B 428179
ENCYCLOPEDIA
OF
CIVIL ENGINEERING
EDWARD CRESY.
TA
145
.C92
1872
LONGMANS & CO.

ARTES
1837
SCIENTIA
LIBRARY
VERITAS
OF THE
UNIVERSITY OF MICHIGAN
VALOVER
KUKU
EXC PLURIBUS
TUEBOR
SI QUARĪS PENINSULAY AMŒNAMÉ
CIRCUMSPICE
COLLEGE
OF
ENGINEERING
TA
WORKS BY SIR WILLIAM FAIRBAIRN, BART.
C.E. LL.D. F.R.S. F.G.S. &c.
Useful Information for Engineers:
Being a FIRST SERIES of Lectures delivered before the Working Engineers
of Yorkshire and Lancashire. With Appendices, containing the results of
Experimental Inquiries into the Strength of Materials, the Causes of Boiler
Explosions, &c. Fourth Edition, revised; with Plates and Woodcuts.
Crown 8vo. price 10s. 6d.
'Sir W. FAIRBAIRN's name is a guarantee
for the soundness of this work. It treats of
steam, fuel, and boilers, the working classes,
as they will one day be called; with an
appendix on wrought iron,-the workman's
jacket stuff. Though a professional book, it
is as much adapted for the general reader as
such a book can be.'
ATHENÆUM.
Useful Information for Engineers,
SECOND SERIES: containing Experimental Researches on the Collapse of
Boiler Flues and the Strength of Materials, and Lectures on Popular
Education and various Subjects connected with Mechanical Engineering,
Iron Ship-building, the Properties of Steam, &c. Second Edition; with
Plates and numerous Woodcuts. Crown 8vo. price 10s. 6d.
Useful Information for Engineers,
6d.
THIRD SERIES, as comprised in a Course of Lectures on the Applied Sciences,
and on other kindred subjects; together with Treatises on the comparative
merits of the Paris and London International Exhibitions, on Roofs, on the
Atlantic Cable, and on the effect of Impact on Girders. With a Plate and
56 Woodcuts. Crown 8vo. price 10s.
'All Sir W. FAIRBAIRN's papers are written
in a clear and popular style, and, as far as
possible, divested of mechanical technicalities,
so that they may be read with interest not
only by amateur or professional engineers,
but by the general public. Much of the
information conveyed possesses a wider appli-
•
cation than is suggested by the title, and
the work is really an attractive one even to
the ordinary reader.
It is not too tech-
nical nor abstruse, and may be read with
pleasure and profit by all who take an interest
in either civil or mechanical engineering.'
GLASGOW HERALD.
A Treatise on Mills and Millwork.
New Editions, carefully revised, of both Volumes. VOL. I. The Principles of
Mechanism and Prime Movers; with 8 Plates and 176 Woodcuts. VOL. II.
Machinery of Transmission, and the Construction and Arrangement of Mills;
with 10 Plates and 146 Woodcuts. 2 vols. 8vo. price 32s. cloth, or separately
16s. each volume.
'THIS valuable work is now complete, and
we doubt not that it will receive from
engineers the reception to which its merits
fully entitle it. It is a book which no
engineer's library should be without.'
SPECTATOR.
"THE whole subject is so ably and syste-
matically treated that we believe there is no
question connected with millwork upon which
the practical man is likely to require informa-
tion that he will not find fully elucidated in Sir
W.FAIRBAIRN's work. It is a work which com-
mends itself to all engaged in the engineering
MINING JOURNAL.
profession.'
'The entire work forms a most valuable
book of reference. The engineer, even if
inexperienced in the construction of any
particular class of machinery, need never be
at a loss for the correct solution of a minute
question of detail. The tables interspersed
give the speeds of all the machines treated of,
from the smallest to the largest; while general
information is put before the reader in a
pleasing and accessible form. We cordially
recommend the book to the mechanical
engineer as one of the best of its kind.’
MECHANICS' MAGAZINE.
'As the most successful and most extensive
master-millwright in the world. Sir W. FAIR-
BAIRN has done good service to the profession
of engineering by the publication of this work.
The subject is one on which there has been
a singular dearth of published information;
most other important branches of engineering
have been treated at length by more or less
able authors, but the mysteries of the mill-
wright's craft have been hitherto preserved
mainly in oral traditions and empirical rules.
No fitter person than Sir W. FAIRBAIRN could
have been found to give this floating informa-
tion a shape. Commencing his work as a
millwright some fifty years ago, he found the
practice of millwork in a most primitive
condition. By the application of new prin-
ciples, by the concentration of motive power,
the substitution of cast-iron wheel-work for the
old and cumbrous forms of wooden gear, the
improvement of water-wheels by the invention
of ventilating buckets, the use of the steam-
engine as a prime mover, and last, not least,
the introduction of wrought-iron shafting of
small diameter, he brought about just such a
revolution in the millwright's art as the
increasing commercial activity of his time
demanded.'
JOURNAL of SCIENCE.
London: LONGMANS and CO.
14-5
692
1872
Works by Sir W. FAIRBAIRN, Bart. C.E.
The Application of Cast and Wrought Iron to Building
Purposes.
Fourth Edition, greatly enlarged, with Corrections and Additions. To which
is added a Short Treatise on Wrought Iron Bridges, with Additions, &c.
With 6 Plates and 118 Woodcuts.
THIS work, which is entirely of a practical
character, has been carefully revised by the
Author. The new edition comprises, in
addition to its former contents, an account of
the most recent improvements in fire-proof
buildings, the employment of wrought-iron
instead of cast-iron beams, and experimental
Iron Ship-Building:
8vo. price 16s.
researches on the effects of vibration on beams,
girders, and bridges. The new APPENDIX
includes, amongst other papers, an account of
the bridge intended to cross the Rhine at
Cologne; followed by some remarks on the
fall of a Cotton Mill arising from defective
beams and defective construction.
Its History and Progress, as comprised in a Series of Experimental
Researches on the Laws of Strain; the Strengths, Forms, and other con-
ditions of the Material; and an Inquiry into the Present and Prospective
State of the Navy, including the Experimental Results on the Resisting
Powers of Armour Plates and Shot at High Velocities. With 4 Plates and
130 Woodcuts. 8vo. price 18s.
'THIS is a complete history of the rise and
progress of Naval Construction from the time
when IRON was first employed for that purpose.
As a work of reference and instruction to
Shipbuilders, it is the most comprehensive
and practical ever published.. It is a
Cyclopædia of facts, figures, and theories on
ship-building in every branch, including even
cupola ships and their armaments.'
.....
SHIPPING GAZETTE.
'Sir W. FAIRBAIRN's treatise begins with
an historical sketch of the progress of naval
construction since IRON was first used for that
purpose. It then treats fully of the law of
strains, properties of the material, and how it
should be jointed to meet the force of wind
and sea. This part of the work includes
experimental researches on cellular construc-
tion, with a view to the construction of
unsinkable ships. The comparative merits of
wood and iron in ship-building; the general
question of the different forms of the con-
struction of ships of war; the questions of
ordnance and its trials before the Iron-plate
Committee; properties of iron armour plates,
and their resistance to shot and shell, are
then successively discussed. Next follows a
treatise on the building of IRON SHIPS; and
the book ends with recapitulations, Mr. TATE
adding a treatise on the strength of materials
considered in relation to the construction of
iron ships,'
EXAMINER.
'A work on the subject of iron ship-building
from such a pen as that of Sir WILLIAM FAIR-
BAIRN is calculated to excite interest in this
part of the world, where that department of
industry is, we may safely say, the most im-
portant and wide-spread branch of manu-
facture. The volume before us has already
been acknowledged by practical men to be
the most comprehensive and valuable ever
published. After a brief account of the rise
and progress of iron ship-building from 1812
(when it was applied to canal boats) to the
present day, when it has culminated in the
Great Eastern, the Professor goes deeply into
the subject-matter of the work, dividing the
latter into fourteen chapters, seven of which
are devoted to the construction of ships of
war and the resistance of armour plates to
projectiles; the letterpress being profusely
illustrated by drawings. Nothing can be of
greater importance to the profession for whom
the treatise is intended than the remarks upon
the law of strains, the jointing of iron plates,
the form of joints, and the comparative merits
of iron and composite ships. We hope we
have now said enough to show the value of
this contribution to scientific literature, in
which the Author pays a high and well-merited
tribute to the Clyde ship-builders for their
energy and enterprise in this branch of trade.'
GREENOCK ADVERTISER.
London: LONGMANS and CO.
ENCYCLOPEDIA
OF
CIVIL ENGINEERING
LONDON: PRINTED BY
SPOTTISWOODE AND CO., NEW-STREET SQUARE
AND PARLIAMENT STREET
AN
ENCYCLOPEDIA
OF
CIVIL ENGINEERING,
HISTORICAL, THEORETICAL, AND
PRACTICAL.
BY
EDWARD CRESY,
Architect and Civil Engineer.
ILLUSTRATED BY UPWARDS OF THREE THOUSAND ENGRAVINGS ON WOOD,
BY R. BRANSTON.
NEW IMPRESSION.
LONDON:
LONGMANS, GREEN, AND CO.
.*
1872.
PREFACE.
CIVIL ENGINEERING must almost necessarily have been coeval with the world's
existence, and that its practical usefulness was fully appreciated by the ancients
seems to be shadowed forth in one of their earliest fables; for when the waters which
covered Thessaly were to be drained, the land rendered serviceable for agriculture,
and the air freed from miasma and pestilential vapours, no mortal could be found
competent to perform the task, and Hercules was implored to cut off the Hydra's
head, or to dam up the watercourses which were the cause of the inundation: but
vain were the several first attempts of the hero to destroy the enemy; two heads
appeared for every one removed; and until the method of searing up the wound
was discovered, he failed in accomplishing his purpose.
The Phoenicians, Egyptians, Greeks, and Romans, gave active employment to
the Civil Engineer, in draining marshes, mining, constructing sewers, bridges,
aqueducts, baths, amphitheatres, roads, canals, moles, harbours, lighthouses, &c. &c.,
the remains of which are not only traceable, but sufficient to justify our conviction
that they were executed by a class of men thoroughly acquainted with the principles
of geometry, and many branches of natural philosophy.
After the destruction of the Roman Empire, all engineering works were under
the direction and superintendence of the Freemasons, Brothers of the Bridge, and
other fraternities; but Civil Engineering can scarcely be said to have taken its place
among the sciences until the desire to recover the submerged lands in Italy called
into action the powers of those philosophers and mathematicians of the seventeenth
century, whose writings laid the foundation of our knowledge of hydrodynamics :
hydraulic architecture as practised in Italy soon spreading over the greater part
of Europe. Galileo, Torricelli, Castelli, Gulielmini, Poleni, Manfredi, Žendrini and
others, became distinguished for the laws they propounded upon the active
properties of water. The torch of theory was then kindled by practice, and again
gave back to the artificer and mechanic a light more brilliant than they had before
enjoyed.
In France, Belidor about the same period collected all the information that might
be useful to the Civil Engineer, which he published under the title of " Architecture
Hydraulique; a work deservedly esteemed, and considered as the primer of the
modern school of engineering in that country.
In England, the profession of the Civil Engineer was scarcely known until the
middle of the last century, when the important discovery of the application of
steam by James Watt, and its rapid development, called into existence a new class
of mechanics, who gave a fresh impetus to manufactures by the improvement of all
kinds of machinery. The vast commercial enterprise which attended this movement,
and its great and growing success, have necessarily led to the enlargement of our
harbours, and the improvement of our inland navigation; the progress, too, of an
enlightened civilisation in its regard for the sanatory condition of the empire,
requires that our towns and cities shall be amply supplied with water, lighted,
drained, &c.; while innumerable other causes are almost daily arising to call for
the reconstruction of our quays, bridges, and every other work executed before
this great and general movement in civilisation was made. During the last half
century hundreds of millions sterling have been devoted to these important objects,
and, great as the amount may appear, it is infinitely less than what will be expended
upon railroads alone if the country remains at peace, and its prosperity unimpaired.
4
338800
iv
PREFACE.
The first portion of the present work is devoted to the history of the past; for it
has been thought that a knowledge of the manner in which others have accom.
plished works similar to those we are called upon to execute at once facilitates our
labour and inspires us with confidence in what we are about to undertake.
In treating of Geology, Mineralogy, and Chemistry, the only aim has been to
point out the nature of these subjects, and give a general idea of the properties of
the materials which form the earth's crust, with an account of their composition, as
far as might be generally serviceable to those who employ them in the arts of
construction, or operate upon them mechanically.
Geometry, as the very foundation of the acquirements of the Civil Engineer,-
embracing, as it does, levelling, surveying, the mensuration of planes and solids;
trigonometry in all its practical applications; drawing, perspective, mapping, laying
down charts, and all the preliminary steps to great undertakings, as well as their
execution, should be made the first study of all who are desirous of becoming
acquainted with the other sciences; for without it, in fact, no portion of them can
be rightly comprehended.
Mechanics are also a most important subject. The ancients, indeed, knew the
principles of the inclined plane, the wedge, the screw, the lever, and the pulley,
and by their application were enabled to move the vast weights accounts of which
are transmitted to us; but the improvements made in machinery in modern times
have undoubtedly enabled us to execute works of vast magnitude with a great
saving of manual labour. From experiments upon the strength and properties of
the metals, and the application of geometry to mechanics, we can construct machines,
which from their variety of movement, and the useful purposes to which they are
applied, are inventions and novelties which belong to the present age. The tools
and engines employed by the Civil Engineer are instances of the advancement in
this branch of physics.
Hydrostatics, with the theory of the motion of fluids, and the various hydraulic
machines that have been invented, facilitate the operations of the Engineer in
raising water, directing its course usefully and efficiently, whether for sanatory,
domestic, or agricultural purposes; and without an almost complete command over
this element, he can scarcely be considered worthy of his high vocation.
The nature of the Atmosphere, and its properties as a moving power, has greatly
occupied the attention of mechanics in all ages, and its services cannot be too
highly appreciated. For the construction of windmills and similar contrivances,
numerous experiments have been made, replete with benefit to the millwright.
Warming and Lighting are daily becoming matters of public attention, and must
therefore occupy the consideration of every man of science; but the Civil Engineer
must beware of fanciful theories: whatever may be bis system, it must be based on
a thorough knowledge of the elements which he is to direct, and he must never lose
sight of the requisite balance to be maintained between the heat generated and the
ventilation. Lighting our coasts has occupied the attention of such philosophers as
Professor Faraday, whose interesting discoveries have greatly improved our light-
houses, and elevated this subject into an important science.
Gas Lighting has its engineers, who have improved the methods of distilling coal,
and laid down principles to direct the proportions of every part of the establishment
where such works are conducted.
Steam, considered as a moving power, is the most extraordinary discovery of this
or any other age. By its application manual and horse labour have been greatly
economised; machinery of every kind is set in motion; and millions of human
beings are transported in a short space of time from one end of the empire to the
other. This branch of our subject, it is unnecessary to add, particularly deserves
our study.
Carpentry, which embraces the construction of timber roofs, bridges, centres,
scaffolding, &c., with a thorough knowledge of the use and properties of timber, has
been treated at considerable length; though not more so than the importance of
the subject demands. Although iron has in this country superseded the employment
of timber in many instances, there are occasions in which the carpenter's art
cannot be dispensed with; moreover, the principles embraced by it are also those
practised by other artificers, and deserve to be understood, if on that account
alone.
Masonry is another branch of artificer's work necessary to be thoroughly


PREFACE.
ν
understood by the Civil Engineer. The construction of every variety of arch
and dome occupies several pages: while the mathematical calculations upon the
strength of stone, the effects of thrust and pressure, are dilated upon in several
parts of the work. The examination of the qualities of the various stones used in
construction, together with an analysis of them, has been also fully detailed from
parliamentary and other documents that may be relied upon. As a science the
mason's art has not in this country been made sufficiently prominent, nor excited
sufficient interest to call forth a treatise on the subject; but a volume would be
necessary to exhibit the varieties of construction, the skill displayed in overcoming
the many difficulties that arise, and the gradual progress of this highly important
branch of the profession.
Stone Bridges, and the principles upon which they are constructed, should be
thoroughly studied by the Hydraulic Engineer, as they embrace all the knowledge
required for the formation of docks, harbours, piers, jetties, quays, &c. which are
among the most triumphant efforts of the engineer. Of the machinery invented
to aid these works, and for which we are indebted to the bridge-builders of the last
century, ample accounts have been given in that portion of the work devoted to
machinery. The stone bridges over the Thames at London are highly deserving
of attention; they may be considered as the result of great study, and the best
examples of the application of science to such structures.
Canals, though now superseded by Railways, ought not on that account to be
entirely neglected: for should steam navigation be still further improved, it is not
improbable that the data which have occasioned their disuse may prove more favour-
able for their future construction, and hence the principles which belong to their
formation should be thoroughly understood by the civil engineer, as there are
many localities where canals would have a decided preference over railways.
Draining and Embanking have from a very early period occupied the attention
of the government as well as individuals. To confine rivers within their banks, and
draw off the surplus waters from the surface of the land, are not only benefits
conferred on agriculture, but on its cultivators, by rendering the atmosphere more
salubrious and agreeable. Towns and cities also require attention to their sewerage,
and the cleansing of the streets; and several local acts of parliament have been
passed to enable these objects to be carried into effect; but one grand compre-
hensive view is still wanting for this to be thoroughly accomplished, and it will
never be attained until the united efforts of a number of engineers, well-instructed
in Geology, shall suggest for every district the best means of attaining it.

Railroads have given an extraordinary impetus to the profession; but it is time
that the principles of their construction should be better comprehended: the public,
at whose expense these highly important works have been executed, having hitherto
generally preferred the mechanic to the artificer, as the director of the chief lines
that have been completed. The construction of a railroad requires a great combi-
nation of talent before it can be brought to perfection. The selection of the country
through which it is to pass, the building of bridges and viaducts, laying down
rails, &c., are even more important considerations than the locomotive engine,
which draws vast loads along the line. We have already had numerous failures,
where the arts of construction have been employed, and it is to be desired that the
engineers entrusted with the expenditure of such vast sums as are embarked in these
speculations would qualify themselves, at once to comprehend these arts, and to
practise them beneficially.
The Principles of Proportion which regulate the quantity of material to be em-
ployed in the arts of construction should be diligently studied both by the Architect
and the Civil Engineer. To this subject the author has devoted the most careful con-
sideration, having measured a vast number of buildings of all ages, for the purpose
of forming an opinion upon the difference of character expressed in the Doric,
Ionic, Byzantine, and Mediæval styles. For economic purposes this enquiry is
worthy of great attention, it being apparent that if an entire building or a portion
in the Byzantine style be cubed, one part out of twelve only is devoted to material;
in St. George's Chapel, Windsor, two parts; in the Chapter-House at Wells four:
in the Ionic porticoes six; in the Doric eight; a variation between a twelfth, a
sixth, a third, a half, and two thirds of the entire cube being employed for supports,
and the remainder for space.
One of the great features of the age is the division of labour, and as the popula-
vi
PREFACE.
tion increases, and the influence of knowledge spreads, it seems likely to be still
further carried out. The province of the Civil Engineer at present extends over the
works performed by the artificer, miner, and mechanic; he is entrusted with the
direction of all that is difficult and scientific in construction, whether upon land or
water, as well as with designing the machinery necessary for these important pur-
poses. This knowledge was formerly demanded of the architect, who in addition was
required to be acquainted with the fine arts. His qualifications, according to Vitru-
vius, were to embrace all that could be known; and many illustrious names could
be adduced to prove that the requirements of the great Roman architect were ful-
filled to the letter.
To design an edifice that shall have "Commodity, Firmness, and Delight," or to
render it both serviceable and expressive of its purpose, requires a variety of talent;
and it is to be feared that the architect who confines his attention solely to that
portion embraced by the fine arts will eventually lose his power: for without
studying the principles of construction, he cannot give character to his design, and
is not qualified to be entrusted with the execution of a work. On the other hand,
should the Civil Engineer be required to act as architect, he must pursue the course
adopted by Sir Christopher Wren, set out upon his travels, and examine and
study those buildings which have received the approbation of the most competent
judges; and he will find that Egyptian, Grecian, Roman, and Medieval architecture,
have each its peculiar principles and character of expression. Equal application is
required for a perfect initiation into the knowledge of architecture as a fine art as
for that of the science of construction. St. Paul's, London, which is a masterpiece
of construction, gives but too strong evidence that the genius of the mathe-
matician had not profited sufficiently from his journey in search of what was con-
sistent and perfect in architecture; he did not even advance so far in that study as
his predecessor Inigo Jones. We admire this splendid edifice, not for its architec-
ture, but for the principles developed in its construction. Those who pass judgment
on a design should be in possession of all the elements necessary for such a task.
They should be acquainted with construction generally and in detail, and should
understand the proper relative proportions of every part of the edifice. The
public are enabled to pronounce the Menai Bridge to be both beautiful and useful:
but before the engineer can decide that it is a perfect work of its kind, he must
be satisfied, not only that every tie rod and strut is rightly proportioned, but that
all of them in their respective characters express their functions, producing a whole
combining security, solidity, and utility.
It is impossible to dismiss this portion of our subject without expressing feelings
of the most painful regret at the position which Architecture now appears to hold in
this country. In France, Germany, and throughout Europe, it occupies its rightful
place, as the chief and most important of the arts of design: there the architect is
prepared for the exercise of his profession by a long course of study, tested by strict
examinations in elementary mathematics and the sciences of construction, while all
the student's talents and energies are called forth by the spirit of emulation
produced by contests for medals and academic honours. Foreign governments
powerfully contribute to the encouragement of successful merit by bestowing
thereon their patronage and protection, by conferring civil orders and decorations,
and by endowing academies and professorships, which enable the man of science
to devote his leisure to the cultivation and advancement of his art.
The Engineers, estimating at its true value the power acquired by combination,
have wisely united "for the general advancement of mechanical science, and more
particularly for promoting the acquisition of that species of knowledge which
constitutes the profession of a Civil Engineer." They have defined the nature and
objects of their Institution; they encourage the student to cultivate the sciences
ancillary to his profession, and, by the distribution of medals and prizes for the most
able memoirs, incite him to the study and description of engineering works at
home and abroad. Nor has the means of furnishing the aspirant with opportunities
for acquiring theoretical knowledge been neglected: the engineering classes at
King's and University Colleges, and at the University of Durham, communicate
much valuable information, which would have been inaccessible in the office
or workshop. For the architect no such means are provided, nor has the Institute
defined the art in a manner to make the public feel its value or necessity. Let
the architects follow the wise example of the engineer, and they will have done
•
PREFACE.
vii
much to acquire for their art the respect and encouragement of their coun-
trymen, and to place it in the elevated position which elsewhere it so deservedly
occupies.
For the information contained in this Encyclopædia, the author is indebted to
several eminent writers, and to numerous tours which he made for the express
purpose of observing the engineering works both of this country and on the con-
tinent. The practical observations are the result of thirty years' employment in
his profession; but he has freely borrowed the opinions suitable to his undertaking
from every trustworthy source to which he has had access, and more especially
from the following foreign authors, a more extended perusal of which he earnestly
recommends to every student.
Gauthey, "Traité de la Construction des Ponts, &c. ;" M. Belidor," Architecture
Hydraulique; " M. Rondelet, "L'Art de Bâtir;" M. Bruyere, "E´tudes relatives à
l'Art des Constructions; " M. Perronet's "Description des Ponts, &c.; " M. Prony's
"Nouveau Architecture Hydraulique," and "Description Hydrographique et His-
torique des Marais Pontins; " M. Boistard's "Observations faites sur différens Tra-
vaux ; "M. Berard's "Statique des Voutes;" M. Hachette's "Traité des Machines ;
MM. Lanz et Bétancourt, "Sur la Composition des Machines; " M. Borgnis, "Traité
complet de Mécanique appliquée aux Arts; " M. Mallet, "Géométrie pratique, &c.
&c;" the several Essays comprised in the "Raccoltà d'Autori Italiani, che trattano
del Moto dell' Acque," whose names are frequently introduced where this subject is
discussed; Alberti, "l'Architectura;" and above all, the "Opera M. Vitruvii
Pollionis," edited by Poleni and Stratico, 4 volumes. He has also to acknow-
ledge assistance received from his eldest son, Edward Cresy, who, whilst studying
his profession, executed nearly the whole of the drawings, so ably cut on wood by
Mr. R. Branston, of St. Andrew's Hill, Doctor's Commons, to whom he offers his
best thanks for his care and attention during the progress of the work.
To conclude: the author's great desire has been to embody in one volume all
the leading principles and multifarious details on which the science of Civil En-
gineering is based; and to produce a work that might at once instruct the pupil,
and prove a useful guide to him in his professional career. The work, he believes,
is the first on the subject which has been published in this country. The labour
bestowed upon its compilation has been of no ordinary kind; and he terminates
it with regret, feeling assured that one individual could not do justice to a subject
involving so many considerations of public importance. Should he, however, be
so fortunate as to awaken in the mind of the young engineer a love for his pro-
fession per se, and a sense of the honourable position in which he may place himself
by careful study and an undeviating course of integrity, he will not think that he
has laboured in vain.


South Darenth, near Dartford, Kent.
January, 1847.
E. CRESY.
CONTENTS.
BOOK I.
HISTORY OF CIVIL ENGINEERING.
CHAP. I.
Phoenician : Ports of Sidon, Tyre, Carthage,
&c.
CRAP. II.
Page 1
Egyptian: Pyramids; Port of Alexandria; Smelting
and refining Metals; Hydraulic Architecture;
Stone Quarries; Obelisks; Bridges
CHAP. III.
7
Grecian.- Ports of Athens, Piræus, Eleusis, Ægina,
rene, Samos, Tenedos, Troas, Chios, Smyrna,
Teos, Ephesus, Crete, Phalasarna, Cyprus, Nea-
paphos, Paros, Delos, Cnidus, Halicarnassus, Cos,
Myndus, Palermo, Syracuse, Agrigentum, Selinus,
Ægesta, Taorminum, Messina, Posidonia, &c.;
Walls of Cities; Gates; arts of Construction 40
CHAP. IV.
Roman Engineering. Walls of Cities, their con-
struction; Gates, &c.: Rome, Circeium, Au-
gusta Prætoria, Nismes, Augustus at Fano,
Autun; Distribution and situation of the Build-
ings within the Walls of Roman Cities; Materials
used in the Arts of Construction; Bricks,
Tiles, and Conduit Pipes of Clay; Sand, Sea-Sand,
Lime, Pozzolana; Stone used by the Romans;
Marble, &c.; Timber; Pavements; Tempering
Lime for Stucco; Stucco Works in damp Places ;
Colours employed for Decoration and Preserva-
tion; Strength of Building, &c. ; Of the Forum
and Basilica: Theatres, Greek and Roman; Am-
phitheatres, &c.; Circus, Riding Schools, &c.;
Baths, their arrangement; Harbours and Build-
ings in Water; Ports of Centocellæ, Ostia,
Claudius, Trajan, Civita Vecchia, Terracina, Adria,
Naples, Cuma, Miseue, Baiæ, Puzzuoli, Portus
Julius, Leghorn, Sinus Lunensis, Genoa, Venice,
Ancona, Antium, Tarentum, Brundusium, &c.:
Roads, their Magnitude, Beauty, and Con-
struction; Bridges; Supply of Water to Towns
and Cities; Instruments used for Levelling;
Conducting of Water; Fire Engines; Forms of
Water-pipes; Piscina; Filters; Aqueducts;
Canals; Drainage of the Pontine Marshes;
Cloacæ; Drainage of the Alban Lake, and the
Lake Fucino; Tombs of the Romans; Mausolii;
Machines and Engines; Principles of Mechanics;
Engines for raising Water; Water Mills; Water
Screw; Hydraulic Organs; Saw Mills; Mea-
suring Distances; Hydraulic Architecture;
Lazarettoes
CHAP. V.
83
Holland and Germany; Drainages and Bridges, 213
CHAP. VI.
France.-Ports and Harbours at Dunkerque, Grave-
lines, Cherbourg; Breakwaters, &c.: Havre,
Dieppe, Marseilles, Rochefort, Toulon, Rouen;
Lighthouse at Cordouan; Navigable Canals;
Bridges; Supply of water; Aqueducts; Abattoirs;
Markets; Bourse; Artesian wells; Railroads 215
CHAP. VII.
America.—Harbours of Quebec, Halifax, Montreal,
Boston, New York, Philadelphia, Baltimore,
Charlestown, New Orleans: Canals: Supply of
Towns with Water; Railroads
293
CHAP. VIII.
*
Britain, Ports and Harbours of: Docks on the
Thames: Chatham, Sheerness, Harwich, Orford,
Southwold, Lowestoft, Yarmouth, Wells; King's
Lynn; Wisbeach; Boston, Grimsby; Barton-
upon-Humber; Goole ; Kingston-upon-Hull;
Lighthouses at Spurn Point; Bridlington harbour,
Scarborough, Whitby, Hartlepool; Sunderland,
Lighthouse at; Harbours at South and North
Shields;
Berwick-upon-Tweed.; Eyemouth;
Dunbar; Leith; Dundee; Bell Rock Lighthouse;
Harbours at Arbroath, Montrose, Gourdon; Stone-
haven, Aberdeen, Peterhead, Frazerburgh ;
Burghead; Findhorn; Banff; Avock; Cullen;
Fortrose; Cromarty; Mahomac; Tain; Wick;
Pulteney Town; Orkney Isles; Kyle; Rhea;
Tobemory; Tarbet; Jura Small Isles; Feoline;
Corran ; Glasgow ; Greenock ; Ardrossan ;
Troon; Ayr; Carlisle; Workington; White-
haven; Ravenglass; Lancaster; Preston; Liver-
pool; Birkenhead;
Aberconway; Bangor ;
Caernarvon; Beaumaris; Holyhead; Aberystwith;
Milford Haven ; Swansea; Cardiff; Bristol;
Bridgewater; Watchet, Minehead; Ilfracombe;
Barnstaple; Bideford; Hartland; Padstow; St.
Ive's; Penzance; Falmouth; Fowey; Plymouth,
Breakwater; Eddystone Lighthouse: Harbours
at Dartmouth; Exmouth; Sidmouth; Axmouth:
Lyme Regis; Weymouth; Poole; Christchurch;
Southampton; Portsmouth; Little Hampton ;
Shoreham; Newhaven; Cuxmere; Hastings
Rye; Folkestone; Dover; Sandwich; Ramsgate;
Broadstairs; Margate; Douglas; Port Patrick;
Belfast; Dublin; Howth; Kingston; Cork;
Jersey, St. Aubin's, &c. : Walls and Gates of
Cities and Towns; Castles, &c. ; Bridges; Roads;
Draining and Embanking; Drainage of Towns ;
Supply of Towns with Water; Rivers, Canals,
and Inland Navigation; Steam Engines; Steam
Boats; Locomotive; Railroads; Atmospheric ;
Electric Telegraphs; Gas Lighting; Prisons,
&c.
306
X
CONTENTS.
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
CHAP. I.
Geology, different Strata; Water; Tidal Currents;
Rivers;
Formation of Deltas; Sand Banks;
Downs; Beach, &c.
617
Plumbers' Blocks; Friction Rollers; Changing of
Motion by several methods, and its application to
a variety of Machines
915
CHAP. XII.
CHAP. II.
Composition and Use of Minerals; Mines; Strength
of Metals; Coal Fields; Boring, &c.; Coke
Making, &c.
CHAP. III.
643
On Stone : Sandstones; Limestones ; Marbles;
Granite; Resistance of Stone to the Crush 697
CHAP. IV.
Bricks and Tiles; their Manufacture and Va-
riety
708
717
725
CHAP. V.
Mortars and Cements; their Composition
CHAP. VI.
Of Pisé; and manner of making
CHAP. VII.
Tar; Pitch; Resin; Glass
728
CHAP. VIII.
Geometry; Shadows; Sciography; Perspective;
Isometrical Perspective; Levelling and the
Instruments used; Compound Levelling; Drawing
the Section or Profile of a Country; Trigo-
nometry; Measuring Heights and Distances;
Piquets; to draw the Map of a Country; Demi-
circles; Geometric Square; Sector; Astrolabe;
Compass and Magnetic Needle; Jacob's Staff;
Plane Tables; Theodolite; Surveying Cross;
Optical Square; Prismatic Compass; Sextant;
Hadley's Quadrant ; Barometer; Chain and Offset
Staff; Gunter's Chain; Parish Surveying; Sub-
terranean Surveying; Maritime Surveying; Tide
Gauges; Sounding; Trigonometrical Surveying ;
Signals and their Construction; Meridian Line;
Mensuration of Superficies, &c.; Copying and
making Plans; to reduce Multilateral Figures to
Triangles and Squares, &c.; Mensuration of
Solids, &c.
CHAP. IX.
Valuation of Property
СНАР. Х.
733
891
Machines, Tools, &c., employed by the Civil En-
gineer the Winch, the Gin, the Capstan, the
Crab, the Jack, the Crane; Tackle for hoisting
Weights
997
CHAP. XIII.
Carriages for transporting Weights, Boats, &c.;
Waggons, Trucks, Railway Carriages, Buffing
Apparatus; Boats for the Transport of Stone, &c.;
Machines for proving the Strength of Materials,
&c.; Making Screw Bolts; the Lathe; Drilling
Machines, Boring Machines, Machines for
punching Boiler Plates, &c. ; Riveting Machines ;
Shears for cutting Iron; Slotting and Key
Grooving; Screw Cutting; Cutting the Teeth
of Wheels; Planing Iron; Forge Bellows:
Hammers; Block Machinery; Saw Mills; Hand
Mills; Horse Mills; Mills for grinding Corn;
Mortar and Cement Mills; Diving
Diving Bells;
Pontoons; Raising Vessels sunk at Sea; the
Hedgehog; Floating Clough; Dredging; Arte-
sian Wells; Boring Instruments; Machines for
measuring the Strength of Men and Animals; the
Dynanometer
1017
CHAP. XIV.
On Piles; Pile-driving, cutting off the heads, &c.;
Pile Engine; Withdrawing Piles; Cutting off
Piles; Steam Pile-driving
1071
CHAP. XV.
Mechanical Agents, or the first movers of Machi-
nery; Velocity with which a man moves; Daily
labour of a man, when moving a load on a Wheel-
barrow ; when acting on pulleys; of a man
pushing or drawing; Swiftness of men; Useful
effect of such moving power; Force developed;
Horse considered as a mover; his tractive power;
Strength of, taken as a dynamic unit; Observation
the daily labour of; the measure of the
1087
greatest effect of an animated mover
on
CHAP. XVI.
Hydrostatics.-Level of liquids and their equilibrium;
On the vertical action of water; Against inclined
surfaces; Centres of impression; Specific gravities,
and Table of
1096
CHAP. XVII.
Value of Artificers' work in Engineering; Ground-
work; Dredging; Fascine work and Fencing;
Carpentry; Masonry ; Bricklayers' work; Smiths',
Tables of various measures,
Painters', &c.; Tables of
895
&c. &c.
CHAP. XI.
Mechanics. Physical Properties of Matter; Me-
ehanical Labour of the Forces; Centre of Gravity;
Action of Bodies when placed over each other;
Equilibrium of an Inclined Plane; the Wedge;
the Screw; the Lever; the Steelyard; the Pulley;
Wheel and Axle; Elementary parts of Machines ;
Wheelwork; of the Plane Epicycloid; Teeth of
Wheels, Construction of; Face Wheels; Strength
of Wheels; Shafts and Axles, Proportion and
Strength of; Journals; Gudgeons; Couplings;
Universal Joints; Bayonet and other Clutches ;
Theory of the Motion of Fluids.-Measurement of
water which flows through Tubes and Pipes;
rectilinear
through
and vertical orifices;
through vertical and circular; through orifices
under pressure; Of the communication of motion
on Fluids when at rest; On the shock of Water
against plane Surfaces; To find the velocity of a
current; Motion of water in Conduit-pipes and
Canals; Quantity discharged by orifices of different
forms from vessels kept constantly full; Quantity
discharged over a weir; On the motion of water
in rivers; Smeaton's experiments relative to un-
dershot Water-wheels; Its dynamic effects; Con-
struction of Undershot wheels; Overshot wheels:
Barker's mill; Tide mills; Breast wheels; Or
Bodies plunged in water; Equilibrium of float-
ation; Sinking bodies; Fountain of Hero; Hy-
draulic ram; Siphon ram; Suction ram; Verra's
1
CONTENTS.
Machine; Hydraulic cane; Machine of Vialon ;
Centrifugal force machine; Archimedean screw;
Suction pump; Forcing pumps; Suction aud
forcing pump;
Double piston pumps; Chain
pumps; Ship pumps; Fire engines; Engines for
raising water; Pistons and Valves; Hydraulic
machines, useful effects of; Persian wheels;
Scoop wheels; Chapelets; Bucket wheels;
Marly machine; Belidor's machine for raising
water by means of a fall; Denisard's and Dueille's
machine; Bucket machines
1126
CHAP. XXIII.
xi
Timber Bridges, Principle of; Piers; Bays and
Arches; Floors and Parapets; Swing Bridges;
Single and double Turning-bridges; Draw-bridges ;
Rolling bridges; Rope bridges; Bridges of boats ;
Floating bridges; Centres of various kinds used
for. Bridges, Tunnels, &c.; Strength of, how
determined; Scaffolding; Suspended scaffolds;
Turning scaffolds : Various kinds
kinds of Knots
used
1348
CHAP. XVIII.
CHAP. XXIV.
Supply of Towns with Water.-Self-cleaning Filters;
Cost of raising water; Laying down mains; Height
1210
that a jet of water will rise
CHAP. XIX.
Atmosphere as a moving Power.—The Air-pump;
Post Windmills; Tower Windmills; Self-adjusting
cap; On the relative effect of Windmill Sails;
Comparison of the Effects of mechanical Agents as
Blowers and Ventilators
CHAP. XX.
1216
Warming and Lighting. Grates; Stoves; Hot
water apparatus; Warming by steam; Warming
by air; Ventilation; Lighthouses; Lighting, Gas-
lighting; Retorts; Hydraulic Mains, Conden-
sers, Purifiers, Gasometers, Meters, Gas gover-
nors; Laying down Mains; Sliding and Hydraulic
valves; Pressure indicator; Quicksilver valves;
Construction of burners; Oil gas apparatus; Beale's
Light, &c.
1223
Masonry, various kinds of Walls; Opus incertum ;
Opus reticulatum ; Pseudisidomum, Diatonus,
Isodomum; Placing the Stone, and the form given
to wrought stone, for Walls, Abutments, Piers, &c.
Dimensions of Stones; Stone Pipes; Arches, how
formed; Varieties of; Vaults, conical, spherical;
Bracing Caissoons; to trace the stones forming
an arch with parallel faces; Development of
perpendicular, oblique, and circular arches on the
plan; Skew arches; Intersecting semicircular
Vaults; Oblique ditto; Descending Vaults inter-
secting at right angles, and obliquely; Groined
Arches; Groined Vaults, on an irregular and on an
hexagonal plan; Hexagonal groined Vaults, with
pointed Ribs; Circular Vaults with groined Ribs;
Gothic Vaults with Ribs uniting in Keys at the
centre; Hanging Keys; Gothic Vaults formed of
inverted Parabolic Conoids; Arris Vaults; Conical
Vaults; Trompes; Spherical Domes; Vaults on a
square plan; Hemispherical Niches; Spheroidal
Vaults; Conoidal Vaults; Pendentives; Groined
Vault over a circular plan;
a circular plan; Construction of
Staircases
1419
·
CHAP. XXI.
;
Steam considered as a Moving Power. - Steam-en-
gine; Atmospheric engine; Single-acting engines ;
Double-acting; Boilers; Materials for making;
Piston-gauge; the Dynanometer; Water-gauge;
Glass-gauge; Feeding apparatus; Safety-valves;
Chimneys; Piston-rods, Beams, cylinders and
metal pipes; Pistons; Valves of various kinds
Four-way cock; Plug-tree; Valves opening by
weights; Eccentric Rollers; Mode of opening
valves, cocks, and slides; the Eccentric; Fly
governor, Centrifugal pump regulator; Parallel
motion; the cycloidal parallel motion; the
Crank; Fly-wheel; the useful effect of an engine;
the portable condensing engine; Application of
Steam-engines for raising Water, for raising Coals
and Ores; to Waterworks; to Steam-boats; Loco-
motive, Boilers, Fire-Box, Axles, Framing; Feed-
pumps; Chimneys; Tenders; Regulator Box;
Safety-valves; Gauges ; Cylinders; Valves;
Drivers; Pumps; Steam-whistle; Dimensions of
parts of Locomotives; Consumption of Fuel; Hy-
draulic Traversing Frames
CHAP. XXII
;
1242
Timber and its Properties. -Different species used
in construction; Felling timber; Seasoning tim-
ber; Causes of Decay in timber; Resistance to a
Transverse strain; Cohesive strength; Resistance
to compression in the direction of its length, or its
vertical bearing strength; For timber placed ver-
tically in Posts, &c.; in an inclined Position ; Joints
and joining timbers; Fishing a beam; Scarfing,
Notching, Cogging, Pinning, Wedging; Tenons;
Mortises; Fox-tail wedging; Bond timbers; Wall-
plates; Dovetailing: Lapping; Girders; Posts;
Kings; Queens; Partitions; Framing; Floors;
Strength of Joists; Girders, &c.; Roofs and cover-
ing of buildings, varieties of; Sheds for Ship-build-
ing; Domes and cupolas
CHAP. XXV,
On Stone Bridges, Situations of; Water-way; Num-
ber and span of Arches; to estimate the quantity
of water to which the bridge must allow a passage;
of the form to be given to the Arches; on their
width; on the breadth of Bridges: Arches, vari-
ous forms of; Semi-circular, formed of three cen-
tres; Elliptical Arches; Thickness to be given to
the Keystones of Arches; to the Abutments; Thick-
ness of Piers; Form of Piers ; Quay Walls ; Founda-
tions; Cofferdams; Sounding the Soil; Excava-
tions; Dragging; Construction of Piers and Abut-
ments; Raising the Centres; Construction of the
Arches; Spandrills and Wingwalls
1477
CHAP. XXVI.
On the Construction of Fascines; Basket-work, &c.
for Jetties; River and Sea Walls; Dock and
Wharf Walls
1522
CHAP. XXVII.
Canals, Cutting; Oblique ditto; Quantity of water
expended by Boats; Locks, form to be given to
the Chambers of; Talus of Walls; Dimensions to
be given to the several parts of a Lock; Wing-
walls; Platform; Pointed Sills; Gates of Locks;
Sluices; Paddles; Iron Lock Gates; Inclined
Planes and Lifts on Canals; Means of making the
water enter and leave the Locks; Bridges and
Towing Paths; Stop Gates and Lets-off; Reser-
voirs and Aqueducts
1533
Chap. XXVIII.
Draining and Embanking; Surface and Subsoil
Draining; Sluicing; Tunnelling
1557
CHAP. XXIX.
1283 On the Construction of Machinery
1561
xii
CONTENTS.
CHAP. XXX.
Railroads, Formation of Cuttings; Gradients; Width
between Rails; Foundations for Stone; Blocks and
Sleepers; Rails of Iron; Chairs; Railway Curves ;
Turn-tables; Passing from Line to Line; Switches;
Crossing-rails; Planes; Engines for double Planes;
Self-acting Planes
CHAP. XXXI.
1566
Principles of Proportion; Architecture; Dorians;
Tetrastyle Porticoes; Hexastyle Porticoes; Octa-
style Temples; Doric Columns; Ionic Proportions;
Ionian Tribes; Pantheon at Rome; Triumphal
Arches; Poliphele's Proportions; Roman ex-
amples; Byzantine, Romanesque, Lombardic, Sax-
on, Norman, Saracenic, and Pointed Architecture;
Proportion of mass and void in Cathedrals; Tra-
cery and Geometric Forms on Mouldings and Win-
dows; Groined Vaults, their thrust, and relativý
dimensions of Piers; Sections of Cathedrals, &c.
&C.
INDEX
1579
1731
SUPPLEMENT
1
1637
CIVIL
ENCYCLOPÆDIA
OF
ENGINEERING.
BOOK I.
HISTORY OF ENGINEERING.
CHAPTER I.
PHOENICIAN ENGINEERING.
As commerce and the art of war equally require the assistance of the engineer, his
employment may be dated from the time when history notices the one, or relates the
success which attended the other. War, in the early ages of the world, being considered
more honourable than the arts of peace, traffic and the handicraft trades would be but
little esteemed; and so few good workmen were then to be met with, that we read of such a
hero as Ulysses being obliged to construct his own boat, as well as to decorate the fur-
niture his rude palace contained. As the knowledge of navigation improved, and traffic
became more general along the shores of the Mediterranean Sea, the inhabitants found that
the high precipitous cliffs, broken into headlands, and the numerous indented islands, by
the assistance of art might be made to afford better protection to their vessels against the
sudden storms to which that sea is subject. To the architect, whose studies comprised
all the sciences which had been developed by society, and united in his employment what
was then known of construction, the lifting of heavy weights, and the arrangement of
machinery, was confided the adaptation and improvement of nature's works; their defence
from aggression of every kind; the formation of the city, the roads, the supply of water,
and all that was deemed necessary or essential for the wants or the pleasures of the inha-
bitants.
To the Phoenicians, who so long enjoyed the dominion of the Mediterranean Sea, we
must give the credit of first encouraging the art of civil engineering: they were among
the earliest descendants of Noah that settled on the coasts, and who made navigation sub-
servient to commerce. These people, named Canaanites, which, in the Eastern language,
signifies merchants, first inhabited a city called Sidon, in consequence of its being built by
the eldest son of Canaan, whose name it bore. The country around not being fruitful, the
inhabitants were obliged to turn their attention to manufactures and commerce, and use
every means to induce other nations to trade with them, and take off their surplus produc-
tions in exchange for the necessaries of life.
In the days of the patriarch Abraham the settlers here had become so powerful a people,
that when Jacob blesses his children, he tells Zebulon "that he shall dwell at the haven of
the sea, and he shall be for a haven of ships, and his border shall be unto Sidon."
The Phoenicians lost the greater part of Canaan which they held, in the time of Joshua,
when the land as far as Sidon was given to the tribe of Asher. The inhabitants were not,
however, destroyed, but suffered to extend their commerce, and to send out colonies to the
shores of Africa and Europe. Cyprus, Rhodes, Greece, Sicily, Sardinia, Gaul, and Spain,
received settlers from the Sidonians, who taught the native inhabitants the first rudiments
of science.
Twelve hundred and fifty years before Christ we find these enterprising merchants
passing through the Straits of Gibraltar, and founding the port of Cadiz, where they
laid up in extensive warehouses the produce they freighted from all parts of the then known
world. Gold, silver, copper, lead, tin, and iron, they supplied in abundance, and these
metals they obtained either by exchange with the natives, or by working the mines which
they discovered.
Sanchoniatho, who was supposed to have been a contemporary of Joshua, has left us
many traditions of the Phoenicians.
.
Б
2
Воок I.
HISTORY OF ENGINEERING.
Sidon is at present a town of considerable importance, known as Saide or Seide. This
ancient port is nearly choked up with sand; the houses which rise from it, and contain
upwards of 15,000 inhabitants, are built along the shore, and impart, as the traveller

HEAVY
SURF
!
2
SCALE OF SEA MILE
3
S
LICABLES
TRACES OF THE ANCIENT CITY
º TOMBS
jur
´KILLA AL BAHN .12
་་་ BERCOUD
GOOD
HOLDING GROUND
CUNS
SAID ISLAND
12
CUNS
SANSOUL ROCK
CUN
ROMAN BAY
MINT ROMAUN
Fig. 1.
SIDON.
approaches, the idea of a place of some extent. Considerable employment is still
given to the spinners of cotton and manufacturers of leather, and at a short distance from
the shore is the island of Said, once connected by a mole with the main land, and forming
a second well-sheltered harbour. The Roman bay is commanded by a modern battery,
and behind this Turkish fortress are traces of the ancient city; and the remains of several
tombs. Homer, in the 15th book of his Odyssey, mentions this city; and in describing the
arrival of one of its ships, tells us how it was freighted, and that it contained toys and
fancies of every sort. The same poet often alludes to the works of art, the mantles of
various hue, the dyes, the silver goblets, the beads of amber rivetted on gold, and other
articles of luxury that were sent from Sidon; and that the fair Sidonians were highly
accomplished in embroidery and other ornamental works.
Sidon was rendered important from the mercantile disposition of its inhabitants, who
were also skilled in producing all kinds of manufactures then in demand; the mountains
of Libanus in their rear afforded them abundance of timber for ship-building, with which
they constructed vessels that carried their surplus produce to the most distant lands.
Had Faccardine, the emir of the Druses, who dreaded the constant visits of the Turkish
fleet, not demolished the ancient mole, we might have had it in our power to describe a
structure of the golden age, or of the time when giants are said to have given their aid:
for vast indeed in dimension are many of the stones that lie scattered along the coast, and
which once formed the mole that shut in their harbours. Some of these stones are reported
to be long enough to have extended through the whole thickness of the mole.
At present
a ledge of rock affords the only shelter to vessels which frequent this port; this is a short
distance from the coast, and stretches itself in front of the citadel towards the north.
This ancient port for a long period enjoyed the sovereignty of the entire Mediterranean;
and as the surrounding country was barren, the inhabitants could not have subsisted
without commerce, which brought in its train the arts. Some of their early bronze and
silver medals bear proof how highly they were advanced, and history attests the success
which attended their navigation. Homer, according to Strabo, speaks only of Sidon, when
he alludes to the inhabitants of Phoenicia.
Tyre, or Sor, called "the daughter of Sidon," stood also on the sea, at a distance of about
200 stadia southward. We must be careful not to confound the three different cities
which had this name. The first in order of time was old Tyre, on the continent; then
Tyre on the island; and Tyre on the peninsula, after the island was joined to the main
land. It had two harbours; one lying north, and the other south, or towards Egypt,
which were formed by the isthmus; the latter was a close harbour, and the opening
through which ships entered was fortified by drawing a chain across it. An artificial
mole still defends this bay; and probably the rocks on the other side were once built
upon, thoroughly to enclose it. Northward, at the head of the island, stretches out, from
a ruined light-house, another mole, which protected the northern harbour. Since the
uniting of the island a gully has been formed, as if the sea had again broken through,
and once more separated it from the continent. Tyre on the island, and old Tyre on
the main land, for a long time constituted one city: according to Pliny, the island was 700
paces from the continent; but, according to Strabo, 30 stadia, or nearly three of our
miles. The same author states that the walls which encompassed it were 150 feet in
height, proportionally broad, and built of large and massive blocks of stone, embedded in
morfar Modern travellers place the island at about a third of a mile distant from the
CHAP. I.
S
PHOENICIAN.
shore. Old Tyre was first destroyed by Nebuchadnezzar, after a siege of thirteen years,
the inhabitants having removed all their treasures to the island. The conqueror was

ROCKS
GULLY AS IF THE
SEA
HAD BROKEN THROUGH
RUINS
LOOSE DRIFT
FOUNTAINS"
'SAND
RUINS
RUINED LIGHTHOUSE
AQUEDUCT.4 FLWIDE SOME PARTS UNDERCROUND
ALL VERY SOLIDLY CONSTRUCTED
CULTIVATED LAND
ØST.PAULSHA
ROAD
TO
A CRE
CRAVES RUINED FORT
BIRKET EL ESKUUNI
ISPRINGS
4 SPRINGS IN TANKS OF
STRONG MASONRY
MILLS
SCALE OF 1 SEA MILE
S
10
1
CABLES
Fig. 2.
TYRE.
therefore obliged to rest satisfied with destroying the town on the main land, after
which he set out towards Egypt. The Tyrians were then compelled to submit
to the rule of the Babylonians; and, for
seventy years, were governed by kings of their
nomination. The Persians then restored to them
their independence, whom they assisted when
Xerxes carried on his wars against the Greeks; and
Herodotus informs us that the kings of both Tyre
and Sidon formed part of the Persian monarch's
council of war.

TOWER
ROADSTED
ARTIFICIAL
MOLE
Fig. 3.
TYRE.
DARSENA
MATIN ROCK
About 332 years before Christ these cities were
destroyed by Alexander, who, in his march towards
Egypt, compelled all the cities of Phoenicia to sub-
mit to him.
Tyre obstinately refused him entrance, when he
immediately commenced the memorable siege, which
ended by his taking the city by force of arms: the
height of the walls, the strength of the navy, and
the abundance of all things for defence, made it a
difficult and almost hopeless attempt.
He began, says Diodorus, by demolishing
old Tyre, and employed his army to carry away
the stones, and raise a mole, 200 feet in breadth,
which was speedily advanced. Whilst this was
doing, the Tyrians determined to send their wives, children, and old men to Carthage,
and keep their young men to defend their walls; but this was not carried into execution:
the walls were covered with new-invented engines, and especially on that side where
the mole was in progress.
When the mole was carried within a short distance, or the cast of a dart, a large whale
was thrown upon it, much to the alarm of all parties: the citizens being struck with the
increase of the mole, sallied out in small boats, accompanied by slingers and archers armed
with engines of all kinds for the discharge of arrows and darts.
A violent storm of wind arose, and destroyed a portion of the work, and broke through
the mole. This was speedily repaired, by causing large trees, cut down in the
mountains, to be thrown in, with their branches entire; on which was heaped a quantity
When the mole was
of earth, to render it strong enough to resist the violence of the sea.
complete, and within a short distance of the walls, Alexander commenced battering them
down, discharging at the same time darts and arrows out of engines at the besieged.
The Tyrians, to guard against these missiles, had contrived wheels with long spokes of
B 2
4
BOOK I.
HISTORY OF ENGINEERING.
0
their battlements, which, turning constantly round, shivered all the darts that came in con-
tact with them to atoms; and they checked the violence of the stones thrown by the
balista, by woolpacks placed in proper situations to receive them.

INER PORT
ALEXANDERS
MOLE
Fig. 4.
TYRE.
The Tyrians did not relax in their exertions. They built within their outer wall
another, ten cubits broad, and five cubits distant from the former, and filled in the space
between with earth and stones. Alexander then constructed a battery, by joining many of
his ships together, and then placing the rams against a portion of the wall, beat down 100
feet of it, when he attempted to pass through the breach, but was repulsed by the Tyrians,
who during the night again rebuilt the wall which had been battered down. The Mace-
donians then approached with towers as high as the battlements of the Tyrian walls, and,
casting out planks, formed a bridge. Here they were again repulsed by the Tyrians, who
had contrived long tridents, or three-forked hooks, to grapple and wound those placed on
the top of the towers; these grapples, attached to ropes, they flung over the shields of the
assailants, and tore them out of their hands. Nets were thrown over those who attempted
to pass over the bridges formed of planks, and they became so entangled, that many of
them tumbled headlong to the ground. They also filled their iron and brazen shields with
sand, and after they had made it scorching hot by placing them over fires, it was by means
of a machine cast upon the besiegers, and getting between their breastplates and coats of
mail, burnt their flesh, and many died in consequence. The Tyrians sent off fire darts,
heavy stones, and all kinds of missiles, and with long poles, armed with sharp knives and
hooks, they cut the cords of the battering rams in pieces: they also discharged out of their
machines masses of red-hot iron; they plucked men off the ramparts with iron instruments
shaped at the end like a man's hand.
Alexander was undismayed, and unwearied in his exertions: he continued to batter the
walls, and discharge ponderous stones out of his engines, and all sorts of missiles from his
wooden towers. Marble wheels placed upon the walls, and kept constantly turned, were
made to throw them off, and render them ineffectual: hides and skins were also sewn
together, which, being soft and pliant, were placed in other situations for the same purpose.
At last, Alexander perceiving that the wall next the arsenal was weaker than the rest, he
brought all his galleys which contained his best engines chained fast together to that
place; here he cast a plank from a wooden tower with one end upon the battlements of the
walls, thus forming a bridge, and alone mounted the rampart, to the astonishment of all,
neither regarding the danger nor the assaults of the Tyrians: his Macedonians quickly fol-
lowed: he came first in contact with the enemy, and killing some with his spear, others
with his sword, and tumbling others down with the boss of his shield, he overcame his
adversaries. During this time the battering rams had made another breach in the wall,
and the Macedonians entering, joined the party fighting with Alexander, and by this means
at last was the city taken.
The Tyrians, throughout this siege, made a most valiant defence; but instead of their
bravery awakening in the breast of the conqueror an admiration for their courage, to
his lasting disgrace he ordered two thousand of the chief inhabitants to be crucified, and
sold thirty thousand for slaves: eight thousand of its chief soldiers perished in the combat,
and the city itself he burnt to the ground.
Nearly twenty years afterwards we again find Tyre able to resist an attack made upon
it by the fleets and armies of Antigonus, who, after a fifteen months' siege, captured it
CHAP. I.
5
PHOENICIAN.
It subsequently fell under the dominion of the Roman empire; and the Latins were not
finally driven from Syria until about a century after the death of Saladin. In the year
1188, Conrad of Montserrat was hailed as the prince and champion of Tyre, which was
then besieged by the conqueror of Jerusalem. The Egyptian fleet was allowed to enter
the ancient harbour, the chain was immediately drawn across the entrance from mole to
mole, and a thousand Turks were slain. Saladin was obliged to burn all his engines, and
make a disgraceful retreat to Damascus. Afterwards, Tyre was a place of rendezvous to
the ships of Genoa, Pisa, and Venice, and eventually it became a part of the Turkish
dominions.
The insular Tyre, destroyed by Alexander, is now "a place for the spreading of nets in
the midst of the sea," as Ezekiel prophesied; the mole which the conqueror raised was
washed away by a storm, and thus the peninsular state of Tyre was destroyed.
Aradus was also a city belonging to the Phoenicians; and another, called Tripoli, was
built by the inhabitants of Aradus and Tyre, and hence its name.
The settlers at a very early period excelled in the sciences, and brought the arts and
manufactures to great perfection. They were the inventors of astronomy, and from them
the Greeks received their letters. The glass, the purple dye, and fine linen, produced
here, was celebrated all over the then known world; they were skilled in the working of
metals and carving of timber; and were so perfect in the arts of construction, that we hear
of them, in the time of Hiram, being employed by king Solomon in the construction of his
temple, more than 1000 years before our era.
As merchants, they had the commerce of the world; as navigators, they were the most
experienced; and the greatest discoverers as well as planters of colonies; and for many
ages they had no competitors.
They carried on considerable trade with Syria; and, having convenient harbours, and
excellent timber furnished them, they built great numbers of ships.
Carthage, according to Velleius, was founded 65 years before Rome; while many writers
imagine that it was built 130 years before the imperial city, by Dido, the sister of
Pygmalion, king of Tyre, and wife of Sichæus; and the Tyrians she carried with her, to
colonise this new settlement, were among the most skilful in the arts of the then known
world: the form of government she introduced was by Aristotle said to be the most perfect
in existence.

NEAPOLIS
NEAP
NOW NABAL
CORUBIS
NOW CORRA
TUNIS
SITE OF
CARTHACE
SOLIMAN
BACRADA NOW.R.MĄJERDEH
LAKEI
(„SI SARĄ
PORTA EARINA..
BIZERTA
C.TY
LA TORRE
P
MAXULA
NOW CAPE BORO
PROM DE MERGURIO
Fig. 5.
CARTHAGE.
Carthage was situated at the extremity of a gulf, upon a peninsula 360 stadia or 45
miles in circumference; and the isthmus which united this peninsula to the continent of
Africa, was 25 stadia or more than 3 miles in breadth. On the west projected a long slip
of land, half a stadium in breadth, which separated the sea from a lake, which was strongly
protected by rocks on both sides.
In the middle of the city was the Acropolis, called Byrsa, where was a temple to Æscu-
lapius. On the south side of the city was a triple wall, 30 cubits in height, and at every 480
B 3
6
BOOK I
HISTORY OF ENGINEERING.
feet was placed a tower, which had its foundations laid at a depth of 30 feet, and was four
stories in height, being carried up two stories higher than the walls.
There were two harbours, so disposed that they communicated with each other,
although they had but one common entrance, which was 70 feet in breadth, secured by
chains. One was devoted to merchant ships, and the inner port, as well as the island
called Cothon, in the midst of it, which was surrounded by spacious quays, was made
secure for the reception of 220 ships of war. Magazines, storehouses, and all the re-
quisites of an extensive arsenal, were constructed around it; and the entrances to the
harbours were decorated with marble porticoes, so that the whole might be said to be
encompassed by two magnificent galleries. Upon the island was the residence of the
governor, facing the mouth of the harbour, so that he could see all that was passing both
within and without the port. When the merchant ships entered, it was not possible for
them to view what the inner port contained, as it was shut in by a double wall, and each
port had its particular gate.
The city had three divisions : Byrsa, Megara, and Cothon. Byrsa was three miles in
circumference, and stood nearly in the centre of Carthage, surrounded by Megara, which
contained the houses of the citizens: these, at the time of the third Punic war, were
numbered at seven hundred thousand. Livy gives twenty-three miles for the measure of
its circumference, and Suidas affirms it was the most powerful city in the world: it enjoyed
the dominion of the sea for more than six hundred years, and had an extensive and lucrative
commerce. The Carthaginians possessed three hundred cities in Africa, and their territory
extended from the western confines of Cyrenaica to the Pillars of Hercules, a distance
of upwards of fifteen hundred miles. Spain, Sicily, and all the islands of the Mediter-
ranean also belonged to them. The Carthaginians, who disputed the empire of the
world with the Romans for a hundred and eighteen years, were destroyed as a nation a
hundred and forty-six years before Christ. Emilianus, the Roman general, made two
attacks, one against Byrsa, and the other against Cothon; and having become master of
the wall which surrounded the port, threw a considerable force into the great square of
the city; soon after which, Asdrubal abandoned the Carthaginian troops, and went over
to the Romans: his wife could not survive such perfidy, and committed herself, children, and
followers to the flames which then enveloped the citadel and temple. Soon after, the
victorious Romans demolished Carthage, as well as the cities dependent upon it, and the
territory was declared a Roman province.
The enormous wealth that had been amassed by this commercial people is stated by
Pliny at upwards of four millions four hundred and seventy thousand pounds weight of
silver, which was carried away by Æmilianus.
Carthage is now at a considerable distance from the sea; the north-east wind and the
Merjedah have closed up its ancient harbour. The place is called El Mersa; the port lies
to the north and north-west of the city, and forms, with the lake of Tunis, the peninsula on
which Carthage was built.

AL
TO
MARSA
MARSHY CROUND
SBIKLEN ROCK
ZZARETTI
BLANDINCFLACZ
FORT
Fig. 6.
CARTHAGE.
ANCIENT
AQUEDUCT
GITY
WALK
RUIN
OF
BURSAY
JOMPE
MR CARTHAGE
HACE
COTHON
EMAINS OF OUAYS
AND BAT HIS
RISALMILK
HALR AL WAD 37, CUNS
FOMM ALWAD MOUTH OF RIVER
CHAP. II.
7
EGYPTIAN.
Upon the other side, Carthage has been a loser by the encroachment of the sea, a corsider
able tract that was land being now under water. The traces of Cothon, though scarcely a
hundred yards square, may be yet seen. Along the shore the openings of the common
sewers remain; and also, at a short distance, the great reservoirs and aqueduct, near the
western wall of the city. There are more than twenty of these water-cisterns, each a
hundred feet in length, and thirty in breadth, and the water was conveyed to them through
earthen pipes, still visible.
CHAP. II.
EGYPTIAN ENGINEERING.
Egypt boasts of as great antiquity as any other nation of the earth. It may be
called the cradle in which the sciences were first nursed, and the source from whence the
Greeks, in after times, drew their knowledge; and we must admit that a great portion of
our modern skill, particularly in engineering, had its rise on the banks of the Nile. This
country is bounded on the east by the Isthmus of Suez and the Red Sea, on the south by
Nubia, on the west by Libya, and on the north by the Mediterranean; its length
from north to south is about 500 miles, its greatest breadth 250, while at some parts it is
very much less. It lies between the twenty-first and thirty-first degrees of north latitude.
The waters of the Nile which pass through it, have their rise in the Gebel Alcomri, and
the course of this noble river measures upwards of 2000 miles, whilst its breadth seldom
exceeds the third of a mile, or its depth twelve feet.
The Delta, which is a luxuriant district, is composed of pure black unctuous mould,
and for the purpose of vegetation needs no manure: it is entirely alluvial, and formed by
deposition of matter brought down by the waters of the Nile. This delta is not wholly
covered by the inundation of the Nile, though throughout the habitations are built upon
mounds raised considerably above the level of the standing water; and it is from the formation
of these earthworks, and the cutting of canals for the irrigation of the land, that the rudi-
ments of civil engineering may have had their origin.
The Nile was perhaps one of the earliest rivers devoted to the purpose of inland naviga-
tion; and, according to Gibbon, "the servitude of rivers is the noblest and most important
victory which man has obtained over the licentiousness of nature;" and, without doubt,
agriculture would first derive advantage from their subjection, occasioning them to be
confined within certain limits by artificial embankments. The earliest cities were founded
on the banks of rivers; and the first operation performed by their inhabitants, both for
salubrity and convenience, would be the cutting of dikes, for the purposes of drainage and
occasional irrigation. In Egypt, before the time of Menes (Herodotus, lib. ii. c. 99. ),
who lived 2320 years before the Christian era, the Nile continued its course along the
sandy mountain on the side of Libya; but this king, by constructing a bank at the distance
of a hundred stadia from Memphis towards the south, diverted the course of the river, and led
it, by means of a new canal, through the middle of the valley: and it seems that in the days
of the historian, during the time of the Persian dominion, this artificial canal was annually
repaired and maintained. At the period referred to, the whole of Egypt, with the exception
of Thebes, was an extensive marsh; and to Menes is attributed the forming of water-
courses, by cutting and embanking, for carrying off the superfluous waters. Herodotus
(lib. ii. cap. 137.) further states, that when Sabacus, the king of Ethiopia, governed Egypt,
he made it a rule not to punish any crime with death; but, according to the magnitude of
the offence, he condemned the criminal to raise the ground near the place to which he
belonged, by which means the situation of the different cities became more and more
elevated: they were somewhat raised under the reign of Sesostris, about 1659 years B. C.,
by the digging of the canals, but they became still more so, under the reign of the Ethi-
opian. To prevent the water of the Nile from continually overflowing the country, and
to maintain a supply for the purposes of irrigation, the lake Moris was formed, which,
according to Herodotus, was 450 miles in circumference (lib. ii. cap. 149.), and was termi-
nated about 1385 years B. C. By some authors it is said to have been in places 300 feet
deep; for six months in the year the Nile supplied this lake with water, by means of a canal,
which during the remaining portion of the year returned to the river. This canal, a stu-
pendous effort of art, is still entire; and, according to Savary, is forty leagues in length:
there were two others, with sluices at their mouths, from the lake to the river, which
were alternately shut and opened, as the Nile increased or decreased: thus the water,
which would have been carried off to the sea, was retained for the moistening the earth
after seed-time. Diodorus Siculus (lib. i. cap. 4.) states the canal to have been 80 furlongs
in length, and 300 feet in breadth, and that the sluices were of such a nature that they
could not be opened or shut at a less charge than 50 talents (12,9167. 138. 4d.); and in
all probability it was necessary to cut through the embankments to attain the object desired.
B 4
HISTORY OF ENGINEERING.
BOOK II.
Among the other benefits conferred by Sesostris on the people of Egypt, we find that
of cutting many canals and deep dikes, at right angles with the river, as far as from
Memphis to the sea, for the quick con-
veyance of corn, other provisions, and
merchandise (Dio. Sic. lib. i. cap. 4.), the
barter of which would supply fresh luxu-
ries to the inhabitants of this agricultural!
country; and thus the advantages arising
from this external commerce would sti-
mulate an ardour for further internal com-
munication; and unquestionably the best
means that could be employed by an in-
telligent governor to procure competence
to every class of citizens, would be the fa-
cilitating the transport of provisions; and
the most simple and efficacious means of
attaining this desirable end, is the uniting
the different provinces of an empire, by
improving the navigation of rivers, and
forming artificial ones, where nature seems
to have denied that assistance. Doubt-
less, the extensive commerce which must
have been carried on under the sway of
this prince, gave rise to many of the canals
with which Egypt was afterwards inter-
sected; for we find from Diodorus Siculus
(lib. i. cap. 4.), that he sent forth a navy
of four hundred sail into the Red Sea,
and was the first Egyptian that built long
ships, which, it is true, were principally
designed for the purposes of conquest;
but the general character of Sesostris gives
the idea that the internal grandeur of his
country and the improvement of his peo-
ple were never neglected. At a later
period, about 610 years before Christ,
Necos, son of Psammeticus, commenced
the difficult undertaking of uniting this
sea with the Mediterranean by means of
a canal, which was opened about twelve
miles to the north-east of the modern
town of Belbays, called by the Romans,
Bubastis Agria; and after a course, nearly
east, of thirty-three miles, it turned to
the south-south-east, and continued sixty-
three miles further, to the extremity of
the Arabian Gulf. This canal was wide
enough for two triremes to pass abreast;
and it is stated that 120,000 Egyptians
perished in the prosecution of the work.
Several monarchs continued it; but, ac-
cording to Pliny (lib. vi. cap. 29.), it pro-
ceeded no further than the lakes called the
Bitter Springs, when it was abandoned,
from fear of the greater height of the waters
of the Red Sea. This author states its
breadth at one hundred feet, and its depth
forty, and the distance from the western
entrance to the Bitter Lakes thirty-seven
miles. Strabo asserts that ships of the
largest size could navigate it. After the
time of the Ptolemies it was neglected,
until the caliph Omar, in 644 a.d., re-
opened it, and cut another canal, called
that of the Prince of the Faithful, south

D

"
141
3319
Mita
1
-----------
ט!
-----------
of Cairo: it was used for more than 120 years, until the commerce of Hexandra was
destroyed.
CHAP. II.
9
EGYPTIAN.
1
By a series of levels, that were carefully taken by the French engineers at the end of the
last century, it was found that the surface of the Arabian Gulf at Suez, at high water, was
thirty-two feet six inches above that of the Mediterranean at Tyneh at low water; and it
is interesting to inquire how the waters were retained in the canal, with such a difference
of level. Diodorus Siculus (lib. i. cap. 1.) states, that gates or sluices were ingeniously
constructed, which opened to afford ships a passage through, and then were quickly
shut again; and Strabo (lib. xvii.) mentions a euriplus (a single or perhaps a double gate),
which Ptolemy II. (Philadelphus) constructed, when he completed this work, and which
afforded an easy passage from the sea to the canal.
Pyramids. Of the numerous pyramids found in Upper and Lower Egypt, only those
of Geezeh are mentioned by Herodotus, and were the first examined by the moderns.
In Nubia, there are remaining upwards of eighty, constructed in stone, and burnt
or unburnt brick; at Abooseer, Abooroash, Sakkarah, Dashour, Assur, Nourri, and many
other places, at a distance of several hundred miles apart. The date of the earliest has been
assumed as upwards of 2000 years, and of the latest as 600 years, before Christ.
The absence of all hieroglyphics, as well as any indication of an arch, in those of Geezeh,
near Cairo, have occasioned most writers to consider their origin as earlier than the others.
These pyramids, nine in all, are built on a projection of the Libyan chain of mountains,
where the calcareous rock has been reduced to a level platform; but what quantity of the
original mountain was left to form a core of the several structures has not as yet been
thoroughly ascertained. Had the emperor Napoleon's orders been carried out, we should,
by the demolition of one of those most ruined, had the means of accurately judging of
their construction.
These royal sepulchres bear so strong a resemblance to earth-works and tumuli, that
they appear to have had a common origin; the sepulchral chambers, which contained the
entombed, are usually hollowed out of the native rock; above which is a mass of super-
structure, either of solid masonry, or, as we suppose, only partly so. The kings of Egypt
appear to have been the first who thought of covering their mounds with regular courses of
masonry. That mountains could be easily transformed into pyramids we can readily con-
ceive; and by a judicious cutting, as much might be taken away as would afford a sufficient
quantity of stone to build up the several courses to the apex; and in all probability such a
practice suggested to Denocrates the idea of converting a mountain into a nobler figure,
and astonishing the world by carrying out a more useful application of such labour.
The platform upon which these pyramids are based is in length about 6890 feet, and in
width, from north to south, about 4920 feet. The rock contains many fossils common to
limestone, as nummulites, belemnites, oysters, &c. &c.; the French engineers took great
pains in ascertaining its height above the mean level of low-water in the Nile, which they
found to be about 164 feet.
What is most interesting in the study of these vast and ancient structures, is the manner
in which the materials were worked, transported, and lifted to their respective levels; and
finding, as we do, among the earlier pictures and bas-reliefs discovered in Egypt, the same
tools represented in the hands of the mason as we use at the present day, as the round-

Fig. 8.
-
GREAT PYRAMID.
4
10
BOOK I.
HISTORY OF ENGINEERING.
headed wooden mallet and chisel, we have no difficulty in accounting for the fine surfaces
and the nicely made joints which, the stones in some instances present to us; and the
causeway extending in length more than 3000 feet, with a breadth of 60, and height of
48 feet, we can also imagine the same facilities for the transport of materials were con-
trived and adopted as by us at the present day. Herodotus says, "that when the Great
Pyramid was designed, that the workmen might more easily move the stone, this cause-
way, which is contiguous to it, was formed: its length was five stadia, its breadth ten
orgyes, and its height eight." This was not the causeway seen by Pococke, the length of
which he traced for upwards of 1400 feet, after which it was buried in the alluvial deposit
of the inundation. It was, at a later time,-probably when used by the caliphs and Mem-
look kings to carry away the stones for the construction of the several mosques they raised,
- repaired and strengthened by sixty-one circular buttresses, placed about 30 feet apart,
and each having a diameter of 14 feet.
The causeway mentioned by Herodotus still remains in part, and reached to the west
side of the canal which communicated with the Nile; and hence the blocks of stone,
brought from the east side of the Nile, were easily moved along this inclined plane, to the
level platform where they were required for the casing of the pyramid.
The base of the Great Pyramid is a square of 764 feet. This measurement was taken
by M. Jomard, on the side to the north, after digging down to the true base; and the total
perpendicular height was also found by him to have been 479 feet. Since that period,
Mr. Perring has given us the following dimensions, from accurate measurement : —
The former base
The present do.
Perpendicular height
Former inclined height
Present do.
Perpendicular height by casing stones
764 ft. 0 in.
746 0
450
9
611
0
568
3
480
9
The total area of the base was 13 acres, 1 rood, 22 poles, and at present it covers
12 acres, 3 roods, and 3 poles. And supposing the rock to average 8 feet in height
only over the whole extent of base, after deducting the hollow passages and chambers,
Mr. Perring calculates that the quantity of stone originally used amounted to 89,028,000
cubic feet, or about 6,848,000 tons.
The present quantity of masonry, supposing it solid, is about 82,111,000 cubic feet, or
6,316,000 tons; the space occupied by the chambers and passages being taken at 56,000
cubic feet. Dr. Clarke observes that the stone used was a grey limestone, and rather
more compact than that called clunch, and that when it was struck with a hammer it
exhaled a fetid odour. Denon describes this pyramid to have had 208 courses in height.
The outside casing stones were found (fig. 9.), at the bottom, in their original position,

Fig. 9.
near the centre; they were quite perfect, and had been hewn to their required angle before
they were built in, and appear to have been afterwards polished down to one uniform
surface. They were cut to an angle of 51° 50′, and were in height 4 feet 11 inches.
At the base they measured & feet 3 inches, and on the inclined side 6 feet 3 inches. Where
they were jointed, the cement which interposed was so remarkably fine a layer, that it
was scarcely perceptible.
CHAP. 11.
11
EGYPTIAN.
The entrance to the Great Pyramid is at a height of 49 feet from the base, and the distance
from its centre is 24 feet 6 inches from the centre of the pyramid. It is now accessible by
means of the accumulation of the rubbish at the base.
The opening by which it is entered is only in breadth 3 feet 6 inches, and in height 3 feet
11 inches. Over it, to discharge the weight, lies a stone lintel, 12 feet 6 inches in length,
and 8 feet 6 inches in height; above which lies another horizontal stone, not quite so
long, over which four others, inclined in the manner of a pediment, act as an arch.
two lower of these inclined stones are 7 feet in height, and the two upper 6 feet 8 inches.
(See fig. 10.)
The passage from the entrance con-
tinues of the same size as the aperture,
and descends, at an angle of 26° 41′, to
the length of 320 feet 10 inches, where
it terminates in a chamber, the roof or
ceiling of which is 90 feet 8 inches below
the base of the pyramid. The length of
this chamber from east to west is 46 feet;
its breadth from north to south, 27 feet
1 inch; and its height 11 feet 6 inches.
The northern side of this room, hollowed
out of the rock, is 8 feet from the centre
of the pyramid northwards, and its eastern
side is 26 feet from the centre of the py-
ramid eastwards. This chamber was left
unfinished; and in the wall opposite the
entrance is a small passage, extending
52 feet in a southerly direction; and in
the floor has been recently excavated a
well 36 feet in depth, which has not led
to any further discoveries in that direc-
tion.
In the inclined passage, at about 100
feet from the entrance, a granite block
closes up the way, which has occasioned
an opening to be made at the side of it:
passing through this is the ascent to the
great gallery, on entering which to the
right is a well, communicating with the
inclined passage which led to the lower
:
Fig. 10.
The

chamber this passage is 28 inches square; at first vertical, then inclines, is again vertical,
and then, with two other inclinations, unites with that below: the well is nearly 200 feet
in depth, and by it the workmen are said to have descended, after they had closed the lower
end of the upper passage with the block of granite above described: they then descended
to the lower passage, followed it to the mouth, and made their exit.
Passing the entrance, and proceeding about 63 feet, instead of a continued descent, there
is an ascent by another passage, which commences at this point, and which is in length
124 feet 4 inches, which conducts to the great gallery of the king's chamber. The angle at
which this passage inclines is about 26° 18', its height is 3 feet 11 inches, and its breadth
3 feet 5 inches.
The great gallery follows in the same inclination with this passage, and is in length
156 feet; the breadth 3 feet 5 inches, besides the breadth of each ramp, which is 1 foot
8 inches; and the vertical height of this inclined gallery is 28 feet.
The
At the foot of the great gallery, or rather where it unites with the passage that
inclines upwards, there is at the point of junction another horizontal passage, 109 feet
11 inches in length, which conducts to what is called the queen's chamber, which measures,
from north to south, 17 feet; from east to west, 18 feet 9 inches; and the height, to the
commencement of the roof, is 14 feet 9 inches; the extreme height is 20 feet 3 inches. The
roof is formed of blocks of calcareous stone, resting, like those over the entrance, with
their ends against each other. This chamber is situated nearly under the apex of the
pyramid; and the stones are so well squared that their joints are hardly discernible.
floor is about 408 feet below the original summit, and 71 feet below that called the king's
chamber, which is at the top of the great gallery, and entered by a horizontal passage, in
length about 22 feet. This horizontal passage is in height 3 feet 8 inches, and in width
3 feet 5 inches: at the end are four portcullises, in granite, each 12 feet 5 inches in height,
which slide in grooves cut in the same stone at the sides, and which, when closed, com-
pletely blocked up the entrance to the king's chamber, which is in length, from east
to west, 34 feet 3 inches, and in breadth, from north to south, 17 feet 1 inch; the height is
12
Book I.
HISTORY OF ENGINEERING.
19 feet. The sides are lined with granite; and the roof, which is flat, is formed of the
same quality of stone, having nine slabs, which cross the breadth of the chamber.
At the upper end is a sarcophagus of similar red granite to the lining of the walls: its
length is 7 feet 6 inches, its breadth 3 feet 3 inches, and height 3 feet 5 inches; so that it
was just admissible through the portal or entrance passage. There are upon it neither
sculpture nor hieroglyphics.
The most remarkable feature or accompaniment of this chamber, is the two air-channels,
or funnels, which pass directly to

the outside, and commence at a
height of 3 feet from the floor.
The air-channel to the north is
233 feet in length, its breadth
is 9 inches, and its height 9
9/12
inches. The length of that on
the south is 174 feet 3 inches,
its breadth 8 inches, and its
height 9 inches. Where they
pass through the outer face of the
pyramids,they are, as measured on
the inclined face, 333 feet 1 inch
from the base. These tubes no
doubt were intended to produce
a free circulation of air through
the chamber, and bear a resem-
blance to the funnel of a chim-
ney by an admission of air the
lamps were probably kept burn-
ing some time after the chamber
was closed.
From the base of the pyramid
to the floor of the king's cham-
ber is 138 feet 9 inches; and the
northern side is distant from the
centre about 16 feet 3 inches
southwards, and the eastern
side is 26 feet 3 inches eastward
of the centre line.
Over this chamber are five
others, which are about 38 feet
by 16, and their heights vary
Fig. 11.
KING'S CHAMBER,
from 1 foot 4 inches to 8 feet 7 inches (fig. 11.); the height from the floor of the king's
chamber to that of the upper of the five is 69 feet 3 inches.
These five chambers were evidently contrived for the purpose of relieving the weight
from the ceiling of the king's chamber below, as they were only entered by cutting or
forcing a passage through the solid mass to arrive at them. These rooms are divided
by immense granite blocks, and the upper one has inclined blocks like those at the
entrance.
The great gallery is formed by projecting the courses of stone as they are laid one over
the other, so that at the top the sides approach nearly, to allow of its being more easily
covered.
The outer stones of this pyramid are laid in regular courses, and we find them, as
described by Herodotus, very strongly cemented together: this author also informs us
how these immense blocks, some more than 30 feet in length, were raised; he says that
after the first course was laid, machines, constructed of short timbers, were placed upon it,
which hoisted from step to step the various blocks as they were brought along the inclined
plane.
Goguet has given the form of such a machine, which consists of a timber frame con-
taining a fulcrum, to which a long lever could be applied, worked by many men at one
time, and capable of raising weights far greater than any we find used here.
Each course being so much within that below, it formed a sort of stairs, so that such a
machine as is now described could be readily applied, and would serve to raise the blocks
from one step to the other.
Such is the manner probably adopted by these early engineers to pile one stone upon
another; and, by the magnitude of the masses they constructed, they hoped to render their
work immortal. They are as solid as they are immense; and all the means that could be
found to render them so were adopted. No timber enters into their construction, and the
stoņes used are of great dimensions, and always solidly bedded.
CHAP. II.
EGYPTIAN.
13
Second Pyramid. — Its construction, though similar, is inferior to that already described,
Fig. 12.
the sarcophagus was sunk.
ול
SECOND PYRAMID.
and by Herodotus is
called that of Chephren.
The lowest tier of
stones was granite, but
the rest has been
brought from the Ara-
bian mountains, the
Troici lapidis mons of
Pliny, or from the
Mokattam limestone
quarries.
The passages are also
similar to those of the
first pyramid, and there
is only one chamber,
in the floor of which

There were two original entrances, but no gallery.
The casing has been removed to within 130 to 150 feet of the present summit.
The original base measured, according to Mr. Perring
The present do.
-
The former perpendicular height was
The present
Former slant height
The present do.
do
Feet. In.
707 9
690 9
454 3
-
447 6
572 6
563 6
The angle is 52° 20′, and the size of the square platform at the top 9 feet.
This pyramid does not rise from the level of the natural rock, but out of an excavation
made in the solid rock, there being a deep cut entirely around it. It was opened by

Fig. 13.
Belzoni, who found the entrance (fig. 13.) on the north side, which was 4 feet high,
3 feet 6 inches in width, and formed of large granite blocks. This entrance was east of a
vertical meridian plane bisecting the pyramid.
At this upper entrance, which was 37 feet 8 inches above the base, the passage descended
at an angle of 25° 55'; its length is 104 feet 10 inches. This passage was cut out of the
solid calcareous rock. After passing a portcullis formed by a block of granite sliding in
grooves, at the end of a horizontal passage was the main chamber, also cut out of the solid
rock, in length 46 feet, and in width, from north to south, 10 feet 2 inches; the height at the
sides, 6 feet, and in the centre, 8 feet 5 inches; the roof slanting, and covered with blocks
of calcareous stone.
Making an allowance of 8 feet of solid rock over the whole area of the pyramid, the
14
BOOK J.
HISTORY OF ENGINEERING.
original quantity of masonry has been estimated at 65,980,000 cubic feet, or 4,883,000 tons;
and the original base has an area of 11 acres, 1 rood, 38 poles.

Fig. 14.
The lower entrance was at a level of 40 feet below the base line, and was completely
filled up with solid masonry, closely jointed and well cemented together: the stones were
10 feet in length, or more. (See fig. 14.)
Third Pyramid, is that of Mycerinus, son of Cheops (fig. 15.). According to Hero-
dotus, its entrance was also, like

that of all the others, on the
north side.
or
Mycerinus, Moscheris,
Mencheres, as he has by other
writers been called, succeeded
Suphis, Saophis, or Cheops, who
was cotemporary with Abra-
ham, about 1920 years before
Christ. The memory of My-
cerinus was greatly revered by
the Egyptians, because he ex-
celled all his predecessors in the
equity with which he adminis-
tered the laws; and Herodotus
observes, that this monarch was
never happy after the oracle at
Butos had informed him that his
----
Fig. 15.
THIRD PYRAMID.
death would be certain at the end of six years. He endeavoured to forget the destiny which
he knew was immutable, and caused a number of lamps to be made, by the light of which,
when evening approached, he passed his hours in the festivity of the banquet.
Before a platform could be obtained for this pyramid, it was necessary, on the western
side, to build up a foundation with two tiers of very large blocks of stone.
This structure
was more carefully executed than the two already described; it varied from them also in
being built in regular steps or stages; the angles between the upright and horizontal faces
being afterwards filled in with polished granite to form a casing.
The entrance was above the level of the base, at a height of 13 feet; and all the passages
and excavations to form chambers were cut in the solid rock.
The exterior presents one continued line to the eye, but the courses of stone diminish in
height as they approach the top.
The base, which is square, is in length on each side
The present perpendicular height
The present inclined height
The former perpendicular height
Feet. In.
354 6
203 0
261 4
218
0
The former inclined height
278 2
The angle at which the casing is laid is 51°, and the square platform at the top is
about 16 feet.
CHAP. II.
15
EGYPTIAN.
The inclined passage is on an angle of 26° 2′, and is in length 104 feet; in breadth, 3 feet
6 inches; and in height, 4 feet: at a distance of 4 feet 3 inches is an ante-room, which, from
north to south, is 12 feet in length, 10 feet 5 inches in breadth, and in height 7 feet. There
are then three portcullises, in
length 13 feet 5 inches; and an
horizontal passage, 41 feet 3
inches in length, 3 feet 6 inches
in breadth, and 5 feet 10 inches
in height. At the end of this is
a large apartment, which had a
flat ceiling, the total length of
which is 46 feet 3 inches, and
breadth 12 feet 7 inches, the
height being about 13 feet 6
inches.
Beyond this was the sepul-
chral chamber, the length of
which, from north to south,
was 21 feet 8 inches; and the
breadth 8 feet 7 inches; the
height at the sides 8 feet 9
inches, and in the centre 11 feet
3 inches.
In this chamber Colonel
Howard Vyse found the stone
sarcophagus which contained
the wooden coffin now in the
British Museum, which has
on it the name of the King
Mencheres or Mycerinus.
The plan of the inclined
passage conducting to the se-
pulchral chamber shows its
direction and the situation of
the portcullis, where an addi-
tional width is given for the
purpose of rendering this part
more secure. The whole
forms apparently an impas-
sable barrier; and without a
knowledge of the construction
of this portion of the gallery,
and the aid of machinery, a
passage could not have been
obtained. Over the great cham-
ber the position of the large
stones which cover it are indi-
cated. The section over the plan
exhibits two inclined galleries,
one above the other, and nearly
parallel: the upper gallery has
not been traced to the outside,
but may conduct to another
chamber not yet discovered.
As the latter inclined gallery
has its communication with the
upper part of the chamber which
contained the sarcophagus, it
is by some supposed to have
been used merely as an air-
shaft; but this is only a conjec-
ture, its dimensions being con-
siderable. The masonry of both
the inclined galleries is exe-
cuted with the same care, these
being apparently cotemporary
with the original structure.

Fig. 10.
PYRAMID OF MYCERINUS,
SECTION
PLAN
16
Book 1.
HISTORY OF ENGINEERING.
The entrance to this inclined passage, which was at the height of 13 feet above the level
of the base, was formed by a square hole (fig. 17.), or rather by the leaving out of one large
stone: the joints of the masonry around it were very imperfect, and many of them seem to
have been disturbed as if injured by attempts to force an opening at some time or other.

Fig. 17.
The ante-room, which occurs in the lower passage, at 104 feet from the entrance, is pecu-
liar for the contrivances which are introduced to prevent any one from proceeding beyond
it. Where the three portcullises are placed (fig. 18), across from east to west, the passage is

PASSACE TO
LARGE
APARTMENT
PORTQULLIS
Fig. 18.
ROOM
ENTRANCE
PASSAGE
13 feet 6 inches in length; after which the passage proceeds to the large apartment in nearly
a horizontal line. Immediately above, in the section of this portion of the pyramid, may
be seen another passage, nearly horizontal at first in its direction, and afterwards inclining
upwards: it however terminates at that part of the pyramid where the artificial construc-
tion commences; which seems to indicate that it never had any communication with the
exterior.

Fig. 19.
□
!
CHAP. II.
EGYPTIAN.
17
The other end of this passage, where it is attached to the large apartment, is very
much cut by ropes, the stone indicating, by the grooves worn in it. that hoisting had
been much practised here:
probably the stones from
the excavations may have
been drawn out by means
of this passage, and after-
wards used in the upper
constructions, which now
effectually close the other
end.

The centre of the py-
ramid is immediately over
the cross, marked on the
plan of the large apartments
in fig. 16. At the bottom
of the southern side of a
passage which leads from
the sepulchral chamber, a
recess has been formed, on
the opposite side of which
is a flight of seven steps
which conducted into the
southern end of a room
that had its floor 3 feet
below the level of that of
the passage. This room
was of a rectangular form,
but was not set out square
with the great chamber; it
contained four niches or
compartments on the east-
ern side, and two on the
northern.
The large apartment
shown on the plan, fig. 16.,
and lying at right angles
with the entrance passage,
had a flat ceiling of very
large and massive stone,
and was divided in its
length by two projections.
or pilasters, one of which
was attached to each side,
and beyond was the recess
R.BRANS TOYS4
Fig 20.
or sepulchral chamber, in which the sarcophagus was found: the hole in front conducts
below. (See fig. 20.)
The original quantity of masonry in this pyramid has been estimated at 9,132,000 cubic
feet, or 702,460 tons, and the extent of its base at 2 acres, 3 roods, 21 poles.
The discovery of the sarcophagus settles the question relative to the destination of
the pyramids. The chamber which contained it is given in fig. 21., and indicated in
the plan, fig. 16., where the recess is shown beyond the two pilasters. All the ancient
writers bear testimony to the extreme anxiety of the Egyptians, in common with other
nations, to preserve their remains until a period unanimously anticipated, when their
bodies should be resuscitated. Indeed, the Egyptians, according to Diodorus Siculus, set
little value on the shortness of this present life, but put a high esteem upon the name and
reputation of a virtuous life, after death; and they called the houses of the living, inns,
because they sojourned there a short time; but the sepulchres of the dead they denomi-
nated lasting habitations, as in them they were to abide for infinite generations. For this
reason they did not bestow much care on the building of their houses; but in beautifying
their sepulchres, they left nothing undone that could be thought of.
When a king died, there was a universal mourning and a rending of garments. Temples
were shut up, and feasts and solemnities stayed, for the space of seventy-two days; casting
dust upon their heads, and girding themselves under the breasts with linen girdles. When
these and other observances had been performed, all things were then prepared in a stately
manner for the funeral; and on the last day, the coffin, with the body inclosed, was brought
C
18
Book I.
HISTORY OF ENGINEERING.
to the entrance of its final sepulchre, where, according to the laws of Egypt, all the actions
of the individual during life were
rehearsed, and any one had free
liberty to expatiate on his faults.
The priests, then, with many thou-
sands of the people, amidst profound
silence, assisted in depositing the
coffin in the sarcophagus prepared
to receive it, which was adorned
with painting.

It is not improbable that the hole
in the pavement in front of the sar-
cophagus (fig. 21.), communicated
with a channel which carried off the
water brought down by the inclined
passage, should any filter through the
walls or rocks with which it was
connected. When Belzoni advanced
some distance along the passage
which led to the apartment con-
taining the splendid sarcophagus in
the museum of Sir John Soane,
be found a well 30 feet in depth,
and 14 feet by 12 feet 3 inches,
which was contrived for the purpose
of receiving the rain water, and
keeping the other chamber dry.
Heavy rains fall at Thebes occasion-
ally, once in every four or five years,
when it may enter through the
porous stone in sufficient quantity
to wash down the rubbish
stantly found deposited within these
passages and chambers.
con-
Fig. 21.
Fourth Pyramid. Its square base is only 102 feet 6 inches long on each side, and its
total height 69 feet 6 inches. It is constructed with large blocks of stone; but it is
doubtful whether the exterior was ever completed. The
The sepulchral chamber measures
19 feet 2 inches from north to south, its breadth 8 feet 9 inches, and its height 10 feet
4 inches. The entrance to this pyramid is by a square aperture. (See fig. 22.)

Fig 22.
The fifth Pyramid was 145 feet 9 inches on each side at the base, and its original
perpendicular height 93 feet 3 inches. Its chamber, from east to west, was 25 feet 6 inches,
its breadth 10 feet 5 inches, and its height 8 feet 9 inches; its entrance is by a descent.
(See fig. 23.)
CHAP. II.
19
EGYPTIAN.

והווווהיי
1 +
MUST
Fig. 23.
The sixth Pyramid measured at its base 102 feet 6 inches, and had a total height of 69
feet 6 inches. It contained, besides its passages, an ante-room, and sepulchral chamber,
which was in length, from north to south, 26 feet, in breadth 11 feet 4 inches, and in height
24 feet: the entrance here is by descent also. (See fig. 24.)

Fig. 24,
The seventh Pyramid had its passage lined with masonry, and its sepulchral chamber
with highly-wrought square slabs of stone: its dimensions were, from east to west, 11 feet
8 inches, and from north to south 9 feet 9 inches.
The length of one side of its square base was 172 feet 6 inches, its perpendicular
height 111 feet, its inclined height 140 feet, and the angle of its side 52° 10′.
When the enterprising Belzoni was in Egypt, he attempted to open most of these
pyramids, and had considerable difficulty in finding out the entrance, which was not
always in the centre, or at an equal distance from the angles; much time was spent in vain
upon the pyramid in question, and it is to Mr. Perring and his patron that we are
indebted for the means of describing the entrance shown above.
The stones in this pyramid, like the others, were laid in distinct courses, diminishing
successively in size as they approached the top: each course was so much within the other
below, that it formed a sort of stair previous to the casing stones being laid upon the
outside, which rendered the work complete. These steps served for the placing of the
€ 2
20
BOOK L
HISTORY OF ENGINEERING.
machines mentioned by Herodotus, by which the stones were successively raised step by
step, and imbedded in their proper places; after which the coating or casing commenced at
top, and the work was finished by progressing downwards; at least so it is reported by the
father of history.

・
Fig. 25.
The eighth Pyramid had a square base, the side of which was 172 feet 6 inches in length,
a perpendicular height of 111 feet, an inclined height of 140 feet, and the angle of its
side was 52° 10′. The sepulchral chamber was in length, from east to west, 12 feet 9
inches, and its breadth 10 feet 3 inches; its entrance is very much broken. (See fig. 26.)

Fig. 26.
The ninth Pyramid measured on each side at its base 160 feet: its perpendicular height
was 101 feet 9 inches, and its inclined height 130 feet 6 inches. The angle that its sides
formed was 52° 10′. Like the others, it had passages, an ante-room, and a sepulchral
chamber, which was in length 12 feet 3 inches, in breadth, from north to south, 3 feet 6
inches, and in height 8 feet 6 inches. The entrance is very much broken, and appears
to have been greatly disturbed; it was by descent, like most of the others; the stones
which formed it were of enormous dimensions, and laid with great care; that which served
as a lintel weighed many tons, and must have required the aid of a powerful lever to
lift it into its place. By means of an inclined plane, these large blocks were rolled from
their quarries, after which the machine mentioned by Herodotus was made use of.
These pyramids astonish us by the enormous manual labour bestowed upon them.
CHAP. II.
21
EGYPTIAN.
Herodotus describes hundreds of thousands of persons as employed for their construction,
who were changed every three months; years were consumed in the preparation of the
material; millions sterling were expended in the purchase of food whilst they were
in progress; and, according to some inscriptions remaining, this food consisted of leeks,
garlic, onions, and other vegetable diet. In the early ages of the world, a rapidly increasing
population required support before means could be found to employ it beneficially, and the
sovereigns of Egypt might have been induced to construct these splendid tombs, to afford
occupation to their subjects.

யராம்
Fig. 27.
Campbell's Tomb, as it is now called, is here given on account of the arch which it
contains, and which, it is asserted, was known at the time of the first Osirtasen, who
reigned when Joseph was in Egypt.


A
A
Fig. 28.
C
Fig. 29.
In the ground plan the chamber A A is 30 feet 6 inches from east to west, and 26 feet
3 inches in the other direction: the depth of this excavation is 53 feet 6 inches.
The part lettered B is the arched tomb, and C is a trench cut all round, 5 feet 4
inches in width; but it is not at an equal distance from the centre excavation on all
sides. It forms a square, measuring on the inside about 57 feet 3 inches. This trench is
cut to the depth of 73 feet, which is a little more than 15 feet 6 inches below the surface
of the inundation in 1838.
c 3
22
Book L
HISTORY OF ENGINEERING.
On a bed of sand, 2 feet 6 inches in thickness, slabs of stone about 5 feet in length
were laid flat, and upon them were carried up a few courses with smaller stones.
In the centre was placed a large block (A) scooped out to receive the sarcophagus,
which contained the body; over this, at B, was another large stone placed, covering the
whole, and on the lower edge was an inscription, or row of hieroglyphics. This sarco-
phagus, of black basalt, is now in the British Museum.
The entrance was by the pit k, and the roof of the chamber was formed of four stones,
the two outer being set edge-

ways, and inclined inwards,
having the two others placed
upon them, forming as it were
the first rudiments of an arch.
Over these was turned an
arch, the radius of which was
6 feet 2 inches, and the span
11 feet, which is a little less
than that of a semicircle. It is
composed of four courses, 3 feet
10 inches thick; the stones are
described to have been 4 feet
long, and 15 inches in breadth;
at the back the joints were
packed with chips, and the whole
had been grouted with fluid
mortar. (See fig. 31.)
66
ა
C
| VIJINI RESITELLITE IRUTTINI IN
EXE331113 13 UPEKE BLI ULCELET ER
IN PELEN KEURINN FEFERSON ESTEEFKEN TOTEND" || (MUNUUMUTAMRITINE
The antiquity of the arch is
said by Mr. Wilkinson, in his
Egypt and Thebes," to be
traced to the time of Amunoph
the First, who reigned 1540
years before Christ; and arches
of stone and brick are met with
in several tombs of a very early
date. He also observes, that if the chambers of the brick pyramids at Memphis, erected
by the successor of the son of Cheops, were vaulted, as he supposes, the antiquity of
the arch might be carried back nearly 700 years prior to the reign of Amunoph, which is
2020 years before our era.
Fig. 30.
When blocks of stone, cut like truncated wedges, are so placed that they support each
other by their mutual pressure,

they constitute an arch in our
acceptation of the term; and it
does not seem improbable that
such a system of construction
should result from the use of
bricks, in a country where
timber was not readily obtained,
to serve as lintels or discharging
pieces. Brick arches seem the
first upon record; here the
opening is gathered over by
three stones set in the or-
dinary Egyptian manner, and
the arch in question, turned
over them, bears no weight, but
acts simply as a covering; there
is no indication of an abutment
necessary to render the work
solid and durable.
21111
RESPITE
PLANETA"
Mr. Wilkinson observes that
arches, or similar constructions,
in brick, were in use 3370 years
ago, as the name of Amunoph is
preserved on the stucco which
coats the interior of the vaulted
tomb at Thebes. The stone arch at Saccara still exists, of the time of the second Psam-
meticus, who reigned about 600 years before our era, and, from its peculiar construction,
there is little doubt that the Egyptians had been long accustomed to the erection
Fig. 31.
CHAP. II.
23
EGYPTIAN.

•
of stone vaults. The want of
timber in that country would
render such construction almost
necessary.
In the time of the first Osir-
tasen, who was cotemporary
with Joseph, the arch was made
use of in the tombs at Beni
Hassan.
In Egypt, then, we must
acknowledge we find the first
rudiments of the arch; and
from that country it was brought
into Europe. The principle of
the arch, with all its voussoirs
radiating to a common centre, is
certainly shown to exist in many
buildings which modern travel-
lers have surveyed in Egypt.
The length of the tomb is
14 feet 9 inches, the breadth is
10 feet 5 inches, the height to
11
Fig. 32.
the springing of the arch is 19 feet 4 inches, and from the springing to the top of the arch
is 7 feet 8 inches. A tube of earthenware in a stone stopper had formed an opening
between the two apartments, and above it another, with a similar stopper in the arch, for
the purposes of ventilation.
The Pyramids of Middle and Lower Egypt are thirty-nine in number: they are situated
on the western side of the river, on desert hills, which form the western boundary of the
Nile. They are comprised within 29° 16′ 56″ and 30° 2′ 30″ north latitude, or a space
equal to about 53 English miles.
Pyramid of Abou Roash is situated five miles to the north-west of those at Gizeh. The
base, which is all that remains, is 320 feet square. The mass, formed of hard chalk, of
which the mountain is composed, has been cut into the form: this was cased with hard
stone, none of which remains. There is an inclined entrance passage, and an apartment
lying east and west, cut out of the solid chalk, and lined with fine calcareous stone from the
Tourah quarries. The passage inclines at an angle of 22º 35′, and is about 160 feet in length.
The chamber is 40 feet by 15, above which was apparently another.
The level space
around the pyramid is about 510 feet above the plain: the northern side has been sloped
away, and an inclined causeway, 4950 feet in length, and 30 in breadth, leads into the plain
below this causeway is in some parts nearly 40 feet in height, and walled with masonry.
Pyramid of Zowyet el Arrian has its base about 300 feet square, and in height its remains
are 61 feet above the rock: the material with which it is built is a hard limestone, in
which are many fossil shells: the blocks

were not squared, nor were they laid in
-
regular courses, clay or loam being used
instead of mortar.
Pyramid of Reegah is situated about
three quarters of a mile north-west from
those of Abouseir; its base measures 123
feet 4 inches square. This pyramid had
two inclinations given to it: the lower
was at an angle of 75° 20′, and the upper,
covered with calcareous stone, an angle
of 52°.
Pyramids of Abouseir are three in
three in
number: they are about seven miles
S. S. E. of those at Gizeh, and three
miles N. N. E. of Saccara. The material
with which they are built is the stone
ound upon the spot, laid in Nile earth
nstead of mortar. The exterior casing
of all of them has been removed. The
interior chambers and passages are similar
to all the others.
The northern pyramid was originally
257 feet square, and the perpendicular
height 162 feet 9 inches; the angle of the
casing being 51° 42′ 35″.
Fig. 33
C 4
་་་་་
24
Book I.
HISTORY OF ENGINEERING.
The passage descended at an angle of 27° 5' for 14 feet, and then went horizontally: at
the distance of 27 feet from the inclined plane, it had been closed by a granite portcullis
1 foot 3 inches in thickness.
The distance from the present entrance to the apartment was in length 71 feet 4 inches;
the apartment measured from north to south 11 feet 8 inches; the height at the sides
was 9 feet 4 inches, and in the centre 12 feet 6 inches. This apartment was in the centre of
the pyramid, and there had been three tiers of roof blocks, the footings of the upper rows
being carried beyond those of the lower, in order that the pressure should be more equally
distributed. These roof blocks were 35 feet in length, 12 feet thick, and 9 feet wide.
The middle Pyramid had for each side of its square base 274 feet, and its perpendicular height
171 feet 4 inches. Here was also an inclined passage and a portcullis; beyond which
a horizontal passage extended 63 feet in length, 5 feet 10 inches in height, and 5 feet 1 inch
in width. The width of the apartment at the end was 14 feet; the roof of which had
been formed of three tiers of blocks, 48 feet 6 inches in length.
Great Pyramid, which was on steps, covered with flat stones, the space between these
and the pyramidal casing being filled up with rubble. The lower parts of the casing, as
well as portions of the entrance passage, were of granite: the mortar in general was formed
of Nile earth, with a small proportion of lime.
•
Its base originally measured 359 feet 9 inches, and perpendicular height 227 feet 10 inches.
The entrance passage inclined 26° 3'; and where it was continued horizontally, it was
constructed of large blocks of Tourah stone, with a roof of inclined stones.
The apartment
was covered with a pointed roof, of three courses of blocks, 45 feet in length.
Small Pyramid, originally measured at its base 75 feet 5 inches on each side: the apart-
ment within was in length, from east to west, 12 feet 2 inches; from north to south 10
feet 6 inches, and in height 8 feet 7 inches. At the south-eastern corner was a recess, 5
feet 1 inch in breadth, and 3 feet 5 inches in depth. The horizontal passage was in length
14 feet, in height 8 feet 7 inches, and in breadth 2 feet 5 inches.
The inclined passage
was 27 feet in length, and 2 feet 10 inches in breadth; the angle being 22° 10′.
Pyramids of Saccara.-The first, much decayed, is a mass of ruins; its present base
measures on each side 210 feet, and its height 59, the platform at the top being about 50
feet square.
The second Pyramid is built with large unsquared stones; the length of the side of the
original base is 231 feet 3 inches, its height 146 feet 6 inches. The angle of the inclined
passage is 26° 35′, and its length 78 feet 9 inches. The horizontal passage to the portcullis
is in length 31 feet 3 inches; the thickness of the portcullis is 2 feet 3 inches, and from
thence to the chamber 26 feet 9 inches, making the total length 60 feet 3 inches: its width is
4 feet 2 inches, and height 6 feet 1 inch. The two principal apartments have pointed roofs,
and are lined with calcareous stone. The outer apartment is in length, from east to west,
13 feet 7 inches, in breadth, from north to south, 10 feet 3 inches; the height at the sides is
10 feet 5 inches, and in the centre 14 feet 2 inches. The inner apartment is in length,
from east to west, 25 feet 7 inches, and in breadth, from north to south, 10 feet 3 inches.
The rooms at the side, one of which runs from east to west, is 18 feet in length and 8 feet
in width. Another, from north to south, is in length 34 feet, and in width 7 feet 3 inches.
The third or Great Pyramid, or that of degrees, stands about 91 feet above the level

---------
Fig. 34.
SACCARA.
CHAP. II.
25
EGYPTIAN.
was
of the plain; an
inclined way, by
which the stone
drawn up,
being cut in the
sides of the rock.
It differs from
most of the other
pyramids in its
construction, and
from its having
four entrances and
several chambers:
originally it had
on the exterior six
steps or truncated
pyramids diminish-
ing upwards. The
core or mass of
masonry is rubble,
enclosed by eleven
walls, each about 9
feet in thickness,
inclining inwards.
These walls are
built of rudely
squared stone, laid
on mortar made of
the gravel of the
desert and lime, or
of Nile earth.
The length of
the sides of the
original base from

1
Fig. 35.
SACCARA.
பட
north to south was 351 feet 2 inches, and from east to west, 393 feet 11 inches. The
total area was 15,372 square yards.
The plan of this pyramid indicates the passages and galleries which led to and from
the square sepulchral chamber, shown nearly in the centre; intricate as they now are,
they appear to have

been set around the
principal room at
regular distances,
whatever may have
been their level or
height, and the re-
gularity with which
the walls are built
with very
very coarse
material, shows
some advancement
in the knowledge
construction.
concrete
rubble employed
here is a very early
indication of the
of
The
or
use of artificial ce-
ments, which have
continued to be
adopted throughout
the civilised world
at all periods: the
due proportion of
lime and the other
compounds expe-
rience soon taught,
it being one of the
II I
Fig 36.
D
D
SACCARA,
ག་
properties of matter to mix only in definite quantities. The concrete of the pyramid
26
BOOK I.
HISTORY OF ENGINEERING.
of the Coliseum, and our feudal castles, differ only in the quality of the lime made use
of, some being so excellent, or so perfectly pure, as to unite with a greater quantity of
stone than the other.
The platform at the top measured originally, from north to south, 42 feet 10 inches, and
from east to west 85 feet 8 inches.
The height of the first step is 37 feet 8 inches; of the second, 35 feet 11 inches; the third,
34 feet 3 inches; the fourth, 32 feet 7 inches; the fifth, 30 feet 10 inches; the sixth, 29 feet
2 inches. The face of each story makes an angle with the horizon of 73° 30′.
At the distance of 52 feet from the pyramid, and 11 feet to the westward of the
centre, is the entrance by means of

a sunk pit; here commences a hori-
zontal passage, 120 feet in length;
this afterwards takes a winding di-
rection, and descends to the large
chamber. The general inclination
is 23° 20′, and the width of this pas-
sage is in the centre 3 feet 5 inches;
its length is 176 feet 5 inches; and
its entrance to the chamber is 7 feet
6 inches above the level of the floor.
There is another passage, 179 feet
6 inches in length, and in breadth
and height 4 feet 2 inches, excavated
out of the rock: this commences
at 5 feet to the eastward of the
northern front, at about 5 feet
distance from the building. This
passage communicates with a recess,
in the upper part of the western side
of the large chamber, where appa-
rently a wooden beam had been in-
troduced, to which a rope had
been suspended: this passage was
nearly straight and lying horizontal.
+
At a distance of 7 feet to the
eastward of the southern front was
another pit, 14 feet square; from
this proceeded a horizontal gallery
166 feet 3 inches long, 10 feet wide,
and 6 feet 4 inches high, with a
recess at the south-western angle of
the large chamber; this recess was
70 feet above the level of the cham-
ber. The whole of the passage was
cut out of the rock, and its covering
or roof was supported by a row of
22 columns, made of compact lime-
stone: these columns, which are
partly covered with hieroglyphics,
have been wedged up above and below with wood, to catch the bearing of the superin-
cumbent weight, to which most of them have yielded.
Fig. 37.
PLAN.
SACCARA.
The large chamber is excavated out of the rock: its western side is 25 feet 6 inches to
the eastward of the centre of the pyramid, from north to south; but it is immediately
under it from east to west. Its dimensions are 24 feet by 23; and its height was 77 fee
from the floor to the ceiling, which was found to have been formed of planks, supported by
a platform of timber, consisting of two principal beams, and cross bearers: one of these beams
remained in its situation, though broken in the middle.
The floor of the chamber was formed with blocks of granite, 10 feet long, 5 feet 4 inches
wide, and the same in height; its entrance was closed by a conical block of granite
(A, fig. 38.), weighing about 4 tons. The granite blocks which compose the floor of the
large chamber are in thickness about 4 feet, and supported on pillars of loose stone
wedged up with wood.
From the south-western angle of the large chamber a passage communicates with the
smaller rooms.
The first is 20 feet 6 inches from north to south, 5 feet 11 inch in width, and
6 feet 5 inches in height; the other is 18 feet 8 inches in length, from east to west, and of
the same width and height as the last.
The sides of these apartments were lined with calcareous stone, and ornamented with
bluish green porcelain; the ceiling and floor was the native rock, smoothed and plastered over
CHAP. II.
27
EGYPTIAN.
The several chambers and galleries which conducted to them were finished and decorated
in a similar manner to the
houses or palaces occupied
by the living, which were
usually coated with a fine
stucco within and with-
out, and ornamented with
devices by the painter.
In some of the tombs,
bronze pins have been no-
ticed in the floors, within
the openings, on which
the wooden doors turned
which shut in the several
chambers; sometimes
holes or mortices in the
pavement and stone lintel
above the opening are
discovered, in which the
pivot at the top and bot-
tom of the door was in-
serted. Many bolts and
bars, which secured the
openings, have also been
found, as have iron keys.
The floors not of stone
were covered with a
composition, and the
ceilings in many instances
exhibit remains of paint-

Fig. 38.
SACCARA.
A
ing; among the designs of some may be traced all that is admired in the ornaments of
Greece and Rome; the fret and other familiar forms are here first met with in all their
variety.
The fourth Pyramid has not been accurately measured, but it is about 220 feet square,
and the height 62 feet, the platform at top being 30 feet.
The fifth Pyramid is the only one entirely constructed with quarried stone, the others
being only cased with that material. The base measures 250 feet, and its height is 40 feet.
The sixth Pyramid measures at present at its base 270 feet, and in height, 80 feet.
The seventh Pyramid at its base is 140 feet.
The eighth 240 feet, and the ninth 245 feet: these have most of them causeways, and are
built on steps.
Pyramids of Dashoors are situated near the village of Mensheeh, and are about three
miles from Dashoors: they consist of two of brick, two of stone, and another, northern brick
Pyramid, is composed of crude bricks, and has been covered with stone from the Mokattam
quarries. This was supposed to have been that described by Herodotus, as built by Asychis,
the successor of Mycerinus.
Many of the stones which formed the casing were at their base 8 feet 3 inches in length,
6 feet in width, and 1 foot 11 inches thick; the ends being sloped with the inclination of
the pyramid they were not laid in regular courses, but in the manner termed polygonal;
several of them were held together by dovetail cramps, made of stone. The body of the
pyramid was built of bricks, which were about 16 inches in length, 8 inches in width, and from
4 to 5 inches thick: they were mostly composed of alluvial earth; some with less sand,
but containing a quantity of straw; and others made from a dark-coloured tenacious earth
without any straw: they were all laid in regular courses, occasionally crossed by others, the
interstices being filled up with dry sand.
The original base measured 350 feet, and the height 215 feet 6 inches, the angle at which
the casing was laid being 51° 20′ 25″. This pyramid has at present baffled all attempts at
discovering its chambers.
The northern stone Pyramid has its exterior casing, the lining of its passages, and chambers
of a white compact limestone, which was brought along the two causeways from the quarries,
lying in a westerly direction, or by two others which conduct to the Nile, where the stone
night have been brought from the opposite side of the river.
The original base measured 719 feet 5 inches, its perpendicular height 342 feet 7 inches,
and the angle of its casing 43° 36′ 11″.
The top was formed of one block of Arabian stone, which rested upon a course formed
of four others, 4 feet 9 inches in thickness: those immediately below averaged 2 feet in
thickness, and near the bottom 3 feet. and were all laid in regular horizontal courses,
23
Book I
HISTORY OF ENGINEERING.
豐
​and well built. The entrance has its centre 12 feet 6 inches to the eastward of the centre
of the northern front, and the bottom of it is 94 feet, higher than the base of the building.
Its
The passage is 3 feet 6 inches wide, 4 feet high, and inclines at an angle of 27° 56′.
original length was 205 feet 6 inches: the lower portion, and a horizontal passage, 24 feet
4 inches long, leads to the first chamber, which is 27 feet 6 inches in length from north to
south, and 12 feet from east to west, having its floor level with the base of the pyramid.
The four lower courses of the walls, to the height of 11 feet 84 inches, are perpendicular; over
these are eleven other courses, each of which overhangs the other nearly 6 inches; so that
the ceiling is only 14 inches in width: the two first courses, which project, are each 3 feet
in thickness, whilst the others are about 2 feet 6 inches: the height of this chamber is 40 feet
4 inches.
From the south-western corner of this chamber is a passage 10 feet 4 inches long, 3 feet
6 inches wide, and 4 feet 6 inches high, which leads to another similar chamber, at the end
of which, at the height of 25 feet 3 inches from the floor, is a passage running southward,
24 feet in length, to another chamber, 27 feet 3 inches long from east to west, and 13 feet
7 inches in breadth: the sides are perpendicular to the height of 12 feet, after which there
are fourteen courses overhanging each other; its total height being 48 feet.
Southern stone Pyramid is singular, from its having two inclinations: the mass or body
is formed of stone, and its casing appears to have been brought from the quarries of
Mokattam.
Its base measured 616 feet 8 inches, and its total present height is 320 feet.
The angle of the casing of the lower portion is 54° 14′ 46″, and that of the upper 42°
59′ 26″, the platform at the top being about 40 feet square.
There are two inclined passages: one has its entrance in the centre of the northern front,
about 35 feet perpendicularly above the base; the other at 44 feet, to the southward of
the centre of the western front, at a perpendicular height of 97 feet 8 inches above the
base.
The entrance from the western front of the pyramid was by a passage 222 feet 8 inches
long, and 3 feet 4 inches wide and high. At the end was a horizontal passage, 65 feet 6
inches in length, and in it were two portcullises: these were slipped down inclined planes


Fig. 39.
DASHOOR.
into their position to cover the opening of the passage: at the eastern end of the horizontal
passage was a chamber, 21 feet 6 inches long, 13 feet 6 inches wide, and 52 feet 6 inches high.
This pyramid was the only one that had its inclined passage from any other quarter than
the north.
Small Pyramid was built of roughly hewn blocks, and was cased with Mokattam stone.
Its base measured 181 feet, and its height 106 feet 9 inches; the angle of its casing being
50° 11′ 41″.
Southern brick Pyramid. The bricks contain a quantity of straw, pieces of broken pot-
tery and stone, and vary in size; they are in length from 13 to 15 inches, and in thick-
ness from 3 to 73 inches.
This pyramid had been cased with stone from the Mokattam quarries: its original
base measured 342 feet 6 inches; and its height, perpendicularly, 267 feet 4 inches, the
angle of its casing being 57° 20′ 2″.
The interior of these brick pyramids has not been examined.
Pyramids of Lisht. The northern at the base now measures 360 feet, and the southern
450 feet.
Pyramid of Meydoom has a base 530 feet square: it is built in three heights or degrees,
forming so many truncated pyramids, the angle being 74° 10′. The lower degree measures
at its base 199 feet, and is 69 feet 6 inches in height; the second is 127 feet, and 32 feet 6
inches high; the upper is about 22 feet 6 inches high.
The blocks are of a compact limestone, about 2 feet thick, laid at right angles, and well
CHAP. II.
29
EGYPTIAN.
put together; the whole being originally cased with others: it has not had its interior
described.


Pyramid of Illahoon is built round a knoll
of rock, which has been faced with crude
brick; the body of the pyramid being formed
of the same material, is supported by stone
walls, which cross the pyramid at its two
diagonals, and others proceeding out of
them, running parallel with the sides. The
bricks are laid in mortar, and measure 16
inches by 8 inches, and are 5 inches or more
in thickness: they are formed of Nile earth
and chopped straw The outer casing was
of stone, and the present base measures
360 feet, and height 130 feet.
The use of unburnt bricks was general
throughout Egypt, and their manufacture
gave employment to a great body of la-
bourers; this simple material, in our own
day, is often found more economical than
stone, quarried or obtained upon the spot;
gardens, and even inclosures to the temples
of the gods, in Egypt, were often surrounded
by walls of crude brick, merely baked in
the sun. The demand being at one period
so great for bricks, the government under-
took to manufacture them, and to supply
the public at a reasonable price; to do
this in a manner to improve the revenue,
the seal of the king or his authorised agent
was stamped upon them, and all persons
forbidden to engage in the manufacture.

Fig. 40.
ILLAHOON.
Pyramid of Howara is constructed of crude bricks, containing chopped straw: they measure
17½ inches by 83, and are 5½ inches thick, laid on a fine gravel: originally it was cased with
Its present base measures 300 feet, and its height 106 feet.
stone.
Southward of this pyramid are the ruins of an extensive labyrinth, as it is supposed.
Pyramids of Biahhmoo are five miles from Medeénet el Faioum: they consist of two masses,
about 30 feet by 22, and about 30 feet in height.
Pyramid of El Koofa, in latitude 25º 10', has its present base 59 feet 6 inches square :
there are 27 courses, built in three several degrees, 38 feet 6 inches in height above the
rock.
Ethiopia. The Island of Meroe, which is formed by the conflux of the Astapus and
Astaboras, according to Diodorus Siculus is in length 375 miles, and in width 125. It
is situated between the twelfth and eighteenth degrees of north latitude, and was long the
seat of empire of the kings of Ethiopia.
The Pyramids at Meroe, which at this day remain, are above 80 in number, and some of
them contain hieroglyphics and sculpture of no ordinary kind: they are all constructed of
red sandstone, from quarries in the neighbouring hills, which lie to the east of them: the
stone is of a soft quality, and of a brownish red tint, and the blocks, which are 2 feet 6
inches long, are laid in regular courses, a foot high.
These pyramids vary in dimension from 20 feet square to 63, and their height is about
the same as the length of their base; at the angles of some, instead of an arris, or sharp
edge, is a bold bead, and in many, at about 12 or 14 feet from the top, is a small window.
But the most singular part of their arrangement is that of having on their east sides a portico
36
BOOK 1.
HISTORY OF ENGINEERING.

کریں کیا کہوں
S
"
Fig. 41.
MEROE.
which contains a room varying in width from 11 feet 6 inches to 12 feet 6 inches; and in
some instances there are two rooms.
The height of these porches in some instances are 18 or 19 feet, and they bear, with their
doorway, 3 feet wide, a strong resemblance to the Egyptian propylon.
Above the doorway is an architrave, over which is a square fillet, and then a bold carved
cornice, ornamented with a winged globe.
One of the best proportioned of these propylons or entrances has the doorway 11 feet
6 inches high, and to the top of the cornice, 14 feet. On each side the wall slightly battered.
At the bottom they measure 7 feet 6 inches in width, and at the top 7 feet.
These porticoes do not much vary in dimensions, although the pyramids to which they
are applied differ.
These pyramids do not appear to contain any passages or rooms, and they are all probably
constructed over wells, in which the dead were deposited.
One of the porches is arched, and consists of four or five stones constructed in a regu-
lar manner, said to be of the highest antiquity. It is stated to be the earliest known,

Fig. 42.
MEROE.
CHAP. 11.
EGYPTIAN.
31
and that in all probability the Egyptians derived their knowledge of this kind of con-
struction from the Ethiopians. Diodorus Siculus informs us that it was from them the
Egyptians learned to honour their kings as gods, to bury their dead with so much pomp,
and also that from them they received their instruction in sculpture as well as in hierogly-
phical representations; that the Egyptians were a colony drawn out by Osiris, after Egypt
was formed by the deposit of the Nile; that the Egyptian laws were the same as those
of Ethiopia, &c. —Lib. iii. cap. 1.
At Gibel el Berkel, three and a half miles east of the small town of Meroe, and about
5200 feet from the Nile, are several remains, among which are those of a fine temple,
said to have been built by Tirhakah, who was the Ethiopian king that assisted Hezekiah
MA

Fig. 43.
GIBEL EL BIRKEL.
when he was at war with Sennacherib, king of Assyria. These several temples are of con-
siderable dimensions, and agree in their architecture and sculpture with what is found in
Egypt.
On the western side of the mountain, from whence the stone was taken for the building
of these several temples, remain seventeen pyramids, which were the burial-places of a
dynasty of unknown kings: they resemble those of Meroe. They vary in height from 35
to 60 feet, and usually consist of from 30 to 60 steps, which recede about 6 inches, so that
they form convenient means to mount to the top.

Fig. 44.
A
GIBEL EL BIRKEL.
Pyramids of Nouri. There are traces of thirty-five, fifteen of which are in tolerable
preservation. They vary in dimension from 20 to 110 feet square. Eight of them are 80
feet square, and four 70; their height is usually as much as the length of their side.
The largest is built up in three stages, and the interior of most of them seem composed of
a conglomerate, or puddingstone, and the casing generally of soft sandstone.
The pyramidal form seems to have been generally adopted by the Egyptians and Ethio-
pians, who considered their palaces only as inns where they tarried for a day, but inade
their sepulchres habitations of rest for ages: there are no such remains in Greece; yet we
find them in Etruria. According to Pliny, the Etruscans built the tomb of Porsenna in
this form, or rather it had five small pyramids. At Rome, the monument of Caius Cestius
is pyramidal, and constructed of marble: its base measures 96 feet, and height 121 feet.
Caius Cestius, who is supposed to have died when Agrippa was consul, was descended from
a noble family, and appointed one of the epulones to prepare the banquets for the gods, at
$2
HISTORY OF ENGINEERING.
BOOK I.
the ceremonies of the lectisternium, so frequently mentioned by Livy the historian.. From
the peculiar form of this monument, and its being the only one at Rome of the kind, we
RIMA.
D-DILDO @
should almost fancy that it had been derived from
some of those in Nubia, with which it so ex-
actly corresponds in arrangement and dimension.
Had Caius Cestius held office under the Roman
general Petronius, in his expedition against
Queen Candace, when he penetrated into Ethiopia,
and took the towns of Pselchis, Premmis, and
Napata, about twenty years before the birth of
Christ, we should have supposed that he had been
struck with the respect paid to the dead in some
of their necropoli, and selected the same form for
his own place of sepulture. In the interesting


ㅁ
​Fig. 45.
Fig. 46.
travels of G. A. Hoskins into Ethiopia, is the description of an elliptical brick arch (fig. 46.),
which he discovered in a tomb at Thebes, situated near the valley of the sepulchre of the
queens. The roof or ceiling was painted upon a plaster ground, and along the centre
was a line of hieroglyphics, which contained the name of Amunoph I., which proves the
existence of the arch in that part of Egypt fifteen centuries and a half before the Christian
Its span is 8 feet 6, and its rise 3 feet 4 inches.
era.
Another brick arch is also described on the road from the Memnonium to the valley of
the Hassaseef, in a small tomb, which is also vaulted.
This has a lower arch of brick resting on a shelf cut on each side of the native rock: the
access to this tomb is through a hole in the ceiling from the floor of another tomb above it,
where the construction of the arch is seen. The whole is covered with plaster, and on
the jambs of the recess are inscribed the titles and prænomen of Thothmes III., Sun, Esta-
blisher of the World, fifth king of the eighteenth dynasty, who reigned fifteen centuries
before Christ.
In the pyramid at Gibel el Berkel is a semicircular arch, the key-stone of which is
1 foot 9 inches in length.
The only stone arch said by Mr. Hoskins to be met with in Egypt is at North Der, at
Thebes. The vaulted tomb at Memphis is of the time of Psammeticus, who reigned im-
mediately after the Ethiopian dynasty; and it is inferred that the Egyptians learned the
use of the arch from the Ethiopians.
Alexandria. — This ancient port was improved by Alexander the Great, after his success
against Tyre, and, according to the historian Gibbon, the undertaking was as noble as
any ever executed by the son of Philip. Having journeyed through Egypt, and observed
the highly productive state of the country, and that it was watered by one of the largest
rivers of the world, which discharged itself by seven mouths into the Mediterranean Sea, he
imagined that its only want was a convenient haven. Pelusium, at the eastern mouth of
the Nile, was not capable of improvement. Canopus, on the eastern side of the western
mouth, was still more inconvenient, although it had a landing-place for ships.
Alexander, who was liberal and magnificent, found among his countrymen engineers
qualified to second his bold ideas, and he had, what is a rare quality among princes, the
talent to select the best fitted to execute them. On this occasion he appointed Dinocrates
his architect and engineer, ho had already acquired great celebrity in the construction
of the temple at Ephesus, dedicated to Diana.
CHAP. II.
$3
EGYPTIAN.
The site selected for the new city was on the western side of the Nile, between the
river and the lake Mareotis,—for which nature had done much, and which seemed
capable of being made by art all that was desirable; and an opportunity was afforded
to humble the Tyrians, to divert that commerce which they had long enjoyed; to
change the current of the Indian trade by Suez, the Nile, and its canal, to the new city of
Alexandria.
In the midst of the capacious bay on the shores of which the city was marked out, and at
some distance from the mainland, lay the island of Pharos, which acted as a natural
breakwater, and which, in the time of Strabo, was of an oblong form; this Dinocrates united
with the mainland by an extensive causeway, or earth wall, and, from its length being
7 stadia, it was called the heptastadium. This grand terrace divided the bay into two
harbours, which communicated with each other by means of two openings left for vessels to
pass from one to the other.

Fig. 47
ALEXANDRIA.
The city was marked out with great regularity: its form was that of a Macedonian
mantie or cloak, and three hundred and twenty years before Christ the walls were con--
D
94
Book I.
HISTORY OF ENGINEERING.
siderably advanced. All the streets were set out at right angles with each other, and more
than a third of the area comprised within the walls was devoted to public purposes.
Every private dwelling had its reservoir of water provided for it, which was supplied by
subterranean conduits from the Nile; all built of stone, with flat terraces at the top,
which answered for their covering, timber being sparingly used in the construction. The
cisterns and conduits were lined with a fine cement, which remains perfect at the
present day.
To render the harbour approachable at all times, a lighthouse was built on a rock some
distance from the eastern extremity of the Isle of Pharos, which was long considered
one of the wonders of the world, and which has given a name to all others. A mole united
the rock with the mainland, and Sostratus of Cnidos, who was so esteemed by Ptolemy
Philadelphus that he was surnamed the friend of kings, was the engineer employed
for its construction. This pharos was in height 450 feet, and could be seen at a distance
of 100 miles. It was formed of several stories, decreasing in dimension towards the top,
where fires were lighted in a species of lantern. The ground-floor was hexagonal; the
sides alternately concave and convex; each a stadium in length; the second and third
stories were of the same form: the fourth was square, with a round tower at each
angle; and the fifth circular, continued to the top, to which a winding staircase
conducted.
The whole, exquisitely wrought in stone, was surrounded entirely by a sea-wall: on
entering the harbour, this wonderful structure was on the right hand, and the pro-
montory of Lochias to the left, where was placed the palace or royal residence, near which
was the island, called Antirhodus, which contained a small harbour, devoted entirely to
the reception of the royal vessels. The ancient causeway now forms the site of part of the
modern town, and is in length about 4000 feet; on the easternmost side is the great har-
bour, and on the western that of Eunostus, or, as it is now called, the ancient port. Here
is a basin or kibotus, which by means of a canal communicates with the Lake Mareotis,
the dimensions of which Strabo says were 300 stadia in length, 100 in breadth, and that
it contained 8 islands.
Alexandria was second in importance only to Rome itself: its circumference was 15 miles,
and its population estimated at 300,000 free inhabitants, besides an equal number of slaves
and dependents. In its streets idleness was unknown: some were employed in blowing
glass, in weaving linen, and manufacturing papyrus.
When Cæsar arrived at Alexandria, he sent to Rhodes, Syria, and Cilicia for his fleet;
and upon reconnoitring the town, he found all the avenues and passes shut up by a triple
wall, 40 feet in height, built of squared stone. The lower portions of the city were de
fended by lofty towers, ten stories in height. There were many timber structures of the
same height, movable on wheels, which could be drawn by horses. We also learn that
he found Alexandria almost hollow underneath, from the many aqueducts that furnished
the private houses with water from the Nile, where, being received into cisterns, it was
allowed to throw down the earthy matter, and become perfectly clear. Ganymed, the
Alexandrian general, to deprive the Romans of a supply in that part of the city of which
they had taken possession, stopped the current through these subterraneous passages
which led from the Nile, and turned salt-water into them, which caused great wonder as
well as inconvenience to the Romans. Cæsar, on the discovery, ordered his soldiers to find
water by digging wells, telling them that on all sea-coasts fresh springs abounded; and the
alacrity used was so great, that they arrived at fresh water in abundance the first night
after the digging commenced.
Smelting and refining metals. The Egyptians began this process by pounding their
golden ore, and reducing it to very small grains; they then put it into a mill, and ground
it to powder; after which it was spread on boards slightly inclined: water was then made
to flow over it, which carried away the earthy particles. After the watering had been
frequently repeated, it was rubbed by the workmen for some time between their
hands, and wiped with small sponges, until nothing was left but the gold. It was then
put into earthen pots, and mixed with certain proportions of lead, salt, tin, and barley meal:
after this it was poured into other vessels, which were luted with great care and placed in a
refining furnace for five days and nights; these were then taken out and suffered to cool,
when the gold was found to be quite pure. They do not appear, according to Pliny, to
have used quicksilver, for the refining of either gold or silver: lead was the menstruum,
and by frequent meltings the pure metal was obtained. The great quantity of gold used by
this people convinces us that the art of mining, smelting, and refining that metal was well
understood.
Forging metals was known in Egypt at the earliest time; most of the arms, tools for
husbandry and the mechanical arts, were usually made of copper or brass, though in the
time of Moses we find iron well known. He describes its hardness, speaks of mines, and
mentions the iron furnaces, and tools for cutting stone, made of iron.
Hydraulics. In the school of Alexandria, which flourished under the patronage of the
CHAP. II.
35
EGYPTIAN.
Ptolemies, the first machines for the purpose of raising water seem to have been in-
vented. After Hippocrates had constructed tables which showed the exact motion of the
sun, Clepsydræ, or water-dials, were brought to great perfection by Scipio Nasica, the
cousin of Scipio Africanus, who about two hundred years before Christ introduced them
into Rome.
Ctesibius, who flourished in the reign of Ptolemy Physcus, an hundred and twenty years
before Christ, brought these machines into very general use, and invented the hydraulic
organ, which was operated upon by air and water. In the clepsydra he introduced,
probably for the first time, toothed wheels: this instrument for the measurement of the
hours was a cylinder resting upon a pedestal; two figures were placed upon the latter,
one of which dropped water from its eyes, whilst the other pointed with a wand to
the hour marked on a vertical line drawn upon the cylinder. This cylinder turned on
its axis once a year, and on it were drawn curved lines, which exhibited the inequality
of the hours on different days, by their being marked at unequal distances.
The manner of working this machine was to allow the water to rise through a tube,
which, passing through one figure, was discharged by the eyes, into a reservoir, M, from
which it passes by a hole near m, into the pipe B, C, D. In this pipe a piece of wood


A
B
Fig. 48.
A
L
B
M
E
D
SECTION.
K
ELEVATION.
floated upon the surface, and by its ascent, as the pipe filled, it raised the small pillar C, D,
on which the other figure rested, and as the float rose in the pipe the wand was made
to point to the different hours. Every twenty-four hours the vessel became filled, as
did the inverted siphon, which communicated with it. The water was then drawn off
by the siphon, and falling in its descent into the buckets of the wheel below, put that into
motion. This wheel had six buckets, and therefore made one revolution every six days.
Its axis carried a pinion of six teeth, working on another wheel of sixty teeth: this
also carried another pinion of ten teeth, and drove a wheel of sixty-one teeth, which by
its axis turned the pillar once round in 366 days.
These machines indicate considerable hydrodynamical knowledge, and derive their
origin from the previous discoveries of Archimedes.
Another clepsydra received the water in a reservoir, which was always kept full, and
descended by a pipe into a hole formed in the great drum. This hole corresponded to
one of the openings in the groove round the circumference of the small drum.
The aper-
tures of the groove in the small drum were of different sizes, to admit different quantities
of water, according to the length of the day; and the proper aperture for the given day
was found by placing the index opposite the sun's place on the zodiac, shown at N, the
index O being used for the night hours. The water which descended through the open-
ings in the small drum was conveyed by the pipe F, through the aperture at G into the
reservoir H. As the water rose in the reservoir, the inverted vessel, suspended by a chain,
which passed round the axis R, and balanced by the counterweight, ascended and moved
the hour hand, which pointed to the dial plate.
D 2
36
HISTORY OF ENGINEERING.
BOOK I.
Hero, the disciple of Ctesibius, wrote a treatise on mechanics, wherein was described at
length the various mechanical powers, which were all reduced to the lever; he left also
another work, called Spiritalia, in which is an account of the forcing pump, which raises
water by the elasticity of the air, and was probably suggested by the Egyptian noria,
a contrivance in which a number of earthen pots were attached to the periphery of
a wheel for the same purpose.
The Great Wall of crude brick, built by Sesostris, on the east side of Egypt, to defend it
against the irruptions of the Syrians and Arabians, extended from Pelusium along the edge
of the desert by Heliopolis, for 1500 stadia, or about 187 Roman miles.
Amasis, who was a great promoter of the arts, erected at Sais a magnificent propylæum,
in honour of Minerva, where stones of prodigious magnitude were used in the construction;
Herodotus says these stones, of amazing thickness, were brought from the quarries of
Memphis, and part from the city of Elephantine, which is distant from Sais a twenty-five
days' journey; but that, in his opinion, the work most to be admired was an edifice which
Amasis brought from Elephantine, constructed of one entire stone. To transport this, 2000
men, all of whom were selected from the sailors, were employed for a period of three years.
The length of this structure on the outside was 21 cubits, its width 14, and its
height 8. Its length inside was 22 cubits and 20 digits, 12 cubits wide, and 5 high.
It was placed at the entrance of the temple, and the reason assigned for its being carried
no further was, that the architect, in consequence of his continual fatigue, was heard to sigh
by Amasis, who, construing it into an evil omen, obliged them to desist. Some affirm,
however, that one of those employed to move it by levers was crushed, for which
reason it was moved no further. This resembled probably the red granite monolith at
Tel-et-mai, which measures in height 21 feet 9 inches, 13 feet in breadth, and 11 feet
7 inches in depth, outsitle; and 10 feet 9 inches, 8 feet, and 8 feet 3 inches, inside.
At Memphis, a colossal recumbent figure, 75 feet long, was, according to Strabo, placed
before the dromos of the temple by this king, as were also masses of granite, 20 feet in
height. At Thebes and other places, as well as the quarries at Syene, are numerous
inscriptions, which indicate the removal of granite blocks of enormous weight, for
the decoration of edifices raised by this prince.
Quarries in Egypt. The granite was obtained from Syene, which is a district reaching
from the island of Philæ, along the whole line of the cataracts; that of the finest quality
is obtained on the banks of the river.
The beautiful pink or rose-coloured granite, the syenite of the ancients, is very hard,
and composed of large crystals, which receive an excellent polish. Two thirds of the
mass is rose-coloured feldspath; sparkling mica and glassy quartz fill up the intermediate
spaces, mixed with hornblende occasionally. Pliny sometimes designates obelisks made of
this granite as Thebaicus lapis, because it came from the region between Thebes and Syene,
Another granite, more resembling that of the ordinary kind, is found contiguous to it,
with particles occasionally much coarser or finer. To these may be added, the fine-
grained granite; the grey, with grey-coloured feldspath; black and white granite,
which has white feldspath with black flakes of mica, and oriental basalt; and a very
dark kind, which is owing to the abundance of mica.
The sandstone quarries of Hadjar Selseleh furnished the chief part of the building stone
for the temples: they are situated in the sandstone district, and, according to some, the
stone resembles the grès de Fontainebleau. When first taken from the quarry it is easily
worked, and may be obtained in lengths of 30 feet or more.
We find stone quarries of great extent on the borders of the valley of the Nile.
Limestone was generally employed in all the early buildings; and quarries, from whence
large quantities were taken, may be seen at Masaralı, where there are tablets remaining,
cut in the time of Ames or Amasis, the leader of the eighteenth dynasty, who ascended
the throne about 1500 years before Christ; and from these quarries all the compact
magnesian limestone used in the construction of the pyramids of Gizeh was taken. There
are other quarries at Téhneh, on the point of a hill, where is a thin deposit of crystallized
carbonate of lime; numerous nautili are found imbedded in the limestone, some of
which are more than 6 inches in diameter.
In examining these excavations, we obtain some knowledge of the early Egyptian
practice of detaching masses of stone, and also a valuable lesson on the saving of both
material and labour. To the Egyptians the difficulty of onstructing a pyramid was scarcely
more than the removal of stone from the quarry, and building it up in the manner in which
it lay previous to its being detached from the original bed; the only difference was, that
the top stones of the quarry became the foundation stones of the pyramid: they were taken
away in layers, all of the same thickness, and built in courses; and as the work proceeded
the quarry might represent as many steps from bottom to top as the pyramid. The stone
was sure to lie the right way of its bed; and it would be scarcely necessary to mark an
oblong stone, after it was detached; its depth being uniform with the others, would
indicate sufficiently its true position.
CHAP. II.
37
EGYPTIAN.

QUARRIES CONTAIN
ENCHORIAL WRITING
IN RED OCHRE
Fig. 49.
BLANK.TABLETS
QUARRIES SUPPOSED ENCHORIAL WRITING,
OF PYRAMIDS
ON ROOF
RAILWAY
MASSARA QUARRIES.
TABLET. OF CLEOPATRA.
TABLET. OF PTOLEMY SOTER
SMALL TABLET
CARTOUCHE
SUPPOSED OF PAVEMENTS
QUARRIES
It was
;
The manner in which a quarry was worked is deserving of our attention.
commenced by levelling the surface of the rock and marking out a square area of sufficient
dimensions to afford the quantity of stone required; around this was cut a deep trench
at parallel distances, 7 or 8 feet apart, according to the size of the stones, other
parallel trenches were made, and then similar lines at right angles, dividing the whole
into as many squares.
After this the blocks were cut to their required thickness: layer
after layer was thus removed, according to the depth of the quarry, or as long as it yielded
good stone.
At other times, after the square was marked out on the top of the intended quarry,
which was usually selected on the side of a hill, or where its face was perpendicular to the
plain below, an horizontal trench was driven through the middle of the square, and then
the masses of rock were detached on each side of this first groove; and as each layer was
removed, new trenches were cut, until the whole assumed the character of a series of steps
on each side of the centre, which rose from the bottom to the top of the quarry,
The same machinery which lifted the stones from
resembling the form of a pyramid.
their beds or steps answered to elevate them to their new position.
Limestone continued in use for many years, after which a fine sandstone was employed,
which was discovered to be of far greater durability. The quarries of Silsilis are extensive,
and situated between Edfoo and Gébel Silsileh. From them most of the sandstone was
obtained which was used in the Egyptian temples and other public buildings.
Tourah and Mussara Stone Quarries — The Troici Lapidis Mons. The Pasha has here a
railroad for conveying stone to the river, which is then transported to Cairo, a distance of
between six and seven miles. These quarries supplied the stone to many of the pyramids and
temples, and afforded employment to a vast number of men. On a range of sand hills, on
the edge of the Desert, which extends the whole length of the quarries, was discovered up-
wards of 150 sarcophagi, made of compact limestone, which no doubt contained the bodies
of those employed in extracting the stone. One sarcophagus was formed of earthenware in
a single piece, having a lid of the same material. Many skeletons without coffins or
sarcophagi were also found these bodies appear to have been interred in their clothes, or
wrappers of coarse woollen cloth. There were also heads of oxen, with the horns, and
several hundred coffins, and many tombs covered with slabs of calcareous stone, where
the bodies were preserved in bitumen, and the coffin not made use of.
Among the
several articles within them was the model of a pyramid in calcareous stone, 26 inches
square at the base, and of the same height; also two pieces of bronze, which resembled the
heads of hatchets. There were several inscriptions to the local divinities, put up when
fresh work was commenced in the quarties, the earliest supposed to refer to the reign of
Amonemhe IV. : another to the time of Necho.
:
At the Tourah quarry is a tablet, dedicated to the Son of the Sun, Amonemhe, beloved
of Phtah, the rampart of the south, and of Anubis: the opening of the quarries is also
alluded to, and orders given for the cutting the good and white stone, which is calcareous,
for the temples of the gods. Some of the tablets are in the form of a propylæon, having the
hieroglyphic inscription on the lintels: one refers to Amenophis II., and has been inter-
preted as commanding the opening of the quarries to draw the good and white stone for
the repairs of the temples for a series of years; the whole apparently being under the direct
superintendence of a military chief, "attached to the heart of the king, for his knowledge
and skill in architecture, one who had adorned the temples in Mesopotamia and in Libya,
and was put over the Bearers of Egypt, of all the gods of the north and of the south.”
Libya and Mesopotamia are said by M. Champollion to have been conquered by Ame-
noph II., or by his predecessors. These tablets are signed by the royal scribe, Saph, the
architect or surveyor engaged to design the public buildings.
Another of these tablets refers to Amenoph III., or Memnon, who is seen offering a
symbolic cye in a basket which he holds in both hands. In the hieroglyphic inscription, he is
D 3
&
33
BOOK 1.
HISTORY OF ENGINEERING.
termed, the "Establisher of the Houses of Stone;" and he orders the opening of the quarries
to procure good and white stone.
In the Massara quarries, which were worked from north to south, are tablets referring
to Amasis, Psammeticus II., and to some of the Ptolemies. Beneath one of the hierogly-
phic inscriptions of Amasis and his wife Nofreareh, is represented a block of stone drawn
by six oxen on a sledge, attended by three men: and the interpretation of the writing is, that
the quarries were opened in the forty-third year of Amonemhe, were again worked in the
twenty-second of Amasis, when the temples of Phtah, and of Amon in Thebes, were built,
the kings of the sixteenth and seventeenth dynasties at that time having their capital at
Abydos. These tablets allude also to Thebes, which superseded Memphis as the capital
after the kings of Egypt had grown more powerful. There are other tablets of the time of
Ptolemy Philadelphus. The quarries at Silsilis are of vast extent, and masses of any di-
mensions might be hewn from them. When a quarry was opened, if the stone could not be
drawn from the perpendicular face, they drove a horizontal shaft into it, at the level which
would afford them the quality they required. They then worked the masses in horizontal
steps, which they made of the necessary depth and width, and in quarries of considerable
extent they left pillars at intervals to support the superincumbent earth. The stone, after it
was quarried, was placed on sledges, and drawn by men or by oxen. Inclined planes were
often used to facilitate its movement. Many instances may be found of a private mark
on the stones, which indicated the number, drawn by the slaves employed for this purpose.
In a grotto between Antinoë and El Bersheh is a painting, where a colossal statue
is moved by a number of men dragging ropes. This painting is a very early pro-
duction, and shows the method employed at that time for moving great masses.
in four rows of forty-three each, pull the ropes attached to the front of the sledge, on
which the statue, a seated figure, is placed. On the knees of the figure stands a man,
directing them to move together, and to pull uniformly. The statue is secured to the
wooden sledge by ropes: these are doubled, and further tightened by the insertion of long pegs,
which were twisted round, and made perfectly secure. Some of the obelisks, brought
from the quarries of Syene to Thebes and Heliopolis, a distance of 800 iniles, are of a single
stone, varying in size from 70 to 93 feet in length, and one of the largest at the great temple
at Karnack has been calculated to weigh upwards of 297 tons, and must have been brought
about 138 miles.
172 men,
In the plain of Qoorneh there are two colossi of Amunoph III., each of a single
block, and 47 feet in height, containing 11,500 cubic feet. At the Memnonium is another
of Remeses II., which, when entire, weighed 887 tons, and which, from the nature of the
stone, was probably brought 138 miles.
The shrine of the goddess Latona, at the Sebennitic mouth of the Nile, in the large city
of Butos, astonished Herodotus, who says that it was 40 cubits or 60 feet in height, breadth,
and thickness, and was cut out of one single stone: after it was hollowed out a stone
4 cubits in thickness formed its roof. The internal dimensions, or the thickness of the walls,
are not given; but if of granite, as those monolithic temples were, the weight must have
been some thousands of tons.
Obelisks, in their removal, required skill and strength; but to elevate them, considerable
knowledge of mechanics must have been brought into application. They are often raised to
a great height, and placed, with the utmost precision, in a perfectly perpendicular position.
Some very large blocks of sandstone, and particularly one which forms the lintel to the
gateway leading to the grand hall at Karnack, is 5 feet two inches square, and 40 feet
10 inches in length; and it seems difficult to understand by what means it was lifted to its
present position; but the Egyptians were learned in the mechanical arts, and were evidently
as capable of raising weights as we are at the present day. In one of the quarries at Syene
there remains a broken obelisk, where it was separated from the rock, and the depth of the
quarry is so small, and the entrance so narrow, that the stone could not be turned 1ound;
it must have been lifted up from its bed, as was the case with all the shafts hewn out of
this quarry.
One of these obelisks, 99 feet in height, and on which 20,000 workmen were employed,
was raised by Rameses. Pliny mentions the method usually adopted to float these
masses from the quarries down the river. Two flat-bottomed boats were lashed together, side
by side, and then had a trench cut for them into the Nile. They were laden at first with as
much ballast as equalled the weight of the obelisk to be transported; when they were
introduced under the weight, the ballast was taken out, and the boats rising as they were
lightened, bore the obelisk in lieu of it.
These large masses of granite may have been detached from their beds in the same
manner as is still practised in the East, where, after cutting a groove in the stone through-
out the entire length, a fire is made upon the rock, which, when sufficiently heated, the
burning ashes are swept suddenly off, and water as cold as it can be obtained is then
poured simultaneously by a number of individuals into the groove, and a clean fracture
takes place throughout the whole line.
CHAP. II.
EGYPTIAN.
39
Another method was, after the groove had been cut, to bore on the line small perpen-
dicular holes, 18 inches or 2 feet apart, into which were introduced as many chisels:
these were beat from one end of the line to the other by a number of men for two or three days
together, when the mass detached itself with a clean fracture, and ropes were afterwards
used to remove the piece so detached.
Metal wedges were sometimes applied to separate large blocks from the quarries, which
were struck simultaneously throughout the line of the intended fracture; and often wooden
wedges in a dry state were introduced into holes made to receive them, when they were
saturated with water, and by their expansion a force was obtained which split off the granite.
Quarries of oriental alabaster are found in the Desert, where, at a latitude of about 28°
40', the mountains which continue to Abyssinia are formed of Egyptian porphyry, various
granites, serpentines, and other primitive rocks; but in the valleys running into the Wadee
Moathil, the oriental alabaster is found among the mountains composed of limestone.
In the division of Ababdeh they obtained the green breschia, slate, micacious, taliose,
and other schists. Near the coast, a short distance from the sea, is another ridge of lime-
stone hills, among which rises Ghareb, a lofty peak of granite, the summit of which is
6000 feet above the level of the sea.
The porphyry quarries that supplied Rome are twenty-seven miles from the Red Sea, near
Gebel e Dokhan, and about twenty-four miles to the south-east are the granite quarries which
were worked in the time of Trajan.
Obelisks, or single blocks of stone. The largest are formed out of the red granite of Syene :
they are at the base of a quadrilateral form, diminishing gradually to the top, which is
finished by a small pyramid: their opposite sides are equal, but vary at times a few inches
in dimension.
These obelisks in their original situation were placed in pairs, one on each side of the
propyla, or entrance to the temple, or in front of the gateways.
At Alexandria are two of red granite, one of which, called Cleopatra's needle, is erect.
They probably decorated the entrance of either a temple or a palace, as Pliny mentions that
was their position. They are 65 feet in height, and about 8 feet wide at the base, and the
weight of one has been calculated at 284 tons. They were of the time of Remeses the Great.
At Luxor, obelisks 80 feet in height are found, generally on the site of most of
the ancient cities, lying on the ground. Such mark the position of Tanis, the Zoan of
antiquity, and of Heliopolis: there are others at Medinet el Faioum, at Axum in
Abyssinia, at Jebel Barkal in Arabia Petræa, and several other places.
At Arles in France there is an obelisk; and at Constantinople are several, of the granite
of Syene.
Obelisks at Rome. Most, and perhaps the whole, of the twelve were taken from Egypt by
Augustus, or the emperors who immediately succeeded him. After having been thrown
down by the enemies of the Imperial City, many of them were again mounted on pedestals,
either by Popes Sixtus V. or Pius VI.
That of St. John Lateran is the most lofty, and the same erected in the Circus Maximus
by the emperor Constantius. It was broken into three pieces, and before it could be again
set up, it was necessary to cut off from the larger end between 2 and 3 feet, so that the
length of the shaft is abridged of that quantity, and now only measures 105 feet 6 inches.
The breadth of the sides is not equal, two being 9 feet 8 inches, and the others 9 feet
only. The circumference at the base is 37 feet 6 inches, and at the top 24 feet 10 inches.
Its solid contents have been estimated at 5960 cubic feet; and as it is composed of red
Egyptian granite, its weight is about 440 tons, or a little more.
It is covered with figures, and originally stood at Heliopolis, from whence it was re-
moved to Alexandria by the father of Constantius; from which place it was taken to
Rome, on a vessel constructed for the express purpose, moved by 300 rowers; and
Ammianus Marcellinus tells us that when it arrived at the banks of the Tiber it was passed
through the gate of Ostia, and the piscinam publicam, on rollers. After its arrival at
Rome a forest of timber was employed for a scaffolding, and by the aid of 1000 men and
much tackle it was suspended in the air, and finally placed on its pedestal. This obelisk
was again raised by Fontana, in the year 1588.
The Vatican obelisk, in front of St. Peter's, in the year 1586 was moved by Fontana, from
the Vatican circus, where it had been placed by the Romans, and dedicated to Augustus
and Tiberius. It is without hieroglyphics, and still entire, being 83 feet 2 inches in height,
each side of the base 8 feet 10 inches, and at the top 5 feet 11 inches. According to Pliny, it
was cut by Nuncoreus, the son of Sesostris, by Herodotus called Pheros, and who is said to
have erected two obelisks, each 100 cubits in height.
Santa Maria Maggiore obelisk, broken into three or more pieces, is without hierogly-
phics, and was erected in its present situation by Fontana. Its height is 48 feet 4 inches.
That of Flaminio del Popolo, re-erected by Fontana, is broken in three places, and has
hieroglyphics. Its length is 78 feet 6 inches. It formerly stood in the Circus Maximus, and
was one of the two crected there by Augustus. The sides are unequal: two are 7 fect 10
D 4
40
BOOK I.
HISTORY OF ENGINEERING.
inches at bottom, and 4 feet 10 inches at the top; the others are 6 feet 11 inches, and 4 feet
1 inch.
That of Piazza Navona, or the Pamphilian obelisk, has some hieroglyphics, is 54 feet
3 inches in height, and has the name of the Emperor Domitian cut on it.
That of Minerveo della Minerva has hieroglyphics, and was placed by Bernini, in 1667,
upon the back of an elephant. It is about 17 feet in height. This was found among the
ruins of the Iseum, in the Campus Martius; its sides incline more than either of the other
obelisks at Rome.
That of the Pantheon has hieroglyphics, and is 19 feet 8 inches in height: it was placed
in its present situation in 1811.
Monte Cavallo, on the Quirinal, has no hieroglyphics, is 47 feet 8 inches in height, and
was broken into two or three pieces.
Sallustiano della Trinita di Monte has hieroglyphics, and was placed in its present
position in 1789: its height is 43 feet 6 inches; it has been much broken, and is joined
together in an imperfect manner.
Monte Citorio. The height of this obelisk is 71 feet 6 inches, and was placed in its
present position in the year 1792. Two sides at top measure 5 feet, the others 5 feet
1 inch, at the base 8 feet. It was found, broken into four pieces, among the rubbish on
the Campus Martius, where it had been erected by C. Cæsar Augustus. Pliny tells us it
was brought from Heliopolis, and was the work of Sesostris; but modern writers have
assigned it to the time of Psammeticus II.
Monte Pincio has hieroglyphics, and is 30 feet in height.
Vella Mattei, on the Coelian hill, is another small obelisk.
There were formerly many other obelisks at Rome, besides the twelve above mentioned.
At Florence there are two, one very small, not more than 5 feet 10 inches high. In a work
by Zoëga, "De Usu et Origine Obeliscorum," is an account of most of the obelisks known,
with much valuable information.
Of the bridges of the Egyptians we have no account left us: occasionally we find a dyke
passed by laying across it large stones one upon another, without any indication of an arch,

DRY
االالا
Fig. 50.
the stability depending upon the goodness of the material employed: in all probability the
narrow streams and watercourses were passed by this simple means; and large rivers that
could not be so forded had a ferry.
CHAP. III.
GRECIAN ENGINEERING.
GREECE, though in its general aspect rugged, has a climate highly propitious; its
mountains contain many valuable metals, and the finest marbles: this celebrated country is
comprised between the thirty-sixth and forty-first degrees of N. latitude. Among its
mountains are Olympus, Ossa, Pindus, Eta, Parnassus, Helicon, Citharon, and Parnes.
Every acropolis has its plain, fruitful in corn, wine, and oil; and the coast is surrounded
by excellent harbours, Agriculture, by the refined Greeks, was left to the management of
their slaves.
Although nature was so bountiful, and the Greeks possessed what might be called a
maritime country, they were slow to use the advantages which their good harbours
afforded, or to benefit from that commerce which the islands by which they were surrounded
were likely to induce. Little progress was made by them in either navigation or commerce
CHAP. III.
41
GRECIAN.
till after Xerxes' expedition to the Peloponnesus. Athens and the other states then
formed a navy, and the expedition of Alexander, when his ships sailed down the Indus, may
be considered as the earliest instance of the Greeks navigating the ocean.
Corinth, Athens, and the smaller states, as Megara, Sicyon, Cos, Cnidus, and others,
devoted themselves to the cultivation of commerce; but the fine arts always most par-
ticularly attracted their attention; and the vigour, chasteness, and grandeur they threw into
their several designs, continue to call forth the admiration of the world.
The seas which surround the coasts of Greece are broken by headlands, islands, and
lofty mountains, and are subject to sudden and violent storms. These, apparently ad
verse to improvements in the arts of navigation, were the cause of making the inhabitants
excellent boatmen. The Greeks depended upon their oars, and seldom hoisted the sail; for
where the seas were landlocked the stoutest vessels experienced the greatest danger:
light vessels could not only creep along the coast, but could in sudden tempestuous weather
seek refuge in shallow water, or upon an emergency be drawn, as at present, out of danger,
on to the beach. The vessels were without decks, and anchors were unknown. When moored,
it was usual to fasten them to some object on the shore; but they were generally hauled
out of the water.
We cannot therefore expect to meet with any important engineering works on the
borders of the Mediterranean. Capacious harbours, formed by nature, were resorted to by
their numerous small craft, and many a retired nook amidst their lofty cliffs was made
inaccessible by throwing a chain across its entrance, thus preventing any molestation from
Wherever their ancient towns are met with on the coast, we find the remains
of jetties, causeways, and landing-places, and, in some instances, the foundations of the
buildings which formed their arsenals. Some ancient pictures, which have been rescued
from baths and tombs, as well as fragments of sculpture and coins, convey to us ideas of the
form of their ships, and their method of protecting them when on shore.
an enemy.
Athens had three ports near each other, the Piræus, Munychia, and Phalerum; and the
first, whilst the city was in a flourishing state, was the emporium of all Greece: it was
formed in a recess of the shore, and protected by a peninsula which extended into the
sea.
A rocky eminence called Munychia separated it from the other ports of Munychia
and Phalerum, which indented the narrow isthmus on the eastern side. The city was
twenty stadia distant from the sea at Phalerum; and from the Piræus forty stadia.
Phalerum was named after Phalerus, who accompanied Jason in the Argonautic
expedition, and from it Theseus sailed when he set out for Crete, and Menestheus for

ΣΑΧΑ
2 ཏི 1:|:ཀ ན ༔ ཙ
Fig. 51.
PIRÆUS.
The
Troy it continued to be the harbour of Athens until the time of Themistocles.
entrance is narrow; its form approaches the circle, and through its clear and transparent
water is perceived a fine sandy bottom.
Munychia is of an oval form, and somewhat larger, having its entrance narrow.
The chief port was the Piræus, which had its entrance flanked by two rocky points, one
belonging to the promontory of Eëtion, the other to that of Alcemus; within were three
stations for shipping.
Themistocles recommended that this triple harbour should be given up, and the more
42
Βουκ Σ
HISTORY OF ENGINEERING.

R
OUTER PORT.!
PIRÆUS.
TOWN
MUNYCHIA
INNERN
PORT.
AONEDUCTS,
MUNYOHIA
CEPH
PHALERUS
LOW
CANDY. SKORE
BAY OF
PHILERUS.
Fig. 52.
THE THREE HARBOURS.
capacious, that of Phalerum, made use of: about 407 years before Christ the great way.
was commenced by him, which was to serve for its protection; it was of hewn stone, put
together without any cement, cramps of iron run with lead being used to the external
courses, to hold them more firmly together. This wall, of a sufficient width to allow loaded
carriages to pass each other, was 40 cubits high.
Hippodamus, to whom the city of Rhodes owed the great beauty of its structures, wat
employed, during the Peloponnesian war, in the construction of this port: he built five
porticoes, which, uniting, formed the long portico-an agora or market; and also another,
farther from the sea, called Hippodamia.
Adjoining the port were constructed dwellings for the mariners, a theatre, and temples
for the use of all who resorted hither; so that the Piræus rivalled Athens itself. All the
ground of Munychia where houses could be built was occupied by them.
About 330 years before Christ, Demetrius of Phaleres ordered Philon, the celebrated
engineer, to enlarge the port of Piræus, to construct an arsenal sufficient to house all the
arms and marine stores, and whatever was required to be preserved for the use of the city.
He succeeded so well in carrying out the wishes of the people of Athens, and in giving an
account to the public assembly of what he had performed, that they, pleased by his
eloquence and happy mode of expression, declared him to be equally a fluent orator and
admirable engineer. Philo also built around the port sheds or roofs for 400 triremes,
which were said to have been first used at Rhodes, and originally contrived by Hippo-
damus. These sheds were necessary to protect their vessels from the action of the weather,
and it is probable they formed the chief constructions.
This port was secured by chains stretched across it, as well as the others: it was a part of
the project of Themistocles to unite the city with the Piræus by long walls. Those on the
side of Phalerum were first commenced, the foundations being formed of massive stones,
mixed with lime wherever the ground was at all soft or marshy. This was completed by
the architect Callicrates in the time of Pericles, who also erected the wall on the other
side, and the fortifications around the port.
About 410 years before Christ, when the Four Hundred Tyrants governed Athens, the
promontory Eetion was walled in, and soon afterwards the long walls built by Themistocles,
with the exception of about 10 stadia on each side, were demolished by the Lacedemonians,
during the reign of the Thirty Tyrants; after their expulsion by Thrasybulus, Munychia
was again fortified. Conon afterwards rebuilt the walls of the Piræus, as well as the long
walls; and, that they might be rendered more secure, a double ditch was cut, under the
direction of Demosthenes.
In this state the port remained until Scylla set fire to the arsenal and armoury, ana
demolished the walls, putting it into a defenceless condition. In the time of Strabo,
who lived under Augustus and Tiberius, the long walls and the fortress of Munychia were
totally destroyed: there was a temple to Jupiter, which retained some curious paintings
as well as statues; and as late as the second century of our era, this temple, another
to Minerva, with bronze statues, a temple to Venus, a portico, and the tomb of The-
mistocles, remained, together with the sheds or coverings which sheltered the triremes.
CHAP. III.
43
GRECIAN.
The walls around the Piræus were constructed with the stone brought from the quarries
close at hand, mentioned by Xenophon.
When the writer visited the Piræus in 1818, there was nothing left to indicate its former
importance; its temples, porticoes, theatre, arsenals, and other magnificent structures,
having all disappeared; the two lions, 10 feet high, of admirable sculpture, which were
taken away by Morosini, now adorn the arsenal at Venice. At the mouth of the port
two ruined piers are to be seen, which were united by a chain, stretched across for its
defence; the deepest water is at the mouth of the inner port, the Aphrodisus of the
old Piræus. It seems difficult to understand how, in the time of Constantine, 200 ships
could have found anchorage here, or that it ever could have contained the whole of
the Athenian navy, which at one period was said to consist of 300 ships of three banks of
oars, the whole length of the harbour, from the outer mouth to the innermost recess, being
not more than a mile and a quarter.
The ground of the peninsula called Munychia is both high and rocky, and not capable of
being applied to cultivation; its shores are indented with four small natural bays. The
walls which fortified it may be traced in various places nearly all round, particularly across
the neck between the port of Munychia and the Piræus. The old harbour of Munychia is
of a circular form, and there are the remains of several walls running into the sea, and parts
of the piers on each side of the mouth, which reduced the entrance to this port, and made
it much less than that of the Piræus. The walls which surrounded it are traceable on the
eastern side of the harbour, and the whole extent of them appears to have been about four
miles.
Between Munychia and Phalerum, and at the top of the cliff, between these two ports,
is an excavation made in the rock, decorated with a pilaster on each side, rather rudely cut,
which probably served for the sentinel placed there to reconnoitre. The port of Pha-
lerum is smaller than that of Munychia, and is in its form elliptical; at its very
narrow mouth are the remains of the two stone piers that formed its entrance; on the
north-east side of this port the land is high and rocky, and beyond is the bay of Phalerum,
two miles or more in length, terminated by the low promontory of Colias, where was
obtained the clay from which the most beautiful pottery was made. From one point of
this bay, which lies south-south-west from Athens, the sea may be computed at a little
more than twenty stadia distant from the city; and Pausanias, who lived in the second
century, gives us an account of two roads which led from thence to the ports, one to
Phalerum, and the other to the Piræus: on the side of the latter, in his time, remained a
part of the walls erected by Conon, and the sepulchral monuments of Menander and Euri-
pides, that of the latter being a cenotaph or mound of earth without his ashes.
These ports were united to Athens by the long walls, traces of which on the right of the
present road, which conducts from Athens to the Piræus, may still be seen. The walls of
Athens, when in its prosperity, together with those which connected the Piræus, were in
length 195 stadia, or 24 miles and 2 furlongs; those enclosing the Piræus and
Munychia comprising of this quantity 60 stadia, the long walls which joined the Piræus to
the city on the north side 40 stadia, and on the south side 35 stadia; and the exterior city
wall, which joined the ends of the two long walls, was 43 stadia; the middle or interior
wall between the long walls was 17 stadia. The circuit of the city wall alone, without
the long walls, was computed at 60 stadia or 7 miles and a half, the portions towards
Hymettus and Pentelicus were constructed of brick.
Thucydides informs us, that when the Athenians raised their walls after their de-
struction by the Persians, they used so much haste, that they united stones of various kinds
and dimensions, many columns taken from tombs, and whatever came first to hand.
The breadth of the walls about the Piræus was sufficient to allow two carriages to pass
upon it, and although so thick, they were entirely built of squared stone throughout, and
cramped with iron run with lead.
Eleusis. The site of the ancient town, with its walls, was a short distance north-east
from the port, where are the remains of three ruined moles: two of these formed the
port, which was an oval; the other, which nearly divided it, seems rather to have
been a landing-place; attached to this is a modern one, which springs from it nearly
at right angles. The sacred way from Athens is still discernible, as is the road from
Megara.
A ridge of the Icarian range of mountains separates Eleusis from the plain of Athens.
Eleusis is situated in the Thriasian plain, where Ceres first gave her instructions in
agriculture; the citadel stands on a low rocky hill, about 300 yards from the sea ;
on the declivity which faces the south-east is formed a terrace, and on this was
founded her celebrated temple, which was backed by the Acropolis. Around the
base, and along the margin of the Bay of Salamis, were numerous villas and residences
of the inhabitants, together forming a picture of a very imposing kind. The propylea
or entrance to the Acropolis equalled in beauty that at Athens. A little beyond the
Sacred Way are some remains of tombs, and at about a mile distant, near the river Cephissus,
44
Book 1
HISTORY OF ENGINEERING.
---------
which is dry in the summer, are considerable ruins; the rise of this river is near
Eleuthera in Mount Citharon, and in its course it passes the hill of Magoula, where the
ancient stone quarries are situated; the river then divides, and both channels enter the

11
*х
1
Fig. 53.
ELEUSIS HARBOUR.
Bay of Salamis at about a distance of 1500 yards from each other. There are some
remains of embankments to confine the water along the eastern side of the western river,
and others to protect the delta formed by the Cephissus. There are some other engineering
works apparent on the shore, and the ruins of an aqueduct which supplied the inhabitants
of the town with water.
Corinth stands on the isthmus, on the side of the Peloponnesus, and its ports were once
celebrated for their convenience and extent; hither resorted ships from Asia and Europe;
it was the centre of commerce, and its citizens became the most wealthy persons of the
world. Around the Peloponnesus the navigation was tedious and dangerous: it was
found more easy to carry the merchandise across the isthmus from one sea to the other,
and sometimes the smaller craft were transported in this way. The merchants attained to
such wealth and luxury, that it was a common saying, that "every man was not rich
enough to live at Corinth."
The port towards Asia was called Cenchreæ, and that towards Italy Lechæum; the
latter lay beneath the city; the road to it was between long walls, 12 stadia or a mile and
a half in length.
In the time of Xerxes, the Peloponnesians destroyed the Scironean way, and erected a wall
entirely across the isthmus, from the port of Cenchree to that of Lechæum.
The isthmus which divided the two seas at Schænus, the narrowest place, is 40
stadia or 5 miles, and here was the Diolcos or drawing-place, where vessels were con-
veyed across on machines a curious and early contrivance, answering the purpose of a
railway.
Demetrius Poliorcetes had the two gulfs surveyed, and it being reported that the water
stood higher in the Corinthian than in that at Cenchreæ, he abandoned the project of cutting
a canal through the isthmus: it was feared by the engineers of the day that such a work, if
carried into execution, would have flooded the island of Ægina, and done considerable mis-
chief; in after times Julius Cæsar and Caligula turned their attention to this subject, and
Nero commenced a cutting from Lechæum, and continued it for a length of 4 stadia, or
CHAP. III.
45
GRECIAN.
half a mile.
Pausanias tells us, that all who have endeavoured to form the Peloponnesus
into an island have failed; that none ever cut away the native rock, which still remains un-
touched; so difficult was it in those days for man to force nature.
The Corinthians were either put to the sword or sold as captives by the Roman army
under the command of Lucius Mummius; and the historian Polybius, present at the
siege, relates that he saw splendid pictures and exquisite works of art destroyed, and
those that were conveyed to Rome became its greatest ornament. The city remained deserted
until Julius Cæsar converted it into a Roman colony, when the sepulchres were ransacked,
and their contents sent to the imperial city, which was said to be filled with the decorations
of the tombs. Strabo, who was at Corinth after this time, describes it thus:
"A lofty
mountain, 3 stadia in perpendicular height, ending in a pointed summit, was the
Acrocorinthus, which was approached by a winding path 30 stadia in length. At the foot of
this citadel, on a level area, was the city, the circuit of which was 40 stadia, and all that
was not sheltered by the lofty mountain, was walled in; the whole circumference was about
85 stadia or 10 miles: the view from the summit is magnificent. To the north
lies Parnassus and Helicon, covered with snow; and below these, to the west, is the Cris-
sæan Gulf, bounded by Phocis, by Boeotia, and the Megaris, and opposite to Phocis, by
Corinthia and Sicyonia. Beyond are the mountains called the Oneian. Pausanias visited
New Corinth after it had flourished 217 years, and he notices several temples, statues, and
the agora or market-place; there was an odeum, a theatre, and gymnasium, all of which
have disappeared.”

The Port of Agina was
once so celebrated, that,
according to Strabo, it
enjoyed naval dominion,
and disputed with Athens
the prize of superior
glory in the battle of Sa-
lamis, when the Persian
fleet was defeated. The
Island of Ægina is sur-
rounded by Attica, Me-
gara, and the Pelopon-
nesus, each distant a
little more than 12 miles
or 100 stadia. Its entire
circumference was 180
stadia or 22 miles.
The port is now diffi-
cult of access, and only
fit for the entry of very
small vessels; a part of
the ancient mole is still
to be seen, constructed
of large stones piled one
on the other, near which,
when the writer visited
it some years ago, were
standing two Doric co-
lumns, which formed part
of the temple of Venus.
A modern lighthouse
and lazaretto occupy the
sites of more ancient
structures, and among
the ruins of the town
may still be traced the
museum and school or
academy. In the interior
of the island are re-
mains of the splendid
C.SKENDINOTÍŲ
о
O
Fig. 54.
(MOLE)
TEMPLE
of
VENUS
ANCIENT MOLE)
ов
LAZZARETTO
SCALE OF.. 茶 ​MILE
LCABLE
Z.CABLES
LICHTHOUSE
C.MYLOS
EGINA.
...
£ ៖
THE TOWN
ais
SCHOOL
MUSEUM
temple of Jupiter Panhellenius, with its numerous columns erect, standing above the north-
eastern coast of the island; it was reckoned among the finest of the Greek places of worship,
and considered famous for its sculpture. Vases of terracotta of great antiquity are found on
the island.
Island of Rhodes, in the Mediterranean Sea, lies nearly opposite the coast of Lycia and
Caria, from which it is distant about twenty miles. It is in circumference about 120 miles,
46
Book I.
HISTORY OF ENGINEERING.
has a fertile soil, produces fine fruits and wines, and has an atmosphere of great serenity,
no day ever passing without sunshine. This island was occupied by a colony of Greeks,
some from Crete, and some from Thessaly, at a very early period; and Homer tells us that
Tlepolemus, son of Hercules, took with him a colony from Argos to Rhodes, and after-
wards joined the expedition against Troy at that time the wealth and power of its in-
habitants were considerable. He divided the island into three independent states, Lindus,
Camirus, and Ialysus: the first of these, which gave birth to Chares, the architect of the
celebrated Colossus, stood on the east coast of the island; Camirus, on the western coast,
and Ialysus on the north side. Some time afterwards, during the Peloponnesian war, these
three states were united, and the city of Rhodes, built in a very advantageous situation,
became the common capital of the island, flourishing in commerce, arts, and arms, and
extending its dominion over a large portion of the contiguous continent.
It was situated
on the east coast, at the foot of a gently rising hill, in the midst of a plain, abounding with
springs and fruit trees. Strabo informs us that in ancient times few places were preferable
to it.
Hippodamus, a native of Miletus, who had gained great reputation by his works at the
Piræus, already alluded to, arranged the plan of the new city, and superintended the
erection of the walls, gates, and public buildings. According to Strabo, its form was that
of a vast amphitheatre, surrounded with walls, like those of Munychia, embellished with
straight and wide streets, large squares, and numerous splendid edifices, among which was the
Haleum, or temple to Apollo.
The haven or harbour was of considerable extent, and the entrance to it was by a passage
between two rocks, 50 feet apart.
The Rhodians, for centuries, were famous for the study of the sciences, and by many,
Rhodes was reckoned equal to Athens for the number of its learned men; the in-
habitants were in amity with all nations, and their merchants, from the trade they carried
on with Egypt, became so enriched, that the whole city was supported by them.
It was
on the occasion of Antigonus not being able to separate them from the cause of Ptolemy,
that he sent his son Demetrius Poliorcetes, or city taker, with ships to intercept the trade
between the ports of Rhodes and Egypt. The Rhodians, however, were successful in all
the combats; at which Antigonus became so incensed, that he furnished Demetrius with
additional ships, and all manner of engines to besiege their city. The fleet consisted of 200
men of war, and 170 vessels, which carried 40,000 soldiers, besides horse and auxiliaries.
A thousand other vessels, belonging to merchants, followed in the train.
Demetrius drew up his fleet, which contained engines of every kind, capable of producing
destruction, in the following manner :-those which discharged darts or arrows, three spans
long, in front; the vessels which contained the cavalry in the second rank, and in the rear the
transports, which contained corn and provisions; the whole sea being, as it were, covered
with vessels. On his arrival, he landed all his men, and took his station within the cast of a
dart from the walls of the city, throwing up an earth wall, fortified by large trees, as a pro-
tection against any sally from the Rhodians; he then commenced dredging the port, and
rendered it sufficiently deep and spacious to hold his fleet. His next operation was
to construct two engines called testudoes, which he placed upon the decks of two
transports, one of which was to guard against the stones thrown by the enemy, and the
other the darts and arrows discharged by the machines on the walls.
Plutarch informs us that Demetrius had a thorough knowledge of mechanics, and that in
every thing he did, there appeared a grandeur of design, and so much invention, that his
enemies, pleased with the beauty of his contrivances, stood looking with admiration at
his galleys of fifteen or sixteen banks of oars, and his engines, which were called helepoles,
in consequence of their employment in taking a city. The largest had a square base, each
side of which measured 48 cubits, and its height was 66 cubits, but it diminished on all
sides towards the top, and therefore resembled the frustum of a pyramid. It consisted of
four stories, each having an opening for the discharge of missiles. Vitruvius informs us
that these engines were made by Epimachus, an Athenian, whom Demetrius Poliorcetes
had in his train, and that it was secured by hair cloths and raw hides, so that it might
withstand the shock of a stone 360 pounds weight, thrown from a ballista. The entire
machine, it is said, weighed 360,000 pounds.
At this time, Diognetus the architect was paid an annual salary for his skill in main-
taining the walls and places of defence; but during the siege, Callias, an architect of
Aradus, arrived and exhibited a model of a wall with a revolving crane, by means of which
he could suspend an helepolis near the spot, and swing it within the walls. When the
Rhodians saw this, they dismissed Diognetus, and appointed Callias to fill his situation,
and to prepare his machine against the helepolis, and swing it within the wall, as he had
promised; when he was obliged to confess his inability. Diognetus was then entreated to
aid his countrymen, and he consented, upon the condition of having the machine if he suc-
ceeded in removing it: this being agreed to, he ordered a hole to be made in that part of
CHAP. III.
47
GRECIAN.
the wall opposite the machine, and water, filth, and mud to be thrown on the other
side and discharged through the hole during the night: when the helepolis advanced,
it sunk in the quagmire, and Demetrius drew off his army.
Diognetus then removed the machine within the walls, and placed it in a public
situation, thus inscribed: - Diognetus presented this to the people out of the spoils of
war."
Demetrius also had upon the sea a floating tower, with loopholes at the sides, from
whence darts could be discharged; this was formed upon a number of boats, which were
attached and floored over with a common platform. The Rhodians had in this memorable
siege contrivances of the same kind, and placed them at the mouth of the small harbour;
in which were engines for the throwing of stones, darts, and arrows of all sizes. Demetrius
was at first prevented entering by a storm, but was afterwards enabled to seize upon the
highest rampart of the great harbour, and throw up a mud wall around it, fenced and
secured with piles and planks as well as stones; here he landed 400 of his men, who were
within five plethras of the walls. Demetrius continued his assault for many days, some-
times burning and destroying the vessels in the harbour, at other times making breaches in
the walls; but the bravery of the Rhodians at last obliged him to desist. The Rhodians
had scarcely repaired the walls which were beaten down by the engines brought against
them, when Demetrius again returned with other battering engines, and with his ships
entered the harbour, throwing firebrands among the Rhodian ships, which were soon ex-
tinguished. The Rhodians then manned three of their strongest vessels with their ablest
men, and ordered them to act against the enemy's vessels which contained the engines;
these they violently charged, and though they were fenced with iron, they broke them in
pieces with the prows of their ships, and shattered them, taking Execestus, who com-
manded the galleys, prisoner. Demetrius made another engine thrice as large as the
former, which was destroyed in a storm as it advanced into the port; he then
abandoned his attacks by sea, confining his assault of the city to the land, and framed
another helepolis much larger than either of the former; its base was square, the length
on each side being 50 cubits, formed of four square pieces of timber, united together by
plates of iron at the angles. Strong transverse timbers were laid from one side to the
other, a cubit apart, on which was the floor for those to stand upon who moved the
engine. The whole rested on eight strong wheels, the fellies 2 cubits in thickness,
also covered with iron; over the spokes were antistreptas, which enabled them to
turn the engine round when required. At each angle was a perpendicular piece of
timber 100 cubits in height, with floors thrown in at regular distances, which tied them
together, and made the machine nine stories. In the lowest were forty-three beds, and
in the highest nine; three of the outer sides were cased with iron plates, to prevent fire
or any other injury to which it might be subjected from the besieged. In the front, each
story had a number of loopholes, guarded with shutters lined with skins stuffed with wool,
which deadened the force of any stone shot against it, and two ladders: to move this vast
machine 3,400 men were appointed, some being placed within, and others around it.
Testudoes, or artificial covers, made of timber covered with raw skins, protected the men
employed in levelling the ground to the city wall, over which this engine was to be moved;
and when the helepolis was against the city wall, its breadth occupied the space of six
divisions between the turrets, and the seven turrets: the workmen and artificers of different
kinds employed are said to have been 30,000.
The Rhodians built within the outer wall of their city another, and employed for its
construction the stones of the theatre, several houses and temples, and in a general as-
sembly proposed to destroy the statues of Antigonus and Demetrius.
The city was,
however, by this time undermined, when the Rhodians cut a deep trench along the wall
that it was intended should be thrown down, commenced countermining, and soon met the
enemy under ground, and prevented any further progress being made.
The helepolis, with eight testudoes made for filling up the trenches, and others con-
taining battering-rams, which were 120 cubits in length, strongly armed with iron, and
resembling the beak of a ship, were moved forward on wheels by the help of a thousand men.
The several stories of the helepolis were filled with archers, and at a given signal the walls
trembled under the strokes of the battering-ram, one of the strongest towers was thrown
down, and the entire wall between it and the next so shaken, that the besieged could not
pass along it.
Ptolemy having sent a fleet with succour, inspired the Rhodians with fresh energy;
they made an attack on the enemy's engines, and by means of fire-balls and weapons of all
kinds, at last succeeded in destroying the iron plates which protected the helepolis, and
then with firebrands set light to it. Demetrius endeavoured to quench the spreading
flames, to move the engines from the reach of the darts discharged against them, and to
make a general reparation of them. The Rhodians, in the mean time, commenced a third
wall, built in the shape of a half moon, which enclosed the gap already made.
Deme-
48
BOOK I.
HISTORY OF ENGINEERING.
trins renewed the attack with all his vigour, and at night determined to carry the city by
assault: a great slaughter on both sides was the result; but the Rhodians were triumphant,
and forced Demetrius to accede to the following terms: "That the city should be subject
to its own laws, and be left without a garrison. Thus the Rhodians, after a twelvemonth's
siege, put an end to the wars, soon afterwards repaired the theatre, and rebuilt the temple
and walls.
""
By some historians it is asserted that Demetrius was at last so reconciled to the Rhodians,
and so much admired the courage they had displayed, that he presented them with all the
engines he had employed, and that it was by the sale of these for 300 talents, that they
raised the famous Colossus on the two rocks at the entrance of the port, which was a
statue of brass, erected in honour of Apollo, the tutelary god of the island; it was 70 cubits
or 125 feet in height, and vessels could pass between its legs.
Pliny describes it as the work of Chares of Lindus, a pupil of Lysippus, and observes
that its thumb was a fathom in circumference; that it was made hollow, and had a lining
of stone, to render it steady on its feet. It stood erect for sixty years, and was thrown
down by an earthquake, which Polybius tells us destroyed the walls and naval arsenals
at the same time. The Colossus, however, lay where it fell for 894 years, until Moavias,
the sixth caliph of the Saracens, sold the metal to a Jew, who loaded 900 camels with
it, the weight being estimated at upwards of 300 tons.
The Rhodians, after its fall, and the injury their city had sustained, solicited help from
the kings of Egypt, Macedon, Syracuse, Syria, Pontus, and Bithynia, to enable them to
restore it. From Hiero and Gelo they received 75 talents of silver, some silver caldrons,
and other presents, which together were valued at 100 talents, and also 50 catapults of
the length of 3 cubits.
Ptolemy engaged to furnish them with 300 talents of silver, a million measures of corn,
timber to build 10 quinqueremes, and 10 triremes, some square pieces of fir, the contents of
which were 40,000 cubits, 1,000 talents of brass coin; 3,000 weight of hemp, 3,000 pieces
of cloth for sails, 3,000 talents for replacing their Colossus; 100 architects, and 350
labourers; with 14 talents by the year for their subsistence; 12,000 measures of corn for
the sacrifices and games, and 20,000 for the 10 triremes.
Antigonus gave them 10,000 pieces of timber that would cut into scantling from 8 to
16 cubits; 5,000 planks of 7 cubits; 3,000 weight of iron; 1,000 measures of pitch, and
,000 measures of tar, as well as 100 talents in money.
Chryseis, his wife, sent 100,000 measures of corn, and 3,000 weight of lead.
Seleucus, the father of Antiochus, gave 10 quinqueremes completely equipped, 200,000
measures of corn, 10,000 cubits of timber, and 1,000 weight of hair and resin.
By all these and other gifts, Polybius tells us, the Rhodians soon restored their city to its
former magnificence; but they were ordered by the oracle at Delphos not to replace the
Colossus, but to use the presents they received for other purposes.
Isene is another ancient port, which once contained a fine harbour: its ruins proclaim

SO
WELLS
AQUEDUCT
Fig. 55,
ISENE.
TOWER
THEATRE
VE
VENETIAN
CHAP. III.
49
GRECIAN.
its importance. Walls of the theatre, aqueduct, and public buildings may yet be traced,
around the site of the castle erected in the middle ages by the Venetians.
Samos was a name common to three islands, Cephalonia, Samothracia, and Samos, which
lay between the continent of Asia and the island of Icaria, being divided from the former by
a strait, which, according to Strabo, was equal to 1000 paces in breadth, and from the latter
by another 8 miles across. At the present day all the vessels going from Constantinople to
Egypt and Syria pass through either one or the other of these straits. The island of
Samos measures about 87 miles in circumference, and from Vitruvius we learn that Samos,
and the thirteen Ionian towns, were built by Ion the Athenian. Samos was very populous,
wealthy, and strongly fortified; and most deserving the notice of an engineer, from the
three remarkable monuments of art mentioned by Herodotus; one of which was a passage
cut through a mountain, 150 orgyia high; the length of which is 7 stadia, and 8 feet in
width and height: by the side is a canal 3 feet in breadth, and 20 cubits deep, also made
by art, which supplied water from a copious spring. Eupalinus, the son of Naustrophus,
an inhabitant of Megara, executed this work. Tournefort observes that in the valley, near
to the aqueduct, are several caverns artificially cut: the spring which fed this canal was
doubtless that of Metelinous, the best in the island: but it does not appear that the levels
were accurately taken, otherwise the depth need not have been so great; and indeed it does
not seem very practicable to dig a trench 20 cubits deep and only 3 wide.
The second was a mole, which projected from the harbour into the sea, 2 stadia in
length, and 20 orgyia, or upwards of 120 feet, in height.
The third was a temple erected by Rhocus, son of Phileus, who was the inventor of the
art of making moulds with clay. Long before the Bacchiades were driven from Corinth,
Rhocus and Theodorus of Samos made casts in brass, and formed statues.
The tunnel through the mountain has been long filled up, but the entrance may still be
discovered; there are no vestiges of the stupendous mole, which must have been a wonder
among the Greeks at such an early period. That the Samians were devoted to maritime
affairs, we learn from their having, 300 years before the Peloponnesian war, employed
Aminocles the Corinthian, the most skilful ship-builder of his time. They traded to
Egypt, Thera, and Spain, and, according to Pliny, they were the first who built vessels for
the transport of cavalry. Samos was famed for its earthenware, and had a considerable
manufacture of it. In all parts of Europe, we find examples of Samian ware; in the
tumuli and monuments of the Romans, vessels of this manufacture are discovered;
sometimes admirable for the beautiful forms they present, the ornaments with which they
are covered, and always for the perfection of the workmanship. Vases, lacryma, lamps,
and cups, made at Samos, the writer has discovered at Athens, Sicily, and in Italy. In the
broken pottery, which the tumuli in France and Italy often afford, fragments of Samian
ware, covered with intricate chasing and highly ornamented, are often found.
Tenedos is a rocky but fertile island; its position, near the mouth of the Hellespont,
has caused it at all times to be a place of considerable importance. Its circumference is
about 10 miles, equal to 80 stadia. The port was enclosed by a mole, but at present
there is no portion to be seen above water; the ancient foundations remain, on which
are piled loose stones, for the purpose of breaking the force of the waves; a ridge of
mountains surrounds the harbour, which gives shelter to vessels bound to Constantinople.
Here the Emperor Justinian erected a magazine, 280 feet in length, 90 feet in breadth,
and many stories in height, for the purpose of warehousing the corn brought from Egypt,
as it often occurred that stormy weather during the Etesian winds prevented the ships
from pursuing their voyage.
On this island still remains an ancient stone building, in which the water used by the
inhabitants was collected, after it was brought from distant springs, in earthen pipes.
Troas. The port has a hill rising around it, in a semicircular form, covered with ruins;
and near the shore are many small columns of granite, injured by the spray of the sea,
and partly buried in the soil, to which were made fast the vessels trading to this port. At
present the smaller basin is dry, and a bar of sand closes up its entrance, but the larger
has shallow water in it. These two basins were both the work of art, and intended
only to receive galleys and small vessels; larger ships being obliged to cast anchor in
the road, outside the mole.
Alexandria Troas is the name given to the town, it being one of the eighteen called after
Alexander the Great, who caused cities and temples to be erected, and improvements to be
made, throughout the countries he subdued: it was first called Antigonia; but its name was
afterwards changed by Lysimachus in honour of the deceased sovereign. Augustus showed
it considerable favour, under whom it increased in wealth, and was benefited by a Roman
colony. The city, which is several miles in circumference, has its wall, of considerable
thickness, still standing; at regular distances it is strengthened by square towers.
aqueduct which supplied it with water may be traced for several miles; the piers are
5 feet 9 inches in width, 3 feet 2 inches in thickness, and the arches, though destroyed, were
upwards of 12 feet in height. This was one of the structures erected at the private cost
E
The
50
CHAP. III.
HISTORY OF ENGINEERING.
of the Athenian Tiberius Claudius Atticus Herodes, who was appointed to preside over the
free cities of Asia. When this munificent and illustrious proconsul found that Troas was
not supplied with water, he requested of the Emperor Hadrian, that he would not allow
this ancient maritime city to be without a plentiful supply, but that he would bestow
300 myriads of drachms to procure it. Hadrian complied, and appointed Atticus Herodes
to superintend the constructions necessary. Upwards of 700 myriads were expended, and
the emperor complained; when Herodes in reply stated, he had given the overplus of the sum
to his son, and he to the city. This munificent Athenian was the grandson of Hipparchus,
who, though wealthy, had his estates confiscated, and his family reduced to the greatest want:
but his father, Julius Atticus, discovered a vast treasure in a house which he inhabited, near
the theatre at Athens; of which he informed the Emperor Nerva, and requested to know
his pleasure in the appropriation of it. The emperor replied, "Use what you have found, and
abuse, if you will, what Mercury has given you." After this Julius married a wealthy lady,
and their son, Atticus Herodes, who was born at Marathon, inherited a vast property: his
education was superintended by the most learned masters; and he became as eminent for
his mental acquirements, as for his wealth: in the year 143 he was made consul with
Torquatus at Rome.
Chios. This island was computed by Strabo to be 900 stadia in circumference, or about
112 miles, and about fifty miles from the island of Mitylene. The ancient city of Chios
had a good port, large enough to admit eighty ships. The present town of Scio occupies the

品
​CITADEL
5
Fig. 56.
+ MILE
CHIOS.
site, and there may still be traced the remains of the ancient mole, which above the level of the
water is now covered with large loose stones. The entrance to the port beyond this mole
is narrow, and encompassed by rocks. A modern citadel takes the place of a part of the
more ancient town, the ruins of which still remain.
Smyrna was founded by Alexander the Great, for the Smyrneans, a people then living in
the neighbourhood of Ephesus; and the situation chosen indicates the judgment which the
Greeks always bestowed upon such occasions. This city, like others of their founding,
is on rising ground, near a plentiful supply of marble, and where in the side hills might be
cut the stadium and the theatre.
The port originally reached to the foot of the Acropolis, at which time it was a spacious
basin in the midst of the city, encompassed with strongly-built and lofty walls, the stones
being laid in regular courses; a great part of which may be still seen. Tamerlane ruined
the ancient port by not allowing the sea its free ingress, and thus permitting the waters of
the rivers to deposit their mud, without means being adopted to remove it.
This emperor,
who ravaged Asia, at the commencement of the fifteenth century, commanded every soldier
in his army to throw a stone into the mouth of the harbour, which soon choked it up. The
ancient city was two miles and a half from the modern Smyrna, and was built on the sea-
shore, with the fine and clear river Menes running at the foot of the walls.
The Gulph of Smyrna, about 10 leagues in length, is well sheltered, and affords ex-
cellent anchorage. The mouth of the Hermus is on the north side, within two leagues
and a half of the modern city. The mountain which bounds the bay of old Smyrna on the
north extends westward to a plain through which the river runs. Near the mouth of the
river is a shoal or sandbank, and the channel is very narrow.
The Hermus appears to
have frequently changed its course, and in time the plains around the modern city will
probably be covered with water, thus placing it in the midst of a vast lake.
Teos. This ancient port is now partly dry, and many sandbanks have been thrown up
CHAP. III.
51
GRECIAN.
above the level of the water; the town itself has long been deserted, though there are
traces of its walls, which appear when perfect to have been 5 miles in circuit. Pliny
describes Teos as an island, and the rocks around it furnished excellent building materials.
It was thirty stadia from Geræ, and fronted the sea on the south.
Ephesus is situated on a plain, watered by the Cayster, and the wall erected by
Lysimachus, which is of excellent masonry, may still be traced in many situations, par-
ticularly at the back of the stadium near Mount Prion, where it remains 20 feet in height;
from thence again over Mount Corissus, where it is nearly entire.
Mount Prion contained the quarries of marble made use of for building the celebrated
temple of Diana.
The port, which received the flux and reflux of the sea, has now its once wide entrance
choked up with the deposits of the river Cayster; and Attalus Philadelphus and his
engineers were of opinion that by contracting the entrance the harbour would have
recovered its depth, and have been rendered capable of receiving vessels of considerable size.
The ancient port is now a morass, and the wall, erected to embank the stream, and by
confining it to give it additional force, is of excellent masonry, formed of large stones in
regular courses throughout, and at the ferry a considerable portion may yet be seen.
Crete. This island, now called Candia, is one of the largest of the Mediterranean, being
287 miles in length, and 65 miles in the widest part. It lies between the thirty-fourth and
thirty-fifth degrees of north latitude, and was by the ancients celebrated for its fertility.
At one time it boasted of its hundred cities, ninety of which were established before the
Trojan war; and after the Dorians had founded the other ten, it was called Hecatompolis.
Gnossus, anciently Ceratus, was the capital, and here Minos held his court: it was
30 furlongs in circumference, but modern travellers have not yet decided where it was
situated.
Gortyna eclipsed all the other cities of Crete in splendour and magnificence, the ruins
are still traceable, six miles from Mount Ida, at the commencement of the plain of
Messaria. Tournefort describes one of the gates, with a beautiful arch, and part of the
wall which Ptolemy Philopater, according to Strabo, erected. There were also some
The walls were
columns of granite fluted in a spiral manner, of exquisite workmanship.
washed by the river Lethe.
Rethymna, now Retimo, had at one time a convenient haven, and Heraclea, which was
opposite the island of Vea, was the seaport of the Gnossians, and occupied the site of the
present Candia.
In the island are many creeks and bays, with several safe and capacious harbours.
Phalasarna, on the western extremity of the island of Crete, has on its northern side
many remains of its city walls, which appear to have extended to the sea, and cutting off
the Acropolis and city, so as to form a small promontory.
The walls near the sea on the north side exhibit the remains of many square towers, the
distance between being about 120 feet, and some 230 feet. One of these towers measures
on the face 36 feet, and projects 20 feet from the wall.
The walls are not continued in regular lines, and in some parts are the remains of
another, placed at a distance of 16 feet from the first; and it seems probable that
originally the whole city had a double wall from one sea to the other, where the distance
is about 500 yards.
Cyprus or Erosa. This island extends from east to west along the coast of Cilicia for
about 180 miles, and is in breadth about 45 miles. It lies between the thirty-fourth and
thirty-fifth degrees of north latitude, and is one of the most productive islands of the Medi-
terranean. It was first peopled by a colony from Phoenicia, about 1045 years before
Christ, and the principal cities were on the north side of the island.
Neapaphos, according to Strabo, was founded by Agapenor, the nephew of Lycurgus.
It was famous for its harbour, which was totally destroyed by an earthquake. There was
an abundance of copper, formerly found in metallic masses, employed by the ancients for
fabricating their agricultural implements and weapons of war; the inhabitants of this
island having been well instructed in the arts by the Phoenicians.
The ancient harbour of Arsinoë, where the modern town of Famagusta stands, is now
choked up with sand. In the Gulf of Larnica stood the town of Citium, still a place of
some trade; but Salines, which takes its name from the Salt Lakes, is the chief port.
Paros, so famous for the whiteness of its marble, is 36 miles in circumference, and has
several safe and capacious harbours, and formerly carried on considerable commerce. The
city of Paros was one of the largest in this archipelago, and the modern Parichia is formed
out of its ruins; the walls which surround it are composed of fragments of temples and
public and private buildings.
This island was first peopled by the Phoenicians.
Delos contained at one time a city which was considered the richest after the de-
struction of Corinth; it became the emporium of commerce, and was as renowned for its
trade as for its celebrated oracle. Among the ruins of Delos, which extend from one coast
E 2
52
CHAP. III.
HISTORY OF ENGINEERING.
to the other, are the remains of a curious arch and many stately buildings. The trunk of the
famous statue of Apollo, which is described by modern travellers, is of a gigantic size,
though cut from a single block of marble; the circumference of the thighs are 9 feet and

Fig. 57.
DELOS.
an inscription tells us that it was dedicated by "the Naxians to Apollo." According to
Plutarch, there was set up by Nicias a large palm tree made of brass, which a violent wind
threw down, and, at the same time, destroyed this celebrated statue.
This island was only 7 or 8 miles in circumference, though there is another island of the
same name, of double this size.
The smaller Delos was the sacred island of Apollo, and in the time of Polycrates it was
united to the island of Rhea by a chain. There was held here an ancient festival, described
in one of the Homeric hymns, as celebrated by the long-robed Ionians; and on one of these
occasions Nicias, who was the Theorist appointed to conduct the sacred chorus, displayed
his wealth and munificence by constructing a bridge, 600 yards or more in length, across
the channel which separated Delos from Rhea; this bridge, hung with tapestry and
paintings, served for the procession to pass. An ancient inscription, brought to England
by the Earl of Sandwich, the date of which is 374 years before Christ, mentions these
ceremonies, and gives some account of the offerings on the occasion.
Plutarch says in the life of Nicias, that he took care to have this bridge constructed
before he left Athens, and that it was magnificently gilded, adorned with garlands and rich
hangings; and then, in the night after his arrival, and before the break of day, he had it
thrown across the strait, ready for the procession and the chorists, who were richly habited,
to pass over. This, in all probability, was a timber construction, resting on boats, or some
other buoyant arrangements.
Cnidus has two harbours, separated by a narrow isthmus, the smaller opening to the
north, the other to the south, near the extremity of which are the remains of the city
walls; inserted in them are many stones of considerable dimensions, which probably formed
a part of the foundation of a tower on the edge of the sea. The broken cliffs extending
along the shores show the ruins of the Acropolis, surrounded with strongly-built walls,
and strengthened with towers at regular distances.
Here are the remains of a theatre with its marble seats, the arches and walls of the
proscenium, and the ruins of one or two magnificent Corinthian temples; also a forum or
agora, with a long colonnade of the Doric order, probably a stoa. An arched gateway of plain
and solid masonry terminates the street which ran from the port towards the Acropolis.
Above are many platforms cut out of the rock, which have served for sites of either temples
or public edifices; and amongst the ruins are several marble slabs, channelled out for
water conduits.
The narrow isthmus, which separates the two harbours, in Strabo's time was an artificial
mole, built over a channel of the sea; and the western part of the town stood on an
island united by this isthmus to the continent. An arch still remains by the side of it, and
probably formed a part of the mole; but the ruins have so accumulated, and the sand so
spread over them, that a neck of land is now formed 60 or 70 yards across.
Strabo tells us that the port on the north was shut in by gates, and two towers may be
traced at the entrance, to which these gates were attached: it contained, he says, twenty
triremes.
CHAP. III.
5:3
GRECIAN
The southern port is much larger, and protected from the sea by a mole of large, rough-
hewn stone, which still remains.

་་་་་་
Southern Port
ป
Fig. 58.
CNIDUS.
Beyond the ports, to the west, the city rose on a hill, the form of which Strabo com-
pares to a theatre, bounded from the mole, on the south, by rocky precipices, and on the
north by the walls, which descended from the ridge to the gates of the northern harbour, in
a semicircular sweep. On this side of the city are still many foundations of ancient houses
to be traced, but no buildings of marble. The entire circuit of the walls is about 3 miles,
including the two ports within them.
Halicarnassus, now the port of Boudroun or Bûdrûn. Its entrance is from the south-

WELL
CULTIVATED
CARDENS
OF FICS AND CORN
Fig. 59.
MOSQUE
SCALE OF 200 YARDS
G
ARSENAL
BAZAAR
700
HALICARNASSUS.
E 3
MO
54
HISTORY OF ENGINEERING.
CHAP. IIL
west; on the right and left of which a great quantity of sand has accumulated, and the
passage, now free, is not more than 60 yards in width: there are some yards for the building
of vessels. The small town now inhabited stands on the east side of this large and deep port.
Off the bay lies the island mentioned by Strabo as Arconnesus (lib. xiv.).
Behind the town are the remains of an edifice of the Doric order, composed of grey
marble, but not of the same proportions as those of the purer days of Greece, which is sup-
posed to have belonged to the agora mentioned by Vitruvius.
Where the modern Turkish fortress called the Castle of Bûdrûn is, at the eastern
end of the greater port, stood the palace of Mausolus, the smaller port being formed by
the island of Arconnesus.
Vi-
According to Vitruvius, Mausolus was a powerful king, and constructed here a mag-
nificent residence, which was standing in the time of Pausanias (lib. viii. cap. 16.).
truvius informs us that it was built of brick, covered with slabs of Proconnesian marble,
so highly polished that they sparkled like glass: he also tells us that this king was born at
Mylasa, and established himself here on account of the situation being so well fortified by
nature, and the port admirably adapted for commerce. The site of the city resembled
an amphitheatre in the lowest part, near the harbour, was built the forum: up the hill.
in the middle of the curve, was a large square, in the centre of which stood the Mausoleum
reckoned among the seven wonders of the world. On the summit of the hill was the
temple of Mars, with its colossal statue sculptured by Leocharis : on the right was the
temple of Venus and Mercury, near the fountain of Salmacis. This place was colonised
by Melas and Arevanias, who were driven out of Argos and Trozene by the Carians and
Lelegæ.
The palace of Mausolus commanded on the right, a view of the forum and the harbour,
as well as the whole circuit of the walls, and on the left, it overlooked a private harbour,
which was so contrived amid the mountains that no enemy could pry into it. From this
palace Mausolus could direct both his soldiers and sailors.
Upon the death of Mausolus, the Rhodians, indignant at his wife, who succeeded to the
government of Caria, fitted out a fleet for the purpose of seizing her kingdom. When the
queen, Artemesia, heard of it, she commanded her fleet to remain quiet in the secret harbour,
and her soldiers to man the walls. On the Rhodian fleet entering the large harbour, she
ordered the citizens and those who were on the ramparts to hail them, and to promise to
surrender up the town. The Rhodians eagerly left their ships, when Queen Artemesia
suuucnly opened a canal, brought her fleet round, and entered the large harbour, whence
the Rhodian fleet, thus abandoned, was easily carried out to sea. The Rhodians, having all
retreat cut off, were surrounded and slain in the forum, Artemesia, then embarking her
own sailors and marines on board the Rhodian ships, set sail for Rhodes; where the
inhabitants, seeing their vessels decorated with laurels, imagined their fellow-citizens had
returned victorious, but received their enemies. When Artemesia had taken Rhodes, she
slew the chief of the citizens, and raised two brazen statues to commemorate her victory:
one of these represented Rhodes, the other herself, imposing a mark of infamy on the city,
which, as it was always contrary to the religion of the Rhodians to remove a trophy, they
encircled with a building.
The remains of walls and square towers are visible for a great extent, continuing for
a distance of six miles from the western horn of the port, along high grounds to a con-
siderable eminence, and then to the eastern promontory, on which the modern castle is
built. On the highest point of this eminence are traces of the ancient walls, indicating
the arx media, mentioned by Vitruvius, where the temple of Mars stood. At the foot
of the hill are the remains of a theatre fronting the south, cut out of the side of the hill,
where the steps show the position of the marble seats.
The modern castle stands on a tongue of land at the eastern extremity of the port,
which it commanded: it is constructed of materials brought from some more ancient
buildings. This may be the site of one of those fortresses described by Strabo, lib. xiv.,
as remaining when Alexander took the city.
The Fort of San Pietro was taken by Philibert de Nailar, the Grand Master of Rhodes,
and was in the possession of the knights until it was surrendered to the Ottomans in the
year 1522.
The Island of Cos, now called Stanchio, was an ancient port, at present defended by a
fortress of considerable strength, with a moat on the land side. Columns of cippolino,
breccia, granite, and marble are found in the modern buildings, which attest the importance
as well as splendour of the former city. The mosque is entirely of marble, brought from
the ruins of temples; and the antiquary, by searching within the walls for inscriptions
and ornaments, may understand the character of the original structures which have been
demolished,
The ancient port is filled up with soft mud, and there are no remains of any mole ;
though probably, by a diligent search among the foundations of the fortress, some might be
CPAP. III.
55
GRECIAN.
discovered. The modern landing-place has extended farther into the sea, which is here
entirely landlocked towards the north. In the wall of the quay, facing the port, are worked
up fragments of ancient statues.

ANCIENT PORT
1.FOOT SOFT MUD.
MOSQUE
ANDING PLACE
Fig. 60.
t
Cos.
SCALE OF A MILZ
The island of Cos gave birth to Apelles and Hippocrates, the members of whose schools
were consulted by the inhabitants of all the neighbouring islands; the remains of an aque-
duct which conveys water for a distance of three miles into the town, still bear the name
of the latter; the top has been destroyed, to allow the women of the island more readily to
obtain it, which is excellent, as it flows from a mountain of limestone, of which this island,
as well as the others in these seas, is composed.
Myndus. Here are the remains of a long stone jetty, built with two parallel walls,
13 feet in width, connecting the island with the mainland; this ancient port is not far
distant from Halicarnassus, and a modern jetty now nearly shuts in the mouth of the
harbour. The part which constituted the island is covered with walls, amid which are the
traces of ancient foundations. The Libs, or south-west wind, often commits great ravages
on this coast, and renders navigation difficult.
Herodotus informs us that the first maritime power in these seas was obtained by Minos
the Cnossian, who, according to Diodorus Siculus, established many cities in Crete, and
founded some equitable laws for the government of the inhabitants. With his fleet he con.
quered all the islands in these seas, and was the first of the Greeks who acquired dominion;
after which he arrived at a high pitch of glory by reason of his justice and valour, and died
in Sicily whilst carrying on a war against Cocalus. Thucydides observes, that this naval
hero commanded the islands called Cyclades, expelled all the Carians from them, and sent
colonies under his own sons to supply their place. The Carians settled on the continent of
Asia, where Myndus was one of their chief ports. Pliny names several free cities near it,
as Palæmyndus, Nariandus, Neapolis, Caryanda, Termera, and Iasus, in the gulf so called.
Rhadamanthus, brother of Minos, also reported to have been the progeny of Jupiter and Eu-
ropa, shared in the government of the islands above mentioned, and Chios became the seat
of government soon afterwards under a son of Minos and Ariadne. The heros or captains
of this fleet had bestowed upon them either an island, or a port upon the continent; and
Diodorus Siculus gives Lemnos to Thoas, Cyrnus to Engyeus, Peparethos to Pamphilus,
Maronea to Euambeus, Paros to Alcæus, Delos to Arrion, and Andros to a hero of the
same name. Neither the ships, nor ports which received them, are described by any ancient
authors in a manner to give us an idea of their form or adaptation.
Some of the paintings taken from the walls of the houses at Herculaneum and Pompeii,
show us the forms of the vessels, character of their landing places, and stupendous moles;
but it has not been possible to identify these representations with what remains at any of the
ancient ports.
Medals also exhibit the ships in use, but not in a manner to convey a very
clear idea of their figure.
E 4
56
CHAP. III.
HISTORY OF ENGINEERING.

Fig. 61.
마
​SCALE OF MILE
MYNDUS.
Palermo.
This harbour is very much exposed to the swell of the sea from the north-eas,
and the anchorage for ships is dangerous when the wind blows from the west. In former

PORT FELICE
CASTEL
AMARE
PORT CALITA
TH OFFICE
ก
Baa
SCALE
Σ
CHURCH/
STABLES
LIGHTHOUSE
BATTERY
MAQAZINE
ARSENAL
BARRACKS
FORTY
MOLE
11 MILE
Fig. 62.
PALERMO.
times the harbour was composed of two long creeks, about 150 feet in breadth, which
extended into the city, and was enclosed towards the sea by a boom; but about 1550 it
became so silted up that it was built over. The Phoenicians, the Greeks, the Romans, and
Normans have all contributed to form this beautiful harbour, which is now shut in by Port
CHAP. III.
57
GRECIAN.
Flemmirium
Mmmm
Cailita, or Health-office, on one side, and the mole terminated with its lighthouse on the
other: here stands Palermo amidst its plains covered with convents, villas, and palaces,
forming one of the most splendid prospects in the world.
The Marina, a raised public walk, more than a mile in length, and 240 feet in breadth,
is defended by a parapet wall.
Syracuse. This ancient maritime city, built upon a rock, may, at the present day, be
traced in many places, as may the excavations in the natural stone, where the walls of both
public and private buildings were raised. The direction of the principal and transverse
streets may be followed by the channels cut to the depth of six inches in the rock by the
carriage wheels.

Port
Desd
FORTYCIA
Port
Neapoli
Acradîna
m
Tica
Fig. 63.
BYRACUSE.
The boundary walls, constructed of stones of large dimensions, worked perfectly square,
and laid without either cramps, cement, or mortar, in many situations remain perfect, to
the height of 6 or 7 feet.
Syracuse was one of the most populous as well as powerful cities of antiquity. When
it was besieged by Marcellus, about 213 years before Christ, it contained 1,800,000 inhabit-
ants. It was divided into four quarters, separated from each other by lofty walls. Cicero,
in one of his orations, observes, that Syracuse was the largest and most magnificent city in
Greece, that its two ports were almost enclosed by nature, and that at their junction an
island was formed, which was united to the city by means of a bridge thrown across the
strait. The first part of the city called Ortygia, was on the island above mentioned.
This, advancing into the sea, covers the entrance to both ports; and on it was situated the
palace of Hiero.
The second part of Syracuse was called Acridina, containing a spacious square, porticoes,
a prytaneum, or building in which the council assembled, a temple dedicated to Jupiter,
and a wide street running from one end to the other, with others at right angles, in which
were the private houses.
The third division was Tyca, which had a temple to Fortune, a gymnasium, and several
public buildings. This quarter was the most populous.
The fourth division was the last built, and called Neapolis: here are the remains of a
large theatre, two temples, one dedicated to Ceres, the other to Proserpine.
The boundary of the ancient walls, according to Strabo, was 180 stadia, or 22½ miles,
including the Epipolæ, one of the suburbs, which commanded the whole city.
The Great Port is about 5 miles in circumference, and to render it more secure against
an enemy, a strong chain was stretched across it from the island to the opposite rock,
Plemmyrium, a distance of about half a mile.
58
CHAP. III.
HISTORY OF ENGINEERING.
On the other side of Ortygia is the lesser port, called formerly the Portus Marmoreus,
in consequence of its being paved with marble. One of the most memorable events in
history is the taking of Syracuse by Marcellus, a little more than two hundred years before
Christ in its defence was employed Archimedes, the greatest engineer among the ancients,
who was singularly skilled, according to Livy, in the science of astronomy and geometry;
and also eminent for his invention and construction of warlike engines, by means of which,
with very slight exertions, he could baffle an enemy.
When Marcellus marched against Syracuse, Appius Claudius commanded the land
forces, and himself the fleet, which consisted of sixty galleys of five banks of oars, full of all
sorts of arms and massive weapons. The consul Appius stationed his army round the
Scythian portico, from whence the wall was continued along the shore to the mole of the
harbour: he employed a great number of artificers for five days to prepare everything
necessary for the siege; but, according to Polybius, he had not calculated upon the great
skill that would be opposed to him, nor had he considered that the mind of a single man
on some occasions was far superior to the force of many hands. Syracuse was a place of
great strength; the wall that encompassed it was built upon lofty hills, whose tops, hanging
over the plain, rendered all approach from without difficult. Towards the sea such a
quantity of instruments for defence had been contrived by Archimedes, that the besiegers
were baffled on all sides. Appius, however, with his blinds and scaling-ladders, advanced
towards that part of the wall which was joined to the hexapylum, on the eastern side of
the city, and at the same time Marcellus directed his course towards Achridina, with his
fleet filled with soldiers armed with bowstrings and javelins, in order to drive the enemy
from the walls.
There were eight other vessels, from one side of which the benches of the rowers had
been removed, from the right side of some, and the left of the others. These vessels were
joined in pairs and rowed by oars on opposite sides, and in them were placed machines
called sambucca or sackbuts. These machines contained a ladder about 4 feet in breadth,
and of a height equal to the walls against which they were to be raised. On either side
was formed a high breastwork or tower. The ladder was laid at length upon the sides in
which the two vessels were joined, but extending far beyond the prows, and at the top of
the masts pulleys were fixed with ropes. At the proper time ropes were attached to the
top of the machines, and while some, standing on the stern of the vessels, drew the ladder
up by the pulleys, others at the prow at the same time assisted in raising it with levers.
The vessels being then rowed near the shore, they endeavoured to fix the machines against
the walls. At the top of the ladder was a small stage, guarded on three sides by blinds,
and containing four men, who, engaging with those upon the walls, were to endeavour to
make fast the machine, and when fixed, these men, being raised above the top of the wall,
threw down the blinds on either side, and advanced to attack the battlements and towers.
The rest at the same time ascended the ladder without any fear that it should fall, because it
was strongly fastened with ropes to the two vessels.
This machine was called a sackbut, because it resembled that instrument when it was
raised.
Archimedes was prepared to meet the attack made by the Romans, and while the
vessels were at a distance, he employed against them catapultæ and balistæ of enormous
size, worked by powerful springs, which discharged darts and stones, throwing them into
great disorder.
When the darts passed beyond them, and the vessels came nearer, he used
other machines proportioned to the distance. Thus repulsed, Marcellus gave over till the
night arrived; but when the vessels again approached, they were exposed to new danger
from another invention of Archimedes. He had made openings in many parts of the wall,
equal in height to the stature of a man, and a palm in breadth, and having stationed archers
on the inside, and small scorpions, he discharged such a multitude of arrows through the
holes, as to disable the soldiers on board.
When they again attempted to raise the sackbuts, there suddenly appeared above the
walls other machines which he had caused to be raised along the whole length on the
inside, and which were concealed from view: these stretched their long beaks far beyond
the battlements, and many carried masses of lead, and stones of ten talents in weight.
When the vessels approached, the beaks were turned by means of ropes and pulleys, and
then let fall their stones on the sackbuts and vessels below, and all attending them were
thus thrown into the greatest danger. The combatants upon the prows of the vessels were
all forced to retire from the discharge of the darts through the openings in the wall, or from
the large stones thrown down upon them.
One of the inventions of Archimedes on this occasion was a large iron hand, hanging by
a chain from the beak of a machine, which was thus applied: — the beak was guided like
the gib of a crane, over the prow of a vessel, and then the hand or grapple was let fall,
which attached itself to the prow; the opposite end of the gib was pulled down on the
inside of the wall, and acting then on the principle of a lever, raised the vessel on its stern,
when the chain was suddenly loosened by means of the pulleys, and the vessels were some
CHAP. III.
59
GRECIAN.
thrown on their sides, some bottom upwards, and others sunk, and as Marcellus jestingly
observed, "his vessels were treated as buckets to draw water.
"
Appius was also obliged to abandon his designs on the land side, for similar obstacles
prevented his success: the iron hands or grapples were employed here to lift men with their
armour into the air, and then dash them against the ground. So wonderful seemed the
power of this one eminent engineer, that they were obliged to withdraw their forces, and at
last attempt to destroy the city by famine: the place was closely blockaded, and all supplies
of provisions cut off both by sea and land.
Archimedes, who was the greatest mechanic among the ancients, was born at Syracuse,
about 290 years before the Christian era, and was nearly related to Hiero, the king of that
city. He was educated in the sciences of his native country, and afterwards travelled into
Egypt, which had been for centuries the resort of many of the Grecian philosophers.
Here he remained for several years, and probably became acquainted with the combinations
of the mechanical powers, which enabled him to produce the wonderful machines he
afterwards used; for in Egypt the lever was applied long before his arrival, in lifting and
moving masses of stone to heights far greater than is usually supposed. The discoveries
of Archimedes in geometry were highly important. In the two books which he wrote upon
the sphere and cylinder, he demonstrated that beautiful theorem, that the surface as well
as the solidity of any sphere is equal to two-thirds of its circumscribing cylinder, and that
the surface of each cylindrical segment, comprehended between planes perpendicular to the
axis, is equal to the superficies of the corresponding spherical segment. In his treatise
upon the circle, he also showed that the ratio of the diameter to the circumference was as 7
is to 22; this result he discovered by taking an arithmetical mean between the paremeters
of the inscribed and circumscribed polygons.
In his treatise on conoids and spheroids, he shows the mutual relation between these
solids, as well as to cylinders and cones of the same base and altitude. The solidity of the
parabolic conoid, he found, was one-half that of the circumscribed cylinder, or three-
fourths of a cone of the same base and height; and that the area of the parabola is four-
thirds that of the inscribed triangle, or two-thirds that of the circumscribed parallelo-
gram. He made us acquainted with the properties of the spiral curve, and the method
of drawing tangents to it: also that the sector of the spiral is one-third of the circular
sector which incloses it, and consequently that a spiral, which has made one revolution, is
equal to one-third of the circle in which it is comprehended.
The fundamental properties of the lever are fully given in his book De Equiponderantibus,
or Isorropica: he there proves that a balance with unequal arms will be in equilibrio if the
two weights in the opposite scales are reciprocally proportional to the arms of the balance.
He shows also that the fulcrum sustains the whole weight, and that there is the centre
of pressure or gravity, and that this centre of gravity is to be found in the parallelogram,
triangle, trapezium, or parabola.
His treatise De iis quæ Vehuntur Influido contains the principles upon which the
science of hydrostatics is founded: he shows that when fluids are in equilibrium, each
particle is equally pressed in every direction: he also inquired into the state of solid bodies
floating in water. It appears singular that it should not have been previously known that
the weight a body lost when floating in water, was only counteracted by the upward
pressure of the liquid.
Archimedes was a man of wonderful sagacity, and laid the foundation of all the sciences,
the prosecution and improvement of which are the boast of the present day. He was slain
by a soldier during the assault made at the taking of Syracuse, about 212 years before
Christ. The ingenious and simple method of raising water by means of a pipe twisted
round a cylinder in the form of a corkscrew, and laid in an inclined position with one end
immersed in the water, which, when made to revolve about its axis, caused the water to
run out at the top, is called the Archimedian screw, and was invented by him whilst he
studied at Alexandria, in the school of the Ptolemies.
When this rich and splendid city fell into the hands of the Romans, Marcellus, viewing
from a height its beauty and extent, is said to have shed tears. The booty found in it was
immense, the royal treasure was carried to Rome, and to the success of Marcellus has been
attributed the subsequent degeneracy of the Romans: the statues and pictures which were
carried away from Syracuse introduced a taste for the fine arts, and led to that effeminacy
of manners which brought about the ruin of the empire.
There remains some part of the temple of Minerva, one of the most ancient in Sicily,
of which Cicero gave a very minute description: he describes the doors of gold and ivory,
and twenty-seven pictures it contained: it was of the Greek Doric hexastyle, and had
fourteen columns on the flank, comprising the outer; their height, including their capital,
was 28 feet 8 inches, and their diameter 6 feet 6 inches. There are also two columns be-
longing to a temple of Diana; and in that portion of the city called Neapolis are the
remains of a Grecian theatre, hewn, as they generally were, out of the solid rock. It has
three ranges of seats, separated by platforms or galleries, which afforded access to them:
60
CHAP. IIL
HISTORY OF ENGINEERING.
the proscenium is entirely destroyed, and the lower seats are buried: from these ruins
the most delightful prospect is obtained of the luxuriant plains below, watered by the
Anapus. The steps are perfect in many places, and there is also a portion of the covered
portico, or loggia, which surrounded the upper part of this once superb edifice.
Beyond is an amphitheatre of an oval form cut out of the native rock in a similar
manner; its longitudinal diameter 316 feet, and its transverse about 214. It was con-
structed no doubt at the time the Romans became masters of this city. Contiguous is one
of those reservoirs for water generally found near an amphitheatre, cut out of the solid
rock, and the aqueduct which supplied it: the reservoir is 57 feet long, 23 wide, and 10
feet deep.
The latomiæ or quarries, where the stone was obtained for the various buildings erected
in the city, are curious: that near the theatre is about three quarters of a mile in circum-
ference, and excavated to a depth of 120 feet below the level of the adjoining ground:
within are many subterraneous grottos cut out of the solid rock, one of which is called the

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CATACOMBS.
Ear of Dionysius, it having been formed by him. This grotto is serpentine on its plan,
about 170 feet in length, 20 to 35 in breadth, and about 60 feet in height: near the top
is a small aperture, which communicates with a chamber 6 feet by 4, said to have been
the place where the tyrant resorted for the purpose of listening to the conversation of the
prisoners confined within it.
The catacombs, or rather subterraneous city, used for the burial place of the ancient
Greek inhabitants, give us some idea of its vast population. The principal street,
which passes through them, is 20 feet wide and 8 feet high, and more than a mile in
length. On both sides are quarried out tombs, with semicircular headed openings: these
formed the sepulchral chambers, and some are admirably worked. Streets at right
angles pass from the main line, and here the ceiling takes a dome or spherical shape, in the
centre of which is an aperture to admit light and air.
There are many of these catacombs or underground works, cut out of the native
rock, to be found along the shores of the Mediterranean; at Malta they extend for
a very considerable distance, and appear to have been resorted to in the middle ages by
the pious, and dedicated to religious purposes. By some writers their excavation is attri-
buted to the Phoenicians, who were in the habit of depositing their corn and merchandise
within them for security when they traded with the native inhabitants. In some instances,
as at Paris, these subterranean streets may have been formed by drawing out the stone for
the purposes of construction.
Agrigentum, inhabited by a Grecian colony, became celebrated for the refinement of its
inhabitants, for the skill displayed in the fine arts, and particularly for the mechanical
powers which were employed in raising ponderous masses of stone for the construction of
their public buildings: it was situated about 18 stadia or 2 miles from the sea, between
CHAP. III.
GRECIAN.
61
two rivers, the Agragas and the Hypsa. Polybius thus describes it: "The city of
Agrigentum surpasses most other cities, not only by its fortifications, but also by the

Fig. 65.
AGRIGENTUM.
beauty and magnificence of its edifices, and being only 18 stadia from the sea, is abundantly
supplied with fish. It is completely fortified both by nature and by art, and its walls are
built upon a rock, which forms an excellent foundation; above all, it has been rendered
inaccessible by the labours of men, where it was not so of itself. Besides, this city is
partly surrounded by rivers, on the south by the Agragas, and on the west by the Hypsa;
and on that side regarding the east is the citadel, which is surrounded by a deep ravine.
There are erected on the heights of this citadel a temple of Minerva, another of Jupiter;
and as Agrigentum was originally colonised from Rhodes, the worship of the god is the
same as that of the Rhodians. Among many other things with which this city is enriched,
are several beautiful temples and magnificent porticoes; as the temple of Jupiter Olympus,
which is the most sumptuous, yielding to none in Greece either in beauty or grandeur.
"Agrigentum was admirably adapted for commerce, from whence it derived all its wealth.
Situated on the southern coast of Sicily, it carried on a vast trade with both Tyre and Sidon.
Its territory was highly fertile, extending over 1000 square miles, and, according to
Diogenes Laertius, this small territory contained 800,000 inhabitants. They exhibited
considerable taste in the fine arts, and it was observed by Plato, they built as if they were
to live for ever, and feasted as though they were to die on the morrow. It is impossible
to account for the great magnificence of this city, where all the merchants were princes.
The most flourishing period in its history was comprised in one century, which terminated
about 405 years before Christ, when the Carthaginians besieged and destroyed it, at which
time, says Diodorus Siculus, the temple of Jupiter was the most considerable on the island,
and that when the Agrigentines were on the point of roofing it in, war put an end to their
operations: after that the city was so far reduced, that they no longer had the means to
finish it."
The length of this temple is 369 feet 6 inches, the breadth 182 feet 8 inches, which by
no means accords with the dimensions left us by Diodorus, who gives 340 feet for the
length, and 60 feet only for the breadth. In the front are seven columns, and double that
number on the flanks, the angles included, disposition usually met with in the early Greek
temples. The columns are built in a wall, and project a little more than half their diameter:
they are 13 feet in diameter, and their projection 7 feet 7 inches; they have eleven flutes;
from centre to centre they measure 26 feet 9 inches; from the outer face of the column to the
face of the internal wall, which united with it, is a thickness of 15 feet. The height of
the steps on which the bases of the columns rest is 14 feet; the base of the column, which
is an unusual feature in the Greek Doric, is 4 feet in height; the column, capital, and base
62
CHAP. III.
HISTORY OF ENGINEERING.
are 61 feet 9 inches in height, the entablature 25 feet 9 inches and the pediment pro-
bably as much more: the whole height may have been 100 feet.
The podium formed a magnificent platform for the reception of the temple: it stands
upon a native rock raised on solid courses: throughout the whole plan to the level of the

CARICATORE
OF
GIRCENTI
TOMONTE
MOUNT TAURUS
CARTHAGINIAN CAMP
Fig. 66.
MOLE HEAD
LIGHT.
AMED FROMANO
RUPA ATHEN,
SPITE DE AGRIGENTUÍ
QUARRY
VALLEY
TEMPLE OF
T OF
A STOR & POLLUS
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CITY WALLS
UNO LUGINA
GIRGENTIı.
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TOMB OF THERON
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S.AMBROSE.
BOINI.ST.LEON.
floor these courses are alternately placed diagonally, and a perpendicular joint separates
them from the wall of the peristyle.
The columns are constructed also in courses, with a core alternately circular ana
octangular; a key or dowel is inserted in their beds; but the writer could find no trace of
metal cramps; their diameter is 13 feet; the flutes are sufficiently large, as Diodorus
observes, to receive a man within them: the echinus of the capital is formed of two
stones only, each weighing at least 21 tons: these are united by plugs or dowels to
the centre stone of the abacus. The abacus is formed of three stones, two of which are
11 feet 9 inches in length, 5 feet wide, and 2 feet 9 inches in depth: the centre stone is 11
feet 9 inches long, 5 feet 9 inches wide, and 2 feet 9 inches deep.
The architrave is 11 feet in height, and is constructed of three courses of stone, each
being about 9 tons in weight; the distance from column to column on the lower course
is 17 feet 8 inches. It required great skill to construct this portion of the work, and
the engineer used all his ingenuity to accomplish it. The two stones forming the
lower course are carried on a beam of hard wood, inserted into a dovetailed channel of
their soffites, the ends of each stone resting on the abacus, acting as a corbel at the same
time.
are
The triglyphs are all of one stone, weighing 12 tons each; the metopes
composed of two stones: on each side of the triglyphs remain the square holes which
sustained the scaffolding. Each end of these large stones had channels cut in them of the
form of a horse-shoe, into which the ropes were placed, by which they were raised, for the
stone was too soft in its quality to permit the use of either the lewis or the forceps.
These triglyphs are 10 feet 2 inches in height, 5 feet 10 inches in width, and 4 feet 10
inches in thickness. In the small portion of this temple remaining, parts of four distinct
giants are to be seen: built up in courses, each composed of twelve, alternately solid,
divided by a vertical joint down to the legs, and occasionally connected with the pilaster
behind them; their height was about 25 feet when entire.
The temple to Jupiter was a compound
a compound of two others, or pseudo-peripteral, the
peristyle being formed by columns inserted in the walls of the naos; the columns of the
east and west fronts were probably insulated as Diodorus expressly mentions porticoes.
On the pediments were sculptured the war of the giants, and the siege of Troy: it was
CHAP. III.
69
GRECIAN.
called the temple of the giants, from having figures in the manner of Caryatides
supporting some part of the edifice. According to Diodorus Siculus, it was the largest
temple in Sicily, and might be compared with the grandest and most magnificent monument
that ever existed.
:
Not far distant from the ruins of this temple, are the remains of the famous Piscina,
which, according to the same writer, was 7 furlongs in circumference, and 20 cubits in
depth the water was conducted into it from the neighbouring streams: this was probably
executed by Pheaces, under whose direction were made the several sewers which carried
off the water from the city, and which were afterwards called by his name; he lived in the
time of Gelon, or about 500 years before Christ. These sewers, therefore, were subsequent
to the great Cloaca at Rome.
This city was surpassed by few in the beauty of its temples, and for the luxuriance of the
country around: there are the remains of a temple to Hercules, Castor and Pollux, Juno
Lucina, and Concord, all in the style of the Greek Doric. The modern town of Girgenti
is near the ancient mole.
Selinus was founded about 725 years before Christ, 107 years after Syracuse; and took
its name from the river Silenus. Its first inhabitants were a colony from Megara, a city on the
eastern coast of Sicily, which was called Megara of Attica, from whence its inhabitants
migrated; 250 years after its foundation it was besieged by Hannibal, carried by assault,
the citizens put to death, and the walls of the city rased to the ground. Soon after this,
Hermocrates repaired the walls, and assembled many of the wandering natives who flea
before Hannibal's army had arrived in the neighbouring states. It became again a place
of importance, and the temples, which had only been robbed of their treasures, remained
nuul a second siege by the Carthaginians, when they were thrown down; the city was
then abandoned, and Strabo enumerates it among the ruined cities of Sicily. The great
quantity of fallen stones which here present themselves lead us to fancy the buildings must
have been the work of giants, as, from the enormous size of some of the blocks which
composed them, it does not seem possible that they should have been moved by men.

PLAN OF SELINOS
Fig. 67.
The plan of the city, which is traceable from the existing walls, is somewhat in the
shape of a horse-shoe, whose two ends are towards the sea: these were terminated by
towers: the port, which lay between them, exhibits no remains. On the western side, the
walls are quite perfect, as are also two vast flights of steps, by which the inhabitants ascended
from the port to the city. The time when the six temples were thrown down, and the
means by which their ruin was accomplished, is unknown: it has been supposed it was the
result of an earthquake, as their immense solidity must have defied all human means. The
columns of the larger temple have all fallen in one uniform direction, thrown down by one
effort; but surely the power which could have raised the immense blocks might also, when
applied to their destruction, be competent to produce this effect.
All these temples were of the Greek Doric order; some of the blocks of stone used
in their construction were immense; one, which formed the architrave of the greater
temple, supposed to be dedicated to Jupiter, is 21 feet in length, 5 feet 8 inches in width,
64
CHAP. 11.
HISTORY OF ENGINEERING.
The
and 6 feet 9 inches in depth, containing 803 cubic feet, weighing probably 50 tons.
manner adopted by the ancients to lift such a ponderous mass, and place it safely upon the
capitals of columns, upwards of 40 feet from the ground, deserves our highest admiration.
Most of these temples, like others of the best periods of Greek architecture, were painted,
either entirely or in part; the Egyptians and the Etrurians probably set this example.
On sandstone, which had not an even surface, previous to painting, they spread a coat of
fine plaster or calcareous composition: the metopes of one of these temples, of a very early
date, are painted red, blue, and green; some of the parts were also gilt; and we fina
similar vestiges in the temples at Athens and elsewhere.
Egesta, according to Cicero, was founded by Eneas, after he fled from Troy. It
has always been considered one of the most ancient towns in Sicily. This city survived
many vicissitudes of fortune, and retained its importance till the Saracenic conquest,
when it was almost destroyed. The temple that remains is situated to the east of the
ancient city, placed upon the brow of a craggy precipice: the solidity of its construc-
tion as well as simplicity of its architecture, have occasioned it to be classed among
the earliest existing monuments of Sicily. The stylobate consists of three steps, the
upper of which is tooled perpendicularly: each stone forming these steps has a knob
projecting, similar to those in the Propylea at Athens, probably left to afford facility in
raising them. The temple is hexastyle peripteral, has fourteen columns in the flanks, including
those at the angles: the columns, unlike all others, are not fluted, although it was not
unusual to work such portions after the buildings were constructed. There is no part of
the cell remaining: the total length is 190 feet, and width 76 feet 8 inches.
There are
considerable ruins of a theatre, which has some stones in its construction of an enormous
size: it is erected upon a very irregular surface, partly resting on the native rock, and partly
on stone piers and solid walls: there is no vestige of an arched corridor, but the seats are
placed upon solid masonry: part of the proscenium wall as well as many of the ancient
steps remain.
At Taorminum is a similar theatre, which, from its fine state of preservation, is worthy of
being studied. The Greeks seem to have found a situation where little was required to
be done but to excavate the seats out of the native rock, and then erect the exterior and
interior portico which surrounded it. This theatre stands upon an eminence overlooking
the sea, almost entire; all that is not excavated out of the rock is formed with brick, and
the columns with which it was adorned were of marble, probably from the neighbour-
ing quarries. The summit of the mountain is of the shape of the portico which
surrounds the theatre, and formed a beautiful promenade: its site is precisely what
Vitruvius recommends, being elevated, and well calculated to convey the sound. The
spectators ascended the rock to the level of the portico by means of several staircases,
then entered the theatre, and descended to their seats. In the interior face of the wall
which surrounds the theatre are niches, which originally contained statues.
The interior, with its orchestra, pulpitum, and proscenium, partly remains: the pulpitum
was ordinarily formed of wood supported by walls, and here such foundations are still
apparent. The proscenium had three doors or entrances, were called aula regia, and
aulæ hospitalia. Some magnificent views of this theatre, made by Lusieri, were forwarded
to England some years ago, and are deposited in the British Museum.
Messina stands upon elevated ground, at the extremity of a range of mountains which
runs through Sicily. There is a broad modern quay, where vessels of almost any burden
may lie close in deep water. At the western extremity is a small fort and a gate: the
other end is closed by the citadel, which is a pentagonal structure, standing on the isthmus
of San Raniero: near this is the Lazaretto. The entire circumference of the port, which
is in the form of a sickle or zancle, is about 4 miles, and is said to owe its formation to the
effects of an earthquake, which opened a chasm, afterwards filled with water, upwards
of 70 fathom in depth.
Near the lighthouse is the pool Charybdis, formed by the crossing, or rather meeting,
of many opposite currents.
The first inhabitants of this celebrated port were the Siculi, driven out by the Cumæans ;
who in their turn gave way to the Samians and Messinians.
The straits which divide Sicily from Calabria are so narrow, that small fishing boats
alone are employed to convey the inhabitants from one side to the other; and many instances
are said to occur in which individuals swam across. St. Francis, in modern times, is
reported to have spread his cloak upon the waters, and with one end raised upon his staff,
to have thus passed from one shore to the other.
From the contiguity of Messina to the coast of Italy, it has at all times enjoyed consi-
derable commerce: here landed the Normans under Maniaces when Sicily cast off the yoke
of the Arabian conquerors in the year 1037; but within the present city there is little
remaining to indicate the Norman sway; there are no vestiges of either of the two churches
or other buildings completed by Count Roger-though in the crypt of the cathedral may
be seen some parts of the work of his son, afterwards king. Richard Cœur de Leon, assisted
CHAP. III.
65
GRECIAN.
the renowned Roger again to expel the Mahometans, and wintered here on his way to
Palestine.

ACQUA
LADRONE
CASTELLA
MESSINA
སཱཨཱ་བྷཔ
CARCURA
INFER
་་་་་ནམ་
لال السنة
UPER
STACATAAN
ROTTO
PT. PACE
PARADISE
/!BAY
SANITA
ROUN
LAKE ENCLISH
CANAL
VĒĻOJUS TOWER
FERLITTO
VERELLI
POINT REZZO
BATT
TELEGRAPH.TOW,
STORE
HOUSES
FOS SA
NAN
APONNARA PALACE
A.COSMO
CHARYBDIS
NIGHTHOUSE
CITADELLO
ARSENAL
FORT CHIM
Fig. 68.
MESSINA.
Posidonia, or Pastum, was happily situated both for the purposes of agriculture and
commerce, placed in the midst of a plain, bounded by the rivers Silarus and Accius on
the north and south, sheltered on the east by the mountain Alburnus, and open to the
bay on the west. The port Alburnus was near the mouth of the Silarus, and some
remains of it may still be traced; it was frequented by merchants of all nations. Strabo
tells us the original inhabitants, driven out of Sybaris on the shores of Tarentum, crossed
the Apennines, and settled in the plains of Posidonia. The Sybarites soon made their
new town both important and powerful; for two centuries they continued in a state
of perfect tranquillity, which was at last disturbed by the tyrant Dionysius of Syracuse,
who invaded the Grecian territories established in Italy: he afterwards, uniting with the
Lucanian aborigines, gained several victories, and Posidonia fell, about the year of Rome
413. Seventy years afterwards it was made a municipal town, and its name changed to
Pæstum.
From the neglect of proper cultivation and the drainage of the marshes, the stagnant
waters, emitting pestilential vapours, obliged the inhabitants to seek a new situation.
The walls which surrounded this city remain to a considerable height in many places, as
do the towers at the angles, and the ancient gates: its form is that of an irregular polygon,
about 3 miles in circumference.
There are three temples, an amphitheatre, and some other buildings. One of the
temples, supposed to have been dedicated to Neptune, possesses in a high degree all
the characteristics of Greek architecture: solidity, combined with grace and simplicity,
prove it to have been erected before the arts were on the decline. The stone used for
its construction, as well as for that of the other buildings, was brought from quarries
in the mountain Alburnus: it is a stalactite formed by a calcareous deposit, of the same
nature as travertino. A thin coat of stucco was laid over the whole to fill up the in-
terstices of this porous stone.
The form of the temple dedicated to Neptune was hexastyle, with fourteen columns on
the flanks, counting those at the angles: the upper step of the stylobate was in length
195 feet 4 inches, and its breadth 78 feet 10 inches: the columns are 6 feet 10 inches in
diameter, and 29 feet in height, including the capitals, while that of the entablature is
12 feet 2 inches. This temple was probably hypethral, as there are two inner rows of
columns, above which is another of less dimensions which supported the roof Those of
F
66
BOOK I.
HISTORY OF ENGINEERING.
the lower range are 4 feet 8 inches in diameter, and 19 feet 9 inches high, and the upper
have their shafts in accordance with the upper diameter of the lower order.
The second temple, or Basilica, as it is sometimes called, is pseudo-dipteral, has nine
columns in the front, and consequently three columns placed between the antæ; thus
differing from all other examples.
The
A range of columns passed through the middle of the cell longitudinally, probably
to support the roof. Its length, measured on the upper step, is 176 feet 9 inches, and its
breadth 80 feet: the diameter of the columns is 4 feet 10 inches, and their height, including
their capitals, 21 feet: the shafts diminish in a curved line, and are channelled with twenty
flutings. The entablature is not perfect, but the frieze was composed of two upright
courses of stone, the exterior one of which, with the whole of the cornice, is gone.
lesser temple is hexastyle-peripteral, with thirteen columns on the flanks, counting those at
the angles: its length, measured upon the upper step, is 108 feet, and its breadth 48 feet.
The columns are 4 feet 3 inches in diameter, and their height, including their capital, 20
feet 6 inches; they are about a diameter apart all round; they have 24 shallow flutings, and
were placed upon circular bases slightly projecting.
Bridges of the Greeks. The Gephyreans, who inhabited Eretria, formed a part of that body
of Phoenicians which, according to Herodotus, Cadmus brought with him into Greece, and
were acquainted with science as well as letters. When the Cadmeans were expelled by the
Argives, they fled to the Encheleans, and the Gephyreans were driven by the Boeotians to find
succour at Athens. They settled on the borders of the Cephissus, a small river which separates
Attica from Eleusis, and here they are said to have built a bridge. Larcher, in his notes
upon the above passage of Herodotus, observes that the author of the Etymologicum Mag-
num pretends that these people were called Gephyreans in consequence of their constructing
this bridge; Gephura signifying originally a dam, dyke, or mound; also the space which
occurred between two hostile armies in Homer; but generally it is significant of a bridge in
other authors. Pindar uses Pontou Gephura for an isthmus. The origin of the compound
word was Gea, earth, and Phero, I bear, as affording a passage from bank to bank.
In another passage in Herodotus we learn that when Croesus passed the river Halys with
his forces, it was by means of bridges, although the Greeks generally asserted that Thales
the Milesian assisted him in cutting another trench for the purpose of dividing the river,
and that then he was enabled to ford it readily; it being much less labour to divert the
waters of the river than to build a bridge.
There were in Greece few rivers which might not have been rendered fordable, and it
seems probable that the usual method adopted in early times to pass a river, was by
throwing in stones or earth to form a dyke or dam, which would occasion the water to
become sufficiently shallow for the passage both of men and cattle. Fords could be more
easily contrived than bridges, and it is certain that the latter were not much used by the
Greeks. When Darius had resolved to make an expedition into Scythia, he prepared a
fleet, and ordered a bridge to be thrown over the Thracian Bosphorus. Gibbon observes,
that the most skilful geographers that have surveyed the Hellespont give sixty miles as
the length of its winding course, and about three miles for the ordinary breadth. But the
narrowest part of the channel is found to be northward of the old Turkish castles, between
the cities of Sestos and Abydus. It was here that the adventurous Leander braved the
passage of the flood, and where the distance between the opposite banks does not exceed
five hundred paces. Xerxes imposed here his stupendous bridge of boats for the purpose of
transporting into Europe his 170 myriads of barbarians.
Herodotus says the breadth of the Bosphorus where the bridge was erected was 4 stadia,
and that Darius was so much delighted with its construction, that he made many valuable
presents to Mandrocles, the Samian, who constructed it. Mandrocles, in consequence, caused
a representation of the bridge, and the king seated on his throne reviewing his army as it passed,
to be made, which was consigned to the temple of Juno, where it remained for some time.
After Darius crossed into Europe, he ordered the Ionians to pass over the Euxine to the
Ister, to erect another bridge, and await his arrival.
When Xerxes passed the Hellespont, 480 years before Christ, numbers were employed
in constructing a bridge betwixt Sestos and Madytus, in the Chersonese of the Hellespont;
and the work was commenced on the side next Abydus. The Phoenicians in his
army used a cordage made of linen, and the Egyptians the bark of the biblos; and
this bridge, which is briefly mentioned by Herodotus, was no sooner completed than de-
stroyed by a tempest. Whether made of boats or floating timber, we are not informed.
After this a bridge was constructed by different architects, who performed it in the
following manner : — -they connected together ships of various kinds, some long vessels of
fifty oars, others three-banked galleys, to the number of 560, on the side towards the Euxine
Sea, and 313 on that of the Hellespont. The former were placed transversely, but the
latter, to diminish the strain of the cables, in the direction of the current, when these
vessels were secured on each side by anchors of great length; on the upper side, because of
the winds which set in from the Euxine; on the lower, towards the Ægean Sea, on account
CHAP. III.
67
GRECIAN.
of the south and south-east winds. They however left openings in three places sufficient to
afford a passage for light vessels, which might have occasion to sail into the Euxine or from
it. Having performed this, they extended cables from shore to shore, stretching them from
large capstans of wood; the cables being made of white flax and biblos: two of one being
united with four of the latter, they were alike in thickness, but those made of the flax were
the strongest, and every cubit in length weighed a talent.
After the boats were fixed, large timbers were laid across the cables, and bound fast to
them; these were floored over, and a platform made in the usual way, upon which was
placed a layer or stratum of earth, and a fence raised on each side to prevent the horses
looking down into the sea.
Polybius, in alluding to the first bridge built by Darius, says that the width of the strait
between Sestos and Abydus was not more than two stadia, that both shores were covered
with inhabitants, and that they sometimes threw a bridge across the strait and passed
from one side to the other on foot; at other times vessels were seen sailing upon it;
and also that the city of Abydus was enclosed by the promontories of Europe, and had a
safe harbour, in which ships might be sheltered from every wind; but that at its entrance
it was not possible for a vessel to anchor, on account of the violence with which the waters
rushed through the strait.
Cyrus is said by Xenophon, when he marched from Sardis, after passing through
Lydia, to have crossed the river Mæander, where it was two plethra in breadth, by a
bridge supported on seven boats. Supposing this distance to have been 200 Greek feet, it
would not have been difficult to throw a timber platform from one boat to the other, and
make a substantial roadway.
The usual method of crossing rivers is perhaps that described by Xenophon in his
march through the desert, when he came to Carmande on the Euphrates: here the soldiers
purchased provisions, and afterwards passed over the river on rafts, made by filling the skins
they used for their tents with dry hay, and sewing them together, so that the water could
not enter. The Roman soldiers, as well as the Greeks, made their tents of skins; and we
learn that Alexander, in his victorious march through Asia, used this method of crossing a
river. In this manner he passed the Oxus, which was a wide, deep, and rapid stream; and
Arrian informs us that this passage occupied five days.
The Mole, which united Chalcis in the island of Euboea with Aulis in Boeotia, is described
by Diodorus Siculus as formed over the Euripus, the name of the straits that separated
the island from the mainland. When Mindarus, the commander of the Peloponnesian fleet,
arrived at Abydus, and had repaired his shattered boats, he sent for succour to the Lace-
demonians, determining to lay siege to the Athenian cities in Asia. The Chalcedonians
and the inhabitants of the island of Euboea, at that time had deserted from the Athenians, and
the latter were greatly alarmed from fear of an invasion, the Athenians being the masters of
the sea they therefore solicited the Boeotians to help them to stop up the Euripus, and
attach the island to the continent. In this narrow strait the sea was supposed to ebb
and flow seven times in twenty-four hours, and Aristotle destroyed himself because he
could not ascertain the cause of this phenomenon. The Boeotians readily consented, as
it would make Euboea part of their continent. All the people that could be assembled took
part in this great work, and commenced a mole at Chalcis, and another at Aulis, on the
Boeotian side; and each was advanced over this unquiet, and then raging passage of the sea,
until the way was so narrow that there was only room for one ship to pass; after which
forts were constructed, and a wooden bridge thrown across the opening.
The port of Aulis would at one time contain fifty ships, and was famous for its manu-
facture of pottery; the opposite port, which is now the town of Vathi, is completely land-
locked, which accounts for the extreme narrowness of the Euripus itself, now crossed
by a wooden bridge: this leads to a Turkish fort, then a marsh, where is another wooden
bridge, which conducts to Negropont.
Walls of cities. There can be no doubt, that in the primitive ages of society, security was
one of the chief considerations, and that no exertion was spared by any of the nations of
antiquity to carry up works of defence. Throughout Greece are remains of cities, where
we have evidence of the labour bestowed upon the walls, which, when in a complete state,
were regarded as the performance of persons something more than human.
The walls of Tiryns and Mycenæ are perhaps the most ancient and the most cele-
brated. Homer mentions the former, a proof of their existence in his time: they are
said to have been constructed by a colony of Lycians, under the direction of Protus,
the brother of Acrisius, long before the Trojan war. The city of Tiryns occupied
a rising ground in the plain of Argos, and was of no great extent, being 220 yards in
length and 60 in breadth, according to Pausanias, it was founded by Tirynthus, the son
of Argus, who employed the Cyclops to construct the walls: these were built of large
masses or blocks of stone, each requiring two oxen to move it: after one was placed, another
was brought, and laid adjoining, the interstices being filled up with fragments and
:
F 2
68
Book 1.
HISTORY OF ENGINEERING.
smaller stones to render the work more solid. Some of these masses measure more than
9 feet in length, 4 feet in breadth, and as much in thickness. It had three gates, the chief
flanked by a solid tower, which could only be ascended by a flight of steps running
parallel with the wall for some distance, and afterwards turning at right angles, before it
reached the gate.
Euripides is among the first who designates the construction with polygonal blocks,
Cyclopean; they were probably the work of the Pelasgi, who were the earliest inhabitants
of Greece of which we have any account. These people may be traced throughout every
part of Greece, Peloponnesus, Thessaly, Attica, Boeotia, Phocis, Macedonia, and even at
Delphos, where the oracle was Pelasgic. Dardanus, the ancestor of Priam, was of this
race.
The Pelasgi remained in possession of Arcadia until the second Messenian war; and
they were finally expelled, or conquered, throughout Greece, it is supposed, at a considerable
time before the Trojan war. After their expulsion the Hellenes were established; Danaus
founding Argos; Cecrops, Athens; and Dardanus, the Phrygian cities. Diodorus allows
the Pelasgi, however, to have retained dominion at sea, from 1088 to 1004 years before
Christ; they are said by Dionysius to have finally settled in Italy at an earlier period, and
that they began to decline about 1170 years before Christ.
In the most ancient part of the walls of Tiryns there is, for the length of 90 feet, a
gallery, supposed at one time to have continued through the whole circuit of the external
walls, which must have been of great advantage to the inhabitants in the defence of their
city. It is 5 feet in width and 12 in height, formed of large stones, laid in horizontal
courses, gathered over towards the top, where they incline against each other, thus pre-
senting in the section of the gallery the form of a pointed arch. At every 9 feet distance
is contrived a recess, to retire during the time it was required for another to pass.
doubtedly this is one of the earliest examples of a practice afterwards universally adopted
both by Greeks and Romans.
Un-
The walls of Tiryns were destroyed, according to Pausanias, for enlarging Argos; what
remains is upwards of 43 feet in height, though originally much higher.
Mycenæ, in the neighbourhood of Tiryns, far exceeds it in extent: according to Pau-
sanias, it was founded by Persicus, and the circuit of its walls followed an irregular line, en-
closing an area, in length about 330 yards, and in breadth 220 yards.

་་
་
CU
LIG
-
initia
TREASURY
Fig. 69.
MYCENÆ.
The walls consist of polygonal blocks, so large and solid, that they have defied the de-
struction offered both by time and by the hand of man. The Argives commenced the
destruction of this city about 468 years before the Christian era; but they could not
break down the whole of the walls, the stones being so firmly united together. The
blocks with which they are built, on the outside present a fair and even face, and their
CHAP. III.
69
GRECIAN.
ends and sides are fitted to each other. And there are evidences that stone-cutting was
new adopted. No mortar or cement was made use of; the massive blocks received their

-
མ༠༠༩{ti།
Fig. 70.
stability from the manner in which they were wedged in, many passing entirely through
the whole thickness of the wall, and bonding it together.
On the north side of the acropolis may still be seen remains of the walls built by
the Pelasgi, and which are usually denominated Cyclopean.
The sites of these early Greek cities were generally chosen upon rising or elevated
ground, and the form of the hill or eminence usually decided that of the city. On the
highest ground was placed the acropolis or citadel: such was the method adopted in setting
out Athens, and, where the wall made an angle, it was sometimes further strengthened by
throwing out some additional work, which may have led to the introduction of towers.

Fig. 71.
Gates or entrances to the Greek cities were of four different kinds: the earliest and the
most usually found, perforating their ancient walls, had its sides perpendicular, and the
opening above closed, by the polygonal blocks advancing until they met in the middle at
top, like the gallery at Tiryns; there are many remains of this kind of gate, as that at
Signa. (See fig. 74.)
In the Isle of Delos is another of great antiquity, which is formed by the inclination of
stones resting one against the other. (See fig. 57.)
This very curious remain forms the part of a gateway, or opening, through the walls of
an ancient fortification, around the lower part of the mount Cynthus. Ten large stones,
inclined towards each other, form the covering to the opening, and very much resemble
some of the examples met with in the pyramids, where the weight over the passages and
galleries is discharged in a similar manner. Should this portion of the walls be as early
as the time of Minos, we must consider that he employed the same construction as the
Dorians, or Cyclopeans as they have been called.
Delos, after having been the abode of pirates, was converted into a colony of Athens by
Erysichthon, son of Cecrops, who erected the first temple to Apollo, afterwards held in
such high veneration by all the Greeks, and even respected by the Persians, who laid waste
F 3
70
HISTORY OF ENGINEERING.
BOOK I
most of the other islands in this sea. Pericles, according to the historian Thucydides,
seized upon the treasury established here by the states of Greece, which amounted to
10,000 talents, for the purpose of defraying the expenses of erecting the Parthenon at
Athens.
Mount Cynthus was the birthplace of Apollo and Diana, and from hence the Hyper-
borei, or most northern people of antiquity, transmitted annual offerings. The altars at
Delos were circular; it being the custom for the votaries of Apollo to run around and
strike them with whips, their arms bound behind them at the same time: they afterwards
bite the olive, which was a symbol of the motion of solar light, and of their desire that its
rays might pervade all space.
Numerous fragments of architecture and sculpture are met with in this favourite island;
among them, heads of bulls arranged on the entablature in a similar manner as found at
Persepolis, which might allude to the worship of the celestial bull, or the sun when occupy-
ing the place of that sign. Before Zoroaster reformed the Persian worship, under the
auspices of Darius Hystaspes, such emblems were common, and formed part of the Mithraic
ceremonies in Persia; and even among many of the Cyclades under Persian rule, where
the religion of the Magi had not been received.
The second sort was like the gate at Arpino; an opening in the form of a lofty pointed
arch, which, from its being inconvenient

for the reception of a wooden door or
entrance, could only be closed by rolling
into it a large stone, or entirely walling
it up. (See fig. 72.)
In this example we have the form
without the principle of the pointed arch;
the stones overhang like corbels, and are
not radiated to their respective centres:
after the form was given, probably the
setting out of the voussoirs according to
the right principle followed.
In many parts of Greece we find open-
ings in the walls so arranged, and the
weight over them similarly disposed; this
system led to the practice adopted in the
conical structures, where a series of con-
centric rings, gradually diminishing, have
the same support as this system of cor-
belling or gathering over. Walls con-
structed of regular masonry, and after-
Fig. 72.
ARPINO.
wards perforated or cut through, would present such an aperture in the course of a short
time; the different courses would chip off till something like the form of the equilateral
triangle was assumed, which, if assisted by a little art, would give the rudiments of a
pointed arch.
Where such was the result of undermining or a settlement, the stone would
incline at the heading joints, and the principle of an arch would be partly developed.
When the writer refers to the sketches he made in his tour through Greece, he finds
abundant examples of openings through walls or entrances, formed by the mere taking out
of stones, originally laid in the Cyclopean manner; some of these exhibit the arch entirely.
In fig. 71. the lower course might be removed, and a segmental figure obtained, the stone
work above remaining unaltered: the mere observance of such an accident would lead to a
knowledge of the arch, and show that superincumbent weight might be safely discharged.
To minds possessing the acuteness of the Greeks, such an accidental circumstance would
not be lost, or the lesson taught thrown away; when once the wedge theory was taken up,
there can be little doubt but the value of pressure on each of the voussoirs of an arch would
be practically understood. The rudeness of the examples left by no means implies that
others of a more perfect and refined character did not exist; their destruction being easy,
may account for our not discovering any remains. No work, which Persian ambition could
desire to annihilate, could be more readily destroyed than the abutments of an arch,
which would bring into ruin all in connection with it; a bridge, or entrance to a city,
had the arch been introduced, could be easily displaced, whilst the rude Cyclopean wall
would exhibit difficulties and danger to any attempting its overthrow, the stones being so
placed upon and against each other, that the removal of their abutments would not be
sufficient for their demolition. It would be required to move each stone in the order in
which it was built up.
The example which follows exhibits a third kind of entrance, where a horizontal
stone is resting on the side walls to discharge the weight, which could not be applied to
very large openings. Such an example exists at Alatri (fig. 73.) in a wall of Cyclopean
construction, where the courses are irregular, and the perpendiculars not kept.
CHAP. III.
71
GRECIAN.
Where a lintel or stone could not be found sufficiently long to extend from one jamb to
another, the upper course on one or both sides required inclining, as in the gate at Signa
(fig. 74.) where the early Greek construction is adopted; to trace the regular arch from
these rudiments is difficult, as we do not discover in any of them the next step by which
the process was completed. Among the researches of modern travellers, an account of a

L
Fig. 73.
ALATRI.
Fig. 74.
SIGNA.
perfect arch is not to be found; and the writer looked through Greece for a specimen, in
vain. That such a form was unknown to them, can hardly be supposed; but it certainly
is curious, that no examples are left us.
By a combination of the second and third kinds, and the introduction of upright posts or
jambs, we have a gateway of the fourth sort, of which we find many examples, particularly
that called the Gate of the Lions at Mycenæ. Pausanias informs us that it existed in his
time. (See fig. 75.)
mm
AN UNUTU KALINTI
• DELETED FIRULLI ANNEN LILA DEM
| {MIN TORBICHAE
TITULATUMAI ALESLIELO
DUNKIN NOMILANS 1
Fig. 75.
MYCENÆ.
This gate, like others of the early Greek cities, which formed the chief entrance,
is not built in the continued line of wall, but recessed at the end of a narrow passage, at
a considerable distance within the outer circuits. This arrangement was undoubtedly
contrived for defence, it not being possible for a number to make an approach through this
narrow defile at the same time.
This gate is 8 feet in width, and the horizontal stone which serves as a lintel is 12 fect
in length; the lions mentioned by Pausanias are cut in relief out of a single stone, 9 feet
in height and about 13 in width: it may date as among the earliest works of sculpture
in Greece.
1

F 4
72
Βουκ Ι.
HISTORY OF ENGINEERING.
Such gates were defended with more ease from their being recessed; at Norina we have
another example (fig. 76. ), which shows more perfectly the method adopted by the Greeks
to annoy an enemy whilst attacking them.

!
Fig. 76.
NORMA.
The Scean Gate had an advanced mole or wall, carried out for some distance on the left
hand on coming out, which was used by the military or guard for the discharge of mis-
siles against those who were attempting to enter without permission. The reason assigned
for the left side being preferred, was, that an attacking party would cover their left sides
with their shields, and hold their spears in their right hand, which would present to the
besieged the only uncovered part that was assailable; consequently, by this arrangement,
the right side of the attacking troops became open to the weapons of the besieged, and the
darts or projectiles from the wall in advance could be brought fully to bear against the
most vulnerable parts of the besiegers.
Delos exhibits an arched gallery, already described, of the same construction as that in
the wall of Tiryns, and among the towns in Greece are found many subterraneous passages,
like that mentioned by Strabo as existing at Preneste, which was underground, and served
usually the purposes of a sewer, conveying the water from the city into a deep valley, and
at other times for a sally port.
These galleries or passages were cut in the rock, sometimes in the natural soil, and often
mined or excavated like a tunnel through the neighbouring country.
Another description of wall which surrounded the cities of Greece showed an im-
provement in construction: these had the courses of stone or marble laid in a more regular
manner; and to which were added towers of a square, circular, or polygonal form, placed at
regular distances. Such were those at Argos, Messene. (See fig. 78.)
Messene was a city at the foot of Mount Ithome, and celebrated for the wars carried
on by its inhabitants against the Spartans, about 700 years before the Christian era. The
Thebans, who under Epaminondas defeated the Spartans abovt 370 years before Christ,
are supposed to have constructed the walls and towers of this city, which remain. Epami-
nondas, according to Pausanias, being assured that the site of Messene was admirably
adapted for a city, desired that the Augurs might be consulted on the subject; and
favourable omens being obtained, he commenced the foundations, and ordered the stone
to be brought from the neighbouring hills. The Gulph of Messene lies a little distance
from the city on the south; to the west spreads Arcadia; and Ithome rises above the
plain with Mount Eva to the south. On the top of Ithome are the remains of the citadel.
After the numerous defeats which the Messenians sustained in their contests with the
Spartans, Pausanias informs us, they abandoned their other fortified cities, and retired to
Ithome, which Homer alludes to
And those that on the steep Ithome dwell.
They increased the citadel, and rendered it, by several engineering works practised on the
steep rocks, difficult of access. From this place they sent messengers in their distress to
Delphos to inquire of the oracle what they were next to do, when they were ordered to
sacrifice a pure virgin to the infernal demons. All their efforts, however, were useless in the
CHAP III.
73
GRECIAN.
battles in which they afterwards engaged; and the inhabitants of Ithome were obliged to
seek refuge at Argos, Sicyon, and Arcadia, or Eleusis, and the Spartans razed the citadel
to its foundation.
The Messenians, after being continually harassed, at last settled at Rhegium, on that part
of the Italian coast opposite to Messina. This event happened about 723 years before Christ.
Anaxilas, one of their leaders, took possession of the territory belonging to the Zanclæi in
Sicily, where he built a city, and strongly fortified it; and the new inhabitants turned their
attention towards maritime affairs. Such, Pausanias tells us, was the end of the wanderings
of the Messenians. We can account for the construction and systems adopted for the defence
of the cities in Sicily, resembling those met with in Greece, when we learn that their builders
were driven out from among the people who occupied the latter country: when they fled,
they carried with them a knowledge of the arts, and laid the foundation for their promul-
gation throughout the new settlement.
The circular court remaining at Messene forms the northern entrance to the city, from
whence the route to Megalopolis took its departure. On each side of the entrance are
the foundations of two

towers which defended
this approach.
Around the walls of
the circle are two niches
or recesses, with square
heads, and slightly de-
corated. The diameter
of the circle is 63 feet,
and the largest aperture
by which it is entered,
'23 feet: the other, about
17 feet, was covered by
a lintel, the dimensions
of which were 18 feet 10
inches by 3 feet 4 inches
high, and 4 feet wide:
such dimensions re-
quired some support
from beneath, or the
weight should have
been discharged from
Fig. 77.
MESSENE.
above, that the lintel might have rested securely, without danger of fracture.
After passing the gates, the
road, formed of large blocks of
stone, conducts to the city; these
blocks are not polygonal, but ob-
long in their form.
The walls which remain at
Messene are of regular blocks
of stone, and at every 7 feet
or more, there were cross walls
at right angles to tie in the two
faces, the thickness being too
much for any other kind of bond.
These walls, as restored, exhibit
an arch over the principal en-
trance, for which there is no au-
thority, although there can be
little doubt but that such an
arrangement was made over the
wide entrances of the Greek
cities.
If we are right with regard to
the time when the arch was used
by the Egyptians, we may cer-
tainly suppose its adoption by a
people who borrowed greatly
from their inventions: we trace
the embrasure and battlements

Fig. 78.
PAPAAAAAAAAAAA
MESSENE.
in Egypt; the arrangement of the masonry, and securing the several blocks, indicates a
similar origin. Time alone, and further research, must clear up this doubtful statement,
and satisfy us upon a subject on which almost all writers differ.
74
Βουκ Ι.
HISTORY OF ENGINEERING.
The internal diameter of the circular tower is 17 feet 4 inches; it projects from the
wall about 16 feet, the thickness of the masonry being a little less than 2 feet.
internal dimensions of the
square tower are 17 feet 8
inches by 16 feet, and the open-
ings on each side 3 feet 4
inches. The thickness of the
walls 20 inches. The platform
or walk along the battlements
was in width 8 feet.
These towers were each two
stories in height, probably
entered by wooden ladders,
as there are no remains of
stone staircases. Square open-
ings for the purpose of assailing
those employed in the attack,
were secured by internal metal
bars. The lower tier of win-
dows was splayed, that the
archers might have a greater
Such
range for their aim.
remains of military architec-
ture among the Greeks, at
once show us that the practice
at this period was the same
throughout all the countries
which bordered the Mediter-
ranean Sea. Pausanias de-
Fig. 79.
FIMID
MESSENE.
The

scribes similar fortifications; those by Homer differ but little from the examples here given.



Fig. 80.
MESSENE.
Fig. 81.
MESSENE.
The battlements have been added from specimens met with in other parts of Greece, and
the section of the wall shows the filling in between the two faces, also the method
adopted to tie the whole together. Some of the apertures, or small windows, are finished
CHAP. III.
75
GRECIAN.
with triangular heads, cut out of the single stone which serves as the lintel. The
towers were only raised a story above the ordinary level of the walls.
Argos had a similar tower, 20 feet 3 inches by 17 feet 7 inches in the clear, with walls about
3 feet 4 inches thick around it, supposed to have been the part of a Pharos, that served to
alarm the inhabitants

of the country around
Tegea and Mantinea.
The external walls
were made to batter
considerably, and if
carried up would have
assumed a funnel-like
appearance, well suit-
ed for the purpose of
a beacon.
Many writers de-
scribe the manner in
which these towers
were set out, what
should be their dia-
meter, distance apart,
and height, as well as
the method of their
construction; and that
pieces of oak timber,
four cubits in length,
were introduced in the
middle of the wall, to
facilitate a repair in case a breach was made.
The walls of Athens were restored after the in-
vasion of Philip, son of Demetrius, in great haste,
when many public buildings were destroyed, and
the materials used for the purpose: we see on the
north side of the acropolis such a wall, where
columns, triglyphs, metopes, and cornices are used,
without order. The long wall of the Piræus, which
has been already mentioned, was not commenced,
according to Thucydides, lib. ii. cap. 75., until those
around the city were completed; but it was set out
near the Piræus of such a width that two carts
Fig. 82.
Fig. 82.
TOWER AT ARGOS.
loaded could conveniently pass. The length of the Phalerian wall to that part of the city
where it joined was 35 furlongs; that part between the long walls and the Phalerian,
35 furlongs; and the length of the long walls down to the Piræus was 40 furlongs; and
the whole compass of the Piræus, together with the Munychia, 60 furlongs.
The engineer's skill was called forth by the early inhabitants of Greece, in the erection of
the walls which surrounded their cities, and in the design and construction of the machines
placed upon them for their defence. The artifice displayed in protecting or defending a
long line of wall so fortified, was often matched by the besiegers, and we find improvement
continually made, both in maintaining and taking a city, by the careful attention of those
upon whom these duties devolved. The architect, well skilled in the arts of design, would
be the best qualified to erect a stone barrier, either against a flood, or an armed body of
men, as well as for raising heavy weights, and transporting them to any required distance;
in the early age of society, he would be the most efficient director for all that now devolves
upon the military and civil engineer. And as we learn from the ancient historians, that the
architect had entrusted to him, not only the defences of the towns and cities, but also their
arrangement, drainage, and general superintendence, we may infer that there existed no
distinction between him and the engineer.
But the most important knowledge to him employed in the defence of a city or pro-
viding for its health and salubrity, would be a thorough acquaintance with the sciences, without
which no great work could be devised or undertaken. Vitruvius, who had the care of all the
engines of war entrusted to him by Augustus, tells us frequently in his writings, that those
selected as engineers deeply studied the opinions of Pythagoras, Empedocles, Epicharmus,
and other philosophers: Metagenes, Ctesiphon, Evangelus, Pæonius, Pephasmenos, Cetras,
Polydus, Diades, Choereas, Agetor, Diognetus, Trypho, and many other eminent names, might
be cited among the Greeks, who were practically acquainted with the use of machinery,
and its applications, to the destruction of towns and cities, when called upon by the great
generals of the age to exert their ingenuity.
76
Book i.
HISTORY OF ENGINEERING.
The construction and demolition of their walls needed the aid of machinery, and among
the Greeks a knowledge of all its proportions was thoroughly understood. The battering-
ram, the balistæ, the catapultæ, the crane, the tortoise for filling up ditches and other
purposes, and the several machines described for defence, show a thorough acquaintance
with the properties of the lever, the wheel and axle, the pulley, the inclined plane, the wedge,
and the screw; and Euclid's Elements, collected about 280 years before Christ, for the
instruction of the pupils assembled at Alexandria, attest their advance in geometry.
The walls which remain in part at Platea more distinctly show the arrangement of the
towers, battlements, and galleries be-

tween them. In some of the towers
are staircases, and the whole is con-
structed of large stones.
J
The double walls of the Pelopon-
nesus, also described by Thucy- -
dides, were formed in portions of a
double circle, one towards Platea,
and the other towards Athens.
They were distant from each other
about 16 feet, and the space so ob-
tained was divided into rooms by
cross walls, which tied and united
the whole together. At every tenth
battlement was a tower, extend-
ing through both walls, and having
its passage through the middle over
the rooms, to which, during incle-
ment weather, the guards might re-
tire, and keep watch through the
loop-holes contrived for the purpose.
(Lib. iii. cap. 21.)
Amidst the discoveries in Lycia,
made by Charles Fellowes, Esq. a few
years ago, and published by that
indefatigable traveller, were several
gates of peculiar construction. That
at Penara is Cyclopean, and formed
Fig. 83.
L L
FTT


of massive upright stones, with
another laid over as a lintel, now
Fig. 84.
PLATEA.
broken. (See fig. 85.) There is also one which forms the entrance to a tomb having a
pointed arch surmounted by the horns of a bull. (See fig. 86.)


Fig. 85.
PENARA.
$10
Fig. 86.
PENARA.
There are great varieties of form given to the ancient portals, and it is curious to trace
the changes from the rude Cyclopean method of discharging a weight over an opening, by
the gradual projection of the stones meeting in the middle, to the formation of an equilateral
triangle, as used by the Egyptians at a very early time, two stones, like the chord of two
arcs, being placed one against the other. The approach to the regular portal is made at the
gate of Penara, and this is rendered beautiful by the improvements added in that at Sidyma,
CHAP. III.
77
GRECIAN.
where a simple cornice with lion's heads protects the massive stones which form the square
portal. (See fig. 87.)
In a tomb at Telmessus in later times we find the bold semicircular arch containing
within the square portal formed of regular voussoirs, and set out with a thorough knowledge
of its construction. This is thought to be of Roman work. (See fig. 88.)
The walls of Etruscan cities exhibit a more perfect construction; the Tyrrhenians in the

Fig. 87.
SIDYMA.
Fig. 88.
TELMESSus.
walls of Volterra, Cortena, Populunia, Roselle, Fiesole, Cosa, Luna, throughout Latium,
and even at Pompeii, followed the manner adopted by the Pelasgi or Cyclops in Greece,
though in the later example there is a nearer approach to regular masonry.
The blocks at Volterra are laid in nearly horizontal courses; and those at Cosa resemble
the construction at Mycena. At Roselle, on the Ombrone, are vast ruins scattered over a
hill, and the walls are nearly a mile and three quarters in circumference, constructed of a
coarse limestone, or large masses of travertine, the outer face of which is perfectly level
throughout. Some of these blocks are 15 feet in length, and their thickness is so great, that
only two of these stones side by side are required for the entire thickness of the wall.
Cosa, near Orbitello, has its walls nearly entire, and those at Luna, an ancient maritime
establishment of the Etruscans, were built in this manner. of pure marble, taken from the
neighbouring quarries of Carrara. Many

of these walls have their horizontal courses
laid nearly parallel, whilst the joints which
should be perpendicular are inclined; so
that the stones are cut more in the form of
a trapezium or rhomboid, their ends, in par-
ticular situations where strength is required,
are dovetailed one within the other
At Circei remains a rude entrance, which
has a Cyclopean character, built up with
stones without cement; and it would seem
that among the Etruscans the progress of
improvement kept pace with the Greeks: we
have entrances to their towns, exhibiting the
same style of construction, and in some in-
stances vastly superior. That at Volterra
has a semicircular arch, adorned with heads.
(Fig. 89.) Another at Tusculum has its
square-headed opening now inclosed within
a regular pointed arch, which seems to have
been constructed at the same time as the
walls themselves, known to be of very great
antiquity. Among the Etruscan remains
this peculiar form of the arch is frequently
found, but in the present example all the
stones radiate to their respective centres, and
leave no doubt as to the principle being
thoroughly known; indeed, it is nothing

Fig. 89.
VOLTERRA,
78
BOOK I.
HISTORY OF ENGINEERING.
more than the result of taking out the middle voussoirs and bringing the other portions of
the arch nearer together, or, in other words, narrowing the original opening, making use
of the same stones which served for a semicircular arch. Such an accidental adaptation may
have been the cause of the pointed arch. In some of the cities of Etruria, particularly at
Tusculum, are the remains of arches similarly constructed with that in fig. 90., but its
date remains uncertain. This example has been adduced as an early specimen of the use of
the pointed arch; it forms a por-
tion of a subterrraean course
or conduit, through which the
water was brought to the re-
servoir distributed to the lower
portion of the city. The aper-
ture, which formed the entrance
to the emissary, is narrower at
top than at bottom, and co-
vered by a single stone lintel.
Had we any authority for affix-
ing a date, we should no longer
be in doubt as to the origin
of the pointed arch; but we
have not evidence by which
we can trace its introduction,
or decide whether it is not
the work of a much later epoch
than that assigned to it.

The great resemblance the
walls of the Etruscan cities
bear to those of Greece indicates
a common origin, or that they
were the work of the same
tribes, though scattered on va-
rious shores. Tarchon, the son
of Tyrrhenus, a Lydian prince,
was supposed by Cato to be
their great leader to the plains
of Italy; and if his followers
were drawn from the shores of
Asia Minor, we have no diffi-
Fig. 90.
TUSCULUM.
culty in accounting for the remains, appertaining to the arts, dug up at Naples, Capua,
Verona, and Padua, resembling those discovered throughout Greece.

Etruria, bounded by the Tiber on the
east, by the Maira on the west, by the Tyr-
rhenian sea on the south, and by the Ap-
penines on the north, according to Polybius
and Herodotus, had its inhabitants from the
Asiatic coast; their language nearly ap-
proached the Hebrew or Phoenician, and
their alphabetic characters were the earliest
used in Italy. Of the inscriptions remaining,
there is enough to indicate, particularly in
the latter period of their institutions, a
Greek connection. Etruscan artists were
always held in high repute, and in the early
history of Rome, we find them selected to
construct what was necessary for the em-
bellishment of the city. If the Pelasgi or
Fig. 91.
TUSCULUM.
Phoenicians were the civilisers of the shores of the Mediterranean, we must follow them, to
account for the similarity of manners and customs. About 2080 years before Christ, they
founded in Egypt the dynasty of the Hucsas, which Sesostris drove out about 500 years
afterwards. Greece received its first colony under Inachus, 1986 before Christ, which was
followed by others under Danaus, Cecrops, Cadmus, Deucalion, Pelops, and various
Phoenician or Pelasgic chiefs. In the course of time, the settlers driven out by Deucalion
from Thessaly, who had settled at Epirus, retired or went over to Italy, carrying all that
was valuable, and established themselves first on the coast. This seems probable, and enables
us to account for the similarity of their habitations and arrangements as well as in their
engineering works.
Treasuries were generally added to the Greek cities at a very early period. According
CHAP. III.
79
GRECIAN.
to Pausanias, Minyas, who governed in Boeotia, erected the first at Orchomenos, and the
wealth contained in that at Delphos is mentioned by Homer, where Achilles rejects the offer
of Agamemnon.
The treasury of Atreus at Mycenæ, and another at Hyrieus, is described by Pausanias.
When the writer measured the first-mentioned building in 1818, there was no portion
the doorway which inclosed its in-

terior, although much might be
traced to indicate its position and
thickness. It was supposed to be
of bronze, and with this metal the
interior, is said to have been cased.
By some the building in question
is considered as a tomb; it is of a
conical shape, about 50 feet in di-
ameter. The courses of stone are
all laid horizontally, and, by gra-
dually projecting one over the other,
assume the character of an arch, or
rather that of a cone (fig. 93.), the
form adopted by Sir Christopher
Wren in the brick construction which
carries the timber dome at St.
Paul's. This method of gathering
over concentric rings has been prac-
tised by people of all nations; we
find it not only in Greece, but in
Italy, where as late as the thirteenth
and fourteenth centuries it was
made use of at Pisa, in the bap-
tistery. Around the Treasury at
Mycena the earth is bedded up to
the stones, and the entrance was
by a passage closed by ornamental
Fig. 92.
MYCENE.
jambs, with a door or gate. Within the first circular chamber was a second, entered by a
square door, which had a large stone for its lintel, the weight above being discharged by a
gradual gathering over of the courses. It is nearly 50 feet in diameter and in height;
two stones cover the entrance passage, one of which is 27 feet long, 16 feet broad, and 4
feet thick.

Sli
Fig. 93.
MYCENÆ.
The Greeks, the inventors of many of the arts of construction, have left us, in their tombs,
forms serviceable to the civil engineer, and which tell us also of the gradual progress made
in architecture.
In Mr. Fellowes's volume, the method adopted by the Lycians of cutting their tombs
out of the solid rock is admirably given; in some examples we have imitations of timber
80
Воок 1
HISTORY OF ENGINEERING.

construction, in which
the covering is carved
to represent rafters, &c.
In another, at Myra, is
a window, admirable for
its lightness and deli-
cate proportions, as is
the other variety here.
selected. The first prin-
ciples of architecture
are indicated. All the
ties to hold in the up-
right timbers, which
bound the figure, are
expressed as they would
exist in a timber con-
struction. The rafters
have the characters of
round timbers, laid
side by side, or as made
out of the tops of the
cedar or fir tree. There
is in this picturesque
Fig. 94.
LYCIA.
fragment a beautiful proportion reigning throughout; it shows the great taste and happy
execution of the masons employed in designing and working these chambers for the re-
ception of the dead. (See fig. 94.) The same may be found executed in the walls of the
Sicilian towns, particularly at Agrigentum, though by no means of so perfect a design.
That architecture had its origin among a people who used timber for their construction has
been generally admitted, and, indeed, most of the parts of the Greek orders seem to have
their proportions from the scantlings of wood.
In the "Antichità della Sicilia per Dominico lo Faso Pietrasanta Duca di Serradifalco."
the engineer and architect will find ample historical and practical information to satisfy him,
upon the embellishment and defence of the early Greek cities, throughout that elegant and
erudite work, we have evidence that every stone has been turned and examined that could
lead to an understanding of its use; the great taste evinced in the arrangement, the correct-
ness of the maps and plans of the several harbours on the coast, render it highly important
that all who take an interest in the study of this subject should have it in their possession; it
contains an ample account of the labours and studies of the civil engineer, throughout Sicily,
during a period the most interesting.
Wherever a staircase, conducting up a slope to one of these sepulchres, required a
parapet to protect the sides, the stones were cut out
of the solid, and formed the last of each course; by
this arrangement considerable strength was obtained,
and, by the manner in which they were placed,
cramps were dispensed with. Stones so united
or tied together, were well adapted for a staircase
between two walls. (See fig. 95.) The science be-
longing to architecture was derived from the Greeks,
and differs materially from the art itself: in the
former, theory and practice constitute the essence;
in the latter, the imagination is necessary. One,
then, is the system of knowledge reduced to practice
and unerring rules, which, on all occasions, must
guide the engineer and architect in the carrying out
of his designs; such a science is deducible from
truths, and their relation to one another. After the rude artificer had discovered the essential
supports requisite for the construction of his cabin or residence, he would then endeavour
Before the
to give it a form pleasing to the eye, or an expression denoting its purpose.
main supports of an edifice assumed the character of columns, or the timber which rested-
on them that of the architrave, a more simple and rude manner of framing was expressed.
The square upright, mortised through to receive the tenons of the horizontal timbers, is
the most simple holding or tieing together that can be well imagined; to execute which,
few tools, or not more than those said to have been invented by Dedalus, were required.
Practice soon taught the strength of the various qualities of timber, and the necessity
of cutting off from the tree all that was sappy or likely to be affected by the weather:
hence squared pilasters, or antæ, were probably first preferred to round trees, which more
resembled a column.

Fig. 95.
CHAP. III.
81
GRECIAN.
+
Timber exposed would require care, whilst that which formed the rafters, and was
protected by the roof or covering, might be allowed to retain its original rotundity,
as the exterior could not be affected by the weather. In these few examples we fancy
we can trace the germ of all that was afterwards rendered beautiful by art, and in them
the rudiments of that fine fancy which guided the Greeks to the excellence we admire in
all their designs.

It was Cadmus,
according to Hero-
dotus, who intro-
duced into Greece
an entire change
in architecture; the
Phoenicians that ac-
companied him had
among them a body
of Gephyrians, who
wherever they went
carried a knowledge
of the sciences and
letters; the poet
Lucan tells us the
Phoenicians were
first acquainted with
the mystery of let-
ters, and could write
down or figure the
thoughts of the
mind; from them
the Egyptians ac-
quired their know-
ledge. To these
Gephyrians, who
came from Eretria,
a city of Euboea, has
been attributed all
the changes which
architecture under-
went in Greece
that they com-
menced buildings of
stone in imitation of
the wood huts for-
merly used. Cad-
mus, who lived about
1500 years before
Christ, introduced
the Egyptian and
Phoenician forms of
worship to the
Greeks; and the
Fig. 96.
MYRA.
system of working and building in stone, as practised by the people of that nation,
may be attributed to the Gephyrians at the same epoch. It has been assumed that the
various elements of Greek architecture were drawn from the buildings constructed by the
inhabitants before the arrival of these scientific colonists, who were struck with the features
presented by the original hut, and engrafted in their designs all that was so pleasing and
agreeable to the eye. Our great author, Vitruvius, tells us distinctly, that the Doric order
had its origin from wooden buildings; and if so, to timber constructions we must refer for
the invention and forms of all we find executed in stone; and the mason called upon to shape
the rock or give its face an architectural arrangement may have had a wooden model for
his imitation, which may also account for the resemblance to timber framing in the ex-
ample before us. The principles of construction ought, however, always to be in ac-
cordance with the material, the property of stone differing from that of wood; the latter may
be applied to tie and hold a building together, by the toughness and strength of its longitu-
dinal fibres, whilst stone, however strong or tough, so used, would readily be torn asunder.
Among the ornamental works of the Greeks we have frequently animals, plants, and
flowers imitated in marble, but always with so much delicacy that the material loses its
character, and seems to become identified with its subject.
G
82
Book I
HISTORY OF ENGINEERING.

The civil engineer, when called
upon to work out masses of rock, has
opportunities afforded him to imitate
these original conceptions, and pro-
duce an effect upon stone which al-
most indicates the employment of an-
other material; not that the eye should
be wantonly deceived at any time.
In these sepulchral abodes the
character aimed at is that of an
habitation; the hewer of stone here
has, perhaps, impressed upon his
material the resemblance of the
dwelling once tenanted by the oc-
cupier of the tomb; from so humble
an effort we have handed down, in an
imperishable material, the style of
construction used by the Lycians at
a very early period, and so uni-
versally adopted by the nations
spread along the shores of the
Mediterranean. We must not in-
quire into the fitness of the material
employed to give expression, but
allow praise to the design, on ac-
count of its conveying to us a re-
semblance of what was most dear to
the deceased when living; here we
have an abode provided for the dead,
far more cheerful in its character than
the pyramid or conical mound of
earth.
Fig. 97.
L
LYCIA.
That the inhabitants of Lycia retain the forms of their earlier constructed buildings, we
have evidence in the ex-

amples before us, where
the several cottages and
storehouses resemble tem-
ples. (See fig.98.) Others
built of mud and straw
are covered with tim-
bers, on which is spread
a layer of stone, above
which is laid a tenacious
earth, kept pressed
and rolled down till it
becomes perfectly water-
Fig. 98.
LYCIA.

Fig. 99.
tight. Plants spring up on this artificial terrace, which may have suggested the various
forms which the Greek architects gave to the covering of their buildings. (See fig. 99.)
The maritime works of the Greeks are now only known to us by reading the accounts
handed down by their historians. Most of their harbours are destroyed, and their
constructions in stone overthrown, yet, by a careful examination of the remains, much
might yet be discovered: the smallness of their vessels did not require very deep water for
their security; shallow seas or inlets from the main were usualy preferred by their ma-
riners, around which they constructed arsenals, magazines for stores, lighthouses, and other
buildings necessary for commerce and for protection.
CHAP. IV.
ROMAN.
83
CHAP. IV.
ROMAN ENGINEERING.
ITALY, whose history is involved in obscurity, at an early period was divided into the
states of Liguria, Gallia Cispadana, Gallia Transpadana, Etruria, Umbria, Sabinum,
Latium, Picenum, the country of the Vestini, Marrucini, Peligni, Marsi, Frentani,
Samnites, Herpini, Campania, Picentini, Magna Græcia, Apulia, and others.
The Etrurians were among the first to distinguish themselves by their victories over the
neighbouring tribes, and by their attention to commerce and the arts of peace, which they
learnt from the Phoenicians. The islands of Corsica, Sardinia, and Elba afforded them
materials for ship-building, and metals for the fabrication of all sorts of tools. Military
architecture by the Tuscans was greatly improved, and the ruins of their towns on or near
the coasts at Luna, Pisa, Leghorn, Civita Vecchia, and many others, prove them to have been
also a maritime people. To them succeeded the Roman Empire, which could boast of
dominion over 1197 cities in Italy, 360 in Spain, 300 in Africa, 500 in Asia, 1200 in Gaul,
and several in Britain. Roads of the best construction were every where made to unite
these cities; and the coasts which did not afford a natural protection to their ships were
furnished with artificial ports. The power which grew up in this vast empire diffused its
advantages over the whole world. Agriculture, which was made a science and lauded by
the poets, introduced plants of every kind to soils of distant lands where they were likely to
flourish. The sciences followed in the train of their conquests, and engineers of talent were
attached to their armies on their march, and established in every great city of their empire.
Emperors distinguished themselves in the prosecution of great and important engineering
works, and all who became enriched by the spoils of their enemies expended some portion
for the benefit of their.country: thus the blessings and luxuries of life became universally
distributed over the whole of Europe. By the Romans civilisation was spread far and
wide; they made use of the talent which every where sprung up, and by their encourage-
ment naturalised it and made it their own.
Architecture and civil engineering are both treated at great length by Vitruvius, and we
cannot do better than follow the order, as well as description, of that able writer, who, it
must be remembered, is our only early guide, without whose labours we should need
an explanation of some of the simple terms made use of in the descriptions left us by other
authors. The inventions of many Greeks would not have been known to us if he had not
handed them down. He lived and wrote when Rome was at its greatest pitch of glory;
and we have no reason to doubt that the rules he gives for construction were different from
what were in those days most approved.
The Romans founded towns wherever their arms were victorious, and paid great atten-
tion to the selection of their site, that it should not be under the influence of noxious or
pestilential vapours, but well provided with all the conveniences necessary to sustain life
and health.
Vitruvius informs us the neighbourhood of marshes was avoided, and that the aspect for
towns should not be directly south or west when founded on the sea-shore, otherwise the
scorching heat of the sun would be inconvenient. By the Greeks air was called Pallas, and
by Homer Glaucopis, which indicates a quality clear and transparent; but the ancients were
not acquainted with its properties, or the manner it which it administered to the nourish-
ment or support of life; the lightest and clearest they considered the healthiest, and, by
inhaling pure air, that their imaginations were improved. On this account the Athenians
were considered more intelligent than the Thebans, who were living in a humid at-
mosphere.
The Romans, in setting out a camp, commenced by sacrificing animals, the livers of which
they carefully examined: if they found any disease, they subjected others to a like test;
if the greater number proved to be healthy, it was then considered that the soil and water
were fit for the use of man, and the encampment was completed. In the same manner,
previous to the foundation of a city, every necessary inquiry was made upon all these sub-
jects, and also upon the best system by which the drainage could be effected. If circum-
stances required it to be established in a marshy situation, near the sea-coast, a northern,
north-eastern, or eastern aspect was preferred, care being taken that none of its foundations
should be so low as to render it incapable of being thoroughly and effectually drained.
The sewers were laid out so as to discharge all superfluous waters into the sea; the lands
G 2
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Book 1.
HISTORY OF ENGINEERING.
round the city were thoroughly drained, and by this means all the cities in Cisalpine Gaul,
Ravenna, Aquileia, and others, were rendered healthy. It is recorded that the inhabitants of
Salopia in Apulia, being continually out of health, applied to Marcus Hostilius for permission
to remove their town to a more healthy spot, when a site near the sea was purchased by
consent of the senate and Roman people, and the new work commenced, each citizen
having a portion of ground allotted him at a moderate price. A communication was after-
wards made between the lake and the sea, by which the former was converted into an
excellent harbour for shipping. The Salopians thus acquired a healthy situation four miles
from their former city, and had all the advantages they desired. The Romans always
thought of the best means for providing the inhabitants with the necessaries of life, and for
holding communication with other portions of the empire. They would not have followed
that advice which the architect gave to Alexander, to cut Mount Athos into the figure of a
man holding a city in one hand, and collecting the waters of the mountain in the other, if
the country around had been barren or unprofitable. A region more accessible both by
land and water would have been preferred by the Roman engineers, where water was of a
quality not injurious to health, and sufficiently abundant for the wants and luxuries of
the citizens. They carefully examined into the health of the people that occupied the
region where a new city was to be founded, they observed the effects on the buildings
which existed, and the trees, whether they indicated, by their bending in one direction, any
prevalent or continued high winds. They also observed the surfaces of the natural stones
and those used in the dwellings of the natives, whether any decomposition had taken
place, or the atmosphere had acted injuriously upon them.
After the site was determined upon, wells were sunk to try the nature of the soil; if fit
to bear the weight of the constructions intended to be put upon it, they commenced
their foundations for the outer walls, which were always based upon a solid stratum; the
workmanship as well as the materials employed for this purpose were the best that could
be obtained on the spot or in the immediate neighbourhood,—square stones, flint or rubble,
burnt or unburnt bricks, bonded together with timber, as that of the olive, or some other
equally imperishable wood. The works were conducted by the military or civil engineers,
and every means adopted that could render them proof against the attack of an enemy.
Vitruvius recommends that the plan of the city should be polygonal, because the angles of a
square or parallelogram are defended with more difficulty. The towers should, he observes,
be also round or polygonal, the square towers being more easily injured at the quoins by the
battering-ram. When the wall which surrounded the city was constructed on the side of a
hill, buttresses were added, distant from each other as much as the height of the wall, or, if
requisite, nearer together. They were gathered in gradually, to give additional strength.
Every precaution was taken against assault by an enemy; angles jutting out were
avoided, as they were considered to assist the enemy when making an assault, and to be in-
jurious to the inhabitants in the defence, and that they were weak against the military
engines brought to act upon them. Whatever form was adopted for the walls, they were
made of such thickness as would permit two armed men to pass each other behind the
parapet, of a sufficient height to prevent the scaling ladder from being applied to them,
and built so firmly as to resist the battering-ram.
Varieties of military engines were employed to demolish or break down the walls, and
some to undermine the foundations; as a security against these, a deep ditch usually
surrounded the outside of the wall. These ditches were often without water, and made
sufficiently wide and steep to defy the approaches of the moveable towers, or tortoise,
brought to act against the fortifications. The city had two walls, if it was of much im-
portance, a space being left about 20 feet in width, or more, between them, which space
was filled with the earth taken out of the ditch, well rammed in: this inner wall was
provided with flights of steps in every convenient position, that it might be easily
mounted from the side towards the city. When there was no ditch, the space between
these two walls was left open, where the soldiers were ordinarily assembled. Cæsar
informs us, that in Gaul most of the walls had beams of timber laid within them at
regular distances, in a parallel direction, braced together and tied diagonally, the spaces
being filled in with large stones, so that neither fire nor the battering-ram could injure
them.
The towers which project from the outer walls, whether round or square, were usually
carried up higher than the wall itself. And the inner wall of these towers, on the face
towards the town, was left open, that, if an enemy got possession of them, he was not
protected from the assaults of the inhabitants: they were often crossed by wooden plat-
forms or bridges, which could be easily demolished, and thus the walk along the top of the
wall, or behind the battlements, destroyed.
The walls and towers externally were finished by a bold projecting cornice, which re-
ceived the battlements, and gave greater width at the top of the wall, as well as prevented
the easy application of the scaling-ladder. Where the city was entered by the inhabitants
on ordinary occasions, the gate was flanked by two towers, larger than the others, and more
CHAP. IV.
85
ROMAN.
strongly fortified.
The floors were of timber, not fastened very securely together, so that
they could be easily removed if necessary.
The city of Rome is of great antiquity at a very early period it occupied only the
Palatine hill, which being cut away at its slopes, a perpendicular face was given to it,
strongly fortified by a stone wall built upon its edge. As the inhabitants increased,
the original city became the citadel, and buildings were constructed around it. Roma
was the name it bore at the time it was inhabited by the Pelasgi, the Tyrrhenians, or
Sicelians. Around the ancient citadel Romulus added a space, which was inclosed by a
wall, called the pomærium, signifying a suburb, or place admitted to the privileges of the
city. Tacitus (Ann. xii. 24.) says it may be a matter of some curiosity to mark out the
foundations of the city, and the boundaries assigned by Romulus. The first outline
began at the ox market, or Forum Boarium, where is still to be seen the brazen statue
of a bull, that animal being commonly employed at the plough. From that place a
furrow was carried on, of sufficient dimensions to include the great altar of Hercules.
boundary stones, fixed at proper distances, the circuit was continued along the foot of Mount
Palatine to the altar of Consus, extending thence to the old Curiæ, next to the chapel of the
Lares, and then to the Roman forum.
By
Another suburb afterwards was added with a wall of earth toward the Subura: this was
on the Carinæ near S. Pietro in Vincoli. At the bottom of the ascent which led to it was
the Porta Janualis mentioned in the Sabine wars.
The Agonian hill, inhabited by the Quirites, and called Quirinal, was a town at a very
early period; this was next united with the Capitoline, on which was the citadel. Where
these two hills joined at the foot stood the Forum Ulpium. The Palatine was separated
from them by a marsh or swamp, the Quirinal being at one period occupied by the
Sabines.
Roma and Quirium were separated by walls, and formed two distinct cities, at first each
having its king and senate of an hundred men; these met together in the comitium situated
between the Palatine and Capitoline hills.
After these two cities were united, the Temple of Janus was built, on the way leading
from the Quirinal to the Palatine, with a door or gate facing each city; this temple was
kept open in time of war, and shut during peace, the object being, in the one case, to afford
succour to each other when harassed by an enemy, and, in the latter, to prevent the inhabi-
tants of either from quarrelling, the result of too frequent an intercourse. The Via Sacra
marks the limits of the two cities; this commenced at the top of the Velia, between
the Quirinal and the Palatine, after making a turn, passed between the latter and the
Capitoline, and, arriving at the temple of Vesta, it bent across the comitium towards the
Palatine gate.
This was the Sacred Way, and seems to have served the purpose of the in-
habitants of both cities during their religious processions. The cities were afterwards united,
and called Populus Romanus et Quirites.
The Capitoline, Quirinal, and Viminal, were first surrounded with walls and incorporated
with Rome, and afterwards the other hills. In the age of Tiberius we find the city consi-
derably increased, and divided into seven districts - the Palatium, Velia, Cermalus, Cœlius,
Fagutal, Oppius, and Cispius, which had each its own festivals.
The Velia was the rising ground between the Palatine and the Carinæ, where is the
temple of Peace and that of Venus and Rome.
Oppius and Cispius are the hills now called the Esquiline. Cermalus is the land at the
foot of the Palatine, subject to be flooded from the Velabrum.
The Fagutal district was probably that plain which lay between the Palatine and the
Cælian, the Septizonium and the Coliseum.
These several districts were not encompassed by a wall; and the Romans never reckoned
more than seven hills, or as many regions.
On the side of the Via del Colosseo, Romulus's pomærium reached the rising ground
that protected the Carina; beyond, in the valley, was the village of Subura. The Cispius
and Cælian hills were fortified by a wall and ditch where the banks could not be cut down
perpendicularly, and the Aventine being insulated was strongly protected. The low land
between the Palatine and Cælian hills was full of springs; these were collected in a ditch
cut from the edge of the Aventine to the Porta Capena, and the earth thrown up
as a wall to protect it: this was done by the Quirites in the time of Ancus, who,
Livy tells us, after the conquest of Politorium, a city of Latium, first numbered its in-
habitants among the Roman citizens. At that time the Romans occupied the ground
around the Palatine, the Sabines the Capitol, and the Albani the Cælian. The Aventine
was allotted to the new citizens; and some time after, on the reduction of the Tellenæ and
Ficana, a considerable addition was made to the inhabitants. Ancus afterwards admitted
many thousands of the Latins as citizens, and allotted them ground near the temple of
Murcia, and united the Aventine to the Palatine. The Janiculum was taken in at the
same time, and joined to the city by a wall, and a wooden bridge, the first built over the
Tiber.
G 3
86
BOOK I.
HISTORY OF ENGINEERING.
Servius Tullius added the Quirinal and Viminal hills, and extended the limits of the
Esquiliæ, where he established his own residence. He also surrounded the city with a
rampart, trenches, and a wall. By this means, the pomærium on each side of the wall was
extended, which space it was the custom of the Etrurian augurs to consecrate. On the
inside of the wall no buildings were admitted, the space being required for defence.

MIH 1
t
F
BEEN
Fig. 100.
WALL OF SERVIUS TULLIUS.
The wall built by Servius Tullius surrounded the entire city, the Colline and Esquiline
region being connected by a mound 7 furlongs in length, formed with the earth thrown out
of a ditch 30 feet in depth, and above 100 feet in breadth: here was raised a wall 50 feet
wide, above 60 feet high, and, although chiefly built of puzzolana, faced, towards
the moat or ditch, with hard stone, and defended with towers. The Colline gate was
situated where the Quirinal was nearly flat, and from thence, up the acclivity of the hill, a
similar wall was constructed.
The Viminal hill, so called from the osiers it produced, was then taken into the city,
which, at this time, measured about 6 miles in circumference. The city of Rome remained
in this state for centuries; but the ramparts which defended its citizens were not suf
ficient in the time of the Emperor Aurelian to satisfy them. Beyond the wall around the
seven hills, numerous buildings which had been constructed in the suburbs were now in-
closed; the city and its inhabitants covered the field of Mars, and also extended their dwellings
for a considerable distance on the various roads which led from it. The new walls, built
by this emperor, and finished by Probus, were in circuit about 21 miles, and comprised
nearly the whole of the suburbs. Probus also built a stone wall from the Rhine to the
RARAS

ARRA

容
​Fig. 101.
AURELIAN'S WALL.
目
​CHAP. IV.
8"
ROMAN.
Danube, of a considerable height, and strengthened it by towers at regular distances: it.
passed from Newstadt and Ratisbon, over hills, valleys, and rivers, as far as Weimpfen
on the Neckar, and terminated at the Rhine, after a winding course of 200 miles. This
wall was overthrown by the Alemanni, and its scattered ruins may be seen in several
places.
A portion of the wall which remains between the Porta S. Giovanni and the Amphi-
theatre Castrenses is constructed in the manner called opera laterizia, and is defended with
square towers, having a base of squared stone of an earlier construction. On the
inside the gallery is carried on a series of arches, and is arrived at by staircases in the
towers; the total thickness of the wall is about 14 feet, and the width of the gallery about
4 feet. The towers are in width about 24 feet, and project 12 feet. (fig. 101.)
Rome was comprised within the circuit of the walls built by Servius Tullius, who also
more strongly fortified the Capitol, by surrounding the edge of the rock with a stone wall,
strengthened by square towers, placed at regular distances. Part of this may be seen
on the western side of the Capitoline hill, but the greater portion was destroyed in the time
of the Caffarelli, when its thickness was found to be upwards of 20 feet, built of
squared blocks of pepperino.
very large
Near the ruins of the baths of Diocletian, and between the Viminal and Esquiline
hills, are the remains of the celebrated Agger of Servius Tullius: it continues for up-
wards of 100 feet in length, and to a height of 30 feet. In the middle was placed the
Viminal gate: the Agger was formed with the earth taken out of the trench in front of
the wall.
The wall here was formed of squared stone laid in regular courses, and strengthened by
square towers, (Dionysio, lib. ix. Strabo, lib. v.): it has been restored and repaired at
various times: the city at present is entered by sixteen gates. Pliny tells us that the
wall of Romulus had only three, and that of Servius Tullius seven. In the part which
Aurelian added on the other side of the river were also three. In the time of Pliny, in
the reign of Vespasian, there were twenty-four gates; and when P. Victor wrote during
the reign of Valentinian, thirty-seven. In the year 1749, the whole circuit of the walls was

MARUNG
QJUICE
Imme
Fig. 102.
GATE OF ST. PAUL.
repaired, and, although built at various times, are to the antiquary highly interesting. In
the present gate leading to St. Paul, out of the walls, the various changes that have been
made may be traced: on the left is the Pyramid of Caius Cestius. (See fig. 102.) A
portion between the Porta del Popolo and Pinciana is built on arches, with deep recesses,
and sometimes with two rows of arches, one above the other. The masonry is composed of
opus reticulatum, which was much used in the time of Vitruvius, who considered it not
very durable.
The Muro Torto remains, although much out of the perpendicular: Procopius, who
wrote in the sixth century, informs us that near the Pincian gate he saw this rent wall,
which seemed to have been long in that state; and that when Belisarius wished to pull
it down, he was prevented by the Romans from doing so. Near the Porta Maggiore is
G 4
88
Book 1
HISTORY OF ENGINEERING.
a part of Aurelian's wall, having open arches at the top, which served as an aqueduct;
this portion is of greater antiquity, probably of the time of Claudius.
In the time of Pope Leo IV. the Vatican was walled in, and six gates admitted to its
enclosure. In the year 1143, Urban VIII. built another wall on the outside of the
Leonine city.
Circeium, or Circeia (fig. 103.), not far from Anxur, is situated on the low land bor-
dering on the sea. The promontory upon which it stands, in the days of the Argonauts, is
said to have been occupied by the Turrheni. The Volscians are reported to have taken
possession of it, in whose hands it remained until Tarquinius Superbus conquered it,
when he sent his son with a Turrhenian colony to settle there. The Volsci again recovered
it, and drove out the Romans, in the time of Coriolanus, and it afterwards became a Roman
municipium.

Fig. 103.
CIRCEIUM.
An area of about 600 feet by 300 is enclosed by a wall of polygonal blocks, laid after
the manner of the cyclopean, and the single gate which enters it at the north-east angle is
curious for the size and disposition of the stones which discharge the weight over the
opening, one of which, nearly 8 feet in length, lies like a lintel in a horizontal position
upon two others which project over the perpendicular line of the jamb, to relieve its
bearing. (See fig. 104.)

Fig. 104.
CIRCEIUM.
Spello in Umbria affords us an excellent example of a gate flanked by polygonal towers:
there are three entrances decorated with simple pilasters, and a gallery above. The stair-
cases within the towers are circular, and the tops have the first indications of machico-
lations. The battlements remain, crowning portions of the walls which once surrounded
this ancient city, and in them we recognise the Greek or Etruscan origin, which was not
departed from during the middle ages. (See fig. 105.)
Chap. IV.
89
ROMAN.

0
J*1 [ ས། ༥/
0
0
0
Fig. 105.
GATE OF spello.
City and Gates of Augusta Prætoria, in the valley of Aosta, between the Alps Graiæ
and Penninæ, or the Great and Little St. Bernard. This city was founded after the defeat
of the Salissi, who inhabited Cisalpine Gaul, and who were continually at war with the
Romans. In the days of Augustus the gate was built it is an admirable specimen of the
entrance to a Roman city. The walls are set out at right angles. The two longer



Fig. 106.
I
GATE AT AOSTA.
90
BOOK I.
HISTORY OF ENGINEERING.
sides have each two gates, and the others one, placed in such a position as to permit the
streets to traverse in a parallel direction. The towers, built on the outside of the wall,
are square, and placed at from 150 to 200 feet apart. The whole city was therefore
contained in a parallelogram, whose sides were 2700 and 2200 feet in length.
The six gates resembled each other, and were defended by towers, in which were stair-
cases to ascend the walls, the breadth of which at top was upwards of 20 feet. The three
openings were closed with wooden gates, and above the archways, the wall, which was
carried over them, was pierced with eleven semicircular-headed apertures, so that the
guard traversing the walk behind the battlements could see who approached, or was about
to enter or go out. (See fig. 106.) An architraved cornice surmounted the whole, bearing
at each end upon a Corinthian pilaster. As the wall was double that surrounded the city,
the space between was strengthened by arches, and the inner was carried up to a con-
siderable height above the outer, both being surmounted with battlements.
Another fine example of a very early gate or entrance to a city is at Perugia, which
has probably undergone very little change since the time of its construction. (See fig. 107.)

ERUSIA
:
TT
Fig. 107.
•
PERUGIA.
The walls at Nismes, erected in the time of Augustus, are 30 feet in height, and, though
varying in thickness, were generally about 9 feet; they are faced on both sides with regular
courses of stone laid in cement; the interior is filled up with rubble, strongly united with
mortar or cement as hard as the stone itself. The walls were covered with flags of free-
stone, which projected over each side; these flags were about 10 feet in length, and formed
a platform for the movement of the soldiers engaged in the defence of the city: an external
and internal parapet was constructed upon them. The towers were generally round, and
the thickness of their walls 5 feet 6 inches, their interior diameter 24 feet 6 inches: they
projected from the walls, as shown in the other examples.
At Nismes the gateways are constructed of stone; one has two entrances of the same
width, each about 12 feet, and 20 feet high; on
on each side was a smaller for foot
passengers, 6 feet in width and 14 feet in height; above the side openings are niches.
A level cornice surmounts the whole, and terminates against the two round towers;
above this was an attic, now destroyed. The towers are 31 feet in diameter.
Another gate remaining has only one entrance, 13 feet in width, and 21 feet in height.
The walls at Pompeii are usually rubble, faced with reticulatum, 20 feet in width,
including the thickness of the two walls which crowned the ramparts: they varied
CHAP. IV.
91
ROMAN.
in height from 25 to 30 feet, according to the inequality of the ground: at unequal
intervals, towers were built, 27 feet by 33 feet, which projected 7 feet from the outer face:
their walls were 3 feet in thickness, also formed of rubble.
Embattled walls were raised upon the inner as well as outer edge of the rampart, that
next the city being some feet higher than the other; these were formed of large stones
2 feet 6 inches thick, and each battlement had a return wall more effectually to protect
the defender. Between these walls was a wide walk that passed through arched door-
ways made through the towers.
The outer walls of the towers have fallen; generally they were divided by a wall, for
the purposes of strength, and arched over at the top, to allow the walk to continue
uninterrupted around the battlements. The entrance to the city from Herculaneum
consisted of an outer and inner wall, each having three arched openings, the space being
left open to the sky: this was about 42 feet in extent, and 47 feet in depth. The lateral
gates for foot passengers were two arched openings on each side. The centre was guarded
by a portcullis about 7 feet distance from the face of the front wall.
In Italy, the south of France, and the towns scattered over Asia, may be found the
walls and defences as set up by the Romans: they afford us the best commentary on
the art of war, and the ingenuity practised by their engineers.
A work of great
interest might be compiled upon this fruitful subject; the architect would find study for
the best construction, and the proportions which many of the entrance gates of these
Roman cities exhibit are extremely beautiful.
The Gate of Augustus at Fano is a fine example of the entrance to a city, the lower
portions of which are of great antiquity. Fanum Fortunæ was the name the city formerly
bore, which, for its sumptuous buildings, was greatly admired. There are three entrances,
flanked by circular towers, which rise to a considerable height, the two upper stories being
lighted by semicircular-headed openings, and crowned with a bold projecting cornice,

A
SULLEDE
LA! Ancasonal A
ነ
Is" Iter
Fig. 108.
FANO.
over which is the battlement. Immediately over the three entrances was a gallery,
formed by seven arches, between Corinthian pilasters, and surmounted by a regular enta-
blature. The repairs these walls underwent during the reign of Constantine somewhat
changed their character, and since that period the upper story was destroyed by a cannonading
which took place when this town opposed Julius II. Various inscriptions remain amid
the several works of restoration,
92
Book I
HISTORY OF ENGINEERING.
The triumphal character of the entrance to a portion of the city of Autun, called St.
Andrè, also deserves our notice. Most of the cities in Provence, and throughout the south

Fig. 109.
GATE OF AUTUN.
of France, were embellished by the emperors at various times; and so similar in design and
construction are these structures to those of the imperial city, that they cannot for a moment
be considered but as erected by Roman engineers.
Architecture on some is more lavishly introduced than on others, and in that at Autun
the Attic is beautifully proportioned and executed.
Distribution and Situation of the Buildings within the Walls.-The circuit being com-
pleted, the next work was to set out the streets, and mark the sites for the public as well as
private dwellings. The Roman engineers are described by Vitruvius to have laid down
first a marble pavement in the centre of the ground comprised within the walls; after they
had made this smooth and polished, they raised upon it a brass gnomon; at the fifth ante-
meridional hour, the shadow that it cast was noticed, and its extreme point accurately
determined. Around the gnomon was then described a circle, the radius of which was
made equal to the length of the shadow. When the sun had passed the meridian, it was
again remarked when the shadow of the gnomon reached the circle. From these two
points on the circumference, two arcs were described, intersecting each other, through
which intersection, and the centre of the gnomon, a line was drawn which indicated the
north and south points. On the circumference to the right and left of the north and south
points, one sixteenth part of the circumference was set out, and lines through the centre of
the gnomon drawn to connect them; one eighth part of the entire area of the circle repre-
sented the region of the north, another the region of the south. The remaining portion
was divided into three equal parts on each side.
The directions of these several lines mark out the wide as well as narrow streets; for it
was considered that if they were set out parallel to the direction of the winds, the latter
would rush through with greater violence, and that during a gale or strong wind, the angles
of the different divisions of the city dissipated it, and prevented it doing any mischief to
either the buildings or inhabitants.
When the city was near the sea, the Forum was placed close to the harbour;
when inland, in the centre. The temples of the gods were mounted on an eminence that
commanded the city: that of Mercury was established in the Forum; of Isis and Serapis, in
the great public square; Hercules, near the Circus; Mars, out of the walls; and of Venus,
near the gate.
Materials used in the Ancient Edifices of Rome. The materials which the Romans em-
ployed were either for the purposes of construction or for ornament. The first, as lime,
pozzolana, clay, and stone, the immediate neighbourhood furnished; those which luxury
CHAP. IV.
93
ROMAN.
called into use were brought from distant parts of Italy or the provinces, as the marbles,
granites, and porphyries.
Vitruvius treats of bricks, but confines himself to the description of those which are
unburnt. Scammozzi imagined that the houses in Rome were originally built of unburnt
brick, and that none are found, he observes, is in consequence of the frequent fires that city
was subject to, which had the effect of thoroughly burning them. Pliny (lib. vii. cap. 56.)
mentions unburnt bricks as having been in use. Gellio Doxius, son of Coelus, was the
inventor of clay houses, taking the example from the nests of swallows. Burnt bricks
came into very general use for public buildings about the time of Augustus, continued
till the fall of the empire, and were considered as durable and solid as stone.
Bricks have undergone various changes, not only in form and colour, but also in the man-
ner in which they were employed. In the time of Augustus, they were made of a red earth,
less than an inch in thickness, of a
triangular shape; they were not equi-
lateral, as the base was the longest side.
Such bricks may be seen in the gardens
of Sallust, the house of Augustus, and
other buildings erected in the time of
Tiberius. In the prætorian camp at
Preneste they were rather thicker, and
of a deeper red colour, or mixed with
yellow. In the time of Nero, these
colours were generally united, as may
be seen in the aqueduct constructed
in his time, near the Porta Maggiore,
where the bricks are somewhat thinner
than those used in the time of Au-
gustus or Tiberius; they were also
thicker at the base, that the face might
allow the edges almost to touch, and
not show any joint or mortar. The
walls, built of brick, by Augustus and
Tiberius, show a joint of mortar almost
equal to the thickness of the brick. Some remains of the Circus Maximus, under the
Palatine, and on the Palatine itself, though of the time of Nero, have large joints, and
are not so regularly laid.

Fig. 110.
Of the time of Vespasian and his successors, we have brick constructions, as in the Coli-
seum, the baths of Titus, and the villa of Domitian at Albano, all of which have more of
the Augustan workmanship than that of the time of Nero. The remains belonging to the
time of Trajan, on the Quirinal, and called the baths of Paulus Emilius, and the villa
of Adrian, prove that the same style was adopted. In the buildings constructed
at the latter period of these reigns, bricks are mixed with the opus reticulatum;
although there is an evident decline in the taste and execution of the ornaments in the time
of Caracalla, the construction was excellent. One of the best examples is the wall at the
back of the great central hall of that emperor's baths. After this period, the construction
declined in excellence, bricks were made of various thicknesses, and the quantity of mortar
was increased. There are scarcely any remains of brick construction between the times of
Caracalla and Diocletian; the walls of Rome, usually attributed to Aurelian, probably
belong to Honorius, as we learn from the inscription remaining over the gate of St. Lo-
renzo, as well as from a passage in Claudian, which affirms such to have been the case.
The baths of Diocletian show a falling off, not only in style, but in construction, which
rapidly deteriorated; in the basilica of Constantine, erected on the Via Sacra, in the time of
Maxentius, and the baths of Constantine, on the Quirinal, we see still greater negligence
in the selection of materials, with an inferiority of workmanship.
After this period, from economy, or desire to save bricks, a mixed construction of
bricks and tufa was introduced, as in the restoration of the tomb of the Scipios, in the circus
called Caracalla's, though of a date much posterior to that emperor; the ruins adjoining to
that circus; and the hippodrome of Constantine on the Via Nomentana. The basilica and
churches founded in the fourth, fifth, and sixth centuries, as those of S. Croce in Gerusa-
leme, S. Giovanni e Paolo, &c. &c., show the same poverty of construction, irregular bricks
being used with quantities of mortar of an inferior quality. With the decline of Roman
institutions, the art of construction lost its excellence; no care was taken in the selection of
the materials, but those purloined from other edifices were indiscriminately employed. For
bricks, they used stone of a similar shape, tufa, pepperino, and a variety of other ma
terials; which practice was adopted at Rome in all the constructions till the end of the
fourteenth century, and which has been denominated Saracenic work.
The bricks which Vitruvius describes as unburnt were formed of white earth or chalk,
94
HISTORY OF ENGINEERING.
Book I.
and red earth or rough sand; which materials were preferred on account of their
lightness. Other kinds, heavier, which do not adhere to the straw, or are dissolved
by wet, were objected to. Bricks were made in the spring or autumn, as the drying then
was more regular; those made during the summer solstice suffered injury from the heat,
the interior seldom drying regularly, and their exterior hardening rapidly cracked. Those
were the best which had been made two years; they were hardly considered dry before
that time. Three kinds were used; by the Greeks called didoron, a foot long and half a
foot wide, pentadoron, and tetradoron. Half bricks were made to work with them, which
enabled the artificers to break the joint, and to have a vertical joint over the middle
of the brick below. Some bricks were moulded of an earth so light that they would
swim on water, as those of Calentum in Spain, Marseilles in Gaul, and Pitane in Asia.
Of Tiles and Conduit Pipes made of Clay. The same earth used for making bricks
served for forming flat and curved tiles, and different sorts of conduit pipes. Roofs were
covered with alternate flat and curved tiles, and tubes or pipes were used to conduct water
from them, as well as to convey it to the fountains. In the thermæ of Antoninus, water
was supplied to the baths by cylindrical pipes, gathered in at one end sufficiently to be
inserted into the adjoining one; in the baths of Titus, square pipes were used for the same
purpose. In the fountain of Egeria, long conical pipes, one end inserted in the other,
are to be seen, which conducted the water from the aqueduct to the fountain.
Tiles, two feet square, with a small foot at each angle, were placed upright against the
walls, at the baths of Livia, thus leaving between the face of the tile and the wall, pressed
against, by the four feet, a narrow space, which prevented any moisture injuring the wall;
they are fixed by T cramps of iron.
The Romans built hollow walls and domes, with pots and tubes of earthenware, which
practice was continued down to the end of the middle ages; they seem, also, as we shall
have occasion hereafter to observe, to have preferred earthenware pipes for their supply of
water to those of metal.
The Sand, used in Roman construction, we find to have been obtained either from the
pit, river, or the sea, as circumstances or convenience permitted. Several sorts were
used, as black, white, deep red, and bright red; that which produced a grating sound,
when rubbed between the fingers, is said by Vitruvius to have been preferred; that
which was earthy, and which did not possess the roughness above named, was fit for the
purpose, if it merely left a stain, or a particle of earth, on a white garment, which could
be easily brushed away. The carbunculum, or bright red sand, was dug out of mountains
of volcanic origin; it was of a much softer nature than tufa, but more solid than the
common earth. The property which all sand has of hardening and consolidating with
lime renders it of great value in construction; it has been observed, that the sand on
the sea-shore, nearest the action of the waves, is the firmest and most solid, and this by the
ancients was accounted for upon the principle, that the larger the masses the farther they
were projected; for the hand cannot throw small bodies to a great distance, in consequence
of their lightness. Several stones driven together on the sea-shore would also have the
lighter particles of sand washed among them, and fill up their interstitial spaces, and thus
form a consolidated mass. Between sabulum and arenam, as used by Vitruvius, there is a
considerable difference: some writers observe that sabulum is a larger kind of sand, or
arenam grossiorem. But arenam is not sabulum, one having the character of earth, the other
of stone. Sabulum has a fine white or yellowish grain, is found in hot climates more
than in cold and temperate ones, as in the deserts of Africa, where the surface of extensive
tracts are agitated by the wind in the same manner as the sea.
Sea-sand was objected to for plastering, or for mixing with mortar, as it dried slowly;
when dug from a pit, and exposed any length of time to the action of the weather, a
vegetation was encouraged, which injured its properties, and rendered it unfit for use. River
sand was always preferred on account of its grit, and was allowed to make the best mortar.
Lime, either burnt from white stone or flint, called by Vitruvius silice, was obtained,
in all probability, from the same calcareous beds as the limestones of the present day, by the
Italians called palombino. That which had a close and hard texture was preferred for
mortar, and the lighter and more porous kinds for plastering. "When slaked for making
mortar," Vitruvius says, "if pit sand be used, three parts of sand are mixed with one of
lime; if river or sea-sand, two parts of sand are given to one of lime." Potsherds reduced
to a fine powder and passed through a sieve were added: when river and sea-sand were
used in the above proportion, the mortar was considered the best. The cause of the mass
becoming solid, according to our Roman authority, was that sand and water added to
lime formed an artificial stone, for all stones were supposed to be compounds of these
elements; those which contained a quantity of air were of a soft nature, those which had
a large proportion of water were tough, of earth hard, and of fire brittle. Stones which
when burnt might make an excellent lime if pounded and added to sand, without burning
did not possess the property of adhesion, nor set hard; passing through the kiln they lost
their natural tenacity, and their pores were left open and inactive. The moisture and air
CHAP. IV.
95
ROMAN.
they contained were driven out, whilst a portion of heat was acquired and retained,
which was dissipated by immersion into water. For this reason limestone was said to be
heavier before than after it was burnt, and that it lost one-third of its weight, although in
bulk it remained the same. The pores of limestone being rendered open by the expulsion
of air and water, enabled the sand more readily to mix with and adhere to it.
Neither pure earth nor sand without lime could form a cement or mortar, or unite
together polished bodies; and the Romans evidently well understood the method of pre-
paring their lime, as well as mixing it with other materials for the composition of their
mortars and cements: all the works left us in which these are employed, time has
hardened into a mass equal in strength to the stone or tile which is imbedded.
Pozzolana, called a species of sand, or arenarium, is found abundantly in the neighbour-
hood of Rome, was used mixed with a proportionate quantity of lime to form a cement.
The colour of Pozzolana varies, and the catacombs were probably formed by the extraction of
this material. The ancient Pulvis Puteolana, mentioned by Vitruvius, was drawn from
the neighbourhood of Pozzuoli, and its application may be seen in the ruins of Caligula's
bridge in the port of Anzio, and in the mole of Pozzuoli. That found about Baiæ,
when mixed with lime and rubble, would harden as well under water as in ordinary
buildings, and this Vitruvius attributes to the heat of the earth, and the sulphur, bitumen,
or alum, which the water holds in solution. Inward and subterraneous fires render this
earth light and dry, but when moisture supervenes, the particles cohere in such a manner,
that neither the waves nor the force of water can disunite them.
Spong or Pompeian pumice-stone, burnt from another species of stone, is acted upon by
the fire in a similar way. Hot springs and heated vapours in the bowels of the earth were
supposed to do what was effected in the lime-kiln, and that the moisture driven out was,
when quickly supplied by water, able again to unite the particles in a more solid state than
before, by means of the heat common to both bodies.
Some lands afford sand-pits in abundance, as the Apennines towards Tuscany, while
on the other side none are to be met with; and some mountains are not earthy, but of
stone. The force of the subterraneous fires, escaping through the chinks, burns that which
is soft and tender: thus the earth of Campania, so burnt, becomes a powder, and that of
Tuscany, which is of a harder quality, is converted into coal. Both of these materials are
of great use, one being serviceable for constructions on land, the other for works under water.
In Tuscany the quality of the material is softer than sandstone, but harder than earth, and
constitutes that sort of sand called carbunculous.
Stones used by the Romans. The practice adopted by the engineers of Italy of the
present day, in the selection of their building materials, has not at all changed since the time
of the republic: the territory of Bolsena and Stratone is still renowned for stone, which
neither fire nor weather will affect; and a beautiful white stone, easily cut with the saw, and
bearing a fine polish, is found throughout Lombardy, and applied in situations where frost
cannot affect it. The limestones of Istria are used in Venice and elsewhere at the
present day.
The ancients do not seem to have thoroughly understood the strength of the several
qualities of stone; but were satisfied that no weight they could expose it to under ordinary
circumstances would be too much for it to bear, or occasion it to crush; if in a mountain
miles high it could carry the superincumbent weight, they had no fear of the result when
used in a structure of ordinary height.
In the Campagna of Rome, a stone is found of a dark colour, which is easily worked, and
resists both the action of fire and the atmosphere, but it has the peculiar property of
absorbing all the water from the mortar or cement in which it is bedded, and therefore is
only applicable to walls or constructions in a dry situation.
Most of the building stones readily obtained are those of recent formation, occasioned by
deposits from water holding lime in considerable quantities dissolved by carbonic acid;
these deposits gave the ancients the notion that stone grew the banks of the river Neva so
increased, that the valley became closed up and formed it into a lake, and in other situations
masses of stone were seen to grow almost daily, from the deposit and evaporation of the
water. Such stone is always soft when first cut from the bed, and hardens as the water it
contains is evaporated from it. From the quality of the water many of the aqueducts
became encrusted in a similar manner, and their channel considerably diminished.
The travertine, the tufa, the pepperino, and the gabina were used in foundations, for ex-
ternal walls, and for the filling in of walls and vaults. The selce was only used for paving
streets, and the internal parts of walls; the pumice stone, from its lightness, for the construction
of arches and domes. Tufa abounds in the neighbourhood of Rome, and particularly where
the ancient excavations were made, beyond the Porta Maggiore, five miles from the Via
Collatina, on the left. Strabo, lib. v. p. 164., describes this material as a volcanic product
of a reddish hue, not very compact, and easily decomposed by the action of the air alone.
In foundations we find it abundantly used, as on the Palatine hill, in the temple of Fortuna
Virilis, and in the aqueduct of Claudius. When used for construction above ground, the
exterior was covered with a coat of plaster: it was quarried in large masses,
96
BOOK I
HISTORY OF ENGINEERING.
Tufa was much employed for reticulated work, which style of construction came into
use at the decline of the republic; and as there are few known examples of the
time of Caracalla, it is supposed

The
that during or after that emperor's
reign it was discontinued.
pepperino is a volcanic production,
found at Albano, by which name it is
sometimes called; it is of a green-
ish brown colour, and the resem-
blance it bears to finely powdered
pepper has given it the modern
name. This stone, having undergone
the action of intense heat, resists the
action of fire, equally with that stone
called gabina. It was on that ac-
count that Nero, after the great con-
flagration in his reign, ordered the
houses to be faced with either one or
other of these stones. Pepperino is
more solid than tufa, and resists the
action of the weather better ; al-
though to a certain degree it be-
comes affected. The walls of Ser-
vius at Rome are built with it, as may
Fig. 111.
be seen in the remains near the Quirinal; also the walls which enclose the forum of Nerva,
and the cell of the temple of Antoninus and Faustina. The gabina is a volcanic pro-
duction, found near Gabii, distant ten miles from Rome. In colour it resembles the pep-
perino; it is harder, though of a more porous texture, and was much used for millstones.
The travertine, or, as it was formerly called, tiburline, is found near Tivoli, on the banks of
the Tiber; the ancient quarries remain, near the bridge of Lucano. This stone is calca-
reous, formed from the mixture of some sulphureous water with that of the Arno. It is very
porous, resists the action of the atmosphere, and becomes harder the longer it is exposed :
it is easily calcined by fire. In the Coliseum, the sepulchre of Metella, and many monu-
ments in the Via Appia, this stone has been used; at first drawing from the quarry it is
white, but the air acting upon it soon gives it a yellow tint, which increases by time: from its
hardness it was used for plinths and substructions, for isolated columns, ornaments, cornices,
capitals, &c.
We see it in the Tabularium, the temple of Fortuna Virilis, the arch of the
Goldsmiths, &c. It was ordinarily quarried in large quadrangular masses, and the smaller
chippings were used for filling in.

Fig. 112.
ARCH OF THE GOLDSMITHS.
CHẤP. IV.
97
ROMAN.
Siliceous stones, or what are called selce by the ancients, cannot be understood to mean
the same as those so designated by mineralogists of the present day: those have an iron
colour, are very hard, and are basaltic, and used only for street paving. Near the sepulchre
of Cecilia Metella, on the Via Appia, and many other localities, it was abundantly
found.
Pumice, brought from the vicinity of Vesuvius, was used in the vaults of the Coliseum,
and in the palace of the Cæsars, the dome of the Pantheon, &c.
The most ancient edifices of Rome were constructed of the Albano stone, put together
with metal cramps. Alba being the first important conquest made by the Romans, it was
most likely they would employ the ex-

cellent material found in that neighbour-
hood, which had become a portion of their
dominions, in preference to seeking for it
out of their territory. This stone was
used not only under their kings, but also
after the decline of their republic. The
Mammertine prison, built under Ancus
Martius, and the Cloaca Maxima, under
the Tarquins; the walls of Servius, re-
maining near the Quirinal; all that por-
tion of the tombs of the Scipios not tufa,
or which have not been restored; one
of the three temples of S. Nicola in Car-
cere; the substruction of the Capitol;
the aqueducts of Appius, Old Anio,
and the Marcian, are all built of it.
After the conquest of Tivoli, in the year
Fig. 113.
of Rome 417, the travertine stone was introduced, and used in conjunction with that of
Albano, and from its greater hardness was better suited to those portions of an edifice most

Teal
لة
Fig. 114.
VIVARIUM.
liable to injury, as arches, architraves, cornices, &c., as seen in the remains of the Vivarium.
In the Tabularium we find it in the Doric capitals, the architraves, and imposts of the in-
ternal arches: in the temple of Fortuna Virilis the isolated columns are formed of it, as
are also the Doric and one of the Ionic temples of St. Nicola in Carcere, the arch of
Dolabella on the Cælian Mount, the façade of the Mammertine prison, which bears the name
of the consuls C. Vibio Ruffinus and M. C. Nerva, who restored it.
Under the kings, and during the republic, it appears from the remains, that the
public buildings were usually of squared stone (fig.115.); but on the decline of the republic,
H
98
Book I
HISTORY OF ENGINEERING.

Fig. 115.
SQUARED STONE.
that kind of construction called opus incerta prevailed, which must not be confounded
with the work we see at Preneste, Cora, and other ancient cities of Latium.
confirms us, and several
ruins still show that the
opus incerta was composed
of small polygonal stones,
set in mortar, specimens
of which may be seen in a
ruin behind the temple of
Romulus, in the temple of
Vesta at Tivoli, of Fortune
at Preneste, and in many
other ruins scattered over
the Campagna; whilst the
walls of the ancient cities
of Latium are formed of
polygonal stones 4 or 5 feet
in diameter, laid together
without any cement.
cement. The
opus incertum is the ex-
ternal coating of the wall,
being backed or filled in
with all sorts of material.
Fig. 116.
(See fig. 116.)
To the opus incertum succeeded the opus
reticulatum, which was in ordinary use at
the time Vitruvius lived, and continued till
the time of Caracalla. At the same time
burnt brick was introduced.
The opus reticulatum (fig. 117.) has the
stones formed like wedges, and put together
to resemble the meshes of a net; the stones
found in the country were used, whatever
they might be composed of, and as the
angles or quoins of their buildings could not
be executed properly with them, they used
for this purpose tiles, or brick, or stone of a
rectangular form like them.
In the gar-
dens of Sallust at Rome, the house of Mæ-
cenas, which afterwards served for the sub-
structions of the baths of Titus, we see the
opus reticulatum used promiscuously with
brick.
Brick was early used for construction,
became general in the time of Augustus,
and continued in use till the fall of the Roman
empire; it is as solid, and perhaps more
durable, than stone.
Thus the Romans used squared stone during
the time of their kings and the republic;
OPUS INCERTUM.
Fig. 117.
OPUS RETICULATUM.
Vitruvius


CHAP. IV.
99
ROMAN.
1
on the decline of the latter, and under Augustus, the opus incertum; the opus reticulatum,
with and without brick, ceased to be used under the Antonines; and brick was after-
wards employed alone to the end of the seventh century—though after the time of
Constantine it was mixed with strata

of volcanic stone, and took the name of
Saracenic work. The brickwork, from
the time of Augustus to Constantine,
was formed of triangular bricks; at cer-
tain heights were introduced courses of
square or rectangular tiles, which passed
through the entire thickness of the wall,
and bonded the whole together; this tied
in the facing, called by the modern
Italians, cortina. Such work may be seen
in the baths of Antoninus, temple of
Venus Erycine, and on the Palatine.
Before stone was used for building, it
was usual to expose it for two years to
the action of the weather, and that which
was most convenient to Rome was drawn,
as Vitruvius says, from the countries of
the Pallienses, Fidenates, and Albanæ;
those which were soft after the two years'
exposure were allowed to be used in the foundations; which perhaps would be contrary
to modern practice; but the excellence of their cement compensated in some degree for
this use of a friable material.
Fig. 118.
BRICK.
The principal Marbles were the Carrara, abundantly used in the structures of the imperial
city, and also in the provinces. Strabo, who wrote in the time of Tiberius, observes, that at
Luna, a city in Etruria, slabs of white as well as veined marble for tables, and shafts of columns
in one single piece, were quarried; and the greater part of the edifices of Rome and other
cities of Italy were enriched with it: it was easy to remove it from the quarries to the sea,
from whence it could be freighted up the Tiber. This passage of Strabo leads us to suppose
that most of the edifices after the time of the emperor Augustus were adorned with this
marble. At the time of Pliny these quarries yielded a kind that surpassed the Parian in
whiteness, and Mamurra, a Roman knight, decorated his house on the Calian mount
with columns of it, which was the first instance of its being so applied at Rome.
The grain, though finer than that of the Greek, is not so pure a white when polished.
The marble brought from Hymettus, near Athens, was as celebrated as the Pentilican.
Xenophon mentions them both as used by the Athenians for their temples, altars,
statues, and other works. Strabo admires its beauty, and Horace intimates that he en-
crusted the walls of his house with it. It was employed at Rome, before any other foreign
marble was introduced, for columns, and Pliny tells us that Lucius Crassus the orator
brought six, not more than 12 feet in height, to decorate the atrium of his house on the
Palatine, 91 years before the Christian era: for which reason it was called by Marcus Brutus
the Palatine Venus.
The Pentilican marble, composed of white with greenish veins, was quarried in the neigh-
bourhood of Athens. By the Roman writers it is seldom mentioned; by the Greeks it was
held in high estimation, though not much employed in the buildings at Rome. Plutarch
implies that the columns of the temple of Jupiter Capitolinus were formed of this marble,
brought from Athens.
The Parian, found in the Isle of Paros, so much admired by the ancients, was chiefly taken
from the quarries of Marpessa, and of a pure white; it was confined to the use of sculp-
ture. Procopius tells us that the walls of the mausoleum of Adrian were covered with
slabs of this marble, which no longer remain. It is also called Ligdino and Licnite.
The Proconnesian marble was white, diversified with black veins, sometimes proceeding
in straight lines, often obliquely and winding; it was found at Proconneso, an island
in Propontis: and at Cizicus it was used for building. In the time of Constantine,
Justinian employed it for incrusting the walls of S. Sophia, as well as for the columns
which adorned that building.
The Tatian marble, according to Pliny, was white and full of spots, and much
used in the time of Nero and Domitian, after which we do not often find it employed. It
resembles the Lesbian, but is clearer. Some have supposed the square blocks of the pyramid
of C. Cestius to be of this marble, though they are more probably from the quarries of
Luna.
The Fengite, called so from its pure whiteness and splendour, was first noticed in the
time of Nero, at Cappadocia, and was employed by that emperor in the construction of the
H 2
100
BOOK I.
HISTORY OF ENGINEERING.
་
Temple of Fortuna Seja, which formed a part of his golden House. Domitian had the walls
of the arcades, through which he alone passed, inlaid with it, that he might observe what
was passing behind him. This was possibly the Marmo Salino.
Of the coloured marbles, the most famous was that of Carystos, the modern Castel Rosso,
a city of the Negropont; it has a greenish colour, with lines and undulations, resembling
the waves of the sea: the quarries at Mount Ocha were called Marmarion: it was much
used in Roman edifices, and was one of the earliest marbles introduced into that city,
and became very common in the time of the emperors. The columns of the temple
of Antoninus and Faustina are formed of it, and in consequence of their resemblance to the
cipollo (onion) are called Cipollino. It was used also for pavements; the Basilica of Con-
stantine, or temple of Peace, has slabs of it; there are many columns still among the
ruins, and in modern churches, made of the Cippolino.
;
The Lacedemonian marble is of a green colour and very hard; it is found at Taigeto in
Laconia, and its quarries were used in the time of Strabo under Augustus and Tiberius
it is likened by some to the emerald and to the verde antique; it bore some resemblance to
the Thessalian, and from a passage in Pausanias we learn that at a village in Laconia, at the
foot of Taygetus, quarries of marble or hard stone were worked, which being cut into form
were polished by immersion in the river, and became so beautiful, that they were applied
to adorn the temples of the gods. The marble we call serpentine is mentioned by
Strabo, and is the ophite of Pliny. The qualities which the ancient writers quoted
give to this marble agree with the serpentine, which is of a grassy colour and very hard,
being especially adapted for tessera; such is that of the grotto of the nymph Egeria.
Lampridius says that Heliogabalus lined the arcades of the Palatine with Lacedæmonian
marble and porphyry, that is, serpentine and porphyry, a method improved upon by Alexander
Severus, from whom it was afterwards called Opus Alexandrinum, and was in great use
during the decline of the arts, most of the early churches being cased with it: one of the
finest examples of which is that of S. Giovanni and Paolo, on the Cælian mount, which
was decorated in the fourth century. The ancient writers mention that the Lacedæmonian
marble was used for incrustation, but do not say it was employed for the shafts of columns :
in the baptistery of the Lateran, before the chapel of St. John the Baptist, are two columns
of red porphyry, of the Corinthian order, with capitals and bases of Lacedæmonian marble.
Serpentine in small pieces is very common in Rome, and was much employed for pavement
in consequence of its hardness. In the baths of Antoninus, the pavement was composed of
small tesseræ, or coarse mosaic, of Lacedæmonian and Numidian marble, viz. serpentine and
giallo antique.
The Atracian or Thessalian was another variety of green marble, obtained from the banks
of the Peneus, 10 miles from Larissa. Paolus Silenziarius says it was a green marble, re-
sembling the emerald, mixed with deep blue spots, a light black and snowy white, and was
much prized by the Greeks. This is no doubt the verde antique, specimens of which are
in the Basilica of the Lateran.
The marble of Chios, from the island of that name, is of various colours, the light black
most predominating, resembling the African. The Arch of Drusus on the Via Appia has
columns of this marble; they are also found in the Pantheon, and in the Basilica Ulpia of
the forum of Trajan, which was partly paved with it.
The Phrygian marble, called Pavonozzetto, very much esteemed, was found near Docimea
in Phrygia. It is white, with purple veins. Twenty-four columns of this marble decorated
the Basilica of Paulus Emilius in the Roman forum, and now form the chief ornament of -
the Basilica of Ostia. This marble is common at Rome, being found in almost all the churches.
The figures of the Prisoner Kings on the arch of Constantine are made of it, as are the
statues found among the ruins of the forum of Trajan. From a passage in Strabo we learn
that quarries which at first only yielded small masses of this marble afterwards produced
columns of one block, and notwithstanding the distance from the sea they were transported
to Rome. During the decline it was used in the decoration of the churches, particularly by
Justinian at S. Sophia at Constantinople.
The Lydian marble was of two kinds, one red mixed with a pale colour, which we
now call red brescia; the other black, called by the ancients basinite and chrysite, both
found in Lydia, a province of Asia Minor.
Nero Antico, or black, quarried at Tenarus, a promontory of Laconia, has a beautiful sur-
face, and is at the present day highly prized. Columns of it at Rome are to be met with as
early as the time of Augustus, at which time it was much used in Greece.
The
Of the Timber used by the Romans. Great attention was paid in the selection of timber
for construction, and all belonging to the fir species were usually cut down when they
put forth their young shoots, that the bark might be more readily stripped.
maple, the ash, the elm, the lime, and the oak were felled in winter, the latter being
considered subject to worm if cut down in the summer. Vitruvius prefers the autumn
for felling of timber; for the fruits being ripened, and the leaves dry, the roots draw
CHAP. IV.
ROMAN.
101
the moisture from the earth; the trees, he says, are then recovered from their exhaustion,
and restored to their pristine solidity. In felling them, he recommends cutting through
the trunk of the tree, then leaving it for a time to allow the juices to drain off, by which
means future decay is prevented. When the tree has drained sufficiently, it may be cut
down and applied to building purposes. Hesiod says, when the trees shed their leaves
is the proper time for felling.
Oak, elm, poplar, cypress, and fir were all used for building, and the holm oak, or esculus,
was greatly preferred. The green oak (cerrus), the cork tree, and the beech were considered
liable to rot, which was accounted for by their containing equal quantities of water,
fire, and earth, which rendered them incapable of balancing the quantity of air
they contained. The white and black poplar, the willow, and the lime tree (tilia) were
also used. The alder was selected for piles, as it was found not to decay under water.
The city of Ravenna had its foundations entirely on such piles. The larch, growing on the
shores of the Adriatic and banks of the Po, was considered not subject to decay, and con-
sequently was highly esteemed; it had considerable density, and would not float in water.
Julius Cæsar first called it Larigna, or larch, after the name of a fortress constructed
entirely of this timber near the Alps, which, when besieged and surrounded with bundles of
fire-wood and torches, was not ignited. A wood that would not burn was considered
admirably adapted for the plates and rafters of dwellings, as they would neither ignite nor
become charred. It was brought down the Po to Ravenna, and used at Ancona, &c.
The palm possessed the peculiar property of bending upwards when any weight was
placed upon it; and the juniper, said by Pliny to have the same properties as the cedar,
and to be even more durable, was also used. The olive was greatly esteemed, as was the
wood of the box tree; for exterior works the chestnut was much employed; for the fittings
of houses, for tables, benches, &c., the fir, as was the pitch pine and cypress; for thin
planks, the beech was in general preferred to either the chestnut, the elm, or the ash.
The mulberry was considered durable, and admired for its getting blacker by age. Cato
advises, for the making of levers, holly, laurel, and elm to be employed; for bars,
the wild cherry tree, or the corneil; for stairs, the wild ash or maple; for water pipes, the
pine, the pitch tree, and the elm, which were buried entirely in the earth to prevent
decay. For the use of the turner, they selected beech, mulberry, and the box, as
well as ebony. Poplar was employed for statues, as was the hornbeam, the service tree,
the elder, and the fig; these, from their dryness and evenness of grain, were easy to
work, and fitted to receive the colour they were to be finished with. Woods which differed
in quality were seldom brought together, as it was supposed that those which were
of a hot nature could not be united by glue to those grown in moist and cold places; wood
of a close texture and fine grain could not be glued together, and oak was said to be unique
in this particular, as it would not unite with itself, or any other wood of the same nature.
The ancients, as Vitruvius advises, did not glue planks of beech and oak together, con-
sidering that woods differing so much could not be firmly united. All this is owing
to the unequal shrinking of the several kinds, which must, whenever it takes place,
detach the planks brought together; were both equally dry, the one would absorb more
moisture than the other, swell or expand in proportion, and have also a tendency by
this action to detach itself.
Pavements, when used for floors, were very highly decorated, much attention being
required to prepare the soil to receive them, and to select the material of which
they were formed.
When on the ground, it was carefully examined, and rendered solid
Fig. 119.
PAVEMENTS.
When laid
between it and the
Holm timber was
After the joists
throughout, after which it was spread over with a layer of some dry material.
upon a timber floor, walls were not built under it, but a space left
floor, that the drying and settling should be equal throughout.
preferred to oak, less likely to split and warp, and thus cause cracks.
were laid, thin boards were fastened down to them by two nails, driven through the edges
of each, which prevented their rising. Fern or straw was then spread over the whole,
to prevent the lime coming in contact with the timber, which would have immediately
H 3
%

102
caused it to decay.
HISTORY OF ENGINEERING.
BOOK I.
Over this was a layer of rubbish, the stones of which were as large
as would lie in a man's hand on this layer the pavement was afterwards laid. New
rubbish required that every three portions should be mixed with one of lime; and old, five
parts to two of lime. Wooden beaters were employed, which by repeated blows reduced it
to the thickness of nine inches. An upper layer, composed of three parts of potsherds and
one of lime, was spread over this to a depth of six inches, on which was laid the slabs of
marble, stone, or tesseræ, care being taken that the whole should lie in a proper inclination :
it was then rubbed off, and the joints or edges of the ovals, triangles, squares, hexagons, or
other figures, made perfectly smooth. After rubbing and polishing, marble dust was
strewed over; then lime and sand run into the joints.
Pavements in the open air had over the first flooring another layer of boards crossing
them, properly secured by nails, so that the joists were doubly covered.
The pavement
first laid was composed of two parts of fresh rubbish, one of potsherds and two of lime.
After the first layer, a composition was spread over it, pounded into a mass, not less than

Fig. 120.
PAVEMENT.
twelve inches thick. The upper layer being spread, the pavement, consisting of tesseræ,
each about two inches thick, was laid on, with an inclination of two inches to ten feet,
to prevent the frost from injuring it at the joints: before the winter it was saturated with
dregs of oil.
When great care was required, the pavement was covered with tiles two
feet square, properly jointed, having small channels an inch in depth cut in the edge
on each side. These, filled with lime, tempered with oil, had the edges rubbed in and
pressed together. The lime in the grooves or channels growing hard, neither water nor
any thing else would pass through. After this precaution, the upper layer was spread and
beaten with sticks; over which, either large tesseræ or angular tiles were laid with the
proper inclination.
Tempering lime for stucco received considerable attention, that the lime should be
of the best quality, and prepared long before required for use. When lime was not
thoroughly slaked, and fresh from the kiln, it was found to blister, and destroy the evenness
of the stucco. After it was properly slaked, and laid in a heap, it was chopped with a
hatchet, when, if any lumps appeared, it was considered not sufficiently slaked; when
the iron of the instrument used came out dry and clean, the lime was considered poor and
weak; but if it had any glutinous substance adhering to it, it indicated richness, and
that it was thoroughly slaked, and properly tempered. This was used to form the com-
partments and last coat of the walls.
Stucco work, for arched ceilings, was executed by setting up parallel ribs about two feet
apart, made of cypress, it not being so liable to rot as other woods. These ribs were cut to
fit the curve, and secured in their place by iron nails: being fixed, Greek reeds, previously
bruised, were tied to them in the required form, with cords made of the Spanish broom.
On the upper side of the arch a composition of lime and sand was laid, to prevent any water,
that might fall from the floor above, penetrating through it.
When Greek reeds could not be obtained, common reeds were used, tied together in
bundles of appropriate lengths, but of equal thickness, observing that between each two
ligatures there should not be a greater distance than two feet. These were bound with
cord to the ribs, and made fast with wooden pins. The remainder of the work was
performed as before described, The arches being prepared and interwoven with the reeds,
a coat was laid on the under side. The sand was afterwards placed on it, and then po-
lished with chalk or marble. When the vault was polished, the cornices were run over
the springing, which were made as light as possible. A small quantity of plaster only was
used, and the stuff was of a uniform quality, such as marble dust; plaster was apt to set
too quickly.
CHAP. IV.
103
ROMAN.
When the cornices were completed, the first coat was laid on the walls as roughly as
possible, and while drying, the sand coat was applied, setting it out in the direction of its
length, by the rule and square, and attending to the perpendicular lines at the angles.
After these two coats were thoroughly dry, a third was laid on, and its perfection greatly
depended on the soundness of the sand coat. Sometimes three sand coats were laid on,
and over them the coat of marble dust, which was so prepared, that when used it did not
stick to the trowel, but came off the iron easily. Whilst the stucco was drying, another
thin coat was well worked and rubbed, and then another still finer than the last. Three
sand coats, and the same number of marble dust coats, rendered the walls solid, and not
liable to crack.
When the work was well beaten, or hand floated, the under coats made perfectly solid,
and afterwards smoothed by the hardness and whiteness of the marble powder, any colours
put upon it exhibited great brilliancy. Colours, when used with care on damp stucco, do
not fade, but are very durable, as the lime, deprived of moisture by burning, becomes
porous and dry, and readily imbibes whatever is placed over it.
The Greek plasterers, Vitruvius continues, not only made their work hard by this means,
but after the plaster was mixed, caused it to be beaten with wooden sticks by a number of
labourers, before they used it. Slabs were often taken from the walls so plastered, and
used for tables, it being thoroughly hardened.
When stucco was applied to timber partitions, the spaces were filled in first with clay,
over which reeds were nailed, side by side, then a coat of clay, and another layer of reeds
nailed on the former, but crossed in the opposite direction, one being upright, the other
horizontal: after this the work was proceeded with in the usual way, finishing with the sand
and marble coats.
Stucco works in damp places. Every precaution was taken to guard against the damp or
moisture creeping up or passing through a wall; and Vitruvius is very particular,
though perhaps not perfectly clear, in his description of the manner in which this was to
be effected.
When apartments were on the ground floor, the walls, to the height of three feet
from the pavement, had a rough coat of mortar spread over them, which was composed
of potsherds instead of sand, to keep out the damp. When continual moisture was dreaded,
a thin wall was built within-side the outer, at as great a distance as was possible, leaving a
space or cavity for the air to circulate freely through. Openings were left both at top
and bottom to assist this circulation, and prevent its becoming stagnant; the wall was
afterwards plastered with potsherd mortar, and finished with the last coats.
When space
was an object, another mode of construction was practised: within the outer wall a channel
was formed, having its ends open to the outer air: on the inner wall of this channel small
piers were built of eight-inch bricks, on the outer edge of the channel, and on these small
piers were laid two-feet tiles, a palm distant from each other. Over these flat tiles, square
bent tiles, edge to edge, were fixed upright from the bottom to the top of the wall, the
insides of which were previously coated with pitch, that any condensed vapour might not
be absorbed, or penetrate the tile. These square tiled flues were open both at top and
bottom, and on the side towards the apartment they were lime-whited over, to make them
adhesive to the first coat of plaster, which from their dryness in burning they would not
readily have done. The first coat being laid on, the coat of pounded potsherds was spread,
and the remainder finished in the ordinary way.
The pavements of their rooms were carefully formed: first, they took out the ground to
the depth of two feet, well rammed the bottom, and spread over the whole dry rubbish or
potsherds, giving the work a fall towards the drain. On this was laid a composition of
charcoal, lime, sand, and ashes, six inches in thickness, inade perfectly level and smooth.
This became hard and solid, and admitted of being rubbed with stone, and polished, when
it acquired the resemblance of a black pavement. "Such," says Vitruvius, "is not only
easily kept clean, but persons walking over it with bare feet are not likely to take cold."
The marble used in plastering, and which produced such a fine stucco, was not calcined,
but simply pounded; the chips, left by the masons, were selected for the purpose; these,
after being reduced to powder, were passed through three varieties of sieves; the larger
particles were used with the sand and lime, then the second in order, and afterwards the
finest; the work was then polished, and made fit to receive the colouring.
The colours used by the Roman painters are vivid even at this day; among them was
red ochre, brought from Sinope in Pontus, Egypt, and the Balearic islands, near the coast
of Spain, and many other places; green chalk from Smyrna; orpiment from Pontus; red
lead from Pontus; vermilion from the Cilbian fields of the Ephesians. This latter
colour peroxidises, and in consequence, immediately after it was used, and sufficiently dry,
it was covered with a mixture of Punic wax and oil, put on with brushes, and afterwards
made to lie in an even manner, by heating the wall, which was done with live coals in-
closed in an iron pan; the whole was then rubbed with rolls of linen cloth.
Lamp black, of the best kind, was formed by burning the lees of wine in a furnace, and
H 4
104
Book I
HISTORY OF ENGINEERING.
grinding it with size; the common sorts, used by plasterers, was charcaol obtained from
burning pine branches, pounded in a mortar with size.
Blue was thus formed: sand was ground with sublimed sulphur, until it acquired the
fineness of flour; to this coarse filings of Cyprian copper were added, and the whole, by
the addition of water, made into a paste, rolled into balls, and afterwards dried; they were
then put into an earthen vessel, and placed in a furnace, when a blue colour appeared.
A purple was obtained by plunging a lump of yellow earth, heated red hot, into vinegar.
White lead, verdigris, and red lead were in common use: purple was obtained from
marine shells, which afforded the scarlet dye; the shells were collected, and broken into
small pieces with iron bars, when the purple colour, which oozed out like tears, was
collected into mortars, and ground. Madder root was employed to tinge chalk, and green
was formed by mixing blue with the herb weld.
The houses at Pompeii are usually constructed of a great variety of inferior material,
and on the strength of the mortar depended their stability; the walls were coated with
plaster, formed precisely after the method described by Vitruvius. After the rough coat, a
second, composed of sand and lime, called arenatum, and then the marmoratum, composed
of sand and pounded marble, which was put on very thin, and rubbed and polished
until a surface was obtained equal to marble. Whilst this coat was in a humid state,
the colours were laid on, which, according to our author, incorporated themselves with the
incrustation, and were not liable to fade: three coats of arenatum, and as many of marmo-
ratum, were used in the best works, which received a polish capable of reflecting objects.
Strength of building. When lintels or beams are loaded, they are apt to sag in the
middle, and cause fracture in the work above; but when posts are introduced, properly
wedged up, this is prevented: by the insertion of two inclined pieces of timber, it may also
be acomplished. (Vitruvius, lib. vi. cap. 11.)
The weight of the wall may be discharged by arches formed of wedges, concentrically
arranged; these, turned over the beams or lintels, relieve the weight, and prevent them
from sagging. In all buildings where piers and arches are used, the outer piers are to be
made wider than the others, that they may resist the thrust of the arches.
Where walls were constructed to resist the pressure of a bank of earth, their thickness
was proportioned to the weight they had to resist, and buttresses were added, which were
placed as far distant from each other as the height of the wall, and made of the same
width; they projected at bottom as much as the wall was thick, and gradually diminished
to the top.
On the inside of the wall, towards the mass of earth, it was indented like the
teeth of a saw, which teeth were made to project from the wall as much as its height; the
pressure of the earth was thus distributed over a larger surface.
The Romans sometimes formed walls entirely of rubble, or blocage, as it is termed by
French writers; depending entirely upon the goodness of the mortar for their strength,

Fig. 131
MINERVA MEDISA.
-
CHAP. IV.
105
ROMAN.
small, irregular formed stones were thrown together, without any apparent order. In the
large vaults of the baths of Caracalla, a species of porous lava was used, which was as light
as pumice-stone. The vaults of the baths of Diocletian, the Coliseum, and the temple of
Minerva Medica, are so constructed. These vaults, as well as those of Caracalla and the
Villa Adriana, were turned on centres, formed of boards laid longitudinally, the marks of
which may be seen where the stucco which finished their soffites has peeled off. On the
boards was first spread a thickness of mortar of more than a foot, on which was laid flat
tiles 2 inches in thickness, and nearly 2 feet square. These tiles were covered by others,
and a second layer of mortar, but not so thick; the tiles were about 8 inches square, and
1 inch in thickness, laid in courses in such a manner as to break joint with the first layer.
Of the Forum and Basilica. No city of the Roman empire, however small, was without
its place of assembly and its market for the sale of all sorts of goods. The forum was
originally intended for this purpose, and was surrounded by a colonnade, over which was a
gallery or covered portico, from whence the gladiatorial shows might be seen, which were
exhibited before the introduction of the amphitheatre. Trades were carried on under its
porticoes, and at the end of it was the senate-house; the curia, where meetings on solemn
and religious matters were held, the comitia for the common people, the treasury, and other
public buildings, adjoined it. Such was the Roman forum, and that at Pompeii, the size of
which was proportioned to its population: its width was usually two-thirds its length;
the columns of the upper colonnade were made one-fourth less than those below, following
the order of nature, which in the fir, cypress, and pine, preserves a gradual diminution
throughout their height.
The basilica, in which all legal business belonging to the city was transacted, had its
precise form and arrangement. Vitruvius, who constructed one at Fano, gives its distri-
bution, and describes what is necessary for its interior.
The middle vault between the columns was 120 feet in length, and 60 feet in width;
the portico, or space between the outer wall and columns being 20 feet in width.
height of the columns,
including their capitals
and bases, 50 feet, and
their diameter 5 feet.
'The columns in the
direction of the breadth
of the vault were four
in number, and on the
side which joined the
forum eight, including
those at the angles in
both cases; on the op-
posite side there were
six, because the two
central were omitted,
that the view of the
Pronaos of the temple
of Augustus might not
be obstructed. The
tribunal was in the
form of the segment of
a circle, the width being
46 feet, and the depth
15 feet.
The two-fold di-
rection of the roof, Vi-
truvius states, pro-
duces an agreeable
effect on the exterior,
as well as from the
lofty vault within; and
for economy such a
building would always
be preferred, no ar-
rangement affording
greater accommoda-
tion, with the same
о о
Fig 122.
о
о о о
о
BASILICA AT FANO,
quantity of material used in its construction.
The

Numerous basilicæ remain to attest the truth of his descriptions, which at Rome now
serve for churches: their form, being convenient for the assénibly of vast numbers, has been
106
BOOK I.
HISTORY OF ENGINEERING.
imitated down to the present time, in all buildings erected for that purpose. The examples
at Pisa show how admirably adapted it was for the Catholic worship, and the Norman and
Saxon ecclesiastics continued to make use of such models for whatever new erections they
undertook.

| | | | |!
TOO!
1
Fig. 123.
BASILICA AT FANO.
was of the greatest
The forum, graced
The basilica, which adjoined the forum, in the Augustine age,
importance: whatever was imposing in architecture was applied to it.
with porticoes, statues, temples, triumphal arches, was by the citizens made their common
place of resort, to which in time were added libraries and places of amusement.
Of the Theatre. The extent of some of the theatres which remain, and the manner of con-
structing them, deserve some attention, as they were first cut out of the sides of a hill, the
proscenium being added to suit the locality, which required great skill on the part of the
engineers who excavated them. In the early examples, the seats were cut out of the solid
rock, and, from the convenience they afforded for the assembly of numbers, were often used
or other purposes than the drama. The seats, elevated one above the other, afforded
the spectators an opportunity of viewing the country, which rendered it necessary in after
times to limit their vision to the theatrical representations, when the whole was inclosed
within a lofty wall. Vitruvius tells us how these buildings were set out : within a circle
was inscribed three squares, the angles of which were to touch the circumference; that
square, the side of which was nearest the scene, and which cuts off a segment of the circle,
marked out the extent of the proscenium, and another line drawn parallel to this last, and
forming a tangent to the circle, determined the front of the scene. Through the centre a
line was drawn parallel, which separated the pulpitum of the proscenium from the orchestra.
In the orchestra, the seats for the senators were placed, and the other portions of the theatre
were so divided, that the angles of the triangles, which touched the circumference, pointed
to the directions of the ascents, and steps between the cunei, on the first precinctories or
stories. Above these the seats were placed, which formed the upper cunei, in the middle of
those below. The angles pointing to the staircases were seven in number, the remaining
five, marked the points of the scene; that in the middle, the royal entrance; those on the
right and left, for the attendants. The seats on which the spectators sat were not less
than 20 inches, or more than 22 inches in height, and their width from 24 to 30 inches.
All the spectators were so situated, that they saw equally well, and the voice of the actor
was heard by all. The seats were so arranged, that a cord drawn from the lowest to the
highest touched the edge of each; and at the top a covered portico sheltered the spectators
during the intervals of the drama from the heat of the sun.
The Proscenium was adorned, towards the theatre, with columns, niches, and statues ;
the stage was formed of wood; beneath which were various machines for adapting the
scenes, and imitating thunder. Painted scenes, and triangular slips, which could be
turned round, with devices upon them, and a quantity of machinery of various kinds, were
introduced, to heighten the effect of the representations.
The top of the scene was level with the roof of the portico, so that the voice was distinctly
conveyed to those on the upper seats.
Behind the scenes were porticoes, which, in case of sudden showers, might be resorted to,
which communicated with verdant and pleasant walks, dug out and drained to the lowest
possible level; to the right and left, sewers were constructed, which served for this purpose.
The walks were carefully formed, taking out the earth to a certain depth: the space was
filled with charcoal, on which a layer of gravel was spread, and Vitruvius tells us that in a
time of siege, these walks were sometimes opened, and the charcoal taken out, and divided
among the inhabitants. thus they contributed to health during peace, and preservation in the
time of war.
CHAP. IV.
107
ROMAN.
Every city had its theatre, fragments of which remain. Herculaneum and Pompeii possess
them in a tolerable perfect state: that of Marcellus at Rome, Arles, Orange, and other
places in France, attest their grandeur and excellent construction; every attention was paid
to the approaches of their seats, and to the shelter and protection of the assembled multitudes
during a heated atmosphere, or inclement weather. Drains were contrived on each story,
which below assumed the character of sewers, maintaining their cleanliness and comfort; all
the rain that fell was collected by earthenware or metal pipes, and carried to the several
conduits, studiously and carefully built up within the outer walls and inner piers. Sicily,
and the provinces generally, boasted, according to their population, of a well arranged
place for theatrical amusement. It became, at an early period of the Roman empire, as
necessary an appendage to the city as the forum.
The Greek Theatres were also formed by excavating the side of a hill: a vast number
of these are remaining in Asia Minor; and the only part constructed, or built from the
foundation, is the wall of the scene. Many of the Roman theatres differ in their construction:
being built with walls radiating to a centre, and arched from one to the other, to support
the inclined plane, on which the marble seats were placed for the spectators. Between these
walls all the spaces which were not left for communication from the several corridors
were occupied by staircases, which served to mount to the precinctories, and for the egress
of the spectators after the amusements were over, or during the intervals which were
allowed between the performances. These buildings, erected for the accommodation of the
people, were the result of the munificence of individuals; and in the smaller provinces,
distant from the seat of empire, there seems to have been frequently a difficulty in completing
them. The citizens of Nicea, after having expended a considerable sum in the erection of
one, could not terminate it, as we learn from one of Pliny's letters to the Emperor Trajan.
Augustus and Tiberius enlarged two theatres at Antioch, by adding a zone, or range of seats
to the upper part of the structure: the former emperor, at his own cost, erected a very large
theatre at Laodicea, placing in it a statue of himself in marble.
At Rome, in the first instance, these structures were of wood, raised at the expense
of
ediles, or other candidates for popular favour, and repaired or renewed as occasion required.
Pompey, Balbus, and Marcellus were the first to build them of stone; and their use seems
to have been for the exhibition of gladiators, more than for the drama. Suetonius, in his
life of Augustus, says, that women were admitted to the upper porticoes to see the games;
but that afterwards, it not being thought decent that they should be present, they were
prohibited from entering. These regulations were soon laid aside, as we learn from the sixth
satire of Juvenal.
Of the Theatre of Marcellus little now remains: twelve or thirteen arcades, with their
Doric columns and entablature, and as many above of the Ionic order, which formed a
part of its magnificent exterior, is all that can be seen. It is of Tiburtine stone, and the
profile of the orders is well proportioned and executed. Augustus is said to have raised
it in honour of his nephew Marcellus; when dedicated, six hundred wild animals were
sacrificed; and for the first time tigers were exhibited confined in cages.
It was a
semicircle, the diameter of which, probably, from out to out, was 270 feet; one half of
this radius was applied to the walls and corridors, over which were the seats, and the other
to the orchestra; the dimensions given to the proscenium, as well as its arrangement, are
not at present known. The building seems to have been set out very regularly, judging
from what remains in the palace of Savelii Orsini, and from the plans left us by the architect,
Baldassare Perruzzi of Sienna, who built the latter.
An outer and two internal corridors sweep round semicircularly, and on the outside were
forty piers with 39 arches. From the inner piers, diverging to the common centre, were 40
walls, constructed as those of the Coliseum, though not with the same material.
The Theatre at Arles was a semicircle of more than 300 feet in diameter, and the proscenium
had a depth of at least 180 feet: its exterior had three orders of Doric pilasters with arches
between, surmounted by a bold modillion cornice; it was built of large masses of stone,
in regular courses. Like the Coliseum, it had two outer corridors, and the walls diverg-
ing from a common centre composed the stairs, vaults, and vomitories, arranged in a similar
manner.
The Amphitheatre was formed of two theatres, or semicircles united in such a manner
that the spectators had an equal view of what passed in the arena: for which reason the
Romans gave them the name of visorium: they were used for gladiatorial shows, combats
of wild beasts, and other games. They were of large dimensions, made in the form of an
oval: the arena or middle space was surrounded by rows of benches elevated one above
the other.
The Etruscans introduced amphitheatres and gladiatorial shows: the Romans borrowed
from them this taste, which degenerated into a fury among that warlike people, with
which they inspired all the nations they subdued. The remains of amphitheatres are
met with throughout the Roman empire. The first were probably mere excavations, the
spectators being elevated on banks of earth; the more persons they wished to accommodate,
108
BOOK I.
HISTORY OF ENGINEERING.
the more necessary it was to deepen the area: this may be seen at Pæstum, which also
shows the manner of construction adopted when formed on the side of a hill; one half of
the seats being on the natural slope, and the upper portions being raised on con-
structions. This method, from its economy, was perhaps the earliest; and thus the first
theatres, as already observed, were formed out of the sides of rocks and hills. The seats were
afterwards made with planks, and removed when the shows were concluded. This being
found inconvenient, others were constructed in a more solid and substantial manner: many
having been destroyed by fire, stone was at last resorted to. The first amphitheatres at
Rome were temporary structures, and situated in the Champ de Mars, without the city.
Statilius Taurus erected the first of stone, A.u.c. 725, which, with the Coliseum, were the
only two within the walls.
The amphitheatres of Castrenses, erected by Tiberius, on the Esquiline hill, of which
some remains are still seen, near S. Croce in Jerusalem, was built of brick, and of the
Corinthian order. Another built by Trajan, in the Campus Martius, was destroyed by
Adrian.

Fig. 124.
CASTRENSE.
Nothing gives us a higher notion of the knowledge possessed by the Romans in the arts
of construction, than the numerous and vast remains of their amphitheatres, erected in
almost all their towns and provinces.
At Fedena, five miles from Rome, Attilus built an amphitheatre, in which, in consequence
of the foundations giving way, 25,000 persons perished.
At Placentia was one of the largest in Italy, built of timber, without the walls of the
city. At Arezzo, Florence, Fisole, Adria, Lucca, Palermo, Cassano, Minturno, Benevento,
Alba, Capua, Pompeii, Puteoli, Otricoli, Catania, Agrigentum, Syracuse, Pæstum, Pola,
Nismes, and Verona, Frejus, Arles, Autun, Saintes, Bordeaux, Orange, Narbonne, Die in
Dauphine, Cahors, Drenaül on the Cher, Toulouse, Lyons, Vienne, Paris, Neri, Grand
Drevant, Bruieres, Valonges, Besançon, Metz, Perigeaux, Nice, Doue sur l'Ilgers in
Poictou. In Spain, at Hispalis near Seville, Tarragona, Saguntum, and many other
places.
At Smyrna is one of stone, in good preservation; also at Sardis, the capital of Lydia,
Jerusalem, Argos, and Melos; Udena, near Tunis, is another, very perfect and beautiful,
and Constantinum, Istria, Tergeste, Ægeda, Parentium, and Pola, each had their amphi-
theatre. Those of Nismes, Udena, the Coliseum, and Verona, are the most perfect that
remain.
Amphitheatre of Vespasian, called Coliseum, finished by the Emperor Titus about the 79th
year of the Christian era, is of an oval form, its diameters being 620 and 513 feet, measured
to the face of the outer wall, from which the semi-columns project. The entire height
of the building is 157 feet, divided by four orders of architecture; the upper has pilasters,
the others half columns. Its entire area may be estimated at 249,804 superficial feet,
or nearly six acres; the cubical contents of the mass and void at nearly 40,000,000 of cube
feet. The arena, 287 feet in length, and 180 feet 3 inches in width, is an area about one-
CHAP. IV.
109
ROMAN.
sixth of the whole, or a little less than an English acre. It has been estimated that 500,000
tons of material were used in the construction of this amphitheatre. Each of the three
lower stories has 80 arches; and medals show that the two upper ranges were decorated
with statues. In the year 1813 the arena was excavated, when substantial walls, finely
worked with pepperino stone, were discovered, that had supported the timber floor: they
were formed into corridors and receptacles for wild animals collected for the shows.
The podium, surrounding the arena, was of a sufficient height to protect the spectators
from attack of the animals: from thence to the summit were steps or seats of marble, which
were 17 inches in height, and about a foot or 13 inches in width.

BERMAINA
افست
Fig. 125.
COLISEUM.
Five corridors of communication extended round the building; the two outer formed of
open arches, which, as well as the piers, were constructed of travertine stone; the whole
paved with thick travertine slabs, extending nearly 6 feet beyond the face of the outer
wall. From the inner corridor arose two varieties of staircases, which conducted to the
Ionic range: from the third corridor other staircases also conducted to the same level.

Fig. 126.
COLISEUM.
110
Book L
HISTORY OF ENGINEERING.
The division walls, which radiate from the third to the two outer corridors, have each four
distinct piers of travertine stone, with spaces between filled with pepperino, the horizontal
joints of which do not always correspond. The walls between the third and fourth cor-
ridors are faced with tiles in regular courses; the outer pier is alone of travertine. and forms
a break.
The vault of the fourth corridor is entirely destroyed; the marble pavement remains,
5 inches thick, which seems to indicate that this was the approach to the podium, where
the emperor and persons of rank were seated.
The rain which fell upon the several seats and the arena, and the water which flowed
through urinals, and other arrangements made for the convenience of the multitude
assembled within the walls, drained into wide and spacious sewers, which were conducted
into the Cloaca Maxima. A large drain in the second corridor, 30 inches wide, received
the water, brought down by perpendicular pipes worked in the solid masonry, or placed in
indents, lined with tile. The drain of the third corridor, 17 inches wide, and 3 feet in
depth, is lined carefully with tile and coated with a fine cement. On the outer side of the
third corridor, a similar drain, with a fall towards the last described, caught all the water
brought by the several branches from the arena.
The total area of this building has been stated to be about 249,840 feet; that of the
arena, within the present podium wall, 40,575 superficial feet: consequently, the area occu-
pied by the walls, piers, and corridors, will be the difference of these two quantities, which
will be found to be 209,229 feet.
The true points of support are the following:
80 outer piers, the area of which is
80 second piers, the area of which is
80 third piers, the area of which is
80 division walls to the third corridor
80 division walls to the fourth corridor
80 portions of the arena wall
·
5,360 ft.
3,600
2,640
-
=
14,400
6,640
9,200
41,840
The points of support are, in area, 41,840 feet, about one-fifth of the mass, or one-sixth of
the total area of the entire amphitheatre, which is about the proportions that exist between
the total area and the points of support in St. Paul's, at London.
The 80 piers and division walls are not set out very exactly; they diminish in thickness
as they radiate to the four centres of the ellipsis.
The
Exterior elevation, consists of 4 stories of different orders formed of travertine stone.
height of the lower, or Doric, including its attic above, is 40 feet 7 inches, which is level
with the pavement of the first story.
The height of the Ionic order and its attic, level with the pavement of the second story,
is 38 feet 7 inches.
The height of the Corinthian order and its attic, nearly corresponding in level with the
pavement of the upper internal corridor, is 40 feet.
The height of the upper wall, with the pilasters and its entablature, is 38 feet 4 inches.
The total height of the present wall is, as stated, 157 feet 6 inches.
The openings of the arches average 14 feet 4 inches, which is the height up to the top of
the impost moulding, on which the semicircular arches rest.
The upper order, above the three ranges of corridors, has its cornice perforated for the
insertion of wooden masts, which supported the velarium; the total number were 240.
The interior portion of this wall is faced with tiles in regular courses, behind which, placed
in indents, and well bedded in cement, are circular earthen pipes, that conveyed the water
from the wooden platform above to the drains below.
The piers are all formed of travertine stone in large blocks, many extending the whole
depth of the pier, which is 8 feet 8 inches; the joints are well worked, and each stone
securely cramped with metal, all of which, that could be removed, have been taken away.
Each of the arches is formed of 11 voussoirs; the key-stone, as well as many of the others,
extending through the whole depth of the wall. These voussoirs have on their sides mor-
tices and tenons, which prevent their sliding, also iron cramps.
The Sections through the building exhibit its construction most perfectly. The back face
of the outer piers and wall above is perpendicular, the outer face retreating on each
story. At the top it is 6 feet 9 inches in thickness; at the Corinthian story, 6 feet 3; at the
Ionic, 8 feet 5; and at the lower, 8 feet 9 inches.
The width of the outer corridor in the clear is 17 feet, that of the second 14 feet 6 inches,
that of the third 14 feet 6 also, and the fourth corridor 11 feet 6 inches.
The main piers are all of travertine stone; the division walls between the third and fourth
corridor, and those between the second and third on the first story, are faced with tiles filled in
with rubble work. The division walls between the second and third corridors have four piers in
CHAP. IV.
111
ROMAN.
travertine, with the three spaces between filled in with pepperino, or a softer stone. The vaults
over the corridors and staircases are turned with rubble, very roughly executed, the good-
ness of the mortar or cement constituting its strength. After the piers and division walls
were carried up to their proper heights, boarded centres were placed, on which the rubble
was laid and grouted together: many of the divisions still show the marks of the planks
used, which were laid longitudinally. The vaults being turned over the entire space,
comprised within 116 feet, or from the face of the present podium to the back of the
wall, which shut out the corridors on the level with the Corinthian order of columns, and
floated to a uniform inclination, received the marble seats, which were 3 feet 5 inches
in width, placed one upon the other, so as to allow a seat of 2 feet 5 inches wide.
Some idea may be formed of the number of persons it contained, by allowing a space of
15 inches to each, or an area of 3 superficial feet: as the total area of seats which covered the
interior was 209,229 feet, the number that might be accommodated was 70,000, without
comprising those seated on the podium, now destroyed.
The staircases conducting to the several vomitories were admirably constructed, and built
of stone.
From the second corridor was the ascent to that immediately over it, by twenty flights
of double staircases, easy in their rise, each having three spacious landings. The same
corridor was arrived at by sixteen other staircases, which commenced in the third corridor:
these had an easy rise, and a wide landing in the middle of the flight. From the last named
corridor, sixteen other staircases led to the seats over the fourth corridor; there being
fifty-two staircases from the ground floor to the corridors and vomitories above.
Sixteen flights of twenty-eight steps conducted from the third corridor of the Ionie order
to the first mezzonine obtained under the vault of the second corridor of this story:
sixteen other staircases led from hence to the corridors of the Corinthian order.
From the second corridor of the Ionic range were sixteen staircases, which led to the
third range of vomitories.
Twenty-four flights passed through the upper mezzonine, and eighteen conducted to the
top of the platform, on which the arrangements were made for the adjustment of the
vela. The fourth corridor, on the ground floor, was paved with marble, 5 inches in thick-
ness; the others with travertine in large slabs; and great attention was paid to the carrying
off the waters, and effectually draining the entire building.
In the year 1818 the writer was occupied for many months in measuring this splendid
edifice; and to the numerous drawings published in the "Roman Antiquities," he must
refer the reader for a more detailed account of its arrangement and distribution, being able
to vouch for the dimensions there given.
The Amphitheatre at Nismes, from some fragments of an inscription found, is supposed to
have been built between the years 77 and 82 of the Christian era.
Its plan is that of an ellipsis, the longer axis of which, measured on the external facing at
the pedestals of the eastern and western entrance, is 437 feet 6 inches; and the short axis,
ineasured also at the faces of the pedestals, 332 feet 6 inches. The interior, measured
within the podium, the longer diameter is 226 feet 8 inches, and the shorter diameter 125 feet
9 inches; from thence it results the thickness or depth of the construction from east to west is
103 feet 4 inches, and from north to south 103 feet, which difference is accounted for by
the projection of the pedestals at the east and west ends.
The four entrances, answering to the four cardinal points, were the only communications
with the arena. It appears by the dimensions, that those to the east and west were
destined for the use of the spectators, the others being reserved for the service of the
arena. The east and west entrances were 13 feet 4 inches wide, and those north and south
only 3 feet 6 inches; the former led to the arena by an inclined plane, the latter by steps.
All the division walls are set out at equal distances on the out as well as on the inside.
The exterior circumference, and interior, around the podium, were divided into sixty equal
parts, setting off from the two axes, on which were the centres of all the stairs, porticoes,
and rampant vaults. Between the centre of each of these sixty divisions a line was traced,
on which the walls were set out. The divisions and their corresponding parts are of
a uniform width, which must have occasioned great difficulty in the execution, although
affording facility for the internal distributions.
The plinth of the exterior porticoes is elevated 7 feet 9 inches above that of the wall of
the podium.
The total height of the amphitheatre is 70 feet; the lower order, 33 feet; the upper, 29
feet 8 inches; and the attic, 6 feet 4 inches.
The foundations of the external pilasters are placed 8 feet 10 inches below the plinth,
and the wall of the podium rests on a simple plinth a foot in height. If to this is added
7 feet 9 inches, the height of the external plinth above the podium, we have a height
of 8 feet 10 inches, which is the depth of the external foundations below the plinths. It is
evident, therefore, that all the foundations were made on a level. After the plan was traced,
the ground was taken out to a depth of three feet, and filled with concrete.
Sixty arcades
1.12
BOOK I.
HISTORY OF ENGINEERING.
formed the elliptical boundary of the amphitheatre. Their openings, with the exception
of those to the north, the east, and west, were all 12 feet 5 inches; the other three 13 feet
2 inches. The width of the external piers, 8 feet, the pilaster of which occupies 3 feet,
and the faces on each side 2 feet 6 inches. The exterior has two orders surmounted by
an attic; the lowest without bases. The pilasters are in height 26 feet 3 inches, from the
zocle to the top of the capital.
The second story, comprising pedestal, column, and entablature, is in height 29 feet 6
inches; the pedestal, 3 feet 6 inches; the column, 20 feet 6 inches; and entablature, 5 feet
6 inches. The column projects two-thirds of its diameter, and at the base is 2 feet 7 inches
in diameter.
The height of the attic is 6 feet, and its face is fair with that of the column below:
two strong stone corbels, pierced with circular holes, between the pedestals, supported
the masts that received the cords of the vela or covering. There are thirty-five ranges
of steps or seats, besides those which divided the whole into precincts.
There are
four precincts, each having its separate staircases and vomitories. The lowest precinct,
nearest the arena, reserved for the principal inhabitants, was formed to receive four seats
only, each 1 foot 8 inches in height, and 2 feet 7 inches in width; to protect the lowest
of these seats, towards the arena, a podium or wall of one stone, 6 feet 6 inches in height,
and 3 feet 3 inches, was built up.
The second precinct was separated from the one mentioned by a wall 3 feet 4 inches in
height; this consisted of eleven seats, and forty-eight vomitories, sixteen of which had their
entrance from the interior gallery of the ground floor, and thirty-two from the gallery of
the entresol.
The third precinct, with ten rows of seats, was separated from the second by a step, in a
similar manner to the others. These were approached by thirty vomitories out of the gallery
of the first story.
The fourth or upper precinct had ten seats, the last of which rested on the attic wall.
They were arrived at by thirty vomitories whose entrances corresponded with the gallery
of the second story.
The Staircases were numerous: twenty-eight conducted from the external gallery of
the ground floor to the gallery of the entresol; a like number from thence to the first
story; thirty-two led from the gallery of the ground floor to the vomitories of the first
and second precinct. A similar number from the gallery of the entresol to the vomitories
of the second precinct. Thirty others from the gallery of the first story communicated,
first, to the thirty vomitories of the third precinct, and then to the double staircases, which
led to the second story, where the thirty vomitories of the fourth precinct were placed.
These last were contrived in the head of the vault of the gallery of the first story, and
received their light from small openings pierced on each side of the capitals of the columns
on the lower story.
The five several galleries held the spectators during the intervals of the exhibition or
violent storms: in a few moments the whole amphitheatre might, by means of the 130
vomitories, have been cleared; and in a small space of time the spectators could, without
confusion, have again taken their seats.
The amphitheatre has been calculated to contain 23,362 spectators, each person occupying
only fifteen inches superficial. The total length of the steps or seats is 30,660 feet; but
some allowance must be made for the loss by vomitories, &c.
For carrying off the superfluous waters, which might collect in such vast edifices, the
most ingenious contrivances were thought of and introduced at the very commencement of
the work, and so admirably arranged as not to weaken the walls or piers which contain them.
Many of these conduits served the double purpose of urinals, and numerous are the pre-
cautions taken to prevent their becoming offensive, and to provide for their proper and
thorough cleansing. The Roman engineers have taught constructors a lesson which has
not been sufficiently appreciated nor imitated in the public buildings of modern times, where
vast numbers remain for many successive hours. By a careful study of the drainage of an
amphitheatre, we shall be enabled to understand the attention paid to the setting out of the
sewers of a city. The Coliseum and many large buildings retain all their pipes and drains,
showing us how admirably this object was carried out; modern practice has not yet devised
a more perfect or effectual method.
Fifty-six drains, constructed within the thickness of the walls which supported the stair-
cases of the ground floor, served for the rain water to pass off, and for the convenience of
the spectators placed in the third and fourth precincts. Their upper opening was on the
landing of the entresol, above the gallery of the first story; half the openings of these
drains were placed opposite the stairs which led to the gallery above, or that of the second
story; the other half was enclosed, and formed into a recess, which concealed them from the
view of those passing by. We presume the first were for the convenience of the men, and
the others for the woinen.
These drains were formed of cylindrical pipes 12 inches in diameter, hollowed out of
the middle of large masses of freestone 20 inches in height, the beds of which were
CHAP. IV. ·
119
ROMAN.
alternately placed square and jutting out, the better to unite them with the adjoining
masonry; almost all the latter formed the thickness of the walls, within which were
the pipes. The upper bed of each
stone, 6 inches round the opening,
is cut in the form of an inverted
cone, as is the lower bed, the other
part of the bed being level: all
these beds or joints, being placed one
within the other, formed an ascend-
ing joint 2 inches in height, and pre-
vented any filtration of water into the
body of the masonry. These drains

carried off all the urine and rain water.
A hole, 2 inches in diameter, sunk
in the middle of a stone, slightly
dished, formed the entrance of all
the drains of the lower stories, from
which it is concluded they were used
for a similar purpose. Besides the
upper openings of these fifty-six
drains, in the landings above the gal-
lery of the first story, there was a
similar number, and also in the pas-
Fig. 127.
DRAINS.
sages of communication with the two corridors of the ground floor; they are at 1 foot 9
inches above the ground, and might serve to cleanse the issue of the gargouille which
poured forth the waters into the outer aqueduct.
The drains communicated by a gutter or channel of
freestone to a well or cesspool, 2 feet 4 inches in dia-
meter, under the stairs of the ground floor, in the
mass of masonry which supported them; the bottom
of this well communicated with a small aqueduct, 13
inches wide by 18 high, having a considerable fall,
the lining formed with the greatest care in moellon
and mortar the base and covering being executed with
large stones. This aqueduct conducted diagonally
to the middle of the under side of the stairs, where it
united with that of the corresponding drain; at this
point the two emptied themselves into one of 18
inches in width by 22 in height, the issue of which
was made under the pavement of the exterior corridor,
in the centre of the portico, which carried the great
stairs of the lower floor, and at 3 feet below the pave-
ment of this same gallery: this issue was formed by
a large stone, so placed against the covering of the
aqueduct, that at the two sides a passage was left for
the water. The external gallery of the ground floor,
under which the drains discharged themselves, and all
the passages which communicated from the two gal-
leries, were entirely filled up with chippings of large
pieces of freestone, from the level of the foundations,
to within 6 inches below the plinths. This latter
height was occupied by an inclined floor of cement,
serving as a pavement to the two corridors as well as
the other passages.
The waters easily filtered through
thin chippings of freestone, and the humidity and
disagreeable odour was prevented from affecting the
galleries, by the interposition of the bed of cement
which covered these fragments. The water and urine
ran off by infiltration into the drains, which could
only serve for the purposes indicated, particularly as
their entrances, still preserved in the vomitories of the
first and second precincts, are only an inch and a
quarter in diameter.

Fig. 128.
UPRIGHT DRAINS.
Sixty-four other drains, found in the passages of the
vomitories of the first and second precinct, corresponding with the interior gallery of the
ground floor, were for the same purpose. A drain placed on each side of the set-off of
these passages, with a hole 2 inches in diameter, formed in freestone, slightly dished out.
I
114
Βουκ Ι.
HISTORY OF ENGINEERING.
received the rain water and conducted it outside. A like number of drains is also contrived
above the set-off of the staircases which led to the entresol and the first story. The
gargouilles, placed over each other, follow the direction of the stairs, then cross the walls
which support them, pass behind the stone jambs of the porticoes and galleries of the
entresols, then return under the landings and the stairs of the ground floor, and are at last
collected in the receptacle connected with the great drains.
The draining so large a building occupied great consideration; the forethought displayed
in these arrangements evinces great ingenuity and simplicity. The surface of the arena
was rather higher in the middle, and sloped
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gradually and uniformly towards the podium.
This form had the double advantage of di-
viding the rain water, and preventing the in-
jury which a collection in the centre would
have occasioned, and of placing the spectacle
on a plane, which by its form brought it
nearer to the spectators. The convexity of
the arena required the oval aqueduct to be
placed at a little distance from the walls of
the podium, to receive and conduct away
all the waters. It was consequently 7 fect
6 inches distant from the wall of the po-
dium, 3 feet 6 inches in width by 4 feet 9
inches in depth. The walls are of moellon
laid in cement. Small channels very close to
each other are cut from the base of the podium, to conduct the water to the aqueduct.
This aqueduct was covered with stone 8 inches thick, which rested on a bed of free-
stone 6 inches high, forming a slight
projection on the internal face; the
upper part is an inch and a half
below the base of the podium, by
which
the sand that co-
vered the arena extended also over
the flags which covered the aqueduct
sufficiently to prevent any injury
occurring to the gladiators when
they fell. These flags rest 8 inches
means
at each end on the bed of freestone
which crowns the walls; they are
also attached by a dovetail half an
inch in depth. The inclination or
fall given to the bottom of the
aqueduct is regular throughout.
Fig. 129.
PLAN OF DRAIN.

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The thickness of its side walls is
18 inches. The outer part is backed
against the concrete in which the
aqueduct is entirely surrounded.
The wall on the side of the podium
is open opposite the two east and
west gates to receive the water of a
second inner aqueduct, which will be
hereafter described. All the waters of the arena flowed into the inner aqueduct, and it
remains to show in what manner that which fell on the seats, in the vomitories and in the
galleries was carried through the opening of the great outer porticoes.
Fig. 130.
SECTION OF PIPES AND PLAN.
he Romans might
All the seats had an inclination of the sixteenth of an inch forward, which facilitated
the flowing of the water from the upper to the lower step, and from one to the other.
The first precinct was defended in front by a parapet which rose 2 inches above the
step, so that the rain water which fell on the four rows of seats and te step of the first
precinct, being stopped by the parapet, could not flow into the arena.
easily have pierced this parapet at the level of the step, and discharg
precinct into the arena; but such an arrangement would have injured
of the podium.
The water of the first precinct was therefore made to pass off b
base of the first seat on the level of the step, to which, for this purp
made towards the seat. Circular openings cut in a conical form,
allowed the passage of the water from the first four rows of seats, and
wall of the podium, by a small conduit made in the stone step; after
at the foot of this wall into a small channel two feet wide, which, tra.
L
the water of this
e ornamental effect
an opening at the
•
a slight fall was
inches in diameter,
arried it behind the
ards it was received
sing the lower part
CHAP. IV.
115
ROMAN.
of the first precinct, and the foundation of the parapet wall of the second, arrived at the great
circular inner aqueduct. Twelve of these discharges sufficed for carrying off the water of
the first precinct, which was only composed of four rows of seats.
The second being protected like the first by a parapet, the same method for discharging
the water as those already explained was adopted, this second precinct receiving also the
water from the cornice of the attic. Twenty-four discharges at the level of the step of this
precinct carried the water behind the wall of the second podium, and through the middle of
the vault which covered the chamber through which the great circular aqueduct passes. At
the summit of this vault, against the wall of the second podium, a large stone pierced with
a hole four inches in diameter received the collected waters. These holes have led some to
presume that they received the posts intended to support the tent which covered the amphi-
theatre. Their nearly horizontal position, and their conical opening, at once show their
destination.
The water which fell on the arena and seats of the amphitheatre was conducted into two
circular aqueducts, that of the arena, and that of the interior. The latter, which followed
the contour of the building, is 30 inches wide; its base, on the same general level as
the foundation, is formed of two walls, faced with dressed stone 6 feet 6 inches high,
having its course through the chambers which receive the water of the first and second
precinct it is arched in the thickness of each wall, under the issues of the vomitories of
the first and second precinct, corresponding to the inner gallery of the ground floor, and
under the passages of the north and south doors. It also communicates with, and empties
itself into, the aqueduct of the arena, under the two great passages of the east and west
doors, by two square openings, 30 inches wide by 20 inches high. The aqueduct under
the great east and west passages is covered with large landings resting on walls built on
each side.
The inner aqueduct received all the water which fell through the openings of the thirty-
two vomitories of the first and second precinct, the entrances of which corresponded to the
inner gallery of the ground floor. This water, which during storms is abundant, was stopped
on the landing of the passage of each vomitory by a step whose tread was hollowed out to a
depth of half an inch. A hole two inches in diameter, opened at each extremity of this step
in the recesses of the vomitories, served as a urinal, as well as received the rain water, and
then passed into the aqueduct immediately below. By this means the water falling through
the openings of the vomitories could never come into the inner gallery on the ground floor.
The rain water driven by the wind into the outer gallery of the ground floor through the
openings of the sixty arches of the façade would soon have inundated this gallery if means
had not been provided for getting rid of it by a rapid and successive discharge. The paving
of the outer gallery, and that of all the passages of communication, had a fall of 6 inches
towards the inner gallery, so that the rain which the wind blew into the outer gallery ran into
the second. At the foot of the piers which divide the passages of the vomitories, it met
with a discharge into a small aqueduct, which conducted it into the great inner circular
aqueduct the smaller opening into the larger by a hole 3 feet high, 18 inches wide, and 16
inches above the base of the great aqueduct. A similar discharge remains in the middle
and at the foot of the first step of the great staircases, which admits under the paving of the
outer gallery, a part of the waters of this same gallery.
:
:
The inner circular aqueduct received all the water of the seats and steps from the attic to
the podium, that of the thirty-two vomitories whose entrances corresponded to the inner
gallery of the ground floor, and that which the wind carried into the outer gallery through
the openings of the entrance porticoes all this water united formed a considerable quantity
during storms; but it was so divided, and so well directed, that it was impossible any
stoppage could take place, or that it could ever inundate the galleries and passages, much
less injure the solidity of the masonry. By such means the Roman engineers, who were
masters in the art of construction, effectually drained the upper galleries and vomitories.
The inconvenience arising from the chance of the water penetrating into the passages and
galleries through the openings of the thirty-two vomitories of the first and second precincts,
was obviated at all the upper stages to which the issues of the other vomitories correspond,
the same pains being taken to get rid of it quickly. The gallery of the half story of the
first floor could easily be inundated by the openings of the thirty-two upper vomitories of
the second precinct, to which this mezzonine gallery was solely destined, but the first step
of the stairs of each vomitory was slightly hollowed and pierced in the middle with a vertical
hole, an inch in diameter. Below this step and hole is a stone cut in the form of a cistern
5 inches deep, 12 long, and 8 wide. At the end of this cistern is a gargouille 4 inches
wide, closed at one extremity, and pierced with a perpendicular hole. The pavement of the
half-story gallery, which throughout is tooled, is formed opposite each vomitory by a
stone similar in all respects to the tread of the first step of the staircase of the vomitory:
this is slightly hollowed and pierced with an aperture which corresponds with a small hole
made through the vault, which carries the inclined winder and the second revolution of the
great staircase of the ground floor. The water which fell in the passages of the vomitories, on
I 2
116
BOOK ì.
HISTORY OF ENGINEERING.
arriving at the first step above the pavement of the gallery of the half-story, was received into
the perpendicular hole with which this first step is pierced, then fell into the cistern placed
below, ran down the gargouille, at the extremity of which it fell into the chambers under
the great staircase, where it was quickly absorbed. If the abundance of water was such
that the first step could not receive it, the excess fell on the stone placed below on a level
with the pavement of the gallery, where it followed the same course as the rest, and ran
under the same vault by a similar contrivance, so that it was impossible any could come
into the half-story gallery.
The water which the wind drove into the first-floor gallery, through the openings of the
porticoes, fell on the first step, by which it descended to the half-story gallery. There it
was received into the hollows of the first step, at the extremity of which were two holes an
inch in diameter, below which were stone gutters communicating with discharges made on
each side of the recesses of this staircase below the winders just mentioned. The water
then followed the course indicated above: a double advantage was thus obtained, that of
cleansing the urinals and getting rid of the water, which, without this precaution, would have
inundated the inner gallery.
The great discharges of the second flight of steps, fifty-six in number, received the water
of the vomitories of the third and fourth precinct.
The construction of the great outer aqueduct, which brought the water from the fountain
of Nismes, is next to be considered.
It was discovered when excavating in the middle of the outer gallery of the ground
floor, opposite the north gate, where an aqueduct was supposed to exist under this
gallery and throughout its circular development. This great aqueduct has a breadth
of 32 inches, and a height of 6 feet from the bottom to the under side of the key-stone
which covers it. Like all the others, it was filled with earth and mud up to the top:
on the north side it was found perfectly preserved, built of tooled stone, as was the
semicircular arch which covers it. This vault has been replaced by landings of freestone,
where it crosses the north passage from the door of the present guard-house to the circular
aqueduct of the arena. It traverses the arena to the centre of the ellipsis, then deviates to
the south-west, leaving the building at the sixth portico east of the south door.
Its con-
struction, precisely the same as that on the north side, is covered with landings. The
excavation was continued from where it issues from the amphitheatre, for a length of 40 feet,
at which distance it was broken and could not be further traced.
Two manholes for descending into this aqueduct existed in the outer gallery on the
ground floor, one at its entrance at the north gate, the other at its issue through the sixth
portico west of the south gate. These manholes are perfectly preserved: they are 2 feet
square, covered with a landing: below the pavement a square hole 30 inches wide,
by 16 inches high, is cut, 3 feet 6 inches above the bottom, on each side of the aqueduct, in
the middle of the outer gallery on the ground floor, to allow the water which filtered
through the pavement to run into the great aqueduct.
Three quarries were worked by the Romans to obtain the stone requisite for the ex-
ternal works of this amphitheatre: the greater part of the seats, and facing of the podium of
the first and second precinct, and some portion of the interior arcades, were of stone, brought
from the quarries of Baruthel; some steps and the worked moellon came from Roque-
maillère. Nearly the whole of the arcades of the lower story, the entresol, the first and
second story, are executed in the stone from the quarries of the Pont du Gard. They are
all calcareous, and of a grain more or less fine. That from the quarries of Baruthel is compact,
firm and fine; its weight about 515 lbs. per cubic foot: when employed as it is found
in the bed, it is an excellent stone, in many instances where this precaution has been
omitted the courses are entirely decomposed.
The stone from Roquemaillère is stronger and harder, and weighs about 460 lbs. per
cubic foot; it is of an excellent quality, and has undergone little change.
That brought from the quarries of the Pont du Gard is a coarse grit, and stands well
when used internally: being porous, when subject to exposure or rain, it is greatly in-
jured: a cubic foot weighs about 333 lbs. The difficulties arising from the oblique
direction of the whole of the constructions, externally and internally, are admirably over-
come. The vaults of all the stories are executed with great precision, as are those of the
corridors; but the same care has not been taken in the construction of the arches of the
exterior, which are oblique on their plan and elevation. The Romans in this example of
oblique work had not quite arrived at perfection, as they have not been sufficiently attentive
to the true setting out of each stone. All the freestone is laid in cement, and the bed cut
with the utmost precision; a hole in the centre of gravity of each stone indicates that it
was lifted by the aid of the Lewis; and it appears, by the nicety of the workmanship, that
the upper stone, previous to being bedded, was suspended by the Lewis, and, water being
thrown over the under bed, was then gradually lowered: all the rough particles that
might remain between were brought down by friction; and when the stones easily worked
against each other, the upper was definitively fixed By no other means can we account
CHAP. IV.
117
ROMAN.
for the excellence of the joint: the small particles of the stone rubbed down, mixing
with the water thrown on the lower, formed a cement, filling up the void between them.
All the workmanship of the amphitheatre is of a colossal kind: many of the stones
contain from 25 to 35 feet cube; their beds are from 12 to 15 feet superficial, which adds
much to the difficulty of the execution.
The facings were not so carefully attended to as the joints and beds, it evidently being
intended they should be dressed after the completion of the work, which was the common
practice with the Romans. In all their constructions they took the precaution of
uniting the stones together by two oak wedges cut in a dovetailed form, placed over each
joint, sunk in the stone to a depth of 21 inches; these were about 4 inches in length, and
all that remains, upon a careful examination, is a ligneous dust, the wedges having perished
long ago.
The cutting of the moellon, employed in the walls and the vaults, is admirable; the
courses are from 5 to 9 inches in height, and the stones are from 8 to 10 inches in length.
Their faces are coarse, and the joints and beds so cut that the stones may be united
closely at the edges with an exactness almost incredible. The edges or arrises of the
moellon are as sharp as if of freestone: the same nicety of execution runs throughout the
vaults where moellon was employed, and the voussoirs, which are from 15 to 20 inches in
height, and from 7 to 9 inches in width, are cut with the greatest care, relatively to their
conical and rampant projection. All the moellon was bedded in cement; but little is to
be seen, on account of the extreme fineness of the joint. The filling up of the masses,
spandrels, &c. was with rubble stones of all shapes, run in a coarse cement, which has
become as hard as the stone itself; this was composed of equal parts of quicklime, gravelly
sand, broken tiles and bricks. Wherever iron is used, it is run with lead; the iron cramps
for placing the stones of the podium are so cased.
·
The velarium or covering. For several ages, the spectators in the amphitheatres were
uncovered, as we find the ancient historians often allude to the necessity of quitting their
seats, on account of the rain which fell. And St. Chrysostom reproves the people (Hom. 4.
e. 16.) for having stood bare-headed with the sun scorching them in the theatre. We
also learn, from many inscriptions which are in the collection made by Gruters, that the
theatres were provided with covered porticoes, to shelter the people assembled. Pliny and
Valerius Maximus both state that Quintus Catulus was the first who contrived a vela, or
shade, for the people assembled in the theatre; and the first of these authors gives the name
of Valerius of Ostia as the engineer employed to execute the work. Lentulus Spinter
(Pliny, 1. 19. c. 1.) formed the vela first of linen cloth, and Dio (lib. 43.) tells us that
Cæsar introduced one of silk, to keep off the heat of the sun's rays at the amphitheatre,
constructed of wood. Silk, in the time of the emperor Aurelian, was in value equal to its
weight of gold, and therefore must have been a great luxury. The emperor Nero spread
over the theatre a vela bespangled with golden stars, on which was represented Phaton
driving the chariot of the sun, the material of which has been supposed was wool, as some-
times, in its description, the word Apuliæ is made use of, and dyed wools were brought
from that country.
Lampridius (in Com. a Militibus, Classiariis) informs us that the management of the vela
was left entirely to sailors, as they were more expert in going aloft amidst ropes, and under-
stood the tackle which regulated the spreading of it better than others. There can be no
doubt that it required considerable dexterity on the part of the engineer to keep steady an
awning containing 113,345 superficial feet, which would be required for the amphitheatre at
Nismes, and for the magnificent Coliseum nearly 250,000 superficial feet, or more than
double; the weight of which, at only one pound per foot, comprising the ropes and
tackle, would amount to 112 tons or thereabouts. So vast a weight disposed and upheld
by tension only creates our wonder and admiration.
At the level of the attic story are 120 projecting consoles, each having a circular
hole about 10 inches in diameter, corresponding with a circular mortice of the same size,
and 6 inches in depth, made in the projection of the cornice of the second order. The
upper opening of the hole in each console has externally a groove 2 inches in height,
destined for an iron collar, to which was attached a tie, which secured it to the wall of the
attic at the level of the top of the console: the holes which contained these have some
portions of the iron run with lead remaining.
The hole of each console received a round mast, which, passing through it, rested in a
hole sunk in the cornice below, the iron collar preventing it from acting against the sides of
the console and fracturing it. The masts alone would not be sufficient to support the
weight of the vela, extending over an elliptical area, the axis of which, in one direction, was
436 feet, and in the other, 331. To aid in the support other posts were introduced through
mortices about 10 inches in length, placed opposite each console, at the projecting part of
the moulding which crowns the interior of the attic; on each side, 4 or 5 inches from the
edge of the attic, are holes still containing the lead which secured the iron ties that beld
13
118
BOOK I.
HISTORY OF ENGINEERING.
these latter posts in their places. Under the mortice holes are others, 8 inches square, and
2 feet in depth, made in the upper step of the attic to receive the second posts.
posts were afterwards securely braced.
Over the centre of the arena
was an oval covering, perma-
nently fixed, which in the
Coliseum was ornamented
with an immense golden
eagle. Round the edge of
this oval covering was at-
tached a large cable. 120 pair
of cords, of equal length,
stretched from the masts on
the exterior to this cable,
were worked by pulleys; thus
forming as many compart-
ments. Each pair of cords
was furnished with rings, to
which the covering was at-
tached, so that it could be
drawn backwards and for-
wards at pleasure. The
whole of these were called
the vela or velaria, and each
single compartment velarium.
The distance between the
ropes on which the vetarium
ran was greater towards the
attic than at the centre; con-
sequently, to make the vela-
rium run freely on its rings,
it was necessary that it should
be of an equal width through-
out when spread, towards
the attic it was stretched,
whilst towards the centre it
sagged, and formed as it were
a fold. To prevent the sun
passing through the opening
thus made by the sagging, an
internal hanging was attached
around the fixed permanent
oval.
Fig. 131.
POSTS OF THE VELA.
The two

The weight of the vela was sufficient to make it drop considerably in the middle, what-
ever caution was used in tightening the ropes: another inconvenience to be guarded
against was, the action of the wind upon it. At the back of the podium wall are remain-
ing many holes, which contained iron rings, run with lead, supposed to have been used
to secure the blocks, through which passed perpendicular ropes, which being kept tight
would obviate this inconvenience,
Amphitheatre at Verona. The longest axis of the ellipsis is 495 feet; the shortest, 396
feet.
That of the arena within the podium is 240 feet, and the shortest diameter 141 feet.
The total circumference of the exterior wall is 1419 feet; the height which remains is about
88 feet, though originally it is said to have been upwards of 130 feet.
There are forty-five ranges of seats or steps remaining, exclusive of the first, and it was
calculated that 22,000 persons could have been accommodated within the walls. The outer
wall is nearly demolished: it had three orders, and an attic built of coloured and white
marble: the three lower had arches separated by pilasters. The mouldings of the upper
story, as well as the capitals and cornices of the other two, are of white marble. All the
seats are of red marble. The stones used in the construction are of large dimensions, and pass
through the entire thickness of the wall; but the courses vary in height. On each story
were seventy-two arches, and each had its number engraved upon it. The staircases are well
contrived, and in some degree resemble those of the Coliseum. There were in all sixty-six
entries, including the two great gates: six led into the arena; twelve straight passages
conducted to the seats over the podium, and each had five steps.
The wedges or cunei above were entered from the outer portico, by eight single stair-
cases and four double ones. The fourth round had sixteen vomitories or openings, and was
ascended by eight smaller staircases.
CHAP. IV.
119
ROMAN.
There were sixteen long rooms of considerable height, and eight smaller under the stairs.
Twenty-eight dens or caves and other rooms were contrived in various parts for the animals
and those who attended.
The Amphitheatre at Pola in Istria, situated out of the town, is not in a very perfect
state. The longest diameter from north to south is 436 feet 6 inches; the other, 346 feet
2 inches its height, 97 feet.
:
The exterior is rusticated, and has two orders of pilasters,
the lower placed on pedestals, above which is an attic. Around the ellipsis are seventy-
two arches, the extreme being both higher and wider than the others. It is built of stone
from the neighbourhood, in appearance resembling marble, and based upon the solid rock.
The architect who constructed this edifice placed it on the side of a hill, to economise the
masonry.
This amphitheatre was probably erected by Diocletian, or by Maximin: the interior is
quite destroyed, not any of the division walls or seats remaining, a wide area extending to
the outer wall.
Amphitheatre at El Jemm in Africa is one of the most perfect, vast, and beautiful remains
of this kind of structure that exists. It is situated at a short distance from the shores of
the Mediterranean Sea, in the beylek of Tunis, from which place it is about eighty miles
distant to the south, and not far from the shore of the ancient Syrtis Minor.
It is probably the ancient Tysdrus or Thysdrus, five miles south-east from Elalia, and
thirty-three miles from Leptiminus. This amphitheatre has four stories, each of the three
lower adorned with sixty-four arches and columns: the upper is a pilastrade, with a square
window in every third interpilaster.
With the exception of one breach, the circuit of the walls is entire; the interior is less
perfect. The inclined plane on which the seats rested remains, as do all the galleries and
their vomitories. Beneath the arena are deep pits of hewn stone. The length of the
building from east to west is 429 feet, the breadth 368 feet.
The arena measures 238 feet by 182 feet. The floor of the first arcade is 33 feet from the
level of the exterior pavement, and the height of the outer wall was probably 100 feet.
The elder Gordian was proclaimed emperor in this city; and on the medals of the
younger Gordian is an amphitheatre, which has occasioned some to attribute this building
to him.
The Amphitheatre at Arles is of an oval form, its greater diameter being 455 feet, and its
smaller 338 feet. It was two stories in height, and had around it sixty arcades, built
of square stone throughout; it is now so occupied by buildings of various kinds, that it can
scarcely be recognised as an amphitheatre.
The Circus. The chariot races of the Romans, which constituted their games during
the time of the republic, supposed to be of Etruscan origin, were celebrated in the circus,
which had an oblong form, terminated with a flat curve at one end, and a semicircle at the
other. The arena was divided longitudinally by a spina, round which the chariots drove.
The first circus was on the site of the Circus Maximus, though the buildings around were
not erected till after the reign of Tarquinius Priscus In the time of Julius Cæsar, it is
said by Dionysius Halicarnassus to have contained 150,000 spectators. It appears to have
been considerably augmented after that period by Trajan, as Pliny tells us it would
accommodate 250,000. It was enlarged by Constantine, by adding to the number of
seats, without increasing the dimensions of the course, so as to contain 360,000.
For a
long time this was the only circus in Rome; but another was formed in the Campus
Martius, without the Flaminian gate, by the consul of that name, of which not a vestige
remains.
Livy mentions the circus Agonalis, where the piazza Navona now stands: this was probably
instituted by Numa Pompilius. The circi of Flora, of Sallust, of Nero, Hadrian, Helio-
gabalus, remain only in name, not one stone being left upon another.
Previous to the games, a procession of the images of the gods, drawn in sacred cars, took
place, and before they commenced, the cars intended for the race were drawn up in front of
the carceres, and prevented from passing out by a rope stretched to two termini: when
the signal for starting was given, which was usually done by the emperor, this was dropped
or withdrawn. A line, or furrow, filled with white chalk, called the alba linea, denoted
the boundary that must be passed to win the victory.
The circus called Caracalla's is distant from Rome about two miles: much of the walls
that supported the seats, and the foundations for the two obelisks which formed the spina,
remain. Its length is 1602 feet, its breadth 260 feet: the length of the spina is 922 feet.
The distance from the carcere, where the horses started, to the first meta or goal, was 550
feet. These structures were in the form of a parallelogram, one end of which was semi-
circular, and the other, where the carceres were placed, was the segment of a circle. Seven
ranges of seats were placed around, on arches, in the same manner as in the theatres and
amphithe tres. The segmental end was so arranged that the horses at starting should all
have an eval
stance to proceed to reach the first meta.
Ridin's, of a circular form, for training, triumphal arches for the victors in the
1 4
120
BOOK I.
HISTORY OF ENGINEERING.
games to pass under, all faced and adorned with marble, formed part of these magnificent
establishments.
The construction of this circus differs so materially from what we see in the baths of this
emperor, that it is very doubtful whether it is not of a much later date. It certainly
remains more perfect than any other known, and by some is considered the work of
Gallienus.
Baths. These monuments of Roman magnificence contained all that could contribute
to the health of the body, the improvement and amusement of the vast population.
Vegetius tells us that the reason the senate ordered the Campus Martius to be formed
near the Tiber was, that, after exercising, the Roman youth might bathe; and 440 years
after the foundation of the city, a piscina publica was constructed at the foot of the capitol
near the Tiber: about the time of Augustus, baths were very generally in use; we find
remains of them in England, and throughout the Roman provinces. As the names of
the various apartments of the thermæ are all of Greek origin, it is inferred that the
invention of them originated with that people: Socrates, Plato, Aristotle, and Hippocrates,
refer to them.
To the original baths in the course of time were added the gymnasium, palæstra,
spheristerium, &c., all foreign to the purposes and arrangement of the bath. At one time
there were more than 800 baths in the imperial city: those of Paulus Emilius, Julius
Cæsar, Agrippa, &c., were for the purpose of bathing only, and most of these were
established by private individuals: but all yielded to the magnificence of the therma which
succeeded them; the most remarkable of which were those of
Agrippa
Nero
Vespasian
Titus
Domitian
Trajan
Adrian
Commodus
Antoninus Caracalla
Alexander Severus
A. D.
10
64
68
Philip
75
Decius
-
90
Aurelian
110
Diocletian
- 120
· 188
Constantine
A. D.
217
- 230
- 245
- 250
- 272
- 295
324
The
Vestiges of these are to be found in various parts of the city, but the immense destruction to
which they have been subject renders it impossible to trace them with any satisfactory result:
those of Titus, Caracalla, and Diocletian, alone yield any instruction to the engineer.
restoration of those of Caracalla by M. Abel Blouet are so complete as to give a new
existence to this species of edifices. They were the most extensive and the most magni-
ficent of the edifices that adorned the capital of the ancient world; situated at the foot of
Mount Aventine, between the walls of Rome and the Triumphal Way: as their name im-
ports, they were founded by Caracalla, and finished in the fourth year of his reign, 217
of the Christian æra.
There seems to have been great symmetry in the arrangements and proportions of the
exterior, but no decoration, that being reserved for the interior, which was regulated
according to prescribed rules. Some idea may be formed of their magnificence, not only
by the debris now visible of the various ornaments throughout the whole of the interior,
but also by the monuments of sculpture which have been found there. The most remark-
able are the Hercules of Glycon, the ancient Torso, the Bull called the Farnese, the Flora,
two gladiators, the two vases of granite in the Piazza Farnese, the two beautiful urns of
green basalt, now in the court of the Museo Vaticano, various terra cottæ, and an infinity
of other sculptures and works of art. The last granite column of the great hall was
removed from these thermæ, in 1564, and given by Pope Pius IV. to the Grand Duke
Cosmo de Medicis; it is now on the Piazza Trinita at Florence, where it supports a statue
of Justice in porphyry.
The general mass of the baths of Caracalla forms on the plan a quadrangle of 1011 feet
by 1080. The principal entrance is on the smallest side, by an external portico, composed
of two stories or rows of arcades one above the other, 53 in each row. These arcades have
their piers ornamented with half columns, Doric above, Ionic below. They lead into a
long gallery, and the piers which form it are ornamented with columns having pilasters
opposite them.
The three other sides of the quadrangle show external walls without decoration, two
of them being backed by Mount Aventine, a part of which was cut away for them.
The decoration was reserved for the internal façades, the enclosure of which contained
the most important body of building, both for its ornament and the richness of its
architecture. It was placed in the centre of this enclosure, between two spaces, that on
the side of the portico being smaller, the other double the first, both having walks planted
with trees. The internal façade of the grand enclosure in face of the portico exhibited
a sort of amphitheatre or range of steps.
The construction of these baths is like most of the Roman works of the kind called
CHAP. IV.
121
ROMAN.
Emplecton, that is to say, masonry faced with triangular bricks, the whole bound together
by rows of large quadrangular tiles, placed at certain distances over each other, and
traversing the whole thickness of the walls; these were coated with cement; sometimes
laminæ of marble were employed entirely to face them. From a review of all that remain
we find that the most complete baths consisted of six principal apartments: the first,
called the Apodyterium, was appropriated to undressing, and had shelves all round
on which to place the clothes, and attendants, called capsarii, took charge of them. This
apartment was also called Spoliatorium: all baths had not an apodyterium, and it
appears from Lucian, that where this apartment was omitted, the frigidarium was used for
its purpose.
The apodyterium is not named either in the gymnasium of Vitruvius, or
in the palæstri described by Lucian; it is probable that there was none in the gymnasium
of the Greeks, and that the frigidarium supplied the defect.
The second apartment was the cold bath, called by the Romans Frigidarium; it was
usually exposed to the north, and used as already stated. Galiani insists that the tepi-
darium and frigidarium were the same, but the paintings that remain to us prove the
contrary, nor is it the opinion of Mercurialis and Baccio.
The third was the Tepidarium: its principal use seems to have been to prevent, by the
temperate air which it contained, the dangerous effects of too sudden a transition from the
extreme of heat to that of cold; thus in the paintings of the baths of Titus, it is seen
between the frigidarium and the comamerata sudatio. According to all historians the
frigidarium was united to the warm bath; hence Pliny calls it the middle chamber (cella
media). Galen gives it the same name, and adds that thus it should be called, not only on
account of its situation, as being the centre, but also with relation to its heat, "this chamber
being as many degrees colder than the third, or the warm bath, as it was warmer than the
first, or frigidarium." Although there were occasional bathers in the frigidarium and the
tepidarium, still they were not generally so used, it being more common to walk through
these halls or chambers at a slow pace, for it was the temperature of the air, and not that
of the water, which induced so many to frequent them.
The fourth apartment was that called Laconicum, from the name of the stove which
warmed it, and which was introduced from Laconia: it sent forth a dry heat, by no
means, says Galen, calculated for warm temperaments. Dion tells us that those who
sweated in the laconicum oiled themselves, and then entered the cold bath; it was originally
intended for old men and infirm persons. According to Vitruvius and the various paintings
which remain from the baths of Titus, it was contiguous to tne tepidarium, and com-
municated to it a more temperate heat; it was a species of stove placed generally in the
angle of the apartment, circular, and surmounted by a little cupola open at top; the
flame of the hypocaustum entered the laconicum, and was lessened or increased by a brazen
shield suspended to a chain, by means of which, says Vitruvius, the degree of heat to be
given to the apartment was regulated. In the baths of Titus, instead of the brazen shield,
a globe is represented attached to a chain, which, placed over the opening through which
the flame arose, served to disperse and increase its power. It is undoubted that the
laconicum was only the stove or furnace: the mistakes which have arisen concerning it were
occasioned by its name being frequently applied to the apartment in which it was placed;
this apartment in the above painting is called comamerata sudatio, and at length the part
was taken for the whole but Vitruvius makes an evident distinction, (lib. 5. chap. 10.)
and he explains himself still more clearly in the following chapter, in which he reckons the
stove among the apartments of the palæstri; "it should have," says he, "in one of its
angles the laconicum, and in the other the warm bath." If, then, the laconicum was to be in
one corner of the stove, it is clear that it was not the stove, but only a part of it; had it
been so, as some insist, of what use was the comamerata sudatio? and why two stoves? The
laconicum, or the stove, according to Vitruvius, had niches called sudationes, in which those
who used these dry baths placed themselves, as shown in several ancient paintings. These
niches were as high to the curve of the head as they were wide.
The fifth apartment was the Balneum, or warm bath, called Thermolousia; it was the
most frequented. Its size, says Vitruvius, "must be proportioned to the number of bathers,
its width a third less than its height," without comprehending the gallery called the schola,
which was continued round, and terminated on the side of the basin, by a little wall of
support; this gallery was large enough to accommodate those who waited for their turns.
The middle was occupied by a basin called piscina, or by a bath called alveum, as shown in
a painting of the ancient balneum : the place in which they bathed was immediately under
,the window from whence the light proceeded, so that no shadow should be cast by the
persons walking about.
The sixth apartment was the Eleothesium or Onctuarium; in it were kept the oils and
perfumes used by the bathers both on going in and out of the bath; it was so constructed
as to receive a considerable quantity of heat from the hypocaustum.
The Hypocaustum was a subterranean furnace, the bottom of which formed an inclined
plane, gradually falling towards the opening, by which the wood was put in; Vitruvius
122
Book I.
HISTORY OF ENGINEERING.
calls it Suspensura. It should be formed, says he, of a pavement made of large tiles
of a foot and a half, laid with such inclination that if a ball were thrown in, it could not
remain, but must return to the mouth of the furnace. By this means the flame rose more
readily, and extended over the whole suspended floor. This was formed of large tiles
placed on little piers two feet high, made of clay, so prepared as to resist the action of
the fire. The hypocaustum extended under the greater number of the apartments before
named.
Besides the apartments especially destined for the use of the bath, there were several
others connected with the exercises used before and after, such as the spheristerium,
conisterium, coryceum, stadium, ephebeum, all of which made part of the gymnasium, but
which did not exist in all baths, particularly in those of private individuals.
The arrangements cited were variable according to the fancy and pleasure of the owner.
See Pliny's Laurentium. The following description taken from the Hippias of Lucian
may give an idea of the various apartments in the ancient baths.
After passing the grand vestibule, we enter a spacious hall, for the use of those domestics
who wait on their masters. On the left are the chambers, where they retire before quitting
the bath; these are the most beautiful and agreeable of all; advancing, we enter the bath
room, intended for the most opulent persons; through this apartment, on either side, are the
places for putting the clothes; the centre of the space is very lofty, and well lighted, and
contains three baths, of cold water, ornamented with Lacedæmonian marble; there are also two
ancient marble statues, one of the Goddess of Health, the other of Esculapius: leaving this
part by an oblong vaulted passage, there is a visible increase of heat throughout the building,
though not disagreeably so, and you are conducted to a well lighted hall, in which are the
oils and essences; it is on the right hand, and communicates with the palestræ; the two
jambs of the doors are encrusted with Phrygian marble: in the contiguous apartment, this
marble shines everywhere, even in the ceiling, consequently this is the finest of all; it is suf-
ficiently large to permit of walking and taking exercise in it, and there are many convenient
situations for sitting down. On leaving this, we enter the warm passage, which is ex-
tremely long; it is encrusted with Numidian marble, and leads to a well lighted and
beautiful hall, painted in purple; here are three warm baths. To go out of it, it is not
necessary to retrace your steps; a shorter way leads to the cold bath across the warm room,
the heat of which diminishes by degrees; all these apartments are well lighted from the
top. Hippias has shown much judgment in constructing the hall which contains the cold
bath, so that it has the north in front; as for the others, which demand a greater degree of
heat, he has exposed them to the south, south-east, and west.
By this description it appears that there was no apodyterium in the bath of Hippias ;
there were only shelves for the clothes at each end of the frigidarium, which contained
three cold baths. The bathers then entered the warm passage which led to the onctuarium,
whence, after anointing themselves, they passed into the spheristerium, which was the largest
and finest apartment; when the exercises were ended, they went to the warm bath, by a
passage in which there was sufficient heat to keep up that which had been produced in the
spheristerium. Thus, when arrived at the warm bath, the bathers found little difference
between it and the heat of their bodies, and after having taken it, they traversed an apart-
ment in which the heat gradually diminished until they arrived at the frigidarium, in which
were their garments.
The following description of the Greek baths is from Vitruvius. After describing the
different apartments of the gymnasium, he says, at the right of the ephebeum was the
coryceum, an apartment for shaving, dressing, &c.; near this was the conisterium, in which
was kept the sand for the use of the wrestlers; in the corner of the peristyle is the loutron
or cold bath; near this latter was the frigidarium, on going out of which was a passage
which led to the propigneum; near the furnace in the corner of the portico further on, but
by the side of the frigidarium, was the vaulted room for the sweating; its length was gene-
rally twice its width, and the laconicum was placed at one of its angles, opposite to that of
the warm bath.
The arrangements of each of the apartments above named differs still more in the
thermes of the Romans, although there is a certain uniformity in the plans: as there were
two peristyles, we are justified in concluding that there was a double set of baths, as Varro
and others prove incontestibly that the women's apartments were separated from those of
the men; the observations of Martial and St. Cyprian by no means contradict this
opinion; the improprieties they refer to relate to females of a licentious character. The
separation of the baths is remarked in those of Caracalla; at least a large portion is pre-
ceded by a vestibule, which enclosed the principal body of the building. This part is
divided into fifty vaulted rooms, separated from each other, but perfectly similar; some of
the baths still remain, and from one nearly entire we can deduce the manner of its arrange-
ment. It is preceded by a small vestibule; the place for the bath is 31 feet long, and 15
feet 3 inches wide. The basin which receives the water is in masonry with a course of
freestone, which separates it 18 inches from the wall at bottom, and from the two return
CHAP. IV.
123
ROMAN.
walls. The open space of the basin, between the edges, is 12 feet wide and 15 feet long;
the descent to it in front was by seven or eight steps, the whole width of the bath, four to
arrive at the edge, and three or four to descend to the bottom, so that those who washed
might seat themselves on the edge. The bath was lighted by an opening in the upper part
of the lower wall. In this part of the thermæ a thousand persons might bathe at once:
the water was only lukewarm, because it came from the warm baths of the thermæ, of
which these latter formed the enclosure; it then flowed out by means of pipes into a large
piscina, for the use of those who wished to exercise themselves in swimming.
In the return of the façades to the right and left were other baths for individuals of
opulence or superior rank. Instead of basins were bathing vessels, of copper, marble,
porphyry, granite, or basalt; there were also seats of marble or porphyry, a great
number of which are still seen in Rome. Olympiodorus asserts that in the therma of
Caracalla there were 1600 seats of this kind.
The rotunda or great hall was 111 feet in diameter; this was supposed to be the cella
solearis or the hall of sandals, of which Spartian speaks in these terms: "Architects and
mechanicians agree in saying that the cella solearis is an inimitable thing." There is reason
to believe that it received the name of solearis because the bars of copper and brass which
formed its floor, according to some, and its ceiling according to others, somewhat resembled
the interlacing of the sandals of the ancient Romans. There were also plates of copper or
brass which ornamented the architraves of the windows and doors, and other parts of the
rotunda: it contained a great number of bathing vessels for warm water.
•
No subject has caused more discussion among the learned than the manner in which the
numerous baths and bathing vessels were supplied with warm water.
For if we suppose,
which is by no means an exaggerated computation, that each vessel in the baths of Dio-
cletian was capable of containing six bathers, eighteen thousand could be accommodated
at once in the building. As there remains no vestige which can decide the various
conjectures as to the means by which the water could be conducted into these vessels, it has
generally been agreed to adhere to the explanation of Vitruvius. Baccius has treated this
subject better than any other modern writer; he has imagined that the water might
come from the reservoirs outside the thermæ, and that they were obliged to make use
of machines to raise it to the height which his examination of the baths of Diocletian
induced him to suppose was necessary: this idea was suggested to him, in consequence
of finding that a vast number of pipes were taken out from an area, where there had
never been any buildings, and were all surrounded by other pipes which came from
the hypocaustum; the various difficulties in which this view of the subject is involved
induced him, after serious reflection, to abandon any further hypothesis.
Piranesi has given the sections of two reservoirs which show that the quantity of water
required to supply the baths of Antoninus Caracalla was easily obtained; it flowed from the
aqueduct of Antoninus Caracalla, a part of which passed by the Appian Way. It appears
by the plan of this vast reservoir, that immediately above the hypocaustum were twenty-
eight vaulted chambers, forming two ranges of fourteen each, and communicating with
each other; the sections show that above these chambers there were twenty-eight
others, although one only communicated with the lower rooms by means of an open-
ing, through which the water passed into the lower chambers immediately over the
hypocaustum. Over all the rooms was a spacious reservoir, not very deep, but which
occupied the whole length of the great reservoir, and in which the water was considerably
warmed by the sun before passing into the chambers; this reservoir did not receive the
water immediately from the aqueduct, but from a cistern, through which it was made
to flow as slowly as possible, so that its surface should not receive the slightest agitation,
which would greatly prevent the effect of the sun's rays upon it. When not required for
the baths in the lower rooms, it flowed out of an opening in the side of the cistern, the
water in the reservoir remaining the while in perfect repose. Thus the cistern answered two
purposes, the preventing any agitation in the reservoir, and the carrying away the surplus
water. When the twenty-eight vaulted apartments, which were immediately above the
hypocaustum, became warmed, the heat they acquired augmented with the greater
rapidity, as there was only one of the chambers which communicated with the outer
air. Pipes were employed to give the water sufficient heat for the use of the bath; there
were also pipes from the hypocaustum, which acted as reservoirs of tepid water to the
lower rooms.
When the hour for the bath arrived, the valves were turned, to allow
the warm water in the lower rooms to flow into the baths, which it did with great rapidity;
it rose in the therma to a perpendicular height equal to the surface of the great
reservoir; its course was accelerated, in consequence of its great tendency to dilate or
expand after being shut up in the rooms. If the pressure of the column of tepid water
was not greater than the diameter of the column of warm water which flowed from the
lower rooms, it was at least equal to it. To prevent the water from cooling in passing
through the subterranean pipes, care was taken to surround them with other pipes which
came from the entrance of the hypocaustum, so that these latter were in the centre of a
124
Book I.
HISTORY OF ENGINEERING.
species of cavity, and acquired a considerable quantity of heat before the water entered
them. Each of the chambers was within the walls, 49 feet 6 inches long, 27 feet 6 inches
wide, and about 30 feet high; the number of superficial feet of the bottom of the chambers
was 38,115, allowing 30 feet for the mean height; the quantity of water contained in
the lower rooms amounted to 1,143,450 cubic feet, and it must be supposed that the upper
rooms contained an equal quantity of water; consequently, if we give to each bather 8 cubic
feet of warm water, supposing that the water preserved its heat for half an hour, sufficient
time for a person to bathe, 18,000 persons consumed 144,000 cubic feet of warm water;
according to this calculation, there was for the space of three hours, or till five o'clock
in the evening, a sufficient quantity of water in the thermæ for 108,000 persons;
it
must, however, be acknowledged that the water cooled gradually in flowing from the
upper rooms. The ancients do not inform us how they discovered the method of heating
such large volumes of water, nor do we know whether it was an invention of the Romans
or Orientals. We may reasonably suppose that it does not date further back than the time
of Augustus, as Dion Cassius informs us, that it was in his reign Mæcenas built the first
warm bath for swimming.
This, or some other similar method, must have been adopted in the thermes of the
Romans. It is evident that the vases described by Vitruvius would have been inadequate
to furnish water to those vast buildings which Ammianus Marcellinus compares to
provinces; but they were used in private baths, as we shall relate.
The water for the baths, says Vitruvius, was heated by means of three copper vessels,
so arranged that it flowed from one into the other; one was called the caldarium, the
other the tepidarium, and the third the frigidarium; these vases were placed so that the

Fig. 132.
FRIGIDARIUM.
TEPIDARIUM.
CALDARIUM.
one which contained the warm water received as much tepid water from the tepidarium, as
the latter did cold water; thus the same quantity was constantly maintained.
"It is not easy," says the Marquis Galiani, "to form a very correct idea of the situation
of these vases on the furnace." Cæsare Cisarano and Caporali have figured them one over the
other, or one within the other, placing the frigidarium on the tepidarium, and this on the
caldarium, which stood immediately over the furnace; but the great difficulty in this
arrangement is that the heat, by the tendency of the flame to ascend, would be more likely
to act upon the frigidarium. Perrault, on the contrary, places the three vases on a level,
and imagines there must have been syphons to conduct the water from one vase to the
other; but without a piston, or some other expedient, the water could not rise to descend
again. This Perrault does not explain. From what we can judge of the paintings in the
ancient baths of Titus, it would appear that the three vases were placed on three steps, so
that the bottom of the water in one is on a level with the opening of the other, whence it is
easy to understand how they can flow one into the other; the Marquis Galiani, however, does
not believe this to be the true arrangement, and imagines that it is made so in the picture
merely to convey a better idea of this transversion from one vessel to the other. The
following are his conjectures on the subject. "I think that these three vases are all on a
level, the caldarium immediately over the furnace, the tepidarium a little further off, so as
to experience the reverberation of the fire, rather than the fire itself; the frigidarium still
more removed, on a heap of masonry which the flames could not touch. There was in the
bottom a tube of communication from one vase to the other. From the caldarium to the
baths was a pipe, whence by a tap the quantity of water required was drawn. Another
pipe brought the water from the reservoir to the frigidarium, and maintained itself at the
same level.
All the drawings hitherto given to illustrate the descriptions of Vitruvius
appear to require the superintendence of a servant to effect the transversion." Nevertheless
this author leaves us to understand, that the operation was effected by itself, and without
CHAP. IV.
125
ROMAN.
the assistance of any one; according to him, it appears clear that three volumes of water
being level, a vase fills in proportion to what it loses, attention being paid to the placing
the bottoms of the vases each a little higher than the other, so that the caldarium should
be the lowest, and the frigidarium the highest; there was no fear that the order of the trans-
version should be reversed; that inconvenience might even be obviated by stoppers placed at
the entrance of the tubes of communication.
"We
There was also another manner of heating the baths, which Seneca describes thus.
have a species of high narrow vases, in the form of dragons and other things, in which pipes
of thin copper are placed in a spiral order, that the water, by frequently circulating through
the same space, may become heated. As the warm water flows out, the cold water flows
in, and all that passes acquires the same degree of heat." Seneca shows the advantage of
this proceeding, and tells us, that the tube through which the fluid descended, having no
communication with the fire, the vapours were not mixed with the smoke.
Probably this was not a general method; there is reason to believe that it was only
adopted by the rich. These vessels derived their name either from the animals which they
represented, or from the quantity of water which they contained; there was necessarily a hole
towards the bottom of the basin to conduct the warm water, and when the proper warmth
was obtained for use, and the tap was turned to let it flow into the lower extremity of the
pipe, the cold water entered the pipe by the upper, and descended as the warm water was
drawn out: when the water which had first been heated had passed through the spiral tubes,
the cold which had come in descended to the bottom of the pipe, after having been warmed
in its passage, in proportion to the length and diameter of the pipe, to the quantity of
water in the vessel, and to the degree of heat at which it had been maintained by means
of the fire. The water was enclosed in such a manner as to prevent its sudden evaporation,
which would have occasioned the introduction of cold water, and this would have abstracted
from the pipe the degree of heat necessary for the use of the bath.
It is improbable that all these refinements of luxury and effeminacy were known to
the Greeks, with whom the baths were only part of the gymnasium, whilst under the
emperors the gymnasium formed part of the baths; it is quite certain that all such delicacies
were not practised among the early Romans; in the best ages of the republic, the pro-
ceedings and customs of the bath were as simple as the edifices which contained them. It
will be interesting to recal the parallel which Seneca has made between the bath of Scipio
Africanus and those of his time.
"There are persons who consider Scipio as unrefined, for not having wide win-
dows to his warm bath. How unhappy was he, say they; he knew not how to enjoy
life! It is true that he did not always bathe in limpid water; it was often troubled, and
even muddy in time of rain. But it was unimportant to him what water he used, for,
using no perfumes, he washed merely to cleanse his body. His bath was small and dark,
according to the custom of the ancients, for our ancestors imagined that a bath could not be
warm without darkness. How delightful is it to compare the manners of Scipio with ours.
This, then, is the hovel in which that great man bathed,—he who was the terror of Carthage,
and to whom we owe it that our city was only once taken: he lived under that humble
roof, he walked on that vile pavement; now, who would bathe thus? We think ourselves
poor and miserable if we do not trample under foot mosaics and precious marbles; the
marbles of Numidia are united to the stones of Thasus; the light is reflected from crystal,
the water flows into the baths by taps of silver, and this is only for the people: what if I
were to describe the baths of our freedmen, the crowds of statues, the multitudes of columns
supporting nothing, only placed there for decoration, and on account of their dearness? With
what noise does the water precipitate itself into the places destined to receive it. Our luxury
has arrived at such a point, that we will no longer walk on any thing but precious stones.
Instead of windows, the bath of Scipio had small openings in the stone walls, which,
without diminishing their strength, only give the requisite light; now the baths would be
called caves, if the windows were not of an immeasurable height, so as to admit the rays
of the sun during the whole day, if we did not burn in bathing, and if from one's seat we
did not see the country or the sea: formerly the baths were of small number, and without
ornament, &c. &c."
We learn by this letter of Seneca to what a point of magnificence luxury was carried in
the edifices destined for the bath, and the recital is quite conformable with the remains that
are still left us; in the greater number we see the rich covering of the walls. In the bath
room or hall recently discovered at Otricoli are still preserved fragments of the rarest mar-
bles; its pavement was formed of that mosaic which is now the principal ornament in the
Musæum Vaticanum. In the baths of Titus the walls were covered with marble to about
the height of 10 feet, to preserve the paintings which decorated the walls from being injured
by the splashing of the water. It appears that in these baths, a portion of the rooms, par-
ticularly those intended for the warm baths, had no window; at least none has been dis-
covered.
When it became a custom to frequent the baths at night, luxury took advantage of the
$126
BOOK I
HISTORY OF ENGINEERING.
necessity, by lighting them with lamps and candelabræ, which contributed greatly to their
decoration. The most magnificent we now see at Rome were found in the therma; their
light was thrown on crystal balls, according to Seneca, placed in the vaulting, or on the
walls, so as to produce the most dazzling reflection: the introduction of glass as a decoration
belongs to the time of Pliny, who calls it a modern invention; it did not exist according to
him in the time of Agrippa, whose baths were decorated with coloured tiles, or a stucco
called Albarium Opus; in one excavation, the vaultings were thrown into compartments of
stucco, painted and gilt.
All the walls and masses composing them were built in rough masonry, filled up with
smaller stones, the facings of which were of brick covered with stucco, ornamented with
paintings, marbles, and precious stones. Generally every apartment was vaulted in the same
kind of masonry; but in order to produce more lightness, tufa, pumice-stone, or extremely
light lava, were used.
The large apartments in the baths of Caracalla were vaulted. The pavement was formed
of masonry covered with stucco or mosaic.
The six apartments of which the ancient baths were composed were thus arranged:
In the first there was nothing remarkable but the shelves or closets, in which were placed
the clothes of the bathers.
In the second was the cold bath, called Lavacrum by the Romans, where was the basin,
in which several persons could bathe at a time. It was of granite or marble, and sometimes
of masonry covered with a strong cement, or capped by an edge of freestone: this cement
acquired by time more hardness than stone; vessels were often made of a single piece, impe-
netrable to water; and as it is in the angles that square vessels generally became injured,
care was taken to round them all internally; the bottom was so hollowed as to be deepest in
the middle; they were finished by an edge or return on three sides only, called the labrum,
and the centre alveum. Vitruvius, lib. 6. cap. 10. says, that the size or capacity of the
basin should be proportioned to the number of persons intended to bathe, but they should
not be less than 6 feet wide, two of which were given to the lower step and the lip; the
length should be one and a half the width. The fourth side of the basin, which was that
by which it was entered, was occupied by the steps which led to the bottom; beyond the
edge or lip, and around the three sides, was a balustrade to separate those who were bathing
from those who waited for their turn, on which account, between the balustrade and the
walls of the hall, there was a gallery called schola, which was required to be sufficiently
wide to accommodate all who were to replace the bathers; this gallery was paved in marble;
the walls, as well as the cement which covered them, required to be made with care and
precaution, on account of the humidity occasioned by the evaporation of the water. Perrault,
in his translation of Vitruvius, imagined that the baths were lighted by an opening in the
centre of the vault; but it appears that Vitruvius himself says, that the bath should be
placed under the light of the window, so that the shadow of those who are around it should
not intercept the rays, which would lead to the supposition that there was no gallery on the
side of the window.
There are several of these cold baths in the thermæ of Caracalla, one of which remains
in a vaulted hall, preceded by a small vestibule with a portico, said to have been added by
Septimius Severus. The apartment is 31 feet long, and 15 feet 3 inches wide; the basin is
in masonry, with an edge in freestone, which separates it 18 inches from the bottom wall,
and the two returns: the hollow of the basin between the edges is 12 feet wide, by 15 feet
long: the descent is in front, by seven or eight steps, which are the whole width of the hall,
viz. four to arrive at the edge of the bath, and three or four to descend to the bottom, so
that those who washed could sit on the edge, which was round the three sides. The bottom
and sides are covered with a very thick and hard cement; the surface being crystallised,
which probably greatly contributed to its hardness; such incrustations are apparent
in all reservoirs and receptacles for water throughout Rome, the water having the property
of petrifying, if we may so term it, the surface of all cements, which are moreover well
mixed, and made with the greatest care.
This hall was lighted by a semicircular window opened at the top of the lower wall,
against which the baths were formed.
Along the side of the therma which is to the north-east there are fifty apartments,
apparently destined for the same purpose, so that a thousand persons might bathe at a time;
the water must have been tepid, for it appears by the pipes and conduits which are left, that
it came from the warm baths of the great thermæ, of which these baths formed, as it were,
the inclosure; between the baths, and at nearly equal distances, were the remains of four large
staircases, of two rampes, which led to the thermæ, the soil of which was 20 feet higher
than that of the baths. The whole edifice was built on the declivity of the mount Aventine,
so that the first served as the substructure or foundation of the upper soil.
All the walls and vaults are in masonry, faced in brick, and covered with cement of
mortar; the pavement is in masonry, which proves that the baths were only destined for
the common people.
CHAP. IV.
127
ROMAN.
Construction and Arrangement of the Furnaces and Conduits for Heat.- Vitruvius gives
very circumstantial detail on this subject. "We must begin," says he, "by making an
inclined area, laid with large bricks 1 feet square. This area should be so disposed,
that a ball thrown in at the door of the furnace should not be able to stop in any part, but
should return to the door; in this manner the flame or heat should extend through all the
turns and voids of the conduits formed under the pavement.

Fig. 133.
HYPOCAUSTUM.
To form the double floor which covers these voids, and which Vitruvius calls Suspensura,
there were constructed at equal distances little brick pillars, 8 inches square, at 2 feet
distant from centre to centre. These pillars should be about 2 feet high, in the part where
the inclination was the
lowest. When well
levelled, bricks 2 feet

square were so placed,
that each pillar re-
ceived the angles of
four bricks, and there
remained round each
pillar 16 inches of
void above this brick
floor, carried by the
pillars, was spread a
layer of broken tile
mixed with chalk, co-
vered with a fine ce-
ment, or a pavement
of mosaic; that the
bricks which rested
on the pillars might
not break before the
whole had acquired
sufficient consistency
to sustain itself inde-
Fig. 134.
PLAN OF PIPES OF TERRA COTTA.

I
O
Fig. 135.
SECTION OF PIPES AT POMPEN.


pendently of the brick,
the space between one
Fig. 136.
Fig. 137.
pillar and the other was arched.
Among the ruins of Pompeii are the remains of a private bath with stoves; the double
floor in suspensura formed nearly in the same manner, with this difference, that instead of
little pillars in brick, they are pipes of terra cotta, made on purpose; these pipes are ter-
minated by two square tiles, with a hole in the middle; they are 19 inches high, and about
4 inches in thickness about the middle: the square at bottom is 8 inches, and that at top
6 inches; no doubt this form was given for the purpose of a greater base; the pipes were
placed upright on an inclined bed, as prescribed by Vitruvius; this is laid in large bricks, 8
inches square, each pipe so placed that it covers the joint where the angles of the tiles
unite, so that they are 18 inches apart from centre to centre. Above the pipes is a plat-
form made by a double row of bricks, also 18 inches square, each placed on four pipes ;
on this double platform is a bed of mortar, made of pozzolana, covered with a mosaic pave-
ment.
The place which served as a stove was small; its plan is a rectangle, 10 feet long, by 5 wide,
terminated by a niche forming a seat at bottom; the entrance is by a very small door,
which is at the other extremity in an angle: as the walls are half demolished, and they have
scarcely more than 2 or 3 feet of elevation, it is not possible to ascertain whether it was
128
Боок І.
HISTORY OF ENGINEERING.
vaulted, which is very probable, but it is still less possible to decide in what manner it was
lighted.
The pavement of this stove, as well as of the warm bath at the side, is raised about 2 feet
6 inches above that of the place in which is the entrance of the furnace. There is also the
remains of a leaden pipe which conveyed the water into the warm baths; its external
diameter is about 2 inches. In these apartments were the vases or kettles in which the
water was warmed; there is no vestige of the laconicum, but at the side of the furnace there
is a square recess in the wall with a bench, the situation of which must have been much
warmer than that of the niche at the bottom, so that persons could place themselves either
in one or the other, according to the greater or less degree of heat desired.
In another part of the same ruins was a stove of a circular plan, with a step and niches
around; it is lighted by a round hole about 1 feet in diameter, made in the middle of the
vault; this hole might have been the situation of the brazen shield, to be raised or lowered
for the purpose of increasing or diminishing the heat.
A bath was discovered at Rome, in which the basin was covered with a coating of cement
so hard, that it was impossible to dissolve it sufficiently to analyse its substance, it was a
Roman palm thick, and capable of resisting not only the heat of the water, but the action
of any heat whatever.
The Romans having introduced the use of the bath wherever they had carried their
arms, we find remains of them in their most distant provinces. At Wroxeter in the
county of Shropshire was discovered a small square room, the pavement of which was con-
structed in the folllowing manner : — there were four rows of pillars in brick 8 inches
square, put together with very fine red cement; they were placed on a bed of bricks a foot
square; the platform above the pillars was formed by bricks 2 feet square, and of extraor-
dinary hardness; the bed above was composed of a mortar of broken tiles and large gravel;
round the internal walls were fixed by iron clamps pipes whose inferior extremity abutted
against the platform of large bricks, which formed the floor above the pillars; the other end
came to the surface of the upper pavement; it was covered by a row of bricks; each pipe
had two opposite holes to communicate the heat.
Six miles from Chester, a part of a bath recognised as Roman construction was discovered.
in which was a hypocaustum surrounded by walls cut in the rock. The lower pavement
was of brick laid in cement; the platform was supported by brick pillars, which appeared to
have been polished, and had in several places holes above which were brick tiles, to distribute
the heat. On some of the bricks were inscribed LEG. XX., whence it was inferred that
this hypocaustum had been constructed by the twentieth legion, which was called the
"Victorious."
With regard to the vaults of the warm baths, Vitruvius says that it is better to make
them in masonry than in carpentry, but when a floor is required, there should be underneath
a filling-up of terra cotta, made in the following manner. Bars or arcs of iron must be sus-
pended to the carpentry with clamps of the same metal, placed sufficiently close, that from
one to the other there may be put flat tiles without edges, so that a vault may be formed
isolated from the floor and entirely suspended by iron; over it should be laid a coating
of clay mixed with hair, and the under side towards the pavement should be first covered
with cement, and then finished with polished stucco; the vault would be better if double, in
order that the vapour, which might penetrate the first, should be stopped by the second,
and thus preserve the carpentry from humidity.
The Therma discovered in 1824 at Pompeii are highly interesting, as they exhibit the
arrangements of such an establishment out of the Imperial city; they occupy an irregular
quadrilateral space north of the forum, and were entered from the street by a small passage
which opened into a court 60 feet in length, on two sides of which was a Doric portico, on
the other a crypt, over which was a second story. At the opposite angle of the court was
another exit, where was situated the latrina; to this succeeded a sort of pronaos with seats,
which was vaulted and lighted at night by a lamp, so placed that its rays fell into the
ehambers around. This lamp was protected by a circular convex glass, the fragments of
which were discovered. From the court the bathers passed to another chamber, in which
were found above 500 lamps, made of terra cotta, with various devices upon them; this
room was the frigidarium, and served also as the spoliatorium, apodyterium, or apolyterium,
or the place where the clothes were left; many holes still remain in the walls in which the
pegs were inserted, on which were hung the garments of the bathers, and which were called
Caprarii, probably from resembling two horns. This spacious chamber is vaulted from a
projecting cornice, decorated with griffins and lyres richly painted. The vault is panelled,
coloured red and white, and the pavement is mosaic. The walls were coloured yellow,
around which was a stone seat with a step a little elevated above the floor. At each end
was a window, similar to the one remaining on the south end, and which opened upon the
cemented roof of one of the chambers. This window had a plate of thick glass, slightly
ground on one side, and secured by copper bars. Another room contained the natatio, or
swimming bath; in the time of Pliny, it was called baptisterium. This chamber is perfect;
CHAP. IV.
129
ROMAN.
nothing is wanting but the water to fit it for its purposes, which gushed from a copper
pipe, about 4 feet from the floor, and fell into the cistern. The plan of this room is a
circle enclosed in a square; in the angles are four alcoves; the diameter is 18 feet
6 inches, and round the whole runs a walk about 2 feet 4 inches wide. The piscina,
12 feet 10 inches in diameter, is surrounded by a seat, 11 inches wide, at about 10
inches below the lip, and 2 feet 4 inches from the bottom; so that the water was about
3 feet in depth. A convenient step led out of the bath, and proper channels were
provided to empty it. The whole of this arrangement was of white marble. The
dome or roof was conical, painted blue, and had an aperture near the top toward
the south-west, which admitted light and air; the side walls were painted yellow
with portions green.
The alcoves, which were 5 feet 2 inches wide, and 2 feet in depth,
were painted blue, and the hemispherical parts red. The cornice surrounding the room
was 8 feet from the floor, 18 inches high, and coloured red; this was ornamented with
stuccoed figures on foot, on horseback, and in chariots.
This
The tepidarium, a beautiful vaulted apartment, discovered in 1824, contained three
bronze seats, inscribed with the name of the donor, Marcus Negidius Vacula. The legs re-
sembled those of the cow, the head of the animal forming an ornament to the upper parts.
This apartment was warmed by a large foculare or brasier given by the same person.
bronze vessel with thirteen battlemented summits, and a lotus at the angles, was 7 feet long,
and 2 feet 6 inches broad. In the centre was a bronze cow. To resist the heat of the embers
the bottom had brass bars, on which were bricks, supporting pumice-stone, for the reception
of the wood ashes or embers. The pavement of the tepidarium was of white mosaic with
two small black borders; the ceiling was painted, the walls crimson.
Under the pave-
ment was a continued hypocaustum to warm the apartment.
Round this room, 4 feet 3 inches above the pavement, and 1 foot 2 inches in height, was
a sinall cornice, on which figures of giants, about 2 feet in height, formed of terra cotta,
were placed, projecting about a foot from the wall, and distant about fifteen inches apart;
their arms stretched out to assist in bearing the superimposed weight of an entablature 1
foot 5 inches in height, which rested upon the heads of these telami.
The caldarium, on account of the steam that was produced by the laconicum, was not
very highly decorated; there was not only an hypocaustum under the floor, but the walls
were constructed so as to allow warm air to circulate around it. This was effected, not by
flues, but by a lining of tiles, connected with the outer wall by cramps of iron, a space of
4 inches being left for the hot air to ascend from the furnace below; it was lighted by win-
dows from the top. The walls are painted yellow, the pilasters and cornice red, and the
alcove blue and red. In the centre of the latter was the labrum, of white marble, 8 feet
in diameter and 8 inches in depth, in the middle of which was placed a brass tube for
throwing up the water. This chamber was 37 feet long and 17 feet 4 inches in width.
From the pavement of the caldarium, which was of white tessera with two small black
borders, the bathers ascended by two steps to a third, also of marble, 16 inches in breadth,
which formed the brink of the vase of hot water. A step, dividing the whole depth of the
cistern, which did not exceed two feet, permitted them to immerse themselves by degrees
in the hot water.
The entire length of this cistern is 15 feet, and the breadth 4 feet, so that ten persons
might at one time occupy it. The hot water entered at the angles immediately from a
cauldron placed on the other side of the wall. In the roof were four openings for the ad-
mission of light, which probably were glazed or closed with vela of linen cloth.
The caldarium was the bath, or the vessel containing the hot water, adjoining which
was the laconicum, for the purpose of producing respiration. The furnace contained
three cauldrons, placed one above another, in which were three varieties of water, that at the
top being the coldest, that immediately over the furnace always boiling, and as it was dis-
charged, a fresh supply was obtained from the middle cauldron, which was in a tepid state.
These cauldrons were supplied by pipes from leaden cisterns called Miliaria.
When we survey the ruins of the baths, we cannot but regret that we have not es-
tablishments in all modern cities, where the inhabitants, both rich and poor, might attain
the first elements of health: cleanliness by the ancients seems to have been much more
considered and encouraged than by us, for there were hot and cold water baths established
in every town. The following verses of one of the poets give some idea of what a Roman
underwent before he commenced his toilet.
"Scabor, suppilor, desquamor, pumicor, ornor,
Expilor, pingor," &c. &c.
And to accommodate the multitude, many of these washing and bathing establishments were
upon such a scale as to resemble towns, where every citizen, whatever his condition, could
enjoy daily, without trouble or expense, the luxury of the bath. Our crowded and
populous manufacturing towns need the use of thermæ more than the provinces of the
Imperial city; the workmen, early and late, should have the opportunity as well as induce-
K
130
Book 1.
HISTORY OF ENGINEERING.
ment to enter the bath; and in all well regulated workshops, it ought to be made a duty of
the first consideration, to adopt habits of cleanliness: were this done, health would be
assured, and longevity be much more frequently met with.
At Bath the Romans had several establishments for bathing; hypocausts and tubulated
tiles are constantly met with when fresh ground is broken. This city in the Itineraries of
Antoninus and Richard of Cirencester is called Aqua Solis; and there are found also
altars to Sulinis Minerva, the Solar Minerva, or the Minerva Medica, which clearly
indicate that it was much resorted to by invalids in those days.
Baths at Baden-weiler, a plan of which is given in the edition of Vitruvius published at
Berlin by Rode, contains a set of baths for men and women, with the apartments required by
those who attended them. A, was the position of the hypocaust, B, the furnace, C, the

K
I
E
B
D
D
A
100
1
K
Fig. 138.
BATHS AT BADEN-WEILER.
caldaria; D, vaulted sudatories; E, tepidaria; F, frigidaria; G, rooms which had
floors, like those of the caldaria, heated by the stoves; H, vestibules; I, elaeothesia, and
K, exedrae. This arrangement forms one of the best illustrations to the description given
us by Vitruvius, although upon so small a scale.
Baths at Stura.-Near Antium, at the mouth of the small river Stura, now called the
Conca, are the remains of some baths built in the sea. A, is a grand court surrounded by

Fig. 139.
M
HE
00
E
D
C
00
蛋蛋
​K
BATHS AT STURA.
L
CHAP. IV.
131
ROMAN.
columns; B, is the vestibule conducting to the baths; C, a hall communicating with the sea
baths; D, is now occupied by the tower of the Stura; E, projects into the sea, at the ex-
tremity of which is the mole; F and G, are large, and H and I, smaller swimming baths, sur-
rounded by rooms for the convenience of the bathers; L, M, are passages and approaches from
the side towards the town.
Baths at Nismes, situated north of the city, are supplied by a clear stream, and have
been decorated with considerable taste: Palladio, Clerisseau, and many French architects,
have shown great skill in their restoration. A, is a large court, surrounded by a covered
peristyle, B; the lower portion of the baths is shown at C; the source of the water is at
D, which is entered by winding stairs at E, E; a bridge over the canal remains at F;

M
H
L
A
10:0
G
ЛЕГИНИАНЕНИНИЙ
E
Fig. 140.
BATHS AT NISMES.
another reservoir is shown at G, which passes by the canal H into different private baths;
I, is the direction given to the waters on issuing from the baths; L, is a small temple
dedicated to the presiding divinity, and M, another small reservoir.
For warming their houses the Romans had a very simple and admirable method; the
word caminus, from the Greek kaminos, whence our word chimney is derived, would in-
dicate that they had flues something like our own. The etymology leads to this sup-
position, but we must take into consideration the various uses and forms to which it
alluded. The terms caminus and focus were applied both to the place in which the fire
was lighted and to the fire itself; hence it is doubtful to which they referred. Focus is used
indifferently for a brasier or any of the portable fireplaces in which charcoal was burnt, or
for a place where wood was consumed.
Vitruvius, in his account of houses to be built in the country, used the word focus when
alluding to the kitchen fireplace. The kitchen, this author states, should be placed in the
warmest part of the court, adjoining to which should be the stalls for the oxen, with the
mangers at the same time towards the fire and towards the east, for oxen with their faces
towards the light and fire do not get rough coated.
The word caminus probably meant at first a furnace for melting metals, in which a
crucible was made use of; and Pliny has the word applied to a smith's forge. It also in-
dicated a hearth.
Seneca, in his 90th Epistle, gives us an account of a method introduced in his day to warm
an apartment. A large stove, or several, were formed in a vault under a building, and
these being filled with burning embers, the heat was conveyed away into the several rooms
by means of pipes built up in the walls, the upper ends of which were ornamented
with a lion's or a dolphin's head, and through their mouths passed the warm air; these
could be shut or opened at pleasure. These pipes, made square, of terra cotta, were laid in
indents in the side walls around the whole apartment in a perpendicular direction, and acted
as so many flues or chimneys from the fireplace below. This was a species of hypocaustum
under the floor, like that described in the baths, and the little smoke produced by burning
wood in the prefurnium passed up the numerous perpendicular flues in the wall; these,
being made of thin burnt clay, radiated all the heat they absorbed into the room, and very
little could have passed away after having circulated through such a length of pipe, where
the draught was so much divided.
The manner of warming our greenhouses bears some resemblance to this method, par-
ticularly where the flues are carried under the pavement, within a walled trench, into which
K 2
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Book I.
HISTORY OF ENGINEERING.
air is admitted, and, after warming, is suffered to pass through apertures in the pavement
prepared for the purpose. In the Roman hypocaustum the fire was laid at the mouth or
at the foot of the prefurnium, and the air passed over it, in the same way that it does in a
malt kiln, into a chamber under the floor of the apartment to be warmed. The floor, being
larger than the top of the kiln, was supported by small pillars, and the heat, instead
of passing through it, was made to circulate around the walls and lose itself in its cir-
cumambulation. These species of hypocausta were common in the country houses of the
Romans. Under the rooms of many of their villas are found a hollow space, from 2
to 3 feet high; the floor being supported upon flat tiles which rest upon a series of small
brick pillars built with fire-clay, or with a cement not containing any calcareous matter
likely to be acted upon by a strong heat. Along the sides are still found the square pipes
of burnt clay which carried off the rarified air from this subterranean chamber into the
apartments around or above the triclinium or room immediately over the space first warmed.
A narrow passage usually led to the mouth of the furnace; this being vaulted, and
having an aperture at the end to admit air, acted as a blower to the furnace or blazing
wood placed at the mouth of the hypocaustum.
De la Valle observes that the Persians warm their apartments by stoves made under ground;
these are a species of cauldron, in size and shape like a small barrel, which are placed in
an iron vessel filled with burning coals. The barrel or stove is covered with a wooden top
over which is laid a carpet; the embers are excited to burn more strongly by means of a
small tube, which acts as a blowpipe: here the air admitted into the barrel becomes
warmed, as it does in the oven of a French poele, and may be diffused throughout the
apartment.
By the introduction of warm air, thus admirably circulating throughout a Roman house,
there was no need of a chimney shaft like those we require to carry off the smoke from a
coal fire; and Vitruvius makes no mention of such contrivance. He says that cornices and
carved mouldings should be omitted in rooms where fires are lighted, because they are
subject to be injured by the smoke. It is true they had open fires, as they have in Italy at
present, made in chafing-dishes or brasiers, which were placed in the middle of the apart-
ment. These are very handsome, and are supported upon a tripod, or made to resemble a
walled town with towers in miniature.
The wood used was the white and common willow, which produced little smoke and
few sparks. They first peeled off the rind, and then laid it some time in water, after
which they exposed it to the sun and air to dry. Sometimes this wood was soaked in oil
lees, or had oil poured upon it, or was partly burnt in the open air, before it was introduced
into an apartment, when it was called ligna cocta, and under such a term it was sold at
Rome. The warehouses called tabernæ coctiliariæ were very numerous, and many persons
were employed to prepare wood for fuel, or to rid it of its smoky qualities.
Harbours and Buildings in Water.-When a harbour was to be formed, the Romans made
choice of such situations as would ensure safety to their vessels in stormy weather, and preferred
those bays which were protected by long promontories jutting considerably into the sea, and
forming curves and angles. Around these, porticoes, arsenals, and market-places were esta-
blished, and the mouth of the harbour was secured by iron chains, suspended by means of
machinery contained in two towers at the entrance. When nature had not so provided, and
the shore was flat, they constructed piers by throwing into the sea heaps of stones, which
they projected to a vast distance in the following manner. An earth was procured between
Cuma and the promontory of Minerva, which, when mixed in one proportion of lime to two
of the earth, had the property of hardening under water. When the situation of the pier
was determined upon, dams were formed in the sea by driving oak piles, secured firmly
together with chain pieces. Between two ranges of piles thus driven, the earth was taken
out, and the bed properly levelled; mortar, composed as above, was then thrown into the
space between the piles, together with a proportional quantity of stones, until it was entirely
filled. If the sea was too deep or violent for this method to be pursued, they constructed
on the margin of the sea a foundation of the greatest possible strength, with courses of
stone laid horizontally throughout rather less than half its length; the remainder, which
was towards the sea, was made to incline. On the side towards the water, and on the flanks
of the inclined plane, walls were built, projecting over the face eighteen inches, after
which the whole was filled with sand to the level of the horizontal part. On this sand
they commenced building a wall, which was raised as high as possible without incurring
danger; this was left for a couple of months exposed to the action of the air, that the whole
might harden. The walls inclosing the sand were then removed, and the sea, washing
against the sand, speedily carried it away; the whole mass then sliding on the inclined plane,
was shot into the water, and this sort of operation was continued until a sufficient number
of artificial blocks were constructed to form the mole or pier required. Sidonius Apolli-
naris, in his panegyric of Anthemius the consul, says: "The new land advances into the
sea, and its mass contracts the old ocean; Dicarhean dust when thrown into the water
becomes solid, and the hard mass sustains fields, thrown into the foreign waves." This kind
CHAP. IV.
133
ROMAN.
of work was accomplished by merely throwing into the ocean the earth obtained from
Puteoli, which, when immersed in the sea, became as solid and compact as a hard rock :
this earth was a compound of alumina, bitumen, and sulphur, not differing much
from that found at Cyzicena, which, when cut into large blocks and sunk under water,
had the property of hardening. The younger Pliny, lib. vi. let. 32., writing from the
neighbourhood of Ostia, describes the progress made at the port of Centocellæ, thus
enabling us to judge of the method by which the Romans conducted such operations.
"The left hand of the port is defended by exceeding strong works, and they are now
employed in carrying on the same on the opposite side. An artificial island, which is
rising at the mouth of the haven, will break the force of the waves, and afford a safe


Fig. 141.
CENTOCELLE.
!
channel to ships on each side. In the construction of this wonderful instance of art, stones
of a most enormous size are transported either in a large sort of pontoon or raft, and, being
piled one upon another, are fixed by their own weight, and gradually accumulate in the
manner of a natural mound. It already lifts its rocky back above the ocean, while the
waves which beat upon it, being tossed to an immense height, foam with a prodigious noise,
and whiten all the sea around. To these stones are added large blocks, which, when the
whole shall be completed, will give it the appearance of an island just emerged from the
sea. The above was written from his villa at Centocellæ.
""
Ostia was formed into a port in the year of Rome 132, by Ancus Martius, who also con-
structed the first wooden bridge over the Tiber; and here, in after times, were three
separate ports, affording secure retreat to vessels on that dangerous coast, constructed by
Augustus, Claudius, and Trajan: the latter, that alluded to by Pliny, was destroyed by the
changes which took place in the bed of the Tiber. The ancient port of Ostia was about
half a league from the sea, and five leagues south-west of Rome, near the mouth of the
Tiber. At Porto, now a small village, and a league from Ostia, on the other side of
the Tiber, are considerable remains of the town which the emperors Claudius and
Trajan caused to be built. The basin of the ancient port of Trajan may be seen,
with fragments of many of the buildings represented on his coins.
The port constructed by Claudius, in advance of that of Trajan, was amongst the
boldest executed by Roman engineers:
:—an oval sheet of water, enclosed from the
ocean by broad and spacious moles, affording a safe haven for vessels which navigated
the western shores of Italy: an artificial island lay between the horns of these two
moles, with towers at each extremity, containing machinery and tackle of various
kinds, by which the boatmen could at all times enter safely. These constructions must
have been a work of prodigious labour; their solidity is attested by the writers of
the time, particularly by Pliny. In the middle of this island stood a pharos, before which
was the colossal statue of the emperor Claudius. Fire was placed, at the approach of
night, in the upper story of this lofty structure, which could be seen from a considerable
distance. Orders of the purest architecture decorated three of the stories, and ingeniously
K 3
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BOOK I.
HISTORY OF ENGINEERING.
@
contrived rooms and staircases served for the use of the officers and men to whom this
part of the port was entrusted. Covered galleries and porticoes standing high above
the sea, and stretching far into the ocean, invited mariners to enter, and produced an
imposing effect to all who navigated these seas.
The port of Claudius united to that of Trajan gives us an
idea of the arrangements in use during the reign of these
emperors: magazines for stores of all kinds, docks, slips, and
other buildings usually found in a modern port, were here
executed in a manner equal to those of the imperial city.

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CAES. AVC-CER-
PM-TR-P-IMP-P·P-
Fig. 142.
O
PHAROS.
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Fig. 143.
SECTION THROUGH CLAUdins' port.
CHAP. IV.
SEA.
OFFE
CLAUDIUS' FORT.
Fig. 144.
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ROMAN.
Temples, triumphal arches, rostral columns, and trophies, occupied the spaces not used
by the mariners, and noble roads conducted the merchandise and warlike stores from thence
to every part of the empire.
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RUM
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Road.
མ་
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SITE OF THE CITY.
TRAJAN'S CANAL.
135

K 4
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BOOK 1.
HISTORY OF ENGINEERING.
Modern nations have neither excelled the Romans in works of this kind, nor rivalled
them in boldness, by lifting out of the ocean walls so lofty and durable as many they
have left us; their engineers formed artificial islands as well as breakwaters, and in what-
ever they undertook, they seem to have blended the arts with a thorough knowledge of
construction. The medals of some of the Roman emperors show the taste bestowed upon
these public works; and no bounds seem to have been set to the area they walled in from
the sea.
One of their ports must have had the character of an extensive island, as its con-
nection with the land could hardly be seen, at the first view, from its length and the
stretching out of its moles. The ports called angiportum were very narrow, and considerable
skill was required to work vessels into them. Juvenal notices the extent of some of the
moles constructed in his day, and observes that such ports as those of Claudius, the work of
nature and of art, were wonderful for the extent of their foundations, laid at the bottom of
the sea.

CLAUDIU
WPORT
--
RAJA)
Fig. 145.
PORT OF Ostia.
We find Roman harbours well calculated to receive and protect the vessels which entered
them: at the mouths of rivers they drove in ranges of piles, planked over, and covered
with pitch; at the extremity of each mole was a tower or contrivance by which a chain or
boom could be stretched across the entrance, and protect the port from any sudden attack
of an enemy.
When an artificial port was formed on the coast, for the security of ships,
they constructed a mole, in a circular shape, or with vast arms, like crabs' claws (chelai),
or, as Cicero terms them, with cornua: Epist. ad Attic. lib. ix. ep. 19. A Roman harbour,
or Claustra, was entirely shut in, and none could gain admission without the consent of the
mariners who occupied the watch towers at its entrance.
That part of the harbour by which you entered was called Ostium and fauces, or the mouth
between the arms of the semicircle: when the vessels had entered, they were made fast to
the shore, or lay at anchor. Where a flat shore presented itself, the vessels on their arrival
were run backwards upon it, with their heads towards the sea, when the rowers, inhibere
remos, hung up their oars out of the reach of the waters, that they might not be broken:
sometimes they were attached to the sides of the vessel; according to Ovid, "to the
ship's sides the seamen hung their oars.”
The port of Ostia, or mouth of the Tiber, having silted up, we trace those of Claudius
and Trajan, and the diversions of the river far from the present shore; the whole features of
the coast are now materially changed, and a wide marsh lies in front of the port of
Claudius.
CHAP. IV.
137
ROMAN.

Fig. 146.
HARBOUR.

CIVITA VECCHIA.
All these ports have long become useless, and the modern one of Civita Vecchia, which is
now at the mouth of the Tiber, is forty miles from Rome, and fourteen leagues distant from
Ostia ; it was the ancient Cen-

tocellæ, so called from its having
an hundred arcades, to which as
many vessels could be moored.
The Roman ships were called
Triremis, Quadriremis, and Quin-
queremis, as they exceeded each
other by a bank of oars: there
were vessels still larger, as the
hexeres, the hepteres, the octeres,
&c.; and the ship Philopater, Plu-
tarch informs us, had forty banks
of oars; three banks of oars were
raised in a sloping direction one
above the other, consequently those
with the greatest number were the
most lofty vessels; when in port
they were placed often under ar-
cades, and protected from the wea-
ther, as we see represented in an ancient picture.
Fig. 147.
商
​ARCADES AT OSTIA.
Terracina. The size of this port and the walls which surround it show that its establish-
ment was calculated for commerce, as well as for the protection of a numerous navy. Two
straight sides united by a gentle curve form this harbour, the entrance to which is 367
feet in width; the length of the other three sides, or its perimeter, is 3705 feet. Its
greatest diameter is 1319 feet, and the least, which is perpendicular to the pass on the
land side, is 1247 feet. Its total area is estimated at 128,107 square yards. Near the
right bank of the port is an accumulation of earth, called Monte Cello, collected from the
frequent cleansing. The canal, which now communicates with the port, and which brings
down the waters from the Pontine marshes, enters through a breach made in a rectilinear part
of the enclosure. The wind, which blows directly into the mouth of the harbour, is the north-
east, but its force is destroyed by the heights of Pisco Montano, on which, probably, was
138
Book I.
HISTORY OF ENGINEERING.
placed the pharos, and by a projection of the shore into the sea, forming a small cape, com-
prised between the Pisco Montano and the Torre Gregoriano; from the latter point to the
extremity of the port, the slope of the shore is from north-west to south-east.
external part of the wall of this enclosure has a considerable talus; the ancient rocks still
remain at its base. The facing on the internal part is perpendicular, and holes in marble
blocks remain, through which the cables were passed when the vessels were moored.
The
The mole, which forms the enclosure, was raised 12 feet in height above low water; its
width at the top is 40 feet, and there are few works more substantial or solid to be met with.
Some remains of columns and their entablature lie at the foot of the mole, and in all
probability they once adorned a structure on the platform which was the residence of the
officers of the port. The foundation or establishment of these works are of great antiquity,
and are said to be the first regular constructions of this kind in Italy. In many parts the
opus reticulatum may be seen: we know that it was restored by Antoninus Pius.
Adria, whence the Adriatic derived its name, was the ancient Atria; it is 32,000 metres
from the sea; Rimini is 1500, and Ravenna 8000. At Rimini terminated the two great
roads, the Emilian and the Flaminian; here was a triumphal arch and a bridge, which were
erected in the time of Augustus. A canal conducts small craft from this once famous port
to the sea.
A variety of methods was employed in the construction of double dams, formed of piles
and planks, chained or tied together, and filled in with clay and marsh weeds, well rammed
in or puddled, to keep out the water. When this was effected, the water was pumped out
by the various machines then in use, and which were most effective for the purpose. The
Archimedean screw and water wheels were employed, after which the foundations were
dragged or dug out; when, if soft, alder, olive, or oak piles, previously charred, were
driven in, and the intervals between their heads filled with charcoal or some other equally
imperishable material. On this, walls of squared stone, in regular courses, were laid,
taking care that the longest were employed as bond-stones, to pass into the thickness of the
wall, and thus tie in the others. The inside of the wall was then filled with rubble or
masonry, and on such work, towers were built. The arsenals around a port usually had
a northern aspect, the heat being supposed to encourage the teredinos and other destructive
worms, and they were generally constructed of a material not likely to take fire. These
buildings were for the purpose of receiving the largest ships, which were drawn on shore,
and protected under them.
Naples is in 40° 50′ north latitude, and 14° 14' east longitude; this city is of Grecian
origin. Livy mentions it as joining with the inhabitants of Palæpolis and the Samnites

JUUULL
SCALE OF
FRET
100
6a0
Fig. 148.
NAPLES.
against the Roman power. It is situated in the bosom of a capacious bay, and the har-
bour is formed by a mole, built in two directions, having its lighthouse at the bend.
Within the mole, the ground is soft, being covered with three or four fathoms of water.
This city, from the number of its inhabitants and its beauty, has been styled the Queen of the
CHAP. IV.
139
ROMAN.
Mediterranean. Its position is in the form of an amphitheatre on the shores of a bay,
shut in by the Isle of Caprea, 17 miles distant to the south, and Procida and Ischia.
Vesuvius on the east may be seen, lifting its fire-scathed summit above the villages of
Portici and Torre del Greco, and on the other side is the grotto of Posilippo. The atmo-
sphere is usually bright and cloudless, and it was made by the wealthy Romans a most
delightful place of residence, the shores of its picturesque bay being covered with their
villas.
On our way from Naples to Pozzuoli, we find, on approaching the latter place, lofty
and precipitous cliffs of indurated tuff, between which and the sea lies a low level tract of
fertile land. This cliff, now far inland, may be seen opposite the island of Nisida, two miles
and a half south-east of Pozzuoli: pursuing our course northwards, we find the sloping
sides of Monte Barbaro, terminating also in an inland cliff, which indicates that the sea
once washed its base. Great has been the change to which this coast has been subjected;
and we have every evidence that the land has been both depressed and upheaved several
times the firm earth and the inconstant sea have frequently changed their relative positions.
The physical causes now in operation, as formerly, enable us to account for the situation of
cliffs where the sea has now retired, and for estuaries, where high tides once rose, being
silted up, and rendered dry land. The volcano and the earthquake on these shores have
effected, in the memory of history, wonderful changes: both, no doubt, have a common
origin; and they continue occasionally to shake the whole district around Vesuvius, to
alter the current and quality of the waters, and the character of the mineral substances that
come within their effects. In this neighbourhood is found the earth puzzolana, so valuable
to us as an hydraulic mortar, and which the ancients made so much use of in the formation
of their moles and breakwaters; they had only to cast it into the sea, between proper limits,
and an island was at once formed.
Cuma, Miseno, Baia, and Pozzuoli. These ports were at one time celebrated for their
commerce with the greater part of the habitable globe. Capua, one of the noblest and most
splendid cities of the Romans, surrounded by plains of great beauty and fertility, was supplied
with its merchandise and luxuries from the vessels which resorted to its coast.
Strabo, lib. v. cap. 4. mentions Cuma as a very ancient city, which, with its amphitheatre
was situated, at N, on a rock overlooking the sea. Miseno occupied the promontory at M,

CUMA.
N
M
H
E
Fig. 149.
CUMA, MISENO, BAIE, AND POZZJOLI.
and its port, which was double, F and G. The town and basin of Baiæ are shown at C,
whilst Pozzuoli stood on the outside of the bay, at H, and was joined to the castle at Baiæ
by the celebrated bridge, E, of Caligula. The lake Avernus, at A, communicated with another
port at Lucrinus, B, or Porto Guilio. The island of Nisida, at I, detached from the main
land, bounded the eastern part of this beautiful bay. Behind the promontory of Miseno, I,
140
BOOK 1.
HISTORY OF ENGINEERING.
lay a large lake, K, called Acherusia, which communicated by means of a canal with the seas
on the western coast.
Cuma was founded by a colony of Greeks from Chalcis in Euboea and from Cumæ
in Eolis: although it was the first Grecian establishment in Italy, for many centuries it
was the chief in power, opulence, and population. Its peculiar situation fitted it for
commerce, and its oracle, sibyl, and teinple, brought to it many votaries and visitors.
When Juvenal wrote, the neighbouring towns of Baia and Puteoli or Puzzuoli were pre-
ferred on account of their salubrity to the marshy district around Cumæ; soon afterwards
its population declined, and in the sixth century we read of it as a mere military post.
The ruins of the ancient city may yet be traced, in a solitary wood, which has grown up
over its once busy streets, where the wild boar is now sought and destroyed by the hunters,
this district forming part of the royal chase belonging to the king of Naples.
The Lake Fusaro, or the ancient Acherusia palus, situated on the south towards Misenus,
is a long and shallow piece of water, called by Strabo a muddy irruption of the sea;
there is a small island with the remains of a castle, and at the end of the lake is a pool,
called l'Aqua Morta.
Baia has a bay, in the form of an amphitheatre, and is situated on the western coast
opposite to Pozzuoli, from whence it is about three miles distant; ruins of Roman villas,
baths and temples, may be seen at the bottom of the sea, which indicate a much larger
extent at one period. Here the emperor Nero had a palace and splendid baths, which
Suetonius tells us contained a reservoir, in which the thermal waters of the surrounding
district were collected. Nero had intended that his palace should have extended over the
whole country lying between Lake Avernus and Misenus, a distance of at least three
miles and a half.
Portus Julius was formed by Augustus, for draining the Lake Avernus, and to admit
the waters of the ocean for the purpose of dispelling the noxious vapours that constantly
hung over the Infernal Basin. When this work was undertaken, the anger of the gods or
infernal divinities was supposed to be raised, and a violent tempest accompanied the descent
of the waters of the lake into the ocean, which was probably no more than the effect of
removing the barrier of earth which confined them, and kept them from flowing into
a lower level. After the waters had passed through the new port, the Lake Avernus was
stripped of its horrors; on the margin are many ruins; near the shore may be traced
those of an extensive mole, that appears to have formed an outer port, and may be a portion
of the harbour of Agrippa, mentioned both by Virgil and Horace.
The Lakes Avernus and Lucrinus being united, formed a most capacious harbour, and
beyond is pointed out some remains of a mole, now crossed by a road, said to have been
constructed by Hercules.
The Lucrine Lake is covered with rushes; the bottom was uplifted in the year 1538,
and now forms a conical hill, instead of deep water as formerly.
The Lake Avernus is about 1½ miles in circuit, surrounded by gardens and woods, and
bears no resemblance to the description left us by the poets.
Pozzuoli or Puteoli, a town of Greek origin, first called Dicæarchia, was erected by the
early settlers at Cuma; the Romans strongly fortified it about two centuries before the
Christian era, and made it a port of considerable importance. Its site, in the centre of a
fine bay, surrounded by lofty coasts, watered by rivers, cannot be surpassed for a commercial
port.
The Romans here purchased all that an extensive commerce with the east could procure
for them: it was injured by the earthquakes to which it was subject. In one of its squares
there still remains a pedestal in marble, on which is represented in bas-relief the fourteen cities
of Asia Minor, which were rebuilt by Tiberius after their destruction by an earthquake.
Behind the city, to the north-east, are the remains of its amphitheatre, and near the coast,
on the western side, those of the temple of Jupiter Serapis, near which are the ruins of the
famous mole that formed the port. Several of its piers remain sunk in deep water, which
supported the open arches, said to have formed a part of Caligula's celebrated bridge, which
extended from the port of Puteoli to Baix. But little reliance can be placed on this
statement, as in all probability the mad scheme of this emperor was nothing more than
a floating raft or bridge of boats, carried across the bay, in imitation of that constructed
by Xerxes. Seneca, Ep. 77. speaks of this mole or pila, and Strabo designates it as a
work carried out far into the sea, at which vessels of considerable burthen might with
great convenience discharge their cargoes.
Antoninus restored this splendid mole after it had received some damage; it had been
probably built long before, in the manner commonly practised by the Romans. It deserves
our attention, both for the economy evinced in the quantity of material employed, and for
the means it afforded of allowing a free current for the waters, consequently diminishing
the chance of the bay silting up. The great strength of this work, exposed at times to
a heavy sea, mainly depended upon the fine cement obtained on this coast, which when used
under water acquires the consistency and strength of marble.
CHAP. IV.
141
ROMAN.
In a picture found at Pompeii is the representation of one of these open moles with
seven arches, which allow the sea to pass freely under them; the upper part or road is

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A ALA
AR
DADO O O DOC
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Fig. 150.
ANCIENT port.
decorated with trophies. There is also shown an island with various buildings con-
structed on it, probably for the purpose of containing the stores required in the equipment
of vessels, or for the residence of the guardians of the port.
At the end of the fifteen arches of the mole at Pozzuoli was the light-
house, of which there are now no remains. In setting out the openings
or piers which sustained the arches, their span was made equal to their
depth, the piers being in width half as much more as that of the apertures;
thus great strength was obtained, and the force of the waves beating against
such a structure would lose a part of their power, being allowed a passage
through to the other side.
The section through one of the arches of this mole exhibits the portion
towards the sea, and by the side is shown the level at which the water
usually stood with reference to the arches, which were not semicircular.
The great distance that some of these open moles were continued into the
sea, where there was a considerable depth of water, would lead us to imagine

Fig. 151.
PLAN AND ELEVATION OF POZzuoli.
that the piers could not have been constructed without the aid of very strong cofferdams;
and we learn that such were used resembling ships, and sunk where the work was to be
executed. There can be no doubt that the Roman engineers were accustomed to drive
piles in deep water, as the descriptions left us of Cæsar's and Trajan's bridges fully
prove: to unite these piles as a barrier against the sea, and afterwards pump out the
water by the machines in use, would not be a difficult task: the tide in the Mediter-
ranean does not rise sufficiently to interrupt the progress of such undertakings, and
where the faces of the piers are worked in regular courses of masonry, no other
method could have been adopted: by heightening the sides of one of their large galleys,
a carpoon might be formed, in which they could pile up their material, and thus effect
their object.
142
Boox I.
HISTORY OF ENGINEERING.


Fig. 152.
MOLE.
SECTION.
The Island of Nisida, or Nesis, is situated at a small distance from the eastern promontory,
and on it is now placed the modern lazaretto to the Bay of Naples.
Misenus with its port occupied the opposite promontory or the western side of
the bay; among the ruins may be traced many hollows in the rock, which probably
served as docks for shipbuilding. The double port of Misenus had but one entrance,
guarded by a mole, in the usual manner of the Roman ports. Near this part of the coast
stood the mansion of Lucullus, afterwards occupied by Tiberius: the poet Phaedrus observes,
"that from its summit might be seen the shores of Sicily." Pliny the younger and his
mother resided here, near the sea, their house being separated from the water only by a
small court.
The Piscina mirabile, a vaulted edifice, divided by four rows of arcades, and situated
near the port, is supposed to have formed part of the great reservoirs constructed to retain
fresh water for the vessels that entered the harbour of Misenus, which lies immediately under
the hill on which it is constructed, and, according to Suetonius, it was one of the works
commenced by Nero. He alludes to it in the following quotation: "Inchoabat piscinam
a Miseno ad Avernum lacum, contectam ; porticibus conclusam, quo quidquid totis Baiis
calidarum esset converteretur."
The port of Misenus is protected by high lands on all sides, and its small haven is
always in a tranquil state: Augustus made it capable of retaining all his fleet. It is
separated from the Mare Morto by a narrow neck of land, through which was cut a canal,
crossed by a bridge, without interrupting the navigation into the inner port thus formed.
The mountains of Procida and Selvaggi afford a shelter from the north along the shores
extend the famous Elysian fields.
The mole at Misenus is a fine example of another system practised by the Romans; a
double range of arches is so set out, that the piers of one line are placed directly
opposite the opening of the others. The force of the waves and currents were by this
arrangement broken; at the same time there was no chance of any deposit being made
between the piers, or within the mole; and no method can be more economical or judicious.

ELEVATION,

Fig. 153.
I LAN.
I
[
OPEN MOLE.
Leghorn, in latitude 43° 35' north, and longitude 10° 16′ east, is a considerable sea-port
belonging to Tuscany. Its outer harbour is defended by a fine mole, half a mile in length,
thrown out in a north-north-west direction; and within the outer is an inner harbour, with
a depth of 8 feet water.
CHAP. IV.
143
ROMAN.
In the outer narbour the rise of the tides is estimated at 14 inches, and at the end of the
mole there is a depth of water of upwards of 18 feet.
South-west of the mole, on a rock, is constructed the lighthouse, which exhibits its light
at a height of 170 feet above the level of the sea.
This port was the ancient Livorno, Liburni portus, or Liburnum, and is situated opposite
the small island of Malora. The town is nearly square, and about 13,000 feet in circuit; the
mole is a favourite promenade, and from it may be seen the islands of Gorgona, Capraia,
and Corsica. The ships are moored beyond the mole, attached to large iron rings.
There are three lazarettos, an arsenal, and extensive warehouses.
The Bay of Spezzia, or Sinus Lunensis. This bay is one of the most magnificent in
Europe, and has a spring of fresh water in the centre; it is encircled by lofty mountains;
the Apennines approach the sea, towards Carrara, and adjoin the Alps beyond Genoa.

Fig. 154.
BAY OF SPEZZIA.
The ancient town of Luna, now called l'Erice, takes its name from Erycis Portus:
the beauty of the bay and the marble quarries in the neighbourhood are often described
by the Latin poets. Pliny, in his thirty-sixth book, giving an account of the various
marbles then in use, enumerates some of a white and sparkling quality, then recently
quarried about Luna. This marble was called lychnite, in consequence, Varro says, of
sparkling in the lamplight when hewed out of the quarry. At a later period, vast quantities
of Luna marble were shipped from this port, and the temples and other public buildings
at Rome were built with it.
From the rising ground around this port, Strabo, lib. v. cap. 3. informs us that the island
of Sardignia might be distinctly seen.
Genoa has a splendid harbour, formed artificially, by the construction of two moles; that
on the east side, called the old, projecting from the centre of the city, is 260 fathoms
in length; its direction is west by south, and near the middle is constructed a modern
battery. The new mole, on the opposite side of the port, projects from the shore 21C
fathoms in an east-south-east direction. The opening between these two moles, which
allows of the passage of ships into the harbour, is in width 350 fathoms. The harbour is in
form a half amphitheatre, its diameter being nearly 8000 fathoms; there are no diffi-
culties to encounter on entering it; and there is a good depth of water near the new mole,
where men of war and larger vessels may anchor at a little distance from the shore.
144
Воок І.
HISTORY OF ENGINEERING.
Within the outer harbour are two smaller, for galleys and merchant ships used by the
coasting trade.

PASSO DI STLAZARO
DORIA
DALACE
LIMBO
SCALO.ST
THOMASO
HARD
CLAY
ARSENAL
GARSINNE
PORSAGG
PONTE LEGN
PONTE SPINOLK
FONTE REAL
PORTA DELLA LANTERNA
LOOSE GROUND
MUD
PONTE DI MERÇANTK
PORTE FRAN
EN ANDRAGGI
OLD
MOLE
LANTERN
PASSO NUUVO
NE
MOLE
HTHOUSE POINT
AND
BATTERY
O.MALARA
ם ם
10000
0000
3003
品
​DONNA
›DI CARIGNANO
20
Fig. 155.
GENOA.
On the west side, without the harbour, on an extreme point of land, is the lighthouse,
a square building of many stories, based upon a rock, which may be seen at sea for many
miles.
The latitude of Genoa is 44° 45′ north, and the longitude 8° 50′ east, and its situation is
on the northern shores of the Mediterranean; the town is about 6 miles in circumfe-
rence, inclosed in a double rampart. By Strabo it was called the Emporium Totius
Liguria: it was at a very early time the chief city of the Ligurians; commerce then, as in
the latter period of its history, was always the favourite pursuit of its inhabitants; the nobles
in the middle ages were both its merchants and defenders, and in the twelfth century they
sent out a fleet consisting of twenty-eight galleys and six other vessels to assist in taking
Cesarea.
Venice, in north latitude 45° 25', and in east longitude 12° 20', is on the north-eastern
coast of Italy: it may be reckoned one of the earliest as well as the most considerable com-
mercial cities of modern Europe, having been established soon after Attila invaded Italy,
in the year 452. It is built upon a number of small islands, near the northern extremity
of the Adriatic Sea, or Gulph of Venice, and separated from the main land by a marshy
lake, about five miles in breadth and covered with water to the depth of 3 feet. A canal, 1200
yards in length, and about 100 feet in breadth, separates the city into two nearly equal
divisions; from this branch off many other canals, which are crossed by upwards of 500
bridges, most of them constructed of stone, and some of great beauty. The inhabitants
pass from house to house in gondolas or small boats, and the merchandise is landed at once
from the barge to the doorways of the warehouses. The Venetian ships of the largest
dimensions were called galeasses or argosies, some of which carried crews of 600 men,
and mounted 50 pieces of cannon; they must have entered many of the ports of England
at a very early period, for we find from our own records, that in the year 1325 they had a
charter, and full liberty to discharge their cargoes, and return in safety. There was a mag-
nificent arsenal situated near the eastern end of the city, defended by a rampart; and before
the entrance were the two lions in granite that once adorned the Piræus at Athens.
The houses are constructed both of brick and stone, and their foundations formed upon
piles; many are more than four stories in height. The bell tower or campanile is the
CHAP. IV.
145
ROMAN.
loftiest of the public buildings, its height being above 300 feet, and it does not exhibit any
settlement.
Ancona was founded by a colony from Syracuse, which settled there about 400 years before
Christ, and the Romans constituted it one of their principal naval stations on the shores of
the Adriatic.

+
-
Fig. 156.
ANCONA,
The emperor Trajan constructed the splendid mole which now remains, as well as the
fine triumphal arch which adorns it.
The mole, a solid mass of masonry, rises to a considerable height above the sea; the
stones that compose it are large, and cramped together firmly with iron; below it is another
mole with a triumphal arch, the work of Vanvitelli. At the extremity is the lighthouse, all
solidly constructed, and equally creditable to him as a civil engineer, as is the arrangement
of the lazaretto.
Antium was once a considerable port, the capital of the Volsci; it was greatly improved
in the time of Nero, and much resorted to by the opulent Romans, who had villas in the
neighbourhood. The road to it runs along the Alban hills, over the Campagna, and then
through a forest which for many miles borders the sea coast.

CAPE OF
ANTIUM
منية المتعلمنا بلدان
-COAST LINE IN 1700.
ANCIENT
COAST: LINE IN 1819
ADEM IN=1822
PORT
::::::::::::
MODERN PORT
PAMPHILE
MOLE
Fig. 157.
PRESENT state of ANTIUM.
The town of Meltuno may be the remains of this once famed port, which had two moles
stretching out into the sea, with a narrow entrance between; at the mouth was an artificial
L
146
BOOK I.
HISTORY OF ENGINEERING.
island, on which was erected the pharos. At the extremity of each of the moles was a
tower, in which was placed the machinery for extending a chain across the opening.

FETT
ל.
Fig. 158.
Nero's port at antium.
Tarentum consists of two ports, the outer called Mare Grande, the inner Mare Piccoli.
A bridge of seven arches unites the present city to the continent on the north side, through

R.LAVANDRA
R.CALERO
TARANTO
LAZZARETTO,VECCHIQ,
CAPUCCINI
MARE
PICCOLO
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CONVENTO.DI.STI.TERESA
IPS.PAULO
10.6.PIETRO
Fig. 159.
R. LUOGO.VIV
R.SAVERN
PULSANO
VILLA NOVA
SATURO
CIARDINODI
S.ERANCISCO
ORRE.DI.SATURO
LE. VIGN
T.DĮ. S. FRANCESCO
TORRE DELLAT
T.DI.TRAMONTANU
APS.VITO.CON.TORRE
TARENTUM.
which the sea flows with great impetuosity; this formerly was the entrance into the harbour,
which will now only admit small boats. In the time of the Romans there were drawbridges,
to enable the military in the citadel to command the inner port. The enemy's fleet in the
second Punic war was so completely blocked up within it, that it could not regain the
sea.
Between the arches of the bridge was a wooden frame, to which nets were attached for
CHAP. IV.
147
ROMAN.
catching fish, and the aqueduct that still supplies the town passes over it; it was built
about 1543. The water is brought from the mountains of Martina, a distance of 14 niles,
where, after being collected into reservoirs, it was led under ground to deep cisterns at Tre-
miti. At La Follia it pursues an open course for 7 miles, then passes an aqueduct con-
structed over 203 arches, then through channelled stones fitted one into the other.
Tarentum has preserved but little of its Grecian foundation, and none of the ancient
walls that enclosed it; fragments of Etruscan vases have been discovered in all directions.
Of the temples, gymnasia, theatres, and other splendid monuments, nothing now remains,
not so much as a single column, to tell us where the city stood.
The moles which protected and shut in these ports were constructed with massive
masonry, and with piers and open arches. That portion which was solid was carried
out progressively, until the arms were completed; these arms were called left and right, and
are described by Suetonius as well as Pliny, in their accounts of the ports of Ostia and
Centocelli. That part between the ends of the two moles was called the mouth, and that
between the island and the moles the jaws or fauces.
Brundusium. Though there is now but little remaining of this once extensive city, the
port, which is double, was reckoned one of the finest in the Adriatic Sea. The outer was
formed by two promontories, which as they advance leave a narrow channel between them.
At the mouth lies an island now called St. Andrew's, which secures the whole from the
violence of the sea. At the bottom of the bay the hills recede in a circle, and form the

ELIGOLO
C CALLDE OTOR DEL PENNA
Fig. 160.
BRUNDUSIUM.
CASTELLO
ORT DEL MARE
TELKOT
TERRA
ÖNVENTO DI
CAPPOCCINI
FIUME
PIL
FIUME
GRANDE
inner harbour, which is 24 miles in length, and 1200 feet in breadth, encompassing a
great part of the city, which has somewhat the form of a stag's head and horns; in the old
Messapian language, the head of a deer being called brundusium.
There is a fine soil, depth of water, and safe anchorage; and the destruction of this place
as a port may be partly owing to the silting up of the channel between the two havens,
which was probably caused when Cæsar attempted to block up Pompey's fleet, by driving
piles into the neck of land between the two ridges of hills, and throwing in earth, trees, and
ruins of houses. When Don Vito Caravelli was employed, at the latter end of the last
century, to improve this port, in deepening the channel, he found several medals, and had
many of the piles which were driven in by Cæsar drawn up: they were small oaks stripped
of their bark, and at that time quite sound.
Cæsar's description of what he did at Brundusium on this occasion is interesting: he
states, as the work could not be carried quite across the port, in consequence of the sea's
depth, he prepared double floats of timber, 30 feet square, which were secured by an anchor
at each corner; these extended to two moles, which he threw up, one on each side the
haven, where the entrance was the narrowest and the water shallow. After the rafts were
securely moored, he covered them with earth and fascines, and made them sufficiently strong
for his legions to pass over with ease, and also have firm footing to defend them. The fronts
and sides of these rafts were protected by parapets or hurdles, and every fourth float had a
tower of four stories constructed on it, the better to guard the work from fire, and protect it
from the boats which might be sent against it.
L 2
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Book I.
HISTORY OF ENGINEERING.
Pompey made use of several ships which were in the port, and fitted upon them towers
of three stories in height, which he filled with engines and darts, and then sent them down
to break through the floats which Cæsar had contrived, and destroy his works: in this,
however, he did not succeed; but before Cæsar had quite completed his blockade, Pompey
found means to embark on board his ships and effect his escape.
Roads. The immense extent of roads constructed by the Romans, their duration and
stability, the obstacles which they surmounted in carrying them over marshes, lakes, and
mountains, have, in all ages, excited astonishment and admiration. Twenty-nine great mili-
tary roads centred in Rome, some of which were carried to the extreme points of the vast
empire. For fifty miles' distance from the capitol, each side was decorated with temples,
baths, hippodromes, tombs, and superb edifices. Buildings used for lodging-houses and for
changing horses were erected at the public cost, at regular distances; and at these several
posts, were maintained relays of horses for the couriers, as well as mules, asses, oxen, and
carriages for the transport of the materials for the army, and mansiones for the lodging of
the soldiers were constructed at distances from 30 to 36 miles.
The whole Roman empire comprised eleven regions, viz. Italy, Spain, Gaul, British Isles,
Illyria, Thrace, Asia Minor, Pontus, the East, Egypt, and Africa, and these were divided
into 113 provinces, traversed by 372 great roads, which, according to the Itinerary of
Antoninus, were together in length 52,964 Roman miles.
Under the kings there were no paved roads, and the first seems to have been commenced
by Appius Claudius, about 442 years after the founding of Rome, whilst he held the office
of censor; this was not only the earliest but the best constructed; and Statius the poet
designates it as the Queen of Roads in his time. Appius Claudius was honoured with
the highest offices which the republic could bestow; he was censor, twice consul, prætor,
curule edile, and lastly dictator, when he conquered the Sabines, and obtained several
victories over them and the Etruscans; after which he erected the temple of Bellona.
The celebrated road, or Appian Way, is mentioned in a variety of inscriptions, and by
most of the ancient authors: Procopius, in his "de Bello Gothico,” says that its length was
so great that it could not be passed by a traveller going at a swift pace in less than five
days; that its breadth was sufficient to allow two chariots to pass without inconvenience,
and that it was paved with large blocks of stone, brought from distant quarries, dressed
and squared with the chisel, and joined very exactly without the aid of metal or any other
material; the work was so perfect, that it seemed as if nature had performed it rather than
man, for the very joints were hardly perceptible. Whether the whole way from Rome to
Brundusium was executed by Appius is doubtful, and it is less certain that it was paved
by him the whole length; the probability is, that his way terminated at Capua.
Strabo, describing Terracina as situated near the shore of the Tyrrhenian Sea, proves that
the paved Appian Way approached it, and Horace, in his Journey to Brundusium, describes
it as paved throughout.
The road from Capua to Brundusium is longer than the portion from Rome to Capua,
and the whole was, according to Strabo, 360 miles in length: that Appius Claudius only
conducted it to Capua, a distance of about 142 Italian miles, is most probable, as
in his time the provinces beyond were not under the dominion of the Romans. It is
difficult to say at what time the latter portion of the work was completed, which it
evidently was before the time of Augustus. Plutarch observes that Julius Cæsar was
appointed commissary of the Appian Way, and that he expended large sums of money
upon it, and to him probably may be attributed its termination.
Quitting Rome the first station on the Appian Way was distant sixteen miles, at Ariciam;
from thence seventeen miles to Tres Taburnæ; eighteen miles to Appii Forum; eighteen
miles to Terracina; sixteen miles to Fundi; thirteen miles to Formiæ; nine miles to
Minturnæ; nine miles to Sinuessa, and twenty-six to Capua; in all 142 miles: and this is
the distance Procopius imagines could be accomplished in five days by an expeditious
traveller.
From Capua to Equotuticum, "ubi campania limitum habet," was a distance of fifty-three
miles, viz. to Caudium twenty-one miles; Beneventum eleven miles, and Equotuticum
twenty-one miles.
From Equotuticum to Hydruntum, where they embarked, was another 235 miles; viz.
to Eeas eighteen miles; to Erdonias nineteen miles; Canusium twenty-six miles; Rubas
twenty-three miles; Bruduntum eleven miles; Barium twelve miles; Turres twenty-one
miles; Egnatiam sixteen miles; Speluncas twenty miles; Brundusium nineteen miles;
Lupias twenty-five miles; and Hydruntum twenty-five miles.
The Domitian Way commenced at Sinuessa, and branched out of the Appian Way,
continuing its course along the sea-shore, crossing the rivers Savo and Volturnus, skirting
Mount Gaunus, and Massicus, fertile in wine; continuing its direction through the marshes
of Linturna, and between the Lakes Avernus and Acherusia, passing by Cumæ, ter-
minated at Pozzuoli,
Strabo, in speaking of these three excellent roads, places first the Appian, which he
CHAP. IV.
ROMAN.
149
describes as far as Sinuesša; Dion carries it beyond: and afterwards says that it united the
seven hills of Rome with Baiæ.
The Domitian Way, though of no very great extent, was of the greatest use, as it
enabled travellers to pass marshes and quicksands, by means of bridges and causeways
constructed at a vast expense. In many portions masses of concrete were thrown into
swampy places, and the distances formerly passed greatly shortened. All the long detours
were avoided, and Statius tells us that a triumphal arch was raised to Domitian by the
senate and Roman people, in gratitude for the benefits bestowed upon them by this work.
The public roads, among the works of Roman magnificence, ranked preeminently high;
vast labour and expense were bestowed upon them, and their construction, as we now
behold them, seems to have been intended to outlast their empire. Such arteries, as they
were termed, which conducted to the heart of the imperial city, were not thought un-
worthy of the attention of the greatest men of the republic; none but those of the highest
rank were even eligible to the office of superintending them, and during the empire
Augustus himself took charge of them. The Romans, however, notwithstanding the good-
ness of their roads, were not very fast travellers, for Augustus, when he went to Præneste,
a distance of only twenty-five miles, usually halted for the night about half-way. And
Horace tells us that he performed his journey to Brundusium, which was distant about
forty-three miles, in the same time, but he observes that an expeditious traveller could
perform the journey in a day.
Among the Romans the various roads were distinguished by the names Via, Actus, Iter,
Semita, Trames, Diverticulum, Divertium, Callais, &c.
Via, answers to our common roads; its breadth was 8 Roman feet, so that carriages could
pass without collision.
Actus, was a road for the passage of a single carriage; it derived its name from a measure
used in surveying land, of which the breadth was 4 feet, and the length 120.
Iter, was a road for pedestrians and horsemen, the breadth of which was 3 feet.
Semita, was only half the breadth of the Iter, and when it crossed fields it was called
Trames, Diverticulum, and Divertium.
Callais, was a road through mountainous districts, for the purpose of attending the
flocks.
These roads, peculiarly adapted for civil purposes, united with other great lines,
which traversed the numerous provinces of the empire, which were called military,
consular, or prætorian, or were named after the consuls and emperors who had con-
structed them, as the Appian, Flaminian, and Domitian; they were sometimes designated

Fig. 161.
ROAD WITH MARGINES.
by the names of the provinces, as the Latian, Tiburtine, Campanian, and Prænestine ways.
The great military roads were divided into three distinct parts; that in the middle was
the most elevated, and called agger, and had a convex form or curve; this was usually
paved with large stones of various shapes.
Most of the roads in the neighbourhood of Rome, as the Appian, Latian, Labicum,
Tiburtine, and the Prænestine, had the paved part 16 Roman feet in width, or 15 feet 6 inches
English; this portion was separated from the two sides, called margines, by a curb, 2 feet
wide and 18 inches high, which served as seats for travellers.
The middle portion was destined for the infantry, and the margines for horses and
carriages: the breadth of each margin was half that of the road in the middle, so that the
entire breadth of these military ways was from 36 to 40 Roman feet.
The streets in the towns were sometimes called Via Militaris, as were the chief of those
in Rome, which were the commencement of the great roads; under these were constructed
L 3
150
HISTORY OF ENGINEERING.
Book I.
vast sewers, which, according to Pliny, ranked among the greatest works ever undertaken.
The subterranean fosses, or continued bridges of great length and breadth, sustained
enormous weights, as columns, obelisks, and other pieces of stone, daily passing over
them. Pliny relates that when M. Scaurus wished to transport 360 marble columns,
each 38 feet long, from the place where they had been used, in his theatre, to the Palatine
Mount, the inspectors of the sewers demanded some security to repair any damage
which might occur. After Scaurus had completed his house, the sewers were examined,
and found not to have sustained any injury; they formed a portion of the roads under

CARRIAGe road.
Fig. 162.
which they passed, and were intended not only to effectually drain all that might be injurious
to health and cleanliness, but also to afford a better foundation.
Over these vaults was laid a bed, on which rested the materials forming the road, which
was paved in the same manner as the bridges.
In Rome there were 31 principal streets, and about 422 lesser. According to
Pancerolus, one is mentioned as made by Heliogabalus from his palace, called Plateas
Antoninianas, which was paved with stone or marble from Lacedæmon, of a beautiful
green colour, mixed with porphyry.
The Materials used by the Romans for road-making were of two kinds; the stones which
formed the mass, and the cement which united them. According to Vitruvius, there were
three sorts of stone quarried, of different degrees of hardness. The soft, when first taken
from the quarry, was easily cut and rendered useful for building purposes, and when
protected from the weather, and not in contact with the ground, had considerable dura-
bility.

That stone which sustained weight, and
the action of frost, without splitting, was
mostly used on the great roads, and was
called Saxum or Silex.
In the formation of their roads, the Ro-
mans used every kind of stone that could
conveniently be obtained; after the line was
set out, excavations were made at the
sides, from whence was extracted any ma-
terial that was serviceable; and, establish-
ing a solid and durable bed, by closing the
ground with iron rammers made for the
purpose, they spread the different strata
which composed the area or mass of the
road. These were called statumen, rudus,
nucleus, and summa crusta, which to-
gether were in thickness about 3 feet.
In the great military roads, the statumen
or lowest bed was formed of two courses
of flat stones laid in mortar: over this was
the rudus, or rubble, well beaten; then
the third layer, called the nucleus, a sort
of beton, was spread; this was formed of
coarse gravel and lime, used hot; on this
was bedded the summa crusta.
Fig. 163.
SECTION.
PLAN.
A

When the road was carried over marshy
districts, a framework of carpentry was provided, called "contignata pavimenta," and the
CHAP. IV.
151
ROMAN.
frame itself contignationes. The joists or sleepers were termed coaxationes or cassationes,
and were made of an oak called esculus, because it was not subject to warp or shrink.
To protect this timber from the effect of the lime mixed with the other materials, they
covered it with a bed of rushes or reeds, and sometimes straw. On this stratum of reeds
or straw was laid the statumen or foundation.
The second bed was made of broken stones mixed with lime, which Isidore calls rudus.
When this material was composed of stones freshly broken, it was called rudus novum; to
three-fourths was added one-fourth of quick-lime. But when the material came from
old buildings, it was called rudus redivivum, and then an additional portion of lime was
used, two parts to five, and the work termed ruderationem; the rammer or beater was
employed to strengthen, equalise, and smooth it. This composition, whether formed of
gravel or debris, was 9 inches in thickness after it was thoroughly rammed. Over this
tarras or ruderation, a cement was laid for the third bed, composed of brick, potsherds,
broken tiles mixed with lime, using one of lime to three of brick. This was spread over
the ruderation in a thin layer, to receive the fourth bed or paving, which served as a
covering to the entire work, and was called in consequence summam crustam. The
third bed or nucleus was the softest layer of the whole, interposed between what was harder.
The stones and cement which formed the road were not less than 6 inches in thickness,
and the entire mass laid upon the framework of carpentry was 15 inches.
The unpaved roads of the Romans were called by Ulpian vias terrenas, to distinguish
them from those dressed with stone or gravel; and they were regulated by similar laws
and ordinances as the others. The road from Spain into Italy, through Nismes, was
of this kind, and only passable during the summer months. In the winter and spring, it
was in a soft state, from the water which came down from the neighbouring mountains,
though Strabo mentions several wooden and stone bridges and ferries.
These roads, so liable to be broken up by the torrents, were exposed to the action of
the sun and wind, all shade being removed, that they might speedily dry.
Appian Way, or road to Capua, a distance of 120 miles, was paved with polygons of lava.
In A.U.C. 451, the first mile, from the Porta Capena to the temple of Mars, was paved as a
way for walking and riding on horseback (semita), with hewn stones (pepperino); and in
A. U. C. 453, the whole road was paved with lava as far as Bovillæ. (Livy x. 23. 47.) Semita,
signifies without any reference to width, a cordonata, or a road up-hill, made with sunken
broad and low steps, where sumpter cattle walk safely and comfortably; carriages, if at all,
can only come down: clivus is a carriage road. A well-known inscription tells us, that there

Fig. 164.
APPIAN WAY.
was a clivus on the Appian road, near the temple of Mars, by the side of which the semita
now necessarily assumed the form of a cordonata.
The Alta Semita, which led from the Subura along St. Agata to the Quirinal Hill, was
such as the locality clearly shows. We find, in the gates of the so-called Cyclopean
towns, Roman or Latin cordonatas, constructed entirely on the same plan as in the present
day.
The Appian Way is remarkable for its foundations, its constructions over deep valleys
L 4
152
BOOK I.
HISTORY OF ENGINEERING.
and hills, its bridges, and for the canal which accompanies it through the Pontine marshes,
for the double object of draining the land and conveying the material of war from Latium
to Terracina; this was important to a state not master of the sea.
The Setian was the military road to Campania from Velitræ to Terracina. To reach
Terracina in one march from Cisterna would be impossible in summer; to encamp
between the two places in the latter season and autumn would be fatal, in the rainy
seasons equally impossible; in the hot months, one single night spent by an army in the
neighbourhood of Cisterna would produce fever.
Forum Appii on the canal was also built by Appius Claudius.
The Pontine marshes were in all probability originally a bay behind the downs on the
sea-coast; when this became filled with mud, by the river flowing into it, a marsh was
slowly but gradually raised.
·
Prænestine Way. Where this magnificent road crosses the low marshy ground, con-
structions of the most solid kind were made, with arches turned in a symmetrical and perfect
manner, rivalling the aqueducts for their beauty. The spandrills were filled in with rubble,

Fig. 165.
VIAS TERRENAS ON THE PRÆNESTINE WAY.
and walls were carried on it, for the support of the level road above; the direction of this
road is given in most of the Itineraries, and a description of the several statues which were
situated upon it.

Fig. 166.
PRÆNESTINE WAY.
The Bridges of the Romans are remarkable for their solidity, and for the almost universal
adoption of the semicircular arch; the stone used in their construction is the hardest that
the neighbourhood afforded; many have stood the force of violent torrents, and at the pre-
sent day exhibit their original design, whilst others have undergone such changes, that
their primitive features can scarcely be discerned.
One peculiar feature of Roman arches of great dimensions, and particularly of their bridges,
is the leaving a projecting stone on each side, at about thirty degrees above the spring-
ing, upon which their centres were strutted, consisting of a longitudinal piece of timber,
with inclined and perpendicular supports. Vitruvius, in lib. vi. cap. 11., observes that care
CHAP. IV.
153
ROMAN
should be taken to discharge the weight of walls by arches consisting of wedges concen-
trically arranged; and further "that on buildings which are constructed on piers and
arches, with wedges whose joints are concentric, the abutments should be wider than the
piers, that they may have more power to resist the action of the wedges, which, when
loaded, press towards the centre, and have a tendency to thrust them out." No particular
rules are laid down for their proportion, which was probably left to the judgment and ex-
perience of the engineer. There is seldom much depth given to the voussoirs, which are of
equal thickness throughout; and when the semicircle was complete, the spandrills were
filled in with a concrete or rubble, which has hardened into a solid mass.
The Pons Milvius, or Emilius, two miles from Rome, on the Flaminian Way, consisting
of four large arches and two smaller, has been altered at various times.
The masonry

es
Fig. 167.
PONS MILVIUS.
of the arches and tower at the extremity, as shown in the figure, with the openings in the
piers, are said to remain as they were when Constantine pursued Maxentius, as he attempted
to escape into the city, after his terrible defeat: being, however, pressed by the crowds who
were flying to the narrow pass, he was forced into the water, and his body, weighed down
by his massive armour, was afterwards found in the bed of the river. The arches vary in
their opening from 51 to 79 feet 9 inches, but the whole of the water-way is in the clear
413 feet 3 inches; the breadth of the bridge is 28 feet 9 inches.
Pope Nicolas V. made some alterations in this bridge, and Piranesi, who has given
an account of the change it then underwent, describes the two arches nearest the city
as the most ancient: when the writer was at Rome, it was repaired under the direction
of Valadier, who recased the ruined tower at the extremity, and gave it the character of a

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Fig. 168.
PONS MILVIUS.
154
BOOK I
HISTORY OF ENGINEERING.
modern fortress. The views representing this bridge show the various alterations that
have been made in it, and will enable the reader to form some idea of its construction.

آپ کے
Fig. 169.
PONS MILVIUS.
Pontus Salarius, Ponte Salaro, on the Teverone, is composed of three semicircular
arches, 54 feet 6 inches to 69 feet span, and of two smaller arches, of 22 feet 4 inches span.
It was built by Tarquinius Priscus 600 years, and restored by Justinian 570 years before
Christ. The breadth is 29 feet: the stones which form the arches are large. It was near
this bridge Manlius Torquatus took the collar of gold from the Gaul.
Ponte Rotto or Senatorius, on the Tiber, was the first stone bridge erected in the
city; another was built on its site, at the time Fulvius was censor, which was completed
by Scipio Africanus, and lasted till 1364. It was entirely rebuilt, in the year 1575, by
Gregory XIII., and was nearly destroyed twenty-three years after by a flood; at present
only one arch remains, to exhibit its former magnificence: the piers are ornamented with
lions' heads holding a metal ring, and they have niches adorned by columns; the arch is
composed of one row of voussoirs, of equal thickness, accompanied by an archivolt, the
mouldings of which follow the curve: it is also decorated with the sculpture of two
marine horses, admirably executed; the span of the arch is 80 feet, and the breadth 42 feet
8 inches.
Seven bridges formerly conducted over the Tiber to the Janiculum and Vatican Mount:
these were, the Pons Sublicius, afterwards called Æmilius, built, as its name implies, of
wood, and erected by Ancus Martius, according to Livy; this bridge stood between the
Aventine and the Ripa Grande, where the foundation of one of its abutments remains.
Pons Palatinus, or Senatorius, now Ponte Rotto; the Pons Fabricius, now Ponte de
Quattro Capi, from a thermæ with four faces placed on it; Pons Cestius, now Ponte di
San Bartolomeo; Pons Junicularis, of which there are no remains, though the Ponte Sisto
occupies its site. Pons Triumphalis, opposite the hospital of Spirito Santo, has a vestige
remaining, and here passed into the Campus Martius the victorious consuls to whom the
senate decreed triumphal honours, followed by their soldiers, captives, and spoils: after
entering the Porta Triumphalis, they passed the circus of Flora and Flaminius, the
theatres of Pompey and Marcellus, the portico of Octavia, and the Circus Maximus, tra-
versed the Via Triumphalis, entered the Via Sacra, passed between the Coliseum and
temple of Venus and Rome, crossed the Roman Forum, and halted at the temple of Capi-
tolinus.
The Pons Elius, or Ponte San Angelo, the ancient piers of which remain, was the
seventh bridge over the Tiber, which, a few miles above Rome to the sea, is in width about
300 feet on an average, therefore not difficult to span by a bridge. Its banks above and
below the imperial city, once adorned by graves and gardens, in which were the villas of
the wealthier Romans, as well as the villages and palaces on its meandering banks, are now
only traceable in their ruins. “Deo gratissimus amnis," the distinguished Tiber, has been
so woven into the recollections of the classic traveller, that it can never be forgotten.
CHAP. IV.
155
ROMAN.
Ponte Sulara, on the Anio, consists of one large arch, nearly semicircular, 95 feet 9
inches span, and two lesser openings. The date of its construction is not ascertained.

Fig. 170.
ртут
PONTUS SALARA.
mess
The Bridge Nomentano, over the Anio or Teverone, near Mons Sacer, so celebrated as the
spot where Menenius Agrippa met the plebeians, and told them the story of the belly
and members; the consequence of their disagreement he likened to the dissension of the

Fig. 171.
101 101
馬刀
​PONTUS NOMENTANO.
156
HISTORY OF ENGINEERING.
BOOK I.
commons and the patricians, and by this fable won over the people from their attempts to put
the consuls to death. The stone arch, a part of the ancient bridge, now sustains a tower,
constructed probably in the fifth or sixth century, which has undergone several changes
during the middle ages, when it was used as a fortress: in its present state it is a very
picturesque object. Many of the Roman bridges had towers either on them, or at their
extremities, encircled with battlements, which served to defend the passage, as also to
collect their dues.
It is to be regretted that Vitruvius has not left an account of the manner of building
bridges in his time, or that he should not in the slightest degree have alluded to the
subject: all that we know of them is by studying the numerous remains which span the
rivers of Europe, where the great roads required them. The vaults are worked much
in the same manner as those of the triumphal arches: large blocks were generally selected,
and truly cut; one course of deep voussoirs supported a mass of rubble, on which the road-
way was laid; precautions were also taken to defend the piers, and to carry off the water
from the road, by means of pipes and drains. All the refinement adopted by modern
constructors is traceable to the examples left us by the Romans, and we cannot too highly
prize their design, and economical use of material: solid stone was employed where
necessary, with a filling in of concrete equally durable, resisting in many instances all the
efforts of time and weather.
Pons Juniculum or Ponte Sisto has been several times rebuilt; the present was executed
in the time of Sixtus IV., in 1478. It is composed of four arches, from 53 feet to 70 feet
span in the distance is seen the Farnese palace.

ичи
Fig. 172.
PONTE SISTO.
Pons Fabricius, and Pons Cestius.
These bridges, now called Ponte Quatro Capi and
Ponte Ferrato, are situate at Rome, on the two arms of the Tiber, which surround the

Fig. 173.
奶
​PONS FABRICIUS AND CESTIUS.
CHAP. IV.
157
ROMAN.
island of St. Bartholomew. The first was repaired in 1680, by Pope Innocent XI. ; the
second, in 380, by the emperors Valens and Valentinian. The Pons Cestius consists of
a single arch, 78 feet 9 inches span: the width is 49 feet 3 inches; the two arches of the
Pons Fabricius are 82 feet span. In the pier which separates them is a passage
accompanied with pilasters: the cornice which surmounts the bridge is ornamented with
mutules; the breadth is 49 feet 3 inches. The Ponte Rotto, in its present state, occupies the
left of the view.
These two bridges were founded, it is said, on a bad soil, by means of a mass of masonry,
consisting of right and inverted arches, carefully cut in freestone. Piranesi gives the
details of this remarkable construction, but does not pretend to guarantee its authenticity.
Bridge at Rimini, built by Augustus, was regarded by Palladio as the finest he had
seen, and most of his designs are copies of it. It consists of five semicircular arches; the
two outer are 23 feet 5 inches span, the three intermediate 28 feet 9 inches. The thickness
of the piers is nearly equal to half the void of the arches; they are formed by a pedestal
rising 13 feet 1 inch above the water; this is surmounted by niches, accompanied by
columns which support an entablature; the cornice which crowns the bridge is sustained
by modillions in very good taste.
Bridge of St. Angelo. This splendid monument, which formerly bore the name of Pons
Ælius, from the prænomen of Hadrian, was constructed by him in a. D. 138, opposite the tomb
which he had erected. The piers were surmounted by eight colossal columns bearing
bronze statues; these columns were destroyed during the troubles in Italy, when a great
crowd occasioned by the procession of the jubilee thrust the parapets into the Tiber: Pope

紅茶
​Fig. 174.
Bridge oF ST. ANGELO.
Clement IX. restored them in 1668, according to Bernini's designs. It was then decorated
with pedestals of white marble, bearing ten colossal statues of angels. The semicircular
arches, from 26 feet 3 inches to 62 feet 4 inches span, have archivolts around them :
they form a water-way of 370 feet 7 inches. The breadth of the bridge is 50 feet 9 inches.
Pons Mammea, on the Teverone, four miles from Rome, consists of three arches, 53 feet
2 inches and 64 feet span. It was erected by Antoninus Pius, about A. D. 147, and restored
in 229 by Mammea, mother of Alexander Severus, whose name it bears. The centre arch
is ornamented with a Roman eagle holding a thunderbolt in his claws, surrounded by a
laurel crown. The cornice is sustained by large consoles; the breadth of the arch is 29 feet
3 inches.
The Berghette Bridge, on the Tiber, consists of three arches, 83 feet 4 inches span. The
upper part of the piers is pierced, and presents semicircular arcades.
Bridge on the Bachiglione, near Vicenza, consists of three arches, one of which is 68 feet
11 inches, and the two others 55 feet 5 inches; it is one of the finest bridges in Italy.
The piers are decorated with niches containing statues, and two composite columns, which
158
Book 1.
HISTORY OF ENGINEERING.
are surmounted by an entablature. The cornice, level over the centre arch, and inclined
over the two others, is sustained by strong modillions. The breadth is 55 feet 9 inches.
Ancient bridge at Vicenza, has been described by Palladio: the centre arch, 34 feet
8 inches span, is very ancient; the two others are modern, their span is 25 feet 11
inches. The width of the piers is 5 feet 9 inches; that of the bridge, 27 feet 7 inches.
The versed sine of the arcs of which the arches consist is two-thirds of their diameter.
They are adorned with archivolts: the cornice is sustained by modillions.
Pilantio Bridge, over the Teverone, near Rome, on the road to Tivoli, is composed of
three arches, arcs of circles. The thickness of the piers is one-fourth the span of the
arches, they have no starlings. It is constructed with very large stones; the total length
is 170 feet 8 inches.
Bridge and Aqueduct of Spoleto, was built near the town which bears that name, in a. n.
741, by Theodoric king of the Goths. It consists of ten large Gothic arches, each 70 feet
3 inches in span, and sustained by piers 11 feet 10 inches thick. The centre arches over
the river Moragia are above 328 feet in height. The others are much lower, the two
slopes on which they are built being very steep. At the upper side of the bridge, thirty
small Gothic arcades sustain an aqueduct, serving to convey water into the town.
monument, of a very bold execution, and built of small hard stones, remains entire, and
still conveys water to Spoleto. The total length is 810 feet 5 inches, the breadth 42 feet
8 inches.
This
Bridge and Aqueduct of Civita Castellana. This work is part of a causeway, constructed
about 400 years B. C., to approach Castellana, 820 feet long, 33 feet wide, and 128 feet
high, pierced in the centre by nine great arches loaded with about 13 feet of earth.
The three centre arches are 87 feet 3 inches in span, the others 63 feet 11 inches. Some of
the piers are strengthened by counterforts, and others by flying buttresses with a detached
base.
Bridge on the Cremera, at Civita Castellana. This bridge, celebrated as the place where
the Veii gained an advantage over the Fabii, B. c. 447, is constructed of brick, stone, and
marble. It consists of three arches, the centre is 74 feet 5 inches span, and the two others
50 feet 2 inches; the breadth is 34 feet 2 inches. The foundation is established on a radier
or timber platform, on account of the instability of the soil, on which are inverted arches of
the same span as those of the bridge.
Trajan's Bridge over the Danube. This colossal work, the most magnificent in Europe,
was built under Trajan by Apollodorus, his architect, about A.D. 120. The rapidity and
depth of the current in the place where it is situated added to the difficulties of the work:
a general foundation was constructed by means of large barges filled with stones, lime, and
sand, sunk at the bottom of the river; sacks of different sizes were thrown into the
interstices, filled with the same materials. On this base the piers were established. The
bridge consisted of twenty semicircular arches, 180 feet 5 inches span.
Their springings
were raised 46 feet above the general level of the river; the thickness of the piers was
64 feet, they were 85 feet 3 inches wide; the stones used were enormous, but it was de-
stroyed a short time after its construction. Some of the piers are still to be seen with the
springings of the arches which they supported.
M. de Marsigli, in his work on the Danube, charges Dion Cassius with having asserted
that the arches of Trajan's bridge were of stone, and says that they are representea as wood
on the bas-reliefs of Trajan's Column.
Bridge near Terni, on the Nera, whose ruins still exist, consisted of seventeen arches,
131 feet 3 inches span; its piers were 27 feet 6 inches thick, and 111 feet 6 inches to the
springing its total length was 2592 feet, and its width 32 feet.
:
It was constructed of
large blocks of stone, and the piers had no starlings; the foundation of intermediate piers
may be seen, which divided the opening of each arch into three parts, intended
probably to support the centres during the construction of the vault, and afterwards
demolished. The bridge has no parapets, and in their place are white marble blocks,
between which chains are suspended as guards.
Bridge of Capo Dorso, believed to have been built in Sicily by the Romans, consists of
one semicircular arch 96 feet span. Its small width may cause us to doubt its Roman
construction, being only 17 feet.
The Bridge de Boisseron, upon the Domitian Way, near Nismes, said to have been con-
structed by C. Domitius Ænobarbus, has five semicircular arches; the centre spans 30 feet
9 inches, the two contiguous 28 feet 9 inches, and the others at the extremities 19 feet 6
inches; the piers are 9 feet 4 inches; the entire width of the bridge, 11 feet 6 inches.
All the arches spring from the same level, consequently the roadway and parapets incline
from the centre. The piers between the springing of the arches are perforated, to afford
more water-way, and to prevent too great a pressure at the time of floods.
In this bridge the projecting voussoirs, on which the timbers, struts, or centres, were
supported at the time of its construction still remain; in almost all the examples where
hard stone was used for the turning an arch, these projecting blocks are to be seen, as in the
CHAP. IV.
159
ROMAN.
Pont du Gard. Few works have undergone less change than the Bridge of Boisseron, or
retains more of the primitive character.


Fig. 175.
NN
BOISSERON.
NN
INN
The Bridge of Sommieres, over the Vidourle, a short distance from Nismes, consists or
seventeen arches, all semicircular, built with a durable stone from the quarries of Pondres,
situated near the city. All the stones which form the level courses are dressed with
great care, and their horizontal and vertical joints worked with precision, little mortar
being used; they appear to have been first bedded, then run with a fine cement or liquid
mortar.


Fig. 176.
SOMMIERES.
The middle arch spans 32 feet, the others 30 feet, and the piers are 10 feet; the whole
length of this fine remain is 620 feet, and the entire width from face to face 22 feet 2
inches.
The Bridge of Ambrussum, upon the Domitian Way, over the Vidourle near Nismes, was
constructed by Augustus about four years before the commencement of the christian era.

Fig. 177.
AMBRUSSUM.
It seems to have resembled in workmanship that at Boisseron. The arches, formed of four
circles of voussoirs, are all destroyed excepting two, which remain in the middle of the
stream.
The Triumphal Bridge of St. Chamas, over the small rivers called Tolubre, has an arch
at each extremity, a perfect and unique example of this kind of bridge. It was built
by Augustus, or in his time, as an inscription on the frieze indicates.
L. DONNIUS. C. FLAVOS. FLAMEN. ROMÆ. ET.
AUGUSTI. TESTAMENTO. FIEREI. JUSSIT. ARBITRATU.
C. DONNEI. VÆNÆ. ET. CATTEI. RUFFI.
By this inscription we learn that it was erected according to the will of Donneius Flavos,
priest of Rome, and Augustus, under the direction of Donneius Væneus and Caffeus
Ruffus. But it does not assert that Donneius Flavos was cotemporary with Augustus, or
which of the emperors of that name is referred to.
160
BOOK I
HISTORY OF ENGINEERING.
The character of the architecture is the best met with in Gaul; the stone was
brought from the neighbouring quarries of Hassissane, and the courses are regularly laid
and jointed.

អ
VIKINIAITCA
Fig. 178.
bridge at ST. CHAMAS.
The span of the arch is 42 feet, and measured on the soffite its breadth is 19 feet 9 inches;
there are 39 voussoirs, 3 feet 5 inches in depth; on each side one projects 13 inches, to
support the centre.
The clear width of the roadway between the parapets is 15 feet 6 inches, and the length
between the triumphal arches at each extremity 74 feet 9 inches.
The opening of each of the triumphal arches is 11 feet 8 inches, and the height to the
springing 9 feet 4 inches; the total height to the top of the cornice 23 feet, and the entire
width, as measured along the frieze, 24 feet, forming nearly a square.

שער.
PER FLAVIO
Fig. 179.
BRIDGE AT ST. CHAMAS.
Some of
The writer in 1817 found this beautiful bridge as perfect as here representea.
the stones had been repaired, and a few of the upper courses had smaller introduced; based
upon a rock, and constructed with the greatest care, it promises to remain as many centuries
as it has already done, a monument of the taste and skill of Roman engineers. Palladio
and other architects have designed bridges with triumphal arches and covered ways, in
CHAP. IV.
161
ROMAN.
imitation, and none have surpassed in merit this simple and unique example, which deserves
much to be studied.
At Vaison are the remains of a bridge of one arch, which, when in a complete state, must
have somewhat resembled the preceding; the voussoirs are admirably worked, having

}
Fig. 180.
VAISON.
retained their original position; the curvature of the arch has not undergone any change,
and the whole is as solid as when first constructed.
The Bridge over the Allier, at Brioude, is also Roman, consisting of one arch; in the
southern part of France are many such remains, particularly on the ancient routes; through

୮
Fig. 181.
།:མས་
Brioude.
Provence, the stones are laid in regular courses, and but little mortar used, the voussoirs
cut very true, and bedded with care.
Bridge at Saintes over the Charente is an ancient structure: above the centre pier, in
1812 was erected a triumphal arch brought from Mediolanum, or Civitas Santonium,

Fig. 182.
SAINTES.
which once formed the termination of a bridge, as at St. Chamas.
The proportions given
to the architecture are not elegant, and on inspecting it, we are induced to believe, that
M
162
Book 1.
HISTORY OF ENGINEERING.
originally its height equalled its entire width: it has been said by some writers, that the
two arches were not so coupled in the situation from whence they were brought, but that a

MMD M
Mi m m
GELL
Fig. 183.
MEDIOLANUM,
single opening terminated each end of the original bridge, as was the practice of the Roman
engineers. In Italy we often have the foundations of piers of triumphal arches, and
pedestals for statues on the abutments of bridges; these not only added weight, where it
could give additional strength, but contributed much to the beauty of the structure; masses
of stone built over the springing of an arch assisted in preventing any spreading or slipping
upon the haunches; a triumphal arch placed at each extremity would have the same use,
and contribute much to the effect. A vast catalogue of Roman bridges might be made,
and it is somewhat remarkable that a selection has not been measured by the modern
engineers, and classed according to the span of their arches and boldness of construction.
The great rivers of Italy, France, Germany, Spain, and Portugal, all afford examples, some
erected where the water is broad, rapid, or deep, or on foundations which presented con-
siderable difficulties. Timber platforms on piles were universally adopted on soft ground,
and a concrete, formed of hydraulic mortar, is found to have been made use of very gene-
rally throughout Italy, wherever it could be applied.
In Italy, the Roman bridges have generally served for foundations for the modern;
many have had their semicircular arches altered during the middle ages, and in some
instances, timber constructions are formed upon the massive piers, which time and the
floods have spared. One great cause of their destruction was the elevation of the beds of
the rivers, in some instances so great, that the openings have entirely silted up, and been
closed by the deposit ; in consequence the structure, not affording sufficient water-way, has
been carried away by the flood.
Pavia over the Tessin.-A covered bridge, of Gothic construction, built of brick, con-
sists of seven arches, each 70 feet span, and 64 feet in height. The piers, whose breadth
is 16 feet, have a rounded form, but longer in the direction of the stream than across
it. The tympanums of the arches are pierced, resembling a curvilinear triangle two
sides of which are parallel to the entrados of the vaults; thus the weight in a great mea-
sure rests against the keystones, the thickness of which is 5 feet 6 inches. The bricks with
which these vaults are constructed have the form given to them suited to their position
as voussoirs, and are pierced in the middle to diminish the weight. The piers are
covered with white marble, the arches have an archivolt, and the whole is crowned with a
Gothic parapet of the same material, worked out to give it the greatest possible light-
each footway has a covering supported by two rows of small coloured marble
columns, 9 inches in diameter, 14 feet 4 inches apart, whose bases and capitals are of
white marble. The vaulted coverings are ornamented with gilt arabesques, on an azure
ground, and sustain two terraces, which are ascended by steps, placed at the extremity of
the bridge. The thrust of the vaults is opposed, as in many other Italian buildings, by
iron rods placed on a level with the springing. This beautiful work was executed by
Galeazzo Visconti, Duke of Milan, to which prince the city owes the Charter House,
Hospital, and Lazaretto.
ness;
Bridge of the Goldsmiths, at Florence, over the Arno, called Ponte Vecchio, was rebuilt in
CHAP. 1V.
163
ROMAN.
1345, after the designs of Taddeo Gaddi; it has three arches, the segments of circles,
from 94 feet 6 inches to 85 feet span; and from 15 feet to 12 feet 10 inches rise. The
thickness of the key-stone is 3 feet 3 inches, the springing line of the arches is 11 feet
5 inches above the level of low water. The thickness of the piers is 20 feet 4 inches, and
the breadth of the bridge 105 feet. It is built on piles, and a general framework;
on the upper side of the bridge is a covered gallery constructed by the Medici, and
forming the continuation of a passage from the Pitti palace to that of the old Ducal.
Under this gallery, on the middle of the bridge, are left open three arcades; the goldsmiths'
shops occupy the sides. The bridge of the Goldsmiths is one of the first modern bridges
where a segment was employed; its springing is near the level of high water.
Bridge of the Carraja at Florence, rebuilt by Taddeo Gaddi, consists of five arches,
which are segments, 57 feet 5 inches to 88 feet span; the versed sines are 12 feet 5 inches
and 26 feet 10 inches; it is built on piles. The facing walls are of squared stone, the rest,
as well as the arches, are in moellon.
Bridge of Alexandrie on the Tenaro, was built anterior to the year 1487, when four of
its arches were taken out, and reconstructed. It has ten arches, segments of circles,
from 52 feet 5 inches to 95 feet 2 inches span. The upper part forms a covered gal-
lery, 24 feet wide, the roof of which is supported by small arches, 7 feet 8 inches span;
during the time Piedmont was occupied by the French, they constructed a general platform
underneath this bridge, to form a movable sluice, by which they could fill the ditches of
the citadel in case of siege.
Ponte Felice, over the Tiber at Rome, was built in 1587, under Sixtus V., by Dominica
Fontana; it is composed of four arches; the two outer are 38 feet 9 inches, and the
two middle 51 feet 2 inches span, nearly semicircular, and supported by piers 24 feet 7
inches thick. Over the arches are sculptured bas-reliefs.
Bridge over the Arno at Pisa, called the middle, was constructed after those at Flo-
rence, in 1660, by François Nave. It is composed of three segmental arches, from 68 feet
to 73 feet 7 inches span, and from 12 feet 2 inches to 14 feet 2 inches in height. The
piers are 19 feet 3 inches in thickness; the outer work is marble, and the rest brick; the
left pier is surrounded by a starling, which serves to strengthen the foundations.
Bridge on the Rialto at Venice was built in 1578 by Michael Angelo, and has a single
arch 96 feet 10 inches span, and 20 feet 7 inches high. The footways are supported by
corbels provided with ballusters; on the two sides are rows of shops, formed by marble
arcades; the interval which separates them constitutes three passages, the middle being
the largest; this bridge is not intended for carriages. The approaches are steep, aided
by marble steps.
Bridge at Vicenza resembles the Rialto; the slope is still more steep, and is only used
by foot passengers; it has a single arch 101 feet 4 inches span, and 30 feet high.
Ponte. Corvo near Aquino, over the Melza; in the fourteenth century, it was in vain
attempted to construct a bridge in this situation; the bad quality of the foundation and the
rapidity of the torrent rendered all the efforts of the kings of Naples useless. Stephano
del Piombino at last proposed to construct one on a circular plan, whose convexity should
be opposed to the action of the current, and this idea was adopted, it being considered that
such a form would ensure solidity. This bridge was raised on a timber framework, whose
surface lay 6 feet 6 inches below the mean level of the water. The piers are formed of
large blocks of stone, securely cramped, and defended by several rows of piles, their base
has four courses of stone, from 13 feet to 16 feet 5 inches long, also cramped, and presenting
large sets-off; as has been observed, the foundations have a circular plan, whose radius is
577 feet 6 inches. The arches are seven in number; they are from 74 feet 5 inches to 93
feet 10 inches span; the thickness of the piers varies from 10 feet 8 inches to 12 feet 9 inches;
the breadth of the bridge is 42 feet 7 inches. The torrent being dry for a considerable part
of the year, the foundations were laid in one campaign; a great number of workmen as
well as soldiers were employed; the following year they raised the piers above the
mean level; Stephano died before the completion, and was succeeded by his son, Au-
gustino, aided by Joconde of Verona, who was afterwards called to Paris to construct the
bridge of Notre Dame; it was finished in 1505. Its solidity is not increased by the
circular form given to its plan, but by the construction of the frame-work, which would
equally have resisted the action of the current had it been in a right line; if some wearing
away had occurred, it would only have been partial, and it is impossible that the bridge
could have been carried away in one piece, which might happen to a dam 30 or 40 feet
long the disposition adopted has the inconvenience of obliging the piers to be inclined
towards the current, which presents more resistance to the stream, and consequently injures
the solidity of the bridge.
Bridge of the Trinity at Florence was constructed in 1750 by Ammanati, a celebrated
architect. This bold work consists of three arches, nearly elliptical, the curve being
The
portions of two parabolic arches, whose angle at the top is masked by an escutcheon.
span of the arches is from 87 feet 7 inches to 95 feet 10 inches; the springings are 7 feet
M 2
164
Bec
HISTORY OF ENGINEERING.
I.
Book 


2
ELEVATION.
PLAN.
Fig. 184.
BRIDGE OF THE TRINITY AT FLORENCE.
:

CHAP. IV.
165
ROMAN.
*
10 inches above low water, and the rise is one-sixth of the span; the arches are 3 feet
2 inches thick. The breadth of the piers is 26 feet 3 inches, and that of the bridge, 33 feet
9 inches. The facings of the piers are worked stone, with well executed mouldings. The
other parts of the structure are of rubble; the foundations rest on a general framework,
surrounded and crossed by several rows of piles. A defect which occurred under one of
the piers of the bridge was repaired in 1811 by the elder Goury.
Bridge of Verona over the Adige consists of three arches, 36, 50, and 160 feet span; the
latter is the largest arch found in Italy.
Bridge on the Marachia, near Rimini, has five arches, from 23 feet 3 inches to 28 feet
9 inches span.
The upper part of the piers has niches and columns, supporting entabla-
tures.
Water. The Romans bestowed unwearied pains to obtain pure and wholesome water;
their military and civil engineers were always on the alert to ascertain its nature and pro-
perties throughout the countries where they were employed. Vitruvius observes that
when C. Julius, the son of Masinissa, lodged with him, they frequently conversed on sub-
jects of natural history, and that he had read most of the Greek authors, as Theophrastus,
Herodotus, &c., with the greatest care and attention, for the purpose of ascertaining the
qualities of the different streams and rivers. The vast sums of money expended to provide
abundance of pure water for the inhabitants of the imperial city and the other towns of
that vast empire, gave employment to many engineers; it is curious to examine the opinions
of Greek and Roman philosophers upon the nature and properties of this element. Thales,
the Milesian, taught that all things originated from, and the priests of Egypt believed
that all things were composed of, water; that it was essentially necessary for the purposes
of life, for pleasure, and for daily use, was universally felt and admitted.
When the Roman engineer wished to discover the source of a stream, he was instructed
to lie down on the ground a little time before sunrise, and to notice where the vapours rose
into the air; he was then to dig at that spot and commence his search. In clay it was
supposed the supply was small, and not of the best quality; but in veins of gravel that it
was well flavoured; when the bulrush, the wild willow, the alder, reeds, ivy, and similar
plants abounded, abundance was always relied on. In situations where these indications
were not met with, they adopted the following plan: a hole three feet square was dug,
at least five feet deep, and in it, about sunset, a brass or leaden vessel was placed, rubbed
inside with oil. Thus prepared it was inserted, and the upper part of the excavation
covered with reeds or leaves, over which the earth was thrown. If on the following
day, on opening the hole, the inside of the vessel exhibited any drops of water, it was ex-
pected that a quantity might be obtained. When the vessel placed in the pit was made of
unburnt clay, it was often found destroyed by the moisture, which was considered a sure
indication of the presence of water. A fleece of wool was often placed in a similar pit,
and when water on the following day could be pressed out of it, an abundant supply
was inferred. Lamps full of oil were placed in the pit and covered over, and when
examined, if not exhausted, but still retaining some of the wick and oil, and presenting a
humid appearance, it was shown that water might be found, as it was supposed that heat
invariably drew moisture towards it. Such were the rude trials recommended previous to
the sinking of a well, which were continued until the head of the spring was found; other
wells were then dug around it, and by means of tunnelling connected with it.
Rain water was considered by Celsus the physician the most pure, and formed of the
lightest vapours.
Aristotle supposed that these vapours rose from the earth, into a cold
region of the air, were then compressed into clouds, and afterwards condensed into rain;
that such water collected into showers was cleansed by its passage through the air. And
Vitruvius tells us further, that showers do not so frequently fall upon plains as upon high
ground, because the vapours are driven to the mountains. The winds convey the water
when heated by the sun, from the low grounds to the higher, and thus keep up a constant
circulation; and he further illustrates this by his observation of the drops of water which
collect on the ceiling of a hot bath; hot vapours ascend at first from their lightness, and do
not fall down, but when condensed, they drop on the heads of the bathers; so it is with
air warmed by the sun, it raises moisture from all places, and gathers it into clouds, whilst
the winds which blow from cold quarters bring dry air and not vapours.
}
Some hot springs produced excellent flavoured water, and many cold ones had both
bad taste and smell; the Romans arranged these, made them serviceable to a variety of
purposes, and had baths supplied with water adapted, as they supposed, to every species
of malady. Some springs, where the water was acid, as those found at Lyncestis in Italy,
the Velinus, and in the Campana near Theanum, had the property of dissolving the stone
which forms in the bladder; eggs placed in such water had their shells softened and
dissolved; lead became white by the application of an acid, and brass verdigris. Pearls
and flint stones, upon which fire would have no effect, were speedily dissolved in the same
way by the application of acids. Such were the qualities and properties they found in some
of the waters, and the Romans seem on all occasions to have exercised their knowledge,
M 3
166
Book I
HISTORY OF ENGINEERING.
when they selected a spring, on which they considered the health of mankind so much
depended. Before an open or running stream was laid on to a town, they examined the
inhabitants of the neighbourhood; if strongly formed, fresh coloured, sound legs, and
without blear eyes, they considered the water good. By throwing a drop of water into a
clean brass vessel, if it left no stain, it was thought pure. And after boiling, if no sedi-
ment was deposited, it was equally so. If in the spring it appeared limpid and transparent,
and no moss or reeds generated near it, the water was considered light and wholesome.
Instruments used by the Romans for Levelling. The libra aquaria and the dioptera were
not for this purpose considered so correct as an instrument called the chorabates, which was
a rod or plank, about 20 feet in length, mounted on a leg at each of its extremities, both of
equal length. The rod and the legs were fastened or secured by diagonal cross pieces or
braces, on which were marked correctly vertical lines. A plumb line attached at each
extremity and acting over these diagonal braces indicated whether the instrument was level.
When the wind prevented the plumb bobs from remaining stationary, a channel cut in the
upper edge of the horizontal rod was filled with water, and if the water touched equally
both extremities, the level was supposed to be correct, and then the observation of the
descent or elevation of the ground was made with accuracy. Vitruvius observes that
although Archimedes asserts that water is not level, but takes the form of a spheroid whose
centre is that of the earth, yet the two ends of the channel on the rod will nevertheless
sustain an equal height of water. If it be inclined towards one side, that end which is
highest will not suffer the water to reach to the edge of the channel on the rod. So that
though water poured in may have a swelling and curve in the middle, yet at its extremities
it will be level. When this instrument was used, if the ground was very unequal, the feet
were propped up, and supported till they were brought level. The other two instruments,
as the water-level and the dioptera, are not very accurately described.
Conducting of Water. This was effected in various ways by the Romans, either in channels
built to convey it, or in earthen or in leaden pipes. When channels or aqueducts were
adopted, they were solidly and substantially executed, with a fall of not less than six inches
in a hundred feet, and arched over at top, to prevent the sun from affecting the water.
When the water arrived at the walls of the city, a reservoir or castellum was built, which
contained three cisterns to receive it. In the reservoir were three pipes of equal diameter,
so connected, that when the water overflowed at the extremities, it was discharged into the
middle one, which supplied the pipes for the fountains; a second pipe supplied the baths,
and a third the private houses. The water for public use was never deficient, nor could it
be diverted if the mains or pipes were properly constructed. The private houses had a
tax levied upon them, which was expended in keeping the aqueduct in repair.
When hills intervened between the spring head and the city, tunnels were driven under
ground, with a fall of one in two hundred; when the material cut through was stone,
a channel was formed in it; when of earth or gravel, side walls were built, and an arch
turned over, through which the water was conducted. Wherever these tunnels were
formed, perpendicular shafts were sunk every 120 feet distance. When the water was
brought in leaden pipes, a reservoir was made near the spring, and other pipes of sufficient
diameter conducted it to the city reservoir; these were made in lengths of not less than ten
feet, out of sheet lead of different widths and weights; hence a sheet of 100 inches wide
would make a pipe weighing 1200 pounds; 80 inches wide, 960 pounds; 50 inches wide,
600 pounds; 40 inches, 480 pounds; 30 inches, 360 pounds; 20 inches, 240 pounds; 15
inches, 180 pounds; 10 inches, 120 pounds; 8 inches, 96 pounds; and 5 inches 60 pounds.
When pipes of this kind were used, the lead varied in weight, though it was generally
at the rate of fifteen pounds per superficial foot; if there was a uniform and proper fall, any
little impediment was made up by means of substructions, or by taking a circuitous course,
provided it was not too far about; the pipes were all laid with a regular and proper current.
If the valleys were long, they took the slope of the hill, and when the water arrived at the
bottom, it was carried across the valley by a low substruction at as great a distance as possible;
a venter here prevented the water on its arriving on the opposite side or acclivity from
bursting or destroying the joints of the pipes. Over the venter were placed lofty upright
pipes, by which the violence of the air escaped. Thus when water was conducted through
leaden pipes, due attention was paid to the fall of its descent, its circuit, its vent, and the
compression of the air. It was, however, always found expedient, after the fall from the
spring was obtained, to build reservoirs, at distances of 20,000 feet, to allow of repairs.
These reservoirs were not made on any descent, nor on the venter, nor on a rise, nor in
valleys, but only on plains.
When economy was considered, earthen tubes were substituted, not less than two inches
in thickness, so made, that one end fitted into the other. The joints were then coated with
a mixture of quick-lime and oil, and on the elbows made by the level part of the venter,
instead of the pipe, was placed a block of red stone, so perforated, that the last length of
inclined pipe, and the first length of the level part, were received into it. On the opposite
sides, where the acclivity commenced, a block of red stone received the last length of the
CHAP. IV.
167
ROMAN.
venters, and the first length of the rising pipe. By this attention the tubes in their ascent
and descent were never put out of order. In aqueducts there is generated a great rush of
air, says Vitruvius, of force sufficient to break stones, unless the water is softly and sparingly
let down from the head, and unless in elbows and bending joints it be restrained by means
of ligatures or a weight of ballast.
When the water was first let down from the head, ashes were put in, which closed the
joints where they were not sufficiently coated; earthen pipes were considered in some
instances preferable, as when damaged, almost any one could repair them, and the water
conducted by them was of greater purity.
purity. The Romans preferred earthen vessels to
silver at their daily meals, the water preserving its flavour better in them.
When wells were dug, they were steined or walled round, to exclude filtration, and tanks
and cisterns were frequently used to collect the rain, which were carefully built with the
purest and roughest sand and broken flint,

гр
among which no single piece weighed more than
a pound; very strong lime and sand, mixed in
the proportions of five of sand and two of lime,
formed the mortar. The flints combined with
the mortar lined the sides and bottom of the
excavation. Several divisions were made in
these cisterns coated with cement, and the waters
passing from one to the other, depositing its im-
purities, was rendered wholesome and fit for use.
Pliny, lib. xxxi. cap. 31., informs us, that
when water is to rise, the pipes must be made
of lead, and that water will always ascend by itself to the height in the castellum from which
it is delivered, or, in other words, find its own level; but that wherever there is a bend
in the pipe, the lead must be increased in thickness at that place.

Fig. 185.
PLAN OF WELL.
Fire Engines.-There can be no doubt but that the Romans had contrivances by which
they could extinguish fires, for we learn by one of Pliny's letters to the Emperor Trajan,
that when the town of Nicomedia, in Bithynia, was almost destroyed by fire, its ravages
were increased by the laziness of the inhabitants, and the want of a proper machine-
sipho―for extinguishing the flames. When Strabo, lib. v., alludes to the subterranean
conduits at Rome, he mentions, that all the houses had siphones or water-pipes, and which
probably could be applied to put out any accidental fire. Apollodorus, the architect, in
his description of warlike machines, mentions the sipho for extinguishing fire, and observes,
that if it is not at hand, leathern bags filled with water may be fastened to hollow canes,
in such a manner as by pressing the bags the water may be forced over the flames. Such
a sipho might throw water to a great height, and in the fourth century they were made use
of. The Romans had many ordinances for the extinguishing of fires, and Ulpian, Digest,
xxxiii. 7. 18., when mentioning those things which ought to belong to a house when sold,
names the siphones, which have been supposed to be fire-engines. Seneca observes that the
height of the houses at Rome rendered it impossible to extinguish fire, in consequence of
the narrowness of the streets.
Form of the Pipes. These were not truly cylindrical, as has been commonly supposed,
but their section that of a pear; the upper part being gathered in formed an edge where
it was soldered. On some found is inscribed the name of the maker, and the situation
they occupied. Where strength was required, over the joint was soldered a capping or
ridge, hooped round with narrow cuttings of lead.
Pliny gives us (lib. xxxiii. cap. 30.), the method adopted for soldering the different
metals; for gold, borax was used; for iron potter's clay (argilla); alum for brass; resin
for lead; and in lib. xxxiv. cap. 48., the same writer tells us that tin is used as a compound
to solder conduit pipes, and that the best common black lead, beaten with hammers
into sheets for the making of the conduit pipes, was brought from Britain, where it was
found on the surface of the ground in great abundance.
To stop the water in the pipe, or to turn it on, a metal cock was used, and many
have been found, similar in their construction to those of modern date.
Vessels resem-
bling a deep pan of lead are met with, supposed to be for the purpose of measuring off a
certain quantity of water.
Pipes of earthenware or terra cotta, called tubuli fictiles, are found in the walls of the
baths and Coliseum of various diameters, none less than two fingers or digits, which was
required to prevent any accumulation of deposit.
Canales lignei, or wooden pipes, were common in ordinary structures, on account of
their economy.
Piscina and cisterns were differently constructed for the reception of
water: that called the Sette Sale, which served the baths of Titus, is one of the most perfect.
The Sette Sale, where the water was collected for the supply of the baths of Titus,
contains nine large reservoirs; it is situated on the Esquiline Hill, in a lonely vineyard near
the Palombara. By some writers it is assumed, that the quantity of water they contained
M 4
1G8
BOOK I.
HISTORY OF ENGINEERING.
was not needed for the baths, but was intended to supply the arena of the Coliseum, when
converted into a naumachia. The walls are solidly built above and below, and all the
arches and vaults well turned; the outer wall is buttressed up, and the spaces between
formed into hemispherical recesses. The stucco which has lined the walls is encrusted
with a tartareous deposit, similar to what we find in the channels of the aqueducts, and the
Piscina mirabile at Baiæ, and is so hard that it bears a polish equal to marble.
J
The

Fig. 186.
THE SETte sale,
various communications between these halls are set out with great regularity, and standing
within either, looking diagonally, a fine effect is obtained.
Piscina were intended for the same purpose as our cisterns, and by Frontinus they
are designated Limaria when they were used for allowing water to deposit its impurities;
such a piscina remains on the Latian

Way, built in the manner already
alluded to the water flowing in and
out of apertures made at right angles
with each other. When a reservoir
was covered by an arch, it was termed
contectis piscinis; such received the
waters of most of the aqueducts, and
kept them from any influence that the
sun's power might produce; when left
exposed, vegetable matter would form
on the surface, and render the water
unwholesome. Frontinus describes a
variety of arrangements to keep water
pure, and in a piscina near the Latian
Way are three divisions, which formed
a perfect system of filtration; from the
Fig. 187.
LIMARIA.
galleries above it could be drawn out in any state of purity, and every precaution was


Fig. 188.
CONTECTIS PISCINIS.
ப
PLAN.
CHAP. IV.
169
ROMAN
taken to provide means to cleanse at proper times each division; these were sometimes
called conceptacula, and had considerable sums of money expended upon them. Sextus Julius
Frontinus, who flourished in the time of Vespasian, was of a patrician family; Tacitus
mentions that he was prætor of Rome, A.D. 70. We find that he held the office of consul
three times, and that during the expedition to Britain, he was the proconsul; he was appointed
by Nero to superintend the Roman aqueducts, and during the period he filled that office,
for the benefit of his successors, he compiled the work, " De Aquæductibus Urbis Romæ,"
which contains an account of the aqueducts built in his time, as well as the names of all
the waters brought to Rome, and by what consuls, from the foundation of the city; from
what places and the miles distant; what distance they ran
under ground, how much above over arches; their height,
their breadth, their laying out, how much without, as
well as within the city; the quantity of water delivered to
each region by measure; the number of public reser-
voirs, as well as private; what was effected at the charge
of the public, and what of private individuals; the
quantity brought from lakes; and also the penalties
imposed on contumacious persons by decrees of the
senate, and by the commands of the emperor.
For 440 years after the foundation of the city, the
Romans were content to use the water drawn from the
Tiber, or from wells and springs; many of the latter
were supposed to be under the protection of deities.


Fig. 189. FILTER.
The Aqua Tepula was conducted to Rome 126 years before Christ, and took its source
on the borders of the Latian Way, from some springs which communicated with the Anio;
its length was 2000 Roman paces.
The Aqua Julia was conducted to Rome in the days of Julius Cæsar, by Agrippa; a
separate canal being added for this purpose to those of Tepula and Marcia. Its length was

PLAN
Fig. 190.
AQUA JULIA AND TEPULA.
15,126 paces, 7000 of which were above ground, and 6472 on arches. Agrippa at his own
expense also repaired the two which were first constructed and found out of order.
•
170
Book I.
HISTORY OF ENGINEERING.
The Anio Vetus, about the year 481 from the foundation of the city, was commenced by
M. Curius Dentatus, and the expenses defrayed by the spoils taken from Pyrrhus.
The

VANHA > GM Mindy Hu
Fig. 191.
VETUS AND CLAUDIA.
water was drawn from the Anio, above Tivoli, and the whole work was completed some time
after the death of Dentatus, by his successor F. Flaccus. The total length of this aqueduct
was 43,000 Roman paces, 221 of which were subterranean.
These two aqueducts in the year 608 from the foundation of the city needing con-
siderable repairs, the Prætor Marius was directed to perform them, and to conduct a further
supply from the neighbourhood of Subiaco, situated among the mountains 20 miles beyond
Tivoli; the water of the Anio was there found in a purer state, and less contaminated
with earthy matter. The length of this aqueduct was 61,710 Roman paces, 7463 above
ground, and the remainder 54,247 subterranean. Where streams or valleys were crossed,
arches were constructed which measured 463 paces.
The Aqua Appia, was the first brought to Rome, in the consulship of Valerius Maximus
and P. Decius, in the year of Rome, 442. Appius Claudius directed this work during the time
that Crassus was censor. This aqueduct commenced in Agro Lucullano, on the Prænestine
Way, between the sixth and eighth mile stone, turning on the left 780 paces; its length
from its head to the Salinas, at the Trigemenian gate, was 11,190 paces. It was conducted
under ground for 11,130 paces, and the whole was arched over. Above ground it was
carried for a distance of 60 paces, (but of this no traces now remain,) to the Capuan gate,
where it united with the old Anio, at the confines of the gardens of Torquatianus.
The Aqua Virgo was introduced a few years afterwards, and some portions of it may be
traced, crossing the three roads, which lead from the gates of Lorenzo, Pia, and Salara.

Fig. 192.
AQUA VIRGO,
CHAP. IV.
171
ROMAN.
It was 14,105 paces in length, 12,865 underground, 1240 above. and 700 on arches, some
of which were of great beauty.
The plan, elevation, and section, is from the work of Alexander Donatus, as it existed in
his time.
This aqueduct had its commencement on the Via Collatina, about eight miles from the city.
The covered piscina, situated near the Pincian Hill, has two stories, and is a curious
and perfect example of a part of the aqueduct; these cisterns in all probability were so
named from having become recep-

tacles for small fish. The con-
ceptacula was the vaulted cistern,
covered in a manner to protect
the water from the sun's influence,
which was preferable to the open
reservoir or limaria. The water
here entered at the top of one alley
and descended by the other to the
lower compartments, where it de-
posited the earthy matter it held.
The contents of this piscina were
accurately known, and the water
could always be let out in any given
quantity.
The plan and elevation of the
stairs which conduct above are
well contrived for the access of
the superintendents to the passages
above.
Fig. 193.
CONCEPTACULA, AQUA virgine.

Fig. 194.
PLAN.
SECTION OF STAIRS.
The arches which decorate some
portion of this aqueduct are not
only well proportioned, but receive
further embellishment from a re-
gular order of Corinthian columns:
where the passage is preserved
through the line, the elevation is
increased by an additional height.
The section at the side shows
the channel for the stream, which
flowed in the attic, built above the order, covered in by a vault carefully worked and
well tied together: here every precaution seems to have been taken to guard against
leakage, which, if it ever happened, would be immediately discovered, by the pouring out
of the water at the defective place; and along the whole line of aqueduct, materials were
deposited, that there might be no delay in the work; there would be also less to perform
than to take up a whole length of mains laid under a solid and hard pavement, rendered
impassable during the progress. Such an inconvenience in crowded streets, the Romans
wisely avoided, and continued to prefer the system of raised aqueducts to those buried in
vaults under ground.

DRENALINI ZALMEIRA DUANES JA RETULI.
! ! ! ! ! ! ! ! ! !
Fig. 195.
AQUA VIRGINE.
172
BOOK I.
HISTORY OF ENGINEERING.
#
The castellum of Aqua Julia is situated near the Porta Esquilina; in it we can trace the
triple immissarium from which the waters were distributed. The castellum (Vitruvius,
lib. viii. cap. 7.) or reservoir, constructed near the walls of the city, had a triple cistern
attached to it to receive the water. Three conduits, of equal dimensions, were connected
in such a manner, that when the water was more than necessary for the supply of the outer,

ப
SECTION
AAAA!
I LAN
Fig. 196.
CASTELLUM AQUA JULIA.
it was discharged into that of the middle, which served all the pipes of the public foun-
tains: one of the mains supplied the baths, the other the private houses. The object of
this contrivance was to provide first for the public wants, then the baths, and afterwards
private individuals.
At the end of each of these three conduits was a receptacle (receptaculum), from whence
the general distribution was made; at the sides were two others (caduca) to take off any
superabundant quantity. By such an arrangement the various supplies were regulated
with the greatest nicety. The total width of this castellum is 115 feet; and the plan and
sections show its general arrangement, its staircases, passages, and receptacles for the water.
No expense was spared in the construction of these stupendous edifices, which, attached to
the numerous aqueducts of Rome, must have resembled palaces. Built of squared stone,
and lined with brick coated with a fine cement, every precaution was taken to prevent
leakage or infiltration. The several conduits and pipes were provided with valves and
corks for shutting off or turning on a supply to any direction. Here the superintendant
could direct the flow of water to the several localities in his neighbourhood, without going
into the castellum: he could also judge of the quantity discharged in each direction, by
the simple instruments he was provided with: experience soon taught him what quantity
flowed through the respective apertures, and he always knew, by guaging the several cisterns
or reservoirs, what had flowed out. A constant flow from the aqueduct enabled him at
the castellum to regulate its distribution, and without great arrangement, when the time
came for supplying the numerous baths, there would have been found a deficiency: there
needed some precautions to prevent this.
As the waters brought by these several conduits deposited a considerable quantity of
earthy matter, it was necessary that the castellum which received it should be provided
with conveniences, by which all the silt that accumulated could be readily removed. For
this purpose chambers were attached to the several cisterns, where the water was not dis-
turbed by the efflux or letting it out, and from them the deposit was washed, by either
letting it off into the public sewers, or removing it by manual labour. In some of the
cisterns or reservoirs discovered, the bottom was made with a considerable fall or inclination
CHAP. IV.
173
ROMAN.
towards a pit sunk in the middle, or like a shallow basin, with a
circular hole in the centre, through which might be scoured out all
the accumulations of sand or lime deposited; these holes were simply
closed or secured by a plug, or by a hard stone in the form of the
frustum of a cone.
The arch which supports the triple aqueduct of Julia, Tepula,
and Martia shows the last-mentioned water conducted through the
lowest channel in the section, and that of Julia in the uppermost :
it is situated near the Porta Esquilina, and on it is the following
inscription

IMP. CAES. DIVI JULI F. AUGVSTVS
PONTIFEX MAXIMVS COS. XI.
TRIBVNIC. POTESTAT. XIX. IMP. XIII.
RIVOS AQVARVM OMNIVM REFECIT.
Underneath is another inscription, showing when it was re-
paired.
IMP. TITVS CAESAR DIVI F. VESPASIANVS AVGVST. PONTIF. MAX.
TRIBVNICIAE POTESTAT. IX. IMP. XV. CENS. COS. VII. DESIGN. VIII.
RIVOM AQVAE MARCIAE VETVSTATE DILAPSVM REFECIT
ET AQVAM QUAE IN VSV ESSE DESIDERAT. REDVXI.
Three streams, conducted by artificial channels one over the
other, and differing in quality, required particular care that they
did not leak one into the other, and that the better should not be
deteriorated by communicating with that which differed from it
in salubrity and clearness: we consequently find that the channel
for each is based upon a thick stone, passing into the sides of the
aqueduct, which is covered with tiles and a coat of cement with the
greatest care: the only chance of any rupture or crack would arise
from a settlement of a division of the arcade, which would imme-
diately be discovered by the leakage, and would speedily be re-
stored. Doors from the outsides admitted the attendants occa-
sionally to examine the several conduits; and it was the duty of
the supervisors and sub-engineers to report constantly upon their
efficiency and condition.
Fig. 197. SECTION OF AQUEDUCT OF AQUA
身
​ANA MINUUT
JULIA TEPULA, AND MARCIA.

Fig. 198.
AQUA JULIA, TEPULA, and marciaA.
And below this, immediately above the middle arch upon the architrave which sup-
ports the cornice, is cut another.
IMP. CAES. M. AURELIUS ANTONINUS PIUS FELIX AUG. PARTHIC MAXIM.
BRIT. MAXIMUS PONTIFEX MAXIMUS.
AQUAM MARCIAM VARIIS KASIBUS IMPEDITAM PURGATO FONTE EXCISIS ET PERFORATIS
MONTIBUS RESTITUTA FORMA ADQUISITO ETIAM FONTE NOVO ANTONINIANO
IN SACRAM URBEM SUAM PERDUCENDAM CURAVIT.
174
Book I
HISTORY OF ENGINEERING.
Seven aqueducts were sufficient to supply Rome until the time of Caligula, when two
others were commenced, which were finished by the emperor Claudius: these were —
Aqua Claudia.
- Few aqueducts exhibit greater beauty of construction or design, and


JIGA. Mu
Fig. 199.
what remains is a mo-
nument of the munifi-
cence of the emperor: it
was extended from the
Porta Maggiore to the
brink of the Cælian Hill
by Nero.
When we examine
this structure through-
out its entire length of
nearly 50 miles, we can-
not allow the Roman
engineers who con-
structed it to have been
ignorant of hydrostatics.
After the source of the
springs had been disco-
vered, to have conducted
the water by a regular
fall to the castellum,
and then distribute it
to the several portions
of the city, could not be
accomplished without a
thorough knowledge of
the levels of the country
through which the aque-
duct was to pass: one
regular fall was main-
tained throughout, that
the water might not be
AQUA CLAUDIA AND ANIO NOVUS.

SECTION.
either unnecessarily agitated or retarded:
and it would be far more difficult to
regulate such a fall on a lofty structure
of arches, than in a system of pipes laid
under ground. Such knowledge indicates
that the Roman engineers were pro-
foundly instructed in the sciences, and
ELEVATION.
PLAN.
Fig. 200. AQUA CLAUDIA AND ANIO NOVus.
CHAP. IV.
175
ROMAN.
thoroughly understood the properties of running water. This aqueduct received two
streams, which flowed from near the Via Sublaceni, a road which follows the valley of the
Anio, above Tivoli. Its total length was 46,406 Roman paces, 36,230 subterranean, and
10,176 on arches.

Fig. 201.
AQUA CLAUDIA AND NOVUS.
The other was the Anio Novus, the most considerable and curious in its construction.
It was in length 58,700 Roman paces, 49,300 under ground, 9400 above, and 6491
carried on arches, some of which exceed in height 100 feet. Before the water was
admitted into this aqueduct, it passed through a reservoir, where the sediment was
collected. Both these aqueducts, after passing on arches and under ground, were united,
although the waters were kept separate.
The Tiber, at Rome, was considered to be 91½ feet above the level of the Mediterranean ;
and the various heights above the level of the Tiber there that these several aqueducts
delivered their water may be thus stated.
The Anio Novus was above the level of the Tiber
The Aqua Claudia
The Aqua Julia
The Aqua Marcia
The Anio Vetus
The Aqua Virgo
The Aqua Appia
Feet.
158.88
148.9
129.4
125.4
-
82.5
34.2
-
27.4
The nine aqueducts which supplied Rome with water in the time of Frontinus are stated
to have furnished a quantity as follows: ---
The Aqua Appia
-
The Anio Vetus
The Aqua Marcia
The Aqua Tepula
The Aqua Julia
The Aqua Virgo
The Aqua Alsietina
The Aqua Claudia
The Anio Novus
-
-
4398 quinariæ
4690
-
1398
2524
14018
-
4607
4738
For construction and architectural arrangement the most beautiful was the Aqua
Claudia, built entirely of squared stone; that of Marcia, which ran almost parallel with
it, had its arches 16 feet span, constructed of different kinds of stone, red, brown, and
yellow; the waters were conducted in canals, one above the other, and the arches in many
places were more than 70 feet in height. Others were of brick and marble, subject to
dilapidations, and cost vast sums to repair.


ㅁ
​ㅁ ​ㅁㅁ
​ㅁ
​ㅁㅁ
​ப
ㅁㅁ
​Fig. 202.
SECTION.
PLAN OF RESERVOIR.
176
BOOK I.
HISTORY OF ENGINEERING.
The reservoirs, attached to most of the aqueducts for cleansing and filtering the waters,
were constructed and attended to with the greatest care. The emperor Nerva formed many
deep reservoirs by the sides of the aqueducts, to collect the sediment in its passage, and also
ordered that the Aqua Marcia should not be used for any other purposes but that of beve-
rage, it being the coolest as well as most transparent of the waters brought to Rome.
When these structures required repair in the first instance slaves were employed, 240
being engaged by Agrippa for that purpose. In the time of Claudius, regular fountaineers
were appointed, to the number of 460 persons, distributed into overlookers, keepers of the
castellum, stone-cutters, masons, plasterers, stuccoers, and others. The works were con-
ducted in the winter, it being thought that the heat of summer would occasion the masonry
to dry too fast for its solidity.
In Rome every house had its fountain, and the water laid on, for the use of the inhabit-
ants, and it was not considered that a dwelling was fit to receive a tenant, however humble
his lot, unless it was provided with an abundant supply of water—an instance of consider-
ation worthy the imitation of modern times.
Aqua Alsietina, in length 22,172 paces, was brought by Augustus to Rome; the water
was of a quality only fitted for the purposes of irrigation, being considered unwhole-
some to drink. 358 arches formed a part of its construction.
Aqua Aniene nuovo and Claudia are carried over the Porta Maggiore on two stone arches,
highly decorated; the water of the Anio Novus flows above that of Claudia, as indicated
in the section.

Fig. 203.
PLAN.
SECTION.
The front, which is situated on the Via Prænestina and Labicana, exhibits the following
three inscriptions.
TI. CLAUDIUS DRUSI F. CAISAR AUGUSTUS GERMANICUS PONTIF. MAXIM.
TRIBUNICIA POTESTATE XII. COS. V. IMPERATOR XXVII. PATER PATRIAE
QUAS CLAUDIAM EX FONTIBVS QUI VOCABANTUR CAERVLEUS ET CURTIUS MILLIARIO XXXXV.
ITEM `ANIENEM NOVUM A MILLIARIO LXII. SUA IMPENSA IN URBEM PERDUCENDAS CURAVIT.
IMP. CAISAR VESPASIANUS AUGUST. PONTIF. MAX. TRIB. POT. II. IMP. VI. COS. III. DESIG. IIII. P.P.
AQUAS CURTIUM ET CAERULEAM. PERDUCTAS A DIVO CLAUDIO ET POSTEA INTERMISSAS DILAPSASQUE
PER ANNOS NOVEM SUA IMPENSA URBI RESTITUIT.
IMP. T. CAISAR DIVI F. VESPASIANUS AUGUSTUS PONTIFEX MAXIMUS. TRIBUNIC.
POTESTATE X. IMPERATOR XVII. PATER PATRIAE CENSOR COS. VIII,
AQUAS CURTIUM ET CAERVLEAM PERDUCTAS A DIVO CLAUDIO ET POSTEA
A DIVO VESPASIANO PATRE SUO URBI RESTITUTAS CUM A CAPITE AQUARUM A SOLO VETUSTATE
DILAPSAE ESSENT NOVA FORMA REDUCENDAS SUA IMPENSA CURAVIT.
Alexander Severus embellished Rome with many stately buildings and magnificent por-
Near Labicana, four miles from the city, are the remains of an aqueduct which
ticoes.


Fig. 204.
ALEXANDRINA.
conveyed the water called Alexandrina to Rome. This emperor was murdered A. D. 235,
and left this fine specimen of construction for our admiration. He was accomplished, fond
CHAP. IV.
177
ROMAN
of literature, moderate at his table, and partial to men of genius, from amongst whom
Ulpian was selected to be his constant companion.
The Aqueduct at Nismes, or the Pont du Gard, was, perhaps, the earliest constructed by the
Romans out of Italy, and is supposed to have been executed by Agrippa, who was governor

Fig. 205.
PONT DU GARD.
of that city in the time of Augustus, and declared curator perpetuus aquarum.
arrangement affords us the best means of judging of such works.
Its perfect
It has three tiers of arches, one above the other; the lowest, under which the river
Gardon passes, is composed of six arches, the second of eleven, and the upper or third
tier of thirty-five, besides two openings made at the side, at the time of the invasion of
Gaul. The arches are semicircular, and rest upon piers more or less elevated. Above the
upper row was the conduit for the water, which passed the valley of the Gardon at a
height of more than 157 feet above the river below.
The length of this splendid monument at the level of the string course surmounting the
first tier is 562 feet, and at the level of the second string course 885 feet; it is nearly the
same length above the crowning stones of the aqueduct, between the extremities where
broken down.
The total height is 161 feet, viz. 66 feet for the first story from the bed of the river to
the first string course, the same to the second string course, and 29 feet to the top of the
stones which cover it. The divisions of the arches and piers of the first and second stories
correspond; the largest arch of the first story, under which, when there is little water in it,
it generally passes, is the centre of the monument, and the second from the left bank of the
Gardon. On the first and second story, on each side, are arches of a smaller space, which
are succeeded by others still less. The difference in the span of these arches, and their all
being semicircular, obliged their springing to commence at different levels, which has a
singular effect. The large arch through which the river passes is 80 feet 5 inches in
diameter; the three on the right side are 63 feet, and the smaller are 51 feet. All the arches
of the upper story are equal in span, 15 feet 9 inches: their piers vary in width, and do
not come immediately over those of the two stories below; consequently, in this tier there
is no symmetry maintained with those beneath them, nor are the perpendiculars kept.
The thickness of the Pont du Gard, from the face of one side to that of the other, is at
the first story 20 feet 9 inches, at the second story 15 feet, at the third 11 feet 9 inches.
Each story forms a considerable set-off, three feet nearly on each side of the first story, and
1 foot 6 inches at the second, where the string course or cymatium was increased a little
more than a foot in its projection, to allow foot passengers to traverse the valley with
more facility,
The lower piers are strengthened and protected by buttresses of a triangular plan, which
directed the waters of the valley in time of floods. The construction of the Pont du Gard
exhibits great skill; the stones are all laid according to their natural beds in the quarry,
and their dimensions are considerable: they were brought from the neighbourhood, on
the left bank of the river, and are of the same quality as those employed in the amphi-
theatre at Nismes. Corbels or projecting stones are left in various parts, for the purpose
of supporting the centres and scaffolding, which were not removed, that they might be ser-
viceable for after repairs.
The foundations were established upon a rock 6 feet above the bed of the river, and the
thickness of the piers is formed of only two or three stones of large dimensions. The
courses are in general 2 feet in height. The key-stone of the large arch is 5 feet 3 inches,
and that of the others 5 feet in depth; those of the arches of the upper story 2 feet 7 inches.
The lower arches are formed of four separate rings in their soffites, those of the range
above of three, and those of the upper or smaller range of single rings or courses of voussoirs:
N
178
BOOK I.
HISTORY OF ENGINEERING.
this kind of construction is unique; the voussoirs seem to be carried side by side, and the
soffites of the arches exhibit the joints not broken, but continuing round in one line. The
thickness of the arch consists of three distinct arches not tied or bonded together.
The whole is of freestone, from the foundations to the third course above the cymatium,
which covers the piers of the third story. Moellon or rubble was employed for the filling
in of the piers, spandrills, and haunches, of the first and second stories.
The stones are laid without cement, and owe their solidity to the weight of each block,
and the nicety observed in the working of their beds and joints. Each stone was dropped
into its place by means of the lewis, the holes for the insertion of which are still seen exactly
placed over the centre of gravity of each. The work above the small arches of the third
story is of masonry filled in with rubble work: here a considerable quantity of cement is
used, which has become as hard as the stone itself, forming one impermeable mass, and pre-
venting any filtration, which would, if suffered, have been detrimental to the structure.
The channel for the water is placed between two walls of masonry, 2 feet 9 inches thick ;
the bottom has an inverted arch, which with the walls are covered with a cement 2 inches
in thickness, composed of fine sand, powdered brick and quick-lime. Its strength is equal
to that of the hardest stone, and there is no apparent change in it, since it was first laid
This layer of cement is covered with a fine mastic, very thin, and of a deep red colour,
laid on with a brush, giving the whole a face as smooth as highly polished marble.
on.
The waters of the Eure and Airan were conducted along this course, which was 4 feet in
width, and 4 feet 9 inches in height. The walls are of moellon or rubble, and had over
them a covering or slab, 2 feet 6 inches in height, formed of two courses of freestone
projecting 2 feet; over these were laid slabs of freestone, which covered in the aqueduct,
12 feet in length, and 3 feet 3 inches in width, projecting over the walls below 9
inches. The fall given to the water is four-hundredths of a foot for every hundred feet,
throughout the entire length of the aqueduct, which brought the waters to the inhabitants
of Nismes, from the sources of the Eure and Airan in the valley of Uzes; after these rivers
have supplied many mills, they fall into the Gardon, near the Pont du Gard.
Several portions of the two aqueducts which conveyed their waters respectively to the
great aqueduct still remain, between Uzes and the village of S. Maximin.
The commencement of the aqueduct was to the south of S. Maximin; it followed all
the sinuosities of the hill, so that the level was always maintained; it was entirely under-
ground, and often cut in the rock itself. The Romans constructed small bridges over the
rivulets, which were permitted to pursue their course to the Gardon. One of these, thrown
across the cascade of the Bord Negré, remains. After having passed the Château d'Argellies
the side of the hill is lower, and the summit is below the level of the waters, conducted to
this point; here the aqueduct is carried on a series of arches, similar to those of the upper
part of the Pont du Gard, with which they unite, passing behind the village of Vers, and
describing on their plan considerable bendings, that they may follow the crest of the hill,
which precaution was necessary, to economise the height of the piers. Thus the waters of
the Eure and Airan arrived at the Pont du Gard by a circuitous flow of 50,855 feet; after
it had passed the Pont du Gard, the aqueduct was lost in the sides of the mountain as far as
Lafoux; it then reappeared, and was carried on arches more or less elevated across the
gorges met with in its passage, some of which remain. It was then carried on the eastern
side of the hill, behind St. Bonnet, under the village of Sarnhac, and crossed the great road
to Nismes near Besonce, to arrive at the mountain of St. Gervasy, which it followed as far
as Nismes. The whole distance from the Pont du Gard is 83,665 feet: whence it results
that the total length of the aqueduct between the extreme points was 134,515 feet.
The relations of both Vitruvius and Pliny on the construction of aqueducts, the engineer
here finds carried into effect in the most admirable manner, and he must be convinced that
the knowledge possessed by the ancients of the laws of hydrodynamics was far greater than
they have received credit for. If their writers have not handed down to us the calculations
made previous to the commencement of these vast and laborious undertakings, the works
show practically their engineers thoroughly understood the art of levelling, and the laws
by which water in its course was governed: though the fall given to the slope of the
channel of this aqueduct is but small, it is regular throughout, and from the masterly manner
in which it is conducted, we cannot but give the constructors the credit of having under-
stood thoroughly the nature and properties attendant upon running water, and that they
must have observed and studied the slopes and beds of the rivulets and larger streams before
they could have arrived at the knowledge displayed in these surprising monuments; as much
care was required, or perhaps more, to set out one of these water conduits, than is demanded
for a modern railway. We find the principles to perform both nearly similar, the locomotive,
in one case, is to be moved along a level or inclined plane at a certain angle, while the water
is to keep one uniform and constant course; both in mountainous districts must be con-
ducted over valleys on artificial constructions, and along the sides of steep hills, and this
must be performed without creating any abrupt turns or angles. In drawing a comparison
between the experience of the men employed in engineering works in times past and at the
CHAP. IV.
179
ROMAN.
present day, the aqueduct and railroad might be taken as a fair test of their ability; to effect
the one is as difficult as the other, and the same kind of talent is required in both; he who
could perform the one might safely be entrusted with the other. If this opinion is correct,
we ought not to be satisfied that during the last two thousand years we have made suf-
ficient progress, and the historian may, perhaps, be induced to say we had not yet arrived
at the excellence attained in former times. When the writer visited this splendid Roman
work in the year 1817, it was about to receive a considerable repair: no monument is
more deserving of being upheld than the Pont du Gard; it is an evidence of the talent and
skill of the Roman engineers in their best days, and worthy of being studied by all who
have the conducting of water to a great and important city.
Aqueduct of Volsci, an ancient city of Etruria, the date of which is not accurately ascer-
tained, though its manner of construction indicates the period of the empire, of which it is
a splendid specimen.

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Fig. 206.
AQUEDUCT NEAR VOLSCI.
Modern writers wonder why aqueducts were built in preference to the humble and ordinary
method of conveyance of water in pipes, and condemn Sextus V., Nicholas V., and Paul
V., who during their sovereignty as Popes used similar means to bring three noble streams.
of water into Rome. In the first place, any metal pipes laid across the Campagna or marshy
land in the neighbourhood of that city, would not only have perished ultimately from the
abundance of carbonic acid contained in the waters of the soil, but this dissolving the lead
or iron would poison all the inhabitants: in the next, the pipes would have been more costly
than masses of masonry, if the bore was sufficient to conduct the quantities which the arched
aqueducts were enabled to do. By taking the levels accurately at first, and allowing the
proper fall throughout, a regular supply was maintained, and the water, perfectly pure
throughout its whole course, was delivered into castelli, or reservoirs at a height above the
level of the city which rendered any mechanical power unnecessary for its elevation: it
could from them be distributed to the baths, fountains, and private houses, by simply
opening the sluices at particular hours appointed for the purpose. The ancient aqueducts
for nearly 2000 years have conveyed running streams constantly, and if an estimate was
made of the cost of their first construction in stone or brick, after the Roman manner,
and another upon our system of pipes, their wear and tear, with the daily and hourly
expense of steam-engine-power to raise the water, the balance would be found greatly in
favour of the ancient method. The purity of the water and its abundance, which could
keep hundreds of fountains of the imperial city, and still does, constantly playing, is another
reason in their favour.
Aqueduct at Lyons. Augustus, Tiberius, and Claudius, all contributed to the embellishment
of this ancient town, then called Lugdunum. A palace erected by the latter emperor in the

Fig. 207.
AQUEDUCT AT LYONS.
10000
hignest part of the city requiring to be supplied with water, an aqueduct was constructed
with arches built of rubble stone, faced with opus reticulatum. The manner in which this
N 2
180
Booz I.
HISTORY OF ENGINEERING.
· A
work was performed was as follows:
level pavement was formed of brick, on
which was raised a frame or caissoon of
timber planks; against the sides of this,
squared stones were laid in regular courses,
and their interior filled in with rubble, in a
dry state, after which a grouting of liquid
cement was poured in to consolidate the
whole. Lime, fine gravel, or sand, mixed
with a due proportion of water formed
this grouting; after a sufficient time had
been allowed for the work to consolidate,
the caissoon was mounted upon another
course or layer of tiles, and similar oper-
ations to the first took place.
The bricks or tiles used are 1 foot
9 inches in length, 12 inches in breadth,
and an inch and a half in thickness.
The whole of the water conduit was
coated with cement; at the bottom its
thickness was 6 inches, at the sides an
inch and a half: 24 inches from the bottom
of the canal, at every 30 inches distance,
iron ties were inserted to hold the side
walls together, and prevent their being
pressed outwards.

L
PLAN OF CASTELLUM.

U
ARCHES IN THE VALLEY,

0000000001
PIER OF ARCHES.
The three aqueducts of the ancient
Lugdunum were traced for many miles
to the source of the waters they conducted,
by M. Delorme, who, in 1759, gave to the
séance de l'Académie an account of his
researches. The Mont de Pile derived its
supply from the river Gierre and some
smaller springs in its vicinity. These
waters having been conducted over eight bridges, across the valley where the ninth was
situated, the syphon was carried over. The valley at the foot of the heights of Soncieu
is very deep, and where the aqueduct crosses, was a large reservoir, constructed on the
south side of the river Garon.
Fig. 208.
LYONS.
Here we have an example showing us that the Romans well knew, when water was
brought down one side of a hill, how to make it rise on the other: why this plan was
adopted in preference to building a series of arches, like the Pont du Gard, we are not
informed; but the arrangement proves that they practically understood that water would
find its level, what precautions to take to expel the air, and the advantages of a venter.
Leaden pipes of large dimensions, bedded on the sides of the valley, conducted the water
to others, laid over a bridge in an inverted curve; they were then continued up the opposite
sides of the valley, and delivered the water into another reservoir, of corresponding level to
the one on the hill before described. The aqueduct then took the name of Chaponest, from
the hill where the last reservoir was situated, and the waters were conducted underground
along the west side of the village. A bridge of 90 arcades carried it to another reservoir, when
it again descended into the valley in similar leaden pipes, passing over the river Baunan in an
inverted curve, and again mounted to a second reservoir at St. Foi. A series of arcades con-
ducted it to level ground, sometimes above, at others below; it continued its current till it
reached the gate of St. Irenee, where was another reservoir; leaden pipes conducted it
through the fosse of St. Irenee, when it mounted once more, and was discharged into another
reservoir, near the Gate of Trion; in this instance the pipes were bedded in a mass of solid
masonry, and not carried over a bridge.
The total length of the course of this aqueduct was 13 leagues, in which distance it had
a fall of upwards of 350 feet.
The reservoir, which emitted the water at the aqueduct bridge of the Garon, was built at
the top of a tower; its length was 14 feet, and its breadth 4 feet 6 inches. On the side towards
the valley 9 oval holes were made, at 9 feet from the bottom, about 12 inches in height,
and a little less in width; through these passed the leaden pipes, which descended into the
valley, crossed over the bridge of arches, and rose on the other side in the regular and uni-
form curve of a great syphon.
When the water reached the reservoir destined to receive it
on the opposite side, it entered at the top, and was emitted at the bottom : the leaden pipes
were 8 inches diameter in the clear, formed of metal of an inch in thickness, and the
water in the emitting reservoir was always a foot lower than in that which received it. One
CHAP. IV.
181
ROMAN.
portion of the aqueduct was formed by opening a trench 5 feet wide and 10 feet deep,
with a uniform fail of 12 inches for every hundred toises. The channel for the water was
lined with masonry, the bottom of which was 12 inches thick; on this two walls, 18 inches
in thickness, were raised to the height of 5 feet; the space between, being two feet in width,
was covered by a semicircular arch, 12 inches in thickness, over which earth was laid to an
average thickness of 2 feet.
At the bottom of the watercourse a coat of cement, 6 inches in depth, was laid, and
the sides were coated in a similar manner, to the thickness of an inch and a half; the width
between the walls being reduced to twenty-one inches. The walls were formed of small
angular stones, laid in mortar, composed of coarse rough sand; the cement used for the
lining was made of very fine sand, lime, and powdered brick; that employed for the first
coat was of a coarser kind, the powdered brick being as large as a pea; but the lime seems
to have been fresh from the kiln, and well-tempered at the time.
Where the aqueduct was tunnelled in the side of the mountain, and its watercourse was
considerably below the surface, putei or wells were sunk, to allow the vapours which
arose to disperse freely; these shafts were made at the distance of an actus, or 120 feet,
many of which are found with their sides steined in very perfect order; they admitted
light and air, and also the workmen who were required to repair any defects, or remove
any deposit that might by accident accumulate within the channel. The putei must not
be confounded with the columnariæ, or vent-pipes, which were perpendicular tubes, the
tops of which rose considerably above the aqueduct, for the purpose of maintaining an
equal pressure and ventilation throughout. Health was the consideration which caused so
many contrivances to maintain the water pure; the ancients knew that pent up, and not
allowed its due proportion of air, it lost that sparkling effect for which it is admired; they
preferred the walled aqueducts on this account, as they delivered the water in a whole-
some state.
Where the works are above ground, the walls, 2 feet in thickness, are faced with reti-
culated work, the size of the lozenges varying from 3 to 6 inches square, and worked
without any intermediate course of brick. The arches were roofed over, to throw off the
rain; and the entrance to the aqueduct was by iron doors placed to open internally. Those
portions underground were approached by man-holes, brought up a little above the level
of the soil, and the entrance of the water into the aqueduct was by a valve, which, sliding
up and down, could be regulated at pleasure.
When the aqueduct was formed above ground, a footing of masonry 6 inches in thickness
was set out, and the span of the arches varied according to their height; all were semi-
a11.

Fig. 209.
ST. JUST AT LYONS.
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circular, and if of 12 feet span, the piers were made equal to half, and where the arches
required to be built to the height of 31 feet, the width of the opening was 15 feet 6 inches,
and the piers 7 feet 9 inches; so that the piers were half the opening, and the opening or
span made equal to half the height.
Where the canal for the water was formed on this portion of the aqueduct, an offset was
made on each side, increasing the thickness to 6 feet.
The piers and masonry throughout are of a corresponding style, formed of small square
stones, laid in a thick bed of mortar, and known as the opus reticulatum, a beautiful kind of
work, described by Vitruvius in lib. ii. cap. 8. : it is, however, very subject to split, from its
not having the necessary bond; its whole strength depends upon its quoins being propor-
tioned to the space given to the reticulated division which must always be regarded as a
simple filling in. The two or three courses of tiles or stones which lay horizontally through
the entire wall serve to tie on the two faces of the work, in part, but there is not that sta
bility in a pier so constructed, as is found with either English or Flemish bond; the cement,
N 3
182
BOOK I
HISTORY OF ENGINEERING.
when excellent, makes up for this defect, but we frequently find in reticulated work-
openings and cracks, which prove it is not calculated to support a heavy and constant
weight. At every 4 feet in height, two courses of brick bonded or tied the work together,
the bricks being 2 inches in thickness, and
twenty-two inches square. The quoins
of the piers are formed of squared stone,
but as these were not properly worked,
they have been detached and created con-
siderable injury.
The voussoirs of the arches are com-
posed of stone, 3 inches in thickness,
and an alternate one of brick; over the
extrados is laid a brick, which by its pro-
jection forms a label, on this two courses
of tile or brick are bedded, which continue
through the whole length without pro-
jecting. On this course of double tile
the water channel is built.
The valley between Soucieu and Cha-
ponost has a depth of nearly 200 feet, and
for nearly 2500 feet the water is con-
ducted over an aqueduct composed of five
stories of arches; that between Chaponost
and St. Foi is nearly 300 feet in depth,
has eight stories of arches, and the third
valley between St. Foi and Fourvieres
had three stories of arches.
Some of the leaden pipes found at the
extremity, where the water entered the
palace, were from 15 to 20 feet in length,
and bore the marks of Tiberius Claudius
Cæsar.

རྔ་རྟsཅཔོ'
བ་ཞུ་བ།
Fig. 210.
PIER AT LYONS.
The Aqueduct near Frejus, called Esterelle, where it passes through the country of Gar-
gallon, or Agreeable Valley, is a noble structure. Its piers are strengthened by buttresses,
the winds of this valley being at times powerful and very destructive: the water is brought
4000

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--
ނކ
Fig. 211.
ESTERELLE ARCHES.
from the river Siagne, running near Mons, 5 miles from Frejus. The country is very
uneven, and full of rocks, which in many parts have been tunnelled. The whole circuit
made by this aqueduct, in consequence of the difficulties presented by the country through
which it passes, is more than ten leagues.
All the provinces in the south of France were as well supplied with water as Rome
itself, and the various engineering works as admirably performed as in the imperial city.
Rich, indeed, is this district with amphitheatres, theatres, temples, baths, and public build-
ings, and no one can doubt, who has travelled through this delightful district, of the pro-
gress made in the arts and civilisation at a very early period.
Aqueduct at Metz, was another beautiful piece of construction that conducted the springs
found in a valley beyond Gorze, now called les Bouillons, for a distance of 11,373 toises, with
a face of about 70 feet. They are first led through a channel 3 feet in breadth, and 6
feet deep, formed in a bed of masonry, composed of rough stones and mortar. On the inte
rior the walls are faced with masonry in regular courses, and where the watercourse is laid
against the side of the hill, an additional wall, varying in thickness from one to two feet, is
CHAP. IV.
183
ROMAN.
built to resist the thrust of the earth. The channel for the water is arched semicircularly,
and the voussoirs are at the top 3 inches thick, and at their intrados only 2: they are
generally 12 inches square.



PARTS OF CASTELLUM.

Fig. 212.
METZ.
The remains at Jouy are considerable, and are
situated at about one league from Metz, in a
beautiful valley, through which the Moselle
flows. There are sixteen arcades, the openings
unequal; six before arriving at that which
forms the entrance to the village, the others
are in a meadow; the aqueduct afterwards
crosses the Moselle. The work is executed
with small stones, in the form of bricks, laid
in regular courses; and in the neighbourhood
is a quarry where many of these stones remain,
and the hatchets which prepared them have
sometimes been found.
The erection of this aqueduct is attributed
to the Roman legions at the time they were
commanded by Drusus, who obtained a victory
over the Germans; he was the son of Livia,
and brother to the Emperor Tiberius; his
monument is at Mayence, where he died at
thirty years of age, in consequence of a fall
from his horse.
The plan of the Castellum and of the Pis-
cina limaria may be accurately traced, the
arches and construction of which are highly
ingenious.
ம

PLAN OF CASTELLUM.
CHANNEL.
Fig 213.
PLAN OF PISCINA -LIMARIA AT METZ.
The length of the series of arcades which crossed the Moselle was about 570 toises; the
thickness of the piers 12 feet, but the opening of the arches, and the width of the piers,
varied; these were sometimes 14, and at others 15 feet.
N 4
184
BOOK I
HISTORY OF ENGINEERING.

PARTAM
111
ሕራ
Fig. 214.
JOUY.
In one part of the aqueduct was a double channel, formed by a division wall, which was
considered serviceable in case of a repair being required.
The quantity of water which flowed to Metz was calculated at upwards of a thousand
cubic feet per minute.
Aqueduct of Evora in Portugal, in the province of Alemtejo, was constructed, as well as
a temple to Diana, by Sertorius. This town, the third of importance in the kingdom,
abounded with Roman remains. The aqueduct is in good preservation, the arches are 13
feet 6 inches in span; the piers 9 feet in breadth, and 4 feet 6 inches in thickness. In some
instances additional strength is given by buttresses. All the work is executed in stone, with
the exception of the arches, which are in tile or brick. The castellum, of fine proportions,
remains very perfect; its form is circular, 12 feet 6 inches in diameter; on the exterior are
eight Ionic columns, between which are as many niches, with hemispherical heads, through
one of which is an entry to the interior. Over this order is another formed of pilasters,
and the chamber was covered by an hemispherical dome.
The Aqueduct at Carthage. Its ruins may be traced for a distance of fifty miles, at the
village of Arriana, near Tunis; one range of arches is entire, 70 feet high, with piers 16
feet square, built of a hard durable limestone, and excellent mortar. Many of the cisterns
for the reception of the water, built of rubble and cement, remain, though converted into
dwellings and stables. Other smaller cisterns, 93 feet in length, 20 in width, and 27 in
height, to the vault, are met with. Temples were erected over the fountains which supplied
this aqueduct; the conduit for water was 6 feet in height, and 4 in width, gathered in at
the top like a pyramid, and lined internally with a beautiful cement, in high preservation.
This aqueduct passed by a tunnel through the hill, and at every 180 feet perpendicular
shafts, 4 feet in diameter, were formed of courses of squared stone, which were carried
up 4 feet above the surface of the ground; these shafts were used for drawing up the soil,
and afterwards left for ventilation.
Near Udena is another aqueduct, built by the Carthaginians; a thousand arches of beau-
tiful masonry remain, which are upwards of 100 feet in height; some writers say this was
the work of the Romans after they had subjugated the country.
The Aqueduct of Segovia, built by Trajan, of squared stone, laid without mortar, extends
upwards of 2220 feet across a valley; in many places it is nearly 100 feet in height.

Fig. 215.
PLAN.
CHAP. IV.
185
ROMAN.
The Aqueduct at Constantinople was erected by Hadrian before the foundation of the new
eity by Constantine; afterwards it bore the name of Valens, as well as that of Theodosius.
It consists of two tiers of arches, built with alternate layers of stone and brick, in a similar
manner to the walls of the city.
The Aqueduct at Lisbon, where it crosses the valley of the Aliantara, about a mile
from the city, consists of thirty-five arches, one of which, measured to the soffite, is 231
feet, and the entire height of the structure at this place is said to be 263 feet. The
span of the principal arch is 108 feet, and the thickness 23 feet 8 inches. A vaulted cor-
ridor, 9½ feet high, and 5 feet in breadth, passes over three arches, on each side of
which corridor is a semicircular channel for the water to flow, 13 inches in diameter.
Aqueducts were built throughout the eastern as well as western provinces, and Pliny, in
one of his letters to the emperor, says, that the inhabitants of the city of Nicomedia had
expended 3,000,229 sesterces (about 24,000l.) in building an aqueduct, which did not
answer the purpose, and, consequently, was abandoned to ruin. A second attempt in
another situation was made, at an expense of more than 2,000,000 of sesterces, which also
failed. Pliny himself then examined some springs from whence the water might be con-
veyed over arches, as was attempted in the first design, and in such a manner, that the
whole city might be supplied; he recommends the use of brick for turning the new arches,
as it was cheaper and easier to carry up a work in that material; he also requested the
emperor to send some engineer skilled in the management of waterworks to undertake the
construction. Trajan, in his reply, observes, that every province is provided with men of
skill and ingenuity, and that Greece supplied most of the architects that came to Rome.
Canals in Italy and the Roman Empire.-Canals in the early history of Italy seem to have
been formed, either for the transport of an army, or for draining a morass or marsh: that
cut through the Pontine marshes, 162 years before Christ, was for the purpose of rendering
the country more salubrious. Before this period the Etruscans had cut many canals, and
they executed the Fossa Phillistina and the Fossa Carbonania, which drew their waters
from the Po; indeed the country watered by this river has always been the scene
where the great undertakings in Italy connected with inland navigation have been car-
ried out.
The consul Caius Marius, about 51 years before Christ, was sent into Provence at the
head of an army, to defend it against the incursions of the northern barbarians, and established
himself in the neighbourhood of Arles, on a spot where he could with facility receive his
supplies by means of the Rhone from the sea. The river was difficult of entry, in conse-
quence of the shoals thrown up at the mouth, and this consul undertook to dig a canal, and
conduct the waters of the Rhone from the left bank, opposite his camp, into a haven called
Fos, where the vessels lay. This canal, called the Fossa Mariana, supplied him with all
that was required, and may be traced to Marseilles, where the inhabitants benefited con-
siderably from it.
The difference of level between two seas was not so readily overcome by the Greeks,
when they attempted to cut through the Isthmus of Corinth, in the time of Demetrius
Poliorcetes, at which period it was the practice to transport light vessels across the isthmus,
a distance of five miles, on machines constructed for the purpose, which was continued in
the wars of the Turks and Venetians. Julius Cæsar, Caligula, and Nero, renewed the at-
tempt to unite the Ionian Sea with the Archipelago, but were frustrated, by finding that the
water in the Corinthian Gulf was much higher than at Cenchreæ, and, consequently, the
Island Egina would have been flooded, and the canal rendered unserviceable.
It was the important part of the business of the Roman proconsuls in the distant parts of
the empire to lay before the emperors the best method of changing the courses of rivers, for
the purpose of more readily communicating from the sea to the centre of the provinces ;
of this we have many examples. Lucius Verus, general of the Roman army in Gaul, under-
took to unite the Saone and the Moselle by a canal, and to open a communication to the
Mediterranean and German Ocean, by means of the Rhone, the Saone, the Moselle, and
the Rhine; his death prevented the execution of this project.
The object of these works was to facilitate, in the first instance, the expediting the pro-
consular legions, which every year were sent from Rome to the remote provinces. The
great Fossa Drusiana, supplied by the Rhine, was executed by Drusus Germanicus, to in-
crease the river Yssel, by which he transported his army into the north.
Corbulon afterwards, either to establish a more convenient passage for his troops into the
British Isles, or to drain the stagnant waters of the Rhine, which overflowed extensive tracts,
made so large a cut in that river at Batavodurum, that he diverted almost all the water
from it, and led it into bis canal, which acquired the name of Fossa Corbulonis, now
called the Leek, the waters of which, under the name of the Meuse, run into the Northern
Sea.
Emilius Scaurus united the waters of the Po, near Placentia, to drain the marshes, and
there is no river in Italy that was not made by the Romans useful for the passage of
troops or provisions. The river Marrechia, near Rimini, was ennobled by Augustus Cæsar
186
BOOK I.
HISTORY OF ENGINEERING.
with a magnificent bridge, that still remains entire, and has defied all the ravages of time; it
is an early instance of a skewed bridge, and was afterwards adapted to form the port of a
canal or basin, for the convenience of the boats provided for the consular army, which marched
by the Emilian way to the provinces.
Pliny's correspondence with the emperor Trajan proves the importance attached to this
subject; the consul in a letter (50.) points out such designs as were worthy the glorious
and immortal name of Trajan, "they being no less useful than magnificent." He describes an
extensive lake near the city of Nicomedia, upon which the commodities of the country were
easily and cheaply transported to the high road, from thence were conveyed on carriages to
the sea-side at great charge and labour; to remedy this inconvenience, he recommends that
a canal should be, if possible, cut from the lake to the sea, observing that one had already
been attempted by one of the kings of the country, but whether for the purpose of draining
the adjacent lands, or making a communication between the lake and the river, was
uncertain: these useful works, in common with all others, fell to decay with the decline
of the Roman empire: during the disastrous period which succeeded, until the time of
Charlemagne, Europe is deficient in any examples of similar undertakings: this sovereign
commenced the projects of uniting the Rhine to the Danube, and of opening a new com-
munication between the German Ocean and the Black Sea.
The Italian republics, in the twelfth century, revived the arts and sciences, and the first
signs of returning activity was to open the navigation by sea and by rivers long neglected.
The Venetians, driven by Attila from the neighbouring lands of Italy, assembled them-
selves in the marshes of the Gulf of the Adriatic, which, in process of time, gave rise to a
new maritime city, preserving a semblance in its laws to the ancient Roman republic;
they soon converted the marshes into ports of great security, and the waters were covered
with numerous fleets, which enabled them to carry on a commerce with the east, by which
they became the merchants of all Europe.
Between the twelfth and fifteenth centuries, various improvements were effected in the
navigation of the Brenta, from Padua to Venice; the Mincio from Mantua to the Po; the
Arno from Pisa to the sea; the Reno from Bologna to Primaro; the Tesino and Adda to
Milan: and on this latter occasion, the Italian architects adopted the use of movable gates
to sustain the falls of the river, and afford a passage to boats, whether the level rose or fell;
for this discovery in the improvement of internal navigation we are indebted to Italy.
Mantua, after the death of the Countess Matilda, became a republic, and one of its first
efforts was to improve the navigation of the Mincio, so celebrated by the poets.
Its waters then overran the country, and becoming stagnant, rendered all the air around it
unwholesome; in its course towards the Po, it formed three arms, and discharged itself with
so much rapidity, that it was useless for navigation. In 1188, Alberto Pitentino erected that
famous structure of stone, resembling a bridge and portico, which unites the gate of
Cepetto with the neighbourhood of the ports, the object of which was to form the upper
lake by the drainage of the marshes; he converted the Mincio into a canal, and restored it
to its ancient course, uniting it with the Po, from whence it had been diverted in the time
of the Romans by Quintus Curtius Hostilius; this great work consumed ten years in the
execution, and the rise and fall was regulated at Governolo, in such a manner that boats
could ascend to Mantua and descend to Po, and the depth of its waters was so equally
maintained, that it was navigable for a distance of twelve miles: it is from this period we
must date the application of locks.
The Lake Maggiore is the source of the Tesino, which in its course is divided into
several streams, but which are again united before it enters the Po, near Pavia. For the
whole distance it is navigable, although at Pan Perduto, where the fall is considerable, it is
sometimes hazardous. Immediately below this spot commences the canal to Milan,
which at Abbiate divides into two channels. The entire length of the excavation is about
32 Italian miles, and its breadth 70 Milanese cubits.
The Canal della Martesana, by some supposed to have been executed by Leonardi da
Vinci, was made in the year 1460, under the Duke Francis Sforza; Leonardi da Vinci
joined the two canals some time during the reign of Francis I. The Canal della Marte-
sana, which is drawn from the Adda, is in length 24 miles, and width about 18 cubits;
but when constructed at first, the water it contained was barely sufficient for navigation
for more than two days in the week, and this, when all the openings for the purposes of
irrigation were closed.
One of the branches of this canal was carried for several miles by a stone dyke, and
afterwards passed through a deep cutting; the other branch had its course through the
rock, after which it was supported on one side by a lofty embankment, where it crossed the
Molgara river by an aqueduct of three stone arches.
Before the introduction of locks, contrivances called conches were in use to moderate
the too great declivity of the rivers, and which were opened to allow vessels to pass
through these openings were 16 or 18 feet in width; a balance lever, loaded at the end,
was made to turn on a pivot, and with it three hanging posts, united by an iron bar,
:
CHAP. IV.
187
ROMAN.
which crossed them immediately above the sill; besides these three perpendicular hanging
posts were two others, let some inches into the side walls. These five posts were all on
the same face, and the spaces between them were all equal. When the balance beam
turned upon its pivot, the three middle posts alone opened, and allowed the boats to
pass, after which the balance beam was turned back to its former position. At a little
distance was placed another balance beam, having attached to it a wide plank, to allow the
lock keeper to pass over, as well as to place in the grooves of the hanging posts the small
planks which served to exclude the water, by closing up the intervals; these were on the
side opposed to the current, and in number sufficient to keep the water at the required
level. Such gates, or contrivances for damming up the waters of a river, were in use at a
very early time in Italy, and two such were constructed at Governolo, in the twelfth
century, to pen up the waters of the Mincio on the side of Mantua.
Zendrini, in his twelfth chapter, Delle Acque Correnti, has informed us of the change
made on this system in the year 1481, by the two brothers Dionisio and Pietro Domenico,
of Viterbo; they were the first who used a lock chamber, inclosed by a double pair of
gates. So important an invention was made known and introduced throughout Europe,
and Leonardi da Vinci united the two canals of Milan by means of six such locks, having
a fall of seventeen braces; this was completed in the year 1497, as an inscription placed
over the last sluice stated.
CATARACTAM IN ELIVO EXTRUCTUM UT PER INÆQUALE SOLUM AD URBES COMMODITATEM
ULTRO UTROQUE NAVES COMMEARENT. ANNO 1497.
All the other canals in Italy soon adopted them, and the whole system of inland navi-
gation was greatly altered as well as benefited.
Zendrini's account of the lock formed by the two brothers, Dionisio and Pietro Do-
menico, clock-makers of Viterbo, is as follows: :-"In the year 1481, they obtained from
the Signiori Contarini a certain site in the Bastia di Stra, a place well known near Padua,
to form in it a soratore of the Piovego, which was a canal from Padua to Stra; and in a
petition made by these two brothers, of the same year, it is expressed that they will so act,
that the boats will pass from the inclosure at Stra without any danger, managing it in such
a way that the water shall flow out with ease, and the boats shall neither be unloaded
nor required to be drawn; the conditions added are, that they shall form the ingegno,
or execute the work, and also maintain it; this being granted with the revenue they
demand, in which is expressly comprised the lock of Stra. The aforesaid brothers being
required to form a buova, for the further perfection of the work."
The State of Venice, according to Zendrini, has the honour of being the first to adopt
this invention; and this is all the information that can be obtained.
In the Milanese territory are several other canals, many for irrigation; near to Ollegio
is a canal, which is fifteen miles in length, used for the purposes of navigation: it passes
Buffolaro, Biagrasso, and Arsago to Milan. At Abiato is a branch eleven miles in length;
its breadth at top is 130 feet, and at bottom forty-six; this canal was made in the thirteenth
century.
The great canal of Tesino and the branch from Pavia unite at Milan: the Muzza,
which commences at Cassano, is in length forty miles, and has its other termination at
Castiglione.
In Piedmont are many considerable canals. The Naviglio d' Inea is in length thirty-eight
miles; this unites the Doria Baltea with the Sessia: whilst another branch, thirteen miles
in length, unites the Gardena river.
A canal passes from Dora Baltea, 27 miles in length, to the Po, which it joins four miles
below Casal.
The Naviglio novo also falls into the Po, ten miles above Turin.
Along the Po, below the Milanese, the canal called Albinia falls into that river, ten miles
above Pavia. At Cremona the Naviglio della Communila unites the Lerico and the Oglio,
whilst other branches connect with the Po.
The Fossa di Puzzola is fifteen miles in length, unites the Mincio with the Tartaro: the
canal of St. George, 6 miles in length, connects the Lake of Mantua with the canal of Puz-
zola;
and that of Martenaro, 8 miles in length, which passes to Borgo Fute, under the same
lake with the Po. The Fossa Maestra is 5 miles in length, and joins Ozoma to the canal
of Montanara. The Fossero, 7 miles in length, commences at the Mincio.
From Secchio to Panaro, by Modena, is a canal 16 miles in length, with several branches
for the purposes of navigation and irrigation.
Fossa Rangone in the papal states is cut parallel to the Panaro, and two branches are
made from it, one to Po mort. From Mansolino is a canal 22 miles in length; a portion
of it is called Condotto di Conti. The Canal from Bologna to Ferrara is called di Naviglio,
and terminates in the extensive marshes after a length of 24 miles. At Primaro, the
Canal di Medicina falls into the Po. From the Great Po to the Po mort is the Canal
188
BOOK I.
HISTORY OF ENGINEERING.
di Bianio, the Naviglio Ferranese. The Gulf of Venice is connected with the Po by a
canal, 6 miles in length, called Val d' Albama.
Besides these are a vast number of branches, which are solely used for the purposes of
irrigation.
Ferrara is connected with Venice by the Po and several canals; the canal Ponfilio con-
ducts to Pont di Lago Oscuro; here the Po is entered, and its navigation continues for
forty miles; when passing four miles along the canal of Cavenella, the village of Laurio is
arrived at. At nine miles upon the Adige are the sluices of Brondo, which are only 28
miles from Venice; soon after the Venetian lagunes are entered. The Bachiglione was
formerly the chief navigation at Padua; at Vicenza it unites with the Rherone, and then
it becomes navigable for vessels of considerable burthen. After passing Padua for fifty miles,
its course is winding, and it then enters the Levant at Bundolo. Between Padua and
Vicenza are several sluices. These sluice gates, or pertuis, as they have been designated,
were thus contrived.
The lower beam of each gate was framed with the head and heel posts, so as to allow a
space of 6 inches between it and the sill. From the middle beam to the top, the gates
were planked over in the ordinary way; the lower part was left open, or in skeleton
framing, and was closed by paddles or sluices, which were moved up and down by a rack
and pinion. When the paddles were let down, they descended three or four inches lower
than the surface of the floor on the lower side, which acted as a rebate, against which
they pressed, and effectually shut the lock. They also had a bearing against the lower cross-
beam of the gate, and the head and heel posts rested on square stones, made fast in the sill.
To make use of gates upon this construction, it was necessary first to raise the paddle as
high as the lower cross-beam, which permitted the water to pass through at the foot of the
gate. The paddles were then elevated to the height of the middle beam, which was placed
at the ordinary level of the water, usually 4 or 5 feet deep upon the sill.
These gates were easily opened, as the boarded part was entirely out of the water, and a
deposit on the floor of the chamber of the lock could form but little obstruction, as from
the scour of the water, the greater part would be washed away. The only serious objection
to this early contrivance in aid of internal navigation is the injury that vessels might
sustain at the time they were passing through, when one half of their length would be out
of the water, producing a considerable strain upon them. The water passing through a
space, walled in on both sides, would, to a certain extent, allow the barge or vessel to
slide down an apparent plane; but, before it could again resume its level position, it would
be subjected to another strain. These side walls were, however, made of considerable
length, a foot being usually allowed for every inch of fall; a timber floor was laid through-
out, to prevent the force of the water from deepening and undermining the foundations.
Bassanallo had a canal 11 miles in length, at the commencement of the thirteenth century;
in its passage it passed two aqueducts, and the vessels loaded with stone to Venice chiefly
navigated it.
The Brenta is navigable fifteen miles above Padua, and it unites with the Bachiglione a
few miles beyond that city. There is also a communication with the Adige by a canal six
miles in length. Another cut, 20 miles in length, passes from Padua to Venice; its fall of
50 feet is divided into four locks.
In the lagunes are several canals; one which skirts them, called the Novella Brenta, is
36 miles in length.
At Leghorn is a fine canal 15 miles in length, 45 feet in breadth, and 4 feet in depth,
which receives its supply from the Arno. Men usually haul the vessels, the fall being
scarcely perceptible.
Drainage. The Pontine marshes derive their name from an ancient town called Po-
metia, whose exact site is not known, and which had totally disappeared before the time of
Pliny. They comprise that part of the Campania or ancient Latium situated on the south-
east of Rome, and on the confines of Naples. Their length is about 42,000 metres, ex-
tending from Cisterna to Terracina; their width is not so much their longitudinal axis
is from south-east to north-west, the direction of the celebrated Appian Way, which, in
crossing their marshes, is almost parallel to the shores of the Tyrrhenian Sea.
:
At the south-eastern extremity is the ancient Auxur or Terracina, the distance of which
place from the house now called Bonificazione, to the port S. Sebastian, or Porta Capenna
at_Rome, where the Appian Way formerly issued, is 91,841 metres, about 621 ancient
miles, each of which is equal to 1471-2 metres.
The distance from the above points to the Porta S. Giovanni, which is the route now
followed, is 101,120 metres: this modern route pursues the Appian Way for 45,000 metres,
which is comprised between Terracina and Cisterna. The shortest distance between the
house of Bonificazione and the gates of S. Sebastian and S. Giovanni, are 90,421 metres, and
to the latter 91,025 metres.
Starting from Terracina, and following the edge of the marsh, we find it separated
from the sea by a narrow down: a similar tract of land, much more considerable, and an
CHAP. IV.
189
ROMAN
alluvial deposit, interposes between the sea and the marshes on their western side, in a
direction parallel to their longitudinal axis. Their eastern side is bounded by a lofty chain
of calcareous mountains, called Monte Lepino, which extend from Terracina to Cori,
Rocca massimi, Monte Ferlino, &c. &c. Their southern limit touches the neck, which joins
the northern extremity of the chain just mentioned to a group of mountains, among which
Artemisia is distinguished, and which has Velletri on the opposite side; Gensanno, Albano,
Castel Gondolfo, &c. on the western side: the height of this neck is the common summit
of the two inclined planes; one descends into the Pontine marshes, the other into the valley
of Sacco, separated by the Lepino mountains from the former, to which it is superior; this
is called the basin of the Lake Celano, formerly the Lake Fucinus and that of the Anieno.
The neck of land at Velletri is covered with a volcanic bed, occupying a considerable
extent on the south-east and north-west of Rome; this has been thrown from several
craters which are now formed into lakes; of these there are at least ten in number: thus
the Pontine marshes are bounded on the north by a volcanic soil, on the east by a cal-
careous chain, and on the south and west by an alluvial deposit.
At the point of the angle formed on the sea-shore by the two latter directions is a
remarkable calcareous pointed hill, detached from the great calcareous chain by the downs
and marshes, to which are attached by a solid and resisting mass two other downs, the
southern and western extremity of which protects the marsh against the action of the waves.
This hill is Circe, or the Monte Circeo, and rises 525 metres above the sea; it is entirely
isolated at the extremity of the vast plain, which it commands, and was probably an island
originally; it now serves as a contrefort to the alluvium of the Pontine marshes, which
were formerly an archipelago of small islands opposite the Gulf of Gaeta and the road of
Terracina. The nucleus of Circe is a primitive rock, whose subterranean union with the
calcareous masses of the Apennines, is now marked by thick beds of alluvium of volcanic
products. The western down, which separates the sea from Machia di Cesterna and the
Machia Terracina, appear to have been first formed, bounded on the north by the Cape
of Astura, and on the south by Monte Circeo; the southern down is much narrower, and
altogether of a later formation. These marshes were probably for a length of time a gulf,
or species of lagune, afterwards covered by alluvium, brought down by the various rivers
that traverse it.
Soundings were made in 1811 near the sources of the Uffente, at the foot of the
mountains Sezze and Piperno, at 16,000 metres distance from the present sea-shore, and
carried to 22 metres of depth under the waters of the river, or 17 metres below the actual
bed, when marine sand, shells, debris of marine plants, in good preservation, were brought
up; this proves that the sea must have once bathed the feet of the mountains which
now bound the eastern side of the marsh, and that its bed had a rapid fall from this ancient
shore. The Pontine marshes may then have afforded to vessels an asylum or harbour,
where the largest might have anchored; one of the principal entrances to which was pro-
bably at a little distance from Terracina, where is the present mouth of the Badino.
The soundings made at the foot of the mountains arrived at the marine sand at 17
metres; other soundings, made near Circe, brought up sands and marine shells at a much
less depth; thus proving that the ancient bed of the sea gradually inclined from Circe to
the shore, at the foot of the mountains, where it again suddenly rose; other observations
show that in the Pontine marshes formerly high beds and islands existed, which greatly
favoured the formation of the downs; for over a large portion of them, a stratum of
very hard matter is found, the breaking up of which is attended with considerable diffi-
culty; this stratum is under the peat, and might have been formed from a deposit of the
waters, which flow from the foot of the mountains, one of the sources of which is called
Aqua Puzza, or stinking water; these waters spread themselves in various directions, and
deposit the earthy matter they hold in solution, thus forming beds of hard stone.
The filling up of the Pontine marshes has been the result of the several rivers and
torrents, which, descending from the mountains, have carried in their course a large quantity
of deposit; the alluvium is of considerable thickness over the greater portion, and is
covered with a thick mud, produced from the decomposition of plants, which apparently has
been going on for ages.
The whole of the land to the north-west, beyond the Cape of Astura, is classic ground;
at every step we find places described and celebrated by the Roman poets. The adventures
of Ulysses and his companions on the Isle of Circe, those of the warrior Camillus and his
father, Metabus, who reigned at Piperno, are to be found in Virgil. The scenes of the
last book of the Eneid were laid in the country situated to the east of Cisterna, Albano,
and Velitri, towards the sea-coast, where Ardea still remains, the ancient capital of the
Rutuli, where Turnus was king, and towards Lavinium, now Pratica, Laurentum, &c. &c.
The waters of the fountain Ferronia, which Horace mentions, still run near Terracina, at
the place where stood the temple of the goddess.
The first inhabitants of this district, the Volsci, were a warlike and powerful people
governed by a king, but afterwards divided into several republics. This latter kind of
190
BOOK. I.
HISTORY OF ENGINEERING.
government produced many private and independent interests, which eventually caused this
people to be subdued by the Romans. There is not a vestige or tradition of any hydraulic
works executed by them, though there are considerable remains both of their sculpture and
architecture.
The first work recorded is the Appian Way, undertaken in the four hundred and forty-
second year from the foundation of Rome, and finished in five years by Appius Claudius,
called Cœcus; during his censorship, which was prolonged beyond the legal term, he also
constructed the first aqueduct.
To form this road, it must have been necessary to drain the marshes to some extent, but
of this we are not informed. A hundred and forty years afterwards, the Consul Cornelius
Cethegus undertook to do this more effectually; but various causes interrupted the
progress of these works until the time of the perpetual dictatorship of Julius Cæsar, who
intended to have performed vast projects, which were prevented by his death. Augustus,
who undertook to turn the course of the Tiber from Ostia, commenced his works on a more
extended plan, and it is supposed that during his reign, the canal on each side of the Appian
Way was formed, which served for the purposes of navigation as well as drainage. This
emperor also cut another large canal along the western side, between the Lakes Monaci,
Caprolace, and Paola, passing the foot of Monte Circeo, and afterwards continued it towards
Terracina. Besides this canal, parallel to the shore, there are on the other side two exca-
vations, evidently made for drainage only, one of which is the Gorgo Leccino, intended
to conduct the water from the upper part of the marsh out of their basin towards Fosse
Verde; the other is the Rio Martino, whose line of direction is more in the centre of the
marshes; this was the greatest work ever undertaken, but history does not mention when
it was executed, or who was its engineer. Nerva and Trajan improved the Appian Way,
constructed many bridges, and several inscriptions show the interest the latter emperor
took in forming the road, but it does not appear that the drainage occupied any portion of
his attention. There is very little mention of these marshes until the time of Theodoric,
who confided their drainage to the Patrician Decius, and several inscriptions found at
Terracina mention works he performed at the end of the sixth and commencement of the
following century.
From the thirteenth to the middle of the eighteenth century, the draining of the Pontine
marshes was a subject that occupied the attention of the successively appointed popes.
Leo X. and Sixtus V. expended vast sums, and the first gave to Julius de Medici, not
only authority, but money to pursue the work; it is to him that we may attribute the
cutting of the canal, Portatorre di Badino, the works being conducted under an engineer
of the name of Jean Scotti: Fiume Sisto was a canal executed under the latter pope, the
course of which nearly follows that of the ancient Fiume Antiquo; this excavation was
performed about the year 1588, under the direction of the civil engineer, Ascanio Fenizi.
In the year 1759, Clement XIII. turned his attention to this important matter, and
ordered a detailed account to be drawn up of the state of the Pontine marshes, and an
estimate to be made of the expense that would be necessary to complete one portion of the
work; but a famine happening in the year 1665, when the inhabitants of the papal states
were much reduced, the funds collected were exhausted for food, and consequently nothing
was done in the way of draining. Clement XIV. Ganganelli, who was his successor, did
nothing; and it was not until Pius VII., in the year 1775, was elected pope, that the
works were recommenced; he altered, during his sovereignty, the character of these
marshes, and performed several very important excavations for the purpose of completing
the drainage.
These marshes contain an area of 1,106,370,000 square metres, though by some it is
estimated at 1,302,610,700 square metres; and it is calculated that the average quantity of
rain that falls into this vast basin amounts to 930,064,042 cubic inches. The volume of
water that is discharged, however, is more than double that quantity, being estimated at
2,352,573,939 cubic metres.
In the calculation from whence the above is taken, the greatest discrepancy seems to
arise in the allowance made for evaporation and infiltration; the water which pours into
them, and so adds to the quantity beyond that produced by the rains, is brought down by
the rivers Ninfa, Cavata, Fiume coperta Cavatella, and Uffente.
The canal Pio, which discharges a considerable quantity, has a very regular fall
throughout; for its first length it is only 00072 metres in a metre, and afterwards
•000068 metres in a metre for the remainder of its course. The fall of these waters in a
length of 3728 metres being 0-734 metres high water, and 525 when at its lowest.
Various methods are adopted to keep open these canals, and for several centuries it was
the practice to drive herds of buffaloes through them, which either trod down, or destroyed
the aquatic plants which are here produced in abundance. A cylinder about 18 inches in
diameter, and 10 feet in length, was afterwards used; this roller, armed with scythes,
by means of a chain was moved along by a punt or boat; twelve buffaloes were attached
to drag it when required for use; another method was to mow down the weeds and plants
CHAP. IV.
191
ROMAN.
by a scythe of a novel form, of iron, about ten feet in length, with a cord attached at
each end. A man walking on each bank, by means of ropes, drew this concave cutting
knife along the bottom, when the plants bending in a contrary direction to the movement
of the scythe, became easily separated; it was found that when the roots were left, the
plants, after cutting, shot up much stronger.
The Cloaca Maxima, or great sewer of Rome, is constructed with large blocks of Albano
stone, called Pepperino; it carried off the waters from the Forum, and drained the public

a
Fig. 216.
CLOACA MAXIMA.
buildings into the Tiber. It is about 14 feet in width, and 32 feet in height; the arch
which covers it is semicircular, and formed of three rings of voussoirs.
the Tiber, the banks are protected by walls of a
similar construction; at present, from the eleva-
tion of the bed of the river, the upper part only,
which is arched over, can be seen; this great
work is said to have been executed in the time
of the kings; its solidity is remarkable, and its
arch is sufficiently strong to bear any weights
that could pass over it. When the habitations
of the Romans were mere huts, it seems extraor-
dinary that so costly a construction for the pur-
poses of drainage should have been executed, but
it shows that in the early history of their city, all
that was undertaken for public utility was carried
out with a spirit and magnificence surpassing any
thing done by other nations who have advanced
more in civilisation and refinement.
ELEVATION.
PLAN.
Where it enters



HHHHHH
One of the chief causes of the unhealthiness of
Rome at the present day is the imperfect state of
its drainage. This vast sewer, buried by the
filling up of the river, no longer serves to convey
the accumulations of filth, or the waters from the
low valleys between the hills, where it is now
suffered to pass off either by evaporation or fil-
tration. When the Coliseum was examined some
years ago, and the earth taken out between the
walls that supported the arena, a quantity of
water drained into the excavations, and remained
there, the Cloaca Maxima no longer carrying it off, as it formerly did in the most effectual
Fig. 217. CLOACA MAXIMA.
192
BOOK I.
HISTORY OF ENGINEERING.


manner; consequently, fearing
the pestilential effects of such
a vast pool, the earth was
again thrown in, and all the
substructions of this interest-
ing building hidden from sight.
Fig. 218.
This sewer is not of larger
dimensions than another dis-
covered in 1742, which passed
under the Comitium and
Forum, 40 palms below the
present surface; every part of
the imperial city had its sewers,
and many are formed of pep-
perino stone, so universally
used before the introduction of
the travertine, which did not
take place till long after. The
Bocca della Verita is a large
marble covering to one of the
sewers of the Forum, which
admitted the surface water
into it. When we recollect
that the quantity of water
conveyed by the aqueducts
into the imperial city sur-
passed that which any modern town receives,
we naturally enquire by what means the baths
and fountains were cleansed, or the surplus
quantity carried off; and on examining the
various buildings, we find admirable and ample
provision for their draining, and what is of far
more importance, a dimension given to the
sewers sufficient to render them effective; their
sectional area was increased as they advanced,
and there appears to have been in Rome one
general direction, which proportioned the parts
as well as the whole. Had Rome been di-
vided into districts, each with its board of di-
rectors, sewers might have been built, as in
London, like an inverted telescope, growing
less as they advanced, instead of greater, or
two sewers might have been conducted into
one, whose sectional area was not equal to
either.


SECTIONS OF ROMAN SEWERS.

Fig. 219. ·BOCCA DELLA VERITA.
Alban Lake.—The plan for piercing a tunnel through the wall of the lava, instead of
directing the course of the stream,

which was running over on the
lowest side of the lake into a re-
gular channel, was adopted for
two reasons; first, as a preventive
against the violent floods that
would have taken place whenever
the waters received any extraor-
dinary increase; and, secondly, as
the space between the level at
which the lake overflowed and
that of the tunnel, where the
banks are six miles round, was of
great value, even supposing that
the land in those days, as now,
was employed to grow wood. The
object was not to gain new land,
but to recover what the pro-
prietors had been deprived of;
indeed, that which was regained
may perhaps not even have em-
SECTION.

Fig. 220.
EMISSARY
PLAN.
CHAP. IV.
193
ROMAN.
braced the whole of what had
been lost in the interior of the
crater, by the rise in the surface of
the lake.
The nature of the stone cut
through to form this tunnel made
the execution a task of great dif-
ficulty. It is a lava as hard as
iron, through which a passage was
broken, high enough for a man to
walk in it, 3 feet 6 inches broad,
and 6000 feet long. On the line
of its course, fifty shafts were
sunk to the bottom of the pro-
jected tunnel, whereby its level
and direction were accurately kept
and determined. After these shafts
were sunk, the workmen com-
menced cutting away till they met,
and the stone was lifted out by
means applied at the top of the
shafts. When the tunnel was
nearly finished, and a thin parti-
tion only separated it from the
lake, a small hole was made
through it, which let off the water

ELEVATION.

Fig. 221. ARCH OF the emiSSARIUM.
by degrees, and enabled the workmen to construct the wall of masonry around the mouth.

Fig. 222.
LAKE ALBANO.

Fig. 223.
194
BOOK 1.
HISTORY OF ENGINEERING.
The Emissarium is one of the most extraordinary among the works of the Romans;
by it was discharged the waters of a lake, which, situated in the bosom of a mountain
often rose to a con-

It
siderable height, and
threatened damage to
the plains below.
was commenced about
398 years before Christ,
at the time the Romans
were besieging Veia;
the waters had then risen
to a height of 310 feet
above their ordinary
level, and Rome itself
was in danger of an in-
undation. The oracle
of Apollo at Delphos
was consulted on this
occasion, and it replied,
that the Romans would
take the town of Veia
when they should have
drained the waters of
the lake, by turning
their course towards the
sea. A prisoner taken
by the Roman soldiers,
who said he was
spired, made the same
answer, and produced
the same impression
among that credulous
in-
Fig. 224.
SECTION.

کر
PLAN
EMISSARIUM.
people not doubting the necessity of the work, they undertook it with vigour, and com-
pleted it in one year; they tunnelled the mountain on the margin of the lake at the place
where is now the Castle Gondolfo, and formed the canal, in which the water usually ran
3 feet in depth: at each extremity is a building or water tower, one at the commencement
of the canal opposite the lake, the other where the canal issues into the plain; these
were constructed so solidly, and with such nicety of workmanship, that at the present day
they serve for the purpose intended, without having needed any repairs. This Roman
work astonishes us, from the difficulty of piercing the mountain, composed of rock, in so
short a time, the canal being so narrow that two or three workmen only could have been
employed at once. This excavation was made by sinking shafts at regular distances, which
descended to the line of the canal; by this means the works at several places were carried
on at the same time. There must have been still greater difficulty after the emissarium
was completed, in opening its communication with the lake, when the water stood at so
great a height above it. This work indicates great knowledge in hydraulic architecture
as well as in levelling. Of the several shafts sunk one only is uncovered, the remainder are
filled up.
When the writer examined this surprising effort of engineering skill in the year 1819, the
arched channel was in a very perfect condition; supplied by the guides with pieces of wood
on which lighted tapers were mounted, he had the opportunity, by floating them along the
gentle current which continued in a straight line, to observe during their progress towards
the discharge into the plains below the finely constructed vault. This work was undertaken
nearly 400 years before the Christian æra, and we have still the means of studying the arch
as constructed at that period, which deserves our highest commendation: an ilex of con-
siderable dimensions had rooted on the blocks of stone which form the side walls encom-
passing the emissarium, which had displaced some of the upper courses.
A wooden penstock was in use to let off the water from the lake, composed of boards
fastened to an outer frame that worked within a groove in the stone at each side, and which
seemed to have been the original arrangement made to comply with the words of the oracle,
Livy, lib. v. cap. 16. -" Roman, beware lest the Alban water be confined in the lake;
beware lest thou suffer it to flow into the sea in a stream; thou shalt form for it a passage
over the fields, and by dispersing it in a multitude of channels get rid of it.”
cr
It was long the custom of the Romans and the Volscians to celebrate together an annual
festival in commemoration of the success of this work; they sacrificed on the occasion a
white bull to Jupiter, whom they called latialis, and by such ceremonies were maintained a
constant inspection and attention to this surprising and early example of tunnelling through
the sides of a mountain.
CHAP. IV,
195
ROMAN.
At the Lake Fucinus is a similar work, of greater magnitude: Pliny says it was one of the
most memorable of the time, and intended to drain the lake; it was commenced by
order of the emperor Claudius: 30,000 men were employed for ten years, and it was

Fig. 225.
LAKE FUCINO.
finished, after a vast expense, in the year A. D. 52. Rocks were pierced through, and many
hydraulic machines applied to draw off the water, which constantly obstructed the workmen.

Fig. 226.
SECTION THROUGH side.
When the canal was perfected through the mountain, a vast assembly of persons was
present to witness the passage of the waters from the lake, and previous to their being con-
ducted into the emissarium or great sewer, the emperor gave a vast naval spectacle or
combat. Narcissus, his freed-man, superintended, and he allowed the waters to rush with
such impetuosity that much mischief was done: we are informed by Tacitus, that the
whole was badly conducted, and that the bed of the emissarium or canal was not sufficiently
deep to allow the water from the lower part of the lake to drain off; this was attempted
to be remedied under the reign of Nero, but the enterprise was abandoned before completed.
The masonry constructed at the mouth of the emissarium is very similar to that already
described: two staircases conduct to the platform below, in which are the conduits and
sluices to let off the water; the channels are lined with masonry in an admirable manner,
and the arch is well executed.
The lake, situated in the country of the Marsi, at the north of the river Liris, is sur-
rounded by a high ridge of mountains called Celano, which are said to be in circuit nearly
50 miles; but the water comprised within their boundary is not more than 10 or 12 feet in
depth. Tacitus, Ann. lib. xii. cap. 56., gives a very interesting account of this work, and
Virgil alludes to the lake (Æn. 7. v. 563.) as being well known:
"Est locus, Italiæ in medio sub montibus altis,
Nobilis, et famå multis memoratus in oris,
Amsancti valles."
The Liris, or, as it is now called, the Garigliano, separates Campania from Latium, and
0 2
196
Book L
HISTORY OF ENGINEERING.

CONDUIT.
SECTION.
PLAN.


Fig. 227.
SECTION.

SECTIONS.
Fig. 228.
falls into the Mediterranean Sea, south of Mola di Gaieta, where was Cicero's famous
Formianum Villa.
The Tombs of the Romans in many instances were in imitation of that which Queen
Artemisia raised at Halicarnassus in honour of her husband Mausolus, which ranked among
the most celebrated constructed by the ancients. All the towns of Italy had beyond the
walls avenues or roads, along which the inhabitants were buried; at Pompeii the Street
of the Tombs conducts the traveller to the city gates.
Tumuli were raised over the dead by Greeks, Etruscans, and Romans. In Greece the
bodies were first consumed, the ashes put into an urn or earthen vessel, and then deposited
in a vault or excavation, made a little below the surface of the ground, sometimes in the
recesses of rocks. At Syracuse and Agrigentum many of these are found in the walls
which surround them, although the sarcophagi or urns, once within them, containing the
burnt remains, have long since disappeared.
In Rome, the practice of burning was not very early introduced; at first the bodies were
consigned to their native earth, although among the Etruscans we find mention made of
the funeral pile. Sylla, it is said, introduced the custom of burning the body, having fear
that his might be ill treated after death. In the Roman sepulchres that have been ex-
amined, the skeleton is found with the arms laid close to the sides, a vase with a narrow
neck placed upon the breast, another on each side of the head, one on each hand, and one
between the legs; a dish once containing eggs, fruit, or birds, and a coin, are also met
with. Neither the Greeks nor Romans were allowed burial within their walls, and
CHAP. IV.
197
ROMAN.
Cicero (De Leg. lib. ii.), observes, "Hominem mortuum in Urbe ne sepelito neve urito.”
Plutarch mentions as an exception to this general rule, that all who had gained a triumph
might be buried in the Forum, and the ashes of Trajan were deposited within his triumphal
column.
Mausoleum of Augustus, though ruined, still exhibits sufficient to indicate its former mag-
nificence: in it was deposited the body of Marcellus, the nephew of Augustus, and those of
J. Cæsar, Augustus, and Ger-

manicus. Strabo (lib. v.) in-
forms us, that it was built upon
immense foundations of white
marble, and covered with ever-
greens; on the top was a statue
of Augustus in bronze; in the
vaults below, the ashes were
deposited, and around were
numerous groves.
The same
author describes the place
where the bodies were burnt:
"in the centre of the plain
stands the tomb itself, finished
in white marble, with iron
palisades round, and poplar
trees planted within. The
inner circular wall still exists
with the opus reticulatum,
but formerly, as it seems, there
were three walls at equal dis-
tances, the intervals between
which were marked out into
certain spaces, so as to produce
a greater number of vaults,
for the interment of each per-
son separately."
This tomb was circular; five
concentric walls formed the
foundations, which were vault-
Fig. 229.
TOMB OF AUGUSTUS.
ed to support the upper stories. Thirteen circular vaults composed the outer range, and in
the centre a cylindrical stairs conducted to the several chambers and gardens above.

Fig. 230.
SECTION OF TOMB OF AUGUSTUS.
The entrance was by a noble portico, and a passage conducted to the several corridors and
staircases; on the outside, the walls were carried through the marble casing, and between
each circle were planted the evergreens alluded to by Strabo: the statue was elevated 400.
feet from the foundations on a pedestal, lifting it above the evergreen forest which covered
the conical structure.
Little now remains of this once splendid mausoleum but a circular mass of brickwork, of
o 3
198
BOOK I.
HISTORY OF ENGINEERING.
enormous thickness; the conical vault has disappeared, and the interior, when the writer
was at Rome, was fitted up with seats to form an amphitheatre, where bull-fights were
occasionally exhibited. In the views given by Pietro Santi Bartoli, in his work on the se-
pulchres of Rome, &c. the entrance and outer walls are shown.
The Tomb of the Scipios, discovered in 1780, in a garden to the left of the Appian Way,
near the gate of S. Sebastian, is one of the most ancient: it is cut out of tufa, and consists
of a series of dark chambers, in one of which is the sarcophagus of L. Scipio Barbatus, the
great-grandfather of Scipio Africanus, who was buried, it is supposed, at Liternum, about
565 years after the building of the city, according to Livy.
The Pyramid of Caius Cestius, which stands near the gate of St. Paul, is partly within
and partly without the walls; its height is 121 feet, its breadth at the base 96; it is con-
structed of white marble, probably from the quarries at Luna. It contains a room about
20 feet by 16, and 17 feet high, upon the walls of which are some paintings, representing
two females sitting, two standing, with a victory between them; there are also vases and
candelabra. Pliny, lib. xxxvi. cap. 13., tells us the tomb of Porsenna was of a pyramidal form,
although the Greeks and Romans seldom used this figure.
From an inscription in the Museum Capitolinum, found near the monument of C. Cestius,
we learn that five persons were named heirs by his will, and that Pontius Claudius Mela
and Pothos erected this pyramid.
Trajan's column was a monument to that emperor, or rather of his victories over the
Dacians. Apollodorus is supposed to have been the architect to whom its construction
was entrusted, about the year 115 of the Christian era. Dion Cassius states that Trajan
himself erected it the year before he set out for Parthia; but from the inscription on it,
it would appear to have been raised by the senate and Roman people, when Trajan had
for the seventeenth time the tribunitian power, which happened the year the emperor was
absent from Rome. Trajan died at Seleucia; his ashes were brought home, and deposited
in a golden ball, on the summit of the column, which was contrary to the usual custom
of allowing a burial within the walls. The pavement from which this splendid marble
column rises is 15 feet below the ordinary level of the streets, the ground having accu-
mulated since its foundation on all sides.
Engineers at the present day are astonished at the simplicity of its construction, and the
dimensions of the blocks of marble that compose it. The column is nearly perfect; its
pedestal consists only of seven blocks; the cornice is a single piece 20 feet square, and 6
feet 4 inches thick. The shaft of the column is composed of nineteen courses, each 5
feet in height, and the entire diameter; in the centre a newel is left, around which are cut
the stairs that conduct to the summit. The capital, or last of the nineteen blocks of the
shaft, is 14 feet square, ornamented with eggs, well sculptured, under which are indications
of doric flutings. The shaft is covered with spiral revolutions of sculpture, representing in
full relief the various exploits of the emperor.
The height of the pedestal is 17 feet 11 inches; that of the shaft, capital, and base, 97 feet
9 inches, and the ancient part of the pedestal remaining above 9 feet 6 inches, making a total
height of 125 feet 1 inch.
The lower diameter of the column is 12 feet 2 inches; the upper 10 feet 9 inches.
One hundred and eighty-two steps conduct to the gallery formed above the abacus, on
which rises the pedestal that supported the statue of the emperor, as some of his coins show.
Two thousand five hundred figures are sculptured on this beautiful monument, among
which the emperor is represented more than fifty times; the figures are 2 feet in height at
the bottom of the shaft, and increase as they mount or get farther from view, being at the
top nearly 4 feet.
Antoninus Pius also had a similar column dedicated to him by Marcus Aurelius. The
height of its present pedestal is 26 feet: the column with its capital and base consists of
19 blocks of white marble. It is in height 97 feet 3 inches, with a pedestal above 6 feet in
height: the lower diameter is 13 feet 2 inches; a similar staircase conducts to the summit,
and a spiral decoration, like that of Trajan's, winds round the outside; but the subjects are
not so well sculptured.
Both these columns are admirably executed, and interesting to the civil as well as mili-
tary engineer for the attempts made by the sculptor to represent the various bridges, ports,
ships, fortifications, implements used to destroy as well as protect; both have been ad-
mirably engraved, from casts taken from the columns when scaffolding was erected around
them to hoist the present statues of St. Peter and St. Paul, which now terminate them ;
the author also measured them, and their dimensions are more fully given in the " Antiqui-
ties of Rome.”
The Mausoleum of Adrian, on the other side of the Tiber, apparently was intended to
rival that of Augustus: it had three stories resting on a square basement. Procopius
informs us that two stories were decorated with columns and statues, and at the top was the
statue of Adrian, "The tomb," he says, " of the emperor stands without the Porta Au-
relia, at about a stone's throw from the walls, and is well worth a visit, for it is built of
Parian marble; the stones with which the basement is constructed are joined alternately to
CHAP. IV.
199
ROMAN.
each other without cement, and its four sides are all equal. In height it tops the walls of
the city; there are also statues on it of men and horses, finished with wonderful skill out of
Parian marble. The inhabitants observing some time ago, that it stood like a tower over-
looking the city, carried out two arms from the walls to the tomb, and by building them
into it united it so that it became a part of the walls." And the same writer tells us that
in his time, during the siege, the Goths under Vitiges, having broken the statues, which
were of marble and of great size, they threw down large stones made out of their fragments
upon the heads of the enemy.
Luitprandus, who wrote in the time of Pope Boniface IV., alludes to this tomb, then a
fortress: "in the entrance to the city, there is a castle of great strength and astonishing
construction. In front of the gate is a bridge over the Tiber, which is the first in going
in or out of Rome: nor is there any other way of passing except over this bridge. But this
cannot be done, except by permission of those that hold the castle, which is so high, that a
church built at the top in honour of the archangel Michael is called St. Angelo: there is a
figure of an angel on the top." The present fortifications were made about 985, by Cres-
cenzio, since whose time it has undergone many changes, though the chamber which con-
tained the porphyry urn, now in the Vatican, and in which were the ashes of the emperor, is
still shown.

Fig. 231.
SECTION OF TOMB of adrian.
The columns which surrounded this fine tomb formed a part of the church of St. Paul.
out-of-the-walls, and in the conflagration, which destroyed that building a few years ago,
they perished.
The tombs of the rich citizens were commonly built of marble, and the ground around,
enclosed with a wall or iron railing, was planted with trees, as Pausanias, lib. ii. 15. mentions
was the practice among the Greeks. Many of these tombs were built during the lifetime
of the Romans, as upon some remain such inscriptions as V F, vivus fecit; V F C, vivus
faciendum curavit; V S P, vivus sibi posuit, and Se vivo fecit; and Pliny severely
(Ep. vi. 10.) censures those friends who neglected to complete the tomb after the decease
of the individual. Sepulchres common to many families, constructed at vast expense under
ground, were called hypogaa; such catacombs are found in the neighbourhood of all large
cities and towns in Italy. In them were recesses and niches for the urns which contained
the ashes of the dead; they were styled columbaria, in consequence of bearing a resemblance
to the arrangement of a dovecote.
0 4
200
HISTORY OF ENGINEERING.
BOOK I.
The Remains of the Tomb of Alexander Severus show two chambers which contained
sarcophagi, and the passages which led to them.

Fig. 232.
Machines and Engines used by the Romans are by Vitruvius divided into three kinds :
the scaling machine, constructed for the purpose of ascending without danger, to view works
of considerable altitude, formed of timber, put together by the carpenter, and braced strongly
in every direction. Ladders of all kinds, particularly those attached to the masts of ships,
all came under this first denomination.
Machines for lifting stones and heavy weights, employed for the purposes of construction,
were made as follows:-
Three pieces of timber, sufficiently strong for the purpose, were connected together at the
top by an iron pin, in such a manner that they could be made to spread extensively at their
feet: when these were raised by means of ropes made fast at the top, which assisted in
keeping them steady, a block was attached in which were two pulleys, turning on axles, one
above the other. Over the upper pulley a leading rope passed, which was let fall, and
made to pass under a lower pulley in a bottom block; it was then returned over the
bottom pulley of the upper block; the rope again descended to the lower block, to the eye
of which it was firmly fastened. The other end of the rope was connected with the axle,
which, as it was wound round, elevated the stone or weight to the required height. The
axle worked in two gudgeons, sockets for which were made in two pieces or cleets
(chelonia), affixed to the back of two of the pieces of timber when they were spread out.
Levers, entering mortices, made at each end of the axle, were used to turn it. Iron
shears were made fast to the lower block, which opened, and their teeth entered two holes
cut in the stone to be raised.
A block containing three pulleys was called trispastos; when the lower system had two
pulleys and the upper three, pentaspastos; and when very heavy masses were elevated,
longer and stouter beams were required; the pins which united them at top, as well as the
axle below, were all made stronger in proportion. When used, guy ropes were attached
to the shoulders or top of the three pieces of timber, and if there was no other place con-
venient to fasten these to, they were fixed to sloping piles driven in the ground, which were
well rammed round. A block slung to the head of the machine had a rope carried round
it to another block, previously fastened to a pile or stake; passing over its pulley, it returned
to the block at the top of the machine, round which the rope passed, and descended to the
axle at bottom, to which it was lashed.
By turning the axle with the levers, the machine was used without any danger, the guy
ropes attached to the piles keeping it perfectly steady.
When heavier weights still were to be raised, the common axle was not strong enough to be
trusted; it was, however, retained, but surrounded with a drum or tympanum; the blocks
employed were constructed after a different manner from that already described; at both
top and bottom were two ranks of pulleys, the rope passing through a hole in the lower
block, so that each end of the rope was equal when extended. It was then bound and
made fast to the lower block, and both parts of the ropes so retained, that neither of them
could swerve either to the right or left. The ends of the rope were then returned to the
outside of the upper block, and passed over its lower pulleys, whence they descended to
the lower block, and, passing round its pulleys on the inner. side, were carried up right and
left, over the tops of the higher pulleys of the upper block; whence descending on the
outer sides, they were secured to the axle on the right and left of the drum wheel, about
which another rope was now wound, and carried to the capstan. When the capstan was
turned, the drum wheel and axle, as well as the ropes fastened to it, being set in motion,
the weights were gently raised, and without danger. Sometimes the drum wheel was
made sufficiently large to allow men to walk within it, by which means greater power was
obtained than with the capstan.
CHAP. IV.
201
ROMAN.
Another machine of an ingenious contrivance, called polyspaston, but which was only
used by the most experienced artificers, was a single pole, maintained in its position by
four guy ropes placed in opposite directions. Under the place where the guy ropes were
attached at top, a couple of checks were fixed, over which was tied the block. Under the
block was placed a piece of timber, about 2 feet long, 6 inches by 4. The blocks had three
pulleys side by side, and three leading ropes were conducted from this part of the machine
down to the lower block, where they passed through its upper pulleys from the side next
the pole. They were then carried to the upper block, passing from the outer sides of the
lower pulley of the upper block. Again descending to the lower block, they passed round
the second rank of pulleys from the inner to the outer sides, and were then returned to the
second rank of pulleys in the higher block, over which they passed and returned to the
lowest, whence they were again carried upwards, and passing round the uppermost pulley
returned to the lower part of the machine.
A third block fixed near the bottom of the pole, called artemo, was made fast at a small
distance from the ground; this had three pulleys, round which the ropes passed for the men
to work them. By this means, three sets of men working without a capstan could raise a
weight to any required height.
A single pole was considered most convenient, as there was dispatch and facility in its
use; the situation of the weight, whether before it or to the right or left, was of no con-
sequence. These machines were generally employed for the loading and unloading ships,
and the ships themselves were usually drawn on shore by blocks and ropes only.
Ctesiphon's method for removing great weights was well known to the Romans, and
Vitruvius tells us that when he was employed to remove the shafts of the columns from
the quarry to the site of the temple of Diana at Ephesus, he did not employ the usual
means, lest the wheels of the carriages should sink into the soft ground which they had to
traverse; he constructed a frame with four pieces of timber, two of which were the length
of the shaft of the column, and the other two were placed at the ends, as transverse pieces,
to secure them together. Iron pivots inserted into the ends of the shafts, run with lead,
worked in gudgeons, were fastened to the transverse pieces, and the pivots having power to
turn freely when the oxen were attached to the frame, the columns rolled round, and
were conveyed the required distance.
Metagenes, his son, adopted the same method to remove the massive entablatures; he
constructed, in addition to the frame, wheels about 12 feet in diameter, and fixed the
ends of the blocks of stone into them; the pivots turning in the gudgeons, when the wheels
revolved, the blocks remained like axles.
Pæonius attempted to remove from the same quarry a base for the statue of Apollo; this
he placed or rather fitted into two wheels, and round their circumference he attached
pieces of timber 2 inches square, forming an entire cylinder. A rope was coiled round
this, and to the end a yoke of oxen was attached; as the rope uncoiled, the stone by means
of the wheels rolled forward; but Pæonius, who had entered into a contract for its removal,
had not sufficient funds to complete the work, much additional labour being required to
prevent its swerving from a direct line.
powers,
Principles of Mechanics. Our knowledge upon this subject is chiefly derived from
Vitruvius, but the study of the mechanical sciences commenced with Archimedes in the
school of Alexandria, established by Ptolemy Philadelphus, and was extended by Ctesibius
and Hero, about 150 years before Christ: these two philosophers first, by an analysis of all
the mechanical engines into their primary elements, reduced the actions of which they were
capable to the combinations of five simple principles, which they called mechanical
and their system was known and practised by the Romans, as it is by us at the present day.
Vitruvius explains fully the nature and difference of direct and circular motion, and
observes, that rectilinear without circular motion, or circular without rectilinear, are of
little use in raising weights. He remarks that the pulleys revolve on axles, which go
across the blocks, and are acted upon by straight ropes which coil round the axle of the
windlass; when that is put in motion by the levers, it causes the weight to ascend.
pivots of the windlass axle being received into or playing in the gudgeons of the cheeks,
and the lever being inserted in the mortice hole prepared for them, are moved in a circular
direction, and thus cause the ascent of the weight. Thus an iron lever applied to a weight
moves what many hands could not do. When a lever is placed under the weight upon a
fulcrum, one man's strength at the end will raise the weight; this is accounted for by the
fore part of the lever being under the weight, and at a shorter distance from the fulcrum or
centre of motion, whilst the longest part, which is from the centre of motion to the head,
being brought into circular motion, the application of a slight power to it will raise
great weights.
The
When the tongue of the lever is placed under the weight, instead of the end being
pressed down, it is lifted up; the tongue then, having the ground for a fulcrum, will act on
that, as in the first instance it did on the weight, and the tongue will press against the side
thereof, as it did on the fulcrum, though by this means the weight will not be so easily
202
Book I.
HISTORY OF ENGINEERING.
moved. If the tongue of the lever be placed too far under the weight, and the end be too
near the centre of pressure, it will have no effect; the distance from the fulcrum to the end
of the lever must be greater than from the fulcrum to the tongue.
The steelyard or stateræ is an instance of this principle, and was in common use among
the Romans, and our author observes, when the handle of suspension, on which as a centre
the beam turns, is placed nearer the end from which the scale hangs, and on the other side
of the centre, the weight will be shifted to the different weights of the beam; the farther
it is from the centre, the greater will be the load in the scale which it is capable of raising,
and that through the equilibrium of the beam; thus a small weight, which, placed near the
centre, would have but a feeble effect, in a moment acquires power to raise a very heavy
load.
The rudder turns a ship, though ever so deeply laden, from the action of the lever, but
Vitruvius also notices that the sails, if only half mast high, will cause the vessel to sail
slower than when the yards are hoisted up to the top of the mast, because, not then being
near the foot of the mast, which is as it were the centre, but at a distance therefrom, they
are acted on by the wind with greater force. For if the fulcrum be placed under the
middle of a lever, it is with difficulty that the weight is moved, and that only when the
power is applied at the extremity of the lever, so when the sails are no higher than the
middle of the mast they have less effect on the motion of the vessel; when, however, raised
to the top of the mast, the impulse they receive from an equal wind higher up causes a
quicker motion to the ship. Perrault disputes this doctrine in his Commentary, and properly
observes that, whether the sails are higher or lower, the motion of the vessel is not affected
by it, for the whole moves together, and there is no fixed point to serve as a fulcrum or
centre of motion; it is not therefore comparable to a lever, nor can it act as such it is
simply pushed forwards by the wind, and the only advantage in having the sails higher is
that the wind is there stronger, while there is a disadvantage from the head of the ship
being plunged deeper in the water, which necessarily impedes its course.
Vitruvius continues: "Oars made fast with rope to the thowls (scalmi), when plunged
into the water and drawn back by hand, impel the vessel with great force, and cause the
prow to cleave the waves, if the blades are at a considerable distance from the centre which
is the thowl.
“So also, when loads are carried by four or six men on a pole, the weights are so placed
in the middle, that each may bear his portion; for if they passed the centre, one set of men
would bear more than the other.
"Oxen also have an equal draft, when the piece which suspends the pole hangs exactly from
the middle of the yoke; and when oxen are not equal in strength, by judiciously shifting
this suspended piece, one may be made to draw more than the other.
"It is the same in the porter's levers as in the yokes, when the suspending tackle is not
in the centre, and one arm of the lever is longer than the other, namely that to which the
tackle is shifted; for, in this case, the lever turning upon the points to which the tackle has
slid, which now becomes its centre, the longer arm will describe a portion of a larger
circle, and the shorter a smaller circle.
CC
Now, as small wheels revolve with more difficulty than larger ones, so levers and yokes
press most on the side which is at the least distance from the fulcrum; and on the contrary,
they ease those who bear that arm which is at the greatest distance from the fulcrum.
"All these machines regulate either rectilinear or circular motion, by means of the centre
or fulcrum, as also waggons, chariots, drum-wheels, wheels of carriages, screws, scorpions,
balistæ, presses, and other instruments, which produce their effects by means of rectilinear
and circular motions."
The_Romans
The
Engines for raising Water. Tympanum. —The Romans were acquainted with various
methods for raising water, and probably after Egypt became a province, many of the
machines used by that people were introduced among them, as we have already seen that
Vitruvius was well informed upon all the sciences taught in the school of Alexandria, and to
him we are indebted for an account of much that otherwise would have been lost.
tympanum he describes might have been long in use, and was calculated not to raise
water to any great height, or beyond that of the radius of the wheel, but to lift a large
quantity in a small period of time. A shaft or axis turned in a lathe, or made cylindrical
by hand, was hooped with iron at each end, to prevent it splitting. This axis was made
to turn on tops of posts cased with iron; into this were fitted eight arms or spokes, for the
purpose of supporting the rim of the tympanum, which was thus formed; the horizontal face
was closely boarded; around it were small apertures about 6 inches in width, to admit the
water. When the tympanum was used, it was moored like a vessel, having another wheel
attached to the side of it on which a number of men could tread, by which means it was
turned round; the water received through the apertures in front of the wheel was elevated
by the arms or division thus raised beyond the horizontal position; it flowed towards the
axis, at the end of which it ran into a trough prepared to conduct it either to gardens, or
to dilute salt in pits.
CHAP. IV.
208
ROMAN.
When this machine was employed to raise water to a higher level, its diameter was
increased to correspond with the requisite height. Round the circumference of the wheel
were attached small wooden buckets, made water-tight by properly pitching them; the
men treading the wheel turned it round, the buckets then mounted to the top full of
water, and as they returned with their heads downwards, they discharged their contents into
a conduit prepared to receive it. Brazen buckets, each holding a gallon, were attached to
a double revolving chain, and when it was required to raise the water still higher, this was
mounted on an axis, and made sufficiently long to descend to the lower level; by turning the
wheel the chain was turned on the axis, and the buckets were brought to the top, where
being inverted, they passed their contents into conduits as before.
Water-mills were introduced at Rome, about 70 years before the Christian æra, as we
learn from Strabo, lib. xii., and the first was erected on the Tiber. Antipater, who lived in
the time of Cicero, in a beautiful epigram, alludes to one of these, where he addresses the
maids who were in the habit of labouring at the mill, and tells them to cease their work,
and to retire to rest, to let the birds sing to the ruddy morning, for Ceres had commanded
the water-nymphs to perform their task, who, obedient to her commands, threw themselves
on the wheel, forced round the axle, and by this means turned the heavy.mill.
Vitruvius describes their construction as similar in principle to the tympanum; that
round their circumference were fixed floats or paddles, which, when acted upon by the
force of the stream, drove the wheel round; attached to this axis was another wheel which
had cogs or teeth, and which turned with the water-wheel; a large horizontal wheel,
toothed also, and corresponding with it, working on an axis, the upper head of which was
made in the form of a dovetail, was inserted in the mill-stone. By this means the teeth
of the drum-wheel, which was made fast to the axis, acting on the teeth of the horizontal
wheel, produced the revolution of the mill-stones; in the machine a suspended hopper sup-
plied the grain by the same revolution.
Public water-mills seem to have been used in the time of Honorius and Arcadius, about
the year A. D. 398, at which time it would seem they were first established.
Mills were erected on the canals and aqueducts which brought water to the city, some
of which were stationed round the Mount Janiculum; we are informed that Belisarius
placed upon the Tiber boats in which were contrived mills driven by the current of
the stream; this was done when the Gothic king Vitiges besieged Rome, and caused the
supply of water from the fourteen large aqueducts to be cut off. Procopius, lib. i. says,
when the aqueducts were cut off by the enemy, the mills were stopped for want of
water; and as cattle could not be found to drive them, the Romans, closely besieged,
were deprived of every kind of food, for with the utmost care they could hardly find suf-
ficient for their horses. Belisarius, however, found a remedy: below the bridge which
reaches the walls of the Janiculum, he extended ropes well fastened and stretched across
the river from both banks; to these he affixed two boats of equal size at the distance of
2 feet from each other, where the current flowed with the greatest velocity under the
arch of the bridge, and placing large mill-stones in one of the boats suspended in the
middle space a machine by which they were turned. He constructed at certain intervals
on the river other machines of the like kind, which, being put in motion by the force of
the water, drove as many mills as were necessary to grind provision for the city. These
mills, called molina or farinaria, were generally after this time common throughout
Europe. Water-wheels put in motion by the current were very early employed to raise
water; around the paddle-wheel buckets were attached, which were carried to the top
without the aid of treading, and discharged as we have already described.
The Water Screw, still used, is said to have been invented by Archimedes when in Egypt,
for the purpose of enabling the inhabitants to free themselves from the stagnant water left
in the ditches after the inundation of the Nile, and Vitruvius says, it was contrived on the
principle of the screw, and raised water with considerable power, but not so high as the
wheel: his instructions for its formation were as follows:
:- a beam, whose thickness in'
inches is equal to its length in feet, is made cylindrical, its two circular ends are
divided into 4 or 8 equal parts, and as many diameters drawn thereon; these lines are
drawn in such a manner, that when the beam is laid in an horizontal position, they cor-
respond with each other. The entire length of the beam is then divided into spaces
equal to one-eighth part of the circumference; thus the circular and longitudinal divisions
will be equal, and the latter intersecting lines, drawn from one end to the other, will be
marked by points. When these lines are accurately drawn, a flexible rule, made of willow,
smeared over with pitch, is attached to the first point of intersection, and made to pass
obliquely through the remaining intersections of the longitudinal and circular divisions;
whence, progressing and winding through each point of intersection, it arrives and stops at
the same line from which it started, receding from the first to the eighth point, to which it
was first attached. Thus as it progresses through the eight points of the circumference, so
it proceeds to the eighth point likewise. Fastening thus similar rules obliquely through
the circumferential and the longitudinal intersections, they will form eight channels round
204
BOOK L
HISTORY OF ENGINEERING.
the shaft, in the form of a screw. To these rules of willow others are attached, also smeared
with liquid pitch, and to these others, until the thickness of the whole be equal to one-
eighth part of the length. The slips or rules fastened all round are saturated with pitch,
and bound with iron hoops, in such a manner that the water will not injure them. The
ends of the shaft or axle, also strengthened with iron hoops, have iron pivots inserted into
them.
On the right and left of the screw are beams, with a cross-piece both at top and bottom,
into which is inserted a gudgeon of iron, in which the pivots turn. Men are employed to
tread it in the usual way, and by this means the screw is made to revolve The inclination
at which the screw is worked is at an angle of forty-five degrees; for if the length is
divided into five parts, three of these will give the height that the head is to be raised; thus
four parts will be the perpendicular to the lower mouth. Although the above is the
description left us of this instrument or machine, as it was in use by the Romans, in all
probability they found out at an after period, that it was not essential to preserve the in-
clination to one angle, but that it might be either more or less than that of forty-five
degrees, for the nearer we approach to a right angle with the cylinder, the more the
head of the cylinder may be elevated, and the higher the water will be raised. It is, how-
ever, necessary that in inclining it, the channels should decline somewhat from the plane of
the horizon, that the water may, as the screw turns, continually descend in its course.
When many channels are used, they must of course be made narrower than where there are
few, in order to preserve the same inclination, so that less water will be raised by each re-
volution of the machine.
How the tread-wheel was attached to the cochlea or screw we are not informed, the men
employed must have been able to preserve their upright position, and probably an additional
wheel was provided for the purpose.
Machine of Ctesibius for raising water to a considerable height. About 150 years before
Christ, the mechanical arts had made considerable progress in the school at Alexandria, and
many of the principles left by Archimedes were studied more fully, and brought into prac-
tice; at this time the common pump seems to have been partially, if not thoroughly,
known; and its principles must have been understood before the more complete forcing-
pump, which was the invention of Ctesibius. Vitruvius has left us a description of this
machine as used in his day. It was made of brass; at the bottom were two buckets, near
each other, with pipes annexed in the shape of a fork, united to a basin in the middle.
this basin were valves, neatly fitted to the apertures of the pipes, which, closing the holes,
prevented the water, which had been forced into the basin by the pressure of the air, from
returning. Above the basin was a cover like an inverted funnel, riveted so securely on
it, that the water could not, under any pressure, force it off. On this was fixed an upright
pipe, called a trumpet.
•
In
Below the lower orifices of the pipes the buckets were furnished with valves, over the
openings below.
Pistons made round and smooth, and well oiled, were fastened to the buckets, and
worked from above with bars and levers, which, by their repeated alternate action, pressed
air into the pipes, and the water being prevented from returning, by the closing of the
valves, was forced into the basin through the mouths of the pipes, whence the force of the
air, which pressed it against the cover, drove it upwards through the pipe; by this means,
water on a lower level might be thrown into a reservoir for the supply of fountains.
Ctesibius, the greatest mechanic of antiquity after Archimedes, invented a clepsydra, or
water-clock, an air-gun, and some others, which, as Vitruvius observes, prove that liquids
in a state of pressure from the air produce a variety of effects, and for their description
refers to the writings of that philosopher, which were extant in his time.
This pump was in all probability the very same in its application of force to the modern
fire-engine.
Hydraulic Organs.-These were blown by the action of water, and it has been doubted
whether they were not played by the fingers, by means of keys; the description given us
of such an organ by Athenæus is that it was invented in the time of Ptolemy Euergetes by
Ctesibius, and that the idea was first given by Plato, who invented a clepsydra or water-dial,
which played upon pipes the hours of the night at a time when they could not be seen by
the index: the descriptions left us by Vitruvius are not sufficiently clear to enable us to
comprehend its construction; that by Claudian indicates that it resembled a modern organ,
blown by water instead of bellows.
Saw Mills for cutting Slabs of Marble were invented, as Pliny tells us, in Caria, to cut the
marble employed to encrust the palace of Mausolus, king of Halicarnassus, as early as 350
years before Christ. The sand which Pliny says was employed for this purpose was the
cutting power, and not the saw, which was used for merely passing down the sand, and
rubbing it against the marble; the coarser the sand employed, the longer the time neces-
sary to polish the marble, and Cornelius Nepos tells us that Mamurra, who was born at
Formia, and employed to superintend the labours of the masons, smiths, and carpenters,
CHAP. IV.
205
ROMAN.
attached to the army of Cæsar in Gaul, was the first Roman who covered the walls of his
house with slabs of marble.
Measuring Distances when Travelling, Vitruvius says, was discovered by the ancients,
and found useful in his time; his account exhibits the manner in which such mechanism
was employed at sea and on land. When adapted to a chariot or travelling carriage, the
wheels were made of such a diameter, that every revolution would advance the carriage
12 feet, thus 400 revolutions passed over 5000 feet, or a Roman mile; the diameter of
the wheels was therefore nearly 4 feet. A drum wheel was securely fixed to the inner
side of the nave of the wheel, which had one small tooth projecting beyond the face of its
circumference; and on the body of the chariot was a small box with a drum wheel,
placed so as to revolve perpendicularly, and fastened to an axle. This latter wheel was
equally divided, on its edge, into 400 parts or teeth, which corresponded with the teeth of
the lower drum wheel; besides this, the upper drum wheel had on its side one tooth pro-
jecting out before the others. Above, in a third enclosure, was another horizontal wheel,
similarly toothed, and which corresponded with that tooth which was fixed to the side of the
second wheel. In the third wheel, just described, were as many holes as are equal to the
number of miles in an ordinary day's journey. In all the holes were placed small balls, and
in the box or lining was made a hole, having a channel, through which each ball might fall
into the box of the chariot, and the brazen vessel placed in it: as the wheel turned round,
it acted on the first drum wheel, the tooth of which, in every revolution, striking the tooth
of the upper wheel, caused it to move on, so that when the lower wheel had revolved 400
times, the upper wheel had revolved but once, and its tooth, on the side, would have acted
on only one tooth of the horizontal wheel; 400 revolutions of the lower wheel caused the
upper wheel to turn but once, and thus showed that 5000 feet, or 1000 paces, had been
performed. By the dropping the balls, and the noise they made, it was known when
they had performed a mile, and at the end of every day's journey, the number of balls col-
lected in the bottom showed the number of miles passed over.
In navigation, nearly the same means were used; but an axis passed across the vessel,
projecting over each side; to this were attached wheels four feet in diameter, with
paddles dipping into the water. That part of the axis within the vessel had a wheel with
a single tooth standing out beyond its face, at which place a box was fixed with a wheel
inside it having 400 teeth, equal and corresponding to the tooth of the first wheel, fixed on
the axis. On the side of this also, projecting from its face, was another tooth. Above, in
a box, was enclosed another horizontal wheel, also toothed, to correspond to the tooth
fastened to the side of the vertical wheel, and which in every revolution, working in the
teeth of the horizontal wheel, and striking one each time, caused it to turn round. In this
horizontal wheel were holes, wherein the round balls were placed, and in the box of the
wheel was a hole with a channel in it, through which the ball descending fell into the
brazen vase, and made it sound. A vessel impelled either by oars or by the wind gave
motion to the paddle wheels, which, driving back the water forced against them, turned
the axle round, and the drum wheel followed, whose teeth in every revolution acted on the
tooth of the second wheel, and produced moderate revolutions. When the wheels were
carried round by the paddles 400 times, the horizontal wheel had made one revolution, by
the striking of that tooth on the side of the vertical wheel, and thus in the turning caused
by the horizontal wheel, every time it brought a ball to the hole it fell through the channel.
By sound and number were found the number of miles the ship had passed.
In the early Italian editions of Vitruvius, particularly that by Cæsar Cesarinus, wood-
cuts exhibit these paddle-wheels attached to the sides of the vessels.
Hydraulic architecture is greatly indebted to the Italian engineers, who have been
successively employed in draining the marshes of Italy, confining the rivers to their natural
bounds, and the ocean to its limits; before the seventeenth century there were scarcely any
principles laid down to direct the civil engineer, and Europe could hardly boast of any
eminent man in that profession. Rome had left marks enough of her greatness: as far
as construction went, or the handling of materials, there could be no want of models to
guide the labours of the artificers; in building, enough was to be found to imitate, both
in the science and the art. But hydraulic architecture had been neglected; the rivers,
in consequence, were left to pursue their natural course, their beds became elevated,
and their openings to the sea silted up all the ancient harbours were for the most part
destroyed or unfit for the reception of vessels of larger burthen, which commerce had intro-
duced.
Lombardy, the richest district in all Italy, and with a soil more fertile than any other in
Europe, is watered by the Po, which receives its supply from both the Alps and Apennines,
and has its course for upwards of a hundred leagues through Sardinica, Pavia, Placentia,
Cremona, Mantua, and Ferrara to the Adriatic Sea; its importance is so great, that it is
navigable to Turin.
The snows which cover the mountains that bound Lombardy during the summer afford
206
HISTORY OF ENGINEERING.
BOOK I.
it abundant water to irrigate the lands of Piedmont, where this practice has been adopted
from time immemorial.
Near Bologna, Ferrara, and towards the Adriatic Sea, the land is often under water, and
the inhabitants of this district are subject to breathe an impure and malignant air in con-
sequence; this is chiefly owing to the attempts made in the middle ages to keep out the
Po, by constantly throwing up dykes, for the purpose of penning back the water in the
river; this naturally, in the course of years, from the deposit, tended to elevate the bed con-
siderably above the country it flowed through.
At the mouth of the Po, vegetation flourished amidst these deposits and overflows, pro-
ducing the worst kinds of malaria, and that portion of the coast of the Adriatic, which
intervenes between Mount Pesaro and the port of. Brondolo, and which formerly exhibited
a deep hollow curve for its section, was by the alluvium elevated to a considerable height;
in consequence all the roads were rendered impassable, and the various streams which
flowed into the sea, at this portion of the coast, as the Po at Goro, the ancient Po of
Primaro, the Lamone, the Ronio, the Savio, Usa, Marrechia, and many others, which
brought down in their course a quantity of deposit, had their beds considerably elevated;
this occasioned the banks which confined them to be raised in proportion, and when these
from neglect gave way, in the time of floods, the whole country became one vast lagune or
swamp.
Ravenna contained upwards of 14,000 inhabitants, and was founded, according to Strabo,
by a colony of Thessalians, on the borders of the sea, from which it is now, in consequence
of the deposit from these rivers, more than two leagues distant, and that place, which
was a port in the time of Augustus, and served him to assemble his fleet, is now land.
Even so late as the time of Theodoric, it was a place of so much importance, that after his
conquest of Italy, he made it his capital, and highly embellished it; it contains his tomb,
which is a curious structure of Istrian stone, 34 feet in diameter, covered by a single
block, placed 40 feet above the floor; the lower part of this circular edifice is now filled
with water.
Ravenna was built, like Venice, in the middle of the waters, and by the Romans it was
united to the main land; it is now situated between the mouths of the ancient Po of
Primaro, of those of Lamone, of the Ronio, and of the Montone, and this once celebrated
marine establishment is now an extensive marsh.
The lagunes of Commachio once formed a portion of the sea; they are now situated
between the ancient beds of the Po of Primaro and of the Po of Volano. When the
tongue of land, or bank, which separates these lagunes from the sea was thrown
up is
not known. Neglect during the middle ages of these great and important rivers was the
chief cause of the changes which have taken place on this coast; their deposits have filled
up the sea where they have discharged themselves: Ravenna is now 8000, Rimini 1500,
and Adria 32,000 metres from the coast; and each of these places ranked as ports in the
time of the Romans.
Rimini was the spot on which the Emilian and Flaminian roads terminated, and in
the time of Augustus it was a port of importance; here was his arch of triumph and his
bridge.
Upwards of 160 square leagues of country was desolated by these overflowings of the
various rivers in the sixteenth century, and it was a constant cause of dispute between the
inhabitants of Bologna and those of Ferrara.
In the twelfth century the Po had passed near Ferrara, and in 1155 it changed its
course, and in the year 1600 it was deemed advisable to separate the Panaro and Rheno,
which flowed over its ancient bed, called the Po di Primaro, and which inundated the
valleys of Commachio. About 1604, the Pope ordered that the Rheno should be turned
into the valley of Santa Martina, but all that could be done could not prevent their being
overflowed, for the banks gave way several times, and a very considerable sum of money
was spent to no purpose.
These terrible inundations alarmed the whole of the inhabitants
of this part of Italy; the evils were daily increasing, and the most eminent scholars of the
day, (for there were no engineers,) were consulted upon the occasion; it may be considered
highly fortunate for Europe and the world in general, that these disasters directed the
labours of the greatest philosophers of the age, when science began to revive, to the study
of hydraulic architecture: all we at present know has its origin in their experiments;
all the useful inventions applicable to modern practice, we owe to the writings of
Francesco Mengotti, Mario Lorgna, Pietro Zuliani, Francesco Focacci, Antonio Tandini,
Isidoro Bernareggi, Barnabita, Giovambatista Masetti, Vittorio Fossombroni, Pietro Paoli,
Antonio Lecchi, Bernardino Ferrari, Giuseppe Bruschetti, Carlo Perea, Eustachio Man-
fredi, Giovanni Poleri, Paolo Frisio, Tommaso Perelli, Giovanni Bacciali, Eustachio
Zanotti, Ruggiero Bosvich, Leonardo Zimines, Bernardino Zendrini, Dominico Gugliel-
mini, Galileo Galilei, Benedetto Castelli, Alfonso Borelli, Evangelista Torricelli, Guido
Grandi, Famiano Mechelini, Tommaso Narducci, Lorenzo Albozi, Geminano Mon-
CHAP. IV.
ROMAN.
207:
tanari, and several others, which are all printed, and form almost an encyclopædia on
the subject.
Galileo Galilei was a native of Pisa, and born in the year 1564; on one of his visits to
the beautiful Duomo, at an early age, he observed the swinging of the large chandelier,
and from thence he set about constructing the first pendulum. Mathematics at this time
was at a very low condition, not only in Italy, but throughout Europe; but Euclid and
Archimedes were now generally revived and studied by all who had any pretensions to
science; after Galileo had studied the writings of the latter, he published his first work,
which was an essay on the hydrostatic balance, in which he proves himself thoroughly
acquainted with the principles of specific gravity. His learning then became generally
known, and in the year 1589 he was named professor of mathematics at Pisa, where he
received a salary of sixty crowns per annum. The phenomena of nature now formed his
chief study, and he began to inquire into the mechanical doctrines of Aristotle, although he
can hardly be considered the first who impugned his high authority. Leonardo da Vinci
had indulged in investigations which astonished his cotemporaries, and which were entirely
unknown to the philosophers of the time.
Galileo succeeded Moleti in the professor's chair at Padua in 1588, and soon after took
up the study of the thermometer, which was to a certain extent the result of the Greek
mathematician Hero's contrivances. Galileo's tube was made of glass, the bulb having the
air expelled by heat, and then filled with water; after which the degrees were marked upon
it, which indicated the expansion of the air when subjected to a change or increase of tem-
perature.
In the year 1609, he invented the telescope, and three years afterwards published his
Discourse on Floating Bodies, after which he turned his attention to the sucking-pump,
and when he found it would not act beyond a certain depth, he imagined some injury had
occurred to it, and sent it to the maker to have it repaired. The maker assured him that
no pump would raise water beyond the depth of eighteen cubits, when Galileo observed,
in his explanation upon this phenomenon, that a rod or column of water, when raised to the
height of eighteen cubits in a pump, its weight overpowers the attraction of the piston and
the cohesion of the particles of the fluid. He died in 1642.
Evangelista Torricelli, born in 1608, was the pupil of Galileo at the same time with Cas-
telli: he became highly interested on the subject of the pump, and made it his particular
study; the year after Galileo's death, he made an experiment upon the vacuum left
between the piston of a pump and the water which it raised; after which he filled a glass
tube with mercury, hermetically sealed at one end, and closed at the other with his finger,
and then inverted it into a basin of mercury, when he was surprised to find, upon the with-
drawal of his finger, that the mercury stood twenty-nine inches in the tube. This indicated
at once that the column of mercury was maintained by the weight of the column of atmo-
sphere, and that the thirty-three feet of water in the pipe of the sucking-pump was sup-
ported in the same manner as the twenty-nine inches of mercury.
Considerable advance was made in the science of hydrodynamics by this able disciple of
Galileo. He was one of the first who showed that when water is let out at the side or
bottom of a vessel, it issues with the same velocity as that which a body would acquire by
falling from the surface of the fluid to the orifice.
Torricelli gave us the means whereby we might measure the density of the atmosphere,
and constructed the first barometer. But it is from his treatise, "De Motu Gravium
naturaliter accelerato," that we learn, for the first time, something of the complex theory
which regulates the motion of fluids, when the orifice has a magnitude which is considerable
compared with the section of the vessel taken horizontally.
Benedetto Castelli was born at Breccia in the year 1577; he was among the distinguished
disciples of Galileo, and may be considered as the originator of a new theory of hydraulics,
relative to running waters, on which subject he compiled a treatise," Della Mesura dell'
Acque correnti," published in 1638.
Urban VIII. having requested him to report upon the means of completing the several
works which were then in progress to drain various parts of the papal dominions, was
the cause of his writing the above treatise. It contains several explanations of various
phenomena relative to rivers; and he states, what some have hesitated to admit, that the
absolute velocity is proportional to the declivity of the bed, or to the height of the water.
He died at Rome, 1644.
Dominico Guglielmini was born at Bologna, 1655: at the age of thirty he had so dis-
tinguished himself in the various branches of science then studied, that he was appointed
chief engineer of the territory belonging to the Bolognese, -a very important office, as it
had under its superintendence the confining of the numerous rivers which intersect that
country in all directions, and which frequently, if neglected, subjected it to inundations. In
the year 1690, he was made professor of mathematics, and four years afterwards a new
chair was created for him, under the title of that of Hydrometry, which, from that period,
208
Book I.
HISTORY OF ENGINEERING.
-
was accounted deserving of being ranked among the cultivated sciences. Among his
writings that "Della Natura de Fiumi," published in 1697, obtained him the greatest
celebrity. It treats of the equilibrium of fluids, the origin of springs, the motion of running
water, either falling perpendicularly or on an inclined plane, together with the consequences
of friction, the resistance offered by the air, &c.; of the beds of rivers, their breadth,
width, and depth, as well as slope, the uniting of rivers, as well as their discharge into the
sea, the consequence of increase after heavy rains, the supplying artificial canals, the drainage
of wet lands, and the precautions that should be taken when the course of a river is altered
or shortened.
Guglielmini, in this work, puts forth a variety of new suggestions well deserving the
attention of all who profess hydraulic architecture. He devoted his life to the pursuit of
the sciences: his naturally robust constitution yielded to over-excitement, and he died at
the age of fifty-four, in the year 1710.
Giovanni Poleni (Marchese) was born at Venice in the year 1683, and at an early age he
distinguished himself in the acquirements of the sciences, and was entrusted by the Venetian
state with the care of all the hydraulic works. His eminence was admitted by those
sovereigns whose territories were subject to inundations throughout Italy, and he was fre-
quently selected as the arbitrator to decide upon the conflicting opinions which arose when
a river running through one state did injury to another. All his decisions were given in a
manner to satisfy, as well as to increase his reputation, and in 1719, we find him appointed
to succeed Niccola Bernoulli in the chair of mathematics at Padua.
Poleni was one of the most celebrated writers on hydraulics; and his work, "Del Moto
misto dell' Acqua," is highly interesting, although the subject, perhaps, had been ably
treated before by some of the Italian philosophers. He in this work, however, has some
ingenious ideas; he supposes the bed of a river to be a rectangular canal, and a per-
pendicular section of it an orifice, and calls that dead water which is between the surface
and a certain point, where all the fluid molecules are in equilibrium, which he supposes are
governed by the same laws as solid bodies.
The water which is between this certain point and the bottom of the canal is called living
water. And he further considers that the motion of the water which flows through the
orifice is occasioned by the action which the living water acquires from its fall, and from
the pressure exerted by the dead water, and thus that motion is produced by the mixed
waters.
Another of his essays is entitled "Delle Pescaie o Cateratte dei lati convergente, &c."
in which are many valuable observations; but his principal work was that which appeared
in the year 1718, entitled "De Castellis per quæ derivantur Fluviorum Acquæ."
He died 1761, aged sixty-eight.
Eustachio Manfredi, was born at Bologna in the year 1674, and died in 1739; he
published some valuable remarks in an edition of the works of Guglielmini on Rivers, also
another entitled "Opere Idraulicke," which relates chiefly to the opinions of the various
engineers upon the proposed change in the course of the Po and the Rheno.
Manfredi was appointed by the Bolognese in 1704 their chief engineer, was equally
eminent with his predecessor Guglielmini, whom he succeeded.
Bernardo Zendrini, was born near Breccia in 1679, and died in 1747; received his
instructions under Dominico Guglielmini at the university of Padua, where he became
learned in mathematics, astronomy, and medicine, which latter he practised for some time
as a profession; among his first scientific treatises was one on the hurricane which happened
at Venice in 1708, in which he enters upon the weight and electricity of the air; the origin
and varieties of gas; the cause of wind, &c. He then excited public attention by his
analysis of a problem which still continues to present extreme difficulties,—if a fluid in
motion is confined within a given channel, the sides of which are susceptible of erosion,
their surface will take the form suitable to the establishment of the resistance and the erosive
power of the fluid; this depends on the relation between the rapidity of the molecules and
the nature of the material that compose the sides. A curved surface is the usual form they
acquire; and the hypothesis of the transverse section being polygonal, with a flat bed and
sloping sides, he says is not that which nature carves out. To have regard to the rapidity
of fluid threads which traverse this section, it must not be supposed that they augment
from the bottom to the surface, where they would attain their maximum force; they on
the contrary augment from the entire surface as well as the sides, to a thread situated
somewhere in the interior of the fluid mass, the position of which depends on its form and
other circumstances. A memoir upon this subject was published in 1715, entitled "Modo
do ritrovare ne' Fiumi là Linea di Corrosione." It contains a description of a very simple
instrument to ascertain the various rapidity of the current. The plains which lie between
the towns of Bologna and Ferrara being at this time inundated by the Reno, the inhabi-
tants of Bologna wished to change the mouth of the river to beyond Ferrara into the Po
of Lombardy, and the most celebrated Italian engineers, Castelli Guglielmini, Gabriel
and Eustachio Manfredi, supported them in their views in opposition to the inhabitants of
CHAP. IV.
209
ROMAN.
Ferrara, who were desirous of conducting the Rheno to the southern extremity of the
Lake Comacchio, and carrying its waters to the sea through the Po di Primaro.
Zendrini was invited, on the death of these celebrated engineers, to confute the opinions
which they had given in their reports, and which the inhabitants of Bologna were
inclined to adopt on this occasion appeared his celebrated work, entitled "Considerazioni
sopra la Scienza delle Acque correnti, e sopra la Storia naturale del Po;" this was published
in 1717. After this work appeared, the Duke of Modena appointed him his chief
engineer; and in the year 1720, by the decrees of Venice, he was nominated superin-
tendent of the waters, rivers, canals, lagunes, and ports belonging to that city.
republic always appointed two of its most eminent philosophers to act as engineers, and
maintain the watercourses of the city in proper condition: some of these were men
famous for their knowledge in hydraulics; among them was Christopher Sabbadino,
nominated Prote in the year 1542.
This
Zendrini occupied himself during the superintendence of these important works at
Venice with compiling an account of the ancient and modern state of the lagunes, which
was published about sixty-four years after his death; it is entitled "Memorie storiche del'
Stato, antico e moderno, delle Lagune di Venezia, &c.," printed at Padua, in two quarto
volumes.
This history comprises the period between 1300 and 1700; Zendrini cites a letter of
Cassiodorus, which gives a tolerably exact account of the state of the lagunes and Venice
between the fifth and sixth centuries, which is highly interesting; and the numerous plates
given are curious with regard to levels, and the means adopted to execute the different
works which were required to keep the canals open.
Zendrini was employed to survey the country round the port of Viareggio in the re-
public of Lucca; his report was printed at the time. In it are many observations
on the level of the sea; he commenced and executed works in this part of Italy, which
ameliorated the condition and health of the inhabitants; the good effects of which were
destroyed by the intestine animosities that happened afterwards.
Clement XII. employed him in 1731, to report upon the state of the country about
Ravenna, which was occasionally inundated by the waters of the Roneo and Montone;
these rivers he turned into new channels, and in 1741 published at Venice an account of
what he had performed.
Soon afterwards appeared his famous work, "Delle Acque correnti," to which subse-
quently was added the work entitled "Relazione per la Diversione de Fiumi Roneo e
Montone."
In the first of these the author gives general observations on the nature of fluids, treats
of their motion when issuing from reservoirs by simple orifices, as well as by pipes; he then
takes up the subject of running water, the methods adopted to ascertain its velocity, and its
effects upon the beds and banks of rivers or canals: he also treats of the breaking down of
dykes and dams, the means by which these effects may be prevented, and the different
methods usually adopted to divide a stream; the `draining of lands: a description is added
of various improvements, that in his opinion might be made in some hydraulic machines.
This work shows distinctly the state of hydraulic knowledge at the time of its pub-
lication; it rectifies many ancient theories, and is enriched with ideas new at the time
they were made known; it was justly considered a chef-d'œuvre by his contemporaries,
and, notwithstanding the progress that has been made since on these subjects, it is a book
which every intelligent engineer should possess. Zendrini died in the year 1747, and the
Venetian senate decreed him great honours.
Lazarettos in Italy. That at Genoa is near the sea, and comprises two spacious courts,
one of which is devoted to goods which are infected, and the other to those which may or
may not be so. In the middle of each of these courts is a chapel; three sides are sur-
rounded by buildings three stories in height; the fourth contains the apartments of the
physicians and medical attendants. At the entrance is a guard-house; three sides of the
courts are occupied by corridors, 10 feet 9 inches in width, separated by doors, so
that the crew and passengers of different vessels may be kept apart. From these corridors
the rooms are entered, which are occupied by those in quarantine; they are 15 feet 7 inches,
by 14 feet 3 inches, and 11 feet 6 inches in height.
On the upper floors there are in front thirty-six rooms, besides twelve occupied by the
governor; on one side are ten, on the other eleven rooms, all of one size, viz. 16 feet 9, by
14 feet 9, and 11 feet 6 inches in height; each has two windows opposite one another, so
that a thorough ventilation can be obtained; they are placed at a height of 6 feet above
the floor, and are 4 feet by 3 feet. The floors are paved with brick, and the rooms are
vaulted; they have a fireplace in one angle, and in another a small closet containing the
urinal and drain. All these upper rooms open into a spacious corridor, 11 feet in width,
the windows of which are towards the court; and there are also doors so contrived, that
they can shut off three or four rooms as may be required.
The windows are barred with iron and have shutters, but are not glazed.
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On the second floor are three ranges of warehouses, 16 feet 6 inches in width, approached
by brick steps from the outside; the floors are of stone, and the windows are 3 feet by 2 feet
9 inches.
In the front are three elevated towers, and through the court flows a clear stream of
spring water, which is conducted from the neighbouring mountains; it then runs through
all the sewers, and scours the drains most effectually.
Leghorn Lazarettos.-There are three; that called San Leopoldo is very conveniently
arranged; at the upper end is the statue of the Grand Duke, at whose expense the buildings
were constructed; it has served as a model for all others in Italy. It contains spacious
rooms, and every sort of accommodation for those whose ill fortune consigns them to the
necessity of a purification; the several courts are so placed, that the cargoes and crews of

OCK
обдо
Fig. 233.
LAZARETTO at LEGHORN.
the vessels arriving at the port may all be separately lodged, though they are not so.
Isolated buildings arranged along an open shore, or on an island in the ocean, afford the
best guarantee for the continued health of the individuals within them; should infection be
brought by the cargoes of one vessel, it is highly necessary that those who without cause
are obliged to undergo the ordeal of a lazaretto should not be exposed to the infection they
have escaped by their own caution, or from being placed in more fortunate circumstances.
The Lazaretto at Varignano in the Bay of Spezzia is situated on a promontory stretching
into the sea, and forming a beautiful object on the coast. The court nearest the gulf is for
aired goods, as are the buildings on each side of the second court. A wide walk divides

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Fig. 234.
LAZARETto at vaRIGNANO.
the great square inland, and a wall at right angles again subdivides it into four courts, one
of which is devoted to the infirmary, and the others to infected goods. Around the whole
is a wall and apartments for the officers and attendants.
The great defect of this establishment is, that the several lodgings set out for the crews
CHAP. IV.
ROMAN.
211
are built against the outer walls, which renders the ventilation imperfect, windows not being
permitted on the outside.
The docks for the shipping are convenient, and there are plentiful supplies of fresh water
but the want of a free circulation of air, and the too great proximity of the different
buildings, are serious objections.
Great attention and skill is demanded in the selection of a site, as well as in the arrange-
ment of hospitals of this kind.
The
In Italy, engineering works continued to be carried on with great success: in Rome la
santa, Napoli la gentile, Genoa la superba, Milano la grande, Ferenze la bella, Bologna la
grassa, Ravenna l'antica, Padua la dotta, and Venezia la ricca, all can boast of objects
worthy the attention of an engineer. The latter city deserves admiration for the various
difficulties overcome in laying the foundations for the noble buildings it contains.
province of the Roman Venetia was bounded by the Adda, the Rhætian and Julian Alps,
and the Po. About 450 years before Christ, the inhabitants of Aquileia and Padua, driven
out by the Huns under Attila, took refuge in the islands along the coast, and laid the first
foundations of the future Venice, on the island of Ripa Alta or Rialto. In A. D. 570, the
patriarch of Aquileia fled before the Lombards with his flock, and settled himself at Grado,
afterwards called New Aquileia; his successors became the first ecclesiastical primates, and
about the middle of the fifteenth century they removed to Venice.
The modern city is built upon two islands, separated from each other by the great ser-
pentine canal, which is crossed by one bridge, called the Rialto; its total area has been es-
timated at one square mile and a half. The two islands are subdivided by many smaller
canals at right angles with the larger, and as the streets or alleys are seldom more than 8 or
9 feet wide, the communication from house to house is chiefly carried on by means of boats,
almost every doorway having a landing stair at the water side.
The houses are of brick, or of Istrian marble, which bears a fine polish; the floors are
composed of fine plaster and pounded brick, into which, when in a soft state, black and white
marbles are imbedded, and when dry, are polished; the foundations of the buildings are
either upon piles or masses of concrete.
The entrance of the Laguna is guarded by the fort of Lido, distant about two or three
miles from Venice; the Laguna is separated from the sea by a line of narrow sandy islands,
which have required the most vigilant attention, in order to prevent the embankments or
barriers from being forced into the channel. There are two other passages through these
narrow sandy deposits, one at the port of Malamocco, and the other at Chiozza, where mas-
sive stone walls have been constructed to defend it against the action of the sea.
Within these sand-banks, produced by the deposits brought into the Adriatic by the
several mouths of the Po, the Laguna forms an extensive bay, a great portion of which is
dry at low water; the tide rises about 3 or 4 feet, and occasions a current sufficient to work
the mills on the island of San Georgio Maggiore. To keep the various canals open, a
dredging machine was used at a very early period, which underwent many changes and
improvements before its introduction became general.
Cassiodorus, appointed præfect of Venice by the Emperor Theodoric, has left us an
interesting account of the lagunes at the commencement of the sixth century, when the
chief exports were fish and salt.
From the summit of the lofty Campanile in the Piazza San Marco, a fine view of the city
rising amidst the Laguna is obtained. To the north lies the Julian Alps, reaching from
the Lake of Garda to Trieste, often covered with snow; to the west is Monte Selice, formed
of porphyry and trap, probably of volcanic origin.
The arsenal was a noble establishment, and contained slips for ship-building, and
arrangements for the manufacture of all that was required for their equipment and efficiency
in time of war. Here the camel was first used for floating large vessels out of the Laguna,
which consisted of four cases, with concave sides, so made as to embrace the whole ship;
they were towed under it, and united securely together; the water was then pumped out of
the camel, and it became sufficiently buoyant to float its burthen in very shallow water;
such a method was adopted by the ancients to move obelisks and heavy masses, where there
was not depth enough for their large craft to navigate.
In constructing the foundations at Venice, every precaution was taken to collect the
waters which rise from the springs at the bottom of the lagunes; they are conducted into
a basin or well left to receive them, in the bed of concrete upon which the walls were
built; where a spring did not occur, the well was converted into a tank to receive that
which fell from the roofs of the buildings during the rainy season. These supplies,
however, frequently failed, and it was then conveyed in boats from the shores of the main
land, and disposed of to the inhabitants. Trade and commerce have departed from Venice,
and its population is in consequence greatly diminished; but the city remains, to interest
the historian, the architect, and the civil engineer. The finest designs of Falladio, and the
manner in which he laid his foundations, may be seen in various parts of the city, and form
the best commentary upon that portion of his treatise on building. All the chief men of
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Book J.
HISTORY OF ENGINEERING.
1
Italy, celebrated for their acquirements in hydraulic architecture, met with employment and
encouragement in Venice, and she must for centuries have been a school for the instruction
of engineers.
Before we leave this portion of our subject, and proceed with an account of the works
executed since the destruction of the eastern and western empire, it is due to the engineers
of Italy to acknowledge how much we are indebted to them for the science handed down
through the middle ages, upon which our modern practice in the arts of construction is
founded.
The ancient writers are scanty in such observations as practical men seek after, and it is
to be regretted that information upon many important and vast undertakings of the em-
perors of Rome is not more fully given.
Cities, harbours, roads, bridges, supplies of water, baths, drainage of vast districts, public
edifices of all denominations, were laid out and executed in a manner never yet surpassed,
the majestic ruins of which are spread far and wide for our wonder and admiration. The
whole circle of the building arts was employed in deep seas, in rapid rivers, and on most
difficult sites, where foundations were raised to bear the extraordinary weights imposed upon
them. We must blush at the expensive but too often ill-directed efforts of the present
day, when we reflect on the well-proportioned and majestic structures which still remain
in and around the Imperial city. It must also be admitted, that we have not improved on
their knowledge of construction; and if Vitruvius, to whom we have so often referred, be
studied by a mind bringing with it a spirit and judgment equal to the information found in
that author, it will be convinced that there is nothing new in the works of modern times.
The builders of later generations too generally present to us only the lifeless form, while
their brethren of yore stamped on their erections all the glow and beauty of vitality.
About the middle of the fifteenth century, the arts were again encouraged. Leon
Battista Alberti wrote his treatise, "De Re Edificatoria," which, from its close resem-
blance to the author alluded to, proves that Vitruvius was held in the highest consideration.
When Alberti was employed by Pope Nicholas V. to repair the aqueducts at Rome,
particularly that of Aqua Virgine, he devoted himself to the study of Frontinus, and
acquired a thorough knowledge of the principles which guided the ancient engineers.
Hydraulic architecture, after the splendid discoveries of Galileo and his successors,
became more refined by the abstract and mathematical reasoning to which it was subjected;
but many of the calculations were formed upon erroneous and inefficient data, and con-
sequently have become of little value, - a very common result when such calculations are
not accompanied by a practical acquaintance with the subject in question. Theory and
practice must go hand in hand; the calculations of the one must be based on the experience
of the other, while the active energies of the practical man may be materially assisted by
the silent process of well-directed reflection. The authors of Italy, during the fifteenth
and seventeenth centuries, revived the writings of the classic period; and in commenting
upon the subjects they described, Palladio and other practical men were required to pro-
vide illustrations: thus were the bridges of Cæsar, Trajan, and the emperors brought under
the notice of the engineers of that period. The baths of the Romans also met with their
share of enquiry, and little was left upon these subjects to the moderns in the way of in-
terpretation; they had only to apply their reasoning to what remained of the structures.
To the Romans we stand indebted for the knowledge that is interesting to us as a
maritime nation. They first established in Britain ports and havens, marked out and
formed roads from one end of our island to the other, which excite wonder even in the
present day for the straightness of their course, and the solid manner in which many of them
are executed. They established beacons on our coast, remains of which may be traced on
some of the heights which girt our isle; within the circuit of the walls of Dover Castle,
their pharos is still shown. It would be impossible to do justice to the people of this
mighty nation: wherever they established themselves they introduced improvement, drained
marshes, cleared lands, brought them into cultivation, and encouraged commerce.
Their stone cutting and artificers' work of all kinds have served us for models; our very
nomenclature upon the subject is derived from them. Of the solidity of their constructions
we have ample proof; and had they been left to the hand of Time alone, we might have
derived many useful lessons from the study of those structures over whose ruins we now
linger with wondering regret.
CHAP V.
213
HOLLAND AND GERMANY.
CHAP. V.
ENGINEERING WORKS IN HOLLAND AND GERMANY.
THE level of a great portion of Holland being below that of the sea, the construction of
dykes, or banks, to keep out the water has given employment to a vast number of indi-
viduals, and called forth the ingenuity of the greatest mathematicians of the age, to
economise their labours, or to direct them in the most efficient manner.
The dykes are in many places raised 30 feet above the ordinary level of the country, and
have sufficient width at the summit to form a roadway: towards the sea, both above and
below the level of the action of the water, is a strong matting of flags, or reeds, which
retains the earth towards the summit of the mound, and on the land side, piles and planking
are adopted, to give the requisite strength; these are filled in with stones covered with earth
and turfed. The matting of flags, of which we have no notice before the end of the six-
teenth century, has been found very successful: they are twisted together in bundles, and
laid horizontally, at distances of three or four yards from each other, and then secured to the
ground by wooden stakes, or by large stones. Above these layers of flags piles are
driven in, to which a number is attached, that the surveyors or engineers entrusted with the
maintenance of the banks may refer. Enormous sums of money have been expended on
these sea-dykes, and when the sea rises to a great height, the inhabitants are obliged to
cover them with sails to prevent their washing away: the water which passes over them is
afterwards pumped out, either by windmills or other means.
The Rhine, the Leck, the Vaert, the Yssel, the Maes, and other rivers which are dis-
charged into the sea on the coast of Holland, have their banks maintained in a similar
manner. The great Lake of Haarlem, 12 miles long and 9 broad, situate between the
towns of Haarlem, Amsterdam, and Leyden, is remarkable for its sluice, which effectually
resists the inroads of the sea.
Where the canals in these districts do not unite but are separated by a dyke, there are
contrivances to transport vessels from one to the other by means of wheels and rollers.
As a great portion of the richest land in Holland has been gained from the sea, it is of the
highest interest to inquire by what means this was effected: the districts in the north consist
of the Zype, the Beenister, the Wormer, and Schermeer. The first was commenced about
the beginning of the sixteenth century, when an extremely strong embankment or mole,
formed of timber, filled in with large stones and covered with earth, was constructed at an
enormous cost.
The draining the lakes of Purmur and Beenister were the next operations carried on,
when many thousand acres of the most profitable land in Europe were redeemed, planted
with orchards, converted into garden ground and meadow. Dugdale, in his "History of
Embanking," gives it as his opinion, that Holland consisted of a three-fold earth; viz.
sandy to the sea, clay to the rivers, and moorish in other places, and that it was the gift of
the ocean, and of the rivers which pass through it, as was Egypt of the Nile; and, quoting
the historian Nannius, states, that "Holland was the gift of the north wind and of the
Rhine, and was in the beginning no other than a more high place than ordinary, over which
the tides do usually flow; whereby through the increase of the sands, which the north
winds, fiercely agitating the waves, stirred up, it first grew to be a shore, and afterwards
raised those sandy heaps, which we daily see both to be made and destroyed." And
further, "that the waters of the Rhine, by this stop, being kept up as it were with a bank,
settled the mud brought down by the stream about the shores, and so by long and frequent
inundations produced those pastures. For it cannot be imagined, saith Bertius, that the
face of this country was always as it now is discerned to be, or that it soon arose from
its former condition, unto this fertile and pleasant state, in which we behold it at present;
there being much time, extraordinary labour, excessive study, vast expenses, and great
diligence necessary thereto. Nature therefore first inviting, the inhabitants bordering near
unto it to make those banks of sand, as a defence against the north wind, and necessity also
spurring them on (than which no master is more ingenious and powerful), in time those
their accustomed endeavours became a second nature to them, it being not unusual to see
the very boys and girls, when they come to the sea-side to recreate themselves, to put
off their stockings and shoes, and taking up the sand with their fingers to make walls
therewith against the ocean, within which, thus encompassing themselves, they disperse the
force of the waves."
The Batavians first occupied these districts, then the Danes and Normans, and after-
wards the Saxons; to each of these people some praise is due for the manner in which the
first embankments have been maintained, and "for the performance of these eminent works,”
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HISTORY OF ENGINEERING.
Book 1.
continues Dugdale, "it required extraordinary knowledge and skill, which ancient times
had not attained to, and foreign nations now admire. The engines of several kinds made
use of for raising the water and casting it off were framed by men of singular judgments in
mathematical learning, and suitable to the depth of the water, er opportune for carrying
it away.
Friseland, which lies very much beneath the surface of the ocean, is preserved by
the wall raised in 1567, by a Portuguese in the employ of Philip II., King of Spain; the
author before alluded to asserts that it would require a volume to give an account of all the
works of this nature in the Low Countries, and the several banks, ditches, and sluices.
The provinces of Belgium which formed a portion of Gaul were in the time of Cæsar
full of woods and fens, which latter were not effectually drained till the work was taken in
hand by Baldwin I., who married Judith, daughter of Charles the Bald.
In the year 1169, Floris, carl of Holland, demanding the Isle of Walcheren, in Zealand,
trom Philip, earl of Flanders, obtained it, on condition that he sent to Count Philip 1000
men expert in making ditches, to stop the breach near unto Dam or Sluse, whereby the
country was drowned at every high sea; "the which the Flemings could by no means fill
up, neither with wood, nor any other matter, for that all sunk as in a gulf without a bottom,
whereby in process of time Bruges and all under its jurisdiction had been in danger of being
lost by inundation, and to become all sea if it were not speedily repaired. Whereupon the
Count Floris sent the best workmen that he could find in his territories, who being
come to the place, they found a great hole, near unto this dam, and at the entrance thereof
a sea-dog, that for six days together did nothing but cry and howl very terribly. They not
knowing what it might signify, resolved to cast this dog into that hole, whereupon a mad-
headed Hollander, getting into the bottom of the dyke, took the dog by the tail, and cast
him into the midst of the gulf with earth, and turf after him, so as, finding a bottom, they
filled it up by little and little." They named the place in consequence Hontsdam, or Dog's
Sluice; dam, in Flemish signifying a sluice, and hont, a dog. The town still has a dog in
its armorial bearings.
The banks from Dam to Sluse thus rescued from the sea, in 1180, all the land that
had been submerged.
At Antwerp the Emperor Napoleon raised on the banks of the Scheldt, which is here
upwards of 2000 feet in breadth, and 40 feet in depth, dockyards, slips for ship-building,
and one of the most magnificent quays in Europe. Engineers were sent from France to
conduct these works, upon which vast sums of money were expended, and Antwerp became
one of the most important ports on the coast; it is situated in an extreme plain on the
eastern bank of the Scheldt, and is divided by eight canals which traverse the city, on
which are warehouses for the reception of goods. The exchange, which was the model for
that constructed by Sir Thomas Gresham in London, and the celebrated warehouse
or magazine, in which all the merchandise that once enriched this distinguished city was
deposited, still remain. Some of the bridges erected in Germany deserve to be mentioned,
and we shall commence with that over the Elbe.
Bridges of Germany.
Bridge over the Elbe, at Dresden, was restored from 1727 to 1731, by Poepelmann, in the
reign of Augustus, Elector of Saxony and King of Poland. The ancient piers, which are
the work of the twelfth and thirteenth centuries, and which were paid for by indulgences,
are the nuclei of the present. Originally there were twenty-four, but several were carried
away at different times, and when the fortifications of Dresden were extended to the Elbe,
some were destroyed. The bridge is now composed of eighteen arches, distributed without
order, nor can this be a matter of surprise when it is considered how they were constructed.
The total length is 1447 feet, the breadth of the road is 25 feet, and that of the footway
4 feet 7 inches. Notwithstanding all its irregularities, it is one of the longest in Europe,
that of St. Esprit and another at Prague only surpassing it, and it may be regarded as one of
the finest. The piers are very thick, being in some instances nearly equal to the span of
the arches, which vary from 40 to 62 fect. They rise to the level of the footway, and serve
as recesses for benches. On one is placed a bronze figure of Christ on the cross, richly
gilt; the parapet consists of an iron railing, strengthened over each pier by pedestals, which
sustain vases.
The bridge is entirely
The roadway is nearly level, and forms a superb promenade.
constructed of squared stones, and the voussoirs are rusticated.
Bridge at Prague, on the Moldaw, was commenced in 1638, by Charles IV., Emperor and
King of Bohemia, who laid the first stone, and finished under Charles VI.
Its length,
1706 feet, is greater than that at Dresden, but it does not equal it in its construction. The
breadth is 35 feet 8 inches. The eighteen semicircular arches of which it is composed are
constructed of squared stone, and ornamented with an archivolt: the piers are surmounted
by pedestals, which support statues; that of St. John Promucena is placed over the very
spot where King Venceslas threw him into the river, for refusing to violate the secret of
confession. The masonry of this bridge is excellent: when the Swedes seized upon Prague,
CHAP. VI.
215
FRANCE.
and were desirous of destroying it, they found the mortar so hard, that they were obliged
to give up the undertaking.
Bridge at Ratisbon, over the Danube, began in 1135, by Henry the Superb, Duke of
Bavaria, consists of fifteen arches, and its total length is 994 feet. The piers rest on piles,
and are defended by jetties and large starlings. It is only 21 feet 4 inches wide; it is
paved with square stone; the footways are only 1 foot in width, and the parapets are
fortne of flag-stones, placed on edge, united by iron cramps, and run with lead. At about
one-third of the length there is a descent upon an island, by means of a staircase contained
between two walls.
The arches are semicircular, and are from 33 feet to 53 feet span.
Bridge of Zwettau, over the Torgau, on the Elbe, was built by King Augustus, in
1730. It consists of twelve arches; of the eleven piers five have starlings; the others
have only a set-off. The fall of this bridge is very considerable.
Bridge at Wurtzbourg, over the Meine, consists of eight semicircular arches, 32 feet 9 inches
span; the starlings of the piers are semicircular, and rise to the level of the parapet; the
work is simple, and very solidly constructed. Statues are placed on the piers, and among
them is that of St. John Promucena, regarded in all Germany as a patron of bridges.
Bridge of Kosen, on the Saal, near Naumbourg, presumed to have been constructed in
the tenth or twelfth century, consists of eight arches; the five in the middle of the current
are pointed, the others are semicircular.
Bridge of Mossen on the Mulde, in Saxe, is composed of three semicircular arches; was
constructed from 1715 to 1718, by Daniel Poepelmann, under the reign of Augustus.
Bridge at Nurembourg, called ABC over the Pregnitz, built under the Emperor
Charles VI., who laid the first stone, was finished in 1728; it is formed of two arches 46
feet span.
In the interior of the pier is a vaulted passage; this pier is surmounted by
two obelisks, erected to the honour of the emperor; the parapets are ornamented with pe-
destals surmounted by a ball.
Bridge of the Boucherie, at Nurembourg, over the Pregnitz, constructed in 1599 by
Peter Carlo, presented many difficulties in its foundations; it consists of a single segmental
arch, 97 feet 2 inches span, and 12 feet 9 inches high; the thickness of the arch is only 4
feet, the breadth of the bridge is 40 feet.
CHAP. VI.
ENGINEERING IN FRANCE.
We have seen that wherever Imperial Rome extended her sway, she has left memorials
of those useful works which have rendered her name immortal among the nations, and it
is not too much to conclude, that after the long night of barbarism which succeeded the
overthrow of her mighty power, when civilisation again dawned, they would be the guide
for whatever improvements might be required, and we have sufficient evidence that they
were the models from which the after inhabitants derived the knowledge they possessed on
the subject; but we can hardly say that the engineer was fully called into practice earlier
than the middle of the seventeenth century, about which period Bernard Forrest de Belidor
wrote his "Architecture hydraulique," which awakened great attention, and laid the foun-
dation for those theoretical studies, which had been entirely neglected by practical men
throughout Europe. This writer, an officer in the artillery, was requested to suggest
some system to guide the military engineer, which eventually led to the establish-
ment in the year 1720, of the Ponts et Chaussées, first composed of an inspector-general, or
chief architectural engineer, three other inspectors, and twenty-one assistant engineers. The
number was afterwards increased to twenty-five and twenty-eight, and in the year 1770,
fifty inspectors were added, taken from the sub-engineers, the numbers of which depended
upon the necessities of the service. This important and erudite body, acquainted both with
theory and practice, directs the education of all who intend to act as civil engineers, or un-
dertake the construction of roads and bridges; and they require those who aspire to the
superintendence of these works to possess a knowledge in geometry, mechanics, mineralogy,
and the natural properties of all the materials employed in the arts of construction.
Among the engineers of this institution are registered the names of the most celebrated
mathematicians of France, who have contributed to the formation of a theory upon what-
ever subject they may have been employed. Such an establishment for carrying out the
P 4
2.6
BOOK I.
HISTORY OF ENGINEERING.
national improvements could not fail of being successful each enterprise submitted to the
board is duly and properly considered, with reference to works, that might be in future
undertaken; one uniform system is laid down for bridges and their construction, and
volumes have been written on the properties of stone, cements, hydraulic mortars, the
thrust and pressure of arches of every kind of curvature. Timber has been examined
thoroughly with respect to its strength, toughness, and powers of resisting, torsion, and
much larger scantling than ever tried in this country, have been tested by the engineers of
France. The best works upon engineering are found among the writers of France and
Italy, and should be studied by all who desire to excel in the profession Rondelet,
Bruyere, Prony, Boistard, Berard, Gauthey, and Perronet, particularly should be enu-
merated for their high attainments and professed knowledge of the subjects upon which
they treat. Before the establishment of this important body, the roads in France were
scarcely defined, and the bridges were left to the control and management of the local
masons, who executed their repairs or reconstruction in a manner devoid of both proportion
and solidity.
Under the Emperor Napoleon, great advances were made in the management of all
public works; his penetrating eye soon discovered what was wanting, and his industrious
and business-like habits changed the routine observed in the building of bridges, the for-
mation of roads, construction of lighthouses, beacons, telegraphs, arsenals, canals, working
of mines, and the reducing of metals.
France is divided into eighteen districts, and placed under the inspection of this estab-
lishinent.
The roads are classed or divided into three orders, as the Royal road, for which the state
provides, the departmental roads, which are kept in repair by the respective provinces, and
the rural roads, which are maintained by the immediate inhabitants of the district through
which they pass.
The Royal roads are subdivided into three classes, the first of which is 42 French feet in
width of this class there are 28, or altogether 1258 leagues; of the second class, which
are 66 feet in width, there are 717 leagues; of the third class there are 5241 leagues.
:
The rivers, as far as used for the purposes of navigation, are under the same direction,
and 1877 leagues are annually reported upon.
The canals finished extend over 370 leagues, and those under construction amount
altogether to near 2000 leagues, and constitute another branch to which the engineers of
this government board have to attend; and that due attention may be paid to this highly
important subject, the duties are divided into lines, and are annually reported upon.
The first line passes by the south and east of France, comprising the Rhone, the Saone,
and the Canal of Monsieur, which unites the latter river with the Rhone.
The second line passes by the south and north of France, and comprises all that is at-
tached to the Rhone and Saone in that quarter; the canal of Bourgoyne, which unites the
Saone to the Yonne; the Seine; the Oise; the canal of Manecamp and Chauny; the Canal
Crozat; the canal of St. Quintin, joining the Oise to the Escaut; the canal of the Somme
or of the Duke d'Angoulême; the course of the Escourt; and all the canals in the neigh-
bourhood of Calais.
The third line, in the centre, on the south, comprises the Rhone, the Canal Lateral,
course of the Saone, Canal du Centre, of Dijon, Chalons on the Saone, which unite the
Loire with the Saone; Canal de Berri; of Dijon; and Bec d'Allier; the canal which joins
the Loire from Bec d'Allier to Briare; the Canal Briare and the Loing; the course of
the Seine and Oise.
The fourth line, passing by the south and north-west, comprises the Rhone, the Saone,
the Canal of Burgundy, the Yonne, and the Seine, to the mouth.
The fifth line, passing from the south to west, through the centre of France, has the
Rhone, the course of the Saone, the Canal of the Centre, the canal de Berri, the branch
canal to the Basse Loire, from Tours to Nantes, and the canal of Nantes to Brest.
The sixth line, passing by the south and south-west, has the canal of Marseilles, to the
port of Bouc by the Lake de Berre; the canal de Bouc to Arles; the branch canal to the
Rhone, from Arles to Tarasçon; the canal de Beaucaire, the canal de la Radelle, the canal
of Mauguio and des Etangs, the canal of Languedoc, and its extension to Moissac by
Montaubon; the Garonne from Moissac to Bordeaux.
Seventh line, passing from La Manche to the sea, by Gascoigny and the Mediterranean,
or the canal from Dunkerque to Bayonne and Marseilles; the canal de Bourbourg, the
navigation of the Aa; the canal of Aire to Bassée, joining the Lys, to the H. Deule; the
canal of Deule; part of the course of the Scarpi; canal of Sensée; the course of the Escaut ;
the canal of St. Quentin; the canal of Crozat; the course of the Oise; canal of the Oise to
the Seine; canal of St. Denis and St. Martin; the Seine as far as the canal of Loing; canals
of Loing and Orleans; the Loire from Orleans to the mouth of the Vienne; the Vienne to
Chatellerault; the canal of Poitou, joining the Vienne to the Charente, by the Clain
river; the Charente to Angoulême; the canal from Angoulême to Libourne; the Dor
CHAP. VI.
217
FRANCE.
dogne from Libourne to Cubzac; the canal of Cubzac to Bourdeaux; the Garonne to the
mouth of the Bayse. When this line is prolonged, it will take a course towards the west,
following the canal of Landes, and the river Adour to Bayonne; and towards the east it will
comprise first the course of the Garonne to Moissac, the canal of Moissac to Toulouse, by
Montauban, the canals of Languedoc, des Etang, Mauguio, La Radelle, Beaucaire, from
Tarasçon to Arles, from Arles to Bouc, and from thence to Marseilles.
Among the ports of France, that of Dunkerque, before its demolition in the year 1714,
was the great school for engineers, and presented more examples for study than any other
in Europe; here was found an assemblage of every kind of hydraulic architecture, of
which single or detached specimens existed elsewhere.
Julius Cæsar found it a mere village inhabited by fishermen, attracted thither by the ex-
cellence of its natural harbour; the neighbouring country, mostly under water, was supposed
at one time to have been an arm of the sea, which extended to St. Omer, anchors and parts
of vessels having been found there whilst constructing the fortifications. The land around
has been rendered serviceable to agriculture by the cutting of several canals, to drain off the
waters, and carry them into the sea. The opinion that the sea has retired is, perhaps, not
correct, for the level of the water is above that of the neighbouring plains, which would be
subject to inundation but for the formation of the dunes or banks of sand, which serve the
purpose of an embankment.
The shore along the entire coast is composed of sand, which
the slightest wind drives in the direction from north to south, depositing it in irregular
ridges, which sometimes rise to small hillocks; these the early inhabitants rendered more
compact by mixing with them layers of bushes, branches of trees, yellow broom, or any
other material which occasioned the sand to bind; in process of time a barrier was formed,
which resisted further encroachments from the sea. At several places the sluices, introduced
for letting off the fresh water, were closed, when the sea again flowed in by constant manual
attention. The name this port bears arose from the circumstance of St. Ely, Bishop of
Meyon, in the seventh century, founding a church on these downs, which was called Dune-
kerque in the Teutonic language.
In the year 863, Charles le Chauve bestowed the town and the country around upon his
son-in-law, Baldwin, who was created Count of Flanders.
Baldwin III., his great-grandson, surrounded the town, which had obtained by that
time some importance, with a strong wall: as a port it was afterwards much frequented, in
consequence of its abundant supply of fresh water, which fed the canals, and formed its
most important defence. In the twelfth century, it acquired the dignity of a maritime
port, and contained several vessels of war, some of which were adapted for long voyages.
Various improvements successively followed, and Dunkerque in the course of a few cen-
turies became a highly important station; in the year 1677, the great Vauban was desired
by Louis XIV. to construct a channel between two jetties, at the head of which were es-
tablished the two forts, Verd and Bonne Esperance, also the famous Risban on one side, and
the Chateau Gaillart. These great works were completed in 1683; and two years after
wards, the basin was lined with a stone wall, and the quays formed. At its entrance a
grand sea lock, 42 feet in width, which allowed vessels of considerable burthen to float
within the harbour was constructed. The fort of Revers was built in 1689, and several
contrivances were adopted, which, aided by the waters of the two canals, deepened the port,
and kept it clean and scoured. M. Clément, who directed these latter operations, became
one of the most eminent civil engineers in Europe. In the year 1701, a new risban, called
the Fort Blanc, was erected at a distance of 800 toises from the town.
Chateaux Verd and Bonne Esperance were situated, the first on the east, the second on the
west on entering the port, at a distance from the town of about 1000 toises. They were
formed of timber, raised on piles, rendered extremely solid, and each mounted with thirty
pieces of cannon. Passing between the two jetties which formed the channel, which was 40
toises in width, on the west, stood the celebrated fort called Risban, constructed of stone,
and containing commodious barracks, a cistern, magazines, and other requisites for a garrison.
It communicated with the town by means of a jetty. On the rampart were forty-six cannon,
which could be placed on three sides; the form of the fort being that of a triangle. To the
east was a smaller, called the Petit Risban or Fort Blanc, also of masonry, which had twenty
pieces of cannon.
Towards the harbour, on the same side, stood the Chateau Gaillard, a timber construc-
tion, and communicating with the eastern jetty by a small bridge. The form was rectan-
gular, and contained twelve pieces of cannon; one side defended the jetty, and the other
crossed the range of Fort Blanc; on the other side of the channel was the battery of Revers,
built of masonry, which had sixteen pieces of cannon.
The jetties, formed of timber and large stones laid on carefully at a vast cost, were the
admiration of all engineers. The basin contained forty line-of-battle ships afloat at the
time of low water; the entrance lock was 42 feet in width, and the whole was surrounded
by arsenals and storehouses for the marine.
The harbour was supplied with every means for cleansing and deepening; its chief sluice
•
218
Book I.
HISTORY OF ENGINEERING.
for this purpose was at the end of the canal of Bergues, in width 26 feet, with a double pair
of gates (Portes Busquées); one of these supported the waters of the canal, the other that of
the sea at high water, so that vessels could pass from the canal to the port, and from the
port to the canal at certain times of the tide; this arrangement was one of the earliest of its
kind. The sluice had others attached to it, which turned when the sea was low and the
harbour dry, to allow the waters which served as a reservoir in the canals to flow out with
so much violence and velocity that they thoroughly scoured the harbour and the channel
between the jetties; its effects were felt to the extent of 1600 toises, the distance of
the sluice from the head of the jetties. At the mouth of the canal of La Moere, a sluice
of a different construction was established, which served a similar purpose; when they
acted singly or together, they produced a force which perfectly answered the desired
purpose.
A third sluice at the canal of Furnes, within the town, contributed to clear the channel,
and from 1701 to 1710, the port was cleaned and scoured out to the depth of 15 feet by
these contrivances.
The grand sluice to the basin at Dunkerque, constructed by Marshal Vauban, in the year
1684, was considered throughout Europe the masterpiece of its kind. Its width was 42
feet, and the gates supported a weight of water, 20 feet in height.
The foundations were laid on a moving sand, into which were driven eight rows of piles;
these carried as many pair of binding pieces, through or between which were driven a double
row of sheet piles, care being taken that those of one row covered the joints of the other.
Between the heads of the piles was laid a foundation of brick, carried up with mortar made
of Dutch tarras, and the whole was brought up 18 inches in height, and made level with
the tops of the binding pieces; other piles were driven under the walls. Between the first
and second row of sheet piles were laid ten cross timbers; between the second and third,
fifteen; between the third and fourth, two; between the fourth and fifth, six; between the
fifth and sixth, two; between the sixth and seventh, eleven; and between the seventh and
eighth rows, ten; these cross timbers extended throughout the whole width of the founda-
tions that were to be occupied by the sluice. Between these timbers the spaces were
filled in with masonry, and the whole brought to a level; a floor of oak plank was then
laid over, dowelled, pinned, and securely caulked at the joints.
On this floor was a second row of cross timbers immediately over those below, excepting
in that part occupied by the four principal pieces which came under the base of the framing
of the pointing sills, which were 54 feet in length, entering at each end 3 feet into
the walls, and their scantling was 24 inches square, or a double thickness. Forty-three lon-
gitudinal timbers at right angles with the two rows of transverse timbers were now halved
down, and securely pinned. On these were laid a third range of transverse timber, which
formed a second grillage, and after the intervals were filled up with masonry, a second floor
of planking was laid over the whole, and pinned and caulked down as the other.
quantity of timber employed in this construction seems, however, to have been more than
was necessary.
The
The masonry of the side walls was then carried up, leaving in each a small aqueduct,
arched with stone; they were 3 feet in width internally, and lined throughout with hard
and durable stone, to resist the violence of the water; these were the more necessary as the
gates, which were curved, had no small sluices for the passage of the water.
The counterforts were made equal to sustain any pressure to which the side walls might
be subjected; and two others were placed to receive the iron ties that secured the collars
of the gates. The aqueducts were closed by paddles, 3 feet 6 inches wide, each of which
sustained a considerable pressure.
In the construction of the side walls, four iron uprights were introduced 6 feet below the
top, at the groove where the paddles worked, two being placed on each side, and the whole
four at an equal distance, occupying a square of 3 feet each way. Each of these iron up-
rights had at the lower end an eye, with an iron key passed through it, 8 feet in length and
3 inches square; these were attached to iron anchors, 7 feet in length and 3 inches square,
the whole for the purpose of rendering it solid. On the top of the masonry were four
solid blocks of timber, 18 inches square; on these was placed the box with a groove in
which was the nut of the screw. The nut was turned by means of levers, and the screw
mounted, which carried with it the paddle below.
The Sluice at the Mouth of the Canal of Bourbourg, used for scouring the harbour of
Dunkerque, had a clear width of 14 feet, and the side walls were sufficient in length to
allow of two sea and two land gates, with a swing bridge between.
After the several rows of piles which carried the binding pieces that confined the sheet
piling were driven, the cross timbers were placed under the sills, their extremities being
allowed to pass through the side walls. Ôn a series of longitudinal timbers was laid a
course of transverse ones; after the intervals were closely filled with masonry, there was
laid a floor of plank. Above this, and immediately over the first transverse timbers, was
another, which was doubly floored; the upper planks crossing the lower at right angles.
1
CHAP. VI.
219
FRANCE.
Between the rows of piles, and particularly in the front towards the sea, was a filling-in of
clay.
The turning gate revolved upon a pivot, at the end of a middle post; on each side of this
post, and framed into it, were five braces; over the skeleton framing towards the side on
which the water was retained, it was closely boarded; and had two openings which were
shut by paddles, worked by a rack and pinion. The top of the middle post had a collar,
through which it passed, and in which it could turn freely round. This turning gate was
made two feet more in width than the lock, and shut against a reveal on each side in the
side walls, constructed for the purpose. To keep this gate firmly closed, a wedge-shaped
piece of timber work was pressed against it, which was moved by means of a rope attached
at the top.
When it was required to open the turning gate, the small paddle was first
removed, and as the water escaped, the gate was gradually slacked by a cable attached
to a capstan. The tide as it mounted shut the gate again, by mere pressure; the
lock-keeper dropped the wedge and closed the paddle, when the water required was ad-
mitted.
Sluice of the Canal of Bergues is a good exemplification of the manner in which M.
Clement laid the timber foundations, where the soil, as in this case, was a moving sand.
The outline of the platform being set out, piles were driven, from 10 to 12 feet in length
and about 11 inches square.
Four double rows of piles were driven to carry the binding pieces, morticed at the head
of the sheet piling, driven in at the two extremities of the platform; others were placed
under the sills, and a single row at the angles, made by the side and cross walls; the
planking was laid against, and not morticed, as in other instances, into these binding pieces.
These ten rows of double and single piles were capped by as many binding pieces; the
piles were driven at every six feet, and so dispersed, that in the double rows, one came
opposite the intervals of the others. The binding pieces, placed four inches apart,
formed a groove or space regulated by the thickness of the planks introduced between them,
which were by this means kept in a line. These were also guided at the foot by another
fixed piece of timber, which prevented their being driven out of place; these pieces were
secured at regular distances by round pins passed through holes made at every six feet, and
were kept in their places by keys passing through their ends. When a sheet pile came in
contact with one of these pins, it was taken out, and a hole cut to allow it to pass; when
the sheet pile was again driven, other square pins were substituted, passing through the
sheet pile and its two binding pieces, the rows of which extended throughout the entire
width of the foundation, and three or four feet beyond the projection of the buttresses, to
prevent the current of water from entering the foundation, which is the main use of sheet
piling. Several divisions are necessary in structures of this kind to ensure perfect success.
With respect to the other piles, as many rows were driven as there were cross timbers
viz. three between the first and second rows of sheet piling, six between the second and
third, five between the third and fourth, six between the fourth and fifth, and three between
the fifth and sixth, these rows being three feet apart from centre to centre. The number of
piles in each row was encreased according to the nature of the bottom, but they were more
frequent under the wing walls than under the platform, where there were scarcely any,
except under the timbers which run lengthwise; sometimes they were omitted, whilst
under the wings and piers, where the lock had several passages through heavy masses of
masonry, more precautions were taken, and a greater number of piles driven, they having
the effect of bearing the additional weight, and also serving to consolidate the soil, which
is compressed in a ratio proportionate, inversely, to the reduction of the volume of earth.
After the piles were driven, they were cut off about 3 feet 6 inches above the bottom
where the filling in masonry commenced; their heads were levelled, except those to which
were attached the binding pieces, which confined the sheet piling. The head of each pile
had a tenon cut on it, which passed through the mortices of the cross timbers, formed a
capping, and were held fast by an iron pin passing through them. The longitudinal and
cross timbers were about 30 feet in length, and 12 inches square. When all the piles were
;
driven and the loose earth taken out between the heads, the spaces were filled with good
masonry to the depth of about three feet, after which the cross timbers were laid, the under
parts of which were filled with mortar and closely bedded. The cross timbers which came
under the two sills, as well as the masonry, were raised a foot higher above the piles than
the others, to form that part of the chamber of the sluice against which the gates rested.
The cross timbers being placed, they formed the first layer, which entered partly into the
masonry; above these was another platform of longitudinal timbers, crossing the others at
right angles, and being halved in and well secured at the intersections by irons.
One line of longitudinal timbers was laid under the face of each wall, both back and
front; the others in the intermediate spaces, so that there were four under each wall. The
platform between the walls was divided into four equal parts, and at each division was laid
a longitudinal timber, and some short lengths under the counterforts.
When the double layer of timber was completed, the voids were filled up with masonry;
220
Book I.
HISTORY OF ENGINEERING.
when brought to a level, a bed of mortar was spread over the whole; and on this, in the
space comprised between the chamber walls, was a floor of three-inch oak plank, secured
down upon the cross timbers, for the purpose of preventing the springs from working
upwards. Under the walls it was omitted, that the masonry might unite more firmly
with the foundations.
The floor was again crossed by other timbers placed directly over those below, and
halved on the five longitudinal pieces forming a third layer, or grille, which extended only
over the chamber; these were pinned down with iron; when these timbers were laid,
others, which formed the sills to the chief parts of the lock, were placed.
The intervals of this timber platform were then filled up with masonry, and levelled as
before. A floor of three-inch oak plank was pinned down to the chief timbers; over
this, in a contrary direction, was another floor two inches thick, a fall being preserved of
one in forty-eight in the direction of its length, to allow the water to run off when repairs
were required.
After six lines of sheet piles had been driven in different directions, the Maréchal Vauban
added a double row at the pointing sills, which, with the other parts of the construction,
were then commenced.
The side walls and their counterforts were set out, and the various courses of facing were
all cramped and worked with care; a backing of clay, 5 or 6 feet in thickness, was rammed
down as low as the first course of masonry, and brought up to the level of high water.
Sluice of the Canal of Bergues, which was used for the purpose of deepening the port of
Dunkerque. It consisted of two gates, one contrived to hang within the other; the lesser
opened seawards, and the whole turned so as to admit boats into the canal. The outer
gate, being scarcely anything more than a margin to the first, carried a triangular piece
of framing, which was requisite in order to render the inner gate secure; this is called
a port busquées, and is more curious than useful. At low water the triangular frame
was unhooked from the great gate, and the lesser one being relieved, opened suddenly
and allowed the water to pass through with violence, pushing any obstructions before it.
At high water the small gate was again closed, and the triangular piece of framing called a
valet was hooked to the outer frame, and effectually prevented its opening.
A turning gate in the canal of Bergues, as designed and executed by M. Clément, in the
year 1705, is an excellent example. The width of the lock was 27 feet 6 inches, so that
each gate was in width half that dimension. The ports were 15 by 17 inches, as were the
horizontal rails: these together formed the skeleton framing, in which revolved the turning
gate, 13 feet 6 inches in width, and 10 feet in height. Where the rails entered the uprights,
they were secured on both sides by strong irons. The upper horizontal rail was 15 by 13,
and the braces 11 by 9.
The gate was supported when closed in a reveal on each side, and turned upon its centre;
when this was required, it was only necessary to raise one of the paddles, and to keep the
other closed, for as the water was allowed to pass through one opening freely, the closed one
receiving the entire weight, was on that side more pressed, and consequently impelled
forward by the weight of water against it. Both sides were then closed, and the force,
being equal over each half, prevented it from turning either way.
Sluice at the Mouth of the Canal of the Moere, about 15 feet in width, was not con-
trived for the purposes of navigation. It had one pair of gates and a sluice gate, raised by
a wheel and capstan, or a wheel termed hérisson, formed by a number of handspikes. The
gates were opened at low tide, and after the water had left the canal, the sluice gate was
raised to a height sufficient to allow the proper quantity of water to pass, and the force with
which it ran out effectually scoured the mouth. The sea again entered the canal, where it
was confined by shutting the gates, when the sluice was afterwards lowered; at the time of
low water it was let out, and the operation continued as long as it was deemed necessary
for scouring purposes.
The vanne of the canal of Moère was about 16 feet in width, and 13 or 14 feet of water
usually pressed against it; its thickness was about 8 inches, and it was firmly secured by
eight bands of solid iron. To raise it, a species of tread-wheel, upwards of 29 feet in
diameter, was placed on each side, worked by men; to the axle that turned round, ropes were
attached, and by the aid of blocks and pulleys, the vanne or gate was lifted to the height
required.
The channel of the port of Dunkerque was at first bounded by jetties constructed with
fascines, which were laid in the year 1679, at the time Louis XIV. became possessed of the
port.
It being found necessary that the sluices should operate more powerfully, and deepen the
channel, the jetties were carried out to a greater distance. Jetties formed with fascines are
admirably adapted to receive the surf, but require a constant outlay to maintain them, and
should therefore only be used as a temporary expedient, or to facilitate the arrangements of
more solid constructions, for which purpose, when properly formed, they are exceedingly
useful. The breadth given to the base was three times that of the height, which here was
CHAP. VI.
221
FRANCE.
25 feet 6 inches. To limit the width of the foundation, two lines were set out not quite
parallel, because the depth increasing as they proceeded, rendered it necessary to increase
the width, at the same time that of the channel was made equal throughout, the difference
being given to the exterior face of the jetty. Some of the earth being removed, the first
bed of fascines was laid, and to prevent the sea from undermining the work, a trench was
dug and filled in with well-rammed clay; fascines united in masses were covered with heaps
of clay, which filled up the inequalities and holes in the shore, before the work was brought
to a level.
When the necessary trenches were cut, several layers of fascines were laid within them
6 or 7 feet in length, and from 18 to 20 inches in circumference; when laid across the
intended jetty they formed a bed of about 12 inches in thickness. The ends of each layer
were dressed to the form required by the slope; small stakes 3 feet in length were driven
through them at the distance of 18 inches, and rows were so formed at every 3 feet. Rods
15 to 16 feet in length were then worked round the heads of the stakes, and the whole
securely wattled together.
The beds of fascines were repeated in a similar manner, until the whole mass was brought
up to the height required, care being taken that the rows of stakes were placed in various
places to unite the upper layer with that below it. This work was only carried on after the
tide had retired, and it was found necessary to load it with large stones, to avoid any
movement that might take place from the rolling in of the sea.
The entire surface was covered with a grillage of fir timber, 4 or 5 inches square, leaving
compartments of 2 feet square. Piles were required to maintain them in their position,
one being driven slantways in each mesh of the square, they were from 12 to 13 feet in
length, and 12 inches in circumference at top, gradually diminishing towards the point; a
hole was bored at the head, through which a stake about 18 inches in length was passed,
to retain the timber grillage, and prevent its moving. The squares were filled with stone,
laid dry, placed on edge, and well rammed with wooden rammers, that the stone might not
fracture. The crevices were filled with smaller pieces of stone, or the chippings from the
quarry.
The whole of the work was protected by piles, to prevent any injury from the
passage of the vessels to and from the harbour, and these also served to support a small
continued line of bridges that communicated with the forts. The slopes and top being
completed with fascines, a series of framing was laid throughout, at distances of 9 feet,
similar to those used in the construction of quays. Each frame being formed of a protect-
ing pile from 36 to 40 feet in length, 16 or 17 inches square at top, and capped with timber
about 12 inches by 8, so as to unite the whole line together. These piles were retained in
their position. by tyes, which ran through the entire width of the jetty; each bay was
strengthened in various directions by cross timbers, 12 inches square.
The jetties so constructed of fascines did not continue more than twenty years, when it
was found necessary to construct them more solidly, and Maréchal Vauban approving of
the plans suggested by M. Clément, he was directed to form them of timber and stone.
The old fascines were removed to within 3 feet of high water mark; those below
had become so consolidated by the deposit of sand and other matter, as to be rendered
strong enough to support the weight intended to be put upon them. Lines were drawn
at every 20 feet, and piles driven at about 2 feet 9 inches apart, which were cut off at a
uniform height, leaving a tenon to mortice into the longitudinal timbers placed over them.
Rows of piles were driven between these lines, and these were repeated at every 8 feet, the
width of each bay. On these rested the sill of the framing, halved on to the longitudinal
timbers, and morticed to the heads of the five intermediate piles, on which was constructed
the framing.
The piles were 9 or 10 inches square, and the long timbers which capped them 13 or
14 inches square, 25 feet long, and their scarfing joints 3 feet long. The transverse timbers
which formed the sill of the frames were 25 feet in length, and 13 inches square; their
ends were dovetailed into the longitudinal timber to the depth of three inches. The middle
horizontal timber was 13 inches square, and the upper one 12 inches square; these were
dovetailed into the side timbers which formed the slopes.
The St. Andrew's crosses were formed of timber, 9 inches square, morticed and tenoned at
the ends. The struts were 9 inches square, dovetailed at the ends, and the upright post
was of the same scantling.
The slant parts of the exterior were 12 inches square. The binding pieces the same
scantling, and 25 feet in length. The whole was planked throughout, and capped at the
top.
After the framing was complete, it was filled in with hard stone, laid carefully by hand
and without mortar, fine gravel being substituted.
The celebrated Risban or fort, which was constructed in masonry to guard the entrance of
the port of Dunkerque, was distant 550 toises from the bastion, and 50 from the mouth of
the canal: the length of each of its three sides was fifty toises, and it rose 46 feet above the
222
BOOK I.
HISTORY OF ENGINEERING.
level of low water. Eighteen embrasures were formed for cannon, and so arranged, that
sixteen could be brought to bear upon vessels in the roadstead: on the other side it com-
manded all the approaches to the citadel.
The lower floor, which was entirely below the ground, served as a deposit for stores; the
upper for the use of the garrison, above which was the magazine for powder.
On the first
floor was a chapel, and on the second a room for the deposit of biscuit.
Over the roof was contrived a lighthouse or beacon, 8 feet in diameter, with a small
dome covered with lead.
On one side of the fort was the lodging for the commandant, consisting of kitchen,
dining-room, and two chambers, with all the necessary offices, from which was a ready
communication with the whole of the ramparts. On the opposite side was a lodging for
six artillery men, a covered shed for the cannon, and the magazine, in which ammunition
was kept adjoining these were the barracks, consisting of twelve rooms capable of accom-
modating an hundred men. Three staircases conducted to the several parts of the ramparts,
and the whole was well provided with water, which was kept in two large cisterns, placed
opposite the governor's house.
Vauban executed this work without a coffer-dam, at the time of low water, the tide rising
about 13 feet. Piles were first driven round the site to be built upon, and four-inch plank
in six feet lengths secured to them, and further kept in their places by binding pieces on
each side. These were surrounded by sheet piles.
The Canal of Mardick, cut after the demolition of the fortifications at Dunkerque, to
discharge the superfluous waters, was completed in the year 1715, under M. Le Blanc; and
the lock he constructed was considered the finest in Europe. It was divided into two
passages, one 47 feet in width, the other 27 feet; its length was 295 feet; that of the
middle wall 32 feet, and each of the side walls without the buttress, 25 feet. It was distant
from the sea 3384 toises: the width of the canal was 50 toises, and its depth 21 feet.
The turning gates employed at this sluice were remarkable for some ingenious con-
trivances in particular, that placed in the widest passage; that in the smaller resembled
one already described in the lock at Bergues.
When required to be closed, one paddle was lowered, and the other raised: each opening
being made a little more than 6 feet square. The weight on the fresh water side being
greater than that towards the sea, it was necessary to provide an additional contrivance to
keep the turning gate secure in the reveals against which it lodged. For this purpose,
two locking bars, moved by a perpendicular rod, were introduced; a simple jack at top
elevated the rod to which the latches or locking bars were attached, and which being raised
relieved the gates.
To raise the paddles, the lock-keeper descended by a ladder, placed on the land side,
against the gate, and by means of a rack and pinion lifted it up; the other paddle
being previously lowered, that the sea might close the gate on that side when the canal had
received the quantity of water required. Capstans and cables were attached to the lower
half of the gate, and facilitated both its opening and shutting. A chain secured to each
side by means of rings prevented the gate from closing, and supported it against the violence
of the water as it rushed through.
Gravelines is situated on the river Aa, which runs through a fertile portion of Artois, and
empties itself into the sea, amidst the sands and dams thrown up on the coast, which being
at this point extremely flat, there was a constant accumulation of stagnant water in the
ditches, for which it was difficult to obtain any outlet. Gravelines became the tomb of all
the garrisons sent there.
At the commencement of the seventeenth century, Philip III., King of Spain, turned his
attention to its improvement, and constructed a canal near Gravelines to carry off the water
by a shorter course; and at about 900 toises from the counterscarp, where high water
flowed, a large sluice with a double pair of gates was formed: this was soon afterwards
destroyed by order of Cardinal Richelieu.
In 1659 it was ceded to the French, and in 1737 Maréchal Vauban commenced im-
proving the drainage of the district. He formed a new lock, divided by a wall of masonry
into two unequal passages, intended to aid the discharge of the waters of the river at the
time of land floods. Its length was 105 feet and its width 100 feet. Coffer-dams were
made use of, and after the earth was taken out to a sufficient depth, piles 8 or 9 feet in
length, and 12 inches square, were driven entirely over the whole site; others were added to
the side and middle walls, altogether amounting to nearly a thousand, all placed in parallel
lines, morticed and tenoned into the longitudinal and cross sleepers above.
After these and the necessary rows of sheet piling were driven in, the ground was
levelled, and the earth taken out to the depth of 30 inches; the spaces were then filled with
masonry. In this was laid the lower grillage or timber platform, composed of twelve longi-
tudinal timbers 12 inches square, so placed that they lay under each side wall, the same
number under the middle wall, one in the narrow passage, and two in the other. These
were secured to the heads of the piles by pins 12 inches in length and 1 inch square. Upon
CHAP. VI.
223
FRANCE.
this was laid a second platform of timber of the same scantling, crossing the first, and securely
pinned to it by barbed irons, 14 inches long and 1 inch square. These cross timbers were
placed 21 inches apart, and the spaces filled up with brick laid in tarras, or mortar made
of lime and sand, with a proportion of one third of Dutch tarras. An oak floor, 3 inches
thick, was laid over the spaces between the intended walls, formed of planks, none of which
were less than 20 feet in length, fastened by spikes, 7 or 8 inches in length, as well as
wooden pins; after which the joints were caulked. In the passages was a range of longi-
tudinal timbers, and three others under each of the three walls, care being taken that one
of these should be under the face of each wall: these longitudinal pieces were secured to
the cross timbers below them by barbed iron pins, 17 to 18 inches long, and 14 inches
square. Upon this third platform was another course of cross timbers, each in one length,
placed immediately over those below: their length was only 4 feet more than the width of
the passages.
These cross timbers were united to the longitudinal ones below by similar
iron pins to those described, 18 inches in length. The spaces between were filled up
with brickwork to the level of the top, on which was laid a coat of mortar and a layer of
moss, over which was another floor of plank, 2 inches in thickness, but not extending beyond
the water-way.
As this work advanced, the main timbers for the pointing sills were laid down, and the
two ends of the platform were secured by rows of sheet piling confined at the head by
binding pieces 12 inches square. The chief timbers under the pointing sills were 28 feet
6 inches long, and nearly 2 feet square. Those of the smaller passage were of the same
scantling, but less in length.
The sill which sustained the heel parts of the great gates was 28 feet long and 2 feet
square. The pointing sills were 10 feet long and 24 inches square, all secured by iron
pins.
The sill of the smaller passage was 23 feet long, and 2 feet by 1 foot 9 inches square;
that of the turning gate was 25 feet 6 inches in length, and 2 feet square: to give it ad-
ditional strength, two timbers of the same scantling were laid at right angles with it in the
middle of the water way. After the whole was carefully set out, and the site for the walls
traced, the masonry was commenced with stone from Landretun, which was laid in regular
courses 10 inches in height, and having their beds not less than 20 inches. These stones
were cramped wherever there was any pressure, particularly where the turning gate was
placed, and the reveal carried up to receive it. The walls were backed with brickwork
laid in cement, to the thickness of from 2 to 3 feet, above which common mortar was used.
The bricks were dipped in water previous to being laid.
The side and middle wall being carried up 4 feet above the level of the highest floods
were finished by a course of flat stones.
The turning gate was composed of two upright posts besides the middle, which had the
pivot on which it turned. There was a bottom, a top rail, and two horizontal between,
which were braced from the middle post; and at each mortice and tenon the joints were
secured by strong irons. The middle or turning post, 17 feet in height, and 18 inches by
16 inches square, worked its gudgeon in a collar. The outer posts were 12 feet 9 inches in
height, 13 inches by 11 inches. The gate was 1 foot more in width than the water way,
that it might rest securely agrinst the reveals prepared to receive it when closed.
One side of the turning gate was wider than the other, that the sea, at the time of flood,
should have the power of shutting it: it was not quite at right angles, but presented an
inclined face to the action of the water. A valet was contrived on the inside to keep the
gate closed, and prevent the fresh water from running out of the canal at the time of low
water. This valet or key to secure the gate was formed of a turning point, 11 feet in
length, and 12 by 7 inches, and a branch 15 feet in length of the same scantling, united by
two ties framed into it and rendered secure by iron straps; when used, a rope or chain
was attached to the upper hook, which pulled it round on its pivot, and when brought
flat against the turning gate, it was secured to the middle post, and prevented the water
from the sea-side from forcing it open.
The Port of Cherbourg, in the department of La Manche, in 49° 38′ north latitude, and
1° 37' west longitude; it is situated on the most northern coast of the peninsula of
Contentin in Normandy, and the bay between Cape de la Hogue and Barfleur, and has the
form of a crescent. There are two harbours which communicate by means of gates, and
at the entrance two piers have been carried out; that on the east side extends nearly half
a mile in length, and the other about half that distance, the width at the entrance being
210 feet. The outer harbour is in length 360 yards, in width 250, and has a depth of
water at low spring tides of 30 feet.
The quay, 200 feet in width, is built of stone, and extends in a straight line from Fort du
Hamet to Fort du Gallet: the inner basin is entered between two circular returns.
Napoleon expended vast sums of money in the construction of docks, slips, and quays,
using the granite obtained from Barfleur.
This port is cleansed by sluicing, at the time the tide is low, or when there is not more than
224
BOOK I.
HISTORY OF ENGINEERING.

POINTE DES FOURGUETS
POINTE ET FORT DE
QUERQUEVUIE
ROCHE
SAUQUEU
LAQUE RRE
ROCHE
CHAVACHAC
ANSE-STÆNNE
POSITION OF THE BREAKWATER
AS DESIGNED BY.M.CESART
BREAKWATER AS EXECUTED
FORMED BY EIGHTEEN
CONES
LINE
OF
SOUNDIN
WATER
CROCHE LA BRUNE
PIPIR
HAPEOUT
ROCKE
-BRETONNÉ
FORT
FORT
MET
LINE.DE
ROCHE NAZAR
Low
WATER
OF:25.
SOUNDINGS OF 25.
ISLE PELEE
AT LOW WATAR
LINE OF SOUNDINGS OF 20.1
FORT DU CALET
ROCHES FLAMAND
LES BECOM:
CHANTE REINË
BATTERIE
CHERBOURG
ONCLE
REDOUTE DE
'TOURLAVILLE
DUMES
Fig. 235.
PORT OF CHERBOURG.
two or three feet water: the gates of the large sluice being opened, the river Yvettes is let
into the inner harbour, and by means of pontoons and other contrivances is made to plough

SECTION.

PLAN OF LOCK.
U
U
D
U
U


TIP
Fig. 236.
LOCK AT CHERBOURG.
CHAP. VI.
225
FRANCE.
mud, and bear it away to sea; and the force is so great that it keeps the outer harbour
scoured, where there is always a depth of 17 or 18 feet of water.
The lock between the outer and inner basin was commenced in 1736, under the direction
of M. de Caux; the foundations and platform were constructed in masonry: its width is
40 feet, and its length 27 toises. It is placed on hard sand, 2 or 3 feet below which is a
stratum of marl or clay, and 7 or 8 feet lower a bank of rock, the thickness of which
could not be ascertained.
To prevent the encroachment of the sea during the process of laying the foundations, it
was necessary to encompass the entire site by a cofferdam, 5 toises in thickness, faced with
stones placed on their edges, supported at every 2 feet by rows of hurdles on a bed of
heathers: this was done especially towards the sea, to prevent the washing away of the
sand. A small lock was made towards the port to allow the water which the machines
had already pumped out to pass off at low tide. An excavation was then made to the
depth of 16 feet, sufficiently wide to allow room for the workmen around the foundations.
Several obstacles occurred to prevent this depth being obtained, occasioned by the innu-
merable springs, which required twelve inclined mills to keep up the pumping, and which
cleared out 180 cube toises per hour during the time of high water: these, however, not
proving sufficient, five more were added, with vertical caps, 16 feet in height, and from 6
to 7 inches in diameter; these latter succeeded so well that the inclined mills were reduced
to four.
The excavation was effected by clearing away the earth for 3 toises in width, at the
extremity of the port, by the inclined mills only; and when arrived at a certain depth, the
piles were driven in, on which were placed the vertical mill. As the column of water
which was to be raised was from 14 to 15 feet, winches were applied proportionate
to the labour to be performed, which were easily moved by twelve men, relieved by the
same number every two hours, so that each mill pumped out 16 cube toises of water per
hour.
When this piece was dug throughout the entire width of the lock, the same system was
adopted for another width, drawing back the mills into the new position, and this was done
so rapidly, that in six months the whole foundation was complete.
The pumps at first used were upon the balance principle, by which, without taking
friction into account, four men raised half a cube foot of water to the height of 15 or 16
feet; but the sand in this instance accumulating, they could not be continued, and the
common mills were substituted.
In digging out a foundation where the springs are numerous, it is desirable if possible to
turn their course, or, if this be not practicable, to conduct them outside by means of a
trough fixed to the masonry, which forms a current for the water: when they arise from a
neighbouring river or the sea, they may be excluded by forming inverted funnels, the sides
of which touch the mainland: a small pipe of 4 or 5 inches in diameter, laid a little higher
than the level of the spring, is attached to the funnels, and the water in the pipe remaining
in equilibrium ceases to flow externally; the masonry is then carried up to the summit,
and the pipe filled with concrete.
After the rows of sheet piling were driven at the extremities of the platform, the first
course of stone on the side of the entrance to the port was laid; it was formed of large
rough blocks throughout the whole extent, and under the platform was placed a course of
squared stone, of from 17 to 18 inches in height. A mass of the ordinary kind, 4 feet in
thickness, was then raised; another a foot in thickness was added, laid in cement, on which
was a bed of cement, 3 or 4 inches in thickness. The portion of the mass at the pointing
sills was formed of several courses united together by cramps run with lead: that which
formed the pointing sill was 2 feet in height, so that, being elevated 16 inches, there
remained eight embedded or bonded to the pavement of the platform. Great care was
taken to select the hardest stone, of from 36 inches to 40 inches cube to bed the pivots:
these stones were so placed as to be tied in by the walls at the side and under the sill.
The whole of the platform was paved with stones from 4 to 6 feet in length, and 2 feet 6
inches to 3 feet in width, and from 18 inches to 20 inches thick, all having a convex surface.
The strongest were selected for the pointed sills, and the whole were laid in cement, and
jointed with mastic; care was taken to unite the lower course of the side walls with the
stone platform, which was done by cutting the stones in such a manner that they formed a
part of the facing as well as the pavement. Bolts run with lead were introduced in the
situation required for the screws which were to secure the quarter circles of iron upon
which the rollers of the gates run.
The pavement being completed all the joints were run with mastic, then the entire
extent of the platform was covered with a bed of clay 2 feet in thickness, that the masonry
might be consolidated, and the salts of the lime prevented from escaping.
The best method of constructing a platform in masonry is to form a course of headers,
dovetailed into the adjoining stones so firmly that no action can detach them; this kind
of work costs considerably more at first, but is infinitely stronger.
Q
926
Book L.
HISTORY OF ENGINEERING.
After the platform was finished, the side and wing walls were carried up with all possible
solidity.
The plan shows only one pair of gates on the side towards the harbour: the omission of
side-gates is a great defect, the vessels entering the port being frequently thrown against the
jetties. The facing of the walls is carried up to the height of the iron collars which confine
the gates, and every method is adopted to fix the ties and iron keys firmly into the masonry.
In the profile and plan are shown the largest, which is fixed, and has three arms, forming a
goose foot; the two extremes are placed horizontally, whilst the middle one inclines ten
degrees below the others, so that the arms being united with the ties, the centre may
have the same inclination, and enable it to bear the weight of the masonry.
The ties,
3 inches square, are each composed of three pieces; their whole strength depending upon
the thickness of the mass in which they are embedded, the pieces should be well tied
together, at the same time easily separated. The ties have several holes pierced in them,
to receive the keys, some of which are placed vertically in the masonry, others horizontally
in large stones introduced for the purpose. The two first are horizontal, and the other is
inclined ten degrees. To give additional strength to the keys two arcs are made in the
stone, one 6 feet or 7 feet radius, and the other from 14 feet to 15 feet, which ties the stone
against which the horizontal keys rest more solidly; grooves being cut to receive the ties,
the vertical keys were fixed into eyes prepared for them.
The side walls were raised to within 6 feet of the entire height.
In arranging the turning bridge, it was necessary that the surface towards the abutments
should be on a level with the pavement; when finished, one half therefore turned on a
platform, and the other into a recess.
The jetties had their foundations laid 12 feet below the ordinary level of the shore;
and the works were carried on without cofferdams during the period of low water. Each
jetty was formed of two stone walls united by transverse walls at every 60 feet; their
intervals were filled with clay mixed with a small portion of lime. The thickness above
the set-off was nearly 30 feet, and at the summit 21 feet; the slope or talus being 4 feet 6
inches. When the walls were within 5 feet of their intended height, an arch was con-
structed, over which was formed the crowning platform.
The lines which limited the width of the jetty having been traced, sheet piling was
driven in to encase the foundations; the earth was then taken out between, and the depth of
the trench made as low as the heads of the sheet piles, and no more earth taken out
than would allow of its being built over in the time of low water, which was about three
hours and a half. Two chapellets were employed to draw the water from the trenches,
which, occupying an hour, left only two hours and a half for work. Twelve feet in length
of sheet piling were driven at each time, tongued and grooved and maintained in their places
by two binding pieces. The thickness of the sheet piles was 6 inches, and their width
13 inches, their length being proportionate to the nature of the soil, which usually re-
quired about 12 feet; they were shod with iron, as the sand into which they entered was
very compact.
As soon as the piles were driven the part of the trench which they enclosed was imme-
diately filled up, to prevent the labour of additional pumping, and the sea from deposit-
ing sand or injuring the works. A dyke, 3 feet in height, was raised throughout the whole
length, formed of fascines and covered with stones. When the foundations were laid, 12
feet in thickness was given to each wall, the first bed of facing wall was laid on plank, 4
feet below the top of the sheet piling, and after the masonry had been carried up 3 feet, its
thickness was reduced to 10 feet for the first set-off, where the heads of the sheet piles were
united to keep them in their place, and to fix the binding pieces firmly to the masonry,
iron ties were introduced at every 8 feet. Two feet above the first set-off was another,
which reduced the two walls to 9 feet in thickness, after which they were carried up with
an external talus equal to one-sixth of their height, the interior face being kept perpendicular,
reducing them to about 3 feet in thickness at 25 feet above the last set-off, without taking
into consideration the addition by filling in solidly the spandrils of the arches. The arch
of the vault, 18 inches in thickness, was formed also of stone well cut and carefully
constructed. At the level of high water, rings and anchors were introduced into the
masonry at regular distances.
Above the vault was laid a paving of a hard stone, 3 feet in length, 8 feet in thickness,
and 18 feet in width; the joints were well secured by cement, and a fall of 4 inches
was given to their surface to throw off the water. On the side towards the sea, a
parapet was built, 3 feet 6 inches high, and 2 feet 6 inches in thickness, coped with stones
strongly cramped. At every 60 feet cannons were placed for the purpose of defence.
The toe of the jetty towards the sea was protected by an additional embankment 16
feet in width, which had in front a row of jointed piles, from 7 inches to 8 inches in
thickness, and of a length proportioned to the nature of the soil. The space between this
and the jetty had other piles driven in, and their heads cut off with an inclination: on
these a platform of timber was laid; the earth was then taken out for a depth of 18 inches;
CHAP. VI.
FRANCE.
227
fascines well bound were laid in, and the coffers of the grillage filled carefully with ma-
sonry.
The celebrated breakwater, commenced by Louis Alexander de Cessart, in the year 1783,
was the most extraordinary work at this port; it was necessary to obtain a sufficiently
extensive harbour for the anchorage of the French fleet after the destruction of Dunkerque,
there being no other refuge on the coasts.
The difficulties were great, both in forming and defending it, some portions being carried
up to the height of 80 feet, as a rampart against the impetuosity of the waves or the attack
of an enemy.
To weaken the power of the sea, Cessart suggested the use of large truncated
wooden cones, base to base, loaded with stone, and placed in a line at half a league from the
shore: they were prepared on land, floated to their destined position, filled with stone, and
sunk; after which, all above the level of low water was to be built up with good masonry,
faced with granite, and laid in mortar composed of puzzolana. When all that belonged to
the construction was complete, the intervals between the tops of the cones was either to be
closed by iron chains suspended from each other, or guarded by a floating boat or pontoon,
and it was supposed that such a construction would present a barrier to the power of the
ocean, and afford at all times protection to 100 sail of the line. Batteries were afterwards
to be erected, which should rake the entrance at each end, and annoy an enemy approaching
the harbour.
Numerous projects and experiments were tried by the engineer, in the port of Havre,
upon the effects of floating a truncated cone of 150 feet diameter at bottom, 60 feet at top,
and 70 feet in height. It was calculated that ninety such cones placed contiguous to each
other would form a perfect breakwater. All the experiments upon the model having

וח
W
HE
Fig. 237.
PLAN OF CONE.
succeeded, the government, after making it a subject of grave discussion, and examining
many competent engineers and nautical men, ordered the works to be commenced. Cessart
being instructed to revise and make various deviations from his original plan, constructed
on a platform previously laid down on the shore a truncated cone, the lower diameter
of which was 150 feet: around this were set up ninety timbers, at a distance of about
Q 2
228
BOOK I.
HISTORY OF ENGINEERING.
5 feet 3 inches from centre to centre, so inclined that at the top they were gathered into
a circle of about 64 feet diameter; the perpendicular height of this cone was nearly
70 feet.
Each of the inclined timbers consisted in length of five or six pieces, arranged alternately:
in those having five the lower length was 25 feet 3 inches, the second length 25 feet 10
inches, the third 25 feet 4 inches, the fourth 24 feet 10 inches, and the fifth 30 feet 10
inches; altogether 132 feet 1 inch. Where six lengths were used, the four lower pieces
were as those already described, the fifth was in length 24 feet, and the sixth 19 feet 7

کممم
inches.
Fig. 238.
J U U U V U T
T T T I I I I I I I
ELEVATION OF CONE.
The scantling of the timbers at bottom was about 13 inches square, gradually dimi-
nishing to 8 inches at the top: where they were joined, a dovetailed scarf was cut, 18 inches in
ength, and the two ends were secured by iron bolts. Square holes or openings were left in
the timbers, 8 feet wide and 9 feet in height; one at the bottom for the purpose of admitting
the casks which floated it, and the other at the fifth course, to remove them when cut from
the base and floated to the surface. After the inclined timbers were hoisted, which was
effected by a very ingenious process, they were bound together by six horizontal timbers
on the outside, and twenty-four on the inside. On the outside beech as well as oak was
used; in the first, third, fifth, and sixth courses oak, and in the second and fourth beech:
these were scarfed at their ends, one 30 inches, and the oak 36 inches in length, and so
placed that they corresponded with the twenty-four internal horizontal timbers in the fol-
lowing order: —
The first external with the first internal, the second with the fourth, the third with the
eighth, the fourth with the twelfth, and the sixth with the twenty-fourth.
All the internal horizontals were halved 4 inches into the inclined timbers, and their
scantling was 13 inches square. Iron bolts with nuts and keys alternately were used to
secure them in their places.
A double course was afterwards added at the bottom to attach the casks, and ninety blocks
were inserted between for the cables. After the slanting or inclined timbers were fitted
together upon the platform, they were hoisted by eight pairs of shears, worked by as many
gangs of men; when the whole ninety were in their place the horizontal timbers were
fixed, which when secured, the next length was raised, and so on till the whole was
completed.
After this part of the operation was performed, other horizontal filling-in pieces were
introduced, varying in scantling from 10 inches by 6 to 12 by 8, at the distance of about
6 feet or 7 feet apart; fifteen of these were placed below water and as many above; the
former were fixed before the cones were floated, the others after they were sunk in their
respective situations; the whole was secured by iron pins, which passed through the
inclined timbers, and were fastened by nuts. Five circular courses, put round the interior
of the cones at the lower 36 feet of their height, prevented any injury when the casks were
attached.
The ninety ends of the timbers at the summit were capped by others 6 inches in thick-
ness and 3 feet in width; besides which other timbers were thrown across, radiating from a
centre, acting as supports as well as forming a platform for the workmen.
This bold undertaking of Cessart attracted the notice of the most learned men of the
time, and numerous publications issued from the press condemnatory_of the principles
avowed by the engineer, and for the purpose of frustrating the work. The sea, it was ob-
served, was subjected to three great movements caused by the various winds, by the tides
CHAP. VI.
229
FRANCE.
and the currents, resulting from the changes of temperature to which the Northern Ocean is
subjected.
When the particles of a fluid are driven in one direction, as they are by the wind, the
adjoining water is required to fill up the vacant space, and restore the equilibrium which
has been destroyed; waves formed by this means, it was observed, and impeded by the
proposed line of timber cones, might render the water on the opposite side comparatively
tranquil, but the force at the two extremities would be so great, that it would be impossible
for a vessel to enter or approach the

harbour. The violent impulse given
to waves in a storm continues long
after the gale which has produced it
has subsided, and an oscillatory motion
remains, and for some time works upon
the great mass of water, which in this
instance, it was said, would be suffi-
ciently powerful to displace any arti-
ficial contrivances in carpentry. The
agitation produced by the wind does
not, however, affect the waters at any
great depth; their surface is alone dis-
turbed, for in the roughest weather at
80 feet the sea is always tranquil.
The force of the tides was still more
likely to be injurious; for, being in-
terrupted in their current, it was urged,
the water would so accumulate in
height, when obstructed by the pier,
that it would have sufficient force to
remove it from its position; and the
currents which set in so violently at
the bottom of the ocean would be
powerful enough to displace any ar-
tificial obstruction. The two polar
currents, which float mountains of
ice from the frigid to the temperate
regions, and which are encoun-
tered as far as the fortieth degree of
latitude, were also supposed to be
capable of driving away a barrier, or
breakwater, placed in their course.
was also maintained, that no obstacles
on land could turn aside the currents,
or oppose a barrier to the grand move-
ment of the ocean, and it was vain to
attempt it: but these arguments did
not weigh with Cessart. When his
timbers were all firmly bolted together,
and secured by the best means he could
contrive, he commenced his prepar-
ations for floating them.
It
The execution of these immense
timber constructions was confided to
ship carpenters, and the whole was
planked and bolted together in the
same manner as the sides of a vessel :
to float them seems, perhaps, the most
ingenious part of the contrivance,
though the method adopted was by no
means new, for casks have been em-
ployed on the English coast for cen-
turies, to buoy masses of stone re-
quired to form a mole or termination
to a jetty. Pliny has described the
·
ם ם
O
D
ם ם
Fig. 239.
ㅁㅁ
​ㅁ
​ㅁㅁ
​од
ם
ច
FRAMING OF CONE,
☐ ☐
ㅁㅁ
​m
口
​means adopted by the ancients to float heavy bodies, and in all probability the system
they practised has never been entirely forgotten: in this instance the casks seem to have
been preferred to vessels; they were more under the control of the engineer, and could be
more easily detached.
Q 3
230
BOOK I.
HISTORY OF ENGINEERING.
The casks were 12 feet in length, 7 feet in diameter, and it was calculated that each was
capable of buoying up 28,000 pounds.

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0
ם
Fig. 241.
PLAN OF CASKS.
When all the casks were fastened to the
bottom, the cones were towed to the position
where the boats were to be attached: it had been
previously ascertained by experiment, that four
men rowing could tow one cask from 15 to 20
toises per minute against tide, and twice as fast
when the tide was in their favour. Upon this
calculation 250 men would be required in calm
weather to tow out the cone, weighing, it was
supposed, upwards of 2,000,000 pounds; but
De Valon's capstan being employed, forty-two
men only were required to do the same
work, and they could in five or six hours move
it a distance of 3000 toises; after which it
would be in a position to float at all times of
the tide, and could be then towed by sailing
boats or by rowing.
By the 6th of June, 1781, all was in readiness
with the first cone; a circuit of strong cables
was placed immediately above the line of im-
mersion, and another above the line of floatation,
crossing the bottom with a grillage of ropes
tending to the centre, to resist the force of the
water, and to prevent the timbers spreading.
For cutting away the casks after the cone had
been floated to its destined position, there were
a number of hatchets or cutting instruments
attached, one over the rope which held each
cask; they were made to move upwards by
a rope, and, from being loaded with lead, dropped
by their own weight, like a pile-driving machine,
and severed the rope upon which they fell.
Thirty-five casks were attached to the inside,
and forty-nine outside. Thirty-one of a smaller
kind were added to increase the buoyancy, and
ladders were provided for the numerous work-
men employed. It would have been practicable
to have floated the cone after it was detached from the platform upon which it had been
framed and put together, by allowing the tide to rise around it, but the following arrange-
ment was preferred.
Fig. 240.
SECTION OF CONE.
In proper situations anchors were fixed, provided with tackle and blocks, that were
CHAP. VI.
281
FRANCE
worked by a capstan on land. There were also four pontoons with similar capstans, and
numerous boats, some with forty, others with eighteen oars to assist.
The pontoons were placed at regular

distances, and the cone was towed out by
attaching the capstan ropes to the double
cable that surrounded it. A few minutes
before 8 in the morning, the sea had risen
9 feet up the cone, and a slight motion
indicated that it was afloat: it stood
perfectly erect, balanced in every part,
and needed no ballast or adjustment.
The water rose a few inches higher,
when a gentle south wind moved it about
its own diameter from the land, which
indicated that little labour would be re-
quired to tow it forwards.
The great towing cable and the hawsers
were fastened to the double cincture of
rope, a signal was given to slacken the
ropes which attached the cone to the
land, and it was immediately moved for-
wards by the rowers; standing out of
the water 54 feet, it glided gently after
the boats. About the middle of the
day the vessels hoisted their sails, when
it proceeded so rapidly that boats loaded
with stones were fastened to it, which
somewhat impeded its progress.
The vessels then reefed their sails, let
go their anchors, and were attached to
the girdle of the cone; the wind growing
stronger, the second pontoon was gained,
at forty minutes past 12; the third soon
after, and at a quarter past 3 it had ar-
rived at its destined position.
The workmen were then ordered to
their posts.
Cessart had arranged that
the cables which held the casks should be
cut at points diametrically opposite to
each other, when he gave from the shore
the signal to do so, which he did at half
past 3; the engineers then let fall four
anchors, and moored the cone to them.
The ropes which held twenty-two of the
casks being cut, it immediately sank
18 feet; the cords had acquired addi-
tional toughness from their strain and
immersion, and although the cutting
knives were loaded with forty pounds of
lead, it required two strokes to separate them.
Fig. 242.
PLAN OF MOORING.
The two ropes which circumscribed the cone, and which were nearly 2 feet in circum-
ference, were then taken off.
Twenty-one cones were put together, but eighteen only were made use of, the other
three being sold during the revolution. According to Cessart, the first was placed in its
situation the 23d of June, 1786, and the last, the 19th of June, 1788.
These were not, however, placed at regular distances from each other.
Cessart's plan
was departed from; and the destruction of the timber work of the cones, a few years after-
wards, was the consequence.
The second cone was placed 513 feet distant from the first, measuring from centre to
centre.
The third was at 159 feet; the fourth at 184 feet; the fifth at 381 feet; the sixth at
416 feet; the seventh at 407 feet; the eighth at 448 feet; the ninth at 453 feet; the tenth
at 492 feet; the eleventh at 737 feet; the twelfth at 817 feet; the thirteenth at 880 feet;
the fourteenth at 905 feet; the fifteenth at 893 feet; the sixteenth at 1845 feet; the seven-
teenth at 1630 feet; and the eighteenth at 1310.
The total length was 12,470 feet, measured from the centre of the two extremes; the
distance of the centre of the first cone to the fort on the Isle of Pelce, 3269 feet; and that
Q 4
232
BOOK I
HISTORY OF ENGINEERING.
of the last cone to the Fort De Querqueville, 7685 feet, making the total width of the
harbour 23,424 feet.
After the cones were placed, they were loaded with stone, and a great quantity were
thrown in around their bases, and between their several intervals for the purpose of breaking
the force of the sea: by the 1st of October, 1795, there had been deposited upwards of
100,000,000 cube feet of stone; or, as Cessart has given it, 381,789 toises, 4 feet, 7 inches
cube.
Each of these conical cases contained as follows: -29,040 cube feet of oak, and 8705
feet of beech, an allowance of 7549 cube feet being made for waste, so that there appears to
have been used for the construction of one entire cone 45,294 cube feet of timber, which
was delivered at the price of about one shilling and ten pence per foot cube.
The total cost including labour, iron work, cordage, and the other materials required,
amounted to about 8418 pounds sterling, or about double the first cost of the timber.
Cessart has given a full and detailed account of the cost of the barrels, vessels, building
sheds, tackle employed, as well as ropes, and all other matters, from the commencement on
April 1, 1783, to January 1, 1791.
The timber and iron work of the eighteen cones
Workmanship and the immersion of the eighteen
Stones thrown into the cones, and to form the dyke
Buildings and various other expences
Expences for superintendence, &c.
Making a total of
·
E
8
£102,600
65,024
620,004
98,312
16,500
902,440
expended upon this breakwater.
The timber of the ones, in consequence of neglect and the work not having been finished,
soon went to dec, and the stones they contained fell into a natural slope with those around
them. From the statement made by Cessart, it appears that those placed near together
lasted three or four years, and almost all the others were entirely destroyed the year of their
immersion, as he had foretold.
The National Assembly in the year 1791 commissioned Cessart to prepare plans for the
completion of the breakwater, when he suggested that the dyke which then existed should
be covered with large masses of stone. The talus or slope towards the bay was found to
have remained at an angle of 45 degrees, while on the other side, having been formed
on too rapid an inclination, it had been destroyed to within 14 feet below low water, and
the stone rolling out to sea had produced a talus of one in ten. He then laid down a plan for
constructing a breakwater by throwing in a further quantity of stone, and covering all those
parts which appeared above low water with blocks of granite, as large as could be ob-
tained; this, however, was not executed, although in the year 1804 a number of large blocks
were raised in the centre, and a battery formed upon them.
Havre de Grace is a sea-port strongly fortified, and situated at the mouth of the Seine,
on its northern bank; it is in 49° 29′ north latitude, and 0° 6' east longitude. The
harbour contains three basins, within the walls of the town, calculated to receive 450
vessels.
On Cape de la Heve, which is two and a half miles from the harbour, on the northern
extremity of the Seine, and nearly 400 feet above the level of the sea, are two lighthouses,
each 50 feet in height, about 325 feet apart. At the mouth of the harbour is a round tower,
constructed by François I., in 1509, over the door of which was his equestrian statue; it
was the intention of the monarch to have made Havre one of his principal ports, and to
have given it the name of François de Grace; he fortified the harbour, which then contained
fifty large vessels, sixty smaller, and twenty-five galleys. This fleet was prepared to
oppose Henry VIII. in his attacks upon Boulogne.
Henry II. made some improvements, and it was decided that the direction of the entrance,
which was south-west, was too much exposed to the south-east and north-east winds; but
no alteration was then made.
De Cessart prepared a design, which was not carried out, for three basins which would
have contained 300 vessels, and the outer port 250 vessels. Honfleur, with its two basins,
contains sixty.
The lock gates which communicate with the basin are 40 feet in width; and getting out
of repair, De Cessart was employed to put in a new platform, and restore the injuries pro-
duced by time.
After having secured the new planking to the old platform by means of iron bolts, he
laid down new sills 44 feet in length, which entered the masonry of the side walls at one
end, and were secured by iron screw bolts at the other. After the grillage was complete,
and thoroughly pinned down to the old work, the intervals were filled in with brick, laid
in cement.
CHAP. VI.
233
FRANCE.

ENTRANCE
Fig. 243.
ARSENAL
INCOVILLE BASIN
JO
OLD BASIN
SLUICE
PERREL
FRANC.L
TOWER
SCOURING
SLUICE
PORT
RESERVOIR
더
​BASIN OF LA BARRE
EXTENSION
OF
PORT
HAVRE De grace.
0
םםם
SAIYAAVA
(a
CANAL OF HARFLEUR
MOUTH OF THE 8BNE

Fig. 244.
LOCK.
Treport is situated in La Manche, at the mouth of the river Bresle, a league from Eu.
The valley, at the extremity of which this river disgorges itself into the sea, is formed by
two hills, 250 feet in height: the entrance of the port is situated at the foot of the west
hill, on the slope of which stands the town.
The village of Merse occupies the foot of the other hill, on the side of the valley, the
breadth of which is here 800 toises.
234
Boor I.
HISTORY OF ENGINEERING.

•
•
RIVER
RESERVOIR OF 20″000, CUBE TOISES
OF WATER FOR SCOURING HARBOUR
BRESLE
Fig. 245.
IT
TREPORT.
MERSE
FISHIN
PORT
EAST TERY
JETTY
The mouth or entrance is exposed to the winds between west-north-west and south-
south-east. This position renders it easy for the access of vessels, as when they miss the
port, they can run out again without being exposed to the danger they incur at Dieppe.
When vessels bound to Havre, Fecamp, or Dieppe, entering the channel by winds blowing
between west-south-west and north-north-west, miss the entrance of these ports, they in-
variably run aground at the mouth of the Saone; this they would avoid by making for

Fig. 246.
ELEVATION OF SCOURING SLUICE.
Treport; its position is therefore most important as a refuge harbour. Du Cessart im-
proved this port in the year 1778, and constructed the scouring sluice by which the harbour
is kept constantly cleansed; it has two passages for the water, each 21 feet in width,
separated by a pier 8 feet thick, terminated at the two sides by walls 10 feet in thickness,
with wing walls and returns.
The platform fills the space between the walls, both above and below; below the apron
is a row of sheet piling, which keeps the earth of the foundation from washing away.
Above these are two rows of sheet piles, which prevent the work from being undermined.
Each of the two passages is closed by two gates, 12 feet in height; a wooden bridge,
13 feet in width, affords a communication across the sluice. The upper platform is con-
structed of timber, so that a reparation can be effectually made, without the walls sustaining
any injury. The pivots and sockets on which the gates move are of cast-iron, each weigh-
ing 193 pounds: the lower rail of the gates is kept 2 inches above the level of the platform,
a sill of the same height fills the space, and prevents the loss of water.
Turning gates made in the ordinary way lose a great quantity of water in the upright
joints, as well as through the space between them and the facing of the piers; to remedy
this De Cessart made a circular indent in the side walls, radiating from the centre of the
turning post, and by this means effectually closed the joint at the side. There is also an
objection in their being centred at two-thirds of their width, the one side being double the
other. The gates open with great velocity, which strains them as well as injures the plat-
form: when the sea is violent the waves striking the gates at low water forces them open,
and they remain so until the water they retain is in equilibrio with the power applied to it.
The wave then suddenly returning, the gate is closed with great force against the shutting
post, which materially injures not only the post but the work. To remedy this incon-
venience De Cessart centred these gates in such a manner that the difference of their sides
CHAP. VI.
235
FRANCE.
was not more than 6 inches, which sufficed to open them. The sea at Treport rises 8 feet
higher at spring than at neap tides; by establishing the top of the gates at the level of

Fig. 247.
PLAN OF SCOURING SLUICE.
high-water spring tides, the sea would only mount 12 feet above the platform once in a
tide; but to retain this weight of water longer, he made the platform 13 feet 10 inches
lower, which gave the advantage of using the sluice five or six times during each tide.
De Cessart proposed the construction of a vast reservoir to contain 20,000 cube toises of
water, and to turn the river, but this project was not fully carried into effect.
Dieppe is situated at a distance of 22 leagues from the English coast, and is the only port
in the Channel where the ordinary spring tides rise 30 feet, and the equinoctial from 32 to
34 feet.

ROADSTEAD
ROCK WORK 250;FE
ABOVE LOW WATER
FORTIFICATIONS
EROM ROUEN TO DIEPPE
INNER
MARBOI
OUTER HARBOUR
QREAT
RESERVOIR
WEST
PIER
ENTRANCE
EAST PIER
ROCK WORK 250. FL
ABOVE LOW WATER
· FROM DIEPPE TO EU
Fig. 248.
DIEPPE.
The town is situated in the midst of a valley, 600 toises in breadth, watered for two
leagues of its length by the river Argues; the valley lies north and south, and the wind
seldom continues to blow in this direction more than forty-eight hours at a time.
It is
236
Book I.
HISTORY OF ENGINEERING.
also sheltered by two hills which rise from 200 to 300 feet above the level of the sea,
affording to the vast basin a calm water, of great value to all vessels that frequent this coast.
The port of Dieppe being situated at the mouth of a river, a deposit of sand had been
allowed to accumulate from time immemorial, and the utility of it as a refuge for ships
was destroyed; the rising of the ocean had also produced another evil; the right bank
of the valley was covered with shingle, as well as with the debris of the left, which
had been washed away; by these obstructions the course of the Argues was changed, and
a mouth opened for it at the foot of the east hill. The works at this port, as the construc-
tion of the timber jetties, were carried on at various times, as necessity suggested, and without
any regular plan being laid down; nevertheless vast sums were expended upon the west
jetty, as well as upon the prolongation of the Polet; and when this costly work was aban-
doned, the gravel accumulated to a height of 12 feet above low water; so that in the year
1775, it had become only a retreat for small fishing boats. Another great inconvenience
was the want of fresh water in the harbour.
De Cessart, who was named engineer-in-chief for the improvement of the port, finding
that off the coast the tide rose to so considerable a height, did not venture to adopt the usual
practice of building in cofferdams, where they could only work at certain hours, but used
caissoons, taking care to surround them with one or more rows of sheet piles, driven until
they ceased to answer the ram. In excavating foundations for marine works, he observes
that it is rare to meet with earth whose particles are sufficiently adherent to prevent filtra-
tion, the deposits on the shore being so various that the water freely passes through them.
The vessels usually frequenting this port required from 15 to 20 feet of water, and
allowing for the plunging of the vessel, the natural ground ought to be at least 22 feet
below the level of high water. Many cofferdams have been constructed of this height, and
the works constantly carried on; he mentions one formed by Thumberg in the Baltic at
Carlscrona, which was 84 toises in circuit, sustained 20 feet of water, and contained a
space of 4000 superficial toises.
The jetties are composed of masonry 50 toises at the base, crowned by a platform 42 feet
above the level of low water, and 7 feet 2 inches below that level, so that the total height
from the foundation to the parapet was 49 feet 2 inches; De Cessart only formed the
earthwork preparatory to this construction, which was sufficiently ingenious to admit of a

Fig. 249.
MOLE.
description: it was partly executed, but in 1793 it was demolished, and the timber sold. A
base of about 50 feet was laid out by driving piles into a hard bottom; these were capped at
the extremities, and the heads filled in with stones; on this were placed three timber
caissoons, 36 feet in height, framed and planked over, and the interior filled with earth: the
slopes were made to vary.
The mole stood 6 feet above the level of high water; on the side towards the sea the in-
elination was at an angle of 60 degrees. The whole may be considered to consist of three
CHAP. VI.
237
FRANCE
prismatic caissoons, two forming the base, the others placed above them; these were boarded
on the outside, and filled with stone, gravel, and earth. The length of the mole was 160
toises; six drains were formed to carry off any water that might find an entry to it.
De Cessart also executed the sluice for scouring the harbour by means of a caissoon, in
length 54 feet 8 inches, in width 93 feet, and in height 15 feet; the area was 5080 feet.
To put the platform together ten rows of piles, each containing eighteen, were driven;
they were in length 10 feet, and 9 inches square, the heads of the piles were capped, and the
whole brought to a level; on this was put the bottom of the caissoon, composed of four
outside timbers, 14 inches square, and four others laid within of the same scantling.
The width was divided into three bays, of 21 feet 4 inches each; these bays were filled in
with timber 10 inches square, nicely jointed, and made level at the bottom; over these were
other transverse timbers securely bolted to the bottom, and between them a course of
4-inch planks, also crossing the lower timbers at right angles. The whole was secured by four
iron bars, 2 inches in thickness, which

were screwed up and rendered the platform
a compact mass.
After this was done, a course of timber
10 inches by 8 was laid around the outside,
and above this, four others of the same
scantling, into which the uprights of the
sides were to be framed; these were 15 feet
in height, and composed of ninety-six up-
right timbers, 12 inches by 6, lined on the
outside with 6-inch planks, and again crossed
by others 4 inches thick; additional strength
was given by forty interties, 18 feet 6 inches
long, and 12 inches by 10. When the cais-
soon was ready to float, a layer of moss and
clay was introduced beneath it, to prevent
any infiltration from taking place.
Fig. 250.
FRAMING.
The weight of the caissoon was 761,342 pounds, and it drew 2 feet 1 inch and 4 lines
of water.

It was towed out by two capstans and
ropes, and in less than ten minutes was
firmly fixed in its place. By some ac-
cident the bottom carried with it some of
the small timbers of the platform, upon
which it was constructed, which pre-
vented the caissoon from being laid on
the bed of moss prepared to receive it.
These were removed by passing small
rollers by means of ropes under the
bottom, which fished out all that ob-
structed it.
אחושית
Fig. 251.
H
CAISSOON.
H
To attach the lower course of masonry
to the timber platform, each alternate
stone was usually fastened by two bolts,
one entering the stone, and the other
the main timber on which it rested, but De Cessart,
not finding this always effectual, adopted another
plan;
after the first course of stones was placed
upon the platform, he secured the second by irons,
and the timbers which were worked into the masonry
to receive the planking of the aprons above and
below the lock, were attached by bent irons placed
at regular distances of 3 feet, 14 lines in thickness.
Bordeaux is a fine harbour on the Garonne, and although situated at a distance of about
seventy miles from its mouth, there is sufficient depth of water in this noble river to enable
large vessels to come up to the quays of the city.

Fig. 252.
ELEVATION.
At the entrance into the river, the distance between Point de la Coubre on the north
and Point de Grave on the south is nearly four leagues; there are, however, extensive
sand-banks which are dangerous to the navigation, and some considerable rocks, on one of
which is placed the celebrated Tour de Cordouan, which has now a revolving light, some-
times showing brilliantly, then feebly, and then eclipsed; in clear weather it may be seen for
eight or nine leagues.
Marseilles is a sea-port of great antiquity, and situated in 43° 17′ north latitude, and
5° 22' east longitude. The harbour, surrounded by strong fortifications, is a capacious
238
Book 1
HISTORY OF ENGINEERING.
basin, 525 fathoms in length, and 150 in breadth; the depth at the entrance is 18 feet, and
in the harbour from 12 to 24 feet, which is maintained by the constant employment of
the dredging machines.
The lighthouse is situated on the Fort St. Jean, which is on the north side of the
entrance to the port, and at some distance from the north of the city is the lazaretto.
On the island de Planier is another lighthouse, 131 feet in height, which from the excel-
lence of its revolving lights may be seen in clear weather at a distance of seven leagues.
There is a slip for ship-building constructed of stone, the length of which is sufficient to
admit a man-of-war, and the width at top 47 feet. The whole is ingeniously roofed in,
with flights of steps descending to the various levels.
Rochefort, a fine maritime city, had its port greatly improved in 1664, under the orders of
Louis XIV. The slips for ship-building were the finest in France; they were connected
with each other and had but one entrance, with a pair of lock gates to shut out the sea.
The first entered was calculated from its depth to receive vessels of the first rate; the
second had its platform 7 feet higher, two vessels could enter, and the water at low tide
being suffered to run out, the gates were closed, and the two vessels were in a situation to
be caulked at the same time. In the side walls were small aqueducts, by which the water
could be admitted, when it was required to float them again out to sea.
To use the upper slip for the construction of a vessel, without being deprived of the
lower one, grooves were contrived in the portion where the separation took place, into
which planks were dropped, which kept the water from entering, as the intervals between
the two ranges of planks were filled with clay in the manner of a cofferdam.
In the construction of this double slip, as great inconvenience was experienced from the
working of the springs, a well was sunk in the bottom of the upper slip, which, by means
of drains, collected all the water that would otherwise pass under and around the works:
from the well it was pumped out by an hydraulic machine made for the express purpose.
It is undoubtedly most important to keep slips perfectly free both from the action of the
springs, and from the water intended to pass through the locks, but this should be accom-
plished without the aid of machines.
At low water they should be perfectly dry, to effect which it is necessary that the
bottom should be laid a foot higher than the ordinary level of low water in the port to
which they belong. Vessels drawing from twenty to thirty feet of water when loaded
require less when their freights are discharged, and the height to which the tide rises must
determine the level to be given to the slip.
To render the entrance gates at Marseilles water-tight, they are stopped at all the
crevices and joints by caulking, and the water is thus effectually shut out. When the
wooden platform is laid too low, it is liable to be covered with mud, and to prevent the
opening of the gates; this was guarded against in the present instance. The length and
width were also made proportionate to the vessels they were intended to receive.
In the slips at Rochefort the entrance lock was first formed with sluices at the bottom,
which allowed the water from the springs to drain off.
To form the foundations the same precautions were adopted for laying the timber
platform as for that of a lock of a canal; planking and piling were made use of throughout,
and the masonry fixed with great care after the heads of the piles were cut off. When all
the intervals between the heads of the piles were filled in, a mass of brickwork or masonry
3 feet in thickness was laid in hydraulic mortar or cement over the whole area; then
cross timbers were so placed upon it, that they formed sleepers to an inclined plane, made
by the longitudinal timbers which rest upon them. All the intervals were again filled up
with masonry, and an inclined floor was then laid, having a fall of 8 or 9 inches from
the upper end.
The piling was carefully executed, and every precaution taken to render the platform
firm and secure.
Toulon, which takes its name from Telo Martius, is a very considerable port, on the
shores of the Mediterranean, and distant from Paris 220 leagues. The arsenal and
magazines are the finest in France, and there is every requisite for a maritime establish-
ment; a quay wall and slip were built in deep water by means of a caissoon, which Belidor
thus describes: "The quay being too narrow, the walls were advanced 40 feet or more
into the sea, where it had 20 feet depth of water. The lines being set out, two machines
were employed to raise the mud between them until a good bottom was obtained, which
was perfectly levelled; the foundations were then formed, 18 inches in width, of a be of
gravel, and chippings of stone, spread level with great care.”
Caissoons, or cases of timber, upwards of 60 feet in length, 13 in width, and 25 in depth,
well caulked and pitched, were made use of in deep water; these were afterwards taken
to pieces, and all except the bottom again served for other caissoons to lengthen out the
work; about 200 feet in length being operated upon at one time.
After these caissoons had been put together on shore, they were launched, floated to
their right situation, and then maintained in an upright position by ropes which passed
CHAP. VI.
239
FRANCE.
through rings attached to piles driven conveniently for the purpose.
When the masons
entered, they commenced their work, by filling up the voids between the bottom timbers with
puzzolana and lime, mixed with gravel and chippings of stone; upon this, properly levelled,
was built a stone wall 8 feet in thickness, the external faces of which were carried up with
blocks from 12 to 14 inches square, dovetailed into each other; the space between being
filled with moellon.
As the caissoons sunk as they were loaded, it became necessary to keep them from swerving
or getting out of their line, and greater attention was required when they had reached
within a short distance of the bottom. Proper examination being made of their position,
when found correct and perpendicular, they were loaded with the rest of the materials
to be employed in the construction, which, when raised within 2 feet below the level of high
water, was allowed to remain for a considerable time to acquire the requisite hardness,
after which the several partitions which separated the caissoons were removed, and the
spaces of 2 feet between them filled up, and the wall completed throughout its whole
length. This portion of the work required that sheet planks shod with iron should be
driven in a manner to surround the several intervals, after which beton was let down into
them, and the facing brought up on both sides to unite with the others, when it was made
good throughout.
In the ports of the Mediterranean slips were made at very early times for the con-
struction and launching of vessels of considerable draught, and also for the purpose of
hauling vessels that needed repair on shore.
When they required careening, a frame made of timber, and called a cradle, was
placed under the vessel and supported it in a state of equilibrium, until it was brought to
the stocks and shored up. This cradle, of a very early invention, was formed of three
longitudinal timbers, 20 inches square, which extended the whole length of the ship, one
being under the keel, and the others at the side a little above. The vessel was girded
with strong cables to these timbers, which were mounted on eight rollers that were turned
by means of handspikes. The form given to the slips was that of a wedge, the inclined
plane of which was in length about 220 feet; the bottom projected into the sea, where
a timber platform terminated it. Its inclination, like that of the stone bottom, was equal
to a fourteenth, the rise being about 5 inches to every 6 feet, which permitted the vessel
when launched to glide easily into the water, without subjecting it to any sudden shock
or interruption. As the vessel had neither its cargo nor ballast, 16 feet water was reckoned
sufficient for it to float.
Another slip at Toulon was commenced by taking out the ground to a solid foundation,
for 220 feet in length, and 60 in width, using for the latter part of the operation the dredging
machines employed for cleansing the harbour. The bottom had a sufficient fall or in-
clination towards the sea, at the point where the slip was commenced.
The stocks were
established 18 feet below high water at one end, and 22 feet at the other; the construction
was carried on by the means of caissoons, 60 feet in length, and of a depth sufficient to
maintain 4 feet above the level of the water at the highest state of the tide. They were
fixed in their places and inclosed in a space 230 feet in length, and about 60 in width, and
in this case the caissoons were not loaded, but the water was suffered gradually to enter and
sink them; afterwards they were loaded with the stone intended for the constructions,
and the openings which admitted the water being closed, the water they contained was
pumped out. Another precaution, taken after the caissoons were grounded, was to
plank and pile around them at the points of their junction, and form a clay dam, so that
when the ends or divisions which separated the caissoons were taken out, the work might
be made good and the wall continued in its construction without any interruption. This
arrangement had very considerable advantages over the preceding, and was another step
towards improvement.
Quay at Rouen, built by De Cessart. The great road from Paris to Havre and Dieppe,
passing along the ancient quay of Rouen, it was found inconveniently narrow, and in 1779,
a new quay was completed, 120 feet in advance of the original wall.
The total length of the new quay was 110 toises; this was divided into seven equal
distances, by caissoons 66 feet in length, 16 feet wide, and 14 feet high, their base containing
1056 square feet. Ninety-two piles were driven, 3 feet 6 inches apart, in the thickness of
the wall, and 3 feet in the length of the caissoon; each pile bore the weight of 18,633 pounds,
for the wall alone, and adding one half more for the weight of merchandize placed on it,
would then have 27,000 pounds.
All the piles were from 12 to 15 inches thick, driven with a ram weighing 1200 pounds,
falling 20 feet, each pile receiving a percussion equal to 300,000 pounds. The heads of the
piles were cut off 6 feet below low water, at 12 feet behind the wall; piles were driven at
every 6 feet, to attach land ties, which supported the masonry; sand and gravel were then
thrown from the inside of the wall, to form a slope on the river side of sixty degrees, which
extended 60 feet into the river, so that vessels of 400 tons could approach the quay at low
water.
-
Book I.
240
HISTORY OF ENGINEERING.
The most ingenious part of this arrangement is the formation of an embankment in the
bed of the river, into which the piles were driven, and of a second embankment over it, in
which the caissoons were placed. After the wall was constructed, the whole was then
backed in by earth brought from the neighbourhood, and the spacious quays thus obtained

Fig. 253.
QUAY WALL, ROUEN.

Fig. 254.
NEW QUAY, rouen.
were paved throughout. To maintain a level above low water, where some difficulties
occurred in cutting off the heads of the piles, arches were turned 7 feet span, and the
whole most ingeniously connected.
Sp
Cordouan Lighthouse. Since the time of the ancients there has never been a more
important and superb pharos erected than that of Cordouan; it is situated on a rock forming
an island at the mouths of the Garonne and Dordogne, and but for the warning it affords,
the vessels entering or leaving would be always in danger of wrecking. It serves as a sea-
mark during the day and a lighthouse at night; there are only two passes, the one called
the pas des anes, between St. Saintonge and the tower of Cordouan, the other between
the tower and Medoc, called the pas des granes, both equally dangerous to vessels that
may be unfortunately surprised by a heavy westerly wind. The tower is in 45° 35′ latitude,
and 16° 53′ longitude, two leagues from Bordeaux. All around it are rocks covered only
3 or 4 feet, against which the billows rise to a great height, and break with tremendous
violence, rendering the access to this tower very difficult; vessels of three tons only can
approach it by a single channel, about 100 feet in width; at 600 feet from the tower there is
a sand on which they can run aground at the moment of low water, of which advantage
must be taken, the rest is nothing but unapproachable rocks. This magnificent tower, 169 feet
high from its foundations, was built in the reign of Henry II. by Louis de Foix, who com
CHAP. VI.
241
FRANCE.
menced it in 1584, and finished it under Henry IV. in 1610. Navigators consider it the
finest in Europe, and the boldest in execution.

原
​I
Fig. 255.
plan of tHE LIGHTHouse at CORDOUAN.
The island upon which it is built, being dry at low water, and wholly covered by the
tide at high water, exhibits a bare rock 500 fathoms in length from north to south, and 250
fathoms in width from east to west; the base of the edifice is a circle of 135 feet
diameter, over the whole extent of which the constructions are of solid masonry, except
where the stone stairs are introduced, which commence at the level of high water; near
them a cavity is formed 20 feet square, which serves as a cistern to hold fresh water, this
rises about 8 feet, including the arches which cover it: the remainder of the area is
entirely composed of solid stonework, brought up to a level platform, which, as the walls
batter all round, reduces the diameter to 125 feet. The staircase, which is carried up in
the solid, commences 4 feet above the rock in the east side, and serves to mount to the
platform; the ascent to it is by a ladder, and the opening is closed by strong wooden
doors.
On the platform is a circle of 100 feet diameter, around which is a wall 12 feet
6 inches in thickness, battering up to the height of 12 feet, where its thickness is only
11 feet; its object being to resist the action of the western seas.
On this circular platform is constructed the tower which forms the lighthouse, the
diameter of which is 50 feet, and the whole is carried up to the height of 115 feet: the
several stories diminish as they approach the summit, on which was originally a stone lan-
tern, or rather dome, supported upon eight stone mullions, with openings between them for
the passage of light.
The 25 feet space between the tower and the outer circular wall was occupied by several
small apartments, which served as lodging rooms for the attendants and store rooms.
The building is composed of four stories, and the apartments they contain were highly
R
742
BOOK I.
HISTORY OF ENGINEERING.
decorated; externally, the lowest is of the Doric, the second the Ionic, the third the
Corinthian, and the uppermost or lantern of the Composite order.
On the ground or lower floor is a vaulted hall, the dimensions of which are 22
feet square, and the height 20 feet; it contained two wardrobes, and many other conve-
niences obtained out of the thickness of the walls.
Over this is the grand saloon 21 feet square, and 20 feet in height, a vestibule, two
wardrobes, and other conveniences, the whole vaulted with flat elliptical arches.
The third story was appropriated to the chapel, which was of a circular form, covered
with a dome; the internal diameter was 31 feet, and the height, including the hemi-
spherical dome, 40 feet. The interior was decorated with paintings and mosaic; the light
was admitted through eight windows, and in the centre was a circular opening 4 et
diameter, protected by a balustrade.

LEVEL,
ப
Fig. 256.
ELEVATION of the LIGHTHOUSE.
The diameter of the lantern, which formed the third story, is 14 feet, and around the
exterior is a stone balcony, the internal diameter of which is 21 feet, forming a solid
covering to the chapel below it. On the outside are eight Corinthian pilasters, which
answer to the mullions, between which are as many glazed windows, 2 feet 6 inches wide,
and 7 feet high.
The inside of this story is 20 feet in height up to the square, which is covered by a hemi-
spherical cupola, making its whole height 27 feet; this cupola, which is formed with
stone, and built very solidly, serves as a basement to the lantern, originally 5 feet
diameter internally, and 9 feet externally, and the height above the cupola 17 feet; in the
middle was an opening 18 inches diameter; through this the smoke passed into a smaller
funnel, 2 feet 6 inches diameter, in which were a number of small holes that allowed its
escape. The upper funnel or turret was capped with solid stone, 31 feet above the floor of
the lantern light.
CHAP. VI.
243
FRANCE.
The total height of the building above the base of the tower, is 146 feet, and above the
surface of the rock 162 feet.
In 1727, the summit underwent a change; the former lantern having been destroyed, one
of iron was substituted. This was done under the direction of M. Betri, engineer-in-
chief at Bordeaux, who contrived a cage of iron, or lantern, formed of four principal
pillars, supporting a cupola, finished with a large ball and vane 36 feet above the
platform; the lantern was entirely open, and the smoke could escape on all sides; the
ceiling, which was circular, was formed into a hollow cone or funnel, the top of
which was bent downwards, about 3 feet; the entire sloping surface of the cone was
covered with tin plates, which became so many reflecting surfaces, and occasioned the light
to be seen from a greater distance.
Reflected light was made use of here for the first time about the year 1780, when

יח
LEVEL
Fig. 257.
SECTION OF THE LIGHTHOUSE.
M. Borda introduced an Argand lamp in the focus of a parabolic mirror; the reflector was
a sheet of copper plated with silver, with a focal length of about 3 or 4 inches; the diameter
of the outer edge was 21 inches.
The curvature of the reflector was truly parabolic; the light issued from a mathematical
point, and the rays were reflected from a mirror, placed exactly parallel to the axis of the ge-
nerating curve; the beam of the projected light was that of a cylinder having a diameter
equal to that of the mirror. The light, however, in this form, was nearly useless, and it
was found necessary to give the rays a divergence, that they might extend to a greater
portion of the horizon. To effect this, the burner, which was about an inch in diameter,
was made to produce the luminous rays at a small distance from the focus, and instead of
being reflected in a mass of cylindrical or parallel rays, they were projected in a cone
having a divergence of about forty degrees.
To obtain a sufficient quantity of light it was necessary to have a number of parabolie
R 2
244
Book 1.
HISTORY OF ENGINEERING.
mirrors; and sometimes as many as eight are employed, mounted upon a frame, their axes
being all parallel to each other, and so placed that the light reflected by them is formea
into one conical beam.
A revolving light was produced by at-
taching the frame to a horizontal axis,
made to turn round by the aid of ma-
chinery.
A stationary light only requires the re-
flectors to be placed round a circular frame,
with their axes on the radii of the circle.
The illumination, however, is not equally
intense at all azimuths, but strongest in the
direction of the several axes, and weakest
in that of the lines bisecting the several
angles formed by each pair of contiguous

axes.
Auguste Fresnel, of the Academy of
Sciences at Paris, advised that refracted
light should be generally introduced into
the lighthouses in France, having a plane
convex mirror with a focal distance of about
3 feet, formed of crown glass, which was
thought less liable to striæ than flint. The
first lens was polygonal, and consisted of
several pieces of glass, separately prepared,
and united together, but afterwards sphe-
rical lenses accurately ground supplied their
place.
The divergence of a cone of light pro-
jected by such a lens, is not more than
5° 9', and is much less than that produced
by the parabolical reflector.
The largest lens at the French light-
houses projects a cone of light equal in
intensity to eight mirrors of the best kind.
The luminous cone in one case is only that
portion of light which falls on the surface
of the lens, and it might be imagined, that
this could never equal in effect that pro-
duced by the parabolic mirror; but the
polish of the latter not being perfect, a
great quantity of incidental light is lost,
which is a chief reason in favour of the lens.
Fig. 258.
LANTERN.
When refracted light is adapted to the revolving system, the frame which carries the lenses
has eight sides, to each of which one is attached; the whole, however, are so arranged, that
all their axes are in the same horizontal plane, and meet in the common focus where the
amp is situated, forming one large octagonal prism.
To prevent any loss of light, a second frame is placed above the first, the sides of which
form the frustum of an octagonal pyramid, and incline fifty degrees; on each of these sides
is another lens, having its focus in the flame of the lamp. The rays which fall on the
inclined lenses are refracted parallel to the axis of the lens, and are then reflected into the
horizontal direction, by plane mirrors, placed above the upper frame. Curved reflectors
are sometimes used, above the frames which contain the principal lenses.
Fresnel also substituted a very elegant contrivance for the upper lenses and mirror : a series
of triangular prisms had their axes arranged in horizontal planes, and so adjusted that the
light falling on the face next the flame was thrown upon the back of the prism, where it
was totally reflected; and by a second refraction at the third side of the prism, it obtained
its horizontal direction.
For fixed lights of this description, a sufficient number of lenses are required to form
with them a cylinder, so that an equal diffusion of light should be spread over every part
of the horizon. Some French lighthouses have a refracting apparatus consisting of a belt
of thirty-two lenses, arranged polygonally.
Such a light is described by Fresnel in his memoir on the subject, published in the year
1822, and his system is applied to most of the lighthouses on the French and Dutch coasts.
The Argand fountain lamp, with a burner an inch in diameter, tipped with silver, is made
use of; and Fresnel invented one with a series of concentric burners; for lights of the first
class, there were usually four, protected from the excessive heat by a superabundant
CHAP VI.
245
FRANCE.
supply of oil, which by means of machinery was made to overflow the wicks continually,
and a sufficient quantity of air was obtained through the aperture of a lofty chimney; the
oil of colza, which is produced by the seed of the wild cabbage, is made use of, and in
some instances coal gas has been employed.
Navigable Canals in France.-Among the first formed since the Roman æra was that of
the Centre or of Charolais, which extended from the Saone to the Loire: its utility will
be seen at a glance on the map; the great facility of execution it presented, and con-
sequently its small expense, compared with that of other canals, had long attracted the
attention of the government, and it was begun at the commencement of the reign of
François I., the epoch of great undertakings. In 1555, Adam de Crapone, who executed the
first canals used for irrigation in France, proposed to Henry II. the cutting that of Charolais,
and some portion of the work was probably done by this engineer. Under Henry IV.
in 1605, it was continued, and the canal of Briare, executed to form a junction of two great
rivers, was commenced, when Sully perceived that, if the latter was united to that of Charo-
lais, it would form an important line of communication: the most ancient account of this
work in detail is by Charles Bernard, printed in 1613, and dedicated to Jeannin, Minister
of Finance under Henry IV. It is there stated, that those who have examined the dif-
ferent projects proposed for joining the two seas in the centre of the kingdom, are agreed
that the Lake of Longpendu, equidistant from the Loire and the Saone, which are only
17 or 18 leagues from each other, should be the point of junction; that from this lake issued
two rivers, one called Bourbince, which flows into the Loire at Digoin, and the other called
the Dheune, which runs into the Saone near Verdun; that the country is sufficiently level;
that there are several other lakes and rivulets, by which the two rivers may be abundantly
supplied, and that with locks and gates they might be made navigable: but he adds that
the Bourbince has 69 feet fall, and the Dheune 75 feet, by which it appears they had not
taken the falls, or not accurately, since that of the Bourbince is four times greater, and
that of the Dheune nearly six times, than what is stated. He makes from six to seven
millions cube metres of earth to be removed, which is nearly the truth. The president Jeannin
also caused a detailed examination to be made of the different projects which had been pro-
posed for the canals of Burgundy, and it was determined to execute that of Charolais, in
preference to one passing through Dijon; and in 1605, the canal of Briare, which forms a
portion of it, was began. In 1612, Descures, Intendant of the river Loire, was sent by
the king to examine the project for the junction of the Saone and the Loire, by the means
of the rivers Bourbince and Dheune. In his report he shows the possibility of uniting
them, and in 1613, the order was given for its commencement, the contract being for
800,000 livres; this was probably for only a portion of it; the project was, however, then
abandoned; the Marquis Effiat made a new attempt in 1627; a procès verbal was drawn
up in 1632 by Gerard, Lieutenant-general of the Charolais, commending its utility; the
canal of Briare begun in 1605 had been discontinued; it was re-undertaken in 1638 by
order of Cardinal de Richelieu by a number of contractors, who finished it in 1642.
As this canal only united two rivers which flowed into the same sea, and the principal
object in view was their junction with the Saone, which flows into the Mediterranean, after
having united with the Rhone, the minister in the same year undertook this last project,
and appropriated for its cost 950,000 livres; the execution, however, was delayed,
probably from the cardinal dying that year; it was renewed in 1655 under Colbert;
the intendant and members for Burgundy were charged to examine the project in
conjunction with Franchini, a skilful engineer, then employed in the water-works at
Versailles. The Sieur Chamois, architect of the king, also assisted. They thought that
by rendering the rivers Dheune and Bourbince navigable by means of locks, the purpose
would be answered; and they made a design which was approved. In 1665 the king
demanded of the States of Burgundy a contribution to defray one-half the expenses of this
canal; 600,000 livres was granted, payable in four years, on condition that the king con-
tributed the remainder, without the province being called upon to furnish a larger sum, and
that the 600,000 livres should be specially employed to re-imburse the proprietors.
king, at their request, established a duty on salt; the act was published in 1666, in the
towns of Dijon, Chalons, Beaune ; at the same time Riquet was superintendant for the pro-
jected canal of Languedoc; he had already made experiments for bringing water to it,
which decided the government on the subject; in 1666, a design was made, and its com-
mencement took place in the same year: the 19th of February, 1667, an order in council
was issued, by which the king postponed for a time the canal of Charolais, and authorised
the members for Burgundy to employ the sum of 600,000 livres, which had been granted
by the states, in establishing manufactories, and partly in liquidating various debts:
the canal of Languedoc was completed in 1682. Louis XIV. was desirous to bring the
river Eure to Versailles, and commanded the aqueduct of Maintenon to be constructed,
which was afterwards abandoned; the expenses incurred by various fortifications preventing
this monarch from employing any money in civil improvements. Vauban, however, studied
the commercial interests of the kingdom, and seeing that the junction of the Saone and
The
R 3
246
BOOK I.
HISTORY OF ENGINEERING.
the Loire was the principal object to which the attention of the government should be
directed, in 1689, employed Thomasin, a royal engineer, to examine the projects of the
canals proposed in Burgundy; this engineer chiefly directed his attention to the canal of
Charolais, and it appears that he took the levels from the Saone to the Loire, but the un-
fortunate termination of the reign of Louis XIV. was not favourable for such works. Under
the Regency, Thomasin was employed in 1719, at the request of Vauban, the nephew of the
Marshal, and the members for Burgundy, to examine two other projects; but he finally
determined on that of Charolais; he laid down a plan in 1720, and made a report which
was approved by Sebastien, member of the academy, and M. Regemort. Many other
engineers were at various times employed in surveying and reporting upon this celebrated
canal, but it was not till 1783 that letters patent were issued, when Gauthey the engineer,
traced out the line, and the work was commenced at the end of April in that year. Com-
panies of pioneers and ground diggers were appointed with clerks of the works over them,
and troops assisted in the various operations. Each regiment employed sent at a time
372 men, commanded by ten officers, two of whom were present; each company of twelve
men encamped together, and the work was so set out, that a certain quantity was completed
every twelve days. The soldiers did not take out the lowest excavations, that being left to
stronger men. At the end of every fortnight, a measurement was taken of the work per-
formed by each company, as well as of that which remained unfinished; and a report was
made by the surveyor, which was sent to the engineer-in-chief, and submitted in case of
dispute to the superior officer of the departments; three hours per day were allowed for
meals; a change took place about every fortnight. The troops were employed for three
years, and performed work to the amount of 288,400 livres, which was about a tenth of the
sum required for the completion. The whole length of the canal was divided into eight
and then into ten stations, to each of which a commissioner was attached, who made every
day a survey of the works in their divisions, numbered the workmen, planted the piquets
for the direction and levels, and took care that the work was executed conformably to the
instructions given; they also measured the masonry, and gave in the accounts of the con-
tractors, no new measurement being made till the former one had been paid. They re-
gistered the number of workmen employed, and the quantity of work done, and at the end
of the month abstracted the whole; the tools, of which they defrayed the expense, were also
under their care, those lost being replaced at the cost of the workmen.
The heights of the various locks were set out by the engineer of the canals, who made
the drawings for their execution. This celebrated canal, uniting the Loire at the Saone,
has its mouth on the first of these rivers at Digoin; it follows the Arroux, then the left
bank of the Bourbince, passing through Paray, Genelarde, Ciry, Blanzy, to the Lake of
Mont Chanin, where the navigation commences; at some distance from the lake, the canal
separates the Lake of Longpendu into two parts, and then passes by the side of the left
bank of the Dheune to St. Julien, where it traverses the valley, following the right bank of
the Seine, and passing through St. Berain, St. Leger, Dennevis, St. Gilles, and Remigny;
it afterwards traverses by Chagny, near the left bank of the Thalie, and passing through
Fragnes and Champfergueil, runs into the Saone at Chalons.
The level of the "point de partage" being determined, the line of the canal was set
out, by fixing stations on the hills, by means of the spirit level, and the platforms of the
locks were determined, the ground between each lock was then accurately levelled, and
profiles were drawn on the ground at the distance of every 64 feet, on which the centre
of the canal was marked; care being taken to regulate the cuttings, and make them
equal to the embankments, agreeable to a table previously constructed, which indicated
the depth they were to dig, according as the fall was greater or less; the points were
set out on the ground, and rectified so as to avoid too great a bend, and form rather
right lines or great curves: the level lines being drawn above or below a lock, a right
line was sought about 390 feet in length, which should unite with the two preceding,
without making too sharp an angle; in the midst of which was placed the lock, except
where the ground offered a proper fall. The ordinary breadth of the canal is 32 feet at
the bottom, and 48 feet at the level of the water, the depth being 5 feet; at this level is a
set-off, 18 inches in width, on which grows the flag or some other aquatic plant; at
18 inches above the water are two other sets-off, one serving as the towing path, having
from 10 to 20 feet of width; the other being 6 feet wide, unless the height exceeded that
dimension; in all cases the width was made equal to the height. The fall of its talus in
good ground is one and a quarter, on sandy ground one and a half, and where subject to
inundation, two. The sets-off have a counter slope of one-forty-eighth to prevent the rain
water entering the canal; at the foot of the bank, on the land side, is a ditch of various
widths to receive the rain water, which is conducted under the aqueducts traversing the
canal; its ordinary width at the bottom is 65 centimetres. In the parts where the canal is
backed by steep hills, two ditches are made at some distance apart, one above the other;
there is also a ditch at the foot of the talus on the valley side, to receive the water which may
filter from the canal, and to prevent cattle from doing injury to the banks. Care was taken
CHAP. VI.
247
FRANCE.
in tracing the canal, that the water was not contained by the made earth to a greater depth
than from 2 to 3 feet; when the earth was not of a nature to hold water, the banks were
lined with clay 2 feet thick, founded on the solid earth or on layers of shells, or in defauit
of these at 4 feet below the bottom of the canal. This lining rises vertically to the level of
the water, at 2 feet distance from the smaller set-off; where the canal is raised above the
land, the bottom is lined 2 feet in thickness; the slope of the banks is either sown with hay
seeds or turfed. In places where stone was common, the interior of the canal to the level
of the water was faced with dry stone, 97 centimetres thick at the summit, giving it a slope
of one and a quarter; in such places the canal is only 33 feet wide at the bottom.
Locks all have a fall of 10 feet, except the two guard locks. The length between the
gates is 108 feet, the breadth of the lock is 17 feet; at 6 feet above the bottom the
facing to the side walls slopes one-sixth; the thickness at the summit is 4 feet, and
at the base 9 feet; the height above the bottom is 16 feet, the water rising to within 18
inches of the summit; the side walls are prolonged by winged and return walls; the platform
at bottom is formed of a concave arc, 9 inches versed sine, its least thickness being 26 inches.
In light soils it is made 3 feet 4 inches; in bad foundations piles were driven, and the
platform laid on arches. The wall over which the water is discharged is curved in front to
give additional strength to the frame of the gates, its projection is 5 feet 3 inches; under it
are the channels through which the water passes to fill the lock; they are 20 inches in
diameter, and spring from the middle of the recess in which the gates are placed; they were
closed by a wooden plug, which was found inconvenient from the pressure of the atmosphere
after the water was lowered, and they were afterwards exchanged for valves, which answered
better. The entrance is furnished with a frame, to which a sector is adjusted, closing it
perfectly. The sector is moved by a lever, acting on a stone arranged for the purpose at
the top of the walls of the lock. The water passes from one lock to the other by channels
formed in recesses made in the side walls, so that it cannot in any way injure the platform
of the lock. All the masonry of the walls is in freestone 14 inches thick, and generally
cramped with iron run with lead. The whole is lined with beton, 8 centimetres thick, to
prevent filtration; at the back of all the walls is a coating of clay 28 inches thick.
Gates of the Locks. The upper gates are 10 feet, and the lower 19 feet in height, so that
the top rail rises 18 inches above the ordinary level of the water. The width of the gates is
10 feet 8 inches, the frame 12 inches square, the sills are 9 inches, and the braces 6 by 7 inches ;
they are covered with deal 2 inches in thickness, and the joints are securely caulked. The
hanging posts are cut partly circular, the diameter being 12 inches, and in part bevelled; the
framework is morticed and tenoned together; the iron work let into the rails is
an inch
wide, and half an inch thick; the pivots and socket are of cast iron; the collars at top are
12 inches in diameter, their height 2 feet, and their thickness about an inch; they carry a
female screw; the male screw passes into timber secured in the masonry; they are 10 feet
long, and an inch thick; the timber under water is pitched, all the other is painted in three oils.
Houses of the Lock-keepers; they are in length 33 feet, and 23 feet wide, outside di-
mensions; they contain a chamber 9 feet square, a smaller one, and a scullery; in this is a
staircase to the garret and cellar; there is also an oven 5 feet in diameter, the cellar is vaulted,
and extends under the smaller chamber and scullery, the height of the chamber is 9 feet.
The aqueducts and drains are five in number, and from 3 to 9 feet span; where a greater
span is made use of, there are several arches, their breadth varies according to that of the
towing path; platforms of timber are laid under all; the height of the piers is at the least
3 feet, and their thickness 20 inches; it is 3 feet 4 inches when the span of the aqueduct is
9 feet. The piers of the arches of 6 feet span are 18 inches thick, and those of the arches
of 9 feet are 21 inches; the thickness of the vaults is 18 inches; the facings of the head and
wing-walls are of freestone, the rest is of moellon. It was attempted to make the aque-
ducts pass as near as possibly under the mur de chute, by which one wall was saved; and
the canal being there more elevated, it was easier to make the aqueduct pass below it.
Experience shows some inconvenience from this arrangement, as it is not possible to construct
the mur de chute as it ought to be—to guard against the pressure or weight of water when
the lock is full; and to prevent the water filtering through the wall, care was taken,
whenever an aqueduct was reconstructed, to place it above the lock, and to separate it
entirely.
Bridges. Those on the great roads are from 25 to 26 feet in width, those for the cross
roads are 18 feet 6 inches, their span is everywhere 25 feet, and their height, from the
bottom of the canal to the soffite of the vault, is 18 feet. The arches are segments of a circle,
one-sixth of their circumference; the thickness of the arch is 2 feet 3 inches on the face,
and 2 feet on the interior; the abutments are perpendicular before and behind, their
thickness is 6 feet 9 inches, that of the wing-wall is 3 feet 6 inches. The slope for bridges
on great roads is one-twenty-fourth, and one-twelfth for those on cross-roads. A quay wall
faces the towing path, in breadth 8 or 9 feet between the parapets; the thickness of
the wall is 3 feet at the summit, 3 feet 6 inches at the base, and its height is 6 feet. The
bridges over the locks are the same height and breadth as the others, but their span is only
R 4
248
Book L
HISTORY OF ENGINEERING.
17 feet; they prevent the lower gates of the lock from opening in the usual way, and are
consequently worked by hooks.
The construction of the bridges is the same as that of the locks, the facings of the walls
being of freestone, and the rest moellon rusticated; there are several skew bridges; those
for uniting the lands of individuals are for the most part constructed of timber, and are
formed over the lock gates; they are composed of three beams, sustained by struts, resting
on the gate post, and by a wheel on the side walls; the roadway is 9 feet wide, and
formed by planking.
Mouths of the Canal in the Loire and the Saone. -The bed of the Loire being subject to
change, the current tends to run from the right bank on which is the lock, and the
margins become silted up; to avoid this a stone dyke is constructed on the opposite side
of a curvilinear form, for the purpose of directing the current to the mouth of the canal,
which is up the stream, and forms an acute angle with the bank; this does not quite answer
the purposes intended, and cleaning the entrance of the canal cost annually from 3000
to 4000 francs; in 1811 a coffer-dam was formed in front, which is too high, and tends to
produce an undermining at the foot of the opposite banks; this has been prevented by
throwing in stones; since the termination of this work, the cleansing costs annually only
300 or 400 francs.
The Mouth of the Saone; the direction of the canal forms a right angle with the bank of
the river, and the guard lock, instead of being placed on the bank, is 200 metres distant
from it; this interval is constantly dragged to allow a passage for the boats.
This canal unites the Loire to the Saone; from Dijon to the summit level there are
thirty locks, rising about 240 feet in 6300 metres; and the length of the summit level is
about 3940 metres; the descent to the Saone is by fifty locks, or 400 feet, in a distance of
4700 metres.
The whole length of the canal is 114,322 metres, the length of each lock 100 feet, and
breadth 16 feet; the breadth of the canal at top 48 feet, at bottom 30 feet, and the average
depth 5 feet 3 inches.
Canal of Languedoc was executed in the reign of Louis XIV. from designs furnished by
François Andreossy, an Italian engineer, by whom locks were introduced into France, pro-
ducing a new epoch in the history of canals, and without which inland navigation never
could have been brought to its present state of perfection.
The canal of Languedoc crosses the isthmus which connects Spain with France, and passes
through the valley between the Pyrenees and the river Rhone; and it appears that a
contract for its completion was made with Paul Riquet on the 14th of October, 1666.
This canal is united with the Garonne below Toulouse, and by means of eight locks
passes round the western side of the city, then along the south side of the river Lers,
and by thirteen locks it ascends to Villefranche, rising another five locks. From the
Garonne to the summit, a distance of nearly 24 miles, it rises by twenty-six locks, a height
of 207 feet; the length of the summit level is 3 miles, after which the canal descends to
Castelnaudary, an ancient town occupying the site of Sostomagus, where the great basin is
constructed; it soon after falls into the Aude near Carcassonne, having crossed several small
streams, and descends by thirty-seven locks. It then traverses the northern side of the
Aude and the town of Treves, to the long level near the Olonzac ; in this latter course it passes
over several streams, and descends by twenty-two locks.
Near Olanzac commences the
long level, and where it crosses the Cesse, the canal of Narbonne branches off; the canal of
Languedoc passes to the north of Capestang by several windings around Mount Ecurene,
and then by a tunnel of 281 yards, under a ridge of mountain called Malpas; eight locks
afterwards ascend to Fonseranne; the level is then 17 miles in length. After passing these
locks it crosses the Orb, near the south side of Bezieres, then the rivers Libron and
Herault, and north of Agde winds round to the Lake Bagnes, enters the Lake Thau,
and passes through to Cette, on the coast of the Mediterranean; there are five locks
during the latter part of its course. The distance from the summit of Naurouse to Cette
the port, is 1214 miles, and the fall 621 feet 6 inches.
The length of the canal altogether is 148 miles, and the lake Thau 94 miles, which
being very shallow at the western end, the canal is carried through it for a considerable
distance by means of artificial dykes.
This canal cost 14,000,000 livres; the king defrayed one-half, and the province of
Languedoc the other. There being some difficulty in making an arrangement with the
proprietors of the lands through which it passed, in 1666, the king issued an edict, which
states "that Paul Riquet, the undertaker of this work, should take all lands and heredita-
ments necessary for the construction of the canal, together with all streams, warehouses,
banks, roadways, locks, &c. &c." which were to be paid for, after a valuation made by com-
petent persons, named by commissaries appointed by the king. The design was fur-
nished by M. Clerville, the most eminent engineer in France, who had also the direction of
the work; the first stone was laid on the 29th July, 1666, at Cette, and in May, 1681, the
communication between the two seas was complete, after fifteen years' labour. The canal
CHAP. VI.
249
FRANCE.
is divided into two principal parts, the starting point being near Castelnaudary; one descends
towards the Mediterranean, being in length 6,165,000 feet, the other, 1,879,000 feet, descends
to the Garonne near Toulouse. After an exact levelling taken between these extreme
points, it was found that the point of setting out was 640 feet above the level of the Me-
diterranean, and 198 feet above the waters of the Garonne. To pass vessels from Cette to
the highest point, there are seventy-four locks, with chambers of a little more than 8 feet
rise, and twenty-six locks to descend to the same point on the Garonne, which is navi-
gable from Toulouse to the sea. There are altogether one hundred locks; the eight near
Beziers form a cascade nearly 1000 feet in length, with a fall of 68 feet equally divided.
There is a circular lock common to three branches of the canal, each having its own
gates communicating to a common chamber; there are forty-five aqueducts, and ninety-
two road bridges; the canal passes above six of these aqueducts, the finest are those of
Repude, Cesse, and Trebes; the thirty-nine others pass under the bed of the canal, for the
drainage of the land.
At the surface the canal is 64 feet in breadth, at the bottom, 34 feet, and 6 feet 4 inches
deep. The vessels which navigate it are 80 feet long, about 18 feet broad, draw 5 feet
4 inches of water and carry about 100 tons.
Canal of Narbonne is connected with the canal of Languedoc, and was commenced
early in 1664; this was extended by Paul Riquet to Beziers. It sets out from the great
level near Argelins, leaving the river Cepe on the right, and all the locks upon it are
placed at regular distances from each other, which has occasioned a useless expenditure.
Canal of Burgundy, intended to unite the Saone with the Seine, was commenced in 1775,
under the direction of Perronet, who has left numerous plans, reports, specifications, and
estimates of this great work. The canal commences at Brianon, and the intention was to
reach a summit level, which would have been 888 feet above its junction with the river
Yonne, and 674 feet above the waters of the Saone. The whole length of the canal was to
have been nearly 148 miles; 13 leagues were completed under Napoleon, and the navi-
gation was perfect from the Soane to Pont de Parry, five leagues west of Dijon; on the
side of the Yonne, the navigation extended to the town of Ancy-le-Franc.
Canal of Malshum, in Alsace, in length eleven leagues, was executed under the direc-
tions of Vauban; it has eleven locks.
Picardy has two principal canals, one called Crozat was completed in 1738.
But the chief canal was that undertaken in 1766, for the purpose of joining the Somme
to the Scheldt, between S. Quintin and Cambray, the cost of which was estimated at twenty
millions of livres ; after repeated alterations in the plans it was completed in 1810; the
length is about 32 miles, and the rise to the summit of the lock of Tronquoi is by
five locks, or 33 feet 6 inches; the summit is 13 miles in length, including two tunnels,
that of Tronquoi 1200 yards, the other called Riqueval 31 miles, each of the tunnels 26
feet 3 inches in width; from the end of the latter tunnel to Cambray is fifteen miles, and
in that distance there are seventeen locks, each 97 feet in length, and 17 feet in breadth ;
the whole fall is about 124 feet.
Canal of Loing was completed in 1724, and proceeds from Montargis to the Seine, a
distance of 33 miles; this was also executed under Regimorte. It has 21 locks, with a
fall of 136 feet 8 inches: it is 44 feet wide at the surface, and 34 feet at the bed, and the
depth of water is 5 feet.

}
Fig. 259.
SKEW ARCH UNDER THE CANAL.
Canal of Briare was begun in 1605, and completed about 37 years afterwards. It
commences a mile from Briare on the Loire, and ascends along the banks of the
250
Book I.
HISTORY OF ENGINEERING.
Trenzi, where there are seven locks, which are supposed to be the first introduced into
France, by the engineer Hugues Cromier; they are from 125 feet in length to 165, and
in breadth 14 feet 6 inches; their rise varies from 5 feet 4 inches to 14 feet; the breadth
of the canal also varies from 25 to 32 feet, the boats draw a little less than 3 feet water.
Canal of Orleans is in length about 45 miles, and has 28 locks, varying from 136 feet
to 178 feet in length, and from 5 feet 6 inches to 12 feet 6 inches rise. The breadth of
the canal varies from 25 feet to 32 feet at the surface, and the depth is about 4 feet 6 inches.
The boats are about 100 feet in length, and nearly 14 in breadth; this work was completed
by Regimorte in 1725.
Bridges. The examples left in the southern districts of France by the Romans have
been partly described; and after the dismemberment of the western empire scarcely any
constructions in stone were commenced till the twelfth century, when necessity produced
throughout France and Germany a religious association, which took the name of "Brothers
of the Bridge; " they established houses of accommodation for travellers, and built bridges
when the rivers were dangerous or difficult to ford. One of the earliest constructed was
at Durance, below the ancient Chartreuse at Bonpas, but due consideration not having been
given to the water-way, it was soon demolished by the floods to which this river is subject.
Another was built at Avignon about 1177, and the funds were obtained by a pretended
miracle, the procès verbal of which is still retained in the Town Hall.
The bridge of St. Esprit and of Guillatiere at Lyons, built at the time Pope Innocent
IV. inhabited France, and that of the Saut du Rhone, on the road from Vienne to Geneva,
were erected by the "Brothers of the Bridge."
During the reigns of Charles VIII., Louis XII., and Francois I., many bridges were
constructed, which sustained mansions or buildings of defence, and it became general
throughout Europe to adopt this system, particularly in cities, where building sites for the
increasing inhabitants could not be obtained.
The Bridge and Chateau of Chenonceaux, commenced by the chamberlain, Thomas
Bohier, who died in 1524, is an excellent example of such structures; upon the piers of
this bridge the architect Ducerceau constructed a gallery for the Queen Catherine de
Medicis, who was charmed with the beauty of the surrounding scenery.

Fig. 260.
CHENONCEAUX.
To the great bridge built on the Rhone succeeded some of single arches of great span:
those of Ceret, Nions, Castellane, Ville Neuve d'Agen, are from 98 to 164 feet span. The
bridge of Vieille Brioude, over the Allier, was the boldest of all; its single arch is above
177 feet. It was built in 1454 at the expense of a lady of that place. In 1545,
Cardinal de Tournon constructed a bridge near the town of that name over the torrent of
the Daux of a single arch, 160 feet span.
These bridges are built very economically, and have nearly the same character. Their
breadth is generally from 13 feet to 16 feet, and few exceed 20 feet. Except those
on the Rhone, which are very well constructed, the faces only of the arches are of
squared stone, and the voussoirs are very small; the rest is of rubble. The haunches
are filled with earth. The piers are always very thick, and above high water their
facings only are of stone. The interior is generally filled with earth or sand; they
seldom have side walls; some portions of walls, founded upon piles, and attached to the
abutments in the line of the heads, generally take their place; the erection of all these
bridges may be dated between the thirteenth and sixteenth centuries, and, considering the
extreme economy of their construction, it is surprising that they have lasted so long.
Arches of great span, consisting of the segment of a circle, whose height is nearly equal
to the diameter, could hardly be erected in towns, where they would encumber the neigh-
bouring houses; in such cases a greater number of arches and less span is far preferable;
the most ancient of the kind now remaining is the bridge of Notre Dame at Paris, built
in 1507. Until this date the city had only wooden bridges, which were frequently carried
away by the ice and inundations, which in 1196 occurred to them all. In 1280, two
CHAP. VI.
251
FRANCE.
more experienced the same fate. In 1412, where the present bridge of Notre Dame now
stands, the first of stone was constructed at Paris; this was soon carried away, and
houses having been built upon it, the magistrates, through whose bad management the
accident had occurred, were condemned to reimburse the proprietors, and not being able
to do so, died in prison. The government, fearing a recurrence, sent for Jocondi, of
Verona, from Italy, whose construction of the Ponte Corvo had gained him great credit.
This architect, who was employed after the death of Bramante, conjointly with Raphael
and Julien de Saint Paul at St. Peter's, built the bridge of Notre Dame as it now exists.
About sixty years afterwards, the Pont Neuf was begun, and during the interim those of
Chatellereau and Toulouse. The breadth of these bridges is very considerable compared
with those which preceded them; they appear to have been the first in which flat arches
were employed, and to have been built and ornamented with considerable attention.
From the completion of the Pont Neuf, in 1604, to 1656, the Pont St. Michel, Hotel
Dieu, Pont au Change, Pont Marie, and La Tournelle, were built. François Blondel
gave the designs for the Pont da Saintes in 1666, and Frére Roman, the architect of the
bridge of Maestricht, was invited to Paris by Louis XIV. in 1683, to commence one of
the piers of the Bridge of the Tuilleries, which was then in progress after forty years'
delay; from this period to that of the bridge at Blois, including those built by Mansard
at the latter end of the reign of Louis XIV., no considerable work of this kind was under-
taken.
Before the time of Louis XIV there was but little commerce, and transport was
mostly effected by mules, which accounts for the narrowness of the bridges, although
many were of great length; the foundations are seldom much deeper than the bed of the
river, and those of Chalons and Macon are built on piles 5 feet long, and many so con-
structed have given way; but those that still remain form a very solid mass, occasioned by
the hardness of the cement: when required to be enlarged, the starlings may be used as
foundations for the new constructions, which is always more economical and safer than
building in a new situation.
After the establishment of the Ponts et Chaussées, the designs for bridges were made
by the engineers attached to it, and submitted to the examination of a board composed
principally of the inspectors-general and some of the divisional inspectors, who, to the
knowledge acquired by study, added that which is the fruit of experience. The bridges
of the last century are, consequently, much more carefully constructed than those of the
preceding, and since this epoch the art has made rapid strides.
The first in order of time is the bridge of Blois, built in 1720, by Pitrou, after the
designs of Gabriel, the royal architect and chief engineer of the Ponts et Chaussées, in
which Pitrou first proposed his trussed centres for great arches. These arches are ellipp-
tical, a form which has since been frequently adopted, as in the bridges of Tours, Moulins,
and Saumur, built nearly at the same time over the Loire and the Allier. The completion
of the last, in 1764, is the epoch of the introduction of the method of founding by cais-
soons; in France its application to bridges was due, as we have seen, to Belie, and Cessa.rt
was the first to practise it.
The bridge of Neuilly, begun in 1768, by Perronet, united the effect produced by great
artists by simple decoration with all that perfection of execution of which this kind of
work is capable. A short time after its construction, the arch of a bridge received the
form of a segment, whose springing is nearly level with high water. The bridge Fauchai d,
projected by Voglie, and built by Limay; the bridge of Pesmes, built in 1772, by Ber-
trand; that of St. Maxence, built in 1784, by Perronet, afforded examples of this kind of
construction, which was followed by several other engineers. In 1787, Perronet began
the Pont de la Concorde at Paris, in which he reduced the thickness of the piers and arches
to less than had ever been done.
The first, as
The bridges hitherto erected in France may be divided into two sections.
we have seen, comprised those constructed from the twelfth to the end of the fifteenth
centuries, all of which are founded on rubble work at but little depth, are extremely
narrow, and although some are very long, they have all the traces of great economy: the
other comprises the bridges from the beginning of the sixteenth to that of the eighteen th
century, when stone bridges were erected in the interior of towns, of greater width and
superior construction and decoration. The third section comprises all bridges from the
establishment of the Ponts et Chaussées to the present time.
Bridge of Avignon, on the Rhone. This has been already mentioned as the second bridge
built in France after the fall of the Roman empire, and constructed by the association
known by the name of " Brothers of the Bridge," in consequence, according to tradition, of
a miracle performed by Saint Benezet. It was begun in 1177, and was not entirely con-
pleted till 1187, although it was rendered passable in 1185.
At Avignon the Rhone divides and forms an island, and it appears that there were at
first two separate bridges over the two arms, in a direction nearly perpendicular to the
current of the river; one of five and the other eight arches: they were then united by
252
HISTORY OF ENGINEERING.
Book I.
eight new arches, built on the island which separated them, in a curved line, so as to unite
the two parts already existing; these latter have many sinuosities, although no reason can
be assigned for such a deviation from the straight line; the whole number of arches was
then twenty-one, of about 180 feet span, and the total length was about 2953 feet.
:
In 1385, Boniface IX., who resided at Avignon, demolished some arches to ensure his
own safety in 1410, the inhabitants of the town, to rid themselves of a Catalan garrison
which Benedict XIII. maintained, blew up the tower which defended the bridge; care-
lessness in repairing a fallen arch, in 1602, caused the fall of three others, and in 1670 the
Rhone having been frozen, the melting of the ice threw down some more, leaving only
four entire on the side of Avignon, where the bridge is 21 feet above the soil, no other
means of ascent remaining than that afforded by the natural inclination of the ground.
The bridge is terminated at each end by two towers; on the Villeneuve side the ascent is
more than one in three. Its breadth is only 13 feet between the parapets, the thickness of
which is a foot. These circumstances render it doubtful whether carriages ever passed
the bridge, mules being formerly the only means for conveying burdens from one place to
the other.
On the second pier is a chapel formerly dedicated to St. Nicholas, patron of navigators,
one part of which is supported on corbels. The piers are constructed of squared stone as
high as the level of the river, and the rest of small rubble work; their upper part and the
haunches of the arches are pierced by round apertures. The remaining arches are well
preserved; they consist of fine squared stones, 2 feet 10 inches high, and so disposed as to
form four separate arcs, which in the first arch present no apparent connection; there is
only one in the second, and seven or eight in the third. The heads are a little distance
from the centre in the first; some iron cramps remain which united the arcs to each other.
Bridge of La Guillotière over the Rhone, at Lyons, consists of eighteen arches from
26 feet to 105 feet span; its total length is 1870 feet; its water-way 1204 feet.
It was
built by Pope Innocent IV. during his sojourn at Lyons, partly at his own cost, and partly
by granting indulgences to those who concurred in this useful enterprise. An inscription
on a tower, since destroyed, preserved the memory of the fact; but on one of the squared
stones of the bridge, the following inscription has since been discovered : —
PONTIFEX ANIMARUM FECIT PONTEM PETRANUM.
Pope Innocent having resided at Lyons about 1245, the foundation of the bridge may
be assigned to that epoch. But the disparity which exists in the construction of the piers
and arches appears to prove that they were built at different, and perhaps very distant,
periods; they are all semicircular.
Bridge of St. Esprit. Its foundation dates from the year 1285, one hundred years after
that of Avignon. The first stone was laid by the prior of the monastery of St. Saturnine
du Port, and the original documents are found in the archives of the hospital; its con-
struction was effected by the alms which the "Brothers of the Bridge" solicited through-
out Christendom. It was completed in 1305; its plan is bent in three directions, and
consists of nineteen great arches and six small, which were afterwards constructed under
the ascent. The span varies from 80 to 109 feet. The total water-way is 2021 feet; the
length 2690 feet.
The piers are more than one-third the span of the arches which they support, and are
carried by a foundation of considerable breadth, presumed to be of rubble work. They
are surrounded with starlings projecting 9 feet 9 inches, and rising about 6 feet 6 inches
above low water; they are formed by double courses of blocks, 6 feet 6 inches long, and
2 feet 3 inches thick, and are further strengthened by jetties, which are maintained with
the greatest care. A tax was formerly imposed on salt ascending the Rhone, to defray
this expense as well as that of the banks above; in 1790 it yielded 28,000 francs, but it
has since been suppressed.
The slope of the jetties being one in one and a half, the surface of the water-way is
rendered exceedingly narrow, notwithstanding the great length of the bridge, a serious
inconvenience, considering the rapidity of the current in floods, and even at ordinary times.
The starlings do not overtop altogether the very high levels; there are holes in the upper
part through which, however, the water but seldom passes.
The arches are constructed of squared stone, the voussoirs are disposed so as to form four
separate arches, united at every four courses by an intermediary one of only three stones,
and their thickness is 5 feet 11 inches. The bridge is very strongly constructed,
and the only injury that has hitherto occurred to it are some slight settlements in
the first arch on the town side; its breadth is 17 feet 6 inches, but that of the roadway
is reduced by the parapets, to 14 feet 11 inches: this is not wide enough to allow of two
carriages passing easily, on account of the great length of their axles. From this cause, or
from fear of other injury being sustained, the passage was not freely opened to the public;
the waggons were unloaded before they were permitted to pass, and the goods transported
CHAP. VI.
253
FRANCE.
on sledges with low wheels, heavy contributions being laid on the merchants by those inte-
rested in the continuance of this manœuvre, so injurious to commerce, and who contrived
to make the public believe that it was necessary for the preservation of the bridge.
It being, however, perceived that the masonry of the arches was as solid as possible, and
that no inconvenience could arise by letting the heaviest waggons proceed, spaces were
formed over the piers to permit them to pass easily, the pavement of the bridge was relieved,
where it lay immediately over the vaults they were covered by a thick bed of gravel, and
the bridge is now perfectly free, without any injury having been sustained.
Bridge of Cêret, on the Tech, was built in 1336, on the road from Perpignan to Pratz
de Mouillon. It consists of a single semicircular arch, 147 feet 8 inches span, of squared
stone, the remainder is of brick. It is remarkable for the arches in the haunches and
abutments, which are from 23 to 26 feet span. This bridge is in good preservation: it is
only 12 feet 9 inches wide.
Bridge of Castellane, on the Verdon, near Sisteron; its arch is a segment of a circle, whose
chord is 115 feet, and its versed sine 28 feet 9 inches. It was built in 1404, from the pro-
duce of indulgences granted by the pope. Its breadth is 6 feet 6 inches, and it is founded
on a rock.
Bridge on the Isere consists of four arches, from 70 feet 2 inches to 91 feet 6 inches
span. The arches are segments of circles, and the piers which support them are very thick,
being 30 feet. The breadth of the bridge is 19 feet 8 inches, it is almost entirely of
rubble work.
Bridge of Villeneuve d'Agen on the Lot. This bridge, of about the same date as the
preceding, consists of a great semicircular arch 114 feet 9 inches span, two others from 29
feet 6 inches to 32 feet 9 inches, and a smaller one of 5 feet 11 inches. The upper part of
the great arch is in a bad state, and tends to separate in several places, but as it is tied
together by iron rods uniting two iron arches, one on each side, it may still last for some
time.
Bridge of Vieille Brioude on the Allier, situated near the Roman bridge, was built in 1454,
by the contractors Grenier and Estone, at the expense of a lady of the place. It consists
of a single arch, the segment of a circle, 133 feet 4 inches span, and 70 feet 4 inches versed
sine. This is the largest arch existing in France, and probably in Europe; it is 16 feet
wide, as are the abutments on which it rests; it is formed of 2 and 3 rows of voussoirs,
placed one upon the other without any tie, one is of volcanic stone, and the other of very
hard sandstone. The stones are only from 8 to 9 inches thick, by 2 feet 2 inches long.
The whole thickness of the circle is 7 feet 5 inches. The bridge is founded on two rocks
rising above low water; its great height and its small width, the steepness of the roads cut
in the rock by which it is approached, as well as some settlements which induced fears for
its solidity, have caused the road to be turned, and another bridge constructed half a
league lower, at Bajace; this was begun in 1750, consisting of three flat arches, rising one
third, from 70 feet 3 inches to 76 feet 8 inches span, with abutments 18 feet, and piers 13
feet 8 inches thick, and was finished in 1753. The foundations were on piles.
The great
arch was 4 feet 9 inches thick, but being, with the exception of the face, constructed of
soft stone, which requires a long exposure to the air in order to harden, it cracked directly
the centres were removed in the upper part, and fell as far as the twelfth or thirteenth
row of voussoirs from the springing, the faces being drawn with it by their connection with
the rest of the arch. One of the small arches was, however, finished, the attendant pier
serving as an abutment until the following year, when the great arch was reconstructed
with better materials, and made 3 feet 3 inches thick.
The soil on which this bridge stands is a compact gravel, into which the piles
are driven with difficulty, yet liable to be carried away by the current; it was attempted
to prevent this by constructing above a coffer of piles, between which all the gravel was
dredged, and its place filled with rubble work. Notwithstanding this precaution the bridge
was carried away by a flood, and as the abutments still remain, it is proposed to reconstruct
it by raising a single pier, and founding it in a caissoon.
Bridge of Sisteron, on the Durance, was constructed in 1500, and is remarkable from
having an arch 85 feet 4 inches span, of an elongated, elliptical form, 57 feet 5 inches in
height. It is probable that it was at first pointed, and that the angle at the two arcs was
afterwards rounded, which conjecture is further strengthened by the circumstance of the
upper and lower parts of the arch being of a different construction.
Bridge of Tournou, on the Daux, built by an Italian engineer in 1545, at the expense of
some cardinal. It has one great segmental arch 156 feet 10 inches span, built like the
bridge of Vieille Brioude, on rock, and only 16 feet 5 inches wide; it is constructed of
pieces of soft, dressed sandstone, except the faces, which are of squared stone.
The
remaining portion is of rough rubble.
Bridge of Claix, on the Draie, consists of a single arch, the segment of a circle, 150 feet
3 inches span; its breadth is 20 feet 4 inches; it was constructed in 1611, near Grenoble,
by the constable Lesdiguières. It is a subject of much admiration with the historians of
254
Book I.
HISTORY OF ENGINEERING.
Dauphiné, who consider it superior to the Rialto at Venice; before the demolition of the
entrance gateway, the following inscription was legible upon it ; —
ROMANOS MOLES, PUDORE SUFFUNDO.
Although built in the 17th century, it is placed in the first section, on account of its anti-
quated construction.
Bridge and Aqueduct of La Crau d'Arles, traverses a marsh, and conveys the water of the
canal of Crapone, erected in 1558 by a gentleman of that name. Its length is 2050 feet;
the arches are semicircular, and their span is 19 feet 2 inches; the thickness of the piers is
12 feet 9 inches, and the width of the aqueduct 17 feet at the upper part; the faces are
slightly inclined.
By the side of the aqueduct is a bridge 32 feet wide, which carries the high road, sus-
tained by arches of the same span as those of the aqueduct; the foundations of the two
constructions are supported in the most dangerous places by timber framework.
Bridge of Nôtre Dame at Paris, on the Seine.-A wooden bridge was constructed here in
1413, under Charles VI., who gave it the name of bridge of Nôtre Dame; it was
It
destroyed the 25th of October, 1499, and rebuilt in stone in 1507 by Frère Joconde.
consists of six semicircular arches, from 31 feet 2 inches to 56 feet 8 inches span. The
piers are 12 feet 9 inches thick. The plinth which crowns the bridge is sustained by mo-
dilions. It is well preserved, and although the stone of Paris is not generally good, this
appears to have been well selected, very little decay being perceptible. It was covered
with houses, which were demolished a few years ago. Its breadth is 77 feet 5 inches.
The pump below one of the arches was constructed by Daniel Jolly, in 1671.
Bridge of Toulouse on the Garonne, was begun in 1543, under Francis I., after the designs
of the architect Souffron. It was not finished till 1632, after the Pont Neuf and Pont de
Chatelleraut. It has seven elliptical arches, from 47 feet to 113 feet span, symmetrically
disposed. The upper part of the pier has openings of a nearly circular form; they are not all
placed on the same level, hence the high water little more than reaches those in the great
arches; the vaults are 2 feet 8 inches thick. It is of brick, except the archivolts and
the starlings, which are of squared stone. Its breadth is 64 feet. The footways are 12
feet 9 inches; the slope of the pavement is about 1 in 26. At the entrance is a triumphal
arch, built by Mansard, which supported an equestrian statue of Louis XIII., destroyed
in 1793.
Bridge of Chattelleraut, on the Vienne, begun in 1560, under Charles IX., and finished
by Sully in 1609. It consists of nine arches, 31 feet 10 inches in span; they are elliptical,
except the centre one, which is semicircular, and elevated on piers 8 feet 6 inches high,
crowned by a plinth. Judging by the heights to which the floods attain, the water-way
appears perfectly proportioned to the volume, to which it gives a passage. The breadth
of the bridge is 71 feet 2 inches; on each side are two footways beyond the parapets, 4 feet.
6 inches wide, formed by flags sustained on consols 3 feet 3 inches apart.
Bridge of Marche Palu, or Little Bridge at Paris. This was much damaged by the floods
of 1649, 1651, and 1659. It was reconstructed in 1695. The 27th April, 1718, two
barges of burning hay were carried against it, and most of the houses consumed by fire. It
was repaired in 1719, and the houses were not rebuilt. It is situated on the lesser arm of
the Seine, next to the bridge of Notre Dame, and consists of three semicircular arches
from 21 feet to 32 feet span.
Pont Neuf, on the Seine.
was Androuet du Cerceau.
year, but the. wars of the League interrupted its progress.
under Henry IV., by G. Marchand, and partially opened in 1604, but not entirely finished
till 1607. The funds were provided by a tax of ten sols on every muid of wine imported
into Paris.
Henry III. laid the first stone, May 21st 1578; the architect
The four piers of the northern part were carried up the same
It was recommenced in 1602,
The bridge consists of two parts abutting at the extremity of the island of the city, and
in the space between stands an equestrian statue of Henry IV. That to the right bank of
the Seine has seven semicircular arches from 46 feet to 62 feet 4 four inches span. The first
is too high, which renders the ascent of the bridge very steep. The second part consists of
five arches, their span varying from 31 feet 3 inches to 48 feet. They are also semicircular,
and have small cornes de vache. The width of the bridge is 72 feet, of which 22 feet
3 inches is given to the road-way, 26 feet for the two footpaths, and 4 feet 3 inches for the
two parapets.
These dimensions are sufficient, although the Pont Neuf is one of the most
frequented bridges in Paris. The starlings of the piers are triangular, and rise to the
cornice, which is very salient, sustained by large consoles ornamented at their feet with
masks of satyrs in very good taste, supposed to be the work of Germain Pilon.
The starlings are surmounted by portions of towers which support the shops erected in
1775 by Soufflot. The bridge was repaired in the course of the same year. The footways
were lowered and widened. The pavement between the footways was reinstated in 1821,
and the ascent diminished.
CHAP. VI.
253
FRANCE.
In 1608, a timber building called the Samaritaine, containing the pumps for raising
water for the service of the Louvre and the Tuilleries, under the direction of a Fleming
named J. Lintlaër, was placed in the tenth arch on the side of the Quai de l'Ecole Militaire.
Henry IV., on this occasion, overcame the obstacles which the municipality of Paris op-
posed to him from fear of the injury which might result to navigation. The pumps were
the first of the kind established in Paris. It was almost entirely reconstructed in 1715
and 1772, and demolished in 1813.
Bridge of St. Michael, at Paris. The first of this name of which we have any account
was of timber, and was replaced by one of stone in 1373. This was partly destroyed in
1408, and rebuilt of timber in 1416. Others shared the same fate, the last, with all the
houses upon it, being carried away by the thaw of 1616. That which now exists was built
in 1618. It consists of four arches, two of 46 feet, and the two others of 32 feet span.
The starlings are surmounted by niches crowned by a cornice, except the centre one, on
which is still the pedestal that supported the statue of Louis XIII.
This bridge is 112 feet wide, and on each side houses were constructed, which were de-
molished in 1809, when the approaches were improved.
Bridges of the Hotel Dieu, at Paris; one called St. Charles, and the other au Double, were
built about 1634 by the governors of the Hotel Dieu. One consists of two arches, 42 feet
span, and the other of two arches 38 feet 4 inches span. They were covered with buildings
welonging to the hospital, leaving a passage only 10 feet 8 inches wide for the use of the
public.
Bridge of Juvisi, near Paris, is remarkable for a serious error of construction.
The piers
on which it is built not being thick enough to resist the thrust of the earth, it is retained
by eight stone arches built from one wall to another, instead of carrying up one arch lower
and larger, which method has been adopted in a similar case, for the causeway at Cravant,
where the arch being too large and too high, a second was constructed, the old walls were
demolished, and the vacant space filled up, by which the original error was entirely
rectified.
Murie's Bridge, at Paris, was built by Christopher Marie, the principal contractor for
bridge-building in France, and united the Isle of St. Louis to the other portions of the city.
It was begun in 1614, and finished in 1635. In 1658 a flood carried away two arches and
the houses upon them. They were rebuilt, first of wood, and then of stone, by means of a
toll granted for ten years. The houses were not rebuilt, and the others were demolished
in 1789.
The Pont Marie consists of five semicircular arches 45 feet 6 inches to 58 feet 5 inches
span. The piers are ornamented like those of St. Michael's Bridge. Its breadth is 77 feet
9 inches.
Bridge of La Tournelle at Paris, also by Christopher Marie, was built of wood in 1614,
and carried away by the ice in 1637, and rebuilt of wood; again carried away in 1651,
re-constructed of stone, and finished in 1656. It consists of six semicircular arches from
51 feet to 58 feet span, and is ornamented in the same manner as the last-mentioned:
the breadth is 53 feet 4 inches.
Bridge of the Exchange, at Paris. A wooden bridge which existed in this place was
carried away by the thaw of 1408, again destroyed in 1510, again at a time not exactly
known, and a fourth time in 1579. Another thaw damaged it greatly in 1616, and threw
down several of the houses built upon it. Lastly, it was burnt in 1621, at the same time with
another wooden bridge called Marchand Bridge, only about 30 feet distant from it. The
stone one now remaining was begun in 1639, and finished in 1647. It consists of
seven semicircular arches, from 35 feet 2 inches to 51 feet 6 inches span. Its breadth is
107 feet: there were two rows of houses demolished in 1788. This is the largest bridge
in Paris.
Bridge of Maestricht, on the Meuse, built in 1683, by Frère Romain, a Dominican friar; it
consists of eight stone arches, from 39 feet to 44 feet span, and a timber platform, which, in
case of siege, could be easily removed. The arches are ornamented with archivolts. The
plan of the starlings is an equilateral triangle on one side, and a half octagon on the other.
The salient angle being, too sharp was destroyed by ice: it has been repaired, and the
angle rounded off.
Bridge of the Tuilleries, or royal bridge. A wooden bridge was constructed in 1632 by a
contractor named Barbier, in the direction of the Rue de Beaune. This was burnt in 1656, as
well as the Machine de Jolly, which raised water from the Seine. Cardinal Mazarine proposed
to pay for its construction by means of a lottery, but this could not be effected, and
it was rebuilt of timber, which was destroyed by a flood the 20th of February, 1684, and
the foundations of that which now exists were laid the 25th of October of the following
Louvois had just succeeded Colbert as superintendent of buildings.
year.
The designs were made by Mansard, and the construction carried on by Gabriel. The
foundation of the first pier on the Tuilleries' side presenting some difficulties, on account of
the bad quality of the soil, Frère Romain was sent for from Maestricht, who was we
256
BOOK I.
HISTORY OF ENGINEERING.
believe, the first to use dredging machines, which he applied in this instance to prepare the
earth on which the pier was to be built, and sunk a large barge filled with stones, sur-
rounding it with piles and a jetty. A kind of chest was then sunk containing courses of
stone cramped together, which were rendered more secure by long guarding piles, and the
space between the walls was filled with rubble and puzzolana, then used for the first time
in Paris.
The foundation was loaded by a weight much greater than what it would have to sustain
after the bridge was built, and as at the end of six months' trial it only indicated a com-
pression of three-fourths of an inch, which was attributed to the contraction of the mortar,
the pier and two collateral arches were carried up in perfect security. In the former
were deposited all the inscriptions and medals.
The bridge consists of five elliptical arches, from 68 feet 9 inches to 77 feet 2 inches span:
the breadth is 55 feet 9 inches: the thickness of the arches 5 feet 6 inches. They are
arranged with more regularity than in any of the preceding bridges of Paris. The two
entrances are widened by forming over half of the last arches recesses, supported on trompes,
which greatly facilitates the passage of carriages. The river is narrower at this point than
at any other, consequently the current has a greatet depth and rapidity, and much of the
bed is every year carried away, to prevent the evil results of which, materials are con-
tinually thrown in.
The cost of this erection was 742,000 livres.
Bridge of Blois, on the Loire, was the first built after the establishment of the Ponts
et Chaussées. It was begun in 1720 by Pitrou on Gabriel's designs. It consists
of 11 elliptical arches, from 54 feet 9 inches to 86 feet 4 inches span. The starlings are
in the shape of an equilateral triangle up the stream, and a semi-hexagon down it. The
three first piers are 16 feet thick, the two centre 17 feet, and the two others 24 feet
6 inches; and these doubtless were intended for abutments in case some of the arches
should be carried away. The other piers, however, appear thick enough to resist the
pressure. The slope of the paving is about 1 in 200: it is too great: the water rises
to the key of the lesser arches, while in the middle arches a considerable space remains
useless. This bridge appearing after its construction not to give sufficient water-way to
the Loire, a new channel for the water has been opened above.
Bridge of Compeigne, on the Oise, was built in 1733 by Hupeau, engineer of the Ponts
et Chaussées. It consists of three elliptical arches rising one-third: two of them are 70
feet 3 inches in span, and the other 76 feet 9 inches. It appears that in this bridge starlings
were used for the first time, whose plan is a triangle formed by two arcs, each equal to one-
sixth of the circumference.
Bridge of Têtes, on the Durance, was built, in 1732, by Henriana, a military engineer, to
connect the road between Brançon and Têtes. The arch is very nearly semicircular, and
has a span of 124 feet 8 inches. The voussoirs are alternately 4 feet 9 inches and 5 feet
4 inches in length. The breadth in the middle is only 16 feet; but it is widened towards
the entrance, and a considerable talus is given to the abutments, which no doubt adds to
the stability of the edifice; and we have many other examples, still it appears more ad-
vantageously applied to timber than to stone bridges.
The thickness of the
Bridge of Cravant, on the Yonne. This was built by M. Advyné in 1760, and has three
elliptical arches, rising a third, from 57 feet 5 inches to 64 feet span.
piers is 12 feet 9 inches.

Fig. 261
CRAVANT bridge,
Bridge of Charmes on the Moselle, built in 1740, consists of ten semicircular arches 64
feet, and two lesser semicircular arches 34 feet 2 inches span. As the stream does not rise
higher than 7 feet 5 inches, the water-way is evidently too great. The lesser arches are
separated from the rest of the bridge by massive piers 128 feet thick. The starlings are of
squared stone, but the arches and spandrils of rusticated rubble.
Bridge of Toul, on the Moselle, built in 1754 by Gourdain, has seven elliptical arches
from 48 feet to 54 feet 6 inches span: it is constructed of squared stone.
CHAP. VI.
257
FRANCE.
Bridge of Trilport, on the Maine, projected and executed by M. Chezy, who began it in
1756 and finished it in 1760; the outlay was 489,000 livres; it consists of three elliptical
arches; the centre is 81 feet span, the two others
76 feet 9 inches. The thickness of the piers is
7 feet 5 inches, that of the abutments 19 feet
2 inches. The breadth of the bridge is 32 feet.
The arches are skewed, their axes making an
angle of 72 degrees with that of the bridge; the
foundations are on piles and a timber framework,
and the water was pumped out by means of a
vertical chain pump and a bucket-wheel driven
by the current.
To avoid the acute angles which the joints of
the voussoirs would have formed with the bridge,
from the skewing of the arches, Chezy introduced
half-voussoirs or cornes de vache on each side
of the bridge, the breadth of which is 5 feet
3 inches at the springing, gradually diminishing
to nothing at the summit of the arch; the half-
voussoir is comprised between the plane of the
head and another vertical plane. The surface of
the intrados is described by a horizontal gene-
rator, perpendicular to the plane of the head,
passing through the intersection of the vertical
plane just mentioned, with the vault of the arch.
The planes of the joint of the voussoir pass
through the intersections of the planes of the
joint of the vault with this same vertical plane,
and through the generators of the voussoirs.
The details and working drawings of these
arches are given in a treatise by M. Bruyère, en-
titled, "Etudes relative à l'Art de Construction."
The bridge of Trilport was destroyed in 1815,
the middle arch was removed, and the two piers
yielded to the pressure of the lateral arches.
Bridge of Port de Piles, on the Creuse, erected
in 1747 by Bayeux: it consists of three ellip-
tical arches rising one-third, and from 99 feet to
103 feet 8 inches span. The voussoirs were laid
on beds of mortar beaten with a mallet, and in their
joints, to the sixth course from the key-stone, long
and wide wooden wedges were introduced, by
means of which the compression was so regulated
that when the centres were removed, the great
arch sank only an inch, and the two others rather
less.
Bridge of the Pope, on the Erieux, constructed
in 1756 by Pitot, consisting of seven arches
nearly semicircular, 48 feet 6 inches span. It is
of squared stone; the abutments are founded on
a rock, but all the piers are built on piles. A
general framework was constructed by driving
two rows of piles capped both up and down the

stream.
Bridge of Orleans, on the Loire, begun in 1751
from designs by M. Hupeau. The work was
carried on under his orders by Soyer, and was
finished in 1760. Pitrou had made a nearly
similar design, except that the situation was a
little different, and the radius of the arches at
the springing was greater, which tended to
increase the water-way.
It consists of nine elliptical arches rising a
fourth, from 98 feet 1 inch to 106 feet 7 inches
in span.
The piers are from 6 feet 3 inches to
10 feet 7 inches high, and from 18 feet 2 inches
ý
the
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Fig. 252
BRIDGE OF TRILPORT ON THE MA¡NE.
258
BOOK I.
HISTORY OF ENGINEERING.
to 19 feet inches thick: the abutments are 23 feet 5 inches thick; the middle arch is
7 feet, and that which joins the abutments 5 feet 10 inches thick. The breadth of the
bridge is 49 feet. The plan of the starlings is formed by two arcs, one-sixth of a
circle up the stream, and a semicircle down it.
The foundations are established on piles carrying a framework and platform of carpentry :
the soil is a bed of sand from 4 feet to 13 feet in thickness, which covers irregular layers of
marl and tufa. A foundation of this kind being very permeable to water, the pumping was
attended with great difficulties. In the sides of the cofferdams, with which the abutment
and piers were successively surrounded, several springs worked, which it was impossible to
exhaust. They were at length enclosed in cisterns, in which the water was allowed to rise
and round which a cofferdam was constructed with planks and clay: the nature of the soil
also rendered pile-driving in some places very irregular; it often occurred that by the side
of a pile which would only drive 6 feet into the tufa, another would go 16 feet, according
to the nature of the beds they traversed.
The arches were constructed on trussed centres, which being found too weak were
strengthened by adding some pieces in the upper part, but after their completion, a settle-
ment was perceptible in the seventh pier from the town, and a load of rubble weighing
1 tons was added to the two arches which it supported; the pier gradually sank 1 foot
7 inches, and the weight remained on it for five months afterwards. The pier and haunches
were then relieved by small vaults in the upper part, which do not appear on the outside,
being concealed by the facings. The same precaution was taken for the fifth, sixth, and
seventh piers. The two arches adjoining the seventh pier have not experienced any accident
and have only a slight irregular curvature, hardly perceptible. The only reason which
can be assigned for the settlement is, that under the bed of tufa there was probably a soil,
so light, that it only acquired sufficient consistence by the weight and compression to which
it was subjected.
The year after the construction of the bridge a sinking of the earth under the tufa took
place under three of the arches and some of the starlings, to the depth of 2 feet 2 inches,
and it was deemed necessary to drive two rows of piles close to each other, and 12 feet
9 inches apart, the whole length of the bridge, and 6 feet 6 inches below the starlings; they
were cut off 3 feet 3 inches below the surface, and the space between was filled with rubble.
All the other portions that had settled were treated in the same manner.
The cost of Hupeau's design amounted to 2,084,000 livres, and the additional outlay
was 587,000 livres. It was opened in 1768 by Perronet, who has published the details of
the construction,
Bridge of Saumur, on the Loire. The designs were made by M. de Voglia, the engineer-
in-chief, and presented to the Ponts et Chaussées in 1753. The works were begun in 1756,
and finished in 1764, under the superintendence of De Cessart.

Fig. 263.
SAUMUR.
This bridge consists of twelve elliptical arches of 64 feet span, rising a third.
are 12 feet 9 inches thick; some are 17 feet high from the springing.
Fig. 264.
PLAN OF PIERS, SAUMUR.
The piers




CHAP. VI.
259
FRANCE.
The first soundings indicated a bed of gravel from 13 to 16 feet thick, and the length of
the piles was fixed at from 26 to 30 feet. The foundations of an abutment and the ad-
joining pier were first laid, but the exhaustion of the water was so difficult, that only one
pier could be finished in the first season, and the piles were cut off 4 feet 4 inches below the
surface. The abutment was finished the next season, and the piles cut off 4 feet 4 inches
below low water.
It being found impossible to establish cofferdams for the piers in the middle of the
river, a proposal was made to adopt the method indicated by Belidor, which consisted in
cutting off the piles under water, and sinking a platform loaded with masonry, by means
of several screws firmly fixed. M. de Cessart invented a saw to perform this operation,
but more careful consideration induced the engineers to use the caissoons, which Labelye
had just employed at Westminster Bridge, and which were merely placed on the ground
carefully levelled. The bottom of these caissoons was composed of pieces from 10 to 11
inches thick, which could rest on the piles throughout; the sides were moveable, and might
be adapted to a new bottom after sinking the former one.
All the other piers and the second abutment were founded in this manner. The piles
of the second pier were cut off 7 feet 6 inches, and some 12 feet 9 inches below the surface.
Care was taken to dredge the sand between the piles as much as possible, and to fill up the
intermediate space with rubble, the upper surface of which was levelled 6 inches below the
heads of the piles, so as not to affect the placing of the caissoons.
The piles were driven by a ram moved by a wheel adapted to a horizontal axle; this
saved one-half the expense and number of men. The saw for cutting off the heads, which
has since been employed in several other places, was completely successful. The invention
of this machine may be considered as a very important era in the art of building under
water, and one of the most powerful methods at the disposal of constructors to overcome
the difficulties which nature opposes to them; it has sometimes cut off twenty-two piles in
a day.
Founding the piers at the bridge of Saumur, by means of a caissoon, by De Cessart in the
year 1757, was thus accomplished.
The bottom of the caissoon was 48 feet in length, and 20 feet in width, from outside to
outside.
The ends were in the form of an isosceles triangle, two sides of which were 13 feet
3 inches.
The outside timber of the frame-work was 18 by 16 inches, scarfed in their length, in the
manner termed traits de Jupiter, and rebated on the inside edge to a sufficient depth to
receive the timbers which crossed from side to side, and were dovetailed at every 3 feet, the

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Fig. 265.
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others between them being laid with square edges; they were secured by wooden pins an
inch in thickness, not driven entirely through, in order that the bottom of the caissoon should
present no inequality to the heads of the piles on which it was to rest. To fasten them,
however, more effectually, a wedge was driven into the points of the pins previous to
their being inserted, which forced them upwards, and formed beneath a second head, ren-
dering their withdrawal almost impossible.
After the first planks were laid and pinned down, another piece, 10 inches in width, and
8 inches in height, was spiked over their ends and united to the main timber by iron bolts,
15 lines in diameter, at every 3 feet; on this was laid another longitudinal timber, 12
inches high and 8 inches in width, bolted through the planks, and laterally through the
main timbers: the space between these outer timbers was then covered with planks.
S 2
260
BOOK I
HISTORY OF ENGINEERING.


Fig. 266.
SECTION OF THE CASSOON.
inches thick, laid longitudinally, and crossing at right angles those previously laid; thus
the bottom became 14 inches thick, and the superficial area of the base 1160 square feet.
The height of the sides was 16 feet above the bottom, and composed of 24 squared
timbers, the scantling of which was 9 by 6 inches, laid on edge; these were of oak, and the
length of each course was 72 feet; at the angles they were lapped one over the other
each two courses were alternately pinned together, making one solid mass.
To strengthen the angles, the timbers were doubled, pieces 4 inches in thickness being
placed vertically; one in the angles, 18 inches in width, between two others 12 inches in





Fig. 267.
JOINTS OF THE CARPENTRY OF THE CAISSOON,
width, well pinned into the outer timbers, the wedge being driven into the heads of the
pins to render them more secure.
CHAP. VI.
261
FRANCE
In addition, there were three knees or curved pieces, 8 feet long and 8 inches square
nicely fitted, and pinned very securely with oak pins.
Within the caissoon were placed perpen-
dicularly other planks at the ends, 4 inches
in thickness, and 12 inches in width, pinned
with great care; between these and the angle
ties were five others, at equal distances apart,
sustained by diagonal sheets, all securely
pinned.
For closing the joints the outer edges of

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Fig. 268. SIDES OF CAISSOON.
Fig. 269. Carpentry of caissoon.
the timbers were all chamfered, and moss of the oak was forced into them by means
of chisels with rounded edges, driven by iron hammers till it became very hard, and
effectually closed the joints. Oak laths soaked in water, an inch in width, rounded on
one side and flat on the other, were nailed over the joint of moss, care being taken to drive
the nails alternately above and below the joint; this manner of caulking with moss
had been previously used with success for all the large barges which navigated the Loire.
To attach the upright sides to the bottom of the platform of the caissoon, De Cessart made
use of a very simple contrivance, so that by drawing a wedge the whole might be released
at one time.
We have observed that the sides were composed of layers or courses of
squared timbers; in the inside and outside of these were others placed perpendicularly, and
dovetailed into the sides of the main timbers of the lower platform, which dovetails were so
cut, that they allowed the timber to be wedged home by an upright piece placed along their
sides, and at the bottom a void of 2 inches in depth was left, which, after the screw which

Fig. 270.
CAISSOON.
s 3
262
Book 1.
HISTORY OF ENGINEERING.
held the main upright in its place was withdrawn, permitted it to descend, and the wedge
piece by its side to be drawn up; when this was done the whole side was easily re-
moved.
This caissoon was constructed in a convenient situation, and commenced by driving
three parallel rows of piles 3 feet from centre to centre, forming twenty-four piles, united
by cross pieces 22 feet in length; the first row was cut off level with the water line, the
second and third 3 feet higher, in order that the inclined plane might facilitate the floating
of the caissoon. The whole was made level to receive the platform by blocking up with
timbers, 30 feet in length, and of a scantling 15 by 12 inches. In the middle was a pro-
jecting bracket and other contrivances, so that when the bottom of the caissoon was raised
to an angle of 20 degrees, it would slide easily into the water.
In laying out the bottom, care was taken to place its centre of gravity 6 inches within on
the land side, and after the caissoon was constructed, it was filled with water by means of a
pump, to prove the caulking.
To fix the upright timbers which were attached to the horizontal layers that formed the
sides of the caissoon, four iron bolts, 20 inches in length and an inch in diameter, were passed
through them, with their heads on the outside and the nuts within, that they might be
easily unscrewed; these were well caulked round with moss to keep the water from pene-

L
OGOO
Fig. 271.
CAISSOON.
trating, and eight chains were attached to them to facilitate their drawing. To prevent the
caissoon from collapsing when placed in the water, five diagonal struts were introduced, which
could be easily moved: after all was prepared, the wedges towards the land were withdrawn,
and the centre of gravity being 6 inches nearer that side, an inclination to move was given to
it; sixteen men at eight jacks raised it a trifle, and then allowed it to slide gently towards
the river; when afloat it drew 24 inches of water; the bottom was forced up about 3 inches
in the centre for every 1000 feet superficial of base, 31 inches for 2080 feet, and 5 inches
for 5084 feet. It was towed to its position on the Loire by six rowers, and before the
heads of the piles were cut off, the lower course of masonry was commenced, 14 inches
in thickness, over the lines previously drawn for the position of each stone. After this
it was found that the caissoon drew 41 inches of water, and remained perfectly level. An
inclined plane was formed of two pieces of timber, on which ran a small carriage, that
brought down the blocks of stone, and facilitated the operation of the masons.
When the heads of the piles were all cut off, the caissoon was towed to its place, every
precaution being taken to moor it in its exact situation; the second course of stone was then
Îaid, 20 inches in height, formed of 30 blocks; the caissoon then drew 61 inches of water, its
position was again verified by stretching a piece of timber across the intended span, and
when half the third course was laid, it was settled on the heads of 116 piles, driven to
receive it; a verification was then made that it had taken up its exact distance from the
piers already constructed on the land.
The fourth, fifth, sixth, and seventh courses of stone were then laid and cramped, and in
the eighth course, which formed the springing of the arches, were introduced three mooring
rings on each side, tied at their ends by irons 14 feet in length.
All the masonry being completed, the joints well dressed, and covered with powdered
lime and fine sand, which hardens in water like puzzolana, the sides of the caissoon were
CHAP. VI.
263
FRANCE.
removed by first taking out the irons at the ends, cables were attached to the rings of the
chains, the bolts which held the upright pieces were withdrawn, and the stays inside were
removed; the water then entered; the upright timbers, which have been described as dove-
tailed at their ends, were driven downwards, and the wedges at their side being released,
were drawn up by hand; these were all taken out in succession, and the sides drawn out by
means of three crabs placed in a barge, after which they were towed away to be applied to
the bottom of another caissoon for the next piers.
To relieve the centres after the arches were turned, De Cessart adopted the plan of cutting
away a portion of the ends of the braces; he removed the wood by making as it were three
mortices, and leaving the whole centre supported upon two tenons at its ends, 2 inches in
width only; these were afterwards cut away, and the whole dropped in a body.
Bridge of Tours, on the Loire, begun 1755 by Bayeux, is the longest bridge in France,
except those of St. Esprit and La Guillotiere, over the Rhone at Lyons.
•
It was finished in 1762, and consists of fifteen elliptical arches, rising a third, and 80 feet
span. The piers are 16 feet thick; the breadth of the bridge is 48 feet; it was founded
partly by cofferdams, and partly by caissoons; the length and water-way appear great when
compared with the neighbouring bridges; several accidents have nevertheless occurred.
The bottom is a sand bank from 6 to 10 feet thick, under which, and from 19 to 23 feet
below low water, is a bed of tufa, in which the piles penetrate about a foot. This foundation
appeared sufficiently secure; the piles of one pier have, however, yielded to the superin-
cumbent weight, and it has sunk about 3 feet, and gone over about as much. The arches
were demolished, and the pier removed, as well as another construction on the old foundation;
this accident is attributed to the bad quality of the timber of the piles, which had remained
a long time underground, and were partly rotten.
A thaw then occasioned the sinking of three other piers, the ice formed a kind of bar
above the bridge, and the water running rapidly under the arches on one side only carried
away the sand between the piles, and laid them bare, and four arches fell in.
The recon-
struction of the piers was very difficult, the ruins of the first pier were removed with great
labour and expense, and the foundations were consolidated and rendered secure; the second
pier was still more difficult, the piles having gone over 3 feet on one side, and it was pro-
posed to suppress the three last arches, which would have given a greater water-way than
was necessary; this plan was therefore not adopted, and a method was suggested for es-
tablishing a cofferdam on the platform of a caissoon, which projected 4 feet 3 inches
beyond the masonry, and the latter faces were thus restored. The interior was then to be
emptied, and the courses and bottom would be easily removed, it being impossible to ar-
range a cofferdam in the usual manner, from the great depth, and the ruins of the arches.
This method did not entirely succeed, because the piles had yielded unequally; those on
the outside having resisted more than the others, the bottom was broken and the pier had
passed through it. These injuries rendered the total exhaustion of the cofferdam im-
possible; the remaining courses were raised piecemeal by multiplying the machines and
pumps, and the bottom of the caissoon being entirely destroyed, it was removed by thirty-
six chains attached to different machines, worked by ninety-six men, who raised about
911 tons at once; it was brought ashore by 150 casks and two boats.
Bridge of Moulins, on the Allier, was begun in 1756, and finished in 1764, under the
direction of M. de Regemorte, and consists of 13 elliptical arches, 64 feet span. The piers
are 11 feet 8 inches thick; the breadth is 42 feet 8 inches. The construction of this bridge
was very difficult; three bridges had been erected in the same situation in 35 years;
two, of stone, had been successively carried away. The last was by Mansard, it
consisted of three great elliptical arches supported by thick piers, which only gave a water-
way of 377 feet. The length was 830 feet. The fall of these bridges was attributable
both to defects in their construction and want of width, a circumstance which the nature of
the bottom rendered very dangerous. The bottom is a coarse sand of great depth, into which
it is difficult to force piles of from 10 to 12 feet, although the floods frequently tear it up to
a depth of 16 or 20 feet.
M. de Regemorte perceived the necessity for increasing the water-way considerably, in
order to diminish the velocity of the current, and the sequel has proved that what he gove
it was far from being too much. In 1790 the water rose to within 3 feet of the crown of
the arch, and it was thought that if the right bank had not given way, it would have run
some risk.
The increase of width did not remove all fear for the safety of the bridge; it
was thought that the least obstacle in one arch might occasion the soil to be carried away
from under the others; to avoid this a framework was constructed under the bridge, 6 feet
6 inches thick, having the upper surface 3 feet 3 inches below the level of the water: the
breadth is 111 feet 6 inches. This precaution set all anxiety at rest. There are few cases
where the arrangements have been made so perfectly in accordance with the natural circum-
stances of the place, or have been worked out in so intelligent a manner. The details of
the construction have been published by M. de Regemorte.
s 4
264
BOOK I.
HISTORY OF ENGINEERING.
Aqueduct of Montpellier, is one of the finest works of the kind in France, and conducts
water from the sources of St. Clement and Boulidou to the town of Montpellier. It was
built in 13 years by Pitou.
There are two tiers of arches, the lower is 70 in number, their span is 27 feet 8 inches,
the thickness of the piers 12 feet 3 inches. Those of the upper tier are only 9 feet. The
greatest height of the aqueduct is 92 feet. It is entirely constructed of squared stone; one
of its terminations is in the Place de Peyrou, which it traverses on three arches, where
there is a reservoir. The total length is 3215 feet.
Aqueduct of Carpentras, on the Auzon, has 33 semicircular arches, 38 feet 4 inches span,
and 12 lesser arches of 25 feet 7 inches, without comprising a segmental arch of 76 feet
9 inches, on which it crosses the Auson. The thickness of the piers is 12 feet 9 inches.
Its width is 7 feet 3 inches above and 17 feet below; the greatest height is 82 feet, and
the total length 2560 feet.
Bridge of Dole, on the Doubs, begun in 1760, and finished in 1764 by Guéret, consists of
11 elliptical arches rising a third, from 52 to 62 feet in span. The piers are from 10 feet
8 inches to 11 feet 6 inches in thickness. Their foundations, 7 feet 6 inches below the
water, are supported by little piles about 13 feet long. The facings are of squared stone,
and the bridge appears to have been carefully built.
A sort of false framework was constructed below bridge, and some jetties made round
the piers; two, however, sunk, which has occasioned the fall of the corresponding arches.
The piles which supported them had been entirely deprived of the materials which re-
tained them, and it had been thought sufficient to place jetties round the piers, without
filling up the void formed in the interior of the foundation.
Bridge of Mantes, on the Seine, where the river is divided into two principal branches,
each about 360 feet wide, and one lesser branch: the old bridge, called that of Limay, was
AAA

Fig. 272.
MANTES.
constructed on the first of these; the second, called Fayol, from the name of the engineer,
is composed of thirteen arches, comprising one for the towage; there is also a third, with
the same number of arches, below which a new bridge was commenced.

Fig. 273.
PLAN OF MANTES BRIDGE.
The stone employed was brought from the quarries of Saillancourt, Cherance and
Veteiul, all of which were of excellent quality. In Perronet's work is shown the con-
struction of the centres, and the methods adopted to supply the various material to the
workmen, which are novel and interesting.
The cofferdam was formed in a similar manner to that constructed at Neuilly; the
piles were shod with iron and driven with heavy rams, some with a force of half a
ton; and after the whole were placed, the dragging commenced, and was continued
until all the mud and sand were removed; the machine used being that contrived
CHAP. VI.
265 ·
FRANCE.
by M. Regemorte for the same purpose at the bridge of Moulins. The space between
the piles was then filled with clay, and, when water-tight, the pumping out was com-
menced, and the whole of the vast interior rendered dry: pumps and chapelets worked
by men, and an undershot-wheel, being constantly in use for this purpose; the whole
was under the directions of M. Hupeau, who made the designs and commenced the
foundations in 1757, and was finished by M. Perronet in 1765; it consists of three eilip-
tical arches, 115 and 128 feet in span. Their springings are 3 feet 3 inches below the
surface, and the platform of the foundations 6 feet 6 inches; the height of the middle
arches 37 feet 3 inches, and of those at the two sides 35 feet 8 inches. The piers are 25 feet
7 inches, and the abutments 28 feet 9 inches; the width is 35 feet 5 inches.

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Fig. 274.
COFFERDAM AT MANTES.
In constructing the arches of this bridge, they commenced by one of the side arches,
which was almost finished, when there were only ten courses of voussoirs on the middle arch.
The inequality of pressure resulting from this on the intermediate pier thrust it in a
horizontal direction. The piles took a slight inclination, and, although the voussoirs of the
great arch were placed with the greatest possible celerity, the motion was not stopped till
the pier had moved 43 inches; the arch was, however, continued, and, to prevent the effect of
pressure on the other pier, care was taken to preserve the distance from the centre by ties
composed of pieces scarfed together. This precaution succeeded perfectly, and after
putting in the key-stones, the first pier was carried back 24 inches towards its proper position.
The details of the construction have been published by M. Perronet.
Bridge of Bord, on the Oeil, built in 1764 by M. Leclerc, is on the road from Moulins to
Autun. It consists of a single arch 69 feet 3 inches span. All the facings are of squared
stone, and the work is very good.
Bridge of Nogent, on the Seine, built between 1766 and 1769, by M. Perronet, consists of
one elliptical arch, 96 feet in span, 29 feet 9 high from the springing to the key. The
thickness of the abutments is 19 feet, they have shoulders and terrace walls. The arch is of
very hard sandstone, and its thickness is from 4 feet 3 inches to 5 feet 2 inches.
The bridge of Nogent has been the subject of an interesting experiment on the motion
and rupture of arches. Before the centres were removed, a portion of the masonry of the
haunches had been constructed, which partly prevented the joints of the voussoirs, which
had opened during the progress of the work, from closing as they generally do; added to
this, the centres were struck immediately after the arch was finished, which increased the
settlement; these different circumstances rendered the points where the acting parts of the
vault separate from the resisting parts very visible, and particular arrangements have been
made with the view of ascertaining them exactly.
It consists
Bridge of Albias, on the Aveyron. This was built in 1770 by M. Boesnier.
of three elliptical arches 76 feet 9 inches and 83 feet in span. Its width is 39 feet.
Bridge of Sorges, on the Anthion, constructed by M. Regemorte; it consists of 7 arches
19 feet 3 inches in span. Gates are attached to them by means of which the water may be
266
Book I
HISTORY OF ENGINEERING.
entirely shut out. The object of this is to prevent the inundation of the Loire, which
covered an extensive country, and made the Anthion flow back to a great height.
Bridge of Carbonne, on the Garonne, constructed in 1770 by M. Saget. It consists of
three equal elliptical arches rising a third, 102 feet in span. The vaults are extradossed,
and with the starlings are of squared stone, the rest is of brick. The width is 25 feet 7
inches.
Bridge of Montignac, on the Vézère, begun in 1766 and finished in 1772 by Tardif. It
has two semicircular arches, 42 feet 8 inches in span, and one elliptical of 66 feet. The
abutments and one pier are founded on a rock. The other pier is supported on piles.
Bridge of Brives, on the Loire, constructed 1772 by Grangent. It consists of five
elliptical arches from 51 to 59 feet in span, and two lesser arches of 10 feet span,
placed behind the abutments. Its breadth is 28 feet 6 inches. It is built on a rock, and
in great floods the water rises to the cordon without injuring it. This is the first bridge
under which the Loire passes, being at this point a rapid torrent.
Bridge of Pesmes, on the Ougnon, constructed 1772 by Bertrand; consists of three seg-
mental arches, 44 feet 9 inches in span. The piers are 6 feet 4 inches thick, and the abut-
ments 12 feet 9 inches. The arches are flattened, and only rise 3 feet 10 inches, or nearly
one-twelfth of the chord. The thickness of the vault at the summit is 3 feet 10 inches.
The height of the piers, 11 feet 8 inches from the platform.
The bridge of Pesmes is the first in France in which arcs of circles were used whose
springings are on a level with high water. The arches sank considerably when the
centres were struck, and the want of thickness in the abutments has occasioned some
important settlements in one of them, the consequences of which were only prevented by
using extraordinary precautions.
Bridge of Pontlieu, on the Huisne, built in 1773 by Voglii. It consists of three elliptical
arches, which rise between a third and fourth of the span, which is 57 feet 4 inches. The
thickness of the abutments is 14 feet 5 inches. This bridge having no plinth, the parapet
forms one, projecting 1 foot 7 inches from the faces of the bridge.
Bridge of Ingersheim, on the Fecht, constructed in 1773 by M. Clinchamp, a military
engineer. It consists of three elliptical arches, rising between a fourth and a fifth, with
a span of from 50 to 60 feet. The thickness of the abutments is 21 feet 3 inches. It is
built on piles 6 feet 6 inches below low water.
Bridge of Drôme, constructed in 1774 by M. Bouchet, on the road from Lyons to Mar-
seilles, with three elliptical arches, rising a third, from 85 to 96 feet span.
This bridge is of very beautiful construction, but the foundations are now too high.
The bed of the river has sunk below bridge, and as the foundations are of squared stone, a
fall is produced which might occasion the earth to wash away; this has been provided
against by driving piles, between which large stones are thrown, to resist the action of the
current. The bridge itself is also too high, the floods never rising above half the height
of the arches, which is the more evident on comparing its height with that of the banks
above the bridge.
Perronet, Jean Rodolphe, a celebrated engineer attached to the Ponts et Chaussées, was
born at Surène, near Paris, in 1708. His father was an officer in the French service, and
a native of Vevei, in Switzerland, after whose death he devoted himself to the study of
architecture, and in 1725 he became a pupil of Debeausire, one of the architects of Paris.
When scarcely seventeen years of age, he was entrusted with the superintendence of the
great sewer of that portion of the quay, called l'Abreuvoirs, between the bridge of
Louis XVI. and the Tuilleries; and also of the projecting footway of the Quai Pelletier, near
the bridge of Notre Dame. In 1747, the minister Trudaine founded the School of the Ponts
et Chaussées, and placed Perronet at its head; he had been for ten years an associate of this
body, and had obtained the office of inspector and engineer-in-chief of the department of
Alençon. In becoming a director of the new establishment in February, 1747, he received
the title of Chief Engineer of the Ponts et Chaussées in France, and in the administration of
this celebrated establishment he fully maintained the high idea his talents had inspired, and
the great works which were entrusted to him confirmed his reputation.
Thirteen bridges
were executed from his designs, and eight which were projected show his ability and in-
vention. All are remarkable for some peculiar beauty, and some are masterpieces, never
having been surpassed, as Neuilly, Nemours, St. Maxence, and that of Louis XVI. at Paris.
Neuilly was the first example of a level bridge, and was commenced in 1768; all the court
were present when the centres were struck, in September, 1772, the whole belonging to the
five arches were lowered in three minutes and a half. St. Maxence is remarkable for the
boldness of its design; that of Nemours, finished in 1805, has undergone some change, but
the design was Perronet's.
That of Louis XVI., at Paris, may be considered as peculiarly his own; it unites every
species of elegance, convenience, solidity, and easy approach; it was to have been decorated
with trophies, but the statues of illustrious men who have done honour to France have been
CHAP. VI.
267
FRANCE.
substituted for them. Perronet was desirous of perforating the piers and abutments, which
would have added to its beauty; but he was obliged to abandon the intention, in conse-
quence of the fears entertained by some that such a construction was insecure: he returned
to this idea in the bridge of Maxence, and experience has proved that these fears were
chimerical. It is a remarkable circumstance, as M. Bertrand has observed, that at the time
Perronet was studying architecture at the Louvre, the Academy having proposed a prize for
a design for a bridge to be constructed opposite the church of the Madelaine, Perronet was
the successful competitor.
His claims to public gratitude are not confined to these works: to him France was
indebted for the Canal de Bourgoyne; he also proposed to render the river Yvette navi-
gable, an extremely bold project, which has been superseded by the execution of the Canal
de l'Ourque.
During the space of thirty years, in the neighbourhood of Paris alone, more than 600
leagues of road were formed and planted with trees; a vast number were widened,
levelled, and rendered convenient for every kind of traffic; and before 1790 nearly
2000 bridges, of various span, were placed under the superintendence of the Ponts et
Chaussées.
He was appointed inspector-general of the salt works in 1757, which he held till
1786.
He invented several ingenious machines; among them a saw for cutting off the heads of
piles under water; a cart, called after him, which unloaded itself; a drag for cleaning har-
bours and rivers; a plane table carrying a pencil; a double pump, with a continued
action; and an odo-metre, applicable to pumping out. This latter instrument, which may
be adapted to all machines, shows the number of turns of the winch made by the workmen
employed, and by this means regulates the quantity of work and price; it is also used for
measuring the distance travelled on foot or on horseback, which renders it peculiarly useful
for military men; and it is so exact as to indicate the retrograde steps.
Perronet was a member of the Royal Societies of London, Stockholm, Berlin, &c., and
several other learned bodies. The court of Russia, in 1778, desired him to prepare a design
for a bridge over the Neva, which was of a very magnificent character.
Perronet bequeathed his bust, in marble, presented by his pupils, his books, his models,
&c., to the Ponts et Chaussées.
His great age, and the respect his services had acquired, preserved him from the revo-
lutionary tempest, and he died universally regretted in 1794.
His published works consist of an account of the bridges of Neuilly, Mantes, Orleans,
&c., several memoirs inserted in the Transactions of the Academy of Sciences, a memoir on
conducting the waters of the Yvette and Bievre to Paris, and on the means which might be
adopted to construct arches of stones from 200 to 500 feet span.
The roads formed by him and various designs were published in three volumes, folio, at
the expense of the government.
M. Lesage published, in 1805, an eloquent discourse upon M. Perronet, who may be
considered the most distinguished civil engineer in France who had been instructed
by the writings of Belidor, in which the first attempts were made to embody what
was known of hydraulic architecture: the Italian philosophers at that time had, by their
discoveries, awakened in the schools of France an inquiry into the principles of science, and
had already pointed out the connection that existed between practice and the mathematical
sciences. It was not, however, the high scientific attainments of Perronet that exalted
his name, or caused him to be the founder of a new era in bridge-building, but his nice
observance of the prevailing modes of construction, which he set about reducing to a
system, and which turned to the best account the movements and employments of workmen
and artificers of every denomination; he showed where labour might be saved by the in-
troduction of machines, and instructed them how many difficulties which occur in laying the
foundations of buildings in water might be overcome, then unknown or forgotten. We
cannot turn over the engravings which represent the labours of this eminent engineer
without acknowledging how much we owe him; he evidently belonged to the school of
utility, upon which is now engrafted in France the refinements of mathematical analysis:
those youths who now aspire to be eminent as civil engineers undergo a scrutinising ex-
amination in the physical sciences, and are not admitted to the post of sub-inspector, nor are
they introduced to any practical employment, until they have shown a perfect acquirement
and thorough knowledge of geometry, mathematics, chemistry, mineralogy, and the sciences
connected with them.
The practical man is considered as the entrepreneur, or contractor, and never charged
with the superintendence of any great work, nor is his opinion valued farther than as regards
his capability of performing what he is entrusted to execute: the design in France is left to
the learned, and the carrying into effect to the artizan.
♫
268
BOOK I.
HISTORY OF ENGINEERING.
Of Perronet's bridges, those at Orleans, Mantes, and Neuilly, exhibit the most profound
knowledge of construction, and the principles of the art. The rise of the arches is
between a third and quarter of their span; and the manner
in which the cofferdams were formed is also deserving of
our attention; although to an English engineer there ap-
pears to be a lavish employment of material, and too much
expended upon the temporary bridges, and tackle to supply
the stone &c. for the construction of the piers.
In the bridge at Neuilly there was a novelty introduced
in the formation of the soffites of the arches, which were
shaped to suit the contracted vein of water, as formed in
the entrance and exit of pipes. This was ingeniously exe-
cuted, by making the general form of the arch elliptical, but
the headers followed the segment of a circle: thus, whilst
the elliptical arch rose a quarter of the span, the segment of
the circle had given to it a ninth rise; by this arrangement
it was supposed the flood waters obtained a better passage,
and also superior lightness of effect given to the bridge.
Mansard, Gabriel, Hupeau, Gautiers, and Perronet, by
means of cofferdams, constructed the piers of bridges on
very rapid and deep streams; and in the published works
of the latter, the engineer will find all the detail of their
operations very beautifully given. Water wheels were
usually employed to work bucket wheels, which threw up
the water as much as twelve feet, and thus kept the interior
of the cofferdams dry.
Bridge of Neuilly, on the Seine. This celebrated work was
built from the designs of M. Perronet, and was conducted
under his superintendence by M. de Chezy; it was begun in
1768, and finished in 1774, and is placed in the axis of the
palace of the Tuilleries, and the centre walk of the Champs
Elysées; the line is prolonged by the road along the rising
ground of Chante Coq, where it divides, one branch to St.
Germain, the other to Bezons.
It consists of five elliptical arches, rising a quarter, 128
feet in span.
Their springings are on a level with low
water, and there is a distance of 7 feet 5 inches between
high water and the neck of the arch. The thickness of the
piers is only 18 feet 10 inches. The plan of the starlings
is a semicircle; they are slightly curved at half their height.
Behind the abutments, the thickness of which is 35 feet
5 inches, are arches for warehouses 15 feet in span. The
roads to the warehouses are paved for a great distance,
and the slopes are sustained by walls extending 331 feet on
each side. The width of the bridge is 48 feet; 31 feet
for the road, and 6 feet 6 inches for each foot pavement. The
arches are brought to a level with the face of the bridge
by cornes de vache, terminated by the prolongation of the
arc which forms the summit of the ellipsis.
The foundations are on piles, and were pumped out by
cofferdams 7 feet 6 inches below low water; the breadth of
the mass on which the piers are built is 22 feet 4 inches; it
projects 2 feet 1 inch round the whole of the foundations.
The facings are of large squared stone, and the mass of
construction is filled in with rubble to 26 feet above low
water.
The river formerly divided into two branches at the point
where the bridge is built; one part of the island was re-
moved to enlarge the arm on the side of Courbevoie, and
the other was filled up; had not this been done, the bridge
must have been in two parts. Compared with the other
Paris bridges, the water-way is too great, and we must
regret that a work so perfect in all its details should have
so great a defect in its general arrangement. The incon-
veniences resulting from this are already perceptible, by an
evident silting up in the islands between which it is situated.


ELEVATION OF THE BRIDGE of Neuilly.
Fig. 275.
Fig. 276.
SECTION OF THE BRIDGE OF NEUILLY.
CHAP. VI.
264
FRANCE.

THE
SECTION.
C
Fig. 277.
PLAN OF COFFERDAM AT NEUILLY.
The bridge was terminated for 2,305,000 livres, and the terraces and roads cost 1,172,000
livres more.
Bridge of Horbourg, on the Ill, constructed in 1775 by M. Clinchamp, and having five
elliptical arches, rising two-fifths, from 55 feet 5 inches to 68 feet 2 inches in span. It is
not quite so flat as Ingersheim, but the general arrangement is very similar.
Bridge of Neuville, on the Ain, built in 1775 from Aubry's designs; it consists of two
elliptical arches 95 feet 9 inches in span, and is carefully constructed and decorated; the
rapidity of the water under the vaults is remarkable. It is built on a rock, which was
even excavated to obtain a solid foundation; great difficulty was experienced in constructing
the bank which abuts against it; this was carried away several times, and could only be
finished by working with great celerity when the water was low. The fall renders the
passage extremely dangerous for the floats of timber which come down the river, and which
run the risk of being broken on the rocks.
Bridge of Fouchard, on the Thouet, at Saumur, was begun in 1774, under the direction
of M. de Voglie, and finished in 1782, under M. de Limay; it consists of three segmental
arches 85 feet 3 inches span, and 8 feet 7 inches high. The piers are 12 feet 9 inches thick

Fig. 278.
ARCH OF THE BRIdge of fOUCHARD.
M
below, and 9 feet 10 inches above, and are 4 feet 3 inches below the surface, and the piers
are 17 feet high. The abutments are formed by a mass 38 feet 4 inches thick con-
270
BOOK I.
HISTORY OF ENGINEERING.
solidated by three buttresses, each 9 feet 2 inches long, and 6 feet 6 inches wide. The
section of the voussoirs is continued for a length of 13 feet beyond the opening.
The arches were raised 1 foot 1 inch higher on the working drawings. They remained
a year on the centres, at the end of which time the mean sinking of the arch was 33 inches;

المبدل بالان
=
ELEVATION.

Fig. 279.
BRIDGE OF FOUCHARD.
forty days after the centres were struck, it was 6½ inches. The parapets and the pavement
having been laid very soon after, a new settlement took place, and the parapets over each
arch assumed a slight curvature, the versed sine of which was 1 inches in 1792, and 13
inches in 1806. These settlements were accompanied with an opening of the joints of the
extrados at the springing of the arches, and are less perceptible in the middle than in
the two other arches. The vaults were placed on trussed centres, according to Perronet's
system.
Bridge of Lavaur, on the Agout, constructed in 1775. It consists of a great elliptical
arch approaching a semicircle, with a span of 160 feet 9 inches. The breadth is 38 feet 4
inches, and it has very high return walls. The thickness of the arch is 10 feet 8 inches at
the key, and is greatly the cause of the wearing away which has taken place. The
accidents cannot be ascribed to a want of strength in the abutments, which are very thick.
The sustaining walls, whose convex form tends to diminish the resistance, could not sustain
the pressure of the earth, and they have been reconstructed and consolidated on the
interior. The water-way appears too great. It is too highly decorated for its situation.
Bridge of Semur, on the Armançon, was built in 1780 by M. Dumorey; it has a single
semicircular arch 76 fect 9 inches span. The retaining walls support more than 43 feet of
earth, they are 9 feet 7 inches thick, and are strengthened by buttresses. Although there was
only a thickness of 13 feet 6 inches of earth between the parapet walls of the bridge, they
were not sufficient; large buttresses were constructed to prevent the thrusting out, which
seemed evident when the earth was only three-fourths of its present height.
Bridge of Navilly, on the Doubs, built in 1780 by M. Gauthey; it consists of five elliptical
arches rising a third, 76 feet 9 inches in span; the piers are 16 feet thick, and are elliptical
on the plan; the height of the piers is 8 feet 6 inches, and the platform is 4 feet 3 inches
was very below low water.
The curvature of the faces of the piers, and the springings of the arches, is prolonged to
the starlings, so that the water does not meet any angle or face opposed to the direction of
the current, and the contraction it undergoes in passing the bridge is as slight as possible.
The arches are constructed with coins of squared stone, the intervals being filled with
worked rubble, so as to form natural caissoons.
Bridge of Chalons, on the Saone, is an old bridge of five semicircular arches, from 42 feet
8 inches to 64 feet span, the breadth is 19 feet 2 inches. It was enlarged by Gauthey to
32 feet; above bridge the starlings were triangular, and the enlargement was effected by
cornes de vache; below they were rectangular, and archivolts were formed.
On the pro-
jecting part of the starlings are obelisks for supporting the lamps, they are set half into the
wall as high as the parapet. Besides the five great arches, there is a smaller one through
which the towing horses pass, and it would be easy, by means of a small iron balcony, to
pass the rope under the next arch, which would prevent any interruption in the towing.
Bridge of St. Maxence, on the Oise, begun in 1774, and finished 1784, after the designs of
M. Perronet; the works were conducted by M. Dausse and M. Dumoustier. It is com-
CHAP. VI.
271
FRANCE
posed of three segmental arches 77 feet, 9 inches in span, and 6 feet 4 inches high. The
thickness of the piers is 9 feet 6 inches; the abutments were to have been 24 feet thick,
strengthened by three buttresses 19 feet long, but they were carried up in a solid mass

ELEVATION.
SAINT MAXENCE, PLAN.

Fig. 280.
SECTION.

HI
FE
TH
FE
Fig. 281,
SAINT MAXENCE, ABUTMENTS,
租
​H
E
肝
​EX
GET
E
272
BOOK I.
HISTORY OF ENGINEERING.
64 feet thick, which rises to the under side of the pavement. The height of the piers
is 19 feet 3 inches, and their foundations are laid in steps which project altogether 6
feet 5 inches. The platform is laid 8 feet 6 inches below low water, which gives a total
height of 27 feet 9 inches to the springings, the thickness of the arches is 4 feet 9 inches at
the summit. The breadth of the bridge is 41 feet 6 inches; the arches were turned on
trussed centres, according to Perronet's system.
The piers are not as usual a solid mass; they, as well as the half piers attached to the
abutments, are composed of two groups of columns, leaving a space of 9 feet 7 inches
between them. The base of the interval is formed by a reversed arch, and the top is
covered by a lunette, which penetrates the vaults of two adjacent arches. The courses of
each column are formed by pentagonal newels, which occupies the centre, and five stones
cut like wedges applied to each side of the newels; an iron rod passing through the axis
of the column traverses the newels from top to bottom; the wedges are united to one
another, and to the newels, by cramps; the courses are bolted together, the five first courses
of voussoirs, the fourteenth, fifteenth, and twenty-sixth rows are entirely cramped; in the
other courses, except the twenty-eighth and the keys, the faces only are cramped. During
the construction, advantage was taken of the force of the current to drive the piles, so that
there were only three men to each engine, and the stones were raised by cranes.
The arch adjoining the left bank was blown up in 1814, but was not entirely destroyed.
On the upper side of the bridge a zone 8 feet 6 inches wide remained, in which the voussoirs,
especially at the summit, were fractured and displaced. The middle arch had suffered a
slight settlement of 3 inches on the upper, and 63 inches on the lower side, in consequence
of which the joints opened at the intrados of the summit, and the extrados of the
springings. The group of columns to the first pier have
of columns to the first pier have gone over inch up the stream,
and 1 inch down it. The arch on the right bank was not injured.
After having strutted the pier, the arch was restored by constructing in succession a first
zone to the front arch, a second in the middle, and a third to the other front, replacing that
which remained after the explosion. Some of the voussoirs were left out to be placed after
it had settled; the whole was finished in 1816, and the details, which are extremely in-
teresting, are given in the "Etudes pour l'Art de Construction," by M. Bruyère.
Bridge of Rumilly, on the Cheran, built in 1785 by M. Garella, consists of a semicircular
arch 128 feet in diameter; the springing is 10 feet 8 inches below low water. The width
is only 23 feet 5 inches. This is the largest semicircular arch constructed in France during
the last century.
Bridge of Vizile, on the Romanche, constructed by M. Bouchet, on the road from
Grenoble to Briançon. It consists of a single elliptical arch 137 feet 5 inches in span, and
38 feet 4 inches high. The thickness of the keystone is 6 feet 4 inches, and that of the
abutments 32 feet.
Bridge of Lempde, on the Alagnon, built 1785, by M. Mauricet, is an elliptical arch
101 feet in span.
Bridge of Homps, on the Aude, constructed 1785 by M. Ducros, consisting of three seg-
mental arches, one-sixth of a circle, with a span of 70 feet 2 inches; the arch on the faces
is flatter than that of the centre of the vault, and small cornes de vaches are constructed,
which terminate on the crowns of the starling.
Bridge of Chateau- Thierry, on the Marne, begun 1765, finished 1786, after a design by
M. Perronet: it consists of three elliptical arches rising a third, 51 feet 2 inches and 47 feet
3 inches in span; the breadth is 35 feet 2 inches; the thickness of the piers is 14 feet
4 inches, and that of the abutments, which are strengthened by return walls, is 15 feet.
The foundation is laid on a frame of carpentry, supported on piles 13 feet 7 inches below
the springing of the arches; the thickness of the keystone is 4 feet in the centre arch, and
3 feet 9 inches in the two others.
Bridge of Mazères, on the Lers, built in 1787, by M. Pertinchamp; it is composed of an
ancient segmental arch, 70 feet 2 inches in span, and two modern semicircular arches,
44 feet 7 inches and 48 feet 6 inches in span. They are decorated with an archivolt, and
the pier, which has no starlings, is faced by pilasters. The decorations have a tolerably
good effect, but the omission of starlings is in most cases attended with inconveniences.
Bridge of Chavannes, at Chalons-on-the-Saône, constructed in 1787, at the extremity of
one of the faubourgs, by M. Gauthey. It consists of seven elliptical arches, rising a third,
42 feet 8 inches in span; the height of the piers is 8 feet 6 inches, and the thickness 15 feet,
the width is 32 feet.
The situation not permitting the pavement to be sufficiently elevated, high floods rise to
the key of the arches, and in order to compensate for the diminution of water-way the river
undergoes in rising, oval openings 8 feet 6 inches wide are made in the upper part of the
piers. The foundation is a coarse gravel, so compact that the piles could not be driven
more than 4 feet 3 inches into it. Constructions raised on such soils being very liable to
settlements, a timber platform was placed under the bridge, 52 feet 6 inches wide, and
3 feet 3 inches thick, the upper surface being 3 feet 3 inches below low water.
CHAP. VI.
273
FRANCE.
Bridge of Rosoi, on the Hyeres, erected in 1787, from a design by M. Perronet, and con-
sisting of two segmental arches equal to one-sixth of a circle, 25 feet 6 inches in span; the
thickness of the abutments is 12 feet 9 inches, and that of the pier 6 feet 4 inches; the
thickness of the keystone is 3 feet. The arches and facings are of very hard sandstone
carefully dressed; the breadth is 35 feet 2 inches.
Bridge of Brunoi, on the Hyères, constructed in 1789, and, like the preceding, from
M. Perronet's designs; it consists of three arcs equal to one-sixth of a circle, and 19 feet 2 inches
The thickness of the piers is 3 feet 9 inches, and that of the abutments 10 feet
in span.

SUSASSSS
25252525252525
ELEVATION.
SECTION.
Fig. 282.
BRIDGE OF BRUNOI.
8 inches; the springings of the arches are 7 feet 5 inches above the last set-off; the
thickness of the keystone is 21 feet. The bridge is entirely constructed of squared stones,
and the foundations are laid on a platform 3 feet 3 inches thick; the total width is 30 feet
4 inches.
Bridge of Louis XVI. at Paris, begun 1787, and finished 1791, from M. Perronet's design.
It has five segmental arches of 75 feet 9 inches, 85 feet 3 inches, and 94 feet span: the per-
pendiculars are 6 feet 4 inches, 8 feet 9 inches, and 9 feet 9 inches. The thickness of the
piers is 9 feet 6 inches. The starlings are formed by columns 9 feet 6 inches in diameter,
rising to the cornice; three-fourths of their radius are, however, hidden within the piers.
The abutments are 51 feet 3 inches thick. The width of the bridge is also 51 feet 3 inches,
and each footway is 8 feet wide. The thicknesses of the keystones are 3 feet 2 inches,
3 feet 3 inches, and 3 feet 8 inches, not comprising 10 inches for the prolongation of the
lower part of the architrave.
The springings of the arches are 19 feet 2 inches above low water. The piers and abut-
ments are built on steps with a projection of 6 feet 4 inches. The platform is 5 feet 6
inches below low water. The stone was from the works at Gare and the ruins of the
Bastille.
This bridge was constructed and decorated with the greatest care. The elevation is
crowned by an entablature supported on modillons; the parapet is formed of balusters.
Above the starlings of each pier are square socles intended for the support of iron obelisks,
but for which colossal marble statues have now been substituted. It is to be regretted that
their proportions, as well as those of the pedestals, are too large. In the bridge of St.
Angelo at Rome this point is much better attended to.
Bridge of Gignac, on the Herault, begun 1777, finished 1793, by M. Garipuy: it consists,
of two semicircular arches 83 feet in span, with cornes de vache, and a great elliptical arch
rising a third, 160 feet 9 inches in span, on piers 8 feet 6 inches high, ornamented with an
archivolt: their thickness is 25 feet 7 inches.
Bridge at the union of the Southern Canal with that of Narbonne. The bridge is built at
the point where the southern canal makes an elbow, so that it is the means of uniting three
branches of canals and three of roads.
The arches are arcs of circles, in order to accommodate the towing-paths of the canals.
The faces of the bridge are curved to facilitate the junction of the roads.
M. Belidor has described a similar bridge situated at the junction of the Ardres and
Calais canals, which unites four arms of canals and four of roads. The arches are semi-
circular.
Bridge of Herault, on the road to Nice. This arch, designed by M. Grangent is 105
feet in span, and 19 feet high; both extremities are on the rock.
T
274
Book 1.
HISTORY OF ENGINEERING.
Bridge of Nemours, on the Loing, constructed by M. Boistard from designs by M. Per-
ronet. It was completed in 1805, and has three segmental arches 53 feet 3 inches in span,
and 3 feet 9 inches high. The thickness of the piers is 7 feet 2 inches, their height 13
feet 10 inches above the water, and 19 feet 2 inches above the platform. The footings pro-
ject 3 feet 2 inches all round. The thickness of the abutments is 16 feet 10 inches, and
they are consolidated by three buttresses 17 feet long, and 6 feet 4 inches thick. The
thickness of the keystone is 3 feet 2 inches. The width of the bridge is 41 feet 6 inches.
This work was constructed with the greatest care, and notwithstanding a considerable
flattening of the arches, no settlement manifested itself. M. Boistard has published some
experiments which he made during its progress, and on the effect of the machines used in
pumping out the water.
Bridge on the Road of the Simplon consists of two bays 42 feet 8 inches in the opening.
They are built partly on a rock and partly on a pier from 20 feet to 23 feet thick and 95
feet high. This arrangement was adopted in order to afford an opportunity of breaking it
down in case of war; otherwise the rocks might have been united by a single arch 98 feet
5 inches in span.
1
Bridge over the Ravines of the Côte de Maires.
This as well as other bridges of the same
kind was built on the road from Viviers to Puy. The two arches, placed one above the
other, are from 33 feet to 40 feet high. Although constructed of granite and basalt, they are
considerably decayed; for after floods the ravines which they traverse bring down masses
of rock from 10 feet to 12 feet square, which break the stone, and in some cases carry it
away. In such localities it would be infinitely preferable to raise a thick wall to block up
the valley, which is soon filled up with debris. The water then falls in cascades to the
bottom of the wall, which, being founded on the rock, cannot be injured.
Bridge of Roanne, on the Loire, was begun in 1789. It consists of seven elliptical
arches rising a third, 76 feet 9 inches in span. The thickness of the piers is 15 feet, and
the bridge is further strengthened by a general ground-work 3 feet 3 inches thick, and 3
feet 3 inches below low water, composed of a bed of beton, 2 feet 1 inch thick, which was
suffered to harden for a year previous to covering it with masonry. Above and below it
rows of piles were driven, and, in addition, on the lower side a jetty of rubble was con-
structed, 8 feet 6 inches deep, maintained in the same manner. The width of the bridge is
38 feet 4 inches, 25 feet 7 inches for the road, and 5 feet 10 inches for each footpath.
There were formerly two wooden bridges, separated by an island, which have been suc-
cessively carried away: one arm being in a great measure filled up, and not allowing a
sufficient water-way, the bridge which crossed it was destroyed by a flood. The other
shared the same fate a few years after, from the effects of a bar formed by poplars, which the
river brought down in great numbers.
Bridge of Bellecour, on the Saône at Lyons, begun at nearly the same time as the prece-
ding. It has 5 elliptical arches, 68 feet 2 inches in span.
It is situated in a very con-
tracted part of the river, where the depth was from 16 to 20 feet below low water, It was
built by caissoons, and the piles are cut off 9 feet 10 inches below the surface.
Bridge of Montlion, on the Durance, commenced in 1805 by M. Delbergue-Cormont; it
is a single elliptical arch, rising one-fourth, and 101 feet 8 inches in span. On one side the
foundations are on the native rock, and on the other on piles.
Bridge of St. Diez, on the Meurthe, constructed from designs by M. Lecreulx, and
consisting of three segmental arches, 39 feet 4 inches in span, and two small semicircular
arches 13 feet span. The height of the first is 3 feet 3 inches. It is raised on piers 5 feet
3 inches both in height and thickness.
Bridge of Montélimart, on the Roubion, is on the road from Lyons to Marseilles, and
consists of three elliptical arches 63 feet 11 inches in span. Its width is 28 feet 9 inches.
Bridge of Maligny, on the Serin, built by M. Werbruge. It consists of a nearly semi-
circular arch, 84 feet 3 inches in span. The foundation is 4 feet below low water; it is
entirely rubble, from 3 to 4 inches thick, and from 10 to 11 inches long, chisel-dressed,
and squared like regular masonry.; the waste was great, the stone being reduced to one-
half its original bulk. To prevent the centres from starting at their summits during
the construction of the arch, and to avoid loading them, the arches were begun in different
places, and were locked together by three keys; they remained fifteen days on the centres.
The bridge was solidly built, but the form has become slightly altered, the two heads having
started from their original position, and assumed a curvature of 7 inches perpendicular.
Bridge of Rieucros, on the Douctoire, begun 1770, finished 1790, by M. Garipuy. It
consists of three elliptical arches, 55 feet 5 inches in span; the piers have no starlings.
Bridge of Mireppis, on the Lers, also the work of M. Garipuy, was begun 1776, and com-
pleted 1790. It has seven arches, one-sixth of a circle, 64 feet span. The plan of the
starlings is a mixtilineal triangle: the width is 25 feet 6 inches; the foundations are 19
feet 8 inches deep, on a solid soil.
Bridge of Frouart, on the Moselle. This fine bridge was constructed in 1788, by
M. Lecreulx, to replace an old one which had been founded at the level of low water, and
CHAP. VI.
27.5
FRANCE.
was carried away by a flood in 1788.
It consists of seven elliptical arches, with a span of
64 feet, and rising between a third and a fourth; the thickness of the piers is 13 feet 10
inches; the plan of the
starlings is semicircular,
and they have a flattened
spherical top.
The abutments are
formed of a mass 35 feet
2 inches thick, and 47 feet
wide; the width of the
bridge is 32 feet. The
foundations were laid by
means of cofferdams, on a
platform 6 feet 6 inches
below low water, and were
surrounded by a row of
piles; the soil is a solid
gravel; the arches were
constructed on trussed
centres. It cost about
440,000 francs.
In placing the voussoirs
around the elliptical arches,
a greater depth was given
to those of the upper part,
which formed the flattest
portion of the arch, or
rather those which had the
longest radius. We find
that most of the bridges
erected at this time in
France had the depths of
the voussoirs proportioned
to their several radii: the
very reverse of this system
was adopted by Mr. Ren-
nie in those he built over
the Thames; that able en-
gineer gave the greatest
length to those voussoirs
which commenced the arch,
and gradually diminished
it towards the key. We
shall find, by a comparison
with one of the arches of
London Bridge, that in
our present example this
difference is very evident;
but those we shall describe
afterwards in France are
constructed in a different
manner, and several writers
upon bridges point out
the necessity of doing
what was, perhaps, first
practised in England, viz.
that of placing the first
voussoir upon an inclined,
in preference to a horizon-
tal bed, as was commonly
done by such an arrange-
ment, there was less pro-
bability of the whole
sliding off the pier, or
along the abutment, and
the pressure of the arch
was delivered below the springing.


ELEVATION.
PLAN.
머
​SECTION.
Fig. 263.
BRIDGE OF FROUART ON THE MOSELLE
T 2
276
BOOK I.
HISTORY OF ENGINEERING.

Fig. 284.
BRIDGE OF FROUART.
Bridge of Rouen, on the Seine: the remains of a stone bridge built by Matilda, wife of
Henry II., Duke of Normandy and King of England, about 1160, are still visible at
Rouen. It was 480 feet long, and composed of thirteen arches; several of these having
fallen, and others carried away, the thoroughfare was closed in 1564, and in 1626 it was
replaced by a bridge of boats.
The new bridge was decided upon in 1810. The designs were made by M. Lemasson,
and the work begun in 1811. In 1812, it was placed under the direction of M. Lamandé,
who proposed several changes, the chief of which related to the manner of founding the
piers.
It consists of two equal parts, which may be considered as two distinct bridges, separated
by a circular mass which forms the lower extremity of the island of La Croix. They are
not in a line with each other, their axes comprising an angle of 146°, which arrangement
was adopted in order that the two bridges might be perpendicular to the current of
the two arms of the river, and directed to the points of commencement of the two new
roads.
Each bridge consists of three segmental arches. The span of the middle one is 101
feet 8 inches, and the versed sine of the arc of the intrados 13 feet 9 inches. The span of
the lateral arches is 85 feet 3 inches, and their versed sine 10 feet 7 inches. The spandrils
are decorated by a semicircular niche, placed over each pier. The springings are 16 feet
9 inches above low water. The thickness of the arches 3 feet 5 inches. The piers, ter-
minated by semicircular starlings, are 10 feet 5 inches thick at the springings, and 11 feet
10 inches at the base. The width of the lowest course of footings is 16 feet 8 inches; the
piles which support it are cut off 9 feet 9 inches below low water. The abutments are
formed by a mass 59 feet thick and 60 feet 9 inches wide, in the middle of which an arch is
constructed, 13 feet span, and 12 feet 4 inches high to the key-stone. This mass was founded
on piles 3 feet 6 inches below the surface. The cornice on each side has a fall of 1 in
34 from the middle of each bridge, which slope extends to the approaches. The
total width is 49 feet 2 inches, of which 29 feet 6 inches is for the roadway and 7 feet
10 inches for each foot pavement. The embankment required was nearly 16 feet in depth,
and extended to the houses.
The abutments were founded by cofferdams, on piles 39 feet 4 inches long, 4 feet 3 inches
apart they are defended by a row of piles touching each other. The depth at low water
is 28 feet 6 inches, and the side rises about 6 feet 6 inches. The piers were founded by
caisscons on piles 49 feet 2 inches long, and 3 feet 3 inches apart.
The foundation is surrounded by a row of piles touching each other, retained by bands;
it is farther strengthened by a similar row 5 feet 2 inches wide, forming a starling round
the piers, the heads of which are 19 feet 8 inches below low water. The interior both of
the piers and the starling was dredged, and filled with concrete, and the exterior defended
by rubble work.
The arches were placed on fixed centres formed by three pairs of principals, supported
by two rows of piles.
Bridge of Sevres, over the Seine, on the road from Paris to Versailles, was designed by
CHAP. VI.
277
FRANCE.
M. Becquey de Beaupré, and executed by M. Vigoureux; it was finished in 1820, allu
consists of nine principal semicircular arches, 59 feet in span, and two
lesser 16 feet 4 inches in span for the towing path. The thickness of
the piers is 11 feet 5 inches; the width of the bridge 42 feet 7 inches.
It occupies the situation of an old wooden bridge, and the axis is in |
the direction of the dome of the Invalides. The piers were founded
by means of caissoons. The arches were constructed on trussed
centres, which did not change their form during the placing of the
voussoirs.
All the arches were keyed in July, 1815, except the first on the
right bank, where there still remained fourteen courses of voussoirs to
place, when orders were given to break down the bridge, and the
centre of this arch was first set on fire, and the fourth blown up by
two discharges, which caused the rupture of some of the inner
voussoirs of the arches, and it was afterwards discovered that settle-
ments had taken place in the third, fourth, fifth, and sixth piers, the
greatest of which was 23 inches. In 1818, the sixth pier was loaded
with 112 tons, without any movement resulting; it was thought fit,
however, to discharge the weight by means of arches in the piers.
The foundation piles were 3 feet 11 inches apart, and each carried a
weight of fifty-two tons; the voidings, however, diminished this weight
by about five tons and a half. A general foundation was also con-
structed by throwing in rubble. The settlements are attributed to
the effect of the explosions; but they would not, perhaps, have taken
place had the piles been less loaded, or the intervals between them
been filled in with hydraulic masonry to a height of 6 or 8 feet
between the ground and the tops of the piles, instead of with ma-
sonry laid in common mortar, which does not harden under water.
In this beautiful example, the roadway is kept perfectly level
throughout, and the arches are all of the same span; this was ren-
dered necessary, as the banks on each side of the river were low, and
it was not deemed advisable to raise the crown of the roadway, which
might have been done on the Paris side, but towards the town of
Sevres, it would have been more difficult to accomplish, as the
houses on each side of the street, and the entrance to the royal park,
would have been equally inconvenienced. The piers, all of the same
dimensions, are of great strength, their width being nearly equal to
a fifth of the span of the arch.
The faces of the voussoirs, which are rusticated and rounded,
increase in depth towards the springing; the effect is improved by this
arrangement, and we have an additional strength given where it is
most required.
For the piers, abutments, and arch stones, the best stone which
could be obtained was made use of, and apparently the atmosphere has
produced little change upon it: as the stones laid in the quarry, so
are they bedded, and their dimensions and proportions are well defined
for their respective situations. In the spandrills and wing-walls,
there does not appear to have been sufficient attention paid to the
backing, and inferior material is said to have been used.
This bridge, which has a decidedly Roman character, is one of the
best where semicircular arches have been preferred to the elliptical;
the same centre would serve for all the arches, and there is some
economy in such an arrangement; but the piers occupy together
upwards of 90 feet, while the breadth between the abutments or
water-way does not exceed 622 feet: by the adoption of a flatter
arch, fewer piers would have been required, and consequently more
water-way would have been obtained: but the whole is deservedly
much admired, and its design seems in harmony with the scenery
around, and with the character of the river: over a stream where
the tide rose considerably, or the navigation was more important, a
bolder design might have been introduced.
The elevation and section through the piers show its solid con-
struction, and the form also of its starlings: over the arch are well
contrived drains, which lead off the waters that fall upon the road-
way, and conduct them behind the spandrills into the stream below:
the blocking course, which forms the parapet, is supported upon a
bold block cornice, and the absence of all balustrade and railing

BRIDGE AT SEVRES.
~ Fig. 285
T 3
278
BOOK I.
HISTORY OF ENGINEERING.

Fig. 286.
PIER OF BRIDGE AT SEVRES.

Fig. 287.
SECTION OF BRIDGe at sevRES.
greatly adds to the effect of the structure.
The roadway is paved throughout, and at the
sides beyond the water channel is a footway, laid with a gentle inclination.
Bridge on the Serrière, near Neufchatel, constructed by M. Ceart; the foundations are on
a rock, and it consists of a semicircular arch 69 feet 3 inches in span. The thickness of
the arch is 5 feet 2 inches; that of the abutment, which does not rest against the rock, and
which forms a pier 14 feet 1 inch high, is 16 feet 5 inches. This bridge, 26 feet 3 inches
wide from one head to the other, is a good example of bridges of one arch constructed
over small rivers in the departments of France: the engineers cotemporary with Ceart, and
particularly those who, like him, had studied the Roman remains in Provence, seem to
have universally adopted the semicircular form for their arches, and to have constructed
their abutments with great solidity: the refinements which have been introduced in modern
times have greatly economised material, the thickness of the voussoirs at the crown has also
been reduced. Boistard and Berard have pointed out how erroneous it is to consider the
strength of an arch as dependent upon the weight of its key-stone: the great depth in the
present example is an unnecessary load, and by its adoption every other portion, down to
its abutments, has been proportionably increased, without the whole acquiring any ad-
ditional strength.
CHAP. VI.
279
FRANCE.
The
Bridge of the Military School, formerly bridge of Jena, on the Seine at Paris, is situated
in the prolongation of the axis of the Military School and of the Champ de Mars.
erection of a bridge in this situation was decided on in 1806,
the arches of which were to have been of cast-iron; but in
1808, Lamandé obtained permission to execute it on the
present design, which is composed of five equal segmental
arches, 91 feet 10 inches span, and 10 feet 9 inches high.
The thickness of the arches is 4 feet 8 inches; their spring-
ings are 20 feet 1 inch above the surface. The piers are
9 feet 10 inches thick, and have semicircular starlings; they
were founded by caissoons on piles cut off 5 feet 4 inches
below the surface, and 3 feet 9 inches apart. The abutments
are formed of a mass 49 feet 2 inches thick, and 59 feet wide,
13 feet 1 inch high at the level of the springing, of rough
stone, bonded horizontally and vertically. The width of the
bridge is 46 feet, that of the road-way 30 feet 7 inches,
and of each footway 7 feet 10 inches; it is crowned by a
level cornice supported on consoles. There are at the
entrance four pedestals for equestrian statues.
The arches were constructed on centres formed by three
courses of principal timbers, disposed according to the system
of M. Perronet, but strengthened by two rows of piles.
The motion of the arch during the placing of the voussoirs
was scarcely perceptible. The centres were easily struck
by first removing the struts applied against the piers, and
then the intermediary piles. The total sinking of the arch
was at most 6 inches.
The semicircular arch having its springing upon the hori-
zontal line, or diameter, its load or weight acts perpendicular,
or in the direction of its gravitation, and it has not that ten-
dency to spread and exert a lateral thrust, and consequently
does not require such solid abutments, as that which is the
portion of a circle or a segment; but the semicircle cannot be
always introduced, as its height would require that all the ap-
proaches should be elevated, and where the banks of a river,
as in the present instance, are low, it is not very practicable.
The segmental arch obviates this objection, and also can
be executed with less material, but the lateral pressure being
augmented, more consideration is required for the strength
of the abutments; in an arch of this description, the thrust
increases as the angular measure of the length of the arc
diminishes. The arches of the bridge of Jena are very
nearly those produced by the side of a hexagon, and its
portion of the circle: they seem to have been set out by
striking a curve round one side of an equilateral triangle,
which is as flat a segment as has hitherto been introduced.
The horizontal thrust of such an arch requires a provision
not only that it may bear its own weight, but also any
which may be added to it; the piers may be made light,
where the arches comprise only sixty degrees, as the weight is
carried to the extremities. In the five arches of this ex-
ample the abutments received the greatest attention; their
thrust, it was considered, acted upon the two extremities of
the bridge, where the masonry was sufficiently strong to resist
it. The flatter the arch or the greater the segment, the
less width is required to be given to the piers, but the
masonry saved in the piers must be given at the abutments.
During the occupation of Paris by the foreign powers in
1814, the Prussian army were desirous of destroying a
monument consecrated to one of Napoleon's most brilliant
victories, and preparations were made for undermining the
lower part of the piers; but this act of barbarism was coun-
termanded, and the evidences of it have since been effaced.
The bridge of the Ecole Militaire combines both sim-
plicity and elegance, and may be considered to possess the
highest degree of beauty that can be imparted to con-
structions of this description.

Fig. 288.
BRIDGE OF JENA.
T 4
280
Boor L
HISTORY OF ENGINEERING.

Fig. 289
SECTION OF BRIDGE OF JENA.

Fig. 290.
BRIDGE OF JENA.
Bridge of Bordeaux, on the Garonne, consists of seventeen stone arches resting on sixteen
piers and two abutments. The length between the abutments is 1590 feet, and the width
48 feet 6 inches. The arches are segments of circles, whose versed sine is one-third of the
chord. The seven middle arches, which are equal, are 86 feet 11 inches span, and the five
first on each side are successively 68 feet 10 inches, 72 feet 6 inches, 76 feet 1 inch, 79 feet
8 inches, and 83 feet 3 inches. The thickness of the piers at the springing of the arches is
13 feet 9 inches.
The Garonne has a general depth of 22 feet, and in some places of 33 feet at low water.
The tide rises twice a day to 13, 16, and even 20 feet above this level. The currents in
both directions have occasionally a velocity of more than 10 feet in a second. The river
flows over a bed of sand and mud easily displaced. The borings gave a resisting soil at
39, 49, and 52 feet below low water. Two hundred and fifty fir piles were driven under
each pier, and cut off 12 feet 3 inches below low water with a circular saw.
Before the piles were driven, a large frame was sunk 1 foot 6 inches below the plane of
cutting off, to regulate their position and their distances apart, formed of strong pieces of
timber placed longitudinally and transversely; the stones which fill the spaces between the
piles, from 3 feet 3 inches to 8 feet 2 inches above the bottom, kept the heads of the piles
steady, and are levelled even with the foundation. All the bases of the piers, and the
water-way under the arches, are covered with a pavement of rubble work, the stones which
compose it being enveloped by the mud which is deposited in their interstices, presents,
as the experience of fifteen years proves, a mass impervious to the erosive action of
water.
The masonry of the piers was raised in a caissoon of a pyramidal form at the base, and
the upper part of the sides rising vertically to a height of 25 feet 10 inches above the plane
of the heads of the piles with a length of 78 feet 8 inches, and a breadth of 27 feet 2 inches
at the level of the same plane.
CHAP. VI.
281
FRANCE.
The centres for the arches were composed of fifteen pair of principals, each of which
formed as it were a single voussoir; the pieces were put together on two boats united and
raised in a body by means of crabs placed on the scaffold of the piers. By this simple and
economical process the whole centre of an arch 86 feet 11 inches in span was placed in three
days.
Before the arches were commenced the piers were proved by loading each with a weight
of 3924 tons, in the form of a pyramid composed of stone blocks and rubble; the weight of
the arches was also diminished by lightening the internal mass of the tympanum and
every portion that was not necessary for the stability of the extrados, by constructing
galleries the lengthways of the bridge; these again were traversed breadthways by vaults
of the same form and span. These precautions effected a diminution of 3280 cubic feet
in the weight borne by the piers; greater facilities were thus afforded for examining the
interior of the bridge, ascertaining if any filtrations or settlements had taken place, and
making any requisite repairs.
this
Squared stone and brick were both employed in the masonry; the archivolts are entirely
of freestone, and they are united by rows of voussoirs in horizontal lines, so as to form
caissoons filled with brick; the heads are relieved by openings, in order to facilitate the
passage of the various substances carried down by the rapid currents of floods, which,
without great precaution, might seriously injure the arches. The Garonne rises occasionally
to very great heights; in 1770, the increase was more than 23 feet above low water
required an extraordinary elevation to be given to the bridge, which, added to the ne-
cessity of uniting two banks sometimes 3 feet under water, have prevented the causeway
from being made entirely on the level, which is only maintained over the seven middle
arches and half of the two next; the remaining portion has a fall of about one in
eighty.
Quay walls, 574 feet long, are retained on each side of the abutments, at the ex-
tremities of which steps descend to the river. The river forming too great an elbow just at
the bridge a dyke has been raised on the right bank above bridge, of rubble work, 16,404
feet long; in some places 46 feet high, and more than 98 feet base. Its effects were such
that in a few months the bar called "la Manufacture" was entirely removed. The bed of
the Garonne was deepened on the left bank, and the property on the right bank increased
by a clayey deposit of 100 hectares in surface, of which several portions are now covered
with vegetation and plantations, and some are under cultivation.
Since 1820, a diving-bell has been used for any repairs that might be required in the
rubble work, and its general stability has thus been satisfactorily ascertained.
Bridge of Libourne, on the Dordogne, consists of nine semicircular arches, each of 65 feet
7 inches span, resting on eight piers 12 feet 6 inches thick at the springing. All that has
been said of the bridge of Bordeaux, both as to form and system of construction, applies to
that of Libourne. The piling, the frame, the rubble work, the caissoons, the centres, the
voussoirs, the mixture of brick and stone, the voiding of the upper mass of the piers, the
double slope from the middle, and the architectural decoration, were projected and executed
on the same principles. The roadway on this bridge like that at Bordeaux is formed by a
brick arch carrying masonry laid in hydraulic mortar, covered with a dressing of broken
stones.
The footways at Bordeaux are paved with small pebbles of different colours laid in con-
crete, forming lozenged-shape compartments. Those of Libourne are paved with brick
laid flat in mortar. Each entrance of both bridges has two lodges, one for receiving toll,
the other for the police. Their architecture is simple; those at Bordeaux are ornamented
with a porch formed by two pilasters and two columns.
The foundation piles at Bordeaux and Libourne were shod, for the first time, with conical
cast-iron shoes, with a wrought axis in the centre; this method has since been employed in
several great hydraulic operations in France, on account of the resistance it affords, and its
great economy.
The two bridges were built from the designs and under the direction of M. C. Des-
champs, inspector-general of the Ponts et Chaussées.
The Pont du Louvre, or des Arts, was the first iron bridge constructed in France under
the auspices of M. de Cessart, inspector-general of the Ponts et Chaussées, and its execution
was confided to M. Didon. It is composed of nine arches, each measuring between the
piers 56 feet 8 inches, the piers being 6 feet 6 inches in width.
The arches are composed of five ribs, placed about 6 feet 8 inches apart; the ribs are cast-
iron, 6 inches deep, and about 3 inches wide, formed in two thicknesses. The chord of the
arch is 60 feet 8 inches, and its versed sine 12 feet.
When iron was first applied to bridges in France, its properties were by no means
understood by the engineers; they, in general, attributed to it a greater strength than it
possessed, and consequently the first constructions in this material were very faulty and
defective: what had been executed in England they greatly admired, and were anxious to
imitate, but the cost of iron being much higher in France, they adopted too strict an
282
BOOK I.
HISTORY OF ENGINEERING.

Fig. 291.
BRIDGE of the Louvre.

་
•
SECTION.

Fig. 292.
PLAN.
CHAP. VI.
283
FRANCE.
economy in its application, and some of their first iron bridges over the Seine gave way,
or were afterwards remodelled or removed.

Fig. 293.
BRIDGE OF THE LOUVRE.

Fig. 294.
BRIDGE OF THE LOUVRE.
Poyet, an architect of considerable eminence, who gave the design for the beautiful
façade of the Chamber of Deputies, turned his attention to constructions of iron, and
laboured much for its general introduction.
This foot-bridge has been greatly admired for its lightness; but, as constructed in the
first instance, its strength was not found sufficient, and some upright supports were added;
the alterations made are shown by the additional strength given to the ribs and platform
above; and also by the diagonal braces of iron introduced in the outer divisions.
Pont du Jardin du Roi, at Paris, commenced in the year 1800, and finished six years after-
wards, was designed by M. Lamnande. It has five arches, resting on stone piers, 9 feet
10 inches in width, and 21 feet in height, above the level of the water. The arches are
parts of circles, the chord of which is 105 feet, and the versed sine 10 feet. There are
seven ribs at the distance of 7 feet apart, formed of a series of voussoirs, 4 feet 9 inches
long, attached to each other by a number of wrought iron bolts.
The spandrils are filled with other frame-work, composed also of portions of circles,
united by radiating and upright piers of iron: the principals are connected with rods of
cast-iron. The timber frame, or platform, which covers this bridge is gravelled, and the
footways are paved with stone.
After its construction, it was perceived that several of its parts near the abutments had
yielded, and a considerable fracture was the consequence: this gave rise to many inquiries
into the properties of the metal employed, and since that period other iron bridges have
been constructed: but there is no treatise on the subject by the French engineers. Where
stone abounds of such excellent quality, there seems to be no inclination to substitute iron
for its use and as that metal is not obtained at a very reasonable rate, it is not probable
that it will be employed so generally as in England.
The iron bridges in which the principles of timber construction have been preferred to
the introduction of the voussoirs, or the practice of the mason, are decidedly superior
in effect: the experiments of Mr. Telford to form a suspended centre for his intended
Menai Bridge gave rise to much of the constructions employed upon iron bridges in
284
Book I.
HISTORY OF ENGINEERING.
France; and no one has done more to explain the principles defined in our examples than
M. Dupin: there is yet wanting, however, such daring efforts as the Southwark Bridge;
and there has been no attempt at the construction of an arch equal in span to those of

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ELEVATION.


Fig. 295.
PONT DU JARDIN DU ROI.
stone, and the state of the iron trade in France does not promise that much will be done
with that material for the purposes of building.
After the bridge had been finished three years, its defective construction was apparent
and it became necessary to introduce a considerable addition of iron work to render it
secure, and to prevent the effects that change of temperature had produced upon the
several voussoirs.
HEA

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6000
18
Fig. 296.
Pont on the Crou, near St. Denis, was built in 1808; its span is 39 feet 3 inches, and its
versed sine 30 inches. It is composed of three principal ribs, a little more than 5 feet
apart. About nine tons of iron were used in it, and the cost was 15,879 francs.
CHAP. VI.
285
FRANCE.

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ELEVATION.
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:
Fig 297.
BRIDGE ON THE CROU.
SECTION.


Fig. 298
BRIDGE ON THE CROU.
Supply of water. Aqueduct of Arcueil, near Paris; this ancient work was repaired in
1613, by Jacques de Mosse, at the command of Mary de Medicis, Queen of Henry IV.,
who required a better supply of water at the Luxembourg, which was collected from
the neighbouring plains, and conducted by the aqueduct to the palace. Its length is
nearly 1250 feet, and its breadth 11 feet 9 inches: it is strengthened at distances of 40
feet by buttresses, between which are nine arches, each 25 feet 7 inches span; the greatest
height is 72 feet, and the whole construction, which is of squared stone, is most admi-
rable.
The fountains which embellish the gardens and public squares at Paris require a great
supply of water, and have always been distinguished for their taste; those of modern Italy
can alone compare with them. The palaces of St. Cloud, Luxembourg, Palais Royal,
Tuilleries, volumes of water are consumed for ornamental purposes, and serve to cool the
atmosphere, and render it refreshing during the warm seasons, and at all times contribute to
the beauty of the scene around: what in London is distributed for domestic comfort, is in
France exhibited in artificial display.
The Cité d'Orleans, in the Rue St. Lazare, the writer constructed, and supplied from
the Canal l'Ourq with water, laying on the same to the several houses in the manner
practised in London, introducing at the same time other luxuries not then common in
Paris. These, however, could not be rendered so efficient as in London, from the want
of the public sewers. Generally, at that time, the houses were supplied by the water-
carriers, who sought for it at the public fountains.
1688.
Aqueduct of Maintenon. This immense work was undertaken 1684, and abandoned in
The levels and calculations were made by Lahire, and the project itself is Vauban's,
who directed the construction; had it been finished, it would have surpassed in grandeur
and magnificence all ancient or modern erections of the same kind.
286
BOOK I.
HISTORY OF ENGINEERING,
span,
It was to have formed part of a canal intended to bring water from the Eure at Pongoin
to Versailles, a distance of nearly twenty-five leagues. The canal passed under ground in
several places for a length of 4233 feet. The length of the aqueduct, which was in
masonry, was 16,090 feet. It was to have presented five parts of different construction.
First, 940 feet of 17 great arches, each 41 feet 8 inches in diameter, with piers 26 feet
7 inches thick, the greatest height 83 feet. Secondly; a length of 4815 feet 9 inches in
two rows of arches, 70 in the lower row, 42 feet 8 inches span, and 140 in the upper, 18
feet 7 inches span, the piers 25 feet 7 inches thick, and the greatest height 135 feet.
Thirdly; 3203 feet 8 inches in 3 tiers of arches, the first 47 arches, 42 feet 7 inches
and 83 feet high, with piers 25 feet 6 inches thick, the height of the first row 97 feet 6
inches, of the second, 90 feet 6 inches. The third formed of little arches, two of which
corresponded to one of the lower rows, its height was 46 feet 4 inches. The piers and
buttresses were inclined. The canal supported by the third row was 7 feet 6 inches wide,
and 4 feet 3 inches deep, with footways of 4 feet. The total height was 90 feet 6 inches.
The breadth of the construction was 21 feet 4 inches at the impost of the arches of the third
row, 30 feet 10 inches at that of the second, and 15 feet 1 inch at the first. Fourthly; 5377
feet 4 inches, of 77 lower arches similar to those of the second part. Fifthly; 575 feet
6 inches, of 11 arcades similar to the first portion. The different parts of the construction
were to have been united by corkscrew staircases. The piers in the upper rows were
pierced with arches.
Forty-seven arches on the first row of the third portion were constructed. The piers are
built of very hard sandstone, and well put together. The interval is filled with masonry of
rough work, which has decayed from the bad quality of the cement. The arches are
mostly of brick, and, where care was not taken to carry the quoins through which strengthen
the piers, this decay is most evident. The whole is in a far worse state than are many of
the buildings of antiquity. Several rivers were rendered navigable, and a canal was dug
for the purpose of transporting the materials; and it is said that 22,000,000 francs were
expended in this useless work.
Aqueduct of Buc, near Versailles, was constructed to bring water from the plain of Sacle
to Versailles. It consists of two rows of arches; the upper are nineteen in number; the
lower range carries a bridge 13 feet 2 inches wide, over which the road crosses the valley,
and is continued on a terrace of earth, so that the lower arches are entirely buried. The
length is 1345 feet, and the height 42 feet 8 inches.
mill-stone, strengthened by quoins of squared stone.
place is supplied by giving a great slope to the sides.
10 inches.

The masonry of the piers is a kind of
There are no buttresses, but their
The thickness of the piers is 13 feet
Aqueduct of Marly, is intended to conduct water from the Machine de Marly to
Versailles, and begins at the reservoir, at the foot of which the machine is placed, and is
2113 feet in length; it consists of a single row of arches 25 feet 6 inches span. The piers
are also 25 feet 6 inches wide; their thickness is 19 feet 2 inches below, and 6 feet 6 inches
above. The greatest height of the aqueduct is 82 feet.
Abattoirs are buildings appropriated to the slaying of animals intended for food, collecting
and cleansing the offal, and preparing the various substances which it yields, as glue,
gelatine, oils, bone, hides, horn, &c.
It must be evident that nothing can be more injurious to health than allowing such
operations to be carried on in densely crowded districts; no where in Europe is there so
thorough a neglect of all sanitory considerations as in England; among the ancients, whom
we profess to surpass in refinement, no slaughter-houses were permitted near the market
where the meat was exposed for sale.
The Emperor Napoleon, about the year 1810, ordered five of these establishments to be
commenced at Paris, and they were executed at the cost of the city. A commission was
formed of five architects, assisted by the vice-president of the council of public works, the
secretary, and a retired master butcher, named Combault, who were instructed to examine
several plans that had been presented, and to report upon their efficiency; but eventually
M. Gauché, one of the five architects, was commissioned to furnish the designs which were
adopted.
The five abattoirs were those of Roule, Villejuif, Grenelle, Menilmontant, and Mont-
martre; their dimensions were defined by the number of persons that each district con-
tained; the two first had each 32 slaughter-houses, that of Grenelle 48, Menilmontant and
Montmartre each 64, making a total of 240.
To each of the abattoirs are attached houses for the melting of tallow; reservoirs and
water laid on by lead pipes wherever required; every means for cleansing; stables, sheds,
for the use of the butchers; inclosures for the cattle; and apartments for the superin-
tendents. A vaulted sewer receives and carries away all superfluous water; there are also
buildings for preparing tripe, trotters, &c. &c.
Scalding-house, used by the butchers for slaughtering. All the abattoirs have two or
more ranges of these, each composed of two buildings divided by a yard. The stalls where the
CHAP. VI.
287
FRANCE.
beasts are knocked down are formed of walls of wrought stone, and are 16 feet wide, and
32 feet in length: each has two entrances, one in the yard, by which the animal enters,
the other on the outer side, to permit the removal of the meat, &c. Each stall is provided
with a supply of water for cleansing, with a drain, and a windlass and pulleys, by which the
carcase can be drawn up to be flayed.
Two pieces of timber are placed across the building at 7 feet of height, fixed into
the wall at one end, and carried or supported at the other by a stirrup iron on these seven
or eight carcases may be suspended, exposed to the air previous to their being taken to
their several destinations. There are pegs and hooks around for the calves, sheep, and
lambs.
The stalls, as well as the yard, are flagged with thick stones, the joints of which are filled
with cement, that nothing offensive may pass through them. The bottom of the doors are
cut, so that the air passes under them freely. The roofs project 3 feet beyond the ex-
ternal walls, which has the double advantage of sheltering the stalls from the sun's rays and
forming a cover for the carts which remove the meat.
Sheds, for the oxen and sheep on their arrival, where they are housed previous to slaugh-
tering: they are 9 feet in width in the interior; one side is occupied by oxen, the other
by sheep, calves, &c. Large stone arches support a floor above, over which are separate
divisions for the several butchers to stow away the forage belonging to them.
on for the use of the cattle.
Melting-houses, where the fat is converted into tallow.
Water is laid
Reservoirs. An abundant supply of water and facilities for distributing it is most essen-
tial in such establishments. In the five abattoirs in Paris 75,000 oxen are slaughtered in
a year, and the mean quantity of water for the service is from 240 to 300 cube metres
per day, to provide which there are two reservoirs to each, each containing 180 cube
metres, formed in masonry, and lined with cement.
Keepers' Apartments. At the entrance of each abattoir are two small houses for the
persons who have the charge of the establishment.
Stables and Sheds, &c. are provided for the carts and horses, commodiously arranged.
Sewers. These are most carefully constructed of a hard gritty sandstone: their dimen-
sions are 3 feet in width and 6 feet in height; to prevent any smell from escaping, a
trap is introduced, which answers admirably well: there are pits for the dung, which is
removed every day. No towns of any importance on the Continent are without these
establishments, as Mantua, Lyons, Blois, Rochefort, La Rochelle, Grenoble, Brussels,
Orleans. Those at Strasburgh, Marseilles, Vicenza, &c., are of considerable extent.
Markets. The great points to be considered in these establishments are position, solidity,
convenience, and health, and in Paris it was decided that their situation should be within
the reach of the greater portion of the population of the district.

Fig. 299.
MARKET.
The strength requisite for an edifice is particularly required in one intended for the
public service, and where the slightest accident might be of great importance.
Convenience and salubrity require that all who attend should be sheltered from the
288
BOOK I
HISTORY OF ENGINEERING,
inclemency of the weather; that the arrangements should be suitable for the provisions
bought and sold; every possible means adopted for thorough ventilation, and every pre-
caution taken to maintain the most perfect cleanliness.
The walls of a market should be carried up to a certain height in masonry or brickwork:
the lower openings should be provided with Louvre boards, to exclude the sun, rain, and
wind, without too much shutting out the light and air. Other openings must be provided
under and in the roof, to afford additional light and air.
A certain width should be given to the markets, so as not to increase the extent of the
outer walls; and pillars internally should not be introduced, as they obstruct and occupy
room; where they are indispensible they should be of stone or iron, and placed as distant
from each other as possible.
The width of the building depends upon the number of stalls, which should be in pairs,
so that one walk approaches two rows.
Experience proves 6 feet 6 inches a sufficient width for the walk, and the same for the
stalls: hence a market may be in width from 6 to 7 metres, from 12 to 13, and from
18 to 20.
The four new markets constructed at Paris, of stone, are of these dimensions.
A public fountain is indispensible, and constitutes one of the chief ornaments.
The architecture should be simple, yet imposing from the mass, the arrangement, and
the proportions.
The divisions should be so arranged that all parts should be equally eligible without any
just grounds for preference; nothing should be sold out of the enclosure, that the entrances
and streets leading to it may be free from all obstructions. The whole should be shut at
night. When the market is of any extent certain accessories are requisite, as vaults, &c.,
for warehousing unsold goods. The market at Naples is a large square, with a semicircular
termination on one side: the butchers' stalls are arranged around it. Those at Florence,
Bologna, and Rimini are admirably contrived, and answer their purpose effectually.
Marché Saint Gervais was built to supply the place of another, which was not open, in the

الماااا
Fig 300.
ROOF OF A MARKET.
Place St. Jean. It was originally intended to have had stalls for the use of those who
attended; but such divisions being found destructive of the good effect and an impediment
to that free intercourse so necessary for those who attended, the idea was abandoned.
M. Labarre was the architect, and the structure is in every way highly commendable,
being well ventilated, and affording convenient and easy access on all sides.
CHAP. VI.
FRANCE.
289

:
The markets first established were
held in an open square, or in the streets,
and it was not until about the latter end
of the last century that any were covered
in the advantages derived by all that
attended were so great, that Napoleon
ordered arrangements to be made for
erecting structures which should exclude
the inclemencies of the weather, and be
convenient to both buyer and seller.
Paris set the example to other great
communities, and hence an important
and beneficial change has been effected
in these establishments throughout Eu-
rope.
L
Fig. 301.


IIIIII
TTTTTTT


Fig. 302.
MARKETS.
Marché Saint Martin was rebuilt on an ancient site between the Rues St. Denis and
St. Martin, a few years since, and is an admirable example of its kind. It entirely covers
the garden of the old convent, now appropriated to the reception of various models, and
known as the Conservatoire des Arts et des Metiers.
The garden was bounded on three sides by the convent walls, affording a favourable
situation for a market. M. Peyre, the architect, was instructed to design a suitable
structure, which being approved was carried up under his superintendence.
Marché Saint Germain was erected from the designs and under the superintendence
of M. Blondel, and is the most important in Paris.
Other smaller markets have been established in imitation of that at Florence, in various
parts of the city, and in most of the towns throughout France. Great taste has been dis-
played in these structures, and the manner in which they are covered is highly creditable
to the engineers, who have displayed a thorough knowledge of ventilation. They are
therefore peculiarly worthy of our attentive

study.
Every large town in France has its market,
conveniently situated, and of dimensions pro-
portionate to the number of its inhabitants.
Vegetables, fish, meat, flowers, all have either
a portion set apart, or a building devoted
entirely to them. The timber roofs, and in
some instances iron, span the entire area; and,
when covered with ornamental tiles, produce
an elegant effect; they are always lofty, well
ventilated, and sufficiently supplied with water.
Italy seems to have afforded the model for
most of these structures; arches resting on
columns, with a simple and bold projecting
cornice, all kept within the laws of proportion,
Fig. 303.
MARKET.
constitute their ordinary design. Their entire area is paved, and, mounted upon a bold
plinth, are easily cleansed.
U
290
を
​Fig. 304.
HISTORY OF ENGINEERING.
O
O
ELEVATION.
O
PLAN OF MARKET.
Book I.


The Bourse at Paris, erected from the designs of M. Brogniart, and completed by
M. Labarre, is a fine model for an exchange, where the public business of a large com-

배미
​Fig. 305.
mercial city is to be carried on.
PLAN OF bourse.
The external character is that of a Greek temple, having
fourteen columns at each end, and twenty at the sides. In the middle is a covered court,

✪ BOURSE ET TRIBUNAL DE COMMERCE O
Fig. 306.
ELEVATION OF BOurse.
where the merchants congregate, and around are a variety of apartments devoted to their
especial use: on the floor above, the several tribunals connected with commerce are held.
The roof is of iron, ingeniously contrived to support the skylight of the great court.
There is throughout great simplicity in the arrangements, and beauty of proportion in
the architecture, with a sufficient quantity of decoration.
CHAP. VI.
291
FRANCE.
The plan, section, and elevation explain its character and proportion: it is executed with
a hard and durable stone, in a most admirable manner. Its length is 212 feet, and width
The roof is formed entirely of iron and copper, and the court or area occupied
by the merchants is 116 feet long and 76 feet broad, and it is calculated will contain 2000
128 feet.

חד
Fig. 307.
SECTION OF BOURSE.
persons. The agens de change, or brokers, have a portion railed off for their especial ac-
commodation; and around the great court are the tribunal and chamber of commerce, the
court of bankruptcy, and several other halls for the convenience of the merchants and others,
and the cost was upwards of 300,000%. sterling.
The exchange marks the importance of a city, and should always be erected in the midst
of the most thronged part, and rendered capable of receiving not only the native, but all
foreign merchants who attend: in its architecture we expect to find that the best talent the
country can produce has been employed, and certainly in this example we are not disap-
pointed.
Artesian wells have long existed in Italy, in Austria, in the Crimea, Siberia, Sahara,
Palmyra, Balbec, Tyre, and Egypt; their modern name arises from their having been im-
memorially used in Artois, one of the departments in France. Belidor mentions one in
1749 at the monastery of St. André, near to Aire, and in the ancient convent of the
Chartreux, at Lillier, in the same neighbourhood, is another more than 700 years old.
About the year 1824, M. Péligot, one of the superintendents of the hospitals at Paris,
suggested the idea of sinking a well upon the Artesian principle, and workmen were sent
from Artois for the purpose; whilst this was being effected, M. Mulot, a smith, became in
terested in the operation, and turned his attention to the subject; he was consequently
employed by the Marchioness de Groslier to sink one at Epinay; success attended his
efforts, and he was nominated to attempt one at Grenelle. The primitive soils, according
to M. Arago, are but rarely stratified, or are found in regular beds. The fissures in granitic
rocks, the crevices separating the contiguous masses, have but little width or depth, and do
not frequently communicate with each other; in such soils the waters of filtration have but
limited outlets, each film or thread terminating its course alone, without receiving any
increase from others in their descent. The springs being numerous in the neighbourhood,
it was not thought probable that any vast quantity of water could be obtained, as the whole
of the rain penetrating the earth was supposed to pass off through various openings in the
sides of the hills.
The secondary soils, which are composed of a variety of rocks, in general take the form
of immense reservoirs or basins, the centre being considerably depressed, or the extreme
boundaries of it greatly elevated: within this basin hills, and often mountains, arise,
apparently destroying its original character. The stratification of the secondary formation
is in regular beds, some of which are of enormous thickness, coinposed of sand or grit, and
very permeable; these permeable beds, as they rise towards the extremities of the basin, be-
come bare on the sides of the mountains and hills. The rain water which falls on the earth,
after penetrating it, forms one continued sheet, which pursues its course with great rapidity
when the beds have a great declivity, and, reaching the lowest point, is accumulated in vast
quantities. One chalky or calcareous stratum, which is furrowed out in all directions, and
particularly in the upper portion, allows the pluvial water to pass with great facility, and
also to circulate through the mass to a great depth: and in this peculiar stratum the wells
both of Grenelle and Rouen have been bored.
The tertiary soils are stratified, and composed of many beds placed over each other, and
U 2
292
Book I
HISTORY OF ENGINEERING.
separated by clean and well defined joints, like the secondary on which they rest; these
basins are of less extent, and derive their form from the rectifying of the beds, the elements
of which they are constituted being the same as those found on the neighbouring hills;
the several beds are arranged in a regular manner, and their separation is formed by a layer
of sand, through which the water freely percolates; in these several sandy fissures it acquires
force as it descends, and at great depths, its pressure being augmented, the flow is rendered
constant.
These soils are undoubtedly the best for sinking Artesian wells, because they have at
their base courses of sand lying on impermeable clays, and are less subject to dislocation or
rupture than rocks of the older formation. Such strata are easily examined, and are
usually found rising from the centre of the basin, and following an inverse direction to that
of the inclination of the water, which like a subterranean river pursues a downward
course till it meets with an outlet. They frequently become broken when the water they
contain weeps into small rivulets, and is carried away on the surface.
Where the well has been bored at Grenelle, the upper stratum or tertiary deposit is 41
metres in thickness; the next is composed of chalk mixed with flint, 99 metres; then a
grey chalk, without any silex, 25 metres; to this succeeded a grey chalk, in which were
iron pyrites, 341 metres; then a wealden clay, grey sand, and a sandy clay, in which were
found ammonites and other fossils; the whole depth bored through being 548 metres, or
about 1798 feet.
The work was commenced on the 30th of November, 1833, by M. Mulot, and water was
obtained in February, 1844, at an expense of 303,000 francs.
The railroads of France, Belgium, and Germany are progressing, and will probably become
the only communications between the various towns and cities of the continent; and in a
few years the diligence and post carriage will only be remembered as ancient modes of
conveyance. The railroads already laid down in Belgium and Prussia are worked in an
admirable manner, and at far less cost than those of England; the engineering difficulties
overcome beyond Liege, on the way to Cologne, the cutting and tunnelling and completing
the lines, rival any that have been hitherto executed. The greater part has been done by
the government: as most of the rails, carriages, and machinery employed upon these under-
takings were first sent from England, no particular description of them is required; and
although the several foreign governments have established manufactories of their own, most
of them are provided with models and workmen from this country.
When the whole of the lines projected are completed, it will be a highly interesting task
for the engineer to draw up an account of their difficulties and cost, and compare them with
what has been performed during the same period of time at home.
;
Of the continental railways completed, first may be cited those in France: that of St. Ger-
mains, 112 miles in length; Versailles, the right bank, 14 miles; the left bank 10 miles
the Strasbourg, which is open from the Rhine to Switzerland, 87 miles; Paris and
Orleans, 82 miles; Paris and Rouen, 84 miles; Rouen and Havre, 57 miles; Montpel-
lier and Cette, 163 miles; Mulhausen and Tham, 112 miles; St. Stevens and Lyons, 31
miles, and many others are in progress.
Of the Belgian railroads complete, there is the north line, from Brussels to Antwerp,
27 miles; west line, Malines to Ostend, 764 miles; east line, Malines to the Prussian
frontier, 822 miles; south line, Brussels to the French frontier, 51 miles; Ghent to the
French frontier and Tournay, 48 miles; and Braine la Compte to Namur, 41 miles.
The whole 326 miles cost about 4,114,354l., or 12,611l. per mile.
Among the German lines opened may be mentioned the Leipzig and Dresden, in length
71½ miles; Leipzig and Magdeburg, 72 miles; Berlin and Potsdam, 18 miles; Berlin and
Stettin, 89 miles; Berlin and Frankfort on the Oder, 48 miles; Altona and Kiel, 63 miles;
Brunswick and Oschersleben, 30 miles; Brunswick and Hanover, 40 miles; Cologne and
Aix-la-Chapelle, 54 miles; Cologne and Bonn, 20 miles; Dusseldorf and Elberfeld, 17
miles; Frankfort and Wiesbaden, 26 miles; Manheim, Carlsruhe, and Kiel, 70 miles;
Nuremberg and Furth, 5 miles; Vienna and Gloggnitz, 53 miles; Breslau and Friburg,
40 miles; Budweis and Gemunden, 120 miles; and several others of great extent, nearly
ready to be opened, and in progress.
CHAP VII.
293
UNITED STATES.
CHAP. VII.
ENGINEERING IN THE UNITED STATES OF AMERICA.
United States. Of late years there have been some extensive engineering works practised
throughout this country which bid fair to rival those of the Old Continent. Admirably
adapted for commerce, its enterprising population are exerting every effort to improve its
harbours, internal navigation, and railroad communication.
The rivers are noble and important, being navigable to a considerable height, intersecting
the country in all directions, and forming deep bays at their mouths. The Hudson for
160 miles will admit vessels of 80 tons, and the Susquehannah, the Potowmac, the Dela-
ware, are all valuable as the means of internal navigation, as are the Catahouche and the
Alabama, which both fall into the Gulf of Mexico.
The Mississippi rises in the latitude of 47° north, and flows south across 18 degrees of
latitude, through a course of 2000 miles. About half way from its source it receives the
Missouri, a larger river, which has a course of 2300 miles. Other noble rivers offer every
facility to trade and commerce; it has been estimated that the inland navigation amounts
to upwards of 23,000 miles, and the basin of this great system of rivers is computed to con-
tain 1,099,000 square miles.
Timber, from its abundance, is generally used in the construction of quays, docks, and
railroads throughout America; and we are indebted to their engineers for some ad-
mirable applications of this material to bridges, &c., which are noticed in our account of
carpentry.
It is not possible to give more than a brief outline of some of their leading works, which
are increasing rapidly over the whole extent of their vast territory.
The harbours of America are mostly capable of receiving the largest class of vessels, and
are all connected by means of inland navigation with the principal towns. In Canada
are the harbours of Quebec, Halifax, and Montreal; and in the United States the chief
are Boston, New York, Philadelphia, Baltimore, Charles Town, and New Orleans, all of
which possess great natural advantages, and afford well-sheltered anchorages in deep
water.
Quebec, the capital of Canada, is situated on the St. Lawrence, about 340 miles from its
mouth. The harbour lies between the town and the island of Orleans, and is very com-
modious, the water being about 28 fathoms deep, with a tide rising from 17 to 18 feet,
and at springs from 23 to 25 feet. It is protected by a citadel built on the headland,
called Cape Diamond, 345 feet above the level of the sea; the fortifications are very strong.
In 1812 the first steamboat that plied on the St. Lawrence was launched at Quebec, and now
the line of steam navigation extends from the Atlantic to Amhurstburg, a distance of more
than 1500 miles. Quebec commands the whole of this internal navigation, which can only
be carried on between April and November, in consequence of the frozen state of the rivers,
large masses of floating ice being kept in constant motion by the tide.
Halifax is the capital of Nova Scotia: the harbour, one of the finest in America, can be
entered at all times, being rarely impeded by ice. There is a very extensive dockyard, and
the port is the seat of a considerable fishery. The town is situated on a peninsula on the
west side of Chebucto Bay.
Boston, one of the largest towns in New England, is the capital of Massachussetts: it is
situated on a peninsula near the bottom of a large and deep bay; it is united to the main-
land towards the south, by a narrow isthmus called the Neck. Charlestown lies on the north
side of the bay, and Dorchester on the south, with both which places Boston communicates
by means of extensive wooden bridges: the bay containing upward of 75 square miles, and
studded with many islands; it extends along 50 miles of coast, between Cape Ann and Cape
Cod. The harbour at its mouth is confined between two necks of land, which allow but
a narrow passage from the Atlantic.
The quays are simply constructed of earth and timber. A row of piles driven close
together forms the face of the quay, secured perpendicularly by walings bolted on to the face
of the quay, and running throughout its whole extent; diagonal ties are made fast to the
insides of the piles, and large pieces of timber, connected with the facing piles, are laid
behind them, which being embedded as well as the braces by the earth filled in, the whole
is rendered tolerably solid; these diagonal timbers serve the double purpose of struts and
ties, and operate against any lateral pressure to which the quay may be subjected. The
filling in with earth is continued to a level of about 5 feet above the ordinary spring tides;
U 3
291
Book I.
HISTORY OF ENGINEERING.
at that height the heads of the piles are cut off level, and the platform of the quay is covered
with planking. The whole of these works are executed with unsquared timber, and are
neither painted nor covered with pitch or tar.
On some of the quays which extend for a considerable distance into the harbour, rows of
warehouses are constructed.
At Boston are the only graving docks which belong to the government of the United
States: one is in length 341 feet, in breadth 80 feet; the depth of water is 30 feet, but the
fall of the tide being only 13 feet, 17 feet are pumped out by means of a steam-engine
whenever a vessel is admitted for repair. These docks are constructed in an admirable
manner in granite, at an expense of upwards of 150,000l. each. They were executed under
the able direction of Mr. Baldwin, the government engineer.
To connect some portions of the neighbourhood of Boston as well as to form a large
basin, an embankment of earth 8000 feet in length has been thrown up, confined between
two stone walls; and the water contained in the basin is made to turn machinery connected
with some manufactories.
New York, the capital of that state, is situated on the southern extremity of Manhattan
Island, at the point of confluence of the Hudson with the east river. The inner bay is
perhaps the finest in the world: it is completely land-locked, and affords excellent anchorage;
the entrance through the narrows is very beautiful and picturesque, the shore being studded
with trees down to the water's edge, mixed with farms, cottages, and villas.
From New York to the Bar between Sandy Nook Point and Schryers Island, which
separates the outer harbour from the Atlantic, is 17 miles.
The tide flows up the Hudson for 160 miles above New York as far as Troy, and these
natural advantages have been further improved by an extensive system of canals, which
connect with the Lakes Erie and Ontario. One omission has, however, rendered this
beautiful harbour a source of serious evil; from there not being any sewers in the town, the
harbour becomes the receptacle of every impurity, and fevers of the worst kind are the con-
stant results of the effluvia.
There are screw and hydraulic docks; the latter are worked with a Bramah's press,
and by means of a timber platform, swung between two frames, the loaded vessels are lifted
above the water. Twenty chains or more, on each side of the timber platforms, pass over
iron pulleys supported above, and the platform bearing the vessel rises by the injection of
water with a cast-iron cylinder attached, which moves a horizontal beam fastened to the
suspended chains.
The cylinder and ram are surrounded by masonry, and rendered perfectly stable; the ex-
ternal diameter of the cylinder is 28 inches, its internal 12 inches, and that of the ram
which works it 11 inches, and 10 feet in length, which has a power sufficient to raise a
vessel of 800 tons. The water is injected into the cylinder by a steam-engine of high pres-
sure and six horse power; when the vessel is to be lowered, it is merely necessary to let
the water escape slowly from the cylinder, and the platform gradually descends.
Philadelphia is the city and sea-port of the state so named, and is at the conflux of the
Delaware and Schuylkill. Vessels of the largest burthen ascend the river as far as New-
castle, but those drawing 18 or 20 feet water cannot reach Philadelphia, in consequence of
a bar a little below the city. The harbour is a vast arm of the sea, navigable for 100
miles from the Atlantic.
Baltimore, a city of Maryland, is on the north side of the Patapsco river, about fourteen
miles above its entrance into the Bay of Chesapeake. The harbour is a fine expanse of
water, and capable of containing upwards of 2000 vessels.
Charlestown in South Carolina, is built upon a point of land between the Ashley and
Cooper rivers; the harbour is spacious and convenient, but the entrance has many sand-
banks. The depth of water on the shallowest part of the bar at ebb-tide is 12 feet, and at
flood from 17 to 18 feet; whilst in the middle channel at low water, it does not exceed 9
feet. A lighthouse has been erected 80 feet in height, with a revolving light.
New Orleans is stiuated on the eastern bank of the great Mississippi, about 105 miles
from its mouth; the depth of water opposite the city is about 70 feet, but the ebb and flow
of the tide do not extend to it.
The Canals in the United States exceed in length more than 3000 miles; wherever in-
ternal navigation cannot be obtained by the removal of obstructions in the great rivers, an
artificial cut is introduced; no labour has been spared to render water conveyance com-
plete. Many of the canals are carried over wide rivers on timber viaducts, and often pass
for miles through dense uninhabited forests. Some are so wide and deep as to admit the
passage of steamers through them. By one the Gulf of Mexico is united to the Mississippi
and St. Lawrence: a river and canal navigation extends from New York to New Orleans,
a distance of upwards of 2700 miles, 672 of which are by the Erie and Ohio canals.
The Erie Canal is one of the most important in the United States; its entire length is
363 miles; after leaving Albany, it passes along the right banks of the Hudson and Mohawk
rivers, crossing the latter at Middleton: it then continues its course for twelve miles on
CHAP. VII.
295
UNITED STATES.
the north bank of the Mohawk, and by the upper aqueduct again crosses it, and is carried
along the southern bank to Utica, distant from Albany 108 miles; still winding along the
southern bank of the Mohawk, another 160 miles, it arrives at Rochester, where by means
of an aqueduct it crosses the Genesee. This aqueduct, formed of eleven arches of hewn
stone is 804 feet in length.
The canal after leaving Rochester runs in a westerly direction towards Lockport, a dis-
tance of 63 miles, where it ascends the mountain ridge by five double combined locks,
each rising 12 feet 6 inches; at Pendleton, which is nine miles farther, it enters Tonne-
wanda Creek, and twelve miles beyond, this magnificent canal terminates at Buffalo.
The breadth at top is 40 feet, at bottom 28 feet, and its depth 4 feet. On the main line
are eighty-four locks, 90 feet in length, and 15 feet in width; the total lockage being 688
feet. There are eight feeders, eighteen aqueducts. From Buffalo to Rochester the fall is
4 feet; then a rise of 630 feet, and again a fall of 62 feet; the total rise and fall being
692 feet.
One of the aqueducts which crosses the Mohawk is 1188 feet in length, and the great
embankment between Palmyra and Pittsford, about 245 miles from Albany, is 72 feet in
height.
Albany, in the state of New York, is situated on the right bank of the Hudson; and in
order to improve the navigation above the town, a dam 1100 feet in length, and 9 feet in
height, has been erected across the river; the lock united with it is in length 115 feet, and
in breadth 30 feet. Albany is the great depôt, and the vessels which navigate the canal
are received in a large basin, the area of which is about thirty-two acres. This basin is
formed by a mound of earth, 4300 feet in length, and 80 feet in breadth at the base, thrown
up in a line with the Hudson, for the purpose of shutting in a part of its waters. The
lower end of the bank is unconnected with the shore, a passage being left for the vessels to
pass; and the upper end is usually closed, in order to prevent the floating ice from entering
and injuring the vessels within; but there are means for allowing the passage of the water
at the upper end which acts as a cleanser, by driving the mud before it. On the top of the
earthen embankment are erected the warehouses, and around it is constructed a timber
wharf for the vessels to load and discharge their freights. Great improvements have re-
cently been made on the canal, which was commenced in the year 1817: it has been in many
parts increased in width, and deepened. A new aqueduct has been erected over the
Genesee river at Rochester, which is 858 feet in length, and 28 feet in height from the base
of the piers to the top of the parapets. It has seven arches 52 feet span, and the six piers
and two abutments on each are 10 feet in thickness.
The width at the base is 75 feet 6 inches, and at the coping 67 feet 8 inches. The clear
width of the water-way is 45 feet, which allows for a double boatway.
The old locks, which were of timber, have been replaced by those of stone: the cutting
through the rock at Lockport extends 21 miles, for a width of 62 feet, with vertical sides.
From the Erie canal branches off the Champlain, the Chenango, the Black River, the
Oswego, the Cayuga and Seneca, the Crooked Lake, the Chemung, and the Genesee
Valley.
The Champlain Canal commences 9 miles from Albany, and is 11 miles in length,
besides a river navigation of 76 miles; the width at top is 40 feet, at bottom 28 feet, and
the depth 4 feet. There are 21 locks, each 90 feet in length, and 14 feet in width ;
the total rise is 134 feet, the fall 54 feet, the lockage being 188 feet.
Chenango Canal is in length 97 miles, its rise from Utica is 706 feet, its fall 303 feet.
The total lockage is 1009 feet; there are 116 lifts, and one guard lock; five are of stone,
and the others of stone faced with timber. There are 19 aqueducts, 52 culverts, 21 waste
weirs, 56 road and 106 occupation bridges, 53 feeder aqueducts, 12 dams, and 7 re-
servoirs.
The Black River Canal is a succession of slack water pools and canals, and the total
length of its navigation is 85 miles; the ascent and descent from Rome to Carthage is
1078 feet.
The Oswego Canal is of a similar kind, and its length is 38 miles: there are 14 locks
constructed of stone, and 6 guard locks, which are in length 90 feet, and breadth 17 feet;
the total descent is 123 feet.
The Cayuga and Seneca Canal is 23 miles in length, and has eleven locks, descending
73 feet.
The Crooked Lane Canal is 73 miles in length, and has twenty-seven lift and one guard
lock, built of timbers; the total lockage being 269 feet.
The Chemung Canal is in length 23 miles, and has one guard lock and 52 lift locks of
timber, which accomplish an ascent and descent of 516 feet; there are 76 bridges,
5 culverts, and 3 aqueducts.
The Genesee Valley Canal, for the first 36 miles after leaving Rochester, passes through a
rich low country, and then rises 95 feet by means of 10 locks. On leaving Mount Norris,
it passes through a natural and precipitous rocky defile, upwards of 400 feet in depth;
V 4
296
Book 1.
HISTORY OF ENGINEERING.
there are then numerous locks, and a tunnel. The summit level is 978 feet above Lake
Erie, and 1546 feet above high water; the total lockage is 1063 feet.
The Ohio Canal extends from Portsmouth to Cleveland, a distance of 307 miles, and the
summit level is 499 feet above the Ohio at Portsmouth, 405 feet above the waters of Lake
Erie, and 973 feet above the Atlantic Ocean. The whole district comprised by the Illinois,
Indiana, Ohio, and Michigan states, is highly favourable for the construction of canals, as
there are few natural impediments. The Ohio valley is one extensive inclined plane,
watered by numerous streams; the hills which are cut through are generally either lime
or sandstone mixed with mineral coal.
The Ohio valley is divided by the river which flows in a deep ravine, and is in length
from the city of Pittsburg to the Mississippi, in a straight line, 548 miles, but measured by
its windings 948 miles. The height of the hills at Pittsburgh is about 1290 feet above
the level of the sea.
The length of the Mississippi river below the point where the Ohio falls into it is 1100
miles, and, allowing 3 inches fall per mile, we shall have 321 feet for the elevation of the
spot where the junction of the two rivers takes place. The whole valley of the Ohio was
at one time a dense forest, the central plain excepted, which, as far as the sources of the
Muskingum, was an open savannah covered with grass.
Lake Erie is said to be 565 feet above the surface of the Gulf of Mexico, and Pittsburgh,
which is 747 feet above the same gulf, is also 830 feet above the tide water in the Atlantic
bays of Chesapeake, Delaware, Hudson, and St. Lawrence. Pittsburgh is therefore 265 feet
above Lake Erie, and distant from it in a straight line 106 miles, and it has been sup-
posed, that if a channel could be cut from the Ohio at Pittsburgh to the lake, the rivers
Allegany and Monongahela would, instead of flowing into the gulf of Mexico, rush into
the Lake Erie, with a fall of 265 feet in 105 miles, or at the rate of 2 feet per mile.
It is a curious fact, that the Allegany river should have its source within 5 miles of the
Lake Erie, and after winding from thence 200 miles should then be 265 feet above the
surface of the lake, while the Ohio does not sink in its course to the level of the lake, until
it arrives at Marietta.
At the surface of the Mississippi, immediately at the mouth of the Ohio, the level is
321 feet above the Gulf of Mexico. Lake Michigan is 35 feet higher than Lake Erie, or
600 feet above the level of high water in the Atlantic.
The Illinois river, which runs from the Lake Michigan, resembles in its course a winding
canal, there being only a fall of 279 feet in the distance of 520 miles, where it unites with
the Ohio, which is about 6 inches in a mile.
The valley of the Ohio, as well as that of the river Allegany, is in its inclination remarkably
gentle; from Olean, in the county of Cataraugus, to the Mississippi, a distance of 1148 miles,
there are no natural impediments in the way of navigation, except those which occur at the
rapids of Louisville.
The Monongahela is more rapid, and the Tennessee and Kanaidha, which rise on the
high table land of Allegany, 2000 feet above the level of the sea, are very rapid in their
course, and impeded by many falls.
The Ohio canal has been admirably executed, and has a lockage of 1185 feet, which is
overcome by 152 locks; the width of the canal at top is 40 feet, and the depth 4 feet.
The canals in the United States are usually constructed on the principle of utility alone,
little attention being paid to minutiæ; their embankments are seldom dressed evenly or
turfed, and timber being exceedingly abundant and easily obtained, it has been used even
for the construction of locks; where, however, these have shown decay, stone has been
substituted, and more finish is given in the general arrangements.
Delaware and Raritan Canal, in the state of New Jersey, is in length 42 miles; it is
75 feet in width at the surface, 7 feet in depth, and has 14 locks, each 100 feet in length, by
24 feet, besides a tide lock at New Brunswick; the total lockage being 116 feet; there are
17 culverts, 29 bridges, and 1 aqueduct.
This canal is supplied with water by a feeder 23 miles in length, and between 50 and
60 feet in width, and 6 feet in depth. Its fall is 2 inches in a mile, and has 1 lift and
2 guard locks; there are 37 bridges, and 15 culverts.
;
Morris Canal, in the same state, commences at New Jersey, and is in length 1013 miles
its ascent is 915 feet, and descent 759 feet, making a total rise and fall of 1674 feet, which
is principally overcome by inclined planes, ingeniously contrived to convey the boats from
one level to another. At each end of these is a lock, in which the boat is adjusted for its
ascent, and another at the top, to elevate it to the level above; when adjusted, the whole is
drawn up by means of machinery, which serves also to lower the boats in their downward
passage.
The elevation at Easton is 161 feet, and summit level 915 feet above the Atlantic.
The width of the canal is 32 feet at top, 20 feet at bottom, and 4 feet deep; the boats
which navigate it are about 70 feet in length, and 8 feet 6 inches in breadth across the
beam; their freight is usually about 30 tons; they are drawn up the inclined planes by
CHAP. VII.
297
UNITED STATES.
being first placed upon a timber carriage, which has beneath it, at each extremity, an iron
truck, running upon four wheels, working upon iron rails laid down on the inclined
planes.
When the boats are placed with their load upon the timber carriage, they are prevented
from falling sideways by a piece of trussed vertical framing, which is coupled at top by
means of chains. The railway extending for some distance into the canal, the carriage is
made to pass under the boat with great facility; when secured, the machinery put in
motion, the whole is drawn by a chain up the inclined plane, to the lock prepared to
receive it, which has gates at each end; after the boat is deposited, one pair is shut and
the other opened, when the water being admitted, it is floated off the car, and continues its
course along the canal. A boat going in the opposite direction is let down into the lock,
passed down the inclined plane, and on its arrival at the lower canal is floated in a similar
manner. There are in all twenty-two of these inclined planes, and the machinery to work
them is admirably contrived to effect the object, without subjecting the boats to any
material injury; their average inclination is two in twenty-one. There are 4 guard locks,
5 dams, 30 culverts, and 12 aqueducts, including one of stone at the little falls of Passaic,
which has an arch of 80 feet span, and another of wood over the river Pompton, which is
236 feet in length, and is supported by nine stone piers; there are also 200 bridges of
different descriptions.
The central division of the Pennsylvania canal forms with the Columbia and Portage
railroad the great chain of communication between the Delaware and Ohio rivers. Its
length is 172 miles, and its total lockage 670 feet 6 inches. Its width at the top is 40 feet
and at bottom 28 feet; the depth being 4 feet. There are 18 dams, 33 aqueducts, 108
locks, besides the two guard and outlet locks at Columbia. The locks are 90 feet in
length and 17 feet in width.
The western division is in length 1044 miles, 21 miles or more consisting of slack water
navigation. The canal is in width 40 feet at top, 28 feet at bottom, and 4 feet deep. Its
lockage is 471 feet, which is performed by 66 locks 90 feet by 15 feet within the chamber.
The average fall is about 8 feet per mile, from Johnstown to Blairsville, and from thence
to Pittsburg about 3 feet.
There are two tunnels, 64 culverts, 39 waste-weirs, and 152 bridges.
By this line the route by railroads and canals is complete to Pittsburg, and is the great
thoroughfare from Philadelphia into the west; the entire distance which can be performed
by it is 394 miles.
Schuylkill navigation is a succession of canals and pools extending from the dam of
Fairmount, near Philadelphia, to Port Carbon, in the county of Schuylkill. The length
by the canals is 58 miles, and by pools 50 miles. The canals are 36 feet wide at top,
22 feet at bottom, and 3 feet 6 inches in depth. There are 129 locks, 80 feet in length and
17 feet in width; 34 dams, and one tunnel 385 feet in length.
It is not possible within our limits to enumerate the whole of the canals in the United
States; they are mostly on the same construction, and executed in a similar manner to
those we have described.
The cost of a canal depends, as in all other countries, upon the nature of the soil and
climate, the price of labour and provisions, as well as other local circumstances.
The excavation of a prism, 3 feet in depth throughout, where the soil is either sand or
gravel costs about six cents per cubic yard, and for clay or stony matter eleven cents.
Excavation of loose rock costs fifty cents, and of solid rock a dollar per cubic yard, the
dollar being worth about 4s. 3d., and the cent a hundredth part; the cost of embankment
is a little more.
It has been found that the resistance to boats 13 feet 6 inches wide, and 3 feet draft, in a
canal 60 feet wide and 6 feet deep, is 81 pounds. In a canal 48 feet wide and 5 feet deep,
100 pounds; and in one 40 feet wide and 4 deep, 130 pounds, and that 18 per cent more
can be transported by the same power on the former than on the latter canal.
The canals of the United States are usually 4 feet in depth; the inner slopes are 12 to 1,
the outer 1 to 1; the towing bank is 10 feet wide at top, and that opposite the towing-
path 6 feet.
When the country is flat, the ground is excavated to the depth of 2 feet 9 inches, which
affords sufficient soil to elevate the banks for a depth of 4 feet of water, and when the
ground is not perfectly level, 3 feet cutting is usually allowed.
The walls of the locks, culverts, and aqueducts are now usually built of stone.
As the canals belong to the different states, the boats are the property of individuals,
who pay a moderate sum per mile for them, and each passenger conveyed by them.
They are about 80 feet in length, 15 in breadth, and weigh about 20 tons, and usually
draw about a foot of water, when the passengers are on board. They have about forty
yards of tow line, and are drawn by three horses, at the rate of a little more than 4 miles
an hour.
Many of the towns in the United States are supplied by means of
Supply of water.
298
BOOK I.
HISTORY OF ENGINEERING.
wheels; at Richmond, water is raised from the James River to a height of 160 feet by two
wheels, 18 feet in diameter, and 10 feet in breadth, with a fall of 10 feet.
There are two
force pumps, with barrels of 9 inches in diameter, and stroke about 6 feet in length; one
wheel can throw upwards of 65,000 cube feet in 24 hours into the two reservoirs, each
of which is nearly 200 feet in length, 100 in breadth, and 10 feet in depth.
The iron main that connects the pumps with the reservoirs is 8 inches in diameter, and
2400 feet in length.
The Fairmount water-works, commenced in 1819, for the supply of the city of Phila-
delphia, are the largest and finest of their kind in America. They are situated on the
east bank of the Schuylkill, two miles north-west from the city, and contain an area of
thirty acres, the greater portion of which is occupied by an oval-shaped mound, 100
feet in height, with the sides variously inclined according to the nature of the formation;
on its summit, at an elevation of 100 feet above mid-tide of the river, and about 50 feet
above the highest ground in the city, are four reservoirs, which contain together 22,000,000
gallons, one of which is divided into three sections and serves as a filter. The reservoirs
have a gravel walk around them, and are arrived at by several inclined planes.
A dam is erected across the Schuylkill, 1600 feet in length, 150 feet wide at the base,
and 12 feet at top, its height varying from 12 to 36 feet. It is formed of earth and stone ;
the length of its overfall is 1204 feet, the eastern embankment 270 feet, and the head
arches through which the water flows into the mill-race 104 feet. At the western end of
the dam is a short canal, with two guard and two lift locks, for the use of the navigation
company.
In January, 1839, the water rose 10 feet 2 inches above the top of the dam, but did not
seriously injure it.
The mill-race is a parallelogram, excavated through a compact mass of gneiss rock, 419
feet in length, and 38 feet in depth; its width is 90 feet, and its depth is 6 feet below the
overfall of the dam. A paved avenue, 253 feet in length, and 26 feet in width, bounds it
on one side, and on the other rocky cliffs 80 feet in height; at the north end are head
arches, which permit the passage of a body of water, 60 feet in width and 6 feet in depth,
into the race.
There is a waste gate to draw off the water, whenever it is required, and
discharge it below the dam.
The buildings which contain the machinery are constructed of stone, and are in length
238 feet, and in width 56 feet. The lower floor is divided into 12 parts, 4 of which
contain the double forcing-pumps. The others are occupied as fore bays, which lead to
the water-wheels.
The water-wheels, five of which have been put in motion, are 15 feet in diameter, and
15 feet in width, and formed of wood with iron shafts, each of which weighs 5 tons; the
wheels work under 1 foot head and 7 feet fall, and each forces 1,250,000 gallons of water
into the receiving basin in the space of 24 hours, with the stroke of the pump of 41 feet,
the diameter of which is 16 inches, the wheel making 11 revolutions in a minute. When
the wheels make 13 revolutions, which they occasionally do, 1,500,000 gallons are pumped
up.
The water-wheels are sunk below the ordinary line of high water; this does not, however,
produce much effect, until there is a depth of 16 inches on the wheel.
The pumps are worked by a crank on the water-wheel, which is connected with the
piston at the end of the slide. They are fed under a natural head of water from the fore
bays of the water-wheel, and are calculated for a 6-feet stroke, but they are generally
worked with not more than five. They are on the construction of the double-forcing, and
are each connected with an iron main 16 inches in diameter, which is carried along the
bottom of the race, to the foot of the mount, and thence up the bank into the reservoir,
92 feet in height.
The lowest estimate of the quantity afforded by the river in dry seasons is 440,000,000
gallons in twenty-four hours, and the average quantity of water raised by each wheel and
pump is 530,000 gallons daily; but when the whole six wheels are put in motion,
5,000,000 gallons can be thrown up in twenty-four hours; and it is calculated that the
average daily consumption is not more than two-thirds of that quantity.
The reservoirs are lined with stone, and paved with brick, underneath which is a bed of
strong tenacious clay, and a thick lining of lime cement, made water-tight; they are in
depth 12 feet. The water is conducted into the city from the centre reservoir by two iron
mains, one 20 inches and the other 22 inches in diameter; each is nearly 10,000 feet in
length. In the year 1821, iron distributing pipes were substituted for those of wood,
which had been laid down only three years previously, for a distance of thirty miles;
up to January, 1840, there were 109 miles of iron main, the greater part of which was
obtained from England.
There are upwards of a thousand fire-plugs throughout the city; the cost to each family
per annum for its supply of water is five dollars; the hotels and public buildings pay in
proportion to their consumption.
CHAP. VII.
299
UNITED STATES.
Cincinnati water-works are on the Ohio; horse-power was originally used, but there
are now two steam-engines, one of which works a double force pump, 10 inches in
diameter, with a four-feet stroke, and throws up into the reservoirs 1000 gallons per
minute; the other works a pump 20 inches in diameter, with an eight-feet stroke, and
throws up 1200 gallons per minute.
From the reservoirs, which are built in stone, and cemented, the water is conducted by
iron mains, 8 or 9 inches in diameter, into the basin, where it is distributed by leaden
pipes.
Pittsburg receives its water from the Ohio, by a steam-engine of eighty-four horse
power, which, by means of its pumps, throws a million and a half of gallons into a re-
servoir, 116 feet above the level of the river, from whence it is distributed by iron mains
15 inches in diameter, into the town.
Albany, on the Hudson, and Troy on the same river, obtain the purest water from the
high ground in the neighbourhood; reservoirs are formed at a sufficient elevation, and of
the requisite capacity, from whence it flows through iron mains to the different quarters of
the town.
Boston originally derived its supply from wells, and according to a report furnished
to the state, there were 2767 for public use, 33 of which were Artesian.
Montreal, and many other towns, are now supplied with water by means of steam power,
which, no doubt, will become universal; and when all the works contemplated at New
York are completed, the town, which is now inadequately served, will be wonderfully
benefited.
The Croton aqueduct, upwards of 40 miles in length, is a subterranean brick tunnel,
ascending at the rate of nearly 14 inches per mile from New York to Croton; after the
trench was cut, and the aqueduct built, the earth was backed over the aqueduct, to a
depth of 4 feet on the crown, where it was levelled down to a width of 8 or 10 feet, the
sides being sloped with a talus of one and a half to one. Wherever a valley is crossed, a
solid wall 15 feet in width at top, with sides battering one-twelfth to one, is built with
stone, on the top of which a bed of concrete is laid, and on it is constructed the covered
aqueduct, which is at bottom 6 feet wide, at top 7 feet, and 8 feet in height; the side
walls being of stone, in courses, 39 inches thick at bottom, and 27 inches at top.
Across the river at Croton is thrown a dam; and 500 or 600 acres of water form
the great reservoir, which for every foot in depth is calculated to contain 100,000,000
gallons of water. The dam is 100 feet in length, 70 feet wide at bottom, 7 feet at top, and
the average height is 40 feet; it is built of stone and hydraulic cement.
The water passes from the reservoir by the corporation tunnel, 180 feet in length, and a
mile further it crosses Lounsberry brook, by a culvert 6 feet in diameter and 66 feet in
length; where it crosses the valley, the grade line is 40 feet above the brook, and 55 to the
top of the aqueduct.
Soon
Five miles beyond, the Indian brook is crossed by a culvert 8 feet in diameter, and
142 feet in length, and the aqueduct is conducted through Benvenue tunnel, 720 feet in
length, and the Ackers brook tunnel, 166 feet in length. At half a mile from Indian
Brook is Hoagshill tunnel, 276 feet in length; from thence to Sing Sing are several
valleys; it then passes through a tunnel 336 feet in length, cut in the solid rock.
after a chasm 70 feet deep, worn by the Indian brook, is crossed by an aqueduct bridge of
88 feet span, with an elliptical arch rising 25 feet, resting on stone abutments; the
aqueduct is lined with cast-iron plates. A mile further are the two state prison farm
tunnels, one 416 feet, the other 375 feet in length; and half a mile further Hollis Brook
tunnel is entered; here, in crossing the valley, the grade line is 35 feet above the stream,
and the top filling of the aqueduct 49 feet. The culvert is 131 feet in length, and 6 feet
in diameter. A mile beyond is Ryders Brook, where the foundation wall is 20 feet high
from the bed of the stream, and 34 feet to the top line of the aqueduct. The culvert is
100 feet in length, and 6 feet in diameter; a viaduct then crosses the road. built of stone,
with an arch 20 feet span. The Austin Farm Tunnel, 186 feet in length, being passed,
there occur several valleys, and when it arrives at Mill River, the grade is about 72 feet
above the surface of the water, and the aqueduct is 87 feet in height. The culvert is
25 feet in diameter, and in length 172 feet. After quitting Mill River, the aqueduct
passes through five culverts, and two miles below is the White Plains Tunnel, which is
246 feet in length. At Jewells Brook the aqueduct crosses by an embankment 62 feet
in height, where there is a culvert 148 feet in length, and 6 feet in diameter, and another
for the road 141 feet in length, and 14 feet in width. At Wiltseys Brook, 18 miles
from the Croton dam, the aqueduct crosses, and the culvert is 137 feet in length, and
6 feet in diameter, and at Dobbs Ferry Tunnel it passes entirely through earth for a length
of 262 feet. At Storms Brook is a culvert 137 feet in length and 6 feet in diameter; as
it proceeds from Dykemans Brook, the top of the embankment is 35 feet above the surface
of the country.
The tunnel at the Saw Mill river is through earth and rock for a distance of 684 feet;
300
BOOK I.
HISTORY OF ENGINEERING.
the foundations are afterwards 42 feet above the valley. The culverts here are 90 feet in
length and 25 feet in diameter, and are double.
At Nodines Run, the aqueduct passes at a considerable elevation by a tunnel in the
solid rock, 810 feet in length; the line then crosses the valley of Tibbetts Brook, where
the culvert is 107 feet in length, and 6 feet in diameter.
At Harlem River, where the aqueduct is to cross, there is a depth of water of 26 feet at
ordinary high tides, and its width is about 610 feet; here it is intended to build a bridge
1420 feet in length, 18 feet in width, between the parapet walls, and 27 feet from out to
out. There are to be sixteen piers of stone, six of which will be in the river, and ten on
land. The river piers are to be 40 feet by 20 feet, and to have a height of 84 feet, to the
springing of the arches diminishing as they rise. The arches are to span 80 feet, whilst
those on land will span only 50 feet. In the centre the arches are projected to be
100 feet above the level of high water; the height to the top of the parapet walls will
consequently be 116 feet, and the total height about 138 feet; when finished, it is intended
to carry the water over in iron mains, 2 or 3 feet in diameter.
At the Manhattan Valley iron pipes or inverted siphons are to be used, as the valley is
upwards of 100 feet below the grade line of the aqueduct.
Twenty-six miles of the works were completed in April, 1840. Ventilators are to be
placed at every mile distant, and the water on its arrival at New York is to be received
into a reservoir 35 acres in area, the northern half of which is to have a depth of
20 feet, and the southern portion 25 feet; and it was estimated that the quantity of water
would be about 160,000,000 gallons. Pipes or mains, 30 inches in diameter, are then to
convey the water to another reservoir on Murray Hill, of five acres, and capable of con-
taining 20,000,000 gallons, the difference of level of which and that of the pool at Croton
being 46 feet, which allows a fall of about 14 inches per mile.
According to the engineer's report, the whole work, with the exception of the bridge
over Harlem Strait, would be completed in 1842; it was proposed, after the cofferdams
were constructed, to lay down pipes which would supply the water, whilst this, the most
difficult part of the operation was in hand.
Various impediments have occurred during the progress of this gigantic undertaking,
which have prolonged it beyond the time specified; it is, however, nearly terminated: its
cost is estimated at two millions sterling.
Railroads. The internal improvements that have taken place in America during the
last thirty years, particularly in the extension of railroads, is truly astonishing; the states
of the Union have endeavoured to rival each other in contributing lines to form one great
national means of communication; it seems intended that railroads should spread through-
out the whole of this vast continent like the meshes of a net, and embrace every spot
occupied by its inhabitants. The progress already made is sufficient to indicate what will
be done in a few years: when the great works now in hand are completed, commerce will
derive such increased advantages, that we may hope, not only that the bond of union be-
tween the states will be thoroughly cemented, but that the whole people will be brought
more closely together, and become as it were one family with a common interest.
The railroads, first projected for the purpose of connecting certain towns and districts,
were designed without regard to any general plan; the lines being undertaken by com-
panies independent of each other, various and often conflicting regulations were adopted ;
and much evil has arisen from this want of unanimity in the several operations. Whenever
chartered companies have united and appointed a board of directors to carry out a plan
suited to their common interests, the most beneficial results have been produced.
The first great chain of railroad commences at Portsmouth, in New Hampshire, and has
almost an uninterrupted course to Pensacola, in Florida. Another line from the same place
extends to Boston, Providence, and Stonington, in Connecticut, where it crosses Long
Island Sound to Greenport, and then continues to Brooklyn, near New York; after
crossing the river Hudson, it proceeds to Jersey, New Brunswick, Trenton, Philadelphia,
Baltimore, Wilmington, and Washington. From thence to Fredericksburg, Richmond,
Petersburg, Gaston, in North Carolina, Raleigh, Columbia, Branchville, and Augusta, in
Georgia, then to West Point, Montgomery, and Pensacola, in Florida. Of this extensive
line of communication nearly the whole is complete, and in the year 1840 upwards of 1600
miles were travelled over.
From Boston commences another grand chain, which passes Worcester, West Stockbridge,
Albany, Schenectady, Utica, Syracuse, Auburn, Rochester, Attica, and Buffalo. The
length of this line is about 530 miles.
From New York lines are in progress which, when finished, will extend upwards of 500
miles.
From Philadelphia is a line to Sunbury, Williamsport, and Erie, on the lake of that name,
a distance of 420 miles.
By means of railroads and canals a distance of 400 miles is accomplished, from Philadel-
phia to Columbia, Hollidaysburg, Johnstown, and Pittsburg.
CHAP. VII.
301
UNITED STATES.
From Baltimore to Wheeling, 280 miles, the canal and railroad extend throughout; and
the same kind of communication exists from Richmond, in Virginia, to Covington and the
Ohio river. From Charlestown to Louisville, Cincinnati, and the Ohio, the line, when
complete, will be upwards of 700 miles.
The great Atlantic line is considered the main trunk to which all others seem united;
the western states are carrying out lines of railroads and canals of not less than 2000 miles
in length.
The first lines laid down were with iron rails and chairs, on stone blocks, which were
frequently so split by the frost, that it was necessary to remove them; the rails also became
deranged, and extremely dangerous for the passage of carriages. Numerous methods have
been adopted in the states to remedy the inconvenience arising from the great changes of
temperature, as will be seen in this brief account of their railroads. The usual breadth be-
tween the rails is 4 feet 8 inches, and when two lines are laid down, the distance maintained
between them is usually 6 feet.
In the southern states, where a line is carried over low and marshy ground, and a diffi-
culty is found in obtaining earth to construct the embankments, a series of timber trusses
are substituted, which often rise 10 or 12 feet above the level of the plain; on these the
longitudinal timbers are laid to carry the rails. Piles of from 14 to 16 inches in diameter,
not sharpened, are first driven in, forming two lines the width of the way; when these are
perpendicular, inclined struts are placed on the outside, which passing at the upper end
under the transverse timbers, and abutting at the lower upon another short pile, render
the woodwork tolerably secure.
Another method is to drive four slanting piles, two one way and two the other, each
pair uniting at top under the longitudinal timbers, and in the middle of the width at bot-
tom, where transverse binding pieces are firmly bolted to them, and secured either by
additional piles or cross sleepers. Occasionally a double series of St. Andrew's crosses are
used, but they have generally been found subject to considerable movement when in con-
nection with the locomotive engine.
The cost of the American railroads is considerably less than in England: many of the
single tracks have not exceeded 4000l. a mile, and, including buildings and all requisite
apparatus, the average expense does not seem to exceed 20,000l. per mile.
One system frequently adopted seems extremely economical sills of white oak 7 feet
10 inches long, and about 9 inches in depth, are laid across the road, at a distance of 5 feet
from centre to centre; and notches are cut at the ends, into which are laid longitudinal
pieces of heart of pine wood, 9 inches in depth, 5 inches in width, and 4 feet 7 inches apart.
On their inner edge, plates of rolled iron 2 inches wide, and half an inch thick, are spiked
down with wrought iron spikes, 5 inches in length; and where the plates form a junction,
there is an additional plate of sheet iron one-twelfth of an inch in thickness; this system is
found to answer when the locomotive engines are from fifteen to twenty horse power, and
the cost per mile in America does not exceed 6001. The locomotive engines, when their
boilers are filled, seldom weigh more than 15 tons, and their driving wheels are placed in the
fore part near the fire-box; they are 5 feet in diameter; the front of the engine running
on four wheels, half the diameter of the large ones.
On the truck which runs on the fore wheels are a number of friction rollers, placed in a
circle, in the centre of which is a vertical pivot, working in a socket of the frame-work
which supports the engine. The friction rollers support the cylinder and part of the
boiler, and the truck of the carriage acting on the pivot aescribes a portion of a circle,
which is of great service when the engine is not running on a level road; at each side of
the engine a guard is usually attached to prevent it being thrown off the rail; this is
nothing more than a strong piece of timber, fixed to the front axle, and supported by two
wheels, of 2 feet in diameter, which run on the rails a few feet in advance. This piece of
timber is on the outside, shod with iron, slightly bent upwards, which clears away any ob-
struction that may be offered to its progress.
The Boston and Lowell railroad is in length about 26½ miles; it has eighteen viaducts,
one of which is 1600 feet in length, and fifty-one bridges. The maximum rise is 1 in
528, or 10 feet per mile, and the least radius of curvature is 3000 feet.
Where the line approaches Lowell, the cutting for 1000 feet is through the solid rock,
which at the top is 60 feet in width, at the bottom 40 feet, and the mean height the same.
At the commencement fish-bellied edge rails, weighing thirty-five pounds per yard, on cast-
iron chairs, were laid down. The chairs were fitted on stone blocks, which rested on stone
cross sills; the bearings were about 3 feet from centre to centre, and the blocks and sills
were carried throughout by a longitudinal wall constructed of rubble, laid dry, 3 feet in
height, 2 feet 6 inches wide at the footing, and 2 feet at the top. The space between these
walls was packed in with clay, and other earth that could be easily obtained.
The construction not being found to answer, the foundations have since been laid in with
sand and gravel; a trench being opened for its reception, 3 feet in depth, and 7 feet in
width, it was well rolled and rammed; sills of stone, 6 feet in length, and 12 by 6 feet
302
BOOK I.
HISTORY OF ENGINEERING.
were then laid down; and the H rail in 15 feet lengths was adopted; the weight of
which was fifty-five pounds per yard.
The Boston and Worcester line is in length forty-four miles, and has several deep cuttings
and high embankments; where it crosses the Charles river is a viaduct of masonry and
trestle work. The rail used is that of the T form, weighing about 38½ pounds to the yard.
The bars are about 15 feet in length, carried by iron chairs, weighing about 15 pounds each
they are tightened by means of two wrought iron keys.
;
The chairs are placed on sleepers of cedars 5 inches square, and in lengths of 7 feet; these
are laid crossways at regular distances of 3 feet from centre to centre, and bedded on piers
of rubble masonry; this was, however, found insecure, and a longitudinal under sill of
chestnut 8 inches by 3 inches has been added throughout.
sea.
The_Western railroad, extending from Worcester to the valley of the Hudson, is in length
more than 116 miles; and the four summits are from 900 to 1500 feet above the level of the
The width of the track is 4 feet 8 inches; the rails are of a parallel form, 3 inches
in depth, 4 inches on the base, and 2 inches at the top; the weight is fifty-five pounds per
yard. They are laid upon sleepers of chestnut, 7 feet in length, 7 inches in depth, and
12 inches wide. These sleepers rest upon others of hemlock wood, laid longitudinally,
8 inches in width, and 3 inches thick, so placed, that they measure 4 feet 10 inches from
centre to centre; where the joints of the iron rails occurs, there are four cross-timbers, 3 feet
in length.
The rails are kept in their place in the usual manner, and the chairs are spiked into the
sleepers.
The maximum inclination is 60 feet in a mile, and the minimum radius of curvature
1146 feet.
The Boston and Providence line is in length 41 miles, and the least radius is 5730 feet ;
the highest inclination is 25 per mile in the direction towards Boston, and on the other side
37 feet 6 inches; the highest elevation is 256 feet above the level of the sea.
The Granite Viaduct at Canton is 700 feet in length, and where it crosses the Neponset
river is 60 feet in height. The wooden bridges on this line are 1200 feet in extent, and
their spans vary from 30 to 125 feet.
The rails are of the H pattern, in lengths of 15 feet, weighing 55 pounds per yard.
The iron chairs weigh ten pounds each, and are only used where the rails join each other;
they are let into the sleepers, and secured by four spikes. The rail is fastened by broad
spikes, four on each sleeper; 6 inches in length, half an inch square, and weighing nine
ounces each. There are cross ties of white cedar under the rails, laid 3 feet from centre to
centre.
Providence and Stonington railroad is 47 miles in length, has rails of the H pattern, in
lengths of 15 feet, weighing fifty-eight pounds per yard, with square ends. The cast-iron
chairs weigh ten pounds each, and are spiked down to the sleepers, with spikes nine ounces
each. The sleepers of white cedar are laid 3 feet apart, are 7 feet in length, and 6 inches
in thickness; they rest on sills of hemlock, 8 inches by 3 inches, and where the joints occur,
there are additional piers 5 feet in length laid under them.
The highest elevation is 302 feet above the level of high water, and the maximum rise
not more than 33 feet in a mile; the minimum radius of curvature 1637 feet.
Norwich and Worcester railroad is in length 58 miles; its maximum grade is 20 feet per
mile, and the average inclination is 11 feet per mile.
Long Island Railroad is in a state of progress, and one portion of the line rises 200 feet
in a mile. The other gradients do not exceed 40 feet in a mile, and the minimum radius
of curvature is 5280 feet. The rails are of the T pattern, weighing thirty-eight pounds
per yard, resting on cast-iron chairs; these are confined on stone blocks, placed on cross
ties of timber. The sleepers are of red cedar, in lengths of 8 feet, and 6 inches square.
The iron chairs weigh fifteen pounds each when they are placed on the sleepers, and
twenty pounds each on the stone blocks. An iron tie crosses the road, and holds the
opposite stone blocks together; it is a bar of half an inch thick, 2 inches in width, and
4 feet 8 inches in length.
The top part of the rail rests on the chair, and is secured by a double key.
Harlem Railroad, twenty-six miles in length, is a double track, and is travelled for
three-fourths of its length by steam power.
The tunnel through which the line passes is cut through a solid rock, composed of
quartz and hornblende, of so compact a nature that masonry was unnecessary. It extends
844 feet, and is in width 24 feet, and 21 feet in height. On this road the plate rail is laid
down; it is 21 inches in width, and five-eighths thick; it is secured to longitudinal
timbers 77 feet long, laid across ties of locust and cedar, placed 3 feet 6 inches apart.
New York and Albany Railroad at one point attains an elevation of 770 feet, but the
gradients seldom exceed 30 feet per mile. The length of this line is 1473 miles, and the
radii of curvature is seldom above 1500 feet.
Camben and Amboy Railroad, in length sixty-one miles; the radii of its curves are
CHAP. VII.
903
UNITED STATES.
about 1800 feet, and the usual gradients 20 feet per mile. The rails are the H pattern,
in lengths of 16 feet, weighing forty-one pounds per square yard. The rails are supported
on stone blocks, 18 inches square, and 12 inches in depth, placed in a continued trench, at
regular distances. Where the rails join, there are cast-iron plates spiked down below
them, which, by means of a notch cut in the rail, prevent its moving endways; the rails
are attached to each other at the ends by an iron plate 4 inches in length, which is riveted
to each rail; the rivet has a play to allow of contraction and expansion.
On the top of the stone blocks is a piece of wood 2 inches in thickness, to adjust the
placing of the rail.
Wherever the clay occurred, it was taken out, being so readily affected by frost, sand
and gravel being substituted.
New Jersey Railroad, thirty-four miles in length, has its least radius of curvature
2000 feet, and the steepest gradient 26 feet per mile. The rails are of the T form, and
weigh thirty-seven pounds per yard; they are in lengths of 18 feet, with square ends.
The rail rests upon its two upper flanches on chairs, a single key keeping it in its place.
The chairs weigh fifteen pounds each, and are placed at equal distances, measuring 3 feet
from centre to centre; they are secured to cross sleepers of cedar wood and chestnut.
There are two timber viaducts, one over the Possaic, the other over the Hackensack,
which are worthy of notice.
At Bergen Hill is a deep cutting, a mile in length, and at one part 50 feet in depth,
35 feet of which is through hard rock; more than 500,000 cubic yards were excavated.
The Viaduct at Raritan is on the plan called after Colonel Long; its length is 1700 feet,
and its spans vary from 112 feet to 145 feet; the depth of the truss being 22 feet, and
the width between the rails at the top 31 feet. There are seven piers and two abutments,
faced with granite, and filled in with blue and red shale stone; this viaduct has two stories
in height; the lower floor is supported by trusses, and a double roadway is carried by
means of joists laid 4 feet apart. The chairs that confine the rails rest on strong pieces,
11 inches in width and 4 inches thick, pinned down to the floor at top, which serves as a
roof. The braces of the truss-framing abut upon thin plates of sheet iron.
Parts of the floors draw up, to allow the passage of vessels at certain appointed times.
Columbia and Philadelphia railroad is 811 miles in length; the maximum gradient is 30
feet per mile, and the minimum radius of curvature 631 feet. The deepest cuttings are
between 30 and 40 feet, and the highest embankment is 80 feet.
There are 75 stone culverts, varying in span from 4 to 25 feet, 20 viaducts, the piers
and abutments of which are stone, the structures above of timber, and 33 bridges.
The Schuylkill viaduct is of timber, formed into distinct trusses, the whole width, from
out to out, being nearly 50 feet, which is sufficient to allow three separate ways, two of 18
feet 6 inches, and the other of 4 feet for foot passengers. There are six piers and seven
spans the whole length of the viaduct is 1045 feet; the height of the floor above the water-
line is 38 feet.
Valley Creek viaduct has four equal spans of 130 feet clear, and the stone piers vary
in
height from 56 to 59 feet. The woodwork consists of a lattice bridge, with the railway
carried over the top.
East Brandywine viaduct has four spans, two of 88 feet 6 inches, and two of 121 feet 6
inches. The clear width is 18 feet 6 inches, and the whole length of the platform 477 feet,
the clear height above the water 30 feet.
The West Brandywine viaduct has a platform 835 feet in length, which is 72 feet above
the water; the line is carried over the top of the framing.
Big Conestoga viaduct is in length 1412 feet, the platform is 60 feet above the water.
The greatest span is 120 feet, and the lattice timber-work is upon Town's plan.
Little Conestoga viaduct has also stone piers and abutments, the length of the platform
is 804 feet, and its elevation above the water 47 feet.
Mill Creek viaduct is 540 feet in length, and is 40 feet high.
Peguea viaduct is a single span of 180 feet, it is in timber, on the plan of Mr. Burr.
The length of the single track is 163 miles, six miles of which have granite sills, on which
are flat iron bars; 16 miles with wooden string pieces, plated in a similar way with
iron; two miles with stone blocks, and sills with edge rails; and 137 miles, with stone
block and edge rail, with timber sills across the track.
The granite track has trenches cut in the line of its direction about 22 inches in depth,
into which is compactly placed layers of broken stone. Granite sills are then laid, varying
in length from 3 to 12 feet, and 12 inches square; into these holes are drilled five-eighths of
an inch in diameter, and 3 inches in depth, into which plugs of locust wood were securely
driven. The iron bars, 15 feet in length, 24 inches wide, and five-eighths of an inch thick,
are spiked to these wooden plugs. As horse-power is used, there is a pathway of broken
stone and gravel 6 inches in depth.
The timber track. — Trenches were dug across the road 4 feet apart, 8 feet in length, 12
inches wide, and 16 inches in depth; broken stone was thrown into them and well rammed,
804
Book I.
HISTORY OF ENGINEERING.
then sills of chestnut and white oak were laid down, in lengths of 7 feet 6 inches, and 7 inches
square, notched, to receive a yellow pine string piece, 6 inches square, which is spiked
down securely. On this are the flat iron bars, and the horse-way is formed as before
described.
Edge Rails on Stone Blocks and Sills.—Trenches were dug in the direction of the length of
the road, 28 inches wide, and 24 in depth; at every 15 feet these were connected by a
cross-trench, 16 inches in width: broken stones were rammed into them, and blocks and
sills were settled by the means of heavy rammers. The granite blocks are 20 inches long,
16 wide, and 12 deep. The sills, also, of stone, 6 feet 6 inches long, and 12 inches
square, are sunk in the trench at every 15 feet. The rails have a bearing on the blocks at
every 3 feet.
The chairs, which are of cast-iron, weigh 15 pounds, and are secured to the
sills and blocks by bolts driven into cedar plugs inserted in the stone. Each chair has two
bolts, weighing 10 ounces each, and between the chair and stone block is a piece of tarred
felt. The rails are of rolled iron, 15 feet in length, parallel top and bottom; their depth is
3 inches, and their weight, per yard, 41 pounds. The rail is fastened to the chair by
two wrought-iron wedges, each weighing 10 ounces. The horse-path is similar to the
others.
Edge Rails on Stone Blocks and Locust Sills.—The locust sills are 15 feet apart on the straight
lines, and 9 feet on the curves, and the remainder of the work is the same as the edge-rail
track already described.
There are turn-outs for the horses at certain intervals.
On this line of railroad all the
bars used belong either to individuals or to companies, whilst the motive power is found
by the state.
The locomotives run daily about 77 miles.
There is an inclined plane at the Philadelphia end 2714 feet in length, and rising 185
feet. Another at Columbia is 1914 feet in length, and rises 90 feet. The cars are moved
up and down by a stationary engine of 60 horse-power, and an endless rope 9 inches in
circumference, which passes round horizontal grooved wheels, placed at the top and bottom
of the planes.
;
Allegany Portage Railroad, its length is a little more than 36½ miles, and its total rise and
fall 2570 feet, of which 2007 feet are overcome by planes, the inclination of which varies
from 40 to 510, or from 7 feet to 10 feet, for every 100 feet base. They are all straight,
both on plan and section. The total length of their base is a little more than 44 miles
the rest of the gradients are about 15 feet per mile. All the embankments are 25 feet in
width; at the top there are four viaducts of considerable extent: that over Connemaugh is
a single arch of 80 feet span, the top of the stone work is 70 feet above the surface of the
water; there are 68 culverts, 85 drains, several bridges, 10 inclined planes, 11 levels, and
one tunnel, 901 feet in length, 20 feet wide, and 19 feet in height to the soffite of the arch.
The edge rails are parallel, and made of rolled iron, weighing 40 pounds per yard; they
are supported by cast-iron chairs, weighing 13 pounds each, and the rail is secured in them
by an iron wedge. The stone blocks under them contain each about 3 feet 6 inches of cube
stone, and are placed on a bed of broken stone, at a distance of 3 feet from centre to
centre. At the head of each inclined plane are two stationary engines of 35 horse-power
each, which work an endless rope, and can draw up four cars loaded with 7000 pounds
weight, and let down four at the same time; from six to ten changes can be made in an
hour. A safety car is in attendance in case of any accident occurring to the rope.
In the formation of this railroad there were
337,220 cube yards of common excavation.
212,034
566,932
210,724
14,8.57
967,060
67,327 perches
13,342
slate or detached rock.
hard pan or indurated clay.
solid rock.
solid rock in the tunnel.
embankments carried over 100 feet.
slope wall.
vert and wall in drains.
Philadelphia and Reading Railroad is 59 miles in length, and in one instance the gradient
is 19 feet to the mile; the others vary from 18 inches to 11 feet in the same distance, there
are three tunnels on the line.
The H rail is used; the weight is 45 pounds 2 ounces per yard; the lengths are 18 feet
9 inches, with square ends. About eight of these lengths weigh a ton; the sleepers upon
which they are secured are of white oak, laid transversely about 7 feet in length; they are
brought to a face on the under as well as upper side, in order that a true bearing might be
obtained throughout; they are 7 inches in depth, and laid at a distance of 3 feet 1 inches
from centre to centre. Under them is a foundation of broken stone, in a trench excavated
to the depth of 14 inches, and in width 12 inches; the length was 2 feet more than that of
the sleepers bedded on them. After these walls were laid, and the timbers placed, the
spaces between them were filled up level with clay, or any other material at hand. The
CHAP. VII.
305
UNITED STATES.
14
rails are let in about of an inch throughout, except at the joinings of the rails, where the
chairs occur. The chairs are 6 inches square at the base, and § of an inch in thickness,
and the rails are bolted down to them securely, the hole in the rail being made a little
larger than the bolt, to allow for expansion. The bolt and nut weigh 7 ounces, and the
chair 10 pounds; the latter is held by four spikes, 6 inches in length, the heads of which
passed over the edge of the chair.
In a mile of road there were 71 tons of rail, 5910 pounds of chairs, 4524 pounds of
spikes, and 481 pounds of bolts and nuts.
About 30 miles from Philadelphia is a tunnel, the length of which is 1932 feet, the width
19 feet, and the internal height 17 feet. The sides are cut quite perpendicular, as high as
10 feet 9 inches, and above this the section is a half oval, rising 6 feet 8 inches; there is no
lining of masonry except at the ends, the rock it passes through being the Grauwacke slate,
and sufficiently strong without it.
Beyond the northern end of the tunnel, the Schuylkill is crossed by a stone bridge,
18 feet 4 inches wide; there are four spans, each 72 feet, and 3 piers of 8 feet; the roadway
is 24 feet above the level of the river. The versed sine of the arches is 16 feet 6 inches; the
arch is the segment of a circle whose radius is 47 feet 6 inches. Below the water the
foundations are carried down to 10 or 12 feet in depth; Roman cement was used instead of
mortar, and the whole of the superstructure is executed with cut stone.
Baltimore and Ohio Railroad extends 80 miles, the road bed is in width 26 feet;
41 miles from Baltimore there is an inclined plane, in length 2150 feet, rising 80; this is
followed by another, 3000 feet in length, and 100 feet rise; the summit is 813 feet above
mid tide, and is called Parr's Spring Ridge. From thence the line descends by an inclined
plane, 3200 feet in length, and 160 feet in height, and by another 1900 feet in length, and
81 feet in height, after which the gradients vary from 37 to 52 feet per mile.
The viaducts are all of stone excepting two; between Baltimore and the Potomac there
are thirty-three.
The rails are sometimes laid on granite sills, and at others on timber sleepers; the iron
rails are in 15 feet lengths, each pierced with eleven oblong holes, to receive iron pins.
Baltimore and Port Deposite Road is 95 miles in length, its maximum inclination is 20
feet per mile, and its minimum radius of curvature 2000 feet.
Under each line of rails is a sill sawed out of white pine, 8 inches by 6 inches, in lengths
of from 12 to 40 feet. These are laid flat in longitudinal trenches; on these, at distances
of 3 feet from centre to centre are cross timbers of white oak and chestnut, 8 feet in length
and about 8 inches by 6; each has four notches, two on the lower side, 8 inches wide, and two
on the upper, 7½ inches, in which is a wedge for the purpose of making fast the longitudinal
piece; the thickness left between the upper and lower notch is always 21 inches. The
lower notches embrace the under sills, and are made to fit, so that no lateral movement can
take place.
The rails are nearly rectangular on their section, and weigh 40 pounds per yard; they
are 2 inches wide at bottom, 24 at top, and 12 inch in height; their length varies from 17
feet 9 inches to 18 feet 3 inches, and their ends are cut obliquely to an angle of about 60°.
Each is vertically perforated by five holes, by means of which they are secured to the
longitudinal timbers; the ends of the rails are lodged on plates of rolled iron, inch in
thickness, and about 53 by 4 inches. On the upper side of these plates are two small
ledges, extending their whole length parallel to each other, through which the rail passes,
and is prevented from having any lateral movement. Two 9-inch bolts keep the plates
secure.
14
Baltimore and Susquehanna railroad is in length 56 miles; its summit level is 1000 feet
above that of high water; its steepest ascent is 84 feet per mile, and descent 59 feet. The
least radius of curvature is 950 feet.
Lexington and Ohio railroad is 923 miles in length, the minimum radius of curvature is
1000 feet, and its maximum inclination 30 feet per mile. Where it descends the valley
of the Green River is an inclined plane 4000 feet in length, and 240 feet in height.
To these may be added the Portland, Saco and Portsmouth in the department of Maine,
in length 50 miles; Concord, in the same department, 35 miles; in Massachussetts, the
Boston and Maine, 17 miles; Berkshire, 21 miles; Felchburg, 50 miles; Naschua and
Lowell, 14 miles; Northampton and Springfield; Old Colony, and some others.
In new
York is the Attica and Buffalo, in length 31 miles; Auburn and Rochester, 78 miles;
Auburn and Syracuse, 26 miles; Buffalo and Magara, 22 miles; Erie, 53 miles; Long
Island, 96 miles; Utica and Schenectady 78 miles; Reading, 94 miles; South Carolina
and Columbia, 202 miles, and a great many others in progress; those already completed
amount to nearly 2700 miles in length.
X
306
BOOK I.
HISTORY OF ENGINEERING.
t
CHAP. VIII.
CIVIL ENGINEERING IN BRITAIN.
AMONG the great nations of antiquity and of modern Europe, we find the engineer trusted
and employed by the governments, and when great works were undertaken, their cost pro-
vided for out of the public funds. The peculiar nature of our constitution has caused a
contrary course to be pursued; the increase of commerce in Britain, and its augmentation of
capital, have directed the attention of individuals not only to the improvement of machinery,
but to the best method of conveying their manufactured goods to the port from whence
they are to be transmitted to foreign lands. Hence arose the necessity of improving the
roads and bridges, forming canals, convenient harbours, lighthouses, &c., and latterly,
spreading over the whole face of the country a network of railway communication.
To commercial enterprise, and not to the government, is due whatever improvements
have been made in the science of engineering: private study, and not an Institute, produced
Brindley, Jessop, Rennie, Chapman, Huddart, Watt, Priestley, Smeaton, and others, who,
in the last century, gave a character to the science, and permanently established it as a
profession. Mechanical knowledge formed the groundwork of their acquirements, and the
increasing wants of the commercial world called them into active operation; the necessity
of an undertaking was no sooner made known than intellect and energy contrived to execute
it. The prosperity of Britain is based upon her industry, and the success which has
attended the speculations of manufacturers has induced the formation of companies for
the establishment of canals, docks, harbours, and other public works.
As it is our boast that the management of public improvements is entrusted to those
who pay for them, the government interferes no further than is necessary for the pro-
tection of private property: when a project is decided on, plans are forwarded to some
public place of meeting in the county or counties interested in it, and notices are trans-
mitted to the inhabitants of the towns and villages, as well as to each individual whose
property is in the slightest degree interfered with. The names of the owners and occupiers
of the soil are registered, with their assent to or dissent from the measure; this document
is forwarded to the office of the justices of the peace of each county, previous to applying to
parliament.
The London Gazette and the country journals then announce the proposition,
and make it as public as possible. A petition drawn up and presented to the houses of
parliament is sent with a draught bill, prepared by the engineers and solicitors of the
company, which is duly considered by a committee of the legislative houses, and if no
important objections are taken, the measure is assented to; when the whole of the
subscribers are summoned to appoint a managing committee, treasurer, engineer, and
assistants, to carry out the work.
Plans and specifications are then advertised of the several portions of the undertaking,
and contractors offer tenders for its performance, the lowest being generally selected; the
contractor is bound to give the work his personal attendance, to submit to the superin-
tendence of an inspector, appointed by the committee of management, and to the works
being measured every month, when an order is given for the amount to be paid; he is also
required to furnish securities for the completion by a certain time; when this is effected, the
management devolves upon a committee appointed by the great body of shareholders.
The engineer thus becomes instrumental in advancing the welfare of the nation; without
him none of these improvements could be carried on, and hence the absolute necessity for
acquiring all the various branches of knowledge connected with the undertakings alluded to.
Science and art are too often considered to have no reference to each other, and hence the
principles of construction have been fostered by the Institute of Civil Engineers, whilst
what relates to taste and fancy has been considered the province of the Royal Academy.
The future historian of Britain will not refer to her architectural remains, but to the
vast works of the engineer, by which to judge of the habits and civilisation of the age.
The architect is too generally confined to the pencil, in other words; to the production of
a beautiful drawing, a point by no means to be undervalued; but of what use is the
creation of designs, when unaccompanied by a knowledge of the construction by which they
can be carried into effect? A picture will not show whether the material has been well
selected or judiciously employed, or if the voids and supports are properly proportioned:
on the other hand the study of the engineer is often too exclusively directed to the display
of mere mechanical skill, without the attempt to produce a good effect; still the demand
for the ability in question is now so great, that without an increased energy on the part of
CHAP, VIII.
307
BRITAIN.
the architect, he will be superseded by the engineer; there is no reason why the labour of
necessity or usefulness should not be embellished by taste, and a great nation has a right to
expect the union of science and art, based on the severest integrity, in those to whom millions
are entrusted for her improvement.
It is not possible to form an estimate of the sums expended by individuals and companies
during the last century on roads, bridges, canals, harbours, docks, and mining operations,
where the services of the engineer were demanded; that the amount exceeds that of the
national debt there can be no doubt, and a thousand million sterling would not be overrating
the total outlay. Many of the bridges have cost upwards of a million, and the railways
completed considerably more than a hundred million; how much of this vast sum has been
improvidently expended cannot now be estimated, but probably more than half.
We may
consider that to the middle of the last century, the drainage of the land, the embankment of
rivers, and the extracting of ores, was performed by individuals who had no claims to the
title of civil engineers; it was his knowledge in mechanics that induced a member of the
Royal Society to select Smeaton as the builder for Eddystone Lighthouse. In the middle
ages towns and cities were walled in, and castles and cathedrals built, by the enterprising
confraternities of Masons, who travelled from place to place under the direction of a
governing body: to them were confided constructions of every kind, and the intelligent head
of the Lodge acted as architect and engineer; old London Bridge, and the walls which
surrounded Dover, Hartlepool, and other harbours, evince their skill in such constructions.
The same causes which led to their dissolution buried for a time the knowledge which had
rendered such important service to the country; but when internal tranquillity was restored,
the whole extent of our coast, and the navigable rivers which discharge themselves into
the ocean, received improvement, though this was often effected by men who had obtained
a reputation abroad; vast tracts of land were redeemed from a state of marsh by engineers
from Holland: all these important undertakings were conducted in a rude and imperfect
manner; the philosopher had not directed his studies to what was useful, and mathematical
knowledge was slighted by the unlearned practitioner.
The Ports and Harbours of Britain first claim our attention, and although it is not
possible to do more than briefly describe them, we may, where information is afforded, give
an account of some of the improvements they have undergone; it must, however, be admitted
that much remains to be performed, before they will answer the growing wants of our
great commercial intercourse.
The Thames, that gentle, deep, majestic king of floods, seems to have been the resort of
commerce at a very early period, and on its banks, where the capital is now situated,
formerly stood Llyn-Din, or the town on the lake. This river, which is of such im-
portance to British commerce, passes through a rich and fertile district; the basin of the
Thames, or the land it drains, has been computed as equal to an eleventh part of England
and Scotland, and as containing nearly a fifth of the entire population. It rises on the
Coteswold hills, and receives its supplies at first from the Lech, the Colne, the Churne, and
the Isis; the latter flows by Cricklade, and is rendered navigable for small craft at
Lechdale, on the confines of Gloucestershire and Berkshire. The Windrush and Evanlode
run into it a little below, and at a short distance further the Thame enters it near Dor-
chester; the whole is then called Thame Isis. After passing Reading, it receives the
Kennet, and below Staines the Wey; when flowing through the metropolis, it has other
tributaries in the Lea, the Ravensbourne, the Darent, and the Medway.
From Lechdale to London Bridge, the distance by the river is 146 miles, with a
total rise from low water mark, at the bridge, of 248 feet; the tide flows up 183 miles, to
Teddington, where is the first lock to aid the navigation. The low water surface of the
river falls about 16 feet 9 inches from Teddington lock to London Bridge, or 103 inches
per mile on an average.
The high water mark at Teddington is 18 inches above the high
water mark at London Bridge, and the time of high water is later by about two hours.
The fall of the bed of the river in this distance is about 12 inches in a mile.
The Thames flows with a regular and steady current, and is of a considerable depth above
Greenwich; at ebb tide it is generally from 12 to 13 feet; the tides at London Bridge rise
ordinarily about 17 feet, and at extreme springs as much as 22 feet. Ships of almost any
tonnage can get up to Deptford; those of 1400 or 1500 tons to Blackwall, whilst St.
Katherine's Docks will not receive vessels of above 800 tons.
The whole course of this noble river measures upwards of 200 miles, and it drains a
surface of country equal to about 5000 square miles; its meandering is considerable, as a
straight line drawn from its two extremities is not much more than half the before-men-
tioned distance. Its velocity varies from mile to 2 miles per hour, and the mean has
been computed at about 2 miles per hour.
On the southern banks, below London Bridge, are many docks, and the government
establishments of Deptford, Greenwich, and Woolwich, and on the Medway, Chatham and
Sheerness. On the northern banks are several docks, belonging to the St. Katherine,
x 2
308
BOOK I.
HISTORY OF ENGINEERING.
London, and East and West India Companies, and many private establishments for ship-
building.
St. Katherine's Docks. A company was incorporated by an act passed 6 Geo. 4. c. 105,
and the docks were opened the 25th of October, 1828. The capital raised by shares
amounted to 1,352,800l. and an additional sum of 800,000l. was borrowed on the security
of the works which had been performed; the engineering department was under the
direction of Mr. Thomas Telford, and the warehouses under that of Mr. Philip Hardwick.

籽
​--
WESTERN.
JUL
་
.
•
་
•
BASIN.
•
、
•
་
·
EASTERN DCCK.
•
*
Fig. 308.
ST. CATHERINE.
These docks occupy a space between Tower Hill and East Smithfield, and communicate
with the river by a lock 180 feet in length, and 45 feet in width; its construction admits
vessels of 600 tons burthen, 3 hours before the time of high water. The depth of water on
the sills at spring tides is 28 feet, at dead neaps 24 feet, at low spring tides 10 feet, and at
low water neap tides 12 feet, Trinity datum.
The area occupied by these docks within the walls is 24 acres, 11 of which are water;
the two docks communicate with each other by a basin, and are surrounded by wide quays
and lofty brick warehouses, where the goods are at once housed by cranes out of the holds
of the vessels.
Between the docks and the Tower is a wharf, having a frontage towards the river of
187 feet.
Before these docks were commenced, numerous borings were made to the depth of
40 feet.
The lock entrance, and the sills under the two middle lock gates, are fixed at a depth of
10 feet under the level of low water mark of an ordinary spring tide.
The vessels pass
from this lock into an entrance basin of about two acres, and thence, through a single pair
of gates, 45 feet in width, into the eastern dock, and by similar means into the western,
each of which contains nearly two acres.
The bottom of the docks and basin is 4 feet above the outer and middle lock sills, and
the height of the quays is 8 feet above the water in the docks, which is always preserved at
the same level by means of two steam engines of 80 horse power each, which can fill the
lock in seven minutes, and the process of lockage may, without affecting the water in the
basin, be continued, as long as there is sufficient depth of water outside the lock gate.
The small area of these docks, and there being but one entrance, suggested the employ-
ment of steam engine pumps, as well as the laying the lock sill so much under the level of
CHAP. VIII.
309
BRITAIN.
low water on the shore; by which means a greater number of vessels can be admitted
every high water.
The two steam engines can be separately worked, but are connected by a line of triple
cranks, which move six double-action pumps. The pumps are 3 feet in diameter, and
have a stroke of 4 feet 6 inches; these are united to a horizontal iron pipe, 3 feet
6 inches in diameter, bent at one end, where it descends into a well, 8 feet in diameter, the
bottom of which is 3 feet below low water mark. Communicating with this well is a
culvert, 8 feet wide, 6 feet 6 inches high, and 170 feet in length, formed, as is the well, of
ashlar masonry; the bottom is laid 2 feet below low water, at spring tides; over the outer
end is placed a grating, to prevent any matter from entering and entangling the pump
valves. The water raised by the pumps can be discharged either into the entrance
lock or the basin.
At spring tides the depth of water on the sills of the outward lock gates is, at the first
hour after flood, 16 feet; at the second hour, 21 feet 2 inches; at the third, 24 feet; at the
fourth, 26 feet 6 inches; and at the fifth hour after flood, and at high water, 28 feet.
At the first hour after high water it is 24 feet 6 inches; at the second, 20 feet 10 inches;
at the third, 18 feet 2 inches; at the fourth, 15 feet 7 inches; at the fifth, 13 feet 2 inches;
at the sixth, 11 feet 3 inches; and at low water, 10 feet.
;
During neap tides, the depth of water at the first hour after flood is 13 feet 6 inches
at the second, 16 feet 10 inches; at the third, 20 feet 3 inches; at the fourth, 22 feet
7 inches; and at the fifth hour, and at high water, 24 feet.
And at the first hour after high water, 21 feet 11 inches; after the second 18 feet; the
third 16 feet 2 inches; the fourth 15 feet 6 inches; the fifth, 14 feet; the sixth, 12 feet
10 inches; and at low water, 12 feet.
The entrance lock is built of grey stock bricks, laid in mortar made with lias lime; the
platforms, hollow quoins, bond stones, and copings of the lock walls, are of Bramley Fall

ப
T
Fig. 309.
SIDE OF Entrance LUCK.
stone, and the whole so cemented that they form a solid mass. As the site of the docks
and
quays is
upon a hard stratum of gravel, it was found necessary to line the bottom of
the docks, and puddle the back of the
walls, as well as to place the counter-
forts upon foundations impervious to

water.
An artificial concrete, composed of
blue lias lime mixed with eight parts
of coarse sand, was kneaded into a thick
mortar, and spread over a bed, a foot
in thickness, of sufficient size to receive
the breadth of the wall of the counter-
forts and puddle. A wooden sill was
laid under the front edge of the wall,
and a row of sheeting piles, 14 feet
in length, and 9 inches in thickness,
was driven along the side of it, their
joints for 3 feet downwards being
closely caulked.
The facing wall of the whole of
11.6
45.0
Fig. 310.
SECTION OF ENTRANCE LOCK.
11.6
x 3
310
BOOK I.
HISTORY OF ENGINEERING.

E
Fig. 311.
PART OF side of LOCK.


45.0
Λ
52.4
10.0
Fig. 312.
LONGITUDINAL SECTION.
Fig. 313.
SECTION IN MIDDLE.
the quay, to within 14 inches of the top, was laid in blue lias lime mortar, and the re-
mainder worked with Dorking lime.
The brickwork was flushed, and every four courses varied in their diagonal direction.
Commercial Docks are situated on the opposite side of the river to the West India
Docks, and nearly opposite their upper entrance. There are six docks, the largest of

off
12 ACRES
93 ACRES
DOCK
SURREY CANAL
3
DOCK
10 ACRES
DOCK
DOCK
181
ACRES
15 ACRES
L
Fig. 314.
RIVER THAMES
COMMERCIAL DOCKS.
山
​CHAP. VIII.
311
BRITAIN.
which, the Greenland, covers 92 acres. The next dock westward, 12 acres, No. 3, 33;
No. 4, 10 acres; No. 5, 15 acres; No. 6, 181 acres. The space comprised altogether by
these spacious docks is 70 acres, of which 58 are water.
London Docks were established by a company of merchants, under the authority of an
Act of Parliament, obtained in June, 1800. The act had for its outline, that the holders
should have 5 per cent. interest annually, guaranteed upon the capital they advanced, and
the dividends were never to exceed 10 per cent. The capital of the company at first was
to be 1,200,000l., with the power of adding another 300,000l., and the interest of all loans
destined to complete this capital was to be paid before the other dividends.
The pro-
prietors of from 500l. to 10,000l. or more had votes in respective proportions, but no one
was to have more than four.
Nine proprietors were sufficient to call a general meeting, independent of the half-yearly
meetings, for the examination of the current accounts.
The basis upon which the purchase of lands or property necessary for the docks, quays,
and warehouses was distinctly established, and the company was empowered to erect a wall
of inclosure, and to supply the basins from the Thames; to construct all necessary bridges,
and to lay down water pipes and form sewers, subject to the superintendence of the com-
missioners of sewers. The company engaged to complete the works in seven years, to
preserve a certain depth of water before the entrance of the docks, but was forbidden to
build any vessels.

JUULU
ST CATHERINES
DOCK
WESTERN
DOCK
RIVER
THAMES
EASTERN
Fig. 315.
Gang
LONDON DOCKS.
The dock rates were fixed at per ton, according to the official guaging of the vessels, as
follows: - For every ship, trading between London and the ports of Great Britain, 1s.;
Ireland, parts of France, Flanders, Germany, and Denmark, 1s. 3d.; to the Baltic, 1s. 6d.,
and to other places in proportion, whilst the highest duties were to eastern Asia and the
East Indies, 2s. 6d. per ton.
The merchandise shipped or unshipped within the docks pays the same duty as in the
port of London, for anchorage, moorage, and housing.
All vessels laden with more than twenty pipes of wine or brandy are obliged to enter
the London Docks; and there are numerous other clauses referrible to the nomination of
officers of management, &c.
The lower communication from the river is by a long cut, which is called the Wapping
entrance, and higher up the river is another called the Hermitage.
Along the sides of the docks, and near the edges of the quays, are erected ranges of
sheds, of a very simple construction: behind these sheds, which first receive the cargoes
from the ships, and in a parallel direction with them, is a line of warehouses, four stories
high, containing beneath them spacious arched vaults: and covering an area of 120,000
square yards. In front of these splendid masses of building, and along the whole length
of the sheds, are iron railways, with others at right angles, which lead from the quays to
the several loop-hole entrances of the warehouses.
These works were commenced in 1800, under the superintendence of Mr. Rennie, and
in five years the establishment was opened for merchant vessels; during the progress, a
steam-engine of twenty horse-power was constantly at work, to pump out the water
which filtered into the excavations. This engine, made by Boulton and Watt, raised nine
X 4
312
Book I.
HISTORY OF ENGINEERING.
Fig. 316.
cubic yards of water per minute to the height of 33 feet, and consumed two bushels of
coals per hour; it turned a drum bearing an endless chain, which glided in an horizontal
direction upon rollers, and passed over a second circular drum; to which was attached an
eccentric pin, the action of which raised the piston of a powerful pump.
In order to prevent the links of the chain from becoming loose by their expansion, and to
make them always press equally upon the two drums, so that they should transmit and
receive motion from each other, there were two parallel upright posts, between which the
chain passed; here was introduced a heavy roller, which mounted or descended in grooves
and rested on the upper part of the chain, thus, by its constant weight, exerting an equal
tension on the two drums.
There are two capacious docks; the western covers an area of 20 acres, being 420
yards long, and 320 yards wide. The eastern dock has an area of about 7 acres. The
entire area within the boundary walls of the whole is a little more than 71 acres.
The tobacco warehouses, on the north side of the tobacco dock, which is more than an
acre in extent, are the largest and most convenient to be met with. They cover 5 acres of
ground, and will contain 24,000 hogsheads of tobacco.
The vaults under the warehouses include an area of 18 acres, and can admit 6000 pipes
of wine.
East India Docks were erected after the passing of the act in July, 1803, which au-
thorised the formation of a company consisting of thirteen directors, elected in fourths every

IMPORT DOCK
EXPORT DOCK
ENTRANCE
EAST INDIA DOCKS.
THAMES
RIVER
year. Every fourth year four nominations are made instead of three: each director to
possess at least twenty shares, and four to be directors of the East India Company.
The
general interests and accounts of the company are laid before two meetings, held in
January and July every year. Persons who do not possess five shares are not allowed to
vote.
The import dock contains 19 acres, the export nearly 10 acres, and the basin 3 acres;
the two docks are connected with the basin by two short locks, making a total superficies of
32 acres. The depth of these docks, measured from the levels of the quays, is 27 feet.
Vessels enter from the Thames by a lock opening in the west side of the basin, over
which is a light iron bridge, 4 feet in breadth, for foot passengers.
The import dock is 1410 feet in length, and 560 feet in breadth.
feet in length, and 463 feet in breadth.
The export dock is 760
The various works were executed under the direction of Mr. Ralph Walker and
Mr. John Rennie.
Fronting the river is a quay nearly 700 feet in length, and the export dock has a lofty
building in which is machinery to mast or unmast the largest vessels.
Since the dissolution of the East India Company as a commercial corporation, these
docks have been opened to vessels from all parts of the globe.
RIVER
CHAP. VIII.
313
BRITAIN
RIVER THAMES
Fig. 317.
Brunswick Wharf, in front of the East India Docks. In 1834 this quay was found to be
in a state of decay, and being required for the accommodation of a large class of steam
vessels, Messrs. Walker and Burgess were employed as engineers to put it into a proper
state, and the new iron piling and wharfing were executed.
A trench 6 feet wide was opened in the direction of the intended line, and the guide
piles were then driven; the main piles, which are of iron, were placed at intervals of
feet, and the intermediate bays were filled in with the iron plates. The piles are each in
two pieces, the upper one fitting into a socket-head formed on the lower, the union being
made perfect by a strong screw bolt: each sheet pile is secured at the top by two bolts to
the uppermost wale of the woodwork immediately behind them; they are of iron 14 inches
in thickness, and the weight of each is 17 cwt.
These plates filling up the spaces over the sheet piling are bolted to the main piles, and
to each other, and the joints stopped with iron cement, and where the mooring rings are
introduced, they are cast concave with a hole to allow a bolt to pass through, which is
secured as well as the land ties from the main piles to the old wharf, which was not
disturbed.
The West India Docks are considerably larger than the London, and are situated about
1 miles below them in the Isle of Dogs, on a peninsula formed by the winding of the
Thames. These docks were commenced on the 12th of July, 1800, and as early as the

LIMEHOUSE
BASIN
IMPORT DOCK
EXPORT DOCK
SOUTH DOCK OR CANAL
WEST INDIA docks.
II
TIMBER DOCK
BASIN
month of September, 1802, vessels entered the import dock. There are two docks, each
about 890 yards in length, running parallel to each other; the largest, 500 feet in breadth,
and destined for vessels returning from the West Indies, contains about 30 acres; the
other, 400 feet broad, about 25 acres. The docks, basins, and locks, together form an area
of 68 acres, whilst the total superficies, including the quays and warehouses, is 140 acres.
204 vessels can be admitted into the import, and 195 into the export dock, forming a
total of 120,000 tons.
At the upper end is the Limehouse basin, containing 2 acres, and at the lower the
Blackwall basin, containing 6 acres.
The docks lie almost from west to east, and the principal entrance, that of the import
dock, is from the west; at the upper and lower end is a basin with three locks; the first
communicates with the Thames, the water being retained by double gates; the second and
third locks also have double gates, and communicate with the export and import docks.
By these arrangements vessels can enter the basin whatever may be the state of the tide,
and remain as long as may be required.
As the water in the docks is very little higher than that in the basin, there is no stress
upon the lock gates, and remaining some time in the basin before it is passed into the docks
the sediment is entirely deposited.
Parallel with the northern quay of the import dock is a range of sheds, 880 yards in length,
which communicate with the warehouses, six stories high. The sheds are supported by cast-
'RESERVOIR
RIVER THAMES
314
BOOK I.
HISTORY OF ENGINEERING.
iron columns, and paved with´ slabs of granite, except at the water's edge, where there are
iron plates for the more easily working of the trucks, which are drawn by two men, who
transport the various casks to the entrance of the large warehouses.
Along the southern quay is a shed with an iron roof covered with slate, and also sup-
ported by iron columns; this shed is 443 yards in length. To counteract the effects of ex-
pansion and contraction, of which the metal is susceptible, the iron tie-beams which rest on
the columns are not closely united, but a sufficient interval is allowed to admit of some
play.
Under the sheds are spacious cellars, with octagonal pillars of stone, supporting flat
brick arches; they are lighted by vertical openings taken from the interior of the sheds above
them. Where two vaults intersect, a cylindrical well is built up, through which the light
descends from a lantern. On a level with the floor of the sheds, plates of cast-iron cover
these wells, and in them are fixed five lens or glass illuminators. Reflectors have also been
most ingeniously introduced to distribute light in various parts.
Iron railways are not used on the quays, but in their stead large slabs nicely fitted toge-
ther, upon which the friction of the wheels is inconsiderable. In the middle of the pave-
ment there are two rows, running parallel with the quays and warehouses, and opposite to
each crane a double row conducts to the warehouse doors, or the sloping passage to the
vault.
East of the docks is the mahogany shed, which is remarkable for the machine used in
piling up the vast logs imported from the West Indies; five men, by the aid of this
machine, move logs weighing as many tons with facility.
William Jessop furnished the plans for the West India docks, and superintended their
execution, as did Mr. Gwilt those for the warehouses.
Deptford is situated on the southern bank of the Thames, not far from the mouth of the
little river Ravensbourne, which rises at Keston, in Kent, near the remains of the Roman
camp.
Henry VIII. established there a royal dock, or king's yard, which has been considerably
improved since that time; at present it comprises upwards of 31 acres, contains wet docks,
slips for men-of-war, basin, mast ponds, and several storehouses. The old storehouse is a
quadrangular pile, and was built in 1543. The roofing, which covers some of the slips, is
a fine example of carpentry. At a short distance on the north is the victualling yard, with
steam mills for grinding corn, ovens for baking biscuits, cattle-sheds, slaughter-houses, a
cooperage, and packing-rooms. There are houses for the residence of all the officers be-
longing to this most important establishment.
Woolwich, on the same bank, farther down the river, has a much more extensive dockyard,
which was established at a very early period. The ship Harry Grace de Dieu, of 1000
tons, was built here in 1512. The dockyard has been enlarged from time to time; at pre-
sent it is about 5 furlongs in length and 1 in breadth. Within this area are dry docks,
mast ponds, slips, smithery, anchor manufactory, model lofts, storehouses of various descrip-
tions, mast houses, sheds for timber, and dwellings for the superior officers. Several of the
largest vessels in the British navy have been built there.
The dry dock, erected under the superintendence of Mr. Walker, is one of the most com-
modious lately built. After the site was excavated, a foot of brickwork was laid over the
whole, then a course of granite 3 feet 6 inches in thickness. The base is 230 feet in length,
and of a proportional breadth; the dock will contain vessels of 300 feet in length, owing to
the excellent manner in which it is arranged.
Another dock, similarly constructed, 360 feet at the base, will admit vessels of 400 feet
in length on the upper deck.
Many timber piers have been carried out from the banks of the Thames within the last
few years, for the convenience of the steamboat passengers, some of which are between 300
and 400 feet in length; the most important of these are at Erith, Greenhithe, and Grays;
it is difficult to say how long the timbers may remain uninjured by the Teredo navalis,
which does great injury below Gravesend.
Gravesend, which contains a population of nearly 20,000 persons, being much resorted to
during the summer months, has grown into considerable importance: steamboats are con-
stantly arriving and departing. In 1833 an act was obtained to construct a new landing-
pier, and thirteen months afterwards the present town pier was opened to the public;
W. T. Clark, Esq. was the engineer employed by the corporation, and Mr. William Wood
contracted to perform the work for 87007. It extends 127 feet from the front of the town
quay, and is 140 feet wide, being built upon cast-iron arches of that span, with a rise of 6
feet; the land arch springing from the stone wall of the quay, and all the others from
columns. The transverse arches and framing, also of cast-iron, are supported by eight
columns on foundations of Bramley fall-stone.
At the extremity of the platform is a T head 76 feet in length, and 30 feet wide, under
which are contrived the steps which communicate with a floating vessel, which rises and falls
with the tide, and is always level with the packets alongside.
1
CHAP. VIII.
BRITAIN.
315
The T head is supported upon cast-iron diagonal framing, 6 feet deep, on 18 columns,
which are protected by transverse timbers, 13 inches square, bolted securely together.
Under each of the columns are three cast-iron piles, 14 feet long and 15 inches in diameter;
these were driven into the bed of the river until their tops were 15 inches under water, at
low water ordinary spring tides.

On the heads of each of the
piles is an iron plate, upon
which the column was placed.
The twenty-six columns of
cast-iron which support the
whole pier are each 18 fect
high and 33 inches in diameter.
The platform of the pier is
enclosed by an open parapet,
and the ends of the T are formed
into pavilions, which afford
shelter in inclement weather.
At the end of the pier is a cast-
iron column 35 feet in height,
including the base and lantern,
which is lighted every evening
with gas.
Particular attention was re-
quired to have the heads of the
iron piles, which were driven
into the chalky bed, perfectly
level before the bases were put
on, and this was effected by
means of a wooden cylinder,
9 feet in diameter, and 9 feet
in length, made of 3-inch
deal battens, firmly keyed and
hooped together, the lower end
being shaped like a sheet pile,
and shod with iron. This
cylinder was lowered over each
set of three piles, and loaded
sufficiently to cause it to sink
through the soft mud of the
shore, when it was driven into
the hard ground. The water was
then pumped out, and the mud
removed low enough to enable
the workmen to reduce the
Fig. 318.
T IT T
town pier, Gravesend,
1998898
heads of the piles to a uniform level by chipping, so that the bases of the columns were
fitted down to the tops of the piles, metal and metal, and this operation was repeated as.
often as was required.
Upon the columns are placed cast-iron ribs, 40 feet in length; each arch is composed of
two, secured together by 1 inch screw bolts and nuts. The whole structure consists of
four such arches, which are strutted by other castings, firmly screwed to them. The
various portions of the iron framing, for the support of the platform, were fitted together
in a temporary manner on shore, previously to their being applied to the columns, which
prevented any cutting or chipping away of the iron work already placed.

Fig. 319.
TOWN PIER, Gravesend.
At the Terrace Gardens, lower down the river, another cast-iron pier has just been com-
pleted, under the direction of Mr. J. B. Redman, which projects into the river 200 feet at
316
Book I.
HISTORY OF ENGINEERING.
high water.
The total length, including the abutments, is 250 feet; it is terminated by a
T head, 90 feet in length, and of the same width as the main portion of the pier, which
is 30 feet. The platform is supported by 22 cast-iron columns, with girders of the same
material.
There are three columns on each tier, with girders of 22 feet span, and three main spans
to where the T head commences; the first two are each 50 feet, the other 51 feet. The
columns are 28 feet in length, except in the first tier, which are shorter; their bases


MUD
SAND
SPRING
TIDES
SILT
SAND
GRAVEL
FLINT
CHALK
CONCRETE
Fig. 320. TERRACE pier.
Fig. 321.
TERRACE PIER.
are laid level with low water spring tides, and their caps 8 feet above the level of high
water spring tides, which rise 20 feet, so that there is never less than 8 feet headway
throughout.
By means of a tide guage, employed whilst the works were in progress, it was found that
the greatest rise of the tide was 22 feet 9 inches, and the lowest ebb was 1 foot 9 inches
CHAP. VIII.
317
BRITAIN.
below the zero on the scale; which gave the total lift of the tide 24 feet 6 inches; but on
October 18, 1841, the tide rose one foot higher.
The excavations for the several works are carried down one foot below the level of low
water spring tides, and rest upon a bed of flints, which cap the chalk.
The first tier of columns, 15 feet long, is placed upon stone bases, which rest on brick
piers 7 feet 6 inches square; and the other columns were fixed by means of cast-iron
cylinders 6 feet in diameter, formed

of segmental plates, firmly bolted
together. When the first cylinder
had been forced into the mud, others
were placed upon them, and secured
by iron bolts, thus forming a species
of coffer-dam.
To base some of the columns, it
was found necessary to have cylin-
ders 7 feet in diameter, supported
with pieces of timber; when these
cylinders were above high water
mark, others, 6 feet in diameter, were
made use of.
·30 ft.
For the foundations of the T
head, the outer cylinders or coffer-
dams were not used, guides being
substituted for them, formed by
placing timbers on the land, bolted
to the fender piles, and so placed
as to enclose a tier of three cylin-
ders; across these timbers planks
were laid down and nailed, so that
there was a square space through
which the cylinders could sink; they
were guided above at the level
of high water by a ring of wrought
iron, held by four guy chains se-
cured to the fender piles; to the
metal ring were attached four iron
rollers, which enabled the cylinder to slide freely through it, by which means they were
placed very correctly.
Fig. 322.
TERRACE PIER SECTION.
The cylinder plates are five-eighths of an inch in thickness, and when placed, they were
weighted with five or ten tons of stone, according to the resistance presented.
After the several cylinders were sunk to their required depth upon the solid chalk, a
floor was formed of two courses of dry brick, and a thickness of 18 or 24 inches of brick-
work was brought up in Roman cement, with two courses of plain tiles, also in cement;
this was done for the purpose of keeping out the spring water, which, in some of the found-
ations, was found to rise in considerable quantities; it was led up through a pipe 6 inches
in diameter, bedded upon the dry courses below, to the mouth of which drains were formed,
from where the water was most abundant. The water was pumped out by this means, and
kept below the level of the work as it proceeded. When the bottom was found sound the
pipe was filled with concrete, formed of Thames sand and Roman cement, and a blank flanch
secured over the top.
After the cement foundation was completed, a cast-iron cross, with a wrought-iron
holding down bolt through it, was bedded on the work; the rest of the brickwork was car-
ried up in mortar, composed of blue lias and puzzolana in equal proportions, with two and
a half measures of clean river sand, and iron hoops were laid between the several courses
to bind the whole together.
The iron bolt was frequently plummed upright as the work proceeded, and a space of
some inches was left around it to afford facility for its adjustment; after which it was filled
up with concrete.
Upon this brickwork was laid a circular base of Bramley Fall stone, bored to pass over
the bolt; and being properly bedded, the columns were lowered and placed upon it. Each
is in one casting, 26 feet long, 4 feet in diameter at bottom, and 3 feet at top; one column,
which rather exceeded 1 inches in thickness, weighed 10 tons, the others averaged about
9 tons each. They are held together at top by cast-iron cross-bracing frames, fitted and
bolted between the caps. The three girders which rest on the first three columns, and those
of the T head, are cast to one section; six of them are 54 feet 9 inches long, and the three,
next the T head 55 feet 9 inches long.
The Doric entablature which surrounds the pier and forms the casing to the external
girders and parapet is 7 feet in height, and rises 2 feet 9 inches above the platform.
918
Book I.
HISTORY OF ENGINEERING.
The platform is of Memel timber; the joints are caulked down upon the girders, and are
covered with 3-inch plank.
The front of the pier is protected by dolphins, one in the centre, and one outside each
wing, and the whole of the piles are sheathed with copper. The dolphins keep the barge
at a parallel distance from the T head, where the platform is approached by two flights of
stairs, with landings at convenient levels between the outer rows of columns, and a trans-
verse flight from above.
The roof of the pier is of iron; the principals are formed of two pieces of wrought angle
iron, with a wood flitch between them, to which the slate boards are nailed; they are
trussed with wrought-iron, with a cast-iron strut on either side. The supporting brackets
are secured to the gutters by two wrought iron bolts, which are carried through the gutter.
Six small skylights are placed over the platform at the entrance, to admit light when the
shutters at the side are closed.
The lighthouse over the T head is supported upon four inclined truss bearers; the centre
of the lantern is 40 feet above the datum level of high water; and the total height from the
base of the outer foundations to the summit of the vane is 82 feet.
The pier, lighted by gas, was opened to the public two years after its commencement, in
April, 1843. Messrs. Fox, Henderson, and Co. were the contractors.
Chatham has a dockyard and arsenal on the banks of the Medway, which were established
about the reign of Queen Elizabeth; and Camden describes it as "stored for the finest fleet
the sun ever beheld, and ready at a minute's warning." James I. formed the ordnance
wharf, on the site of the old dock; since which time capacious wet docks, slips, mast
houses, rope walks, sail lofts, smiths' shops, and other buildings, have been erected
upon a very extensive scale, and some of the largest ships in the navy have been con-
structed there. Near the town of Rochester is a victualling office, composed of several
extensive ranges of building, appropriated to the use of the shipping at Chatham, Sheer-
ness, and the Nore.
Sheerness is another dockyard on the Medway, near where that river unites with the
Thames; it is the chief town of the Isle of Sheppy, and situated at its extreme southern
point. This yard was chiefly established for the repair of vessels that were but partially
damaged; but during the last fifty years vast sums of money have been expended upon it
to render the docks complete, and fitted for other uses.

DINANG
BOAT
BASIN
STORE
SAW PITS
HOUSE
LITTLE
BASIN.
RIVER
MEDWAY..
DOCK
BASIN.
DOCK
DOCK.
Fig. 323.
SHEERNESS.
It is well supplied with spring water from a well sunk in 1781, 328 feet in depth. When
the workmen had penetrated through the chalk, and were trying the strata with an auger,
it suddenly dropped, and the water gushed up with such velocity, that the men could with
difficulty be drawn out; in six hours the water rose 190 feet, and in a few days was within
8 feet of the top, and though constantly in use, it has never been lowered more than
CHAP. VIII.
319
BRITAIN.
200 feet; its quality is soft, and its temperature higher than that obtained from ordinary
wells.
Docks and slips have been constructed upon the best principles, and a sea-wall, founded
upon a solid bed, is built along the entire frontage.
After quitting the Thames, and continuing on the line of coast northward, we arrive at
the river Crouch, which has left many deltas; one of these, called Foulness, advances con-
siderably into the sea; the river itself is navigable for more than eleven miles.
Ten miles north of the Crouch lies Blackwater Bay, into which the Chelmar and other
small streams empty themselves; some years ago the Chelmar was made navigable for
small vessels to Chelmsford; the Colne carries small craft to Wivenhoe and Colchester,
which are employed in the oyster trade.
One of the streams which pour forth their waters into this spacious bay is the Idumanum,
on which Maldon is situated.
Fifteen miles farther north is another bay, into which fall the Stour and Orwell; both
are of a considerable width at their mouth, and the first is navigable for 28 miles to
Sudbury, where the Flemings established a manufactory for cloth in the fourteenth cen-
tury.
Harwich, a populous sea-port and a market town, is situated at the north-east extremity
of Essex, on a point of land bounded on the east by the sea, and on the north by the
estuaries of the Stour and Orwell. The inhabitants are chiefly employed in ship-building,
and vessels of considerable burthen have been launched from the convenient yards established
here. The harbour is deep and spacious, and the anchorage good. More than 100
sail of the line and 400 colliers are reported to have been seen riding in safety at one
time.
Numerous vessels are fitted out from this port engaged in the fishery trade, and there is
a constant communication between it and the ports of Holland and Germany.
On the south side of Harwich the cliff which divides Orwell haven from the bay con-
tains a stratum of a blue clay, about a foot in thickness, on which is another of the same
thickness, of stone, containing numerous fossils.
Immediately opposite to Harwich, and at the south-east extremity of Suffolk, is a strong
fortification, called Langard Fort; it is built upon a point of land united to Walton Colness,
except at the time of high water, when it becomes an island, nearly a mile distant from the
shore.
The Orwell is navigable to Ipswich, but the port is still much silted up, although in the
reign of George III. an act of parliament was obtained to improve the course up to Stow-
market.
The Deben discharges itself at Felix Stow, north of Harwich Bay, and is navigable to
Woodbridge, a distance of ten miles.
Orford, situated on the confluence of the Alde and Ore, was once a place of considerable
importance: the keep of the ancient castle remains; its plan is polygonal, having 18 sides
described within a circle whose radius is 27 feet; three square towers, placed around it at
equal distances, flank the walls, each measuring about 22 feet in width, projectimg 12 feet,
and 90 feet high. The walls at the base are 20 feet in thickness; the whole is surrounded
by ditches, and was formerly by a circular wall 40 or 50 feet in height; this Norman castle
is chiefly built of Caen stone.
The decline of the town is ascribed to the loss of its harbour, occasioned by the bar
thrown up, at the mouth, which has caused the sea to retire altogether. The accumulations
of sand on this coast have also destroyed the importance that Aldborough once possessed,
which is situated on the same river.
Southwold, on an eminence overlooking the German Ocean, is nearly surrounded on
every side by the river Blith, which here discharges itself into the sea.
The herring
fishery once contributed to its wealth and importance. About the middle of the last
century a pier was erected on the north side of the port, and a few years afterwards another
on the south. Two docks were also laid down by the Free British fishery, and numerous
magazines for depositing stores were constructed.
Southwold Bay, or Sole Bay, as it is commonly called, was rendered celebrated in 1672,
by the action fought in it between the combined fleets of England and France against the
Dutch, commanded by De Ruyter.
Lowestoft is situated on the easternmost part of the English coast, upon a lofty eminence
commanding a fine view over the German Ocean; and near the edge of the cliff, north of
the town, stands the upper lighthouse, erected in 1676, which is a circular tower of brick,
40 feet in height, and 20 in diameter. This lighthouse originally had its upper story or
chamber glazed all round, and within was kept burning a coal fire, which was visible at
night for a great distance at sea. In 1778 the brethren of the Trinity House altered this
arrangement, and erected at the summit one of the newly contrived cylindrical lanterns.
Another lighthouse, of timber, is placed below, so that vessels coming into Lowestoft
roads are directed to the Stanford Channel,, which lies between the Holme and Barnard
320
Book I.
HISTORY OF ENGINEERING.
sands.
This channel is mile broad and mile from the shore, and is continually changing
11
its direction; it is, therefore, necessary constantly to move the position of this timber light-
house, in order that it may be placed in such a manner that it covers the great lighthouse,
to vessels entering. The herring fishery forms the principal trade, and the ships employed
are about 40 tons burthen.
Farmouth is admirably situated for the commerce of the north of Europe, and for the
inland navigation of the county of Suffolk, from which it is separated by the Waveney.
The town, which is in the county of Norfolk, is placed upon a bank of sand that became
firm ground, and was first inhabited about the time of the Norman conquest, when a wall
was built around the town, and a broad moat formed outside.
The haven has been a constant source of expense; the present is the seventh which has been
formed, and it is yet subject to all the inconveniences of the former. It was executed under
the direction of Joas Johnson, a Dutchman of some experience, who commenced his ope-
rations by driving and hedging down on the north side large stakes and piles to render the
foundations firm; upon the south side the same system was adopted, that the refluent tide
might be forced to run out by a north-east channel. Piers and a jetty were erected to
prevent an overflow, and to preserve a sufficient depth of water for vessels to float at all
times.
The north pier, which was the principal, was made 40 feet wide at bottom, 20 feet at top,
and 235 yards long. The whole was executed with timber of large scantling braced
together, and bound with iron. This pier was defended by a jetty, 265 yards long, 16 feet
wide at the base, and 8 feet above. The south pier, 340 yards long, 30 feet broad, and 30
high, 24 feet of which were under water, was built to prevent the waters of the old haven
from running out southward.
The haven measures between the two piers 1111 yards, and is constantly receiving some
improvement. There are two lighthouses on the coast for the benefit of Yarmouth Roads,
one at Caister and another at Garleston; this coast is very dangerous, and it is recorded
that more than 200 sail of vessels and 1000 men perished in one night, in the year 1692.
Numerous sand-banks on this coast are continually shifting, but the sea has not
encroached upon the shore since the sixteenth century. The great estuary, in the time of the
Saxons, reached as far as Norwich, which was then situated on an arm of the sea. Since
Yarmouth was first occupied, the sands have wonderfully increased, and a line of dunes is
formed across the entrance of the entire estuary, which increasing both in breadth and
height effectually has shut out the tides, and narrowed the passage of the river, which has
varied its course several times; the tides at the river's mouth now only rise 3 or 4 feet, and
at springs 8 or 9. Thousands of acres have been reclaimed in consequence, which are
interspersed with upwards of sixty fresh water lakes, varying in depth from 10 to 30 feet,
and in extent from 1 acre to 1000. The Yare passes through some, and by depositing its
earthy matter tends to render them a productive soil, if the sea does not again break in upon
them, which sooner or later must be the case, as the shore about Yarmouth is constantly
wearing away by the current which sets on it from the north-west, preventing any per-
manent delta from forming on this coast.
The Waveney, which separates Suffolk from Norfolk, is navigable for 25 miles to
Bungay; and the Yare, which also empties itself here, for 22 miles is navigable to
Norwich.
Wells, a small sea-port town on the coast of Norfolk, possesses a good harbour with a
deep channel, but difficult of access, in consequence of the shifting sands.
About the year
1719 the river which constitutes the harbour was improved, and a considerable quantity of
land, redeemed from the marshy state, was rendered valuable for agricultural purposes by
embanking it, and preventing the sea from any longer overflowing. Holkham marsh,
including the creeks, consisting of 560 acres, was embanked at the expense of Lord
Leicester, and 108 acres, called Wells marsh, at the expense of Sir Charles Turner; soon
after, upwards of 1500 acres more were reclaimed; and in the year 1738, immediately
below the town a sluice was formed called Friestone, after the name of the builder; it was
constructed with fascines, stakes, piles, &c.; these in a very few years went to decay, the
mouth widened, and it became necessary to reconstruct it, which was effectually done
in the year 1765, when the harbour and channel down to the pool or mouth, which opened
into the German Ocean, were perfectly scoured.
This second sluice soon required repairs, in consequence of the timber of which it was
composed being eaten by the worm.
In the year 1782, so much mischief had accrued, that it became necessary, to prevent the
loss of the harbour, that something effectual should be undertaken, and Mr. John Smeaton
was called in to report upon the best means of performing the necessary works.
This en-
gineer found that as long as the sluice had been maintained in proper order, it had answered
the intention of clearing and keeping in good condition the whole of the harbour and channel
which intervened between the mouth of the sluice and the upper or south end of the pool;
that since its decay the pool had so filled up, that at low water there was not more than 6 feet
CHAP. VIII.
821
BRITAIN.
depth; and that about twenty years before this survey, the direction of the harbour out to
sea was north-west, and that vessels could be easily brought, during all the time of flood, in
the direction of the channel. The entrance had veered, so as to be north-east or north-

Fig. 324.
WELLS Harbour.
east by north, which rendered it difficult for vessels to enter. The distance from the
quay to the channel was then between three or four miles, and the course of the waters
was through broad and open sands, from the northward or out end of the pool to its
outfall into the sea; the sand is perfectly clean, and so free from any particles of other
matter that produce tenacity, that when dried by the sun it is moved easily by the wind,
and is also considerably acted upon during storms; these sands now extend very consi-
derably more in breadth than formerly.
Smeaton observed that the annual rains did not, in any way, increase the waters of the
ocean, so as to cause it to swell its limits, exhalation raised by the power of the sun
and winds keeping it at a constant level, but that the floods and rivers carried with them
earthy matter, which was left either in the channels of rivers, or was borne out to sea;
that these matters were not returned to the land, as water is by evaporation, but was
left to a slow increase, and by the flux of the tides, and the agitation of the winds, was con-
stantly in a state of motion, not only about the mouths of rivers, but in more distant parts;
that there is no power of nature to return these particles of earthy matter to the coasts or
high grounds, from whence they may have been disintegrated, and that, by their accumu-
lation in the ocean, they must always be on the increase, and so continue, till the place of
their reception is entirely filled up.
At one period probably the whole of this coast presented nothing more than a naked
sand, lying against the bare shore, upon which the town of Wells now stands; in the
course of time, the breadth of this sand increasing, and the declivity becoming too smal
for the tidal water left by the flood to make its retreat, so as to keep pace in its return
with the ebb at sea, a body of water would be left behind, which having a sensible
declivity towards the sea, made its way into the lowest slades, and there cut a gully, which
was again enlarged by the influx and efflux of the tide; a scour thus produced would keep
the passage open, by letting a certain quantity of water in and out; but the breadth of the
sands gradually increasing, a greater body and surface of water would require a passage,
which would increase its power of scouring: the gully by this means would be widened
into a fleet or creek in the course of time. By this process, the sand furthest distant from
low water being mixed with clayey matter, brought in by the tide, is on the constant
rise, and after the salt water has left it, and it has been some time exposed to the action
of the sun and air, the surface is fitted for vegetation. and in time becomes a salt
marsh.
These marshes at Wells having increased in height as well as in breadth, a greater body
of water is left upon them; the gullies or creeks multiplied with the increase of breadth,
and the larger ones increase in size and depth: at Wells, these having been collected into
one now serve to scour the channel.
Y
322
Book I
HISTORY OF ENGINEERING.
The marshes increasing in breadth and height have a greater surface of water upon them,
but not an increased depth; and yet, there is more water requiring a passage to the sea
than before; for as long as the depth of water is considerable upon these salt marshes, the
water makes its way to sea, by settling gradually, and passes off, in the nearest direction
over the marsh surfaces, without having any need for the gullics and creeks as drain.
last foot in depth, over the whole surface, is what produces the scour, in the several gullies;
and this is increased to a great degree, in consequence of the water having retreated from
the gullies, and allowing the full force of their draining off to operate upon their
channel.
The
Whilst the neap tides were suffered to cover the surface of the marshes, the scour would
be on the increase, and the harbour improved; but as soon as this scour was diminished,
the gullies would become choked up, and the harbour in proportion injured.
The elevation of the surface of the salt marshes, from the fresh deposit of mud at every
time they were overflowed, would not stop at the neap tides, but would gradually rise
higher and higher towards the high water of spring tides, until they became so high that
no embankments were necessary; and the same effect would happen in all the creeks and
gullies, which would elevate their beds in the same proportion. The surface of the
marshes, rising higher and higher from the neap to the spring tide mark, they became less
overflowed, and the gullies, not having so much water down them, would grow less
capacious; the creeks would suffer from the same cause, and eventually the main channel.
The tide water, however, at the same time flowing in through the creeks and gullies to
the several extremities of its branches, must flow back the same way, and their extremities
would be the first to silt up; this progress continuing, and there being no natural tendency
at work as a remedy, it alone could be changed by employing human ingenuity and labour
The harbour of Wells was kept open by the reflow of the tidal water, or, as it is called, the
back water; and whatever has cut off or diminished this has been a detriment to the
scour, and to the maintenance of the channel.
When a backwater, assisted by a large freshwater river, makes its way through moveable
sands, its direction will be that where there is the greatest declivity; and if that happens
to be in the shortest direction, it has no natural tendency to gain a longer course, which
would necessarily lessen its force; and wherever we find water flowing in a course that is
not the shortest, we may conclude that it has a more speedy descent in that direction
than in any other, and thus it is that many streams have a meandering course.
"The
bar at the mouth of the harbour appears not to have been noticed by Smeaton, as of
much importance to the hindrance of the navigation, nor did he fancy that it formed any
injury to the entrance for the shipping. Between Hunstanton and Weybourne on this
coast are numerous low dunes or hills 50 or 60 feet in height, which are formed along the
shore, and are composed of blown sand; these in the course of time are united into a solid
and compact mass by the roots of the Marram, or Arundo arenaria; and such is the present
set of the tides along this shore, that the harbour is now securely defended by these natural
barriers.
"The harbours of Wells, Clay, and many others, arc defended from all encroachments by
the ocean, by such deposits which have entirely altered the contour of the coast.
King's Lynn Harbour was a place of importance at the time of the Norman conquest.
It is situated on the Great Ouse river, where its breadth is very considerable; the town is
on the eastern bank, at a distance of about 10 miles from the ocean, and four small rivers
or fleets divide it into several parts.
"Mr. John Smeaton, who reported upon the state and improvement of this river harbour,
in the year 1767, found that the course of the Ouse was in as good a condition as it had been
described in former accounts, and that there was no material cause of complaint. A bar
had formed itself on the upper mouth of the west channel, and the current at low water was
confined to the east channel, which was proportionally improved in consequence; nature, in
spite of all the objections made to the contrary, had taken this course, and Smeaton was not
willing to propose any thing which should counteract her intentions.
"It had been suggested some years before to build two jetties, to prevent too much swell
running into the harbour, which should serve also to remove the bar forming in the east
channel; but Smeaton was of opinion, that where a channel must be maintained through a
vast mass of sand, capable of shifting by winds, seas, currents, and other powers, the more
directly the waters make their passage out to sea the better. Any check given to the
indraught of the raging tides, which was complained of, would also check the moderate ones,
and the greater the efflux, which in some measure depends upon the influx, the better the
channel would be made and maintained. Too great tides may be a partial evil, though a
fault on the right side, and in this, as well as in many affairs of human life, the judgment
consists in choosing the least of two evils.
"It was not wise to affect the indraught of the tides, or to diminish the quantity of fresh
water coming down the river from above, but to leave nature to do what was required; for
CHAP. VIII.
323
BRITAIN.
wherever there are many acting forces and disturbing causes, the goodness of the channel
may by turns be better or worse; but the grand principles of preservation being main-
tained, after a wrong turn happens, a right one will succeed, as experience has shown in
the present case; when nature tends rightly, leave her alone; it is time enough to help
her when we are sure she is going wrong."

Fig. 325.
ان
KING'S LYNN.
Having already discouraged all attempts to prevent the free influx and efflux of the tides
and land waters, in order to preserve the channel out to sea in the most effectual manner,
upon which the navigation and drainage by the Ouse entirely depend, he then speaks of
the banks of the river, and says that they ought to be made stout and high enough to stand
against all extremes; he disapproves of all jetties built into the stream, as a defence for
saving the banks and foreshores from the action of the water, as they seldom failed of pro-
ducing a deep pit, either opposite to or on the downstream side of the jetty, which tends to
undermine the banks as well as the jetty itself.
"All works attempted for the preservation of the foot or bank of foreshores, when too
hard a set of the water tends to undermine them, ought to be disposed parallel, or according
to the direction of the stream, so that the water, instead of being stopped or thrown off,
shall glide gently by, with the least interruption possible; for thereby the water gets away
with the least action upon the banks, and wears them or their defences the least. On
this account, all angles and sudden turns should be avoided, and when a turn must be
made, let it have as easy a sweep as possible, keeping it near to the natural bend of the river,
cutting or rounding off all small sudden turns, angles or exuberances, which may happen
in the general sweep.
"All jetties do mischief, and wherever the sides of a river or foreshore grind away by too
great stress of water, the most infallible, secure, and lasting method of remedying this is,
after the irregularities of the curve are taken away, as low as the water will admit being
performed by hand, to line up the foot with rubble stones thrown in promiscuously so as to
form their own natural slope against the shore, till they appear above low water. This
being done, nature will form for herself such a slope to neap tide high water mark as will
need no artificial defence.
“The base of the banks and foreshores being secured, and the slope being naturally formed
up to the high water mark of neap tides, it will be then sufficiently defended against waves
and currents; above this there is no better way of finishing the wall than by turfing it.
No wood should be used at the foot of the turf about neap tide high water mark, but the
whole reliance should be upon a lay of rubble stone, and if some of this be broken, to
fill up the interstices of the larger pieces, this will form a more complete union between
the rubble and turf than if composed of large stones only.
“Boarded wharfing is not calculated to stand long against the action of the waves, and
soon goes to decay; when the sea dashes against the end of a faggot or a stone, these
Y 2
324
BOOK I.
HISTORY OF ENGINEERING.
having no solid connection with their neighbours, the impression goes no farther, but the
tremulous motion raised in one part of a boarded wharfing is communicated over a large
area, which in time loosens the earth behind, and, as the tides enter by degrees, brings
the whole to ruin.
"Wherever the foreshores are not broad enough, from low water to neap tide high water
mark, to stand by a natural slope, they should be reduced to a slope of two to one, that is
to batter two feet to one perpendicular; and this being covered a foot thick with rubble
stones of all sizes, bedded together and footed upon the rubble, thrown in to support the
ground under low water mark, will make a lasting and durable defence, and will resist any
ordinary force, but, if exposed to the waves of the open sea, the cover must be increased in
weight and thickness. This method will answer if the batter is three to five, or even one
to one, but the first inclination is preferable.
"Banks, to be secure against inundations, must not only be high enough, but sufficiently
strong, and experience here is the best guide. They are proof only when they stand at
least a foot higher than the level the waters are known to rise. It is not, however,
necessary to preserve the same slope above the high water mark of equinoctial spring tides
to the extremest height as below that mark, because they will seldom come to such a
stress, yet they ought to be sufficient to answer if they are put to it.
"In order to do this, they should be at least 3 feet broad at the extreme height, and three
times as much broader at the level of the equinoctial spring tide mark, as the extreme
height exceeds their height.
"The artificial banks below that mark should be at least four times as much broader in
their base or seat, upon the natural level of the ground, as the perpendicular height of the
said extreme tide mark is above the natural level of the ground, whereon each part of the
said bank stands: when the earth is loose, sandy, or moorish, the bases or seats and tops
should be respectively broader."
The harbour has undergone considerable improvement at various times, since Mr.
Smeaton was called upon to make his report, but the anchorage is not good, in conse-
quence of the oozy bed of the river, which has several times changed its direction. The
Great Ouse now carries its water by a new cut from Littleport Chain to Rebeck, and the
Little Ouse is a narrow stream.
There can be no doubt that the harbour has sustained considerable damage from the
obstructions, which prevented the ascent of the tides up the river; it is not a quarter of a
mile in breadth at Lynn, though six miles below its width is four times as much; on
some occasions the tide flows in so rapidly, that it has received the name of the Bore, and
its violence frequently changes the curvature of the channel.
This town, distant ten miles from the coast, enjoys considerable commercial advantages,
and by means of the Ouse and its tributary rivers communicates its navigation with eight
counties; its inhabitants have received from various sovereigns as many as fifteen charters;
four small rivers, called fleets, divide the town, which is surrounded by a deep ditch,
flanked by a strong wall which originally was strengthened by nine bastions.
Wisbeach, the most northern town in Cambridgeshire, derives its name from its situation
on the banks of the Ouse, or Wis, which flows through it into the sea, about 8 miles
distance. All the waters, which were directed by a channel, cut in the reign of Edward I.
to benefit Lynn, once passed through this place; the town, however, from its situation,
carries on considerable trade.
Boston, situated on the Witham, about 5 miles from its mouth, is an important port of
the gulf called the Wash; some few years ago the channel of the river was considerably
deepened, and an iron bridge of a single arch, 86 feet span, designed by Mr. Rennie, was
thrown across it; the width of the carriage way was 39 feet, and the abutments are so kept
down, that there is not much rise from the horizontal direction.
The tower of the church, somewhat resembling that of the cathedral at Antwerp, 282
feet in height, has a lantern at top, which formerly served as a guide to the navigators of
the Boston deeps.
The whole of the country around Boston is subject to inundations; in 1820, a high
spring tide, accompanied by a violent tempest, broke through the sea embankment, and did
considerable damage.
Grimsby, formerly the emporium resorted to by merchants from Norway and the
western islands, had its commerce destroyed by the silting up of its famous harbour: this,
however, has been partly improved, and a dry dock, constructed at a vast expense, has
restored some of its former prosperity.
Barton-upon-Humber, about three quarters of a mile from its banks, carries on considerable
trade, from its position on the Ancholme canal and the basin of the Humber.
Port of Goole, Yorkshire, is on the Ouse, at some distance from where it falls into the
Humber, and near to where the Dutch river forms a junction with the former; this port,
therefore, is considerably more inland than Hull, and has two wet docks and a basin. The
CHAP. VIII.
325
BRITAIN.
ship dock is 600 feet in length, and 200 feet in width, and will contain fifty-four sail of
square-rigged vessels, seventeen of which can lie at the quay at the same time.
The barge dock is 900 feet in length, and 150 feet in width, and will contain 200 sail.
The basin is 250 feet by 200 feet, has a depth of water of 19 feet, and the timber
pond is calculated to contain 3000 loads.
The warehouses are capacious for bonding goods of all kinds: it was made a bonding
port in the year 1828.
A canal unites Goole with Ferry Bridge, at which place it joins the river Aire, so that
Leeds and Wakefield are by this means connected.
Kingston-upon-Hull, was first made of importance by King Edward I. ; when he returned
from his expedition into Scotland, this monarch made inquiries concerning the depth of
the river, the height to which the tides flowed, and afterwards sent for the Abbot of Meaux,
who was lord of the soil, and exchanged some lands for what he possessed. The manor-
house being converted into a palace, obtained for the town its royal appellation. A new
harbour being formed in 1299, a charter was granted to the inhabitants of the borough,
who constructed new walls around the town, 2610 yards in circuit, and of considerable
strength. From this period the commerce improved, and the merchants became
wealthy.
The old dock was the first constructed, an act for which was obtained in April, 1774.
Previous to this period, the only harbour for vessels was that portion of the river Hull
which extended from the North bridge to the end of the Garrison jetty, a distance of
2940 feet, and the width at high water of spring tides averaged about 165 feet; the total

CASTLE STREET
NEW
ROAD.
QUAY
DOCK!
10
QUAY
JUNCTION
DOCK
HUM BER
QUAY
BASIN.
QUAY
பபட
பப்ப
THE
HUMBER
QUMA
OLD
DOCK.
QUAY
~OLD HARBOUR.
CARRISON
RIVER HULL
Fig. 326.
HULL DOCKS.
area might be estimated at 11 acres, the depth of which was 22 feet This harbour was
found inadequate to the growing trade of Hull, as well as inconvenient, from the violence
of the stream some hours before low water preventing vessels from coming up; the fall
being from 4 to 5 feet, from the outer end of the old dock basin to the harbour month, and
the velocity of the ebb from 3 to 4 miles per hour.
The old dock, formed under the superintendence of Mr. Grundy, the engineer, is in length
1703 feet, and in width 254, containing an area of nearly 10 acres.
The walls are of brick, coped with stone from Bramley Fall; and in front, at every 10
feet, are oak fenders, 9 by 7 inches, tenoned into three oak sills, 12 inches by 6; these are
POND
Y 3
$26
BOOK I.
HISTORY OF ENGINEERING.
built into the brickwork, and secured by oak brackets on each side, as well as by strong
iron bolts.
The walls are built upon longitudinal sleepers, 12 inches by 6, laid flat, and trenailed
on to pile heads; across these are laid 3-inch planks, all of fir timber.
The piling having given way, and the walls bulged out in some places, a great portion
was obliged to be rebuilt.
Lock and basin. The original lock, 36' feet 6 inches in width, 24 feet 6 inches deep,
and 200 feet in length, was built upon a wooden floor; 4-inch planks were laid upon
transverse and longitudinal joists, bedded on 1245 bearing piles, 12 feet in length: across
the lock were six rows of grooved sheet piling, 14 feet in length. The walls, constructed
of brick, were faced with Mexborough stone, and the hollow quoins and coping were of
Bramley Fall, all set in puzzolana.
The basin was constructed in the same manner, and was in length 212 feet, and in
width 80 feet.
The entrance lock and basin, in the year 1814, was entirely rebuilt, under the direction
of Mr. Rennie, the old one having become decayed. After the water was drawn out of
the dock to within 4 or 5 feet of the bottom, a coffer-dam was made at the outer end
of the basin, next the harbour, and a dam of clay on the side next the dock, and the lock
and basin walls were removed, when the piles, sleepers, and planks were found perfectly
sound, although in many places the foundations had considerably gone down.
The new lock is 120 feet 9 inches in length, within the gates, 38 feet wide at the top, and
24 feet 6 inches high, above the sills.
The inverted arch is brick laid in puzzolana, as well as the side walls, which were
faced with Bramley Fall stone; the lowest course was all headers, 4 feet in length, and
18 inches in thickness. The hollow quoins are of Rotherham stone, and the coping of
coarse sandstone from Bramley Fall, 15 inches in thickness, and 4 feet in width.
The gates are constructed of English oak, except the planking, which is of fir, 21 inches
in thickness. They are each 23 feet wide, 24 feet 3 inches high above the pointing sill,
16 inches thick at the heel, and 14 inches at the head. There are 10 bars or ribs, slightly
curved, tenoned into the heel-posts, and secured by iron straps and screw bolts.
The sluices are of cast-iron, 2 feet 6 inches square in the clear, and are worked by a
wrought-iron screw and brass nut, with bevel gear at top.
To move the gates, at the side of the lock, is placed machinery which turns a cast-iron
roller, round which is a revolving chain made of 7-inch iron; these chains are fixed from
2 to 4 feet above the bottom sill for shutting, and 7 feet for opening the gates; to assist the
latter operation, there is a counterbalance weight, which prevents the chains from running
off the roller.
In front of the lock walls, at about 10 feet above the sills, is placed one horizontal
and two vertical rollers, with another large horizontal one, at the foot of each wall, around
which the chain turns whilst working the gates.
The heel-post has a cast-iron socket at the bottom, 3½ inches in diameter, and 12 deep :
this turns on a cast-iron pivot securely fixed on the bottom.
The brass friction roller, which moves on a segment of cast-iron, is 10 inches in diameter,
and 4 inches in length, fitted into a cast-iron box or frame near the meeting post; to
this is attached a wrought-iron regulating rod, which reaches to the top of the gate, to
adjust the roller.
The bridge over the lock, of cast-iron, is 15 feet in width, the road for carriages being 7
feet 6, and the entire length 81 feet. It is formed of six ribs, 1 inch in thickness in
1½
the middle, and 3 inches thick at the flanch; they are 9 inches deep where they meet in
the middle, and increase a little towards the sides. The bridge turns on a cast-iron shaft,
8 inches square, with four round bearings, working in plummer blocks, fixed in cast-iron
carriages bolted firmly into the masonry.
To open this balance bridge, a lever is applied to lift a cast-iron flap, which turns on an
axis 4 inches square: when this flap is lifted, the bridge rises, and the flap forms a
barrier against passengers, and when the bridge is again lowered, it forms part of the
roadway.
The bridge is covered with oak plank, 3 inches in thickness, bolted to the iron ribs, and
where the wheels of the carriages pass it is lined with 1 inch elm. The footways are also
ined in the same way, and stand up about 5 inches above the road on each side, guarded
by a cast-iron curb, and wrought-iron bars and chains.
As this bridge ascends, the outer end descends into a cavity, prepared for the purpose,
and one man can raise or lower each portion in half a minute; its weight, exclusive of the
timber, is about 80 tons.
Basin of entrance is 213 feet in length, 80 feet 6 inches in width at the top, and 71 feet
at the bottom. It is cased with brick, and coped with stone from Bramley Fall; 14 feet
from the bottom is a bond course of the same stone, passing through the whole thickness.
CHAP. VIII.
327
BRITAIN.
The side walls are supported by brick inverted arches, which are built across the bottom, 6
feet wide and 18 inches deep; the spaces between are 10 feet in width, and the whole is
levelled down with earth to the top of the lock sills.
The Humber dock, in length 914 feet, and in breadth 342, was designed and completed
under the superintendence of Mr. Rennie and Mr. William Chapman; the act of par-
liament for its establishment was obtained in 1802, and it was commenced soon after. It
comprises an area of a little more than 7 acres. To keep out the tide, during the exe-
cution of the work, at the south end a coffer-dam was formed; its span was 280 feet, and
its versed sine about 140. It was constructed of two rows of Dantzic piles, 7 feet 6 inches
apart; the piles were of whole timber, and well bolted and braced together. In the
middle, at the bottom, was a trunk, and in the space between the rows of piles, bricks laid
in sand were built up to the level of high water. The perpendicular head of water pressing
against it being sometimes 30 feet in height, shores and braces were required to counteract
its efforts to drive in the dam.
The water was pumped out by a steam-engine of six horse-power, which worked two
eleven-inch pumps; this engine also raised two rams of 7 cwt. each, for driving the
various piles. After the water was pumped out, the excavation was carried to an average
depth of 24 feet, the soil being alluvial and stiff clay. To excavate the basin, on the
outside the coffer-dam, which at every tide was overflowed, horse-runs were established
to remove the soil; and what could not be moved by this means was conveyed away in
ballast lighters.
The foundations of the dock walls are piled, with a row of 6-inch grooved sheeting
piles in front; the other piles are 9 inches and those under the counterforts 8 inches in
diameter. To drive them, a ringing engine, with a ram of 4 cwt. worked by fifteen or
sixteen men, was employed. On the heads of the piles were bolted longitudinal sleepers of
half timber; and the sheeting piles were securely spiked to an inner waling of the same
scantling. Over the sleepers was laid a transverse covering of 4-inch plank, on which was
commenced the wall. The piles were of Norway and the other timber Memel. The dock
walls were built of brick made out of the excavated clay, and where the bottom of the
fenders terminate is a course of stone, 15 inches thick, passing entirely through the wall;
and between the tides are worked three other courses, all of Barnsley stone. The whole is
coped with stone from the same quarries, 15 inches thick, and 4 feet in width, the joints
being secured by square dowels. Warmsworth blue lime and sharp fresh water sand were
used for the mortar, the lime being previously ground dry, and afterwards mixed, and used
hot.
The oak fenders to protect this wall are 12 inches square, and project from the brickwork
8 inches, the rest being sunk into the brickwork. At their feet they are dovetailed into
stone corbels, and at the top they are secured by oak ties and wrought-iron fastenings.
The two rows of horizontal fenders are 7 inches square, tenoned into the upright ones; and
pieces are laid under and above them, of an angular shape, to prevent vessels catching as
the tide rises or falls.
The entrance lock within the gates is in length 158 feet, its top width 42 feet, and its
height above the pointing sills 31 feet. The average depth of water at high water
spring tides is 26 feet, and at neaps 20. The foundations are built upon four rows of
bearing piles, with two others under the counterforts. These piles are from 15 to 20 feet
long, and on the heads is securely bolted sleepers of half timber, laid longitudinally. These
are again crossed by others of the same scantling, laid on edge, and the interval covered
with 4-inch close planking; the spaces between are filled up with solid brickwork, on which
is constructed the inverted arches and the side walls.
Across the platform are five rows of 6-inch grooved sheeting piles, from 15 to 20 feet in
length; the bearing piles are distant about 3 or 4 feet each way; on these lay longitudinal
sleepers, 12 inches square, with two courses of transverse sleepers close together, for 13 feet
in length, from the main sill, on which the pointing sills are bolted. The other part of the
platform is covered with 6-inch close elm plank, into which the cast-iron segments in which
the gates traverse are sunk. At the tail of the lock is an apron, about 50 feet in length,
covered with 4-inch plank; this is spiked to the transverse sills, which are bolted to the heads
of the bearing piles; the outer end is protected by a row of 6-inch grooved sheeting piles.
Norway timber was used for the piles, the planking is of Dantzic, and the pointing and
main sills are of English oak.
The side walls have six counterforts on each side, each 6 feet square; the walls are in
width at the top 6 feet 9 inches, and are built of brick, faced with stone, from Bramley Fall.
The hollow quoins are of stone from Dundee, and for some length a part of the wing-walls
are faced with the same material. A Bramley Fall stone coping, 13 inches thick, and
4 feet wide, terminates the wall.
The lock gates are in height above the pointing sills 31 feet 4
25 feet 6 inches, measured on the curve; they camber 143 inches.
inches, and in breadth
At the head they are
Y 4
328
BOOK I.
HISTORY OF ENGINEERING.
in thickness 14 inches, and at the heel 16 inches; each gate, which may be considered a
solid mass of oak timber, the planking only being fir, has two cast-iron sluices, 3 feet
square, with a rod, worked at the top by an iron screw.
To open and shut the gates, there is a 6-inch iron pinion, which works in a cog wheel,
4 feet diameter, round the cast-iron axis of which the gate chain winds.
Over the centre of this lock is an iron swivel bridge, in length 81 feet 9 inches, and in
breadth 12 feet 3 inches; it forms a segment of a circle, and meets in the middle. It is
composed of six cast-iron ribs, 2 inches thick at top, and 24 inches on the lower edge, united
and braced together, and covered with 24-inch oak plank. A cast-iron plate, 11 feet
9 inches diameter, is firmly bedded on a pier of brickwork on each side: this has a pivot in
the centre, which works in a socket underneath the bridge; revolving between this circular
plate and another on the underside of the bridge are twenty conical rollers, 10 inches in
diameter at one end, and 93 inches at the other; these are 6 inches long, and are fitted into
a frame. A man can open and shut this bridge by means of the machinery attached,
which consists of two 8-inch bevel pinions, one of which receives the handle; at the bottom
of the other is a vertical shaft, which has fixed on it a 9-inch pinion, which works in a
spur-wheel, 4 feet in diameter; on the axis of this is another pinion, 12 inches in diameter;
this works in a toothed segment at the outer end of the bridge, and turns it.
The entrance basin to this dock, 267 feet in length, and 435 feet in breadth, has its
walls constructed in a similar way to those to which it belongs; at the top they are in
thickness 6 feet, at the bottom 10 feet; they are faced with stone from Bramley Fall, and
have a similar coping. The walls rest on three rows of piles from 16 feet to 18 feet long,
and in front is a row of sheeting piles, with transverse sleepers, closely planked over.
The mooring posts are placed 30 feet apart, and about 12 feet from the sides of the lock.
The Junction Dock, 645 feet in length, and 407 feet in breadth, was commenced in
1826, from the designs of Mr. James Walker, and contains an area equal to 6 acres. Two
coffer-dams were employed; that next the Humber dock was 220 feet in length, forming a
curve, the versed sine of which was 61 feet. It was formed of two rows of close piles,
6 feet apart, and after the mud was taken out, filled in with well puddled clay the piles
were of whole timber, about 40 feet in length. In front, on each side, were forty-two gauge
piles with two rows of waling pieces, 13 inches by 8, well bolted. Rough iron tie rods
were also introduced to prevent the work from yielding; against this dam was a pressure
occasionally of 28 feet of water, which found its way along the cross braces, but was
speedily stopped.
:
The other coffer-dam, at the west end of the old dock, a curve of 115 feet in length, with
a versed sine of 14 feet, was formed in a similar manner.
The water was pumped out by two six-horse steam-engines, and the sides of the dock
were excavated with a slope of one horizontal to one vertical. The average depth of the
excavation was 19 feet, and the quantity of clay and earth removed was about 300,000
cubic yards.
;
Under the dock walls were driven 2401 piles, containing 18,500 cubic feet of timber,
and 2140 feet in length of sheet piling, 12 feet in depth, and which cubed to 12,840 feet
on the heads of some of these piles it has been calculated there is a superincumbent
weight of 20 tons.
Below the sleepers, the space is filled up with brick rubbish puddled or grouted with
hot lime and sand, and at the foot of the wall is a similar bed of concrete.
The wall is of brick, partly faced with Bramley Fall stone, in 12-inch courses; this
extends from the coping about 11 feet 9 inches downwards; the two lowest courses are,
however, of stone from Barnsley or Whitby, both fine sandstones, and each 15 inches
thick; every two stretchers have one header, which are each 3 feet 6 inches long: the whole
is coped with similar stone, 4 feet in width, and each joint is secured with a 4-inch square
dowel.
The walls are curved about 7 feet on the east and west sides.
The locks within the gates are in length 120 feet, and in width at the top 36 feet
6 inches: they are in height above the pointing sills 25 feet.
The lock gates, formed of English and African oak, are cased with 3-inch fir planking ;
they are hung at top with a wrought-iron collar, in a cast-iron anchor, let into the stone-
work; the heel-post has an iron socket, which turns on a brass pivot; the outer end of
the gate is supported on a brass roller, 12 inches diameter, and 4 inches wide; to this is
attached an adjusting screw: the roller moves in a brass segment, let into and screwed
down to the platform. To work these gates, on each side is the machinery, which is fixed
into a cast-iron box; it consists of a 7-inch pinion, which works in a spur-wheel 4 feet
diameter, on the axis of which is a cast-iron roller, 3 feet long, and from 12 inches to
9 inches diameter; a three-quarter inch chain winds round this, and passing under a roller
at the bottom of the wall, and over another, in the face of the walls, is fastened to the gate.
There is attached, as in the other locks, a counterbalance weight and chain.
Each gate
CHAP. VIII.
329
BRITAIN.
weighs upwards of 20 tons, and has two sets of sluices, working on brass facings, in iron
grooves, and so constructed that one set is raised whilst the other is lowered; this is
effected by having the sluice rod attached to a rack that turns a spur-wheel working in
another rack attached to the other sluice rod; thus a capacious opening is obtained without
weakening the gates.
The bridges over are on the balance or lifting principle, and are moved by means of four
crabs, two on each side; the handle is applied to a 6-inch pinion, which drives a spur-
wheel 4 feet in diameter, on the axis of which is a 12-inch pinion, working in a toothed
segment, the radius being 5 feet 9 inches; this is attached to the outer rib of the bridge.
Each bridge weighs nearly 100 tons, and it can be opened or shut by three men in less than
a minute.
Cleansing the Docks of the mud deposited by the waters of the Humber, is a matter of
considerable moment, as it is said the quantity annually deposited in the Humber Dock
was 36,000 tons. The dredging machine employed is placed on a flat-bottomed vessel,
80 feet in length and 20 feet in breadth, drawing 5 feet water. It is worked by a steam-
engine of six-horse power; its stroke is 2 feet, forty times a minute; by means of a bell
crank, motion is given to four cog-wheels; on the axis of the upper one is a square
tumbler, with a corresponding one at the lower end of the bucket-frame.
There are
twenty-nine iron buckets, revolving on an endless chain, which deposit the mud they bring
up, by means of a spout, into lighters. This endless chain turns on an axis at the upper
end, and the lower end passes through an opening in the middle of the boats, and is raised
or lowered by a crab, and tackling fixed over it; by this means, the buckets are placed at
the proper level for dredging. An engine man and three assistants are required to manage
this machine, and two others to attend the lighters. Sixty tons per hour is sometimes
raised, but usually twelve boats, each of 500 tons, are employed, and the ordinary work
performed is about 45 tons per hour. The mud boats are flat-bottomed, and draw 4 feet
water; they are in length 48 feet in width 17 feet 6 inches, and carry about 40 tons.
The tide basin is scoured by two cast-iron mains, 4 feet in diameter next the lock, and
diminishing to 2 feet 6 inches. At the outer end, branching out of these on each side, are
ten 18-inch pipes, which discharge through the basin wall, about 5 feet above the level
of the sills; other mains are connected with the docks, but they only scour where the water
is discharged, and leave the bed in furrows, to be cleared away by other means.
In consequence of the waves of the Humber acting with violence against the outer gates
of the dock, it was found necessary to build two piers to protect them. The main piles
are 14 inches square, the outer waling the same scantling, and the inner wales 12 inches by
6; the cap sill 12 inches by 10; joists 7 inches by 4; ties 12 inches by 6; sheet piling
6 inches in thickness, and the planking 3 inches in thickness.
Spurn Point Lighthouses were commenced near the Humber mouth by John Smeaton, in
the year 1771; they were built of brick, and his instructions were to make the largest
90 feet in height from the mean surface of the ground to the centre of the light, and
the smallest 50 feet high; both were to be provided with inclosed lanterns for fire-lights.
The original lighthouse was a strong brick building of an octangular form, 60 feet high:
the light was hoisted on a swape, a provincial term for a lever, fixed upon a centre which
could be turned in any direction by the hand. A naked coal fire was employed, which

口
​"
Fig. 327.
FLANS OF spurn POINT LIGHTHOUSE.
burnt with unequal force; during the storm of 1703, the draught was so great that it
melted down the iron bars on which it was laid like lead. In the year 1777, the two new
lighthouses were completed; in design they did not differ, but the lower one con-
-----
330
BOOK I.
HISTORY OF ENGINEERING.
sisted of fewer apartments, there being only a coal vault, a dwelling room, pipe room,
and lantern.
In the larger one there was a coal vault, a smith's shop, and machine for hoisting the
coals. A vacant room, a dwelling room,

with two fireplaces, to be used according to
the direction of the wind, two chambers, one
over the other, a pipe room, wherein were
two of the eight pipes that conveyed air from
the external hopper mouths to the receptacle,
which was lined with thick plate iron; the
bottom being stone, when the door was shut,
the air ascended through a large funnel and
the hearth to the fire-grate.
The flame was seen in every direction,
through the windows of the lantern, and
the smoke was collected in its passage through
the decagon conical roof, composed of ten
Elland edge flag-stones, and then through the
copper funnel at the top.
The coals to supply the fire were drawn up
in a tub through an opening by means of a
roll, wheel, pinion, and wrench. A rope from
thence, ascending through all the floors, passed
over a large pulley suspended from the roof,
and thence downwards through the hole in
an arch to a large square wooden pipe, ter-
minating in a hopper mouth, proper for
receiving the burthen.
The ashes and hot cinders, passing through
the grate, fell into the bottom of the recep-
tacle, and by heating the air therein pro-
moted a sufficient draught in the calmest
weather, which could be augmented and
regulated, when there was a breeze, as any of
the air-pipes could be enclosed at pleasure.
The ashes and cinders were thrown into a
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​Fig. 328.
SPURN POINT
Fig 329.
SECTION OF LIGHTHOUSE.
CHAP. VIII.
331
BRITAIN.
hopper, and conveyed down a square wooden pipe, through a funnel formed in the brick-
work, and from thence into a bingstead in the court-yard.
The corner pillars of the lantern were of cast-iron, the sash frames of oak.

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Fig. 330.
The year after the completion of the lighthouses, the lower one was washed away, and
totally destroyed, when a new swape light was erected: in the year 1816 the coal fires
SPURN HEad tempoRARY LIGHT.
3:32
BOOK I.
HISTORY OF ENGINEERING.
were discontinued, and a new brick building was erected, with lamps and reflectors. In the
year 1828 this was destroyed, and a wooden tower erected further inland, which was
removed, three years afterwards, 50 yards further inland, to avoid the encroachment of the
sea.
The swape, including the walls on which it stood, exhibits at the height of 56 feet.
The fire basket of iron turning upon its axis places itself level, in every position of the
mast. This loaded with a weight counterbalances the iron work and fuel at the top; the
whole being steadied and clipped into an iron frame, that turns in equilibrio upon the
horizontal axis, supported by pillars and braces.
To renew the fire, the attendant, laying hold of one of the winches of the roll, turns it
round, so as to wind the rope upon it, which, after going obliquely towards the ground, passes
a pulley in a stud, fixed therein, at some yards' distance, and thence rising obliquely upward,
it lays hold of the mast by a small chain.
By the motion of the roll the fire basket is brought to the ground, where it is fed with
coals. While the rope is winding upon the roll, the rope, being coiled thereon the
contrary way, was unwinding; and this being attached to the extreme of the lower end of
the mast, and at equal distanee, in rising carries the rope with it. The fuel being renewed,
the winch is turned the contrary way round, by which that end of the mast is brought
down, and the fire basket carried up into the position shown. The lower end of the mast
is steadied against the cross piece, the roll being then fastened.
The projecting part is a small umbrella of sheet iron, to throw off the cinders.
Bridlington Quay opens directly upon the harbour, which is formed by two piers,
extending a considerable distance into the sea; that to the north is a promenade, from
whence a fine view of Flamborough Head and the spacious bay is obtained. South-
westerly winds occasion a considerable deposit here, and the force of the waves is very much
broken by the Smithick sand, which extends in a direction nearly north-east and south-west
across the bay, on which there is only from 12 to 20 feet of water at the recess of the
tide.
Scarborough is the only port on this coast, between the Humber and Tynemouth haven,
where ships can find refuge in violent gales; it is easy of access, and has a sufficient depth
of water at full tide for vessels of considerable burthen. As there is no natural stream to
scour the harbour, it is subject to be warped up by the sand which is deposited in it, and is
only cleansed by the violent agitation of the sea, produced by the strong gales from the east.
Quay Street once bounded the old harbour, and is now only reached by the water at high
spring tides, which proves how much deposit has taken place.
Whitby, at a very early period, had timber piers for the protection of its shipping, but it
was not till about 1702, when two acts of parliament were obtained for the improvement of
the port, that the present east pier was built, 200 yards westerly to the channel of the Eske,
which affords a great security against the violence of the sea, when the wind is at north-
east, which flows over the rock with a strong current into the harbour. About the same
time, a staith was erected on the west side of the river, the Scotch head built, and the
western pier formed, which extended 200 yards towards the sea, contiguous to the channel
of the Eske.
The sand that daily warped into the harbour, around the west pier, and the bed of sand
that continually lay at the head of that pier, seemed to threaten its destruction, when it was
proposed to lengthen the pier on the west, and extend it sufficiently towards the north, that
its head might shelter the east pier from the run of the sea, setting along the coast. An
act of parliament was obtained to carry out this project, but it was only partly effected. The
western pier is regularly built of stone, brought from a quarry near Woodlands, four miles
south-west of Whitby, and extends 520 yards into the sea, where it is terminated by a
circular head. One of the other piers, which extends from the east cliff, so contracts the
entrance, that in hard blowing weather the harbour is difficult of access.
The town is built on two declivities, on the banks of the Eske, which empties itself into
the harbour; a drawbridge is so constructed, that the inner harbour can be entered by
vessels of 200 tons burthen. There are several dry docks, and ship-building is extensively
carried on; the depth of water in the harbour at neap tides is 12 feet, at common tides 18,
and 24 in the great equinoctial springs.
Hartlepool, situated on a promontory, is nearly surrounded by the German Ocean, and in
front is a capacious bay, favourable for the reception of vessels at all times. "Few places,"
says Mr. Hutchinson, "give so perfect an idea of the fortifications of a former period; a
long extended wall, strengthened by demi-bastions, are placed at intervals, some rounded,
others square; various gates and sally ports, secured by machicolations and the portcullis ;
some of the gates defended by angular, others by square turrets, all the variety of style ap-
pearing as they had successively grown into use." As the wall runs along the edge of the
creek, behind the point of land which projects into the sea, and from thence turns to cross
the isthmus to the opposite cliff, the figure it forms is not regular, giving first a triangle,
and then running with a sweep or bend north and eastward.
CHAP. VIII.
BRITAIN.
883
At the ness end or north-east point of the wall to the sea, it finished with an acute angle,
rising on the brow of lofty rocks; the foundation has of late years wasted by the washing

SLAKE
HARBOUR
VICTORIA
NOCK
LOCK
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RAILWAY
STATION
OLD
HARBOUR
JETTY
PIER
Fig. 331.
HARTLEPOUL.
of the waves, and that part of the wall has now fallen; it was exactly similar to the ness or
point of the Roman wall, opposite to the castle at Carlisle. The whole of the wall is much
broken for a considerable distance from the sea. At about twenty paces are the remains of a
square bastion; from thence about forty paces is a round bastion, projecting from the wall,
about two-thirds of a circle, in girth nearly 30 feet: in the front of the bastion, at the dis-
tance of about 5 yards, is a high ridge of earth, probably cast up by assailants. From the
second bastion, at about 40 paces, is a square bastion, about 10 feet in front, and projecting
about 7 feet from the line of the wall; from thence, at 46 paces, is a second bastion some-
what larger than that before mentioned, making a projection of about 10 feet, not so pro-
minent as the others. In all the portion described, the wall forms a straight line, the
ground gradually inclines, and falls from the edge of the cliffs; where the wall begins at a
distance of 30 paces, it forms an obtuse angle, guarded with a turret or bastion, from
whence is a kind of horn work, projecting into the field for a considerable distance, of an
angular figure, having two terraces, one above another, with the remains of the glacis, the
mason's work appearing through the broken turf; from whence there is an extensive pro-
spect of the sea and coast towards Sunderland, commanding Hawthorn Hive, or the Beacon
Point, Essington, Elwich beacon, and a long tract of country. Thirteen paces from the angle,
there is the appearance of a sally-port; but the wall has been repaired and altered in
modern times, so that it is not possible to ascertain more concerning it. At the distance of
about 60 paces is a round bastion, and 80 paces further, the great Land gate, the chief
entrance of the town from Durham, opening upon a road, formed over a level marsh,
easily broken up or flooded in a siege. This gate seems to have been strengthened by a wet
ditch, and probably a drawbridge.
The whole wall, towers, and gateways are of excellent masonry, built of limestone, of so
soft a nature in the bed or quarry, that it may be squared with an adze, but when exposed
to the air becomes remarkably hard and durable: the arch of the gateway is ribbed, and
besides double gates had a portcullis; the width of the passage is 10 feet, and of the whole
gateway tower about 30 feet; the projection is not much above a foot from the face of the
wall; it appears to have had a strong tower for its superstructure, entered at each side from
the parapet of the wall. The approach to the town from this gate was by the side of the
haven, which must have made a fine appearance; as the basin, if we may judge from the
334
Book I.
HISTORY OF ENGINEERING.
present slake or morass, consisted of several acres, where a hundred sail might be moored.
From this gateway commences the wall, which secured the haven, and runs in a direct line,
the water at high tide coming up to the gate. It is somewhat more than 8 feet thick, faced
on each side with dressed stone; the parapet is guarded by a breast-wall and embrasure,
now greatly decayed. There is a water gate in the wall, formed by a low pointed arch,
above 24 feet in span, and 10 feet high, for the small craft to pass in and out of the haven,
without removing the boom chains afterwards noted; the gateway projects from the wall
about 18 inches; it has had flood gates, and also a watch tower, as we apprehend from the
remains of the superstructure.
From thence, at about the distance of seventeen paces, is a
square bastion about 8 feet in front; and nearly a hundred paces distant is another square
bastion, and from thence about seventy paces is a lofty round tower, remaining very perfect,
save the parapet and embrasures; opposite to it, at the distance of 36 feet, stood another
tower, exactly similar in dimensions, as the fascia and foundations plainly show. This
was the grand entrance into the haven, and by the space between the towers one may
judge of the size of those vessels which were moored therein, a thirty-gun ship being 32 feet
wide.
This entrance was guarded by large boom chains, stretched from tower to tower, the re-
mains of the hoops belonging to such chains being still visible in the walls of the tower.
At ten paces distant are the foundations of a round bastion, near which is a modern gate,
where, it is presumed, was formerly a small doorway, for the convenience of persons landing
from boats; at 24 paces distant the wall forms an angle; this angle is defended by a half
moon.
The entrance into the haven had the peculiar security that vessels coming from the sea
must necessarily double the cape or point of the isthmus, and then proceed along the whole
range and stretch of the south wall, within reach of the engines and instruments of war,
and
At the distance of 60 paces
pass the half moon which guarded the angle of the wall.
from the angle is a square bastion, and near it is a large breach in the wall; from the
square bastion, about 120 paces, is a round bastion, and next stands the gateway, now
called the water-gate, which only communicates with the land at low water, and leads to
the High Street; the arch of this gateway is pointed, about 8 feet in width, and defended on
each hand by angular terraces, with fronts projecting, a figure not commonly met with in
old fortifications. From this gate the wall advances to, and abuts upon, the rock near its
point, where the pier and mole begins; the whole of this south part being much more
modern than the north and west sides."
Bishop Pudsey, in the year 1189, probably raised the walls and increased the forti-
fications of Hartlepool, and by the Normans it was always held as an important place of
security.
The docks were greatly improved by the late Mr. Rennie; a considerable sum of money
has since been expended upon them, and they afford us now one of the best examples of a
sluicing harbour that exists. The eastern dock next the entrance is 460 feet wide, the west
dock 230 feet wide next the entrance, and 1075 feet in length, and the tidal harbour
upwards of 700 feet in width, between the slake bank and quay wall.
The scouring sluice and tunnels between the slake and the tidal harbour were built in a
most admirable manner; the channel for the water was 15 feet in width, having a flat arch
at bottom as an invert, 22 inches in thickness, and another above, to cover the watercourse,
2 feet 3 inches deep, rising about 18 inches. The height of the side walls, between the
springing of the top and bottom arch was 4 feet, and their thickness 5 feet 6 inches. The
side walls, throughout their entire length, were further strengthened by external buttresses,
3 feet 6 inches thick, and 4 feet projection.
Sheeting piles were driven in at each end of the sluice, and also under the sluice gates or
paddles. The entire foundation of the tunnel was floored with 3-inch plank, laid on stout
timbers. The gates of the sluice are of cast-iron, lifted by well-arranged machinery, and
the whole is made to operate most effectively.
The retaining walls have a curved face, the radius from which they are struck being 80
feet. The toe of the wall in the interior of the dock is 5 feet below low water, and those
of the quay next the tide harbour 7 feet. The exterior quay walls are founded on piles,
well protected, and carried up with excellent stone in regular courses, and coped through-
out with stone 3 feet 6 inches in width. Oak fenders, 12 inches by 10, are fixed opposite
each counterfort, at a level of 6 feet above low water, strong iron shoes being cast to retain
them.
The retaining walls of the docks are at the base 12 feet in width, and diminish gradually
to the top, where they are only 6 feet in width. The tops of the fenders are capped with
cast-iron bollards; holding down stones, with Lewis eye-bolts, are everywhere provided for
the fastening of the hawsers in a perfectly secure manner.
The bank wall between the tide harbour and the slake has a slope 4 to 1 next the tide-
harbour, and 2 to 1 next the slake or reservoir, with a puddle wall carried up in the interior
to prevent the water percolating.
CHAP. VIIL
335
BRITAIN.
The frames of all the sluices are made of cast-iron, as are the sluice gates.
There are also some admirable cast-iron turning bridges, 45 feet 6 inches span, which work
upon pivots and conical rollers, about 9 inches in diameter; each leaf of these bridges is made
to open by a sector rack, attached to the tail plate of each leaf, having a pinion with a spur
and pinion, working into each other.
Sunderland, 20 miles south-east of the town of Berwick-upon-Tweed, occupies the right
bank of the mouth of the Wear, and Wearmouth the other, and the two towns are united
by an iron bridge of 236 feet span, and 98 feet from the underside to the level of high
water.
The Wear is not navigable to Durham, as it is not swelled by many tributary streams.
From Sunderland bridge to the sea, a distance of a mile, the Wear forms an extensive
dock, which is full of vessels engaged in the extensive coal trade carried on here. This is
kept constantly open by the dredging machine, and there is a floating dock formed with
convex gates; where the river empties itself into the ocean, the passage is confined by two
piers, and from the force with which the tidal water mounts, there is never any obstruction
at the mouth. The piers are composed of stone, laid in short horizontal courses, terminated
at equal intervals by vertical timbers, so that if any part is broken through and carried
away, it can be easily repaired.
At the end of the southern pier is a lighthouse, built of timber, and at the distance of
90 feet from the point of the north pier stands the great lighthouse.
The entrance to the harbour lies east-north-east; and on the eastern side is a ledge of
rocks, which extends a quarter of a mile to seaward; this is covered at high water; the
harbour is sheltered on all sides, except from the north-east.
The tide ebbs about 100 yards from the head of the north pier, and the harbour is dry at
low water; spring tides rise about 18 feet; between the jetties at the entrance there is 6
feet at low water; neap tides rise only 9 feet, at which time there is only 6 or 7 feet
water in the harbour.
Removal of the Lighthouse at Sunderland. This building, which is octagonal on the
plan, is of stone; its height is 62 feet 2 inches from the base to the cornice, and the
lantern above was 16 feet, making a total height of 76 feet 2 inches. Its breadth at the
base was 15 feet, and it diminished to 8 feet 6 inches. The lighthouse was erected in
1802, at an expense of 1400 pounds sterling; and in consequence of a breach made by
the sea in the year 1841, it was required to be moved to a foundation prepared to receive it,
a distance of 447 feet.
This operation was performed very successfully, in the following manner :-
holes were
cut through the stone walls on the north and south sides of the building, through which
were passed six timbers, intended to be framed into a temporary platform. Where these
main timbers came in contact with the masonry, they had spread over them a sheet of lead,
to prevent their being unequally acted upon. Screws were then placed under these
timbers, and they were forced to a bearing; after this upright timbers were introduced
under them, and the screws were taken away. Four other timbers were then introduced,
laid parallel to the first, which were screwed up and supported in a similar manner.
A hole was then cut on the eastern side, opposite the door, and through it were intro-
duced two transverse timbers, which were firmly screwed to the others, and when shored
up, the screws under them were taken away.
Timbers were then introduced with rails fixed to them; those in the centre, below the
upper beams, were first fixed, and then bedded on the stone pavement around; the
sheave balks to each were then threaded through the building, wedged to the timbers
above, as well as to the rails below, by a series of wedges. The other rails and sheave
balks were then similarly fixed underneath each timber, and when all the wheels were
brought to a proper bearing, the stone work, which had been allowed to remain at four
angles of the building, was cut away, and then two other timbers were introduced and
secured.
The octagonal lighthouse had a three-inch plank from bottom to top laid against it at
each angle, and these were hooped round with five iron hoops 24 inches broad, and 78 inch
thick; ropes and wedges were employed as well at regular distances, the whole made
to embrace the building, and by means of screws were drawn closely up to the upright
planks.
Under the cornice a hole was cut on each of the eight sides, where the walls were 10
inches in thickness; through these were pushed horizontal timbers from the inside,
and these were drawn back until they met in the centre. Iron plates covered the joints
above and below the timbers, and screwed bolts passed through both.
This upper timber platform was connected to that below by a large chain, which
passed round a strong bar of iron at the top, and another at the bottom, which was
tightened by a screw. Eight upright timbers, a foot square, were tenoned into the hori-
zontal timbers under the cornice, and brought close to the outer wall of the building,
at the base, where they were secured by stirrup straps and bolts; these uprights were
336
BOOK I.
HISTORY OF ENGINEERING,
ROCKS
united by three tiers of chock pieces; three iron straps passed round these as well as the
uprights, and the whole screwed tightly together.
After this, raking braces were added, and the whole firmly bound together; then diagonal
braces, to prevent the timbers from springing or twisting.
When the whole of these works was completed, five pulling screws were attached
to the glacis of the pier, and the chains were fastened to them; 24 men were employed to
turn these screws, four forcing screws, worked by three men at each, being applied
behind the cradle to help propel. The total number of men employed amounted to fifty.
The platform or cradle that carried the whole weight, which was 338 tons, was supported
on 144 wheels, which moved on eight parallel lines of rails.
The cradle timbers were of American oak, and all the rest was Memel; the cast-iron
rails upon which the wheels moved were laid upon a plank of African oak 1½ inches in
thickness.
There were employed, during the operation at the winches, 18 men, and their power
may be estimated as equal to 562 pounds. The radius of the handles of the winches was
14 inches, worked by a cog-wheel of 44 inches diameter, turning a spur-wheel of 30 inches,
and a barrel of 10 inches in diameter. The additional power of the two-fold and three-
fold sheave blocks, made the whole power of the 18 men equal to 52,480 pounds, whilst the
gross weight was 757,120 pounds.
The speed with which the whole was moved was about 84 feet per hour, when at
the quickest; and the time occupied to move the whole distance was 13 hours 24
minutes.
The foundations prepared to receive the lighthouse after its removal were formed of
solid blocks of stone, and when it had arrived over its destined position, the timber uprights
were again wedged under its cradles, and the various sheaves and railway timbers drawn
out. The masons then underpinned it by degrees, striking the upright supports as the
building had obtained its proper bearing.
Mortar, composed of blue lias lime, sand, and puzzolana, was made use of, and great
çare was taken to pin up the last course; a sheet of lead being introduced to equalise the
pressure.
Since its completion the works have stood remarkably well, and no settlement has taken
place. The accomplishment of so arduous and novel a task as removing a lighthouse
reflects the highest credit upon the engineer, John Murray.
From this port upwards of 1,300,000 tons of coal are annually shipped, and it is
reckoned in importance the fourth port of the United Kingdom.
South Shields and North Shields occupy the banks at the mouth of the Tyne. Tyne-
mouth, which is about 1 miles distant from the former, has a lighthouse 61 feet high,
which rises 168 feet above the level of the sea.

SAND HILLS
HICH WATER ORDINARY SPRING
HERD
SAND
HOW WATERSPRINGETIDE
UPPER.
ĮDLICHTHOUSE.
LOWER.
(EICHT HOUSE.
TIDES
SCALP
MIDDINGS
IGH WAT
TIDES
SPRING
Fig. 332.
BERWICK UPON TWEED.
PRIORS HAVEN
。 LICHTHOUSE -
Newcastle is situated on the Tyne, and on the banks are many yards for ship-building.
The average rise of the spring tides at North Shields is about 14 feet, at Hepburn
CHAP. VIII.
337
BRITAIN.
about 12, and at Newcastle 11 feet 6 inches. The velocity of the current of the flowing
tides in springs above Shields is about 3 knots an hour at half flood, but about half ebb it
is increased half a knot.
Jarrai Slake, which is covered at half flood, contains nearly 350 acres.
Berwick-upon-Tweed, is on the left bank of the river, and has a pier, erected under the
direction of the late Mr. Rennie, at the end of which is a lighthouse. The harbour is by
no means a convenient one; and the river, which is here crossed by a bridge of fifteen
arches, is the second in point of importance to any in Scotland.

0
D
RIVER
BERWICK
TWEED
AHOSPITAL
SAND
BERWICK
BAY
Fig. 333.
BERWICK-UPON-TWEED.
Here, originally, was a pier, constructed in the reign of Elizabeth, which afforded shelter
from storms from the north-easterly wind. Spring tides rise here about 15 feet, and neaps
about 9 feet; and at high water of an ordinary spring tide, there is 19 or 20 feet water on
the bar, and from 14 to 15 feet at the quay; at neap tides there is not so much by 3 or 4
feet.
Eyemouth Harbour, is advantageously situated at the corner of a bay, where ships can
work in and out at all times of the tide, and lie at anchor secure from all winds, except the
northerly or north-easterly.
.
Mr. John Smeaton, in the year 1767, who was consulted upon the best means of im-
proving it, found that the mouth of the river being open to northerly winds, the vessels
could not lie secure without going beyond the elbow of the quay, where there was but very
shallow water, and the breadth was much contracted. At a full sea, the mouth of the
harbour being wide admitted the waters with so much impetuosity, that they found their
way round the elbow and disturbed the quiet of the vessels which took shelter there. To
enlarge the harbour, and to increase its security, he advised the construction of a north
pier to defend the mouth, and which was to be based upon a natural ledge of rocks.
The entrance to the harbour was at right angles with the direction into and out of the
bay; and at spring tides there was 20 feet of water; and between the pier heads, there
was several feet at low water, at the lowest ebbs; and at neap tides it was calculated
there never would be less than 16 or 17 feet in the harbour, which would be capable of
receiving vessels of from 300 to 400 tons burthen.
The length of the pier from the elbow and round the head into the flank was to be 240
feet, its mean height 22 feet, and the mean thickness of the two walls 5 feet. The length
within, from the elbow to the said flank, was 132 feet, and the mean thickness of the walls
3 feet. The width of the base was 30 feet, and as the casing walls were built with falling-
in faces, the interior was filled in with rough stones placed by hand, and well packed. The
faces of the wall and parapets only were built in regular courses of freestone, which were
laid in mortar, hammer-jointed and faced.
Dunbar Harbour, though situated advantageously at the bottom of a bay, was with
difficulty to be entered, as the passage for vessels was extremely narrow; and the sloping
of the rocks on the starboard or north-west side, going in, contributed to increase the evil,
for vessels being obliged to keep close to the pier were often driven on it by the recoil of
the sea from the rocks. John Smeaton, in 1772, to remedy this inconvenience, recom-
mended that the rocks should be sloped off, level with the bottom of the rest of the pas-
Ꮓ
338
BOOK I.
HISTORY OF ENGINEERING.
sage, and the face built up above high-water mark; by which the passage to the harbour
would be widened to 5 yards, and in the narrowest part from 45 to 60 feet.
The sea
would also be prevented by this means from breaking upon the sloping rocks, and the new
pier being carried up sufficiently above high water mark, by means of rope, vessels might
he towed when they did not come in with sufficient fresh way to keep them clear of the
entry.
He also advised that a pier should be carried out upon the ledge of rocks which at low
water were dry, on the south-east side of the entry from the north angle of the present pier
to the Beacon rock, which would defend the passage from the surge of the sea, and serve as
a help, by its projection, to the throwing a rope on board a ship on the larboard side. As
the construction of a pier that would resist the full stroke of the sea ought to be of great
strength, and consequently its expense might be objected to, he devised a gangway, to
extend as far as the Beacon rock, where men could give the necessary assistance by heaving
a rope on board, which might be executed at a moderate cost.
This structure was proposed to be composed of few materials, for it was found that it
was generally better to elude the force of the sea than to resist it, and the less matter opposed
to its action the better, provided that be securely and permanently fixed. The rocks were to
be bored by a jumper, 1 inch diameter; to these the eye-bolts were to be forged, a little
tapering, and larger than the holes, so that they might be driven tight, by means of an iron
maul; and if they were found too small, strips of iron plate were to be introduced, and
in a short time the rust would prevent their being moved or drawn out.
As this proposed pier would receive the full stroke of the sea, when the wind was
south-easterly, it was not only necessary that it should be built very firmly, but in such a
manner that the ordinary seas should not break over it; he therefore proposed that it
should be raised 9 feet above high water at spring tides, which is 22 feet above the low
water line at the pier head, and that it should have an inclination, as it continued from
the south-west towards the land. Such a height would carry it considerably above the
rocks, where it was built, and therefore, instead of so large a quantity of backings as would
be necessary to make the whole good to that level with the land, he proposed it to be
built upon the other side.
The rocks at the foot of the pier were to be removed before the pier was built, and
where the pier was founded, the rocks were to be cut off level, so that the lower course of
stone had a proper bearing.
Dunbar had its harbour originally at Belhaven, some distance from the town, though
within its liberties.
Cromwell began the eastern pier of the present harbour, and some years afterwards the
latter was deepened by taking away, over its whole surface, 8 feet of the solid rock. After
this work of great labour and expense, a new pier was built. Between the harbour and
the fortress are some basaltic rocks which dip towards the south, and are crystallised into
either triangles or hexagonal figures like those at the Giant's Causeway.
Leith, the port of Edinburgh, stands at the mouth of a small river of that name; the
harbour at neap tides has about 8 feet water, and at high spring tides nearly 16 feet.
There is a communication with Edinburgh by a causeway nearly two miles in length, and
50 feet in breadth. In 1777 great improvements were made in the harbour; the pier was
continued to a considerable distance into the sea; a quay, basin, and docks, were at the
same time constructed at a great expense; and in 1801, Mr. Rennie commenced a new
dock, since which others have been suggested and partly carried out, and to raise the
vessels there are slips with iron ways; the ship is supported by a cradle which runs upon
wheels.
Adjoining to Edinburgh, on the north, is the Frith of Forth, or ancient Bodotria, which
is from five to seven miles in breadth; the largest of its bays is that of Musselburgh,
which advances several miles to the south of the village, whilst the harbour of Leith
occupies the angle or peninsula formed by the line of the Frith of Forth on the north, and
the Bay of Musselburgh on the east.
The trade of Leith is considerable, and one of the docks for building ships formed at the
entrance of the new basin presents three quadruple rows of steps, 29 inches high, and
11 inches in breadth, which gives a total depth of 21 feet. The division of the rows is
marked by a bench 20 inches in breadth. The breadth of the dock at bottom is 44 feet,
and the entrance to it is about 35 feet; the entire breadth at the top or level of the ground
is 70 feet.
An iron bridge, 12 feet 6 inches in width, composed of 6 ribs, and which cost 1365l., is
placed over the entrance to the basin.
On the south side of the Forth, at Newhaven, is the chain pier constructed by Captain
Brown,
Leith is protected by a fort, which was considerably strengthened by Cromwell; since
whose time a battery has been constructed on an eminence behind the docks, which extends
to Newhaven; this is surrounded by an intrenchment, and defended by bastions. In the
CHAP. VIII.
339
BRITAIN.
year 1485 a law was passed, prohibiting the inhabitants of Leith from engaging in any
commercial intercourse with the people of Edinburgh, and also forbidding the latter to
admit the former into partnership, on pain of forfeiting the privileges of the city, so great
was the jealousy between the two rivals for commercial advantages; and it was not till the

AVIEN PIER
LOW
WATER
SPRING TIDES
OTOWER
HARBOUR
DOCK.
DOCK.
SAND
PORT
FORT
DOCK
STREET
CUSTOM
HOUSE
Fig. 334.
LEITH HARBOUR.
citizens of Edinburgh purchased the surrounding land of the feudal lord that any thing
like unity or harmony was established, and their common interests found to be identical.
Dundee Harbour is entirely formed by art, and by considerable difficulty it has been made
to answer the purpose of sheltering vessels, and render them safe and quiet; but the

OVERGATE:
NETHERGATE
MICH
WATER
YEAMANS
SHORE
EQUINOCTIAL
SPRINGS
LOW WATER
HICH ST
HARBOURD
BUOT
HARD GROUND
Fig. 335.
SHORE
CHARBOU
SEACATE
DUNDEE
IRON
FOUNDRY
CEORCE GRAY DUNDEE
CAS
COMPANY!
PAVING
POWDER
MAGAZINE
MUSSE
THE BRYCES
FOWLER
Rock
GRYCES
ELEVATION OF FERRY PIER .N.SIDE
DUNDEE HARBOUR.
EXCON
ROCK
SECTION
WATER
FORT
➡CAROLINA

means adopted to make the entrance convenient and easy of access has rendered it more
liable to the deposit of mud and sand; the method formerly employed to cleanse the
harbour from the silt was by allowing a quantity of water to pass through sluices from
the basin, and at the same time causing a number of men to throw into the current the
z 2
* 340
BOOK I.
HISTORY OF ENGINEERING.
mud, that it might be washed out to the mouth, and afterwards carried away by the
tides.
John Smeaton, in the year 1769, finding that during spring-tides, at the tide of ebb
a strong current set past the end of the pier, which was diverted from the harbour mouth,
suggested that openings should be made, by which the water might pass, for the purpose
of clearing away the mud accumulated near the middle of the harbour: he recommended
two sets of tunnels to be made, three and three together, 12 feet wide each; these tunnels
to be arched over, so as to form a level platform at top, and the passage for the water to
be made through the rocks, down to the level of low water mark. He also suggested
that the channel should be turned, and that the small pier already constructed should be
removed, and the rock levelled, that the water in its passage from the tunnels should meet
with no impediment; and then the tidal water would pass with more force, and act more
efficiently in scouring away the deposits.

Fig. 336.
SECTION OF SLIP LONGITUDINALLY.
Thus, by means of strong currents, and the aid of men, as before, it was calculated that
the harbour might be kept tolerably clean; and he advised that the sluices should be made
larger, as well as the basin; and that the water should not be let off in small quantities, as
that was not making the best use of it, for a quantity of water, when a certain power was
given, would move that very expeditiously, which, applied in a less degree, suffered the
matter to remain.

Fig. 337.
SLIP AT DUNDEE.
The water in the basin, discharged at once in a body, would remove obstacles, which
would remain, if the capacities of the openings were only such as to allow the waters to
be a quarter of an hour running out.

Fig. 338.
•
SECTION OF SLIP TRANSVERSELY.
Smeaton recommended that the sluices should be made quite water-tight, and that the
doors should not be cut, so as to form a valve to let in the water, but that one door should
CHAP. VIII.
841
BRITAIN.
be opened at a time by hand, for this purpose; and to prevent any accident he suggested
that a small tunnel with a valve should be used, in part to let in, and effectually to keep
in the water. Without the use of men, it was imagined the harbour might by this means
be kept clean; and occasionally they might be employed to remove what the sluices could
not effectually do.
This harbour, which is on the left bank of the Tay, is often greatly inconvenienced by
the quantities of sand deposited within it. When the tide ebbs, it is brought down the
river, and when it flows it is brought from what has previously been carried out to sea.
Mr. Telford, in 1815, repaired and extended the quay, and constructed a new dock, 250
yards long, and 150 yards broad.
An act of parliament was obtained in the year 1815, for the improvement of this
harbour, and the management vested in commissioners. Mr. Telford was employed to
carry on the several works, and a floating dock, 750 feet in length, and 450 feet in
breadth, with an entrance lock, 210 feet long between the gates, and 55 feet in width, has
been constructed, as well as a graving-dock, the floor of which is in length 265 feet, and
breadth at bottom 40 feet, and at top 68 feet.
On the site of the entrance lock, at ordinary spring tides, is a depth of water of 19 feet,
and at neaps, of 14 feet. And the total cost of these works was 119,8351.
The ferries at Dundee required proper landing-places. One was formed on the north,
nearly 150 yards in length, which has a parapet and raised footpath, as well as an inclined
slip for carriages and cattle, 30 feet in width; it is supported on arches, so that the flux
and reflux of the tide is not prevented from scouring the back of the protecting pier of the
western harbour.
On the south side are two connected slips with a protecting wall between them, so that
there is shelter provided against all winds; and in every state of the tide, embarkation may
go on, and boats be under shelter.
The cost of these slips and approaches was 24,600l.
Bell Rock Lighthouse is situated in west longitude 2º 22′, and north longitude 56° 29′,
eleven miles south-west from the Redhead in Forfarshire. The rock on which it stands is
a red sandstone, of a fine grain, and containing minute specks of mica; the surface is very
rugged, and full of cavities, owing to the fracture and overlapping of the strata.
It con-
sists of an upper and lower level, being highest at the north-east end, which is partially
left by the tide at low water of neaps, whilst the lower level is only seen at spring tides;
at which time its dimensions are about 427 feet in length, and 230 feet in breadth.
The ordinary rise of spring tides is about 15 feet, and of neap tides 9 feet; but the state
of the weather varies this materially. The course of the flood tide in moderate weather is
south-west, and of the ebb tide north-east; and the spring tides have a velocity of about
3 miles an hour near the rock; and neap tides about 1 miles.
This celebrated rock is 11 miles from the nearest land, and is the obstacle to the
navigation of the firths of Forth and Tay; it is also dangerous to all vessels trafficking
the North Sea and German Ocean. In the year 1806 an act of parliament was passed to
construct upon it a lighthouse, and Mr. Robert Stevenson was appointed engineer to carry
the same into effect. The design approved of by the commissioners was one on the same
principle as the celebrated Eddystone.
A work-yard was established at Arbroath, and a quantity of granite was procured from
Aberdeen for the outside casing, and sandstone from Dundee; these materials being
prepared, and implements for lifting heavy blocks being provided, the works were begun
on the rock on the 17th of August, 1807. The workmen commenced by boring a number
of holes, to receive the lower ends of six large beams and six smaller ones, which were to
support a wooden beacon, or temporary residence for the workmen during the summer
months. Pieces of Memel timber 50 feet in length were placed round a circle 36 feet in
diameter, and met together at the top, on which was constructed a wooden house, which
consisted of three floors. The lower one was store-house and kitchen; the second, in
which the beams crossed, was made into two cabins: one was occupied by the engineer,
the other by his foreman; the upper room was fitted up with three rows of beds for thirty
workmen.
Below these three apartments, at a height of 25 feet from the rock, was a temporary
floor, on which the mortar was prepared, and a smith's forge for sharpening the picks and
workmen's tools was fixed. The violence of the sea at times, however, was sufficient to
lift this floor, and send all that rested upon it adrift: yet during the five years that
operations were carried on, this beacon, which was immersed every tide from 8 to 12 feet
in water, was found of the greatest utility.
During the first part of the work, it was necessary at every tide to go to and fro in
row boats, each of which contained sixteen persons. In the winter months, the workmen
were employed on shore preparing the various stones, which, after being carefully fitted
together, were all numbered and marked as they were to be placed in the building; and
z 3
342
Boox I.
HISTORY OF ENGINEERING.
this was highly necessary, as the several courses were dovetailed together, so as to form
one mass, from the centre to the circumference. The stones were all bored for trenails of
oak and joggles of stone, in the same way as practised at the Eddystone.
The lighthouse is 42 feet in diameter at the base, and 13 feet at the top. The part
constructed in masonry is 100 feet in height, and including the light room it is 115 feet;
the mortar used was sand, pulverised lime, and puzzolana, in equal quantities.
The
ascent from the rock to the top of the solid part, or lowest 30 feet, is by a trap ladder; and
from the entrance doorway a circular staircase leads to the first apartment, which con-
tains the fuel, water, and stores. The other apartments are approached by wooden stairs;
they consist of a light store-room, a kitchen, bed-room, library, and light room; in all, six
stories.
The three lower rooms have two windows each, and the upper four, all glazed with thick
plate-glass, and guarded on the outside from the violence of the spray of the sea by wooden
shutters. The light-room, which is 88 feet above the medium level of the tide, has around
it a projecting balcony with an iron railing; the interior dimensions of this octagonal
room is 12 feet in diameter, and 15 feet in height. It is framed of cast-iron, and glazed
with plate-glass, each plate being 30 by 27 inches; it is terminated with a dome roof, with
a circular ball; and the light used is from oil, with Argand burners, placed in the focus
of silver plated reflectors, hollowed to the parabolic curve by hammering only. These
reflectors measure 24 inches across, and the light is so powerful that it may be seen, when
the atmosphere is clear, 6 or 7 leagues.
The above lighthouse is the most important in the northern division; the others, erected
on the points or promontories connected with the main land, or upon the islands on the
coast of Scotland, including the Isle of Man, are more rudely constructed. That at the
Mull of Kintyre in Argyleshire, almost inaccessible by sea, from the rocky and precipitous
state of the coast, stands 240 feet above the level of the sea, and so difficult is the approach,
that the stores cannot be landed nearer than at a spot six miles distant.
The Pentland Skerries in Orkney consist of two islands surrounded by a reef of sunken
rock: one of these is about 15 acres, and has been entirely stripped of its soil by the sea
washing over it; the other, called the Great Skerry, contains 75 acres: on both are light-
houses, not, however, remarkable for their construction.
The methods adopted till lately on these coasts for distinguishing one light from another,
where the distance and bearing by the compass were not sufficiently marked, was effected
by double and single stationary lights, a method expensive and not to be relied on as a
guide to the navigator, from the frequency with which they were made to occur on the
coast in many districts; the revolving light has been substituted to great advantage, which
varies its character by the different tints given to the glass.
These several lighthouses are under the direction of a board of commissioners, except
those of the Tay, which come under the management of the Trinity House; the Com-
missioners of the Northern Lighthouses were established about the year 1780, and six years
afterwards a bill was brought before parliament, to enable them to erect several new
buildings on the coast, which had become frequented by the vessels engaged in the fisheries.
Arbroath, which stands on the river Brothwick, has a small harbour of a rectangular
form, defended from the sea by a wall of hewn stone on the north, and by a pier on the
south side. The entrance is closed by a floating boom, which slides between a double row
of piles, and is made to ascend by a capstan.
Montrose is situated in a fine bay, and at its quay vessels of 400 tons burthen ride in
perfect security, sheltered on the north by the town, and on the south by lofty hills.
The town is situated on the north bank of the South Esk, a torrent which descends with
considerable violence from the Grampian Hills, and forms a vast bay, near where it dis-
gorges itself into the sea; over the entrance, which is very narrow, is the bridge leading to
Montrose, 244 yards in length; the piers are of timber, and have been considerably injured
by the ravages of the worms, of the genus Oniscus, particularly on the side towards the sea.
An opening is formed in the middle of the bridge, by lifting a portion to admit vessels into
the bay.
At the mouth of the river on one side are dangerous rocks, and on the other a shallow
bottom of sand, without consistence, extending several miles into the bay, which, by an
easterly wind, is blown into the harbour, and again removed by the Esk, as the tide ebbs,
driving it outwards.
The North Esk runs parallel with the South Esk, and empties itself a little to the north
of Montrose; it is crossed by the stone bridge of Money Kirk, of four arches, built at the
cost of 10,000l., after the design of Mr. Stevenson.
Gourdon is a small fishing town, two miles south of Bervie, in the county of Kincardine-
shire.
Bervie, the ancient port on the river of that name, has an elegant bridge, on the
abutments of which is built the town hall. King David, in 1342, made it a royal town or
borough, in consequence of the reception given him by the inhabitants after a violent storm.
CHAP. VIII.
843
BRITAIN.
A pier, 350 feet in length, was constructed here under Mr. Telford's direction, on one side
of the harbour, which is defended by the west rock on the opposite side.
Nature has

MARSH DYKE
VIÊ
ROAD
WEST
ROCK
HARCOUR
VILLACE OF
COURDON
PIER
SECTION THROUCH AB
HICH WATER
EAST
WESS
0
ORDINARY SPRINC
·BOTTOM OF NAVICATION CHANNEL
Fig. 339.
GOURDON HARBOUR.
done much in scooping out many natural bays on this coast, some of which have deep
water.
Stonehaven, 15 miles from Aberdeen, has a secure harbour or a natural formed basin,
sheltered on the south-east by a high rock, which runs into the sea, and on the north-east
by a quay.
Aberdeen Harbour, which is 106 miles from Edinburgh, was extremely difficult to enter,
in consequence of a bar formed just outside the mouth of the Dee, composed of a shifting
bed of sand, gravel, and shingle, deposited on the north side of the entry; this, with a
north-easterly wind, was driven into the main channel, and choked it up; the quantity
driven depended upon the state of the tides, the land speats, and floods or freshes of the
river, which here falls into the sea.

MILI BARN
ΦΥΛΥ
WATERLOO
QUAY
wer DCCK OF 18 ACRES
INCHES. 36. Acres
TIDE HARBOUR
CAPSTAN JETTY
NEW CHANNEL FOR THE RIVER DEE
NEW CHANNEL FOR THE FLOOD WATER
CAPSTANO
TOWER
OBSERVATOR
CAPSTAN
JETTY
Fig. 340.
ABERDEEN HARBOUR.
CAPSTAN
When Mr. John Smeaton, in the year 1769, sounded at the mouth of the harbour, he
found 4 feet upon the bar at low water; on the sixth day after new moon, and at high
z 4
344
BOOK I.
HISTORY OF ENGINEERING..
water, full 14 feet; but at ordinary spring tides there was the same depth upon the bar at
high water, and at low water it was left with only the run of the river over it.
The neap
tides usually made 10 feet water upon the bar. Outside this bar the water gradually
deepened, and ships rode conveniently at low water, protected from all winds, except the
north-easterly and easterly, which blew into the harbour's mouth.
The bar, according to Smeaton, was thus formed; the whole coast, which stretches away
northerly, is for miles a flat and sandy shore, and the north-east wind acting obliquely upon
it brings the sand and gravel intermixed coastwise towards the south; and as the coast,
from the south side of the entry, stretches away nearly east for mile, these sands would
be deposited in the angle of the coast formed at the harbour's mouth, if the waters of the
Dee did not force its way through them, which they do, and maintain more or less an open
channel; a hard gale of wind at north-east, bringing the sand and gravel coastwise south-
ward, puts also in agitation that which has been previously lodged on the bank on the
north side of the mouth of the harbour, and at the same time forces it into the entry, and
if at that time it happens to be spring tides, and little fresh water in the river, a strong

၁
•
0000
000
Fig. 341.
PLAN OF BEARING AND SHEETING PILES.
tide of flood is the consequence; this, together with the wind, carries the gravel and sand
into the channel of the river, and the fresh water being short at the time, the reflux will
be languid, and, impeded by the impetus of the sea, and it cannot return.

Fig. 342.
SECTION of pier.
A continuance of land floods, either at spring or neaps, when the wind is moderate from
the north-east, scours the sand and gravel away from the mouth of the harbour, and carries

Fig. 343.
PLAN OF THE PLATFORM.
다
​it into the roadway, from whence it gets round the point of Girdleness; and if there is with
a strong land fresh low spring ebbs, which give the current the greatest fall to sea, and at
the same time run bare over the bar, with a moderate wind to the north-east, the stony
CHAP. VIII.
345
BRITAIN.
body of the bar will be cleared of sand, and the harbour's mouth found in the best
state.
To prevent this constant state of fluctuation that the harbour was subject to, Smeaton
recommended the erection of the north pier, which not only confined the land freshes till
they arrived at deep water, but prevented the sand and gravel from being driven in. The
first stretch of this pier carried out was 400 feet; this part not being subject to be over-
flowed by the tide, the base was 20 feet, the width at top 12 feet, and the height
12 feet.
The second stretch, another 400 feet, with a mean base of 28 feet, 14 feet 6 inches at
top, and 20 feet high; the third stretch was 546 feet beyond the last, having at a mean
36 feet base, 24 feet top.
The sides at a medium were 4 feet 6 inches thick, filled in with rough stones.
The pier head was to have had a base of 60 feet diameter, 48 feet at top, and 24 feet
high.
The parapet, the whole length of which was 1400 feet, had a base of 4 feet 6 inches, and
3 feet width at top, and was in height 4 feet, and the estimated cost was 10,000l.
In the year 1778 Smeaton found the pier completed according to his suggestions, and it
had produced the increase of depth and freedom of passage he expected; but the swell at
high water, meeting with nothing to control it, made its way through the clear passage
between the two piers, where meeting with nothing to break or disperse it in the bay, they
turned round along the shore, and spent their fury upon any objects they came in contact
with. To remedy this inconvenience, he suggested that at the commencement of the old
Sandness Point, a deposit should be made of rough stones, projecting towards the middle of
the open space, rising towards the pier, and sloping towards the low water; this was to be
of rough granite.
This catch pier he fancied would have the effect of quieting the harbour, and leave a
clear water-way of 300 feet of navigable channel, and it was not thought requisite to carry
this breakwater higher than spring tide mark, the seas being suffered to break over it at
high water.
There is nothing which tends to quash and disperse a wave when it is raised so well
as allowing its breaking upon a sloping beach; on this account the continuance of the
south piers so far to the westward has an injurious effect, in preventing the seas from
spending and breaking, as they would do, upon the naturally sloped shore; and this south
pier was required to be removed, as the use of the new catch pier was to throw the seas
more effectually over to the south side, and, unless there was a sloping beach for them to
break upon, they would again be reflected back from the side towards the north, and pro-
duce effects disagreeable to some part of the harbour.
This catch pier was formed of blocks of split granite, which was done at the quarries ;
they were cut into wedge-like pieces, and made of parallel shapes, and each alternate stone
composing the circular end of the pier was a header, and the others tended towards
the centre, whilst those lying between were retained in the manner of a dovetail; and the
header stones themselves being anchored at their tails, that is, at their inward or smaller
ends, to an anchor or cross stone, by means of an iron cramp to each, the whole were held
compactly together. It was particularly requisite that the wedge stones should be made
to fit properly.
The wedge-like header stones which formed the turn to the head, and which held the in-
termediate stones between them, were tied to the anchor stones at their tails by iron cramps,
an inch square, turned down and rounded at each end, to go into jumper-holes, and fixed in
them with wood wedges without lead, as the weight of the courses above them was sufficient
to keep them from starting.
The
This harbour seems to have been viewed by Smeaton as a tide harbour.
River Dee, which admitted the tide to flow upwards about 2 miles, and spread itself
over some very flat ground, did not acquire sufficient strength, to carry out all the deposits
that were borne down from the country above, through which the river flowed. The
tide, meeting the fresh water, occasioned the sand, stones, and mud, to be deposited, and
at last a bar was formed, which almost obstructed the entrance for large vessels.
Smeaton finding the river spread over a space upwards of 500 yards in breadth, imme-
diately had recourse to confine it in a narrower channel; and for this purpose it was that
he founded the north pier, which continues 700 feet eastward from ordinary high water
mark, and then starts off to the north for another 500 feet, in order that the current
might have a proper direction given to it.
Another pier was also built on the south side of the river about half the length of the
other, and two small jetties and a small basin were formed by Mr. Smeaton, in conformity
with the act of parliament obtained in 1773.
In the year 1810, another act for the improvement of this port was obtained, and Mr.
Telford employed to carry out its object. He commenced by ascertaining the quality of
346
Book I.
HISTORY OF ENGINEERING.
the soil by boring, the nature of the land floods and tides, and drew up a report upon the
subject; his object being to provide wharfage and floating docks, and new ground for ship-
building on the mud banks called the Links, to place locks and graving docks capable of
admitting vessels on the best foundations, and to provide the means of scouring the docks,
and cause the flux and reflux of the tide, as well as the land floods, to act most effectually
on the existing bar and prevent future accumulations there, so as to preserve 4 feet addi-
tional depth of water, and by this means admit large vessels at neap tides, and form a com-
munication between the Aberdeenshire canal and the new harbour.
The pier on the south side, which was constructed by Smeaton, having been destroyed
in 1807, Mr. Telford commenced his works of improvement by erecting another in cut
granite, and finished it with a slope of five horizontal to one perpendicular; this was
completed in October, 1809.
In the following year the north pier was commenced, and by the aid of a railway its
entire extension of 300 feet was completed within the twelvemonth; this was found so
beneficial to the harbour, that it was afterwards extended another 865 feet beyond Mr.
Smeaton's head, which was performed in three seasons, in the full expanse of the German
Ocean.
The outer head having in the following winter received considerable injury, its slope
was altered, and made five to one, since which it has stood perfectly well.
The foundations resting on loose sand and gravel, it was found necessary to consolidate
the work under low water by dropping from lighters large stones, and filling the interstices
up with smaller, until it was brought to within a few feet of low water, at which level the
ashlar line commenced. The stones were not laid horizontally, but at an angle of 45°,
and in this way was the masonry worked, until it arrived within 18 inches of the top,
when it was built level.
I
4j1.6
By this means the work was more rapidly advanced, and less liable to temporary de-
rangement, for while the ashlar wall was being carried up on both sides, the middle
was built, which was performed by a care-
ful backing of large rubble stone to within
18 inches of the top, when the whole was
coped with granite, 18 inches in depth,
over which, on the north side, was added
a cut granite parapet the whole length of
the pier. The outsides of the pier are
built with roughly dressed granite ashlar,
the headers being 3 feet 6 inches in length,
and the hearting of large rubble, the in-
terstices being filled up with smaller stones.

The rocks in the neighbourhood are
chiefly a gneiss formation, and as it is diffi-
cult to dress this stone into a regular shape,
the masons call them heathens; some of
these, of large dimensions, weighing from
5 to 30 tons, were slung by the aid of
machinery between the bows of two lighters,
which had counterweights at the stern, and
by this means floated to the pier head, and
deposited in the situations allotted them.
A railway laid down along the old pier,
with a double crane at the end, movable
on rollers, and advanced as the work pro-
ceeded, was found of the greatest con-
venience.
Besides this, six lighters of 40 tons each,
with a crane mounted on each, were em-
ployed to bring the stone used in the lower
part of the work.
16 feet
20 feet
12 feet
Fig. 344.
TRANSVERSE SECTION.
PUDDLE
The pier on the south side was carried
out, to correspond in extension with the
other; it was not, however, made parallel
with the north pier, but formed a solid breakwater from the south shore, in a north-east
direction, with a space at its entrance of 250 feet. Within this breakwater there was a
sloping beach, that the surge might spend itself freely, and not agitate the waters within
the harbour. The length of the breakwater is 800 feet, and it is constructed of large
rubble stones, as they came from the quarry, except the head, which is formed of roughly
dressed ashlar, laid to a slope of 450 where exposed most to the sea's action, and about
CHAP. VIII.
947
BRITAIN.
half that slope on the inside. It is raised 5 or 6 feet above the level of high water at
ordinary spring tides, and the top is covered with large blocks of roughly hammered
stone. The breakwater is protected by a shoeing of rubble stone; by narrowing the
entrance, it materially deepens the channel; a permanent depth of 5 or 6 feet water has
been obtained.
By means of a dredging machine, worked by a steam-engine, the interior of the harbour
was deepened; an additional 3 or 4 feet of water has been obtained, throughout the whole
extent, for more than a mile in length, so that vessels of any description arrive at the quays,
and there is no necessity for lighters.
In the year 1815, 900 feet in length of the new wharfs and the capstan towers were
built, as well as the embankment formed, on the south side of the wet dock; the works
remained in this state till 1830, when 1350 feet of new wharf was built, and the embank-
ment of the wet dock was proceeded with, as well as other portions of the work.
The whole breadth of the new wharf is 100 feet, and its foundations are laid on a plat-
form of timber, resting on piles, with a row of sheet piling in front; the outside face of the
other wharfs is built with granite ashlar, backed with hammer-dressed masonry, laid in
lime mortar, and the outside joints pointed with Parker's cement.
The general bottom of the harbour is sand and gravel, so that it was necessary to have
coffer-dams, for the purpose of constructing the foundations for the various buildings
erected, and chain pumps were used.
The right bank of the new channel was completed in 1832, its length being 1630 feet,
and that of the spill or water bank, 4107 feet.
The cost of these works was as follows:
£
Extending the piers and breakwater
81,955
Dredging the inner harbour
17,999
Constructing new wharfs and common sewer
39,738
Forming a new channel for the river, including the cap tan, towers, and jetty,
also constructing bulwark and embankment
15,398
Making a communication bridge to the Inches
5,500
£160,590
Since these works were performed, a new channel for the Dee has been opened, and a
spill water channel formed, by which means the river is kept entirely out of the harbour.
A cast-iron turn bridge has been constructed across that part of the harbour called the
Inches, which, by means of an embankment, has been considerably enlarged. A wall
has been built, 3200 feet in length, forming a spacious quay, 100 feet in breadth, and
paved throughout; this is in addition to the 920 feet length previously built.
A quay
wall 1200 feet in length has been also built on the Inches.
There is now altogether 6290 feet of quay berthage to this harbour, and a building slip,
of a size sufficient to receive the largest steamers, has been built according to a patent
obtained by Mr. Morton.
Mr. Morton's mechanical slip was patented in the year 1818, and it has been put down
at most of the ship-building ports in the kingdom; the patentee, in giving his evidence
before a Select Committee appointed to inquire into its merits, enumerates about forty
slips built a few years after its invention.
The chief feature is that of placing a complete wheel carriage underneath the bottom
of the vessel, which carriage has a long straight beam extending beneath the whole
length of the keel, with blocks fitted upon it for the vessel's keel to rest upon. As
all vessels are straight at the underside of the keel, or have some determined curvature,
it is easy to dress the blocks, which are placed on the middle beam of the carriage, to
either a straight or curved line, before the ship is taken up; and the slip is so constructed,
that the form of the carriage undergoes no alteration when the weight of the ship is
placed upon it; and the carriage is substantially borne by three parallel lines of iron
railway, founded upon either timber and piles or masonry, upon which it traverses upon
numerous wheels or trucks of cast-iron.
The ship, when placed upon the carriage, is kept in its perpendicular position by cross
bearers, on which is adapted other timbers fitted to the curvature of its sides, forming a
cradle; it is then, by means of tackle, drawn up an inclined plane, by men working at a
capstan, or at winches with cog-wheels, the chain being attached to the carriage, and
exerting no strain on the ship.
Between the railways is laid a cast-iron rack having serrated teeth, into which strong
palls catch, and which prevent the carriage from running down the inclined plane, in case
the tackle gives way.
Previously to this system being adopted, it usually cost 170% to haul up a ship of
348
BOOK I.
HISTORY OF ENGINEERING.
500 tons, and by Mr. Morton's principle this was reduced to 31, without any risk
whatever.
A durable and substantial slip may be constructed, under ordinary circumstances, at the
tenth part of the expense of a dry dock; and the apparatus employed may be moved from
one place to another. The vessel may be hauled up at the rate of 21 feet per minute, by
6 men to every 100 tons, so that the expense of taking up and launching a vessel of 500
tons does not exceed 60s.
Peterhead, is situated on the most easterly point of Scotland.
The town is built upon
the edge of an extensive bay, which affords to the vessels frequenting this coast a very

WEST
JETTY
BATTERY
TOWN OF
PETERHEAD
QUAY
PORT HENRY
SOR
FISHERMAN,
HARBOU
SOUTH
HARBOUR
QUAY
BALLA
HICH
VAT
GRAVING
DOOK
GREEN 19LAND
FISH TOWN
NORTH BAY
70 F1
Fig 345.
PETERHEAD HARBOUR.
secure anchorage. Besides the old south harbour with its south pier, west jetty, and
ballast quay, there is a new harbour formed to the north, with a capacious graving-dock,
excavated out of Green Island. The north jetty is carried out 470 feet, and its interior
wall was constructed on caissoons, as was the jetty-head which bears to the west, in length
80 feet. This portion in 1819 was partly destroyed by the violence of the sea, and has
since been reconstructed upon a broader and firmer foundation.
Peterhead, so famous for its sea bathing, had its harbour considerably deepened by
Smeaton, who recommended blasting 30,000 cubic yards of rock, but this operation has not
been attended with the success that was expected: wooden boxes or cases were made use
of by the workmen employed for this purpose; these movable cofferdams had occasionally
the water pumped out of them, and enabled the operation to be carried on at all times
without difficulty.
There is 18 feet water at the entrance at the top of an ordinary spring tide, but only
14 feet at the eastern extremity of the pier.
The granite found here, called by the people who work it Pacey Whin, is the best
material for building that can be obtained; it is scattered over the whole face of the
country in large irregular lumps, and is so hard that it resists the finest tempered edge
tool; but is admirably split into blocks of any size required, by the masons accustomed to
the work, who are perfectly aware that they cannot split the stone in any other direction
than that of its natural "greet," which they ascertain with great facility, and with such
certainty, as seldom to be mistaken. After it is split they draw a straight line in the
direction of the "greet," and then sink a row of holes along it with a weighty hammer,
having blunt points at both ends, and highly tempered; with this pick they unite the holes
and form grooves, into which they place a wedge made of the best steel, with a point cut
over square, so as to leave a triangular cavity below it; they then strike the wedges in
succession with a heavy hammer along the whole line, till the stone splits asunder; the
fissure going through to the bottom of the stone, in the direction of the line first marked
out, cleaving it into two parts, nearly as straight, though not so smooth, as if cut with a
When the stone is cut into a number of slabs, they are split into lengths at right
saw.
CHAP. VIII.
349
BRITAIN.
angles with the former cutting; they are picked over their surface, and smoothed by a
tooi in shape of a small hatchet, with much labour, and at a cost of 6d. per superficial
foot.
head.
Frazerburgh harbour lies at the foot of Mount Kennaird, and is 50 miles from Burgh-
The jetty has three bends; the first is in length 272 feet, the second 440 feet, and
the end, which returns at nearly right angles, 100 feet.
The thickness of the pier at top is 33 feet 7 inches without the parapet wall, which is 4
feet 6 inches in addition; towards the sea the height is 20 feet 6 inches above low water,
and batters considerably; towards the harbour the face is curved.
This harbour, lately so much improved, is now one of the best on the eastern coast.

TOWN OF
ERASERBURGH
272-2
SECTION
THROUGH A.B.
33.7
440.7
100.0
Fig. 346.
FRAZERBURGH.
Burghhead, in the county of Moray, has a small harbour well sheltered by a rocky
promontory from the north. The trustees, who have the management, expended upon this

570.FL
ROMAN STATION
AFTERWARDS
DANISH. FORT
TOWN OF
BURCH-HEAD
IL
Fig. 347.
BURGHHEAD.
rectangular dock 6000%, and the commissioners 2000l.; but the whole is dry at ebb
tide.
Findhorn is another port on the coast, the bay of which contains upwards of 1000 acres
of stiff clay, which is only covered by the flux of the tide, as a bar of sand crosses the
mouth of the river, and prevents all violence of the surge; this sand is constantly moving,
and the present harbour is at least of a mile farther down the firth than it was 150 years
ago.
350
BOOK I.
HISTORY OF ENGINEERING.
Banff, is situated on the side of a steep declivity at the mouth of the Doveran, which
rises in Aberdeenshire. A new harbour has been recently formed here, and at the same

مل النار
HARBOU
BOBBY
OLD HARBOUR
Fig. 348.
BANFF.
time that the jetty of Peterhead was thrown down, a portion of this pier, which was laid
The new harbour has a fine quay 370 feet in length, on
upon caissoons, was destroyed.
which was expended upwards
of 14,000l., the commis-
sioners for public roads ad-
vancing half the amount.
The harbour is, notwith-
standing the improvements
made on it, still inconvenient,
from the continual shifting
of the sand-banks at the
mouth of the river.
The section through the
pier shows its dimensions.
LOW
Fig. 349.
RIGH
SECTION OF PIER

20.-FT
WATER
WATER
Avock, upon the northern shore of the Bay of Inverness, had in 1811 a dry dock con-
structed; and within the bay are many other small harbours, convenient for fishing vessels,

**WATER
Fig. 350.
AVOCK HARBOUR.
1
150.Fb
J
70.F
150. Ft
CHAP. VIII.
351
BRITAIN.
Cullen, is another port in Banffshire, to the west of which the river Spey enters the
ocean, and forms the north-western boundary to the country. The harbour was by no
means convenient until the construction of the jetty, which is 250 feet in length.

Low
300.F*
MARK
MARK
Fig. 351.
FISHING VILLAGE
CULLEN HARBOUR.
Fortrose is at the entrance of the bay, opposite to Fort George, and stands upon the
Moray Frith, which, at the south-western point, is exceedingly narrow: after passing the

150 Ft
120.Ft
60.Ft
18 Ft
HICH
WATER
LOW
WATER
SECTION OF PIER
Fig. 352.
TOP OF PARAPET
TOP OF PIER
·SURFACE OF
BEACH
FORTROSE HARBOUR.
2.6
SURFACE OF BEACH
SECTION of mound
HICHIWATER SPRINCO
352
BOOK I.
HISTORY OF ENGINEERING.
ferry between the two forts it widens considerably. On the side of Fortrose a jetty has
been built for the convenience of disembarkation, and a mound has been formed on the
other side upon a tongue of land. The pier is raised 18 feet above the level of low water,
and is 22 feet thick at top: both sides are faced with squared stone, and filled in with
rubble.
Cromarty stands on the inner extremity of the bay, on the banks of the Petter. Two
quays have been recently constructed at Dingwall, where vessels drawing 9 feet water may
discharge their cargoes.
The Bay of Cromarty has several landing-places, lately built for the convenience of those
who frequent this magnificent coast, as Invergordon, Balinghead, &c. &c.
Mahomac, in the Firth of Dornock, which is separated from that of Murray by a
prominent tongue of land, has a pier recently constructed for its protection, 450 feet in

MARK
Fig. 353.
IN
TER
NEW PIER
VILLAGE
OF
PORTMAHOLMACK
HIGH
WATER
SECTION
18.
SPRING
TIDES
MAHOMAC.
LOW
WATER
30.9
SPRING
TEDES
length, with an end or jetty of 68 feet, returned at right angles. The wall towards the
sea batters, and has a parapet for its defence; that towards the harbour is curved on the
face, both built of squared stone and filled in with rubble.
Tain is another harbour in this gulf, which is exceedingly narrow.
Wick, in the county of Caithness, has a small harbour protected by a jetty at the mouth
of a small river; beyond this resort for fishing boats is seen Cape Duncansby, which
terminates the western coast.
Harbour of Pulteney Town. Caithness in Scotland, situated in the latitude of 58° 26'
north, and 3º 5′ west longitude, has been improved by the British Fisheries Society, partly
under the late Mr. Telford. A stone bridge connects the improvements with the town of
Wick, formed of three arches, having a clear water-way of 156 feet, which was built
in 1805.
The rise of the tide at neaps is 5 feet, and at ordinary springs only 9 feet 6 inches; at
extraordinary springs, from the lowest ebb to the highest flow, 13 feet.
The north harbour, only adapted for small vessels, being found very insufficient for the
growing trade of this improving fishing port, in 1823 the south harbour was undertaken;
the quays are built with stone of a hard quality, and vary in length from 3 feet to 20 feet,
and 3 feet 8 inches in breadth, and in thickness from 8 to 15 inches. These were set on
edge, and the courses placed diagonally in the slope; in the front walls the courses were
laid flat, and perfectly horizontal.
The foundations of the slope were formed of stones weighing from 15 to 20 tons each,
which were floated to their place by means of casks made of fir; each weighed about 25 cwt.,
and displaced about 445 cubic feet of water, so that two of these casks would lift 34½ tons
of stone.
Four of these casks were made use of, and sometimes they were found useful to lift the
vessels loaded with stones; when the water was low in the harbour, they exercised a lift
equal to 44 tons, by means of chains passed under the keel. These casks, which did not
cost more than 87. each, were found of great service in moving the stone, which cost only
18. 6d. per ton, when they were moved three miles, and lowered into their respective
situations. When the casks were applied to stones under low water, a wooden frame was
made use of for boring holes in the stone, for the insertion of a Lewis of rather a novel
form: the shank which was inserted was about 2 inches in diameter at the bottom, and
tapered upwards, diminishing to 1 inch at the top, where, into the eye, welded at the
CHAP. VIII.
353
BRITAIN.
top, was inserted the ring, into which was secured the chains. This shank being dropped
into the hole prepared to receive it, a wedge was driven in, and by this means secured it
most effectually.
After the stones were thus prepared and attached to the casks, at the flow of the tide, they
were floated to their destination.
These casks were strutted inside in the manner of the spokes of a wheel, and hooped
strongly round on the outside; the stones were attached to them by means of chains, which
were passed round each of a pair of casks, the chains being drawn through the eye of the
lewis; each stone has inserted in it two lewises, so that it was firmly and securely held by
the two casks to which it was suspended. One lewis, even if placed immediately over its
centre of gravity, would have been inefficient to prevent the unsteady motion of the stone,
and its derangement would have constantly taken place; this ingenious part of the operation
was superintended by Mr. James Bremmer, in a most masterly manner.
The south harbour was completed in 1830, at a cost of 20,9001.
The Orkney Isles, being much frequented by vessels employed in the fisheries, consider-
able attention has been paid by the Government to some of the ports and landing places
during the last few years. These remarkable islands, forming the group known to the
ancients by the name of Orcades, are situated between Caithness and Shetland; from the
former they are about four miles distant, and from the latter, upwards of twenty leagues;
they are separated from one another by sounds, friths, and ferries, some of which are only
a mile in breadth, and others more than five; though so connected, the whole are of
considerable extent, being seventy miles across from the south-west point to that at the
north-east, and forty miles in the other direction. The islands are sixty-seven in number,
thirty-nine of which, called Holms, are not inhabited, but afford occasional pasturage for
cattle.
Lobsters and crabs are found in great abundance, and the cockle, which, as an article of
food, is greatly esteemed. The turbot, sole, flounder, plaice, holibut, ling, whiting,
haddock, cod, and numerous other marketable fish, are taken during the season, and
forwarded to the different cities and towns of the empire.
The coasts of the whole of these islands, with a few exceptions, may be seen at a distance
of ten leagues, where the sea is fifty-two fathoms in depth, which continues within a league
of the shore, where it is not less than fifty fathoms. The flood tide comes from the north-
west, it is high water at full and new moon about half an hour after nine, the ordinary
spring tides rise 8 feet perpendicular, and extraordinary ones 14 feet.
At the quadratures
the usual neap tides rise 3 feet, and sometimes 6 feet. The greatest rapidity of the spring
tides is nine miles an hour, whilst the neaps have only a fourth of that velocity.
Kirkwall Bay is in one of the Orkney Islands, called the Mainland or Pomona, which
forms the centre of the group; its latitude is 58° 33', and its longitude 0° 25' west; the
town is built upon a neck of land, washed on one side by the bay, and on the other by the
sea, which flows at the backs of the houses at high water. This ancient town was formerly

Low
-WATER
HARBOUR
THÍCH
WATER
BASIN
ONLY COVERED AT
HICH WATER
91.F
PIER 961.
MARK
Fig. 354.
KIRKWALL. BAY.
a place of great resort, and contributed with the boroughs of Wick, Dornock, Tain, and
Dingwall, to choose a burgess to represent them in parliament. The harbour is broad, safe.
and capacious, with a bottom of clay so firm, and a depth of water so convenient, that
vessels of considerable tonnage take anchorage here.
The new pier extends beyond ordinary low water, and returns at the head 91 feet.
Kyle, in the Isle of Sky, is situated on the shore of the narrow channel which divides it
from Inverness; this island, the largest of the Hebrides, lies at a distance of about 18 miles
south-west from Harris: on the south-east it approaches near to Glenelg, on the coast of
Scotland. The length of the island is between 50 and 60 miles, and its breadth 40 miles.
A a
354
BOOK I.
HISTORY OF ENGINEERING.

350 . F
#HIGH
OLD CASTLE
FISHERMEN
HOUSES
Fig. 355.
KYLE HARBOUR.
At the village of Portree or Rhea is a newly constructed landing quay; the country
around is mountainous, and some of the highest land is covered with snow at midsummer.

FERRY RIER
CATTL
198 H4 BH 20
BULWARK .120.F$
Fig. 356.
RHEA FERRY.
ZMIGANINI
CHAP. VIII.
$55
BRITAIN.
There are many fertile plains, and rivers abounding with fish, and sometimes the Mytilus
margaritifera found here contains pearls of considerable value.
Tobermory, in the Isle of Mull, is a considerable port, with a pier continuing eastwards
for 300 feet, or a little beyond low water mark. The British Society for the Encouragement

ELEVATION
PRESENT
WHARP
MOUND
OF RUBBLE
STONES
SECTION
18.0.
HCIH
WATER
LOW
WATER
Fig. 357.
TOBERMORY HARBOUR.
of the Fisheries have an establishment here; the bay is well sheltered from the ocean by the
small Isle of Calve, and it is situated in the track of the shipping which pass from the south
northwards.
Tarbet is situated on a small isthmus in the sound of Islay; the strait or sound of Jura
is a large and deep gulf, extending along the western coast of a tongue of land, 60 miles
in length, which the canal of Crenan divides from the county of Argyle; this canal,

UNHIDEHITI OF
ملام
EAST TARDET
ATE
R·K
ས་ས
Fig. 358.
EAST TARBET.
9 miles in length, enables vessels to avoid a very dangerous navigation; the coasting vessels
pass through the peninsula of Cantyre to the extremity of Loch Fine, and then by the canai
of Crenan.
AA 2
256
BOOK I.
HISTORY OF ENGINEERING.
Jura Small Isles pier, situated between the ferries of Lagg and Feoline, and constructed
under the direction of his Majesty's commissioners, is extremely well executed, and can be
approached at all times;
the double bend given to

it
secures the safety of
passengers landing at all
times. The width at top
is 16 feet, and the two
faces are carried up with
squared stone.
FROM FEOLINE TO
LUCO
STORE HOUSE
|LEVEL or DOOR STEP
HCIH WATER
LOW WATER

SECTION
16.
There are two very fine
harbours on the east side
of the island, that to the
south, where the above pier
is situated, and another to
the north, called Lewland-
man's Bay: they are with-
in a few miles of each
other; the island of Jura,
30 miles in length, and 7
miles in breadth upon an
average, is the most rugged
of the western group, being
composed of rocks piled
one on the other, in most
admired disorder: Mr.
Pennant, who ascended
Bienn-an-Oir, with con-
siderable difficulty, de-
scribes the grandeur of the
prospect from the summit.
Sir Joseph Banks found the
height of Bienn Sheunta
to be 2359 feet above the
level of the sea, and Bienn-an-Oir, 2420 feet. The stones forming these mountains are
white and red granite, and the shores are covered with a fine sand, great quantities of which
are annually carried away in vessels employed for the purpose, to be used in the manu-
facture of glass. In this island are several cairns, rude obelisks, and duns; the climate,
like that of the other western
isles, is extremely moist: the
winds blowing from the west are
loaded with vapour, drawn from
the broad surface of the Atlantic
ocean, and when they are inter-
cepted by the high lands, the
rain often descends in torrents;
but although the climate is ap-
parently so unfavourable, there
are instances of great longevity
among the inhabitants. Gillour
Mac Craen is said to have
kept 180 Christmasses in his own
house; he died in the reign of
Charles I..
At Feoline we have an admi-
rable specimen of a stone land-
ing-place for all states of the tide.
Upon a base of not more than
50 feet are two inclined planes,
with a jetty dividing them, in-
tended to be used at high water,
and to protect those landing
from boats at either high or low
water; when the wind blows
Fig. 359.
HICH WATER
LOW WATER
12... 0
SMALL ISLES PIER.
20.
ELEVATION

46..6
SECTION
12.0
from the south, the lofty jetty
screens the north landing-place,
Fig. 360.
FEOLINE.
and so with that on the other side when the wind is in the contrary direction.
CHAP. VIII.
35T
BRITAIN.
Corran Ferry incloses a basin for the vessels to receive their freight, and is most admirably
adapted for the convenience of shipping cattle; the whole is built of stone, and the walk
around is of a sufficient width to be serviceable at all times.

+
PE
Fig. 361.
CORRAN FERRY.
Port Glasgow is 20 miles from the city, on the Clyde, and is built around a basin, which
was the first excavated in Scotland: its form is that of a rectangle, but it is not inclosed by
lock gates. Beyond this dock is a wide quay, extending along the Clyde for a considerable
distance.
The river Clyde has been improved greatly since the period when the inhabitants of
Dumbarton, Renfrew, and Glasgow, undertook jointly to remove the deposits in the river
by statute labour. Smeaton, in 1755 and 1758, directed his attention to the clearing away
of the numerous obstructions in its navigation, and afterwards an act of parliament was
obtained for the construction of locks, which was never carried into effect.
In 1769 the river was sounded by Mr. J. Watt; and Mr. J. Goulbourne, of Chester, com-
menced his improvements by inclosing the river between two artificial embankments, when
water was obtained of sufficient depth for vessels drawing 7 feet to reach Glasgow. To
contract the bed of the river, walls of stone were built, in a direction at right angles with
the stream, at some distance from each other; these were united by dikes, which were
thrown up to make the bed of the river one uniform width throughout.
The government of the river Clyde is placed by act of Parliament under the magistrates
and council of the city; and all the revenue, arising from tonnage, craneage, and harbour
dues, collected at the Broomielaw, are kept distinct from the funds of the corporation, and
are laid out in deepening and improving the river and harbour.
In 1808 a company was incorporated for supplying the city of Glasgow and its suburbs
with water, and works of some magnitude were soon after established at Cranston Hill,
about a mile below the city; filtering beds are attached to the great reservoirs, and by
means of powerful steam engines and iron mains, water is delivered throughout the streets
and lanes of the city in a pure state.
The first steam boat introduced on a navigable river in Great Britain plied between
Glasgow and Greenock in the year 1811; it was the property and contrivance of Mr. Henry
Bell, an engineer of this city; the name given to the boat was the Comet, and the distance,
twenty-two miles, was performed in three hours and a half, with an engine of three horse
power.
Greenock, on the gulf of the Clyde, has an open basin, around which are many yards for
ship-building.
Androssan. To defend the harbour from the violence of the sea, a long pier has been
constructed upon a ridge of rocks, which may be seen at low water; it forms a salient angle,
whose sides extend from the land towards the west, and from the west towards the north
at some distance from the mole stands a lighthouse, to protect vessels from the shoals at
the entrance of the harbour.
A wet dock has been constructed within the mole, capable of holding 100 vessels, drawing
16 feet water; a building dock, of stone, has been added.
;
AA 3
968
Book I.
HISTORY OF ENGINEERING.

PRODICA CASTLE-
LAMLASH
5.END OF ARRAN·
AILSA CRAIC-
HORSE
ISL
PROPOSE!
EAGLE
ROCK
WEST
CUMBRAES
PENCORSE
TRANGE
DOCK
DOCK
7
CANAL
OLD
CASTLE
CAMPBELLS
ROCK
Fig. 362.
CASTLE
CRATC
These works were directed by Mr. Telford, who employed chains and wooden cranes for
raising the large masses of stone used.
Troon has a mole, built in the form of a horse-shoe, the outside and inside courses of
which are composed of granite, cut at right angles with the joints, and left rough externally.
The several courses lie with an inclination of 45°, which occasions the seas to glide off
more easily. There is a large wet dock, of a quadrangular figure, also built of granite, and
the entrance is from the north. To the east is a building dock, with gates 36 feet wide.
Ayr Harbour is at the mouth of the river of that name, where it falls into the wide and
open part of the Firth of Clyde, where the coast is flat, and composed of drift sand, which
has formed a bar before the mouth of the harbour; the river, which is of a considerable
width and force, and subject to great speats in rainy seasons, drives the sand out to sea, and
prevents the entrance from being entirely choked up.
By the erection of the north and south dikes or walls, the channel of the river has been
confined, and made to pass over the flat sands, which has maintained a tolerable depth of
water in the harbour.
When Smeaton saw this harbour in the year 1772, he advised the raising of these walls
to the level of high water mark, and that they should be so lengthened that a greater force
might be obtained, and the back waters being driven in a north-west direction might be
prevented from acting on the banks; he calculated that by judicious management a con-
siderable additional depth of water might be obtained.
The harbour commences below a bridge of four arches, and two piers of stone and timber
extend 550 yards right and left of the river, to which the vessels are moored.
リ
​ROAD FROM GREENOCK
BURNFOOT
CHAP. VIII.
859
BRITAIN.
In the town of Ayr, Cromwell established a fortress.
Carlisle on the Eden is situated some distance beyond Maryport, which is at the mouth of
that river, the banks of which are protected by stone quays and wooden piers.
Workington is a small port at the mouth of the Derwent, here crossed by a bridge of
three arches, which does not interrupt the passage of small vessels to Cockermouth, a town
on its banks, where the Cocker enters.
Whitehaven is a port with a lighthouse and mole, of considerable business, and the coal
works in the neighbourhood give employment to numerous coasting vessels.
Ravenglass, at the mouth of the Esk, has a deep gulf, extending to Ulverstone, where are
numerous manufactories.
Lancaster on the Loyne has a harbour, whose entrance is obstructed by a bar thrown up
by this torrent stream. On the left bank of the river there is a long quay for the accommo-
dation of the shipping.
Preston, situated on the Ribble, at a short distance from the sea, carries on a considerable
trade.
Liverpool, on the Mersey, ranks next to London in point of importance and commercial
wealth, although Leland tells us that in his time (Henry VIII.), "Lyverpoole, a paved
towne, hath but a chapel. Walton, a four miles off, not far from the Le, is paroche
chirch." Irish merchants then resorted to it, on account of its small port dues. From the
time of William III. this place has continued to increase in importance. Situated on the
eastern bank of the estuary, it has long been considered the key of its commerce: the river
gradually widens towards the sea, and at spring tides the water rises 30 feet, and at dead
neaps only 13 feet.
The shore, however, is remarkably flat, and though vessels rode safely in the offing,
it was found necessary to form a more secure place for them; and in the reign of Queen
Anne the first floating dock for ships, called the Old Dock, was constructed; in the reign
of George II. the Salt House Dock was formed, and a pier erected.
In the following reign St. George's Dock was formed; piers to secure the outer harbour,
and two new lighthouses, were built. The King's, Queen's, and other docks have been
since added, as have graving-docks and dry basins for the convenience of the shipping
resorting here.
These docks were the first constructed in England for the accommodation of merchandise,
and consist of wet, dry, and graving; the latter, by means of flood-gates, can admit or
exclude the entrance of water at pleasure.
The Old Dock is 198 yards by 85 yards; Salthouse Dock 213 yards by 102 yards;
St. George's Dock 246 yards by 100 yards; King's Dock 272 yards by 95 yards;
Queen's Dock 280 yards by 120 yards.
The principal basin of the West India Dock measures 2600 feet by 510 feet, and is
29 feet deep; contiguous to it is another of the same length, 400 feet wide; the first
contains 30 acres, and will hold nearly 300 sail; the latter contains 24 acres, and is used
for the vessels about to proceed outwards.
The London Dock, for unlading, is 1262 feet long, 699 feet wide, and contains about
20 acres.
The East India Dock, for unlading, is 1410 feet long, by 560 feet wide, and contains
18 acres; that for loading is 780 feet long, 520 feet wide, and contains 9 acres.
Between all these docks there is a communication, so that vessels pass from one to
the other, and into the several graving-docks, without going into the river.
Large tunnels pass from one dock to the other, for the purpose of scouring them; so
that when a dock is to be cleansed, it is left dry at low water by closing the gates; the
sluices are then opened in different directions, and a number of navigators enter with
spades and shovels, to throw the mud into the channels or currents made by the sluices;
this, continued for several days or a fortnight, once in the year, keeps them tolerably free
from accumulation.
Formerly such an operation was effected by means of flat-bottomed boats, and the
sluicing here introduced was a vast improvement.
The Bridgewater Dock is for the use of the barges that belong to the several canals.
The five old docks, without including the Bridgewater basin, and the two others, have
3600 yards in length of quay, or a superficies of 28 acres. The dimensions of these
docks were increased by the late Mr. Rennie to an area of 62 acres; this was effected by
suppressing one dock, enlarging three others, and constructing two new ones, one to the
north, and the other to the south.
The new bridges are on the best principle, and the cranes of superior construction: the
capstans for opening and shutting the gates, the rollers and chains, are all of iron.
The distance between the quay at Manchester and these docks is 33 miles; but the
channel or natural course in the Mersey was 15 miles further; but this has been lessened
considerably, and reduced now to a little more than 41 miles.
At Manchester the river is 108 feet in width, at Warrington 140 feet, at Fidler's
AA 4
360
BOOK I.
HISTORY OF ENGINEERING.
Ferry 170 feet, and at Cuerdly Point 650 feet: from thence it rapidly widens to 3500 feet;
it is then narrowed at Runcorn Gap to 1200 feet, and at a short distance beyond its
width is 4200 feet, after which it extends to nearly 21
miles, and is again diminished at Liverpool to 3300 feet.
The level of the highest tide intersects the bed of the
river at Woolston, a distance, by the course of the
channel, of nearly 26 miles; and the bed of the river
at Manchester is 49 feet above the bed of the river at
Woolstan. At Warrington is the first weir, after which
the distance to Manchester is divided into ten pools.

The
At Liverpool, the spring tides rise 33 feet, at Run-
corn 16 feet 6 inches, and at Warrington 8 feet.
lowest of the neap tides at Liverpool is 23 feet 6 inches,
and the depth of water with a high spring tide is 89 feet;
but the bed of the river rises so much that at 9 miles
there is only 33 feet.
Birkenhead, on the Mersey, nearly opposite to Liver-
pool, on the Cheshire coast, is becoming a port of great
importance; the formation of numerous docks, and the
rapid increase of its inhabitants, have occasioned a new
market, a town hall, and various other public edifices
to be erected. The area of the market is 430 feet in
length, and 130 feet in breadth; its roof is supported
by forty-six cast-iron columns, 25 feet in height.
Aberconway has a small port or dry harbour, and its
ancient town of Conway, surrounded by high walls
12 feet in thickness, with twenty-four circular and semi-
circular towers, give us some idea of a Greek or Roman
city. The walls and four gateways remain, now in-
closing a wretched collection of dwellings. On the
eastern side of the wall of the town is a quay of some
extent; and here was a ferry of so much importance
that it formed the landing-place for those who returned
from Ireland. The spring tides rise about 12 feet, and
at low water the river Conway is not more than 150 feet
in breadth. The sandy bed of the river still produces
the pearl oyster or muscle, as it did in the time of the
Romans, and the limestone in the neighbourhood abounds
with copper ore.
Bangor, so famous for its slate quarries, is situated at
the Menai Straits, which separate the Isle of Anglesea
from the main land.
Caernarvon, the Segontium of the Romans, is highly
interesting to the antiquary for the remains of the ancient
city, which occupies an oblong square, containing seven
acres at a short distance from the present town.
The port affords excellent anchorage in 10 or 12
fathoms of water, although the Aber sand bank forms a
dangerous bar to vessels entering. The quay is of con-
siderable extent on the side of the castle, and has lately
been greatly improved.
Beaumaris, a port of the Isle of Anglesea, has con-
siderable trade, and in the neighbourhood are rich and
extensive copper mines.
Menai lighthouse, constructed on a sunken rock about
200 yards from the coast of Anglesea, was designed by
Messrs. Walker and Burgess, and its total cost is said
to have been 12,800l.
It resembles a circular tower, 40 feet in diameter,
75 feet in height, and 20 feet 6 inches in diameter at top,
where it is capped by a castellated parapet of Anglesea
marble. The base of this tower is solid to the height of
22 feet 6 inches, after which the walls diminish at regular
sets-off, of 9 inches each, and at the level of high water
the diameter is 22 feet.
BRUNSWICK
·DOCK.
CANNING
ALTHOUSE
KINGS
DOCK.
QUEEN
DOCK
GEORGE
CLABENCO
NISVS)
BASIN
PRINCES DOCK
LIVERPOOL DOCKS.
LOW WATER SPRING TIDES
Fig. 363.
The interior is divided into six stories; all the stones are laid perfectly water-tight,
and are each secured to the one below by a slate joggle, and two oak trenails passing
CHAP. VIII.
361
BRITAIN.
entirely through it, and entering 8 inches into the lower stone. On the upper bed of
each course is a projecting fillet, which enters a groove formed to receive it in the upper
course, and by this means no water can be admitted. A gallery is formed above by pro-
jecting the courses inside and out; this supports the lantern, which is of cast-iron.
The light is stationary, red, dioptric, of the first order, without mirrors. The burner
has four concentric wicks, the largest of which is 34 inches in diameter, and consumes a
pint of oil per hour. The mortar used in the construction consisted of three of sand, one
of lime, and one of pozzolana. A foot-bridge unites this lighthouse with the shore.
On a
rock at a short distance is a beacon formed of a cone of masonry, 20 feet in diameter at the
base, and 37 feet high: on the top is a staff and globe, which rise 13 feet above the apex;
the globe, 4 feet in diameter, formed of copper bands, is 36 feet above high water mark.
Lighthouse lamps, as now supplied with oil, are of the Argand or Fresnel construction,
and great attention is requisite to the ventilation of the chambers; where a quantity of oil
is burnt in a short space of time a great quantity of carbonic acid is produced, which
renders the atmosphere unwholesome. A pound of oil in combustion produces 1.06 pounds
of water, and 2.86 pounds of carbonic acid; this increase of weight being due to the
absorption of oxygen from the atmosphere, one part of hydrogen taking eight parts by
weight of oxygen to form water. An Argand gas-burner in four hours, when placed in
the window of a shop, produces 24 pints of water. Lighthouses are now usually fitted with
one large central lamp, the outer wick of which is 3 or 4 inches in diameter, or with many
single Argand burners, each having a parabolic reflector, Professor Faraday has contrived
a method to keep the air in the chamber pure, and to ventilate the lamps by flues which
maintain fresh air within the lantern; this is performed by means of a chimney or copper
tube, 4 inches in diameter, not in one length, but in three or four; the lower end of each
portion, for about 1½ inch, is opened out into a conical form, measuring 5 inches in dia-
meter at the lowest part. When these pipes are put together to form the chimney, the
upper end of the bottom piece is inserted about inch into the cone of the next piece
above, and fixed there by three ties or pins, leaving at the same time plenty of air-way.
After the ventilating chimney is thus completed, it is placed in such a manner, that the
lamp chimney enters about inch into the lower cone, and the top of the ventilating
chimney enters into the cowl or head of the lantern. The ventilating flue, thus ingeniously
contrived, is found to carry off all the products of combustion into the cowl; none passes
into the conical apertures from the flue into the air of the lantern, but a portion of the
air passes from the lantern by these apertures into the flue, and thus ventilates it.
A sudden gust of wind striking the cowl does not in any degree affect the steadiness of
the flame, the ventilating flue carrying up every thing, and bringing nothing down. In
lighthouses, where many separate lamps and reflectors are made use of, a system of
gathering pipes is resorted to; these are brought together behind the reflectors, and enter
one large pipe, which passes off to the cowl at top. A seven-eighth inch pipe is found
sufficient for a single lamp, and this is made to pass downwards through the aperture in the
reflector over the lamp, and dips an inch into the lamp glasses, when the draught upwards
is such, that not only do all the products of combustion enter the tube, but air also
passes down between the top edge of the lamp-glass and the tube, and is finally carried off
with the smoke. The tube should not dip more than inch into the lamp-glass, or the
whole of the burnt air would not escape.
Holyhead, or the Caer Cybi of the Britons, is situated on a small island at the north-west
extremity of Anglesea; here are the remains of many Roman constructions, as well as
British. This port, being the nearest to Dublin, has occasioned it at all times to be much
frequented; latterly it has undergone considerable improvement, and a new lighthouse been
erected. The piers in front of the port are upwards of 1300 yards in length, and the
base 90 yards in breadth. The slope towards the sea is made 5 to 1, and the breadth at
top is 8 feet.
At 8 feet below the top a way is formed, 48 feet in breadth, which answers
the purpose of a quay. At the end of the pier the quay is 47 feet above the level of low
water mark, and 6 feet above high water. All the masonry is executed with granite
obtained in the vicinity, and towards the head of the pier is formed a jetty or spur which
advances 60 feet, and has a width of 164 feet.
It appears from Tacitus (in Vita Agricolæ), that the Romans had a settlement here, and
carried on a considerable trade with the people of Ireland. No place could be more
advantageously situated for such a purpose, as it projects far into the Mare Vergivum of
Ptolemy, and lies in the neighbourhood of the Roman stations on the western shores of
Flavia Cæsariensis: Mr. Pennant has described a Pharos at the summit of the mountain
called Pen Caer Cybi, 10 feet in diameter, and at no great distance a regularly faced wall,
10 feet in height and 6 feet in thickness, which surrounds three sides of a parallelogram,
the fourth being open to the harbour. At each angle was a circular tower. By some these
fortifications are supposed to be the work of the celebrated chieftain Caswallon Law-hir,
for the purpose of repelling the Picts, who infested these coasts after the final departure of
the Romans.
362
BOOK L
HISTORY OF ENGINEERING.

TOWN
du
BLACK
ROCK!
HOLYHEAD,
THE SOUND
CUSTOMS
ENGINEER'S
PHOUSE HARBOUR
MASTERS
OFFICE
ROYAL
HOTEL
THE BAY.
TRUE NORTO
THE
PLATTERSE
-WEST
OUICHTHOUSE,
THE
PIER
YNYS RUG
OR
PARRY'S
ISLAND
TO
PENRHO'S
SOUTH
ENGINE
HOUSE
TURKEY SHORE.
Fig. 364.
DIEW ROAD TO LONDON
HOLYHEAD HARBOUR.
Towards the south is another pier, and within is a wet dock, containing upwards of 22
acres, with a depth of water of 19 feet. To the south of the port, on the rocks, stands one
lighthouse, and another is placed at the head of the mole.
Aberystwith has a small port, and in the neighbourhood are extensive lead mines, which
afford employment to the shipping.
Milford Haven, surrounded by lofty mountains, penetrates far inland, and has sufficient
depth of water for the largest vessels of war. At Pembroke is an arsenal.
Swansea, an excellent seaport, formed by the construction of moles, by Captain Huddart,
is situated on the western side of the river Tawe.
Cardiff is a port at the mouth of the Taff, about three miles from Rumney Bridge, and
the town was once surrounded by thick and lofty walls. The new cut to the quays admits
EAST
CHAP. VIII.
963
BRITAIN.
shipping of 200 tons; in the neighbourhood are many canals and railroads, which greatly
contribute to the business of this port.
Bristol is one of the most important cities of the empire, and the great emporium of the
western counties; in the eleventh century, we find its inhabitants trading with Ireland,
Norway, and every part of Europe: though the city is situated at a distance of 8 miles
from the ocean, yet the Avon and Frome are of sufficient importance to allow vessels of
any burthen to arrive at it. The quay and harbour have received improvements at various
times, and a company was established in 1804, that undertook the formation of extensive
docks, which were completed about five years afterwards, covering 82 acres of ground;
they extend 21 miles, and at all hours vessels may pass from Dunhead to the quays, and
discharge their cargoes while afloat: the arms of Bristol, which consist of a ship and a
castle, have the motto Virtute et industriâ, which should be ever remembered by commercial
men.
The Frome, below its junction with the Avon, resembles a vast basin, which traverses the
greater part of the city; around this artificial port are a range of quays. The vessels
coming up the Avon are first admitted by a lock into an entrance dock, called Cum-
berland lock, which can be made dry; then, by a second and third lock, they enter the great
basin.
The Cumberland dock is built of stone, and its subterranean aqueducts, with elliptical
openings, are admirably contrived for sluicing and clearing away the mud.
Here are
docks for building and careening vessels, spacious timber-yards, and numerous basins,
where ships may always remain afloat.
This port is greatly indebted to the skill and knowledge displayed by its engineer,
Mr. William Jessop, whose father was engaged to superintend the erection of the Eddystone
lighthouse, under the direction of Mr. Smeaton: the engineer employed at Bristol was born
at Plymouth, in the year 1745, and died in 1814; the improvements he made were highly
important, and chiefly consisted of the conversion of the river Avon into an immense
floating dock, which extended over 70 acres; this was effected by diverting the river
Avon for a length of two miles, and then cutting a canal to carry off its waters at the back
of the city; by such a project three miles of the rivers Avon and Frome were converted
into a deep wet dock, an entrance basin, with double lock chambers opening into the
Avon below, and a single chamber into the old river above.
Bridgewater is a port where the tide rises 40 feet, and frequently occasions damage to
the shipping. The most considerable portion of the town formerly occupied the east
side of the river; now it is on the western; there is an ancient bridge of three arches,
built in the reign of Edward I., to the north of which is the quay.
Watchet and Minehead are two small ports on this coast, and from the first named is
shipped the lime so celebrated for hydraulic purposes.
Ilfracombe has its port, surrounded by a semicircle of hills, which contribute much to its
security.
Barnstaple, at the mouth of the Taw, is a town of importance, and vessels can safely
anchor under its long and spacious quay, which extends for a considerable distance be-
yond a bridge of sixteen arches, which crosses the river. At the mouth of the Tawe a
bar is thrown up, which prevents vessels exceeding 200 tons entering the river.
Bideford is another port, south of Bristol, where merchant vessels may anchor alongside a
spacious quay, built at the side of the river.
Hartland is a small artificial port, built in the reign of Elizabeth, for the convenience or
the fishermen frequenting this coast.
Padstow, on the south bank of the Camel, is the best port on this coast; here is a
channel for ships at low water, 18 feet deep, and 400 feet in width; and vessels can at all
times come alongside the quay, and to the custom-house built adjoining it.
St. Ive's Harbour is situated five leagues north-east of Cape Cornwall, and upon the entry
of the British Channel lies nearly opposite Mount's Bay; this harbour is in depth about 2
miles, and in width 4 miles, having in the middle, at low water, full 10 fathoms. The
bottom is clean, and composed of a fine white sand, or the fragments of sea-shells; under-
neath this is a blue clay, forming excellent anchorage ground. A bold rocky promontory,
called the Island, is situated at the north-west corner of the bay; this is joined by a narrow
neck to the main land, and projecting towards the east forms an harbour on the north-west
side of the bay, which is well defended from all winds, except those from the north-east.
This interior harbour is almost left dry at low spring tides; but the fine soft sand that
lines the bottom of this bay affords an easy bed for ships when left by the tides; for larger
vessels there is an excellent road, where they may ride safe from all north-westerly,
westerly, south-westerly, southerly, and south-easterly winds, in 6 or 7 fathoms of water,
at low spring-tides. Mr. Smeaton visited this port in the year 1766, and furnished a
design for a pier, 60 fathoms in length; and he advised that if upon an examination of the
soil, there should not be found any rock upon which the foundations might be laid, they
should work upon the principle the French call pierre perdu, or cast-stones, that is to
964
BOOK I.
HISTORY OF ENGINEERING.
say, by dropping a large quantity of rough stones in a proper direction and width, so as
to form an artificial rock or base for the pier; these stones, sinking by degrees into the sand,

SECTION OF PIER.
Fig. 365.
ST. IVES HARBOUR.
and being followed by others, will rest upon the former, and so on, till the lowest become
firm; for the sand, lying very close and compact, will bear any weight when not affected
by the action of the sea. By this method more stone is required than if the pier be built
upon a regular base; but the whole being of very rough stone, and executed without
timber work, it will be cheaper and more secure than any thing can be made upon a foun-
dation of piles and timber upon sand.
The pier, so raised to half tide, or even to the top, was to act as a breakwater or defence
against the sea, and Smeaton estimated that the cost would be 7s. 6d. per cube yard.
The highest spring-tides being 26 feet above the surface of the sand, the pier was to be
carried up solid to the height of 30 feet; and supposing the settlement in the sand to be
6 feet, the whole height would be 36 feet. The pier was to batter half its height on
each side, and as the top was to be 24 feet in breadth, the base would be 60 feet, and the
mean breadth 42 feet; this multiplied by 36 feet, the height, gave a sectional area of
168 yards.
Smeaton recommended that the shores should be planted with sea rushes, which were
found to entangle the sand, prevent its blowing about, and retain it in the north bay, where
it arises, and by this means the breadth of the neck of land that joins the island would be
increased.
Penzance harbour has a mole to protect it, but the port is dry at low water.
Falmouth has a spacious port and quay, from whence the packets bound to Spain, Por-
tugal, and the West Indies, take their departure.
Fowey is a small port at the mouth of a river of that name, and the town is built upon
its western bank.
Plymouth Sound, on entering, has to the east the celebrated breakwater; after passing
which a natural basin is arrived at, into which the Tamar and Plym discharge themselves,
forming the harbour, comprehending the three divisions of the Hamoaze, the Catwater, and
the Sound.
CHAP. VIII.
365
BRITAIN.
RAME
HEAD
In the time of the Saxons, this haven was called Tameorweth; by the Normans South
Town, and in the reign of Henry VI. it received the name of Plymouth. We have an

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Fig. 366.
PLYMOUTH SOUND.
account of the town in the reign of Elizabeth, and of its new charter, then granted at the
request of Sir Francis Drake, who brought water to all the houses by means of leaden
pipes from a reservoir which he formed above the town, the property of which he vested
in the mayor and commonalty, and their successors for ever. The water was conveyed
to the reservoir, through a winding channel of 24 miles, from some springs at Dartmoor:
this enterprise of the gallant admiral is perhaps the earliest example in England of sup-
plying a town with water brought from a distance.
Plymouth has had at various times considerable fortifications erected around it for its
security: its most ancient fort, built in the reign of Edward III., is by Leland styled
"a strong castel quadrate, having at each corner a great round tower." This fortress,
which stood on the south of the town, near the pier, is now nearly demolished, as are the
numerous block-houses which were erected at different points of the harbour in the time
of Queen Elizabeth. Some traces of them may perhaps yet be seen on the site of the
fort which occupied Hoe Cliff, where the citadel now stands. The view from the citadel
comprehends Maker Tower, Mount Edgcumbe, the town of Dock, now Devonport, Mount
Wise, and the Tamar, the beautiful bay of Causand, the Sound, the Bristol Channel, and,
in fine weather, Eddystone lighthouse, the scenery around Saltram, Plympton, Mary Vale,
and the lofty hills of Dartmoor.
St. Nicholas Isle, also fortified, is connected to the south-west shore by a range of
rocks, which are uncovered at low tides. Near the Devil's Point is the victualling offices,
where are granaries, bakehouses, and every requisite for the supply of a large navy. The
docks, situated about 2 miles from Plymouth, on the eastern bank of the Hamoaze, are
defended by strong fortifications, and acknowledged to be the finest examples of a maritime
establishment in the world: they contain upwards of 72 acres, and are surrounded by a
stone wall 30 feet high. Basins, docks, slips, rigging houses, artificers' shops, mast-houses
and ponds, rope-houses, mould lofts, and all that can be deemed necessary for the navy of
a great nation, are provided on a most perfect and extensive scale.
The basin, made in the reign of William III., has within it a dock 198 feet in length,
66 feet wide, and 23 feet deep.
Adjoining the south jetty are the rigging-houses, 480 feet in length, three stories high;
and on the other two sides, forming a square, are various store-houses. Beyond these, to
3S6
BOOK I.
HISTORY OF ENGINEERING.
the south, is a slip for hauling up and graving the bottoms of ships, and farther on is a
canal 70 feet wide, which has a basin at the upper end for small boats. An anchor manu-
factory and smith's workshops adjoin the wharf, near which are three slips; northward
lie the mast-house and pond. The rope-makers' buildings are 1200 feet in length, and
two stories in height; in the upper twine is made, and in the lower cables are layed or
twisted together, the largest of which are more than 24 inches in circumference, and weigh
upwards of 8 tons.
The double dock, situated near the north jetty, will contain two vessels, lying one a-head
of the other, but divided by gates. The Union dock, 240 feet in length, 87 feet wide, and
27 feet deep, is faced with Portland stone, having blocks of granite to support the shores.
The New Union or North New dock is 260 feet long, 85 feet wide, and 28 feet deep,
and these, as well as the whole of the work executed before the year 1790, were by
Mr. Barlby.
Plymouth Breakwater is composed of three arms or bends; the centre is in length 3000
feet, and each of the others 1050 feet, both inclining on an angle of 20 degrees. The length

Fig. 367.
PLYMOUTH BREAKWAater.
of the whole, measured at the top, is 5100 feet, and at low water line 5310 feet. At
the western extremity, a circular foundation was prepared, to receive the lighthouse,
570 feet in diameter. The general depth of water varies from 36 to 60 feet at low water
spring tides, which generally rises about 18 feet, and at neaps from 12 to 14 feet.

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45.0
Fig. 368.
SECTION THROUGH BREAKWATER,
This work was executed by Mr. Rennie, in the centre of Plymouth Sound, the first
stone being deposited on August 12. 1812. The entrance into the harbour on the eastern
side is mile in width, and here there are 6 or 7 fathoms of water: the western, which is
1242
the entrance most used by the shipping, is about the same width, and varies in depth from
7 to 9 fathoms at low water spring tides.

450
Fig. 369.
SECTION THROUGH BREAKWATER.
The work is chiefly composed of limestone obtained at Oreston, about 4 miles distant,
where the quarry is situated at the mouth of the river Laira.
The exterior slope, below the line of low water, was formed by the sea, and is now
ascertained to lie at from 3 to 4 feet horizontal to 1 of perpendicular; and from the
low water line upwards, it is 5 to 1. The inner slope is 2 feet horizontal to 1 of per-
pendicular from the base to the top, which is laid 2 feet above high water spring tides.
The width here is 45 feet, and in the centre it forms a ridge 12 inches higher. Beyond
the slope towards the sea there is an additional work or foreshore 30 feet in width at the
east end, 50 feet in the centre, and 70 feet at the west end; this rises about 5 feet above
the level of low water, and is intended to diminish the force of the sea, and to prevent the
undermining of the chief work beyond it.
The stone was raised in large blocks, some of which contained 10 tons, and were thrown
into the sea, in the direction set out for the breakwater, care being taken that the greater
number were deposited upon the outer slope. After a number of these large masses had
been lowered, a smaller class of stones, quarry rubbish, rubble, and lime screenings, were
thrown in to fill up the interstices, and close all the cavities; these found their position,
by the action of the sea, and the great mass became as it advanced perfectly wedged
together; in the storm which occurred in November, 1824, the sea made the outer slope
CHAP. VIII.
367
BRITAIN.
•
5 feet to 1 perpendicular, and drove all the rubble from the outer to the inner slope,
making its area equal to the other. Time was requisite to give the whole its perfect con-
solidation, which being obtained, and no movement in the masses being apparent, the
slope on the side towards the sea down to the foreshore was cased with regular courses
of masonry, which was dowelled, joggled, dovetailed, and cramped together, to lay the
lower courses of which the diving bell was made use of. The three lower courses were
all granite, laid horizontally on their natural beds; these were dovetailed, lewised, and
bolted to each other. The mortar was compounded of one part of Italian puzzolana, one
part Aberthaw lime, mixed with two parts of fine sharp freshwater sand: this com-
position, before it was used, was well worked together in a mill, with as little water as
possible: this, when applied to the masonry, speedily became hard. Roman cement was
employed for the outer joints and for some distance within, and to increase its setting.
For the interior of the work, a concrete was made use of, composed as the first, but with
a greater quantity of sand.
To transport the stone from the quarries to the breakwater, vessels of about 60 tons'
burthen were employed; these had two railways laid along them, parallel to each other,
and towards the stern they formed an inclined plane, which prevented the trucks from
running too far. The blocks of stone were placed upon trucks, and then in parallel lines
on the railways. After the vessel had arrived at its destination, the trucks were dis-
charged of their load by heaving them up; this was done by windlasses placed on the
deck; when the truck had arrived at the inclined plane, it was tilted over by its own
weight, and the stone was at once let go, and deposited into the sea; the truck then made
way for another, and after the whole was discharged, the vessel returned, to be again
freighted at the quarry: to economise time, steam-tugs were made use of, and consequently
many voyages were performed in a day. To guide the vessels, and to enable them to shoot
out their load in the proper place, buoys were laid down in the line at every 30 feet; an
account was kept of the quantity deposited, and the level it rose to, so that at all times the
actual state of the work was known.
This important work is so situated, that vessels can enter the Sound with either an
easterly or westerly wind; and the two entrances are so set out, that the tidal and
fresh water keep them at all times clear, and prevent any deposit or accumulation of sand
from obstructing them.
The heaviest gales are those from the south and west, when the breakwater is exposed
to the whole violence of the vast Atlantic; hitherto it has been found to stand against this
power, and effectually to check the waves which uninterruptedly roll through the Bay of
Biscay. 3,369,261 tons of stone are computed to have been used in this stupendous un-
dertaking from the year 1812 to March, 1841, when it was completed at a cost of nearly
1 million sterling. A calculation has also been made upon the entire cubical contents as
compared with the quantity of stone deposited, and it is found that the interstices occupy
about 37 per cent. of the whole, which arises from the employment of large blocks of stones.
Messrs. Walker and Burgess have constructed at the western end a lighthouse, designed
by the late Mr. Rennie. The dimension of this lighthouse, which is circular, is 14 feet
clear diameter, and the centre of the light is placed 55 feet above the top of the breakwater.
It is built of granite, and divided by floors into store, dwelling, bed, and watch rooms.
The lantern is 12 feet in width, and 7 feet 6 inches high, in which is a dioptric fixed light
with mirrors; the south side shows red lights, and the north white, which distinguishes it
from the other lights on the coast.
Where this lighthouse is placed, the diameter of the head of the breakwater is 390 feet at
the level of low water, and at the top 75 feet. All the lower courses are secured with slate
dowels, and vertical and horizontal dowels 18 inches long and 6 inches square at the centre,
sunk 8 inches into the lower course of stone; both ends are also dovetailed, and secured in
their places by plugs of copper, and by wedges driven into the lower stone.
Eddystone Lighthouse is built upon a rock, which lies nearly south-west from the middle
of Plymouth Sound, according to the true meridian; and the nearest point of land is the
promontory called Ramhead, which is distant about 10 miles, and bears from thence south,
scarcely one point west, or, by the compass, south-west by south, allowing two points of
variation of the north end of the magnetic needle to the westward. These rocks have
derived their name from the set or current of the tides which are observed there. An
eddy of the tide is a current setting in a direction contrary to the main stream, and is
occasioned by some obstruction; this eddy may be either a smoothness on the surface of
the water, or a current in the opposite direction to the tide, according to the velocity of the
stream, or the size of the island or rock which interposes to produce it.
The rocks are situated in west longitude 4º 5', and north latitude 50° 10', and consist
of three principal ridges, called the House, South, and East Reefs. They lie north and
south, in which direction their greatest extent is 600 or 700 feet; there is also a small
rock, called the North-east, seen only in spring tides, which lies about 1000 feet from the
House Rock. They are either granite or gneiss, called in Cornwall moorstone; they
908
BOOK I.
HISTORY OF ENGINEERING.
abound with felspar, which is of a brownish colour, and contain a number of irregular-
shaped white specks; they dip towards the north-west, at the rate of about one perpen-
dicular to two horizontal.
On the days of full moon it is high water at
the Eddystone at a quarter past five o'clock;
the tide of flood sets easterly, or up Channel,
and the ebb tide sets westerly; spring tides
rise from 16 to 18 feet, and neap tides from
10 to 11 feet: at these rocks, and upon the
opposite shores, it is high water about 21 hours
sooner than in the middle of the Channel.
The first lighthouse was commenced in the
year 1696 under the general powers lodged in
the Masters, Wardens, and Assistants of the
Trinity House, who were empowered in the
reign of Elizabeth to erect and set up beacons,
marks, and signs for the sea, needful for avoid-
ing the dangers, and to renew, continue, and
maintain the same.
Mr. Henry Winstanley, of Littlebury, in
the county of Essex, was the engineer bold
enough to undertake this building, which oc-
cupied three years in constructing; he com-
menced by making twelve holes in the rock,
and introducing as many irons 3 inches in
diameter, around which he carried up a mass
of masonry 14 feet in diameter, 12 feet high
upon the upper side, and 17 feet on the lower;
on this was constructed the upper stories,
which were probably of timber.
The base was afterwards increased, so that
its diameter was 24 feet; above this, the
structure had a polygonal form of twelve
sides, and the upper or look-out room had
eight; the whole underwent a thorough
change, or reconstruction, and the lighthouse,
as completed in 1699, bore no resemblance to
the first design.
On November 26. 1703, a violent storm
carried away the lighthouse; and Mr. Win-
stanley, the workmen employed in its repair,
and the light-keepers, all perished.
Mr. John Rudyerd, a silk-mercer upon
Ludgate Hill, was in the year 1706 em-
ployed to reconstruct it; and whatever he
required as a mechanist was ably supplied by
two shipwrights from the king's yard at
Woolwich. A circle was the form he selected
for the plan of the new building, and after
making a number of holes in the rock by
means of jumpers, he inserted the iron
branches, to hold his work firmly to the foun-
dations prepared for it. The holes were 21
inches in diameter, and the extremities of the
two which formed the breadth for the branch
at the surface of the rock were about 7 inches,
and these holes were bored slanting, so that at
the bottom they were full 81 inches apart.
Between every two holes was bored a third,
and afterwards the rock between them was
broken away by square-faced pummels, when
a hole of a dovetailed shape was obtained
21 inches wide, 7 inches broad at top, and
8 inches at bottom, and in depth 15 or 16
inches. These holes were not exactly alike
in dimension, and it became necessary to
forge an iron expressly to fit each.

Fig. 370.
WINSTANLEY'S LIGHTHouse.
CHAP. VIII.
369
BRITAIN.
The main pieces of each branch were, at the surface of the rock, 4 inches in breadth,
and at the bottom 6 inches; when introduced into the hole, there was space left to

admit a key, which, at the
bottom, was 2 inches, and
at the top 3 inches, which,
when driven, fixed the
whole in the manner of a
dovetail or lewis.
The holes being fitted
with the branches, a quan-
tity of melted tallow was
poured into each; the
branch and key being
heated to a blue heat was
put into the tallow, and
the key firmly driven, so
that the space which the
iron did not occupy was
filled with tallow; after
this was done, and whilst
the iron was warm, a
quantity of pewter, made
red-hot, was poured in
from a ladle, which being
heavier than the tallow
drove it out. Many years
afterwards, when these
irons were cut out, the
iron, pewter, and tallow
were found unaffected by
the action of the sea-water,
which apparently
apparently
never penetrated into the
holes which contained
them.
had
After these irons were
fixed, a layer of squared
oak timber was placed
lengthways upon the low-
est step of the rock, and of
a depth to reach to the
level of the next above.
Over these were laid cross-
wise another layer of
timber; and above this,
others, taking care to cross
each alternate course, until
a mass of timber was piled
up two complete courses
higher than the highest
part of the rock, and these
were all trenailed together.
In the middle of this series
of timber platforms stood
an upright mast, which
was firmly secured to the
rock by two stout irons;
this mast served as a centre
for guiding all the rest
of the superstructure, as
there were altogether 36
of these branch irons, in
each of which was bored a
hole, seven-eighths of an
inch in diameter, aud
through these 252 holes
Fig. 371.
WINSTANLEY'S LIGHTHOUSE.
passed as many bearded spikes, or jag bolts, which held the several layers of timber together.
B b
370
Book I.
HISTORY OF ENGINEERING.
Two courses of solid oak timber, squared, were laid one upon the other, to form the
basement; and on this five courses of Cornish moorstone, each a foot in thickness; these
were well jointed, but laid without any mortar or cement, and retained in their place
by iron cramps; the outer courses being

further bound together by upright ones,
which also prevented their being lifted by
the action of the waves.
After this 5 feet of moorstone was laid
on, which weighed 120 tons; two other
courses of timber crossed them, and where
the timbers presented their ends, circular
or compass timbers were laid, which were
scarfed together, each course breaking joint
over the other; these outside timbers were
jag-bolted to the interior parallel pieces.
Above the basement so constructed, a
well-hole, 6 feet 9 inches square, was left
for the stairs; and at 8 feet above the
highest part of the rock commenced the
step of the entrance doorway.
After constructing the building with
courses of moorstone and layers of compass
timbers up to the top of the central mast,
the height of which was 33 feet, a floor
was laid over the whole, composed of 3-inch
oak plank.
The upper part of the building com-
prised four rooms, one over the other,
formed of upright timbers, having a kerb
or circle of compass timber on each floor,
to which the upright timbers were screwed
or connected, and upon which the floor
timbers rested. These upright timbers
were jag-bolted and trenailed to
another, and in this manner the whole was
carried up to the height of 34 feet above
the floor, which was placed over the top of
the central mast. The floor of the lantern
was made of 3-inch oak plank, around
which was fixed the balcony.
one
The whole building was in form the
frustum of a cone, 22 feet 8 inches in di-
ameter at the bottom, and 14 feet 3 inches
at the top, and the height above the cir-
cular base was 61 feet; so that the base
was a little more in diameter than one-
third of its height, and the diameter at
top was somewhat less than two-thirds of
the base at the greatest circle.
The up-
All
用
​用
​right timbers were united at the ends by
scarfing and overlapping; they varied in
length from 10 to 20 feet, but were so
united that no two scarfings came close
together. The number of uprights around
the entire building were 71, their breadth
at the bottom nearly 12 inches, and their
thickness 9 inches, diminishing towards the
top, both in breadth and thickness.
the outside seams were well caulked with
oakum, and well pitched. The weight of
the various beds of moorstone was calcu-
lated to be 270 tons, and served to act as
ballast to keep steady this work of ship-
carpentry. All the windows, shutters, and
doors, were composed of double plank,
crossed and clamped together; they shut into a rabbet, so that there was no crevice left for
the sea-water to penetrate.
Fig. 372.
RUDYERD'S LIGHTHOUSE.
CHAP. VIII.
371
BRITAIN.
This building, finished in the year 1709, was repaired at various times, and answered
perfectly its purpose; but in December, 1755, it was totally destroyed by fire. The Earl
of Macclesfield, then President of the Royal Society, being requested by the proprietors to
recommend an engineer to reconstruct it, named Mr. John Smeaton, a philosophical in-
strument maker, as a man capable of executing the work; he was at that time in the north
of England, but upon being made acquainted with his nomination, waited upon the pro-
prietors, and having received their instructions, commenced his designs, though he admits
that he was a total stranger to such structures. Smeaton has, however, informed us
that he reflected much, previously to making his design, upon the several structures that
had occupied the rock, and that he had a wish to retain as much of Rudyerd's as was con-
sistent with the different nature of the material he had in view; and he observes further,
"It appeared most evidently that had it not been for the moorstone courses, inlaid with
the frame of the building, and acting therein like the ballast of the ship, it had long ago
been overset, notwithstanding all the branches and iron work contrived to retain it; and
that in reality the violent agitation, rocking, or vibration, which the late building was
subject to, must have been owing to the narrowness of the base on which it rested, and
which the quantity of vibration it had been constantly subject to, had rendered, in regard
to its seat, in some degree rounding, like the rockers of a cradle. It seemed, therefore, a
primary point of improvement to procure, if possible, an enlargement of the base; it also
seemed desirable to adhere strictly to the conical form, where the necessary consequence
would be, that the diameter of every part being proportionably increased by an enlargement
of the base, the action of the sea upon the building would be greater in the same pro-
portion; but as the strength increases in proportion to the increased weight of the materials,
the total absolute strength to resist the action of the sea would be greater by a proportional
enlargement of every part, but would require a greater quantity of materials; on the other
hand, if we could enlarge the base, and at the same time rather diminish than increase the
size of the waist and upper works; as great strength and stiffness would arise from a
larger base, accompanied with a less resistance to the acting power, though consisting of a
less quantity of materials, as if a similar conical figure had been preserved. A stone edifice
having been determined upon, the engineer gave to it the form of the waist or bole of a
large spreading oak; and made a model, by roughly turning a piece of wood, with a small
degree of tapering, and then fitting it to the oblique surface of another block, which re-
sembled that of the Eddystone rock; and found that by arranging the several curves
carefully, they could be firmly united, to form an efficient foundation. The model having
given ample satisfaction, it was ordered that the works should be proceeded with.

Fig. 373.
In the year 1757, all the necessary preparations being made, and the rock cut away for
the reception of the first course, Mr. Smeaton, on the 12th of June, laid the first stone of
the new lighthouse, which was of moorstone or granite, and weighed 24 tons. In the
་་
BB 2
372
BOOK I.
HISTORY OF ENGINEERING.
first course there were altogether 4 stones, in the second 13, in the third 25, in the
fourth 28, in the fifth 26, and in the sixth 26; these six courses brought the platform up
N
W
F

Fig. 374.
FIRST COURSE OF MASONRY
level with the top of the rock, and the laying of these 123 stones occupied 61 days; the
whole were of moorstone, and cemented together with lime and puzzolana.
PE
E

0
D
0
D
Fig. 375.
SECOND COURSE OF MASONRY
CHAP. VIII.
373
BRITAIN.
Each stone was separately. worked on land, marked or numbered, and lines were drawn
across the middle of each, tending to the centre as well as to the concentric circles,
E

N
Fig. 876.
W
THIRD COURSE.
S
to denote their position in the contrary direction; they also had a notch cut in the edges
where they were to unite with those adjoining.
Each stone had cut, from the bottom to the top of the course, two grooves, 3 inches in
N
W
Fig. 377.
FOURTH COURSE.
·
E

n
BB 3
374
BOOK I.
HISTORY OF ENGINEERING.
width, and 1 inch in depth, into which oak wedges, somewhat less than 3 inches in breadth,
1 inch thick at the head, nearly 3 inch at the point, and 6 inches long, were introduced
2

N
Fig. 378.
FIFTH COURSE.
1
S
The mortar used was compounded of blue lias lime and puzzolana, in equal quantities,
being prepared by beating it up in a strong wooden bucket made for the purpose, each

N...
Fig. 379.
E
W
SIXTH COURSE.
--S
mortar beater having his own bucket, which he placed upon any level part of the work,
and with a rammer or wooden pestle first beat the lime alone, using a quarter of a peck
CHAP. VIII.
375
BRITAIN.
at a time, to which, when formed with sea-water into a thin paste, he gradually added the
puzzolana, and at the same time kept continually beating it.
When the mason had fitted the stone to its place, it was hoisted by a light movable
triangle, furnished with a double tackle; then properly bedded, afterwards beat down with
a heavy wooden maul, and levelled with a spirit level.
The carpenter then placed
the oak wedges in the grooves
prepared for them, one upon
its head, and the other with
its point downwards, so that
the two wedges were head
and point together; then, by
means of an iron bar, 21
inches broad, inch thick,
and 2 feet long they were
driven down one wedge upon
the other, very gently at first,
so that the opposite pair of
wedges being equally tight-
ened, would equally resist
each other, and the stone,
therefore, keep its place; as
the wood, when first inserted,
was in a dry state, by its
swelling with the moisture,
it became tighter. To pre-
vent the stones from being
broken by driving these
wedges, a couple of others
were pitched at the top of
each groove, the dormant
wedge, or that with the point
upward, being held in the
hand, while the drift wedge,
or that with its point down-
wards, was driven by the
hammer; the whole that re-
mained above the surface was
then cut off with the saw; a
couple of thin wedges were
also moderately driven at the
butt end of the stone, the
tendency of which was to
force it out of its dovetail;
these were calculated to unite
the mass, and prevent any
violent agitation of the sea
from displacing them.
The oak wedges served
effectually to bind the stones
together in their several
courses; but to prevent
their being lifted up be
fore the mortar became
hard, oak trenails were
used. A couple of holes,
13 inches in diameter, were
bored on shore, through
the external or projecting
end of each stone; after
they were placed, and the
wedges fixed, one of the
tinners, or Cornish men,
with a jumper continued
the hole into the course

Fig. 380.
WW!
חור
EDDYSTONE LIGHTHOUSE.
below, and bored it about 8 or 9 inches in depth; but the lower hole was not so large in
diameter as the one above by inch. The trenails, being nicely planed down to drive freely
BB 4
976
Book I.
HISTORY OF ENGINEERING.
through the upper hole, drove stiffly into the lower; after driving as far as possible, a saw-
cut was made in the end to the depth of a couple of inches, into which a wedge, of inch
18

R-
Fig. 381.
SEVENTH COURSE.
Each trenail was
in thickness at bottom, and double that at the square end, was driven.
then cut off even with the top of the stone, and its upper end wedged cross and cross.
E

N
S
Fig. 342.
W
FOURTEENTH COURSE.
CHAP VIII.
377
BRITAIN.
There were two trenails to each stone; and it was found impossible, by ordinary means, to
pull them asunder, or lift the stones after their introduction.

N
Fig. 383
FIFTEENTH COURSE.
E

N
S
Fig. 384.
W
EIGHTEENTH COURSE.
378
BOOK 1.
HISTORY OF ENGINEERING.
>
K

N
9
N
Fig. 385.
X
Fig. 386.
W
TWENTY-THIRD COURSE.
E

W
TWENTY-FOURTH COURSE,
S
CHAP. VIII.
379
BRITAIN.
A quantity of liquid grout, made of the puzzolana mortar, was then poured into the
joints by means of iron ladles.
CC
E
Smeaton informs us, in his interesting account, of the pains he took to consider how the
blocks of stone could be bonded to the rock and to one another, so that the whole and each
individual piece should form but one mass, and be proof against the violence of the sea;
and he plainly saw that every portion of the work was liable to be acted upon by storms.
Cramping, as generally performed, amounts to no more than a bond upon the upper
surface of a course of stone, without having any direct power to hold it down, in case of its
being lifted upwards by an action greater than its own weight, as might be expected fre-
quently to happen at the Eddystone, whenever the mortar of the ground bed it was set
upon was washed out of the joint, or attacked by the sea, before it had time to harden;
and though upright cramps, to confine the stones down to the course below, might in
some degree answer the end, yet as this must be done to each individual stone, the quantity
of iron, and the great trouble and loss of time that would necessarily attend this method,
would in reality render it im-
practicable; for it appeared
that Mr. Winstanley had found
the fixing 12 great irons and
Mr. Rudyerd 35 attended with
such a consumption of time,
(which arose in great measure
from the difficulty of getting
and keeping the holes dry,
so as to admit of the pouring
in of melted lead,) that any
method which required still
more in putting the work to-
gether upon the rock would N
in consequence inevitably, and
to a very great degree, pro-
crastinate the completion of
the building. It therefore
seemed of the utmost conse-
quence to avoid this, even by
any quantity of time and mo-
derate expence that might be
necessary for its performance
on shore, provided it pre-
vented hindrance of business
upon the rock; because of
time upon the rock there was
likely to be a great scarcity,
but on the shore a very suffi-
cient plenty.

"This made me turn my
thoughts to what could be
done in the way of dovetailing.
In speaking, however, of this
as a term of art, I must ob-
serve that it had been princi-
pally applied to works of car-
pentry; its application in the
Fig. 387.
D
W
TWENTY-NINTH COURSE.
masonry way had been but very slight and sparing; for in regard to the small pieces
of stone that had been let in with a double dovetail across the joint of larger pieces, and
generally to save iron, it was a kind of work even more objectionable than cramping;
for though it would not require melted lead, yet being only a superficial bond, and con-
sisting of far more brittle materials than iron, it was not likely to answer our end at
all. Somewhat more to my purpose, I had occasionally observed in many places in
the streets of London, that in fixing the kerbs of the walking paths, the long pieces
or stretchers were retained between two headers or bond pieces, whose heads, being
cut dovetail-wise, adapted themselves to and confined in the stretchers; which expedient,
though chiefly intended to save iron and lead, nevertheless appeared to me capable of more
firmness than any superficial fastening could be, as the tie was as good at the bottom as at
top, which was the very thing I wanted; and therefore if the tail of the header was made to
have an adequate bond with the interior parts, the work would in itself be perfect. Some-
thing of this kind I also remember to have seen in Belidor's description of the stone floor
of the great sluice at Cherbourgh" (this is shown in fig. 236.), "where the tails of the
880
Book I.
HISTORY OF ENGINEERING.
upright headers are cut into dovetails, for their insertion into the mass of rough masonry
below.
"From these beginnings, I was readily led to think, that if the blocks themselves were,
both inside and out, all formed into large dovetails, they might be managed so as mutually
to lock one another together, being primarily engrafted into the rock; and in the round and
entire courses above the top of the rock they might all proceed from, and be locked to, one
large centre stone.
"It is obvious that this method of dovetailing, while the slope of the rock was making
good by cutting the steps formed by Mr. Rudyerd also into dovetails, it might be said that
the foundation stones of every course were engrafted into, or rather rooted into the rock;
which would not only keep all the stones in one course together, but prevent the courses
themselves, as one stone, from moving or sliding upon each other. But after losing hold of
the rock by getting above it, then, though every stone in the same course would be bonded
in the strongest manner with every other, and might be considered as consisting of a single
stone, which would weigh a
considerable number of tons,
and would be further retained
to the floor below by the ce-
ment, so that, when completed,
the sea would have no action
upon it but edgeways; yet as
a force, if sufficiently great,
might move it, notwithstand-
ing its weight and the small
hold of the sea upon it, and
break the cement, before time
had given it that hardness
which it might be expected N
to acquire afterwards, I had
formed more expedients than
one for fixing the courses to
one another, so as absolutely
to prevent their shifting."
The six lower courses of
stone, already described, were
thus engrafted in dovetail re-
cesses, cut out of the solid rock,
and were therefore perfectly
immovable from any force
acting horizontally against
them; as the work would
not now have this natural ad-
vantage, it was necessary in
the seventh course to adopt
some means which should pro-
duce a similar effect; in the
course number six, at the
centre, a hole was cut, I foot
square, and eight others, 1 foot
square and 6 inches deep, were
disposed at regular distances
round the centre; into these
Fig. 388.
E

W
FORTY-THIRD COUrse.
S
were introduced cubes of marble, which were to act as joggles. A plug of strong hard
marble, from the Plymouth rocks, 1 foot square and 22 inches in length, were set in
mortar in the central cavity, and there fixed by wedges; this plug stood up 9 inches, and
the centre stone of the seventh course, which had a square hole made in it, covered this
plug, and, after being properly grouted, was held firmly together.
After this centre stone was fixed, the four that surrounded it were placed, united by as
many dovetails, projecting from the four sides of the centre stone; these were secured by
dovetailed wedges and grouted as before, and each held down by a couple of trenails. The
whole formed a circular stone 10 feet in diameter, and weighing 7 tons, which was held by
a centre plug and 12 trenails, the circumference of which admitted eight dovetailed recesses
to be made in it, and to receive eight other stones of about 12 cwt. each, and in this
manner did the work proceed until the whole of the solid part was complete. One
plug in the middle, of a foot square, and each joggle of a foot cube, with the trenails, added
to the strength of each course.
On the fourteenth course was set out the winding staircase and entrance doorway.
CHAP. VIII.
881
BRITAIN.
The building was carried up solid as high as there was any reason to suppose it would
be exposed to the heavy stroke of the sea; that is, 35 feet 4 inches above its base, and
27 feet above the top of the rock, or common spring tide high water mark.
At this height it was reduced to 16 feet 8 inches in diameter, the rooms here occupying
12 feet 4 inches, and the walls 26 inches or 13 inches thick.
These were built with single blocks of granite or moorstone, and 16 were used in
each course, cramped together with iron, and joggled at each joint. The joggles were
made of sawn marble, 8 inches long, 4 inches broad, and 3 thick; each end of each block,
therefore, occupies 4 inches in length, 4 inches in breadth, and 1½ inch in the height of
each joggle. To prevent any water or moisture passing through the upright joints, a
groove was made in the end of each stone, into which an upright piece of stone, 6 inches
broad and 2 inches thick, was slid into the cavity or groove prepared for it; these were
mostly of Purbeck, selected for their firmness, and were run in with mortar; they also
served to bond the work together. When in their places, the cramps were let in, which
were flat bars of iron, 13 inches in length, 2 inches broad, and § inch thick, and were
turned down at each end about 3 inches in length, forming a cylinder 11 inch in diameter.
E

N.
-
*
*
*
*
*
*
*
*
A
-
----
-----------------
mar én do a de un me a 4 t - -
--
-S
Fig. 389.
W
FORTY-SIXTH COURSE.
The cramps being previously fitted to the stones, all that was necessary was to put each
into a kettle of lead made red hot, and let it remain till it had acquired the same
state. About a spoonful of oil was then poured into the cramp holes, and the cramp
put into its place; the ebullition of the oil caused by the heat of the iron gave an oily
surface to the whole cramp, as well as to the cavity of the stone; then the hot lead
being poured in, the unctuous matter caused the metal to run into and occupy the most
minute cavity, and thus defend the cramp from any action that might be produced from
the salts of the sea.
At the twenty-eighth course was introduced the vaulted floor which formed the ceiling
to the upper store-room; here was the first circular iron chain, which was lodged in
a groove cut round the middle of the upper surface of this course.
The ordinary way of fixing the several courses by joggles and joint stones, and also the
bonding them together by cramps, has been already described; by a reference to the section,
it will be seen that each floor rests upon two courses, and that the circumference of the
floors is not supported upon the sloping abutments of an arch, in lines tending towards the
centre of the sphere, of which the underside of the floor was a portion, but upon a triple
ledge carried round the two supporting courses: if each floor had been composed of a
382.
Book 1.
HISTORY OF ENGINEERING.
single stone, lying upon the horizontal bearings furnished by the ledges, it would, while it
remained entire, have no lateral pressure or tendency to thrust out the sides of the en-
compassing walls, and the several pieces of which the floors were composed might have the
property of a whole stone; the

centre stone was made large
enough to admit of a man hole,
with dovetails on its four sides,
like those of the entire, solid, by
means of which the others were
connected with it, consequently
the whole, like a single stone,
rested upon the ledge, without
any tendency to spread the walls,
which was further provided
against by an iron hoop or cir-
cular chain. Sir Christopher
Wren, in the construction of the
cupola of St. Paul's, had already
adopted with success the same
construction, and to this Smeaton
refers for his model.
Each of the four floors had
two endless chains, the bars of
which are composed of links 11
inch square, and the grooves that
received them were 4 inches in
depth and width, and when
placed each chain was run with
11 cwt. of lead.
The height of the six
Ft. In.
foundation courses to
the top of the rock
8 49
The height of the eight
-
12 01
The height of the ten
courses to the entry
door
courses of the well hole
to the store-room floor 15 21
The height of the four
rooms to the balcony
floor
Height of the main co-
lumn, containing forty-
six courses
-
34 4/1/
-
70 0
The lantern is formed mostly
of copper; there are 16 frames
with 9 panes each, and the bal-
cony is covered with thick plates
of lead; there were 16 sheets
put together with strong ribbed
joints; the whole of this work
was very securely braced, and the
copper funnel adapted to let out
the smoke from the candles.
metal conductor, to guard against
the effects of lightning, was added.
A
Fig. 390.
LANTERN OF EDDYSTONE LIGHTHOUSE.
The lower diameter, immediately above the rock, is 25 feet, and the upper 15 feet, in-
cluding the thickness of the walls; the height of the lantern is about 24 feet, and the
diameter 9.
The building was completed in October, 1759; and upon the rock the workmen were
employed 2674 hours; the number of pieces of stones used was 1493, independent of 75
large cubic joggles and centre plug-stones, 162 cubic joggles of 6 inches, used in the well-
hole courses, 399 flat joggles in the courses of the rooms and lantern, 399 joint stones in
ditto, 1800 oak trenails. 1 inch in diameter, used in the solid, 4570 pair of oak wedges for*
CHAP. VIII.
983
BRITAIN.
steadying the stones of the solid, 8 large circular chains, two used at each vaulted floor, 221
strong iron cramps in the walls of the rooms and lantern, and 5 others in the foundation.

The whole time occupied
between the first stroke upon
the rock and leaving the light-
house complete was 3 years, 9
weeks, and 3 days.
The stone employed was
partly obtained from the neigh-
bouring coasts, and from the Isle
of Portland.
For the lower part of the
building Smeaton contracted
for 240 tons of moorstone or
granite, which was considered
to be preferable in point of
duration, the price of which
was 25s. per ton, roughed out
according to the moulds, and
4d. per foot superficial for
working the beds; this was the
price delivered into the yard,
and did not comprise the ex-
pense of carriage to the rock;
the rest of the stone was brought
from the Isle of Portland.
The lantern, as originally
contrived by Smeaton, contained
a chandelier 6 feet 4 inches in
diameter, made for 16 candles ;
and a smaller, 3 feet 4 inches
in diameter, for 8; they were
so disposed as to affect each
other as little as possible by
their heat.
In the year 1807 the Trinity
House had the building tho-
roughly examined and some
trifling repairs performed, re-
moved the chandeliers and
introduced in their place a
reflector frame, fitted up with
Argand burners and parabolic
reflectors, formed of copper,
covered with highly polished
silver.
The Granite used for this work
was obtained from the quarry,
by splitting it with a number
of wedges, applied to holes or
notches, cut or pooled into the
surface, made at a distance of
about 4 inches apart, or ac-
cording to the size required
or the strength of the stone.
These pool-holes were sunk with
the point of a pick, in the way
hard stones are usually quarried.
The harder the granite, the
more exactly it may be made to
split to the size required; in
many parts of Devonshire and
Cornwall, the moorstone or
granite is split into posts, 12
ΟΙ 14 feet in length, and a
scantling of 8 or 9 inches square,
and the sides perfectly even.
Fig. 391.
SECTION OF EDDYSTONE LIGHTHOUSE,
884
Book I.
HISTORY OF ENGINEERING.
At the Beare quarries, on the sea coast, near the south-east corner of Devonshire,
Smeaton found the bed of freestone was of considerable thickness, and with so great a cover
of earth upon it, that it was
worked in underground ca-
vities, the superincumbent
earth being supported by
pillars, formed of the de-
tached parts of the stratum
left standing. This calca-
reous stone resembled the
Bath, but its bed was so
thick, that blocks of any
size might be drawn from it.
It is very compact, free from
fissures, and yet so soft that
it can be cut with the com-
mon saw; after exposure it
becomes hard, and in the
buildings at Beare, where it
is used, is covered with a
mossy coating, and remains
perfectly sound and free
from decay.

:
Sand and limestone have
each their peculiar lichen,
and their respective qualities
may be known by a careful
examination of the plants
produced upon their sur-
faces granite and gneiss
rocks are often found co-
vered with Lecanora gelida,
Lecidea petræa, Silacea, La-
picida, Verrucaria glaucina,
&c. The rock crystal is
known by its being the ha-
bitat of Lecanora fusco-atra
var. dendricata. The rocks
of porphyry exhibit on their
surface the Lecidea pustu-
lata and confluens, Parmelia
ciliaris and furfuracea, and
the Gyrophora deusta. The
mica slate rocks are found
covered with Cornicularia
tristis and exilis, Gyrophora
polyphylla, and of the va-
riety frigida of Lecanora
tartarea. The clay slate
abounds with such lichens
as Lecidea cupularis, Leca-
nora decipiens, &c. Sand-
stone near the sea is fre-
quently found covered with
the Ramalina scopulorum,
Lecanora parella and atra.
Limestone is furnished with
the Lecidea immersa, Col-
lema nigra, Verrucaria mu-
ralis, Urecolaria calcarea,
and Thelotrema exanthe-
matica. And any one ac-
quainted with the charac-
teristics of the several lichens
may at once distinguish the
variety of stone used in a
building, where, in the
Fig. 392.
ELEVATION OF EDDYSTONE LIGHTHOUSE.
course of time, they generally are covered with specimens of one kind or the other.
CHAP. VIII.
385
BRITAIN.
The stone which Smeaton selected from the Isle of Portland was obtained where it lay
in beds nearly parallel with the surface of the land, and is covered with a small quantity
of earth.
There are several beds, varying in thickness from 2 to 4 feet and upwards: these are
covered with a stratum called a cap, which is formed of shells of various kinds; some of
them, as the Cornua Ammonis, are upwards of two feet in diameter; this capping is very
hard, and is usually detached by blasting with gunpowder.
After this cap has been removed, the quarry-men proceed to cross-cut the large flats,
which are laid bare with wedges, and split off the Portland, not in a very even manner,
but in masses, the quarry-men, with a tool called a kevel, which is at one end a hammer
and at the other an axe, whose edge is short and narrow, like a pick, reduce it to something
like a cube, or regular shape. The face of the kevel is not at the hammer end quite flat,
but a little hollowed out, which gives rather a sharp edge to two of its opposite sides,
which are parallel to the handle; and by this means it is made to bite more keenly upon
the stone, and to bring off a spawl or large shivers. The edge at the pick end is about
half an inch in breadth.
Dartmouth Harbour is not only beautifully situated, but very safe for vessels, and
capacious enough to hold 500 sail. It is defended by a fort, situated where the ancient
castle stood.
The Dart is navigable to Totness, where are numerous manufactories.
Exmouth, at the mouth of the Exe, is situated near the shore, where the cliffs open as it
were to receive it. It is sheltered from the north-east and south-east winds by lofty hills;
this was the birth-place of Sir Walter Raleigh, who was the author of the History of the
World, as well as its greatest navigator.
Sidmouth was formerly a good sea-port, where the small river Sid flows toward the ocean
and loses itself among the pebbles on the beach, in consequence of the alluvium with which
the harbour is almost choked up.
Axmouth, on the river of that name, is another small port, monthly resorted to by fishermen.
Lyme Regis, situated on the river Lyme, near the west bay, in a cavity between two
rocky hills, has a spacious quay, and round the harbour are several forts for its defence;
the chief is called the Cobb, which is very ancient, and composed of fragments of rock, in
huge masses piled together; this fabric is of the greatest importance on this coast, as there
is between Start Point and the Portland Road no other shelter for shipping. The Cobb,
distant about mile from the town, is in the shape of a half moon, with a bar in the
middle of the concave part. The stones are not cut or bedded in cement, and the surge
plays in and out through the interstices. When a reparation is requisite, the new stone
obtained on the coast, of as large a size as possible, is floated by means of casks chained
together, with a man mounted on one to steer them. Such is the description given by
Lord Keeper Guildford in his time, and reported in North's life of that nobleman.
This is a very early example of a breakwater formed with pierre perdu.
Weymouth is situated within a fine bay, admirably protected by lofty hills on all sides.
Leland observes, "that the tounlet of Waymouth, lyeth strait agayn Milton (Melcombe)
on the other side of the haven, and at this place the haven is but a small brede; and the
trajectus is by a bote, or a rope bent over the haven, so that in the ferry bote they use no
oars."
He mentions also, that there is "a trajectus into Portland, by a long causey of
pebble and sand.
Poole, on the north side of the bay, stands on a peninsula, connected by a narrow isthmus
with the main land, which is & mile long, and mile in breadth. This is surrounded by a
spacious quay.
At the east end of the bay, about 3 miles north-west of Studland, is the Isle of Brownsea,
1½ in length, and 2 in breadth.
94
Christchurch Harbour, Hampshire, is situated at the bottom of a deep bay, lying between
the Isles of Wight and Purbeck, and at the mouths of the Avon and Stour. These rivers
form in their passage to the sea an inland basin, which is defended from all winds; in
former times the mouth of this harbour was much more extensive, as the heads of land
which bounded it, being formed of loose sand and iron-stone, have been, to a very con-
siderable extent, washed away; much of this sand now forms a range of hommacks or sand
hills, extending from Christchurch Head north-eastward, to the south point that now con-
stitutes the harbour's mouth; here a bank has been thrown up, which separates the basin
of Christchurch from the sea; the sands have thus driven the mouth of the river to the
north-east.
The two rivers, which drain a considerable track of country in time of floods, pour down
a quantity of water and keep the channel open, but in consequence of the small rise of the
tides, which is not more than from 5 to 7 feet spring tides, and from 4 to 6 at neaps, it is
not very practicable to obtain a very great depth of water in the harbour, and the increase
of the sands, their constant motion, and the flatness of the bottom of the bay, also contribute
to prevent any great improvement being carried out.
C c
386
BOOK I.
HISTORY OF ENGINEERING.
Christchurch quay lies 2 miles up the river from the harbour's mouth, about a furlong
from which, in the reign of Charles II., was carried out a pier or jetty in a straight line,

Fig. 393.
formed of round lumps of iron-stone, its direction being south-east, and its extent, beyona
high water mark, 770 feet; its top gradually declines from the shore towards the sea, the
whole being uncovered at low water, but at high water the greatest part is covered.
This pier was intended to secure a better passage to the harbour, and was made by cutting
through the hommacks, to let the water out, and to direct its course to the south-west side
of the pier.
Smeaton, in the year 1764, reported upon the condition of the harbour, and designed and
estimated for an additional pier.
Southampton has of late years risen into considerable importance, from its regular com-
munications with the coasts of France, Spain, and Portugal; it ranks among those towns
which have a Roman origin, and was of great extent when the Saxon kings resided at
Winchester; the walls and gates which remain are probably some of the constructions of
that time. In Domesday Book, Southampton or Huntune is styled a burgh.
The Test, Anton, and Ilchin, here unite and form the Southwater, in which vessels of
1500 tons may sail.·
Spacious and commodious docks have been formed since the railway has been completed,
which opens a direct communication with the metropolis.
Portsmouth and Gosport had their origin, it is supposed, by the retiring of the sea;
according to Camden, Portchester on this account was deserted for the Isle of Portsea;
Edward IV. improved its fortifications, and increased the size of its port, and Leland
notices having seen "in a great dok for shippes, in which lyeth part of the rybbes of the
Henry Grace de Dieu, one of the biggest shippes that hath been made in hominum memoria.”
The dock-yard and gun-wharf on the side of Portsea are very extensive, and contain all
that a navy can require; storehouses, residences for the officers, anchor manufactories, docks,
basins, jetty heads, rigging houses, &c. &c., where first-rate ships of war are constructed and
refitted with an extraordinary expedition. In time of war upwards of 5000 artificers were
employed here, and the activity of the whole establishment had nowhere its parallel.
Barracks, magazines, forts, mills, victualling yards, and other extensive establishments,
surround this important depot.
Government has been furnished with a most complete survey of this harbour and its
various lakes by naval officers, and it appears that the soundings entirely over are nearly
the same as they were sixty years ago. The bar, off the south sea landmarks, is also un-
changed in its dimensions, and is composed of flint, chalk, and gravel; this concrete could
be easily removed, and without very great expense.
Little Hampton is formed by the channel of the Arun, which flows into the sea between
two piers, composed of piles with an extension of Dicker work.
The depth of water in the entrance between the piers is 2 or 3 feet below the level of
high water, but a bar extends outside the Dicker work across the mouth, which rises about
2 feet above the general surface, and is left dry at low water.
The lift of average spring tides is about 16 feet, and of neaps 11 feet.
The larger vessels which enter usually remain near the river's mouth, but a vessel of
13 feet draught, when she has passed the bar, can proceed to Arundel Bridge, a distance of
6 miles, the bottom continuing of an uniform level throughout that extent.
The tide flows 25 miles up the river, but the backwater is of little use to cleanse the
mouth, from the narrowness of the channel and sluggishness of the stream.
Shoreham is at the mouth of the Adur, which formerly entered the sea nearly at right
CHAP. VIII.
387
BRITAIN.
angles with the line of coast, but it has, by the accumulation of the shingle, been diverted
very considerably. This shingle now forms an embankment nearly 300 yards in width, and
an artificial channel has been cut through it, about a mile from the town, the opening is
preserved by wooden piers 218 feet apart, and which run in a south-west direction across
the shingle into the sea. Within this entrance a third pier has been built out from the
shore nearly across the harbour, for the purpose of diverting the waters on the ebb, from
the eastern and western sides of the inlet, directly to the mouth.
The great body of water which thus ebbs and flows through the entrance serves to keep
the channel open, and, though the width is so considerable, the stream runs between the
pier heads at the rate of 5 or 6 miles an hour. The harbour mouth is nevertheless subject
to a bar, which rises occasionally above the low water level, and shifts its position from 60
to 160 feet from the pier heads.
The lift of spring tides is about 15 feet, and neaps about 9 feet; the depth of water near
the bar at high water is from 14 to 17 feet, according to the tides.
Newhaven is formed in the channel of the Ouse at its entrance into the sea, by wooden
piers carried out in a southerly direction across the beach. The river is navigable as far
as Lewes, and open to the flow and ebb of the tide 4 miles higher, or 12 miles altogether,
and affords a powerful backwater for scouring the entrance.
The average rise of spring tide at the harbour's mouth is from 19 to 20 feet, and of
neaps about 14 to 15 feet. The bar, however, is left dry at low water spring tides; but
within the pier there is about 2 feet water at such time, and this depth continues uniform
for a mile up the channel. The distance between the pier heads is 106 feet: on the western
side of the harbour, the wooden pier, which extends about 250 yards, has been continued
onwards by a stone embankment nearly mile in a straight line; and the bar, which
formerly extended from the western side nearly across the mouth of the harbour, has been
considerably reduced since the completion of this work; the eastern pier has been extended,
and other improvements have been made by straightening and deepening the river above
the town.
During flood tide and fine weather, the harbour is easy of access from the indraught and
eddy tide which set towards the mouth; but from the rapidity of the stream during the
ebb, it is not considered safe for a sailing vessel to enter, and the flag at the pier head is
consequently lowered at high water.
The piers only extend to the line of low water on the beach, and this harbour, like others
on the south coast, is greatly affected by the accumulation of beach and shingle, which cannot
be effectually scoured or washed away by any means yet attempted. The latitude of New-
haven is 50° 48′ north, and its longitude 0° 5' east of Greenwich; it lies directly in the course
of vessels sailing up or down the channel. The original name of Newhaven was Meeching.
Cuzmere Haven, on the western side of Beachy Head, is an artificial harbour; the shingle
beach crosses the entrance, and rises several feet above low water, and the interior of the
haven is left dry at three quarters ebb.
Hastings has a small tidal harbour for the use of coasting vessels; here the coast runs,
with little deviation, in a straight line nearly east by south, and is entirely exposed to the
prevailing southerly and westerly winds. There is no natural breakwater, nor the facility
of forming one; the shore is composed of shingle, and not above 4 fathoms of water at the
distance of mile from the beach, which would give but a limited area of 12 feet at
low water, in proportion to the size of the harbour, were piers to be carried out to such
an extent.
In Jeakes's History of the Cinque Ports, we find that before the Conquest three only
were incorporated, viz. Dover, Sandwich, and Romney; the Conqueror is supposed to have
added Hastings and Hythe: the arms of the cinque ports are, per pale gules and azure,
three demi lions, or, impaling azure, three semi ships argent. The chief prerogatives of
these ports, in addition to their naval jurisdiction, are some ceremonies and honours at the
coronation; the Lord Warden's power extends from Redcliff, near Seaford, to Shoe Beacon,
near the Isle of Sheppey, and he has free warren over a considerable district in Kent.
Hastings formerly had a pier, which was destroyed by a storm in the time of Elizabeth,
who granted a contribution towards making a new harbour; the remains of this pier may
be traced at low water, and it was called previous to its demolition the Strade, because
vessels were wound up and let down the acclivity by a strong capstan, worked by three or
four horses.
Boat-building is carried on to some extent, from the facility of obtaining fine oak timber,
and the pleasure-boats constructed are said to be superior to all others.
Rye Harbour, one of the ancient cinque ports, stands on the edge of Sussex towards Kent,
and is supposed by some to have been the Portus Novus of Ptolemy. The town was walled
about in the reign of Edward III., and is now under the government of a mayor and
jurats. As long as the tide was suffered to flow up the Rother, there was a good tide
harbour; but a sluice placed some years ago about 6 miles above the town, and another at
3 miles, stopped the mud and sand brought in by the spring tides from running out, and
C c 2
388
BOOK I.
HISTORY OF ENGİNEERING.
the whole became silted up.
Before this, the harbour was sufficiently capacious and deep
to shelter large vessels at low water; the sea being suffered at every tide to overflow what
are now extensive marshes in the neighbourhood, by which means a vast body of water was
collected, which, draining off, opened and maintained a spacious channel. In all similar
situations, where the land has been walled in and converted to the purposes of agriculture,
the tidal waters, from being confined and lessened in quantity, have lost their power of
cleansing, and wherever there is not a sufficient quantity of land or flood waters to supply
the purpose of scouring, the tendency must be to silt up. Besides this, a quantity of
shingle or beach, derived probably from the constant wearing away of the chalk cliffs on
this coast, was thrown up to the westward, which, being driven on the shore, was then
carried by the currents in a direction nearly west-south-west and east-north-east; the wind
at any point between south and south-west, now causes the sea to strike the shore ob-
liquely, and to heap up greater quantities of beach, and drive it along the shore in the
direction of east-north-east to the bottom of the bay or mouth of the harbour.
Thus, by the silting within, and the throwing up the shingle at the mouth, a surface of
several hundred acres of land is formed, and the harbour has lost its value.
As early
as the year 1698, a report was drawn up, which states the harbour to be entirely lost, and
in no condition to be preserved for any purpose of navigation. In the year 1719 the
Admiralty Board, under whose direction the former report was made, sent down three
competent gentlemen to make another survey, after which a new harbour was projected,
which was partly carried into effect by Captain Perry, who had previously executed many
considerable engineering works in Russia.
The mouth of the new harbour was put 2 miles westward of the old one, where the
coast for several miles extends itself in a straight line, its entrance is nearly at right angles
with the coast, and points south-south-east, or rather south-east by south.
In the year 1763, Mr. John Smeaton reported upon its then condition, and found that
there was no increase of beach in the harbour; and at the foot of the beach, which is low
water mark at neap tides, there was a fine firm sand, regularly inclined towards low water,
which at spring tides was about 257 yards from the foot of the beach; and from thence
inclined by very regular and gradual soundings, so as to make 20 feet at low water spring
tides, and about 23 feet at low water neap tides, at the distance of 1 mile right out of the
harbour's mouth; these soundings gradually increasing further out, where the bay formed
excellent anchorage ground.
The tides here he found to have the greatest rise of any along this coast, for the common
spring rose above low water mark 23 feet, and neap tides about 14 feet, viz. 17 feet above
low water mark spring tides.
The direction of the tides was nearly along shore, and very gentle in consequence of
their distance from the main channel tide, which was of great importance to the harbour.
The design of the new harbour was that of an extended canal; it had two stone piers
projecting into the sea, as far as the foot of the beach, and the distance between them, which
formed the mouth, was 120 feet; but a quantity of beach having collected at the back of
the west head, it was prolonged by constructions in timber and stone, until it overlaid the
east pier 210 feet.
From the pier head the harbour enlarged to a width of 200 feet, and at the distance of
730 yards within the pier is a large stone sluice. Between the pier head and the sluice,
the harbour is formed into the arch of a circle of about 45°; so that no part of the mouth
can be seen from the sluice, nor any part of the sluice from the mouth of the harbour.
The sluice was built of Portland stone, and consisted of two openings, one of 40 feet, shut
by folding gates pointing to landward, the other had 30 feet clear water-way, shut by 5
draw-gates of 6 feet wide each.
By this contrivance the tide received into the canal above the sluice was shut in, and
kept the vessels afloat during the whole time of tide, or was let off at low water by means
of the draw-gates, for the purpose of scouring out the harbour. The length of the canal
above the sluice is about mile, and at the surface had a mean width of 150 feet, at the
14
bottom 70 feet, which was the level of the sill of the sluice.
The canal, exclusive of the harbour, would contain about 200 sail of vessels, but not a
sufficiency of water to answer all the purposes of keeping the outer harbour clean; it was
constantly receiving deposits of mud from the Rother and its branches, which brought the
waters from upwards of 100,000 acres of land.
When Smeaton examined the harbour, he found that the bottom of the channel, between
the pier-heads, was about 6 feet above low water mark at spring tides, and about 3 feet
above the sill of the sluice, and that in the course of a few years, as the scouring force was
inefficient, the whole would be filled up, if some effectual means were not adopted to prevent
it. He therefore advised that the Winchelsea channel should be widened and others made.
the Rother dammed across, and new sluices built upon it, and that the tidal waters shoula
be suffered to pass the great sluice into all these proposed new channels, and which
were calculated to contain five times as much water as the original canal above the sluice.
CHAP. VIII.
389
BRITAIN.
In order that the drainage of the lands might in no way be injured, the tides were never
to be shut in by the great sluice, so as to pen upon the aprons of any of the sluices for
drainage, at a time when the levels were under water.
Smeaton's instructions were in part followed, and considerable sums of money were ex-
pended in endeavouring to arrest the movement of the beach from the west towards the
east; the groins raised to stop it filled as soon as they were carried out, and the surplus
beach was forced into the harbour's mouth.
The stone sluice falling to decay some years after was carried away by a river flood,
when the inhabitants of Rye opposed its restoration; the absence of the impediment having
given in one year 3 feet additional water in the harbour channel at the town quay.
The piers, wharf, and sluices, were in a few years completely silted up, when the masonry
was dug out, and the stones sold. This harbour has been entirely ruined in consequence
of excluding the tide, and depriving it of the benefits of its natural backwater; in shutting
out the sea and preventing its flooding the lands which were originally covered, much
valuable pasture has been gained and improved, but Rye, as a port of importance, has
ceased to exist.
A wooden pier on piles has been carried out on the eastern side, and embankments have
been thrown up on the western, leaving an entrance between of 160 feet in width.
The average rise of spring tides is about 17 feet, and during neap tides from 9 to 12 feet
at the pier-heads, whilst the lift in the bay is 22 feet; at low water the harbour is left dry.
The depth of the channel up the river gradually decreases to the town, where there is
14 feet water at the top of spring tides, but during neaps seldom more than 9 feet.
The approach from the bay to the entrance of the harbour is very intricate and difficult,
from the accumulation of sand and the winding course of the channel; the shingle, which
extends on both sides of the harbour's mouth, accumulates with winds either from the
westward or eastward of south, and forms banks, which, with the sand, block out the sea,
and render the channel uncertain.
Folkestone. This artificial harbour, formed by rubble stone piers, encloses an area of
14 acres; the western arm extends in a south-south-west direction, 140 yards across the
beach, and is united with the main pier, which is carried in a straight line east and by south
about 317 yards; a projecting pier has since been run out from the shore on the eastern
side, towards the south-west, 236 yards, leaving an entrance of 123 feet in width, open to
the east and by south.
Near the eastern extremity of the main pier, a groin has been constructed, which extends
at right angles 130 feet seaward, intended to stop the accumulation of shingle, but in spite
of this caution, it forms a bar at the harbour's mouth.
The rise of the spring tides is about 18 or 20 feet, and neaps 12 or 14 feet, but the
harbour is entirely dry at low water, and the greater part of the interior is blocked up by a
bank of shingle, which rises several feet above the level of high water, leaving only a narrow
channel alongside the main pier.
At the north-western side, a small stream is pent up, for scouring the harbour at low
water, which, with the assistance of manual labour, keeps the watercourse open, so as to
allow vessels of 10 or 12 feet draught to come alongside the pier at high water.
Folkestone was the Lapis Populi of the Romans, the Folcestane of the Saxons, and the
Fulchestan of Domesday Book; in the time of Leland it was "mervelusly sore wasted with
the violence of the se," since whose time greater ravages have been committed on the
whole extent of the coast. This town ranks among the Cinque Ports, and formerly was a
place of considerable importance.
Dover Harbour, or Portum Dubris, is of great antiquity, deriving its name probably from
the British word Dwfyrrha, which signifies a steep and hilly place; this by the Saxons was
changed into Dorfa and Dofris, which in Domesday Book is made Dovere. The Romans
had a town on the south side of the river which flows into this harbour, and the Watling
Street took its departure from it, where Biggin Gate formerly stood. The straits of Dover
have always been the medium of intercourse between this country and the continent, and
no port in England is of more importance; it is worthy of remark, that before the pier
was carried out there were no banks or shelves of beach to be seen, but all was clean sea
between Archcliff Tower and Castle Cliff.
In ancient times the sea flowed over the greater part of the valley in which the town is
now situated, and the harbour was considerably more inland, towards the north-east, than at
present. Little is recorded of it until the time of Henry VII., when a round tower was
built on the south-west side, to which vessels were moored to rings let into it, and as they
rested secure here, it was called the Little Paradise. In the following reign the pier was
commenced under the direction of Sir John Thompson, who held the living of St. James in
the town of Dover; it was carried out on the south-west side of the bay, directly eastward
into the sea, for a distance of 131 rods. It was formed of two rows of main piles, 26 feet
in length, shod with iron, and driven into the main chalk; these were fastened together by
fc 3
390
Book I.
HISTORY OF ENGINEERING.
iron bolts and ties. The whole of the space between was filled in with large stones, some
weighing 20 tons, which were freighted on rafts, supported by empty casks, from the
neighbourhood of Folkestone; at this time more than 80,000l. were expended. Soon after
the formation of this pier, a vast bar or shelf was formed across the harbour, by an immense

口
​PENT.
BASIN.
ALE TRAD
Goop!
дая
HARBOUR
DILP
FOW-WATERS THE
CASTLE
Fig. 394.
DOVER HARBOUR.
quantity of beach being thrown up, which totally impeded the passage, there being only a
small outlet left for the current of the water of the river. Every exertion was made to
improve the entrance into this port, and it appears from a survey made about 1652, that it
had 22 feet water at spring tides. Since that time various acts of parliament have been
passed, and enormous sums of money expended ; jetties have been erected towards the east,
to prevent encroachments of the sea, and though the south-west winds still throw
up large
quantities of beach at the mouth of the harbour, they are partly dissipated by sluicing, the
depth of water at spring tides varying from 18 to 20 feet, and at neaps about 14 feet.
•
This harbour has undergone many changes, the mouth at present being in a very different
position to what it was formerly, which seems to have been occasioned by the constant
motion of the beach or shingle, which is driven coastwise from west to east: the British
Channel opens towards the west, and contracts eastward, so that the seas are much more
violent and heavy from the south-western than from the south-eastern quarter. The violent
storms, however, at south-east move the shingle westward, though the general prevalence
is the other way, from west to east.
This shingle or beach is composed of flints produced by the destruction of the chalk
cliffs, which when undermined are precipitated in large quantities into the sea; the chalk
is dissolved, and the flints, rounded by attrition, form a constant succession of beach, an
immense quantity of which is in continual motion along the coast, from west to east, part
of which lodges and fills up every recess where it can be deposited and lie quiet.
This beach was the cause of the destruction of the old harbour, and it seems that the
mouth has been shut up more than once, and has remained so for years; the mouth of the
present harbour is nothing more than a cut through the beach to allow the land waters,
pent up on the inside of the harbour, to have a passage, which in time was improved
and defended by two piers composed of wooden piles, filled in with rough and heavy stones;
after passing these, vessels arrive in a capacious harbour, defended from all winds, but
having an open communication with the sea, the water flows and ebbs, and at low water
spring tides the harbour is dry; it is divided by a dam or cross wall, in which, when
Smeaton made his survey in 1769, was an opening 38 feet wide at top, and about 36 feet
at bottom; in this was placed a large pair of gates pointing to landward, through which
vessels at high water might pass from the outer to the inner harbour or basin, and be kept
afloat.
Besides these great gates, there were two other openings in the cross wall, 12 feet wide,
furnished with a pair of draw-gates.
The interior harbour was again divided by a second cross-wall with an opening of
·
CHAP. VIII.
391
BRITAIN.
20 feet for the passage of smaller vessels, which was also furnished with a pair of gates
pointing to Landward; this cross-wall had three draw-gates, through which the water
could pass for the purpose of scouring out the basin.
This upper reservoir is called the Pent, and here the fresh water river which springs
from the chalk hills north of Dover empties itself, and makes its way through both sets of
gates through all the three harbours, and lastly through the pier heads into the sea.
Smeaton observed that no arrangement could be more judicious, and that it corresponded
with what had been done so effectually at Cherbourg, where immense sums of money had
been expended, which was in a most perfect state before it was destroyed by the English.
When there are hard gales of wind and seas from the south-western quarter, a quantity
of beach is brought round the western head, and lodges itself between the heads; the basin
and pent are then filled, partly by taking in the sea water, and partly by fresh water afforded
by the river, and there retained until low water.
The draw-gates of the sluices in the cross-wall are then opened with all expedition, and
the body of water contained in the basin or pent, by making its way through the pier-
heads, cuts down and removes the bar of the beach, which at the time of spring. tides is
done with great effect, and at two tides the mouth is effectually cleared.
When there are hard gales from the south-western quarter, and at the same time short
or low neap tides, such a quantity of beach is accumulated, that it is with difficulty an
entry can be made into the harbour.
The natural direction of the entry is east-south-east by the true meridian, and by the
magnetic meridian, when Smeaton took his observations, it was south-east.
The western head was carried out in the natural direction of the harbour's entry, for
about 30 feet in a line at or about south-south-east, when it suddenly turned to south-
south-west, in which direction, after being carried 60 or 70 feet, it terminated by a salient
angle, pointing to the same quarter. The line of direction of this flank of the pier being
continued in an opposite direction, cut within the eastern pier-head about 60 feet, so that
all the winds betwixt south-south-west and east-south-east occasioned the sea to strike
obliquely, and, acting in the manner of a tunnel, bring the seas, when the wind is south or
south-south-west, and the beach into the harbour's mouth; the south-eastern seas are so
short, that they do not much affect it, but by the pier turning so much to the west, it
greatly facilitates the beach, after it has passed round this salient point, to get along its
flank, whose line of direction being overlapped by the eastern head is thereby caught and
retained when the wind is more to the west than the south-south-west direction of this
flank.
To lessen as much as possible the quantity of beach from getting round and lodging
between the pier-heads, Smeaton recommended that the first mentioned line of head should
be prolonged in its direction, south-south-east, until it was advanced sufficiently far to come
into a south-south-west direction with the extremity of the east head, which would require
an addition of about 90 feet. This additional work would form a sort of triangle, the base
of which would be the south-west flank, whose projection forwards towards the south-east,
in a line perpendicular to the base, would be but little above 60 feet further out.
By the elongation of these piers, it was not thought that the beach would be effectually
prevented from entering the harbour's mouth, but that it would be lessened in quantity, and
more readily removed.
The outer harbour at present contains 7 acres, the inner basin 6 acres, and the pent
11 acres; a wet dock of 1 acres opens into the western side of the outer harbour, which
again communicates with a graving-dock.
The entrance between the pier-heads, now formed of stone and brick, faced with timber
piles, is 110 feet in width, and opens to the south-south-east. The rise of average spring
tides is from 18 to 19 feet, and of neaps from 12 to 13 feet; but the depth of high water
in the harbour at spring tides is only 17 or 18 feet, in the basin from 16 to 17 feet, and
about 3 feet less during neaps. The harbour therefore is left dry at low water.
Vessels on entering, when the south-westerly gales prevail, find great difficulty, as there
is then a heavy sea at the harbour's mouth, from the bar of shingle which is thrown up, and
which renders it inaccessible for several weeks together. In addition to three sluices or
culverts connected with the inner basin by means of a pipe, there is in the western pier a
brick reservoir, communicating by means of a tunnel 30 feet in width, and 16 high, with
the inner basin and pent. From this reservoir five new sluices, 7 feet in diameter, lead to
the extremity of the pier-head, and from the powerful volume of water thus discharged,
and the impetus acquired by the proximity of the reservoir, it has been found sufficient,
with the assistance of the sluices in the cross-wall between the basin and the outer
harbour, to remove the shingle from the pier-head, and keep the channel clear to a level
below the bottom of the harbour; but this shingle again returns or is thrown up with
particular winds.
The tide flows from the south-west, at the rate of four miles per hour.
C C 4
392
BOOK I.
HISTORY OF ENGINEERING.
Sandwich Haven was a flourishing sea-port at the time the Isle of Thanet was surrounded
with navigable water. Great changes have occurred by the silting up of the channels,
which have been caused by the deposit of mud from the sea water, which is suspended
in the water as long as it is agitated and kept in motion, but immediately it becomes at
rest in an arm of the sea, or within shore, it subsides and is deposited.
Wherever the quantity and agitation of the water is too little, or the mud too great to be
kept in motion, then its natural tendency is to rest. Every creek, inlet, or bay," says
Smeaton, "that has not a sufficiency of fresh water to keep it open, by being discharged
through it, has a tendency to become land. While such a creek or bay remains deep,
a quantity of tide water flowing in and out twice a day, tends to keep the mud in
agitation and from settling; but as the tide of ebb is naturally weaker than the flood,
the ebb will not carry out all that the flood has brought in; and when the deposition
is so far advanced as to contract the breadth of the water, and render it to a certain
degree shallow, the quantity of water flowing in and out being lessened, its power is
weakened."
the
The natural means whereby an inlet is kept open is the discharge of a freshwater river
through it, which opposing the influx of the tide, and adding to the force of its ebb, will
always maintain a certain channel, in proportion to the quantity of land water that requires
to be discharged. The tendency of nature is to contract the channel to such a size that
power of the stream can just maintain it, and in this state the wide extended arm of
the sea, anciently flowing by Sandwich, and up the general valleys, as now called, seems
to have been at the period that the new cut at Stonar was projected and executed.
The Stour was never adequate to keep open so large an arm of the sea as that through
which it flowed, and the force of its current was impaired by its meandering course. The
declivity of its bed in time becoming less, and the drainage of the lands more imperfect,
they turned the river through the narrow neck of land at Stonar, where in the space of
of a mile there was a fall of a fathom.
The land floods, after heavy rains, are the clearers of the channels of rivers to sea, and
this is chiefly effected when the tide is out, and most of all when they happen at the low
ebb of a spring tide; at such a time more is done in a few hours than in months where the
reflow is leisurely and moderate; one tears away all deposit with violence, the other grinds
away but small particles of mud or sand, and a gentle reflow does not disturb a particle;
but, on the contrary, if the preceding tide of flood has brought any silt with it, such a
reflow will allow it to be deposited, and where nothing is done towards its removal in one
tide, no number of repetitions will effect it. As long as the top waters are drawn off
through the flood-gates of Stonar and the dribbling of the floods, and the ordinary current of
the river left to go quietly round by Sandwich, no improvement can take place in the
harbour.
John Smeaton, who made his report in the year 1789, observes fully upon the greas
injury sustained by the harbour, in consequence of the changes made for the sole purpose
of draining the land, and improving its condition; he professes himself as great a friend to
drainage as to navigation, and observes that the flooding of low grounds in the valleys of
rivers is an advantage, provided it is done at suitable seasons of the year, and that the soil
and manure brought down from the high lands and deposited on the surface of the low
lands greatly improve their fertility; that the lands are not injured by the height or depth
of water which remains upon them for a short time, but the contrary: the damage arises
from the continuance of a small depth of water, which must be entirely removed from the
soil before its fertilising powers can be called forth.
For the improvement of this harbour, he suggested that during the winter months,
instead of drawing the gates when the water was just above the mark, after a dry season,
they should remain shut for a few days, that the water might be permitted to overflow the
meadows, and run again in its ancient course; and that as much of the top waters as could
be made to pass Sandwich Bridge should be directed or allured that way in order that the
whole channel of the Stour should be kept open.
A scouring power, acting by intervals, through Sandwich Harbour, together with the
aid of the hedge-hog and spade in some particular places, might keep it clear.
The harbour has, however, grown both narrower and shallower, and the contraction
of its section is a natural consequence of the loss of the force of the top waters of the land
floods.
Whenever a fresh water river makes its way to the sea through the loose sand and silt
that the sea has deposited, its course is continually varying; and when curved, the water,
acting on the side, tends to increase its departure from a straight line; to alter this by the
spade is a useless and endless work, and jetties are inefficient, as they will make fresh.
curves where there were none before.
Ramsgate Harbour.-As early as the reign of Edward VI. an attempt was made to form
an harbour from Sandwich into the Downs, and traces of a canal may be seen between
CHAP. VIII.
393
BRITAIN.
Sandwich and Sandown Castle, which formed a part of the project. In the reign of
Elizabeth, a commission was appointed to make a new survey; but nothing more was at-
tempted until the year 1736, when M. Labelye, the engineer to Westminster Bridge, laid
down a scheme for sheltering ships in the Downs, by means of a navigable canal and basin
in the direction of the old cut, and by aid of sluices, which joined the river Stour.

T
Fig. 395.
M
RAMSGATE Harbour.
Parliament was afterwards applied to, and an order in consequence issued from the Ad-
miralty by which five persons were named to report upon the means of making a better
and more commodious harbour than the present haven of Sandwich; they proposed that
two stone piers should be carried out, each 2096 feet in length from the shore, to 12 feet
depth of water, at low water, and that a clear opening should be left between the heads of
these piers of 300 feet, to narrow from that to 100 feet, and that the middle line should
point south-south-east, half east by the compass, that is nearly south-east by the true
meridian. The estimate for this work was 389,1687. 13s. 2d. exclusive of the value of the
ground to be purchased.
This grand project, however, was never undertaken, and it was not until a violent storm,
on the 16th December, 1748, when several vessels were wrecked, and a few found safety
in the little harbour of Ramsgate, that attention was turned to this port, and soon after an
act of parliament was passed, when Mr. Robins and Mr. Turner, engineers of Gosport, were
appointed to mark out the site of Ramsgate harbour. It was found that in consequence of
the pier constructed in 1715, having been lengthened, a bar had been cast up, which was
about 2 feet 6 inches in thickness, and as this accumulation was the result of 34 years, it
was reasonably presumed that when a greater depth of water was made by two piers in-
stead of one, the filling up would be less considerable than before.
394
BOOK I.
HISTORY OF ENGINEERING.
It was also observed that the sea-weed which drove in came from the westward; and
that from the east there was a drift of large shingle, which it was thought would be of
advantage to the new piers. When vessels broke loose from their anchors in the Downs, it
was usually from three-quarter flood to one-quarter ebb, when the current of the tide is to
the north and north-east, which carried them right into the harbour at Ramsgate. The
Goodwin Sands constitute the Downs as a roadway, and at low water these sands form a
breakwater to all the easterly winds, and even at high water they are too shallow to admit
the great seas to pass, without being broken and dispersed, and it is not till the tide turns
to the north, which is at about three-quarter flood, that the combined force of wind and
tide causes the ships to break from their moorings. The most advisable bearing for the
entrance to the new harbour was then determined to be south-south-west; for if placed
full south, the tide near high water would run so across it, that it would be difficult for
vessels to get in; and if at south-west, there would be too great an indraught of sullage.
-
At the commencement of the works, Mr. Etheridge, who had been employed as foreman
under Mr. King, the carpenter at Westminster Bridge, held the appointment of resident
engineer; he laid the foundations of the piers in cases or caissoons, and showed the method
of excavating a trench under water, and levelling it, which, being attended with certainty
and dispatch, is the practice still followed; and the whole progressed under this engineer's
superintendence until the works were ordered to be stopped; in the year 1755 a staircase
called Jacob's Ladder was made from the top to the bottom of the cliff, which was the
last work executed by Mr. Etheridge.
The east pier was, at this time, carried out 757 feet from the shore, and the west 849
feet.
In the year 1774, the works being incomplete, Mr. John Smeaton was called in to make a
report, when he found that a large mass of silt, consisting partly of mud and chiefly of very fine
sand, had been brought into the harbour by the tide; the tide water upon this part of the
coast being charged with these matters whenever agitated by the wind, and accompanied
by a quick flowing tide. This silty water, finding repose in the harbour, deposited its
heavy matter, and the water only was taken back at the ebb tide; this is the tendency
of all harbours, unless artificial methods are found to prevent it.
The most natural means to disperse it is by a fresh-water river, which continually tends
towards the sea, and in time of floods carries with it whatever forms an obstruction to its
course; where this means does not exist, such a harbour as that at Ramsgate must in
course of time become dry land: when Smeaton made his report, there was found to be
268,700 cube yards of silt in the harbour; that the two barges with ten men each took out
about 70 tons of silt per day; supposing 1 ton of silt to be 1 cube yard, it was calculated
that they would be 12 years in clearing it out, even if there were no fresh accumulations.
The whole harbour contained 46 acres, and the external harbour, where the greatest
quantity of silt was deposited, was about 30 acres; and supposing that the whole was
covered to the depth of inch per day, there would be 410 cube yards, which, at the rate
of clearing 70 tons per day, would require a week. It was calculated, that all which had
been deposited was the result of 12 years, which was the time when the curves enclosing
the harbour were raised to the level of half tide; the increase of silt was thought to be at
least inch per week.
183
Smeaton, therefore, proposed to make use of an artificial backwater and sluices, and
constructed a basin to take in the sea water, the tide having considerable rise and fall.
To prevent the basin itself from silting up, he advised that it should be divided into
two parts, by a partition with a sluice or sluices capable of retaining the water in either
while the other was empty, so that they might be used for alternately cleansing each other.
The harbour at Ramsgate was admirably suited for the execution of this plan; the
bottom was composed of a hard chalk, and declined with an even fall towards the sea.
The set of the tide runs across the harbour's mouth, so that when the sand was washed out
by the artificial current, the natural current of the tides would carry it away, and effectually
prevent any bar being formed.
Two basins of 4 acres each were proposed, and four draw-gates were to be made in the
westernmost and five in the easternmost basin, the whole pointed in three different directions;
two towards the curve of the western pier, four towards the harbour's mouth, and three
towards the curve of the eastern piers. To give these sluices their full effect, it was sug-
gested to construct a caissoon, shaped like the pier of a bridge, which being floated to its
place, and there sunk in a proper direction, might be used to divert the current to the right
or left, as was required.
Before this plan was put into execution, the committee of management ordered a
lighter of 50 tons to be scuttled, 17 inches deep, and 14 inches broad on the starboard bar,
and when placed at the end of the cross-wall to be filled with water. When the sluice was
opened at low water, it ran out in a few minutes, and made a cavity in the sand some feet
in depth and width; and afterwards, the water being confined in a channel guarded by
CHAP. VIII.
395
BRITAIN.
planks, a cavity was made in the sand when the water was discharged from the sluice, 7 feet
wide and 6 feet deep; it was again tried, and the hole, after three discharges, was found to
be 10 feet wide upon the surface of the sand, 6 feet deep to the chalk, and 3 feet wide upon
the bed of the chalk, the channel being full 100 feet in length.
The piles were driven, and part planked, for the cross-wall to enclose the basin, in the
year 1779, and soon after the sluices were completed; when all the men employed about
the works applied themselves with handles to start the sluices; the spindles upon which
the wheels were fixed broke upon the first attempt; but two of the sluices were raised at
last by means of tackle blocks, when the force and power of the stream was so great, that it
not only forced up the chalk to the depth of 6 or 7 feet, but carried away pieces weighing
from 3 to 4 cwt. to a distance of 60 or 70 feet, and in its course cleared away the silt
down to the chalk to low water mark, the stream continuing 200 or 300 feet beyond the
harbour's mouth.
They could not raise more than two sluices at this time, but after some alteration this
was rendered easy; the planking of the sluices was put to draw cross ways of the plank,
which operating on a rough groove of stone caused considerable friction; when they were
altered, and the spindles repaired and made of wrought-iron, the water was again pent up
in the basin, and the whole discharged together, and it was found to have such power, that
there was fear lest the cross wall should have been undermined; they therefore were
obliged to construct proper aprons to prevent this.
The committee further reported, that since the cross wall had been built, the sea which
before broke and spent itself upon the shore had now become so agitated that vessels
were unsafe; that the sea mostly ranged along the western pier, and that the cross wall
stopping and repelling the swell, it returned, not having any vent or outlet, and that this
was the cause of the great disturbance and agitation complained of. To remedy this the
committee then ordered that 200 or 300 feet of the cross wall should be taken down, and
that from thence a wall should be built up towards the cliffs, and also that 80 or 100 feet
of the timber pier should be taken away, beginning at the end of the cross wall, the opening
to extend towards Jacob's Ladder; it was also recommended that another sluice should
be made from the angle in the old pier, to scour the upper or northern angle of the
east pier.
In the year 1781 the sixth sluice being completed, a new channel was dug through the
sand, and a couple of barges were laid so as to direct the water through it; in a few
minutes the bank was considerably diminished, and the water of this sluice flowed so high
that it overtopped the conduit wall, and it was the general opinion, that by these means
the harbour might be kept cleansed; in the channel under the east pier there was found
19 feet water at spring tide.
Mr. Smeaton afterwards gave a design for a new dock, and the first stone was laid
July 31. 1784, but the walls were carried up without any timber floor; after this dock
was built, the natural springs which rise in the chalk bed broke not only through the
cement, but in many places issued with such violence as to break the paving-stones with
which it was covered. It was then proposed to take up the whole of the pavement, and
to do what had been done at Plymouth on a similar occasion,-lay down large blocks of
stone 3 feet by 4, and 2 feet 6 inches deep, each stone weighing 1½ tons. After these blocks
of Portland stone were all laid, and the dock shut in at the time of high water, the whole
pavement was again hoisted, and 100 feet of the north wall lifted with it.
Mr. Smeaton was then requested to examine its state, and he reported to the committee,
that on the day he arrived the tide rose 13 feet 4 inches upon the apron of the gates of the
dock, but that before it had risen 2 feet it began to spring through several joints of the
stone floor, which had been laid with the solid Portland blocks 2 feet 6 inches in thickness,
in the form of an arch. As the height of the tide increased upon the apron, the leakage
through the joints increased, so that when it was high water, there was a depth of 5 feet
3 inches water upon the floor.
The cause of these derangements was owing, he states, to the pressure of the water under
the bottom, endeavouring like a vessel swimming in the water to buoy it upwards; and
which, with 8 feet pressure, was calculated to produce that of 1000 tons over the entire
area of the floor; and he was of opinion that had the wooden floor been introduced
according to the original plan, it would have been subjected to the upright pressure only,
and not to a lateral pressure as in stone arches. It was found that it was produced by the
springs issuing from the area of the chalk on which the dock was founded, and that this
would not have been the case had the soil been a compact clay or rock that would not have
suffered the water to percolate through its pores.
Mr. Smeaton, who hitherto had been only occasionally consulted, was in the year 1788
appointed engineer to the harbour, and Mr. John Gwynn, who had already executed many
works under him, resident surveyor. They immediately commenced rebuilding the dock,
a timber floor was laid throughout, and an additional thickness given to the walls; here
396
BOOK I.
HISTORY OF ENGINEERING.
Smeaton again turned his attention to the formation of a diving-bell, to be used in laying
the foundations of a new advanced pier. Instead of the form of a bell, he used a square
iron chest weighington; it was 4 feet 6 inches high and long, and 3 feet in width; and
there was sufficient room for two men to work under it, who were supplied with a constant
influx of fresh air, by a forcing air-pump placed in a boat upon the water's surface.
The advanced pier was built in caissoons, twelve of which being fixed, extending 120
feet, the masons commenced their work; this constituted about one-third of the intended
length.
The timber breakwater, at the external angle of the east pier, being washed away,
it was determined that its reconstruction should be of stone, and in the year 1790 this work
was commenced.
In the year 1791, the dry dock built in the basin was tried for the first time, since it had
been found necessary to introduce a timber floor, which was constructed in a new and
peculiar manner, ou account of the springs in the chalk rising so powerfully under it as to
force up the stone floor, with which it had before been twice tried; the experiment showed
that its construction was complete, and all that could be desired; and the advanced pier
was very nearly finished.
The harbour now contains between its substantial stone piers an area of 42 acres,
the piers extending 1310 feet into the sea. The inner basin is used as a wet dock, and
contains a dry dock, where vessels of from 300 to 400 tons can be repaired.
The entrance to the outer harbour is 200 feet wide, and opens to the south-west. The
average rise of spring-tides at the pier heads is from 13 to 14 feet, and of neap tides 9
feet, giving to the entrance 19 feet at high water of spring-tides, and 16 of neaps.
The sluices for scouring the harbour are very powerful, and are constructed through the
cross-wall of the inner basin; the water they discharge serves to keep open the channel,
and the gullies which extend round the harbour at the foot of the piers, in certain portions
of which, near the entrance, the depth increases to about 6 feet at low water. The mud in
the middle of the harbour serves as grounding banks, and affords a soft bed, on which
vessels entering can ground with safety. The opening of the gates of communication
between the outer and inner harbour is 42 feet. In the outer harbour has been laid
down one of Morton's patent slips, on which steam-vessels of too great beam to enter
the graving-dock in the inner basin can be hauled up and repaired.
There is no natural breakwater to this tidal harbour, so essential for the purpose of
scouring, nor does the line of cliff offer shelter against any winds but those which blow from
off the land; it is, however, at present the best to be found on the south-eastern coast of
England, and affords a place of refuge to vessels of considerable draught of water that run
for protection at tide time.
The entire management of this harbour is vested by parliament in trustees.
Broadstairs had a wooden pier in the time of Henry VIII., erected for the security of
the fishing boats; this pier is now about 100 yards in length, and extends from the northern
side of a small bay. The entrance faces the south-west, and the harbour is much exposed
to the sea, which is driven in by winds from the eastward.
At spring-tides there is about 16 feet water at the pier-head, and 10 feet at neaps; but
the whole harbour is dry at low water, and during spring-tides nearly 100 yards outside
the pier is left uncovered.
Margate had a pier at a very early period, near which was a small creek; the land on each
side was, in the course of time, washed away by the sea, when it was necessary to protect
the shores by additional piling and piers.
The harbour is situated in a small bay, between two extensive flats of chalk rocks, the
Nayland on the west, and the Fulsam on the east, both of which are covered before high
water. The artificial harbour is formed by a stone pier, which commences on the eastern
side of the bay, and extends 800 feet to the westward, in an irregular course, leaving the
entrance open to the north-west.
The rise of average spring-tides at the pier-head is about 13 feet, and that of neap
tides 8 feet; but spring-tides ebb outside of the pier-head, and leave the harbour dry at low
water.
A wooden jetty has been run out from the root of the pier, over the Fulsam rocks, to
the distance of 1100 feet, for the convenience of passengers landing from the steam-packets
at low water.
Douglas, in the Isle of Man, has an extensive bay on the eastern side, its width, between
Douglas Head on the south, and Banks How, on the north, being 21 miles. Between the
head and Quarry Point it is only 1 mile and 5 furlongs wide, and about 7 furlongs in
depth, at right angles with this line, and which may properly be considered the bay. It is
bounded by steep and perpendicular rocks of clay-slate, and has a depth of water at low
spring-tides of from 2 to 5 fathoms.
The southern shores of the bay stretch as far as Douglas Head, on which the lighthouse
CHAP. VIII.
397
BRITAIN.
is placed. The town lies at the south-west extremity of the bay, at the mouth of a small
river, which has a course of 10 miles, and which discharges itself into a smaller bay, sepa-
rated from the greater by the Pollock Rocks, which ebb dry about 800 feet beyond high
water mark, and are, upon an average, 15 feet above low water; there is another rocky
island which is dry at low water, upon which there is a small tower of refuge for the
mariners that may be driven upon it. St. Mary's, or the Connister Rock, is another shoal,
between which and the Pollock the channel is not more than 300 feet in width, which
is nearly dry at low water of extraordinary tides. The harbour is formed of a pier, which
extends, from high to low water mark, a distance of 650 feet, terminated by a circular head
and a lighthouse. Quay walls are continued from thence along both sides of the river for
a distance of nearly 2000 feet, and the harbour comprised may be computed at 11 acres;
it is dry at low water of spring-tides, and the bottom is composed of fine shingle.
The tides vary here considerably; the height of the springs occur two days after full and
change of the moon at noon, when the tide rises from 19 to 20 feet, and extraordinary
equinoctial tides rise 3 feet higher, and the neaps from 10 to 14 feet.
Port Patrick Harbour is the nearest port in Great Britain to Ireland, and is only 7
leagues from the opposite harbour of Donaghadee: when John Smeaton was called upon
to report upon its condition, in 1770, he found it as nature had left it, with the addition only
of a small platform for the convenience of the landing and shipping of passengers; it had,
however, many advantages-it was easy of access, vessels of considerable size could remain
afloat at low water, and they were protected from storms coming from seven-eighths of the
whole compass, and had the other eighth, he observed, been as well guarded as the rest, the
harbour would be complete.
The harbour is formed by two ledges of rocks running out almost parallel from the shore,
so as to inclose between them a small bay of about 220 feet clear width, and about 550 feet
in depth. The bottom is covered with a clean sand, and the soundings gradually increase
from the shore to 20 feet at low water in the mouth of the bay, leaving from 9 to 10 feet
at dead low water mark in the middle of the harbour.
As the Irish coast extends from the south-west to north-west, and being so very near,
the swell, when the wind is right, is not considerable; from the north-west and north points,
the fetch of the sea is not of great lengths, being to a certain degree land-locked by the
Ila, Mull of Cantire, &c., &c.; and being well screened by the ledge of rocks, immediately
on the north side of the harbour, which rise considerably above high water, no violence is
experienced on that side. The land lies from north to south, so that nothing can happen
from the eastern point; it is only from south to south-west inclusive that the harbour lies
unprotected.
The rocks, which run out in the direction west by south on the south side of the harbour,
point to the lighthouse of Donaghadee, and would, if higher, afford considerable shelter in
all these winds; but the Irish Sea being open from these points, and the rocks being in a
great measure covered at high water neap tides, and at three-fourth flood at spring tides,
the seas break over them with so much violence in times of storms, that vessels lying there
were beat against the sandy beach at the bottom of the bay, where they were retained by
ropes as their only means of protection.
The vessels entering this port were, in consequence, obliged to be built very strong, and
of so flat a construction that they would not sail except with wind on the beam or abaft.
All the westerly winds prevent their sailing from Port Patrick to Donaghadee, and all the
easterly winds from their returning, so that they cannot go and return unless the winds are
southerly or northerly, and not then, if it were not from the strong current of the tides,
which up and down this narrow channel change twice each way in 24 hours; so that
sailing at a proper time of the tide, they are prevented by the current from sailing to lee-
ward, but could vessels constructed upon proper principles be protected here, they would
be enabled to turn to windward, and consequently make their passage good in all winds in
moderate weather, an advantage that arises from the particular set of the tides.
For the improvement of this harbour, Smeaton proposed to run out a pier from the point
of the rocks upon the mainland, crossing the gully between that point and the detached
rocks called the South Ledge, and then follow their general direction. This pier was to be
raised 6 feet above the high water of a spring tide, with a parapet 6 feet upon that; so that
the whole being raised 12 feet above high water, vessels would be effectually screened from
the south and south-westerly winds, as well as from those nearer the west.
The flow of the tides here was reckoned to be 15 feet at spring tides, and 12 feet at neap
tides, but these varied with the winds.
When the work was advanced sufficiently to break off from that part intended for the
interior harbour the great seas that roll in with the southerly and south-west winds, an
additional pier was proposed, the position of which was nearly north-east, and this extended
from the main pier 175 feet, leaving an opening into the interior harbour of 100 feet,
between the pier head and the nearest point of the platform rocks, which served the effect
398
Book I.
HISTORY OF ENGINEERING.
of a counter pier.
from 30 to 40 tons.
Vessels then could at all times enter, and shelter be obtained for any of
The width of this pier at the base is described to be 40 feet, and after fixing up leading
marks from the first erected pier to the shore, stones were dropped in between them to
form the foundation. These stones, which were rough masses of rock, were suspended by
tackle in slings, and hooked or secured by a loop made of as many turns of rope yarn
as would hold it, and by cutting the loop when the stone was in its proper position, it
was dropped. After the outlines were established, the internal stones were tumbled into
the area comprised between them.
The first stones dropped penetrated the sand, the second and third courses also dis-
appeared in the same way, but after they had settled to a firm base, the rest of the
construction was carried on by dropping the stones in a similar manner, taking care that
the faces fell back on each side, and that the wall diminished in thickness gradually; and
when any settlement occurred, or the stones were displaced by a storm, they were imme-
diately set right and the injury repaired.
The diameter of the circular part of the head was 2 feet more than the common breadth
of the pier, and the foundation was 43 feet.
The masonry of the upper parts was built with stones laid flat on their beds with
mortar; the joints of the head of the pier radiated from a common centre, and every third
course was securely cramped, and the centre stones retained by iron dogs. The cap or pier
head had every stone cut like a dovetail, and was so put together that its strength was suffi-
cient to resist the force of the seas opposed to it.
Belfast is situated on the river Laggan, near where it discharges itself into an inlet of the
Irish Channel. The tides flow for a short distance up this river, but ebbs entirely out at
low water, leaving a narrow and winding course through the sands for the river to flow
out.
Spring tides rise in the roadstead 12 feet, and neaps 8, so that vessels which draw 10 feet
water cannot reach the quays at neap tides, but are obliged to lighten their cargoes at
Garmoyle.
Bay of Dublin. On entering the nearest point of land, on the north and south are the
promontory of Howth, and the island of Dalky, which are distant from each other 63 miles;
from the line uniting these points, to the end of the lighthouse of the south wall, the
distance is 33 miles; from the same line to Ringsend, 63 miles.
·
Towards the south Howth presents a bold ascent, interspersed with rocks and adorned
with heaths of various colours; the mountains of Wicklow rise beyond in harmonious
confusion, and the whole produces, on approaching this beautiful bay, great picturesque
attractions.
On the north and west are two dangerous sand banks, produced by the channel of the
Liffey, and which extend to the lighthouse on the south wall. The channel between them
is not very wide, and the entrance is difficult, the depth of water at the recess of spring-
tides not being more than 5 feet. Near the northern extreme line of the banks called the
South Bull, a pier has been constructed, which is much admired; it commences at the vil-
It is
lage of Ringsend, and continues as far as the pigeon-house, a distance of 7938 feet.
formed by two stone walls, filled in with gravel, and completed about 1756.
The Pigeon House, before the harbour at Howth was constructed, was the place where
the packets received and landed passengers; and there is here an artificial basin, 900 feet in
length, and 450 feet in breadth, which is nearly dry at low water.
Beyond the Pigeon House the pier is continued eastward 9816 feet, where it is terminated
with a lighthouse; this division of the pier was originally timber, but in 1796 two parallel
walls of hewn granite were built, without the aid of cement, and the intermediate space
filled in with shingle and gravel; it is 32 feet broad at bottom, and tapers to 28 feet at top.
As it is merely a sea-wall, parapets have been dispensed with; the lighthouse at its
eastern extremity, built in 1768, is a truncated cone, three stories in height, with a stair-
case on the outside, which leads to an octangular lantern; the whole is built of the moun-
tain granite.
The pier secures the harbour from the sands of the South Bull, and with the quay walls
forms one continued barrier, from the lighthouse on the east, to Barrack Bridge, at the op-
posite point of the compass, a distance of 6 miles.
The situation of Dublin Bay cannot, however, be considered favourable to the formation
of a deep or commodious harbour; were it not for the discharge of the waters of the
Liffey and Dodder, there would be scarcely accommodation for the smallest class of
vessels.
The Liffey, being confined to a narrow course, the channel it cut through the sands
was of very small width, regular in its depth, but constantly altering its direction.
Captain John Perry, who was employed to stop the breach made in the Thames wall at
Dagenham, at the commencement of the last century, made some improvements in this
harbour by forming a pier of drift work, damming up the waters of the two rivers before
CHAP. VIII.
399
BRITAIN.
mentioned, and constructing a stone sluice in the embankment, of sufficient width to adinit
vessels within at the high water of spring tides.

IRISHTOWN
SANDY
MOUNT
BALDOYCE
OF CUSH
CLONTARF
CLONTARE
BANK NORTH
DUBLIN AND KINGSTOWN RAILWAY
NORTH
BULL.
THE
[RELANDS STACK'
EYE
HOWTH
"RALSCADDON
ENTOSE OF
HOWTH,
CUSNA
ROCK
FRESHWATEK JAY
BATTERY
MAUDYO
BLACK
SMUOY
• WHITE
FOOLBEG.
LIGHT.
SHEEP HOLE`RTZ
DRUMLOCK
BAILY
LIGHTHOUSE
RULL.
WILLIAMSTOWN'
BLACKROCK!
LIGHT
KINGSTOWN HOUSE
HARBOUR.
DUBLIN
BAY
NW.
-NE
BURFORD
BANKI
W-
-E
KINGSTOWN
TOWERO
TOWER
MAIDEN ROCK.
FLARE R.
МАРАЛЬ
BELI
-SE
MUCLUN R.
➜DALKEY ISLAND
SLANDS ENQU
Fig. 396.
BAY OF dublin.
In the year 1711, when the soundings were taken, there was from 19 to 21 feet water on
the bar at high water; and in the year 1800, Captain Bligh found that little alteration had
taken place in either the soundings or set of the tides.
Howth. The ancient name of this small port was Ben-hy-dair, or the Promontory of the
Oaks, or, as some imagine, of birds; this is connected with the main land by a sandy
isthmus, about mile in width.
124
The new harbour is formed on the north side of the peninsula, in the sound, between the
promontory and the island termed Ireland's Eye. From the northern shore of Howth, on
the one side, and the south-east point of the island on the other, are two ledges of rock,
which are mile apart.
Between the north-west end of the island and the sands of Baldoyle there is a similar
passage, and by these two passages the sound or harbour is entered.
Ireland's Eye is distant about a mile towards the north from the shore, and is little more
than a mile in circuit.
In this harbour, a pier has been formed on the ridge projecting from the main land,
200 feet in width at the base, and 85 feet at high water mark; it is 38 feet in height, and
runs 1503 feet from the shore, where it forms an obtuse angle with its first direction,
and proceeds north-west for the distance of 990 feet, at the extremity of which stands the
lighthouse.
On the west has been raised a pier 170 feet wide at the base, and 80 feet broad at high
water mark; it is 36 feet in height, and runs 2020 feet on the north-east, to meet the
return of the other, the entrance between being 300 feet in width, and the area inclosed not
less than 52 acres.
The inside of the pier is faced with cut granite, and under low water, was built by
400
BOOK I.
HISTORY OF ENGINEERING.
means of the diving-bell. The first stone was laid in 1807, and the whole was completed
for the sum of 305,000l., under the direction of the late Mr. Rennie.

SPIT OF BALDOYLE.
ROAD TO DUBLIN
LICHTHOUSE
VATER
RUIN
CHURCH
YARD
MARTELL
TOWER
ORDNANCE
GROUND
CATHOLIC
PEL
CHA
TOWN OF
HOTEL
HOWTH
110
BALSCADDAM
BAY
Fig. 397.
HOWTH HARBOUR.
Kingstown, formerly called Dunleary, is distant from Dublin 5 miles; here is a small
bay, naturally formed by an indentation of the coast, and from an early time there was a
pier of rude construction, which afforded shelter to vessels under stress of weather.

RESERVOIR
DUNLEARY.
QUAY
Fig. 398.
KINGSTOWN HARBOUR,
PIER
CHAP. VIII.
401
BRITAIN.
The new pier is formed half a mile further to the east, or nearer to Dalkey, at the com-
mencement of a rocky tract, called Codling Rocks, to the westward of which, within shelter
of the pier, the bottom is of fine sand.
The first stone of the new pier was laid in 1817; it extends 2800 feet, and has four arms,
the first running directly from the shore, to the distance of 1500 feet, in a north-east direc-
tion; the next continues north, the third north-west, and the fourth west, each 500 feet in
length. The base of the pier is about 200 feet in breadth, terminating in a perpendicular
face towards the harbour, and battering towards the sea; on the top runs a quay, 50 feet in
width, which is protected by a parapet wall, 8 feet high. At the extremity is placed the
lighthouse. The depth of water at the pier-head is 24 feet at the lowest springs, which at
all times is sufficient to shelter large trading vessels and ships of war. The estimate for
the completion of these works, as laid before Parliament, was 505,000l.
The Harbour of Cork, 8 miles from the city, is one of the most capacious and secure in
the British empire. The outward entrance is barely half a league, but having passed a
bank, called the Turbot, on which there is 30 feet water, the entrance narrows to half a mile.
In this great basin lie the two islands of Spike and Halbowlin, placed as it were to form
bulwarks against the winds and the ocean; so that vessels may lie in the harbour land-locked.
Extensive barracks and a dockyard are formed on these islands, which are distant from
Dublin about 125 miles.
Jersey Harbour.-St. Helliers, when Smeaton reported upon it in 1788, had a pier, which
he denominated a screen, and he suggested some improvements, which have since been par-
tially carried into effect; but he observed, "that no small harbour could be made quiet,

Fig. 399.
JERSEY HARBOUR.
for the magnitude of the waves are supposed the same to all, and the necessary width of the
mouth for a ship to enter the same: seas, then, that will inevitably sweep round the heads,
will affect a smaller harbour more than a large one, though of similar constructions ;
for the effect of the waves in disturbing a harbour is greater in proportion as the lineal
width of the mouth is to the whole area of the harbour: for this reason St. Helliers must
pen-
always be defective. Another circumstance tends to render such a harbour unquiet, and
that is, when they are bounded by walls. The waves of the sea follow the laws of the
dulum, which, when once set vibrating, would never cease if not stopped by friction and the
resistance of the air. The same would happen to the libration of the water if there were
nothing to stop it; for, meeting with walls and objects comparatively smooth, the waves
are not destroyed, but reflected into another direction, and from that into another, till they
are gradually dispelled by friction. The speediest way by which waves are destroyed
(that is, by friction,) is by forming a surf, and breaking upon a sloping beach, sand, or
rocks, in which the harbour of St. Helliers is defective."
The catch pier, suggested by this engineer, extended into the harbour 550 feet, and the
spring-tides rise here upwards of 40 feet, but the neaps run very short.
There not being in the inner harbour any backwater to scour away the sand, it accumu-
lates in large quantities, and Smeaton advised the making of arches through the pier, as was
practised by the Romans, and which had the effect of disturbing the deposit, which was'
partly carried out to sea on the retreat of the tide.
Dd
402
Book I
HISTORY OF ENGINEERING.
St. Aubin's Harbour is also in the Island of Jersey, and upon it Mr. Smeaton also drew
He observes : —
up a valuable report when he visited the last mentioned harbour.
" Ex+
perience having shown that the new pier of St. Aubin, called the Upper Pier, intended to
bring up ships and vessels close to the town, for the convenience of fitting them out,
loading and unloading, is, from its situation, liable to fill, from the great quantity of gravel
which the sea washes in from the back of it, and that the depth of water is, from that

Fig. 400.
ST. AUBIN'S.
99
action of the sea, diminishing more and more. And he further states, "that where a
sloping shore is interrupted by the erection of a wall, as a wall has not that tendency to
spend and destroy the waves of the sea that a sloping shore constantly has; wherever walls
are erected in the confines of a harbour, it is rendered, in a degree, less tranquil by this
means.
19
The reason of the gravel accumulating at this upper pier seems to have arisen from the
west end of the Island of Jersey lying so exposed to the Atlantic, without any land to
shelter it; the south-westerly winds, therefore, drove forward the gravel brought coast-
wise, towards the bottom of St. Aubin's Bay, where it met the upper pier.
Smeaton suggested that a pier should be carried out in a north-easterly direction, which,
flanking the current with a considerable obliquity, might prevent this accumulation.
Having now enumerated most of the harbours of Great Britain, upon which vast sums
have been expended, it is a subject of regret that few answer the purpose of sheltering
vessels at all times from the heavy gales our 2000 miles of coast are subject to.
Milford Haven, Portsmouth, Plymouth, Cork, and a few others, may be entered at all
times of the tide, whilst the harbours on the eastern shores in particular are nearly all
choked up, and incapable of receiving large vessels, excepting at the highest state of the
tide. A good harbour requires a depth of water which will permit the largest vessels at
all times to enter, and that it should be easy of access, with quay and piers, at which ships
could load and unload their cargoes without inconvenience.
Most of our harbours being formed by piers, not sufficiently carried out from the main
land, are consequently dry at low water, have bars at their entrances, and do not afford any
shelter to ships of the largest class.
Mere tidal harbours are serviceable only to coasters, as their draught of water is usually
very inefficient.
It has been very properly observed by the parliamentary commissioners, that deep water
harbours can only be formed in the sea by means of breakwaters detached from the main
land. Dover Bay affords an excellent site for such a harbour of refuge, there being at a
distance of 400 fathoms from the shore a depth of 2 fathoms at low water of spring tides,
and but 6 fathoms at 1100 yards, which affords sufficient space for the construction of a
capacious deep water harbour, without getting into such a depth for the site of the piers or
breakwaters as would add greatly to the expense. A breakwater at a distance of about
1000 yards from the shore, with piers projected from the land towards the eastern and
western ends, having four entrances, according to the plan there given, would form a most
effectual harbour. It is also suggested that the piers should be built with hard chalk,
CHAP. VIII.
403
BRITAIN.
and faced with stone; the space inclosed to be about 450 acres, the expense of which is
estimated at two millions sterling.
Other sites, as Margate Sound, off Long Nore Spit, at Foreness, and off Beachy Head,
have been considered equally eligible for the construction of a harbour of refuge.
River harbours are subject to constant silting up, and to deposits at the mouth, which
sluicing very inadequately removes; therefore to form a perfect establishment to receive
vessels at all times, it should be at a distance from the main land, with entrances to suit
the prevailing currents and winds: to form a hollow island in the ocean, which should
enfold within its arms the ships of Britain, and protect them against the elements, often so
fatal to many, would, indeed, be worthy of the nation, and rival the great works performed
by the Romans.
To see an artificial zone rise from the ocean, covered with buildings containing all that
our marine required, and within its circuit ships from all nations riding in safety, would call
forth admiration equal to that expressed by Pliny when the port in view of his villa was
being formed: a nation's wealth could not be more beneficially employed than in such a
work, and though millions might be expended in its formation, in a few years it would be
repaid by the securities it offered and afforded. To execute such a project is by no
means difficult, as our shores and tidal currents are so thoroughly known.
To attempt to form a harbour on any part of the coast where there is an accumulation of
beach, which is moved forwards by the prevailing winds, and lodged in layers along the
shore until it rises to nearly high water mark, is useless; no breakwater can be provided
sufficient to scour and keep open a passage for vessels in such situations, and a good
harbour cannot be obtained.
Under Beachy Head, Dungeness, and several projecting parts of the coast, the beach
finds shelter, and forms a bold face, where the water is deep, to the shore, and where, as in
the Isle of Portland, a vessel may lie afloat with her bowsprit over the beach, such situ-
ations might be rendered fit to hold a large navy.
Walls and Gates of Cities and Towns.-There can be little doubt but that the Romans
walled in our chief towns, and taught the Britons a more secure method of defending
themselves against a foe who menaced their dwellings than was afforded by earth-works
and timber constructions, which Cæsar describes as surrounding their camps and places
of resort.
London was encompassed with walls as early as the third century; and in all pro-
bability, Helena, the mother of Constantine, added considerably to their strength in the
following century. Maitland imagines that the greater portion was rebuilt by Theodosius,
who was governor of Britain in 379 a.d.
The direct course of the city walls was as follows: beginning at the Tower, they con-
tinued by the Minories, between Poor Jury Lane and the Vineyard, to Aldgate; they then
curved to the north-west, between Shoemaker Row, Bevis Marks, Camomile Street,
and Houndsditch, to Bishop's Gate; from thence in a straight line by Fore Street to
Cripple Gate. They then turned southward to Monkwell and Castle Street, Noble Street,
Dolphin Court, to Alder's Gate; then south-west, by St. Botolph's, Christ's Hospital, and
Old Newgate and southward to Ludgate; from thence to Little Bridge Street and the
Thames. Stow makes the whole circuit of these walls about 2 miles 1 furlong. Another
wall was continued along the banks of the Thames, 1 mile 120 yards in length, to the
Tower. These walls were defended at different distances by strong towers and bastions,
three of which remained when Maitland wrote his history, in the vicinity of Hounsditch and
Aldgate; the height of the walls was about 22 feet, and that of the towers 40 feet. The area
comprised within them is computed at 380 acres. A portion of the foundations was
measured in 1707 by Dr. Woodward, in Camomile Street, near Bishopsgate, who states
them to be about 8 feet below the roadway, and that to the height of 10 feet they were
composed of Kentish rag-stone, with single layers of broad tile interposed, at the distance
of 2 feet from each other. The tiles were Roman, 17 inches long, 11 inches in breadth,
and 14 in thickness; the mortar was very firm and hard, and the entire thickness of the
wall was 9 feet. A portion still remains near Tower Hill.
Numerous tesselated pavements, coins, and other Roman remains, are constantly dis-
covered over the entire area of the ancient city.
York was strongly fortified by the Romans, but the walls which they constructed were
probably rebuilt in the reign of Edward I.; in that of Edward III. an order was again
issued to strengthen them, and the following is Leland's description of them in the time of
Henry VIII.
"The towne of Yorke standeth by west and est of Ouse River, running
Thus
through it, but that part that lyeth by est is twice as gret in building as the other.
goeth the waul, from the ripe of Ouse, of the est part of the cite of York.
Fyrst a great
towre, with a chain of yron to cast over the Ouse, then another towre, and so to Bowdam
Gate; from Bowdam Gate or Bar, to Goodram Gate or Bar, ten towres, thence foure
toweres to Laythorp a postern-gate; and soe by a space of two flite shotts, the blind and
deep water of Fosse, coming out of the Forest of Galtres, defendeth this part of the cite
DD 2
404
BOOK I.
HISTORY OF ENGINEERING.
without waules: then to Waumgate three toweres, and thence to Fishergate stopped up,
since the communes burned it yn the time of King Henry VII. Thence to the ripe of
Fosse have three towres, and in the three a postern, and thence over Fosse by a bridge,

Fig. 401.
INSIDE OF THE CITY WALLS, YORK.
to the Castelle. The west part of the cite is thus ynclosed; first a turrit and soe the
waule, runneth over the side of the dungeon of the castelle on the west side of Ouse, right
against the Castelle on the east ripe. The plotte of this castelle is now called Ould
Baile, and the area and
ditches of it doe mani-
festly appeare. Betwixt
the beginnyng of the first
parte of this west waulle,
and Micklegate, be nine
towres, and betwixt it and
the ripe agayne of Ouse,
be eleven towres; and at
this eleven towres be a
postern-gate, and the towre
of it is right agayne the
est towre, to draw over
the Chain on Ouse betwixt
them.
The four gates or bars,
by which this city is entered,
are admirable examples of
those castellated defences
of which there are some
traces in all our walled
towns.
Bootham Bar stands on
the north-west side, on the
way to Durham, Newcastle,
and Edinburgh. On the
front are two shields with
the city arms, and another
much defaced. This bar
suffered considerably in the
time of Charles I.

Fig. 402.
BOOTHAM BAR.
--
CHAP. VIII.
405
BRITAIN.
Monk Bar is the en-
trance from the Scarbo-
rough road; the lower
arches are circular, and
built of a hard grit-stone,
probably at a very early
period; the upper por-
tions with the pointed
arch, and the picturesque
towers at the angles, are
of the time of Edward
III., and bear the shield
of France and England.
In this tower are two
stories of vaulted cham-
bers.
The plan shows its
general arrangement: A,
is the bar, B, the bar-
bican, C, the groove of
the portcullis, D, the city
walls, E, the guard room,
F, the stairs, G, the gates,
H, the sally port: the
clear width between the
walls is about 25 feet;
the thickness of the
walls 6 feet 3 inches, and
the total length about
50 feet; the thickness of
the two walls equals half
the clear opening, and
the entire length
length is
double the entire width.
The view of this bar
towards the city shows
the room over the gate-
way, which has a stone
arch of considerable
strength; there is a se-
cond room, similarly
arched, containing the
portcullis and windlass.
Such entrances graced
and adorned all our large
towns, and Leland de-
scribes the walls of New-
castle-on-Tyne as having
the pre-eminence. "The
strength and magnifi-
cence of the wauling of
this towne far passeth all
the wauls of the cities of
England, and of most of
the touns of Europe."
General Roy, in the
"Military Antiquities of
the Romans in Britain,"
and Mr. King, in his
"Munimenta Antiqua,"
have shown a great va-
riety of examples of the
fortifications of the
middle ages; and it will
be found that the whole
were designed and ex-
ecuted after the models

Fig. 403.
MONK BAR.

Fig. 404.
fי
Autall
3
MONK BAR, INSIDE.
ED 3
406
Book 1.
HISTORY OF ENGINEERING.

:
of others, erected during the period of
the lower empire of Rome: most
cities and towns were defended by
castellated walls, a castle, or citadel.
In England the Romans constructed
a vast number of fortresses; for in
every province they conquered, they
marked out a camp, and founded mi-
litary strongholds: to these succeeded
the Anglo-Saxon tower and castle,
which was made of considerable extent
and strength in the time of King
Alfred Arundel Castle exhibits much
of the construction of that monarch.
When the Danes arrived, some change
was introduced in the style; they, it is
said, founded Norwich, and threw up
those high mounds of earth at Castle-
ton and Coningsburgh. The Saxon
princes have left us much of their
constructions at Winchester, Exeter,
Canterbury, Bamborough, Durham,
Porchester, Pevensey, Castleton,
Guildford, Corff, Bridgenorth, and
Goodrich, and in them we discover
that the builders have made use of the
H
B
D
C
Fig. 405.
--A-
----------------
PLAN OF MONK BAR.
E
D
tiles and materials which had formed a portion of the Roman fortresses that probably
occupied their sites; this is observable at Colchester, Arundel, and Eynesford Castles in
particular. When the
Normans arrived, they
introduced various means
of defence by military
stratagems, as concealed
sally ports, galleries under
ground, doorways and
staircases which led to
nothing, and dungeons
only to be approached by
trap doors. Even the
bishop's palaces were for-
tified and made strong-
holds, and the citizens of
large towns adopted the
same means of defence, as
was practised by all the
inmates of the larger re-
ligious houses throughout
Britain.
Micklegate Bar. The
royal arms displayed are
those in use before the
time of Henry V. This
beautiful gate forms the
chief entrance from Lon-
don; it is built of grey
grit-stone, and the towers,
which probably are of a
later period, are of fine
limestone. The portion
which is of grit-stone is
supposed to be Roman,
though Sir H. C. Engle-
field (Archæologia, vol. vi.)
has refuted this opinion.
The upper parts were
probably built in the time

Tonal
Fig. 406.
MICKLEGATE BAR.
MANU
of Edward III.; the outwork or barbican, with its angular towers complete, must have
added much to the beauty of the entrance.
CHAP. VIII.
407
BRITAIN.
The portcullises of some gates were of oak covered with iron, and Leland mentions one
at Pembroke composed "ex solido ferro."
The Magècolles or machecoulis, under the parapet over the gate, between the salient
towers at the angle, contributed greatly to the defence of the entrance: they were intro-
duced into Spain by the Arabs, and subsequently adopted by the Normans and Lombards
wherever they established themselves.
The gateways of Caernarvon, Pembroke, Raby, Warwick, Canterbury, and many others,
exhibit the perfection of this style, and are models of proportion and construction.
Walmgate Bar is the entrance from Hull; on the front are the arms of Henry V.
The fronts and sides are embattled, and the barbican was similar to the other bar this

ARC.
Fig. 407.
WALMGATE BAR.
gate suffered greatly in the siege of 1644, and has since been subjected to still greater
injury.
The walls adjoining the bar are built upon arches in the foundations, and appear to
be of great antiquity.
Chester was a Roman city; its walls were rebuilt by Ethelred and Ethelfleda, about the
year 608, and their form is so entirely Roman, that the Saxons made no great changes in
the system adopted by their great precursors.
These walls are about 13 miles in circumference; the top is paved sufficiently wide
for two persons to walk abreast; there are four gates or principal entrances over the
north-east bridge and water-gates, besides several posterns. Around the walls were for-
merly several towers; that called the New, which projected towards the Dee, erected
in 1322, was 24 feet in height, and we learn from the archives of the city that the
architect was John Helpstone. To the exterior are attached large iron rings for holding
the vessels, which, before the harbour was choked up with sands, were admitted up to the
walls. Leading to the water tower was another, called Bonewaldesthorne, and the
Phoenix tower, from which Charles I. saw his army defeated on Rowton Heath. The
Gobelin's tower is nearly destroyed, and the Sadler's tower was taken down in 1780.
Chester is divided by four principal streets, crossing each other at right angles, and the
road for carriages is on a level with the basement of the houses, over which are covered
galleries or rows, for the accommodation of the foot passengers; these galleries are approached
by flights of steps at the intersection and ends of the streets, and the houses extend over
them, being supported on stone and timber pillars.
Winchester. The Saxon walls on the north side of the city are built of flint and hard
mortar; at regular distances the ruins of the towers that formerly flanked them may
be traced, and in some situations they remain to their full height, being crenated, em-
battled, and coped with freestone. The form of this ancient city was that of a paral
DD 4
408
Book I.
HISTORY OF ENGINEERING.
lelogram, rounded at the angles, and its gates terminated the principal streets, which
crossed at right angles: West Gate, which was the entrance from Rumsey, remains nearly
perfect. A ditch, or rather running water, protects the walls on the outside.
At Southampton portions of the walls are said to be Roman, Saxon, and Norman, and it
is extremely difficult to discriminate between the works of the several people. The en-
closures of a town were usually set out of a sufficient thickness to allow of a walk at the
top, which was guarded externally by an embattled parapet. The wall was constructed of
the material the country afforded, either stone quarried in the neighbourhood, or flints
picked from the surface of the land. Bricks and tiles are occasionally found in the arches
to the drains or other openings, and sometimes forming a course through the entire thick-
ness; these walls, like those of the churches and castles of the same epoch, were con-
structed between cases of timber framework, in a similar manner to the pisé walls; and
there is sufficient evidence that after the facing was laid on both sides, the filling in or
stuffing was made with every variety of material that could be collected, sometimes
imbedded in mortar, at others run with liquid grouting, in either case making a hard
concrete, capable of enduring for centuries.
Rochester, situated on the Watling Street, was fortified by the Romans, and much of the
walls constructed by King Ethelbert remain: they were built in the direction of the four
cardinal points, and extend from east to west about half a mile, but from north to south
not more than a quarter; they are 4 feet in thickness, and on the east side the height was
30 feet. Edward I., in the year 1290, gave permission to the monks of the convent "to
pull down part of the south wall, and to fill up the ditch without the wall, on condition
that they built a new stone wall, 5 rod and 5 feet from the former, 16 feet high and well
embattled, to stand on their own ground, and to be repaired by them." There were several
gates, all of which are destroyed.
It is not possible to enumerate all our city and town walls; they varied in height and
thickness according to their locality or importance. Their general character was Roman,
and their gates and approaches were defended in the same manner as those of the castles of
the wealthier and more powerful barons. What a different spectacle to the traveller must
England have then presented! Walled and fortified towns, resembling many on the con-
tinent; castles defying admission; religious establishments and colleges within enclosures,
resembling fortresses.
The gates of cities and towns throughout Europe during the middle ages bore a strong
resemblance to each other. Those at Constantinople, perhaps, served as the prototype of
many. The walls of this city extend, on the western side 3 miles, and are fortified by
100 towers. The battlements, machicolations, and entrance gates, are of the same character
as those of the castles and walls constructed in England by Edward I. That sovereign,
when engaged in the holy wars, as they were falsely termed, had the opportunity of
observing the arrangement of the castles in Asia, and the fortifications of the cities, which
were surrounded with lofty embattled walls, strengthened by towers of various forms, out
of which projected machicolations, galleries, and various other contrivances, both for
defence and ornament.
Caernarvon Castle, both a garrison and a palace, has a beautiful entrance, built by
Edward I. after his return from the Crusades. It is an hundred feet in height; the gateway
has a succession of sharply pointed ribbed arches; there are grooves for three portcullises,
above which are circular holes for the discharge of missiles, or for pouring down molten
lead.
The Eagle tower has three angular turrets; that appropriated to Queen Eleanor is
polygonal, and contains four stories.
There can be no doubt that for the style of our castles we are indebted to the inhabitants
of Asia; many towns in India are still surrounded by lofty stone walls, embattled, machi-
colated, defended by round towers, and with gateways and barbicans in every particular
resembling our own.
The Castles of England afford study for the engineer of the most instructive kind; in
them all the arts and science of the age are exhibited, and as their plans and forms are
adapted to peculiar situations, they do not resemble each other: hitherto they have been
regarded solely as contributing to the picturesque character of the country, and as afford-
ing subjects to the artist and the historian; they have not been sufficiently studied by
the engineer with regard to their construction, nor have they been accurately measured
for the purpose of examining their merits as places of defence. A perfect collection of
English castles has never been made, which, as they crumble away or are removed to
make room for modern changes, will hereafter be regretted. Hertmonceaux, Bodiam,
and some others, have been very accurately described, which only tends to awaken feelings
of regret that more have not had the same attention bestowed upon them.
The square,
the circular, the polygonal keeps, which occupy a portion of the area within the outer
walls, are generally fine examples of the contrivances of our ancestors; in them were
apartments of noble dimensions, well secured and defended from outward attack. Warwick
CHAP. VIII.
409
BRITAIN.
Ragland, Barnard, Richmond, Pontefract, Ludlow, Goodrich, Caernarvon, Conway
Chepstow, Caerphilly, and others, might be enumerated, all of which had accommodation
within the circuit of their walls to lodge a considerable body of men.
It is not possible in the present work to do more than select one or two examples, as
illustrations of this highly interesting subject; but from measurements, the keep of
Coningsburgh and gateway of Saltwood Castle have been selected, as exhibiting in their
arrangement and construction the chief and peculiar features belonging to castles of that
date.
Coningsburgh Castle, Yorkshire, is a fine example of a fortress at a very early period of
our history; and when the sketches of the keep were made, it was, as far as the masonry
is concerned, in a perfect condition. It is an evidence that the engineers then understood
the setting out of geometrical forms, and the arrangements necessary for the weapons of
attack and defence then made use of: Vauban himself could not have contrived a tower
capable of greater resistance.

Fig. 408.
С
PLAN.
10
20
40
50
60
FIRST STORY.
In the time of Edward the Confessor, Arundel Castle is said to have existed, and
Domesday Book enumerates forty-nine, after which the Normans laid the foundations of
many, and that at Coningsburgh is supposed to have been erected by W. de Warrein
about 1070.


Fig. 409.
SECOND STORY.
THIRD STORY.
A Norman fortress was a considerable engineering work; a deep ditch was generally cut,
the earth taken out and carried within the circuit, to form in some convenient situation a
mound, on the summit of which was built a keep or lofty tower, containing several stories
appropriated to different purposes.
In the wall on the inner edge of the ditch was an entrance gateway, before which was
410
BOOK I.
HISTORY OF ENGINEERING.
a barbican or watch tower, communicating by means of hidden passages with the strong
tower on the mound.
The Normans constructed a castle in every lordship, and when material was not
easily obtained, they frequently imported stone from Caen for casing the walls, and for the
ornamental portions of the interior, the internal and external facing being filled in with a
concrete composed of pebbles, flint, or chalk, run with fluid mortar. The great thickness
given to the walls enabled their engineers to practise within them staircases, guard-rooms,
chapels, and every kind of accessory apartment that the inhabitants could require during a
siege. The keeps of London and Dover, Hedingham, Norwich, Porchester, Scarborough,
Colchester, and others, though dismantled, convey to us an idea of the great discernment
and skill of those under whose direction they were raised.
At the entrance story of Coningsburgh, the internal diameter is 22 feet 1 inch, the
thickness of the walls where the buttresses are attached the same. Between the buttresses
it is only 13 feet 7 inches. The entire diameter, measured through to the flat outer face
of the buttresses, is three times that of the interior. The six buttresses are half hexagons,
and on this floor solid throughout; each of their sides internally measure 8 feet 10 inches,
the distance apart is 12 feet 4 inches, and from angle to angle in a straight line 26 feet.
The entrance, 24 feet from the ground, is approached by a lofty flight of steps, and is
only 4 feet 4 inches in width; after passing through half the length of this passage, on the
right, in the middle of the wall, is a stone staircase conducting to the apartment above, to
which the only light admitted is from the aperture shown between the buttresses.
In the centre of the floor of this apartment is a circular hole communicating with a lower
apartment, at the bottom of which was probably the well that supplied the tenants of the
keep with water during a siege.
Some writers suppose that this keep was constructed by the Saxons, and that William
the Conqueror bestowed it upon the husband of his sister Gundred, but of this we have no
direct evidence: the castles of the Saxons were often entered as this was, by an aperture at
a considerable height from the ground, either by ropes or a wooden ladder. The reader
is referred to the "Archæologia" for a description of a castle at Eynsford in Kent, by the
author. The only entrance is at the top of the wall, and no one could have gained ad-
mittance without being hauled up, or supplied with a wooden ladder.
The first story has a fireplace of a curious construction, perhaps the earliest example we
can produce of such a contrivance in England. Light is admitted over the entrance door-
way by a double opening; and in one of the buttresses is a closet, entered through a
passage 2 feet 6 inches in width.
A staircase in the thickness of the wall conducts to the floor above. The mantel
of the fireplace is formed of nine stones, so cut as to hang on each other, and preserve a
level line below, show-

ing all the properties of
a flat arch. Above this
arch runs a level mould-
ing, on which the ma-
sonry rests,
rests, bevelled
over so as to gather the
flue into the thickness
of the wall; the chimney
at Coningsburgh seems
to have been built up
at the same time as this
portion of the keep; the
opening is 7 feet 3 inches,
and depth 18 inches;
on each side is a triple
column, with capitals
and bases.
The thickness of the
walls at this story is
13 feet 6 inches, and
around the interior face
the stone corbels that
carried the timber floor
still remain.
The second story,
27 feet in diameter, ap-
pears to have been en-
tirely devoted to the
baron and his family;
Fig. 410.
CHIMNEY OF CONINGSburgh Castle.
CHAP. VIII.
411
BRITAIN
there is a fireplace, closet, chapel, and other conveniences, hollowed out of the buttresses
and walls.
The chapel, with an inner room adjoining, remains in a very perfect state, and the
architecture which decorates it is in the pure Norman style; the zig-zag is peculiar, and
the ornaments comprised in the plain faces have a truly Greek character. The light is
admitted by quatrefoil openings, of a very early date; the whole is vaulted, with the ribs
resting on very enriched capitals attached to the walls. There are several niches worked
out of the walls in various places; some contain stone sinks or troughs, and a water-closet
at the end of a winding passage in this floor is contrived with admirable skill.
The clear width of the fireplace on this floor is only 5 feet 4 inches, and height about the
same; the weight of the breast of the chimney is discharged by a flat arch of eight stones,
constructed like that below. The corbels around the walls remain, on which the timbers
rested which carried the oak floor.
The light in this apartment is nearly sufficient for any modern building. The conve-
niences attached, and easy access to the rooms above and below, give an excellent idea of
what the barons considered essential to their wants; and a family at the present day
would have no difficulty in finding accommodation in a structure so arranged.

טויטי
VITA
Fig. 411.
CONINGSBURGH CASTLE, YORKSHIRE.
The upper floor has within one of the buttresses an oven, sufficiently large to have cooked
all the provisions for the entire garrison; the other five buttresses have recesses within
them, for the protection of the guard, who were constantly on the watch to announce the
approach of an enemy, and prepare for defence against an attack. The battlements and
machicolations around, which must have greatly added to the effect of the upper portion,
have long disappeared.
The thickness of the main wall is here 12 feet 4 inches, and the outer face is perpendicular
from the level of the ground floor, the diminution in thickness being always caused by
giving an addition to the internal diameter.
The village of Coningsburgh, situated a short distance from this beautiful remain, is 51
miles from Doncaster, on the road to Sheffield; it was no doubt a British station, as the site
was called Caer Conan, or the Royal Town. By the Saxons it was known as Cyning or Conan
Byrgh, and it very probably formed the stronghold of Hengist when he was defeated in
487 by Ambrosius. The tumulus near the entrance has been supposed to cover the body
of the Saxon chieftain.
*
Saltwood Castle, Kent. This entrance gateway is in a very perfect state, and shows the
style of architecture adopted for such edifices in the 14th century.
Archbishop
Courtenay resided here, and under his directions the castle received many additions
and embellishments; his arms are quartered on the shields over the gateway, whence we
may infer that it was built during the time he possessed it.
The gateways of cities, religious houses, and castles, during this epoch, combined
architectural beauty with defence. The lofty towers, which flanked the entrance, were
carried up high above the battlements of the curtain walls that shut in the court-yards;
412
BOOK I.
HISTORY OF ENGINEERING.
FEIEGES
these were crowned with a parapet, resting on corbels, and in the centre division between
the towers were deep and projecting machicolations, from which might be hurled a variety
of missiles upon the heads of those who had crossed the drawbridge, or were endeavouring
to force the portcullis or fire the gates.


Fig. 412.
GROUND PLAN OF SALTWOod castle, and first STORY PLAN.
Catapultæ, mangonels, balistæ, springals, tribuli, arcubalistæ, multones, barfreni,
skaffauts, and various other instruments and machines were here lodged, ready either for
defence or attack.
All
On comparing these defences with those attached to the entrances of Roman or Greek
cities, we find that the orders of architecture are omitted, but many oriental contrivances are
substituted, which give a peculiar effect and character; there is the same solidity of con-
struction and quality of material in both, as well as great similarity of workmanship.
the vaults and arches, winding stairs and passages, are formed in the same manner; concrete
is universally employed, to fill in between the outer faces of the walls in the castles of the
middle ages as in those of the Roman fortress. The construction is Roman, and the
military features are mostly of eastern origin.
The lower or entrance floor of Saltwood Gateway has considerable strength; it is
flanked by two circular towers, which contain hexagonal apartments.
From out to out this gateway measures 56 feet 6 inches, and the space between the
towers is 12 feet 2 inches. The entire depth, from the face of the wall between the towers
to that at the rear, is 56 feet 6 inches.
The floor above contained many convenient apartments, admirably proportioned, and so
arranged as to be used for defence when occasion required. Each of the towers had a
chamber, 13 feet 2 inches in diameter, lighted by two narrow windows, between which was
a fireplace, the flue being continued to the summit of the tower.
A spacious room, 29 feet by 17 feet, and another 16 feet by 15 feet, occupied the space
over the gateway; the walls are 5 feet in thickness, except where the towers unite with the
straight portions, and there is a square mass of masonry and rubble, solid throughout,
except where hollowed out for the purposes of obtaining a guard room, 8 feet by 4 feet.
Bridges. — We have no evidence of any bridges of consequence being erected previous to
the Norman conquest, and the names of our principal towns on the banks of rivers, having
the word ford attached to them, seems to confirm the opinion that none existed. Following
the course of the Watling Street, or great Roman road over the Medway, we meet with
Aylesford; over the Darent, Dartford; the Cray, Crayford; the Ravensbourne, Deepford ;
and so with most other rivers in England. The capital in all probability would first have
a bridge in preference to a ferry, which is noticed over the Thames. We have an account
of a timber bridge constructed by Etheldred in 1002, which lasted many years, and also of
another built in 1165.
The first stone bridge was begun in 1176, by the celebrated Peter of Colechurch, who
continued the work during the reigns of Henry II., Richard I., until the second year of
the reign of King John, when he died, and was buried in the crypt of the chapel erected
over the centre pier.
It appears to have been the custom with the society called the Brothers of the Bridge,
when any member died during the superintendence of any important work, to have his
CHAP. VIII.
413
BRITAIN.
remains entombed within the structure; and as all great bridges were provided with a
chapel and crypt, every means was afforded for the performance of the annual rites that were
usually instituted. The great bridge at Avignon, when built by S. Benezet, or Johannes
Benedictus, the first brother and founder of the order, had such a chapel, where he was
buried in 1222.
At the death of Peter of Colechurch, the work was not delayed; another brother, of the
name of Isembert, master of the fraternity at Xaintes, and who had recently completed
bridges at that place and Rochelle, was appointed to carry it on; in a few years the bridge
and its chapel were entirely completed; the latter he endowed with two priests and four
clerks, constantly to perform service therein. The chapel was dedicated to St. Thomas of
Canterbury, and contained a table, on which were inscribed the names of all the lands and
gifts given for its support.
This stone bridge was 926 feet in length, 15 feet in width, and 60 feet in height above
the level of the water. It contained a drawbridge, and nineteen broad pointed arches, with
massive piers, varying in solidity from 25 to 34 feet, raised upon strong elm piles, covered
with thick planks, bolted together.
The breadth of the first arch on the city side was 10 feet, the second 15, the third 25, the
fourth 21, the fifth 27, the sixth 29 feet 6 inches, the seventh the same, the eighth 26 feet,
the ninth 32 feet 9 inches, the tenth 25 feet 6 inches, the eleventh 16 feet, the twelfth
24 feet 6 inches, the thirteenth 25 feet 8 inches, and the breadth of the drawbridge, or
fourteenth arch, 29 feet 4 inches. The breadth of the chapel which stood on the centre
pier was 20 feet, and its length 60. Mr. George Vertue engraved this bridge and its
stately chapel and crypt, and published them in 1748; after his death his widow presented
the plates to the Society of Antiquaries.
The water-way between the piers was not more than 336 feet 9 inches, and if we make
some allowance for the footings or increased size of some of the starlings, we shall find that
nearly two-thirds of the stream was occupied by piers, and only one-third allowed for
water-way.
When the bridge was demolished, the tomb of Peter of Colechurch was found embedded
in the tenth pier from the city side; it was 7 feet in length, 30 inches wide, and 24 in
height; it was also discovered that the piers were formed upon piles driven into the bed of
the river, cut off at low water-mark, with a filling in between the heads of stone and chalk :
on the top of the piles blocks of Kentish rag were bedded in pitch.
The Traitor's Gate, at the north end, was built about 1426; in 1437 the great stone gate,
on the Southwark side, fell into the river, and according to Stowe destroyed two of the
arches adjoining.
Monnou Bridge, over the river of that name, where it joins the Wye at Monmouth, as it
existed some years ago, was a fine example of a fortified bridge; the arches were constructed
much in the same manner as the severy or division of a cathedral church; ribs were framed

Fig. 413.
MONNOU BRIDGE.
IINI
ނ
--
from one abutment to the other; after they were gathered over, and united at the top of
the vault, the spaces between were filled in with masonry; the whole bore some resem-
414
Book 1.
HISTORY OF ENGINEERING.
blance to a work in carpentry, and though executed in stone could only be deemed the
centre or contrivance on which was laid a bed of beton or concrete, which hardened into a
mass, and formed the solid construction of the bridge. The mason and carpenter during
the middle ages employed the same principles; wood and stone were often treated in a
similar manner, and the same mouldings and forms were given to both, without reference
to their different qualities.
Bishop Auckland Bridge over the Wear, erected in 1388, has two segmental arches, the
largest of which spans 100 feet 5 inches, and has a rise of 22 feet; the other has 91 feet
5 inches span, and rises 20 feet. Each of these arches is built of three rows of voussoirs,
22 inches in depth: this example is, perhaps, the earliest in England where the segment
was introduced. The three rows of voussoirs performed the office of as many ribs, and by
this arrangement a simple centre might be made to serve for the execution of the whole.
There are several small bridges remaining, in which the Gothic ribs are admirably pre-
served; that which crosses the moat at the palace at Eltham is a fine example: another
over the Darenth at Eynesford in Kent, though small, is a good specimen.
Rochester Bridge, Kent. In a line with the principal streets of Rochester and Strood
formerly stood a wooden bridge, which is mentioned as existing at the commencement of
the 13th century. Lambard, the historian of this county, has given several regulations for
its repair, copied from manuscripts in the library of Rochester Cathedral, which were
collected by Bishop Ernulphus, who was elected to that see in the year 1115.
From these ancient writings we learn that the bridge consisted of nine stone piers,
placed at equal distances, and the width of the river was 26½ rods, or 440 feet, nearly the
same breadth as it is at present.
These ten divisions were each 43 feet from the centre of one pier to the centre of the
other, so that the cills or beams were 43 feet long; and each bay had three of these timbers
to make out the width of the bridge. Across these beams were thick plankings, probably
about 10 feet in extent. It would appear that the sides were not protected, as in the
Registrum Roff. mention is made of a rash young man, son of Earl Aufrid, who, in the
reign of Edward I., not alighting from his horse, as was customary, when passing the
A wooden
bridge, the beast took fright, leaped into the river, and both were drowned.
tower, constructed with marvellous skill at the east end of the bridge, was used as a gate as
well as a defence.
This bridge was probably erected at the cost of the proprietors of the manor, who after-
wards kept it in repair. The manors are all mentioned, and two of the holders were
annually elected as wardens and overseers of the bridge.
This wooden structure was burnt in 1264, by Simon Montfort, Earl of Leicester, but
the timber work was soon after restored, for in the year 1281 we find, that after a severe
frost, the ice struck with such impetuosity against the stone piers, that some of them were
swept away, and the others much damaged; in this state it was left until the reign of
Edward III., when it was again put into repair.
Sir Robert Knolles, after his return from France, where he had attended Edward III.,
in all his successful campaigns, founded a stone bridge at his own cost, probably about the
year 1387, for it was completed in the fifteenth year of Richard II., as appears by a statute
made "for repairing and supporting the new stone bridge of Rochester," which is stated
to contain more in length than the old bridge. The sum of the various portions allotted to
the places and manors for the repairs in future amounts to 566 feet, 1 inch. This
bridge was considered one of the finest at that time in England; the breadth was 14 feet;
it had stone parapets and eleven arches, resting on substantial piers, well secured on each
side with starlings. At the east end, and fronting the passage over the bridge, is a chapel
which was erected by Sir John de Cobham.
It appears that after this bridge was completed over the river, at about 40 yards
higher up the stream than the old bridge, it was enacted by two statutes, one made in the
fifteenth, and the other in the twenty-first year of Richard II., that it should be repaired
by the manors and places there specified. The statutes also enact that the persons,
manors, places, and bounds, should be considered as a community, and that they should
choose two men annually, who should be called wardens, and have the superintendency
of, and provide for the repairs of the said bridge. It also allowed them to purchase lands
to the amount of 2001. per annum, and to hold them as wardens of the said bridge; they
were to be accountable to auditors to examine the receipts, disbursements, &c.; and in the
ninth year of Henry V. a statute was made confirming the two former acts, and allowing
the wardens to have a common seal, and to plead in any court by the name of the War-
dens of the New Bridge at Rochester.
Sixty years after it was finished, it required some repair, which was partly done by the
prior and convent of Rochester, assisted by Henry VI.; and in the year 1489, John
Morton, Archbishop of Canterbury, published a remission from purgatory for forty days
of all manner of fines, to such persons who would give any thing towards the repairs, as at
that time the bridge was very much broken.
CHAP. VIII.
415
BRITAIN.
Lambard says that in the time of Elizabeth, the revenues were converted to private
uses, and that the county was charged with a toll, and fifteenth, to supply the public wants;
yet the bridge went out of repair, and was threatened with absolute destruction.
Sir William Cecil obtained from Queen Elizabeth permission for certain knights and
gentlemen of the county to examine and report upon the defects, and a statute was passed
in the eighteenth year of that queen's reign, for the perpetual maintenance of Rochester
Bridge. Another statute, passed nine years after, makes some further provisions, the
former funds proving inadequate. About the middle of the eighteenth century three of the
arches were rebuilt, and the approaches greatly improved, out of the funds derived from the
estates belonging to the bridge.
Timber bridges of very simple construction were long made use of over the wide rivers
in England, but no skill was exhibited in the framing, nor any further mechanical principle
than that of strength; trees merely squared, were laid side by side, at right angles with the
stream, supported on a single row of perpindicular piles, or several rows parallel to each
other, capped and cross braced, and sometimes planked over to the height that the water
rose, the space between being filled in with stones. The roadway was cross-planked,
covered with chalk and gravel, and frequently required repair, in consequence of the air not
being admitted to the upper side of the planking.
Battersea Bridge over the Thames, nearly 900 feet in length, still remains an example of
such rude and primitive style of construction, and several others might be named.
Croyland Triangular Bridge is alluded to in a charter of the year 943, under the title of
"The Triangular Bridge of Croyland," and though the present structure does not warrant
so early a date being assigned to it, the construction is nevertheless curious; its style belongs
to that in use at the commencement of the 14th century.
This bridge is situated on the west side of the abbey, at the confluence of three streams,
the Welland, the Nyne, and the Catwater or Catch-water Drain, all which unite and pass
under it, and proceed thence by Spalding to the German Ocean. Three pointed arches,
having their bases or abutments placed on the points of an equilateral triangle, meet in the
middle, and thus form three distinct watercourses, as well as three roadways; the singu-
larity of its arrangement has always made it an object of the greatest curiosity, and it is,
perhaps, unique as a specimen of bridge building, though its utility is somewhat destroyed
by the steepness of the ascent, which is almost too great for horses.
Each arch has three stone ribs, and the whole nine meet together in the centre; the
bridge is of stone, and had it not been raised on such lofty abutments, long ere this the
torrents which flow occasionally under it must have swept it away; the roadways are paved
with pebbles, and have more the character of steps, so that carriages generally pass under,
and not over it; the construction is thus rather calculated to excite wonder for its pecu-
liarities, than admiration for its utility. When Croyland was established, and the arts began
to revive in Europe, we find the same skill evinced in the construction of bridges,
so necessary for the security and convenience of the neighbourhood, as in the religious
edifices themselves, and this might have arisen from the example set by the fraternity before
alluded to, the Order of the Brothers of the Bridge. Croyland Abbey, which is near the
bridge, was situated in a morass, and the foundations of its stone church were laid, according
to Ingulphus, who was abbot at the commencement of the eleventh century, on innumerable
large timber piles, driven into the ground, the softer parts being covered with earth brought
in boats from a distance of several miles.
Bridge over the Ouse at York, taken down some years ago, was remarkable for the span of
its pointed arch; it was constructed in the reign of Elizabeth. The chapel and abutments
were probably built before the commencement of the thirteenth century.
Laythorpe Postern and Bridge belong to the same period; the tower had gates defended
by a portcullis.
Many of the chapels constructed in bridges during the thirteenth century, like this
example, were rich in architectural embellishment, and endowed with estates of considerable
extent for the maintenance of the bridge, and for the support of the priests appointed to
perform the service within them. The chapel sometimes occupied the middle pier, and
each extremity of the bridge was protected by a machicolated and strongly embattled
gateway. The chapels were usually dedicated to St. Nicholas, he being the patron saint
of sailors, and the Brothers of the Bridge scarcely ever terminated their work without
creating some memorial to this favourite saint, or votive offering to that Holy Spirit which
presided over them and their designs.
The bridges being very narrow, it was necessary, as the use of wheeled carriages became
more general, to destroy these highly ornamented and picturesque structures, to obtain a
convenient access to the cities and towns with which they communicated. The passengers
seated on the roof of the mail and ordinary coaches could not pass without danger under
the arches of the gateways, and where it was not practicable to turn the thoroughfare, they
were necessarily demolished.
It would be an endless task to enumerate all the bridges erected in England by the free-
416
BOOK I.
HISTORY OF ENGINEERING.
masons of the middle ages; many were built, as has been observed, in the same manner as
the vaults of the chapter houses and cathedral churches; after the piers were carried above

注
​"IHE
Fig. 414.
OUSE BRIDGE, AND ST. WILLIAM'S CHAPEL, YORK.
the level of the stream, ribs of stone spanned the opening from one pier to the other, and
supported a rubble construction laid above them, an arrangement combining both economy

Π
Fig. 415
OUSE BRIDGE, AND ST. WILLIAM'S CHAPEL, YORK.
and convenience. In subsequent instances we see one or more rings of voussoirs spanning
a river, upon which slabs of stone are laid, and the bridge completed; but it must be borne
in mind that such ribs simply serve the purpose of centres, and cannot have the strength
of our modern bridges, where a wedge-like form is given to every portion of the stone.
Between the towers of Lincoln cathedral, and above the vaulting, is a stone girder, com-
posed of numerous voussoirs, arranged within the segment of an arch, whose radius is
91 feet; the abutments are extremely solid, and the girder, which exhibits a horizontal
surface above and concave below, is about 20 inches deep at its abutments, and 11 inches in
CHAP. VIII.
BRITAIN.
417
the centre; the shallow depth given at the key proves that there strength is not required,
so long as the extremities are well maintained in their position. The arrangement of the
stones, as in this curious girder, is a strong proof that at its introduction the theory of the
arch was understood, and, its use not being apparent, we are tempted to imagine that it was
so placed as a model for study, and an evidence of its practical strength.
After the reign of Henry VIII. bridge-building underwent a considerable change;
timber constructions again became very common, and some of the principal rivers were
crossed by them. In the year 1636, Inigo Jones erected a bridge at Llanwast in Den-
bighshire, after the method practised in Italy, which was the model for some of the suc-
ceeding structures.
It was formed of three segmental arches, the middle spanning 58 feet, with a versed sine
of 17, and the breadth of the soffite of the arch 14 feet. The depth of the voussoirs,
measured on the face, was 18 inches, the piers were 10 feet in thickness. The pointed arch
was no longer used, and the defences of towers and gateways were unnecessary: the passage
was made more convenient, and the roadway approached a horizontal line, in consequence
of the substitution of vehicles for the pack-horse for the transit of merchandize.
At the commencement of the eighteenth century we find evidences of an attempt to
improve the bridges throughout England, but there is no account of any principles by
which the engineer could be directed, nor are there any names upon record to whom such
constructions were particularly entrusted; what had been done in Italy does not seem to have
found many imitators here, and though Newton had discovered the principles upon which
mechanical science was based, it was long before the equilibrium of the arch occupied the
consideration of practical men. Dr. Hooke had, however, drawn attention to the figure
which a heavy chain or rope assumes when suspended at the two ends, and shown the pro-
perties of the catenaria; but it was not then applied to the construction of bridges.
One of the first essays on the subject was written by Isaac Gadsdon, and published in
1739; he sets forth very clearly the nature and properties of arches, mechanically considered,
with respect to their shape and duration; and, as this essay is interspersed with some
remarks on the intended bridge at Westminster, some portion of its contents may be in-
teresting as evidences of the state of knowledge on this subject at the period he wrote.
By the word arch is to be understood some regular curve or crooked line, which, when
applied to practice in building, is always put with the convex side uppermost, in order to
support some weight. But without the abutments it would not support itself, for the
action of gravity pressing upon it would soon tumble it down; and if a flexible or mal-
leable body, would soon reduce it to a straight line. From hence it is plain that the
strength of all arches depends upon the abutments, and that dependency is in proportion to
the height they rise from the chord line of their respective arches.
"The truth of this will plainly appear by setting up two pieces of wood in the shape of
levers, one against the other, in the nature of a pediment. The pediment requires a greater

A
Fig. 416.
0
e e
a
B
C
Fig. 417.
weight or resisting power, to be
placed at the foot e, e, to keep it
from falling in the arch A, than in
the other; therefore the arch B
will support a greater weight
than the arch A, if their abut-
ments are equal. The reason of
this is, that the lines a, a, are
nearer a perpendicular than the lines o, o, for if those before-mentioned pieces of wood were
placed perpendicular one against the other, with a hinge at the top, and wheels put in the
bottom, for the sake of experiment, to take off the friction, they would in that position want
no abutment to keep them together at bottom; but if they are a small space asunder at
the bottom, they will want an abutment to keep them in that position, otherwise they will
run one from the other, and the further they recede from each other, the greater must be
the resisting power or abutment be to keep 10 9 8 7 6 5 4 3 2 1

them from falling. From what has been
said, it appears that gravity acts on these
two levers, according as they are elevated
or depressed, and if so, it must be in some
proportion, which proportion may very
nearly be determined by the following
figure G, where the theory depends upon
that of the steelyard, which, for the better
understanding of what is to follow, I shall
endeavour to explain by the figure E
"Let the line cand o represent the beam,
and O the centre of a pair of steelyards,
2
G
א
Fig. 418.
4 5 6 7 8 9 10
and suppose two weights, as n and r, were to be hung at equal distances from the centre
E e
418
BOOK I
HISTORY OF ENGINEERING.
.
E
b
a
2
3 4 5 6 7 8 9 i
C
d
Fig. 419.
But
O, and the other part of the beam cut off, they would
then hang in equilibrio, that is, n and r would be equal.
But if the other part of the beam was to be added, and
the weight n was carried on the beam as far as the
number 10, and suppose the weight was but one pound
each, then I say that the weight r must have 9 pounds
added to it to make it balance the weight n, when re-
moved so far from the centre. But here it is necessary a
to observe, that in making these instruments, the weight
that is occasioned by the length of the beam is always
accounted for before they begin to divide, and it is very
easy to discover what weight did belong to a pair of
steelyards, supposing it to be lost, by taking the dis-
tance between the centres of the hooks, that is, between
O and r, and apply it to the proper edge, and the di-
vision there will tell you what the weight should be,
for it is that distance multiplied into the whole length, as you may see in the figure.
here in this present case the beam is only imaginary, for it is the distance from the centre
that occasions all those different gravitations, for if we suppose the circle a, b, c, d, to be a
wheel, and o its centre, and a weight of one pound to be fixed at its periphery at b, and the
wheel to be turned round, the weight when it is got to a will be 3 pounds, and at z 5 pounds,
and the gravitation of such a weight will increase in the same proportion as if it was carried
along the beam e, as you may see by the divisions. By this useful instrument may also be
discovered the power of the lever, from a perpendicular to a horizontal position, and may
very justly be called a scale, to measure all mechanical powers that act from centres, and
notwithstanding our present subject be two levers set up one against another, yet I believe
the next figure will make it appear very plain that they also depend on the same theory,
and are subject to the same laws of gravitation. For as the two levers a, a, in the figure G,
support one another at the top, and prevent their falling or acting like levers, yet I conceive
that gravity will act on the bottoms, when the friction is taken off by wheels, in the same
proportion as if they were turned end to end, according to the left hand side of the figure G
when turned upside down, that is, to put the confined end downwards, and let the upper
ends fall one from the other: I say, in the fall of such a lever, the gravitation would be
increased in the same proportion as is there set down, for if the lever a, by falling from the
perpendicular line G, should have gained a force of 1 pound, it would at e have gained
3 pounds, at z 5 pounds, and so on in proportion, as was gained by the weight at the peri-
phery of the wheel in figure E, until it becomes horizontal. In the same proportion I
conceive gravity to act at the bottom of the two levers, a, a, that is, if at a they should want
an abutment of 1 pound at each foot to keep them in their position, at e they would want
3, and at z 5, and so on in the same proportion, as they are set down in the right
hand side of the figure G, until they become so far extended, as to lie level on the plane they
moved on: from what has been demonstrated from figure G, it is plain that gravity acts on
pediments, according as their sides are elevated or depressed; and if so, it must certainly
act on all arches in the same proportion, as their inscribed pediments are to one another in
respect to their height. And from hence may be discovered how much weight one arch
will bear more than another that is the same width, and hath the same abutments to support
it; that is, if the lower arch D will bear
500 pounds weight, the arch a will bear
600, and the arch b 700, and so on ac-
cording to what height you rise may
the weight be increased, which will
always be in proportion, as the sides
of the inscribed pediments are to one
another, when their chord lines or
widths are the same. Notwithstanding
I have given this method to show how
much one arch will bear more than
another of the same width and abut-
ment, yet I do not pretend to know


1
b
2
3
D
6
Fig. 420.
how much weight any arch will bear, for there is no arch that I know of that can be said
to bear all the weight that is built perpendicularly over it, because that part hath commu-
nication with the rest of the building, and cemented to it in such a manner, that takes off a
considerable part of the weight that would otherwise press upon it if that communication
was destroyed; and I may venture to say, that it is from this reason that arches some-
times become so loose, that their keystones are almost ready to drop for want of sufficient
weight to keep their parts together. From this observation it is plain that all arches want
CHAP. VIII.
419
BRITAIN.
a weight proportionable to the height they rise, to keep their parts firm in the situation
they are first placed, for it is very reasonable to think, that the arches of London Bridge
would not have remained so entire to this day, if it was not for the weight of houses that
are erected thereon, which must certainly prevent those frequent shocks and shakings that
it must otherwise have suffered, by loaded carts and cars, and other vehicles of burden, that
daily pass and repass thereon.
A
"But to proceed to make some observations on the shape of arches in respect to their
duration. I think the most common sort that are to be found amongst our modern
buildings are either semicircles, segments, or semi-ellipses, which I must own have an
agreeable effect on the eye, because they are part of regular figures, and make a good ap-
pearance in a building if they are well proportioned and well introduced; but this is not
always observed by our modern builders, for I have often seen a passage of 3 feet wide with
a semicircular arch, and a gateway of 10 with an elliptical one, whose height from the
springing hath not exceeded 20 inches; such a one cannot be supposed to be of any long
duration without very strong abutments, unless the weight be discharged by a concealed
breastsummer, or very little laid thereon: in such cases ornament is consulted more than
strength, for the arch of 3 feet being a semicircle will bear above ten times more weight
than the elliptical one of 10 feet with the same abutments, by reason of its flatness and
double centres, which must render it very weak and unfit to support a great burthen, I
mean such an ellipsis whose transverse diameter is placed bori-
zontal; but if you take an ellipsis the other way for an arch, and let
the conjugate diameter be horizontal, then it will become altogether
as strong, and may very justly be esteemed the best sort to support
a great burthen, excepting those formed by the catenarian, which I
shall endeavour to prove the strongest of all, and the most durable.
But for the truth of what I have asserted in respect to the elliptical
arches, I must refer to a very easy and familiar experiment, which
is, to take an egg, and try whether it will not bear a great deal
more weight on the ends than it will on the sides before it burst;
such an experiment seems to me to put this matter out of the reach of contradiction, and
will justify the theory I have hitherto endeavoured to explain, namely, that all arches will
bear a weight proportionable to the height they rise from their springing, if their chord
lines or openings are the same, let the shape be what it will, although it must be allowed
that some sort of shape will bear more weight than another of the same height and abut-
ments; for if the elliptical arch was a segment of a circle of the same height, it would add
much to its strength, by reason that a curve would be more uniform, and approach nearer
to a catenarian than it was before, in the flat elliptical form, for it is my opinion that the
strength of all arches would be increased the nearer they approach that firm arch of nature,
for so I must call it, by reason it is formed by action of gravity, which must be allowed to
be a natural cause.

B
Fig. 421.
“This curve or arch may be discovered by suspending a chain, or flexible line, that is not
very light, from two horizontal points or nails; the curve or arch that such a line or chain
will form is called the catenarian. This line, as I before observed, is formed by the action
of gravity, which acts on all bodies according to their density or quantity of matter they
contain, if their form and shape are the same; therefore, if gravity by its action on a slack
line or chain form the arch a, it is very plain that if it were turned
upside down it would form the arch K, which, consequently,
must resist that action in the same proportion as the other gave
way, that is, K would become an arch of equal strength in all
its parts, and for that reason must be certainly the best shape
for any arch that is to bear a great burthen.
D
K

A
Fig. 422.
"But as the properties of the catenarian arches are so far con-
cealed that it would be very difficult to assign any centres that
would strike the same, for if they are very flat they appear like
segments of large circles, but if you endeavour to form a semi-
circle by letting the line drop half its opening, it will then appear
elliptical, and as you drop it lower, it seems to approach the
hyperbola, so that the distant appearances it makes in these dif-
ferent stations must render it very difficult to find out proper centres to strike them out.
But those that have occasion to apply them to practice, may observe the following method,
which may answer the purpose very well if it be carefully observed, that it is to take such
a line as before mentioned, and rub it with chalk or charcoal until it be fit to leave an im-
pression; then, on some flat plane or board that is large enough for the use, fix in two nails
horizontally, according to the width or span of your arch, and from thence let the line fall
as far below the horizontal line as you would have the arch to rise above it; then carefully
press the line hard enough to leave the impression, and that will be the arch required then
·
EE 2
420
Boox I
HISTORY OF ENGINEERING.
G
2
C
X
move the nails from o to K, according to the
margin you intend to show in the front, and K
from them let fall the arch m, and that will limit
the border or margin, which may be divided, and
a mould made to fit the curve in the same manner
as if the arch was in any other form, as you may
see in the figure, which in practice must be turned
upside down; but, as I observed before, that the
lower the line was let fall, the nearer it approached
an hyperbola, therefore it cannot be expected that
the lines n and m will be parallel or appear con-
centric like arches struck from the same centre,
but those that should think it disagreeable for the margin of an arch to be wider at top,
may easily prevent it by making the moulds parallel to the inward arch, which would be a
matter of indifference in respect to its strength.

1?
Fig. 423.
"But, notwithstanding all those distant appearances before-mentioned, that are made by
the catenarian line, yet I cannot help thinking that they are all of the hyperbola kind, for
as the hyperbola is that section of the cone cut any where when parallel to its axis, I say
that it is no hard matter to imagine a cone large enough that will admit of the flattest as
well as the highest arches to be cut off by such a section; now, I believe it will appear
from what I have already said, that catenarian arches are the best shape for duration, and
for that reason the most proper form for the new bridge on the river Thames, if it be built
with stone.
"A cask or tub may very justly be said to have the same properties as an arch, for the
staves may be considered as so many stones, whose joints point to one common centre, and
the hoops that circumscribe them as their weight or pressure; then I think it cannot be
denied that the tighter these hoops are drove on round such a vessel, the more compact it
must keep the staves, and the stronger the vessel will be for such a weight or pressure;
therefore it appears to me that weight on an arch will have the same effect as a hoop hath
on a tub, if the weight be well proportioned.
"But in order to give my opinion in this affair, the actions of gravity on solid bodies ought
to be understood, and the shape of the arch well considered before a judgment can be formed
about the weight it will carry, or on what part to bestow it to the best advantage; therefore
I shall lay down the following theorems:
"I. When any weight presses on the sides or haunches of an arch, the weight on the
crown must be considered as an abutment to that weight on the haunches, and in proportion
to the height they rise from the chord lines of their respective segments will the weight on
the crown be required.
"II. And as the weight on the crown is an abutment to the weight on the haunches, so is
the weight on the haunches an abutment to the weight on the crown.
"III. And as the weight on the haunches wants to reduce the curvature thereof to a
straight line, contrary to that doth the weight on the crown want to make it rise higher or
push it out at foot, if there is no abutment placed there to prevent it, and both would
produce that effect if it was not for a counterbalance of power, as will be best explained by
the following figure.
d
b
10 9 8 7 6
5
"If the segment aec will bear five hundred weight, the semicircle a b c will bear six with
the same abutment, and the cate-
narian a dc will bear the weight in
respect to the abutments below, but
if they are both considered as having
no weight on their haunches, the
catenarian must be the strongest by
reason that the curvature of its
haunches are nearer a right line
than those of the semicircle, for was
there as much weight laid on the
crown of the catenarian arch as it
would just bear, the same weight if
applied to the semicircle would
occasion it to burst out and fall
down, which plainly sheweth that
the semicircle wants a greater weight on its haunches to counterbalance the same weight on
the crown; and how much more weight is required on the haunches of the semicircle to
counterbalance the same weights on the crowns of both may be nearly discovered by the
same method, for drawing the chord line o, will cut off one haunch of both, which may be
considered as whole arches, and the difference of weight be discovered in the same manner,
for if the haunch of the catenarian requires nine hundred weight, the semicircle will require

α
6
5
4
3
2
1
с
Fig. 424.
CHAP. VIII.
421
BRITAIN.
ten, to enable it to support the same weight on the crown as the catenarian, and the haunch
of the segment aec is likewise subject to the same rule, and requires but seven, by reason
the haunch is not so much elevated, which gives the weight a greater gravitation.
"In like manner may the difference of weight be discovered in any two arches, which will
always be in proportion as the chord lines of their respective segments are to one another,
or in proportion as the sides of the inscribed pediments are to one another, which implies
the same thing. To shew the application of the steelyard to the nature and properties of
the arch, let a b c represent the arch proposed: now if we suppose that the half arch
bc was in one stone, and its weight 28 tons, and that it was by some power to be lifted
upon its pier w, until it come to its centre of gravity, which may be supposed to be at d,
then it is very plain that the pier must bear all its weight, and if from thence it was to be
let down to a horizontal position as at x, and a support put under the end at o, the
support o would bear 141 tons, and the pier w would bear the same weight; and was it from
thence to be lifted up to its proper place at B and there supported, then will the pier w bear
201 tons, and the support at B bear 84 tons, for the end B being elevated, the support o is
released of 6 tons weight,

which consequently must be
added to the pier, for as this
half arch is supposed to be in
one stone, it may be considered
as a lever, and be subject to the
same laws of gravitation as hath
before been demonstrated, and
may be explained by the
figure.
"This method seems to me to
give some insight whereby the
real weight of the abutments
may be discovered; for if the
support o was taken away, and
the other half arch, A B, was
set up against it, in its proper a
position, that must certainly
throw the whole weight of both
on their respective piers; but
as A B is set at the same angle
A
1
B
----
38
28
O
21.
14
7
Fig. 425.
n
as B C, they would thrust each other down, if there was not an abutment placed at A and
C to prevent it. Now, if we consider that before A B was set up against B C, the
support o supported 81 tons, the thrust of AB must be equal to that weight, if there
was no friction at c; and if so, it appears very plain to me, that a weight of 8 tons,
placed at A and C, will be a sufficient abutment for the arch, A B C; for as such a
weight is a counterbalance to the thrust, there will be the friction of A B C on the
piers, for a further security; which, considering the great weight of A B C, may perhaps
be equal to 2 tons more, but this must be referred to experiment.
"And if the arch A B C was to be considered in parts as the half A B, the weight
or pressure would still be the same; for drawing parallel lines, from the joints to the
chord lines, plainly sheweth how the weight is diminished, as appears by the figure. By
what I have endeavoured to demonstrate, it appears very plain, that the centre which is
to support the arch, A B C, will be released of 12 ton weight, in the thickness of the
whole breadth, which is supposed to be 40 feet, and the number being multiplied by 12,
the product is 480, which being deducted from 2320, which is supposed to be the
weight of the whole, the remainder is 1840, which will be nearly the weight, when
that of the key-stone is deducted out, that will lie on the centre, before it can be relieved
by the keystone. How much of the spandrills' weight will press on the arch is very diffi-
cult to discover, because it hath a communication with the upper pier or breast-work,
which takes off a great deal of the pressure; but if that communication be destroyed,
and it be considered as one stone, and no friction on the arch, it could then be only
said to lean on the arch, and what weight that leaning is may in some measure be dis-
covered by the same rule as the former; that is, to draw a line as d, in such a manner that
if the spandrill was lifted up on its lower point, until that line become perpendicular, it
would then be the centre of gravity, and if the line d was continued to cut the arch P,
and from thence let fall a perpendicular to the chord line, which if divided according to the
weight of the whole spandrill, it will give the weight that will press on the arch if the line
d be so drawn as the quantity of matter on both sides are equal, which ought to be regarded
in the half arch, B C, as well as in the present case.
"This method will not exactly discover the weight or pressure of any arch, but it will be
EE 3
422
Book 1.
HISTORY OF ENGINEERING.
near enough, I believe, to let a man know what he is about when he either designs or
erects one.
"In respect to arches, their strength doth not so much depend on
their shape, as the weight they bear being well adapted to them; for
although it must be granted that catenarian arches, if considered inde-
pendent of any weight but their own, are the strongest of all others, yet
if the weight on their crowns is not proportionable to the height they
rise, they may be said to be weaker than a semicircle, or arches of any
other form, when their weight and abutments are well proportioned."
Westminster Bridge was the commencement of an entirely new system
for laying foundations in deep water, as well as the construction of
centres for arches required to span great rivers. An act of parliament
for its erection was passed in 1736, and another fixing its site, two years
afterwards. The first design was a curious wooden structure, by Mr.
James King, resting on stone piers.
The two large middle piers were contracted for soon after, and the
wooden superstructure was to have been placed upon them and com-
pleted in a year after all the piers were finished, for the sum of 28,000l.
Mr. Charles Labelye, a native of Switzerland, presented to the com-
missioners, in 1738, a design for a stone bridge, which was approved of,
and preferred to many others, and it was resolved that the piers should
be erected as high as the springing of the arches, viz. about a foot above
the level of low water mark, and over these broad piers, smaller ones of
solid stone, each to be the width of the bridge in length.
The design for the stone bridge consisted of thirteen semicircular
arches, springing about a foot above the level of low water mark; the
middle arch 76 feet span, and the others decreasing in width equally on
each side by 4 feet, the two next the middle arch being 72 feet wide,
and so on to the least of the large arches, which are 52 feet wide.
two small ones nearest the abutments are 25 feet wide.

The
The length of every pier is 70 feet from point to point, and each end
terminates with a salient angle. The two middle piers are 17 feet
wide at the springing of the arches, and the others decrease in breadth
equally on each side by 1 foot, the two next the largest being 16 feet
wide, and so on to the two least of each side, which are 12 feet wide at
the springing of the arches.
The piers are 4 feet wider at their foundations than at their top, and
each of them is laid on a strong grating of timber, the same shape as the
pier, about 80 feet long, 28 feet wide, and 2 feet thick.
The depths and heights of every pier are different, and none of their
foundations are at a less depth than 5 feet under the bed of the river,
nor at a greater than 14 feet. This difference of depth is occasioned
by the nature of the ground, for although all the piers and abutments
are laid on a bed of gravel, which on boring was found harder as the
depth increased, it was still more difficult to penetrate on the Surrey
side than on the Westminster.
In July, 1738, Labelye, with a company of London masons, arrived at
the Isle of Portland, and commenced quarrying and working into proper
scantling all the stone necessary for the two largest piers. About the
same time the carpenters began to make and erect on the Surrey
shore twelve frames of timber, supported in a vertical position,
parallel one to another, and kept in their proper places by short piles
driven into the ground. These frames reached about 2 feet above the
common high water mark, and were braced together so as to be kept
upright and steady, till the caissoon should be formed and finished on
the top of them. The ground sills or bottom pieces of these frames
were made cylindrical, that by taking the braces away they might serve
as so many axes or centre pieces, round which the frames could revolve
all together, for the lowering or launching of the finished caissoons at
high water without danger of racking or straining.
In September the engine for driving the piles, which was contrived by
Mr. James Vauloüé, a watchmaker, was completed, and on the 13th of
that month the first pile was driven.
WESTMINSTER Bridge,
Fig. 426.
The piles were of fir, 13 or 14 inches square, and 34 feet in length,
shod with iron: round their tops were thick iron hoops, which were
taken off after driving, and used again; they were driven 13 or 14 feet
below the surface of the bed of the river, and were placed about 7 fect asunder, in lines
CHAP. VIII.
423
BRITAIN.
parallel to the two short sides of each end of the piers, and about 30 feet distance from
them; the use of which fenders or guard piles was to secure the works from the approach
of barges; the smaller boats were prevented passing between the piles by booms or long
pieces of timber, which floated up and down with the tide alongside the piles, to which
they were fastened by wooden rings, and proper iron work. By means of these booms
the boats and vessels were secured from damage during the progress of the works.
By the 26th of October, 1738, all the piles necessary for building the two middle piers
were driven, and were found to stand so firmly, that the plates, whale pieces, ties, and
braces, originally intended to

be introduced were omitted.
The number of piles used for
building the first large pier
was thirty-four long and
twenty-two short ones; and
for the other large pier
twenty-six long ones only.
The engine employed to
drive the piles had a ram or
weight of 1700 lbs., and the
height of the strokes at a
Fig. 427.
WESTMINSTER BRIDGE.
mean was 20 feet perpendicular: with two horses, it gave 48 strokes per hour, and with
three horses, 70 strokes per hour. When it had worked sufficiently long for the gudgeons

P
Fig. 428.
WESTMINSTER BRIDGE,
or pivots to be rubbed smooth, and the stiffness of the ropes destroyed, three horses, going
at a common pace, gave 5 strokes in 2 minutes, on the ram being raised from 8 to 10 feet.
At the commencement of October, the grating for the first pier was finished, and the
sides of the caissoon were placed upon it; these were made of fir timber, laid horizontally
and close, one over the other, pinned with oaken trunnels, and framed together at all the
corners of the caissoon, except the two points or salient angles, where they were secured
by proper iron work, which being unscrewed permitted two halves to be removed from the
caissoon, which were planked across the timbers, inside and outside, with 3-inch planks in
a vertical position; their thickness being 18 inches at bottom and 15 inches at top, and for
further strength, every angle but the two points had three oaken knee timbers, properly
bolted and secured. The bottom was formed of squared timbers, planked on the underside
with 3-inch planking, and across the upper was laid timber 9 inches square, making the
entire bottom 2 feet thick.
The length of each caissoon from point to point was 80 feet, the breadth 30, the height,
including the thickness of the bottom, 18 feet, and the form that of the intended piers;
it contained 150 loads of timber, and in capacity was equal to a man-of-war of forty guns.
After the pier was built sufficiently above low water, and the masons could work with-
E E 4
424
BOOK I.
HISTORY OF ENGINEERING.
out it, the wedges being drawn up, liberty was given to clear the straps from the mortises,
when the sides by their own buoyancy quitted the grating under the foundation of the pier.
The sides of the caissoons were prevented from being pressed inwards by means of a
ground timber or ribbon, 14 inches wide, and 7 inches thick, pinned upon the upper row of
timber of the grating, which exactly filled the space contained between the sides of the
caissoon and the first course or lower plinth of the stone pier; and the top of the sides was
secured by a number of beams laid across, which also served to support a floor, on which
the masons and labourers stood to hoist the stones out of the lighters, and lower them into
the caissoon.
In October the ballast men commenced making the excavation for the westernmost of
the two piers; when they dragged and excavated a pit 6 feet in depth, of the shape of the

Fig. 429.
WESTMINSTER BRIDGE.
caissoon, and 5 feet wider all around, with a slope of such a form that the ground would
not fall into it; short grooved piles, reaching 4 feet above low water mark, were also driven
before the two ends, and partly along the sides of the intended piers, parallel to the fenders

Fig. 430.
WESTMINSTER BRIDGE.
or guard piles, and at a distance of 15 feet from the sides of the caissoon, to prevent any
silting. Two rows of boards let into grooves were also applied between these piles.
Gauges formed of flat stones, 15 inches square, and 3 inches thick, with a wooden pole
CHAP. VIII.
425
BRITAIN.
or stem fixed in the middle, 18 feet in length, divided into feet and inches, were used to
examine the level of the bottom, and to ascertain if the bed was ready to receive the
caissoon.
The caissoon being finished, with a sluice towards the bottom, all the seams well
caulked, and the bottom and outsides pitched over, on the 15th January, 1739, it was
launched and fixed in its position, by means of a lighter that had been previously moored
200 feet distance from the shore; from the head and stern of which two cables passed to
the two ends of the caissoon, guiding its motion, after it was launched, without any person
on board to direct it.
The masons then began hoisting the stone into the caissoon, and as soon as the first
course was laid, the gate of the sluice was raised near the time of low water, and the
caissoon was sunk to ascertain how it sat and grounded. Some loose stones having fallen
in, the sluice was again shut, and after two hours' pumping, the caissoon floated; the
ground was again levelled, and two days afterwards it sunk to its proper bed when it was
a second time raised, and after the masons had cramped the stone of the first course, and
set and cramped the second course, the gate of the sluice was raised, and the caissoon sunk,
when it was found to bed itself, and set perfectly level on the hard gravel. The water was
then pumped out of it, and it floated as before.
The third course of stones being cramped, the caissoon was sunk for the last time; the
stone-work of this pier was brought up within 2 feet of the common low water mark.
About two hours before low water, the sluice was let down, and by the help of four pumps
of 8 inches square, three men to each, and a small spare pump of 3 inches in diameter,
worked by one man, the water was pumped out without waiting for the lowest ebb of the
tide, for the masons to set and cramp stones of the succeeding courses; before the tide had
again flowed or risen sufficiently high to endanger the caissoon and stone-work, the masons
desisted for that tide, and the sluice was again opened. By the masons working at every
low water, night and day, the first course of the solid shaft was finished by March 24th.
The sides of the caissoon were floated off over the sides of the pier on the 30th March,
and applied to the caissoon of the other large pier.
When this was done, the masons placed their crab or engine, with which they hoisted the
stone, on a temporary floor, fastened to some fender piles, which guarded the north point of
the pier.
On the 20th April the last stone of the torus or cordon was cramped, when the sheers
and the crab, as well as the other necessary apparatus were taken away, and the first pier
was so far completed.
This new method of building piers having succeeded so well, the commissioners con-
tracted for the two abutments, including the two small arches and the two abutment piers
close in-shore, and it was decided that the wooden structure might be dispensed with.
In April, 1740, the masons' work for the three middle arches was contracted for by
Andrew Jelfe and Samuel Tuffnell, who had already built the pier.
Mr. James King also contracted to supply the three centres, and subsequently five
others, his design for them being preferred by Labelye to his own.
The Portland stone was brought by sea upwards of 250 miles, and the Purbeck from
Sandwich in Dorsetshire, a distance of 220 miles. The moorstone was from Devonshire or
Cornwall, and the Kentish rag from Maidstone.
The soffite of every arch is turned, and built quite through, the same as in the fronts,
with large Portland blocks, over which, bonded in with the Portland, is another arch of
Purbeck stone, 4 or 5 times thicker on the reins than over the key.
The breadth of the Thames where the bridge is built is 1220 feet. The length of the two
abutments is 226 feet, the section of the twelve piers 174 feet, and the span or opening of
the thirteen arches 800 feet, the voids or water-way being double that of the solids.
The breadth of the bridge is 44 feet, which was also the clear width of way at the top;
the parapet walls being fixed over the sally or projection of a cordon or rustic cornice,
which serves also as a weathering to the stone work.
The road-way is 30 feet in breadth, and each foot-way 6 feet. Over each pier are
recesses for shelter. The piers are terminated by a right angle at each end. The spandrills
of the arches were filled in with regular rubble stones, with proper bond, and the joints of
the work preserve a tendency to the centre.
The entire construction of this bridge occupied 11 years and 9 months; it was completed
the 10th day of November, 1750, and the total sum expended upon it is said to have been
something under 400,000 pounds. Some delay occurred from the unequal settlement of
one of the piers, occasioned by the removal of some gravel from the bed of the river intended
for the roadway of the bridge; this took place near the third pier on the western side of
the centre arch; the gravel slipping from under the platform, in consequence of the hole
made below the foundations, the pier sunk so much that it was necessary to take down the
two arches which rested upon it.
On the pier being examined, it was found to have settled 18 inches at one end, and that
426
BOOK L
HISTORY OF ENGINEERING.
it was loaded with 700 tons; after casing it round with strong piles, to prevent a further
slipping of the gravel, it was taken down to the level of low water, and rebuilt; to lighten
the work which rested upon it, arches were constructed in the spandrills.
The
Bridge over the Taaf, near Llantrissart, in South Wales, was commenced in 1746 by
William Edwards, a country mason; it consisted of three arches, and was admirably
executed; two years and a half after its completion, it was carried away by a flood, and as
the builder had engaged to maintain it for seven years, he commenced rebuilding it.
second bridge was of one arch, the span or chord of which was 140 feet, its height 35 feet,
the segment being that of a circle of 175 feet; the breadth is 15 feet, and the thickness of
the arch 2 feet 6 inches. When completed, with the exception of the parapets, the
thrust was so great that it pressed in the haunches, and the middle of the bridge sprung
up, when the key-stones were forced out. This second misfortune did not quell the
courage of our mason, and he undertook his task a third time.
In each of the haunches he introduced three cylindrical holes through the whole thick-
ness, and by this means so reduced the weight that no farther danger was anticipated. The
holes or cylinders rise above each other, ascending with the form of the arch; the diameter
of the lowest is 9 feet, the second 6, and the uppermost 3 feet; this was finished in the
year 1755; the chord line and versed sine were the same as those of the second bridge
which fell four years before; besides the cylindrical holes, the spaces between them were
left hollow, and filled up with charcoal.
The fame of this latter work spread far and wide, and Edwards was employed to build
the bridge at Usk in Monmouthshire, another of three arches over the Tawy, and Pont ar
Tawy, over the same river, ten miles above Swansea; this had but one arch, its chord being
80 feet; over each haunch was one cylindrical hole.
Bettws Bridge, in Caermarthenshire, consisting of one arch 45 feet span.
Londonvery Bridge, in the same county, with one arch 84 feet in the span, and one
cylinder over the haunches.
Wychbree Bridge over the Tawy, 2 miles above Morriston, which has one arch, 95 feet
span, 20 feet in height, with two cylinders over the haunches to relieve them.
Aberaven Bridge, in Glamorganshire, consisting of one arch, 70 feet span, 15 feet high,
but without any cylindrical holes.
Glasbury Bridge, near Hay in Brecknockshire, over the Wye, which consisted of five
arches.
Edwards, born in 1719, was the youngest son of a farmer residing in Glamorgan-
shire, and some of his first works in the art of construction were the stone walls for the
inclosure of the lands on which he was employed; they were so well built, that they
attracted considerable attention. An opportunity being afforded him of seeing the tools
used by the regular masons, he procured some of them, and commenced squaring the stone
for building a workshop, which was so well executed, that it met with the approbation
of all who saw it, and it is said that he there introduced the properties of the arch. His
first bridges, consisting of only one arch, were evidently too high, which he avoided by
flattening the arch, as he became better acquainted with the subject; he proceeded, however,
with caution and judgment, having no other guide than his own experience, and he at
length learnt that where the abutments are prevented from spreading, arches of little rise are
perfectly secure.
As the Castle of Caerphilly was in the parish in which he lived, it is more than probable
he derived all his knowledge of construction from that ruin, all his masonry, and the
manner of hewing and dressing the stone, being so similar to what he doubtless admired
there.
The science of bridge-building had already considerably advanced, and various ideas
were then published on the form of arches, in which the merits of the circular, elliptical,
and cycloidal curves were discussed. The elliptical seems to have been considered as pos-
sessing particular advantages for forming the intrados of an arch, as at its springing the
curvature was more considerable, and it rose more perpendicularly, affording an extensive
and commodious opening for vessels to pass; and towards the summit or crown the curv-
ature decreased, so as to form almost a horizontal line, which was the best adapted for the
roadway; on this account it was probably preferred for some of the bridges afterwards
constructed. The cause of the stability of an arch was not at this time sufficiently under-
stood, nor had the engineers given attention to the subject of increasing or decreasing the
depth of the voussoirs, or what constituted the absolute weight to be provided for in the
abutments: it was not then the practice to consider, that for an arch of equilibration it was
necessary to have the curvature of the intrados different from that of the extrados; the
principles of the catenarian had not been applied, but in the course of a few years it was
generally adopted by our most celebrated builders; and the laws which nature has laid
down prescribe the form to be given to the extrados of an arch intended to be lasting.
Dr. David Gregory had, in the Philosophical Transactions for 1697, stated, "that none but
the catenary was the figure of a true legitimate arch, and that when an arch of any other
CHAP. VIII.
427
BRITAIN.
figure is supported, it must be because in its thickness some catenary was included;
notwithstanding, no attempt was yet made to introduce its form into the arches of bridges,
nor had the cathedral vaulting been sufficiently noticed by our engineers.
Blackfriars Bridge. — During the time that the improvements of
London Bridge were carrying on, the Common Council undertook to
open a new and magnificent entrance into the centre of the metropolis,
by a stone bridge at Blackfriars. After discussing this project for
several years, it was at last referred to a particular committee, and
a report was made in answer thereto, in September, 1754; this was
followed by a design, made by Mr. Dance, the surveyor to the city
works, the estimate for which was £185,950, exclusive of purchases of
property, and if the foundations for the bridge required piling, the cost
would be increased.
The City afterwards applied to parliament, and obtained an act to
erect a bridge, with a grant of a reversionary toll, and a power to
borrow £160,000 upon the credit thereof. This act was passed in the
year 1756, and two years afterwards, twelve aldermen and twenty-four
commoners were appointed to carry the same into effect. Designs
were afterwards advertised for, and on the 4th of October, 1759,
many drawings and models were received by the committee; objections
were made to the form of the arches in the design presented by Mr.
Robert Mylne, as deficient in strength and stability, which objections
were ordered to be laid before eight gentlemen of the most approved
knowledge in building, geometry, and mechanics, for their opinion and
advice. In February, 1760, their opinions were delivered in, and it
was then determined that Mr. Robert Mylne's design should be
adopted.
The proceedings of the commissioners for Westminster bridge were
then consulted, and the committee advertised for proposals, which were
to be accompanied with a specification of different prices for peace and
war, a caution never before practised, but by which a saving was made
of £5,839.
After the proposal had been received, and all duly examined, the
masons' work was given to Mr. Joseph Dixon, the carpenters' work to
Mr. John Spencer, the smiths' work to Mr. Bryant, and the ballast
work to Mr. Cox and three others.
In forming the contracts particular care was taken not to admit a
doubt, about either the manner of execution or payment; explicit rules
were laid down for the admeasurement of every species of work; the
first stone was laid on the 31st day of October, 1760.
A careful examination was made by boring for the foundation of
every pier, and the piling was in proportion to the respective textures
and solidities, the architect having convinced the committee of the
practicability of driving piles under water, and of cutting them level
with the bed of the foundations, by an invention of his own.
In fixing the position of the bridge, it was desirable that two objects
should be obtained; one, that its direction across the river should be
at right angles with the streams of ebb and flood, the other, that its
situation, with regard to the bed of the river, should fully answer the
purpose of navigation. The great inequality in the bed of the river,
where the depth of stream was thrown towards the Surrey shore,
made it expedient to place the great arch nearer the latter than the
former, as otherwise most of the arches on the London side would at low
water have stood upon dry ground, and a great part of the bridge
would have been rendered useless to the navigation, and in consequence
of this position being taken, the northern abutments were extended to a
greater length than the southern.
As soon as a part of the bridge was passable, a temporary arrange-
ment was added, by which the public were enabled to cross, and the
toll received was added to the building fund.
In December, 1770, the surveyor applied by a memorial, as the
bridge was nearly finished, for the monies due to him to be settled and
paid; and the committee, after several days' consideration, determined
that he was entitled to receive a commission of five per cent. on works
done, of one per cent. on purchases made, being the same as allowed at
London Bridge.

BLACKFRIARS BRIDGE.
Fig. 431.
428
BOOK I.
HISTORY OF ENGINEERING.

Fig. 432.
BLACKFRIARS BRIDGE.

Fig. 433.
BLACKFRIARS BRIDge.
The total cost for the building and completing Blackfriars Bridge, and making the
avenues thereto, was as follows: -
To Joseph Dixon, mason
To Messrs. Cox and Co.
To Dixon and Spencer, carpenter
To William Bryant, blacksmith
To sundry other artificers
-
£ S. d.
· 111,569 2 81
35,844 8 5
10,687 16
T
3,555 11
4
9,194 14 111
£ s. d.
170,851 13 111
Surveyor's commission of 5 per cent. on all artificers' bills,
and 1 per cent. on the purchases and sales of premises 9130 1 0
5 years' salary for his constant attendance on the
meetings of the committee, and for inspecting and
taking care of the bridge, streets, roads, sewers, new
buildings, and various matters relating thereto, from
1 June, 1773, to 1 June, 1778
By salaries and gratuities to the clerks of the committee
from Michaelmas, 1758, to Michaelmas, 1778
By ditto to the chamberlain's clerk, for keeping the
accounts from Michaelmas, 1760, to Christmas, 1777
By ditto to the hall keeper and his man for summoning
the committee from Midsummer, 1759, to Michael-
mas 1776
525 0 0
1683 2 6
693 15 O
Incidental expenses
Interest paid on £144,000
Purchase of ground and premises
1
433 0 0
12,464 18 6
4,507 8 8
Cash to Watermen's Company for the purchase of the Sunday ferry
25,920 0 0
35,584 1 11
12,250 17 6
Total
£261,579
061
CHAP. VIII.
429
BRITAIN.
The bridge consists of nine elliptical arches; the middle one is 100 feet span, and the others
decrease gradually to 98 feet, 93 feet, 83 feet, and the two outer ones each 70 feet, leaving
a clear water-way of 788 feet. The breadth across the bridge is 43 feet 6 inches, and the
total length from wharf to wharf is 995 feet. The breadth of the carriage-way was 28 feet,
and that of the footpath on each side 7 feet; this, however, has recently undergone con-
siderable alteration, and the effect of the original design is entirely destroyed. The piers
were built in caissoons, like those at Westminster, but previously to their being moored
and placed in their respective situations, the whole of the space to be occupied by them was
closely piled over. They are smaller in proportion to the arches than those of Westminster
bridge, and the whole work shows that considerable advances had been made in buildings
of this character. The Ionic columns resting on the piers, which diminish in height, taking the
curvature of the roadway, have been censured, but there is much to admire, if we take into
consideration the period of its erection. The caissoons were made of fir timbers, as were
all the piles; the sides and bottom of the former were constructed like those at Westmin-
ster, but their form was rectangular; their length was 86 feet, their breadth 33 feet, and
their entire height 29 feet. The sides were secured to the bottom by strong iron straps,
six on each side, and three at each end, 20 feet in length. At one end a portion about 10
feet was hung on short hinges, and a floor at 16 feet from the bottom served to brace and
secure the sides, and to receive the machinery which worked a chain pump. Level with
the top was a similar floor, on which was placed the capstan for lifting the stone; there was
also a triangle for the same purpose, and a windlass for lifting the mortar. Four upright
pieces of timber were secured to each side of the caissoon, which, with the assistance of
barges, enabled them to be removed. When the stone-work was built up to the level of
low water, a barge was laid alongside, and fixed to the upright pieces, so that when the tide
raised the barges they lifted up the caissoon, care being taken to disengage the long iron
straps and the movable piece at one end; and when the caissoon was sufficiently raised to
clear the bed of the river, it was floated off. The height of the caissoon rendered barges
necessary, particularly as all the machines were attached to the upper floor.
Many stone bridges were erected in England during the eighteenth century, some of
which exhibited considerable talent, particularly those executed under the directions of
Mr. Gwynn, a native of Shrewsbury. Kew, Maidenhead, Henley, and Oxford had stone
bridges over the Thames, but one of the boldest designs was by Sir Thomas Robinson,
who, in 1762, constructed a single arch at Winstone, over the Tees, with a span of 108
feet 9 inches; the versed sine being 45 feet, the diameter of the circle of curvature at the
vertex 112 feet, and the height of the key-stone 3 feet.
:
The bridges built by John Smeaton do not display any boldness of design, nor remark-
able science in their construction; we have already noticed much that he performed for
the improvement of our harbours, and also his great undertaking and masterpiece, the
Eddystone lighthouse. This celebrated man, and perhaps first practical civil engineer in
England, was born at Austhorpe, near Leeds, on the 28th of May, 1729; he very early dis-
played a fondness for mechanics, and at twenty-one we find him employed as a mathematical
instrument maker. About 1750 he transmitted to the Royal Society an account of the
improvements in the mariner's compass by Dr. Knight, and two years afterwards he
furnished the same society with those he had made on the air-pump, and an engine for
raising water by fire, a subject upon which the French philosophers were then busily en-
gaged he was soon afterwards admitted as a member, when he introduced his ideas upon
the pyrometer, and several other subjects. About this period he was induced to travel
into Holland and the Netherlands, where he had the opportunity of examining the system
of draining and management of locks on the canals, and several important engineering
works then progressing under the direction of very able men: and on his return to England
he occupied himself in inquiries relative to the powers of water and wind, on their appli-
cation to machinery, where circular motion was required; and after great patience and
labour he was enabled to exhibit their results to the learned men of the society in several
models of undershot, breast, and overshot wheels, which he accompanied with calculations of
their relative value: the novelty as well as utility of his observations obtained for him the
Copley gold medal, and, what was far more important, he was selected as the builder of the
Eddystone lighthouse by the Earl of Macclesfield, who was then president. We have
already seen with what diligence he set about preparing himself for that great work, and
how ably he accomplished the very arduous and difficult task: after its completion, the
public seem not to have encouraged his talent as he merited, for we do not find him em-
ployed again until 1761, when he was associated with Mr. James Brindley in surveying for
several canals in Staffordshire. Among his reports dated after this year are some on
canals, improvements of rivers and harbours, draining, and a description of many useful
inventions and applications of foreign methods for constructions in water. His reports are
exceedingly valuable, and show that he was admirably qualified for all he undertook. He
was a great observer of nature, and applied his mind diligently to examine her works:
430
Book I,
HISTORY OF ENGINEERING
when called upon to shorten the course of a river, or improve its channel, he directed his
attention to the causes which had produced the results he was required to amend. This
eminent engineer died the 16th of September, 1792, to whom we are indebted for many
improvements in air and water-mills; before his examination into the force of water, our
machinery was in a very rude state; he called forth the inquiries from which the present
generation are now reaping advantage.
Bristol Bridge.—When Smeaton was consulted upon the rebuilding of this bridge in
1762, he observed, that no limit was yet fixed for the span of arches, or the proportion of
their rise, since the widest and flattest that had been attempted upon right principles had
succeeded as well as the narrowest and highest, provided the abutments were good, and the
stone and cement of a firm texture.
One of the peculiarities in this engineer's designs was that of perforating the spandrills
of his arches by a circular opening, and also employing segmental or elliptical arches in
preference to semicircular. The skill with which he managed his centres cannot be too
highly admired; the strength is always greatest where most required, and there is no un-
necessary quantity of timber made use of. Of the various bridges that are mentioned in his
reports are those of Perth, Stoneham Creek, Glasgow, Dumbarton, Old London, Howick,
Aberdeen, Edinburgh, Coldstream, Newcastle, Hexham, Berwick, Banff, Dumballock,
Braan, Altgran, Bewlic, Conon, Sutton, Walton, Harraton, Carlton Ferry, and Montrose,
and others, several of which he entirely rebuilt. The utmost span given to his arches was
75 feet, the width of the piers being made about a fifth; the same proportions we shall
find at Perth bridge, which he built about the time that Blackfriars was completed.
Bridge over the River Tay, at Perth.-In 1763 Smeaton was consulted by the justices of
the peace for the county on the practicability of building this bridge; and, after the necessary
surveys, he gave a design for one of stone, having seven principal arches, extending 605 feet
9 inches, and in the whole length 893 feet. The width is 22 feet in the clear between the
parapets; the span of the two outer arches 70 feet, the next 72 feet 10 inches, the next
74 feet 6 inches, and the centre arch 75 feet, leaving a water-way of 509 feet 9 inches. The
piers of the middle arch were in width 17 feet, the other four isolated piers each 16 feet.
An estimate accompanied the design, supposing the foundations to be laid 8 feet under the
bottom of the deepest part of the river, which was based upon the information he had
received, that there was a stratum of hard gravel 8 feet below the bed of the river, upon
which the piers were to be placed, without either piles or grating. The river at its ebb had
not more than 2 feet depth of water, and at ordinary spring-tides did not rise more than
8 feet above this mark, and he considered that a dam capable of keeping out the water 4 feet
above its low state would enable the men to work nine or ten successive days between each
spring-tide; and that a dam of this height was not only less expensive in its construction, but
also less likely to be injured, than another raised high enough to keep out the spring-tides.
A sluice made in this dam let the water in and out, and it was so formed, that a clear space
of 16 feet was left round the pier for the convenience of the workmen. The dam was ellip-
tical, the better to resist the tides and floods.
Cofferdams, materials in, and cost.
26 gage piles, of 10 feet long, at 10s.
-
2328 feet supl. of plank piling, 91 feet long, at 1s. 2d.
122 feet cube of timber in strong pieces for supporting the
pile heads, at 3s.
Extra work to sluice for letting in and out the water
Timber work in one cofferdam
To pile shoes for 26 gage piles, at 1s.
£ s. d.
£ s. d.
13 O 0
135 16 0
18 6 0
2 10 0
•
169 12 0
1 6 0
To plank pile shoeing 245 running, at 6d.
To 25 bolts for the string pieces, at 28.
6 2 6
To extra iron work about the shuttle, and contingencies
2 10
200
Iron work about one cofferdam
11 18 6
A cofferdam complete
181 10 6
A cofferdam complete
The materials for the first pier are supposed to be of half value towards
each succeeding pier, which will therefore be No. 6, at 907. 158. 3d.
Cofferdams for the whole
181 10 6
544 11 6
726 2 0
CHAP. VIII.
431
BRITAIN.
Excavation and Drainage.
To excavation of the matter, 722 yards for each pier, at 6d.
To drawing off the water, supposed equal to 50 days, at 20s.
per day per pier
£ s.
d.
£ s. d.
-
18
1 0
50 0 0
68 1 0
The excavation and drainage of six piers, the two abutment piers, and
foundations for the wing-walls, being supposed equivalent to two piers,
the whole will be equivalent to eight piers, at 68%. Is. each
Masonry in the piers and abutments, below the springing of the arches.
To 1080 feet supl. of ashler in each pier below water, at 7d.
To 1176 ditto above water, at 8d.
The whole pier in solid contains 467 cube yards, including
labour, carriage, tarras mortar, six inches in the outside
joints, and all materials, at 5s. per yard
-
N. B. The ashler being at least 20 inches bed, and cubed
into the solid, at 5s. per yard, is supposed to pay for the
tarras mortar and extra labour in setting thereof.
To capping the pier with solid blocks, jointed between the
springer stones, 600 cube feet, at 6d.
To capping the ends of the piers, 148 feet supl., at 8d.
To six piers and two abutment piers, each reckoned as a pier,
that is No. 8., at 2071. 7s. 8d.
-
To walling in the west land stool, to bring it up to the
springers to be at a medium 5 feet thick, containing 490
cube yards, at 5s.
-
To hammer-dressing that part of the wall that comes in view
below the plinth, containing 666 feet supl., at 1½d.
To working the plinth, being before reckoned as solid, con-
taining 990 feet supl., at 3d.
To 78 cube yards of masonry, in the east land stool, to bring
it up to the height of the springers, at 5s.
To setting under the west abutment arch, to prevent the
water from affecting the foundations, 1353 feet at 4d.
31 10 0
39 4 0
116 15 0
15 0 0
4 18 0
1659 1 4
122 10 0
4 3 3
12 7 6
19 10 0
22 11 0
G
544 8 0
Masonry in the piers, and abutments below the springing of the arches 1840 3 1
Centering for the arches.
To timber in one rib 416 feet cube, and for six ribs
To timber in 30 bearing piles and 5 capt-trees, for supporting
the ribs
-
2496 cube ft.
750
To stays and bracings between the ribs to keep them upright
To covering for the centres in square scantlings
To additional work to make the centres fit the large arches
75
525
188
To timber in a centre complete
4034 at 3s.
605 2 0
To iron work in the six ribs, 1852 lbs. at 5d.
To ditto in pile shoes and hoops, 662 lbs. at 5d.
To spikes, nails, and other contingent articles
£38 11 8
13 15 10
5. 0 0
The iron work for one centre
One centre complete
To a set of piles and cap pieces, ready prepared for driving in the second
arch before the first centre is struck, containing 750 feet, at 2s.
To 5 booms, containing 375 feet of timber, at 2s., to be fixed as struts
between the piers of the second arch while the centre is taking down
from the first and putting up in the second
To taking down the centre, drawing the piles, driving ditto, and setting
up the centre 6 times, repairing and making good what is wanting, at
9d. per cube foot upon the timber, which being 4034 feet, comes to
1517. 5s. 6d. each time, and for 6 times
Taking down and putting up the booms 5 times, at 6d. per foot
To centering for one of the small arches, at 20s. per square
To taking down, removing, and setting up ditto in the other arch
Centering for the bridge complete
-
57 7 6
662 9 6
75 0 0
37 10 0
907 13 0
46 17 6
20 0 0
500
1754 10 0
432
Book I.
HISTORY OF ENGINEERING.
Masonry in the superstructure.
To 15,850 feet supl. in the soffite of the main arches, being 3 feet thick,
set in place and mortar included, at 20d.
To 2000 feet supl. in the soffite of the abutment arches, at 1s.
To blocking up the spandrills of the arches solid 6 feet high, containing
473 cube yards, at 58.
£
8. d.
-
1320 16 8
100 0 0
To cube masonry in the spandrill walls, abutments, and wing-walls, from
the top of the piers to the top of the cordon, containing 3776 yards,
at 5s.
To hammer-dressing the plain superficies thereof, containing 33,984 feet
at lid.
In the parapet, 11,856 feet supl. on both sides, being 15 inches thick, stone,
workmanship, mortar, and setting ditto, at 6d.
To 18,382 feet supl. in the faces of the arches, bands and keys, the cordon,
mutules, capping, and pedestals, which being before reckoned in solid,
except their projecting parts, and all square work, at 4d.
118 5 0
944 0 0
212 8 0
269 8 0
306 7 4
To 2160 feet supl. in the 12 eyes, and 640 feet in the terminating pillars,
in the whole 2800 feet supl. of circular work (being before included
in the solid), at 6d.
70 0 0
The walking path, being 4 feet wide, contains 3641 feet supl. of stone,
working and laying, at 7d.
106 12 0
Masonry in the superstructure
3447 17 0
410 11 0
·
1000 0 0
Gravel.
To 10,948 cube yards, to fill up the spandrills and wing-walls, and form
the road, at 9d.
Contingencies.
To piling engines, pumps, and other utensils, supervisal, unforeseen acci-
dents, and expences
Abstract.
To cofferdams
Excavations and drainage
Masonry in the piers and abutments
Centering for the arches
Masonry in the superstructure
-
Gravelling the bridge
Contingencies
-
1
Total
#
726 2 0
544 8 0
1840 3 1
1754 10 0
3447 17 0
410 11
0
1000 0 0
·
£9723 11 1
In the batterdeaus and centres there remained at least 5763 cube feet of timber, which
if sold at 9d. per foot cube would amount to 214l. 2s. 3d., besides iron work, engines, and
utensils; which, it was presumed, would be sufficient to make the road to and from the
bridge.
The prices in the preceding estimate include all labour, carriage, mortar, and setting up
in place, unless otherwise particularly expressed.
Description and method of fixing the foundation of the second pier and the cofferdam.
The gravel proving harder than was expected in this last pier, much time being occupied
in driving the piles of the cofferdam down to their proper depth, and so much difficulty being
experienced in drawing them, that they were severely injured when drawn, it was proposed
that for this pier there should be as many additional piles, as should set the whole at the
distance of 9 feet from the sheeting of the base of the pier, and that they should be driven
no further than to fix them firmly in the ground, even should that happen at only 2 feet.
To prevent the filtration under the bottom of the piles, gravel and corn-mould earth
were thrown in on the outside, after being well mixed together; and this was sloped
against the piles, and extended to a width of 6 feet all round.
Method of forming the excavation. The pumps being fixed, and the water pumped out,
the excavation was made to the size of the pier; and after having got down a space in the
middle to its proper depth, the width and depth were increased, till the area was clear for
driving the piles, upon which the foundation frame was to rest, and no more, leaving the
matter on the outside of the area to form its own slope towards the cofferdam, so that the
rest of the area remained solid, to support the sheeting of the dam.
The depth of the excavation was determined after the following rule. It must be exca-
vated at least 3 feet at a medium below the natural surface of the gravel where the pier
stands; but if this did not carry down the base of the pier within 2 feet of the level at which
CHAP. VIII.
458
BRITAIN.
the base of the first pier was fixed, the depth of the excavation must be increased, till it is
within 2 feet of the former depth.
Method of fixing the foundation according to the plan. The excavation completed, let
the 21 piles upon which the frame is to rest be driven into their proper places; these
piles are to be 10-inch heads, and 6 feet long, supposing the gravel of equal strength with
the last; the pile heads are then to be reduced to a level, and the frame laid thereon,
and trenailed down upon the pile heads. Then the sheeting piles are to be driven; and
these may be of oak, elm, beech, or fir, and about 6 feet in length, as these piles are to be
rebated, and if possible driven without splitting.
To save timber, it was recommended to groove the piles on both sides, and to nail in
the tongue, which might be of hard wood if fir piles were used; these tongues were to be
1½ inches in thickness, and 13 inches broad; and to be let in 3 inch where it fastens, and to
stand out 1 inch. The tops of the sheeting piles, being reduced to the same level as the
string pieces to which they were to be spiked as they were driven; the outside was to be
reduced to a regular breadth, and the notched stones taken in a line.
When this was per-
formed, the rest of the bearing piles were to be driven, beginning with the outside rows,
and cut to a level with the tops of the string pieces; the piles were to be 6 feet, more
or less as found requisite.
The setting was to be completed by first underpinning the string pieces and tie-beams
as firmly and equally as possible, by driving stones under them, and then the other spaces
to be set and well driven down as before; but before ramming down, the joints were to be
filled, by sweeping in dry lime mixed with sand and small gravel, so that the whole when
driven down should be thoroughly compacted together.
After the pier was raised above low water, the matter was to be taken out 4 feet in width
all around, down to the level of the top of the notch course, and then filled with good
lagging as before, standing somewhat higher than the natural bed of the river, and the rest
of the space covered with rubble to the sides of the dam.
The bearing piles were to be driven until the ram made them descend 1 inch for every
20 blows, and the sheeting piling, until it required 40 blows to drive the same quantity;
and the latter were to be driven to a regular depth throughout.
Coldstream Bridge over the Tweed, designed in 1763 by John Smeaton, has five arches.
That in the centre is in span 60 feet 8 inches, the two adjoining 60 feet 5 inches, and each
of those on the land sides 48 feet. They are all parts of the same circle; the smallest
arches being one-third, and the others rising higher in proportion to their span. The height
of the piers above low water, including the impost, which is 2 feet, is 12 feet precisely, so
that the shaft of the piers before the impost was put on is 10 feet.

Fig. 434.
COLDSTREAM BRIDGE.
The engineer in one of his reports upon this bridge remarks, that he found the gravel of
the Tweed lie very open, and not wrecked up with sand and matter in the usual manner,
and though generally objecting to piling foundations, which are tedious and expensive,
and getting down to the rock, would from the nature of the gravel make the drainage
exceedingly so, he in this case recommended piling the foundation 3 feet below the bed of
the river; in general he observes that in similar cases it was usual to lay down a grating
and build upon it without any piles at all; but that here the floods might take away the
gravel and leave the grating bare, which would eventually undermine the pier; and that
to defend the foundations in the usual way, by building starlings round the piers, ter-
minating above low water, would also be objectionable, as the water-way would be too
much contracted.
Hexham Bridge, as designed by John Smeaton, had nine elliptical arches of different
spans, and extended 518 feet between the abutments, and 568 feet comprising them; the
width measured on the soffite 20 feet, and the clear between the parapets 18 feet.
The span of the centre arch was 51 feet, the piers 12 feet 6 inches; the adjoining arches
50 feet 7 inches; the piers 12 feet; the next arches 49 feet 11 inches, the piers 11 feet
6 inches; the next arches 48 feet, the pier 11 feet 6 inches, and the two outer arches span
37 feet. This bridge, which was destroyed by a flood in 1782, was a considerable loss to the
contractors. Five of the piers were built in a caissoon, the internal width of which was
16 feet, the length on the flat side 22 feet; the bottom was formed of 3-inch plank laid
crosswise, and the sides of 3-inch plank placed upright, supported by three ribs of timber,
two on the inside and one on the out, all secured at the angles by iron bolts in a proper
manner.
F f
434
BOOK I.
HISTORY OF ENGINEERING.
On the upper rim iron studs were screwed, over which an iron chain could be cast when
the caissoon was moored, a pile being driven above and below bridge for this purpose.
All the joints of the planking and sides, and the cross and upper planking of the bottom
were grooved about 2 inch in depth; and a lath 1½ inches in breadth, and inch thick, was
14427
let into it with tar; and over the joints was nailed a
strip of thick flannel covered with tar, 3 inches in
breadth upon the outer edge.
During the excavation, the floods carried away the
gravel under the caissoon, the fourth pier from the
south abutment settled about 18 inches;
in many
places, the gravel was removed to the depth of 30
inches, and several of the stones were driven out of
the cutwater of the pier.
This damage was remedied by enclosing the se-
veral foundations with a row of sheet piling, which
prevented the gravel from further washing from
under the base of the piers; and then filling up the
cavities below the bed of the river with rough rubble
stones, and the inside of the piles with smaller
quarry rubble and clean sand, in the proportions of
2 of stone to 1 of sand.
To underpin the piers effectually, it was necessary
to make use of a diving machine, the principal part
of which was an air-chest, 3 feet 6 inches in length,
4 feet 6 inches in depth, and 2 feet in width, pro-
vided with a copper air-pump which threw in a
gallon of air at a stroke; it was sunk with the
proper tackle, by attaching 16 pigs of lead to it.
A board was put across for a man to sit on, with
another for his feet, and a pane of glass inserted at
top to admit the light.
The pump was formed of a copper cylinder 10
inches in diameter, and 12 inches high; wired at
top, and a flanch at bottom 14 inch broad, by which
it was screwed down to the top of the air-chest; the
copper is described as being the thickness of a half-
penny. The sides of the air-chest had 21 plank for
the ends and bottoms, and 13 inches for the sides.
Kelso Bridge, over the Tweed, consists of five
arches, each 72 feet span, with a versed sine of 20
feet 9 inches; the diameter of the circle of curvature
at the vertex being 114 feet.
This beautiful work, completed by Mr. Rennie
about the year 1799, was the model for Waterloo
Bridge; the estimate for its construction was 12,8761.,
which was not exceeded.
The old bridge at Kelso was constructed of six
semicircular arches, with a water-way of 318 feet,
where the river was 561 feet in width.
The roadway of this bridge is perfectly level; over
each pier are two columns, which sustain an en-
tablature that runs the entire length; these columns
project about three quarters of their diameter, and
are of graceful proportions. The width of the
bridge measured on the soffite of the arches is 26
feet.
The scenery around this structure is admired
for its beauty, and the conflux of the Tweed and the
Teviot rivers is enriched by the engineer; at the
period this bridge was constructed, similar works
were carried on in France, but none excel this
example in simplicity or style of execution.
objections made to the introduction of columns
at the bridge of Blackfriars do not hold good in
the Kelso Bridge, for they are of one proportion
throughout, and are not diminished in height
towards the abutments to adapt them to the cur-
vature of a cornice, which rakes with an inclined

The
Fig. 435.
bridge at Kelso,
CHAP. VIII.
435
BRITAIN.
roadway; there can be no doubt, however, that it would have been better to have omitted
the columns altogether, as they can hardly be supposed fit decorations for the piers of a
bridge.

BRIDGE OVER THE RIVER CREE.
Fig. 436.
Bridge over the River Cree at- Newton Stewart, executed
also by Mr. Rennie, consists of five arches, all segments
of circles; that in the middle is 50 feet span, with a
versed sine of 6 feet 6 inches, its two piers are 8 feet in
thickness; the arch on each side of the centre is 46 feet
span, with a versed sine of 2 feet 9 inches, and the outer
piers are diminished in width 6 inches; the two arches
on the land sides are 39 feet in width, with a versed sine
of 4 feet 9 inches.
The roadway, which takes the same curve as the cor-
nice of the bridge, is 20 feet in width between the para-
pets.
Bridge over the Esk at Musselburgh was also con-
structed from designs by Mr. Rennie, about the year
1803. It consists of five segmental arches of considera-
ble radii; that in the middle is 45 feet span, with a
versed sine of 6 feet 6 inches; the arches on each side of
the centre are 42 feet span, with a versed sine of 5 feet;
the outer arches, or those adjoining the abutments, are
37 feet span, with a versed sine of 3 feet. The piers
are all 7 feet in width above the set-off, and are rusticated
to the underside of the cornice, which has a circular form,
and follows the curvature of the road.

curves.
In the bridges over the Cree and Esk the flat seg-
mental arches produce the most elegant and pleasing
effect. Ammanati, in his beautiful design executed at
Florence (Fig. 184.), had already shown how much
grace could be obtained by the introduction of arches
that approached the elliptical form. Perronet, some
years afterwards, also with great success, adopted others
which formed a portion of the circle, or were very flat
St. Maxence on the Oise (Fig. 280.), and
Brunoi on the Hyeres (Fig. 282.), executed by that
celebrated engineer, served as models for many ex-
ecuted in France; among which may be reckoned
that of Jena at Paris, erected in 1808 by Lamande
(Fig. 288.); but all these bridges, though their arches
are of an increased span, and of bolder construction, do
not surpass the examples we are describing. The cur-
vature given to the roadway, to accommodate the level
of the banks of the river, differs from the French ex-
amples, but is admirably accomplished in the Kelso
bridge, where the effect is improved by the cornice being
maintained horizontally throughout. The enormous
sums of money that have recently been expended to
lower the crowns of Westminster and Blackfriars
bridges, so as to render the draught over them less
laborious, ought to satisfy those who are partial to a
curved line of road, that utility and elegance equally
recommend its discontinuance; and that, wherever a
level surface can be obtained, without too much increas-
ing the expense of the abutments, it should be adopted.
Independent of this the eye is better satisfied with such
an arrangement, as the ends of the bridge, where all the
strength is required, gain importance by elevating it
above the ordinary level of the shore, and an idea is
conveyed of power to resist the combined thrust of the
arches, by the additional loading it receives from the
increase of height. A reference to Waterloo Bridge
will convince the most fastidious that the level line not
only possesses the greatest convenience, but beauty also;
the latter arising out of the fitness of the several parts
for the uses to which they are devoted,
BRIDGE OVER THE ESK.
Fig. 437.
FF 2
436
BOOK I.
HISTORY OF ENGINEERING.
It is
Stoneleigh. Bridge, in the county of Warwick, was constructed by Mr. Rennie.
built of stone, and the centre arch is 92 feet span, with a versed sine of 13 feet. The
abutments are solid, and very ornamental; they have an opening in the middle of each
12 feet wide, with a semicircular head. The Doric entablature, which runs through the
I

Fig. 438.
STONELEIgh bridge.
entire length of the bridge, has a good effect; it is surmounted by a balustrade, and the
roadway is kept horizontal.
Wellington Bridge, over the river Aire, at Leeds, erectea under the direction of Mr.
Rennie. It spans the river where it is 100 feet in width, and the banks 8 feet in height.
The arch is the segment of a circle, 91 feet radius, with a versed sine of 15 feet. Coffer-
dams were made use of to construct the abutments, which were protected by sheet piling
and wales; each of these abutments is in length 30 feet, and 28 feet in width at the bot-
tom, diminishing by offsets to 27 feet in length and 21 feet in width where the arch springs.
These abutments are built with radiating courses within, but on the face they are horizontal,
and the stones used are from 14 to 18 inches in thickness, and were accurately cut from
templates made to suit each course. All the lower courses of the footings were laid without
mortar, but had their joints well grouted; the others, up to the water-line, were laid in
mortar, made from magnesian limestone; the proportions used were, one of lime, one of
clean river sand, and one of forge scale, well mixed and tempered, and used quite hot. The
masonry of the arch was put together with mortar, of equal proportions of lime`and sand.
After the abutments were completed, the piles were driven to carry the centre, the lagging
of which was laid 5 inches higher than the proposed arch, to allow for its settlement.
There were six of these ribs or centres, of Memel timber, and the whole contained 2220
cube feet. The striking wedges were of oak, 6 inches in width, and 9 inches in height; the
middle one being the largest. The voussoirs in front were 7 feet on the bed at the
springing, diminishing to 4 feet at the crown; but the interior arch stones were on an
average 3 feet in length, and 18 inches thick. After the arch was turned to the extent of
one-third on each side, the centre was loaded at the crown with 20 tons of stone, and the
haunches were not further loaded until after the key was placed, which was about three or
four weeks from its commencement. The centre was enabled to bear the weight of a thou-
sand tons, yet it was found that the wedges were forced into the timber, and it was necessary
to cut them out. The arch, during the progress of the work, was squeezed down 21 inches,
and after the centre was struck another 2½ inches. The stone used was a coarse red sand-
stone, or millstone grit, from Bramley Fall, a quarry about four miles above the bridge. It
was delivered scappled, ready for dressing, at 9d. per cube foot; the dressing and setting,
exclusive of the cornice, cost 41d. per cube foot, including the mortar 15d., and the cornice
and parapet walls about 4d. extra. The total quantity of masonry was 80,000 cube feet,
and the entire cost of the bridge was 75301.
Waterloo Bridge, commenced on the 11th of October, 1811, after the designs of Mr.
Rennie, may be considered to form a new era in the art of bridge-building. Caissoons in
this instance were abandoned, and cofferdams made use of instead, for laying in the
foundations. The width of the Thames in this part is 1326 feet at high water, which is
spanned by nine equal semi-elliptical arches of 120 feet opening, with a versed sine of
32 feet, and a rise of 35 feet above the surface water of spring-tides, so that the clear
water-way is 1080 feet. The diameter of the circle of curvature at the vertex of these
arches is 225 feet, the depth of the key-stone 4 feet 6 inches. The abutments are 40 feet
in thickness at their base, and gradually diminish to 30 feet at the springing of the arches,
and are 140 feet in length, including the stairs. The piers are 30 feet wide at their
base, diminishing to 20 feet at the springing of the arches, and their extreme length is
CHAP. VIII.
437
BRITAIN.
87 feet. The sides of the bridge are defended by an open balustrade; the carriage road is
28 feet wide, and the footpath on each side 7 feet.
The roadway is nearly horizontal throughout, and
level with the terrace at the back of Somerset House.
This was nearly the first bridge so constructed, and great
credit is due to the engineer in thus triumphing over
the vulgar prejudice, that it was necessary to incline
the thoroughfares to obtain a greater elevation of the
middle arch in the arrangements at Blackfriars the
columns are made to diminish in height towards the
abutments; in the present case they are of the same
altitude throughout; consequently the entablature is
not distorted, and from the excellent effect produced
by this level line of cornice being preserved, the bridge
is justly considered the most beautiful structure of the
kind.
The cofferdams were formed of three concentric rows
of piles, placed about 3 feet 6 inches apart; the stratum
into which they were driven was gravel; each elm or
beech pile was 12 inches in diameter, and about 20 feet
in length.
The form given to the cofferdams was that of an
ellipsis; and the heads of the piles, after they were driven
into the gravel, were cut off, about 5 feet above the level
of high water mark spring tides; to secure them more
effectually, wrought-iron screw-bolts were passed through
them, as well as three rows of waling pieces, the ends
of which were covered by stout cleets. Cross and dia-
gonal braces of whole timber connected and strutted the
several rows of piles; the dam was braced longitudinally
in several places, and struts were introduced in every
position where they were not found to interfere with the
masons in their work. The water which accumulated
or passed into the cofferdam could be let out at low tide
by means of a short tunnel formed in the end; and a
sluice, moved by iron racks and wheels, enabled the
workmen to open or close the mouth of the tunnel at
pleasure. The spaces between the piles were filled with
well puddled clay, that had been beaten and prepared
for the purpose before it was put on board the lighter
which conveyed it to the cofferdam. In the execution
of this work great attention was paid by the engineer
to obtain a perfect command over the water at all times,
and thus prevent any interruption to the men employed
upon the masonry of the piers, which was completely
effected by means of a steam-engine erected for the
purpose: neither hand-buckets, pumps and machines
worked by men or horses, nor the numerous contrivances
described by the French engineers, could have emptied
the space comprised within the area of a cofferdam in
so short a time as it was accomplished by this; hence
the labour was continued almost without interruption,
on many occasions being proceeded with for twenty-
four successive hours, a most important advantage in
constructions of this kind. The application of the
steam-engine to bridge-building has wonderfully eco-
nomised both labour and time; piles are driven, their
heads cut off by its power: manual labour has thus
been greatly abridged, and the use of horses almost
rendered unnecessary; in the present instance, the stone
and other materials were so laid upon the temporary
platforms or timber constructions, as to be within the
command of the power of the engine at all times, and
heavy weights were moved by very simple tackle and
machinery.


Fig. 439.
WATERLOO bridge.
The arches being all equal, and of an elliptical form, produce an admirable effect; the
depth of the key-stone is between a twenty-sixth and twenty-seventh of the span, which is
FF 3
438
BOOK I..
HISTORY OF ENGINEERING.

Fig. 440.
Elevation of arch, WATERLOO bridge.
exceedingly small as compared with all previous examples, and it is no more than a fiftieth
of the diameter of its circle of curvature. In the theory of the arch the thickness given to
the voussoirs forms the most important consideration; and here we have them admirably
proportioned, so as to diminish the pressure on the arch, and increase in strength towards
the springing, that is to say, in proportion to the accumulated tangential pressure. At
sixty degrees from the top the voussoirs are lengthened, and continue to receive some
addition down to the springing.
The bridge at Neuilly, built by Perronet, is at the crown 4 feet 8 inches in thickness,
and its span is 128 feet, with a versed sine of 32 feet the crown of the arch being the
portion of a circle whose radius is 150 feet, its horizontal thrust is very considerable, and
the key-stone is made 4 feet 8 inches in height; nevertheless, the arch sunk when the
centre was struck nearly 2 feet, whilst those of Waterloo descended only a few inches.
The form given to the starlings at Waterloo Bridge is well contrived to split the stream
in its current, and carry the water quietly under the arches.

Fig. 441.
WATERLOO bridge.
The centres made use of were admirably contrived, and put together in such a manner
that they could be readily dropped, if required, by means of the wedges introduced upon
the heads of the inclined piles. The piers and abutments being raised to their necessary
height, to receive the arches, the timber centres or ribs were set up, framed together, as
represented in the elevation of the arch: these centres were remarkable for their strength,
and calculated to support the weight of the voussoirs placed upon them, throughout the
entire progress of the construction of the arch until finally keyed by the introduction of
the last stone. The form of the arches has undergone no change, which is the best
indication that can be adduced of the excellent manner in which the centres were framed
and supported. They were laid upon whole timbers, which capped the piles; and under
each set of ribs the wedges were introduced, which were made to extend across the entire
CHAP. VIII.
439
BRITAIN.
width; so that when it was required to ease the centre, wedges were driven along each
other, and slid down the inclined plane into larger spaces than they had previously occu-
pied: the whole centre, consequently, could by this means be made to descend very gently,
and remain so during any part of the operations.
The inclined piles, which carried the weight of the ribs of the centre, had their bearing
on the offsets of the stone piers, which afforded a most effectual and perfect abutment;
and it must be acknowledged, that the skill shown in putting together a centre of such
vast weight and dimensions is a strong evidence that improvement in bridge-building has
been greater here than on the Continent.
The section through the piers shows their construction, which is of solid granite
throughout; over the spandrills are rows of columns, which carry the roadway, and a pipe
conducts the water from the channels of each gutter to an opening immediately above the
last set-off, where the pluvial waters are discharged into the river.

Fig. 442.
SECTION THROUGH PIER of WATERLOO BRIDGE.
Great attention was paid to have the spandrills of the arches constructed with solid
masonry, laid in regular horizontal courses, and of one uniform thickness throughout, and
where bedded upon the extrados of the arch, they were very carefully worked, so that the
whole was made solid and secure before any course was proceeded with, the last executed
was dressed on the surface, and rendered perfectly even, that the layer of fine mortar intro-
duced under the beds should have a uniform thickness: over these were constructed in-
verted arches, the stones of which increased in dimension with the radius, and these also
were carefully dressed, so that they should perform their office effectually, contributing
additional strength at the back of the main arches, where these were likely to spring,
without adding unnecessarily to the weight on the piers: this feature in the construction
of the arches of a bridge was, perhaps, first introduced at Westminster, but was not there
so admirably executed as in the present example.
FF 4
440
BOOK I..
HISTORY OF ENGINEERING.
The section through the arch exhibits the twenty-four voussoirs which lock the whole,
the top of which is level with the upper portion of the architrave that rests on the two
Doric columns.

Fig. 443.
SECTION Through arch of waTERLOO BRIDGE.
The abutments are of singular beauty, and comprise within them staircases to descend
to the river at all times of the tide; from the increase in their width, both above and below

Fig. 444.
ABUTMENTS of wateRLOO BRIDGE.
the bridge, greater security is given to the structure, and the eye is pleased by the
additional masonry.
CHAP. VIII.
BRITAIN
441

వి
IB
B
ען
Fig. 445.
SECTION THROUGH THE STAIRS of WATERLOO BRIDGE.
The section through the stairs, arch above,
and solid masonry resting on the piles below,
give some idea of the precautions taken by
the engineer to render his abutments per-
fectly solid; beyond these, and continuing
for an immense distance on the Surrey side,
is a series of brick arches, on which the
roadway is carried, which gradually inclines
towards the obelisk in St. George's Fields.
On the Strand side the ground rising rapidly,
the same extent of arches was not required.

Waterloo Bridge is an imposing and beau-
tiful structure, which has received most un-
qualified praise from all capable of judging
of its merits: as the works were generally
constructed in a similar manner to those of
London Bridge, it has not been thought ne-
cessary to enter more upon them here, but to refer to that specification for further inform-
ation upon the subject; the whole surface of the piers and abutments, as well as the arches,
are of Cornish granite, and the filling in is of Cragleith and Derbyshire stone.
Fig. 446.
PLAN OF STAIRS.
London Bridge, at the commencement of the nineteenth century, was in such a state of
dilapidation as to require either that a large sum of money should be expended upon it, or
that a new structure should be erected; an application was made to parliament on the
subject, when a select committee was appointed to consider what was necessary to be done.
On the 28th of July, 1800, this committee reported, that notwithstanding large sums
had annually been expended upon the bridge, the methods hitherto adopted for its secu-
rity had not proved effectual; that the bed of the river suffered injury from increasing
shoals, partly from its natural course being obstructed, and partly from the dispersion of
materials employed to strengthen the piers. That the bridge was in such a state that it
could not be substantially repaired; that its foundations were daily undermining, from the
force of the agitated water rushing through the confined arches; and the committee was
of opinion, from the enquiries they had instituted, that the rebuilding of London Bridge
upon improved principles would be a measure of economy.
442
BOOK I.
HISTORY OF ENGINEERING.
The report made by Mr. Robert Mylne on the state of the River Thames and its bed,
on the structure of London Bridge, and the navigation of the river above and below it,
in the year 1800, contains the principal information on those subjects furnished to the
select committee.
In this report he states, that whilst the alterations were making at London Bridge in
1761 and 1762, and during the removal of the pier under the great arch of 70 feet span,
he was consulted by Parsons, the contractor, as to the best manner of performing his
contract; and he advised that a hole should be made in the ashler works forming one side
of the old pier, on which the two Gothic arches rested, which was to be removed. On
examination it was found that the pier rested on four rows of piles, driven closely together
round its outer edge; the tops of which were at a very considerable depth below the
present low water mark. Around these and forming the starlings were others, which he
drew up by means of powerful screws fastened to the heads, and then, by destroying some
of the ashler work, he was enabled to displace and draw some of the outside quadruple
row, on which the foundations of the pier were laid; the pier quickly became a ruin, and
dissolved away in the midst of that impetuous agent, the fall under the bridge. The outer
piles being carried away, the heart or middle of the work was borne off so suddenly, as
hardly to leave any time to consider and measure its substance and texture. All that
could float was dispersed up and down the river; but some of the original piles were pre-
served, which were stated to have been there about 586 years. The original bed of the
river, under the substance of the pier, had never been exposed to such a rapid stream
before; it was then much higher in level than any parts above as well as below the bridge;
its substance was soon worn away by the powerful friction, and in proportion as the space
and depth were enlarged, the violence of the stream increased in power, by the current
being drawn from both shores and from the small arches, augmenting the volume of
water, which was greater than had ever before existed. This corrosion at both sides of the
old pier spread across the bottom of the locks adjoining, and attacked the stability of the
starlings under the old piers of the new arch; unfortunately the outer faces of these
starlings were so close to the stone piers, and only 6 feet broad underneath the haunches of
the great arch, that no pile engine could act, and there was but little space to stand and
perform any efficient works. Mr. Smeaton was immediately called in, and he advised the
only probable remedy for the urgency of the case, which was to throw as much stone as
possible into the vacuities of the foundation, to preserve it from further corrosion;
accordingly, the stones belonging to the old city gates, which had recently been pulled
down and sold, and which were stored up at no great distance, were repurchased and thrown
into the gulf which had been formed from the deep water above to the deep water below
the bridge. This remedy seems to have been suggested from the manner in which Gautier
states the bridge of St. Esprit to be supported, and maintained at a constant and great
expense, yet the whole of the advice was not followed. Increased velocity formed ad-
ditional danger, and eddies were thus created, in which all sorts of vessels became entangled.
After a great deal of discussion, a compromise was effected between those who contended
for having the current as gentle as possible under and through the bridge, and those who
were for maintaining as strong a current as might be, in order to work the water wheels
attached to the bridge. And the report further states, "that if the bridge was totally
removed, and nature restored to its full power and original possessions at this place, there
cannot be any doubt but the navigation would be here, as at any place upwards to Fulham
Bridge, free, open, and unencumbered for all the variety of craft which navigate that
extent of the river. Boats would pass up or down against the stream, equally as well as
they do now any where else; and a greater quantity of tidal water being admitted, by the
removal of that which obstructs its influx at present, the intercourse inland would be en-
larged and extended by as much further as the tide would certainly flow. The reflow of
that newly and enlarged quantity of water would scour out the sand shoals and muddy
shores, and hurry off the filth produced from the common sewers, which through a certain
sluggishness in the stream is not cleared away at present. The west country barges, and
other large craft, would not be detained in certain parts of the river for want of water in
dry seasons. The upper end of the tidal water would swell the natural waters a long way
further up, and thereby release the craft from a demurrage, which increases the cost of the
voyage, this question pervading the inland trade as far as Reading and Oxford. If the
pass at London Bridge was free, the land floods of the Thames would have a ready passage
to the tide way and the sea, and thereby pass off the useless superabundance more readily,
and in such a manner that the shores and towing paths would be used, and barges pass
more freely under the floors of the scaffold bridges at Chelsea, Fulham, and Kingston.
The high waters of the tides respectively would be so much higher in this district, and the
velocity so much stronger upwards, that the voyage would be done in less time, and with
more safety, through a deeper water at each period of the tide. Some of the walls, it
is true, would be found between this bridge and Kew not quite adequate thereto, and
would have to be raised by their respective owners."
The area or space of water-way of the whole river at London Bridge before the same was
CHAP. VIII.
443
BRITAIN.
built was, by Mr. Mylne's measurements, " 19,586 feet superficial nearly, taking the width
equal to the length of the bridge, and the depth from the face of its bed, underneath the
arches, up to the visible marks of the flow of the tide on the modern stone-work. It is
reasonable to suppose, the bridge being removed, that would be the space through which
the tidal waters would flow. The water-way of all the arches or locks added together,
taken from the surface of the starlings (which are 1 foot 10 inches out of a level endways,
and not altogether on a level with one another across the river) down to the floors of the
locks respectively, was, in 1767, 3530 feet superficial. The water-way of all the said arches
above the starlings to high water mark, above mentioned, deducting the triangular spaces at
the haunches of each arch, forms a space of 4470 feet superficial. Now, these added toge-
ther form the whole space of 8005 feet nearly, and this is very much diminished in its
powers by being divided into nineteen parts, one very large, and many others exceedingly
small. It is further diminished in its effects by stages and piles, stretching 290 feet along
the bridge; and by as much as the water-wheels at their periphery do not move so fast as
the current of the stream in the face arches, and thereby producing a considerable retard-
ation of the due effect there would be if they were not there. Many of the floors of the
locks have been raised to a degree of no small danger, and the outsides of the starling have
been covered with planking since 1767, all of which last make considerable deductions from
the quantity of 8005 feet; yet if that space alone be deducted out of the area of the whole,
there remains of solids in this bridge 11,581 feet superficial. This is nearly a proportion
of the solid parts, occupying three-fifths of the river, and leaving only two-fifths for the
passage of the whole river."
The water-way at Westminster Bridge was, before it was built, 19,010 feet superficial,
and now 14,768 feet, so that the piers occupy 4242 feet superficial only.
The water-way at Blackfriars was, between the present shores before the bridge was built,
19,083 feet superficial; the water-way of all the arches or openings is 15,081 feet super-
ficial, and the piers occupy a space of 4001 feet superficial. The proportions then are as
follows:-
London Bridge
Westminster Bridge
Blackfriars Bridge
-
•
Area of River.
19,586
19,010
Solid.
11,581
19,083
4,242
4,001
Water-way.
8,005
14,768
15,082
When the committee of the House of Commons had determined upon the erection of a
new bridge, Mr. George Rennie, at the desire of his father the late Mr. Rennie, made the
design as it is now executed; and as the country lost the services of Mr. Rennie by his death
in 1821, the execution of this important undertaking devolved upon his sons, and Mr.
George Rennie holding at that time a situation under the government, his brother Sir John,
who was his junior, was named the acting engineer. Messrs. Joliffe and Banks were the
contractors, and the cost, including the approaches, amounted to £1,458,311 8s. 11 d.
The first pile for the cofferdam was driven on the 15th of March, 1824, and the dam was
finally closed on the 1st of April the following year, and after the water had been pumped
out 29 feet below low water mark, it was found remarkably tight.
On the 27th of April the workmen commenced their excavations in a stiff blue clay,
after which the sills and planking were laid ready for the foundations, which were com-
menced on the 15th of June: the first stone laid was a piece of Aberdeen granite, 5 feet
g of an inch long, 3 feet 63 inches broad, and 2 feet 10 inches deep, containing 50 feet
7 inches cube, and weighing 4 tons.
The cofferdam for the second pier was completed soon after, and pumped out by the
24th of August; in 1826 the foundations on the Southwark side, comprising the abutment
and wing-walls, were carried up, and the second pier was commenced.
The coffer-dams of the first and second piers being no longer required, a portion of the
piles were cut off on both sides, to prepare them for the support of the centres; and after
the horizontal wedges were fixed on the heads of the coffer-dam piles, on the 30th September
the first rib was set up by means of large sheer poles and powerful hoisting tackle, and
by the 10th November, the whole ten ribs were placed.
When the masonry of the second pier was sufficiently advanced, the centre, which had
been framed in the Isle of Dogs, was floated up the river, and being hoisted upon a large
double barge, was raised into its place by means of screws, assisted by the tide. The
cofferdam of the third pier had by this time advanced, and soon afterwards that of the
fourth pier, when it became necessary to provide more water-way by removing the pier
between the fifth and sixth locks of the old bridge, and forming a wooden tressel frame of
whole timbers for the traffic to pass. This was performed at the cost of 8000l. by demo-
lishing one half of the arch at a time, after which the pier below was taken away 4 feet
below low water mark. By the 4th of August, 1827, the first arch was completed; by the
end of the year the second arch was keyed in, the foundation of the third pier completed,
and that of the fourth laid. In 1828, the water being pumped out of the north abutment
dam, and the excavations made, the first pile was driven on the 1st of February, and the
444
Book I
HISTORY OF ENGINEERING.



व
Fig. 447.
LONDON BRIDGE.
CHAP VIII.
445
BRITAIN.
C
entire foundations completed on the 1st of March following; the masonry was then carried
up to the springing of the arches.
The first arch turned having now stood the entire winter, the wedges were struck
2 inches back on each side, and the crown lowered § of an inch; the wedges were
then driven back 4 inches more on the following day, when the crown of the arch sank
another half inch. On the third day they were driven back 6 inches, when the crown of
the whole arch was clear, and shortly after the wedges were entirely driven back, when the
soffite of the arch was accurately examined, and found to have preserved its form entire,
although it had lowered 1½ inch. By this time the centres of all the other arches were
placed, and the masonry considerably advanced in 1829 and 1830 the centres of the middle,
fourth, and fifth arches were shifted back, and when released of their load, the middle arch
sank 2½ inches, the fourth 24 inches, and the fifth 13 inch.
The centre arch is 152 feet span, and rises 29 feet 6 inches above Trinity high water
mark; the arches on either side span 140 feet, and rise 27 feet 6 inches above the same
line, and the abutment arches span 130 feet each, and rise above the same line 24 feet
6 inches. The entire water-way being 692 feet, the total length of the bridge 1005 feet, its
width from out to out 56 feet, and its height above low water 60 feet. The two centre
piers are 24 feet in thickness, and the two others 2 feet less.
So important a national work requires us to enter more into particulars, and to give the
specification and forms of the contract, which are perfect models of their kind, and will serve
as such for similar undertakings.
66
Cofferdams for the abutments.-These dams are to be of a circular form, and of the size
and dimensions in every respect as shown in the drawings exhibited; they are to be com-
posed entirely of the best Memel, Dantzic, Riga, or Stettin, fir timber. The piles are to be
composed entirely of whole timbers, that is, none to be less than 12 inches square when
measured in the work, and as much larger as the timber will allow; the main part of the
dam is to be composed of two rows of piles, not less than 5 feet apart, the inner row to be
driven not less than 10 feet, and the outer row not less than 8 feet below the lowest parts
of the foundations, that is, the square parts of the piles are to be driven to this depth besides
the shoes, and when driven, both rows are not to be less than 5 feet above high water mark
of spring tides, according to the Trinity House standard. These two rows of piles are to
be properly secured together with three rows of double waleing, not less than 12 inches
square each; these three rows of waleing are to be secured together with the best wrought-
iron screw bolts, 2 inches diameter, passing through each set of waleings at every 10 feet,
and having their ends secured with the best wrought-iron plates, not less than 10 inches
long by 8 inches wide, and 1 inch thick, and wrought-iron screw nuts 5 inches square, and
2 inches thick, and wooden cleats not less than 12 inches square and 3 feet long, the whole
to be well fitted and screwed up to their bearings. There is to be a third or outer row of
piles, to be composed entirely of whole timbers as before, and to be not less than 6 feet
asunder from the main rows of piles; these piles are to be driven not less than 8 feet below
the lowest part of the foundation, that is, the square part of the piles are to be of this depth
besides the shoes, and their heads are not to extend higher than the level of half-tides, or
7 feet below high water mark of spring tides, according to the Trinity House standard,
except that there are to be two piles at such distance as are shown in the drawings, to be
of the full height of the inner rows. This outer row of piles is to be connected together
with not less than three rows of double whole timber waleings, as before described, and to
be connected to the main dam with long wrought-iron screw-bolts, 2 inches diameter, passing
through the three rows of piles at each row of waleings, and at the centre of every space
between the bolts belonging to the inner rows of piles, and having their ends secured with
cleats and nuts as before described, and well fitted and screwed up to their bearings: the
whole of the three rows of piles above described are to be planed and straightened on the
edges, and the joints of the two inner rows are to be caulked and covered over with pitch,
so as to be perfectly water-tight; they are also to be braced firmly together by transverse
and diagonal braces, composed of half-timbers firmly fitted and spiked together, and having
their ends supported by cleats where required; the whole of the piles are to be properly
hooped and shod with the best wrought-iron, and the hoops and shoes to average 56 pounds
weight each. The spaces between the three rows of piles are to be well fitted with the
best tough well-beaten clay, thoroughly puddled, so as to be impervious to water;
the space
between the two inner rows of piles is to be filled with the above clay to the level of not
less than 2 feet above high water of spring tides, according to the Trinity House standard,
and the space between the outer and middle row of piles is only to be filled with clay up to
the level of 2 feet below the upper waleing of the second row of piles, and to incline
downwards to the heads of the outer row of piles; besides the diagonal and transverse
braces above described, there is to be a series of main, transverse, and longitudinal bracings
for the interior of the dam; at the level of each row of waleings these transverse and longi-
tudinal braces are to be composed entirely of double whole timbers, firmly scarfed, bolted,
and strapped together with the best wrought-iron bolts and straps, and supported by piles,
>
446
BOOK I.
HISTORY OF ENGINEERING.
as described in the drawings; the minor transverse and diagonal braces are to be composed
of whole timbers only.
"The whole of these braces are to be firmly united together with wrought-iron straps and
ties at their ends, in order that their dams may be firm and immovable in every part; there
is to be a tunnel, not less than 3 feet square, placed towards the centre of the dam, and at
the level of low water mark of spring tides, it is to be secured with a proper sluice worked
by machinery, as shown in the drawings, in order that it may be raised or lowered at
pleasure; this tunnel is to be properly secured on all sides to the piles, and to have its
joints well caulked, so that it may remain perfectly water-tight. There will be two of these
dams.
"Pier Cofferdams.—These dams are to be of an elliptical form, of the size and dimensions
as shown in the drawings; they are to be composed entirely of the best Dantzic, Memel, Riga,
or Stettin fir, all the piles to be composed of whole timbers, and none to be less than 12
inches square when in the work, the main dam to have two rows of piles, not less than 5 feet
asunder, and when driven to be not less than 5 feet above high water mark of spring tides,
according to the Trinity House standard; they are to be properly secured and connected

Fig. '48.
PLAN OF COFFERDAM, LONDON KRidge.
together with three rows of double whole timber waleings, having the best wrought-iron
screw bolts, 2 inches diameter, passing through them at every 10 feet, and well secured at
their ends with wrought-iron plates and nuts, and wooden cleats as before described; there
is also to be a third or outer row of whole timber piles, not less than 6 feet from the second
row; the heads of this row of piles are not to extend higher than the level of half tides, that
is, seven feet below high water mark of spring tides, according to the Trinity House
standard, only that there are to be two piles at such distances as shown in the drawings, to
the full height of the inner rows; this row of piles is to be connected together with three
rows of double whole timber waleings, not less than 12 inches square, and to be secured to
the main dam with long wrought-iron screw bolts, 2 inches diameter, with plates, cleats, and
nuts as before described, passing through three rows of piles at each row of waleings; at the
centre of every space between the bolts belonging to the two main rows of piles, the two
outer rows of piles are to be driven not less than 8 feet below the lowest part of the
foundation, and the inner row not less than 10 feet, that is, the square part of the piles are
to be of this depth besides the shoes; the spaces between the three rows of piles are to be
properly filled with tough well-beaten clay as before described, the whole of the exterior
joints being previously well caulked and covered with pitch. There are also to be proper
sets of cross and diagonal half-timber braces to connect the rows of piles together, and the
whole dam is to be braced longitudinally and transversely with double and single whole
timber braces, struts, and wrought-iron straps and ties; at the upper, middle, and lower
tiers of waleings, as shown in the drawings, there is to be a tunnel at one end of the dam,
3 feet square, secured by a sluice worked by proper machinery, as shown in the drawings,
in order that the sluice may be raised and lowered when required, the above tunnel to be
CHAP. VIII.
447
BRITAIN.
well fitted and secured to the piles as before described; the whole of the piles are to be
straightened and planed on the edges, and shod with good wrought-iron shoes, and properiy

Fig. 449.
FRAMING OF THE TIMBERS of cofferdam.
headed and hooped with strong wrought-iron hoops of the same weight as before described,
so as to prevent the piles from splitting whilst driving. There will be required four pier
dams.
"Foundations. -The earth for the foundations of the abutments is to be excavated to
such a depth, that the tops of the platforms at the front shall not be less than 34 feet
6 inches below high water mark, according to the Trinity House standard, and at the back
25 feet below the said Trinity House high water mark, and as shown in the drawings.
"The earth for the foundations of the two side piers is to be excavated to such a depth,
that the tops of the platforms shall not be less than 40 feet below the said Trinity House
high water mark.
"The earth for the foundations of the middle piers is to be excavated to such a depth
that the tops of the platforms shall not be less than 43 feet below the said Trinity House
high water mark. When the earth has been excavated to the required depth, piles are to
be driven to sustain the weight of the superstructure; these are to be of elm, fir, or beech
timber, not less, on an average, than 12 inches diameter in the middle, and 20 feet long,
properly shod with good wrought-iron shoes, not less than 35 pounds weight each, and
good wrought-iron hoops 30 pounds weight each, so as to prevent the piles from splitting
whilst driving. The piles under the foundations of the abutments are to be driven at right
angles to the inclination of the foundations, and those for the piers are to be driven perpen-
dicular, as shown in the drawings; all these piles are to be driven not less than 18 feet
below the under side of the respective platforms of the piers and abutments, that is, the
square parts of the piles, besides the shoes are to be driven to this depth. The piles are to
be driven in rows about 4 feet asunder from centre to centre, as shown in the drawings.
When all the piles are driven to the requisite depth, their heads are to be cut off level and
even, and the earth from between is to be excavated to the depth of 9 inches below the pile-
heads, and the spaces between are to be filled with Kentish ragstone, well beat down and
racked in with sharp gravel and lime screenings to the level of the pile-heads, in the pro-
portion of one part of lime to five parts of gravel, after which sills of beech, elm, or fir
timber, not less than 12 inches square each, are to be laid and fitted solidly on the pile-
heads, in the transverse direction of the foundations, and firmly spiked to each pile with
jagged wrought-iron spikes 18 inches long, and 1 inches square; between these sills,
except at the extremities, which are to be filled with square blocks of stone, the spaces are
to be built up with good sound brickwork, composed of the best sound, hard, well-burnt
grey stock bricks, set in mortar, composed of four parts of clean sharp river sand to one
part of well-burnt Merstham, Dorking, or other lime equally good; above these sills there
are to be laid and properly fitted other rows of sills longitudinally over the pile-heads below,
448
BOOK I.
HISTORY OF ENGINEERING.
and at right angles to the other sills: these rows of sills are to be of the same materials and
dimensions as the former, and to be firmly spiked down to the lower rows of sills with

Fig. 450.
4
•
•
•
SECTION THROUGH PIER OF LONDON BRIDGE,
18-inch jagged spikes, as before described. The spaces between the upper rows of sills are
to be well fitted and built up level with Bramley Fall, Painshaw, or other stone equally good,

Fig. 451.
set in and grouted with mortar similar to that above described, and when made level with the
top of the sills, the whole of the foundations are to be covered with 6-inch beech, elm, or fir
planks, to be bedded in mortar, as before described, and to be well-fitted, close-jointed, and
firmly spiked down to the sills with the best wrought-iron jagged spikes, 12 inches long,
and inch square, and upon this platform the masonry hereinafter to be described is to be
3 å
built. Along the front of the abutments, and on each return, and round the entire found-
ation of the piers, sheeting piling is to be driven to the depth of not less than 12 feet below
the top of the above described platforms of the abutments, and 14 feet below the top of the
platforms of the piers, that is, the square parts of the piles are to be of this depth, besides
CHAP. VIII.
449
BRITAIN.
the shoes.
These piles are to be of clean beech, elm, or fir timber, not less than 6 inches
thick, except those for the piers, which are to be fir timber, not less than 12 inches square,
the whole to be well straightened, planed, ploughed, and tongued on the edges, and driven
perfectly close, and to be connected together with half timber fir waleings, well bolted and
secured to the piles. These piles are to be hooped and shod with wrought-iron hoops and
shoes, averaging 26 pounds weight each for the small and 36 pounds weight each for the
large piles. The above sheet piling to be pitched not less than 18 feet long each pile, and
to be commenced previous to the main foundation, in order to facilitate getting down to
the required depth for the foundation.
“Stairs. The foundations for the stair walls in front are to be excavated to such a depth
that the upper side or top of the platform may not be less than 34 feet 6 inches below the
said Trinity House standard high water mark, decreasing backwards in depth according
to the inclination of the abutments, as shown in the drawings; bearing piles of beech, elm,
or fir timber, not less than 12 inches diameter in the middle, are then to be driven not less
than 12 feet below the under side of the platform of the foundation, that is, the square parts
of the piles are to be of this depth, besides the shoes, and 4 feet from centre to centre; the
heads of these piles are then to be cut off and levelled, and the earth from between is to be
excavated to the depth of 9 inches below, and the spaces are to be filled with Kentish rag-
stone as before described, well beat down, and racked in with sharp gravel. One tier of
sills not less than 12 inches square is then to be laid and solidly fitted on them, and well
spiked down to the piles with 18-inch best wrought-iron jagged spikes, not less than
1 inches square; between the sills there is to be brickwork well bedded in mortar com-
posed of three parts of clean sharp river sand to one part of the best lime, and the whole is
to be well grouted and made solid to the level of the top of the sills. The whole area of
the foundations is then to be covered with a flooring of 6-inch beech, elm, or fir plank,
well bedded in mortar as before described, properly jointed, and firmly spiked down to the
sills with the best wrought-iron jagged spikes 12 inches long, and of an inch square;
934
the whole of the sills and planking are to be laid so that they may break joint not less than
4 feet beyond each other.

B
HE
BHE
CHE
Fig. 452.
SECTION THROUGH STAIRS OF LONDON BRIDGE,
"All piles that break or split in driving, or that are wrong placed, or that do not
go in their proper direction, are to be taken out and replaced at the expense of the con-
tractor.
"The masonry of the abutments up to the springing of the arches is to be built or com-
G g
450
Book I.
HISTORY OF ENGINEERING.
posed of ashler, in courses of not less than 15 inches nor more than 24 inches thick in the
front, and the beds in the interior are to incline parallel backwards, as shown in the
drawings; but the courses next to those under the springing of the arches are to be of the
thickness and projection as shown in the drawings. The exterior stone, for an average
depth of 5 feet 6 inches to within 3 feet below the springing of the arches, is to be com-
posed of the best English, Scotch, Irish, Jersey, or Guernsey granite, to be approved of
by the principal engineer; the interior stone is to be composed of one half of the best
Bramley Fall, and the remainder of Painshaw, Derbyshire, or other stone equally good.
"The masonry is to be formed of header and stretcher courses alternately; the headers to
be on an average 5½ feet long, but not less than 41 feet long, and of the average breadth
of 3 feet, but no stone to be less than 2 feet 3 inches wide.
“The stretchers to be on an average 5 feet long, and none less than 4 feet, and an average
width of 3 feet, but none to be less than 2 feet 3 inches wide. The backing or hearting
to be laid in courses of headers and stretchers alternately, the headers being opposite to the
stretchers in front, and in size and thickness suitable thereto, so that the whole masonry,
exterior and interior, may be completely solid and bonded together throughout every part,
and double joggles to be used where and when considered necessary by the principal
engineer, according to the mode shown in the drawings, and the upper bed of each course
is to be dressed off smooth and even before the next course is commenced. The whole of
the exterior stone is to be smooth and fine hammer-dressed on the face.
"The horizontal beds are to be fine dressed and rusticated 2 inches each way; but the
upright or vertical joints are to be plain and perfectly straight and fine dressed for at least
15 inches inwards; the remainder of the stone to preserve its full dimension, and to be
fine picked and straight between the whole of the backing or hearting, to be straight
dressed in the beds and joints, and the upper bed of each course to be dressed off smooth
previous to commencing the next course; all the backing belonging to each course is
to preserve an equal thickness, and upon no account must it be permitted to run one
course into another, except where joggles or dowels are directed to be used; the whole
of the above described masonry is to be set flush in beds of the respective kinds of mortar
hereinafter to be described, and properly grouted.
“The masonry of the piers up to the springing of the arches is to be built or composed
of ashler, laid in horizontal courses of not less than 15 nor more than 24 inches thick,
except the course next to those under the springing, which is to be of the thickness and
projection as shown in the drawings. The whole of the exterior stone for 5 feet 6 inches
inwards, except within 3 feet of the springing (which is to be of granite), is to be composed
of the best granite as before described. The interior stone is to be composed of one half
of Bramley Fall, and the remainder of Painshaw, Derbyshire, or other stone equally good.
“The masonry is to be formed with headers and stretcher-courses alternately, the headers
to be on an average 5 feet long, but none less than 4 feet long, and on the average breadth
of 3 feet, but none less than 2 feet 3 inches. The stretchers to be on an average of 5 feet
in length, and none less than 4 feet long, and an average width of 3 feet, but none to be
less than 2 feet 3 inches wide. The backing or hearting is to be laid in courses cor-
responding in thickness with the outside courses of ashler, header and stretcher alter-
nately, the headers being opposite the stretchers in front, and in size and thickness suitable
thereto, so that the whole of the masonry, exterior and interior, may be solid and bonded
together throughout every part, and dowels and joggles are to be used where and when
considered necessary by the principal engineer, and the upper bed of each course is to be
dressed off smooth and even before the next course is commenced; the whole of the
exterior stone is to be smooth, and fine hammer-dressed on the face; the horizontal beds
are to be perfectly straight and fine dressed, and rusticated 2 inches each way, but the
upright or vertical joints are to be perfectly straight and fine dressed for at least 15 inches
inwards; the remainder of the stone to preserve its full dimensions, and to be fair picked
and squared between. The whole of the backing or hearting is to be fair dressed on the
beds and joints, and the upper bed of each course is to be dressed off smooth; and
previous to commencing the next course, all the backing belonging to each course is to
preserve an equal thickness, and upon no account must it be permitted to run one course
into another, except where joggles or dowels are directed to be used; the whole of the
above described masonry is to be set flush in beds of the respective kinds of mortar herein-
after to be described, and properly grouted.
These walls are to be con-
"The stair walls to the level of the springing of the arches.
structed agreeably to the drawings, and to be composed of hard, well-burnt stock bricks
for the interior; the exterior, to the level of the bed of the river or adjoining ground, to
be composed of the best Bramley Fall stone or other stone equally good, laid in courses
not less than 15 nor more than 24 inches thick, to be laid header and stretcher alter-
nately, and on an average depth, the bed not less than 3 feet 6 inches, and above the bed
of the river, to the level of the springing of the arches; the exterior to be composed
of the best granite as before described, and in courses not less than 15 nor more than
CHAP. VIII.
451
BRITAIN.
21 inches thick, laid header and stretcher alternately, and an average depth on the bed of
not less than 3 feet 6 inches; the upper bed of each course to be dressed smooth and even
before the next course is commenced; the faces, beds, and joints of the exterior stone-
work, as well as the setting, to be executed similar to that described for the abutments
and piers.
"The Centres. There are to be four complete sets of centres, on which the arches are to
be turned; each set of centres is to consist of eight ribs properly braced together, and to
be executed according to the drawings; they are to be composed of the best Dantzic, Memel,
Riga, Stettin fir timber, except the springing pieces, which are to be of elm, and the

200
र
Fig. 453.
PIER OF LONDON BRIDGE.
striking wedges are to be of oak of the best quality, entirely free from sap or wane, and
cased on the upper and lower sides with fine sheet copper, one-tenth of an inch thick, and to
be well greased previous to being put in their places.
"The iron work to be composed of the very best English iron, and to be executed as
described in the drawings; the supports or trussels for carrying the centre to be of the
best fir timber of the quality above described; the trussels and centres when fixed to
be firm and strongly braced longitudinally and diagonally, so as to make them firm and
secure.
"The covering of the centre for carrying the arch-stone is to be of good sound fir, half
timber, 7 inches thick, to be carefully laid, properly levelled, and firmly packed and
wedged up to the curvature of the respective arches.
“ Arches. The arches are to be of semi-ellipses. The centre arch to be 152 feet span in
the clear, and 29 feet 6 inches rise when finished; the voussoirs, or arch-stones, to be 4 feet
9 inches deep at the crown, and not less than 10 feet at the springing. The two arches
next the centre are to be 140 feet span each, and 27 feet 6 inches rise; the voussoirs at
the crown to be 4 feet 7 inches deep, increasing to not less than 9 feet at the springing; the
two side arches to be 130 feet span each, and 24 feet 6 inches rise; the voussoirs, or arch
stones, at the crown to be 4 feet 6 inches deep, increasing to not less than 8 feet 6 inches at
the springing.
"The whole of the arch-stones are to be headers, except where the engineer shall allow
stretchers to be used. They are all to be 18 inches thick at the intrados or inside of the
curve, and to increase in thickness to the extrados or outside of the curve, according to the
radius of curvature at the respective places where they are to be used. Of these arch-
stones none are to be less than 2 feet 6 inches wide, and none of them to overlap at the
joints in their respective courses less than 15 inches. The length of the arch-stone is to
GG 2
452
BOOK I.
HISTORY OF ENGINEERING.
increase where the inverted or the abutting arches on the piers commence, agreeably to the
ratio shown in the drawings, and in the abutments they are to be continued on the same
line of radius to the full extremity of the abutments, diminishing from the top of the

Fig. 454.
Elevation of centre ARCH, LONDON BRIDGE.
abutments until they come to the regular depth of the arches, as shown in the drawings;
the outside or quoins of the arches are to continue in length to meet the horizontal courses
in the spandrils between the arches.
"The arch-stones are all to be dressed perfectly smooth and straight on the beds, sides,
and faces, without any deficiency whatever. The faces and soffits are to be fine-dressed
and rusticated as before described; the extrados to be formed according to the drawings,
and rough hammer-dressed, except where the inverted arches join, and these are to be
smooth dressed, so as to bear and fit solidly in every part.
"The whole of the arches, interior and exterior, are to be composed of the best granite as
before described; there are to be four sets of connecting bars, composed of the very best
wrought-iron in each arch, of the forms, dimensions, and position shown in the drawings;
the whole of the arch-stones are to be properly bedded and jointed in mortar hereafter to
be described.
“Solid spandrils over the piers to the under side of the inverted arches; these are to be
made up with solid masonry in horizontal courses, corresponding in thickness, and closely
fitted to the extrados or back part of the arch-stones at their respective places as shown in
the drawings; these are to be composed of the best granite as before described.
"The top bed of each course is to be dressed off smooth and even before the next course is
commenced; the whole of the above courses of stone are to be firmly squared and dressed
in their beds and joints, so that they may fit solid and close in every part, and they are to
be set in beds of fine mortar hereafter to be described.
"Inverted Arches. The inverted arches over the piers are to be constructed as shown in
the drawings, and the depth of these inverted or abutting arches is to be 6 feet in the
middle for the two centre piers, and 5 feet for the two side piers; these inverted arches are
to be composed of courses not less than 18 inches thick at the soffit, and increasing in
thickness according to the radius, and they are to rest on the solid spandrils before
described, and to be close and accurately fitted to them and the extremities or extrados of the
arch-stones; they are to be composed of the very best granite as before described; the whole
of the above described inverted arch-stones are to be finely dressed in every part without
any deficiencies whatever; they are to be set in fine mortar hereafter to be described:
there is to be a circular opening of 18 inches diameter through the centre of each pier and
through the solid spandril and inverted arches, and through the pier below the level of
low-water mark, as shown in the drawings, where it is to communicate with the river to
carry off the leakage or soakage water that may accumulate from above.
"The outside spandril walls, between the arches and against the abutments, are to be 5
feet thick, and fronted with granite, as before described, in courses of suitable thickness to
those of the arch-stones, against which they are to abut, and fit closely as represented in the
drawings.
CHAP. VIII.
453
BRITAIN.
"These courses are to be laid headers and stretchers alternately; the headers not to be less
than 2 feet 6 inches wide in the face, and run generally through the whole thickness
of the wall, but no stone to be less in the bed than 3 feet 6 inches long; the stretchers are

阿
​Fig. 455.
SECTION THROUGH ABUTMENTS OF LONDON bridge.
not to be longer than 5 feet, nor less in breadth, on an average, than 2 feet 6 inches, and no
stone less than 2 feet broad: and whenever a header or stretcher is used less than the
dimensions above given, the next stone is to exceed the average dimensions as much as the
stone in question is under it. The backing is to be of the best Bramley Fall, Painshaw,
Derbyshire, or other stone equally good, and laid in courses in thickness corresponding to
those in front. The top of each course throughout to be dressed off smooth and even
before the next course is commenced. The horizontal joints or beds of all the spandril
courses are to be rusticated as before; the vertical joints to be plain and fair-dressed, and
the outside face to be fair hammer-dressed; the interior joints to be square, close, and well-
fitted. The covering or cap-stones on the point of the piers to be fair-dressed on the exte-
rior and on the beds and joints, and they are to be secured to the facia course below with
proper sized stone dowels 6 inches square, and to be of the best granite, as before described.
The whole to be set in mortar hereafter to be described.
"Buttresses.-There is to be a rectangular buttress over each pier and abutment, as shown
in the drawings, the outside to be faced with the best granite for at least 3 feet 6 inches in-
wards; the plinth or lower part to be plain and fair-dressed on the face; the faces and
beds and joints to be properly dressed, and secured to the course below with sufficient
stone dowels, and the masonry above to be in courses corresponding with those of the span-
dril walls, and header and stretcher courses alternately; the backing to be composed of the
best Bramley Fall, Painshaw, Derbyshire, or other stone equally good, laid in courses equal
in thickness with the front or outside courses, and to be straight, square, and fair punched in
the joints, and dressed on the beds; the top beds of each course to be dressed off smooth
before the next course is commenced, and the horizontal joints of the outside courses are to
be rusticated as before, and the faces hammer-dressed in every respect as the spandril
walls.
"The outside of the abutments and wing-walls above the springing of the arches is to be
executed in every respect as described in the drawings, to be faced with the best granite, as
before mentioned; to be upon the average not less than 3 feet 6 inches, and to be backed
with Bramley Fall, Painshaw, Derbyshire, or Red Castle stone. The wing-walls to be of
the thickness described, and the backing to be in courses corresponding in thickness with
GG 3
454
BOOK I.
HISTORY OF ENGINEERING.
those in front. The horizontal joints to be rusticated, and to be in every respect executed
in the same manner as the spandril walls and buttresses over the piers, the whole to be set
in mortar hereinafter to be described.
"Waterman's Stairs.-The walls above the level of the springing of the arches are to be
executed as described in the drawings; they are to be composed of the best hard grey stock
bricks for the interior, the exterior to be composed of the best granite, as before described,
and in courses of not less than 15 nor more than 21 inches thick, laid header and stretcher
alternately, and average depth in the bed of not less than 3 feet 6 inches, the upper bed of
each course to be dressed smooth and even before the next course is commenced, and the
horizontal joints are to be rusticated as before.
"Interior Spandril Walls.-Previous to these spandril walls being commenced, the whole of
the joints on the back of the arches and of the inverted arches are to be well cleared out, and if
any opening can be found it is to be properly filled with grout, and afterwards the joints are to
be well and firmly pointed with Roman cement, and the whole surface of the arches between
the termination of the inner spandril walls on each side of the crown of the arches to be covered
with a sufficient coating of Roman cement of the best quality; the interior spandril walls
are to be composed of the best hard well-burnt grey stock bricks, laid flush in mortar of
three parts clean sharp river sand to one part of well-burnt Merstham, Dorking, or other
lime equally good; the interior mortar to be composed of four parts of sand to one part of
lime; these are to be six in number over each pier, and to extend from arch to arch, the
walls to be 2 feet 3 inches thick; on the tops of these walls are to be stone corbels 18
inches deep, projecting on each side over the walls not less than 12 inches, and there are to
be corbels projecting 12 inches from the inner side of the retaining outside spandril walls;
these are to be composed of Bramley Fall, Painshaw, or Derbyshire stone.
"The whole surface over these walls, and for 1 foot on each of the retaining or outside
spandril walls, to be covered with good strong Yorkshire landings not less than 9 inches
thick, the longitudinal joints in all cases to be over the centre of the interior spandril walls:
these coverings are to be fair-dressed, and close and well-jointed, and firmly and solidly
bedded on the corbels underneath, in mortar hereafter described.
"Roadway over the Bridge.—When the whole of the arches and spandril wall coverings
have been carried up to the level for receiving the roadway, the whole surface of the bridge
is to be covered with a bed of sound, tough, well-beaten clay, 15 inches thick, thoroughly
puddled, and well-beaten together, so as to become perfectly impervious to water. The
clay is then to be covered with 3 inches of fine sand; there is then to be a course 12
inches thick of fine flint stones, broken into small pieces, so that none are to be larger in
size than 2 inches diameter; the whole is then to be well-dressed and rolled. The foot
paving is to be composed of granite, as before described. These stones are to be the whole
length of the footpath, that is, 7 feet 6 inches long, 8 inches thick, and 3 feet and upwards
wide; on the one end they are to be properly bedded on the cornice; and at the other end
they are to be supported by curbstones not less than 4 feet long, 9 inches wide, and 12
inches deep, set edgeways, to be of the best granite, as before described, and properly bedded
and jointed, and set in mortar. The intermediate spaces are to be filled with fine gravel or
sand, so that the paving may be bedded throughout. Along the front of these stones there
are to be gutters or watercourses, paved with granite pitching paving 9 inches deep on
each side, for the width of 5 feet 6 inches from the outside of the foot paving. It must be
observed that the roadway is to be curved 6 inches in its transverse direction, and the
clay and pavement is to incline inwards towards the gutters, as shown in the drawings.
"Cornice and Parapets. The cornice and parapets are to be constructed of the best
granite, as before described, and are to be executed in every respect agreeably to the
drawings; they are both to be finely dressed and jointed; none of the stones belonging to
the cornice, plinth, dado, or coping of the parapet to be less than 4 feet 6 inches long, and
to be bonded and dowelled properly over each other, the coping to be dowelled at every
joint by a projecting dowell 2 inches square, fitted into an equal recess in the adjacent
stone. All the stone is to be perfectly free of blemish and deficiencies of any kind
whatever.
CC
Approaches. The approaches are to be formed of solid embankments and arches where
the height will admit, as shown in the drawings; in the former case the embankments are
to be supported on the sides with brick retaining walls, as shown, and where arches are
adopted the piers are to be founded 6 feet below high water mark, according to the Trinity
House standard, and the retaining walls 3 feet below the said high water mark; the un-
sound earth, for at least 6 inches below, is to be removed, and to be replaced with sound
gravel and lime, in the proportion of five parts of the former to one of the latter, to be well
mixed and puddled together, and to be allowed time to harden; there is then to be laid
Yorkshire landings 6 inches thick, and not less than 2 feet wide, and at every 6 feet to be
4 feet wide each for the whole width of the foundations; upon the top of these landings
there is to be laid a course of Bramley Fall, Derbyshire, Painshaw, Red Castle stone, 15
inches thick, 4 feet wide, and not less than 4 feet long, to be so laid as to break bond over
CHAP. VIII.
455
BRITAIN.
the landings, not less than 18 inches each stone. The piers are then to commence, and to
be 4 feet wide at the bottom, and set off until at 4 feet high, they are to be reduced to 2
feet 3 inches wide. The cross walls, where necessary, are to be done in the same manner.
The retaining walls above and below the springing of the arches are to be 2 feet 3 inches
thick, and to batter, as shown in the drawings, at the springing of the arches; over each
pier there is to be a complete course of Bramley Fall, Painshaw, or Derbyshire stone, 18
inches thick, well-dressed and bedded in mortar, hereafter to be described.
"The arches are all to be semicircular, 16 feet span each, and 18 inches deep at the crown,
and increasing in the haunches, as shown in the drawings. The brickwork is to be com-
posed of the best hard well-burnt grey stock bricks laid flush in mortar of three parts of
clean sharp river sand to one of the best well-burnt Dorking, Merstham, or other lime
equally good, the interior mortar to be composed of four parts of sand to one of lime.
"The roadway to be formed with 18 inches of sound tough clay, well-beaten and puddled
together, so as to be impervious to water, 3 inches of sand and 12 inches of flints, broken
equally into small pieces about 2 inches diameter, and mixed with a small portion of chalk
at the surface, and well-dressed and rolled together; the clay, sand, and flint are to be laid
inclining towards the gutters.
"On each side of the road is to be a foot pavement 9 feet wide, to be composed of the
best Yorkshire landings, 4 inches thick, and laid in courses not less than 2 feet 3 inches
wide, and no stone to contain less than 4 superficial feet; they are to be fair-tooled on their
upper beds, and squared in their lower beds; the joints are to be properly dressed and set
in mortar, before described; at their side they are to be bordered by curbstones of the best
granite, as before mentioned, not less than 12 inches wide, and 9 inches thick, and + feet
long, to break bond well with the landings, and to be properly fitted to them, the whole of
the paving to be laid in the best manner. There is to be a paved gutter on each side of the
road, to be done with the best granite pitching paving, as before, not less than 4 feet wide
and 9 inches deep, done in the best manner.
“Mortar.—The mortar of the different parts of the bridge is to be composed of two kinds,
namely, lime mortar and pozzolano mortar; the former is to be composed of the very best
Dorking, Mersthamn, or other lime equally good, well-burnt and ground up in a mortar
mill on the spot to a fine powder in its dry state, and afterwards mixed with the requisite
proportions of clean sharp river sand and water under the mortar mill. The lime mortar
for the whole exterior of the bridge and arches, with the exception hereafter to be mentioned,
is to be composed of three parts of sand and one part of lime; the exterior must be understood
to extend 3 feet inwards; the interior mortar to be composed of four parts of sand to one
part of lime, except where otherwise mentioned. The exterior mortar for the piers and
abutments, from the foundations up to the Trinity House high water mark of spring-tides,
is to be composed of one part of the best pozzolano, one part Dorking or Merstham lime,
and two parts of sand, to be well-mixed and ground up together under the mortar mill, as
before described.
"The whole of the workmanship and materials above described to be of the best descrip-
tion of the respective kinds, and to be executed to the entire satisfaction of the principal
engineer appointed to direct and superintend the works, who shall have full power during
the progress of the work to reject all improper workmanship and materials, or to make
such alterations or additions in the plans and specifications alluded to, as the nature of the
foundations or the circumstances may, in his opinion, require; proper allowances being
made to the contractor where additions are made, or deductions where diminished, according
to the scale of prices to be delivered in and approved of at the time of making the contract;
and if any difference should arise between the engineer and the contractor as to any matter,
clause, or thing in the specification or plans above alluded to, the same to be decided by the
principal engineer, without reference to any other party or parties whatsoever."
The contract contained the following covenants on the part of the contractors:
"To execute and perform in a substantial, perfect, and workmanlike manner, and to the
satisfaction, and according to the directions, of the principal engineer for the time being,
without reference to any other person or persons, all the cofferdams, excavations,
foundations, abutments, piers, centres, arches, spandrils, buttresses, stairs, walls, cornices,
parapets, embankments, and other works of every description, which shall be required to
be done and executed in and about the building, executing, constructing, finishing, and
completing the new bridge, and the approaches thereto, and the road and footway over the
same, according to the plans, and under and subject to the directions, rules, regulations, and
explanations and restrictions mentioned or referred to in the above specification, with such
alterations, if any, as may from time to time be directed by the principal engineer in manner
hereinafter mentioned.
"To find and provide all the stone, timber, iron, bricks, mortar, lime, sand, chalk, gravel,
clay, and other materials necessary for executing the works of the kinds and descriptions
mentioned in the specification, to be directed by the principal engineer, or the resident
GG 4
456
BOOK I.
HISTORY OF ENGINEERING.
engineer acting under his directions, and of such quality as shall be approved of by the
principal or resident engineer.
"To find, provide, and erect from time to time to the satisfaction, and according to the
directions of the principal engineer, such steam engine, or steam engines, with proper pumps
and machinery of every description, as shall be necessary to keep the works clear of water.
"To find and provide to the satisfaction, and according to the direction, of the principal
engineer, or the resident engineer acting under his direction, all such places for depositing
and working materials, and all such temporary roads, railways, gangways, stages, scaffold-
ings, pile engines, cranes, crabs, blocks, shears, tackles, chains, barrows, ropes, planks, and
all such other engines, machines, tools, implements, utensils, and labour, as shall be necessary
for the execution of the said works, as well at the said intended bridge as at the place or
places to be provided for by the contractor for depositing and working materials; and also
all such boats, barges, carriages, and labour as shall be requisite for conveying the said
materials, engines, machinery, and implements to and from the places where the same
respectively are to be used for clearing away superfluous earth and rubbish.
"To drive and provide such guard piles, dolphins, moorings, and other fences and pro-
tectors as shall be necessary for the safety of the works, to bear all risk and responsibility
whatever attending the execution of the works, and without any delay to make good all
damages of every description which may happen to the works, or any parts thereof,
during the progress of the same; and pay the expenses of, or make good all settlements
or defects which may happen to any wharfs or buildings near the works, and all
other damages which may be occasioned by, or in consequence of, the works or any
of them.
"To make and contract according to the satisfaction and according to the directions of
the principal engineer, or the resident engineer acting under his directions, such works as
shall be necessary for preventing the possibility of injury or damage to the present bridge
or the starlings thereof, by the execution of the works, or in consequence of removing the
nosings of the western extremity of the sterlings of the present bridge, which the contractor,
with the approbation of the principal engineer, is authorized to take away for the more
convenient erection of the cofferdams, or in consequence of any alteration in the present
bridge, which shall be made with the approbation of the committee and of the principal
engineer.
"In case any injury or damage shall happen to the present bridge, or the sterlings
thereof, during the progress of the works, the contractor is without any delay to make good
and repair the same.
"To construct, remove, and fix the cofferdams, guard piles, and moorings, and other
temporary works in such places, at such times, and in such manner as the principal
engineer, or the resident engineer acting under his directions, shall direct.
"The execution of the works to be arranged in such manner that a free and sufficient
passage shall at all times be preserved for such vessels as can now pass through the present
London Bridge.
"To provide during the progress of the works such watchmen, gate-keepers, and other
persons as may be necessary for the protection thereof.
"The contractor shall constantly attend to the works during the progress thereof, and to
the due execution thereof in manner aforesaid.
"All the works shall be performed, finished, and completed to the full and entire satis-
faction of the principal engineer in the manner aforesaid, and according to the true intent
and meaning of the contract, in or before the
day of
day of
"To clear away before the said
all the dams, scaffolding
materials, and rubbish, and remove all other obstructions occasioned by the building of the
bridge, except such part thereof (if any) as shall be directed to be left for any further time
by the principal engineer.
"In case the principal engineer shall, at any time or times during the progress of the said
works, think proper to cause any alterations in, or variations from, the original plans and
the above specification to be made on account of the nature of the foundations, or any other
circumstances, either by increasing the works, or the scale of magnitude thereof, or altering
the quality of any part thereof, or omitting some part, or diminishing the works, or the scale
of magnitude thereof, or altering the quality of any part of the works, or the materials to
be used therein, or otherwise; and shall give notice in writing to the contractor of such
alterations or variations, the contractor is to execute, perform, and complete the works
according to such alterations or variations in the manner, and within the time, in which the
works ought to be completed according to the true intent and meaning of the contract; and
such alterations and variations shall not vacate or lessen the validity of any of the covenants
or agreements contained in the contract, but such sum of money shall be added to or
deducted from the sum agreed to be paid to the contractor, as the principal engineer shall
estimate to be the value of such alterations or variations, according to the measurements
thereof, at the prices mentioned in the scale of prices to be delivered by the contractor at
CHAP. VIII.
457
BRITAIN.
the time of making his tender, and to be approved by the principal engineer, and in case
any works or materials shall be included in any alteration or variation, the price of which
is not mentioned in the said scale of prices, or cannot be determined according thereto,
then the value thereof shall be estimated by the principal engineer at a fair and reasonable
price.
"In case any day work shall be required by every such alteration or variation as is not pro-
vided for by the said specification or the said scale of prices, the contractor is to deliver in
every week to the principal engineer, or the resident engineer acting under his direction, an
account of such day work as shall have been performed on account thereof; and in case any
day work shall have been done of which such account shall not be delivered in within one
week after the same shall have been performed, the contractor shall not be entitled to any
payment or compensation in respect thereof.
"If any materials provided to be used in or about the works shall not be approved of by
the principal engineer, or the resident engineer acting under his direction, previous to their
being brought into use, he shall be at liberty to reject the same, and if the contractor, his
executors or administrators, shall not, within twenty-four hours next after notice of such rejec-
tion shall have been given or left at his usual or last place of residence, or with his foreman or
clerk of the works, clear away and remove the same, it shall be lawful for the principal
engineer, or the resident engineer acting under his direction, to order the same to be carted
to the city greenyard, and forthwith to sell the same, and out of the money arising from such
sale to pay all expenses occasioned by such removal and sale, and to pay the surplus only
(if any) to the contractor.
"In case the principal engineer, or the resident engineer acting under his direction, shall
disapprove of the workmanship or execution of any parts or part of the works, the same shall
be immediately taken down and re-executed, or altered to his satisfaction, and in case the
contractor shall not within three days after notice in writing of such disapprobation shall
have been given to him, or left at his usual or last place of abode, or with his foreman or
clerk of the works, proceed to take down, alter, amend, or rectify such disapproved part of
the works, then it shall be lawful for the principal engineer, or the resident engineer acting
under his direction, to employ other workmen to take down and amend and rectify the
same, and that the contractor shall permit the mayor and commonalty and citizens of the
city of London, or the committee, to retain out of the money which may be due to the
contractor on account of the works, the amount of the bills of such other workmen, for and
in respect of their work, labour, and materials which may have been done, performed, and used
in and about the rectifying or amending such part of the works; and in case the monies due
on account of the works shall not be sufficient to satisfy the bills of the said other workmen,
then the contractor shall, on demand, pay unto the said mayor and commonalty and
citizens, or their successors, or to the said committee, so much of the amount of the bills as
the said monies shall be insufficient to satisfy.
"In case the contractor shall refuse or neglect to perform the works, or any of them, in
manner hereinbefore described, or in the specification mentioned, or to obey and comply
with any orders or directions to be given by the principal engineer, or the resident engineer
acting under his directions, or in case at any time during the progress of the said works
there shall appear to the principal engineer to be any unnecessary delay in the carrying on
of the works, or any part thereof, either by not employing sufficient number of workmen, or
otherwise howsoever, or in case any of the works shall not be performed to the satisfaction
of the said principal engineer, or shall not be finished within the time hereinbefore men-
tioned for completing the same, or in case the said contractor shall depart this life before
the said works shall be fully completed, then, and in any such case, it shall be lawful for
the said committee, if they shall think proper, any time before the said works shall be com-
pleted, by any writing signed by their clerk, to be given to the contractor, his executors and
administrators, or left at his or their usual place of residence, to revoke and make the con-
tract void, and every clause, matter, or thing therein contained, so far as relates to the
subsequent part of the works, and the same shall be thereon null and void; and in case such
declaration as last aforesaid shall be made during the progress of the works, that only part
of the money to be paid to the contractor shall be paid in respect of such part of the works
which shall have been executed, as shall be estimated by the principal engineer to be the
value of such part according to the scale of prices before mentioned, and in consequence
of
any omission in the scale of prices, any part of the works cannot be estimated thereby,
the value of such part thereof shall be determined according to the judgment of the
principal engineer.
"In case the said committee, in pursuance of the powers before given them, shall make the
contract void, the contractor, his executors or administrators, shall not remove or be entitled
to remove or take away any of the dams or engines made or erected and placed in or upon
or rear to the works for the purposes thereof, or any of the materials found or provided for
carrying on the same, until the principal engineer, or the resident engineer acting under his
direction, shall permit the same to be removed, but the value of such materials, and of the
458
Book I
HISTORY OF ENGINEERING.
use and employment and wear and tear, or the purchase (as such engineer may think most
expedient) of such engines, dams, and works as the said principal engineer shall think
proper to be retained shall be estimated
and determined by the principal engineer,
and shall be paid or allowed to the con-
tractor, his executors or administrators, to-
gether with such sum of money as he or
they shall be entitled to in respect of the
part of the works which shall have been
executed.
"The direction, certificate, valuation,
and opinion of the principal engineer re-
specting the execution of the works, the
quality of the materials employed, the
value of the works executed, any alter-
ations or variations from the plans and
specification hereinbefore mentioned or re-
ferred to, or of any part of the works which
shall have been executed, or of any engines,
dams, machinery, or materials, or the con-
struction of any matter, clause, and thing
contained in the contract, specification, or
scale of prices, or either of them, or other-
wise, respecting the premises, shall be final
and conclusive on the contractor without
reference to any other party or parties
whomsoever."
This splendid bridge, which has not its
equal in the world, reflects the highest
credit on all concerned in its erection, and,
as long as it majestically spans the Thames,
will be considered a masterpiece of con-
struction. It was opened to the public on
the 1st of August, 1831, with great pomp,
after having been in progress seven years
and three months.
The general depth at which the found-
ation of the piers is laid below low water is
about 29 feet 6 inches, and the total quan-
tity of stone used in constructing the
bridge and its abutments was 120,000 tons;
the number of piles of 20 feet in length
under the piers and their abutments was
2092, and the total number for the coffer-
dams 7708. There were four sets of timber
centres, each weighing on an average 800
tons.
The amount of Messrs. Joliffe and Bank's
estimate for the bridge alone, including an
extra set of centres, was only 425,081l. 9s. 2d.,
the remainder of the sum previously men-
tioned being swallowed up in the purchase
of land, houses, compensations, and law ex-
penses.
Staines Bridge is a very beautiful struc-
ture of five segmental arches of equal span,
with a smaller through the abutments,
which serve for the use of the towing-
horses; it was completed in the year 1832,
under the directions of Mr. George and
Sir John Rennie, sons of the eminent en-
gineer to whose works we have already
alluded.
The span of each arch is 74 feet, and
the versed sine 9 feet 3 inches; the dia-
meter of the circle of curvature at the
vertex is 156 feet, and the height of the key-stone is 3 feet.

Fig. 456.
ELEVATION OF STAINES BRIDGE.
CHAP. VIII.
459
BRITAIN.
The cofferdams, though much smaller, were constructed in a similar manner to those of
London Bridge; a double row of piles, diagonally braced and firmly bolted together, con-
fined the clay and puddle, which kept out the water during the progress of the works.

Fig. 457.
STAINES BRidge; cofferdams.
Under the piers piles were driven, as shown in the plan, which were crossed with strong
timbers, and planked over for the footings of the piers; a row of sheet piling was driven

Fig. 458.
STAINES Bridge; ArCH AND ABUTMENT.
all around at the toe or outside of the planking, to maintain the solidity of this portion of
the structure.


Fig. 459.
SECTION OF ARCHES.
460
BOOK I.
HISTORY OF ENGINEERING.
PART OF COFFERDAM.
The arches are light and elegant, and remarkable for their boldness and little rise; the
voussoirs are admirably proportioned, increasing in depth towards the abutments, where

Fig. 460.
SECTION of pier.
greater strength becomes necessary; the abutments are admirably constructed, the several
courses which receive the thrust or pressure of the arches being made to radiate to the centre
of the circle, from whence the segment of the arch is struck.
The section through the arch exhibits the foundations, sheet piling, and manner that the
crown supports the roadway, which has a footway on each side, and paved channel to col-
lect the water which falls upon the bridge, and which is conducted into pipes and carried
off below. The piles are shod with iron, and driven till they come into a hard bed of
gravel, and the cofferdams were securely tied together with iron bars, which could be
screwed tighter, when necessary, by means of the nuts at their ends.
Hyde Park Bridge, erected from the designs and under the superintendence of Mr. George
Rennie, is a beautiful structure of three arches, each 40 feet span, with a versed sine of

Fig. 461.
ELEVATION OF PART OF HYDE PARK BRIDGE.
4 feet 10 inches; the radius from which the arches are struck was 45 feet, and the round of
the segment is 42 feet. It was commenced in 1824. The construction does not materially
differ from the bridge last described.

Fig. 462.
SECTION.
CHAP. VIII.
461
BRITAIN.

Fig. 463.
PLAN.
It must be admitted, after the description given of the bridges erected in England at the
commencement of the present century, that our engineers have exhibited great science, and
introduced such a method of construction as has greatly economised material. The thrust
and pressure of the arch on its several points are better understood, and the nature of the
materials employed is also more thoroughly known: the qualities of all used in such con-
structions have been tested by Mr. George Rennie upon a large scale, and their capacities
of expansion and contraction under the various changes of temperature examined and
reported upon most satisfactorily by that eminent engineer. He has also subjected the
metals, stone, timber, and brick, to severe pressure, and ascertained their relative strengths
and fitness for construction.
Chester Bridge, for which an act was obtained in 1825, is one of the last designs of Mr.
Harrison, an architect of that city; it has one segmental arch of stone over the Dee 200
feet span, the largest yet constructed; the key-stone is 54 feet above the level of low water
mark, and the roadway is 33 feet in width.
This bridge is situated between the castle and the village of Overlegh, immediately at the
head of the harbour, where the tide rises 12 feet at ordinary springs. The abutments are
founded on the solid rock, except for a small portion, where it was necessary to pile. The arch
is the segment of a circle whose radius is 140 feet, and the rise, or versed sine, 42 feet. The
voussoirs at the crown are 4 feet deep, and increase towards the springing, where they are
6 feet. The centre, executed by Mr. Trubshaw, the contractor, consisted of six ribs in
width; the span of the arch was divided into four spaces by three piers, at regular dis-
tances, built up in the river, from which the timbers spread like a fan towards the soffite,
so that each timber received its weight in the direction of its length; the lower ends of
these radiating supports rested on cast-iron shoes, placed on the tops of the stone piers, and
the upper ends were bound together by two thicknesses of 4-inch plank, cut and arranged
to follow the form of the arch; on these were laid the lagging or covering, 4 inches thick,
which was supported over each rib by a pair of folding wedges 16 inches long, and 1 foot
broad, tapering about 1½ inches; each course of voussoirs had six pair of striking wedges.
The horizontal timbers of the centre were 13 inches deep, and the six ribs were tied toge-
ther transversely near the top by bolts of inch iron; the timber used was fir, and the
quantity required about 10,000 cube feet. When the centre was removed the crown sunk
only 21 inches. The cost of the bridge was 42,4004, and the approaches 7500l., making a
total of 49,9007.
One of the chief bridge-builders at the end of the last and commencement of the present
century was Thomas Telford, who rendered his name celebrated throughout Europe by
the erection of the Menai suspension bridge; he was born at Westkirk, in the district of
Eskdale, the 9th of August, 1757, and died the 2d of September, 1834, aged 77. Few men
have done more to advance the profession of the civil engineer: he commenced life as a mason,
on the property of the Duke of Buccleuch, and afterwards worked at Somerset House, under
Sir William Chambers, about 1787; his talent and industry gained him the good opinion
of Sir William Pultenay, for whom he had done some repairs at Shrewsbury Castle, and by
him he was appointed surveyor to the county of Salop. His first public work was a
bridge over the Severn, at Montford, four miles west of Shrewsbury; it consists of three
elliptical arches, one of 58 feet, the others 55 feet span, and measuring 20 feet across the
soffite; here he made use of cofferdams for the construction of the piers, and the whole was
satisfactorily performed with the red sandstone of the country for 5,800.
Buildwas Bridge, mentioned among those constructed of iron, was his next work, after
which he built upwards of forty stone bridges in the county of Shropshire, the span of the
arches varying: two were 85 feet span; three of iron, 55 feet; one of stone, 50 feet; four
of stone, 40 feet; two of stone, 35 feet; one of iron, 27 feet; two of stone, 24 feet; nine
of stone, 20 feet; and sixteen less than 24 feet span. For the last twenty-eight years of
his life he was engineer under the commissioners for making the Highland roads,
bridges, &c.
462
Book I.
HISTORY OF ENGINEERING.
:
Gloucester Stone Bridge, built by Mr. Telford, has but one arch, of 150 feet span and
85 feet rise. The idea of this bridge is taken from that over the Seine at Neuilly built by
Perronet. The voussoirs or external arch-stones have the same chord as the inner arch,
but its segment only rises 13 feet. By this means the arch has the form of a funnel, which
suits the contracted passage of the waters, and lessens the flat surface opposed to the
current when the waters rise above the springing of the ellipse, that being at 4 feet above
the level of low water.
This work was commenced in July, 1826, upon a soil, the stratification of which was
found by boring through to be from the surface of the ground, 11 feet of loam, 12 feet of
blue silt, 5 feet of peat moss, 5 feet of brown clay, 3 feet of strong coarse indurated gravel,
and 8 feet of finer gravel or coarse sand, in all 44 feet.

Fig. 464.
GLOUCESTER BRIDge.
The foundations were laid upon the indurated gravel, at about 15 feet below the bed of
the river. A space of 40 feet square was excavated to the depth of 33 feet below the
surface of the meadow, and a very strong cofferdam was made to protect it, as the floods
occasionally rise 6 feet or more above the banks of the river. The cofferdam was formed
of piles of Memel timber, 32 feet in length, with a space of 5 feet between the outer and
inner circumference of piles; this space was filled with clay worked into water-tight puddle.
This
After the gravel was made level, a course of large and flat bedded rubble stone was laid
over the whole space, and upon this was carefully bedded the timber platform.
consisted of thirteen pieces of Memel timber made straight and level; those laid at right
angles with the stream were 37 feet in length, and those placed up and down the stream,
40 feet in length. These pieces of timber were crossed, and laid at equal distances, the
square spaces between them being filled with rubble masonry well grouted. Upon these
pieces of timber, or sleepers, was a covering of 4-inch beech plank, planed, closely jointed,
and spiked down, thus forming a level platform, 40 feet by 37 feet, and upon this the
masonry was laid.
The stone employed for backing above low water mark was brought from the quarries
at Highley and Alveley, 6 miles from Bewdley; its thickness varies from 14 to 24 inches,
and its weight from one to three tons. They were squared on all sides, and well bedded;
every course was brought to a level and grouted before any of the next were set. All the
external masonry was from the quarries of Colford and Quitchurch in the Forest of
Dean.
The abutment on the west side of the river was of the same dimensions, the only
difference being, that the gravel was found at 27 feet below the surface of the meadow.
No piling or platform was used to the wing-walls, and they are in consequence defective
on the eastern side.
The centre was supported by six parallel rows of piles, fixed in the current of the river,
each row being connected by cross braces and caps; each supported a rib which formed
the actual centering. The whole was steadied by diagonal braces; and between the caps
of the piles, and the ribs which rested on them, the wedges were placed by which the
centering was slacked or lowered after the masonry was keyed.
The depth of the arch-stones at the springing is 5 feet 6 inches, and at the key 4 feet
6 inches; this sunk 10 inches after striking the centre. The thickness of the abutments at
the springing of the ellipse is 27 feet 2 inches, besides the wing-walls, which are 7 feet
each, the spandrill walls are 3 feet 6 inches thick, exclusive of the pilasters.
The four longitudinal walls of the interior, which support the platform of the roadway,
are each 2 feet thick; the width of the carriage-way is 27 feet, with a footpath of 4 feet on
each side.
Centering.-A platform was prepared, perfectly level, rather larger than the intended
centre, on which it was struck out the full size, the centres of the different radii being
fixed. Dantzic timber was employed in scantling 15 inches square.
The piles were of Memel, with wrought-iron shoes, and caps at the top to the proper
CHAP. VIII.
463
BRITAIN.
height. On these were laid another tier of beams, lengthways to the centre, one under
each rib; upon these beams the wedges were fixed, which were of three thicknesses, the
bottom one being bolted down to the beams; the tongue or driving piece in the middle
was of oak, well hooped at the driving end; the top side of the upper piece was laid
perfectly level and straight, both transverse and longitudinally. The wedges were rubbed
with soft soap and black lead before they were laid upon each other.
Each rib of the centre was then brought and put together upon a scaffold made upon
the top of the wedge pieces, and lifted up whole, by means of two barges on the river and
two cranes on shore. The scaffold was extended 30 feet beyond the striking end of the
wedges, to lay the last ribs upon, previously to raising, and for the workmen to stand upon
for finally striking. After the ribs were properly braced,
After the ribs were properly braced, they were covered with the
4-inch sheeting piles which had been used in the cofferdams.
This centre was so well formed, that when the arch was keyed, its sinking was not more
than an inch, and it was struck in the short space of three hours. This was performed by
placing beams upon the top of the work directly over the ends of the wedges; to these
beams was fixed a tackle, and at its lower end was slung a heavy ram of 12 cwt., with
which the piles were driven; this ram was swung to and fro, so as to strike the driving end
of the tongue-piece of the wedge. This operation required eight men to pull it back, and
two men to bring it forward; after twenty or thirty blows the wedges started, they then
slid easily, and pieces were put in to stop their going further than was required. The
covering was then taken off, and the ribs were let down, in the same order in which they
were put up; and when taken to pieces were carried on shore. The bearing piles were
then drawn by two 42 feet levers and strong chains.
Bewdley Bridge, over the Severn, in Worcestershire, being injured by the great flood of
1795, an act of parliament was obtained to raise money, and levy a toll, that a new bridge
might be constructed; and Mr. Telford furnished the design for one of stone, of three

V G Q G Q G 6 5
O OD SUUTOS!
Fig. 465.
BEWDLEY Bridge.
arches, the centre having a span of 60 feet, and the two outer 52 feet each; the breadth,
measured across the soffite, is 28 feet. The versed sine of the centre arch is 18 feet, and
that of the two others, 16 feet 9 inches each. This bridge was completed in 1798, at an
expense of 92641.
Bridge at Tongueland, near Kircudbright in Scotland, over the river Dee, has but one
arch with a span of 112 feet; the width measured across the soffite is 24 feet. The depth
of water at ordinary spring tides is 30 feet, and it required considerable skill to support the
centre to an arch of such magnitude. In order that the arch should not be unnecessarily

ME
Fig. 466.
TONGUELAND BRIDGE.
loaded, a number of longitudinal walls were carried up to the level of the road, where they
were covered with flat stones, by which means the state of the arch may be at any time
examined; this system is a considerable improvement upon the usual practice of filling in
the spandrills with loose earth, which frequently produced an external pressure and destroyed
the work.
The foundations of this bridge were laid in March, 1805, and completed in November,
1806, at the cost of 77107.
Glasgow Bridge, built by Mr. Telford, consists of seven segmental arches, diminishing
in their span towards the abutments; that in the centre has an opening of 58 feet 6 inches,
and a versed sine of 10 feet 9 inches; the two adjoining are 57 feet 9 inches, with versed
464
BOOK I.
HISTORY OF ENGINEERING.
sines of 10 feet 5 inches; the next two 55 feet 6 inches, with versed sines of 9 feet 8 inches
and the two adjoining the abutments are each 52 feet, with versed sines of 8 feet 3 inches.




Fig. 467
GLASGOW BRIDGE,
CHAP. VIII.
465
BRITAIN.
The piers of the centre arch are 9 feet in thickness, the next 8 feet 6 inches, and the other
8 feet; the water-way in the clear is 389 feet, the thickness of the piers 51 feet, and the
clear width between the abutments 440 feet.
The clear width between the parapets of the bridge is 58 feet, and measured on the
soffite of the arches 60 feet.
The subjoined specification shows the manner in which the works were executed, and
requires nothing further. to convey a clear notion of its construction.
Cofferdams. Before any works can be proceeded with, it is necessary that all the stones
that lie upon the bed of the river, where the cofferdams are to be constructed, should be
cleared away; and afterwards the foundation deepened as far as practicable with safety, so
as not to alter the level of the water above bridge by too much lowering the bed.
The cofferdams are to be formed by driving two rows of gauged piles at a parallel dis-
tance of 5 or 6 feet apart; the area comprised within the inner row being not only sufficient
to allow the foundations of the pier to be laid, but also a width of a 3 or 4 feet clear space
entirely around it, for the convenience of the masons and other workmen employed.
“The timber employed may be either Dantzic, Memel, or red American pine, care being
taken to select that which is perfectly sound; these gauge piles, when about 30 feet in
length, are to be made of whole timber, about 12 inches square, pointed and shod with iron,
each shoe weighing about 12 pounds; the heads also to be hooped with the best scrap iron,
not less than 3 inches in breadth, and § inch in thickness, to prevent their splitting when
under the weight of the pile-driving machine. A bench mark is established, to the
level of which all the piles are to be driven, and which serves as a guide to the work-
men.
"That each row of gauge piles are to be closely wedged together, and driven 6 feet
apart from centre to centre; care being taken that they are quite perpendicular, and
truly range with each other. Double waling pieces, 12 by 9 inches, are to be laid hori-
zontally on each side, and secured to the heads of the gauge piles by -inch iron screw
bolts; and at 8 or 9 feet below them to be attached another horizontal row, forming a
double groove to receive the sheeting piles, which are to be wedged in closely between the
gauge piles.
“The dam sheeting piles, 12 by 6 inches, are also to be shod with wrought-iron shoes, of
about 9 pounds weight, and to be hooped with the best scrap iron, 21 inches broad, and
inch thick. These sheeting piles are to be driven down to the level of the gauge piles,
and in a manner that the last firmly wedges all the rest in the bay, and makes them join
closely together.
"The engines employed to drive the gauge piles are to carry a ram of not less than 12
cwt., and for the dam sheeting pile 2 cwt. less; and it is necessary to construct scaffolding
and proper stages for the performance of these works in the most convenient situations.
"After the dam is completed, the soil is then to be taken out between the two rows of
piles to the depth determined by the engineer, and a sluice trough introduced, for the
purpose of letting water into the dam, when it rises on the outside to a height which
would endanger its stability; in rivers subject to floods this is of the highest importance,
otherwise the dam might at such times be liable to be blown.
"After the soil has been removed between the two rows of piles, the gauge piles of the
respective rows are then to be connected by round iron screw bolts, made to pass through
them, as well as through the centres of the two rows of waling pieces. Each of these
screw bolts is 14 inch diameter, and is provided with a wrought-iron washer 3 inch thick,
and 4 inches square, placed under the head of the nutt, to prevent the wood of the waling
yielding to the strain.
"When this is performed, pounded clay well puddled is to be introduced between the
two rows of piling, and the whole worked together, until the dam has become perfectly
water-tight; then the pumping out of the water to be commenced by means of a steam-
engine.
"In pumping out the water, and excavating the soil from the interior of the dam, it is
necessary to guard against and prevent the sand from blowing up through the bottom:
this may sometimes be done by driving the foundation piles, which consolidates the sand
and allows of its being taken out to the required depth; at other times it may be requisite
to drive extra piles all around, before it would be safe to take out all the earth to the re-
quired depth.
"As the works of excavation proceed, the dam will require bracing, otherwise the
outward pressure would force it inwards, which is to be done according to the directions
given by the engineer.
Piling for the foundations. The outside rows of foundation piles are to be either
Memel, Dantzic, or sound American red pine; and the gauge piles 12 by 12 or more,
as the length exceeds 30 feet, to be driven 6 feet from centre to centre. Waling pieces
are to be bolted to them as before directed, for keeping the intermediate sheet piling
between them in a regular line. After these sheet pilings have been driven to the required
Hh
466
Book 1.
HISTORY OF ENGINEERING.
depth opposite to each joint, others of the same thickness and half the breadth are to be
driven, and then the whole firmly united by walings and iron bolts.
"The piles driven inside, and which support the foundations, are to be made of beech
or newly-cut Scotch fir cleared of its bark, shod and hooped as before described; after
they are driven to a bench mark, all the heads to be cut off to an exact level, to receive
the sleepers and the timber platform; but before this is established, the soil is to be taken

ם
•
a
Fig. 468
GLASGOW BRIDGE.
out between the heads of the piles to the depth of 1 foot or more, and the space filled in
with hand-set rubble, well packed, and laid flush in good water-lime mortar.
"Foundation sleepers.— Upon each transverse row of piles is to be laid a sleeper, extending
across the whole width of the pier or abutment, secured to the head of each pile by a
wrought-iron ragged bolt of 2-inch round iron, 15 inches in length or more, according
to the depth of the sleepers, and between each row of sleepers filled in with hand-set
rubble, laid in good water-lime mortar.
Platforms. Upon the sleepers are to be laid two floors of Dantzic, Memel, or Ame-
rican red pine planking, to cross each other at right angles, spiked down with long spikes,
and firmly united to the sleepers.
"Masonry.—After the foundation platforms are completed, then the mason to commence
with his work.
—
"Dressing of ashlar. -The whole of the stones which compose the piers and abutments
must be truly squared throughout, and should have chisel drafts round the faces, beds,
backs, and end joints, and be truly pick-dressed down the drafts. The outside face work,
from the bottom of the foundation to the level of low water line, should be broached in
horizontal lines, not coarser than eighteen to a foot.
"Granite facings should be of uniform colour and quality, and laid in alternate courses of
headers and stretchers; the headers, where they have 2 feet in length of face, are to have as
much on the bed; the stretchers should be 6 inches longer, and not less than a foot in
width on the bed. Each stone should be truly squared, and fair dressed on the beds and
joints, full throughout, the backs scapelled, and the fronts rough picked; the front arris
being axed or chisel drafted, so as to make a close joint on the face.
“Ashlar hearting. — The hearting masonry to the piers or abutments to be squared ashlar,
well dressed, and laid in courses of uniform thickness throughout, and agreeing with that of
CHAP. VIII.
467
BRITAIN.
the facing; no stone should contain less in its bed than 4 superficial feet, and should be of
a size to break joint at least a foot with the stones adjoining.
"Freestone masonry of piers and abutments should be laid in alternate courses of headers
and stretchers; the headers not to present an outside face of less than 2 feet, and all to
extend at least 3 feet in length into the body of the work; the stretchers not less than
3 feet in length, and in breadth 2 feet on the bed.
"No stone used in the interior of the work to have less than 4 superficial feet on its bed,

•
•
Fig. 469.
GLASGOW BRIDGE; PLan of pier.
The whole to be square
and to be of the same thickness as the courses on the outside.
dressed throughout, to be laid on its natural bed, flushed in with good lime mortar used
fresh, and of a quality that will harden under water.
"Arch-stones or voussoirs must be of the dimensions designed, and should break joint with
the adjoining stones at least 1 foot; their beds should be truly radiated, chisel drafted
round the edges, and neatly picked dressed within the drafts. The soffite faces neatly

口
​Fig. 470.
GLASGOW BRIDGE.
broached in horizontal lines parallel to the beds, all carefully bedded, by bringing each
stone down to its place with a wooden maul.

Fig. 471.
SECTION OF ARCH OF GLASGOW bridge.
Spandrill facing, if of granite masonry, to have its stretchers 12 inches on the bed, and
one fourth of each course made headers, passing at least 1 foot 9 inches into the solid wall,
no course being less than 14 inches in height, the courses beneath generally being made
HH 2
468
BOOK I.
HISTORY OF ENGINEERING.
more; each stone should be at least 30 inches in length, and break joint 1 foot with those
adjoining.
"Rubble backing of spandrills to consist of hammer-dressed rubble masonry, laid in regular
courses on their natural bed, not more than two stones in thickness for one of outside
ashlar; all properly bonded with the facing stones, as well as among the others they are
laid with.
“Interior spandrills to be of good rubble masonry, hammer-dressed, and laid flush in good
water-lime mortar.
"Spandrill hearting to be built up solid between the backs of the arch-stones to the level
of the water, and composed of good hammer-dressed rubble masonry, laid in regular
courses on horizontal beds, well flushed in water-lime mortar.
"Cross walls over each pier and abutment may be either of rubble masonry or brick.
"Gutters and curb-stones. The gutter stone of granite, 14 inches wide, and 9 inches
deep, to have cut in it a triangular water channel, 8 inches wide and 4 inches deep; the
curb, 15 inches deep, and 12 wide, formed also of granite, should have its outer angle
rounded off, and the interior angle checked down about 4 inches, to receive and support
the footpath pavement.
"The gutter and curb-stones should not be less than 3 feet in length, and axed on the faces
which are seen; their joints being arris chisel drafted, or neatly axed, so as to make a
close joint, and the whole set in good water-lime mortar.
"Footpath pavement should be laid in regular courses, and if possible the stones to be of
the length of the whole width between the curb-stone and parapet wall; they should never
exceed three stones in width; where this cannot be accomplished, the joints should alternate,
and the surface be neatly broached, and made with an inclination of an inch to 3 feet, or
1 in 36, towards the curb-stone, the top of which should be laid 6 inches above the gutter
stone.
"Road concrete. The stone shivers and dry rubbish having been well pounded, and
filled in between the wing walls, the whole is then to be covered with a bed of lime and
gravel concrete well mixed, in the proportions of four measures of clean gravel to one
measure of water-lime mortar, used fresh. This bed of concrete should not be less than
9 inches in thickness on the outside, and 12 inches in the middle of the roadway, the
surface forming a uniform curve. Upon this may be laid the paving or metal for the
road.
“Drain pipes, of iron, 6 or 8 inches diameter, are to be introduced to carry off the water,
passing through the arch-stones of the bridge, and continued down the abutments.
""
Number and dimensions of bridges built under the Highland Road and Bridge Act of
1803, by Thomas Telford; —
1,075 bridges of one arch, varying from 4 feet span up to 65 feet, and affording a water-
way of 10,198 feet.
13 bridges of two arches, with a water-way of 643 feet.
16 bridges of three arches, with a water-way of 1236 feet.
2 bridges of five arches, with a water-way of 522 feet.
11 others with forty-three arches, and having a water-way of 2387 feet.
Making a total of 1117 bridges, 1202 arches, and 14,686 feet of water-way.
"General specification for the bridges. — Required that they should be built over each river
or stream with stone and lime mortar, and that the foundations should be sunk to and laid
on the rock, wherever practicable; where this could not be done, then the foundations were
required to be sunk 2 feet at least below the lowest part of the bed of the river; and wher-
ever the ground was loose a platform of timber was to be laid under the foundations of the
masonry; this platform was to consist of two thicknesses, of 3-inch plank, laid crossing
each other, and if necessary a row of pile planking driven all round the outside. If the
ground was hard, instead of this timber platform, an inverted arch or pavement was to be
laid and wedged between the abutments, the entire width of the bridge, and well secured
above and below by means of rows of piles sunk deeply into the bed of the river.
"The span of the arch to be according to the table annexed. The breadth of the road-
way between the parapets to be 18 feet in the narrowest part.
"The parapets to be not less than 18 inches in thickness, of the height mentioned in the
table, coped with hammer-dressed stones, set on edge in lime mortar, not less than 9 inches
in depth, with a large stone at each extremity of the parapet.
"Wherever the ground required them, retaining walls are to be used, of dry stone of
sufficient thickness, as described for breastwork, to support the made-up ground, and these
walls to run from the extremity of the parapets into firm ground, unless the distance
exceed 20 yards.
"When the bridges are not set upon rock, bulwarks of dry stone are to be introduced
above and below the abutments, 10 yards in length. The dimensions of the masonry to be
as set out in the table below.
“The spandrills of the arches to be filled with stone or coarse gravel, so that the rise and
CHAP. VIII.
469
BRITAIN.
fall of the roadway over the bridge should not exceed one in twenty-four in the steepest
places.
"The roadway to be formed of properly cleansed gravel to cover the top of the arch at
least 14 inches.
"Each bridge of one arch to be built so that the parapets when finished should have a
curve horizontally of not less than 3 feet in 36 feet in length; and all the bridges to batter
vertically at least 1 foot in 12 of height, and this height also to have a concave curve of
4 inches.

Span of
Arch.
Thickness of
the Walls of
the Abut-
ments on an
Average.
|_ Length_of
Parapets from
the Face of
Abutments
with Wings
under.
Height of
Parapets
above the
Crown of the
Thickness of
Spandrills and
Wings on an
Average.
Thickness of
the inverted
Arch.
Rise of
Arch.
Depth of
Arch Stones.
Height of
Abutments
from Bed of
River to the
Springing.
Arch.
Ft. In.
Ft. In.
4 0
1
6
Ft. In.
1 0
6 0
2 0
1
8
0
3
0
1
10 0
3
6
1
12 0
4
0
1 4
1000♡+
2
3
2224
Ft. In.
6
Ft. In.
Ft. In.
6
6
3
0
3
18
0
6
0
1
6
3
24 0
8
0
1
9
4
0
30 0
12 0
2
4 0
1222 ∞ † LO LO
6
9 0
Ft. In.
1 2'
Ft. In.
0
10 0
2 2
12 0
3
2
6
12
3 2
3
0
14 0
3
2
4
6
18
3
2
5
0
24 0
4 2
1122222
£60
Ft. In.
O 9
1
0
0
1
0
2
0
1
0
2 6
1
9
1
4
9
1
4
5
6
30
4 2
3
0
1
6
50 0
15
O
2 6
6 0
6 6 36 O
4 8
3 6
1 6
"The spandrills were all to be filled up between the outside walls with solid masonry,
above the level of the springing of the arches, up to one-third of the height of the rise of
the arches."
Dunkeld Bridge, erected in 1809, has five large arches, and two smaller ones. The
middle arch is 90 feet span, with a rise of 30 feet; the two adjoining arches are 84 feet span,
and the other two 74 feet; the two smaller or land arches being only 20 feet span. The
breadth, measured across the soffite of the arch, is 27 feet, that of the roadway between the
parapets 25 feet. The thickness of each of the two middle piers is 16 feet, that of the
two next 14 feet, and that of each of the two side piers 20 feet, and of the land abutments
7 feet. The cost of this bridge was 13,361l.
Allness Bridge, on the Fearn Road, county of Ross, has one stone arch of 60 feet span
and 20 feet rise.
Helmsdale Bridge, on the Dunrobin road, Sutherland, has two stone arches, each 70 feet
span, with a rise of 25 feet.
Conan Bridge, near the town of Dingwall, consists of five arches of 65 feet, two of 55 feet,
and two of 45 feet span. The cost was 6,8547., and the water-way 265 feet.
Potarch Bridge, over the River Dee, near Kincardine O'Neal, has three arches, the
middle spanning 70 feet, the others 60 feet.
Lovat Bridge has five arches, the middle spanning 60 feet, two 50 feet, and two others
40 feet, the cost of which was 88027.; the water-way 240 feet.
Ballater Bridge, over the Dee, has five arches, the middle one spanning 60 feet, and the
total water-way being 238 feet. The cost was 42241.
Alford Bridge has three arches, the middle arch spanning 48 feet, the others 40 feet; the
whole water-way being 128 feet, and the cost 2000%.
Fairness Bridge has three arches, the middle spanning 55 feet, the other two 36 feet,
the total water-way being 127 feet; the cost was 1255l. These were all erected by Mr.
Telford.
Bridge at Edinburgh, over the valley of the North Loch, was built by Mr. Mylne, and
consists of three arches each 72 feet span, and two smaller 20 feet span. The height
from the surface of the ground to the springing of the arches is 17 feet 6 inches; the
arches are semicircular, and the thickness of the voussoirs 2 feet 9 inches. From the top of
the voussoirs to the top of the parapet is 9 feet 9 inches, making the entire height 65 feet.
The breadth across the soffite of the arches is 42 feet 3 inches. The cornice and parapet
curve downwards, which produces a bad effect.
Bridge over the Teviott, erected by Mr. Elliot, consists of three arches; the middle spans
65 feet, and rises 17 feet: the whole are segments, and the width over the parapets is
23 feet. This bridge was completed in 1795.
Peas Bridge, on the road from Berwick to Edinburgh, was designed by David Hender-
son; it has 4 arches, the span of the greatest being 55 feet, and the entire height of the
bridge 124 feet; it is constructed over a deep dingle.
Bridge at Fochabers, over the Spey, was built by Mr. G. Burn; it consists of four arches,
the two in the middle span 95 feet, and the breadth over the parapets is 21 feet 6 inches:
as the number of arches are here even, a pier occupies the middle of the river,
ян 3
470
BOOK I.
HISTORY OF ENGINEERING.
Hutcheson Bridge, over the Clyde at Glasgow, erected after the designs of Robert
Stevenson of Edinburgh, consists of five segmental arches, whose radius is 65 feet. The
middle arch spans 79 feet, and its versed sine is 13 feet 4 inches. The arches on each side
are 74 feet 6 inches wide, and the outer 65 feet, and their versed sines are 11 feet 9 inches
and 8 feet 8 inches. The rise of the road from each side is about one in thirty, and the
breadth of the bridge, measured over the soffite of the arches, is 38 feet.
The entire width between the faces of the abutments is 404 feet, 358 feet being occupied
by the arches, the rest is taken up by the piers. The bed of the river consisting for 27 feet
of gravel, sand, and mud, cofferdams were made use of, composed of two rows of piles 3 feet
apart, filled in between with clay.
The cost of this bridge was 23,000l. The voussoirs measure in length 3 feet across the
soffite; the depth of the keystone is 3 feet 6 inches, and the other voussoirs gradually
increase in dimensions, being at the springing of the central arch 4 feet 6 inches; the
others diminish in proportion.
One of the earliest bridges constructed across the Clyde was built by William Rae, who
about the middle of the fourteenth century was Bishop of Glasgow; the next was the
Broomielaw, opened in the year 1772; and the importance of the navigation between
Greenock and the city, and the improvements made around Paisley, rendered necessary
the Hutcheson Bridge, so called from two brothers, George and Thomas, who died in
1640 and 1641, bequeathing considerable sums of money to purchase land, the rental of
which was to be appropriated for the relief of the aged and infirm, and also for the edu-
cation of the young.
Hutcheson Bridge is a fine piece of construction; the stones used are all of excellent
quality; the heights of the courses vary from 12 to 16 inches, and are composed of alternate
headers and stretchers; the former bond into the wall, 3 feet 6 inches, and on the outer
face are not less than 2 feet in length; the stretchers are 2 feet in breadth on the bed, and
3 feet 6 inches on the outer face; the beds are droved round the outward edges to the
breadth of 3 inches, and broached with mallet and iron within these draughts. The outward
faces of the courses, below the level of summer water mark, have 1 inch chisel draughts
round the edges, and are picked and hammer-dressed between; above the summer water-
mark the face work of the abutments and piers are neatly broached, and the horizontal
joints are chamfered to the breadth of 1 inch on the beds and faces; the hearting stones of
the abutments and piers have also 1 inch chisel draughts round the edges of the horizontal
beds, and are broached between, the vertical joints being dressed square with the pick or
hammer.
The springing course of the arches is 4 feet in thickness, and on the piers as well as the
abutments consist of three rows of stone; the two outer are worked off on the faces to
form the voussoirs, which have a soffite 9 inches in breadth, and a bed of 3 feet 6 inches on
the pier; no stone being less in length than 2 feet 6 inches. On the piers the middle or
closing row of stone is laid in two courses, and exactly fills the space up.
The beds of all the voussoirs have their edges all droved round to the depth of 3 inches,
between which draughts they are broached. The end joints are all chisel draughted and
broached between; and the face work of the soffites is broached, and the bed joints across
the arches; and the heads of the ring courses are chamfered to the breadth and depth of
1 inch on each side of the soffites.
Stone Bridge, over the Whitadder at Allanton, executed from designs furnished by Messrs.
R. Stevenson & Sons, has two arches, each spanning 75 feet, with a versed sine of 11 feet
6 inches, being segments of circles, the radius of which is 66-89 feet for intrados and
72-42 feet for extrados. The voussoirs are 3 feet deep at the springing, and 6 inches less
at the crown. The breadth of the bridge measured across the soffite is 22 feet 1 inch,
between the parapets 20 feet, and the width of the roadway 15 feet. The foundations are
on a sandstone rock, and the whole of the masonry is of broached ashlar; the stone
generally used is a soft red sandstone, and the mortar one part lime, two parts sand.
bridge was completed in 1842, at an expense, including its approaches, of 6,0581.
This
Railway Bridges. It would not be possible to enumerate the whole of the viaducts
constructed since the introduction of railways. Structures in timber, brick, iron, and stone
of various designs have been erected, and in some instances there is a novelty of principle
accompanied by great boldness of execution.
The brick bridge at Maidenhead, constructed by Mr. Brunel for the Great Western
Railroad, is one of the best examples in that material; it is composed of two elliptical
arches spanning the Thames, each 128 feet, with a versed sine of 24 feet 3 inches. The
piers between the two arches are 30 feet in width. The arch is 5 feet 3 inches high in the
middle, and gradually increases in thickness towards the abutments; at about from the
14
springing it is 7 feet 2 inches high.
+
The width of the bridge, measured on the soffite, is 36 feet, and of the piers, in the same
direction, 43 feet 3 inches. The clear width between the parapets is also 36 feet, as the
thickness of the parapet walls is obtained in the projection of the cornice.
CHAP. VIII.
471
BRITAIN.
Six longitudinal walls rest on the back of the brick arch, which carry the platform on which
the rails are fixed. Besides these two grand brick arches on each bank of the river are four
others with semicircular heads; that on the abutments spans 21 feet, the six others are
each 28 feet.
Skew Bridges.
One on the London and Birmingham line carries the railway 23 feet
7 inches above the level of the road, and the angle it makes is 32°, the square span of the
arch being 21 feet, and the oblique span 39 feet 8 inches. The arch, 2 feet 6 inches thick,
is the segment of a cylinder, the internal radius of which is 12 feet 6 inches, the versed
sine 5 feet 8 inches. The angle at which the coursing joints of the soffite cross the axis
of the cylinder is 53° 25', and that of the extrados is 58° 15′; the angle of the voussoirs
consequently is 4° 50'. The joints of the face of the arch all converge to a point, 32 feet
6 inches below the axis of the cylinder, or 45 feet below the crown of the arch.
Midland Counties Railway, presents another variety of skewed brick bridge, the span of
which is 42 feet 6 inches, and versed sine 11 feet; the whole consists of six arches, 2 bricks
in depth, and 4 feet in thickness: the total width of the bridge, measured through at right
angles with the face, being 24 feet.


Fig 472.
BRIDGE OVER THE LOUGHBOROUGH AND STANFORD road.
Another skew bridge on this line, over the Nottingham and Sawley Road, is of a different
construction; the whole depth of the bridge, measured square with the face, is 27 feet, and
span 53 feet, with a versed sine of 7 feet.
the

Fig. 473.
BRIDGE Over the NOTTINGHAM AND SAWLEY road.
A great variety of skew or oblique bridges has been erected in brick for several rail-
ways, and by means of such arches the engineer has been enabled to avoid all awkward
and injurious turns in the lines of rails to be carried over them; the lines of pressure are
HH 4
472
BOOK 1.
HISTORY OF ENGINEERING.
delivered upon the abutments, and are generally contained in vertical planes, lying parallel
to the sides of the roadway: such arches, intersected by numerous planes, transmit their
pressure from one to the other, in a direction perpendicular to those pressures.
Bridge over the Ouse near York, constructed for the Great North of England Railway,
consists of three arches, each 66 feet span; the piers are 10 feet in thickness, and the arch
measured on the soffite 28 feet 7 inches. The thickness at the keystone is 3 feet 6 inches,
and the voussoirs gradually increase towards the springing.
This is another excellent example of a bridge of three arches, the curvature of which in
the outer is continued to the footings of the abutments; by which means the voussoirs at
the springing are extended considerably in length. The centering made use of was well

་་་་་

Fig. 474.
BRIDGE OVER THE OUSE; PLAN AND ELEVATION.
put together, and rested upon piles inclined towards the foundations on which they were
placed; and the piers are capped with a single stone, from which the voussoirs commence,
their thickness gradually decreasing towards the key, which lessens the pressure and
increases the strength of the arch. The starlings or cutwaters are formed of two arcs of

0
Fig. 475.
Bridge OVER THE OUSE; ARCH and centre.
60 degrees, described from the two angles of the piers, which perhaps are the best
adapted for a rapid stream. It is generally supposed by most practical men that the
strongest angle is that formed by an isosceles right-angled triangle, having its right angle
facing the stream.
CHAP. VIII.
473
BRITAIN.

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Fig. 476.
Bridges in Ireland.
BRIDGE OVER THE OUSE, SECTIONS AND PLAN.
Queen's Bridge, Dublin, over the Liffey, was finished in the year
1768, under the superintendence of Colonel Vallency; it consists of three arches, that in
the middle spans 46 feet, and each of the others 35 feet; the piers are 7 feet in thickness,
and the breadth between the parapets is 35 feet.
Essex Bridge, in 1753, was commenced after a design of Mr. George Semple; it con-
sists of five arches, one 58 feet span, three of 45 feet, and one of 37 feet; the thickness of
the piers on each side of the centre arch is 6 feet, the breadth between the parapets 48 feet :
a very interesting account of the building of this bridge was published by the architect in
1780.
Previous to the work being commenced, the above ingenious architect directed his
attention to the nature of the foundations of the old bridge, and found that where the
piers were built upon a bed of sharp gravel, the lime had so penetrated that the whole
surface seemed petrified or converted into stone; he then enters fully into the nature of
the construction of walls, called by the Italians Reimpiuta, or cofferwork, and recommends
that no stone used among the stuffing should in weight exceed 1 pound; but he more
particularly dwells upon the nature and properties of lime, mortar, and grout, details
many experiments that he had made, and informs us that he had heard a Scotch mason
affirm, that in 100 years good mortar would become as hard as stone. In these descrip-
tions we have the author's opinion upon the manner adopted in building the walls of
churches and castles. "After the masons had laid the outside courses with large stones
laid on the flat in swimming beds of mortar, they hearted their walls with their spawls and
smallest stones; and as they laid them in, they poured in plenty of boiling grout, or hot
lime, liquid among them, so as to incorporate them together, as if it were with melted lead,
whereby the heat of it exhausted the moisture of the outside mortar, and united most
firmly both it and the stones, and filled every pore, and so set that it grew hard imme-
diately; and this method was taught to our ancient masons by the Romish clergy that
came to plant Christianity in these countries; and this mortar," he affirms, “so run
together, was harder to break than the stones that were imbedded it."
There are many
very sensible and useful remarks contained in his curious work, which relate to a variety
of subjects connected with constructions in water, and which would interest the civil
engineer.
Sarah's Bridge was built by Mr. Stevens, in 1792; it consists of one arch, 110 feet span,
with a rise of 22 feet; the breadth between the railing is 37 feet
Carlisle Bridge consists of three arches, the middle 50 feet span, the others 40 feet each ;
the thickness of the piers 10 feet, and the breadth between the parapets 63 feet.
Wellesley Bridge, at Limerick, erected after the designs of Alexander Nimmo, consists of
five segmental arches, each 70 feet span, with a versed sine of 8 feet 6 inches; the piers are
each 10 feet in thickness, and the soffite of the arch, measured from one face to the other, is
43 feet.
This bridge bears considerable resemblance to some of those constructed by Perronet,
474
-BOOK J.
HISTORY OF ENGINEERING.
where the archivolt is made to partake of a different sweep to that of the soffite, in order
to produce a greater lightness in
the elevation, or the soffites of
the arches are shaped to suit the
contracted vein of water as
formed in the entrance or exit of
pipes. The roadway over this
bridge is maintained throughout
at a perfect level, and there is no
break or distortion in the cornice
or the balustrade: we have seen
in some of those constructed by
Mr. Rennie how much attention
was paid to have the lines per-
fectly horizontal, and although
in France the slopes to the sides
of bridges had been long aban-
doned, it was some time before
the system underwent a change
in England: in the bridge at
Limerick the approaches are
well managed, and the effect of
the structure is much to be ad-
mired. The piers are elegantly
capped and proportioned, and for
the omission of columns, or of any
useless ornament, the engineer
deserves great praise: simplicity
and proportion, coupled with
good construction, are all that
have been aimed at, and in this
example we find nothing extra-
neous. The section through the
arch and pier shows the con-
struction, and that every means
has been adopted to lighten the
weight, and to strengthen the
parts which sustain it: the cur-
vature of the intrados meets
with a gentle inclination on the
sides of the pier, and the alter-
ation from the perpendicular
line is a great improvement, not
affecting the width of water-way,
but adding to the strength of the
footings of the piers.

It is not possible to enumerate
all the stone and brick bridges
that have been constructed with-
in the last half century,—those
for the canals and the railroads
alone amount to several thou-
sands: it is enough, perhaps, for
our purpose to have described
examples of each variety, and
thus exhibited the different
phases of the science.
Every county in the king-
dom has had its civil engineer,
and some of the works executed
are highly creditable, although
they do not generally show an
acquaintance with the higher
principles of construction. To
the late Mr. Rennie we stand
indebted for our most beautiful
Fig. 477.
WELLESLEY BRIDGE, NEAR LIMERICK.
bridges, and for the introduction of scientific principles: that eminent engineer had
CHAP. VIII.
475
BRITAIN.

Fig. 478.
SECTION OF ARCH AND PIER.
attentively studied the various forms of curvature given to the arch by the French and
Italian architects, but did not adopt either until he had practically tested the properties
of all. The result of his observations is seen in the magnificent bridges that cross the
Thames, which are monuments of his constructive skill; they have never been equalled,
and cannot be surpassed. England may certainly now boast that her engineers have
advanced in the knowledge of the principles which direct the bridge-builder; in tracing
the history of the art through the last six or seven centuries, we find not a gradual
progress, for it does not appear until the construction of Westminster Bridge, or a little
time previously, that much change had been made, or that the proportions for the stones
forming the voussoirs had been at all considered; and when Semple published his work
very little was known. The bridge at Blackfriars possesses considerable merit, and indi-
cates a march in the theory of construction; but until the latter end of the last century
the science was not matured. We have only to compare the old with the new London
bridges, and we shall be satisfied that in the former we have construction alone, whilst in
the latter it is directed by highly scientific principles, producing an effect which is admired
by the most unpractised eye, with an immense economy in the materials.
Iron Bridges. Before we proceed with a description of several constructed previous to
the close of the eighteenth century, we shall endeavour to show the opinions of some of the
learned men on the principles of such construction; and we cannot do better than refer to
a report which was laid before Parliament on the subject of one of the boldest conceptions
ever formed, which was to span the Thames by a single arch of cast-iron, the segment of a
circle 1450 feet in diameter. This arch was to have an opening of 600 feet, with a versed
sine of 65 feet. It was to consist of seven ribs, having a roadway over the centre, 45 feet
in width, and which towards the abutments was increased to double that dimension. It
was computed to require for its execution 6500 tons of iron, 432,000 cubic feet of granite,
and 20,029 cubic feet of brickwork for its abutments; the total cost of which was estimated
at 262,2891.
The originality of such a cast-iron arch was greatly admired, and Messrs. Telford and
Douglas, who had presented the designs, were called upon to submit them to several
scientific and practical men, that their opinions might be taken before any risk was
encountered in the construction. To keep the attention of those consulted to the subject,
several questions were drawn up, and their answers will enable us to form a tolerably clear
idea of the state of science at that time in England.
Some licence has been taken with the arrangement of the report, and portions are
omitted, those only being retained which are applicable to iron bridges.
The Parliament, however, after having received the various opinions, thought the
experiment far too bold, and the bridge was not erected.
The first question was, What parts of the arch are to be considered as wedges which act
on each other by gravity and pressure, and what part merely as weight, acting by its
gravity only, similar to the walls and other loading commonly erected on the arches of
stone bridges; or does the whole act as one frame of iron, which cannot be destroyed but
by crushing its parts?
Dr. Nevil Maskelyne, the Astronomer Royal, answered this question, by stating, that he
considered the whole of the iron bridge as one great frame of iron, which could be destroyed
only by breaking or crushing its parts by the weight of the whole, or by weights laid on it,
or by passing over it. However, the wedging of the parts together, by the convergence of
the frames to their centre of curvature, may be useful to secure the bridge from the con-
sequence of the decay or failure of any of the parts in future times, as well as for the con-
venience of easier putting it together.
The Rev. A. Robertson, Savilian Professor of Geometry, supposed AB DEF to
represent the bridge, bde the under part of the arch, and a cf the upper, bde and acf
being concentric. Let c d, nk, m h, and lg, &c. be straight lines, and let the direction of
each be to the centre of the circle; then will c n k d, n m hk, m l g h, &c., represent portions
of the arched part of the bridge, and these portions only can be considered as wedges.
476
Book I
HISTORY OF ENGINEERING.
a
B
D
E
n
m
h
k
It is evident, that the strength of the
arched part of the bridge will be as the
length c d of the side of one of these wedges;
as is the excess of n c, the upper or back
part of the wedge, above kd, so will it be
increased as c d is lengthened. The height
of d and D the highest point in bde, and
the highest point of the bridge above the
horizontal line A F, limit the lengthening
of cd, the side of the wedge. These
wedges act upon one another by their
own gravity and the gravity of the matter over them. The sides cd, nk, &c., of the
wedges being accurately directed to the centre of the circle, occasioned him to consider the
whole of the arched part of the bridge equally strong, as one piece of cast-iron, of the same
form, dimensions, and weight; and that if the iron work above the arched part of the
bridge be firmly connected together, and with the arched part, the whole may be considered
as one piece of cast-iron, of the same dimensions and weight.

b
Fig. 479.
Mr. Playfair, Professor of Mathematics at Edinburgh, in his consideration of this ques-
tion, remarked, that iron bridges admit of being constructed more exactly on the principles
of equilibrium than stone bridges, but that the equilibrium may be more safely dispensed
with in the former than in the latter; as the frames of iron in the form of truncated
wedges may be made of any depth, so that the whole mass from the interior to the exterior
curve of the bridge may consist of such wedges, and every single ounce of matter may con-
tribute to support itself. In bridges of stone, on the contrary, the depth of the wedges or
key-stone is necessarily limited to a few feet. All the superincumbent load, being merely
dead weight, the exact distribution of which, according to the law required by the equi-
librium, is extremely difficult, or rather impossible to be attained. The truth of the second
assertion, that an exact equilibrium of the parts may more safely be dispensed with in
bridges of iron than in bridges of stone, depends partly on this, that the materials which
compose the former are much lighter for their strength than those which compose the
latter, iron being hardly three times heavier than stone, and more than an hundred times as
strong. It depends also on this other circumstance, that the whole mass being connected,
especially if it consist of truncated wedges, extending from the interior to the exterior curve
of the bridge, even though an exact equilibrium does not take place, every part of the mass
contributes its share to the support of the whole.
The whole bridge, if we except the road over it, the parapet, and the framework, that
immediately support them, is to be regarded as a system of wedges, resting against two
immovable abutments, each of which wedges, whether the whole be in perfect equilibrium
or not, contribute to its own support. This holds in the strictest sense in this instance, as
the bridge consists of 63 wedge-form frames of iron, each 10 feet thick at its lower
extremity, with the inclined sides all converging to the same point. This is without,
doubt a most advantageous construction.
Mr. J. Robeson, Professor of Natural Philosophy at Edinburgh, observed that in this
question was involved several others, and that taking the whole structure together, he
thought that it must not be considered as in the condition of an arch of masonry, each part
acting merely by its weight, and the whole maintaining its form by being equilibrated; and
observed, I see, however, that the ingenious inventors have had this very much in their
thoughts, because the profile is plainly divisible into several arch frames of different radii,
all having a common tangent at the crown. The undermost may be considered as the
main arch, which the superior ones are only intended to relieve, while they stiffen it, and
connect it with the road-way. But in this way of considering the structure, it is very far
from being fit for supporting itself by mere equilibrium. The main arch is abundantly
able to do this, if alone, because a catenusea of the same span and base will not deviate
from one of its circles 3 inches in any part. But when the upper arches are taken in, the
road at and towards the haunches is vastly too great. I do not think, however, that this
great want of equilibrium will make the bridge unable for its load, because the crown is
still by far the weakest part, the total strength at the haunches being vastly greater than
is necessary. I think the bridge abundantly strong, if united in a proper manner, but I
think that it is rather in the condition of a frame of iron consisting of two pieces, leaning
on each other in the middle. I think that our mathematical theories of arch vaulting are
extremely defective, and that their defects arise from the very anxiety of the mathematicians
to make them perfect. The joints are supposed to be without cement, perfectly polished,
and therefore every where perpendicular to the curve or soffite of the arch; and the mutual
pressure is supposed to be everywhere perpendicular to those joints. But the mutual
friction of the parts and the connection of straps or of joggles introduces a force which has
no place in those theories. It enables a load on one part to act on a far distant part trans-
versely with the energy of a lever. By attending carefully to the way that old arches fail,
CHAP. VIII.
477
BRITAIN.
I think that they almost all act like the rafters,
DA, BE, of a mansard or kerb roof, from which
the middle tie-beam has been taken away.
The
D
A
C

Fig. 480.
crown breaks in by the opening below and crush-
ing above, and it springs at some intermediate
points, by the joints opening there on the upper
side. Sir Christopher Wren considered an arch
entirely in this way, and makes no use what-
ever of the mathematical theory of cymlibration, although then carefully studied by the
great mechanicians. The drawings do not clearly show how the different arch-stones
or frames are united, yet plainly point out something like joggles in one frame fitting
concavities in the one adjoining, by which they are prevented sliding on each other. I
highly approve of this plan, because it connects at least half of this rib of frames: as a
straight line can be drawn through, causing it to act as one rafter, I am confident that this
ring alone, if con-
sidered as consisting
of six pieces, the joints
of which a b c are
connected with the
roadway by uprights,
aa', bb', and truss
rafters, a g, fg, ah, bh
abutting on the arch,
would make it firm
enough, stiff enough,
and a great deal lighter
b
Ci
V
h ச

g
Fig. 481.
than by the plan proposed. But I do not mean to prefer this method, because, although six
points of bearing may be perfectly sufficient, it is far preferable, with so brittle a material as
cast-iron, to make the bearings as numerous as possible, that no one point may be much
more strained or compressed than another; yet I think that this is overdone in the pro-
posed plan, and that it might be much lighter in the haunches.
I should certainly construct the main or lowest ring as an arch of equilibration, making
each of its frames bear on its neighbour, as a stone in an arch of masonry. I think that any
cement would be inefficient, and would be hazardous in the extreme; I know no practicable
cement whose cohesion will be of any significancy, none that will not be a little compressed
by the enormous horizontal thrust of near 10,000 tons. The consequence of the compres-
sion, by the arch taking its set, will be almost certain destruction, as I shall show by-and-
by. The frames should all abut on each other with perfect accuracy. If they are to
have this form, the radial joints must all be ground on each other lengthways, so that
they may touch all over; should cement be put on such a joint, the smallest hard bit
about the middle would cause the piece to snap without remedy. Grinding will procure
a full contact and bearing, therefore the joggles should be loop pieces, like pound balls,
that the grinding may be practicable. Perhaps this form may be still more secure against
snapping, and not unsuitable to the style of ornament, which is very pure Gothic.
I
own that I prefer Mr. Burdon's construction of the ring, as the most susceptible of ac-
curacy in the execution, the firmest union, by means of the wrought-iron straps, and
perfectly free from snapping. I foresee immense difficulty in casting everything true, so
as to have the radiated joints all straight, and all bearing, and for this reason am disposed
to prefer a construction with loose pieces, butting endways, like rafters. The different
expansion of different fonts of iron by heat will have some effect here; whenever a joint
seems open, or not in an exact line with the rest of that radial joint, it should be filled up
with a plate of good copper. A forged iron plate would perhaps exfoliate with the weather.
I look upon this circumstance of accurate joining as the most important of all in this
particular construction, and I apprehend that it was this difficulty that induced Mr. Burdon
to fill up the haunches of his arch at Wearmouth with a series of circles, which serve
merely to prevent the main arch from rising in the haunches, and to support the roadway.
But if it can be attained, the bridge will be both stiffer and stronger.
That the hazard from the compression of cement or the closing of bad joints may clearly
appear, we must now consider the weight of the whole, and the different thrusts excited in
its different parts. I consider it as two masses resting on the abutments, and leaning on
each other in the middle; I suppose the carriage-way to have 2 feet of gravel, each cubic
foot weighing 109 pounds. The footpaths may be paved hollow with free-stone, so as not
to require more than 18 inches in thickness. One half of this, including the increasing
width at the ends, will weigh about 1800 tons; this added to 3250 tons of iron work
makes 5050 tons. I think that its centre of gravity is situated at nearly two-fifths of
the half-breadth of the arch from the abutments, that is, at about 120 feet. We have,
therefore,
478
Book 1.
HISTORY OF ENGINEERING.
5:2 whole weight : vertical weight at the crown, 13: 30= weight at the crown: horizontal thrust.
65: 60 = whole weight: horizontal thrust.
Therefore the proportion of 13 to 30 is that of twice the height (65 feet) to the half of the
span (300 feet). As the same load at the crown is produced by the other half of the bridge,
this must be doubled, or say as 65: 60 :: 10100 tons : 9323; 10,000 tons being the whole
weight, and 9323 the horizontal thrust. Some mathematicians consider the horizontal
thrust as only the half of this quantity, but this is a mistake.
Now this thrust is the same in every part of the arch, as is well-known; therefore the
whole of this thrust is borne by the middle joint of the seven ribs, and amounts to above
1300 tons on each joint. Did the whole joint bear alike, there would be little danger, but
when the arch is set up on its mold, and the middle frame or key-stone nicely fitted in, and
the scaffolding removed, every thing comes into a new situation, all settles. The joints are
squeezed close, and even the solid metal of the whole bridge suffers a compression: this is
equivalent, as far as relates to the figure of the arch, to a yielding of the abutments. One
inch of compression in the half arch will cause the crown to sink nearly 5 inches. A total
compression of 3 inches in above 300 feet is no unreasonable supposition; this will produce
a sinking of 15 inches at the crown: should this take place without a change of shape in
the half arch, it is evident that the enormous pressure of 9000 tons will be borne by the
upper end of the joints of the key-frame, and the lower end of the same joints will be much
less pressed. The frames will be hanging by their upper angles, and the upper rail of the
frame will be strained with the greatest part of the thrust. I should fear exceedingly that
so brittle a substance as cast-iron would be very apt to chip off at the upper angles of the
frames at the crown of the arch; if any cement be admitted into the joints, I apprehend
that the sinking and the inequality of pressure will be vastly greater. If, indeed, the inter-
mediate half arch between the crown and the abutments shall bend a little, this will tend to
equalise the pressure on the joints at the crown. It may even bend so much, if ill-joined,
as to make the middle joints bear most on the lower angles; but this is highly improbable,
because the general shape of the half arch makes it almost incapable of bending, even though
the radial joints are not very accurate.
The method that occurs to me as the most effectual to prevent this risk is to form a
middle piece of the arch, so as to keep the mutual pressure diffused over the whole joints,
even though the whole arch should settle considerably. Thus, instead of making the joints
straight lines, I would make them arches of circles of about 25 or 30 feet radius, or still less
radius and more curvature, so as to lengthen as much as possible those joints which are to
bear so great a strain. I would not, however, make more than two of these joints, because
if these be allowed to slide a little on each other, having no joggles, the joints will keep
close, like the joints of a sector. It will not hurt the style of ornament if this middle
piece should differ greatly from the rest. I would also make this middle piece (cr key)
entirely of wrought-iron, as much better suited for preventing chipping at the angles, and
for affording fixtures for diagonal ties, which may be found necessary for stiffening this
weakest part of the arch. For if such ties or struts be attached to parts of cast-iron, and
much greater strain be exerted there than in other parts, they are in great danger of snap-
ping. It should be carefully kept in mind in this structure, that when a bar is sustaining
a very great compression endways, or in the direction of its length, it is more easily broken
across by any transverse strain. I have made many experiments on this kind of strain; a
piece of white marble inch square and 3 inches between the props bore 38 pounds.
1-4
When compressed endways with 300 pounds, it broke with 14 pounds. The effect is
much more remarkable in timber and softer bodies, but is considerable in all, and this
circumstance will make it hazardous to employ ties in the bridge. We extend their
action to considerable distances, so as to create great strains on particular points. Yet
I think that ties may be usefully and safely employed, diverging from the lower side of this
middle piece, and connecting it with several frames on each side, in order to stiffen, by
supporting the middle points.
The part of the arch which requires the greatest accuracy in the construction is about
80 or 100 feet on each side of the middle and the lowest ring of frames all over, if those be
close-jointed; the rest is free from all risk. The portion mentioned of the middle must be
carefully jointed up to the roadway, so as to make one mass; this being set on the arch-ring
will tend to force it up a little at the.haunches; but the work above it will effectually pre-
vent this, although not executed with such accuracy.
In the forming of this profile, by which the haunches are filled up, it is asked whether it
is more advisable to cast the frames in long masses or in smaller frames. In carrying the
principle of masonry through the whole, one is prompted to cast the pieces, so as to inter-
rupt the lines of joint, or to break joint, as masons call it. I should think this hazardous.
If one half of a radial joint be closer than the other half, there is a great risk of the sides of
the frames snapping in the middle. Plates of copper should be employed for making up
all such deficiencies, or even tin-foil, such as is used for the silvering of mirrors; perhaps
some way might be fallen upon to apply heat to the pieces when set in their places, so as to
CHAP. VIII.
479
BRITAIN.
make the tin take hold of the iron, but this is not necessary. The great pressure and the
bullet joggles will prevent all change of figure.
After all, I own I still prefer Mr. Burdon's construction of the arch. His method of
combining the abutments of the cast-iron rails of his frames with the wrought-iron straps
seems finely calculated for procuring a close union of the parts. A judicious artist will
perceive, that by a proper forming of the holes in the three pieces (the cast-iron rail between
the two wrought-iron straps), the drawing of the keys into these holes will draw the two
cast-iron ends closer together, and press them hard into each other. Thus, when keys are
drawn into the holes, the two parts of the cast-iron bar which is between the straps will
be forced hard together. I observe, also, that Mr. Burdon's arch has three rails, and the
London arch has but two; at least the middle rail of pierced work does not seem to form
a line of abutment supporting the middle of each subjoint. I think that this mode of
framing at Wearmouth might be extended to the next circle, which is in the middle of
the Gothic arcade. The effect of the straps which form this circle would be prodigious in
strengthening the whole.
Dr. Milner on this question supposes the whole mass of the bridge to be cut into a great
number of thin slices, bounded by planes parallel to each other, and all of them parallel to
the plane of the arch of the bridge; then it may be said, that all those parts of the iron
work, whether they be called ribs, bars, rods, braces, frames, or by any other names, all that
can be properly considered as lying in the above-mentioned planes, or so extending between
any
of them in the direction of the said plane, as to contribute to the formation of the arch,
and also to the strength of it, considered as a geometrical curved line, or rather as a bent
iron rod of small thickness; all the parts of the work coming under this description act as
wedges, both by gravity and pressure, but all the parts which serve merely to bind together
the above-mentioned slices, and which act in directions perpendicular to the said parallel
planes, which are the boundaries of the slices of the bridge, are to be considered as weight
only; and such portions of iron as come under neither of these descriptions must be divided
by just reasoning, upon the well-known principles of the resolution of forces, and a due con-
sideration of all the circumstances, and then be placed part to one account, and part to the
other.
It appears that in regard to an iron bridge of the magnitude of that proposed, not only
the weight of the iron made use of, but also its elasticity, and still more its cohesion, are
powers which enter into every part of the investigation of the construction. The con-
sideration of these powers presents a very difficult subject, but unless something be settled
respecting them, every conclusion that pretends to any thing like precision must be ab-
solutely fallacious. How should the steps in an argument be probable, when the premises
are all conjecture? As far as mere weight is concerned, the mathematicians very readily
determine curves of equilibration as they are called, and it certainly deserves very seriously
to be considered, whether after all it may not be the safest way to dispose of the weight in
such proportion as to make all in perfect equilibrio, on the supposition that there was
neither cohesion nor elasticity in the materials.
If the natural powers of the iron in regard to its cohesion, elasticity, and strength in
general, under all the circumstances in which it may be employed in this occasion, could
be ascertained with any tolerable degree of exactness, then it would be undoubtedly the best
method to take into consideration all those powers so estimated, and also the gravity of the
materials, and reduce the whole to a rigid calculation proceeding upon a sound theory, and
to rely upon the conclusion in practice; but if there be too much reason to suspect that the
powers above-mentioned cannot be estimated from any known facts, with the requisite
degree of probability of being near the truth, then the question will be whether in that
case it may not be most prudent to compute merely upon the weight of the materials and
their action as wedges, considered as the data, and so to determine the curve of equilibration.
To a bridge constructed upon the principles last-mentioned, so that the tangential forces
should be in perfect equilibrio, and destroy each other at every point of the curve, there
might still be superadded all the advantage which a good mechanic can give to it, by making
the most skilful use of the powers of cohesion, elasticity, &c. of the metal.
There are, however, two objections to be offered, the first is, that though the above-men-
tioned powers of cohesion, elasticity, &c., may be allowed to be entirely beyond the reach of
computation; when we have in view a structure like this, yet we may still be sure that these
powers are very considerable. We may in many cases be quite sure that a power is very
great, though we are unable to say how great; and under such circumstances, it is not to
be dissembled that no person can foresee whether the effect of a great unknown power may
not be to overturn in a great measure the geometrical reasoning itself, respecting the curves
of equilibration; or whether, therefore, it might not be better to hazard and compute upon
some hypothesis or conjecture, respecting the strength and effect of these powers, rather
than to leave them entirely in the dark, and proceed upon the partial consideration of mere
weight and wedge action, when we are sure that other powers are actually present. The
second objection arises from a considerable practical difficulty which must occur in executing
480
BOOK I.
HISTORY OF ENGINEERING.
the work, so that each point of the curve of the bridge shall feel the precise degree of
vertical pressure which theory shall assign to it, and unless this difficulty can be got over,
all the reasoning concerning curves of equilibration will be of no use. The engineers will
be the best judges how far it can be removed, and it will no doubt occur to them, that this
matter is much easier to manage in the case of stone bridges.
Dr. Charles Hutton, of the Royal Military Academy at Woolwich, states it as his opinion
that all the small frames or parts ought to be so connected together, at least vertically, as
that the whole may act as one frame of iron, which can only be destroyed by crushing its
parts. For by this means the pressure and strain will be taken off from every particular
arch or course of voussoirs, and from every single voussoir or frame, and distributed
uniformly throughout the whole mass. Hence it will happen that any particular part
which may by chance be damaged or be weaker than the rest will be relieved and prevented
from fracture; or if broken, prevented from dropping out and drawing other parts after it
which may be next to it, either above or on the sides of it. By this means also the effect
of any partial or local pressure, or stroke or shock, whether vertical or horizontal, will be
distributed over or among a great number of the adjacent parts, and so break and divert the
effect from the immediate places of action. By this means also will be obviated any dan-
gerous effects arising from the continual expansion or contraction of the metal, by the
varying temperature of the atmosphere, in consequence of which the bridge will altogether
in one mass, in a small and insensible degree, keep perpetually and silently rising and
sinking, as the arch lengthens by the expansion, or shortens by the contraction of the metal.
This unity of mass will be accomplished by connecting the several courses of arch pieces
together vertically, or the lower courses to the next above them, and also by placing the
pieces together in such a way as to break joint, after the manner of common or wall
masonry, and that, perhaps, in the longitudinal and transverse joints as well as the vertical
ones.
Mr. Attwood, of Sloane Street, states that, according to the plan of the bridge, the interior
curve is a circular arc, and the whole of the iron-work between the arc and exterior ter-
mination on the road is divided into sections of a wedge-like form, the sides of which being
prolonged unite in the centre of the circular arch. The sides of the sections considered as
plane surfaces, which are projected into the aforesaid lines, are placed contiguous after the
manner in which blocks of stone are disposed which form the arches of a stone bridge;
but in the plan of the iron bridge, the wedge-like form of the sections, instead of being
confined to the arch adjacent to the interior curve, as in the case of stone bridges, is ex-
tended throughout the whole structure as far as the road. The ties and fastenings applied
to prevent the sections from changing their places in the direction of the sides of the
wedges coincide with the lines in which the surfaces of the contiguous sections are united.
For these reasons I suppose that the whole iron-work is to be considered as consisting of
sections, which act as wedges by their pressure and gravity. It may also be observed, that
if the iron-work above the immediate arch be divided by circular arcs or lines of division,
drawn from centres situated in the vertical line which bisects the entire arc, the said cir-
cular arcs will divide the whole of the iron-works into separate arches, the sections of
which may be adjusted so as to form so many distinct arches of equilibration. These
arches when united will become a single arch of equilibration.
Colonel Twiss, of Woolwich, states, that every part of a bridge, whether formed in the
shape of a wedge, or laid on in horizontal joints, such as the walls and other loading usually
erected upon the arches of stone bridges, should be all considered as acting by gravity, and
every heavy body so situated, being prevented from falling vertically, will produce a lateral
pressure, varying according to circumstances; in considering the strength of arches, I never
can suppose the whole to act as one frame, which can only be destroyed by crushing its
parts.
Mr. William Jessop, of Newark, says, respecting the practicability of constructing an arch
of iron of 600 feet span, and the weight that such a material is capable of sustaining before
it will crush with the pressure, I am inclined to believe that those who may critically in-
vestigate this matter will remove all doubts on these heads. I can easily conceive that a
cube of Portland stone, of 6 inches for instance, would require no great weight to crush it;
that such a cube of granite or marble, though much stronger, might also be crushed; but
I feel it difficult to form any conception of a weight that would crush such a cube of iron,
and though a similar arch of stone would have more surface in contact, yet as its com-
parative weight (allowing for the difference of specific gravity) would be nearly in pro-
portion to the surface of its section, its advantages on the one hand, of having more points
of bearing, will, in my opinion, be much inferior to the advantage, which, on the other
hand, will be derived from the greater hardness and tenacity of the materials, and the great
decrease of absolute weight.
Presuming then, that there should be no doubt on this part of the subject, it will next be
required that all its parts should contribute their due proportion of resistance to the
pressure, and that when so constructed, every part should have a disposition to remain at
CHAP VIII.
481
BRITAIN.
rest, and that the whole should be so framed, as to be capable of resisting any force tending
to alter its form or position, whether from external violence, or from imperfection, or in-
equality in its parts. Although the parts of the bridge may be so put together as to
become one united frame, I should think it right, nevertheless, so to construct the arch,
that independent of the framing between the arch and the roadway, it should be equal to
the support of the superincumbent weight; and in order that it should be so, it ought to
have such a curvature as to counteract the unequal pressure created by the increase of
width at the ends of the bridge, or an increased weight on the crown of the arch, or both;
it is, therefore, advisable, that instead of the three circular members or segments above the
arch, uniting into one on the crown of the arch, and thereby diminishing their weight, each
of these segments might be continued distinctly, but resting on or touching each other at
the crown; and in the plan also, each rib should be continued independent of the others.
Mr. John Rennie, of Stamford Street, observes that were the arch a semicircle, ellipsis,
or other curve, in which some of the frames or voussoirs had but a small inclination to the
horizon, the friction arising from the gravity of those frames would be greater than their
weight would overcome, and of course would act by pressure only; but in the present case,
the arch is so flat, that I apprehend every frame may be considered as a wedge, if its sur-
face were perfectly smooth and straight, and not prevented from sliding by joggles or other
contrivances; but as each frame is proposed to be connected by proper joggles or con-
trivances to the other, and the whole loaded so as to be in equilibrio, except as far as the
materials will yield by the weight of the superstructure, I apprehend it may in a great
degree be considered as a single frame, which can only be destroyed by crushing its parts.
Mr. John Southern, Engineer, Soho, near Birmingham, observes, that the design repre-
sents the parts as one frame; but I do not think it possible to execute it so as to have
that effect, nor even that parts can be combined so accurately as to form wedges of so
great a length as to reach from the arch to the road; nor do I think it desirable that it
should be so constructed; because, as settlement will certainly take place in some degree,
when the centres are struck, an immense pressure may possibly be brought on some of the
eccentric arches in the spandrills, which are evidently not calculated for such an effect. It
is better that the construction should be such as to direct the pressure of force on those
parts intended and able to bear it. I therefore consider the lower part only of the bridge,
or the arch, constituted by the concentric curves, and which I desire to distinguish by the
name of arch, as answering the end of wedges or arch stones; all the superincumbent
matter I consider as weight, the pressure of the greatest part of which is, however, increased
by the declination from the perpendicular of the members or pillars which point to the
centre of the arch, and which communicate to it this pressure. The eccentric members,
which form arches in the spandrills, of less curvature than the principal arch, can only be
used in keeping the long pillars from bending under the pressure they sustain. Indeed,
were the whole pressure of the bridge, by any accident, to come upon any one of these
spandrill arches, and were it made strong enough to resist the pressure, the pushing or hori
zontal force acting against the abutments to overset them, would be increased in proportion
to the flatness or radius of the said arch.
The second question propounded by the committee was, whether the strength of the arch
is affected, and in what manner, by the proposed increase of its width towards the two
abutments, when considered both vertically and horizontally; and if so, what form should
the bridge gradually acquire?
Dr. Nevil Maskelyne apprehended that the strength of the bridge would be somewhat
increased vertically, and also horizontally, according to the length of the bridge, by the
increase of its width towards the extremities or abutments; but that it is increased princi-
pally in the direction of its width, so as better to resist the stroke of the mast of a ship
going up or down the river.
The Rev. A. Robertson stated that the arch will certainly be affected by increasing the
width of the bridge towards the abutments. Such a form will decrease the strength of
the arch, to bear the roadway and any weight upon it, and on the other hand it will
increase the strength of the bridge to resist any force tending to press it out of the vertical
plane. The following are the reasons for this opinion: If the weights of the several
parts be so proportioned, as to give the whole the greatest possible degree of strength, the
quantity of matter over any point in the arch must be fixed according to the weight at the
crown or at the abutment; it can neither be increased nor diminished, if that law is
observed by which a maximum of strength is obtained. If, therefore, the bridge increase
in width from the crown to the abutments, the quantity of iron being in an horizontal, it
must be decreased in a vertical direction. Consequently, the strength of the bridge will
.continually diminish in a vertical direction from the crown to the abutments.
Mr. Playfair thought that the proposed increase of width at the extremities, though
necessary to steady the bridge in the horizontal direction, and to preserve it in the same
vertical plane, is an additional load towards the haunches of the bridge, and tends still
more to remove the distribution of the weight from that which the equilibrium requires.
JI
482
Book I.
HISTORY OF ENGINEERING.
Though there seems to be in the manner of framing, and in the strength of the materials,
abundant provision made to supply this want of equilibrium, yet as the tendency of
so great an increase of pressure at the haunches must be to make the arch spring at the
crown, it may perhaps be expedient to make the wedges near the crown deeper and heavier,
in comparison of the rest, than is proposed in the plan. I am aware, at the same time,
that the power of the iron bars that compose the framework of the bridge, to resist ex-
tension as well as compression, and to draw as well as to thrust (quite different from what
happens in stone, where it is the latter only which takes place), may render this pre-
caution unnecessary.
Those who have had experience in the construction of arches of
iron are the only good judges in this case.
Mr. J. Robeson did not think the mode of widening the bridge towards the ends can be
materially improved. This additional width does contribute to increase the load on the
haunches, which are already overloaded; but they are so stiff, if united with moderate
care, that they are vastly stronger than is necessary, and will not be sensibly affected by
this addition. It is in some degree hanging work, that is, hanging by the rest, and not by
any regular abutment. This might be given it, as in the Pont Admirable between Calais
and Ardres, which I examined with great attention many years ago. But this would
require a most difficult framing, with oblique angles, each frame and each tie requiring a
mould for itself, and it would not be one fiftieth stronger.
Dr. Charles Hutton says, there can be no doubt but the bridge will be greatly strengthened
by an increase of its width towards the two extremities or abutments, especially if the courses
or parts be connected together in the manner mentioned in the answer to the first question;
for thus the extent of the base of the arch at the impost being enlarged, the strength or
resistance of the abutment will be increased in a much higher degree than the weight and
thrust of the arch, and consequently will resist and support it more firmly. The arch
itself will thus also acquire a great increase of strength and stability, both from the quantity
and disposition of the materials, as well vertically as horizontally, by which, in the latter
direction in particular, the arch will be better enabled to preserve its true vertical position,
and to resist the force or shock of any thing striking against it in the horizontal direction
and for the better security in these particulars, considering the immense stretch of the
arch, it will be perhaps advisable to enlarge the width in the middle to 50 feet instead of
45 feet, and at the extremities to 100 feet instead of 90 feet, as proposed in the design.
As to the form of this width or enlargement, the side of the arch might be bounded by a
circular arch or by any curve that will look more graceful, perhaps a very eccentric ellipse
will answer as well as any other curve, or better.
;
Mr. Atwood observed, that the proposed increase of breadth near the abutment does not
appear to affect the strength of the bridge in a vertical direction; but a more effectual
resistance will be opposed in consequence of this form to any force which may be applied
horizontally, and perpendicular to the plane of the arch to alter its position in that
direction.
Colonel Twiss stated, that the increasing breadth of the arch at the abutments seems
to afford no advantage in the vertical section, on the supposition that no force except
gravity could act upon it; but considering the length and breadth, it appears a wise pre-
caution to resist any force acting in a horizontal direction, such as wind, the masts of
vessels, &c., and as a guard against vibration; perhaps the strongest form of widening the
bridge would be by constructing the sides in straight lines from the centre to the abut-
ments, but the present proposal is cheaper, and may answer the object.
Mr. William Jessop says, that widening the bridge towards the ends will be attended with
many inconveniences, and a great extra expense; it is worth consideration whether it may
not have sufficient strength to counteract any lateral bias by other means. I am much
disposed to believe that if the braces which connect the ribs with each other, instead of
being rectangular with the ribs, were to be connected diagonally, so as to form triangles,
little more would be wanted to give it the necessary stiffness; but when, in addition to this
I consider that the whole covering of the bridge under the roadway may be of iron plates,
or reticular gratings with flanches, so that they may be put together with screw bolts and
nutts of cast-iron, or with eye bolts and cotters, and form one great iron plate or grating of
45 feet in width; I have no conception of its being capable of any sensible flexibility edge.
ways; and by liagonal braces, in a vertical as well as horizontal position, which I conceive
may be applied without much difficulty, and without the aid of malleable iron. I should
have no apprehension of its being liable to any material injury from any external violence,
and upon the whole I believe, that an arch of 600 feet span, similar to that in question,
.with such improvements as it may be susceptible of, is practicable, and capable of being
rendered a durable edifice.
Mr. J. Rennie observed, that the strength of the arch will be very much increased
horizontally, by the increase of width towards its two extremities. But I do not think any
advantage will arise to it vertically from this increase, but rather on the contrary; for, as
the additional width will also increase the weight, it cannot be made in equilibrium unless
CHAP. VIII.
489
BRITAIN.
the iron work is made lighter. Vertical ribs seem the most natural and easy method, and
if well braced might probably answer the purpose; but the increase of width towards the
extremities is certainly the strongest method of steadying the arch. If the bridge was to
be made 50 feet wide at the crown, and 100 feet at the extremities, it would, in my opinion,
be sufficient.
Mr. James Watt, of Heathfield, near Birmingham, thought that the width of the road-
way of the bridge ought not to be less than 60 feet, including the parapets on each side.
In respect to the effects of storms and common accidents, such an arch would be sufficiently
stable, without being widened at the ends; but it would be more convenient if it were
90 feet wide at each end, such extra width decreasing gradually, so that, at 150 feet from
each end, it should be reduced to the width of 60 feet, from which points the sides would be
parallel for 300 feet of the length. It appears to me, that the uprights which stand upon
the arch and support the roadway should be perpendicular, as well as the faces of the
abutments above the spring of the arch, as the uprights would in that position be stronger.
The segments of flat arches in the spandrills, if they acted at all as arches, would have a pre-
judicial effect, as they would push with great force against the abutments, in points where
they were less able to resist than at the spring of the real arch. One reason for enlarging
the width of the bridge to 60 feet is, the very great concourse of carriages and passengers,
which may be expected in that situation, and which I apprehend would be greater than
now cross at either London or Blackfriars Bridge, and surely 60 feet is narrow enough for
any principal street in London, as this should be considered.
Mr. John Southern observed, that the pillars that carried the road being radii from the
centre, the weight per foot long of the road ought to decrease from the crown, or summit
of the bridge, towards the abutments, in order to obtain the equilibrium of the arch; and
consequently, instead of increasing in width, the road ought to decrease towards the abut-
ments, supposing it to have the same depth of section. If it keep the same width, or
have parallel sides, it ought to get thinner towards the abutments, and still more so if it
widen.
By the plan it appears to be twice the width at the abutments that it is at the crown, in
which case the thickness at the crown should be, to that at the abutments, nearly as two
and two-thirds to one, in order to affect the equilibrium: this is, however, on the suppo-
sition that the weight of the arch is of little consideration in comparison with that of the
road, by which I mean the sleeper plates, Cornish flags, pavement, &c.
It is hence evident that the road may take any form in the plan, by making its thickness
correspond with the weight demanded by the equilibrium; but I must prefer parallel sides,
because of the great, if not insuperable difficulty of making them curved; and because I do
not perceive that much advantage can be gained towards horizontal stability by that form,
which seems, as I conceive, to be the main object, but which may be better attained by
diagonal braces.
Mr. William Reynolds, of Colebrooke Dale, says, I have no doubt but the strength of the
bridge is very materially affected by the increase of width towards the extremities, and
which will operate in a favourable manner in every respect, as it not only strengthens the
lateral bearing, but gives a greater abutment to the pressure endways, which will be very
advantageous.
Mr. Charles Bage, of Shrewsbury, observed, it was an excellent thought to make the
bridge wider at the ends than in the centre, not only for the convenience of the passage over
it, but for the opportunity it affords of giving firmness to resist tempests, or any other
horizontal pressure.
The third question to be answered was highly important, as it demanded in what propor-
tion should the weight be distributed from the centre to the abutments, to make the arch
uniformly strong?
Dr. Nevil Maskelyne apprehended this question to relate to the principle of equilibration.
But considering the question to be relative to the strength of cohesion of a perpendicular
section of the bridge, as opposed to the stress arising from the weight acting against it to
overcome it, it appears to me to make the bridge equally strong from one end to the other;
the thickness of the rib frames should be diminished more and more in going from the
centre to the extremities of the bridge, and that in the inverse ratio of the square of the
height of the perpendicular section above the arch. This it is evident will much diminish
the quantity of materials and weight of the bridge, and thereby further strengthen the
bridge, and lessen the expense. This subtraction of the materials, however, in going
towards the ends, is contrary to what is required for an arch of equilibration, at least of a
circular one.
18845
Rev. A. Robertson, previous to answering this third query, stated the following particulars
relating to the circle, of which the arch of the bridge would be a part. The diameter is
or 1449, feet, the circumference 4554-10103763. The length of the arch of the
bridge will be 618-59872427 feet, and its magnitude 48° 54'. Having ascertained these
13
II 2
484
Book I.
HISTORY OF ENGINEERING.
+
particulars, I proceeded, with a view to answer this third question, to calculate the propor-
tional weight at the extremity of every fifth foot from the crown of the bridge, the weight
at the crown being supposed to be one These are put down in the following table: the
first column contains the length of arches in feet from the crown; the second column contains
the weights at the extremities of these lengths; the length of arch and the weights at the
extremity of that length being in the same line, and adjoining to one another. If therefore
it be determined upon that the weight at the crown shall be any number as n, the weight
at the extremity of every fifth foot may be obtained by multiplying the number in the
second column of the first table by n. As the length of half the arch is 309-299, the last
length is not a complete multiple of 5.
If the weight over a portion of the arch at the abutment be given, the weight at the
crown may be ascertained. Thus if the weight over a portion of the arch of 10 feet at the
abutment be r, the weight x divided by 11-9911 will give the weight at the crown.

1st Col.
2d Col.
1st Col.
2d Col.
1st Col.
2d Col.
1st Col.
2d Col.
5
1.00007
85
1.0209
165
1.0816
245
1.1909
10
1.00027
90
1.0211
170
1.0866
250
1.1997
15
1.00063
95
1.0262
175
1.0923
255
1.2088
20
1.00114
100
1.0290
180
1.0979
260
1.2181
25
1·00178
105
1.0321
185
1.1039
265
1.2277
30
1.00256
110
1.0353
190
1.1099
270
1.2375
35
1.00367
115
1.0386
195
1.1162
275
1.2477
40
1.00458
120
1.0422
200
1.1226
280
1.2582
45
1·00581
125
1.0451
205
1.1293
285
1.2689
50
1.00717
130
1·0497
210
1.1371
290
1.2799
55
1.00870
135
1.0537
215
1.1433
295
1.2913
60
1.01034
140
1.0579
220
1.1507
300
1.3030
65
1·01210
145
1.0623
225
1.1583
305
1.3150
70
1.01410
150
1·0669
230
1.1661
309.299
1-3256
75
1.01620
155
1.0716
23.5
1.1741
80
1.01850
160
1.0765
240
1.1824
:
From the form of the bridge, and the law by which the weights over the several parts
must be regulated, it is evident from the table, that proceeding from the crown to either
of the abutments the quantity of metal must be less and less in proportion than the spaces
occupied; or, in other words, if I may use the expression, the metal must become more and
more rarified.
It therefore follows, that proceeding from either abutment to the crown,
the metal must become more and more condensed. The limit of condensation at the
crown, however, is that of solidity, and therefore a greater weight cannot be laid over a
given portion of the arch at the abutment, than that which, regulated according to the
established law, will render it necessary to use solid blocks of metal at the crown.
Mr. Playfair replied, that the distribution of the weight, so that these wedge-form frames
may be in equilibrio, and may support themselves even if they were not connected but by
their mutual pressure, can easily be determined, but will give a construction hardly ap-
plicable in practice. The equilibrium of the parts would require that the weights of the
wedge, at the spring of the arch, should not exceed the weight of that at the crown, in a
greater proportion than that of six to five, and that at all the intermediate points, this dif-
ference of one-fifth should diminish, as the square of the distance from the crown diminishes.
Thus the crown wedge being of the weight a, the wedge at the abutment should be of the
weight a +; the first wedge from the crown, a+
the second a +
α
α
5+31
312;
4a
;;
5+312
the
oa
third a+
; and so on for all the other thirty-one frames that compose one-half of the
5+31º
bridge, computing the distance from the crown by the space between the crown and the
middle point on the base of each frame. This is obviously so remote from the proposed
figure of the bridge, and from any that it can possibly have, that the notion of making
the parts balance one another, or support themselves by their weight alone, must be entirely
abandoned. It may be abandoned too without any loss to the firmness and stability of the
bridge, agreeably to what has been already remarked. The perfect balance of the parts
is only necessary, if the frames are unconnected and free to slip on one another; the moment
that any connection by diagonal braces or other means is established between them, the prin-
ciple of equilibrium is in effect departed from, and therefore has never been had recourse
to in any instance of an iron bridge hitherto constructed. When therefore it is asserted
that the iron bridge over the Thames is not meant to stand on the principle of equili-
trium. I do not mean in the slightest degree to object to its construction.
CHAP. VIII.
485
BRITAIN.
b
Mr. J. Robeson could not answer this question without considering the manner of acting
of every bar almost, to see what are in a state of compression, and what are on the stretch.
Did the main ring alone act, and act like masonry, the load on
every point of it should be as the cube of a line, drawn from the
centre of the arch through the point, till it meet a horizontal line.
Thus the weights on a, b, and c, should be as o d³, o e³, o ƒ³, o being
the centre, and fd horizontal. But in a mass of frame-work like
this, the equilibration theory is of very little use.
Dr. Charles Hutton says, to make the arch uniformly strong
throughout, it ought to be made an arch of equilibration, so as to
be equally balanced in every part of its extent. When the materials
Fig. 482.
of an arch are uniform and solid, then to find the weight over every part of the curve, so as
to put the arch in equilibrio, is the same thing as to find the vertical thickness of the arch
in every part, or the height of the extrados, or back of the arch, over every point of the
intrados or soffite of the under curves of the arch. In the case of the present design, a
strict mathematical precision is not to be expected, or attained by mere calculation on ac-
count of the open frame-works of iron in parts of various shapes and sizes.
We must,
therefore, be content with a near approach to that point of perfection, which can be accom-
plished in a degree sufficient to answer all the purposes of safety and convenience. Now
this can be conveniently done by a comparison of the present design of a bridge with the
example of a similar intrados curve in the 4th prop. of my Treatise on Bridges. By that ex-
ample it appears that the weight above every point on the soffite curve should increase
exactly in proportion as the cube of the secant of the number of degrees in the arch, from
the centre or middle to the several points in going towards the abutments. This proportion,
though it require an infinite weight or thickness at the extremities of a whole semicircle.
where the arch rises perpendicular to the horizon; yet for a small part of the circle near
the vertex, the necessary increase of weight or thickness towards the extremities is in a
degree very consistent with the convenient use and structure of such a bridge, as will be
evident by a glance of the figure and curve of that example. For as the whole extent of
the soffite arch in the present design is but about 48° 54′ or 24° 27′ on each side from the
middle point to the abutments, that is little more than the fourth part of the arch in that
example, therefore, by cutting out the fourth part of the arch, it will give us a tolerable
idea of the requisite shape of the whole structure, and increase in the thickness when the
materials are solid, or at least the increase in weight over every point in the soffite, that is,
the figure exhibits a curve for the scale of such increase. Or if we compute the numeral
values of the weights or thickness by the rule in that example, in the proportion of the cube
of the secants, they will be as in the annexed table, which is computed for every degree in
the arch from the middle, supposing the middle thickness or weight to be 10. And the

Degree.
Weight or
Height.
Degree.
Weight or
Height.
Degree.
Weight or
Height.
Degree.
Weight or
Height.
0
10.000
7
10.227
14
10.947
21
12.290
1
10.000
8
10.298
15
11.096
22
12.546
2
10.018
9
10.379
16
11.258
23
12.821
3
10.041
10
10.470
17
11.434
24
13.116
4
10.073
11
10.572
18
11.625
24/
13.272
5
10.115
12
10.685
19
11.831
6
10.166
13
10.810
20
12.052
true representation of the figure as constructed from these numbers, or the extrados curve
determining the true scale of weight or thickness over every such point in the soffite
curve, is here exhibited. Here the thickness or height in the middle being supposed 10,
the vertical thickness or height of the outer curve above the inner at the extremities is
13-272, or nearly 18, and the other intermediate thicknesses at every degree from the
vertex are as denoted by the numbers in the latter column of the table. If the thickness
at the top be supposed 7, 8, or 12, or any other number instead of 10, all the other numbers
must be changed in the same proportion. Now the upper curve in this figure is con-
structed from these computed tabular numbers, and exhibits an exact scale of the increase
of weight or thickness, so as to make the whole an arch of equilibration, or of uniform
strength throughout when the materials are of uniform shape and weight; and in this case
the upper curve does not sensibly differ from a circular arch in any part of it; but as the
convenient passage over the bridge requires that the height or thickness at the extremities
or imposts should be a great deal more than in proportion to these numbers, denoting the
equilibrium of weight, it therefore follows that the frame-work of the pieces above the
arch in the filling-up of the flanks ought to be lighter and lighter, or cast of a form more
11 3
486
Book I.
HISTORY OF ENGINEERING.
and more light and open as in the design, so as to bring the loading in those parts as near
to the equilibrium weight as the strength and stability of the iron frames will permit.
Mr. J. Rennie observed, that different methods may be adopted of rendering the arch
equally strong throughout. It may be balanced by the weight of the frames and loading
charged on them towards the extremities, so as to counterbalance that at the crown of the
arch, or it may partly be done by weight, and partly by longitudinal braces, placed in such
a direction as to answer the same purpose. The latter method will be found very useful
in this arch, particularly if put in addition to the weight which forms the equilibrio, for, as
I apprehend, it will be impossible to prevent the iron from yielding in some degree; this
yielding will be greatest where the depths of the materials are least, which is at the crown
of the arch, in which cases the braces will act in opposition to it, with more effect than the
simple gravity of whatever load may be placed upon it.
Mr. Attwood stated that the distribution of weight among the sections, so as to form an
arch of equilibration, depends on the angles of the sections which form the entire arch. If
the angles should be equal, and of the magnitude stated, the weight of each section and the
pressure on it appears from calculation to be as set forth in the table which follows.
dimensions of the proposed bridge being
Height of the middle arch
Span
Radius
Number of wedges which form the arch
Angle of each wedge or section
-
65 feet.
600
- 724-8
- 63
The
46′ 34″-314.
The inclination of the successive abutments to the vertical line is calculated from the
angle of each section, 46′ 34″-314, a degree of exactness not necessary, except to prevent the
small errors from accumulating. The angles of the abutments, entered in the second column
of the table, are expressed to the nearest minute of a degree. The weight of the highest or
middle section, denoted by the letter A, is assumed equal to unity, the weight of all the
other sections being in proportion to it.
Angular Distances of
Sections. the Abutments from Weights of the Sections.
the Vertical Line.
Pressure on the Sec-
tions next following.
Sums of the Weights of
the Sections, deducting
the Weight of half the
first Section.
I
Ꭱ
ARCARFGH-K-ZZOLOFQ=PPBX>N<MUAREG
0.23'
1.000
73.82
⚫500
1.10
1.000
73.83
1.500
1.56
1.001
73.86
2.501
D
2.43
1.002
73.90
3.503
3.30
1.003
73.95
4.506
4.16
1.005
74.02
5.510
Ꮐ
5.3
1.007
74.10
6.517
5.49
1.009
74.20
7.526
6.36
1.012
74.31
8.538
C
7.22
1.015
74.43
9.553
8.9
1.019
74.57
10.57
8.56
1.023
74.72
11.59
9.42
1·027
74.89
12.62
10.29
1.032
75.07
13.65
11.15
1.037
75.26
14.69
12.2
1.043
75.47
15.73
12.48
1.049
75.70
16.78
13.35
1.055
75.94
17.84
T
14.22
1.062
76.20
18.90
15.8
1.069
76.47
19.97
V
15.55
1·077
76.76
21.04
W
16.41
1.086
77.06
22.13
17.28
1.094
77.38
23.22
Y
18.14
1.104
77.72
24.33
19.1
1·114
78.08
25.44
19.48
1.124
78.45
26.57
20.34
1.135
78.84
27.70
21.21
1.147
79.25
28.85
D
22.7
1.159
79.68
30.01
22.54
1·172
80.13
31.18
23.40
1.185
80.60
32.36
Ꮐ
24.29
1.199
81.09
33.56
CHAP. VIII.
487
BRITAIN.
Mr. John Southern stated that the weight of a foot long of the road, at any point a, ought
to be to the weight of the same length at d, as the cube of the cosine of the arch c b is to
the cube of the radius, or as the line de is to the line df, wherein d is the
centre of the arch c b, b, the summit or crown, a b, a tangent to the curve at
b, ce
parallel to a b, a ƒ at right angles to da, and c a and b f continuations of
the radii dc and db respectively. In the case of the proposed bridge,
wherein the point c at the abutment is about 24 degrees from b, the weight
of a foot long of the road, at the abutment to that at the crown, is as three
to four nearly.
As the weight of the arch will not, in fact, be inconsiderable, this difference
will not be so great as this rule makes it, but unless the real or the relative
weights of the parts of the bridge were given, it is not easy to express the
ratio required.
The fourth question demanded, What pressure will each part of the bridge
receive, supposing it divided into any given number of equal sections, the
weight of the middle section being known; and on what part, and with what
force, will the whole act upon the abutments?

Fig. 483.
b
e
Dr. Nevil Maskelyne, upon the supposition that the whole acts as one frame of iron, stated
that there would be no horizontal thrust acting on the abutments, and the bridge will rest
and press perpendicular to the horizon upon the two abutments, each of which will support
half its weight, and if the thickness of the rib frames be made in the proportion mentioned
in the answer to the third question, the stress will be alike on every part.
Rev. A. Robertson said, proceeding from the crown to either of the abutments, and sup-
posing half the bridge to be divided into sixty-two sections, each of them, except the last,
over a portion of the arch 5 feet in length, the weights of the several sections will be as ex-
pressed in the second column of the following table. The first column of the table contains
the numbers of the sections of half the bridge, reckoning from the crown. The second
column contains the weights of each of the sections, the weight of cach section being on the
same line with its number. The third column contains the whole weight of 123, &c. sections,
reckoning from the crown of the bridge in this table the weight at the crown is supposed
to be 1. If, therefore, any weight be determined upon for the crown, the weight of any
section, regulated according to this determination, may be obtained by multiplying the
weight so determined upon, by the weight of the same section in the table.

1st Col. 2d Col.
3d Col.
123 4456789
4.9969
5.0009
4.9969 22
9.9978 23
1st Col. 2d Col.
5.0120
3d Col.
1st Col.
2d Col.
3d Col.
5.1228
110.8500 43
115.9728 44
5.4374
221·5345
5.4791
227·0136
5.0022
15.0000 24
5.1342
121-1070 45
5.4990
232.5126
5.0031
20.0031 25
5.1459
126.2529 46
5.5311
238.0437
5'0052
25.0083 26
5.1585
131·4114 47
5.5524
243.5961
5.0075
30.0158 27
5.1713
136.5827 48
5.5743
249.1704
5.0105
35.0263 28
5.1847
141.7674 49
5.6047
254.7751
5.0150
40.0413 29
5.1987
146.9661 50
5.6319
260-4070
50164
45.0577 30
5.2134
152.1795 51
5.6600
266 0670
10
5.0220
50.0797 31
5.2247
157.4047 52
5.6887
271-7557
11
5-0231
55.1028 32
5.2437 162.6484 53
5.7182
277-4739
12
5.0324
60.1352 33
5.2604
167.9088 54
5.7484
283-2223
13
5-0375
65.1727 34
5.2652
173-1740 55
5-7797
289.0020
14
50439
70.2166 35
5.3067
178.4807 56
5.8114
294.8134
15
5.0509
75.2675 36
5.3127
183-7934 57
5.8399
300-6533
16
5'0580
80.3255 37
5.3314
189.1248 58
5.8778
306.5311
17
5'0656
85.3911 38
5.3504
194.4752 59
5.9120
312-4431
18
5.0740
90-4651 39
19
5.0827
95.5478 40
20
21
5:0937 100-6415 41
5'0965 105.7380 42
5.3704 199.8456 60
5.3909 205.2365 61
5.4082 210.6447 62
5.4524 216.0971
5.9400
318-3831
5.9908 324-3739
5.1764 329-5503
The pressure against each abutment, in a direction parallel to the horizon, is 724-8,
the weight at the crown being 1. If, therefore, a weight be determined upon for the
crown, the pressure at each abutment will be found to be 724-8 times this weight. If
the weight over a certain portion of the arch adjoining to the abutment be given, the
weight at the crown may be found as mentioned above, and the horizontal pressure at
the abutment may then be determined. Thus, if the weight of matter over a portion of the
arch 10 feet in length, adjoining to the abutment, be 340 tons, the weight at the crown will
be 28.354, and the horizontal pressure at each abutment will be 20550.9792 tons. In this
II 4
488
Book L.
HISTORY OF ENGINEERING.
case the weight of half the bridge will be 28.354 x 3295503, which is equal to 9344·0692062
tons; the weight of the whole bridge will therefore be 18688-1384124 tons. As the law
which secures a maximum of strength produces an equilibration throughout the whole
arch, the horizontal pressure throughout is the same as against the abutment. In adjusting
the strength of the abutment to resist the horizontal pressure, the pressure must be sup-
posed to act in the line from which the arch springs.
Mr. Playfair observed, the pressure on the abutments will be found by multiplying half
the weight of the bridge by the number 2.41605, or by multiplying the weight of the
whole bridge by 1.20802; the pressure on each abutment will therefore exceed the whole
weight of the bridge by about 1. This immense pressure must be counteracted by abut-
ments of great size, and of the most solid structure; it would be worth while to compare
this pressure with the thrust against the abutments or piers of some well-known stone
bridge, such as that of Westminster or Blackfriars; one would be enabled by that means to
form some notion of the comparative strength required in the abutments. The rule above
laid down gives the pressure in the direction perpendicular to the face of the abutment;
of that pressure one part is directed downwards, and may be had by multiplying the
foregoing number by 4139, and hence the perpendicular pressure on the abutment is found
nearly equal to the weight of half the bridge.
The other part, that which acts on the abutment horizontally, and which it is of most
consequence to know, is found by multiplying the pressure formerly computed, namely,
that which is perpendicular to the face of the abutment, by 91, which brings out the hori-
zontal thrust against the abutment, equal to the whole weight of the bridge multiplied by
1'099, or nearly equal to the whole weight increased by one tenth part.
The horizontal thrust at the crown may be found by multiplying the weight of the
bridge by 1.188; I would not, however, have it understood that this last number is accurate,
as the investigation of it involves the knowledge of the centre of gravity of the bridge, the
exact determination of which would require more data and more time than I am in pos-
session of.
Mr. J. Robeson. I cannot conceive any physical division of this frame, which will
enable me to answer this question; I do not believe it possible to divide it into great
wedges, which will abut on each other like so many stones.
Dr. Milner observed, that the construction of the arch of this bridge required the in-
genuous and mutual communication of the theorists and the practitioners, for computing
the horizontal drift or shoot of the bridge, and its action against the abutments.
Dr. Charles Hutton. By the equal sections mentioned in the question may be
understood either vertical sections of equal weight, or those perpendicular to the curve, of
equal weight or of equal length; and whichever of these is intended, their thrust or
pressure in direction of the curve may be easily computed, if wanted for the purpose of
making experiments on the strength of the frames, to know whether they will bear those
pressures, or what degree of pressure they will bear without being crushed to pieces. But
as it is evident that the frames next the abutment will suffer the greatest pressure of any,
I shall here give a computation of the actual pressure there, which may be sufficient, since,
if the frames at the abutments are capable of sustaining that greatest pressure, we may safely
conclude that all the others, from thence to the vertex, will be more than capable of sus-
taining the lesser loads or pressures to which they are subject, and this computation will
answer the latter and most essential part of the question, viz. On what part, and with what
force, will the whole act on the abutments? Now, from the nature of an arch, it appears
that the whole pressure on the abutments will be chiefly on the lower parts of the impost,
where the lower frame rests on it, and where we shall, therefore, in our computation,
suppose it to act; and in the calculation, the whole weight of the half-arch A O must be
supposed united in its centre of gravity N. Then, if a vertical line N M be drawn through
the centre of gravity N, by computation, it is found that DM is nearly equal to 160 feet,
and consequently ME is equal to 140 feet; also if N O be perpendicular to the impost, or
G
152
B

1:0
A
6:5
រ
H
E
140
160
M
D
Fig. 484.
F
in the direction of the arch at OE, we shall have this proportion, viz. as MN (60) is to the
weight of half the arch (3250 tons), so is NO (152) to the pressure on the impost in the
direction of the arch at O, and so is ME (140) to the horizontal thrust or pressure in the
direction M E.
This gives 8233 tons for the pressure on the impost at O in the direction
CHAP. VIII.
489
BRITAIN.
of the arch, and 7583 tons for the horizontal thrust in direction ME, being the pressures at
each end of the bridge. We may therefore estimate the greatest pressure on the east, or
abutment frame, at about 8000 or 9000 tʊns.
Mr. Atwood. The weight of the highest or middle sections being denoted by unity,
the proportions of the pressures on all the other sections in respect to unity will be found ir.
the fourth column of the table. If the highest section should weigh 100 tons, it appears
from the table that the pressure on the first section, or rather the pressure between the first
and second section, will be 7300 tons, and the pressure on each of the abutments will be
8100 tons. It may be -dded, that according to these dimensions, the weight of each semi-
arch will be 3350 tons, and the weight of the entire arch 67CO tons.
The fifth question proposed was, What additional weight will the whole bridge sustain,
and what will be the effect of a given weight placed on any of the fore-mentioned sections?
Dr. Nevil Maskelyne stated, that an additional weight laid upon any part of the bridge
will be supported by the two abutments, each bearing its share in the inverse ratio of its
horizontal distance from the weight. The stress of the weight on the part it lies on is as
the weight, and the product of the horizontal distances from the two ends of the base, and
its stress upon the centre of the bridge will be to the stress there arising from the
of the whole bridge, as the weight laid on is to the whole weight of the bridge.
pressure
Let us suppose the additional weight laid upon any part of the bridge to be that of a
loaded waggon, which we will suppose to be 7 tons; there is no doubt but that this bridge
may easily be made strong enough to support this by the connection of its parts; but as the
load might be laid on, so as to press upon the iron plate in the interval between two ad-
jacent ribs, it will be proper to calculate the thickness it may be necessary to give to the
plate to sustain such pressure. I find that if the interval of the ribs be 6 feet, a plate of 8
inches thick will be above four times stronger than what would barely support the weight.
Rev. A. Robertson. The maximum weight which the bridge will sustain depends upon
the strength of cast-iron, and, as far as I know, experiments have not been made to ascer-
tain the strength of cast-iron. As far, therefore, as relates to the first part of this query,
there are not data sufficient for determining by calculation the weight required.
D
H
Ꮮ
ரு
F
The effect of a given weight placed over a given point of the arch may be ascertained
in the following manner. Let A, B, D, E, F,
represent the bridge, and suppose a given weight
to be placed upon the point H, in the roadway;
let the straight line H, K, be perpendicular to
the horizontal line A, F, and meet it in K; then
the effect of the weight on H, will be as the
rectangle under the parts A K, K F, of the
horizontal line. The pressure of a given weight
will therefore be greatest when it is over the
middle part cr crown of the arch.

K
Fig. 485.
Mr. J. Robeson.—The only portion of the arch which can be sensibly affected by an
occasional load is the crown, and 40 or 50 feet on each side of it. This is already carrying
above 300 tons of roadway; I imagine that any load which can occasionally collect in that
portion will be a mere trifle in comparison to this load. We have already seen, that it
will increase the mutual compression about of its own weight. If laid on at 180 feet
from the crown, this must be increased in the proportion of 2 to 5, because it is supposed
to lie on the crown; but I do not think that this increased compression is of any im-
portance. The chief risk is from the vertical strain, and it was for this reason that I
recommended diagonal ties, diverging from the lower angle of the middle joint. If a
very strong horizontal transverse tie of wrought-iron went across the bridge in this place,
ties could be attached to it, and to the underside of the roadway, at considerable distances
on each side, which would suspend the intervening portion from parts which have a more
extensive vertical connection, and would, in short, make it a more obtuse wedge.
Dr. Charles Hutton. It is perhaps not possible to pronounce exactly what additional
weight the bridge will sustain without breaking, as it depends on so many circumstances,
some of which are not known. But considering the great dimensions and strength of the
arch-frames and of the whole fabric, we are authorised to conclude, that there is no possible
weight which can pass over any part of the bridge, even heavy loaded waggons, whose pressure
can be great enough to cause any danger to such strong and massy materials, and especially
when it is considered that by connecting all the frames together, by proper bond and
otherwise, as mentioned in the answer to the first question, the local additional pressure
will soon be distributed through the whole series of the iron framing.
Mr. Atwood. The sections being adjusted to equilibrium are to be tied or joined
together by a method described in a detached drawing; this is intended to prevent any
change in the positions of the sections, in consequence of occasional weight which may be
brought to press on any part of the arch: any such additional force of weight, if not
490
Book J.
HISTORY OF ENGINEERING.
opposed, would cause the sections immediately under the additional weight to descend
from their places, which cannot happen without the elevation of some other sections,
in consequence of which the form of the arch would be altered; but this change is pre-
vented by the fastenings which oppose equally the descent of any section, in consequence
of additional weight superincumbent on it, and the ascent of other sections from the
excess of pressure caused by the aforesaid superadded weight. But the form of the arch
will be preserved entire, notwithstanding the occasional addition of any weight whatever,
until the stress on the joinings should be so great as to cause them to give way, or to break
or crush the substance of the iron frames which compose the sections. This point of
security must therefore depend on the cohesive force of the iron, and affords no data for
precise calculation; but the circumstances of the construction afford some grounds for
forming a probable conjecture on the subject. The force necessary to cause a change in
the positions of the sections depends on the following circumstances:-1. On the massive
weight of the sections; 2. on the strength of the joinings, which resists in a certain degree
any force applied to separate the sections; 3. the pressure between the surfaces of the
contiguous sections, which increases the effectual strength of the ties or fastenings.
According to the dimensions stated in the table, the weight of each section is from 100 to
120 tons. And since the sections united by the fastenings are bound or pressed together
with a force or pressure from 7300 to 8100 tons, if 30 or 40 tons should be the greatest
occasional weight that may probably bear on the same part of the arch, it does not seem
probable that the form of the arch would be sensibly changed by the addition of such a
weight. 6. The horizontal force, which might be sufficient to press the arch out of the
vertical plane, must depend on many circumstances, some of which can be estimated by con-
jecture only. The principal of these are the following:
1. The motive force, such as the force of the wind in tempestuous weather, which may
be in very high winds at the rate of 8 or 10 pounds on a square foot of surface, when the
wind unfringes directly against it, according to the experiments of Colonel Beaufoy for
ascertaining this point. 2. The magnitude of the areas which may be estimated to be
subject to this force of pressure. 3. The angle at which the wind may strike upon it.
4. The effect of any force in pressing the arch out of the vertical plane will be the less in
proportion as the massive weight of the iron used in the construction is greater. The
strength of the ties or fastenings will also, as in a former instance, add to the stability of
the arch, against any force that may press against it.
Mr. John Southern. An additional weight or force brought upon any part of the arch
will distort the curve of equilibration, (an imaginary line, which if the bridge be properly
constructed passes through the centre of the frames of the arch,) will render it (the curve
of equilibration) prominent opposite the additional force, and will depress it at distant
points of the arch; but if these distortions of the imaginary curve keep within the limits
of the frames of the arch, no change of position of the parts will ensue, nor will any tension
be brought upon the limits of the frames; but if the distortion go beyond the said limits,
the joints of the frame will open under the prominent and above the depressed parts of the
curve, and the bridge fall, unless those openings be prevented by means which bring on
tension in the limbs. The force which will bring on this degree of distortion of the equilibrial
curve is in proportion to the weight of the bridge, and nearly the depth of the frame
jointly; and I am induced to believe from an experiment I have made, that if the frames
be 8 feet deep, the weight which would produce this effect would not be less than 100 feet
long of the road.
The Sixth Question. Supposing the bridge executed in the best manner, what horizontal
force will it require, when applied to any particular part, to overturn it or press it out of
the vertical position?
Dr. Nevil Maskelyne. — Suppose the largest ship that could strike against it to be of
80 tons, and the bridge to be 7000 tons. The ship then is an eighty-seventh of the bridge;
let the ship be going at the rate of 5 miles an hour, or 7.2 feet in a second. This stroke
then tends to communicate a velocity of an inch in a second to the whole bridge, if it were
free to move. The friction upon the buttresses, or the connection with them, would imme-
diately overcome this motion; but suppose the bridge was free to vibrate upon the middle
line of its base as an axis, it would swing to and fro like a pendulum, each vibration taking
up about 4 seconds, and as in that time the centre of gravity would not be moved by the
velocity acquired by the stroke above 4 inches, it is plain that this small removal from the
centre of the base, which is itself 45 feet, can no way endanger the oversetting of the
bridge; nor even if it were ten or twenty times greater, but as was said before, the con-
nection with the buttresses will soon bring it to rest.
•
Rev. A. Robertson. The power of the bridge to resist any force tending to press it out
of the vertical plane will consist of four particulars; the strength of the iron of which it
is composed, its width, and the resistance at the abutments, and the inertia of its matters.
The absolute effect of the strength of the iron and the width cannot be calculated, for the
reasons already mentioned; but, cæteris paribus, an increase of width will give the bridge an
CHAP. VIII.
491
BRITAIN.
increase of power, both at the abutment and in the middle, to resist any force tending to
press it out of the vertical plane. In estimating that part of the power which arises from the
inertia of matter, we are to suppose the two halves quite unconnected at the middle of the
whole, and that each of the halves may be made to revolve about its adjoining abutment
in a vertical position, as about an axis. The inertia of each half will then be obtained by
multiplying its weight by the square of the distance of its centre of gyration from the
abutment.
If the weight of the crown be 1, I find that the inertia of each half of the bridge will
be 9245488-995. If the weight over a portion of the arch, of the length of 10 feet, ad-
joining to either abutment, be 340 tons, the inertia of each half of the bridge will be
262146827·94741 tons.
Mr. J. Robeson.-What force will push the arch out of the vertical plane, the breadth
being so considerable in proportion to the length, and the compression at the crown so
great? I cannot conceive any force as likely to occur which will put it in any danger.
Even the curved form of the sides is favourable to its strength in this particular, for, sup-
posing it pressed from the west side, if the abutments at the east side at the corners do not
yield, the whole of the eastern surface, being a concave, must resist as an arch, and although
this resistance is not well directed, and allows a twist, it is still considerable. The chief
risk is from a ship's mast-head striking the arch near the crown, but the chief risk will be
to the ship. The mast-head or rigging, which will then be confusedly bundled about it,
may catch, but the ship will be carried through by the current, and may very probably
cant round with her broadside to the stream; in this situation, her mast being held fast, she
will very likely be heeled down, and take in water and fill.
As, independent of the curved form (horizontally) of the sides, a pressure of one side
tends to open the joints on the other; this points out another advantage of the connection
by straps, in the manner practised at Wearmouth Bridge.
I cannot form a precise opinion of the effect of these oblique ribs, which appear in the
plan, two on each side of the middle rib. They are intended for stiffening the bridge
horizontally, but I do not see them in the profile, and must therefore suppose them to
range along with the other ribs, so as to be hid by them. I think that their effect would
have been twice as great, had they been twice as oblique or gone across from side to side.
I observe that they are connected with the cross ties as they go along. If these cross ties
which connect the different ribs are of cast-iron, I think that this connection with the
oblique tie-ribs exposes them to a great risk of snapping. For the obliquity of these ties
occasions the strain of compression to be considerably different, both in magnitude and
direction, from the strain of the same kind on the ribs; this difference acts transversely on
the cross ties and tends to break them. The underside of the roadway is a very convenient
place for diagonal framing, in order to stiffen the bridge horizontally. But whatever is
done with this intention must have a very extensive connection with the abutments.
straps to which these braces are attached should embrace a great part of the masonry,
that one part may not easily be torn from another.
The
Dr. Charles Hutton.—This question will be much better answered by means of experiments
made on a proper model, than by theoretical calculations à priori. But when the bridge is
executed in the best manner, with the frames properly bonded and connected together, it
seems more likely that any violent shock, such as a ship driving against it, would break
any particular frame, rather than overturn such a mass of bonded materials, or even move
it sensibly out of the vertical position.
Mr. John Southern.—If the bridge should be considered as a single frame, having strength
to keep itself together against a horizontal force applied at the crown, that could under these
circumstances overset it; and supposing it free from the top of the abutments, and simply
resting upon the end of the arch as feet, this horizontal force applied to the vertex would
be more than two-thirds the whole weight of the bridge; but though this supposition of
the unity of the parts of the bridge fail us, there is no doubt in my mind of the practi-
cability of making the bridge strong enough, by the application of diagonal braces, to resist
any force that can possibly apply to overset it.
The Seventh Question.-Supposing the span of the arch to remain the same, and to spring
10 feet lower, what additional strength would it give to the bridge? or, making the
strength the same, what saving may be made in the materials? or if, instead of a circular
arch, as in the drawings, the bridge should be made in the form of an elliptical arch, what
would be the difference in effect, as to strength, duration, and expense?
Dr. Nevil Maskelyne.—In the proposed bridge of 600 feet in the span and 65 feet high,
the radius of the arch is 725 feet, and the length of the arch 618 feet 6 inches; and in the
bridge proposed in the question, the height being 75 feet to the same span as before, the
radius of the arch will be 637 feet 6 inches, and the length of the arch 625 feet, and the
arch more curved by about one-seventh, and consequently stronger by about one-seventh,
whether for sustaining its own weight or a weight laid on it. But as it already contains
more materials than the bridge of 65 feet height, it does not appear to me to be probable
492
BOOK I.
HISTORY OF ENGINEERING.
that a reduction can be made in the materials, so as to make them less than in the other
bridge, though it may reduce them to an equality in the two bridges. If an elliptical
arch was adopted instead of the circular one, a bridge might be made sufficiently strong,
equally durable, more convenient, and with great reduction of expense.
Rev. A. Robertson.-Supposing the span of the arch to remain the same, and the arch to
spring 10 feet lower, the crown of the arch would be 75 feet, and the diameter of the circle
would be 1275 feet. Let A B D, E B G, be the two arches, whose strength are to be
compared, A E, D G being each equal to 10
feet, and perpendicular to the horizon. Take
any point H in the arch, A B D, and draw the
straight line H K perpendicular to the
horizontal line E G, and cutting the arch
E B G in F. Then the diameter of the
circle of which A B D is a part being
A
18845
13
E
B

H
F
D
K
G
Fig. 486.
feet, and the diameter of the circle of which
E B G is a part being 1275, the strength of the
upper arch at H will be to the strength of the under arch at F, as 1275 to
51 to 58 nearly.
18845
or as
13
The span and height being the same, if the arch consisted of the flat side of an ellipse it
would be weaker than the circular arch: if it consisted of the other side of an ellipse, it would
be stronger.
Mr. Playfair.-Were the entire elevation of the arch to be 75 feet instead of 65 feet, a
considerable addition would be made to the strength of the bridge. The radius of the
arch as at present proposed is 725 feet nearly; if the elevation were 75 feet, the span
remaining 600, the radius would be shortened to 637 feet 6 inches, and the strength of
this latter arch, in as far at least as it depends on the wedge-form figure of the frames,
would be to that of the former in the inverse of that proportion, or as 725 to 637, or as 8 to
7 nearly.
In this I suppose the weight and strength of the iron frame-work to remain the same.
As more weight would no doubt be required in this second construction than in the first,
the real advantage gained would not be so great as has been just stated, or as a seventh
part.
As to the elliptic arch, I do not think that any advantage would be obtained by intro-
ducing it in the room of the circular. An elliptic arch, indeed, might be so employed as
greatly to lessen the horizontal thrust on the abutments, but the curvature at the crown
would be rendered so small that the bridge would be greatly weakened at that point,
deriving there no advantage from its figure, and depending on the mere strength of the
iron.
Mr. J. Robeson.-Making the arch spring 10 feet lower will diminish the thrust on the
abutment one-fifth, as also at the crown, and by giving more curvature at the crown will
make longer joints. This will greatly strengthen the bridge, but this advantage will be
lost by making it elliptical, not from a want of equilibration, because this structure should
not be compared with masonry, but for want of long joints near the crown, and an oppor-
tunity of using better disposed diagonal braces. Such a degree of ellipticity as will be
sensible to the eye and graceful will certainly make the bridge extremely weak in the
middle.
Dr. Charles Hutton. -Should the arch spring 10 feet lower than in the design, the
bridge would be more stable, because the thrust or pressure on the abutments would be
directed lower down, and more into the solid earth, and in general, the lower the springing
of the arch, the more firm the abutments and stable the bridge, if the height of the crown
above the springing of the bridge be the same. But the greatest advantage would be by
making the bridge in the form of an elliptical arch instead of the circular one, in all the
articles of strength, duration, convenience, and expense. For, as the elliptical flanks
require less filling up than the circular, this will produce a great saving in the iron work,
and this same reduction of materials in the flanks towards the abutments is the very cause
of greater strength by reducing the weight there, nearer to the case of equilibration, since
that very extraordinary mass employed in the flanks of the circular arch destroys the
equilibrium of the whole by an overload in that part. The elliptical arch will also be
much more convenient, as it will allow of a greater height of navigation way between the
water and the soffite of the arch. The elliptical arch is also a much more graceful and
beautiful form than the circular arch.
Mr. Atwood.—It does not appear to me that there would be any material difference in
the strength and duration of the arch, whether it is constructed in an elliptical or circular
form, all the parts being executed equally well in both cases. The expense, it may be pre-
CHAP. VIII.
493
BRITAIN.
suined, will principally depend on the quantity of materials used, to be determined by the
degree of strength, arising from massive weight, it may be proposed to give to the
structure; and the distribution of the mass among the several sections will be regulated
according to the principle adopted for establishing the equilibrium, which, it appears to
me, will be to all practical purposes the same, whatever be the form of the arch.
Colonel Twiss.- Increasing the rise of the arch 10 feet, and leaving the span the same,
would strengthen the bridge, chiefly by increasing the width of the back part of the
voussoir; but I cannot state the exact proportion, nor do I believe any theory can;
neither do I think that theory can answer the second part of this question, but I am of
opinion, that when an arch can be built to answer its object, and yet contain less than
sixty degrees, that in all such cases the segment of a circle is to be preferred to an
elliptical one.
Mr. John Southern. The span of the arch remaining the same, as also the weight of the
road, the stress or compressing force, which the arch frames would suffer, and also the hori-
zontal push against the abutments, would be lessened, by increasing the altitude, or versed
sine of the arch, nearly in the inverse proportion of the altitude, or more accurately, in the
present instance, as eight to seven. It would appear, therefore, that the members of the
arch might be lessened in section to sustain the same road, but as the road itself is supposed
to be the same weight, the whole quantity of materials of the bridge would not be lessened
by increasing the altitude of the arch in any such ratio as the above; and the force that
would break up the bridge would rather be lessened, supposing the depth of the arch
frames the same.
The elliptical arch is better adapted to resist the pressure of a road of uniform thickness,
which is supported by pillars, pointing to the centre of the arch, especially if it widen
towards the abutments; but for the same altitude, as it implies a less degree of curvature
at the crown, it necessarily induces a greater compressing force on the arch frames, which,
of course, will be transmitted to the abutments. The degree of ellipticity which the case
would demand is, I think, too trifling to afford greater convenience for vessels to pass
under; it cannot be more durable, being made of the same materials, but it will certainly
be much more expensive and difficult to execute well than the arch of a circle.
Fourteen other questions were submitted to these professors and others by the select
committee, but they were chiefly of a nature relating to the material and cost, which were
not very satisfactorily answered; and Mr. John Playfair concludes his report by observing,
"That it is not from theoretical men that the most valuable information in such a case as
the present is to be expected. When a mechanical combination becomes in a certain
degree complicated, it baffles the efforts of the geometer, and refuses to submit even to the
most approved methods of investigation. This holds good particularly of bridges, when
the principles of mechanics, aided by all the resources of the higher geometry, have not yet
gone further than to determine the equilibrium of a set of smooth wedges, acting on one
another by pressure only, and in such circumstances as, except in a philosophical experi-
ment, can hardly ever be realised. It is, therefore, from men educated in the school of
daily practice and experience, and who, to a knowledge of general principles, have added,
from the habits of their profession, a certain feeling of the justness or insufficiency of any
mechanical contrivance, that the soundest opinions on a matter of this kind can be
obtained."
Iron Bridges.- Colebrook Dale, over the Severn, was the first erected in England, and
was completed after the designs of Abraham Derby, in the year 1777. It is situated
between the villages of Madeley and Brosely in Shropshire, and where the river is both
narrow and rapid.
The abutments are of stone, and were built up about 10 feet above the common low
water mark; they are finished off with a platform of squared freestone, in breadth 10 feet,
which is made to answer both for a base for the springing of the arch and for a towing
pathi.
Cast-iron plates, 4 inches in thickness, formed with sockets to receive the ribs, are laid
upon this platform, and to save metal the plates are cast with considerable openings. On
these rest the five principal or lower ribs, which form the arch; they are 9 inches by 64;
above them is a second row, cut off at the top by the horizontal bearing pieces, 6 by
6 inches; and above these is a third row, 6 inches by 6 inches. Between the ribs are
upright standards, 15 inches by 6 inches, with an open space in the middle, 5 inches
in breadth. The back standards are 9 inches by 6 inches, with projections for the braces;
the diagonals and horizontal ties are 6 inches by 4 inches, and the cast-iron tie bolts are
in diameter 21 inches.
The covering plates, which reach quite across the bridge, are 26 feet in length, and 1
inch in thickness.
The great ribs are each cast in two pieces, meet at the keys, and are 70 feet in length.
being one-half of the entire circumference of the arch, which has a clear span of 100 feet 6
inches, and a rise of 45 feet.
494
BOOK I.
HISTORY OF ENGINEERING.
In the spandrills are introduced rings of cast-iron, and a railing of the same metal runs
along each side of the roadway.
The ribs are nearly semicircular; the height from the ordinary low water to the springing
plate is about 10 feet, making a total height from low water to the soffite of the arch of 55
feet.
The weight of the whole of the iron work is 378 tons.

H
UTUTUTU U
Fig. 487.
COLEBROOK DALE BRIDGE.
Behind the iron work, at each extremity of the arch, the abutments are carried up
perpendicularly, and the square stone facing backed with rubble work.
Iron Bridge at Buildwas, finished in the year 1796, after the designs of Mr. Telford, is
situated about three miles above that at Colebrook Dale. In this example the portion that
sustains the road is, as it were, suspended from two large ribs, placed on each side of the

Fig. 488.
BUILDWAS BRIDGE.
bridge; the span of the arch is 130 feet, and the versed sine of the ribs, which bear the
covering plates, is 17 feet; the breadth across the soffites is 18 feet, and the height from the
ordinary low water to the soffite is 30 feet.
This novel mode of construction, which allows the roadway to be kept low, on the sus-
pending principle, was perhaps the first adopted in this country. The bearing-ribs have a
curve of one-eighth of their span, or 17 in 130; they rise about one-fourth of their span,
The
or 34 feet, and are maintained securely, both by horizontal ties and cast-iron braces.
whole is covered with 46 plates of iron, 1 inch in thickness, each 18 feet in length; they
CHAP. VIII.
495
BRITAIN.
are cast with flanches at the sides, 4 inches in depth, and are screwed together, and, being
laid according to the curvature of the ribs, and secured firmly at the abutments, form an
arch in themselves, and thus in some degree relieve the ribs of the weight they would
otherwise sustain. As there is only one rib in the middle of the bridge, others are placed


Fig. 489.
BUILDWAS BRIDGE.
at right angles, 4 inches in depth, cast with flanches, which serve to support the 18 feet
plates that extend across. The suspending ribs are 18 inches in depth, and, exclusive of
the moulding, 25 inches in thickness. The bearing ribs are 15 inches in depth, and 21
inches in thickness, and each is cast in three pieces, of about 50 feet; the braces are 6 by 3
inches. The principal king-posts are 10 by 4 inches. The springing plates are 3 feet
broad, and 3 inches thick, cast with openings to save metal. The uprights against the
abutments are 4 inches square. The strongest uprights in the railing are 3 inches square,
and those between them 1 inch; they are placed 6 inches from centre to centre, and their
height above the road is 4 feet 9 inches.
In each spandrill are three circular arches, formed with hard bricks, which are con-
cealed by a covering of iron plates, an inch in thickness. The abutments are carefully
built of squared masonry, filled in with rubble; the foundations are laid upon the solid
rock.
The whole weight of iron is 173 tons, and the cost was about 60007., including the abut-
ments, the masonry of the wing-walls, (which have a curve both on the plan and vertically,)
and the towing path, which is about 10 feet above the level of low water.
Sunderland Iron Bridge, over the Wear, was formed in part out of another contrived by the
celebrated Thomas Payne, which was put up at the Yorkshire Stingo, Lisson Grove, and
afterwards carried back to Rotheram; it was opened to the public in the year 1796, and
was cast at Rotheram, under the superintendence of Mr. Thomas Wilson. It is composed of
one arch, the segment of a circle, the chord line being 236 feet, and the versed sine 34 feet;
the height from the surface of the ordinary low water to the soffite of the arch is 100 feet, the
springing line is 60 feet above the level of low water, the width of the roadway is 32 feet,

Д
Fig. 490.
SUNDERLAND BRIDGE.
and the whole is carried upon six ribs, each composed of 125 small frames, about 2 feet in
length and 5 feet in depth, in the direction of the radius. In each of these frames are three
pieces 4 inches square, following the curve of the arch, and connected, in the direction of
the radius, by two other pieces 4 by 3 inches. In each side of the larger pieces is a groove
3 inch in depth and 3 inches broad, in the middle of which is a hole opposite each cross-
piece.
·
496
BOOK I.
HISTORY OF ENGINEERING.
After the abutments were built, and a timber scaffolding constructed across the Wear,
six of the frames were placed on the abutments, in the manner of voussoirs, and wrought-
iron bars were fitted into the grooves, so as to hold several of them together. Hollow pipes
of cast-iron, 4 inches in diameter, fitted to reach between each two frames, were introduced
entirely across the soffite; upon the ends of these pipes were flanches, having holes drilled
into them to answer to those in the 4-inch pieces of the frames, as well as to those of the

Fig. 491.
SUNDERLAND BRIDGE.
wrought-iron bars; through these holes wrought-iron bolts were passed, which brought all
the parts together by means of forelocks. The frames do not meet at the upright pieces.
but only on the three points of the 4-inch pieces; at the ends of the hollow pipes are small
projecting pieces, embracing both the upper and lower edge of the frames, which oppose
each other. When the whole of the frames were placed upon the centre, and the arch
keyed, in the manner of a stone bridge, the upright pillars were fixed; between them were

Scaffolding.
Fig. 492.
SUNDERLAND BRIDGE,
cast-iron circles, resting upon the extrados of the voussoirs.
timber platform, and the railing is of cast-iron.
The road is carried upon a
This magnificent bridge, from its elevation and lightness of construction, is perhaps the
boldest attempt that had hitherto been made to cross a river, and at once proved what could
be accomplished by the aid of cast-iron; some objections have been made to the number
of joints in the main ribs, which might possibly have been lessened, and considerable
CHAP. VIII.
497
BRITAIN.


Q
=
Fig. 493
VOUSSOIRS OF SUNDERLAND Bridge.
expense saved in the braces, ties, and bolts; the circles placed in the spandrills are also
ill-adapted to support the roadway, the
pressure they receive being unequal.
Iron Bridge over the Witham, at
Boston in Lincolnshire, executed from
the designs of Mr. Rennie, has one
arch, with a span of 85 feet, and a rise
of 5 feet 6 inches; its breadth is 36
feet. It is composed of eight ribs, each
consisting of eleven frames, of a depth,
in the direction of the radius, of 3 feet.
At the joints cast-iron gratings are in-
troduced across the arch which connect
the frames together, in a similar way
to those practised in the aqueduct at
Pontcysyte. In the direction of the
curves are two pieces of iron 7 by 41
inches, and these are connected in each
frame in the direction of the radius
by pieces 4 by 3 inches. Upon the
back of the ribs pillars 4 by 3 inches
are perpendicularly placed to support
the roadway. The rise of the arch is
only one-fifteenth of its span; the
frames are nearly four times the length
of those at Sunderland, and being con-
nected with cast-iron gratings instead
of wrought-iron is a decided improve-
ment; but the pieces in the frames,
which are in the direction of the ra-
dius, are perhaps not sufficiently
strong, in proportion to the main pieces
in the direction of the curve.
Two Cast-iron Bridges over the Avon,
at Bristol, built after the designs of
Mr. Jessop, each consisting of a single
arch of 100 feet span; the rise 12 feet
6 inches, or one-eighth, the breadth
Fig. 494. SECTION THROUGH SUNDERLAND bridge.
30 feet. There are six ribs, each
composed of two pieces, meeting in the middle, and connected crosswise by nine cast-iron
ties, dovetailed and wedged into the ribs, their cross sections being T-shaped. The abut-
ments that receive the ribs are laid in courses following the direction of the radius, and on
them are plates 32 feet in length, 2 feet 4 inches in breadth, and 4 inches in thickness;
each plate has five apertures 5 feet long, and 20 inches in width. The ribs in the direction
of the radius are 28 inches in depth and 2 inches in thickness, and have each 80 apertures
K k
D


498
BOOK I.
HISTORY OF ENGINEERING.
12 inches square, separated by bars 3 inches broad, excepting opposite the cross-ties, where
the solid metal is 12 inches in breadth. In the middle, where the ribs meet, are flanches
2 inches thick and 8 inches broad, which are connected by 3-inch cast-iron screw bolts.
Between the ribs and the bearers of the roadway are perpendicular supports, the horizontal
section of which is T-shaped. The road is carried upon cast-iron plates, and protected by
railing of the same metal.
Iron Bridge over an Arm of the Sea at Bonar, in the county of Sutherland, in Scotland,
under the direction of Mr. Telford, consists of one arch 150 feet span, and rises 20 feet;
it is 16 feet in width, and has four ribs. The springing plates are laid in the direction
of the abutments, and are 16 feet in length, 3 feet in breadth, and 4 inches in thickness;
they are all cast with sockets and shoulder pieces to receive the ribs; in each plate
are three apertures, 3 feet in length and 18 inches in width. Each rib is composed of five
pieces, 3 feet in depth in the direction of the radius, and 2 inches in thickness. In the
ribs are triangular apertures formed by the pieces in the direction of the radius, and the
St. Andrew's cross or diagonals between them, but all parts are of equal dimensions.
Where the ribs join a cast-iron grating passes across the whole arch, upon which are cast
joggles to receive the ends of the ribs, which are flanched and fixed in the gratings with
cast-iron screw bolts. The ribs are preserved in their vertical position by covering the
whole with grated flanched plates, secured together and to the top of the ribs by cast-iron
screws and pins. The spandrills are filled in with lozenge-work, each triangular form being
cast in one frame, with a joggle above and below, which pass into the sockets formed in the
top of the ribs, and in the bearers of the roadway. Where these lozenges meet in the
middle of their height each has a cast-iron tie, which passes by a notch from each side,
and meets in the middle of the breadth of the arch, where they are secured by forelocks.
Towards the abutments the lozenges are halved, in order to suit the inclined surface. The
covering plates are cast in a reticulated form. the holes or apertures being larger on the
under surface than the upper, the better to support the materials of the roadway.
From the experiments made by Dulong and Petit it seems that the temperature of
iron is nearly equable, between 320 and 212°; the rate of expansion increasing with the
temperature: it is therefore most important that due allowance should be made for the
metal's expansion and contraction wherever it is introduced. The arches of the Southwark
Bridge are said to rise and fall an inch within the range of our atmospheric tempera-
ture in most of the first constructed French bridges, sufficient attention was not paid
to this quality of the metal, and hence the cause of many of the failures where it was em-
ployed.
In the construction of an iron bridge it is highly important that the distinction between
ties and struts should be well understood; and that cast should not be made use of, where
wrought-iron alone can be efficient. M. Duleau, who made several experiments on the
malleable iron of Perigord, found that its elasticity was greatly affected by the various
weights to which he subjected it, and that there was a point at which it would not again
recover its form; and he concluded that a bar of wrought-iron might be safely strained
until the extension, at the point of the greatest strain, is equal to of its original
length, without losing its elasticity, and that the load upon a square inch which pro-
duces this extension is 8540 pounds. In some of his experiments, however, he found
the extension was three times this without permanent loss of elasticity; and thus has
the art of construction in iron been latterly directed by the French engineers, who have
consequently been very successful. Navier, Rondelet, and others, have calculated the re-
sistance of iron to compression and tension, and upon their data the use of iron is applied.
The greatest load they found a bar of malleable iron whose length was 11.8 feet and
scantling 1.21 inches square would bear without doubling was 4400 pounds; and upon
these results their iron-bridge-builders proceed in proportioning their metal.
Southwark Iron Bridge, over the Thames, at London, was commenced after the designs
of Mr. Rennie on the 23d of September, 1814, and completed in April, 1819. The whole
was cast at the iron works at Rotheram, in Yorkshire, and weighed 5780 tons; the ex-
penses, amounting to about 800,000l., were defrayed by a joint-stock company.
There are three arches, the middle one spans 240 feet, and has a rise of 24 feet; it
is composed of eight ribs strongly secured by diagonal braces, each in the direction of
the radius, being 6 feet in depth at the top of the arch, and gradually increasing to 8 feet
where it rests upon the abutments. The two other arches each span 210 feet. The
masonry of the abutments is constructed of stone from Bramley Fall and Whitby; a
vertical bond was adopted, running through every two courses at intervals; the masonry
of the piers was carried up in the same manner, with horizontal and vertical courses to the
springing of the arches, where they radiated to receive the iron-work. The piers are
24 feet in breadth, 56 feet 6 inches in length, and 60 feet high from the bed of the river to
the top of the parapet; the length of the starlings is 74 feet 6 inches. The middle arch
settled at the vertex after the centre was struck 17 inches; the entire width of the soffite is
44 feet 4 inches. The foundations of the piers are laid 10 feet below the actual bed of the
CHAP. VIII
497
BRITAIN.
river; they are 36 feet in width at the base, and 24 feet at the point where the vertical
part of the piers commences; the whole rests upon ten rows of piles.
At high tides the lowest course of masonry is 36
feet below the surface of the water; considerable care
was consequently requisite in the construction of the
cofferdam. It was formed of three rows of piles repre-
senting on the plan three oblong octagons, one within
the other; the clear width of that on the inside was 60
feet, and the length nearly double; the thickness was
about 6 feet. The piles were 13 or 14 inches square,
and 50 feet in length; of this 15 feet 8 inches were
driven into the bed of the river, 28 feet allowed for high
tides, and 6 feet above high water. Traverses were
fixed inside the dam 60 feet in length, pressing at each
end against longitudinal timbers, which prevented the
rows of piles from being forced in by the pressure of the
water from without. On the inside of the dam, around
the space left for the pier, a range of planks was driven,
6 or 8 inches in width, united closely together without
either nails or grooves, in order to prevent the ground
being washed away between the piles. The piles of the
abutments were driven 3 feet 4 inches distant from each
other, and covered with a strong frame of timber
planked all over. Below were sixteen or eighteen
isolated piles, to protect the dams against the craft
navigating the river in the service of the works. The
first piles were driven to form the figure of the three
octagons, and others were then forced into the intervals,
so as to close them, and when the three rows were
thus completed, the gravelly earth to form the dam
was thrown in. A steam-engine of fourteen horse-
power, erected on the banks of the river, gave motion
to the several pumps, and by means of scaffolding
reaching from the shore to the cofferdams the alternate
movements were transmitted.
To build the abutments a dam was constructed in
front of them, and when the water was pumped out the
ground was prepared, at a slope of two in fifteen towards
the bed of the river; the piles were then driven perpen-
dicular to this inclination. A timber floor rested on
the head of these piles, like that of the piers, and on
this was laid the first course of Portland stone, each
course being on a plane more and more inclined towards
the river; the stones were prevented from sliding by
dice and the power of their own weight; by this
means the plane of the upper course was made exactly
perpendicular to the springing of the arch, and capable
of more effectually resisting the pressure of the first
rib. The total width of each abutment is 80 feet.
Each arch is composed of eight ribs of the same form
and dimension; each rib is divided into two parts; that
which forms the lowest contour of the arch is massive,
and the other, which rests upon it, consists of open work.
These iron voussoirs are in thickness 23 inches, but ad-
ditional strength is given to them by a rim of 4 inches
in width, which enables the joints to bear greater ver-
tical pressure. Transverse plates of iron of the same
breadth and thickness as the voussoirs, and isolating
them from each other, traverse all the ribs at right
angles, in numbers equal to the joints between the vous-
soirs of each rib; and on the abutments, where the
lowest voussoirs rest, are similar plates to carry the
arch. Thus the whole becomes a centre to support first
the spandrills, and afterwards the roadway. The span-
drills are formed of open work resting vertically upon
the voussoirs, and those on the outside have a lozenge

Fig. 495.
SOUTHWARK BRIDGE.
KK 2
500
BOOK I.
HISTORY OF ENGINEERING.

KEKAYAAVAVAAVAVAAVAZZ
AAAAAAAV
AVAVAVAVAVAVAVAV
Fig. 496.
PLAN AND ELEVATION OF ARCH.
figure introduced between them, diminishing in size as they approach the summit of
the arch; these lozenges are contiguous to each other, and united at the extremities of

VAVAVA
Fig. 497.
ABUTMENT AND SPRINGING Of Arch.
CHAP. VIII.
501
BRITAIN

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魚湯
​NNNNNN
NNNNNN
Fig. 498.
ABUTMENT AND SPRINGING Of arch.
their smaller diagonals, which form a part of a polygon, or rather a segment of a circle, and
divide the space comprised between the centre and the platform into two equal portions.

Fig 499.
SECTION THROUGH bridge.
KK 3
A
f
502
HISTORY OF ENGINEERING.
Book I.
As the lozenges diminish in size, the iron-work of which they are formed is also relatively
lessened in dimension; the lower points of the lozenges rest upon the centre, the upper

Fig. 500.
PLAN OF PIER.
support the bridge road. The vertical sides which compose the ribs are united with screw
bolts, passing through the rims raised on the outside, which are occasionally increased in

Fig. 501.
PLAN SHOWING STAIRS.
CHAP. VIIL
503
BRITAIN.
thickness. There are two lozenges and four half lozenges cast in one piece; that portion
next the abutment has one complete lozenge and two halves. The lower parts of the

N
-
•
Fig. 502.
FOUNDATION COURSES.
lozenges are connected together by an arch on the extrados of the voussoirs, and the upper
portions are united in a similar manner; the entire space between the road and the vous-
soirs is divided into four distinct series of triangles. That part of the ribs upon which the
first series rests has a number of grooves made in the extrados of the voussoirs to receive
them, and they are secured by iron bolts passing through the bases and the voussoirs.
Weight of the Materials of Half the Middle Arch.

No. 1
1 2 3 4 5 6 7
Voussoirs.
Diagonals.
Transverse.
St. Andrew's
Cross.
Lozenges.
Total.
Tons
62
Cwts.
18
Tons Cwts.
6
11
Tons Cwts.
11 0
Tons Cuts.
9 10
Tons Cwts.
Tons Cwts.
26 4
112 3
60 9
2
12
10 13
8
15
20
3
102
12
54
15
2 13
10 2
8 2
32
16
108
8
3
51
2 11
9 17
24
5
87 16
50 17
2 18
9 15
51
25 12
2 2
2
13
9 15
}
1
32
14
95
19
24
15
88 5
2
12
20
+
7
48
11
643 14
Tons Cwts.
152 0
77
3
650
0
13
0
0
Plates that cover the bridge under the road
Cornices and railing
Road and pavement
Plates resting on the piers and abutments
Total weight of iron in the three arches
Weight of a half pier
The price of casting, transport, and fixing, was 187. per ton.
5,584
11,000 O
Of Mr. Telford's iron bridges, that over the river Spey at Craig-Ellachie consists
of one arch of 150 feet span, with a rise of 20 feet. Subsidiary to this main arch, but at
some distance from it, are three others, built of stone, 15 feet span each, under the eastern
end of approach; the total water-way is 195 feet. This bridge is beautifully situated about
12 miles above Fochabers, where the Spey, rushing among lofty rocks, has cut a deep
passage for its waters, and the slender arch, amidst the birch trees and native firs, renders
this spot truly interesting; the total cost of the bridge and its approaches, including the
rock-blasting on the east side of the river, was not more than 82007.
K K 4
504
BOOK 1.
HISTORY OF ENGINEERING.

*
Fig. 503.
CRAIG ELLACHIE.
Tewkesbury Bridge, of one arch of cast-iron, was constructed by Mr. Telford over the
Severn, at about a mile above its confluence with the Avon; the bed of the river was
found by boring to consist of alluvial matter to a great depth.
The masonry of the abutments was laid 6 feet under low water level, upon strong wooden
platforms, surrounded by sheet piling about 10 feet in depth; it was carried up to 16 feet
above low water, which, allowing 3 feet of masonry to receive the cast-iron springing plates,
determined the lower edge of the large ribs to be 13 feet above low water level, the water,
in the time of floods, never rising more than 18 feet.
The span of the arch is 170 feet, and its rise about one-tenth of the span, or 17 feet; the
breadth, measured across the soffite, is 27 feet; it consists of six main ribs, each 3 feet deep,
the thickness of the two outer ones being 24 inches, and that of the four interior 2 inches.
They were all cast in lengths of 22 feet, and are connected at each joint by grated cross-
plates, 3 feet in depth, and 2 inches in thickness, to which they are severally screwed.
The whole of the ribs thus united in one arch are placed upon springing plates 3 feet in
breadth, and 4 inches in thickness, embedded in the stone abutments; their upper edges
are covered with grated plates 1 inch in thickness, and upon the six ribs is a perpendicular
lozenge framing to support the roadway bearers, which are connected by wrought-iron rods
or cross ties, 1½ inches in diameter, passing through cast-iron tubes with flanches adjusted to
the lozenge frames, and retaining them in a perpendicular position, while the wrought-iron
bolts, being screwed to the outer ribs of the bridge, prevent them from bending outwards,
and the interior of the spandrills are further secured by diagonal braces. The roadway
bearers support plates 4 feet 6 inches in breadth, and 1 inch in thickness, with flanches
4 inches in depth at each juncture, by which they are screwed together. Upon the road
plates are skirtings to retain the gravel of the footpaths, which are also adapted to receive
the bars of the side railing.
The whole is cast from No. 2 Shropshire iron of the best quality, and the work was com-
pleted in April, 1826. The cost of the iron-work was 4500l., and that of the masonry, em-
banked approaches, and land arches, 10,000Z.
Manchester and Birmingham Railway.-At Fairfield Street is a bridge whose span in a
straight line is 128 feet 9 inches, with a versed sine of 12 feet; the width, measured from
face to face, is 31 feet.

Fig. 504,
FAIRFIELD STREET Bridge.
Six ribs of iron abut on as many independent walls, each of which are 5 feet 10 inches
thick, and project before each other 12 feet 11 inches. The transverse sections show the
construction of the piers, the faces of which are rusticated; an ornamental stone parapet and
cornice crown this viaduct, and present a novel and agreeable character.
This bridge, executed after the designs of Mr. George Watson Buck, is remarkable for
its acute angle, which is about 24 degrees. The weight of the iron work employed in
the six ribs was 540 tons, and the whole was admirably screwed together; the remainder
of the viaduct is formed with brick arches of 45 feet span. Iron ribs have enabled the
engineer to cross rivers and roads in situations where arches of masonry or brick could
not have been introduced: in the present instance, the level of the viaduct would not have
permitted a rise sufficient; but wherever they can be introduced, there is no doubt that a
considerable portion of the expense of iron structures would be saved. For oblique
bridges iron constructions are particularly well adapted, and, as in this instance, beau-
tiful in their effect; timber has been employed, as we shall hereafter see, for the same pur-
CHAP VIII.
515
BRITAIN.

100
Fig. 505.
PLAN OP PIER.
of

Fig. 506.
SECTION OF PIER.
pose, where greater economy was necessary. The masonry of the abutments was well
executed, and great care taken to allow for the expansion and contraction of the iron,

n
•
Fig. 507.
PLAN.
which was found considerable; it is even reported that the heat of the sun affected the
length of some of the outer ribs, during the progress of hoisting them to their situation:
and that the dimensions of one, taken by the workmen when
on the ground, was increased so much, that it would not
answer the position for which it was designed until its tem-
perature had been lowered. One of the first considerations
of the engineer, when he employs iron for construction,
should be its properties of increasing and diminishing; and
he should always provide a means by which the metal can
accommodate itself, without thrusting out the works on
which it rests or may be in contact.
At the Kildare Canal, in Ireland, the first skew bridges
were introduced by Mr. Chapman, in the year 1787; before
that time their advantages do not appear to have been much
noticed in England. One executed by that engineer at
Finlay Bridge, near the town of Naas, in Ireland, deviated
51 degrees from a rectangle with the canal, and formed an
acute angle of 39 degrees with its abutments: its span in an
oblique direction was 25 feet, and its rise 5 feet 6 inches.
The only difference of construction is, that in common bridges the courses are all parallel
with the abutments, and in the skewed arches they run obliquely to them. The face of
the abutments making an oblique angle to the sides of the bridge, it became necessary

Fig. 508.
SECTION.
-506
HISTORY OF ENGINEERING.
Book I.
that the courses of the arch, except a few at the springing, should stand square, with the
outside of the bridge; all these difficulties are, however, overcome by iron ribs, applied as
in the present example.
Lary Bridge, near Plymouth, completed in 1827, is of cast-iron, and is built over the
estuary of the river Plym, and connected with Plymouth Sound by the Catwater. The
width of the estuary is from

500 to 600 feet; the tide
rushes with a velocity of
3 feet 6 inches per second,
and flows on an average
16 feet perpendicular.
There are five arches; that
in the centre spans 100 feet,
and rises 14 feet 6 inches;
the next are 95 feet span,
and rise 13 feet 3 inches; the
other arches are 81 feet span,
and rise 10 feet 6 inches
;
the piers are 10 feet and
9 feet 6 inches; the road-
way between the abutments
is 24 feet wide, supported
upon five cast-iron equi-
distant ribs, each at the
springing 2 feet 6 inches
deep, and at the apex 2 feet
2 inches. The
The masonry cost
13,3657., and the iron-work
27,1261.
Cast Iron Bridge over
the Avon, 7 miles north of
Tewkesbury, over which the
Birmingham and Gloucester
railway passes, was
pleted in the year 1840.
This bridge has three arches,
com-
each of 57 feet span, and a
Fig. 509.
ARCH OF LARY BRIDGE.

Fig. 510.
24....0.
SECTION THROUGH PIER.
versed sine of 5 feet 2 inches; the distance between the centres of the piers is 66 feet
6 inches, the breadth of the cutwaters 8 feet 6 inches, the clear water-way is 173 feet
6 inches.
The two piers are formed of cast-iron caissoons, filled in with solid masonry and concrete
to the height of 12 feet; after which hollow masonry is used to support a capping plate of
iron, on which is placed eight columns over each pier, supporting the entablatures and
arches, all which are of cast-iron. The caissoons are 41 feet 6 inches in length at the base,
and 16 feet in width; their ends are semicircular, and they taper upwards for 12 feet all
round, the dimensions at the top being 34 feet 6 inches by 8 feet 6 inches, after which
they rise perpendicularly 8 feet 9 inches. They have cast-iron flanched plates, of about of
an inch in thickness, put together with screw-bolts and iron cement; each caissoon when
put together contains about 28 tons of iron. The total weight of the iron work in this
bri`ge is 520 tons, and the cost is stated at about 10,0007.
Cast-iron Bridge at Portumna, over the Shannon, which unites the counties of Galway and
Tipperary. The total length is 558 feet 6 inches, exclusive of the island; the width between.
the railing is 17 feet.
The abutments are of masonry, of Portumna limestone, built with hydraulic mortar; the
sheeting piles are of beech and larch, whilst the main piles and waling pieces which support
the roadway girders are of Memel timber.
There are thirteen openings, each of 18 feet 6 inches span, between the Tipperary shore
and the island, and twelve openings of a similar span between the island and the outer pier
of the swivel bridge, which adjoins the Galway shore, and is 40 feet 6 inches span.
The cast-iron girders are 20 feet in length, 17 inches deep, and 1½ inch thick, with a
flanch at the top 8 inches wide, to receive the plates which carry the roadway; there is also
another flanch at the bottom 4 inches in width. The roadway plates are of an inch in
thickness, secured by bolts and plates put together with iron cement. On the outside
girders, cast-iron plates are affixed, which carry the railing of wrought-iron; each girder
was proved by passing along it a weight of 12 tons, whilst it was mounted on two piers at
20 feet apart.
The swivel bridge has two leaves, with a clear opening of 40 feet.
The total cost of the bridge, including abutments, cofferdams, and superintendence, was
24,1317., it was executed under the superintendence of Mr. Rhodes.
•
CHAP. VIII.
507
BRITAIN.
Suspension Bridges, of iron, do not appear to have been introduced before the year 1741,
when one was built across the Tees for the use of the miners; its length was 70 feet, and
was suspended above the level of the river at a height of 60 feet: Scamozzi “Del Idea
Archi," published in 1615, conveys some notion of these structures, but their true princi-
ples were not made known till they obtained the attention of Bernouilli. Hutchinson, in
his " Antiquities of Durham," gives the following account of the winch bridge: -" It is sus-
pended on iron chains, and stretched from rock to rock, over a chasm 60 feet deep; its
width is 2 feet, with a hand-rail on one side, and it is planked in such a manner, that the
traveller experiences all the tremulous motion of the chains.”
When Mr. Telford was called upon to report upon the practicability of forming a
bridge at Runcorn, he commenced a series of experiments upon the tension of iron, and
from that period engineers seem to have studied the principles of suspension bridges. These
important experiments occasioned iron to be more universally introduced into construction;
and we now find that the skill of the carpenter is not always required to cover in a build-
ing with timber.
Mr. Telford commenced his experiments by proving what force would pull asunder
lengthwise pieces of iron from 1½ inches to of an inch in diameter. The experiments

Fig. 511.
MACHINE FOR PROVING THE STRENGTH of iron.
were made upon those of the largest diameter, by means of an excellent hydrostatic machine,
and on those of the smaller by attaching weights perpendicularly, and repeating them at
various times.
20
He then made several experiments upon different diameters, fromto of an inch
drawn horizontally, and with different degrees of curvature; and this was performed
between points 900, 225, 140, and 139 feet 6 inches apart, and was repeated 200 times. In
the experiments made upon of an inch and under, the wire was drawn over pulleys; some-
times both ends were fixed, and sometimes one end only, the other having weights attached
perpendicularly to show the effects when compared with those loaded upon the curved
part of the wire; these last were disposed at 4, and divisions of the distance over which
it was stretched. These experiments being completed, it was ascertained what blow would
break the wire when stretched nearly horizontally and at different curvatures, which was
done by dropping weights from a given height. The several wires were weighed, and
the weight of 100 feet in length of each noted.
50
The result of the experiments was, that a bar of good malleable charcoal-iron 1 inch
square will suspend 27 tons, and that an iron wire, of an inch in diameter, 200 feet
in length, weighing 3 pounds 3 ounces, will suspend 700 pounds; and that the latter, with
a curvature or versed sine of part of the chord line, will support of the weight sus-
pended perpendicularly, when disposed equally at 4,, and its length, and with a curva-
93174
ture of of the chord, it will bear of the aforesaid perpendicular weight disposed in a
20
similar way.
A wire of an inch in diameter, drawn very tight between points, 31 feet
6 inches apart, resisted the impulse of 20 pounds weight, falling from a height of 7 feet
9 inches.
20
A bar of good English malleable iron 1 inch square will suspend from 27 to 30 tons
before it breaks, and will bear from 15 to 16 tons before its length is at all extended.
With a curvature of of the length, malleable iron, besides its own weight, sustained of
13
what broke it perpendicularly. An inch bar would therefore bear of 15 tons without
deranging its parts; but it is better in practice to assume that an inch square in section
should only bear 4 tons.
Galushiel Bridge was constructed in the year 1816, at a cost of 407., and is 112 feet in
length; it is suspended from iron wires of very small diameter.
Peebles, over the Tweed, called King's Meadow Bridge, was constructed in 1816, for the
508
Book I.
HISTORY OF ENGINEERING.
sum of 1601; its length is 110 feet, and its breadth 4 feet. Columns of cast-iron 9 feet
high, fixed securely in the soil, were placed at each angle of the bridge, and supported the
suspending wires, which were inch in diameter. The floor is carried by five oblique
wires, which are secured to an iron bar 10 feet in height, and of a sectional area of 21 inches,
inserted in the top of the column; the way over is formed of frames of wrought-iron
covered with 1-inch deal; on each side are chains, which serve as ties, of 2-inch iron; the
·length of the links is 5 feet, they are fixed at one end into masonry underground, and
at the other to the iron bar inserted in the columns, which prevents them from being pulled
over.
torrent.
Dryburgh Bridges were erected in the year 1817, about 18 feet above the low water of a
The supports were 260 feet from each other; and about a year after its erection
it was destroyed by a high wind, which gave an undulating motion to the roadway, and
at last broke the suspension chains. A new bridge, which cost 7201., was immediately
commenced, with perpendicular suspension rods inch in diameter, having at the top a
cross-head, by which they were kept between the oval links of the suspension chains;
at the lower end they pass through the side beams of the flooring, to which they are
screwed. Chains of nearly 1 inch in diameter pass under the roadway, and extend from one
abutment to the other. On each side a diagonal trellis firmly joined together forms a
parapet, and prevents the effects of any undulatory motion. The two suspension chains are
each 1 inches in diameter, and the length of the bars composing them is 10 feet. At each
extremity of the bar is an eye, through which passes an oval ring 9 inches in length, connect-
ing the two contiguous bars; these suspension chains are secured to the head of wooden
pillars 28 feet high above the level of the roadway; the space between them, which forms
the approach to the bridge, is 9 feet. The two pillars at the extremities are connected by
braces forming a St. Andrew's cross, and by transverse beams, over which the suspension
chains rest; each pair of chains is 12 feet distant from the other where they pass over
the pillars, and only 4 feet 6 inches in the middle of the bridge. By this arrangement they
obtain an oblique power, both horizontally and vertically, and thus prevent, to a certain
degree, any oscillatory motion.
2
The suspension chains are under the platform, which they support by upright rods of
cast-iron, kept in their places by small arches of the same material, in a horizontal line under
the flooring, also of cast-iron, over which is a layer of small stones. The chains pass over
each abutment, descending behind it, and are secured in masonry where a passage is left to
examine and repair them. The lower extremity of the chains rests upon the base of a
conical tube of cast-iron, through which it passes, and the tube being strongly bedded in
the masonry keeps it secure.
Suspension Bridge over the Tweed, at Kelso, in Scotland, was finished in July, 1820, by
Captain Brown. It is 300 feet in length, and 18 feet in width, and has a carriage-road
in the middle; the total cost, including the masonry, timber, and iron-work, was only
50,000l.
The roadway, 27 feet above the level of low water, presents a gentle rise towards the
middle, where it is 2 feet higher than at the extremities. There are twelve suspension.
chains, arranged in pairs; the diameter of the iron with which they are made is 2 inches.
The links are composed of bars 15 feet long, terminated with an eye at each end; two short
flat links are applied at each side of the two contiguous bars, and bolts well-riveted traverse
the two links as well as the eye of the bar. The vertical suspension rods are 1 inch in
diameter, and pass through a saddle-cap; the bolts are cylindrical, having for their base an
ellipsis, the two axes of which are 2 inches and 24 inches. The three chains are placed almost
perpendicularly over each other, and the suspension rods are fastened first to the upper, and
next to the middle chain, and then to the lower. The chains which correspond with each
other right and left of the bridge have their joints so placed that the suspending rods also
perfectly correspond. The lower ends of the suspension rods traverse a longitudinal piece
of iron, at the extremity of which the timbers for the floor rest, and under which the rod is
strongly riveted. The timbers are 15 inches deep and 7 inches wide, and are covered with
plank 4 inches thick.
The parapets are formed into lozenges, the sides of which are 6 inches; the height is 5 feet.
The distance between the points of support for the chains is 437 feet, although that between
the abutments is only 360 feet; the angle formed by the chains with the vertical line at the
points of suspension is equal to 78 degrees. The weight of each chain, with its suspending
rods, bolts, links, &c., is about 900 pounds. The twelve chains and all the iron-work used
in the bridge weighs 13,000 pounds.
The masonry of the abutments against the steep rock which borders the river is 20 feet
high, and the isolated pier on the other side is 60 feet, and of a pyramidal form; its thick-
ness is 17 feet 6 inches, and at half its height the width is 36 feet; it is square at the bottom
to the height of 10 feet, when the slope commences diminishing about a twelfth part. The
road passes through this pier by an arched gateway 12 feet wide and 17 feet high. The
pairs of chains run through the masonry of the piers, the openings for which are 2 feet wide,
CHAP. VIII.
509
BRITAIN.
one above the other. They pass over rollers on the English side of the river, and cast-iron
bedded in the masonry on the other; the rollers have axles resting on iron embedded in
the masonry,
and the chains, instead of being formed of bars 15 feet long, are composed of
very short links, so that they may work freely over the rollers. After the chains have
traversed the masonry of the piers, they are further strengthened by long links passing
24 feet underground, and are attached to masses of cast-iron 6 feet long, 5 feet wide, 5
inches thick in the middle, and 2 inches at the edges; to these they are secured by strong
oval bolts, and the masses of iron are loaded with stone to the level of the road; the corre-
sponding masses on the English side of the river are not buried as on the other, but are above
the level of the foundation of the piers. They are placed nearly vertical, corresponding with
the strain of the chains. A horizontal arch, the stones of which are embedded in the rocks,
keeps the iron plates in their right position.
Menai Bridge, over the strait which separates the Isle of Anglesea from the county of
Caernarvon; erected by Mr. Telford.
The work was commenced in May, 1819, and the rock called Ynys-y-moch, which was
accessible at low water, was, by blasting, brought to an even surface; on this was laid the
foundation for the west main pier on the Anglesea side. A temporary causeway, on which


A M
Tig. 512.
TRANSVERSE SECTION AND ELEVATION ON THE CAERNARVON SIDE.
was a railroad for sledges, drawn by horses, was made, at a considerable elevation above
the level of high water, over the space between the Anglesea shore and the rock.
The tide through the strait runs with great velocity, and being now shut out, the
current in the centre of the channel is greatly increased in velocity. The rise at ordinary
spring tides is about 22 feet; it sometimes exceeds 30, and winds from the range of
mountains in the vicinity of Snowdon are frequently strong and violent; the breadth of the
estuary at high water is 918, and at low water 480 feet.
The first stone was laid upon the Ynys-y-moch rock on the 10th of August, 1819, and
in the autumn of the same year the main pier on the Caernarvon side of the strait was com-
menced; the beach, being first excavated to the depth of 7 feet where the solid rock sustains
the east main pier, a greater mass of masonry is given to the foundations of this pier than to
the other on the Ynys-y-moch rock.
The height of the main piers, from the level of high water spring tides to the roadway, is
100 feet; from that of low water spring tide 121 feet; from thence to the top 53 feet.
510
BOOK I.
HISTORY OF ENGINEERING.
The two arches, through which the road passes, are 9 feet in width, and 15 feet to the
springing of the arches.
The width of the piers, taken on the transverse section at the base, is 66 feet 3 inches;
at the set-off, above the high water line, 58 feet 2 inches, diminishing at the top to a width
of 33 feet 8 inches, as measured at the bottom of the hollow which forms the cornice or
capping. Their depth, as measured in front, immediately above the set-off, above the high
water line, is 40 feet 11 inches. The construction of the pier is exhibited in the sections.
The resident engineer was Mr. W. A. Provis, the prover of the iron-work Mr. J. Provis,
the contractor for the masonry Mr. J. Wilson, the iron-founder Mr. Hazeldine, and the
superintendent engineer of the iron and timber work Mr. T. Rhodes.
The masonry of the piers above the level of the roadway was strengthened by drilling
holes through the stones of each course, and, after the insertion of iron bolts, fixing them
with Parker's cement; wherever arches spring over the roadways, iron horizontal ties were
introduced to prevent any spreading. In May and June, 1824, the two pyramidal piers
were constructed, and the cast-iron saddle plates fixed on their summits.
The Abutments, Piers, and Arches were commenced in the year 1820, and by March, 1822,
all the piers were carried up to the level of the springing course, and the centres for the
arches fixed; by the end of the year, the whole of the arches were turned, and the spandrills
built to the level of the cornice.

НИАНЕНННННІ
1
!!
HIGH WATER
Fig. 513.
SECTION AND ELEVATION OF MAIN PIER.
The span of the side arches is 52 feet 6 inches, and their versed sine 26 feet 3 inches,
forming semi-circles; the height of the small piers above the level of high water, to where
the arches spring, is 65 feet.
There are four of these arches on the island side, and on that towards Caernarvonshire
three; the distance from the centre of one pier to that of the other is 579 feet 10 inches.
The span of the catenary is 570 feet, and its versed sine 43 feet.
Materials employed. For the masonry the grey marble was employed, which was
obtained on the shores of Penmon, at the north-east extremity of the island of Anglesea,
7 miles from Beaumaris, and the price paid by the government to Lord Bulkley was 6d.
per ton.
This fine stone bears a beautiful polish, and the natural layers or shelves afforded blocks
of any required dimensions, which could be drawn from the quarry without blasting; it
CHAP VIII.
511
BRITAIN.
was removed by small vessels from the Bay of Beaumaris to Bangor Ferry, a distance of 12
miles.
The iron was all of the best Shropshire manufacture, supplied from Upton Forge, by
Mr. Hazeldine of Shrewsbury. The bars were repeatedly drawn between cast-iron rollers,
grooved in various shapes, and afterwards proved at the works, previous to being shipped
for the Menai Straits.
An accurate and powerful machine was used for proving each bar, which was tested by a
strain of 11 tons to every square inch of transverse section; during the trial, it was
frequently struck by a hammer, and its length was observed by an unvarying iron gauge.
After proof, each piece of iron was cleansed, put into a stove, at a gentle heat, and then
immersed in a trough containing

linseed oil, where it remained for a
short time, and was again returned
to the stove, when, after drying, it
came out covered with a varnish,
upon which a coat of oil paint was
added, and it was sent off to the
works.

D
Iron work. There are four sets
of main chains, each composed of
four so that there are altogether
16 chains, which have a similar and
uniform tension. Each consists of 5
chain bars in length, each 10 feet
long, 3 inches wide, and 1 inch in
thickness, with 6 chain plates at each
end 16 inches long, 8 inches broad,
and 1 inch thick; the joints being
secured by 2 bolts weighing


cwt.
In the cross section of the chain
there are 80 chain bars, and the
number there in one chain is 935, in
the sixteen, 14,960.
The entire length of the chains is
Fig 514.
•
TINE
•
UPPER LINKS AND JOINTS.
1710 feet from where they are fastened to the rock on each side.
The number of chain plates to each chain is 1122, in all 17,952; each chain has 374 bolts,
amounting in all to 5984.

10
E
Fig. 515.
טון ער
O
for tightENING THE MAIN CHAINS.

D
Fig. 516.
ELEVATION OF CHAINS.
The vertical rods suspended from the chains are placed 5 feet distance apart, and are
1 inch square; there are 199 to each line, and in the whole four lines 796.
These carry
512
Book 1:
HISTORY OF ENGINEERING.
111 sleepers; the number of trussed rods and king-posts which support the suspended road
is altogether 444.

Fig. 517.
1 I
PLAN OF CHAINS.
0
оо
Iron frames to which the suspension chains are made fast. Three oblique circular cavities
were blasted in the solid rock on the Anglesea side, 6 feet in diameter, care being taken to
leave a considerable portion of rock between the openings; through these the suspension
chains pass down an inclined plane of not less than 60 feet in length.

XXXXXX
HH
་
0000
auben
Fig. 518.
SECTION THROUGH MAIN CHAINS AND ROADWAY.
At the lower ends of these inclined tunnels is another at right angles, which connects them
together, through which the workmen passed to fix the iron plates into the natural rock,
and a passage is left on the south-west side of the bridge, which communicates with these
subterraneous chambers.
On the Caernarvonshire side there is the same arrangement, but the depth of earth
was considerable before the native rock could be arrived at, which occasions a different
length to be given to the catenary on this side to that on the other.
The flat cast-iron plates were let into the natural rock, and so firmly secured that they
CHAP. VIII.
513
BRITAIN.
are perfectly immoveable, and, unless the entire mass of rock were to give way, would bear
any stress that might be given them.

0000
SECTION.
可
​0
PLAN.
Fig. 519.
Saddles AND TIES for carRYING CHAINS,
The saddles and ties which carry the main chains through the front of the Caernarvon-
shire toll-house are formed of cast-iron plates; they are 3 feet 5 inches wide; the holes
through which the chains pass are 2 feet 4 inches in width; the four plates, with the
passage for the sixteen chains, are admirably put together, two being in the middle, and
one at each extremity; the cast-iron blocks or saddles are 8 feet 7 inches in width across
the bottom, in the direction of the chains, and 7 feet in height, the spaces between the
four bars which hold the chains being each 7 inches. These saddles were all cast with
holes, in order that the tackle might be adjusted and attached by which they could be
hoisted. The frame for raising these castings was made of timber; the platform at bottom
was 30 feet in extent, and its total height was 74 feet; an additional timber was fixed to
the sides to a height of 26 feet; the blocks were secured by ropes to the top, and passed
as shown in the figure, which represents the action of elevating a part of the iron work.
At the side is a section of the frame-work, to the top of which is attached two guy-ropes.
There was also an ingenious machine or clam made use of for holding the ropes of the
hoisting tackle whilst fleeting them on the capstan, and which was found of the most
essential service. The plan of the saddles shows their position; the parallelogram, upon
which the four are placed, measures 37 feet 6 inches in length, and 14 feet in width.
The
The plan of the great pyramid exhibits the planking of the two carriage-ways.
mass of masonry in the middle is 6 feet in width; the space for the traffic on each side
9 feet, and the thickness of the exterior walls at the greatest 9 feet, and in the less 6 feet.
The pavement, as it is laid over the planking, is partly shown in the figure. The trans-


HOHOHOHO
O
Q
(OHOHOHO
Fig. 520
ELEVATION.
SECTIONS.

METHOD OF SECURING MAIN CHAINS TO THE ROCK.
I LAN.
L1
514
BOOK I.
HISTORY OF ENGINEERING.


52
Fig. 521.
PLAN OF THE SADDLES.
Fig. 522.
PLAN OF GREAT PYRAMID.
verse section through the main chains, exhibiting a little more than one half of the entire
width; the middle footway and one passage for carriages, also represents the position of
the several lines of chains where they cross or pass over the saddles; the sections and
elevation of the main pier show the position of the main chains in the other direction,
or in a line at right angles with the passage across the stream.
The suspension chains were first firmly secured to the flat cast-iron plates; the chain bars,
each 10 feet in length, were then laid down by placing the five together, which constituted
one breadth; and the consecutive lengths were thus carried on, united by flat iron plates
and bolts, until the apex of the suspension piers was arrived at, the whole chain being
supported by a timber framework placed underneath.
On the apex of each of the suspension piers was a cast-iron saddle, in which were
wrought-iron rollers and brass bushes, which as the temperature varied allowed some play
to the chains, and regulated any contraction or expansion of the iron; as the rollers were
self-acting, no derangement could very well take place from this cause.
Mr. Davies Gilbert furnished Mr. Telford at various times with information highly
useful for the completion of this bridge; that gentleman calculated the dimensions to be
given to the several bars of a catenary arch formed in iron or steel upon the suspension
principle. He assumed the tenacity of iron to be 50,000 for a square inch, and its specific
gravity 7-8, and Mr. James Jardine formed the following table for the construction of the
chains. The first column shows the distance between the points of support; the second,
the length of curve, or chain, between the points of support; the third, the axis of curve,
or versed sine, of the chain; the fourth, the angle, nearly, between horizontal line and
curve, at the point of support; the fifth, the tension, or strain, on each chain by its own
weight, at either point of support; the sixth, the tension or strain on the sixteen chains by
their own weight, at either point of support; the seventh, the weight of one chain; and
the eighth column the weight of the sixteen chains.

Feet.
Feet.
Feet.
Angle.
Tons.
Tons.
Tons.
Tons.
500
560
565.6
35
14° 0'
20.87
333.9
10.10
161.6
567.5
40
15 54
18.53
296.5
10.13
162.1
560
569.5
45
17 52
16.57
265.1
10.17
162.7
The transverse section through the main chains and roadway shows the positions of the
several parts, and the cast-iron pipes 3 inches in diameter, strutted or braced with diagonal
bars; within the pipes is a wrought-iron bolt, 14 inch in diameter, which connects together
the four lines of suspending chains. The footpath in the middle of the transverse section
is 4 feet in width, and the two other divisions are each 12 feet: between the oak guards of
each carriage-way is a width of 7 feet 6 inches; the iron truss-rods and king-posts intro-
duced beneath the roadway bars add very considerably to the strength of the platforms.
In the arrangement of the several parts of this bridge the greatest attention was paid to
the manner in which they were united together, and also to allow of any portion being
taken out and reinstated, in case of accidental fracture or injury of any kind; in this
stupendous undertaking the constant stress upon particular parts, where destructive in its
effects, could be easily remedied without endangering the entire work.
CHAP. VIII.
515
BRITAIN.
The chains were supported on the scaffolding, whilst the lengthening took place on the
Caernarvonshire side, until the chain bars, suspended from the apex in a perpendicular
direction, nearly reached the level of high water mark.
The most difficult part of the whole operation then com-
menced, that of conveying the first suspension chain across the
Strait, and making a junction; this was performed on the 26th
of April, 1825.

A
Fig. 524.
Clam for holding the rope of THE HOISTING TACKLE WHILST FLEETING IT ON THE CAPSTAN.
n
O
Fig. 523.
FRAME FOR RAISING CASTINGS ON TO THE PYRAMIDS.
At half flood tide, a raft prepared for the purpose, which
carried the portion of the chain intended to be drawn over,
was moved from Trebroth Mill, on the Caernarvonshire side,
by four boats assisted by the tide, to the centre of the river, and between the two
main piers, where the raft was made fast to several buoys, anchored for the purpose.
One
LL 2
516
Book 1.
HISTORY OF ENGINEERING.
end of the chain was then made fast to that which hung perpendicularly from the apex of
the pier, on the Caernarvonshire side. The other end of the chain to be suspended was

"

Fig. 525.
MAIN TAckle for RAISING THE CHAINS.
fastened to two blocks of great power, the tension of the chain at this time being equal to
40 tons.



Fig. 526.
Jood
SADDLES FOR CARRYING THE MAIN CHAINS.
SECTION.
After the blocks were made fast to the chain, two capstans and two preventive capstans,
each worked by 32 men, commenced raising, and within two hours and twenty minutes
from the movement of the raft from the

shore the last bolt was fixed, which com-
pleted the entire length of the first chain,
three of the men employed passing along
it. And by the 9th of July the other
fifteen chains were secured, and the entire
line of suspension completed.
Vertical rods.—These are placed at
equal distances of 5 feet, and are fastened
to the sixteen suspension chains. The
iron sleepers or transverse roadway bars
are bolted to the lower ends, and to each
of these 111 sleepers four vertical rods are
attached transversely, making altogether
444.
Fig. 527.
Saddle.
©
Timber roadway.-The first tier of planks
was laid across the iron sleepers on the
24th of September, 1825, there being three
altogether, the lowest 3 inches thick, the
middle and upper each 2 inches; the last is laid transversely to the width of 8 feet, with
side guides to prevent any injury from the carriage wheels. The planks are all spiked
together, and between each layer was a coating of Borrodaile's patent felt saturated with
boiled tar.
CHAP. VIII.
517
BRITAIN.
Weight of the Iron.
Lbs.
64 large chain bars, each 7½ feet long, 4 inches wide, 1½ inches thick, and each
bar weighing 150 pounds; for the five
48,000
384 chain plates, 18 inches long, 10 inches broad, 1½ inches thick, and each
weighing 126 lbs.
28,000
128 large bolts, each weighing 126 lbs.
16,128
123 chain bars, 10 feet long, 34 inches wide, 1 inch thick, each weighing 124 lbs. ;
for the five
76,260
738 chain plates, 16 inches long, 8 inches broad, and 1 inch thick, each weighing
32 lbs.
23,616
246 bolts, each weighing 56 lbs.
597 connecting rods and bolts, each weighing 37 lbs.
16 steadying ties, each weighing 1225 lbs.
13,776
16,119
19,600
Total weight of one chain (121 tons 299 lbs.)
-
242,299
And for the whole sixteen chains, 3,876,784 lbs., or 1,938 tons 784 lbs.
2 cast-iron plates under the saddles, each weighing 46,080 lbs.
92,160
8 saddles, each weighing 3248 lbs.
25,984
20 tie bars for the saddles, 20 feet long by 3 inches square, each weighing
600 lbs.
12,000
64 rollers, each weighing 335 lbs.
21,440
16 guide plates and brass bushes, each 373 lbs.
5,968
199 suspension rods, averaging 331 feet in length, 1 inch square, and each rod
weighing 111 lbs. ; for the four sets
88,356
-
111 sleepers, each weighing 334 lbs.
222 trussed rods, each weighing 40 lbs.
222 king posts, each weighing 7 lbs.
Anglesea side.
Suspended portion,
Caernarvon side.
98 side rails, each of 80 lbs. weight
98 foot rails, each of 50 lbs. weight
222 side rails, each of 10 lbs. weight
74 foot rails, each of 50 lbs. weight
[74 side rails, each of 65 lbs. weight
6 cast-iron frames for fastening in the rock, each weighing 2240 lbs.
24 round bolts, 9 feet by 6 inches, each weighing 444 lbs.
37,074
8,880
1,554
7,840
4,900
14,430
5,920
3,700
13,440
10,656
78 side rails of road, weight 80 lbs. each
6,240
Side of Anglesea.
24
39 hand-rails, weight of each 104 lbs.
24 centre do. weight 50 lbs. each
78 cast-iron stanchions to support rails, weight 176 lbs.
do. weight of each 100 lbs.
1,200
13,728
-
2,400
4,056
Side of Caernarvon.
484 cast-iron parapet rails, weight of each 31 lbs.
4 sets of cast-iron saddles, weight of each 2016 lbs.
8 gate posts, weight of each 533 lbs.
38 side rails of road, weight 80 lbs. each
40 cast-iron stanchions, weight of each 176 lbs.
38 hand-rails, weight of each 104 lbs.
3,040
7,040
3,952
15,004
8,064
4,264
4 toll gates, weight of each 325 lbs.
1,300
2 lamp-posts, weight of each 300 lbs.
600
12 tie bars in the pier arches, weight of each 533 lbs.
6,296
32 cast-iron saddles about the toll-house on the side of Caernarvonshire, weight
of each 416 lbs.
13,312
4 plates under the last-mentioned saddles, weight of each 900 lbs.
240 segment saddle bars on the piers, and near the Anglesea toll-gate, weight of
each 200 lbs.
3,600
48,000
Add to this the weight of the sixteen chains
496,468
3,876,784
Total weight of iron
-
4,373,282
Or 2186 tons, 1282 lbs.
Conway Bridge is upon the same principle as that over the Menai Strait. The distance
between the points of suspension is 327 feet; the depression or versed sine of curvature
of the main chains is 22 feet 6 inches; the number of chains is eight, each having five
bars, 3 inches by 1 inch, making together a total of 130 square inches of transverse section.
The roadway is in breadth 17 feet 6 inches, and is 15 feet above the level of high water;
it consists of a carriage-way without any separate footpath.
L L3
518
Book I.
HISTORY OF ENGINEERING.
The main chains were hoisted in the following manner; six strong rope cables were
stretched across the tops of the supporting pyramids, which were made to carry a temporary
platform; on this was laid the chain which was to be united with that portion to be
brought up
from the fixed points in the rock galleries to the top of the pyramidal towers.
When this junction was made, the platforms of wood were removed, the rope cables were
slackened, and the chain lowered to its proper curvature. The side railing was then fixed,
and the road platform constructed in a similar way to that over the Menai, the several
parts of the chains, and method of fixing them, being alike.
The Union Suspension Bridge, over the Tweed, five miles from Berwick, constructed by
Capt. S. Brown, R. N., was the first large bar chain bridge executed in Great Britain; it
was finished about 1820.
The chord line, or distance between the points of suspension, is 449 feet, and the de-
flection 30 feet. There are twelve main chains placed in pairs, and forming three ranges,
one under the other, on each side of the bridge, and about 19 inches apart. Each link is
formed of a rod 2 inches in diameter, and 15 feet in length, with an eye at each end for
welding. On the Scotch side of the Tweed the suspension pier is of ashlar stone, formed
like a pyramid, 60 feet in height, 36 feet in breadth, and 17 feet 6 inches thick at bottom.
The arched opening is 12 feet wide and 17 feet high. On the other side of the river the
pier is built on the rock, which is precipitous. The roadway is 387 feet in length, and
18 feet wide between the parapets, and is supported by vertical rods, 1 inch in diameter,
and placed 5 feet apart. The chains contain 38 square inches of iron, and its strength has
been computed equal to bear 1104 tons.
The Newhaven Suspension Pier was also erected by Capt. S. Brown, R. N., in 1821, by
order of the Trinity Pier Company; its extreme length is 700 feet, and its width 4 feet.
It has three divisions, each 209 feet span, with 14 feet deflection. The pier-head is 60 feet
wide, and 50 feet long, supported upon 46 piles driven about 8 feet into the clay. The
land pier is of solid masonry, 6 feet square, and 20 feet high; the main bars pass over the
top, and the back-stays form an angle of 45 degrees to the chord line. There are two main
chains formed of rods 1 inch and 17 inch in diameter, and 10 feet in length The road-
way is supported by two longitudinal iron side bars, which are held up by the vertical
rods. The cast-iron standards that support the main chains are triangular frames cast in
one piece, and the main chains lie on cast-iron saddles.
Brighton Chain Pier, opened in November, 1823, was designed by Capt. S. Brown, R. N.,
who first suggested that the chains should be made of straight wrought-iron rods or bars,
from 5 to 15 feet in length, with either welded eyes, or holes drilled at their ends, by which
they might be connected either by short links or pins; this invention he patented in 1817.
The Brighton pier extends into the sea 1014 feet from the face of the esplanade wall,
and its entire length is 1136 feet, formed with four openings, each spanning 255 feet, with
a deflection of 18 feet. The extreme breadth of the platform is 13 feet, and in the clear
width 12 feet 8 inches.
The pyramidal suspension towers are made of cast-iron, united by an arch at the top;
they are 10 feet apart and 25 feet high, and each weighs about 15 tons: they are placed on
piles driven firmly into the chalk, which stand out about 13 feet above high water; these
groups of piles are 256 feet distant from each other, and leave a clear opening of 227 feet
The pier-head has the form of a T, and 150 piles were used, besides braces and diagonals ;
over them the platform is 80 feet by 40 feet, which is paved with granite 12 inches thick,
the weight of which is upwards of 200 tons.
The four main chains on each
Each of the ordinary groups of piles consists of twenty.
side, which carry the platform, are formed of wrought-iron, round eye-bolts, about 2 inches
in diameter, 10 feet long, and weighing 112 lbs. each; they are united by open coupling
links 1 inches deep, and 1 inch thick, with bolt pins 2 inches in diameter. The total
area of the section of the iron in the chains is 25 square inches. The platform is suspended
by vertical rods 1 inch in diameter and 5 feet apart.
The
Montrose Suspension Bridge, over the River Esk, was completed in the year 1829.
iron work was provided by Captain Samuel Brown for the sum of 94307., and the masonry
of the towers cost 90801.; this was exclusive of the land arches, which were a part of the
old bridge.
From the centre of one tower to that of the other was 432 feet; the deflection of the
chain, or versed sine of the catenary, 42 feet; the length of the suspended roadway 412 feet,
and the width 12 feet; height of the roadway above the low water line 21 feet, and that
of the towers 68 feet. The dimensions of the base of the tower at the level of the roadway
are 40 feet by 20 feet: the archways through them 16 feet in width, and 24 feet in height;
they are built of red sandstone ashlar, and are carried on piles. On each side were two
main chains 12 inches apart, each composed of four bars of iron 5 inches in width, 1 inch
in thickness, and 10 feet in length, united by plates and wrought-iron pins. The roadway
was suspended by 14-inch perpendicular rods, placed 5 feet apart; these had at their lower
ends stirrup irons, which carried cast-iron bearers, over which the road was formed.
A
CHAP. VIII.
519
BRITAIN.
flooring of 3-inch plank, well caulked, was laid upon these bearers, and then 14 inch
boarded floor above, laid transversely; over this was a fine coating of sand and gravel,
cemented by tar.
There were no joints to the suspending rods, and the main chains rested upon detached
cast-iron saddles, built into the masonry of the towers, and their ends were secured by cast-
iron plates let into the masonry 10 feet under ground. The roadway of this bridge, which
weighed 203 tons 9 cwt., was destroyed on the 11th of October, 1838, when the platform
fell in one mass, in consequence of the failure of the suspension rods, which having no joints
were twisted off close to the floor by the undulatory motion. It was afterwards repaired,
when suspension rods of 1½ inch diameter were introduced, with flexible joints at the level
of the platform.
Cross timbers were introduced instead of the cast-iron bearers; these were of Memel,
13 inches by 3½, laid edgeways and bolted together, as well as trussed with an iron rod 1½
inch in diameter; every sixth beam was trussed on the under side to give it more strength.
Each side of the carriage-way, both above and below the cross beams, was bolted to two
sets of longitudinal timbers, four in each set, and at every 10 feet they were united together
by cast-iron boxes.
The planking of the footway was composed of battens 2 inches in thickness, laid trans-
versely, and that of the roadway of four thicknesses of 2 inch Memel, over which was laid
gravel, sand, and tar. During the storm which destroyed this bridge, the undulatory motion
was observed to be the greatest at about midway between the towers and the centre of the
roadway, but the waves of the platform did not follow those of the chains; no oscillatory
motion was seen either in the roadway or in the chains; after the event, the chains, saddles,
and fastenings were all found quite sound. The weight of the new roadway was 226 tons,
17 cwt., or 47·5 pounds per square foot.
The platform is 212 feet in length, and 27 feet in width, and cost 40267., or 7s. 3d. per foot
superficial. The injury done to the bridge by the storm was the cause of many pre-
cautionary measures being resorted to, not only for preventing any upward heave, but also
to confine, as much as possible, the undulatory motion: in the first suspension bridges
these principles were entirely neglected; the idea of the roadway being lifted up from a
force exerted beneath it does not seem to have suggested itself. The weight of the
structure, it was supposed, would always be sufficient to count act any upheaving: but on
the repairs being entrusted to Mr. Rendel, he was led to unclude that the wind might
act at the same moment on the upper side at one end, and the lower side at the other;
therefore, unless the platform had considerable rigidity, undulation commenced, and then
oscillation; to counteract this effect, a mode of trussing which should withstand this action
was necessary. Here is adopted a system of vertical diagonal trussing 10 feet in depth,
5 feet above, and 5 feet below the platform, which effectually prevents undulation as well
as oscillation.
The stretching strain, of malleable iron bars, is found to be three-fourths of the breaking
strain, or, as some experiments have proved, nearly one half. Iron bars 1 inch square
stretch when 16 tons is applied to them, so that the stretching strain may be fairly taken
as six-tenths of their strength, and they will support 9 tons per square inch without
stretching at all. Mr. George Rennie has shown us, however, that the ultimate strength
of cohesion of cast steel is 134,256 pounds per square inch.
Hammersmith Suspension Bridge, erected after the design of W. Tiernay Clark, forms a
communication from the Surrey side of the Thames with Hammersmith; it was completed
in 1824. The distance between the points of support is 422 feet 3 inches; the deflection
of the chains 29 feet 3 inches; and the tension on the iron at the points of suspension is
1.857 times the entire weight suspended. The piers are of stone, 22 feet thick, 46 feet
wide at the top, and 72 feet at the water-line, and their height above the level of the road
is 48 feet; through each pier is an arched opening 14 feet wide. The platform is divided
into a carriage-way 20 feet in width, with a footpath on each side 5 feet wide. There are
eight main chains arranged in four double lines, viz. two small chains, one under the other
on the outside of each footpath, and two large ones on each side of the carriage-way. The
small chains each contain three lines of bars 8 feet 10 inches long from centre to centre of
the eyes, 5 inches broad, and 1 inch thick. They are united by screw-bolts 23 inches in
diameter, and coupling plates 151 inches long, 8 inches broad, and 1 inch thick. The
large chains contain six lines of bars, of the same dimension as those described; all the
chains pass through openings in the main piers, and over rollers and iron carriages, each of
which carries two sets of rollers one under the other. From the piers the chains or
backstays pass down at the same angle as the chains of the central opening. The abutments
are in length 45 feet, in width 40 feet, and 15 feet deep, and the weight of each is computed
at 2160 tons. The chains are carried through tunnels 2 feet wide, where the smaller enter
the abutments, and 3 feet for the larger chains. The chains are secured to strong holding-
plates, which are bedded in the brickwork, and are all of hammered iron; the vertical rods,
1 inch square and 5 fect apart, are attached to the coupling plates of the main chains by
L L 4
520
Book 1.
HISTORY OF ENGINEERING.

Fig. 528.
HAMMERSMITH BUSPENSION Bridge.
short links and inch-round screw-bolts. The roadway is formed of transverse joists 12
inches by 4, on which longitudinal beams are laid, and then the planking.
Marlow Bridge is nearly similar in its construction; its total length is 426 feet, and the
carriage-way is 20 feet broad, the height of the platform is 12 feet above the water; there
are four main chains composed of flat bars; the deflection is 18 feet, and the section of the
iron in the chains altogether is 64 square inches.
Norfolk Bridge, at New Shoreham in Sussex, is another beautiful suspension bridge by
the same engineer. The chord line between the piers is 284 feet, and the deflection of the
chains 20 feet 2 inches; the breadth of the platform within the parapets is 28 feet 6 inches,
the width of the carriage-way being 20 feet. There are on each side three lines of chains,
the sectional area of the whole being 84 square inches. The bars are 8 feet 10 inches long,
61 broad, and 1 inches thick, with eyes 8 inches in breadth; where the chains are sus-
pended are rollers of cast-iron, all 10 inches in diameter, with 23 wrought-iron pivots.
There is a central arched opening through the main piers, and the abutments, which are
solid, weigh 900 tons; the backstays are not put at the saine angle as the central chains;
the platform of timber is in length 268 feet, and the total weight suspended in the central
opening is about 356 tons, or at the rate of 62 pounds per square foot.
Micklewood Bridge, designed by Mr. James Smith of Doune, differs in its construction
from most others; the platform is not suspended, but supported upon iron frames, which
rest upon the chains. The span is 103 feet, and there are two supporting chains on each
side about 23 inches in diameter, and 1 foot apart, which are fastened to iron frames. The
joists which support the platform rest upon iron uprights, set on the chains, the lower
ends being made like a fork to embrace them. There are twenty cross joints, the scantling
of which is 12 inches by 5, and the whole is cross-braced and secured.
Broughton, near Manchester; this suspension bridge has 145 feet 6 inches span, with a de-
flection of 12 feet 6 inches; the platform is 18 feet 3 inches wide, and 143 feet 3 inches in
length; it is supported by four chains, two on each side, formed of rods 2 inches in diameter,
and 4 feet 6 inches long, united by coupling links of inch-square iron and pins 2 inches
in diameter. The vertical suspension rods, 1 inch in diameter, spread out at top like a
fork, where they are pinned to an iron plate.
The main chains are supported by four cast-iron suspension frames, each carrying a pair
of chains, and the points of suspension are movable to allow for contraction.
Suspension Bridge over the Avon at Twerton, near Bath, is in length 230 feet, and the
width of the roadway 14 feet; it was executed under the direction of Thomas Motley.
There are two pair of pyramids, placed on a bed of concrete, 22 feet by 12, and formed
of six courses of Bath stone 30 inches deep, having two blocks on each course; the
dimensions of the pyramids at their base is 5 feet 6 inches by 4 feet 6 inches, and at top
CHAP. VIII.
521
BRITAIN.
3 feet by 2 feet 6 inches. The distance or span of the middle compartment is 120 feet from
centre to centre, and between them and the land 55 feet at each end. At the base of each
pyramid, level with the roadway, is a cast-iron bed, secured by iron bolts inserted into other
iron plates worked in the foundation; an iron bar, 3 inches by 1 inch, passes through the
centre of the pyramids into a cast-iron plate at the top.
The suspending bars average 2 inches by 1 inch, and are placed 2 feet 6 inches apart;
these are fastened by gibes and keys into a cast-iron plate, which passes up the side of the
pyramid from the base to the top. The main beam is formed of two wrought-iron bars,
7 inches by g of an inch, arranged in lengths of 18 feet, breaking joint, and connected by
brace plates. At the edge of each suspending bar an upright piece of iron, about 12 inches
long, is welded, to which the upright supports are attached; in these uprights are eyes
through which the suspending bars, which are all arranged parallel, pass, and are made
tight by wedges above and below the bar. These suspending bars are attached to a
round bolt 2 inches in diameter, which passes transversely, and connects the two ribs or
beams. At the abutments the ribs are secured by cast-iron bolts and plates. The weight
of the suspending and upright bars is 7 tons, and the total quantity of wrought-iron is
18 tons, and of cast-iron 5 tons. The floor is of Memel joists and oak platform, and the
cost was 2500l. As there are twenty-four suspending bars, whose united sections equal
48 inches, and one inch will support 20 tons, this bridge would carry 960 tons, but as the
leverage is as 4 to 1, we must only allow one quarter, including the weight of the
materials.
Turning or Swing Bridges.—There have been a great variety constructed over the various
canals and dock entrances: among the best in design are those at the West India Docks.
The roadway is carried upon cast-iron plates, which are secured to the ribs by iron bolts
and nuts, the ribs being cast with flanches to receive them.

13
D
L
Fig. 529.
ST. CATHERine's dock swing bridge,
At St. Catherine's Docks the bridge is equally divided in its length, one half being made
to swing each way, the tails working round three parts of a circle; the clear opening be-
tween the walls being 44 feet 9 inches, and the rise in the middle 3 feet 8 inches. The
turning is effected by a wheel working horizontally on a number of rollers that run
upon a bed of cast-iron, and so nicely is the whole balanced, that by means of a rack and
pinion it is easily worked. Iron bridges of this kind are generally adopted in pre-
ference to those of timber, which were formerly used; although more costly in the first
instance, there is greater economy in the end, and from the superior quality of the
machinery applied, and the nice adaptation of the parts, and perfect balance maintained,
there is little labour required to open and shut them. On canals in particular where a
single lock-keeper or attendant is on duty, it becomes indispensable to provide the means
of turning a bridge with the least possible labour, and to so great perfection have our
engineers brought the construction of these swing bridges, that they may be manœuvred
almost by a child. The ribs, when rightly proportioned and put together, are calculated
to bear any weight they may be subjected to, and, when properly balanced at their turning
end, there is no danger of their getting out of order, or sagging.
522
Book I.
HISTORY OF ENGINEERING.
The Thames Tunnel. — Having described some of the stone, iron, and suspension bridges
constructed over the rivers of Great Britain, our attention is drawn to a method of passing
under the current, so as not to interrupt navigation: this has been
accomplished by Sir Mark Isambard Brunel, a native of France, after
sixteen years' constant labour and attention; the Thames having broken
in upon the work three several times.
Before it was commenced, and as early as the year 1798, Mr.
Dodd proposed a communication between Gravesend and the Essex
coast by a passage under the Thames; another at Rotherhithe was
projected by Mr. Chapman in 1804, and three years afterwards a
shaft, 11 feet in diameter, was sunk at a distance of 315 feet from the
river. Mr. Trevithick, who thoroughly understood the difficulties
of such an undertaking, was then engaged to drive a way under the
navigable part of the Thames, and after great labour he formed a drift
way, 5 feet in height, 2 feet 6 inches in breadth at top, and 3 feet at
bottom, for a distance of 1046 feet under the river. Early in the year
1808 the water broke in upon the workmen, although there was at
least a thickness of 25 feet between them and the bed of the river;
this, perhaps, might have been prevented, if precautions had been
taken to line the way with brick as the work proceeded. After this
event a company was formed to carry out the plans which were pro-
jected by Mr. Brunel in 1823: a shaft was afterwards sunk, by first
driving 24 piles, with a shoulder projecting on the side of each, within
the circle intended to receive it; on these was laid the timber curb,
which also partly rested on one of iron; 48 wrought-iron bolts,
2 inches in diameter, passed upwards through this to a height of
40 feet, or to the top of the intended shaft. The curb or rather tower
was built upon it with bricks laid in cement, and as the work pro-
ceeded it was bound together by 26 circular timber hoops inch
thick when the brickwork was completed, on the top was placed
another wooden curb, through which the long iron bolts passed, and
their ends being formed into screws, the whole was by nuts held in
one entire mass. The construction of this brick curb was completed in
three weeks, and in seven or eight days, when the cement had hardened,
16 of the piles on which it rested were driven by pairs opposite to each
other, inch at a time, and then the whole gradually sunk, carrying
with it the other 8 piles; after this effect was produced, the 16 piles
were drawn out by opening the ground at the back; the whole weight
of the brick shaft, which was 910 tons, then rested on the 8 piles, and
these were eventually drawn, when a bed of gravel was arrived at for
a foundation. Mr. Brunel commenced this work on the 1st of Janu-
ary, 1826, and by the 27th of April in the following year 540 feet
of the tunnel were completed. On the 18th of May the river broke
in and filled it. After this irruption only 50 feet was advanced
in 1827, when, upon a second irruption, the work was totally aban-
doned. In 1835 the government made some advances of money, and a
new shield was provided, a masterpiece of ingenuity and contrivance,
executed by Messrs. Rennie, which was fixed March, 1836; the work
was resumed and continued until the 11th of June, when the water
again broke in, and retarded any further progress for six weeks;
after which it was continued until completed, in 1842, without any
serious interruptions.
There is a double tunnel throughout the whole distance between the
shores of Rotherhithe and Wapping, through a blue tenacious clay.
On the Rotherhithe side, at 150 feet from the river, is a shaft 50 feet in
diameter, 42 feet in height, and 3 feet in thickness; this was built on
the surface, and the ground excavated afterwards, the earth and water
being drawn out at the top by means of a steam-engine. It was sunk
in its place bodily, and passed through a bed of gravel and sand 26 feet
deep, causing great difficulty in the first attempts: when this 50 feet
shaft had descended 65 feet, it was followed by another from the lower
level, of 25 feet diameter, which was carried down 80 feet for the pur-
pose of effectually draining the works.

PLAN OF THE THAMES TUNNEL.
Fig. 530.
The tunnel was commenced at a depth of 63 feet, with a fall of 2 feet 3 inches in every
100 feet. The part excavated was 38 feet in width, and 22 feet 6 inches in height, having
a sectional area of 850 feet; the bottom at the deepest part of the river was laid 76 feet
below high water. The excavation was carried on by means of the shield, which was
CHAP. VIII.
523
BRITAIN.


Fig. 531.
THAMES TUNNEL.
composed of twelve frames close together, each having three cells, one above the other,
in which the miners worked. As the work advanced, polling boards were pressed firm
against the earth by means of screws, and closed the whole area of the excavation in front:
this shield weighed 180 tons; the mass of earth removed was 63,000 tons; the weight of
the brickwork 26,160 tons, and it is stated that the cost was not less than 12001. for every
yard advanced.
Roads. The Romans intersected Great Britain with roads, set out in straight lines from
one city to another, and from their military stations and camps to the coast; they were often
paved, and remained for centuries in the best possible condition, and were the principal
media of communication. Some of the great lines may be traced, as may the remains of the
sepulchres at their margins, containing coins, vases, ornaments of the dress, and arms.
name of street is still applied to them, particularly the chief, as Watling, Ikeneld, and Ermine.
The Roman roads were, however, narrow, and as manufactures were introduced, and a
consequent increase of traffic took place, we find a desire to improve these means of com-
munication.
The
In the year 1285 the owners of lands were enjoined to widen the roads, by cutting down
trees on each side to a certain width; in 1346 a law was passed to levy a toll on some
leading out of London, which were reported to be impassable. In the reign of Henry VIII.
laws were enacted binding the several parishes to take care of the roads, and annually to
select qualified persons to superintend them: but simple as are the principles of road-
making, those appointed are seldom sufficiently instructed on the subject, and being rate-
payers are too much interested to allow of the requisite outlay, thus many of the parish
roads are in a wretched condition, the system adopted by most parish surveyors being
merely to fill up the ruts and inequalities with stones picked from the surface of the land,
or gravel dug in some convenient spot: this operation, repeated in the spring and autumn,
constitutes their whole duty; no attention being paid to the nature of the soil, or the
selection of the material that will bind with it to form a hard exterior crust.
Stage-coach travelling had certainly arisen to a very great perfection before railroads were
introduced; the carriages were easy, well-constructed, and drawn by a superior breed of
horses. Considerable capital had been employed in the improvement of the turnpike roads;
hills were levelled or cut through, valleys filled up, and as straight a line as possible
was obtained; their repair was never neglected for an instant; immediately any part of the
crust was broken or worn away, it was the signal for a general spreading of fresh material
the smooth surface of the road being previously broken up into furrows to a depth of 2 or 3
inches; this process, called lifting, was followed by spreading the stones 3 or 4 inches deep,
and raking them even until the whole was consolidated into one entire mass.
;
The same system should be adopted by the superintendents of all parish roads; an
engineer or director should be set over a district or county to see justice done to the
public, and to instruct those who are too generally incompetent to perform the duties im-
posed upon them.
The footways or paths that lead from one village or town to another, equally important
to public convenience, and which hitherto have never been repaired, deserve to be
scrupulously regarded and maintained in the best possible condition: no proprietor should
be allowed to divert them out of a direct line, and the straightest course should be taken.
Towns, Streets of. In all large towns it has been found advisable to pave the streets
and footways, and in consequence laws have been established to regulate the expenses, and
to elect persons competent to collect and disburse the necessary funds; various local acts
were obtained before the passing of one (which comprised nearly all the measures then
deemed requisite) in the year 1817 (57 Geo. 3. c. 29.), which contains provisions for the
524
BOOK I.
HISTORY OF ENGINEERING.
guidance of the authorities with respect to the convenience, safety, and cleanliness of the
towns.
The corporation of the city of London appoint their own commissioners, and Westmin-
ster and the other parishes within the bills of mortality are under the jurisdiction of local
commissioners or their vestries.
All inhabited houses and shops are rated according to the value at which they are
assessed for the poor-rate to provide funds for the purposes of paving, &c.; and public
buildings pay a shilling per square yard over half the public way in front or belonging to
them.
The commissioners of paving regulate the duties of the scavengers and dustmen, levy fines
for the deposit of rubbish of any kind, either on the footways or streets, and are empowered
to cleanse the public thoroughfares, to contract for the watering of the streets, and provide
all that is requisite for the purpose; for which the inhabitants deriving the advantage pay
a tax not exceeding one-fortieth part of the rental. When new streets are formed, or old
ones improved, the commissioners may purchase the ground necessary, or call a jury (stat.
3 Geo. 1. c. 25.) for fixing the value.
Parish Roads. All that was excellent in the old statutes, or authorized by custom for
the regulations of parochial roads, was embodied in an act passed in 1773 (15 Geo. 3. C.
78.), under which a surveyor is annually chosen, whose duty it is to maintain the roads of
his parish in good order. The act states that on the 2d of September every year, or the
Monday following if it should fall on a Sunday, a meeting for the nomination of ten candi-
dates for the situation of surveyor shall take place; they must possess property or income
to the annual amount of 100l., or be occupiers of land or houses of the yearly value of 30%.
Three days after the meeting the constable presents the list to a justice of the peace, and it is
subsequently laid before a Special Quarter Sessions held the first week in October. The
justices then appoint one or more surveyors of roads for each parish; should the candidates
appear to them incompetent, they have the privilege of electing a respectable house or lease-
holder who may not be included in the original list.
A surveyor so chosen manages all the executive part as well as the expenditure, for which
he is personally responsible, and his office is somewhat similar to the ædile of ancient
Rome, his only reward being the exact performance of his duty; but a professional sur-
veyor may be appointed with a salary if the parish, or more than two-thirds of those
qualified to vote, agree. Surveyors chosen from among the parishioners often exhibit great
zeal, and some knowledge of their subject; but the professional man, who devotes his life to
the practice of such works, must be better qualified for the task, and his attention will
necessarily be more concentrated upon it, and were such offices filled by persons selected for
their knowledge as civil engineers, there can be little doubt that, with perfect integrity, the
highways in each parish would be maintained at a cheaper rate and in better order. The
magistrates of each county might have the power to nominate an engineer-in-chief, or an
officer from whom some general instructions should proceed.
Laws relative to Public Roads. By the act 13 Geo. 3. c. 78. s. 63., it is deemed
unlawful to dig a ditch, plant a hedge, trees, or shrubs, or fix a paling within at least 15
feet from the centre of the road. The ditches and drains on each side are to be maintained
and kept in repair by the owners of the adjoining ground. They must also make the
bridges or lay the pipes where the communications take place with their property. The
surveyors may procure gravel, sand, chalk, or stone from the commons, and from every
river or stream throughout the parish, but he is restricted from injuring any private or
public buildings.
Turnpike Roads were established after the return of Charles II., and acts were passed in
the second year of his reign for widening and repairing some of the public roads: the first
relates to that from London to Scotland, which passed through Hertford, Cambridge, and
Huntingdon. Many subsequent acts followed, but all the important laws were combined
in the 13 Geo. 3. c. 84., which was again modified by the 3 Geo. 4. c. 126., containing all
the regulations requisite for this important subject; it arranges the collection of the road
tax, and places the receipt and employment of the funds under the direction of trustees:
a trustee must have an income of 100l. per annum arising from landed property, or be
presumptive heir to some one having an income of double that amount; and within ten
miles of London the qualification is 10,000l. personal property after the payment of all debts.
The revenue arising from the tolls is paid into the hands of a treasurer by the receivers,
who are to present their accounts to the trustees whenever called upon, but always
at their annual meetings, which are held for the express purpose of examining and passing
accounts; besides this there are as many special meetings called as may be deemed
necessary, three members being sufficient for ordinary purposes, and seven to alter or
revoke an order made by a preceding assembly. The trustees have the power of short-
ening, improving, or altering the direction of a road; but they may not deviate more than
100 yards from the old line without consent of the proprietor of the land crossed by the
new line. They may borrow the money necessary for making, repairing, or improving
the roads, the interest and capital being paid out of the tolls.
CHAP. VIII.
525
BRITAIN.
The act for each trust limits the rate of the tolls and the number of turnpikes; the
trustees having the power of diminishing the toll with the consent of the creditors of
the road, and, also, of letting it out by public auction, after having stated by advertisement
the net produce during the preceding year. On the erection of a new turnpike the trus-
tees, on proper notice, decide in what situation it shall be placed. All the works for the
support of toll roads are under the direction of surveyors appointed by the trustees, as are
also the treasurer and other officers. The surveyor has the right, after having obtained the
authority of a justice of the peace, to collect in any field stones necessary for his purpose,
but he is also bound to pay for the same. The trustees order the fixing of all milestones,
finger-posts, and railings in dangerous places, and may prosecute any individual who wilfully
damages them.
In the year 1819 it was suggested to the Committee of Inquiry into the State of the
Public Roads, that the whole should be placed under the management of government; but,
upon the ground that this was contrary to the public interest, the idea was abandoned, and
the construction and maintenance of all parish roads are still left to the parish authorities,
and those of turnpike roads to the various trustees, the government alone interfering when
improvements essential to the general prosperity, and which are too costly for the local
districts, are to be carried out.
The narrowest limits which the law permits to be given to by-roads are as follows:—
footpaths 6 feet, horse-roads 8 feet, and carriage-roads 20 feet; their width may be
increased to 30 feet, viz. 16 feet 6 inches for the horse-road, and the rest given to the foot-
ways and ditches.
The width of turnpike roads, determined by act of parliament, is 60 feet for the
approaches to populous towns, though in many places this is reduced to less than 20 feet.
The total length of the paved streets and turnpike roads in England and Wales, as
reported by the Committee of the House of Lords in 1829, was 19,798 miles, and that of
the cross-roads and other highways 95,000 miles.
It is curious to refer to the progress made in turnpike legislation, which may be thus
stated: from 1700 to 1710, twelve turnpike acts were passed; from 1710 to 1720, twenty-
one; from 1720 to 1730, seventy-one; from 1730 to 1740, thirty-one; from 1740 to 1750,
twenty-nine; from 1750 to 1760, one hundred and eighty-five; from 1760 to 1770, one
hundred and seventy-five, making up to this period five hundred and thirty acts of parlia-
ment which had received the royal assent. These acts were limited to a duration of
twenty-one years, as it was presumed that at the end of that period the tolls imposed would
not be required: the clerks of the several trusts always take care, however, that some cre-
ditors of the road should remain unpaid, by which means they contrive to keep the trust
alive, and prevent their own office becoming extinct. The renewal of the Turnpike Act
is also profitable to the clerk, and since 1830 the term has been prolonged to thirty-one
years; at present the trusts in existence exceed 1100.
The General Turnpike Act now in force, the 3 Geo. 4. c. 126., was passed in the year
1822.
By a statement made to Parliament of the income and expenditure of the 1111 trusts
of England and Wales from the 1st of January, 1835, to 31st of December, 1835, it appears
that the
Bonded mortgage debt was
Revenue received from tolls
Money borrowed on security of tolls
Manual labour
Farm labour
Materials for surface repairs
1
₤
7,116,702
1,469,317
165,474
397,665
134,861
215,835
301,508
211,808
132,983
Interest of debt
Improvements
Debt paid off
Wherever the government has undertaken the formation of roads, engineers have been
appointed to make a careful survey of the country, and take the levels of the line to be set
out; and some of the best roads in the world have been the result of this arrangement;
those in Scotland, the Glasgow and Carlisle, and the Holyhead, which were made under
the able superintendence of Mr. Telford, may be enumerated as examples. A brief account
of the methods adopted may give an idea of the great care bestowed upon them by that
eminent engineer.
The Highland Roads and Bridges, executed under the direction of Mr. Telford, by the
aid of parliamentary grants, constitute so great an improvement, that they deserve our
particular attention; the whole were completed in a short space of time, when the work
done and money expended are considered.
As the Highland road was chiefly for the accommodation of cattle, hard substances
526
HISTORY OF ENGINEERING.
Book I.
were rejected; they were often formed along steep hill-sides and rocky precipices, and are
always sufficiently wide to admit of two carts passing. Wherever the land-owners required
a road, an application was made to the parliamentary commissioners, accompanied by the
offer of defraying half the expenses; the district was then surveyed, and the cost estimated,
after which the memorialists were called upon to deposit half the amount in the Bank of
Scotland; detailed working drawings and specifications were prepared, and the ground
marked out, and contractors were found to undertake the work under proper surveyors.
Where the length of road did not exceed ten miles, it was generally contracted for by one
person, but it was frequently divided among many, separate tenders being given for dif
ferent lots. The general superintendent and special inspector were appointed by the chief
engineer, Mr. Telford, to whom the inspector made a regular monthly statement, which
was afterwards sent to the commissioners.
When the roads were completed, those who contributed the moiety of the expense were
invited to survey them, and to join in the certificate that the whole was executed agreeably
to the contract and specification, after which the last eighth of the total sum retained was
paid to the contractors.
There were 920 miles of new road, and 1117 bridges, built in the course of 18 years,
under 120 contracts, witnout recourse being had to a court of law in any one instance.
Many of these roads were originally mere tracks, and it was sometimes necessary to carry
the lime for making the mortar in sacks on the backs of horses for upwards of twenty
miles. The stones for the arches of the bridges were brought by sea, many districts not
affording sufficient to cover a drain 2 feet in width.
The setting out these roads, and constructing the bridges throughout the most unfre-
quented parts of Scotland, called into practice a new class of engineers, hitherto unknown,
who soon systematised the labours they had to perform, and introduced a nomenclature
and method by which others could direct similar operations. An evident improvement
took place on all our mail-coach roads, which was imitated by those who had the charge of
other trusts. Material was sought for where it could be most easily obtained, and ex-
periments were tried upon its quality before contracts were entered into for its employ-
ment; many surveyors, who were before incompetent to judge of the quality of the metal
with which they formed the crust of a road, turned their attention to its chemical and me-
chanical properties. Small, smooth, round pebbles were no longer heaped together to be
spread over the middle of the carriage-way, but limestone or granite broken into angular
masses was carefully laid over the whole to one uniform depth. Every precaution was
taken for draining and keeping the road clean; the manner in which these operations
were carried out cannot be better understood than by referring to the following instructions
drawn up by Mr. Telford, which may be serviceable to those who have similar works to
perform, and as there is now every probability of railroads becoming general, it is peculiarly
necessary to preserve documents which relate to so direct an evidence of our progress in
civilisation.
"General specification for the Highland Roads.-The road to be formed to the full breadth
of 20 feet in the clear, including the side drain and green margin, except on places where
there is an absolute necessity for cutting the whole breadth of the road in solid rock; and
in those places the breadth of the road shall be 18 in the clear, between the parapets which
may be necessary for a safeguard, and those parapets are to be 2 feet in thickness at the
bottom, so that in rock the cutting will be 20 feet in breadth, and in all cases the road is to
be so laid out, that there shall be no quick bendings, nor its upper side interrupted by points
of rock.
"On dry bottomed ground, gravel of a proper quality, out of which all stones, above the
size of a hen's egg, shall have been previously taken, shall be laid to the depth of 14 inches
in the middle, and 9 inches at the sides; but the stones which are taken out of the gravel,
and do not exceed 4 inches in size, may be laid for that thickness below the gravel, and in
that case 10 inches only of cleansed gravel will be required.
"On mossy ground or swampy soils, if the moss or soft matter is not more than 2 feet in
thickness, and a hard bottom below this moss or soft matter, it is to be wholly removed,

Fig. 532.
SECTION ACROSS ROAD.
and the road formed on the harder substance as above described; but when the moss or
soft matter is more than 2 feet in depth, the contractors are to have their option of either
removing it, or forming the road upon the top of it in the following manner.
"Where the surface is level, and covered with sound sward or heath, there must be laid
two rows of swarded turf, with the swarded side of the one downwards, and of the other
CHAP. VIII.
527
BRITAIN.
which is to receive the gravel upwards; or otherwise, where turf cannot be readily pro-
cured, the surface of the moss or soft matter may be covered with a layer of brushwood or
heath, which, when compressed, shall not be less than 6 inches in thickness; upon the sur-
face so compressed and prepared, there shall be laid gravel, cleansed as before described, to
the thickness of 18 inches in the middle and 18 inches at the sides.
"In all cases, whatever be the nature of the soil, the road is on all the flat ground to be
brought to a perfect level from side to side, before the gravel is laid on; but in all cases
where the road is to be raised on the one side by moved ground, while the upper side is on
the natural ground, the lower side of the road, when finished, is to be from 4 to 6 inches
higher than the upper side, in proportion to the quantity of moved ground on the lower side.
"In side cuttings in steep banks, even if there is no moved ground on the lower side, still
the lower surface of the finished road is to be on at least 4 inches higher level than the
upper side.
Where the ground is level or flat, the road is to be gravelled to 18 feet in
width, and to have a border of green turf on each side, I foot in width.
“When the road is formed on a sloping bank, where no parapets are necessary, there is to
be a border of green turf on the lower side of the road, 1 foot in breadth in the clear.
"The drains are to be formed perfectly regular, and so as the course of the water shall not
be interrupted by points of rocks or sudden turnings, and where the soil is soft and loose,
these drains on the upper side of the road are to be paved with small stones, not less than
4 inches in depth. These pavements are to be made at the places pointed out by the in-
spector; they are to be carried to the extent, and made in the shape, he shall direct.
"Where the parapets are necessary, the road is to be gravelled to the breadth of 18 feet
as before described. And also the said contractors bind themselves and their foresaids to
make in a sufficient manner all back drains, of such dimensions, and in such directions, as
shall be necessary for effectually collecting and conducting the water in a proper manner
from the higher grounds to the nearest bridges or covered drains, especially where the
road is formed along steep and sloping banks, and the ground is wet and swampy, and that
at the places which shall be pointed out by the said surveyor, so that the road shall always
be kept free from water.
"Where the road is to be formed upon level ground, and particularly where it is mossy
and swampy, side drains are to be made of sufficient depth to drain the ground, and in all
cases quite sufficient to carry off the water. These side drains to be made with a slope
from the road to within 1 foot of the farther side of the drain, so that if the depth at th
farther side be 30 inches, the width at top shall be 6 feet, and so more or less in proportion
to the depth, and which side drains shall be made at the places approved of by the sur-
veyors: and also to make covered drains of dry stones at all places were necessary; the
inside walls of these drains are not to be less than 2 feet in thickness, and the stones for
that length to be laid regular: these covered drains shall in no instance (without particular
directions in writing from the principal engineer employed by the commissioners) be
less than 2 feet square; they are to be properly secured in the bottom by paving with.
stones set on edge; the pavement as well as the sides are to be secured at both ends of the
drains by stone work, so that it shall appear evident there is no risk that they shall be in-
jured by the water, where it enters into or issues from the drain. The stones with which
the two feet drains are covered are to be not less than 3 feet in length and 4 inches in
thickness, and laid so close together on stones of equal length overlapping each joint, as
shall effectually prevent the gravel from passing down into the drain, and leaving a hole in
the road. But in case it shall be discovered during the execution of the road, that instead
of some of the 2 feet, the road may be better protected by making a greater number of
drains of smaller dimensions, the contractors, upon receiving instructions in writing from
the principal engineer, shall execute them in such a manner, and counting two drains of
18 inches, or three drains of 12 inches, in lieu of one drain 2 feet square, and in case of
drains of 18 inches being made, the stones of the covers shall not be less than 30 inches in
length; if 12 inches the covers to be 2 feet in length; and in order to secure the due ex-
ecution of the said covered drains, it is expressly declared that the same shall be subjected
to the inspection and approval of the resident surveyor before the covers are laid on, that he
may be satisfied that the bottoms are properly paved, and the sides are built in a sufficient
manner; and after the said drains are covered, the backs of the buildings are to made up
with stones to the level of the upper beds of the covers, and the said drains shall be con-
structed, so that they shall have a sufficient covering of gravel, not exceeding 12 inches, to
the satisfaction of the surveyor, without causing any swell on the road. And also the said
contractors bind and oblige themselves, and their foresaids, to build and erect breastworks of
stone at all places where necessary on the lower side of the road, along the side of water-
courses, or on sloping banks, or on rocks; the foundation of the said breastwork must be
cut into the rock or solid ground for the whole breadth of the base of the wall or breast-
work which is to be placed on it, as hereafter described, and its direction is to be dipping
into the hill at a right angle with the slope of the face of the breastwork. If it shall be
necessary to make the breastwork 3 feet in height, from the foundation to the level of the
528
Book I.
HISTORY OF ENGINEERING.
lower side of the road, the breadth of the foundation shall be 24 inches, and 18 inches at
the top, or level of the lower side of the road. If the height is 4 feet, the breadth of the
foundation is to be 30 inches, and at the top 24 inches. If the height is 6 feet, the breadth
at the foundation is to be 3 feet, and 2 feet at the top. If the height is 8 feet, the breadth
of the foundation is to be 4 feet, and at the top 2 feet, and so on in proportion to any
greater or lesser height. In forming these breastworks, the stones are to be laid in regular
manner, quite through the thickness here described; the slope which is necessary to bring
the wall to its thickness at the top is all to be taken off the outside, and the stones are to
be laid mostly lengthwise into the wall; the space behind the breastwork and natural
ground, up to the level of the top of the formed roadway, is to be filled up with coarse
gravel or stones, (neither sand, sods, nor moss, to be used,) and if with stones they are to be
covered and brought to the levels formerly described, with a layer of strong swarded turf,
before the cleansed gravel is laid on.
"At all times, when the nature of the cutting makes it possible, the resident over seer
shall have an opportunity of examining the breastwork when completed, before the inner
side shall be filled up with stones or gravel as aforesaid, and also, where it shall be necessary
for the due execution of the said road, to erect parapet walls above breastworks, or upon
rock, they are to be built with stones laid in good lime mortar, agreeably to the ground report.
"These parapets are to be 2 feet wide at the foundation, and 18 inches at the top. The
height above the finished roadway is to be 2 feet 9 inches, including a coping of stones 9
inches deep. These coping stones are to be chosen, so as to meet one another in close
regular beds or upright joints, to be firmly wedged together, and pointed with lime mortar.
"At each extremity of the parapets the copings are to be well secured with the ends
turned down under the roadway, and also where it shall be necessary in forming the road,
to cut and remove earth from the higher side, to the depth of 2 feet or more, the road must
be formed 21 feet 6 inches wide, and, to prevent the earth from falling into the drain on the
upper side of the road, a wall of dry stones must be erected of a height according to the
depth of the cut. The foundation of those retaining walls is to be laid in all cases 6 inches
below the bottom of the drain, on the upper side of the road; there the thickness is to be
from 15 to 18 inches to the height of 4 feet; above that height they are to be of the
13
thickness. The stones with which they are constructed are to be laid in a regular and
workmanlike manner for the whole thickness of the wall; they are to be carried to such a
height, that the slope from them to the solid ground of the bank above is not to be less
than two horizontal to one perpendicular, and that slope to be covered with turf laid flat.
"And further, the contractors are to be bound to cut down all heights, fill up all hollows,
and blast all rocks upon the said line of roads, as pointed out by the said reports, and
which shall be requisite and necessary for the same: and further the said line of road shall
be formed and prepared for the gravel for one mile at least per advance to the satisfaction
of the surveyor employed by the said commissioners before any of the cleansed gravel is
laid on."
Every necessary precaution was taken to render these roads efficient, and where the
foundations were of a soft nature, concrete was spread entirely over the surface, made with
hard stone, or gravel mixed with lime in the proportion of one of the latter to four of the
former; and the greatest care was used, when the water was added, that the lime was
properly slaked and saturated. The depth of the bed of concrete varied according to cir-
cumstances: in some instances, 6 inches was found sufficient, in others more than double
that depth was required; and before this became thoroughly set or hard, the broken stone
was laid on, in order that it might bed itself, and unite firmly with the upper surface; for
it is very important that there should be a junction between the two bodies, otherwise
the stones would be in constant motion, and never form a firm and durable crust; by
laying the courses of broken stones on at intervals, the roadway is rendered perfectly solid,
and in one mass from bottom to top.
Glasgow and Carlisle Road differs materially from those in the Highlands, as it was
necessary to provide for the transit of the mail, and heavy coaches and carts carrying 3 or 4
tons; it was made with the utmost care, all the ascents and descents set out with an easy

wwww
Fig. 533.
SECTION of road.
and regular slope, never exceeding a rise of 1 in 30.
Telford, after the act of parliament was passed in 1816.
These works were directed by Mr.
The old road, which had become impassable, was in length 102 miles; the present is not
more than 93, and in order to gain this 9 miles, it was necessary to reconstruct 69 miles
entirely, and to build fifteen new bridges; exclusive of the bridges, the expense of the road-
CHAF. VIII.
599
BRITAIN.
making was about 1000l. per mile. It was specified that the breadth was
to be 34 feet between the fences, 18 of which were to be metalled, and the
remaining 8 feet on each side to be covered with gravel. In all embank-
ments the width on the top to be 30 feet, and the side slopes 1½ horizontal
to 1 perpendicular; in all cuttings above 5 feet, the width between the
lower skirts of the slopes 30 feet, all below that depth to be 34 feet. The
slopes of all the cuttings to be at the same rates as the embankments.
The surface of the road longitudinally or lengthwise, in all cases where
there were cuttings and embankments, to be formed as shown, and in no in-
stances the ascents or descents to exceed 1 in 30, and the changes from one to
the other to be made in regular curves, to the satisfaction of the inspector.
Where there were side cuttings and a part of the road made on moved
ground, the surface of the lower part, or moved ground, to be higher than
that of the upper side, to allow for consolidation, so that when finished it
might have the proper level.
In the middle of the road a metal bed to be formed, and in all cases
where the ground was nearly level, the metal to be laid upon the natural
surface of the ground, so as to have a curvature of 4 inches, in the middle
18 feet, and the sides or shouldering to be made with moved ground, but on
no account the metal bed to be cut out of the natural ground, unless that
be loose gravel or rock.
The metalling to consist of two beds or layers, viz. a bottom course of
stones, each 7 inches in depth, to be carefully set by hand, with broadest
end downwards, all cross-bonded or jointed, and no stone to be more than
3 inches wide on the top. These stones to be either good whinstone,
limestone, or hard freestone; the vacuities between to be carefully filled
with smaller stones packed by the hand, so as to bring the whole to an even
and firm surface.

Fig. 534
SECTION of road.
The top course or bed to be 7 inches in depth, to consist of properly
broken stones, none to exceed 6 ounces in weight, and each to pass through
a circular ring 2 inches in diameter in their largest dimensions. These
to be of hard whinstone, the quality of both bottom and top metal
to be determined by the inspector. In every 100 yards in length on
each side of the road, upon an average, there was to be a small drain from
the bed of the bottom layer to the outside ditch, as directed by the inspector.
Where the height of the embankments exceeded 3 feet, they were to
stand from one to three months, in proportion as they increased in depth, as
determined by the inspector. Over the upper bed or course of metal to be a
binding of gravel, of 1 inch in thickness upon an average; the cross
section of the finished roadway to have a curvature of 6 inches; in the middle
18 feet, and from that on each side a declivity at the rate of an inch in a
foot, to within 18 inches of the fences; the remaining space of 18 inches
to have a curvature of 3 inches, making in all about 9 inches on each side
below the finished roadway.
Fig. 535.
In passing morassy ground all the surface upon which the road was to be placed, viz.
between the fences, to be brought to a curvature of 12 inches in the middle, and to be
secured with two rows of good swarded turf, the lower end to be laid with the swarded side
downwards, and the upper one with it upwards. The metalling upon the said mossy
ground to be made 20 feet in width; a drain to be cut alongside of the road, 4 feet wide
at the top, 18 inches at the bottom, and 3 feet deep.
Cross drains, nine to be made in every mile in length, placed in situations marked out
by the inspectors; 18 inches wide, 16 inches high at the upper end, and 22 inches high at
M m
TRANSVERSE SECTION OF ROAD.

580
BOOK I.
HISTORY OF ENGINEERING.
the lower end; their bottoms to be paved with flat or small pebble stones, 4 inches in
depth. The foundations of the side walls to be laid at least 6 inches below the level of
the bottom of the drain, and these not to be less than 18 inches in thickness, laid in regular
courses, faced on both sides, in the manner of a good stone dyke. The top of each to be
properly levelled, and covered with a firm turf 2 inches in thickness, to form a bed for the
covers. The covers to be 2 feet 6 inches in length, and 4 inches in thickness; their side
joints to be made straight, so as to unite closely; the parts which lie on the turf to be flat.

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Fig. 536.
Section, SHOWING DRAINS.
These drains must be of a length, not only to cross the road, but the fences on each
side, also the slopes of the embankments, and pass fairly into the fields or natural water-
courses; from the ends of the drain, wing-walls to be extended 5 feet in a curved direction
into the solid ground, there to be of the same thickness as the side walls, founded at the
same depth, and carried to the same height, and coped with two rows of swarded turf. The
bottom between the wing-walls to be paved with stones not less than 6 inches in depth, and
well secured at the extremities by stones 12 inches in depth, and these to be well secured at
the upper ends, and connected with the firm ground and side drains. The whole body of
the drain to be at such a depth as to admit of a turf being laid over the covers, and the
full quantity of road metal and binding, without raising the longitudinal line of road. At
each end of the cross drains, the water which passes along the side of the road to be intro-
duced by a proper opening, protected by a stone cover; this entrance to be paved at least
5 feet in length. In passing through morassy ground, the bottom of the drains to be laid
with flat stones quite across, and at least 12 inches under each side wall, to be continued
quite to the extremity of the wing-walls.
To keep this road in repair after it was made required at the least 80 cubic yards of
broken stone per mile, and at the most 120 per annum; the cost of which varied from 201.
to 467. per mile.
Holyhead Road.-The embankment over the Stanley sands near Holyhead is 1300 yards
in length, 16 feet in height, and 34 feet in width at the top, including the roadway and
parapets.
The slope towards the sea is three horizontal to one perpendicular, and on the other
side at the rate of two to one; the breadth at the base is 114 feet; both sides are coated
with rubble stone, which has proved an effectual protection against the most violent storms.
In one part of the foundation was a hard rock, where an arch was turned which admitted
the flood tide to cover the space to the westward of the mound.

Fig. 537.
SECTION OF ROAD.
The embankment for the eastern approach to Conway Bridge is 666 yards in length,
and the breadth at the top 30 feet; its greatest height is 54 feet, the slope on the sea-side
is 3 horizontal to 1 perpendicular, on the other side 2 to 1; the greatest breadth at the
bottom is 300 feet.
The tide flows ten miles above the site of this embankment, and during its construction,
the velocity of the current swept away the gravel and earth to the depth of 34 feet, the
bottom being hard clay and rock; here a casing of rubble-stone was sunk at the outward
extremity of the base on the seaward side, and by persevering in this manner the mound was
completed and then protected by a rubble coating.
Railroads have now superseded in a great measure the use of the old turnpike roads, and
probably ere long there will not be traffic enough to contribute the toll for their maintenance;
we may then anticipate that they will fall into the condition of parish roads, and become
again impassable, if the legislature does not provide for the contrary; the next generation
will almost require a guide-post at every turning to indicate the route, for few will be
found on the way to whom the inquisitive traveller may apply for information, and
Pennant's Journey from Chester to London will become as unintelligible as the Itinerary
of Antoninus.
CHAP. VIII.
531
BRITAIN.
Draining and embanking are among the most important operations of the civil engineer;
the salubrity of a city or of an extensive district depends in a great measure upon the
manner in which its superfluous waters are conducted from the surface, and from the
various strata beneath, and we shall find that the laws now in force do not sufficiently bear
upon this subject, nor do they respond to the present wants and wishes of the population.
When the first regulations were made with regard to sewers, the construction of our houses
differed as much as did the habits of those who occupied them; the legal enactments now
comprise little more than what refers to the carrying off the water from the surface of the
soil, or forming banks to rivers for the purposes of guarding against their overflow. An
island like Great Britain requires more than ordinary attention to remove the abundance
of moisture condensed upon the surface, and a knowledge of the falls of the several streams,
brooks, and other supplies to the rivers which form the arteries of the whole system, is the
first thing to be obtained. The rate of motion of water dependent on its fall into the sea,
the nature of the soil it runs through, and the length of its course, all require to be studied
before any instructions can be given, or a comprehensive plan be arranged for effectually
draining any district.
To lay down a map of the whole country, on which should be marked the height of every
town and village above the level of the sea, as well as the boundary of every basin drained,
would be a great work, but the advantages derived from such a labour would more than
compensate for its cost; and if the natural drains, which are the rivers, were shown, with
all their tributaries, a comprehensive system might be based upon the knowledge so ob.
tained, and there would be no difficulty in framing laws which would effectually conduce
to the general salubrity, and essentially increase the interest both of the proprietors and the
cultivators of the soil. Dugdale, in his History of Embanking, tells us that draining a
district or a country has a divine origin, "for in the beginning the waters were gathered
together, and the dry land appeared, and that after the deluge the waters were dried up
from off the earth, and the face of the ground was dry."
All nations seem to have regarded the subject of drainage as one of primary importance,
and at a very early period we find it practised in England, but it was principally confined
to surface drainage of marshy districts, not forming a part of one grand whole, which is left
for the present generation to contrive and carry out.
When sewers are to be made in a city or town distant from the sea, it is requisite to
ascertain what will be the result when they unite with the river into which they are to
empty, and how the bed of that river is likely to be changed in the course of time by the
silting up of the mouth, or by the throwing up of other impediments to its free and natural
discharge. To have the sewage of a town under the management of one set of commis-
sioners, and the great trunk into which they are discharged under another, whose object,
perhaps, is only to maintain the navigation open, or to construct and keep in repair the
banks which confine it, is not likely to work well for the inhabitants of the places so
drained.
This is rendered obvious upon examining the state of many of our large and populous
towns, situated at the mouths of rivers, which pour their waters into another still larger.
The Thames, for instance, receives the Medway, the Darent, and others; and if we look
into the condition of the towns on their banks, we shall find that in consequence of the
elevation of the beds of these rivers, which at first formed a natural drainage, the whole of
the buildings, as well as the surrounding, and once fertile, district, is too often in the midst
of a mass of stagnant water and decomposing vegetable matter, producing periodical
diseases among the inhabitants.
The streamlets or brooks, which fall into these natural drains, and which once afforded
abundant supply of wholesome water, have also become the receptacles of all that is filthy,
being converted into common sewers, from the surface of which arise exhalations highly
injurious. Never was it more necessary that some comprehensive plan should be laid
down to remedy this increasing evil, and to establish some power which should prevent
further mischief and bring back the whole to a healthy state of management. This could
be readily done if the country were divided into districts, not according to hundreds or
parishes, but in reference to their natural position: the whole of the land drained by a
river of any importance should be under one controlling power; the valley on each side of
the Medway, for instance, or that watered by the Darent, after being accurately surveyed,
could have such local laws established as would at once show the necessity of maintaining
them inviolable, and that any infringement would be injurious to the interests of all.
The various mills erected on the rivers have all assisted to destroy the effectual draining
of the lands on their banks; the outbreaks of the springs have in many instances been
penned upon, by creating a head of water, and a whole village has by this means been
placed in a morass, its soil, once loose and dry, becoming saturated with water; this is
particularly the case on the banks of those rivers where mills and factories have been long
established; and we often find the sill, over which the supply to their water-wheels formerly
ran, at a depth of 8 or 10 feet below its present level. Now, it must be evident, that had
MM 2
532
Book I.
HISTORY OF ENGINEERING.
some control been exercised over this increase in the several falls of water, the natural
drainage of the district would have been better maintained. To effect it now, it would be
absolutely necessary, in almost every valley in the kingdom, after taking the fall from one
end to the other, to open a new channel to carry off those waters that have been deprived of
their natural outlets.
Romney Marsh, in Kent, which contains upwards of 24,000 acres of rich land, and which
was probably obtained from the sea when the Romans occupied England, is the first
district of the drainage of which we have any historical mention.
It is defended against
the sea by an artificial wall of great strength, extending in length across the opening
upwards of 6000 yards, and upon its maintenance depends the efficient drainage of the
whole level. There are three grand sluices within it, which allow the fresh water to pass
off at the lowest state of the tide.
From Tacitus we learn that the inhabitants of Britain were made to toil in clearing
woods, banking fens, and making causeways, and to the Romans we are perhaps indebted
for the first regulations upon these subjects; certain it is, that for the conservation of this
marsh the first statutes and ordinances were framed, and they formed the basis of all others
that were made for the preservation of sea banks and marshes throughout the kingdom.
At first, probably, the whole was governed by customary laws, but we find that as early as
the forty-first year of King Henry III., these were confirmed; previous to that time the
whole management was entrusted to twenty-four jurats, who were appointed by as many
townships or manors, and a bailiff named out of their own body, who, like the Saxon
reeve, presided over, as well as executed, the powers which were lodged in the whole body.
These twenty-four jurats named the quantity of work to be performed by the several owners
of the adjoining lands; and, if not promptly attended to, the bailiff took the manage-
ment into his own hands, and charged the party that had refused, with the sum expended.
Henry III., upon some complaints being made, sent his chief justice, Henry de Bathe, to
Romney Marsh, to lay down some more efficient laws for the guidance of the jurats than
those in operation; and his first ordinances were to this effect: :-"That twelve lawful men
should be made choice of by the commonalty of the said marsh, viz. six of the fee of the
Archbishop of Canterbury and six of the barony, who, being sworn, should measure both
the new banks and the old, and those other which ought to be new made, the measure to
be, by one and the same perch, scil. of 20 feet. And that afterwards the said jurats should
likewise, according to the same perch, measure by acres all the lands and tenements which
were subject to danger within the said marsh. And all the said measures being so made,
that then twenty-four men, first elected by the commonalty and sworn, having respect to
the quantity of the banks of those lands, which lay subject to peril, upon their oaths to
appoint out every man his share and portion of the same banks, which should so belong to
him, and to be made and sustained; so that, according to the proportion of the acres
subject to danger, there should be assigned to every man his share of perches; and that the
said assignation should be made by certain limits, so that it might be known where, and
by what places, and how much, each man should be obliged to maintain.
"And that, when necessity should happen, by occasion whereof it might be requisite to
withstand or resist the danger or violence of the sea, in repairing of the before specified
banks, that the said twenty-four jurats should meet together and view the places of danger,
and consider to whom the defence of the same should be assigned, and within what time to
be repaired.
"And that the common bailiff of the said marsh should give notice to those unto whose
defence the said places should be assigned, that they should defend and repair them within
the time assigned by the said twenty-four jurats; and if they neglected so to do, that then
the said common bailiff should, at his own charge, make good the said repairs by the over-
sight of the twenty-four jurats; and that afterwards the party so neglecting should be
obliged to render to the said bailiff double the charge so laid out by him about those
repairs, which double to be reserved for the benefit of the said banks and the repair of
them; and that the party so neglecting should be distrained for the same, by his lands
situate within the said marsh.
Moreover, in case any parcel of land should be held in common by partners, so that a
certain place could not be assigned to each partner for his own proportion, viz. a whole
or a half perch, in respect of the small quantity of land; that then it should be ordained
by the oaths of the twenty-four jurats, and viewed what proportion of the said land so
held in common he might be able to defend; and, therefore, upon a certain portion
so to be defended by the said partners in common, to be assigned to them.
And if any
of the said partners should neglect to defend his portion, after admonition given to
them by the bailiff, the said portion of the party so neglecting to be assigned to the other
partners, who ought to make the like defence; which partners to hold the portion of the
party so neglecting in their hands, until he should pay his proportion of the costs laid out
about the same defence, by the oversight of the twenty-four jurats; and also double
towards the commodities of the said banks, and the repair of them as aforesaid.
CHAP. VIII.
533
BRITAIN.
"And that if all the partners should happen to be negligent in the premises, then that
the common bailiff before mentioned should make good the whole defence, at his own
proper costs, and afterwards distrain all those partners in double the charges so by him ex-
pended in the said defence, by view of the twenty-four jurats as aforesaid; saving to the
chief lords in the said marsh the right which they have against their tenants touching
this defence according to their feoffments.
“And that all lands in the said marsh be kept and maintained against the violence of the
sea, and the floods of the fresh waters, with banks and sewers, by the oath and con-
sideration of twenty-four jurats at the least, for their preservation, as anciently had been
accustomed.”
Such were the first laws formed for the guidance of the commissioners of sewers, and we
learn that soon after their publication, Henry III. was informed that his haven at Rumenale
or Romney was likely to be destroyed, unless the river of Newendene, whereupon the said
haven was founded, was again turned into its original channel, from whence it had been
diverted by the overflowings of the sea. . Various obstructions in the old course of that
river were removed, a new channel was opened, and a sluice built at the town of Apeltre,
"to allow the salt water to enter into the said river, by the inundation of the sea from the
parts of Winchelsea, and that it might join the fresh water of the river in its ancient course,
and thus in its descent be made to scour out the haven.' Another sluice was also made
at Sneregate, and a third in the port itself, where the water passed off into the sea to pre-
vent the tide from entering the river; the whole of these works were performed under
Nicholas de Handloo and twenty-four jurats, named by the sheriff of the county of
Kent.
""
Edward I., in the sixteenth year of his reign, finding that the sea banks and water-
gangs on the coast needed reparation, issued a commission to John de Lovetot and Henry
de Apuldrefeld, to inquire by whose default this damage had occurred, and, together with
the bailiffs and others, to distrain upon all those whose negligence had been the cause.
These commissioners confirmed the ordinances of Henry de Bathe, and assigned the
election of the king's bailiff to the lords of the marsh in future.
In the eighteenth year of the same reign, some controversies and differences again arising
relative to those upon whom the expenses of repairing and maintaining the sea-walls should
fall, another commission was appointed, in which were named John de Lovet, Robert de
Septuaus, Thomas de Gudinton, and Henry de Appletrefeld.
Some few years afterwards, Henry de Appletrefeld and Bertram de Tancrey were
desired to make a general survey of the whole coast of Kent, examine its banks and ditches,
which by reason of the roughness of the sea were in many places broken, and after making
their report, they extended the ordinances of Henry de Bathe by common assent to every
hundred and township throughout Kent, as well as the coast bordering the Thames and
other waters, wherever there were marsh lands subject to inundation.
The ordinances now so generally promulgated were, "That through all other maritime
places in the said county liable to the danger of the sea, the river of Thames, or any other
water, wherein the marsh law had not formerly been established and used, and that divers
perils, through defect of banks and water-gangs, had there happened: lest therefore for the
future the like or worse might accrue.
"That in every hundred and town, as well by the sea coast as bordering on the Thames
and other waters, in which the marsh lands are subject to inundation, there be chosen and
sworn twelve or six lawful men, according to the largeness of the hundreds or towns, and
who have lands in danger of the sea, the Thames, and other waters; which men to be
assigned keepers of the banks and water-gangs in the hundreds and towns aforesaid, who
upon their oath shall keep safe the said banks and water-gangs; and when, and as often as
need requireth, repair them, as also shall, in respect of the raging of the sea, raise the said
banks higher by 4 feet at the least than formerly they were, and make them of thickness
answerable to that height.
"For the reparation of which banks and water-gangs, when need shall so require, the charge
to be raised in manner following, viz., that all and singular persons having lands liable to
the danger, whether situate near or afar off, forasmuch as they have preservation by those
banks and water-gangs, they shall contribute for the quantity of their lands and tenements,
either by number of acres or carucates, according to the proportion of what they hold, so
that no tenant of these lands or tenements, be he rich or poor, or of what order, state,
dignity, or condition soever, either within liberties or without, any favour shall be showed
in this matter.
"That in every place for the levying of the said costs and charges, and faithfully laying
it out upon the said banks and water-gangs, two lawful persons out of the said sworn men
be assigned, who, together with the bailiff of the liberties or lords of the fee, shall make
distresses for the same.
“And when the before specified banks shall be, according to the ordinances of the jurat,
M M 3
534
BOOK I.
HISTORY OF ENGINEERING.
so repaired at the common charges, that there shall be assigned to every man his peculiar
portion of the bank by certain places and bounds, to be sustained at his own proper cost,
according to the quantity of his tenement, and number of acres subject to that danger, so
that it may be known where, and by what places, and to what portion every man is so
obliged to make defence. And if any shall be negligent in paying their portions of the
said contributions at the day appointed by the jurats for that purpose, or in his portion for
repair of the banks, that he be distrained by his goods and chattels wheresoever they should
be found, within liberties or without, till he have contributed his share, and paid his charge
of the said banks with double costs, which double to be reserved for the common benefit of
the like repair in these parts.
"And that these distresses shall be made by the collectors of the said costs, together with
the bailiffs of the liberties or lords of the fee, and being so made, to be kept for the space
of three days at the most, if they upon whom they shall be made be stubborn or negligent
for so long time, and then forthwith sold, in respect of the perilous rage of the sea imminent.
And if as well the collectors as tenants shall be found negligent in performing the premises,
that then every lord of the fee within the compass of the fee shall cause the said banks and
water-
r-gangs to be repaired at his own proper charge, and the costs that he shall be at
therein, together with the double thereof, he shall cause to be levied upon the goods and
chattels of those that are negligent for his own use.
“And that no shrieve of Kent for the time being, or his bailiff or officer, shall take any
distress touching the banks and water-gangs in any marshes, nor thenceforth meddle at all
neither with the distresses taken by the lords of the fee, bailiff of liberties, or collectors of
the costs or contributions to the said banks and water-gangs, nor distrain them by writ of
replevin, nor deliver them by surety or pledge any manner of way.
"And it was also ordained and concluded, that if the jurats so chosen for the custody of
the banks and water-gangs, whether they shall be of the marsh of Rumenale, or of other
maritime lands, do refuse to come at the summons of their bailiffs, for the necessary repair
of the said banks and water-gangs, they shall, for that their negligence, be punished by their
bailiffs, as in this marsh of Rumenale they had been heretofore accustomed.
"And that the collectors also of the costs bestowed in repair and support of the banks
and water-gangs, after the said repairs are perfected, shall forthwith make their account
before the jurats and bailiff of that county, as well within the marsh of Rumenale as
without, of all monies assessed and levied for the before specified repairs; as also for the
double, whensoever it may fortune to be levied; and if they shall not do so, then to be dis-
trained by the bailiffs of the country or place, to make account thereupon, saving always to
the chief lords of the fees their right which they have, and hitherto had wont to have,
touching the defence of their lands according to their feoffments, and of levying the double
according to ancient custom used, as it is contained in the ordinance of the said Henry de
Bathe."
These ordinances were held in such high esteem, that they were constantly confirmed and
issued by the crown wherever it was necessary in the thirty-fifth year of Edward III.,
some further penal statutes were annexed, and in the sixth year of Henry VI. several com-
missioners of sewers were appointed and empowered in various parts of the kingdom, “ to
make and ordain necessary and convenable statutes and ordinances, for the salvation and
conservation of the sea banks and marshes, and the parts adjoining, according to the laws
and customs of Romney marsh.”
In the succeeding reigns the same statutes were continued, with some minor alterations
and additions, and no material change took place until that act was passed in the twenty-third
year of Henry VIII., in which it is provided, "that commissioners of sewers shall be
directed in all parts within this realm from time to time, where and when need shall require,
to be formed of such substantial and indifferent persons as shall be named by the lord chan-
cellor and the two chief-justices for the time being; any six commissioners, of whom three
must be a quorum, may act as the king's justices, to survey the walls, ditches, banks, gutters,
sewers, gates, calcies, bridges, streams, and other defences, lying within the limits assigned,
and also all fishgarths, milldams, locks, ebbing wears, keeps, floodgates, and other like
annoyances, and the same cause to be made, corrected, repaired, amended, put down, or
reformed, as case shall require, after their wisdoms and discretions, as well according to the
statutes and ordinances already made, as by the authority of the present ordinances, after
ascertaining by a jury the persons equitably liable to the charge of such works, and the
proportions in which they ought to be assessed."
The commissioners are empowered to appoint keepers, bailiffs, surveyors, collectors, ex-
penditors, and other ministers and officers, who shall account to them, and also to impress
workmen, take materials, waggons, carts, &c., to make statutes and ordinances for the safe-
guard, conservation, redress, correction and reformation of the premises, after the laws
and customs of Romney Marsh in the county of Kent, or otherwise. This statute was
made perpetual by the third and fourth of Edward VI., and is the existing statute of
sewers.
CHAP. VIII.
535
BRITAIN.
Under these several acts the various breaches whicn took place from time to time in the
Thames banks were repaired, but in spite of the several commissions, it appears from a re-
presentation made to parliament in the fifth year of Elizabeth, that upwards of 2000 acres
of land had laid thirty years under water in the parishes of Erith, Lesnes, and Plumstead,
which in former times were excellent pastures. It was also represented, "that one Jacobus
Aconytus, an Italian, and servant to the queen, had undertaken at his own charges the
recovery thereof, in consideration of a moiety of it for his charges; but that the lords and
owners thereof were many, and had several kind of estates therein, whereby their assents
and good assurances could not be procured. It was therefore enacted that the said Jacobus
and his assigns, and their servants, factors, and labourers, &c., should at the cost and charges
of the said Jacobus after the tenth day of March, in the year 1572, for the term of four
years then next following, inn, fence, and win the said grounds or any parcel of them; and
that having so won and fenced the same or any of them, that he the said Jacobus and his
heirs, or such person or persons and their heirs as he or his executors should nominate, by
their writing enrolled in one of the said queen's courts of record at Westminster, or by his
the said Jacobus's last will and testament, in consideration of such recompense, should have
and enjoy the one moiety thereof, to be severed from the residue, within two years next
after the said winning thereof, by four or more discreet commissioners, to be nominated and
appointed by the lord chancellor, and being so severed, lots to be cast for concluding of each
portion to either parties.
After the two years had expired, "there were only 600 acres won and inned with walls,
banks, &c., which afterwards, by the violence of the floods, were again overflowed and lost,”
and Jacobus Aconytus then deputed John Baptista Castilion, John Gresham, and others,
to undertake the work, and after many years' fruitless attempts, it was enacted that William
Burrell of Ratcliff, in the county of Middlesex, gentleman, should have power to enter
upon the work, and to take reed and earth, in any part of the said drowned marsh, so as he
the said William, nor any employed therein under him, should not dig within twenty rods
of any wall already made within that marsh, and that immediately after his accomplishment
of the same, he the said William, his heirs and assigns, to have the one-half of all the said
grounds so to be inned, according to the purport and true meaning of the said recited in-
denture, the other moiety to belong to the owners of the said marsh grounds,according to
the several proportion of their quantities which they had in those grounds, to be holden of
Edmund Cooke, Esq., his heirs and assigns, as of his manor of Lesnes and Fants in free
soccage by fealty, and one penny rent for every acre, and not in chief, nor by knight's service.
And that in consideration of the great charge of this work, the said inned marshes to be dis-
charged from all tithes and tenths whatsoever, for and during the term of seven years next
after the inning, winning, and fencing the same.
We are not informed how long the work was in operation, but it was effectually accom-
plished, after considerable difficulty, early in the 17th century.
In the month of September, 1621, the whole of Dagenham Level, on the Essex side of the
river Thames, was thrown under water by an extensive breach being made in the walls; this
was speedily repaired by Cornelius Vermuden, of Saint Martin's Dyke, in the island of
Tholen, near the mouth of the Scheldt, a gentleman expert in the art of banking and draining ;
and as many of the owners refused to pay their proportion of the expenses, a portion of the
land reclaimed was assigned to Vermuden by the king's letters patent, which recited, "that
where any person should be assessed by the commissioners of sewers to any lot, and refuse
or neglect to pay the same, the land to be leased, or passed in fee simple, in recompense to
the undertaker."
Drainage of the Fens in Lincolnshire, one of the most important, as well as one of the
earliest works, in this branch of engineering, executed in England. These fens were entirely
inundated by the sea, though there is strong evidence for believing that previous to their
being covered with water, they formed a woody country, "oak trees being frequently found
at a depth of 3 feet or more beneath the surface, lying near their roots, which still stand as
they grew in the firm earth below the moor, and the bodies for the most part north-west
from the roots, not cut down with axes, but burnt asunder somewhat near the ground. Some
of these trees are 5 yards in circumference, and 16 in length, and many have acorns
remaining near them. There are also fir trees which lie 1 foot or 18 inches deeper; many of
them are more than 30 yards in length," and according to Dugdale, one was taken out in
the year 1653, “36 yards long without the top, which was lying near the root, which stood
likewise as it grew, having been burnt and not hewn down, which tree bore at the bottom
10 inches square, and at the top 8."
A ladder of fir was found in the moors at Thurne, with about forty staves, which were
33 inches asunder, and at Haxey Carr a hedge with stakes and binders. So many trees
are found here, that the inhabitants have, on an average, taken up, says the same author,
2000 cart-loads in a year.
No memorial is left which can lead to a conjecture of when this vast inundation took
place; but without doubt it was occasioned by the elevation of the beds of the several rivers
M M 4
536
Book I.
HISTORY OF ENGINEERING.
flowing through it, the chief of which are the Trent, the Ancholme, the Witham, the
Welland, the Glen, and several tributary streams. In the reign of Henry II. the whole of
this district was one vast lake, for we find an account of shipping traversing it in all direc-
tions. The great bay or estuary into which these different rivers are discharged is very
shallow, and full of shifting sands and silt, and the rivers flowing through a soft soil bring
down a great deal of mud, particularly in times of flood, which is met by the tide, also
charged with silt, and prevented from being carried away; thus both are deposited at the
mouth.
In wet seasons the rivers, from the greater quantity of water, run to seaward with
increased velocity, and of consequence drive the silt further out; when this quantity is
lessened, and the tides are stronger from the effects of the wind, the silt is driven less power-
fully outwards, and settles near the mouths, which chokes them up, and prevents their free
discharge from the fens. Such may be some of the causes for the inundations that have
taken place. There is no doubt that much was effected by the Romans in this district to
confine the course of the several rivers, and prevent their frequent overflow.
The marshes on the river Ancholme are mentioned in the sixteenth year of King
Edward I., who directs his writ to the sheriff of the county of Lincolnshire, to inquire
"whether it would be hurtful to him, or any other, if the course of that river, then ob-
structed from a place called Bishop's Brigge to the river Humber, were opened, so that the
current of the same might be reduced into its due and ancient channel," and commissioners
were afterwards appointed to cause the channel to be scoured and cleansed.
The Island of Ancholme, which contains some of the most fertile land in the county, was
formerly nothing but fen, occasioned by the silt thrown up the Trent with the tides of the
Humber. The obstructions which the Dun and Idle met with forced back their waters
over the neighbouring lands, so that the centre of this district, which was somewhat more
elevated, formed an island. One of the works performed here to prevent inundation in the
reign of Henry V. was a strong sluice of wood, made upon the Trent at the head of a
sewer, called the Mazedyke, which was of a sufficient height and breadth to keep out the
tidal water, as well as to prevent the fresh water descending from the west part of the same
sluice to the sewer into the Trent, and from thence into the Humber. This sluice was
destroyed by some of the inhabitants of the lordship of Hatfield, and rebuilt by John de
Shireburne with stone, sufficiently strong, as he thought, for defence against the sea-tides and
fresh waters. The jurors, however, condemned it, being inadequate for its purpose, and
both too high and broad; they also ordered in lieu of it, "that sluices of strong timber
should be set up, which should consist of two flood-gates, each containing in itself 4 feet in
breadth, and 6 feet in height; and also a bridge upon the said sluices, in length and
breadth sufficient for carts and other carriages, which for the future might pass that
way."
No great engineering works appear to have been undertaken to rescue this vast fen or
lake, which extended over upwards of 60,000 acres, till the beginning of the reign of King
Charles I. That monarch seems to have authorised the draining of all the surrounding
marshes of the Isle of Ancholme, as well as those of Hatfield Chase and Dykesmarsh, which
were overflowed by the Idel, Bickersdyke, Turne, Done, and Ayre rivers, in conse-
quence of their being obstructed by silt, so that boats could navigate the country at all
times.
Haxey Carr had boats laden with twenty quarters of corn usually passing over it from
the river Idel to Trent. The king being the owner, not only of Hatfield Chase, Dykes-
marsh, and other townships so inundated, contracted under the great seal with Cornelius
Vermuden of the city of London, in the second year of his reign, "that the said Cornelius
should at his own charge drain and lay the same dry, beginning the work within three
months after the said king should have agreed with those persons that had interest of com-
mon therein, and finish it with all possible expedition.
"That the said Cornelius, in consideration thereof, should have to him and his heirs for
ever one full third part of the said surrounded grounds, to hold of the said king, his heirs
and successors, as of his manor of East Greenwich in free and common soccage.
"That he the said Cornelius should pay and satisfy to the owners of all lands lying
within the same level, and so surrounded, such sums of money as the said lands should be
thought worth by four commissioners, whereof two to be named by the Lord Treasurer of
England for the time being, and the other two by him the said Cornelius.
"That the said work being finished, there should be, for the better preservation thereof,
a corporation made to make acts and ordinances to that end, as occasion should require,
consisting of such persons as he the said Cornelius and his heirs did nominate.
"That within three years after they should be finished, six commissioners to be ap-
pointed, viz. three by the Lord Treasurer of England, three by the said Cornelius, his heirs,
&c., to view them, and to estimate what the future yearly charge might amount unto for
the perpetual maintaining of them: whereupon the said Cornelius to convey and assure the
inheritance of lands to such a value as might be thought sufficient to support that charge;
CHAP. VIII.
537
BRITAIN.
and that whereas divers did claim common of pasture in sundry of the said grounds, it was
agreed that the king should issue out his commission under the great seal of England to
certain persons to treat and conclude with those commoners, by way of compensation in
land or money concerning the same. Commissions were accordingly directed to several
gentleinen of those counties to treat with the several parties who had right of common; and
the whole being submitted to Sir John Bankes, the Attorney-General, he made an award,
viz. that of 13,400 acres belonging to that manor, which was then to be drained with the
rest of the level, 6000 should be allotted to the commoners as their part or portion,
lying next to the towns, and so preserved for ever at the charge of the said Cornelius Ver-
muyden, and the remaining 7400 acres to be set out in the remotest parts of those wastes
to Sir C. Vermuyden and his participants for their third part, and for the said king's part in
right of his interest as lord of the soil, which by consent was decreed in the Exchequer
Chamber, and possession thereupon established with the said Cornelius Vermuyden and his
participants, and to their assigns."
When this agreement was made the work was commenced, and in five years, after an ex-
penditure of 55,8251., it was completed; the water which had overflowed the entire level being
conveyed into the Trent through Snow sewer and Althorpe river, by a sluice, which allowed
the issue of the drained water at every ebb, and kept back the tide at the flow. These fen
lands are rendered more difficult to drain in consequence of there being no calcareous strata
separating the Kimmeridge and Oxford clays, as is usually the case, but which are here
found in contact, and extend to a very considerable depth. These strata, not allowing the
water to percolate, can only be drained by conducting it away on the surface, a great
obstruction to which, is the low level of the entire district, which has little fall towards the
ocean, indeed in many parts is absolutely below it.
Soon after the drainage of this district, the town of Sandtoft was built and inhabited by
200 French families, or Walloon protestants, who had fled from their native country to
enjoy the free exercise of their religion, in the year 1642, and the inhabitants who had been
deprived of their rights of common broke down the fences and inclosures of 4000 acres,
destroyed all the corn growing, and demolished the houses; they pulled up the flood-gates
of Snow river, let in the tides from the Trent, and again laid the greater part of Hatfield
Chase under water.
The inhabitants of the island of Ancholme three years afterwards threw down many of
the banks that had been constructed to keep the rivers in their course, filled up many of
the drains, and altogether laid waste 74,000 acres; and it was not till the year 1656 these
injuries were redressed.
The marshes which lie on the north-west of Lincolnshire, upon the borders of the river
Ancholme, were drained in the year 1639, at the expense of Sir John Munson," a person,"
says Dugdale, "eminently qualified with learning, and sundry ample endowments, who, out
of a noble desire to serve his country, undertook the work and accomplished it."
The low lands on the south side of the Humber, and on the sea-coast in the province of
Lindsey, were very ineffectually drained in the time of Henry III., although we find that
a sewer was opened for the purpose betwixt the towns of Brunthorpe and Orreby, which
was regularly scoured, cleansed, and repaired, by casting out the earth on each side, and that
various bridges were built over it for the convenience of the adjoining landowners.
In the reign of Edward I. a writ was issued to John Beeke and the sheriff of the
county, to inquire if the river Friskney could be diverted and brought to the town of
Grimesby, for the better opening of that port, which was then silted up; and in the suc-
ceeding reigns many new sewers were cut, and more effectual drainage obtained; flood-
gates were made at the various dams to keep out the sea; these were in pairs, generally
from 12 to 20 feet in width, and made of timber.
The manner in which the earth walls were set out in the time of Elizabeth in this dis-
trict seems to have been by falls, for one then newly made at Skegnes by order of the com-
missioners that sat at Partenay, and which was commenced at a place called Ransom
Hyrne, is described as having forty falls in length, from the north end of the said Ransom
Hyrne towards the south, and joining on, and closed to the old bank; this sea-bank
measured 50 feet in the skirt, 14 feet broad at the top, and was 12 feet in height.
The Marshes of Witham lie on the borders of the river of that name, which extends from
Lincoln to Boston; but its fall is so small, and the current so slow, that it could not be
kept open either for the purposes of navigation or drainage, without constant cleansing
from both mud and weeds. The navigation to Lincoln, which is now only sufficient for
the passage of small craft, was attempted to be improved in the reign of Henry VII. by
Mayhave Hake of Graveling, who brought with him from Flanders fourteen masons and
labourers, to make a proper sluice and dam near the town of Boston. Mayhave Hake
received four shillings a day, the masons and stone hewers five shillings per week, and the
labourers four. The iron work required was made at Calais: among the items mentioned
for making this sluice were, small cramps and large, chains, hookes, bolts, scherys, maunds,
pannes, troughs, water scoops; and the price of the iron seems to have been two pence per
538
BOOK I
HISTORY OF ENGINEERING.
.
pound. After the work was completed, the engineer received in addition to his pay the
reward of fifty pounds.
To the north, and north-east of the Wetham, lie other large fenny districts, called Wild-
more Fen, West and East Fens; these are drained by an outfall, at Wainfleet Haven.
No general survey having been made during the middle ages, or any of the levels
properly taken, the country comprised within this great fenny district was but very
imperfectly drained. All the sluices were much too small, and the water courses so confined
that they could not carry away the superabundant waters to the sea. The commissioners
appear generally to have been guided by the wishes of the inhabitants of the particular
district where any inquiry was instituted, and they were often misled by either the pre-
judice or ignorance of the engineers consulted.
In the summer time there is so much deposit at the mouths of the several rivers or
washes, that the floods of winter cannot scour it away, though these often pour down in
such abundance that they over-ride the gates, and flow over the fens.
At the latter end of the last century considerable attention was paid to this district, and
vast sums of money expended for its improvement. Deeping Fen, which was drained by
three wind engines above Spalding, where the waters were lifted into the river Welland,
has now a deep canal cut, which conveys them into the Witham, below Boston.
The fen which extends from Tattershall to Lincoln has been greatly improved by
embanking and draining, under an act passed in the year 1787, and a new cut has been
made from Bishop Bridge to the Humber, for the drainage of the Ancholme district. The
Wildmore, East, and West Fens have outlets at Anton's Gowt, and Maudfoster; one 2 miles
above Boston, the other a little below it; these are consequently more effectually drained;
besides which, there is a cut from Midlam Drain at Swinecoat's inclosure, which continues
for 11 miles, with a fall of from 3 to 4 inches per mile, and for 13 miles with little more
than 2 inches per mile during neap tides.
Catch-water drains have been made, which skirt the high lands near the Witham, in
Coningsby, and receive all the waters that can be collected; the locks are so constructed
that the navigation is not impeded.
The Bedford Level. Mr. Samuel Wells published in 1830, in two octavo volumes, a
complete history, accompanied by a map, of this singularly interesting district.
The great fen comprehends the low lands on each side of the bay called the Wash, and is
about 60 miles in length, and from 20 to 30 in breadth.
The area of the Bedford Level contains about 530 square miles, or 340,000 English
acres, and on the east are the high lands of Norfolk, Suffolk and the wolds of Lincoln,
which consist of chalk: westward the high grounds are composed of sandstone and oolite,
and the substratum of the level is alluvial marle or sand, formed by deposition of the
upland waters, wherever met by the tide. This deposit, when its accumulation is above the
level of neap tides, forms a salt marsh, only overflowed by spring tides: when the surface
is elevated, by vegetation partially intercepting the sediment of the upland streams, it then
becomes fen, through which the rivers are constantly forming new channels.
Eleven rivers bring off the waters from the high lands, and form the natural drainage;
these are the Witham, the Glen, the Welland, the Nene, the Cam, the Great Ouse, the Lark,
the Brandon or Little Ouse, the Stoke, and the Wessey. All these are collected into four
outfalls, viz. the Witham, the Welland, the Nene, and the Ouse. History tells us that the
Romans commenced the drainage of this highly productive soil, and formed embankments
still visible at Wisbeach and Lynn, and in the Carr dyke, which extends from Peterborough
to Lincoln. Around Horsey, near Stand Ground, Erith, Bodsey, and Worlich, numerous
lines of forts or stations may be still traced.
In the reign of Henry VIII. an act was passed for regulating the commissioners of
sewers, but it specifies no powers for making new drains; other acts were passed in the
reign of Elizabeth, in 1572, and five years later; but in the forty-third of Elizabeth, 1600,
a general drainage act was passed which extended over all the marshes and drowned lands
of England.
During the reign of James I. the crown lands were taxed for the purpose of drainage,
and two commissioners were appointed to treat with the parties interested: Richard Atkins
was employed to bore the fens 11 feet deep; and a plan of drainage was laid down, by
forming a new channel for the Nene, from the town of March to Salter's Lode. Also to
cut straight the channel from Ouse to Erith, where the Ouse at low water was 10 feet
below the soil of the fens. The first of these is now called Popham's Eau, and the latter
the Bedford River. Land drained under Hayward's survey, made at that time, amounted
to 307,242 acres.
Sir John Popham, the Lord Chief Justice, and others, undertook, in 1605, to drain all
the fens between the Ouse and the Deeping, and were to retain for their trouble and outlay
130,000 acres. Popham's Eau, which was executed under Atkins's direction upon an en-
larged scale, was opened in 1606: seven years afterwards the banks yielded to a very high
tide, and considerable damage was done to them, to repair which cost 40,000l.
CHAP. VIII.
539
BRITAIN.
In the year 1631, Sir Nicholas Vermuyden was consulted upon the subject, and his first
work in England was to complete the embankment of the Dagenham marshes; after which
he drained Hatfield Chase.
Ninety-five thousand acres were to be given as a reward for draining the great level,
which was undertaken by a company of adventurers, with the Earl of Bedford at their head,
he at that time possessing 20,000 acres in Thorney and Wittlesey.
The works were entrusted to Vermuyden, and carried into effect in the following order:
The old Bedford river, 21 miles in length, and 70 feet in width, was improved from Erith
to Salter's Lode; same cut from Feltwell in Norfolk to the river Ouse; Sandy's Cut, near
Ely, 2 miles in length, and 40 feet in width; Bevill's Leam, 10 miles long, and 40 feet in
width, from Wittlesey Mere to Guyhorn; Morton's Leam; Peakirk Drain, 10 miles long
and 17 feet wide; New South Eau, from Crowland to Clowes' Crop; Hell's Cut, near
Peterborough, 2 miles long and 50 feet wide; Shire Drain, from Clowes' Crop to Tyd and
the sea; two sluices on the Shire drain; a clow or clough at Clowes' Cross, a kind of
sluice, in which the aperture is closed by a sliding board in the manner of a porte coulise
a great sasse, or navigable sluice, through which any thing could pass at pleasure, at the end
of the well creek at Salter's Lode; another stone sluice at the mouth of the Bedford
river; a sluice at Erith; a larger one at the Horse Shoe, below Wisbeach, to keep the tide
out of Morton's Leam.
In the year 1635 a charter of corporation was granted to the Earl of Bedford and others,
and the work having been declared complete, the 95,000 acres were set out by his Majesty's
surveyor, which were, however, only summer lands.
The law by which this allotment was made was reversed, and the Earl of Bedford died
in 1641, the victim of disappointment.
Vermuyden divided the fens into the North, Middle, and South Levels; the space between
the Welland and Nene was called the North Level; and the first of these rivers was pro-
tected by a bank 70 feet wide at the base, and 80 feet high. The Middle Level eastward of
the Nene, was protected by Stand Ground Sluice; and the waters of the Ouse were
confined for some distance by a bank 60 feet wide at the base, 10 feet at the top, and 8 feet
in height. In the South Level a new river channel was made. 120 feet in width, and 10 feet
in depth, with sluices at each end.
Vermuyden, who had studied in Holland, seems entirely to have mistaken the nature of
the English fen district, his whole scheme being directed to keep out the sea, sluices
being placed at the ends of all his canals, as well as those of the natural rivers, for this
purpose. His object should have been, by raising the embankments of the great drains,
to allow the tidal waters to flow freely up them, and thereby prevent the mouths of
natural and artificial outlets from being choked up.
The sea never rises above a certain known level, and banks may be always formed to keep it
out; in these districts there is more to be dreaded from the freshes after heavy rains, and
to collect and allow them a free passage into the ocean is the most important consideration.
The passages or drains should be cut as straight as possible, the current being regulated by
the declivity of the bed, and this will be greater as the line is shorter: 3 or 4 inches per
mile constitutes a moderate current; consequently if the distance is doubled with the same
fall, scarcely any current is obtained. All obstacles, as sluices, which prevent the tide
entering or the drainage water from freely passing off, should be avoided. Three inches
fall per mile makes a slow movement, 4 inches a moderate velocity, and sufficient for all
draining operations, so that any sill laid down at the mouth of a river, 3 feet above the
proper level, will have the effect, where the fall is 3 inches to a mile, of obstructing the
natural drainage for 12 miles above it. A drainage outlet obstructed by sand banks has
the same effect, the fall being lessened in consequence of the deposit at the mouth. Free
ingress should always be given to tidal water, and the banks of the river raised sufficiently
high to obtain a good and perfect fall, and the course should be as straight as circumstances
will allow, that none of the advantages be lost. An increased downfall, as well as tidal
water, may be also rendered efficacious in removing old sand banks, and is the best method
of scouring a harbour..
The Eau Branch cut, opened in 1821, and excavated under the direction of Mr. Rennie,
was one of the greatest improvements effected in this district: its cost was 33,000 pounds;
and the first winter it was opened the river channel from Denver Sluice to Lynn was scoured
5 feet, since which time it has gradually deepened itself nearly 15 feet on an average: all ·
the outfall sluices on each side of the river, and the beds of the drains have been lowered,
and the windmills used are no longer required.
This was originally projected by Nathaniel Kinderley, about 1720, and was intended to
conduct the Ouse by a direct cut from Eau Bank to Lynn, a distance of only 2 miles,
instead of allowing it to flow 5 miles. The tide in Eau Bank flows three hours, and rises
in that time 15 feet; thus leaving nine hours' ebb.
The Nene Outfall is a new tidal channel, carried through the light sands which border
the Lincolnshire coast; that portion which is artificially formed commences about 6 miles
540
BOOK I,
HISTORY OF ENGINEERING.
from Wisbeach, near Buckworth sluice, and extends a distance of 6 miles to Crabhole,
from which place a natural channel 1 mile in length opens into the German Ocean at
Wisbeck Eye.
The excavation was commenced under Mr. Rennie's direction in August, 1827, when
the old channel was closed up, and the course of the new river became deepened 12 feet
and upwards by the scour of the tidal current, the sides being secured by a thick coating of
stones.
The breadth of the bottom of the river is 200 feet at the lower end, and 140 feet at the
upper, near Kinderley Cut; the depth from the surface of the ground adjacent to the bed
of the river is 24 feet throughout, and the width at the top varies from 200 to 300 feet.
An ordinary spring tide rises 22 feet at the lower extremity, and 18 feet at Kenderley Cut
junction.
Over the channel at Sutton wash a bridge has been constructed, and an embankment
carried across the estuary to Cross Keys in Norfolk. 1500 acres of land embanked from
the sea are under cultivation, and 6000 more are rapidly becoming fit for the same purpose.
The water in the new channel ebbs out every day 10 feet lower than formerly, opposite
the South Holland and North Level sluices, which are outlets for 100,000 acres of land,
lying between the Nene and Welland, now efficiently drained without the aid of windmills
or steam engines.
The North Level, containing 48,000 acres, benefitted materially from this work; a new
sluice was built for the discharge of the waters into the Nene Outfall, at a level 8 feet
below that which conveyed them into the old channel of the river. The width of the
waterway of the old sluice was only 17 feet; the new one was increased to 36 feet.
A new main drain 84 miles in length was made from the last mentioned sluice to Clowes'
Cross, 8 feet deeper, and of a capacity six times greater than the old one; the declivity of
the bed is throughout 4 inches per mile.
From Clowes' Cross the new drainage is turned into the two channels called New South
Eau, and the New Wryde, which now receive the waters from the whole of the North
Level.
The Wisbeck district contains 15000 acres, and benefits materially from the Nene Out-
fall all the drains are navigable, which was not the case with with the old ones. The
total expense of the Nene Outfall was 200,000l., and that of the North Level drains about
150,000l.
The Nene Outfall, projected by Mr. Rennie, was completed by Mr. Telford and Sir John
Rennie; and the scheme of the North Level drainage was entirely the work of Mr. Telford,
who first made use of the natural outfall, to which no previous attention had been paid,
and removed all the drains and sluices which acted as obstructions; he also returned to the
better principle of admitting the influx and reflux of the tide; thus maintaining the channel
clear by the constant scouring. The fall given in some instances is 4 inches, and in others
3 inches per mile, and the banks or side slopes have a fall of 2 to 1.
A catch-water drain was executed by Mr. Rennie, for the purpose of draining the
Wildmore Fen, which had no outlet, and comprised upwards of 75,000 acres.
The lower
part of this fen was a watery waste, containing 15,000 acres; it is now inhabited, and its
land highly productive. The whole cost of this work was 650,000l. The wind-
mills and their machinery erected by the Dutch engineer to lift the water from the lower
ditches into the upper, that it might pass off to the sea, are no longer necessary, and the
annual expense of maintaining them is consequently saved.
All the outfalls of the rivers of this district were affected by the tides, and particularly
by those which flowed up the Ouse: at Lynn, where the water was always thick and
muddy, a large proportion of silt was left behind. In deepening the Wisbeach river at
the beginning of the seventeenth century, beds of stones 8 or 10 feet below the then bottom
was arrived at by the workmen in sinking for a sluice, and in it were the remains of several
boats.
These stoppages must, at a very early period, have produced a most unhealthy stagna-
tion of waters, and a vast deposit. On sinking the foundation of Skyrbeck Sluice, near
Boston, at a depth of 16 feet, a smith's forge was discovered, with all the tools, horse-shoes,
and various other things. The country about the monastery of Croyland is described before
any material change was made by draining, in the history of the religious hermit who first
resided there; the writer of the life of S. Guthlake has beautifully personified all the
demons which haunt a morass; and this of Croyland must have been most abundant in
whatever could render it wretched. When the saint awoke in the dead of the night, he
discovered his wooden cell full of black troops of unclean spirits, which crept in under the
door, and at chinks and holes, and coming in, both out of the sky, and from the earth,
filled the air as it were with dark clouds. In their looks they were cruel, and of form
terrible, having great heads, long necks, lean faces, pale countenances, ill-favoured beards,
rough ears, wrinkled foreheads, fierce eyes, stinking mouths, teeth like horses, spitting fire
out of their throats, crooked jaws, broad lips, loud voices, burnt hair, great cheeks, high
CHAP. VIII.
541
BRITAIN.
breasts, rugged thighs, bunched knees, bended legs, swollen ankles, preposterous feet, open
mouths, and hoarse cries. A vivid and too correct a description of a population, born and
dwelling in such a pestilential marsh, and one which should animate not only a govern-
ment, but every individual of the community to lend his aid in reversing it ought to be
felt as a stain upon the national philanthropy that many portions of the saint's dream are
still realities.
:
In the time of Edward the Confessor, a firm causeway was made of wood and gravel
across Deeping Fen, which reached from the town of that name to Spalding, for the use
of passengers, and is described by Ingulphus as most sumptuous and valuable; various
earth-banks were also thrown up by the Saxons to protect their habitations from inun-
dation; but nothing appears to have been done by that people upon an extensive scale in
the way of draining. The Romans are supposed to have constructed the Carr or Caer dyke,
which acts as a vast catch-water drain to the whole North Level, and which would, if in a
good condition, drain upwards of 12,000 acres. This great work extended originally from the
river Nene, below Peterborough, to the city of Lincoln, and also to the Trent at Torksey.
The fens adjoining the Wash are said now to contain 217 square miles, between the hills
on the south and south-east, and the rivers Ouse and Cam; 394 square miles between
these rivers and the Nene; 389 square miles between the Nene and Glen rivers, 414 square
miles between the Glen and Old Witham; and 201 square miles between the Old Witham
and Tetney drain; making a total of 1615 square miles, or 1,033,360 acres.
The fens are generally lower the more distant they are from the sea: the difficulty of
drawing off the water is therefore considerably increased: but this has been most admirably
effected, by paying due attention to the outfall, by preventing the upland waters from
running or spreading over them, collecting it in catch-water drains, discharging it in the
best manner, and always taking for a cut the shortest possible course towards the sea.
Much has been done to effect the drawing off the waters by improving the outfalls; but
to get rid of it entirely, mechanical means are requisite. The Dutch mills pumped up
considerable quantities; but not being regular in their movements, the steam engine
has been generally adopted; at Deeping Fen, near Spalding, one supplies the place of forty-
four windmills.
It is generally found necessary to raise the water from 3 to 4 feet; and for this purpose
scooped wheels are made use of, the float-boards of which dip 5 feet below the water's sur-
face, or 6 feet 6 inches below the land. The main drains are twelve inches deeper than the
wheel track, and the scoop-wheels are made of cast iron, with wooden float-boards, like the
undershot wheel of a water-mill; but with this difference, that they are moved by steam
power, and lift the water. The float-boards move on a trough of masonry, into which they
fit exactly, the lower end being open to the main drain, and the upper communicating with
the river, which is kept out when the wheel is not at work by lock gates. The float-
boards do not radiate from the centre of the wheel, but form an angle of 45 degrees with the
horizon, at the point where they deliver the water. The diameter of the wheels is so con-
trived, that the surface of the water in the outfall river is never more in height than 4 or
5 feet above its axis, which prevents the water passing over the float-boards, and finding its
way back again. The speed given to the circumference of these wheels is about 6 feet per
second.
At Pode Hole, in Deeping Fen, a steam-engine of eighty horse power, and a water wheel
of 28 feet diameter, with the float-boards of 5 feet 6 inches in depth, and 5 feet wide, moving
at the rate of 6 feet per second, discharged 165 cubic feet of water per second; the float-
boards dipping 3 feet 4 inches, and the average consumption of coal being 10 pounds per
horse power per hour. The expense annually in this district does not exceed 2s. 6d. per
acre, independent of the first cost of the engine and machinery attached, which may be cal-
culated at 20s. per acre.
Deeping Fen, consisting of 25,000 acres, has two steam engines of about 140 horse power.
Marchwest Fen, containing about 3600 acres, has a 40 horse engine: the same power is
applied to Misterton Sas.
Littleport Fen, near Ely, has two steam engines of 110 horse power, to drain 28,000 acres :
there were formerly seventy-five windmills. The scoop-wheel is 35 feet in diameter, and
weighs 54 tons; the pinion is 4 feet in diameter, weighs 33 cwt., and makes thirteen revo-
lutions in a minute: when the tide is high, this pinion works into a wheel 24 feet in
diameter, having internal teeth; the float-boards on the scoop-wheel then move with a ve-
locity of 212 feet per minute, and discharge in that time 3519 cubic feet of water. When
the tide is low, the pinion is made to work in another wheel 16 feet in diameter, which has
external teeth; the float-boards then move at the rate of 318 feet per minute, and deliver
5278 cubic feet of water in that time.
Middle Fen, near Soham, has 7000 acres drained by an engine of 60 horse power, and
Waterbeach Level has a similar engine to drain 5600 acres. Öther engines are employed
in various districts; and it is surprising that so small a quantity of mechanical power is
found adequate to drain such an extent of marshy land so effectually. It has been estimated
542
BOOK I
HISTORY OF ENGINEERING.
that on an average upon every 1000 acres, 7,260,000 cubic feet of water are annually raised
and carried off; and a ten-horse steam engine performs this work in less than 232 hours.
The quantity of rain is computed at 26 inches; and if 3 inches fall in a month, allowing
1 inch or to be evaporated or absorbed, we shall have 7260 cube feet of water to the acre
to be carried away by means of machinery, before the land can be rendered fertile.
The high lands which pour their waters over these fens comprise not less than 12,000
acres, and during a rainy season, as much as 40,000 cubic feet of water is sent down from
them per minute, which is considerably augmented by that from the fens.
This vast
quantity was impeded in its passage to the sea by the narrowness of the three sluices through
which it had to pass, viz. the Austins, which had an opening of 14 feet, Maudfoster, 13 feet,
and Tichtoft, 4 feet. When the late Mr. Rennie was called in to survey and improve this
extensive district, he commenced his operations upon a bold and noble scale: he shortened
the course of all the rivers, made new cuts and drains in various directions, gave their beds
an inclination of from 3 to 5 inches in a mile, formed a catch-water drain at the skirt of all
the high grounds around the fens, and conducted the upland waters by an inclined bed of
6 inches to a mile, through a separate outlet into the head of the Eau Bank cut, into which
all the drainage waters were conducted.
Thus the Great Level, as it is commonly called, is now more effectually drained, and once
more redeemed from the state into which it had fallen after the dissolution of the religious
houses in the time of Henry VIII., whose fraternities had paid great attention to keeping
open the passages for the water, and the repair of the several banks, although not sufficiently
aware of the advantages arising from opening and cleansing the natural outfalls of the drains,
which the daily flowing of the tides choked up. It would be exceedingly advantageous if
such a level could be placed under one direction, and not governed by persons interested in
one district alone, and that, perhaps, the most remote from the point at which the waters
are discharged into the ocean: no management could be effectual or beneficial to the whole
body of proprietors, but one which should be established upon a system embracing the
entire district to be drained.
Accurate maps and levels, meteorological observations, and the geological structure of the
different portions of the district, together with a knowledge of the machinery in use for
every kind of hydraulic work, should be acquired by the board, or the individual charged
with so important and often costly work.
In the middle ages, before science was called in to assist at these operations, the rural
engineer was content to confine the rivers with embankments of earth, raised 5 feet above
the level of the land adjoining: these had sometimes a base of 18 feet, and a surface at top
the same as the height: others with the same base and 6 feet high, had a width of 12 feet
at the top, and these were calculated to keep out water in almost any situation: towards
the water they were usually clayed to 11 feet in thickness, not only up the side, but over the
entire top.
Sea banks were made 12 feet in breadth at top, and carried up 2 feet in height above the
highest tides: these were sloped and turfed, and strengthened in various places with stakes,
piles, and timber: sometimes rows of piles were driven parallel to the river at distances of
2 and 3 feet apart; and after uniting their heads by a plank, or weaving rods around them,
the parallel spaces between were filled up with chalk or some other hard substance: thus
the side of a wall towards a tidal river represented so many steps of piling and chalk, which
frequently became more tightly bound together by the sea-weed. At times this method
of defending the shore would be swept away altogether by the force of the tides when
acted on by the winds, and a frightful breach would be the result, inundating extensive
districts, and destroying property to a great amount.
Banks were sometimes made of sand. with twigs of the broom placed in horizontal layers,
which, when properly clayed on the surface, and turfed, were found to stand in many
situations remarkably well.
Loughs Swilly and Foyle, in Ireland. The first of these lakes has a communication with
the Irish Channel by a narrow course. above which it spreads over a considerable tract of
land, and afterwards narrowing again its breadth, joins the river Foyle about 4 miles above
the town of Londonderry, where the channel is deep enough to allow the navigation of vessels
of 600 tons burthen.
Lands of 25,000 acres, overspread by the tide, all alluvial, and gradually deposited, were
undertaken to be reclaimed under the direction of Mr. Macneil, by the construction of a
sea wall 14 miles in length.
Lough Swilly, from its width at the mouth, is more subject to be acted upon by the
winds than Lough Foyle, and the highest tides rise 18 feet: here the first embankments were
made, which reclaimed about 2000 acres. They were commenced as follows: -the soundings
being accurately taken, the wall was set out in the most favourable position; a tide gauge
was established, on which was permanently marked the height of high and low water. The
slopes given to the embankment varied on the side towards the sea from 3 and 4 to 1, and
CHAP. VIII.
543
BRITAIN.
on the land side from 2 to 1. Culverts, 4 feet in diameter, founded on piles and cross
timbers, with sluices and flood-gates on each side the wall, served to let out the water when
the wall was completed, the gates being put at the lowest level of spring tides. The wing
walls of these culverts, built of rubble masonry, were founded on a bed of concrete; these
flood gates can be used either to admit the tidal waters for the purposes of irrigation, or
for the passage of the land water; to carry away the silt that may accumulate in the channel
catchwater drains are puddled, which collect the land waters on all sides, and convey them
to the sluices with a proper fall.
The embankment contains within it a bed of puddle, 4 feet 6 inches in width at bottom,
and 3 feet at top, and on the water side is placed a strong facing of fascines 6 feet thick at
bottom, and 4 feet at top, embedded in the soil, and laid in an oblique direction, with a dip
towards the land side; they are all held down by irons, which pass at right angles through
their entire height. On the land side they are covered with sods of turf; the cost of this
kind of embankment, including the sluices and puddle in the centre, is about 12 pounds per
yard run.
Drainage of Toums.- Much has lately been written on the value of manures, and attention
has been directed to the great waste which is permitted, by the sewers of the metropolis
discharging their contents into the Thames, to be carried away by the current and the
tide, injuring the quality of the water, and rendering the district through which it passes
unhealthy; numerous plans have been suggested, by which much that is valuable to the
agriculturist could be saved and made serviceable to the growth and improvement of vege-
tation. In Paris, where there are no sewers, every means is taken to prevent waste of that
which is important to the wine-grower, and a considerable trade is carried on in the capital
by collecting all that will serve for manure, and arrangements made to convey it to the most
southern provinces. A vast portion of London might have its sewage directed into large
reservoirs in the marshes, at a distance on each side of the Thames, where the contents
might be separated and dispersed throughout the neighbouring district, or be conveyed by
water to any part of the empire in need of it. The expense of such a scheme would be so
small, compared with the immense advantages, that it is surprising public attention has not
been directed to it; it has been computed that 1,000,000 tons of manure might easily be
obtained annually, the value of which would be very considerable.
To carry out such a system, the property of individuals would perhaps be interfered with,
and objections would be made to changing the character of the sewers; the most economical
method is that of having movable casks placed in the vaults under the pavement, into
which all the pipes of the dwelling might drain; and if these casks were arranged so that
one was devoted to retain the solid matters and the other the liquid, or pipes laid to
carry off the latter into the sewer, the valuable portions useful for manure could be easily
carted away as often as it was found convenient. Such is the method practised by the
company in Paris, and no inconvenience or annoyance is found to arise from it; the casks
are the property of the company, who keep them in an excellent state of repair.
Before the fire of London, little or no attention was paid to carrying off the surplus
waters from the city; it was suffered either to run upon the surface, or through the channels
which the small streams had formed. After that calamity, it was enacted "that the
number and places for all common sewers, drains, and vaults, should be directed by some
one or more appointed under the common seal," and from this period we may date the
authority of the commissioners of sewers in the metropolis; for some of the larger towns in
the kingdom, similar enactments were obtained soon after.
Although the sewers in the city exceed in length 15 miles, it is still not thoroughly
drained; one of the best constructed is that which carries off the waters from Moorfields,
which is 7 feet in width, and 8 feet 6 inches in height. The other sewers vary in their
dimensions; some are 4 feet 3 inches high, and 2 feet 3 inches in width, and others 5 feet by
3 feet, but none are made less than will enable men to enter and thoroughly cleanse them.
The whole drainage of the city is into the Thames.
Westminster and a portion of Middlesex is under another commission, who have the
control over 134 miles of arched or covered sewers, of which 93 are constructed with curved,
the rest with flat bottoms.
Holborn and Finsbury districts comprise the northern parts of the metropolis.
The Tower Hamlets commission extends over 45 miles of sewer, and since the year
1830, upwards of 11 miles of new sewers have been built under its direction.
Surrey and Kent commission takes in the southern side of the metropolis; since the year
1820, nearly 21 miles of sewer have been constructed; previously the greater portion was
only a surface drainage.
The Regent Street has a commission which manages its drainage, and there is so general
a desire throughout the metropolis to have all the sewers covered or inclosed, that the open
ones are fast disappearing, although the commissioners have no power whatever to make
new covered sewers, by which the effluvia arising from them, so prejudicial to health, shall
be confined.
544
BOOK I.
HISTORY OF ENGINEERING.
There is also a great want of uniformity in the practice of the several commissions
and their officers, which requires immediate improvement; among other points none
is more important than the form given to the sewer, which differs in all the various
districts. That used in Westminster has a curved bottom, perpendicular sides, and a semicir-
cular top; that in Finsbury is the section of an egg, with the small end downwards. For
every foot of the Westminster of the first class, 261 bricks would be required, and for the
egg-shaped only 175, besides which for the latter there would be less digging. Others
are built nearly cylindrical.
Recently, however, the egg-shaped sewer has been introduced by the commissioners for
Westminster, with the large end downwards, which is certainly not the right position either
for strength or utility; with the small end downwards, and carefully constructed, there
would be less chance of compression or of the sides becoming foul.
Cast-iron inverts, bedded in lengths, are often used where the foundations are sandy or of
a loose nature; they contain 8 or 9 feet superficial, are well adapted to take an extended
bearing, and sustain the brickwork put upon them.
The outlets of many of the sewers which discharge into the Thames are protected
by self-acting valves, which exclude the tidal water, and, in some instances, pen-stocks,
under the direction and management of a resident attendant, are added, for still greater
security.
Supply of towns with water.—The historian Stow most justly considered that, after the
requisite arrangements for the defence of a city, the next subject requiring attention was a
plentiful supply of good and wholesome water; and it appears that London, at the time of
the Conquest, and for 200 years afterwards, received its water from the Thames, from the
river of the Wells on the west, the stream which ran through Walbrook, and another
through the ward of Langbourn, on the east. The suburbs were supplied by the Old-
bourne, which fell into a stream called Wells, and numerous common wells, as the Holy,
Clements, Clarks, Skinners, Fags, Tode, Loder, and Rads, well. In West Smithfield was
a sheet of water called Horse Pool, and numerous wells were scattered over other dis-
tricts.
These various streams and wells were constantly cleansed by the authorities of the city
of London, but not being sufficient for the uses of the inhabitants, Henry III. granted to
the citizens and their successors the liberty to convey water from the town of Tyburn to
the city by pipes made of lead: and the first leaden cistern, built round with stone, called
the Great Conduit in Westcheap, was erected in the year 1285; the whole length of leaden
pipe then laid down from Paddington to the cross in Cheap was 1096 rods.
In the year 1401 a cistern was formed at Cornhill, and 22 years after bosses of water
were made at Billingsgate, near Paul's Wharf; about 10 years after, Newgate and Ludgate
gaols were supplied. Other conduits were afterwards established, at the expense of the
city, and numerous leaden pipes laid down. These were annually visited by the Lord
Mayor and wardens of the twelve companies; "they hunted the hare and dined at the head
of the Conduit, and after dinner they hunted the fox, finishing the day with blowing of horns
and merry-making.”
A great portion of the citizens had, however, no other means of procuring this important
article of domestic comfort than by fetching it from the Thames by the lanes that led
down to the water-side. These lanes, in the course of time, were walled up at the end by
those who occupied dwellings near, which became so great a grievance that an inquisition
was established, several presentments were made by persons appointed out of the wards to
inquire into the matter, and the evil complained of was considerably abated.
In the year 1582, Peter Morice, a Dutchman, showed the citizens that he could, “ with
pipes of lead and a most artificial forcier, standing near London Bridge, convey water into
men's houses." This "forcier" is described by Stow as the first mill made to supply
the city with Thames water, and he adds that it remained a long time the property of a
Mr. Morice." The houses in and about Gracechurch Street were the first benefited by
this "new device," and the water was remarkable for its clearness. Six years afterwards,
Bevis Bulman set up another forcier near Broken Wharf, and conveyed the water to the
neighbouring houses. In the year 1610, pipes of wood and stone were laid down by
Thomas Hayes, to supply Thames water to the conduit at Aldersgate.
Such were the only means adopted for the supplying water to the metropolis until the
year 1608, when Mr. Middleton commenced his important work of bringing the New River
from Chadwell and Amwell to Islington. Stow tells us that whilst the work was in pro-
gress, he frequently, by favour of the owner, did divers times ride and see it, and diligently
observed that admirable art, pains, and industry were bestowed for the passage of it, by
reason that all the grounds were not of a like nature, some being oozy and very muddy,
others again as stiff, craggy, and stony. The depth of the trench in some places descended
full 30 feet, if not more, whereas in other places it required a sprightful art again to mount
it over the valley, in a trough between a couple of hills, and the trough all the while borne
up by wooden arches, some of them fixed in the ground very deep, and rising in height
CHAP. VIII.
545
BRITAIN.
above 23 feet: being brought to the intended cistern, on Michaelmas day, 1613, Sir
Thomas Middleton, the brother of Mr. Hugh Middleton, being Lord Mayor, rode with
many worthy aldermen to see the first opening of the river into the cistern. Sixty of the
labourers were present with their tools, all habited well, and wearing green Monmouth
caps; the foreman delivered a speech, which embodied in verse an account of the obstacles
against which the projector had contended, and made honourable mention of the overseer,
the clerk, the mathematician, the master of the timber-work, the measurer, the bricklayer,
the engineer, the borer, and the pavior: after this was delivered, the whole went in proces-
sion to the floodgates, which when opened, allowed the stream to flow gallantly into the
cistern, amidst the sounds of drums and trumpets. Wooden mains were at first laid
down in the streets, and from them leaden pipes conveyed the water to the houses.
Stow also tells us that as early as 1580 a person of the name of Russel propounded to
bring Istelworth or the Uxbridge river to London; and that by a geometrical instrument
he laid this scheme before Lord Burgley, whom he told in his paper, " that he moved this
not by skill or art of learning, which he did not profess, but only by an assured and infallibly
grounded consideration taken by the difference of the height of the said Uxbridge river at
the place or head appointed and the river Thames, right below the same towards Lalam ;
which was, he said, to be compared to the difference between the upper end of Holborn,
which was a point of the new water, and Thames right against it below the Strand. Which
thing rightly noted did show the easy possibility, and sufficient current to that place with
discreet leading; for that the country lay well for that purpose, yet very dark, and seeming
hard to all that took not with them the consideration aforesaid. So," added he, "it hath
pleased God to bestow this blessing, and to appoint me an instrument, in a time best
pleasing unto his will, showing that in all ages, neither power, wisdom, learning, or
strength can perform an act until the time appointed, and the instrument to effect it."
Lord Burgley was so pleased with the project, that "he drew with his own hand on
Russel's paper the river and the town adjacent, describing the river Istelworth and another
river, how they fell into Uxbridge river, and how that run by St. Giles."
In the year 1591, the same historian tells us, that Frederick Genebelli, an Italian, pro-
posed to establish water-works in London, which should cleanse all the filthy ditches, and
afford to the inhabitants a plentiful supply of wholesome water.
The works before alluded to, and first established at London Bridge by Peter Maurice,
were erected near the first arch on the north side, after a lease had been granted him by
the city. They consisted of a water-wheel worked by means of the tide; by this motion
a number of force-pumps raised the necessary quantity of water to the top of a wooden
building, where a cistern, elevated 120 feet, allowed it to flow by numerous leaden pipes
into the dwelling-houses of Thames, Gracechurch, and New Fish Streets, as far also as the
Standard in Cornhill: from the latter place it was again conducted by four other leaden
pipes to Bishopsgate, Aldgate, the Bridge, and Wallbrook.
The highest point at which the water was delivered was the Standard in Cornhill; and
the quantity thrown up by this first simple machinery of Maurice was estimated at
3,170,000 imperial barrels per annum, or an average quantity of 216 gallons per minute;
the wheel working 16 pumps, each 7 inches in diameter, and having a stroke of 30.
chinery of a similar kind was put up in the other arches, and also on the Southwark side
of the river, for the use of the inhabitants of that district.
Ma-
Mr. Beighton, in the Philosophical Transactions, gives us some account of the state of
these works as they existed in the year 1731. At that time the water-wheels which
drove the pumps were placed under the arches of the bridge, and moved by the current
of the stream; the dimensions were, 19 feet for the length of the axle, the diameter
of which was 3 feet; there were eight rings to each, four arms, twenty-six floats, the
length of which was 14 feet, and the depth 18 inches. These axles turned on two
gudgeons in brasses, or two large levers, which were placed in a horizontal position, and
therefore supported the weight of the wheel, which, by means of the levers, might be
made to rise or fall with the tide in the following manner. The levers were 16 feet
long, divided by the fulcrum at 10 feet from one end and 6 feet from the other. At the
extremity was a sector or arc of a circle, described from the fulcrum of the lever, and to
the bottom of this arch was fixed a long triple chain, similar to that of a watch ; but the
links were arched to a circle of 12 inches in diameter, with notches or teeth to take hold of
the leaves of a pinion of cast-iron, 10 inches in diameter, with eight teeth, moving on an
axis, fixed up over the arch at a considerable height; the chain went up to the pinion and
turned over it. To the loose end of this chain was attached a large weight, to counterpoise
the great weight of the water-wheel, which prevented the chain from sliding on the pinion.
On the same axis as the pinion was a cog-wheel 6 feet in diameter, with forty-eight cogs.
To this was applied a trundle or pinion with six teeth; and upon the same axis was fixed a
second cog-wheel of fifty-one cogs, turned by a trundle of six rounds, on the axis of which
was a winch or windlass. The other lever was provided with a similar chain and wheel-
work; and the axis of the last mentioned trundle was prolonged until the two winches
N n
546
Book I.
HISTORY OF ENGINEERING.
nearly met, so that one man, with the two windlasses, raised or let down the wheel, as there
was occasion, the quantity of water within his power to raise being fifty tons, which was
more than the weight of the water-wheel.

E alina
Fig. 538.
WATER-WHEEL AT LONDON BRIDGE WORKS.
Near each end of the great axis of the water-wheel, a cog-wheel was fixed 8 feet in
diameter, with forty-four cogs, working into a trundle of 4 feet 6 inches in diameter, and
twenty rounds, whose axis or spindle was of cast-iron, 4 inches in diameter, lying in brasses,
supported by strong timber framing at each end.
As the fulcrum of the levers was in the line of the axis of the trundle, in whatever situation
the water-wheel was raised or let down, the great cog-wheel was always equidistant from
the trundle, and worked and geared with it.
A quadruple crank of cast-iron was attached to the end of the axis of the trundle, the
metal being 6 inches square; each of the necks was distant 12 inches from the centre of
motion; the gudgeons of the cranks were sustained on brasses at each end, by two head-
stocks, fastened down by caps. One end of the axis was placed close to that of the axis of
the trundle where it was 6 inches in diameter; at the other end was a slit: the crank ter-
minated in the same manner, and an iron wedge was fixed one half into the slit at the end
of the axis, and the other into that in the end of the crank, by which the axis turned the
crank about with it. To each of the four necks of the crank was united an iron spear or
rod, jointed at the upper end to its respective lever, and within 9 feet of the centre. The
levers were 24 feet long, moving on centres in the middle of their length, and supported by
the frame; at each end of each lever a rod was jointed, which descended into the pump-
barrel, the forcers being fastened to it. Each end of the four levers worked a quadruple
forcing-pump, which consisted of four cast-iron barrels or cylinders 4 feet 9 inches long, 7
inches bore above, and 9 inches below, where the valves were placed; the four barrels were
fastened by screwed flanches over four holes in a hollow trunk of cast-iron, which had four
valves in it; just over these holes, at the joining on of the bottom of the barrels, and at one
end of the hollow trunk, was a sucking pipe and grate touching the water, which supplied
all the four pumps alternately. To carry away the water which they forced out, there pro-
ceeded from the lower part of each pump-barrel a neck, turning upwards archways, whose
upper part was cast with a flanch, to screw up to the under side of another square trunk,
which received the necks of all the four barrels, which necks had bores of 7 inches in
diameter, and over the holes in the trunk communicating with them were placed four valves
at the jointings or flanches. The square forcing-trunk was cast with four bosses or pro-
tuberances, standing out against the valves, to give room for their opening and shutting;
and on the upper side of the trunk were four holes, stopped with plugs, to take out when
the valves required cleansing. One end of this trunk was stopped by a large plug, and to
the other the iron pipes were joined by flanches, through which the water was forced up 120
feet, or to any height or place required. In addition to this four-barrelled pump, there
was a similar one at the opposite ends of the levers. At the other end of the water-wheel
CHAP. VIII.
547
BRITAIN.
was placed work of a like kind, and, according to the calculation made by Mr. Beighton,
the effect was as follows:-
In the first arch next the city was one wheel, with double work of sixteen forcers.
In the third arch there were three wheels, with fifty-two forcers, and one revolution of
each wheel made two strokes and a fifth, so that one turn of the four wheels made 114
strokes.
When the river was in its best state the wheels went six times round in a minute, and
but four and a half at middle water.
The number of strokes then in a minute was six times 114, or 684. The 2 feet 6-inch
stroke in a 7-inch bore raising three gallons of water per minute, made the whole quantity
raised in that time 2052 gallons, or in the day 46,896 hogsheads were raised to the height
of 120 feet.
The power by which the wheels were moved was thus calculated:
column of water on a forcer 7 inches in diameter, and 120 feet in height,
7 x7=49 pounds average in a yard nearly.
40 yards high.
1960 pounds in one forcer.
8 forcers always lifting.
the weight of the
15680 pounds, the weight at one time on the engine.
This is equivalent to seven tons weight: then as the crank pulls the lever 3 feet from the
forcer, and 8.3 feet from the centre,
7 tons.
11.3
8.3)79·1(9.5 tons to the crank.
Wallower 2.2)9.5(4·3 tons on the trundle,
The spur-wheel
The radius of great wheel
4
10)17-2(1.72 tons.
20
The force of the floats 18 cwt. 14 lbs.
34.40 cwt
But, to allow friction and velocity, may be reckoned at 1½ tons.
The ladles or paddles, 14 feet long, 18 inches deep
The fall of water sometimes
22.4 square feet.
2.0 feet.
44.8
Contents in a cube foot
6 gallons.
Pounds to a gallon
268.8
10
112)2688(24 cwt.
The velocity of the water 4 feet in 21" of time,
21" 4 feet: 60": 685 feet per minute.
The quantity expended on the wheel, according to the velocity of the stream, was 1433
hogsheads per second, and the velocity of the wheel was to the velocity of the water
as 1 to 22″.
In the year 1767 it was discovered that the supply of water was diminished to 2716
hogsheads in the twelve hours. Mr. Smeaton was employed to make some improvements,
and he placed a machine in the fifth arch, considerably larger than either of the others.
The diameter of the water-wheel to the extremity of the floats
The diameter of ditto in the rings out and out
Width of the wheel or length of floats
-
Number of floats twenty-four, width of each
Diameter of spur-wheels
Number of cogs eighty, number in the lantern twenty-three.
Ft. In
32 O
27 0
15
6
4 6
14 O
Diameter of the water-
wheel gudgeons 7 inches, and the length of the cylindrical part 7 inches.
When the tide was low the water was forced up by the aid of a fire-engine, as they were
NN 2
548
Book I.
HISTORY OF ENGINEERING.
then called, to the top of the tower, 120 feet high, and in this condition the works remained
until the parliamentary inquiry of 1821, when it appeared that 29,516,333 hogsheads of
water per annum was supplied to 32,071 houses, which paid a rental for the same of
35,3581.
Smeaton also erected an atmospheric engine of ten horse-power to assist the wheels at
neap tides.
It is greatly to be regretted that no arrangement was then or has since been made
by the proprietors of small tenements for supplying their tenants with water; there is a
natural objection on their parts to pay the usual demand of the companies, which to
them would be a considerable item; but if it were rendered imperative that every small
dwelling should be supplied, there can be little doubt that the companies would lessen their
charge, and the landlord would be indemnified by an increased rent of a few shillings,
which would not be felt by the occupants; and efficient drainage for the surplus should
also be provided. The increasing luxuries of the middle classes require this attention to
the necessities of those who compose the next grade in the social system, and it is surely
not too much to ask for them the means by which the first claim to personal respect,
cleanliness, can be secured, and without which frequently the intellectual and moral health
is ruined.
Minor works were established during the seventeenth century for the supply of various
districts the Merchants' Waterworks had a windmill in Tottenham Court Fields, an over-
shot wheel worked by the common sewers in St. Martin's Lane, and another by that in
Hartshorn Lane. Each of these had 6-inch mains, from which smaller pipes branched off to
the neighbouring houses.
At Shadwell, a horse-wheel was put up in the year 1660, and two atmospheric engines
were subsequently erected, which drew water from the Thames, and supplied it to the
inhabitants of that district through two mains of 6 inches in diameter.
To the original
projector succeeded a company, which was incorporated in the reign of William and Mary.
Two of the earliest manufactured engines by Bolton and Watt were put up at these works,
and in the year 1808 they were purchased by the East London Company.
The York Buildings' Water-works were established at the bottom of Villiers Street, in
the Strand, in the year 1691. A horse-wheel was first employed to pump up the water
from the Thames; one of Savery's engines was afterwards introduced, for which one of
Newcomen's was substituted. About 1804, the company erected an engine of 70 horse
power, took up all the wooden pipes that had been previously used for the distribution of
water, and laid down cast-iron. Newcomen's engine is said to have raised daily 356,000
gallons to a height of 102 feet, or 3,137,000 barrels per annum.
West Ham Works, established in the year 1743, obtained their water from the river Lea
by means of a fire-engine of 6 horse power; they now form a portion of the East London.
The Banks-end Works, in Southwark, or Old Borough water-works, were founded in
the year 1756; and when London Bridge was rebuilt were purchased by Mr. Edwards,
and became the foundation of the present Southwark Water Company. Other works were
established at Rotherhithe, where a wheel was turned by the tide water collected in the
ditches, and at Lea Bridge, which were called the Hackney water-works.
The Lambeth Water-works were established in 1785, and in 1805 the South London
were commenced.
At present the metropolis is chiefly supplied with water by the New River, the
Chelsea, the Grand Junction, the West Middlesex, the Southwark, and the East London
Water Companies. The power made use of is universally the steam-engine; and if we con-
sider what is effected by the most economical of these engines, we shall not be surprised
at the quantity daily distributed in London. Taylor's engine at the United Mines is said
to have raised, in 1841, 92,500,000 pounds weight of water 1 foot high by each bushel of
coal consumed, and in the following year nearly 100,000,000. The bushel of coals weighed
94 pounds, so that a pound of coal raised 1,000,000 of pounds, or 16,000 cubic feet of
water, 1 foot high. It would require either a man to labour 4 hours or a horse of an
hour to perform the same quantity of work as a pound of coal so applied.
The New River Company is now the oldest remaining in the metropolis; to it was trans-
ferred by an act of parliament the London Bridge water-works, when the old bridge was
demolished. This work, projected and carried out by one individual, Sir Hugh Middleton,
as before observed, was commenced by an open canal 40 miles in length, into which was
collected various springs which rise near Ware and Amwell, in Hertfordshire. The dis-
tance of these springs from the metropolis is not more than 20 miles in a straight direction,
but the circuitous way by which they are conducted was preferred in order to obtain a
fall of 3 inches per mile throughout their whole course.
The timber aqueduct over the valley at Bush Hill, 660 feet in length, was removed in
the year 1785, and an earthen embankment substituted in lieu of it; the same change has
taken place with the open wooden trough at Hornsey and other places. After the water
has arrived at Stoke Newington, it is conducted for more than 200 yards by a subter
CHAP. VIII.
549
BRITAIN.
raneous tunnel; at Islington its width is about 14 feet 6 inches, and its average depth
4 feet 6 inches. Two hundred bridges were constructed in its varied course for the con-
venience of the proprietors of the adjoining lands. The supply from the Hertfordshire
springs being found inadequate to the demand of the company, a considerable addition was
obtained from the river Lea, on the banks of which is a sluice; and in order that the
guardians may know what quantity to let out, a guage is fixed across it, composed of a
large stone, under which the water flows out in a regular manner.
The first distribution of water, as we have seen, was by leaden pipes, which abundantly sup-
plied the conduits in various parts of the city; these were mostly destroyed during the
great fire; from them the inhabitants received their several quantities by the aid of water-
carriers. After the destruction of this system, a new arrangement was made to lay the water
on to the houses, and this was admirably accomplished by wooden pipes or mains, of elm
timber, and at the end of the last century, when they were removed to make way for iron,
the New River Company had upwards of 400 miles of wooden pipe.
When water-closets were more generally introduced at the commencement of the present
century, a more abundant supply of water was required, which was first poured into the
cistern, usually placed in the basement, from whence by means of force-pumps it was thrown
into the tank to feed the closet; this system was afterwards further improved by supplying
water at a higher pressure by the use of steam-power, and which could be more easily
effected through the introduction of iron pipes. Twenty miles per annum of wooden pipes,
6 or 7 inches bore, with their 3-inch service pipes, were annually removed until the whole
of the districts supplied by this company were furnished with cast-iron mains; these vary
in diameter from 1 to 3 feet, and the services are generally 4 inches.
When the iron mains were first laid down, they were supposed to impart a chalybeate
quality to the water, and they were in consequence dressed in the interior with a pre-
paration of lime-water, which entirely removed the evil. They were screwed together at
the joints, which prevented their free expansion and contraction, and often occasioned them
to be broken by the varied temperature of the water, rendering them very defective in the
winter season. Cylindrical socket joints were then introduced, and the pipes cast in lengths of
9 feet, which entirely obviated all inconvenience. These joints being accurately turned in
a lathe no stuffing is required; a little whiting and tallow is used, and they are at once
formed and the pipes driven up; joints so made answer well to a suction pipe of a steam-
engine 30 inches in diameter.
The tenant's communication pipes are united to the mains by flange joints, which are
cast with the pipes, and all the cross branches are slightly curved, which materially reduces
the friction to which they were subject when lying at an angle. Screw cocks have also
taken the place of the valve-cock, so that the water is now gradually shut off, and not as
formerly in an instant, which frequently occasioned the bursting of the pipes. At the New
River head, Pentonville, there are two powerful steam-engines as well as an engine for
forcing the water to a higher reservoir near the works, and another near Tottenham
Court Road.
The works are about 85 feet above the level of the Thames, and all the houses above
this were formerly supplied by a windmill, afterwards by a horse-mill, then by a fire-engine,
and in 1820 by three steam-engines of 63 horse power. Mr. Mylne, the engineer to the
company stated, in the year 1844, when he gave his evidence to the Commissioners of
Inquiry into the State of Large Towns, that the average annual quantity of water supplied
for the last three years had been 614,087,768 cubic feet: deducting from this the larger
consumers, and street watering, amounting to about 33,529,400 cubic feet, there would
remain 580,558,368 cubic feet per annum, equal to 46 cubic feet per tenement each alter-
nate day; the number of tenements supplied being 81,555.
Chelsea Water-works were established in the year 1724: about two years afterwards the
basin in the Green Park was built for the supply of Whitehall, and another for Westminster
in Hyde Park. The water was at first obtained from the Thames by means of a wheel
throwing it into settling ponds, which was worked from other ponds in the same manner
as a tide mill, and in the middle of the last century 1700 tons of water were so raised
daily, which not being adequate to the increasing demand, the works were enlarged, and
about the year 1810, they were removed from the site which now forms the Belgrave basin
to their present situation. They occupy nearly 7 acres of land; the water was originally
obtained froin a dolphin, which stood about 50 feet from the bank; this was a brick
structure below, and iron above, into which the mains entered, and drew their supply; but
being situated near the mouth of a large sewer, it was removed, and the main pipes are
now supplied from the Surrey side of the river; the water is received into settling reser-
voirs, lined with stone and brick, the first of which is 100 feet in length, 70 feet in width,
and 10 feet in depth; from thence it is forced up into one 300 feet in length, 160 in
breadth, beyond which is another, 540 by 140 feet; from these the water flows into
two filters constructed below them, one of which is 240 by 180 feet, and the other 351 by
180 feet.
NN 3
550
BOOK I.
HISTORY OF ENGINEERING.
The mode of filtration is by the descent of the water, which, in its way, is made to
pass through fine and coarse river sand, broken shells and pebbles, and small and large
gravel. These several materials are laid in a reservoir, disposed in ridges, which show an
undulated surface; and the whole depth of the beds is about 5 feet. The upper layer
is fine sand, the second coarse sand, the third pebbles and shells, the fourth fine gravel,
and the fifth large gravel; built within these with cement blocks are eleven brick tunnels
for collecting the filtered water, partially open-jointed, with spaces of 1½ inch on the bed,
with the heading joint of each brick also open.
The bed of the filtering works consists of loam, sand, and gravel, which overlie the
London clay to the depth of 30 feet; the two latter strata contained powerful land springs,
so that it was necessary to form a bottom with clay and cement walling. The bed covers
an area of an acre, and there is an elevated reservoir of nearly the same size.
The cost
The water is let in by nine brick tunnels, and the ends of the pipes are fitted with
curved boards to diffuse the currents of water, and prevent the surface of sand from being dis-
turbed; this is scraped every fortnight, and from a careful examination, it appears that the
sediment penetrates to the depth of from 6 to 9 inches, to which depth the sand is frequently
removed, and fresh supplied by carefully lifting portions in succession. The quantity of
water filtered is from 300,000 to 400,000 cubic feet daily, or 2,300,000 gallons.
of the filter, exclusive of the land, was 11,700%, and the annual expenditure for raising the
water on the filtering bed is 800l., for cleansing and renewal a similar sum. A steam-
engine of 120 horse power raised, in the year 1834, 4,640,000 gallons of water per day, a
portion of which was carried to the height of 135 feet: 13,892 houses were supplied in
the year with 15,750 hogsheads of water.
The West Middlesex Water-works were established in the year 1806, and are situated on
the banks of the Thames at Hammersmith; they obtain their supply by means of steam-
engines, the power of which is equal to raising 6,000,000 gallons per day to the height of
122 feet; the water is pumped into a reservoir at Notting Hill, and another at Primrose
Hill.
The number of houses and buildings supplied are 16,000, and the total quantity of
water annually is 20,000,000 hogsheads; the average daily consumption 2,250,000 gallons,
or about 360,000 cubic feet. This company supplies that part of the metropolis which
lies west of Tottenham Court and Hampstead Roads and the north of Oxford Street, the
Edgeware Road, the Regent's Canal, Bayswater, Kensington, Hammersmith, Fulham, and
Chiswick.
The Grand Junction Water-works, established in the year 1810, are situated at Chelsea,
and at first derived their waters from the Thames, with which they filled three reservoirs
at Paddington; at present they are empowered to draw their supply from the same river,
at a little above Kew Bridge, on the Surrey side. A steam-engine, of 500 horse-power,
drives the water through a main, 30 inches in diameter, for a distance of 6 miles, to
Paddington, where it is subjected to filtration. The total quantity supplied annually
was 21,702,567 hogsheads to 7,700 houses; the daily consumption being estimated at
2,800,000 gallons, or upwards of 450,000 feet. The highest elevation is 151 feet 9 inches,
and the average quantity raised per day 3,744,213 gallons. This company supplies the dis-
trict included within Oxford Street, Princes Street, St. James's Park, Hyde Park, the
Edgeware and Uxbridge Roads, and the Regent's Canal. After making due allowance
for watering the streets and waste, the average consumption of each house, when Mr.
Telford made his report, was estimated at 180 gallons per day, or 25 gallons per day for
each person.
Southwark, and the south side of the Thames is supplied by the Lambeth, the Southwark
Companies, and the Vauxhall or South London.
The Lambeth Water-works are upon the Thames, between Westminster and Waterloo
bridges; they have no reservoirs, the water being forced immediately from the river into
the mains, and thence distributed to about 16,000 tenants, who consume about 1,244,000
gallons daily, or nearly 200,000 cube feet.
The Southwark Water-works are upon the banks of the Thames between Southwark and
London bridges, and take their supply from the middle of the river opposite their
engines; 7000 tenants receive about 720,000 gallons of water, or 115,000 cubic feet,
daily.
The Vauxhall or South London Water-works are in Kennington Lane, and have an engine
on the river at the foot of Vauxhall Bridge; they obtain the water from the Thames, and
have reservoirs for the service of their upper engine. They supply about 10,000 tenants
with about 1,000,000 gallons daily, or about 160,000 cubic feet.
Each of these establishments has two engines; the aggregate power of the six may
be estimated at about 235 horses; the whole of the water furnished amounts to nearly
3,000,000 gallons, or 485,000 cubic feet daily, which is distributed among 33,000 tenants.
East London Company, established in the year 1807, and situated at Old Ford, on the
CHAP. VIII.
551
BRITAIN.
In
river Lea, a little above Bow Bridge, draws its water from above the influence of the
tide, and is carried by an aqueduct into settling reservoirs, which are upwards of 18 acres
in extent; it then flows into another, from which it is pumped up by steam-engines of suffi-
cient power to throw up 11,293,776 gallons per day: the highest elevation is 107 feet.
the year 1820 the total quantity supplied annually was 29,516,333 hogsheads; and the
company had laid down in the streets 400 miles of iron pipes, one half of which were in
use at one time. When the water is at rest any matter mechanically suspended in it
settles in the pipes, to avoid which, before the turncock gives the supply to any street, he
starts the end plug of the service for three or four minutes, and lets a part of the water run
out, which removes the deposit. The number of houses served is 50,000, and there are as
many tanks and waterbutts in the district in addition.
It may be well to remark, that the quantities given are not to be considered as
fixed, they are necessarily daily increasing; but in the year 1826 the total annually
distributed to the metropolis by these public companies amounted to 155,381,038 hogs-
heads, the number of houses being 120,000, and the rental paid for the same 175,890l.
The daily supply is stated to be equal to the contents of a lake of 50 acres, 3 feet in
depth.
Trent Waterworks, at Nottingham, were established in the year 1830, under the direction
of Mr. Thomas Hawkesley; 8000 houses are supplied by this company, and the expen-
diture was about 30,000l.; the water can be thrown to any level; the annual average
charge is 7s. 6d., and the quantity supplied to each house is about 80 or 90 gallons per
day, at a cost of not much more than a farthing. The greatest pressure at which the
water is kept upon the pipes is about 120 feet, but the average is not more than 80 feet.
The pipes are charged so as to deliver water to the tops of all the houses within a proper
distance of the superior reservoir: they are generally inch in diameter, and each foot in
length weighs 23 pounds.
It has been estimated by Mr. Hawkesley that the company sell 1000 gallons of water at
something under 3d., and that the total or general charges, exclusive of the interest on
capital, amounts to 1·42, or a little less than 1d.; this is made up by a charge of 3d. upon
the quantity for salaries, taxes, rent, repairs, &c., another d. for attendance upon the
machinery, and a trifle less than d. to defray the cost of coals, hemp, leather, oil, tallow,
repairs, &c.
•
The construction of the filter is thus described :—the reservoir, which lies on the banks
of the Trent, about a mile from the town, is excavated in a natural stratum of clean sand and
gravel, through which the water slowly percolates to a distance of 150 feet from the river.
The adventitious solid matter is generally deposited on the bed of the river, from which it
is washed away by the action of the stream. The river at times is exceedingly thick, and
of the colour of tea, from the admixture of peat and other vegetable matters; but after
filtration through the bed, the water becomes perfectly pellucid.
The reservoir being exposed to the action of the sun produces vegetation of the conferva
genus, which is removed at intervals of about three weeks in summer, and six weeks in
winter, by pumping out the water and the use of the broom; after which operation a pin
may easily be distinguished at the bottom, a depth of 9 feet. To prevent the small
communication pipes from being choked by the accidental introduction of leaves and other
extraneous substances, the water is drawn through large sieves of fine strainer cloth.
addition to the reservoir there is a filter tunnel, passing through a similar stratum for a con-
siderable distance up the adjoining lands, 4 feet in diameter, and half a brick thick, and
being laid without mortar or cement cost only 10s. per foot, including an excavation to the
depth of 12 feet.
In
Greenock Water Supply, under the direction of Mr. Thom, engineer. A company incor-
porated by an act of parliament in the year 1825 undertook these works, and the reservoirs
they have formed contain 310,000,000 cubic feet of water, into which annually drains more
than double that quantity; their capacity is calculated for the consumption of more than
six months.
There is above the town a filter, the basin of which contains one day's supply of water to
the inhabitants; the conduit pipe is 15 inches square, perfectly water-tight, being of stone
built with cement; the cost was one-third of that of an iron pipe of equal capacity. In it
cesspools are formed, into which some of the sediment is deposited in its course before it
enters the three filters. Each of these are 50 feet in length, 12 feet wide, and 8 feet
deep, and the water percolates through them either upwards or downwards at pleasure.
When it passes downwards, and the lodgment of the silt is considerable, by shutting one
sluice and opening another, the water is made to pass upwards with sufficient force to carry
the sediment with it into a waste drain. After this is cleansed, the sluices are again changed,
and the filter operates as before.
By this arrangement of the several beds, a return current of water may be forced
upwards, and thus cleanse them from the deposit; there is also less average pressure and
NN 4
552
BOOK I
HISTORY OF ENGINEERING.
pumping required, and the cost of cleansing is lessened materially. The return of the water
upward cannot, however, entirely remove all that has been previously lodged, nor can it
serve the purpose of so effectually cleansing as to obviate the necessity for renewing the
several materials. Experiment has shown that, when the upward current is applied under
a pressure of 26 feet head, it does not remove one-tenth part of what has been deposited: it
seems necessary to produce great agitation between all the particles before the impurities
will detach themselves from the grains of sand.
Impurities usually found in Water, are the mineral or saline, the vegetable, the animal, and
mechanical. The saline are earthy salts, salts of lime, and salts of magnesia; common salt
is also usually present, and sometimes bicarbonates of soda and potash. The most important
of the earthy salts is the bicarbonate of lime. The whole saline matter consists of two por-
tions, the neutral and the alkaline. The latter are entirely bicarbonates, as those of lime
and magnesia, to which sometimes are added those of potash and soda. The neutral por-
tion consists of the neutral salts, of earths and alkalies, such as gypsum and common salt.
Salts of iron are sometimes found, giving an inky taste to the water, and a yellowish tint to
linen washed in it.
The earthy salts and iron salts are the principal cause of hardness, which effect is often
also produced by an excess of carbonic acid, at least when it is in a greater quantity than
is sufficient to form the bicarbonates present.
Filtration has no effect upon the hardness of water, but it is softened by exposure to the
air, and sometimes by the process of boiling, when the earthy bicarbonates are decomposed.
The New River water contains, according to Mr. Clark's evidence, given before the Com-
missioners of Inquiry into the State of Large Towns, 13 grains or more of carbonate of lime
in every gallon. In the middle of May, water taken from the Thames at Mortlake con-
tained 14 grains, that from the East London Waterworks upwards of 16 grains, that of
the Vauxhall Company, on the Surrey side of the river, 13 grains.
Thomas Clarke's, M D., Process for Purifying Water. -To understand its nature, it is
necessary to advert to a few chemical properties of the familiar substance chalk, which
at once forms the bulk of the impurity that the process will separate from water, and
is the material whence the ingredient for effecting the separation is obtained. In water
chalk is almost or altogether insoluble; but it may be rendered soluble by either of two
processes of a very opposite kind. When burned, as in a kiln, it loses weight: if dry and
pure, only 9 ounces will remain out of 16; these 9 ounces will be soluble in water, but
they will require not less than 40 gallons of water for entire solution. Burnt chalk or
quicklime, when held in solution, forms lime-water, which is perfectly clear and colourless.
The 7 ounces lost when the chalk is converted into lime is carbonic acid gas. The other
mode of rendering chalk soluble in water is nearly the reverse. In the former mode, a
pound of pure chalk becomes dissolved in consequence of losing 7 ounces of carbonic acid.
To dissolve in the second mode, not only must the pound of chalk not lose the 7 ounces
of carbonic acid that it contains, but it must combine with 7 additional ounces of that
acid.
In such a state of combination chalk exists in the waters of London, dissolved, invisible,
and colourless, like salt in water. A pound of chalk dissolved in 560 gallons of water by 7
ounces of carbonic acid would form a solution not sensibly different in ordinary use from the
filtered water of the Thames in the average state of that river. Chalk, or carbonate of lime,
becomes a bicarbonate when it is dissolved in water by carbonic acid. Any lime-water may
be mixed with another, and any solution of bicarbonate of lime with another, without any
change being produced; the clearness of the mixed solutions would be undisturbed; not so,
however, if lime-water be mixed with a solution of bicarbonate of lime. Very soon a hazi-
ness appears, this deepens into a whiteness, and the mixture soon acquires the appearance of
a well-mixed whitewash. When the white matter ceases to be produced, it subsides, and
in process of time leaves the water above perfectly clear; the subsided matter being nothing
but chalk. What occurs in this operation will be understood, if we suppose that 16 ounces
of chalk, after being converted by burning into 9 ounces of quicklime, is dissolved, so as to
form 40 gallons of lime-water; that another 16 ounces is dissolved by 7 ounces of extra car-
bonic acid, so as to form 560 gallons of a solution of bicarbonate of lime, and that the two
solutions are mixed, making up together 600 gallons. The 9 ounces of quicklime from the
16 of chalk unite with the 7 extra ounces of carbonic acid that hold the other 16 ounces of
chalk in solution. These 9 ounces of quicklime and 7 ounces of carbonic acid form 16
ounces of chalk, which being insoluble in water become visible at the same time that the
other pound of chalk, being deprived of the extra 7 ounces of carbonic acid that kept it in
solution, reappears.
Both pounds of chalk are found at the bottom after subsidence. The
600 gallons of water will remain above clear and colourless, without holding in solution any
sensible quantity either of quicklime or of bicarbonate of lime.
The weight of chalk separated from the whole waters with which the several companies
in London supply the public annually is estimated by Dr. Clarke to be equal to 9000 tons,
and that to purify it after the above method would cost only 10l. per day.
CHAP. VIII.
558
BRITAIN.
Few subjects have more perplexed the civil engineer than the theory of filtration, and
many thousand pounds have been uselessly expended to obtain pure and wholesome water.
The two processes generally adopted are, first, either that which acts entirely on the
surface, in the same manner as passing water through filtering paper, or by a layer or
number of layers of various qualities of sand or other material.
By the first of these methods minute impurities may be retained, and as the filtration
proceeds, the quantity of water that passes is comparatively small; its passage is gradually
lessened by the deposit of impure matter upon the filtering surface, and the pores through
which it passes become stopped. By the second the sand is usually selected of different
sized grains, and the mud or foreign matter which the water holds mechanically in the
course of time fills up the vacuities that exist between the particles, destroys its porous
quality, and prevents its use as a filter. Water passing through sand, therefore, deposits
its impurities between the grains, and if these are not frequently changed, the mass will
become impermeable, and cease to do the work required. Such a filter would therefore
answer admirably for a short time, or until the whole of the interstices were closed, and ex-
periment has proved that the quantity of water passed through diminishes each succeeding
week. A filter should be so constructed, that the material used should be unchanged, im-
putrescent, and without any alteration in its mechanical structure, allowing the water at all
times to pass freely.
M. Maurras's system of filtration is effected by means of a water-tight iron box, about
5 feet 6 inches square, with a filtering surface within it equal to 60 superficial feet, which,
with a 12 feet 6 inches head of water, it is calculated will filtrate 150,000 gallons in the
space of 24 hours.
The water is introduced at the top, and makes its exit at the bottom, after having passed
through several layers or beds of coarse and fine sand; it at first percolates a coarse sand,
which lies both at top and bottom, then a fine sand, and afterwards meets in the centre of
the box, where it makes its exit.
The principal part of the arrangement, however, consists of a number of horizontal closed
iron boxes, the upper and lower sides of which are pierced with small holes, for the passage
of the water under pressure: these are placed one over the other, and between them are
alternate layers of coarser and finer sand, through which the water is first made to pass; they
are tightly packed with riddled sand, which cannot escape through the fine holes made for
the passage of the water, in consequence of its large grain, whilst its interstices are suffi-
ciently small to allow the finer sand of the filtering beds between the boxes to enter and be
retained, and although that of the smallest grain has been used under a pressure of a column
of water of 60 feet, it has been found that none has escaped.
The machine is cleansed by reversing the current of the water, which, by an arrangement
of sluice cocks, is effected very easily; when the water is admitted at bottom and forced
upwards, a violent agitation takes place throughout the pores of the sand, and the accu-
mulation of deposited matter is thoroughly dislodged and carried away.
The filtering sand, of various degrees of fineness, cannot escape, and can be changed at
pleasure.
Of
In most parts of England water is obtained from wells, some of which are Artesian.
the quantity of water which descends in rain in our latitude, one-third has been estimated
as passing off by evaporation, the remaining two-thirds being required for the support of
animal and vegetable life, and to supply the subterraneous springs. Rain water either runs
off upon the surface or percolates the strata, being received in the fissures or vaults of the
earth, where it forms subterraneous reservoirs.
Where beds of gravel rest upon a substratum of clay, the lower portions contain water;
if the clay is thin, and has fissures or openings in it, the water passes through, and continues
to descend till it meets some other layer, which will retain it.
Some wells are supplied by water descending in the strata, others by its ascent from
below by means of hydrostatic pressure, which is the case with Artesian wells, or perpe-
tually flowing springs: these are numerous in the neighbourhood of London, where they
are formed by penetrating the chalk or the plastic clay formation. At Sheerness, the sandy
strata of the plastic clay formation was reached after boring through the London clay
330 feet, and in many districts the chalk has been pierced to a considerable depth beneath
the clay, and abundance of water obtained, which is generally perfectly clear and bright, for
by its passage through the various strata, it is deprived of all that it held mechanically, as
well as other impurities, which are taken up by one earth or the other.
The district called the London Basin may be considered as a continuous seam of chalk,
varying in thickness, and sometimes covered with sand and gravel alternating with plastic
clay, over which is a thick stratum of London clay. Under the chalk basin is a substratum
of clay, through which water will not pass, and consequently a large supply is always to be
found in it. The surface of the water in this subterranean reservoir does not stand at one
uniform level, but rises in a distance of 14 miles, as between Watford and the highest spring
in the chalk hills, as much as 300 feet. The molecular attraction of the particles of chalk
554
Book I.
HISTORY OF ENGINEERING.
through which this sheet of water is spread, and the obstruction presented by friction to its
descent, may in some degree account for its inclined position, though on the other hand it
appears, that when the floods at Watford affect the wells in that neighbourhood, the same
influence extends to those in London a few hours afterwards; and a steam-engine employed to
pump water from a well near Watford lowers that in all the wells to a considerable distance
around it.
The Reverend J. C. Clutterbuck has shown that if a line were drawn from a point
3 miles south of the Colne at the level of that river, which is 170 feet above Trinity high
water-mark, to the mean tide level in the Thames below London Bridge, the dip would be
180 feet in 14 miles, or an average inclination of 13 feet in each mile; the uniformity of
this inclination is proved by the wells at Hendon union workhouse, Cricklewood, and at
Kilburn, in which 20 years ago the water stood much higher than at present, the exhausting
of the wells in and about London by means of powerful machinery having reduced its
level considerably. The level at which the water stands in the chalk is subject to periodical
change; there is also another supply to that portion of the London Basin beneath the
plastic clays, which is not fed by infiltration, but probably by means of hydrostatic pressure
from higher sources.
This periodical change observed in the height of water in the chalk, is called the oscil-
lation of the water level, and is caused by an irruption of rain water, which finds its way
from the surface of the London and plastic clays into the chalk through fissures, and at
last arrives at the sand above the plastic clay formation.
The water level line generally inclines about 10 feet in a mile when most depressed, and
after heavy rains, when the clays throw their water from their surface, the irruption of the
water may be seen at the outcrop of the sand of the plastic clay formation; the level will
then be raised in proportion to the quantity of water which passes through the sand into
the chalk beneath it, the elevation of level extending towards the Colne, in a ratio increasing
with the distance from the river; the fixed summit will remain unaltered, until the level
at the point of irruption has attained an elevation at which the water can flow towards the
south. After a period of dry weather, the level will decline in the same ratio as it has risen
until it regains the original level with a regular inclination.
The same effects may be observed in all chalk districts where no streams are found on the
surface; the valleys which lie between the rounded hills seldom exhibit any running water,
but wherever wells are sunk and the water-bearing stratum is arrived at, an abundant
supply may be obtained. Taking the level of the water in the wells on the highest ridge, and
drawing from thence a line to the surface of those found in the lowest, or that of the river
into which they drain, we find that the surface of the water of all the intermediate sinkings
corresponds with the slant line of drainage within the chalk, and if by means of pump-
ing or tunneling, we exhaust the water on any part of this line, all the supplies above are
affected. In whole districts the wells have by this means been rendered dry, and it is
only by sinking them deeper, or out of the influence of such effects, that water can be
again obtained.
Canals. Where rivers abounded with shoals, we find it a very early custom to contract
the channel, and thus obtain deep water, or sufficient to float small vessels. Another mode,
called flashing, was applied to shallow streams, and consisted in penning up for a time the
river itself within reservoirs, which had openings cut in them, to allow of the passage of
boats.
Wears and sluices were made use of when the rise in the bed of the river was con-
siderable; there was an opening in the wear, closed by a flood-gate, which allowed the
passage of vessels: this commonly consisted of two abutments of stone, projecting from
each bank, in which was a groove to receive a plank, or timber, which was let down and
drawn up at pleasure; or a sill was laid at the bottom, with a groove, into which per-
pendicular planks were dropped, and maintained at top by one or two strong horizontal
timbers, resting on the abutments. To open this it was necessary to draw out one plank or
paddle at a time, and then remove the horizontal timbers; after the boat was hauled
through, the whole was replaced, and the water in the head or reservoir again permitted
to rise.
Inclined planes and rolling bridges were also in use for transferring boats from one
pond to another across a wear.
We have already seen that in Italy, France, Holland, and Germany, canals were esta-
blished at a very early period, and it is remarkable that we do not find much attention paid
to the subject in England, until about the middle of the sixteenth century, when it was
proposed to render the Isis and Avon navigable by means of sasses, and then to unite the
two streams by a canal of about 3 miles in length; but nothing of importance was under-
taken until James Brindley connected Liverpool with London, Bristol with Hull, and
several other districts by canals; he was a native of Tunstal in the parish of Wormhill in
Derbyshire, and the date of his birth is said to be about the year 1716. He served his
apprenticeship to a millwright at Macclesfield, where he acquired a thorough knowledge
CHAP. VIII.
555
BRITAIN.
of his business as practised at that time.
For some years after he was employed in making
improvements in the machinery of several mills in Cheshire and Lancashire, where he gave
considerable satisfaction to his employers. About the year 1758, the Duke of Bridgewater
turned his attention to the subject of inland navigation, and petitioned parliament to grant
him permission to cut a canal; having previously observed some of the most important on
the continent, he was desirous of benefiting from their introduction into his coal-fields in
South Lancashire. The Duke, having obtained his act, employed Brindley to execute a
canal from Worsley to Manchester, a distance of 10 miles. This is the first canal of any
importance in England, and the skill displayed in carrying it over the river Irwell by an
aqueduct at Barton excited much astonishment at the time. This aqueduct consists of
three semicircular arches, one in the centre being 63 feet span, and 39 feet in height
above the river; it is entirely built of dressed stones, and the channel for the water is
puddled at the sides to prevent leakage. Across the meadows at Stratford the canal,
which is 24 feet in breadth at top, is carried on an embankment, 900 yards in length, and
17 feet high, with a breadth at the base of 112 feet, the slopes being two to one.
Legislation relative to rivers and canals.—There is no general administration to regulate
water conveyance: the whole management of this important branch of commerce is either
under the control of municipal authority or special commissioners chosen by virtue of acts
of parliament from among the inhabitants of the various districts to which the water transit
belongs. We find that at an early period of our history the navigable rivers throughout
the kingdom were considered as contributing to the advantages of trade, and every means
were adopted to prevent private individuals from appropriating them to their own use.
In Magna Charta, cap. 16., a clause is inserted, making the course of the Thames and all
other rivers free of duty to those that navigated them, and enacting that any obstructions to
the transit should be removed.
In the reign of Edward the Third a special act was made (1351) to demolish all dams
which impeded navigation, without allowing any compensation to the owners or persons
who had constructed them. Twenty years afterwards another act was passed, ordaining
that a fine of 100 marks should be paid by any individual who injured the navigation of the
rivers.
In 1427 (6 Henry 6th, ch. 5.) commissioners were appointed for the management of
rivers, either for the purposes of internal navigation or drainage, the removing of any
obstructions in the streams, and preventing inundations. By this act the chancellor
nominates commissioners to superintend the repairs of all dykes, bridges, roads, and the
damage done by natural or artificial streams of water. They have the right to construct
any works, to destroy any ponds, dams, or mills, or reclaim land, and institute inquiries
or actions at law, on account of injury to any water-conveyance; with the power of fixing
the amount of fines according to the damage sustained, of levying taxes for the execution
of the several works on the property which is to be benefited; and the law enjoins perfect
equality in the territorial tax, without any exemption to either the church, the nobility, or
the king.
Individuals refusing to pay their portion of the tax are liable to have their property
confiscated; or the commissioners may seize the land of any one refusing, and let it at a
life-rent or for a term of years. They may put in requisition horses, waggons, oxen,
and workmen, by paying suitable wages, and may take any timber requisite at their own
estimate of its value. The commissioners appoint bailiffs, collectors, treasurers, and super-
intendents, who are answerable to them, and whose salaries they fix.
Commissioners, previous to taking the necessary oath, must show that they are possessed
of a clear annual income equal to forty marks, or landed property to the value of 100%., or
that they are freemen of a city or an incorporated borough, or members of one of the four
principal Inns of Court.
When any seizure is made by order of the commissioners the party may prosecute
the agent executing the order, and a jury then decides upon the question according to
law. If the agent gain the cause, he receives triple the amount of the expense of the
action.
In the
There are besides several special laws for the management of currents of water.
year 1423 (Henry 6th) a committee was appointed to examine the course of the river Lea,
and to render it fit for the purposes of navigation. In the following year, the parliament
authorised the chancellor to select a committee out of the adjoining parishes, who were
qualified to correct the defects of the river, by the execution of any works, or the removal
of anything which impeded the navigation (3 Henry 6th, cap. 5.).
The river Thames is under the direction of the mayor and corporation of the city of Lon-
don, who, as conservators, have the management of all that regards the navigation, from the
mouth of the river to as high as the flood tide extends, (4 Henry 7th, cap. 15.). They also
exercise an inspection over all stagnant waters and currents which communicate with the
Thames. One half of the fines paid by persons convicted of having in any way damaged the
banks or injured the bed of the Thames goes to the city of London, (27 Henry 8th, cap. 18.).
356
Book I
HISTORY OF ENGINEERING.
Parliament gave to the corporation of London (13 Elizabeth, cap. 18.) the right of
rendering the river Lea navigable from Ware to the Thames.
In the 21st year of James the First, cap. 42., a very important act was passed, which had
for its object the diminishing the price of fuel and other articles of necessity in the city of
Oxford; to facilitate the conveyance of produce to Oxford, and to prevent the high roads
which conducted to that city from being broken up during the winter. These works were
consigned to the superintendence of eight commissioners, four of whom were to be appointed
by the city, and four by the university.
Various other acts of parliament have been made to protect the works necessary for
water conveyance, (1 George 2nd, cap. 19. sect. 2. and 8 George 2nd, cap. 20. sect. 1.).
In the reign of Charles I., Vermuyden, a Dutch engineer, was authorised to drain the
land at the mouth of the Trent, which was performed in 5 years, at an expense of £55,825,
and to him may perhaps be attributed the introduction of the first lock in England, which
is on the river Idle, and called Misterton Sas: after the Restoration inland navigation appears
to have received increased attention, which may, in some measure, be attributable to the
opportunities afforded the exiles in the Low Countries of seeing the great advantages to be
derived from facility of communication; but it was not until the commencement of the
eighteenth century that this important object was conducted upon any thing like prin-
ciple.
Previous to the commencement of this century, various acts of parliament were passed,
relating to the improvement of the navigation of different rivers, either by straightening,
widening or deepening their channels, forming banks with towing paths, as well as jetties
and sluices, penning up water, and making flushes to overcome the rapid part of the
streams or the shallows. This was accomplished by pound locks, which were necessary
where mill-weirs were established, as the boats could not make their ascent or descent with-
out, for in all the acts of parliament special care was taken of the mills.
In 1776, in order to overcome all the difficulties attendant upon the use of the natural
streams, a separate cut with pound locks was made from the Mersey by the proprietors of
the Sankey navigation, who had previously obtained an act of parliament for the purpose.
Soon after (33 George 2nd) the Duke of Bridgewater obtained an act for his celebrated
canal, and since that period upwards of 2400 miles of artificial canal have been made in
England.
Aberdare Canal is a branch of the Cardiff canal; the act was passed 33 George 3. c. 95. ;
it passes the iron-works of Abernant, Aberdare, and Herwain, and proceeds to the summit
of a precipice near the valley of Neath, where an inclined plane unites with the Neath
canal; various railroads now communicate with it.
Aberdeenshire Canal proceeds from Aberdeen to Inverury.
Aire and Culder Navigation was perfected about fifty years before any other act passed for
making canals, and it is important in the history of inland navigation; 1699 was the year
the royal assent was given to the first act of parliament. The river Aire rises in Malham
Tarn, a few miles from Settle, in the district of Craven, in Yorkshire; it passes nearly a
mile underground, and afterwards issues from the base of a lofty rock; it then bends its
course through Airedale to Leeds: at Castleford it unites with the Calder, and the two
rivers retaining the same appellation join the Ouse, a short distance from Howden.
Aire is navigable at Leeds, and the distance to its junction with the Calder is about
11 miles, in which distance there is a fall of 43 feet 6 inches, made with 6 locks; from the
junction of the two rivers to Weeland the distance is 18 miles; here there is a fall of
34 feet 6 inches, and 4 locks.
The
The Calder has its rise near Todmorden, and becomes navigable at Wakefield; its
course thence to Castleford is about 12 miles, with a fall of 28 feet 3 inches, made by four
locks. The total length of the navigation from Wakefield to Weeland is 31½ miles, with
a fall of nearly 63 feet; numerous railroads communicate with it. The canal from
Haddlesey to Selby was opened in 1788; its length is 5 miles, and the only lock is into
the tide-way of the river Ouse. From Leeds to Selby the distance is 30 miles, on which
there are ten locks; from Wakefield to Selby is 31½ miles, with eight locks. The old
locks, which have been generally removed, were about 60 feet in length, and 15 feet in
width; those now in use are increased 3 feet in width, so that vessels of 100 tons navigate
these rivers and canals.
Another canal, uniting Knottingley to Goole, was opened in the year 1826, after surveys
and designs made by Mr. Rennie. The length of this canal from Ferrybridge to Goole is
18 miles, and the fall to low water mark at the latter place 28 feet 9 inches; its width
at the surface is 60 feet, and at the bottom 40 feet; the depth is 7 feet. The locks are in
length 70 feet, and in width 19 feet, and vessels of 100 tons can now proceed to the towns
of Leeds and Wakefield in 8 hours, and from Castleford to Goole there are steam-packets
for passengers.
Alford Canal, in Lincolnshire, runs into the German Ocean at Anderby, where it has a
sea lock, which maintains the water 14 feet 8 inches above the low water of spring tides,
CHAP. VIII.
557
BRITAIN.
being equal to high water-mark neap tides. The spring tides averaging about 18 feet
6 inches; there is a rise of 7 feet 9 inches by one lock, and the canal is then a dead level.
Ancholme River Navigation begins at Ferraby Sluice, on the Humber, and terminates at
Bishop Briggs; the works were much improved in 1801, under the superintendence of
Mr. Rennie. The canal from Caistor falls into the line about 5 miles above Bishop Briggs.
Andover Canal commences near that town, and enters the tide-way of Southampton
Water at Redbridge.
Arun River Navigation. The river Arun rises at a place called Haslemere, at an
elevation of 920 feet above the level of the sea at low water; the navigation commences at
Billinghurst, and is suited for vessels drawing 3 feet water.
Ashby-de-la-Zouch Canal commences near Nuneaton, in Warwickshire, and terminates
in the parish from whence it takes its name; it is level throughout, the whole line was
completed in 1805. Various railroads are made to communicate with it.
Ashton-under-Lyne Canal commences near Manchester, and proceeds to Clayton, thence
to Fairfield, a distance of 33 miles, with a rise of 162 feet 6 inches, by eighteen locks.
From Fairfield for a distance of 21 miles it is perfectly level. At the aqueduct of Ducken-
field is a branch to the Huddersfield canal, and another 2 miles in length to Waterhouses,
which crosses the river Medlock by an aqueduct, having previously gone through a con-
siderable length of tunnel. The branch from the aqueduct to Holinwood is 13 miles in
length, and by means of eight locks rises 83 feet. A collateral branch proceeds from the
Hollenwood branch, about a mile in length, to Fairbottom Colliery. Several short canals
unite with these.
From this canal Manchester derives considerable advantage; it unites that town with
Ashton-under-Lyne; by means of Huddersfield canal and other branches, it connects the
German Ocean with the Irish Sea, and by the Rochdale canal it unites with the Mersey.
Avon River rises near Devizes, and falls into the sea at the Bay of Christchurch; it is
navigable to Salisbury; in the year 1771, the works were much injured by a flood, and
were repaired by Mr. Brindley.
Avon River rises near Warwick, and becomes navigable at Stratford-upon-Avon, from
whence it flows 43 miles 3 furlongs to Tewkesbury, and then into the river Severn, bene-
fiting in its course the towns of Stratford, Evesham, and Pershore.
Avon and Frome Rivers. The Avon from the Hanham Mills to the Severn, at King's
Road, is navigable for a distance of 15 miles; a part of its course was through the middle
of the city of Bristol, and this has been converted into a floating dock and harbour, by
cutting a new channel for the navigation 2 miles in length.
The Frome river rises near Wickwar, in Gloucestershire, and falls into the floating dock
at Bristol.
The Avon is subject to high and rapid tides, occasionally rising as much as 50 feet.
Smeaton proposed great improvements in the harbour of Bristol, but they were not carried
into effect until after the passing of the act of the 48 George 3., when William Jessop
was appointed engineer. A part of the Avon has been rendered navigable to Bath; the
distance from Hanham Mills to that city being 11 miles, with a fall of 30 feet, by six locks.
Barnsley Canal commences from the river Calder of a mile below the bridge at
Wakefield; it rises in the distance of 23 miles a height of 117 feet by means of fifteen locks.
There is a reservoir 40 feet in depth, and in area 127 acres, to supply this canal; near
Burton it crosses the Dearne by an aqueduct of five arches of stone, 30 feet span each;
at a distance of 10 miles from its commencement, it unites with the Dearne and Dove
canal. From Barugh Mill to Barnby Basin, where the canal terminates, there is a rise of
40 feet by five locks; its engineer was Mr. William Jessop.
Basingstoke Canal has its commencement on the river Way, 3 miles from where it unites.
with the Thames: at Ash it enters the county of Southampton; in this distance of 15
miles it rises 195 feet by means of twenty-nine locks. Throughout this length the canal
is 36 feet wide, and 4 feet deep, the locks admitting vessels 72 feet long and 13 feet wide,
which carry 50 tons.
By means of an aqueduct about a mile from Winchester, the canal crosses a valley of a
mile in width. At Grewell Hill it passes by a tunnel through the chalk for more than
mile, and terminates at Basingstoke; the last 22 miles its width is 38 feet, and its depth
5 feet 6 inches. At Aldershot is a reservoir, which with the river Lodden supplies a part
of the canal.
Baybridge Canal commences at West Grinstead, and terminates at the place from whence
it takes its name, in the connty of Sussex.
Beverley Beck commences from the river Hull, and extends to Beverley.
Birmingham Canal was originally planned and executed by James Brindley; the first act
was obtained in the year 1766, and under it the canal was completed, which commences in
the river Trent, at Wilden Ferry in Derbyshire, passes through the Potteries, and through
Cheshire to the river Mersey at Runcorn. In the same year another act was passed, to
branch off a canal from Heywood near Stafford, and proceed by Wolverhampton to the
558
BOOK I.
HISTORY OF ENGINEERING.
river Severn at Stourport, near the town of Bewdley. A communication was then made
with the ports of Bristol, Hull, and Liverpool, and the Severn, the Humber, and the
Mersey. In 1768, another act authorised a canal to be made from Birmingham, through
the mining district of Oldbury and Bilstone, to the Staffordshire and Worcestershire
canal, 3 miles east of Wolverhampton, a total distance of 22 miles.
The act for the communication with Hull was passed in 1783, when the Fazeley canal,
20 miles in length, was made. The Coventry, Oxford, and Grand Junction canals, after-
wards united London to these ports.
The Birmingham summit is
The Staffordshire and Worcestershire
At the Fazeley Junction
Feet.
464
Inches.
5 above low water at Liverpool.
352
3
219
0
Ditto.
Ditto.
In the year 1824, Mr. Telford was applied to on the subject of improving these canals,
then deemed inadequate to the growing industry of the district; he found them little
better than crooked ditches, and with scarcely the appearance of a towing path.
Aided by
the celebrated James Watt, he succeeded in cutting off the numerous bends in the
canals, and making one nearly straight from Birmingham to the summit at Smethwick,
where a new cut was made 70 feet in depth, and the length of the main line from Bir-
mingham to Autherley reduced from 22 to 14 miles. The canal was enlarged to 40 feet
in width, with perpendicular banks and walled sides, and the bridges to 52 feet in breadth
between the abutments, so that the hauling-paths were continued without contracting the
water-way of the canal.
Embankment at Rotten Park forms a reservoir of 80 acres, with a depth of 45 feet at the
head of the retaining bank, the bottom of which is above the Birmingham summit, so that
all the water it contains is rendered serviceable. The feeders of this great supply are from
the old reservoirs at Oldbury and its neighbourhood.
Mr. Telford also removed the six locks, three ascending, and three descending, which
were on the line between Birmingham and the Collieries; to effect this 1,697,000 cubic
yards of earth were excavated in the distance of 2 miles; the slopes of the banks are 11
horizontal to 1 perpendicular.
The greatest depth of cutting is 71 feet; the water-way of the canal is 40 feet in width,
and 5 feet 6 inches in depth. The whole is walled with stone, there is a towing-path on
each side 12 feet in width. Over this cutting are numerous brick and stone bridges, the
construction of which show great ingenuity; several are built askew. At the point where
the cutting is deepest is an iron bridge, 150 feet span, over which is the public roadway,
26 feet in width; the other two bridges are only 52 feet span.
An aqueduct of two arches near Spon Lane carries the canal across the new works; and
at Smethwick is an elegant iron aqueduct, through which the surplus water is conveyed,
from the upper level of the old canal across the new works into a feeder, which carries the
water to the reservoir before mentioned.
At Smethwick the upper level descends into the improved new line of canal, and between
this place and the town of Birmingham, a distance of 43 miles, nearly miles have been
saved; the quantity of earth removed to complete the three embankments and the inter-
vening deep cutting was 370,000 yards. Here the canal is also walled on each side, has a
double towing path, and is 40 feet in width at the surface of the water: there are several
brick skew bridges, some upwards of 50 feet span; at Bloomfield is an excavation, extend-
ing towards Deepfield, where the cutting is 90 feet in depth, and the canal 24 feet in width,
and 5 in depth; the sides are walled, and the towing path is continued on each side. To
effect this more than 1,000,000 yards of rock and earth were removed.
Birmingham Canals. The old Birmingham commences near that town, and at Smeth-
wick there are three locks, rising in all 19 feet 9 inches; at Autherley it locks down by
means of 21 locks, 132 feet.
Birmingham and Fazeley Canal commences near Farmer's Bridge in Birmingham, and
passes by part of the Coventry Canal to near Tamworth; this distance of 15 miles has a
fall of 248 feet; the canal afterwards forms a part of the old Coventry, and continues
another 5 miles to Whittington Brook, where it communicates with the Wyrley and
Essington canal. It is united to the Warwick and Birmingham by the Digbeth branch,
which is in length 1 mile 2 furlongs, and has a fall of 40 feet by six locks; there is a short
tunnel at Curdwath, and at Salford bridge an aqueduct of seven arches of 18 feet span each.
By these canals a communication was effected between London and Hull.
Birmingham and Liverpool Junction Canal was commenced under an act passed in the
year 1806.
The whole length is 39 miles, besides the Newport branch of 9; its width at
the surface is 36 feet, at the bottom 16, and its depth 5 feet.
This canal leaves the Staffordshire and Worcestershire canal about 3 miles from Wolver-
hampton; nearly opposite to Autherley, it passes on a level for 3 miles with one lock ;
thence on to Market Drayton, a distance of 15 miles, where is the second level; near the
last mentioned town are five more locks, and 5 miles beyond there, at Adderly, five others.
CHAP. VIII.
559
BRITAIN.

Fig. 539.
SECTION OF CANAL where puddled.
At Audlem in Cheshire are fifteen locks in one chain; 12 miles north of the river Weaver
are two more, making twenty-eight locks in all upon the main line, besides those on the

Fig. 540.
Newport branch.
SECTION OF CANAL.
These locks are 82 feet in length, and 7 feet 6 inches in width, and
admit a boat 7 feet wide, carrying 24 tons.
At Nantwich is a cast-

iron aqueduct, the arches
of which span 30 feet
and rise 4 feet.
Thirteen miles from
the south end of the
main line, in the town-
ship of Norbury, the
Newport branch com-
mences, which falls into
the Shrewsbury canal,
in the township of Wap-
penhall. This canal is
11 miles in length, and
has a fall of 139 feet, by
similar locks to those of
the main line: its sup-
ply of water is thus
obtained; its summit
being upon a level with
the Staffordshire canal,
and under that of the
Fig. 541.
AQUEDUCT.
Birmingham canal, communicating with the latter at Autherley, every boat passing to or

Fig. 542.
PLAN OF AQUEDUCT.
560
Book I.
HISTORY OF ENGINEERING.
from the Staffordshire into the Birmingham and Liverpool Junction, brings with it a lock-
full of water, and as this is received into the summit level, it serves throughout the whole

000
Fig 543.
side of aQUEDUCT.
passage to the Mersey. To provide for evaporation, there is a reservoir of fifty acres at
Belvide, and another of the same size at Knighton; these two reservoirs are shallow, but
they will allow a foot in depth to be drawn off, if required for lockage water.


1
Fig.544.
PLAN AND SECTION of lock.
The Cheshire marl used for the embankments stood very well where the height did not
exceed 10 or 12 feet, but was found hazardous beyond that, not retaining its shape, and
slips and bulges occurring to a great extent.
Blyth River rises near Laxfield, and terminates at Southwold in Suffolk.
Borrowstounness Canal proceeds along the south side of the Firth of Forth, and unites
with the Forth and Clyde canal near the mouth of the Carron rivers.
Bradford Canal commences near Shipley, and terminates at Hoppy Bridge.
Brecknock and Abergavenny Canal commences near Pontypool; it crosses the Avon by
an aqueduct, and then, by a tunnel 220 yards in length, it proceeds to Abergavenny and
Brecon.
Bridgewater Canal (the Duke's) extends from Worsley to Manchester. From Castlefield
it proceeds to Longford Bridge, a distance of 34 miles; 18 miles further it joins the Trent
and Mersey, and at 54 miles arrives at Runcorn; it then falls into the Mersey by ten locks,
which are together 82 feet 6 inches.
The Worsley branch is 5 miles, and from thence to Leigh 6 miles. This canal, executed
at the expense of the Duke of Bridgewater, who has been justly called the father of British
inland navigation, is on one level the greatest part of its length: this is done by means of
lofty and wide embankments; one of these, over Stretford meadows, is at the base 112 feet
wide, and 17 feet high; the Barton aqueduct, which is 39 feet above the Mersey and Irwell
navigation, is 200 yards in length.
CHAP. VIII.
561
BRITAIN.
Excepting for a distance of 600 yards at Runcorn, where the rise is 82 feet, the rest of
the navigation for 73 miles is on one level, which is effected by means of tunnels, aque-
ducts and embankments of considerable magnitude, and as all this was performed in the
infancy of canal operations, it reflects the highest honour on the projector and his en-
gineer.
Bridgewater aud Taunton Canal commences on the Avon, 6 miles below Bristol, and ter-
minates near the town of Taunton.
Britton Canal commences 3 miles below the town of Neath, and terminates at the pool
called Swansea Harbour.
Bude Harbour and Canal: this canal commences at the Port of Padstow, and after
passing through a considerable length of tunnel, terminates at Thornbury; there are
several branches, as the Launceston, Moreton Hall, Verworthy, Druxton Bridge, &c.
Bure or North River becomes navigable at Coleshill, in Norfolk, and continues so to
Aylsham.
Bure, Yure, and Waveney Rivers, and Yarmouth Haven. The navigation of the Bure com-
mences at Coleshill, and continues for 134 miles to a place where it unites with the Yare.
The Ant river branch commences at Wayford Bridge, and after an 8 miles course enters
the Bure. The Thurne River branch begins at Huckling Broad, and running 7 miles,
falls into the Bure at Thurne. Eight miles from Yarmouth, there is a cut from the town-
ship of Tunstal 1 mile in length.
The Yare becomes navigable at Norwich, and after receiving the Bure at Yarmouth, falls
into the roads of that place, a distance of about 32 miles. The Waveney is navigable at
Bungay, and falls into the Yare at Burgh Flatt, after a course of 25 miles.
Bury, Loughor, and Lledi Rivers.-The Bury is a wide estuary, terminating at Worm's
Head, on the southern coast of Caermarthenshire, its course is about 12 miles. The
Loughor, from the ford to the estuary of the Bury, is 2 miles. The Lliedi falls into the
Bury near Llanelly.
Caistor Canal commences near Creampoke, and terminates 3 miles west of the town of
Caistor in the county of Lincoln.
Calder and Hebbel navigation commences about 2 miles from Halifax, at Sowerby Wharf,
and terminates a little below the bridge at Wakefield, at Fall Ing, where it unites with the
Aire and Calder navigation.
Caledonian Canal. The Highlands of Scotland are divided by a series of lakes, called
Lochs Ness, Oich, Lochi, Eil, and Lynnhe, which run in a direction from north-east to south-
west, and from their contiguity afforded a favourable opportunity of uniting the seas of the
eastern and western coast. Twenty-one miles only of canal was requisite to obtain a navi-
gable line for the entire extent, upwards of 100 miles.
In 1802, a survey of the coasts and the interior of the country was made by Mr. Telford,
by order of the Lords of the Treasury, for the purpose of forming the canal from Inverness
to Fort William. After Mr. Jessop's and Mr. Rennie's opinion had been taken on the
possibility of effecting this desirable line of communication, an act was passed directing
the works, and regulating the expenditure; Mr. Telford was appointed engineer.
The length of the excavations for the canal is 21 miles; that of the intermediate lakes
374 miles, making a total of 583 miles.
The breadth of the canal at the top is 122, at the bottom 50, and the depth 20 feet.
From each side of the flat bottom the sloping sides are in height to the breadth as two to
three. The slopes are continued to within 2 feet of the level of the water, where the bank
is 6 feet wide. There are twenty-three locks, 40 feet wide, and 172 feet in length. The
entrance is 10 miles from Fort George, and 1 mile to the north-west of the river Ness,
where the tide-way of Beauley Water is from 5 to 7 fathoms in depth.
The tide-lock is 400 yards from high-water mark, at the end of an embankment; its cham-
ber is in length 170 feet, in width 40, and the rise 8 feet. The canal is afterwards formed
upon a flat and muddy shore, by artificial banks, until it reaches high-water mark at Clach-
nacharry, where a similar lock is constructed on a foundation of hard clay. South of this
is a large floating dock, 967 yards in length, and 162 in breadth, the area being computed
at 32 English acres.
At the south end of the basin are the four united Muirtown locks, each in length 180
feet, in breadth 40, together rising 32 feet, and bringing the waters of the canal to the level
of those of Loch Ness, The canal here measures 120 feet at the surface, 50 feet at the
bottom, and in depth 20; and by an easy bend winds to Torvaine on the Ness river.
Before the canal enters the Loch of Doughfour, 6 miles from its starting point at Clach-
nacharry, it passes a regulating lock, 170 feet in length, and 40 feet in width, and then
unites with Loch Ness, at a small outlet, at Bona Ferry. Loch Ness is nowhere less than
a mile in breadth; its depth varies from 5 to 129 fathoms; its whole length is about 22
miles.
Fort Augustus is situated at the south-west end of Loch Ness, and on its north side the
canal ascends by five connected locks a height of 40 feet, each lock being 180 feet in
0 o
562
BOOK I.
HISTORY OF ENGINEERING.
length; it then proceeds to the north-east corner of Loch Oich, after having passed the
lifting lock at Kytra, which is 170 feet in length, and 40 feet in breadth.
Between the western end of Loch Oich, and the east end of Loch Lochy, forty feet
depth of cutting was required, and near the latter place is a regulating as well as a lifting
lock; the difference between the surface of the water in these two locks is nearly ten
feet.
At the south-west end of Loch Lochy is another regulating lock; the whole length of
the Loch is not less than 10 miles, and its ordinary level is continued along the canal to
within 1 mile of Loch Eil, where there are eight connected locks, each 180 feet in length,
and 40 feet in width, falling altogether 64 feet; this work forms a mass of masonry 1500
feet in length; each of the locks rises 8 feet.
The canal continues on a level, until it arrives at the two connected locks at Corpach,
which fall 15 feet, where there is a single sea-lock, which enters the tide-way of Loch
Eil. This is situated at the western extremity of the canal, within 300 feet of high-
water-mark. The rock being covered at three-quarters flood, it was necessary to lay the
sill in such a position on the rock that a depth of 21 feet water might be obtained upon it
at high-water of neap
neap tides.
Water-tight mounds, faced with rubble-stone, were formed
for this purpose from the shore, beyond the extremity of the lock-pit, which were con-
nected by a wooden cofferdam. A foundation was arrived at after boring to a depth of
63 feet below the lower water line of spring tides; a sufficient space was enclosed with a
cofferdam, which was framed on the eastern bank, and afterwards put together on the beach,
near high-water mark.
The leading frame was made by fixing together, end to end, two pieces of timber,
crossed by others 20 feet long, 13 inches broad, and 6 inches thick, laid on opposite
sides of the first beams, across the joinings, and fastened by four screw bolts, which passed
through the whole. When these beams were so fished together, their whole length was
95 feet.
To unite the two sides, two others, each 63 feet in length, were laid with mutual
inclination, the ends being 63 feet apart; these were secured to the two long beams at the
ends by halving, or corking down; after which two iron screw bolts were passed through
each. Another beam, 38 feet in length, was laid across each angle, and also screwed to the
other beams at the two ends.
When the spring tide was at its height, the first leading beam was floated off, and at
low water was sunk into its proper situation by attaching several large stones to it at its
upper side, three mortises were cut on each side and three in the front, to receive the
standards, which were to be tenoned into them, and which, after being placed upright,
were cut off to the level of one foot below high-water neap tides, that they might receive
the middle leading frame, which was made on shore, floated to its place, and sunk by means
of guide piles, driven by a pile engine, placed upon the deck of a sloop, and then secured
by screws to the tops of the upright standards already mentioned.
On the top of this second frame upright standards were placed in mortises, which were
cut off at high-water spring tide. The upper leading frame was then floated off, and
placed upon the last-mentioned standards, and also bolted to the piles. On this was
formed a temporary scaffold, by laying large timbers across, and driving piles within the
space to support them; when this was done, the whole was loaded with large stones, and a
pile engine; fixed piles were driven at from 15 to 20 feet apart, entirely around the whole,
and these were so securely bolted to the upper frame, that the storms had no effect upon
them.
In March, 1808, the main framing piles were fixed to the rock by iron dowells, and this
was performed by means of a cylinder, 8 feet long, and 22 inches internal diameter, formed
of 3-inch plank. The joints were closely united and dowelled together, and the who'e
hooped with iron, and shod at the lower end with a circular iron shoe. On its upper end
were two strong iron eyes, fixed by means of clamps, which were riveted to the sides of the
cylinder, and through them passed the iron chain which lifted it up.
At low water the cylinder was placed where the main pile was to lie, there being then
only 3 feet of water, and 8 of silt and gravel on the rock; it was then placed upright,
close to the inside of the lower leading frame, and on its top was a block of ash timber, 2
feet in height, on the under side of which a piecer turned, 6 inches in length, ntting
exactly to the top of the cylinder; this prevented the block from shifting, as well as the
crushing of the cylinder whilst being driven. This block and the pile 12 inches square,
placed on the top of it, were hooped with iron: the pile was as much above the top of the
upper scaffold as it was necessary to sink the cylinder in the mud. When all was perpen-
dicularly placed, a pile-engine, 30 feet in height, was applied to drive it, with a ram of 1008
pounds weight. When the cylinder had descended some depth into the mud, it was
found necessary to empty the contents; this was effected by an auger, which filled at two
complete turns, when it was lifted out by a purchase at the top of the pile-engine, and the
sand cleaned out by means of a shovel.
CHAP. VIII.
563
BRITAIN.
When the cylinder had reached the rock, a frame, which fitted it, was introduced into
the upper end, and sunk by means of two half hundred weights, and in the middle of the
frame, through a hole 4 inches square, was passed a funnel which tapered to 3 inches at
the bottom; this was driven down to the rock, and the sand enclosed in the funnel was
cleared out, by a cylindrical iron tube, 3 inches diameter, and 3 feet in length, which had
a valve fixed within 2 inches of the bottom, resting on a small ring, fastened to the inside
of the tube, on the top of which was a screw, by which it was attached to a set of boring-
rods.
It was then passed down to the bottom of the square wooden pipe, and working by
short and quick strokes, the sand and gravel were brought by the agitation of the water
above the valve; the tube was then drawn out and emptied; this was continued until the
whole surface of the rock within the square tube was perfectly clean.
Through the square directing pipe a jumper was then passed, worked by a lever on the
upper scaffold, until a hole 20 inches in depth, and 23 in diameter, was bored into the rock,
into which an iron dowel, 2 inches square, might be placed; this was effected by fastening
it to a square socket, made in the end of 13-inch square iron bar, a small cord being
attached to it, to prevent its falling out of the socket whilst lowering the square directing
pipe to the rock when it had arrived there, it was driven into the hole in the rock by
striking the head of the bar several times with a haminer. After it was driven 18 inches
into the hole, the timber was lifted up by a sudden jerk, which broke the cord, and left the
dowell in its place, the frame and square directing pipe being also lifted out of the
cylinder. The pile to be let down had two hoops round its lower end, and a hole cut to
receive the end of the iron dowell already placed upright in the rock.
On the lower end of this pile were nailed four other pieces, so as to increase its size to 22
inches, the diameter of the cylinder, by which means it could be securely placed exactly
over the iron dowell by a stroke of the pile-engine.
To the chain fixed at the top of the cylinder a lever was applied, 50 feet in length, the
fulcrum of which was laid on the top of the main piles, and the other end lifted by ropes
and blocks from the mast of a sloop. It required a purchase of 50 tons to start the
cylinder; it was lifted up over the tops of the piles by the aid of ropes and blocks. The
head of the pile so fixed was then forced against the inner side of the leading frame, and a
screw bolt put through both. The apparatus was then shifted to the others, until the
whole of the main piles were fixed. Temporary leading beams were then fastened to the
heads of the first piles, at 15 or 20 feet apart, round the outside of the main leading
frames, and these spaces filled up by driving other piles, side by side, down to the rock.
The lower temporary leading frame was then taken off, the inside braces put in, which
rested on brackets fastened to the main piles.
The outer row of piles was placed in front of the cofferdam, by means of a float made of
pieces of fir timber 1 foot square, and 40 or 50 feet in length, fastened together by spiking
others across them. This float, 14 feet in length, filled the space between the rows of piles.
and was not only kept steady by them, but served to regulate and maintain their parallel
distance.
When the outer row was driven, a leading beam made by fishing was bolted to the
outside of the piles, on a level with the inside leading frame; a temporary leading frame
was then fixed on the inside of the outer row of piles, 1 foot lower than the outside beam;
a scaffold was erected on the top, and an outside leading beam bolted, at the same level
with the leading frame on the inside.
The space between the first-mentioned piles was now filled up by others set close
together, and driven down to the rock. The bank and puddles on each side of the dam
being by this time brought forward as far as the inner row of piles, the connecting bolts
were placed through each pile opposite the middle of the leading frame, through which it
passed, across the puddle, and through the front leading beam on the outside of the outer
row of piles. Each of these connecting bolts was fastened by a strong cotterel through
each end, with a strong iron plate under them; two of these bolts passed through each
of the main piles in front of the dam, one through each of the leading frames and the
other I foot below low water of ordinary spring tides, at which level the leading beams on
the outer row of piles was fixed. The two rows of piles were maintained in their position
by pieces of timber being joined on each side of the main pile on the inside of the dam, and
spiked down on the outside of the leading beams. When the banks and cofferdam were
finished, and the engine commanded the water, the works were proceeded with in the usual
way, and after enough of the rock had been removed the masonry was commenced. The
locks on this canal are of unusually large dimensions; the whole work, forming a junction
between the two seas, was opened at the end of the year 1823.
Artificial embankments have already been described, as made for the canal, 400 yards in
length beyond high water-mark on the shore of Loch Beauley at Clachnacharry, where the
foundations were of mud so soft that an iron rod could be thrust down 55 feet with ease.
002
564
Book I.
HISTORY OF ENGINEERING.
In this situation it was not deemed practicable to form a wooden cofferdam sufficiently
large to construct a lock 170 feet in length, and 40 feet in width, besides the necessary wing-
walls, and the following method was therefore adopted. An iron railway was laid down,
on which the heavy mountain clay found close by was carted, and the two banks of the
canal were first formed as far as where the depth of water at an ordinary neap tide was
20 feet; and when the site of the intended lock was approached, the banks were united into
one mass; the mountain clay compressed the soft mud beneath and squeezed out the water.
Upon this great mound of earth a quantity of stone was laid, which was afterwards used in
the construction, and remained for six months, at which period the mound had sunk 11 feet,
and it being considered that no further material sinking would take place, a lock pit was
excavated in the solid mound, and the water was kept down by a steam-engine of nine
horse power.
When the lock pit was excavated, rubble stone masonry was laid with
hydraulic mortar to the thickness of 2 feet in the middle of the lock chamber, increasing to
5 feet thick on each side; upon this an inverted arch of square masonry was struck, and on
it was built the side walls; the chamber walls, counterforts, recesses, and wing-walls were
then carried up.
The masonry of the bottom part was built in lengths of 18 feet, in order that the mud
might be prevented from again rising up in the space newly compressed. The mud was
easily penetrated by piles, but after they had been driven a few hours, no power could either
drive them further or draw them out. The whole of the masonry was completed in 1812,
the rise of the lock being 6 feet 8 inches. The system adopted was found to have been
far less expensive than a cofferdam.
The five connected locks at Fort Augustus have their foundation on a coarse open gravel,
and to construct them it was found necessary to turn the river Oich. A trial pit was
then sunk by means of a steam-engine of six-horse power; but when a depth of 18 feet was
obtained, the water accumulated so fast, that a pump well and an engine of 36 horse-power
were required, which enabled the lock bottom wings and forebay walls to be constructed,
though during the progress of these works, a third engine of nine horse-power was used,
and when the depth arrived at was 25 feet below the surface of Loch Ness, the whole three
engines were required to keep the waters down.
There is a let-off or outfall between Corpach and Loch Lochy, at Strone, which consists
of three sluices, each 4 feet broad and 3 feet high, the sills being on a level with the bottom
of the canal, and the inside faces of the water surface ranging with the bank line; the water
falls 9 feet before it reaches the rock on which it falls; the frames and sluice doors are of
cast-iron, the working parts being faced with copper; the sluice doors are raised and lowered
by rack-work, enclosed in cast-iron cylinders, placed over the centre of each, and rising
1 foot above the surface of the canal when full.
The length of the canal operated upon by this let-off is 6 miles, where it is 80 feet wide
at the surface, 50 feet at the bottom, and 10 feet deep, and the three sluices when opened
lower the water as follows:
From 10 feet to the depth of
9 feet
9
8
8
7
7
6
5
6
5
4
hr. min.
-
1 39
1
42
1
45
122
49
6
2 38
The freshwater lakes form 37 miles of its length, and vessels are admitted drawing
15 feet water.
The total expenditure from its commencement in 1803 to May, 1829, was
For work performed by contract and measurement
Ditto, by day work
-
£
652,494
68,099
Expenses of management for timber, machinery, shipping, land purchased, &c. 261,766
£982,359
The price of Baltic timber at its commencement was 2s. 6d., and got up to 7s. per foot
cube. The lock gates are of English oak and cast-iron; there are fourteen locks on the
west side, and thirteen on the east side of the summit. The turn-bridges are all cast-
iron.
Carlisle Canal, 114 miles in length, was executed under the direction of William Chapman,
a native of Whitby, at a cost of about 120,000%. It commences on the south-eastern side
of Carlisle, and falls into the sea through a height of 70 feet, by means of 9 locks. At
Carlisle there is a basin of considerable extent, and the first reach is 4 miles in length: it
then falls 46 feet by 6 locks, in the length of the next 1½ miles: it is then nearly level to
Bowness, and afterwards falls into the sea by three locks, the lift of each being 8 feet
between these are two basins, called the Upper and Lower Solway; the latter is on a level
;
CHAP. VIII.
565
BRITAIN.
.
with high water of the lowest neaps, and the other is 15 feet 6 inches higher. The depth
of water in the canal is 8 feet; the locks are 17 feet wide and 74 feet long, and the supply
is drawn from a reservoir, into which the waters of the Eden are pumped up.
Mr. Chapman showed considerable ability as an engineer in the execution of this work,
and was very extensively employed till his death, which took place 29th May, 1832, in his
83d year.
Chesterfield Canal commences at Stockwith in Nottinghamshire, and terminates at
Chesterfield. From the Trent to Worksop, a distance of 24 miles, it rises 250 feet, and in
the next 9 miles it rises 85 feet. Between the summit and Chesterfield, a distance of
13 miles, the fall is 45 feet; between Wales and Harthill is a tunnel 2850 yards in length,
12 feet high, and 9 feet 3 inches wide.
Coventry Canal commences on Fradley Heath, and ends at Coventry; it is joined in its
course by the Wyrley and Essington Canal, and by the Birmingham and Fazely. The first
11 miles is level; near Tamworth there is a rise of 14 feet 6 inches by two locks; from
thence to Grendon, 6½ miles, it is level; from the latter place to Atherstone, a distance of
21 miles, there is a rise of 81 feet 6 inches; it is afterwards level to Coventry.
Crinan Canal crosses an isthmus in Argyleshire, commencing at Ardreshaig in Loch
Gelph, and falls into Loch Crinan near Duntroon Castle.
Cromford Canal, the engineer to which was Mr. William Jessop, commences near Langley
Bridge, in the county of Northampton. The top width of the canal is 26 feet, and the
boats employed upon it are 80 feet in length, 7 feet 2 inches wide, and 3 feet 4 inches deep;
when loaded with 22 tons, they draw 2 feet of water, and when empty about 9 inches.
The tunnel at Ripley is 9 feet wide at the surface of the water, and from thence to the
crown of the arch it is 8 feet high: for the construction of this tunnel, which is 2966 yards
in length, thirty-three shafts were sunk, some of which were 210 feet in depth; the cost
of this work averaged 77. for each yard in length. There is an aqueduct bridge near
Wigwell over the Derwent, 200 yards long, and 30 feet high, the arch over the river
having a span of 80 feet; near Fritchly is another aqueduct, 200 yards long and 50 feet
high, and the two cost 60007 The reservoir of 50 acres over the Ripley tunnel is 12 feet
in depth, and contains 2800 locksfull of water, which is discharged by a large pipe and
cock in one of the tunnel pits; the embankment of this reservoir is 200 yards long, 156 feet
wide at the base, and 12 feet wide at the top: there are two other reservoirs, one containing
20 and the other 15 acres. The engineer has informed us that for cutting and wheeling
the clay, the price usually paid for a stage of 20 yards was 3d. per cube yard, for gravel
4 d., and that the entire cost of the canal was 80,000l.; it was completed in 1793.
Dearne and Dove Canal commences near Swinton, and near Dunn passes through a short
tunnel, and terminates near Barnsley.
Derby Canal commences on the Trent, near Swarkstone, and terminates at Little Eaton;
there is a branch to Erewash Canal.
Dorset and Somerset Canal commences at Gains Cross, and terminates in the Kennet and
Avon Canal at Wedbrook.
Droitwich Canal commences in the town of that name, and terminates at Hawford Bridge,
where the Salwarp river falls into the Severn; this work is said to have been by Brindley,
and is most admirably executed.
Dudley Canal proceeds from the Worcester and Birmingham Canal, at a place near Selby
Oak, and near Stonehouse enters the Lapal tunnel, which is 3776 yards long; beyond
Hales Owen is another tunnel 623 yards long, and at Dudley Woodside a third 2926 yards
in length, a short distance beyond which the canal communicates with the Birmingham.
There is a branch canal two miles in length, called the Black Delph, which falls into the
Stourbridge Canal.
Edinburgh and Glasgow Union Canal has its commencement two miles west of Falkirk,
at the sixteenth lock of Forth and Clyde navigation. Over the Avon is an aqueduct 80
feet above the surface of the river; this canal terminates by a basin at the Lothian road; it
is fed at one place by a suspension aqueduct, which crosses the Almond river.
Ellesmere and Chester Canal leaves the tideway of the Mersey at Ellesmere Port, crosses
the river Ceiriog by a stone aqueduct, and at Pont Cysyllte by an iron one, and falls into
the Montgomeryshire Canal.
The Llanymynech branch leaves at Francton common, out of which is another, which
terminates at Weston Lullingfield. The main line of the canal rises 46 feet in the first 83
miles; from Chester to the Harleston locks is 153 miles, with a rise of 131 feet, by means
of eleven locks. From these locks to Francton Common it rises 115 feet in a distance of 25
miles; from Francton Common to its termination in the Montgomeryshire Canal, it is 111
miles, with a fall of 52 feet. The branch from Wardle Green to Middlewich is in length
10 miles, with a fall of 44 feet 4 inches by four locks; that to Ruabon Brook Railway
is 11 miles in length, with a rise of 13 feet. The aqueduct over the Dee, at Pont
Cysyllte, has a height of 125 feet; the pillars are 52 feet apart. The trough through
which the vessels pass is 320 feet long, 20 feet wide, and 6 feet deep, formed entirely of cast-
003
566
BOOK I.
HISTORY OF ENGINEERING.
iron plates. The original plans for this undertaking were made by Mr. William Jessop.
This canal unites the Severn, Dee, and Mersey, and consists of a series of navigations,
commencing from the river Dee, in the Vale of Llangollen, passing near Ellesmere,
Whitchurch, Nantwich, and Chester, to Ellesmere Port, on the Mersey, in one direction;
through the middle of Shropshire, towards Shrewsbury, on the Severn, in another; and in
a third, by the town of Oswestry to the Montgomeryshire Canal at Llanymynech; the
whole length, including the Chester Canal, being 103 miles. An act of parliament was ob-
tained for this work in 1793. Mr. Telford was employed, and it was the occasion of his
attention being more particularly called to the study of civil engineering.
Ellesmere Port, on the Cheshire side of the Mersey, is 12 miles from Liverpool; here the
canal commences; from thence to Chester is 9 miles, and from Chester to Nantwich 20
miles. For the whole of this distance the locks will admit barges whose beam is 14
feet. The perpendicular rise from low water in the Mersey to Nantwich is 177 feet.
From Nantwich to Whitchurch is 16 miles, with a rise of 132 feet; from thence to
Ellesmere, Chirk, Pont-y-cysyllte, and to the river Dee 13 miles; above Llangollen (in-
cluding the Prees branch) the distance is 384 miles, and the rise only 13 feet, in all 322 feet
above low water at Liverpool. About 32 miles west of Ellesmere, at Francton, the canal
descends 30 feet, and from thence passes on a level to Weston Llulling fields in one
direction, and in another 10 miles to Llanymynech, with a fall of 19 feet, where it joins
the Montgomeryshire Canal.
The greater part of the fifty-one locks are only calculated for boats of 7 feet beam. They
are of the usual form, but the gates are chiefly of cast-iron. For locks of 14 feet beam, the
lower gates, which are in
two leaves, have cast
heads, heels, and ribs in
separate pieces, with
flanches, which are fast-
ened together with nuts
and screws; the whole is
then covered with wooden
planking. The price of
the lower pair of gates so
formed in locks, with a
rise of & feet 6 inches,
was 1021., and for the

Fig. 545.
CAST-IRON LOCK; PLAN AND SECTION.
upper gates, where each valve was cast in a single piece, 597. 10s.: at this time iron was
computed at 147. per ton delivered. These gates show no
symptom of decay, even at the present day.
Cast-iron Locks opposite Beeston Castle, Cheshire.
Here are two locks rising 17 feet, built entirely with cast-
iron upon a stratum of quicksand: they answered the
purpose admirably, and, for this peculiar and difficult
foundation, were the best that could be adopted, though
the cost in the first instance was considerable.

Fig. 546.
SECTION OF LOCK.
The aqueduct over the valley of the Ceiriog, between Chirk Castle and the village, is
710 feet in length; the surface of the water in the canal is 70 feet above the level of that

Fig. 547.
of the river below.
AQUEDUCT OVER THe ceiriog.
There are altogether 10 arches, each of 40 feet span; the total breadth
at the top is 22 feet, that of the water is 11 feet, and the depth 5 feet.
The piers are 33 feet in depth, and 13 in width, or a little less than a third of the span of
the arches which rest on them; these are all constructed in stone, and in the spandrills are
longitudinal walls, supporting the cast-iron plates which form the bottom of the canal.
These plates have flanges cast on their edges, and are united by means of nuts and screws;
on these the sides of the canal, which are 5 feet 6 inches thick, are built with ashlar
inasonry, backed with hard burnt bricks laid in Parker's cement; the outside was faced
with rubble stone-work, like the piers and arches.
Under the towing-path, and beneath the gravel, a thin bea of clay was laid, and the outer
edge protected by an iron railing; the iron bottom plate forms a continued tie, and prevents
the walls from splitting. This work was completed in 1801, at a cost of 20,8987.; the
whole, with the exception of quoins, coping and lining the sides of the water-way, which is
of ashlar masonry, is of rubble work laid in good lime mortar.
CHAP. VIII.
567
BRITAIN.
Aqueduct of Pont-y-Cysyllte is 4 miles from Chirk, over the river Dee; an earthen em-
bankment was pushed forward until the perpendicular height became 75 feet. The distance

Fig. 548.
AQUEDUCT over the dee at PONT-Y-CYSYLLTE.
between the end of this and the north bank is 1007 feet, and the river Dee is 127 feet
below the water level of the canal carried over it.

Fig. 549.
AQUEDUCT over the dee at pont-Y-CYSYLLTE.
To construct an aqueduct upon the usual principles, with piers and arches, 100 feet in
height, and of a sufficient breadth and strength to afford room for a puddled water-way,
would have been, not only extremely hazardous, but expensive. Telford, who had already
carried the Shrewsbury canal by a cast-iron trough 16 feet above the level of the ground,
formed the idea of doing the same in the present instance, and made a model of a portion
set on two piers, with the towing path and side rails, which was approved of and finally
adopted. The foundation on which the piers are erected is a hard sandstone rock; their
height above low water in the river is 121 feet, at the bottom they are 20 fect by 12, and
at the top 13 feet by 7 feet 6 inches. For a height of 70 feet from the foundations, they
are built solid, and the remaining 50 feet hollow, the walls being only 2 feet in thickness,
with one cross inner wall; by this means the centre of gravity is thrown lower in the pier,
and the masonry economised.
The width of the water-way is 11 feet 10 inches, of which the towing-path covers 4 feet
8 inches, leaving 7 feet 2 inches for the boat; as the towing-path stands upon iron pillars,
the water fluctuates and recedes freely as the boat passes.
There are eighteen of these stone piers, besides those of the abutments, and the total
expense, including the embankment, was 47,0187.
The embankment cost
Masonry
Iron work
£ S. d.
-
8,570 15 8
-
21,162 13 5
-
17,284 17 5
£47,018 6 7
The
This aqueduct almost rivals the works of a similar kind left us by the Romans.
introduction of iron, however, for the watercourse, is a novelty with which they were un-
acquainted; in this instance it has proved admirably well fitted for the purpose to which
it is applied; had a stone or brick channel been constructed at this great elevation, it
could not have been rendered so secure for the passage of boats, as there would have been
a constant leakage from the motion and friction of the water within it. The cast-iron
plates which form the sides are strongly riveted and secured to those at the bottom, and
0 0 4
568
Book I.
HISTORY OF ENGINEERING.
wherever possible, ties and braces are introduced: the platform which supports the towing
path adds greatly to the strength of the side to which it is attached, and the water passing
under it prevents in a great measure any injurious consequences from the swell occasioned
by the boats in their transit. The span of the arches is 45 feet, and their rise above the
springinr 7 feet 6 inches.
Upon this canal are two short tunnels, one 500, the other 200 yards in length, both in
the rugged ground which lies between the rivers Dee and Ceiriog; they are each 14 feet
7 inches high, 14 feet wide, and the towing-path covers 4 feet 9 inches, leaving 9 feet
3 inches water-way; this path also stands upon pillars, so that the water is allowed its swell
without great interruption.
The general summit of the canal is supplied by a navigable feeder 6 miles in length,
carried along the bank of Llangollen valley from the river Dee at Llandisilio; a constant
supply of water being ensured by a regulating weir, which dams up the Lake of Bala Pool,
4 miles in length, situated about 20 miles from Llandisilio.
Adjacent to Mantwick, where the Ellesmere canal unites with the Chester, the distance
to the Trent and Mersey, or Grand Trunk canal, at Middlewick, is only 11 miles; in 1826,
an act was passed to unite them by a canal, and the works were speedily completed. This
branch of 11 miles has a fall of 44 feet; the locks are 82 feet in length, and 7 feet 6 inches
in width. The canal is 16 feet wide at the bottom, 36 feet at the surface, and 5 feet deep,
and obtains its chief supply from the Dee.
Erewash Canal, proceeds from the Trent, near the village of Sawley, and terminates at
Langley bridge, by uniting with the Cromford canal. From the Trent to where the
Derby branch locks down is 31 miles; from thence to Nutbrook 2½ miles; from thence to
Cromford canal 6 miles, with a total rise of about 100 feet from the Trent.
Exeter Canal, was probably the first pound-lock canal established in England, for we
find that in 1563 the corporation of the city employed John Trew of Glamorganshire to
form a canal, which should restore the navigation already rendered difficult in the river,
in consequence of a weir constructed across it in the time of Henry III. The length of
this canal was 9360 feet, the breadth 16 feet, and depth 3 feet; and several pools or
chambers were formed, 300 feet in length, 80 feet in breadth at the top, and 50 feet at the
bottom, with the sides walled for the purpose of passing the vessels; each pair of gates
was 25 feet in height, and each leaf 20 feet in breadth, furnished with iron and brass
work, that they might be moved with facility; specifications of the work remain among
the papers of the corporation.
The most ancient method of navigating rivers was by flashes of land-waters, so collected
that boats could be carried over the shoals: in this canal we find the first improvements
were made by John Trew, who constructed a number of pools or locks, the vestiges of
which may still be seen, consisting of the chamber-walls, partly buried in the western part
of the canal, which was cut in 1699. In one of the specifications above alluded to is the
following entry :-" for digging a pool between the said two gates, which must be 300 feet
in length at least, and about 80 feet in breadth, at the top or surface of the water, and 50
feet broad at the bottom, and for walling the same on both sides, for the convenient and
necessary passing of ships one after the other." These pools, or pylls, had each a pair of
sluices, and were no other than pound locks, and frequent mention is made of these pairs of
sluices in the several conveyances by the Corporation. There can be no doubt that on the
whole canal there were at least seven sluices; the pools were fed by the river Ex, which
had a stake weir constructed across it long before the one of stone.
After the works were executed, we find that the Corporation were by no means satisfied
with Mr. Trew, for the canal could not be entered at all "tide and tides; "it was afterwards
considerably deepened, and other sluices added.
The two Brothers of Viterbo, as we have already seen, had built a lock chamber, with a
double pair of gates, at the Canal della Martesana, as early as 1481, and it seems extra-
ordinary that so novel an invention had not found its way from Italy into England until
more than 80 years afterwards: the canals in France for the purposes of irrigation may
have suggested the idea of a sluice that could be opened for the passage of boats; Adam de
Crapone, employed by Henry II. of France for these works, had, in all probability, seen
the gates which shut the locks in Italy.
Previous to this discovery it was not possible to form an artificial canal, except in a per-
fectly level district, and we find attention at once directed to the improvement of inland
navigation throughout Europe immediately afterwards; in the Low Countries and in Hol-
land the greatest advantage was taken of the discovery, and a most complete system was
established for the passage of vessels of very considerable tonnage.
Forth and Clyde Canal has its course from the river Forth, in Grangemouth harbour,
and passes the Loggie water by a stone aqueduct, and the Kelvin by another, when it locks
down in Bowling's Bay. There is a branch to the Monkland Canal at Glasgow 23 miles
in length. On this canal are thirty-three draw-bridges, ten large and thirty-three small
aqueducts. There is a reservoir at Kelmananmuir, the area of which is 70 acres, which
CHAP. VIII
569
BRITAIN.
has a depth of water at the sluice of 22 feet. Another reservoir at Kilsyth comprises
50 acres, and has a depth of 24 feet.
The aqueduct at Kelvin is in length 429 feet, and in height above the stream 65 feet;
a small junction canal has been cut opposite the river Cart, which unites the Forth and
Clyde with the river Clyde. The lock chambers are in length 68 feet in width, at the
gates 15 feet, and in the centre 17 feet. The walls are curved and batter; the retaining

لسلسلة
F
Fig. 550.
PLAN AND SECTION OF LOCK OF FORTH AND CART.
walls are in freestone, coped with whinstone; they were puddled at the back to a thickness
of 2 feet.

不
​Fig. 551.
ELEVATION OF TAIL.
TRANSVERSE sectION.
Foss Navigation commences near Newburgh Hall, 4 miles from Easingwold, and falls
into the Ouse on the south side of the city of York.
Foss Dyke Navigation begins at Torksey on the Trent, and ends at Lincoln High
bridge; it is level throughout. At Torksey is a double lock with gates pointed both ways,
for the purpose of damming up the Trent, and keeping out the flood waters. At the
other end is another lock, for preventing the water of the Witham from entering during
the time of floods. Torksey being the site of a Roman town, it is supposed that this
work was a continuation of Caerdike, made by the Romans; Domesday Book mentions the
place as important.
Glamorganshire Canal, sometimes called the Cardiff, from commencing near that town
on the Taff, near the place where that river enters the Penarth harbour, which river it
crosses by an aqueduct, and terminates at Merthyr Tydvil.
Glasgow, Paisley, and Ardrossan Canal, begins at Port Eglington, west of the town of
Glasgow, and terminates at Johnstone.
Glenkenns Canal runs from the Dee near Kirkcudbright, and terminates in Loch Ken,
near Glenlochar bridge.
Gloucester and Berkeley Canal passes from the Severn, at Sharpness Point, and terminates
near the city of Gloucester. This spacious ship-canal is level throughout, and capable of
floating vessels of 400 tons burthen, there being at least 18 feet water. Near the outer
harbour, in the Severn, is a breakwater.
An act of parliament was obtained for a ship-canal from the city of Gloucester to the
open estuary at Berkeley Pill, in the year 1793, and the works were commenced under the
direction of Robert Mylne, the architect of Blackfriars bridge, when a basin and entrance
lock was made at Gloucester, and about 8 miles of the canal on the low ground was com-
570
Book 1.
HISTORY OF ENGINEERING.
pleted; but it was not until the year 1818, that it was proceeded with under the direction
of Mr. Thomas Telford. The proposed entrance at Berkeley Pill being considered too
much exposed to the south-west winds, it was determined that one should be formed
under a projecting headland called Sharpness Point, where, restrained by a rocky shore on
each side, the river channel was the only passage for the flux and reflux of the tide, thus
securing deep water free from sand and mud banks, to which the flat shores of the Severn
are subject.
An entrance basin and extensive piers of masonry were constructed, and by a large tide-
lock the canal was raised to the same level as that of the Gloucester basin. Near the Sharp-
ness Point, the canal is carried for the distance of a mile along the face of a very steep bank
of rock marl; the outer bank being formed of and secured by a sea-wall.
In addition to the sea-lock, which admitted vessels of 300 tons burthen, another was
constructed for barges of 70 or 80 tons. It is high water at spring tides at this entrance
at 7 o'clock, and the depth upon the lock-sills is from 26 to 28 feet, at neap tides from
14 to 16 feet. The length of this canal is about 16 miles, its depth 18 feet; it is supplied
with water from the river Frome.
Grand Junction Canal, one of the principal engineering works of Mr. William Jessop, forms
an important link in the system of inland navigation, by which the capital is connected with
the iron and coal fields of the midland counties. Within a mile of its commencement, it
rises 37 feet to its first summit; this summit level is 43 miles long, and has a tunnel 2045
yards in length, through which the canal enters the marlstone ridge of the lias formation;
it then falls 60 feet into the valley of the Nene, and continues on a level for 13 miles to
Gayton, from which place there is a branch to Northampton. On this level the famous
Blisworth tunnel is situated, 3080 yards in length, which was completed in March, 1805.
Its internal width is 16 feet, the depth below the water-line to the inverted arch 7 feet, and
the soffite or crown of the arch is 11 feet above the same line. The side walls are segments
of a circle of 20 feet radius, the top arch one of 8 feet radius; the side and top walls are
2 bricks thick, and the bottom or inverted arch 14 bricks. The mortar was composed of
1 bushel of Southam lime (blue lias) to 3 of good sand: 6 inches under the water-line on
each side of the tunnel, slide rails of fir 5 inches square, to keep the barges off the walls
are fixed by pieces of oak let into the wall below them; these rails project 9 inches from
the wall, and at every 9 feet a chock of wood is fixed upon the rail for the bargemen to set
their pole against. This tunnel was contracted for at 157. 13s. for every running yard, the
scil being a hard blue clay, interspersed with two or three thin rocks.
Sufficient headings
having been driven at the company's expense several years before, the same contractors were
paid 10d. per cube yard for excavating the deep cutting at one end of this tunnel, and
11d. per cube yard for the other. The expenses of driving the above headings was 36s.
to 42s. 6d. per yard run; nineteen tunnel pits, some 60 feet in depth, were sunk for the
use of the tunnel, which cost above 30s. including steining, for every yard in depth.
The canal next falls into the valley of the Ouse, where its level is 172 feet below that
of the Braunston summit. Following the line of the Ouse, it passes close to the town of
Stony Stratford, whence a branch goes off to Buckingham; it then continues to Lin-
ford Magna, Fenny Stratford, and Leighton Buzzard, through the sands and gault clay
of the green sandstone formation, and rises to the summit level at Tring by a lockage of
192 feet: it attains this level near Marsworth, 51 miles distance from Braunston. The
summit level, 33 miles in length, is carried through a chalk cutting of 30 feet in depth, and
passing by Berkhamstead and Hemel Hempsted, the canal falls into the valley of the
Colne, and continues by King's Langley and Harefield to Uxbridge. Near King's Langley
is a deep cutting, on a level of the canal, 127 feet below the Tring summit. From Uxbridge
it passes through a flat district, and after crossing the river Cran and Brent, terminates in
the river Thames at Brentford. The total cost of this great undertaking was 2,000,000%.
sterling: its entire length from Braunston to Brentford is 90 miles, the width of the canal
at bottom is 28 feet, at the water surface 42 feet, and its depth 4 feet 6 inches: the length
of the lock chambers is 80 feet, and their breadth 14 feet 6 inches.
The reservoirs which supply the canal at
Daventry contains
Drayton
Marsworth
Stanhope End
Tring
Locks of Water.
7205
1337
994
2296
1016
1413
1413
1856
Old Wilston (covers 40 acres)
New Wilston
Weston
Each lock contains about 9000 cubic feet of water.
As these reservoirs are at various levels, steam-power is required to raise the water
from one to the other. The principal engine at Tring is estimated as a 70 horse-power,
CHAP. VIII.
571
BRITAIN.
its consumption of coals is about 1 cwt. per hour, with a 40 feet lift; this engine works
at a pressure of 24 pounds, makes ten strokes per minute, and pumps up sufficient for
eighty locks in 24 hours.
Mr. Jessop's estimate for the completion of this canal was nearly quadrupled; the follow-
ing are the lengths and lockage, as stated on the map which accompanied this report:—
From the Oxford canal to near Braunston Mill
From Braunston Mill to the end of Long Buckby parish
From the end of Long Buckby to the end of Whilton parish
From the end of Whilton parish to Stoke
From Stoke to the river Ouse
-
From the river Ouse to near Marsworth
From Marsworth to near Cow Roast
From Cow Roast to Two Waters
From Two Waters to near Langleybury
From near Langleybury to the river Thames
295
Miles. Furl. Ch.
0 7 3.20
4 2 0.30
0
5.10
Feet.
37 rise
level.
60 fall.
13
3 5.90
level.
6 4
25 1
3 6
4.10
112 fall.
6.
0.50
192 rise.
6 6 0.50
level.
127 fall.
4 6 2.40
level,
23
6 5.60
268 fall.
90 1 3.60
There is a branch from Uxbridge to Paddington, level throughout and 20 miles in length,
at which latter place is a basin 400 yards long, and 30 yards broad. The barges have
generally square heads and sterns, flat bottoms, and carry 60 tons; there are some with sharp
heads and sterns, which carry 25 tons.
Grand Union Canal unites the Leicester Union about 4 miles from Market Harborough
to the Grand Junction, at Long Buckby.
Grand Junction Canal unites the Severn with the Bristol Channel.
Grantham Canal, from the town of that name to the Trent Bridge at Nottingham.
There are two reservoirs, one of 20 acres, and 9 feet deep, at Denton; the other, of 60 acres,
at Knipton, both executed under the directions of Mr. William Jessop.
Gresley Canal, from Apedale to Newcastle-under-Lyne.
Hartlepool Canal is a cut through the solid rock to a depth of 19 feet; its length is not
more than 300 yards.
Hereford and Gloucester Canal, from. Hereford to the tideway of the Severn at Gloucester
There are tunnels at Hereford, Asperton, and Oxenhall; the first 440 yards long, the
second 1320 yards, and the third 2192 yards.
Horncastle Navigation begins in the Old Witham river.
Huddersfield Canal connects the river Calder, between a bridge called Coopers, and the
river Colne to Huddersfield. Near Marsden there is a rise of 436 feet, made by forty-two
locks; here its summit elevation is 656 feet above the level of the sea. It has afterwards
a descent of 334 feet 6 inches, divided by thirty-three locks. The tunnel at Scout, through
a sand rock, is 204 yards long, and that at Standedge, called the Marsden tunnel, is 5550
yards in length, 17 feet high, and 9 feet wide, with a depth of water of 8 feet; each of these
has a towing-path. Mr. Outram was the original engineer, but Messrs. Clowes & Nicholas
Brown were afterwards employed.
Hull and Leven Canal unites the Hull river with Leven Bridge.
Ivelchester and Langport Canal connects these two towns.
Kennet and Avon connects the Kennet navigation at Newbury with the Avon, where
the latter river becomes navigable to Bristol. This canal at its highest elevation is 474
feet above the level of the sea. There are two aqueducts over the Avon.
Kidwelly Canal, from the harbour of that name.
Lancaster Canal has its commencement at Kirkby Kendal. The tunnel at Hincaster
is 800 yards long, and that at Whittle Hills is 300 yards. The aqueduct of stone over
the Lune is 51 feet above the level of the water, and has five arches of 70 feet span each.
At Barkmill, the Leeds and Liverpool canal crosses it by an aqueduct 60 feet high. There
are two others belonging to the Lancaster canal, one at Garstang over the Wyre, the
other at Bethorn over the Beeloo. This great work was the first of the kind undertaken
by Mr. Rennie, and established his reputation as an engineer.
Leeds and Liverpool Canal, uniting these towns, is one of the boldest works executed,
particularly for the time; its rise to the branch of the Bradford canal is 155 feet 7 inches.
It soon after crosses the Aire by an aqueduct of considerable length, and again rises 88
feet 8 inches. The Bingley locks at this place consist of five rises; and every boat requires
five locksfull of water, which might be economised by dividing them. At Skipton the
elevation of the canal above the waters of the Aire at Leeds bridge is 272 feet 6 inches.
Gargrave it again crosses the Aire by another long aqueduct. At Rainhill Rock it rises
411 feet 4 inches above the Aire at Leeds, which is its greatest height. At Foulbridge
the great tunnel commences, the length of which is 1640 yards; the height is 18 feet, and
the width 17 feet. Near the tunnel is a reservoir, comprising 104 acres, and containing
At
572
Book I.
HISTORY OF ENGINEERING.
1,200,000 cubic yards of water. At Barrowford, it locks down 70 feet, then crosses Colne
Water by an aqueduct. At Burnley there is an embankment 60 feet high, and 1256 yards
long; and two aqueducts, one over the Broun, the other over the Calder: there is also a
road under the canal. At Gannah is another tunnel, 559 yards in length. Another
aqueduct crosses the Henburn, and at Grimshaw Park there is a fall of 54 feet 3 inches,
by six locks. An aqueduct passes Roddlesworth Water, and at Cophurst Valley is
another fall of 64 feet 6 inches, by seven locks. Near Kirkless there are twenty-three
locks, which bring the canal down 214 feet 6 inches from the Lancaster canal to the Wigan
basin; from thence there is a fall to Newburgh of 30 feet.
The Lady's Walk, Liverpool, to Leeds Bridge, is 127 miles, and has a lockage of 844 feet
6 inches, viz. from Leeds to the summit level 411 feet 4 inches, and then a fall of 433 feet
2 inches into the basin at Liverpool, which is 21 feet 10 inches above the Aire at Leeds,
and 56 feet above low water in the Mersey.
To James Brindley and Robert Whitworth the engineering works upon this line were
entrusted, and the manner in which the whole were executed deserves the highest com-
mendation. The locks are formed to receive boats 70 feet in length, and with 14 feet beam,
and the least depth of water in the canal is 4 feet 6 inches. By means of its water con-
veyance a communication is at once opened between Liverpool and Yorkshire, and agri-
culture is benefited by it to a considerable degree.
Leicester Navigation. — From its commencement, at the basin of the Loughborough canal,
to its junction with the Leicestershire and Northamptonshire Union canal, there is a rise
of 45 feet; the whole was superintended by Mr. William Jessop.
Leicestershire and Northamptonshire Union Canal. Where this navigation commences
with the Leicester, it is 175 feet above the level of the sea. It rises 160 feet to the tunnel
at Saddington, and falls into the Grand Union canal at Gumley Hall.
Leominster or Kington Canal proceeds from the latter place at an elevation of 505 feet
above the level of the sea. It crosses the Lugg by an aqueduct at Kingsland, and by
another over the Rea passes the tunnel at Sousant, 1250 yards long, and unites with the
Severn and the Stafford and Worcester canal. The tunnel at Pensax is 3850 yards long.
Leven Canal communicates with Kingston-upon-Hull.
Liskeard and Loe Canal terminates at Moorswater, 156 miles above the level of
the sea.
London and Cambridge Canal has its commencement at Bishop Stortford canal; twelve
locks raise it 72 feet, and there is a tunnel 340 yards in length; ten locks then descend
to a second tunnel, 418 yards in length. At about 13½ miles from its commencement
is a third tunnel, 704 yards long; the canal locks down by twenty-two locks the next
12 miles. Eight other locks occur before it falls into the Cam at Clayhithe sluice.
On the Whaddon branch are thirteen locks.
Louth Canal commences at the sea lock in Tetney Haven, and terminates in the river
Ludd.
Macclesfield Canal proceeds from the Peak Forest canal, and joins the navigation from
the Trent to the Mersey; it is 29 miles in length, and passes from the north end of the
Harecastle tunnel, to the Peak Forest canal at Marple; it is 32 feet wide at the surface,
16 feet at the bottom, and 5 feet 4 inches deep. It continues to a little beyond Congleton,
a distance of 10 miles, upon a level, where it rises 114 feet by eleven locks, which occupy in
succession nearly a mile in length; the canal then proceeds on a level to Marple. The
dimensions of the locks are 84 feet in length, and 7 feet 6 inches in breadth.
As this canal crosses several deep ravines, it was necessary to have ten considerable em-
bankments, some of which are 80 feet in height. The aqueducts, whenever introduced, are
of cast-iron. These works were executed in conformity with an act of parliament passed
in 1825.
Manchester, Bolton, and Bury Canal has its commencement in the Mersey and Irwell
navigation, where there is a rise of 68 feet 4 inches by six locks. After leaving the Salford
basin, and proceeding some miles, it again falls by twelve locks; it crosses the Irwell by an
aqueduct near Clifton Hall, and again near Bolton: there is a third aqueduct over the
Roach.
Market Weighton Canal locks down into the Humber, opposite the mouth of the Trent,
at the Fossdyke Clough.
Monkland Canal proceeds to Glasgow, where it joins the Forth and Clyde canal, at a
point 156 feet above the level of the sea.
Monmouthshire Canal commences on the Usk river, near Newport: from Crynda Farm
to Crumlin Bridge the canal rises 358 feet.
Montgomeryshire Canal has a lockage of 225 feet from Llanymynoch to Newton, where it
unites with the Severn. The branch from Garth Mill was made by Mr. Josias Jessop, and
has six locks, of 8 feet each; it is 15 feet wide at bottom, and 6 feet deep: the Guilsfield
branch was by Mr. G. W. Buck.
Neuth Canal commences near Abernant, and terminates in the river Neath.
CHAF. VIII.
573
BRITAIN.
Newcastle-under-Lyne extends to Stoke-upon-Trent.
Newport Pagnell Canal extends to the Grand Junction at Great Linford.
North Walsham and Dilham Canal commences at Wayford Bridge, and terminates at
Altingham.
North Wilts Canal proceeds from Swindon, which is 345 feet above the level of the sea,
to the Thames and Severn canal, at Weymoor Bridge.
Norwich and Lowestoft Navigation, improved under the direction of Mr. William Cubitt.
The sluice and lock between the Lake Lothing and the sea had their foundations laid at
30 feet below the level of spring tides, and upon these the side walls were constructed.
The substructions are 10 feet in thickness, 50 feet in width between the walls, and
450 in length, the whole built as an inverted arch, grooved and filled up solid to its chord
line. The floor of the lock agrees with this line, and is 12 feet below the low water of
spring tides. The lake was deepened by a dredging machine, which lifted from two to
four tons per minute from depths of 10 or 12 feet.
Nottingham Canal unites the Cromford canal with the Trent, and has some collateral
cuts. At Amsworth is a large reservoir, with a regulating, self-acting, sluice which lets
out 3000 cubic feet per hour. This canal, executed under the direction of Mr. William
Jessop, cost 75,000l.
Nutbrook, or Shepley Canal, extends from Shepley to the Erewash Canal.
Oakham Canal from the town of that name to the Melton Mowbray Navigation.
Oxford Canal begins at Longford on the Coventry canal, where it is 315 feet above the
level of the sea; its summit level at Marston wharf is 387 feet: its termination is in the
Thames at Oxford, where it is 192 feet above the level of the sea. Over the valley at
Brinklow it passes by an aqueduct of twelve arches, each of 22 feet span, and at Casford
and Clifton are two others. At Newbold is a tunnel 125 yards long, and another at Fenny
Compton, 1188 yards long.
Peak Forest Canal begins near Ashton-under-Lyne, crosses the Mersey by an aqueduct
90 feet high, with three arches of 60 feet span each; then rises 212 feet by sixteen locks,
and afterwards joins the Macclesfield Canal: there is an inclined plane of 515 yards long,
and 204 feet fall.
Pocklington Canal commences on the river Derwent at East Cottingwith, and terminates
at Street Bridge.
Portsmouth and Arundel Canal, from Ford to Chichester harbour. It is supplied with
water from the harbour by a steam-engine. At the east end are two locks, one of 5, the
other of 7 feet, and a basin at the termination at Portsea: from the main line of the canal
in Chichester harbour to the canal at Cosham is 15 miles; to Portchester Lake it is 11
'miles.
Regent's Canal unites the Paddington branch of the Grand Junction with the Commer-
cial Road Basin, which locks into the Thames. It passes under the Edgeware Road by a
short tunnel, and by another under White Conduit Street. By this canal the London and
Liverpool are united. The locks have all double chambers. The tunnel at Maida Hill is
370 yards long, and the other at Islington 900 yards.
Rochdale Canal. From the Calder navigation at Sowerby Bridge, it proceeds until it
locks down in the Duke of Bridgewater's canal, at Castlefield, Manchester. It has several
reservoirs, a tunnel of 70 yards in length, 8 aqueducts, and forty-nine locks. Its total rise
is 275 feet, and fall 438 feet.
Rye, or Royal Military Canal commences near the castle at Sandgate, and terminates at
Cliff End.
Salisbury and Southampton Canal, intended to unite these two places.
Sankey Canal commences at the mouth of Sankey Brook, in the Mersey, and terminates
at St. Helen's. It has eight single locks of 6 feet fall each, and two double locks of 15 feet
each; there are eighteen several bridges, and near St. Helen's is a tunnel; this was the
second canal made in England, that at Exeter being the first.
Sheffield Canal connects that town with the river Dunn.
It commences in the township
of Tensley, passing by an aqueduct over the road to Attercliffe and Sheffield.
Shrewsbury Canal commences in Castle Foregate basin, and terminates in the Ketley
canal; part of the ascent is by locks, and the other by inclined planes. At Langdon is
the first aqueduct, of cast-iron, over the Tern. The inclined plane at Wombridge is 223
yards long, and 75 feet perpendicular fall.
It
Shropshire Canal. -From the Severn at Coalport to the Donnington Wood canal.
rises 207 feet by an inclined plane. At Windmill Farm is another inclined plane, of 120
feet.
The summit of this canal is 333 feet above the Severn at Coalport, and 120 feet
above the summit of the Shrewsbury canal. The inclined planes, introduced by Mr. William
Reynolds of the Ketley iron-works, is an epoch in canal history; and the Shropshire canal
passing over a rugged country with a great scarcity of water, the system usually adopted
was not found practicable. On the banks of the Severn, up the face of a steep bank, an
inclined plane, 350 yards in length, and 207 feet of perpendicular height, was constructed,
574
BOOK I.
HISTORY OF ENGINEERING.
with a strong double railroad upon it, to receive boats with their carriages. When the
boats arrive at this height, with their load of five tons, they pass along a level canal for 14
miles, and then descend by an inclined plane, 600 yards in length, and 126 of perpen-
dicular height; they then, by another level line of canal, which is the summit, proceed to
Rodwardine Wood inclined plane, which is 320 yards long, and 120 feet perpendicular
fall.
Other inclined planes succeed; the whole works were completed in 1792.
Somersetshire Coal Canal commences at Limpley Stoke, in the Kennet and Avon canal,
and terminates at Paulton.
Staffordshire and Worcestershire Canal. — From the river Severn at Stourport, and unites
with the Trent and Mersey navigation, near Haywood in Staffordshire. Aqueducts con-
duct it over the river Trent and Sow Penk, Smester and Stour; there are also three tun-
nels, one under the town of Kidderminster.
Stamforth and Keadby Canal, from the Don at Fishlake, to the river Trent at Keadby in
Lincolnshire.
Stourbridge Canal. From Stewponey on the Staffordshire and Worcestershire canal to
Stourbridge.
Stafford-upon-Avon Canal commences at King's Norton, and at 6 miles from Birmingham
joins the Worcester and Birmingham. It has four branches, one to the Tamworth quarries,
2 miles long, another to the Warwick and Birmingham canal, 13 miles long, and one at
Temple Grafton Lime Walks, 4 miles in length, and the other 1 mile in length 'to Aston
Cantslow. Near Milepole Hill is a tunnel, 320 yards in length, and several small
aqueducts.
Swansea Canal, from the harbour, where the Tawe river falls into the Pen Tawe.
Tavistock Canal, from the tideway of the Tamar, at Morwelham Quay Basin, to Tavi-
stock. Under the Morwelham dam is a tunnel, 2646 yards long; this tunnel has 460 feet
height of earth and rock above it. The locks are made for boats 12 feet 6 inches long,
and 5 feet wide. At Crebar there is an aqueduct 200 yards long, and 60 feet above the
river.
Thames and Medway Canal commences at Gravesend, and by a tunnel through the chalk,
it enters the Medway at Frinsbury.

The chalk formation,
through which this tunnel
is driven, was by no means
favourable to its exe-
cution in some places it
was found so soft that it
crumbled before the miner,
and in others so dense that
it was necessary to blast
it with gunpowder; where
the chalk was mixed with
veins of earth, it required
a considerable number of
stout yellow pine spars
9 inches in diameter to
support it; these were fre-
quently crushed beneath
Fig. 552.
THAMES AND MEDWAY TUNNEL.
the weight to which they were opposed, and some serious accidents occurred. The thick-
ness of the brickwork varied according to circumstances; at the summit of the tunnel it
was 14 inches, and generally at the springing 18 inches. The space above the brick arch
was filled in with chalk and lime mortar as the vaulting advanced, and the chalk above
was pinned up as securely as possible.
The length of the tunnel is 24 miles, and the entire length of the canal nearly 7 miles
the passage round the Nore and up the Medway is thus avoided, and a distance of nearly
50 miles saved in the navigation.
Whilst this tunnel was in progress the water in the surrounding wells, for a very con-
siderable distance, sank so low that it was necessary to deepen them to obtain a supply
When the salt water was admitted into the canal it affected all the fresh which pervaded the
chalk district, and materially injured the quality of that which was drawn from the newly
deepened wells, and great expense was incurred by the company, who were assessed in
considerable damages for these injurious effects. The entrance from the Thames at
Gravesend is through a basin; the canal is 50 feet wide and 7 feet deep to where the tunnel
commences, a distance of 43 miles. Mr. William Tiernay Clark, the engineer, commenced
the works in April, 1819. The width of water-way in the tunnel at top is 21 feet 6
inches, and at bottom 20 feet; the depth is 8 feet; the towing-path is 3 feet above the
water, and 6 feet higher the footing of the brick arch, the clear width of which is about 30
feet; the occasional perpendicular shafts are 8 feet in diameter.
CHAP. VIII.
575
BRITAIN.

--
Fig. 553.
THAMES AND MEDWAY TUNNEL.
;
Thames and Severn Canal, from the Stroudwater canal at Wallbridge, near Stroud
beyond Sapperton it passes the Tarlton tunnel, which is 2 miles and 3 furlongs in length;
the span of the arch is 15 feet in the clear, and the highest point of the rock above it is
250 feet. In some portions masonry has been dispensed with, the rock being sufficiently
hard to maintain itself. The canal passes the head of the Thames, and Sedlington St.
Mary, where there is a branch to Cirencester. At Latton it is joined by a branch from
the Wilts and Berks canal, and at Lechlade terminates in the Thames and Isis navigation
Trent and Mersey commences at Wilden Ferry, where the Derwent joins the Trent;
joins the Coventry and Fazeley canal at Fradley; at Haywood Mill the Staffordshire and
Worcestershire canal; and at Stoke, the Newcastle-under-Lyne canal. It afterwards
passes the Harecastle tunnel, 2880 yards in length, and is joined by the Macclesfield
canal, and at Preston Brook unites with the Duke of Bridgewater's canal, and is then
continued to Runcorn Gap, on the river Mersey. Mr. Brindley projected this canal, and
commenced the works, which were completed by Mr. Henshall. There are altogether
one hundred and twenty aqueducts, six tunnels, and ninety-one locks. The lockage from
Harecastle summit to the Trent is 316 feet, and that from the summit of the Duke's
canal is 326 feet.
Tetney Haven Navigation was projected by Mr. John Grundy, engineer, in 1761, when
Mr. Smeaton was consulted upon the practicability of carrying it into effect. A navigable
canal was to be formed from Tetney Haven to the upper end of Avingham-out-Fen, and
from thence to join the River Lud, or Louth River, between Ringers Drain and Avingham
Mill; and from thence, partly by the course of the river, but chiefly by a new canal up to
the town of Louth.
576
Book I
HISTORY OF ENGINEERING.
Harecastle tunnel, upon this canal. was constructed by James Brindley, for a distance
of 2888 yards. at a level of 197 feet from the highest summit of the hill above it. This
tunnel would only permit a 7 feet boat, with a moderate lading, to pass through it, and
then only by employing leggers to propel it, a class of men who, lying upon their backs
upon the freight, pushed against the sides and top of the roof with their feet, and thus
moved the boat onwards. The tunnel is only 9 feet in width, and 12 feet in height, and
occupied nearly eleven years to complete; and to pass a boat through it occupied two hours.
In the year 1824 Mr. Telford commenced another tunnel, at a distance of 26 yards from
that already described; its length is 2926 yards, its width 14 feet, and height 16 feet, of


Fig. 554.
ELEVATION OF TOWIng path.
PLAN OF TOWING PATH.


Fig. 555.
HARECASTLE TUNNEL.
which 4 feet 9 inches is covered by the towing path, leaving 9 feet 3 inches for the passage
of the boat; the path is supported by pillars, and the water flows under it.
There are
altogether fifteen shafts sunk from the surface, the deepest of which is 179 feet; they
were so well set out, and the headings so accurately driven, that the whole length may be
seen at one view.
The bricks were made from clay of superior quality, after being triturated by machinery ;
the mortar was of Barrow lias limestone, ground in a mill, and when set is quite im-
pervious to water. The first brick was laid on the 21st of February, 1825, and the last on
the 25th of November of the following year, and the whole was opened after not quite
three years from the commencement of the works. The total number of bricks used was
8,814,000 in all, for shafts, culverts, &c. The total cost of all the works connected with
this tunnel was 112,6812
Sinking 15 shafts 9 feet aiameter
Driving heading through hill
-
Driving cross-heading to carry off water
Driving headings in coal measures to drain sand at north end
Excavating body of tunnel, turning brickwork, including timber,
£
1,610
7,057
470
540
length 29261 yards
43,435
Expense of towing path
9,600
Expense of railway, 6 miles
7,000
Expense of providing bricks, mortar, centering
22,750
Labour upon mortar and centering
1,537
Carriage of materials
4,060
Expense of open cutting, entrances and turn-over bridges at each
end, workshops, mills, engines, pumps, damages of land fences, &c.
14.622
£112,681
River Witham Navigation, from the city of Lincoln through Boston, to its outfail into
the sea, a distance of about 43 miles. The River Witham, from Lincoln to Boston, runs
in a very crooked course, until it reaches the extensive fens of that district called Holland
on the south, and Wildmore and West Fens on the north, and then passes through the high
marshes into the great bay called Metari's Estuarium. This river was formerly navigable
for large vessels, from its outfall at the Scalp to Boston, and from thence to Lincoln
barges and other smaller boats could float at all times of the year. In the year 1744
CHAP. VIII.
577
BRITAIN.
surveys and levels were taken by the Messrs. Grundy, engineers, for the purpose of improving
the drainage of the low lands consisting of 100,000 acres, and rendering the transit of vessels
more convenient; nothing, however, was done until some years afterwards, when John
Grundy, the son, Mr. Langley Edwards, and Mr. John Smeaton, were called upon to make
a report upon the state of the drainage, &c. In 1761 they surveyed it carefully, and found
the river had so great a tendency to silt up, that they imagined in twenty years there
would be no drainage at all. They therefore advised the formation of another river, of
sufficient depth or capacity to drain all the neighbouring fens and low grounds, and which
should also serve to restore the lost navigation from the sea to Lincoln. It was decided
that the river should be cut in the shortest direction possible consistent with the lowest
surface, so that it might act as an effectual drain; that its dimensions should be sufficiently
large to receive and discharge all the upland waters, branch rivers, and drains; that its
banks should be strong and high enough to confine any flood waters within them, and
force them down to sea without overflowing the fens; that the bottom should be made
with a declivity from Lincoln to the sea at 5 inches per mile; that all the living waters
should be collected, in order to obtain a reflowing force capable of driving out any de-
posits left by the tides, by which means the outfall might be preserved open and clean;
that the tides should not be suffered to flow into this new river, so that its depth and
dimensions might be preserved. A lock, with two pair of doors pointing to landward for the
purposes of navigation, and one pair pointing to seaward to keep out the tides, was provided.
Ülverstone Canal commences in Morecombe Bay at Hammerside Hill, and terminates at
Ulverstone. At its entrance is a sea lock 112 feet long.
Warwick and Birmingham Canal commences at Saltisford, and unites with the Digbeth
Branch of the Birmingham Canal near Birmingham. At Hatton is a rise of 146 feet by
twenty locks.
At Knowles Wharf there is a rise of 42 feet by seven locks; and at the
Digbeth Branch is a fall of 42 feet by five locks. At Haseley there is a tunnel 300 yards
in length, and another at Rowington. It crosses the Blythe River, the Cole, and the Rea
by three aqueducts.
Warwick and Napton Canal proceeds from the Warwick and Birmingham in the parish
of Budbrook, and terminates at its junction with the Oxford Canal near Napton-on-the-
Hill. It crosses the Avon three times by aqueducts, viz. near Warwick Bridge, Radford,
and Long Itchington.
Wey and Arun Junction Canal unites the Wey near Shalford Powder Mills with the
Arun at New Bridge.
Wilts and Berks Canal begins at Abingdon on the Thames, and unites at Leamington
with the Kennet and Avon Canal. The branch to Wantage isinile in length; the
Longcot Branch mile, to Colne 3 miles 1 furlong, and that to Chippenham 2 milec.
Where the canals lock into the Thames, it is 180 feet above the level of the sea.
River Weaver Navigation.— This river has its rise in the south-west part of Cheshire,
and, after a circuitous course, falls into the Mersey at Runcorn, about 50 miles above
Liverpool. From the western tide-lock on the Mersey to Winsford the distance is 24
miles, and the rise 52 feet only. There are 10 locks, each 80 feet in length, and 18 in
breadth, and the vessels employed on this canal are from 60 to 70 feet in length, and 17 feet
in breadth, drawing from 5 feet 6 inches to 6 feet 6 inches water, when loaded with about
70 tons. These works were all executed according to the conditions of an act passed in
the year 1734.
In the year 1807, another act was obtained, and Mr. Telford employed to make a canal
from near Frodsham Bridge to

the Mersey at Weston Point,
below Runcorn, a distance of 3
miles 6 furlongs.
The works which he executed
were the protecting piers at
Weston Point, a sea-wall about
1 mile in length, two river weirs
at Winnington and Saltersford,
and reconstructing the locks at
Wetton Brook, near Northwick.

Fig. 556. SECTION OY WEIR AT SALTERSFORD.
HHH
Piers at Weston Point were constructed with the sandstone of the neighbourhood, and by
their formation the entrance into the basin was extended, affording greater facility to
vessels, both for entering and departing, than when the entrance was at a considerable dis-
tance from low water-mark. The cost of these protecting piers was 78357.
Sea Bank. For 2000 yards the canal skirts a steep bank exposed to the south-western
gales, from a reach of upwards of ten miles of sea; and the original bank which pro-
tected the canal had its upper slope paved with rubble stone, pitched on edge without
mortar; the waves worked into this, and softened the marl which formed the banks of the
canal, causing the rubble paving to sink into it.
PP
573
BOOK I.
HISTORY OF ENGINEERING.

M
Fig. 557.
SALTERSFORD WEIR.
Mr. Telford had the old paving broken into small masses, and laid in water lime mortar
well grouted, upon the banks after they had been shaped with the proper declivity.

Fig. 558.
ELEVATION OF SALtersford Weir.
Upon this bed of broken stone in mortar was set a pavement of scabled or roughly
dressed stones, about 18 inches in depth; these were laid in mortar, and all the joints grouted
well in, which no storms have penetrated or deranged. The whole cost was 17,000ī.
Grand Western Canal has a contrivance which to a certain extent supersedes the use of the
lock; this is by means of a lift, which has some advantages in the saving both of time and water.
These lifts are 46 feet in height, and consist of two chambers, with a pier of masonry
between them; they are of sufficient dimensions for each to contain a timber cradle, in
which the boat required to ascend or descend is placed. The cradle, when on a level with
the canal, allows the boat to swim into it, by simply raising up a water-tight gate at the
end. The two cradles which work in the chambers, when full of water, or when either or
both of them contain a boat, balance each other on very strong chains, which pass over three
cast-iron wheels, and are so arranged that the water in the upper cradle is kept about 2
inches below that in the pond, which gives it a slight preponderance, sufficient to set the
machinery in motion. It is necessary to pay particular attention to the strength of the
materials. The boats in this instance weigh about 8 tons, and pass up and down the
46 feet in about 3 minutes, consuming 2 tons of water only, whereas in the ordinary way
3 tons would be required.
Wisbech Canal runs from the Nene river to the old river at Outwell.
Worcester and Birmingham unites Birmingham with the river Severn at Deglis, a little
below Worcester. The tunnel at Westheath is 2700 yards long, 18 feet high, and 18 feet
6 inches clear width, with a depth of water of 7 feet 6 inches. The tunnel at Tardebig is
500 yards long; that at Shortwood 400; that at Oddingley 120, and that at Edgbaston
110 yards long.
Wyrley and Essington Canal, from Wyrley Bank to Birch Hill in the parish of Walsall :
there are several branches from this canal; one connects the Coventry Canal, near Hudders-
field, another Hayhead lime-works, another Lord's Hay, and another Essington Wood
colliery.
CHAP. VIII.
879
BRITAIN.





Name of Canal.
Date.
Length.
Top
Breadth.
Breadth.
Bottom
Depth.
Total
Rise.
Number of
Locks.
Total
Fall.
Number of
Locks.
Length of
Locks.
Breadth of
Locks.
'T'unnels.
Length of
Length of
Aqueducts.
Tonnage of
Boats.
Engineer.
Aberdare
Aberdeenshire
1793
miles feet. ft.in. ft.in.ft. in.
61
1796 18 23
t
40 0
3 9169 0 17
ft. in.
feet. ft.in. feet. miles tons.
57 90
Capt. George Tay-
lor.
Aire and Calder
-1699
Aire
11
43 6 6
Calder
12/
28 3
United rivers
181
34 6
Canal to Selby
1788 5
60 18 0
to Goole
1826 18
60 40 0
60 40 0
7 0
28 9
70 19 0
Mr. Rennie.
Alford
1826
63
8 0
79
Tierney Clarke.
Ancholme
1767 19
6 0
1
Andover
1789 22
-
176 4
Robert
Whit-
worth.
Arun (river)
1785 26
1
·
Robert
Whit-
worth.
Ashby de la Zouch -1794 26
Ashton-under-Lyne 1792
Avon (river)
Avon (river)
Avon and Frome
Barnsley
31 15 0 5 0
1664 36
-
1751 43
1700 15
1793 15
Basingstoke
Baybridge
Birmingham
Birmingham
Fazely
70 7 0
5 0257 0 20
66 15 0
1778 37 38
1825 3 28
1768 22
5 6195 0 29
4 0 14 0
223
72 13 0
19 9
3
132
21
and
·
1783 201
1
·
248
Digbeth Branch -1783| 14
Walsall Branch -1794 4
Birmingham and
Liverpool Junc-
1
Mr. Jessop, Mr.
Gott.
May Upton.
Brindley.
tion
Blyth River
Borrowstowness
Bradford
Brecknock
1826 39
1757
1768
1771
8968
and
·
174 9 27
80
7 6
T. Telford.
4
7 0
50 86 3 10
66 15 2
of
Abergavenny -1793 33
Bridgewater, Duke
-
Bridgewater and
Taunton
Britton Canal
Bude Harbour and
Canal
68 0
-1737 73
82 0 10
18
•
1811 42
4골
​1774 45%
$
•
Brindley.
Mr. Rennie.
Edmund Leach.
Bure, or North
River
1773 9
0 6
Bure, Yare, &c.
1670 86
Caistor
1793 4
•
6
Calder and Hebble -1758 22
192 6 28
Caledonian
1803 23 40
20 0 94 0 27
180 40 0
Carlisle
1819 114
Chesterfield
Coventry
1771 46
70 0 9
335 0 65
45 0
1
1768 37
•
-
Crinan
1799 9
12 0 58 0.
7
59 Ol 8
Cromford
1789 18
Dearne and Dove
1793
Derby
Dorset and Somer.
set
Droitwich
Dudley
Edinburgh and Glas-
gow
Ellesmere and Ches-
80 0
4 6127 0 24
1793 9 44 24 0 5 0 29 0
DO LO
-
1
94
53 14 4
90 15 0
Smeaton
T. Telford.
W. Chapman.
Brindley.
James Brindley.
Mr. Rennie
William Jessop
60 Whitworth.
Grand Junction
Grand Union
Grand Western
Grantham
Gresley
Hereford and Glou-
cester
Hertford Union
-
1796 40
-1768 5
1776 13
59 6
8
5 0 31 0
5
13 0 2
7 06325
-1817 13
5 0
110 0
ter
61
Erewash
1777 11
(380 0
100 0
226 0
Forth and Clyde
-1768 35
155 0 20 156 0 19
74 20 0
Foss
Foss Dyke
1793 12
11
47 8
Glamorganshire
Glasgow, Paisley,
and Ardrossan
1796 25
611 0
1806 11
102 6
-
64 0
Glenkenns
1802 252
1
1
1
Gloucester
and
Berkeley
(1793 163 70
-1793 90 43
18 0
5
0
90
82 14 6
|T. Telford.
Brindley.
Smeaton.
William Jessop.
1810 45
|1796 35
James Jardine.
Mr. Rennie.
T. Telford.
Mr. Barnes.
Mr. R. Bevan.
-
1793 33
-
1775
1791 35
1824
·
197 6
147 6
195 6
•
195 6
Horncastle
Huddersfield
1792 11
1794 19
t
1
Joseph Clowes.
Mr. Outram.
PP 2
· 580
BOOK 1.
HISTORY OF ENGINEERING.


Naine of Canal.
Date.
Length.
Top
Breadth.
Bottom
Breadth.
Depth.
Total
Rise.
Number of
Locks.
Total
Fall.
Number of
Locks.
Length of
Locks.
Breadth of
Locks.
Length of
Tunnels.
Length of
Aqueducts.
Tonnage of
Boats.

miles feet. ft.in.ft.in. ft. In.
ft. in.
Hull and Leven
-1801 3
1
•
Ivelchester
and
Langport
Kennet and Avon
-1795 7
1794 57 44 24 0 5 0210 0 31 404 6 48 80 14 0
Kidwelly
-1766
Lancaster
1792 76
Leeds and Liver-
pool
Leicester
Leicestershire and
1720 1083 42 27 0 5 0
1791 14
Northamptonshire 1793 17
45 0
Leominster
Kington
Leven Canal
-
and
-1791 46
1801 3
Liskeard and Loo |1825
London and Cam-
bridge Junction
Louth
7100
48 0
496 0
156 0 25
1812 283 44 24 0 6 0 72 0 12 165 9 32
-
11763 14
Macclesfield Canal 1826 29
Manchester, Bolton,
and Bury
1791 15
Market Weighton 1772 11
Monkland Canal
Monmouthshire Ca-
113 9
189 6 18
1
-1770
nal
1792 17
Montgomeryshire
Canal
1794 27
Neath Canal
|1791| 14
Newcastle-under-
Lyne
1795 3
Delham
Newport Pagnel
North Walsham and
North Wilts
Nottingham Canal -1792 15
Nutbrook, or Shep-
ley
Oakham Canal
1793 41
1793 15
Oxford Canal
1769 84
Peak Forest Canal -1794 143
1814 14
1812 7
-
1813 81
1
50 9 7
58 6
126 0
Engineer.
feet. ft.in. feet. miles tons.
1
70 15 6
1
1
·
Mr. Rennie.
Mr. Rennie.
Mr. Rennie.
Mr. Brindley.
William Jessop.
John Varley.
Thomas Dadford.
William Jessop.
Mr. Rennie.
Mr. Smeaton.
Mr. Telford.
Mr. Whitworth.
Mr. J. Dadford.
Mr. J. Dadford.
110 22 6
72 16 0
1
Benjamin Outram.
George Leather.
Mr. Rennie.
Mr. Morgan.
Mr. Rennie.
Royal Engineers.
John Eyes.
T. Telford.
- Henry
Reynolds
and Henry Wil
liams.
Pocklington Canal 1815 8
4
Portsmouth
and
Arundel
1817 14 33 19 6 4 6
Regent's Canal
1812 8
90 0 12
2
Rochdale Canal
1794 31
275 0
438 0
Rye, or Royal Mili-
tary
St. Columb
1807 30 72 36 0 9 0
1773 6
·
Salisburyand South-
ampton
1795
Sankey Canal
|1755| 12 | 48
57
78 0 10
Sheffield
1815 4
Shrewsbury
1793 17
·
154 0
22 0
Shropshire -
-1788 7
::
Somersetshire Coal
Canal
1794 8
Staffordshire and
294 0
100 6
Stainforth and Kead-
1793 15
Worcestershire - 1766 47
by Canal -
Stourbridge Canal -1776 5 28
Stratford-upon-
Avon
Swansea Canal
1793 23
1794 17
1
Tavistock Canal 1803 4 16
Thames and Med.
way
5 0191 3 16
309 0
373 0
8 0 3 0 256 6)
-1800 83 50 28 0 7 0
Thames and Severn 1783 30 42 30 0 5 0243 0 28 134 0 14
Trent and Mersey -1766 93
Ulverstone Canal 1793 165 30 015 0
Warwick and Bir-
•
Mr. James Brind-
ley.
Thomas Sheasby.
Mr. John Taylor
and J. Hitchins
R. Whitworth.
Brindley.
- Mr. Rennie.
mingham.
1793 221
208 0 27
42 0 5
Warwick and Nap-
ton
1794 14
134 6
Wey and Arun
1813 18'
Wilts and Berks
Wisbech Canal
mingham.
Wyrley and Essing-
ton
-1795 52
168 0
-
181 0
-
1794 6
Worcester and Bir-
|1791] 22 | 42
6 0
1428 0, 71 81 15 0
-1791 24
.330 0 40
William Pitt.
CHAP. VIII.
581
BRITAIN
Steam Engine.— The application of steam to draining, mining, manufactures, machinery,
railroads, and navigation has so changed the labours of the civil engineer, that it is
necessary to notice, however briefly, its inventors and progress.
Windmills are no longer employed to exhaust the water from our fens, nor are the rude
constructions of complicated machinery under our bridges now required to throw up
water to our houses. The miner is enabled to penetrate to greater depths in the bowels of
the earth in search of the ore, and the civil engineer has an efficient agent on all occasions
where great power is required; in the various operations of pile-driving, exhausting water,
dredging and cleansing the bottoms of rivers or harbours, moving weights, and in con-
structions, it is equally important, and thus new elements have been introduced into his
employment since the days of Perronet and Smeaton.
It is not necessary to give a detail of the various opinions relative to the invention of the
steam engine; in the history of the progress of the useful arts none has been more keenly
contested: different nations, as well as individuals, have put in their claims; but the
efficacy of this useful machine depends on several physical properties, and on a variety of
mechanical arrangements, to render them available; and suppose these all to have been
known in the early age of science, they were not combined until James Watt devoted his
mind to the subject: previous to this period, the steam engine possessed extremely limited
power, and was inferior to other mechanical contrivances as a prime mover: but since his
genius matured it, it has become the source of wealth to the British nation, as well as
beneficial to the progress of civilisation and the comfort of the whole human race, and a mo-
nument to his fame. It must be evident that the engine as it now exists is not the exclusive
invention of one individual, but the result of discoveries made during the two previous
centuries its progress from its commencement is a curious history, attesting the slow
working of the human mind, and how long a period often intervenes before the genius
springs up who can mature and render useful the so-called dreams of philosophers.
:
It is difficult to assign a time when the properties of steam first attracted attention;
as early as 130 years before Christ we find some mention in the writings of Hero of
Alexandria of a philosophical toy, called an æolipile, the principle of which was nearly
the same as that which produces the motion in Barker's mill; in America, a few years
ago, an engine was constructed of 21-horse power upon this system, and its only fault
was stated to be the consuming too much fuel. This kind of engine was first made by
Mr. Avery.
At the commencement of the seventeenth century Baptista Porta, who invented the
camera obscura, gives in a commentary on the Pneumatica of Hero the design for a steam
fountain, which raised water in a similar way to the steam-engine, the steam being formed
in a separate vessel from that which contained the water to be raised.
A tube introduced the steam into the cistern, which was nearly filled with water, the
end of the tube being above the level of the water; the steam occupied the space above the
water, and by its elastic power forced the water through the bent tube.
Solomon de Caus, an engineer and architect in the employment of Louis XIII. of France,
showed that water might be raised by the aid of fire higher than its own level; his publi-
cation is said to be the first instance in which steam is mentioned as a moving power.
In a copper ball, well soldered together, was a vent-hole, through which the water also
entered, and a perpendicular tube, which approached nearly to the bottom of the ball,
and was carefully soldered in. The ball, filled with water, and placed upon the fire, soon
formed a quantity of steam, which having no escape pressed on the surface of the water,
and occasioned it to mount in the perpendicular tube.
Giovanni Branca, an Italian engineer, formed a steam windmill, which seems to be one
of the first instances of an attempt to render this power practically useful; and in a work
published about 1629, there is a representation of this invention. It consists of a boiler
with a spout directed towards a horizontal wheel, and the steam which issues from it
is made to strike against the flat vanes or floats contrived on its circumference, pro-
ducing a rotary motion in the wheel, which he proposed to transmit to machinery that
should raise buckets, grind corn, &c. The specific gravity of steam being low, no great
power could have been obtained by it when so applied; and being so rapidly condensed,
and so much resisted by the air, which is twice its weight, its force could not be great.
Edward Somerset, Marquis of Worcester, who was confined in the Tower for being im-
plicated in a plot at the time of the Stuarts, one day observing the lid of the pot in which
his dinner was cooked suddenly fly off, asked his attendant, "What is to be done in such
a melancholy den, unless we have the liberty of thought?" and probably this circumstance,
trifling as it may appear, gave rise to his consideration of steam as a convenient motive
power.
In his Century of Invention, published in 1663, hẹ shows “an admirable and
most forcible way to drive up water by fire, not by drawing or sucking it upwards, for
that must be, as the philosopher calleth it, ‘intra sphaerum activitatis,' which is but at such a
distance. But this way hath no bounder if the vessel be strong enough; for I have taken
a piece of a whole cannon whereof the end was burst, and filled it three quarters full of
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HISTORY OF ENGINEERING.
water, stopping and screwing up the broken end, as also the touch-hole, and making a
constant fire under it: within twenty-four hours it burst and made a great crack; thus
having a way to make my vessels, so that they are strengthened by the force within them,
and the one to fill after the other, I have seen the water run like a constant fountain stream
40 feet high; one vessel of water rarified by fire driveth up 40 of cold water: and the
man that tends the work is but to turn two cocks, that one vessel of water being consumed,
another begins to force and refill with cold water, and so successively; the fire being
attended and kept constant, which the self-same person may likewise abundantly perform
in the interim between the necessity of turning the said cocks." The Marquis called this
a semi-omnipotent engine, and says he intended to have a model of it buried with him.
Sir Samuel Morland, in the year 1683, exhibited to Louis XIV. some new principles on
the power of fire, by "which when water is evaporated, it will acquire a space equal to 2000
times what it was before; and that in such a state it might be made highly useful for
raising water.”
In the Philosophical Transactions for 1697 is a notice of a method for draining mines,
where there is not the conveniency of a near river to play an engine, with air-pumps and
cylinders connected by an air-pipe; which no doubt refers to the inventions of Denis
Papin, a Frenchman, who first showed that a piston working tight in a cylinder might be
raised by boiling a little water under it, and that by cooling and condensing the vapour
which had raised it, a vacuum would be formed below, when the atmospheric pressure
would force it down.
The first engine applied in England to practical purposes was made by Thomas Savery,
for which he obtained a patent in the year 1698; and he suggested that it could be used
for working mills, raising water to houses for domestic purposes, and extinguishing fires,
supplying cities with water, draining fens and marshes, propelling ships, &c. This engine,
though so highly creditable to the genius of its inventor, had some considerable defects,
particularly in its application to the drainage of mines, the depths of which had been greatly
increased; rendering it highly desirable that some process of working them, less expensive
and difficult than that ordinarily adopted, should be resorted to.
The lift of Savery's engine was limited to 90 feet perpendicular, so that to raise water
from the bottom of a mine it was necessary to place one at every 90 feet of depth; the
water being successively raised into reservoirs, one above the other. It was also found
that sufficient strength could not be given to an engine of this description, when made upon
a large scale, and that the consumption of fuel was very great.
Thomas Newcomen, a blacksmith at Dartmouth, and John Cawley, a plumber of the same
place, endeavoured to overcome the defects in Savery's engine, and to them we are indebted
for the first atmospheric engine, for which they took out a patent in 1705. Here the piston
was pressed down in a cylinder by the atmospheric pressure, a vacuum being previously
formed below the piston, by filling the space with steam, which was then condensed. In
this engine there were three principal parts; the boiler, which generated the steam, the
cylinder, in which the steam was condensed, and the beam, whose movements followed the
alternate admission and condensation of the steam, communicating the motion to the
rod of the pump.
An engine of this construction raised a load of 7 or 7 pounds for
every square inch of the surface of the piston.
This engine, which soon came into general use, received several improvements from
Mr. Beighton, an engineer, who fixed a rod to the beam, called a plug-frame, with pins or
catches in it, which opened and shut the valves with great precision and regularity; so that
no attendant was required for that purpose, and the engine thus worked itself. The
celebrated John Smeaton also applied all his knowledge in mechanics to proportion the
various parts, which enabled him to construct machines of greater power, and to perform
more work with the same amount of fuel. A crank and fly-wheel was added, which, from
the reciprocating vertical motion of the piston, produced a continued circular motion.
The atmospheric engine had considerable advantages, arising from the almost unlimited
power which could be commanded, which depended on the range of surface of the piston,
from the low degree of temperature and pressure at which the steam was produced, so
that there was little risk of explosion, from the simple mode by which the steam was
condensed, and from the power which the engine possessed of opening and shutting
its valves.
It had also its disadvantages, arising from the alternate heating and cooling of the
cylinder, during which process a considerable quantity of steam was lost, and the air
rushing in whilst the piston was under atmospheric pressure.
Newcomen's was, however, the first really efficient steam-engine applied safely and pro-
fitably to many very important purposes, and no doubt to it Mr. Watt was indebted for
many valuable suggestions; it was exclusively used for sixty years, and, according to Mr.
Carr, was the chief hydraulic engine for upwards of an hundred. In the coal mines it
was universally adopted, as it was also in those of Cornwall, Cumberland, and elsewhere.
The great improvements made in the steam-engine by Mr. James Watt were condensing
CHAP. VII.
583
BRITAIN.
the steam in a separate vessel; removing the air and water from the condenser by an air-
pump; producing the movement by the aid of steam instead of atmospheric pressure;
giving the piston an impulse or moving power both in ascending and descending; con-
verting the alternate rectilinear motion of the piston into a continued circular motion, so
as to adapt the engine for impelling machinery, and working the steam expansively, and
thus greatly economising the fuel: this important engine, as completed by these and other
improvements, soon superseded all other inventions of the kind, the principles which he esta-
blished being those in use throughout the world at the present day. His first work is known
as the single-acting steam-engine, in contradistinction to the double-acting engine, as it was
afterwards called, in consequence of that beautiful arrangement which allowed the steam
to enter alternately above and below the piston, at the same time forming the vacuum
alternately, by which a moving force was communicated to the piston in its ascent as well
as in its descent; thus constituting a continuous moving power.
To the genius and sagacity of James Watt the whole world owes a debt of gratitude;
and Dr. Darwin, in his " Botanic Garden," has well asked, "Why, if at Rome a civic
crown was given to him who saved the life of a single citizen, is not the projector of the
steam-engine considered worthy of being covered with garlands of oak?"
——
Steamboat Engine. About the year 1736, Jonathan Hulls took out a patent for "a
new-invented machine for conveying vessels or ships out of or into any harbour, port, or
river, against wind or tide, or in a calm." The power was procured by the pressure of
the atmosphere against a vacuum, and, by some curious machinery, motion was given to a
paddle-wheel, the continued rotation of which was provided før. This was probably the
first attempt to apply the power of steam to navigation, and which has led to vessels so
propelled crossing the Atlantic Ocean, and making the voyage to India.
In the year 1775, M. Perier had a small steamboat on the Seine, and seven or eight
years afterwards the Marquis of Jouffray constructed one at Lyons, 140 feet in length,
and 15 feet in width, which navigated the Saone for some time: about the same period
they were introduced into Scotland as canal boats, and on the Forth and Clyde canal there
was one which plied with much success. But it was not until Mr. Fulton, an American,
had studied the subject, that a really efficient vessel was built; in the year 1807 he
launched one at New York, containing an engine made by Bolton and Watt for the
purpose, and a voyage was performed between that city and Albany, a distance of 160
miles, in thirty hours.
་
After Fulton had shown that steam might be applied as a moving power to ships,
numerous other attempts were speedily made, and the first steamboat in Europe, after the
appearance of Fulton's, was " The Comet," which plied between Glasgow and Greenock.
"The Great Western," built expressly to cross the Atlantic, had two engines, each of
225 horse-power; her burthen 1340 tons; her paddle-wheels made 273,000 revolutions;
her consumption of coal was 1 tons per hour. "The British Queen," of 1862 tons, since
employed in the Atlantic navigation, had the diameter of the paddle-wheels 30 feet, and the
power of her engine was 500 horse.
These large vessels usually make the voyage from Falmouth to New York in seventeen
or eighteen days, their least speed being 89 miles per day; and the average for the whole
voyage has been 190 miles daily.
Locomotive Engines. After the great improvements made in the steam-engine by Mr.
James Watt, those of high-pressure ceased to be generally used by manufacturers; but
in the patent obtained in the year 1784, he explains that his newly-invented engine was
calculated to propel carriages; and the manner by which he proposed to effect this was, by
having a boiler made of wood, like a cask, to contain in the inside an iron furnace, which
was to be entirely surrounded by water: this simple apparatus was to be placed on a car-
riage, and the wheels worked by means of a piston, the reciprocating motion being converted
into a rotary one by toothed wheels and a sun and planet motion. The wheels differed in
their proportions, in order that the variable resistance offered by the road might be more
easily overcome. The cylinder was to be 7 inches in diameter, the length of the
stroke 12 inches, and the number per minute 60. This carriage was to carry two persons,
but it was never executed, as the inventor always manifested an objection to high-pressure
steam.
In the year 1802, a patent was taken out by Richard Trevithick for a locomotive car-
riage; this was the first attempt to adapt the power either to the common road or a
railroad, and its principle was high-pressure. The carriage had two small wheels in front,
which served the purpose of guiding it, and two larger ones behind, by which it was driven.
The cylinder, boiler, and fire were all enclosed in a case, and placed low down in the rear
of the axle, and the large wheels could either be worked together or singly, or one could
go one way whilst the other moved in an opposite direction; their motion was produced by
a spur-gear, which had a fly-wheel added to it. The piston rod, outside the cylinder, was
double, and drove a cross piece, working in guides on the opposite side of the cranked
axle to the cylinder, and the crank of the axle revolved between the double parts of the
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HISTORY OF ENGINEERING.
piston-rod. To this axle was attached the first of the toothed wheels, and to the axle, on
which were the driving wheels, was the other, similar in size to the first, and worked by it.
The steam cocks were open and shut by a connection with the crank axle. The force-
pump, by which a supply of hot water contained in the casing which enclosed the cylin-
drical fire-box, &c., was injected into the boiler, was also worked from it, as was a pair of
bellows.
Two years afterwards he obtained another patent, in which he specified the boiler as
cylindrical, with flat ends, and an engine was built in conformity to it, which worked on
a tram-road at Merthyr Tydvil, in South Wales. The wheels, though quite smooth,
were found to have sufficient adhesion when the carriage drew ten tons of bar-iron, and its
supply of coals, at the rate of five miles an hour.
In the year 1811 Mr. Blenkinsop took out a patent for the first double-cylindered
engine. Here the boiler was circular, and the tube, which was connected with the fire,
passed through the centre, and was bent up, to form the chimney. The cylinders, partly
in the boiler, were vertical, and 8 inches in diameter. The piston rods worked the con-
necting rods by means of cross heads; the two cranks were placed below the boiler, and
made to work two shafts fixed across the engine, on which were small-toothed wheels,
working into a larger one between them.
On the axis of this, and outside the framing, were the driving wheels, one of which was
toothed and worked in a rack on one side of the railway: there were two pair of plain-
flanged wheels, one before, and one behind, the driving pair. This engine weighed 5 tons,
drew 94 tons on a level at 3 miles per hour; its consumption of water per hour was
50 gallons, and of coal 75 pounds.
In the following year another patent was taken out by the Messrs. Chapman, in which
mention is made for the first time of fanners to excite combustion, but we have no account
of the idea being carried into effect.
Numerous patents were taken out at various times by Mr. George Stephenson, Mr.
Locke, and others, none of which were practically applied until April, 1829, when the
directors of the Liverpool and Manchester railway offered a premium of 5001. for the
best locomotive engine. It was to draw on a level plane three times its own weight,
at the rate of 10 miles per hour, which weight was not to be more than 6 tons.
The price
of the engine was restricted to 550%., the height of the chimney to be 15 feet, and the pressure
on the boiler to be 50 pounds per square inch: it was to consume its own smoke; the whole
weight of boiler and engine was to be supported on springs, and if the weight exceeded 41
tons, the engine was to have 6 wheels.
In October the trial was made by three competitors, who owned the " Rocket," the
"Novelty," and the "Sans Pareil;" the ground chosen was on the Manchester side of Rain-
hill Bridge, about 9 miles from Liverpool, where the road was level. The "Rocket," the
production of Mr. Robert Stephenson, the engineer of the London and Birmingham rail-
way, was the only engine which performed the required distance of 70 miles with the
given load and at the stipulated speed. It was constructed with four wheels not coupled ;
the boiler was 6 feet long and 3 feet in diameter, and contained twenty-five copper tubes,
3 inches in diameter, through which the heated air from the furnace passed to the
chimney.
The furnace at the after end of the engine was 2 feet wide, and 3 feet high; it had an
external casing, between which and the fire-box was a space of 3 inches filled with water,
and communicating with the boiler. The cylinders were placed on each side of the boiler,
in an angular position, one end being nearly level with the top of the boiler at its after-end,
and the other pointing towards the centre of the foremost or driving pair of wheels, with
which the connection was made from the piston-rod to a pin on the outside of the wheel.
The weight of the engine was 4 tons 5 cwt. The prize was of course awarded to Mr.
Robert Stevenson, and from this time we may date the successful application of locomotives
to railroads.
:
Prior to this competition the greatest load drawn by locomotives was 431 tons, engine
and tender included, 15 tons at 10 miles an hour, or 284 tons of goods, including waggons,
while the "Rocket" and tender, weighing only 7½ tons, drew 44 tons gross, at the rate of 14
per hour this great result is principally to be attributed to the introduction of tubes
in the boiler, by which the evaporating power was increased to three times that of the
older engines, with 40 per cent. less consumption of fuel, the invention of Mr. Seguin.
Since the period above alluded to numerous patents have been taken out for improving
almost every portion of the locomotive engine.
Railways.- - Iron railroads were not in use much before the commencement of the 17th
century previous to that time we find wooden rails employed at the coal works near New-
castle, where one horse was enabled to draw 4 or 5 chaldrons in carts, with four rollers fitted
to the rails, on which they ran with ease. These roads were about 6 feet in breadth:
across them oak sleepers were laid from 4 to 8 inches square, at a distance of 2 or 3 feet
apart; on their ends, the only parts perfectly squared, longitudinal timbers were pegged
down, 6 or 7 inches in breadth, and 5 inches in depth, extending the whole length of the
CHAP. VIII.
585
BRITAIN.
way, at about 4 feet distance from each other. This single road required frequent repairs,
causing constant impediments to the carts; another rail was therefore added to that pegged
upon the sleepers, and as this upper rail wore away it was kept renewed. Between the
rails the roadway was made level with the tops of the sleepers with ashes, so that they
were in some degree protected from the horses' feet.
Cast-iron rails were substituted for wooden at the Norfolk colliery, near Sheffield, about
the year 1776, and were, perhaps, the first plate rails on record; they were secured to the
wooden sleepers by nailing only, and it does not appear that stone bearers for the ends of
the rails were used before the year 1800. We have an account also of a railroad laid down
as early as 1767 at the Colebrooke Dale iron-works, where cast-iron wheels, turned in a
lathe, were applied, when it was soon discovered, that if these were running on a pair of
iron plates, a great advantage would be obtained over those employed upon common roads.
The plates were at first of cast-iron, very flat and smooth on the upper surface to receive
the wheels, but having a flanch or feather rising vertically on one side, for the purpose
of guiding them, which were cylindrical, and preventing them from getting off; these
were sometimes placed on the inner, and sometimes on the outer edge of the rails, most
generally on the former.
Another variety of rail was afterwards made use of, without vertical flanches, the flanch
being formed upon one side of each wheel, and the wheels arranged in pairs upon the same
axle, so that the flanches embraced the two parallel rails, or they were placed inwards and
fitted between the lines of rail.
Wrought-iron bars were then adopted, 2 or 3 inches in width, and of an inch in thickness,
lying upon longitudinal sleepers of timber, and fastened by spikes or bolts, upon which
ran similar wheels to those last described.
Cast-iron bars were next introduced, with their edges upwards, on which ran cylindrical
wheels, with either a flanch or groove around them, to keep them on the rail. These and
a variety of other methods were adopted until the present edge-rail superseded all others.
Mr. Jessop used this rail at Loughborough in Leicestershire, and instead of nailing the
ends of the rails, he united them in a block of cast-iron, made to receive them, which was
called a chair; these were placed upon stone blocks firmly fixed in the ground.
In October, 1820, a patent was obtained by Mr. John Berkinshaw of the Bedlington iron-
works, Durham, for an improvement, capable of extensive application, which was that of
forming rails of wrought-iron, by passing them when red-hot through rollers grooved in
the required form; by this means wrought-iron bars, with rounded tops of any form, with
flanches, may be produced in lengths of 18 feet or under, and when fixed on chairs 3 feet
distance from each other make an admirable and permanent railroad.
Mr. Blenkinsop was the first to introduce the locomotive at the collieries in the north of
England: one wheel of the engine had strong cogs or teeth around its periphery, which
fitted into a toothed rack on the rail; this was considered necessary to prevent the wheei
from slipping or turning round without advancing.
In 1829 the directors of the Manchester and Liverpool line employed Mr. James Walker
and Mr. Rastrick to enquire whether it were possible to use the locomotive on a public
railroad, and a very valuable report was made upon the power of such engines, the quantity
of work they are capable of performing, their consumption of fuel, their annual cost, the
friction of ropes in stationary engines, the cost of such ropes, the wear and tear of waggons,
the accommodation to the public, and the comparative safety of the two modes.
In the year 1830, when the London and Birmingham was projected, it was considered that
one line of rails would be sufficient for the traffic, and that the whole might be constructed
for 6000l. per mile; it was at first intended that the carriages should be drawn by horses at
the rate of 8 miles per hour. Fifteen years' experience has shown how little the success which
has attended railway transit was then anticipated; since that time more than 73,000,000%.
sterling has been expended upon the leading lines, the interest of which at 5 per cent.,
requires that the profits should not be less than 10,000l. per day. Five times that capital will
be required to complete the various railroads now in progress, and those projected. The
power of steam has triumphed over the prejudices which obstructed the progress of the first
speculations, and it is now generally admitted that railroads are not only necessary, but in-
dispensible; and when a system, uniting public utility with safety, and founded on integrity,
shall be established over the whole of Great Britain, the price of the necessaries of life will
no doubt be rendered more equal, intelligence will be spread, and the arts of civilisation
carried through the length and breadth of the land.
The execution of railways has called into active employment a very different class of men
from those engaged in repairing the common roads, and the artizans who manage the steam
power, and superintend the property of the companies, are far more intelligent than were
the great mass of attendants on the old system. All the arts of construction have been
essentially improved; new principles have suggested themselves, and other materials have
been made use of: iron has been wrought into every possible form, and its strength tested
to serve the purposes of the railway engineer; the carpenter has exerted his skill to perfect
the works with which he was entrusted, and many novelties have been introduced in the art
586
BOOK I.
HISTORY OF ENGINEERING.
of framing; he has applied timber and iron in conjunction to roof in buildings of a span
which some years since would have seemed to defy his power. The mason and bricklayer
have revived the principles of skew arches adopted by the Romans, and in some instances
improved upon them, and a beneficial impetus has been given to every branch of the
building art. Other sciences have participated in these advantages: in geology many new
facts have been brought to light from the deep cuttings and tunnels driven through the
hills and mountains. It is scarcely possible to enumerate the advantages which the
country has already derived from these works, and it would be daring to prophesy what
may be the result of a more perfect system. Had the great success attendant upon rail-
ways been foreseen, and an accurate survey made of the levels throughout the whole of
Great Britain, vast sums might have been saved, the lines would have been laid down more
in unison with the general benefit, and due attention would have been paid to any future
or branch lines that might have been required.
To detail all the engineering works upon the various lines would require volumes, and
all that can be done is briefly to enumerate those executed, with such observations on their
length, gauge of rail, and cost as could be obtained: the government has been careful in
providing for the public, and numerous acts of parliament have been framed; the first was
passed in 1838, to provide for the conveyance of the mails by railroads; the next which re-
ceived the royal assent was in August, 1840, for the better regulation of railways. This
important act determines that no railroad shall be opened to the public until a month's
notice has been given to the Board of Trade, and that all railway companies shall deliver
returns of the traffic in passengers according to the several classes; also of cattle and goods,
as well as accidents on the line, and a table of tolls and charges. A third act received the
royal assent in July, 1842, which was for the better regulating of railways, and for the con-
veyance of troops.
Another very important act received the royal assent in August, 1844, which attached
certain conditions to the construction of future railways authorised or to be authorised by
any act of the present or succeeding sessions of parliament, and for other purposes in relation
to railways. This act, called Mr. Gladstone's, provided, that if after twenty-one years
from the passing of the act for the construction of any future railway, the profits shall
exceed ten per cent. the Treasury may revise the scale of tolls, and fix a new scale upon
three months' notice being given it also empowers the Lords of the Treasury to appoint
an inspector, and to examine the accounts of any company, and ensures a daily train each
way to carry passengers for one penny per mile, the average rate of speed being twelve
miles an hour for the whole distance, including stoppages: such train to take up and set
down passengers at every station: the carriages to have seats, and to be covered, and half
a hundred-weight of luggage to be allowed to each passenger. It also stipulates that the
Lords of the Treasury shall have electrical telegraphs laid down at the sides of the rail-
way, to which several other useful provisions are added.
The Surrey Iron Railway Company, was the first incorporated by act of parliament, and
passed in 1801. Its length is nine miles, and the cost of its construction was about 60,0007. ;
it had a double line of rails throughout the whole line, which extended from the town of
Wandsworth to Croydon, with a branch to Carshalton. This railway was not intended to
convey passengers; and horses were employed as the motive power.
The Caermarthenshire Tram-road was commenced in the year 1802; it is 16 miles in
length, extending from the lime works of Castell-y-Garreg to Llanelly.
Sirhowey Tramroad extends from the Monmouthshire canal, near Newport, to Sirhowey
furnaces, a distance of 11 miles.
Croydon, Merstham, and Godstone Railway was a continuation of the Surrey railway; its
length was nearly 16 miles, and is said to have cost 90,000l. The line was double through-
out, with a pathway on each side, 24 feet in width.
Oystermouth Railway proceeds from that place to the town of Swansea, a distance of 6
miles.
Kilmarnock Railway is in length 93 miles, and extends to Troon.
Bullo-pill, or Forest of Dean Railway, is in length 7 miles; it commences on the Severn,
near the town of Neconham; there are three short lines to various coal-mines in the
forest.
The Severn and Wye Railway connects the two rivers; the extent, including its nine
branches, is 26 miles.
Monmouth Railway proceeds from that town to a place in the Forest of Dean, called
Howler Slade.
Berwick and Kelso Railway has never been completed, but was intended to unite the town
of Berwick with Kelso.
The Hay Railway is in length 24 miles, through a mountainous district; it commences
on the Brecknock and Abergavenny canal, and terminates at Parton Cross in Herefordshire.
Llanfihangel Railway is 6 miles in length, commencing on the same canal, and ending
at Llanfihangel Crucorney, in Monmouthshire.
CHAP. VIII.
587
BRITAIN.
It
The Grossmont Tramroad is about 7 miles in length, and has a rise of 166 feet.
commences at the Llanfihangel railway, and terminates at Llangua Bridge.
Penrhynmaur Railway, a little more than 7 miles in length, commences at that place, and
terminates at Red Wharf, near Llanbedrgoch, in the county of Anglesea.
Mamhilad Railway, after a course of 5 miles, ends at Usk Bridge, in the county of Mon-
mouth.
Gloucester and Cheltenham Railway extends from the basin of the Gloucester and
Berkeley canal to the Knapp toll-gate at Cheltenham, the distance being 9 miles.
Mansfield and Pinxton Railway, 8 miles in length, commences at the first mentioned
town, and ends near Alfreton, in Derbyshire, after passing through a country abounding in
minerals.
Kington Railway is 14 miles in length, and may be considered as a continuation of the
Hay railway, which it joins at Parton Cross, in Herefordshire; it passes by Kington, and
terminates at Burlinjob, in Radnorshire.
Plymouth and Dartmouth is in length altogether 30 miles: this railway commences at
the Sound at Sutton Pool, and terminates near the prison at Dartmoor, in the parish of
Lydford.
Stratford and Moreton. — This tramroad is in length 16 miles, exclusive of a branch of
21 miles; it extends from Stratford-upon-Avon to Moreton in the Marsh, the branch
leading to Shipston-upon-Stour, in Worcestershire.
The above railroads were established solely for the use of miners, or the transport of
coals and minerals, and some for that of merchandise. We now arrive at the period when
it was considered that they might be rendered available for passengers.
Stockton and Darlington Railway, being the first on which the locomotive steam-engine
was employed, excited considerable interest, and led to the great changes which have taken
place in the transit of passengers, and the establishment of the numerous lines which have
since been laid down. Its length was 25 miles 30 chains; it was opened throughout in
September, 1835: it commences on the left bank of the Tees at Stockton, and proceeds in
a southerly direction for 4 miles, where there is a branch to Yarm Bridge; the main line
turns to the west, and afterwards to the north-west, by the town of Darlington, from
whence its course is nearly north, to the point of junction with the Clarence railway.
then passes West Auckland, and ends at Bishop Auckland. The main line has five branches,
making together 15 miles, the whole extent being 40 miles. At the fifth branch, which
extends across the river Tees, is a suspension bridge, 240 feet in length between the piers,
and 30 feet above low water-mark. The gauge of the way is 4 feet 8 inches, ruling
gradients 1 in 104, rise in feet per mile 50, and cost per mile 90007. The total sum ex-
pended to July, 1844, was 450,000l.
It
Durham and Sunderland, open throughout 28th of June, 1839, is in length 13 miles 20
chains; its termini are in the two towns above named; the gauge of way is 4 feet 8 inches,
ruling gradients 1 in 60, rise in feet per mile 88, and cost per mile 14,2817. The total
sum expended to August, 1844, was 301,2487., and the cost of working the previous six
months 11,3341.
Redruth and Chasewater Railway.
The length of the main line is 94 miles, and that of
the four branches rather more than 5 miles additional. It commences at Redruth in Corn-
wall, and ends at Point Quay, in the parish of Feock.
It com-
Monkland and Kirkintilloch is 10 miles in length, with a branch of about 3 mile.
mences at Palace Craig, and terminates at Kirkintilloch, in Dumbartonshire.
Rumney Railway is in length 212 miles, and extends from Bedwelty, in the county of
Monmouth, to Bassaleg, in the same county.
West Lothian, with its two branches, is in length 23 miles; it commences at Ryall, on the
banks of the Edinburgh and Glasgow Union canal, and ends at Shotts.
Cromford and High Peak Railway, originally planned by Joseph Jessop, was executed
under the direction of Thomas Woodhouse, engineer. An act was obtained in the year
1825, having for its object a junction between the Cromford and the Peak Forest canals,
through a very mountainous and rugged district, where many obstacles occurred to prevent
its being effected; the railway was substituted in lieu of it.
As Derbyshire is intersected by a lofty range of mountains, which extend northerly into
Yorkshire and southerly into Staffordshire, the waters which run to the eastern and
western coasts are divided, and over these mountains, which are of a limestone formation,
the railway is carried: it ascends to a level of 992 feet above the Cromford Canal, and 1270
feet above the level of the sea. The railway commences at the Cromford Canal, where it
ascends, by two inclined planes, to an elevation of 465 feet; the lower one being 580 yards
long, rising 204 feet, the upper one 711 yards long, and rising 261 feet. Each of these
inclined planes has two stationary steam-engines of 20 horse-power, which work endless
chains, directed and supported by pulleys, for the purpose of drawing up the waggons,
two of which, containing five or six tons each, are drawn up at a time, with a velocity
of four miles an hour: 123,000 cubic yards of excavation, principally through grit or free-
588
BOOK I.
HISTORY OF ENGINEERING.
The railway pro-
stone rock, were necessary for the execution of this portion of the work.
ceeds from the top of the upper plane for a mile nearly level, after which, at Middleton, it
mounts another inclined plane of 253 feet rise in 708 yards: here the cutting was some-
times 43 feet in depth, through a solid limestone rock, where it was necessary to remove
32,000 cubic yards, and the waggons were again drawn up by means of two other engines
of 20 horse-power each. The railway continues level from thence, and at the distance of a
mile the limestone rock is cut through to a depth of 68 feet. In the centre of these cut-
tings there is a tunnel of arched masonry 105 yards in length, and the Via Gellia embank-
ment was formed out of these cuttings, which amounted to 168,000 cubic yards. At the
end of the embankment the Hopton inclined plane commences, which rises 98 feet in 457
yards, where are two other stationary steam-engines: there is then a level for 12 miles, with
the exception of 2 miles, which have a rise of 10 feet each, in order to lessen the depth of
cutting at Haven Lodge.
The chief cuttings in this length were, Carsington, 20,000 cubic yards; Bressington,
58,000; the Minington embankment, 78,000; Pike Hall and Burncliff, 40,000 yards;
the cutting near the Manchester road and Haven Lodge, 125,000 cubic yards; and at the
Hurdlow inland plane, 38,000 cubic yards: most of these cuttings were through limestone
rock, and were blasted with gunpowder, the material being applied to form the several
embankments.
At 16 miles from the commencement, the railway ascends by the Hurdlow inclined plane
to its greatest elevation; this plane rises 168 feet in a length of 850 yards: there are two en-
gines of 10-horse-power each. It then continues level for nearly 20 miles, and the excavations
in this length were, at Hurdlow and Brierlow, 57,000 cubic yards; at Hindlow, 26,000;
at Hill Head and Harpur Hill, 44,000; south of Turncliffe, 46,000; north of Turncliffe,
47,000; and at Ladmanlow and Burbage, 62,000 cubic yards.
At Buxton there is a tunnel 580 yards long, 21 feet in width, and 16 feet in height;
this was driven from the two ends, without any pit or shaft being sunk; the strata passed
through was hard clunch or shale, to remove which gunpowder was employed. The whole
of the tunnel is arched with masonry.
At Upper Goyt is another inclined plane, which descends 266 feet in a length of 660
yards; and the lower plane descends 191 feet in 455 yards, which brings the railway into
the valley of the river Goyt. Here are two engines of 20-horse-power each, and the
excavations were about 30,000 cube yards. After this, there is a level of 21 miles, which
was effected by 74,000 cubic yards of cutting. To this succeeds the Shallcross inclined
plane, 817 yards in length, with a descent of 240 feet, where there are two other engines
of 20-horse-power.
At Whaley is another inclined plane, falling 42 feet in a length of 180 yards, which
required a cutting of 18,000 cubic yards; here the railway, after having traversed 33 miles,
communicates with the Peak Forest Canal.
There are altogether fifty-two bridges, some of which are cast-iron.
The cast-iron rails
were in 4-feet lengths, having a pedestal at one end, and the opposite end adapted to it,
which admits of a little movement at the joint; each rail weighed 84 pounds; so that for
a mile of single road about 100 tons of rail were required.
The cost of completing the railway was 150,000l., and of the engines, reservoirs, and
machinery, 30,000l.
Nantle Railway joins the town of that name to the shipping quay at Caernarvon.
Portland Railway is in length 2 miles; it commences at the Priory Lands, and terminates
at the castle.
Duffryn Llynvi and Port Cawl Railway is in length 16 miles; it commences at Llan-
goneyd, and terminates at a bay called Pwll Cawl, at Newton Nottage, in Glamorganshire.
From its commencement it is one continual descent, at first 50 feet in a mile, then 15, and
afterwards 28 feet.
Ballochney Railway.—The main line is 4 miles in length, with a branch of 1½ miles, to the
village of Clerkston.
Dulais Railway is 83 miles in length, commencing at Aber Dulais, and terminating at
Swm Dulais, in the parish of Cadoxtone-juxta-Neath, in Glamorganshire.
Dundee and Newtyle Railway unites these two towns by a line 11 miles in length. The
district through which it passes is very hilly, and the height of 544 feet is overcome by
stationary engines, and five inclined planes; here coaches and passengers are drawn by
locomotives.
Edinburgh and Dalkeith.—The main line is in length 103 miles, and the three branches
61 miles. It commences on the south side of the city of Edinburgh, and terminates near
Newbattle Abbey on the banks of the South Eske river.
Garnkirk and Glasgow is 84 miles in length; it commences at Cargill Colliery, near
Gartsbarrie Bridge, in Lanarkshire, and terminates on the road between Glasgow field and
Keppoch. The locomotive engine is here employed for the transport of coals and other
articles of commerce.
CHAP. VIII.
589
BRITAIN
Heck and Wentbridge is 7½ miles from its commencement at Heckbridge to Wentbridge,
in the West Riding of the county of Yorkshire.
Liverpool and Manchester, opened throughout on the 15th of September, 1830, is in length
38 miles 23 chains; its termini are Lime Street, Liverpool, and Hunt's Bank, Manchester.
The gauge of its way is 4 feet 8 inches, ruling gradients 1 in 89, rise in feet per mile 59,
and its cost per mile 50,9237. The total sum expended to June, 1845, was 1,798,5067., and
the cost of working for six previous months was 65,610l.
Canterbury and Whitstable Railway: its total length is about 6 miles; there are a number
of inclined planes, at far too great an angle to permit the use of locomotives, except on a
very small portion of the line, consequently, two stationary engines of 25-horse power, and
another of 15 are made use of. Near Canterbury is a tunnel mile in length, 12 feet in
width, and the same in height; and the highest elevation of the line is midway, 220 feet
above the level of the sea at Whitstable.
Johnstone and Ardrossan Railway is 223 miles in length, it commences at the canal wharf
at the first mentioned place, and terminates in the harbour at the latter.
Bristol and Gloucestershire. — This railway is in length 22 miles 10 chains; it commences
near the floating dock at Cuckold's Pitt, on the east side of Bristol, and terminates at
Gloucester. The gauge of its way is 7 feet, the ruling gradients 1 in 330, and the cost per
mile 22,7007. It was opened throughout on the 8th of July, 1845.
Bolton and Leigh is a part of the Liverpool and Manchester line; its length is 9 miles.
Bridgend Railway is 4 miles in length, and in that distance rises 190 feet. It proceeds
from Bridgend to the village of Ceffn Gribbwr, in Glamorganshire.
Llanelly Railway, in the county of Glamorgan.
Clarence Railway commences at Samphire Beacon, on the river Tees, and after a course
of 15 miles unites with the Stockton and Darlington railway. There are also six branches,
which together extend more than 30 miles.
Warrington and Newton is attached to the Liverpool and Manchester line; its length is
4 miles.
Wishaw and Coltness Railway commences at Chapel, and at Old Monkland unites the
Monkland and Kirkintilloch railway; it has several branches to the neighbouring col-
lieries.
Leeds and Selby, in length 20 miles, forming a portion of the York and North Midland.
Leicester and Swannington is 153 miles in length. At its commencement is a tunnel
13 miles in length; it forms a portion of the Midland railway.
Dublin and Kingstown.—This railway is 6 miles and 4 chains in length; at its com-
mencement, the rails are placed at an elevation of 20 feet from the ground, and are carried
across the streets of Dublin upon flat arches of an elliptical form. The breadth of this
viaduct is 60 feet between the parapets, and contains four lines of rails, which, after passing
this arched road, are brought to the level of the ground, and the boundary on each side is
marked by a green sod bank, protected by a quickset hedge and a deep ditch.
From Mercon to Blackrock, the road is elevated across the strand at high water, it
having the appearance of a long mole stretching across the sea; it passes through a deep
cutting among the granite rocks, and along the edge of the cliff. The cost of the work,
including the locomotive-engines and carriages, was upwards of 40,COOl. per mile. The
width of the gauge is 4 feet 8 inches, ruling gradients 1 in 440, and rise in feet per
mile 12. The total sum expended to February, 1845, was 359,000%.
London and Greenwich was the first railway which started from the metropolis; its length
is 3 miles 60 chains; the rails are laid throughout on a viaduct composed of more than a
1000 brick arches, each of 18 feet span, 22 feet in height, and 25 feet in width from side
to side. The termini are at London Bridge and Greenwich; the gauge of its way is 4 feet
8½ inches on a level, and it was opened throughout 24th of December, 1838.
It cost per
mile 266,3221., and the total sum expended up to June, 1845, was 986,682l.; and the cost
of working for the previous six months was 15,384l.
Grand Junction Railway is in length 82 miles, and the whole passes without a tunnel
from Birmingham to Newton in Lancashire, where it unites with the Liverpool and Man-
chester line. Its course is through or near the towns of Walsall, Bilston, Wolverhampton,
Penkridge, and Stafford, the Potteries, Nantwich, Middlewich, Northwich, and Warring-
ton.
The cost is stated to have been 1,500,000l. sterling, or 18,180l. per mile; it was
opened throughout, 4th of July, 1837. The Birmingham terminus is 371 feet 5 inches
above the level of low water at Liverpool, which difference of level is increased in the
first 15 miles to 422 feet, giving a rise of 3 feet 6 inches per mile.
From Wolverhampton to Stafford is 15 miles, in which distance there is a fall of 157 feet,
or 10 feet 6 inches per mile. From Stafford to the Whitmore station is 14 miles, in which
length there is a rise of 116 feet, or about 8 feet per mile. From thence to Warrington is
35 miles, on a descent of 331 feet, or 9 feet 6 inches per mile. The remaining 43 miles to
Newton is again a rise of 60 feet, or 12 feet 8 inches per mile. The greatest inclination is
in the 3 miles between Madeley and Crewe, where it is 1 in 180.
590
BOOK I.
HISTORY OF ENGINEERING.
At Vale Royal, about 64 miles from Birmingham, the river Weaver is crossed by a viaduct
of stone; there are five arches each 63 feet span, and 60 feet in height, with parapets of
12 feet, making the total height 72 feet above the river; the length of this viaduct is 456
feet.
Four miles beyond is the Dutton viaduct, composed also of twenty stone arches, each
spanning 60 feet. Where the railway crosses the Mersey and Irwell canal, there is a bridge
of stone having twelve arches; the two in the centre are 75 feet span; that which crosses
the canal is 40 feet, and the others are 16 feet 6 inches. The gauge of its way is 4 feet
84 inches, ruling gradients 1 in 177, rise in feet per mile 29. The total sum expended to
June, 1845, was 2,597,3177., and the cost of working for the previous six months was
96,3361.
The Newcastle and Carlisle: its length is 62 miles. In the first 423 miles from the
first named place, there is a rise of 10 feet 3 inches in a mile, or 1 in 515; in the next 6
miles there is a fall of 5 inches in a mile; and in the remaining distance, a fall of 390 feet,
which is 30 feet in a mile, or 1 in 176. The level at Carlisle is 45 feet higher than at
Newcastle. At Middle Gelt Bridge, near Brampton, is a viaduct which crosses two
public roads and the river Gelt, at the height of 80 feet above the bed of the river, over
which it is carried in an oblique direction, so as to prevent any bend in the inclination of
the rails. The arches, which are three in number, are each 33 feet span, and are built at
an angle of 45 degrees.
•
This railway was opened throughout on the 18th of June, 1839; the gauge of its rails
is 4 feet 8 inches, ruling gradients 1 in 106, rise in feet per mile 50, and cost per mile
17,8381. The total sum expended to December, 1844, was 1,252,845l., and the cost of
working for the previous six months 64,5017.
Newcastle and Darlington has its termini at Rainton; it is in length 23 miles, and was
opened throughout 18th of June, 1844. The gauge of the way is 4 feet 8 inches, and the
cost per mile 20,000l. The total sum expended to June, 1845, was 1,156,378., and the
cost of working for the previous six months 19,1387.
London and Birmingham Line was opened for public use throughout its entire length on
the 17th of September, 1838. The London terminus is at Euston Square, and occupies
7 acres; a short distance beyond, at Park Street, Camden Town, is a plot of 33 acres of
ground covered with buildings of various kinds for the use of the engines, waggons, car-
riages, and luggage department. These two stations are united by a deep cutting, over
which are seven bridges: the distance, which is 1 miles, being an inclined plane, the
carriages are drawn up it by two stationary engines of 60 horse-power each, by means of
an endless rope wound round two cylinders; the trains on their arrival from Birmingham
are propelled from Park Street to Euston Square by their own momentum.
The tunnel at Primrose Hill is 1120 yards in length, clear width and height 22 feet;
the constructions throughout are of brick; there are five ventilating shafts placed at regular
distances. Kensall Green tunnel, 3 miles beyond, is in length 320 yards.
The river Brent is crossed by a viaduct of seven arches, and a little beyond Watford
is another tunnel, 1 mile and 70 yards in length, 25 feet high, and 24 feet wide; beyond
Leighton Buzzard is another tunnel, 272 yards long.
At Blisworth, about 5 miles from Castle Thorpe, is a cutting 2 miles in length, at
an average depth of 50 feet, through blue limestone rock; the quantity removed is said
to have been 1,200,000 cube yards. Five miles beyond, where the railroad passes under
the Old Watling Street, is Weedon tunnel, 418 yards long. To this succeeds the Kilsby
tunnel, 2398 yards in length. At Beechwood, near Hampton-in-Arden, is another tunnel,
300 yards long. According to a statement made by the engineer, Mr. Robert Stephenson,
the works were taken by public contract; the company provided blank tenders, to be
filled up with schedules of prices, on which an estimate was founded: at the end of every
month, the work was measured up, priced according to the list, and the amount paid, with
the exception of 20 per cent., which was withheld until the contract was finished according
to the tenders.
The stone blocks for the chairs were delivered at 6s. each, and the price for the
excavation of ordinary materials was from 1s. to 1s. 6d. per yard; the average price of the
cutting 13d. the highest price paid being 14d., which was clay, sand, and marl, with a lead of
14 miles only. If the lead was 3 miles, 17d. or 2d. per mile extra for the leading. Through
the rocks in Northamptonshire it was 2s. 3d. per cube yard. The average lead upon the
whole line was 1 mile; 1d. per yard was added for stock found by the company, as
waggons, rails, &c.
At Chalk Farm the company found all the materials, and paid the contractor 74d. per cube
yard, with a lead of about 600 or 800 yards; be afterwards had 8d. One shilling and two-
pence farthing per cube yard is the true cost, after adding interest of money, &c.: this
amount does not include the resodding of the slopes, nor any expenses which might arise
from slips, &c.
The London clay is as easily worked in fine dry weather as any other material, but in
wet weather the labour is exceedingly great. The waggons generally held two cubic
CHAP. VIII.
591
BRITAIN.
yards, and some dexterity was always required in filling them; if too full, they frequently
tilted on the road; the number of boxes in one train varied from 8 to 16, and the locomotive
which led them averaged 25 journeys a day, 3 in an hour being the utmost; they worked
from 6 to 6, two hours being allowed for rest; the distance run was a mile, which was done
with ease in 4 minutes.
Eleven horses were employed to lead the waggons to and fro, from the end of the line,
after the engine had left them, a distance of 600 yards. The engine went down a per-
manent road, but the boxes passed along a temporary one to the end, the rope being
attached diagonally, to prevent any waste of power: the Scotch fir sleepers employed cost
3s. to 3s. 6d., larch sleepers 6s. to 6s. 6d., oak sleepers at Coventry 7s. 6d. A mile re-
quired 3000 sleepers; thus the saving in a double line, if Scotch fir could be used, would
be 1200l. per mile, compared with larch it would be 3007., and with oak 6007. Oak
sleepers, upon a permanent road, will answer as well as stone, and also upon embankments
for the first 4 or 5 years, after which it is advisable to replace them with stone.
Fourpence-halfpenny per cube yard was charged for locomotive power. The locomotive
was let at of 1d. per ton per mile at the Stockton and Darlington Railway, but the fire
cost the engine-man from 3s. 6d. to 4s. per ton, while at Willesden it cost 2s. 6d. ; at
Liverpool and Manchester of a penny was paid for the loan of the engine.
Embankment at Willesden Green.—The extreme height is 13 feet, the slope 3 to 1; at the
end were 6 roadways. The expenses of working on dark nights were nearly double those
of the day, in which period from 1000 to 1200 cube yards of earth were generally thrown
out. The Birmingham line is 111 miles long, and contains 12,500,000 cube yards of
excavation, which on an average may be taken at 14d. per cube yard. The price for
fencing was 4s. per double yard, for tunnelling 30l. per yard, ballasting, laying the per-
manent way, and rails, 4000l. per mile.
Mr. Robert Stephenson was paid a salary, and an allowance for travelling expenses, pre-
paring the specifications, and furnishing an estimate. Only 13 miles of the road is per-
fectly level, the rest is by a series of inclined planes, the least favourable inclination being
1 in 330, or 16 feet in a mile. The whole length is 164 miles 20 chains, which includes
a branch to Leamington and Warwick of 9 miles, and another to Northampton and Peter-
borough of 44 miles. The Birmingham station covers 10 acres of ground, and is about
250 feet above the level of the London. The gauge of the railway is 4 feet 8 inches; the
ruling gradients are 1 in 330; rise 16 feet per mile. Its cost per mile was 52,8821.: the
total sum expended upon the works to June, 1845, was 6,997,0651., and the cost of
working for the six months terminating at that time was 192,9157.
Manchester and Birmingham, opened throughout 10th May, 1842, is in length 31 miles;
the gauge of its way is 4 feet 2 inches, ruling gradients 1 in 378, rise in feet per mile 13.
Its cost per mile was 61,6241., and the total sum expended to July, 1845, was 2,031,375,
and the cost of working for the previous six months was 34,7897.
South-Western or London and Southampton was opened for its whole length on May 11th,
1840; its length is 94 miles 10 chains, including the branch to Gosport, of 15 miles 61
chains, and there is no tunnel of any extent. The average earthwork per mile was about
142,000 cubic yards. The gradients nowhere exceed 1.in 250, being rather more than 21
feet per mile, and the gauge of the way is 4 feet 8 inches.
The report of the company, as made up to June 30th, 1840, was as follows:-
Expenditure in raising the capital and procuring the act
Land, compensation, &c.
Works of road and station
-
£ S. d.
41,467 2 0
291,200 2 5
1,114,605 5 2
Rails, chairs, and sleepers
Waggons, tools, and stores
Engines and carriages
Surveying and engineering
Salaries, rent, incidental expenses, &c.
Directors' experses
Debentures, bond stamps, brokerage, &c.
340,006 0 7
59,566 4 4
140,325 16
0
33,448 19
7
24,729 3 6
5,350 0 O
3,687 11 10
£2,054,386 5 5 5
The cost per mile was 27,8747., and the total sum expended by the company up to June,
1845, was 2,620,7247., and the cost of working for the previous six months 83,055l.
Great Western Railway is 205 miles 20 chains in length; the termini are at Paddington,
London, and Temple Mead, Bristol. Mr. Brunel was the engineer.
The Box tunnel, between Cheltenham and Bath, is in one part 400 feet below the surface;
it is 9680 feet in length, 35 in width, and 39 high. There are 13 shafts, varying in depth
from 80 to 306 feet. The quantity excavated was 414,000 cubic yards. and the brickwork
and masonry more than 54,000 cubic yards. Thirty millions of bricks were used; a ton
592
BOOK I,
HISTORY OF ENGINEERING.
of gunpowder and the same weight of candles were consumed every week for 2 years,
1100 men and 250 horses being constantly employed.
The rock is freestone, and the water poured in with such violence that, notwithstanding
the constant use of the pumps, it filled the tunnel, and rose to a height of 56 feet in the
shaft; this difficulty was at length overcome by means of an additional engine of 50-horse-
power, discharging 32,000 hogsheads per day.
The inclined plane through this tunnel is 1 in 100; instead of the ordinary rails thin
plates of iron are substituted, their inner edges being supported upon a thick felt, which
causes the rails to bend under the weight of the passing engines, and retard its progress.
The bridge at Maidenhead, crossing the Thames, has 10 brick arches; the two principal
are 128 feet span, the others are from 15 to 25.
The gauge of the way is 7 feet, the ruling gradients 1 in 100, rise in feet per mile 52.
It cost per mile 56,3721., and the total sum expended upon the entire work to June, 1845,
was 7,717,043l., and the cost of working for the previous six months was 158,3671.
The cost to the 30th June, 1841, when the railroad was opened, was thus stated :—
Expenses before the act
Land and compensation
Works
-
Permanent way, timber rails, &c.
Premises in Princes Street, Bank
Engines and carriages
Engineering, surveying, &c. &c.
Land valuers, &c.
Law charges, conveyancing, &c.
Parliamentary expenses
Stamps for debentures
Office expenses, direction, salaries, &c.
£ S. d.
89,197 11 3
720,523 16 3
3.427,429 12
3
926,052 9 11
19,600 4 5
386,900 8 4
139,859 3 0
16,528 10 10
55,815 9 6
29,104 5 4
10,357 6 0
55,751 10 0
£5,877,120 7 8
2
Preston and Wyre Railway, for the purpose of connecting the town of Preston with the
mouth of the river Wyre, is 19 miles in length, was opened on the 16th of July, 1840.
The gradients nowhere exceed 7 or 8 feet per mile. The gauge of the way is 4 feet 8 inches,
the ruling gradients are 1 in 264, rise in feet per mile 20, and the cost per mile 22,2611.
The total sum expended to February, 1845, was 490,030Z., and the cost of working for the
previous six months 7,5811.
North Union has its termini at Preston and Peak Side station, on the Liverpool and
Manchester railway; its length is 46 miles 30 chains, and was opened throughout the 31st
October, 1838. The gauge of its way is 7 feet 8 inches, its ruling gradients 1 in 100, its
rise in feet per mile 52, and its cost per mile 27,3261. The total sum expended to June.
1845, was 1,060,550l., and the cost of working for the previous six months 27,010l.
London and Croydon Railway was opened on the 1st of June, 1839, the whole distance
between the two termini being 10 miles. This railway may be said to commence where
it unites with the London and Greenwich, at Corbett's Lane, although it has an independent
station at the London terminus. The distance from the station to Corbett's Lane is 1 mile
60 chains, and the rails branch off in a curve of 90 chains radius; the railway then proceeds
along an embankment, 20 feet in height, to New Cross, where it enters a deep cutting; at
New Cross is a station, occupying three acres of ground, where there are numerous offices,
stationary pumping engines, workshops, and sheds for the carriages, and locomotives.
The high Dover road here crosses the railway by a bridge of one arch, 30 feet span, and
a height to the crown of the arch of 14 feet 6 inches.
The railway from this station rises up an inclined plane for the length of 2 miles and
50 chains, and during its course passes under six brick bridges; the cutting is in some
places 60 and 80 feet in depth. After arriving at the Dartmouth Arms station, the line is
nearly level, the greatest deviation from the horizontal being 1 in 660.
The Croydon station occupies an area of seven acres, and contains offices, waiting-rooms,
sheds, &c. The gauge of its rails is 4 feet 8 inches; ruling gradients 1 in 100; rise in
feet per mile 52 feet.
mile 52 feet. The cost per mile was 80,4002, and the total sum expended to July,
1845, was 842,5927, and the cost of working for the previous six months was 18,7221.
Brandling Junction connects Gateshead with South Shields, in Durham; it was opened
to the public the 5th of September, 1839; this railway now forms part of the property of
the Newcastle and Darlington Junction railway.
Hull and Selby Railway is 31 miles in length, and commences at the Humber dock, and
crossing the Ouse by an iron bridge joins the Leeds and Selby line, on the east side of the
Doncaster road; this line is said to be the most level of any hitherto executed, and was
opened throughout on the 1st of July, 1840.
CHAP. VIII.
593
BRITAIN.
There are iron bridges over the Derwent, at Wreple, and the Ouse, at Selby. The
greater part of the line is laid with longitudinal timbers and cross sleepers. Messrs.
Walker and Burgess were the engineers. The gauge of its way is 4 feet 8 inches, ruling
gradients 1 in 240, rise in feet per mile 22, and cost per mile 22,290. The total sum
expended to June, 1845, was 702,1737.. and the cost of working for the previous six months
20,5871.
Bristol and Exeter Railway is 76 miles in length, and chiefly through a level country;
its termini are at the stations of the Great Western at Bristol and at the depôt Exeter
it was opened throughout on the 1st of May, 1844: the gauge of its way was 7 feet, ruling
gradients 1 in 227, rise in feet per mile 41, and the cost per mile 23,6761. The sum ex-
pended to June, 184.5, was 2,136,546l.
The gauge of its
Midland Counties Railway is in length 57 miles, including the branch to Derby, of 9
miles. The amount of the earth-work on this line averaged 110,000 cubic yards per mile.
There are two short tunnels near Leicester and Redhill; beyond the latter, over the Trent,
is an iron bridge of three arches, each spanning 100 feet. Where this railway unites
with the Birmingham, at Rugby, is an extensive viaduct. The cost of work to the open-
ing of the line was 1,287,0871 5s. 11d.; and the total sum expended up to June, 1844,
1,742,7292; and the cost of working for the previous six months, 40,830%. The acting
engineer was Mr. Woodhouse, the consulting engineer Mr. Vignoles.
rail is 4 feet 8 inches, ruling gradients 1 in 330, rise in feet per mile 16.
Birmingham and Derby Junction Line is 38 miles in length; it was opened throughout
its whole length on the 12th of August, 1839. After leaving the Hampton station, there
is a mile of deep cutting, and then a lofty embankment; the river Blythe is then crossed
several times. Between Kingsbury and Tamworth, over the Anker, is a viaduct of
eighteen arches, each of 30 feet span, and one oblique arch, of 60 feet span; its elevation
above the river is 23 feet, and the cost was 18,000Z. Before entering Tamworth is a lofty
embankment, rising 30 feet, and midway between Tamworth and Burton-on-Trent is a
viaduct, mile in length, built upon a thousand piles, driven 15 feet below the bed of
the river. The gauge of its way is 4 feet 9 inches, ruling gradients 1 in 339, rise in feet
per mile 15, and cost per mile 24,6331. The total sum expended to June, 1844, was
1,212,645%, and the cost of working for the previous six months, 23,563l.
An act was passed in 1844 for consolidating the Midland Counties, North Midland, and
Birmingham and Derby railways; the total sums expended upon which amounted to the
30th of June, 1845, to 6,327,690l. 16s. 8d.
Manchester and Leeds Railway is in length 56 miles 40 chains, whilst the distance
between the termini in a straight line is only 35 miles; Mr. George Stephenson was the
engineer. At Littleborough, near Rochdale, is a tunnel nearly 1 miles in length, lined
with brick. The summit tunnel at Littleborough, 2869 yards in length, 21 feet 6 inches
in height from the level of the rails, besides a depth of about 6 feet from the rails to the
centre of the invert; the width at the level of the rails is 22 feet, and the widest part 24
feet.
There are fourteen air-shafts, averaging in depth 177 feet; and in order to complete
this portion of the work, besides the 1000 men usually employed, there were thirteen
steam-engines, in united power equal to 100 horses. The average rate of progress was
about 127 yards of length each month; 23,000,000 bricks were used in lining the
tunnel, and 8000 tons of Roman cement; its inclination is towards Manchester, and at one
point it is 400 feet below the surface. In the centre is a large culvert or drain to carry
off the water, covered with flag-stones. The rails are supported at short intervals, the
sleepers being placed only 2 feet 6 inches apart. The total cost was 251,000l. At Charles-
town is another tunnel 250 yards in length. At Horbury is a deep rock cutting of nearly
70 feet, and at Sowerby Bridge another of 80 feet.
In September, 1841, the items of expenses were thus stated:-
Parliamentary expenses
Engineering ditto
-
Land and compensation, &c.
Works, including permanent way
Stations
Directions and travelling expenses
Office expenses, salaries, advertising, &c.
Stamps and interest on loans
Law charges
Locomotive-engines, carriages
ச
S. d.
48,500 5 9
40,359
7
3
295,935 14 9
-
1,821,015
3 5
168,562 15 2
88,841
12,602 18 2
6,827 19 1
16 10
10,266 18 3
152,586 0 6
83,771 6 4
£2,728,270
This railway was opened throughout on the 1st of March, 1841.
1 10
The gauge of its rail
On account of branches
Q q
594
Book I.
HISTORY OF ENGINEERING.
is 4 feet 8 inches, ruling gradients 1 in 150, rise in feet per mile 35, and cost per mile
46,9687. The total sum expended to June, 1845, was 3,372,2404, and the cost of working
for the previous six months 92,934
Sheffield and Manchester, opened throughout 14th of July, 1845, is 40 miles 66 chains in
length; the gauge of way is 4 feet 8 inches, ruling gradients 1 in 220, rise in feet per
mile 44, and the total sum expended to June, 1845, was 1,249,9321.
Manchester, Bolton, and Bury, opened the 29th of May, 1838, is in length 10 miles; the
gauge of its way is 4 feet 8 inches, ruling gradients 1 in 160, rise in feet per mile 33, and
cost per mile 67,000l. The total sum expended to June, 1845, was 813,980%., and the cost
of working for the previous six months 97721.
Newcastle and Shields Railway is 6 miles in length, and was opened on the 18th of June,
1839; it commences at the back of Pilgrim Street, Newcastle, and ends at Little Bedford
Street, North Shields. The line commences with an embankment, and then passes under
the Shields road by a tunnel 70 yards in length; there are altogether twenty-four bridges;
one over the Ouseburn has nine arches, two of which at the ends are of stone, the others
are of timber resting on stone piers. These wooden arches are formed in eleven thick-
nesses of Dantzic 3-inch deals bent over each other; between each is a layer of felt dipped
in tar, the whole being held together by oak trenails and iron bolts. Each of the five
arches consists of three ribs lying parallel to each other, on which are transverse timbers
that carry the road. The three centre arches have each a span of 116 feet, and the others
110 feet; the total length of this viaduct is 750 feet, and its height above the water 180 feet.
The viaduct at Willingdon Dean has seven timber arches, five of which span 120 feet
each, and the two exterior each 115 feet; the whole length is 1050 feet, and the height to the
top of the rails 82 feet. These two viaducts cost 26,000l. The gauge of the way is
4 feet 8 inches, ruling gradients 1 in 180, rise in feet per mile 29, and cost per mile
44,2331. The total sum expended to December, 1844, was 290,730%.
Aylesbury Railway is a straight line of 7½ miles, and branches off from the London and
Birmingham line at Chiddington, 35 miles from London; it was opened throughout, the
10th of June, 1839; its gauge is 4 feet 8 inches, ruling gradients 1 in 118, rise in feet
per mile 44, and cost per mile 7500%. The total sum expended to February, 1845, was
60,0811.
Yarmouth and Norwich, opened throughout the 1st of May, 1845, is in length 20 miles;
the gauge of its way is 4 feet 8 inches, and is nearly on a level. It cost per mile 11,578,
and the total sum expended to June, 1845, was 259,040l.
Arbroath and Forfar was opened on January 3, 1839. Its length is 15 miles, and
extends from the harbour at Arbroath, where it joins the railway from Dundee to Forfar,
in the vale of Strathmore. Its guage is 4 feet 8 inches, ruling gradients 1 in 130, rise in
feet per mile 40, and cost per mile 92131.; the total sum expended to May, 1844, was 135,4162
Dundee and Arbroath, opened July 8, 1840, is 16 miles 50 chains in length; its guage
is 4 feet 8 inches, and nearly level throughout. It cost per mile 8570l., and the total sum
expended to June, 1844, was 153,416l.
Ulster Railway was opened in August, 1839.
York and North Midland was opened on June 30, 1840; its length is 71 miles 10 chains;
the gauge of its way is 4 feet 8 inches, the ruling gradients 1 in 484, and rise in feet per
mile 10; Mr. George Stephenson was the engineer. The cost per mile was 23,9007, and
the total sum expended to June, 1845, was 1,279,950l.
This railway commences in the city of York, and passes through the city wall by an
arch of 70 feet span, which affords room for four lines of rails. After crossing several
skew-bridges, and a bridge 274 feet in length over the river Wharfe, which has one arch of 60
feet, and eight of 15 feet span, the main line passes under the Leeds and Selby line near
Sherburn, and over the river Aire by a brick bridge, with piers of stone from Bramley
Fall; the arches are 65 feet 6 inches span, and built at an angle of 60 degrees; its total
length is 313 feet, and its width between the parapet 30 feet.
The Methley branch crosses the Calder by a similar bridge of 3 arches, each spanning
50 feet, and built at an angle of 75 degrees.
Lancaster and Preston Junction, (Mr. Locke, engineer,) is a little more than 20 miles in
length; it was opened June 30, 1840. The gauge of its way is 4 feet 8 inches, ruling
gradients 1 in 500, rise in feet per mile 10, and cost per mile 20,1927. The total sum ex-
pended to June, 1845, was 462,4671.
North Midland Railway; its length is 72 miles 29 chains; it was executed under the
direction of Messrs. George and Robert Stevenson, and Mr. F. Swanwick, engineer.
This railway commences at Derby, where the station covers an area of 26 acres, and has
very capacious sheds, offices, workshops, &c. The principal carriage-shed is 450 feet in
length, and 140 feet in width, covering 9 separate tracks; one portion extends upwards of
1000 feet, and is 42 feet in width.
The Melford tunnel is 836 yards in length, that at Claycross 1 mile, that at Chevet 600
yards. At Bule Bridge, where the river Amber is crossed, is a viaduct, and the turnpike
CHAP. VIII.
595
BRITAIN.
road, the railway; and the Cromford Canal, intersect each other at three different levels.
There are numerous bridges; two over the Derwent are constructed of timber, one 400,
the other 450 feet in length, containing together 200,000 cubic feet of Baltic timber.
The steepest inclination on this line is a slope of 1 in 264, or 20 feet per mile; this
occurs for 2 miles near Wakefield. The gauge of the way is 4 feet 8 inches, ruling
gradients 1 in 330, rise in feet per mile 16. The total sum expended to June, 1844, was
3,346,1387., and the cost of working for the previous six months 56,6261. It was opened
throughout on June 30; 1840.
Chester and Birkenhead is 14 miles in length, and the gradients are about 16 feet in a
mile. Mr. Stephenson was the engineer, and Mr. Dixon the sub-engineer; its termini are
at Monk's Ferry, opposite Liverpool, and at Brook Street, Chester; it was opened through-
out September 22, 1840. The gauge of its way is 4 feet 8 inches, ruling gradients 1 in
I
330, rise in feet per mile 13, and cost per mile 34,1987. The total sum expended to June,
1845, was 511,0467., and the cost of working for the previous six months 81881.
Chester and Crewe was opened October 1, 1840, Mr. Stephenson being engineer. This
railway commences at Brook Street, Chester, and unites with the Grand Junction Railway
at Crewe, about 53 miles from Birmingham. An aqueduct conveys the Ellesmere Canal
over the line at Christleton, and over the Weaver is an extensive viaduct.
This railway
now forms a portion of the Grand Junction.
Stockton and Hartlepool railway, 8 miles in length, was opened in December, 1840.
Messrs. Leather and Sons were the engineers. At Greatham Meadows is a viaduct, 700
yards in length, and 30 feet high, of 92 brick arches, and an embankment along the sea-
shore for mile, the sides of which are formed of clay puddling in a curvilinear form,
which allows the sea to fall easily upon it.
Northern and Eastern terminates at its junction with the Eastern Counties, 3 miles from
Shoreditch, and at Ely it unites with the Norfolk railway; its length is 70 miles 10 chains,
and was opened in July, 1845; its gauge is 4 feet 8 inches, ruling gradients 1 in 330, rise
in feet per mile 16; total expended 1,122,4987., or per mile 31,2561.
Eastern Counties terminates at Shoreditch, London, and at Colchester; its length is 151
miles 10 chains; it was opened throughout March 20, 1843; its gauge is 4 feet 81 inches,
and its ruling gradients 1 in 100, rise in feet per mile 52. The total sum expended to
July 4, 1845, was 2,954,755l., or 46,3551. per mile, and the cost of working for the pre-
vious six months 92,9741.
Glasgow, Paisley, Kilmarnock, and Ayr, (Mr. Miller, engineer,) was partly opened Sep-
tember 19, 1840; its length is 40 miles. There are a number of bridges on the joint line,
and an extensive viaduct at Paisley. Over the Cart is a stone bridge of one arch, 85 feet
span, and at Tradeston the line crosses the Polloc and Govan railway by a bridge. At Ark-
leston is a short tunnel, and another at Two-mile House.,
From Glasgow to Paisley the distance is nearly 7 miles, and from Paisley to Ayr 33½
miles. At Bishopton is a considerable cutting, and a tunnel through the solid whinstone rock.
The gauge is 4 feet 8 inches, the ruling gradients 1 in 440, rise in feet per mile 12,
and cost per mile 20,6077.
mile 20,6071. The total sum expended to January, 1845, was 1,071,2577., and
the cost of working for the previous six months 21,706l.
Edinburgh and Glasgow, opened throughout February 18, 1842, is in length 46 miles.
Its gauge is 4 feet 8 inches, ruling gradients 1 in 880, rise in feet per mile 12, and cost per
mile 35,0241. The total sum expended to January, 1845, was 1,686,556l., and the cost for
working for the previous six months 30,7831.
194
Taff Vule Railway, (Mr. I. K. Brunel, engineer, with Mr. Bush,) was opened on October
8, 1840; its length is about 24 miles; it extends from the port of Cardiff to Merthyr
Tydvil, and cost per mile 25,000l. This line has but one track, and is worked by loco-
motives, except at Navigation House, where there is an inclined plane, and a stationary
engine of 50-horse power. The inclined plane is mile in length, and rises generally 1 in
20, but near the top 1 in 18. There are two short tunnels; the principal one was blasted
through the rock, and is 250 yards in length. Near Quaker's Yard is a viaduct, which
crosses the Taff, the length of which is 600 feet, and the height above the river 100; it has
six arches. Some of the bridges are large; one has an arch of 100 feet span, and 60 feet
in height; this crosses the Rhondda at its confluence with the Taaf.
Glasgow, Paisley, and Greenock, (Messrs. Locke and Errington engineers,) opened
throughout on the 24th of March, 1841, is in length 22 miles 22 chains, and passes for
2300 yards through a hard whinstone rock, in blasting which 314 tons of gunpowder were
used. There are two tunnels, one of 320, the other of 340 yards long, between which is
an open cutting, of 70 feet in depth. A thousand men, three steam-engines, and a number
of horses, were constantly employed in this work. Gauge of way 4 feet 8 inches; ruling
gradients 1 in 330, rise in feet per mile 16, and cost per mile 35,015. Total sum ex-
pended to January, 1845, was 797,6431., and the cost of working for the previous six
months 16,6801.
Blackwall Line. Messrs. George Stephenson and G. P. Bidder were the engineers. The
Q Q 2
596
Book L
HISTORY OF ENGINEERING.
length of the entire line is 3 miles and 1230 yards; its termini are in Fenchurch Street,
London, and Blackwall. It crosses the Minories by trussed cast-iron girders, which have
a clear space of 63 feet in width, and 18 feet in height: each of these six girders weighs 15
tons. Över Vine Street is a similar construction, 30 feet in span. The greater part of
the line runs upon brick arches, about 18 feet above the level of the streets, one of which,
crossing Crutched Friars, is oblique, and spans 53 feet 6 inches.
At the London terminus is a long platform, the first portion of which has an inclination
of 1 in 100, and the remainder to the Minories, 1 in 240. On this slope, notwithstanding
the curvature of the line, the trains descend by gravity. Wire ropes are used, worked by
powerful steam-engines, stationed at each end of the line, and turning a barrel, to which a
rope of about 6 miles long is attached. An electric telegraph gives the signal when the
engines are to be put in motion, and the train is drawn forward, unwinding the rope at the
other cylinder as it proceeds; carriages are stopped at any intermediate station, by means of
a brake, after being detached from the rope, while the rest of the train proceeds. When
the carriages are prepared for returning, they are again attached to the rope, and
are drawn simultaneously by the engines. There are two lines of railway, one used for
travelling in each direction. The gauge of its way is 5 feet, ruling gradients 1 in 106, rise
in feet per mile 50, and was finally opened on the 2nd of August, 1841.
mile was 288,1777., and the total sum expended to June, 1845, was 1,083,951l., and the
cost of working for the previous six months 24,4941.
The cost per
Slamannan Railway was opened in August, 1840; it was a communication between
Ballochney and the adjoining railways and the Union Canal at Causeway End, near Lin-
lithgow.
Maryport and Carlisle Railway, open throughout in January, 1845, is in length 28 miles
3 chains; the gauge of its way is 4 feet 8 inches, ruling gradients 1 in 209, rise in feet per
mile 25, and cost per mile 11,500%. The total sum expended to June, 1845, was 345,7201.,
and the cost of working for the previous six months 5,3907.
Birmingham and Gloucester. Captain W. S. Moorsom, engineer. The total length is 55
miles 73 chains, and was opened throughout on the 17th of December, 1840. Its termini
are at the Spa Road, Gloucester, and Camp Hill, Birmingham. The gauge of its way.
is 4 feet 8 inches, ruling gradients 1 in 37, rise in feet per mile 142, and its cost per
mile 26,9341. The total sum expended to December, 1844, was 1,527,2671.; and the cost
of working for the previous six months 44,7391.
London and Brighton Railway.
G
Mr. Rastrick, engineer. The total length of the main
line is 41 miles; the distance run over the Greenwich and Croydon lines 94 miles, making
50 miles. This railway; from its junction with the Croydon line, rises for 8 miles about
20 feet per mile, or 1 in 264. At Merstham is a tunnel 1780 yards long, after which the
line falls, at the rate of 1 in 264, for the distance of 7 miles. From this point at the
Horley station, it rises for about 6 miles, and passes through Balcombe tunnel, 1122 yards
long. It then falls for another 8 miles, and rises for 5½ miles, where is the Clayton
tunnel, through chalk, 14 miles long, from whence there is another fall to the terminus at
Brighton.
Across the valley of the Ouse is an aqueduct, 1437 feet in length, and the height varies
from 40 to 96 feet; it is formed of thirty-seven brick arches, of 30 feet span. The other
tunnels at Patcham and Hayward Heath are 480 and 230 yards long.
The rails are laid
to a gauge of 4 feet 8 inches, and are supported by wooden sleepers. The expenditure to
the 30th of June, 1841, was thus stated:~
Parliamentary expenses (which does not include the contest)
Land and compensation
Law, and surveying charges thereon
Engineering and surveying
Works
Stations
London joint station on account
Rails, chains, sleepers
Engines and carriages
Direction
Law expenses
Office expenses, salaries, &c.
Interest, stamps, commission on mortgage bonds
£ S. d.
3,780 10 11
386,725 7 9
16,185 11 10
31,030 15
O
1,159,328 9 2
42,523 4 8
25,754 2 1
176,872 3
4
45,438 13
9
8,400 0 0
15,969 3 11
31,023 11
0
7,975 3 11
£1,951,906 17 4
The assent was given to the bill for the formation of this railroad on the 15th of July,
1837, and it was finally opened to the public on the 21st of September, 1841. The total
sum expended to June, 1845, was 2,653,6724,, and the cost of working for the previous six
months, 66,9331.
CHAP. VIII.
597
BRITAIN.
J
South-Eastern Railway. -Its termini are near London Bridge and Dover; its length
is 88 miles 10 chains; the gauge of its way is 4 feet 83 inches; the ruling gradients 1 in
264, and the rise 20 feet per mile. It was opened throughout on the 6th of February,
1844. The total sum expended up to July, 1845, was 4,306,4781., and the cost for the
previous six months was 123,462l. Assent was given to the bill on the 21st of June, 1836.
Ulster Railway, in length 36 miles, has its termini at Belfast and Armagh; its gauge is
5 feet 6 inches.
Dublin and Drogheda, in length 37 miles, was opened throughout the 26th of May,
1844; its gauge is 5 feet 3 inches, and it cost per mile 16,5337 The total sum expended
to December, 1844, was 579,2531.
Great North of England Railway, (Mr. Robert Stephenson engineer,) has its termini at
Darlington and at York; its length is 45 miles 19 chains, and was opened throughout in
1842. The gauge of its way is 4 feet 8 inches, ruling gradients 1 in 330, rise in feet per
mile 16, and the cost per mile 26,855. The total sum expended to June, 1845, was
1,296,2007., and the cost of working for the previous six months 31,0317.
Railways.
Cost of
working for
Six Months.
Length.
Total Sum
expended.
Returns for
the same
Time.
Great Western
London and Birmingham
South Eastern
Miles. Chains.
205 20
£
7,717,043
£
158,367
£
433,296
164
20
6,997,065
192,915 452,881
88 10
4,306,478
123,462 160,402
Manchester and Leeds
56 40
3,372,240
92,934
153,279
North Midland
772 29
3,346,138
56,626
112,866
Eastern Counties
51 10
2,954,755
92,974 114,807
London and Brighton
South Western
30 20
94 10
2,653,672
66,933 109,831
2,620,724
83,055 169,789
Grand Junction
82 50
2,597,317
96,336 226,326
Bristol and Exeter
76 10
2,136,546
44,951
Manchester and Birmingham
31 0
2,031,375
34,789
72,540
Liverpool and Manchester
38 23
1,798,506
65,610
134,124
Midland Counties
47 36
1,742,729
40,830 68,153
Edinburgh and Glasgow
46
0
1,686,556
30,783 61,047
Birmingham and Gloucester
53
30
1,527,267
44,739
70,096
Great North of England
York and North Midland
Newcastle and Carlisle
45 19
1,296,200
31,031
59,899
71
10
1,279,950
28,484
77,791
61 67
1,252,845
64,501 78,484
Birmingham and Derby
38 68
1,212,645
23,563
36,063
Sheffield and Manchester
40 66
1,249,932
9,629 18,746
Newcastle and Darlington
23 0
1,156,378
19,138
70,276
Northern and Eastern
79 10
London and Blackwall
3 38
1,122,498
1,083,951
19,647 45,759
24,494 29,525
Glasgow, Paisley, Kilmarnock, and
Ayr
40. O
1,071,257
21,706 42,720
North Union
46 30
1,060,550
27,010 51,404
London and Greenwich
3 60
986,682
15,384 18,058
London and Croydon
10 26
842,592
18,722 36,027
Manchester, Bolton, and Bury
10 0
813,980
9,772 25,038
Glasgow, Paisley, and Greenock
22 22
797,643
16,680 23,447
Hull and Selby
30 51
702,173
20,587 35,054
Bristol and Gloucester
22 10
667,822
19,685 27,544
Taff Vale
24 40
623,102
18,543 24,894
Dublin and Drogheda
32
0
579,253
13,313 21,572
Chester and Birkenhead
14 72
511,046
8,188
15,570
Preston and Wyre
19 60
490,030
7,581
13,537
Lancaster and Preston
20 18
462,467
13,832
Stockton and Darlington
25 30
450,000
Dublin and Kingston
6 4
359,000
29,263
53,740
Ulster
36 0
358,353
5,190
14,743
Maryport and Carlisle
28 S
345,720
5,390
8,406
Durham and Sunderland
13 20
301,248
11,334
17,347
Yarmouth and Norwich
Newcastle and North Shields
Dundee and Arbroath
20 40
259,040
5,289
7,286
6 79
290,730
15,022
19,152
16
50
153,416
8,633 13,987
Arbroath and Forfar
-
15 15
135,416
Q Q S
598
Book I.
HISTORY OF ENGINEERING.
In the preceding table is shown the length, total sum expended, cost of working
for six months, and the returns for the same time upon forty-five of the principal railroads
completed; and as the works upon them were mostly of a similar kind, it was deemed
advisable to reserve the descriptions which relate to the detail to that portion of the volume
devoted to theory and practice. The various locomotive-engines, the different forms of
the rails, and the machinery, is described under the separate heads of machines and their
movers. For the construction of these railways the civil engineer and architect have
contributed their labours; for the machines and engines afterwards applied to it, we are
indebted to the several manufacturers now established throughout England. By the united
labours of the civil and mechanical engineers a new era has opened upon us, which
eventually will lead to the most beneficial results.
Atmospheric Railway. -Dr. Papin exercised his skill in attempts to derive mechanical
power from the motion of a piston in a cylinder, and thus produce a vacuum. He first
made his experiments with gunpowder, and afterwards with steam; he placed a cylinder
containing a little water and a piston over a small fire; as soon as steam was created the
piston of course rose, and after the fire was taken from under it the steam cooled down,
and the piston again descended. Papin, however, applied his discovery, if it might be so
termed, only to mere models; he made no attempt to gain a succession of strokes for his
piston, nor to produce rapidity of motion; he thought it might be so worked, but did not
point out any method by which it could be performed.
Mr. Valence in the year 1824 was the first to impel a piston through a tunnel, which
he did at Brighton, and immediately afterwards took out a patent to secure his invention.
This was to be applied to the transmission of railway carriages, and the plan consisted of
a series of cylinders of large diameters, within which they were to pass with passengers or
goods, being propelled by the pressure of the air upon a disc which was placed in front
of the first carriage: the cylinders were exhausted by air-pumps placed at their ends; the
atmosphere then pressing with all its power against the disc, pushed it forwards in the
vacuum already produced by the air-pumps.
Mr. Medhurst in 1827 endeavoured to carry out a project he had described sixteen or
seventeen years before, as a method of rapidly conveying goods and passengers through a
tube of 30 feet diameter, by the power and velocity of the air.
Pinkus in 1834 took out a patent for an extended cylinder or main 40 inches in
diameter, with a longitudinal opening along the upper side, through which an arm extended
from the piston to the leading carriage, which, with the rest of the train, ran upon the rails
on the outside of the main. The aperture of the cylinders in advance of the pistons was
closed air-tight, by a flexible cord which was raised by a grooved wheel in the centre
of the carriage, and pressed down by two other wheels at the ends as the train advanced.
In front of the piston a partial vacuum was produced by means of air-pumps, and
the atmosphere was supposed to rush into the cylinder through the groove, which was
laid open by the raising of the cord.
Mr. Samuel Clegg, who had been engaged in making some of the arrangements to carry
out Mr. Pinkus's invention at Wormwood Scrubbs, and to demonstrate the principles of the
pneumatic railway, discovered that the vacuum might be improved, and in conjunction
with Mr. Samuda took out a fresh patent. It is now proposed that the moving power
shall be through a continuous pipe laid between the rails, and divided by separating
valves into convenient lengths for the purpose of exhaustion. A partial vacuum is formed
in this pipe by air-pumps, which are worked by steam-engines placed at various distances;
the separating valves are opened as the train progresses. At the top of the pipe or
main is a continuous groove covered with a valve, made of stout leather riveted between
two iron plates, that at the top being wider than the other, to allow of the valve closing
and effectually covering the groove; when the valve falls the edge lies upon a compo-
sition of bees-wax and tallow, which is passed over by a heater made fast to the frame of
the leading carriage. The pipe is exhausted in front of the piston, which is attached
to the carriage by a connecting plate, serving to draw the train as well as to sustain the
piston when in motion. This plate has also attached to it a frame on four wheels,
which lifts and sustains the continuous valve, whilst the plate is in motion along it; this
is kept open beyond the plate by means of the two outer wheels, and the atmosphere is
thus admitted behind the piston. The main or pipe is of iron cast in 9 feet lengths, and
put together with socket joints, caulked carefully with yarn and a cement made of whiting,
boiled linseed oil, olive oil, or any other, the drying qualities of which are not rapid;
tallow is afterwards used and tarred yarn, to make the joint perfect; the whole is in a soft
state, and is not affected by either the contraction or expansion of the metal. The heater,
which is described as passing over the valve, consists of a trough filled with charcoal, and
at the bottom is a copper blade, which rests on the surface of the composition, and being
always hot slightly melts it; thus by closing it, the joint is rendered again air-tight as the
train passes along. The entire main is separated into lengths of 3 miles each, by valves
which open in a direction to suit the passage of the trains; these valves act in a semi-
CHAP. VIII.
599
BRITAIN.
circular valve-box placed underneath the pipe; the valve is opened by the wheel of the first
carriage depressing a lever on the outside of the pipe, which disengages a catch that
occasions a weight to move a slide valve across two openings of the valve-box on either
side. In one position of the valve the air in the chamber finds its way into the exhausted
tube; and on the other, the valve which is attached to the same fulcrum as the first is
opened by the external pressure; this is a very ingenious part of the contrivance. The
disc in the inclined position is a little larger than that in the pipe, and thus keeps it
closed until the slide is moved. To the fulcrum of this valve is attached the weight, by
which the action of the wheel is disengaged; there are two sets of these valves, to allow
of a transit in either direction.
When the first steam-engine is worked, a vacuum is made in the first length of the pipe;
the piston is then introduced, and the valve opened; when the train begins to move a
signal is given by means of an electric telegraph, and the second engine is set to work, so
that when the first length of pipe is passed through, the second is exhausted, and after
passing the branch connected with the first pump, the exit valve of the first division is
opened, as well as that of the second, and the train passes on without any interruption
whatever; the third engine then does its work in a similar manner, and so on.
When of
a vacuum are produced before the train enters the section of pipe it is to pass over, it is
propelled by nearly twice the power required to work the air-pump during its motion;
for the mean pressure on the piston of the air-pump, working at this degree of vacuum, is
only 5 pounds per inch, whilst that on the piston in motion is 10 pounds.
Experiments were made on the Dalkey railroad, upon the amount of leakage of the
main there laid down, which was 15 inches in diameter; the total contents of this main or
pipe were estimated as containing 10,680 cubic feet, and in the space of 41 seconds it
was not found more than 356 cubic feet, an inch of mercury being all the reduction which
took place in the vacuum; this leakage has been estimated as equal to 10 horse-power per
mile, or 30 horse-power for each section of 3 miles.
The Electric Telegraph, adopted on some of the lines of railroads, is remarkable for the
great ingenuity displayed in applying electricity to communicate intelligence from one
point to another; telegraphs so set in motion were the invention of Messrs. Cooke and
Wheatstone.
When the required communication is to be made, the operator upon the machine com-
mences by sounding a bell, which he does by a very simple apparatus. In connection with
the instrument are two coils of wire, the ends of which, passing through the bottom of the
frame, are attached to the general wires of communication; a piece of soft iron is fastened
to a lever, which is firmly held against a pin. The electric current attracts the iron by
magnetic influence, releases the pin, and, giving motion to the wheels of the machine,
produces a loud and clear ringing, which is attended to at the station where the information
is to be conveyed. The communication is then made by letters, every word being spelt,
each letter having the distinct motion of a pointer or index applied to it, which works on
a dial divided into five circles, each containing a number of letters, all indicated by needles.
The left-hand needle moved twice gives A, three times B; once to the right and once to the
left, C ; once to the left and once to the right, D; once to the right E, twice F, three times G.
The order is then taken up by the right-hand needle moving once to the left for H, twice
for I, three times for K, once to the right and once to the left for L, once to the left and
once to the right for M, once to the right for N, twice for O, and three times for P. The
remaining signs are made by the two needles conjointly, so that the simultaneous movement
of the two once to the left indicates R, twice for S, three times for T, once to the right and
once to the left for U, once to the right for W, twice for X, and three times for Y. At
the end of each word the left hand needle moving once to the right to the cross, indicates
the word is complete, and when the receiver understands it, he moves the same pointer
twice to the left and twice to the right, which indicates yes. When not understood, the
needle E is pointed twice to the right and twice to the left, which indicates no, and then
the original word is repeated. Doubling the motions for each letter, figures are obtained.
The signals are given by two magnetic needles or pointers, each suspended vertically on
its axis, passed through the dial; behind the dial is fixed another pointer on each cor-
responding axis. A portion of the conducting wire, many yards in length, is coiled round
the galvanometer frame, in which the magnet moves, so as to subject the magnet to the
multiplied deflecting force of the electric current; the motion of the pointers is limited by
a fixed stop or pin at either side.
When a communication is to be made, the conductor turns the handle to the right or
left, so as to break the electric circuit, and press the wire against pins connected with the
battery poles; the coils of wire thus receiving the full deflective force attract the magnetic
needles to either side, according to the course of the current; thus, if the stream of
electricity first passes into the coil, the upper part of the needle will be attracted to the
left, thus giving the whole motion necessary to the pointers. The movement of the handles,
and consequent deflection of the pointers at either end of the line, are simultaneous, and
QQ 4
600
Book I.
HISTORY OF ENGINEERING.
there is no time lost between the sending and the receipt of the intelligence. To convey
the wires from one station to another, posts 16 or 17 feet high are fixed in the ground at
every 400 or 500 yards, which support them in the air. Three wires on the lines, one ap-
paratus and one set of wires at each station, are all that is required to complete the
machine.
The battery at each station is about 2 feet in length, and 6 inches in width: if the wires
connected with it were kept continually attached to the signal wires, they would produce
constant motion at the other end; to obviate this another wire conducts the electricity into
the earth when the telegraph is not at work, and an attendant is always present at each
dial; when a signal is made, he attaches the wire again to the battery. The wires are all
copper and coated with zinc.
Gas Lighting. About the year 1739, there is a notice in the Philosophical Transactions
of the discovery of coal-gas by the Rev. John Clayton, Dean of Kildare; this gas, called
"the spirit of coal," was obtained from a retort placed in an open fire, and Dr. Clayton
observes, that "at first there comes over only film, afterwards a black oil, and then a
spirit arose which could not be condensed, and it broke the lute as well as the glasses.
This spirit caught fire at the flame of a candle, and continued burning with violence as it
issued out in a stream; a quantity was collected in bladders, and a hole being made, the
gas as it issued was lighted, and allowed to burn out for the amusement of his friends."
In the year 1767, Dr. Richard Watson, afterwards Bishop of Llandaff, made some ex-
periments upon the distillation of pit coal; he allowed the gas to mount by curved tubes,
and describes, in the second volume of his chemical essays, its great inflammability as well
as elasticity; he also found that it retained the former property after it had passed through
a great quantity of water.
These discoveries do not appear to have been applied to the purpose of lighting until
some years afterwards: in the streets of the metropolis, as well as those of most of the pro-
vincial towns of importance, oil lamps were used, though very inadequate to their purpose,
and it is difficult to say how or by whom coal gas was first introduced as an illuminator.
Mr. Murdoch, Mr. Southern, Mr. Clegg, and Mr. Henry Creighton, all resided at Soho,
near Birmingham, at the same time; and without doubt Mr. Murdoch used coal-gas for the
purpose of lighting his house and offices at Redruth in Cornwall in the year 1792, and four
or five years afterwards he introduced the system into Scotland. In the year 1798 he con-
structed an apparatus upon an extensive scale at the great manufactory of Bolton and Watt,
near Birmingham, where the first attempts were made to purify the gas; and at the peace of
1802, the manufactory at Soho was illuminated by it with a variety of devices on the
exterior, to the astonishment of all who beheld it.
Various manufactories were afterwards lighted with coal-gas, but it was not used in the
streets till the year 1807, when a portion of Pall Mall in London was illuminated by Mr.
Winsor, who proposed the establishment of a national light and heat company.
The retort
used on this occasion to distil the coal was an iron vessel, with a cover well-fitted and luted
to the top; in the centre of the lid was a pipe, which conveyed the gas to a condensing
vessel of a conical form; this was divided into two or three separate compartments by plates
bored with a number of holes, so that the gas might spread, and more readily purify itself
from the sulphuretted hydrogen and ammonia, which it did, though very imperfectly. The
pipes laid down as mains were lead, with copper burners to the branch pipes, which were
argands, jets, and batswing, as in present use.
Dr. William Henry gave a series of lectures at Manchester in the year 1804, and during
the course he exhibited the mode of producing gas from coal, and its use as a material for
yielding light. Mr. Samuel Clegg at this time, having left Soho, began to direct his atten.
tion to the construction of gas-light apparatus, and one of his first works was lighting a
cotton-mill near Halifax in Yorkshire. The subject was soon afterwards taken up by Mr.
Josiah Pemberton, of Birmingham. His apparatus consisted of a cast-iron vessel, like a
cottage pot, and would contain from 15 to 30 pounds weight of coal; a strong cover with
a pipe fitted on carried the gas to the purifying cistern, ascending and descending in its
passage through the water; it was thus well condensed and washed before it entered the
gasometer, which was suspended by a weight over a large wooden vat. The pipes that
carried the gas were made of tinned iron or copper.
In the year 1809, an application was made to parliament for the establishment of the
present London and Westminster Chartered Gas Light and Coke Company: this was opposed
by Mr. Murdoch, on the ground of his having a priority of right to the discovery, but it was
eventually embodied by legal authority, and having a large capital at command, the works
for lighting the streets were commenced; but the subscribers becoming dissatisfied with the
proceedings, a change of management took place, and in 1812 a charter was granted
for the term of twenty-one years The following year, by the assistance of Mr. Samuel
Clegg, great improvements were introduced throughout all the operations, and to him we
are indebted for the horizontal rotative retort for purifying coal-gas with cream of lime
for the rotative gas-meters, and for the self-acting governor: he also greatly improved the
CHAP. VIII.
601
BRITAIN.
retorts, and the manufacture of gas was rendered so perfect, that its general adoption was
the consequent result.
In 1817, this gas company had three stations, which consumed daily 25 chaldrons of coals,
producing 300,000 cubic feet of gas, which was equal to the supply of 75,000 Argand
lamps, each yielding the light of six candles. At the City gas works in Dorset Street,
Blackfriars, 3 chaldrons of coals were daily carbonised, which was equal to the supply of
1500 Argand lamps, so that the two companies supplied 76,500 lights. During the last
few years many new companies have been established, and there is scarcely a town in the
kingdom without this invaluable addition to its comfort.
In the year 1834, in the city of London and its suburbs alone there were 168,000 gas
lamps, which consumed nightly 4,200,000 cubic feet of gas; requiring for its manufacture
10,800,000 cubic feet of coal. And by a document laid before parliament three years after-
wards, it appears that there were eighteen establishments, besides twelve chartered com-
panies, employing a capital of 2,800,000l., whose yearly revenue was 450,000l.; that they
annually consumed 180,000 tons of coals, and made 1,460,000,000 cubic feet of
gas, which
was supplied to 134,300 private burners, used by 40,000 consumers, and 30,400 street lights:
176 gas-holders, which contained 5,500,000 cubic feet of gas, were employed; 890 tons of
coals were consumed in the retorts during the longest night, or 7,120,000 cubic feet of gas.
In the five years between 1822 and 1827, the quantity of gas made was doubled; and from
that time to the year 1837, it had again doubled itself.
Prisons, according to Palladio, "should consist of three descriptions: one for those who
are kept confined until a reformation of manners can be effected; another for criminals who
are to be tried, as well as those already condemned, and a third for debtors; these ought to be
well secured and guarded against internal and external violence, healthy and commodious,
because they are for the safe keeping, not for the torment and pain of criminals, or of other
men; their walls therefore in the middle should be formed of massive stone, bound together
with cramps, with bolts of iron or other metal, and then lined on both sides with brick, to
prevent any humidity, and to make them healthy. Passages should be made all round
them, and the rooms for the keepers should be near at hand."
At Milan and other towns of Italy, there are such prisons, but in England little attention
was paid to the subject until taken up by the philanthropic John Howard, towards the
latter end of the last century. This illustrious individual, after visiting most of the places
of confinement in Europe, induced the government to establish penitentiary houses, upon
the principle of some already founded in Holland, where it was considered, that if offenders
convicted of crimes, for which transportation had been usually inflicted, were ordered to
solitary imprisonment, accompanied by well-regulated labour and religious instruction, it
might be the means, not only of deterring others from the commission of the like crimes,
but also of reforming the individuals, and inuring them to habits of industry. The reform-
ation and amendment of the prisoners was here for the first time made the chief end
of imprisonment; and to carry out this excellent idea, Dr. Fothergill was associated
with Howard to devise a plan and provide a site for a structure in which it could be
fully developed. The cloth-hall at Halifax was the model for the building, whilst the
regulations were to be those of the Rasp and Spin houses in Holland. The plans and
elevations are given by Howard in his account of prisons, and consist of six courts, each
surrounded by three stories or tiers of open galleries, around which are distributed the cells
for the prisoners; a portion of ground near Islington was selected for its erection, the
neighbourhood being considered healthy, and a supply of water could be easily obtained;
it was also sufficiently removed from any habitation.
Regulations were laid down for security, health, diet, clothing, lodging, firing, re-
ligious instruction, employment, rewards, punishments, sickness, and general government.
These works were, however, not carried out during the life-time of Howard, and after
his death were abandoned for some time. In the year 1770, the mortality among the
prisoners at Newgate was so great from the gaol distemper, that Mr. Akerman, the then
keeper, stated, that independently of the prisoners, nearly two sets of servants had died
since he had been in office; and that in the year 1750, two of the judges at the Old Bailey,
the Lord Mayor, several of the jury, and others, to the number of sixty persons, died of the
same disease; after this had occurred, a large ventilator, with sails like a windmill, was
placed on the top of Newgate to produce a circulation of fresh air.
Parliament subsequently granted 50,000l. to construct a new gaol; this was completed
under the superintendence of Mr. George Dance, a little before the riots of 1780. This
prison, which has a frontage of nearly 300 feet, is admired for its appropriate and massive
character. The centre is occupied by the keeper's house, with the entrances on each side;
the walls are of Portland stone, rusticated and continued up to a height of 50 feet, the
whole producing by its magnitude and boldness of detail a very characteristic façade. The
interior distribution is defective, in consequence of the want of space, the site on which it
is erected being far too small to allow of a proper ventilation or a requisite supply of air.
602
Book I.
HISTORY OF ENGINEERING.
This prison has three distinct arrangements, which are called stations. The first, in the
north wing, has three yards, with sleeping and day rooms attached: the first yard and
rooms are occupied by adult convicts; the second by boys, who have a school-room; and
the third is an infirmary.
+
The principal wards and rooms in the stations are 38 feet by 15, and 24 feet by 15.
The two connected with the press-yard, for males under sentence of death, are 31 feet by
There are three tiers of condemned cells, five in each tier, strongly arched, 9 feet by 7.
In each cell is a barrack bedstead. The chapel will contain 350 persons.
18.
Other prisons have since been erected about the metropolis, as well as in several of
the counties in England; there are also numerous bridewells and penitentiaries, upon
which enormous sums of money have been expended, but that most deserving of notice
is the Model Prison lately erected at Pentonville, in which all Howard's ideas are carried
out. It was reserved for the present day to execute the plans suggested by this philan-
thropist, upon the site he had selected. The first stone was laid on the 10th of April,
1840, and the whole was completed in the autumn of 1842. It is adapted for the recep-
tion of 520 prisoners upon the separate system, each having a cell 13 feet by 7, and 9 feet
in height.

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| | | | | | | | | | | | | | | | |||
A
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Fig. 559.
PLAN OF the model PRISON.
The plan exhibits a central hall, open from the floor to the roof, from which branch
five blocks of building, each having on the ground floor a corridor, which extends the
whole length, with galleries above, in which are the entrances to the cells, arranged on
each side against the outer walls. From the central hall the doors of all the cells may be
seen, as the galleries are formed of open iron-work. The Eastern Penitentiary at Phi-
ladelphia, designed by Mr Haviland, seems to have been the prototype for this arrange-
ment. As there are no female prisoners there is but one class of cells.
The boundary wall is upwards of 20 feet in height, and solidly constructed, and on the
outside is an open space of considerable width. The basement is not sunk into the earth,
except in one portion, where it has an open area; over the whole surface of the walls a
course of slate in cement was laid 6 inches above the ground line, and the walls stand on a
CHAP. VIII.
603
BRITAIN.
bed of concrete 3 feet in depth and as much in width, so that every precaution is taken to
prevent the ascent of moisture. Under the entrance building is a ward for the reception
of prisoners, where they are examined by the medical attendant. The access to this ward
is from the ground floor, near the entrance door; and the accommodation consists of a
receiving room, a number of cells in which prisoners can be locked up for twenty-four
hours if necessary, an examining room, clothing stores, bath, and a closet for fumigating
and purifying clothes. This ward has no connection with the rest of the basement, but
prisoners, after being examined, cleansed, and dressed, are taken into the prison through
the entrance passage on the ground floor. The basement under the great central hall is
used for the distribution of materials, and is surrounded by a covered passage, which
communicates with the kitchen, yards and stores, &c. Adjoining the kitchen is a room
in which the provisions are weighed out and arranged in trays, after which they are
hoisted by an apparatus to the different stories, and distributed to the wards.
maining portion of the basement is used for offices, punishment cells, and the attendants.
The ground plan shows the distribution of the building, the exercising yards, the entrance
gates, and two front barriers; the well for supplying the prison with water; the houses for
the governor, chaplain, and gate porters.
The re-
Besides the 520 separate cells, there are twenty others on the basement used as work-
shops, &c.; a chapel, which contains stalls for 256 prisoners; a board room for the com-
missioners, A; offices for secretary, B, governor, H, chaplain, D, physician, E, governor's
clerk, N O P, clerk of the works, &c., waiting room, G, visiting room for prisoners' friends,
L M, schoolmaster's room, library, surgery, offices for the steward and clerk, kitchen and
scullery, stores for provisions, &c., stores for manufactured articles, dwellings for go-
vernor, chaplain, assistant chaplain, steward, and manufacturer, principal schoolmaster,
clerk of the works, four principal warders, twelve warders, two gate-keepers, one mes-
senger, an engineer, and apartments for the deputy-governor, resident medical officer, and
infirmary warden. The total area, including the boundary wall, is 6 acres 10 perches;
there is a garden of 2 acres in the rear, and a terrace and road 75 feet broad in front.
The chapel is 72 feet 6 inches in length, 40 feet in width, and 26 feet in height to the
under side of the cornice, above which is a coved ceiling. It occupies a portion of the
upper part of the building, and is entered on the level of the first and second galleries.
The rows of seats are so disposed that the prisoners are effectually separated from each
other, whilst, at the same time, each has a view of the officiating clergyman, and can be
seen by the attendant inspector. Each prisoner, as he enters, closes the door after him, and
when a row is filled the officer fastens the whole of the doors in the row by a handle and
crank, which are shown in the cut.
There are four entrances, and, by means of a sliding partition drawn across the gallery,
the whole can be filled in seven minutes. When service is over, a signal is made by means
of a letter, which designates each row, and the prisoners occupying the seat corresponding
with it retire.
The plan of the stalls shows the doors shut, half shut, and entirely open, in the three
different rows; the clear space allowed each prisoner is in width 20 inches, and in depth
32, the width of the seat being 9 inches out of it.
The section shows the stepping up, so that each prisoner may obtain a view of the clergy-


SHUT.
DOORS OPEN.
HALF SHUT.
HO
H
H
Fig. 560.
PLAN OF STALLS.
Fig. 561.
SECTION OF STALLS.
604
BOOK I.
HISTORY OF ENGINEERING.
;
man: the heights of the divisions up to the top of the reading-desk is 4 feet 6 inches, the
width of the reading-desk 16 inches, and the height of the doors above the floor of each
6 feet. By this arrangement the prisoners on the rear and front are prevented from seeing
each other.
The fastenings for the hall doors are shown in plan and profile with the jointed handle;
they are made of brass. When the doors are closed, the handle falls downwards, and when
open its position is as shown in the
figure to the left. On the plan the
fastenings, when the doors of seats are
closed, assume the horizontal direction.

The cells are each divided by a wall
two bricks in thickness; the external
walls are two bricks and a half. The
ceilings are formed of half brick arches,
worked in cement, over which is laid
a bed of concrete, about 6 inches in
depth; this is levelled, and on it is
placed the floor of asphalte for the cells
above. The whole thickness from the
floor of one cell to the ceiling of the
other is 12 inches. In the upper cells,
for the purpose of greater security, is
a brick arch, nine inches thick, worked
in two courses in cement, with a layer
of hoop iron laid diagonally at intervals
of 4 inches.
کے کچھ کھانے کی توام
Fig. 562.
HANDLES TO DOORS OF CHAPEL.
The cells are 13 feet in length, 7 feet
in breadth, and 9 feet in height to the
under side of the arched ceiling. The
window-frame, which is fixed, is of
cast-iron, glazed with fluted glass,
having outside two strong iron bars so
placed that they do not intercept the
light. The door has a spring lock, and
a small trap is contrived for the intro-
duction of provisions; there is another
opening, covered by a movable flap, for
the purpose of inspection.
These cells are well adapted to carry out the reformation and amendment of their inmates.
to such the philanthropic Howard, who did not approve of any suffering capitally but
for murder, setting houses on fire, or house-breaking attended with acts of cruelty, would
have consigned all those unhappy wretches who had committed less heinous faults, that
they might, by regular and steady discipline, have the chance of becoming useful members
of society, and he ardently indulged in the hope that it was possible, in the course of five
years, to effect this; and with such accommodation and treatment as the prisoners receive,
with airy apartments, warmed, ventilated, and plentifully supplied with water, they cannot
but enjoy better health than falls to the lot of many mechanics and day labourers, who,
neglecting cleanliness, and not receiving wholesome and proper food, often die at a pre-
mature age.
In these cells there is ample space for any work assigned to the prisoner,
and as a proper degree of labour is conducive to health, he that has led an idle life pre-
viously may not only acquire industrious habits, but with them strength of mind and
body: there are many who would fancy the inmates of these solitary rooms far too com-
fortable, but they should remember that the object is to reform the prisoner, to oblige
him to reflect, review his past life, and form resolutions to amend, which may tend to his
becoming a better citizen. Punishment, unaccompanied by sympathy for the distresses of
the offender, is not likely to be a corrective; the human heart is not so to be softened; on
the contrary, a feeling of anger will be induced, leading to the commission of greater
crimes, until the last dread penalty of the law is inflicted.
Habits of decency, order, and regularity being obtained, the prisoner has advanced
towards the threshold of religion, for which he is infinitely better prepared than he would
have been by the most rigorous severity. Experience gives us daily proof that criminals
may be reformed, and if so, every county and populous district in the United Kingdom
should have its penitentiary-house or prison: the hulks and common gaols would no
longer contaminate the young, who are often sent thither for faults arising from a neglect
of education, and where they imbibe ideas imparted by the most abandoned, and return to
society a greater nuisance and dread than before they were committed. The bettering-houses
in Holland proverbially benefit those who enter them, and there are few instances in which
CHAP. VIII.
605
BRITAIN.
solitary confinement, with careful supervision, has any other effect than that of amelior.
ating the condition of the prisoners. The grand object of education should be to make

Fig. 563.
SECTION OF CELL.
B
B
Fig. 564.
plan of cell.
pro-
men think, and the opportunity to do so can only be afforded when they are removed
from haunts in which they see and hear what stimulates them to actions of wrong, and
receive no inducement to do what is right: notions on these subjects may possibly
never have been presented to them, and when committed to the care and superintendence
of the officers of such establishments, they may, for the first time, be led to comprehend
that their own means of subsistence is not necessarily connected with injury and outrage
towards their fellow-creatures; and what may be the result of such a dawn in the mind,
no one can predict. Cleanliness in this establishment is strictly attended to; all the
visions with which the prisoners are served are of the best quality of their kinds, and the
proportions duly given out to each. Water is abundantly supplied from triangular
cisterns, fixed in the angle of each cell; the gaslight is immediately over the table, seen in
the section, to the right of which is placed a three-legged stool; under the window is the
earthenware basin and water-closet: these are all shown on the plan, and are more es-
pecially detailed in the several figures which succeed. The works for all these conveniences,
particularly those of the plumber, are admirably executed, creditable alike to the workman
and the architect. In the management of such apparently simple details far greater in-
genuity is required than is generally imagined or is usually bestowed upon them, and at this
prison they are models of their kind,
The double supply cock, which communicates with the washing-basin and soil-pan, is
606
HISTORY OF ENGINEERING.
BOOK I
enclosed in an iron frame, which protects it from injury. The pan and parts connected
with it, are of strong glazed earthenware.

Fig. 565.
EARTHENWARE SOIL PAN.
Fig. 566. SECTION OF SOIL PAN, TRAP, BASIN, ETC.
The cells are lighted with gas, and the water-troughs and service-pipe are well contrived.
The troughs are of iron, 6 inches in depth and 4 inches wide; these are cast in lengths of
8 feet 6 inches, which correspond with the width of the cell; they are supported on
brackets, and in order to limit the quantity of water, there is a division to which each
prisoner has access, containing a cubic foot, or six gallons. The troughs are supplied from
cisterns placed on a level with each range.


በወ
Fig. 567.
GAS LIGHTS AND WATER CISTERNS,
By a reference to the plan of these arrangements it will be seen that the greatest
economy has been adopted. The pipes are all trapped in such a manner that no effluvia
can pass along the soil-pipes or find its entry into the adjoining cell; the party-wall
between the two is of a sufficient thickness to prevent all sound, and the junction of the
two wastes takes place on the outside of the building: wherever the water that has been
used for washing or other purposes is allowed to run away, it is made available for puri-
fication; the waste of the wash-hand basin passes through the pan of the closet, which is
united to a D trap.
CHAP. VIII.
607
BRITAIN.
The gas-burner is provided with a pipe for the escape of the unconsumed carburetted hy
drogen, which, when the light is burning, also contributes much to the purification of the
air in the cell. No opportunity seems to have been lost for rendering everything necessary
for the prisoner's use available

WALL
EXTERNAL
for maintaining a free and
regular ventilation: the quan-
tity of air necessary for com-
bustion, as well as to supply
the loss of that which is de-
teriorated by respiration, has
all been provided for; and a
very small room, in which
these matters have been con-
sidered, is far more healthy
than one of large dimensions
where they have been ne-
glected. In our crowded
bridewells and prisons no pro-
vision was made either for
ventilation or for the removal
of accumulated filth: to walk
through such a building pro-
duced feelings the very op-
posite to those which we ex-
perience in this well-ordered
and cleanly model prison;
many were without a common
sewer; cesspools
cesspools were the
only receptacles, covered with
temporary boards, or some
other material easily taken up,
for the purposes of constantly
removing the contents: hence it could hardly oe supposed that gaol fever could be
eradicated, or that the walls, with the constant lime-whitening to which they were subject,
could be free from putrescence or infectious miasma: when contrasted with the under-
ground dungeon of the middle ages, our receptacles for prisoners may be considered as an
important progress in civilisation.
Fig. 568. PLAN OF BASINS IN THE TWO ADJOINING Cells.
The interior of the frame, from which the supply-pipes and cocks branch to the several
basins, is shown in the annexed figure.
49

Fig. 569.
PLAN OF WATER CISTERN.
Fig. 570. FRAME SHOWING THE SUPPLY COCKS.
The central hall and corridors, which are open from the pavement to the roof, enable
the officers on duty to see all that passes to the door of each cell. Each block or wing is
called a division, and distinguished by letters, A, B, C, D. The cells on the ground floor,
and on the level of the galleries of each division, are wards in the division to which they
belong. The ground floor is No. 1., the first gallery No. 2., and the upper gallery No. 3.
Ward. The cells in each ward are numbered consecutively, the odd numbers being on the
left-hand side when looking from the centre hall, and the even numbers on the other.
Each prisoner has a small brass plate, which is suspended to his button, on which is en-
graved the designation of his cell, the letter of his division, and the number of his ward.
GUS
Book I.
HISTORY OF ENGINEERING,


Fig. 571.
ELEVATION of part of CORRIDOR.
The prisoners can communicate at any time with the officers of the prison by means of
a large bell or gong in the centre of each line of cells.
A handle attached to a label and

1
Fig. 572.
LABEL IN the corriDOR WHEN shut and open.
CHAP. VIII.
609
BRITAIN.
crank is placed in every cell, and a single wire and crank communicates with the bells.
When the handle is turned the label flies open, a single stroke is sounded, and a pendulum
connected vibrates with it; thus the attention of the officer on duty is attracted, and the
label, which remains open, indicates the cell where his presence is required.


Fig. 573.
ELEVATION OF GONG.
SIDE ELEVATION.
The exercising yards radiate from a central point, round which there is a passage of
communication, and an inspection into each is obtained through a large orifice in the door,
covered by open wirework. The space within the passage forms a room with windows
above, which command each yard. The yards have an open railing on the outside, to allow
a free circulation of air, and one portion is roofed in to afford shelter, if required. In the
centre space is a water-closet, and there is an easy access to all the cells. There are alto-
gether 114 exercising yards, which exceeds a fourth of the prisoners, so that each has one
hour's exercise in every four hours.
The baths are very simple in their arrangement; there are eight, which admit of thirty-
two prisoners bathing each hour, and every one must bathe once in fourteen days.
The advantages which the prisoners derive from this judiciously arranged portion of the
Model Prison are incalculable, and worthy of imitation by the directors and governors of
all the gaols throughout the world. The expense attendant upon cold, tepid, or a warm
bath, is so inconsiderable, compared with the comfort derived from them, that it seems
extraordinary any establishment should be without them. Numerous plans have been
submitted to the government at various times to establish public baths, and in some large
towns in the neighbourhood of the factories they have been erected at a considerable
expense, and found highly beneficial: the health of all the labourers and artisans resorting
to them has been so infinitely superior to those neglecting this benefit, that the absolute
necessity of their introduction in all prisons is most obvious, where confinement prevents
that exercise which produces free circulation, and consequent healthy state of skin; for
this the bath is an excellent substitute. But perhaps one of its most important services
in prisons is the producing notions of cleanliness in the prisoners, which they may carry
with them when restored to society; and the squalid misery, so often the companion
of poverty, may thus become less common, through the influence of those to whom we
should not generally look for reformations, the discipline of the prison would then
become a blessing instead of a curse.
The ample supply of good water throughout the Model Prison, and the judicious manner
in which it is distributed, tends to promote the comfort of those occupying the solitary
cells. By a reference to the cost of the pipes and hydraulic arrangements, it does not
appear that each cell has had expended upon it more than 40s., and this amount includes
all the requisites for a prisoner with regard to the supply of water. Such beneficial
results are rarely found united in our public buildings with so much economy, and are
deserving the consideration of those who have the management of our hospitals, union
workhouses, and similar establishments. By a reference to the evidence taken before the
Commissioners of Inquiry into the State of Large Towns and Populous Districts, we see
many valuable hints to benefit the residences of the poor, but none in which the estimate
is so small, and productive of such vast advantage.
The hoisting machine, by which the trays containing provisions or materials are raised
from the basement to the level of the ground floor and galleries above, is fixed in the base-
ment on each side the central hall, and affords a direct communication between the kitchen
Rr
610
BOOK I.
HISTORY OF ENGINEERING.
and the wards. The trays are conveyed along the ground floor in a small truck, and along
the galleries, or upper wards, by a light trussed iron carriage, which traverses on the top of
the gallery railing. The front and side views of the machine are at the top of the figure;
the power which hoists it is placed on the floor line of the basement; its profile and

0 0 1 0
www
Fig. 574.
MACHINES FOR RAISING PROVISIONS.
arrangement are shown below, as are also the plan, side, and end elevation of the iron car-
riage which traverses the galleries.
The different rations or allowances for the prisoners, being placed in large trays, are
thus conveniently mounted from the basement floor, where the kitchen and magazines for
the provisions are situated. When they have arrived at the level of the gallery where
they are intended to be distributed, the horizontal bar at the top of the balcony on each
side becomes a railroad, upon which the light iron carriages make their passage from one
end of the corridors to another: the officers in attendance who have the distribution stay
the carriage at the door of each cell, and give out the requisite meal. There is immense
convenience derived from this simple arrangement, the whole passes so steadily that it
arrives at its destination exactly in the same state in which it sets out; there is no confusion
or waste by any article being broken or spilt by the way; by these mechanical means the
food is served to the prisoners with such despatch, that it runs no risk of being cooled in
its passage up long flights of stairs, or through the corridors.
The plan in the accompanying figure shows the position of the four wheels which run
CHAP. VIII.
611
BRITAIN.
upon the top of the railing of the balcony, in front of the doors of the cells; the whole is
firmly braced together and bound by screws: the upper part of the figure represents the
elevation of the iron framing, and the two wheels placed upon the edge of the railing: the
middle figure is the section or

elevation of the carriage in the
other direction. By the bracing
or trussing introduced beneath
the frame, it is rendered capable
of carrying a considerable weight,
and from the care used in ar-
ranging it, there is no apparent
tendency to force out the vertical
position of the balcony railing.
When the crab or windlass in the
basement is worked, the whole
mounts in a perfectly steady
manner, without any irregular
action, and thus continues to
the end of its destination: the
materials given out to the pri-
soners from the warehouses be-
low to be manufactured are all
hoisted in the same manner, and
when wrought so descend to
other depôts. So ingenious a
contrivance would be of the
greatest service in our public
establishments, and ought to be
more generally introduced :
some years ago the writer con-
trived similar machinery for the
great laundry at the top of the
Burlington Hotel in Cork Street,
# 1
SECTION.

Fig. 575.
PLAN AND SECTION of carriAGE.
which he erected, and which has been found of essential service to that establishment, from
the great economy of labour.
In detailing the several contrivances here introduced, we are struck with the differences
presented to us in comparing them with the general state of prisons up to the end of the
last century: let us take for example the description given by a French writer of the Con-
ciergerie, which was formerly a portion of the Palais de Justice, and still preserves its
ancient feudal character: "the towers, the entrance court, the dark corridor by which the
prisoners pass, produce a sensation of melancholy and terror; those condemned to remain
there, if not provided with sufficient money to pay for the hire of a bed, must lie in dark,
damp, and fetid cells, straw only being allowed, amidst a number of other wretched indi-
viduals: the vast court, constructed in the thirteenth century, in which the prisoners take
exercise, is sunk 10 or 12 feet below the level of the neighbouring streets; their food is
confined to one ration of poor bread and thin soup." In other prisons, we find the cells
were not sufficient in height for the inmates to stand upright. The minister Necker
interested himself most ardently in endeavouring to remedy many of these evils, and was
successful in some particulars. In the House of Correction at Ghent, commenced in 1773,
during the reign of Maria Theresa, great improvements were introduced, which awakened
consideration to the subject throughout the continent; fire-places were constructed, and
the cells were made of a dimension sufficiently ample for the number they were to contain ;
light and air were admitted, and cleanliness was encouraged and enforced; exercise was
allowed to the unhappy individuals, and they were no longer punished by their allowance
of food being withheld.
Regulating cistern, pipes and cocks for the distribution of water. The cisterns are placed
in the roof, which has a rising main, together with a service-pipe, and two rows of troughs,
divided into compartments, containing six gallons, or one day's supply for each cell.
There
are also regulating cisterns, and ball-cocks for turning on and shutting off the water to the
troughs.
The supply pipe for the upper troughs is connected with the main service pipe, and
runs to the extreme end, where it fills another trough, which then overflows, and supplies
another, and so on, till all are filled. The last is furnished with a waste-pipe, to convey the
surplus water into the regulating cisterns, which, raising the ball as it fills the cistern, acts
upon the stop-cock to which it is attached, and shuts off all further supply to the troughs
on the roof. The troughs under the upper gallery floor, for the use of the cells beneath,
R R 2
612
Book I.
HISTORY OF ENGINEERING.

L
-------
:.
Fig. 576.
PIPES TO CISTERN In roof.
are supplied by a pipe fixed under the troughs; the water is allowed to flow successively
into the cisterns, and is shut off as above.
Ventilating. An artificial system of ventilation has been adopted, with a view to
produce at all times and seasons an abundant supply of fresh and wholesome air; this
has been attended with some difficulty in a prison where each prisoner has a separate
cell, and the window of that cell necessarily obliged, for the sake of security, to be closed.
Health is of the first importance, and considerable attention has been paid to the subject;
but there yet seems to be something wanting, on entering one of these cells, to make it ap-
parent that a pure and agreeable atmosphere is breathed. The objects aimed at have been
the withdrawal of a stated quantity of foul air from each cell; the supply of an equal
quantity of fresh air, without subjecting the prisoner to a draught; the means of warming it,
when necessary, without injuring its qualities, or affecting its hygrometrical condition, and
the avoidance of additional facilities for the transmission of sound by the air channels or
Aues.
The apparatus for warming the air is placed in the centre of the basement story of each
wing: it consists of a case or boiler, to which a number of pipes for the circulation of hot
water are attached. In connection with it there is a large flue open to the external air,
which is introduced through this opening, and, after passing over the surface of the boiler,
turns, right and left, along a main flue, which runs horizontally under the floor of the cor-
ridor, and from thence passes upwards, through small flues in the wall, which terminate
CHAP VIII.
613
BRITAIN.

TRANSVERSE SECTION OF PRISON.
Fig. 577.
respectively in a grating placed close under the arched ceiling of each cell, into which a
current of air is thus introduced.
It is very difficult to lay down a plan for the ventilation of public buildings, particularly
as the sites and uses present so much variety: the various improvements that have been
suggested on this subject for deep mines, and in some instances carried into effect, have
turned the attention of the architect and civil engineer to adopt some method that shall insure
a stream of pure and properly tempered air to follow the exhaustion that takes place in our
churches, halls of assembly, or wherever great masses of people meet together and are
confined for any length of time; in a future part of the work the subject will be more fully
treated. It does not appear that attempts were made to renovate the atmosphere of
the cells of our prisons until practised here: much has been judiciously effected, but,
with all the precautions hitherto adopted, none have yet been found to answer perfectly.
Temperature and pressure exert so many influences, and, in conjunction with radiation
and evaporation, so change the properties of the air, that it is exceedingly difficult to
construct by means of pipes, valves, or machinery, contrivances that shall counteract or
mitigate them. The section of the windows represents by the arrow-heads the current
that the air takes in its passage, and the escape of the foul air to the outside of the cell
the handle attached to the valve that admits the warm air is at the prisoner's command; he
can consequently introduce the desired quantity at pleasure; the windows are so formed
that thorough ventilation is obtained.
:
The window frames are formed of iron: their plan shows the manner in which they
་་་་
RR 3
614
Book I.
HISTORY OF ENGINEERING.

are rebated to receive the glass,
and the section at the side of
the opening shows its position ;
the whole is barred to prevent the
prisoner making his escape, at the
same time in such a way that the
light is by no means obstructed.
In the plan and section of the cell
previously given, its position and
height from the floor may be seen;
as it is placed immediately opposite
the door by which the prisoner
enters, which is also provided with
a grating, there can be obtained a
thorough current of air, if it is
desired; the parts marked B and
C in the plan of the cell show
also the situation of the fresh and
foul air shafts or pipes obtained in
the thickness of the wall. The→→→→
external walls, in which these win-
dow openings are made, is 1 foot
10 inches, and that of the walls
between the cells is 18 inches in
thickness. The whole of these fit.
tings are executed in a most sub-
stantial manner, and the frame is
so strongly bedded in the brick-
work of the outer wall, that it
would be difficult to disturb or
displace it.
SECTION.
Fig. 578.
PLAN OF CELL WINDOW.
The foul air is removed by means of a grating, placed near the floor of each cell, on the
side next the outer wall, and diagonally opposite the point where the fresh air is introduced;
this grating covers a flue in the outer wall, opening at its upper extremity into a horizontal
foul air-flue in the roof, communicating with a vertical shaft, raised upwards of 25 feet above
the ridge. Thus, by the outer air passing

the warming apparatus to the top of each
cell, and thence from the floor upwards,
through the extracting flues and venti-
lating shafts, it again passes off into the
outer air at a considerable height above
the building. An uniformity of action is
obtained by making each pair of flues used
for the foul air of equal length on all the
stories, and introducing fresh air into them.
Each cell contains 800 cubic feet, and a
ventilation is obtained of 30 cubic feet
per minute, at a cost during the winter
months of less than a farthing per cell,
and during the summer at half that
expense.
HANDLE TO ADMIT WARM AIR.

Fig. 579. Regulators in THE WARM air flues.
The ascending principle of ventilation
in this case extracts the foul air from the
cells in consequence of the superior alti-
tude of the shaft; had it been required to
pass downwards below the floor of the
cells into flues in the basement, a power
must have been produced to overcome the tendency of air to rise when at a high tem
perature; the ventilation must then have been produced by force, instead of being as it is
merely assisted. From the diffusion which takes place, it is stated that the difference of
temperature at the ceiling or floor of the cell can hardly be detected, and that it seldom
exceeds a degree.
The main flues in the roof, for the extraction of foul air, are connected with the vertical
shaft, and during the suminer a small fire is maintained at the bottom of this shaft, which
raises the temperature of the column of air within it above that of the exterior, or the
general temperature of the cells, and thus makes it specifically lighter. In this state it
CHAP. VIII.
615
BRITAIN.
easily rises, and the vacuum is filled from the adjoining foul air-flues, which derive their
supply from the cells, the cells in return receiving a corresponding supply of fresh air to
replace that which has been drawn up the vertical shaft. One hundred weight of coal per
day for each wing, containing 130 cells, has been the consumption. The principle here

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Fig. 580.
PLAN OF VENTILATING FLUES.
adopted is similar to that used in deep mines, the ventilating chimney serving the purpose
of the upcast shaft.
Warming is effected by an apparatus where the whole radiating surface derives its heat
from the circulation of hot water, and it is calculated that the area of the whole is sufficient
to maintain a temperature of 60 degrees, when the external air is at 32. There is a
provision for increasing the radiating surface in the main flues as its temperature becomes
lowered by an increased distance from the boiler, so that the most remote cells are equally
warmed.
The apparatus consists of a double iron case; the space between being filled with water
becomes the boiler; the fire is lighted in the interior, but is not brought in contact with
either the sides or top: from the top of the boiler a rising main communicates with the
various circulating pipes, and the return pipes are introduced at the bottom. The external
case of the boiler is covered with vertical plates 7 inches deep, and § of an inch thick, placed
about 5 inches apart, and disposed in zigzag lines over the whole surface. The apparatus
is set in brickwork, and the plates occupy the interior of the air-flue which surrounds
the boiler; they are useful both as radiators and keeping the air longer in contact with
it. A slide valve placed in the main flue-pipe regulates the circulation, and lowers the
temperature if required. The pipes being disposed in flues formed of brick, they can only
be moderately heated, and impart in consequence a genial warmth to the current of air
passing through them.
The cost of erection of the Pentonville model prison was as follows:
Messrs. Grissell and Peto's contract, &c. for the building
₤ S. d.
70,115 14
6
Asphalte for cells, roads, and paths
Water-closets, fittings, basins, cocks, &c.
2,503 8 9
9
Locks, fastenings, bells, &c.
1
1,154 10
941 5 9
Superintendence
689 4 11
Sundries
361 10 9
75,765 15
4
Additional expenses for fittings, furniture, &c., Artesian well and
machinery, heating and cooking apparatus
8,402 12
2
£84,168 12 2
Which, divided by 520, the number of cells, gives for each 1617. 17s. 2 d.
Besides the prison the following are to be added : —--
Detached residence for seven families, complete
Archway and terrace wall
Wall enclosing garden
Stables and road -
1
F
S.
d.
1,892 7
1
2,856 5 2
739 10 7
415 0 O
£5,903 2 10
R R 4
616
HISTORY OF ENGINEERING.
The total amounts of the several trades were as follows: -
Excavator and bricklayer
Carpenter and joiner
Mason
Plasterer
Painter
Glazier
Plumber
Slater
ச
36,140
BOOK I.
3.
d
0 41
10,670 12 2
5,793 13 33
6,252 5 31
1,306 3 11
1,347 12 11
2,466 13 5
1,733 5 7
Smith and founder
Sundries, including the warming apparatus, &c.
9,958 4 83
754 6 0
£76,423 2 9
Items of the cost of the Artesian well, sunk 370 feet in depth, with the
30 feet cast-iron cylinders, 5 feet in diameter, pipes for bore, &c.
Building for the cranks, stages, and ladders
A three-throw pump and raising main to the top of the well only
Machinery
F
8.
d.
1,060 0 0
299 6 101
165 2 2
76 6 2
£1,600 15 21
Major J. Jebb, of the Royal Engineers, gave the design for this model prison, and to
him the country is indebted for the admirable arrangements which it contains, and for the
regulations and able management which prevail within it.
617
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
CHAPTER I.
GEOLOGY.
GEOLOGY and Mineralogy are equally important to the civil engineer, and it is in proportion
to his acquaintance with these comparatively modern sciences, that he is rendered skilful in
the formation of roads, canals, harbours, mining operations, building of bridges, or forming
foundations of any kind, and draining; wherever the scene of his labours may lie, he cannot
be entirely successful, without a careful consideration of the various layers or strata com-
posing the earth's crust.
When Smeaton was called upon to construct the Eddystone lighthouse, he commenced
by examining the structure of the rock on which it was to be based; and as far as was
possible endeavoured to imitate nature in his arrangement of the first and subsequent
courses. Had the builders of the Leaning Tower at Pisa been equally careful, or had they
been acquainted with the composition of the earth on which they laid their foundations, the
world would never have had the opportunity of supposing that its inclination was the effect
of design, instead of the consequence of an insecure base, which might have been con-
solidated by art; had the alluvial matter on which the footings are laid been converted
into a mass of conglomerate or artificial rock, this famed Campanile would have stood as
upright as the Eddystone lighthouse, a position which would certainly have been more in
unison with the beauty of its architecture, though perhaps not so conducive to its celebrity.
For all the purposes of building, it is necessary that the constructor should be acquainted
with the formation and properties of the matter with which he has to deal; he should
understand the cause of the durability of a substance, whatever it may be, as well as what
disintegrates or destroys it.
On examining the geological structure of England, we shall find that it exhibits nearly
all the variety of strata discoverable on the continent of Europe, in the same successive
order; the dip, though occasionally broken, generally inclines towards the east or south-
east, and in this direction is the drainage effected. It is possible that before the rocks,
which make up the greater portion of our island, were deposited, the general outline
was marked out or defined on the bed of the ocean, and this platform, after having been
elevated by some disturbing forces, and the protrusion of igneous rocks, then received the
several deposits, the succession of which with the variety of plants and animals of extinct
genera, the disturbance of the several strata after their formation, sometimes by their
elevation, at others by their depression, afford ample subject for consideration and en-
quiry; and from the talent and ability of the various geologists, who are giving free scope
to their researches, and diligently observing all that is opened to their view in the several
mining districts, or where any deep cutting is made, we may hope in time to obtain a clear
and satisfactory solution of those phenomena which are at present involved in doubt and
obscurity.
In travelling through a country the geologist knows by the strike of a stratum, or series
of strata, in a range of hills, with a steep fall on one side, and a gradual rising on the other,
that the latter indicates the dip; the prevailing strike being generally found to extend over
the whole tract of country; and as by the inclination of the strata the drainage of the district
is effected, so the various rivulets may be accounted for, and their sources ascertained.
To the miner an acquaintance with geology seems indispensible, to enable him to trace
the various disruptured strata, which often baffle the observations of others. A correct
estimate of the mineral veins, and the circumstances under which they have been formed, as
well as their general direction, can only be ascertained by a study of this science, and a
practical acquaintance with the various rocks in which they abound; but the mechanical
contrivances by which the miner is to test his theories, and make them profitable, are pro-
vided by the civil engineer: both private and public interest, therefore, demand that he
should be acquainted with these subjects, for if not conversant with the matter to be worked
upon, it is scarcely possible that he should apply the proper means, certainly not with the
requisite economy. On the coal fields, which are a most important study, we have scarcely
any thing written that is practically useful, although the subject of ventilation, and the pre-
vention of accidents in mines, has obtained much consideration.
618
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
To the civil engineer the geological map, with the heights of the sections above a certain
level now forming, will be of great utility, enabling him to investigate the geological
features of particular districts. In many cases several portions of the same district have
been examined and reported upon, and sections of the strata have been surveyed and laid
down, showing the position of the beds, to a scale of 40 feet to an inch: the details are given
with full investigation into their mineral deposits, and notice taken of their organic remains.
The geological structure is shown in different directions, to a scale of 6 inches to the mile,
with the relative heights and distances. The maps are duly verified and coloured, to
exhibit the detail with the boundaries of the coal fields and districts of different formations.
The agricultural character of the country is defined, and for the mining districts contour
lines distinguish the dip of the various beds of rock or coal, and as the faults in a district
are known, the means of ascertaining exactly where the vein is again to be met with are
clearly given. These contour lines are highly useful, as they assist in affording information
on the subject of drawing off the water, which, if suffered to accumulate, would put a stop
to mining operations. The miner and agriculturist are interested in the completion of this
general survey, which will at once attest the importance of geology to all practical men.
For the supply of water, the selection of building materials or the metals, this map promises
to afford a clear and useful guide, and to establish principles which will direct all operations
where either the architect or engineer are employed.
The advances made of late years in geological knowledge have unquestionably produced
greater certainty in all mining operations. To obtain a mineral ore deposited in veins,
different means must be adopted to those required when it is in alternate beds: and it is
rare to find the process the same in any two districts. In the tin and copper mines, for in-
stance, in the west of England, the ore is drawn from fissures in the carboniferous or newer
Paleozoic system, or from those cracks in igneous rocks which crop out near the surface,
and such minerals are often of great value. In Sweden the ore is obtained in large lumps,
and used for the manufacture of the best quality of steel; differing materially from that
regularly bedded in the stratification, and constituting a part of the fossiliferous stratified
rocks.
Veins usually traverse the strata in a direction by no means agreeing with, or having any
reference to, their deposition; they have more the resemblance of fissures or cracks, which
have been subsequently made in the rocks, and have by some mechanical means been filled
up with mineral substances, which are generally, in such cases, either copper, lead, tin, or
other metals, united with sulphur, carbonic acid, and other bodies, with argillaceous or
siliceous substances; and such veins usually pass through the strata of rocks in a down-
ward direction, often beyond the reach of the miner; they are also found extending
horizontally, and diminishing in their course until absolutely lost. They differ in name
according to the district: they are called pipe-veins when their direction is nearly parallel
with the beds and the ore makes no shoots in a lode; where shoots occur, the vein dips
from the neighbouring granite, which is the case whether the rock containing the ore be
in itself crystalline or the effect of stratification. Shoot-veins implies a state where
masses of ore occur in stratified rocks, and take an oblique direction, conformable to the
dip of the beds.
Flats is another term given to those lateral extensions which are parallel to stratification,
as in those veins which spread over layers of any particular rock. There are other terms
expressing the condition in which the ores are met with, as that made use of in Germany,
called stockwork, which indicates the working in floors one below the other.
Veins are found in a vertical position, and seldom at a greater angle than 10°, though in
Cornwall they are met with occasionally at 45°; they affect the mineral character of the
rocks that contain them by softening them, probably by the water, which circulates more
freely around and within them. The dip or inclination of a lode is called the slope, and
the intersection of the vein with the surface the strike; and in a mine the terms applied to
a house are used, the floor, the roof, and the walls. The ores found in the metalliferous
veins have no relation whatever to the rocks through which these run, the contents of a vein
being silex, fluor spar, or carbonate of lime, which the miners call vein-stone, in which is
the ore from whence the metal is extracted; and the more intelligent the geologist, the less
difficulty will he have in deciding whether a vein will be productive, and deserving the
labour of the miner.
Crystalline quartz, fluor spar, and carbonate of lime, contain ore in one form or another,
either in small veins, or in crystalline masses, or disseminated crystals. At other times a
rich ore is discovered in an earthy and powdery state; when the fissures are filled with clay
or sandstone, they rarely abound with ore in a sufficient quantity to make it worth pre-
serving. A change in the nature of the rock indicates to the miner what he is to expect for
his toil, there being in most districts an order in the arrangement of the ores in veins. In
the older rocks, when a vein contains copper, and it passes from a slaty formation, without
altering its direction, into granite, it at first increases in richness, and afterwards gradually
СНАР. І.
619
GEOLOGY.
diminishes. Granite is often found to yield tin ore in abundance, whilst in the same dis-
trict the slate abounds with copper, lead, and tin.
In
In Derbyshire the lead is obtained from the carboniferous limestone and toadstone rocks,
and the veins, which are valuable in the first, become poor as they pass into the other.
Cornwall copper is most abundant where the granite and kellas unite; and in Alston Moor
the veins of lead are richest in the limestone, a bed of which measuring 70 feet in thickness
being much more abundant than those in other districts which extend to a depth of 1000
feet, through eight varieties of limestone, eighteen of grit, and twenty-six of shale.
In a country abounding with ores, both the geologist and the miner have a guide to lead
them to the veins: they are characterised by their positions and contents. In Cornwall
the earliest are those of tin; they underlie to the north, and are traversed by others of a
second class, and of smaller value: from these two all the tin ore is obtained; and the
width of the lodes varies from that of a mere thread to 30 or 40 feet in thickness; the most
productive lie east and west. The copper lodes in Cornwall also lie east and west, and
traverse the tin; there are others termed contra, because they cross at right angles.
The Slides consist of imperfectly formed veins, and run in various directions, though the
most productive are usually east and west, and the cross courses north and south.
Lead in England is found in veins running from east to west, which are traversed by
cross courses at right angles to them less productive. Out of 300 observations made in
Cornwall, the direction taken by most of the veins was between west and south-west or west
and north-west. Mineral veins, as has been observed, are quite independent of the rock in
which they are found, and differ also from them in age; being filled up long after the
fissure was caused, or the disturbing force of the several strata applied. The three chief
mining districts of England are found in mountainous regions: the granite rocks in
Cornwall rise to an elevation of 1300 feet above the level of the sea, in which are the tin,
and a considerable proportion of the copper used in commerce.
In
The Devonshire mica slate and granite dykes offer to the traveller a surface of country
barren, and apparently unprofitable, but under it is a variety of minerals; and in Derby-
shire the region around the Peak affords abundance of lead. The high moors of the north
in Northumberland, Durham, and Cumberland, yield a rich return of the same ore.
the Island of Elba iron ore is obtained from veins in sedimentary rocks, which are con-
tiguous to igneous rocks. Wherever the metals are found, their deposit seems owing to
electric or magnetic influences; but the hypotheses on this subject are not at present satis-
factory. After the mineral vein is found, the engineering operations commence, which must
be carried on to a considerable extent before any advantages can be derived. A pit or shaft
is sunk, and an horizontal gallery or tunnel driven, through which the drainage of the mine
is effected, and which is called the adit level; the horizontal drivings, the downward sinkings,
and the upward risings, are set out with reference to the locality or direction of the strike of
the vein. There are usually two sets of galleries, both horizontal, at right angles to each
other, one being in the direction of the strike of the vein, and the other at right angles to it,
which serve the double purpose of extracting the ore and carrying off the water, which rises
from the springs or drains from the several strata. The great adit or drain in Cornwall,
which receives the water from the Gwennap and Redruth mines, is nearly 30 miles in length,
and discharges its waters into the sea, about 40 feet above high water-mark.
When the works are extensive, many shafts are requisite, though there is usually one of
greater diameter than the others, which communicates with all the horizontal galleries;
this principal shaft is generally double, or divided into two compartments, one of which is
devoted to the engine, which pumps the waters from the deep workings into the adit level;
the other is called the whim shaft, through which the ores are drawn up. The workings
of the several lodes are commonly connected by horizontal shafts, or by cross-cuts, so that
their contents may be brought to the shaft and drawn up. From the extraordinary depth
that many of these shafts are sunk, the greatest care is requisite; that of the Dolcoath Mine
in Cornwall is upwards of 240 fathoms in depth, 210 of which are below the adit level,
this being 30 below the surface. The total amount of sinking of these shafts in Cornwall has
been estimated at 12 miles of perpendicular height, and the horizontal galleries as extending
altogether to 40 miles in length. It is not only necessary for the engineer to direct his at-
tention to the best method of extricating the ores, or draining off the water, but also to
introduce a supply of fresh air into the workings, to lower the high temperature which
is encountered at the greater depths beneath the earth's surface This is effected by making
use of the several shafts and galleries which have communication with them; the currents
of air, produced by the variations of temperature, set in different directions; these by me-
chanical contrivances are made to keep up a constant ventilation; where gunpowder is used
to blast the rocks, a considerable quantity of gas is evolved, which is injurious to the at-
mosphere of the mine, and therefore requires to be dissipated by ventilation, the gas
which is evolved at each explosion being equal to at least five thousand times the volume
of the powder made use of.
620
Book 1.
THEORY AND PRACTICE OF ENGINEERING.
In the formation of a railroad or a canal, a vast advantage is gained by an acquaintance
with the structure of the land to be operated upon. The setting out of the line depends
upon the geological character of the country; and in carrying the work into execution,
much labour and expense may be saved, by understanding how the various soils passed
over should be worked.
The clay, which alternates with occasional sand when deeply cut, is often dangerous,
and is maintained in its position with great difficulty; the water carrying away particles
of sand, leaves the clay to slide down upon its slippery bed after the layer of sand is
washed away. Wherever clay is cut through in the direction of its line of strike, it has
a tendency to slip, which can only be avoided by draining or drawing off the water of each
bed cut through, or by giving a greater inclination to the rise side of the bed than to the
dip side.
Chalk offers but little difficulty, as it will stand nearly perpendicular, but it is preferable,
on account of the drainage, to make the cutting through it at right angles to the strike of
the beds. Where sandy or loamy earth occurs, the slope of the excavations should always
be made, if possible, in conformity with the dip of the bed, and so in other loose soils.
In tunnelling the geologist is the best pioneer; he alone can point out the state of the
various strata and the nature of the rock to be cut through, the probable amount of water
contained by them, and the best method of draining it off.
Even in making and repairing the common highways, a scientific acquaintance with the
subject will render the selection of the materials a much more secure and easy task; it too
frequently occurs that no consideration is made of either the friction or pressure; it is suffi-
cient that the ruts are filled up, whether usefully and durably is not considered.
The ordinary flint when used should be broken to a regular and moderate size; lime-
stone forms a smooth, but not so durable a road; whinstone, where it can be obtained, is
preferable to either.
In the formation of harbours, or the works which appertain to them, where the violence
of the ocean is to be resisted, it is impossible, without a study of the coast, to effect anything
that shall be permanent, except by experiments causing an unnecessary outlay. The
geologist observes the forces by which the projecting headlands are gradually worn away,
and the earthy matter deposited by the various currents, and is thus enabled to direct the
best means of resisting the injuries to which most harbours are subject, and providing
against their silting up, and the formation of bars or other impediments to the vessels
seeking shelter.
In the selection of materials for the purposes of building, geology has been of great
assistance, pointing out to us that a stone which resists the action of the air may be de-
composed by water, and one that is porous and impermeable to water may be disintegrated
by frost or the action of the atmosphere.
Limestones are divided into argillaceous, crystalline, and another variety, which compose
the several Oolites. The Magnesian Limestones require great care when used for building
purposes; they are obtained from the beds which overlie the lower new red sandstone, from
which they are separated by the coal measures.
The sandstones employed in building are of various qualities, those taken from the older
rocks are mostly preferred. The Craigleith is of excellent quality, of a light grey colour,
and a fine grain; it contains 98 per cent. of silica, and not more than one per cent. of car-
bonate of lime; it is heavy, and its particles are firmly bound together; the beds are in
some instances 10 feet in thickness; it is much more difficult to work than Portland stone.
There are many varieties of gritstone, some where quartz grains are united with argillo-
siliceous cement, but those containing iron are subject to decomposition, and they absorb
upwards of a fourth part of their bulk of water. All stone should be applied in a building
as it is found in the natural bed, for being usually laminated it is liable to split, if loaded
or pressed in a direction opposite to the planes of deposition.
As this subject is more fully considered in the sequel, we shall proceed with some
account of the different strata in the order they appear, commencing at the earth's surface,
and noticing the organic bodies that are found in the several beds, for the purpose of
identifying the strata. This order and arrangement belongs more immediately to the
palæontologist: a brief account therefore of the various classes and orders of these organic
remains will be sufficient.
Organic remains or fossils, which are found in every stratified formation, are numerous,
and endless in their variety; they consist of both animal and vegetable productions, and the
study of them is termed Palæontology, or a description of what had existence some ages
past. The animals found are divided into the Vertebrated and Invertebrated.
The first form four classes, Mammalia, Birds, Reptiles, and Fishes.
The Mammalia are divided into nine orders; first, Man, or Bimana; second, Quadrumana ;
third, Carnivora, which is subdivided into four families, the Cheroptera, the Insectivora, the
Plantigrada and Digitigrada, and the Amphibia; fourth order, the Marsupials; fifth, the
CHAP. I.
621
GEOLOGY.
Rodentia; sixth, the Edentata, which have three tribes, viz. the Sloths, the ordinary
Armadillo and the Ant-eater, and the Monotremata; seventh, the Pachydermata, which is
subdivided into Proboscidiana, Pachyderms, and Solipedes; eighth, the Ruminants; and
ninth, the Cetacia
The Birds or Oviparous Vertebrata are rarely found in a fossil state.
REPTILES are in great abundance and variety, and are divided into eight orders, viz.
the Dinosauria, or land saurians; the Enaliosaurians, or those of the sea; Crocodilia; La-
certilia, or lizards; Pterosauria, or flying saurians; Chelonia or tortoises, &c.; Ophidia or
serpents; and Batrachia or frogs.
FISHES are divided into Ganoidians, Placoidians, Ctenoidians, and Cycloidians.
The INVERTEBRATA are divided into four classes: the first is the Mollusca, which is sub-
divided into seven orders; the Cephalopoda, the Pteropoda, the Gasteropoda, the Conchi-
fera, the Brachiopoda, the Tunicata, and the Cirrhopoda.
The second class is the Articulata, which comprises five orders, viz. the Crustaceans,
the Arachnidans, the Insecta, the Myriapoda, and the Annelidans.
The third class, or Radiata, is divided into two groups; one of which has received the
term Nematoneura, which is divided into five orders, viz. the Echinodermata, the Epizoa,
the Rotifera, the Bryozoa, and the Cælelmintha.
The second group of Radiata is called Acrita, and comprises five orders, viz. the
Sterelmintha, the Acalephæ, the Polygastrica, the Polyps, and the Sponges.
Lamarck has made another arrangement, dividing the Mollusca into two classes, Con-
chifera and Mollusca, and the whole into families.
The 1st family in his classification is the Tubicolide, among which is the Asper-
gillum, Clavagella, Teredo, &c.
The 2nd family is the Pholadida, of which is the Pholas, Gastrochæna, &c.
3rd. Solenide, which contains the Solen, Panopæa, &c.
4th. - Myida; the Mya, Anatina.
5th. Mactride; Mactra, Crassatella, Erycina, Lutraria, Ungulina, Solemya,
Amphidesma.
6th. Corbulida; Corbula, Pandora.
7th.-Lithophagida; Saxicava, Petricola, Venerupis.
8th. - Nymphida; Sanguinolaria, Psammobia, Tellina, Corbis, Lucina, Donax,
Capsa, Crassina.
9th.
Conchida, which are fluviatile and marine; among the first are Cyclas,
Cyrena, Galathea; among the latter Cyprina, Cytherea, Venus, Venericardia.
10th. Cardiida; Cardium, Cardita, Isocardia, &c.
11th.
12th.
13th.
14th.
15th.
16th.
Arcida; Cucullæa, Arca, Pectunculus, Nucula, Trigonia, and Castalia.
Naiida; Unio, Hyria, Anodon, and Iridina.
Chamida; Dieras, Chama, Etheria.
Tridacnida; Tridacna, Hippopus.
Mytilida; Modiola, Mytilus, Pinna.
Mulleida; Crenatula, Perna, Malleus, Avicula.
17th. — Pectinida; Pedum, Lima, Plagiostoma, Pecten, Plicatula, Spondylus,
Podopsis.
18th. Ostreida; Gryphæa, Ostrea, Vulsella, Placuna, Anomia.
19th.
Rudista; Sphærulites, Radiolites, Calceola, Birostrites, Discina, Crania.
20th. Brachiopoda; Orbicula, Terebratula, Lingula, &c.
The second class are the Mollusca,
The first order of which are the Pteropoda; Hyalæa, Clio, Cleodora, Limacina, Cym-
bulia, Pneumodermon.
2nd Order.- Gasteropoda.
21st Family. Tritonida; Glaucus, Eolis, Tritonia, Scyllæa, Tethys, Doris.
Phyllidida; Phyllidida, Chitonellus, Chiton, Patella.
22nd.
23rd.
24th.
25th.
3rd Order,
Semi-phyllidida; Pleurobranchus, Umbrella.
Calyptræide; Parmophorus, Emarginula, Fissurella, Pileopsis, Calyp-
træa, Crepidula, Ancylus.
Bullida; Bulla, Aplysia, Dolabella.
Trachilopoda.
26th Family. Helicida; Helix, Bulimus, Achatina.
27th.
28th.
29th.
Limnaida; Planorbis, Physa, Limnæa.
Melanida; Melania, Melanopsis, Pirena.
·Peristomida; Valvata, Paludina, Ampullariæ.
30th. Neritida; Navicella, Neretina, Nerita, Natica.
31st. -Janthinida; Janthina.
32nd. Macrostomida; Sigaretus, Stomatella, Haliotis.
33rd.-Plicacide Tornatella, Pyramidella.
•
1
622
THEORY AND PRACTICE OF ENGINEERING.
34th.
Scalarida; Vermetus, Scalariæ, Delphinula.
Book II.
35th. Turbinidæ ; Solarium, Rotella, Trochus, Monodonta, Turbo, Planaxis,
Phasianella, Turritella.
The Zoophaga form the next section.
36th Family. Canalifera; Cerithium, Pleurotoma, Turbinella, Cancellaria,
Fasciolaria, Fusus, Pyrula.
37th. — Alata; Rostellaria, Pteroceras, Strombus.
38th. ·Purpurifera; Cassis, Cassidaria.
39th.
40th.
Columellida; Columella, Mitra, Voluta, Marginella, Valvaria.
Convolutida; Ovula, Cypræa, Terebellum, Ancillaria, Oliva, Conus.
The fourth Order.-Cephalopoda.
41st Family. Orthoceratida ; Belemnites, Orthoceras, Nodosaria, Hip-
purites, Conilites.
42nd.
43rd.
44th.
45th.
46th.
Lituolitida; Spirula, Spirulina, Lituola.
Crasticide; Renulina, Cristellaria, Orbiculina.
Spherulide; Meliola, Gyrogona, Melonia.
Radiolidida; Rotalia, Lenticulina, Placentula.
Nautilida; Discorbis, Siderolites, Polystomella, Vorticialis, Nummu-
lites, Nautilus.
47th. — Ammonitida; Ammonites, Orbulites, Ammonoceras, Turrulites, Bac-
culites.
48th. · Argonauta.
49th.
C
Genus Octopus, Laligopsis, Loligo, Sepia.
Fifth Order, Heteropoda.
50th Family.-Genera Carinaria, Pterotrachea, Phylliroe.
Plantæ or Fossil plants; these are either terrestrial, fluviatile, or marine: when met
with in the blue clay they are often converted into jet, and sometimes their interior is
changed into carbonate of lime; in these cases their structure is very distinct. In a lime-
stone which contains silica, or in calcareous sandstone, they are often found silicified; in the
coal-shales they are converted into coal; in millstone grits there are only impressions of
the plants, and the space they occupied contains a brown or yellow powder.
The races of plants found in the different strata all differ; the most numerous belong to
the following classes: Agamia; Cryptogamia cellulosa and vasculosa; Phanerogamia
gymnospermia, monocotyledonia, and dicotyledonia.
In the Newer Tertiary or Pliocene are found Zoophyta, Infusoria, Foraminifera, Mollusca
acephala, Mollusca gasteropoda, Reptilia, Mammalia, &c.
In the Middle Tertiary or Miocene, Zoophyta, Mollusca acephala, Mollusca gasteropoda,
and Mollusca pteropoda.
In the Older Tertiary or Eocene are Plantæ, Zoophyta, the Mollusca, and Pisces.
In the Cretaceous system are Zoophyta, Radiata, Mollusca acephala, Mollusca brachiopoda,
Mollusca cephalopoda, Pisces, and Reptilia.
In the Wealden formation are Plantæ, Crustacea, and Reptilia.
In the Oolitic system are found Plantæ, Zoophyta, Radiata, Insecta, Crustacea, Mollusca
acephala, Mollusca gasteropoda, Mollusca cephalopoda, Pisces, and Reptilia.
In the Lias are Radiata, Mollusca acephala, Mollusca brachiopoda, Mollusca gaste-
ropoda, Mollusca cephalopoda, Pisces, and Reptilia.
In the New Red Sandstone are Radiata, Mollusca acephala, Mollusca brachiopoda,
Mollusca gasteropoda, Mollusca cephalopoda, and Reptilia.
In the Carboniferous system and Magnesian Limestone are Plantæ, Zoophyta, Radiata,
Mollusca brachiopoda, gasteropoda, pteropoda, cephalopoda, and Pisces.
In the Devonian system and Old Red Sandstone are Zoophyta, Crustacea, Mollusca
brachiopoda, gasteropoda, cephalopoda, and Pisces.
In the Silurian and Sub-silurian are Zoophyta, Crustacea, and the Mollusca brachio-
poda, pteropoda, and cephalopoda.
In the British Isles we find the Pleistocene or superficial deposits, or what by some are
termed Diluvium and Alluvium, to consist of gravel and other transported materials, which
usually cover the regularly stratified rocks; these in fact form the upper surface of our
island, and therefore the first operated upon by the civil engineer.
The Newer Tertiary or Pliocene are the Norwich or Mammaliferous Crag, and the Till of
the valley of the Clyde.
The Middle Tertiary or Miocene are the Coralline and Red Crag, the Older Tertiary or
Eocene, the Bagshot sand, and London clay.
The Newer Secondary Period, embraces first the Cretaceous System, which comprises the
Upper Chalk with flints, the Lower Chalk without any, Marl, Upper Green Sand, Gault,
and Lower Green Sand.
The Middle Secondary comprises first the Wealden formation, which contains the Weald
clay, Hastings sand, and beds of Purbeck marble.
CHAP. I.
623
GEOLOGY.
Secondly, the upper Oolitic Series, as Portland stone, Portland sand, and Kimmeridge
clay.
Thirdly, the middle Oolitic, as the Upper Calc grit, Coral Rag, Lower Cale grit,
Oxford clay, and Keiloway rock.
Fourthly, the lower Oolitic, or Cornbrach, Forest marble, Great Oolite, and Bradford
clay, Stonesfield slate and Fuller's earth, Inferior oolite, and Calcareous sand.
Fifthly, the Liassic group of Upper lias shale and Marlstone, Lower lias shale, and
Lower lias limestone.
The Older Secondary, or New Red Sandstone formation, or Triassic system, comprises the
Saliferous marls, the Red sandstones, and Conglomerates.
The Newer Paleozoic period or Magnesian Limestone, or Permian System, comprises
the Magnesian limestone and the Lower Red Sandstone.
The Carboniferous system, which comes also under this head, contains the Upper coal
grits, Coal measures, Millstone grit, Carboniferous limestone, and Lower carboniferous
shales.
The Middle Palæozoic Period, Devonian system, or Old Red Sandstone formation, includes
the slate and limestones in Devonshire, as well as the Conglomerate, Cornstone, and Till
stone of Herefordshire and Scotland.
The Older Paleozoic or Upper Silurian, are the Ludlow and Wenlock Series, and Upper
Cambrian rocks, and the Lower Silurian or Protozoic Series, comprises the Caradoc,
sandstone, and Llardillo flags, as well as the Older Cambrian fossiliferous slates.
Stratification is found to be universal in the rocks of aqueous origin which compose the
earth's crust; and this character is the first to attract the attention of the geologist; it con-
stitutes the bed of all stones, and has been formed entirely by mechanical means. It is
nothing more than the deposit of the solid matter, brought down by the rivers, and spread
out over the bed of the sea. The mountains and high lands are continually crumbling
away, and their particles are for a time mechanically suspended in the running streams and
rivers, and are thus borne away to form fresh land.
We find that the several strata, varying in thickness, are often disturbed from the hori-
zontal position in which they were deposited by some subterraneous movement, and the
materials that constitute them are usually sand, clay, limestone, and iron; the successive
layers have the appearance of having been formed under water, as they are alternately sand
and mud, which have been allowed to settle at regular intervals.
The dip of a stratum is its inclination with the horizon, and is always at right angles
with the strike; the angle which the dip makes with the horizon is its amount of deviation
from the level plane.
The strike is the direction in which a stratum lies, or the line of intersection of the plane
of the bed with the horizon.
Faults are occasioned by the breaking away or settling of one portion of the earth's crust
from another, and this is sometimes found to occur to the extent of several hundred feet or
more.
Denudation occurs when a portion of a valley is washed away by a flood, and Elevation is
a term given to the upheaving of a portion of the earth's crust.
Cleavage: this is perhaps best illustrated by examining slate, which is not stratified in the
ordinary way, but is found to have three sorts of stratification, independent of each other,
and occurring in different directions; one is the bedding, which it is often difficult to as-
certain; the other is the cleavage plane; and the third is the divisional plane or joint.
Cleavage takes place easily on those argillaceous rocks where the planes are parallel to
each other; and these are often found to exist without being the result of stratification;
probably the cause of these masses being so divisible into planes is a partial crystallisation,
for when clay moistened with acidulated water is subjected to voltaic action for some time, it
will show a laminated structure, the planes of the lamina being found at right angles to the
electric forces.
It is now necessary to give a description of each stratum, commencing with the
Tertiary Series, which were probably occasioned by the deposits from large rivers into
estuaries, as they consist of beds of gravel, clay, sand, and friable sandstone, and were
formed after the present land had become divided into bays and gulfs, or lagoons of various
extent and depth; arenaceous deposits prevail; argillaceous types are found in particular
districts; calcareous rocks, having a marine as well as freshwater formation, lie spread out
in many basins, and marl as well as gypsum are found locally accumulated. Conglomerate
containing fragments or entire boulders constitute some of the arenaceous rocks, and are
of various colours, probably produced by the oxide of iron which they contain; some of
these sands, which are rarely hard enough to constitute stone, are variously tinted, others
are colourless; the green colour is produced by a silicate of iron.
The flints left by the destruction of the chalk, after being subjected to the action of
water, occur in the state of rounded pebbles, accompanied with layers of lignite and sul-
624
BOOK IT.
THEORY AND PRACTICE OF ENGINEERING.
phuret of iron and clay; the whole being subjected to long abrasion, and exposure to the
oxygenating processes of the atmosphere.
The Argillaceous Sediments consist of a variety of light greenish and blue marls, with beds
of gypsum, and those which are found accompanying the coloured sands of Alum Bay, in
the Isle of Wight, are singular from the variety as well as richness of their tints.
The limestone is soft, marly, and generally abounds in shells. The whole of this forma-
tion was in all probability derived from the detritus of those rocks that surrounded the
seas where they were deposited; or different rivers emptying themselves into the same
estuary might each bring with it sedimentary matter taken up in its course, either argil-
laceous, calcareous, or siliceous, more or less finely comminuted. The velocity of the
several streams would influence the deposits, and distribute them at several distances
and depths; but in all cases the tertiary formation is the result of stratiform deposits,
and the most striking features consist in the repeated alternations of marine and freshwater
beds.
The marine formations of this series are divided into Newer Pliocene, Older Pliocene,
Miocene, and Eocene, and alternating with these there intervenes a fourfold series of other
strata, or freshwater formation.
The Newer Pliocene consists of lacustrine and fluviatile deposits, and the majority of shells
found in it bears a great resemblance to those of the living species; this system in Sicily
alternates with volcanic beds, and is constituted of hills, rising in some cases upwards of
2000 feet above the level of the sea; and the species of shells found in them are similar to
those inhabiting the Mediterranean Sea.
The great limestone formation, which is the uppermost of these strata in Sicily, bears some
resemblance to the calcaire grossier of the Paris basin, and consists of a yellowish white
calcareous rock, often containing leaves of plants, reeds, &c. as if a river of fresh water
with carbonate of lime in solution had floated down these vegetable remains. Its thick-
ness is sometimes 800 feet; in some situations it is of a more compact character, and may
have been precipitated from the waters of mineral springs.
The Older Pliocene. The Norfolk Crag formation comes under this division, and re-
sembles a raised sea beach; it is composed of layers of sand and pebbles, mixed with marine
shells, and occupies much of the low ground of the eastern coast of England; the pebbles
found in it are much worn and abraded, and resemble those on the margin of a sea in-
fluenced by tides. This crag is usually considered the uppermost of the British strata, and
consists of several layers.
The Miocene comprises the Red and Coralline Crag, the latter being formed of calcareous
sand, derived from corals in a state of decomposition, among which are embedded sponges,
corals, and shells in good preservation: this formation in Suffolk is quarried and used for
the purposes of building; it is not stratified, its bed does not exceed 10 or 12 feet in
thickness, and it is of a soft nature. The Red Crag, which is uppermost, has a deep
ferruginous colour, and is formed of layers of siliceous sand, mixed with broken shells,
and was probably cotemporaneous in its formation with the coralline: among the shells
are the genera Buccinum and Murex, exclusive of Polypi, Radiaria, and Crustacea; some
hundreds of species of invertebrated animals are found, among which are Annulata, Cirrhi-.
peda, Conchifera, and Mollusca. In the Suffolk Crag is the Fusus contrarius and the
Fusus bulbi; and in many parts of the cliffs of Norfolk and Suffolk, sand and shingle
alternate without any organic remains; whilst in others there are abundant remains of the
bones of terrestrial quadrupeds, as well as Ammonites, vertebræ of Ichthyosauri, and drift
wood, sometimes lying in confused masses, at other times in regular strata. From the
mixture of these terrestrial and marine remains, there can be but little doubt that the crag
formation was partly deposited at the mouth of a river: the bones of the mammalian re-
mains are ascertained to belong to the leopard, the bear, the hog, and a large kind of deer;
some of the Mammalia of the Norwich crag are of a more recent date, such as the teeth of
the Mastodon longirostris, the elephant's tusk, the bones of the horse, the hog, and the field
mouse, mixed with those of birds and fishes.
P
Eocene. In this formation may be classed the Bagshot sands, which are of an ochreous
colour, and are found alternating with foliated green clay, green sand, and various coloured
foliated marls; a few shells are occasionally met with in the marls, of the genera Trochus,
Pecten, and Crassatella; though organic remains are rare, remains of fishes do occur; the
greatest elevation above the level of the sea is 465 feet.
The fresh-water formations of the Isle of Wight are divided into an upper and lower
deposit, the bed separating them containing marine remains; the shells belonging to genera
Murex, Buccinum, Natica, Venus, Nucula, and Corbula.
The upper fresh-water formation, composed of yellowish marl, contains shells of the
genera Limnea, Planorbis, and Helix.
London Clay has either a bluish or black colour, and sometimes passes into calcareous
marl, having a depth of more than 1000 feet in thickness. Argillaceous limestone con-
taining calcareous spar occurs in numerous layers, as well as ovate or flattish masses, called
CHAP. I.
625
GEOLOGY.
Septaria. In some localities these occur at upwards of 200 feet in depth. The shells of
the Paris basin are also found in it, but there are no remains of terrestrial mammalia,
although there are those of the tortoise and crocodile, which indicate the deposition to have
been made at no great distance from land; many of the shells found in the clay bear a
strong resemblance to the testaceous fauna of the tropics, though they cannot be identified
with any species now living. The fish found in it appear to have belonged to a warm
climate: among
them is the sword-fish, Tetrapterus priscus, about 8 feet in length; and the
saw-fish, Prestis bisulcatus, 10 feet in length, both of which were found in the Isle of Sheppey,
where more than fifty other species of fish have been discovered; the nodules of calcareous
stone in that island are formed into Roman cement, and the fossil Flora resemble those on
the shores of the Mediterranean. The shells are the Dentalium striatum, Paludinum
lenta, Crassatella sulcata, Venericardia planicosta, Conus scrabriculus, Voluta dubia, &c.
The London and Croydon Railway, during its execution, laid open a complete section of
the London clay, down to its junction with the plastic clay. At New Cross the plastic
clay was decomposed sandstone, with fossils, black sand, clay and sand, occupying a depth
of a little more than 30 inches; then a layer of strong blue clay of 10 inches or more;
then a layer of loose ferruginous sand, about 1 foot in depth; afterwards fine sand to the
depth of 2 feet or more; then a stratum of flint shingle, of the same depth, on this lies
the London clay, in many places more than 15 feet in depth, and above it the top yellow
clay.
The cutting near to that at New Cross is nearly 80 feet, and the rails are laid on the
top of the plastic clay. About three or four years ago a great movement was observed
in the embankment of the western slope, which forms the inside of the curve, taken by
the line of rail: the yellow clay became, from the great fall of rain, in a semi-fluid
state, and was in motion throughout its whole thickness; in a few hours more than
50,000 cubic yards slipped on the surface of the blue clay, and covered the rails for a
considerable distance. The blue clay is stiff and insoluble, and so compact that it is
impervious to water; but the yellow clay above is mixed with a variety of other matter
soluble in water, as lime, fullers' earth, and bands of septaria; these being dissolved
occasioned faults and fissures within, which became filled with water, caused an
pansion of the mass, and at last its falling down, from not being able to sustain its own
weight on the steep slopes at which it had been cut. The strata also dipped in a manner
to favour the slipping, which chemical action may have aided, for the iron pyrites found
in the yellow clay may have been decomposed by exposure to the atmosphere, and sul-
phuric acid evolved, which, entering into combination with the carbonate of lime, would
form crystals of silenite, materially affecting the bulk of the whole mass, and assisting the
separation of the clay.
To remove this slip stages were erected at each end, sufficiently high to permit the
waggons to run under them, and advance gradually into the slip, a way being cut by
working a gullet down to the rails. Two sets of waggons were made use of, which, when
filled, were drawn away by locomotives to the nearest embankment, where the contents
were either carted or wheeled to their destination. When the whole was cleared, a cutting
was commenced at each side where the slips took place, and after removing above 250,000
cubic yards of clay, the slopes were trimmed back to what was considered a safe
inclination. This was effected by cutting benches and intermediate slopes; on the west
side there are three benches, and on the other two; these benches vary in dimensions up
to 65 feet in breadth, and the several slopes are cut with an inclination of 2 to 1.
Drains are formed both on the benches and in the slopes, to carry off the surface water.
Some of the earth on this line is very untractable: at Forest Hill a continued rain
resolved it into mud; and after all attempts to drain it were found ineffectual, a bench
70 feet in width was cleared about 20 feet up the slope, and on this 100,000 cubic yards
of clay were run; at the back of the benching was a retaining wall of gravel, nearly
double its width, and varying from 5 to 12 feet in height; the clay taken out was then
thrown in front of it, to gain additional weight, and a greater firmness in the soil has been
the result. Drains of gravel seem to be in most cases efficacious, the water, which is the
general cause of all slips, being by this means entirely drained off; care is also required to
secure the foot, and to make the slopes in such soils from 3 and 4 to 1.
Retaining walls on the London and Birmingham line, near the Euston Square station,
were forced inwards from the expansion of the clay behind them: they were of brick, 5 feet
6 inches thick at bottom, and 2 feet 6 inches at top, with a curved face, and whenever taken
down for the purpose of repairs, the face of the clay appeared to stand perfectly straight,
the expansion and the force obtained by it being attributable to the action of the atmo-
sphere, which causes a constant contraction and expansion, if the clay be exposed even for a
few hours; it is from the same influence that the sides of wells sunk in it so frequently
give way; when dried, it occupies a seventh or eighth less space than when in its bed.
During the heat of summer it will shrink, and form cracks or fissures, which, when the rain
falls, become filled with water, the hydrostatic action of which occasion masses to break off
S s
626
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
and slip. This water should, therefore, be collected as much as possible at the surface, and
carried away by drains.
Clay in a moist situation requires a slope of at least 3 to 1, to enable it to stand; when
kept dry, 2 to 1 has been found sufficient. Where sleepers have been laid upon it in mines
or at the bottom of tunnels, they frequently rise up, and are broken, by the mere expansion
of the clay; this occurred in the tunnel of the Manchester and Bolton railway. Houses
or buildings of any kind placed upon it are in constant motion: when the weather is dry,
the foundations contract, when wet expand, so that the walls are never at rest; when the
clay is moist, a heavy wall will sink, and continue to do so until out of the influences that
produce these changes.
Whenever a slope is made at the side of a cutting in clay it is advisable to have at the
toe a footing of concrete or a wall built up to guard against the mass sliding from it.
The
difference in the colour of the yellow clay and the blue beneath arises from the iron they
contain. When this is excluded from the air, it is found as a protoxide; in the upper clay
it is a peroxide..
The London clay is more or less pervious, abounding with fissures in all directions,
many of which hold a slimy earth and abundance of water: this often passes down to the
lower stratum on which it rests, which, if composed of sand, is washed away, and then the
whole superincumbent mass either settles or moves forward; it is supposed to contain 10
per cent. of water. Where canals have been cut through clay, and the embankments
formed of the material thrown out, they have remained firm as long as their weight
balanced the upward tendency of the water in the substratum of the bed of the canal; but
when the increased weight of the mass destroyed that equilibrium, the embankments sunk,
and forced the bottom upwards. The greatest depth of the London clay is estimated at
700 feet, and its greatest elevation above the sea at 760 feet.
Plastic clay belongs to this formation, and is of various colours; it is so called from
its being used in the potteries; it is found in different degrees of thickness, and contains
lignites, amber, and shells, both freshwater and marine. The number of tertiary fossils is
considerable; the greater proportion are terrestrial; the fishes are so nearly related to
existing forms that it is difficult to class them, crocodiles and snakes agreeing with those
met with at the present day.
Upper Secondary. Cretaceous.
Upper Chalk had its surface furrowed by the action of the waves and currents before any
of the sands or clays were deposited upon it, deep indentations being frequently observed, in
which are imbedded sand, gravel, and flint.
The stratification of chalk is often obscure, where layers of flint are wanting; where they
occur they form strata of from 4 to 7 or 8 inches in thickness, and the distance between
these beds varies from 2 to many feet.
Lower Chulk is harder and less white than the upper, and is sometimes varied by green
grains, generally with fewer flints, and often without any. The organic remains of the
cretaceous system are nearly all marine; the plants are few, and exclusively marine, with
the exception of fragments of coniferous trees, which have evidently floated in the sea, as
some specimens have been perforated by Teredines.
Among the fossil shells are the Terebratulæ, which live in deep and tranquil seas, and
the extinct species of Crania and Catillus, the Belemnite, Ammonite, Baculite, and Tur-
rilite, of the family Cephalopoda, which resemble the cuttle-fish. Sea Urchins, Corals,
Sponges, &c., are also dispersed through the chalk and flint; the latter of which owe
their irregular shape to the inclosed zoophytes, as the hollows on their outer face are
caused by branches of a sponge, which may be sometimes discovered by breaking the flint.
Fish and Crustacea are found, but no bones of land animals, terrestrial or fluvial shells,
plants, sand, or pebbles, indicating a formation in a deep sea at a great distance from land.
Fossil fishes, with the air-bladder distended, have been discovered in the Sussex chalk,
leading to the conclusion that their destruction and envelopement were sudden.
The chalk formation in England is of great extent; it is chiefly of carbonate of lime in a
fine granular state; the greatest height which it attains above the level of the sea is about
1000 feet.
Greensand generally forms the base of the chalk hills, and consists of small grains of
silicate of iron agreeing in composition with chlorite; the greensand deposits are a suc-
cession of ordinary beds of sand, clay, marl, and impure sandstone, probably the detritus of
former rocks, the nature of which may be traced in the pebbles of quartz, quartzose sand-
stone, jasper, flinty slate, and grains of chlorite and mica.
The upper greensand is a formation of sand and loam, frequently mixed with chert,
which passes downward into clay and marl called Gault. Below the gault is the lower
greensand, which is partly ferruginous sand and sandstone, with some limestone; among
the latter may be mentioned the Kentish rag, used for building and repairing the roads, and
among the sandstones that called firestone, which derives its green hue from grains of sili-
cate of iron.
CHAP. I.
627
GEOLOGY.
The fossils of the greensand are marine; among them is the Pecten quinquecostatus,
several forms of the Cephalopoda, as the Hamite, Scaphite, and others, which distinguish
this formation from the chalk. A specimen of a Saurian named the Iguanodon Mantelli
was discovered at Maidstone.
OOLITIC SYSTEM. Wealden formation is almost peculiar to the counties of Kent,
Sussex, and the Isle of Wight; it is a local freshwater or estuary deposit, composed of
coloured sands and clays, with lignites, conglomerates, and calcareous masses, interspersed
throughout the sands, limestone and ironstone in the clay. It is divided into four several
groups, viz.: —
The uppermost or weald clay is blue and stiff, with Septaria, argillaceous iron-stone,
and beds of shelly limestone, called Sussex or Petworth marble (fossil Cyprides). These
beds of limestone are made up of a few species of the univalve called Paludina, a fresh-
water snail, common in rivers and lakes; the shells are sometimes decomposed, and their
casts alone remain, the interstices being filled up with indurated marl, or calcareous con-
cretions. In the coarser varieties are cavities left by the decomposition of the shells; in the
more compact masses a crystalline calcareous infiltration of various colours has permeated
the mass, and given it a beauty equal to foreign marble. There are a few bivalves trace-
able in this limestone, though some blocks containing large specimens (Unio) interspersed
with univalves, and fragments of reptiles, bones, &c. of various tints of green, blue, grey,
&c. have been found in Western Sussex. The Petworth and Bethersden stone or marble
are extensions of the same bed. These marbles were most extensively employed during
the middle ages for tombstones, altars, fonts, monuments, and the decorative portions of
churches and cathedrals. Columns of it, highly polished, are distinguishable features in
the early Pointed architecture.
Secondly.—The Hastings sand, which consists of irregular alternations of sand and sand-
stone, sometimes calcareous, of a grey, yellowish, or ferruginous colour, with concretions of
ironstone and layers of lignite, the sandstone often having a conglomerate form, and con.
taining pebbles of quartz and jasper.
Thirdly. The Ashburnham beds, clays, shales, bluish grey limestones and sandstones.
Fourthly. The Purbeck beds, clay, sandstone, and shelly limestones, with layers of vege-
table mould, and remains of trees in a vertical position. The Purbeck is found in the deep
valleys of eastern Sussex, but emerges on the Dorsetshire coast, and from the northern brow
of the Isle of Portland. The Isle of Purbeck is an irregular oval, 7 miles in breadth, and
12 miles in length; on the eastern promontory the chalk is in a vertical position, and
beds of sandstone and limestone are seen underlying this displaced strata; towards
the southern extremity of the island appears the Portland limestone. The Purbeck beds
are a sort of calcareous marble, of various thickness, and of a mottled colour; they abound
in organic remains, the chief of which is a congeries of the shell Paludina, intermixed with
minute crustaceous coverings of a species of Cypris; this marble bears a high polish; it is
finer grained than the Petworth, and was much used in the decorative portions of Salisbury
and Wells Cathedrals; it has unfortunately been generally placed in a contrary position
to its true bed, which accounts for the long slender columns into which it was con-
verted flaking off and crumbling away. The fossils found in the Wealden formation are
exclusively of a genera either fluviatile or lacustrine, such as Melanopoca, Paludina,
Neritina, Cyclas, Unio, and others; these occur in such quantities that the surface of each
layer of marl is sometimes entirely covered with the valves of Cyclas, and beds of limestone
are composed solely of Paludina.
The species of Bulla, that of an Oyster and Exogyra, which are met with, indicate the
occasional presence of salt water. The fishes of the Wealden belong to the genera Pycnodus
and Hybodus, as well as a species of Lepidotus; the general form of the latter resembles
the carp, although of a distinct kind, and somewhat allied to the pike.
Of
Among the vertebrated animals the reptiles are the most numerous, such as the Trio-
nyx and Emys genera, found at the present day in the fresh-water of tropical regions.
Saurians there are five genera, the Crocodile, Plesiosaurus, Megalosaurus, Iguanodon, and
the Hylæosaurus. The Iguanodon, which was herbivorous, had its teeth formed like the
modern Iguanas, found in America and the West Indies; its entire length has been com-
puted at 70 feet. No skeleton of a mammiferous quadruped has been discovered: the
birds belong to the order Grallæ. Of vegetable remains there are numerous varieties, all
having the character of tropical productions; their resemblance to the living genera of
Cycas, Zamia, and Esquesata, is very great; there are specimens of Coniferæ allied to the
Araucaria, as well as many varieties of tropical ferns.
G
Upper Oolite. Portland Oolite. This is a marine formation, or limestone, abounding
in Ammonites, Trigoniæ, and other exuviæ: it occurs immediately below the Purbeck
bed, from which it is separated by a vegetable soil, called the dirt-bed, of from 12 to 18
inches in thickness, containing a large portion of earthy lignite, with rounded pebbles or
gravel interspersed. Trunks of trees, nearly allied to the Zamias and Cycas, are also
buried in it, and there is every evidence that when these were growing the Portland beds
£ s 2
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BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
:
were in a softer state than they are now found, many of the roots having penetrated,
leaving cavities resembling them in shape. In all probability the Oolitic beds which were
formed in the sea first became dry land, were then covered by a forest, and afterwards
submerged beneath a body of fresh water, from the sediment of which fluviatile shells
were deposited.
The cap of the Portland Oolite is light-coloured, and of a fine grain, but shattered and
full of fissures, which occasions it to fall into masses too small for any useful purpose, although
it is not destitute of hardness.
The skull cap is compact and open in its texture, hard, and its grain well cemented
together; it is useful for structures where ornament is not required. The Roche of
both the top and bottom beds forms a portion of the stone with which it is in contact, and
resembles it in its composition. The best beds are those called the top, which are situated
about midway between the top and bottom of the quarry. Their thickness varies from 5
to 7 feet, although occasionally blocks of much greater dimensions are obtained. The
bottom bed averages about 6 feet in depth, but the particles are not so well cemented
together. They are in a loose state of combination; it is, however, often preferred, from
the facility with which it may be worked, and from its fine grain.
Kimmeridge clay is of a blue colour, and consists in a great part of bituminous shale,
sometimes forming an impure coal, several hundred feet in thickness, whilst in others it
resembles peat. The impressions of plants are rarely found in it, but Ammonites, Ostrea
deltoida, Gryphæa virgula, are mixed with the shale, and the bitumen it contains may be
attributable to their animal origin.
Middle Oolite. Upper Calcareous grit is a deposite full of comminuted shells, having an
oblique lamination; it is a freestone of rather close texture.
Coral rag, or Coralline Oolite consists of two beds of calcareous sand separated by
another of limestone; the lowest is of a yellowish colour, and contains about thirty per cent.
of calcareous matter. The limestone is almost wholly composed of corals.
The upper
arenaceous deposit is close in its texture, full of comminuted shells, forming a calcareous
freestone, which is useful for many purposes. Among the organic remains are the Am-
monites vertebralis, Plagiostoma rigidum, Clypeus dimidiatus, Cidaris florigemma, Astrea
tabulifera, and Caryophylla annulata, and frequently masses of coral as they were formed
in the sea.
Lower calcareous grit is a yellowish quartzose sand, containing a considerable quantity of
calcareous matter.
Oxford clay is an argillaceous deposit of a dark blue colour, which, when exposed to
the action of the air, becomes brown; it contains Septaria, and concretions of argillaceous
limestone separated by veins of calcareous spar; among the organic remains is the
Gryphæa dilatata.
Kelloway rock is a calcareous sandstone abounding in fossils, among which is the Ammo-
nites calloviensis.
LOWER OOLITE.
Cornbrash limestone is a coarse and impure limestone, though it has considerable hardness,
and is of a compact nature. It has sometimes a crystalline appearance, and contains many
500 feet in thickness in the neighbourhood of Bath.
shells, &c.
Forest marble is found associated with clay and sand; it is limestone of a bluish tint.
with particles of oolite occurring in thin beds. In Wichwood Forest in Oxfordshire, it
becomes a coarse kind of marble, which is worked for inferior purposes.
Bath Oolite occurs in beds of from 100 to 200 feet in thickness, and is calcareous; when
freed from fossils it is easily sawn and worked with the chisel; it contains various corals,
as the Eunomia radiata, several of which have been found of great dimensions, indicating a
growth of many centuries, as the large brain coral, the Meandrina. The stone lilies
(Crinoideans) are also common. The upper surface of the Bath or Great Oolite once
abounded with a forest of these beautiful zoophytes; and there is every appearance that
the deep marine waters in which they were produced were invaded by deposites of mud,
which threw down and destroyed them; the stumps of some are found in their original
position. Among the other fossils are the Trigonia gibbosa, Ostrea Marshii, Orbicula
reflexa, Ammonites striatulus, &c.
Stonesfield slute is remarkable for its marine and terrestrial remains: it is calcareous,
and consists of two beds of thinly laminated oolitic limestone, of about 2 feet in thickness,
separated by calcareous limestone; it has the quality of splitting or separating into
plates when struck with a mallet; after being exposed during a winter it is occasionally
used for roofing. It is obtained from the quarries by driving a gallery into the side of the
hill, about 6 feet in height, and as it is exhausted the sandstone is piled or built up to
support the superincumbent earth. The Stonesfield slate is rich in organic remains,
containing Belemnites, Trigoniæ, and other marine shells, many impressions of ferns,
Cycadeæ, and other terrestrial plants, several insects, and many genera of reptiles, as
the Plesiosaurus, Crocodile, and Pterodactyl, and the jaws of two mammiferous quadrupeds
allied to the Opossum (Didelphys).
CHAP. I.
629
GEOLOGY
Fullers' earth beds are deposites of calcareo-argillaceous beds, mixed with frequent courses
of soft rubble-stone, containing a considerable proportion of calcareous matter. Blue and
yellow clays, called fullers' earth, are found with them; these clays are of a blue colour,
changing near the surface to yellow; they are often laminated, but generally resemble a
mass of argillaceous sediment, divided by lamina of shelly limestone or lines of Septaria;
pyrites and jet lie in many of them; from these clays the transition to either sandstone or
limestone is usually very gentle.
Inferior Oolite possesses a brown tinge or colour from the oxide of iron it contains,
which is also mixed with much siliceous matter; it sometimes passes into a ferruginous
sandstone, as in Northamptonshire and the adjoining counties. The arenaceous deposites
of this system are not found to be micaceous or felspathic, as those of an earlier date:
yellow tint is the prevailing one, sometimes of a deep colour; the grain is usually fine, and
quartz pebbles occur as well as portions of carbonate of lime.
Sandstone, which is the lowest portion of the oolitic system, is always stratified, though
often coarse-grained, and exhibiting an oblique lamination, the finer sorts splitting easily
into flags or slates. Shells, and plates of oxide or carbonate of iron, are found in them,
which appear the result of molecular arrangement round nuclei of other matters which
have served as centres of attraction.
LIAS FORMATION is usually found stratified in conformity with the rocks of the oolitic
group; it is of considerable thickness, varying from 500 to 1000 feet, and of an uniform
lithological character. It is of marine origin, and consists of an alternation of thin beds of
limestone, with a light brown weathered surface, separated by dark-coloured, narrow,
argillaceous partings, having a striped appearance; its prevailing colour is blue, though
some beds, called White Lias, have a yellowish-white tint. The organic remains are
principally marine or littoral. Among the shells are the Gryphæa, Cephalopoda,
Ammonite, Belemnite, and Nautilus; the fossil fish are the Lepidotus, &c. ; of the reptiles
there are several species of Ichthyosaurus and Plesiosaurus, and among the plants of
Zamias and Coniferæ.
Upper Lias shales. - Marlstone, Lower Lias shale, Lias Limestone, and Lower Lias Marls,
are its subdivisions.
POIKILITIC or New Red Sundstone formation is a great mass of arenaceous and argillaceous
deposit, immediately below the blue lias; gypseous and rock salt, with some organic
remains, are contained in it. The rocks are generally granular, of a yellow colour, and
sandy nature, but not micaceous; some of them are a coarse breccia, containing fragments
of limestone; others are conglomerates of various pebbles; many a coarse red grit, used for
building; the grains of this red sandstone consist mostly of clear quartz, the exterior
coated with red oxide of iron.
Variegated Marls are red, blue, green, or white; they are laminated, contain gypsum
and rock salt; white and grey sandstones of a peculiar character are occasionally found
among these marls.
Variegated Sandstone, so named from the white and mottled partitions contained in them;
the lower part is a quartzose conglomerate.
The red sandstones and red marls, which form so considerable a thickness in England,
are perhaps the result of the disintegration of various crystalline or metamorphic schists,
and often of porphyritic trap rock, containing much oxide of iron; the red colouring
matter with which this alluvium is tinted may have been furnished by the decomposition of
hornblende or mica, which contains oxide of iron in large quantities. Fossil remains are
rarely found in any stratified rocks where this oxide of iron abounds.
Magnesian Limestones vary in their character, and are sometimes loaded with magnesia,
having either a white, yellow, grey, or smoky colour, occasionally red. The texture is
compact, and sometimes oolitic, the cells being lined with crystallised carbonate of lime.
Some of these limestones have a fine sandy grain, others are quite powdery, containing
crystallised balls. Plates and strings of spar are very common in them, and it is this pecu-
liarity which causes magnesian limestone, when used in building, to decay, the stone
perishing between the ribs of spar, and crumbling away. The fine-grained limestone of
Knottingley are thin-bedded, or flag-like, and it is often difficult to trace the beds in the
powdery magnesian rocks; they are frequently traversed by vertical divisions from top to
bottom, which are in some places filled with pebbles or clay.
Marl slates are laminated impure calcareous rocks, of a soft argillaceous or sandy
nature.
Lower Red Sandstone, with red and purple marls and micaceous beds; the grits are
white or yellow, and either of a pebbly or sandy nature. The repetition of clay, sand-
stone, and oolitic limestone, shows the new conditions imposed upon the land and sea, and
the loose grits that the deposits were made at no great distance from land.
The red sandstone appears to have accumulated in a situation unfavourable to either the
reception of vegetable or animal exuviæ.
The magnesian limestone and red sandstone are variously tinted with oxide of iron, the
ss 3
630
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
ocean.
clays with green or blue by the protoxide; and these colours are supposed to be the result
of volcanic influence on the particles which formed the first deposits at the bottom of the
The limestone is found of various densities, arising from the degree of consolidation
to which its particles have been subjected. Some claim a corallaginous origin, and have
their particles in different degrees of aggregation. The globular concretions of others may
be owing to the submarine springs yielding carbonate of lime, mingled with magnesia,
which after deposition were consolidated.
The origin of the gypsum and rock salt have been variously accounted for, and from the
absence of all marine exuviæ, it does not seem to have been deposited by the sea under
ordinary circumstances.
The fossils belonging to the saliferous or Poikilitic system are in Britain confined to about
50 species, the great proportion of which belong to the magnesian limestone, and contain
fishes, zoophytes, and mollusca; in the lower red sandstone are many plants, and in the
marls marine shells.
Carboniferous System.Arenaceous, argillaceous, and calcareous rocks, associated with
beds of chert, ironstone, and coal, are the six substances which compose it: it is of great
thickness, and exhibits throughout proofs of slow and successive deposits.
Coal Measures, or the upper part of the carboniferous system, consists of alternations of
argillaceous and arenaceous strata, with beds of coal and ironstone, the latter yielding 30
per cent. of iron; the sandstones are micaceous, and both coarse and fine-grained, alternating
with shale. The coal is often found in 50 seams or beds, varying in thickness from 1 inch
to 6 feet or more. The rocks with which it is associated are of various colours, and there
is almost every possible gradation between the sandstones and argillaceous deposits;
the latter being laminated are called plate or bass; when the lamination is less perfect,
shale; and when quite unobservable it takes the name of clunch, bend, or some other
peculiar to the locality; they are all more or less bituminous, and of a dark colour.
The limestones are compact, oolitic, or granularly crystallised, and mostly formed of
pure carbonate of lime, except the granular varieties, which contain magnesia. The
whole are of marine origin, though there are some exceptions. All are, however, the result
of aqueous deposition, as lamination occurs throughout the whole of the six substances
which compose this system.
Coal is of vegetable origin, which has been most satisfactorily proved by a microscopic
examination of many varieties, after cutting them into thin plates. Impressions of plants
and trunks of trees are frequently met with in the sandstone and shale; leaves, branches,
and fruits occur in the nodules of clay ironstone, the vegetable itself having served as
the nucleus round which the carbonate of iron has concreted.
The latest of the carboniferous deposits is said to be that in the neighbourhood of
Shrewsbury, which was of freshwater origin: it consists of shales and sandstones, about
150 feet in thickness, with coal and traces of plants, including a bed of limestone of from
2 to 9 feet in thickness, of a cellular texture. The fossils contained in it are small
bivalves, having the form of Cyclas, a small Cypris, and the Microconchus of an extinct
genus.
In the lower coal measures of Colebrook Dale the strata often change materially within
very short distances; beds of sandstone passing horizontally into clay, and clay into sand-
stone; the strata are from 700 to 800 feet in thickness, and more than 50 terrestrial plants
have been found, besides various fishes and Trilobites, as well as 40 species of Mollusca,
among which are two or three of the freshwater genus Unio, and others of marine forms, as
the Nautilus, Orthoceras, Sperifer, and Productus, from whence it is inferred that these
deposits were made in a bay of the sea or estuary, into which some large river poured its
flood.
In the South of England the carboniferous strata consists of three formations, viz.—
Coal formation, a mass of more than 1000 yards in thickness, composed of alternations of
shales and sandstones of various kinds, with about 50 feet of coal in beds, a portion of iron-
stone, and sometimes thin layers of limestone.
Mountain Limestone, formed of calcareous rocks, with few partings of argillaceous matter,
and with few grits, no coal, some chert nodules, and occasionally layers of red oxide of
iron; the whole from 500 to 1500 feet in thickness.
Old Red Sandstone, composed of arenaceous rocks, from 500 to 10,000 feet in thick-
ness, contains some conglomerates of extreme coarseness, and sandstones of many kinds :
among the argillaceous beds is concretionary limestone irregularly developed. In the
North of England this triple system is somewhat modified, and consists of the millstone
grit group, composed of quartzose and felspathic gritstones, and some bad coal, with shales
and sandstones.
Limestone shale formed of a series of laminated shales or plates, mostly bituminous, with
some ironstone, and thin black limestone, but no coal; the thickness is 1000 feet or more.
Mountain Limestone formation, where the old red sandstone is almost absent; some mill-
stone grit and limestone shale are found about the South Wales coal-field. In the north-
СНАР. І.
631
GEOLOGY.
western part of Yorkshire the series is still more varied and complicated. After the coal
formation we have the millstone grit, or series of grit-stones, separated by shales, and
several other flaggy and freestone grits, cherts, thin limestone, ironstone, and several coal-
seams, 1000 feet in thickness.
Yoredale rocks are a series of five or more limestones, with many freestones, flagstones,
abundance of plates, some ironstone, chert, and several coal seams, 1000 feet in thickness.
Scar Limestone, divided by grits and slates, with some beds of coal 800 feet in thickness.
Alternations of Red Sandstone, clay, and limestone, 100 feet red sandstones, and conglo-
merates, very limited in their range and of variable thickness.
Pursuing this system in Northumberland, we find the scar limestone interfered with by
the interposition of various grits and abundance of coal. The usual thickness of coal in
England and Scotland is about 50 or 60 feet, divided into 20 or more beds, alternating
with from 20 to 50 or 100 times as great a quantity of sandstones and shales. Though in
some districts the coal is deposited in beds above one another, with but little earthy matter
intervening, in which the different beds are traceable, and possessing various qualities, pro-
bably arising from the differences of the vegetable matter that comprise them, and the
manner in which the accumulation has taken place.
In the coal tracts of the Tyne and Wear there is very little limestone; in Yorkshire the
total thickness of the coal formation is from 1000 to 1500 yards; in Lancashire a greater
thickness, whilst in South Staffordshire it does not exceed 1000 feet. The most variable
are the sandstones and shales, the most regular the coal beds and ironstones.
The organic remains in the coal formation consist of many varieties of plants in fine pre-
servation; abundance of zoophytes, mollusca, crustacea, many fishes, but, as far as has yet
been ascertained, neither reptiles, birds, nor mammalia. Many of the plants are of terrestrial
growth, whilst all the zoophytes, nearly all the mollusca, crustacea, and fishes are cf marine
origin. The plants are somewhat similar to existing species, as the large group of ferns,
though others are quite dissimilar, as in the furrowed stem of the Sigillaria, &c. &c.
The following may be taken as a brief summary of the plants:
Cryptogamia vasculosa
Phanerogamia monocotyledoniæ
Equisetaceæ
Silices
Lycopodiacea
20 species.
100
60
10
Coniferæ
Cachacea
Undetermined
10
50
50
300 species.
The remains of these plants usually compose the coal seams, and one cause of the differ-
ence among them is the various structural composition of the plants themselves, which are
generally confined to arenaceous or argillaceous deposits; they abound in the upper part of
the carboniferous system, and they also occur in the midst of the millstone grit, in the sand-
stones and shales, and also among limestones, where coal-beds are found, but they are rare,
or almost wholly unknown, in the midst of the undivided limestone, and in the old red sand-
stone. Among the Zoophytes are 40 species of the Polyparia, 40 of the Crinoidea, and 3
of the Eschenida. The Mollusca consist of 326 species, among which are of the Conchifera
40 species of the Plagymyona, 28 of the Mesomyona, 100 of the Brachopoda; Gastero-
poda 92 species; Cephalopoda monothalamia 10, and Cephalopoda polythalamia 69, 10
species of which are of estuary formation, and about 60 per cent. belong to species of
extinct genera.
The fishes of the carboniferous system are mostly of the Ganoid division, and both the
plants and animals are very distinct from existing types.
Carboniferous and Mountain Limestone lies beneath the coal measures, and sometimes
alternates with the shales and sandstones of the coal; it is destitute of land plants, and
usually abounds with corals of large size, several of which belong to the lamelliferous class,
which enter largely into the structure of coral reefs: there are many Crinoides, Echinides,
&c., associated with the Zoophytes. Among the Mollusca are Brachiopoda, several of
which are referrible to the Spirifera and Productæ; Univalve and Bivalve shells, such as
Turritella, Buccinum, Patella, Isocardia, Nucula and Pecten, abound; but the Cephalopoda
differ widely from living genera.
The Carboniferous limestone has a sub-crystalline texture, and some of the varieties take
a fine polish, their surfaces being ornamented by the sections of inclosed Crinoidea, corals
and shells; the prevailing colour is a bluish grey, the organic remains being of a pure
white, but some varieties have a ground of red, others nearly black, the shells which are
embedded being of a deep ochreous colour.
The Derbyshire marbles and those of St. Vincent's rocks are among the finest examples
of mountain limestone; in Gloucestershire, Somersetshire, Shropshire, Derbyshire, and
S54
632
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
North and South Wales, it is a calcareous mass, interposed between the old red sandstone,
or where this is wanting, the more ancient slate rock below, and the sandstones and shales
of the coal above. The Derbyshire or Encrinital marble is formed of crinoideal remains,
composed of stems and detached ossicula of one species of Encrinite.
It is in the mountain limestone that the principal lead mines are situated; in Derbyshire
the metal occurs in numerous veins which traverse the rock, and extend in some instances
into the ancient volcanic bed, The perpendicular or rake veins are from 2 to 40 feet wide,
and others are chasms or hollows in the rocks, several hundred feet wide, which also contain
metallic ores and spar; manganese, iron, copper, zinc, &c., are also found, but that which
most predominates is galena, or the sulphuret of lead; it is accompanied with fluor and
calcareous spar, sulphate and carbonate of barytes, iron pyrites, &c. &c.
Millstone Grit is a siliceous conglomerate, or quartzose sandstone, and is composed of the
detritus of the primary rocks. Fragments of granite, from the size of a pea to a large
pebble, are cemented together by a crystalline paste.
Old Red Sandstone : this is of enormous thickness, and has been stated at 10,000 feet; it
consists of many varieties and alternations of tile, stone, limestone, marl, conglomerates,
shales, and sandstones; the latter of various states of induration, which, when schistose, are
employed for roofing. The conglomerates contain abundance of quartz pebbles; the red
colour predominates in the cementing material and the marls, and is derived from the
peroxide of iron. The formation of the stratas has evidently resulted from the waste and
degradation of the ancient slate rocks, the detritus being cemented together by red sand or
marl into coarse conglomerates.
Among the organic remains are ancient forms of the Terebratulæ, Spiriferæ, Productæ,
&c.; Nautili, Ammonites, and Orthocoralite, &c; Fishes, Fuci, &c.; some of the fishes
belong to the genus Cephalaspis and Onchus.
Among the tile-stones the Ichthyodorulites of the genus Onchus has been found, and a
species of Dipterus, with Mollusca of the genera Avicula, Area, Cucullæa, Terebratulæ,
Lingula, Turbo, Trochus, Turritella, Bellerophon, Orthoceras, and others.
UPPER SILURIAN is chiefly found in Shropshire, Radnorshire, and Herefordshire, par-
ticularly at Wooltrope.
Upper Ludlow Rocks are formed of a grey thin bedded limestone, slightly micaceous.
The Aymestry Limestone is sub-crystalline, and either a grey or blue argillaceous limestone,
highly fossiliferous; among the most numerous of the fossils is a species of Brachopoda,
viz. the Terebratula navicula.
Lower Ludlow Rocks are composed of sandy shales and flags, with concretions of earthy
limestone. The organic remains found in them are Corals, Terebratula leptena or pro-
ducta, Orthis, Pentamerius Knightii, Lingula, Orbicula, Bellerophon, &c. &c.
Wenlock Formation. The limestone of this formation is of a grey and blue colour, highly
concretionary and subcrystalline. The shale is argillaceous, of a dark liver colour, with
nodules of earthy limestone, and sometimes micaceous. The organic remains are chiefly of
the lower order of marine animals, as Corals and Crinoidea, among which are Producta
depressa, Spirifera lineata, Euomphilus rugosus, Orthoceras annulatum, Consularia qua-
drisulcata, Calymene Blumenbachii, (variolata, Asaphus caudatus).
LOWER SILURIAN. Caradoc Flags are thin-bedded impure shelly limestones, finely
laminated, slightly micaceous greenish sandstone.
The Sandstone is thick-bedded, and a freestone of various colours, as white, red, green,
and purple. The grits are quartzose and conglomerate, the limestones sandy and gritty.
Among the fossils are a few Crinoidea, Pentameris levis, Orthis, Terebratula, Leptæna,
Nucula, &c.
Llandillo Flags are dark-coloured, and chiefly calcareous, with some sandstone and schist ;
the fossils are several varieties of Trilobites, Asaphus Buchii, &c.
The Silurian system is composed of sedimentary deposits, which are either calcareous,
arenaceous, or argillaceous; the latter rocks are less indurated and less complicated in
their joints of cleavage, retaining in many places their original lamination. The arenaceous
rocks take the character of ordinary sandstone and conglomerate, and the calcareous are
only partly crystalline. The whole of these rocks seem to have accumulated in a regular
and tranquil manner, as they all show the lamina of their deposition in the sandstone the
beds are distinctly marked; in the limestones are evidences of regular stratification, though
nodular and concave on their surfaces, and sometimes partially lenticular, indicating that
their origin may have been similar to that of the coral reefs.
:
The joints and fissures which occur in the Silurian system are usually at right angles
with the planes of stratification; the organic remains are only those of Invertebrata, 500 or
600 species of shells, and 14 or 15 species of plants; each of the four formations of this system
contains distinct and characteristic species of fossils.
CAMBRIAN SYSTEM. Upper Cambrian, or Plynlymmon Rocks.-In Cumberland they
are formed of a dark limestone, containing corals and shells; in Wales of beds of conglo-
merate, greywacke and grey wacke slate, &c. The green slates and porphyries rest upon
CHAP. I.
633
GEOLOGY.
the Skiddaw rock, and for the most part contain crystals of chiastolite and hornblende,
without any fossils.
Lower Cambrian consists of slates of various colours, with their cleavage at right angles
to their stratification; they are found with conglomerates, porphyry, and greenstone, among
which are a few organic remains. In the rocks of this system are the first traces of fossil
remains, and among them the first evidences of organic life; those found belong to the
genera Cyathophyllum, Terebratula, Spirifera, Leptæna, or Producta. Some of the
Cambrian and Welsh rocks have a mechanical origin: they contain marine organic remains,
and have evidently been deposited by water; but it is extraordinary that they are not only
stratified, but have cleavage planes inclined at a very considerable angle to the planes of the
strata, and are never coincident, although in some cases they seem almost parallel with them.
In Wales the cleavage planes occasionally dip towards the same point of the compass as
those of stratification, but more generally in an opposite direction. The joints are un-
doubtedly natural fissures, which traverse these rocks in straight and well-defined lines,
the whole mass being frequently split by them into regular and symmetrical shaped blocks,
which affords great facility in removing them from the quarry. These natural fissures have
been produced since the deposition of the strata.
Slate is an argillaceous deposit, and the clay slate resembles in a great degree decomposed
felspar, which has been deprived of its potash by the action of water, and under particular
circumstances powdered blue slate, acted upon by great heat and an alkali, has been trans-
formed into white and glassy crystalline grains of felspar.
In greywacke slate the lamina of deposition show, on all the vertical planes, being parallel,
or nearly so, to the plane of stratification, which differs from the clay slate, for their lamina,
as has been stated, cross the planes of stratification, so that it may be split almost indefinitely
into thin plates, in a nearly vertical direction; there are instances where the lamina of
deposition remain in clay slate; across the cleavage plane are often seen stripes of colour,
different from the mass, which are evidently the marks of deposition interrupted by water.
The most cleavable slate rock in the quarry shows a stratified deposition, although it is
perfectly crystalline in its regular structure.
Cleavage has been thought, and probably is, the result of some agency after the sediment
was deposited; it is most perfect in the ancient argillaceous strata, where the rocks are of the
finest grain and uniform in their character. Heat operating upon argillaceous sediment, so
as to overcome the natural horizontal lamination, is supposed to have induced a new, almost
crystalline fissility in vertical or highly inclined planes, having one general direction. The
lower slates are universally cleavable, whilst the upper are only partially so, and the polarity
of the cleavage is the result of some general agency, which no doubt directed the molecular
attraction.
Gneiss System.—The materials which compose these rocks are siliceous, argillaceous, and
calcareous, in a different state of aggregation to those before described. The siliceous
strata is composed of the same materials as those found in the secondary sandstones, quartz,
felspar, and mica, but are not so worn by attrition, and bear some resemblance to granite.
The Argillaceous Strata do not much differ from the common clays, but from their
indurated character must have undergone different changes; the prevalent colours are blue,
red, purple, grey, and yellow; the green varieties contain chlorite.
>
Primary Limestone is met with in irregular beds, alternating with all the members of the
primary series; it has a highly crystalline texture, is compact, and both large and fine
grained; the purest and whitest are sometimes called saccharine limestone. In the
mountains at Carrara it is abundantly found, and contains no fossils; it was once supposed
that this marble was formed before the existence of organic beings, but it has been proved
to be a mere change of the limestone of the oolitic period. The calcareous rocks around
the bay of Spezia contain abundant fossils of the oolitic system, and exhibit a difference of
character in proportion as they have been acted upon more or less by the Trappean and
Plutonic rocks.
Quartz Rock, being divided by natural joints, breaks into rectangular or rhomboidal forms;
its structure is rarely compact and crystalline throughout; it is sometimes mixed with
felspar, and sometimes with mica; it is of a white colour, but when impure it is either
red or yellow.
Talcose Schist consists of talc alone, or quartz and tale; it is found in thin beds, and often
passes into argillaceous schist.
Chlorite Schist is distinguishable by its green colour, and is saponaceous to the touch; its
chief ingredients are chlorite and quartz, sometimes mixed with felspar and hornblende. It
is most frequently found with mica schist, into which it passes.
Hornblende Schist is chiefly composed of felspar and hornblende, containing occasionally
grains of quartz; it is rarely met with in large masses, but is usually associated with
gneiss.
Mica Schist is a crystalline compound of quartz and mica in different proportions; its
texture is foliated or laminar, and it may sometimes be split into coarse plates. When it
634
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
has a granular texture, the quartz grains are united by a crystalline cement of the same
mineral.
Gneiss is composed of quartz, fefspar, mica, and hornblende, the same ingredients which
are found in granite, although the proportions vary. The character in which gneiss most
differs is in its having the mica and hornblende arranged in planes parallel to the stratifica-
tion, so that it may often be cleaved into plates. Its stratification is, however, irregular
and contorted; it usually rests upon granite. The whole of the rocks of the gneiss system,
after being deposited by water, have been acted upon by heat, and acquired a highly crys-
talline character; they are wholly devoid of organic remains, and in Britain contain no dis-
tinct fragments of other rocks, either angular or rounded.
PLUTONIC OR UNSTRATIFIED ROCKS. Granite is a compound crystalline rock, containing
quartz, felspar, and mica; each of these bodies are composed of several elementary sub-
stances; they are intimately joined together, but without any base or cement: they vary
in quantity: felspar usually predominates, and mica is less frequently present; they differ
also in magnitude, alternating from large to small grains. In some varieties the con-
cretions of felspar and quartz are several inches in size, and the mica occurs in plates
upwards of a foot square, whilst in others the grain is so small that the granite appears
nearly compact. The crystals of granite are seldom arranged regularly, as in gneiss, but
are united in a confused crystallisation.
The Graphic Granite is a variety compounded of felspar and quartz, arranged so as to
produce a laminar structure. The felspar crystals seem first to have been formed, and
afterwards the darker-coloured quartz.
Aberdeen Granite sometimes has the mica replaced by hornblende, and there are varieties
composed of hornblende and felspar.
Porphyritic Granite contains large crystals of felspar, held together in a granitic base in
which are specks of mica of an hexagonal form. The uniform character of granite seems
to indicate that, after its elements were mixed together, they were crystallised at the same
time and under the same process.
The minerals which constitute the granitic as well as
the volcanic rocks are silica, alumina, magnesia, lime, soda, potash, and iron, and the
presence of these seven elements in certain proportions is more favourable to the granitic
structure: the fine grain it sometimes assumes is perhaps owing to the manner in which it
has cooled.
Granite composed of quartz two parts, felspar two parts, and mica one part, is repre-
sented in the first colt mn. Porphyritic granite in column the second, and composed of two
parts quartz, three parts felspar, and one part mica. In the third column is shown a binary
granite of three parts felspar and two parts quartz.
Silica
Alumina
Potash
Magnesia
Lime
Oxide of iron
·
Oxide of manganese
Fluoric acid
No. 1.
74.84
No. 2.
No. 3.
73.04
75.1
-
12.80
13.83
10.9
7.48
8.51
9.8
0.99
0.83
0.37
0.44
0.5
1.93
1.73
0.4
0.12
0.10
0.21
0.18
Granite, when reduced to very fine grains, cannot be distinguished from felspar
porphyry.
:
Syenite is a compound of compact or crystallised felspar, united with hornblende and
quartz where the proportions are equal the first column shows the ingredients; when
composed of equal proportions of quartz, felspar, and mica, they are found in the second
column; and when of schorl rock and quartz in equal parts in the third column.
Silica
Alumina
Potash
Lime
Magnesia
Oxide of iron
-
Oxide of manganese
Fluoric acid
No. 1.
No. 2.
69-91
63.96
No. 3.
68.01
10-37
14.32
17.91
4.55
5.94
0.35 soda.
4.86
3.73
0.14
6.26
5.94
2.22
2.69
4.06
6.85
0.07
0.21
0.81
0.50
0.65
1.79
Greenstone is composed also of compact and crystallised felspar, hornblende, or augite :
its texture is sometimes earthy, but when crystalline it resembles syenite, the difference
being only its green colour; its compounds are found in the first column.
Hypersthene rock is of a white or red colour, and the felspar is compact or crystallised;
its compounds are in the second column.
CHAP. I.
635
GEOLOGY.
Diallage or Serpentine may be considered as a hydrated subsilicate of magnesia; its com-.
pounds are in the third column. It should be observed that the felspar and hornblende are
in equal quantities in the greenstone; the felspar and hypersthene in equal parts in
column two; and in the third column the proportions are two-thirds of common felspar
and one-third of diallage.
-
Silica
Alumina
Potash
Lime
Magnesia
Oxide of iron
Oxide of manganese
Fluoric acid
Water
-
No. 1.
54.86
No. 2.
No. 3.
59.14
58.42
15.56
10.59
13.86
6.83
6.83
9.10
7.29
1.13
4.87
9.39
7.00
8.13
4.03
12.62
2.00
0.11
0.75
0.20
1.06
Water. This important element occupies about three-fourths of the whole surface of the
globe, and geological researches having dispelled the many fanciful theories that existed on
this interesting subject, it is generally agreed that within its depths the various matters
and crystallised bodies which now constitute the dry land have been precipitated, from
the disintegration of other lands no longer existing. Of the period of time during which
these changes were going on it would be useless to speculate; the "Medals of Creation
will enable us to class in some measure the great transitions, but they afford us no fixed
dates.
""
At all temperatures above 32° water remains in a liquid state; when cooled below this it
is congealed, and becomes solid, forming prismatic crystals, which lie across each other at
angles of 60° and 120°. During the formation of ice the mass is increased in bulk a ninth
part, and its expansive powers become greater, which, acting mechanically upon rocks or other
earthy matter, breaks them up into smaller masses, and it thus becomes a powerful agent in
the destruction of cliffs, or even mountains, though by slow degrees, and by successive
operations. When the temperature of water is raised to 212º, it passes off into steam,
though it is found in a state of vapour at all temperatures under pressure.
The atmosphere contains a large quantity of water, and it may be called the great
receptacle of that element; all the moisture carried away by evaporation from the ocean
and land enters the atmosphere as vapour, where it floats, until, being driven against higher
land, it is converted into water in the form of rain or snow by condensation, and again
drained off to the ocean.
Water in its ordinary state is frequently found to contain foreign matter, which renders
it totally unfit for domestic uses. Rain water, if collected with care, is the most pure, but
in it there are small quantities of carbonic acid and atmospheric air, as well as appreciable
traces of vegetable and animal matter, which occasion it, when kept for a length of time, to
become putrid.
Water is sometimes designated hard and soft, and these states may be ascertained by
dropping into it a solution of soap dissolved in alcohol, which will produce at once a milky
effect, if it contains any earthy or metallic salts, the presence of which constitutes its
hardness, and throw them down in a flocculent precipitate.
There are five great seas or basins from whence the earth derives the supply of moisture
so necessary for its fertility, and the existence of its various inhabitants.
The Pacific Ocean is of vast extent, and derives its name from the quiet of its waters,
particularly between 10° and 30° of north latitude, where it is almost always calm. This
sea extends 3700 leagues from east to west, and 2700 in the other direction. The coasts
of America and Asia are its boundaries, and in the midst of this world of waters rise up
numerous islands and coral reefs, which have their foundation at immense depths, and
present a perpendicular face from the bottom to their surface.
The Atlantic Ocean, which receives the waters of some of the largest rivers of the world,
is not more than half the area of the Pacific.
The Indian Ocean is in length and breadth about 1500 leagues.
The Arctic Ocean surrounds the north pole, and is a vast circular basin, which, by means
of two channels, connects the Pacific and the Atlantic.
The Antarctic unites the Indian Ocean and the Pacific.
The Mediterranean is 2300 miles in length, and 650 in breadth; the Straits of Gibraltar
uniting it with the Atlantic, and the Dardanelles with the Black Sea, beyond which is the
Sea of Azoph: still further lies the Caspian, which has apparently no communication with
the ocean.
The Baltic Sea is 1200 miles in length, and nearly 100 in breadth, and unites with the
German Ocean.
+
The water in the northern and southern hemispheres differs considerably in quantity · in
the former the proportions between land and water are as 72 to 100, and in the latter only
636
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
as 15 to 100. It is impossible with our present means to define the height at which the
waters stand, or the level of the ocean, from the constant motion to which it is subjected
from winds and currents. Its greatest depth has never been fathomed, and it has rarely
been sounded beyond a mile; 800 or 900 fathoms were reached by the sea-clamms by Cap..
tain Parry in latitude 74° 30′ north, and 78° 1' west longitude.
The specific gravity of sea-water is the same in nearly all latitudes when examined at a
distance, from the discharge of fresh-water poured in by the rivers; its mean is about
1-02757, though, from the impurities it holds in solution, this must necessarily differ; these
consist of muriate of lime, magnesia, potash, and other matters.
The colour of the sea varies, probably from the different animal and vegetable matters
diffused through it in a putrescent state; it is often a blue green, and at the Tropics an
azure blue, in the Mediterranean of a beautiful purple tinge.
The temperature differs according to the latitudes and depths, and seasons of the year:
at the equator it is from 80° to 82°; at the temperate zones it is higher in the winter than
in summer. The decrease of heat is calculated at about one degree for each degree of lati-
tude. The cold increases with the depth in the tropical seas, whilst in higher latitudes the
reverse law is observed.
The prevailing currents have two directions; those which originate in the Tropics go
round the globe in a western direction, and those of the polar seas in the direction of the
equator.
Between thirty degrees north and the same of south latitude, the western current moves
with a velocity of about ten miles a-day; in the Atlantic it takes two directions, one of
which passes to the Cape Verde Islands round the Gulf of Mexico, through the Bahama
channel, and along the coasts of North America; it again alters its course at Newfoundland,
and proceeds in a south-eastern direction to the Canary Islands, and then joins the stream
from whence it took its departure.
The North Atlantic Ocean has a current between 11° and 43°, extending 3800 leagues,
its velocity increasing as its breadth and depth becomes contracted; at the Bahama channel
its breadth is 51 leagues, and its motion is as much as five miles per hour. This current
returns to the Azores at the rate of seven or eight miles per day, where its breadth has
been computed at 160 leagues. The space comprised between these two currents is still
water, and is 140 leagues in breadth. These currents exercise a very powerful effect on the
coasts, causing a continual erosion on those that are bold and rugged, whose detritus falls
down into the ocean, and is carried away to be deposited in less turbulent waters, and
perhaps become the foundation of some future island.
The waves of the sea depend upon the force of the wind, which, by depressing or moving
a body of water, at once alters its equilibrium. When water is placed in a bent tube, and
made to ascend and descend alternately, its motion agrees with that of the pendulum,
which Newton compared to the action of the waves, and found that their velocity was as
the square roots of their breadths, as taken between the tops of their ridges; and he also
found that waves moved through a space equal to their breadth in the same time in which
a pendulum oscillated, whose length was equal to its breadth. Waves, whose breadth are
391 inches, will move over that distance in a second of time, and their motion is progressive;
but an object floating on their surface seems to make little way, and their motion does
not appear to be so considerable.
The tidal currents, which alternately move in opposite directions, exercise a considerable
destroying action on the land, as well as on the formations in progress at the bottom of the
ocean. The motion of the tides and currents is produced by different means; the first is from
the influence of the sun and moon, and their height and velocity depend upon the coasts within
which they are enclosed. In narrow seas they rise higher, but when the waters meet with
no obstruction and can freely expand, they do not exhibit so much elevation. In the
Bristol Channel, where the passage is narrow, the tide runs at the rate of 14 miles an hour.
In the ocean are permanent currents from 50 to 250 miles in breadth, which constantly
flow in the same direction, in consequence of the influence of particular winds, or from the
expansion and contraction that the waters of the sea are subjected to when acted upon by
heat or cold, which change the condition of their temperature.
The currents towards the Tropics from the poles are produced by the increase of specific
gravity of the water as it becomes colder, which occasions it to sink, and thus allows that
which is warmer, and consequently lighter, to float at the surface. Thus rising and de-
scending currents are produced, the lower parts of the ocean in high latitudes become of
higher specific gravity than those at the same depth between the Tropics; the cold water
rushing to occupy the lower place of that more highly rarified, which, in its turn, moves
forward in the opposite direction.
The tides are not affected entirely by the moon's influence; the sun has considerable
power, which has been estimated at about one-fourth of the whole. When the sun and
moon are in conjunction or opposition, and exert their combined influence in elevating the
waters of the ocean in the same direction, they rise to the height called a spring-tide; this
CHAP. I.
637
GEOLOGY.
effect is shown in the diagram, where the sun, S, and the moon, M, are supposed to be drawing
the waters of the earth, A B C D. The moon's action alone is shown by the spheroid
ch gf, and the combined effect of both sun and moon by the spheroid E F G H. When
the moon is in quadrature with the sun, the action of the one diminishes the effect of the
་
h
HD
20
A
C
M
H
BF
k D
M


E
A
G
g
S
G
Fig. 581.
Fig. 582.
other, as shown in the figure e f g h; the moon would have produced the effect, but as the
sun's attraction depresses the water at e and g, and raises it at ƒ and h, the combined effect
of the two luminaries will be that shown at E F G H, and such an effect is called a
neap-tide.
The highest spring-tide does not occur immediately after the new or full moon, but
about the third or fourth tide afterwards, and the lowest neap about the same time after
the quarters.
The magnitude of a tide is the difference between the highest flood and the lowest ebb
during the same day.
The high and low state of the tide occur twice during a lunar day, or at the rate of
12 hours 25 minutes and 14 seconds. The tide is, however, 9 or 10 minutes longer ebbing
than flowing, and the higher it is at the ebb, the lower it generally sinks on the same
day.
The atmosphere is subject to elevations and depressions like those of the sea, and
cause variations that affect the winds and weather; but their influence cannot be very great,
for the addition of a few feet to the height of the atmosphere would be productive of little
change. The height of an aerial tide must correspond with the height of the observable
tides of the ocean, and the alteration of atmospheric pressure may be measured by the dif
ference between the actual form and the spheroid of equilibrium. Near the equator there
is a periodical variation in the state of the atmosphere far greater than in our climate, but
which is not caused by the action of the moon, as it happens regularly at the same hour
of both day and night. The atmosphere is affected by a current from east to west, like
that of the sea, which is attributed to the attraction of both sun and moon. Since Newton
explained his theory of the tides, and the effects of the laws of gravitation, the theory has
been much improved by the labours of later mathematicians: but no problems are
more difficult to solve than those which belongs to such investigations; and the causes and
circumstances upon which they are dependent are so remote, that it is more than probable
they will remain for a length of time unknown to us; and it is absolutely necessary, before
we can arrive at a conclusion, that we should have ascertained the depth of the sea
throughout the globe.
The great wave which follows the moon, or the tide, is an undulation in which there is not
much progressive motion, except where it approaches the shore; and the usual time of high
water is about two or three hours after the moon is on the meridian.
Where the passage of this wave is confined, the tides are not the result immediately of
the sun and moon; the narrowing the mass of water elevates their level considerably; this
is very evident where the waters of the Atlantic are opposed by the coast of Ireland, and
divided into three different branches, one passing up the British Channel, another west of
Ireland and Scotland, and the third into the Irish Channel. The first of these moves at a
rate of 50 miles an hour, and passes through the Dover Straits, so as to reach the Nore at
midnight during spring tides.
The second branch is more rapid, reaching the north of Ireland six hours before; three
hours afterwards it has arrived at the Orkney Islands, and three hours more, or at twelve
o'clock, we find the same wave, extending eastward to the Naze of Norway; twelve hours
afterwards, it has progressed through the German Ocean, and arrived at the Nore, meeting
the morning tide, that left the mouth of the channel only eight hours previously, so that
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THEORY AND PRACTICE OF ENGINEERING.
these two tides make the circuit of Britain in twenty-eight hours, during which period the
primitive tide has made the circuit of the globe, and nearly 45° in addition.
High water on the Thames at London
bridge takes place at the moment when it
is low water at the mouth of the river, the
surface of the water at London being 40 feet
above its level at the German Ocean at the
same time.
Large rivers in which the tides occur do
not have a regular descent of surface towards
the sea, but a varied outline produced by con-
tinual motion.
The Bore, which is an accumulation of water
in large rivers at the time of flood, arises from
the narrowness of the outlet preventing the
entire discharge of the water before the
return of the next tide, which it meets as it
flows in an opposite direction, and conse-
quently causes an elevation of water above
its natural level, and which is often extremely
dangerous to small craft and to navigation.
The wave so formed rolls with great violence
up the river, pressed forwards by the accu-
mulating force of the tide, until it is lost or
dies away.
In the river Severn the bore
often rises 10 feet, and in the Amazon it is
said to mount upwards of 100.
A variety of instruments are made use of
in our harbours to measure the tides; that
which is found to answer the best is formed
of a pole, 24 feet in length, and 6 inches in
diameter, supported upon legs firmly lashed
together with ropes, ballasted with pig-iron
laid over the bottom. On the pole is placed
a perpendicular graduated scale, made of deal
or other wood, and the whole is kept steady
by several guy ropes attached to the top.
Measuring rods, made of inch deal, with
a cork float at the bottom, in the form of a
cube of 3 inches, work in boxes attached to
the pole: these rods, graduated in feet and
inches, pass through staples which steady
them; and as the water is admitted into the
boxes through a hole in the bottom, the rods
rise with it, indicating to what height in a
given time the tide rises or falls.

Origin of Rivers. The condensation of
vapour on the tops of the highest mountains is
the origin of some of the largest rivers, and
the source of all is dependent upon meteorolo-
gical causes. That water which falls from the
clouds and enters some depth into the earth
again issues forth as a spring, and, gaining
strength in its course by the addition of other
streamlets, continues to flow on till it reaches
the ocean, after being sometimes diverted in
its course by the various obstacles that are
opposed to it. On tracing the descent of a
river, we perceive that the gradation from
masses of rock to grains of fine sand is almost
imperceptible. At its commencement the water trickles drop by drop from the ledges of
the rock, whose cold and rugged sides have condensed the vapour brought from the ocean;
these drops unite, and run down the acclivities in small veins, which in their course receive
others, until by accumulation they attain the character of a river. The quantity of rain
that falls must affect the state of a river. This varies in different districts; in the neigh-
bourhood of Paris it annually amounts to 18 or 20 inches; at Milan, in the north of Italy,
to 40, and in many mountainous districts to 90 or 100 inches; the summits of the Alps
Fig. 583.
TIDE GAUGE.
CHAP. I.
639
GEOLOGY.
and Apennines, and all mountainous regions, are usually covered with snow, so that there
is a perpetual humidity in the loftier regions of the earth, until we arrive at that station
where, for the greatest part of the year, the whole is congealed by extreme cold.
The Seine has in the summer not more than 3 feet depth of water, though in time of
high floods it has been known to rise nearly 23 feet. The Po, in Italy, during floods does
not increase in breadth, but quadruples its height, so that the quantity of water poured
down in one day is equal to eight times that which flows on ordinary occasions.
river Thames drains an area of a little more than 5000 square miles, and taking the average
depth of rain that falls in a year at 24 inches, it has been computed that 239,765,120,000
cubic feet of water annually pass down this great natural drainage into the ocean, to be
again returned by evaporation.
The
Were it not for floods, the beds of rivers and their banks would undergo little alteration:
when, however, they occur, as they do in many districts periodically, the large stones are
moved forward, and rounded by attrition, whilst their debris, and the fine gravels and sands
whose specific gravity varies little from that of the water, are carried along by the force
of the current, and are not deposited till they meet with still water, or are taken out to sea,
where the motion of the fresh water is opposed or staid altogether.
Beds of rivers are constantly raised by the stones, gravel and sand brought down at the
time of flood: this is evident, when we take into consideration the enormous quantities of
ballast dredged from our rivers, in order to keep their channels open for the purposes of
navigation. It thus becomes necessary to elevate the banks, which is often continued
beyond the limits that are beneficial to the drainage of the neighbouring land.
When a
bar or shoal is thrown up, if not cleared away, it acts like a dam or artificial wall, pre-
venting first the free passage of the heavy stones, which are consequently deposited until
the bed is raised to the level of the impediment. In many instances where the foundations
of buildings have been laid considerably above the level of the water, we find them now
sunk one or more stories below it, and the whole drainage of a city destroyed by either
natural impediments in the slope of rivers, or some artificial contrivance to benefit
machinery constructed on its banks. Throughout England the proprietors of mills have
been suffered to increase their fall, not by dredging the bed of the tail-water, but by raising
the banks through which the water was conducted to the sill; thus destroying the use
of a river as the natural drain of a country, by elevating its bed above the ordinary level
of that part of the valley where the mill is situated. Wherever a head of water is created
in a valley, it does an infinite mischief in penning back, by its weight, the springs which
endeavour to find a vent at the foot of the hills, and which the river, when left to itself,
would carry off.
Mill-dams, when thrown across a stream, occasion a deposition of all that is brought down,
and thus elevate the upper parts of the beds, as well as affect all the tributary streams that are
within its influence. When a succession of drains occur, they materially change the natural
slope of the bed; for whatever the water tumbles over occasions it to acquire an increased
velocity, and deepens the channel for some distance, pushing as it were the bed forwards,
so that if the section of such a stream were taken, we should find ascending concavities
rising to the level of each successive dam instead of a regular slope. When the velocity of
a stream depends upon its fall, it is materially altered by the introduction of a dam; and
when the velocity is diminished the natural slopes in the bed are all changed, and new
depositions are the consequence. In muddy streams, where no impediment occurs in the
way, or any dam offers itself to oppose the force of the floods, the whole trunk becomes
scoured out, and the natural slope is maintained. Where the slope of the bed of a river
varies, there we always have a difference in the velocity of the running waters.
By aug-
menting the force of a stream, any deposits may be pushed onwards; and this may be done
by uniting several others with it, thus increasing its height, or by making the course
shorter through which it flows, which has the effect of distributing its fall over a less
distance. Gravels will not always move forwards with the ordinary power that is exerted
upon them; they will generally accumulate to such a degree as to drive the river from its
channel, and find some new course. This is not the case with rivers flowing over a bed
of sand, where the current is seldom changed from its original direction. When a river
through a gravel is shortened, by making it flow in a straighter direction, the bed in the
upper part is lowered, and the portions pushed forward elevate the bed below the point
where the cut terminated, which will be the case with every successive portion, until in
the course of time it ceases to admit the vessels or boats, which formerly navigated it, to
the serious injury of the surrounding neighbourhood; such are the too frequent results, when
improvements, so called, are suggested or undertaken by persons ignorant of the elements
which they have to manage.
In straight rivers we find the gravel more easily pushed forward than in those which
have a meandering course, and it is first deposited at the bottom, at the greatest distance,
where it gradually raises the lower parts, and then those higher up the stream: this in time
requires the embankments to be elevated, to prevent an overflow when floods occur.
640
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THEORY AND PRACTICE OF ENGINEERING.
Rivers that carry gravels should never have their course shortened without well considering
all the consequences likely to ensue. When it is required to alter the course of a river, to
shorten it, or to unite other streams with it, the new bed should always be made to pass
below the utmost limits of the gravel. In all cases let nature be the guide; she often
brings together, amidst rocks and mountain precipices, various streams, but seldom or never
whilst they bear down gravel does she unite them in the plains with those which carry
mud or sand. Wherever any cut has been made to shorten a river flowing over gravel,
its success has been uncertain; and when it is attempted, care should always be taken that
the fall of the new channel is not less than that of the old one. Streams may be united
without much danger if they all carry the same substances, and there is sufficient fall and
velocity to bear them to their utmost limits; the success of the undertaking may then be
relied upon.
The velocity with which water moves arises from the pressure of the upper parts, and is
in proportion to the number of pressing particles, or as the height. These velocities are
computed to be as the square roots of their heights, but it is not possible, for any practical
purposes, to make use of the solutions of such hydraulic problems; the difficulties seem
to increase with the several conditions of the examples, and the better way for the engineer
is to resort to direct experiment. The velocity of water has but one law, and is always pro-
portional to the square root of the height; this law is the same which belongs to all falling
bodies, passing in a second of time through a given space. If a parabola be formed with
its abscissa made to represent the space the falling body passes in a second of time, and the
corresponding semi-ordinate to represent double that space, or what it would fall in two
seconds; then all the other semi-ordinates will express velocities corresponding with the
height of their respective abscissas; and by dividing the square of the semi-ordinate by its
abscissa, the parameter of the parabola will be obtained.
To ascertain the velocity at the surface of a river, it is only necessary to measure the
space through which a floating body moves in any given time, or to notice the float-boards
of a wheel, and count the number of times they strike the surface of the stream, and then
count its revolutions in a given time, or to measure with a quadrant how far a weight
suspended from its centre is diverted from the perpendicular by the force of the stream ;
it being ascertained that the tangents of the elevations of pendulums ought to be pro-
portional to the stroke and force of the stream, viz. to the velocity and the number of par-
ticles which strike it in a given time, or, in other words, to the square of the velocity.
After this has been done, ascertain what height will correspond with this velocity, or from
what height a body must fall to acquire a velocity equal to that with which the surface
of the river is moving, and then add this height to the whole height of the section, to obtain
the effective height, with which the actual velocity agrees.
The space run through in a second by a floating body at the surface, divided by the
same parameter, will give the height due to the velocity of the surface, which, added to the
actual height of the river, will give the whole effective or equivalent height.
The square-root of the product of the equivalent height by the parameter will give the
velocity at the bottom of the section.
Two-thirds of the product of the velocity at the bottom, by the whole equivalent height,
minus two-thirds of the product of the velocity at the surface, by the height added to the
actual height, will give the mean velocity.
Finally the product of the mean velocity by the actual breadth and the actual height
will give the quantity of water that passes in one second through the rectangular sec-
tion.
Where the section is a trapezium it is necessary to calculate the quantity of water which
passes through all the perpendiculars of the triangle formed about the greatest inscribed
rectangle, but the method of calculation is the same.
When the height of the water is stated, as well as the figure or form of the opening
described through which it flows, it will be easy to ascertain the quantity given out in any
certain time.
Supposing the aperture to be square, one side of which touches the surface of the water
at rest in a cistern or reservoir, or a circle inscribed in the square, or a triangle with the
vertex upwards, or downwards, or with one having the same height and vertex, but with
only half its base; then the quantity of water flowing through these apertures in equal
times will be as 5, 4, 3, 2, and 1, and it has been found that through a circular hole 1 inch
in diameter, immersed below the surface of the water, there will flow out 13½ pints in 1
minute of time.
The velocity of a river depends on its fall, or on the pressure of its upper parts: all the
particles of which it is composed in descending are moved forwards by the ordinary laws.
The acceleration from pressure puts them in motion, and the slope of the bed contributes
chiefly to their progressive advancement, by the pressure of the higher parts of the stream
and its current in the plains, where the slope of its bed is trifling, and the body of water is
materially increased.
СНАР. І.
641
GEOLOGY.
Rivers near their discharge often obtain a much greater velocity than they had at their
commencement, from the increase of their body of water.
The slopes or beds of rivers differ materially in their inclination, and we often find
them cutting deep chasms through lofty mountains, or taking their course through ravines
or fissures caused by some convulsive movement of the earth itself. Where the river
passes over or through a district of alkaline or calcareous rocks, which are soluble in water,
the carbonic acid of the water dissolves them, and wears away by degrees these apparently
hard and indestructible substances, often acting at the base of a hill or mountain, under-
mining them, and masses fall into the torrent, to be carried lower down the next flood.
When two rivers fall into one channel, the height of the water does not increase in pro-
portion to the body by which it is augmented; so that when a considerable quantity of
water is added to a stream, there is only an increase of velocity. If the height of the
sections of twenty or more tributary streams were added to that of the trunk they fall
into, this fact would be made evident. When the Mayne, which is more than half the
size of the Rhine, unites with that stream, there is no apparent increase, and where divided
into two or more channels, its height is not lowered. The Inn falls into the Danube, and
both rivers, nearly equal in size, then pursue one course, without becoming either broader
or deeper.
The Po has no apparent increase after it has received the Secchio and Panaro; and the
Tiber receiving the Teverone is neither deepened nor widened, and so it is with other rivers.
Pliny, in one of his letters to the emperor Trajan, observes that the canal cut by Nerva to
draw off the superfluous waters of the Tiber, did not in any degree prevent the inundations
of which it was the cause. The two sections above and below this canal, called the
Fiumicino, are nearly of the same breadth; the depth in the upper is 7 feet 4 inches, and
the whole section is a rectangle; the depth of the lower is 6 feet 8 inches on one side, and
13 on the other; but when the areas of the two sections are accurately computed, they
are found to be similar.
Rivers which carry sands in the lower parts of their beds have less slope than at the
upper; their declivity diminishes in proportion to the distance they have run from their
sources; this is caused by the diminution of the size of the particles as they progress, which
consequently require less force to push them forward, and are borne to the very ex-
tremity before they are deposited; where these light substances are floated, less declivity
is needed to keep the bed of the stream clear of obstruction. The body of water being
the same, the slope of the bottom may be said to diminish in proportion as the matter
brought down becomes smaller, and is more easily moved onwards on this account.
Rivers which are increased by their union with others that are less require less fall than
before; for if the slopes of all the small streams which unite to form one be measured, it
will be found that their declivity is much greater before than after their junction, so that
the greater the ordinary body of water in a river, the less will be the slope of its bed.
Whenever the freshes of a tributary stream fall into another, the recipient flows back,
depositing its sediment above the mouth, as well as below it, if the assistance which the
former receives from the low waters is insufficient to compensate for the difference of fall
which the tributary encounters in passing from its own into the common bed.
It appears to be a common law that the greater the quantity of water a river carries, the
less will be its fall, and the greater the force of the stream, the less will be the slope of its
bed, and the slope of the bottom of rivers diminishes in proportion, as the body of water is
increased.
Tacitus relates in his Annals, that when a proposition was made to the Roman senate to
divert into other channels all the rivers which flowed into the Tiber, the opinion of Piso
was followed; he advised that no alteration should be made, since every one might see that
nature knew how to provide for her wants much better than could be done by art; she
assigned to rivers their sources, boundaries, and limits the most suitable. Nature, however,
exhibits at times singular phenomena, where rivers discharge themselves into the sea, by
spreading their waters over its surface. At a considerable distance from the land, they
often run over a bottom having a very small declivity, but which at the mouth of the river
is bent downwards, forming a deep concavity; this is the case with some of the largest
rivers, where the tides are apparent at a considerable distance up them.
The sea-water during the time of flood-tide, entering the river, and at ebb returning,
helps to produce this effect, and to render the section of the bed a concave line, by sweeping
away
all the deposits lodged where this action takes place; so that shoals are not formed so
long as a river can keep its mouth open on a flat shore, the particles brought down being
deposited either above or below the spot where they discharge themselves.
Deltas at the mouth of rivers arise from the deposit of the detritus they carry in
their course; this in time rises to the surface, forms a bar, turning the river into another
channel. On a flat coast there is usually the most deposit, and sometimes what is brought
down is carried into a current in the ocean, and afterwards deposited on some other coast,
Tt
642
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
or formed into islands elsewhere; the quantity of earthy matter depends upon the nature
of the river that discharges itself.
The Rhone, which passes through the Lake of Geneva, there deposits much of the matter
it brings down from the glaciers of Mont Blanc, but it acquires in its after-course a con-
siderable accession from the tributary streams of the Alps of Dauphiny. This river pours
itself into the Mediterranean, which it discolours for a distance of 7 miles from its mouth,
depositing a fine sediment in horizontal strata along the whole shore over which its
water spreads: since the time this coast was under the dominion of the Romans its
harbours have been silted up, and are now a league from the shore.
The Po has poured out so much sediment, received from the Alps and Pyrenees, that
where it is discharged in the sea not under the influence of a tide, it has added to the coast,
for a length of 100 miles, a breadth of land in some places as much as 20 miles. Adria, a
town of importance, and which gave the name to the sea that washed its walls, is now 20
miles within land; this increase of land has been more rapid as the embankments of the
various rivers have been elevated.
The Nile, which discharges 250 times as much water as the Thames, deposits its detritus
in its course over the fertile lands of Egypt, which it irrigates; therefore its delta is small
in comparison with that formed by other large rivers. The land of Egypt is calculated to
have been raised above 6 feet in height since the commencement of the Christian æra; and
the earth deposited is about half argillaceous, a fourth carbonate of lime, and the remainder
carbonate of magnesia and oxide of iron. The delta of the Nile at its termination has a
depth of sea of 2000 feet or more. The seven mouths of this noble river are no longer
open; five of them are silted up, as is the Lake Maræotis.
The Mississippi empties itself into the Gulf of Mexico after a course of 3000 miles, and
often brings down with it whole forests, and large quantities of alluvial matter.
The Ganges and Brahmapoutra, which bring the water from the Himalaya mountains, are
discharged into the Bay of Bengal; the delta at the mouth reaches 200 miles along the
coast, and commences 220 miles from the sea. The tide extends its influence to the head
of this delta when the river is low, and the sea for a distance of 60 miles in times of floods
is discoloured by the alluvial matter, which chiefly consists of sand and silt borne by
the tidal current to a distance of 400 miles. In one direction a tract of land 40 miles
square and 114 miles in depth has been washed away in the course of a few years;
and it has been stated, on the authority of Major Rennel, that the deposits forming the
Sunderbunds equal in extent the area of the whole of Wales.
The Delta of the Niger stretches 300 miles along the coast, and extends 170 miles into the
interior.
Quantity of Water discharged by Rivers. This is found to be the annual produce of the rain
that falls over the several districts, in which they act as a natural drain, after deducting
about for filtration and evaporation, and the total expenditure of a river may be deduced
by the products of its mean section and mean velocity. Buffon estimated the area of all
the land to be equal to 63,728,938 square miles, and the mean quantity of rain to be equal
to 36 inches; if then we calculate the quantity carried down by such a river as the Po, we
shall find that it would be necessary to have 1400 such rivers; the Po having a mean
breadth of 1000 feet, and its waters moving with a velocity of 4 miles an hour.
The annual discharge of the Rhine at Bayle is estimated at 1,046,763,676,000 cubic feet.
The Tay at Perth, in Scotland, 100,000,000,000 cubic feet. The Thames, which drains
upwards of 5000 square miles, according to Dr. Halley's observation made at Kingston
Bridge, 239,765,120,000 cubic feet per annum; but it is doubted whether any of these
calculations are to be depended upon.
Sand Banks. The Dogger Bank is 350 miles in length, and that in the Firth of Forth
110 miles, and their average height is about 80 feet. The area of these two banks is about
of the German Ocean, and almost equal in extent to of England and Scotland; they
are formed of sand mixed with broken shells and corals, and have been thrown up by the
tidal current.
Downs or Dunes are formed on a low coast, where the bottom is composed of sand: this
being driven by the waves towards the shore is left dry on every reflux of the tide; the
winds which blow from the sea then carry them inland, and form sandy flats and hills.
These sometimes occur at the mouths of rivers, and such a sand flood, as it is termed,
effectually stops the passage of the water, driving it into some new channel.
The Beach may be divided into three portions: viz. that comprised between high water
of spring and neap tides; that between high water at neaps and the extreme low water of
spring tides; and the expanse of sand and gravel, of greater or less extent in proportion to
the flatness or steepness of the shore, never laid dry, but covered at the lowest ebb by
shallow water. These are termed high water, low water, and littoral sea beaches.
first is usually composed of shingle or round pebbles, thrown up more or less steep. The
second or low water beach usually presents a gently sloping surface, strewed with pebbles
or patches of sand.
The
CHAP. II.
645
COMPOSITION AND USE OF MINERALS.
CHAP. II.
OF THE COMPOSITION AND USE OF MINERALS.
THE Constituents of minerals are resolved into fifty-four elementary bodies; and these are
either gaseous, fluid, or in a solid state.
In the gaseous bodies the particles that compose them have no cohesion; they yield
readily to pressure, and when that is removed, they expand again into their original volume.
The fluids are not elastic, and do not yield to ordinary pressure.
The solids may be changed into fluids, and fluids into gaseous bodies by the agency of
heat.
Gazzolytes.
Oxygen.
Hydrogen.
Nitrogen.
Halogens.
Chlorine.
Iodine.
Bromine.
Fluorine.
Metalloids.
Sulphur.
Selenium.
Phosphorus.
Metallic Bases of the Earths.
Aluminum.
Silicum.
Yttrium.
Glucinum.
Zirconium.
Thorium.
Common Metals whose Oxides cannot be
reduced by heat alone.
Iron.
Lead.
Copper.
Zinc.
Antimony.
Tin.
Bismuth.
Manganese.
Chromium.
Carbon.
Boron.
Metallic Bases of the Alkalies.
Potassium.
Sodium.
Lithium.
Metallic Bases of the Alkaline Earths.
Barium.
Strontium.
Calcium.
Magnesium.
Cobalt.
Arsenic.
Nickel.
Common Metals whose Oxides are reduced
by heat alone.
Mercury.
Silver.
Gold.
Platinum.
Palladium.
These bodies all combine with each other with reference to their weights, and the
absolute quantity of matter they contain; this constitutes the basis of the Atomic theory,
proposed by the late Dr. Dalton, who established that great and important principle,
which teaches that all bodies combine in definite proportions by weight, and never other-
wise. Water, for instance, is composed of one volume of oxygen united with two volumes
of hydrogen, the relative weights of which are as 1 to 8; the two volumes of hydrogen
being considered as one atom or unity. All bodies which assume the gaseous form may
have their atomic weight easily determined; carbon, for instance, which is incapable of
assuming the gaseous form, will combine with oxygen and form carbonic acid gas, one
volume of which weighs twenty-two times as much as the two volumes of hydrogen which
we take as a standard. Twenty-two parts of carbonic acid contain sixteen of oxygen,
therefore the other six must be carbon, which is the number or proportion in which this
body combines with others Carbonate of lime contains twenty-two parts of carbonic
acid, and twenty-eight parts of lime, therefore the latter number is its atomic weight.
Atomic weights for almost all the bodies are now established, as is the relation in which
they combine with each other; one of hydrogen combines with six of carbon, and with
eight of oxygen, or, as has been stated, six of carbon combine with eight of oxygen. The
equivalent or number for water, for instance, is usually stated thus, 9-oxygen 8+ hydro-
Sliding scales are made use of by chemists for aiding the calculations with
respect to different combinations, and it must always be borne in mind, that these
gen 1.
TT 2
€44
Book II
THEORY AND PRACTICE OF ENGINEERING.
are either exactly double, triple, or some multiple by a whole number of the smallest
proportion in which the body enters into combination with the other substance. Fourteen
of nitrogen can only combine with 8, 16, 24, 32, or 40 of oxygen, but with no inter-
mediate proportion.
13
Oxygen is an invisible and permanently elastic gas, without taste, colour, or smell; its
specific gravity, as compared with air, is 1.111 to 1·000; compared with hydrogen as 16 to 1,
hydrogen being unity. At mean temperature and pressure 100 cubic inches of oxygen weigh
34.60 grains. When water is freed from air 100 cubic inches will absorb 3.5 cubic inches
of oxygen; it forms of the weight of the atmosphere, & of the weight of water, and is so
abundant a principle in the mineral kingdom, that in silex it forms 50 per cent., in alumina
47, in lime 28, in magnesia 40, in potash 17, and in soda 25 per cent.; in the sulphate
and carbonates of lime, the two most abundant acids, it is the essential ingredient. Oxygen
does not occur in nature except in combination with other bodies, and it is then said that
the body so containing it is oxidised, or is in a state of oxidation; its combining number
is 8.
Hydrogen is the lightest form of matter known, its specific gravity, as compared with
oxygen, being as 1 to 16; 100 cubic inches of pure hydrogen gas at a mean temperature
and pressure weigh 2.1318 grains, and as compared with atmospheric air its specific gravity
is as '0694 to 1. It does not form a very important element in the composition of rocks,
though it occurs in the animal and vegetable kingdoms in abundance. It is one of the
elements of water, constituting about 11 per cent. of that compound, or of the water of the
globe. Pure water, when exposed to the action of voltaic electricity, is resolved into two
volumes of hydrogen, disengaged at the negative pole, and one volume of oxygen at the
positive. Water therefore, consisting of one volume of hydrogen, and half a volume of
oxygen, their relative weights are as 1 to 8.
Equivalent.
Volumes.
Hydrogen
Oxygen -
1
1
11.1
1.0
1
8
88.9
0.5
1
9
100.0
Pure water, at the temperature of 62°, has its specific gravity equal to 1·000; a cubic
inch weighs 252.5 grains, and a cubic foot 998.217 ounces avoirdupois, so that the specific
gravity of any substance in reference to water is nearly the absolute weight of 1 cubic foot
of such substance in ounces avoirdupois.
Water is about 815 times the weight of atmospheric air, and at 32º it freezes, ice being
of the specific gravity of 0·94. It boils at 212°, when the barometer is at 30°: 100 cubic
inches of steam weigh 19,062 grains, the specific gravity of steam being 6249.
At a mean
pressure, and at a temperature of 212°, the bulk of steam is 1700 times greater than that
of water.
Pure hydrogen condenses half its bulk of oxygen when detonated by the electric spark,
and is much employed by the chemist as a deoxidating agent; it refracts light powerfully,
and is an imperfect conductor of electricity.
Water has the power of absorbing many of the gases, 500 cubic inches absorbing of
Sulphuretted hydrogen
Carbonic oxide
Nitrous do.
Olefiant gas
Oxygen
Hydrogen
Nitrogen
-
Volumes.
- 233
-
- 100
- 76
-
12.5
3.7
1.56
1.56
Water absorbs oxygen and nitrogen from the air, condensing more of the former than the
latter, and air at the surface of the earth is always found to contain water, but is scarcely
ever in a pure state.
Peroxide of Hydrogen, or oxygenated water, is liquid, transparent, and inodorous; its
specific gravity is 1-45, and it is decomposed by all metals except iron, tin, antimony, and
tellurium. Silver and oxide of silver decompose it as well as platinum and gold. Lead
and mercury more slowly disengage the oxygen.
Hydrogen
Oxygen -
-
·
1
2
Equivalent.
1
Volume.
5.9
1
16
94.1
1
1
17
100.0
Nitrogen or Azote is a colourless gas, without either taste or smell, incapable of sup-
porting combustion or respiration. It has no action upon vegetable colours, or upon
CHAP. II.
645
COMPOSITION AND USE OF MINERALS.
lime water, nor does water absorb it, except after it has been boiled for a considerable time.
Nitrogen forms four-fifths, by bulk, of atmospheric air, and is found in coal, in the nitrates,
and abounds in the materials of the animal kingdom. Its specific gravity, as compared with
air, is 0.976. At a mean temperature and pressure, 100 cubic inches weigh 30 16 grains.
Its specific gravity, in reference to hydrogen, is 14 to 1.
Nitrous Oxide or Protoxide of Nitrogen, gaseous, colourless, with a sweet taste and slight
odour, supports combustion brilliantly, and acts powerfully on the animal economy when
inhaled. When agitated with water it is absorbed, taking up an equal bulk, and when
heated it is evolved unchanged.
At a pressure of fifty atmospheres, this gas has been obtained in a liquid form.
Nitrogen
Oxygen
1
1
1
14
8
22
63.3
36.7
100.0
1.0
0.5
}
1.0
30.16
17.05
47.21
By passing it through a bright red heat in a porcelain tube, it is resolved into oxygen,
nitrogen, and nitrous acid.
Nitric Oxide or Deutoxide of Nitrogen is a colourless, uncondensible gas, and cannot be
respired. When mixed with air, it combines with the oxygen, producing red fumes of
nitrous acid. Its specific gravity, compared with hydrogen, is 15 to 1. 100 cubic inches
weigh 32.137 grains, and compared with air, its specific gravity is as 1.038 to 1000.
is permanent over water. It is fatal to animals when breathed.
It
Nitrogen
Oxygen
·
1
2
14
16
1
30
46.67
53.33
1
1
100.00
2
Hyponitrous Acid forms distinct salts by combining with the salifiable bases. It is
liquid, green and very volatile.
Nitrogen
Oxygen
1
14
36.8
1.0
3
24
63.2
1.5
4
38
100.0
Nitrous Acid is used as an oxidating agent, particularly when mixed with nitric acid.
Its specific gravity, as compared with hydrogen, is as 46 to 1; to air 3·19 to 1, and 100 cubic
inches weigh 98.8 grains. When liquid it is of an orange colour, specific gravity 1·452,
and boils at 82°, and a red heat decomposes it.
When nitrous acid is poured into water, it is quickly decomposed, nitric oxide is dis-
engaged, and the fluid assumes a greenish colour.
Nitrogen
Oxygen
·
1
14
4
32
1
46
30.4
1
69.6
2
100.0
1
Nitrous acid does not unite with bases, but forms with them hyponitrites and nitrates.
Nitric Acid is transparent and colourless when pure, and is decomposed when passed in
vapour through a red-hot tube. Its specific gravity varies between 14 and 1·5, and it
always contains water.
Nitrogen
Oxygen
1
14
25.9
5
40
74.1
1
54
100.0
The salts called Nitrates are compounds of the anhydrous acid and a salifiable base;
they are soluble in water, and crystallisable. The liquid nitric acid in its utmost state of
concentration consists of
Anhydrous nitric acid 1
Water
54
75
2
18
25
1
72
100
Nitric Acid is used to oxydise and dissolve the metals, and to separate them from those
which are not acted upon by it, as gold and platinum.
TT 3
646
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Aqua regia is a mixture of nitric and muriatic acids, which has the power of dissolving
gold and platinum. Nitrogen and hydrogen combine (N +3 H) to form ammonia; and
this gaseous compound is obtained from a mixture of quicklime and muriate of ammonia
the specific gravity of ammonia, as compared with hydrogen, is as 8-5 to 1; with air as
590 to 1, and 100 cubical inches weigh about 18 grains: water at a temperature of 50°
will take up 670 times its volume of ammonia.
Ammonia and muriatic acid constitute the sal ammonia of commerce, or the muriate of
ammonia. It is constituted of
Ammonia
Muriatic acid
-
-
1
17
1
37
54
31.5
68.5
100.0
1
Muriate of ammonia has been found serviceable in removing the incrustations formed at
the bottom of boilers, which chiefly consist of carbonate of lime. A small quantity of
sal ammoniac added to water in a boiler dissolves the carbonate formed, and converts it
into a soluble muriate, without affecting the boiler.
Sal ammoniac is made use of in tinning, to prevent the oxidation of the surface of the
copper or other metal on which it is laid.
Atmospheric air, or the atmosphere, comprising all those gaseous matters which sur-
round the earth, is essentially composed of oxygen and azote, in the proportions of nearly
one of the former to four of the latter; to which is added carbonic acid gas, and water
in the state of vapour; or the quantity of each may, under ordinary circumstances, be
stated thus,
Oxygen
Nitrogen or Azote
Aqueous vapour
Carbonic acid
210
775
14.2
.8
1000.0
The pressure or weight of the atmosphere upon all parts of the surface of the earth is
estimated at 15 pounds upon a square inch, which is equal to a column of mercury of the same
area, 30 inches high; this pressure decreases as we ascend above the earth in regular geo-
metrical progression; for at three miles the density is only equal to a column of mercury,
15 inches high, and at 6 only 7 inches; at 9 miles of elevation 33, and at 15 miles only
1 inch. It has been consequently assumed that the atmosphere does not extend to a height
of more than 45 miles, and that the greatest portion of it is comprised within 15 miles.
Chlorine, at common temperatures and pressures, is a gaseous fluid, but may be con-
densed into a liquid form at a temperature of 60°, and a pressure of four atmospheres.
Chlorine gas is of a greenish yellow colour; its specific gravity, as compared with air, is
2.47, and 100 cubic inches at mean temperature weigh 76.59 grains. At a temperature
of 60°, water dissolves two volumes of chlorine, and the solution has a specific gravity of
1.008. Chlorine has never been found pure, but in common and rock salt, it is combined
with sodium in the proportion of 60 per cent. ; it has a violent action on some of the metals,
which, when thrown into it in a state of powder, are burnt, and enter into combination
with it.
Chlorine destroys most animal and vegetable colouring matters, as well as odorous
effluvia, by decomposing them, removing the hydrogen present, or by combining with the
oxygen. Water absorbs about 1½ times its volume of chlorine.
Protoxide of Chlorine (hypochlorous acid) is pernicious to respiration; water dissolves ten
volumes of this gas, which is of deep yellow colour; it destroys most vegetable colours, pre-
viously reddening the blues. The aqueous solution is rapidly decomposed by iron filings,
but the other metals have little or no action upon it. Silver, however, combines with the
chlorine, evolving at the same time a portion of its oxygen. Bromine, iodine, sulphur,
phosphorus, selenium, and arsenic, are converted by it into their respective acids, chlorine
being evolved.
Chlorine
Oxygen
-
1
1
1
36
8
44
81.75
18.25
100.00
Peroxide of Chlorine is gaseous, transparent, and of a very deep greenish yellow colour.
Its specific gravity, as compared with air, is 2.360; as compared with hydrogen it is 34
to 1.
Chlorine
1
36
52.9
1
Oxygen
1
32
47.1
2
1
1
68
100.0
2
CHAP. II.
647
COMPOSITION AND USE OF MINERALS.
Chloric Acid is a sour, colourless liquid; it reddens vegetable blues; the compounds of
chloric acid, giving off oxygen with facility when heat is applied, promote the rapid defla-
gration of inflammable matter. It is decomposed by muriatic and sulphurous acids, and by
sulphuretted hydrogen.
Chlorine
Oxygen
1
36
47.4
45
5
40
52.6
55
1
76
100.0
100
This acid cannot exist independent, without water or some other base.
Perchloric Acid is a very stable compound, and is not decomposed by sulphuric or mu-
riatic acid. Its specific gravity is 1·6, and it boils at 392°.
Chlorine
Oxygen
-
1
36
7
56
1
92
39.2
1.0
60.8
3.5
100.0
Hydrochloric or Muriatic Acid.—This gas is unrespirable, is inflammable, and has a strong
attraction for water, which takes up 480 times its bulk of muriatic acid gas, and forms the
liquid muriatic acid. Its specific gravity is 1.269, as compared with air. Muriatic acid
gas consists of
Hydrogen
Chlorine
1
1
36
1
37
2.75
97.25
100.00
1
1
2
Iodine has a bluish black colour, pungent odour, and acrid taste, melts at 227°, and is
vaporised at 350°. Its vapour is of a fine purple colour. In a state of vapour 100
cubical inches weigh 264-75 grains. Its specific gravity, compared with air, is 8·7, and with
hydrogen 125. It renders vegetable colour yellow.
Oxide of Iodine. An alkali poured into its solution is rendered colourless.
Iodic acid; 1 of iodine and 5 of oxygen.
Bromine, at common temperatures and pressures, is a deep reddish-brown liquid, of a
disagreeable odour; its specific gravity is 3°; 100 cubic inches of its vapour weigh 168
grains.
Bromic acid is sour, inodorous, first reddens, and then destroys the blue of litmus.
Bromine
Oxygen
1
78
5
40
1
118
66.1
33.9
100.0
Fluorine is not found in an insulated state, but its equivalent number has been considered
16. It is a component of fluor spar, but supposed not to combine with either oxygen,
chlorine, iodine, or bromine.
Fluor Spar is composed of one-third of fluoric acid and two-thirds of lime; fluoric
acid dissolves silica, and corrodes glass.
Sulphur is a mineral product, and found crystallised and massive, most frequently
in combination with iron, silver, lead, copper, &c. Its specific gravity varies from 1970
to 2, or is twice the weight of water.
Sulphur is found in beds in the blue clay formation on the southern coast of Sicily, and
in the gypsum of the salt deposits in Switzerland. The sulphurites and pyrites of the
metals afford it in abundance. It begins to fuse at a temperature of 216°, and between
230° and 270° it is perfectly liquid; between 300° and 400° it becomes viscid, but regains
its fluidity when cooled. It boils at 600°, and then sublimes into an orange-coloured
vapour; when heated to 300° and poured into warm water, it acquires the consistency of
soft wax, and hardens on cooling.
Sulphurous Acid, at common temperatures, is a gaseous body, obtained by burning
sulphur in oxygen gas; its specific gravity is 2.22; 100 cubic inches weigh between 68
and 69 grains: its specific gravity, as compared with hydrogen, is as 32 to 1.
is one of those most easily condensed.
This gas
Sulphur
Oxygen
1
16
50
2
16
50
1
32
100
This acid consists of 100 volumes of oxygen gas, and 16-6 of the vapour of sulphur,
condensed into 100 volumes. It is gaseous, transparent, colourless, with a pungent and
suffocating odour, and water absorbs about 33 times its volume.
TT 4
648
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Sulphuric Acid is a limpid, colourless, and inodorous liquid, and has great chemical powers,
displacing most other acids; it is decomposed by several metals, which become oxidised,
and evolve sulphurous acid. When the metals are dissolved in diluted sulphuric acid, the
water only is decomposed, and the oxygen, being transferred to the metal, forms a metallic
oxide, which unites with the sulphuric acid to form a sulphate, whilst the hydrogen is
evolved. The specific gravity of sulphuric acid is 1·84. Liquid sulphuric acid is a com-
pound of one atom of dry or anhydrous sulphuric acid, and one of water.
Anhydrous Sulphuric Acid. When caustic lime or baryta is heated in its vapour they
become ignited, and are converted into sulphates.
Sulphur
Oxygen
40
1
16
3
24
60
1
40
100
The common or liquid sulphuric acid is composed of
Dry sulphuric acid
Water
-
1
40
81
1
9
19
1
49
100
Sulphuretted Hydrogen Gas, under a pressure of seventeen atmospheres, at 50°, takes a
liquid form; it has a peculiar fetid odour, and is so diffusible that a very small portion
escaping is sufficient to be perceptible in a large space. Its specific gravity, as compared
with air, is 1.17 to 1; and compared with hydrogen, as 17 to 1. 100 cubic inches weigh
36 grains.
Sulphur
Hydrogen
1
16
94.1
1
1
5.9
1
17
100.0
The decomposition of the sulphurets is caused by exposure to the atmosphere; the
oxygen combines with the metals to form an oxide, and the sulphur to form sulphuric
acid.
Selenium is a brittle, solid, opaque body, of a metallic lustre, resembling lead in its
aspect; it has a ruby colour; its specific gravity is 4.32; it becomes semi-fluid at a
temperature of 212°, and boils at 650°.
Oxide of Selenium, -selenious oxide.
Selenium
Oxygen
Selenious Acid.
Selenium
Oxygen
1
40
83.3
1
8
16.7
1
48
100.0
1
40
71.43
2
16
28.57
1
56
100.00
Selenic Acid is a colourless liquid, which, at a temperature of 554°, is rapidly resolved
into selenious acid and oxygen; it has a strong attraction for water, and when mixed with
it evolves great heat.
Selenium
Oxygen
1
40
62.5
3
24
37.5
1
64
100-0
Selenium combines with hydrogen, nitrogen, sulphur, and phosphorus.
Phosphorus is solid, semi-transparent, colourless, or of a light yellow tinge; it shines in
the dark, and, when pure, its specific gravity is 1.770. It is insoluble in water, and out of
the contact of air it melts at 105°.
Oxide of Phosphorus.
Phosphorus
Oxygen
8 I
3
48
85-78
1
8
14.22
1
56
100.00
Phosphoric Acid consists of 44 of phosphorus and 56 of oxygen, and enters into the com-
CHAP. II.
649.
COMPOSITION AND USE OF MINERALS.
position of several minerals, forming phosphates; its combining proportion is said to be 18.
Phosphorus combines also with hydrogen and sulphur.
:
Carbon of this the diamond is a specimen in its purest state, but it is usually found in
charcoal, prepared from burnt wood; in ivory black, or animal charcoal; lamp black,
or vegetable charcoal; or in plumbago, which is a compound of iron and charcoal. It
is solid, black, porous and brittle, and when heated in air or oxygen produces carbonic acid.
It is quite insoluble in water, and destroys the putrescent qualities of both animal and ve-
getable matters.
Carbon and Oxygen do not combine at common temperatures, though there are ex-
ceptions to this rule in organic bodies.
Carbonic Oxide (gaseous oxide of carbon). — The specific gravity of this gas, compared
with hydrogen, is as 14 to 1, and to atmospheric air, as 0.972 to 1000, 100 cubic inches
weighing 30-2 grains; when burnt with oxygen it produces carbonic acid.
Carbon
Oxygen
1
1
1
6
8
14
42.9
57.1
100.0
Carbonic Acid (fixed air) is gaseous, transparent, and colourless, and absorbed by an
equal bulk of water; it is found to exist in a vast number of minerals, as a Carbonate,
where it is united as a salifiable base, and particularly in lime, magnesia, &c.; it is contained
in mineral waters and the atmosphere, and is distributed throughout the globe. Its
specific gravity is about 1·52, and from its density it may be poured out of one vessel into
another. As compared with hydrogen it is as 22 to 1; and 100 cubic inches weigh 47-25
grains, and when subjected to great pressure it becomes liquid, and is then limpid, colour-
less, and extremely fluid; it has been obtained in a solid form.
Carbon
Oxygen
-
1
2
1
6
27.27
16
72.73
22
100.00
Carbonic acid unites with ammonia, chlorine, iodine, bromine, and hydrogen, and with
the latter forms the several important compounds called the hydrocarbons and hydro-
carburets.
Carburetted Hydrogen, or fire-damp, is a species of hydrocarbon, found in the cavities
of coal mines, in stagnant pools of water, produced by the decomposition of vegetable
matter; the specific gravity of this gas is 0.555, and compared with hydrogen it is as
8 to 1; 100 cubic inches weigh from 16 to 17 grains; 100 volumes of this gas require 200
of oxygen for its perfect combustion, the result of which is water and 100 volumes of car-
bonic acid.
Boron is a deep olive-coloured substance, insoluble in water and infusible; its specific
gravity is about 2. Neither air nor water act upon it, but when heated to redness it takes
fire, and burns into boracic acid.
Boracic acid is found native among volcanic products, and also in borax.
Boron
Oxygen
1
6
1 ·
20
48
68
29.41
70.59
100.00
Fluoride of Boron has a specific gravity of 2.371, and water takes up about 700 times its
volume of this gas.
Boron
Fluorine
·
1
20
6
108
1
128
16
84
100
Potassium is a white metal of great lustre, but soon loses its brightness by exposure to
the air, and is converted into an oxide. Its attraction for oxygen exceeds that of all other
bodies, and in consequence it is the most powerful de-oxidising agent we possess ; at ordinary
temperatures it is solid, but becomes partially fluid at 50°, and completely so at 150°; it is
lighter than water, and for a moment floats upon it, but soon after its contact it becomes
inflamed.
Protoxide of Potassium, or Potassa, is found combined with many of the earthy minerals,
and particularly with mica and felspar
Potassium
Oxygen
1
40
83.34
1
8
16.66
1
48
100.00
650
THEORY AND PRACTICE OF ENGINEERING.
Book II.
Peroxide of Potassium :
Potassium
Oxygen
1
40
62.4
3
24
37.6
1
64
100.0
Potassium combines with chlorine, iodine, bromine, hydrogen, and nitric acid to form
Nitrate of Potassa. Saltpetre is an abundant mineral production, being found in many
soils, and particularly in old plaster rubbish, which sometimes, after washing, affords 5 per
cent. of this product; it is also found in situations where animal or vegetable matter has
been left in a putrefied state in contact with calcareous soils. Upon newly-built walls it
sometimes shows itself, and is the result probably of the mortar containing hair, or other
animal matter. Mortar made of lime, wood-ashes, and cow-dung produces in a short time
efflorescent nitre.
Oxygen
Nitrogen
Potassium
6
48
47.10
1
14
13.75
1
40
39.15
1
102
100.00
Gunpowder is a mixture of nitre, sulphur, and charcoal in the following proportions:
Saltpetre
Charcoal
Sulphur
-
-
Common.
75
12.5
12.5
Shooting
Shooting.
Miners'
Powder.
Powder.
78
76
65
12
15
15
10
9
20
Potassium unites with sulphur, selenium, carbon, cyanogen, and boron.
Sodium is soft and malleable, and its globules may be welded together by pressure; in
colour it resembles silver, but soon has its lustre changed by exposure to the air; it fuses
at 190°, and becomes volatile at a white heat; its specific gravity is 0.9348; when thrown
into water hydrogen is given out, and the metal rapidly oxidises.
Sodium and Oxygen. Soda.
Sodium
Oxygen
Peroxide of Sodium.
Sodium
Oxygen
1
24
75
1
8
25
1
32
100
1
24
66.7
12
33.3
I
1
36
100.0
Chloride of Sodium.- Common salt exists as a fossil, and is found abundantly in solution.
It is taken up nearly in the same quantities both by hot and cold water; in solution
it deposits crystals during evaporation, though it does not do so by cooling; 100 parts of
water at 58° dissolve 36 of salt.
Common Salt is the source of soda, muriatic acid, and chlorine.
Sodium
Chlorine
1
1
1
24
40
36
60
60
100
Chloride of Soda is a powerful bleaching agent; when exposed to the air it absorbs car-
bonic acid, and evolves chlorine, which occasions it to be used as a disinfectant.
Soda and Nitric Acid.- Nitrate of soda resembles common nitre; it is found native in
Peru, forming a stratum of many miles in extent, covered with clay and alluvium.
Soda
Nitric acid
1
1
32
54
37.2
62.8
I
1
888
86
100.0
Sulphuret of Sodium is composed of
Sodium
1
24
60
Sulphur
16
40
1
40
히
​|
100
?
CHAP. II.
651
COMPOSITION AND USE OF MINERALS.
Sulphate of Soda.— Glauber's salt is a natural product present in many mineral waters.
Dry sulphate of soda
Water
1
10
1
72
90
162
44.4
55.6
100.0
Carbonate of Soda is a very important salt, obtained by burning sea plants, the ashes
of which produce the alkali called soda. Its specific gravity in the crystalline form is
1.62; it is soluble in twice its weight of water at 60°, and in less than its own weight
at 212°.
Soda
Carbonic acid
Water
1
32
22.25
1
22
15.25
-
10
90
62.50
1
144
100.00
It is manufactured in large quantities by heating carbonate of lime, charcoal, and
sulphate of soda, the charcoal tending to produce sulphuret of sodium, and the lime to
remove sulphur or sulphuric acid. The carbonic acid of the carbonate of lime, and that
from the flame of the furnace, being made to pass over the soda, give it the carbonic acid.
It is then crystallised.
Borate of Soda, Borax, is soluble in 20 parts of water at 60°, and in six parts of boiling
water; at a red heat it forms a transparent glass, which by exposure to the air becomes
opaque: the anhydrous borax consists of
Soda
Boracic acid
Crystallised borax.
Soda
Boracic acid
Water
1
32
31.4
1
68
68.6
1
100
100.0
1
32
16.85
1
68
35.80
·
10
90
47.35
1
190
100.00
Lithium, when first discovered, was supposed to be soda, but differs from it, and has
peculiar properties. Lithia, or protoxide of lithium, is not very soluble in water, and con-
verts vegetable blues green.
Barium is metallic and of a dark grey colour, heavier than water, and attracts oxy-
gen with great rapidity. Its specific gravity is 2°, and when gently heated, burns with
a red light.
Oxide of Barium, Baryta, is the heaviest of all the earths, its specific gravity being 4,
and in all its leading properties bears a strong resemblance to lime. It is poisonous, as
are all its compounds. Carbonic acid has a much greater attraction for baryta than for
lime.
Barium
Oxygen
1
69
89.6
1
8
10.4
1
77
100.0
Nitrate of Baryta is composed of
Barium
1
77
58.7
Nitric acid
-
1
54
41.3
I
1
131
100.0
Sulphate of Baryta, or Heavy Spar, is found in great abundance in nature; when heated
it decrepitates, and at a very high temperature is fused into a white enamel. It is harder
than carbonate of lime, but not so hard as fluor spar.
Sulphate of baryta in an anhydrous state consists of
Baryta
Sulphuric acid
Carbonate of Baryta is also poisonous.
Baryta
Carbonic acid
Its specific gravity is 4·7.
1
77
63.8
1
40
34.2
1
117
100.0
•
1
77
777-7
1
22
1
99
218
22.3
100.0
652
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Strontium is nearly as heavy as barium, and is a substance of rare occurrence.
Protoxide of Strontium, Strontia, is a substance of a greyish colour, is distinguishable from
lime by the insolubility of the sulphate; it is extremely infusible, but is less caustic than
the fixed alkalies and baryta.
Strontium
Oxygen
-
1
44
84.6
1
8
15.4
1
52
10Û·Ù
Calcium has a white colour and a metallic lustre; when heated in the air, it is oxidated
and converted into lime.
Calcium and Oxygen-Oxide of Calcium-Quick Lime, is extremely infusible, but gives
out a brilliant light when intensely heated; pure lime is of a pale grey tint, and has a
specific gravity of 2.3.
Calcium
Oxygen
-
1
1
20
71.4
8
28.6
1
28
100.0
Hydrate of Lime—Slaked Lime, is a compound of
Lime
-
1
28
75.6
Water
1
9
24.4
1
37
100.0
Nitrate of Lime is formed by neutralising nitric acid, diluted with water, by lime; is
found in old plaster, and in mortar: in the anhydrous state it consists of
Lime
Nitric acid
Sulphuret of Calcium is soluble in water.
Calcium
Sulphur
·
1
1
1
1
28
54
1
82
།སྐྱ
-
15880
20
16
36
1
34.1
65.9
100.0
Sulphate of Lime is found abundantly under the form of gypsum, selenite, alabaster, &c.
all of which contain water of crystallisation, which is driven off before it can be made into
plaster of Paris. It is soluble in 500 parts of cold water, and more so in boiling water,
hard water being produced. Anhydrous sulphate of lime consists of
Lime
Sulphuric acid
1
28
41.1
1
40
58.9
1
68
100.0
The crystallised sulphate of lime consists of
Anhydrous sulphate of lime
Water
12
68
79
18
21
1
86
100
Native sulphate of lime or selenite is crystallised: the fibrous and earthy is called gyp-
sum, and the granular or massive alabaster; the variety called satin gypsum is used
for ornamental purposes.
purposes. Massive and granular gypsum is applied to architecture.
Marbre de Bergamo is a variety of sulphate of lime, called anhydrous gypsum, which
sometimes contains common salt.
Chloride of lime, or bleaching powder, destroys vegetable and animal colouring matters.
and various effluvia. It is a dry white powder, smells of chlorine, and has an acrid taste :
when exposed to the air it absorbs carbonic acid, and evolves chlorine. It probably consists
of a chloride of lime, containing one proportion of chlorine and one of lime, with a pro-
portion of hydrate of lime.
Carbonate of Lime. Heat expels the carbonic acid, whilst muriatic and the other
acids decompose it; it is the most abundant compound of the globe.
Lime
Carbonic acid
1
1
1
28
22
50
56
44
100
It occurs native in various forms, and in the Iceland spar is extremely pure and trans-
CHAP. II.
653
COMPOSITION AND USE OF MINERALS.
parent. White granular limestone, or primitive marble, is another variety; and among the
inferior limestones are several, as the oolite, common limestone, &c.
Magnesium fuses at a red heat, then burns, uniting with the oxygen of the air to form
magnesia.
Oxide of magnesium, or magnesia, consists of—
Magnesium
Oxygen
1
12
59.3
8
40.7
20
100.
Its specific gravity is 2·3, it is almost infusible, and nearly insoluble in water.
Aluminum is difficult of fusion, requiring a higher temperature to melt it than cast-iron,
and it is not oxidised by exposure to the air; water at a common temperature does not act
upon it, nor is it affected by nitric or sulphuric acids; but in hot sulphuric acid it rapidly
dissolves, and sulphurous acid is evolved. Sir Humphry Davy found that potassa was
formed by passing the vapour of potassium over alumina at a white heat.
When chloride of aluminum mixed with potassium is heated in a platinum crucible by
means of a spirit lamp, and the substances begin to act, the temperature rises suddenly to
rednets, and then care must be had that the chloride does not pass off in an undecomposed
state, or that there is an excess of alkali in the residue. After the whole is cooled down,
and washed with cold water, pure aluminum is found in the state of finely divided grey
substance, with a small degree of metallic lustre. Aluminous rocks are abundant in every
formation.
Oxide of Aluminum.-Alumina is an insipid and insoluble compound, with a specific
gravity of 2. It has a strong attraction for moisture, and will absorb about one-third of
its own weight, which may be again expelled by ignition. Alumina is rendered plastic
when mixed with water, and has a strong affinity for various organic compounds; and
moist alumina is readily soluble in most of the acids. When ammonia is put to a solution
of alum, in infusion of cochineal or madder, the aluminous earth is precipitated with the
red colouring matter, and in this way the colour lake is formed. Alumina is known by
its solubility in caustic potassa, and by its octohedral crystals of alum, which are formed
on evaporating the sulphuric solution, with the addition of sulphate of potassa, and by
the blue colour which it has when moistened with nitrate of cobalt strongly heated.
Alumina does not combine with carbonic acid, but with other acids and the alkalies, and
with the latter its compounds are soluble in water.
The different hydrates of alumina are found in a native state, though their distinct
atomic compounds are not yet ascertained. Alumina as a protoxide may be thus
stated
Aluminum
Oxygen
1
1
1
10
55.5
8
44.5
18
100.0
Many chemists, however, consider its proportions to consist of two equivalents of alumina
and three of oxygen.
Alumina exists in all kinds of clay, and from an analysis made by Professor Faraday of
the blue alluvial clay of the Medway, in its dark-coloured and moist state, it was found
that 100 parts whose specific gravity was 1·46, contained -
Water
Sand
Finer
า Silica
particles Alumina
Peroxide of iron
Carbonate of Lime
Fragments of wood
Organic matter
-
50.9
14
14.8
-
10.8
3.4
1.5
1.5
3.1
100.0
In the brown pit clay of Upner, he also found, its specific gravity being 2.07,
Water
Sand
Finer 1 Silica
particles Alumina
Peroxide of iron
Carbonate of lime
19
30.5
29.8
16.5
3.7
•5
100.0
654
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
Berthier has given a table of the compositions of various clays, and among them, that at
Stourbridge, which contains
Silica
Alumina
Oxide of iron
Water
•637
•207
•040
•103
•987
And those met with in the county of Devonshire, used for pottery,
Silica
Alumina
Water
•496
•374
•112
•982
Clay in general may be considered as a silicate of alumina, or a compound of silica,
alumina, and water; and the best for pottery are those where the proportions are three of
silica to one of alumina, or by weight 48 to 18.
Sulphate of Alumina and Potassa, or common alum, consists of three equivalents of
sulphate of alumina, one of sulphate of potassa, and twenty-five of water; its crystals are
octobedrous. Aluminous slate, which is an argillaceous slaty rock, containing sulphuret
of iron, when roasted so as to oxidise the iron and acidify the sulphur, produces a sulphate
of alumina, and when to this sulphate of potassa is added, alum is obtained.
Alum reddens vegetable blues, and dissolves in five parts of cold water, and in rather
more of its own weight in boiling water: in its crystallised state it consists of—
Sulphate of alumina
Sulphate of potassa
Water
3
174
1
88
25
225
1
487
35.73
18.07
46.20
100.
Silicium is a simple non-metallic combustible, and has a strong resemblance to boron.
It may be perfectly oxidised, and converted into silica or silicic acid by mixing it with dry
carbonate of potassa, and heating it to redness, when a silicate of potassa is obtained.
Silica is the most common, as well as the most abundant, of the earths; it constitutes the
chief portion of hard stones and minerals. It is found in solution in many springs, but
the water must be raised to a high temperature before it will hold any quantity in solution;
and retaining a greater heat under the pressure of the sea than in the atmosphere, sub-
marine springs are probably more charged with silex than those to which we have access.
The waters of Ireland hold silex in solution in consequence of the presence of the
alkali soda. The deposition of silica in an insoluble state is from the water, when cooled
down, not being so able to retain it as at a high temperature, the evaporation of the
water decomposing the compounds of silica and soda which at first existed. Fragments of
wood and plants are often found completely silicified, or converted into stone, called
petrifactions.
Oxide of Silica, Silica, or Silicic Acid. It exists nearly pure in flint, and quite so in
rock crystal; it is a white powder, insoluble in water, and infusible except by intense heat;
its specific gravity is 2·66.
Silicium
Oxygen
1
1
1
∞ ∞
8
50
8
50
16
100
Fluo-silicic acid (Fluoride of Silicium). — The only acid body which acts energetically on
silica is the hydrofluoric acid; it is gaseous, transparent, and colourless. Water condenses
365 times its volume; its specific gravity is 3 61 compared with air; 100 cubic inches of
the gas weigh 112 grains
Silicium
Fluorine
1
8
30.8
1
18
69.2
1
26
100.0
Silicate of Potassa. — To obtain this compound silica is generally fused with the carbonate
of potassa, the carbonic acid being expelled by the heat; with 3 of carbonate of potassa
and 1 of silica, a glass is formed which is soluble in water; if there is an excess of silica, it
is insoluble. Plate glass is made from soda and siliceous matter. Common flint glass
contains 50 of silica, 34 of the oxide of lead, and 14 of potassa.
Yttrium, Glucinum, Zirconium, Thorinium, are all extremely rare metals.
CHAP. II.
655
COMPOSITION AND USE OF MINERALS.
Antimony is found native, and its principal ore is the sulphuret; the most common is
crystallised into four and six-sided prisms; it is of a white colour, brittle, and of a crys-
talline texture; fuses at about 800°, and its specific gravity is 6·712; it is prepared from
the sulphuret by heating it in a crucible with iron filings, when a sulphuret of iron and
the metallic antimony are formed.
The composition of the oxides has been differently stated, and it seems that there are
three distinct varieties. The oxygen in the protoxide is to that of the peroxide as 1-5 to
2.5, and that in the three oxides one atom of antimony is united with 1.5, 2, and 2·5 of
oxygen.
Sulphuret of antimony is artificially produced by fusing the metal with sulphur; it has
a dark grey metallic colour, and a specific gravity of 4·36.
Antimony
Sulphur
-
1
65
73
11/1/0
24
27
1
1888
89
100
Bismuth is found native, combined with oxygen, arsenic, and sulphur; it occurs crys-
tallised into cubes and octohedra; it is a brittle white metal with a reddish tint; its specific
gravity is 9.85; it is fusible at 496°, and always crystallises when cooling.
Protoxide of bismuth is obtained by dissolving bismuth in nitric acid, which is
precipitated by dilution with water, and heated, when dry, to a dull redness.
Bismuth
Oxygen
1
1
1
72
8
80
90
10
100'
Chloride of Bismuth, or Butter of Bismuth, is of a grey colour, and fuses at 480°; when
exposed to air it deliquesces.
Bismuth
Chlorine
1
72
66.6
1
36
33.4
1
108
100.0
Fusible metal is a com-
Alloys of bismuth are formed with gold, platinum, and silver.
pound of 8 of bismuth, 5 of lead, and 3 of tin, which liquefies at the temperature of
boiling water. Soft solders contain bismuth.
Manganese has a powerful affinity for oxygen, attracting it from air and water; in its
appearance it resembles iron. It is a hard grey metal, brittle and granular; the specific
gravity of which is 6.8.
Oxide or Protoxide of Manganese :
Manganese
Oxygen
1
28
77.75
1
8
22.25
1
36
100.00
Manganesic Acid. When peroxide of manganese (which is 1 of manganese and 2 of
oxygen) and nitre are heated, a compound is obtained called Chamelion. It consists of
manganesious acid and potassa, gives in water a green-coloured solution, which becomes
purple and red by exposure to the air; the red colour is formed by the manganesious
compound attracting oxygen.
Chromium. — In a metallic state its colour resembles that of iron; it is brittle, difficult
of fusion, and is not easily acted upon by the acids. Its specific gravity is 6.
Protoxide of Chromium is of a green colour, and when fused with borax produces that
used in porcelain and enamel painting; the emerald receives its tint from it.
Chromium
Oxygen
1
28
11/
12
1
40
70
30
100
Chromate of Lead, in its native state, is of a deep orange colour, approaching to redness,
but when reduced to a fine powder is yellow; its primitive crystal is an oblique prism.
Its specific gravity is 6. In an anhydrous state it consists of
Oxide of lead
Chromic acid
1
112
68.29
1
52
31.71
1
164
100.00
+
656
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
The Dichromate of Lead, which contains two of oxide of lead and one of chromic acid,
forms valuable pigments, used in oil and water-colours, dyeing, &c.
Chromic Acid, which is a compound containing three of oxygen, combines with potassa,
mercury, silver, chlorine, fluorine, &c.
Cobalt. This mineral is of a grey colour with a reddish tint, is very heavy and brittle.
It is found native, combined with iron, nickel, arsenic, sulphur, &c. Its specific gravity is
8-5, and it is used to give a blue colour to glass; it crystallises into cubes, octohedrons,
and dodecahedrons.
Oxide of Cobalt, or protoxide, is obtained by heating the carbonate of cobalt out of the
contact of air; it is of a greenish grey colour, and imparts a blue tint to glass and
enamel.
Cobalt
Oxygen
1
30
78.9
1
8
21.1
1
38
100.0
Smalt is a blue-coloured vitreous compound, produced by fusing zaffre, which is an
impure oxide which remains after the arseniuret of cobalt has been heated to expel the
arsenic, the cobalt becoming oxidated; this is mixed with twice its weight of finely-
powdered flint. Smalt and azure blue are formed by fusing zaffre with glass, which in
a hot state is dropped into water, and afterwards reduced to a fine powder.
Arsenic is of steel grey colour, brilliant lustre, crystalline texture, brittle, and soon
tarnishes on exposure to the air. Its specific gravity is 5.8, and it is readily volatilised at
a temperature of 360°; and when exposed freely to the air produces arsenious acid.
Arsenious Acid (white arsenic). It is white, semi-transparent, brittle, and becomes
opaque by exposure to the air; it condenses into small octohedral crystals. It is soluble
in sixteen of water at a temperature of 212°, a portion being again deposited in crystals as
the solution cools. It is nearly tasteless, but highly poisonous. When arsenious acid is
slowly sublimed, octohedral and tetrahedral crystals are formed, derived from a rhombic
prism.
Arsenic
Oxygen
1
38
76
1 1/2
12
24
1
18
50
100
The arsenious acid combines with bases and forms the
Arsenites. Those of potassa and soda are easily soluble and uncrystallisable; those of
lime, strontia, baryta, and magnesia, are more difficult.
Scheele's Green, a fine apple-green colour and used as a pigment, is a mixture of this
acid with a solution of sulphate of copper. With lead, antimony, and bismuth, white pre-
cipitates are formed.
Nickel is a brilliant white metal, both ductile and malleable, and not oxidised by ex-
posure to the air or moisture at common temperatures. Its specific gravity is 8.5.
Protoxide of Nickel consists of
Nickel
Oxygen
-
1
28
77.77
1
8
22.23
1
36
100.00
Nickel combines with chlorine, iodine, fluorine, sulphur, &c.
Meteoric Stones have a black surface, when broken exhibit a coarse texture and a grey
colour; they are compounds of silica, magnesia, iron, and nickel.
Mercury has much the same colour and brilliancy as silver; it is liquid, forms round
globules, which when brought in contact readily unite together; exposed to the air it
quickly tarnishes; at 40° it loses its liquid state, and becomes solid and malleable, and in
the frozen state its specific gravity is 15-6. At a temperature of 670° it boils, and becomes
vapour; at 60° its specific gravity is 13.5.
Native Cinnabar is the principal ore of mercury, and occurs massive and crystallised in
six-sided prisms, rhombs and octohedra. It is sometimes of a steel grey, and at others a
bright red colour; it is a bi-sulphuret of mercury.
Oxide or Protoxide of Mercury is insoluble in water and muriatic acid, but is dissolvea
by acetic acid.
Mercury
Oxygen
1
200
96.1
1
8
3.9
1
208
1000
Mercury combines with chlorine in two proportions.
CHAP. II.
657
COMPOSITION AND USE OF MINERALS.
Protochloride of Mercury, or Calomel
Mercury
Chlorine
1
200
84.74
-
1
36
15.36
I
1
236
100.00
Perchloride of Mercury, or Corrosive Sublimate, has an acrid nauseous taste; its specific
gravity is 5.2. It is soluble in twenty parts of water at a temperature of 60°; boiling
water takes up about half its weight, and as it cools quadrangular prismatic crystals are
formed. It dissolves without decomposition in muriatic acid, but is insoluble in concentrated
nitric and sulphuric acids.
Mercury
Chlorine
13
2
1
200
72
272
73.53
26.47
100 00
Bisulphuret of Mercury, Cinnabar, or Vermilion, may be manufactured by mixing 8 parts of
mercury in an iron pot with 1 of sulphur, and combining them at a moderate heat; this is
put into a glass subliming vessel, and heated in a sand-bath to redness, after which it is
rubbed down into a fine powder.
Mercury
Sulphur
12
1
200
86.2
32
13.8
232
100.0
Silver occurs native, and crystallised in cubes and octohedra; pure it has a brilliant
white colour, and when polished a bright lustre, is extremely ductile and malleable.
At a
bright red heat it melts, and when pure absorbs oxygen, which as it cools it again evolves.
The tarnish of silver is produced by the vapours of sulphur, and it is most apparent when
the metal is alloyed with copper.
When the argentiferous sulphuret of lead is placed in the reverberatory furnace, and a
current of air suffered to pass over its surface, the lead is converted into litharge, and the
silver is left in the metallic state.
The sulphurets of silver are reduced by amalgamation; when these ores are washed and
ground, they are mixed with common salt, and roasted; sulphate of soda and chloride of
silver are thus formed; it is then reduced to a fine powder, and agitated with mercury,
water, and iron filings; thus the chloride of silver is decomposed, and the chloride of iron
being washed away, the silver and mercury combine into an amalgam, when the mercury
is partly pressed out, and the remainder driven off by distillation; the specific gravity of
silver is 10.5.
Oxide of Silver is of a dark olive hue, and when employed in glass or enamel painting,
gives a yellow colour.
Silver
Oxygen
1
1
108
8
1
116
93.103
6.897
100.000
Chloride of Silver is formed by adding to a solution of chlorine of muriatic acid or
common salt a solution of nitrate of silver; it is precipitated in the form of a heavy
powder, of a white colour, which by exposure to light becomes black.
Silver
Chlorine
J
-
1
1
1
108
75
36
25
144
100
When found native, it is crystallised in cubes and octohedra.
Nitrate of Silver.—Silver is readily dissolved with nitric acid, when diluted with three
parts of water. Nitrate of silver should be a clear and colourless solution; by exposure to
light it becomes deep purple, and all animal substances, when tinged with it, are of a deep
yellow colour. Ivory, marble, and other substances when soaked in this solution, and
afterwards exposed to a strong light, become black.
Nitrate of silver is an anhydrous salt, and consists of
Oxide of silver
Nitric acid
1
1
1
116
68.23
54
31.77
170
100-00
Alloys of Silver. The standard silver consists of 11·10 silver and 6·90 copper. Amalgam
of silver is used for plating; when applied to copper, the mercury is evaporated by heat,
U 11
6.58
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
and afterwards the silver is burnished. A plate of silver is sometimes applied to a plate of
copper, and beaten or drawn out. Brass is silvered by a mixture of chloride of silver,
chalk, and pearlash; when the metal is thoroughly cleaned, the above mixture, moistened
with water, is rubbed over it: clock dials and scales for thermometers are silvered in this
manner.
Gold is found native and in a metallic state; it is either massive or crystallised in cubes
and octohedra; it melts at a bright red heat, 2016°, and when fused is of a brilliant
green colour; its specific gravity is 19.3. It is the most malleable and ductile of the
metals, and is not tarnished or affected by the action of either air or moisture. It is
Gold
separated from copper by cupellation, and from silver by nitric or sulphuric acids.
is so malleable that it may be beaten into leaves two hundred and eighty-two thousandths
of an inch in thickness, and a grain of it may be made to cover 56 inches of surface; its
ductility is so great, that the same quantity may be drawn out into 500 feet in length.
The Protoxide of Gold consists of
Gold
Oxygen
200
96.25
8
3.75
208
100.00
The Peroxide consists of
Gold
Oxygen
1
200
89.5
3
24
10.5
1
224
100.0
The Perchloride of Gold is decomposable at a red heat, and is soluble in water, alcohol
and sulphuric ether; the latter solution is used for gilding. The aqueous solution, or
muriate of gold, is decomposed by several vegetable acids.
Protochloride of tin, added to a dilute solution of chloride of gold, occasions a change of
colour; the purple powder produced from the compound is used in enamel and glass
painting to produce a fine red colour.
Gold
Chlorine
13
1
200
65
108
35
308
100
Platinum resembles silver, but has a less brilliant lustre; it is dissolved by chlorine and
nitro-muriatic acid; its affinity for oxygen is extremely feeble; its specific gravity is
In a minute state of division it promotes the union of the hydrogen and oxygen
gases, absorbing them in large quantities.
Protoxide of Platinum.
21.5.
Platinum
Oxygen
-
1
96
1
8
92.31
7.69
1
104
100.00
Palladium, Rhodium, Osmium, and Iridium, have all been obtained from the ores of
platinum; but they have not perhaps been either of them perfectly examined.
Having described the composition of several minerals that compose the earth's crust, it
is necessary to examine somewhat more in detail the methods adopted in extracting the
ores of lead, iron, copper, and tin, and their conversion into a state to render them useful to
the engineer. The report of the commissioners appointed to examine the mines, published
in 1842, affords information of a highly interesting character, and which we have taken
chiefly for our guide upon this subject.
Lead is seldom or ever found in a pure state, but in combination with carbonic, sulphuric,
phosphoric, arsenic, chromic, and other acids, together with oxygen and chlorine. It has a
colour of a bluish white, is flexible and soft, melts at a temperature of 612°, and when air
is admitted freely with heat it is converted into an oxide. At common temperatures air
and water act slowly upon it; its specific gravity is 114.
be
Oxides of Lead. When air or water is charged with carbonic or other acids, they will
oxidate lead; if the acid be either phosphoric, arsenic, sulphuric, or the hydriodic, an
insoluble crust is formed on the surface of the lead, which protects it, and water may
retained in a cistern or pipes made of it with perfect safety. Carbonic acid in abundance
forms a carbonate, which, instead of encrusting the lead, mixes in a minute state of division
with the water, and is highly poisonous.
Protoxide of Lead, Massicot, or yellow lead, is insoluble, fusible at a red heat, and com-
bines with many earthy and saline substances; when heated with charcoal it is decomposed,
CHAP. II.
659
COMPOSITION AND USE OF MINERALS.
metallic lead being obtained.
At a high red heat it fuses, and forms what is termed
litharge, which is a lamellar vitreous mass of reddish brown colour.
Lead
Oxygen
1
1
1
104
8
112
92.857
7.143
100.000
Deutoxide of Lead, Red Lead, Minium, is a common red pigment, produced by exposing
the protoxide to the action of heat at 700°, and air sufficient to oxidise without fusing
it; its fine red colour loses its brilliancy by exposure to light.
Lead
Oxygen
1
1 1/2
1
104
89.66
12
10.34
116
100.00
Peroxide of Lead.-Lead 104 with oxygen 16 = 120.
Chloride of Lead is obtained by heating laminated lead in chlorine; the gas is absorbed,
and chloride of lead is formed; its specific gravity is 5.13.
Patent Yellow is formed from the compound of chloride and oxide of lead.
Lead
Chlorine
1
1
1
104
36
140
74.3
25.7
100-0
Sulphuret of Lead, the galena of mineralogists, is found native, and is the chief source
whence pure lead is obtained; its primitive form is that of the cube; it often contains a
Galena is reduced by a simple pro-
sufficient quantity of silver to be worth extracting.
cess; the ore is broken and washed, then roasted in a reverberatory furnace, the temper-
When the fumes of the sulphur are
ature being sufficient to soften but not to fuse it.
driven off it is then fused; the lead sinks to the bottom of the fuel which has reduced
it, and is run out and moulded into pigs. Sulphuret of lead has a colour and lustre
resembling pure lead; it is brittle, and requires a white heat for fusion; its specific gravity
is 7.58.
Lead
Sulphur
1
:
1
1
104
86.66
16
13.34
120
100.00
Sulphate of Lead in its native state is crystallised into prisms and octohedra.
Oxide of lead
Sulphuric acid
1
1
1
112
40
152
73.68
26.32
100.00
Carbonate of Lead, White Lead, or Ceruse, is prepared by exposing sheet lead to the action
of the vapour of vinegar, or by decomposing the acetate of lead by a carbonate; its specific
gravity is 64: when found native it is one of the most beautiful of metallic ores; it is soft
and brittle, sometimes tinged with carbonate of copper, and has a green colour; its primitive
form is the octohedron, though it is found prismatic and tabular.
Oxide of lead
Carbonic acid
1
1
1
112
83.58
22
16.42
134
100.00
Alloys of Lead.
Plumber's Solder contains equal parts of lead and tin, or, according to
Mirrors are made in Sweden containing 0.39 of lead,
others, two of lead and one of tin.
This
and 61 of tin. Common pewter consists of 80 parts of tin and 20 of lead.
Of the Mines that produce Lead-Northumberland, Durham, and Cumberland.
country, although politically distributed amongst the three counties, is one and the same in
all its characteristic features. From it flow the Tyne, the Wear, and the Tees, and many
branches which fall into these rivers. Along their banks are dales or valleys highly cul-
tivated, but beyond them rise dark fells, covered with peat moss and heath, and between
one vale and another is a wide range of high moorland, extending sometimes for many
miles. In these upland districts are no inhabitants; thousands of black-faced sheep are
scattered over them, and grouse are found in abundance.
The rivers do not, as in rich, flat, clayey lands, form for themselves a winding serpentine
The channel, of
course, but flow onward in a straight line, and with a rapid current.
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THEORY AND PRACTICE OF ENGINEERING.
which the water occupies but a small portion in dry weather, is covered with boulders,
some of an hundred weight, and small pebbles, and here and there an accumulation of sand.
After rain, and in winter, the stream flows in a powerful flood. At short distances, on both
sides of the rivers, are vales or gullets, with the banks feathered with wood, through which,
with thundering noise, the smaller streams, called Burns, rush over the stones to join the
great stream below. These deep fissures are of importance, as they often lay open to view
veins of ore, and direct the operations of the miner to the places where it is met with in
sufficient plenty to reward his toil.
Weardale is held by many to be the most beautiful of these vales. It gradually contracts
into narrower spaces, and the hills become loftier on proceeding westward from the low
country; it is 15 miles in length, and considered to commence about 3 miles below the
village of Stanhope, where the grass lands are interspersed with fields of wheat, oats,
and turnips, the soil being fertile, and the crops abundant; there is much woodland,
but gradually, as we ascend, this is less frequent; for some miles there is a considerable
show of trees by the river banks, and thick plantations on the sides of the ravines, through
which, over rocks and stones, the burns dash downwards: towards the upper part of the
dale the trees are solitary, near habitations, or occasionally on the river-side. Beyond is
Wearhead, a hamlet where two burns meet, and which give a name to the Wear; each
rises a mile or two higher up to the centre of a wild, treeless, heath-covered hollow in
the mountain.
:
Both sides of the dale, for mile, back from the river at Wearhead, and still farther
down are clothed with the most beautiful green and rich vegetation. The whole of
the dale is well inclosed with stone fences, and subdivided into holdings of about 5 acres
each. Houses are distributed on both sides of the river, and form a continuous scattered
village these houses, built of blocks of stratified hard sandstone, are covered with slate,
and as lime is abundant, they are whitewashed, and present a clean, neat appearance, with
the fronts towards the sun. Here and there is a little hamlet by the road-side, the residence
of tradesmen, to whose stores and workshops the population of both sides of the vale resort.
There is much travelling backwards and forwards along the road, but seldom do the inhabit-
ants of the dale pass far beyond its bounds. They see few but themselves, and intermarry,
so that, by nearer or more remote relationship and affinity, they constitute but one great
family, and an attachment subsists between them which nothing can overcome: hence it
is that, although by removing only 20 miles lower down, into the coal country, a young
man might nearly double his income, and have the prospect of adding many years of health
and strength to his life, he will not remove. He clings to his beloved dale, and follows
an occupation which in most instances allows but a short life, the last years of which are
spent in sickness and in sorrow; and this, too, is the effect on a population well educated,
and of intellectual capacity and acquirement surpassing any met with elsewhere in
England.
The river Tees rises in a hollow, near the foot of Cross Fell, and is soon augmented by
other mountain torrents; for many miles it flows through a desolate valley, with a little
grass land on each side, a few houses, with only now and then a solitary tree; gradually
the vale widens, and for 3 or 4 miles before arriving at Middleton-in-Teesdale it is well
adorned with wood. On the Yorkshire side the rude hills approach very near the river, and
in some places present lofty cliffs. Middleton is a pleasant village, einbosomed in woods, with
the Tees flowing on its south side, and the Yorkshire hills receding for several miles.
Below Middleton, and down to Barnard Castle, the country is beautiful, and the grass
lands are interspersed with fields of grain.
From Stanhope it is ten miles in a northerly direction to the mines and washing-
floors on the Derwent. A turnpike road, then one made by the parish of Stanhope, and
another by that of Edmondbyers, conducts to the parish of Hunstonworth. The fell is
altogether uninhabited, and it may be stated as a proof of the severity of the climate in
winter, that there are high posts of wood painted white, with the top black, to enable the
traveller to find his way amidst the snow.
The Vale of the Derwent, near the works of the Derwent Company, is not 100 yards
wide; the miners and washers come from a distance, and for a time remain in the lodging
shops provided for their use.
The upper part of West and East Allendale, where the mines and washing-floors are
situate, are wild, narrow vales, inclosed within lofty dark fells. From Weardale to Alston
Moor the road lies over a high uncultivated dreary tract, which conducts to the busy
village of Nenthead, with its smelting mills and washing floors, on which may usually
be seen a multitude of children engaged at work. The little river Nent flows five miles
to the town of Alston Moor, through a narrow vale, divided into small holdings, and
studded with houses like Weardale, but with very little wood.
The town of Alston is situated on the side of a hill close to the river Tyne, beautifully
surrounded with wood. The vale of the Tyne below the town is richly cultivated, and
ascends for about five miles between lofty hills, where the river rises in a hollow at the foot
CHAP. II.
661
COMPOSITION AND USE OF MINERALS.
of Cross Fell, which lofty mountain on the south, and others on the west, give an interesting
grandeur to the prospect from every place in the vicinity of Alston.
The whole of the lead country possesses great beauty, though of a diversified character.
Mining is the sole resource of the inhabitants, who are universally so attached to the
country, and to each other, that they continue to engage in an employment which ið
remunerates their toil, and brings many of them to an untimely grave.
The Lead Country, in a geological sense, is below the coal measures and above the old
red sandstone; the former consists of many strata of siliceous sandstone, limestone, clay,
shale, with beds of indurated clay between them. The lead is found in all these strata,
though not often in clay or in clay-shale, and a vein will descend from the surface down
through all the strata, until it is so deep that it can no longer be followed on account of water
and other difficulties. Amongst the most remarkable beds is the encrinital limestone,
with abundance of its peculiar fossil remains; it may be seen in the bottom of a large
burn which falls into the Wear, some miles below Stanhope, near Frosterly Bridge, at Bishop's
Crag. Limestone boulders gathered from the bed of the Wear supply the lime-kilns; and
there are large quarries worked about two miles below Stanhope, and near the commencement
of the railway, adjacent to which are also beds of limestone of excellent quality, which
are carried by the railway to furnaces in the coal districts. In this country the mines
now worked all afford lead. There was a considerable quantity of copper found in one
near Garrigill Gate, in Alston Moor, and in some other mines, but none is obtained at
present. Much farther west, in Caldbeck Fells, is a mine called Roughton Gill, in which
there are ores of copper and lead in the same veins, in the proportion of copper and
lead. The population of this country has been devoted to mining as far back as records
can be obtained. As Cumberland was not surveyed by the Conqueror, we have no
account of it in "Domesday Book;" but in the Record Office, in the Tower of London,
in the Patent Roll of the 20th of Henry III., A. D. 1235, is a copy of a charter, which
shows that the mines were then worked, and had been so during the time of the former
kings of England.
Working the Mines.
The entrance into the mines is generally by a level driven into
the sides of the hills; in former times shafts were frequently sunk from the top, which
is now seldom the case. The level is made about 6 feet, sometimes 7 feet high, and from
3 to 4 feet wide; where necessary it is arched with stone, and a railway for the waggons
is laid at the bottom. By means of this level, the water is brought out of the mine; carts
are drawn in by horses to a certain distance, and the ore put into them; the miners walk
into their work, or at least to the places where they ascend or descend. The level is
usually driven into the hill as far as possible in the stratum called plate or clay-shale,
that stratum being softer and more economically worked than any other. The object in
penetrating through the hill by a level is to arrive at a vein of ore, and when the working
can be got on the first level it is most advantageous to all parties. In the level of the
mine at Stanhope Burn, after proceeding nearly mile, there are several chambers in
which the men work, breaking down the lead ore by hammers and picks, drilling holes,
charging with gunpowder, and firing it; this extends through the vein of limestone rock as
far as 200 fathoms. The tools used by the miners are few and simple, as,
The Jumper, an iron chisel pointed with steel, the usual length of which is 18 inches,
and sometimes 2 feet; one miner holds it against the rock, whilst another or a boy strikes
the end with a hammer; from time to time the dust has to be taken out of the hole.
The Hammer is used for striking the end of the jumper.
The Pricker. After the cartridge is put into the hole, the pricker, which is a thin iron
rod with the outside end formed into a ring, is driven into it and through the cartridge.
When made of iron sparks are produced in siliceous rocks, or even in limestone, both
from the hammer and the spade: a copper-pointed pricker obviates this risk.
The Driver. This is a piece of iron with a broad head, to drive the shale down along
the side of the pricker; the head is usually of copper.
The Scraper is for taking out the dust from the hole made by the jumper and hammer.
In breaking down the rock, the lead miners use a pick very like that employed in the
coal mines, as well as a great hammer. They first drill a hole in the rock with the jumper
and hammer, then insert a cartridge of gunpowder, in the same way as if charging a gun,
although the hole may be bored perpendicularly, horizontally, downwards, or sidewards;
boys and young persons drill the holes, but are seldom trusted to charge it with the powder.
They then drive a pricker through the cartridge, keeping it there for a time, and place
what is called plate, or pieces of black shale, at the sides of the pricker, which with
the driver they force down as far as it will go, continuing this work until they have filled
up the entire hole round the pricker, which is then drawn out by inserting the scraper
in the ring at the end, leaving a hole open down to the powder, into which the men thrust
a squib to which they apply a match: all except one man retire and get into the level, or
some place where the stone directly coming from the explosion cannot hit them, and
turn their backs to prevent any piece being reflected into their faces; the man who lights
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THEORY AND PRACTICE OF ENGINEERING.
the match runs away, and after the shot has gone off with much noise, smoke, and dust,
the men return and find a chasm made; then with hammers and picks they strike upon
every projecting piece of rock, and bring it down. The chamber where they work is filled
with smoke by every additional shot fired: if the rock be wet, the patent fuse, being a slow
match inside a rope, is found convenient for blasting. When the miners have cut out the
ore which is near the level, it is arched over, and they proceed working upwards; the
deads or rubbish, or the rock not containing the ore, is let down behind them, as they
ascend; different sets of men work above each other, protected by scaffolding. When
the ore is removed, it is let down a channel, through an opening called a hopper, into the
cart or waggon in the level.
In some mines there is much work in the first level, and it is frequently necessary to
ascend and make another; this is effected by drilling and blasting out the rock by gun-
powder, and placing scaffolding, by which the miners climb to their work.
In this upward
work they make a small-landing place, and go from one stage to another, so that they are
able to place ladders or pieces of wood from side to side, and afterwards climb up, having
halting-places all the way. When arrived at the height thought best to fall in with the veins,
they move forward horizontally, or in a line parallel to the first level driven in from the
air;
it may be necessary to work upwards a second time, and form another flight of
ladders, and, after getting to a certain height, again to move forward, and so on several
times, until the place of working be 500 or 600 feet above the first level.
The miner who works in such a remote situation walks into the level, as far as the first
descent by the ladders, down which he goes, with a load of tools on his back. He then
proceeds to the second flight of ladders, and descends to the third, until he comes to the
place where he has to perform his work: no air being admitted except from the level by
which he has entered, there is nothing to produce a current; the air enters slowly about
him, merely by the effect of a difference of temperature, and means are taken to diminish
an evil which cannot be removed. Sometimes a body of air is forced by a fall of water
from the top surface of the hill, an opening being made for it to descend to the level with
great violence, driving a body of air before it, and running out along the bottom of the level
from the mine. Machines or fanners, worked by boys, are used, and the air is carried
along pipes to places to which it would otherwise very slowly penetrate. Forcing-pumps
are sometimes employed to drive it in a similar way, and a supply is obtained by running
a second level from the air into the hill, making a communication with the first; in this case
the air put in action enters at one level, and goes out by the other. Sometimes a shaft is
carried up or let down from the open air into the level, when a current is produced.
Few mines have two levels communicating with the open air, or shafts from the outer
air down to the levels, the sum required for the purpose being so great that the pro-
prietor prefers to discontinue working rather than submit to the expense; but the men
and boys, having no other means of existence, are often allowed to work in the mine with
all these inconveniences. The ore dug out of the level, which is entered from the open
air, is brought out by a horse and cart, the wheels of which run upon a railway; but
that dug in the shafts, above the first levels, is let down holes or channels made for the
purpose from one to another, and down to the first or chief level, when it is brought out:
when taken from the low levels it is hoisted up by whinseys from one to another, until
brought to the first level, where it is carried out to the open day; boys are employed to
drive the horses for the whinseys and carts.
The water is raised from great depths by steam-engines or by an hydraulic engine
or great water-wheel, which works a pump; that at the surface falls into the buckets of
the wheel, and by its gravity causes it to revolve, the water being discharged into the
level. The pump brings up the water from a great depth below, and discharges it into
the level, where it runs out. This machine is cheaper than the steam-engine, as it
requires no fuel, and very little attendance, and works day and night.
In the parish of Stanhope steam power is not used, but water power equal to that of
120 horses: in the mines of Allendale, there are 14 water-wheels, possessing a power
equal to 300 horses. It is obvious that the hydraulic machine can be used only on the
side of a hill, where there is a stream of water on the surface, which very often occurs in
the lead country. The lengths of the levels, driven into the hills, are various: some
are half a mile, and some double that distance; there are some much longer, as that nearly
5 miles in length, called the Nent Force Level; it begins near Alston, close by the fall of
the Nent, and extends forward to Nent Head. For a long time there was water in this
level deep enough to carry boats, by which the ore was brought out, which is now per-
formed by carts, to the foot of a shaft near Nent Head, where it is hoisted up by a
whimsey; several shafts, for the purpose of ventilation, are let down into this level.
Of Hushing.. A quantity of ore is obtained by a method called hushing: where a
great ravine has been formed by the streams on the side of a hill, and water comes down
over the stones, clay, and earth, if ore has been discovered, it is a good place for hushing.
A dam is made at the upper part, with a channel for the water, some of the larger stones
CHAP. II.
COMPOSITION AND USE OF MINERALS.
663
being laid on one side; when the dam is let out, the flood of water, rushing down, tears
up the earth and stones, and lays bare new surfaces, when men and boys go into the ravine,
and pick up all the ore left by the water. Hushing is chiefly carried on where the
ravines disclose new veins, and the water running along tears up the stones containing the
metal. Rainy weather, which enables a dam of water quickly to be collected, is favour-
able to hushing. The work is as easy as washing the ore, and wages much the same.
according to the ages of the boys or persons employed. There are many hushing places
on the road-side from Weardale to Nent Head, in Alston Moor.
Washing the Lead Ore. The object of washing the ore after it has been brought from
the mine is to separate the lead from the limestone, sandstone, barytes, or other matter
with which it is united or mixed up. Some men, and very many boys under 13, and
young persons under 18, are employed; as this operation depends on a supply of water,
it is necessarily suspended by the frost, and when it has permanently set in, the work is
discontinued altogether until the spring; it is also partially liable to be interrupted in dry
weather, in places where water is not abundant. It is a great advantage to a mine when
it is situated near a river, or a large and copious burn of never-failing water; but frequently
it is necessary to take advantage of the smallest streamlets, and artificial means are used
to collect water by dams, the outlets of which can be stopped up at nights, or when the
people are not employed. In East Allendale, there is a dam which covers 7 acres of land,
but in general they are not so large.
Formerly the washing of the ore was a very simple and rude operation. It was placed
on a buddle or sunk space of ground, with a gentle declivity, so that water coming at one
end might slowly flow over the stony bottom to the other, carrying off the loose dirt,
clay, or pulverised stone; the solid pieces of ore were broken by a rude instrument
called a bucker, not yet entirely out of use. This instrument consists of a flat piece
of iron, about the size of a man's hand; at the back is a broad ring, through which is
thrust a piece of wood for a handle. The boy takes this in his hand, and striking the
ore, breaks it into pieces, by which means the water carries off the earthy matter,
and leaves the metal behind. The large pieces of lead, thus separated from extraneous
matter, are carried away in a state fit for the smelting mill: other pieces are put into
sieves. In the distant fells, which will not afford the expense of machinery, and where,
also, there may be but a small supply of water, this mode is still in use; a few persons are
also employed as auxiliaries to washing establishments, working at buddles along the side
of a gill, taking advantage of the streams of water which flow down after a heavy fall
of rain.
It is obvious that in this mode of washing many small particles of lead must be carried
away, although this is in part obviated by the water falling into pits, and depositing
much of the lead. About forty years ago crushing-mills were introduced, and other im
provements have since been made, by which the lead is separated from the earthy matter
at much less expense, and a greater proportion of lead is obtained: mines are thus rendered
more profitable, and some, which, on the old system, would not have yielded a profit, can
now be worked to advantage. Preliminary to the operation of the crushing-mill the larger
portion of ores are picked out, and sometimes large pieces of pure Galena, without any
earthy matter, which may be broken with the hammer from the stone, are carried at once
to the bingstead, requiring no washing. The orcs are at all times placed upon bars of iron,
called a grating, and a stream of water flows upon them; the smaller pieces are carried by
the water through the bars, and down an inclined plane to a place below; those too large to
get through remain upon the grating; some of these are dead pieces of stone containing no
metal, which are picked off by boys and thrown aside; the remaining matter of ore and
stone goes to the crushing mill. Much depends on the nature of the stratum from which
the ore is obtained; some found in a stratum of barytes comes out in dust or small frag-
ments, and may be carried by the waggons, so as at once to be let down, by opening the
hole in the bottom of the hopper, which is over the mill; where the pieces are of a
larger size, they must previously be broken and grated. The crushing mills require a
plentiful supply of water to drive the wheel, as well as to perform the other subordinate
operations; they are of various powers, and have the great water-wheel in the middle: on
one side are the wheels which break the bouse ore, or the ore in its rough state, and on the
other side are the chat mills, for breaking and bruising the ore which has been crushed or
ground into sinaller pieces.
The Bouse Ore is discharged from the hopper by a machine called a shoe, or a boy or young
person gradually lets it out. In either case it falls between two rollers, deeply fluted, which
revolve and work into each other; a body of water falls down between them at the same
time. In passing between these fluted rollers the ore is crushed into smaller pieces, which
with the rest fall down two inclined planes, one to the right and the other to the left, with
a pair of rollers at the extremity of each: these are smooth, and between them the ore
passes along with a body of water, and is further ground, and falls into pits below. A
certain portion of the ore still escapes, as, when a large piece comes between the rollers,
U U 4
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BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
they are forced to recede sufficiently to let it pass through, when other pieces of stone
slip through unbroken, although but for this contrivance the mill might be damaged
or choked up. The rollers are, however, immediately brought back to their right position
by means of levers, at the end of which are attached large weights, usually stones, for
effecting this purpose, and the depression of the lever brings up the roller attached to it
to its proper position.
From the pits below the crushing-mill the broken ore is drawn up to the chat mill,
on the right side, by means of iron buckets on an endless chain, much in the same way as
we see, on a larger scale, the ballast dragged up into the barges from the bottom of the
river Thames. Every bucket, on arriving at the top, discharges its load upon a grating,
by the bars of which the larger pieces are retained, and are passed again through the
crushing mill, or sent to the stamping mill; the smaller pieces are made to pass the
three pair of chat rolls, which are exactly on the same plan with the crushing rolls, only
on a smaller scale, and adapted to ore of a smaller size. As the crushed ore comes down
from the chat mill, a boy stirs it, and the small lead, with the dirt adhering to it, is carried
by the stream of water to pits lower down.
The stamping mill is used for breaking the hard refractory pieces of ore, which resist the
rollers of the crushing and chat mills. In some establishments the stampers are separate
and distinct from the crushing-mill, and in others the same water-wheel turns the rollers of
the crushing-mill, and raises the stampers, the broken ore being carried down an inclined
plane by a stream of water. When the matrix of an ore is soft and easily broken, the
stamping mill may be dispensed with, but for very hard ore it is exceedingly useful.
After the ore has come from the chat mill and the smaller portion has been carried off
by water, it is taken up and put into a sieve, to undergo the process called hutching. The
sieve, made of iron wire, is let into a box which is full of water. From the stalks or chains
of the sieve proceed a long lever which rests upon a fulcrum; this is moved up and down
by a boy, who places his two hands above his head, and pulls the end of the lever, and in
consequence the sieve with the ore upon it is raised up and down with an agitated motion
in the water contained in the box, which occasions the very small lead or dust, called
Smiddum, to fall through the sieve, and sink to the bottom of the box; and of that portion
which remains above the sieve, the lead, being the heaviest, works down to the lowest place
next the wires of the sieve. Immediately above the lead are the larger pieces of stone,
with portions of ore called chats, and above the chats are lighter pieces of stone called
cuttings: the cuttings are removed by a limp or broad piece of iron, and given to the
cutting cleaners, when it is again put into a sieve and treated as before; the chats are
sent back to the mill to be ground again.
It has been already stated that when the ore is laid on the grating, the smaller portions
are carried through the bars to a pit below; by a stream of water, part of this matter
is sludge or slime, but there is another portion much too large and weighty to be
thus carried off: this is taken out of the pits, again put in the sieves, and hutched or
jerked up and down in the water on the sieve, by the boy pulling the end of the lever
and when sufficiently hutched, the stony matter is carried off by the limp, and the clean ore
lying at the bottom is taken to the bingstead.
;
The Smiddum is taken from the bottom of the boxes, in which the sieves were agitated,
and removed to a running buddle, or space of ground with a stone floor made a little lower
than the ground about it, and having a little declivity, over which water runs very gently;
upon the upper end of this buddle is put the smiddum, and the water let in upon it.
The boys and young persons then stir it with an instrument called a colrake, and the water
carries away dirt, and the fragments of stone or cuttings, and the lighter ore or smiddum
tails are brought to the lower end of the buddle, whilst the weightier ore is left at the upper.
The two are thus separated, and the weightier ore is removed to the bingstead.
It is a necessary consequence of the grating and crushing of the ore under the action of
water, that a quantity of finely pulverised earthy matter has been collected, and much lead,
in the form of minute detached particles, been brought away with it, carried down the
stream with the water, and lodged in the pits into which it flows, where all this matter
is merely mechanically diffused through it. This mass is more or less stiff, and that portion
which is coarse and contains larger grains of lead, is called sludge, that consisting of smaller
and finer particles slime: it is put into trunks and again agitated with water, then laid on
the floors of the buddles, and streams of water made to pass over and through it, being
stirred and rubbed against the bottom of the buddles whilst the water is flowing, the object
being to separate the lead from the clayey matter. The last process is to put the slime
into the dolly-tub, where by means of a handle the board is turned round which agitates
the slime; the lead then falls to the bottom, and the other matter above is taken away.
Many particles of the lead are, however, carried down in the muddy water of the river or
burn, and the cattle for many miles below a washing place are not allowed to drink of it.
The apparatus of the Roughton Gill Mine, invented by Mr. John Leathart, of Alston,
in Cumberland, and put up in 1840, is found to be of use in facilitating these operations
CHAP. II.
665
COMPOSITION AND USE OF MINERALS.
and also for washing poorer lead. Its principle is that of separating the different kinds of
ore, by passing them through plates full of holes of various sizes.
12
The ore when brought from the mine is grated, that is to say, those portions are thrown
aside which are considered not to contain lead, and the large pieces of ore are broken up
with hammers, and made to pass through the crushing mill; after which it comes on to a
separator, or broad plate with holes in it, of inch in diameter; that which remains on the
plate and cannot get through the ¦ inch holes is sent back to the crushing mill to be re-
14
ground; that which passes through the holes is carried by the water down to plate No. 2.,
the holes of which are inch in diameter; what remains on this plate, or is too large to
pass through the holes, is taken to the sieve or the shaking apparatus, where the small
portions called smiddum go through, the cuttings are thrown out, and the small ore at the
bottom is taken to the bingstead.
The chats which come out of the sieves or shaking apparatus are ground, and come to a
plate No. 1., and the rough, which cannot pass through the holes, is taken off and sent back
to the chat mill again; what falls through is carried by the water to the surface of plate
No. 2., which is laid in an inclined position; the smiddum passes over and the sludge goes
through; the former is then put into the shaking apparatus, to be separated in the same
manner as in other washing-places; the cuttings are taken out, and the lead is removed
to the bingstead
The Sludge Separator is carried by water to the surface of plate No. 1.; the holes are of
an inch in diameter; the rough sludge is carried off by the water and the small falls
through the holes, and runs into trunks or buddles, the rough passing through another
buddle.
The slime is made to pass over plate No. 1., when the lead drops through, and is carried
to the inclined plate No. 2.; the rough passes over, and the small, which falls through, is
afterwards treated as we have already described. The lead which remains at the upper end
of the buddle or trunk is put into the dolly-tub, and the matter at the lower end is put into
another separator of the same kind.
The cuttings which come from the sieves are carried by water to a small grate; the
stones remain above the grate, and are then removed and thrown away; what falls through
goes on to an inclined plate with holes in it; the rough is put back again to undergo the
same operation.
The Smelting Mills are buildings for reducing the crude ore to lead, and separating the
silver contained in it.
The operations consist of roasting the ore; smelting the roasted ore at the smelting hearth;
roasting and smelting the ore in one operation at the smelting furnace; refining the metal, by
exposing the lead to the flames of a reverberatory furnace, by which it is converted into
litharge, and the silver left behind; separating the silver and lead, removing the greater
part of the latter, and sending to the refining furnace the portion containing the silver.
Roasting the ore in a reverberatory furnace is precisely the same in principle as that adopted
for puddling iron, and at the balling furnace used for heating the iron before passing through
the polls. A bing of lead ore is introduced at one time, and heated to ignition, but not to
melting; too little or too much heat is considered equally bad. The flame of the fire
strikes against the ore, and when it shows a yellow flame, it is stirred with a paddle or
iron rod with a broad end. The stirring must be repeated five, six, or seven times in a
heat. This depends on the nature of the ore, varying from one hour and a half to three
hours. A barrow, containing a bing of ore, is wheeled from the bingstead, and placed
over the furnace ready to be let in when required. When the ore is sufficiently roasted
it is raked forward by degrees and let fall into a cistern, and the heated water which flies
up is prevented by an iron plate from reaching the workmen. A reverberatory furnace is
one in which the flame and heat are carried forward by the draught of air, and dashed
against the bodies to be smelted.
When one heat is over, another bing is let into the furnace, and the same work is re-
peated. Two men are engaged eight hours at a time; they are succeeded by two others,
who work eight hours; the first set return and work another eight hours: in this manner
they proceed day and night for four days in the week, it being considered a great saving of
fuel not to let the furnace cool.
Roasting the ore drives off the sulphur from the galena or sulphuret of lead, of which it
is composed as well as the antimony and other matter more volatile than the lead. The
small dust ore is made to adhere together, whereas, if it were to be put into the smelting
hearth, and exposed to the blast, a great portion would be lost.
The roasted ore is let fall into water to prevent its forming unwieldy lumps, as it would
do if left to cool in a heap. The ore is then taken from the water and carried to the
smelting-house.
Of the Smelting Hearth.
Its usual dimensions are 22 inches long and 22 broad, and
about the same in depth; but these vary at different places. It is made of cast-iron, and
charged with half-melted matter of former operations, with peat and coal, and the roasted
666
Book II.
THEORY AND PRACTICE OF ENGINEERING.
ore.
A large bellows throws its blast into the hearth, whilst two men working together
stir the melted lead, and gradually add more ore. There is a small channel in the hearth
in which the melted lead flows into a pot at the side of the brickwork in which the
hearth is fixed, from which the men lift up large ladles of the metal, and pour it into
moulds. At most smelting-mills the smelters are divided into three sets of two men each,
who come in turns, ten hours each set at a time, so that each works ten hours and rests
twenty. Lime is sprinkled on the edge of the hearth when melted slag is running off, which
has the effect of uniting with the slag, and converting it into a solid.
Smelting-furnace is of the same description as the roasting-furnace, already described;
the roasting and smelting are both done in one heat, which occupies about five hours,
coal being mixed with the ore to smelt it. A bing of ore is roasted and smelted at one
shift; the smelting furnace, requiring more fuel than the smelting hearth, is not used where
coals cannot be readily procured. The process of roasting being effected, the doors of the
furnace are shut, and the heat is then increased sufficiently to melt the ore.
Of the horizontal Chimneys. — It is important that the chimneys of smelting mills should
carry off the effluvia, so highly injurious to the workmen. About twenty years ago hori-
zontal chimneys were first used, some of which were more than 100 yards in length.
The chimney at the Derwent Company's mines is a mile from the smelting mills, and
proceeds under ground the whole of the way up the side of the hill to the foot of a
lofty turret, carrying off the destructive smoke, but which, falling upon the ground, renders
the grass poisonous to the horses and cows partaking of it.
To prevent the land from being injured by the smelting-hearths an arched tunnel, a mile
long, is usually conducted to a chimney shaft, which at the end of the year is cleaned, and
the matter smelted, by which means a sufficient quantity of lead is obtained to remunerate
the expense of making the tunnel.
The chimney in Allendale is 3 miles in length, from which many thousand pounds
worth of lead are obtained, the farthest smoke being the richest in lead. This tunnel or
chimney is 3 feet wide and 6 feet high, so that it may be effectually cleansed.
The smelting mills are generally placed in a low situation, on account of the water ne-
cessary to turn the wheels which give motion to the blasts. It is obvious that a tunnel
carried from such a situation up the side of a hill to a great height will have a strong
draught of air, and consequently draw off the smoke and effluvia from the metal, and
the noxious matter so ruinous to the health of the workmen.
Refining the Lead and Silver. The process of refining the lead and silver depends on the
principle, that lead exposed to heat readily imbibes oxygen from the atmosphere, and
becomes oxide of lead, whilst the silver remains unaltered. It is carried on in a rever-
beratory furnace, which allows the flames from the fuel to strike against the lead and silver;
the lead is converted into litharge, and the silver, formed into a plate, remains below. Before
the metal is put into the furnace a test is made from the ashes of bones or those of ferns
or brakes (Pteris aquilina). This plant, when burnt, yields a vegetable alkali, or potash,
which constitutes its value as a test. A mixture is made of the bone and fern ashes, beat
up with water, and afterwards moulded into an oval form, and placed within an iron frame
in the furnace, with the pig of lead upon it: some of the litharge is absorbed by this
mixture, and its quality tested The flames change the lead into a semi-vitrified oxide or
litharge, the melted lead abstracting oxygen from the air. On one side is an opening, and
at the other the blast of a large bellows is introduced, which blows the litharge from the
su face, and occasions it to fall through an opening into an iron vessel placed to receive it,
which, when nearly full, is removed, and another put in its place. The test absorbs in
two or three days such litharge as is below the silver, with a part of the silver.
Of the Separation of Lead and Silver. The present mode of separating these two metals
was discovered by Hugh Lee Pattinson, of Alston, an agent employed by the trustees of
Greenwich Hospital to test the lead paid to them as their royalty, to ascertain the quantity
of silver it contained, and to determine its value. In the course of conducting his opera-
tions he observed that part of the lead crystallised before the rest, which induced him to
attempt to discover the cause; and on analysis he found that the portion which continued
longest liquid contained a larger proportion of silver.
The operation, as now practised, may be thus described. Three cast-iron pots are set
in brick along the middle of the chamber; when the lead is melted in pot No. 1., it is
stirred with an iron rod, and every now and then the lead which adheres to the rod is removed
with a great hammer. On the other side a man with another rod, at the end of which is a
ladle full of holes, dips it into the pot of melted lead No. 1., and, pressing it on the edge
of the pot as a fulcrum, raises up the ladle nearly full of lead, curled, crisping, and frosted,
which runs out in a liquid metal from the holes in his ladle. This is held above the
surface, and shaken till no more metal will run out, and then the lead is emptied into pot
No. 2. This operation is continued until there be very little liquid metal left in pot No. 1.,
if there be a breeze of wind through the room, the lead cools faster, and the work goes on
more rapidly. The metal in pot No. 1. is then brought into moulds and cast into pigs,
CHAP. II.
667
COMPOSITION AND USE OF MINERALS.
and that put into pot No. 2. is melted, and is treated in the same way as the lead in pot
No. 1. The lead taken away is then put into pot No. 3., and melted and treated in the
same manner, when it is found to contain so little silver that it will not defray the expense
of melting it a fourth time.
In some mines the lead is richer, as at Greenside, where there are five pots in the
separating room; the lead of this mine contains from 12 to 14 ounces of silver to the ton,
and there is sufficient silver, after it has been melted and separated the third and fourth
time, to cover the expense, and yield a profit in melting it again.
Of the reducing Furnace. Under the new system, before the remaining lead and silver
is subjected to refining, comparatively little litharge is made, although there is more than
can be sold at a remunerating price, either to the glass-makers or the colour-makers ;
much, therefore, is reduced to metal in the reverberatory furnace, at the bottom of which
is placed a layer of coals, and the litharge, mixed with small coal, is put in and exposed
to the flames. During the combustion the small coal abstracts the oxygen from the
litharge, and pure lead is the result, which is cast into pigs of 12 stones each, and is in a
malleable state,
Reducing the Slag. The slag is put into a furnace, mixed with coke and heated by
fuel beneath the oxygen of the slag enters into combination with the fuel, and the
lead is separated and cast into pigs. This is less valuable than the other, and is easily
broken.
Cast Lead is manufactured by melting the pig-lead in a large iron vessel, and then ladling
it out on a table 18 or 20 feet in length, which has been previously covered with fine
pressed and beaten sand, brought to a level and smooth surface by passing a strike
over it.
The table has a rising edge all around it, on the top of which is a movable
strike, which determines the thickness to be given to the sheet; this strike, when the metal
is in a liquid state, sweeping before it the superabundant lead. When a very thin sheet is
required to be cast, a linen cloth is stretched over another of wool, on which is poured
the lead, care being taken that the heat is not sufficient to set fire to the paper, and it is
requisite, as the lead cools rapidly, to be very adroit in passing the strike over it.
Milled Lead is first cast in sheets, and then passed under rollers, placed at such a distance
apart as is required for its thickness, the space between each pair of rollers it passes
through diminishing gradually: the weight in pounds of a superficial foot is
When of a sixteenth of an inch in thickness
a twelfth
a tenth
an eighth
a sixth
a fifth
-
-
lbs.
331
5 6
71
10
12
143
193
a quarter
a third
a half
·
1
29
The weight of a cubic foot of lead is 709 pounds, and Smeaton found that a bar 12
inches long, 1 inch square, and weighing 4·94 pounds, was expanded by 1 degree of heat
2500. Lead melts at 612 degrees, and will bear a weight of 1500 pounds on each square inch,
without altering its form materially. Compared with cast-iron its strength is 096; its
extensibility 2.5 times, and its stiffness 0385 times.
62300*
Casting of Leaden Pipes is comparatively a recent invention; for those used in water-
works were commonly made of sheet lead wrapped round a wooden or iron core, and where

IMF CAES ADRIANI AVC,
DO

Fig 584.
LXMVOII
PIPES FOund at LYONS.
668
Book II.
THEORY AND PRACTICE OF ENGINEERING.
the edges met, they were soldered together: pipes so made are very liable to burst,
from the soldered joint giving way. Some of the pipes found at Lyons, near the Roman
aqueducts, were evidently made in this manner, and perfectly agree in form with those
Vitruvius describes.
Pipes are sometimes cast in an iron mould made in two halves, and afterwards united to
form a hollow cylinder, into which a core or iron rod, the size of the intended bore, is intro-
duced; the two halves of the iron mould are secured in their position by screws or wedges,
which make the core that occupies the centre fit in such a manner that there is an equal
distance all round to receive the melted metal, which enters it by means of a spout, care
being taken to allow the air to escape. The mould is fixed to a long bench, and a rack
moved by toothed wheels and pinions is fitted to one end of it, in a line with the centre
of the mould, which by means of a hook connected with an eye at the end of the core
enables it to be drawn out when the pipe is cast: when this is done, the iron halves which
form the mould are separated, and the pipe is moved onwards, an inch or two of its end
alone occupying the mould; the halves are then again secured together with the core
between them, and its end entered again, an inch or more into the first piece of pipe; the
mould is filled with melted lead, the heat of which unites it with the end of the first piece,
so as to double its length, and the core being again drawn out is ready to be used for
another piece. Any length of pipe may be thus cast, but the metal is very subject to air
bubbles, and the joinings are far from sound. The usual method now is, to cast the lead
in an iron mould upon a cylindrical rod of the size of the intended bore, leaving around the
core a space three or four times the thickness of the intended pipe; after they are cast in
short lengths, they are drawn through holes of steel plates, and reduced to the thickness
required. Another process is to reduce the pipe by passing it through two rollers of a
flatting mill, in each of which semicircular grooves are formed all round, so that the two

បណ
日
​
I
Fig. 585.
MACHINE FOR FORMING LEAD PIPES.
rollers when united have circular cavities between them, which gradually diminish in
diameter from one end of the rollers to the other. The pipe after passing through the
largest cavity, then the others to the smallest, is diminished in its thickness or substance;
and by this process also hardened and rendered stronger.
The section shows the two half moulds screwed up in their place, with the core or treblet
in its position; and great care is required that the interior surface of the former is truly
cylindrical, and that the latter is accurately turned in a lathe, so that an equal space
is left around or between the two, or the metal will be cast unequal in thickness. The
inclined plane on which the process is conducted is necessary, in order that when the metal
is poured in at the cup at the lower extremity, the air may pass out at a hole or vent left
at the upper end, where the hook is connected with the rack. The core has a neck or
smaller part at the end, which prevents its being drawn through the pipe; and by means
of the rack and pinion, the pipe is drawn to its required length.
The other machine has a strong timber framework with a cog-wheel moved by a
steam-engine or water-wheel, and which can be put in motion by the handles or levers
shown above the stage. The drum of the cog-wheel has a pair of spiral grooves formed
on its circumference, for the reception of two chains, the ends of which are hooked to a
little carriage on wheels, and which has at the back a double claw to engage in the notches
made at the end of the core or treblet. In the middle of the bed is a cast-iron frame,
CHAP. II.
669
COMPOSITION AND USE OF MINERALS.
securely fixed on a short cross-bearer; in this is a notch in the upright side nearest the
roller, which allows the treblet and pipe to pass through, and also forms a hold for the steel
plate through which the pipe is drawn: these steel plates or whirtles vary according to
the sizes of the pipes, and are movable at pleasure; they are made rounding on one side,
to allow a more ready exit and entry of the pipe, and diminish gradually, from the size
of the rough cast pipe to that required. When the lead pipe is fitted to the treblet, it is
laid upon the rollers on the bench, and the end of the treblet being put through the largest
set of whirtles, it is hooked on to the carriage, and the whirtle lodged against the cheeks
of the frame. The drum is then put into gear by means of the handles and levers, and,
winding up the double chains, the pipe is drawn through the whirtle, and diminished in
size as it is lengthened. After the pipe is drawn entirely through, the roller is cast off by
shifting the levers; the treblet is then unhooked from the carriage, and pushed back into
its former position, and a smaller whirtle being put on, the pipe is drawn through as
before; the operation is repeated through smaller whirtles, until the pipe has acquired
its proper thickness: this is sometimes performed through a dozen, when it is made
perfectly even and smooth; the elevation and two sections of the whirtles are shown above
the machine. By this means lead pipes are drawn out in lengths of from 10 to 12 feet;
after which, by a process termed burning, they are united together; this is performed by
passing through one pipe an iron core, which enters a few inches into the other, and a
small iron mould put together in two halves over the ends of the two pipes, which are
brought close together. Melted lead is then poured into the mould, which runs out by
a hole in the bottom; when the stream of lead has run a sufficient time to fuse the ends of
both pipes, a slider is made to pass over the hole, and the mould being left full is suffered
to cool, when the pipe is removed.
Zinc or Spelter has a crystalline texture, is brittle at ordinary temperatures, and of a
bluish white colour: at 300°, it is both malleable and ductile, and at a white heat is
converted into vapour.
When pure zinc is exposed to air and moisture, it acquires a dull
colour from partial oxidisement; and great electric action takes place when it is in contact
with copper, and the zinc decays in consequence. Its specific gravity is 7, and it has a
great attraction for oxygen; the weight of a cubic foot is 4394 pounds.
Oxide of Zinc is obtained by intensely heating the metal exposed to air; it takes fire
at a red heat, if the air is freely admitted, burning with a very bright flame.
Zinc
Oxygen
-
1
1
1
32
80
8
20
40
100
Sulphuret of Zinc (Blende) is found native, and is a brittle soft metal of a brown and
Elack colour; its primitive form is a rhomboidal dodecahedron, and it is a most abundant
mineral. The pure metal is obtained from it by roasting the ore, and afterwards distilling
it when mixed with charcoal.
Zinc
Sulphur
1
32
66.5
1
16
33.5
1
48
100.0
Carbonate of Zinc (Calamine): when found crystallised, its primitive form is an obtuse
rhomboid.
Oxide of zinc
Carbonic acid
-
1
40
64.5
1
22
35.5
1
62
100.0
Zinc is obtained from the sulphuret and carbonate; the ore when broken is submitted to
a dull red heat in a reverberatory furnace, when the carbonic acid is driven off from the
calamine, and the sulphur from the blende: it is then mixed with of its weight of powdered
10
charcoal, being first ground and thoroughly washed, and distilled by the application of a
red heat; the metal being put into earthen pots with iron tubes cemented into the lower
parts, dipping into water, where it is collected, and afterwards cast into cakes. A bar
of zinc 12 inches long, and 1 inch square, weighing 3.05 pounds, expands in length at one
degree of heat and melts at 648°; it will bear, without permanent alteration, a
pressure on a square inch of 5700 pounds.
Zinc is used for the preservation of iron, by electro deposition. The iron is first rendered
perfectly clean and free from oxide, by placing it in a bath of heated sulphuric acid and
water; then in a cold solution of sulphate of zinc. The positive pole of a galvanic
battery is attached to a zinc plate, and the negative to the iron to be covered; the pure
metal is deposited, and the zinc and iron are amalgamated. Wooden troughs are em-
670
Book f1.
THEORY AND PRACTICE OF ENGINEERING.
ployed for the process, and iron plates so covered are extensively used for roofing, and do
not after many months exhibit any signs of decay. The iron being coated with zinc in a
cold solution does not in any way change its condition; but when the zincing of iron is
performed, by steeping it in a bath of melted zinc, a combination takes place between the
two metals, and a brittle alloy is the consequence, the iron losing all its tenacity.
Tin is usually prepared from the native oxide, its oxygen being removed by charcoal: the
purer kinds are called grain tin, and the others block tin. The common ores are known
under the name of mine tin, and furnish a less pure metal than the stream tin. Tin has a
silvery white colour; its specific gravity is 7-3, and air and moisture have little effect upon
it: it melts at 442°, and is converted into a white oxide by exposure to heat and air.
The specific gravity of the native peroxide of tin is 7, and its primitive crystal an obtuse
octohedron.
Protoxide of Tin: specific gravity 6·6:
Tin
Oxygen
1
58
87.8
1
8
12.2
1
66
100.0
Bisulphuret of Tin, (Aurum musivum, Mosaic Gold,) is a mixture formed by heating per-
oxide of tin, which contains two of oxygen and one of tin, with its weight of sulphur.
Bisulphuret of tin is also formed by decomposing perchloride of tin by sulphuretted hydro-
gen; it is quite insoluble in the acids, except nitro-muriatic; it forms the bronze powder
used by paper-stainers.
Tin -
Sulphur
1 2
1
58
64.4
32
35.6
90
100.0
The weight of a cubic foot of cast tin is 455.7 pounds, and the weight of a bar 12 inches
long and an inch square is 3·165 pounds; it expands, according to Smeaton, at one degree
of heat and melts at 442°.
72510'
It will bear on a square inch 2880 pounds without any
permanent alteration, and an extension of length of 10 Compared with cast-iron, its
strength is 0.182 times, its extensibility 0.75 times, and its stiffness 0.25 times, cast-iron
being considered as unity.
1600
Copper is found native, and of its ores the most remarkable are the oxide, sulphuret, sul-
phate, carbonate, chloride, arseniate, and phosphate. It has a red and brilliant colour, is
malleable and ductile, melts at a dull white heat, or at 2548°, and in oxygen gas burns with
a green light; when long exposed to moist air a green crust of the carbonate is formed
upon its surface. The weight of a bar 12 inches long and 1 inch square is 3-81 pounds, and
its length is increased by one degree of heat 10900. Its specific gravity is 8.8, and the cohe-
sive force of a square inch is 33,000 pounds when hammered. Copper is principally pre-
pared from the native sulphuret of copper and iron, which is heated with a flux of charcoal
and siliceous matter; the sulphur is first expelled, and the metals oxidated; the oxidated
iron forms a slag with the flux, and the charcoal reduces the oxide of copper. When the
ore is broken, it is heated in another reverberatory furnace, where it is fused, and the re-
mainder of the slag removed from it, when it is cast into pigs, which are again broken up
and melted with a portion of charcoal. The metal is rendered malleable by constantly
stirring it when in the furnace with a pole of green wood, and it is afterwards cast into
cakes 18 inches by 12, the weight of a cubic foot of which is 549 pounds.
Oxide of Copper is black, insoluble in water, but with acids forms coloured salts.
Copper
Oxygen
1
1
1
32
8
40
80
20
100
Sulphate of Copper (Blue Vitriol) is formed by dissolving peroxide of copper in diluted
sulphuric acid; its crystals are of a fine blue colour, and in rhomboidal prisms. The com-
mon blue vitriol is obtained by exposing roasted sulphuret of copper to air and moisture,
but it is often impure, from the iron and zinc it contains. When animal substances are im-
bued with it and dried, they remain as it were preserved, and it has been employed in a
state of solution to immerse timber for the purpose of preventing the dry rot.
The crys-
tallised sulphate of copper contains
Oxide of copper
Sulphuric acid
Water
1
40
32
1
40
32
5
45
36
1
125
100
CHAP. II.
€71
COMPOSITION AND USE OF MINERALS.
Sulphuret of Copper is an artificial compound.
Copper
Sulphur
1
32
50
1
16
50
1
48
100
Carbonate of Copper (Malachite) is found native, but never regularly crystallised; it is of
a fine green colour, but sometimes of a beautiful blue.
Oxide of copper
Carbonic acid
2
1
1
80
78.43
22
21.57
102
100.00
ALLOYS OF COPPER.
Ormolu is an alloy of copper and zinc in equal quantities,
melted at the lowest temperature at which copper will fuse; they are then stirred
together, and when thoroughly mixed, a further quantity of zinc is added in small quan-
tities, until the alloy has attained in the melting pot the desired colour. It should be
observed that the zinc will fly off in vapour if the temperature is too high, and the residue
will become spelter, or hard solder only; but when the operation is properly managed the
alloy will acquire first a brassy yellow, then, by adding a little more zinc, a purple or violet
hue, and afterwards become perfectly white, which is the proper hue for the compound in a
fused state.
Sterling or Standard Gold consists of 11 of gold and 1 of copper specific gravity
17.157.
Brass is an alloy of copper and zinc, usually in the proportions of from 12 to 18
per cent. of zinc; its specific gravity varies from 7-8 to 8.4. It may be also made by mixing
50 parts of oxide of copper, 100 of calamine, 400 of black flux, and 30 of charcoal powder;
these melted in a crucible till the blue flame is no longer seen, a button of brass of a golden
colour is found at the bottom, weighing about one-sixth more than the pure copper ob-
tained from the same quantity of oxide.
Pinchbeck, or Dutch Gold, contains more copper than exists in brass; a little tin is some-
times added.
Speculum Metal is an alloy of copper, tin, and arsenic.
Bell Metal and Bronze: the former consists of 3 parts of copper and 1 of tin, the latter of
from 8 to 12 of tin with 100 of copper; when a shrill sound is required zinc in a small
proportion is added, and sometimes lead. Bronze requires its texture to be softened when
heated, and then suddenly cooled.
Tinned Copper.—Vessels intended to be tinned have their surface cleaned and washed
with sal-ammoniac; a bit of tin then rubbed over it unites and covers the copper.
Gun Metal: copper 663, tin 336; another variety, copper 764, tin 236.
Bronze for Statues usually contains 0·20 parts of tin. In an ancient Egyptian poniard
was found 85 copper, 14 tin, and 1 iron: in a mirror 62 copper, 32 tin, 6 lead.
German Metal: copper 534, nickel 175, zinc 291; it resembles silver of 18 carats; it is
employed in the manufacture of all ornamental works where silver is used: 90 parts of
copper, 5 of zinc, and 5 of antimony, is the best alloy to make plummer's blocks for the iron
or steel gudgeons of machinery to run in.
The Copper and Tin Mines in Devonshire and Cornwall may be considered to commence
at Dartmoor and terminate at the Land's End. The surface of the country is gently undu-
lating, the loftiest hills rarely exceeding 1000 feet above the level of the sea, and the planes
at their bases are in general from 100 to 200 feet above high-water. The highest peaks are
granite, and the lower hills and the plains consist of various slates. The granite may be said
to occupy Dartmoor, the neighbourhood of Rough Tor and Brownwilly, the Hengsbarrow
district, the Cairn Bren range, which is separated from that of Wendron by a narrow slip of
slate near Pendarvis, and the western tract, which extends from St. Ive's to the Land's End.
Granite is also found at Kithill, Brenge, and St. Michael's Mount, and in a few other localities.
All the other parts of Cornwall (except the Lizard district, which is of serpentine,) may be
considered to consist of slate of various kinds.
The granite, in general cross-grained and of porphyritic structure, contains felspar,
quartz, and mica; but in some places the mica is replaced by talc; the rock is then called
China-stone, the felspathic portions of which, when decomposed, are washed out and pre-
pared as porcelain earth for the manufacture of earthenware. In some of the granite schorl
abounds. In the year 1838, 28,000 tons of this porcelain clay and China-stone were exported
from Coruwall to the Potteries.
The slates are in general felspathic, and near the granite their structure is often com-
pact, whilst at greater distances they are lamellar and schistose in their structure, and still
farther off they become fissile, and make excellent roofing slates. The laminæ of the slates
usually dip from the granite, round the flanks of which they are symmetrically arranged,
672
THEORY AND PRACTICE OF ENGINEERING.
BOOK II.
which has occasioned it to be observed, that the granite peaks rise like islands in an ocean
of slate. The range or bearing of the masses of granite is about north-east and south-west,
and the mines occur on both sides of it. Both the granitic tracts and the slates in their
vicinity are intersected by veins or dykes of a porphyritic felspar rock (provincially called
Elvan). These veins have been traced for miles, passing uninterruptedly through both
granite and slate; their usual direction is about 20° south of west, and they are generally
several fathoms in width where they fall in contact with the veins they appear as if they
had been portions of the strata.
The schistose varieties of the slate formation, considerably above the granite, contain
beds of limestone, which coincide in position with the slaty laminæ, but are more generally
irregular and unconformable. The metalliferous veins or lodes have an average direction
of 4 degrees south of true west, but the general bearings are not the same in other parts
of Cornwall: those of St. Just, for example, run about 35° north of west; in the same
district, and even in the same mine, (as at Dolcoath, East Wheel Crofty, &c.), there are
often two series of lodes, one bearing nearly east and west, whilst the others, called counter-
lodes, are nearly south-east and north-west.
The dip or inclination of the lodes is about 60° or 70° from the horizon, and four out of
six may be said to incline towards the nearest mass of granite; the lodes near Dart-
moor are for the most part flatter than those in the west of Cornwall. Taken on the
whole they appear tolerably straight in direction and in inclination, but when examined
in detail, it will be found that they exhibit almost continual curvatures or irregularities;
still, however, these flexures seem projected on certain lines, which have considerable con-
stancy.
The width of the lodes on the average is about 3 feet, but they vary from a mere line to
40 or 50 feet; each lode seems to have a natural or casual breadth of its own. The
composition of the lodes is as variable as the nature of the rocks through which they pass;
the greater number is composed of earthy matter, of the nature of the contiguous rock,
mixed with large quantities of quartz. These ingredients are sometimes in separate
veins, but for the most part are mixed without regularity or order; through them the
metallic ores are dispersed, sometimes thickly, or in irregular lumps connected with each
other by small veins of ore; in other cases the ore is very sparingly sprinkled through
the earthy matter of the vein, and in some rare instances forms the larger part of its
contents. The masses of ore in the lodes usually dip from the granite, and the deepest
parts of the mines are consequently farthest from where that rock appears at the surface.
There is a second series of veins which run nearly at right angles to the lodes, called
cross-courses when they are composed of quartz, and flucans when of clay. The general
direction of the former is somewhere about south-east and north-west: their dimensions
are variable, being perhaps on an average 2 feet; their dip fluctuates, but as a general
rule, it is greater from the horizon than that of the lodes. It has been already mentioned
that quartz and clay form the larger part of their ingredients: this clay is invariably of
the same character as the contiguous rock.
Tin and copper ores are occasionally found in small quantities in the cross veins, and in
two or three instances silver and its ores have occurred to some amount. The chief metallic
produce of this class of veins is lead ore, but they seldom yield it in the neighbourhood of
lodes which are productive of other metals; it being a general law in Cornwall, that
two series of veins, at right angles to each other, are seldom found productive in the same
district.
Both the lodes and cross veins ramify and divide, and whilst the one which is rich will
sometimes within a short distance dwindle away, that which is small will often enlarge
and become productive.
As these two varieties of veins run at right angles to each other, they of course
frequently meet and intersect. There are a few cases of the lodes traversing the cross
veins, but in the larger number of instances the cross veins cut through the lodes, and
occasionally simply intersect them, but generally a displacement attends their contact;
the separated portions of the lodes not occurring exactly opposite to each other on both
sides of the cross vein. These displacements are called heaves, and although they are usually
for a few feet or fathoms only, yet some cases are on record where the discordances are as
much as 20, 30, or 40 fathoms, and in one instance 72 fathoms. It is not easy to lay down
a rule for finding again the second portion, but it is perhaps rather more frequent to
discover it on the side of the obtuse angle formed at the intersection than on the acute. It
is obvious that on whatever portion of the lode we approach the cross veins, the other
will be found towards the same hand; the separated portions are more commonly found
towards the right hand than the left. These heaves are the most intricate and baffling pheno-
mena with which the Cornish miners have to contend.
There is a third series of veins bearing parallel to the lodes, which are generally of small
size, and consist of clay, called slides. These are confined to the slate districts, and seldom
metalliferous: they interscet the lodes on the lines of their inclinations, and cut off the lower
CHAP. II.
673
COMPOSITION AND USE OF MINERALS.
from the upper parts, producing similar displacements vertically as those which the cross
veins occasion horizontally.
Taking the granite and slate with the lodes which traverse them, it appears that
the largest part of the tin ore obtained in the west of England is from lodes in the gra-
nite, and that of copper ore from veins in the slate, though the richest masses of tin ore yet
discovered have been in slate, whilst the bunches of copper ore found in the granite have in
a few instances been as large as any which have occurred in slate.
It is a prevailing and apparently well-founded opinion among practical miners, that the
lodes are most productive near the junction of the granite and slate rocks; accordingly
the mines, instead of being irregularly distributed over the face of the country, are clustered
together near the lines of these junctions, and the heaps of rubbish separated from the
ores may be traced in such situations for considerable distances on the lines of the chief
lodes, rising in some cases amidst rich fields, and destroying the vegetation like streams of
lava from a volcano.
The St. Just mines form one group near the Land's End, those near St. Ive's another, at
the opposite ends of the same granite mass; those of Breage a third, subordinate to the
granite of Godolphin and Tregoning hills. The Crowan and Gwinear mines stand at the
western extremity of the Cairn Brea and Wendron granite, whilst those of Camborne and
Redruth skirt it on the north, and those of Wendron on the south, and the Gwennap dis-
trict occupies its eastern flank. In like manner many of the St. Agnes mines are located
near a small patch of granite at Cligger Point; those of St. Austell are grouped on the
skirts of the Hengsborough granite; whilst the mines near Callington and Tavistock are
contiguous to the Kithill and Dartmoor ranges.
TIN ORE is also found in deposits generally considered diluvial, mixed with the debris of
different rocks, covered with an alluvial bed. Repeated washing by means of running
water being the chief process to which such tin is subjected, the designation of stream-work
is commonly applied to this method of obtaining the ore. In a solitary instance at Carnon,
this stratum of tin stuff is removed by subterraneous excavation, the alluvial bank or over-
burthen being too thick to be taken off, and it is subject likewise to be covered by the sea at
high water.
Mines of iron and manganese, giving employment to a considerable number of persons,
fall also within the district above described; among them those near Lostwithiel are the
most important. The ore lies in a vein, nearly vertical, and of an average thickness of
10 feet. The greater part of this mine is worked open to the surface, and the access to the
underground part is by levels: the greatest depth does not exceed 50 fathoms. The
manganese mines, which are chiefly situated on the borders of the two counties, are like-
wise very superficial, the workings being seldom carried more than from 20 to 30 fathoms
from the surface. Antimony has also been raised to some extent, but the foreign ores of
this metal have of late years almost monopolised the market, and very few persons
are now employed in obtaining it. The mines of tin, copper, and lead, with the latter of
which metals silver is generally united, are those which present the characteristic features
of the mining of the west of England.
When it is known or thought probable that a lode which will repay the cost of working
exists in a particular locality, the usual course of proceeding is to sink a shaft vertically
to a certain depth, which shall intersect the lode. If this cannot be done, a gallery or
level is driven or excavated at right angles to the shaft, in the assumed direction of the
lode, and continued till it is reached: in either case, when reached, a level is driven hori-
zontally along its course, the miner working upwards and removing the rock from above.
It must depend on the thickness of the vein and its inclination, whether it is necessary to
excavate any of the adjoining rock, and to what extent. Meantime the shaft being sunk
still deeper, another gallery or level is carried along the vein or lode, usually about 10
fathoms below the former, and the metalliferous stone intervening between the two levels is
subsequently removed. This process is repeated again and again, and as the workings become
more extensive in length, additional shafts become necessary. Horse and water power are
made use of for effecting the earlier operations, but the steam-engine is employed in most
of these mines; and as they increase in depth and extent, very powerful machinery is needed
to raise the excavated rock and the water. Shorter shafts, called winzes, are formed at
intervals between the levels, for the purpose of ventilation. In proportion to the dip or
inclination of the vein, there must be an advance in a horizontal direction, as the
depth of the workings increases, which renders a communication necessary from the
lower levels to the surface, in a more direct manner than can be furnished by the shafts.
At a very early stage of this process, a separation is established between the shafts by which
the men pass to and from their work, and those in which machinery is employed. This
separation is effected by a boarded division in a single shaft, or by devoting two distinct
shafts to these purposes; excepting the occasional raising of men and boys in buckets through
short distances, ladders are the universal means of ascent and descent in these mines.
Many of the shorter shafts, or winzes, are provided with ladders, so that the course taken
X x
674
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
by the miner is commonly not one of continuous descent and ascent, but varied by his
traversing at different intervals a considerable length of horizontal galleries.
Mr. De la Beche in his geological report has estimated the value of the mineral exported
produce of Cornwall and Devon in 1837, as follows:-
·
Copper
Tin
Manganese
Lead
China-stone and clay
Granite
952,855
415,518
40,000
3,000
43,000
24,500
The smallest height of the levels in Carnon mine from which a
stuff is removed is 5 feet, and the thickness of the vein of ore 3 feet;
13 fathoms from the surface of the ground.
£ 1,478,873
horizontal bed of tin
and the ore is about
St. Ive's Consols well illustrate the character of the greater part of the tin mines. The
smallest height of the levels is seldom less than 6 feet; the thickness of the bed or vein of
ore is from a few inches to 10 feet, and sometimes more than double that in width. The
lodes in this district enter the rock at the surface, at an angle of 50°, 60°, or 70°, from the
horizon, and sometimes almost vertically, and if productive, from any given level to
another, are regularly cut away, after first supporting the sides and roof of the level
with timber frame-work fitted to the angle of the lode, which in few cases proves otherwise
than completely safe and secure. The workings below the level or surface of the ground
vary from 30 to 147 fathoms, and 20 fathoms from the adit.
In the Charlestown tin mines the smallest height of the levels is 7 feet, and the thick-
ness of the bed or vein of ore is from 3 to 10 feet. In the copper mines in the central
district, in the United Mines for instance, the levels in the ancient workings do not
exceed 5 feet high and 2 feet wide; but those made recently are about 7 feet high and
4 feet wide. The veins are nearly perpendicular, and vary from 1 inch to 9 feet wide:
the ores are got from between 40 to 220 fathoms from the surface. In the Consolidated
Mines of this district, the deepest, the smallest height of the level is 6 feet, and width
21 feet: the openings in the platform, from one ladder to the other, 18 by 12 inches; the
thickness of the vein of ore varies considerably, sometimes being 8 feet, at others a few
inches only. The veins do not incline much from the perpendicular, and consequently the
levels are driven 6 feet high, and the ground above is worked afterwards. The ore is sometimes
found nearer the surface than the adit level; but in general it is worked from 20 fathoms
from the surface, to the 260 fathom level below the adit, the deepest point being nearly
300 fathoms from the surface.
In the large copper mines of the Levant in the western district, the height of all the
levels is 6 feet, and from thence to the next level 10 fathoms or 60 feet; the thickness
or width of the whole vein, where the ore is found, is on an average about 4 feet. The
vein, almost perpendicular, having a small declination only, is worked by the side at first,
and taken down afterwards. The adit or sea level is 30 fathoms under the surface, and
the ore in work from 70 to 230 fathoms below the adit.
In the Eastern Cornwall district, the Fowey Consols copper mine is the most con-
siderable; the smallest height of the levels is not less than 6 feet, and often 7 feet or more,
where air-pipes are required for ventilation. There are no horseways in these Cornish
mines; the twenty lodes vary in thickness from 8 feet to only a few inches. When the
lodes are perpendicular, and of a sufficient size for the levels to be driven, they do not cut
away any of the overlay or underlay, as the lode is very rarely perpendicular. The
air of these shafts and levels is more condensed than that on the surface, with a
temperature higher in proportion to the depth. There is no reason to believe that any
gas except carbonic acid is generated from the strata in these mines: where they have
been carried beneath beds of alluvium, which are periodically submerged, some of the
inflammable compounds of hydrogen are at times emitted. The natural temperature at
different depths, and in different strata, is given by Mr. Henwood, who personally
inspected 200 mines in Cornwall and Devon, and made several hundred observations
on the temperature of the streams of water which flowed from the unbroken rocks.
Depth in Fathoms.
Surface to 50
50
to 100
100
to 150
150
to 200
200 and upwards
-
In Slate.
57° Fahr.
61.3
68
78
85.6
In Granite.
51.6°
55.8
65.5
81.3
When work is carried on, there is of course a rapid exchange of oxygen for carbonic
acid, by means of the respiration of the miners, the burning of candles, and the blasting
CHAP. II.
675
COMPOSITION AND USE OF MINERALS.
which takes place; when the gases generated by the explosion of gunpowder are diffused
a thick smoke fills the shaft or level. The following analysis shows the extent of impurity
of the air in the places in which the men are employed.
From eighteen samples the summary of the analysis was, oxygen 17.067, carbonic acid
085, nitrogen 82.848, and in one instance the quantity of oxygen was reduced to 14·5],
and in another the carbonic acid was 0·23. These results exhibit a lessening in the pro-
portion of the vital ingredient of the air from its usual per centage, 21, and an increase in a
directly noxious ingredient, carbonic acid gas, from 0·05, its ordinary amount, calculated to
produce effects sufficiently injurious to those who for hours together inhale such a fluid.
Ventilation is produced by the sinking of various shafts at short intervals, beneath the
lowest levels, and establishing free communication between them as speedily as possible.
But no method hitherto introduced is adequate to maintaining the air in a state of purity;
every mine is more or less wet, as it constitutes a receptacle for the waters permeating
the strata through which it passes.
The Adit is the drain through which the water, lying above its level, and a great part of
that raised by machinery, is discharged. One or more of the deepest shafts are appro-
priated as wells, from whence the water is raised by steam power, a preliminary process
involving the greatest difficulty and outlay connected with the working of many mines.
Such a well or pit at the bottom of the engine shaft is called the sump, and when the water
has been so far removed as to admit of the workings being carried on in the lowest levels,
it is said to be in fork. Mines in slate are generally more wet than those in granite.
When the mine is situated near the coast, its drain or adit generally opens on the surface,
at a point a little above the level of the sea, and when inland the deepest valley in the
neighbourhood is the place of its discharge. In some cases a large common adit has been
driven a little above high water into the centre of an upland mining district, and the separate
adits of the several mines opened into this general drain. In many mines a large quantity
of water is constantly poured through the interstices and fissures of the strata, and it is often
at a temperature so much lower than that of the air in which the miners are at work, that
they are subject to very serious chills from this cause.
Ladders are the universal means of ascent and descent, the distance between the levels
being generally 60 feet; a single ladder in former times reached from one to the other, but
the most usual length at present is from 4 to 5 fathoms. In the perpendicular shafts the
inclination is commonly such that the ladder may nearly traverse the breadth of the shaft ;
from 18 to 21 inches in the fathom is the inclination which experience has determined to
be the best calculated to facilitate the progress of the miner, being that which enables him
to stand upright on the ladder with the leg clear from the stave above, so that the effort is
divided between the upper and lower extremities. The distance between the staves
is generally 12 inches, in some old ladders they were 14 inches apart, but 10 inches is
found the best for facilitating the climbing, by which one-fourth of the labour is
estimated to be saved. The staves are of wood, though iron is in some instances preferred,
in others it becomes slippery and rough from the corrosive action of water impregnated
with
copper, &c.
Each ladder usually terminates on a sollar or platform, which leads to
that below, which is generally placed parallel to that above; trap doors are provided
over each man-hole to prevent accidents, but closing them obstructs the free ventilation.
The principal tools used by the miners are picks for working the rocks, borers and mallets
for making the holes for blasting; these are often sent up and down in the bucket (kibble)
in which the ore or rubbish is drawn to the surface, but the miner very commonly carries with
him from 10 to 20 lbs. weight of tools, there being a constant necessity for hardening and
sharpening them, which is done at the smith's shop; in some mines this is established un-
derground, which is very advantageous, the weight of coal sent down being only one-fortieth
of that of the tools sent up.
The dress of the miner is of woollen, consisting generally of trowsers, shirt, and jacket;
he does not wear stockings, but puts on a pair of thick shoes, and covers his head with a
strong felt cap, hemispherical on the crown, and broad-brimmed, about 2 pounds in weight;
on this he usually sticks his candle by means of a lump of clay, attaching another to a
button. These habiliments are, unless the miner lives near at hand, usually kept at the
mines in the changing-houses, where the ordinary dress is left until he comes up from his
work.
The great body of the miners underground are employed in excavating the rock,
whether for the sinking of shafts, the driving of levels, or the removing of the veins of
ore, which operations require the almost constant application of the explosive force of
gunpowder. The greatest part of the work consists in beating the borer, that is, in driving
an iron cylinder terminating in a wedge-shaped point, by blows with a heavy hammer
(mallet), whilst it is turned by another hand. The necessity or advantage of making
the hole in a particular direction often constrains the miner to assume every variety of
posture; he is even compelled at times to lie on his side. When the rock has
been bored to a sufficient depth, the charge is introduced and rammed down with a
X X 2
676
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
tumping iron, a particular clay being used for wadding, a certain length of safety fuse
keeping up the communication with the powder; when fire is applied the miners retire till
the explosion has taken place. It is not often that the safety fuse misses fire, but accidents
now and then arise from its burning more slowly than usual, which may occur from too
tight ramming down, when the impatience of the miner induces him too early to
examine into the cause of the delay, and the explosion takes place before he withdraws.
After the blasting the pick comes into requisition for the removal of the partially separated
angular pieces of rock; in soft ground the use of gunpowder is only occasionally re-
quired. These works are done by the piece; the miner contracts to excavate the
rock in a certain situation at so much per solid fathom; this is denominated tut-work; or
he undertakes to excavate the vein, and to fit the ore for the market, at the price of so much
in the pound of the sum for which the ore is sold; then it is called tribute. Both these
contracts are to a certain extent speculative; but whilst the former involves only the un-
certainty of the nature of the ground, which in these strata is not ordinarily great, the latter
is dependent on the character of the vein, as well as on its size and richness, which are ex-
ceedingly variable in the majority of mines; the consequence is, that while the tut-workman
receives pay approaching, in the regularity of amount, to that of the daily labourer, the
tributer is on one occasion absolutely a loser, and on another receives a sum unusually large
for a person in his rank of life; he is in fact a co-adventurer with the owners, but one who
risks nothing but his time and labour.
The methods by which the contracts are let tends, however, to equalise, in a great
measure, the average monthly earnings during periods of considerable length; at certain
stated times, generally at an interval of two months, the work to be done in different
levels is put up to be contracted for. Each place of work (pitch) requires a certain number
of men and boys, determined by the agent, the partnerships between the individuals being
entirely voluntary. The greater part of the men who are employed in a particular mine
are generally present on these occasions; at any rate one of each party is there to com-
pete for the contract. The agent, who acts as auctioneer, commonly standing in the
window of the counting-house of the mine, names a particular place of work, as the 140
West of Doctor's Shaft; some one immediately names a price, and in a great majority of
cases this is one of the party who has been working in the place in question, and no one
underbids him, but the agent states a lower price, which is accepted. Where the contract
is taken by the party which had it before, it is generally throughout the mining districts
a rule not to disturb those who have been in possession of a pitch: it is the assurance
springing from this, which sometimes induces a party of miners when a new pitch, one
which has not hitherto been worked, is set up, to take it for nothing, or next to nothing.
They expect to establish themselves in the mine, and on the next setting day, they pro-
bably obtain a remunerating price.
There is of course an opposition of interests between the owners, whom the agent
represents, and the labourers, and the object of the latter is to make the former believe the
ground harder, and the veins poorer than they are. He, on the other hand, forms his own
judgment on these points by an accurate examination within a day or two of the setting,
and fixes his price for the most part so that average wages may be gained by the men.
It is clear, however, that where a tribute pitch is at present poor, he must be cautious in
giving a higher price, as there is always a possibility of a rapid increase in the size of the
lode, and the value of its produce. The contracts are generally good from one setting-day
to another, or for two months; but longer terms are often given, where the work to be
done is known to be of equable value.
The setting-day is usually the pay-day likewise; accounts are given to each party,
stating the value of their work, and the deductions to be made from it. The sum due to
the concern is received by one of its members, and divided afterwards among them. One
considerable item in these bills is what is called the subsist, which is an advance made on
account at the end of the first month of the contract, for the subsistence of the men and
payment of the boys. Its amount is commonly determined by the value of the work
already done: but in some mines the sum advanced is always nearly the same, and where
the men are relied upon for continuing at their work, this pay is allowed for a number of
successive months, until at length their contract becomes more profitable, and they are
enabled to discharge the arrears.
The most common ore of copper is the yellow sulphuret (bisulphuret), or rather copper
pyrites, which is frequently combined with stony matter, blende, galena, mundic, oxide of
tin, wolfram, and other substances in a smaller degree. The existence of either of these is
matter of consideration for the smelter, in making a proper mixture of ores for the furnace.
The smelting of copper ores in the West of England has been entirely discontinued, it being
found more profitable to send them to Wales, as a return freight for the ships bringing
coals to the mines.
The Crushing Mill is not generally adopted on account of the difficulty of bringing the
ore to exactly the proper size. The average quantity of copper contained in the ore is
CHAP. II.
677
COMPOSITION AND USE OF MINERALS.
nace.
rather less than 9 parts in 100; if it is pulverised too finely, which is difficult to prevent,
especially when it is not very hard, there is a chance of loss in smelting, from the particles
being carried up the chimney by the force of the draughts. For this reason copper ore, which
has been pulverised in the stamping mill, generally sells rather lower than the other ores.
In tin and lead ores there is also danger from the same cause as well as some loss, as
they contain about two-thirds of their weight of metal when they are put into the fur-
The other ores of copper are found in comparatively such small quantities that the
large operation in preparing them for sale scarcely applies. The Grey Ore, chiefly a
sulphuret with a small admixture of iron, is the second in importance, but relatively of rare
occurrence. It requires no difference of treatment from that of the richer portions
of the bisulphuret. The black ores, of which but a very small quantity is found (usually
oxide of copper), are permitted to touch the water as little as possible, as they are often
found in particles so fine as easily to be carried off by a small stream.
There is probably no metal which exists in so few varieties as tin: except a little
sulphuret, which has been found in combination with sulphuret of copper, all the tin ore is
in the state of oxide. The tin and copper are sometimes so intimately mixed in the
ore, and it is so difficult to separate them, that it becomes a subject of debate whether it
should be sampled as copper ore, or carried to the smelting-house as tin. The tin ores
raised in the west of England are smelted there, and the metal is brought to different
degrees of purity for various purposes.
stamping mill, as it merely requires some re-
Parcels may be frequently seen, the greatest
The richest stream tin is not taken to the
duction of size to prepare it for the furnace.
part of which consist of small pebbles, just as they were found in the stream, which
require little or no calcination. But with this exception tin ore is all subjected to the
stamping mill.
The ore is in itself so rich, and consequently so heavy, that it is easily
separated from the stony particles by the power of gravity.
This mode would not be advantageous for the copper ores, as the trouble of effecting
their separation would be far too great; none therefore of these ores are subjected to the
stamping mill, except some of the halvans, which have been thrown aside from the other
processes, to separate which pulverisation and subsequent dressing by water must be
employed.
The tin ore, which has connected with it the largest quantity of copper and iron pyrites,
naturally yields the greatest proportion of arsenic. Copper ore is calcined by partial de-
composition, to get rid of the sulphur and arsenic contained in it, and tin ore to decompose
the ores of other metals connected with it, and to expel the sulphur and arsenic they
contain; afterwards the tin ores are taken to the stamps, and a series of washings succeed,
sometimes 100, before they are prepared for the calcining furnace. The portion of copper
ores subjected to similar processes is comparatively very small, simple selection and pulver-
ising being the only preparation necessary.
In the preparation or dressing of the copper ores, the first step is the separation of the
larger pieces raised from the smaller by a sieve called riddle or griddle. When this has been
done, the process of picking the valuable portions of the latter from the worthless succeeds ;
and this is the work which female children are first employed upon, whilst some of the
youngest boys are engaged in washing up, or cleansing the stones previously to this selection:
this is done in wooden troughs, through which a stream of water flows immediately in
front of the pickers. The girls are seated or half recline on a table, and a small heap
of the mineral being thrown before them, they select and it put into a basket, or otherwise
separate the valuable pieces, and throw back the others into what are called the boxes,
whence they are wheeled by boys to a large heap, which is again subjected to examination.
This picking is carried on under a shed (hutch), open on both sides, for the convenience
of washing in front, and of the carrying away the rejected portion at the back.
The Riddling, mentioned as the first part of the separation of the larger from the smaller
pieces of ore, is performed by girls of sixteen years old or more: the very large masses
are broken or ragged by men; those somewhat sınaller are spalled by stout girls with
long-handled hammers, much in the way in which the larger pieces of stone are bioken for
the repair of roads. The riddling and spalling are performed in the open air.
The fragments are next to be cobbed; this process is performed by girls, who are
seated a little above the ground with an iron anvil at their side; they break the stones
with a short-handled hammer, to about the size usual in the repair of roads, rejecting
as they proceed the worthless and very inferior parts. The stones of ore are now taken
to be bruised or bucked, where the further reduction of sizes is effected by the mill,
called a crusher or grinder, now employed in pulverising of probably full half the copper ores
raised. The manual process of bucking consists of pulverising by a sort of combined move-
ment of percussion and trituration the pieces of ore already reduced to the weight of an
ounce or two, being chiefly those brought from the cobbers; this is done with a broad
square hammer 2 or 3 pounds in weight, worked with both hands, or sometimes with one
only, whilst the other is employed in sweeping the ore within convenient range; the bucker
x x 3
678
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
stands by a sort of counter, having iron anvils let into it at intervals. The pulverised ore
is allowed to fall on the ground, from which it is afterwards swept up and measured into
barrows, for each of which a certain price is paid. The substitute for this method of pul-
verising copper ores is the crushing-mill; this consists of two parallel cylinders of iron placed
nearly in contact, one of which is made to revolve, whilst the other is fixed so as only to
yield to great pressure: the stones of ore thrown in from above are ground between these
rollers, and a cylindrical sieve is placed beneath, which being inclined at an angle of 45°,
and turning on its axis, allows the particles which have been sufficiently pulverised to pass
through its holes, whilst the larger pieces fall out at the bottom and are returned to the
mill. The working of this machine is attended with the suspension in the air of a great
quantity of mineral dust, often of a very suffocating nature; when inhaled even cursorily it is
found to produce ill effects upon the lungs; the ores are wetted for the purpose of
lessening the escape of this dust, and any consequent loss. A further separation of the
more valuable part of the pulverised ore is effected by the process called jigging, which
consists of keeping the whole of the mineral particles suspended in water, for a time
sufficient to allow of the subsidence of the more ponderous portion; this is done by the
agitation of the water in the sieve in which the broken ore is placed; the more finely
pulverised part passes through the interstices of the sieve, and the heavier pieces of
larger size occupy the bottom, sufficiently separated to admit of the light and worthless
stone being removed from the top with a piece of wood. The agitation of the water was
formerly produced by hand labour, and in many instances boys are employed at this
work the jigger is obliged to bend forward over the water, across which he generally strides
and shakes the sieve (usually 1 or 2 feet in diameter) beneath the surface of the water;
when the separation of the several portions of the mineral is judged to be effected, the sieve
is lifted out and the refuse removed.
Machinery has superseded this process in a large proportion of the works: two methods
are in use, by one of which a succession of sieves are kept in motion under water, by means
of a connection with a water-wheel or steam-engine; and in the other, the water itself, in
which a number of sieves are immersed, is kept in a state of agitation by the motion of a body
in the centre. Whichever of these contrivances is adopted, the only manual operations required
are the supply of the mineral, and the removal of the worthless portions from the surface.
The inferior portions of the copper ores, from which the metalliferous particles cannot
be extracted by the methods described, is subjected to the stamping mill, as are almost all
the ores of tin; the mineral is reduced by the action of these heavy hammers to a fine
powder, which is carried by a stream of water through the perforations, made in a set of
plates of iron surrounding the boxes in which the stamps work. A series of washings of
this powder succeeds, the principle of which is the carrying off the lighter particles by a
current of water of graduated power, and allowing the more ponderous to remain and
subside. The number of these washings, amounting in some tin mines to about 100 from
first to last, causes the employment of a large number of boys and girls. The operations
called trunking, buddling, &c., chiefly fall to the lot of the former, together with the clear-
ing out of the slime pits, in which the mineral mud is collected, and wheeling this slime
for further dressing, all of which are carried on in the open air. The more delicate
manipulations are generally intrusted to females: among these what is called framing in
some districts, and recking or rucking in others, employs a great number; in this the girl
stands at the side of a very shallow wooden frame inclined at a moderate angle, and open
at the foot at the head of this, on a ledge more or less raised, a portion of the metal-
liferous mud is extended, and being divided by a light rake, a gentle stream of water is
allowed to find its way through it, and to carry it gradually to the frame below; by a
skilful direction of the current, the lighter portion is carried off at the bottom, and the
heavier is thrown beneath the frame by tilting it into a vertical direction upon the
pivot upon which it hangs, and throwing water with the shovel upon its surface to
wash off any portion which might adhere to it. The tin ores, after these successive
cleanings, are removed to the calcining furnace, and are subjected to several further
washings: in some of these the girls sit within and at the lower part of a long wooden
trough, and direct the gentle current of water with a light brush or feather over the sur-
face of the ore.
Sampling finally preparing and dividing the ores for sale: this division into separate
parcels is done by females; the general heap, containing some hundred tons, is sur-
rounded by a number of pairs of girls with handbarrows, which are filled from the edge
of the heap by a party stationed round in a regular succession, directed by a girl appointed
to the post; the barrows are then carried off rapidly, as the germs of a certain number of
distinct parcels, and to each of these a barrow-full is added in regular order, so that the
total number in every one is the same: those who fill the barrows exchange places after a
time with those who carry them; the latter have during their turn by far the harder work,
the barrows usually containing about 1½ cwt.
IRON. The ores of iron are extensively diffused throughout the mineral kingdom in
CHAP. II.
679:
COMPOSITION AND USE OF MINERALS.
every part of the globe, and are found in small quantities in some animal and vegetable ·
bodies, in several mineral waters, and in every soil; it is also met with in combination with
sulphur and with several acids. It is of a bluish grey colour, and a dull fibrous fracture,
capable of being brought to a brilliant polish; it is fusible at a white heat, is extremely
ductile, but cannot be hammered into very thin plates. It is the most tenacious as well
as the hardest of the malleable metals. It is oxidated by air and by water, and by
many other acids; but air in a dry state, or water free from air and acid, exert but little
influence over it; the rust being occasioned by an exposure to a moist atmosphere. It is
easily moulded into any shape, drawn into wires of the greatest fineness and strength,
rolled into sheets or plates, hardened or softened, welded by heat and rendered permanently
magnetic, and converted into tools of every description; indeed it is scarcely possible to
limit the various purposes to which it may be applied, and it may be justly considered as
the most useful of all the metals: its specific gravity is 7·77. It is obtained in England
principally from the carbonate of iron of the coal formation, which usually yields about
30 per cent. of cast metal, or sometimes as much as 40 per cent.
The carbonate of iron consists of two varieties, the compact and the sparry. The
compact comprises most of the clay iron-stones, and those found in the coal measures of a
flat spheroidal form; its colour is either a yellowish brown, brick red, or reddish grey,
with a fracture close-grained; it yields a yellowish brown powder; it will not effervesce
with either of the acids, and it has a slightly argillaceous smell when breathed upon.
The
slaty clay between the seams of coal affords abundant supply of this ore; it is frequently
found in continuous beds, sometimes 18 inches in thickness. The sparry carbonate of
iron has a lamellar fracture, a yellowish grey colour or brownish red; it slightly effervesces
with nitric acid, and changes to a reddish brown: its primitive form, when crystal-
lised, is an obtuse rhomboid, and the crystals often contain quantities of carbonate of lime.
This ore is found in the mountains of gneiss, in combination or mixed with quartz,
copper pyrites, oxide of iron, and carbonate of lime of different varieties. Natural steel is
produced from it, and in England and Scotland it produces from 30 to 33 per cent. of cast
metal.
The richest specimen, analysed by Dr. Colquhoun, which had a specific gravity of 3·05,
gave, in 100 parts,
Carbonic acid
Protoxide of iron
-
Lime
Magnesia
Silica
Alumina
-
Peroxide of iron
-
Carbonaceous matter
Loss
35.17
53.03
3.33
1.77
1.4
•63
•23
3.03
1.41
100.00
and its contents in metallic iron were 41.25.
Three-fourths of the iron manufactured in Great Britain is obtained from the coal fields
of Dudley and South Wales; the former is very favourably situated, as the ore, the limestone
flux, and the clay for making fire-bricks, are all obtained with the coal. At Merthyr Tydvil
in Wales, the iron-stone is found in abundance in about sixteen beds of slate clay, in nodules
of various size, both below and above the coal seams; in this district there are upwards
of thirty blast furnaces, and the iron is chiefly converted into bars.
Of the Assay of Iron Ores.-To obtain all the iron contained in the ore, it must be first
deoxidised, and the temperature so raised that the metals and earths will melt, when a
button of iron will be found at the bottom of the crucible; to effect this, and to overcome
any refractory earth, borax is usually added as a flux, taking care that the ore is finely
powdered before being mixed with it; it is then placed in a crucible which is previously
coated or lined with hard-rammed damp charcoal dust. The ore and flux is also covered
with the same material. The crucible is then closed with a well-luted lid and fire-clay,
and placed in a furnace, where the heat should be moderate at first, in order that the
moisture of the damp charcoal should be slowly passed off, and the deoxidation completed.
This is effected within the hour, when more fire is applied until a white heat is obtained,
which is kept up for a quarter of an hour; the crucible being then allowed to cool, the
button of cast-iron is weighed, and the result denotes the quality of the ore from which it
has been obtained. This method of assaying is called the dry way, and requires a tempe-
rature of 150° of Wedgewood.
To effect the assay in the humid way 100 grains of the ore, finely powdered, are digested
with nitro-muriatic acid, when, of the numerous compounds mixed with the iron, silica or
alumina will alone be thrown down. Any effervescence that takes place in the cold dilute
XX 4
680
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
indicates by the loss of weight the quantity of carbonic acid gas which has escaped. The acid
contents are then evaporated to dryness and digested in water, when the silica is alone
found insoluble. The solution somewhat acidulated, and oxalate of ammonia added, the
lime is precipitated in the form of an oxalate. Alumina and the oxide of iron are also
precipitated by ammonia. The manganese may be thrown down by hydrosulphuret of
potash, and the magnesia by carbonate of soda. The red oxide of iron contains 69.34 of
metal, and 30.66 of oxygen.
To ascertain the quantity of iron contained in 100 parts without reference to the other
materials comprised in the ore, a more simple method may be adopted. Hot nitric or
muriatic acid is poured upon the ore, the solution filtered, and supersaturated with am-
monia, when the iron oxide and alumina are alone thrown down. This red precipitate,
digested with potash lye, gives the oxide of iron nearly pure.
Native iron is occasionally found, and is considered as of meteoric origin, in consequence
of its containing a small quantity of nickel, the usual alloy of meteoric stones.
Iron and Oxygen.-Heat, air, and moisture, have the effect of oxidising iron, and con-
verting it, according to circumstances, into either a protoxide or peroxide, and the two
latter are salifiable bases.
Protoxide of Iron is seldom found pure; it is of a dark colour, and usually contains a
small quantity of the peroxide; it is obtained by burning iron in oxygen, which when
heated red-hot drops in the state of oxide. It is insoluble in water, tasteless, and of a
black colour. Its equivalent is 28, and it contains
Iron
Oxygen
1
28
77.6
1
8
22.4
1
36
100.0
Peroxide of Iron is in the state of a red powder, when sulphate of iron is decomposed at a
very high temperature; the colour varies according to the method adopted to obtain it;
sometimes it is of a yellow brown, which acquires a darker tint by heating. Iron rust
consists of the peroxide in union with water, and traces of carbonic acid and ammonia are
found in it, the acid being derived from the air, the ammonia from the nitrogen of the air
combining with the hydrogen of the water.
Iron
Oxygen
1
28
70
11/1
12
30
1
40
100
Iron and Carbon.-Cast-iron and steel are bodies which contain more or less carbon, and,
as already observed, it is from the carbonates of iron in a native state that the chief metal is
obtained. The clay iron ore of our coal districts is an impure protocarbonate of iron.
The Protocarbonate of Iron consists of
Protoxide of iron
Carbonic acid
-
1
36
62
1
22
38
58
100
Iron unites with chlorine in two proportions, viz. the protochloride and a perchloride.
Native Sulphurets of Iron. Among these are the magnetic pyrites, which is a proto-
sulphuret of iron, and the common pyrites, which is a bisulphuret, crystallised in a
variety of forms, having their origin in a cube; their colour is a brass yellow; they are
used to produce green vitriol, or sulphate of iron, and as a source of sulphur in the pro-
duction of sulphuric acid.
The Bisulphuret of Iron contains
Iron
Sulphur
12
1
28
46.6
32
53.4
60
100'0
Sulphates of Iron are used in the preparation of ink, Prussian blue, peroxide of iron, and
carbonate of iron.
Protophosphate of Iron is found native in the state of a blue earthy powder, and sometimes
in prismatic crystals; it is said to contain
Phosphoric acid
Protoxide of iron
Water
31
41
28
100
CHAP. II.
681
COMPOSITION AND USE OF MINERALS.
Iron combines with cyanogen, and forms several important compounds, uniting in
various proportions with other bodies. Prussian Blue is a ferrosesquicyanuret of iron, and
has a peculiarly rich colour, of an intense blue with a copper tint on its surface; it is in-
soluble in water, in alcohol, and in dilute acids; the anhydrous variety consists of
Iron
Carbon
Nitrogen
7
196
45.5
- 18
108
25.2
- 9
126
29.3
1
430
100-
Alloys of Iron. — Iron and potassium form a white soft alloy, which effervesces in water;
that of iron and manganese is white, hard, and brittle, and is said to give a peculiar
character to steel.
Salts of Iron are generally soluble in water, and the solution by exposure to the air
becomes of a reddish brown; with ferrocyanuret of potassium, a pale or deep blue preci-
pitate; and with the hydrosulphuret of ammonia a black precipitate.
The Persalts of Iron, as the permuriate and the persulphate, furnish a red precipitate,
when the solutions are concentrated, upon the addition of sulphocyanic acid and the soluble
sulphocyanates: none of the metals precipitate iron in a metallic state, zinc and cadmium
excepted.
The weight of a cubic foot of cast-iron is 450-5 pounds avoirdupois, and of wrought
468.8 pounds, the weight of a cubic inch of the former being 260 pounds, and of the
latter 281. It has been found that 93,000 pounds upon a square inch of wrought iron is
sufficient to crush it, and that it will bear 15,000 pounds without any apparent change in
its particles.
The quantity of pig-iron, manufactured in South Staffordshire in the year 1839, was es-
timated by Mr. Mushet as amounting to 346,2133 tons, and in Shropshire 80,940 tons,
being together nearly two-thirds of the whole quantity made in the United Kingdom. The
materials for its manufacture are coals, ironstone, and limestone; the first, when intended
for the cold-blast furnace, previously to its application, is made into coke; the ironstone
undergoes roasting and calcining, and the limestone is broken into small lumps: after
these operations they are mixed, or thrown into the blast furnace, in certain definite pro-
portions.
The Coke is made by burning the coal in large heaps 4 or 5 feet high in the open air, the
pieces being placed side by side, care being taken that they lie sufficiently loose near the
ground to admit of a free current beneath them; these heaps contain as much as 20 or 21
tons. In some parts of Staffordshire, a brick funnel 2 feet in diameter, with occasional side
apertures, is carried up to the height of 4 or 5 feet, and around which the coal or slack is
heaped and continually watered. After the fire has been burning for 4 days, the coke is
sufficiently made, and water is thrown over it to extinguish the fire and carry off the
sulphur: 2 tons of coal so treated produce 1 ton of coke. In Shropshire the heaps do not
generally contain more than 13 or 14 tons, and are suffered to burn 10 or 12 days, when a
light blue lambent flame makes its appearance; the sides are covered with wet coke dust,
and afterwards the top.
Calcining the Ironstone. The ironstone in Staffordshire and Colebrook Dale is argil-
iaceous. In some pits it is in bands 1, 2, or 3 inches thick, with measures of indurated
clay, perhaps several feet thick, between; in others it is in boulders distributed through a
bed of indurated clay, or of clay and sand. The boulders vary in size from that of a small
apple to masses weighing many hundred weight. The usual form is that of a flattened
spheroid; after the ironstone is taken out of the pit, it is laid in heaps exposed to the sun
and air, for the purpose of evaporating as much of the water as possible. Before calcination
the larger boulders are broken into pieces about the size of a man's fist, that the fire may
act equally on all.
The ironstone is burnt on the ground like the coke, a layer of coals of several inches in
height is laid down with the points touching the ground, so as to admit the air below; upon
this is a layer of ironstone, then another of coals alternately, until the heap, becoming
narrower with every layer, terminates in a point, after which small coal is spread over the
whole, and fire is introduced at the bottom: this gradually spreads along the ground,
penetrating upwards through the whole heap, and lambent flames are seen issuing between
the pieces of the ironstone; in ten or twelve days the operation may be completed, and the
ironstone being cooled is ready for the furnace.
The effects of calcining the ironstone are, to drive off first the remaining water, which
would materially diminish the quantity of iron produced in the furnace, and injure its
quality; secondly, the sulphur, which would produce the same effect; thirdly, the carbonic
acid, which adds considerably to its weight, as it does to that of chalk or limestone. If the
fire be continued too long, the ironstone, and all metals similarly treated, imbibe oxygen,
and its quality is injured.
682
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Blast Furrace generally resembles externally a round tower, or it is square at the bottom,
and circular at the upper part; occasionally it is entirely square, but in either case its
internal construction is the same. The exterior of the roof is flat, and from its centre rises
a cylindrical structure, which serves as a chimney, from 20 to 25 feet high; it has an
opening at the side called the filling place, into which the coke, ironstone, and limestone, are
thrown. In many furnaces the external wall round the top is raised 10 or 15 feet higher
than the floor, to protect the people employed from the cutting blasts of the wind. In
Staffordshire, when the ground is level, the blast furnaces rise like the towers of an ancient
castle, and the ascent to the top is by an inclined plane; the materials and the fillers are
sometimes hoisted by the steam-engine, working ropes over a pulley at the top.
In Shropshire advantage is often taken of the difference of level of the ground, and the
furnaces are built on the lowest part, so that the top may be even with the surface above; by
such an arrangement

the materials can be
wheeled and thrown
into the furnace without
any difficulty.
In these furnaces A
represents the regu-
lating cylinder, 8 feet
in diameter and height;
B, the floating piston
loaded with weights,
proportionate to the
power of the machine;
C, the valve, 26 inches
long and 11 inches wide,
by which the air is
passed from the pump-
ing cylinder into the
regulator: D, the aper-
ture by which the blast
is forced into the fur-
nace, its pipe being 18
inches in diameter; the
wider this can be made
the less is the friction,
and the more powerful
the blast; E is the
blowing or pumping
cylinder, 9 feet high,
and 6 feet in diameter,
the piston within it
having a stroke of from
5 to 7 feet; F, the
TO
E
A
B
Fig. 586.
S
N
M
R
L
H
I
T
SECTION OF IRON FURNACE.
K.
D
blowing piston with its valve or valves, of which there are sometimes several distributed over
the surface of the piston, the area of each being proportioned to the number; G is a pier of
stone or masonry supporting the regulating cylinder, to which is attached the flanch and
blowing cylinder; H is the safety-valve or cock, by the simple turning of which the blast
may be admitted to or shut off from the furnace, passing to a collateral tube on the opposite
side. I, the tuyere, by which the blast enters the furnace; the end of the taper pipe which
approaches the tuyere receives small pipes of various diameters, from 2 to 3 inches, called
nose pipes; these are applied at pleasure, as the strength and velocity of the blast may
require. K, the bottom of the hearth, 2 feet square. L, the top of the hearth 2 feet 6 inches
square. K, L, the height of the hearth, 6 feet 6 inches; L is also the bottom of the boshes,
and where they terminate of the same size as the top of the hearth, only the former is round
and the latter square. M, the top of the boshes, 12 feet diameter, and 8 feet perpendicular
height. N, the top of the furnace at which the materials are charged, commonly 3 feet
diameter; M N, the internal cavity of the furnace, from the top of the boshes upwards,
30 feet high; NK, total height of the internal parts of the furnace, 44 feet.
lining; this is done in the nicest manner with fire-bricks made on purpose, 13 inches long
and 3 inches thick. PP, a vacancy round the outside of the first lining, 3 inches broad,
and filled with coal dust; this space is allowed for the expansion which might take place
in consequence of the swelling of the materials by heat when descending to the bottom of
the furnace. QQ, the second lining, similar to the first. R, cast-iron lintel, on which the
bottom of the arch is supported. RS, the rise of the arch; ST, the height of the arch on
the outside, 14 feet and 18 feet wide. V V, the extremes of the hearth, 10 feet square; this
OO, the
CHAP. II.
683
COMPOSITION AND USE OF MINERALS.
and the bosh-stones are always made from a coarse-gritted freestone, whose fracture presents
large rounded grains of quartz, connected by a cement less pure. The height of the entire
furnace is 55 feet, and its diameter at bottom 38 feet.
The cost of a pair of blast furnaces in the Dudley district is about 18007.; when 40 feet
in height they require for their construction 160,000 bricks, 3900 fire-bricks, and 825 boshes.
A furnace 50 or 60 feet in height will produce 60 or 70 tons of cast-iron per week; from
50 to 55 feet high, 60 tons; and two of 45 feet in height together, 100 tons. 3½ tons of
coal, including the coal of calcination, are required to obtain a ton of cast-iron, and the
workmen's wages amount to about 15 shillings; 14 tons of coke, 16 of roasted ore, and
63 tons of limestone, being thrown into the furnace every 24 hours, allow a run of 7 tons
of pig-iron every 12 hours. In many parts of Wales these furnaces are of much larger
dimensions; that at the Plymouth iron works at Duffryn, near Merthyr, is 18 feet in diameter
in the boshes, and 10 feet at
the top or filling place, the
height being 40 feet; it
contains 7000 cubic feet,
and when at work 150 tons
of ignited materials for the
smelting of the iron. In
some of the largest furnaces
20,000 cubic feet of atmo-
spheric air is forced into
them every minute, by a
pressure of 1½ lb. upon each
square foot: their form
varies in different districts,
and when built against a

Fig. 587.
SECTIONS OF IRON FURNACE,
side hill they have a flat wall, and the blast is admitted at the front.
The air apparatus is put in motion by a steam-engine, and the noise may be heard for
many miles; the rod is made to force down the piston to the blowing cylinder, E, when
two valves open, which allows the air to pass above the piston; by drawing it back
the valves are shut
by the pressure of
the air above them,
which being brought
into a smaller space
forces open the
valve as the pis-
ton rises air rushes
into the vessel, and

:
as the piston begins
Fig. 588.
PLANS OF IRON FURNACES.
The
to descend, the valve is shut close by the force of the air. The heavy weights upon the
piston now press it down, and force the air through the opening, and along the pipe
with great violence into the furnace, with a constant and unintermitting stream.
air in the furnaces becomes very much heated, and passes up with great force through
the materials, which by the heat are gradually melted, and slowly subside downwards,
whilst fresh materials are put on at the top; about 36 hours is the time that it takes for
a charge to get down to the hearth. Instead of the regulator, just described, several furnaces
have a large vessel or a reservoir, made of plates of wrought-iron in the form of a cylinder,
rounded at each end; the usual length is about 20 feet, and the diameter 8 feet.
air is forced into this precisely in the same way as in the vessel, and passes from it in a
continuous and powerful stream into the blast furnace. The diagram shows only one
air-blast directed towards the furnace, but in practice there is one from the other side, and
generally another from the back of the furnace; the melted metal is let out from the front;
a roof over head shelters the men engaged under it in the operation of casting; this is
called the casting-house.
The
The hot blast has been used with effect in Staffordshire and Shropshire; the general
principle is, that instead of forcing the air into the blast furnace at the temperature of the
atmosphere, it is previously raised to from 600° to 700° Fahrenheit by traversing a number
of tubes which pass through a large fire made in a building at the back of the furnace.
practice the air is considered sufficiently hot when a jet striking against a piece of lead will
melt it and cause it to fall in drops.
In
The effects of this invention in the iron trade have been very great: the operations of the
furnace go on more rapidly, a greater quantity of iron is made from the ironstone, and there
is a saving in fuel and limestone; raw coals may also be used instead of coke, which
diminishes the expense.
In Staffordshire some hot-blast furnaces are worked with raw coals only, but in others a
684
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
mixture of two parts raw coal and one part coke is preferred. At those of Woombridge in
Shropshire, the proportion is half coal and half coke; but even this is a great advantage.
The iron produced by the hot-blast is not only less expensive, but for some purposes it is
infinitely superior, for instance in fine castings, ornamented on the surface with delicate
figures when poured into the moulds it will enter into every line, however fine, almost
like a Daguerreotype. For all articles, on the contrary, that are made by passing wrought-
iron through the rollers, a stronger iron is better adapted.
:
In the districts of Staffordshire and Shropshire about one-third of the furnaces are blown
by the hot-blast, and two-thirds by the cold blast: that part of a furnace which first requires to
be repaired is the hearth, or lower part of the interior, into which the iron glides down from
the melted materials. The hearth is made of sandstone, which resists heat; the most noted
quarries of which in Staffordshire are at Gornal, about two miles from Dudley, and
belong to the geological formation called the millstone grit. A furnace may require to be
renewed in four years, and sometimes it may last seven or eight. A new furnace takes con-
siderable time to dry thoroughly, and afterwards to heat, and then to be gradually charged
with materials, ironstone, limestone, coke, or coal, so as to bring it into a proper state for
the making of iron. When it is intended to discontinue a furnace, it must be blown out, as
it is called, for if the blowing were suddenly to cease, the melted and half-melted materials
would all vitrefy into one solid mass, and adhere to the sides of the furnace, which would
involve the taking it down: hence it becomes necessary to continue putting on fuel and
blowing until the whole contents has descended in a melted state to the bottom, and been let
off. A furnace in full operation is charged by a set of hands, consisting of men, young people,
and boys: the boys fill coke into baskets or barrows, and ironstone and limestone into what
are cal ed boxes, though they resemble baskets. The young persons and men convey these
materials to the filling place at the top of the furnace, and a certain proportion of each is
thrown in, according to the orders given from time to time; to ascertain the proper quan-
tities, an acquaintance with the peculiar qualities of those found in the district is necessary.
A skilful and trustworthy person is required to superintend the weighing of the ironstone
and limestone, for which proper machines are provided; for the coal or coke the eye is
sufficient. There are generally two furnaces together, sometimes three, and when one is
charged the people proceed to the other; they have never many minutes to rest, until after
4 or 5 o'clock in the afternoon, when the furnace is usually quite full; the blast is then
stopped for a time, until the melted iron and cinder be let off. In about ten hours, some-
times a little more, a hole is bored in the sand and clay at the bottom of the hearth; the
liquid iron flows out, and runs into a broad mould, with a number of smaller on one side,
prepared for it in sand, on the floor in front of the hearth; these moulds are called the sow
and pigs, and in conformity with this expression the iron is called pig-iron, and also crude-
iron. Sand is sprinkled over it to prevent its cooling too rapidly, which would injure its
quality. The cinder or liquid mass, composed of the clay and lime, with silex and a por-
tion of iron, is then let off, and flows round a piece of iron, by which it is held fast when
cooled, and to which a crane pulling a chain is attached; the whole mass is hoisted upon a
waggon, and carried off from the surface to the further part of the cinder hill. If intended
to be used as road materials water is thrown on it before it is quite cooled, and it readily
breaks. The cinder has to be let off several times in the course of the twelve hours, gene-
rally every hour and a half, or every two hours; in some furnaces it is allowed to keep
continually running off. The furnace-master observes from time to time the appearance of
the melted cinder, and from it he is able to ascertain the condition of the furnace, and gives
his orders accordingly, as to the proportion of the several materials. The people are re-
lieved every twelve hours; the day set takes the nightwork every alternate week; the change
is effected by the set at work during the day on the Sunday continuing all night till
6 o'clock on the Monday morning, that is called the double turn.
Moulding and Casting.—The pig-iron is found to be of various qualities, dependent on the
quantity of carbon which has entered into combination with it during the process of smelt-
ing. The iron called No. 1. in commerce is highly carbonated, the most fusible of all, and
most fluid when melted, and therefore the best adapted for fine castings, giving a smooth
surface, and filling up the finest parts of the figure moulded. That called No. 2. is less
fluid when melted, but better adapted for articles requiring strength and durability. The
No. 3. is used for castings where very great strength is demanded; it may also be made into
bar-iron. In order to be made into articles of cast-iron, the pig-iron has to be melted a
second time. Moulds in the form of the articles to be cast are made of a mixture of sand
and clay in boxes, laid on the floor of the foundery: the iron is melted in a furnace,
let out into large pans, and then carried and poured into the moulds and left to cool.
A great deal of casting is made from the iron as it comes from the blast furnace, as water-
pipes, rails for tramways, broad flat pieces of iron for the flooring in front of the iron
furnaces, &c. &c.
Refining of Iron. The furnace is generally small, being about 3 feet square at the base
in the inside; the bottom is of hearth brick, and the front, back, and sides are of cast-iron,
CHAP. II.
685
COMPOSITION AND USE OF MINERALS.
made hollow, so as to allow of a constant stream of water flowing through them to resist
the neat of the iron; holes in the sides admit blasts of air, in the same way as in the blast-
furnace. The pig-iron is laid in the refinery with the coke, and blasts of air passing through
the flames are dashed against it, and the iron is melted; in about two hours or less, the
metal is ready to be let off into a mould. In the process of refining a portion of the worst
parts of the iron is left behind; the chemical change is effected by a separation of a part of
the carbon united to the pig-iron; when cooled the iron is broken into pieces of a manage-
able size. Much less iron is now melted in the refinery than formerly, a method of con-
verting pig-iron into malleable iron having been discovered without refining, which for many
purposes answers exceedingly well, and is more economical.
Malleable or Wrought-Iron.-There are several kinds of pig-iron unfit for casting, but
which undergo other processes in order to be made into malleable or wrought-iron, which
is not brittle, like the former, and is so ductile that it can be drawn out to a considerable
length, and to the fineness of wire. It may be welded, that is, two or more pieces may be
hammered together into one: it is the iron ordinarily used by blacksmiths.
For its con-
version into malleable, the pig-iron has to be puddled, and then beat under the forge ham-
mer, and passed through rolls or hollows in two iron cylinders, rolling round near to each
other, which force it into long bars; it is then cut into pieces by a pair of shears, the pieces
are laid over each other, heated in a furnace, and again passed between the rollers, by which
it is forced into the shape intended.
Puddling Iron.-To undergo this process the iron is put into a furnace, the fire being at
one end, and a chimney of sufficient height to produce a strong draught at the other. The
flames raised by the draught are drawn upon the iron, pass on, and the heated air goes
up the chimney. In some iron works each puddling furnace has a chimney to itself, and
twenty or thirty or more such chimneys may be seen; but in others the air from all the
puddling chimneys is conveyed to one more lofty than the rest, creating a still stronger
draught. In about half an hour or less the iron becomes soft; it is then heated until it
is fluid, when it soon begins to boil. The puddler now stirs it with iron rods, bringing
every portion of the iron under the action of the flames: after a time the boiling and
fermentation cease, and the iron becomes thick and adhesive. The puddler now divides it
into parts, and rolls each part separately, until it has acquired something like the form of a
ball, when the pieces are taken out to be subjected to the action of the great forge hammer.
The puddle furnaces, the forge hammers, and the puddle rolls are employed day and night,
on account of the great labour and expense of fuel in heating the furnaces if allowed to
cool, in order to bring them again into a fit state for working: two sets of hands are con-
sequently required, who take the night and day work alternately.
Forging the Iron. The iron being in ill-shaped masses, called balls, one is taken from the
puddling furnace, by means of a rod of iron, with a sort of hook at the end, and is then laid
down to be forged, which is effected either by squeezing it forcibly between large pieces of
iron, worked by the steam-engine, called the squeezers, or subjecting it to the blows of the
forge hammers, by which means the cinder mixed up with the pure iron is driven off in a
shower to a considerable distance, and a piece of iron is formed, somewhat resembling a
brick, but from four to six times as large. This is immediately passed between the
Puddle Rolls, two huge cylinders, in which are grooves, similar in shape to the mass itself,
so that when they revolve the iron passes through them, and is squeezed into a longer form.
A boy on the side opposite to the workman lays hold with the tongs of the end of the
iron, and places the end which comes out last against the upper cylinder, the motion of
which carries it back again to the side where the workman called the roller stands, who
then places the piece in the next groove, which as it passes through is still further elon-
gated, and this process is repeated four times, when the iron becomes a bar, although a thick
one. On a line with the two cylinders already mentioned are two others, their grooves
being flat and broad, such as a bar may be laid upon, and there is a corresponding flat
piece of iron in the upper cylinder to press upon it.
The bar is now under the care of a second workman, who places it in the groove, through
which it passes, and is elongated. It thus goes on through successive operations, becoming
longer and more slender, until at last it is 10 or 12 feet long. It is then withdrawn, and
laid on a large flat piece of iron, and beaten by boys with wooden mallets, while it cools;
others stand by the bar, in order to keep it straight.
The usual method until lately was to puddle only the refined iron, or that which had
been smelted first in the blast furnace, and then again in the refining furnace. Of late
years a practice has been introduced of puddling a mixture of pig-iron and refined iron, in
Staffordshire called plate, thereby saving the expense of refining, and also the loss of
metal always occasioned by that process; still greater economy is effected by dispensing
with the refined iron altogether, the loss upon which amounts to about 12 per cent.,
which added to the expense of refining will make altogether a difference of 2 pounds per
ton. It is true that the iron so manufactured will not be so good, and may lose some-
thing more in passing through the rolls, but for most purposes it answers sufficiently
1
686
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
well; though there are many cases in which that made by the less economical
indispensable.
process
is
Rolling Mills.-The iron having undergone so many operations, having been smelted from
the ironstone, refined, puddled, forged, and drawn through puddle rolls, might be supposed
to be brought to a perfect state of manufacture; but there is still another process before it
is fit for sale and common use.
The puddle bars are cut into pieces of equal length by shears, made of hard steel and
moved by the steam-engine, with apparently as much ease as if they were cutting paper :
four or five, sometimes as many as seven or eight, of these pieces are laid upon each other
and placed in a balling furnace, very similar to that in which it is puddled, and
are heated by a hot blast, driven against them with sufficient force to render the iron soft,
so as to be capable of welding or uniting together, but not to become fluid; they are
then taken from the furnace, and passed between rolls, just in the same manner as in the
puddle rolls, the inclosed space between the rolls becoming smaller and smaller, until the
bar is drawn out to the intended length and size, when it is finished wrought-iron. This
process is applicable to every variety of purpose, from the rails for a railway to the small
bars or rods for making nails, plates for the boilers of steam-engines, and the various por-
tions of iron boats or ships, and other things requiring great strength. Some of the
plates are afterwards tinned for culinary vessels, &c., by being dipped into a solution of
tin in sulphuric acid, which is called pickle; when withdrawn they are found coated with
tin; the acid having a stronger affinity for the iron unites with it, and the tin is deposited
on the surface. The plates are afterwards rubbed and polished.
Steel is a carburet of iron, and of great value, in consequence of its being readily
tempered to any degree between extreme hardness to softness. These different states are
produced by raising the temperature, and then suddenly plunging the metal into cold
water, or some other fluid; the hardness is destroyed by heating to redness, and then
leaving it gradually to cool. At a white heat it becomes less malleable than at a red heat,
and brought to a very high degree it fuses, and returns to its original state of pig-iron. Its
increase in weight is from 4 to 12 ounces per hundred weight; there are three different
qualities, as natural steel, steel of cementation, and cast steel; the first acquires some
peculiar properties from the manner in which the ore is treated.
Steel of Cementation, bar of blistered steel, is manufactured in bars, and none is superior
to that made from Swedish iron; the furnace employed for this purpose has an hearth of
an oblong quadrangular form, divided by a grate into two parts, on each side of which is a
chest built of firestone grit; these are each from 10 to 15 feet in length, and from 2 to 3
feet in width and depth; the sides are 3 or 4 inches in thickness, and the space between
them is about 12. These chests do not rest upon the sole of the furnace, but are so placed
that the flame plays freely all round them; the heat is regulated by an opening in the arch,
or sides of the furnace, which conducts to the chimney.
The breadth of the grate varies according to the nature and quantity of the fuel em-
ployed; the whole furnace is constructed under a conical hood or chimney, 50 feet high,
which has a thorough draught, produced by numerous air-holes at the bottom of the grate.
The furnace being prepared, bars of iron of a proper quality, a little less in length than the
chests or troughs, are put upon the bottom, on which has been previously spread a layer of
charcoal dust; layers of iron bars and charcoal are then alternately put in, and the whole
covered over with clay to exclude the air, which, if allowed to enter, would destroy the pro-
cess; the bars are not suffered to touch each other in the trough, and the fire is continued
for three or four days, till the temperature of 100 degrees by Wedgewood is obtained, at
which it is steadily maintained for six or ten days if necessary. When the cementation is
complete, the workman draws out a bar, and examines the blisters on it: if not sufficiently
changed, the air is again excluded, and the process continued, but if in the required state
the fire is put out, and the steel is left to cool for eight days, when the process for making
blistered steel is completed.
The blisters are formed by the bursting of vesicles on the surface, filled with carbon in
a gaseous state; on the interior blistered steel is irregular in its texture, has a white
colour like frosted silver, and exhibits crystalline angles and facettes, which inrcease in size
the longer the cementation has been continued, or the greater the quantity of carbon
applied.
The imbibing of the carbonaceous matter renders the steel unfit for any useful purpose,
until it has undergone the operation of tilting, which is performed by submitting it to a
powerful hammer, weighing 2 cwt., lifted by machinery, and giving from 300 to 400
blows per minute. Hammering improves the malleability, and renders the steel peculiarly
adapted to the manufacturing of edge-tools and cutting instruments of all kinds; this
property has acquired for it the name of shear steel.
Cast-steel is made from blistered steel broken into small pieces and packed in fire-clay
crucibles, with a small quantity of powdered coke; the crucibles contain about 30
pounds of steel, and generally serve for three charges. They are placed in a furnace the
CHAP. II.
687
COMPOSITION AND USE OF MINERALS.
cavity of which is like a square prism lined with fire-bricks, and the smoke is conducted
into a lofty chimney. Cast-steel will not bear more than a cherry red heat without
becoming very brittle; it cannot be welded together, but will unite with iron through the
intervention of a fine film of vitreous boracic acid, and the latter metal may be plated with
cast-steel, by pouring the liquid steel from the crucible upon a bar of iron laid in a mould
with the upper face polished; the adhesion becomes so perfect, that the two metals may be
rolled out together, and instruments made of it will have the toughness of iron combined
with the hardness of steel.
According to Mr. Mushet, carbon combines with iron in the following proportions to
form the different carburets:
Soft cast-steel
Common cast-steel
White cast-iron
Black cast-iron
T20
100
23
1
13
and the specific gravity of steel varies from 7.31 to 7.91, which is that of the best ham-
mered: so great is the affinity of iron for carbon, that it will absorb it from carburetted
hydrogen or coal gas, and thus become converted into steel.
Hardening Steel is performed by putting it into a charcoal fire, and when the metal has
acquired a red heat, it is suddenly plunged into cold water; where these plates are required
to be hardened, they are plunged into oil and tallow, or bees-wax and resin, as the water
would render them too brittle, and cause them to crack.
Tempering is effected by again submitting the metal to the action of fire; as the heat
increases it becomes softer, and when the requisite degree is arrived at, it is withdrawn and
quenched in cold water. To an experienced workman, the degree of temper is indicated
by the colour; for springs or where elasticity is the object, it is quenched when the colour
assumes a fine blue: when a fine edge is required it is brought to a straw colour, whilst
the back of the instrument is left blue. For magnets, the ends of the bar only are brought
to a blue colour, as the harder the whole bar is left the better is the magnetism retained,
although communicated with more difficulty in the first instance. The heat required by
Fahrenheit's scale to produce
Very pale straw yellow, was
Light purple
Dark blue
Pale blue
and for all a free access of oxygen is required.
430°
530
570
590
Alloys of steel with platinum, gold, and nickel, may be made when the heat is sufficiently
powerful.
Founding or Casting of Iron. Iron intended for the foundery receives a high charge of
carbon, whilst the bar or malleable iron must be deprived of it; consequently a different
process must be adopted in the manufacture of these two varieties: that intended for the
whitesmith, as already described, is put into a furnace where it is exposed to air and heat
only, without the fuel coming in contact with it; that for the foundery must be remelted
in close contact with the fuel, and excluded almost entirely from the air; hence as it melts
it takes up an additional quantity of carbon when cast into pigs. There are varieties of
pig-iron; the grey, which is the best, another of a medium quality, and one which is not
much superior to the forge-iron. The finest soft iron, when struck with a hammer,
scarcely yields any sound, like a mass of lead; its fracture shows little lustre and is coarsely
granular, whilst the inferior quality is very brittle, easily broken by the hammer, and gives out
a sound like a bell; its fracture is shining and of a silvery whiteness, with no granular appear-
ance. Iron which after casting is required to be turned on the lathe, filed, or drilled, should
be of the purest quality: where, however, great strength is required, and the casting is to be
used as when taken from the mould, the medium quality should be preferred; when it is
to be applied to the ram of a pile-driving engine, or for an anvil, the third quality should
be selected on account of its hardness. These three varieties of iron owe their qualities to
the carbon, the best containing the greatest proportion; when this is running from the
furnace, a large quantity of carburet of iron floats on its surface, denoting it to be a
superior kind.
The Cupola and Air Furnace.—The first is used for small, the latter for large castings;
the cupola requires a blowing machine of some kind, whilst the air-furnace has a sufficient
draught created by means of a lofty chimney.
The open Sand Casting is applicable to flat plates, where one side is rough or uneven;
the mould is made of sand of a peculiar kind, having its grains of an equal size, and not of
a nature to vitrefy when highly heated; this is mixed with enough loam to give it when
moistened the property of being moulded into the form required; it must also be
sufficiently open to allow the escape of air or steam when the hot iron is poured into it.
688
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
The sand is usually passed through a sieve, and the surface made hard and level by
continuous beating with a rammer, and then smoothed by a trowel: an edge of the same
material to confine the casting is formed around it, by first laying laths of the thickness
of the intended plate on the prepared bed, and then making the border or edge close to
them; the laths are then removed, and the metal is poured into it. To prevent the casting
from cracking as it cools, the moment it sets it is covered with a thickness of 3 or 4 inches
of dry sand.
Fig. 589.
FLASK CASTING.
Flush or Box Castings require a more perfect model or pattern, which is usually made
with boxes or flasks as they are
termed, either out of wood or
metal, put together in such a
manner as to admit of being
lengthened or shortened, and thus
adapted by bolts and screw fasten-
ings to an endless variety of forms
and sizes. To make a casting
two boxes are required; one is
placed nearly on a level with the
floor of the foundery, which is
previously covered with sand and
which forms the bottom : into
this is put the moulding sand,
which is well rammed in until a sufficient bed is made for the introduction of the
previously prepared pattern, the centre line of which should about range with the top of
the box; the whole is then filled up level with moist sand; this being pressed or rammed
in and made smooth at the top, a quantity of perfectly dry sand is sprinkled over the
surface, to occasion a parting or separation when the upper box is placed upon it; before
this is filled, it is necessary to provide a vent for the escape of the air when the metal
is poured in, and for the gate, a funnel-shaped channel that is to admit it: these two
openings are preserved by placing two upright rods, slightly tapering, in the position
required previously to filling the upper box with sand, which when rammed in, the box
is to be lifted up and the pattern taken out, leaving its impression in the sand: this
requires some skill and adroitness on the part of the workmen, who, by moistening the
pattern with a little water, consolidate the sand immediately around it, and its liberation
is rendered easy; should any breaking down of the sides of the mould take place, it must
be repaired and made perfect. When the casting is to be hollow, as in cylindrical pipes or
columns, it is necessary to introduce a core which shall corre-
spond in dimensions with the void required, and the formation
of this core demands considerable skill: a core barrel is made
by twisting hay bands round an iron column, wetted and bound
carefully from one end to the other; this is covered with well-
tempered wet loam mixed with cow hair; were clay used it
would burn into a brick or hard substance. When the core
is thus prepared, it is rendered true by turning in a lathe, after
which it is hardened in a stove or oven constructed of bricks with
racks or shelves in it, and closed with iron doors: when the
core is taken out, it is covered with finely ground coal-dust
mixed with water, and when dried it is ready to introduce into
the previously prepared mould; the heat of the metal poured
in burns away the hay, which separates the iron core from its
coating of loam, and when the iron begins to set the barrel
is withdrawn, and the loam is scraped or chiseled out.
The process adopted by John Weichard Valvasor, of Carniola,
of casting statues very thin is given in the Philosophical Trans-
actions, vol. xvi.: he first formed with good clay that endured
the fire, and would not crack either in drying or burning, the
figure or statue to be cast: when the model was quite dry, small
holes of moderate depth were made over its entire surface, into
which were placed small pieces of metal, to keep the core and
mould from touching each other, or from falling together; a
portion of the clay was then scraped away to as much as was in-
tended to constitute the thickness of the statue, and the mould
was placed in a furnace and heated red-hot: when cold, it was
rubbed over with an earth used by the German potters to colour
their tiles, resembling black lead, for the purpose of making the
metal flow freely over it; yellow wax, mixed with pitch or resin, Fig. 590. STAtue casting.
was then spread over, to the thickness of the metal to be given to


CHAP. II.
689
COMPOSITION AND USE OF MINERALS.
The
the statue, which was performed with great care, and constituted a perfect model.
whole statue was then covered with smaller pieces of wax, in the direction intended for the
channels of the metal, and of the necessary size; some being, as shown, considerably larger
than the others; the whole was then coated with similar clay to that which formed the
core. The great channels met at the top of the model, and formed apertures where the
metal was to be poured in, but there were others provided by which the air could escape
when the metal entered; at the bottom, or at the feet of the statue, a hole or two was left,
where the great channels and waxen statue join; the wax forming the covering and the
channels then ran out, and the mould was again submitted to a red heat after this it was
placed in a pit, and the same process adopted as for casting bells: to ascertain the quantity
of metal, it is only necessary to weigh the wax, and compare it with the weight of
metal to be used.
The statue of Lord Hopetoun, erected in 1834 at Edinburgh, was cast in a somewhat
similar manner at the Royal Arsenal at Woolwich: a model made in plaster of Paris was
covered over with a thin shell, composed of a number of pieces fitted nicely together, and
which could be taken asunder, and after the model was removed again built up; the work
was commenced at the bottom by covering a portion of the shell with sand to about
1 or 1 inches in thickness, to which was added about 12 inches of plaster of Paris, which
uniting with the sand, formed one block; the remaining part of the statue being com-
pleted with similar blocks, so arranged that they could be removed readily without disturbing
the sand when the whole was finished: tubes were introduced with the plaster for the ad-
mission of the metal and for the escape of the air, and iron rings let into the blocks for the
convenience of removing them. After the shell was complete, the whole was taken to pieces
and removed to the casting pit, where it was carefully rebuilt, and the interior filled
with the material to form the core; it was then a second time taken to pieces, leaving the
core of the shape and dimensions of the original statue; from this sufficient was scraped off
to allow for the intended thickness of the metal; the shell was then put together as before,
and a space left between it and the core for the operation of casting.
Green or dry Sand Castings.—In this
process after the mould is made, the
flask is placed in the stove, and there
kept till the sand becomes perfectly
dry before it is used a fire of char-
coal is made all round it to heat
the sand previous to the metal being
poured into it, the casting of which is
always of a superior kind, in conse-
quence of its not being cooled down
too rapidly; all castings intended to
be turned or filed should be made by
this process, moist sand rendering the
surface of the iron refractory and hard,
as well as injuring its quality.
up



Loam work is employed where large
cisterns or cylinders are required,
and is effected without moulds or
patterns, by modelling in loam
the object required. Supposing
the work to be that of a steam-engine
cylinder, upon a plate of metal is built
a mould with very soft bricks laid in
beds of loam; this being completed,
it is plastered over with loam and
hair, about an inch in thickness,
dressed perfectly even by a striking
board, which works on a pivot, and
traverses freely round the whole cir-
cumference: when dry, this is dressed over with a coating of coal and charcoal powder
mixed with water.

Fig. 591.
LOAM WORK CASTING.
The intended thickness of the metal is then set out, and another coat of loam without
hair is put on, and being worked true by the striking board, which is adjusted for the
purpose, represents the place of the metal; any bands or ribs may be moulded upon it, by
cutting out their profile in the striking board. When this coat is dry it receives its black
wash, which prevents one coat of loam from adhering to the other.
Two semicircular plates of iron, having projecting arms and their insides made to the
curvature, are now placed on the foundation plate; on these are built the external case of
the mould, or the jacket, in two cylindrical halves, in the same manner as the core, but of
Y y
690
THEORY AND PRACTICE OF ENGINEERING. BOOK II.
greater thickness: the several parts, when dry, are then easily removed by a crane, con-
veniently placed for the purpose, over a pit sunk in the ground deep enough to hold the
casting. The two halves of the jacket are first removed laterally: the intermediate coat of
loam which occupies the place of the metal is then broken away, and the core is lowered
into the pit, by means of chains attached to the iron plate upon which the core was built.
The two jacket pieces are then lowered and properly placed; the pit is filled up with sand
solidly around it, and a cake of loam is placed over the whole, with the vent and gate holes ;
it is then ready for the reception of the melted iron, which is usually run at once from the
furnace to the gate of the mould by means of a channel. To get the casting out of the
pit the sand is first removed, the jackets broken to pieces, and then by means of the crane
it is hauled up.
Great care is requisite in withdrawing the pattern from the mould, and if attention be
paid by the pattern maker to form the lower portions a little smaller than those above,
the difficulty will be lessened materially; regard must be had also to the contraction of the
metal in cooling, which varies under different circumstances.
Of the Strength of Cast-iron Beams. From grey cast-iron yielding so easily to the file
when the external crust is removed, and being slightly malleable in a cold state, it is
preferred by the engineer whenever iron is to be employed in construction; it is also less
liable to fracture when it receives a blow than the hard metal: it has a granulated fracture,
of a grey colour, with some metallic lustre, and is softer and tougher than the white cast-
iron, which is, however, less liable to rust, and less soluble in acids; the white cast-iron,
when cast smooth, makes excellent bearings for pivots or gudgeons, and is very durable;
it may be employed where hardness is required, and brittleness is not a consideration.
Soft grey iron was considered by Mr. Tredgold the best for constructions of all kinds, and
his calculations were made upon it. When the weight laid upon an iron beam is dis-
tributed equally over it, the deflection is found to be the same as when five-eighths of the
load is applied at the middle; in calculating, therefore, the strength of a brestsummer or
any other beam, which is to be uniformly loaded, we must take only of the load as sus-
pended to its centre.
In putting an inch square bar of cast-iron upon supports 3 feet apart it broke wben
850 lbs. were suspended from the middle; and as cast-iron has its elasticity destroyed by
about of the weight that will produce fracture, its permanent load should never exceed
}}
that amount, so that 850 lbs. may be considered the weight which an inch square bar of
cast-iron will bear when its length does not exceed 1 foot.
The transverse strength of a beam is as its breadth to the square of its depth, and in-
versely as its length; so that a beam increased to twice its width will carry twice the
weight; increased to twice the depth, it will sustain four times; thus by doubling its
breadth its strength is doubled, doubling its depth its strength is quadrupled. A plate
of cast-iron, 2 inches thick and 8 inches broad, will carry twice as much as one 2 inches
thick and 4 inches in breadth, and the same placed on edge four times.
The strength of a rectangular beam of iron, supported at both ends and loaded in the
middle, is found by multiplying 850 lbs. by the breadth and square of the depth in inches,
and then dividing this product by the length in feet: the quotient gives the weight in
avoirdupois pounds.
A bar of iron an inch in breadth, 4 inches deep, and 20 feet bearing, will sustain 680 lbs., for
850 × 1 × 4º
20
13600
20
= 680 lbs.
The breadth of a beam is found by multiplying the length in feet between the supports,
by the weight to be supported in lbs., and dividing this product by 850, multiplied by the
square of the depth: the quotient thus found expresses the breadth.
20 ft. x 680
850 x 16
1 inch, the breadth required.
The depth is found by multiplying the length by the weight to be supported in lbs. and
dividing this product by 850 multiplied by the breadth: the square root of the quotient is
the depth required,
20 x 680
850 × 1
=
16, the square root of which is 4 inches.
The weight of the beam may be found by multiplying the area of the section in inches
by the length in feet, and that product by 3.2, which will give the weight in pounds; 3.2
lbs. being the weight of an inch square bar 12 inches long,
1 x 4 × 20 × 3·2 = 256 lbs.
As iron differs much in its quality, the breaking weight of an inch square bar has been
found to vary materially; some writers have therefore made their constant number 925 or
1000, instead of 850, which was preferred by Mr. Tredgold.
When the weight is placed on the axis of an upright column, or over the centre of the
section of a short rectangular block of iron, to find the area that will resist any given pres-
CHAP. II.
691
COMPOSITION AND USE OF
OF MINERALS.
sure; divide the pressure or weight in pounds by 15,000, and the quotient will be the area
of the section of the block in inches.
For story posts of warehouses or other buildings, the following table was calculated by
Mr. Tredgold.
A Table showing the Weight that may be placed with Safety on Cast-iron cylindrical Columns
from 1 to 12 Inches Diameter.

Feet. 12 Feet. 14
Feet.
Length or 2 Feet. 4 Feet. 6 Feet. 8 Feet. 10 Feet. 12 Feet. 14 Feet. 16 Feet. 18 Feet. 20 Feet. 22 Feet. 24 Feet.
Height.
Diameter
in Inches.j Cwt.
Cwt.
Cwt.
Cwt.
Cwt.
Cwt.
Cwt.
Cwt.
Cwt.
Cwt.
Cwt.
Cwt.
1
18
12
8
5
3
2
2
1
1
1
1/1/20
44
36
28
19
16
12
9
7
6
5
4
3
2
82
72
60
49
40
32
26
22
18
15
13
11
2
129 119
105
91
77
65
55
47
40
34
28
25
3
188
178
163
145
128
111
97
84
73
64
56
49
3/1/2
257
247
232
214
191 172
156 135 119 106
94
83
4
337 326
310
288
266
242
220
198 178 160
144 130
4/1/
429
418
400
379
354
327
301
275 251
229
208
189
5
530 522
501 479
452
6
616
607
592 573
550
7
1040 1032 | 1013
989
959 924
8
1344 1333 1315 1289
1259 | 1224 |
9
1727 1716 1697 1672
1640 1603
10
11
12
365 337
469
440 413 386 360
887 848 808 765 725 686
1185 | 1142 | 1097 1052 1005 959
1561 | 1515 | 1467 1416 1364 1311
2133 2122 2130 2077 2045 2007
| |
1964 1916 1865 1811 1755 1697
2580 2570 2550 2520 2490 2450 2410 2380 2230 2250 2190 2130
| | | | | |
3074 3050 3040 3020 2970 2930 2900 2830 2780 2730 2670 2600
A Table showing the Depths of square Beams or Bars of Cast-iron of different Lengths, to
sustain Weights (its own being included) of from 1 to 500 Tons when supported at the
Ends and loaded in the Middle; the Deflection not to exceed one-fortieth part of an Inch
for each Foot in Length.
427
394
310
285 262
525 497
1603
|

Lengths in Feet.
Tons.
4 6 8 10 12 14 16 18
1
2
3
4
5
6
7
8
28
36 38 40
20 | 22 24 | 26
30 32 34
2.5 3.0 3·5′ 3·9 4·3 4.6 4.9 5.2 5.5 5.8 6.0 6-3 6-5 6-8 7.0 7.2 7.4 7.5 7.8
2.9 3.5 4.1 4.7 5.1 5.5 5.9 6.2 6.5 6.8 7-2 7-6 7-7 8-0 8.3 8.5 8.7 9.0 9-2
33 40 4.6 5.1 5.7 6.1 6.5 6.9 7.3 7.6 7.9 8.3 8.6 8.9 9.2 9.4 9.7 10.0 10.1
3.5 4.3 4.9 5.5 6.0 6.5 7.0 7.4 7.8 8.2 8.5 8-9 9-2 9-5 9-8 10-1 10-4 10-7 11.0
| 10·410-711-0
4.5 5.2 5.8 6-4 6-9 7.4 7.8 8.2 8.6 9.0 9-4 9-7 10-1 10-4 10.7 11.0 11-211-6
|
55 61 6.7 7.2 7.7 8.2 8.6 9.0 9.4 9-8 10-2 10.5 10.9 11.2 11.5 11.9 12.1
|
5-7 6-3 6-9 7.5 8.0 8.5 8-9 9-4 9-8 10-2 10.6 11.0 11.3 11-7 12.0 12-312-7
| |
5.9 6.6 7.2 7.8 8.3 8.8 9-3 9-7 10-1 10-6 10-9 11-3 11.7 12.0 12.4 12.8 13-1
| | |
6.0 6.8 7.4 8.0 8.5 9.0 9.5 10·0| 10·4| 10·9] 11·3| 11·7 12·0| 12·4 | 12·8 | 13∙1 | 13.5
6.9 7-6 8-2 8-8 9-3 9-8 10-3| 10·7] 11·2] 11·6| 12·0 12·4 12·8 | 13∙1 | 13.5 | 13-8
7.1 7.8 8.4 9.0 9.5 10-0 10-5 11.0 11.5 11.9 12.3 12.7 131 13.5 13-814-2
7.2 7.9 8.6 9.2 9.7 10·2 10-8 11·2| 11·7] 12·1| 12′5] 13·0] 13·4 | 13·7 | 14.1 | 14-5
7.4 8.1 8.8 9.4 9.9 10·4 11·0] 11.5 11·9 12·4] 12·8 13·2] 13.6 14.0 14·4 | 14·7
7.5 8.3 8.9 9.5 10.1 10-6 11-111-7 12-1 12-6 13.0 13.4 13-8 14-2 14.6 15.0
7-7 8-4 9-1 9-7 103 10-8 11-4 11.9 12.3 12-8 13.2 13.7 14-1 14-5 14.9 15-3
7.8 8.5 9.2 9.8 10.4 11.0 11.5 12-0 12.5 13.0 13.5 13.9 14.3 14.7 15.1 15.5
7-9 8-7 9-4 10.0 10·6 11·2 11·7| 12·2| 12·7| 13·2] 13·7| 14∙1| 14·5 | 14·9 | 15-4 | 15-8
8.0 8.8 9.5 10-1 10.8 11-3 11-9 12-4 12-9 13-4 13-9 14.3 14.7 15-1 15.6 16-0
8.1 8.9 9.6 10.3| 10·9| 11·5 12∙0 12·6 13·1| 13-6 14-1 14.5 15-0 | 15·4 | 15·8 | 16-2
9.0 9-7 10-4 11.0 11.6 12.2 12-7 13.2 13-8 14.2 14-7 15.1 15-6 16-0 16-4
10.8 11.5 12·2 12·9 13·5| 14∙1| 14·7 15-2 15-7 16·3 16·8 | 173 | 17·7 | 18-2
12.4 13.1 13-8 14.5 15.1 15.7 16.4 16.9 17.5 18.0 18.5 19-119.5
13.9 14.6 15-3 16-0 16-6 17-3 17-9 18.5 19.0 19.6 20-120-7
14.5 15-3 16.0 16.7 17.4 18-1 18-7 19-3 19-9 20.5 21.1 21-6
15 1 15.9 16·7 17·4] 18·2 18-8 19-5 20∙1 | 20·8 | 21·3 | 22·0 | 22-5
17.2 18.0 18-7 19-4 20-1 20-721-4 | 22·0 | 22·6 | 23-2
17.8 18.6 19.3 20·0 20·7| 21-4 22-1 | 22·7 | 23·3 | 23-9
19.0 19.8 20-6 21-3 22.0 22.6 23-3 23.9 24.5
20.3 21.0 21.8 22.5 23-2 23.8 24.5 25.1
20-8 21.5 22.3 23-0 23-7 24-4 25.0 25-7
22-022-723·5 24·2 | 24·9 | 25.5 26.3
23-223-9 24·6 | 25·4 | 26·0 | 26-7
23.6 24.3 25.0 25.8 26.5 27-2
26.2 27-0 | 27-7 28.5 29-2
27.6 28.5 29-4 30-1 31-0
28.9 29-930-731-532-0
30.0 31.0 32.0 33-0 33.7
31-132-0 32.9 33.9 34-7
32.0 33.1 | 34-0 | 34-8 35-8
33-8 | 34.8 | 35-7 36-7
9
10
11
12
13
14
15
16
17
18
19
20
30
40
50
60
70
80
90
100
110
120
130
140
150
200
250
300
350
400
450
500
Deflection
in Inches.
1 15 *2 25
•3 35
4 45 •5 55
.6 65
די
75 8 8.5
⚫9
•95❘ 1.0
YY 2
Table showing the Weight or Pressure a Beam of Cast-iron, 1 Inch in Breadth, will sustain, without destroying its elastic Force, when it is supported at the Ends, and loaded in the Middle of its Length, and
also the Deflection in the Middle which that Weight will produce.
Calculated by Mr. Tredgold.
Lengths. 1 Foot. 2 Feet. 3 Feet. 4 Feet. 5 Feet.
Depth. lbs. defl. lbs defl. lbs.defl. lbs.
1 in. 850 02 425 08 283 18 212
1912-014 956 053 637 12 477
6 Feet. 7 Feet.
defl. lbs. defl. lbs. defl. lb defl.
32 170 •5 142 72 121 98
21 383 33 320 .48 273 65
1700 04 1132 09 848 16 680 25 568 36 484 49 425 .64
2656·032 1769 0721325 |·128|1062| •20 887 *29 756 39
2547 06 1908 111530 167 1278 •24 1089 -33|
3467-052 2597 |·092|2082 |•143|1739| •205| 1482| •28 1298-365| 1164] •46| 1041| •57|
8 Feet.
lbs.defl.
9 Feet.
10 Feet.
12 Feet.
14 Feet.
16 Feet.
18 Feet.
20 Feet.
22 Feet.
106 1.28]
lbs. defl.
95|1.62
lbs. defl. lbs. defl. lbs. defl. lbs. defl. lbs. defl. lbs. defl. lbs. defl.
85 2.0
24 Feet.
lbs. defl.
26 Feet.
28 Feet.
30 Feet.
lbs. defl.
lbs. defl.
lbs. defl.
239 •85
214 1.08
1921.34
•
380 81
340 1.0
283 1.44
243 1·96
212 2.56
189 3.24
1704.
1544-84
142 5.76
131 676 121 7.84
113 9.0
662 51
594 65
531 .8
954-426
855 54
765 66
637 96
546 1.31
4781-71
425 2.16
382 2.67
347 3-23
318 3-84
•
·
•
|•125|2272
3392 08 2720j 125 2272 18 1936 245 1700 32 1520405 1360 5 1133 72 971 98
4293 071 3442 111 2875 16 2450 217 2146 284 1924 36 1721 443
849/1.28
5
6
7
4250
•
•
618 2.42
10621·6 966 1.93
15301-34 13601-61
29 3471 41 2975 58 2603 73 2314 93 20821·14 1893 1.38
7551-62
680 2·08
294 4.51 273 5.23
523 3.38 485 3.92
255 6.0
453 4.50
1180 1.29
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
127
28
130
135
287*****
32
33
34
36
·
•
566 2.88
13560144 3050196 2650*256 2375 32 2125 4 1771
·4 1771 ·58 1518 78 13281-02
885 2.30 817 2.70 759 3·14 708 3.6
5112 12 4356163 3816213 3420 27 3060 33 2548 48 2184 65 1912 85 1699 1.08
1274 1.92 1176 2.25 1092 2·61| 1019 3.0
6958·103 5929 14 5194183] 4655) ·23| 4165
1735 1.65 1602 1.93 1487 2-24 1388 2:57
9088 ·09 7744·123] 6784 ∙16 6080203| 5440 25 4532 36 3884 49 339664 3020 81| 27201·00 24721·21 2264 1·44 2092 1.69 1940 1·96 1812 2-25|
9801-109 8586-142 7695 18 6885 22 5733 32 4914 44 4302 57 3825 72 3438 89 31231-07 2862 1.28 2646 1.50 2457 1-74 2295 2.0
1210009810600 128 9500·162 8500| 2 7083 288 6071-392 5312-512 4722-648 4250 *8] 3863968] 3541|1·152| 3269|1·352) 30351·568 2833 1·8
26 7346 36 6428 47 571459 5142 73 4675 88 4285] 1.05 3955 1.23 36731-425 3428 1.64]
6796 •54 6120 67 5560] ·81| 5096| *96 4704 1.13 4368 1.31 4076] 1.5
2210260 307 8978 39 7980 49 7182 61 6529 74 5985 886 5525 1-04 5130 1.21 4788 1·38
2810412 36 9255 46 8330 57 7573 69 6941 824 6408 965 5950 1.12 5553 1·28]
19 13660 26 11952 34 10624 43 9562-533 8692-645 7967
75 7355
•96829 1.03| 6374| 1·2]
18128 18 15536 24513584 32 12080-403|10880 59888 63 9056]
72 8368 •84 7760 •98 7248 1.13
20500 17 17500 2315353] •313647
·
12826 117 11495 1510285-182 8570
15264107 13680·135|12240 1710192
16100 125 14400154 11971]
18600-115|16700 143 13883
15937
•
•
•
•
·
•
24 8736 33 7648| ·43
•
•
21 11900
•
•
❤
•
•
*64 10584
-607|11725
607 11725
•75 9828
673 9447
79 8773
•92 8188] 1·06]|
87 9180
825|10161|
784 11332|
1.0
*95
•9
7512495
*86
71|13713) ·815]
D
*7110887
64513387
61514693
5916059
576 13076 67612140
*55 14417
52515823
517286
*48 18816
•46 20432
22100
42723832|
38 12282 47 11166-567 10235
22932 •1619656 •217|17208*284|15700 36|13752 44212492 ·54|11448|
25404 152 21800 207 19053 27 16935 34 15242 42 13857 51 12702
28332.144 24284 195 21248 256 18888-324 17000 *4 15452-48414164
31230 138 26770·186 23428 245 20825 3118742 38217036 •4515618|
34500 131 29300 -178 25712·235 22855 295 20570·365 18700 •44|17146
37600 127 32000 1728103 225 24980 282 22482 35 20439 42 18735
407681234944 163 30592 216 27184 27 24480 335 22240-40220384
37700 15633203 21 29514 26 26562 32 24148-387 22135
40900 15 35912-197 31922 25 28730 307 26118 375 23941-443
44000·143 38728 19 34425 24 30982 297 28166 3625819
47300 1441650*183 37022 23 33320 286 30290347 27766
44678-176 39714 223 35742 275 32493-333 29785
47808 170 42498-216 38250 266 34767 322 31869
51053 164 45380·207 40882-257 37148 31 34035
54400 1648371*202 43520 ·25 39563·302|36266|
•
•
·
·
•
·
·
•
►
•
51425 196 46282 24242075 293 38568
54586 19 49130 235 44663 283 40941
57847-185 52062 228 47329 276 43385
[61200 1855080' 222/50073 269|45900
* The first column shows weight in pounds: the second the deflection in inches.
•68 14988 78
565|17492] •665|16304|
•75
•5418793 625|17708| •72
*52/20521] *607|19153] *695|
•521130 *58 20655
667
•41/25630
•48 23800
•5621213
•
645
395 27494
.462 25530
*54/23828
•62
384 29421
450 27315
522 25497
•GO
37 31417
435 29173
505 27288
•58)
•36,33477
•35 35602
336,37792
329 40048
•4231086
*4929013
•56
•41/33058
395 35093
47 30855 545
•46 32753
⚫53
3242369
38637187
375 39343
448 34708
435 36720
514
•5




CHAP. 11.
693
COMPOSITION AND USE OF MINERALS.
The direct cohesion of cast-iron has been variously estimated: Captain Brown found
that a bar 1 inch square broke with a force of 11.35 tons, and estimated its cohesion at
7.26 per square inch. Mr. George Rennie found it to be 8·104 and 8·14 tons, when he
made his experiments upon a bar only of an inch square.
10
A bar of malleable iron admits of considerable torsion without having its strength much
diminished, but cast-iron fractures easily when submitted to twisting.
The cohesive power of cast-iron has by some writers been estimated at 10 tons per square
inch of section; by others at 18,000 or 19,000 pounds avoirdupois, one-third of which may
be taken as the permanent cohesive strength for practical purposes. Mr. George Rennie
has given us some experiments, which he made upon the resistance of inch iron bars, when
14
subjected to a wrenching force; he made use of a wrought-iron lever, 2 feet in length,
having an arched head of about 60 degrees, and 4 feet in diameter, of which the lever
represented the radius; in the centre round which it moved was a square hole that
received the iron bar to be twisted: the lever was balanced, and a scale hung on the
arched head, the other end of the bar being fixed in a square hole in a piece of iron, and
that again in a strong vice; it was found that inch bars cast horizontal twisted when
9 lbs. 15 ounces were placed in the scale, and that 10 lbs. 10 ounces were required to those
bars which were cast in a vertical position, to produce the same effect.
6
70
Numerous experiments have been made upon the vertical strength of iron wires of dif
ferent diameters, but there is a great discrepancy among them; in those from to of
an inch in diameter, their strength per square inch has been estimated at from 30 to 40
tons; the mean strength of iron wire, which does not exceed the length of an inch in
diameter, will not support more than 36 tons load.
The cohesive strength of wrought-iron being from 55,000 pounds per square inch to
70,000; when it is required to find its ultimate cohesive strength, the area of its section
must be multiplied by the relative cohesive strength, or rather by one-third of what it is
supposed to be, when applied to practical purposes.
As the transverse strength of wrought or malleable inch-round iron bars, 12 inches long,
loaded in the middle, and lying loose at the ends is equal to 3152 lbs. avoirdupois, and for
an inch square bar 4013 lbs., to find their ultimate strength, it is only necessary to mul-
tiply this strength of the square bar by the breadth, and the square of the depth in inches,
and divide the product by the length in feet; the quotient will be the weight in pounds
avoirdupois.
When malleable iron is subjected to the force of tension, its absolute resistance has been
found to vary from 50,000 pounds to 80,000 pounds per square inch of section according to
its quality, and its strength to resist torsion 15,360 lbs.: this is directly as the cube of one
side, and inversely as the force applied, multiplied into the length of the lever; for if we
multiply the strength of an inch-iron bar by the cube of one side in inches, and divide the
product by the length of the lever in inches, the quotient will give the ultimate strength of
the bar in pounds avoirdupois, or if the bar is round, the cube of its diameter must be divided
by the length of the lever or the diameter or side of a square bar may be found by mul-
tiplying the force applied in pounds by the length of the lever in inches, dividing the pro-
duct by one-third of the ultimate strength of an inch bar, when the cube root of the
quotient will be the diameter or side of the square in inches, capable of resisting perma-
nently that force.
:
In revolving shafts for machinery, the strength is directly as the cube of their diameters
and revolutions, and inversely as the resistance they have to overcome. A forty-horse-
power steam-engine making 25 revolutions a minute is found to require a wrought-iron
shaft 8 inches in diameter; the cube 8 multiplied by 25, and divided by 40, is equal to
320, a constant number or multiplier for all others; as for example, an engine 65 horse
power making 23 revolutions per minute,
3 65 × 320
23
=9.67 inches diameter nearly.
200 is the constant multiplier or number made use of in general for all second movers, and
100, for that of shafts connecting the smaller parts of machinery.
Corrugated Iron is employed in the covering of buildings, and it was first used at the
Eastern Counties Railway shed at the London terminus, built in 1840. The plan is a
rectangle, being 230 feet in length, and the width is divided into three spaces; that in the
middle is 36 feet in width, and those on each side 20 feet 6 inches: the rows of cast-iron
columns seventeen in each, and distant 13 feet 6 inches from one another; over their
capitals they are connected by a cast-iron elliptical girder of an inch in thickness with
open panels; over this is a cast-iron gutter. The centre roof rises 9 feet, and that of the
side roofs 4 feet, the springing line above the rails being 22 feet 6 inches.
The corrugated wrought-iron is of the sheets called No. 16. wire gauge, or in thickness
the fourteenth of an inch; and the arch is formed by curving the sheets of iron in the
transverse direction to the arches themselves, and riveting them together in the direction
of their length.
Y Y 3
694
Book II.
THEORY AND PRACTICE OF ENGINEERING.
The superficial content of the middle span is 10,235 feet, and that of the two side roofs
10,810 feet, each being a little more than half that in the centre. As the weight of this
corrugated iron is 3 pounds per superficial foot, the whole weight is 28 tons: the cost of
erection was 61. 10s per square of 100 feet, or 13657.
The water is carried off from the roof down the curves of corrugation, first into the gutter,
then through the hollow columns, and afterwards by drains. A single sheet of this iron was
found to bear 700 pounds weight in a vertical position without bending. Many other
roofs of this description have been executed, and apparently stand well; one at the London
docks is 225 feet in length, and 40 feet span. St. Catherine's Docks, the Birmingham,
Blackwall, and numerous other railways, have made use of them.
Galvanised iron, as it has been termed in France, is made by covering the metal with a
coat of tin by a peculiar process, and for a time it resists the corrosive effects of the atmo-
sphere as well as that of water: the surface of the iron is first rendered perfectly clean by the
joint action of dilute acid and friction; after which, it is plunged into a bath of melted zinc,
and moved about until entirely covered with the alloy; it is then taken out and immersed
in a bath of tin, which covers it with a thin coat of alloy. It is stated that when iron thus
heated is exposed to humidity, the zinc slowly oxidises, and protects the former from rusting
within it whilst the outer tinned surface remains.
Coal is found in many parts of the British Islands. The culmiferous series in Devonshire
lies in a great basin, the axis of which extends 50 miles from east to west, with an average
breadth of 30 miles; the upper beds of slate of the Devonian system are occupied by dark
coloured limestone, over which occurs a stratum of siliceous flagstones; over these are sand-
stones, carbonaceous and calcareous slates, which are surmounted by a bed of thick
sandstone.
The South Wales coal field extends about 90 miles along the shores of the Bristol
Channel; its greatest breadth is not more than 20 miles; the number of bands of coal is
considerable; their thickness varies from 18 inches to 9 feet, and the whole taken together
amount to a depth of 95 feet in the deepest part they lie about 13,000 feet below the
surface.
The Somersetshire and Bristol coal field is of small extent; that of South Staffordshire
has only eleven seams, but the main bed in the middle is upwards of 30 feet in thickness;
this seam crops out near Bilston. The coal in the northern portion contains numerous
impressions of plants.
The Shrewsbury coal field is not very extensive: that in Flintshire is under the new red
sandstone; this latter is about 40 miles in length, and 3 in breadth. But the most im-
portant of all are those in the north of England, which form three districts: in the first is
comprised Yorkshire, Derbyshire, and Nottinghamshire; in the second, Lancashire; and
in the third, Durham and Newcastle.
In the first the beds vary from 2 to 5 feet in thickness, and are of a bituminous qua-
lity. In the Lancashire district, the extent from north to south is 46 miles, and about
40 in width: in some parts there are 75 seams, forming altogether 150 feet of workable
coal.
Coal Fields.-The chief in England is the Newcastle, and lies between the rivers Coquet
and Tees, its length being nearly 50 miles, and its breadth upwards of 20; the area of this
district, so important to British trade and manufactures, is computed at 800 square miles.
It is divided by a great fault, which crosses it north of the Tyne, where the strata are
thrown downwards on the one side, and uplifted to a height of 90 fathoms on the other;
this fault is termed the main dyke. The most valuable working is the high main, where
the coal is 6 feet in thickness.
Boring is first resorted to for the purpose of ascertaining the best position for sinking the
shaft by which the coal is to be drawn up; this is performed in the ordinary way by means
of successive iron rods and machinery to work them, the cost of which is 12 shillings per
fathom for the first ten, and an additional 6 shillings for each 5 fathoms beyond.
The shafts are cylindrical, and seldom less than 10 feet in diameter; these are divided by
a wall; some of the larger shafts are formed into three compartments, one of which is used
for ventilation, another for drainage, and the third for drawing up the coal. Great expense
and caution are necessary in the works appertaining to this part of the operation; the
whole of the shafts require to be cased or lined with good bricks or stone, and where the
springs are abundant there must be a tubing or a crib formed of whole deals attached to
circular ribs or curbs; metal castings are now sometimes substituted, as better calculated
to resist the extraordinary pressure to which the curb is subjected.
These shafts commonly extend to the depth of 150 feet, and sometimes as much as 1800;
that at the Wearmouth Colliery, near Sunderland, passes through the capping of magnesian
limestone, the lower beds of which, with the lower new red sandstone, overlap the coal
measures. After the shaft had been sunk 330 feet, the workmen tapped a spring, which
poured out 3,000 gallons of water per minute; this, however, being subdued by the
working of a steam-engine of 200 horse-power, a strong metal cylinder was introduced, and
carefully placed around the shaft; the sinking was then continued to the depth of 1578
CHAP. II.
695
COMPOSITION AND USE OF MINERALS.
feet, when a very valuable seam of coal was arrived at; during
the ten years employed in sinking this pit upwards of 100,0007.
were expended.
In Staffordshire the coal is drawn out by means of a
number of pits, which are not required to be of great depth.
When the shaft is first sunk, two galleries are driven, one
in an horizontal line along the strike of the coal seam, the
other on the rise of the bed, at right angles to it. The
first is termed the drift or watercourse, and the other the
winning headway, through which the coal is brought to the
shaft to be hauled up these cuttings are 9 or 10 feet in width,
6 feet in height, and are made convenient for the passage of
the waggons, which in some cases run upon rail or tramroads.
After the drift and winning headway are completed, other gal-
leries, varying in dimension, are set out parallel to the latter;
some are 9 or 10 feet in width, intersected by others at right
angles, the pillars of coal which are left between the galleries
for the purpose of support being generally 8 or 9 yards in thick-
ness; and in the old method of mining these pillars were left, but
since panel work was introduced, fifty years ago, they have been
extracted: this is performed by dividing the entire mine into
panels, separated by walls of coal from 40 to 50 yards in thick-
ness, and then extracting the coal from each in succession, com-
mencing work in that most distant from the shaft, shutting off all
communication with the others till the whole panel is worked
Pillars about 24 yards by 12 are at first left between the
boards, as the largest galleries are called, and the transverse gal-
leries or rooms, and when the first are completed the miners
attack the pillars; the roof being supported by posts of Scotch
fir, which are removed as the work proceeds, and the roof is then
suffered to fall in. Thus the whole of the coal is now removed,
and by allowing the galleries to be filled up, all danger from an
accumulation of the noxious gases is prevented.

out.
The tools used by the collier are a mattock having both ends
of the head pointed, and several kinds of chisels, crow bars, and
hammers. The coal is generally blasted, and then broken
up into
small masses; the blasting is effected by piercing the lower part
of the seam with a hole about 1 inch in diameter and 3 feet in
depth, into which the cartridges are introduced, and the hole is
plugged up with coal dust; the men who obtain the coal are
called hewers, and those who load the waggons or corves the
putters, who also conduct the horses to the bottom of the shaft,
where the coal is drawn up.
In the Dudley coal field, where the thickness of the seam is as
much as 30 or 40 feet, it is worked in chambers, which are called
sides of work.
The strata of coal in England usually lie horizontal; in Wales
and in Scotland they are inclined, sometimes at a considerable
angle; where this is found to be from 450 to 60°, as in Pembroke-
shire, the mine is worked by an adit level, which passes out on a
hill side. Windlasses placed along the inclined vein draw up the
coal after it has been extracted from the stalls; two sets of
carts are used for the purpose, so attached to the windlasses that
those which are full draw up the empty.
The whim for raising coals from the shaft is now generally
100
-
coal minE SHAFT.
Fig. 592.
worked by a steam-engine, which gives motion to a hollow drum on which the rope
winds that brings up the materials.

Fig. 593.
WHIM FOR RAISING coal.
YY 4
696
BOOK Il.
THEORY AND PRACTICE OF ENGINEERING.
The ventilation of coal mines is effected by means of rarefaction; a furnace is placed at
the bottom of the pit, which produces a rapid ascending column of warm air, and as this
rises up the shaft its place is supplied by a current of cold air, which passes down one of
the other compartments of the shaft, and is made to traverse the several workings of the
mine before it is permitted to arrive at the furnace, where in its turn it becomes rarefied.
In the Wallsend colliery the quantity of fresh air thus admitted varies from 2000 to 3000
cubic feet per minute; in some of the coal mines the air has so many miles of gallery to
traverse that it is 12 hours before it arrives at the furnace, the rate at which it progresses
being about 2 feet per second or a little more. The wall of separation in the shaft is called
the brattice, and is of two kinds: one is permanent, and usually 2 or 3 feet in thickness;
the other is of a more temporary kind, composed of 3-inch deals, so attached to a skeleton
frame that it can be easily removed. Where the galleries are shut off, to prevent the cur-
rent of air from passing, the wall is called a stopping; this is sometimes effected by
trap-doors, made either single, double, or triple, as may be most convenient; the air
course is called either the intake or return as it receives or emits the air.
Lighting Coal Mines.-The means of effecting this, without subjecting the workmen
to the dreadful calamities arising from the explosive nature of the gas when mixed with
atmospheric air, had long occupied the anxious attention of scientific men, but without
success, until the experiments of Sir Humphry Davy happily led him to construct a
lamp by which the lives of incalculable numbers have been preserved. He found that no
mixture of fire-damp would explode in tubes with a diameter of less than of an inch;
and also that a much stronger heat was required to effect this than with mixtures of
common inflammable gas, and that neither charcoal nor iron made red-hot would produce
an explosion. Upon these principles Sir Humphry formed the lamp called after him:
the flame is enclosed within a wire gauze of very small meshes, there being as many as
784 to the square inch; the security which it affords to those for whose use it was invented
is not, however, sufficiently estimated, in consequence of its not affording a great abundance
of light, and in many instances there has been much difficulty in enforcing its introduction.
Besides the fire-damp there is another noxious gas, called the choke or black damp; this
is a carbonic acid, and from its density will not rise to the surface, but sinks to the bottom
of the mine. The heavy carburetted hydrogen is also found; this, when mixed with certain
proportions of common air, is exploded by either charcoal or iron heated to a dull red heat.
The Scotch Coal Fields are about 100 miles in length, and 30 in breadth; and the
number of beds are said to be 337, 84 of which are coal; the total thickness of all these
layers is computed at not less than 5000 feet.
The Coal Fields in Ireland are nearly 150 miles in length, and 120 in breadth, covering
a surface of more than 10,000 square miles. The coal is anthracitic, being often found in
the state of pure anthracite.
The first charter for the licence of digging coal was granted by Henry III., in the year
1239, and it is there called sea-coal; it became a common fuel soon afterwards, and a
considerable quantity appears to have been exported to France. When Mr. Taylor, a few
years ago, gave his evidence on the coal mines before the Committee of the House of
Lords, he stated that the annual consumption of coal in Great Britain amounted to
19,540,000 tons.
Coking of Pit Coal. The most common method is to throw up the coals in heaps of
about 40 tons as loosely as possible, and cover them with the smaller pieces; fire is then
applied at various parts, and the mass is suffered to burn until the whole is ignited; when
this is effected, it is covered up with dust and ashes to exclude the air, and the heap is
suffered gradually to cool: water is often poured over it to accelerate this last part of the
process, which is said to improve the quality of the coke by making it harder.
Ovens are used for making the better quality of coke; the best are usually elliptical in
their form, about 12 feet in their longest diameter, and 11 feet in the other; the walls are
3 feet in thickness; the mouth is usually lessened towards the inside to about 2 feet
6 inches, that on the outer side being a foot more. At the back is the entrance into the flue
which conducts to the chimney; this is regulated by means of fire bricks, which can be
moved to increase or diminish the draught, so as entirely to consume the smoke.
A series of eighteen ovens, with a flue at the back 1 foot 9 inches wide, and 2 feet 6
inches high, have been constructed at the station of the Birmingham railway; and the flues
are conducted into a chimney 11 feet clear diameter at bottom, 17 feet outside, and 115
feet in height. These ovens are each charged with 3 tons of good coal, and entirely
consume the smoke from the moment they are first lighted up; in about 40 hours it is
sufficiently coked, when it is thrown out upon the ground and watered; it is then put
into iron canisters and covered up: good coal will yield 80 per cent. of coke, weighing
14 cwt. per chaldron. The loss of weight when coals are coked in the ordinary manner
is about 25 per cent., and coal which thus loses in weight gains † in bulk.
14
CHAP II.
697
ON STONE.
CHAP. III.
ON STONE.
GREAT attention has been deservedly paid to the quality of the materials made use of in
building, and the knowledge on the subject has been greatly advanced by the mineralogist
and chemist. Vitruvius asserted that all bodies consist and spring from earth, air, fire,
and water, but has not given us the quantity of each that enters into their composition:
these original elements, he observes, are not only indivisible, but also incapable of change
or of destruction; this is not exactly the case, for we find that stone is acted upon chemi-
cally as well as mechanically, and that it exhibits, when applied to buildings, the same
decomposition to which it is subject when attached to its native rocks. Stone is variously
acted upon in different situations: in cities, when exposed to the influence of the smoke
of coal, some varieties are rapidly decomposed; other kinds are affected by the alternations
of dryness and humidity; particular streams rapidly destroy some limestones, and materially
injure the granites.
The limestones used by the Egyptians, Greeks, and Romans, have endured to this day:
the sandstones employed in their temples and public edifices in many situations exhibit no
decomposition, and the granite of all varieties remains perfectly entire; showing that the
architects of antiquity knew how to select their material, and to apply it in such a manner
that it was not subjected to any greater action by exposure than it had to encounter in its
natural bed.
Stone Quarries.—The stone found near the surface, and which has been exposed to the
action of the atmosphere, is not so sound as that which is taken from a depth, where it has
been subjected to great pressure, and the greater the depth, generally speaking, the greater
is its hardness and density. On opening a quarry, the first consideration is the means of
raising and delivering the stone in the least expensive manner; an excavation is usually made
in the side of a hill, in preference to uncallowing the top, in order that the road leading
from it should have as gentle an inclination as possible; for if the quarry be sunk very
low, the difficulty and expense of drawing out the blocks of stone are seriously increased.
The stone is generally found in beds or masses, divided by joints, at which divisions the
natural adhesion is broken, and there is no difficulty in detaching the blocks, nor risk of
breaking them: where vertical pressures exist, which is often the case, their removal is
facilitated; but it is sometimes necessary to break the contiguous blocks, or blast them
with gunpowder. Wedges of steel, driven in by a heavy sledge hammer, are often used to
separate the stone from its bed: in order that the edges may not be broken, or rendered
ragged by removal, they are elevated to the platform or truck by an instrument called the
lewis, which consists of three pieces of strong iron, formed and held together by a shackle
and screw bolt; two sides are parallel to each other, or the pieces are of the same thickness
throughout, which varies from 1 to 3 inches, according to the weight it is destined to
carry. The two pieces outside spread out, and at the bottom are twice the thickness that
they are above; the middle piece is of the same size at top and bottom, consequently when
the three pieces are put together, the width at the bottom is one third more than at the
top; by taking out the screw-pin, and withdrawing the central piece, the two others are
brought together, and introduced into a sunk groove in the stone, cut like a dovetail, or
spreading at the bottom, of a sufficient dimension to take in the whole lewis, which is
placed in separate pieces, the middle being the last; the bolt and shackle are then attached,
and the lewis now occupying the whole cavity, no force can detach it; by this means
enormous masses are lifted perpendicularly by blocks and falls, worked by a piece of
machinery called a crab. The upper block, which sustains the weight, is attached to a
crane or strong beam of timber, fixed as perpendicularly as possible, with its block over the
stone, every precaution being taken to prevent its lower extremity from slipping.
crab is so placed as to have the draught of the rope as nearly as possible in the direction of
the pole, the top of which is either secured or moved by guy ropes, worked also by blocks
and falls fastened to the ground; where the weights are great, two poles are sometimes
used for more security.
The
When the stone in the quarry does not exhibit any natural joints or fissures, but appa-
rently forms one compact mass, a line of holes is drilled at short and regular distances, into
which are put conical steel pins, rather larger than the holes, which, being struck simul-
taneously by the hammers of the miners, produce a separation in the direction desired.
Wooden pegs are occasionally substituted, where the cleavage is easy, around which a clay
wall is built, filled with water; in a short time the pegs swell and separate the stone.
698
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
To drill the holes in very hard stone, it is necessary to have a steel cold chisel about 2 feet
long, and the breadth of the hole required, the edge being double bevelled, and not too
sharp; a workman holds this instrument where the hole is to be made, whilst another
strikes it, taking care that the drill is turned partly round, or kept revolving during the
succession of blows; as the indentations are made, the powdered stone or dust is removed
from the hole. When rocks are blasted by gunpowder, the holes are drilled to a greater
depth, usually 16 or 18 inches deep, and an inch or more in diameter; the powder is
introduced into them, sewed up in a linen bag, with a cartridge made of tin; dry sand is
put upon it and rammed down, and the top of the hole is filled with moistened sand. A
train of powder in a fine tin tube is connected with the holes, to which is attached a slow
match or some wild-fire, so arranged as, when fired, to give the workmen time to retire out
of all danger from the scattering of the fragments, which occasionally is attended with
great violence. Voltaic electricity, conducted by means of wires, has been effectually
applied to the ignition of the gunpowder, which is attended with infinitely less casualties,
inasmuch as if ignition does not immediately take place, it is not to be feared afterwards.
In the selection of stone for the purposes of construction, regard must not only be had
to the colour and texture, but also to its power of withstanding the exposure to atmo-
spheric agency, or the decomposing effects of water. Stones are composed of various earthy
substances in such a state of hardness as not to be softened by immersion in water under
ordinary circumstances; they may be classed under three distinct divisions, viz. the sand-
stones, limestones, and granites.
Sandstones are formed of angular or rounded grains of different earths or minerals, which
are either held together by a cement or base, or joined without any such basis by simple
juxta-position: when the grains composing them are small, they are called sandstone, but
when they increase in dimension, they are designated conglomerate, if the particles are
rounded; if angular, they take the name of brescia. The consolidation of the various
sandstones seems to have taken place not during the time they were forming under water,
but when they were upheaved, or had the water drawn from them; this is implied from the
fact that most sandstones, when first taken from the quarry, are softer than after exposure to
the air; no doubt the water which they contain is speedily evaporated, and the minerals it
holds in solution become deposited, and by their crystallisation give greater hardness and
consistency to the mass, binding it more firmly together, and rendering it more difficult to
cut; some varieties are so plastic, when first taken from the quarry, that they may be easily
compressed, and afterwards, from the loss of the water they contain, become perfectly hard.
Sandstones are divided into three varieties, according as the quartz or siliceous grains com-
posing them are cemented by siliceous, argillaceous, or calcareous matter.
In the siliceous kinds the particles are cemented by a base of quartz: in the argillaceous
by a base of clay, usually impregnated with a red oxide of iron, which gives that tint to the
whole rock; and in the calcareous kinds by a marly or calcareous cement, and it must be
obvious that the quality of sandstone entirely depends upon the durability of its cementing
properties. As the particles which are held together, being silex in nearly a pure state, are
not acted upon by either air or water, its decomposition is found to commence by the de-
struction of its base, which liberates the grains in the sandstone, or permits them to crumble
into fine sand: when the base is highly impregnated with silica, it is very hard, has almost
the character of porphyry, and seems to defy decomposition.
In the varieties of sandstone with small grains, set in an argillaceous or calcareous base,
the colours vary from red, grey, green, yellow, and brown, and are arranged in zones or
bands dependent upon the oxidation of the iron in the base or cement. This variety of
sandstone is found alternating with beds of red-coloured clay, or marl, which is sometimes
slaty, or mixed with sand and mica, passing into sandstone slate; the beds are of great
thickness.
From sandstone being formed in strata, and laminated, it is obvious that when applied to
building purposes, they should be so placed as to correspond with their natural beds, for if
in any other position, or vertical to their planes of stratification, any weight placed upon
them would tend to cleave or split them into laminæ.
The sandstones that have undergone an analysis consist of:


Cragleith.
Darley Dale.
Heddon.
Kenton.
Mansfield.
Silica
98.3
98.40
95.1
93.1
49.4
Carbonate of lime
1.1
0.36
0.8
2.0
26.5
magnesia
0.0
0.0
0.0
0.0
16.1
Iron alumina
0.6
1.30
2.3
4.4
3.2
Water and loss
0.0
1.94
1.8
0.5
4.8
Bitumen
0.0
0.0
0.0
0.0
0.0
Specific gravity of dry
masses
2.232
2.628
2.229
2.247
2.338
CHAP. III.
699
ON STONE.

Cragleith.
Darley Dale.
Heddon.
Kenton.
Mansfield.
Specific gravity of parti-
cles
Absorbent powers, when
saturated under the ex-
hausted receiver of an
2.646
2.993
2.643
2.625
2.756
air-pump
0.143
0.156
0.143
0.151
Disintegration-Quantity
of matter disintegrated
Cohesive powers
0.6 grs.
111
0.121 grs.
100
10.1 grs.
7.9 grs.
7.1 grs.
56
70
72
As a general remark it may be inferred that those stones which have the greatest specific
gravity possess the greatest cohesive strength, absorb the least quantity of water, and disin-
tegrate the least by the process which imitates the effects of weather, though we are not
able to compare stones of different classes together, for while sandstones absorb the least
water, they disintegrate more than the magnesian limestone, which absorbs a great quantity
of water.

Names of the
Quarries
specified.
Weight in ordi-
nary Slata in,
Grain.
Weight when
well-dried in
Grains.
Cohesive Powers.
Specific Gravity
of the Solid
Particles.
Bulk of Water
absorbed ;
total Bulk
considered as
Unity.
Cragleith
-
4746.2 4737.4 4880-0
Ditto
4557.1 4553.8 4765-10
4594.0 4588.3
4698-7 4695.6 4859.0 163.4 0.080
Ditto
-
4737.8 4734.3
Ditto
Darley Dale
Ditto
Ditto
Heddon
4685.2 4678.3 4826.5 148-2
0.6
60
111
1
1
2.266
2.646
0.143
88
100
2.230
2.666
0.163
211-2
0-104 10-1 26
56
Ditto
1
2.229 2.565 0.156
Kenton
4658.4 4647.9 4848.5 200-6
0.099 7.9
48
70
Ditto
4595.4 4581.5
Ditto
1
2.045 2.706 0.244
Mansfield
4700.2 4695.3 4906.0 210-7 0-104
7.1
28
Ditto
Ditto
-
4733.5 4719.4
1
72
2.338
2.756
0.151
Results of experiments upon cubes of 2 inches in diameter.
Results of experiments
on cubes of 1 inch in
diameter.
In the foregoing table the first column gives the name of the quarry where the specimen
was procured.
The second indicates the weights of the specimens in the state in which they are usually
employed for the purposes of building, subjected only to the atmospheric influences since
taken from their respective quarries and worked.
The third contains the weights of the same specimens, after having been perfectly dried,
by exposure in heated air for several days: their relative specific gravities are indicated
by these numbers, subject to the errors arising from differences in the sizes of the cubes,
which, on account of the accuracy of the measurements, varied but little from each other;
the specific gravities, however, taken by the most certain method, will be found in columns
10 and 12.
The fourth exhibits the weight of one set of the above-mentioned cubes, after having been
immersed in water for several days, so as to become completely saturated, such weights
having been ascertained immediately after the cubes were taken out of the water, and
wiped.
The fifth shows the difference of weight between the same specimen in its dried and in
its saturated state, and indicates, therefore, the quantity (by weight) of water absorbed by
each stone.
The sixth shows the relative bulk of water absorbed, 8 cubic inches, or the bulk of the
cube being taken as unity.
The seventh gives the quantity of disintegration of the several stones in grains, after
having been simultaneously subjected to Brard's process for eight successive days; the
measures thus obtained may be considered very closely to represent the action of the atmo-
sphere during successive winters on the various stones submitted to examination.
The eighth and ninth columns contain the results relating to the cohesive strength of the
stones, or their resistance to pressure. These experiments were made at the manufactory
of Messrs. Bramah and Robinson with a 6-inch hydrostatic press, the pump of which was
1 inch in diameter: according to previous trials by Messrs. Bramah and Robinson, 1 pound
weight at the end of the pump lever produced a pressure on the face of the cube equal to
700
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
2.53 cwt., or 71.06 lbs. on the square inch. The experiments with the stones were
cautiously made; the weight on the lever was successively increased by a single pound,
and in order to ensure greater accuracy, a minute was allowed to elapse previous to the
application of each additional weight. The eighth column shows the pressure at which the
stone commenced to crack, and the ninth the pressure at which it was crushed. The unit
assumed is the pound weight placed at the end of the lever; the employment of this unity
in the table is preferred to stating the calculated weights, because it is not wished to give
a greater appearance of accuracy than can strictly be adjudged to the experiments; but if
absolute measures be required, the pressure either upon the face of the cubes employed on
1 square inch of the surface may be estimated, as nearly as the means employed enabled it
to be ascertained, by multiplying the figures in the table by either of the values of the
unit above stated. The results having been obtained with the same press, and under the
same circumstances, it is presumed that no objection can be made to them as comparative
experiments.
The tenth indicates the specific gravities of the stones, accurately taken by the means
usually employed.
The eleventh contains the specific gravities of the solid materials of which each stone is
composed, on the supposition that the water absorbed, when the atmospheric pressure is
removed, completely replaces the air which before occupied the pores.
The twelfth shows the bulk of water absorbed by the stones when saturated under the
exhausted receiver of an air-pump, their entire bulk being taken as unity. The quantity
of water absorbed in this process may be considered to represent space occupied by the
pores or interstices in the substance, unless we suppose that in some cases the adhesion
between air and the solid particles is so great that the entire removal of the atmospheric
pressure is not sufficient to counteract the force. It is certain when this pressure is not
removed, long immersion in water will not occasion the displacement of all the air contained
within its pores.
Sandstones on the continent, as well as in England, are less used in architecture than
calcareous stones; there are nevertheless some kinds which are sufficiently solid, and may
be safely employed in those districts where calcareous stones are wanting. At Paris the
sandstones found in the environs are only used for paving, in consequence of the difficulty
with which they are worked: many of the sandstones, which appear to be very friable, and
readily affected by the air, are used with advantage in constructions under water.
Limestones, or Calcareous Stones, are the most generally used in the construction of
edifices, and are called calcareous, because, when exposed to heat, they are reducible to
lime; they are also distinguishable by being soluble in acids, in which they strongly effer-
vesce a drop of nitric acid falling on a calcareous stone, it bubbles and hisses, like hot
iron plunged into water; when struck with the steel it emits no sparks.
Limestones are most frequently used, not only because most abundant, but also because
more easily worked than all others, and possessing sufficient tenacity to resist pressure, and
preserve the mouldings, arrises, &c. The varieties are not, however, indifferently used;
some have not sufficient cohesive power, as, for example, chalk, several granular calcareous
stones, simple or micaceous, from the primitive and intermediate strata, which do not resist
pressure; others, having their parts sufficiently compact, are too fragile, or, according to
the opinions of the workmen, too dry, such as those which are very compact and formed of
fine grains having a conchoidal or shelly fracture; these varieties are frequently filled with
fissures injurious to their solidity, whether open or filled with calcareous spar. Calcareous
stones, most suitable for construction, are the compact, with unequal fracture, flat, or
irregular, of an earthy tinge, and these formed of shells, united by a cement, partly earthy,
partly crystalline. These varieties abound in the secondary and tertiary formations, in de-
posits analogous to those of the Jura, and similar to those in the environs of Paris; of these
the greater number of the monuments of the civilised world have been constructed; the
finest houses of Amsterdam and the mosques of Constantinople are built of this material.
The stones of the secondary formation are also in general use; those in the second bed
of tertiary formation are abundantly employed in Paris. The workmen class this under
several varieties according to their application.
The calcareous tufa or travertine used in Italy is whitish or yellowish, and is found in
the substructions of most of the ancient temples, in the Coliseum and other public buildings
in Rome: it must always be placed in the same position as in their natural beds, where it
is deposited in horizontal layers; when laid improperly these exfoliate and split vertically;
stone of a very compact and homogeneous structure, and forming beds of great thickness,
will alone allow of their natural position being reversed.
Calcareous spar is found in crystalline masses, or in colourless crystals; it is easily dissolved
by muriatic acid; its specific gravity is 2.7; it loses 46 per cent. by the expulsion of car-
bonic acid. The stalactitic carbonate of lime, or concretionary limestone, is formed of
zones which have a fibrous structure arising from the successive deposits of the crystalline
limestone from its solvent water. The stalagmite or alabaster limestone does not exhibit
concentric zones, but spreads out in a waving and parallel direction. The stalactites are
CHAP. III.
701
ON STONE.
formed from the roofs of caverns in the limestone rocks, where the water percolates
through them, which is charged with carbonate of lime held in suspension by an excess of
carbonic acid, which is precipitated by exposure to air.
Limestones are comprised under three denominations, the simple, the oolite, and the mag-
nesian; these are the varieties usually employed in construction: the most crystalline are
the most durable; some contain a quantity of silica; on many the atmosphere has a power-
fully decomposing effect; water being first absorbed acts mechanically on the external faces
of the stone, occasioning afterwards, by chemical action, an entire change in the constituent
parts.
Of the various limestones examined by the Commissioners appointed by the Government
previously to the erection of the Houses of Parliament, their composition is as follows: —

Chilmark.
Silica
Carbonate of lime
of magnesia
Iron alumina
Water and loss
Bitumen
Specific gravities of dry masses
of particles
Absorbent powers, when saturated under the ex-
hausted receiver of an air-pump
Disintegration quantity of matter disintegrated
Cohesive powers
Name of the
Quarry from
whence Speci-
mens were
procured.
Barnack.
Hum Hill.
0.0
10.4
4.7
93.4
79.0
79.3
3.8
3.7
5.2
1.3
2.0
8.3
1.5
4.2
2.5
a trace
a trace
a trace
2.090
2.481
2.260
2.627
2.621
2.695
0.204
0.053
0.147
16.6 grs.
25.
9.8 grs.
101.
9.5 grs.
57.

Weight in ordi-
nary State in
Grains.
Weight when
well-dried in
Grains.
Weight when
saturated with
Water in Grains.
Weight of Water
absorbed in
Grains.
Bulk of Water ab-
sorbed, 2 Cube
Inches con-
sidered as
Unity.
Weight of Parti-
cles disintegrated
in Grains.
Weight pro-
ducing First
Fracture.
Cohesive Powers.
Crushing
Weight.
Specific Gravity
of the dry Speci-
mens.
Specific Gravity
of the Solid
Particles.
Bulk of Water
absorbed ;
total Bulk
considered as
Unity.
Barnack
4443-9
Ditto
Ditto
4442.3 4729-4 287.1 0.141
4235.4 4233.5
16.6
16
25
2.182
2.687
0.180
Chilmark
Ditto
Ditto
Ham Hill
4907.1 4897-0 5072-4
174.4
0.086
5.6
36
90
4935-9 4925.3
1
·
2.366 2.658
0.109
-
4700-3 4695.5 4930-0
234.5 0.115
9.5
22
57
Ditto
[
4685.3
4683-5
Ditto
2.260
2.695 0.147
M
Results of experiments upon cubes of 2 inches sides in duplicates.
Results of experiments
upon cubes of 1-inch
sides.
Oolite. This is composed of oviform bodies cemented by calcareous matter of various
coherency, and is liable to decomposition as the cementing qualities are chemically or
mechanically acted upon that of Bath and Portland is extensively employed in building;
it is worked with great ease, and has a good colour, which it, however, loses when long
exposed to the action of the atmosphere; the same cause renders it unfit for fine carving,
the delicate portions and arrises soon crumbling away.
The oolites examined by the Commissioners are the following:


I
Ancaster.
Bath Box.
Portland.
Kelton.
Silica
Carbonate of lime
Iron alumina
0.0
93.59
0.0
94.52
1 20
95.16
2.0
92.17
of magnesia
I
2.90
2.50
1.20
4.10
0.80
1.20
0.50
0.90
Water and loss
2.71
1.78
1.94
2.83
Bitumen
a trace
a trace
a trace
a trace
Specific gravities of dry masses
2.182
1.839
of particles -
2.687
2.675
2.145
2.702
2.045
2.706
Absorbent powers
when saturated
under the exhausted receiver of an
air-pump
0.180
0.312
0.206
0.244
Disintegration-quantity of matter
disintegrated
7.1
10.
2.7
3.3
Cohesive powers
33.
21.
30.
36.
702
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

Names of Quar-
ries from
whence Speci-
mens are pro-
cured.
Ancaster
Ditto
Ditto
Bath Box
Ditto
Ditto
Portland
Ditto
Ditto
Ketton
Ditto
Ditto
Weight
in ordi-
nary State.
Weight when
well-dried in
Grains.
Weight when
saturated with
Water in Grains.
Weight of Water
absorbed in
Grains.
Bulk of Water
absorbed; 2 Cube |
Inches con-
Cohesive Powers.
Bulk of Water
absorbed ; total
Bulk con-
sidered as
Unity.
-
-
4585-4
4543-1 4512.0
3767.8 3766-8 4109-0
4584.0
4920-3
336.3
0.166
7.2
24
33
2.182
2-687 0.180
342-4
0.169 20.0
18
21
3876.3
3875.5
-
-
4302.9 4300-4 4375-1
0.135
275-1
1
1.839
2.675
0.312
2.7
30
55
4306.9 4305.0
2.145
2.702 0.206
4412.8
4313.2
4409-7 4715-6 305.9 0.151 3.3
22
36
4309.5
2.045
2.706
0.244
Results of experiments upon cubes of 2-inch sides in duplicate.
Results of experiments
upon cubes of 1-inch
sides.
Magnesian Limestone or Dolomite, when of a crystalline character, and with nearly
equivalent proportions of carbonate of lime and carbonate of magnesia, is preferred to most
others, on account of the uniformity of its texture, and the facility with which it is worked.
Like common limestone it can be formed into mortar, though it remains much longer
caustic than quicklime made from the latter; this constitutes the important difference be-
tween magnesian and common limestones when employed in agriculture; the lime made
from the magnesian variety is hot and injurious to the fertility of the soil.

Bolsover.
Huddlestone. Roach Abbey. Park Nook.
Silica
Carbonate of lime
3.6
2.53
0.8
0.0
51.1
54.19
57.5
55.7
of magnesia
40-2
41.37
39.4
41.6
Iron alumina
1.8
0.30
0.7
0.4
Water and loss
3.3
1.61
1.6
2.3
Specific gravities of dry masses
2.316
2.147
2.134
2.138
of particles
2.833
2.867
2.840
2.847
Absorbent powers when
saturated
under the exhausted receiver of an
air-pump
0.182
0.239
0.248
0.249
-
Disintegration
quantity of matter
disintegrated
Cohesive powers
1.5 grs.
117
1.9 grs.
61
0.6 grs.
1.8 grs.
55
61

Name of
Quarry from
whence the
Specimen was
procured.
Weight in ordi-
nary State in
Grains.
Weight when
well-dried in
Grains.
Weight when
saturated with
Water in Grains.
Cohesive Powers.
Bulk of Water
absorbed; total
Bulk con-
sidered as
Unity.
Bolsover
Ditto
Ditto
4890-8 4881-4 5042.0 160.6 0.079
5052.2 5043.0
1.5
70
117
2.316
2.833
0.182
Huddlestone 4493-5 4491.4 4735-0 243-6 0.120 1.9
34
61
Ditto
-
4447·4 4445.9
4424-6 4422.5
Ditto
Roach Abbey 4408-3 4406-0 4754.7 348.7 0-172
Ditto
1
2.147
2-867
0.239
0.6
24
55
Ditto
2.134
2.844
0.248
-
Park Nook · 4356.6 4336-3 4784-7 448.4
0 221 1.8
26
61
Ditto
Ditto
4519.2 4509.3
-
·
-
2.138
2.847 0.249
Results of experiments upon cubes of 2-inch sides in duplicate.
Results of experiments
upon cubes of 1-inch
sides.
The purity of all the limestones is readily determined by measuring the quantity of
carbonic acid which is evolved during their solution in dilute nitric or muriatic acid:
perfect carbonate of lime loses as much as 46 per cent, and when a smaller proportion is
driven off, we may infer that there is less weight of calcareous carbonate. Marls or other
earths containing lime may also be similarly tested by effervescing them with acids.
CHAP III.
703
ON STONE.
Statuary Marble—primitive Limestone. Of this entire mountains are sometimes formed:
in other instances it is found in beds; its specific gravity is 2.7; it can be sawn into thin
slabs, and will receive a brilliant polish: these qualities are only found in three varieties
of limestone, the saccharoid, foliated, and the carboniferous: it never contains the remains
of organised bodies, but sometimes quartz, mica, hornblende, and other substances.
The white marble of Carrara is a fine grain, even and close, of equal colour, resembling
white sugar; crystals are occasionally embedded in it, which prevent the working of the
chisel: when diversified with spots and greenish or greyish veins, it is called Cipollinaccio;
that of a coarser grain resembling salt, and thence called Saligno, is more difficult to work,
and often contains a great deal of moisture: those which sound like a bell under the tool
are called Campane; being exceedingly dry they are very hard. As these marbles are
blasted, it is common to find them shaky in the interior of their mass, and containing
veins: the Carrara marble will not admit of so fine a polish as that of Paros, but most
modern statues are formed of it; probably the situation of the quarries affording greater
facility for the working and transport. The Paros statuary is milk-white, greyish, and
opaque; its texture varies from fine-grained to coarse; it is more difficult to work than
the fine Carrara. The true Paros, with crystalline grains, is that which the Roman
masons called Marmo greco a specchioni; that which they designated Paros is probably
Coralitique. Pliny says that several marbles exceeded the Paros in whiteness; the Luni
or Carrara had this advantage over it; but as this was the case with several others, it
would be difficult to decide which were from Carrara and which from the Greek quarries.
The works executed in Parian marble retain all the delicacy of wax with the soft lustre of
their original polish.
The Pentelican marble obtained from the mountains in the neighbourhood of Athens,
and exclusively used in the temples there, is of a yellowish white, close-grained, frequently
interspersed with greenish stripes, which causes it to decompose when exposed to the air;
it is found in beds, and so easily separated that the ancients used it as bricks and tiles;
the Romans call it Marmo cipolla; but it must not be confounded with the Cipollino, or
marble of Caryste, which is undulated from a greyish white to green, and is not a
statuary marble.
The quarries at Pentelicus were admirably situated both for working
and transporting the blocks of which the beautiful structures at Athens were constructed;
being at a considerable elevation, a regular inclined plane was made from the entrance of
the quarry to the city, and masses of marble were moved upon rollers with little labour,
care only being required to guide them. The various tinted marbles, or those having
coloured veins, are of the same crystalline character, affected by an oxide of iron; but the
blue and green tints are occasioned by minute particles of hornblende, as in the siate blue
variety called Turchino. The black marbles receive their dark colour from charcoal mixed
occasionally with sulphur and bitumen.
The Giallo Antico is a beautiful marble, of a regular yellow colour with light violet veins ;
it is extremely rare, and is supposed to have been brought from Numidia; there are
several varieties; the black marble of the ancients called after Lucullus, from his having
introduced it, was a very fine unmixed black; when exposed to a high temperature in an
open crucible it burns white; with sulphuric acid it forms a black-coloured mass, and
when dissolved in nitrous and muriatic acids it leaves an insoluble black-coloured substance;
it is composed of
Lime
Carbonic acid
Black oxide of carbon
Magnesia and oxide of manganese
Oxide of iron
Silica
Sulphur
Potash and water, &c.
1
·
53.38
41 50
•75
•12
•25
1.13
+25
2.62
100.00
The Rosso Antico is an Egyptian marble, the quarries of which are said to have been on
the borders of the Red Sea; the best specimens are of a deep red without either black or
white veins; the grain is very fine, compact, and takes a fine polish; it seems to be dotted
or strewed over with very fine grains of sand. It has been occasionally used for the
purpose of sharpening tools; pieces of it for this application have been found in the
excavations of Herculaneum and Pompeii.
The Verde Antico is a kind of brescia, whose base or cement is a mixture of talc and
limestone, the dark green fragments consisting of serpentine with spots of a lighter shade,
pure white and fine black; the colours should be very distinct to constitute a fine specimen.
It was found in Laconia and Thessalonica; several columns are extant, of great beauty and
of large dimensions.
704
Book II.
THEORY AND PRACTICE OF ENGINEERING.
The Cipollino has greenish rings or zones produced by green talc; the fracture is
granular and shining.
Alabaster Sulphate of Lime. -There are two varieties, the gypseous, which is a semi-
crystalline sulphate, and the calcareous, which is a carbonate. The word alabaster is
derived from the Greek, and signifies vases of perfumes, called at first alabastra, from
having no handles, and this kind of stone being often used for the purpose the name
became applied to it. The Oriental alabaster is a carbonate of lime, frequently variegated
with beautiful colours, and is susceptible of a high polish.
The common alabaster is composed of sulphuric acid and lime, though some varieties
effervesce with acids, and contain a portion of the carbonate; it is much softer than marble,
and usually forms the lowest bed of the gypsum quarries. At Carrara it is worked into
vases, statues, and ornamental models, &c.; the hardest variety is preferred, particularly
that which has a granular texture and a pure white colour; it does not polish so readily
as marble, but it is easier to work. When carved it is smoothed down with pumice-stone,
and afterwards polished with a mixture of chalk, soap, and milk, the hand being used to
give it the last finish.
Granite ranks as the most durable among all the stones selected for the purposes of
building, but it is difficult and expensive to work. The Egyptians employed this material
in enormous masses: we have an account of an edifice hewn out of a single mass of granite,
and moved from the city of Sais to the Isle of Elephanta, which, after deducting the void,
is stated to have been upwards of 1222 cube cubits; its weight therefore would be upwards
of 200 tons. The temple of Latona at Buto, mentioned by Herodotus, had the sides of a
single stone, and the roof also in one piece.
The obelisks at Rome were quarried in Egypt, and transported at a great cost to the
imperial city of twelve which remain eleven are erect; they are a large-grained red
granite, covered with hieroglyphics with the exception of three, and the granite of which
they are composed is of so imperishable a nature, that after exposure to the action of the
atmosphere for 3000 years, the hieroglyphics are still entire; they are in relief, but this
was effected by sinking the surface of the granite around them, the sinking forming the
outline; so that the figure, not projecting beyond the ordinary surface, is not exposed to
decomposition, but in some degree protected. Poggio mentions that in 1430, these obelisks
were all prostrate, with the exception of that of the Vatican, which was in one single block,
unbroken, and without hieroglyphics; its height is about 84 feet, and its weight may be
taken at 300 tons. It was moved by Fontana to the Piazza of St Peter's, and is the
largest mass of granite known to have been applied to purposes of art, with the exception
of that at St. Petersburg for the statue of Peter the Great. Granite was also largely
employed by the Romans for the shafts of columns; those of the Pantheon are of one
single piece with statuary marble, capitals, and base. Egypt, as well as the island of Elba,
supplied them with abundance of this material, not only for their temples, baths, and fori,
but also for fountains, the basins of which were hollowed out of large masses.
In England, granite does not seem to have been brought into use for the purposes of
construction much before the commencement of the present century. The bridges at
London over the Thames, erected by the Messrs. Rennie, may perhaps be mentioned as
instances of its first application upon a large scale: its beauty and durability render it
superior to all other material for works considered national, or intended as monuments of
art to be bequeathed to future generations. In the selection of granite, attention should
be paid to its quality, which evidently varies as it is produced from different quarries,
that obtained from the surface being usually more or less in a state of decomposition :
the quartz, mica, and felspar, composing the granite, do not seem to be held together by
any base or cement, and the size of the crystals or grains differs in the various specimens,
as do the proportions of the ingredients themselves. As the quartz, mica, and felspar,
contain several elementary substances, to determine their constituents it is necessary to
reduce a given quantity of granite to a powder, and then to fuse it in a platinum crucible
with three or four times its weight of alkali, which will decompose it by uniting with one
or more of the constituents. The mass so fused is soluble in dilute muriatic acid by
the application of different re-agents; the constituents are precipitated, after which it may
be filtered, carefully dried, and weighed.
The quartz may be considered pure silex; it is an indestructible body, sufficiently hard
to scratch glass, and when struck with steel will produce fire; it is also infusible before
the blow-pipe; it is whitish, yellowish, or greyish white. The form of its crystals are
generally six-sided prisms or pyramids; they may be cleared parallel to the faces of the
primitive crystal, which is a rhomboid; its specific gravity is 2.6 to 2.7.
Mica, as found in granite, is confusedly crystallised, and its primary form is said to be
a right rhomboidal prism; its colour varies from white, yellow, green, brown to almost
black; in some instances it is so very transparent that it is used as a substitute for glass; its
specific gravity is about 2.0 to 2.5. The analyses of mica vary, but Klaproth gives that
of two varieties, the first from Zinnwald, the latter from Siberia.
CHAP. III.
705
ON STONE.
*
Alumina
Silica
Oxide of iron
of manganese
Magnesia
Potassa
20.00
34.25
47.00
48.00
15.50
4.50
1.75
0.00
0.00
0.50
14.50
8.75
98.25
96.00
Felspar in the granite is found in rhomboidal crystals, and can be cleaved with facility
into an acute-angled parallelopipedon; its prevailing colour is white, sometimes flesh red
and green; its specific gravity is 2.54: when heated it gives out no water; before the
blow-pipe it fuses into a white enamel; it is insoluble in acids.
Silica
Alumina
Potassa
Oxide of iron
Water
64.50
19.75
11.50
1.75
•75
99.25
From an examination of these ingredients, it appears that granite contains more than
its weight of pure silica, and the remaining third is alumina, potassa, and oxide of iron: the
felspar is the first to decompose, the next is the mica, but the quartz is imperishable.
The quartz may be known by its grey and translucent colour, the felspar by its greyish
white or flesh-red tint, and the mica by its grey or black colour.
On the Resistance of Stone to the Crush. The resistance of stone to the crush may be
considered first with respect to the weight it is capable of sustaining; second, supposing
it placed between two horizontal surfaces, what weight could it carry without being crushed
or split under it? third, in supposing it held vertically by the upper part, what weight
could be suspended at the lower extremity without the stone yielding? It very rarely
occurs that weights are suspended at the extremities of the stones; on the contrary,
whether in the construction of piers or of the vaults, they are pressed between two parallel
surfaces. Although some experiments have been made on the resistance of stones held at
one of their extremities, their strength, when thus applied, is not yet ascertained; but
not so the resistance of stones bedded level; our knowledge on this subject, if not complete,
is very far advanced.
But a short time has elapsed since it was first attempted to discover the weight stones are
capable of sustaining; and if we consider the great thickness which the ancients have every-
where given to the points of support of their edifices, we shall be induced to think that
they had little idea of the resistance of the material they used. The boldness of the
architects of the middle ages, who sometimes carried immense masses on slender and lofty
columns, would on the contrary lead us to believe that they had studied the properties of
stone in this respect; but no traces remain to us of any researches, and, according to the
state of the sciences in the ages in which they worked, it is natural to believe, that, with-
out much reflection, they sought to excel each other in lightness till they arrived at limits
which they might possibly have carried still further. As an example of the smallest surface
of the points of support of Gothic architecture, we may cite two columns in the church of
Toussaints at Angiers; their diameter is only 12 inches, and their height 25 feet; they
support pointed arches, the mouldings of which are in freestone, and the weight carried
by each is 35 tons.
The discussions to which the dome of St. Genevieve gave rise were the occasion of the
first experiments made on the resistance of stones; Mons. Patte published in 1770 a
memoir, in which he raised doubts on the solidity of the piers of this dome, and asserted
that they had not sufficient surface to enable the tower which supported the cupola to
resist the thrust. Mons. Gauthey replied the following year to these assertions, showing
that they were not in agreement with the rules then known for calculating the thrusts of
vaults, and proved by applying these rules in a more exact manner, not only that the thickness
of the piers was sufficient to carry the vaults projected by Soufflot, but that the solid mass
of masonry might be suppressed, and the columns attached to them only preserved. This
assertion supposed, however, that the stone of which the columns were composed would
not crush under the weight it would have to sustain; and as this latter difficulty could not
be resolved without knowing exactly the strength of the stone, Gauthey undertook for
this object experiments which might then be regarded as entirely new; they were published
in 1774, in the Journal de Physique of the Abbé Rozier.
The construction of the piers of the church of St. Genevieve, considered with relation to
Z z
706
Book II.
THEORY AND PRACTICE OF ENGINEERING.
the strength of the stone compared to the weight which it supports, is holder than that of
the columns of the church of Toussaints at Angiers: these piers are constructed in hard
stone of Bagneux in the lower part, and in that of Mont Souris in the superior part:
the beds formed of the stone of Bagneux are considerably split, those in the stone of
Mont Souris have resisted much better. The weight supported by a surface of 9 square
inches in the pillars of the church of St. Genevieve is 16 cwt.; the weight under which a
cube of 2 inches in hard stone of Bagneux was crushed is 137 cwt.; the weights supported
by a similar cube in the stone of Mont Souris was 68 cwt. Hence the pressure supported
by the stone of Bagneux in the piers of St. Genevieve is from eight to nine times less
than that which is necessary to crush it, and the pressure supported by the stone of
Mont Souris is only four times less; it may then appear astonishing that the latter has
resisted better than the preceding.
The pressure supported by the key-stone of the vaults of the bridge at Neuilly is 127
tons per 3 feet 3 inches of length, and it appears that the weight carried is fourteen times
less than that which will crush it: but we must observe that by the settlement in these
vaults, the weight is not equally distributed on the whole height of the key; the principal
effort is near the upper edge, and although we cannot exactly judge of the total weight car-
ried by the adjacent parts of this arris, we may presume, on account of the great flatness
of the vault, that this portion is very considerable, and that the bridge of Neuilly is as
bold an edifice in this respect as it is in every other.
We may add from Mons. Rondelet an indication of the pressure exercised on a surface
of 9 square inches in the edifices regarded as the boldest : —
Piers of the dome of St.
Piers of the dome of St.
Piers of the dome of the
Peter's at Rome
Paul's at London
Invalides
Piers of the dome of St. Genevieve
Columns of St. Paul's without the walls
Piers of the tower of the church of St. Méry
Columns of the church of Toussaints d'Angers
Pounds
Avoirdupois.
-
10221
1190
922
1840
1235
-
1837
2767/1/2
In the pier of the Chapter House at Elgin the stone supports a weight of 5½ tons on each
9 square inches: it was formerly loaded with a heavy roof covered with lead; the stone,
which is a red grit, has resisted this pressure for several centuries; it is estimated that
the resistance is from 7725 lbs. avoirdupois to 23925 lbs. on 9 square inches, whilst that
of brick is 9150 lbs. ; consequently, 1520 lbs. for 9 square inches is a pressure which may
be admitted with security for the voussoirs of an arch. This pressure would be perhaps
too considerable for calcareous stones, and as a general rule, stones should not be made to
carry a weight more than of that which has crushed them in small experimental cubes;
this weight would be too great if we were not assured that the pressure would be equally
spread over the whole surface of the joints: the voussoirs of the arches near the key, and
the points of fracture, are exposed to inequalities in the partition of the powers they exert
as supports, and we shall see by-and-by how we can appreciate these effects.
The parts
of a block of stone comprehended between the beds of a quarry are not exactly homo-
geneous experiments have shown that the weight and the specific resistance are more consi-
derable in the middle of the stone, and diminish proportionably in its approach to the upper
and lower beds.
By the experiments of Gauthey it appears, that the strength of the stone augments in a
greater relation than the surface of its base; the results reported by Mons. Rondelet agres
in general with this assertion. But as no experiments were made on surfaces of any con-
siderable dimension, or differing much from each other, it does not appear possible to judge
exactly of the manner in which the resistance of the stone does augment relatively to the
surface of its base, and it is proper in the application to suppose the relation constant,
which, moreover, cannot induce any dangerous error as this hypothesis, is favourable to the
resistance.
We know a little more positively the influence which form has on the resistance of stone.
The experiments which have been made with a view to discover this influence have shown
that the different solids, the bases of which had equal area, resisted best, as their figure
approached a circle; and in general that for figures differing from each other, the resistance
was nearly in the inverse ratio of the perimeter.
When the base of solids remains the same, height influences their strength: a very thin
stone easily fractures: if it is in the form of a cube it carries a considerable weight, but
if the height is augmented, the strength, which first augmented also, finishes by diminishing;
if a vertical prism is divided in several parts longitudinally, it will resist less than if it
were in a single piece.
On the Pressure to which Stones are exposed in Vaults. — The thickness which it is necessary
to give to the vaults of bridges involves many considerations: and the pressure to which
CHAP. III.
707
ON STONE.
the voussoirs are exposed, and the degree of resistance of the stone, deserve enquiry; it is
necessary to direct our particular attention to these objects when we are projecting arches
of considerable span.
Suppose Q the horizontal thrust of the arch, a the
pressure that the two halves exert against each
other, and which is the greatest possible force it
will be necessary to apply horizontally in N to pre-
vent a portion, mn and N M, of the arch turning from
top to bottom on the edge m.

B
y
A
N
N.
Q
M
G
q p
D
X
The co-ordinates AO, NO, of the point M,
counted from the point A, are designated by ab, and
the length of the joint MN by c. The co-ordinates
Ap, pm from the point m, are named x and y, the
length mn of the joint z, and the angle which this
joint forms with the vertical, 0. We represent by
G the weight of the portion of the arch in NM, as
well as the parts of the construction which it sup-
ports, and by cc the horizontal distance from the centre of gravity of this weight to the
point A.
The value of the horizontal thrust at Q being known, we shall easily ascertain
the pressure exerted perpendicularly against any joint, mn; in effect, this pressure can be
no other than the result of the forces QG, to which is submitted the portion of the vault
mn NM, discomposed perpendicularly at mn; that is to say, it is expressed by
Fig. 594,
G Sin. 0 + Q Cosin. 0
It is not, however, right to consider the horizontal thrust Q a force applied to the arris
N, as the voussoirs at the summits of vaults necessarily lean against each other through the
whole or a portion of the height of the superficies of the joint; the pressure then being
extended over a certain space below the arris N, it acts to prevent the descent of the portion
of the vault mn M N, with an arm of a lever less than is supposed, when we consider it as
applied in N; consequently we find, as the effect of this supposition, the value of Q smaller
than it really should be.
The value of the normal pressure exercised on each joint should be exactly known, or we
cannot deduce from it the efforts supported by the stone, since we are ignorant of the man-
ner in which this pressure is spread over the surface of the joint; far from being able to
admit that the pressure is equally distributed over all that surface, we know on the contrary
that in all the arches, with the exception of a small number of joints, the pressure is prin-
cipally exercised near one of the edges: this circumstance takes place above all at the summit,
when the pressure exerts itself near the upper edge; at the joints of rupture, placed in the
haunches, when it exercises itself near the bottom edge; and at the inferior joints below
the springing, when the pressure exerts itself at the exterior edge. We suppose here, con-
formably to what has so often taken place, that the inferior parts of the vault have a ten-
dency to thrust outwards.
The manner in which the pressure is spread over the surface of the joints is besides more
uncertain, as it depends on the precautions with which the voussoirs are cut and placed,
on the disposition of the wedges, on the consistency of the mortar, and the settlement of the
vault, according to which the joints are more or less open.
ZZ2
708
THEORY AND PRACTICE OF ENGINEERING. BOOK II,
CHAP. IV.
BRICKS AND TILES.
WHERE stone cannot be procured, bricks form an admirable substitute, being easily made
from clay or argillaceous earth, which is found in most situations where stone is wanting:
some advantages are derived from the use of this material over stone, which is not ob-
tained from the quarry in a state or shape fitted for use, whilst the brick is of a con-
venient size, and easily carried to the place where it is employed. An absorbent brick
readily adheres to the mortar in which it is bedded, and in a short time becomes a solid
mass; whilst it often happens that hard stones are less adhesive, and their surfaces do not
combine with the mortar in which they are laid.
Unburnt bricks are of great antiquity: the first were probably masses of clay, dried in the
air by exposure to the sun; afterwards these masses were moulded into regular and uniform
shapes, improved also in strength by mixing chopped straw with them: such bricks were
not calculated to resist the humidity of our climate, although some found among the ruins
of Babylon are as durable as if they had been burnt, which is entirely owing to the dryness
of the air.
The remains of what is considered a part of the famous tower of Babel are perhaps
among the most ancient specimens of unburnt brick: these bricks are 12 inches square,
and 4 inches in thickness, are bedded in bitumen mixed with sand, the joints of which are
about 8 inches in thickness; and although they have stood the exposure to the dryness and
heat of the climate, when soaked in water have quickly decomposed, which is sufficient proof
that straw, reed, and such vegetable matter mixed with the clay, do not constitute a sound
brick at Bagdad, where the bitumen is obtained from a lake in the neighbourhood, bricks
are still used in most of the buildings.
The immense edifices of unburnt brick constructed by the Egyptians remain almost
entire one distant about 10 leagues from Cairo, and measured by Dr. Pococke, in 1738,
was about 150 feet in height, with its base rectangular, one side being 210 feet and the other
157 feet. This brick pyramid was supposed to be that mentioned by Herodotus as built
by Asychius, who is said to have inscribed on it the following: "Do not disparage my
worth, by comparing me with pyramids composed of stone: I am as much superior to them
as Jove is to the rest of the deities; I am formed of bricks, made of mud that adhered
to the ends of poles, and drawn up from the bottom of the lake."
These bricks are composed of a black, argillaceous earth, containing small pebbles, shells
and chopped straw, and were of two dimensions, the largest 15 inches long, 7 inches broad,
and about 4 inches thick.
The Greeks as well as the Romans used, as we have seen, unburnt bricks: Vitruvius
mentions the wall of Athens, on the sides towards Hymettus and Pentelicus; the walls of the
temples of Jupiter and Hercules, the columns and entablature of which were of stone; the
palace of King Attalus at Tralles, that of Croesus at Sardis, and of Mausolus at Halicar
nassus: that author also describes the manner in which unburnt bricks were made, and
observes that gravelly, pebbly, or sandy clay is unfit for the purpose, and that the most
proper is a red earth, of a chalky nature, or containing sand; and that the proper season for
making them is the spring and autumn, as they dry more equally. When plaster is laid
on bricks which are not perfectly dry, they shrink, and the plaster no longer adheres to
them the inhabitants of Utica would allow no bricks to be used which were not at least
five years old, and had been approved by a magistrate.
The three sorts of bricks in use were the doron, the tetradoron, and the pentadoron.
The word doron signifies palm, designating a gift that might be borne on the palm of
the hand, and it is supposed that the Roman palm was equal to it. The tetradoron is a
cube of four palms, and the pentadoron five: there were half bricks of each sort: the least
thickness the Greeks are supposed to have given to their walls was that of the doron, or one
brick, to their ordinary walls a brick and a half, and to their thickest two bricks.
building a wall there are alternate courses of whole bricks and half bricks, so that the joints
are regularly broken.
In
In neither Athens nor Rome are found any remains of unburnt bricks, and the form of
those mentioned by Vitruvius is not quite certain, though it is generally believed that they
were cubical; it does not seem very practicable to build a wall and keep the courses
regular where the three varieties are to be used; they seem intended for as many different
kinds of work. The unburnt bricks still used by the nations of the east are made by treading
the clay with the feet, and mixing chopped straw, after it has been duly prepared; it is then
CHAP. IV.
709
BRICKS AND TILES.
put into small wooden moulds, and, in order to give them firmness, they are plunged into
a vessel of water, in which is a quantity of chopped straw, and after two or three hours' im-
mersion, they are laid out in the shade, where they remain until they become dry. When
walls are constructed with them they are coated with a layer of clay and chopped straw,
which protects them from the rain; sometimes a coat of lime and plaster, beaten and mixed
together is substituted, where a better effect is desired.
Brick-making. The earth usually selected by brick-makers is of a tenacious character,
and partakes of the quality of loam; a stiff clay makes a brick that falls to pieces in
burning, whilst a milder earth is made by adding a quantity of sand to that which is too
strong. The clay dug in the autumn is wheeled in barrows to a piece of ground previously
levelled to receive it, where it has a quantity of breeze added, which renders it partly com-
bustible, when submitted to the heat, which converts the clay into a brick. It is necessary
that the brick should become red-hot throughout, and which would be difficult without
the breeze, which also gives colour, hardness, and durability. After this mixture of clay,
sand, and breeze is rendered ready for use by being worked together with the spade, and
continually softened by water, it is exposed to the action of the frost, and usually small
heaps are thrown up, so that the weather may penetrate them, and form one uniform, soft,
and yielding mass: it is then tempered by adding water, or spreading it to dry; then the
whole mass is pressed down, and preserved by a covering to prevent the sun or air further
affecting it.
The clay is now generally wheeled at the commencement of the spring from the place
where it has been exposed to the action of the frost to the pug-mill, where chalk, sand, or
other materials are incorporated with it, the mill being supplied with a quantity of water,
which reduces the whole into a thin paste, running through a sieve or wire strainer into a
reservoir formed for the purpose; when this is full the whole is suffered to subside, and
the water is gradually drawn off: after it has acquired sufficient consistence, this finely
divided paste is moved by barrows, and mixed with sifted breeze; a few days' exposure
to the air makes it sufficiently dry for the moulder's use.
The pug mill is a conical tub, secured by iron hoops, about 6 feet in diameter at the
top, and as much in height: the bottom is made of day, or some other material imper-
vious to water, and constructed so as to be perfectly firm and steady. The clay is put into
it, and then, by means of revolving rakes, with iron teeth, like those of the harrow, and
made in such a form that in their revolution, they lift up the clay, which falls down again
towards the bottom; the masses so separated, and supplied with abundance of water,
are soon reduced into a paste. The whole is prevented from adhering to the bottom by a
constantly revolving scraper, which allows the pugged clay to find its way to the orifice at
the bottom, where it is discharged.
A long beam of timber, keyed on the upright shaft, has a yoke, to which a horse is at-
tached, that walks round in a track not exceeding 16 feet in diameter; if larger the proper
motion would not be maintained. A pump worked by hand, or by the machinery, throws
the required quantity of water into the mill; the clay is put in from barrows, wheeled
a platform made for the purpose.
up
The Moulder's Bench is usually attended by a lad or assistant, who cuts the clay into por-
tions sufficient to fill the mould; these are taken up by the moulder, and thrust into it,
which is previously passed through a mass of sand, to prevent the clay from adhering to it :
after the clay has been well forced down, a flat wooden strike is made use of to remove all
that is superfluous; the brick is then turned out upon a board, and taken away by a boy to
the track in a barrow, covered with thin laths or strips of wood: one moulder's bench
will supply 5000 bricks or more per day.
The bricks are then laid upon each other in the hacks, arranged on their edge, and placed
diagonally, so that the sun and air pass freely around them; they remain here some time,
after which their position is changed, and in a week or 10 days, if the weather be favourable,
they are fit to be burnt.
The clamp is the general system adopted for burning them, which is formed by making
a foundation of place bricks, and then arranging those to be burnt in layers, with a stratum
of breeze or cinders, 2 or 3 inches in thickness between them.
A fireplace is generally at the west-end, about 3 feet in height, from which various
flues branch out that run in a straight direction throughout the clamp; these flues, filled
with coals or breeze, are placed at distances of 5 or 6 feet apart when the weather is
favourable a month is sufficient to burn off a considerable quantity.
Kilns containing 20,000 are in the country often preferred for burning bricks; these are
made 13 feet in length, 11 feet in width, and 12 feet in height; the outer walls incline
inwards as they rise, and are a brick and a half in thickness throughout.
The furnace is formed of three arches, which have apertures at the top to allow the
heat to pass through to the charge, which is placed on a floor of lattice; a moderate and
gentle heat is applied for the first three or four days, to drive off the water; the mouth
of the furnace is then blocked up by a shinlog composed of brick, and room only left to
zz 3
710
Book II.
THEORY AND PRACTICE OF ENGINEERING.
introduce the necessary quantity of wood for the purpose of maintaining the fire; when the
flame has made its entire way through the whole of the layers, and appears at the top, the
fuel is more sparingly applied, and in a short time the fire is suffered to go out, and the
kiln gradually cools. Forty-eight hours is sufficient to burn off a kiln of bricks, if care is
paid to the raising and slacking the heat, which requires some skill on the part of the
burner.
Murls, or malms, stocks, and place-bricks are so named, according to their fineness or
quality. The first is of bright uniform yellow colour, partly obtained by washing chalk
with a fine clay; from these are selected the cutters for arches, which, from their fine tex-
ture, are calculated for rubbing.
Seconds is another term for a second quality of malm, which are used for gauged work,
and the facings of walls.
Stocks are either red or grey, the first being the kiln-burnt, the other that usually from
the clamp.
Place-bricks are of an inferior quality, and, from the fire not having thoroughly burnt
them, are generally fit only for purposes of building where soundness is not a requisite.
Floating bricks, in imitation of those made by the ancients, were formed by M. Fabbroni
out of a material which consisted of 55 parts of siliceous earth, 15 of magnesia, 14 of water,
12 of alumina, 3 of lime, and 1 of iron: this kind of brick does not become altered by
fire, being infusible, and although it loses part of its weight, it is not in any way
diminished in size: as these bricks are found to float on water, they have been very much
used where lightness of construction was desirable.
Fire-bricks, used for furnaces and the lining of stoves where great heat is generated, are
moulded in various parts of England. At Hedgerley, near Windsor, where the loam con-
tains a considerable amount of sand, they were made in large quantities; Welsh lumps
and Stourbridge bricks are a similar quality, and will stand the action of great heat.
Retorts for a variety of purposes are made with a mixture of clay and iron, particularly
for the manufacture of gas; the iron retort receiving a casing of prepared clay, which
permits the fire to act first on the clay, and thus prevents the rapid destruction of the
metal.
Retorts or bricks made of one part pure clay and three parts of coarse and pure sand,
slowly dried and annealed, will resist a very high temperature, and are not readily fused;
but if in contact with any metals in a fusible state, which are suffered to oxidise, they will
then act upon the earthy matter, and cause it rapidly to fuse.
A long continued white heat will soften the compound made of any of the siliceous and
aluminous earths; therefore clay and sand are not so well adapted to bear a great heat as an
entire clay; coarsely powdered and burnt clay being substituted for sand, the vessels which
contain glass in the furnace, and which are subjected to intense heats, are thus made, and
resist for a length of time the action of the saline fluxes they contain.
Windsor loam, or a mixture of clay and sand, made by beating a thin paste, is employed
as a lute to unite the joints of fire-bricks, or to set them in instead of common mortar; and
if it is required that vitrefaction should take place with the clay so used, borax or red lead,
mixed in small portions, will produce the effect; such a compound will destroy the porosity
of earthenware, when exposed to high temperatures.
The strength of brickwork depends entirely upon the manner in which the bricks are
laid; at present the practice in England is confined to what is called Old English and
Flemish Bond. The first, which is the preferable mode, bas a course of stretchers, and
then a course of headers; the latter is alternate header and stretcher.
In the Old English the stretching courses bind the wall together in the longitudinal,
and the heading courses in the transverse direction; so that if any fracture occurs, it does
not break at the joints, but as a solid mass.
The Flemish bond, introduced into England about the reign of William and Mary, is,
however, frequently preferred, because it presents a more regular face; wherever strength
is an object it should be rejected, and the old English practice followed. Each course
being alternately headers and stretchers, should have every brick in the same course laid in
the same direction, and in no instance is a brick to be placed its whole length along the
side of another, but to be so situated that the end of one may extend to the middle of
those it adjoins, except in the outside of the stretching course, where three-quarter bricks
must be used, to prevent a continued upright joint in the face of the work: and where a
wall crosses another at right angles, all the bricks of the same level course should lie in
the same parallel direction, in order that the angles may be completely bonded.
In Flemish bond, to prevent the wall splitting, it is necessary to make use of iron hoops,
in the horizontal joints between the two courses, and some bricklayers, to attain the same
end, lay diagonal courses at certain heights from each other, but the latter system is far from
efficacious; others lay all heading courses within the outside Flemish bond, making the
face-work alternately of 9 and 4 inches in thickness; this prevents splitting, but destroys
the stretching bond.
CHAP. IV.
711
BRICKS AND TILES.
Tiles are formed of a reddish or grey-coloured clay, which fuses at a red heat: these clays
are probably mixtures rather than compounds of silica, alumina, and water.
The common kind of tiles is made of the blue clay, obtained near London at a greater
depth than the ordinary brick earth; this is excavated in the autumn, and exposed to the air
during the winter, to properly temper it: after the tiles are moulded to their shape, they
are burnt in kilns, surrounded by a conical structure with an opening at top.
A kiln 20 feet square, with 3 furnaces, is calculated to burn about 34,000 tiles at one
time; the space which contains them above the arches of the fireplace being 14 feet 6
inches square, and about 8 feet in height, this square chamber being open at the upper sur-
face around it is built the frustum of a cone, with a clear diameter of 32 feet at bottom
and 3 feet at top, the walls of which are of brick, 18 inches in thickness at bottom, and
diminishing by three regular internal sets-off to 9 inches at the top: an entrance is usually
left at opposite sides for the charging and unloading the kiln, the bottom of which is
generally sunk about 10 feet below the ordinary surface of the ground, and a vaulted pas-
sage leads to the furnace, where the fuel is applied: such a kiln is adapted for the burning
of bricks as well as tiles, and is found to answer for both admirably well.
The Earth used for making tiles should be pure and tough, and free from any foreign
matter: after constant turning over and tempering, it is brought to a proper consistence
and moulded into the desired shape.
Plain Tiles are usually made § of an inch in thickness, 10 inches long, and 61 wide,
weighing from 2 to 21 pounds each: these when laid lap over each other, and the part
uncovered is called the gauge, which is generally 6½ inches: when so laid, 740 tiles will
suffice to cover 100 superficial feet; they are hung upon the lath by two oak pins in-
serted in holes perforated by the moulders before burning.
Plain tiles are now made so that they may be placed side by side, in courses perfectly
flat, without overlapping: this is a far more economical method, decreasing the weight
nearly half: a groove is run in the edges which receives a corresponding fillet, both at the
sides and at the top and bottom, communicating with each other, and should any water
enter the joints it is carried down to the eaves in a continued line.
Pan Tiles, first used in Flanders, have a wavy or convex and concave surface one way,
and are made 14 inches in length and 10 inches in breadth; their gauge is usually 10
inches, and 170 are sufficient to cover 100 superficial feet; these tiles weigh from 5 to 51
lbs. each.
Ridge and Hip Tiles are formed cylindrically, 13 inches in length, and girth 16, weighing
on an average 5 pounds.
Gutter Tiles are nearly the same size and thickness.
Mathematical Tiles, for covering the upright surface of cottages, instead of lathing and
plastering the outsides, are much in use in the counties of Kent and Sussex: these tiles are
intended to resemble courses of brick, and are made to overlap each other; the face of
each consists of two planes, the size of a common brick, and when placed in their proper
position, they form a double thickness of tile; they are nailed on, and a fine mortar is in-
troduced where they rest on each other, which is pointed in the same manner as ordinary
brickwork.
Weather Tiles differ from these: they lap over each other, and are made of various
patterns, but having their size and thickness that of the common plain tile; they resemble
the plates of chain mail, when in their position, and their exposed edges often receive a
variety of outline, and form great diversity of pattern; when put on with proper nails, they
are found very durable and keep out the weather. Various machines have been invented for
the manufacture of tiles, one of which, patented by Mr. Hunt, has two wooden cylinders.
round which revolve bands of cloth, which press the clay into one regular thickness through.
out; this is conducted by a continued web over a covered wheel, curved on the rim, which
gives the cylindrical form to the tile; they then pass through iron moulds, and are cut off
to the length required.
The Flat Tiles are made in somewhat similar manner: by this machine drain tiles, and
the sole pieces on which they rest, are moulded with the greatest correctness.
The Brick-making Machine, patented by the same inventor, has also two cylinders, each
covered with an endless web, which are so placed that they form a sort of hopper on their two
upper cylindrical surfaces, the ends being enclosed by two iron plates: well tempered
clay from the pug mill is thrown into this hopper, and at the lower part it acquires the form
and dimensions of a brick: beneath is worked an endless chain, by the movement of the
cylinders, and at various marked intervals are laid the palette boards under the hopper;
the clay is brought down by a slight pressure, and enters a frame, which has a wire stretched
across it, which projects through the mass, and cuts off the requisite thickness; this is
immediately removed by the forward motion of the endless chain; and this operation
is renewed as often as a new palette board is advanced under the hopper: such a machine
produces about 1200 bricks per hour, and is worked by two men and three boys.
Bricks usually made with machinery are found to dry with more difficulty, in con-
z z 4
712
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
sequence of the great pressure that has been made use of; the clay, being more compact,
dries on the outside long before the centre parts with its humidity, and in consequence the
surface is apt to peel off. This machine does not exercise more than a slight pressure, and
the bricks made with it are uniform in size and quality.
The Marble Tiles, which covered the Greek and Roman temples, have been imitated in
clay, and when properly made have an elegant effect: flat tiles with raised sides extend

Fig. 595.
ROMAN TILES.
from rafter to rafter, the upper ends having a rib that enters a groove formed on the under-
side of the tile placed above it; after these are laid, the joints in the direction of the
rafters are covered with other tiles, formed like the half of a frustum of a cone, and made
to lap over each other; the ends over the eaves or cornice are closed by an ornament, as an
eagle, honeysuckle, or flower.
In other examples the long joints are covered by rib tiles, with a fine arris or edge at the
top, which is calculated to produce considerable strength, and keep out the weather equally
well.

Fig. 596,
GREEK TILES.
The architects in Paris have made use of such to cover both public and private buildings,
and some of the manufacturers produce them in all their varied forms by machines of a
very simple kind: those which covered the temple of Jupiter Stator at Rome were of
marble, and of considerable dimension, and since their discovery they have served as
models for imitation.
The Sunk Tile, with its lateral raised fillets, being laid side by side, had the upper edge
overlapped by the succeeding course; the longitudinal joints, or those in the direction
of the rafters, were covered by a rib, cut on the underside to saddle the fillets of the two
tiles with the joint between them. The lower ends were covered by a perpendicular orna-
mental tile or antifissa, the sculpture of which constantly varied: on some of those at the
Temple of Vesta at Rome, which the writer discovered, is the representation of an eagle,
and on others the honeysuckle.
In Flanders, where moulding in clay was at a very early period carried to great perfec-
tion, are many varieties of pattern; and they are contrived not only to produce a good
effect as they lie, but to keep out the weather: the wavy, which is the most common,
are laid on or taken off with very little trouble; they are made with a projecting knob
:
CHAP. IV.
713
BRICKS AND TILES.
on the underside, for the purpose of hanging on the lath; the tail of the next overlapping,
and by its weight keeping the other in its place.

Fig. 597.
SEMICIRCULAR FORMED TILES.
The semicircular formed Tile lies like the plates of chain mail one over the other, and
forms an admirable covering both for effect and utility. In these the fillet which bounds

Z
Fig. 598.
WAVY TILES .
the concave sides is elevated above the tile, and that dotted is raised beneath it, so that when
placed it covers the others and keeps all the joints tight, as well as serves to hang them all
together; this is a very ingenious and excellent mode of forming the tile.
Most buildings might be improved by making their covering more ornamental, and when
a graceful form is given to the tile, it contributes greatly to the effect. In the example
three are made use of, and that which lies undermost forms the gutter, which conveys
away the water that falls upon the roof; the wavy character of the arrangement is well
adapted for rustic building, and worthy of imitation.
These plates of clay baked in a kiln have been long used for covering the roofs of houses,
and the moderns have generally adopted only one kind, whilst the ancients employed two :
that placed in regular rows was called imbrex, and that which covered the joints of two so
714
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
laid side by side, the tegula; the ends at the eaves being finished with those ornaments
we have termed the antefissæ. Pliny mentions them under the term persona, probably from
their resemblance to masks, and says they were invented by a Sicyonian potter named
Dibutades, who was established at Corinth, where they were called protypes, from being
stamped in front only: other tiles fixed upon the ridge, executed by the same artist, were
termed ectypes.
Many very ornamental tiles were made use of, some of which were covered with plates of
metal, either silver or bronze.


ביר
Fig. 599.
CONVEX TILES WITH COVERED JOINTS.
A more simple application consists of forming the tiles in such a manner that the cover-
ing to the joints can be dispensed with; this is accomplished by making the lower tile

Fig. 600.
CONVEX TILES LAID WITHOUT COVERED JOINTS.
with grooves at the edges, in such a manner that a portion of the upper may enter and keep
out the weather.
Tiles are sometimes laid diagonally, and with an undulating surface: the joints are
then sufficiently covered, and do not require any further protection.
CHAP. IV.
715
BRICKS AND TILES.
Throughout France there are many varieties of pattern, and in laying their plain tiles, par-
ticularly in Paris, they vary the arrangements; in some instances, a square plain tile is laid


Fig 601.
DIAGONALLY LAID TILES.
diagonally, in others they have undulatory or polygonal surfaces, forming channels to con-
duct off the water, and producing a good effect.
The Tiles, which cover some of the abattoirs, are made in a similar manner to those
manufactured in Burgundy; a concave tile is laid, with its position alternately reversed,

Fig. 602.
FLAT TILES LAID SIDE BY SIDE.
and those which present a convex back, and form the outer surface of the roof, abut against
a cylindrical tile which covers the joint.
The Flat Tiles, one edge of which has a fillet, and the other a semicircular turn, seem
to combine the use of the two tiles in the former example and to produce a much better
716
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
effect; they are more in accordance with the ancients; by forming them in such a manner that
the ribs become portions of cones, they will fit each other and make a very strong covering.


Fig. 603.
TILES IN IMITATION OF THE ANTIQUE.
Numerous other specimens might be given of the ornamental tile: among them the fol-
lowing show the great variety of pattern that may be produced; and it is to be regretted

Fig. 604.
TILES ALTERNATELY CONVEX AND CONCAVE.
that the covering of our buildings should continue to exhibit the monotonous plain and
pantile, when so many picturesque designs might be substituted for them.
To tiles as a covering for a roof there are some objections, and generally slate is now pre-
ferred; but their manufacture is capable of great improvement, and when their surfaces
are glazed, so as to render them impervious to wet, they are upon an equality with slate.
Tiles, in the ordinary state, when exposed to moisture or to rain, will imbibe about a
seventh of its weight of water, while slate, if of a good quality, will not take up more than
a two-hundredth part: if tiles remain saturated with water for any length of time, they
certainly injure the timber on which they are laid, and will probably occasion the rooms
constructed in the roof to be affected by damp.
Pavements are frequently formed of glazed tiles; those in imitation of the ancient
tesseræ have a good effect: in the middle ages our churches were paved with a square
tile, each of which had a different pattern, or formed figures and devices resembling those
of a carpet.
CHAP. V.
MORTAR AND CEMENTS.
717
CHAP. V.
MORTAR AND CEMENTS.
CALCAREOUS Mortars and cements are said to acquire their hardness by the slow absorption
of carbonic acid from the atmosphere, though few mortars that have been submitted to the
process of analysis have exhibited the quantity of acid necessary for the full saturation of
the lime, every 28 parts by weight requiring 22 of carbonic acid. This idea was probably
suggested by noticing that the outer surface of a lump of mortar first exhibited the greatest
hardness, and then the portion nearest to it, and at last the centre. According to one
theory a chemical affinity exists among the ingredients that compose the mortar, so that the
lime acting upon the alumina and sand or silica enters into combination with them ; while
another supposes that the particles are only affected by mechanical agency, and that the
lime adds to their cohesive properties. The minute state of the lime, and its extreme
division, allows it to spread over the entire surface of the particles of sand, bringing them
more closely into contact, or it fills up their interstitial spaces, forming a matrix to hold
them together.
Lime is superior in its adhesive power to that of its cohesive, and therefore attaches
itself to hard bodies in preference to its own softer particles. The hydrates of lime and
alumina, when powdered and mixed with water, possess great adhesive powers, which is not
the case with anhydrous substances, as carbon and silica: those bodies which harden
quickest have the strongest affinity for water, though some substances which will not harden
in this liquid will in others. Lime-paste slowly dried acquires considerable cohesive pro-
perties rich limes, when mixed with sand or grains of silex to form ordinary mortar,
being very soluble in water, remain in a soft state when excluded from the air for a length
of time; but when a small portion of puzzolana is added in a finely comminuted state,
the lime loses its solubility, and in a short time hardens under water, probably occasioned
by a chemical combination taking place between the lime and puzzolana.
:
Hydraulic Mortars are composed of silica and caustic lime in general, and their peculiar
property may be attributed to their forming a hydrated silicate of lime; when clay and
magnesia are added, double silicates of greater consistency and strength are produced: the
silica should always be in such a state that it is easily converted into a gelatinous paste by
the addition of an acid, and should be prepared by calcining it with an alkaline earth at
a bright red heat, after which it will dissolve in acids. Sand of the quartzose kind, when
mixed with lime in the ordinary way, will not form hydraulic mortar; but if after, when
reduced to fine grains, it be burnt with the lime, it becomes suitable for the purpose of
building in water: those limestones which contain 10 per cent. of clay, when strongly
burnt, form good hydraulic mortars; but if this proportion be increased to double or more,
it requires to be well ground before it will set. Marls which contain 30 per cent. of clay
make an excellent mortar without adding any other ingredient; when the proportion of
clay is greater, it must not be subjected to any great or prolonged heat; if strongly cal-
cined it becomes vitrefied, and requires pounding, or grinding very fine, as well as an
addition of some strong lime to make an hydraulic mortar. When 1 part of silica and
4 of caustic potassa are fused together and slowly cooled, a part of the compound may be
poured out of the crucible before the whole has solidified, and pearly crystals are formed in
the residuary portion, composed of 1 atom of silica and 1 of potassa: when 1 part of silica
and 2 of carbonate of potassa are fused together, the carbonic acid is expelled, and a
bisilicate of potassa is formed; these silicates are soluble in water; this solution may be
also obtained by digesting gelatinous hydrate of silica, or very finely divided silica, in
solution of potassa.
In Holland a substance called terras or trass has been from time immemorial used as a
water cement; it consists of a substance called Wakke, a species of basalt, and has been
employed in forming mounds or barriers against the irruption of the sea: according to
Morveau compact basalt, after burning, made a similar cement to the Dutch terras; and a
material very nearly resembling it is found in great abundance near the port of Leith, and
in the vicinity of Edinburgh.
The Mortar made use of by the Egyptians was formed of sand and lime, nearly in the pro-
portions we now adopt: 100 grains taken from the pyramid of Cheops were carefully
analysed; after being reduced to a fine powder, dried thoroughly, and immersed in 6 ounces
of pure water for some time, they were heated to remove the soluble salts: when filtered
after this operation the mortar was found to have lost 18 grains, which consisted of 15·3
sulphate of lime, and 3.2 of soda. The residue of 81½ grains had 4 cubic inches of dilute
718
THEORY AND PRACTICE OF ENGINEERING. BOOK II.
·
muriatic acid poured upon them, and there was then a loss of 4-7 grains of carbonic
acid, the total weight of which in the mortar was 5 64 grains; and on completing the
process the constituents were found to be
Sulphate of lime and soda
Carbonic acid
Lime
Alumina
Alumina and crystals of selenite
Water and loss
Grains.
-
18.5
5.64
10.7
0.3
-
54.7
10.16
100.00
This mortar does not appear to contain any siliceous matter, and is a compound of rich
lime and coarsely powdered gypsum, as a substitute for sand, in the proportion by weight
of 1 of lime to 5 of gypsum: it possessed considerable tenacity, and its specific gravity
was about 1.98.
The Greeks used a fine mortar, and well understood the composition of stuccoes; some
that remain at the present day cannot be surpassed for whiteness, hardness, or polish:
their floors were made of a cement resembling the finest marble, which dried so rapidly
after washing, that there was no danger of any injurious effects, even when walked on
without the sandal.
The Romans, according to Vitruvius, paid great attention to the selection of their limes,
and considered that of the finest quality which was made from the hardest and purest
marble for hydraulic purposes they generally made use of puzzolana, being perfectly
aware that common lime and sand would not set under water: all Roman mortars ex-
posed to the action of the atmosphere seem to be alike; they are composed of pounded tile
or brick, coarse sand or gravel, and lime, the latter often occurring in small lumps, as if not
properly slaked: their artificial hydraulic mortars were composed of pure lime and large
proportions of pounded brick, which, when broken, resemble a brescia of which lime is the
matrix: with this they lined their reservoirs, first preparing it by beating, and floated it
on the walls by means of sandstones, which they rubbed over the surface; upon this was
laid a fine coat of plaster, and then one of red lead and oil; the first rough coating dried
the plaster rapidly, by absorbing its superabundant water. These cements or mortars very
frequently exhibit on their surface a coating of carbonate of lime, particularly in the con-
duits of the aqueducts, some of which are extremely hard, and of considerable thickness. We
have many remains of limestone quarries worked by the Romans; one, called Calcariæ in the
Roman Itineraries, is situated at Tadcaster in Yorkshire.
Lime is the essential ingredient of all calcareous cements, and is never found in a natural
state quite pure; it is usually that of an earthy salt, which crystallised is called calcareous
spar; when massive, limestone is found combined with carbonic acid in the proportions of
46 to 54 of lime. This gas, which is sparingly soluble in water, is a permanently elastic
fluid under the ordinary pressure and temperature of the atmosphere. The whitest lime--
stones, as the white granular marble, for instance, are nearly pure, only containing a small
quantity of siliceous earth; this, when subjected to calcination, falls into a coarse powder,
and, as it cannot be burnt in an ordinary kiln, is not in use for the purpose of making
mortar.
Chalk, in consequence of its requiring less fuel to convert it into lime, is preferred; but
as it is subject to be only superficially burnt, and to contain, in consequence, a quantity of
core, it is not so eligible for the builder.
Oolite Limestone is the next in quality, and superior to this is the grey limestone, which
requires longer time, as well as more fuel to convert it. The swinestones and bituminous
limestones, which are of a dark brown colour, become frequently black when heated red-
hot, the carbonic acid is converted into carbonic oxide, which, having no attraction for lime,
flies off, leaving the lime perfectly white, very caustic, and more porous than that produced
from the compact limestones; this kind, when exposed to air, or the action of water,
crumbles into a fine powder, and is useful for mortar.
The Magnesian Limestone is found in the new red sandstone formation in thick beds,
either of a reddish or yellowish tinge; they are compounds of carbonates of lime and mag-
nesia, in the proportions probably of three-fifths of carbonate of lime and two-fifths of the
carbonate of magnesia: after burning it retains its causticity for a long time.
Grey Chalk or Chalk Marl, which contains a large proportion of iron and clay, formed
the bottom bed of the great chalk deposit, and contains no flints; that which is used for
hydraulic mortar has from 10 to 25 per cent. of clay, and when burnt has a pale yellow
colour.
The blue limestone, or the dark dove colour, when burnt into lime, becomes buff; it is
found both in the transition and mountain limestone deposits, and constitutes nearly the
whole of the lias formation: its position is between the lower oolite and the new red
sandstone, and its entire thickness is 250 feet. Watchet, Aberthaw, and Barrow in
CHAP. V
719
MORTAR AND CEMENTS.
Leicestershire, are all on the same bed, and Smeaton found, upon a careful analysis, that
the proportions of iron and clay in each were the same, or about 11 or 12 per cent.
For the Eddystone lighthouse he used equal measures of Aberthaw lime, in the state of
hydrate, and of fine powdered puzzolana, proportions which when reduced to weight, and
allowing 24 per cent. for water, agree with those stated by Vitruvius to be in use among
the Romans. The Dorking lime is used for land and water cements, as is the Merstham,
both of which are obtained from the chalk marl, as is the Halling on the Medway.
In the cements made from lias the oxide of iron they contain appears to combine with
the lime during the process of burning, and sets without difficulty when mixed with a large
proportion of sand.
The Tournay mortar is a lias cement, and thus formed: after the lumps of lias are
withdrawn from the kiln, what remains with the ashes of the slaty coal, in the propor-
tion of three of ashes and one of lime, is sprinkled with water, just sufficient to slack the
lime. It is then beaten by an iron pestle for half an hour; this is repeated three or four
times, until it attains the consistence of mortar. It is then placed under cover, and in a few
days beaten again, either with stone or brick; it acquires in a short time great hardness.
The coal ash in this instance is burnt clay in a state of fine division, and therefore ready to
combine rapidly with the argillo-ferruginous lime, which, being in a state of hydrate, and
allowed to be some time in contact with the ash, a combination takes place, which is
further increased by beating, the lime parting with its water, and combining with the
ash.
As it is of the utmost importance to understand the nature of the hydraulic limestones,
M. Berthier recommends the following method of analysis: after the specimen has been
reduced to a fine powder, it is passed through a hair-sieve, and a given quantity is put into
a vessel; muriatic or nitric acid, diluted with a small quantity of water, is poured upon it,
taking care to stir the whole with a glass or wooden rod. When the effervescence has
begun, the solution is to be evaporated by a gentle heat, until the whole becomes a thick
paste; this is put again into a small quantity of water, and filtered; all the clay contained
in the paste will remain in the filter, and the substance which has passed through must be
dried in the sun or by the fire, and afterwards weighed: or the specimen to be examined
may be calcined to redness in an earthenware or metal crucible, and very clear water being
poured into the solution, a precipitate will be formed, which is magnesia; this, washed in
pure water, and dried speedily, is to be then weighed. The clay may be thus estimated, as
well as any fine sand that it may contain.
The only apparent difference between lime obtained from limestones and chalk is that of
the greater retention or expulsion of the carbonic acid gas, and both Smeaton and Higgins
have proved that when chalk or stone lime is equally fresh from the kiln, their qualities as
cements are nearly equal;. but as chalk lime absorbs carbonic acid more rapidly from its
spongy texture, it loses much of its cementing quality, and does not make so good mortar
as the lime from stone.
Limestones are sometimes found wholly composed of lime and carbonic acid: the best
hydraulic limestones contain silica, alumina, magnesia, iron, and manganese; the silica
being the most abundant.
The rich or fat Limes are those which in slaking double their volume, and after having
been immersed for a length of time retain their consistency, and in pure water will dis-
solve to the last particle; they are derived from the pure limestones, which contain from
0.1 to 0·6 of silica, alumina, magnesia, and iron; they absorb in slacking nearly 300 per
cent. of their weight of water.
The poor Limes do not much augment their volume, and only partly dissolve, leaving a
residue, which has little or no consistency; they are produced from the limestone in which
silica is present in the state of sand, magnesia, the oxides of iron and manganese, and absorb
about 200 per cent. of water.
The moderately hydraulic Limes set in 15 or 20 days after they are immersed, and then
continue to become harder in quality; at the end of a twelvemonth they acquire the con-
sistence of soap, in pure water dissolve with difficulty, and expand in slaking.
From Limestone, united with Clay, Magnesia, Iron, and Manganese, in the proportion of
not more than 15 or 18 parts out of 100 of the whole, are obtained the hydraulic limes; these
set after six or seven days' immersion, and continue to acquire hardness; such lime absorbs,
on slacking, 250 per cent. of its weight in water. Some of the best hydraulic limes are
obtained from limestones which have, in addition, a greater amount of silica, or where it
occupies nearly half the whole quantity of the other substances; these kinds set on the
second or third day after immersion, and in a month become hard and perfectly insoluble.
Lime is said to set when it will bear without depression a rod the twentieth part of an inch
in diameter, loaded with a weight of 10 or 11 ounces avoirdupois, or when it will resist
any indentation made by the finger moderately pressed.
By these observations it would seem that there are no definite proportions between
the quantities of silica and alumina or of magnesia which unites with the calcareous
matter; but it is well ascertained that no good hydraulic mortar can be made without
720
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
:
silica, and that the best limestone for the purpose is that which contains a certain quantity,
with alumina in the proportions usually found in clay. Limestones are made into lime
by driving off the carbonic acid and water by burning them in open kilns.
When limestone is in a pure state it will bear a white heat, but that which contains the
properties to render it an useful hydraulic lime easily fuses; its calcination, therefore,
requires more care; the heat should never exceed redness, and the burning should not pro-
ceed too rapidly; if exposed to too great a heat, they become covered with an enamel, and
the carbonic acid is not driven off, and consequently they will not slack. The forms of kilns
used for this purpose vary in different districts, as they are cylindrical, conical, egg-shaped,
or prismatic.
Flare Kilns, intended for burning scares or faggots, have the limestone, with which they
are fed, resting on one or two vaults, built up dry with the materials of the charge: a
small fire is lighted beneath the vaults or arches, and this is gradually increased, as the
draught gains strength. The air which rushes constantly through the flame passes through
the charge, and by degrees renders the whole of the mass incandescent: the lime required
for this kind of burning varies according to the size and quality of wood used.
Vicat, who made many experiments upon lime and mortars, ascertained that if lime was
plunged into water for a few seconds, and then withdrawn, it decrepitated and fell into a
fine powder, which might be kept in a dry place for a considerable time, and would not
again heat when water was added to it.
When lime was slacked in the common manner 100 parts by weight of common fat or rich
lime absorbed 236 per cent. of its weight of water, and its volume was increased to 310;
when slacked by plunging for a few seconds, it absorbed 131 per cent. of water, and its
bulk increased to 104; and when slacked by mere exposure to the air, it absorbed 148
per cent. of water, and its volume was augmented to 176. The same lime, therefore, will
produce cream of lime of the same consistence, with different portions of water as either of
the above processes are adopted.
The great quantity of water absorbed by the common process shows us that the particles
of lime are minutely subdivided, and, therefore, in a state to take up a greater quantity of
sand.
The quantity of water absorbed by the hydrate of lime has a material influence on its
hardness. One hundred parts of rich lime, by weight, imbibing 137 parts by weight of
water, acquired a hardness of '126; of 183 parts, 222; and when 315 parts, by weight, 068,
so that the middle quantity gave the best result. The greatest tenacity in the common
limes was obtained by the usual method of slaking, the next by spontaneous evaporation,
and the least by immersion. The greatest tenacity of the hydraulic limes is also found to
be in the same order.
Water has no action on the hydrates of the hydraulic lime, but it dissolves and decomposes
the rich lime; the latter, if slacked and made into balls and then exposed to the air, will in
a month or two be covered with a carbonate of lime; if these balls are then broken and
plunged into water the interior lime will dissolve, and the shell or carbonate will remain.
The solidification of common mortar is therefore accounted for by the reformation of a
carbonate of lime, the hydrate of lime attracting carbonic acid from the atmosphere: the
water which holds the lime in solution for any length of time combines with the carbonic
acid, and as evaporation proceeds slowly crystallisation takes place; this, according to some
opinions, constitutes the hardness of old mortar.
Where coal is used the limestone and coal are indiscriminately mixed, the quantity of the
latter varying with the hardness of the limestone to be reduced: 1 bushel of coal will make 4
or 5 bushels of lime, the magnesian limestone requiring still less. Where there is any
aluminous earth in the limestone, the fire must be kept down by means of a damper
introduced in the kiln, or there will be danger of the lime becoming vitrefied in consequence
of its affinity for silex and alumina: a white heat will often convert lime into glass; good
lime may be made with a slow red heat.
Common lime, when slacked under water, takes up more than it can solidify, and,
as it cannot then throw off the superfluous quantity, remains in a state of paste :
hydraulic limes, on the contrary, when slacked, and brought to the consistence of cream, if
plunged into water, in setting give up the superfluous quantity, and if made into a thick
paste before immersion, then absorb sufficient to set them. The hydraulic limes, when
mixed with sand, make an excellent mortar for buildings that are out of the water, and
the richest, which take up a greater quantity of sand, would be found the most economical
for general purposes.
When Limestone is to be converted into lime, it is not unusual to sprinkle it with water
before it is thrown into the kiln, which aids the process. The carbonate of lime, if heated
too violently, and in a close vessel, melts and crystallises again into a state of carbonate;
when it contains any mixture of alumina, and is burnt in contact with charcoal, it is not so
well adapted for hydraulic mortar as when burnt with coal. The best fuel is the blaze
from wood or furze, for it has been found that charcoal has the effect of depriving it of
CHAP. V.
721
MORTAR AND CEMENTS.
the strength which it acquires from the flare or flame heat: pure lime and clay thus
heated in a kiln will produce good hydraulic lime.
When water is thrown upon a subcarbonate, however, it will form a hydrocarbonate,
which will not set under water, and with an excess of base is more difficult to reduce into
lime than a neutral carbonate by a second calcination; this will in some degree account
for the difficulty of converting limestone into lime, when it has been chilled before
calcination is complete.
Artificial hydraulic lime, which is so necessary for all engineering works, is now generally
prepared by mixing with a rich lime a certain proportion of alumina or clay, and then
subjecting it to the process of calcination: with lime so prepared the beton, a mass
composed of hydraulic lime and rubble, is made, the lime being slacked previous to its
mixture; this sets under water, and is universally employed in France, where the piers of
bridges are founded on a beton composed of sand, flint, and artificial hydraulic lime; it is
often applied at great depths in a caissoon without a bottom, and after it has been deposited
8 months, has been found hard enough to bear 2500 tons on a surface of less than 100
square yards.
Chalk is sometimes used, which being quickly reduced to a powder is formed
into a paste by the addition of water, but does not produce so good an artificial lime, in
consequence perhaps of the less perfect state of the combination of the materials. Cal-
careous substances cannot, without slaking or subjecting them to heat, be reduced to the
same state of fineness. The proportion of lime and clay for the manufacture of hydraulic
lime must vary according to their quality; but 20 parts of dry clay added to 80 of rich
unslacked lime, or 140 of carbonate of lime, is found to be a good proportion; the finest
and softest clays are always preferred.
Parker's cement was first patented in 1796: it contains 45 per cent. of clay, and 55 of car-
bonate of lime, according to Sir Humphry Davy, and the mineral substance used for its
manufacture is a reniform limestone, found in nodules in beds of clay; they are most
abundant in the argillaceous strata, which alternate with those of oolite, and the clay
stratum, which reposes on the chalk and often on the London clay. In Kent they are
found on the coast of the Isle of Sheppey, and are called Septaria; the siliceous clay of
which they are composed contains veins of calespar; after these Septaria or cement-stones
are collected, they are subjected to calcination in kilns, and the cement is packed in casks;
their analysis shows usually 55 parts of lime, 38 of alumina, and 7 of oxide of iron.
In Yorkshire there is a cement made for hydraulic purposes, which contains 34 parts
of clay, and 62 of the carbonate of lime, and that obtained at Harwich, which sets very
quickly, has 47 parts of clay, and 49 of carbonate of lime.
When this material is properly burnt it is of a light brown colour; the cement, when
taken from the kiln, requires grinding before it is fit for use, and when mixed with water
it regains all the carbonic acid that was driven off by burning. The stone or septaria
of which this invaluable cement is made is fine grained, and susceptible of polish, its spe
cific gravity being about 2·59.
Its components after a careful analysis are found to be,
Carbonate of lime
of magnesia
of iron
of manganese
f silica
Clay
Water
{
alumina
I
657
5
60
19
180
66
13
1000
Two measures of sand and one of good cement powder form an excellent composition
for ordinary building purposes, though many prefer equal measures of each; cement,
however, unites more readily and powerfully with brick or stones when it is perfectly pure
and unmixed with sand: for the lining of reservoirs or cisterns it is used pure, and if
mixed with sand is seldom found to be water-tight; hence where a thickness is required,
it is better to dub out with tiles as much as is necessary, using only pure cement.
Kilns for burning Parker's Cement. That in Her Majesty's dockyard at Sheerness
is circular, 17 feet in diameter from out to out, and about 21 feet 6 inches in height: an
inverted cone occupies the middle, which has a clear diameter at top of 8 feet, and at
bottom of 5 feet 6 inches, where there is a conical mass of brickwork, which spreads
the cement as it falls through the ash-holes or eyes; there are four of these placed at re-
gular distances, each 30 inches in width, and 18 inches in height, to the crown of the flat
arch that covers them; within are fire-holes a foot square, which have iron bars to sup-
port the brickwork above them. Around the entire cylindrical kiln are four wrought-iron
hoops 3 of an inch in thickness, and 3 inches in width, for the purpose of holding the work
3 A
722
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
together: these are placed at regular distances from above the lower arches to the top,
and are held by vertical iron bolts where they join: the kiln will hold a charge of 30
tons of broken cement-stones measuring 26 cubic feet to the ton, as well as the fuel re-
quired for burning it. When used the bottom is covered with wood, and the coals and
cement-stones are arranged in alternate layers, each about a foot in thickness: after it
has been lighted three days the lower part may be drawn, and then by constantly filling
up, this may be done every twenty-four hours: the cement-stones and coals are thrown
in from the top, and every ton of cement-stone yields 21 bushels of cement powder. In
the mill for grinding this cement, the materials are thrown by a labourer into a sieve
containing seventeen wires to an inch, which is shaken by the machinery attached to the
steam-engine, after which it is packed into casks and kept ready for use: two tons of cement
powder are ground during the day.
are the
In France the materials selected for the manufacture of hydraulic mortar
chalk of the country, and a clay which contains 63 parts of silica, 28 of alumina, and 7 of
oxide of iron; after they are reduced into small lumps they are ground in a mill, the
stones are placed on their edges, and followed by a strong wheel to which is attached
a set of rakes; these are moved by a 2 horse-wheel in a circular basin 13 feet in diameter;
in the middle is the pivot of the vertical axle which supports the machinery: water is al-
lowed to flow into this basin as required, and the proportions of chalk are three measures
to one of clay. When this has been subjected to the action of the mill for an hour and
a half, it is drawn out in the state of a thin pulp into four or five successive reservoirs,
in the last of which it stands until it has obtained its requisite consistency; the mass
is then cut out into prisms, which are placed on shelves to dry, and in a short time they
are sufficiently so to be subjected to the process of calcination.
*
Smeaton's observations on water cements show that the quality of lime does not depend
either upon its hardness or its colour, for the white lias of Somersetshire, though
approaching to a flinty hardness, and having a chalky appearance, he says, is not equal to
the clunch lime, obtained near Lewes in Sussex, which is of great repute for all works
executed in water. This clunch lime is a species of chalk, not found, like the lias, in thin
strata, but in thick masses. It is considerably harder and heavier than common chalk, but
yet of the lowest degree of what may be termed stony hardness, and inclining to a yellowish
ash colour. When analysed, it contains three parts out of sixteen of its weight of yellowish
clay, with a small quantity of sand, seemingly of the crystal kind, not quite transparent,
but mixed with red spots: hence the fitness of lime for water building seems neither to
depend upon the hardness of the stone, the thickness of the stratum, nor the bed or matrix
in which it is found, but in burning and falling down into a powder of a buff-coloured
tinge, and in containing a considerable quantity of clay; and he found all the water limes
to agree in these particulars, among which that obtained at Dorking, he supposed, was
stronger than that made from common chalk, it containing one-seventeenth part of light-
coloured clay of a yellowish tinge.
Sutton lime in Lancashire, he observed, had this buff cast, the stone itself being of a deep
brown colour, its quality as a water lime not depending upon its colour before it is
burnt: this limestone was found to contain three parts out of sixteen of its weight of
brown or red clay, and one part out of forty-two of fine brown sand, making a lime very
superior to all others for water-building.
The mortar used at the Eddystone lighthouse was composed of equal measures of puzzo-
lana and blue lias lime, slaked into a powder, forming a very strong cement, and setting
well under water, though requiring considerable time to do so: in this sand was altogether
omitted, and when two bushels of slaked lime powder were added to two bushels of puzzo-
lana, the whole occupied 2.32 cube feet. For the common face mortar, to two bushels of
lime powder were added one bushel of puzzolana and three bushels of common sand,
which occupied 4.67 cubic feet.
Smeaton also used a water-lime and minion, or siftings of the ironstone, after calcination
at the iron furnaces, which were ground in a mill before being added to the powdered
lime; this minion or forged scales, he considered, when well pulverised, and sifted clean
from dirt and glassy slag, equivalent to as much puzzolana or tarras. Two bushels of lime,
two bushels of minion, and one of sand was the proportion for face mortar; and for backing
mortar, two of lime, bushel of minion, and three bushels of common sand, occupying 4·17
cubic feet.
14
When common lime was mixed with minion for ordinary face mortar he employed two
bushels of lime, the same quantity of minion, and two bushels of sand, making 4.75 cubic
feet, and for common lime, mixed with tarras, his proportions were for tarras mortar two
bushels of powdered lime, and one of tarras or 1.67 cubic feet; and for the backing mortar,
to the same quantity of powdered lime, only bushel of tarras, and three bushels of sand, or
14
3.50 cubic feet.
Puzzolana, obtained near Naples, is of a violet red colour, and of volcanic origin: it
is sometimes found in coarse grains in slag, pumice, or tufa, and often of a yellow, grey, or
CHAP. V.
723
MORTAR AND CEMENTS.
black colour: it is composed of silica and alumina, with a small quantity of other
matters; a portion analysed by M. Berthier contained silica 44·5, alumina 15, lime 8-8,
magnesia 4·7, oxide of iron 12, soda 4, potash 1.4, water 9.2, in 100 parts, and the only
preparation to which it was subjected was grinding and sifting; when reduced to a fine
powder, it is beaten with a due proportion of lime to a proper consistency.
Puzzolana was obtained by the Romans near Baiæ, and, mixed with lime and small
stones, Vitruvius tells us it acquired great hardness from the moisture it absorbed, and
that it would resist the dashing of the waves and the action of sea-water. Acids will,
however, act upon it, though some specimens are not at all affected by them; others,
when washed with sulphuric acid, become covered with an aluminous efflorescence; puz-
zolana thrown into limpid lime-water decomposes it more or less, but a sufficient quan-
tity restores it to a state of purity.
We find the mortars or cements used by the Romans in this island composed of chalk
lime, sand, pounded brick or tile dust, occasionally mixed with ashes of wood or charcoal,
the residue of the hearth where the lime was burnt, and the carbonic acid of the chalk driven
off; their mortar is remarkably hard, generally of a pinkish tint, and often when broken
exhibits cavities which contain crystals of the carbonate of lime. This kind of mortar is
perhaps the most ancient of the artificial puzzolanas known, and we find it through-
out Europe in every place occupied by the Romans; its weight and durability have
occasioned it to be considered as more excellent in quality than that made at the present
day; but this apparent advantage is entirely owing to time, which has permitted it to ab-
sorb from the atmosphere a greater quantity of carbonic acid, and to become in consequence
more solid, and capable of bearing greater weight.
Numerous experiments were made during the last century by the French chemists upon
the ochreous clays, in order to form a substance that would answer the same purpose as
the Italian puzzolanas; and M. Bruyere has shown us that by a mixture of powdered clay
and lime, in the proportion of three of the first to one of the latter, an active cement is
formed, which sets under water in a few hours, but never arrives at a very great degree of
hardness: all kinds of clay composed of silica and alumina, and a little oxide of iron, and
no carbonate of lime, if soft and fine in their textures, will produce, by proper treatment,
a very active and energetic puzzolana.
A clay which does not effervesce in nitric acid, and when burnt has a brick-red colour, if
after it is pulverised, it is thinly spread in a layer on a plate of iron, and heated to redness,
allowed to remain about twenty minutes, taking care continually to stir or move it with a
rod, so that all the particles may be properly and thoroughly calcined, forms an excellent
artificial puzzolana, which, mixed into a stiff paste with half its weight of lime, becomes
very hard in water.
Pipe clay, which contains a considerable quantity of silica, but no carbonate of lime, after
burning, will set, with the same proportion of lime as in the preceding example, into a very
hard cement, after it has been immersed five or six months.
Clay calcined at too great an heat loses its quality as a puzzolana, and it never should
be so great as is required to burn a sound brick; the artificial puzzolanas, made by the
ancients by pulverising old tiles, bricks, and the residue of their potteries, shows us that
those materials in which there had been a deficiency of burning were employed in preference.
Sand varies in the size of its particles, and where rubble-work is employed, after the
coarse stones are filled in with the finer sorts, the interstices are run in with some cementing
substance; to estimate the exact amount of all these spaces, a measure is made of each of
the varieties, and afterwards of the quantity of water to fill them up. In pebbles of about
half an inch in diameter, the void is equal to half the measure which contains them; in
gravels, five-twelfths; common sand, two-fifths; fine sand, one-third; and very fine sand,
two-sevenths.
To ascertain what proportion of each, when mixed, would approximate a solid mass, or
fill up all the voids, requires more consideration, though this is commonly done by first
filling a measure with the larger stones, and then by degrees adding the finer; and when
all in the proportions of their bulk have been calculated, they may be put together, and if
the measure, when duly shaken, is no more than full, we are sure the interstices are filled up.
The sand usually preferred for making mortar has a sharp grit, and is obtained from
rivers; the proportions with which it is compounded with the lime varies in different
districts according to the quality. Mortar for ordinary constructions is composed of one
part of stone lime and three of sand mixed together; the lime, being in a perfectly dry
state, is thrown into a basin formed by heaping up the sand around it; water is then
sprinkled or thrown on to slack the lime, and it is immediately covered over with sand;
after remaining some time in this state, and the whole of the lime has been reduced to
powder, it is turned together, then passed through a wire screen, where all the core, or that
portion of the lime which has not slaked, is taken out. The whole has then more water
poured upon it, and being triturated or larryed, is rendered fit for the workman,
3A 2
724
Book II,
THEORY AND PRACTICE OF ENGINEERING.
The lime is sometimes placed in the middle of a heap of sand, and after water has been
thrown on it, it is amalgamated together by hoes; after remaining in this state a few hours,
it sets and is fit for use: by this means the lime takes up a larger quantity of sand; 72
bushels of good stone lime, and 18 yards of sand, when formed into mortar will have a
cubical content of 315 feet.
Sand is the produce of the spontaneous disintegration of the granitic, schistose, or cal-
careous rocks, and their specific gravity is the same as that of quartz, a cubic foot of which
would weigh 162½ pounds, but when in the state of sand it does not weigh more than 75
pounds, so that the interstitial parts are more than equal to the sand itself: the proportion
of lime to fill up these spaces between the particles of sand must be ascertained before we
can have a solid mass, and the difference between the weight in its loose and compact
state ought to give us the quantity of lime requisite to bind the particles firmly together.
Concrete is of very ancient use, and formed the foundations as well as hearting of the
walls in the remotest ages, and among all nations: it is made by mixing lime, coarse gravel
and sand together, with a moderate quantity of water. The lime should be reduced to the
state of a fine powder, which is done immediately it is brought from the kiln, by grinding
it in a mill, or by pounding it; when used it is slaked and not before, the ordinary
method employed is to mix it with the other ingredients as quickly as possible, and then
add the water immediately before it is put into the barrow and wheeled to its destination,
or where it is to be thrown down.
Neither gravel nor sand alone will form a perfect concrete, for when large pebbles are
mixed with quicklime and water, they are not in any way held or cemented together, but
when fine sand is used in the ordinary proportions of common mortar a concrete is formed;
and a mixture of coarse with the fine sand renders the mass still more compact: when all
the materials are properly mixed together, the lime combines with the fine sand only, and
cements the pebbles or larger stones together, forming a rubble, so that the proportions of
sand ought to be precisely those required to make mortar of the best quality.
In the sea wall at Brighton the proportions were six parts of large shingle and well-sifted
sand, and one part of grey chalk lime fresh from the kiln; these were not mixed together
at one time, but three parts of sand and one part of lime were first made into mortar of
the ordinary kind, which was thrown with an equal quantity of beach shingle into a pug-
mill, where they were well mixed together before being used.
Artificial stone has been formed of concrete, and the process patented by Mr. Ranger;
the moulds have at the bottom a flat board, made larger than the size of the intended
stone to be cast; the four sides are held together by iron cramps, tightened up by means
of wedges: when the moulds are prepared they are laid out to receive the mixture of
gravel, sand, quicklime, and boiling water, which is thrown into them as rapidly as
possible, and kept constantly rammed down until the mould is full; the surface is then
floated over with mortar and rendered quite smooth.
Boiling water has the advantage of causing the lime to slack more rapidly, and therefore
fewer moulds are required; in half an hour these artificial stones are sufficiently set to
allow of the moulds being taken to pieces, after the trenails are drawn which kept the sides
together; two holes are left in the concrete block to attach any tackle that may be required
to hoist them to their destined position: when the boards which form the mould are all
withdrawn, the blocks are put up to acquire hardness, which they do in two or three months.
Whenever concrete is used for the foundation of a building, it should be thrown from as
great a height as possible, which compresses it into a more solid mass: its depth when
laid in trenches, or spread over an entire surface, should never be less than 4 or 5 feet, and
where great weights are to be borne not less than 6 feet.
The hydraulic mortar in the construction of the Menai Bridge in North Wales, made
of Aberthaw lime and sand, was found to answer admirably well; it was composed of
one measure of lime to two of sand; that used by Perronet at the bridge of Neuilly in
France had equal measures of lime and pounded tile from the Neuilly kilns, ground
very fine.
The artificial hydraulic lime made by Guyton de Morveau at Lena, in Sweden, consisted,
according to Bergman, of ninety parts of carbonate of lime, six of clay, and four of oxide
of manganese.
General Treussart's system for making artificial puzzolana is, first to reduce soft red
bricks to powder and mix them with common lime which has been some time slaked, in the
proportion of two measures of brick-dust to one of lime paste, with the addition of as much
water as is necessary to incorporate them thoroughly. Common lime, sand, and brick-dust
in equal quantities he also found to make a good hydraulic mortar he observes that all
hydraulic limes set much quicker in summer than in winter, and may be considered good
when either as hydrates, or mixed with sand, they set in the course of eight or ten days ir,
the summer, and acquire a hardness sufficient to resist the pressure of the finger.
:
CHAP. VI.
725
PISE.
CHAP. VI,
OF PISÉ.
THIS method of construction is far more simple than that where unburnt bricks are em-
ployed, and by no means so costly; it is universally adopted in the departments of the Ain,
Rhone, and Isère, in France, and forms fire-proof houses, far preferable for cottages to
timber framing, and well suited for barns, stables, or sheds attached to a farm.
Walls properly carried up in this material form one entire mass, and covered with a fine
coat of plaster will endure for ages, and present an agreeable appearance. Rondelet informs
us that he repaired, in 1764, an ancient chateau in the department of Ain, which had
endured for upwards of 500 years, and that the walls had attained a hardness and com-
pactness equal to ordinary stone; when desired to increase the size of the windows and
other apertures, the workmen were obliged absolutely to use the same tools as in a quarry.
The Romans practised this system at a very early period in Gaul, and we find men-
tion made of it by Pliny, who in admiration observes: "What shall we say, do we not
see in Africa and in Spain walls of earth called formacei, having the form given to them
by planks and boards placed on each face: and between which prepared earth has been
rammed? The earth so rammed, I can assure you, does continue for years in an imperishable
state, and is neither affected by the beating rain, by wind, nor by fire, and neither mortar
nor cement is used in them. In various parts of Spain we see the high watch-towers built
by Hannibal, upon the summits of mountains, with this material."-Pliny, lib. 35. cap. 14.
Manner of making Pisé. The ants probably suggested the process of preparing earth for
building purposes, and in the tropical climates we discover these industrious insects almost
rivalling man in the arrangement and strength of their habitations: the elevation of their
houses exceeds in height 500 times that of the builders. The termites, which are scarcely
a quarter of an inch in size, pile up dwellings 7 feet high, and sometimes as much as 20.
Bishop Heber describes some in India which were as much as 7 or 8 feet in circumference;
within were numerous galleries and cells, the principal of which was occupied by the king
and queen, placed nearly in the centre; its floor was more than 1 inch in thickness, formed
of clay, and the roof one solid well-turned oval arch of considerable strength.
The Termes mordax and Atrox, or turret-building ants, form their habitations with
a well-tempered black earth, often 3 feet in height, in form of a conical mushroom :
all the varieties of ants select a fine clay for their cells, galleries, and bridges; lining
their rooms with a composition formed of wood and gum, which these insects seem to
have the instinct to prepare in a very fine state, and to lay on like a coat of cement :
thus it is that man may receive instruction from a close observation of the habits of the
animal creation. All earth is suited for pisé-work, but the best is clay which contains
small gravel, and of such a consistence that it can be dug with the common spade:
every kind of earth that will sustain itself, with a small slope, is adapted for the purpose,
and may be successfully used. To prepare it, after beating thoroughly, it must be passed.
through a screen to take away the stones beyond the size of a common hazel nut; and
if not moist it must be watered, and turned over with a shovel until it has acquired a
regular consistence, which is known by moulding it by the hand, or between the fingers,
and then throwing it into a vessel, when, if it retains the shape given to it, it may be
considered as fit for use. After the earth is thus prepared, it is put into a frame or move-
able box, where it is forced down and beaten with a rammer. There is some attention
necessary for the construction of this box, which is formed of deal planks put together, with
their joints ploughed and tongued, and further strengthened with clamps on the outside,
fastened on with clenched nails. These sides or frames rest, when in their places, on
cross-pieces or putlocks, which pass entirely through the thickness of the wall; near the
ends are mortises, into which upright pieces are placed, wedged firmly at the bottom up to
the sides, already set, to the distance which is to constitute the thickness of the wall,
usually about 20 inches at bottom, and gradually diminished as the height is increased;
the diminution or inclination is uniform throughout, and in a house of two stories does not
exceed I foot. The sides or frames are made 10 feet in length, and 3 feet high; the uprights
5 feet long, comprising the tenons, so that they stand up sufficiently above the sides to allow
of being secured by ropes. The wedges are 9 inches in length, 11 at the base, and 20
inches at top, made to fit the mortises exactly, which should be deep enough to permit
the bottom to be 2 inches below that of the wall, that the frame may hold within it a
portion of the wall already made. The frames at top are steadied by small stieks, which
3 A 3
726
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
press them against the outside uprights, held together by the cords at their upper ends;
between each pair of uprights it is found necessary to have a strut or one of these sticks;
when placed, the cords above are tightened by twisting them with a small piece of wood

Fig. 605.
PISE-WORK.
introduced between them. When the frames are thus fixed, the earth is thrown in, and
worked in the same manner as concrete or common mortar; first well wetting the parts
about the putlocks, to enable their being easily withdrawn; as many workmen are then em-
ployed as there are divisions, one being placed in each compartment.
After the bottom is well-cleaned and lightly sprinkled with water, the labourers bring to
the masons the prepared earth in wicker baskets, and tread it with their feet so as to form a
bed of an uniform thickness of not more than 3 or 4 inches; they then ram it down, reducing
it to little less than half its former thickness; this first bed being compressed, the labourers
bring more earth, and form another, spread out and beat in the same manner, and so on till
the whole case is filled.
The rammer is a block of wood 10 inches high; at the middle of its height it is square,
and 6 inches by 5, diminishing in thickness, and terminated by rounded edges at the bot-
tom: towards the upper part it is terminated by a circular surface 4 inches in diameter,
in the centre of which a hole is sunk 1 inch in diameter and 2 inches deep; the circular
part at the top being rounded off from the square below, the flat portion of the rammer
at bottom must be perfectly smooth and even; a block of ash, elm, or hazel, is usually pre-
ferred; the handle is 4 feet 2 inches long, and in ramming it is turned round at each stroke
to make the work solid and to unite it with that previously done.
When a wall is commenced, the first frame is put at one of its extremities, and the end is
inclosed by two planks united by cleets, secured at the top by two iron cramps; the other
part, where there is no end, is terminated by a fall of about 60°. The section of the wall
serves to unite the first constructed with that which follows.
CHAP. VI.
727
PISÉ.
After the first stratum is finished, the case or frame is taken down, and placed further
along, so that the plank entirely covers the inclined part, which terminates the preceding,
uniting it with that


about to be made, and
the same process is
continued. Lintels
are placed over all
apertures, and when
the walls are finished,
previously to covering
them with plaster, it
is necessary to let
them remain to dry,
according to the cli-
mate and time of
year. Experience has
shown that in an or-
dinary climate walls
of 18 or 20 inches
in thickness finished
about the commence-


Fig. 606.
TOOLS USED FOR PISE-WORK.
D
""
7
ment of May, are sufficiently dry in September or October for plastering; those finished
in July or August may generally be completed before the frost and rain have any effect
upon the work: although pisé is formed of earth scarcely wetted, whilst the unburnt
bricks of the ancients were kneaded with straw and water, it is nevertheless prudent to
regard Vitruvius's observation, "not to apply plaster unless the middle is dry.'
The pisé
which is made during the hot months soon dries in the exterior; but the moisture is con-
fined to the centre, from whence it escapes slowly, rising by degrees to the surface; if
covered with plaster, it insinuates itself between this and the pisé, occasioning the outer
coat to fall off. There is no fear of the action of the air when it is well done, for the drier
it is the better the plaster adheres; in the department of Isère there are ancient houses of
pisé that have never been plastered on the exterior, and which still resist all the inclemencies
of the weather: when the earth is poor, or not consistent enough, by being wetted with
lime-water, or grouting formed of mortar, it hardens, the surface becomes improved, and
a building might be carried up with its walls so even as not to require any coat of
plaster.
The Cob Walls, in Devonshire, formed of clay and chopped straw, are generally 2 feet
in thickness, based upon either brick or stone foundations, 3 or 4 feet in height above the
level of the soil. Houses so built are warm and healthy, and usually covered with thatch :
like pisé-work they require to be carried up at several times, for if hurried the walls will
not settle equally, but bulge and incline from the perpendicular. The earth selected
is loam mixed with a certain proportion of straw, the whole being well beaten and
pounded before it is used. The first height of 4 feet being carried up all round, and the
divisions or walls brought to the same level, they are left some weeks to dry and settle,
each succeeding rise being diminished in height as it is carried up. The workman stands
on the wall to receive the cob, which is pitched up to him, or brought from below, he
treading and pressing it down as it is thrown in: after a rise has been made in the wall,
the sides are carefully pared down before the next addition is made to it; this is per-
formed by an iron cob parer, which in shape bears some resemblance to a baker's peel. At
the openings which are to be afterwards cut out, as the doors and windows, lintels are in-
troduced, due allowance being made for settlement; these rest at their ends on templates
or cross-pieces, to which they are secured. When the earth has sufficiently settled and
dried, the apertures are cut out, and the sides or reveals carefully dressed; the whole
is then coated with a fine stucco or plaster; if kept dry at top and at its foundation, and
no water allowed to drip upon it, it will remain sound for centuries: where this con-
struction is adopted for garden walls, it is necessary to thatch the top, or cover it with
tiles, to prevent the destructive effects of every shower of rain.
728
THEORY AND PRACTICE OF ENGINEERING. BOOK II
CHAP. VII.
TAR, PITCH, RESIN, &c.
BITUMEN or asphaltum is used in the composition of hydraulic cements, and for varnishes
and japans: it is a black substance found in the earth; in external character it bears some
resemblance to coal; it is a compound of carbon, hydrogen, and oxygen, and generally
obtained from the secondary and alluvial formations; its average density is 1·16, and it melts
at the temperature of boiling water.
The island of Trinidad contains a tar lake, 3 miles in circumference, and asphaltum is
produced in great abundance from springs in many parts of Asia; it is also obtained in con-
siderable quantities near Antibes in France, where it is made into a varnish by dissolving
2 portions of asphaltum with 12 parts of fused amber, 2 parts of resin, 6 parts of linseed
oil varnish, and 12 parts of oil of turpentine.
Bitumen has been applied as a covering for roofs and floors, and lining cisterns, and con-
siderable quantities have been imported from the borders of the Lower Rhine: to every
pound of bitumen when melted is added 4 or 5 pounds of powdered limestone, chalk or
burnt clay; when thoroughly mixed and combined, it is poured out and spread into
moulds, previously smeared with a thin coating of loam to prevent adhesion; after the
whole has cooled, the mould is taken to pieces, and the bricks or contents are 18 inches
in length, a foot broad, and 4 inches thick, weighing about 70 lbs.
Asphaltum may be decomposed by alcohol and caustic potash; its origin is but little known;
by some chemists it is supposed to be the product of coals decomposed by volcanic heat or
by spontaneous combustion.
Resins.—The Juice of Pine and Fir Trees, like that of the Pistacea terebinthus, has an austere
stringent taste; it is viscid and transparent, readily inflammable, and easily becomes concrete.
In distillation with water, it yields a highly penetrating essential oil, and the liquor is
found to be impregnated with an acid, a brittle resinous matter remaining behind: diges-
tion with rectified spirit of wine completely dissolves all the resinous parts, with which some
portion of the insipid gum, or mucilage is also taken up. If this solution be filtered, and
diluted largely with water, it becomes turbid, and throws off the greatest part of the oil,
the gummy substance being retained: if the solution be subjected to distillation, the spirit
carries with it some of the lighter oil, so as to be sensibly impregnated with its terebinthi-
nate odour, and it leaves behind an extract, differing from the resin separated by water, in
having an admixture of mucilage. The native juice becomes miscible in water by the me-
diation of the yolk or white of an egg, or by that of vegetable mucilage, and forms a milky
liquor: exposed to the immediate action of fire, the roots and other hard parts of the tree
produce a thick, black, empyreumatic fluid, which, containing a proportion of saline ana
other matter, mixed with the resinous and oily, proves soluble in aqueous liquors, and ac-
cording to its several modifications constitutes the varieties of tar and pitch. The resinous
residue of the several processes to which the matter extracted from pines may be subjected
constitutes the varieties of resin, colophony, &c. &c. There are also other products, both
natural and artificial, much employed in medicine and the arts.
Tar and Pitch are extensively used for the purpose of retarding the decomposition of
wood, cordage, and other articles.
Tar mixed with grease or clay is used for greasing wheels, &c.
Yellow Resin in the proportion of 3 cwt. to 10 cwt. of tallow, for common yellow soap.
Shoemakers' Wax is a composition of pitch, oil, and suet, but it is also made of resin, bees.
wax and tallow.
Turpentine in all its different forms, is extensively employed in painting.
Tar and Pitch, with a mixture of tow or beaten cables, used for paying over the seams
of the sides and decks of ships after they are caulked, to preserve the oakum from any wet.
Oakum is formed of untwisted old ropes steeped in tar, and in ship-building is indis-.
pensible.
Lampblack is used by painters, modellers, and other artists.
Turpentine made from the Scotch fir is so inferior to that obtained from the silver fir
that the latter is generally preferred.
Tar is procured from the Scotch pine in great quantities in the north of Europe, and is
considered superior to that produced in the United States from P. resinosa, Strobus
Australis, &c. The process by which tar is obtained is very simple; it is chiefly from the
roots of the Scotch pine. A conical cavity is made in the ground, generally on the side of
& bank; and the roots, together with logs and billets of wood, neatly trussed in a stack of
CHAP. VII.
729
PITCH, TAR, RESIN, ETC.
the same conical shape, are let into this cavity; the whole is then covered with turf to
prevent the volatile parts from being dissipated, which by means of a heavy wooden mallet,
and a wooden stamper worked by two men, is beaten down and rendered as firm as possible
above the wood; the stack of billets is then kindled, and a slow combustion of the pine
takes place as in making charcoal during this combustion the tar exudes, and a cast-iron
pan being fixed at the bottom of the funnel, with a spout which projects through the side
of the bank, barrels are placed beneath the spout to collect the fluid as it comes away; as
fast as these barrels are filled they are bunged, and are then ready for immediate exportation.
The turpentine melted by fire mixes with the sap and juices of the pine, while the wood
itself becoming charred is converted into charcoal.
Pitch is made by putting the tar without any addition into large copper vessels fixed in
masonry to prevent any danger from it taking fire, and is there suffered to boil for some
time, after which it is let out, and when cold hardens and becomes pitch. Tar and char-
coal are obtained in Russia, much in the same manner as in Sweden, from the bottoms
of the trunks and roots of trees: in Germany the process is conducted with very great
accuracy.
Resin. The resinous matter which exudes from the pinaster is called by several names
in France, even in its raw state: that which encrusts on the sides of the wound is called
barras; it is nearly as white as wax, and is used for mixing with that substance for making
tapers, to which it gives suppleness and elasticity: the barras is collected only once in
the year at the end of the season, and is scraped off with an iron rake: the principal
substance which flows from the tree is called galipot, or résine molle; this having been
collected in the hollow cut of the tree, or in the trough attached to it, is put into large
pits or reservoirs capable of containing 150 or 200 barrels each, which pits are dug in the
earth, and lined with planks made of the pine trees, fitted so close together as to prevent
the liquid oozing through: it is afterwards melted in large copper caldrons set in brick-
work to free it from the impurities mixed with it, with a proper chimney to convey away
the smoke, as should it be suffered to come in contact with the resin, the whole would
probably take fire; it is also necessary to keep continually stirring the caldron to prevent
the resin from burning to the bottom.
When the matter is to be made into brown resin, some of the barras is to be mixed
with it, and when it is thought to be sufficiently boiled a little is poured upon a piece of
wood; when it becomes cold, if it will crumble between the fingers, the resin is ready.
It is then poured through a filter made of straw laid horizontally, 4 or 5 inches thick, and
run into barrels, where it is left to harden: in this state it is brown and brittle, and
called by the French crai sec, which is the brown resin of the shops.
Yellow Resin. -When the resinous matter is boiling a quantity of cold water is added,
a few drops at a time; this makes the resin swell, and a trough having been previously
fixed to one side of the caldron, the matter flows through it to a vessel placed to receive it;
from this the operator raises it by a ladleful at a time and puts it back into the caldron,
repeating the operation several times, till the resin has become yellow and as clear as
wax; it is then filtered through straw into moulds hollowed in the sand, where it is
formed into cakes, as sold in the shops. To make these moulds, a circle is first traced
in the sand with a forked stick which acts like a pair of compasses; the sand is then
hollowed out with a knife, and the bottom and sides of the mould are well beaten with
wooden mallets to make them perfectly hard and smooth; the cakes of resin generally
weigh from 150 to 200 lbs. each.
Lamp-black is made from the waste materials used in preparing the resin, which are
carefully preserved; the straw and pieces of wood are all burnt in a close furnace, or,
when the wood of the pine tree is burned for tar, lamp-black is formed on the cover of
the furnace.
Pinus Australis, (the long-leaved pine): four-fifths of the houses in Carolina, Georgia,
and the Floridas, are built with it; no other species is exported from the southern states
to the West Indies, and it is preferred before all other pines in naval architecture: it is
sent in large quantities to Liverpool, where it is called the Georgia pitch-pine, and is sold
25 to 30 per cent. higher than any other pine imported from the United States, where it
supplies nearly all the resinous matter used for ship-building. The resinous products are
turpentine, scrapings, spirit of turpentine, resin, tar, and pitch.
Turpentine is the raw sap of the tree obtained by making incisions in the trunk; it
begins to distil in the month of March when the circulation commences, and it flows with
increasing abundance as the weather becomes warmer, so that July and August are the
most productive months. The sap is collected in boxes, or notches cut in the tree, 3 or 4
inches from the ground, of a size to hold about 3 pints of sap, but proportioned to the
dimension of the tree, the rule being that the cavity shall not exceed of its diameter :
these cavities are made in January or February, commencing with the south side, which
is thought the best, and going round the tree. The next operation is clearing the
ground from the leaves and herbage: about the middle of March, a notch is made in the
730
Book II
THEORY AND PRACTICE OF ENGINEERING.
tree with two oblique gutters to conduct the sap which flows from the wood into the box
or cavity below; in about a fortnight the box becomes full, and a wooden shovel transports
it into a pail, and it is then put into a cask: the edges of the wound are chipped every
week, and the boxes after the first generally fill in about three weeks. The sap thus
procured is used as turpentine without any preparation, and is called pure dripping.
The Scrapings are the crusts of resin that are formed on the sides of the wounds;
these are often mixed with the turpentine, which in this state is used in the manufacture
of yellow soap, and is called Boston turpentine; in five or six years the tree is abandoned,
and the bark never becomes sufficiently healed to allow of the same place being wounded
twice.
Spirits of Turpentine are principally made in North Carolina, and obtained by dis-
tilling the turpentine in large copper retorts: six barrels of turpentine afford 122 quarts of
the spirit; the residium after the distillation is resin, which is sold at the price of the
turpentine.
As soon as vegetation ceases in any part of a pine tree its consistence changes, the sap
wood decays, and the heart becomes surcharged with resinous juice to such a degree as to
double its weight in one year; this accumulation increases.
Tar of the southern states of America is made from the dead wood of Pinus australis,
obtained from trees prostrated by time, by fires annually kindled in the forests, or from the
tops of those that are felled for timber, &c. : dead wood is productive of tar for several
years after it has fallen from the tree. To procure the tar a kiln is formed in a part of
the forest abounding in dead wood, which is collected, stripped of the sap wood, and cut
into billets of 2 or 3 feet long, and about 3 inches thick, a tedious and difficult task,
rendered so by the numerous knots with which the wood abounds. The next step is to
prepare a place for piling the billets, and for this purpose a circular mound is raised,
slightly declining from the circumference in the centre, and surrounded by a shallow ditch;
the diameter of the pile is proportioned to the quantity of wood which it is to receive; to
contain 100 barrels of tar it should be 18 or 20 feet wide: in the middle is a hole with a
conduit leading to the ditch, in which is formed a receptacle for the tar as it flows out.
Upon the surface of the mound, after it has been beaten hard and coated with clay, the
wood is laid round, in a circle like rays. The pile when finished may be compared to a
cone truncated at 3 of its height and reversed, being 20 feet in diameter below, 25 or 30
feet above, and 10 or 12 feet high; it is then strewed over with pine leaves covered with
earth, and held together at the sides with a slight cincture of wood; this covering is
necessary in order that the fire kindled at the top may penetrate downwards towards the
bottom with a slow and gradual combustion, for if the whole mass were rapidly inflamed
the operation would fail, and the tar would be consumed instead of distilled; in fine, the
same process is observed as in Europe for making charcoal; a kiln which is to afford 100
or 130 barrels of tar is eight or nine days in burning.
Strasburgh Turpentine, to be good, ought to be clear, free from impurities, transparent,
and of the consistence of syrup, with a strong resinous smell, and rather a bitter taste: it
is the only turpentine produced by any kind of pine or fir tree, which is used in the
preparation of clear varnishes, and its oil sells at a higher price than any other.
The pro-
portions for making the oil are 5 lbs. of liquid resinous juice to 4 pints of water distilled
in a copper alembic; this is the essential oil of turpentine; and if 1 pint of it be redistilled
with 4 pints of water it is called rectified or æthereal oil of turpentine.
Lamp-black. The apparatus employed for this purpose consists of a furnace, a chimney,
and a small chamber or box for collecting the soot: the furnace is about 2 feet 6 inches
wide, 3 or 4 feet long, and 2 feet 6 inches high, and it is usually set in brick on each of the
long sides this furnace has an opening near the bottom, which can be shut up at pleasure,
by means of a little door attached to it. The furnace has a brick chimney made almost
horizontal, to conduct the smoke into the chamber or box: the chimney is from 14 to
16 inches long, and 12 inches broad and high; at the place where the pipe of the chimney
terminates is constructed a chamber or box, into which the pipe should enter some inches,
so as to carry the smoke into its centre. This chamber is generally about 12 feet square,
and 9 feet high in the roof; there is a door on one side, and in the upper part or ceiling
an opening 5 or 6 feet square. The walls of the chamber are lined with thin planks of
wood or plastered very smooth, and the door is fitted closely into a groove: over the
opening in the roof is placed a flannel bag, supported by rods of wood in the form of a
pyramid, composed of four pieces of coarse flannel sewed together.
When the lamp-black is to be made, a little of the straw through which the resin and tar
have been strained, and some of the other refuse, are put into the furnace ano lighted, fresh
straw, impregnated with tar, being strewed over the fire, as fast as the other is consumed.
The smoke passes into the chamber, and deposits its soot on the walls, and on the flannel
bag, from both of which it is detached, after the whole of the straw and refuse have been
burned, by striking the outsides smartly with a stick. The flannel pyramid acts as a filter
to the lighter part of the smoke, retaining the soot, and permitting the heated air to escape
CHAP. VII.
731
TAR, PITCH, RESIN, ETC.
into the atmosphere. The door of the chamber is then opened, and the lamp-black, being
swept up, is packed in small barrels made of the wood of the spruce fir for sale.
In the Landes the furnace and the chimney are in the open air, and the chamber only
covered with a tile roof; but in Germany the whole apparatus is constructed in a barn-like
building, about 24 feet long, 12 feet wide, and 10 feet high.
Glass. This transparent, impermeable, and brittle substance, consists of many varieties,
which are differently composed, and applicable to as many purposes: the manufacture of
glass is of the highest importance, and now that all restrictions are withdrawn to its
improvement, we may expect to find it rendered not only cheaper but better.
It was
known not only to the Egyptians, but also to the Phoenicians, whom Pliny says were the
inventors of the manufacture; both Sidon and Alexandria were famous for the production
of beautiful glass, which was cut, engraved, and tinted with a variety of colours, some
specimens of which equalled the precious stones in brilliancy of effect. Rome was also
celebrated for its manufacture, and Nero is reported to have given as much as 6000
sesterces for two glass cups: before Colbert introduced an establishment into France for
blown mirror-glass, Europe generally was indebted to Venice for all that appeared in
commerce: it was not made in London until 1557. Glass is made by fusing silica with
a due proportion of alkali, which serves as a flux to the silica, and makes the whole
transparent: it may be said to consist of one or more salts, which are silicates, with bases
of potash, soda, lime, oxide of iron, alumina, or oxide of lead.
The silica ordinarily made use of is sea-sand, which consists chiefly of quartz, and the
finest quality is obtained on the coast of Norfolk, near Lynn: the common black flint is
also used; after it has been heated red-hot, and plunged into cold water, it breaks to pieces,
and becomes so brittle that it is easily ground into a fine powder. The alkali is either
potash or soda in a state of carbonate: borax is the flux for the finer sorts of glass, but
for the more common kind lime is substituted: two oxides of lead are used, viz. litharge
and minium, which give to the glass greater powers of refracting light, and that of sud-
denly changing its temperature without cracking. The white oxide of arsenic is also a
flux, and in any large quantity will give the glass a milky hue, which increases with time.
Soluble Glass is a simple silicate of potash or soda, or of both these alkalies; crown glass
is a silicate of potash and lime; common window-glass is a silicate of soda and lime, or red
potash; bottle glass is composed of silicate of soda, lime, alumina, and iron.
The common crown glass for ordinary windows is compounded after the following pro-
portions; 450 pounds of kelp, dried and ground, 325 pounds of Lynn sand, and 25 pounds
of slacked and sifted lime. The kelp, which is the alkali, differs so much in quality that
its proportions continually vary arsenic is added to facilitate the fusion, and oxide of
cobalt with ground flint introduced to improve the colour. By measure, five parts of fine
sand and eleven parts of ground kelp or soda is another proportion for common crown glass.
Flint Glass is composed of silex, to which is added carbonate of potash and red lead or
litharge, the latter giving the glass its great specific gravity, its superior transparency, its
ductility and powers of refraction. The materials after preparation are put into a crucible
of Stourbridge clay, which holds about 1600 lbs. weight of fused glass; a double stopper
covers the mouth of the crucible, and as it is not luted, the carbonic acid gas, or excess of
oxygen, has the means of escaping: a strong, rapid, and intense heat for sixty hours is
required to drive off the gases and to fuse the metal, during which process the surface is
regularly skimmed of all the impurities that arise.
Flint plate glass, for optical purposes, is thus prepared; seven pounds of the metal is taken
out of the pot when at a certain point of fusion, in a conical-shaped ladle, and then blown
into a hollow cylinder, which is cut open and flattened into a sheet 20 inches by 14, and
varying in thickness from 3 to of an inch; the plate is then annealed, and afterwards cut
and ground into the required form.
When glass is not sufficiently annealed, it is put into tepid water, which is heated and
maintained for some hours at a boiling point, and is then suffered to become gradually cold;
unannealed flint glass, heated and suddenly cooled in water, resembles in its appearance a
mass of crystals, from whence it has been supposed that the process of annealing renders the
glass incapable of polarisation, in consequence of its becoming more compact. A barometer
tube 40 inches in length, unannealed, heated, and suddenly cooled, would contract of an
inch, and if done by the usual manner, its contraction would be double, or . The red tint
given to glass by manganese is destroyed by annealing, and the best fuel for melting glass
in the furnace is oven-burnt coke mixed with screened coal: in plate glass there is no
lead; in consequence it is purer, and more homogeneous than common flint glass.
Plate Glass.-Common salt or the muriate of soda is decomposed by the subcarbonate
of potash, when both salts are in a state of solution and subjected to heat; an alkali so
obtained is dried by being continually boiled: 1 pound of pure soda, and 4 pounds of
sand, produce a hard glass, which neither water nor the mineral acids will affect. The best
plates are formed out of 720 pounds of Lynn sand, 450 of alkaline salt, 80 of slacked quick-
732
THEORY AND PRACTICE OF ENGINEERING.
Book II.
lime, 25 of nitre, and 425 pounds of broken plate glass; this generally, if well managed,
produces 1200 pounds weight of plate glass.
On the continent the best mirrors are formed with 300 pounds of white quartz sand,
100 pounds of dry carbonate of soda, 43 pounds of lime slacked in the air, and 300 pounds
weight of old glass; per cent. of the weight of soda is added in manganese. The atomic
constitution of glass consists of five atoms of silicic acid, one of oxide of lead, and one of
potash.
After the materials are thoroughly prepared and refined, they are put into a cistern,
the temperatare of which is previously raised to that of the glass, and when the cistern
is full, it remains for a considerable time in the furnace, until all the air-bubbles are
dispersed; after this operation it is ready for casting. The table for this purpose is formed
of a cast-iron plate, supported on pillars of considerable strength; the metal is then suffered
to flow readily and equally from the furnace into a cistern, which is carried to the table,
it being first heated with hot ashes and carefully cleaned. The surface of the metal has
the scum taken off by a copper instrument, and the cistern that holds it is then hoisted
and swung by means of a crane over the end of the casting-table, where it is overset,
and the metal immediately flows equally over it. A copper roller is passed over the fluid,
and the surface is thus rendered comparatively smooth; by means of this roller the
necessary thickness is given to the plate, as it runs upon a fillet placed on the edges of
the table: after plates are cast, they are taken to the annealing chamber, where they
remain for twelve or fifteen days, placed in a horizontal position.
CHAP. VIII.
533
GEOMETRY
CHAP. VIII.
GEOMETRY.
GEOMETRY, derived from the Greek words which signify land and the method of measuring
it, is employed in estimating the length of a line, the area or superficial contents of a figure,
and the cubical or solid contents of a body, and is usually divided into theoretical and
practical. Egypt gave birth to the study; from thence it was imported into Greece, and
among the refined and intelligent inhabitants of that classic land it arrived to a degree of
perfection that succeeding ages have but little improved.
Theoretical geometry is founded on ideas, or those perceptions of the mind which
resolve and demonstrate the truth of any proposition; it is the method of defining exactly
the notions we form of any particular figure.
Practical geometry, so important to the civil engineer, is that division which enables
him, by the aid of various mathematical instruments, to carry into operation the principles
taught by theory, and to trace and define the boundaries of any figure that may be
required to be set out for mechanical or other purposes. This branch is subdivided into
Trigonometry, Planeometry, and Stereometry.
A
B
Trigonometry is the art of measuring heights and distances by means of triangles; for
example, it enables us to ascertain the distance between the two spires A and B, which are
separated by a wide and deep river, and con-
sequently inaccessible. It shows us an easy
method of laying down the map of a country,
and defining upon it the inequalities of the
surface, as the depths of valleys or the heights of
mountains; it enables the mariner to map an
inaccessible coast, to form a chart which shall
guide him through deep and safe channels, and
to shun the rocks and shoals which would destroy
his vessel.
Planeometry is applied to ascertaining the area
or superficial contents of any surface; it shows the
land surveyor the method of finding the number
of acres contained in a given district of country,
or of subdividing it into any number of equal
or unequal parts.
Stereometry or mensuration is the art by which
we ascertain the contents of a cube, or any solid
figure; that is to say, the quantity of cube feet
or yards it may contain.

Fig. 607.
The elements of practical geometry, or leading
definitions, may be thus described: :—a point is
the extremity of a line without dimensions, or
even length, breadth, or thickness; hence, by
some it is merely held as an idea; but Euclid, the earliest and ablest teacher of the science,
considered it the beginning or nucleus of all quantity. It is therefore the smallest portion
of matter, or of an object, that the eye can distinguish, or which may be defined or ex-
pressed by a pencil, or instrument of any kind.
A point may be established at any given place, and may be marked by a stake or staff,
or by the end of a pair of compasses.
The point of junction is that where two lines meet, as at
Q. The point of intersection is where two or more lines
cross each other, as at A.
The point of incidence, A, is that from whence the
line PA is reflected back from the line A C or BC. A
point has neither length, breadth, nor thickness; a line
has length only; a surface has length and breadth, and
a solid has, in addition, thickness: one dimension is
required then for a line, two for an area, and three
for a solid body. The edges which bound a solid
are lines, and where they unite may be considered
points; these may all be imaginary, but they are
necessary to establish, before we can arrive at the true
B

с
Ω
A
Fig. 608.
784
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
S
estimate of quantity, or the contents of either surfaces or
solids.
Tangent point is that at F, where the straight
line V X touches the curve of the circle N, at a part of
its circumference GO F, or at G, where two circles touch
each other, without cutting; N is the central point of
the circle: right lines drawn from this point to the cir-
cumference are its radii; the two points which bound
each being the centre, and a dot on the circumference.
The diameter passes through the centre, comprises twice
the radius, and may be defined as bounded by two points,
situated somewhere on the outline of the circle. This
circumference may be also supposed to be divided by
points into a number of degrees, and the divisions
between by others, ad infinitum, until the entire figure is
composed of points, or forming a polygon with an in-
finite number of sides.
Station point is the place from whence an observation
is made, and the spot immediately beneath the centre
of the instrument used; R is such a point.
Distance point is a stone or hole in an object, re-
marked in taking an observation; V in the tower serves
for such a point of sight, and is used to denote the hori-
zontal or level line by which the height of the tower T
may be ascertained.
Inaccessible point is one that cannot be approached, as
S, the water which surrounds the tower not permitting
an easy access to it.
Lines have length only, and are the boundaries of
all figures; they may be considered to pass from one
body to another, without being visible; CD is an ima-
ginary line from the point of the pyramid to the stone.
A right line, as that of GH, is straight, and lies
evenly between two points, neither ascending nor de-
scending, but is the shortest distance between the ob-
jects.
A curved line has no portion of a right line, but is
concave on one side and convex on the other.
GH is a perpendicular line standing on KL, the
angles formed on each side being equal; GHL and
GHK both being right angles. The plummet makes,
when it is dropped, a perpendicular line, as at N.
The column L is a perpendicular line standing on its
base M, or rather it diverges or tends to the centre of
the earth, the line with which it is perpendicular being
a tangent to the earth's circumference: falling bodies
tend towards a point at its centre, and our ideas of a
perpendicular line must always be with reference to a
limited base, or it must be considered a diverging line;
for the sides of buildings continued to a great height,
and maintained perpendicularly, would, according to our
usual notions, require that the area of the upper floor
or top should be larger than the one below: the walls or
lines that bound them, to be upright, must be radii, and
consequently diverge from each other as they are con-
tinued upwards; in practice it is not necessary to have
any other guide than the plummet, which dropped from
a height falls to the centre, and any material disposed
within such a line gravitates to the same point. Spires
of churches are rarely found to have the point at their
apex directly over the centre of the area of their base;
that at Salisbury is nearly 2 feet inclined beyond it; it
is extremely difficult to ascertain one point by the
plummet that is directly over another, when the height
is considerable. Columns are rarely found placed truly
perpendicular; their internal faces, as those towards the
cell of a temple, are sometimes less inclined or diminished
K
R
V

X
F
N
Fig. 609.
Fig. 610.
C
Fig. 611,
G
Fig. 612.
M
L
Fig. 614.
Ꮐ
G
[]
T


Fig. 613.
D
H
inut.


CHAP. VIII.
735
GEOMETRY.
than those on the outside; hence some have supposed
that such an arrangement was intended to produce a
better effect.
The line OP, in the triangle OQR, is a perpen-
dicular, because it falls at right angles with the base;
OPQ and OPR being both right angles. In prac-
tice, a perpendicular or right angle is set out by the
numbers 3, 4, and 5; for example, if QP is made 3
feet, PO 4 feet, and QO 5 feet, OP will be perpen-
dicular; or if O P is made 3000 feet, PR 4000, and RO
5000, the result will be the same.
ST is perpendicular to the side T, because it is at
right angles with it; hence the radius of a polygon,
when it falls on the middle of one of its sides, is also
its perpendicular.
An inclined line, as VX, is that which is neither pa-
rallel nor perpendicular with another, as that of Y Z.
Parallel lines are those like AB, CD, and E F, which
may be drawn to any length, and yet never approach.
All lines which preserve an equal distance from each
other are called parallel lines.
The two curved lines ST, VX are parallel, although
they are not of an equal length.
Some
This subject has ever been considered difficult of ex-
planation, and much has been written upon it.
writers have exerted themselves to demonstrate that
two parallel lines, when they meet a third, are equally
inclined to it, or make the alternate angles with it equal.
Euclid has shown that if a straight line meet two
straight lines, so as to make the interior angles on the
same side of it less than two right angles, these straight
lines, being continually produced, will at length meet on
the side on which the angles are which are less than two
right angles; but this is not so evident, and many
celebrated geometricians have attempted to make our
author more clear upon this point. Some have as-
serted “that straight lines are parallel which preserve
always the same distance from each other;" but the
Y
A
Q
0

R
P
Fig. 615.
Fig. 616.
E-
V
Fig. 618.
S
X
T

א
Z
B
D
Fig. 617.
F
T
X
correct definition would be, that "two straight lines are parallel when there are two points
in the one from which the perpendicular drawn to the other, and on the same side of it, are
equal." The difficulty in such a statement consists in
showing that all the perpendiculars drawn from the one
of these lines to the other are equal.
Parallel lines by some are said to be those which
make equal angles with a third line towards the same
parts, or make the exterior angle equal to the interior
and opposite; this definition requires only that it should
be proved that all the straight lines which are equally
inclined to one given straight line are equally inclined to
all the other straight lines which fall upon them.
N
Ordinates are lines in a parabola, RPQ, which are
drawn parallel with the base, as GH, IK, LM, NO, P
and are derived from the Latin ordine. A straight line
drawn from any point in a curve perpendicularly to
another straight line, which is called the absciss, is an
ordinate. The absciss and ordinate together are called
the co-ordinates of the point. The situation of a point
in a plane is determined, when its distances from two
straight lines in the same plane are known; and when a
series of points are so situated in respect of each other
that the co-ordinates of each have the same mathematical
relation, they form a curve, the nature of which is ex-
pressed by the relation of the co-ordinates.
Horizontal line, or apparent line of level, is that which
cuts or touches at right angles a line supposed to
pass through the centre of the earth; the line ab,
resting on the perpendicular cd, is horizontal, and all
lines parallel with this are deemed horizontal.
α
L
G
Fig. 619.
Fig. 620.
R

d
H
K
V

736
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Level line is that traced out by the instrument made
use of by bricklayers and other artisans; the face glis
level when the plummet hanging at e falls perpendicular
over a line traced to f, which is set out at right angles
with it; the line of true level is, however, a curved line,
which is at all points equally distant from the centre
of the earth; for example, in a length of 5000 feet,
an allowance must be made of nearly six-tenths of
a foot, to reduce the line levelled to its true level.
The plane of the sensible horizon is indicated in two
manners, first by the direction of the plummet or plumb
line, to which it is perpendicular, and by the surface of
a fluid at rest: levels are therefore formed either by
means of the plummet line, or by the use of a fluid applied
in an instrument made to contain it.
The Gunner's Level is a triangle with a scale, on which
the plumb line falls; by which arrangement the inclin-
ation of a straight line to the horizon can be measured.
The plummet hangs from the point where the two equal
legs of the level join at right angles, and this plays over
a quadrant that is divided into twice forty-five degrees
from the middle; so that when the plane on which the
ends or legs of the level rest is horizontal, the thread of the
plummet falls over zero; when it falls over any other
point, the degree marked on the scale indicates the in-
clination of the line to the horizon.
Diagonal line, as that in the figure ABCD, which
is drawn from A to C, cutting it into two parts, and
dividing the rhombus into equal portions.
Master Line is a term given to that which is set out or
boned through a country or field to be mapped, (this
latter technical expression being possibly derived from
the French word borner, to limit or confine within
bounds,) and from which spring a number of triangles or
other figures. IF is a base or master_line, being the
longest which can be traced in the plot E F G H I.
The use of a map is to exhibit the boundaries of a
country, and the relative position of the several parts,
in reference to their just and proper proportions; this
may be done very accurately on a globe, but without the
same spherical surface; it is not possible to represent
any considerable area in such a manner that the dis-
tance of places shall retain the same proportions which
they have on the globe; for small maps, or the plans
of an estate, lines may be boned through for the con-
struction of angles or other figures without difficulty.
Heights.It is highly important that we should have
the means of determining accurately the relative altitudes
of points on the earth's surface: when it is required to
ascertain the height of one point or station relatively to
another, and also the relative heights of a number of
points above a common horizontal plane, as for tracing
the line of a railway, levelling is practised.
The height of a figure is a perpendicular let fall from
its highest point, as QT in the triangle QRS, or the
line ab in the inclined pyramid c.

E
Y
D
Fig. 621.

Fig. 622.
Fig. 623.
Y
Sa
b
Fig. 624.
M
с
C

F
N
P
H

R

Line of heights is that which descends from the top to
the bottom of a building; OP, for instance, is such a
line, from whence the observer, placed with the instru-
ment YM, is enabled to mark out at N, or any other point, a determined distance or
measurement.
Scales are right lines of any length,
divided into equal parts; the scale A B,
for instance, is set out or divided into
50 feet, and one portion attached sub-
divided into feet; the other is marked
Fig. 625.
100
200
300
400
500
10
Fig. 626.
30
40
50
with 500, each portion containing 100, and this again subdivided into tens.
A
CHAP. VIII.
787
GEOMETRY.

Plans always have a scale attached to them; in that of
the fort Fits length and divisions are made with refer-
ence to one of its sides, as H or I, which may be
supposed either 50 or 500 feet in extent.
In the figures
M, N, the scales K and L may be made to agree with
the length of either of its sides, and by reducing or
enlarging the scale, the figures to be traced may be made
larger or smaller, care being taken to set out the angles
correctly.
Working drawings are usually upon a large scale, as
they are intended for the artizans to set out their respective
labours; they should be of a size to express accurately the
parts of the machine or other object to be executed: an out-
line is generally sufficient for the purpose; sometimes a
quarter scale is required, where the parts are intricate or
small, at other times a 12th or 24th part of the real size:
for fortifications or earth works the plans are made upon
a scale of so many chains or feet to an inch, and when
laid down accurately, they may be diminished or in-
creased by adopting different scales. A very easy and
simple method of performing this is by covering the
designs with squares or lines parallel and at right angles
with each other; when the plan is irregular, as that
shown at M and N, it is necessary to bound them by a
square, or, taking the longest sides for a base line, to
construct one upon it, and then set out accurately all the
angles, or, according to the degrees they measure, a dia-
gonal line may be drawn from the points of the two
extreme angles, and then parallelograms and squares may
be constructed on each side of it to embrace the other
portions of the plan, and afterwards the figure which
bounds the whole may be reduced or enlarged; the sub-
ordinate parts will all have the same relative value to
each other, and one will be a fac-simile of the other,
though on a different scale.
Wavy or curved Lines rise and fall, as indicated at
ACEDFB, and when a circle is struck from the centre
V, the line N is a curve.
We may suppose the surface of the earth to present a
wavy or curved form, which it is required to ascertain;
this is performed, as we shall hereafter see, by means of an
instrument called the level; the wavy line is measured
from another, which is set out by means of upright staves
and rods with great accuracy, and where the inequalities
are numerous, it is requisite to make the measurements
frequently; when the eye of an observer is placed
on a level with the plane which presents an undu-
latory surface, it is difficult to measure the rise and fall
without establishing a number of fixed points, or placing
in each hollow a perpendicular staff that can be seen
from the station point; if these rods were all so cut
that the eye could see their tops in one continued line, the
level might be established, or the inequalities measured
sufficiently for ordinary purposes, but where great nicety
is required, instruments carefully adjusted are necessary,
as the eye is easily deceived in long distances.
Spherical Lines are those which may be traced on the
globe L.
Spiral Lines proceed with a regular and gradual en-
largement of distance round the volute P to the ter-
mination at O. This name is given to all those curves
which have the peculiar property of receding from
the centre while they continue to revolve about it;
there are many varieties, as the equable, the hyperbolic,
the logarithmic, spiral, and others: the first was ably
treated upon by Archimedes, who also showed the rules
by which it could be generated.
H
Fig. 627.
F

M
Scale K
N
1
Scale L
Fig. 628.

B
D
C
F
E
Fig. 629.

N
Fig. 630.

Fig. 631.
Fig. 632.
L

P
3 B
738
BOOK IT.
THEORY AND PRACTICE OF ENGINEERING.
Of Angles. -Two right lines drawn from the same
point, and diverging from each other, form an angle; the
two lines A B and CB form the angle ABC, because
these two lines touch each other, or cross at the point
B. An angle is commonly designated by three letters,
and it is usual to place in the middle letters which mark
the point of divergence, which in this case is B.
At the point D several angles unite, as the angle
EDF, FDG, GDH, HDI.
The magnitude of an angle does not depend on the
lines which bound it, but upon their divergence from
each other; the lines which proceed from the point
D though continued to an indefinite length, do not in
ary degree alter the angle; it is only greater than
ar other when lines of equal length are placed at a
greater distance apart.
Opposite Angles are those formed by the intersecting of
two right lines; the angle RPO is opposite the angle
SPQ, and for the same reason the latter is opposite the
former.
The angle LIM is not opposite to that of MIN, be-
cause it is not formed by the same prolonged lines.
Euclid defines a plane angle to be the inclination of two
lines to one another which meet together, but are not
in the same direction: Apollonius, however, gives a
somewhat more obscure definition; he calls it the col-
lection of space about a point. Euclid's idea in strict-
ness can only apply to acute angles, and from it we can
form but very inadequate notions of angular magnitude.
The angular point B, it must be remembered, is always
considered to be the point of the angle ABC.
The solid angle is formed by the meeting of two plane
angles, which are not in the same plane, in one point;
such magnitudes admit of no accurate comparison one
with another; no multiple or submultiple of such angles
can be taken, and we have no method of expounding the
ratio which one bears to another; on this account our
reasoning is limited to the plane angles which contain
them.
The visual angle is formed by two rays of light, or
two straight lines drawn from the extreme points of an
object to the centre of the eye, which we may suppose
at B.
A Curvilinear Angle is formed by two curves, as the
cog of a wheel; the lines DEF form such an angle struck
from the centres F and D.
A mixed Angle has a curved side united with a straight
line, as GH I.
The Central Angle of a figure is that which is formed
on the centre of a figure by the intersection of two lines;
the angle LKM is a central angle, because it is formed
from the centre of the pentagon POMLN, by the
meeting of the two right lines LK and MK.
The Angles of a Polygon are those formed by the sides
of the figure, as NLM.
The Angle of a demi-polygon is that which is made by
the line drawn from the centre and the side, as K ML.
The Angle of a Circumference is that of which the
summit bases on the circumference, as LMN.
The opposite Angle to a side is that which is over against
the side which serves for a base, as LKM.
A Salient Angle is that whose point is towards the
outside of the figure, as OPN.
A re-entering Angle is that whose point is towards the
inside of the figure, as OQ M.
Adjacent Angles are those formed at the extremities of
the same side, as KML and KLM.
A
R.
C
Fig. 633.
F
Fig. 634.
Fig. 635.
P
E
ID
Z
H
B


(
Ι
M

Fig. 636,
E
F
Fig. 637.
G
Fig. 638.
M
Fig. 639.
P
K
H
B


CHAP. VIII.
739
GEOMETRY.
•
An Inaccessible Angle is formed by two lines which meet in
a point, as A B C, the point of the pyramid B being supposed
inaccessible, or which cannot be reached so as to measure it.
A solid Angle is the point where more than two planes or
superficies of a solid touch each other. The point E is a
solid angle between the three faces H, I, K: all points or
angles of solid rectilinear bodies, of whatsoever figure, are solid,
as more than two faces meet each other.
The cube is bounded by six squares, and constitutes
one of the five regular Platonic bodies, which being placed
beside each other fill up the space about a point; there are
here eight solid angles formed by the junction of the six
planes. The duplication of this solid, or the finding of the
side of a cube, containing exactly twice as much as another,
was for a long time a problem of difficulty, and which cannot
be solved by means of the straight line and circle, which were
the only lines the ancients made use of in constructing their
geometrical solids.
The Opening, or Size of an Angle, is measured by the num-
ber of degrees of the circumference of a circle contained
between the two sides, the circle always having the summit
of the angle for a centre. LMN is of 60 degrees opening,
because there are so many contained between the lines LM
and N M, or 60 parts out of 360 of the circumference, which
is described, taking M as a centre.
no 1
--
2
In geometry generally, the term right is applied to such
angles as have one line perpendicular to the other, as
where the angle is one of 90 degrees. The Platonic
school of mathematicians was frequently employed to dis-
cover rational numbers, which should designate the sides of
a right-angled triangle: Pythagoras gave the formula n
n² + 1
and n
where n is odd: Plato gave 2n, n²— 1, and n² + 1
2
where n is either odd or even. For practical purposes the
numbers 3, 4, and 5, effect this: suppose P Q to be 4 feet,
PO 3 feet, and the distance from Q to O to be 5 feet, then we
know that we have a right angle, for if to the square of 4 we
add the square of 3, and then extract the square root, we
obtain 5.
The Angle OPQ is for the same reason one of 90 degrees,
because the distance between OP and PQ is a quarter of the
circumference of the circle which encloses it.
A Right Angle is that made by a right line falling perpen-
dicularly on another, and which contains in its opening a
quarter of the circumference; ABC is a right angle, because
the line AB falls perpendicularly on that of BC; a right
angle is square, and is used as such by all workmen.
The square G, formed with either wood or metal,
enables us to set out very accurately a right angle, or any
other figure which has its sides perpendicular to the base; for
drawing we have one limb fixed into a cross piece that gives
it the form of a T: with such a square we can construct, by
means of a drawing board nicely adjusted, lines both parallel
and perpendicular.
The square used by mechanics is formed like an L, and
should be a true right angle; this can always be ascertained
by drawing a line along the edge of the blade, and then re-
versing it; if the line and blade in the new position correspond,
the square is pronounced to be true.
A rule or square, formed of wood or ivory, like a right-
angled triangle, is used for drawing perpendicular lines; this
is laid with one side to the given line, and the perpendicular
required is drawn by the edge of that at right angles to the
first.
T squares are sometimes made of two equal pieces, kept
together by a screw; the blade is fixed into one of these, flush
Fig. 640.
F
H E
1
K
Fig. 641.
I,
B

N
M
Fig. 642.
P
Fig. 643.
Fig 644.
E
1
2 L
C
G
F
Fig. 645.
Ꮐ




3 B 2
740
THEORY AND PRACTICE OF ENGINEERING. BOOK IL
with its inner face: if the other be applied to the edge of
the drawing board, the former, with the blade, can be turned
on the screw as a centre to any angle; the screw being
then tightened, parallels forming that angle with the side
of the board can be drawn; and, if applied to an adjoining
side, the blade will be at a right angle to its first position ;
these bevel squares are exceedingly useful to architectural
draughtsmen and engineers.
An Obtuse Angle is greater than a right angle, and con-
tains more than a quarter of a circle or 90 degrees; the
angle HIK exceeds the angle LIK, or that of the quarter
of a circle described from I as a centre.
The magnitude of an angle does not depend on the lines
by which it is formed, but, as has been observed, upon their
distance from each other; the obtuse is therefore greater than
the acute, in consequence of the lines which constitute it
being farther apart, or diverging more than those of the
acute the legs of a pair of compasses may be made to
exhibit this; when separated but little, we have an acute
angle, and opened more and more we obtain the obtuse,
the rule joint upon which the limbs move being considered
the point of the angle.
When a point of the compasses is applied to N, and
a circumference described, the arc contained between the
lines which diverge from the centre, as M and P, serve to
measure the angle.
An Acute Angle is less than a right angle, as M N O, be-
cause also it is less than a quarter circle or 90 degrees.
A Right-angled Triangle has two sides at 90 degrees
from each other, and the line which unites them is called
the hypothenuse, as KL.
An Obtuse-angled Triangle is that which has its angle
greater than a right one.
An Acute-angled Triangle is that which has its angle less
than a right angle: consequently an equilateral triangle
is acute; in general every triangle has two acute angles.
The triangle NOP is obtuse angled; ABC an equi-
lateral triangle: RQS an isosceles triangle; FED a right
angle; and LMK a scalene triangle.
Rectilinear Figures are those which are contained or
bounded by right lines, as TKL M.
In the square the right lines which form the sides fall
upon parallel lines, and make the alternate angles equal, and
the lines being perpendicular to one of the two which are
parallel, it necessarily follows it must be so to the other.
In a quadrilateral figure the surface is comprised within
four equal right lines, which are called its sides, with all its
angles right ones.
Curvilinear Figures are such as are bounded by curved
lines, as NOP.

All
A plane figure contained by one line, called the circum-
ference, is such that all straight lines drawn from the
centre to it are equal to one another. The straight line
and the circle are the only figures admitted into plane or
elementary geometry, all questions in mathematics depending
on the intersections of straight lines with straight lines,
straight lines with circles, or of circles with circles.
figures are formed by the intersections of planes with solids,
and are termed problems, for the understanding of which
it is necessary to have them bounded by straight lines and
circles. The circle is a very important figure in trigonometry
or the measurement of angles, and the ratio that the cir-
cumference bears to the diameter is a calculation that long
exercised the heads of the learned: in the two concentric
circles of the figure, their relative circumferences are in pro-
portion to their diameters, as NO and P.
C
H
Fig. 646.
Fig. 647.
M
K
Fig. 648.
N
Fig. 649.
A
}'
N
P
M
X
L
K



B
R
Fig. 650.
D

K
E
Fig. 651.
L
Σ
M

K
T
Fig. 652.

N
P
Cont
Fig. 653.
CHAP. VIII.
743
GEOMETRY.
Mixed Figures are bounded both by lines and parts.
of eircles, as QR S.
Regular Figures are all formed of equilateral and equi-
angular polygons; circles can be described within and about
such figures; such can also be explained by geometrical
methods in particular instances. General expressions for
the radii of the circles explained within and about them,
and for their areas and angles can be given: thus if we
denote the number of the sides of the polygon T by the
expression n, and if uº represent the nth part of 1800, we
shall have a being the side R={} a cosec. uº, r={}; a cot. uº,
area= in a³ cot uº.
That figure which has its sides all of equal length, and
its angles equal, as those of the hexagon T, &c., is regular.
Figure, in geometry, is often used in two different
senses: in one it implies a space bounded on all sides,
whether by lines or planes; in another it signifies the
representation only of the object of a theorem or problem,
and enables us to render its demonstration or solution
more easily understood.
An Irregular Figure is that whose sides are unequal,
and its angles various, as V, the sides XY, YZ, Z5,
being all unequal.
Triangles are figures contained within three sides,
and form three angles, as A B C.
The following are some of the properties of plane tri-
angles: the greater side is opposite the greater angle, and
the difference of any two is less than the third side.
Compasses have been formed with three legs for the
construction of maps, by which three points can be taken
off at one time; these have two legs that open in the
usual manner, and the third made to turn round an ex-
tension of the central pin of the other two, besides having
a motion of its own on the central joint.
A Rectilineal Triangle is formed by three right lines, as
ABC.
A Spherical Triangle, T, is that which has its three
sides curved.
Equilateral figures inscribable in circles are necessarily
equiangular, but the converse does not always hold true:
when the number of sides is odd, the equiangular figure
inscribed in a circle is always equilateral; but when the
number of sides is even, they may either be all equal, or
one half equal to each other, and the other half equal to
each other, though not to the former, the two sets being
placed alternately this was well understood by the
masons of the middle ages, as we see expressed
in the tracery of the windows, and the mosaic patterns
they have left us on the pavements and walls of their
several buildings. Pisa is rich in such illustrations, and
it seems to have been a favourite study to construct equi-
lateral and other angles within the circle when the cathe-
dral in that city was built.

:
An Equilateral Triangle has its three sides equal,
as DEF.
An Isosceles Triangle has two of its sides equal, and
of the same length, the third being either greater or
less: V and Y are mixed triangles. Among the pro-
perties of the isosceles triangle is one in particular, viz.
the angles at the base are always equal, and as the demon-
stration given by Euclid is the first, and somewhat in-
tricate and difficult for learners, it has been termed the
pons asinorum.
A Scalene Triangle has its three sides unequal, as GHI.
A cone or cylinder is said to be scalene if its axis is
inclined towards its base; but the term oblique would be
more appropriate.
R
Fig. 654.

Fig. 655.
X
Fig. 656.
C
Fig. 657.
Fig. 658
V
T
A
T
D
F
E
Fig. 659.
Fig. 660.
H
Fig. 661.
Y
V
B
Z
*



3 B 3
742
BOOK 11
THEORY AND PRACTICE OF ENGINEERING.

triangle are equal to
From the summit of
The three internal angles of every
two right angles, or to 180 degrees.
the angles NOP describe circles, each divided into 360 de-
grees, and if we add the degrees contained between the
lines of the three angles, as PNO 68, NOP 60, O P N 52,
we shall find the contents of the three angles together 180
degrees, or the double of two right angles.
A Common Triangle is that which is comprised between
two triangles, of which it contains an equal portion, and
which has for its base the same as that of the two tri-
angles comprised between the same parallels. The triangle
GHI is common with respect to YHI and ZIH, because
it is comprised between two triangles
FIGURES OF FOUR SIDES, OR QUADRILATERALS: ——
A Square has four equal sides, and four right angles, as
A B C D.
In the rectangle ABCD, the side B C is parallel to the
side A D, and the side A B parallel to the side DC. The
line A B is perpendicular to the two lines BC, AD, the
two other lines are therefore parallel: in like manner the
line A D is perpendicular to the two lines AB, DC; the
two lines A B, DC, are therefore parallel.
A Parallelogram has four right angles, but its sides are
unequal, two being shorter than the others, as E F G H.
The opposite sides of rectangles are equal; and a line
falling upon parallel lines, as we have seen, make the alter-
nate angles equal.
By superposition the relative proportions of the square
and parallelogram can be ascertained; this method was
very much used by the ancient geometricians: when two
figures so applied are found to coincide and to fill up the
saine space, we infer that they are equal each to each.
When Euclid endeavoured to prove that two triangles
which have two sides of the one equal to two sides of the
other, and also the angles contained by those sides, equal, he
supposes one triangle to be placed over the other : on such
a principle we compare rectilineal figures, for if it be shown
that the square when placed over the parallelogram occupies
only two-thirds of that figure, we infer that it requires half
entirely its area in addition to cover it. It is easily de-
monstrated also that any two equal rectilineal figures may,
by resolving them into parts, be applied by superposition
one above the other, so as entirely to agree in quantity.
A parallelogram is bisected by each of its diagonals, for
the triangles into which it is divided are equal to one another:
and, consequently, if one angle of a parallelogram be a right
angle, all its angles will be right angles. Hence we learn that
a rhombus has all its sides equal to one another; that a rect-
angle has all its angles right angles; and that a square has
all its sides equal, and all its angles right angles.
Euclid has clearly shown that the opposite sides and
angles of parallelograms are equal, and that their diagonals
bisect one another; and, conversely, if in any quadrilateral
figure, the opposite sides be equal, or if the opposite angles
be equal, or if the diagonals bisect one another, that quad-
rilateral shall be a parallelogram. The same writer has also
proved that the complements of the parallelograms which
are about the diagonals of any parallelogram are equal to
one another.
A Rhombus has its four sides equal, but not at right
angles, as KL MN.
The rhombus has the peculiar property of its diagonals
angles; and therefore whenever a quadrilateral has all its
bisect one another at right angles, it is a rhombus.
P
52
Fig. 662.
Y
G
380
N
68
H
Fig. 663.
A
D
Fig. 664.
E
H
Fig. 665.
K
N
Fig. 666.
R
Fig. 667.
L
60
C
P
G
2
א




crossing each other at right
sides equal, or its diagonals
A Rhomboid has its opposite sides and angles equal, as OPQR, without being equi-
lateral or rectangular. The diagonals of all quadrilaterals are straight lines, which join
the opposite angles, and consequently would divide the figure into four triangles.
CHAP. VIII.
GEOMETRY
743
A Trapezium is any other figure whose opposite four sides
are not parallel, as ABCD.
A Scalene Trapezium has two of its sides parallel, but its
four sides unequal, as E F G H.
A Rectangular Trapezium has two of its sides parallel, and
two right angles, as I KLM.
An Irregular Trapezium has none of its sides parallel, as
PQNO.
When one pair of opposite sides, as in the figure A B CD,
are parallel, it is called a Trapezoid, and
called a Trapezoid, and among the remarkable
elementary properties of this trapezium are the following
The sum of any three sides is greater than the fourth side:
the sum of the squares of the diagonals is equal to the sum of
the squares of the sides, and four times the square of the line
joining the middle points of the diagonals. The lines joining
the middle points of the sides form a parallelogram; and if the
figure can be inscribed within a circle, the sum of each pair of
opposite angles in two right angles, and the sum of the rectan-
gles of each pair of opposite sides, are equal to the rectangle of
the diagonals.
When a diagonal is drawn in a parallelogram, and two other
right lines parallel with the sides are made to cut it, the two
parallelograms which the diagonal does not cut are called the
supplements or complements. In the figure RSTZ the pa-
rallelograms RXY and XVT are such.
Land surveying requires that every plane figure should be
resolved into some of the forms we have described, or con-
sidered as composed of a certain number of triangles; for com-
puting the area of which it is necessary that we should have
the length of at least one side; and when this is ascertained,
together with any two of its other parts, those remaining and
the area may be computed by the rules of trigonometry.
Polygons which are regular have their angles equal each to
each, because they are contained the same number of times in
the same number of right angles, and their sides about the
equal angles are to one another in the same ratio.
If the circumference of a circle be divided into any number
of equal parts, the chords joining the points of division
include a regular polygon inscribed in the circle, and the
tangents drawn through those points include a regular poly-
of the same number of sides circumscribed about the
gon
circle: therefore when we have a regular polygon inscribed
in a circle, by drawing tangents through the angular points, we
can readily construct another on the outside.
Pentagon is bounded by five sides, and having within it as
many angles; it is called regular when they are all equal, as the
figure A.
In the regular pentagon, if we inscribe within it a triangle,
whose base corresponds with one side, and its point that where
two opposite sides meet, we shall have an isosceles triangle:
in such a triangle we have the angles of the greater double
that of the less.
An Irregular Pentagon is where the sides and angles vary,
as B.
Hexagon is a rectilinear figure of six sides and as many
equal angles; this is called also irregular when the sides are
unequal, as in the figure D.
The side of a regular hexagon is equal to the radius of the
circle in which it is inscribed, and it will also be found
that the side of a regular decagon is equal to the
greater segment of the radius divided medially,
and the side square of a regular pentagon is greater
than the square of the radius by the side square of a
regular decagon inscribed in the same circle.
hexagon is composed of six equilateral triangles, and
its figure was much adopted formerly by architects,
from the facility which it affords for subdivision.
The
M
P
D
B
A

Fig. 668.
f
H
E
G
Fig. 669.
Fig. 670.
N
Fig. 671.
R
Y
Fig. 672
Fig. 673.
Fig. 674.
B
A
X
C
D
Fig. 675.
S
C


T
K
L





3 B 4
744
THEORY AND PRACTICE Of engineeriNG. Book II.

Heptagon is bounded by seven sides, E, and as many equal
angles; it is called irregular, F, when these are not equal.
Heptagonal numbers are those where the difference of
the terms of the corresponding arithmetical progression is
5. Thus arithmeticals being called 1, 6, 11, 16, the hep-
tagonals written under them would be 1, 7, 18, 34, &c., the
latter being formed by the continual addition of the terms
of the first: among the properties of these numbers is one
very remarkable, viz. that if any heptagonal number is
multiplied by 40, and 9 added to the product, the sum is
a square number.
Octagon is bounded by eight sides and angles, as A, and
when these vary it is termed an irregular one, as B. It
has been found that any regular figure, which has the
number of its sides denoted by 2+1 and prime, may
be inscribed in a circle without any other aid than that of
plane geometry, that is, by the intersections of the straight
line and circle only; and it is clear that by dividing the
subtended arcs into two, four, or more equal parts, a re-
gular figure of twice four times, &c., the number of sides
of any may be inscribed. An octagon for instance may be
drawn by bisecting the arcs which are subtended by the
sides of a square.
Nonagon is bounded by nine sides, as C, and has nine equal
angles; when irregular, as the figure D, these all vary.
This figure, by some geometricians called the Enneagon,
has not yet had any rule laid down for its construction,
and can only be inscribed approximatively.
Decagon has ten equal sides and angles, E; when they
vary, as in the figure F, it is not regular.
This figure is the double of the pentagon; and Euclid
has shown in his fourth book of the Elements, that the
side of a regular decagon is equal to the greater segment
of the radius of the circumscribing circle, divided by a
medial section, or so that the rectangle contained by the
whole radius and one of the parts is equal to the square
of the other part.
Undecagon has eleven equal sides and angles, and this
may be the form of such a figure as H, which also has
eleven sides, arranged neither within a circle nor after any
particular form.
This figure, also termed the endecagon, has no regular
rule laid down for its construction; it can only be set out
or inscribed within the circle by approximation.
Duodecagon has twelve sides and angles equal, and is
regular when so drawn as H, and irregular as shown in the
side figure.
A regular Polygon has all its sides equal, and likewise all
its angles equal; and the centre is the same with the
common centre of the inscribed and circumscribed circles,
and the perpendicular, which is drawn from the centre to
any one of the sides, is called the apothem: if any two
adjoining angles of a regular polygon be bisected, the inter-
section of the bisecting lines will be the common centre
of two circles, the one circumscribing, the other inscribed
in the polygon. The area of a regular polygon is equal
to half the rectangle under the perimeter and apothem.
An Equilateral Figure has all its sides equal, as in the
square, pentagon, and hexagon, A, B, C.
Those figures of four, five, and six sides when lines are
drawn from their several angles to the centres, or when
they are inscribed within circles, may have their separate
and relative values easily calculated.
Equiangular Figures are those which have their relative
angles equal; the figures RST and V X Y are so, the angle
R being equal to the angle V, the angle S to that of Y,
an:l that of T to X.

F
E
Fig. 676.

B
Fig. 677.
C
Fig. 678.
A

D

E
F
Fig. 679.

H
G
Fig. 680.

H
H
Fig. 681.

B
Fig. 682.
R
T
Fig. 683.
10
A
V
C
CHAP. VIII.
745
GEOMETRY.
Equal Figures contain equal quantities: the square G,
for example, contains as much as the parallelogram D.
Equilateral figures are those which have their sides
equal to each other, and such, when inscribed in circles,
are consequently equiangular, but the converse does not
always hold true.
In the square F, by drawing lines across from the
divisions made on the respective sides, it may be made
into nine equal parts, and if the length of one was set out
equal to the divisions in G or D this figure would be in
proportion of nine to four when compared with them.
Isoperimetrical figures are such as have equal perimeters
or circumferences. Problems which relate to them are
extremely difficult of solution, and require a peculiar
analysis; as, among curves having the same length, to
determine that of which some assigned property is a
maximum or a minimum; for example, among those
having the same perimeter, to find that which has the
greatest area; this constitutes one of the simplest ques-
tions of the kind, and the curve to which the property be-
longs is proved by elementary geometry to be a circle.
In the figure G, the circumference equals the three
sides of that shown at E, as well as the four of F in the
preceding diagram.


:
Figures are similar when their relative angles are
equal the side LK is to KM as ON is to NP, and
they are said to be similar when their angles and sides
exactly agree, as in the figure Q.
Centres are the points in the middle of a figure: A,
for example, in the pentagon BCDEF.
Centre, in geometry and mechanics, has a variety of
significations, and is numerously applied. The centre of
a circle or an ellipse is the middle of any diameter; centre
of a curve is the point where two diameters intersect each
other; and in mechanics we have to treat of the centres
of attraction, equilibrium, gravity, oscillation, &c.
The centre of conversion is the point in a body about
which it turns when a force is applied to any part of it,
or unequal forces to its different parts. A rod, struck at
one of its extremities in the direction perpendicular to
its length, will turn it round, but there will be one point
in it which remains at rest, or about which the other points
turn; this is the centre. The point or fulcrum upon
which a lever turns is its centre of equilibrium.
H
The Centre of an irregular figure is that marked by a S
star in the middle of HIKLMNOPQRS, or there
may be found the centre of each moiety of the figure, as
GT, and then the star taken as a mean.
The Point V is the centre of the circle XZ910, it
being equidistant from the circumference in every part.
The Foci or centres of an ellipsis are the points by which
it is described, as 1 and 2.
The focus of the parabola is a point in the axis, having
this property, that a radius drawn from it to any point in
the curve makes the same angle with the tangent at that
point that the tangent makes with the axis. Hence a
ray of light proceeding from the focus, and reflected by
the curve, proceeds in a direction parallel to the axis; or
if parallel rays fall on the concave side of a parabola, they
are reflected into the focus.
In the ellipse the two foci are situated in the greater
axis, at equal distances from the centre, and if from both
foci straight lines be drawn to the same point in the cir-
cumference, the two lines make equal angles with the
tangent at that point: a ray of light, therefore, issuing
from the one focus is reflected by the curve into the
other. There is a similar property in the hyperbola, but
Ꭱ
J
3
3
G
F
3
12
3
Fig. 684,
12
G
E
12
Fig. 685.
I
Fig. 686.
K
M
Fig. 687.
R
C
F
A
E
D
Fig. 688.
H
•
D


N
P



L
K
M
G
T
N
Fig. 689.
X
Fig. 690.
3
Fig. 691.
V
9
P

N

746
THEORY AND PRACTICE OF ENGINEERING. BOOK IL

with this difference, that one line falls on the concave and
the other on the convex: or, the two lines drawn from
the foci to any point in the hyperbola, make equal angles
with the tangent on its opposite sides.
The Centre of a globe, AZ 10, is that point which is
equidistant from every part of its surface. The point Y is
the pole of the circle 4.
Lahire was the first who proposed the globular pro-
jection, or the delineation of the terrestrial surface or any
part of it on a plane; it is important that this subject
should be thoroughly understood. The projection of any
circle on the sphere, which does not pass through the eye,
is a circle, and circles whose planes pass through the eye
are projected into straight lines. The angle made on the
surface of the sphere by two circles which cut each other,
and the angle made by their projections, is equal.
Gnomonic or central projection is that where the eye is
situated at the centre of the sphere, and the plane of pro-
jection is a plane which touches the sphere at any point
assumed at pleasure: the point of contact is called the
principal point, and the projections of all the other points
on the sphere are at the extremities of the tangents of the
arcs intercepted between them and the principal point.
As the tangents increase very rapidly when the arcs ex-
ceed 45°, and at 90° become infinite, the central projec-
tion cannot be adopted for an entire hemisphere.
The Centre of a geometric square is 11, or the point
from which the greater circle is struck.
And the Centre of a rule S is in A, or the pivot on
which it turns.
The Circumference is that line which bounds a circle
whose centre is A.
As we have seen there is a point in a circle, from
whence a line may be drawn equidistant around it, and
which is the circumference; the rectification of the circle,
or the determination of the ratio that the circumference
bears to the diameter cannot be expressed in finite numbers.
Archimedes in his treatise De Dimensione Circuli showed
that they were as 7 is to 22, or 113 to 355: De Lagnay
found when the diameter was 1, that the circumference
was 3.14159265358979323846264338327950288.
areas of all circles are to one another in the ratio of the
squares of their diameters, or the area is one-fourth of
the circumference: Archimedes makes it nearly in the
proportion of 14 to 11: the ratio the area of a circle bears
to the square of its diameter has been thus expressed,
2 × 4×4 × 6 × 6 × 8 × &c.
3 x 3 x 5 x 5 x 7 x 7 x &c.
8 24 48
The
which is the same as X X x &c; the denominators
9 25
25 49
being the square of the odd numbers, and the numerators
differing from the denominators by unity.
Circles have similar circumferences when their dia-
meters or radii are equal, as in those of CD and F G, or
VB equal radius V E.
The greatest Circumference of a sphere is that which
is struck from the pole T as its centre, and which cuts
it into two equal parts, the plane passing through the
centre H.
The curved surface of a Sphere is equal to the rectangle
contained by its versed sine, and the sphere's circumference:
10
Fig. 692.
11
Fig. 693
Fig. 694.
Fig. 695.
B
Y
5
A
C
V
Fig. 696.
E
F
כדי
Fig. 697.
1
T
Fig. 698.
H
A
G
V
N


A




for the fluxion of the surface is obviously equal to the rectangle contained by the
fluxion of the circumference, and the circumference of the circle of which the radius is the
sine; it varies therefore as the sine; but the fluxion of the cosine, or of the versed sine,
varies as the sine, consequently the surface varies as the versed sine. Now where the
tangent becomes parallel to the axis, the fluxion of the surface becomes equal to the rect-
angle contained by the sphere's circumference and the fluxion of the versed sine.
CHAP. VIII.
747
GEOMETRY.
The Sphere is divided then into two equal portions, as
shown by the sections H of the globe K.
The sphere is described by the revolution of a semi-
circle about its diameter, or it may be defined as a body
bounded by a surface of which every point is equally dis-
tant from the centre. The curve surface of either of
these zones or half globes is equal to twice the area of
one of its great circles, or rather of the section made by
the plane passing through the centre: the curve sur-
face of a zone or portion contained between two parallel
planes is equal to the curved surface of a cylinder
of the same height with the height of the zone, or the dis-
tance between the planes, and of the same diameter
with the sphere, from whence we learn that the whole
surface of the sphere is equal to the curved surface of the
circumscribing cylinder.
The solid content of a globe is equal to that of a
cone whose altitude is the radius, and whose base is
equal to the surface of the sphere; hence the content of
the sphere is one-third of the product of its radius into
its surface, and the sphere is also equal to two-thirds of
its circumscribing cylinder. Hence the cone, the sphere,
and the cylinder, whose diameters and heights are equal,
are in the proportions of 1, 2, and 3, or the cylinder
is equal to the sphere and cone taken together; the cone
is equal to a third part of the cylinder, and the sphere is
double the cone.
In the Globe P the great circle dotted at M, the other
at N, and the outer circumference QR P, are all equal
to one another, because the planes by which it is cut
pass through its centre.
The globe is by this means cut into four equal parts,
and the content of each, as well as their superficies, may
be easily ascertained.
A small Circle inscribed on a globe, as that shown at
B on the globe A, must be struck from another centre.
Globular projection, or the representation of the
boundaries of planes which pass through the globe at
right angles with its diameter, belongs more immediately
to spherical geometry: a circle whose plane passes
through its poles is called the meridian, and which cuts
the planes of the equator, and all circles parallel to it at
right angles.
The plane of the horizon of any place touches the
earth's surface, and divides the whole expanse of the
heavens into two hemispheres. The earth's surface was
by the ancient astronomers divided into five zones,
founded on the different lengths of the longest day, as we
proceed from the equator towards either of the poles :
these were also denominated climates, and were each of
such a breadth that the longest day at the boundary
nearest the pole exceeded the longest day at the boundary
nearer the equator by a certain space of time, as half an
hour or an hour: within the polar circle the climates
were supposed of such a breadth as to make the longest
day at the opposite sides differ by a month.
The Circle B of the globe C has its centre in the middle
of the plane D, and the section made is common to both
figures.
Fig. 699.
K

H
P
M
R
Fig. 700.
B
Fig. 701.
Р
Fig. 702.
A
B
L
H



C

H
F
GI
***
Fig. 703.
K
оо


M-
Fig. 704.
Small equal Circles of the same globe have their Fig. 705.
K
N
Q
centres equidistant from its centre. In the globe E the circles F and G are equal to one
another, because they are equally distant from the middle of the sphere. H and I are
also so in the figure HIKL, and the two portions cut off are equal.
An Arc is that portion of a circle which is less than a quarter of its periphery; the
dotted portion EF is an arc of the circle EFGH, as is AD, CB of the other circle
drawn in lines.
The Point K of the arc I KL is the summit, and the line MN, as it touches the point
P of the arc O Q, is also its summit.
748
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

Circles of all sizes are divided into 360 degrees, as F
is the centre of the circle BCD, to which they all
radiate.
Degrees are divisions which may be shown by right
or curved lines, and are here drawn on the circum-
ference of the circle E DC, as well as on the parallelogram,
ADLCBK.
By geometricians degrees are understood to be the 360th
part of the circumference of a circle, or of four right angles:
each of these degrees is divided into 60 minutes, and each
minute into 60 seconds, and we find such a division re-
cognised by the ancients. The Chinese divide the circle
into 365 parts, so that the sun daily describes one of
these degrees.
The French mathematicians in some instances divide
the quadrant or right angle into 100 degrees, and each
degree into an hundred minutes, which suits better their
decimal method of computation. A degree of latitude is
understood to be that distance an observer must advance
along the meridian on the surface of the earth to the north
or south, in order to produce a variation of one degree in
the altitude of the pole; the exact measurement of one of
these degrees has been a study of the greatest interest, as
by it is ascertained the dimensions of the globe itself.
290
At the present day this problem has acquired greater
importance, in consequence of the discovery of the earth's
ellipticity; for it is by the comparison of the lengths of 20
the meridional degrees at different latitudes, that we are
enabled to ascertain accurately its true figure.
The great irregularities of the surface of the earth render
it difficult, but as the length of a degree depends on the
radius of the circle on which it is measured, it will readily
appear that the terrestrial degrees at different places, if
measured on the external surface, must be unequal. To
obviate this, and to reduce all the degrees to the same
radius, the surface of the sea is supposed to be continued
all round under the continents, and to this surface or
level all the measurements are made to refer. The prin-
ciple adopted is the following: two stations being as-
sumed on the same or nearly the same meridian, the
distance between them must be found with great exact-
ness in feet or yards; this being done, the latitude of each
of the stations is then determined, the difference of the two
latitudes being the length of the celestial arc intercepted
between the two stations, and by comparing this with the
terrestrial measure, the number of yards or feet corre-
sponding to a degree is known.
An error of a second made in the measurement of the
celestial arc corresponds to 100 feet on the ground, so that
great nicety of observation is required before it can be as-
certained with precision.
From measurements made at various stations, the di-
mensions and ellipticity of the earth are found to be,
250
A
340
820
350_360_10
C
310
300
290
70
180
B
F
D 90
88
1300
170
280
270
260
260
240
230
130
220
210
E
150
200
760
190 180 170
Fig. 706.

8004
240
310
E F
360
810
230
K
A
B
120
130
230
140
220
210
150
160
200
190.
Fig. 707.

A
D
B
C
Fig. 708.
N

I
H
F
Equatorial diameter
Polar
ditto
Difference of diameters
Feet.
41,843,330
41,704,788
138,542
Miles.
7924.87
Fig. 709.
7898.63
26.24

A Circle is a plane bounded by a single line, called
its circumference: the area dotted is a plane so cir-
cumscribed by a line ABCD struck from the centre
E, and equal circles are those struck from similar radii,
as HNI and FL G.
A Semicircle always contains 180 degrees, and is divided,
as OPQ.
A Protractor is such a figure, and used to set out de-
grees its simplest form is a semicircular limb of metal
60
50
70 80 90 10011020
40
120
30
140
150
160
170
180
20
Fig. 710.
CHAP. VIII.
749
GEOMETRY.

divided into 180 degrees, and subtended by a diameter,
in the middle of which is a notch to mark the centre:
when this notch is placed at the angle of any figure, and
the diameter laid along a given straight line, an angle of
any number of degrees may be marked off.
For complicated or large surveys the protractor is in
the form of the entire circle, having its rim connected with
the centre by four radial bars; over the centre is a disc of
glass, on which two lines are drawn, crossing each other at
right angles, their centre of intersection denoting that of
the instrument. Round the centre, and concentric with
the circle, is fitted a collar, which carries two arms; one
of these has a vernier at its extremity adapted to the
divided circle, and the other a milled head, which turns a
pinion, working in a toothed rack round the exterior edge
of the instrument. The rack and pinion give motion to the
arms, each of which carries a fine steel pricker, which is
pressed down when the protractor is placed in its required
position.
The Quadrant contains 90 degrees, and is divided as
shown at ABC. This instrument, when attached to an
artificial globe, is made of a thin pliable slip of brass, which
when applied to its surface serves as a scale for measuring
distances between points in degrees: it is graduated into
minutes and seconds, and at one end is a nutt furnished with
a screw, by which it can be attached to the brass meridian
of the globe at any point. This point being placed in the
zenith, and the quadrant applied to the globe, its zero
coincides with the horizon, and consequently the altitude
of any point along its graduated edge is indicated by the
corresponding division.
A Segment is a less portion, as DEFG. The segment
of a circle is a part of the area comprised between an arc
and its chord, and segments of different circles are said
to be similar when their arcs have the same ratio to the cir-
cumference of their respective circles, or when they con-
tain the same number of degrees.
A Sector is that portion which by two right lines
passing through the centre, as KI, LI in the figure
VN.
A small sector is indicated by the dotted por-
tion M, and the greater sector by N.
Such a figure is a portion of the area of a circle, bounded
by two radii and the intercepted arc: sectors of different
circles are said to be similar when the sides or radii in-
clude equal angles. The area of a sector is equal to that
of a triangle whose base is equal to the length of the con-
tained arc, and altitude equal to the radius of the
circle.
Cylindrical Ring is bounded by two circles, and void in
the middle, as QO: its section, when solid, is that of a
circle, the area of which multiplied by the length of its
diameter gives its contents.
Ovals have both a long and short diameter, which divide
them into four equal parts: the line CE is the conjugate
and BD the transverse diameters: F, F, are the foci.
The Oval or Ellipse somewhat resembles the transverse
section of an egg, and a variety of forms are given to
it it is produced by cutting the cone by a plane passing
obliquely through its opposite sides. The name of ellipse is
derived from one of its properties ascertained, viz. that the
squares of the ordinates are less than the rectangles under
the respective abscissa and the parameter, or differ from
them in defect.
The ellipse is the curve in which the planets perform
their several revolutions about the sun, and its properties
enter into every investigation where physical astronomy is
concerned. The curve it forms is defined by means of an
C
Fig. 711.
A
10
Fig. 712.
S

20
30
40
50
60
70
80
90
F

E
Γ
Ꮐ
Fig. 713.
K
Fig. 714.
Q
H

N

0
Fig. 715.
1}

F
A
F
Fig. 716.
ن
R
750
Book II.
THEORY AND PRACTICE OF ENGINEERING.
equation between the radius vector, which is a line drawn
from the focus to the curve, and the angle which it makes
with the transverse axis: this is termed the polar equation
to the ellipse.
It is the property of this figure, that if a circle be de-
scribed upon either axis, and from any point of that axis
an ordinate be drawn, both to the circle and ellipse, then
the ordinate of the circle is to the ordinate of the ellipse,
as the axis to the other axis. Hence the whole area of
the circle is to the whole area of the ellipse in the same
proportion, and consequently the area of an ellipse is a
mean proportional between the areas of the two circles
described upon its transverse and conjugate axes.
The Oval G approaches nearer a circle than that shown
at H, the transverse diameter N O being greater than that
of P Q
An Ellipsis may be described by working a thread
round the two foci Y Z, and holding it at S, so that it
may pass TV X S, and thus form a true oval.
A Parabola is a part of an oval cut off by a straight
line, as shown in the figure 4567, or at 123. Spiral
lines, as at S, bent in the manner of a volute, are struck
from a variety of centres.
The parabola is also formed by the intersection of the
cone with a plane parallel to one of its sides, and the
term is applied to all algebraic curves of a higher order
determined by an equation of the form ym+n=amîn.
The curve whose equation is y³ —a²x is called the cubical
parabola, and that which has for its equation y =ax³, the
semi-cubical parabola; this latter curve was the first that
was rectified or found equal in length to an assignable
straight line.
A figure is said to be inscribed within another when it
is bounded, as that of the triangle DEF is by the lines
ABC.
It is extremely useful at times to bound a regular as
well as an irregular figure within another whose dimen-
sions are known or can be easily computed: in an
early Italian edition of Vitruvius, we see the sections
of the cathedral of Milan covered entirely with equilateral
triangles, for the purpose of accurately calculating its
quantity: our freemasons, particularly those who were
not thoroughly skilled in computation, could not adopt
a more simple means of ascertaining the area of a body
than by applying an equilateral triangle to it; six such
would form a hexagon, as the four in the cut do that of
the triangle of similar sides; this figure is capable of sub-
division as well as multiplication, and presuming that the
base of a pillar was comprised within any such form, the
proportion of its relative parts could be easily computed.
Bounding an irregular figure with a parallelogram, and
afterwards dividing it into a number of equilateral tri-
angles, its area could be obtained, and with as much pre-
cision as by numbers.
The Parallelogram LMNO has inscribed within it the
irregular figure HIK.
The Circle may have inscribed within it the square
PQS R
In computing the relative areas of the two figures, we
have to consider only that the diameter of the circle is
the same as the diagonal of the square; to obtain which
we have to square two of the sides and add them to-
gether, and then extract the square root, which will be
the diameter of the circumscribing circle: when the
square is formed on the outside of the circle, then the
side of the square is the same as the diameter, and their
areas may be easily found by the ordinary rules.
I
L
R
Y
Fig. 717.
2
3
Fig. 718.
A
Р

Q
N
H
G
K
V
5
D
E
Fig. 719.
0
Fig. 720.
1
P
Fig. 721.
F
X
Z
7



G

M
+
H
1
T
Z
CHAP. V111.
GEOMETRY.
751
The Circle X is inscribed within the pentagon 1 2 3 4 5, whose
sides are each the base of an isosceles triangle, the property of
which is to have each of its angles at the base double that at
the vertex; and if any two adjoining angles of a regular
polygon be bisected, the intersection of the bisecting lines will
be the common centre of the two circles, the one within, and
the other circumscribing the polygon.
The regular polygons, which have the same number of sides,
are similar figures; for their angles are equal, each to each,
because they are contained the same number of times in the
same number of right angles, and their sides about the equal
angles are to one another in the same ratio: it will also be
evident that the area of a regular polygon is equal to half
the rectangle under its perimeter and apothem, which is a per-
pendicular let fall from the centre to the middle of one of the
sides; therefore the sum of the sides multiplied by the length
of the apothem will be the area.
When the pentagon, hexagon, or heptagon, or either of
them, are formed into triangles uniting in the centre, those
must have equal bases and equal altitudes, and consequently
are equal one to another; and whatever the shape of the
polygon, it must contain as many of these triangles as it has
sides, therefore it must be equal to half the rectangle under
the perimeter and apothem.
The Circle Z is inscribed within the hexagon Y.
The Circle B contains inscribed within it a regular heptagon.
The Axis is the straight line, real or imaginary, about which
a body turns, in which sense it is sometimes called the axis
of rotation or of oscillation, according to the motion of the
body: it is, however, a straight line about which the parts of
a figure are symmetrically disposed.
The axis in peritrochio is one of the five mechanical powers,
consisting of a peritrochium or wheel fixed immovably to an
axle, so that both turn together round the axis of motion.
The power is applied to the circumference, and the weight
raised by the rope is wound round the axle: the power
gained is the same as that gained by the lever, the longer arm
of which is equal to the radius of the wheel, and the shorter
equal to the radius of the axle.
The Axis of a Circle is a right line, A B, drawn through
the centre C, so as to divide X into two equal parts: E F is
the chord, and C D the radius.
The Axis of a Globe is a line passing through its centre
I, on which it can move as on two pivots.
Axis of a Cylinder is the line 47 passing through its
middle vertically, and round which the plane 4567 may
traverse to generate the figure.
The axis of a column or frustum of a cone is a straight
line drawn through its centre, and in the middle of its solid
mass: all weight placed upon it should have regard to its
true position.
The straight line which divides a conic section symmetrically
is called the axis: in the ellipse and hyperbola the axis cuts the
curve in two points, which are termed the principal vertices of
the ellipse or hyperbola: and a straight line intercepted be-
tween them is called the principal diameter or transverse axis.
The axis of any circle of the sphere is that diameter which
is perpendicular to the plane of the circle; its extremities are
called the poles.
It is therefore evident that parallel circles have the same axis
and poles, for a straight line which is perpendicular to one of
two parallel planes is perpendicular to the other likewise: it
may also be observed that two parallel circles cannot both of
them pass through the centre of the sphere, or they cannot both
be great circles of the sphere.
Axis of revolution may be considered that straight line
about which the figure revolves.

5
Fig. 722.
Y
Fig. 723.
R
Fig. 724.
E
X
3
N
Q
A



Y
I
00
8
F
X
C
B
Fig. 725.
G
Fig. 726.
Fig. 727.
Z
4
D


752
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
3
If a
The Axis of the Ellipsis M is shown at KL.
moving or generating circle roll along the concave circum-
ference of a fixed circle in the same plane, and the radius
of the former be half that of the latter, any given point
in the plane of the generating circle within or without it
will describe an ellipse; such a curve has been proved
to be an epicycloid; when the circle revolves on the in-
side of the circumference, the curve is sometimes called
the hypocycloid. The revolving circle is the generating
circle, the circle on which the revolution is performed
the fundamental circle, and the portion of the fundamental
circle on which the epicycloid rests is the base.
The Axis of the Parabola P is the perpendicular line
NO, which falls upon the line Q R.
The Axes of Spheroids are the two lines which cross at
right angles, TV being that which is horizontal.
Solids have length, breadth, and thickness.
The mass
A has length from B to C, breadth from B to D, and
thickness from D to E.
The boundaries of solids are surfaces, and all the regular
solids are terminated by regular and equal planes; they
are five in number, as the tetraedron, the hexaedron, the
octaedron, the dodecaedron, and the icosaedron; these are
also called Platonic bodies, on account of their being
treated of and described by Plato: besides these five there
can be no other solids bounded by like equal and regular
plane figures, and whose solid angles are all equal:
three of these, as the tetraedron, octaedron, and icosaedron,
are contained by equilateral triangles; one, viz. the cube
or hexaedron by squares, and the other, the dodecaedron,
by pentagons. The sphere may be inscribed in either of
these, as may also another around or circumscribing it,
the common centre of which may be found by bisecting
any three of the dihedral angles, or by bisecting any three
of the edges by planes at right angles with them.
The solid content of any regular polyedron is equal
to one-third of the product of its convex surface and apo-
them, which is the radius of the inscribed sphere.
The regular polyedrons of 6, 8, 12, and 20 faces, have for
every face a
face opposite and parallel to it, and the oppo-
site edges of those faces likewise parallel; also the straight
line which joins two opposite angles passes through the
centre of the polyedron: any one of them may be in-
scribed in a regular polyedron which has a greater
number of faces, by taking for its vertices certain of the
vertices of the latter, or of the centres of its faces, or of
the middle points of its edges.
Similar and equal bodies are those which have all
these dimensions of one size, the square OKL and PMN
being the same in both, as well as the other sides.
In the Cube A the sides BCD are all equal. The
hexaedron or cube has six faces, eight solid angles, and
twelve edges; the centres of its faces are the vertices of
an inscribed regular octaedron; four of its vertices are
the vertices of an inscribed octaedron; its adjoining faces
are at right angles to each other, and the diameter of a
circumscribed sphere is to the edge as the hypothenuse
to the lesser side of a right-angled triangle whose sides
are as the side and diagonal of a square. The diameter of
the inscribed sphere is equal to the edge of the cube.
The Sphere has its surface represented by F.
As a
line according to Euclid is generated by the motion of a
point, so a surface is generated by the motion of a line:
if the generating line be a straight line, and move, subject
to the condition of having always two consecutive positions
in the same plane, the surface generated is developable,
and can be stretched out on a plane, as that of a cylinder.

K
T
Fig. 728.
Fig. 729,
Fig. 730.
C
Fig. 731.
Fig. 732.
P
Ꭱ
Fig. 733.
P
M
N
0
R
B
A
K
L
H
M
N
A
B
C
D
Fig. 734.
E
Fig. 735,
F
E
V
L






CHAP. VIII.
GEOMETRY.
753
Р
Z
Y
ر
Fig. 738.
The Column G has a circular plane at top and bottom
and a cylindrical surface; the irregular figure P is bounded
by numerous planes running through QRS, &c.
To draw accurately such figures, it is necessary to intersect
them by planes in a vertical as well as in a horizontal direc-
tion: the form P indicates the taste which prevailed in the
time of Louis XIV., and which took precedence over the
simple shaft previously in use; to ascertain the quantity or
weight of such irregular figures the greatest care in their
measurement is required.
The difference between the diameters at O and N in the
column HI is termed its diminution, and the proportions
which govern this in architecture should always be drawn from
a study of nature. Smeaton, in preferring the trunk of the
oak for his model of the Eddystone lighthouse to the column,
showed that he had thought well on the subject, and by adopting
the curve line for its section, he produced less resistance to the
waves as they rose up its sides: where columns carry weights
they must be proportioned to the load, and many writers have
urged that eight or nine diameters is as much as should at any
time be depended upon for stone or timber; when used as posts
the ancients varied their marble columns from four to ten
diameters in height, but on no occasion do they appear to load
them, when applied to temples, beyond their own weight.
K is an irregular cylinder, hollowed in the extent of its
height, and formed of different horizontal planes.
The contents of such forms are not very easily obtained, to
acquire which a variety of dimensions are necessary to model
them the turning lathe is employed: their curvature can thus
be fashioned to the purposes for which they are intended.
A Cylinder has three superficies, formed by a rectangular
parallelogram; the solid A is generated by turning the paral-
lelogram Z B C on its axis BC.
The cylinder is a solid figure, the surface of which is partly
plane and partly curved, the plane portions being two equal
and parallel circles, and the curved portion such that any point
being taken in the circumference of either circle, the straight
line which is drawn through it, parallel to the line joining their
centres, lies wholly in the surface.
The base of a cylinder is the circular ends R and S, that at
Q is shown in perspective.
Wherever a cylinder is made use of, either for support or as
a gudgeon attached to machinery, we must recollect that its
stiffness, when compared to that of its circumscribing prism, is
as three times its mass to four times that of the prism. When
a cylinder is compared with a prism of the same length and
weight, its vibrations, according to Dr. Young, will be less
frequent, in the ratio of 300 to 307, or nearly of 43 to 44: then
it may be said that the stiffness of a cylinder is to that of its
circumscribing prism, as three times the bulk of the cylinder
to four times that of the prism; the authority before cited
also observes that the force of each stratum of the cylinder may
be considered as acting on a lever, of which the length is equal
to its distance x from the axis, for though there is no fixed
fulcrum at the axis, yet the whole force is exactly the same as
if such a fulcrum were placed there, since the opposite actions
of the opposite parts would remove all pressure from the
fulcrums; the tension of each stratum being also as the
distance x, and the breadth being called 2y, the fluxion of the
force on either side of the axis will be 2xyx, while that of
the force of the prism is 2x and its fluent x³. But the
2
3
fluent of 2x²y x, or 2√(1-xx) x²x, calling the radius unity,
is } (z—y³x), z being the area of the portion of the section in-
cluded between the stratum and the axis, of which the fluxion
is yx, for the fluxion of z — y³ x is yx — y³ x—3 y² x y = y x²x
N
I
H


Fig. 736.


K
Fig. 737.
R
S
Fig. 739.
Fig. 740
Fig. 741.
D
a

о

3 C
#54
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

Sy³x
У
= 1 and y=0
= y x²x + 3y x²x=4y xx, and when z
the fluent becomes z, while the force of the prism is expressed
by
2
3
When the ends of a cylinder are not parallel it is an
irregular figure, and it is said to be inclined when placed
on one of its ends which is cut in a plane out of right
angles with its lengths.
Ballusters are a species of cylinder, which usually are
made to swell in the middle; that as I has additional
strength to that shown at E, the diameter at F being the
same as at its base H.
A regular Polyedron has all its faces or planes equal, as A.
The apothem of such a figure is a perpendicular drawn from
the centre to any one of the faces, and is equal to the radius
of the inscribed sphere. Cubes, or cubic numbers, are those
formed by the multiplication of any number into twice
itself, thus 8 and 27 are cubes, the first being equal to
2 × 2 × 2, and the second to 3 × 3 × 3: the number thus pro-
duced by multiplication is called its power, and the original
number its root; this is called the square root if the power
is square, and the cube root when the power is a cube.
These powers are distinguished from one another by the
number of times that the given number has been multiplied
by itself: the square is called the second power, the cube
the third power, and when multiplied again the fourth
power, or biquadrate. The first, second, third, fourth, and
fifth powers of 10, are 100, 1000, 10,000, 100,000, &c, which
in algebra may be represented by a, aa, aaa, aaaa, aaaaa, or
a100 when a is raised to the hundredth power, a³ when a is
cubed, and aª, a³, &c. when raised to the fourth or fifth
powers: such terms are also in geometric progression,
because each term is once greater than the preceding.
Vitruvius informs us that the ancients called 10 a perfect
number, but that mathematicians, on the other hand, pre-
ferred 6, the number of sides of the cube; its divisors equal
its number, for a sixth part is 1, a third 2, a half 3, two-
thirds 4, &c.
An irregular cube has them unequal, as those of CD in the
figure B.
A Pyramid is bounded by many planes, and terminating
at a point, as in those at G and E. They are called pyra-
mids from the resemblance they bear to a spire of flame;
but the etymology of the term is perhaps derivable from
the Egyptian words, which signify the separating or setting
apart from common use, which was the case with such build-
ings: the word pyramid, therefore, may denote a sacred fane
or place set apart for some religious use.
In geometry a pyramid is a solid contained by a plane
polygonal base and other planes meeting in a point, which
is called the vertex; the planes which meet in the vertex are
called the sides, which are all triangles, and the slant height
is the length of one of these sides measured from the point
to the middle of one side of its base: every pyramid is
equivalent to one third of a prism having the same base and
altitude; consequently those which have similar bases and
altitudes are equal: the solid content is found by multiplying
the area of its base by one-third of its perpendicular height.
The base of a pyramid is the plane opposite to its apex
or points, or the side on which it rests; FGH is the base
of the figure E.
F, H, M, are pyramids with square bases, and the figure
M is usually designated, when the top H is removed, the frus-
tum: when a pyramid is cut by a plane parallel to its base, the
frustum, as M, which is the part comprehended between
the base and the section, is equal to the sum of three
Fig 742.
Fig. 743.
G
Fig. 744.
A
D
[2]
B
C
F E
E
F
H
G
Fig. 745.
Fig. 746.
H
E
H


M
CHAP. VIII.
*ES
GEOMETRY
pyramids, having for their common altitude that of the frus-
tum, and of which the bases are respectively the lower base
of the frustum, the upper base of the frustum, and a mean
proportional between them.
A truncated Body is that of a pyramid, where L is so
called, when the top M is broken off.
Obelisks are of this form, and may have any number of
faces, one of which is a triangle or other rectilineal figure,
and the rest triangles which have a common vertex, and for
their bases the sides of the first triangle or rectilineal figure :
the altitude of such pyramids is the perpendicular distance
of the vertex from the base, and the truncated pyramid is
said to be triangular, quadrilateral, or pentagonal, according
to the figure of its base. When the pyramid has a part of
its summit cut off by a plane parallel to its base, the part
next the base is called the frustum, and sometimes a trun-
cated pyramid.
A Prism is a solid composed of many planes, of which
the two opposite are equal; K, T, and S are instances of
triangular, square, and hexagonal prisms.
The prism is a solid contained by planes, of which two
that are opposite are equal, similar and parallel, and all the
rest are parallelograms. A right prism has its sides perpen-
dicular to its ends; an oblique prism is that of which the
sides are oblique to the ends.
Tetraedron has four equal sides, formed by four equilateral
triangles, H and I, or it is a triangular pyramid having four
equal and equilateral faces, which are the least number pos-
sible for a solid. If we assume a =
If we assume a = the linear edge, b
the whole superficies, c = to the solid content, r= the
radius of the inscribed sphere, R = the radius of the circum-
scribed sphere, then the following relations hold true,
a = 2 r√6, b = 24 r² / 3, c = 8 r³ √ 3, R = 3 r.
Hexaedron is a solid which is bounded by six equal sides,
as E and A.
This is one of the five regular or Platonic
solids, the whole surface of which is equal to twenty-four
times the square of the radius of the inscribed sphere, and to
eight times the square of the radius of the circumscribed
sphere, and its solid content is eight times the cube of the
inscribed sphere.
Dodecaedron is composed of twelve equal, equilateral, and
equiangular pentagons, as the figure F.
The surface of the dodecaedron is found by multiplying
the square of its side or linear edge into the number
20-64578, and its solidity by multiplying the cube of its
side by 7-66312.
Icosaedron is a solid composed by twenty equal, equilateral,
and equiangular triangles, as the figure G, and may be
regarded as formed of twenty equal and similar triangular
pyramids, whose vertices all meet at the same point; hence
the content of one of these pyramids multiplied by 20, gives
the whole content of the icosaedron.
Parallelopipedon is a solid composed of six plane quad-
rangles, of which the opposite sides are parallel, four of
which are equal to one another.
All the faces of one of the above named solids cannot be
seen at the same time; in the cube A, we can from the
point X only see the three faces A, D, and C, and the eye
may be so placed above it that only the top face may be seen.
In the representation of the several solids, it is necessary
that we should attend to some rules, and that they should
always be drawn, either as they appear to the eye, or ac-
cording to a recognised scale. Isometrical perspective gives
us, as we shall hereafter see, such a method of showing the
various sides of a cube or other figure, and ascertaining from
a scale its relative dimensions. When it is required that a
solid should be projected in the plane of a picture with its
P
Fig. 747.
K
Fig. 748.
H
Fig. 749.
發
​Fig. 750.
G
Fig. 751.
Fig. 752.
X
C
Fig. 753
A
T
B
D
F
A
S



3 c 2
¹756
BOOK II.
THEORY AND PRACTICE OF ENGINEERING. -
actual dimensions, we may obtain the requisite measures
from the properties of similar triangles; for instance, to
find the position of the image of either of the right lines in
the cube, we must determine the point in which a line
parallel to it, passing through the place of the eye, cuts
the plane of the picture; this, which is called the vanishing
point, is shown at X, and all the lines which are under the
same parallel will tend to it; when the lines are, however,
parallel with the plane of the picture, the distance of their
vanishing point becomes infinite, as we shall see when
treating of the laws of perspective. In treating diagrams,
geometricians usually make all lines which are on the
return of a cube, or which represent its sides, tend to one
point, and draw the face in front, as D, perfectly square.
When a cube is represented with its sides equal, it is
said to be geometrically drawn, but when shown as at
K it is in perspective.
A Sphere is a body comprised within a single super-
ficies, in which all the lines drawn from a central point
equal one another.
LMNO is an hemisphere or half globe; a segment
either less than a portion cut off, as at Q, or greater,
as that part of the sphere at R.
The zone is a portion taken out of the
shown at S.
Fig. 754.
Fig. 755.
K

A

L
N
P
R
M
middle, as
Fig. 756.
The sector of a sphere has a portion of the outer
surface, and terminates in a point as at T.
The globe R, when cut in two, has the parts or planes
shown as at T, V, which are called its sections, and S is an
hemisphere.
B is an armillary sphere, and used by astronomers to
show the motion of the earth, and the relative position
of the sun, moon, and stars, &c. This is an ancient astro-
nomical machine composed of an assemblage of hoops or
circles, representing the different circles of the system of
the world, as the equator, the ecliptic, the colures, &c.,
arranged in their regular position.
D shows the mounting of the sphere used to represent
the earth, which is usually represented as round, or a true
globe; this was inferred from the figure of its shadow, as
seen on the moon's disc in lunar eclipses. The hypothesis
of its being a true sphere is sufficient to explain the general
appearance of the heavens as seen from different points of
its surface: Eratosthenes, upwards of 2000 years ago,
made the attempt to ascertain its diameter: he knew that
on the day of the summer solstice the sun illuminated the
bottom of a well at Syené; at the same instant he observed
at Alexandria that the sun was 7° 12′ from the zenith, and
it was supposed that Syené was due south from that place,
and, therefore, that both were under the same meridian.
Having determined the distance between the two places to
be 5000 stadia, and accurately measured the sun's altitude,
he found the earth's circumference to be 250,000 stadia:
this method, which is not accurate, was afterwards adopted
by many other philosophers.
Artificial globes are used for explaining the rotation of
the earth, the latitude and longitude, and the situation of
places with respect to each other; they are, however,
limited to general explanation: it is often highly necessary
for the engineer to determine the meridian, or to draw a
meridian line, and this requires the aid of a good telescope,
a well-regulated clock, and the sextant, or an instrument
for determining the altitude of the sun or star. By the
sextant we can determine two instants of time; when the
star has the same altitude, the clock will give the interval
of time between them, and half this interval will be the
time between each observation and the passage of the star
over the meridian. If we next day note the time of the
Fig. 757.
T
T

R
Fig. 758.
B

Fig. 759.
Fig 769.
C
D

CHAP. VIII.
757
GEOMETRY.

clock when the star again attains that altitude, and add to
that time the above mentioned half interval, we shall have
the time by the clock when the star will be on the meridian;
if at that instant a telescope, movable in a vertical plane,
be directed to the star, so that in passing the meridian the
star may be on the axis of the telescope, the position of the
plane of the meridian will be obtained. If a meridian circle
pass through the zenith of any place, the arc intercepted be-
tween the zenith and the equator is called the latitude of that
place: assuming this or any other meridian circle that passes
through the zenith of any particular place as the first me-
ridian, the arc of the equator intercepted between the first
meridian and the meridian circle passing through the zenith
of any other place is called the longitude of that place: by
the zenith is meant the top of the heaven, or vertical point
directly over head, or it may be defined as the pole of the
horizon, from which it is 90° distant.
When a cavity is made through a globe, as at E, it is
said to be pierced.
In the globe L it is comprised over its whole surface;
the coating of a sphere is its superficies. In a part of a
globe the area of the base or section must be added to that
contained over the convex portion to obtain its superficies.
In the figure EFGHIK, the upper and lower faces, as
well as those of the ends, must be added together to make
up the total surface or entire superficies.
And when it contains a cavity in the centre, as a shell,
it is a hollow globe or sphere.
A Spheroid is an oblong sphere formed by the turning
of an ellipse round its axis: if the generating ellipse
revolves about its major axis the spheroid is said to be
prolate, and about its minor, oblate.
Supposing 2 a the axis of revolution, and 2b the dia-
meter of the generating ellipse perpendicular to the axis,
then the origin of the co-ordinates being at the centre, and
r being taken on the semi-axis a, the equation of the sphe-
roid is
Fig. 761.
Fig. 762.
Fig. 763.
E

L

M

G
E
I
H
Fig. 764.
K

x
as
+
= 1.
b⁹
The solid content of such a figure is equal to two-thirds
of its circumscribing cylinder.
A Paraboloid is the half of such a figure, and is
described by the revolution of a half parabola round its
axis: sometimes the term is used to express the parabolas
of the higher orders, and sometimes the solid formed by
the rotation of a parabola about its axis, or the parabolic
conoid. In the parabola the parameter of its axis is a
third proportional to the abscissa and its ordinate. The
focus is that point in the axis where the ordinate is equal
to the semi-parameter; the diameter is a line within the
curve terminated thereby, and is parallel to the axis;
an ordinate to any diameter is a line contained by
the curve, and that diameter parallel to a tangent at
the extremity of the diameter. In a parabola the ab-
scissas are proportional to the squares of their ordi-
nates; and as the parameter of the axis is to the sum of
any two ordinates, so is the difference of these ordinates to
the difference of their abscissas. The distance between
the vertex of the curve and the focus is equal to one-fourth
of the parameter; the radius vector is equal to the sum of
the distances between the focus and the vertex, and be-
tween the ordinate and the vertex.
The parabolic curve is that which some mathematicians
call the curve of equilibrium for an arch, because it sustains
a load uniformly when distributed over its length; it should
be comprised in the depths of all flat arches, and it is
the best form for suspension bridges. It is the curve
described by a cannon ball, and by a jet of water when it
F
Fig. 765,

Fig. 766.
Fig. 767.
Fig 768.
G

V
D

H
3 c 3
753
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.

issues from a hole made in the side of a cistern or reservoir,
and it forms the best curve for the reflection of light.
The mouldings found in Greek temples, so worthily
admired, are all of this form; they result from the inter-
section of conic surfaces by planes parallel to the side of
the cone in general.
VX is the base of the parabola Y. The parabola is a
curve consisting of two similar sides, which may be produced
indefinitely, by being drawn in such a manner with regard
to the axis passing through the vertex, that the abscissæ are
to each other as the squares of the ordinates; so that if the
former be 1, 4, 9, the latter will be 1, 2, 3, &c.
When a
body or projectile is thrown in a horizontal direction,
its path through the air will be half of a parabola, whose
vertex lies in the point of projection.
When a body is thrown obliquely upwards, its path is
that of a complete parabola, whose vertex will be the
highest point reached by the body, which ascends one side
and descends by the other: if the projectile forms any
angle whatever with that of gravity, a body set in motion
by these forces will not follow the direction of either of
them, but will adopt a middle course proportional to both
the forces; the course of the body, which is determined by
the laws relative to the parallelogram of forces and the
earth's attraction, will be that of a curved line resembling
the parabola.
The base of a paraboloid, as Z, is its circular end; in the
frustum of a cone it is at 3, and the top at 2 shows the
base of the part cut off, and 1 the slant height.
In the parabola NOP the superficial content may be
obtained by considering it as the portion of an oval.
A Cone is a body comprised within two superficies, and
is formed by revolving a right-angled triangle on its axis,
as that at X. So is formed the paraboloid C when one
side of the figure is curved.
The base of a cone is the circle on which the figure
stands: NO is the slant height.
If a body be thrown vertically upwards, it will be re-
tarded in an uniform manner, and not arrive either per-
pendicularly or at the apex of the cone, but will, by the
influence of gravity, assume the parabolic curve, which is
one of the sections of the cone. This is in consequence of
the effect of the projectile force becoming every moment
less powerful by the earth's attraction on the ascending
body, and which is exactly in the same ratio as it accele-
rates its descent. The laws which regard the latter are in
inverse application; a body will therefore lose its velocity
after a certain time, and return to the surface of the earth
in precisely the same time as was occupied by its ascent;
the projectile force is momentary, and the action of gravity
permanent; the motion is consequently a compound one,
the forces acting sometimes in the same vertical, and some-
times in an opposite or oblique direction.
When a ball or other body is projected, its force as well
as angle may be ascertained by using a spiral steel spring,
which may be strained according to various degrees of
tension; this spring, placed in a tube, and made movable
about a pivot, may be made to act at any required angles
by means of a graduated scale.
The base of an angle is DC: B is the summit of
the angle A.
The base of any solid is the side on which it rests:
LM is the base of the figure K.
The amount of the weight of such a body is proportional
to the mass, the measure of which, estimated by that of
some other body which serves as an unit, is termed its ab-
solute weight. Gravity and weight in mechanics always
are to each other in the relation of action and re-action.
Fig 769.
D
Z
Fig. 770.
N
Fig. 771.
Χ
Fig. 772.
N
Fig. 773.
D
Fig. 774.
L
Fig. 775.
Y
Р
R
1
ON
2
3
Z
X



C
K
M
CHAP. VIII.
759
GEOMETRY.
The superficies is that which has length and breadth :
ABCD in the parallelogram bounds its area, and indi-
cates its quantity.
A B is the boundary of the straight line as CD is of the
curved: E F G H are the boundaries of the parallelogram.
Boundaries. It is curious to observe the principles
adopted by the ancient geographers in their description of
a country to express its form: Strabo tells us that Spain
resembled a hide spread out, and we also learn that Alex-
Britain
andria was in the form of a Macedonian cloak.
was represented by them as contained within a triangle,
of which the base or longest side was that opposite to Gaul.
The Greeks considered the several continents to be
bounded by the sea. The general outline of a country
must be obtained before we can accurately estimate
its area, and in our descriptions we must notice its
boundaries; England, for instance, is bounded on the
south by the English Channel, on the east by the German
Ocean, on the north by Scotland, on the west by the Irish
Sea and St. George's Channel: in mapping a country or
an estate, it is necessary that we should remark on the
boundary lines, where it touches or comes in contact with
the adjoining lands not comprised in our survey: from
an accurate map of England and Wales, with its outline
properly defined, the area was computed to be 57,960
square miles.

A.
A
B
C
Fig. 770.
G
Fig. 777.
K
Fig 778.
ها.
Fig. 779.
L
M
R
P
S
R
T
B
F
D

H
The term England is derived probably from its trian-
gular form: the base of the triangle is a line drawn from
the South Foreland in Kent to the Land's End in Corn-
wall; the eastern side, by a line drawn from Berwick to
the South Foreland, and the western or longest side, by a
line drawn from Berwick to the Land's End. In the
maps which were drawn during the last century there
was no approach to the accurate form of either England
or Wales, nor was there any attempt made by the surveyors
of that time to exhibit the rising ground, mountain chains,
or principal features of the country. From such inac-
curate surveys we cannot be surprised at the differences
which appear in the various calculations of the area which
have been made. Sir William Petty estimates the area
of England and Wales at 28,000,000 acres, Gregory King
Arthur Young
39,000,000, Dr. Halley 39,938,500, Arthur
46,916,000, Dr. Beeke 38,498,572, and Mr. M'Culloch
at 36,999,680; the latter is much nearer the truth, as the
statute acres he has given were deduced from the aggregate
Fig. 780.
measurements of the several counties in England and
It is of the
Wales of these Wales comprises 4,752,000, and England 32,247,680 acres.
utmost importance that the boundaries of all kingdoms and states should be clearly defined;
before this is done, or an outline of their coasts or form is obtained, it is not possible to
compute their area, or to lay down a system of taxation or rates that the inhabitants should
contribute to the state. The boundaries which relate to a district should also be well
defined, as should those which nature has prescribed, as the basin or valley drained by a
particular river: sufficient attention has not been paid to this part of the subject of map-
ping, for all rivers have a limit or boundary, in their drainage of the superfluous waters, and
the high ground from which they draw their supply is capable of being defined and having
its outline established. In making the surveys for the parishes throughout England this
might have been attended to, and the information conveyed would then have been invaluable
to the engineer in all his future surveys, and to the government in controlling him.
Of areas and solids it is not necessary to say any more of their boundaries than that the
lines and surfaces which contain them are so called; as, for example, A B is the boundary
of the straight line, &c.
LMN is the boundary line of the half circle, as K is that of the whole figure I.
PQR are the boundaries of the quarter circle, and R is that of the segment cut off S.
When the curved line of a segment is less than half the circumference, as at R, it is the
small segment.
The boundaries of a sector are TV X, the radius or lines TV and TX comprising a
part of the external circumference.

3c4
780
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
The boundaries of a vessel of any kind, whether those of a vase,
cup, or box, are those surfaces and lines which are visible to the
eye; they comprise all within and with-
out, and whatever presents a face.
Zones or Girdles are those bands which
encompass or surround a sphere, as that
between B and D.
GLI, HMK, indicate the zone be-
tween F and E: a zone may embrace only
a portion of a sphere, as that indicated at
C in the two halves, A, A.
Y
Fig. 781.
The globe is divided into five zones by the two tropics
and the two polar circles; that comprised between the
tropics is called the torrid, its breadth being 47°, or twice
the sun's greatest declination; this is divided into two
equal parts by the equator. That zone included between
the tropic of Cancer and the arctic circle is called the
north temperate zone, and that between the tropic of
Capricorn and the antarctic circle the south temperate
zone: each of these are in breadth 43°; that portion com-
prised between the arctic circle and the north pole is the
north frigid zone, and that between the antarctic circle
and south pole the south frigid zone.
•
This division of the earth into zones probably arose
from the difference observed in the temperature, which is
higher in the equatorial regions than in any other part of
the earth, in consequence of the sun's rays being more
direct; to every point of the earth's surface whose zenith
lies between the tropics, the sun is vertical twice in the
year in the polar regions the temperature is lowest, in
consequence of the obliquity with which the sun's rays
fall, and the length of the winter night. In the countries
situated between these two regions there is a medium
temperature, increasing as the zenith approaches the
nearer of the two tropics, and diminishing as it approaches
the nearer of the polar circles.
Zones are sometimes irregular, as N on the globe Y,
the widths of OQ and PR being different.
S is a zone on the globe T, as is V on that of X.
Plans are of various form, as those of A, B, and C: any
figure having superficial contents is so designated.
The surveyor of land determines by measurement both
the boundaries and superficial content of any portion of
the earth's surface; the object being to ascertain the
content of a single field, or the relative distances and
bearings of the various buildings or other objects around
or within it. In measuring land, all the lines and surfaces
whose contents are to be found are reduced to the same
horizontal plane, on the principle that as corn grows ver-
tically, no greater quantity can be produced on the slant
side of a hill than would grow on the area which its base
covers: when the lines measured are not horizontal, they
must be multiplied by the cosines of their respective
inclinations to the horizon. When a country is surveyed,
or a large geometrical map is to be formed, it is necessary
to have regard to the earth's curvature and many other
circumstances.
Ichnographic plans, as shown at D, are made use of to
exhibit the foundations of the walls of a building, or the
arrangements of the several divisions or compartments.
This term, derived from the Greek, signifies a model,
and the drawing of it: in architecture it usually indicates
the ground plan, as of a fortress, garden, or building:
when either of these are laid down properly to a scale,
any portion, as well as the whole quantity may be esti-
mated, and if the walls or points of supports are distin-
guished by colour, their proportions with regard to void
Fig. 783.
Fig. 782.
A
G LI
F
E
HMK
N



B
D

P
N
Q
T
R
Y
Fig. 784.
X

A
B
с
Fig. 785.

Fig. 786.
D
CHAP. VIII.
761
GEOMETRY.
may be also calculated; this is an important preliminary before any constructions are com-
menced, and great accuracy in the drawing is requisite to make the estimates correctly.
An orthographic plan shows the extent as well as eleva-
tion of the several portions of the building.
A scenographic plan represents the whole in perspective.
Vitruvius informs us that architecture depends on fit-
ness and arrangement, and also on proportion, uniformity,
consistency, and economy: the first relates to the nice
adjustment of the dimensions of the several parts to the
whole, as well as to their use. Ordination is the word
we have rendered into fitness, and in it is comprised the
terms we are now using, as Ichnography, Orthography,
and Scenography; as the first relates to the plan drawn
geometrically, so does the second to the elevation; the
last exhibits the front and receding side properly shadowed,
the lines being drawn to their proper vanishing points.
After such a description as is contained in the author
above cited, it is not possible to fancy that the Romans
were unacquainted with our method of making designs,
and particularly when he further observes that the three
systems of preparing them are the result of thought and
invention, the first being an effort of the mind, ever in-
cited by the pleasure attendant on success in compassing
an object, whilst the other is the effect of this effort, which
shows a new light on things the most recondite, and pro-
duces them to answer the intended purpose: such are the
ends of arrangement. Proportion is that agreeable har-
mony which results from one and all parts agreeing
with each other and the whole: uniformity is the parity
or likeness of the parts to one another: consistency is
the result found when the work exhibits a suitable detail,
and economy is the due and proper application of the
means afforded, and prudently employing it. The second
chapter of the first book of Vitruvius should be studied
by all who are desirous of becoming civil engineers.

G-D
DEEN 0-0-0
ご
​Fig. 787.
C
E
A

Fig. 788.
E
H
C
D
F
A
E
Of different sites or situations of planes with regard to
the horizon, which is said to be either sensible or rational;
the first is a plane which is a tangent to the earth's surface
at the place of the spectator, extended on all sides till it
is bounded by the sky; the latter is a plane, parallel to
the former, but passing through the centre of the earth.
These two terms are only relative, as they vary with the
spectator's position; for when his eye is in the plane of the
sensible horizon he can only see what is above it, but when
it is raised above the horizon he can observe what is beneath.
it. The sensible horizon is therefore properly defined to
be the conical surface which has its apex in the
eye of
the spectator, and embraces the portion of the earth over
which the eye can reach; the visual rays, which are tan-
gents to the earth, are situated in this surface, and point
below the true sensible horizon, or the rational horizon
which is parallel to it; and the angle which a visual ray makes with the plane of the
horizon is termed its dip or depression, and which is easily estimated from the known dimen-
sions of the earth, and the height of the eye above its surface. An inclined plane is that
which is neither horizontal nor vertical, but which slopes on the horizon, as the cliff at D.
A may be considered the true level or the surface of the waters; B is the horizontal plane
parallel with A; C is a vertical plane perpendicular to A, or parallel to the plummet let fall
at E; D may be called an inclined plane.

B
G
Fig. 789.
Of Sines, Tangents, and Secants.—The sine of any arc of a circle is the straight line drawn
from one extremity of the arc perpendicular to the radius, passing through the other ex-
tremity. The sine of an arc is the half of the chord of the double arc. The tangent to a
curve is a straight line which meets or touches the curve without intersecting it; the
arc and its tangent have always a certain relation to each other, and when the one is
given in parts of the radius, the other can always be computed by means of an infinite
series; the Arabians were the first to introduce tangents into trigonometry, and which
render important service in simplifying many calculations. The secant is a straight line
drawn from the centre of a circle to one extremity of an arc, and produced until it meets
the tangent to the other extremity. The secant of an arc is a third proportional to the
762
Book II.
THEORY AND PRACTICE OF ENGINEERING.
cosine and the radius, hence if the radius be taken as unit, the secant is the reciprocal of
the cosine. The cosecant and cosine is the complement of an angle or arc.
The sides of the triangle ABC are sines,
because its sides are enclosed in the circle
EFGBD, which has for its radius one of the
sides A.
A tangent is a right line which falls perpen-
dicularly on the end of the radius, where it
touches the circle, as HF: AH is a secant.
To trace a line or any figure on the ground,
the engineer is provided with staves or rods of
various lengths which enable him to station
the holder at any particular point where the
observation is required to be made; such a staff
or piquet is made use of, with various devices on
the point, to set out a straight line through any
district that is to be surveyed. Any one sta-
tioned at either of the extremities of the line
AD could direct others at the intermediate
stations F, C, H, B, E, to plant their rods in the
direct line; which when set out is to serve as
the base or diagonal of a figure, from which the
country around is to be mapped or levelled.
Sometimes these piquets have placed upon
them boards, either coloured or pierced with
holes, or with curved tops, which enable them
to be more readily distinguished.
The staves made use of for levelling have a
vane which slides up and down with facility, and
can readily be lengthened; these are accurately
divided in their height into hundredths of a foot,
and are alternately coloured black and white:
the lines denoting the tenths are drawn through
the whole breadth, and every and foot is
further distinguished by one or two conspicuous
dots or marks.
Smaller stumps or pins are made use of to
mark out the line or figure after the survey is
commenced; Q is a form made use of for one
description of marks, and P for another.
When the excavator commences his labour,
he is generally instructed to leave witnesses of his
work in the shape of small cones of earth, by
which the depth of his excavation can always be
obtained. B is the natural and original level of
the man A. At every extreme height as well as
depth, these marks should be left for the engineer
to make his survey when he is desirous of verify-
ing the quantity of earth which has been removed.
In measuring such an excavation, it is the
hole made in the ground that is to be measured,
and not the earth removed, and when great
depths are taken out, allowances in price are
made accordingly; in large excavations the
workmen are usually distributed in gangs; one
digs, another fills, and a third wheels the earth
away: when the distance exceeds twenty yards,
a fourth man is employed, a stage being con-
sidered that distance. The first man, who has
to wheel the earth out of the work, generally has
an inclined plane to mount, whilst the second
runs his barrow along level ground; when this
is the case, the stage or run is limited to a less
distance, and when the level is an inclined plane,
then the run is extended to twenty-five yards.
There is a considerable advantage obtained in
dividing the moving of earth into separate stages,
but the engineer who has the direction of the

D
Fig. 790.
N
Fig. 791.
Fig. 792.
Fig. 793.
B
F
L
H
A



CHAP. VIII.
763
GEOMETRY.
work should always set them out proportionably, which sometimes is rather a difficult
task to perform. As the excavation proceeds it should be measured, as it is expedient
that this should be done before any of the marks are obliterated or destroyed, which they are
constantly subject to, particularly where horses and carts are employed in any great numbers.
Rules, Sight Vanes, &c. - Rules are required of different
lengths and thicknesses, with straight and bevelled edges,
either to draw lines on paper in pencil or with ink; but
when a line is to be drawn on the ground, it may be done
more readily by stretching a line, as at C, from one stump
to another.
A
B
C
Parallel Rules. There are several kinds in use; the
best consists of a single rule with an axis, carrying two
small rollers fixed at each extremity: these must be
made of precisely equal diameters, and should be as far
apart as the length of the rule will permit: an instru-
ment rolling on two such wheels will be moved parallel
to any position it was first placed in, and consequently parallels to any line to which
its edge is set may be drawn. The edges of the wheels are grooved very truly, to prevent
them from slipping instead of rolling, which would affect the parallelism.

Fig. 794.
The second variety consists of two plain rules connected by two equal pieces of brass
turning on centres, and these must be truly parallel, so that in every position the four
centres of motion may form a parallelogram: when used, the edge of one being set
to any line, the other rule must be firmly held down by the hand, and the first moved
till the same edge is brought to where the required parallel to the given line is to be
drawn. The faces of these rules are generally provided with scales.
E, D, or any other very long line, may be accurately set
out by means of piquets placed at short distances, and
making use of an instrument with an eye-hole, as at B, H,
and which is made to traverse along the line, and having
attached to this instrument a plummet so that its per-
pendicular may always be maintained; parallel lines may
afterwards be drawn in any number. Take also the shortest
distance between the point A and the given line D E, by
placing one foot of the compasses on the point A, and
describing with the other an arc which shall touch the
given line D E in the point F, than the interval A F will
be the shortest distance from the point A; then with the
same distance, from the point G, strike a similar curve, and
lines may be thus drawn or set out parallel to each other.
To draw through the point A a line parallel to K I,
first draw from the point A the line A K, till it touches
the right line K I in any point K; from this point A,
and with any radius as O P, describe the arc O P, then
with the same radius from A strike the arc Q N, and by
setting off the same angle from N to Q, as that of O P,
and then through Q drawing the line A Q, we have the
parallel line required.
Another method may be pursued with a pair of com-
passes: after a straight edge is laid down, points may be
marked at the required distance, through which the line
may be afterwards traced.
If through the piquet Q a line parallel to the railing
B S is to be drawn, and you then place two piquets at B,
S, and with the same length of cord strike two portions of
a circle, as at Q T, a line drawn through two other pi-
quets placed at the extremity of this radius will be at
once equally distant from the railing and parallel with it.
Perpendicular lines are those placed upon another in
such a manner that the adjacent angles formed by their
intersections are equal, and consequently each is a right
angle. A straight line is perpendicular to a curve at a
given point, when it is perpendicular to the tangent to the
curve at that point, in which case it is sometimes called a
normal to that curve.
E
B
D
نا
Fig. 795.
B
F
H
D

H
A
E
G P
F

K
I
Fig. 796.
S
Fig. 797.
A
N
OE

B
A straight line is perpendicular to a plane when it is at right angles with every straight
line in the plane passing through the point of intersection: a plane is perpendicular to a
planc, when any straight line in the first, which is perpendicular to the common in-
tersection of the two planes, is also perpendicular to the second plane.
764
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
To draw a perpendicular at the end of a line: place one
foot of the compasses in the point A, and the other in the
point C; then from C as a centre, and with the radius C A,
describe the arc DAE; from the point F, where the circle
cuts the right line A B, draw a line through the point C
till it cuts DAE in G: a right line drawn from the point
A to the point G will be perpendicular to the line AB.
When the perpendicular is to be raised in the middle of a
line, or let fall from I and K, equally distant from H,
strike curves intersecting at N and O, and a line drawn
through these points of intersection will be the right line
or perpendicular required.
Should the point not be in the middle, as is the case at
X, on the line YZ, the points 1 and 2 must be set out at
equal distances from it, and then arcs of intersection struck.
Or if it should be required to drop a perpendicular to
the line QR, from a point situated at P, then from P as a
centre strike the curve ST, and where it crosses the line
QR, with the same radius form the intersecting curves at
V, and draw the line PV, which will be the perpendicular
required.

in
S
D
M
H
C
3
1
2
X
P
Scale is a term applied to a mathematical instrument,
containing an assemblage of lines and figures, by means of
which certain proportional quantities can be taken;
mensuration it signifies a line or rule of a definite length,
divided into a given number of equal parts, and is used for
measuring other linear magnitudes. An ordinary scale is
usually set out by stepping the compasses along a given
line, very lightly from one end to the other; the distance
between the points being previously determined on. Some-
times it is required to find out the scale by dividing the
given line into a certain number of parts, and considerable
nicety is necessary accurately to perform this: practice alone can effect it.
6 10
*
Fig. 798.
E
B
F
T
R
K
70
PID
B
N
M
K
401
80:
T
EQ Y
Fig. 799.
X
100:
R
H
To construct a scale, considerable care is requisite that all the portions or divisions may
be set out equally: to form one of 80 feet for
instance, it is only required to step the com-
passes so many times along the line; or after 10
feet have been set out at one end, to take its
extent, and then set out the remaining 80 feet.
But when it is required to make a scale of 140
feet upon a given line, as GH, then it is better
from G as a centre, first to strike the arc HS,
and from H as a centre the arc G O, and then
drawing the lines GB and H E, at the same
angle from the line GH; these may be sub-
divided into the same number of equal parts;
then, by uniting the points KY, LX, MV,
NT, OS, PR, they will cross the line GH, and leave all the divisions equal.
When it is required to divide a long line into a consi-
derable number of equal parts, it is best, if the number
will admit of it, to resolve it into two factors, and first to
divide the line into the number of equal parts indicated by
the small factor, then subdivide each of these parts into the
number expressed by the larger; thus, in dividing a line into
150 equal parts, it is better to divide it first into fifties, and
then into tens; it is advisable always, when the number of
divisions is considerable, to adopt a small number at the
commencement, and continue to subdivide them into the
required portions, and when all is performed, to verify them
over the whole length of line.


A
M
•
P
/D │E. | F | G\1\1
K
'I
N
R
To construct two scales on two lines of unequal length,
as suppose it is required to divide each of the lines MN
and QR into ten equal parts; take, or step along the line
AK, ten parts, all equal, but of any length; then from the
points A and K at the extremity of the line, strike arcs
which intersect at L; from this point draw lines through C,
D, E, F, G, H, and S; then from the point L, with M
and N as radii, strike arcs which will cut at O and P, and with O and R as radii, other
Q
Fig. 800.
CHAP. VIII.
765
GEOMETRY.
arcs cutting at S and T: then OP and ST will be the scales required; for as LA K is au
equilateral triangle, the subdivisions on both lines, though of unequal length, must be equal.
Or, the straight line ab may first be divided into five equal
parts, and afterwards subdivided from a andb; an equilateral
triangle may be set out; then parallel lines, as cd, being
drawn, scales of any length may be taken from it, all equally
divided.
A scale divided into hundredths is very useful, particu-
larly where the chain is made use of: ten equal distances
are set out by as many horizontal lines, then from B to L,
the equal distances, L, M, N, O, P, Q, are set out. Another
division is set out, divided into tenths or hundredths at one
end; on each horizontal is expressed a tenth by the sloping
lines; on the horizontal line 22, may be measured two-
tentlis, on the line 33 that of three-tenths, and by descend-
ing, four, five, and six-tenths. Supposing, for instance, it
is required to take off four chains thirty links, or three-
tenths, placing the compasses on the fourth line horizontal
a
C
n
p
q
ሪ

f
g
h
i
d
m
″
38
Fig. 801.
B
8
9
10
F# / 44OD ** 2 L
Q
Р
K
0
F
Y
X
V
D
N
N
M
L 10 80 80 70 90 100

L
2
3
5
6
7
8
10
ㄖ
​T
S
R 10 30 50 70 90:100
G
Fig. 802.
H
of PX, and extending them to the slant line numbered 30, you have the dimensions re.
quired, and so for any other within the limit of the scale, for it will be readily perceived

1
2
3
4
5
6
7
8
G
1
1
2
3
4
5
i
6
1122
18
24
30
FG
J.
20
40
60
80
100
120
140
160
180
200.
!
Fig. 803.
that the last division to the right contains the decimal arrangement. A B, CD, EF, GH,
are scales of the same length, made to suit different measures, as those used in other
1
2
3
1
2
C
E
5
6
7
8
9
10

B .
4
5
6
D
6
12
18
24
30
36
F
24
48
72.
96
120
144
168
192
216
H
G
Fig. 804.
countries; or the first may be called a scale of tenths, the second feet, the third six times
that scale, and the fourth six times that of the third.
Scales are often used as ratios, or for drawing lines which shall be in relative proportion
766
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
A
C.
I
.B
D
L
to each other; so that the first shall bear the same proportion to the second that it does to
the third. A third proportional is required
to the lines AB and CD, the first of which
is double the length of the latter; draw any
angle less than a right angle, as E, F, G.
Carry the line AB from F to H on FG;
carry CD on FE from F to I, and draw the
line IH; then carry CD from H to K on
the line towards G; make LK parallel to
IH, then IL is the third proportional re-
quired.

When a fourth
a fourth proportional is required,
an angle, as SFV, is set out at pleasure;
from the point F, the line MN must be set
out towards the point V, which will termi-
nate at X. Carry the line OP on FS,
where it will terminate at Y, draw the line
YX; then carry QR towards V, and it will
end at Z. Draw IZ parallel to YX, and
the length YI will be the fourth proportional,
as shown.
A mean proportional, found between the
lines AB and KG, is found to be CD:
for example, draw the line EP at pleasure,
and set upon it the line AB and KG,
which will be found to terminate at H;
then divide EH into two equal parts by
the point I; from this point as a centre,
describe a semicircle. From the point G,
which answers to the length of the line AB,
raise a perpendicular, which will cut the
semicircle at K; the line G K is the mean
proportional to the line AB, CD: or the
line A B is to K G, as KG is to CD. Should
it be required to find a mean proportional
to the lines LM and OQ, draw the line
EP at pleasure, and carry on it the two
lines LM, OQ. Describe a semicircle, and
raise a perpendicular as before: then from
E as a centre, as with the radius EK, de-
scribe an arc K R, which cuts the line EP in
S; then the line ES is a mean proportional
between the two given lines L M and OQ;
that is to say, LM is to E'S, as ES is to OQ.
Arithmetical Proportion is when four mag-
nitudes are proportionals; A, B, C, D may
A C.
represent them numerically: then
BD
Three straight lines are in harmonical
progression, when the first is to the third,
as the difference of the first and second to
the difference of the second and third.
Pythagoras is said first to have noticed in
chords of the same thickness and tension the
sounds of the fifth and its octave. These
lengths are as 1, 3, and, the first of which
is to the third, as the difference of the first
and second is to the difference of the second
and third.
2 8
G
F
ti
K
Fig. 805.
M
N
P

Q
R
Y
Y.
T
X
2
Fig. 806.
५.
♡
V

P
•
E
I G
R
H
L
-M
S
A
K
C
Fig. 807.
A
M
مس
Fig. 808.
D
10
Q
B
G
D

B
10
15
20
25 30
M... P
R
L
K
H
If a musical string is called CO, and its
parts DO, EO, FO, GO, AO, BO, CO,
be in proportion to one another as the num-
bers 1, 8, 4, 3, 3, 3,,, their vibrations will
exhibit the system of eight sounds, which are expressed by the notes C, D, E, F, G, A, B, C.
Harmonical Proportion, as it relates to architecture, is that where three numbers are in
such relation, that the first is to the third, as the difference of the first and second, is
to the difference of the second and third; thus 2, 3, and 6, are such numbers, because
2:6:: 1:3; and four numbers are said to be in harmonical proportion when the first is
CHAP. VIII.
767
GEOMETRY.
to the fourth, as the difference of the first and second, is to the difference of the third and
fourth; 9, 12, 16, 24, are such; for 9: 24 :: 3 : 8.
To trace on the ground a straight line equal in length to a circle, it is only necessary
to divide the diameter AC of the circle into eight equal parts, and prolonging the line
to F, upon which six of the divisions are to be set out.
Through the point C, at right angles, draw G H, and from F as a centre, with the radius
FA, describe IAK, when AK will be the length sought.
When it is required to draw a straight line equal to a portion of the curve, as that of L,
it may be done by dividing it into small portions as shown, set out from M, and transferring
them to a straight line, as OP: by this means, it may be performed with sufficient accu-
racy for ordinary purposes.
To draw either on the ground or on paper angles of any kind, a protractor is some-
times made use of: this is a semicircular limb of metal, divided into 180°, and subtended
by a diameter, in the middle of which is a line and dot to mark the centre of the circle, to
which all the divisions of the degrees radiate.
By this simple instrument an angle of any number of degrees may be set out by laying
its straight edge on a line previously ruled upon a sheet of paper, and then marking off the
angle required; lines then drawn from the dot or centre will fully express it.
E
A
When this instrument is made use of for surveying on a large scale, it is formed into an
entire circle, with four arms radiating from the centre. A circular disk of glass is placed
over a hole in the centre, on which two lines are drawn,
crossing each other at right angles: round this is a small
circular ring of brass, which carries two arms, one of
which has attached to it a vernier, which moves over the
outer circle, divided into degrees, and the other a head,
which can be moved round, and made to turn a small
pinion that works in a toothed rack round the outer edge
of the protractor. The arms are moved by this rack
and pinion entirely round the whole circumference, and
the vernier can be set to any particular angle. The
arms are made to extend over the outer rim, and each
carries a fine point, which is pressed down when the in-
strument is to be used, and these make a small dot or hole
in the paper.
To draw an angle of 30° on the line B C, for instance at
the point B, the demicircle has its dot or centre laid at B;
the number of degrees are counted off from D to E, and
then, moving the protractor, a line is drawn from B
through E, and ABC is the angle required.
Or from the point G, on the right line IH, it is re-
quired to set out an angle of 90°. Place the centre of the
přotractor at the point G, and its diameter IK along the
line IH; then counting off the number of degrees, and
mark the point, as at L, remove the instrument, and draw
the line GF through L, and HGF will be the angle
required.
The same may be done by placing the protractor at N,
and its diameter along the line OP, and counting from
this line OP on the circumference of the protractor 144°,
as from R to S, draw then the right line NM through S,
and the obtuse angle of 144º is obtained.
As this is a right angle it is only necessary to raise a
line perpendicular to another to obtain it: the side of
a square makes an angle of 90°, and its diagonal one
of 45°, or the half.
The division of an angle into any number of equal
parts is termed its angular section; and its trisection
requires the aid of solid geometry, being equivalent to
the solution of a cubic equation; the general division of
an angle into any proposed number of equal parts, is a
problem which mathematicians have not yet solved.
To draw on a right line an angle equal to any given
angle, as on the line A B, from the point A, to draw an
Place one foot
angle equal to the given angle CDE.

.C
B
D
Fig. 809.
Fig. 810.
R
Fig. 811.
C
E
F
Fig. 812.
L
H
1
F

L
H
K
M

P
N


--
A
of the compasses on the point D, and strike the arc Fig. 813.
FG: with the same radius, from the point A, strike a similar arc from H to F; then
take the height from F to G, and transfer it from H to K: draw the line AL through
K, and you have what is required.
768
·BOOK II
THEORY AND PRACTICE OF ENGINEERING.
When angles are to be set out upon the ground, lines
or cords are made use of; and if an angle of 144 degrees
is to be set out from the line OP, the centre of the pro-
tractor must be placed at the point N, or where the angle
is required, and then the number of degrees counted from
R to S, and then a string or cord attached to the point
N is stretched over the division at S towards M, and
OM is the angle required. Or, what would be the same
thing, the smaller angle of 36° may be counted off from the
base line towards S.
By the same means, on the line MN, from the point O,
an angle equal to CDE may be drawn, and so of other
angles; but sometimes it may be required to make on the
cord ST, at its extremity S, an angle equal to PRQ; we
must then fix a stump or piquet at the point R, and
another at each of the points P and Q, V and X. Then,
with a cord, we must measure the distance from R to X,
and set it off from S towards Y, and place a piquet there;
from X we must take the distance to V, and set it off from
Y to Z, describing an arc at Z. Then the length RY is set
off from the piquet S, and an arc described cutting the other
at Z: through this point of intersection a line is to be
stretched, and then the angle Z SY will equal that of V R X.
An Equilateral Triangle upon the base line A B is formed
by striking arcs of a circle, having the same radius from
the points A and B: where these intersect at E, BC and
AD are drawn, and the figure is complete.
Before any of these figures can be set out, it is neces-
sary that a straight line should be first established, and
the engineer commences by marking the two ends of the
required line, by fixing at each point a piquet staff. Then
taking up a position at a short distance behind one of
them, and closing one eye, he looks along the edge of one
staff, and directs his attendant to place between the two
piquets first set up other intermediate ones at regular dis-
tances, taking care that they are all so placed that they
are in the line between the two first. This kind of ad-
justment, which is termed boning a line through, requires
considerable practice before it can be relied upon; and the
assistant who follows the direction of the engineer must
well understand the signals that are made to him by the
motion of the hand to the right or the left, or the difficulty
will be increased. The same practice is adopted in setting
out a base or any other straight line when an instrument
is used; and all lines which are to be measured should be
previously set out in this manner, for then those who
carry the chain will be guided in the right direction, and
not be subject to a deviation, which, whether to the right
or left, would increase the dimensions beyond the truth.
All diagonals and angles require the same precautions to
be taken, where accuracy is desired. After a base line is
established, perpendiculars and angles may be raised upon
any point of it in the manner already described.
In an Isosceles Triangle the angles at the base are equal
to one another, and if the equal sides are produced, the
angles upon the other side of the base are likewise equal:
to set out such an angle from the point F, with any radius
greater than the base FG, describe the arc H, and from
the point G describe with the same radius the arc I, cut-
ting each other at K: draw FK and GK: KGF is the
isosceles required. The isosceles triangle, which has the
two equal sides less than the base, may be set out in a
similar manner, using, however, from the points M and N
a radius less than its length, which will intersect each
other at L: LMN will then be the isosceles required.

め
​M
x
N
G
R
X
Fig. 814.
A
Fig. 815.
M
F
Fig. 816.
Fig. 817.
D
Fig. 818.
Z
E
K
L
Y
T
H
G
B
¿





A Scalene Triangle may be formed on the line OP of
any required dimension; from the point O strike the arc which will intersect another struck
with a different radius from P: and then by drawing through S the lines OS, PS, the
angle is formed.
CHAP. VIII.
769
GEOMETRY.

Triangles, similar and equal to others, may be set out
on straight lines by taking the length of the base of the
given triangle, CED, and carrying the length DE on the
line AB from A to F. Then from the points A and F,
and with the radius AF, describe the arcs which shall cut
each other at G: draw the lines GA, GF, when one will
be like the other.
If two triangles have two sides of the one equal to two
sides of the other, each to each, and likewise the included
angles equal; their other angles shall be equal each to each,
viz. those to which the equal sides are opposite, and the
base or third side of the one shall be equal to the base or
third side of the other. And if two triangles have two
angles of the one equal to two angles of the other, each to
each, and likewise the sides lying between equal; their
other sides shall be equal each to each; viz. those to which
the equal angles are opposite, and the third angle of the
one shall be equal to the third angle of the other.
An isosceles triangle may be similarly imitated: take
the length of the base LM, and mark it out from H to
N; then from the points H and N, with the radius LK
or MK, describe the arcs at 0; where they intersect at
P, the lines HP and NP are to be drawn. The two
isosceles triangles will then be similar.
In an isosceles triangle, if a straight line be dropped or
drawn from the vertex to any point in the base, or in the
'base produced; the square of this straight line shall be
less or greater than the square of either of the two sides,
by the rectangle under the segments of the base, or of the
base produced.
The scalene triangle X Y Z may be set out at STQ in a
similar way; and either of these operations may be per-
formed on the ground by means of cords and piquets.
Whatever the form of the triangle, the square of the
side which is opposite to any given angle is greater or less
than the squares of the sides containing that angle, by
twice the rectangle contained by either of those sides, and
that part of it which is intercepted between the perpendicular
let fall upon it from the opposite angle and the given
angle; greater when the given angle is greater than a
right angle, and less when it is less.
In every triangle the squares of the two sides are together
double of the squares of half the base, and of the straight
line which is drawn from the vertex to the bisection of the
base: every triangle is a mean proportional between two
rectangles, the sides of which are equal to the semi-peri-
meter of the triangle and the excesses of the semi-perimeter
above the three sides.
To draw a triangle similar to another, either with or
without a scale, as that shown at ABC, the side A B
measuring 90 feet, the side AC 70, and BC 42, make
a scale of any convenient length, divided into feet, and then
draw a similar triangle, using for radius the dimensions
taken from the scale; by this means the figure may be
enlarged or reduced according to pleasure, or to the di-
mensions determined by the divisions of the scale. In the
present example, 70 feet radius taken from the scale is made
to cut that of 42: the two centres, being F and H, also
set out at 90 feet distance on the base line G from the
same scale.
H
A
D
Q
B
C
F
E
Fig. 819.
K
P

0
N
L
M
Fig. 820.
1

T
R

Z
Fig. 821.

}
90
H
G
D
70
K
70
Fig. 822.
42
A
90
B
It must appear evident, if we make the three angles of
the one triangle equal to those of the other, whatever may
be the difference of the size, their shape will be similar; we
may in one instance use a scale where each minute of a
degree is an inch, and in the other a foot; still if we employ the same scale to each by
which it was set out, the area or content will be the same.
In doubling or quadrupling the contents of a figure, it is only necessary to prepare cor◄
S D
770
Book II.
THEORY AND PRACTICE OF ENGINEERING.
T
rectly the scales by which they may be set out; irregular forms may always be cut up
into squares or triangles, and master lines may be drawn
generally from the extreme points upon which the out-
lines may be constructed.
The triangle TRS may be enlarged to YPG in a si-
milar manner, or without a scale, by taking care to make
their angles correspond.
A Square may be constructed on the line AB, by setting
out first the length of its side from A to C, and then using
these points for radii, striking two arcs which will cross
each other at F. Then divide the line FA in P; set off
the distance FP towards H and G on the arcs struck from
A and C; then draw AG, CH, and GH, and the four
sides will be equal.
A square may easily be set out by means of the pro-
tractor, whose diameter being laid on the line IK, the
perpendicular LI can be marked out: then from I as a
centre, and L as a centre, strike the arcs NO, MO; unite
KO, LO, and the square is formed.
Every rectilineal figure may be divided into triangles,
and every triangle being equal to half the rectangle under
its base and altitude, contains half as many square units as
is denoted by the products of the numbers which express
how often the corresponding unit is contained in its base
and altitude. Suppose the linear unit to be a foot, and it
is required to find how many square feet there are in a tri-
angle whose altitude and base are 10 feet, the rectangle
of the sides of which is 100 feet; therefore the triangle
contains half that area, or 50 feet. It is on this account
we say that a rectangle is equal to the product of its base
and altitude; a triangle to half the product of its base and
altitude.
The length of a line or a side is the linear units it con-
tains: the area or superficies is the number of square units
on its surface. A square whose side is 22 yards long is
the tenth part of an acre, therefore 22 × 22 × 10=4840
square yards, which is the magnitude of the statute acre.
The chain employed to measure land is of this length, so
that 10 square chains make an acre. In Ireland 121 Irish
acres are equal to 196 English, and 48 Scotch are equal to
61 English, and in France 40-466 acres are equivalent to
1000 English acres.
In setting out any given area the simplest method is to
resolve the whole either into squares or triangles; in the
figure the radius represented is 22 yards: it is evident
we should have an area of the tenth of an acre within the
square AGH C, and the square root of 4840 would give us
the length of the side that would contain the acre, which is
10 chains or 220 yards.
The Parallelogram ABCF may be also set out in a
similar manner, using for radius the length of their
respective sides, and through the points of intersection
drawing the lines which are to bound the figure.

P
D
Ꮐ
A
L
A
C
K
S
X Y
Fig. 823.
P
Fig. 824.
N
M
Fig. 825.
B
Fig. 826.
H
K
E
F
D
Ꭰ;
K
1
M
Q
N-PO
S
R
G
Ù
Fig. 827.
L
G

B



Trapezoids may be made either larger or smaller than
others, as well as similar, by dividing them first into tri-
angles by the diagonals MK and GP, and then taking
care that the angles are made equal. At the point G, on
the side GP, the angle PGQ is made equal to the angle
KMI, and at the point P the angle GPR is made
equal to MK I. Then the triangle SPG is similar to
IKM, and the trapezoid SPHG is similar to that of IK ML.
that shall be equal to a given circle, it is only necessary to draw a line equal to the circum-
ference, and at one end to erect a perpendicular equal to radius, and then to unite this right
angle by drawing an hypotenuse.
To draw a triangle
The area of a circle being equal to half the product of the radius and the circum-
ference, and the area of the triangle being equal to half the product of its height and
base, the surface or area of a triangle so constructed and that of the circle must be equal.
CHAP. VIII,
771
GEOMETRY.
METHOD OF Drawing MultiLATERAL FIGURES.-The Pen-
tagon A is drawn by describing a circle from the point B of
the given size: then from the centre B draw the two diameters
CD and EF at right angles, and from the point G, which
is half the radius of E B, describe the arc CH; the length
CH will be the side of the pentagon, which may be traced
round the circle.
To inscribe a regular pentagon within a circle, divide the
radius B F medially in the point H, so that BH may be
the greater segment: draw the radius B C, at right angles to
BF, and join CH: then because the square of CH is greater
than the square B H by the square of the radius C B, and
that BH is the side of the inscribed decagon, CH is the
side of the inscribed pentagon. Therefore a chord equal to
CH will subtend a fifth part of the circumference, and if
the circumference be divided into five parts with chords, each
equal to CH, a regular pentagon will be inscribed. To in-
scribe a regular decagon, divide the radius medially, and
divide the circumference into ten parts with chords each
equal to the greater segment of the radius so divided.
The Hexagon has its sides equal to its radius, and is made
up by six equilateral triangles; the diameter of the circle
which contains it, when cut by a perpendicular passing
through the centre, forms right angles with the two sides it
touches.
The Heptagon M. On a circle of any given diameter fix the
point N: with the radius NO describe the arc PO Q, and
draw the chord line PQ; the half of this chord will be the
side of the figure required.
It must be admitted that we have no exact rule for setting
out this figure, and we can only inscribe it within a circle
approximatively. This is sometimes done by continuing the
series 4, 8, 16, &c., which represents the number of parts
into which the circumference may be divided by continued
bisections, until a number be found which is greater or less
by 1 than a multiple of 7. 64 is such a number, being
greater by 1 than 9 × 7. Now, if the circumference be
divided into 64 parts, and an arc be taken equal to 9 of
those parts, which is less than a seventh part of the circum-
ference by a seventh part, the error may be made up by a
little calculation, and the side obtained near enough for
most practical purposes.
The Octagon S. Describe a circle, and draw the two
diameters V X and YZ at right angles through its centre;
then divide one quarter of its circumference into two equal
parts, and so on with the rest.
The octagon may also be set out by two squares, so
placed that their diagonals are at right angles with each
other, and also by bisecting the arcs which are subtended
by the sides of a square.
The Nonagon B. Describe a circle, and carry two-
thirds of its radius nine times round it.
The same method may be adopted for this figure as de-
scribed for the heptagon: seven times the arc, which is as-
sumed as the seventh of the circumference, falls short but
little of the whole circumference; and 9 times the arc by
about the same, therefore both are near enough for all
practical purposes.
C
K
C

A
E
H
B:
G
Fig. 828.

Fig. 829.

Fig 830,
A
S
M
R

2
Τ
X
Fig. 831.

Fig. 832.
D
Any polygon may be decomposed into triangles, by
drawing straight lines from one of its angular points to each
of its opposite angles, and the area of the polygon is the sum
of the areas of all the component triangles: their area may
be found without this process, which, when the number of
sides is considerable, leads to some labour; the theorem was established by L'Huilier, who
found that the double of the surface of any rectilinear figure is equal to the sum of the
rectangles of its sides, taken two and two, excepting one, multiplied by the sine of the sum
of the supplements of the interior angles contained between each pair of sides.
3D 2
772
Воок 11
THEORY AND PRACTICE OF ENGINEERING
To investigate the general property of polygons, we must
divide them into two classes, convex and concave, the first
being those in which all the interior angles are less than two
right angles, and the second those which have one or more
re-entering angles. If we term those the interior angles of
the polygon which belong to the interior of the figure,
whether less or greater than two right angles, and those
exterior angles which are obtained by subtracting each in-
terior angle from four right angles, we shall have the two
classes.
The Decagon. Describe a circle, and divide the radius
into two equal parts, as at M: from this point, with the
radius MH, mark the point N; the distance GN will be the
side of the decagon.
By a reference to the pentagon we have also the means
to set out this figure, the operation being nearly the same.
The Undecagon. Draw a circle, and cut it in the centre, P,
by two lines, QR and ST, drawn at right angles from the
point R; with the radius RP, mark on the circumference the
point V, and draw the right line VQ; it will cut the radius
PS in X; the length PX will be one side of the undecagon.
The area of the circle was computed by means of in-
scribed and circumscribed polygons; and of all plane figures
having equal perimeters, the circle contains the greatest
area; and consequently, of all plane figures containing equal
areas, it has the least perimeter. The circle, therefore, is a
maximum of area and a minimum of perimeter.
The Dodecagon is formed by carrying the length of one
half the radius round the circle.
Another method may be described for the setting out of
these figures.
On the line A B set out two equal parts, and at their di-
vision, or the point D, elevate the perpendicular line CD;
then from the point A, with the radius A B, describe the arc
BE, which will cut the perpendicular CD in the point F.
Then describe from the point F, with the radius FA or
FB, a circle: the length AB carried six times round forms
the hexagon. By dividing
BF into зix equal parts
in the points L, M, N, O, P,
and F, and from the point
F taking the radius FP,
and describing the arc PQ,
which cuts the perpendicu
lar C Din R: from this point
R as a centre, with the ra-
dius RA, describe a circle,
and carry the length AB
seven times round it, and it
will form a heptagon.
To form an octagon take
the second division F O and
work before, and so on with
all the other figures. Thus
the whole of the regular
polygons may be drawn by
increasing the diameters of
the circles by one division
each time, which will give
several points on the per-
pendicular CD, whence cir-
cles may be described on
which may be carried the
line AB as many times as
may be necessary to con-
struct the required poly-
gon.
Fig. 836.
C
R
Q
K
S
F
II

L
M
G
N
Fig. 833.
1

K
T
Fig. 834
u

Y
Fig. 835.
M
B
b

GEOMETRY
773
H
of
METHOD OF DRAWING POLYGONS ON RIGHT LINES BY MEANS
OF DEGREES. —For the Pentagon divide 360 degrees by 5, and
the quotient gives 72 degrees for the angle in the centre
of the pentagon; then subtract these 72 degrees from 180,
the value of the three angles of a triangle, there remains 108
degrees for the angle of the figure, the half of which, 54,
will be the angle of the demi-polygon. Then make at the
point A on the given line A B the angle B A C of 54 degrees
by placing the centre of a protractor on the point A, and
making its diameter coincide with AB: count 54 degrees on
the circumference, which will terminate at D, and having re-
moved the protractor, draw from the point A through the
point D a line ADC, which will form an angle BAC of
54 degrees. The same process must be repeated at the point
B, the other extremity of the given line AB, in order to
draw the line BE, which will cut A Cin F and form a centre,
from which, with the radius FA, a circumference may be de-
scribed, on which, if we apply the line AB five times, we
shall form the pentagon AGHIB, and by a similar method
all the other polygons.
METHOD OF DESCRIBING CIRCLES, OVALS, PARABOLAS, SPIRAL
LINES, ETC. The following table of factors is sometimes made
use of to construct a circle geometrically: suppose c to be the
circumference of a circle, the diameter of which is unity, and
r the side of a square equal in area to it, and let a be the area of
the circle: then c=3.14159; 2c
3.14159; 2c = 6·28319; = 1.57080;
2

C
P
A
E
Fig. 837.
K
Fig 838.
C
D
B

M
R
L

с
=0·26180;
12
с
360
=
0.00873; = 0.31831;
2
E
=0·63662;
B
A
360
с
=114.59156; x=0·88623; and a=0·78540.
To describe a Circle.-Place one foot of the compasses in the
place where the centre is to be, and with the radius required
describe the circle: to set out a circle on the ground, fix a
piquet or staff in the place where the centre is to be, as at A,
and tie the end of a cord to the piquet by a slip knot, so as to
turn round easily. Then to the other end of this cord attach
a staff, B, at the distance required for the radius, and then
describe the circle by stretching the cord AB equally, and
being careful to keep the staff B perfectly perpendicular, and
not to allow the cord to touch the ground.
To divide a Circle.-Divide the diameter A B into as many
parts as it is required; then from the point A, with the length
of the diameter, describe B C, and from the point B, with the
same radius, describe A C. From their point of intersection,
through the division marked 2, draw the right line CD until
it touches the circle: the line AD will be one-fifth of the
circumference, the diameter having been previously divided
into five equal parts. By this means any circumference may
be divided, so as to inscribe any regular polygon, remem-
bering that we must always draw the line CD through the
second point of the division of the diameter AB, whatever
the diameter of the circle may be divided into: to form an
equilateral triangle it must be drawn through both points of
division.
To draw a Circle through three given Points.-It is necessary
that the three given points should not be in the same line.
Let it be required to draw a circle through A, B, and C. If
on the ground, take the distance between AB with a cord,
or if on paper with the compasses, and describe above and
below, from the points AC, the arcs D E and HI, and
with the same radius from the point B intersect them: then
draw lines through their points of intersection, and where they
cross will be the centre, from which a circle may be described,
that will pass through the three given points.
This method of describing circumferences of circles is of
D
Fig. 839.
E

D
Fig. 840.
Fig 841.
B
F
3
4
en!
B
5
F
G

30 3
774
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
service to architects and others, enabling them to discover the entire form, when any portion
of the figure has been destroyed.
To find the centre of a circle or any portion of it, take
any three points in the circumference of the circle, as A, B,
and C: then from the points A, B, with the radius A B,
describe four arcs intersecting at E and D, through which
points of intersection draw at pleasure the right line
ED; then from the points B and C with the radius
BC, describe four other arcs intersecting at F and G, and
through these points draw the line FG cutting ED in
H, which will be the centre of the circle A B C.
To find the centre of a portion of a circle, as that of
IKL, draw the right line IL, and divide it into two
equal parts in the point M; then raise a perpendicular
from the point M, and prolong it towards the base until
it cuts the portion of the circle IKL in K; then measure
the distance I M, which here is found to be 6 parts, and
the distance MK 4 parts; then multiply 63 by itself; the
product 44 must then be divided by 4, and the quotient
11} must be counted as the line M N from M to C; then
divide the length KO into two equal parts in the point
P, which will be the centre of the circle. The centres of
basins or reservoirs of water may be thus found, even
when portions of them have been destroyed.

+
Method of describing Ellipses.-To draw the oval A, trace
a right line CD of the length required for the oval, and
divide this line into four equal parts by the points E, F, G;
from the points E, F, and G, with one of these divisions
as radius, describe three equal circles: on the point F,
the centre of the line CD, let fall the perpendicular H I,
which will cut the circumference of the circle FG in K
and L; from the point K through the centre E, draw
the right line KE, until it cuts the circle CF in M, and
in like manner from the point I, through the centre G,
draw the right line LG until it cuts the circle FD in
M; then from the point K, with the radius KM, draw
the line MO, and from the point L the line PN. The
curved line CPNDOM is the oval.
When it is required to draw a more rounded figure, as
B, whose diameter is the same as CD, it is only ne-
cessary to divide the line CD into three equal parts in
Q R, and from the two points Q, R, with the radius of one
part, as QC, describe the circles CR and QD; then at
their points of intersection, S, T, draw the perpendicular
ST across CD; then take two equal parts out of the
three, and with the compasses, from the point S describe
the arc VX, and from the point T the arc YZ: the
line CYZDX V is the oval required.
To draw an Oval when the two diameters are given,
as CD for the longer, and E F for the smaller, take half
the smaller diameter, as GE, and set it off on the greater
diameter CD from G to H, and from G to I: divide
GH into three equal parts, and carry two parts on to the
smaller diameter E F from G to K, and from G to L.
From the two points K and L, draw four right lines of
any length through the points H and I: from the point
H as a centre, with the radius HC, describe the arc
NCM, and from the point I, with the same radius, de-
scribe the arc O'DP; then from the point L, with the
radius LM, describe the arc MEO, and from the
point K, with the radius K N, describe the circle NFP;
the line CMEODPFN will form the oval A on the two
given diameters.
To draw an oval similar to B, the two diameters of
which, QR and ST, cross at right angles in the point
V, take with a thread or cord the length of the greatest
diameter QR, and double the thread; place its two ex-
C
0
P
M
F
"
Fig. 842.
Fig. 843.
Fig. 844.
Y
X
N
B
L
E
P
M
6
4
**
H
H
K


K
N
L
T
Q
R
Fig. 845.
M
Z
D

B
D

Q
B
T
L
Fig. 846
R
CHAP. VIII.
775
GEOMETRY
Draw in any part of the
tremities X and Y on the greatest diameter QR, equally distant from the centre V, so
that the fold or angle of the thread exactly reaches the point S and the point T; then
place a pencil-point at the end of the doubled thread, and move it round until the
extremities QR and ST have been passed through, which will form the oval required.
To find the Centres of an Oval.
oval the right line CD, and at any distance its parallel
EF; divide these two parallel lines into two parts in
G and H, and trace through these points the lines
IGHK; then bisect this right line in the point L,
which will be the centre required.
To find the two Diameters of an Oval when the centre is
known, it is required to find the lengths of the longer
and shorter diameters of an oval whose centre is at L.
Describe from the centre L a circle which shall exceed
the oval both above and below, and note where the
circle cuts the oval, as in the points MNOP, in order
to draw through those points M and P the right line
MP, to which a parallel line must be drawn, passing
through the centre L, to the circumference of the oval,
as QR, which will be the lesser diameter of the oval ;
then cut the lesser diameter QR at right angles in the
centre L by the right line ST, which will be the greater
diameter of the oval.

•
Method of drawing Parabolas, &c. Trace the right line
A B, of the length required for its base, and divide it
into two equal parts in the point C; from this point
raise a perpendicular CD, of the length required for the
axis of the parabola; divide this axis into several equal
parts in the points E, F, G, H, I, and D: through these
points of the axis CD, draw transverse lines parallel with
the base AB; prolong the axis CD to infinity, as to K.
Divide the first space ID into two equal parts, as at L;
take the length DI, and set it off from D towards M;
then take the distance MI, and set it off from L to the
extremities of the first transverse line, at the points N and
0;
O; then take the length MH, and set it off on the
second transverse line, as at P and A: take also the
distance MG, and set it off from L, to the extremities
of the transverse line C, as at the points R and S, and do
the same with all the other lines: then through these ex-
tremities so marked off, trace the line A X T, &c., which
will give the parabola.
Method of describing Spiral Lines, which are either
simple or compound; the first are those which are
formed by a single line, and the latter those which have
a double one. A simple spiral is drawn by tracing the line
CD, and making upon it the position of the eye of the
spiral G; then from this point G, with the radius GE,
describe the semicircle EHF; and from the point E as
a centre, with the radius EF, describe the semicircle
FIK; then from the point G, taken again as a centre,
with the radius GK, describe the semicircle KLM;
then from E as a centre, with a radius EM, describe the
semicircle MNO. The same process must be repeated
alternately from the centres G and E; and thus semi-
circles must be traced at the interval where the preceding
circle ceased, until the spiral is of the size required.
To draw a compound spiral, a simple one must be
first drawn; then set off from the point E to P, the ex-
tent to be given to the width of the band, as EP; then
from the point G, with the radius G P, describe the semi-
circle PQR, and from the point E as a centre, with the
radius ER, describe the semicircle RST: in like manner
also, from the point G as a centre, with the radius GT,
describe that of TV X, which must be continued alter-
nately from the centres E and G, until the several spirals
answer to the former.
с
E
A
D
G
Fig. 847.
K
L
H

K
M
H
G
D
T
X
Fig. 848.
R
Р
A
L

D
M
N
L
Q
S
V
Y
C
B
Fig. 849.

N
I
0/K/EGT M
Fig. 850.
H
I
B

RX
3 D 4
776
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
The Construction of Solids comes more under the denomi-
nation of descriptive geometry, and on the Continent it has
for many years formed a branch of study for engineers, both
civil and military: it cannot be too highly esteemed, as it
consists in the application of all the known rules of projec-
tion, to exhibit on a plane the figures of the solids, as weli
as to show their method of construction. The plane surfaces
of all solids are bounded by edges, which can be expressed
by straight lines: and in the construction of a solid we have
to regard three varieties of angle: the first are those where
the lines meet which bound the figure; the second, those
which result from several faces meeting to form a solid
angle; and thirdly, those which are formed by two planes
or faces.
We shall find that cubes contain six equal planes, twelve
edges, and eight solid angles, and that in all solids with
plane surfaces, the edges terminate in solid angles formed
by them, or where they unite with each other: and to find
the projections of the right lines which represent those edges,
it is necessary that we should know the position of the solid
angles where they meet, and these are formed generally of
several plane angles.
To make a Triangular Pyramid, draw the triangle DEF
of the required dimensions, and then fix the point G where
the summit is required, and unite lines from each of the
points DEF of the base in this point, which will give the
figure required. All other pyramids, as those with square
or polygonal bases, are set out in the same manner.
Pyramids may be regarded as solids standing on polygonal
bases, their planes or faces being triangular, and meeting in
a point at the top, where they form a solid angle.
To construct a Pyramid or a Tetraedron in relief, in card, or
other material, the base must be set out as at I; then at the
sides the other triangles must be formed. These three outer
triangles are then raised and united at the top, which will
form the tetraedron required. If the faces which meet at the
apex are required to be longer than the equilateral tri-
angle, after the base is set out, the isosceles triangle must be
traced of the height required, and when cut out, united at
the point or summit as before.
It will easily be seen that a tetraedron may be inscribed
in a tetraedron, an octaedron in a cube, and a cube in an
octaedron, an icosaedron in a dodecaedron, and a dode.
caedron in an icosaedron.
The mutual relation between the regular solids is very
curious: when lines are drawn from the centre of the cir-
cumscribed solid to its different angular points, these lines
will be perpendicular respectively to the faces of the inscribed
solid; so that if we cleave or cut away the solid angles of the
circumscribed figure by planes perpendicular to these lines,
and if we continue the process until we arrive at the centres
of the several faces, we shall obtain the regular solid, which
is inscribed, and which forms, as it were, the nucleus of the
other. By cutting away the solid angles of the tetraedron,
we also form the octaedron.
To find the inclination of the two adjoining planes of a
tetraedron, we have only to consider that the required in-
clination is that of two angles of equilateral triangles, which,
together with a third, form a solid angle, and therefore may
be easily constructed: in a cube the angle of inclination
will be a right angle.
To draw or construct Prisms. Set out its base of the
number of sides given; then from the angles of the base
DCH, &c., elevate perpendiculars of the height to be given
to the prism, in such a manner that we join the points
I, C, N, &c. Hollow prisms may also be set out, by giving
the thickness and drawing as it were one prism within the
other.
G
a
с
E
B
C
L
K
M
N
I
P
Fig. 851.
K
P
H
Fig. 852.
Fig. 853.
K
L
D
P4
E
R
K
M
A


CHAP. VIII.
soy y
GEOMETRY.
To construct a Prism.
T its sides XY, of the length required, and also the top
V of the size and form of the base, and then the whole
may be folded together to form the prism or figure
required. In the figure shown at S, we have a simple right
prism, the faces being all perpendicular to the ends; the
developments are consequently all rectangles which are
joined together at the edges and enclosed at each end.
Form on each side of the base
V shows the plan of an hexagonal prism, and its manner
of uniting the sides Z to form a regular figure.
To draw an inclined prism, we commence by tracing the
profile parallel to its degree of inclination, and then de-
scribing on its axis the plane which is perpendicular to it;
afterwards by lengthening the lines which represent the
edges, we may project the horizontal section, as is shown in
the development of right and oblique cylinders.
The Tetraedron. The three triangles which surround
that in the middle, and which are made to meet in a point
at the summit, form a figure with four faces. To form
this out of paper or card, it is only necessary to partly cut
through the lines to enable it to fold.
A sphere may be circumscribed about a given tetraedron,
as well as inscribed within it.
The sphere or globe may be considered the chief or
primary figure, and the standard of proportion to the tri-
angular prism, the cylinder, and the cone: the discovery of
the diagram of a sphere inclosed within a cylinder on a
tomb at Syracuse led Cicero to pronounce it as that of
Archimedes. In the triangle we might inscribe a circle,
which would represent the base of the three secondary
figures, and among the Saxon-sculptured ornaments we
find the globe encompassed by an equilateral triangle,
which is readily effected by sinking the stone without
the circle, and then rounding off its edges to produce the
hemisphere. Taquet, in his Theorems of Archimedes, has
added "Una tribus ratio est to the diagrams in which is
represented the prism, the cylinder, and globe. Length,
breadth, and depth constitute a geometrical solid, and these
three dimensions belong to the parallelopipedon, the tetra-
edron, and the sphere: the first of these figures is said to
be cubic, plinthic, and oblong; the second, equiangular,
obtuse, or acute; and the third, right, oblate, and ovate; of
these varieties there are many subdivisions. The sphere is
the most perfect of the whole, as it comprehends all others
in its centre, diameter, radii, and circumference.
"3
To draw a Hexaedron or Cube, or to construct one, an
exact square must be set out for a base; then on the sides
the four squares RSTP, each equal to O, and attached
to P another square Q, which, when folded together, forms
the top.
Care must be taken to make allowances for the
joining or uniting at the angles.
Cubes are variously represented: the top D may be shown
of the same dimensions as the front C, or the double cube
may be drawn with its top, I KLM, double the face or
front GHIK; it may be shaded, as N, and the dotted lines
EF omitted.
Z
Fig. 854.
Fig. 855.
C
S

L
M
E
G
Fig. 856.
V
T

D


Mr. Peter Nicholson, in his Practical Treatise on Stone-
cutting, says, "Every stone bounded by six quadrilateral
planes or faces forms a solid, of which the surfaces terminate
on eight points, every three surfaces in one point: every
three planes thus terminating is termed a solid angle or
trihedral. The angles formed by the intersections of the
faces with one another, or the three plane angles, are called sides of the trihedral, and
the angles of inclination, by way of distinction, simply angles. The three sides, as
well as the three angles, are each called a part, so that the whole trihedral consists of six
parts, and if any three of these be given, the remaining three can be found: therefore,
if bodies constructed of stone, which are intended to have their solid angles to consist
778
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
The
of three plane triangles, the construction of such may be reduced to the consideration
of the trihedral: as to the remaining surface, which encloses the solid, completely
making a fourth side to the trihedral, it may be of any form whatever, regular, or irregular,
or consisting of many surfaces; it or they have nothing to do in the construction.
portions of the trihedral, which may be obtained from three given parts, are the very same
as the three found in a spherical
triangle from three given parts:
this is in fact spherical trigono-
metry.
This figure is easily compre-
hended by the plan, on which, in
the form of the cross, the six
squares that are to make the sides
are set out Q becomes the top,
Sone end, and P the other, RT the
sides, and D the bottom. A piece
of card-board, partly cut through,
where the lines are drawn, may be
folded on the contrary side so as
to exhibit this figure. It will ap-
pear at once evident that each face
has one opposite to it as well as
parallel, and that the opposite
edges are parallel; the straight
line which joins two opposite
angles passes through the centre
of the cube.
R
A
Fig. 857.
V
Q
Р
S
#

To draw and construct an Octaedron. Trace the
square NOPQ of the given dimensions: on each side
construct an equilateral triangle, which being folded to-
gether will form one half of the octaedron; this repeated
and joined to the first half constitutes the entire figure.
The equilateral triangle, the square, and the pentagon,
are the only forms which enter into the regular poly-
edrons, whose angles and sides are equal; the solid
angles of all, when cut away, regularly form figures, also
symmetrical.
The angles of the tetraedron may be so
taken off, that we may obtain a polyedron of eight faces,
composed of four hexagons and four equilateral triangles,
forming a polyedron of fourteen faces.
When it is required to show a bird's-eye view of the
octaedron, it may be drawn either in simple outline, or
it may be shaded to express its figure. The square
CDEF, by its dotted diagonals, shows the plan of its
sides; GHIKL its solid form, and M the figure with
its sides tinted.
To construct the octaedron on card board, it is only
necessary to cut partly through lines which unite the
triangles with the side of the square, and then to bring
them into the position shown at NOPQ, and uniting
the edges RR to form one half, as TR.
Similar oper-
ation for the other half V must then be performed, and
the two brought base to base, to complete the model
of the entire octaedron.
S
R
D
T
P
T
Q
K
A
Fig. 858.

Fig. 859.
C
D

G
F
IX
L
H
Fig. 860.
R
R
Ω
N
M

R
N
S
R
R
K
T
P
K
These regular solids have all been admirably cut by the
aid of machinery, and are very useful in enabling us to com-
prehend the structure of minerals, or to project the form
into which a stone requires to be shaped for particular
situations in masonry. In the academy of the Greeks
consideration was deservedly given to the five Platonic
bodies, so designated after their great discoverer, who
always taught by example or with models before him.
In France great attention has been paid to the subject of
projection, and to the right understanding of the regular
and irregular solids; rules are laid down in every treatise
upon carpentry and masonry to enable the student to per-
form these operations, and it is in proportion as he com-
prehends form, that he can construct with strength and economy. If it were necessary in the
Fig. 861.
CHAP. VIII.
779
GEOMETRY.
A
Grecian schools to have a thorough and clear notion of form before an object could be rightly
comprehended, it is equally so at the present day : let us remember what the
artizans of Athens have left us, and then seek for the rules by which they
were guided, and have before us the precepts of Plato in all our inquiries:
that great philosopher in his " Phædo" observes: "If we are not able to find
out truth, this must be owing to one of two reasons; either that there is no
truth in the nature of things themselves, or that the mind of man is, from
some radical defect, unable to discover it; upon the latter supposition, the
inconstancy and uncertainty of human opinions can easily be accounted
for, and therefore we ought to ascribe all our errors to the defectiveness
of our own minds, and not to affirm, gratuitously, that
there is any defect in the nature of things: truth is fre-
quently difficult of access; therefore, before we arrive at it,
we must proceed with great caution, examining carefully
every step we take; and after all our efforts we shall often
find ourselves disappointed, and forced to confess our igno-

rance.
The Dodecaedron is formed round a pentagon in a similar
manner, as CA.
The dodecaedron may have its angles so cut away
as to produce a solid having twelve pentagons, united by
twenty hexagons, and having altogether thirty-two sides;
in this shape it nearly approaches that of the globe.
represents the solid resting on one of its angles.
A
C
N
H
P
D
I
Fig. 863,
To draw the dodecaedron, describe first a circle of the dimen-
sions to be given it, and divide it into ten equal parts, as shown at
DEFGKIHL MN: these are to be united by lines, as shown
in the figure; then from five alternate points, as E, G, I, L, N, draw
other lines to the centre; then set out PQRST to show the
pentagon at top, and omit the dotted lines to render the figure
complete.
Fig. 862.

E
R
G

V
X
T
&c
}
Z
Fig. 864.
To construct the dodecaedron in card, draw first the pentagon
T of the size or dimensions of the face; then on each of its sides
construct the other pentagons V, X, Y, Z, &c. of the same size;
then, after cutting through the lines partly by which the latter
are united to T, they may be folded and united together to resemble half the solid, as
shown at A; a similar process must be adopted for the other half, and then the two united
to complete the dodecaedron.
The Icosaedron is formed by drawing twenty equal and equilateral triangles, and uniting
them in a manner to form the figure Q, A, and B.
This figure is formed of
A
Fig 865.
B

C


L
H
D
F
Fig. 866.
Fig. 867.
twenty pyramids, whose bases
are the twenty equal and
equilateral triangles, the sum-
mits of which terminate in
the centre of the body, as
shown at A; this figure re-
presents one half of the ico-
saedron, and the figure B
the other. To draw this
form, trace a circle of the
dimensions to be given to it,
and divide it into six equal parts, as shown at
CDEFGH, then draw the sides CD, DE, EF,
FG, GH, and HC, to complete the hexagon, in
which is then to be inscribed the equilateral
triangle HDF, and the parallelogram HDEG:
then, from the point L, the centre of the side
HD, raise the perpendicular L C, and from the same
point L, draw the right lines LI, LK, to the points
I and K, which are the points where the two sides
HF and DF of the equilateral triangle HDF cut
the side GE of the parallelogram HDE G.
To construct it on card, twenty equal and equi-
lateral triangles must be placed as shown at MN,
and then, when the lines are partly cut through, they
may be folded, as shown at Q.
N
M
Fig. 868.
Fig. 869.
E

780
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Cylinders are formed by drawing
a parallelogram equal to its external
face, and folding it together, adding
the top and base.
A and B show two cylinders
placed in a vertical position; and
they are drawn by first making the
circles BC and FG equal, and
afterwards uniting them by the
straight lines FB, C G, taking care
that the centres E and Dare in the
same perpendicular line.
A cylinder lying in a hori-
zontal position, as H, may be con-
structed around the centres D, E, in
a similar manner; BF and CG
being drawn to unite the ends.
Columns, which differ from cy-
linders by their entasis, or swelling
at a certain part of their height, or
diminishing like the frustums of
elongated cones, may be formed in
the same manner; their summits P
and Q must, in that case, be made
of the dimensions calculated for
their upper diameters.
E
F
G
D
H

B
F
C
B
G
D
Fig. 871.
N
K
Fig. 870.
M
Z
א
A hollow cylinder, or one constructed in card, is commenced
by drawing the parallelogram R, which has its sides ST, VX,
the length of its circumference, and those of XT and VS the
height of the figure: simply bending such a card, and uniting
its edges, completes the figure, and by covering the two ends
with circular cards, formed of the proper dimensions, a solid
cylinder may be represented. The cylinder is a solid figure,
the surface of which is partly plane and partly curved, the
plane portions being two equal and parallel circles, and the
curved portion such that any point being taken in the circum-
ference of either circle, the straight line, which is drawn
through it, parallel to the line joining their centres, lies wholly
in the surface.
Right and Oblique Cylinders may be treated
as prisms with polygonal bases. The setting
out a right cylinder is obtained by having a
rectangle of the height required, and also the
circumference of the circle which serves for its
base: the twelve perpendicular lines may re-
present the edges of a prism, and their distance
apart is such that the whole bend round the
plan is shown at the top and bottom. In the
oblique cylinder, the same principles of setting
out are attended to as already described for an
oblique prism.
Fig. 874.
l'ig. 872.

R
T

X
TX
Fig. 873.


In making plans and elevations for the con-
struction of an arch or vault, we may generally
suppose that the vertical projection of a point
is above the ground line, and that the hori-
zontal projection is below: if the point be above
the horizontal and before the vertical plane,
its vertical projection will be above, and its horizontal projection below, the ground
line: if the point be situated before the vertical and below the horizontal plane, the two
projections will be below the ground line: if the point be situated above the horizontal
and behind the vertical plane, the two projections will be above the ground line; and if the
point be situated above the horizontal and behind the vertical plane, the vertical projection
will be below, and the horizontal above the ground line.
To construct a mould for a, cylindrical oblique arch terminating upon the face of a wall,
in a plane at oblique angles to the springing plane of a vault, so that the coursing joints
may be in planes parallel to the lines of the intrados of the vault, we must let the
vertical plane of projection be perpendicular to the axis of the intrados, and conse-
CHAP. VIII.
781
GEOMETRY.
quently it will also be perpendicular to all the joints of which their planes are parallel to
the axis.
The vertical projection of the intrados will be a curve similar to the curve of the right
section of the intrados. The vertical projections of the coursing joints will be radiant
straight lines, intersecting the curved projection of the intrados.
The vertical pro-
jections of all the joints, which are in vertical planes parallel to the axis, will be straight
lines perpendicular to the ground line: the vertical projection of all the joints, horizontal
planes parallel to the ground line.
In practice we may mould a cylinder to the form of the opening, which is to be arched
or vaulted over, and after its ends have been cut to suit the faces of the walls with which
it is to unite, we may make a correct model of this, and trace upon it the direction of each
course, showing its plan and situation; or we may cover it with plastic clay, of a thickness
correspondent with the first course of masonry, upon which we may define each particular
joint, and thus arrive at a thorough knowledge of all the planes and their projections.
Models at all times serve to help us to the right knowledge of form, and when cor-
rectly made, there is no difficulty in giving their representation upon paper, whatever may
be their situation with respect to the plane on which they are to be drawn. The same prin-
ciples apply to cones and all other figures, whether right or oblique.
Cones are constructed by
describing a circle of a radius
equal to its slant height, and
then dividing the circum-
ference into six equal parts;
taking one of these parts, and
uniting it together at the
edge, the cone required is
formed. When it is required
to form a less acute cone, a
greater portion of the circle
may be taken, or that portion
which equals the circum-
ference of the base.
Σ
L
K
A
H


Ꭱ
F
G
To draw a cone, either
perpendicular to the horizon
or reclining, a circle, G, must
be first described, of the ex-
tent to be given to the base,
as E FCD: GH must be set
out of the required height, and the perpendicular drawn,
after which the sides H F, and HD, HC, and H E.
Fig. 875.
E
C

B
H
E
Fig. 876.
X
R
I
Y
In France the epure made by the engineers and architects
for the use of the workmen are of the size of the objects to
be formed; these, corresponding with our working drawings,
are set out with the greatest precision. The position of
every part or its plane must be carefully studied before any
figure can be worked. If in the cone X it were required to
take out a portion, as that of TS in the cone Y, it is only
requisite to set out upon the card of which it is formed the
dimension TS on its outer edge, and then lines drawn to the
centre, from which the curvature is struck, will represent the
omitted part. By a similar method the conical covering of Fig. 877.
a tower or building may have developed upon it all the
apertures or ornaments which form its decoration; which,
when drawn upon the. flat surface, will be in their true
position after the card is folded together, if projected truly.
To cut out a piece of paper or card, so that it can be
folded up into the form of an oblique pyramid: the position
of the point must be shown on the plan or horizontal pro-
jection, which corresponds with the apex of the pyramid;
from this point must be described the arc of a circle, upon
which are to be transferred the horizontal projections of the
inclined arrises: then on the perpendicular raised from the
plan to the apex is to be set the height of the pyramid
above the plane of projection; from a point so established,
lines, as dotted, are to be drawn to their seat on the horizontal
plane, which will show the real lengths of the edges of the
pyramids the small section shows the form at one-third
from the top.
Fig. 879.
G


T S
Fig. 878.

782
THEORY AND PRACTICE OF ENGINEERING. BOOK IL

To draw an Oblique Prism, we must commence by
tracing the profile of the prism parallel to the degree of
its inclination: having defined the inclined axis of the
prism in the direction of its length, and lines to show
the surfaces by which it is terminated, upon the axis so
drawn, the polygon which forms the plane of the prism
is to be drawn perpendicular to the axis: thus the four
edges of the prism will be obtained.
Right and Oblique Cones may be formed in a similar
manner: thus the base of a cone is the sector of a circle
whose radius is equal to the side, and the arc equal to
the circumference of the circle which is its base.
If we regard the cone as a polygon with an indefinite
number of sides, we shall have little difficulty in de-
veloping it; in the example we have shown twelve sides,
and the lines may be imagined to show the edges or
arrises.
•
t
Fig. 880.
The Cone may be formed by setting out its superficies, and bending it round until it
unites at the edges.
The Base is a regular polygon, of an in-
finite number of sides, and consequently its
development is the sector of a circle, whose
radius is equal to the side of the cone, and
the arc equal to the circumference of the
circle which forms its base.
The ancients made considerable progress
in the discovery of the properties of conic
sections: Archimedes incidentally refers to
the subject, but his writings do not explain
the whole of the theory relating to it; he
treats, however, of the areas of the sections,
and the solids formed by their revolution
about an axis; he also shows that the area of
a parabola is two-thirds that of its circum-
scribing parallelogram, and this for a long
time was the only true quadrature of a
curvilineal space known. This great geo-
metrician also pointed out what was the
proportion of elliptic areas to their circum-

Fig. 881.
scribing circles, and of solids formed by the revolution of the different sections to their cir-
cumscribing cylinders.
Apollonius, the Greek geometer, cultivated the science of conic sections, and made con-
siderable advances on the subject: before his time the different curves were defined by sup-
posing right cones to be cut by planes perpendicular to their sides, by which method it was
necessary to have three different cones to produce the three sections, as a right-angled cone
for the parabola, an acute-angled cone for an ellipse, and an obtuse-angled cone for the hy-
perbola. Apollonius showed that the three sections might be obtained from any one cone,
whether right or oblique.
In setting out a series of courses or zones on the cone, it is necessary to define all the
divisions intended on the base, as well as on the slant lines, and then form each portion
separately; where a cone is to be cased with masonry the thickness of the stone, when
applied, forms an outer cone, consequently two developments are required.


Fig. 882.
Upon a cone so set out may be traced the varieties of curves or sections which produce
CHAP. VII1.
783
GEOMETRY

the ellipsis, hyperbola, and parabola,
so useful in the study of conic sec-
tions, or in the development of
mouldings used by the Greeks.
The base of the cone may be divided
into a number of equal parts, and
from each point on them lines may
be drawn to the apex, and either of
the above-named figures may thus
be portrayed.
To set out an oblique cone, the
position of the apex must be found
on the plan, and the same method
Fig. 883.
A
Fig. 885.
Fig. 884.
R
Y
of proceeding must then be adopted as in the preceding example: after the seat of
all the lines has been found upon the plan, and their respective heights set out on the
planes which represent the vertical, they may be transferred to the figure.
Globes are constructed by drawing the paral-
lelogram E F G H, which has its greater side EF
twice the smaller one E H. Divide the small sides
EH and FG each into two equal parts in the
points I and K, and draw the line IK; divide this
length into twelve equal parts, and prolong it at
pleasure. Take nine parts from the twelve on
IK, and placing one foot of the compasses on any
division, as 7, observe where the other foot cuts the
line IK, as at L: from the point L as a centre,
with the radius L7, describe the arc M7 N: then
with the same radius L7, placing one foot on the
point 6, observe where the other foot falls at O,
and from this point O as a centre, with the radius
06, describe the arc M6 N, which will form the
spindle M7 N 6. Twelve of these spindles made
with the same radius, and according to the same
rules, cut and folded together, will form the globe
Q.
When it is required to cover a dome or any
portion of a globe, these spindles or gores must be
carefully drawn, and if the boarding or material is
to be applied from the base towards the top, the
diagram will show the method for cutting it out;
if it is to be bent round, so as to exhibit horizontal
joints, the several portions will be those of cones, as
already described. Timber domes are frequently
formed by adopting both processes, and many upon
a small scale exist in Italy, hooped round with thin
board, the first formation being that of a number
of gores, cut as shown in the figure E F G H; three
or four thicknesses of bent plank screwed firmly
together will form a dome of sufficient strength to
sustain a covering of lead or copper, and, when
assisted by an iron hoop at the base, will endure a
considerable weight without yielding.
When the base of a dome is polygonal, the forms
to be given to the gores may be easily found by a
similar process.


N
H
9
10
11
L
E

Fig. 886.
F
M
Fig. 887.
To project a Sphere orthographically on the Plane
of the Equator: the centre from which the circle is
struck that represents the equator will be the projection of the pole; and the two diameters
which are perpendicular to each other will be projections of meridians 90° distant from each
other: each quadrant of the circle must then be divided on its circumference into six
equal parts, and lines drawn as radii from these points will be the projections of meridians of
15º, 30°, &c. &c., dividing the equator into twenty-four equal parts, any one of which may
be assumed as the first meridian. To project the parallels of latitude, divide one of the
quadrants into nine equal parts, and drop from the points of division as many perpendi-
culars, which will cut the diameter of the circle; then from the pole as a centre, describe
other circles through these points on the diameter, which will be the projections of parallels
of latitude at the distance of ten degrees.
By a series of parallel circles, crossed by others perpendicular to them, we may fɔrm a
784
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
sphere into a polyedron, and these bands can be made to exhibit the faces of the truncated
pyramids of which they are a portion.
The mineralogist has taken the regular tetraedron, the cube, the rhombic dodecaedron, the
octaedron, the six-sided prism, and the parallelopiped, as the primary forms upon which the
several crystals are found in the first four, which are called the regular geometrical solids,
we find all the planes of each equal and similar; the cubical crystal of fluors may have each
of its solid angles removed

easily, when its figure will
exhibit eight triangular
smooth planes instead, and
then continuing to remove
the several layers which
compose these eight trian-
gular planes, we arrive at
the eight triangular planes
of a regular octaedron By
a study of the structure of
a mineral substance, we
shall arrive at a tolerably
good idea of the principles
of descriptive geometry:
the sphere may be in the
present instance considered
the nucleus upon which
the parallel deposits are
formed.
Fig. 888.
The sphere is a polyedron, having a great number of plane faces, formed by trun-
cated pyramids whose base is a polygon, and its development by conic zones is obtained
in the same manner as for truncated pyramids, with this difference, that all the arrises are
arcs of circles, described from the summits of cones, instead of being polygons.



Fig. 889.
On Shadows.-That part of a body from which light is intercepted by any object inter-
vening is said to be in shadow. The rays of light, which we receive from the sun, proceed
in straight lines, and opaque objects, not transmitting through them the light they receive,
necessarily have their opposite sides to the luminary in shadow: a shadow becomes
apparently darker as the illuminating powers which produce it are increased. A stream of
light may be supposed to proceed from every luminous body which falls on all the objects
around, and is again reflected by them to others, until it is entirely imperceptible.
Shadows are produced by depriving the object of the direct rays of light, and the artist
generally represents on his drawing a shadow equal in depth to the projection of the ob-
ject which casts it, or at an angle of 45°.
Light is either transmitted, absorbed, thrown back, or reflected, and the latter is always
so thrown that the angle of reflection is equal to the angle of incidence.
Some colours reflect light stronger than others, and on this subject the painter must
carefully study nature to obtain his knowledge: in a lofty building those parts nearest
the ground receive the greatest portion of reflected light, and the upper the less, consequently
they are darker: and the strength of colours is heightened or lessened from this cause.
All shadows thrown from one object to another are darker than the object itself. and those
parts which do not receive the direct light receive their brightness from reflection, and the
shadow gets no reflection except from the object in shade.
The cornice of a building, which casts a shadow on its perpendicular face, receives on its
under side or soffite a proportionate quantity of reflected light, either from the ground be-
neath it or the upright face of the wall; consequently it is not so dark as the shadow it casts,
and hence the beautiful relief between one and the other: there is the positive light, the
intermediate, and the shadow.
CHAP. VIII.
785
GEOMETRY.
All Opaque Bodies which are lighted up on one side cast a shadow on the opposite; and
those which receive their light from bodies larger than themselves cast a shadow as at A:

B
C
A

Fig. 890.
those that are of equal magnitude as those at B, and those that receive their rays from a
smaller light, as that of a candle or lamp, as shown at C.
All luminaries, as the sun, emit a stream of light by which objects are rendered visible,
and those bodies which cannot be penetrated by it are called opaque bodies: the part which
is deprived of light, or which does not receive it, is said to be in shade, and that part of
any surface on which a shade is projected is called the shadow.
The side of the body, as that of a prism, which is not opposite the light, is
that which is in shade, as A K. Should the top of the prism receive the direct
light, then the side K ought to have a teint, to distinguish it from the face
which is so strongly illuminated: but if the rays fall at an angle of 45 degrees,
the horizontal and vertical faces which receive them may be supposed equally
bright.
K
A

Sciography, or the principles upon which shadows are projected, will be the
better understood as we advance in our knowledge of descriptive geometry,
which explains as well as removes all the difficulty of understanding the
position of the several planes, or their relation to each other: as the rays of
the sun are reflected in all directions, the projecture of the prism prevents a
part of the reflected rays from proceeding to the plane behind the prism, and
consequently that plane would be a little darker than the face of the prism
which is parallel to it; but as the side of the prism adjoining to the plane will throw a
reflection, it is difficult to distinguish any difference between them. The difference of
Fig. 891.
light between the side of the prism which is perpendicular to the plane and the plane
depends on the position of the luminary; if its plane be equally inclined to both, there will
be the same light on each; but when it is more inclined to one than the other, then that
which is the most oblique will be the darkest.
In a cube that is doubly inclined, as in the
figure, its projection upon a horizontal plane is a
regular hexagon, and upon a vertical plane a rect-
angle; thus showing the variety of shadows such
a solid may cast. By dropping perpendiculars
from the solid angles of the cube, we may, upon the
horizontal plane, where the hexagon is shown, set
out the seat of every portion of the cube which is
obliquely placed above: by parallel lines we de-
scribe upon the vertical plane the quadrangular
figure which the cube exhibits, and which is similar
to a section seen diagonally. In stone cutting, as
we shall hereafter find, it is highly important that
we understand the form of a cube in every position,
and this is only to be exhibited by imagining a
variety of planes, upon which the figure may be
drawn: the cube may be made to contain the sphere
or portions of it, the planes of which can be found


Fig. 892.
in every direction, and afford the student an opportunity of study and practice in drawing.
3 E
786
THEORY AND PRACTICE OF ENGINEERING.
*
* Book II.


It is not possible thoroughly to compre-
hend the seat of a shadow upon either a ver-
tical or horizontal plane, without using the
methods already described for projecting
them: by the various positions in which the
cube is placed, we can perceive that its
shadow is dependent upon the same prin-
ciples as those already described for the for-
mation of a solid.
The geometrical form of the cube, shown
in the figure, would be as here represented.
The diagonal lines dotted on the plan show
the position of the upper edges of the cube;
the perpendicular dotted line on side pro-
jection shows its diagonal: by a variety of
inclinations the projections of the cube may
be made to exhibit the parts of machinery,
for on every side may be drawn a wheel
or other figure, and its projection found either
upon the vertical or horizontal plane.
Fig. 893.


:
1
Fig. 894.

A sphere or ball, whether its projection be on a ver-
tical or horizontal plane, is always found to be circular.
To project a curved line, when the surface in which it
lies is curved, and it is not perpendicular to the plane of
the projection, it is better to form a polygon, and then
from each of its angles to drop a perpendicular, from
which parallel lines may be drawn to the chords which
subtend the arcs. But as the curved line has a double
flexure, it is necessary to inscribe within it another poly-
gon, which shall represent the surface in which the curved
line is situated. If the plane on which the shadow of the
globe is represented was not in perspective, the form of it
would be circular; its diameters in every direction being
the same, so must be that of its shadow.
4
0
t
Fig. 895.
The cone, when projected upon a perpendicular face, assumes the character of the pyramid,
and on the horizontal plane the circle. The projection of any of these figures is exceedingly
simple, and needs but little further observation.
In the shadow of the cone the same rules must be adopted,
the seat having been found on the horizontal can be readily,
by means of parallel lines, transferred to the vertical; the
direction of the vertical plane does not alter the height of the
projected shadow, though its breadth depends upon its position.
The shadows of curved lines being projections of those
curves, they may be treated as such: that of a circle, in any
position where the luminary is not in its plane, will be a conic
section if the shadow be received on a plane, and the form of
the curve, which will represent it, will depend on the relative
position of the circle, the luminary, and the plane of the
shadow; therefore the shadow of a circle can only be ob-
tained by establishing a sufficient number of points in its
curve, and then drawing lines through them. To find the shadow of any point it is ne-


Fig. 896.
CHAP. VIII.
787
GEOMETRY.
cessary to fix its position on the plane of the shadow, and this can only be effected by the
ordinary rules of projection: if we regard the cylinder of rays which produces the shadow
of a circle as a solid capable of being cut by a plane in any
direction, we shall find no difficulty in fixing the points of
each ray upon the plane so cutting it, and through them
tracing the form of the shadow.
A pyramid may be projected on a plane or upright wall,
by continuing the lines of its base, and then drawing per-
pendiculars to them.
The figure more clearly shows the orthographical pro-
jection on two planes at right angles with each other, one of
which is termed the horizontal, the other vertical: it simply
depends upon representing a point on any space by drawing
a perpendicular from it to both the vertical and horizontal
planes, that on which the perpendicular falls being termed
the projection of the proposed point; if we then imagine
lines made up of points, we shall have no difficulty whatever in projecting the entire outline
of any figure.
Fig. 897.
We may suppose the figure to represent a building, and if it be required to show the
position on the plan of the tiles or slates with which it is covered, we have only to drop
perpendiculars from them to the plane below, and find where their lines intersect: the apex
of the pyramid, which may be the point of a hipped roof, would fall where the diagonals
of the square cross on the plan below;
it is therefore not difficult to transfer
the seat of a point from one plane
to another.
----
----------------
Fig. 898.
In the cylinder it is necessary,
before we can project it, to
imagine its surface covered by a
system of lines or a series of
points, after which each may be
projected to a vertical or hori-
zontal plane, and when these are
united by lines, the figure will be
projected. Cylinders may be re-
garded as prisms whose bases are
either circular or elliptical, and
these may be resolved into poly-
gons which have straight lines for
sides, uniting in as many points.
Solids, which have a double
curvature, require that we should
consider them as inclosed within
a single surface, and
surface, and as such
bodies present neither angles
nor lines, they must be re-
presented by some apparent
curve which will bound their
superficies: this may accurately
be shown by a series of tan-
gents made parallel to a line
drawn from the centre of the
Fig. 899
solid, perpendicular to the plane of projection. When such solids are cut by other planes,
we must by points and lines find their true figure upon them.
?







3 E 2
788
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

And the ring LB, which has its face in shade, casts a cir-
cular shadow on the ground, which is darker than the ob-
ject that has defined it: the globe M C receives its light
in front.
In a polygonal or circular ring, the boundaries of light and
shade may be accurately defined, by having its ichnography
and elevation properly drawn out. If the seat of the sun's
rays be drawn on any plane, on which a cylinder is laid, with
its axis perpendicular to the seat and parallel to the plane,
the lightest line on the cylinder will be nearer to the plane
in this position than in any other; but if the axis of the
cylinder make oblique angles, then the line of light will be
higher on the cylinder. And, should the axis of the cylinder
be parallel to the seat of the sun, the lightest line on the
cylinder will be at its greatest distance from the plane: these
rules cannot be so well understood as by a reference to the
model of a polygonal ring laid in a position to receive the
sun's rays, and then its several planes may be traced geome-
trically, and the principles of light and shadow rendered clear.
In shading the globe, we must first consider the point upon
which the rays of light directly fall, and then gradually
diminish its effects until the shade commences.
But we
must not forget that the outer edges receive a reflected light,
and that no part of the surface which bounds the figure is
black. When the sun's rays fall upon a reflecting plane, the
angles made by them will produce reflected light, which is
received by every part of the object within its influence: the
globe standing over a sheet of white paper would conse-
quently have all its under side illuminated and rendered
brighter. To project its shadow it is necessary to draw out
the several planes, and pursue the course adopted in descrip-
tive geometry.
As the light of the sun falls perpendicularly or from above,
the top edges and the interior of a hollow body will re-
ceive a portion of it, and the sides N, O, P will be of different
shades, as they are more or less removed from the position to
receive the direct rays of light.
E, F, D, will show the ordinary manner of shading solid
bodies, the light being presumed ordinarily to proceed from
the left hand, and where two objects are shown, as H, I, their
several planes which are on the same parallels must be shaded
in the same manner. As the rays of light proceed in
straight lines, every opaque object on which they fall throws
a shadow on the side opposite the luminous body; and this
shadow is darker in proportion as the illumination is stronger.
Shadows are either right or versed, according to the position
of the planes which receive them: that which is thrown by
an upright body, as the prism which is projected on the
plane of the horizon, is a right shadow; that on a vertical
plane, as a beam fixed perpendicular to the face of a wall,
is a versed shadow. In both instances the length of the
shadow is to the height of the opaque body, as the cosine to
the sine of the angle which the luminous ray makes with the
plane. The altitudes of objects may be thus taken by
measuring the shadows they produce, and which was fre-
quently done by the ancients.
Sciography, or the science which teaches the projection of
shadows, has been very successfully studied by many artists,
and it will only be necessary to allude to a few more simple
architectural forms to make the subject perfectly clear.
I.
B
Q
M
C
Fig. 900.

N
Fig. 901.
E

:
F

2
D

Fig. 902.

Fig. 903.
I
A cylinder, having an abacus or square tile laid upon it,
would, when the sun is at an angle of 45°, form a shadow
in depth equal to its projection. A line drawn from the
centre to the angle of the abacus is the seat or plane of a ray of light; perpendicular
lines represent the surface of the cylinder, and when parallel lines to the rays of light are
projected and made to intersect with those that are perpendicular, the points of intersec-
tion express the extent of the shadow, and a line drawn through them indicates it.
CHAP. VIII.
789
GEOMETRY.
When the abacus is circular, then the cylinder beneath it will receive its shadow in
the same manner; the process of projecting it is the same as in the preceding example.
A prism with a polygonal base and a projection breaking round its top, when attached
to a wall, will cast a similar shadow; it will not be difficult to cast the shadow upon
the base, shaft, and capital of a column, if we suppose them to be cut into planes parallel
with its axis, for the purpose of marking the points which receive the shadows; for it
must be evident that if a ray of light enter any of these planes, every part of that ray
will be in that plane, and the projecting parts upon the edges of those planes will
cast a shadow at the several points of intersection.
In shading mouldings, it must be remembered that where the end or side of a building
on which they occur is in shade, they will not receive any reflected light, either from the
ground or the surface of the building: and such mouldings will have a contrary effect to
others in shadow, situate on the light side of an object.
An ovolo laid level, whose greatest projection is above, when on the dark side of a
building, will be lightest above, and gradually becoming darker towards its lowest edge.
The cavetto will be the reverse of this when in the same situation; it will be continually
lighter and lighter towards the under edge.
Perspective is the art of drawing the forms of objects as they are seen this method of
delineation differs materially from that called geometric, and is in fact the section of a
pyramid of rays, proceeding from the object to the eye; suppose for example a line drawn
from every point or angle of a cube to the eye, or threads substituted for such lines,
and that they in their passage pass through a transparent plane, as a sheet of glass or
paper; the holes made in this plane will indicate the boundary and form of the object,
and consequently its perspective representation.
Vignola, Seragatti, Brook Taylor, Priestley, and the Maltons, have by their writings
rendered this subject perfectly clear, and the Young Painter's Maulstick by James Malton
is an admirable practical treatise; and Sir Joshua Reynolds, in the first Discourse he
delivered at the Royal Academy, showed its importance: for it had been by many supposed
to bound the artist with laws that might cripple the beauty of the forms he was called upon
to draw, but the President emphatically stated that "Every opportunity should be taken to
discountenance that false and vulgar opinion, that rules are the fetters of genius; they are
fetters only to men of no genius; as that armour, which upon the strong is an ornament
and defence, upon the weak becomes a load, and cripples the body which it was made to
protect. How much liberty may be taken to break through these rules, and as the poet
expresses it, 'To snatch a grace beyond the reach of art,' may be a subsequent consideration
when the pupils become masters themselves: it is then where their genius has received its
utmost improvement, that rules may possibly be dispensed with: but let us not destroy the
scaffold until we have raised the building."
To the civil and military engineer a knowledge of the rules of perspective is highly im-
portant, to enable him correctly to delineate all the objects within his sight, and to all it is
the principles of the art of seeing, and should be generally understood.
Drawing is as useful as the art of writing, and oftentimes the pencil in the hand of an
experienced draughtsman can explain more than the pen of a ready writer: and in giving
directions to a workman, a drawing accurately made is often all he requires; to those who
are desirous of forming a clear and distinct notion of form, the study of perspective is neces-
sary, for every thing we see is seen perspectively, and no object appears as it really is from
any one point of view except it be the sphere.
In the geometrical representation of a building all the forms are drawn exactly as they
are, and it is necessary that such drawings should be made before we can exhibit its per-
spective effect.

Fig. 904.
A visual ray is an imaginary line extended from the eye to any particular point, and a
3 E 3
790
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
number of these rays is called a pyramid: to find the perspective of the small house in
the accompanying figure, it is only necessary to find the points of intersection of the visual
rays, made with the visible angles of the object as they pierce the plane which cuts them.
The point of view or point of sight is the eye of the observer.
The plane of delineation or picture is the canvass or paper upon which the subject is
drawn.
The original object is the house or any other to be drawn.
The original lines are the boundaries of the original objects, or of planes in those objects.
The horizontal planes are any planes placed truly level, that is, to which the plumb line
is perpendicular.
The horizontal line is a line on the plane of delineation level with the eye of the observer,
or point of view, and is supposed to be obtained by a horizontal plane passing through the
eye of the observer produced till it cuts the plane of delineation.
Vertical planes are planes perpendicular to horizontal planes.
Ground plane is that upon which the objects to be drawn are placed, and also that
on which the observer stands.
Ground line is that on which the plane of delineation rests on the ground line.
Station point is that on the ground plane perpendicularly under the point of sight or
point of view.

Κ
R
M
G
Fig. 905.
L
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B
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If
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X C
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Vanishing point is a point on the plane of delineation, which is the point of union or
CHAP. VIII.
791
GEOMETRY,
point of convergency that two or more lines will have, which are the representations of two
or more parallel lines in an original object, placed inclined to the plane of delineation.
Vanishing line is a line on the picture or plane of delineation supposed to be obtained by
a plane passing through the eye parallel to any plane in an original object, and produced
until it cuts the picture: the horizontal line is, therefore, the vanishing line of all horizontal
planes, and all horizontal lines have their vanishing points in the horizontal line.
To find the vanishing point of a line as well as all the others, the diagram introduced
may be sufficient.
The plan of a church is shown at ABCDE, and at the side an elevation on which the
several heights are drawn: it is required to put this in perspective on a plane or sheet of
paper, standing vertically on its edge upon the ground line, RT, the situation of the draughts-
man being at S, the station point. `ST and SR are drawn parallel to the ends of the
building through the station point S: and where they cut the ground line, RT, they fix
the extent of the vanishing point. The line VZ is the horizontal line, and perpendiculars
dropped upon it from the points R and T determine the vanishing points V, Z.
On the plan, FE and FA are prolonged to the ground line RT: these dropped serve
to set out the heights of the several parts: X Y is the height OP, which, when drawn
through to its vanishing point, V, marks um, as the perspective height of the same line:
X W shows the height ON, which is also drawn through the vanishing point in the same
manner, and where it cuts the prolonged perpendiculars um at v, a line is drawn to its
vanishing point z, and at o is found the point of the gable of the roof.
Lines having been drawn from the points A,B,C,D,E,F,G,H, of the plan to the station
point S, the corresponding small letters on the ground line RT show where the perpen-
diculars are to be dropped, on which the several heights are to be perspectively marked off.
mo p qu
show the end ED: ikmu the side E F, rski the side A F, rsyt the end A B. 00
is the height of the spectator, which, of course, may be varied at pleasure, and were the
horizontal line V Z dropped to half the height, the perspective representation would be
varied materially: the top of the tower bae, as well as the ridges wx and oz, would then
all incline downwards towards the vanishing points, Z, V, which are supposed to be imme-
diately over the points RT of the ground line.
Sometimes, to enlarge the perspective representation, the lines are not drawn immediately to
the station point, but are prolonged upon the ground line, and then crossed to the vanishing
points, which have been previously found. In this example we have the effect of the
capital above and below the horizontal line, and the small letters show the position on the
plan, and the corresponding large ones; those of the plan above and elevation are shown
in perspective.
For convenience the plan to be put into perspective may be placed either above or below
the line, and in the diagram three systems are shown of drawing a figure; the angle of
vision or angle of view being the same in all.
The Young Painter's Maulstick contains, among many other valuable hints, one with
regard to the best angle for vision, or that within which objects should be viewed, so as to
obtain the most agreeable representation; for as the angle of vision is enlarged or lessened
by viewing the objects near or remote, their appearance will be altered. Objects may be
placed too near the eye for their proper observance, and as the eye can contemplate only a
point at one time, it is by its celerity and continual motion that it becomes perfectly
sensible of a whole or of many forms; but when an object, or many objects widely ex-
tended, are placed too near the traverses of the eye, to contemplate them becomes
painful. In taking a view of a building turning the head should be avoided, as no view
should comprise a greater extent than the eye can agreeably contemplate at one glance, or
that can be seen by a pleasing and satisfactory traverse of the eye alone, which necessarily
confines the extent of the matter, and of course the angle of vision, to certain limits.
eye rests with composure on what it can contemplate with little trouble; not only too great
an extent, but too many objects, however they may interest and delight at first, soon
distract and tire the organ of vision. Smallness of object has nothing to do with the
angle of view; a cube or miniature being placed too near the eye may form a large
angle of view, and cause pain in observing it: a large extent of view, or a large picture.
may be contemplated with as much ease as a small one; it is only to place the observer
at a greater distance.
The
Isometrical Perspective is sometimes used to represent buildings, and is of great use in
diagrams and drawings of machinery, as all perpendicular lines in them may be measured
by a scale; the principles may be explained in the representation of a cube, into which
figure all others may be resolved.
The square or side of the cube is crossed by diagonal lines, and then another, as A C, is
set out from A D, at an angle of thirty degrees; and where this cuts the other diagonal, as
at B, you have the length of the side, as A B, for the radius of a circle which is to contain
the isometrical cube; and if on this a scale is marked, all other parts may be measured by it.
The sides, as well as radius and height in the figure, all exactly correspond in length, and,
3 E 4
792
THEORY AND PRACTICE OF ENGINEERING. Book II.

consequently a straight
edge or ruler, with a tri-
angle having angles of 30,
90, and 60 degrees, will
enable us to set out or sub-
divide a cube into any
number of parts.
The cube is contained
in a circle, and its centre
becomes one angle of the
upper face: lines drawn
from the angles 'of the
hexagon indicate the whole
of the sides. One quarter
of such a cube may be
shown as extracted or cut
out by dividing the sides
into two, and raising three
perpendiculars; or it may
be represented as seen from
the other angle.
A mortise and tenon,
or groove and tongue, are
easily set out, as is a
Greek cross, or three
steps.
By cutting a cube
into a series of planes the
interior of a building may
be represented, and a scale
applied, and in this exam-
ple three sections are
shown, which may be sup-
posed 100 feet in width,
and the same in height;
consequently 50 feet a-
part. Two others interven-
ing would have been more
in unison with the pro-
portions found in churches,
and could be easily in-
troduced by dividing the
side of the cube into four
instead of two, and re-
peating the method here
laid down of drawing the
respective lines.
Where wheels are to be
shown they must first be
inclosed within a square,
and then there is no diffi.
culty in representing any
combination of them.
For minerals this method
of drawing is very useful,
and is becoming general.
Curved lines and surfaces
may be illustrated by this
system and shown with
great accuracy; suppose
in the upper square we
were to trace a circle, and
beneath it in the lower
plane another, of similar
dimensions: uniting these
A
C
B
BaD
-
Fig. 906.


Fig. 907.


Fig. 908.


Fig. 909.
by drawing two perpen-
dicular lines, we have the representation of a cylinder; between the planes which express
its top and bottom, we may have any other number we require by setting out parallel
CHAP. VIII.
793
GEOMETRY.


squares
circles.
with inscribed
The cone may be shown
inverted by drawing two
lines from the circum-
ference of the circle on the
upper plane to a point in
the centre of the lower ;
or it may be exhibited on
its base by making the
apex terminate in the centre
of the upper square, using
the lower circle for its
base.
Fig. 910.
Setting out Points or Lines. To set out lines on the ground, where the situation is
inaccessible, as supposing it were required to draw through the point A a line parallel to
the inaccessible wall B C. Unite two straight edges or rulers about 3 feet in length by a
screw, on which they could be made to open and shut like a pair of compasses.
Place the
end of this instrument against a piquet at A, and bone along the edge of the two
rules, and open them until they cut the inaccessible points B and C ; then secure the open-
ing of the two rules, by screwing on a cross piece which shall embrace the two arms.
B
A
Fig. 911.
C
G

---------------------------
L
E
H
Then changing the position, walk to the side through which the parallel is to be drawn,
looking along the two open arms of the rules till BC is seen, which will be the case when
the station E is arrived at.
Then removing the transverse rule from above the two others, and placing their head on
the piquet E, open them, so that by boning along their sides the point B and the piquet A
are discovered, and by which the angle BE A is obtained; this being found, fix the rules, and
proceed to the station A, so as to see the point C along the limb of the angle BEA. Then
a cord drawn along the other limb at F will be the parallel to the wall required.
If it be required to let fall a perpendicular from any inaccessible place, as at B, from
the point G, first mark out the parallel line, and then, by means of a square LIH,
advance along the line, till the boning edge of the perpendicular comes opposite the
point G.
Of Levelling and Levelling Instruments. To the architect, as well as the civil engineer,
this term is understood rather to mean the difference which exists between two planes or
heights than the idea of a perfectly horizontal surface; the object generally being to dis-
cover how much ground must be elevated or removed to facilitate the running of water, or
the construction of a railroad over valleys or mountains. A level line infers a plane or
surface parallel with the horizon of the place where it exists; so that if water were placed
upon its surface, it would remain at rest, having no inducement either to mount or descend,
794
Book II
THEORY AND PRACTICE OF ENGINEERING.
But in reality when we look at a distant object, our eye is in the direction of a tangent to
the surface of the earth, which is not the true level; this follows the earth's curvature,
and in constructing a canal the bottom should not be a straight line, but concentric :
any drops of water placed in succession upon such a curved line, from their being
equidistant from the centre of the earth, will remain in the position in which they are
placed.
In the levelling for the foundation of a building where the dimensions are small in com-
parison to the circumference of the earth, they are generally treated as straight lines, and
in practice this is sufficiently accurate; but all plummets gravitating towards the earth's
centre, it stands to reason that a succession of lines taken with the common level must be
polygonal.
Telescopes, used to distinguish distant objects, consist of
a number of glasses placed in a cylindrical tube, with
their centres in a straight line.
The Eye-Glass is placed in a small tube, which can be
drawn out, and adjusted to different observations, and it
has in its focus a thread marked E, which serves to
regulate the sight.
The Object Glass, at the other end of the telescope, is
shown at C.
The Optical Axis is the line proceeding from the
eye when looking through the glasses, and which passes
through them at right angles. The glasses are spherical,
and of a convex form, their centre being thicker than
their edges.
Fig. 912.
A
D
E
B
F
G
C
K
Fig. 913.
I
B
TT
The Focus of a Glass is the point in which the rays
reflected from an object, having passed through a glass,
unite in a point. In practice it is highly important that
the cross hairs in the telescope should be properly adjusted,
which is done by attaching them to a brass ring, and
the eye tube must be drawn out until these hairs appear to occupy the focus of the glass,
and can be distinctly seen. The telescope has a screw attached to the instrument, on
which it rests, and which elevates and depresses it in a manner to be directed to any
object. The horizontal hair in the telescope being in apparent contact with the object,
the vertical one must be treated in the same manner until it also cuts it.
The Spirit Level with a Telescope is made of brass about 12 or 18 inches in length,
sometimes of a cylindrical form, and at others that of a parallelogram; it encloses a tele-
scope D E, in which is a tube F, having an eye-glass, with a thread fastened in its focus,
and which draws out to suit the various sights: at the other end of the telescope the
object-glass is inclosed in a small frame, and which can be moved either up or down by a
screw. This telescope is placed in the tube B C in a manner that it can be turned on its

A
F
D
X
H
Z
M
O
N
G
C
E
K
Fig. 914.
axis half round, and back to its original position: against one side of the tube BC the
spirit level H is attached at its two ends by the screws K and H; at H are two rings, one
of which clasps the tube, and the other end is attached to the screw L, by which the level
HI can be elevated or depressed at pleasure, so as to make the level agree with the visual
ray of the telescope: below the square tube BC is a plate of brass, which can be elevated
or depressed by the screws MN; to the centre of this plate the joint is attached, by which
the level can be turned in any direction, and roughly adjusted.
To centre the Telescope, it must first be mounted on a stand, and pointed towards the object,
in order to observe where the thread of the telescope cuts, and which need not be on a level
CHAP. VIII.
795
GEOMETRY.
with the instrument.
Then the telescope must
be turned half round, or the other side up-
wards, in order to see if the thread cuts the same
point; if it does, it is sufficient proof that the
telescope is properly centred, and has its sight
parallel to the points of support; but if this
point of sight or visual ray cuts above or below,
then the screw must be turned which elevates

A
Fig. 915.
or depresses the object glass, until the visual ray coincides with an intermediate point,
and then again reverse the telescope, to see if it is properly centred.
M
L
K
I
To rectify the Level, or to make the spirit level attached agree with the telescope, two
piquets, as G and H, are planted not more than 300 feet apart; then from the station G
observe the piquet H, the spirit level being adjusted until the bubble of air is in its centre,
as at K; the card I must then be raised or lowered until it coincides with the visual ray of
the observer at G. The observer at G must
then place against his piquet another card K, at
the height of his eye; when looking at the card
I, he must then move the level to the piquet H,
and place it horizontally at the same height
as the centre of the card I, to observe the pi-
quet G; then if its visual ray coincides with the
centre of the card K, it is a proof that the visual
ray is parallel to the horizon, and that the level
is rectified. But if it happen that the visual ray
cuts above or below the centre of the card K, as in the figure shown at L, then keeping
the eye at the same height, lower the telescope until the visual ray cuts an intermediate
point, as M; keep the telescope in this position, and adjust the spirit level until the
bubble is in the centre, which is done by means of adjusting screws. Then proceeding to
the piquet G, keeping the level at the same height as the centre of the card M, and bone
the middle of the card I, which if the visual ray cuts in the centre, it proves that the
visual ray is parallel to the horizon, and consequently that the visual ray of the telescope
attached to this level agrees with the spirit level.
To rectify the Level by a single Station.
Having centred the telescope of the spirit level,
place it on its stand; then knowing two points
which are on a true level, and at a short
distance apart, place the eye-piece of the
telescope at the height of one of these points, so
that the air bubble may be in the middle of the
glass tube; then if on boning the second point
it cuts the thread of the telescope, it is a proof
that the level is properly rectified and fit for

use.
It is known that the point A at the corner
of the house B is on a true level with the
cill of the window of the inn D at C: centre
the telescope to that level in such a manner
that the thread always cuts the same point
when turned either way.
G
Fig. 916.
Fig. 917.
H

B
D
с
The Spirit Level in general use, of the most convenient and improved form, has a telescope
ab, supported at each end, and a spirit level below it, inclosed in a brass tube, with a piece
of glass let in at the upper side, to observe the position of the air bubble: the instrument
has a compass usually attached to it. By means of the socket F, and the screw below, the
telescope may be raised or lowered at pleasure; on the plate M are four levelling screws,
which pass through the upper plate, and by which it may be adjusted. The cross hairs in
the telescope are fixed to a brass ring placed within the tube, and are kept in their position
by four small screws, as seen at o on. The eye tube at a is to be drawn out until these
hairs appear exactly in the focus of the glass, and are clearly seen. The telescope is then
directed to some vertical object or piquet, and by turning the screw g it is raised or
lowered to the required point. Clear and distinct vision of an object is obtained by
turning the screw B, which by its connection with a rack and pinion contained in the
tube which carries the object-glass, either lengthens or shortens it: when this has been
done so that the horizontal hair is observed to be in contact with the object, turn the
telescope half round, so that the spirit level is above, and see if the same point of
contact is preserved; should it not be so, then the screw oo must be turned until it
is right in both positions: the horizontal hair being adjusted, the vertical one must
also be treated in the same manner; when both are properly adjusted, their intersection
796
Boox II.
THEORY AND PRACTICE OF ENGINEERING.
appears in the centre of the telescope. The spirit level must then be adjusted in a
manner that it shall be exactly parallel with the axis of the telescope, or what is called its
line of collimation. The end of the level next the eye-glass has a screw by which it may
be elevated or depressed at pleasure; having by means of this screw got the bubble in its
right place, the telescope must be reversed again and again, until it is seen that the bubble
steadily maintains its position. To take an observation, the three legs of the stand are
opened and placed firmly on the ground, with the lower plate of the instrument as nearly
level as the eye directs; then by turning the various screws the level can be soon brought
into its proper position: three adjustments are always required for the Y spirit level: the
first regards the wires of the telescope, which should be made to coincide very exactly with
the axis of the rings on which the telescope turns; the second adjustment brings the level
parallel to this axis; and the third sets the telescope perpendicular to the vertical axis, so
that the level may preserve its position when the instrument is turned round upon the staves.

D
TOYNA.
H
K
BE
OZAREMURIYDIV
Fig. 918.
A A, the ends of the telescope.
Spirit level.
C, screw for adjusting the telescope.
E, screws for elevating the instrument.
G, the frame.
I, screw to secure the instrument.
L, rack for side motion.
B, the screw.
D, the spirit level.
F, the Y's which support.
H, the compass.
K, screw to elevate the instrument.
To adjust the line of collimation, the eye-piece being drawn out, you should direct the
telescope to some fixed object, care being taken that you get a distinct view of the cross
wires, and that you notice where their intersection cuts: after this, by turning the telescope
round on its axis, you must observe whether the wires cut the same object in the same
place: should they do so, the instrument is fit for observation; but if this is not the case,
the wires must be moved by turning the small screws near the eye-end of the telescope until
half the quantity of error is got over, and then trials must be made again, till the adjust-
ment is correct. To place the level parallel to the line of collimation, the telescope must
be moved till it lies in the direction of two of the parallel plate screws, and by then moving
the screws the air-bubble is brought to the middle of the glass tube: the telescope should
then be reversed endwise, that is to say, one end brought in the place of the other, and
then the air-bubble examined again; if it be not in its proper place, the parallel plate-screws
must be used to make it: repeated trials are needed to effect this properly. To set the
telescope in a perpendicular position with its vertical axis, it should be first placed over
two of the parallel plate-screws; then by unscrewing one, and screwing up the other, the
air-bubble may be brought to the centre of the tube; then the instrument must be turned
half round, and if not correct, then again adjusted; then turn the telescope one quarter
round, and by repeated trials its adjustment may be completed.
The
Troughton's improved Level is preferred by many to that of the Y, in consequence of its
adjustments not being so likely, after they are once perfected, to derangement.
telescope rests at once upon a horizontal bar made to turn round upon the head of the
staves which support it, in the same manner as in the theodolite. The spirit level is
placed on the top of the telescope, and over it the compass-box: the wire plate has
CHAP. VIII.
797
GEOMETRY.
three threads, two of which are vertical and the third horizontal; there is also some-
times a micrometer scale, fixed perpendicularly on the diaphragm in lieu of the wires:
one edge of a fine slip of pearl with straight edges is applied for this purpose, which is
divided into hundredth parts of an inch, and again subdivided into lesser quantities: in the
fixing of this pearl micrometer the divided edge is placed so that it intersects the line of
collimation, the central division indicating the point upon the staff where the level falls.
The telescope generally shows the object inverted, consequently fewer glasses are required;
and in this as in the Y level, the line of collimation and the level must be made parallel
with each other, and the telescope brought into a position exactly perpendicular to the
vertical axis, and so that the air-bubble when turned round horizontally should always
preserve its position in the middle. This kind of spirit level being firmly fixed in its cell,
the line of collimation has its adjustment given by the aid of two screws near the eye-end

A
D
B
Fig. 919.
A B, the telescope.
TROUGHTON'S IMPROVED LEVEL.
E F, the spirit level.
ef, capstan screws for adjusting the level.
CD, horizontal bar.
G, the compass-box.
of the telescope. A bench mark made against a wall should be every now and then
examined by the instrument placed at the same height from the ground, and any error in
its collimation then would be readily discovered.
Mr. Gravatt's Level is another modification of the above, and has an object glass of larger
aperture and shorter focal length; it also has a diaphragm with cross wires, and the spirit
level is placed above the telescope; there is also a small mirror so fixed on a hinge that the
position of the air-bubble can be seen at all times by the observer; at the same time he
reads off the staff.
E
T
F D
Levels were formerly constructed with two telescopes, as A B and CD, each about 20
inches in length, placed in such a manner that when the eye-glass of AB was at A, that
of CD was at D: each of these was so con-
trived that they could be elevated or depressed
at pleasure, by screws placed at F and E.
GI and HK were pivots placed at right angles
with the bottom, and were the points on which
the levels were supported: by turning the
rule EF round on its pivots, the two tele-
scopes were made to change their positions.
To the support of the level IK is attached a
weight at X, of a square form, and weighing
3 or 4 pounds, which is placed there to maintain
the telescopes in a state of equilibrium, but so
as not to prevent their motion on their axis at
Q. At R is attached three rings which hold
the eye or handle V: by means of the handle
at T, which passes through the upper part of the box at S, the levels are raised or de-
pressed when required; the box Z, which contains this spirit level, is made of mahogany,
and is furnished with a screw at Y to adjust the level.

I
L
Fig. 920.
2
N
Such a box placed on its stand was much in use in France, and its rectification was
effected in the ordinary way, by centring the two telescopes in such a manner as to make
their visual rays always in a parallel with the pivots on which the circular motion of the
telescope was made: the level being mounted on its stand at the same height as the
object to be observed, the weight was permitted to remain at the bottom of the box, so
that the telescopes were not subject to motion or to oscillate: then looking through the
798
BOOK II.
THEORY AND PRACTICE OF ENGINEERING,
b
eye-glass of the telescope AB, at any line
parallel to the horizon, as that of the line ab,
on the house C, so as to cover it exactly with
the thread of the telescope; then turning the
telescopes half round on the two pivots G, H, so
that the telescope A B, which was on the left,
comes on the right hand; then looking through
the same telescope AB, if the thread still
covers the horizontal line ab, it is a proof that
the telescope AB is well centred, and that its
visual rays are parallel to the two pivots G and
H: should it either cut above or below, the
screw at E must then be turned until the visual
ray cuts half way between e and ƒ; then turn the
telescope round on the pivots, so that the telescope through which the observation has
been made may pass from right to left; on looking through it, if the thread cuts the
line ef, it is a proof it is well centred. The same rule must be observed with the other
telescope, and both being properly centred, it is only then necessary to have the two visual
rays parallel with the horizon, and this is done by putting the weight into equilibrium :
after this is done, point the telescope towards the object, as the house C, and if in looking
through the eye-glass of the telescope AB, its thread cuts the object in any point, as G,
and having turned the whole level to make the eye-glass D of the telescope CD come to
the same point, it is then a proof the visual rays are parallel with the horizon.
The weight
N, by being advanced or pushed back, changes at once the equilibrium of the level, and by
the whole it may be truly and correctly adjusted.

Fig. 921.
Level lines and points are all equidistant from the centre
of the earth; the points B, K, L, and C, are equidistant
from the centre of the globe A. There are two de-
scriptions of levels, one called the true, the other the ap-
parent: the true level is that which follows the circum-
ference; the apparent is that which is drawn perpen-
dicular to the radius of the circle: BGIF, which is so
drawn at the end of A B, is the apparent level.
The term levelling implies the idea of bringing any
thing to a level or flat; but, as engineers use it, it simply
means the process by which the quantity of deviation from
a true level is ascertained, the object being to find out if
the surface be raised or sunk, or what is the slope or in-
clination. Level lines or level planes are supposed to be
perfectly flat, or parallel with the horizon where they exist,
and a sheet of water at rest may be supposed
to have its surface level, for if any part of
the plane on which it rested was lower than
another, it would run in that direction.
It therefore follows that some allowance
should be made in levelling through very long
distances, as from E to D, D to E, and B to A,
and for this very accurate tables have been com-
pleted for all distances within the range of an
observation.
27
A
B
G
I F

'H
K
Τ
E
с
A
Fig. 922.
D

B
C
E
Fig. 923.
H
G
F

K
M
J
We have also to make some allowances for
the refraction, which varies from to of the
angle subtended by the horizontal distance of
objects. In the ordinary state of the atmo-
sphere, the refraction is about a fourteenth of
the horizontal angle, and the radius of the cur-
vature of the ray seven times that of the earth.
The effect of refraction may be allowed for by
computing the correction for curvature, and
then taking one-seventh for the quantity by which the object is rendered higher by the
refraction than it ought to be.
Fig. 924.
N
Numerous tables have been drawn up to enable the engineer to correct the curvature and
refraction for distances in chains, feet, or miles; the corrections for refraction are taken
usually from one-seventh up to a twelfth of the apparent above the true level, which is
affected by the state of the atmosphere.
Suppose a spring to issue from the earth at G, the water would not flow along the line
HF, which is the apparent level, but would flow towards K and L, in the circle N, and
CHAP. VIII.
799
GEOMETRY.
thus it is apparent the true level is the earth's curvature: all bodies at an equal distance
from its centre are supposed to be level.
In levelling for a Railroad or a Canal, it is often necessary to
place the levelling staves 300 or 400 yards apart, and then it is
important to make some allowance for the curvature of the earth, as we
shall hereafter describe; but before we proceed, it is necessary to
describe the staff or target made use of for determining the height of
the several objects above or below the level line. The most common
form is that of a rod 1 inches square, and 6 feet 6 inches long, made of
mahogany, and inlaid on its face with a white wood to receive the
divisions and figures: the staff consists of two pieces dovetailed into
each other throughout their whole length, so that one half of the rod
slides upon the other, in consequence of which the rod can be pulled
out or extended to 12 feet long, and yet will leave a foot of the two
halves joined together for maintaining the straight line of the instru
ment: the divisions begin to count from the bottom of the staff.
The vane is a thin piece of mahogany 10 inches long and 3 wide,
having projections behind, which form a socket for fitting the rod,
and enable it to slide up and down; this motion is rendered more
certain by the addition of a flat spring placed in the socket. In the
centre of the vane is pierced a hole, through which may be read off
the figure on the staff, and the edges of this hole being chamfered,
the horizontal wires which cross it can be distinctly perceived as they
lie over the divisions of the scale beneath: when this staff is placed
in a truly vertical position, its vane can be elevated or depressed, as
the signal is given by the engineer who is at the levelling instrument ;
for the telescope cannot be altered by elevation or depression, there-
fore the vane is moved upon the staff until it is brought into exact
coincidence with the horizontal hair of the instrument: so that when
the cross-wire of the vane is raised so high as to intersect 6 feet, there
is a stop to prevent its being pushed higher : when a greater height
is required, the vane is put to this height, and then it is raised by
sliding up the front portion of the staff, which carries the vane with
Several methods of marking these rods
are adopted, but all begin to count from
the bottom of the staff: some have a double
scale of divisions running up the middle
of the front; on some the side consists
of feet and inches divided into tenths,
and others of feet divided into hundredth
parts, without regard to inches. When the
levels can be taken in inches and tenths, or
in feet and hundredths, the calculations are
rendered more easy and simple, and it
has been suggested that the decimal di-
vision should be adopted for rules and
scales generally.

ל
•
་ ་ ་ ་ ་
3
it.
Fig 925.



The staves now in use are generally
without vanes, having their graduations
distinctly marked in feet, tenths, and
hundredths; these were introduced by
Mr. William Gravatt, and are made of
three pieces of mahogany with joints at the
ends, to enable them to be united in one
length of 17 feet or more; such staves
can be packed up with the stand of
the instrument, and are more portable.
Mr. Sopwith of Newcastle has improved
upon these, by adding a spring catch
to that which slides, so that it is more
easily retained in its place; but, however
correctly these may be graduated, if the
attendant who holds them is not very careful, errors of great magnitude may result, for
when the face is turned from the last forward station to become the next back, an
error of an eighth of an inch is sometimes the result of carelessly placing it on the
ground: to remedy this the greatest attention should be observed, and the stave should be
[31
Fig.926.
800
Book II.
THEORY AND PRACTICE OF ENGINEERING.
pressed firmly into the ground at each station, and then on turning the face, there will not
be much change apparent in the level taken.
When it is required to know whether the
points E, E, are elevated or lower than the
points C and G, place piquets at D, E, and
having properly rectified the level, place it
against the piquet at B C, and bone the line E
through the telescope, and the card must be
raised or lowered until the visual ray meets
the centre of it at E; then measure the
height that the centre of the eye-glass at C is
above the base B, and set off from the base of
the piquet D this same height BC, and the
height then up to the point at E on the card,
will be the difference of the levels.
If the observed height fall lower than the
sight point, as at K, it proves that the ground
is lower than at I, as much as the difference is
between K and H.
When it is required to find the difference
between the levels of the spring at A and
another at B, piquets of the required length
must be fixed at the stations D, C, and B, and
the level may be placed at C; then by taking
the necessary observations, measuring off the
heights on the piquets, and deducting the height
of the stand, it may be easily computed; or, sup-
pose the height from B to F to be 16 feet, and
that of AD 10 feet, the difference will be the
variation in the level.
If it be required to ascertain whether a
well at the station at F is above or below
the level at B; after rectifying the level,
place it at D, where both piquets can be
seen when the observations have been made on
the piquets, their difference can easily be cal-
culated, which will be the variation in the level.
If it be necessary to plant piquets in a line
from the trunk of the tree A to the descent
at B, where hills as F, G, and H, intervene; a
piquet must be placed at A D, and another at
BE, and then the level must be stationed
between the two objects AB, at any place
where the piquet A D can be seen.
From the station F, bone the piquet A D,
and then looking through the other end of
the level place in a line the piquets Q, R, S; and
if this be found not to cut the piquet B, then
from the last of these piquets bone R and Q,
and take up another station, as at G, boning
through the piquets P, O, N; we must continue
our observations until by boning from the
piquets A D and B E, we find BE in the visual
ray with the other piquets; then a line drawn
through the foot of the piquets planted on the
hills and valleys between the two stations A
and B, as A, N, O, P, and B, will mark the
shortest road required.
may
When the district through which the levels
are to be taken is much intercepted by trees
or buildings, it is often found very useful to
leave at convenient intervals marks which
be cut in posts, stumps of trees, or painted on
a fence or building: such a bench-mark will
be valuable for future reference, and during the
survey to check the levels made in different
directions; and it should always be establish-
ed at the end of every day's labour.
1
D
F
I
C
G
Fig. 927.
Fig. 928.
Fig. 929.
Fig. 930.
F
MILAS
G
C
D
- E
I
D
E

K

G C

B

S
E
P
B
H
N
Fig. 931.
CHAP. VIIL
801
GEOMETRY.
If it be required to ascertain whether there
is any fall from the point A to the little
hillock at G, piquets may be placed first at
A and K, and the level F, having made the
necessary observations at the station E, may
be removed to I, where the piquets H and D
can be observed; then by a simple calculation
the difference in the levels may be found.
C
F
H

A
Fig. 932.
D
K
F
E
B
The difference between the levels of two houses E and O may also be found by planting
piquets at G and L, and the level at D, H, and C: so may the inequalities of a country.
B
N

C
J
L
E
C
G
H
F
Fig. 933.
as from A to C, be marked, and a canal set out upon a dead level, K, O, P, being piquets, and
LHT the position of the level used for making the observations: M and Q show the depth
of cutting.
In this latter example D, F, H, and T show the position of the level for taking the ob-
servations, and KA, ON, PR the station of the piquet.
A
Fig. 934.
T

B
H
L
P
G
F.
E
M
Q
R
8
The ordinary method of levelling the foundations of a
building, or an area of moderate extent, for the pur-
pose of forming a drain or watercourse, is by a level
10 or 12 feet in length, formed of wood, and having attached
at A a string which holds a plummet that falls into a
hole below; this simple instrument is blocked up until
it is brought perfectly level; then the difference in the
heights of the blocks is taken, which added together
constitutes the variety in the level.
The level shown at B has an upright straight edge,
which when placed against a wall or building at once
indicates, by the play of the plummet, how much in that
length it is out of the perpendicular.
These implements all depend upon the circumstances of
a level line being a tangent to the earth's curvature and of
a plumb line disposing itself into the direction of a radius
of the earth, of course perpendicular to the middle of that
tangent, and that the level direction is a right line. To
prove the correctness of such an instrument it should be
placed upon a surface known or ascertained to be perfectly
level, and such may always be formed by wedging up a
plank at one end or the other: after finding that the
plummet hangs in its proper vertical direction, it should
be reversed by turning the two ends of the level in an op-
posite direction or position, when, if the plummet retains
the same place over the line, the instrument may be
depended upon.
C and E are other varieties of levels which are in use
for ascertaining how much a stone or other body may
be out of a level; the plummet in the one falls over
a mark on the cross piece towards D, when it is perfectly
level at the feet, and in the other over a graduated arc
of a circle.
Fig. 935.
Fig. 936.
C
D
Fig. 937.
B
A
E
C



3 F
802
BɔOK. II.
THEORY AND PRACTICE OF ENGINEERING.
Small spirit levels are also used, which are made of
glass, and mounted on brass tubes; M and V are small
brass plates which have an upright and horizontal cut
made through them, so that the eye can see from one to
the other, and when the bottom OKP is placed upon
any surface, by looking through MN a level may be ob-
tained: sometimes a glass tube F is placed on the top of
a box H, which is furnished with an eye-hole at O.

K
F
Fig. 938.
L 1
N
H
P
The earth's diameter being nearly 41,796,480 feet, or
7916 miles, it has been estimated that the height of the
apparent above the true level for every mile is a little
more than 8 inches. To find the difference between the true and apparent level, the dis-
tance levelled should be squared, and its product then divided by the mean diameter of the
earth, when its quotient will be the difference required: for the differences of the heights
of the apparent levels at different distances are as the squares of those distances; in short
lengths the differences are small, but they increase rapidly as the distances increase: in ten
chains it is ⚫12 of an inch; in twenty chains 5; in thirty 1·12; in forty 2; in fifty 3·12;
and in 100, 12.50 inches.
Compound Levelling is usually adopted where great accuracy is required, and this is per-
formed by taking back and forward sights; by this means errors are easily corrected: the
height obtained at a back or forward observation is deducted from the other, so that when
these heights are compared together, the result may be depended upon, it being obtained
upon the spot, sufficient correctness is arrived at in setting out a canal or railroad,
it is usual to go over the same ground a second time in an opposite direction, beginning
the first operation where the latter ended; and if the results turn out the same in
both cases the correctness is sufficiently ascertained. It is, however, necessary to measure
and set off the distances with the chain, and to reduce all the sloping measures to their
horizontal value: the distance between the sights ought to be short, and the piquet-bearer
should be careful to hold his staff upright, and to place it on the same spot for a forward
or back observation.
Drawing a Section or Profile of a Country after it has been levelled, to enable an estimate
of the expense to be made, for the construction of a canal, railroad, or other work,
is the next point to be considered. This drawing, to be useful, should be on a large
scale, that is to say, from 8 to 16 inches to a mile: in the first instance an inch represents a
furlong, and each chain the tenth of an inch; when this scale is doubled, it is usually called
5 chains to an inch. A straight line representing the base or level is first drawn, which
may represent the horizon; on this is set out the several distances that have been
measured upon the ground; the profile lines are then laid down, and after the heights are
accurately set out, the surface of the country may be traced through them: by such a
section a sufficient knowledge of the expense may be acquired for the formation of any en-
gineering work that may be constructed.
In the year 1742 it was proposed to the Academy of Sciences at Paris, to show on all
maps by the means of contour lines the respective levels of the districts surveyed. The idea
seems to have been suggested by the marks left around a hill after the waters on an inun-
dation had been drawn off; supposing the valleys around a number of hills were to be
inundated, and the water suffered for a sufficient length of time to stand at one level, then
if piquets or stumps were driven around the margin, to mark the extent of the surface
of the water, and their position mapped and a line traced through them, then such a contour
line would show the various spots which were at the same level, and if it were possible
to lower the surface by degrees, and draw off a foot of its depth at each time, and mark its
various boundaries in a similar manner and map them as before, such a series of contour
lines would accurately express the height of the ground, and show where the relative levels
were to be found: we can imagine Shooter's Hill, which is 400 feet in height, immersed
in water, and that it could be lowered or drawn off a yard in depth each time; then
if stumps could be driven to mark the water's edge, as this was done, and these stumps
or the figure they comprised mapped, we should then have expressed by contour lines
the extent of the level planes at every yard of elevation.
In public surveys where three chains are used to an inch, such a series of lines laid down
would be found of the greatest possible service to the engineer about to cut a road
or canal through the country so mapped, as he would at once see all the points which
were upon the same level: for the supply of a town with water such a survey would be
of the greatest importance, and facilitate the operations of the engineer.
The engineer, when surveying a country through which a railroad or canal is to pass,
must not only pay the greatest attention to the levels of the several districts, but also notice
the manner in which the earth's strata are disposed; if he has an eye to judge accurately, he
may, like Brindley, perform much of his task by walking over the intended line, and get a
thorough knowledge of the difficulties he has to overcome: general ideas are too frequently
CHAP. VIII.
803
GEOMETRY.
thrown aside, and the entire attention devoted to minutiæ: in taking the levels of a
valley through which a stream discharges itself into the sea, and where there are many mill
weirs, and their fall can be ascertained, it will be of considerable service previously to
decide the level of the river's mouth, its entrance into the sea, and also the slope of its bed,
which may be calculated by adding the several falls together, and taking an average in-
clination per mile of the stream: although this is not a very accurate way of proceeding, it
will serve as a check to gross errors.
Inland districts are not necessarily higher than the level of the ocean, and in the fens of
Lincolnshire and elsewhere, the slope of the streams is so inconsiderable as to be hardly
perceptible, the fall being frequently less than 2 inches to the mile; the Thames from
Lechdale to London bridge is 146 miles, and in this distance the rise from low-water
mark is 248 feet, consequently its fall averages about 20 inches per mile, though for a part
of its course the slope of the bed is not more than a foot. Surveys made through a country
where the falls of the rivers are known may be
frequently rendered more accurate by com-
paring the levels as taken with the instru-
ment with those observed in the manner al-
luded to.
Trigonometry teaches the method of measuring
all kinds of distances as well as heights by
triangles; it enables the engineer to ascertain
how many feet or yards there are in a right
line from one place to another; to measure the
breadth of a river; the length of a line of for-
tification; the opening of a breach; the distance
of a fort even when water intervenes, or the
surrounding country is inaccessible: it also
enables him to measure the heights of hills,
mountains, and buildings of every kind with
great precision: formerly these two branches
of trigonometry were called longimetry and
altimetry.
By the first was understood the method of
measuring in a right line from one place to
another, as to find the width of a river, or the
distance of one building from another, as the
distance of the castle A from the church B:
it is evident from the stations at G and H,
two angles may be measured; that by computa
tion afterwards the distance may be known
accurately.
By the second the height of the tower at C
from the point D may be found from the sta-
tion points where the instrument is placed.
A

Fig. 939
For suppose the circumference of a circle
divided into 360 equal parts or degrecs, these
each into minutes, and these into seconds, it will
be easy to measure the angle taken by the
demicircle with the points C and D; its mag-
nitude may be expressed by degrees, minutes,
and seconds; this division of the circle, called
usually the sexagesimal, was that adopted by
the ancients. Supposing the point occupied by
the demicircle to be marked by the letter B, the ratio that CD bears
to CB is called the sine of the angle, and the ratio of BD to BC the
cosine of the angle, or, as they are usually written,
DC
BC
=sin. A; =cos. A.
BD
BC
Fig. 940.
The ratio which the sine of an angle bears to the cosine is called the
tangent of the angle; the inverse of the ratio the cotangent; the ratio of
unity to the cosine of an angle the secant, and that of unity to the sine
the cosecant. The difference between unity and the cosine is termed
the versed sine, and the difference between unity and the sine of an an-
gle the coversed sine.
The depth of all places may also be found, as the depth and width
of all ditches and cavities, as that of EF, and the breadth at the
bottom.
H
E
B
C


Fig. 941.
3 F 2
804
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
The demicircle is placed at E, and the angle
that the bottom of the well or surface of the
water makes with the perpendicular line E F is
accurately measured; then by means of a scale
or trigonometrical calculation, when the diameter
is ascertained, its depth can be readily found;
or, if the angle be taken, and the depth ascer-
tained by measurement, the width at bottom may
be found. Whenever it is required to measure
a distance or space that is not accessible, care
must be taken not to make the angle more
acute than absolutely necessary, and the same
rule must be observed in planting over piquets
to measure angles between other objects: in all
instances we must endeavour to obtain them as
large as possible.
By means of the triangle ACB we can as-
certain the distance from A to B, and by the
triangle DFE that from the windmill to the
church.
A

Fig. 942.
D
F
B
The exact situation of these points may
always be determined by means of the triangle;
but we cannot by instruments measure them
exactly to resolve its value by construction, it
is only necessary to establish the data of the
things given, and then measure the lines and
angles that are unknown; if the data be suf-
ficient this representation on paper affords us
the means of finding the lines and angles that are not given, and when these unknown quan-
tities are drawn out proportionate to a scale of the known, it is only requisite to measure
them by the same scale to ascertain their values. Suppose it is required that the distance
between the inaccessible points A, B, should be known, as we can take up a station at C, and
measure the distance from C to A and from C to B, the three terms of the triangle A B C,
viz. the length of two sides and the angle comprised can be found. The distance from the
windmill, D, to the church, E, may be also calculated when the angle from F is known,
together with the length, FD and FE.
The knowledge of the three angles is not
enough to enable us to obtain the length of
each side, as there may be many triangles like
LMV and GHI equal to each other, and
the length of their sides different: we must,
therefore, always be enabled to measure a base
line; as when the distance from one place to
another is required, we must place our piquets
in such positions with regard to our instruments
that the angles made are not too acute or too
obtuse.
Trigonometry being based on the know-
ledge of sides and angles, it is necessary
to be very exact in our observations, as well
as in the measurement of the line from which
we calculate our angles, for if the ground-work
be insecure, the building up will be in jeo-
pardy.
To find the distance between one place and
another without actually measuring it may
be done when it is allowed to approach them,
as from the point F to that at G: a piquet
planted at I was found to be by measurement
50 yards from F; the same distance was set
out in a straight line towards K, where
another piquet was planted. The distance
from G to I was then measured, which was
found to be 60 yards, and this distance was
set out towards L, and a piquet planted: then

F
Fig. 943.
1
Fig. 944.
H
L
M
N

FRALTENS
50
60
G
the distance from L to Kwas measured, which was found to be 102 yards, the exact dis
tance from F to G, afterwards measured with a cord.
CHAP. VIII.
805
GEOMETRY.
To measure the Distance between two Objects
inaccessible from one to the other, but accessible
from a station, as the distance from the tower
A to the tree B, supposing it to be possible to
place a piquet at C, whence we can proceed
to the two objects A and B. Measure in a
right line from A to the piquet C how many
feet it is, as 70: then measure in a right line
on A C prolonged to D 70 feet, so that A CD
may be 140 feet. Then from the point B
measure BC, in a right line, and call it 100
feet; measure the same distance on BC pro-
longed; then measure the distance ED, 150
feet, and which is that of the inaccessible
length or distance A B.
By means of a Piquet to measure the Dis-
tance from one Object to another, when it is
only possible to approach one of them, as to
measure the opening or bar of a river. - Plant
at the point A a perpendicular piquet, 4 or 5
feet high, as at A C; place on the summit C,
the blade of a knife with its back turned to
the piquet; elevate or depress this blade until
you see, looking along the back of it, the
point B: then keeping the knife at the same
opening, turn round to the land side, opposite
a level piece of ground; replace the knife in
the piquet C, and its back against this piquet,
in order to look along the back of the blade
until the visual ray cuts the ground, as at D:
the distance AD will be that of the bar or
entrance of the river A B.
An observation similarly made at E G, and
tried along the ground from H to I, where
the base may be measured, gives the width of
the river.
By means of piquets, the length of the ridge
of a roof may be found, as that of the church at
NO. Piquets placed at PR on the line ab, drawn
on the ground parallel to the ridge having on their
tops two latbs arranged like a cross: these must
be moved along the line till they are perceived to be
opposite the points N, O, and then the distance
PP being measured, the length of the ridge will
be similar.
To enable the observer to be more accurate, the
piquets placed at P and R on the base line a may
be mounted with cross staves, the arms ST and
YX being in a line, and Y Z and Z2 at right
angles with it: should the distance of the objects
be considerable, the observations so made would
be far from accurate; when within a few feet or
yards, the dimension measured on the ground
between the feet of the piquets might be suffi-
ciently near the truth for ordinary purposes.
This practice somewhat corresponds to the com-
mon method of boning, or booming as it is some-
times termed, which often leads to very erroneous
calculations. In Holland, wherever difficulties
are offered to the navigation of a channel by
the overflowing of the coast, and the course
not distinctly known, poles are set up to enable
the sailors to steer in a straight direction, from
whence probably we have the term; and in this
manner lines are set out with booms or spars
when a canal is to be cut; but without great care
it is scarcely practicable to make a very long
line straight by such means.
E
A
B

Fig. 945.

Fig. 946.
Fig. 947.
الله
N
N
F

E
G

2
S
X
T
Y
Y
Z
a
P
på
B
b
3 F 3
Fig. 948.
806
Book II.
THEORY AND PRACTICE OF ENGINEERING
B
By means of Piquets to measure the Distance between inaccessible Places, as that from
the tower A to the windmill D. Trace on the ground, where you are to perform the
operation, a line parallel to the given length
to be measured, as the line SV; then attach
two rules at right angles, placed in the form
of a cross, on the heads of the two piquets,
each 4 or 5 feet in height. Place these

8
K
E
M
H
G
L
D
V
two piquets at any points on the line SV,
and look along them in such a manner as to
discover the objects as well as the piquets, as
at C; by the rule IK you may see the tower
A, and by the rule E F the piquet D. Then
from the piquet D, observe by the rule LM
the mill B, and by the rule H G the piquet
C, which may be done by bringing these two piquets nearer together or further apart,
always keeping them in the line S V, until you can discover the objects before named, which
nappens when at the points C and D : then the length CD will be equal to the inaccessible
length, A B, between the tower A and mill B.
Fig. 949.
B
To find the Height of an Object, AB, when it can be approached.- Place a mirror at C
horizontally at any place on the ground, with its
back downwards, so that the glass may be upper-
most; retire from the mirror at a distance pre-
cisely equal to the height of the eye from the
ground, as at D, and standing perfectly upright,
observe if the top of the proposed height can be
seen in the middle of the mirror; if not, see if the
mirror be too near or too far from the object,
and place it either nearer or farther from it.
When the view of the object in the mirror has
been obtained, measure on the ground the dis-
tance from the centre of the mirror to the foot
of the proposed height, as from C to A, and it
will be the height required.
To measure by means of two Piquets Heights to
which the Foot is accessible. Take two piquets, as
E, C, one of which is half the length of the other ;
elevate them perpendicularly in the ground, on a
level with the foot or base of the height which
is required to be ascertained, and so that the shorter
piquet may be its own length distant from the
longer one; look along their tops, and walk either
backwards or forwards, keeping them the same
distance apart, until by the same visual ray the
summit of the object to be measured can be seen.
The distance from the foot of the object to the foot
of the short piquet, viz. from C to A, added to
its length, gives the height of the object.
To measure a Height, when the Base is accessible
by means of a Piquet. Retire from the foot of
the height to be measured as much as the height
is supposed to be; plant a piquet upright on the
ground, as at DE, on the same level as the foot of
height, and as high as the eye: lie down on the
ground with the feet against the piquet, and look
along its top until in the same visual ray the sum-
mit of the height to be ascertained is seen.
distance from the foot of the height, A to C, to
the place where the eye was when lying on the
ground, will be the required height.

The
C
A
Fig. 950.
B

A
Fig. 951.
E
D
Fig. 952
B
D
ECG

Examples might be multiplied of measuring
heights by means of the piquet, and it is inen-
tioned in several ancient writers. We may imagine that Archimedes and Apollonius, who
enriched geometry with so many new theorems, made use of the staff or piquet for several
purposes, particularly where the properties of similar angles were to be exhibited: seventeen
centuries have passed since these great men taught in the academies: the principles
they have left us have been but little added to, although they have been varied in their
application. Wherever the piquet is employed, its perpendicular position should be
CHAP. VIII.
807
GEOMETRY.
regarded, and maintained, as the slightest inclination would affect the truth of the observa-
tions made with it.
To measure by means of a Piquet and the Rule
of Three a Height of which the Foot is accessible.
Place on the ground at some distance a piquet
CE, of any length; then retire from this piquet
till, by lowering the eye to the ground, as at
D, the top of the piquet and the summit of the
height, B, to be measured, is seen in the same
visual ray.
State the question by placing in the first term
the distance from the point where the eye was
placed when on the ground from the piquet; in the
second term, the distance from the same point to
the base of the required height, and for the third
term, the height of the upright piquet: the quo-
tient will be the required height.
From DC we will suppose 5 feet, and from D
to A 25 feet, and the height of the piquet, CE, 6
feet: then we shall have

E
A
C
B
5: 25 :: 6 : 30 feet for the height of A B.
For if a line be drawn in a triangle parallel to one
of its sides, it will cut the two other sides propor-
tionally; and the line which bisects any angle of
a triangle divides the opposite sides into two seg-
ments which are proportional to two other adja-
cent sides let the angle DEA of the triangle
DAE be bisected by the line CE, making the
two angles at E so bisected equal: then the segment DC will be to the segment CA, as
the side DE is to the side EA, or DC will be to CA, as DE is to E A, and the line EC
being drawn perpendicular or parallel to B A, cuts the two other sides proportionally,
making DC to CA, as is DE to E B, or to its equal E A.
:
Fig 953.
When the sun shines, if we set up vertically a staff of any known length, and measure
the length of its shadow upon a horizontal or other plane, and measure also the length of
the shadow of the object whose height is required, we may, by a similar rule, obtain it: as
the length of the shadow of the staff is to the length of the staff itself, so is the length of
the shadow of the object to the object's height.
To draw the Map of a Country à la Cavaliere. We must be placed on an eminence
which gives an opportunity of seeing the country to be mapped, and have some attendant
acquainted with the names of all the places and objects before and around, as well as their
distances from each other, that their relative positions may be set down. To transfer this
rough map, or to draw it out fair, we must begin by drawing a line from the top to the
bottomn, and on this form a scale divided into as many miles as there are between the most
distant places; then mark the site of the different places which come on this line, by taking
in the compasses the distance right or left from the first position, performing the same
operation with all the others: rivers may then be traced, as well as the various objects between
them.
It would be advisable in mapping a country always to work upon a meridian line, and
before any survey is commenced, its direction should be accurately laid down: where a
number of parishes are surveyed, it is important that general instructions should be im-
plicitly followed, that the whole when brought together may be examined: for example,
all writing and figuring should be placed in the same direction; the top of the paper on
which the representation is made should be considered north, and whatever the form of the
plan, this rule should never be departed from: upon a sketch so made, a series of triangles
may be extended at any time, and the respective sides calculated with precision. From an
eminence or lofty site numerous towns and villages may be seen, and after the meridian
line is established, their bearings from each other may be noticed upon the divisions of a
card, which if drawn within a circle will serve to make the sketch. From a table showing
the distance in miles of one place from another, this may be rectified and brought to ap-
proach the truth or a circle may be traced on the ground, and after dividing it into
360 degrees, piquets may be set upon that part of its circumference which is in a line with
the object, and the observer being stationed in the centre of the figure, the divisions of the
circle may be noticed, and thus the sketch of a country may be made where instruments
cannot readily be obtained, or a hasty survey is to be laid down.
If an estate could be seen at once, and its meridian line be determined, there would be
no difficulty in mapping it, and approximating its area, by walking across it in the longest
direction, afterwards triangulating it from this line as a base, and then uniting it with the
3 F 4
808
BOOK II.
THEORY AND PRACTICE OF ENGINEERING
meridian line already drawn. Either the time or the steps taken may be counted from
one position or station to another; the writer found Sir William Gill's Itinerary of Greece
a sure guide, although it contained only the bearings of the places, and the time occupied
in riding or walking; when the traveller has no better map, he must find his course by such
general directions, which have often proved his only security.
Of Demicircles and their Construction.. They
are usually made either of copper or of wood,
and are 12 inches in length, 8 inches wide, and
an inch in thickness; usually a sheet of white
paper is glued on their surface, upon which
the divisions are marked. To graduate the
demicircle, divide its diameter AB into two
equal parts in the point C; from this point,
with the radius CA, describe the semicircle
ADB, and from the point C elevate the per-
pendicular CI on the diameter A B, which will
cut the demicircle ADB in two equal parts
in D.
To graduate the semicircle AD B, open the
compasses to the extent of the radius CA,
and carry the opening three times on the semi-
circle AD B, viz. from A to E, from E to F,
and from F to B; also carry the same extent
A C, on the semicircle, from D to G and H:
then the summit ADB will be divided into
six equal parts. To have the ten degrees,
M P Q
K
L
A
10
20
0

70 80 90 100 110
50
40
140
150
160
170
780]
D
E
Fig. 954.
C
H
divide each of these six parts into three other equal parts, as AG is divided in the
points K, L, and G, and each of these must again be divided, and so on till the whole is
divided into 180 degrees.
Demicircles with sights (à pinnules) used for
measuring angles, distances, &c., are usually
about 15 inches in diameter; the degrees are
numbered from each extremity of their dia-
meter, where a sight is attached by a screw, as
at C and D. At the centre E is a movable
rule with a sight at each of its extremities ;
in the middle of the semicircle is a compass
to show the cardinal points.
A telescope is frequently added to them,
by which the angles of objects at a con-
siderable distance may be very accurately
taken, and the whole is placed on a stand:
with such an instrument it is possible to
determine the position of the several head-
lands and principal objects on a coast, to
complete a maritime survey, and afterwards
to lay them accurately down upon paper.
Suppose two boats are anchored at a known
distance from each other, and the bearings
of the several objects taken from each; then
if the measured distance between the boats
be drawn out to serve as a scale, and the
various lines laid down according to the ob-
served angles, their points of intersection would
denote the positions of the objects that have
been noticed; or the same might be done on
land, by selecting a plain on which a base
line could be measured, and then fixing station
staves at the extremities; from these station
staves the angles which the prominent features
of the country make with each other may be
taken, and the whole may be laid down to
any scale, by adopting a similar process to that
previously described.
Fig. 955.
Fig. 956.
EN
B
G
Fig. 957.
A

B
E
이
​G
K


K
H
The instrument called the station pointer does not materially differ from a demicircle,
over the centre of which moves a number of arms that can be directed to any object; ge-
nerally three rulers, connected by a common centre, are so arranged that they can be turned
CHAP. VIII
809
GEOMETRY.
so as to open and form at one time two angles of any given inclination; the middle ruler,
which is double, has a fine wire or thread stretched in the opening, the others have
one similarly placed from end to end, so adjusted that the three tend to the centre of the
instrument: they can readily be directed towards an object, and their angles accurately
measured: such a station pointer may be made by graduating an arc of a circle on a sheet
of glass ground on one side, upon which, with a pencil, all the angles may be marked; this
laid upon paper, may be easily set off and traced.
When the demicircle is to be used, it has its plane
placed horizontally for taking distances, and upright
for heights; having a joint which works upon a
movable socket, it can be easily adjusted; a plumb
line at once indicates whether it is truly vertical or
horizontal.
To take an angle with this instrument, we turn
it in such a manner that the object A is seen through
the sights on its diameter, and then, without moving
the demicircle, we look along the alhidade or mov-
able rule, and when through its sights the object C
is seen, the angle ABC can be laid down. The
number of degrees contained in this angle may be
counted off between H and I, which may then be
written down.
The demicircle now yields to the azimuth instru-
ment, which measures angles with greater facility,
whether vertical or horizontal, serving also the pur-
poses of the theodolite; it does not possess the
power of repetition, but should an error occur,
it may be reduced or rectified by measuring the
same angle upon different parts of the arc, which
may be accomplished by turning the instrument
on its stand, and adjusting it as required: such ob-
servations frequently repeated, and a mean result
taken, are free from any great error.
To take the height of an object the demicircle is
turned or placed upright, and adjusted by the plumb
passing through its centre, when its base will be ho-
rizontal and at right angles with the height to be
taken. The alhidade is then turned until through
its sights the object O is seen; the angle MNO
will be ascertained, and the degrees may be counted
off.
Distances between places inaccessible may be ascer-
tained and measured in the following manner : when
the angle ABC is taken, measure on the ground
the distance between BA and BC, and construct
upon paper with a scale the angle taken, and pro-
ceed as has been before described.
It will appear evident that if upon the angle
GEF, the dimensions are set off from E to F and
E to G that have been previously taken from B
to A and from B to C, by the scale the distance
between the objects may be accurately measured.
We may infer that this instrument was used first by
the Arabians, from the index or ruler which carried
the sights being called an alidade or alhidade,
which, on the limb of the instrument, showed the
number of degrees or minutes that the object was
above the horizon.
K
A
L
B
Fig. 953.
Fig. 959.
Fig. 960.
Fig. 961.
G
C
A
*
B
Η
E
B
D


M
A


Besides the altitude and azimuth circle, we have
now mural and reflecting circles for measuring
the altitudes and azimuths of stars: the mural
is so called because it is supported by a long
axis passing into a wall, to which the plane of the
circle is parallel; the reflecting circle carries a
mirror, by which an object is seen by reflected
vision; another object is viewed directly the two are
brought to coincide, and the angular distance be-
tween them is measured by the inclination of the mirror to the axis of the telescope,

Fig. 962.
E
810
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
the repeating or multiplying circle is so contrived, that the observation made may be
repeated or multiplied by reading it off successively on different parts of the graduated
limb: the number of values thus found afford a mean result.
Place
Distances between places where one only is accessible may also be found.
the demicircle at the foot of the tower A, and measure the angle CAB; then place
the instrument at C, and measure the angle ACB; by setting out these angles on paper,
the distance between A and B may be found by a scale of parts, or by calculation.
A
Fig. 963.
C
B
G
E


K
30
112
Fig. 964.
34
L
M
L-'.
30
83
112
To ascertain the distance from the piquet at
M to the angle of the building at N: place the
demicircle at P, and measure the angle MPN;
then draw the line RS, of the length or dis-
tance that P is from M, and construct from the
point R a similar angle to that observed from
P. Suppose it has been found by measure-
ment that the angle taken at P was 112º,
the length of the line PM was 83 feet, and the
angle PMN 30°; if all these are accurately
drawn out by a scale, the distance may be
easily ascertained. R to T being the same as
the measured distance from P to M, and R to
I that of P to N, it is evident that by the
scale the distance from T to I on the line X may be taken off.
Distances between places inaccessible on all
sides, as between A and B, may be found by
placing the demicircle on a point C, where both
objects may be seen, as well as a piquet at D.
The demicircle is then turned in such a manner
that the piquet D is visible through the sights
of the diameter, and the steeple B through the
sights of the alhidade. The degrees contained
between the diameter and the alhidade must
then be read off; keep the diameter in the
same line CD, and move the alhidade until
through its sights the tower A is seen; then read
off again the degrees contained between it
and the base line; remove now the demicircle
to the piquet D, and measure this distance
from the new station; repeat the operation,
and lay the angles so taken down upon paper
with a proper scale, as K FIMHN, and the dis-
tance between A B may be truly ascertained.

M
K
D
T
R
Fig. 965.
A
123
32°
ર
E
10 20 80
40 50 60 70
Fig. 966.
X
B

G
N
If it were required to ascertain how many yards distance it was between the points M, L,
of a fortified town, by placing a piquet at N, and then measuring the angle, and the distance
from N to L, and from N to M, the same might be laid down accurately on paper by

M
Fig. 967.
64
117
N
L
CHAP. VIII.
811
GEOMETRY.
means of a scale: the opening of the angle,
117½ degrees, could be set out at Q, and
the distance OS made 67 yards, and OV
on the line T 64; then by the scale P
the distance from V to S will be found
112 yards, which will be that also from M
to L.
To find the length of a building, as from
T to L, select two stations, as Y and P,
and plant two piquets: at the first take
the angle PYL, which will be found to
be one of 30°, and measure the distance
between the two piquets, which is here
45 yards: then from the piquet P, con-
struct the triangle YPL, which is also one
of 30°.
Then set out a scale, and draw bd equal
to YP, and the angles bdg, answering to
YPL, and kbh equal to LYT; the whole
may then be measured, and in this case
the distance from i to k will be found 102
yards, which is the length of the building
TL.
Maps may be laid down by means of
the demicircle, and all the towns at A, B, C,
D, E, F, G, H, be accurately measured, and
put at their proper distances from each
other. First place the instrument at H,
and a piquet at N; after having taken
all the angles, move the instrument to N,
and make a similar observation : measure
the distance from H to N, which here is
200 yards, and then lay down the several
T
T
P
R

112
V
S
117
Fig. 968.
Fig. 969.
Fig. 970.
120
30
KC

60
197
d
k
9
I

angles as observed accurately upon paper, and the lines at their intersection will give the
positions of the towns.
This system was practised in
France as early as the seven-
teenth century, when a base
line was measured from the
town stationed at N and L,
and all the others shown on
the map accurately laid down
from drawing a series of angles
taken at the two stations.

Picard, in 1670, called the
attention of the moderns to the
measurement of a degree of
the meridian, and his observ-
ations were confined to a line
stretching between the parallels
of Malvoisine and Amiens: this
was succeeded by the very ac-
curate observations and the
trigonometrical survey made
by Delambre and Mechain; the
terrestrial arch it embraced ex-
tended over nearly 10 degrees,
and it was
was almost exactly
bisected in the parallel of 45
degrees: these observations, made during the great revolution, led to a more exact method
of measuring, and to the adoption of the trigonometrical system of surveying. After the
labours of Delambre and Mechain, Biot and Arago carried a train of triangles southward
as far as Tormentera, which is a small island near Ivica, in the Mediterranean.
H
200
Fig. 971.
N
It must always be borne in mind, that the magnitude of the angles of the connecting
triangles are affected by the earth's curvature, and these must undergo a correction corre-
spondent with it before the length of the unknown sides can be accurately obtained; for we
know that triangles drawn on the surface of the globe cannot be regarded as plane, neither
can horizontal angles at one station be considered as in the same plane with those at
812
THEORY AND PRACTICE OF ENGINEERING. Book II.

AUTEIUL
PASSY
ISSA
VANVRE
VAUGIRARD
PARIS
OBSERVATORY
RIVER SEINE
MON TROUCE
GENTILLI
AVRI
CHA
CHATILLON
N
BACNEUX
Scale
K
ARCEUL
BOURC DE LA REINE
CONFLANT
VILLE JUIFUE
L
MARNE
VITRI
Fig. 972.
another: NL, the original base from whence the triangulation commences, may represent
the meridian line; but before we commence our computations we must correct any imper-
fections in our instrument, or carelessness in taking our survey; we shall afterwards find
much advantage by adopting the approximating theorem of Legendre, who first demon-
strated that if each of the angles of a small spherical triangle be diminished by a third part
of the spherical excess, their sines become proportional to the opposite sides of the triangle,
considered as spherical. The situations of Paris and the several towns in its neighbourhood
were accurately laid down by the observations made from this base line, and hence com-
menced the method now adopted in making a trigonometrical survey.
In 1784 the British government turned its attention to this interesting subject, and by
Mr. Fox's direction, who was then minister, it was ordered that by means of a series of
triangles, the difference in the longitude between the observatories of London and Paris
should be ascertained: the meridian of Paris having been already continued to Dunkirk,
the Royal Society undertook, with the assistance of General Roy, to complete the task;
and he commenced laying down a base line, rather more than 5 miles in length, upon
Hounslow Heath.
To connect the triangulations between Paris and Dunkirk, Cassini, Mechain, and
Legendre were employed by the French government, and, as a check on their operations,
another base line was laid down in Romney Marsh in Kent, where a steel chain, constructed
on purpose by the celebrated Ramsden, was made use of. Romney Marsh is 60 miles from
Hounslow, and when the two bases were united, by calculating the sides of all the triangles
taken, so great an accuracy had been observed, that there was only the apparent error of
28 inches: the junction of the two observatories of Paris and Greenwich was completed
in 1788.
B
E
M
L
N
Heights may be mea-
sured by the demicircle.
The height of the tower
at A, the top of which we
will suppose is not to be
approached, may be mea-
sured by placing the in-
strument at C, in such a
manner that by elevating
its plane perpendicular to
the horizon, through the pinnules of the diameter, which are parallel with the horizon,
the tower A B is seen in some point, as at E. Then elevate the alhidade of the demi-
circle until the top of the tower is visible through its pinnules: remark then on the demi-
circle how many degrees are intercepted between the diameter and the alhidade, in order
to ascertain the angle E DB, which is here supposed to be 20°.


90
45
A
Fig. 973.
20
H
45
K
Fig. 974.
Then measure on the ground the distance from the station to the tower, and afterwards
construct a scale and lay down a similar figure, the lines M, H, showing the plan of the
CHAP. VIII.
813
GEOMETRY.
tower, the distance, KH, being 45 yards; the angle taken at K, 20° being first set out,
it will then easily be perceived that the height may be ascertained by the scale.
P
10
20
The height of the observatory O P from the station at R, may also be accurately ascer-
tained by constructing the angle YTV, and setting off the distance TX, and then
measuring by the scale the
height Xa. The angle
ZXT is here a right angle,
and the distance from T
to X is 17 yards.


Inaccessible heights may
be measured by having two
stations, as C and D: after
the distance between them
is ascertained, take the
angles BCD from the sta-
tion C, and the angle BDC
Fig. 975.
R
a
X
א
Z
80
Fig. 976.
B


M
L
N
C
D
G
H
A
12
0
Fig. 977.
Fig. 978.
from the station D: then construct the angle LGO, and the angle GIM, and by means
of the scale the height ON may be measured, which will correspond to the height A B.
The height from P to R may be ascertained in a similar way: from the point S
measure the angle

TSR, and from the
point T the angle
STR, also the dis-
tance between the sta-
tions S,T: then con-
struct a scale Q, draw
the line VK, and set
off the measurement
of the distance taken
between S and T,
which is VX: at V
and X set out the
R
P
Q
T
Fig. 979.
术
​
X
Fig. 980.
angles taken at the two respective stations; the height Z Y will be that of P R.
N
The height of the tower A B, which is inaccessible, may also be found by means
of the demicircle placed at DC: after the observations have been made, draw the line

B
A
K
N
M

H
D
C
P
Fig. 981.
Fig. 982.
GH by the scale: from the point G draw the angle G K L equal to the angle CD A, and
the angle IN M equal to DA B: the dimension or length of line PO by the scale will
be the height of the tower A B.
The height from one portion of a building to another may also be readily found, as the
difference between the levels at R and S: place the piquets at V and T, and measure the
four angles TV R, TVS, VTS, VTR, and also the distance between V and T.
814
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Then by aid of a scale up the base line, ZY, set out the angles so taken at a and Y, as
ca Y, ƒYa, and draw the line gƒ from the point where the lines e,b cross, to where the lines
cd intersect each other, and this line of measured by the scale will be the height required.

T
Fig. 988.
S

א
7.
u
Fig. 984.
L
9
Keep-
B
E\ D
The height of the tower A B may be ascertained from the station at D in a similar
manner. First take the height of the tower
CD, and then place the demicircle at D, in
such a position that its diameter shall be paral-
lel to the wall of the tower, DC: turn the
alhidade towards the point A, at the foot of
the great tower, and measure the angle CDA,
the angle DCA being a right angle.
ing the demicircle at D, place it in such a
manner that its graduated limb shall be up-
permost, its plane perpendicular, and its dia-
meter parallel with the horizon, as well as
with the ray DE: then turn its alhidade
until the top of the tower B is seen the
degrees intercepted between the diameter and
the alhidade will be those of the angle E D B.
Construct a scale K, and set out the figure
NIK on the base line FG: make GI on the line H, the height of the small tower; and
the height K N, on the line KL, will be the height by the scale.

A C
L
N
H
M
F
G.
K
Fig. 985.
The height of the tower OP may also be obtained by placing the demicircle at R,
on the top of a lower
building, the height of
which must be measured.
Having observed the two
angles PRT and TRO,
keeping TR as a level
line, and setting off the
same angle from Z by
the scale, making XZ the
height of the low build-
ing, and raising a perpen-
dicular on the line YZ,
where the angle cuts the
ground: where this cuts
the line 42, as at 8, will
be by the scale the height
of the tower OP.

Fig. 986
2
I

T
R
Y
X
O
Fig. 987.
We must always bear in mind when measuring angles, that the circumferences of
different circles are proportional to their radii, and that similar arcs of circles are also
proportional to their radii, and vice versâ. Two arcs of different circles, which bear
the same ratio to their respective radii, must be similar, and therefore consist of the
same number of degrees, minutes, and seconds; it follows, then, that an arc of one
second of all circles is contained the same number of times in their radii, and from the
calculation of the ratio of the circumference of a circle to its diameter, it is ascertained that
this number differs from 206265 by only a fraction; therefore the radius of any circle
CHAP. VIII.
815
GEOMETRY.
π
differs from an are of that number of seconds only the fraction of a second.
In plane
geometry we consider angles as belonging to triangles which do not exceed 180 degrees,
but we may fancy them of unlimited increase or diminution: if a line, for instance, revolve
round a central point, it will in a revolution move through 360 degrees, and in a revolution
and a quarter, that number with the addition of 90. If we call 180 degrees π, the revolving
radius in every revolution will move through the angle 2 π, and in every quarter of a re-
volution and in every half revolution through 7. In general, if n be an integer, the radius
2
after a number of complete revolutions will have moved through an angle expressed by
If it has exceeded a complete number of revolutions by an angle w, the angle
which it has described will be expressed by 2 n π + w, and if it fall short of a complete
number, it will be expressed by 2 n π-w. If the angle it has described exceed an exact
number of revolutions by half a revolution, we shall get its expression by changing w
into π in the former formula, which gives 2 nπ + T = = (2 n + 1) π. If, in like manner, the
angle which the revolving radius has moved through exceed or fall short of a complete
number of revolutions by a right angle, its expression will be found by changing w into
in each of the formula, which gives
2 n π.
IN
2nπ +
π
2
(2 n + 1) π, and 2 n π —
- ( 2 n − 1) π.
2
The angle
2
- w is called the complement of w, and the angle -w the supplement of w.
To find the length of the inclined line AB, fix two piquets, one at C and the other
at D, and measure the angles

DCA and DCB, the first
being 27°, the other 42°.
Then from the piquet D,
measure the angles CDB,
120°, and CDA, 142°: then
measure the distance be-
tween the piquet CD, which
is 9 yards: construct the
scale E, and set off on the
line FG nine parts taken
from the scales, and then con-
struct the two angles IF H
C
D
Fig. 988,
B
F
G
E
Fig. 989.
K

L
H
and KG L, and the distance from their points of intersection will be the length required.
Heights that are in-
clined and inaccessible
may also be measured,
as that of the Leaning
Tower at Pisa. From
the stations R and S,
from whence may be
seen the base and sum-
mit, plant two piquets :
then place the demi-
circle at the piquet R,
and measure the angles
SRO and SR P:
place the demicircle at
the piquet S, and mea-
sure the angles RSP

R
S
Fig. 990.
P

and RSO, and measure the distances between
the piquets R, S: lay this down upon paper, and
from the points where these angles unite or cut, B
as at c and d, measure the length cd by the scale,
and it will give the inclination of the tower, or
rather its inclined height.
Depths which are inaccessible can also be as-
certained, as that of the well A: measure the
diameter AB, and at the point B measure the
angle ABC with the demicircle and by a scale
of parts; the perpendicular A C, or depth, may
be ascertained by drawing the right angle CFI,
and setting out the angle HLK, and from the
scale taking the height L F.
10 15
Fig. 991.
b
Y
d

A
H

G
F
Fig. 992.
Fig. 993
816
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
To measure the depth of a shaft, as MN, the
width or diameter at top M O being 9 feet: place
the demicircle at O in such a manner that the
degrees may be downwards, and its diameter
parallel with the horizon, as is the line OM.
Then turn the alhidade until the bottom of the
shaft at N is seen; measure the angles MON
and OMN; draw the scale P, and the right
line RS, and set off the 9 feet from R to T,
then draw the angle TRY; and the height RY
on the perpendicular RV, as measured by the
scale, will be the depth required of M N
The breadth of a ditch may
also be found, as that of AB.
Being stationed at C above
the point A, take the depth
CA, and measure the angle
ACB. Then with a scale
set out on the line EF, and
from E draw the angle GEH,
and at the point G the angle
EGI, which answer to those
previously measured. From
the point L, where the two
angles cut, measure the length
GL by the scale, which will be
the breadth required.

Fig. 996.
B
M
S
T
R

Y
X
Fig. 994.
Fig. 995.

E

C
L
1.
G
A
H
The width of the ditch at N may also be found
in like manner: from the point N, measure the
angle KNM and the angle NKM, and draw the
scale O. Draw the line PR, and set off the
height taken from N to K, as PS. At the point
P, draw the angle SPT, and from the point S
the angle PSV; then from the point X, where
they cross, measure SX by the scale, and the
breadth of the ditch will be ascertained.
The various methods of measuring heights by
angles are supposed to have had their origin in
Egypt, from whence they were introduced into
Greece by Thales: there can be no doubt that after
Pythagoras had discovered that celebrated pro-
position concerning the square of the hypotenuse,
trigonometry made rapid advances: we have mention
made by Vitruvius of many philosophers who ad-
vanced the science of computation by clearer de-
finitions in geometry.
The Geometric Square is an instrument for mea-
suring distances and heights, &c., and is valuable
for its portability as well as for the facility, by the
common rule of three, of solving most of the
problems arising from its use: it is made of
brass about 12 inches square, or of wood 15 or 18
inches square: it is graduated from top to bottom,
and from bottom to top, and may be called a quad-
rant of 90 degrees. The two sides of the square
which are opposite to the angle of the centre D, as
on the sides AB and BC, are each divided into
100 equal parts, which commence at the two extre-
mities of the quadrant, so that in both divisions the
hundred-point finishes at the angle B, which is
opposite to the centre D, and to facilitate the count-
ing these degrees they are divided into tenths by
short lines tending to the centre.
A
D
Fig. 997.

M
K
Р
V
X
T
Fig. 998.
60/70
70, 80:90
20 30/10/50/60
10
10
201
Fig. 999.
30
40
מז
R
100\\90\80 \70\\\60
50 40
\30 120
80
60
70
108
४
120
B
N

The side DC represents the horizon at the centre D is fixed an alhidade by means
of a screw, which equals the diagonal of the square A B C D, on which the same divisions
are marked as on the side of the square, and as the alhidade is longer than the side of the
square, it will contain more than 100 equal parts: two sights are attached to it, and a socket
joint to one side for the purpose of turning or elevating it when required.
CHAP. VIII.
GEOMETRY.
817
Distances between objects when
one is accessible are measured
by placing the geometric square
at the station R, in such a man-
ner that by boning along its side
DA, we can discover the point
T, and by the other side DC,
the piquet or point X at any
distance from it; the line D T
will then make a right angle
with the line DX. Place the
centre of the square at the pi-
quet X, and turn it in such
manner that by boning along the
line DA the piquet R is seen,
and by the sights of the alhidade
the point T: then remark the

A
D
22
A
Fig. 1000.
number of equal parts in the angle made on the side CB, as at Y.
R
Place, in the first term of a rule of three sum, the number of equal parts from the point.
C of the square to the point Y. In the second term, place the number of feet between the
two stations or centres of the geometric squares D, D; and lastly, for the third term, the
number 100 for the number of equal parts into which the side CB is divided. The quotient
will give the distance in feet from the piquet R to the point T: if it be desired to find
the length of the hypotenuse X T, place in the first term the value of DC of the square;
in the second the number of feet from R to T, and in the third term the number of parts
marked on the alhidade, which are counted from the centre of the square to the place where
the alhidade is on the side CB, as at the point Y. The quotient will give the distance X T.
Distances between objects which are
inaccessible are found by the geo-
metric square, by first placing it at
the point R, where a piquet is fixed,
and then boning a line along its side
DA, until the point T is visible.
Then in the visual ray formed by
the side of the square DC plant
the piquet V. Place the geometric A
square at the piquet V in such a
manner that by boning along its side
DA the piquet R is seen, and by the
alhidade the point S; then count
the number of divisions comprised
between the points C and Y, where
the alhidade rests. Then by the
rule of three proceed as before.

D
D A
Fig. 1001.
Heights may be measured by the geometric square
when the foot is accessible, as by placing the instru-
ment at the point R, and fixing its plane perpen-
dicular to the horizon, in such a manner that the
side CD shall be parallel to it: elevate the alhidade,
until the point P is obtained through its sights,
and remark when it stands on the side CB of the
square, as at the point B, where the 100 divisions of
the side CB are finished.
T

B
A
D
R
Then by the rule of three, place for the first term
100 for the side of the square CD; in the second
the number of feet from the centre D of the square
to the point O, and for the third term 100, the
number of parts comprised from the point C to
the point where the alhidade is at the angle B, as
before mentioned. The quotient, which in this
case is the distance, will be the height, to which,
however, must be added the height the foot of the square is from the ground, when the
observation is taken.
F g. 1002.
If it be required to measure a building with such accuracy that the proportions of
its several ornaments and detail should be expressed in a drawing, the only method that
can be adopted is, to take the dimensions of each portion in feet and inches with rules
or rods prepared for the purpose.
$
3 G
818
THEORY AND PRACTICE OF ENGINEERING.
BOOK II.
}
To find the height of the upper part of a tower,
as that from 0 to P. First find the height from
the ground at S to O, then measure the distance to
the station R. Elevate then the alhidade until you
catch the point P; remark where it stands on the
side A B, as at Z; let R be distant 38 feet from S,
and the height SO, for example, be 34 feet, and the
number of parts on the instrument from A to Z
40. Then as 40: 38: 100: 95, to which add the
height of the square, and we obtain the whole
height of the tower; from this sum subtract the
height SO, and the remainder will be the height
from 0 to P.
It is a well-known property of a right-angled tri-
angle, that if the ratio of any pair of its sides be
known, the angles and ratios of the other sides may
be found; this is indeed the principle upon which
trigonometry is formed; as there are three pairs of
sides in a right-angled triangle, differently related to
either of its acute angles, so there are three ratios
which will determine the angle.
Let w be the angle, y the opposite side, and r the
containing side, and v the hypotenuse; the angle
w may be indifferently determined by any of the
three numbers,
y y, r
y
The first is the sine of the
T
angle w, the second is the tangent, and the third
Y
X
Z/ B
A
D
P

S
R
Fig. 1003.
*
is the secant.
x
•
Heights of Objects which are
not accessible may also be taken,
for instance placing the geo-
metric square at the station V,
so that its centre is level with
the point R: turn its plane
obliquely in such a manner that
by boning along the side DA,
the point Tis seen, and by boning
along the side DC, a piquet
can be placed in the visual ray, as
at X, measured at a certain
distance from the station V.
Then remove the square to the
piquet X, and turn it in such a
manner that by
that by boning along
its side DA, we see in the line
the piquet V, and by the sights
of the alhidade the point T.
Remark the number of divi-
sions from C to Y, where the
alhidade stands, and state the
rule of three sum by placing
for a first term the number of
divisions from C to Y; in the
second term the distance in feet
from the two stations V and X;
and lastly 100 for the third term,
being the side AD: the quotient
gives the line VT. For the
second operation, place the
square at V, so that its centre
shall be exactly in the same
place as before, and its plane per-

1
B
Fig. 1004.
B
C
4
Z
B
A
D
V
pendicular to the horizon, and its side DC parallel to it. Then elevate the alhidade until
the point T is seen through its sights, and remark where the alhidade stands on the
side CB, as at the point Z.
CHAP. VIII.
819
GEOMETRY.
By the rule of three, place for a first term the parts on the alhidade, in the second the
distance in feet from V to T, and in the third the number of parts in the instrument
counted from C to Z. The quotient thus obtained, added to that found by the first opera-
tion, gives the height of R to T.
E
Fig. 1005.
Of the Sector, and its uses for mea-
suring distances, &c. This is a more
complicated instrument than the
others previously described, and is
usually made of either ivory, wood,
brass, or silver, having its two
limbs DB and DC 6 or 8 inches in
length, when used for drawing, and
12, 15, or more, for making sur-
veys; the largest sectors are the
most accurate, on account of their
divisions being larger. The limbs
of the sector are perfectly flat, and
contain all the lines necessary to be
drawn on them; they are united at
one end by a rule joint with a dot
in the centre of the screw, round
which it works: when the in-
strument is closed, the two limbs are
called the upper and lower each
face of the sector has a particular
name, as that which has the line of
equal parts is called the face of
equal parts, and another the face of
chords. By the line of chords, the
opening of angles is ascertained
in making a survey, and upon this
the sights F, F, are placed with
screws for directing the visual rays.
For surveying, the instrument is
placed upon a staff by means of a
joint with one or more screws, by
which any motion may be given it,
and a plumb bob is attached, which
indicates on the ground the precise
centre after an observation has been
taken. The sector has two faces,
one of which is that of equal parts,
the other that of chords, and each
face has two branches, which are
again divided by three lines; be-
sides the lines of equal parts which
it contains, there are also the line
of plans and polygons; on the
face B, which is the reverse of
A, the line of chords is added
to those of solids and metals.
The lines of equal parts is generally
drawn from
from the centre of the
sector to the third part of the
four into which the end of each
branch is divided, and its length is
that of the sectors, which is divided
generally into 200 equal parts or
more. This length is first divided
in half, so that it may have the 100
marked in the middle; and each of
these 100 is again divided in 50
points, and so on until the 200 parts are set out.

Fig. 1006.
F
F
H
ક
G
A
F
B
A
B
Chords
* Metals } ©→X2
Saltas
Chords
C


» Metals [*
Solias
The division of the line of plans is set out from the calculations of equal sides of equal
squarea, as it comprises between its points the lengths of equal sides of a certain number of
square planes, which commonly are enumerated up to 64, and a tolerable skill in the use
of the square root is required to find the distances of these points: the first point on the
3 G 2
$20
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
line of plans is placed opposite the 25th division on the line of equal parts, and the second
point opposite 35½, and continued as in the following table.
128416
1 opposite 25 17 opposite 103
33 opposite 143 49 opposite
175
35
18
106
34
146 50
1767
3
431 19
109 35
148
51
178/1
50 20
1117 36
150 52
1801/1
5
564
21
114
37
152
53
182
6122
1171
38
154
54
1837
7
66
23
119 39
156
55
185
8
703
24
1221 40
158
56
187/1
9
75
25
125 41
160
57
189
10
79
26
1271/
42
162
58
1903
11
8227
130
43
164
59
1921
12
86
28
13211
44
166 60
193
13
14
15
16
∞ THE LO C
90 29
135
45
1677 61
1952
93
30
137
46
169/1
62
197
96 31
1391 47
100
32
141/1/20 48
1711 63
173/1 64
1981/
200
The lines of polygons are constructed by the division of circles, or by the proportion it
bears to the line of equal parts.

12 is opposite 60 9 is opposite
806 is opposite 116 4 is opposite
163
11
65 8
88 5
136 3
200
10
72 7
101
The division of the line of chords or angles is so named from its forming all kinds of
angles, either on paper or on the ground; it is generally the same length as that of the
equal parts, and is always di-
vided into 180°, the number of
degrees which a demicircle con-

*ains.
From
The line of chords is set
out by describing from its middle,
K, as a centre, with the radius
KH, the semicircie HLC,
which must be divided into 180
parts or degrees, so that the line
of chords shall be the diameter
of the demicircle HLC.
the point H, the centre of the
sectors, place one foot of a pair
of compasses, opening them
to the first point of the division
of the demicircle, and describe
an are from thence cutting the
line of chords at the first point
10
30
L
100
90
110
80
120
70
130
60
50
10
40
150
\180
170
_130 140 150||160
H
10
20
30
40
50
60 70 80
90 100 110 740
K
C
B
Fig. 1007.
of its division: then from the same centre H, describe an arc from all the other division"
of the demicircle cutting the line of chords HC: it will then be found that this line will
be divided into 180°, commencing their enumeration from the centre of the sector at H.
The ancients worked their trigonometry by means of chords and arcs, which, with the
chords of their supplemental arcs and the constant diameter, formed all kinds of right-
angled triangles. Beginning with the radius, and the arc whose chord is equal to the
radius, they divided them both into sixty equal parts, and estimated all other arcs and
chords by those parts; viz. all ares by 60ths of that arc, and all chords by 60ths of its
chord or of the radius: this method is as ancient as the writings of Ptolemy, who used
the sexagenary arithmetic for this division of chords and arcs.
Menelaus, at the commencement of the Christian æra, wrote six books on the chords of
arcs, and his system of trigonometry was greatly improved in the following century by
Claudius Ptolemæus, who taught astronomy at Alexandria: in the first book of his
Almagest he has a table of arcs and chords, with their method of construction; it contains
three columns; in the first are the arcs for every half degree, in the second the chords,
expressed in degrees, minutes, and seconds, of which degrees the radius contains 60, and
in the third column are the differences of the chords, answering to one minute of the arcs,
or the thirtieth part of the differences between the chords in the second column. In this
table we discover the property of any quadrilateral inscribed within a circle, viz. that the
CHAP. VIII.
821
GEOMETRY.
rectangle under the two diagonals is equal to the sum of the two rectangles under the
opposite sides. This system of computation by chords was changed for that of sines by
the Arabians, who improved the science left by the Greek school.
The division of the line of solids is drawn below that of the chords, and of the same length.
As the line of planes is founded on the knowledge of the equal sides of perfect squares,
that of solids is founded on the cube roots of the equal sides of cubes, which are also
marked up to 64. The first point of the line of solids is placed opposite the division 50
of the line of equal parts, and is as follows:—
1 opposite
50
1234567
17 opposite 1281 33 opposite 160 49
63 18
1873/
189
1901/
191
opposite 183}}
72
19
1341 34
133 35
162 50
184
1632 51
1853/
79 20
135 36
165 52
1863
85
21
138
37
166 53
91
22
140
38
1681 54
95
23
142
39
169 55
8
100
24
144
40
171
56
9
108 25
146
41
172 57
1923
10
111 26
148
42
174 58
1933
11
114
27
150
43
175 59
194
12
116 28
1517 44
1761 60
195
13
117 29
153 45
178 61
196
14
120
30
1551 46
1791 62
197
15
123
31
157 47
1802 63
1982
16
126 32
1587 48
182 64
200
The division of the line of metals is divided according to the differences in the calibre of
the balls, and each metal is distinguished by its particular sign: that of gold the sign is
put opposite 146 of the line of equal parts, that of lead 172, that of silver 179, that of
copper 1873, that of iron 195, and that of tin 200.
A
#
Fig. 1008.
To divide a right line into two or more equal parts by the sector,
take its length with a pair of compasses, and carry it to the line of
equal parts, then keeping the sector open, carry from the line of
equal parts the number which exactly divides it. Supposing it is
required to divide the line into five parts, which shall be equal, take its length and set it
off on the line of equal parts on the sector at the opening of a number divisible into as
many parts as the line is to be divided, viz. it must be remarked, first, what number is
divisible by 5, and having observed that 200 is one of those numbers, as 40 is the fifth;
place, therefore, the two points of the compasses containing the
length of the line to be divided on each point of the 200, which
is usually at the extremity of the sector, and keeping it open,
then take the distance between the two 40 on the line of equal
parts, which distance will be only one-fifth of the length of the
line.
:
To divide a circle by applying a right line as often as is re-
quired divide 360 by the number of times it is required to ap-
ply the given line, and the quotient thus obtained is so many
degrees. Then open the sector and carry the length of the given
line to the line of chords, where the figures answer to the number
of degrees previously obtained: keep the sector open, and take the
opening between the two 60° on the same line of chords: this opening
will be a radius to describe a circle, which may be divided by the
given line into as many parts as is required, or into five, as shown
at CDEFH.
To divide a circle into equal parts by the sector, take in your
compasses the length of the radius, and carry it to the two 60° on
the line of chords; then divide 360 by the number, as already
described. For example, it is required to divide the circle
ABCDE into five equal parts: take the length of its radius
FB, and carry it to the two 60° on the line of chords, opening and
shutting the sector, until the two points of the compasses, open to
the extent FB, fall exactly on the two 60° of the line of chords.
Keeping the sector at this opening, divide 360 by 5, the number
of equal parts required: we shall have 72 as the quotient, which
must be taken from the line of chords as before; this opening will
then precisely divide the circle into five equal parts.
H
B
A
Fig. 1009.
C
F
Fig. 1010.
A
B
F
B


E
D
C
Fig. 1011.
3 G 3
822
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
D
A
B
C
Fig. 1012.
To draw any angle on a right line. From the point or extremity of the given line
describe an arc of any radius, keeping the compasses open;
apply it to the sector, opening it until the points fall upon the
two 60° of the line of chords: then take the opening on the
same line of chords of the degrees of the proposed angle:
place one foot of the compasses where the arc touches the
given line, and let the other fall on the arc through this
point, and that of the extremity of the given line whence the
arc is described; draw a right line, and it will be the required
angle. As, if it is required to construct at the point A, on
the line AB, an angle of 56°, describe from the point A,
the arc CD, of any radius: then with the same opening of
the compasses carried to the two 60° on the sector, and
placed on the line of chords, which must be done by
opening the limbs of the sector: then take the distance be-
tween the two 56° on the same line, which will be equal
to the required angle, and apply it to the arc, when it will
touch the point E: then draw a right line through this point
from that of A, and the angle BAE will be one of 56°.
By the same means the opening of any rectilineal angle may
be measured, and its degrees ascertained: great care must
be taken always to plumb down the centres of the piquets, as
that of CE is found to be at D.


A
E
B
D
Fig. 1013.
When the sector is used for surveying, the larger it is made, the less C
liable it will be to error, and too much care cannot be observed in placing
the piquet, the centre of which, if planted obliquely in the ground as shown
at C, will produce considerable error.
E
• F
An angle in geometry denotes the inclination of one straight line to
another, and in this simple acceptation must be less than two right angles;
but in trigonometry the term angle has a more extended signification. Let
A B be a fixed line and A a given point in it, and suppose A E to revolve
in one plane about A; then the whole angular space described by AE in
its revolution about A is called an angle, which may therefore in this case
be of any magnitude; or if with the centre A and any radius, we describe a
circular arc, subtending any angle A CD, this are cannot, according to the
geometrical definition of an angle be greater than the semi-circumference of the circle; but
according to the trigonometrical definition, the subtending arc may be of any magnitude,
consisting of any number of circumferences, or any portion of a circumference.
To form and measure angles by the sector :
from the point A to form and measure the angle
BAC. Place the sector at the station A, the face
of the chords being uppermost, and bone by its
sights one of the objects as B, and by the other limb
the object C, and the angle BAC will be formed.
To measure this angle, take in the compasses the
distance between the two 60º on the line of chords,
and putting one foot in the centre of the sector,
let the other fall on line of chords which will be at
65°, which indicates the angle.
To measure distances by the sector, by forming
a triangle of which the two sides are known as well
as the comprised angle: as to find the distance
between BC, when the two sides DB and DC,
with the comprised angle BDC, are known.
Place the sector at D, in order to form and mea-
sure the angle BDC, which we will suppose to
be 83°: then measure the length of its sides, DB
and BC, the first of which is 80 and the second
75 feet; this being done, remove the sector from its
stand, and turn the under side uppermost, keeping
it
open at the angle BDC, 83°. Then place one
foot of the compasses on the line of equal parts at
the figure 80, the number of feet contained in the
side DB, and open the other limb to 75 the
number contained in DC: this opening of the
compasses, measured from the centre of the scale
along the line of equal parts, will give 108 feet
for the distance from B to C.
B
B
Fig. 1015.
Fig. 1016.
83
D
Fig. 1014.

C

CHAP. VIII.
823
GEOMETRY.

The length of the building from I to K may
be similarly found, by placing the sector at L,
and then measuring the angle ILK, and the
length LI and LK.
To measure distances with the sector by forming
a triangle, two angles of which as well as the
adjacent side are known: as to find the distance
A B, from the base line A C: construct and mea-
sure the angle CAB, 84° from the station A,
and the angle A CB, 47°, and the base line
134 feet: then to obtain the other angle, A B C,
add together the two known angles, and sub-
tract them from 180°, the value of three angles
of any triangle, and the remainder, 49°, is the
value of the angle ABC. To obtain the
length of AB, take in the compasses the
length of the side A C, 134 feet, from the centre
of the sector along the side of equal parts; then
turning the face of the sector, place one limb
of the compasses open to 134 at the 98 point
on the line of chords, which is twice 49, the
value of the inaccessible angle ABC; then
leaving the sector open, take from the same line
of chords the value of twice the angle opposite
the side A B, which will be 94°; this measured
on the sector from the centre along the line
of equal parts gives 129 feet for the side A B.
The side CB may also be found by taking
twice the angle CAB, 168°, instead of twice
the angle ACB, and following out the same
method.
When angles are greater than 124, its double
not being contained on the line of chords, we
must, to find this double, subtract 124 from
180, the remainder, 551, doubled will give 111
for the double required.
To measure distances with a sector when the
objects are inaccessible, as that of the side
AB: select two stations at pleasure, as C
and D, 42 feet apart, or any other distance.
From the station C, form and measure with
the sector the angle DCB, which in this case
we will suppose to be 4010, and then the angle
DCA, 7610 from the station D form and
measure the angle CDA, 7610 and the angle
CDB, 12410.
These three angles, with the distance between
the stations C and D, form several triangles
which may be done by the preceding rules,
and it will be found that the side CA is 91
feet long, and the side DA also the same di-
mension. The same rules apply to the other
triangles, and the sides CB and DB may be
found; and lastly the triangle DAB may be
found, the side ĎA 91 feet, DB 108 feet, and
the angle ADB 48°; then following the
principle which has been previously explained,
viz. the method of measuring by the sector the
distances formed by a triangle of which we know
the length of two sides, and the angle comprised
by them, it will be seen that the length AB
is 84 feet.
Fig. 1017.

B
47
134
84
A
C
Fig. 1018.

A
B
Fig. 1019.
D
To obtain heights or distances by means of
trigonometry, it is only necessary that the
length of one line should be ascertained by
measurement, the magnitude of the angles being taken by observation; the sector, as well
as the other instruments, are graduated with great precision, but all observations require
3 G 4
824
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
correction by other methods, which do not depend upon the accuracy of the instrument
nor the mechanical skill; one of the most important is the principle of repetition, by which
any error in the graduation, and in reading off the number of degrees, to which a single
observation is liable, is divided among many repeated observations, so that by a sufficient
number of repetitions the required angle can be accurately obtained, or nearly so: another
method for correcting erroneous graduation and reading off, consists in taking the mean of
several readings upon different parts of the instrument.
To find by the sector the three angles of a triangle, when the three
sides are known. Take in the compasses from the centre of
the line of equal parts the length of the side opposite to the angle
to be ascertained, and carry this opening to the same equal
parts, and open the sector in such a manner that each foot of the
compasses answers to the two other known sides. Keep the sector
at this opening, and turn it over; take in the compasses the
distance between the 60° on the line of chords, which being mea-
sured from the centre of the same line will give the required
angle.

B
Fig. 1020.
By the
In the triangle ABC the three sides of which are known,
viz. A B 10 feet, BC 7, and CA 13 feet, it is required to know the
angle ABC. The side CA opposite the required angle being
13, take in the compasses the distance between the centre of A
the sector and the 13 point in the line of equal parts. Apply
this length to the sector, opening and shutting it until each foot of
the compasses (open to the 13 parts) answers precisely to 10 feet
of AB and the 7 of B C: keep the sector at this opening, and
turn it over, taking in the compasses the distance between the
two 60º on the line of chords; place one foot in the centre of the sector, and the other leg
falling on the same line of chords will indicate 98° 31′ for the angle ABC.
same process it will be found that the angle BCA is 49° 15′ and CA B 32° 14′.
To measure with the sector heights whose feet are ac-
cessible. The height of the line AB, whose foot B is
accessible, is found by taking a station at any distance,
as at F, 40 feet, and planting the sector there, mounted
on its foot, with its line of chords or visual ray
parallel with the horizon. Then lift the other limb
of the sector, until the top on the point B is discovered
through its sights: this will give 23° for the angle
DCB, and as the visual ray cuts the line AB in a
right angle at the point D, a triangle will be formed
of which two angles and the adjacent sides are known,
viz. the angle DCB, 23°, the angle CDB, 90°, with
the adjacent side DC 40 feet. The angle CD B
will be found by taking the known angle DCB 23°
from 90°; the remainder, 67°, will be the unknown
angle CBD. To have the side DB, take in the com-
passes from the centre of the sector, and along the
line of equal parts, the value of the known side DC,
40 feet, and carry this to twice the angle CBD,
67134 on the line of chords. Take in the com-
passes on the same line twice the angle which is op-
posite to the required side BD, which will be 46, the
angle DCB being 23, and keeping this opening,
turn the sector to measure it on the line of equal
parts, which will give 16 for the number of feet from
D to B, to which sum the height of the sector EC
must be added for the whole height of the line A B.

D
C
A
E
Fig. 1021.
G

B
Fig. 1022.
F
In like manner, by placing the sector at B, the height F G may be ascertained.
The sector is still much employed in France, where it is called the compass of proportion:
its principle depends upon the fourth proposition of Euclid's sixth book, in which it is shown
that equiangular triangles have their homologous sides proportionals. The scales now put
upon sectors are divided into single and double; the former has a line with inches divided
into eighths or tenths, a second into decimals containing 100 parts, a third into chords, on a
fourth are sines, on a fifth tangents, on a sixth rhumbs, on a seventh and eighth latitudes
and hours, &c. &c. The double scale contains a line of lines, a line of chords, another of
sines, a fourth of tangents to 45°, a fifth of secants, a sixth of tangents above 45°, and a
seventh of polygons.
The single scales may be used when the sector is either open or shut, but the double
require it to be opened.
CHAP. VIII.
825
GEOMETRY.
To measure with the sector inaccessible heights, as that of the line A B.
B
G
Place two piquets
or stations, as at CD, in a right line with the inaccessible line AB: measure the distance
between the stations C and D, which is 72 feet.
Place the sector at these stations, mounted on
its foot, to form and measure the acute angle
BCD 29°, and the obtuse angle CDB 130°, with
the adjacent side DC, 72 feet. To find the
sides BC and BD, follow the previous rule, and
the unknown angle ABC will be 21°, the side
BC 153 feet, and BD 97. To get the height GB
and afterwards the whole height AB, observe
the triangle DB G, in which the angles GDB
and BDG are required: we shall have the first,
GDB, by subtracting from 180° the angle CD B,
130°; the remainder 50° will be the value of the
angle GDB, and if from 90° we subtract this
50, we shall have 40° for the angle D BG. In the triangle DBG, find the two angles
G D B 50°, and D B G 40°, with the adjacent side DB 97 feet. The length GB is known,
by the method before cited for measuring distances by means of a triangle, where two angles
and the adjacent sides are known, and it will be found that the height G B is 74 feet,
to which add 5 feet for the height of the sector, it will be found that the height A B is 79
feet.

Fig. 1023.
A
F
E
D
ரு
D
Of the Astrolabe and its application. This instrument is of wood or brass, and
consists of a round plane, a foot or 18 inches in diameter, having two faces, one of
which is sunk and called the sea, the other
the altimetric scale; it is an ancient invention,
and is said to have been in use as early
as the days of Ptolemy. The sunk face
of the astrolabe contains several lines or
bands of metal; the first has engraved on it
several stars, and on the others are circles
of azimuth, &c. for different elevations of the
pole, serving to examine and ascertain the
motions of the stars. On the other face, C
which is used by geometricians, and which
comes more under our notice, are several
graduated circles, serving to take the heights of
various objects above the horizon. These
circles are divided into four equal parts by
the two diameters A B and CD, of which
A B, descending from the ring of the in-
strument, represents vertical lines, and the
diameter CD, which cuts A B at a right an-
gle in the point E, represents the horizon or
the level of sea or land. Below the horizontal line CD is an oblong figure FGHI, which
is called the altimetric scale, and is composed of two geometric squares, each having
two of their sides divided into twelve equal parts. We count from the horizontal line
CD, or from the points F and G, the divisions on the sides FI and GH, on which versed
shadow is written, and those on the other two sides which compose the long side IH, on
which right shadow is written, from right to left of the vertical line A B.

Fig. 1024.
B
At the centre of the astrolabe is an alhidade fitted with sights, and at the vertical point
A of the instrument a ring passes through a movable socket, which serves to suspend the
astrolabe in a vertical position.
Plant
Measuring distances with the astrolabe, when only
one of the objects is accessible: as the distance
from the station M to the inaccessible point N,
its edge being level with the ground at M.
the staff M O, about 5 feet in length, perpendicular
at the station M, and divide it into twelve equal
parts, without comprising the portion which is
planted in the earth. Then, holding the astrolabe
by its ring, raise or lower it until in the same
visual ray, when looking from the top of the staff
O, through the sights of the alhidade, the point N
is discovered. Observe then at what point of the
altimetric scale the alhidade is standing, as at the
third point of the side GH, versed shadow. Then

M.
Fig. 1025.
826
Book Il.
THEORY AND PRACTICE OF ENGINEERING.
divide 12, the number of parts into which the staff MO is graduated, by 3, the division of
the altimetric scale on which is the alhidade: the quotient will give 4, for the number of
times that the staff MO would measure in the length MN, and as this staff is 5 feet out
of ground, the distance MN will be 20 feet.
When a great length is to be measured, the observer must be mounted at a considerable
height, as the astrolabe can only measure twelve times
the length of the staff added to the height on which
it is mounted.
The width of the river from P to R may be ascer-
tained by placing the observer at S, which we will
suppose to be 12 feet above the level of the water; then
suspending the astrolabe, raise or lower its alhidade
until the point R is seen; remark at what point
of the scale the alhidade stands, as in this case it
is found at 1: divide the height 12 by 1, and the
quotient will be 12, which denotes that PR contains
12 times the height of PS, or 144, which is the
width PR.

Fig. 1026.
Measuring Heights, whose foot is accessible with the astrolabe, as the height KL.
Then
L
Place
the alhidade of the astrolabe in such a position that the line of the alhidade which answers
to the visual ray of the two sights shall be
exactly in one of the right angles of the alti-
metric scale, which is found by one of the versed
shadows and one of the right shadows.
suspend the astrolabe from a staff, and holding it
in the hand, look at the point L from the end
of another staff, through the sights of the alhidade,
moving the staff nearer or farther from the line
KL, until the point N is seen: lay the staff N,
down on the ground in a right line with KN, as
at NV, the length VK will be precisely the
height of KL.
Measuring inaccessible Heights with the Astrolabe.
It may happen that in taking up the two dif-
ferent stations for measuring inaccessible heights,
the.alhidade, which serves to guide the sight, may
in the same operation fall in four different ways
on the sides of the altimetric scale, viz.: when in
two stations the alhidade is on the same side as
the versed shadow; then observe at the first station,
which is generally the nearest to the object, at
what point on the side versed shadow the alhidade
stands; with this number divide 12, and write down
the quotient separately: remark at the second
station B at what point on the same side versed
shadow the alhidade stands, and with this number
divide 12 again, and subtract this from the first,
or vice versâ if it is greater, and with the re-
mainder divide the number of feet between the
stations, and the quotient will give the height
required by adding that of the staff to it.

M
N
Fig. 1027.
K
Secondly. When the alhidade at the first
station stands at the point 12, or the angle in
which the right shadow and the versed shadow
meet, and at the second station on the side versed shadow; then remark the number at
which the alhidade stands on the side versed shadow at the second station, and with
this number multiply the distance between the two stations, and divide this product by the
remainder of the points which the alhidade makes on the side versed shadow, to make 12
of the division; this quotient added to the height of the staff will give the required
height.
Thirdly. When the alhidade stands at the first station on the right shadow, and at the
second on the versed shadow; then divide 12 by the number to which the alhidade
points at each station, subtract the quotients from each other, the remainder will mark that
the distance to be known is as many times greater as there are parts to be added to
the remainder, besides the height of the staff.
Fourthly. When the alhidade stands on the ombra at both stations, divide 12 by the
number at which the alhidade stands at both stations, and subtract one from the other;
CHAP. VIII.
827
GEOMETRY.
multiply the distance between the two stations by 12, and divide this product by the
remainder from the subtraction of the two quotients; the quotient of this last division
added to the height of the staff gives the required height.
For measuring inaccessible Heights with an Astrolabe, as that of AB, select two stations as
C and D), distant from each other in this case 36 feet; suspend the astrolabe at the station
C, look at the point A through
the sights, and observe at what
point on the altimetric scale the
alhidade stands, as at the 6
point on the versed shadow.
Perform a similar operation at
the station D, that is to say, ob-
serve the point A through the
sight of the alhidade, noting at
what point it stands, as at the
third point of the versed shadow,
which shows that the first of the
preceding observations must be

Fig. 1028.
C
D
followed; divide 12 by 6, the number of divisions which the alhidade indicated on the
versed shadow at the first station, and the quotient will give 2: then divide 12 by 3,
the number indicated by the alhidade on the side versed shadow of the second station,
the quotient will give 4; subtract these two quotients from each other, as 4—2—2, with
which divide the number of feet distant between the stations C, D, 36, which leaves 18
to be added to the height of the staff 5, making 23 feet for the required height, A B.
A
Or if it is required to measure the height AB, in another case, choose the two stations.
C and D, which here are 27 feet apart; then suspend the astrolabe at the station C:
by the staff and by the sights of the alhidade bone
the point A, and mark where the alhidade stands
on the altimetric scale, which at the first station
will be at the right angle figure 12, where the
right and the versed shadows meet: suspend the
astrolabe at the second station, and bone the line
A through the alhidade, remarking where it stands
on the altimetric scale, as at the 8 point in the versed
shadow, in which case
which case we must, to finish the
operation, employ the second of the previous general
rules therefore, multiply the distance between the
two stations C and D, which is 27 feet, by the
number of the side versed shadow at which the
alhidade stood, viz. 8 × 271=220÷4, the number
of points necessary to make up 12=55+ 5, the
height of the staff, and we have 60 feet for the
required height AB, which is found without approaching the
line.

B
Fig. 1029.
Another method to find the height PR may be described,
which is an example coming under the third system. Take a
station at any point S, and having planted the staff per-
pendicularly, suspend the astrolabe from the left hand, elevating
or depressing it until the point R is seen from the top of the
staff, and by looking through the sights of the alhidades:
observe at what point on the altimetric scale the alhidade
stands, as at the 4th point of the right shadow, then, according
to the third rule, we have 12÷4=3; then retire in a straight
line to the station S, and plant the staff perpendicular to, and on
a level with the point P, suspending the astrolabe also, until the
point R is seen, by looking along the staff T, and through the
sights of alhidade: after having observed where the alhidade
stands, as at 10 on the versed shadow, this number 10 will serve
to divide 12, the number of parts on the staff T; the quotient
will be 1, which subtracted from 3, the quotient of the first
division, there remains 2; this number 2 denotes that the
height RP is twice as great as the distance between the
station S and T; that is to say, if the distance ST is 8 feet,
the height from P to R will be 16+5, when the height of
the staff is added: if the difference had been 1 only, then the
distance between the two stations with the height of the staff
would be equal to the required height. Lastly, if the difference
P
Fig. 1030.
C
D

S
R
828
BOOK 11
THEORY AND PRACTICE OF ENGINEERING.
were 3, we must triple the distance between the two stations in order to have a sum,
to which the length of the staff must be added, to obtain the required height.
N
To illustrate the fourth remark, select the two stations R and S, in order that the
height from M to N may be obtained; these stations
are 40 feet distant from each other: at the station
R suspend the astrolabe; bone through the sights of
the alhidade the point N, and observe at what divi-
sion, and on what side of the altimetric scale, the alhi-
dade is, as at the third point of the side right shadow;
suspend then the astrolabe at the second station S,
and bone the point N through the alhidade, and having
observed that it stands at the 10 point of the right
shadow, adopt the fourth rule, previously given; ac-
cordingly divide 12 by 34-3, being the number
of points on the side right shadow indicated by the
alhidade at station R: divide 12 by 10, the num-
ber indicated on the side right shadow of the alti-
metric scale at the second station S; the quotient 1,
rejecting the remainder of this division, which is of little
account, must be subtracted from the first quotient 4,
and 3 remains: then multiply 40 feet, the distance
between the two stations by 12, in order to divide the
product 480 by 8, the remainder from the subtraction
of the two quotients; the quotient of this last division
will give 160 feet, to which add 5 feet, the height of the
staff, which gives 165 feet for the total height of the
line VN; if then we subtract the height from the
ground to the point M, viz. V to M, we shall obtain the
height MN.

S
S
Fig. 1031.
R
V
M
M
Measuring Depths by the Astrolabe. Required the depth of a well, as from PM to ON:
first measure the opening of the mouth PM, which is 34 inches; then suspend the astro-
labe, disposing it in such a manner that the vertical line
AB of the altimetric scale, which divides the right shadow
into two equal parts, shall be plumb or on the same line
with the wall of the well PO: then turn the alhidade of
the astrolabe until the bottom of the well N is seen through
the sights of the alhidade: remark at what point on the
right shadow the alhidade stands; if on the 4th point, as
in this case, the depth MN is half the number 12, which
is half the division of the long square; therefore, if the
diameter of the well MP is 34 inches, the depth MN will
be 102 inches, and if we subtract 6 inches for the height of
the astrolabe, there will remain 96 inches for the depth of
the well. If the alhidade fell on the 6th point of the
right shadow instead of on the 4th, the depth of the well
would only be twice the diameter of the mouth: if on the
point 12, where the right and versed shadow makes a right
angle, the depth would be precisely equal to the diameter
of the well: if on the 1st point of the right shadow, the
depth of the well would be twelve times the diameter of
the mouth, and so on with the other points, taking their
relation to the number 12.
Measuring Heights or Depths with the Astrolabe, when
the station is either above or below, as to get the height
OP. We must so place ourselves at R that we can see
the point 0; and at R suspend the astrolabe in such a
manner that the line AB shall be perpendicular to the
horizon; then turn the alhidade until by means of its sights
we discover the point 0; observe then where the alhidade
stands on the right shadow at the 2 point, counting from
the vertical line A B, which indicates that the depth or
height OP will be six times greater than the distance
RP, because 2 is the sixth of 12, the division of the side of
the square used in this operation. Therefore if we measure
the distance RP, and find it 12 feet, we shall have to
multiply 12 by 6, and the product 72 feet will be the height
of OP.

N
Fig. 1032.
R

P
Fig. 1033.
CRAP, VIII.
829
GEOMETRY.
A
O
B
E
Of the Compass and the Magnetic Needle. This is usually made of brass or wood in
the shape of a small circular box, about 4 or 5 inches in diameter, mounted in a
square mahogany case, as shown at GHKI. Each side is
divided, and a line drawn across it at right angles; at C, the
centre, several circles are described, the outer one divided
into 360 degrees; in the centre is suspended the needle; on the
top are two sights, through which the observations are to be
taken; the box is covered with glass set in a brass rim, the
margin of which is divided into 360 degrees. The compass
when used is attached by a joint, which enables it to be moved
in any direction on the stand provided for it; a ball and socket
is usually found to be the most convenient for the purpose.
D
Fig. 1034.

G
F
'The mariner's compass has a circular card attached to its needle,
which turns with it, on the circumference of which are marked
the degrees, and also the thirty-two points or rhumbs likewise
divided into half and quarter points. The pivot rises from the
centre of the bottom of a circular box, called the compass-box,
which contains the needle and its card, and is covered with a
glass top to prevent the needle from being disturbed by the
agitation of the air. The notation is marked out by dividing
the circumference into four quadrants by two diameters at right
angles, the extremities of which are the four cardinal points marked N, S, E, W. Bisecting
each of the quadrants, the several points of bisection are denoted by placing the two letters
at the extremity of the quadrant in juxtaposition; thus NE denotes the point which is
half way between north and east, and so with NW, SE, SW. Let the octants next be
bisected, the points of division are denoted by prefixing to each of the above combinations,
first the one and then the other of the two cardinal points of which it is formed. Thus
NE gives NNE and ENE, and so with the others: sixteen points having thus been
A
B
G
Fig. 1035.


H
E
N
N
M.
W
C
E
W
S
C
K
H
B
LUG
¡.
Fig. 1036.
C
E
K
Fig. 1037.
fixed, their distances are to be bisected, and each of the points so found is expressed by that
one of the preceding points already named to which it is nearest, followed by the name of
the cardinal point towards which its departure from the nearest points leads it, the two
being separated by the little letter b; thus the point half-way between N and NNE is
NhĚ, that which is half-way between NNE and NE is NEbN: the whole of the
thirty-two points are thus established.
The variation of the needle is its deviation
from the north; and to find the true meridian of
a place by the sun, we may fix a piquet upon a
horizontal plane, either perpendicular or inclined,
as that at AB, with a plumb attached, as BC:
from the point C, which is found by the plumb,
and with the radius at which the point of the
shadow D finishes before noon, describe the arc
DF; then in the afternoon observe where the
shadow touches the arc a second time, as at F,
and draw the line DF; bisect this line, and raise
the perpendicular CG, and this line will be the
meridian. By placing the compass at I and K,
its variation may then be observed from the true
meridian.
H
B
D
A
Fig. 1038.
G
I

K
830
THEORY AND PRACTICE OF ENGINEERING. BOOK IJ.
The meridian may also be found by the plane table,
as that shown at MLON; describe on it the arc
of a circle MPO, and sink it to the depth of an inch,
and then within it describe another arc, as Z, parallel
with the first at L, place a small piquet or staff.
Place this plane table on a level plane about nine
o'clock in the morning, as is done at X, so that it
stands on its side NO; and having OL towards the
sun, turn it until the extremity of the staff at L casts
its shadow on the circle at Z, and then mark on the
ground the line RX; and after some space of time,
observe another point where it cuts the circle: at
three o'clock place the plane table on its side NO,
with OL towards the sun, taking care that one
corner of the plane table touches the line RX, as at
the point R; and observe as before where the shadow
of the staff touches the circle Z, and having remarked
this point, draw along the foot of the plane table the
line RS; from the point of intersection, R, describe
the arc X S, which bisected in T will be the meridian
required.

M
Q
Z
N
Fig. 1039.
S
T
Fig. 1040.
X
R
I

The dip of the needle is subject to variations, to
account for which numerous hypotheses have been
suggested. Halley once supposed the earth a great
magnet, with four poles or points of attraction, two
being near each pole; but on reflecting that no
magnet was known to possess more than two poles, he abandoned that idea, and imagined
the earth to consist of an external shell, which contained the magnetic power, having its
two fixed poles distant from the poles of rotation, and an inner globe separated from the
outer crust by a fluid, also having two poles, and the same axis of diurnal rotation as the
shell. The general opinion now is, that the magnetism of the earth is owing to its
temperature; that the globe itself is a great magnet, and the intensity of its magnetism at
any point is inversely as the temperature of that point. Those who are desirous of making
accurate observations upon the variations to which the needle is subject must have recourse
to one of the instruments made expressly for the purpose, as Colonel Beaufoy's variation
instrument, so generally employed in his numerous magnetical experiments, or Dolland's
dipping needle remarkable for its simple construction, and the adaptation of adjustable
agate planes, on which the pivots of the needle rest: for the purpose of proving whether
these planes are horizontal, there is a contrivance on the under side, by which their level
can be truly ascertained.
Ꮀ
A vessel constructed of iron having caused considerable disturbance of the needle, a
number of experiments were undertaken by Mr. Barlow of the Royal Military Academy
at Woolwich, who found that the attracting power of iron is not resident in the mass, but
on the surface; so that a hollow shell of about four pounds weight acts as strongly on the
needle, at the same distance, as a solid iron ball of 200 pounds; this being established, it
occurred at once that a thin iron plate of five or six pounds weight might be made to
represent and counteract the whole amount of the attraction of the vessel, and thereby
leave the needle perfectly undisturbed; the action of the ship and that of the plate, as
regards their effect on the needle, neutralising each other; upon this principle Barlow's
correcting plate is made, which, mounted on a tripod stand or fixed pedestal, determines
the variation of the compass in a ship, as dependent upon the local attraction of the vessel.
Maps drawn by the Compass. The instrument used for this pur-
pose has its rim divided into 360 degrees, and against one of its
sides parallel to the meridian is a movable rule or alhidade, the upper
edge of which is furnished with a groove to bone the objects either
vertically or otherwise, without disturbing the horizontal position of
the compass.
When a map is to be laid down, two stations are se-
lected from whence the whole of the country can be seen: place
the compass, for instance, at the point A, and turn it in such a
manner that it points north, and that by boning along the alhidade
the point B is seen; remark then how much the needle declines
from the meridian of the compass: turn the north side of the compass towards the
next object to be boned, as C, remarking the degrees indicated, as 22° W.; write this down
on the side of the visual ray, and proceed with the other. angles of the position, as that of D,
which is 7° W.: then place the compass at the second station B, in such a manner that the
north side is towards D, and observe the degrees which are indicated by the needle, as 15°
W.; figure this down against the visual ray, from B to D: then turning the north side of the

D
Fig. 1041.
E
CHAP. VIII.
831
GEOMETRY.

compass, bone its position through the sights of alhidade, and remarking
that the needle indicated 45° W., write this against the visual ray.
Draw out the map, tracing a line AB, on the paper, and set out
upon it 1600 feet, the distance measured from A to B; against the
line A B, used as the base, place the side of the alhidade of the com-
pass, and turn the sheet of paper, keeping the compass against
the side AB, until the needle points at the same degree as when
boning to A: without removing the paper, observe what is the degree
of the ray to C, and having found it to be 22° W., place the side of
the alhidade against the side A, and turning the compass, with the
side of the alhidade always against the point A, and the paper un-
moved until the needle makes 22° W., as found from the point A to C,
draw a right line along the side of the albidade of the compass,
which must also be done for the other positions as 7° W., for the
point D: then observe, where the station B is marked, what is the
degree on the line which goes towards C, and having found it 45° W.,
place the side of the alhidade on the sheet of paper at the point B,
the extremity of the line AB; and doing the same at the point B,
we shall have second rays which will cut the first in several points,
and give the positions of the places to be set down on the map.
The compass is also used to mark the meridian on maps;
this is done by placing against the line drawn from one plane
to another, as from A to B, one of the sides of the compass,
and then observing the place where the needle points, and
marking its direction, as KL; this is afterwards again proved
by placing the box against this second line, and finally
drawing E F parallel to it.
The compass should be extremely susceptible and possess-
ing an intensity of directive force; the first of these is ob-
tained by constructing the needle of the material and form
best suited to receive and retain the magnetic power. Shear
steel has been found best adapted to receive the greatest
amount of magnetic force, and the best form is that of a
lozenge or rhomboid cut out in the middle, so as to diminish
the extent of surface in proportion to the mass, it being as-
certained that the directive force of the needle when mag-
netised to saturation depends not on the extent of surface,
but on the mass.
A
H
N
E
L
Fig. 1043.
В
32
A
Fig. 1042.

N
B
K
To measure Angles with a Compass, attach a long rule
to its north side, and present it against one of the sides
of the angles to be measured, and observe how many degrees
the north point of the needle declines from the north point of
the compass, beginning to count these degrees from the
smallest arc there is from the north point of the card, to the
degree where the north point of the needle stops, in order to
figure on one side the degree of declination, supposing that the north point of the needle
does not coincide with the north point of the compass: then present the same side of the
compass to the other side of the angle, and count
from the smallest arc how much the north point
of the needle is distant from the north point
of the card; subtract the degrees from each other,
and the remainder from 180°, and this remainder
will be the angle required. As in the salient
angle BAC, apply the long side marked north
of the compass to the side AB, and observe
how many degrees the north point of the needle
declines from the north point of the card; and
since they coincide, it is a proof there is no
declination; write therefore, north to the side
AB: then apply the same side of the compass to
the other side A C, to count how much the north
point of the needle declines from the north point of the card, as 90°, write down AC 90°
above mark north, in order to subtract this from 90°, which being subtracted from 180° still
leaves 90° for the angle BAC. But if the angle required was CDA, when the nort!
point of the needle is 36° from the north point of the card, having placed the north side
of the compass against the other side DB, it will be seen that the declination of the
needle would be 92°; subtract the 36° from 920, there will remain 56°, which being sub-
tracted from 180° leaves 124° for the angle CDB.

B
Fig. 1044.
D
C
Z
A
B
852
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
To make Surveys under Ground, as in Mines,
with the Compass. Supposing it required to
make an opening at A, and after a shaft has been
sunk to the required depth, to cut a road in the
mine which shall continue in the direction of and
terminate at a point directly under B: we must
place ourselves above the opening A, as at C, and
then measure in a right line the distance from
A to B, which in this case is 28 feet; then place
the north side of the compass at the point C, on
the line CB, and observe at what degree the
needle points, as to the 7° E. of N., and figure
this down: then having removed the compass,
draw on the ground at the point C, and on the
line CB, the perpendicular C G, and lay a staff
along this line CG, which carries at its salient
extremity a plumb-line, to mark the point H on
the ground at A, and also several others, as IK,
&c., drawing back the rod on the line CG; take
care to observe how much the rod was advanced
from the point C, where it marked the point
H, as 9 feet: then from the entrance A, draw a
right line through the points H, I, K, measuring
back 9 feet from H, which will give the point
R, answering to the point C above ground:
place the side of the compass marked north at
the point R, and turn the compass till the needle
stops 70 E. of N., which being remarked, draw
a line along the north side as RS, in order to
dig according to this line from the point R 28
feet, which will coincide with the point B; but
should it not be practicable to continue in a
straight line on account of the hardness of the
rock, or for some other cause, several detours at
right angles may be made to the right and left,
as shown at O, P, &c., taking care that the
number of small detours, P, compensate for the
detour O, to find again at V the right line RS.
It is by the aid of geometry that the miner
studies the situation of the mineral deposits on
the surface and in the interior of the ground: he
also determines the several relations of the veins
and rocks, and becomes capable of directing all
the operations which are to be performed.
Wherever iron does not interfere with the mag-
netic needle, the compass is employed to
measure the direction of a metallic vein, and
its graduated circle serves to notice the in-
clination or dip, which is called the clinometer.
The distance from one point to another is mea-
sured with a staff or chain; for some surveys
the dials of the compasses are graduated into
hours, generally twice twelve; thus the whole
limb is divided into 24 spaces, each of which
contains fifteen degrees or one hour, which is
subdivided into eight parts.
R
C
K
Fig. 1045.
I
G
S
1
A
H
L
N
M
L
G
C
D
T
HALJALFAMETUM/FLOTMINE
K
B
B


The Jacob's Staff, an instrument used by geo-
metricians to measure distances and heights, is
a long rod or square staff with a cross, as shown
at DE; it is usually made of the wood of the wild
cherry, pear tree, or ebony, these three trees
having fewer knots or veins, which allows the cur-
sor to move freely up and down the rod : the rod
itself is divided usually into four equal parts, as
at M, or five as at L, and is commonly 3 or 4 feet in length: the cursor has a square bole
made in the middle, and is allowed to have but little play; it is provided with a small
screw to keep it at any required point. In order to measure distances, it should be in.
H
Fig. 1046.
CHAP. VIII.
833
GEOMETRY
length equal to one of the parts the rod is divided into,
and when we wish to measure a height, we must add
half the thickness of the rod to the extremity of half the
cursor which is used to take the height. In order to
bone more easily along the rod of Jacob's staff, four
small holes are pierced aside the hole in the cursor, as
shown at K; this instrument when used is mounted on
a stand fixed to the ground.
To measure the Distance between two Objects one of
which is accessible. Place the cursor on the second
division of Jacob's staff, fix a piquet on the ground near
the accessible object, and place the end of the rod near
the piquet; bone along it until you discover a point of
the inaccessible object, and bone with the extremities of
the cursor two other points, one to the right, the other
to the left of the inaccessible object, and in the same
line with the first inaccessible point: run the cursor to
the third division of the staff, and retire in a right line
from the first station, and from the first inaccessible
point, in such a manner that by boning along the rod
you can discover the piquet and the point in the inac-
cessiblę object, and also the two points to the right and
left of the inaccessible point by boning along the ex-
tremities of the cursor; the distance between the latter
station and the piquet at the inaccessible object will be
half the distance between the two objects. The breadth
of a river may be found by placing the cursor on the
second division of the rod or staff, as at H, and then
placing a piquet at A, against which the end, M, of
Jacob's staff, is required to bone; which is done by
placing it in such a manner that by looking along
the staff MN, you can see the point B, and also
the two points E and F by the extremities C and
D of the cursor: run the cursor on the third point
of the rod, as to G, and retire in a right line from
the accessible object A, until by boning along the
staff M N, and by the extremities of its cursor CD,
you discover the inaccessible point B, and also the
two others E and F: the distance KA, being
doubled, will give the breadth of the river from Ã
to B, that is to say, if it is 30 feet from K to A, it
will be 60 feet from A to B.

Fig. 1047.
L
H
N
M
N
C'
M
N
K
M

To measure Distances between two inaccessible
Objects. Fix the cursor on the second division
of the staff, and place yourself about midway
between the two objects which are inaccessible,
bone along the staff, and by the two extremities of
the cursor, which should be placed in a direction
parallel to the line between the two objects, until
you discover the two inaccessible objects by the
visual rays; plant a piquet at the place where the
observation was made: then run the cursor on
the third division of the staff, and retire from the
first station, boning by the staff and by two
extremities of the cursor until you discover by
the visual rays the inaccessible objects; the distance
between the stations will be equal to that between
the objects. As, for instance, it is required to as-
certain the distance from A to B: run the cursor
on the third division of the staff M N as to H;
then being at about an equal distance from both
objects, bone by the staff MN and by the two
extremities of the cursor, CD, which is parallel
with the line AB, the two objects A and B; that is to say, you must discover by the visual
ray MC the object A, and by the ray MD the object B, which will be the case when
you are at L, where you must place a piquet for the first station, Then run the cursor
CD on the third division of the staff MN, as to G, and retiring from the piquet or station
Fig. 1048.
(
D
K
3 H
894
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
L, bone the piquet L and the inaccessible objects A and B, as was done at the first station,
which being observed at the station K, plant there a piquet for the second station. The
distance between these two stations or piquets L, K, will be equal to that between the inac-
cessible objects A, B; that is to say, if it be 180 feet from L to K, it will be 180 feet from
A to B.
To measure accessible as well as inaccessible Heights. Place the cursor on the second
grand division of the staff, holding the staff horizontal with the cursor perpendicular to the
horizon; advance to or retire from the ob-

MD
D
N
H
C
B
ject whose height is required, until by
boning along the staff and the two ex-
tremities of the cursor the foot and the
summit are discovered at the same time,
which when observed, plant a piquet at
the station of the same height as the staff
is held. Then run the cursor on the third
great division of the staff, and advance or
retire from the piquet until at the same
time the foot and the summit of the object
are discovered, remembering to keep the staff
horizontal, as at the first station, and bone
by the two extremities of the cursor; then
plant a piquet at this station: the distance between the two piquets will be that between
the objects.
K
Fig. 1049.
The height of an object, A B, being required, fix the cursor at the second division of the
staff MN, as at H; then holding the staff horizontal, bone from its extremity M along
the two extremities C and D of the cursor, until the foot A and the summit B are seen,
which will be the case at L, where a piquet must be planted, of the height the staff M N
is held. Run the cursor CD to the third great division of the staff, as at G; then ap-
proaching or retiring from the piquet L, holding the staff horizontal, and at the height of
the piquet L, bone from the end of the staff M, by the two extremities C and D of the
cursor, until the foot A and the summit B are seen, which will be at the station K,
where a piquet must be planted for the second station. Then, measure in a right line
the distance between the two piquets K, L, which will be the height required; that is to
say, if the distance KL is 80 feet, the height AB will be 80 feet: small heights can
only be measured by this means, as the instrument must be placed opposite the middle
of the height required.
B
L
A
To measure Lengths when they are accessible about midway.—Stand opposite the middle
of the required length, and dispose the staff and cursor parallel to the horizon; bone
the two objects by this end of the staff
and the two extremities of the cursor, which
should be placed parallel to the distance be-
tween the two objects; this may be done by
moving the cursor nearer to or further from
the eye: count how many small divisions
there are on the rod between the end of
the staff boned and the place where the.
cursor stopped; measure how far it is from
the station whence the two objects were
boned to the middle of the line drawn
between them: by the rule of three place
as a first term the number of small parts
at which the cursor stopped on the rod;
in the second term the number of feet
from the station to the middle of the dis-
tance between the objects; and in the third,
30 for the length of the cursor: the quotient
will be the answer. The distance from
A to B is required, which to obtain we
must place ourselves at the station K, oppo-
site the middle of the distance between A
and B, and dispose the staff in such a way that the rod and cursor may be parallel to
the horizon, in order that, when boning from the end of the cursor C and D, the two
objects A and B may be discovered, either by advancing or retiring the cursor back, as to the
60 division. Then measure how far it is from the station K to the point L, which is
the middle between the two objects A and B, or 450 feet. Then by the rule of three,
placing as a first term 60, the number at which the cursor stands, and in the second term
450, the number of feet from the station K to the middle L, between the two objects

Fig. 1050.
C
K
D
M
CHAP. VIII.
835
GEOMETRY.
A and B, and in the third term 30, the length of the cursor; the quotient gives 225, the
number of feet from A to B.
To measure Heights by Jacob's Staff and Arithmetic. In this case its rod is placed parallel,
and its cursor perpendicular to the horizon; then boning from the end of the rod by the
elevated end of the cursor, the summit of the height to be found, which is done by moving
the cursor nearer to or farther from the eye, and remarking the number of small divisions
on the rod, comprised between the end boned and the place where the cursor stops;
then measure the distance from the station to the foot of the required height; put for a
first term the number of small divisions
at which the cursor stands; for the second
the distance in feet from the station; and for
the third term half the length of the cursor,
the quotient will be the height sought.
A
B

Fig. 1051.
M
C
The height A B is required. The staff
MN is to be first placed parallel with the
horizon, and CD perpendicular to it; in
order that by boning from the end M, by
the elevated arm D of the cursor, the point B
may be seen. Count how many divisions
there are on the rod between M and the cursor D, as 45; then measure the distance on
the ground to A, which here is 600 feet; then 45: 600 :: 15: 200, to which quotient must
be added the height of the stand, to obtain the height of the tower A B, 15 being half the
length of the cursor CD.
The Plane Table, and the method used for
measuring heights and distances, &c. with it.
This instrument is of great antiquity, and
was clearly in use when Vitruvius compiled
his book; it is usually made of a plate of
brass, either of a round or square form, on
which is placed a sheet of paper to draw the
lines necessary to form plans or maps, as
well as to obtain the distance between ob-
jects. The plane table A for mapping is of
brass, 10 or 12 inches in diameter, and on
its edge is a circle B, capable of containing
six sheets of paper, and having a diameter
sufficient for measuring the 360 degrees. In
the centre at C a point is placed, the upper
part of which is sunk to receive a screw.
On the centre is placed a brass alhidade,
FG, which fits into the hole C, and which
is furnished with a telescope.
The plane table is often used for forming
a sketch map, and for filling up the details
of a survey, where the principal points have
already been fixed by the theodolite, but
observations made with it cannot be relied
upon where great accuracy is demanded: in
many plane tables the divisions into 360
degrees is dispensed with, and the reverse
face of the frame is divided into equal parts,
as inches and tenths, which are very con-
venient for ruling parallel lines, setting out
squares and other purposes. On one side is
screwed a compass-box, with a magnetic
needle to indicate the bearings, and to enable
the engineer to place the instrument at any
new station parallel to its former position.
The brass rule or index with a sloping edge
and perpendicular sight vanes at each ex-
tremity is all that is required to complete
the apparatus.
H
A

E
F
G
Fig. 1052.
Ꭱ
Fig. 1053.
i
M

K
The modern plane table is commonly made of wood in order that pins may be readily
fixed in it its size for taking distances is about 2 feet in length, and 18 inches in width,
and about 1 inch in thickness; its station line being only 6 inches When used a rule
LM is placed on its edge to serve for the sights, and we require a stand to place the table
on, some piquets, pins, and a chain to measure distances with: a sheet of paper is then
3 H 2
836
BOOK II
THEORY AND PRACTICE OF ENGINEERING.

placed on the plane table, folding down the edges, which are secured
either with mathematical pins or by paste; sometimes the plane
table is sunk, and by means of a frame the paper is kept flat.
When the paper is laid over the table T, the frame V passes
over it, and keeps it perfectly stretched and in its place.
To take the Distance between two Objects, as A and B, which are each
accessible from one to the other, the plane table is placed at any point,
as C, opposite the middle of the two objects: draw a scale near one
of the long sides of the table, and fix a pin, D, at about an inch
from this scale within the table, where the station line generally is;
then turn the plane table in such a manner that one of its sides
shall be nearly parallel to the two objects A and B : place against
the pin D the side of a rule which may be moved in such a manner
that when boning along the face of this rule from the pin D, the
visual ray may cut the point A draw on the paper from the
pin D along the side of the rule the line DE: then shift the rule
to the other side of the pin, and in a similar manner draw the line
DF: measure how far it is from the station C to
the object A, as 64 feet, and take from the scale G 64
parts, and set them off on the line D E from D to H,
to answer to the 64 feet from the station C to the ob-
ject A likewise take 66 parts from the scale G, and
set them off on the line D F from D to I, to answer to
the 66 feet from D to B: draw the line HI, which
being measured by the scale G, will give 51 parts for
the number of feet from A to B.
A
Fig. 1055.
V
Fig. 1054.
E
F
D
G
C
T


B
To measure the Distance between inaccessible Objects,
as that of A and B: place the two piquets, C and D,
at pleasure, and draw on the plane table a scale, E,
of any length or division, as into 600 equal parts, and
measure the distance between the two stations Cand
D, as 563 feet: take from the scale 563 parts, which
will give the station line F G on the table, on which
fix the pins F and G: place the plane table at one of :
the stations, as at C, in such a manner that the station.
point F shall be above the piquet C, and the plane
table towards the objects A and B: bone the piquet
D by the two pins F and G, keeping the table in this
position; place a rule against the pin F, and bone the
object A along the side which touches the pin and
draw the line F H. Then turn the rule against the
pin, until the object B is seen, drawing in the plane
table the line FI: remove the plane table from this
situation to the piquet D, placing it in such a manner
that the point G of the station, line shall be exactly
above the piquet D, so that by boning along the pins
F and G the piquet C may be discovered: place the
rule against the pin G, and bone the object A along
it, drawing on the table the line from the pin G,
along this rule a line GK, and remark where it cuts
FH at L: turn the rule until the object B is dis-
covered, keeping the rule against the pin G, and draw
on the plane table along the rule a line G M, and
observe where the line GM cuts F I, as at N: the
length L N measured by the scale F will give 342 feet for the inaccessible distance A B.
In this figure two stations are selected as the extremities of the base line, the distance
between which is accurately measured, and represented by a line drawn on paper, according
to the assumed scale: if the modern plane table be used, it is set up at one of these
stations, and a fine needle or pin being stuck into the table at one extremity of the line
drawn on the paper, the edge of the index is brought to press gently on the pin, and co-
incide with the line and the table turned round, till the object of the second station is
bisected through the sight vanes; the table is then clamped, and the direction of the mag-
netic meridian marked; the fiducial edge of the index, still kept in contact with the up-
right pin which serves as a centre, is then directed successively to the objects A and B, and
lines drawn on the paper in the direction of each: when this is done, the table is re-
moved to the other station, and the pin placed at the correspondent point on the paper,
which forms a second centre. The edge of the ruler is then directed to A and B as before,

(
Fig. 1056.
KH
D
CHAP. VIII.
837
GEOMETRY
when the intersection of the several lines drawn from the second centre, with those drawn
from the first, marks on the paper the position of A and B.
F
M
To measure the Bends of Rivers, as that of
ABC: plant at pleasure the two piquets H and
I, and measure the distance between them, as
200 feet: draw on the plane table the station
line KL, which divide into 200 equal parts, to
serve as a scale and to answer to the 200 feet
from H to I: place the plane table mounted on
its stand at the piquet I, and its point L above
the piquet I in such a manner that it shall be
towards the river, and its line L K on the line
IH between the stations: then place the rule
against the pin L, and bone the point A by the
rule, and draw on the plane table along the side
of the rule the line LM, which as well as the
others must have its name written against it :
keep the rule against the pin and turn it towards
the point B, and draw along the rule on the
plane table LN, and continue in succession to
turn the rule towards the point C, and draw
on the plane table a line LG, and this in
continuation for the sinuosities D, E, F, &c.
where piquets must be previously planted, if
there were not some objects fixed which would
answer the purpose: then taking the plane table
from the station I, place it at the piquet H,
disposing it in such a manner that when boning
by the two pins K, L, the piquet I can be discovered, and place the rule against the pin K,
and bone the point A, drawing along the rule on the plane table a line KP, and do the
same with the line K Q, KR, and so on for the other sinuosities, DE F, where piquets also
must be planted in this manner all the windings of a sea coast can be traced, by taking
up two stations in a boat securely moored or anchored.

:
To take the Plan of any
can be
H
Place where entrance
obtained, as that of the citadel
ABCDEFGHI: the angles
being distinguishable, plant
about the middle of the plot two
piquets K and L, at any distance
apart, but in such a manner that
all the angles from both piquets
can be discovered: then draw
about the middle of the plane
table a station line M N, about a
third of its length, which must
have two pins at its two ex-
tremities: move the plane
table on its stand at the piquet
K, so that the station point M
on the plane table comes ex-
actly above the piquet K, and G
bone along the two pins, M, N,
till the piquet L is seen in the
same visual ray place the rule
against the pin M, and bone
from it the angles at A, B, C, D,
&c., and draw from the pin
M, along the rule, the lines
Fig. 1058.
A
A)
Fig. 1057.
'R
·
B
H
K
M

N
6
L
E
F
MO, MP, MQ, MR, MS, MT, MV, MX, and MY: then remove the plane table to the
station L, and place it in such a manner that the point N on the station line shall be above
the piquet L, and that when boning along the station line, MN, the piquet K can be dis-
covered in the same visual ray: then place the rule against the pin N, to bone from this pin
all the angles at A, B, C,D, &c. to be taken, and draw on the table the lines 1, 2, 3, 4, &c.,
remarking where these last lines cut the former, in order to draw lines through these points
of intersection, which shall form a figure similar to ABCDEFGHI.
A scale may
3 н 3
838
Book II:
THEORY AND PRACTICE OF ENGINEERING.
be made by measuring one of the sides on the ground, as E F, in feet, and dividing its
corresponding sides on the plane table into as many equal parts.
B
•
C
To take the Plan of a Place where entrance is denied, as that of the town ABCDEF:
plant piquets or other marks which may be distinguished, and having measured one of the
sides as E F, 236 feet, draw on the
plane table a station line GH,
which divide into 336 parts, and
fix a pin at each extremity of it:
place the plane table at the station
F, so as to be towards the angle or
point G, on the station line pre-
cisely. Place the rule against
the pin G, and turn it until the
angle B is seen; then draw along
the rule, the line GK; turn the
rule towards the point C, and draw
the line GL, in the same way bone
the line D, and draw the line G M.
But for the angle E it is not ne-
cessary to bone it, as we have it
already laid down. Remove the
plane table from F to E, and turn
it in such a manner that the point

Fig. 1059.
K
L
M
IL
.
ட்
P
U
H corresponds rightly on the station line and the side FE, so that by putting the rule
against the pin H the angle A may be boned, and draw the line H N; in like manner
continue to draw the other lines HO, HP, HQ, to the angles B, C and D, in order to remark
where these lines cut those of the first station, on the points R, S, T, V, that by drawing
through these points of intersection right lines, we may form with the station line GH
a plan RSTV HG similar in all respects with that of the town ABCDEF.
To draw from a given Point a Line parallel to an inaccessible Length, as that of the line
BC: plant a piquet at D, the point through which the line is to pass, and another as at E:
measure the distance between these two piquets as
50 feet; divide the station line FG on the plane
table into 50 parts, to answer to the 50 feet from
D to E.
HM
K
A

H
50
F
L
E
Place the plane table mounted on its foot in
such a manner that the point G on the station
line shall be above the piquet E, so that when
boning by the two pins on the station line G F,
the piquet D may be seen in the same visual
ray; place the rule against the pin G, in order
to bone the two points B and C, which will enable
the lines GH and GI to be drawn on the plane table. Then remove the plane table
from the station E and place it at D, disposing it in such a manner that when boning by the
two pins F and G, we can discover the piquet E, and placing the rule against the pin F,
the two points B and C.
Fig. 1060.
Draw the lines F K and FL on the plane table, observing where they cut the lines GH
and GI, in the points M and N, in order to draw the line M N, which will be parallel to
the inaccessible line BC.
Draw on the ground from the point D a line D O, parallel to this line MN, and the line
DO will also be parallel to the line BC.
C
To measure the Height of accessible Places, as that of the line BC.
any distance from the foot of the tower or line BC, as at 40 feet.
into 40 parts corresponding with the 40 feet from B
to D: dispose then the plane of the table in such a
manner as to be quite perpendicular with the horizon,
and its station line parallel to it, and the point F on
its station line over the piquet D. Place the rule
above the pin F, lowering or raising it until we
discover by the side which touches the pin the point
C; then draw along the rule on the same side as the
pin the line FH; from the point E, on the station
line, elevate the perpendicular E I, and remark where
this perpendicular cuts the line FH on the plane
table, as at K: the height EK measured on the
station line EF will give a height, to which add
that from the point F on the station line to the sta-
tion point D, and we will have the precise height BC.
B
A
Fig. 1061.
Plant a piquet D at
Divide its station line

K
E
AL
1
CHAP. VIII.
GEOMETRY.
839
To measure the Heights of inaccessible Places, as that of BC: plant three piquets D, E, F, at
any distance convenient, but in such a manner that their summits are in a horizontal line,
or that a cord passed through their

heads may be level, and looking
along it some point G may be esta-
blished. Measure the distance be-
tween the two piquets D, F, as 27
feet, in order to divide on the plane
table the station line HI into 27
equal parts, to serve as a scale, and
to answer to the 27 feet. Having
mounted the plane table on its stand
with its plane perpendicular to the
horizon, place the point I on the
station line IH, precisely against
the level of the piquet F, in such a
manner that the station line IH
should be in the visual ray, which
passes above the piquets D, E, F, or
along the cord D˚F. Place the end
Fig. 1062.
L
K
G
E
B
of the rule against the pin I, lowering or elevating it until you see the point C, and draw
along the rule a line I K. Place the plane table perpendicular at the station D, in such a
manner that the point H on the station line HI cuts against the head of the piquet D, and
that the station line HI shall be in the same line with the heads of the piquets D, E, F.
Then place the rule against the pin H, elevating or depressing it until we discover the
point C, drawing on the plane table the line HL cutting IK in M.
From the point M let fall a perpendicular M N, on the station line HI, which measured
on the line I I, which serves as a scale, gives 30 feet, to which 5 is to be added for the
height the station line is above the ground, making altogether 35 feet for the height of
B C.
To measure the Height of inaccessible Places, when they are at a considerable elevation, as
that of the line B C, situated on the slope BD. Plant two piquets E and F in such a
manner that their summits are
in a right line with the point B.
Measure the distance between the
two piquets E and F, as 68 feet;
divide the station line GH into
68 parts, and place a pin at each
extremity of the station line.
Place the point H in the station
line, precisely over the piquet F,
and make the station line GH
coincide precisely with the visual
ray passing over the heads of the
two piquets E, F. Place the rule
against the plane of the table
until we get the point C, draw-
ing along the rule a line HI.
In like manner bone the point B
and D, drawing along the side of
the rule the lines HK and HL.
Then transport the plane table

H
F
I
K
M
P
N
E
R
L
Fig. 1063.
D
C
B
A
to the piquets E, placing the point G on the station line GH, precisely above the head of
the piquet E, and make the station line coincide with the visual ray of the two piquets E
and F. Place the rule against the pin G, in order to elevate and depress the rule till we
discover the point C, drawing along the rule a line GM, and boning also the points B
and D; draw the lines G N and GO, and observe where the lines GM of this station
cut HI of the first in P, where GN cuts GK in Q, and GO cuts HL in R: draw
the right lines PQ and QR. The line PQ will represent the height BC, and QR
that of the slope BD, so that if we measure P Q and QR, we shall obtain the entire
height.
By the mensuration and protraction of lines and angles are determined the lengths,
heights, depths, and distances of objects. Accessible lines are measured by applying to
them some certain measure a number of times, as a foot, yard, or chain; but inaccessible
lines can only be measured by angles. for taking which, when the plane table is used, the
lines are calculated from the principle of similar triangles, or some other geometrical pro-
perty, without regard to the measure of the angles: this method is not so accurate for
3 н 4
840
BOOK II.
TIIEORY AND PRACTICE OF ENGINEERING.
seen.
F
&
C
D
taking angles of elevation or of depression as by the theodolite or quadrant, which latter
is divided into degrees, and furnished with a plummet suspended from the centre.
To draw the Map of a Country with the Square
Plane Table. Choose two stations, as A and B,
and plant two piquets where the whole of
the country it is intended to map may be
Then, having measured the base or station
line A B, draw on the plane table the line L K,
near one of its sides, and placing the plane table
mounted on its feet at the station A, turn it in
such a manner that the point K of the station
line shall be above the point A, with the plane
table turned towards the places to be taken,
and in such a manner that we discover the pi- H
quet B in the visual ray of the two piquets K
and L Place the rule against the pin K, and
turn it, boning it towards the places to be taken,
and draw the lines K, C, D, E, I; remove the table
from A to B, so that this point D may be above
the piquet B, and that we can discover the pi-
quet A in the same visual ray with the pins
LK; so that by placing the rule against the pin
L we can bone the places, observing the lines.
L, C, D, E, F, in order to note where the lines drawn
from the second station cut those from the first; these L
points will give the just position of the places in
the country required to be mapped. But if it be re-
quired to find how far these places are from each other,
it will only be necessary to measure the distance be-
tween the stations A and B, and to divide the station
line into the same number of equal parts, and then it
will serve for a scale for the whole. If from the two

Ι.
stations A and B we cannot see all the other places,
F, G, H, then one or more other stations will be necessary.
B
K
K
A
Fig. 1064.

C
€
E
F
Fig. 1065.
D
To draw the Map of a Country with the Round Plane Table, which is furnished with cards,
each of which has a radius or semi-diameter marked upon it, to answer and serve as station
lines, and mounting its stand in some elevated ground, piquets are planted to show the
station points, and the distance being measured between them, as in the line A B, 742 feet,
serves as a scale. Place the plane table at the piquet A in such a manner that, when
boning along its rule or telescope, we can see the piquet B. Then draw along the rule
a station line, on which write station from A to B; which being for all the objects whose
position we would have, take the card from the table, by turning the screw which holds
the alhidade or rule, and place a fresh card on the plane table; then go to the piquet B,
placing the centre of the plane table above it, and turn it until we discover by the side of
the rule the station A, and draw the station line, writing on it as before, station from B to
A; bone from this station B all the objects boned from A, and draw all the lines to
the visual rays, writing the name of the object on them as before. Having marked on the
cards all the places of the map intended to be laid down, draw about the middle of a sheet
of paper the line CD, to serve as a station line, remarking that the map will be large
or small in proportion to it; place the centre of the card drawn at the station A on
the point C, and make the radius of the card on which is written station from A to
B coincide with the line CD; prolong it to infinity on the map to be made by means of
rules; draw all the lines marked on the card, and likewise place its centre drawn at the
station D over the point D, making its radius coincide with the line CD; prolong on
the paper all the lines marked on the card B and the points of intersection, which the
lines prolonged from the centre B make with those from the centre A, which will show
the positions on the required map. To form a scale, set off the length CD, and divide
it into as many feet as were measured from A to B.
•
The Theodolite has been brought to such perfection, and is so complete an instrument for
the taking of large or small surveys, that it has almost superseded all others; formerly they
consisted of a whole or half circle, about 10 inches in diameter, divided into 360 degrees,
but angles that were vertical and horizontal could not be taken by it at the same time.
The theodolite now in use consists of two circular brass plates, which turn one upon the
other, and have a horizontal action by means of an upright axis, which is made of two
parts, external and internal; the former is secured to the lower, the latter to the upper
plate. The lower plate has its circumference divided into 360 degrees, which are again
subdivided, and at the extremities of a diameter of the upper plate are fixed two
CHAP. VIII.
841
GEOMETRY
verniers; with these horizontal
plates and their divisions, all
angles in a plane parallel to
the horizon are taken in de-
grees and minutes, and they
are adjusted by four parallel
plate screws, g, set in pairs op-
posite to each other; these
screws are to be moved ac-
cording as the two spirit levels
placed at right angles a in-
dicate, and the whole brought
to a perfect level. These
spirit levels are usually filled
with spirits of wine, and are
hermetically sealed; the tube
is slightly curved, and is
placed with its convex side
upwards, so that the air bub-
ble, when level, occupies the
highest central part. These
two plates, called the upper
and lower horizontal, are,
when adjusted, retained in
their position by clamp screws,

h.
By
E
m
Fig. 1066.
K
IC
H
F
A, B, the horizontal limbs.
C
D
G
A, the vernier plate, which turns.
C, the vertical axis.
D, the ball or socket movement.
dd, spirit levels.
P
L
A
I
B
On the upper plate rests a
frame, on which are the angular
receptacles called Y's, into
which the telescope is placed;
and they are so fixed, that
by turning the telescope to ob-
serve an object, the horizontal
motion is communicated to one
or both of the circular plates.
The telescope has in the focus
of the eye-piece and object-
glass three lines formed of
very fine wire, one of which
is horizontal, the others cross-
ing its middle or central point
diagonally, so as to divide the
glass into an hexagon.
means of these wires an object
or any part of it may be
pointed at. From the lower
part of this telescope is sus-
pended a spirit level, which
being more delicate than those
fixed on the vernier plate is
used finally to adjust the cir-
cular plates, and to bring
them to a true horizontal po-
sition. The under part of the
telescope has a vertical semi-
circular arc e, for the purpose
of taking altitudes, the axis of
which rests on two points in
the frame which supports it,
so that when the upper plate
is horizontal, the semicircular
arc attached to the telescope is in a vertical plane; the angle of inclination being indicated
by a fixed index and vernier attached to the upper plate. This vertical arc is adjusted
and retained at any required angle by means of a clamp and tangent screw. One side
of the arc is divided into degrees and parts, and the other shows the difference between an
hypotenuse of 100 units, and the base in right-angled triangles, calculated to degrees of
inclination of the hypotenuse, from 0 to 45. To the upper plate is attached a compass,
which serves to notice the bearings of the different stations, and also is a check to the angles
E, a magnifier to read off the degrees.
F & G. Plates are held together by the ball D.
ff, is a screw to adjust the level or line of collimation.
b, b, are milled screws to adjust the instrument, and set in level.
g. is a screw to adjust the telescope laterally.
H, a clamping screw, by which means the collar c may be tightened
to the axis C. and kept from moving.
J, the magnet box.
I, is a slow-motion screw, by which the instrument is moved more
exactly than could be done by the hand.
i, i, clips, to reverse the telescope by screws j,j.
K & L are frames into which the pivots are placed, on which the
vertical arc M is turned round, and on which the telescope is fixed.
N is a microscope for reading off the degrees.
O is a clamp screw.
P a slow-motion screw, by which the vertical arc and telescope are
moved.
Q, a milled screw for moving the object-glass of the telescope.
842
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
taken.
This instrument, by means of a screw, is fixed on three legs; beneath the centre
of the staff head is a hook, to which is attached a plummet, that very much aids the observer
in placing the instrument in a horizontal position.
To adjust the theodolite properly is highly important, and the first point to be attended
to is, to draw out the tube of the eye-piece till the cross wires are clearly and distinctly
seen: the next adjustment is that of the line of collimation, the term given to the line
passing through the point of intersection of the cross wires, fixed in the focus of the
object and eye-glasses, and the centre of those glasses; this, when properly adjusted,
should coincide with the axes of the cylindrical rings, in which the telescope turns:
this is performed by making the cross wires coincide with a well-defined part of some
object in the distance, and turning the telescope half round till the level is at
the top; when on looking through it, the same point should be covered by the
centre of the wires, which, if it is not, must be acquired by moving the centre half
the amount of the deviation, by means of the diaphragm screws, and correcting the
other half by elevating or depressing the telescope: when the wires and the object
remain perfect in both positions of the telescope, the line of collimation in altitude or
depression is correct. This process must also be resorted to, to adjust the line of collima-
tion in the vertical plane. After this, the level attached to the telescope is fixed in a
position parallel to the rectified line of collimation, or longitudinal axis of the telescope:
to effect this, open the clips that retain the telescope, and bring the vertical arc at or near
zero; then turning the tangent screw, bring the air-bubble of the level to the centre of
the tube;` then reverse the telescope, and if the bubble does not return to the middle, bring
it there, one half by turning the screw placed at one end of the tube, to elevate or depress
that end of the level, and the other half by the tangent screw that acts on the vertical arc.
The circular plates must also be adjusted until they are perfectly horizontal, as any devia-
tion would produce in the measurement of an angle a proportionate error. The bubble
of the level under the telescope must be brought to the middle of the tube by the tangent
screw of the vertical arc; then turn the upper plate 180 degrees from its former position.
Should the bubble not return to the middle, half the difference is to be corrected by the
parallel plate screws, and half by elevating or depressing the telescope by means of the
-tangent screw this operation is repeated over the other pair of parallel plate screws,
until the air bubble of the spirit level attached to the telescope remains permanently in the
centre of the tube, in whatever position it is turned. The two small levels on the vernier
plate are then to be adjusted by the screws adapted for the purpose. The vernier of the
vertical arc is next to be looked to, and should point to zero after all the other adjustments
are effected, and any deviation from that point must be rectified by the screws which are
attached to it should the deviations, however, be small, note the amount, and apply it by
adding or subtracting from each vertical angle observed. This deviation may be readily
discovered by repeating the observation of the altitude or depression in the reversed
positions both of the telescope and vernier plates; the two readings having equal and
opposite errors, half their difference will be the index errors. When the theodolite has
been thoroughly and properly adjusted, it is placed exactly over the station from whence
the angles are to be taken; and this is done by observing the direction of the plumb line
which is suspended to it: it is then set level by the parallel plate screws bringing the
telescope with the vertical arc clamped at zero over each pair alternately.
Clamp the
lower horizontal limb in any position, and direct the telescope to the object, moving it
until the cross wires correspond with it; then clamp the upper limb, and by the tangent
screw make the intersection of the wires exactly bisect the object; then read off the two
verniers, noting the degrees, minutes, and seconds of both, and take the mean of the two
observations. Then release the upper plate, and move it round, until the telescope is
directed to the second object, whose angle is required, from the first already observed,
and by the clamp and tangent screws make the cross wires bisect the object. Then read
off the verniers, and the difference between their mean and the mean of the first reading will
be the angle required.
:
To measure angles of elevation or depression, unclamp the vertical arc, and direct the
intersection of the cross wires of the telescope to the object: note the reading of the
vertical arc, and repeat the operation with the telescope turned half round in its Y's with the
level uppermost; the mean of the two readings will correct the error in the line of colli-
mation. The magnetic bearing of an object is taken by simply reading the angle made by
the needle with the common compass, which is ordinarily attached to the theodolite, and
usually four or five inches in diameter: the angle cannot be obtained with any truth
nearer than by degrees. The telescope shows the objects seen through it in an inverted
position; the reason for this inversion is that objects are seen more clearly by the omission
of some of the glasses: a second eye-piece is usually provided, which, when applied, shows
the objects in their true and natural position.
The Circumferenter is sometimes used where great accuracy is not required in the survey:
it is a simple instrument, and consists of a flat bar of brass, B B, about 15 inches in length,
CHAP. VIII.
843
GEOMETRY.
with sights, C, C, at its opposite ends, and two narrow slits b,c for observations; in the
middle of the bar is a circular brass box, A, containing a magnetic needle, and covered
with glass. The ends of the needle play over a brass circle, g, which is divided into
360 equal degrees, in such a manner that the two numbers of 90° are at right angles
to the lines drawn through the sights. This instrument is usually supported on a
staff or tripod, E, and when firmly fixed in the ground it can be turned in any direction by
means of its socket joint. When the magnetic needle is well balanced, and moves
freely in its horizontal position, the sight can be turned towards the object to be sur-
veyed, and the needle will retain its position

of due north and south; consequently the
number of degrees which the angle contains,
after moving from one object to another, can
be counted off. The length of the mag-
netic needle increases the accuracy of the
circumferenter, for if made too small it will
be apt to follow the motion of the instrument
when turned round.
This instrument is chiefly used in mines
and coalpits, and sometimes has a spirit
level attached to it; aa are screws to ad-
just and turn it round, which is performed
by moving the vertical screws at m; F is a
spirit level; but by the free play of the needle
it may be generally ascertained whether
the circumferenter is nearly or perfectly level.
When this is the case, by clamping the
ball and socket joint tight, and turning the
sights to the respective objects, the mea-
surement in degrees of the angle made may be
relied upon.
The needle should not be suf-
D
E
mun
0
fered to play longer than is necessary, but
be lifted off its centre, otherwise the delicate
point upon which it turns would soon be
destroyed. This instrument usually has the
east and west marked contrary to their true
positions, in order that by the reading off the needle, the actual direction of the line is
shown.
Fig. 1067.
A
The Surveying Cross, employed for establishing perpendicular lines, is a better arrange-
ment than the cross staff, being more carefully made; it consists of four sights, fixed at
right angles upon a brass
cross, which can be screwed
to a tripod or single staff;
by placing it with reference
to a given line, perpendi-
culars can easily be traced on
the ground or set out.

A Circular Box of brass,
called the optical square,
is a
more convenient in-
strument for the same pur-
pose; this contains the two
principal glasses of the sex-
tant, viz. the index and ho-
rizon glasses, fixed at an angle
of 45°; so that viewing an
object by direct vision, any
other forming a right angle
with it at the place of the
WD

Ba
Fig. 1068.
observer will be seen by reflection to coincide with the object viewed. Placing the in-
strument in such a position as to look through any given line, we are enabled to direct
a station staff to be placed perpendicular to the given line. There are several varieties
of this instrument, some of which are fitted for the pocket, and extremely useful to the sur-
veyor.
Prismatic Compass is a similar instrument, but differs from the circumferenter, by
having a floating card attached to the needle graduated to 15′ of a degree; but angles
cannot be taken with it of less than half a degree: these graduations commence at the
north point, and are numbered 5°, 10°, 20°, &c. round the circle up to 360°.
A sight
844
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
vane is fixed perpendicularly with a fine wire stretched across it, opposite to which is a
prism: on applying the eye to the latter, and bisecting any object with the wire in the
sight vane, the division on the card coinciding with the thread, and reflected to the eye
of the observer, will show the angle formed by the object with the meridian. The instru-
ment must be carefully used when the observation is made, and the card must have free play
on its centre, otherwise the results will not be true: each angle as taken should be
registered down, which is more simple than first taking one object at 15, and others at
20, 30, and so on, where one is to be subtracted from the other before the angles between
any two given points can be ascertained.
The Box or Pocket Sextant is used for laying out angles, and for filling in the details
of a survey, where the theodolite is employed in setting out the long lines, and laying
out the larger triangles: it is usually divided to 140° on a silver plate, although a greater
angle than 110° should not be taken with it: to the sight is attached a small telescope,
which often requires time to arrange, and is inconvenient. To take plain sights, there
is an aperture opposite the half-silvered or horizon-glass, which answers the purpose
better. When an observation is made, take the sextant in the right hand, and
apply the eye to the small aperture, looking through the unsilvered part of the horizon-
glass to some object or station marked on the line. Then with the left hand, turn the
screw which carries the silver glass, until it reflects the object, the angle of which
is to be ascertained; when these two objects are, as it were, in conjunction, viz. the
object viewed direct through the unsilvered glass, and the reflected object appearing as one,
the desired angle will be given. The index or vernier being placed at zero, before the
screw, which turns the silver glass is moved, the object viewed direct and by reflection being
the same, is a proof that the instrument is correct: should this not be the case, the defect of
the instrument must be set right by means of two screws, one in the upper part, over the
horizon-glass, and the other at the side of it; these screws must be turned until the object
viewed direct and reflected appear, as they really are, one, the vernier standing at zero.
There is attached to the vernier a small magnifying glass, which enables the angle when
required to be read off.
The Sextant in maritime surveys is of great service, and in all situations where the theo-
dolite cannot be placed on a firm footing, or where the angular distance between two bodies
in motion is required, it is of the greatest utility, and almost the only instrument used
at sea for taking the altitudes of objects, or the angles they make with one another when
employed it is taken in the right hand, and its face placed in the plane of the two objects,
the angular distance of which is required: when the altitude of an object is required, the in-
strument is held vertically, and when oblique angles are to be measured, in an oblique plane.
The sextant is a modification of the quadrant, and seems to have been the invention of
Newton: the principle of its construction may be thus described. Let A, B, be two mirrors
moving on axes, parallel to each other, the second mirror, B, being
half silvered, so that it admits the passage of rays of light
through half its area. Suppose a ray of light to pass from the
object C, and reflected on the mirror at A, and after a second re-
flection from the half-silvered glass B, enter the eye at E. Also
let a second object D be seen by direct vision through the half-
silvered glass B: it is required the angle subtended at the eye E
by the objects C and D. Produce the plane of the mirrors until
they intersect in F: the angle AFB is equal to half the angle
CED. For producing AB to G, we have GBE = to BAC
+ AEB. Then, as the angle of incidence is equal to the angle
of reflection,
HBA FBE
=
=
GBF: therefore
GBE 2 GBF BAE+AEB: but
2 GBF 2 BAF +2 A FB: therefore
BAE+AEB 2 BAF +2 AFB.
= -
C

H
G
Fig. 1069.
K
But because CAI =
BAE = 2 BAF:
BAFFAE,
taking equals from equals, we have A E B, or CED equal to 2 AFB.
When the two mirrors are parallel to each other, and the angle formed equal to zero, the
distant object seen by direct vision and its reflected image will seem to coincide.
In constructing the sextant, the arc is graduated to 10 minutes of a degree: these are
again subdivided into 10 seconds by the vernier, which moves round an arc, the axis of which
is at the centre of the circle: over this centre, and attached to the arm carrying the vernier,
is placed a mirror, perpendicular to the plane of the instrument, which moves with the index.
The Index is adjusted by clamp as well as tangent screws: another half-silvered glass is
attached to the frame, nearly opposite the first, with its plane perpendicular to the plane of
the instrument, and the zero on the limb is so placed that the vernier indicates zero when
these two mirrors are in a parallel position to each other: glasses of different tints are
CHAP. VIII.
845
GEOMETRY.
attached to the instrument, for the purpose of taking observations with the sun, and
moderating intense light. Before used, the index and horizon glasses must be so adjusted
that they are perpendicular to the plane of the instrument, as well as parallel with each
other; when the index division of the vernier is at O on the arc, and the optical axis of sight
or telescope, parallel to the plane of the instrument.
The Index Glass is adjusted by moving the index to the middle of the limb, and holding
the instrument in a horizontal position with the divided limb away from the observer, and
the glass to the eye; look obliquely down the glass, so as to see the circular arc, by
direct view and by reflection in the glass at the same time, and if they appear to form
one continued arc of a circle, the index glass is in adjustment.
The Horizon Glass is in its right position, when by a sweep with the index the reflected
image of any object passes over or covers its image when seen directly; any error in this
effect may be rectified by turning a screw, placed at the lower end of the frame for this
purpose.
The Parallelism of the planes of the two glasses, when the index is at zero, may be
readily ascertained, by setting the zero on the index at the zero on the limb; when, on
taking an observation, it is observed that the object seen by direct vision and that reflected
coincide and appear as one, the glasses are parallel to each other: any deviation is called
the index error, which does not often occur in a well-made instrument.
Hadley's Quadrant is often made use of in the same manner for determining the time, lati-
tude and longitude of a place, and is as useful to the land-surveyor as the navigator: its arc
is graduated to minutes of a degree, and the vernier at the extremity of the movable limb
into seconds, which can be seen by the aid of a magnifier attached.
The telescope at the sides can be moved upwards or downwards by a milled screw
beneath it and it can be so placed that the field of view is bisected by the line that sepa-
rates the silvered from the unsilvered part on the horizon glass: it is adjusted by sliding the

A
B
Fig. 1070.
tube at the eye end of the telescope, so as to make the focus suit the eye of the observer.
The inverting telescope is furnished with two wires parallel to each other, between which
the observations are to be made, the wires being first brought parallel.
A more simple instrument is made on the continent, con-
sisting of two side branches or radii, at right angles, as
at A, having the limb E B divided into 90°, and each sub-
divided into 60'. GF is the telescope, which is rectified
by the frames H, H. At P is a joint into which the qua-
drant is screwed; S is the foot or stem, 5 feet in length,
which has a screw at T to secure it.
A M and IK represent bars of brass, on which the instru-
ment traverses: V, V, are four screws by which the stand can
be elevated.
When this quadrant is used for taking heights, after the
observation is made by the telescope, the angle is ascer-
tained upon the quarter circle by a plummet or bob at-
tached to a fine silk, which works in the box B; this
hanging always perpendicularly, the number of degrees
is counted up to it.

F
H
P K
H
N
E
M
13
Fig. 1071.
The Barometer is frequently used for measuring the heights of mountains, it being found
that the mercurial column invariably depends on, and is in proportion to, the atmospheric
846
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
pressure; if we therefore know the law by
which the altitudes increase, it is possible
to determine the difference between the
elevation of two places when their mean
barometrical altitude are given; it being
an established law of nature, that the pres-
sure of the atmosphere decreases in a
geometrical progression, as the height of
the place of observation increases in an
arithmetical progression. To measure
the height of any place, the altitude of
the mercury must be measured simul-
taneously at both the lower and upper
stations; the logarithms of these two
barometric altitudes being found, the less
is to be subtracted from the greater; the
difference will be proportional to the
difference of the elevation of the two
places: to find the real height, this loga-
rithmic difference must be multiplied by
a constant number found by previous ex-
periments. Professor Littron, in the
Transactions of the Astronomical Society,
has given the necessary formulæ and
tables, by which great exactness may be
arrived at in the measurement of heights;
but the system is somewhat complicated,
and needs great care, accurate observation,
and considerable calculation.


em-
The Chain and Offset Staff are
ployed alone in land-surveying, or in con-
junction with the theodolite, or other
instrument for measuring angles: when
the chain alone is employed, no other
figure can be used than the triangle,
and the correctness of the survey depends
upon the accuracy with which its sides.
are measured. The length of the chain
must be accurately tested to ensure cor-
rectness, before any of the distances are
taken; to do this it must be stretched on
a level piece of ground, and with an ac-
curate rod it must be carefully measured,
and if any error is apparent, it must be
rectified equally on both sides of the cen-
⚫tre: after this has been done, it may be
applied upon a wall, and a permanent
mark made upon it, which will serve at
any future time to compare it with; long
chains enable us to measure with greater
accuracy than shorter ones, and angles
formed by them are less obtuse.
R
a
n
in
R
FAHRENHEIT
CORRECTION
и:124 MOHINT STOV
THO: JONES.
AUD.OSUBST?-
103
30
36
89
829
|1|91|
92
87
27%
198
199
26
101
102
255
Gunter's Chain, as it is called, has been
found the most convenient where the
computation of acres is required, and is in
general use by land-surveyors; its length
is 66 feet, and it is divided into 100 links:
ten of these square chains equal an acre,
and as the chain is divided into 100, the
contents expressed in chains and links are
converted into acres and decimals of an
acre, by dividing by 10; an acre being
equal to 66 feet multiplied by 66 feet, and
then again multiplied by 10, 43,560 feet
being equal to 100,000 square links. The
rood is one fourth of an acre, and the rod or perch one fortieth of a rood; thus, after re-
ducing the area to square links by cutting off the last five figures, we obtain the acres in
R, R, section.
n, section of glass.
Fig. 1072.
a, box.
c, t, brass box.
CHAP. VIII.
847
GEOMETRY,
the remaining figures; the decimal figures cut off are multiplied by 4, to bring them into
roods, and the decimal part of the last product multiplied by 40 gives the poles or perches.
The chain now in use is of 100 feet, and divided into as many links: whichever chain
is adopted for the measurement of distances, it is divided every ten links by brass marks,
notched in a manner to distinguish them, and to enable the number of links at any
part of the chain to be read off conveniently: ten arrows accompany this chain, and when
used two persons are employed, one of whom leads and takes the ten arrows with him :
when the chain has been stretched in the proper direction, an arrow is stuck in the
ground where the chain terminates; and these are collected by the follower as he
proceeds, and when ten have been taken up, they are given to the leader to be used again,
care being taken to notice each exchange from the follower to the leader; for when
the line is entirely measured, the number of changes added to the number of arrows in
the follower's hand, and to the number of links or feet extending from the last arrow put
down to the extremity of the line, gives the entire length: the only care to ensure correct-
ness is, that the line so measured is perfectly straight, and that the ends of the chain are
made to coincide with the arrows placed in the ground as accurately as possible.
links of the chain being pliable, and united by rings that are not welded, render it extremely
liable to get out of order; therefore, it is essential that it should during an extensive mea-
surement be frequently applied to some standard, to examine and test its correctness: this
is very important, more particularly so, as it has been advised that no person should be
admitted to give evidence in any court of justice with any other than a stamped measure:
when the chain is used in wet weather, it often becomes shorter from the collection of
particles of dirt getting into the joints or rings, and defective by the bending of the
links. When the survey is made with a chain of 100 feet, and it is required to plot it to
a scale of five chains to an inch, the scale must be divided into the 330 parts of an inch,
there being that number of feet contained in five chains, making 33 divisions, each re-
presenting 10. A scale double the length of Gunter's, divided into 100 links, is found
both correct and convenient, each link being double the ordinary length.
The
The Offset Staff is a rod ten links in length, marked at each link by a notch or by
brass nails; the follower carries this, and is employed by the surveyor for taking offsets,
but where these offsets are considerable, a tape 100 feet in length is the most con
venient they should always be taken at right angles to the main line, and formerly
the cross staff was employed; at present, an instrument called the optical square is
found the most convenient for this purpose, it is a small circular box about 2 inches
in diameter, which makes a right angle with both accuracy and expedition; it has two
glasses fixed at an angle of 45° from each other, and one of them acts as a mirror; the
other is half silvered, so as to admit direct vision of one object and reflected vision of the
other; so placed at right angles to a line passing from the observer to the first object, the
image of the second is reflected from the first mirror: the principle is, that the angle
made by the first and last direction of a ray of light which has suffered two reflections in
one plane, is equal to twice the angle of inclination of the reflecting surfaces. With
this little instrument right angles may be accurately set out, by the observer simply
standing over the given point and looking through it along the line, having some one with
a marking rod in the direction where the perpendicular is to be set out, and by motioning
him to the right or left, until the rod he holds is seen by reflection to coincide with a staff
fixed on the line where the observer is looking; when this is the case the rod is fixed in
the ground: a perpendicular line is often set out by the use of the chain only, by measuring
on the base line a distance of 40 feet; then at the extremities of this distance measuring
as an hypotenuse 50, and as a perpendicular 30: when the sides of a triangle are in the
proportions of 30, 40, and 50, it is a right angle, and has the two short sides perpendicular
to each other.
To survey a Plot of Ground with the Chain, we are confined to the use of the triangle,
it being the only figure the sides of which cannot be altered. The field to be measured
is then divided into a series of triangles of as large a description as can well be obtained;
much of the judgment of the surveyor is called into play upon the adoption of the triangle,
or laying out the sides of the figure, which should approach as nearly as possible that of
the equilateral: the sides of the triangles are then measured, also a line from one of
the points to the middle of its opposite sides which enables the surveyor to detect any
error that may have been committed in the measurement of the three sides: the general
combination of these triangles must be laid down so that the largest come as nearly
to the boundary of the spot as possible; and when their figure is determined, pickets are
placed on the ground at their angles; these are called station points, and are measured
to and from, and all the lines connecting them are denominated station lines, which are
to be distinguished from the simple offset lines.
The Field Book should commence with a rough sketch made of the land to be plotted,
and which should be the result of a careful walk over the ground previous to the measure-
ments being taken: it is ruled into three columns; in the middle one is to be set down
849
Book II
THEORY AND PRACTICE OF ENGINEERING.
all the distances measured on the station line, at which any mark, offset, or other notice
is made: in the right hand column are placed all the measurements of the offsets in that
direction, and in the left hand column those on that side of the station line. The middle
column represents the station line, and whenever it passes a road or boundary, it must
be marked obliquely to denote this deviation. The entries in the field-book are usually
commenced at the bottom of the page for convenience, the surveyor keeping his face in
the direction of the distant station: wherever fences or other objects, as rivers or streams,
are crossed, they must be sketched in the field-book in as accurate a manner as the time will
permit; by this much subsequent labour is saved. On commencing the measurement
along the station line, the letter corresponding to the starting point is placed at the bottom
of the middle column of the field-book, and on each side is written the letters whence
the measurement is taken, and at every new distance this is again to be observed.
When the whole of the measurements have been made and entered in the field book, the
contents may be ascertained by computing the areas which are enclosed in the measurement
of the respective triangles; but it will be first necessary to reduce all lines measured over
steep hills to a horizontal plane; should the inclined plane or slope not be very steep, the
difference may be rectified by holding the chain horizontal whilst measuring, which may be
judged of by the eye; or if the slope be steep, half the length of the chain may be used: when
the angle of inclination is 4°, an allowance of 1 in 15 is made, 6° 1 in 91, in 7° 1 in 8, in 10°
1 in 6, and in 20° 1 in 23, or 6 feet for every 100 feet; this, however, may be readily ascer-
tained by careful observation. The angles of inclination should always be observed where
perfect accuracy is required, and the proper deductions made when the work is laid down
or mapped.
Parish surveying. Where it is required to obtain the area of the whole by some other
means than that of adding together the contents of each enclosure, it seems the simplest
method to commence by measuring two straight lines through the entire length and breadth
of the parish; to connect the ends of these by other measured lines, and upon them as
base lines to construct triangles and measure the offsets. The contents of the entire
parish may then be ascertained by calculation; the lines measured to accomplish this
should be shown on the plan when finished. These main lines should pass over the most
remarkable objects, as the church, the mill, the manor house, and their extremities
should be marked by a stone or permanent boundary, that may be referred to on all
future occasions. This boundary should be shown on the plan by a dotted line, and
when a fence constitutes the boundary, the dotted line should be shown on both sides
of it when this boundary passes through a field, the whole field should be shown.
The plan should be drawn to a scale of 3 chains to 1 inch, and the north point should
always be at the top of the plan.
:
To measure the base or principal line, which should be the longest that can be obtained,
the theodolite is placed at one extremity, and the angle formed by this line with the
magnetic meridian must be first accurately obtained: then all the angles of the several
prominent objects; at this spot a pole must be placed perpendicularly, and proceeding
along the line, the roads, rivers, &c., must be noted as they are crossed, and all convenient
offsets should be taken. Poles should be set up at all the prominent stations, which serve
to guide the measurement and insure its being in a straight line: these must be constantly
boned, or the true course will be departed from.
Where objects occur which are not accessible, angles must be taken with the theodolite,
either to the right or left of the line, exactly at 60°, and then measured out to any length
until clear of the obstruction: another angle of 60° must be taken and measured, the
same distance as before; these forming two sides and angles of an equilateral triangle,
the remaining angle and side will be the same, and the distance, if measured through,
will be found to agree.
After measuring up to the other extremity of the base line, the theodolite is placed upon
it, and the angle of one of the side lines taken with considerable accuracy; these side lines
must then be measured, and the theodolite placed at their extremities, so as to measure
the angles made with its transverse lines: and so proceed with the respective lines and angles,
till the whole is completed. From the extremities of the two principal lines, measure
the distances one from the other, or the length of these tie lines, taking at the same time
their angles very accurately. These angles and tie lines form four principal stations or
boundary points to the parish, and should be marked permanently. The whole of the
outline between these four stations or the natural boundary may be surveyed, and afterwards
the portions within for the filling up. The sextant is employed usefully in taking all
the interior angles, and uniting them with the main lines which run through and traverse
the parish: these two instruments are now the only ones employed.
To compute the area or contents of the parish, the whole should, after it is mapped, be
thrown into triangles, and each enclosure treated in a similar manner: but the most
correct method would be to divide it into squares of about a chain. by which means the
small parcels would have their quantities easily ascertained.
CHAP. VIII.
849
GEOMETRY.
Subterranean Surveying is performed with the miner's compass, which for observations
of horizontal angles is by no means sufficiently accurate. The circumferenter or half'
theodolite is more so, and may be used with greater certainty, though the common theodolite
should always be preferred: it is often of more importance to have an accurate plan of the
works in a mine, than of the land above it. The surveys of pits or mines being not only
made to direct the working, but for the sinking of shafts, ventilation, or for the raising
the produce, after the situation of the shafts are determined on above ground, the work-
ings below must be either set out on the surface, or the survey must take place beneath.
To adapt the theodolite to mining observations, the stand on which it rests should be so
formed, that it can be readily disengaged.
The survey is commenced with the assistance of two men, who carry the chain, and two
others the lamps, one of which is placed at the starting point from whence the measure-
ment is to commence, and the theodolite is advanced in the direction of the line, as far as
it is possible to obtain a sight of the lamp at the point advanced from. The vernier of the
theodolite being fixed at zero, the telescope is directed towards the light, and the angle of
inclination noted down, another lamp is advanced along the line and the same observations
taken the distances are then carefully measured from one station to the other, as practised
in roadway surveying all underground surveys should be made to agree with those taken
on the surface, which may be readily done by comparing the adits and shafts, both as to
their distances and bearings to each other.
:
Care must be taken to notice whether the needle is affected when the theodolite is used,
which is sometimes the case; when the instrument is elevated 2 or 3 feet above the
tram plates of a railway, there does not seem to be any sensible attraction between them
and the needle.
Maritime Surveying, comprises the laying down charts with accurate representations of
the coasts and harbours, and is one of the most important applications of the science, as it en-
ables the mariner to pursue his voyage and return to his port without encountering those
dangers which beset him in the shape of rocks and shoals, shallows and flats. The first
thing to be performed for the construction of a map or chart is to refer to some fixed points
on the shore of the coast to be laid down; these are ascertained with great precision by
means of a trigometrical survey on shore.
Tide Gauges are erected in well-chosen localities in a vertical position, and divided into
feet and tenths: the zero point of each gauge corresponds with a bench mark permanently
fixed, so that should any be displaced by the violence of the sea, they can, by means of a
spirit level, be refitted in their original position.
These gauges serve after a series of observations to give the lowest point of the lowest
tide at full and change of the moon, and to the level of this lowest point the depths of all
the soundings are referred: they serve also to show the rise and fall of the tide, by which
means all the registered soundings are reduced to the lowest level: this is very essential,
as it is not practicable to take all the soundings over an extensive bay at the precise time of
low water: near the shore these observations may be made with reference to some permanent
marks made on the walls of the quays.
A second gauge is placed further out at sea, so that when the tide has left the first, the
second may be observed. Then the zero division of the first gauge must be compared, by
means of the spirit level, with some division of the second; and this, as well as each succes-
sive gauge, must be denoted by some number or letter, and entries made to record the time
of changing from one gauge to another. A situation should be selected where the base of
the tide gauge is not left dry at low water.
When an observation is to be made, a person with a well-regulated watch is stationed at
each tide gauge for the purpose of registering the height at every quarter of an hour or
other stated intervals. A meridian line is marked upon each station, so that the observer
may regulate his watch by the course of the sun.
The time of high water at the full and change of the moon should be carefully marked
on the tide gauge, and this time may be either mean or apparent, but whichever is selec-
ted must be noted; the instant to be registered is that when the surface of the water is
the highest, but if the water is perfectly calm, its change when near the highest point is
slow, and it almost seems stationary for some moments. To prevent the effect of waves
rendering the surface uncertain, an upright pipe is sometimes fixed by the side of the gauge
in such a situation that at low tide the water only reaches the lower part: the bottom of
the pipe must be stopped, and a number of small holes drilled in it near the bottom about
a quarter of an inch in diameter. A float is then placed on the pipe which carries a light
rod, and by means of feet and inches marked on it, the rise of the tide can easily be read off.
In narrow channels or at the mouths of rivers, a great many gauges are requisite, and no
precise number can be mentioned, as that must depend altogether upon circumstances.
Churches, lighthouses, are then made use of on land, to serve as vertices to the triangles
about to be laid down, and it is usual to place signals upon them; and those which serve to
be viewed from the sea are painted white, when the ground falls behind them, but of a
8 I
850
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
N
The first
fro
darker colour, when they are projected against the sky. All this being arranged, the opera-
tions for the survey may commence at sea. There are three methods adopted for deter-
mining, by reference to fixed points on shore, the locality of any station at sea.
consists in observing by means of the compass the bearing of two or
more points on shore, by which means the position of the observer is
determined when the position and bearings of the points on shore are
given with respect to each other. Suppose A B to be two objects on
shore, and S the position of the observer, from which the angles and
meridian is observed. In the triangle ASN the angles at S and N
are given, consequently the angle at A is known; in the same manner the
angle at B is known. Then on the side A B, and the adjacent angles
A and B being given, the point S may be found: with the compass,
however, the angles cannot be determined nearer than within one or
two degrees; when two compasses are employed, one at a height of
2 or 3 feet above the other, the mean between the two observations
made will perhaps approach the truth.

AT
Fig. 1073.
B
The second method is by observing at the same period of time from
two or more stations on shore the bearing of the observer at sea, and this is only to be done
by means of well preconcerted signals.
The third method consists in measuring from the boat by means of the sextant the angles
subtended by three or more objects on shore, the positions of which are given; from these
data the position of the observer is determined.
An instrument called a Station Pointer is used to insure greater accuracy in taking
angles; this is formed of three rules which revolve on a common centre, in such a
manner that two triangles can be set out with it; the middle rule is double, and has a
fine wire stretched along its openings; the others have also a fine wire, which is stretched
from end to end, and so adjusted that all the three wires tend to the centre of the in-
strument; in the centre is an opening through which a steel pin may be passed:
attached to the middle limb are two verniers, with arcs of about 1000 each, and when all
the limbs are closed, the verniers mark zero, and as the limbs are opened the verniers mark
on the corresponding arcs the angles they respectively form: the angles subtended by
three stations on the shore at the place of the observer at sea are the measures to which
the verniers are to be set; and when so set the instrument is laid on the plan, and moved
till the three wires pass through the three stations; the centre of the instrument then
occupies the relative place of the observer, and a dot marked by the steel pin determines
the point on the plan: a graduated circle on paper or on glass may serve this purpose
as well; by drawing on the upper surface lines diverging from the centre at the given
angles, the circle being moved until these radii pass through the stations, the centre of
the circle will give the point required. Excepting in a case where the observer is in the
circumference of the circle passing through the three stations, the measure of two angles
is sufficient to determine his position; it is as well to observe as many angles as possible,
and where accuracy is required, the observations of two angles only should never be con-
sidered sufficient. The angles are taken with the sextant or the reflecting circle, and
measured in the plane of the objects: should this plane be inclined to the horizon, the
angles of elevation of each station above the horizon should be observed, to give the
necessary data for reducing the hypotenusal to the horizontal angle: when the difference
of elevation is great, an ideal vertical line may be drawn from the higher object downwards
until it apparently meets the base, and the results will be
sufficiently near the truth; as in the height of a mountain, the
line BC may be dropped. It is not usual to apply a telescope
to the sextant, as the objects are brought readily into the field
of the mirrors by the unassisted eye; and time is a great object, A
and perhaps the most important of all in making the obser-
vations. Sea-water destroying the silver on glass, metallic re-
flectors are generally substituted.
હ
C
Fig. 1074.
B

Sounding Lines, to ascertain the depths, are formed of strong
pliable cord or lead line, divided into feet by different coloured
pieces of cloth or other marks; the lead fastened at the extremity is like the frustum of a
cone, with its base so hollowed out that grease may be introduced into it, which serves,
when let down upon sand or mud, to show the nature of the bed lines of different lengths
and strength are used, and leads differing in weight according to the depth of the water to
be sounded; these lines are liable to sudden changes, and must be constantly compared with
some known standard; deep soundings must be taken when the boat is still, and the depth
measured in a vertical position: in shallow water sounding rods are substituted, and where
hard rocks occur they are perhaps more convenient. Sunken rocks, reefs, and shallows, re-
quire great accuracy in the survey, and it is necessary to cast anchor, in order to get the
angles and their measurement with more certainty: when the shoal or reef is so far out
at sea, that only two objects on shore can be seen, an assistant boat must be moored
CHAP. VIII.
851
GEOMETRY.
A
between the observer and the coast, in such a position that one additional station can be
seen from it: at the time of a given signal, angles are observed from the assistant boat to
three objects on shore, and to the distant boat; and from the latter, angles at the same
time measured to the two stations on shore, and to the assistant boat: suppose D to be
the distant station, from whence A and B can be seen, and E the position of the assistant
boat from whence A, B, and C can be seen; then at the same
moment of time, the angles are observed from E and from D;
their mean show the position of D; for the point E is fixed in
position by the observed angles CE A, A E B, and it becomes
therefore a fixed station with reference to D, from which two
angles are observed to three stations fixed in position. Breakers
and currents must also be observed at that time when the tide
is favourable, or when a perfect calm allows them to be re-
cognised.
To reduce soundings after they have been taken consists in
deducting from the depths, as noted down, proportionate quantities
varying with the time, so that all may agree with the lowest
level of the tide; the whole are then written on the chart in
fathoms and quarter fathoms.
Maritime Surveying without the aid of Triangulation on Shore,
is not in its results so accurate as that where they can be adopted;
but where free access to a country is not attainable, this method
is resorted to as the nearest approaching to the excellence of the
first instead of commencing with the measurement of a short
base, and a series of triangles spread over a great area, a much
longer base is established; sometimes one of 50 miles or more:
upon this all the observations are made, and the details laid down
as quickly as they are taken, and all errors corrected during the
progress of the work.

B
Fig. 1075.
P
7
с
On the choice of direction for this base line much of the success
depends: elevated land, or some mountain or conspicuous object, should terminate each
extremity; and the more numerous the intermediate objects that can be seen from the ends
of this base line, the greater will be the correctness of the survey. The latitude and
longitude of the first station being taken and determined by astronomical observations, and
the bearing of the several objects by the compass, the same is to be done at the chief
stations along the line selected for the base. The stations are determined by the chrono-
meter and measurement of the rate of sailing; from them the observations are made which
are to be laid down on the chart: the distance between the primary stations, whose lati-
tudes and longitudes have been determined, is obtained by supposing P to represent the
pole of the earth: the angle P is known by the difference of longitude between the two
stations B and A; the sides PA and PB are also given, being the respective co-latitudes
of the two stations. In the spherical triangle ABP are two sides and the contained angle,
from which we may obtain the length of the opposite side AB: a line joining any two
of these stations is the arc of a circle on the surface of the earth, and must therefore be re-
duced to its chord, which is equal to twice the sine of half the arc. When a survey of a
coast is made at night, and intersections cannot be obtained, observation
must be taken within a few miles from the shore by anchoring the vessel
at one or more intermediate stations: the position of the vessel is deter-
mined by a careful observation of the angles subtended between the sun and
primary stations, noting the time also when the observation is made: the
time gives the sun's azimuth, and from it is deduced the azimuth of the
two primary stations from the vessel; those intermediate are obtained
by the intersection of their lines of direction as observed at the different B
stations. The details and soundings are then to be taken, with the filling-
in as it can be obtained; by this means a very accurate map may be
laid down it is often necessary to make a survey of the coast when a
ship is under sail, and although the system adopted may vary in its
details, the general principles are the same. The angular distances
between prominent points of land as observed from the vessel, should be
taken when at anchor, and the outline of the coast sketched: astronomical
observations must be made at the same time to determine the position of
the vessel, and the bearing by the compass noted: continuing a series of such observations
in sailing from one point to another, and having special care not to lose sight of the points
to which angles have been observed, as this would lead to confusion and great difficulty
when the whole is to be laid down on paper. A reckoning of the ship's rate of
sailing must be carefully noted by the log line; though much reliance cannot be
placed upon it, it may help, in some degree, to check any error arising from the astro-
nomical observations: when sailing, care must be paid that the vessel has all its bearings

Fig. 1076.
A
312
852
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
accurately noted when she changes her course; then, proceeding in the same manner as
already described, the soundings and remarks will enable a tolerably correct sketch of the
coast to be made. Distances are sometimes measured by sound, which travels at the rate
of 1090 feet per second of time; a chronometer will enable a distance of several miles
to be determined with considerable accuracy: the time between the flash and the report
of a gun being found, the distance may be calculated by the above rule.
Trigonometrical Surveying.—The survey of a country, when carried on upon an extensive
scale, has much of the labour of admeasurement abridged, by merely applying the rods or
chains to a base line, and calculating the other distances by triangles; the difficulties which
attend the operations of a trigonometrical survey of a country must not, however, be
underrated, particularly when the object is to determine the distances as well as the positions
of places with the greatest precision. Upwards of one million sterling had been granted in
the year 1841 by the Houses of Parliament at several times to carry out the Ordnance
surveys of the United Kingdom. A general survey seems to have been commenced in
the year 1783, in consequence of an application made by the French government to
Mr. Fox, then Secretary of State of the Foreign Department, to carry a chain of triangles
from London to Dover, which could be connected with those of the French arc of the
meridian already extended to Dunkirk; so that by actual measurement the relative
positions of the observatories at Paris and Greenwich might be determined.
This ap-
plication was laid before the Royal Society by Cassini de Thiery, and the great advan-
tages which would result from it were highly appreciated by that body. The English
government, in consequence, employed General Roy for the operation, who had already
commenced a survey of the neighbourhood of London, for the express purpose of connecting
the private observatories with that of Greenwich: as early as 1747, a survey of the High-
lands of Scotland was undertaken by this officer, which was considerably advanced by the
end of the year 1755. To obtain an accurate base line, so that by its measurement all
the other triangles constructed on it should be computed, was the first part of the opera-
tion and for this purpose General Roy selected a line on Hounslow Heath, in consequence
of the level surface the ground presented, and its proximity to the Royal Observatory at
Greenwich. The terminal points of this base line were marked by wooden pipes sunk in
the ground, and the measurement was commenced in June, 1784.
:
;
The first mode was with deal rods, which had been employed previously in other countries:
but it was soon evident that from the alternations of dryness and humidity, they were subject
to sudden and irregular changes, and by no means fit for a purpose where such great
precision was necessary. These rods were cut out of an old mast of Riga timber, and
made 20 feet 3 inches in length, tipped with bell-metal, to prevent their ends from being
injured; they were 2 inches in depth, and 14 inch broad, and rendered inflexible to a cer-
tain degree by trussing; when, however, applied to the standard during the measurement,
they were found each to have increased the fifteenth part of an inch, and were conse-
quently laid aside: glass rods were then substituted, as tubes of this metal could be easily
procured of the length required. Three hollow tubes, 20 feet in length and 1 inch in dia-
meter, perfectly straight, were provided, and converted into measuring rods by Ramsden
they were placed in cases made fast in the middle, and braced at several other points, to
prevent their shaking or bending, but not their free expansion and contraction; the ends of
these rods were smoothly ground, at right angles to the axis of the tube; one end had a
fixed metal button attached to it, for making the contacts, and the other a movable slider
which could be pressed outwards by a slender spring, and against which the fixed extremity
of the succeeding rod was placed, and then pressed until a fine line on the slider was
brought into exact coincidence with another fine line on the glass rod, when the distance
between the two extremities was exactly 20 feet. To ascertain precisely the expansion
to which these glass rods were subject, they were submitted to a microscopic pyro-
meter, when their expansion could be ascertained for every degree of temperature from 32°
to 212º of Fahrenheit's thermometer.
After much calculation upon the expansion and contraction of the rods they were
applied to the base line, which was not over perfectly level ground; consequently it
became necessary to divide the whole distance into inclined lines, each containing about
600 feet. This was done by placing the rods exactly in straight lines, stretching from one
extremity of the hypotenuse to the other, and then determining the relative heights of
the two extremities by means of the spirit level, for the purpose of reducing the horizon;
the cases containing the glass rods being throughout supported upon trestles, which were
about 30 inches in height. After the measurement was completed, its true length was
reduced to that of the level of the sea, the mean semi-diameter of the earth being estimated
at 3,492,915 fathoms: infinite pains were evidently taken throughout the whole operation,
and the means employed seem to have been the best that could be suggested.
The true length of the base was fixed at 27404-0137 feet, but when the Ordnance
survey was commenced in 1791, it was thought necessary to remeasure this line, from an
idea that as the ends of the two consecutive rods, having been made to rest on the same
trestle, when one was removed the trestle would have a tendency to incline forward, which
CHAP VIII.
853
GEOMETRY
would shorten to a certain degree the measurement, or the flexure of the rods would
produce the same effects. Two steel chains, each 100 feet in length, and containing forty
links, made by Ramsden, were selected to remeasure the line: the links were in
the form of a parallelogram, ofinch square and 30 inches in length. When used,
they were strained over five boxes placed at equal distances upon bricks, and stretched in a
straight line by weights of 56 pounds: to bring the extremities of the two chains
together over the same point, they were supported at each end by an upright piece of
wood or post; that of the preceding end had attached to it a pulley over which passed
the rope which stretched the chain, whilst to the end that followed was applied a screw ap-
paratus, by which the chain could be drawn back against the weight: another upright or
post at each end, not connected with the others or with the chain, supported a scale.
The chain being placed, the scale at the preceding end was moved by means of screws,
until one of its divisions exactly agreed with the mark on the handle of the chain: the
scale remaining in its place, the chain was then carried forward, and again adjusted by the
screw scale in a similar manner: after 38 of these chains had been used, one in con-
sequence of the links being bent was laid aside, and the base line was measured by the
other; the one laid aside being repaired, was retained as a standard. Experiments out of
number were made previously, to ascertain the rate of expansion, and a thermometer was
placed at each of the five boxes when the measurement was taken, in order to insure
aceuracy; the chains, after the measurement, were again compared, when it was found that
that which had been used had lengthened through the rubbing of the joints 0373 of an inch.
The length of the base line was by means of the chains found to be 27404-3155 feet,
being about 23 inches more than that measured with the glass rods. The mean of the two
results, 27404.2 feet, was then assumed for all the future calculations. Rods seem, how-
ever, in general, to have a preference over the chain, where great accuracy is required,
as they cannot be considered so flexible, nor are they so likely to increase in length, as
the chains when slightly strained may do at the joints: great care must be taken at
the commencement of such an operation, in ascertaining the exact length of the foot, to
be marked on those measuring rods or chains, and some standard should be applied to for
the purpose.
Such a standard is now adopted as constitutes the yard at 36·000659 inches,
the length of the pendulum vibrating seconds being taken at 39.13929 inches; this is
called the imperial measure, and as it was supposed to be a correct and unalterable
quantity, it was prescribed by Act of Parliament that the length of the standard yard
should be restored by reference to the length of a pendulum, should accident occur to
injure the legal standard deposited in the House of Commons.
a
In Ireland another method was adopted to measure the base line set out on the
plains of Magellan, which is between 7 and 8 miles in length, and where the greatest
possible error is not supposed to exceed 2 inches. Two bars, each 10 feet long, one of
brass, the other of iron, were placed parallel to each other, and riveted at their centres, it
having been previously ascertained by experiment that they expanded or contracted in the
proportion of three to five; some nonconducting substance was spread over the brass bar,
which equalised the two metals in their susceptibility as to change of temperature:
tongue of iron, with a minute dot of platina, was fixed across each extremity of these two
combined bars, and this tongue had the dots so placed that under every change of con-
traction or expansion they remained at the constant distance of 10 feet. The tongues were
perpendicular to the rods, at the temperature of 60 degrees of Fahrenheit, and the ex-
pansion of the two bars of brass and iron taking place from their common centre, as the
inclination of the tongues became changed, the platinum dots remained unalterably fixed
at the exact distance of 10 feet. When the base line is accurately taken, it should
be reduced to its proper measure at the level of the sea, and as this is constantly changing,
some elevation must be established that can be referred to, and that made use of by the
Ordnance surveyors is low water mark.
=
Suppose R to the radius of the earth at the level of the sea; R+h equal to the radius at
the level of the measured base; Ato the measured base A B, and a=to the reduced base ab.
Then, as similar arcs are in the same ratio as their radii, we have R+h: R:: A: a, and
R. A
A=
R+h
and the difference between the measured and reduced base is
A-a-A-
Ꭱ Ꭺ
R+h
reducing both terms to a common denominator :
A-α=
AR+Ah-AR
whence
R+h
A-
·a:
A h
R+ h
difference required.
The elevation of Hounslow Heath is about 102 feet above the level of the sea, and the
31 3
854
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
The
measured base 27405-6677 feet, after due correction made for temperature, &c.
radius R being taken at 7,002,667 yards; the length of this line at the level of the sea is
thus found:-
A, the measured base, is equal to
h, the height,
-
27405-6677 feet
102
21008001
=0·133 feet.
Hence the reduced base will be 27405·6677 −0·133 =
=
R, the radius of the earth,
27405.6677 × 102
-
21008001
27405-5347 feet.
Before a base is reduced to its length at the level of the sea, it is necessary to consider
its horizontal value, as all lines measured over the earth's surface must be treated as con-
centric, and are more or less inclined to the horizon.
Signals, and their Construction. When the base has been set out, permanent signals
must be established; they should be constructed in a durable manner, and have perfect
steadiness.
In ordinary surveys straight poles fixed in trees or firmly in the ground may serve
sufficiently for all purposes, and when greater security is required, they may be held in a
vertical position by ropes, in the same manner as a ship's mast, and such an arrangement
may be easily rendered more lofty by means of an additional mast, and the help of guys
and stays.
These masts have each a bunting flag, usually either red or white when pro-
jected against a dark ground, and green and red when against the sky; sometimes a cir-
cular disk of sheet-iron is found a better substitute for the flag, and may be attached to the
top of the pole.
The
The parabolic reflector has been successfully employed in Ireland, and for the illuminating
power, a ball of chalk lime was submitted to a stream of oxygen directed through the
flame of alcohol; the light was estimated at 83 times the intensity of the brightest part of
the flame of an Argand burner of the best construction, supplied with the finest oil.
direction of this light was marked by placing a guiding light at the distance of every
15 miles, which was a 15-inch parabolic reflector illumined by an Argand lamp: by this
means the former light, though 66 miles distant, was perceived, larger and brighter than
the guiding lights. Plano-convex lenses, 2 or more feet feet in diameter, illumined by an
Argand burner, with four concentric wicks, the lens composed of a series of concentric
rings reduced in thickness and cemented together at the edges, are often used, and their ap-
pearance at a distance of 48 miles is stated to resemble a star of the first magnitude.
Summits of mountains are usually selected for stations, and the signals constructed upon
them are built either pyramidically or conical, with a pillar in the centre. The selection
of stations depends much upon the nature of the country to be surveyed; they ought to be
placed in such positions as to be visible from each other, that the errors of observation
may have as little effect as possible on the distances measured: the triangles should be
equilateral; the smallest errors are likely to occur when the angle opposite to the
measured side is less than a right angle, and the angles adjacent to that angle are nearly
equal: in general no angle should be less than 30 degrees, and then the calculated sides in
a series of triangles will not be very different from those obtained by actual measurement.
When a great survey is undertaken, the sides of the first triangles should be of greater
length than the original measured base, and which is readily accomplished; triangles whose
sides were from 70 to 90 miles in length were adopted in Ireland, though in England
those whose sides were from 12 to 18 miles were considered preferable.
Calculation of the sides of Triangles. — All the angles and the triangles which are taken
in a trigonometrical survey by the theodolite are spherical, as they form a part of the
surface of a spheroid: it is evident that as every object used for pointing the telescope of
a theodolite has some certain elevation not only above the soil, but above the level of the
sea, and as these elevations differ in every instance, a reduction to the horizon at all the
measured angles is necessary; but by the construction of the theodolite, this reduction is
made by reading off the horizontal angles. Ramsden's large instrument, 3 feet in diameter,
was the first by which this spherical excess was observed; it is in all trigonometrical ob-
servations small, not exceeding 4 or 5 seconds in the largest triangles employed: if the
earth's surface was a plane, the sum of the three angles would be exactly 180°, and the
excess above 180° is so far from being a proof of incorrectness in the work, that it is
essential to its accuracy, whilst it offers at the same time another proof of the earth's
sphericity. The true way to judge of a trigonometrical survey is to consider the net work
of triangles as the bases of so many pyramids converging to the centre of the sphere: the
theodolite accurately measures the angles included by the planes of these pyramids, and the
surface of an imaginary sphere at the level of the sea intersects them in an assemblage of
spherical triangles, above whose angles in the radii prolonged, the real stations of the ob-
servations are raised by the superficial inequalities of mountain and valley. When the
triangles are so large as to make the difference between the chords and their arcs perceptible,
the condition of the sphericity must be ascertained, or else, when all the triangles are laid
CHAP. VIII.
855
GEOMETRY.
down, they would occupy a greater area than they ought: the triangles must, therefore,
be considered as spherical, and treated as such, when their sides are to be calculated; when
angular distances are measured by a theodolite, the plane of the instrument is so adjusted
to the horizon that the angle observed is the horizontal angle of the station. The three
summits of the triangle so measured are equally distant from the earth's centre, which is
not the case when the sextant and repeating circle are used for the purpose of measuring
angles. The centre of the theodolite being placed directly under the centre of the signal
destroys the necessity of any calculation for reducing the observed angie to the centre of
the station.
In all spherical angles the three angles together exceed 180°, by what is called the
spherical excess, which is proportional to the area of the triangle; ABC, being the angles
of a spherical triangle, r the radius of the sphere expressed in feet, x=3.14159, the pro-
portion the circumference has to the diameter, and S the number of square feet contained
in the area of the triangle; then by trigonometry,
Let E denote the spherical excess,
E
=
:
S=
r² X.
A+B+C-180°
180°
A+B+C-180°; then E
Sx 180°
r2 x
in degrees, or
S x 648000,
as expressed in seconds: in any triangle which can be measured on the
r2 x
surface of the earth, S is very small in comparison with r², and therefore E is a very small
quantity in practice it seldom exceeds four or five seconds; but in the triangle of a side of
100 miles in length, it would amount to more than thirty or forty an approximate value
of S is sufficient then to compute the value of E with precision; and for this purpose, we
must consider the triangle a plane one: let abc be the number of feet in the respective
sides opposite to ABC: we shall have for the area S=ab sin. C. Substituting this in the
ab sin. C × 648000
formula for the spherical excess, we obtain in seconds, E=
: this formula
2r2 x
is deduced on the hypothesis that the surface of the triangle is spherical; but it equally
applies to triangles on the surface of a spheroid; for the spherical excess is the same for
triangles on a spheroid and sphere, when the latitude of the stations and their differences
of longitude are the same. To compute the spherical excess of any triangle, the value of r,
the radius, should be ascertained; the curvature of the arc joining any two points or
stations on a spheroid varies with the latitude, and also with the direction of the arc in
respect of the meridian: the value of r may then be considered sufficiently near the truth,
by assuming its value that which corresponds to the curvature of the meridian at the
mean latitude of the stations, and even to suppose it constant for all the triangles within
similar parallels of latitudes. To calculate the two remaining sides of the triangles after
the three spherical angles have been determined, one side being always known either by
measurement or computation, three different methods have been adopted: the first is to
transform the side whose length is already known in feet into an arc of a circle, which is
done by comparing it with the radius of the earth, and solving the triangle by spherical trigo-
nometry. But this process is not generally adopted; that which was followed in calculating
the triangles of the Ordnance survey was to consider, as the distance of any two stations
mutually visible from each other is very small in comparison of the whole circumference
of the earth, the chord of the intercepted arc will differ from the arc itself, by a quantity
which may be computed from the known ratio of the chord to the radius of the earth, but
which in general is so small as to be insensible. If, therefore, from the observed spherical
angles we deduce in each case the corresponding angles formed by the chords, and with
these compute the sides by plane trigonometry, we shall obtain the chords of the arcs
intercepted between the stations, and thence the arcs themselves. The third method was
after the demonstration, that a triangle on a sphere or spheroid, which is small in comparison
with the whole spherical surface, differs insensibly from a plane triangle, of which the sides
are respectively equal in length to the sides of the triangle on the sphere, and whose angles
are respectively equal to those of the spherical triangle, each diminished by one third of
the spherical excess.
Tables for the reduction of spherical angles to the plane of the chords, and likewise for
the computation of the spherical excess, are given by Delambre in his Base Metrique.
To determine the Meridian Line the theodolite is fixed at one of the stations; and some
hours before mid-day the telescope is directed, in such a manner that the cross-wires shall
touch the upper or lower limb of the sun in the east; and then the horizontal and vertical
readings of the arc are to be set down; this operation is to be repeated several times: in
the afternoon, the vertical arc being clamped to the last reading off, the horizontal angle
at the time of the sun's limb touching the intersection of the cross-wires is to be noted;
the vertical arc being clamped in succession in the descending series of the vertical angles,
all the horizontal readings at the time of each successive intersection are entered: the
3 1 4
856
Book II.
THEORY AND PRACTICE OF ENGINEERING.
point on the horizontal limb half-way between all the readings will give the angle to
which the vernier is to be placed, in order that the telescope may point to the position
occupied by the sun at noon.
D
B
On the Mensuration of Distances, Heights, &c., by the calculation of Sines, Tangents, and
Secants. By the terms sines, tangents, and secants, is understood the knowledge of the
sides and angles of triangles, by means of which, and the assistance of tables calculated for
the purpose, we can obtain the length of the unknown sides and angles.
A Sine is the side of a right-angled triangle, the
hypotenuse of which has served as a radius to describe
a circle comprising the right-angled triangle, as A B C.
the hypotenuse of which, AB, is the radius of the
circle DBEF G, which encloses the triangle ABC,
the side of which, BC, is the sine of the angle CAB;
for the same reason the side AC is the sine of the
angle ABC, and the hypotenuse A B that of the angle
ABC. Every angle of a triangle is the sine of its
opposite side, as in that of A BC: the angle CAB is
the sine of the side B C, which is opposite to it; and
the angle ABC is the sine of the side A C; and the
angle BCA is the sine of the hypotenuse A B.

G
E
A
C
Fig. 1077.
F
Total sine, radius, sine of 90°, or entire sine, is the
hypotenuse of a right-angled triangle, which serves
as a radius to describe a circle enclosing a right-
angled triangle. In the triangle ABC, the hypote-
nuse AB is a total sine, and the two other sides AC and BC are only sines; so that
the total sine AB, being commonly divided into 100,000 parts which are equal, the
two other sides or sines being each smaller, must have less than that number.
Right Sine of an Angle is a line which falls perpendicular from the point where the
hypotenuse cuts the circle, on to the extremity of another line, which forms an angle
with the hypotenuse, as the line BC is the right sine of the angle CA B.
Sine of an Arc is the right line drawn from one extremity of the arc perpendicularly to
the radius which answers to the other extremity, as the right line BC is the sine of the
arc BE.
Versed Sine is the remaining portion of the radius which is comprised between the line
of the right sine of an angle and one of the same sine, as the line CE is a versed sine.
Sine of the Complement of an Arc is a right line drawn from the extremity of an arc,
perpendicular to the radius, which does not touch the arc, but which together with the arc
terminate a quarter circle: the line BH is the sine of the complement of the arc BE;
because the right line BH is drawn from the extremity B of the arc BE, perpendicular
to the radius AD, which does not touch the arc D B, which bounds it.
The reason why each side of a right-angled triangle inclosed within a circle is called a
sine is said to be from the word sinus, signifying the heart, the most inward part of man;
thus, sines, which are likewise enclosed or rather found inscribed in a circle, are called so; and
as the heart is the most important part of man, so are sines in a circle those which produce
the most useful acquirements in mathematics.
Tangents and Secants. -A tangent is a line which
touches the circumference of a circle, but does not
cut it if prolonged, as BC: tangent of an angle is a
line perpendicular to the extremity of a radius at the
point on which it touches the circle, and this perpen-
dicular terminates at the other line, which forms the
angle of the tangent with the radius; the right line
BC is the tangent of the angle BAC, because it is
perpendicular to the extremity of the radius A C, at
the point C, where it touches the circle DCEF;
and the perpendicular BC terminates at the line C
A B, which together with the radius AC forms the
angle B A C of the tangent BC.
A Secant is a line which is drawn from the centre
into the circumference of a circle, as the line AB is
a secant; for being drawn from the centre A, it cuts
the circumference of the circle DCEF in the point
G.
B

G
دع
D
F
A
E
Fig. 1078..
Secant of an Angle is a line drawn from the centre
of a circle, which cutting the circumference extends to the tangent; as the right line A B is
the secant of the angle CAB, because it is a line drawn from the centre of a circle into
its circumference DCEF, in the point G, and extends beyond the circle to the tangent B C.
CHAP. VIII.
857
GEOMETRY
In practical geometry
Of Tables of Sines, TangenTS AND SECANTS, AND OF LOGARITHMS.
the instruments mostly used have their degrees usually divided into six equal parts, and con-
sequently the tables are calculated to answer them by having their degrees divided into six
equal parts of 10 minutes each.
The sines, tangents, &c., are comprised in two sets of tables; the first contains the sums
of progression of common sines and tangents for the 90 degrees of the quadrant, for the
100,000 parts into which its radius or entire sine is supposed to be divided. The second
table contains the logarithms from 1 to 10,000: in the first table the first column contains
the minutes of degrees, the second the sines auswering in order to the minutes, the third and
fourth the tangents and secants, the fifth the degrees, the sixth and seventh the logarithmic
sines and tangents. The first column of minutes contains six divisions; the first is the
minute, and then follows 10, 20, 30, 40, 50, 60, which answer to the five columns against
them. The second column contains the sums of sines according to the progression of
degrees and minutes of the radius or total sine, and the other columns contain tangents,
secants, sines, logarithmic sines, and tangents; whilst the fifth serves to mark the degrees
from top to bottom to 45 degrees for the left-hand columns, and from bottom to top from
45 to 90 degrees for those on the right-hand.
To find the Sine of an Arc, or the degrees of a given angle and its complement.-Every arc in
´a given angle may have less or more than 90°, and its degrees may have minutes or not.
Required the sine of an arc of 24°, or simply the sine of 24°, look in the table under the
head of degrees for this number, and against it is found 40673 for its sine; but if it is re-
quired to find the sine of 24° 10′, we must further seek for 10′ under the head of minutes,
where, opposite to 24°, also in the column of sines, is 40939, which will be sine of 24° 10′.
If it is required to seek the sine of 60° in the table which goes from 45 to 90; when the
sine is 140°, or exceeds a quadrant, or 90°, we must take the complement by subtracting
140° from 180°, the value of a demicircle, and the remainder 40° must be sought in the
column of sines, which will give 64278.
To find the Degrees and Minutes of a given Sine, as that of the sine 40673.- Seek the sine in
the column of sines, and the figure opposite in the column of degrees will give 24°, and
opposite this sine 40673 in the column of minutes is an 0, which signifies that the sine has
no minutes; if the given sine had been 40939, seek it in the column of sines, and having
found it in the left-hand columns, observe what degrees and minutes correspond with it,
and having remarked it to be 24° 10′, set it down as the sine required. The rules above
given for finding sines apply also to tangents and secants, both simple and logarithmic :
when the distances measured are in feet or inches, it is necessary to reduce these dimen-
sions into seconds, because these small fractions become less considerable, as fractions of
lines in great distances are of little importance in a practical point of view.
A
D
K
To distinguish when observing objects, if the Sides of the Triangles formed are either Sines,
Tangents, or Secants. In a right-angled triangle, when we know the hypotenuse, or the
side opposite the right angle, the sides of this triangle are considered the sines, because, if
from one extremity of the hypotenuse, with its length as a radius, we describe a circle,
it will inclose the whole triangle, and there will be neither tangent nor secant; supposing it
required to find the distance from A to C, by employing a
right-angled triangle A CB, of which the two angles BA C
and A BC are known with the hypotenuse BC; it is evident
that if from the point B, the extremity of the hypotenuse
BC, and with the radius or length BC, we describe a circle,
as DCEF, it will enclose the triangle A CB, and its sides
AC and AB will be sines, because they are enclosed in the
circle DCEF. Observe also, that in the same right-angled tri-
angle A C B, that it is a general rule when one of the two sides
are known which form a right angle, as for example B A, we can
use it as a radius or total sine, to describe a circle, as A GHI;
that the other side A C of the right angle BAC is a tangent,
because it falls perpendicularly on the extremity of the radius
BA at the point A, where it touches the circle; and that the
side B C, which is opposite to the right angle B A C, is a secant, because it cuts the circle
AGHI in K.

L
B
G
H
E
Fig. 1079.
M
In trigonometry, all the sides of acute and obtuse-angled triangles are called sines,
because these triangles, having no right angle, can have neither
tangent nor secant of angles: if it be required to find the
distance L M by the obtuse-angled triangle L M N, it is clear
that having no right angle, it can be neither the tangent nor
secant of an angle.
To measure lengths by the calculations of Sines, forming a
right-angled triangle, of which the hypotenuse and two angles

Fig. 1080.
are known, viz. right and acute.—To find the unknown angle, subtract the acute angle from
8.58
Book II
THEORY AND PRACTICE OF ENGINEERING.
Į
A
C
90
50
Fig. 1081.
B
90°, the remainder will be the unknown angle; to find the two other unknown sides,
proceed by the rule of three, placing in the first term 10,000,
in the second the value of the known hypotenuse, and. in
the third the sine of the angle opposite to the side required:
the quotient will give the unknown side. As to find the
length A B by forming a triangle ABC, of which the hy-
potenuse CB is 108 feet, the acute angle ACB 50°, and
the right angle CAB 90°. To find the unknown angle
CBA, subtract the acute angle A CB, 50°, from 90°, the
remainder, 40°, will be the angle CBA; then place for the
first term 10.000, in the second the length of the hypotenuse
reduced to seconds, as 15552, and the third term the sine of
the angle ACB 50°, which sought for in the tables is found
to be 76604; the quotient will give 11913 seconds, and the
remainder 45408 is about one half second more, consequently the length of A B is 82 feet,
4 inches, 8 seconds, 94 thirds. To obtain the side A C, you must adopt the same method.
Another example may be given where the length of the hypotenuse is not known. From
90° subtract the known acute angle, the remainder will be the
unknown angle; to find the length of the unknown side
which forms the right angle and is a tangent, place in the
first term, as before, 10000, in the second the known side, in
the third the tangent of the angle opposite to the required
angle: the quotient will be the length. The height AC of
the triangle A B C, of which the side A B is 11913-5 seconds,
the angle CBA 40°, and C A B 90°, it is required to find the
height AC; subtract from 90° the acute angle 40°, and the
remainder 50° will be the acute angle AC B.
Then place

C

A
90
Fig. 1082.
40
B
in the first term 10,000, in the second 11913.5, and in the
third the tangent of the angle, 40°, which will be 83909, ac-
cording to the tables; the quotient gives 9996 seconds for the
height A C, which reduced to feet is 75 feet 5 inches. If the length of the hypotenuse is
required, place in the first term 10000, in the second the length of the side AB, 11913-5,
and in the third place the secant of the angle, 40°, which is 130540 in the table, and the
quotient gives 15551, with a remainder of 88290, or nearly one-third of a second, conse-
quently the hypotenuse is in length 15551 seconds, or 108 feet nearly.
B
A
90
Required the length A B of the third triangle, having formed the right-angled triangle
ABC, of which the hypotenuse CB is 108 feet, 15551 seconds, and the side CA is
69 feet 5 inches. First find the acute angle A CB opposite the required side A B by the
unknown angle CBA, which you can obtain by the simple
rule of three, placing in the first term the value of the hypo-
tenuse CB, in the second term 10000, and in the third
term the length of the side A C; the quotient will give 64277
for the sine, which being sought in the table and not found,
seek the nearest number to it, 64278, which will give 40° for
the angle C B A; subtract from 90°, the angle C B A, 40°, and
the remainder, 50°, will be the angle A C B. To find the side
A B, adopt the rule given for the first triangle, that is to say,
by the rule of three, placing in the first term 10000, in the
second the length of the hypotenuse, and in the third the
sine of the angle A CB 50, opposite the required side AB,
which sought in the tables will be 76604; the quotient of the sum will give 11913 seconds;
there will remain 45408, which is half a second, and which reduced into feet gives 82 feet,
8 inches, and 9 seconds.

Fig. 1083.
C
Required the distance from B to C, having formed the right-angled triangle ABC, of which
the side A B is 82 feet, 8 inches, 9 seconds, or 11913
seconds; and the side A C is 69 feet, 5 inches, and half B
a second, and the angle B A C a right angle of 90°.
It will be seen that since we do not know the hypote-
nuse, B C, we must work by tangents and secants.
To find the required side B C, we must know one of
the two acute angles, as C B A, opposite to the short
side A C, 9996 seconds. To find this by proportion,
place in the first term the length of the side AB, 119131
seconds; in the second term 10000, and in the third
term the side A C, 9996 seconds; the quotient will give 83912, which, being a tangent,
seek the nearest number to it, 83909, in the table, it will give 40 degrees for the angle
CBA.

90
A
Fig. 1084.
CHAP. VIII.
859
GEOMETRY.
If you desire to measure the acute angle A C B, it will only be necessary to subtract 40°
from 90°, the remainder, 50°, is the angle. To have the length of the hypotenuse, or side
B C, follow the rule given for the second triangle by proportion, placing in the first term
10000, in the second the value of the side A B, 11913 seconds, and in the third the
secant of the angle C B A, 40°, which is 130540: the quotient will give 15552 lines for
the distance B C, which, reduced into feet, will give 108 feet.
A
It is required to find the distance A B, having formed an acute-angled triangle, A B C,
the angle A C B is supposed to be 79°, the angle C B A, 37°, and the length of the
side C B, 58 feet. To find the angle C A B, add
together the two known angles, 79° and 37°, and subtract
their sum, 116°, from 180°, the remainder, 64°, will be the
value of the angle C A B. To obtain the length of the
side A B by proportion, place in the first term the sine
of the angle C A B, 64°, opposite the known side, A B,
58 feet; the sine will be 89879; in the second term the
length of the side CB 58 feet; in the third term the sine
of the angle A C B, 79°, opposite the required side; this
sine will be 98162; the quotient will give 63 feet for the
side A B, and since there remains 31019, reduce them
into inches and seconds. If the side A C is required, place for the first term the sine of
the angle C A B, 64°, viz. 89879, for the second term the value of the side C B, 58,
and in the third term the sine of the angle C B A, 37°, which is 60181; the quotient will
give 38 feet for the length of the side A C: what remains must be reduced into inches and
seconds.

с
Fig. 1085.
37
B
C
18
Required the distance from A to B, the side A C
having 46, C B 66, and the angle C A B, 81°. First find A
the angle CB A, opposite the known side A C, by pro-
portion: place in the first term the length of the other
side, C B, 66, opposite the known angle, C A B, 81º.
In the second term the sine of the angle, C A B, 81º, which
is 98768, and in the third term the length of the known
side, A C, 46, opposite the angle sought, C BA; the
quotient, 68838, will be the sine: seek the nearest number
in the table, 68835, which will give 43° 30′ for the angle
CBA. Add the sums of the two triangles C A B, 81º,
and C B A, 43° 30′, their sum, 124° 30′, subtracted from
180°, leaves 55° 30′ for the angle A C B. Then find the
length of the side A B, by the rule before given. Place in the first term the sine, 98768,
of the angle C A B, 81°, opposite the side C B, 66; in the second term, the value of the
known side, CB, 66, and in the third term, the sine, 82412, of the angle A C B, 55° 30′,
opposite the required side, A B; the quotient will give 55 for the length of A B, with a
remainder.

R
Fig. 1086.
69
A
Measuring Lengths by the calculation of Sines, forming an acute-angled triangle, of which
two sides and the comprised angle are known. Required the distance from A to B, by
forming an acute-angled triangle A B C, the side of which A C is 63 chains, BC 30 chains,
and the angle ACB comprised by these two sides 69°. To find the two angles C A B and
CBA, add together the two sides, A C 60 chains, and
BC 30 chains; their sum will be 90°; subtract the
short side, BC, 30, from the long side, A C, 60; there
remains 30: subtract from 180° the known angle A CB
69°; the remainder, 111°, will be the value of the two
unknown angles, C A B and CBA, of which take the
half, 55° 30. Place in the first term the sum of the two
sides, A C 60 and B C 30=90; in the second, the dif-
ference of the two sides 30, and in the third term the
tangent of half the two unknown angles 55° 30′, which
is 145500; the quotient will give another tangent, 48500, the nearest number to which
in the tables, 48413, will give 25° 50′, to which add half the value of the unknown
angle 55° 30, and it will give 81° 20′ for the greatest angle of the two, viz. CBA, but if
you subtract the 25° 50′ from 55° 30′, it will give 29° 40′ for the angle CA B. To find
the side A B by proportion, place in the first term the sine of the angle CAB 29° 40′
opposite the side BC, 30 chains; this sine will be 49495; in the second term the side
BC 30 chains, and in the third term the sum of the angle ACB 69° opposite the side
required; this sine will be 93358; the quotient will give 56 chains for A B.
would reduce the remainder 29020 chains into feet, you will have 14 feet more, which
gives 54 chains 14 feet for the distance from A to B.

C
Fig. 1087.
If you
Measuring Lengths by forming an Obtuse-Angled Triangle, of which two angles and the
860
THEORY AND PRACTICE OF ENGINEERING.
Book II.
A
33
109
B
adjacent side are known. This method is almost the same as that for the fifth triangle,
only instead of taking the sine of the obtuse angle, we take the sine of its complement, as
will be seen in the following example. Required the
distance from A to B, having formed the obtuse-angled
triangle ABC, of which the angle CAB 33°, ACB
109°, and the adjacent side AC 52 feet. To find the
unknown angle CBA, add together the value of the
two known angles CAB 33°, and A CB 109°, and
subtract their sum, 142°, from 180°; the remainder,
38°, will be the value of the unknown angle CBA.
To find the length of the unknown side AB by the
rule of three, place in the first term the sine of the angle CB, 38°, opposite the known sine
A C; this sine will be 61566; in the second term the value of the known side AC 52,
and in the third term the sine of the angle ACB 109, opposite the side required. But
since this angle A CB is 109° and we have no sine above 90° we must take the sine of the
complement of 109°; that is to say, we must subtract the obtuse angle A CB 109° from
180°; the remainder will be 71°, and the sine of 71° will be 94551, which must be put in
the third term; the quotient will give 79 with a remainder for the length A B.

Fig. 1098.
It will be seen that all the other difficulties which might attend the obtuse-angled
triangle are reduced to the rules for the acute-angled triangle, provided it is remem-
bered that to have the sines of obtuse-angled triangles the complement of 180° must
be taken.
A
50
90
Fig. 1089.
B
40
To find the three Angles of a Triangle, when the three sides are known, by the calculation
of sines.— Since this difficulty may occur in the three kinds of triangles, right, acute, and
obtuse-angled we will commence with the first, viz. the right-
angled. In the triangle ABC, the three angles of which
we wish to ascertain, let it be supposed that the side A B is
11913 seconds, A C 9996, and CB 15552; to find the three
angles, let fall a perpendicular AD from the angle CAB to
the side CB; add together the two sides A B 11913 and
AC 9996; their sum will be 21909; subtract the shorter
side A C from the mean AB, to have their difference 1917:
then by proportion, placing in the first term the greatest side
CB, 15552, in the second the sum of the two sides A B and
A C, 21909, and in the third term the difference 1917; the
quotient will give 2700, with a remainder of 9153, which is
nearly two-thirds of the difference between the two segments
CD and DB, and this difference being subtracted from the half length CB leaves
128513, of which take half for the small segments CD, and if to this half, 642511, you add
the difference, 27001, between the two segments, you will have for the other segment, DB,
9125 Before proceeding further, value the small portions of the two segments CD and
DB, and it will give 64253 for CD, and 91261 for DB. To find the angles of the two
right-angled triangles, ADC and ABD, of which we know the hypotenuse and one
side, follow the rule of the third triangle. To find the two acute angles DAC and DCA
of the right-angled triangle ADC: by proportion, place in the first term the hypotenuse
A C, 9996, in the second 100000, and in the third the side CD, 6425; to have the
opposite angle D A C, the quotient will give 64282, which will be a sine; seek the nearest
number in the table, 64278, which will give 40° for the angle DA C, which subtracted
from 90° leaves 50° for the other angle DCA: by the same rule it will be found
that the angle DAB in the right-angled triangle ABD is 50° and DBA 40°: add
these together; their sum will be 90° for the third angle CAB of the right-angled
triangle.
Mensuration of Distances, Heights, &c. by Logarithms, which facilitates the calculations of
sines, and avoids the necessity of calling in the aid of proportion, addition, and subtraction
with them, hold the place of multiplication and division, as has been seen in preceding
examples; here we shall repeat them, to show the convenience of logarithms in calculating
sines, tangents, and secants. We have already mentioned that sines give halves, thirds,
quarters, &c., by reason of their remainder, after their division; logarithms only give
integers, which obliges us to reduce the value of the known sides into small measures, as far
as 4000 (the number given in the ordinary tables), which is a sufficient quantity to be
appreciated in mensuration.
Measuring Lengths, by forming a right-angled triangle, of which the hypotenuse, with
the right and acute angles are known. To find the third angle, subtract from 90° the
value of the known acute angle; the remainder is the third unknown angle: then to find
the side opposite to the acute angle just ascertained, seek in the logarithms, in the column
of numbers, the number of the length of the hypotenuse figured apart. Then seek in
the table of sines, in the column of logarithmic sines, the logarithmic sine of the acute

CHAP. VIII.
801
GEOMETRY.
angle opposite to the side to be known, to add to the lo-
garithm already figured a part, and subtract their sum from
the logarithm of the sine 100000000, which is the end of the
column of logarithmic sines, where the 89° 60′ of the tables
of sines end; the remainder of this subtraction will be a
logarithm, which sought in the table of logarithms will give
the value of the required side.
A

90
Fig. 1090.
50
C
Let it be required to find the distance AB: having formed
the right-angled triangle A B C, of which the hypotenuse
CB is known to be 1296 inches, and the acute angle ACB
50°, with the right angle CAB 90º. To find the third ang'e
CBA, subtract the acute angle ACB 50° from 90°; the
remainder, 40°, will be the acute angle CB A. To find the
inaccessible side A B, seek in the column of numbers the sum of the hypotenuse BC,
1296, which will give the logarithm 31126050. Then seek in the column of sines of
logarithms the logarithmic sine of the angle A CB, 50°, opposite the side required, AB;
the logarithmic sine will be 98842540, which add to the logarithm figured aside, and
from their sum, 129968590, subtract the total logarithmic sine 100000000; the remainder,
29968590, will be a logarithm, which being sought, or its nearest number, 29969492, wil
give opposite in the column of numbers 993 for the length of the side A B in inches:
according to the same rule it will be found that the side AC is 833 inches long.
Measuring Lengths, by forming a right-angled triangle, of which one of the sides which
form the right angle is known, with the adjacent right and acute angles. To have the
third unknown angle subtract the known acute angle from 90°; to have the other side,
forming the right angle, which is a tangent, seek in the column of numbers the length of
the known side, and write down the logarithm opposite it.
Then seek in the table of sines the tangential logarithm of
the angle opposite the side to be found, which add to the
logarithm written down, and from their sum subtract the
total logarithmic sine 100000000; the remainder will be a
logarithm, which being sought in the column of logarithms,
will give in the opposite column of numbers the side re-
quired.

A
Fig. 1091.
40
Required the height AC of the right-angled triangle
ABC, where the side AB is 993 inches, the right angle
CAB 90°, and the acute angle CBA 40°. We know that
by subtracting the acute angle CBA, 40°, from 90°, the
remainder 500 will be the unknown angle ACB. To have
the height AC, which is a tangent, seek in the column of numbers the side A B, 993
inches, to take its logarithm 29969492: seek in the table of sines the tangential logarithm
of the angle CBA 40°, opposite the side required; the tangential logarithm will be
99228135, which add to the logarithm before found; their sum will be 129207627 ;
subtract the total logarithmic sine 100000000 from it; the remainder, 2920762, will be
the logarithm, which sought in the table of sines will give 833 inches, opposite its nearest
number, 29205430, for the height required of A C. To have also the hypotenuse CB;
add the total logarithmic sine, 100000000, to the logarithm 29206450, and from their
sum, 12906450, subtract the logarithmic sine 98080675, of the angle CBA 40°; the
remainder, 31125775, is a logarithm, which sought in its nearest number, 31126050, in
the table, will give 1296 for the hypotenuse CB.
A
9J
B
Of measuring Lengths by forming a right-angled Triangle, of which the hypotenuse and
one of the sides which form the right angle and this angle are known. To find the third
unknown side, add to the length of the hypotenuse that
of the known side; seek their sum in the column of numbers
and figure the logarithm, which is opposite, by itself; then
subtract the known side from the value of the hypotenuse;
seek the remainder in the column of numbers, take the lo-
garithm opposite, to figure it above or below the last loga-
rithm; add the two together, and take half their sum, which
being a logarithm, seek it or the nearest number to it in
the table, the number opposite marks the length of the
unknown side.
Required the distance from A to B having formed a
right-angled triangle ABC, of which the hypotenuse
CB is 1296 inches, and the side AC 833 inches, with the
right angle CA B, 90º.

C
Fig. 1092.
To find the side. A B, add the hypotenuse 1296 to the side AC 833; seek their sum in
the column of numbers, which will give the logarithm 33281757. Then subtract the side
862
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
A C, 833, from the hypotenuse CB, 1296; their remainder, 463, seek in the column of num-
bers; write the logarithm, 26655810, which is opposite, below the first logarithm; add these
two together, their sum will be 59937567, and its half 299687831 will be a logarithm; seek
this or its nearest number 29969492 in the column of logarithms, which will give in the
column of numbers 993 for the number of inches from A to B.
Of measuring Lengths by forming a right-angled Triangle of which the two sides forming the
right angle and the latter are known. - Required the distance B C, having formed a
right-angled triangle A B C, of which the side AB is 82 P

One
Q
feet, 8 inches, 9½ seconds, or rather more than 993 inches,
the side AC 833 inches; and the angle B A C 90.
of the two acute angles must be found, say C B A, opposite
to the shortest known side A C, 833 inches. Write down
the total logarithmic sine 100000000. Then seek in the
column of numbers the figure 833, the value of the side
A C, which is that opposite the angle required, CB A; and
take the logarithmic sine, and add them together: their
sum will be 129206450. Seek in the column of numbers,
the figures of the other side AB, 993 inches, and having
found them, take the opposite logarithm, 29969492, which
write below the sum 129206450; subtract one from the
other, the remainder, 99236958, will be a tangential logarithm, which, or the nearest num-
ber to it, 99238135, you must seek in the column of tangential logarithms; in the opposite
column of degrees will be found 40° for the angle C B A: if you subtract this angle from
90° there will remain 50° for the other acute angle A CB. Lastly, to find the distance
BC, which is a secant, add to the total logarithmic sine 100000000, the logarithm
29969492 of the side A B, 993 inches, and from their sum 129969492, subtract the loga-
rithmic sine of the angle AC B, 50°, which is 98842540, the remainder 31126952 is a
logarithm; which, or its nearest number 31126050, will give 1296 for the required distance
B C, in inches.
Fig. 1093.
A
Measuring Lengths by forming an acute-angled Triangle, of which two angles and the adjacent
angle are known: to find the third angle, add together the value of the two known angles,
and subtract their sum from 180°; the remainder will be the
unknown angle. To find the two unknown sides, as that
which is opposite to the least angle, seek the logarithmic
sine of the angle, and write it down: then seek in the column
of numbers the value of the known side, figure its logarithm
below the logarithmic sine before found, add the two toge-
ther, and from their sum subtract the logarithmic sine of
the angle opposite the known side; the remainder will be a
logarithm; which being sought in the column of logarithms
will give in that of numbers the length of the unknown side.

C
79
Fig. 1094.
37
B
Required, in the acute-angled triangle ABC, the dis-
tance from A to B the angle A CB, being 79°, CB A,
70°, and the adjacent side CD, 3480 inches. To find the
angle C A B, add together the two angles AC B 79° and CBA 37°: subtract their sum
116° from 180°, the remainder 64° will be the unknown angle CB A. To have the length of
the side A B, seek in the table the logarithmic sine of the angle A CB, 79°, opposite the side
A B required to be found; this logarithmic sine will be 99919466: then seek in the column
of numbers the length of the known side CB, 3480 inches, which will give opposite the lo-
garithm 35415792, which write below the logarithmic sine 99919466; add them together,
their sum will be 135335258. Lastly, seek in the table the logarithm of the angle C A B 64°,
and it will be 99536602, which subtract from the sum 135335258, the remainder, 35798656,
will be a logarithm, the nearest number to which, 35797836, will give 380 for the distance
in inches from A to B.
B
A
Of measuring Lengths, by forming an acute-angled triangle, of which two sides and the
comprised angle are known. Required the distance from A to B of the acute-angled tri-
angle A B C, of which the side A C is 1440 feet, CB 720,
and the angle ABC 69°. To find one of the two unknown
angles, subtract the short side B C, 720, from the long one
A C, 1440, their difference, 720, will give the logarithm,
28573325. Subtract the known angle ACB 69° from
180°, the remainder 111° is the value of the two unknown
angles, of which take the half, 55° 30', their tangential lo-
garithm in the table of sines will be 101628657, which add
to the logarithm 28573325; their sum will be 130201982.
Then add together the sides AC 1440, and BC 720; their
sum, 2160, will give the logarithm 33344537, which must

C
69
Fig. 1095.
CHAT. VIII.
863
GEOMETRY.
be written below the sum total 130201982, and subtracted from it; the remainder, 96557445,
will be a tangential logarithm, the nearest number to which, 96849681, will give 25° 50′,
which being added to the 55° 30′, the approximating value of the two angles, will give 81°
20 for the greater angle CB A, and 25° 50′, being subtracted from 55° 30′ there will remain
29° 40′ for the angle CA B. To find the third side A B take the logarithmic sine of the
angle A CB, 69°, opposite the side A B; this sine will be 99701517. Then seek in the
column of numbers the logarithm of the side BC, 720, which will be 28573325; figure it
below the logarithmic sine 99701517, and add them together; the sum will be 128274842.
Seek the logarithmic sine of the angle C A B, 29° 40', opposite the known side BC; it will
be 96945642, which subtract from the sum 128274842, the remainder, 31329200, will be a
logarithm, the nearest number to which in the table will give 1358 for the distance in feet
from A to B.
B
33
109
A
Fig. 1096.
C
Measuring Lengths by forming an obtuse-angled Triangle, of which two angles and the adjacent
side are known: the rules for the first acute-angled triangle must be applied here; never-
theless, since in the table of sines there are no logarithmic
sines for obtuse angles, we must subtract the obtuse angle
from 180°, and take the logarithmic sine for the remainder
or complement. Required the distance A B, having
formed the obtuse-angled triangle, A B C, of which the
angle CAB is 33°, the angle A CB 109°, and the adja-
cent side AC 312 feet. To find the third angle CBA,
add the two angles CA B, 33º, and A C B, 109°, together,
and subtract their sum 142° from 180°, the remainder 38° will be the required angle CB A.
To have the length of the required side A B, seek the logarithmic sine of the angle A CB,
109°, opposite the required side A B; but since the angle A CB 109° is obtuse, subtract
109° from 180°, the remainder 71° is its complement; the logarithmic sine of which is
99756701. Then seek in the column of numbers the side AC 312; write down the loga.
rithm which is opposite 24941546, below the logarithmic sine 99756701, and add them
together; their sum will be 124698247. Seek the logarithmic sine of the angle CB A 38°
opposite the side A C, it will be 97893420, which subtract from the sum 124698247, the
remainder 26804827 will be a logarithm, the nearest number to which in the table, 26803355,
will give 479 for the distance A B in feet.
By the same rule it will be found, that the side CB is 276 feet, remarking that there is
no sine of the complement to be taken for the angle C A B because it does not exceed 90º.
As for the other obtuse triangles, they are solved like acute-angled, only taking the com-
plements of the obtuse angles.
MENSURATION OF SUPERFICIES AND SURVEYING. Of Bevels
and Recipiangles. — A bevel may be compared to a pair of
large compasses, and is usually made of iron or wood: the
iron bevel A, used by stone masons, has each of its branches
about 2 feet long, smooth and pointed, and its head, which is
round, will open to any angle required.
The carpenter's bevel, B, made of wood, is commonly
shorter than the stone-mason's; the extremity which forms its
head is cut at right angles, so that opening them to the square
mark they may serve more easily to express a right angle.
The Recipiangle C consists of two long rules of wood,
which have their branches parallel at their edges, and are
attached together at the middle of their ends by a double-
headed screw, which forms the head of the instrument.
When used for taking salient and re-entering angles, the
centre of a protractor of wood or horn, 6 or 8 inches in
diameter, is applied at D to the point at which the branches
cross, to observe how much the branches are opened, and
which give the required angle; in default of this instrument
we use a bevel.
The recipiangle E, made of wood, copper, &c., is com-
posed of two plates, each about a line in thickness,12 inches
long, and 3 inches wide: sometimes its length is increased
by adding slips of wood or flat rulers. At the extremity
of one of the two plates is described a demi-circle, equal to its
breadth, divided into 180°; and at the extremity of the second
blade, towards its centre, is a small tongue or round head,
which is attached to the centre of its semicircle on the
other limb by a double-headed screw.
The instruments described are extremely simple and have
this fault, that it is difficult to apply the centre of a protractor


Ꭰ
A
Fig. 1097.

Fig. 1098.
Fig. 1099.
E
Fig. 1100.
C
B


864
BOOK II.
THEORY AND PRACTICE OF ENGINEERING,
precisely to the point where their limbs cross; and that marked E can only carry a small
protractor, on account of the size of the circle on which it is mounted; wherefore the
demicircle, having its sines very small, cannot give the just value of an angle, and we
cannot observe halves and quarters of degrees, which are necessary to set out the angles
precisely.
D
A
E
Of the Parallelogrammic Recipiangle. The two limbs A B and A C, of any length
and breadth, are joined together at the point A by a double-headed screw; they are
pierced in the centre of their breadth at the points D and E, equidistant from the centre
A; and to these holes are attached two small
rules, DF and E F, joined at the centre F, in
such a manner that the four rules A D, D F,
FE, and E A, when the four centres of motion
are of an equal length, form a perfect square.
On the rule E FG, which is longer than D F,
is attached a protractor with two hinges G
and H. The centre of the protractor should
be above the centre of the screw F, and the
line of its diameter, if prolonged, should pass
through the centre of the screw E: its radius
should be rather less than the side FD, to
allow a small line to be seen on the piece at-
tached to the screw D, which serves to indicate
the angle on the margin of the protractor. The
recipiangle is used for taking re-entering angles,
but when salient angles are required, it is only
necessary to open the long rules AB and A C
in a right line, and then the centre F will coin-
cide with the centre A, so that the same sides of
the long rules which have served to take the
re-entering angles will also serve to take the
salient. When taking small re-entering angles
and salient angles, the protractor must be ele-
vated perpendicularly on its rules by means of
two hinges, and then laid down to measure the
angle.

Fig. 1101.
G
H
C
To draw the Outline of any Place or to take its Plan. As we can only take the plan of a
place by the knowledge of the length of its sides and the measurement of its angles, the
first thing to be done is to pass round it, and observe whether it is closed or not; if it is
accessible and open, as most hamlets and villages are, an artificial outline must be made by
planting piquets near the places to be taken, and on the most elevated ground. It must
also be observed that in placing these piquets it is not necessary to plant them at equal
distances, or that the outline should be formed with regular sides; all that the plan is to
comprise should be so set out that its angles may be taken. If the place is only partly open,
or if several trees or houses interfere, their position and measurement must be taken in the
manner described hereafter. The outline of the plan being roughly sketched out on paper,
when the measurements are taken, the sides and angles may be correctly set down in
their true and relative positions.
When the plans of a large extent of country containing several towns and villages have
been taken, the measurements of which differ, they must be reduced to one uniform scale;
and if any marsh or water intervenes, which cannot actually be measured, recourse must be
had to the trigonometric method.
H
- Required the plan of the
B
A
To take the plan of any rectilineal Figure with the Recipiangle.
ground A, of which the figure BCDEFGH has been
drawn, and the length of the sides written along them, as
BC 150, CD 81, &c. First take the angles of the
ground, as BH G, with a recipiangle; then, having mea-
sured it from the angle, retain its opening, and apply the
centre of a protractor to the point where the two branches
cross, and the diameter of the protractor along one limb,
and remark how many degrees are comprised between the
limbs, as 93°, which write down on its corresponding
angle: then, to obtain the re-entering angle, as GFE,
place the head of the recipiangle in the angle required,
and make the two branches of the instrument touch the two sides of the angle; then remove
it, keeping it open, and place a protractor on the point where the two limbs cross, with its
diameter along one of the limbs: the degree intercepted between the two limbs will be the
required angle, GFE, 110°, which write down in the corresponding angle of the drawing:

Fig. 1102.
F
E
CHAP. VIII.
865
GEOMETRY
if the salient angle BHG is required, take it between the limbs of the instrument, and
observe on the demi-circle which is at the head, how many degrees are covered, and the
number, as 93°, will be the required angle. Sometimes cords are attached to the several
piquets, that the recipient may be more accurately applied where the angles are to be
taken.
C
E
L
H
M
D
To draw out the Plan after the Angles are taken, commence with the line AB, which
serves as a scale, and draw it of any length convenient, divided into any number of parts,
as 150°; then at the upper part of the paper draw
the line CD, on which set off 150 parts from
the scale, to answer to the 150 feet of the
scale A B at the point. E draw an angle of
121° equal to BCD on the ground, by placing
the centre of the protractor at the point E, and
its radius turned towards the side to be drawn,
on the plan, and its diameter along the side
CD; count from this line 121°, as to F, and
draw through it a line, FG, which will form
with CE an angle CEG, equal to BCD on the
To determine the side E G, take
ground.
81 parts from the scale A B, answering to the
81 feet from C to D on the ground, and set
them off on the line E G, from E to H. At the

Fig. 1103.
K
N
60
90
8+
120
150
B
point H draw an angle of 113º, answering to the angle CDE on the ground, and set off
on the line HI, 73 parts of the scale, from H to K, to correspond with the 73 feet from D
to E on the ground; then, at the point K, draw an angle H KL, with the protractor of
89º equal to DEF, and set off 55 parts of the scale A B from K to M, answering to the
35 feet of E F: from the point M, draw a re-entering angle, K M N, 110°, equalling EFG,
by placing the centre of the protractor at M, its radius towards the plan to be drawn, and
its diameter along K M, to count 110° from this line on the protractor: continue these
operations for the sides and angles already set down on the rough plan, and the work will
be complete.
A
C.
Q'A
B
L N
! R
P
H
S
M
E
F
Ꮐ
V
T
S
→
h
a
k i
d
X
12
Q
9
e
b
mo"
1
To take the Plans of Streets and various other Places, &c.—To take the plan of a quay near
the river side, draw a scale, as IK, and on a sheet of paper of any length, draw an oblique
line, as at ab, to unite the quay,
A L, which is skewed, the length of
which is to be measured: set off the
same quantity of feet taken from the
scale, from c on the line ab; the line
ac will represent the border of the
quay, AL; after having measured
on the ground how far the descent,
R, is from the barrier, A, take a
like distance from the scale, and
set it off on ab, which will represent
the descent of the point R: then re-
mark that the border of the quay, AL,
makes an angle with the other border,
M N, which angle may be formed by
stretching two cords, ALS and MNP,
along the two borders, which will
intersect at Q, and form the required
angle, LQN, which will serve as a
fixed point: then measure the dis-
tance from the point Q, to the bor-
der of the quay, L, and from the point, Q, to the border, N, and measure the angle, LQN:
then take from the scale IK, the value of the distance LQ, and set it off on the line ab
from c to d, and from this point, d, draw with a protractor adc, equal to LQN, and by
means of the scale set off the distance G N on the line de, from d to f: measure also the
border of the quay, NM; take a like distance from the scale, set off on fe, from ƒ to g,
and do the same for the other parts of the quay. To have the breadth of the quay, place
a square against the parapet, at the openings and descent, RL, MN, &c., opposite the
streets which lead to the quay, with the other side of the square towards the houses, so
that by stretching a cord, RS, along the square, the exact width of the quay may be
obtained: then draw perpendicular lines on the paper representing the quay, and its
descents, he fgn; set off the distances on them of the different breadths of the quay, at
the points i,k,l,m,o, through which draw the line to indicate the width of the street

I
+
Fig 1104.
K
3 K
866
BOOK IL.
THEORY AND PRACTICE OF ENGINEERING.
extent of the houses, &c. Lastly, to have the angles of the
streets, take them with a recipiangle, and their length and
breadth by means of a cord and square; then draw with a
protractor the various angles, as before described, and
set off the breadths and lengths till the whole is com-
pleted. It must always be borne in mind that the three
internal angles of every triangle are equal to two right
angles, and make 180°. In the right-angled triangle,
all its three angles taken together make 180°, as is seen
by the space of a circle described from the point of each
angle, comprised by the sides of the same angle. The
same is the case with the obtuse-angled triangle and the
acute. To have the angle of the centre of a regular
figure, divide 360° by the number of sides of the figure,
the quotient will give the angle.
In the regular hexagon abcdef, to have the central
angle aib, divide 360° by 6, the number of sides of the
hexagon, the quotient will give 60° for the angle,
where it will be seen that whatever number of sides a
regular or irregular figure may have, the central angles
together equal 360°, because they occupy a circle de-
scribed from the centre of the figure, and which is divided
into that number of degrees.
To find the Polygonal Angles of a regular Figure, sub-
tract from 180° one of the central angles, the remainder
will be the polygonal angle.
In a regular hexagon subtract 60°, the central angle,
from 1800, the remainder, 120°, will be the polygonal
angle: multiply 120° by 6, the number of sides in a
hexagon, and we have 720° for the six polygonal
angles.
To have all the polygonal angles of an irregular
figure, it is a rule for those of the same number of sides,
both regular and irregular, that the sum total of the poly-
gonal angles of the regular figures is equal to that of all
the polygonal angles of the irregular figure.

36
48
90
70
a
Fig. 1105.
a
e
115
30
с

360
Fig. 1106.
60
d
If in a regular hexagon six lines are drawn from its
centre to its six polygonal angles, the hexagon will be
divided into six equal triangles; and as already stated,
the three angles of a triangle are equal to 180°: we shall,
therefore, have for the angles of the six triangles 1080°, and as the six central angles of
the hexagon are equal to 360°; if from 1080° we subtract 360°, there remains 720° for
the six polygonal angles of a regular hexagon. By the same rule it will be found that the
six polygonal angles of an irregular hexagon are together equal to 7200, which is easily
seen by drawing lines from its centre to its six polygonal angles, dividing the hexagon into
six triangles, each of which is equal to 180°; we therefore have 1080° for the angles
of the six triangles of the hexagon, and if we subtract 360° from 1080°, there remains
720° for the polygonal angles, which are equal to those of the regular hexagon.
B
1
121
To find in plans laid down, if the sum of the polygonal angles is correct, multiply
180° by the number of sides of the plan; from the product subtract 360°, the remainder
will be the value of all the polygonal angles of the figure.
In taking the polygonal angles of the irregular hexagon,
the addition of the six polygonal angles gives 720, and
if it is not known whether the sum is correct, to ascer-
tain it, by the preceding rule multiply 180° by 6, the
number of sides of the proposed hexagon; from the
product 1080° subtract 360°, the value of all the central
angles, the remainder, 720°, will be the number of degrees
of the six angles of the irregular polygon; and since the
sum of the angles of the polygon which have been taken
agree exactly with this, it proves that they have been cor-
rectly taken.

A
113) D
93
G
150
F
126
E
Fig. 1107.
To find whether the Polygonal Angles have each separately been correctly taken by the
second of the preceding rules it may be found if the polygon is regular; but if not, for
example, in the angle DEF, take on the ground each angle of the complement, by means
of a cord stretched in the line of the angle of the polygon required, and if, by adding toge
ther, the value of these two angles is equal to 180°, it may be concluded that the angle is
CHAP. VIII.
867
GEOMETRY.
correctly taken; but if the sum of the addition is more or less than 180°, measure the angles
again, to ascertain whence the error has occurred, and by successive operations correct it.
B
H
41
טן
16
121
103
D
A
16 E
G
150
100126
117
33
F
To find the salient and re-entering Angle of a Plan, if correctly taken, it is requisite
to ascertain if the right angles of the irregular plan are equally so, viz. the salient
angle, IBD, 76°, the re-entering angle B DC, 121º the
angle DCE, 103°, CEF, 1130, EFG, 89°, the re-entering
angle FGH, 110°, GHI, 117°, and the salient angle
HIB, 93°. Trace outside the two re-entering angles the
lines BC and HF, which form an artificial boun-
dary, BCE FHI; measure all the angles of this
as if it were the true one, except the two CEF, 113°, I (93
and HIB, 103°, which are already known, and having
found, by taking these angles, that IBC is 117°, BCE
121°, EFH 126°, and FHI 150°, which, together with
the two angles CEF, 113°, and HIB, 93°, make 720°;
then this shows that the angles are properly taken, be-
cause the polygonal angles of a hexagon, whether regular or irregular, together make
720°. But since the artificial boundary B CEFHI has the angle IB C, 117°, greater than
IBD, 76°, BCE, 121º, greater than DCE, 103°, EFH, 126°, greater than EFG, 89°, and
FHI, 150°, greater than GHI, 117°, therefore we must ascertain if the four angles IBD,
76°, DCE, 103°, EFG, 89°, and GHI, 117°, are correctly taken. For the first two angles
IBD and DCE, measure in the artificial triangle BCD, the angles DB C, 41°, and
DCB, 18°; then subtract DBC, 41°, from IBC, 117°; the remainder, 76°, being equal to the
angle IBD, as measured, shows it has been accurately taken. If from the angle BCE,
121°, the angle DCB 18° is subtracted, there will remain 103° for the angle DCE.
Pursue the same course for the angle EFG and GHI, and the first will be found 89°, and
the second 117°.

Fig. 1108.
To ascertain if the re-entering angles are properly taken, beginning with DB C, add
to the artificial triangle B CD, the two angles DB C, 41°, and DCB, 18°, subtract their
sum 59° from 180°, the remainder, 121º, will be the value of the re-entering angle B DC,
which was before found the value of that angle: the same rule must be followed for the
artificial triangle GFH, to ascertain if the re-entering angle F G H, 110°, has also been cor-
rectly taken. Lastly, to verify the two angles CEF and HIB, have recourse to the method
before given, by using the complement of the angle
T
K
B
D
A
E
F
Taking the Plan of Places wholly or the part of
a circular figure: such a plan must be enclosed
within a cord, or in some other manner, so that
it may touch the enclosure as much as possible,
as in the figure BCDEFGHIKL: if the en-
closure or boundary is very irregular, and full of
retreats or sinuosities, as the lower part of the plan,
their exact plan must be taken independently:
then remark where the two cords of the artificial
boundary form an angle, as at G, and stretch
another cord BV, through the middle of the
angle, to the undulations of which measure the
length; then stretch cords from the sides of the
angles to the undulations, at right angles to the
sides, the length of which must be written down,
as well as their distances from each other. If the
artificial boundary whose plan is required has
towers, or other projections, they must be sur-
rounded by cords, and the length of their sides and angles figured down, that their circum-
ference may be defined: to lay such a plan on paper, draw a circle of any length or divisions,
as 180 feet place on one of the sides the length BC, 180 feet; draw with a protractor from
the point C, the angle B CD, 101°: continue to draw in succession the length of the sides
and angles, until you have the measurement of the whole of the artificial boundary.

R
H
Fig. 1109.
V 8
To have the Circular Boundary, observe at what distance from the angles the rea.
boundary touches the lines shown by the cords, as at the points M, N, O, P; then take from
the scale their relative distances, and mark them on the sides of the artificial boundary
through which the real outline must be traced.
To have the Circular Boundary correct, observe that the angles of the artificial boun-
dary are divided into two by a right line drawn from the angle to the boundary, the
length of which is figured; this must also be set out on the paper at the respective angles :
remark also, that to the right and left of each angle of the artificial boundary, where cords
are stretched, their distance and length must be set down; and when these lines are properly
laid down, the natural boundary may be traced through them.
3K 2
868
Book II,
THEORY AND PRACTICE OF ENGINEERING.
X
B
K
Fig. 1111.
N
C
E
12338
26
60
LOS
160
01
D
G
A
28
82 F
66
76
*15
86
67
H
Fig. 1110.
M
T
L
R/Q
To trace on the Ground a Plan drawn on Paper. Having
drawn on paper the plan to be laid down, the angles of
which are indicated by the letters BCD, E FG, HIK:
drive a stump into the ground at the point where it is in-
tended to have one angle of the plan, as at L, where
a cord LM must be stretched, towards the place in-
tended to trace the plan; on the line set off LM, 52
feet from L to M, answering for the 52 feet from B to C;
and at this point N, drive a large stump into the ground;
above the large stump or piquet, place a demicircle with its
diameter in the line LN, for the purpose of forming the
angle LNC, 123º, equal to BCD on the paper, setting off
also 36 feet from N to P, the length of CD: drive another stump into the ground
at P, and stretch a cord horizontally between the two piquets P and N; drive other stumps
between the two, and mark the two lines forming
the angles on the head of each stump: at the
point P draw a re-entering angle NPQ, 105º,
to equalise CDE, and set off 86 feet on PQ,
from P to R, answering to DE on the plan; and
continue in the same manner to form the angles,
RFN, RST, STL, &c., according to the plan,
with the lengths of their sides: when there
are re-entering angles on the plan, take care
to observe if the sides of the plan on the
ground agree with those on the paper, which may
be rectified by means of fixed points; for ex-
ample, if the side RS was prolonged, it would
exactly fall on the side TV, at the distance of
15 feet from V in L, as is marked from H to X,
on the side HG of the plan; if it falls near T,
some of the sides or angles are too small, if near V the contrary is the case.
Drawing and measuring Angles on the Ground by a divided Port Crayon
and two Cords. The divided port crayon may be of any length, from
5 to 6 inches, and ¦ of an inch square; the longest are the most conve-
1/4
nient, on account of the two equal and parallel lines engraved on them:
the line BC must be divided into 180 equal parts, according to the line
of chords on a sector; and DE, which is parallel to it, and of the
same length, should be divided into 60 equal parts: the two cords may be
made of fine twine about 36 feet long, as F, G, H, which must be divided
into two at G, and a ring attached there; and also its two extremities, F
and H, made large enough to receive a small stump; divide FG and G H
each into 30 equal parts to serve as feet, &c.: the second cord FI,
which is longer than the first, must
be divided into 60 parts, equal to
those on the other cord.
draw an angle on the ground,
as one of 40°, at fig. 1115, plant
a stump at the point where the
angle is to be drawn, pass the
ring G of the cord over the
stump, stretching the side FG 22
towards the place it is required
to fix one side of the angle, and
drive a stump through the ring
F; then remark the port crayon
on the line of chords BC, where
40° coincides with the line DE,
divide into 60 equal parts; having
observed that it is at the 21st,
stretch the cord FI, until its 21st
point touches the ring H, where a
stump must be driven; so that on taking up the cord the stump FGH remaining, the
three points of the required angle are given.


16
17
15
To
18
14
27
26
19
25
28
20
12
11
24
29
19
13
21
330
#
15
1
23
16
24
17
20
18
19
26
27
F
28
29
30
Fig. 1112.
21
A

B
D
30
10
120

6030
70
80
22
10
90
300
110
180
130
110
150
180
60
770
E
Fig. 1113.
One cord may be considered as passing the whole length of the spiral figure, its first ring
at H, its second at G, and a third at the extremity, F, comprising 60 feet: the other cord
containing 30 feet, or half the former quantity, has one ring at H and the other at G; by
the application of these two cords angles may be set out on the ground: sometimes, instead
CHAP. VIII.
869
GEOMETRY.
of the port-crayon a flat piece of brass or wood is divided longitudinally into two columns,
called BC and DE; the first is marked with the 180 degrees, as taken from the line of
chords on a sector; and on DE are arranged the 60 equal parts; when these columns ave
placed side by side it is more easy to read them off.
This instrument is now seldom made use of, but in France it was much employed,
and considered sufficiently accurate for all ordinary surveys, or for setting out angles either
salient or re-entering: spiral lines were frequently set out with it, and the gardener em-
ployed under Le Nostre marked out the fanciful forms which were then in fashion with
this simple instrument.
M
To measure salient and re-entering Angles, as that of the angle LMN, drive a stump
at M, over which place the
ring G, straining FG and GH
against the sides of the angle,
and drive a stump into each of
the rings F and H.

Stretch the cord FI, which
must be attached to the stump
F, until it touches the extre-
mity H of the cord F G H, and Q
remark how many divisions of
the cord FI there are from F
to H; then note on the line
DE of the port crayon what
division or degree of the line
which answers to 50, as 112,
which will be the required
angle. To find the salient
angle OPQ, either prolong OP
to R, and QP to S, to form
F
R
Fig. 1114.
G
N
P
G

40
H
F
H
F
E
Fig. 1115.
G
A
8
the re-entering angle RPS, which may be measured by the preceding rule; or place the
ring G of the cord at the salient angle P, and stretch the side GF along QP, and GH
along OP, of the salient angle OPQ; so that by measuring with the divided cord the
distance FH, number of divisions are obtained, which sought on the line of cords denote
the degrees of the angle RPS, as well as the salient angle OPQ, which is equal to it.
To reduce or enlarge a Plan on a given scale without using a
scale or protractor: as, to reduce the plan A, which has for its
base FE, to another plan having the base HI. Draw a line
K L, and from the point K as a centre, with the base FE as
a radius, describe an arc NM, on which set off the given base
HI from N to O, and draw a right line KP through 0: take
the distance F G from the plan A, and describe from the point
K, an arc QR, of which take the chord RQ, and from the
point H of the given base, describe with this distance the arc
S: from the plan A take the distance EG, and from the
point K describe the arc TV, of which take the cord VT,
and carry to the point I of the given base HI; and from this
point I describe the arc X, which will cut the arc S in Y;
from the point H, draw a right line
HY to the point Y, which will make
the side HY homologous or relative
to FG, on the plan A: to have the
side relative to GB, it is only neces-
sary to follow the same rule, that is
to say, from the point K, with the
distance GB, describe the arc ab, and
carry its chord ba, to the other point
Y, the extremity of the line HY, and
from the point Y describe the arc c;
then take the distance EB, from the
plan A, and with it describe an arc
from the point K; so that by taking
its chord ed, from the point I of the
given base an arc may be described, and
observing where the arc cuts c, as at g;
then draw the line Yg, which will be homologous to GB. All the other relative sides may
be found by the same rules, so as to reduce the plan A to another whose base is HI; by
this means, plans may be diminished or increased, provided the base is not double the other

ROZ
K

b
N
V
L
Fig. 1116.
T
H
S D
X
DY
Fig. 1117.
g
C
3 K Y
870
Book II
THEORY AND PRACTICE OF ENGINEERING.
F
H
G
A
To draw by means of a Scale and
Protractor a Plan, greater, equal, or
smaller than a given Plan.—It is
required to copy the plan A, which
is bounded by six sides, B C, DE,
&c.; the scale H being divided into
100 parts of the same size. Draw
a scale K of the same length as H,
viz. into 100 parts; measure how
many parts of this are contained by
the side BC, as 80; draw the line
LN, on which set off 80 parts, as
taken from the scale from L to N :
then with the protractor measure
the angle CB G of 117°, and draw
another equal to it at the point
N, having its diameter along LN,
and count 117 degrees on its circum-
ference, beginning at L; having removed the protractor,
draw the right line N P, off 60 equal parts, to answer to
the side BG; at the point P draw the angle NPQ
equal to BGF on the plan A, and set off as many
parts on PQ as are equal to G F on the plan A: con-
tinue to draw the relative sides and angles of the
plan A, until you have the plan LNPQRS equal
to it.
E
Fig. 1118.
Copying Plans by means of Squares. To copy the
plan A, it may be inclosed in squares, as HIKL:
divide the two opposite sides HI and KL into the
same number of parts, as into five, and draw right
lines through the opposite points of these two lines :
divide also the sides HL and IK into any num-
ber of parts, and draw lines through the opposite
points, which crossing the first will form several squares.
To copy the plan A precisely the same size, draw
the squares equal, and then tracing the map or plan
through all the corresponding parts, they will be alike.
If it be required to copy a plan without drawing,
squares on the originals or on the copy, fine threads
stretched across may be made to answer the same pur-
pose, and on the paper on which the drawing is to be
made, fill up the squares in the manner of the original:
thus the copy may be completed without ruling any
lines on the original.
G
B
R
C
P


K
I
Fig. 119.
A
H
1
C
B
1
2
3
4
5
6
7
E
8
F
L
Fig. 1120.
N
M
1
2
3
4
5
Q
7
པ
8
Fig. 1121.
LO
L
L

K
P
D

The Cross Staff is commonly of copper or brass; there are both simple and com-
pound: the simple one, A, is a circle of brass, 4 or 5 inches in diameter, divided
by two lines at right angles, which have their extremities mounted with sights; the
space between the arms is hollow, to render it lighter, and more portable; below the
cross is fixed a joint with a dowel to fit into a socket joint, fixed on the staff which
supports it.
The cross staff, F, is compound, 6 or 8 inches in diameter; it has four sights, and
an alhidade is fitted to its centre by a two-headed screw, as KL, whose extremities
H
K
A
B
AR
A
L
F

요
​

Fig. 1122.
Fig. 1123.
Fig. 1124.
K
G
CHAT. VIII.
871
GEOMETRY.
are charged with sights, and work on a circle described on the cross, which is divided into
360 degrees. This alhidade serving to form angles has a magnetic needle at its centre,
to mark the point of the compass, by placing one side of the square against the object to be
taken. When the double cross has not an alhidade, four more sights are screwed in the
intervals of the others, so that the cross has eight sights: it is to be remarked that large
squares are to be preferred to small, as they direct the visual rays better.
To ascertain whether the cross staff is accurate, mount it on its stand, and plant it on a
level piece of ground; then, boning by the sights A C, place a piquet with its card in
the line with the visual ray; and, without removing the cross staff, bone through the
sights C, A, and plant a piquet H in the visual ray; bone through all the other sights,
and if they cut the same points, as well as the piquets placed at right angles, it may be
considered correct.
A
To measure acute-angled Triangles.-Let fall from an angle of the triangle a perpendicular
to the side opposite the angle, and multiply this perpendicular
by the length of the side opposite the angle; half the product
will give the content or superficies of the triangle required.
To measure the acute-angled triangle ABC, plant piquets at
A B C, and place the cross staff at some point on the
side BC, so that by looking along the sights of one diameter,
the two piquets B and C may be seen, and without removing
the staff, look also at the piquet A, through the sights of the
other diameter; if at D it cannot be seen, the staff is too
far to the right, and must be advanced to the left, as at E;
then from the point E the two piquets B and C may be seen
through the two sights of the diameter, which is in a line with
BC, and through the other sights the piquet A; measure the
perpendicular EA, which is 24 feet, and BC 52: then mul-
tiply the length EA, 80 feet, by BC, 52, and take half the
product 4160, we have 2080 superficial feet for the content of
A B C, the acute-angled triangle.

It is very
To measure right-angled Triangles.- Multiply the two sides
which form the right angle together, and half the product will
be the superficial content. Measure the side BC, which is 144
feet 5 inches, and A B 125 feet; multiply 144 feet 5 inches by
125 feet, and the product 18104 feet 6 inches divided gives
9052 feet 3 inches for the superficial content. For if a parallel-
ogram and triangle be upon the same base, and between the
same parallels, the parallelogram will be double the triangle,
as shown by Euclid in his 41st prop. Book I.
manifest that triangles are the halves of parallelograms upon the
same base, or upon equal bases and between the same parallels :
and because these parallelograms are equal to one another, the
triangles which are their halves are also equal: on this account
it is said that the rectangle is equal to the product of its base
and altitude, and the triangle to half the product of its base and
altitude. When the two straight lines which form a rectangle
are of such a length that one contains exactly the same number of
feet or divisions that there are in the other, or side adjoining it;
then the rectangle under these two straight lines is contained as
many times in the given rectangle as is expressed by the product
of the two numbers, which denote how often the feet or divisions
are contained in the two sides.
To measure obtuse-angled Triangles. After having planted
piquets at the three angles A, B, C, place the cross staff at some
point on the side BC, as at D, in such a manner that by look-
ing along the sights of one diameter, the two piquets B and
Care seen, and by those on the other diameter the piquet A ;
if the piquet is not seen, the square is not exactly opposite
the angle A, and must be advanced to For E. Then measure
the perpendicular F A, which is 220 feet, and BC 663 feet,
which multiplied produces 145860, the half of which, 72930,
feet is the superficial content required.
To measure inaccessible Angles.-First find by the trigono-
metric rules the length of the sides of the triangle, viz. AB
68, BC 70, CA 28, and draw a similar triangle DHE;
raise a perpendicular on the side DE, as HG, and proceed
as before described.
3 K 4
B
A
C
B.
C
A
C
D
E
Fig. 1125.
Fig. 1126,
A
Fig. 1127.
E
Fig. 1128.
D


E
3

R
872
Book II
THEORY AND PRACTICE OF ENGINEERING.
To measure any Triangle, as that of
ABC. Multiply the length of BD,
the perpendicular, by the base AC,
and half their product will be the area :
this will be evident if we observe that
in measuring the square we multiply
the two sides which form a right angle
together; the product will be the area
of the square, as that of A B C D.
In any triangle the difference of the
squares of the two sides is equal to the
difference of the squares of the seg-
ments of the base, or of the two lines
or distances included between the ex-
tremes of the base and the perpendi-
cular. Let ACB be any triangle,
having BD perpendicular to A C, then
will the difference of the squares A B,
A
B

1
D
C
Fig. 1129.
A
B

C
D
Fig. 1130.
BC be equal to the difference of the squares of AD, CD; that is, A B³ — CB³ —
AD2-CD2.
For since A B² is equal to A D³+B D³,
and CB2 is equal to CD2+ BD²,
therefore the difference between A B² and CD'
is equal to the difference between A D²+BD2,
and CD2+ BD,
or equal to the difference between AD and CD2, by taking away the
common square BD2.
The rectangle of the sum and difference of the two sides of any triangle is equal to the
rectangle of the sum and difference of the distances between the perpendicular and the two
extremes of the base, or equal to the rectangle of the base and the difference or sum of the
segments, according as the perpendicular falls within or without the triangle.
To measure Rhomboidal Figures. Let fall a perpendicular
from one angle to the opposite side, and this perpendicular
multiplied by the side gives the area required; but when
this cannot be done, prolong one side; let fall a perpen-
dicular on the side of the rhombus, and proceed as before.
A
C
B

For example, to measure the rhombus AB CD, whose
side A B is 30 feet long; as this figure has no right angle,
it is necessary that one should be established; this is effected
by placing the cross staff on CD, in such a position that a
piquet at A may be seen through one of the pinnules on
one diameter, and DC through those of the other, as at E;
then measure the perpendicular, 27 feet, which multiplied by 30, the length of the side AB,
produces 810 feet as the superficial area of the figure A B C D.
To measure a Trapezium. Add together the two
parallel sides, and multiply their sum by the length of
a perpendicular line contained between their two
sides, and which is the height of the trapezium; the
product will give the area.
D
E
Fig. 1131.
F

K
Fig. 1132.
H
To ascertain the content of the figure FGHI,
where the two sides FG and IH are parallel, the
shortest being 30 feet 9 inches, and the longest 60 feet:
place the cross staff on IH, as at K, so that through
the pinnules of one diameter the piquets I and H may be seen; then through the other
view the piquet F, where KL, which is 20 feet, is the perpendicular. Add together the
two parallel sides, which will be 90 feet 9 inches; this multiplied by 20 will produce 1815
square feet, the half of which will be the area sought.
M
R
To measure the Trapezoid MNOP, whose side MN is 4
feet. Plant piquets at the four angles: draw from the
angle P the diagonal PN, which will divide it into two
triangles; find their superficial content, and add them
together for the area of the trapezoid. For example, find
the area of the triangle PN M, the base of which, PN, is 6
feet 6 inches, and the perpendicular R M 2 feet; these mul-
tiplied together produce 13 feet, the half of which, 6 feet 6
inches, is the area of the triangle; proceed in the same
manner for the area of the other part of the figure, and add them together.
P
Fig. 1133.
N

CHAP. VIII.
879
GEOMETRY.
Add all the sides
To measure a regular Polygon.
together, and multiply the sum by a perpendicular let fall
from the centre to one side; half the product will be the
area.
To find the superficial content of the pentagon ABCDE, E
measure one side DC, which is 22 feet, and then multiply
it by 5, the number of the sides: multiply its product 110
by 15, the height of the perpendicular FG; take half this
product of 1650, which is 825 superficial feet, for the area.
When the figure is inaccessible, surround it by the square
or rectangle FGHI, whose side FG is 35 feet 3 inches, and
FI 33 feet 6 inches 4 parts; when these two sides are mul-
tiplied together, their product will be the area of the rect-
angle: then measure the four triangles FAE, AGB,
EDI, and BHC; when their areas are found and added
together, deduct the sum from that already found for the
whole rectangle, and the remainder will be the area of the
pentagon. Similar polygons inscribed in circles have, as we
have already seen, their perimeter in the same ratio as the
diameters of those circles; for if we imagine the number of
sides to be infinite, or so numerous that they coincide with
the circumference of the circle, then the perimeter of such
a polygon may be regarded the same as the circumference
of the circle.
To measure an irregular Poly-
gon.
Plant piquets at all the
angles of the irregular polygon,
and one in the centre of the
figure, in order that cords may
be stretched from thence to the
angles; by this means the ir-
regular figure will be divided
into triangles, which may be
measured separately, and the
whole added together.
F
E
Fig. 1136.
G
E
B
F
C
F
E
D
υ
Fig. 1134.
D
A

B
F
G
A
G

Fig. 1135.
A
Fig. 1137.
•
B
H
B


D
C
To measure the irregular hexagon ABCDEF, plant piquets at all the angles, and one
in the centre; then stretch cords to the several angles, and when they are defined the
lengths of their sides may be obtained, and their areas found, which added together will be
that of the whole.
If the hexagon ABCDEF
has a piece of water in the cen-
tre, and is inaccessible, then
cords may be stretched from op-
posite angles, and by this means
measured, and the area found.
If the entire area is inaccessible,
then the whole figure may be
bounded by a rectangle, and all
the outer angles measured.
as
In measuring land, take
few dimensions as possible;
measure, for instance, FC, and drop
perpendiculars from A, B, D, E,
and measure them. If the
figures are very irregular,
GHIKLMN OP Q R S T V X,
form it into trapeziums and
angles.
as
It must always be borne in
mind that a vast number of small
figures tend to confuse the sur-
veyor and render his calculations
more difficult; it is therefore ad-
visable not to have a greater
number of triangles than is abso-
lutely necessary, for in finding
their area it is impossible to avoid
E
D
Fig. 1138.
A
P
B
N
S T

X
R
V
G

M
Fig. 1139.
K
H
874
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
fractions or decimal quantities, which, when added or taken away, often materially affect
the whole quantity.
To measure the Circle. This cannot be
done in any other manner than by ap-
proximation, as we cannot find the quadra-
ture of the circle, or the superficial con-
tent of a square, which shall contain
precisely that of a given circle.
If a
triangle A has three equal sides, each 14
feet 8 inches long, its circumference will
be 44 feet: if the square B has each of
its four sides 11 feet long, its circum-
ference will be 44 feet; and if the circle C
has its circumference 44 feet, these three
figures will be isoperimetrical. If you
measure the triangle A and the square
B by the rules given already, you will
find that the square contains 121 feet
superficial, the triangle 45 feet 4 inches,
and the circle 154 superficial feet.
Of
all who have written on the subject, none
have given rules which approximate
nearer to truth than Archimedes; he
states the circumference of a circle is 34
the diameter, that is to say, the circum-
ference ABCD will be 22 feet if its
diameter AC is 7 feet, so that the
diameter is to the circumference as 7 to
22, and the circumference to the diameter
as 22 to 7. This is shown in the circle
ABCD, which, reduced to a straight
line, as AF, is three times the diameter
A C, and of FE.
The second approximation is that the
area of a circle is equal to a right-angled
triangle formed of the circumference and
radius of a circle; that is to say, the
right-angled triangle GIH contains the
same area as the circle K, because the
triangle has its side HI equal to the cir-
cumference of a circle, and GH, which
forms a right angle with it, equal to the
radius GK. The other supposition of
this great mathematician is, that the
superficies of a circle is to the square of
its diameter as 11 to 14; that is to say,
if the circle M contains 11 superficial feet,
the square HPON drawn on its dia-
meter will contain 14, and it will be
seen that the circle Q, inscribed in the
square RSV T, is less than the square by
a certain quantity.
P
H
R
T
A
Fig. 1140.
Fig. 1141.
C
B
M
Q
Zon
H
A


1
G
Fig. 1143.
N
S
A
V
Fig. 1142.
D
Fig. 1144.
K
F
442
E
B



B
The relation of 7 to 12, which Archimedes gives as the ratio of the diameter of a circle
to the circumference, holds good with a greater number of figures, as of 100 to 314, and
the larger the number of figures the nearer is the truth approached.
To find the Circumference of a Circle when the Diameter is given. By proportion, place in
the first term 7, in the second 22, and in the third the length of the diameter: the quotient
will give the circumference. If we require the circumference of the circle ABCD,
according to Archimedes, we should place for a first term 7, for the second 22, and for a
third the length of its diameter; the quotient would be the circumference sought: if the
diameter be 15 feet for instance, then, 7: 22 :: 15: 47 ft. 1 in. 8p.; or, 100: 314: 15:
47 ft. 1 in. 2 p.
To find the Diameter of a Circle when the Circumference is given. Place in the first term
22, in the second 7, and in the third the known circumference, and the quotient will be the
diameter.
To find the Area of a Circle when the Diameter is given. First find the circumference, and
CHAP. VIII.
873
GEOMETRY
multiply it by the radius, and half the product will be the area: or, multiply the square
of the diameter by 7854, and the product is the area.
To find the Area of a Circle when neither the Diameter nor
the Circumference are given. When the arc E C F is given, to
find the area of the circle ABCD: draw the chord or
right line EF, and divide it into two equal parts, from
whence draw a perpendicular G C, and measure FG; then
multiply E C by itself, and divide the product by GC; the
quotient will give E G, to which add GC; the sum will be
the diameter AC: then by proportion proceed as before
described.
To measure a Circular Ring, as ABCD.-First ascertain
the area of the whole circle, and then of the part contained
in the lesser one, and deduct one from the other; the
remainder will be the area of the ring.
The diameter of the interior circle we will suppose 9 feet;
its circumference then will be found to be 28 feet 3 inches
5 parts; and if we consider the breadth of the circular ring
to be 3 feet, we shall have 15 feet for the diameter of the
outer circle, the circumference of which will be 47 feet
1 inch 8 parts; the arc of this circle will be found equal to
176 feet 3 inches: if we then deduct from it the area of
the inner circle, we shall obtain superficial content of the
circular ring.

B
The areas or spaces of circles are to each other as the
squares of their diameters or of their radii, for, as before
observed, similar polygons inscribed in circles are to each
other as the squares of the diameters of the circles; for,
conceiving the number of sides of the polygons to be in-
creased more and more, or the length of the sides to become less
and less, the polygon approaches nearer and nearer to the circle,
till in the end it coincides and becomes in effect equal; hence
the areas of circles, which are the same as polygons, must be
to each other as the squares of the diameters of the circles.
To find the Area of a Spiral. Add together the exterior and
the interior circumference, and multiply their sum by the breadth
of the band, and half the product will be the area. To measure
such a spiral as A, whose breadth BH is 3 feet, its exterior cir-
cumference BCD 25 feet 1 inch 8 parts, and its interior 15 feet
8 inches 7 parts; add these together, and multiply their sum, 40
feet 10 inches 3 parts, by 3 feet, the product of which divided will
give the area of the band.
B
Fig. 1145.
Fig. 1146.
To find the Area of Sectors. Multiply the arc CDE by BC,
the radius of the circle; take half the product, which will be the
superficial content of the section. By the same rule the area of
the sector X may be ascertained; for example, to measure the
figure A, we multiply the arc CDE, 15ft. 8 in. 6p., by DC 7 ft.
6 in. which is the radius of the circle. Half the product will be the
content of the segment; and if, on adding the area of the sector
X, we find the sum equal the content of the whole circle, we
are sure that the calculation is correct.
The sector of a circle is a portion of the area of the circle
bounded by two radii and the intercepted arc, and sectors are
said to be similar when the sides or radii include equal angles.
The area of a sector, then, must be equal to that of a triangle
whose base is equal to the length of the contained arc, and
altitude equal to the radius of the circle.
A
C
F
G

D
K
A
H
B
C
Fig. 1147.
F
X
Fig. 1148.
B
C
A
D
B
E
F
C
E
A
D
D



To find the Area of a Segment.— Form on the arc CDE a
sector BEDC, and find the area by the preceding rules; then
find the area of the triangle, and subtract it from the area of the
whole; the remainder will be the area of the segment. For
example, the line CE, 12 feet 5 inches 8 parts, and its arc CDE,
12 feet 8 inches 6 parts, to ascertain its area: form on the arc
CDE the sector BEDC, and find its superficies; then that of the triangle BE C, and
subtract it from the area of the whole sector, when the remainder will be that of
the segment A. Should the segment be small, add half the length of the chord to the
height of the arc, and multiply the sum by the whole height of the arc.
Fig. 1149.
876
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
To find the Area of an Oval.-Multiply the length of the
greater diameter CD by the lesser EF; their product will
serve for the third term, whose first is 14 and second 11;
the quotient will be the area sought: or, multiply the two
diameters together, and their product by 785, which divided
by 1000 gives the area: or, multiply the two diameters toge-
ther, and extract the square root, which will be the diameter
of a circle whose area is equal to that of the ellipsis.
To find the Area of a Sphere or Globe. Multiply its cir-
cumference by the diameter; the product will be the superficial
content; or, the surface of a sphere is equal to the diameter squared,
multiplied by 3.141593, and the surface of a spherical segment is
equal to the circumference of the sphere, multiplied by the height
of the segment: the sphere is a solid bounded by one curve
surface, which is everywhere equally distant from the centre; it E
may be conceived to be generated by the rotation of a semicircle
about its diameter, which remains fixed: the axis of the sphere
being a right line about which the semicircle revolves, and the
centre the same as that of the revolving circle.
Archimedes gives another rule for finding the superficies of
a globe, which is that of multiplying the superficies of their great
circles by 4; thus in the globe A the area of its greatest circle
is 176; this multiplied by 4 gives 704 for the superficial content.
The diameter squared, its product multiplied by 314, and then
divided by 100, the quotient will be the superficies of a sphere.
There are some peculiar properties belonging to spheres; for
two will cut one another, or touch one another, or one of them E
will fall wholly without the other, according as the distance
between their centres is, first, less than the sum, and greater than
the difference of their radii; secondly, equal to the sum, or to
the difference of their radii; or thirdly, greater than the sum, or
less than the difference of their radii; for the sections of two
spheres made by a plane passing through their centre, and through
any point which is supposed to be common to the two surfaces,
will be circles having the same radii and centres with the spheres
respectively. If two spheres cut one another, they do so in a
circle, the plane of which is perpendicular to the line joining their
centres, and its centre is that line. If three spheres be described
whose centres do not lie in the same straight line, the surfaces of
the three cannot have more than two points in common, which
points lie in a straight line perpendicular to the plane of the
centres, and at equal distances on either side of that plane. If
the centres of three spheres lie in the same straight line, their
circles of intersection cannot meet one another, because their
planes are perpendicular to this straight line, and therefore
parallel and accordingly, the surfaces can have no point in com-
mon, unless each of them passes through the same point of the
straight line in which the centres lie, for then each of them will
touch the other two in that point. When a point is equally dis-
tant from the three angles of a triangle, it must lie in a perpen-
dicular to the plane of the triangle, which passes through the
centre of the circumscribing circle.
To find the superficial Content of Segments of Spheres.-Multiply
the circumference of the entire sphere by the axis A of FG for
the area.
E
A
E

F
Fig. 1150.
B
A
D
Fig. 1151.
B
<<
C
A
F
C
G
D
Fig. 1152.
B K
G
H
C
D
L
Fig. 1153.
B
Сс
H
G
F
D
Fig. 1154.
E
D



To measure the superficies of regular zones, as of BKDL, we
must multiply the circumference by the height of the segment.
The superficial content of the irregular zone BCED may be also found by ascertaining,
first, those portions which are of a regular breadth, and then those which are not.
If we
Suppose it is required to ascertain the superficial content of the zone BCDE, the
diameter of which is 15 feet, and the greatest circumference 47 feet 1 inch 8 parts.
follow the rules already laid down, we shall find the area of the great segment CEF, which
is formed from the segment BDG, and the irregular zone BCED, by multiplying the
circumference of the globe BCEDFG by the length of the part of the diameter FI
comprised within the great segment CEF, which will give 565 superficial feet for its
content. Then, after subtracting the superficial content already found, of the smaller
segment BDG from that of the great segment CEF, there will remain 329 superficial feet
for the area of the irregular zone BCED. which surrounds the globe.
CHAP. VIII.
877
GEOMETRY.
To find the Superficies of Cones, it is only necessary to mul-
tiply the length of the side by the circumference, and take half
the product. Thus in the cone A, whose side B E is 24 feet,
and the circumference of the base BCD 19 feet, 24 × 19 =
456
228. To measure the superficies of the truncated cone
2
A, whose diameter at the base BE is 8 feet, and at CG 6 feet:
add together these diameters, and take the half for a mean,
which is 7 feet; this multiplied by 8, the length of the side BC,
gives the product 56, from which the square root is to be ex-
tracted.
can
It must be borne in mind that
with a radius of 7 feet 6 inches,
which is equal to HI, we
describe a circle HKLM, which
shall contain an area equal to the
superficies of the cone A.
To find the Area of a Cylinder.
Multiply the height by the circum-
ference; the product will be the
area, to which add that of the two
ends.
K
H
I
L
Fig. 1155.
M
Sub-
F

A

B
D
C
C
D
A
B
E
F
Fig. 1156.
L
To measure the cylinder A, multiply the height B C, which is 21 feet, by the circum-
ference CDE, which is 44 feet, and the product, 924 feet, will be the superficies of the
cylinder, without comprising the area of the two ends.
If the cylinder be irregular, as that at F, multiply
the less height, I K, 13 feet, by the circumference,
GHI, 44 feet, and the product will be 572.
tract the shortest height, IK, 13 feet, from the
longest, GL, 21; multiply the remainder, 8, by the
circumference, and take half the product, 176, and
add it to 572, which will be 748, the superficies of
the cylinder.
Mixed or irregular Figures, as ovals or parabolas,
must be divided into small segments, triangles, and
squares before their area can be ascertained. The
oval shown at A for instance may be divided into
two segments, BCF
and BCG, and the area
found by the preceding
rules.

Figures bounded by
several curved lines
must be enclosed with-
in a triangle, as that at
FDBG, by the lines
I and K: the area of
the equilateral triangle
being found, the seg-
ments may be after-
wards found, and their
area deducted: when
the form is very much
varied, as that com-
N
H
M
Fig. 1159.
K
D
I
A

B
K
F
C
E
1
G
D
H
Fig. 1157.
K
Α
B
F
H
L
Fig. 1160.
G
prised within the irregular line HIKLMN, it must be similarly
treated, dividing it into triangles, segments of circles, or any
other regular figures.
On
Fig. 1158.


E
B
On flut and round Superficies.We at once see in the diagrams
G and II the effect of houses so placed that they radiate from
a centre, and are drawn perpendicular to the base line.
hilly or mountainous land no more grass or trees can grow than
would do on its base if the whole were levelled: trees rise
perpendicular, or tend to the centre of the earth, and not to the
surface on which they stand; consequently the superficial con-
tent or area of a mountain is that of its base; so it is with a field,
where no more blades of corn can stand upon uneven ground
than would on the level plane comprised within the same boundary
Fig. 1161.
Fig. 1162.
AF

G

G
H
In carrying a fence
878
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
over a hill composed of upright paling, we shall discover that, although more rails might be
required to pass over the convex surface, as there are more houses shown on G than on H,
there would not be more posts or upright pales.
The conversion or reducing of Plane Figures of one kind to that of another is found ex-
tremely useful in practice, as it often saves considerable trouble in the calculation, par-
ticularly where they are very irregular: this subject has not
received the attention it demands in the ordinary works which
treat upon the measurement of land.
To reduce a Triangle to a Rectangle. If the triangle be
equilateral, as A B C, and it is required to form a rectangle on
the side CB; divide the other two sides AC and AB into
two equal parts in the points D and E; through them draw
the line DE, parallel to the side CB: from the point A drop
a perpendicular A F to CB; remark where it cuts DE at G;
set off DG from D to H, and EG from E to I; draw the
right lines HC and IB: the parallelogram HIBC will be
equal to the equilateral triangle A B C on the given side CB.
A

H
G
E
C
To reduce a Rectangle to a Triangle, as the figure ABCD to an
isosceles triangle. Bisect the base DC of the square in E, and
elevate a perpendicular E F, twice the length of the side of the
square; draw the upright lines FD and FC; the superficies of the
isosceles triangle will be equal to that of the square.
If it be required to reduce the parallelogram GHIK to a scalene
triangle, it is only necessary to divide the base of the parallelogram
into two unequal parts, as at L, and elevate
a perpendicular LM, twice the length of
the side of the square; then draw the right
line MK and MI: the superficies of the
scalene will be equal to that of the rectangle.
G
K
M
Fig. 1164.
To elevate or depress a Triangle on
given length, without altering its superficial
content, as to elevate the point A of the
triangle A B C, so that it may be at the dis-
tance DE from the base C B. Draw a per-
pendicular to the base CB, through the
point A, and set off the given length from F to G, and
draw a line HI through G at right angles to FG; prolong
A C until it cuts HI in K; from this point K draw a right
line KB; make AL parallel to KB, and draw the right line
KL; the triangle KLC will be equal to ABC.
H
C
Fig. 1163.
F

A
Ᏼ

D
E
Fig. 1165.
K
Ι

A
Z
FL
B
Fig. 1166.
To prove that the triangle KLC is equal to the triangle
A B C, and that it is the height of the line given: it must be
remarked that the line KL has cut the side A B in Z, and that
by its construction the lines KB and AL are parallel, which
occasions the two triangles A B L and A KL, which are on the
same base A L, and between the same parallels K B and A L,
are equal to each other, agreeably to the 37th proposition of
Euclid's First Book; so that the triangle AZ L being cut off, the two
triangles Z BL and Z KA will remain equal to each other. If from
the triangle ABC we cut off the triangle Z B L, to make Z K A equal,
we shall have the triangle KLC equal to A B C, and the height of the
line already given; since the line H GI, which is parallel to the base
CFB, is removed from it the distance of the given line by the per-
pendicular G F, which is equal to it.
To reduce Trapeziums and Trapezoids to Triangles, as the figure
ABCD to a triangle, whose height shall be equal to the trapezium:
fix a point in one side of the trapezium, for the summit of the triangle,
as E on AB; from this point E draw to the extremities of the base
DC the right lines ED and EC, and prolong the line DC either
way; from A draw a line parallel to ED, cutting the line in F, and
likewise from B draw B G, parallel to EC; draw EF and EG, to
have the triangle E F G equal to the trapezium A B CD.
To prove that the triangle E G F is equal to the trapezium A B C D,
and of the same height, we have only to observe that the lines E F and
F G cut the sides AD, BC at the points P and R, and that by the
construction the lines ED and A F are parallel, which causes the two
triangles AED and FDE to be upon the same base E D, and
between the same parallels ED and A F.

B
E
A
C
R
Fig. 1167.
D
F
CHAP. VIII.
879
GEOMETRY
To reduce Multilateral Figures to Triangles, as the regular pentagon
ABCDE to a triangle. Prolong the base DC, and on it set off twice
the length of DC to F and G; from the centre H of the pentagon draw
the right lines HF and HG: the area of the triangle HGF will be
equal to that of the pentagon.
To prove that the triangle H G F is equal to the pentagon A B C D E.
Draw from the centre H the two right lines HD and HC; then remark
that the base F G of the triangle H G F contains five times the base of
the triangle H CD, so that the triangle H G F is composed of five equal
triangles according to the 38th proposition of Euclid's First Book: but
the triangle H C D is also the fifth part of the regular pentagon A B C D E,
so that the triangle HCD being the fifth part of the pentagon
ABCDE, it is also of the triangle HGF: then, by the ninth proposition
of Euclid's Fifth Book, the triangle HGF is equal to the pentagon
ABCDE.
A
B
G

C
H
D
Fig. 1168.
Rectangles, it must be remembered, which have the same or equal
altitudes, are to one another as their bases: for if the base of one of the
rectangles be divided into any number of equal parts, the rectangle itself
will be divided into as many equal rectangles by straight lines drawn
parallel to its side through the points of division; also the base of the
other rectangle will contain a certain number of parts equal to those into
which the first base is divided, exactly or with an excess less than one of those parts, and
that rectangle will contain as many rectangles equal to those into which the first rectangle is
divided exactly, or with a corresponding excess less than one of them; and this will be the
case, whatsoever be the number of parts in the first base and rectangle,
N
1
N
K
To reduce the Superficies of the irregular Pentagon I KLMN to a Triangle: prolong any
side of the pentagon on either hand as
the base ML: then from the op-
posite angle to the side ML, as the
angle I, draw the right lines I M
and IL; from the point N draw NO,
parallel to I M, and draw the line IO;
the triangle IPO will be equal to
the pentagon IKL MN.


Y
L
Fig. 1169.
T
X
If the area
of the figure be reduced to an irre-
gular hexagon, QRSTVX,
hexagon, QR STV X, you
must prolong one of the sides TS, on either hand, and from the
point X draw the line X T, from the point V the right line V Y,
parallel to XT, and from the point X draw the line X Y, which,
with the four other sides, will form an irregular pentagon,
XQRSY, from which a triangle may be drawn according to the
preceding rule.
To prove that the triangle IPO is equal to the irregular pen-
tagon IKLMN: it must be remarked that the two triangles
IMN, IMO, are equal, because they are on the same base IM,
and between the same parallels NO and IM, so that if
we take the triangle IMO for its equal IMN, we shall
have the trapezoid I K L O equal to the pentagon IK L M N;
the triangles IKL and IPL are also equal, so that in
placing the triangle IPL for its equal I KL, we have the
triangle IPO equal to the irregular pentagon IK LM N.
To reduce an irregular Heptagon, as ABCDEFG, with
a re-entering angle to a triangle: prolong the base EF on
each hand; draw from the point A a line AF, and from
the point C another parallel to it, viz. GH, and draw H H:
then from the angle C draw the right line CE, and from
D draw DI parallel to it, and then draw CI; from the
point B draw BI, and from the point C the line CK,
parallel to it, and draw BK; from the point A draw A K
and BL parallel to it, and draw AL: the triangle ALH
will be equal to the irregular heptagon A B C D E F G.
Any two rectangles are to one another in the ratio which
is compounded of the ratios of their sides: this is clearly
shown in the 23d Prop. of Euclid's Sixth Book; and it also
is made apparent by the same proposition, that any two
parallelograms whatever are to one another in the ratio
which is compounded of their bases and altitudes, for the
rectangles to which they are equal are in that ratio.
F
A
Fig. 1170.
B
G
E
C
I
L
F
Fig. 1171,
Q

830
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
To reduce a Square to a Parallelogram on a given length,
as the square ABCD to a parallelogram which shall be
of the length EF: prolong the side A of the square, and
on it set the given length E F, from B to G, and prolong
the other three sides; draw the right line GC till it cuts
AD prolonged in H: through the point H draw a line
parallel to A G, as HI, and from G draw a line parallel to
the side BCI, as is GL, cutting the side CD prolonged
in M: then the parallelogram CMLI will be equal to the
square ABCD.
D
H
E
P
A
}}}
G

Fig. 1172.
The complements of the parallelograms which are about the
diameter of any parallelogram are equal to one another: let
HAGL be a parallelogram, of which the diameter is HG;
and DI, MB parallelograms about HG, that is through which
HG passes; and AC, CL, the other parallelograms, which
make up the whole figure HAGL, which are therefore called
the complements. The complement AC is equal to the com-
plement CL, because HAGL is a parallelogram, and HG
its diameter; the triangle H A G is equal to the triangle HLG;
and because DCIH is a parallelogram, the diameter of which is
HC, the triangle HDC is equal to the triangle HIC; by the
same reason the triangle CB G is equal to the triangle CMG:
then because the triangle HDC is equal to the triangle HIC,
and the triangle CBL to CMG, the triangle HDC, together
with the triangle CB G, is equal to the triangle HIC, together
with the triangle CMG: but the whole triangle HA G is equal
to the whole HLG; therefore the remaining complement AC is
equal to the remaining complement CL.
F
A
B
M
C
I
L
B

Fig. 1173.
E
F
A
B
G
To reduce a Rectangle to a Square. - Prolong one of the long sides of the rectangle, as
AB to H, and set off the width A G on it, from A to E to find a mean proportional
between A and A E, divide E B in F, and from the point F, with the radius FH, describe
a semicircle: prolong A D till it cuts the semicircle in G: AG will be the mean pro-
portional, and the square A CIH constructed on it will equal ABCD.
To lengthen or shorten a Parallelogram on a given
length. It is required to reduce the parallelogram A B CD,
to one which shall be of the length EF: prolong the
four sides of the parallelogram to infinity, and set off the
given length from B to G, and from C to H, and then
draw GH parallel to BC; draw the diagonal GC, till
it cuts AD prolonged in I, and draw through this point
H, a line parallel to DCH, cutting B C prolonged in K,
and GH in L; then the parallelogram CHLK will be
equal to ABCD.

D
H
C
M
I
L
Fig. 1174.
The straight lines which join the extremities of two
equal and parallel straight lines towards the same parts are also themselves equal and
parallel: let BG and CM be equal and parallel straight lines, and joined towards the same
parts by the straight lines BC, GM; BC, GM are also equal and parallel; join GC: and
because BG is parallel to CM, and CG meets them, the alternate angles BGC, GCM are
equal; and because BG is equal to CM and GC common to the two triangles BGC, MCG,
the two sides BG, GC are equal to the two M C, CG, and the angle BGC is equal to the
angle GCM: therefore the base BC is equal to the base
GM, and the triangle BGC to the triangle GCM, and
the other angles to the other angles, each to each, to
which the equal sides are opposite: therefore the angle
BCG is equal to the angle CGM, and because the
straight line GC meets the two straight lines BC, GM,
and makes the alternate angles BCG, CGM equal to one
another, BC is parallel to GM, and it was shown to be
equal to it.
To reduce the Area of a Circle to that of a Square, &c. It
is required to reduce the circle HIK to a square: divide
the diameter KI of the circle into 14 equal parts, and
count off 11 of these parts to L; at this point L, and in
KI, elevate a perpendicular LM; remark where it cuts
the circle in H, and draw KH; then a square con-
structed as KH, as is NOHK, will be equal to the
circle HIK.

1
H
N
M
R
L
Fig. 1175.
CHAP. VIII.
281
GEOMETRY.
To reduce the Area of a Square to that of a Circle, divide one
side of the square, as CD, into two equal parts in E: at this
point E, draw E F perpendicular to DC, half the length of DE;
from the point F as a centre, with the radius FD, describe the
circle DCG, which will be equal to the square A B C D.
Similar four-sided figures, or of any number of sides, are
to one another in the duplicate ratio of their homologous
sides, and universally similar rectilineal figures are to one
another in the duplicate ratio of their homologous sides, and
according to cor. 2. attached to the 20th prop. of Euclid's
Sixth Book, if three straight lines be proportionals, as the third
is to the third, so is any rectilineal figure upon the first, to a
similar and similarly described rectilineal figure upon the second:
and the same geometrician teaches us in the 9th prop. of his
Fifth Book, that magnitudes which have the same ratio to
the same magnitude are equal to one another, and those to
which the same magnitude has the same ratio are equal to
one another.
To reduce a circle to an Oval on a
given Length, as the circle ABCD,
to an oval, whose greatest diameter
shall be equal to EF; draw a right
line GH, and set off the given
length E F, from G to I; at the
point I elevate a perpendicular IK,
of the same length as the diameter
of the circle DB: draw the right
line G K, and bisect it in L; from
L draw the perpendicular LM;
from the point N, where it cuts
GI, with the radius GN, describe
a semicircle GKO, and 10 will
be the shortest diameter of the oval:
then draw the two diameters of the
oval at right angles to each other;
take the given length EF with a
thread, fold it in half, and place the
two extremities on the diameter ·
QR, at the points Y and X, equi-
distant from V; so that the fold or
angle of the thread may coincide
with the point S, the width of the
required oval; so that by moving

D
Fig. 1177.
A
C
S
Z
L
A
E
C
Fig. 1176.

G

B
Q
R
X
V
Y
T
Fig. 1178.
N
M
II
Fig. 1179.
L
K

a pencil through the points S, R, T, and Q, you will describe an oval equal to the given
circle ABCD.
To unite several Figures
into One, and increasing the
Content of others. To re-
duce several figures into a
triangle whose height shall
be equal to a given height,
as that of the triangle
ABC, and the square
DEFG: draw a right
line HI, and on this line
at the point H, make such
an angle as it is desired the
triangle should have, as
IHK: take the height
AT of the triangle ABC,
and draw a line RS parallel
to HI; at the distance A T,
set off the line CB on
HI, from H to M: reduce
C
D
A

K
S

R
B
T
E
II
M
V I
Fig. 1181.
N
FP
Fig. 1180.
the square DEFG, to a triangle DNG, and make the triangle DNG equal in height
to ABC, as is the triangle OPG; set off the base GP on HI from M to Q, and draw
LQ; the triangle LQH will be equal to the square DEF G, and the triangle A B C.
3 L
882
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
To reduce two Squares into One. If two squares touch
at one angle, and the two sides of one angle are in a line
with the two sides of another angle, as at ABG and EBC,
draw a right line GC, on which form the square CGH1;
its area will be equal to that of the two squares; but if the
two squares do not touch, as KLMN and OPQR, draw
a right angle STV, and set off the side VKL on TS, from
T to X, and the side OP on TV, from T to Y; draw the
right line X Y, on which erect the square XYZ, &c., and
it will be equal to KLMN and OPQR.
Euclid, in his 47th prop. of Book I. demonstrates, that in
any right-angled triangle the square which is described upon
the side subtending the right angle, is equal to the squares
described upon the sides which contain the right angle.
To reduce a Square into several equal Squares, as that of
ABCD into two equal squares: divide one side into two
equal parts, as AB, in E; from E with a radius AE,
describe the circle AGB: elevate a perpendicular E F
from E, observe where it cuts the demicircle, as at G,
in order to draw the lines AG and GB; the squares
constructed on these lines will contain half ABCD.
H
Ꭱ
D
S
E

A
G
G
X
F
H
Р

K
L
IC
T
N
M
Y
N
&c.
Ꮓ
Fig. 1182.
A
F
K
G
E
B
In any right-angled triangle the square which is described
upon the side subtending the right angle is equal to the
squares described upon the sides which contain the right angle.
Let G AB be a right-angled triangle, having the right
angle A GB; the square described upon the side AB
is equal to the squares described upon AG, G B. On
AB describe the square ADCB, and on AG, GB,
the squares IA, K B, and through G draw GL parallel
to AD or B C, and join GD, HB. Then, because each
of the angles AG B, AGI, is a right angle, the two
straight lines GB, GI, upon the opposite side GI,
make with it at the point G the adjacent angles, equal
to two right angles; therefore, BG is in the same
straight line with GI: for the same reason GA and
GK are in the same straight line; and because the
angle D A B is equal to the angle H A G, each of them
being a right angle, add to each the angle GA B, and
the whole angle DAG is equal to the whole HAB:
and because the two sides GA, AD are equal to the
two HA, A B, each to each, and the angle D A G equal
to the angle HAB; therefore the base GD is equal to the base HB, and the triangle
GAD to the angle H A B. Now the parallelogram AL is double of the triangle G A D,
because they are upon the same base A D, and between the same parallels AD, GL; and
the square I A is double of the triangle HA B, because these also are upon the same base
HA, and between the same parallels H A,
IB. But the double of equals are equal
to one another, therefore the whole square
ADCB is equal to the two squares IA,
K B, and the square ADCB is described
upon the straight line A B, and the squares
IA, KB upon A G, GB. Wherefore the
square upon the side A B is equal to the
squares upon the sides A G, GB.

To reduce several Figures to a Rectangle
of a given length, as the trapezoid ABCD
and the pentagon EFGHI to a rect-
angle of the width KL: first reduce the
figures to triangles of the same height,
and twice the breadth KL, as are the
two triangles PCQ and RSO: set off
the base CQ from K to T, and SO from
T to V; at the point T elevate the per-
pendicular TX, equal in height to PCQ,
and draw the right line KX and XV;
reduce the triangle X K V to a rectangle,
which will be equal to the two figures
ABCD and EFGHI.
P
B
A
L
C
Fig. 1183.

D
C
Υ
R
F
G
Fig. 1184.
E
ta
H
I
X

Fig. 1185.
T
L
CHAP VIII.
889
GEOMETRY.
To reduce rectilineal Figures to one which shall be similar
to a given Figure, as those of the trapezium and pentagon
to a figure similar to MabN: reduce the trapezium and
pentagon to triangles, and the figure ab NM to a triangle
MaR: reduce the two triangles to the same height, as
Ma R; draw a triangle equal to these three triangles, by
setting off the bases from a to b, b to c, and c to d, and
elevate the perpendicular ce at the point c, of the height,
of the triangle Ma R; then draw from the point e the lines
ea and ed, which with the right line ad will form a
triangle equal to the three: then reduce the triangle
eda to a rectangle fgda, and remark where fg cuts ce in
h, and prolong af and dg: take the base
ba, and set off on fg, from h to i, and
draw ci until it cuts dg prolonged in
k; draw a line parallel to fg through k,
until it cuts af prolonged in l; from the
point draw lc, remark where it cuts
fg in m: draw a perpendicular nm to
fg, through the point m, and at i, the
perpendicular oip.

h
0
ཁ་
(L
८
c9
μ
Fig. 1186.
M
N
X
b
Fig. 1187.
Fig. 1188.
d


Find a mean proportional between the
length be and cp, by bisecting bp in 9,
and from q as a centre, with the radius qb
describe a semicircle, and remark where it
cuts the perpendicular ce in r; the length or will be a mean proportional between bc and
cp: set off this mean proportional cr from z to c; divide the figure Mab N into two
triangles by means of the diagonal M, and draw on the line CZ, at the point Z, an
angle CZs, equal to ba M; and at the point C, an angle CZs, equal to ab M, and remark
where the two lines Cs and Ct intersect at u; from this point u draw the angle Cux, equal
to b Mn, and at the point C an angle equal to MbN; the figure u Z Cz will be equal to
the two triangles, and similar to the figure ab NM.
K
E
The above principles are drawn from Prop. 1. of Euclid's Sixth Book, wherein he states
that triangles and parallelograms of the same altitude are one to another as their bases, and
he observes in the cor. attached, "Let their figures be placed so as to have their bases in
the same straight line, and having drawn
perpendiculars from the vertices of the
triangles to the bases, the straight line which
joins the vertices is parallel to that in
which their bases are, because the perpen-
diculars are both equal and parallel to one
another.


To reduce several Circles to a single one, as
the superficies of the two circles A and B
to one: draw the diameter CD and EF;
draw a line GH, on which set off CD
from G to I, and elevate a perpendicular
from this point I, on which set off the
other diameter EF from I to L: draw
GL; bisect it in M: from M as a centre
with the radius ML, describe the circle
GNLI, which will be equal to the two
given circles A and B.
B
N
F
C
M
Fig. 1189.
To draw a Square the Double or Quadruple of another. To double
the square ABCD, prolong the side DE toward the place you
wish the square extended: from D as a centre, with the radius DE,
describe an arc BE, cutting DC prolonged in F: on DF construct
a square GHFD, which will be double the square A B CD.
H
G
D
A
Fig. 1190.
D
B
H

F
C
E
Vitruvius has given us the method practised in his time for
doubling the square: that valuable author observes, "If there be an
area or field whose form is a square, and it is required to set out
another field, whose form is also to be square, but double its area, as
this cannot be accomplished by any numbers or multiplication, it
may be found exactly by drawing lines for the purpose, and the
demonstration is as follows: A square plot of ground, 10 feet
long by 10 feet wide contains 100 feet; if we have to double this, that is, to set out a plot
also square, which shall contain 200 feet, we must find the length of a side of this
Fig. 1191.
3 L 2
884
Book II.
THEORY AND PRACTICE OF ENGINEERING.
square, so that its area may be double, that is 200 feet. By numbers this cannot be done,
for if the sides are made 14 feet, these multiplied into each other give 196 feet; if 15 feet
they give a product of 225 feet. Since, therefore, we cannot find them by the aid of numbers,
in the square of 10 feet a diagonal is to be drawn from angle to angle, so that the
square may be divided into two equal triangles of 50 feet area each: on this diagonal,
another square being described, it will be found that whereas in the first square there were
two triangles, each containing 50 feet, so in the larger square formed on the diagonal, there
will be four triangles of equal size and number of feet to those in the larger square; in this
way, Plato demonstrated the method of doubling the square. Rules for extracting the
square root have since been discovered, and we no longer admit it to be impossible to an-
swer this question by figures, for the square root of 200, which is 14.14211356, would be the
length of the side of the square that would contain the superficial area of 200 feet.
A
G
P
M
N
B
H
C L
E
F
To construct rectilineal Figures similar and double to given
Figures of the same Number of Sides. It is required to draw a
rectangle similar to and double the square ABCD: prolong
the line DC, and set off the base from C to E, and from E to
F: find a mean proportional between E F and E D, by elevating o
a perpendicular to E F, at the point E, and bisecting DF in H:
from H as a centre, with the radius HD, describe the semi-
circle DIF, cutting E G in I; the right line EI will be the
mean proportional required: set off the mean proportional on
DC prolonged from D to L, and on this length construct a
rectangle similar to ABCD; which is done by forming at the point L an angle DLM,
equal to DCB: draw the diagonal DB, until it cuts LM in N; through N draw a line
parallel to A B, and remark where the line NO cuts DA; prolong it in P, the figure
PNLD will be similar to and double A B C D.
To double, triple, or quadruple the Circle. -To draw a circle,
whose superficies shall be double that of B, draw the diameter
CD: elevate the perpendicular DE at the point D; on it set
off the radius BD from D to E, in order to draw BF, which
will serve as a radius to describe from A as a centre, a circle
which will be double the given circle B.
If it be required to have the circle tripled: from F elevate the
perpendicular FK, on which set off the radius BD from F to E,
and draw BL; it will be a radius for describing a circle M N O,
which will be triple the given circle B.
If it be required to have the circle quadrupled, elevate the
perpendicular LB from the point L, and set off the radius BD
upon it; from L to A draw BQ, and it will serve as a
radius to describe a circle, which will be the quadruple of the
given circle B. .
Geodesy is synonymous with land-surveying, and compre-
hends all those trigonometrical and geometrical operations which
more particularly have for their object the determination of the
magnitude and figure of the whole or any part of the earth's
surface. The 37th prop. of the First Book of Euclid states that
triangles upon the same base, and between the same parallels,
are equal to one another: upon this proposition, most of the
following rules are founded.
To divide triangular Figures into several equal Parts which
shall all unite at one Angle. It is required to divide the triangle
ABC into two equal parts both uniting at the angle A:
divide the line CB into two equal parts at D, and draw the
right line AD; this right line will divide the triangle into two
equal parts.
To divide the triangle ABC into two equal parts, uniting
in the centre of the side A C: bisect AC in D; draw DB; it
will divide A B C into two equal parts.
To divide the Isosceles Triangle into three equal parts
meeting in the point H on the side EG: divide the side
EF opposite the point H, into three equal parts in the
points 1,2,3; draw HI and also G K parallel to it from the
point G, cutting EF in L; from L draw LH to the given
point H, fron the given point H draw H 2, and from the
point G draw GN parallel to H2, cutting E F in N, from
N draw NH: then will the triangle E F G be divided into
three equal parts by the lines HI and HN.

G
D
C
P
Fig. 1192.
K
Fig. 1193.
A
B
E


D
C
B
A
D
Fig. 1194.
Fig. 1195.
E
1
B

K
E
2
V M
CHAP. VIII.
885
GEOMETRY.
To divide the Triangle EFG into four equal parts
meeting at the point H, on the side FG: divide GF
into four equal parts in the points 1,2,3,4; from the point
E draw the right line E 1; from the point H draw the
right line H1, and through E a line parallel to it,
cutting GF in K, and draw HK: set off the line G K
on GF from K to L, and draw HL: set off KL from
L to M on GF, and draw HM and HF; draw MN
parallel to it, cutting E F in O; draw HO: the lines
HO, HL, and H K, will divide the triangle EFG into
four equal parts.
H
E

9
F
G
1
K2
3
L 4
M
Fig. 1196.
To prove that the triangle EFG is divided into four
equal parts, H KG, HLK, HO FL, HE O, it is only
requisite to remark that the triangle E F G has its base G F divided into four equal parts
by the points 1, 2, 3, and 4, and which form the triangles EIG, E21, E32, and EFs,
the heights and bases of which are all equal, and each forms a fourth of the triangle EFG.
This must be so, for the triangles HEK and IEK are upon the same base E K, and
between the same parallels H1 and E K, so that cutting off the common triangle PEK,
the two triangles HEP and IKP, which are equal, will remain; if from the triangle
EIG we cut off the triangle HEP to take its equal IK P, we shall have the triangle
HKG equal to EIG, and consequently to a quarter of the triangle E F G.
It is to be observed that the three triangles HK G, HLK, and H M L, being of the
same height, and having their bases G K, KL, and L M equal, are equal each to each; and
as the triangle HKG has been proved to be the fourth of the great triangle E F G, the two
other triangles HLK and H ML are also each the fourth of this great triangle: but as
the triangle H ML comes out of the triangle EFG, that it may be comprised within it,
the right line H F, and its parallel MN are drawn, which form the triangles HOM and
FOM, which being on the same base O M, and between the same parallels HF and OM,
are equal, so that in cutting off from these two equal triangles the common triangle QO M
there will remain the two triangles HOQ and FM Q, which are equal; if from the
triangle H M L we cut off the triangle F M Q, to take its equal HOQ, we have the figure
HOFL equal to the triangle H ML, and dividing into four the great triangle E F G ; and
as we have proved that the three figures HKG,
HLK, and HOFL, are each a quarter,
the remainder HEO is the fourth quarter.
K

S/O A
L E
F
Q
C 3
Fig. 1197.
2
1
BNH M 1
To divide the Triangle ABC into three
equal parts uniting at the point D: draw
through the point A a line AF parallel to
the line BC: divide CB into three equal
parts in the points 1, 2, 3; draw A D, and
through 1 a line 1 F, parallel to AD, cutting
AB in G: from D draw D G and D1: set
off B1 from B to H, and DG from H to I,
and on this line III draw the triangle KIH
equal and similar to A GD: elevate the triangle KIH
to the height of A B C, and you will have LMH: set
off H M from B to N, and HN from A to C, and draw
OC: take the shortest distance from D to A C, as
DP, to draw a line parallel to AC at the distance, as
QR, cutting A E in S; from which point S, draw SC,
and through C another parallel to it, as CT, cutting
AC in V; draw VD: the lines 1 D, DG, and DV
will divide the triangle ABC into three equal parts
uniting at the point D.
To divide Triangles into equal Parts by lines parallel to
their sides: as to divide ABC into two equal parts
parallel to A C; prolong one side CB, and bisect it in
D; set off BD from B to E: find a mean proportional
between CB and B E, as BH: set off BH on BC from
B to I: through I draw IK parallel to AC: the line
IK will divide the triangle ABC into two equal parts.
To divide Figures of four Sides into several equal parts,
as the square A B C D into three equal parts, all uniting
at A: draw the diagonal BD, and divide it into three
equal parts, in 1,2,3: from A draw the line A1, A2:
draw A C and 1 E and 2 F parallel to AC: then draw
AE and A F; these two lines will divide the square
ABCD into three equal parts uniting in the angle A.

3L 3
a
H
A
K
L
C
I D F
B
Fig. 1198.
A
D
2
Fig 1199.
R
B

F
C
8
886
Book II.
THEORY AND PRACTICE OF ENGINEERING.
To divide Figures of four Sides into several equal parts
uniting at a point on one side; as to divide the four-
sided figure ABCD into two equal parts uniting at E:
reduce the quadrilateral ABCD to a triangle, A FD,
and bisect the line D F in G: draw GE, and through
A a line parallel thereto HA; draw HE, and it will
divide the four-sided figure into two equal parts.
To divide Figures of four Sides into several equal parts
uniting at a point in their superficies: as to divide
ABCD into two equal parts, uniting at the point E:
divide the trapezoid ABCD into two equal parts,
uniting by a line, F G, passing through the point E;
reduce the trapezoid A BCD, to a triangle AHD, and
FBCG to a triangle FIG: draw AK parallel to
DH: elevate the triangle FIG to the same height as
AHD, and you will have the triangle LMG: bisect
the base DH in N, and draw A N, forming the two
equal triangles AHN and AND: set the base M G of
the triangle LMG on the line HN of the triangle
AH N, and remark if these two lines are equal: but
since the base M G is shorter by the distance ON, set
off this distance ON from G to P, and draw LP,
forming the triangle L.GP: then remarking the figure
FBCQ only contains I M G, or its equal, AH O, you
must add to this figure the triangle A ON or L G P,
lowering the height to E on the side DH, as is the
triangle E GQ, which will give you the irregular
pentagon FBCQE for one half, and AEFQD for
the other half of the trapezoid A B C D.
To divide Figures of four Sides into several equal parts
by lines parallel to one of their sides: as to divide the
trapezoid HIKL into two equal parts by a line
parallel to HL: reduce the trapezoid HIKL to a
triangle HML: bisect its base LM in N: prolong
LK and HI till it cuts LK prolonged in 0: find a
mean proportional between OL and ON, as PQ,
which set off from O to R, and draw RS parallel to
HL; it will divide the trapezoid into two equal parts.
To divide Pentagonal Figures into several equal parts
abutting at one angle: as the regular pentagon
ABCDE into two equal parts abutting on the angle
A. Reduce the pentagon ABCDE to a triangle,
AFG: bisect the base GF in I, and draw A I, it will
divide the pentagon ABCDE into two equal parts.
To divide Pentagons into several equal parts, abutting
at a given point on their sides; as to divide the
irregular pentagon ABCDE into two equal parts
uniting at the point F. Reduce the pentagon to a
triangle, AGE: bisect the base EG in H, and draw
AH forming the triangle AHE: half the triangle
AGE, or the pentagon ABCDE: then lower the
triangle A HE to F, as FIE: draw FD, and through
I its parallel IK, and draw FK, which will divide the
pentagon into two equal parts.
D
A
A

H
T
Fig. 1200.
D Q P
L
E
B
G C
B
E
K

G
NC
O M
H
Fig. 1201.
Р
H

n
L
K
K
M
Fig. 1202.
A

F
G
A
E
E
B
1) I
с
F
Fig. 1203.

Fig. 1204.
A
B
L
D H
تح
K
B
To divide Pentagonal Figures into several equal parts
uniting at a point in their superficies: as to divide the
irregular pentagon ABCDE into two equal parts,
abutting at the point F. Divide the pentagon into two
equal parts by a line passing through the given point,
as GH; then reduce the pentagon to a triangle, AIE,
and the figure GBCDH to a triangle GKH, which
you must elevate as high as AIE, as is done in the
triangle LMH: divide the base EI into two equal
parts in N, and draw NA, which will form the triangle
AIN: set the base IN on the base MH; it will be
greater by the distance HO: draw OL forming the
triangle LMO: lower the triangle LHO to the point
F, as F II P, which will give you GBCDPF for half the pentagon A B C D E.

C
E P
HND
M K
Fig. 1205.
CHAP. VIII.
887
GEOMETRY.
To divide Pentagons by lines parallel to their sides
into several equal parts, as the irregular pentagon,
ABCDE, into two equal parts, by a line parallel
to E D: reduce the pentagon to a triangle, AFG;
bisect its base G F in H, and draw A H: reduce the
trapezoid, AHDE, to a triangle, EID; prolong the
base ID, and the side A E, until they intersect in K:
find a mean proportional, L M, between KI and K I);
set off the mean proportional on K I, from K to N;
through the point N draw a line, N O, parallel to
E D, and it will divide the irregular pentagon into two
equal parts.
K
L
0 4

E
G D HN
C F
M
Fig. 1206.
Z
A
F
B
K
To divide Hexagons into several equal parts, uniting at one of their angles: first reduce
the irregular hexagon, as A B C D E F, to a pentagon: then to a trapezoid, and lastly to
a triangle. To reduce the hexagon, ABCDEF, to a
pentagon, prolong the side DC to I: draw A C, and from
B a line parallel thereto B K, and divide A K, which will
reduce the hexagon to the pentagon, A K D E F. To
reduce this to a trapezoid, prolong the side E D, and draw
A D, and from K draw K G parallel to A D; draw A G,
which will reduce the pentagon to the trapezoid, A GEF:
reduce the trapezoid to a triangle by drawing from A the
right line A E, and through F its parallel F H, and draw
A H, which will form the triangle A G H, equal to the trapezoid A G E F: then divide
the base, HG, into two equal parts in L, and draw A L, which will divide the hexagon into
two equal parts.

H E
Fig. 1207.
G
To prove that the irregular hexagon ABCDEF is divided into two equal parts ABCDL
and ALEF, which join at the point A.
The angle AGF is equal to the irregular hexagon ABCDEF, and the triangle A GH
has its base equally divided at the point L, so that the two triangles A GL and ALH,
having the same height and base, are equal; and as they are the moieties of the triangle
A GH, they are also the moieties of the hexagon A B C DEF, which is equal to the
triangle A G H.
The two triangles A EF and AE H being upon the same base A E, and between the
same parallels FH and A E, they are equal: AEF and AEH are also equal, as are
FAZ and HEZ.
If from the triangle ALH, which is the half of the hexagon A B C DE F, we cut off
the triangle HEZ, and take its equal FAZ, we shall have the figure A LEF equal to the
triangle A L H, and also the moiety of the figure A B C D E F.
Y
P
Z
S
R
T
X
A
B
To divide Multilateral Figures, having re-entering angles. into several equal parts, uniting
at one angle, as to divide the irregular heptagon, A B C D E F G, into six equal parts,
uniting at the angle B: reduce the
irregular heptagon to a triangle B N M,
draw B D in CN; divide M N into
six equal parts, in the points 1, 2, 3, 4, 5, 6,
and draw right lines to them from B;
draw E B, and through 2 a line 2 0,
parallel to E B, and draw O B. Reduce
the irregular pentagon A B OFG to a
trapezoid, B OF P, by prolonging F G,
and from G draw the right line G B,
and from A, A P, parallel to B G, and
draw PB: set off the base of one of the
small triangles, as 43, and F G, from
P to Q. Take also the length of its
side 4 B, and describe from the point
P an arc R; take the length of its other
side, 3 B, and from the point A describe
the second arc S, cutting the first in T:
then draw the two lines Q T and P T,
which will form the triangle Q P T
equal to B 43. Through B draw a line parallel to F Q, as B V, cutting PT in X: then
lower the triangle T P Q to X, and you will have X P Y equal to TPQ. If, then, you
set off the base Y P from P to Z, and draw Z B, you will have the two triangles BZP
and X P Y equal to each other. The triangles B G A and B G P being equal, if to the
triangle B Z G you add the triangle B G P, you will have the triangle BZ P; and if to the
triangle BZ G you add B G A, you will have the trapezoid B Z GA equal to B Z P, and

M
Fig. 1208.
א
C
E
3
4
5D No
3 L 4
888
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
consequently a sixth of the heptagon, A B C D E F G: there will remain the trapezoid
BOFZ for the last sixth. Thus the irregular heptagon will be divided into six equal
parts by the lines B, Z, 0, 3, 4, 5.
A
L
T
V
B
To divide Figures of unequal Dimensions by similar Lines, as to divide the figure
A B C D into three parts similar to three divisions on the plan E F G H: measure the
length E I of the plan, E F G H, with the scale K, as
45: measure likewise on the figure A B C D 45, from
A to L then take with a protractor the angle EI M,
105°, and from the angle A L N also 105°, on the side
A B, at the point L. Measure the length F O, 40°,
with the scale K, and set off 40° from B to P; at the
point P draw the angle B P Q equal to F OM: then,
having found that the distance GR is 70 parts, set off
the same number from C to S. At the point S draw
the angle CST equal to G R M: the lines L, N, P, Q
and S, T, intersecting at V, will divide the figure
A B C D similarly to E FH G.
MENSURATION OF SOLIDS.-Determine the value of the
spaces included by contiguous surfaces, and the sum of the
measure of those including surfaces is the whole surface or
superficies of the body; the rules for performing such
operations we have already described. The measure of a solid
is called its solidity, capacity, or content, and is usually measured
by cubes, whose sides are inches, feet, or yards: hence the
solidity of a body is said to be so many cubic inches, feet,
yards, &c., as will fill its capacity or space, or another of an
equal magnitude.

N
P
C
S
D
E
I
F
M
G
II R
Fig. 1209.

The cube A may be supposed to contain a solid foot, con-
sequently 1728 cubic inches; for if the area of its base were
divided into square inches, it would contain 144, and as the
cube is 12 inches in height, it would permit of 12 layers of
cubical inches being piled up to complete the figure, or 144
cubes x 12=1728: consequently, to find the solid content of a
cube, we only have to multiply the area of its base by its
height.
Of a Parallelopipedon. -Multiply the area of one end by the
length, and the product is the solid content.
Inclined Parallelopipedons are cubed in a similar manner.
The solid content of a rectangular parallelopipedon is said to
be equal to the product of its three dimensions, that is, as
ABX ACx AD, when AB,
Fig. 1212
A C, AD, are the three edges:
this expression being inter-
preted in the same sense with
the product of the two dimen-
sions or sides, which is said to
constitute the area of a rect-
angle, viz. that the number of
cubical units in the parallelopiped is equal to the product of
the numbers which denote how often the corresponding linear
unit is contained in the three edges: it is on this account
said that the solid content of a rectangular parallelopiped is
equal to the product of its base and altitude. The cube is
considered a unit in the mensuration of all other solids, their
content being the same with the content of rectangular
parallelopipeds equal to them.
Prisms in general have their solid content found by mul-
tiplying the area of their base by their height.
L
F
M
A
Fig. 1210.
Fig. 1211.
Fig. 1213.
Fig. 1214.
K
G

N



Fig. 1215.
To find the solid content of an irregular solid whose sides
are parallel, we must first measure it in detail, find the con-
tent of the several parts, and add them together: the present
example might be taken as three parallelopipedons; or the solid content of the parts
cut out might be ascertained, which, deducted from the solid content obtained by mul-
tiplying the area of its base by its height, would give the content of the irregular solid.
As all prisms and cylinders are equal to parallelopipedons of equal bases and altitudes,
it is only necessary to multiply the base or end by the height to obtain the solid
content.
CHAP. VIII.
889
GEOMETRY.


Pyramid, or Cones: multiply the area of their base by one
third of their height for the solid content.
To find the solidity of the frustum of a cone or pyramid,
add into one sum the area of the two ends, and the mean pro-
portional between them, and take two-thirds of the sum for
a mean area, which being multiplied by the perpendicular
height will give its content.
Suppose we call a² the area of the base of the frustum of a
pyramid, b² the area of the top, h the perpendicular height,
and c the height of the pyramid when the frustum is made
complete.
Then c+h the height of the whole pyramid.
=
Then a² (c+h) is the content of the whole pyramid, and
bc the content of the top part: therefore the difference
} a² (c + h) — { bc is the content of the frustum.
But the quantity c being no dimension of the frustum, it
must be expelled from this formula, by substituting its value
in the following manner,
a² : b² :: (c + h) 2: c², or a b :: c + h : c ;
hence, a-bb::h: c, and a- b: a :: h: c+h;
hence therefore, c=
α
b h
b
ah
and c+h=
a b
;
then these values of c and c+h being substituted for them in
the expression for the content of the frustum gives that con-
- 162 ×
bh
a-b
=}h ×
a³ — b³
a-b
ah
tent={a² ×
=}}h × (a² + ab + b²),
a-b
which is the rule above given, ab being the mean between a²
and b².
Tetraedron. — Multiply the area of the base by one-third
of the perpendicular height for its solidity. Required the
superficies and solidity of the tetraedron, whose linear edge
is 3 inches.
32
1·73205 × 3² = 15.588 for its superficies,
0·11785 × 3² = 3.18195 for its solidity.
-
Hexaedron is the same thing as the cube, already described.
Octaedron. Multiply the square of its side by the diagonal,
Fig. 1216.
Fig. 1217.

A
Fig. 1218.
Fig. 1219.
and one third of the product will give the solid content.
Required the superficies and solidity of an octaedron, A, the linear
sides of which at BEC is each 2 inches: taking from the table
3.46410 × 2²=13.85640 for the superficial content,
0·47140 × 2º −3·77120 for its solidity.
Dodecaedron.—Multiply the content of one of its pyramids, E, by 12,
because the figure is composed of twelve equal pyramids having a regular
pentagon for the base, their summits being the centre of the dodecaedron.
Required the superficies and solid content of a dodecaedron, whose
linear edges are 2 inches.
20·64573 × 2²=82·58292 for the superficies,
7·66312 × 2²=61·30466 for its solidity.
Icosaedron. — Multiply the content of one of its pyramids, N, by 20,
because it contains twenty equal pyramids having equilateral triangles
for bases, and their summits in the centre of the body.
Required the superficies and solid content of the icosaedron N.
8·66025 × 2²=34·64100 for the superficies,
2.18169 × 2²=17.43352 for the solidity.
X
The side of any of the five Platonic bodies being given, to find the
diameter of a sphere that may either be inscribed in that body or cir-
cumscribed about it, or that is equal to it: As the respective number in
the following table, under the title inscribed, circumscribed or equal is
to 1, so is the side of the given Platonic body to the diameter of its
inscribed, circumscribed, or equal sphere.
The side of any one of the five Platonic bodies being given, to find the
side of the other four bodies that may be equal in solidity to that of the
given body: As the number under the title equal, in the third column of
the second table. which stands against the given Platonic body, is to the
number under the same title against the body whose side is sought, so is
the side of the given Platonic body to the side of the body sought.
B

C
A
E

E
Fig. 1220.

Z
Fig 1221.
890
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
To find either the Surface or solid Content of any of the regular Bodies, multiply the
tabular area, taken from the following table, by the square of the linear edge of the solid,
for the superficial content; and for the solid content, multiply the tabular solidity by the
cube of the linear edge.

Number of
Sides.
Name.
4
Tetraedron
6
Hexaedron
8
Octaedron
12
Dodecaedron
20
Icosaedron
-
Surface.
Solidity.
1·7320508
0.1178513
6·0000000
1·0000000
3.4641016
0.4714045
20.6457288
7.6631189
8.6602540
2.1816950
The diameter of a sphere being given, to find the side of any of the Platonic bodies
that may be either inscribed on the sphere, or circumscribed about the sphere, or that is
equal to the sphere.
Multiply the given diameter of the sphere by the proper or corresponding number in the
following table, and the product will be the side of the Platonic body required:

The diameter of a sphere being
1, the side of a
Tetraedron
Hexaedron
Octaedron
Dodecaedron
Icosaedron
That may be in-
scribed in the sphere
is,
That may be circum-
scribed about the
sphere is,
That equal to the
sphere is,
0.816497
2.44948
1.64417
0.577350
1.00000
0.88610
0.707107
1.22474
1.03576
0.525731
0.66158
0.62153
0.356822
0.44903
0.40883
To find the Solid Content of a Sphere. Multiply the cube of the
diameter by 5236, and the product will be the solidity.

s=
·
Or we may put d=the diameter, c=the circumference, and s=the
surface of the sphere or its circumscribing cylinder; also a=3·1416,
thens the base of the cylinder, or one great circle of the sphere,
and d is the height of the cylinder; therefore ds is the content of the
1444
cylinder but of the cylinder is the sphere; that is of ds, or ds
is the sphere.
6
Again, because the surface sa d², therefore { d: s=a d² = 5236 d³
the content; also d being = c÷a, therefore ¦ a d³=} c³ ÷ a² — •01688.
Then if we cube the diameter of a globe, and multiply it by ·5236, or
cube the circumference and multiply it by 01688, we shall obtain the
solid content.
To find the Solidity of a spherical Segment, or Plano-convex Portion
of a Sphere. To three times the square of the radius of the base or
flat side, add the square of the versed sine or height; then multiply
the sum by the height, and the product so obtained by 5236 for the
solid content; or, from three times the diameter of the sphere take
double the height of the segment; then multiply the remainder by the
square of the height, and the product by the decimal 5236 for the
content.
To find the Content of a solid Ellipse or Spheroid. Multiply the
square of the transverse by the square of the conjugate diameter, and
the product by ·5236.
To find the Solidity of a Parabolic Conoid. Multiply the square of
the diameter of the base by the height or length of the axis, and the
product by -3927: two such solids united at the başe form a parabolic
spindle.
P
T
Fig. 1222.

X
Fig. 1223.
T
A S
V
Fig. 1224.
E

To find the Content of a cylindrical Ring. Add to the diameter of
the cylinder of which the ring is formed the extent of the inner diameter
of the ring; then multiply the sum by the square of the thickness on
the diameter of the ring, and the product by 2.4674, which is one fourth of the square of
3.1416, and it will give the solidity.
To find the convex Surface of a Sphere. — Multiply the diameter of the sphere by its
circumference; or multiply 3.1416 by the square of the diameter, and the product will be
the convex surface required.
CHAP IX.
891
VALUATIONS OF PROPERTY.
CHAP. IX.
VALUATIONS OF PROPERTY.
In forming a valuation of either land or houses great attention should be paid to their
locality, as well as to their quality. Land is not uniform in this particular, as it
consists of several varieties; and it is necessary, when surveying an estate, so to
apportion it, that land of the same description and value be classed under the same
head or denomination: where the soil, however, differs materially in the same en-
closure, this is not very easily to be done; but in all cases, it must be noticed what are
the propertions of the good to the bad, and valued accordingly. Not only the nature and
depth of the soil, but the quality of the subsoil should be thoroughly examined by digging
into it, and the description fully entered in a book prepared for the purpose; for if the
valuator is governed by the appearance of the crops, and forms his opinion of the value
of the land by the quality and quantity of produce, he will often err, by putting a high price
on light or bad land highly manured; which is unjust, inasmuch as this value is only
temporary, and dependant upon the skill and capital bestowed upon it.
Pasture Lands in their value depend on the quality of the herbage; and on them, as
well as on all tillage lands, the nature of the prevalent indigenous plants should be noticed,
as they almost always indicate a particular quality of soil and subsoil, and are often
much better tests of the quality than by digging at the surface, or sinking holes. Woods
and plantations should be estimated according to the agricultural value of the land
on which they grow, without reference to the timber and uncultivated lands: in valuing land,
it is always better at the commencement to put the price which it is worth under ordinary
circumstances, and afterwards to add or diminish according to those which are local, and
which are dependant upon elevation, steepness, exposure to injurious winds; different varieties
or patches of soil, ill-shaped fields, bad fences, and the state of the roads, &c., &c. Climate
in a great degree depends upon elevation; in mountainous districts, not only must a
deduction be made for height, but also for situation, whether upon interior or exterior de-
clivities, the climate being much more moist in the bosom of the mountain, and more liable
to frost and snow than on the exterior at the same elevation. When lands are so steep
and hilly that they inconvenience the farmer in ploughing, manuring, &c., a deduction of
from one to four shillings per acre should be made: and where it is too steep to plough,
and must be cultivated by the spade, it may be valued as under pasture: considerations
should also be made when large stones or rocks produce difficulties in the way of the plough.
The character of the prevailing winds should be well ascertained, as they affect the crops;
if the land varies in quality, they will not ripen at one and the same time, and for such
situations a proper reduction should be made: land in an ordinary situation, within 3 or
4 miles of a market town, with good roads, and not particularly sheltered or exposed, or
remarkably level or hilly, and whose greatest elevation does not exceed 300 feet above
the level of the sea, the chief matters which are required to be taken under consideration
are the means of obtaining manure or limestone, which adds to or diminishes the value.
The neighbourhood of large and populous cities also affects the value of land, and the
distance must always be noticed, as well as the local advantages or disadvantages obtained;
the distance from market, and the difficulty of access, materially lessens value, and ought
always to be taken into account.
The soils are usually classed as either clay, sandy, or calcareous, or compounds of one or
all, except where composed of peat or the primitive earths, which contain saline compounds
and the oxide of iron; such always retain water.
Argillaceous Earth forms the basis of clay, and is usually combined with siliceous sand,
as in potter's and pipe-clay, where the proportions of sand are 60 per cent. clay used for
brick-making is not only combined with siliceous but also with calcareous earth, the
siliceous most abounding; the colour of this kind of clay is either yellow, blue, brown or
red, which it derives from an oxide of iron.
Siliceous Earth is found pure in the flint and in transparent siliceous sand; the colours
of the varieties are dependant upon the different proportions of oxide of iron.
Calcareous Earth or Lime is sometimes in the form of limestone, where pure lime is
combined with carbonic acid in nearly equal proportions, or in a state combined with
sulphuric acid, when it is called gypsum. Calcareous earth may always be detected by
pouring a few drops of oil of vitriol or diluted muriatic acid on a small portion, and
892
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
if the soil contain lime an effervescence will take place, by the briskness and duration
of which the proportion of lime contained in it may be ascertained; but where it is
necessary to know the exact quantity of lime in an earth, this may be found by putting
half an ounce of the soil into a glass, and pouring upon it dilute muriatic acid, letting it
stand for four-and-twenty hours; after which pour off the clear liquid, adding water and
stirring it: when the earthy matter has subsided, pour off the clear water, and suffer the
residuum to dry till it acquire the same consistence it had previous to pouring on the
dilute acid; when weighed, whatever it has lost in weight will be the proportion of lime
contained in the soil. For practical purposes, however, the valuator may divide the ar-
gillaceous soils into clayey, clayey loam, and argillaceous alluvial: the siliceous soils
into sandy, gravelly, slaty, rocky, &c.; the calcareous into limestone, limestone gravel,
chalk, and marl: the peat into moor, peat, and bog.
Clay, when either blue or yellow, and in its quality tenacious or lying upon a
retentive subsoil, is nearly unfit for tillage; while on an open subsoil it is capable of
improvement, and when clays contain a due admixture of sand, lime, and vegetable
matter they are well suited to the growth of wheat, and may be classed among the most
productive: such may degenerate into a cold stiff clay when there is little or no sand
or vegetable matter, and their value is diminished accordingly.
Loamy soils are a compound of argillaceous and siliceous earths, and frequently contain
some proportion of lime and vegetable as well as animal matters; from being friable they are
soon reduced to a finely pulverised state: when a fine loam is mixed with sand, gravel,
clay, or peat, it is to be so designated, and the term loam is only to be understood as com-
prehending soils of a fine tilth, not forming clods when ploughed in wet weather.
A stiff clay, with either sand, peat, lime, chalk, or stable manure added to it, in
the course of time will become a rich loam, but it is only by numerous ploughings and
exposure to frost that a due mixture can take place.
A strong clayey loam contains about one-third part and sometimes more of clay, the other
ingredients consisting of sand, gravel, lime, &c., the sand predominating.
A friable clayey loam contains less clay and more sand: such a soil is easily cultivated
in wet weather.
Sandy or gravelly loams are those where either predominates; both render the soil open
and free, though not sufficiently retentive of moisture.
Argillaceous alluvial soils, usually on the banks of great rivers or near the sea-shore,
are evidently derived from the deposits of water: they are composed of fine argillaceous
loam, or other earths arranged in layers, with alternate beds of clay, shells, sand, &c.
The value of these soils depends in a great measure on the quantity of lime they contain.
Rich alluvial soils are the most productive of any when not subject to floods.
Siliceous soils comprise sands of all gradations from open sandy loam to pure sand.
white shelly sands, when near the sea, are very productive, although there is not a great
portion of earthy matter found in them.
Gravelly soils are those where coarse sand or gravel abounds; a due admixture of loam
renders them sufficiently retentive of moisture; such produce excellent crops.
Slaty soils occur on the sides of mountains, and are composed of the debris of slate rock
either coarse or fine-grained.
Rocky soils are found abounding with fragments of rock intermixed with mould, where
the substratum is rock.
Calcareous or limestone soils contain an unusual quantity of finely pulverised limestone ;
these form excellent grazing lands.
Limestone gravel soils occur in limestone districts; these are sometimes calcareous and
often composed of calcareous sand.
Marly soils consist of two kinds; that which contains clayey marl or calcareous matter
combined with clay and white marl, which is a deposit from water, usually found at the
bottom of lakes and rivers.
Moory, peaty, or boggy soils vary in their quality; some contain very little earthy
matter, and when burnt the ashes which remain scarcely amount to a tenth or twelfth of
the original weight; the value of peat soils is dependant upon their production of red or
yellow ashes when burnt: in deep bogs these are light and white, and do not amount to
more than an eightieth part of the original weight, and are of little use as a manure.
Where peat earth yields a small quantity of white ashes its value is trifling, unless
covered with a heavy coat of loamy earth or clay; a solidity is then given to the soil, and
crops may be produced upon it.
It is of the utmost importance that due attention should be paid to the nature of the
soil, and of all the ingredients of which it is composed; and the person who has to fix a
value should thoroughly understand what is meant by the following terms, and should so
arrange his field-book that the whole of the lands surveyed should come under one or other
of these qualities.
Stiff, when the soil contains above one-half of tenacious clay, and which in dry weather
CHAP. IX.
893
VALUATIONS OF PROPERTY,
cracks and opens, and has a tendency to form into large and hard lumps when ploughed in
wet weather.
Friable, where it is loose and open, as sandy, gravelly, and meory lands.
Strong, where a considerable portion of clay abounds, and there is a tendency to form
clods or lumps.
Deep, where the soil exceeds 10 inches in depth.
Shallow, where the depth is less than 8 inches.
Dry, where the soil is friable and the subsoil
porrus.
Wet, where the soil or subsoil is tenacious, or where springs are numerous.
Sharp, where there is a moderate proportion of gravel.
Fine or soft, where there is no gravel, but chiefly composed of fine sand or light earth
without gravel.
Cold, where the soil rests on a tenacious clay subsoil, and has a tendency when in pasture
to produce rushes and other aquatic plants.
Sandy or gravelly, when either abound.
Slaty, where that substratum is intermixed with the soil.
Worn, where the soil has been long under cultivation without either rest or manure.
Poor, where the land is of a bad quality.
Hungry, where there is a considerable proportion of gravel or coarse sand resting on a
gravelly subsoil: on such lands manure does not produce the usual effect.
Colours of soils should also be noticed, as well as the inclination of the various lands:
all these qualities, however, for the purposes of valuation may be classed under five heads,
as, A, prime land, rich loamy earth; B, medium; C, poor clayey, shallow or stony arable;
D, cultivated moors; and E, natural pastures, &c. : and each of these letters may again
be subdivided into No. 1, 2, and 3; so that A 1 down to E3 may comprise every quality
found upon an estate or within a district, and a value proportioned accordingly.
The valuator should also be aware that in mountain districts the farmers usually
divide their pasture lands into two qualities, called inside and outside grazing, to which is
sometimes added another called the remote. The quality and quantity of the herbage must
be ascertained, as well as the usual price paid in the neighbourhood for grazing.
Valuation of Houses. The value of a house depends partly upon what it would reason-
ably let for by the year, and upon the state of repair in which it may be found: all
dwelling-houses with the outbuildings dependant on them are valued as one building;
but, as in the country houses are seldom let separate from the land, and there is some
little difficulty in coming at a fair letting value, it is advisable to establish a table which,
when the dimensions of the buildings are ascertained, may indicate the value: this ought
to be well considered, and the state of the repairs noticed before any building is classed
in it. New buildings, those that are neither new nor old, and old buildings, have a different
value; and the table must be so made as to meet these three denominations: after the
number of cube feet in each building is ascertained, its value may be estimated by reference
to the price per cube foot determined upon, which price must depend upon circumstances,
and upon the judgment of the valuators. The table of value should embrace every class
and variety of dwelling-house, as well as the different denominations of offices and out-
buildings. To ascertain the cubical content of a building, measure its length, breadth,
and height, multiply them together, and enter the product into the field-book for future
calculation: it is, however, as well to note what the valuator supposes such a house or
premises would let for by the year in any ordinary situation, as a check to his estimate:
large houses in the country ought not to be so calculated, as it rarely happens that they
let for any thing like their value; the smaller the tenement the more probability there is
of a tenant, and of obtaining a return for the outlay or cost of the building.
Houses or mansions belonging to an estate are of little worth when the lands are taken
from them; and in making an estimate of such property, there are numerous considerations
before a just value can be put upon them: where houses are situated in a town, it is only
necessary for the valuator to note down the variety of situations, as the leading streets,
squares, &c.; then those in the next and succeeding degrees; supposing he commences
with the main or chief street, and continues his survey till he has comprised all the larger
houses, and the smaller tenements in the courts and alleys, he must proceed with the yards,
warehouses, manufactories, wharves, and other establishments, taking care to class them
all under their various and respective heads: the cubical dimensions of the buildings being
ascertained, and the area of the premises, a just classification as to locality and value is
then required. When the tenant has a lease obliging him to keep the premises in repair,
certain allowances are to be made; and in all smaller tenements let by the week or year,
some allowance must be made for loss of rent, and for greater wear and tear.
:
In large cities, towns, villages, and hamlets, the value of property, particularly houses,
varies after the valuator has satisfied himself upon the terms at which the various classes
of houses or tenements are let, he will have no difficulty in arriving at a close approximation;
in all these cases considerable knowledge and judgment are required, and these kind of
894
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
valuations should never be entrusted to the uninitiated, or to those who have not inade
buildings their particular study.
Mills and buildings, where there is water-power, require to be valued under two heads:
first, the buildings by their cubical content; then the water-power; to establish that of the
latter, it must be first ascertained whether the water acts by its weight or gravity, as
with a breast or overshot wheel, or by impulse, as in undershot wheels. In the former,
or gravity wheels, their diameter must be ascertained, as well as the breadth, the
depth of the shrouding, and the number of buckets; also the velocity of the wheel, or
the number of revolutions it makes in a minute when at work; the fall of water perpen-
dicularly, which is the difference of level between the centre of the column of water as
delivered on the wheel and its lower periphery: the section of the water in the trough
where it is conducted to the wheel, and its velocity, must be determined by ascertaining
the number of seconds a floating body requires to pass through a given distance. In
undershot water-wheels, their diameter must be taken, the breadth, the depth of the
floatboards, and their number; also the velocity of the wheel, its fall, and the section and
velocity of water in approaching the wheel.
In Corn and Flour-mills the valuator must examine their actual state, and whether the
millstones are new or old, whether the mills are ever stopped by back-water in floods,
or retarded from other causes: in estimating the value, the power of a horse is equal to
raising 33000 lbs. 1 foot high in a minute. One pair of millstones in a flour-mill, with its
attendant bolting and other machinery, worked by a water-wheel, is considered to be
equal to an 8-horse power. The value of the water-power capable of working a pair of
millstones with the attendant machinery night and day all the year round, in some situations
is valued at 207. per annum, and sometimes more or less, according to circumstances.
The full amount of working time is usual'y taken at twenty-two hours during the day and
night, two hours being allowed for the change of men and other contingencies: millstones
not actually at work should not be counted. It often happens that a mill has abundance
of water for only six months in the year, and is at a considerable distance from a market
town; wherever this is the case, and land carriage is considerable, an allowance must be
made for every mile of additional distance of a shilling or more in the pound; where a mill
is 10 miles from a market town, it can be rarely worked to advantage. To determine
the value of a flour-mill, the number of pair of millstones usually worked at a time must
be ascertained, as well as their diameter. The force necessary to work a pair of corn mill-
stones grinding meal, together with a pair of shelling and attendant machinery, is taken some-
times at only 6-horse power: the number of pairs of grinding mill-stones, shelling-stones,
and other machinery in the mill, as well as the ordinary working time, must be also
ascertained. To determine the water-power of corn-mills where there is one pair of
stones, tables are usually made, calculated upon the performance of an 8-horse power engine.
Bleaching Mills. In beetling mills in a single long engine the wiper beam, or that which
is furnished with cogs for lifting the beetles, is usually 10 feet long, and makes 30 revolu-
tions in a minute; being furnished with two sets of cogs on its circumference, it raises
the beetle sixty times in a minute; such a wiper beam working beetles of 4 feet 4 inches in
length, and 3 inches in depth from front to rear, making thirty revolutions, or lifting the
beetles sixty times in a minute I foot high, is equal to one-horse power. In this calculation
the power necessary for working the traverse beam, which holds the linen, is included; an
allowance is made for the guide slips, which retain the beetles in a perpendicular position.
Tables may be made upon the above data for any length of beetles, where the number
of inches from front to rear are given; and the horse-power may be set down.
determine the value of the other machinery in a bleaching mill, it is usual to consider
a pair of rub boards equal to two-thirds of a horse-power; a pair of wash feet equal to one
horse-power; a starching mangle, one horse-power; a drying and squeezing machine equal
to one horse-power; and a calender from three to eight horse-power, according to its
quality.
To
Flax Mills. Six stocks are considered to require the power necessary to turn a pair of
corn millstones with shelling-stones, fans, sifters, and other attendant machinery; therefore
each stock is equal to one horse. The bruising machine, consisting of three rollers, may
be considered equal to one and a half stocks.
Spinning Mills.
Coarse yarns require a greater proportionate power than fine; this
is chiefly owing to the additional trouble necessary to prepare the coarser kinds for the
spindle; the spindles and their machinery are also heavier.
Yarn is distinguished by its degrees of fineness, and known by the number of leas or
cuts it yields to the pound: a bundle is twenty hanks; a hank is twelve leas or cuts, and
a cut is 300 yards in length.
Tow is usually spun at from 2 to 5 leas to the pound, and in the dry way, including
the carding and preparation, it requires a horse-power to 40 throstle spindles.
Coarse Yarn, from 13 to 18 leas to the pound, including the preparation, requires a horse-
'power to 80 spindles.
CHAP. X.
895
VALUE OF ARTIFICERS' WORKS.
Yarns spun from 20 to 60 leas to the pound require nearly the same preparation and
machinery, and a horse-power is equal to 120 spindles in the wet and warm way.
In Yarns spun from 60 to 100 leas to the pound, a horse-power will work 200 spin-
dles, including all the preparation; but the spindles and attendant machinery will be lighter
than in the other cases.
In Cotton Mills the throstle spindle is used for the coarser yarns, and for the finer kinds
the mule spirdle.
With Throstle Spindles few manufacturers spin a coarser kind than 10 leas to the pound,
none higher than 30; taking 20 as a fair average, the horse-power would drive 180
spindles.
With Mule Spindles, at an average of 50 leas to the pound, a horse-power, including the
preparations, will turn 500 spindles, and this is varied up to 1000 spindles to the horse-
power; but in this latter case the cotton must be clean, of superior quality, and spun to the
finer degrees. By inquiries based upon the foregoing, the number of horse-power may be
obtained, and consequently the value of the water-power.
Paper Mills, saw mills and others containing machinery driven by water, may be all
estimated, and their value determined by calculating in the same manner.
Before the valuator commences any survey, he must be provided with good maps, having
a field scale, and proper measuring rods or tape for taking the dimensions of the buildings
that are upon the estate.
Where the district is mountainous or hilly, it is also necessary that he should carefully
examine the crops, and make due allowance for the difference of elevation, and where land
lies in the interior of a mountain, or is surrounded by high land, some consideration should
be allowed: land also which has a southern aspect is of more value than that which lies to
the north, and Vitruvius explains to us why that species of fir known at Rome by the name
of supernas is not so good as that which is called infernas, whose durability in buildings is so
great; "the hither side of the Apennines towards Tuscany and Campania is in point of
climate extremely mild, being continually warmed by the sun's rays; the further side,
which lies towards the upper sea, is exposed to the north, and is inclosed by thick and
gloomy shadow. The trees, therefore, which grow at that part being nourished by continual
moisture, not only grow to a great size, but their fibres, being too much saturated with it,
swell out considerably, and then are unfit for building: those which grow in sunny places
are more solid, and, in consequence of the closeness of their pores, are exceedingly lasting.
The infernas, as those firs are called which are brought from warm open parts, are preferable
to the sort called supernas, which come from a closely and thick-wooded country."
CHAP. X.
VALUE OF ARTIFICERS' WORKS IN ENGINEERING.
THE exact valuation of the price of work being one of the most important elements in
the execution of great enterprises, the basis upon which it should be founded, it is our first
duty to consider.
The price of work depends upon several elements, which may be classed as follows:
The prime cost of the materials :
The waste which occurs in converting them to use:
The manual labour :
The incidental expences, such as tools, machines, workshops, &c. &c. ; and persons em-
ployed as clerks of the works, foreman, &c. :
The interest of money on capital, and the profit thereon.
The principal materials employed are stone, brick, lime, sand, and other substances which
unite with lime; timber, iron, lead, copper, &c.
The price of these comprehend, first, that of the material itself, then its conversion and
carriage. The only method of estimating its value is to acquire a correct knowledge
of these three objects, and particularly the manual labour consumed in its conversion, which
generally forms the chief item: usually the price current of the materials is the one acted
upon; and these vary according to circumstances. The loss which materials suffer in their
employments depends in part upon their quality, and on the workmen, as well as the care
and diligence of those who direct them. The manual labour is not so difficult to ascertain.
The execution of work may be divided into three operations,-preparing the materials,
their carriage, and fixing; each of these may be subdivided and separately calculated :
among the tools employed, some are found by the workmen, and the wear and tear forms a
portion of the labour; some of the machines used in large works are provided by the go-
vernment, or the company that promotes them.
896
Book II.
THEORY AND PRACTICE OF ENGINEERING.
The expense of overlooking workmen consists in the payment of foremen and clerks, who
do not labour, but keep the account of the various materials and time.
Gauthey in his valuable work, "Traité de la Construction des Ponts," has given us the
following data upon which we may form our calculations, and it is to be regretted we have
not had similar experiments made upon the labours of English workmen.
Ground Work: under this title is comprehended the digging and removal of earth, laying
the turf, ballasting and dredging, &c. Excepting charges made for cutting turf, the only
expense for these works is the labour; they are generally performed by a lower grade of
workmen, and in companies. The price required is given in hours; the price of an hour
depends upon the value of a day's work, and the number of hours or effective hours it
contains, which is usually ten.
Excavating. The time employed in digging depends upon the nature of the soil; and
the mean results, which serve as comparisons, are as follows:
Vegetable earth, per cube metre,
Loam,
Clay,
Stony earth
or 35.3 cubic feet En-
glish, or one and a
third cube yards.
}
Parts of an
Hour.
· 0.60
-
0.90
H
1.50
- 2.00
2.50
Tufa,
Removal of Earth comprises loading and unloading: when the barrows or carts cannot
approach close to the workmen, it is necessary to throw the earth with a shovel, either
horizontally or vertically on scaffolds raised 2 metres over each other.
For throwing a cube metre (or 1} cube yards English) with a shovel :
Vegetable earth, loam, or sand
Hard earth, clay, and tufa
Mud
Parts of an
·
Hour.
0.65
-
0.75
0.80
When the removal takes place by barrows, it is executed by relays; if the ground is
level, or slightly inclined, each relay is 30 metres in length, and 20 when the inclination is
1 in 12
For loading in barrows a cube Vegetable earth, loam, and sand
metre, or 1 cube yards En-Clay, stony ground, and tufa
glish.
For removal to a relay
Mud
Vegetable earth and loam
Clay, stony earth, sand, mud
·
0.60
-
0.70
·
0.75
·
0.45
0.55
The specific gravity of vegetable earth and loam is 1·5, and each barrow contains 0·04
cube metres.
It is most advantageous to use carts when the distance is from 150 to 200 metres:
when this distance is not very great, trucks drawn by men are preferred; some of a very
ingenious construction, used at the bridge of Neuilly, contained 0-2 cube metres of loam,
and were drawn by three men.
Vegetable earth, loam, and sand
A cube metre drawn by trucks Clay, hard stony earth
For the removal, each cube
supposing five trucks employed,
load,
Time for loading a truck, con-
taining 0·2 cube inches
Time to go a distance of an
hundred metres, and return,
the ground being level, or
nearly 110 yards English
Mud
-
Parts of an
Hour.
0.63
0.73
0.78
metre of earth is estimated in the following manner :
drawn by three men, and three workmen employed to
Vegetable earth, loam, and sand
Clay, hard stony earth, and tufa
Mud
Vegetable earth and loam
Clay, stony earth, sand and mud
Time of unloading
Parts of an
-
Hour.
0.042
-
· 0.049
0.052
-
0.060
-
0.070
-
0.030
If the road is bad, or the rise and fall considerable, some additional allowance must be
made. When carts drawn by horses are used, it is advantageous to have as many men to
load as is practicable; our calculations suppose three employed for that purpose.
To load a cube metre in a cart
Vegetable earth, loam, and sand
Clay, stony earth, &c.
Mud
-
-
Parts of an
Hour.
0.65
0.75
0.80
CHAP. X.
897
VALUE OF ARTIFICERS' WORKS.
The price of transport varies with the number of horses employed; during the time of
loading the horse is unemployed, and this evil is increased in proportion to the size of the
carts, and to the shortness of the distance; the carts should be made in proportion; and
small ones used where the distance is not great. A cart with one horse should be employed
where the distance does not exceed 313 metres; two horses where it does not 1104 metres;
three horses to 2111 metres; and four horses to 3873.
Supposing each horse to draw half a cube metre of earth, the following estimate may
be made :-
Time of loading a one-
horse cart containing 0.5
metre
Ditto two-horse cart, con-
taining a cube metre
Ditto three-horse cart,
containing 1.5 cube
metres
Ditto four horse cart, con-
taining 2 cube metres
Time to go a distance
of 100 metres, and to
return
Time for unloading
୮
Vegetable earth, loam and sand
Clay, stony earth, and tufa -
Mud
-
Vegetable earth, loam, and sand
Clay, stony earth, and tufa
Mud
Vegetable earth, loam, and sand
Clay, stony earth, and tufa
Mud
Vegetable earth, loam, and sand
Clay, stony earth, and tufa
Mud
-
Vegetable earth and loam
Clay, stony earth, sand, and mud
Hours for two
one-horse carts,
-
0.108
-
0.123
•
0.133
300 metres dis-
0.217
-
0.230
- 0.267
0.325
- 0.353
- 0'400
-
0.434
·
0.460
0.434
·
-
tance.
One cart from
300 to
metres.
1100
Two-thirds of
a cart of three
horses from 1100
to 2000 metres.
Half a cart of
0.060 four horses, from
0.070 | 2000
to 4000
0.050 J
metres.
Earth is sometimes removed by boats, which generally contain from 40 to 50 cube
metres from what has been already stated, the loading and unloading may be easily cal-
culated; as for the transport, it varies according to circumstances, and can only be estimated
by the daily hire of the boat, and the number of journeys it can make. When the
earth is shot from a cart or a truck it requires levelling, and a man is necessary for the
purpose.
For levelling without ( Vegetable earth, loam, &c.
throwing a cube metre Clay, stony earth, and tufa
When more care is required, or a talus is to be dressed,
Square metre of surface Vegetable earth, loam, &c.
Clay, stony earth, and tufa
0.15 Hour of a ground
0.25 digger.
J
0.10 Hour of a ground
0.13 digger.
J
Rammer.- Earth requires ramming, when used for cofferdams, or filling in behind
walls, where it is necessary to produce immediate cohesion, that the thrust may be
diminished; and also where it is intended to lay down a pavement. Vegetable earth,
loam, and clay are alone susceptible of being rammed; the latter is not so well suited for
this purpose.
The operation is performed by laying the earth in beds of from 15 to 20
centimetres in thickness, and the ramming a cube metre of earth usually occupies 0·5 of an
hour of the ground digger.
Some experiments have been made on the loss arising from the earth employed in
cofferdams, which is caused by the joints of the sheet piles; the result is, that in those of
from 3 to 4 metres in height, the volume of earth carried into the part below the water
is one half more than the void filled in the cofferdam, or the loss is one-third of the
original volume; above the level of the waters, the loss is only one-fourth of the same
volume.
Laying down Turf, the thickness of which is usually 10 centimetres, comprises three
operations; taking up, removing, and laying down. The men usually employed, being of
a superior grade, have more wages than the groundmen: to cut and remove a sufficient
quantity of turf for one square metre requires 0·5 of an hour of the workmen; the removal
may be estimated according to what has preceded. Laying it down depends generally
on skill, but on a mean it takes 0-8 of an hour for a square metre. The value of
the turf is governed by various circumstances, which require to be added.
Dredging is either performed by machines or by hand moving sand is the only
material upon which any calculation with regard to price can be formed. To remove
with hand drags a cube metre of moving sand, at a mean depth of 1·5 metre under water,
requires ten hours for a workman. This valuation implies that the labour is performed
by men skilled in this employ, who usually receive twice as much as an ordinary
labourer. When the machine is used, the time necessary to drag a cube metre at the
depth of two or three metres under water may be estimated at an hour of the machine
worked by five men; an allowance for the use of the machine must be added.
Incidental charges for Groundwork, &c. comprise superintendants, providing planks,
3 M
898
Book II.
THEORY AND PRACTICE OF ENGINEERING.
scaffolds, wheelbarrows, trucks, &c. ; the other tools belong to the workmen; the carts are
usually hired by the day, in the price of which the value is comprised. It has been found
that these incidental expenses amount to about one-twentieth of the labour. Suppose
a cube metre of loam dug, thrown out, removed in wheelbarrows to 150 metres distance,
and rammed. Taking the price of the labourer per day at two francs, or 20 pence
English,
Digging
Throwing out
Loading the barrow
Removal at five relays at 0.45 hour for each
Ramming
Time employed by the workman
4.90 hours of the workmen is worth at 0.20 franc
for the incidental expenses
for profit
Total
0.90
0.65
0.60
2.25
0.50
-
4.90
Francs.
- 0·980
- 0·049
-
0.103
- 1·132
If the same quantity of earth be removed in carts, it will require levelling down after
being shot; and supposing the value per day for a cart and one horse be nine francs, the
detail will be as follows.
Digging
Throwing out
-
0.90
0.65
Loading the cart
Levelling
0.65
0.15
Ramming
•
0.50
Time employed by the workmen
I
2.85
2.85 hours of the workmen at 0·20 francs is worth
Francs.
0.570
Removing in the cart
0.108
Time in going 150 metres at 0·06 of an hour for 100 metres
Unloading
0.090
0.050
Time employed by the carts -
- 0.248
0.248 hour of two carts with one horse, at 1.80 francs, is worth
0.446
Total
1.016
for incidental expenses
0.051
for profit -
1
0.107
1.174
Whence it appears that for this distance there is a saving of 4 centimes per cube metre
by using barrows in preference to carts.
J
Fascine Work and Fencing. The materials used are branches of trees, stakes, and
gravel to fill the intervening spaces: the price of the branches is at per cube metre, and
regulated by the price of timber: the fascines are usually 2.5 metres in length, and
30 centimetres in diameter: the stakes are 1.5 metres in length, and 5 centimetres in
diameter; when hurdles are employed, they are made with the longest rods that can be
obtained, but not more than from 2 or 3 centimetres diameter at the largest end; the
distance between the stakes varies according to the strength required; it is usually
about 50 centimetres. With regard to the quantity of material for the execution of
these works, a fascine with its four stakes will require two cube metres of branches;
there will be 1 fascines in the cube metre of each row, the thickness of which will be
reduced, after placing and driving in the stakes, to 20 centimetres; it will then require 63
fascines for every cube metre of work performed: if hurdle rods are used across the fascines
to tie them together, there will be 0·1 cube metre of branches for a square metre of each
row, or 0.5 cube metre for a cube metre of work: if the spaces are filled with gravel, it
will require about 0·1 cube metre for every cube metre of work. To make a fascine
with its four stakes employs half an hour; for placing and driving them an hour, which
CHAP. X.
899
VALUE OF ARTIFICERS' WORKS.
together, for a cube metre of work, occupies ten hours of labour; placing rods for hurdles
on a square metre 0·65 hours, which amounts for a cube metre of work to 3.25 hours: the
time necessary for spreading the sand is about 0·25 hours per square metre, which
amounts to 0.75 hours for a cube metre of work. The workmen usually have higher
wages than the labourer; and the incidental expenses to be added are one-twentieth.
Carpentry. — The labour of this work includes the setting out at large the price of
the timber, &c., the carriages, sawing, framing, and taking it to pieces in the yard;
removing it to its destination, and raising the same in its place. The following calcu-
lations suppose the use of oak timber; with regard to fir, birch, chesnut, and other qualities,
it will be easy to form a judgment of the proportion according to which it will be necessary
to reduce the quantity of labour, which depends on the hardness and specific gravity of the
timber.
To make a mortise requires
To make a tenon
S at least
at most
at least
at most
Halving the ends of plates or other timbers
For a square metre in joints at the ends of brestsummer, &c.
which gives for one joint, supposing the piece to be 25 cen-
timetres square, and at the joint 50 centimetres in length
Supposing the piece 35 centimetres square, and at the joint 1
metre in length
Mean.
Hours of a
Carpenter.
1·001
1.50
2.00
3.25
-
1.25
1.75
2.25
1.00
1.00
10.50
-
1.31
2.50
3.68
5.00
6.00
1.00
3.00
1·40
5.00
10.50
12.50
1.50
0.20
0.15
For common framing
dovetailing
boring a metre in length for bolts
boring the timber when fixed
sawing a square metre of timber on tressels
sawing in the yard a square metre of the ends of timber
cutting off the heads of piles with the hand-saw for a square metre
sawing a square metre of planking with ditto
lining out and squaring for use
-
To fix a kilogramme of iron when the iron is to be let in
drive in or pull out an iron pin
-
Carpenter's work may be divided into several kinds: as that for foundations or scaffold-
ing, which do not require timber to be squared or prepared; it is equally useless to reduce
it to one thickness, except where planks are required to unite in a very exact manner: the
labour is reduced to framing done on the spot, and fixing.
Temporary bridges and centres to vaults require that the timbers should be prepared
after a working drawing, and the framing put together in the yard, but not wrought on
the face with regard to the carpentry of timber bridges, it is done agreeably to a drawing;
the framing prepared and put together in the yard, and the faces wrought.
There are also works executed after a drawing that do not require to be wrought
entirely, as horizontal sleepers or joists and binding pieces, which are generally faced in
the yard, cut to a length and fitted at the place, the price of which differs from that of
the timber.
Parts of an
Hour.
Planking and Piling.
Preparing a pile for scaffolding, forming the head, and fixing the shoe
Letting in the shoe, weighing 5 kilogrammes at 0·20 hours for each
Do. for a pile used in foundations
1.25
1·00
2.50
Letting in the shoe, weighing 10 kilogrammes at 0·20 hours for each
To sharpen and prepare a lineal metre of sheet-planking, and putting on the
shoes if not let in
2.00
0.20
If the joints are grooved and tongued
-
0.80
For fixing the sheet piles
0.20
which gives for a sheet pile, 5 metres long, if the joints
are square, 5 metres at 0·20 hours for each
1.00
1.20
Put into the frame or placed -
0.20
If the joints are grooved and tongued, 5 metres at 0.80 hours for
each
4.00
4.20
Put into the frame
0.20
If the shoes of the weight of 5 kilogrammes are let in, we must add 5 kilo-
grammes at 0.20 hours for each
1.00
3 м 2
900
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Scaffolding. — Labour for fixing the heads on the top of the piles, including the mortise
and tenons: piles 22 centimetres in diameter are placed 3 metres apart; the heads are 22
centimetres square, formed of pieces 5 metres in length; hence the labour of each run-
ning metre will comprise for the construction as follows:-
Hours of a
Carpenter.
Sawing the third of a pile, forming a surface of 0·013 square
metres, at the rate of 10·50 hours per square metre
A third of framing, mortised and tenoned at the rate of 2.25
hours for each
0·14
1.35
0.75
A fifth of framing for the end, at the rate of 1·3 hour for each
Placing and adjusting
0.26
0.20
Which amounts per cube metre to
27.89
Hours of a
And for the removing, unframing, &c., for a running metre
Which amounts per cube metre to, for a carpenter
Ditto
for a labourer
Workmanship of a Cube Metre of capping placed on the heads of the piles, fixed by iron
pins.
Supposing the dimensions of the timbers and their distances apart to be the same as before:
the labour for the construction will comprise,
Labourer.
0.04
0.06
0.83
1.24
Hours of a
Carpenter.
Sawing the piles, as before
0.14
Piercing one third of a hole, allowing a length of 7 centimetres
at an hour per metre
0.07
0.69
Placing a third of a pin at 0·06 hours for each
0.02
Framing at the ends, as above
-
0.26
Placing and adjusting
-
0.20
Which amounts at per cube metre to
14.25
And for the unframing, &c., and taking out the third of a pin at
0.06 hours
0.02
0.06
Removing, &c.
0.04
Hours of a labourer
0.06
Which amounts for a carpenter per cube metre to
1.24
Ditto for a labourer
ditto
1.24
Labour upon a Square Metre of Waling Pieces, which secure the piles in a longitudinal direction,
the piles being at 3 metres apart as before, and the pieces 25 centimetres in width.
Hours of a
Carpenter.
The running metre contains a third of a pin at 0·06 hours for
each
0.02
0.12
Raising and adjusting
0.10
which amounts per square metre to
0.48
For the demolition a third of the pin pulled out at 0.06 hours
for one
0.02
0.06
Removing and stowing away
0.04
Hours for a labourer
0.06
which amounts for a square metre to
0.24
Hours of a labourer
0.24
Labour for a Square Metre of Planks placed on a scaffold to form a floor.
The construction consisting in the arrangement on the scaffold will employ
For a labourer
0.02
0.08
The removing may be considered at the same price.
Cofferdams.- Labour for a cube metre of waling pieces bolted to the piles; the timber
being 16 centimetres square, and 5 metres in length, and the distance between the piles
1.3 metres; it will then require 39-06 running metres to form a cube metre; the running
metre will contain,
0.77 holes for bolts, 46 centimetres in length, giving 35 centi-
metres at the rate of 3 hours per metre
joint at the end, at 1.30 hours for each
Putting it in its place
S
which amounts per cube metre to
.
Hours of a
Carpenter.
1.05
1.51
0.26
0.20
58.98
CHAP. X.
901
VALUE OF ARTIFICERS' WORKS.
Removing the bolts at 0·77 bolts at 0·6 hours for each
Taking down and putting away
Do. for a labourer
Hours of a
Carpenter.
0.05
0.05
}
0.10
0.10
3.91
3.90
Which amounts per cube metre for a carpenter to
Do.
for a labourer
When the timbers are used again the labour will be the same.
Labour for a Cube Metre of Entretoise (or entertyes) bolted to the piles, the scantling
being as the timbers above, and their length each four metres: the running metre will
comprise,
Half a hole of a bolt, 40 centimetres long, giving 20 centi-
metres, at 3 hours per metre
Hours of a
Carpenter.
·
0.60
Half letting in at the meeting of the piles, at the rate 0-50
1.05
hour for each
0.25
Putting it in place
0.20
which amounts per cube metre to
41.10
For demolition, half a bolt to remove at 0-06 hour for each
Removing and putting away
0.03
0.08
0.05
For a labourer
0.10
3.12 for a carpenter.
which amounts per cube metre to
Do.
do.
The labour is the same when the timber is employed again.
3.91 for a labourer.
Labour for a Cube Metre of Entretoise nailed against the piles, supposing the length of
cach entretoise 2 metres, and its scantling from 10 to 15 centimetres: it will require
66.67 running metres to form one cube metre; and the running metre will comprise when
constructed,
Placing an iron pin
Fixing or putting in place
which amounts per cube metre to
For demolition
Removing and putting away
Do. for a labourer
which amounts per cube metre to
Do.
do.
Hours of a
Carpenter.
0.06
0.15
}
0.21
14.00
0.06
0.05
}
0.11
0.10
7.33 for a carpenter.
6.67 for a labourer.
Labour for a Cube Metre of Deals framed in panels to slide, supposing the cross pieces
are 2 metres apart, and the deals 25 centimetres wide and 8 centimetres thick, it will re-
12.5 square metres to form a cube metre.
The square metre contains, when constructed, as follows,—
Placing 4 pins at 0·06 hour for each
Framing the deals
·
Placing the sliding planks
which amount at per cube metre to
Demolition
Removing, putting away, &c.
For a labourer
Per cube metre
Do.
do.
1
Hours of a
Carpenter.
0.24
0.50
1.04
0.30
13.13
0.24
0.44
0.20
0.60
5.50 for a carpenter.
7.50 for a labourer.
If the sliding planks are used again without being demolished, the labour will be re-
duced to the mere placing.
Carpentry for Foundations. Labour for a Cube Metre (or 7 of a load of timber English
nearly), of capping placed on piles, into which they are mortised and tenoned; the piles
being distant 125 metres, and the cappings composed of timber 5 metres in length, 10
running metres being required to form a cube metre; the labour of which will comprise,
8 mortises and tenons, at 3.25 hours each
2 joints at the end, 2.50 hours each
Placing and adjusting
I
...
Hours.
26.00
Hours of a
Carpenter.
5.00
2.00
}
33.00
3M 3
902
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Labour for a Cube Metre of Sleepers tenoned and mortised to the heads of piles, and
halved at the ends to the cappings; the piles being at the same distance, and the scantling
of the timber as before, each sleeper being 5 metres long.
8 mortices and tenons as above
4 halvings at 5 hours each
Placing and adjusting
26.00
20.00
3.00
Hours of a
Carpenter.
Labour for a Cube Metre of binding Pieces, let into the piles, and bolted to them.
8 notches or halvings at an hour each
49.00
Hours of a
Carpenter.
8.00
8 holes for bolts, each 50 centimetres in length, giving 4
metres at the rate of 3 hours for piercing on the plane,
27.00
and fixing the bolt
12.00
2 joints at the end, 2.50 each
5.00
Placing and adjustment
2.00
Labour for a Cube Metre of Capping or Sleepers, fixed to the piles by iron pins.
Hours of a
Carpenter.
8 bolt-holes 30 centimetres in length, giving together 2-4
metres, at the rate of 1 hour each for piercing
2·4
2.40
5.60
8 iron pins, driven in at 0·15 hour for each
1.20
Placing and adjustment
2.00
For the Labour when the Sleepers are under Water.
Hours of a
Carpenter.
Piercing the holes
2.40
8 iron pins driven in, 0·50 hour each
4.00
10.40
Placing and adjustment
4.00
Labour for a Cube Metre of Platform, with deals or planks, the thickness of which are
10 centimetres, and their width 25 centimetres.
Hours of a
Carpenter.
8 metres of joints in length to prepare, forming 0-8 square
metres, at the rate of 0·15 of an hour per square metre
1.20
1.20
Placing and adjusting a square metre of floor
0.90
Which amounts per cube metre to
21.00
The Labour when the Deals are framed together, and afterwards sunk under water.
Hours of a
Carpenter.
Preparing the edges and adjusting the planks as before
Sinking and placing under water
2.10
3.10
1:00
Which amounts per cube metre to
31.00
If the platforms are in compartments, add per square
metre
0.15
And per metre cube
1.50
Labour on Timber in the Yard. The first operation is tracing the form by applying
the mould, and ascertaining the proper timbers for the purpose; so that none be selected
that would occasion much waste; it is then sawn, and the face over which the saw has
passed is considered perfect; hence, there is economy in the employment of large timbers:
if the faces are dressed with the axe or the adze, and the deals are formed from large tim-
bers, then
To select a cube metre of timber apply it to the mould,
and line it out, for the least
for the most
3.00
6.00
Hours of a
Carpenter.
4.50
As for the cutting, it must be estimated according to the nature of the works, they being
too various to be analysed: some general results will enable a judgment to be formed,
which may approximate near enough for practice.
For the labour employed in cutting a cube metre of timber for the principals of a bridge,
the total length of which is 36 metres, the scantling 30 centimetres, which form a cube of
3.24 metres.
For cutting a Cube Metre of Timber at the Yard. — Timber not wrought when used for
centres or temporary bridges.
CHAP. X.
903
VALUE OF ARTIFICERS' WORKS.
Hours of a
Carpenter.
fat least
Above 25 centimetres scantling {
at most
ſ at least
Less than 25 centimetres scantling {
at most
Timber wrought all round for Bridges, Palisades, &c. &c.
Above 25 centimetres, at least
ditto
ditto
at most
Below, 25 centimetres square, at least
Timber rebated, &c. &c. above 25 centimetres
ditto
below
at most
ditto
as capstans, &c.
Timber used for machines, as cranes, pile-engines, &c. &c.
ditto,
10.
15.
20.
20.
25.
30.
Carpenters.
- 30
40
50
·
40
50
-
60
60
70
90
150
The timbers having been cut and framed, the holes for the bolts bored, the timbers are
numbered, taken to pieces, and laid aside in the yard, to be removed to their destination.
Per cube metre at least
ditto
at most
Labour of Cutting consists of
Hours of a
Carpenter.
:
1.00
2.00
}
1.50
Four pieces of framing, mortised and tenoned at the extremities of the braces, at
3.25 hours for each
8 notches for the two courses of waling pieces, 1 hour each
1 notch for the small timbers on the piles
-
Hours.
-
13.00
8.00
0.50
5.00
2 end joints for the beams or sleepers at 2.50 hours each
9 holes for bolts, 60 centimetres each, for uniting the upper timbers to the sleepers,
and for the binding pieces, making 5·40 metres, at the rate of 1 hour per
metre
For cutting the pieces to a length, 20 ends, each having 0·09 square metres, and to-
gether 1.80 square metres, at the rate of 5 hours per metre
43.20 square metres of surface of face, to wrought at 1.5 hour per metre
5.40
9.00
- 64.80
Total
105.70
By dividing 105-70 hours by 3-24 cube metres, we shall have for the labour upon each
cube metre, 32-62 hours: it will be seen that this limit is placed between 30 and 50
hours, as previously given. If the timber was not wrought, the labour would only be 40·9,
which divided by 3 24 cube metres, gives for each 12·62 hours, a number placed between 10
and 20, as already cited.
Raising or putting up Timbers already framed. The expense varies according to the work:
if the timbers are of small scantling, the pieces are numerous, and caution great for the
removal; carpenters are alone employed. When they are less important, machines worked
by labourers are employed; there is some difficulty in fixing a value for this kind of work.
For the raising a Cube Metre of Timber.
When small timbers are used, and carpenters employed to raise it by hand,
above 25 centimetres square
below
ditto
Hours.
- 20
-
· 30
:}
25
When the timbers are of an ordinary scantling, portions being already framed, and put
together, the labour being performed by carpenters.
Timber above 25 centimetres square
ditto below
ditto
For large pieces of carpentry, such as the principals used in centring, &c. &c. raised
by machines worked by labourers
Above 25 centimetres square
-
101
- 20
}
15
Hours.
carpenter
labourer
·
€ 5.0
10.0
·
For the striking the centres of vaults, removing temporary bridges, taking framing to
pieces, and placing them in boats, &c.
Hours.
For each cube metre, for a carpenter
2.0
ditto
for a labourer -
4.0
3 M 4
904
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
Carpenter's Work for the upper Parts.—The planks laid on the centres for the construction
of vaults do not require any preparation at the yard, and therefore must be put at a dif-
ferent price to that of the centres.
For the Labour of a Cube Metre of Planks, supposing the principals or ribs 2 inches dis-
tance, and the scantling 20 centimetres, we have 25 running inches for a cube metre.
Piercing 13.5 holes in each, 20 centimetres long, making 2·70 metres at an
hour per metre
13.5 pins driving in at 00·6 hour for each
Putting in place
S
Hours.
-
2.70
7.01
-
0.81
3.50
Timber used for floors and other parts of wooden bridges require no other prepa-
ration at the yards than reducing them to their proper scantlings; they must be valued
accordingly.
Labour on a Cube Metre of Joists, supposing the principals at 15 metres distant, the scant-
ling from 25 to 30 centimetres square, which gives 136 running metres to a cube metre,
and 5 metres of length for the pieces, two of which will form the width of the bridge, each
running metre will comprise:
Two thirds of a notch at the meeting of the sleepers at the rate of 0.5
hour for each
- 0.33
-
Sawing the ends, having 0.15 metres square, at 5 hours per square metre - 0.75
} of the joint at the other end, at 1·30 hour
4 wrought faces, 1·10 square metre at 1 hour
small pins, driving at 0·06 hours
Putting in place or fixing
Hours of a
Carpenter.
0.26
2.78
- 1.10
- 0·04
-
0.30
Which gives per cube metre
-
37.53
Laying the planks on the floors of wooden bridges may be valued in the same manner
as in the platform for foundations.
Carriage of Timbers. —Large timbers are usually moved by means of a truck; smaller,
and planks, &c. are loaded on carts, &c. when the distance is trifling, they may with
advantage be carried by hand: the price of this portion of labour is not subject to much
variation. The proportion of price is always relative to the weight and size of the timbers
moved :-
Per cube metre
For loading
0.20
Unloading
0.15
For going, &c., or returning, a
distance of 100 metres
0.06
Hours of a truck
served by 10
labourers.
Waste upon Timber depends on the nature of the work, and the arrangements made
between the merchant and contractor. Supposing the timber to be squared, the loss is
then divided into three portions: first, on the round timber, as it has been felled; second,
when squared or dressed on four sides, and reduced to a more regular figure: third, when
sawn into planks and deals.
Round timber is seldom employed except for piles. The loss which is sustained on it
arises from the length being usually greater than required; something is cut from the
extremities to form the head and point, and such timber loses three-fourths of its value. The
waste may be estimated at one-tenth of the primitive volume.
The waste upon square timber depends on the nature of the works. It may be estimated
at one-eighth, which is near enough for timber prepared on its four faces, and at a tenth
for rough timbers of the primitive volume. If the works contain circular pieces it is rare
to find timber crooked enough naturally; regard must then be had to the waste sustained,
and a price put accordingly. The waste on sawn timber is about an eighth of the volume,
when the joints are wrought, and at a tenth when laid rough.
;
Waste on Timbers in temporary Constructions. The cost of scaffolding centres and tem-
porary bridges may, with respect to labour, be estimated in the manner before described ;
the timber used is generally taken away by the contractor, and an allowance made to him
for the use and waste of one half. The diminution of value which timber sustains in the
above works arises from the change produced in the quality, and from the adaptation to
particular purposes, such as injury from piercing holes, mortices, &c.
Suppose a scaffold pile, five metres in length, cost 75 francs, and as the timber of this pile
cut into lengths of a metre is only fit for fire-wood, its value would not be more than 25
francs the cube metre, and diminishing the length of the pile from five metres to one, the
price of the cube metre will diminish in proportion.
Estimating, as above, one tenth for the loss sustained in the pile for forming the head
and point, which is abridging it one tenth of its length; reducing it from 5 metres to 4.5
metres, which is the quantity it would be taken at in the estimate. When used, the head
СНАР. Х.
905
VALUE OF ARTIFICERS' WORKS.
and point are injured, and before it can be used again as a pile, or converted to any other
purpose, it must be reworked, and reduced to 4 metres in length. The length of the
pile will then have diminished a quarter of the interval from 1 metre to 5 metres: the
price of the cube metre of timber must then be diminished a quarter of the interval between.
75 and 25 francs; that is to say, it will be reduced to 62 50; consequently, if the pile is
25 centimetres in diameter, it will be worth 4 × 0.48=0·192 cube metres, at 62.50 francs;
that is to say, 12 francs: but, according to ordinary custom, the contractors will take it at
4·50 × 0·048=0·216 cube metres at 37.50 francs, that is to say, for 8·10 francs.
་
A piece 30 centimetres square, employed as a binding piece to a centre, and in which
notches 10 centimetres in depth have been cut, and at the extremities a joint 50 centi-
metres long, will have sustained a loss of one metre in length, which will reduce the price
of a cube metre of such timber to 62.50 francs. The notches do not affect the value, because
a cube metre of timber 30 by 20 centimetres square is not essentially worth less than a cube
metre of timber 30 by 30: but the piece must be considered as having lost one-third of
its thickness; thus it is not worth more than 4 × 0·030 × 0·20=0·24 cube metres at 62.50
francs; that is to say, 15 francs.
According to custom, in the first example the contractor would be a considerable gainer;
in the second, he would neither gain nor lose. As in carpentry, there are few timbers
which belong to the second example, but many of the first which are little injured,
it follows that the contractor obtains an advantage, if care be taken that the pieces
be as little notched as possible, and the binding pieces attached by bolts: hence it
appears that if an account is not taken of the loss which each work sustains, and a gene-
ral proportion adopted, the contractor should take the timber back at two-thirds; that is
to say, allowing one-third for use and waste; nevertheless it must be observed, that it
often happens that the timber remains a long time on hand before it can be again used :
this requires consideration, and perhaps a further allowance to be made.
There are temporary works executed with timber that has been previously employed for
the same purpose, as cofferdams: on examining, if it requires any change in construc-
tion, the extra labour must be taken and valued accordingly: as for the loss sustained by
recutting the timber, the proportion is the same as has been already given, or at about
a fourth of the primitive volume.
Incidental Expenses for Carpenter's Work are considerable, independent of the expenses of
management, which comprise the payment of the foreman, who marks out the timber,
regulates the employment of the men, and that of the clerk, who enters an account of the
time and materials: besides these, there is the rent and expenses in the yard, the cost
of sheds for laying out the moulds, the machines, as pile-engines, crabs, scaffold-poles,
blocks, and pulleys, windlasses, trucks, &c.; keeping them in order, and above all, the
cordage and ropes, which are a considerable item of expense; the tools also which are not
provided by the workmen but found by the master, of which there are several. These inci-
dental expenses may be estimated at one tenth of the value of labour.
For the price of a cube metre of timber used in the platform of a foundation, supposing
it framed, and fixed under water; the price of the timber per cube metre delivered at the
yard being 75 francs: the carpenter's day's work 3.5 francs, and the labourer's 2 francs. The
platform, 10 centimetres in thickness, may be formed out of timbers 30 centimetres square,
by putting two cuts into it, or of timber 20 centimetres square with one cut; conse-
quently, in the first instance, there will be 6.667, in the second 5, and the mean 5.833
square metres of sawing for a cube metre of platform. The price of the cube metre will
then be valued as follows: —
Francs
Francs,
A cube metre of timber furnished
75.00
5-833 square metres of sawing at the rate of 1·4 hour of a
carpenter, valued 0·49 franc per square metre
77.86
2.86
An eighth for loss
9.73
Carriage, distance 200 metres, 0.47 hours of a truck,
worked by 10 labourers, worth 2 francs
0.94
8.29
Labour for framing, sinking and adjustment under water,
31 hours of a carpenter at 0.35 francs
7.35
A tenth of the labour for incidental expenses
0.83
Total
96-71
A tenth for the contractor's profit -
9.67
Total
106.38
For the principals of a centre used in a stone bridge, composed of two arches, which are
separately centred, the dimensions being unequal, so that it would be required to recut
906
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
the timbers to adapt them for the second centre. The manner of establishing this price depends
in some degree upon the arrangement made with the contractors. Supposing the contrac-
tors take the timber back at two-thirds its original value, and the volume is equal to that
which has been used, the price of the cube metre of timber for the first centre will be
Francs.
A cube metre of timber delivered
75.00
A tenth for waste
7.50
Hours.
Labour at the yard, lining out and gauging -
3.00
Cutting and framing
15.00
Taking to pieces, numbering, &c.
1.00
Total
19.00
Francs.
19 hours of a carpenter at 0·35 francs value
6.65
Carriage
0.94
Raising: 5 hours of a carpenter
1.75
10 hours of a labourer at 0.2 francs
2.00
13.78
Striking the centre: 2 hours of a carpenter
0.70
4 hours of a labourer at 0.2 franc
Second crrriage
·
One tenth of labour for incidental expenses
0.80
0.94
1.38
Total
97.66
One tenth for profit
Total
Deduct two-thirds of the value of the timber
Remains
9.77
107.48
50.00
57.43
With regard to the second centre, admit that in reworking the timber, a loss of a fifteenth
takes place, the price of the cube metre will be.
Loss or waste, one fifteenth on 75 francs
Labour (as above)
Incidental expenses
Profit
Total
Total
Francs.
5.00
13.78
1.38
20.16
2.02
22.18
Suppose, after an exact account is taken of the loss timber is subject to in the forming
of centres, it be ascertained that after the execution of the first centre it has lost two-fifths
of the primitive value, and after that of the second a fifth of the second value, the price
of the cube metre of timber of the first centre would be
Loss on the value of the timber, two-fifths of 75
·
Labour, as before
Incidental expenses
One-tenth profit
Total
Total
Francs.
30.00
13.78
1.38
45.16
4.52
49.68
And observing that when the timber has sustained a loss of 30 francs out of 75 francs,
it is only worth 45, the price of the cube metre for the second centre will be-
Loss on the value, one-fifth of 45 francs
Labour, as before
Incidental expenses, ditto
One tenth for profit
Francs.
9.00
•
13.78
1.38
Total
24.16
242
Total
26.58
CHAP. X.
907
VALUE OF ARTIFICERS' WORKS
Masonry, valuation of.— Mortar, cutting and laying the stone.
Forming the Mortar.—The proportion of the materials used depends on their quality,
as does also the waste, and which experience can alone value: it must be first ascertained
how much a given measure of well burnt quicklime will produce when slaked; observing
that quicklime always suffers a loss of about a tenth, on account of the core, which arises
often from not being properly burnt. Secondly, the proportion of slaked limes and sand,
or other materials used instead. Thirdly, the relation of the volume of the mixture after
trituration, with the volume of the materials mixed. As to the labour, the slaking of the
lime depends on the quantity as well as distance from whence the water is brought; it may
be valued in general at eight hours of a labourer for every cube metre of quicklime; if the
water is laid on, five hours of a labourer is sufficient.
Making the mortar requires care, and an account must be taken of the time employed
for its due mixture; it may be considered that from 12 to 20 hours of a labourer is
required for a cube metre. The waste in mortar may be computed at one-twentieth of its
volume.
Rubble Work or Moëllon comprises the carriage of the stone from the yard where it is
measured to the spot where it is to be used, and its adaptation, whether rough, piquet or
hammer-dressed, in mass or faced, in walls or vaults. The removal is performed by
barrows when the distance is not considerable.
Loading the barrows, per cube metre
Hour of a
Labourer.
0.8
·
0.6
Removal with one relay of from 20 to 30 metres, the specific gravity of the
stone being 2
-
When the distance is greater, carts are employed, containing 0.21 cube metres, which
are drawn by four men.
To load a cart containing a cube metre of moëllon 0·83 hours of a labourer.
The time employed for each
cube metre of moellon.
Hours of
4.767 carts,
drawn each by
four men.
Loading the carts containing 0.21 cube metres,
three labourers to load
100 metres going and returning
Unloading
0.0.58
0.060
0.030
When the distance is considerable, the removal of the moellon is performed in carts
drawn by horses: it will be easy to estimate it upon that of the removal of earth,
reckoning 0.85 hours of a labourer for loading a cube metre in the carts, and observing
that each horse which draws half a cube metre of earth weighing 1500 kilogrammes, can
only draw
1.5
2
0.5 0.375 cube metres of moellon.
10
06
A man with a barrow, working ten hours, will remove = 16.7 cube metres of stone
to a distance of 30 metres of level ground, or 20 metres when inclined. The specific
gravity of stone being 2, the daily effective labour will be equal to 16·7 × 2 × 30=1000
kilogrammes moved 1000 metres on horizontal ground, and 16-7 × 2 × 20=668 kilogramines
moved 1000 metres on inclined ground.
For the removal by carts, a man in 10 hours would remove
metres of moellon, 100 metres distance.
10 x 021
0.148 x 4
−3·547 cube
The daily effective labour then would be 3.547 × 2 × 100=709 kilogrammes carried
1000 metres with respect to water carriage the value of transport depends upon various
circumstances.
The labour required to execute a cube metre of moellon, including the labourers
assisting the mason, as well as those making the scaffold :—
Per cube metre
Measuring the stone
Throwing the stone and watering, without adjusting
Ditto with adjustment
Hours of a
Labourer.
0·70
0.80
1.00
Hours of a
Masses placed dry by hand
Per cube metre
Masses placed rough
Masses for walls requiring scaffolds
Mason and his
Labourer.
4.00
4:50
6.50
908
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
For placing a Square Metre : —
Hours of a
Mason.
Facing a wall of moellon laid dry
the same rough in mortar for walls
in vaults
hammer dressed, joints in mortar
vaults and circular on plan
the moellon cut for straight walls
vaults and circular parts
To repoint the joints carefully with mortar or cement, without scaffolding
With scaffolding
0.50
-
1.00
1.50
9.00
-
10.00
11.00
-
12.00
Mason and
Labourer.
1.00
1.25
The quantity of mortar used bears a proportion of about, or at the most, of the
volume of the masonry: as the mortar only fills the voids left by the stones, it does not
augment the volume; the mortar or cement used for pointing may be estimated at from
0.10 to 0·02 cube metres, per square metre of facing.
Brickwork.—The carriage of bricks may be estimated in the same way as moellon: the
work requires more attention, and the labour is dearer,
It requires for a Cube Metre,
For rough brickwork
For ditto, requiring scaffold
For the laying of faced Work, per Square Metre,
Rough brick, joints struck, without adjustment, mortar, lime, and sand
Vaults, &c.
Per square metre, pointing without scaffolding
Per square metre, pointing with scaffolding
Hours of a
Bricklayer and
Labourer.
5.00
7.00
Bricklayer's
Hours.
1.20
1.80
Bricklayer
and Labourer.
-
1.25
1.50
Bricks are usually sold by the thousand; the loss which they sustain in carriage is
about 1
The quantity of mortar used varies in different works.
20°
in,
Works in rough Stone. Stones larger than rubble or moellon are used for filling
where rivers are rapid; they are also used to advantage in the lower beds of piers exe-
cuted in moellon, and placed dry; above all, in forming the foundations of walls, where a
timber platform is not considered necessary: when these stones are used rough, and
placed without arrangement, the price is that of moellon, or a little more; when the faces
are dressed, and each stone placed on wedges, the facing being plummed, the price approaches
that of worked stone.
With regard to carriage, if the stones are too large for a cart, waggons for the purpose
are appointed, and the charge for transport depends upon the dimensions. The waste
varies between and of the primitive volume, and the quantity of mortar between
and
Stone squared, and laid in Courses. The first operation is cutting the stone, paying
great attention to the joints and beds, which is oftentimes neglected, and that of the
facings seen the time required depends upon the nature and properties of the stone.
The principal object is to face the stone, and the time necessary to execute a square metre
being known, it may be used as a unit in the value of other work.
For squaring a Metre of upright facing,
Of granite
Calcareous stone, hard
-
do. of another quality, soft
Hours of a
Stone cutter.
28.00
9.00
3.50
The granite and soft calcareous stone are the extremes of hardness and softness of
stone employed in hydraulic constructions.
These valuations suppose the faces only rusticated, that is to say, raised or worked with
chisel, and dressed with the point and the hammer (matting hammer) if it be axed or cut
with the hammer on one side, and toothed on the other, then smoothed with the rip (a
scratching tool) and mallet, we must add another three-fourths. The time necessary for
cutting straight facings being known, the labour of curved facings may be estimated thus:
CHAP. X.
909
VALUE OF ARTIFICERS' WORKS.
m
T= (1 + 77 T):
T=the time of cutting the face straight.
T'=the time of cutting a curved face.
7 the radius of curve of the surface of this facing.
m=0·75.
Then the price of the curved facing will require the time necessary to reduce the stone to
a plane face and a curved one. But if the reducing has for its object the execution of some
parts in projection, as obtuse angles or retreats, it cannot be valued as if cutting a face;
but an allowance of ten times the labour is required for mere plain work: after cutting the
face, the beds and joints require the next consideration: both are valued at the same
price, which is an erroneous system; the joints requiring much more reducing than the
beds.
of the time necessary for
cutting the face.
For cutting the joints}
the
0-8
0.3 J
Cutting mouldings for cornices is valued thus, a price for reducing the stone, and after-
wards according to the girth of the mouldings, as moulded work: other expenses are
incurred in cutting stone besides the labour, as tools and oil, &c. ; for cutting granite, ten
points are allowed for every square metre for the calcareous stones: this expense is trifling.
Stone suffers a waste, which varies from a tenth to a fourth. The carriage is performed
by a truck, or low waggon, drawn either by men or horses.
Supposing the specific gravity of stone to be 2, a man can draw 0·055 cube metres, and
six men are required to load and unload the blocks of stone; these six men will be suf-
ficient for the service of the truck, when the volume of the stone does not exceed 0.38 cube
metres; if the stones are heavier, a greater number of labourers must be employed, who
will lose their time after loading, unloading, and during their return; and as it costs
more to move a truck with men than with horses, there is a point where, relative to the
weight, it becomes preferable to use the latter. The volume of stone that may be drawn
by a horse being 0.4 cube metres, it is easy to determine the size of the stones which re-
quire one or more horses, and
When the stone is between 0-60 and 0.80 cube metres 1 horse
0·89 and 1∙18
1·29 and 1·58
1·69 and 1·98
2 do.
3 do.
4 do.
Upon this basis the charge for transport may be easily obtained, when the time of loading
and unloading is also known, which is in proportion to the dimensions of the stone; an hour
is required for a block for every cube metre; and the time necessary for going and re-
turning are 100 metres, 0·6 hour.
When the stone arrives, the masons receive it, and sometimes it is requisite to move it by
machines when a block is 0 75 metres cube, and it is required to be raised & metres; for at-
taching and detaching the tackle, 0.50 hours is allowed for two men and six boys.
For mounting to 8 metres at the rate of 0·1 hour per metre, 0·80; the same number of
men and boys being employed. To bed the stone requires a mason, two assistants, and a
labourer: when great rapidity is necessary, there are in addition two others to lay the
cement, and an additional labourer.
For a cube metre
of stone.
for the placing
J for the grouting
-
·
3.00 hours of a mason, 2 assist-
2.00 ants, and a labourer.
It is not necessary to add anything for the construction of vaults; the experiments made
at the bridge of Nemours indicated that placing the voussoirs is less costly than that of
the courses of the facings of walls; bedding the cube metre of stone at this bridge required
for the piers 2.94, for the abutments 3, and for the vaults 2.67 hours. The quantity of
mortar required varies from a tenth to a twentieth of the volume of the masonry.
After the work is done, the stone requires re-dressing and pointing, which ordinarily
amounts to about a twentieth of the primitive cutting; a running metre of joint occupies
half an hour for a mason and labourer; the mortar used in the joints may be estimated at
0.001 cube metre.
Beton. The preparation of various species, and of mortar used for composing the backs
of vaults, may be estimated in the same way as moellon: with regard to beton, some
allowance must be made when it is thrown from a height into the water; the labour is
about the same as that for throwing earth with a shovel, or stones for foundations: where it
is thrown into an inclosure with ease, an allowance must be made.
The covering of the backs of arches of bridges is so important for their preservation, that
great care should be used. The labour to spread and level each layer should be valued
for a cube metre at 4·5 hours of a mason, served by a labourer; and that of the beating at
1.5 hours of a labourer for every square metre of each of the layers beaten. The labour
910
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
for stucco, with which the facings in moellon are sometimes covered, is nearly the same as
that of the pointing, the quantity of mortar being a little greater.
Incidental Expenses on Mason's Work consist in the maintenance of the machines used,
timber and cordage for scaffolding, saws, sieves, roller, pincers, &c. The tools for cutting
and laying the stones belong to the workmen: these incidental expenses amount to about
one tenth of the labour.
Iron-work. — A smith usually works, winter and summer, twelve hours per day.
There is employed in the
manufacture of a kilo-
gramme of iron
Loss of iron may be va-
lued at
For iron of large dimensions, as ties, &c.
For cramps, &c.
For pins, bolts, &c.
For the first
For the second
For the third
-
1
Smith and
his Assistant.
0.10
0·40
0.70
Of the Pri-
mitive Weight.
0.03
0.08
0.10
For the first
The volume of coal used
for a kilogramme.
For the second
For the third
Cube Metres.
0.0001
0.0006
0.0010
Making the screw ends of bolts, according to their size, requires from 0-2 to 0.5 hours of
a smith for the screw and its nutt: with regard to the placing or fixing ironwork, if it is
done by the smith it may be valued at
Hours of a Smith
and his Help.
For a kilogramme of iron,
including carriage
For the first class
For the second
For the third
0.04
0.20
0.40
As for running in with lead, &c. it is difficult to fix a price.
Incidental Expenses. These are considerable: as all the tools are furnished by the con-
tractor, they are generally put at one-fifth in ordinary buildings, but in bridges, &c. one-
seventh is sufficient.
The labour
Painter's Work. The colours usually employed are lamp-black, red and yellow ochre,
linseed oil, turpentine, &c.: to cause them to dry quickly, litharge is added.
of the painter is employed to grind the colours and to lay them on.
For grinding a kilogramme
of colour in oil
Red ochre
Yellow ochre
Lamp-black
The quantity of oil necessary for the above :-
Red ochre
Lamp-black
For grinding a kilogramme Yellow ochre
-
Hours of a
Grinder.
8.5
6.5
8.5
Kilogrammes
of Oil.
0.5
0.5
0.8
The colours being ground, they must then be mixed with a sufficient quantity of oil to
be in a condition to lay on.
To mix a kilogramme
Red ochre
Yellow ochre
Lamp-black
Kilogrammes
of Oil.
0.62
0.73
1.17
If turpentine is used for the above quantity, half the oil is employed with the same
quantity of turpentine: sometimes one-eighth of litharge is added.
To paint a square metre two coats requires
Red or yellow on timber
Olive colours
Black
The waste may be valued at a twentieth of the original weight.
Time necessary to mix and apply the colours
For a square metre
{
Without scaffolding
With a flying scaffolding
Kilogrammes of
prepared Colour.
0.12
0.11
0.08
Hours of a
Painter.
0.2
0.5
CHAP. X.
911
TABLE OF VARIOUS MEASURES.
To find the value of painting a square metre, the price of the colour ground, and the
labour of painting:
One coat-0·11 kilogrammes of colour at 2·17 francs
One-twentieth of loss, 2·51
0.2 hours of a painter at 0·45 francs
One-seventh of labour for incidental expenses
One-tenth for profit, 1.03
Total
Francs.
0.239
0.012
0.090
0.013
0.03.5
0.389
Eng. ft.
1.095
1·144
1.135
1.090
1.421
730.8
Greek foot
{
1.009
1.006
1·007
Phyleterian foot
1.167
Pitching, applied to new timber or to that already pitched: in the latter case some allow-
ance must be made for scraping off.
Per square metre com- [ Clearing off
prising heating the Pitching without scaffolding
pitch.
Pitching with scaffolding
1
Hours of
a Man.
0.01
0.07
0.10
Upon a square metre about 0.0003 cube metre of pitch is required for new timber;
0.0002 when it has already been pitched.
The incidental expenses may be valued at one-seventh of the labour.
Tables of various Measures in English Feet and Decimals, from Folkes, Raper, Shuckburgh,
Vega, Hutton, Ozama, Cavallo, Young, &c.
Arabian foot
ANCIENT MEASURES.
Babylonian foot
Drusian foot
Egyptian foot
stadium-
-
Augsburg foot
Austria, see Vienna.
Avignon, see Arles.
Barcelona foot
Bavarian foot
Bergamo foot
I
Eng. ft.
•972
•992
-944
•968
1.431
•992
•962
1.015
[1.244
Basel foot
Berlin foot
Bern foot
Besançon foot
Hebrew foot
Bologna foot
1.212
common cubit
1.817
Bourg en Bresse foot
sacred cubit
2.002
Brabant ell in Germany
1.250
1 030
2.268
great cubit=6 common
Bremen foot
•955
Macedonian foot
·
1.160
Brescia foot
1.560
Natural foot
•814
braccio
2.092
=
Ptolemaic Greek foot
Breslau foot
1.125
Roman foot
{
•970
Bruges foot
•749
•967
Brussels foot
1
•966
-{
•902
•954
before Titus
*970
.965
•9672
after Titus
Castilian vara
•9681
greater ell
lesser ell
Chamberry foot
2.278
2.245
2.746
-
1.107
•9696
China mathematical foot
1.127
Roman mile of Pliny
Strabo
4840.5
4903,
imperial foot
{
Sicilian foot of Archimedes
•730
li
1.051
1.050
*606
Cologne foot
•903
MODERN MEASURES.
Constantinople foot
2.195
1.165
Eng. ft.
Copenhagen foot (Denmark)
1.049
Attdorf foot
•775
Cracau foot
1.169
•927
greater ell
2.024
Amsterdam foot
•930
lesser ell
1-855
•931
Dantzig foot
•923
Amsterdam ell
2.233
Dauphiné foot
1.119
Ancona foot
1.282
Delft foot
•547
Antwerp foot
•940
Denmark old foot
1.047
Aquileia foot
Arles foot
i.128
new foot
1·036
•888
Dijon foot
1.030
912
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Dortrecht foot
Eng. ft.
•771
Eng. ft
Naples carro=2 botti.
Dresden foot
•929
tumulo of wheat 3 cubic palms
ell 2 feet
•
1.857
or 40 rotoli.
Edinburgh, see Scotland.
Ferrara foot
1.317
Nuremberg town foot
-{
•996
·997
Florence foot
⚫995
1.900
braccio
-
1.910
-
country foot
artillery foot
ell
•907
•961
2.166
barilo of wine weighs 140
Florence pounds = 20
fiaschi.
cogno = 10 barili.
rubbio of wheat 640 Rom.
lbs.
Franche Comté foot
Genoa palm
canna
Geneva foot
German mile degree.
- T5
Grenoble, see Dauphiné.
Halle foot
Hamburgh foot
Padua foot
1.406
Palermo foot
Paris old foot
•747
{
1.066
1.172
point
line
.0888
•812
•800
ell 44 French inches.
sonde 5 French feet.
.817
toise 6 French feet
76.736
-
7.300
1.919
perch 18 French feet.
perch royale 22 Fr. feet.
league 2282 toises
=
deg.
•977
square foot or inch
•933
cubic foot or inch
1.1358
1.21061
⚫903
1.101
1.06.578
Eng. in.
0148
Heidelberg foot
Inspruck foot
Ireland perch 7 yards.
acre 7840 sq. yds. Eng.
Italy, old common mile
Leghorn foot
Leipzig foot
ell
Leyden foot
Liege foot
5299.
•992
1.034
·
1.833
1.023
•944
Lisbon foot
Lombardy mile¿ degree.
Lucca braccio
Lyons, see Dauphiné.
•952
-
1.958
•915
Madrid foot
•918
3.263
vara
arpent, 100 square perches,
about Eng. acre.
930
measure royale about §.
pint 48 cubic inches
litron -
boisseau 1190 = 16 litrons.
minat 2 boisseau, nearly
=
a bushel Eng., 2380
cubic in. English.
mine 2 minats, 4760
-
cubic in. English.
septier = 2 mines, 9520
cubic in. English.
muids=12 septiers.
ton of shipping 42 cubic ft.
metre 3.07844 Fr. ft.
Eng. c. in.
58.11
74.375
Eng. ft.
3.281
3.285
Eng. in.
Maestricht foot
•916
millimetre -
⚫03937
Malta palm
•915
Mantua brasso
1.521
centimetre
decimetre
-
braccio
2.092
metre
Marseilles foot
•814
Mechlin foot
Mentz foot
•753
•988
Milan decimal foot
braccio
Modena foot
Monaco foot
Montpellier pan
•855
Aliprand foot
1.426
·
1.725
decametre
hecatometre
kilometre
myriametre
⚫39371
3.93708
39.37079
398-70790
3937-07900
39370-79000
393707.90000
8 kilometres are nearly 5 miles.
1 inch is 0254 metre.
Moravian foot
ell
Moscow foot
Munich foot
Naples palm
canna
mile=3 degree or
60*
barilo of wine=60 carafe.
carafa Parisian pint.
batto 12 barili.
=
-{
2.081
1000 feet are nearly 305 metres.
771
•777
Eng. in.
•971
2.594
123
1 centimetre is
⚫39371
•78742
-
1.18113
.928
•947
⚫861
·859
7
6.908
8
9
10
45 6
1.57483-
1.96854
2.36225
2.75596
3.14966
3.54337
3.93708
1 square centimetre·155006
square inches.
СНАР. Х.
913
TABLE OF VARIOUS MEASURES.
Paris, I are or square decametre=
3.95 English perches.
Scotland, gallon
cubic in.
827.23
1 hectare=2 acres, 1 r. 35-4 perches
English.
hogshead (16 gallons) 13235-7
gallon of the Unicr
Eng. cubic in.
barrel
799.
millilitre
-
•06103
Lippie or feed English
centilitre
-
•61028
barrel
200-345
decilitre
litre or cubic decimetre
decalitre
- 6·10279
61.02791
610.27900
pint jug of Stirling
103.72
Aberdeen
105.30
firlot of Linlithgow
hectolitre
kilolitre
myrialitre
6102.79000
61027.90000
610279-00000
(31 pints)
3205.5
2150.
firlot for wheat
2197.3
1 litre is nearly 21 wine pints.
firlot of Edinburgh
1 kilolitre, 1 tun 123 wine gals.
1 decistre of firewood 3.5317
cubic feet English.
1 stere or cubic metre 35-3171.
Parma foot
braccio
Pavia foot
Piedmont old mile=1 mile Eng.
Placentia, see Parma.
Prague foot
ell
Provence, see Marseilles.
Rhinland foot
Riga, see Hamburg.
Rome palm
foot
oncia
foot
deto foot
palmo
palmo di architettura
canna di architettura
staiolo
braccio dei mercanti
canna dei mercanti
braccio del tessitor
braccio di architettura
mile degree.
Rouen, see Paris.
Russian arschin
1½ per cent more.
Seville, see Barcelona.
Eng. ft.
vara
Eng. ft.
Sienna foot
1.869
2.242
1.540
2.760
1.239
Spain league=4 miles English.
Stettin foot
1.224
Stockholm foot
-
1.073
Strasburg town foot
•956
-{
•987
country foot
•969
•972
1.948
Toledo, see Madrid.
Trent foot
-
1.201
Trieste ell for woollens
for silk
-
2.220
-
-
1.030
2.107
Turin foot
•733
•966
ras
-
trabuco
•0805
-
f 1.676
1.681
1.958
10.085
⚫0604
Tuscany mile
•2515
see Florence.
·7325
Tyrol foot
ell
7.325
Valladolid foot
4.212
- {2
2.7876
2.856
Venice foot
#
-
6.5365
2.0868
braccio of silk
ell
2.561
braccio of cloth
5329.
1.096
2.639
•908
1.137
1.140
1.167
2.108
2.089
2.250
-{
2.3333
2.3625
mile or of a degree.
moggio of wheat weighs
528 Venice pounds.
Verona foot
-
•1458
Vicenza foot
3508.
Vienna foot
ell
--
3.100
post mile
vershock, arschin
werst
f
Savoy, see Chambery.
Scotland, ell 37 Scotch inches (37.2
fall, 6 ells (223-2 Eng. in.) 18.600
Eng. inches)
furlong
mile
link
chain
rood
acre 55353-6 sq. ft.=
gill
1·27 of English acre.
mutchkin
choppin
pint
quart
-
1.117
-
1.136
1.037
2.557
24888.
744.
5952.
·
Eng. in
8.93
892.8
1339.2
cubic in.
- 6.462
25.85
- 51.7
103.4
206.8
yoke of land 1600
square fathoms.
metz or bushel 1.9471
cube feet of Vienna,
eimer = 40 kannen =
1.792 cube ft. of Vienna.
fass=10 eimer.
Vienne Dauphiné
Ulm foot
-
Urbino foot
Utrecht foot
Warsaw foot
Wesel, see Dordrecht.
Zurich foot
·་
-
1.058
•826
1.162
741
1.169
:}-
•979
.984
3 N
914
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
''
Table of various Weights.
ANCIENT WEIGHTS.
Pounds.
Erg.grs
Eng. grs.
Dresden
7210.
8.2
Dublin
Attic obolus
7774.
9.1
Florence
5287 ·
51.9
drachma
ounce pound
440.0
54.6
France, see Paris.
lesser mina
greater mina
medical mina
talent=60 mina=} cwt.
old Greek drachm-
old Greek mina
Egyptian mina
Ptolemaic mina of Cleopatra
Alexandrian mina of Dioscorides
3892.
Geneva
8407.
5189.
5464.
Genoa = 12 ounces
{
ƒ 4426 ·
6638.
6994.
rotolo = 18 ounces.
-{
146.5
62.5
rubo=25 pounds.
cantaro=6 rubi.
peso 5 cantari.
=
6425.
Germany apothecaries -
5523.
8326.
Hamburg
-
7315.
8958.
Ireland, see Dublin.
9992.
Konisberg
-
5968.
Roman denarius=
oz.
= oz.
ounce
=
51.9
Leghorn
5146.
62.5
Leyden
7038.
415.1
Liege-
7089.
avoirdupois oz.
pound of 10 oz.
437.2
Lille
6544.
4151·
Lisbon
-
7005.
pound of 12 oz. -
{
f 4981.
London avoirdupois
7000.
5246.
troy
5760.
Lucca
5273.
MODERN WEIGHTS.
Lyon silk
6946.
Pounds.
Eng. grs.
town weight
6432.
Aleppo rotolo
30985.
Madrid
6544.
Alexandria
6159.
Marseilles
6041
Alicant
6909.
Melun
4441.
Amsterdam
7461.
Messina
4844.
Amsterdam commercial
-
7636.
stone 16 pounds.
ounce pound.
Montpellier
Namur
Nancy
6218.
7174.
7038.
drop ounce.
Antwerp
7048.
Avignon
6217·
Basel
7713.
Naples = 12 oncie
rotolo=33}|o.
staro = 101 r.
cantaro 100 r.
4952.
Bayonne
7461.
oncia=30 trapezi.
Bergamo
f 4664.
trapeso = 20 mini.
11660.
Nuremberg
7871.
Bergen
7833.
Paris (1·08 lb.)
7561•
Berlin
7232.
marc=pound.
Bern
6722.
ounce=marc.
Bilboa, see Bayonne.
gronounce.
Bois le Duc
7105.
denier
gros.
Bordeaux, see Bayonne.
Bourg
7074.
grain = denier
G
Brabant
7249.
milligramme
Brescia
4497.
centigramme
Brussels heavy pound
7602.
decigramme
light pound
7201.
gramme
Cadiz
7038.
China kin
-{
9223.
5802.
leangkin.
tsien leang.
Cologne-
-{
Constantinople
7220.
7218.
7578.
Copenhagen
6941.
sous,
Cracau commercial
6252.
mint mark
3071.
TO
Damascus
25613.
decagramme
hecatogramme
kilogramme, 2 lb. 3 oz.
avoirdupois
myriogramme
-
quintal 10 myriogrammes.
millier = 1000 chiliogrammes
= 1 ton.
5 grammes of copper.
franc, 5 grammes of silver with
To of copper.
Prague commercial pound
Eng. grs.
•8203
0154
•1543
1.5433
15.4330
154.3300
1543.3000
15433-0000
154330 0000
Dantzig -
6574.
Revel -
$947.
6574.
CHAP. XI.
915
MECHANICS.
Riga
Rome = 12 oncie
oncia 8 dramme.
=
dramma=3 scrupoli.
scrupolo= 12 oboli.
obolo 4 silique.
siliqua 12 grani.
=
Eng. grs.
6149.
-
5257.
Vicenza
Eng. grs.
Vienna, commercial
apothecaries 420 Fr. gram.
miut mark 280-64 Fr. gram.
6879.
8648.
carat of the jewellers 206085
Fr. gram.
Apothecaries Grains of different Countries
Rouen
7772.
Saragossa
4707.
Scotland troy pound Dutch
7621-8
Austria
iron pound,troy
9527.25
Bern
Seville, see Cadiz.
France
Smyrna, commercial pound
6544.
Genoa
Stettin
-
6782.
Germany
-
Stockholm
9211.
Strasburg
Toulouse
Turin
Tunis
7277.
Hanover
6323.
Holland
4940.
Naples
7140.
Piedmont
Tyrol
8693.
Venice
f4215.
·
6827.
L5374.
Portugal
Spain
Sweden
Rome
Verona
4676.
Venice
CHAP. XI.
from Veya.
-
1.125
•956
•981
·850
•958
•959
•978
•989
·860
•824
-
•864
•909
.925
•955
•809
MECHANICS.
As quantity, space, and number are understood and comprised in mathematics, so their
application more immediately belongs to mechanics and hydrodynamics: but before we
enter into the principles which affect falling bodies or those which belong to bodies re-
volving round a centre, or the general laws of machinery, it is necessary to describe the
physical properties, or those external signs by which matter is recognised either in its solid,
liquid, or aeriform condition.
Extension is that property by which a body occupies a certain space: by it is understood
its volume or figure; the measure of the extension and compression of uniform elastic
bodies is proportionable to the force which produces it; when, for instance, a weight is
suspended to a bar of iron, causing it to be prolonged, if twice that weight be added, the
effect will be doubled, and it was proved by Dr. Hooke, that the application of these
weights in a contrary direction would shorten the bar in the same proportion.
Dr. Young
has suggested that the elasticity of a substance may be expressed by the weight of a certain
column of the same substance, which he calls the modulus of elasticity, and of which the
weight is such that any addition to it would increase it in the same proportion as the weight
added would shorten by its pressure a portion of the substance of equal diameter.
Impenetrability implies that a body is so compact in its structure as not to allow another
to pass through it.
Matter may be understood to comprehend whatever occupies space, and possesses ex-
tension and impenetrability; such are all bodies that have magnitude, or that comprise
length, breadth, and thickness, as well as those which have surfaces only.
Porosity is that property which indicates that there are interstitial spaces lying between
the particles or molecules of matter, usually called pores.
Mass and Density are estimated according to their various properties of porosity; the
mass comprises the material particles, and the greater their quantity the less porous the
body or substance will be: density, on the other hand, expresses the relation of the masses
when the volumes are equal; or, of any two bodies, that is the most dense which with equal
bulk contains the greater mass.
Compressibility implies that the body may be diminished by pressure without the mass
being lessened by forcing the particles which compose it closer together and diminishing
the size of the pores.
Dilatability is the reverse of the former: the pores are increased by throwing the particles
farther from each other, which is affected by heat, or raising the temperature of a body.
Elasticity is the power of a body to resume its original state, as in the case of a spring,
or when compression has taken place.
3 N 2
916
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Motion is a successive and continuous changing of place, and may be accelerated,
retarded, or made either absolute or relative.
Repose is the state of matter when in perfect rest.
Space is indefinite, unlimited, and of the extent which all bodies may be supposed to occupy.
Divisibility.— All bodies may be brought into the fluid state by heat, but there are
other means by which matter may be divided. Stone, metals, and timber may have their
particles separated by a blow, by friction, grinding, filing, sawing, splitting, &c. &c. The
several divisions so obtained may be in many instances rendered smaller by sublimation;
by passing the finest portions through sieves, and throwing them into water, they may be
subjected to decantation; blowing will produce the same effect, the air put in motion by
the bellows carrying the particles to a distance proportionable to their fineness; this is the
case in all powder manufactories, and thus is corn winnowed from the chaff.
Sublimation is vapourising bodies by means of heat in close vessels, and condensing the
vapour so formed by cold applications.
Inertia. As matter in itself is inert or inanimate, it cannot produce motion, or change
that position which is imposed upon it, so that it remains in perfect repose, unless acted
upon by an animated mover, or weight or pressure be applied to it: when, however, put
in motion, in a certain direction, it will continue to move in it, unless obliged to deviate
by some efficient cause; nor will its rapidity increase unless some acceleration be given.
:
A weight or heavy body thrown from a height continues to fall with an accelerated
movement derived from its own weight, which acts continually on it, in the same manner
as when it is in repose, and this is rendered evident by the movement of a ball which, when
thrown upwards, diminishes in rapidity instead of augmenting a cannon ball propelled
obliquely changes at each instant of time, the weight operating to bring it to the earth.
Inertia obliges a body in constant motion, with a certain rapidity, and in a certain direction,
to preserve its line of course, which would be uniform, and in a rectilinear direction, if
nothing occurred to derange it.
Force. This term is applied to causes which modify the actual state of bodies, or
would do so, if other forces did not interfere to destroy the effect of the first: the
resistance of the air, heat, and weight change the state of bodies: different effects of
forces are produced: sometimes leaving bodies in a state of repose, sometimes changing
their form, by breaking or impressing them with movement; at other times accelerating
or retarding that which they possess, or changing its direction; when bodies suddenly
change their state, either in direction or movement, it arises from an increased force, pro-
ducing an effect in a smaller portion of time, the duration of which cannot be measured by
the means we possess. The ball discharged from a gun will pass through a pane of glass,
a door panel, a sheet of paper, with so much rapidity, that the parts carried away have not
time to communicate movement to those adjacent.
A cannon attached to a vertical cord, and nicely balanced, sends the ball to its
destination, in the same manner that it would do if mounted on its carriage; which is a
proof that the cannon had not deviated in any appreciable manner before the ball had left
it, although it recoiled afterwards. The forces which give motion are called moving; those
that hasten movement accelerating, and those that keep it back, retarding forces.
Measure and Nature of Force.—When a body at rest, or free to move is drawn or forced
forward, it may be said to be pressed in that direction; the effort is called pressure, and
analogous to the force exercised in supporting a weight. Two forces are equal, when,
being substituted for each other, and under the same circumstances, they produce the same
effect, or destroy that of a third when opposed to them. A body suspended by a thread
assumes a perpendicular direction; and if two forces be applied for the same purpose, they
will be equal to each other, as well as to the weight of the body, and may be measured or
compared by means of the balance, or other instrument used for that purpose, among
which is the dynometer. The farther we remove a body from the surface of the earth, the
less is its apparent weight; so that at the summit of a mountain, the body suspended to a
thread will have apparently diminished in weight 1 part in 700 for a height of 3 miles.
The nearer we approach the equator the greater is the diminution of weight, although not
to so appreciable a difference as to be of importance in mechanics: the plumb line, or the
weight at the end of a thread, is not, strictly speaking, perpendicular, nor are a succession of
them in parallel lines, as they all tend towards the centre of the earth; but as the distance
is so great, it is unnecessary to take the variation into our consideration. We may estimate
weight as a constant force, and invariable in its direction, as far as concerns the labour of
the mechanic.
The Manner in which Force acts upon a Body.
When force is applied to any point on
the surface of a body, it exerts a pressure against the molecules nearest to this point; and
the body is either compressed, or in some degree gives way. The molecules, when brought
in closer contact, after the force is removed, in virtue of their elasticity, make an effort to
return to their original state; by pressing against each other, the force is conveyed to the
extreme molecule, and if this can be driven no further, then compression takes place, and
the form of the body undergoes a change: should this extreme molecule have the power,
CHAP. XI.
917
MECHANICS.
however, to move, it will advance, and the movement will be communicated to the parts of
the whole body, and these approaching nearer and nearer, in consequence of a series of com-
pressions, indicate clearly that time is necessary before any force can communicate its total
effect; for rapidity of movement is not instantaneous, as has been too often supposed. The
same happens when an inverse force is employed to destroy the movement of a body; the
molecules nearest the point of action are first stopped, and then the others in succession.
As each molecule is to a certain degree elastic, it cannot be compressed without a reaction
taking place, for the force which presses against a body is repulsed in the same manner as
it is exerted in forcing that body forward; this reaction is equal, though contrary to,
the action itself.
When a body is pressed by the finger, or drawn by a thread, or pushed with a rod, we
have by the same effort pressed, drawn or pushed the body in contrary directions. In all
cases, the action of the force is transmitted to the point of resistance by a series of reactions,
equal and opposite, destroying each other: but we admit generally that the force applied
to a given point exerts itself over the whole.
Inertia of Matter, measured by means of the Forces. When an external force acts on a
body free to move, or destroys the motion imposed upon it, the resistance offered is equal
to the force applied; by this resistance we measure the inertia of matter; in the same
body the resistance is increased, according to the degree of rapidity impressed or destroyed,
and this quality is augmented in proportion to the matter contained in each body. If a
weight be drawn by a cord, the cord extends, elongates, and perhaps snaps, when suddenly
pulled; if it be suspended, and in the line of suspension a spring balance is introduced, the
spring will indicate the weight of the body; this weight taken away, the spring will again
resume its state when in repose; the variations of the movement of a body and the force of
inertia are thus measured. This measurement may be expressed by making lines equal in
length to the force, in pounds or any other weight; or a number of divisions marked upon
a given line may show the intensity of the force; and thus mechanics inay be studied by
figures in geometry.
Equilibrium of Forces. When two or more forces are applied, they reciprocally destroy
each other, so that they leave the body to which they are applied in the same state as pre-
vious to their application, whether in action or repose; and if they neither modify the
direction nor the intensity of the rapidity when the body is in motion, then there is an
equilibrium between the forces. This equilibrium is static in the first instance, and
dynamic in the second; if a cord be drawn or stretched with equal force at each end, it is
in a state of equilibrium; but if a greater force be applied at one end, then it is dynamic;
there is no true static equilibrium, the earth attracting all bodies to a certain degree.
Influence of Inertia on the state of Equilibrium.-When a body is acted on by several external
forces, and preserves a uniform movement, it is considered in equilibrio. When the
rapidity is augmented or diminished, the equilibrium has no place in these forces; but if
regard be had to the force of inertia of the different molecules, and we substitute an
exterior force equal to those originally applied, there will then be an equilibrium between
all these forces a horse drawing a carriage destroys at every instant the resistance offered
to his action, and if his movement is uniform, all the obstacles presented by the inequality
of the road are overcome: if his rapidity be increased, the inertia put in motion is added
to the preceding resistance, and the horse causes an equilibrium to take place among all
these forces: if, however, the rapidity be diminished, the inertia which keeps the carriage
in motion adds its action to that of the horse, and destroys or maintains the resistances in
equilibrio.
When two forces are directly opposed, the less will destroy the greater to an amount
equal to its value. Three men pulling a cord in the same direction, with the force of 20,
34, and 50 pounds, in all 104 pounds; and two others pulling in an opposite direction,
with a force of 24 and 38 pounds, total 62 pounds; the cord will really be drawn with a
force of 104-62 or 42 pounds, acting in the direction of the three men.
Mechanical Labour of the Forces. The most simple state of equilibrium is when two
equal forces destroy each other, and this is the case in works of industry. To work is to
overcome or destroy resistance, such as the force of adhesion, which exists between the mole-
cules of bodies, the force of springs, of weight, the inertia of matter, &c., &c. : to polish a
body by friction, to divide it into parts, to raise weights, draw a carriage, bend a spring,
propel a ball, are all works in which labour is constantly renewed, to overcome the re-
sistance offered: in mechanical labour, resistance is overcome at the same time that it is
reproduced. To remove a portion of matter from a mass by means of any tool, it is
requisite not only to produce an effect directly opposed to the resistance presented, but
the tool must be made to advance in the direction of the resistance; the greater this ad-
vancement is, the greater will be the quantity of matter removed; at the same time it must
be taken into account that the greater the length or thickness acted upon, the greater will
be the resistance, so that the work increases with the intensity of the effort and the length
of the direction.
3 N 3
918
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Measure of Labour when the Resistance offered is constant. Supposing the resistance to be
uniform, as well as the effort, which is directly opposed to it, and that at the same instant
of time it remains the same, it is evident that the work or labour is proportionate to the
length of way made; if on a road it will become double or triple, in proportion as the
carriage passes over it: so that if we take labour as unity, or that which vanquishes
resistance along a yard of road, the total labour will be the number of yards passed over.
But should the labour increase at each yard, so that the second should be double, and con-
tinue in this proportion, then the labour will be increased in a corresponding manner. As,
for example, 1 pound for the first yard, 2, 3, 4 for the second; the labour for each yard
would then be 2, 3, or 4 pounds: taking for unity that force which overcomes the
resistance of 1 pound along 1 yard, any labour may be measured by the number of pounds,
which express the various resistances of each yard run over. Suppose a moving power
employed to draw a body along a horizontal plane, the labour must be sufficient to over-
come the constant friction which exerts itself, and if this friction be equal to 40 pounds,
and the distance passed over 100 yards, then the labour will be measured by multiplying
40 by 100 or 4000 pounds. The rate at which a body moves, or the length of time which
it takes to move from one point to another, is called the velocity; and this is always
proportionate to the force which puts it in motion. The absolute velocity is measured by
the space over which the body moves in any particular period of time, as 10 miles in an
hour; the distance divided by the time gives the velocity per hour. Space is also equal to
velocity multiplied by the time; if the velocity be 10 miles an hour, and the time 10 hours,
then 100 miles will have been passed over.
The Value of the mean Effort. When we have found the value of the mechanical labour
of a variable resistance for any length of way run over by its point of action, and divide
that value by the distance, we obtain the mean effort of resistance; or the constant effort,
which, being repeated along the road, will produce the same quantity of labour: we have
already shown that for a constant resistance the labour is measured by the product of that
resistance, and the total road passed over.
Vurious Examples of mechanical Labour. When a mover is employed in pressing a
spring, at each instant it developes an effort which increases as its point of action has gone
over a greater distance in the proper direction: this effort may be measured for each posi-
tion of the spring, or for each position of the point of action: we may then designate it as
a curve, which gives laws to these efforts, and by approximation calculate the sum of the
mechanical labour employed at each instant of time, which, united, compose the total
labour. For example, the labour of drawing a body along a plane offering a constant
resistance, and which is indicated by compressing a spring, the resistance of which varies
at each instant of time. This may be applied to a horse working in a mill, a man
drawing water from a well, sawing or planing timber, polishing metal, &c. The work
done may always be measured by the efforts, equal and opposite, or those contrary to the
resistance of the tool employed, the length of that resistance, if it be constant,
or by the sum of the products which measure the partial labour, if the resistance be
variable.
In seeking to appreciate mechanical labour, care must be taken not to confound that
which the mover effectually expends, and that which immediately results from the work
performed; for it is easy to imagine that a portion of the first effect is destroyed by
other resistances than those arising from the work: it is only to this latter resistance that
the measure of labour can be applied. To show this, we will instance the whitesmith, in
the operation of filing a bar of metal, on which he must first lean sufficiently to make his
file bite; he must constantly support the weight of the file, he must exercise another effort
to make the file slide over the bar, and this, with a certain rapidity backwards and forwards
to overcome the inertia of the matter contained in it, so that the quantity of work done is
the result of all these varied circumstances. This apparent complication disappears when
we separate from the result all that is not indispensible to it, bearing in mind what actually
takes place, where the grains of metal are taken away by the file. We then only see á
resistance which supposes an effort equal and contrary to the direction of the way which
the point of action of the file describes, and the quantity of labour which is measured, as we
have before described. The labour of the mover may be reduced to that only, by sup-
posing the file placed flat on a level bar loaded with a certain weight, and that the mover
is employed in regularly drawing this file in the direction of its length, taking into account
the inertia in the first instance.
The most simple labour is that of raising a perpendicular weight, provided the inertia be
not taken into consideration. The unit of labouring force is sometimes considered to be that
which raises a pound one foot in height: a cube metre of water, which weighs 1000
kilogrammes, raised one metre in height, is the unit in France; and this is denominated a
kilogrammetre. Bolton and Watt's dynamical unit was one-horse power, equal to raising
33,000 pounds one foot iu height in a minute, which the French estimate at 75 kilograin-
metres per second,
CHAP. XI.
919
MECHANICS.
The metre is 3.28 feet, the kilogramme 2.2 pounds, the kilogrammètre 7·216 dynams,
and the horse power is 525 dynams, which nearly coincides with Bolton and Watt's
dynamical unit.
Mechanical power is the term used by Smeaton; momentum of activity by Carnot; dynamic
effect by Monge, Hachette, Coulomb, and others, all signifying the quantity of action or
mechanical labour.
It is evident that labour is judged of by its quantity, or rather that of the work per-
formed, which must be proportioned to the mechanical labour required. Labour, then, is
the quantity of action, which pays itself in force.
Labouring force is measured by the product of the resistance overcome, and the space
through which it is overcome.
Parallelogram of Forces. Independently of the action of simultaneous forces, the action
of force on a body, whether at rest or in motion, is always the same, and impresses on it
the same degree of velocity in both circumstances. A body left to itself is moved by
gravity with the same degree of velocity at each instant of time: when it leaves the
state of rest by having motion imposed upon it by force of any kind. as a shell, in its
passage through the air, it describes a parabola; the velocity of the projectile at each in-
stant is always the resultant of the velocity which it received at the instant immediately
preceding that which we have considered; and the very slight velocity which gravity
impresses on it during the interval of time, also very small, separates these two suc-
ceeding instants: thus where two forces are applied to the same body, they will impress
upon it at each instant, and simultaneously, the degrees of velocity common to each, and
these degrees, according to the general laws of nature, are proportionate to the intensity of
the forces.
A
B
A single force which is equivalent to two or more forces is called the resultant, and
relatively to it, they are called the components.
A force acting on a body at A, in the direction
of AB, as well as in that of A C, when these
forces are equal, and act together, the body will
in the same time be moved through the distance
A D, or the diagonal of the parallelogram. The
forces in the direction AB, AC, AD are re-
spectively proportional to the lines which represent
them. The two oblique forces A B, A C, are equivalent to the single direct force A D,
which may be compounded of these two, by drawing the diagonal of the parallelogram
A D.

C
Fig. 1225.
о
A
:
D
A body acted upon by two forces at the same time will pass through the same point, as
it would do if these forces were to act separately and successively and if any new motion
be impressed, this does not alter its motion in lines parallel to its former direction.
Suppose three forces A, B, C, acting against one
another at the point D, and whose direction is on the
same plane; if they are all in equilibrio their forces
will be to each other respectively as the three sides.
of a triangle, drawn parallel to their lines of direction,
DI, CI, CD. The three forces A, B, C, are to each
other as the sines of the angles through which their
respective lines of direction pass when produced.
DI: CI:: CDB: CDA
CI: CD:: CDA: AD B.

and
It must be evident that if the force C alters its
direction from that applied in either direction, its
diagonal and corresponding sides are affected, the
parallelogram DHCI is changed in form, and the
whole proportions vary. The united effects of two
forces moving in the direction of the sides of a
parallelogram are expressed by a diagonal drawn in that figure.
Fig. 1226.
H

If a body acts against another by any force whatever, that
force is exerted in the direction of a line perpendicular to the
surface on which it acts. Suppose the ball B strike the body C in
an oblique direction, so as to form the angle ABD: the magni-
tude of the stroke will be directly as the velocity, and the sine of
the angle of incidence A BD, and the body C receives the stroke
in the direction EB, perpendicular to the surface D B.
The magnitude of the stroke is represented by BE, and the
motion impressed on the body that receives it is equal to the
magnitude of the stroke, and to the motion lost in the striking
body,
D
C
B
E
Fig. 1227.
3 N 4
920
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
If an elastic body A impinges a hard and elastic body, CF, at B,
it will be so reflected from it that the angle of reflection will be
equal to the angle of incidence. The motion at B, parallel to the
surface, not being altered by the stroke, elastic bodies recovering
their figure in the same time that they lose it by the stroke;
therefore the velocity in the direction of BE is the same after as
before the stroke, and we have two equal and similar triangles.
But as no two bodies in nature are perfectly elastic, one angle will
be more acute than the other: a non-elastic body striking another
in a similar state loses half as much motion as if both were per-
fectly elastic; non-elastic bodies only stop, but elastic recede with.
the same velocity that they meet with.

B
F
E
Fig. 1228.
On the force of Gravity.—The earth, whose diameter is about 8000 miles, has from its
magnitude the power of attracting all smaller bodies to its surface; so that when put in
motion they tend, if unopposed in their descent, in a straight line towards its centre: this
is sometimes called the earth's attraction, or terrestrial gravity, and the force by which the
body is attracted is called weight.
The force of gravity acts equally on bodies in motion and at rest: when put in motion
it draws them down, and destroys in some measure the forces which put them into motion,
and the same quantity of force is required to keep them in uniform motion directly
upwards, suspended, or at rest; when they descend uniformly that force which is suf-
ficient to prevent their acceleration in descending is equal to their weight.
When a heavy body falls from any height, as it approaches the ground it increases in
velocity; this is rendered evident from the force with which it strikes the ground, that
force increasing in proportion to the height from whence it has fallen, and also to its
velocity at the moment it reaches the ground. The velocities of falling bodies are the
accumulated effects of the attraction of the earth during the entire time of their descent:
at each instant a new impulse is given which increases the velocity, so that the final
velocity is the sum of all which have been communicated. Gravity is, then, a uniform
force or attraction, which affects all bodies equally, whatever may be their position. The
velocity of a falling body is as the time of its falling from a state of rest, the force of gravity
being the quantity of matter.
All bodies falling by their own weight gain equal velocities in equal times, and when
the same bodies are thrown or propelled upwards, they lose as much in an equal time:
when a body falls through a certain space in a given time, it will afterwards descend
through four times that space in the next similar period of time; through nine times that
space in the third, sixteen times in the fourth, &c.: or, to ascertain the space through which
a body will fall in a given number of seconds, multiply the space in the first second of
time by the squares of the total number of seconds it was in falling; thus the spaces through
which a body falls is as the square of the time from the commencement to the fall, or the
velocity is as the square root of the height fallen, and it is absolutely necessary, before we
can compute any velocity, that we should know how much it would fall through in a
second of time. The velocity acquired in a second, and the space fallen through in a
second, are the elements upon which the whole calculations are formed: when one of
these elements are known, the other may be immediately found, as there is a remarkable
relation between the space through which a body falls, and the velocity it acquires in any
given time. In the latitude of London a body will fall in a single second 193 inches, or
about 16 feet. Taking any equal parts of time, the spaces described by a falling body in
each successive part of time will be the odd numbers 1, 3, 5, 7, 9, 11, &c.
The spaces, velocities, and times may be judged of by the following table: the space
fallen through in the first second of time is considered the unit of length:

Space fallen
through in the last
second of the Fall.
Seconds from the Velocity acquired
beginning of thej at the end of
Descent.
Space fallen
through.
that Time.
123456
24
1
4
6
9
8
16
10
25
13579
12
36
11
7
14
49
13
8
16
64
15
Between the three quantities, the height, the time, and the final velocity, there are fixed
relations. The time counted from the commencement of the fall and the final velocity are
CHAP. XI.
921
MECHANICS.
in proportion to one another; for as one increases, so does the other. The height being
equal to half the space which would be moved through in the time of the fall with the
final velocity, must have a fixed proportion, and the time and final velocity are proportional
to the product of the two numbers which express them.
The phenomena of falling bodies were experimented upon by Mr. George Atwood, who
constructed for the purpose a very ingenious machine, which still bears his name.
The gravitating forces of bodies are to each other, first, directly as their masses, and,
secondly, inversely as the squares of their distances: for if the mass of one body is double
that of another, its gravity will be doubled, and with a distance twice as great, its gravity
will be as many times less. Putting M and m for the masses; D and d for the distances,
and G and 9 for the forces of gravity of two bodies; first we have G: g:: M:m:
M
Or, G =
g M
>
and if g=1, G=
m
m
de
Secondly: G:g:: d² : D²; or, G=g·D; and if g=1, and d=1, G:
2
From whence it follows that G: g:: Md² : m D²;
1
Da
Or, G=g
M ď²
m D2
M
; whence, if m and d are = 1,
==
1, G=g
•
D2°
The latter expression is usually taken for the above laws, M representing the attracting
mass, and D the distance at which it acts upon some other body, as compared with the
attracting force g of this second body, whose mass is equal to 1, and whose distance is equal
to 1, which are considered the units of measurement.
Terrestrial gravitation is the attraction exercised on all bodies by the earth; and occasions
the common musket-ball, which proceeds at the rate of 1280 feet in a second, or the 24 pound
cannon-ball, which has double that velocity, to fall at last to a place of rest.
The Centre of Gravity of a Body is a point through which a single force, equivalent to
the gravitation of all its particles, passes, and in whatever situation the body is placed,
its centre of gravity tends to descend in a line perpendicular to the horizon, called the line
of direction of the weight. If a line be drawn from the centre of gravity of a body perpen-
dicular to the horizon, and this perpendicular fall within the base upon which the body rests,
it will stand, but if it falls without the base the body will fall down.
Hence it follows that if the centre of gravity of a body be supported, the whole body is
supported, and the centre of gravity must be considered as the place of the body: if it be
sustained by any lever or beam, its place is at the point where the beam is cut by a line
drawn from the centre of gravity perpendicular to the horizon.
All the gravity of a body, or the force with which it endeavours to descend, being collected
into the centre of that body or its centre of gravity, whatever sustains that centre of gravity
sustains the whole weight, and the descent of a body must be estimated by the descent of its
centre of gravity. Also the larger the base is upon which a body stands, and the farther
the centre of gravity lies within it, the firmer will it stand, and the more difficult will be its
removal. If, on the contrary, the centre of gravity be moved out of this situation, and made
to approach to the extent of its base, its tendency to fall will be increased: a body laid
upon an inclined plane, and having one end gradually elevated, will continue to slide as long
as the perpendicular falls within the base; but if the perpendicular fall without it, it will
roll over.
The centres of gravity of plane figures and solids are determined—
In the Triangle, by drawing two lines from any two of its angles to the middle of its
opposite sides; the point of their intersection is the centre of gravity; the distance, there-
fore, of the centre of gravity from the vertex is two-thirds of the line bisecting the opposite
side.
In the Trapezium, by dividing it into triangles, then finding the centre of gravity of
each, and uniting the centres so found; the point of their common junction is the centre of
gravity sought.
For the Arc of a Circle, as arc: sine of half the arc :: radius: to the distance of its
centre of gravity from the centre.
For the Sector of a Circle, as arc: chord :: radius to the distance of its centre of
gravity from the centre: for the parabolic space the distance of the centre of gravity
from the vertex is at two-fifths of the axis.
In the Cones and Pyramids, the distance of the centre of gravity from the vertex is three-
fourths of the axis.
In a Paraboloid the distance of the centre of gravity from the vertex is at two-thirds of
its axis.
For the Segment of a Sphere let r be radius, x=to the height of the segment, then the dis
tances of the centre of gravity from the vertex is
8 r-3 x
12 r- 4 x
r.
922
THEORY AND PRACTICE OF ENGINEERING.
Book 11.
If two weights on any machine are in equilibrio, and moved by any means, the centre of
gravity of the weight and the power will always be in the same horizontal right line: in
the lever the centre of gravity is at the fulcrum; and therefore neither ascends nor descends.
In the wheel and axis, and in the pulley, the weight and power approach or recede from
each other by spaces which are reciprocally as the bodies, and their centre of gravity is
therefore at rest.
Upon the inclined plane, the perpendicular velocities of the power and weights are
reciprocally as their quantities, and the distances of the centre of gravity from each being
in the same ratio, is also at rest.
In the combination of any of these powers, or of any machine whatever, where the
equilibrium continues, the ascent and descent of the power and weight being reciprocally
as their quantities, the centre of gravity neither ascends nor descends.
E
F
To show the value of ascertaining the centre of gravity in a body in the arts of con-
struction, we will suppose a piece of timber supported at the two ends B and C, as in the
following diagram. If G be the centre of gravity of the whole weight sustained, and the
line FGH be drawn perpendicular to the horizon, and C F and BH drawn, then the
weight of the whole body is as
FH; the pressure at the top
C, as BH; thrust of the pres-
sure at the base B, as FB.
The pressure and the thrust
are also in the direction of the
respective lines which represent
them. If the beam support any
weight, the beam and weight
must be considered as one body,
whose centre of gravity is G.
Then the end C is supported by
the plane BCE, and the other
end B may be supposed to be
sustained by a plane perpen-
dicular to BF; therefore the
weight and forces at C and B
are respectively as FH, BH,
and FB. The angles BCF and


B
D
A
9
Fig. 1229.
B
D
A
Fig. 1230.
BDF are right angles, and a circle described upon the diameter B F will pass through CD.
If BC be any beam bearing any weight, G, the centre of gravity of the whole, and if it
lean against a perpendicular wall CA, and be supported in that position, draw BA, CF,
parallel, FGD perpendicular to the horizon, and draw FB.
Then the whole weight is represented by the line
The pressure at the top, C, by
Thrust at the bottom, B, by
and the same by the several directions.
-
FD
BD
FB
If the point which constitutes the centre of gravity be supported by a force equal to the
weight of the body, it will remain in equilibrio in every possible position; and if the centre
of gravity be either vertically above or vertically below the point of support, the body will
be in equilibrio, but will not, as before, be indifferent to any position. When the centre is
vertically above a point of support, the smallest inclination will altogether destroy the
equilibrium; when it is vertically below a point of suspension, if the equilibrium be dis-
turbed, it will after some oscillations be restored.
If a body rest upon a horizontal plane, and the vertical line passing through the centre
of gravity be within the base, as we have already seen, the body will stand, if without it
will fall, and when that line is within the base, the farther the point in which it meets it is
from the perimeter on any side, the firmer will be the stability of the body, for the weight
may be considered as acting entirely on the centre of gravity; consequently, the more dis-
tant any point in the perimeter of the base is from the vertical of the centre, the longer is
the vertical lever by which the weight acts, and the greater the momentum to resist that
of a given force similarly applied, tending to produce a rotation about an axis passing
through that point. When the centre of gravity is high, the body is more easily overturned
than it would be were the centre lower: a carriage loaded will overturn more readily
on a declivity, and when the weight is piled up very high, the chance of accident is still
further increased, because its centre of gravity is more easily thrown outside its base, or
beyond the wheels or points of support. In every body possessing weight, there is a point
through which the resultant of the gravitation of its individual particles will pass,
whatever be the position of any given points in it with respect to the constant vertical
direction of this force, that point is the centre of gravity.
CHAP. XI.
923
MECHANICS.
If a heavy beam, or one bearing a weight, be sustained at C, and movable about a
point C, whilst the other end B lies upon the wall BE, and if HGF be drawn through
the centre of gravity, G perpendicular to the horizon, and B F, CH perpendicular to B C,
and CF be drawn, then-
The whole weight will be equal to
Pressure at B
Force acting at C
-
HF
HC
CF

H
B
A
B
F
Fig. 1231,
A
**
Fig. 1232.
11

C
G
E
If a heavy beam, BC, whose centre of gravity is G, be supported upon two posts, B A
and CD, and be movable about the points A, B, C, D, and if A B, DC produced meet in
any point, H, of the line G F drawn perpendicular to the horizon, and if from any point
F in the line G F, FE be drawn parallel to A B, then
The whole weight will be represented by the line
Pressure at C
Thrust at B
and in these directions.
HD
HE
EF
By the construction of these four diagrams the triangle of pressure is formed, repre-
senting the several forces in which the line of gravity, or the plumb line, passing through
the centre of gravity, measures the absolute weight, and the other sides the correspond-
ing pressures.
The Action of Bodies when placed over each other. When two bodies touch each other at
the point of contact, a depression or sinking may be imagined, perpendicular to the surface
of contact, which indicates the reaction of the two bodies in the perpendicular line com-
mon to both suppose, for instance, that a body A be solicited by forces the resultant
of which is confounded with that perpendicular, and that the other body B remains fixed,
the reaction of the latter will destroy the resultant, and the body A will remain in repose:
but it is evident that the equilibrium will subsist if the body B be replaced by a force
equal to the reaction which it exerts against the body A, if this latter be considered as
free, and solicited by this new force concurrently with the other forces given. This
property, that all bodies resist each other according to the common perpendicular which
passes through their point of contact, extends in most cases to where one body is placed
on others: the reaction of the latter are so many true forces at the respective point by
which the first bodies rest on the other, and thus the equilibrium is restored or brought
back to conditions analogous to those which would have taken place if it had been free.
A simple instance of this is shown by a body placed on a single point, or by several on a
plane.
When a body rests on a plane at a single point, and is drawn by any forces whatever,
their resultant must be perpendicular to the plane, and must pass by the point of support.
The condition of passing by the fulcrum will not be sufficient for it alone, for if this
resultant be decomposed in two forces, the one perpendicular to the plane, and the other
situated in the plane, both passing by the point on which it rests, the first will be destroyed
by the resistance of the plane, but the other component will cause the body to move along
924
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
the plane, and they will no longer be in equilibrio: thus the equilibrium of a body which
rests on a plane by a single point is submitted to two conditions; first, the result of the
forces applied to bodies passes by the point of support, and, secondly, its direction is per-
pendicular to the plane.
A
G
B
m
G
Fig. 1233.
C
Equilibrium of an inclined Plane. Let us represent any plane cut perpendicularly to
its horizontal, and following the line of its greatest inclination, A B. Although this plane
be supposed to be indefinitely prolonged, its in-
clination is sufficient to define its base A C and its
height BC. Let us imagine a heavy body placed
on this plane of which G shall be the centre of
gravity: the equilibrium of this body in the plane
will require, first, that the resultant of its weight
should pass by one of the points of the base which
supports the body; secondly, that that resultant be
perpendicular to the plane: this latter condition
cannot be generally satisfied with regard to any plane whatever, because the action of
gravity is always vertical; hence this action will be decomposed into two others, the one
perpendicular to the plane, which will be destroyed by its resistance, and the other parallel
to the plane, which will cause the body to move or descend according to its length. We
must, however, remark that if the vertical of the centre of gravity meets the interior of the
base of support of the body, this latter will only slide in the direction of the plane; but it
will roll if the vertical falls without the base. This will happen with a base, because
the vertical always passes outside its point of support on the plane.
Let us suppose that a force, p, parallel to the
plane, is opposed to the descent of the ball: call
P the weight of the latter; we know that the
body ought to remain in equilibrio under the
action of the two forces p and P; consequently their
resultant, GM, will be perpendicular to A B, and
will pass by the point of support m, and then let GM
be the intensity of this resultant; it will be such
that the sides of the parallelogram G G' M N will
represent, the one G G' equal M N the vertical force
P, and the other G N the force p, parallel to AB.
The triangle G MN is similar to the triangle
A B C, for GM and M N are perpendicular to
AB and AC; moreover they are rectangles, the
one in G, the other in C: we shall have the pro-
portion


A
Fig. 1234.
GN: MN:: BC: A B,-
Or p: P:: BC: A B.
G
P
m
p
B
N
C
M
GI
Then the force parallel to the plane which holds the body, is to the weight of this body, as
the height of the plane is to its length and we have
BC
p=Px A B
B
Suppose, instead of drawing in the direction of the plane, the force p, which retains the
body on the plane, was horizontal and acted in the direction of the power, which prevents a
nut from descending along the screw; G M, the
resultant of the weight of the body and of this new
force, will not be the less perpendicular to AB; and
the triangle G M N, representing the two forces
which draw the body as well as their resultant,
will be similar to the triangle ABC: but as GN
is perpendicular to B C, and the right angle of the
first triangle is in N, we shall have the proportion,
as GN: MN:: BC: AC;

Or, p: P:: BC: AC,
which shows us that the horizontal force retaining
the body in the plane is to the weight of the body
as the height of the plane is to its base: or, that
p=Px
BC
A C
G
P
G
M
Fig. 1235.
p
It will be remarked, that in the value of p the numerator is the same for two cases in pro-
portion to the height of the plane; but the denominator is only the side of the plane
parallel to the force applied.
CHAP. XI.
925
MECHANICS.
Quantity of Work on an inclined Plane. The inclined plane is a machine of the greatest
utility in the arts, and facilitates the removal of the heaviest burthens to a considerable
height. If, for example, it be required to build a tower of stone, a number of men
would be necessary to raise the materials vertically; but by means of slopes or inclined planes,
men, horses, or carriages could readily ascend it, and the power required to draw the
weights would be much reduced.
P
F
To move a stone along an inclined plane A B, the workmen are accustomed to turn
it on its edges perpendicular to the inclinations, or if it be cylindrical, they roll it along,
so that in its different operations the resistance of
the friction is avoided; the effort, F, which is here
parallel to the length of the plane, A B, has then
only to overcome the resistance of the weight, P,
of the body; and as we have shown, we shall
have

F=
B C
A B
x P.
A
Fig. 1236.
C
If the inclination of the plane be such that its length, A B, is 100 times its correspond-
ing height, BC, the effort required to be exercised against the body is in the proportion
of 1 to 100, and consequently the labour is the same whether the body be raised
directly or along an inclined plane, this latter having no other use than that of facilitating
the elevation of the burthen. When a body descends along an inclined plane, its relative
gravity, or the force which accelerates its motion, is to the absolute force of gravity, as the
height of the inclined plane is to its length; or, the force urging the body to descend in
the direction of the plane, is to the whole force of gravity, as the height of the plane is to
its length.
An inclined plane is any plane surface
which forms an angle with the horizon,
and is measured by ABC. The line AB
is the length of the plane B C, the length
of its base, CA, its height.
There is, then, in an inclined plane an
equilibrium when the power is to the
weight, as the height of the inclined plane,
is to the length of its base multiplied by
the cosine of the angle which the direction.
of the power makes with the inclined plane.

Fig. 1237.
C
A
IT
B
When a body W is placed upon a horizontal plane, it is obvious that it cannot be in equili-
brio, unless a perpendicular let fall from its centre of gravity cuts the plane within the base
of its body when the plane becomes inclined to the horizon, the same condition is
necessary, and another force, P, is requisite to prevent it sliding down the plane in virtue
of its gravity. In order that an equilibrium may take place, the resultant of the two forces
P and W must be in a line perpendicular to the plane, and their direction must lie in the
same plane, and as the direction of W is in a vertical plane passing through the centre of
gravity of the body, the direction of P must be in the same plane.
The weight, power, and pressure on the plane are then respectively as radius, the sine,
and cosine of the plane's elevation: for if a cylinder be sustained upon an inclined plane by
a power holding one end of a cord parallel to the plane, whilst the other end is fixed, the
power is to the weight of the cylinder, as half the height is to the length of the plane: this
is obvious, for half the relative weight of the cylinder is sustained by the end of the rope
which is fixed.
The Wedge is a solid with three planes inclined to each
other, and two triangular sides: to free it from friction
the faces should be polished, and the force which acts upon
it is directed perpendicularly. That the three forces act-
ing on the three planes may be in equilibrio, each of
them must be in proportion to the length of the plane
on which it acts, and they must be applied at such parts
that their directions meet in one part; otherwise they will
be in opposition, and produce a rotary motion.
The shore C, for instance, when placed against a smooth
vertical surface, as the wall of a building, or employed to
raise a weight by means of any force applied at the foot by
drawing it along the surface, AB; the horizontal force
applied will be to the weight, as the distance, A B, is
to the perpendicular height of the wall: and on this
principle the equilibrium of arches, domes and roofs is
estimated.

A
Fig. 1238.
B
926
Noox II
THEORY AND PRACTICE OF ENGINEERING.
The
The edge C, called the cutting
edge of the wedge, is the most acute
angle of the triangle ABC.
face BA is the head, and AC and
BC are the sides.
The use of the wedge consists in
driving it, by the cutting side C, into
the substance to be split, so that
when driven it rests on its sides in two
places, a, b. Suppose the force F,
which causes it to descend perpen-
dicular to the head, (if it were ob-
lique, the wedge would turn,) has the
power of resisting or overcoming the
matter to which the wedge is applied,
which resistance may be represented
as two forces Q and R applied at ab,
C
Fig. 1239
A
B
F

B

a
12
R
Fig. 1240.
perpendicular to the respective sides AC and BC. The force F, which produces the
equilibrium, will be equal, and directly opposed to their resultant, and as this passes by
the point of concurrence of the forces Q and R, it is necessary that the three forces F, Q,
and R should be in the same point, or the wedge would be overthrown. If these re-
sistances then be given, the diagonal of the parallelogram constructed on their intensities,
and at their point of concurrence, will give the intensity of the force F to be perpen-
dicularly applied at the head of the wedge required to overcome these resistances. Taking
on the direction of Q, from the point O, a line or distance Om, equal to the force, and
carrying through the point m a line perpendicular to B C, as mn, we shall have the tri-
angle Ŏmn, two sides of which represent the two resistances Q and R, and the third their
resultant or the power F, which is equal or directly opposed to it: the triangle Omn is
equal to the angle C, the angle mnO is equal to the angle B, and the angle mOn is
equal to the angle A. Thus the sides On and A B, opposed to these angles, are homo-
logous; the same is the case with the sides mO and AC, and the sides mn and BC;
we shall then have the following proportions; On:
m 0::mn:: AB: AC: BC, or, replacing the dimen-
sions On, m O, mn by the forces F, Q, and R, which they
represent, F: 0: R::AB: AC: BC, which indicate
that in the equilibrium of the wedge, the perpendicular
power at the head, and the two resistances perpendicular
to the sides, are proportioned to that head and these sides;
as when a force is applied to drive it, that force is to the
resistance which the parts of the body oppose to it, as
the head of the wedge is to the sum of its sides.
Several forms are given to the wedge; among them is
one resembling the triangle ABC, with the rectangle in
A, the points of support being at a and b, and the
resistances in the direction Q and R.
The power
F, which is perpendicular to ab, cannot concur at the
common point of the direction of these resistances,
unless they are applied according to the direction of
the line Fb, parallel to the side AC, and passing by the
point of application of the resistance which is perpen-
dicular to the hypotenuse.
A
a
Fig. 1241.
F

b
R
In the example where the wedge is an isosceles triangle, which is the common form
given it, we have AC equal to BC, and, agreeable to what has been already stated, the
relations which satisfy the equilibrium are
FX AC
Q=
and R
>
AB
Fx BC
AB
We see, on account of A C being equal to BC, we have
Q= R, whence we have the proportion of
FQ:AB: AC.
When it is required to split bodies, wedges are used,
the heads of which are small in proportion to their sides;
if ten times less, as A B is the tenth of AC, F will be the
tenth of the reaction, Q, to be overcome; thus the advantage
drawn from the wedge is, that in diminishing the head, or
the angle of cutting, we can with a small force overcome
considerable resistance, as ten times or an hundred times,
by making the head a tenth or an hundredth part of its side.
A
Fig. 1242.
F

b
B
R
CHAP. XI.
927
MECHANICS.
Divers forms of the wedge are given to workmen's tools, and great loss of labour is oc-
casioned by those most constantly in use, which have not always the prismatic form: when
they are pyramidal, having three or four faces, the equilibrium between the power and
the resistance is analogous to those of the prism; the first is equal and opposed to the
resultant of three or four forces, which depend on the length of each face, and the sides
which form the head.
The wedge is also a truncated prism, and often nothing more than a cone with a
cylindrical head; but the condition of its equilibrium is the same as that of the isosceles
wedge, viz. the power is to the resistance, as the diameter of the head, is to the length of
the side of the cone.
Chisels, knives, nails, files, &c. are half flat prisms, the surfaces of which are striated or
cut into furrows at a certain angle, and crossed at another, so as to form small
pyramids or wedges, the points of which carry off the particles to be filed.
Saws are
an assemblage of wedges, the lower face of which is slightly inclined towards the
cutting edges and in the thickness of the blade; one tooth also inclines differently to the
other, viz. one to the right, the other to the left, that the saw may clear itself, and work
more freely. All wedges act on their cutting side, or on their pointed extremities, and
there is a proper angle for every tool according to its use, which practice can alone de-
termine. The chief matter for the workman to consider, when he is setting a cutting instru-
ment to act upon any surface, should be that he endeavour to make its end form the least
possible angle with the face to be cut; it should, therefore, be kept nearly parallel with the
surface it is employed upon, and should it be required to be made very sharp, the acute-
ness given to it must be obtained by taking away from the front part of the cutting
instrument against which the shavings slide. The carpenter's axe has the bevelled surface
outwards, and the flat side is that which is placed against the wood to be cut, so that the
angle between the face of the tool next the wood and its surface forms the least angle possible.
The Screw depends for its action on the same principles as those of the inclined plane,
and to have an idea of the form of the square thread screw, suppose a cylinder BCED
A

B
C


d
D
E
A
Fig. 1244.
Fig. 1243.
Fig. 1245.
drawn with the axis at A vertical.
x
កម្ល
W
b
If there be attached to the surface of this cylinder
or newel a rectangle, as abcd, and which represents the profile of the thread of the screw,
when the cylinder turns on its axis, this rect-
angle will form an annulus or ring, as long as
it remains in a horizontal position: but sup-
posing when it turns, the rectangle is made
to descend, and for each quarter of a revolution
it descends a fourth of the vertical height, a
square thread will be projected on the newel,
called a helix; when this has passed entirely
round its height, it is termed the step of the
screw, and is measured by the interval aa', be-
tween the upper surfaces of two consecutive
threads; the inclination or stiffness of the helix
diminishes towards the external edge of the
thread. When this has been formed, another
body, cut in an opposite manner, and called the
nut is applied to it; these together have a double
movement of rotation, and act as on an in-
clined plane.
The screw is nothing more than a cylinder, b, having a rectangular or triangular prism,
as ad, wrapped or coiled round it, in such a manner that one of the faces of the prism is


Fig. 1246,
a'
Fig. 1247.
928
THEORY AND PRACTICE OF ENGINEERING. Book II.
#
applied to the convex or concave surface of the cylinder, and one of the sides of the prism
always forms an acute angle with the axis of the cylinder, this angle being everywhere the
same.
To raise a weight by the nut and screw, the first may be
fixed, and the latter left free, or the reverse; in the first instance
a lever is applied to the head, which not only turns in the nut,
but raises the weight Q attached to its extremity; but when
the screw has the nut movable, the power is so applied, that
in turning the nut round the screw, it is elevated, raising at
the same time the weight attached to it, as in the press.
Calling F the power, and Q the resistance to be overcome, it
is evident that the first should act in the plane of the move-
ment of its lever, or perpendicular to the axis of this move-
ment, as in the wheel and axle; and if we abstract the
friction, its labour should be equal to that of the resistance
produced in the same time. It must be remarked that when
this latter rises to a certain height, the point of application of
the power must run over a certain arc, and in virtue of the
property of the screw, the relation between these two quan-
tities is always the same at the end of any given time, what-
ever may be the height to which the resistance has mounted,
and the arc described by the power, provided that the arc and
the height be simultaneous. We will now consider what takes
place in a complete revolution: the power has described a cir-
cumference, whilst the resistance is raised one turn of the
screw. If we call h the height of the turn, and R the distance
from the point of application of the power of the axis, h and
2 PR will be the space described by the resistance Q, and by
the power F in their proper directions; thus F and 2 PR will
be the labour of the power, and Qh that of the resistance at
the end of a complete revolution, and we shall have for the
condition of the equilibrium independently of friction,

F× 2 PR=Qh, or
FQh: 2 PR,
Q
Fig. 1248.
Fig. 1249.
R

R
which indicates that the power is to the resistance, as the turn of the screw is to the
circumference described by the point of application of the power: so that the power of the
screw increases as the distance between the threads diminishes.
In the endless or perpetual Screw, there will be an
equilibrium, when the power is to the weight, as the
distance of the threads multiplied by the radius of the
axle, is to the distance of the power from the axis of
the screw multiplied by the wheels' radius. Suppose
P the power, and x its effect on the toothed-wheel:
let R be the radius of the wheel, D the distance be-
tween the threads of the screw, r the radius of the axle,
W the weight, and C the circumference described by
the power,

PxC=xxD;
and by the properties of the wheel and axle,
x × R=Wxr:
multiplying these equalities,
we then have PxCxR=WxDxr,
PxCxx × R= x <D× W ×r;
or, P: W:: D×r: C × R.
Q
Fig. 1250.
The power, then, is to the weight, as the distance between the threads multiplied by the
radius of the axle, is to the circumference described by the power multiplied by the radius
of the wheel.
A
C
B
The Lever is of three kinds, and may be called an inflexible bar, capable of moving round
a fixed pivot or fulcrum; its properties are various.
A lever of the first kind has the power and
the weight on opposite sides of the fulcrum, as
in the balance, steelyards, scissors, &c. Supposing
two equal weights fixed at the ends of the equal
arms of the lever, it is evident there will be a per-
fect equilibrium, since there is no reason why either
should preponderate.
P: W-BC: AC.

P
Fig. 1251.
WI
CHAP. XI.
929
MECHANICS.
In a lever of the second kind, the weight is
placed between the power and the fulcrum, as
in cutting instruments which move round the
point of the blade, &c.

P: W=BC: AC.
In a lever of the third kind, the power is
placed between the weight and the fulcrum, as
in fire-tongs, &c.
P: W=BC: AC;
B
W
Wx BC
hence we have P=
AC
PXAC
W =
BC
WX BC
AC=
P
BC=
PXAC
W
Fig. 1252

B
よ
​Fig. 1253.
P
The weight supported by the fulcrum C is equal to the sum of the power and weight, or
P+W, when they act on different sides of the fulcrum, and therefore in the same direction;
and to the difference, P-W, when they act on the same side of the fulcrum, and therefore
in different directions. If the power P is shifted along the arm CA of the lever AB of
the first class, the weight W, which is capable of maintaining an equilibrium, will be pro-
portionate to CA, the distance of the power P from the fulcrum; for since P: W-BC
: AC, we have W: A C=P: BC; and if a be another value of W, and a C another value
of A C, we shall then have w: a C=P: BC. In a lever of the second kind the power
must be less than the weight, since it must be further from the fulcrum; and in one of the
third kind it must be greater than the weight, as it is nearer to the fulcrum. When the
centre of gravity of the lever or bar is not immediately over the fulcrum, the weight of the
bar must be taken into account. Of levers of the first kind there are many examples, as
the crowbar, scissors, snuffers, &c., where two levers are riveted together in elevating
a ladder the first process partakes of a lever of the second kind, and afterwards of the
third. When a man raises a stone by the application of the crowbar resting on a fulcrum
between himself and the stone, he presses down the end of the lever, and the utmost force
he can apply is equal to the whole weight of the body; but when he thrusts the
lever under the stone so that its extremity bears on the ground, it becomes a lever of the
second class; and in order to raise the stone he must draw the end of the lever upwards,
and in this direction a powerful man can exert a force equal to twice his weight.
The Roman Steelyard is usually
formed of a bar of iron resting upon
an edge or pivot, and having one arm
longer than the other. To graduate
this machine or the arm CB: let us
suppose M to be the weight of it when
united to its centre of gravity u, N the
weight of CA united in its centre of

+
Fig. 1254.
B
A
+
P
gravity v, and O the weight of the scale: let P, P', P", be the different weights employed:
an equilibrium is obtained by placing the constant weight, W, at the different distancer
a,b,c; consequently, there will be an equilibrium in the following cases: -
PxCA+Nx Cn+0xCA=Wx Ca + M × Cm ;
P'x CA+Nx Cn+0x CA=Wx Cb + Mx Cm;
P" × CA+Nx Cn+O× CA=Wx Cc+ M× Cm.
X
By subtracting the first equation from the second, and the second from the third, we have.
P'-PX CA=Pxab
P-P'x CA=Pxbc
ab=
bc=
P-PXCA
P
P"-PX CA
P
&c.
If the weights are in arithmetical progression, the distances ab, bc, will be equal, or form
a scale of equal parts; and if ab be made equal to CA, then W=P'-PW-P" — P', &c.
on the counterweight equal to the difference of the arithmetical progression of the bodies
3 0
930
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
weighed. In constructing a steelyard for practical purposes, the arm should be made
sufficiently strong to prevent its bending, and it is necessary that the scale be graduated
by experiment: supposing it is required to graduate the bar to indicate pounds, let one
pound be suspended at P, and let the counterpoise be moved until the bar rests in the
horizontal position; then try two pounds in the same manner: these two divisions being
established, let the whole length of the bar be divided into equal divisions, and each division
will give the number of pounds it will sustain; care being taken that the centre of gravity
of the bar is at or under the fulcrum on which it is suspended.
The Danish and Swedish Steelyard is a bar or lever, with a constant fixed weight at one
extremity, and a scale for holding the body to be weighed at the other. The point of
suspension, therefore, varies, and is usually a ring moving along the bar, and placed in the
position where the equilibrium takes place for instance, suppose the weight, W, is that
of the whole apparatus, with the exception of the ring, to be united in its centre of gravity;
D and P, to be that of the body to be weighed. An equilibrium will take place, when
W \ CD = P × CB, which, since CD = BD-CB, gives
x
CB=
W × BD
X
W+P '
from which the lever may be readily graduated. There are many applications of the
principles of the lever to the balance for commercial purposes, and the sensibility of a pair
of scales is made much more delicate, the more the length of the arms is increased, and the
weight of the bar is diminished. The bent lever balance is graduated upon a quadrant
attached to it, and an index which is acted upon by the body to be weighed. Supposing
the scale be loaded successively, the divisions on the quadrant may be made to exhibit the
respective weights by noticing the successive positions of the index.
The Pulley will have an equilibrium when each of the two powers is to the weight, as
the radius of the pulley is to the arch of the circumference, which the rope surrounds.
Let the powers, P, P, attached to the ropes which pass over the circles, M,N, and round
the pulley, CE, whose centre is D, be in equilibrio with the weight W;
then P: P' :: W=CD: DF, CE.
M
N
P and P' being equal, and in equilibrio, may be represented by the equal lines W A
and WB; then drawing A F parallel to MW, and BF parallel to NW, the diagonal,
W F, will represent the resultant of the
two powers, P, P': but as this resultant
is in equilibrio with the weight, W,
acting in the same direction FW, we
shall have W F for the measure of the
weight, W. By joining CD, D E, and
drawing CE, two isosceles triangles are
formed, WBF and CDE, which are simi-
lar, because the angles A and D comprised
between equal sides are both the supple-
ment of the same angle, CWE. The
figure CDEW, which is quadrilateral,
having C and E right angles, we have
WB: BF::WF=DC: DE: CE;
therefore P: W or P: W as radius,
is to the chord of the arc embraced by
the rope.
Each of the powers is to the
weight, as radius is to twice the cosine
of the angle which each rope forms
with the direction of the weight. As
the angle DCH is equal to CW D,
CE is equal to twice its cosine, or
twice CH.

'P/
Fig. 1255.
C
E
H
F
:7
B
W
The pulley is a cylindrical piece of
wood, or any other hard substance, with a groove cut out of its rim for the rope to pass
over. The cylinder moves round an axis, which works in a frame called the block. A
system of pulleys, or a number combined together, called a muffle, is either fixed or move-
able, according as the block which contains the pulleys is so. When a rope used to trans-
mit force has its direction altered, if the angle be too sudden, the probability is that it will
break; instead, therefore, of bending it over a single angle, the change of direction is
generally produced by deflecting it over several angles, each of which is less sharp than a
single one could be, and this is most perfectly done when the rope is bent over the surface
of a curve or pulley. If the rope were employed to sustain a fixed body, and not to move
a weight, no inconvenience could arise from its rigidity; but when motion is required, it is
CHAP. XI.
931
MECHANICS.
necessary that the surface on which it rests should move also, so that the friction is removed
in a great degree by the curved surface rolling on with the rope.
H
When two cords or ropes, suffering the same tension in every part of their length, are
parallel, there will be equilibrium of the forces, if each P and P' is one half of the weight, W ;
for the arch embraced by the rope being 180 degrees, the chord of which
is equal to twice the radius, therefore each of the powers is only one half
the resistance, and when one of these chords is fixed, then one power,
P, only being in action, it will be in equilibrio and equal to half
W. A system of pulleys with four ropes shows the weight to be 16
times the power, upon the same principle; for supposing the first to
carry the weight W, and the cord which passes round to have one end
fixed at M, and the other attached to the block of the second pulley, and
other cords to pass round the various other pulleys in a similar manner;
the tension of the first rope is equal to the powers. The first movable
pulley sustains a weight equal to twice the power, but the weight which
it bears is the tension of the second rope; hence the tension of the second
rope is twice that of the first, the tension of the third twice that of the second,
and so on.
If there be four ropes, the tension of the first is P, the second
2 P, the third 2 × 2P, or 4 P; that of the fourth 2 × 2 × 2, or 8 P. Each
rope added to this system doubles its power, so that W= 2º P, ¤
expressing the number of distinct ropes there may be applied; or,
if a be the number of movable pulleys employed, there will be an
equilibrium when

P: W-1: 2ª—1.
To determine the ratio of the power to the resistance when there
is an equilibrium with any number of fixed or movable pulleys, and
when the cords are parallel.
Spanish Bartons consist of two ropes and two movable pulleys;
and by such an arrangement there is a considerable gain of power.
The tension of the rope P B is equal to the power, and this rope
being finally attached to the pulley, which sustains the weight, sup-
ports the part of the weight equal to the power :
the
the rope
from A
to B balances the united tensions of both parts of the rope, extend-
ing from B to the weight and power, and therefore its tension is
twice the power; being brought under the pulley which sustains
the weight W, and finally attached to the fixed point, it sustains a
part of the weight equal to four times the power: thus the
whole weight must be equal to five times the power.
The rope I
passes by F over the wheel A, and it is attached to the wheel B.
Another system of two ropes is here shown, which does not pos-
sess the
power of the other: the tension of the rope extending from
the power to the fixed point is equal to the power, and the tension of
that extending from the pulley A to the weight is obviously equal
to twice the power: thus the weight is four times
the power. H is the point at which is suspended
the rope that passes under the wheel, G C, and
over that at A. B is the fixed wheel over which
the rope attached to A and E passes:
as the
wheel A is caused to descend by the power P,
so that of GC, to which the weight W is attached,
rises.
Гн
H
D
B
E P
F
с
Gе
W
Fig. 1256

ぼ
​Fig. 1257.
A
C
A
ल
Да
E


In a system of four ropes the weight is sixteen
times the power, for the tension of the rope
EC is evidently equal to the power, because it
sustains it; D being a movable pulley, must
sustain a weight equal to twice the power: but
the weight which it sustains is the tension of the
second rope; hence the tension of the second
rope is twice that of the first: in like manner
the tension of the third rope is twice that of
the second, and so on, the weight being equal
to twice the tension of the last rope. The four
ropes, then, of this example have the tension
of the first equal to P, of the second equal to
2 P, that of the third 4 P, that of the fourth
8 P, therefore the weight W will be 16 P: each rope so added doubling its effect, and the
G
W
Fig. 1258.
Fig. 1259.
W
3 0 2
932
BOOK II:
THEORY AND PRACTICE OF ENGINEERING.
n
condition of such an effect may be thus expressed: W=2º P, " expressing the number of
distinct ropes.
More power may be gained by an arrangement in which each
rope is finally attached to the weight. The first rope sustains a part
of the weight which is equal to the power: the tension of the
second rope is twice that of the first, and therefore sustains a part
of the weight equal to twice the power; the third sustains a part
equal to four times, and so on, the part sustained by each rope
being double that sustained by the preceding one. C is the fixed
pulley, B and A are the movable, and the three ropes are attached
to the weight W, at D, E, and F.
When a rope passes over a single wheel or fixed pulley, as its
tension is uniform throughout the length, it follows that in such a
case the power and weight are equal; for the latter stretches that'
portion of the rope which is between the weight and the pulley,
while the former stretches that between the power and the pulley :
and because the tension throughout the whole length is the same,
the weight must be equal to the power; no mechanical advantage
is therefore gained from the single pulley, but there are various ap-
plications of it where considerable benefit is derived.
In directing the power against the resistance, two fixed pulleys
are often found useful; thus, in elevating a weight, the rope may
be carried over the pulley at top, and returning downwards, brought
by means of another on an horizontal plane or the ground.
A single pulley merely serves to change the direction of motion;
that placed on the ground, around which the rope passes, may
wind round a windlass, or have the power applied in a horizontal
direction, which may be calculated according to the general rule.
The mechanical power of pulleys admits of being almost inde-
finitely increased by combination; systems of pulleys may be
divided into two classes, those in which a single rope is used, and
those which consist of several distinct ropes. In both cases the
weight is attached to a movable block, in which are fixed two or
more wheels, and whatever the system, every wheel has a separate
axle, and there is a distinct wheel for every turn of the rope at each
block: each wheel is attended with friction on its axle, and also
between the sheave and block, which destroys a great part of the
power employed. When the pulley is heavy, and acts in the same
direction as the resistance, its weight must be considered as part of
that resistance; and if its direction differs from that of gravity, in
which the weight of the pulley acts, an allowance must be made for
the loss of power. A parallelogram may be drawn
to express this, of which one side will represent the
weight of the pulley, the other the resistance; its
diagonal will then show the real resistance and its
direction, which will be greater or less than the
other, according as the direction of gravity coincides
with or opposes that of the resistance.
Whatever the arrangement of the pulley one law
holds good, viz. that as force is diminished, velocity
increases, or the power passes over a space greater
than that gone over by the weight, by as many
times as the weight exceeds the power.
It matters not how these several wheels are ar-
ranged; they may be combined in a variety of
ways so as to gain an advantage, or as it is termed
a purchase, which is more or less according to
the number of the pulleys, and their mode of com-
bination: the purchase gained is computed by
comparing the celerity of the weight raised with
that of the moving power, according to the prin-
ciple of virtual velocities: where the several portions
of the cords are parallel to each other, and the
weight rises an inch, the blocks will approach each
other by that quantity, and consequently the length
of cord connecting a single pair of pulleys would
be shortened two inches.

P
A
C
B
D
E F
W
Fig. 1260.

Fig. 1261.


W
Fig. 1262.
Fig. 1263.
CHAP. XI.
933
MECHANICS.
Suppose the pulleys in each
block to be n, then while the
weight ascends an inch, the
power descends 2n inches; and
consequently, when there is
equilibrium, the power is to
the weight as 1 to 2n.
By mariners the case which
contains the wheel or sheeve of
the pulley is called the block;
two or more blocks with the
rope constitute a tackle.
When each block contains
six sheeves, the ropes are made
to pass from one to the other,
as expressed in the section, and
the power is to be calculated
in the ordinary way.
There are many systems of
pulleys which are worked by a
single rope; in all of this kind
there is one movable block in
which wheels or sheeves are
fixed over which the rope runs,
and to which the weight is
attached: the weight here is
raised by the lower block, and
the rope, instead of being finally
attached to the fixed block at
top, passes over a second wheel
in that block, and then under a
second in the lower. The
weight here is equally distri-
buted among four ropes, each




Fig. 1264.
10
Fig. 1265.
:
of which is stretched by the force of the power; hence in this case the weight is four times
the power.

When passed over the third wheel its
increase of power may be estimated in a
similar manner. M is the fixed point;
the weight W is suspended on the sheeve
which contains the three lower wheels
comprised within RS, as the three upper
are between M and N: the rope after
passing over AB and under VT, rises to
C, and then descends and follows its course,
as represented in the former example.
In White's pulley, all the wheels in the
same block are reduced to one; or rather,
instead of using separate wheels, several
grooves are cut round circles of different
diameters upon the same wheel: as all
circles are proportional to their diameters,
it follows that such wheels come under the
same law in the lower block of a pulley
so contrived the diameters of the several
cylinders are as the odd numbers, 1, 3, 5,
7, 9, &c.; whilst those on the upper block,
which is fixed, are as the even ones, 2, 4, 6,
8, &c.: in such an arrangement the uni-
versal law of mechanics is followed, viz.
that as force is diminished, velocity in-
creases; or, the power must pass over a
space greater than that gone over by the
weight, by as many times as the weight
exceeds the power.
M
A
B


P
T
W
Fig. 1266.
Fig. 1267.
Fig. 1268.
White's pulley is so arranged, that the successive wheels revolve in the same time,
although they be of different diameters, and are so constructed that their several circum-
303
934
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
ferences are adapted to the length of rope which passed over them at the same time;
this will be evident if we consider the circumference of one wheel to be 1 foot, and that it
make one revolution while the lower block is raised 1 foot: in this time 3 feet of rope
would pass over the circumference of the corresponding wheel; and if the circumference
of the latter be 3 feet, it will revolve once during the ascent of the weight: from thence it
follows, that the several wheels will revolve in the same time, if their circumferences be as
above stated.
In the single movable pulley when the power descends through a
space of 2 feet, the rope will have passed over in the same length or
be shortened as much; thus the weight ascends through a foot while
the power descends 2 feet, or the velocity of the power is twice that of
the weight.
The laws of the equilibrium of pulleys are sometimes supposed to be
the same as those which belong to the lever; but this can only be the case
where two equal weights suspended by a rope pass over a single pulley :
a pulley ought rather to be considered as a cylinder moving on an axis,
the sole object being to change the direction of the rope without any
unnecessary friction, for when a rope has its course altered by passing
over a smooth surface, it communicates to it the entire force which is
acting upon it without any friction, and the resistance of such a surface
being in a direction perpendicular to itself and to the rope, the force ap-
plied remains undisturbed: a fixed pulley, therefore, on this account
has no mechanical advantage. By a movable pulley the weight may
be suspended by two forces, each equivalent to half the weight applied
in a vertical direction to the extremities of the rope; and these forces
may be derived from two weights if the rope passes over two fixed pul-
leys in a proper direction, and if one of the ends be attached to a fixed
point, and the other to the weight, the equilibrium will still be main-
tained.

W
Fig. 1269.
T
When two ropes are wound round two cylinders which move on the same axis, there will
be an equilibrium when the weights which are suspended to them are inversely as the radii
of the cylinders; this will be apparent, if we consider that every section of the cylinder
perpendicular to the axis is a circle, and the ropes, being tangents to the circles, will be at
the distances of the radii from the vertical plane: therefore by similar triangles the right
line joining the weights will be divided in the ratio of
the radii, and the centre of gravity will be in the vertical
plane; and the point of the axis immediately over it is
the centre of suspension. When a rope is wound round
a cylinder in contrary directions, the first perpendicular,
and the other in an oblique position, there will be an
equilibrium when the forces are as the perpendicular
distance of any point of the oblique rope from the axis, to
its distance from the point of contact.
The common pulley consists of a wheel with a groove
made on its edge or circumference which confines the
rope; this wheel is usually put into an iron frame,
where it turns with a metal pin, the diameter of which
is about a twelfth that of the wheel; the thickness of the
wheel is made a fifth of its diameter.


Sometimes the groove
on the wheel is made of
portions of cones, SO
arranged that they hold
more securely the rope
which is passed
them.
over
When there is a great
strain upon machinery,
and its motions are re-
quired to be regular,
belts and ropes cannot
be safely employed, and
chains are more advan-
tageous, which act as
ropes by simple friction
Fig. 1271.
Fig. 1270.


on the surfaces around which they pass. When ropes are used, they generally move in
grooves cut in the circumference of the sheaves or wooden wheels.
CHAP. XI.
985
MECHANICS.

Some pulleys are made to revolve on rollers;
the pivot that passes through their centre is made
to turn upon two other rollers at each bearing;
there are many varieties of friction rollers.
The most efficacious method perhaps of diminish-
ing friction is by the application of friction-wheels:
for any friction arising from one body being
dragged over another may be changed into that
which arises from one body rolling upon another :
when the moving force is not exerted in a per-
pendicular direction, but obliquely, as in the
gudgeon of a wheel, it will press with greater
force on one part of the socket than on any
other.
Some are so mounted that the
pulley contains four others that are
movable, and which revolve round
a fixed cylinder in the middle; the
four wheels are retained in their
position by two cords which pass
over their thickness, and hold them
together.
The force of friction, which re-
sists the sliding of different bodies
on each other, is closely connected
with lateral adhesions; the friction
of all solid bodies may be regarded
as a uniform retarding force, neither
increasing nor diminishing as the
velocity of their bodies is changed;
when bodies are in contact with each
Fig. 1273.
Fig. 1272.



other and at rest, their adhesion is greater than their friction, and this is required to le
first overcome.



Sometimes eight small wheels
are arranged in a manner to form a
regular polygon, being held together
by irons which are riveted over
their respective centres, the rivet
forming the pin upon which they
revolve around the fixed centre.
When wheels are fixed on the
same pivots, and turn with the same
velocity, there is considerable friction
and consequently wear, for the rope
passing over the wheels with different
degrees of velocity, it cannot but
slide variously in the different
grooves, with the exception of one
only. The object then in any ar-
Fig. 1274.
rangement of pulleys ought to be the making them all revolve on their axles at one time,
so as to avoid unequal wear, and at the same time their grooves on their exterior should
have different velocities, equal to those of the rope which passes over them.
Chains of a variety of
forms have been applied
instead of ropes to
pulleys; that which is
commonly used was in-
vented by De Vaucan-
son, a celebrated me-
chanic ; each chain
carries a tooth, which
passes into a notch made
edge of the


on the edge
pulley.
Other pulleys have had
the same principle ap-
plied, but in a manner
Fig. 1275.
Fig. 1276.
304
996
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
that they can be made to turn only one way,
which is serviceable in the raising of weights;
the click enters a new notch whenever the
pulley moves round, and prevents its receding.

M. Coulomb made several experiments on
the simple pulley, where the friction of the axis
and the rigidity of the rope produced a joint
resistance; when lignum vitæ, moved on iron,
was either a fifth or seventh of the weight in
all velocities, besides the rigidity of the rope,
the mean was a sixth, or with a small weight
a trifle more. For axes of iron on copper,
where the velocity was small, not quite a
twelfth, the friction being always a little less
than that on plane surfaces: when the axis was
green oak, and the pulley was of lignum vitæ,
the friction with tallow was a twenty-sixth, and
without it a seventeenth; with a pulley of
elm a thirty-third in the first state, and a
twentieth in the other: with the axis of box, and the pulley of lignum vitæ, it was a
twenty-third and fourteenth with a pulley of elm, a twenty-ninth and twentieth; and
with an axis of iron, and a pulley of lignum vitæ with tallow, it was a twentieth.
There are some which are contrived with a
spring at top, which enables the click or
ratchet which holds the wheel to be lifted up,
so that the pulley may turn in a contrary
direction.
Fig. 1277.

In all these contrivances we must have
remembrance that the ropes are subject to
considerable rigidity; and this is supposed to
vary as the diameter, as the curvature, and as
the tension. Coulomb found the power of the
diameter expressing the rigidity to be generally
1.7 or 1.8, never less than 14, and that a
constant quantity must be supposed to be
added to the weight. Small wet ropes are
more flexible than dry; and when large, less
So. Ropes that are tarred are stiffer by about
one-sixth, and in cold weather somewhat more;
and in general after a little rest, the stiffness of all ropes is increased.
Fig. 1278.
In a rope of three strands each of two yarns, 12 lines in circumference, 6 inches of
which weighed 21 gros, or 125 grains English, being bent on a fixed axis 4 inches in
diameter, required a constant force of the tenth of a pound French, and a fifty-fourth of the
weight, to overcome the rigidity: the same rope tarred required the fifth of a pound and a
fiftieth of the weight. In a rope of five yarns, the circumference 20 lines, and the weight
61 gros, the rigidity was equal to half a pound, and a twenty-third of the weight; when
tarred, the rope required one pound and one twenty-
one parts of the weight to move it. With strands of
ten yarns, a circumference of 28 lines, and a weight of
121 gros, for 6 inches, the untarred rope showed a
rigidity of two pounds and a thirteenth of the weight,
and the tarred rope of 2-3 pounds, and a tenth of the
weight. These experiments were made on a roller
which was allowed to move in a horizontal plane,
while the rope was coiled around it; it was therefore
necessary to make some allowance for the friction it
was liable to, which varied as its weight, and in-
versely as its diameter.
It has been found convenient at times to mount one
pulley in such a manner that it has an eccentric motion,
which prevents the cord or rope from slipping so easily
from off the edge: the pivot upon which the wheel is
mounted is placed a little out of the centre, by which
means the revolution is changed from that of the regular
pulleys, and when the rope attached to it is pulled it
presses the eccentric against that which passes over the
edge of the lower pulley, and prevents its slipping off.


Fig. 1279.
CHAP. XI.
937
MECHANICS.

•
In a muffle of pulleys, when three are fixed and
three movable, there will always be an equilibrium
when the weight is to the power, as the number of
ropes which bear the lower muffle is to unity: there
is the same proportion between the power and the re-
sistance when the pulleys are in different places, or
when the fixed pulleys are placed on one axis, and all
the movable ones upon another.
In all movable pulleys whose number is N, when sus-
pended on separate ropes, the extremities of each of
which are attached to the weight, there will be an
equilibrium when P: W=1: 2n − 1. In a combin-
ation of pulleys in which two are supported by one
rope, there will be an equilibrium when P: W=1 : 4,
and all others in the same proportion.
-
There are several arrangements made in the pulleys
used to raise weights: in some single-wheeled pulleys
there are means provided to release the rope; a part
of the sheeve opens at the edge sufficiently to pass
the rope over, or to disengage it: the weight being
attached to the movable block, the fixed one serves
only to apply the power in the desired direction; the
former alone diminishing the power acquired, dividing
the weight equally among all the pulleys; every mov-
Fig. 1280,
able pulley requires the application of a force equal to half the weight to produce equi
librium.





Fig, 1281.
阿
​8
USED AT THe menai bridge.
The pulley is of great antiquity, and was used by the ancients: we learn from Vitruvius
that Ctesibius, whose father was a barber, was born at Alexandria, and that being endowed
with extraordinary talent and industry, he acquired great reputation for his mechanical
contrivances: wishing to suspend a mirror in his father's shop in such a way that it might
be easily lowered and raised by means of a cord, he used the following expedient: -fixing
a wooden tube on the under side of the beam he attached a pulley to it, in such a manner
that the cord passed and made an angle in descending into the wood which he had hollowed
out; there he placed small tubes, within which a leaden ball attached to the cord was made
to descend. It happened that the weight in its descent in the tube pressed on the enclosed
air, and violently driving out at its mouth the quantity of air compressed in the tubes,
produced by its obstruction and contact hollow sounds; this afterwards led to his invention
of the organ.
The block or sheeve was much in use by the Romans, and known under the name of
trochlea, though it was sometimes called rechamus. From the description handed down to
us by the author above quoted, it would appear that the pulleys were not placed as we have
938
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
•
them, side by side, but under one another; for it is stated that in the trochlea are two pulleys
turning on an axis; through the upper pulley the drawing rope is passed; then it descends
and passes round the under pulley of an inferior trochlea, and returns to the under pulley
of the superior trochlea, when it descends to the inferior, and in a hole therein the end of
the rope is fixed, the other end of the rope passing to the bottom of the machine. The
blocks used in hoisting the various parts of the Menai bridge were of different forms, as
shown above, and were admirably suited to their various purposes; they were well pro-
portioned to their works, and the ropes could be taken out easily, as indicated in the single
pulley.
Wheel and Axle consists of a cylinder which revolves about its axis, having a wheel of
larger diameter affixed to it; the weight is suspended by a cord which is wound round the
axle; the power applied acts on the periphery of the wheel. The equilibrium is established
when the power is such a multiple of the weight that acts on the axle, as the diameter of the
axle is of the diameter of the wheel; thus, if the diameter of the axle be 1 foot, and that of
the wheel 10 feet, a power of 1 cwt. will be an equipoise of 10 cwt. or ton: when the
power has turned the wheel once round, the axle has revolved once also; the power has
gone over a space indicated by the circumference of the wheel, whilst the weight has
been raised a height equal to the circumference of the axle.
The wheel and axle bears so strong a resemblance to the lever,
that it is not improperly called a continual one; for if two cords
perfectly flexible are wound round two cylinders in opposite directions
there will be an equilibrium if the drums or rollers are of a similar
diameter; and the forces which operate upon any cylinders are
universally as their radii, or as their diameters, of which they are the
halves: weights in turning round a cylinder exert the same power as
the arms or spokes of a lever equal in length to their semi-diameter:
the cylinder is often united to a winch or lever; and in this case the
radii of the cylinder must be compared with the length of the winch.
Let us consider the wheel and axle to consist of a cylindrical axis
CD, of any diameter, to which is fixed a wheel A B of a larger
diameter, and having its plane perpendicular to the axis, as well as
its centre corresponding: the pivots F and D are those on which the
axle moves when the wheel is made to revolve.

F
B
P
W
Fig. 1282.
There will be perfect equilibrium when the power is to the weight, as the axle is to the
radius of the wheel. Let AB be the axle, O the wheel, W the weight applied to the
point E, and let the power P be applied to the point
M in the direction M C.
Let O be the centre of the wheel, and K that of
the axle; through E draw a plane perpendicular to
the axis A B, cutting it at K; therefore the radius
KE of the cylinder will be perpendicular to EW:
through O draw OF, parallel to KE, and this
radius will be horizontal and in the plane of the
wheel: let two forces W', W", each of which is equal
to W, be applied in opposite directions to the point
F, and in the vertical line GH, the one W' acting in
the direction FG, and the other W" in the direction
FH. These two opposite forces destroying each
other, the equilibrium of the machine is not altered.
K
D
W/H/

G
M
C
H
P
W/
W
Fig. 1283.
B
Join FE, meeting in the axis D, and bisecting
KO in D; then KE FO. Let us consider the
state of the forces W acting at E, and W' acting
at F.
Since W'W, the effect of these forces
will be the same as 2 W acting on D: but as the point D is in the axis of the cylinder,
which axis is immovable, the force 2 W can have no effect in altering the equilibrium or
turning the machine round its axis.
The other forces, therefore, are P applied at M, and W" applied at F, and acting in the
direction of FH. We may now consider MOF as a bent lever whose fulcrum is 0; and
since the forces at M and F, in the direction MC, FH, perpendicular to the arms of the
lever, are in equilibrio, these forces will be inversely as the length of the arms, viz.
P: W" OF. OM; but since FO-EK and W'W we have
=
P: W=EK: OM.
When, therefore, there is an equilibrium in a wheel and axle, the power is to the weight,
as the radius of the axle is to the radius of the wheel.
In the windlass the axle is horizontal, and in the capstan it is vertical, and the advantages
gained on the latter application is evident, as it affords the means for a number of workmen
CHAP. XI.
939
MECHANICS.
to apply levers or handspikes, and to walk around it without any interruption, the spokes
or levers supplying the place of a wheel. When the axle is horizontal, the weight of the
machine presses upon the pivots upon which it turns; and when its centre of gravity is
equally distant from them, its pressure is distributed equally between them. When, how-
ever, the axle is vertical, the whole weight rests upon one pivot, the friction in the two
cases varying.
In a machine composed of several wheels and axles connected together by ropes, which
pass from the wheel of the one to the axle of the other, the power is to the weight, as the
product of the radii of all the axles, is to the product of the radii of all the wheels.
When toothed wheels and pinions are used, the power will always be to the resistance,
as the product of the radii of all the pinions, is to the product of the radii of all the wheels.
In all the combinations of the simple mechanical powers, the condition of equilibrium
may be easily computed by tracing and calculating the effects of all its separate parts, the
effect produced at one part being always considered as the power which is applied to the
next part.
The relation between power and effect may be found by considering that if the
points of the machine to which the power and resistance are applied be made to describe
an infinitely small space, the power will be to the weight or resistance as the space
described by the point to which the weight or resistance is applied, is to the space described
by the point to which the power is applied; then
We shall then have
P the power,
W = the weight,
p=the
the space described by the power,
w=the space described by the weight.
P: W=w: P,
or, what is the same, the power is to the weight, as the velocity of the weight, is to the
velocity of the power; consequently whatever is gained in power is lost in time.
Elementary Parts of Machines.-A system of wheelwork is composed of two parts, each
turning on a fixed axis: considering two points in this system, the distance of whose axis
of rotation is invariable, and supposing a force applied to the first causes it to describe an
arc of a circle in any given time, the machine transmits this rotary motion to the second
point, which will describe in the same time another arc of a circle. The form of the
wheelwork depends on the several positions of the two axes of rotation, and on the relation
of the arcs of the same radius described in the same time by two points invariably fixed on
these axes.
We shall consider the case in which this relation is constant, and determine
the form of the wheelwork by two hypotheses, of two parallel axes of rotation of two inter-
secting axes, and indicate the researches made on the form of wheelwork in the case in
which the two axes do not cut.
S
a
-When a point
B
On Wheelwork having an uniform Rotation round two parallel Axes.
describes a circle, the measure of its absolute velocity is the
arc which it describes in an unit of time, the relation of this
velocity to the radius of the arc is the measure of its angular
velocity. The two parallel axes of rotation being given, draw
a plane perpendicular to them, and cutting them in two points
as A and d; join these two points by a right line Ad. The
relation of the angular velocities of the two fixed points to the
parallel axis, Dd and a being known, divide the right line Ad
into two parts, A B and Bd touching each other in the point
B. Whatever is the force of P applied tangentially to the
circle of the radius A B, it is evident that the transmission of
the motion of rotation of this first circle to the second Bd will
be made by the point of contact B, and that the arcs described
in the same time by two determined points of the two circles
will be of the same length; whence it follows that the absolute
velocities of these two points are equal, but the arcs of the
same length and different radii; measure on the circum-
ferences to which they belong angles which are to each other
as the inverse ratio of the radii of these circles; whence it follows, that the angular and
simultaneous velocities of any two points taken on the circumferences of the radii Bd,
aB
AB are to each other in the ratio of these radii.
Bd

Fig. 1284.
Supposing the axis of rotation A and d, invariably fixed to two given points, and con-
sequently to two circles of the radii AB, Bd: then the rotary motion of these two points
will be made in the same time as those of the circles, and the arcs of the same radius,
similar to those which they describe simultaneously around the parallel axes A and d, will
be to each other in the inverse ratio of the radii A B, Bd. Designating the two given
points by M M which turn, the one round the axis A, and the other round the axis d, the
´940
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
3
Bd
angular velocities of these two points will be in the constant given ratio ( of the radii Bđ,
AB
A B, whatever their absolute velocity may be.
A machine composed only of the two circles A and d, which should revolve and touch at
the point B would only transmit the motion of the first circle to the second by simple
friction at the point of contact, and as soon as the contact should cease, which would happen
in a short time, the transmission of motion would no longer take place.
Of the Plane Epicycloid.-When two circles which touch are in the same plane, and one
rolls on the other without ceasing to touch, a certain point in the movable circle describes
a curve called a plane epicycloid. The movable circle may roll either on the exterior or
interior of the fixed one; in the latter case, if the movable circle has a radius of the fixed
circle for its diameter the epicycloid would become a right line; this right line is the radius
of the fixed circle which passes through, and in which it is touched by the movable circle,
considered in its first position.
F
G
H
A
B
CA
K
D
Let B be the point in which the movable circle in its first position A HK B touches the
fixed circle BEFG, in another position ACD; it touches
the fixed circle in D, and taking the arc DC of the same
length as BD, the point C, the extremity of the arc DC, will
be one of the points of the line described through the movable
point B of the circle AHKB; further, this point will be on
the radius A B. Let us suppose that it is at C; beyond this
radius the angle B A D has for its measure either the entire arc
B D, or half the arc CD. This arc CD is only half the radius
of BD; then in order that it should have twice the number of
degrees of the arc B D, it is necessary that the two arcs should
be of the same length as DB. Then these two arcs which
belong to the same circle are equal, and the points C and C'
are the same; whence it follows that the epicycloid described
through the point B of the circle A H K B is reduced to a right line AB.
When the movable circle is of infinite radius, it becomes a right line; and the plane
epicycloid a development of the fixed circle; if the radius of the fixed circle is infinite,
the epicycloid becomes a cycloid.

E
Fig. 1285.
Roemer, a Danish mathematician, was the first to adopt the epicycloidal curve to the
teeth of wheels, in 1674, about which time De Lahire published a work upon the
same subject, and demonstrated that if a tooth of either a wheel or pinion be formed by a
portion of an exterior epicycloid, described by a generating circle of any dimensions what-
ever, the tooth of its follower will be properly formed by a portion of an interior epicycloid
described by the same generating circle. The object here was to obtain a uniform pressure
and velocity throughout the machine, so that the wheels, whatever might be their position,
should act uniformly and equally, and that the surfaces of the teeth touching at a point
should roll over each other and avoid all friction.
The cycloid and epicycloid have been treated on by numerous writers, and Camus in
particular has applied their principles to the forms of the surfaces of the teeth of wheels and
pinions acting against each other under different circumstances, as the wheel and trundle,
the wheel and pinion, the rack and pinion, conductor or conducted, spur or bevel gear, and
others. De Lahire thought the involute of a circle the best of the exterior epicycloids,
and considered the generating straight line as a curve of infinite radius, which it is when
applied to a pinion acting on a rack.
M. Hachette investigated this question with great ability, and decided the form of curves
most applicable to the teeth of wheels: and that the mechanical effect which one wheel
produces upon another should be the same in all positions, for which it is necessary that
the line perpendicular to the surfaces of the teeth at the point of contact should intersect
the line joining the centres at a fixed point that divides the line into two parts, the ratio of
which is the mechanical power.
The teeth ought to work a little before and after the line of centres, and some mathe-
maticians have preferred a union of the epicycloid with the hypercloid to effect this more
perfectly, as their line of action is nearly perpendicular to the radius, which causes less
friction as well as strain upon the axles.
The teeth of wheels have been made so small since the introduction of iron for
their manufacture, that their form is not so important; such excellence of workmanship is
arrived at, that they are now set out with the template and dividers only. The practical
rule made use of by millwrights for finding the depth of the teeth from the bottom to the
pitch line, and from thence to the top of the tooth, is simply to multiply the pitch by 5,
and divide by 9, and vice versâ.
Sometimes the curves of the exterior and interior surfaces of the teeth are set out by a
tracer, fixed in the radius line of one of two pieces of board, the edges of which are made
to resemble the primitive circles of the wheels: then by fixing a template to one edge, and
CHAP. XI.
911
MECHANICS.
diviamg the teeth accurately, the tracer will, by the rolling of the two circles, describe the
curves sought. The teeth of wheels are usually set out by arcs of circles after their centre
and radius are accurately determined.
Iron was first cast into wheels and used in machinery about the year 1782, at the works
at Colebrook Dale, though wrought-iron had been partially employed long before on the
continent.
E
b
E
When two wheels engage each other the smallest is called the pinion, and the number
of their teeth being determined, the line uniting their centres is termed the line of their
centres, and if this line be divided in the ratio of the number of teeth in each wheel, this
point limits the circle, or what practically is called the pitch line. If from each centre a
circle is described, passing through this common point, the diameters of these circles are
named primitive or proportional, and the circles themselves the pitch lines; the pitch of
the teeth being the distance from each other, as measured across this line as a chord, and
not along its circumference. Suppose CD the line
of centres, EE the pitch line of the smaller wheel,
FF that of the larger, and the centre A to be
in the line of centres CD. Let A be the stave of
a trundle, from the centre of which describe the
are be, which shows the form of the tooth, which
within the pitch line may be drawn circular. The
radius for describing the teeth is equal to the
pitch, minus half the diameter of the stave of the
trundle, and the centres of these arcs will be in the
proportional circle, which we have called the pitch
line.

Fig. 1286.
D
TT
D
F

:
Having set off upon the proportional circles the
points G, 2 L, and Oo H, according to the thick-
ness of the teeth and leaves, draw lines from these
points towards the centre of their respective circles,
to serve as the sides of the spaces between the
teeth and between the leaves; the depth of which
spaces must be such as to give room for the action
of the curved part of the teeth and leaves. Then
describe upon the extremity of the sides of each
tooth epicycloids, such as QD, LD, with the generating circle Y, the diameter of which
is equal to the proportional radius of the pinion, upon the circumference of the propor-
tional circle of the wheel as a base.
Fig. 1287.
The mode of forming the teeth being shown, that of the leaves will be obvious, V V being
the generating circle of the epicycloid upon the circumference of the circle of the pro-
portional pinion as a base. When the teeth are small, and do not begin to act till they
arrive at the line of the centres, the teeth of the wheel when the wheel drives the pinion,
or the leaves of the pinion when the pinion drives the wheel, may be described by a
circular arc, of which the radius is equal to the pitch, and of which the centre is in the
pitch line of the wheel or pinion.
Another method is shown, which may be considered more simple :
Let A A represent the pitch ine, the circle
BB the bottom of the teeth, and DD the
top.
After the pitch line is described, it is divided
into the number of teeth the wheel is to have;
with a radius equal to one and a quarter of these
divisions, strike circles upon the pitch line A;
thus the curved part of each side of the cog
is formed. The remaining portion of the tooth
within the pitch line A is bounded by two
straight lines, drawn from the point gmn towards
the centre of the wheel; the spaces between, as
well as the teeth, are all equal.

D
A
B
m
g-
D
g
n
Fig. 1288.
B
Another method may be shown, which re-
quires, however, to be executed with attention.
Let the tooth GCH have the form of a curve traced by the extremity of a thread FC,
unlapped from the circumference, and let the acting face of the tooth b be formed in a
similar manner: then the line FCE, drawn perpendicularly to the touching point C, is
in the direction of the threads, by which the two acting faces are formed; this line, being
the common tangent to the circumferences of the two wheels, will always cut the line A B
in the point D: thus the teeth can act on each other at the same time, and the pressure is
spread over a number, instead of being confined to one.
942
THEORY AND PRACTICE OF ENGINEERING. BOOK IL

When a wheel and pinion act
with each other, the teeth of the
small wheel may be made to
represent the staves of a trundle;
suppose the teeth divided on the
pitch lines EE, FF: on the
wheel C form circles, which may
represent staves; the centre of
one of these staves or teeth being
placed on the line of centres at A,
draw the line AB, uniting the
centres of these teeth.
a
Ꮐ
CR
B
E
Fig. 1289.
Fig. 1290.
E
B
A
Then the radius Ab from A as
centre will describe bc, the
curve of the tooth of the conducting wheel, and the curve ba that of the other wheel.
Radius being equal to pitch, diminished by half the diameter of the circle of the stave teeth,
and as the centres will always be in the pitch lines, the other teeth may be easily drawn.
Bevelled Gear, or conical wheels, are usually frustra of fluted cones; the axis or shaft
of the leader or driver is placed at an angle of 45 degrees with the axis of the shaft
of the follower or driver. To form a pair of conical wheels there must be set out on the
frustra regular series of teeth at equal distances, projecting as much above the surface as
the hollow between them descends. These teeth must be directed towards the apex, so
that when they are in contact, they shall touch each other along the whole length; when
the point of contact is along the line of centres, there is little or no friction. Wheels of
this kind are used to communicate motion in any direction that is required, and the action
of the teeth is the same as in the common spur-wheels; the diminution of the teeth being in
the same ratio in both cases, but requiring more attention in the setting out than the common
teeth.
Supposing it is required to determine the diameter of two wheels that shall change a
motion into a direction of the angle above mentioned, and in which the axle shall move
with four times the velocity; the wheel mounted on the axis that is to revolve four times
more rapidly, must have one-fourth the number of teeth, and one-fourth the diameter.
Let the cone ACD have its slant height at
right angles to CBD; the cone will then inter-
sect the teeth at right angles.
If AB show the original direction of the
motion to be changed, through the point O
draw COD at an angle of 45 degrees to the line
A B. The axle CD is required to move four
times more rapidly than AB; the wheel which
it carries must have only one-fourth the number
of teeth. Draw cd at any distance parallel to
CD, and ab parallel to AB, so that Au= Bb
=4Cc=4Dd, and join the points of intersection
i in 0: draw Om, so that the angle BOm equals
BOi, and On, so that DOn equals DOi, and
these lines show the size and position of the cones
of which the wheels are to be formed. The
angle BOD is in fact divided into two angles,
whose sines are to one another as the number of
revolutions of one wheel is to the number of re-
volutions of the other.
The surface of the cone may be developed on
a plane by rolling it round its apex, and by this
means the true impression of its teeth taken; the
pitch circumference of CD will be the sector of
a circle, the slant height BC being radius.

d
D
B
Fig. 1291.
I
B
α
C

The wheel and pinion may be either situated
on the same plane, or their planes may form an
angle, in which case one of them becomes the
crown wheel, or both of them may be bevelled,
and their teeth cut obliquely according to the
relative magnitude of the wheels, the angle of the
bevel must be different, in order that their
velocities may be in the same proportion at both
ends of their oblique faces; for which purpose,
becomes necessary that the teeth must be directed to the point where the axes would meet
Some mechanics have considered that the angles should be as the diameters of the wheel,
it
Fig. 1292.
CHAP. XI.
943
MECHANICS.
for in reality the tangent of the angle must be to the radius as one diameter to the other.
Hence we see that the bevel of the wheels must be such, if we suppose their shafts pro-
duced, till they meet a line drawn from that point to the meeting of the circumference of
the wheels will determine the angle or bevel of their edges, so that they will work freely
and equally together. When the acting faces of the teeth on the large wheel have the form
of a spherical epicycloid, whose generating circle is the primitive circumference of the
pinion, and whose base is the primitive circumference of the wheel, and if they drive the
smaller wheel by acting upon infinitely small pins in its circumference, the motion of both
will be found uniform. If the acting faces of the teeth of the large wheel have the form of
spherical epicycloids, whose generating arch has a radius equal to half the primitive radius
of the smaller wheel, and whose base is the primitive circumference of the wheel, and if
they drive the small wheel or pinion by acting upon rectilineal leaves directed to its
centre, the motion will be uniform. If a bevelled wheel drives a conical lantern with
conical spindles, it will be done uniformly, when the acting faces of the teeth of the bevelled
wheel have the form of a curve drawn parallel to the spherical epicycloid and distant from
it by the radius of the spindle.
Strength of the teeth of wheels may be calculated upon the principle of a beam fixed at
one end, and sustaining pressure at the other; when the pressure at the pitch line is given,
multiply it by the length in inches of the tooth to this line, and divide the product by
2544 times the square of the thickness, and the quotient will be the breadth in inches;
it is usual in practice to make the breadth of the wheel and teeth two or three times the
pitch of the teeth.
The table gives the radii of wheels, the pitch being an inch, and the teeth of various
numbers. When it is required to find the radius for any other pitch, it is only ne-
cessary to multiply the number in the tables by the proposed pitch of the wheel, and the
product will be the primitive or proportionate radius, viz. the radius measured from the
centre to the pitch line.
The table is founded upon the following principles: divide 360 degrees by twice the
number of teeth, and it will give half the angle the pitch subtends at the centre, and the
cosecant of this angle to a radius equal to half the pitch is the radius sought, thus:—
180°
Primitive radius equal to half p x cosecant number of teeth
To determine the diameter of any wheel where the pitch and number of teeth are given,
it is only necessary to multiply the number of the teeth by the pitch, and divide this
product by 3.1416.
0
1
2
3
4
5
6
7
8
9
6.055 6.214
10 1.668 1.774 1.932 2.089 2.247 2.405 2.563 2.721 2.879 3.038
20 3.196 3.355 3.513 3.672 3.830 3.989 4.148 4.307 4.465 4.624
30 4.783 4.942 5.101 5.260 5'419 5.578 5.737 5.896
40 6.373 6.532 6.643 6.850 7·009 7.168 7.327 7.486 7.695 7.804
50 7.963 8.122 8.231 8.440 8.599 8.753 8.962 9.076 9.235 9.399
60 9.553 9.712 9.872 10.031 10.190 10.349 10.508 10.662 10.826 10.935
70 11.144 11·303 11·463 11-622 11-73111.940 12-099 12-758 12-417 12.676
80 12.735 12.895 13.054 13.213 13.370 13-531 13-690 13.849 14-008 14.168
90 14.327 14.436 14.645 14.804 | 14.963 15.122 15-281 15.441 15-600 15.759
100 15.918 16.072 16.236 16.395 16.554 16.713 16.873 17.032 17-191 17.350
110 17.504 17.668 17.987 17-827 18.146 18 305 18 464 18.623 18-782 18.941
120 19.101 19-260 19.419 19.578 19-737 19.896 20-055 20-214 20.374 20.533
130 20.692 20-851 21 010 21∙169 21 ·328 | 21·488 | 21·647 | 21·806 | 21·460 22·124
140 22.283 22·442 | 22·602 | 22·761|22·920 | 23·074 | 23·288 | 23:397 23.556 23·716
23.875 24 034 24-193 24-352 24.511 24 620 24.830 24.989 25.148 25.307
25.466 25.625 25.784 25.944 26.103 26 262 26.421 26.580 26.739 26.894
170 27-058 27-217 | 27-376 27.535 27·694 | 27·853 | 27.931 28·172 28-331 | 28-490
180 28.699 28-808 28.967 | 29·126 | 29·286 | 29°445 | 29 604 | 29-763 | 29·922 | 30·086
190 30.241 30-400 30.559 30-718 30.877 31 036 31 196 31 355 31.514 31-673
200 31·832 31·992 | 32·150 32-310| 32·469 | 32·628 32.787 | 32·846 | 33·105 | 33-264
210 33.424 33.583 | 33·742 | 33·901 34·060 | 34-219 34.278 34.537 34.697 34-856
220 35-015 35·174 35-333 | 35·492 35.652 | 35·811 | 35·970 | 36·129 | 36·288 | 36·447
230 36.607 36-766 36 925 37 084 37-243 37.402 37-561 37.720 37.88038-039
240 38.198 38-357 38-516 | 38·725 38-835 | 38·994 39·153 39.312 39-471 39-631
250 39.790 39-949 | 40·108 | 40·262 40·426 | 40·585 | 40·744 | 40·90441·063 | 41·222
260 41.381 41-541 41-699 | 41858 42019 42.177 42-336 42.495 42-65442-813
270 42.973 43-132 43.291 43-450 43.609 43.768 43-927 44 087 44-23144-405
280 44.564 44-723 44.882 45·042 45 201 45 360 45-519 45.678 45-83745.996
290 46.156 46.315 46-474 46‍633 46·792 46·751 47·111 47-270 47·429 47 588
150
160

944
Book II.
THEORY AND PRACTICE OF ENGINEERING.
In the foregoing table, supposing it is required to find the radius of a wheel having 105
teeth, look for 100 in the first column, and under 5 in the top, we find 16-713, and sup-
posing the pitch to be more than one inch, we multiply this number found by the pitch in
inches. For a greater number of teeth than is given in the table, take half the given
number, and double the quantity in the columns, and for any less number, the general rule
may be applied.
The following table contains the pitch and dimensions of teeth of wheels already executed,
and satisfactorily performing their work, with their power and velocity per second.



Pitch of
Inches.
Thickness Breadth of
Teeth in of Teeth in
Inches.
Teeth in
Inches.
Length of
Teeth in
Inches.
Horse-power Horse-power Horse-power Horse-power
at 2-27 Feet at 3 Feet per at 6 Feet per at 11 Feet per
per Second.
Second. Second. Second.
4.2
2.
8.
2.40
13.33
17.61
35.23
64.6
3.99
1.9
7.6
2.28
13.03
15.90
31.80
58.30
3.78
1.8
7.2
2.16
10.80
14.27
28.54
52.32
3.57
1.7
6.8
2.04
9.63
12.72
25.54
46.68
3.36
1.6
6.4
1.92
8.53
11.27
22.54
41.32
3.15
1.5
6.
1.80
7.50
9.91
19.82
36.33
2.94
1.4
5.6
1.68
6.53
8.63
17.26
31.64
2.73
1.3
5.2
1.56
5.63
7.44
14.88
27.28
2.52
1.2
4.8
1.44
4.80
6.34
12.68
23.22
2.31
1.1
4.4
1.32
4.03
5.32
10.64
19.54
2.10
1.
4.
1.20
3.33
4.40
8.81
16.15
1.89
•9
3.6
1.08
2.70
3.57
7.14
13.09
1.68
⚫8
3.2
•96
2.13
2.81
5.62
10.33
1.47
1.26
76
2.8
•84
1.63
2.15
4.30
7.88
2.4
•72
1.20
1.59
3.18
5.83
1.05
•5
2.
•60
⚫83
1.10
2.20
4.03
The thickness of the teeth, as given in the second column, varies one-tenth of an inch in
each line; and it must be further observed that the breadth of the teeth is always four times
as much as their thickness. The strength of the teeth is ascertained by multiplying the
square of their thickness into their breadth taken in inches and tenths. The pitch is found
by multiplying the thickness of the teeth by 2.1.
Construction of Wheels.-When of wood, they are usually
formed of three thicknesses, and the joints broke over each
other; the middle thickness is made in six or eight pieces:
a solid rim is formed by bolting them together; this is
mortised for the cogs, the tenons of which have a pin
driven through to hold them in their place. The arms are
mortised sometimes through the shafts, but which weakens
them, and is not the best manner; they may be halved into
each other, and form a frame with a square opening in the
eentre; the arms may be secured to the middle thickness of the
rím by bolting them well together.
A wheel of this kind may be easily attached or removed to
the shaft by the adjustment of wedges, which are inserted
around the shaft, and which close up the square hole left in
the framing.
Face Wheels have stays and braces attached to the back of
the rim, some distance along the shaft into which they are
mortised, in order that greater strength may be obtained:
this is necessary, as the face wheel, when acting with a trundle,
has its teeth thrown off, and requires a stay to prevent it.
The trundles usually are surrounded with iron, to prevent
them from splitting, and small pinions are made out of a
solid block of wood, with the cogs fitted into it.
Iron wheels are more usually adopted, and have their
teeth cast with them, or mortices left for the insertion of
wooden cogs: it has been found that wheels work with less
noise and friction when wooden and iron cogs are used together.
When this practice is adopted, the thickness to be given to
the wooden cogs must be a little more than the space between
them; and the space in the wheel corresponding to it must be
made a little more than its teeth. The iron teeth generally
given to the smaller wheel are chipped with a cold chisel,

Fig. 1293.

Fig. 1294.
CHAP. XI.
945
MECHANICS.
hammered, and afterwards filed into the true form: when iron wheels are under ten feet
in diameter, they are cast entire; when larger, the arms are cast in separate pieces, and
they are attached to the rims by flanches, and securely bolted together: these flanches
should be cast at right angles to the circumference, and the arms are secured to the boss
by means of two projecting pieces cast upon it, and which fit into the nave or boss.
In the construction of fly-wheels the greatest quantity of cast-iron possible is given to
the rim and arms, in order that the momentum generated in the rim should not destroy it :
they are usually cast in a number of pieces, and bolted together, using every means to
resist the tendency they have to fracture.
Strength of Wheels. We must first ascertain the weight which acts on the rim of the
wheel, then the length of the arm or lever, and the part supported by each arm, must he
taken as a fraction of the whole. Suppose, then,-
+=
the weight, or straining power in pounds.
the radius in feet.
b and d = the breadth and depth of the arms in inches.
n = the number of arms.
a = the quantity of allowable deflection.
год 3
2656 na
=
= bď³.
The breadth or depth being given, the other dimensions may be found:-in a wheel 6
feet radius the number of arms eight, the weight acting on its circumference 1600 pounds,
and the allowed deflection a tenth of an inch: then-
bd3
1600 x 6³
2656 × 8 × 1
= 163.
Hence when the breadth is 21 inches, then-
d= 3
3/16
2.5
4.03 inches in depth.
When a wheel is so strained that the arms break, the fracture takes place near the axle,
and here then should the greatest strength be given.
fot
Shafts or Axles are employed either in a horizontal or vertical position, and the arbour or
spindle on which they turn is called a gudgeon. A horizontal shaft
has a support between the first mover and the work to be per-
formed; the cylindrical portion revolving on this support is called
the journal; that which supports it, or in which the journal
revolves, is called the carriage, but when it is not a part of the
framework, it is called a plummer's block; the lower gudgeons
of upright shafts rest upon steps or bearings.
When shafts are made of cast-iron, their strength may be thus
calculated; suppose r to the radius of the wheel in feet, at the
circumference of which the power is applied, s=to the side of a
square, or d to the diameter of the shaft in inches, t-to the
thickness of the metal in a hollow cylinder, w-to the weight in
pounds. In cast-iron shafts,

Square
Solid cylindrical
Hollow cylindrical
In wrought-iron shafts,
rw=150 s3
rw=125 d³
-
rw=125 d³ (1—p¹)
Solid cylindrical
Square
Hollow cylindrical
Where
Fig. 1295.

Fig. 1296.
-
-
rw=168 s 83
rw=140 d³
=140d³ (1—p¹)
d-2t
pd
then for cast-iron shafts, where the length does not exceed one-fourth of e, we have
3
d:
rx w
S= 3
d=
150
w
3/*125
rx w
for a square shaft,
125 (1—p¹)
for a solid cylinder,
for a hollow cylinder.
The same formula answers for malleable iron, if we use the number 168 for the first,
140 for the second, and 140 (1-p¹) for the third divisors: when the shafts are cylindrical
and of cast-iron of great length, multiply the weight in pounds by r in feet, and divide the
product by the cube of the length in feet, multiplied by 5.2; add 5148 to the quotient,
3 P
946
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
extract the square root, and subtract 72; then multiply by the square of the length in feet,
and the result will be d, or the diameter in inches.
The lateral strain and twisting to which shafts are subjected must be estimated, and it
commonly happens that one of these forces exceeds the other, and therefore the greater
power is the one to provide against; the resistance to a lateral strain is measured
by its resistance to resist flexure, and which may be about one-hundredth part of an inch
for each foot in length, before it materially affects the regularity of the motion of the
machine.
For the lateral stress on cast-iron shafts, the weight w in pounds, acting in the middle of
the length l in feet,
3/20 x 1
d.
wxi
500
For malleable iron the result must be multiplied by 0.935, for oak 1.83, for fir 1.72, and
for shafts to resist torsion, we have in horse-power h, that the shaft will drive, making turns
per minute,
3/240 × h
3/240 x
d for cast-iron.
For malleable iron multiply the result by 0·963, for oak by 2.238, and for fir 2.06; these
are for shafts of first movers, for second movers multiply the first by 0.8, and for third by
0.793. To show the application of the preceding rule, suppose the length of a shaft, from
the water-wheel to the cogwheel, to be 6 feet, the radius of the water-wheel 9 feet, and the
greatest force it will be exposed to 2000 pounds.
9 × 2000
5.2 × 63
✔/16+5184=72·12
subtract 72
= 16 nearly.
•12: then 12 × 6º =4·32 inches.
Practical men usually estimate the size of shafts or journals by the number of horse-powers,
and the speed of the fly-wheels.
Rightly to proportion the shafts of mills to the stress they are subjected to is of great
practical importance; timber formerly was entirely used for the axles of mills, and since
the application of iron to this purpose, machinery has undergone an entire change. Tables
giving the proportions have been established, so that now the mechanic is guided with
greater certainty in his work. It must always be borne in mind that the stiffness of a
shaft or beam is the property it has to resist bending or flexure, and that strength is that
which resists breaking or fracture: the stiffness, then, is determined by the force which
causes it to recede, its transverse strength by the pressure required to break it.
This distinction is expressed when we say that beams of equal length have their lateral
stiffness as the breadth and cube of their depth, and their lateral strength as the breadth
and square of the depth.
Lateral stress, which produces fracture, or which tends to break a body across, is pro-
portional to the rectangle of the parts of the beam, and is the greatest when loaded in the
middle; the rectangle being the product of the parts multiplied into each other.
When
a shaft is loaded exactly in the middle, half the weight is borne on each end, but we may
generally consider the weight which is spread over any part of a beam as united in its
centre of gravity.
When timber is submitted to a transverse strain, the effect of the weight is greatest in a
certain and determinate point, where if sound, defects in other portions are not so important;
but if placed in a position to receive pressure endwise, the defective parts at once come
under its influence; hence it is of the utmost importance in making experiments upon the
strength of materials, that they should be subjected to every species of trial previously to
their application to the purposes of construction, or to machinery of any kind. In the
Philosophical Transactions for 1818, Mr. George Rennie describes the apparatus he used
in his experiments relating to torsion: it consisted of a wrought-iron lever 2 feet long,
having an arched head of about 60°, and 4 feet in diameter, of which the lever represented
the radius; in the centre, round which it moved, was a square hole to receive the
end of the bar to be twisted: the lever was balanced, and a scale hung on the arched
head, the other end of the bar being fixed in the square hole in a piece of iron, and that
again in a vice.
Cylindrical shafts of cast-iron, having the stress applied to them in the middle, and equal
to W hundred-weights, and the flexure not exceeding as many hundred parts of an inch as
the shaft is long in feet, then the fourth root of half the stress in hundred weights, mul-
tiplied by the square root of the length in feet, gives the diameter in inches, and it has been
found, that when the cube of the length in feet is multiplied by 007, the square root of the
product will be the diameter in inches.
CHAP. XI.
947
MECHANICS.
Shafts of Cast-Iron to resist Lateral Pressure.

Diameter in
Diameter in
Diameter in
Diameter in
Diameter in
Length in Feet
Inches.
Inches.
Inches.
Inches.
Inches.
246∞
•237
•31
•44
•54
•62
·67
⚫88
1.24
1.5
1.76
1.23
1.61
2.28
2.79
3.22
8
1.9
2.48
3.51
4.30
4.96
10
2.65
3.47
4.9
6.0
6.93
12
3.48
4.55
6.44
7.89
9.10
14
4.38
5.74
8.12
9.94
11.48
16
5.36
7.01
9.92
12.15
14.02
Own weight
only.
Stress equal to
its own weight,
or n=1.
Stress double its
own weight,
or n = 2.
Stress three times
its own weight,
or n = 3.
Stress four times
its own weight,
or n=4.
When shafts of cast-iron are hollow, they will resist more twisting than solid ones con-
taining the same quantity of metal, for circles are to each other as the squares of their
diameters, and to compute the diameters of a hollow cylindrical shaft, where the thickness
of the metal is two-tenths of the entire diameter, which is found to be usually adopted in
practice; the cube of the length in feet, multiplied by 009, and the product again mul-
tiplied by the number of times the weight of the shaft is contained in the stress; from the
latter product extract the square root, which will be the diameter in inches. It has been
found that the square of the exterior diameter in inches, multiplied by 1·6 times the length
in feet, gives nearly the weight of the shaft in pounds.
Hollow Shafts of Cast-Iron to resist lateral Stress, though it is necessary to consider Torsion
as well.

Length.
Exterior
Diameter
Interior Exterior Interior
Diameter Diameter Diameter
Exterior Interior
Exterior
Diameter Diameter Diameter
Interior
Diameter
in Inches. in Inches. | in Inches. | in Inches.
in Inches. | in Inches. | in Inches.
in Inches.
4
1.5
0.9
1.9
1.1
2.2
1.3
2.4
1.4
6
2.8
1.6
3.5
2.1
4.0
2.4
4.5
2.7
8
4.3
2.5
5.3
3.1
6.1
3.6
6.9
4.1
10
6.0
3.6
7.4
4.4
8.5
5.0
9.5
5.7
12
7.9
4.7
9.8
5.8
11.2
6.7
12.6
7.5
14
10.0
6.0
12.3
7.3
14.2
8.5
15.9
9.5
16
12.2
7.3
15.0
9.0
17.3
10.3
19.4
11.6
Stress four times the
weight of the shaft.
Stress six times the
weight of the shaft.
Stress eight times the
weight of the shaft.
Stress ten times the
weight of the shaft.
When the diameter of a shaft is found for cast-iron, by multiplying this diameter by '935,
the product will give a diameter for a shaft of equal stiffness made of wrought-iron; and a
shaft of fir should be 1·716 times the diameter of a cast-iron one, and of oak 1·83 times, in
order to be of equal stiffness.
Shafts of cast-iron to resist torsion may have their diameter, when cylindrical, according
to the following table, which is found by dividing 240 times the number of horse-power by
the number of revolutions per minute, and extracting the cube root of the quotient for the
diameter in inches.
Revolutions of the Shafts in a Minute.



Diameter of
Shafts in
Inches.
LO
5
10
20
30
40
50
Horse-power. Horse-power. Horse-power. Horse-power. Horse-power. Horse-power.
2 3 4 5 6
0.17
0.33
0.66
0.99
1.33
1.66
0.56
1.13
2.25
3.37
4.5
5.62
1.33
2.66
5.33
7.99
10.66.
13.33
2.6
5.2
10.4
15.6
20.8
26.0
4.5
9.0
18.00
27-0
36.0
45.0
7
7.15
14.3
28.6
42.9
57.2
71.5
8
10.66
21.33
42.66
64.0
85.0
106.6
10
20.83
41.66
83.33
125.0
166.0
208.3
12
36.00
72.0
144.0
216.0
288·0
360·0
14
63.83
127.66
255.33
383.0
510-0
638.3
16
85.33
170.66
341.33
512.0
6820
853.3
3r 2
948
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
When the cylindrical shafts are hollow, the diameter must be multiplied by 1·05, and
when the shafts are laid horizontally, something should be added to what is given in the
foregoing tables, as they are calculated for vertical shafts.
When the shaft is of wrought-iron, multiply the diameter found by 0.963, if of oak by
2.238, when of fir by 2·06.
In the following table is given the dimensions of several shafts, subject to torsion and
lateral pressure, and which have been found to work well in practice.

Horse-
power.
Revolutions
per
Minute.
Inches.
Diameter of Length Section
Journals in of
Shaft.
Diameters
of the
of
Middle.
Journals.
Cast-iron lying shaft
20
20
18
22
16
22
14
24
12
25
10
25
8
27
A A Gr or or are of
6
28
5
30
4
32
3
34
31
2
36
230
1
40
2
Malleable iron lying shaft
6
28
3
5
30
31
43 2
4
32
2
34
2
2
36
12/20
1
40
1
11
53
11
10.6
79390
plini Ca
777
7.368
6.889
6 621
10
6.153
a σ a ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ ∞ 7
14
9.6
6
5.768
9
633
5.428
9
6
4.904
8.6
4.414
8.6
8
8
4
8
3
8
∞ ∞O A LA C
4.061
3.484
1.203
2.802
31
2.154
8.6
8
8
8
8
7.6

The cross-tailed gudgeon, which is made of
cast-iron, must be turned very true; it consists
of four leaves, which form a cross, and which are
let into the end of a wooden shaft; the front
edge of each leaf is made thinner than the back,
so that when it is inserted, and a pair of strong
hoops are driven tight upon the end of the shaft,
the wood is closed all round the cross and holds
it fast screws are occasionally added to secure
the cross.
An octangular wooden shaft is generally used
for a water-wheel, made of a sufficient length to
reach across the pit in which the wheel works;
the gudgeon at each end supports it, and allows
it to revolve upon its proper bearings.
proper bearings. A cast-
iron box in this case is fitted upon the end of the
shaft and tightly wedged; this prevents the shaft
from splitting as effectually as hooping. Upon
the end of this iron box is a projecting flanch, on
the face of which are four grooves or notches,
into which the arms of the iron cross enter; this
is also part of the gudgeon on which the shaft
revolves.
The best shape for cast-iron shafts is tubular
or hollow cylindrical; and care should be taken
that at each extremity the metal should be
thicker; the gudgeon should have three arms
cast or wrought on it, so that it can be attached
to the end of the shaft by screws or bolts.
The end of the wooden shaft is sometimes
fitted into a cross piece and box, for the purpose
of more readily putting on a new gudgeon when
required; by simply taking out the screw-bolts
this is easily performed.
[
Fig. 1297.

Fig. 1298.

Fig. 1299.

EL
Fig. 1300.
CHAP. XI.
949
MECHANICS.
The strength of a gudgeon is limited by the
strain it will bear, and the calculated stress
should include every kind of force acting on the
shaft; the diameter should always be determined,
so that the gudgeon may be capable of resisting
the whole if occasion required. If w represents
the stress upon the gudgeon in hundred weights,
(112 w × √7) *
and its length in inches, then
=or 0·42(w l)³
in inches.

=
5
d, the diameter of the gudgeon
Fig. 1301.
Journals are those parts of a shaft which revolve between the points where the power and
resistance are applied, and these have sometimes to carry a fly-wheel, as well as to resist
great torsion; to proportion the stress they have to sustain, we must consider the horses-
power to which the resistance is equal directly, and the number of revolutions the shaft
makes inversely.
Gudgeons are the ends or extremities of a horizontal shaft which runs in the collar, and
in order to avoid friction, are usually made of a diameter as small as possible, so that their
strength is sufficient. The cube root of the weight of a water-wheel
in hundred weights is found to be nearly equal to the diameter in
inches of a cast-iron gudgeon sufficiently strong to support it:
gudgeons of cast and wrought-iron are in the proportions of 9 to 14;
the diameters of journals or gudgeons, when of one or the other,
serve, when determined upon, in some degree to proportion the shaft.
The axis of the gudgeon should always be in the line with the axis
of the shaft, in order that the motion should be uniform and regular :
when the water-wheels are formed of timber, their diameter in feet
must be multiplied by the width in feet, and to this product the
square of half the diameter must be added. The diameter of the
gudgeon in inches will be the cube root of this sum.
Gudgeons when applied to water-wheels, spindles to grindstones
or to other wheels, may be all calculated upon the above principles.
Fig. 1302.
Couplings may be considered to have either one or two bearings, and serve for the con-
veyance of motion by connecting a series of shafts. The square coupling box is the most
simple, and is formed by making it exactly of the dimensions of the ends of the shaft it is to
contain, so that when motion is given to one shaft it may convey it to the other; it should
also be so contrived that it may be slipped over one shaft, and
the other be disengaged, by which means the motion may be
discontinued. The square coupling box is now only generally
employed in small machines, and has given way to a cylin-
drical one, in which pins at right angles are inserted through
them into the shaft to hold them firmly together; these may
be turned with great accuracy, and are found to get out of
order less often than the square coupling.
When a shaft has two bearings, the common coupling used
is that here shown: the shafts are terminated with circular
heads, with such alternate indentations, that they not only fit,
but give motion to one another; and should any settlement
take place, the joints will not be so much deranged as to mate-
rially affect the motion.

E
In another variety, calculated to connect a long line of
shafts, where there is a heavy strain, Murray's coupling-box is
used successfully; and when the shafts are out of line the
motion is continued in the same
manner as by an universal joint.
The two shafts to be united are
shown at A and B, and their necks
or collars lying on the bearings at
C and D. The boxes E and F
are fixed on by wedges, and one
of them has a projecting piece at-
tached to both sides of it, as shown
at a.
The box F has two similar
pieces, shown at b, b. When the
shaft A and box E are turned round,
they cut against the screws c, c of
A
C
DB
E
Fig. 1305.
Fig. 1303.

1
Fig. 1304.

3 r 3
950
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
the cross, which is of iron, and contained within the
boxes, and cause them to revolve; at the same time the
other two screws d, d press against the pieces b, b and
put the box F and shaft B into motion.
Where there is only one bearing for every length of a
shaft this may be used.
be used. The two shafts have at each end
a pivot fitted into a coupling piece, bored to receive the
ends of them, with a neck turned on the outside, which
works in a bearing. The two shafts are connected
with the coupling piece by means of keys passed through
each shaft, and there are notches within the coupling-
box which receive the ends of the shafts. The shafts
do not fit tight any where but at the pivots, so that
there is some freedom of motion allowed, and a slight
deviation from a right line does not produce much
strain.

A
D
E
B<
D
E
Fig. 1306.

Fig. 1307

Hooke's universal Joint is a beautiful means of uniting shafts which in-
cline towards each other. By this motion the rotary may be conveyed,
when there is considerable inclination from one shaft to another: when
this angle is more than 15 degrees of inclination, then bevelled wheels
are used to prevent the friction and great irregularity of motion which
are the consequences of too great an inclination.
Fig. 1308.
This ingenious contrivance consists of two shafts or axes, terminating
in a semicircle, and connected by means of a cross: as the branches
have motion round their pivots, it is obvious that when one shaft is
turned round, a similar motion will be communicated to the other; such
joints are used when the inclination of the shaft does not exceed 40° or
rather 140°, its complement. When the inclination is between 50° and 90°, the double
universal joint is employed, which has two crosses, with their extremities moving on their
pivots in the semicircles at the ends of the rafts. These joints may be constructed with
four pins, fastened at right angles upon the circumference of a
hoop or a solid ball.
Friction Couplings are employed when the connection is merely
the contact of the surface, and is not applicable to heavy ma-
chinery; it is employed much in boring instruments. The shaft
A has at the end a circular plate, which fits into a loose box at
the end of the shaft B. A collar of leather bb within the end of
the hollow part of the shaft B, screwed up by the nuts a, a, causes
the box D to press against this collar, and the friction produced
puts the shaft B in motion.
Engagement and Disengagement of Machinery is usually performed
by either bands, belts, or chains, the particular object being to com-
municate motion as steadily as possible, for if given suddenly, frac-
ture of the machinery is too often the consequence. The fast and
loose pulley is one of the most simple used, and consists of two
pulleys, one fixed on the axle, the other loose, so that the belt
which conveys the motion may be placed upon either of them, thus
putting the pulley either in or out of motion. The belt inclining to
that part of the pulley which has the greatest diameter, it is requisite
to have the rim rounded towards the middle, in order to prevent its
slipping off.

A
D
Fig. 1309.
Fig. 1310.
E
P
B
D
B


The common Clutch or Gland has a pulley revolving upon
a shaft, to which it can be connected when it is required to give
motion to the machinery. The axle has a gland or cross-piece
attached firmly to it, and upon the wheel, and is so formed as to
be able to slide along the shaft when motion is required; by
moving the handle the wheel is pressed towards the gland, and
the cogs or teeth at the side engage the gland, turning it
round and thus put the axle it is connected with into motion.
The pulley P, made to revolve upon the shaft AB, is often
used for disengaging or re-engaging a machine, moved by a
belt or band. DE is a cross-piece or gland attached to the
axle, for the purpose of receiving the teeth of the pulley, P,
when it is slided along the shaft for the purpose of engaging it,
and which is easily performed by the handle EG. It is necessary that the teeth placed at the
side of the pulley should be made of sufficient strength, and that they nicely fit the gland they
are intended to engage, otherwise the motion in some machines would be rendered irregular.
E
F
G
Fig. 1311.
CHAP. XI.
931
MECHANICS.

Another method commonly in use is here represented: the
shaft to which the machinery is attached can be put out of
motion by the means of the revolving wheel C. The end of the
shaft A is square; the clutch D is made to slide freely upon it
by aid of the handle EF, so that by engaging the revolving
wheel C, which is always in motion, the shaft may be made to
revolve. The teeth of the clutch should be made of a sufficient
strength to prevent fracture.
Fig. 1313.
A
R
C
Fig 1312.
D
D
Fig. 1314,
E
D
Ꭺ
The Bayonet Clutch has its arms A A fixed securely to the
shaft, or is cast upon it. These arms have holes drilled through
them, through which the shanks f,f of the bayonet pass. The
sliding of the bayonets back upon the shaft puts the whole out of
motion, and when they are brought together pass through the
holes in the opposite wheel, they carry the shaft around with
them. It is perfectly easy by such
means to throw the work out of
gear, during the time the mill may
be in motion; but great care should
be adopted in throwing them into
gear, as the teeth are subject to be
broken, particularly when high velo-
cities are employed. They are
consequently only made use of in
such machines as roiling mills, and
others where there is a slow velocity.
The shaft on which the cog-wheel is
placed, we may suppose engaged; in
turning the machinery we can stop the works by pushing back the shanks f, f, which are
firmly fixed by nuts to the arm DD, and made to slide upon the shaft; around the central
part, g, is a circular groove, like that of a pulley, into which a fork may be introduced
when it is required to slide the bayonets either forwards or backwards.
The friction clutch is another modification, and which
enables the machinery to be brought into motion more gra-
dually. AB is the part of the shaft put into motion by the
mill, and the bayonet is made to slide on the square part of
the shaft. The bayonet CDE is made to slide on the
square part of the shaft, or to pass through the arms of a
cross H I, that is secured firmly to the shaft; FG is the part
of the shaft to be connected, and upon it is fastened a drum
or pulley, with a hook on the outside, and which is made to
press gently upon the drum by screws. When the machine
is required to be put in motion, the hoop LM is turned
round by the bayonet clutch, and by the friction of the hoop
LM upon the drum, a gradual and easy action is obtained. This simple and ingenious
contrivance is applicable to large machines, and particularly where any shock or strain given
to the works would be injurious.


H
L

TH
C
A
E
B
Fig. 1315.
D
M
Friction destroys, but does not generate motion, it is therefore unlike gravity, or any
other force which, while retarding motion in one direction, accelerates it in another. The
force of friction may be said to destroy the law of continuity and motion, and it is of the
utmost importance that every means should be adopted to diminish its influence in practical
mechanics as much as possible. If power be applied to a machine of any kind, an equi-
librium takes place when the velocity of the power is to the velocity of the resistance, as
the weight is to the power; in this state the machine may be considered at rest, and
incapable of performing any work. If we increase the power, the machine will move with
more and more velocity, its motion gradually increasing as long as the power exceeds the
resistance; but should the power be lessened, or the resistance increased, the motion of the
machine will be diminished until it arrive at a state of uniform motion. This increase of
resistance may be produced by an increase of friction, which generally accompanies an
increased velocity, or by the resistance of the air, which is always greater as the velocity
augments. The power of a machine is therefore diminished by an increase of velocity, and
from this cause it is that machines acquire a uniform motion. The force which opposes
the production of motion in a machine is the resistance, and the chief of that to be over-
come arises from the work to be performed; but there is, in addition, the resistance from
friction, and from the inertia of the parts of the machinery, a considerable quantity of the
moving power being employed to overcome the first obstacles to motion. An axle with a
wheel at each extremity, moved by two currents of water running with different velocities,
has at first a slow motion, but if the fall of either be increased, the work will be performed
3r4
952
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
by that without reference to the other; a diminution of the impelling power accompanies
an increase of velocity, and in every machine there is an inertia to be overcome, before we
arrive at a motion which will produce the useful effect.
Plumber's Blocks and Steps are the bearings
upon which the gudgeons of shafts revolve.
The pillows or brasses are made of gun metal,
or a composition of copper and tin, which when
working with cast-iron acts with little friction.
The internal brass or pillow is fitted within an
iron frame or casting, one half attached to the
lower plate, the other to the upper, and by
means of screws and nuts are securely drawn
together. In order that the two halves of the
brasses may be true, they are turned previously in
a lathe, or bored out of the solid, and afterwards
separated and put into their respective situations.
Friction Rollers, or wheels, are used to diminish
friction, and their effect is produced by converting
a sliding into a rolling motion. Wheels are
sometimes employed for this purpose, but the
stress is then thrown on their axles, and is not
borne on the surface as in the rollers. Friction
rollers consist of an iron plate bolted down to
the framing, upon which are cast circular rings,
whose interior surface is accurately turned;
the gudgeon rests in the middle of six rollers,
placed at equal distances, and of such a diameter
as exactly to fill up the space between the gudgeon
and the outer ring. When the revolution of the
gudgeon takes place, as the rollers are free to
move, they roll round in the same direction, but
with a velocity in proportion to the difference of the
diameter of the gudgeon and the ring. A groove
is formed in these rollers, and an iron ring made to fit upon them,
so that they are kept asunder at their proper distances, and truly
parallel after the gudgeon is introduced in the middle. The
notches in the ring are not made to fit the rollers tightly, but to
allow sufficient play, and little friction. The sides of the ring are
boxed up, that no dust or dirt can enter to derange the rollers.
Conical Friction Rollers, if not executed very accurately, will
wear out of adjustment, and are not of frequent introduction;
they are sometimes used to vertical shafts; two conical friction
rollers introduced under the end of a shaft, also made conical
around the pivot, to play on them, prevents the weight from
resting upon the pivot.
Having described some of the first movers employed in the
construction of machines, the effect of which is usually rectili-
near, it is now necessary to consider them as acting tangentially
on the circumference of a circle, producing rotary motion;
also to describe the great variety of contrivances to vary these
motions, and adapt them to the construction
of machines.
Alternate cones are frequently made use of
for changing the velocity of motion, when
this is required to be gradually and uniformly
accelerated: one cone gives motion to the
other by a belt, carried along by a guide,
by which means the motion is accelerated
or retarded. One of the earliest methods
adopted for the transmission of rotary motion,
with or without a change of speed, is by
bands or straps. A series of pulleys or
grooves in one common pulley, corresponding
with others in another such wheel, so as to
preserve always the same length of band,
allows a great variety of speed to be obtained
by merely shifting the band from one pair of
opposite grooves to another.

Fig. 1316.

Fig 1317



Fig. 1318.
Fig. 1319
CHAP. XI.
953
MECHANICS.
Continuous rectilinear motion, with a uniform velocity, or which varies according to given laws
may be changed into a continuous rectilinear motion, with a velocity
of the same nature as that of the movement which produces it, constant
or variable, according to a given law, in the same plane or different
planes.
An endless cord turning round two fixed pulleys gives the idea of
rectilinear motion, which is nothing more than the circular and conti-
nuous movement of a circle whose radius is infinite.
To make a right
line pass over the distance ab with a certain velocity, whilst the point
c goes over the same distance with the same velocity, a single pulley
may be employed, or two pulleys, if the motion is to be communicated
in different planes.
The conversion of rectilinear motion from one direction to another,
with either increased or diminished velocity, is usually effected by
pulleys and blocks.
If it be required that the point a should pass over three or four times
the space of the point c, combinations of pulleys must be employed.
To transform rectilinear movement into circular, as to make the
distance ab traverse in a straight line, and with a certain velocity,
to the point a, whilst the point e traverses the distance cd with
the same rapidity and reciprocally; this is effected generally
by means of a reversing pulley, e, or by two, if the two points
are to be moved in different planes. If the point c is required to
run through two or three times less space than the point a, it is
effected by means of the muffle generally employed to move heavy
weights.
Rectilinear motion is changed into con-
tinuous rectilinear by the mules of the
spinning jennies. The chariot or carriage
B, mounted on four wheels, has placed
upon it a system of spindles, which are
made to revolve by its motion; the power
is applied at d, and the carriage is made
to maintain its parallelism by means of
two cords, m t, sp, the ends of which,
n and u, are attached to two fixed points,
and pass through two pulleys sm, tp. In
like manner the extremities r and u of the
second are attached to two other fixed
points, and pass through two pulleys placed on the same axis
as the first; the points u q and nr being so situated that they
are perfectly parallel, and the cords equally stretched. The
carriage B, in its primitive position, is made perpendicular
to the line uq and nr, and when rightly arranged the perfec-
tion of the work is easily maintained.
The same problem is performed by the motion of a rule
mounted on two channelled or grooved wheels placed near its
extremities, and which are equal in diameter, and with their
planes truly parallel.

Fig. 1322.
a
a
Fig. 1320.
a
Fig. 1321
B
H
72
Fig. 1323.
น
୯
C




α
a
a
HO
d
HHH
с
d
¿
The parallel rule has a variety of forms given to it, but that
most generally used by engineers
or draughtsmen has two wheels,
as c and d, fixed upon a rod, and
which, when rolled either back-
wards or forwards, preserves a
parallel distance: it was the in-
vention of Mr. Dollond at the
latter end of the last century.
To make one line move in a
parallel direction to another there
are several methods: the simple
rule, made to run upon wheels, or
the double, working by means of



d
Fig. 1324.
Fig. 1325.
two bars riveted on them, are the ordinary examples: and Ramsden's movable sights with
three rules is another variety.
The rule ab has a horizontal groove running from one end to the other, in which is engaged
a sınall fixed cylinder, but which does not traverse it; d is another rule, made freely to
954
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
slide between the two small bridges p and q, and which has a
perpendicular rod ef, from one part of which, at a greater or
less distance from the rule c d, rises another cylinder, which is
inserted, like the first, in the longitudinal groove m of the
rule ab; but on the opposite side to that on which is the
cylinder c, and in such a manner that when the rules are in
motion they do not meet.

If we move the rule so
A G, parallel to the rule C
go over the right line ab.
that its point a goes over the line
D, the point a will in the same time
T
q
A
B
g
Fig. 1326.
It is thus by the continual rectilineal motion of the point a we
can communicate to the rule d a motion of the same kind with the relative velocity we
require, and even in a contrary direction by placing the cylinder a conveniently in the rod ef.
Let A be a wedge which may slide in the direction of its
length between four pillars, whilst another wedge B is retained
by pins, or, what is better for the diminution of friction, by
rollers fixed in the same wedge, and which touch the pillars;
it is clear if we push the wedge A, B will rise, preserving its
parallelism. Supposing the force applied to the wedge A in the
direction of the base ab, and a rule lp, perpendicular to the
inclined plane ab; the extremity of this rule has a friction
roller at 1, it leans on the inclined plane, and the rule slides
between the bridges c,g.

p
До
9
B
q
A
a
Fig. 1327.
It is evident that, the inclination of the plane being arbitrary,
we may transform a continuous rectilinear motion into another, which will form a given angle
with the first; the velocity of the first will be to that of the second, as the radius is to the
sine cba. If the angle cba were zero, the rule lp would rest motionless, which happens
when rectilinear motion is changed to another also rectilineal, but the direction of which is
perpendicular to the first; we obtain this result by means of the second wedge B, and if we
add a third, C, which forms one body with the second, we may change the direction of motion
at pleasure, as well as the ratio of velocities; the line cb may have any curvature, and in
this case the continuous rectilinear would be transformed into an alternate rectilinear motion.
Montgolfier's Hydraulic Ram. The current of a river or
waterfall is a mover, acting in a constant rectilinear direction,
and communicates alternate motion to a valve; this, seconded
by a reservoir of air, causes a continuous flowing of water,
which may be regarded
be regarded as a continuous rectilinear motion.

I
I
Fig. 1328.
This machine, first constructed in 1797, has been brought
to very great perfection since, and in some cases usefully em-
ployed. The large pipe, which is called the body of the ram,
passes through the side of the reservoir, from which the fall of
water is obtained; this pipe generally is formed with a trum-
pet mouth at one end, and at the other the opening can
be closed by valves, through which, when open, the water
issues with a velocity dependent upon the height at which it
stands in the reservoir from whence the supply is drawn.
The valve is made of metal, with a hollow cup or dish attached
to its lower surface, and its seat is made a little wider than the diameter of the pipe, which
consists of a short cylinder screwed by a flanch into the upper surface of the ram; this
cylinder is so formed as to have an inverted cap or annular space round the upper, for
containing air, which cannot escape when it is compressed by the water. From this annular
space there is a small pipe, communicating with the open air, furnished with valves, one of
which opens inwards to admit air, and prevent its return, whilst the other admits a certain
quantity of air, and then shuts and prevents any further entrance. When these valves are
opened by hydrostatic pressure, a portion of the water flows into the air-vessel, and con-
denses the air it contains, and the water in it is thrown to a height sufficient to balance
the elasticity of the air shut up in the chamber.
Continuous rectilinear motion with a uniform velocity, or which varies
according to a given law, may be changed into alternate rectilinear motion,
with a velocity of the same nature as that of the movement which produces it,
constant or variable according to a given law, in the same or in different planes.
This machine consists of two cylindrical pipes a and b, whose axes are
in the same vertical direction; they are separated from each other by
an interval dependent on a condition we are about to indicate.
The upper extremity of the pipe a is closed by a plate in which is
pierced a circular orifice answering to that in the pipe b. C is a circular
diaphragm whose diameter is smaller than that of the orifice dd,
a little below which it is placed.
א
Fig. 1329.
CHAP. XI.
955
MECHANICS.
The water from a reservoir enters through the pipe a, and tends to rush out through the
annular orifice formed by the diaphragm and the edges of the circular orifice dd, with the
velocity due to the weight of a column of water of a constant and equal height: the dispersion
of the annular orifice through which the water endeavours to escape increases the effect of
the ordinary contraction of the fluid vein, and forms a cone whose summit entering a certain
portion of the tube b, determines the distance which should separate the two tubes a,b.
On the diaphragm a small cone, f, of water will be formed; the water rushes into the pipe
b, and remounts to a height equal to 3h, when the pipe is cylindrical. But if it be conical,
it rises to greater and variable heights, by reason of the qualities of the cone; arrived at its
maximum of elevation it descends, introduces itself into the stationary cone of water, causes
the fluid vein to diverge, and obliges it to rush beyond in a parabolic curve through the
interval which separates the two tubes until the tube b is entirely full.
The directions of the jet d'eau return to their former position; then the contraction of
the vein takes place, and the first effect recommences; this alternate motion takes place in
perfectly equal intervals of time; but without the diaphragm the machine would produce
no effect.
Continuous rectilinear motion with a uniform velocity, or varying
according to a given law, may be changed into a continuous circular
motion with a velocity of the same nature with that of the motion which
produces it, constant or varying according to a given law, in the same
plane or in different planes.
A Cylinder turning on its axis, and a cord which envelopes its sur-
face, gives the solution of this problem and that which is reciprocal
to it.
An endless Chain furnished with teeth, which engage a toothed
wheel attached to the cylinder, has been substituted for the cord
employed in the preceding figure.
Nut and Screw, as applied to the Press. If on the same
cylinder two screws be traced in a contrary direction, they will
at the same time communicate two rectilinear motions in op-
posite directions to the two nuts (female screw).
If the nut be fixed and the screw turn, the screw will have
a rotary and rectilinear motion, which is employed for pene-
trating hard bodies, for uniting them together, for raising
heavy weights, &c. M. Zureda contrived a very ingenious
machine of this kind, where a cylinder turning round its axis
by means of a handle; on the surface of the cylinder two
opposite grooves were cut, like the threads of a screw, and
which united or ran into each other at both ends of the cy-
linder. A rod running along the top of a frame, with its other
end in the groove, was made, by turning the handle, to follow
the spiral direction of the grooves, until it reached the end of
the groove, where it communicated with the opposite groove;
it then returned through it to its original position.
When the screw of the machine in the figure turns without
changing its place, the nut must not turn, but have a motion
given to it in the direction of the screw, and in this case the
circular and rectilinear movements are divided.

Fig. 1330.


Fig. 1331.

Fig. 1332.
The screw is one of the most useful machines in the arts; it is an auxiliary in almost
every machine, and readily changes form wherever it may be required; a system of two
parallel screws is often used at the edges of a long plank to communicate a rectilinear
movement, and preserve its parallelism; and the same principle, applied in an opposite
direction, forms the press. When motion is to be generated, the male and female screw are
always joined; that is, whenever the screw is to be used as a simple mechanical power;
when joined with an axis in peritrochio,
there is no occasion for a female, but in
that case the screw becomes a portion of a
compound engine.
Circular Motion transformed to rectilinear,
as illustrated by Prony. gh is an axis
divided into three parts, ab, cd, ef; the two
screws ab, ef, are of the same gauge, they
traverse in two fixed supports k,n, in which
are two female screws; this axis moves
horizontally, and passes over at each turn
a space equal to one turn of the screw;
ed is another screw, whose dista ce b.-
g
m
k
n
k

m
Fig. 1333.
1
956
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
tween the threads is greater or less than the other; into it is introduced a nut n, in
which is fixed the thread of the micrometer; this nut cannot turn at the same time with
the axis, for it is prevented by the bar mm; but at each turn of the axis it passes over a
space equal to the distance between the threads of the screw; it participates consequently
in two opposite movements, that of the absolute change of this axis, and that round the axis
itself, so that it only advances by the difference of these two motions. Let a be the dif-
ference between the threads of the screws, ab, cf; g that of the screw cd; after n revolu-
tions of the axis, the support n will have gone over a space equal na-nà, equal n (a−à);
but a-à may be as small as we please, a and à also as large as circumstances require.
A spiral enveloping a cylinder presented to a current of air
or water changes the rectilinear motion of these fluids into a
circular one, and the screw of Archimedes may be considered
as the inverse of the problem. The simplest method of pro-
ducing a rectilineal alternating motion from a circular con-
tinuous one consists in raising a beam or stamper vertically, as
that of an oil mill, by wheels formed into an irregular outline,
or carrying on their circumference wipers or spirals. The
stamper is thus raised to a certain height, and descends through
the same height by its own weight, when the succeeding wiper begins to act upon it, and
raises it a second time. In the vertical wheel with floats, in the undershot, breast, and
overshot bucket wheels, we have at once an example of rectilinear converted into circular
continuous motion.

Fig. 1334.


Fig. 1335.
UNDERSHOT WHEEL.
Fig. 1336. ovERSHOT WHEEL.
d
Horizontal Windmills are composed, first, of a wheel formed by six sail-beams, fixed to
the axle c; secondly, of vanes, a,b,d,e,f,g fixed to these sail beams by their pivots, placed in
such a manner that their surfaces are divided into two unequal
parts by the axis of rotation. If we place in the sail-beams
the obstacles r, formed by vertical cords, in such a manner that
the distance between each obstacle and the pivots of the vanes
belonging to the same sail-beams are smaller than the largest
vane, so that they can freely turn, without being able to
pass beyond the direction of the sail-beams, which is performed
by stops, and other cords placed between those we have men-
tioned and the points of rotation, it will be seen that in whatever
position the vanes are in calm weather, immediately the wind
blows, they present themselves to it, so as to turn the axis c always
in the same direction-a circumstance which would give a
decided advantage to this kind of sail over vertical sails, but for
great inconveniences which have thrown discredit on them: of
these the chief is the resistance resulting from the action between
the wind and the part of the wheel which moves in a contrary
direction to it. The continual friction of the vane against the
cords also diminishes the effect of these machines, and tends to
destroy it it has been attempted to obviate this by multiplying
the number of vanes on the same sail-beam; but the incon-
veniences from the sails.of the horizontal mill are greater than
the advantages.


C
Fig. 1337.
Windmill with a vertical Wheel. These mills are composed of a turning axle b inclined
to the horizon from 8 to 15 degrees: second, of four pieces of wood, c,d,e,f, each 40 feet
long, perpendicular to the axle b; they are fixed to the axle at its upper extremity: third,
by four sails sustained by these four pieces of wood: each sail commences at 6 feet 6 inches
from the turning axle b, and terminates at the extremity of the arms which sustain it;
consequently it is 32 feet long, their breadth rather more than 6 feet 6 inches. According
to Monge and Hachette, each sail may be regarded as an irregular surface engendered by
the motion of a right line perpendicular to the picce which sustains the sail, and which at
the coinmencement of the sail, viz. nearest the turning axle, would form with it an angle of
CHAP. XI.
957
MECHANICS.
60° on the windward side of this right line, passing over the whole length of the piece sus-
taining the sail, and remaining always perpendicular to it, but uniformly increasing the angle
which it forms with the turning axle b, in such a manner that at the extremity of the sail
the angle, which was 60° at the commencement, would become 78° if the axle b were
inclined 8° with the horizon, or 84° if the inclination were 15, and in proportion for inter-
mediate inclinations. The position of the generating line serves to fix the direction of the
cross pieces; together they form a frame which receives the sail-cloth: each sail may
also be regarded as an irregular surface produced by the motion of a right line perpen-
dicular to the piece sustaining the sail, and subject to touch in all its positions the right
line drawn through the corresponding extremities of the position which the generating
line should have at the two extremities of the sail, as previously stated.
The dimensions we have given are those mostly employed in Flanders, principally
near the town of Lille. Coulomb estimates the total effect of these mills working
the whole year 8 hours per day, as raising a weight of 1000 lbs. 218 feet per minute.
Supposing a man employing his strength in the most convenient manner can only
elevate, when working 8 hours a day, a weight of 60lbs. 1 foot per second, which
gives 1,728,000 lbs. elevated a foot for the daily effect; we shall have for 8 hours' work
per day a weight of 1000 lbs. elevated 3 of a foot per minute and as the mill working
8 hours per day raises 1000lbs. 218 feet in a minute, its effect is equivalent to the daily
work of 61 men.
Euler found the angle of 54° 44′ the best for the sail to form with the axis in
the intermediate part, and one of 80° at its extremity, and that the velocity of the
extremity of the sail should be to that of the wind=2+ : 1. Mills with a horizontal
axis, the wheel of which we call a fly, carry four arms each 36 feet in length, perpen-
dicular to the axle of motion, on which is spread a sail more or less inclined to the
plane of motion of the wheel; it is generally of a rectangular form, and instead of
being a single plane, it is constructed with an irregular surface perpendicular to the
corresponding arms. The arm itself is rectilinear, so that the surface of the sail applied to
the laths offers a concavity to the action of the wind; the axle should always be parallel to
the direction of the wind, and as the wind blows in level countries at an angle of 18° with
the horizon, the axle is fixed at that angle.
The arms are thicker near the axle than at the extremities, and the laths which receive
the sails are fixed at right angles to these arms: as the axle must always be directed
towards the wind, a lever is made use of for that purpose which turns the framework
supporting the mill round a fixed vertical axle; sometimes the mill carries a sail on the
side opposed to the axle, which occasions the mill to set itself. The reason the wind
causes the sails to turn, it must be remarked, is that the action is resolved into two others,
one in the direction of the sail, and the other perpendicular to it; from the latter, the
pressure is received by the sail, which is decomposed into two new actions, one of which,
parallel to the axis, produces no effect, the other, situate on the plane of motion, turns
the sail. If two opposite sails were inclined in the same direction with regard to the plane
of motion, the pressure they would experience would turn the axle in two contrary
directions, in such a manner that the latter would not move; for this reason the inclinations
are made equal but contrary to the two opposite sails.
A Mill with a horizontal Axis.-The sails being rectangular, the most advantageous form is
that called the Dutch, which offers to the wind a surface slightly concave, and whose elements
are disposed as follows: -the radius of the sail is divided into 6+ parts; the first is
set out from the centre at a distance equal to 3 of the unity of the divisions, being designated
as No. 1., and that which answers to the extremity of the sail as No. 6.; the breadth of
the sails must not exceed of the length, but generally it is or . Experience has
taught that we ought rather to diminish the angle they make with the plane of motion
than increase it; according to Smeaton the sails which enlarge towards their extremities
are more advantageous than those which are parallel throughout: the best form is that
of a trapezium; at the extremity of the radius, a bar equal to a third of this radius
divided at the point where it intersects, in the ratio of 3 to 2. With sails so constructed
we have the best effect, and maintain the velocity of rotation in a constant ratio to that of
the wind; this velocity of rotation, measured at the extremity of the sail, should be, accord-
ing to Smeaton 2.6 or 2.7 times that of the wind, which agrees with Coulomb's experi-
ments, from which he deduced the ratio 2·5 or 2·6. The sails being established according
to the Dutch method, and their velocity being in the ratios of that assigned before 2·6, the
work transmitted increases as the surface of the sails, which is a little less rapidly than the
cube of the velocity of the wind, and we shall have for the work transmitted in a second
according to Coulomb, P=2·60 V P=0·13. a. V 3 kilogrammes; a formula in which P is
the effect in kilogrammes at the extremities of the sails, and in the direction of the motion
of rotation of this extremity, V the velocity of the wind in metres, a the surface of a single
sail in square metres. Regard has not been paid in the experiments to the variation of the
density of the air according to the temperature.
958
BOOK II
THEORY AND PRACTICE OF ENGINEERING.

m
d
h
C
Fig. 1338.
(1
p
k
N
Verzy's Steam-engine whose Motion is continuous. Let cdef be
a section perpendicular to the axis o, of a cylinder whose height
is equal to the distance mn, which separates it from another
cylinder ghikql, which penetrates the first in such a manner that
they have the same axis, and that the surface of the latter adjusts
itself exactly to the upper and lower edges of the first; there
will be between the two cylinders a circular channel whose
horizontal section will be mgdhknpqmg, and the height equal
to the plane pq, which is attached to the external cylinder,
the continuity of which it interrupts: the bases of the inner
cylinder are closed by plates of metal, making a small rebate: at
the crowns of the outer cylinder they are below the axis o,
so that the inner eylinder may freely turn round its axis,
supposing the outer one fixed: in the curved surface of the
inner cylinder two openings are made diametrically opposite to each other, equal in height
and in breadth to those of the circular canal; two angular valves are opened which turn on
their axis, and tend to close these openings as well as the canal, by means of two spiral
springs which are in the upper part of the axis, and whose elastic force may be increased or
diminished at pleasure; the axes extend beyond the upper base, and have each a handle
whose positions are projected in the directions, g,m,k,n; the curved surface of the outer
cylinder is pierced by two circular holes, one where the tube a abuts, which conducts the
steam, and the other communicating with the condenser by means of the tube b: suppose
then the steam enters at a, the plane pq opposes its passage, whilst the two sides of the
angular valve present the same surface to the steam, consequently it does not change its
situation, and its edge will lean on that of the inner cylinder with all the force of the spring
grs; and this cylinder will turn in the direction of abc. Before me arrives at the hole b,
which communicates with the injector, the handle at k will meet the obstacle o, at which is
a small bar fixed to the upper crown of the great cylinder; this forces the angular valve
ikn to turn inwards; thus going without difficulty past the fixed plane pq, in such a
manner that when it shall have taken up its first position mr will have passed the hole b,
and the vacuum will be formed, the inner cylinder having made only a half revolution :
the action of the steam will continue to communicate a continuous motion of rotation to
the axis o, which may be applied to any required use.
H
Fig. 1339.
p

E
Universal Windmill. This machine has for its object the
immediate transformation of the rectilinear motion of the
wind to circular, and is more curious than useful.
Let aceg
be the equator of a sphere whose radius is kl, and kpep the
vertical projection of the meridian, which cuts the equator in
the diameter ke. In the upper part of the plane of the equator
draw the two diameters ae, cg, perpendicular to each other ;
and in the lower part of the same plane the two other diameters
dh,bf, which form angles of 45° with the preceding: in the
upper part of the plane of the equator are constructed four
curves formed by the surfaces of cones whose summits are at
e,g, a, and c, and whose bases are oppositely curved; which
results from the intersection of the surface of the sphere with
the right cylinders, which cut the equator in the curves l,e,f,
&c., tangential to the lines lg, hl, al, bl, &c., and through the
corresponding parts of the surfaces of the two meridians cg, a e,
and of the equator. In the lower part of the plane of the
equator are also placed four curves constructed according to
the same principles; the summits of the cones are at dl, hb: c
the curves l, g, h are traced by geometrical principles, viz. from
the summit g of the triangle lgh, the line EM is drawn to
the middle of its base; at M is elevated a perpendicular Me
equal Me: the circle lef drawn tangential at ƒ and 7 to
the two sides gl, hl of the isosceles triangle Igh: from each
point N of the line lf, two lines were drawn, one parallel to
ME', which is terminated at n' in the arc of the circle; and
the other Nn equal to the first, and parallel to ME, which gives a point n belonging to
the line Le F, required to be drawn.

d
b
Fig. 1340.
a
M
እ
It must be observed that, in consequence of the very small angle at which the sail of the
vertical windmill is inclined to the direction of its motion, which generally is not more than
20°, and of which angle the sine, which represents the force to give motion to the sails,
scarcely exceeds one-third of the radius, much of the power of the wind is lost: on this ac-
count horizontal sails were introduced, under the notion that more power could be acquired ;
numerous contrivances for this purpose are contained in the Repertory of Arts.
CHAP. XI.
9.59
MECHANICS.
b
T
S
Fig. 1341.
1.20
d
Danaide, Marquis Mannoury d'Ectot: this machine may be classed among hydraulic
wheels; it consists of a cylindrical cistern of wood, dd, whose bottom is pierced in its
centre by a circular orifice r, through which passes a vertical iron axle p, retained above by
a collar, and resting at its lower part on a pivot which allows it to turn on itself, drawing
with it the cistern to which it is firmly attached by means of
four iron crosses, two of which, c, c, are shown in the section,
and the two others dd, e e, in the section b; this axle directed
in the axis of the cistern does not completely close the central
orifice which it traverses. On the other hand it leaves around
its circumference a circle through which the water can escape
by a circular diaphragm s fixed to the vertical axis p, and to the
crosses immediately below the latter: divide the cistern into two
equal parts, which cannot communicate with each other, except
by the circle which remains between the circular diaphragm
and the inner surface of the cistern: the lower part cd, de is
divided into eight cases by as many diaphragms, four of
which go from the axle p to the circumference, and the
four others do not touch the axle, so as not to obstruct the
orificer; these diaphragms formed by plane surfaces descend
from the circular diaphragm to the base of the cistern; the
water enters at the upper part of the cistern by the conduit
pipe b, which is bent conveniently to allow it to issue through
an orifice x in the form of steam, which strikes tangentially the
concave surface of this part through its whole height, puts the
cistern in motion, descends to the lower part by the circle con-
Fig. 1342.
structed between the diaphragm s and the inner surface of the cistern, engages in the
partitions before indicated, and then issues through the orifice r to fall into the discharge
pipe r. Such is the description and play of this machine, executed with the greatest
success in different manufactories; an improvement was made in it, by substituting for
the diaphragm t with plane surfaces, others in a spiral form, prolonged to the upper edge n
of the cistern through the hollow crown in the centre; the form given to these new
diaphragms allows the edge n to be suppressed, which prevents the water from spreading
beyond; by this modification the loss of active force is considerably diminished.


19
a
$
Fig. 1343.
Machine of Cagniard Latour is composed of two cisterns, a and b, the first filled
with water at the ordinary temperature, and the second with water at 750 centigrade;
in the first cistern is plunged an Archimedean screw C, in the
second a bucket wheel d; a tube communicates the bottom
of the first cistern with that of the second; if we turn the
screw in a direction contrary to that necessary for elevating the
water contained in the cistern, it will cause the atmospheric air
to descend, and following the direction of the tube of com-
munication, will escape at the orifice e, the distance of which
from the cistern b should be less than that of the orifice r
from the surface of the cistern c; the cold air thus carried to the
bottom of the cistern filled with hot water dilates, enters the buckets whose opening is
turned downwards, and drives the wheel d. In the machine executed by Cagniard, the
effect produced consists of raising, by means of a cord attached to the axle of the wheel, a
weight of 15 lbs. with a uniform vertical velocity of 1 inch per second, while the moving
force applied to the screw is only 3 lbs. with the same velocity: the effect of heat is to
quintuple the natural effect of the moving power; the effect of the moving power being
quintupled, we may take from it a force with which to supply the moving power, and
there will then remain a disposable force of four times the moving power. The Archi-
medean screw thus employed forms an excellent blowing engine.
A Gin, where a muffle is not employed, we obtain the ratio of
velocities required but by substituting for the ordinary cylinder
another whose axle is composed of two parts, a and e, of different
diameters; a cord, after being turned on the part a of the axle,
passes through the movable pulley which supports the weight
p, reascends and passes through another pulley, and is then
attached to the other part e of the cylinder, round which it is
enveloped in a direction contrary to that in which it is wound
round the part a; by turning the cylinder the cord winds on
the part a while it unwinds from the part e, the power being
applied at the extremity of the lever c. It may be easily con-
ceived that at each turn of the cylinder, the weight d only
goes over a space equal to half the differences of the two cir-
cumferences of the cylinders a and e, a quantity which we may
render as small as we please.


α o
Fig. 1344.
960
Book II.
THEORY AND PRACTICE OF ENGINEERING.
J
Continuous rectilinear motion with a uniform velocity, or varying according to a given law,
may be changed into circular alternate motion with a velocity of the
same nature as that of the motion which produces it, in the same plane
or in different planes. Fig. 1345. represents a method invented by
Perrault of applying a fall of water to the movement of a clock:
the water which flows through c falls into a small chest e,
which turns round an axis a, and is divided by a partition into two
parts when the base is horizontal the water flows in such a
manner as to be divided into two equal parts; by the partition in
any other position the fall is into the elevated part; in that repre-
sented by the figure the fall takes place in the side e; when this
part is full, the chest turns on its axis and leans on the obstacle
r, emptying the water whose weight has decided its motion; the
other part is filled in its turn, and restores the chest to its primi-
tive position.

a
Fig. 1345.
Continuous rectilinear motion is converted into circular motion
by means of a descending weight attached to a cord wound on an
axle, as we have already described: but to convert a reciprocating
rectilinear motion into a continuous circular for a long time baffled the skill of our
mechanics; it is, however, now generally effected by means of a crank applied in three
different manners: first, where the moving force may be uniform, and in a straight line;
second, where the moving force may be uniform, and in a curved line; and, thirdly, where
in either case the force may be variable. A crank increases also the velocity of the moving
force in the usual construction, in the ratio of the circumference of a circle to twice its dia-
meter; but this ratio, as well as the action of the power, varies for the crank motion which
converted the reciprocating motion of a piston rod into a rotary
one, a patent was granted in 1769, 1778, and 1781; that invented by
Steed was the most simple. Mr. Watt in 1781 obtained a patent
for five other kinds of crank, one of which was the sun-and-
planet-wheel motion, which he applied to his expansive steam-
engines: the "Annals of Science" show how great was the diffi-
culty of converting a reciprocating rectilinear motion into a
circular one, and by what patient investigation and labour it was
overcome.
:

Let
To transform circular alternate into continuous rectilinear.
a c be a lever turning on its axis e; rr a bar which may ascend
and descend freely, and whose edges are ratchet-toothed; dn, dn
are two small levers turning on their axes d, d, and whose ex-
tremities n and n are furnished with small cylinders, which engage
the teeth of the bar; the circular alternate motion of the lever c
will cause the bar to mount.
A boat at anchor in the middle of a river attached to a cable
sufficiently long will go from one bank to the other with a
circular alternate motion by means of its rudder, a method often
employed in crossing a ferry.
A sector surmounted by a sail whose centre of gravity is very
much below that of oscillation, by means of a counterpoise, con-
tinually balances itself with a circular alternate motion, when the
wind strikes the sail. This method of applying the action of the
wind has often been proposed, and models on this principle are
found at Paris.
Continuous rectilinear motion with a uniform velocity, or which varies
according to a given law, may be changed into continuous in a given
curve, with a velocity of the same nature as that of the motion which
produces it, constant or variable according to a given law, in the same
plane or in different planes.
Rectilinear continuous motion with a uniform velocity, or which
varies according to a given law, may be changed into alternate in a
given curve with a velocity of the same nature as that of the motion which
produces it, constant or variable according to a given law, in the
same plane or in different planes.
Continuous rectilinear motion may be changed into continuous circular
by the means before indicated.
(L
d
l
72
Fig. 1346.
Fig. 1347.
Fig. 1348.
2

Circular continuous motion, with a uniform velocity, or which varies according to a given
law, may be changed into alternate rectilinear, with the velocity of the same nature with that of
the motion which produces it; constant or variable, according to a given law, in the same plane
or in different planes.
CHAP. XI.
961
MECHANICS.
WW
Let ABDE be a wheel, which turns round its centre C in the same direction ABDE
with a uniform velocity, m n a rule
which is obliged to preserve always
the same direction, whilst its ex-
tremity, m, follows the centre of a
curve drawn on its surface, the
other n should make a determinate
number of alternate motions of a
given extent, returning at each revo-
lution of the wheel to the same point
of departure with a velocity alto-
gether uniform, which varies ac-
cording to a certain law, or is
arbitrary.

If the ratio of the velocities is
uniform and follows given laws, the
curve which it would trace would be
uniform, and easy to construct.
If the ratio of the velocity is ar-
bitrary, there is an infinity of curves,
which may satisfy the conditions of
the problem either by rectilinear
polygons or curves: rectilinear po-
lygons give two acute angles;
therefore curves are preferred,
taking care to choose those which
form the most obtuse angles; for
this purpose it is necessary to di-
minish the velocity by changing the
direction, and that the curve should
have the greatest possible extent, by
giving the circle the greatest radius
that circumstances may allow.
If it be required that during the
revolution of the wheel ABDE, the
extremity, n, of the rod, mn, make
three alternate movements, whilst
the point A describes the arc from
O to 5, from 5 to 9, from 9 to 10,
from 10 to 13, from 13 to 19, and
from 19 to 24.
:
18
If it be required that the motion
should be uniform, divide the centre
space, which the point n should go
over, and which for greater clear-
ness is drawn above the figure, in
such a manner, if it be possible,
that the equal divisions fall at the
extremities of the rectilinear oscil-
lations in the figure it is divided
into 24 equal parts. The circle
ABDE is divided into the same
number of equal parts, and radii are
drawn to the points of division: from
the point 5, the furthest from the
space that the point n should go over,
goover,
we have taken a distance which
enters a little into the circumference
of the wheel, and this distance gives
the length of the rod mn: the ex-
tremity n is supposed at o, the other
extremity, m, is at a, which will be
one of the points of the curve; we
have taken with the compasses the
distance o 1, which we have set off
from a tor, and the distancer C=Cq
has given the point q of the curve,
9
17
20
16
15
22
14
Fig. 1349.
Fig. 1350
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rd
10
11
10
$
7
6

962
Book II.
THEORY AND PRACTICE OF ENGINEERING.
so that when the division 1 of the circle is found at A, the extremity n of the rod will be
at 1 figure a of its course: in this manner we have drawn the whole curve a qb c d e fa;
at one corner of the figure we have drawn a portion, scdt, of the curve, which corre-
sponds to the part sed of the curve of uniform motion, to show that angles become more
obtuse when greater extent is given to the figure; if the problem were subject to no law of
velocities, it is evident that the rectilinear polygon abcdef would satisfy these conditions,
but in the application to the arts acute angles not being the most convenient, curvilinear
polygons are preferred, represented by the dark lines; the march of the extremity n of the
rod is indicated by the numbers which mark its place in the line 0, 1, 2, 3, 4, 5, 6, &c.
Fig. 1350. is a peculiar example in which we obtain at each revolution of the wheel a
single alternation with a uniform velocity, the curve being symmetrical, and all its
diameters equal: advantage is taken of this circumstance to fix the rule, a b, to the curve
by means of two bolts, m, m, furnished with pulleys to prevent friction; the alternations for
the directing the silk in the bobbins for the spinning machines are moved by this same
curve; it is used in various hydraulic machines to give a uniform motion to the pistons
of
pumps.
ř
Let bbb be a plate of metal, in which are cut the slits a, a, a, &c. : behind and near this
plate imagine another in which is placed the spiral slit, marked by the double dotted
line, and drawn according to the same principles as the heart-
shaped curve (fig. 1350.): hence it is evident if the small
cylinders traverse the intersection of the slits with the spiral,
and that they cause the plate behind to turn, all these cylinders
would retire from, or approach the centre of the plates by the
same distance; suppose elbows added to these small cylinders
in the direction of the radii, whose length should be such
that their extremities terminate in the circumference of a
circle, whose centre should be the same as that of the plate, it
is evident that the extremities of the elbows, whether they ap-
proach or whether they retire from the centre will always be
found in the circumference of a circle concentric to the first:
two similar mechanisms may be placed above each other, as is
seen in the figure, and the extremity of the elbows may be
joined by bars, which will form a sort of cylinder, whose
diameter may be increased or diminished at pleasure by the
instantaneous motion of rotation communicated to the plates
cut in a spiral shape. Such is the ingenious mechanism
adopted for lathes and other machines, in which it is required
to change the ratio of the power to the resistance according to
necessity, and that almost instantaneously.
The wheel a has its circumference cut in the shape of teeth,
which may vary in form at pleasure. The rod a leans con-
stantly against the teeth of the wheel a, by means of a
spring or weight, and slides between the tenons c, d, preserving
its position perpendicular to the plane of the wheel; when
the wheel turns, it will communicate to the rod an alternate
rectilinear motion, and we can vary this motion as we re-
quire. The tracing of the teeth of the wheel offers no
difficulty.
M. Zureda, an eminent engineer in Spain, has applied this
to a machine for pricking holes in leather and making
cards; it has also been employed in the manufacture of
fishing nets, as shown in Leupold's Theatrum Machi-
narum, vol. ii. fig. 3. plate 36. If all the teeth in the
wheel a were reduced to one, the surface of the wheel
would be an inclined plane, and the oscillations of the
rod b would be performed in every revolution of the wheel.



፩.
Fig. 1351.
a
Fig. 1352.
a
m
a
a

C
d
b

n
h
The circle a turning round its axis, with a point or pin
fixed on its surface, traverses the groove n of the lever n,
whose centre of rotation is at m: it results from this that
its circular uniform motion is changed from continuous to
circular alternate, which the extremities of the lever, n, pass
over, but not with uniform velocities If we fix at the
lower extremity a toothed arc of a circle, which engages
a rack b, we have a rectilinear alternaté, but not uniform
motion. By means of the pulley g, and the cord fixed at o, sustaining the weight h, we
obtain a rectilinear, but not uniform motion. The intersection of the groove drawn on the
lever n, with the other groove drawn on the fixed rule x, where a small cylinder may be
·
Fig. 1353.
CHAP. XI.
963
MECHANICS.
placed, serves to communicate to the latter body a recti-
linear alternate, but not uniform motion.
a is a wheel partly toothed, which turns in the same
direction on a fixed axis; bc is a frame, two of whose
opposite sides are cut into a rack; to the extremities of
this frame the bars b s, ct are fixed, which form a single
body, and which pass through the tenons at the end in
such a manner that the rack and the two bars which may
be regarded as one, st, may require an alternate rectilinear
motion from the circular motion of the wheel a. We
may also apply the frame which contains the two racks
to a bar, by a simple change of construction: this
motion is applied to the alternate motions of pistons of
pumps, sawing machines, &c. By suppressing one of
the two racks, and furnishing the whole wheel with
teeth, we transform alternate circular to alternate rectilinear
motion.
The frames of the preceding machine is enlarged by
prolonging the two racks in such a manner that they abut
on the two small sides, where they unite in the form of a half
circle, and the whole wheel is furnished with teeth.
It is ne-
cessary in this case to employ two cross pieces to communicate
at the end of each oscillation a slight lateral movement to the
frame, to facilitate the change of gear: in general this motion
presents difficulties in execution, and it does not appear
capable of producing great effects.
This motion is applied to transform the circular continuous
motion of a horizontal axis to vertical alternate rectilinear,
which work the piston of a pump, producing a slight balancing
in the frame.

Fig 1354.
b
$


A
Fig. 1355.

Fig. 1356
Fig. 1357 is a modification of
the same motion; having re-
duced the teeth of the rack to
one, the number of that of the
wheel is also diminished, and in
their place arms terminated by
small wheels are substituted, to
diminish friction. It will be
easily seen that the rectilinear
form of the tooth of the rack
occasions an inequality of the velocity in the alternate motion; this
may be varied at pleasure, or the law of velocity rendered uniform,
by giving a convenient form to the teeth. This construction is pre-
ferable to that of fig. 1354. for machines exposed to very great efforts,
which small teeth could not resist.

Fig. 1357.
In fig. 1359. a is a wheel turning on its axis, n,m two cheeks to keep
steady the sliding bar pqrs, which is in the shape of a T; a pivot
traverses the groove, and the circular motion of a communicates an
alternate motion to the bar. This alternate rectilinear motion, very
slow at the end, and accelerated towards the middle of the oscillation,
is very simple and of easy execution; it is a modification of fig. 1354.,
and is employed for churns. The circular continuous motion of the
wheel can be transformed to rectilinear alternate.
Fig. 1358.

q
n
a
Fig. 1359.
m
The contrivances that have been devised for converting a cir-
cular continuous motion into a rectilinear alternate motion are
very numerous, and many highly ingenious; the simplest methods of
producing a rectilinear alternating motion from a circular continuous
one are those shown in figs. 1361, 1362, &c., where a beam or stamper is raised vertically
by wheels formed into an irregular outline, or carrying on their circumference wipers or
spirals; the stamper is thus raised to a certain height, and descends through the same
height by its own weight, when the succeeding wiper begins to act upon it, and raise it a
second time. The same is produced by the rack and pinion, provided the pinion has teeth
only on a part of its circumference: the toothed wheel elevates the rack, which descends
when the last tooth has ceased to act, and by the time the last tooth has ceased to act, and by
the time the rack has performed its work, the toothed part of the pinion has come round
again, for the purpose of raising the rack a second time,
342
964
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
It is easy to render the alternate rectilinear motion of the
rule pqrs of fig. 1359. uniform, by substituting for the rec-
tilinear groove another drawn in a convenient manner, as
here shown. Divide the distance Cs into a certain number
of equal parts, for example into six, and divide the quarter
of the circle s D into the same number of parts: it is
evident the conditions of the problem will be answered
if the point of the rule which answers to that where the
pivot s is, found also in the division of the radius s C,
at the same time that the pivot coincides with the divisions
of the arc s D. We must then determine the positions
of the divisions of the curve in such a manner that each
of these points should be placed relatively to the point s,
as the points of the arc s D are placed with regard to the
points of the radius s C, which does not offer the least dif-
ficulty. We do the same with regard to the three other
portions of the circumference, but it must be remarked that
there are three different cases to consider; that whilst the
pivot s goes over the second portion of its course, the rule
pq advances towards its extremity q an equal space, larger
or smaller than that it goes over, whilst the same pivot
goes over its first space s D. In the first of these three
cases we have the form of the figure 8 placed horizontally,
that is to say, the points m and n touch; in the second
its form is that indicated by the figure; in the third the
branches intersect in two points.
The second of these three cases is that to be preferred
in practice: we envelope this curve by another to form a
groove capable of containing the pivot s, furnished with its
friction roller; the rectilinear groove of the preceding
figure may be cut through, but that of which we are
speaking ought not to be, in order to tie the interior
nut or surface, enveloped by the one curve, with that
. terminated by the other.
Fig. 1361. a is a vertical rule sliding between two
rings n,m; at its lower extremity is attached a pestle; one
of the sides of the rule is furnished with a rack in which
the toothed portion of the wheel c engages the other part,
which is not furnished with teeth. Suppose the pestle
c falls by its own weight on the body o; if the wheel
c turns from left to right, its teeth will oblige the pestle
to rise, but it will fall again immediately afterwards by
the deficiency of the teeth in a part of the wheel, and
this alternate motion will last as long as the wheel shall
continue to move. It is also a particular motion of
fig. 1354.

R
D
Fig. 1360.
n
m
ల
Fig. 1361.
n
121
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11
101
Fig. 1362.
F


Fig. 1362. is a modification of the preceding; we reduce the teeth of the rack to one,
and furnish the wheel with wipers, whose curvature is such that the resistance becomes
constant.
12
The circular motion of the wheel a communicates by the intervention of the rule m a
rectilinear alternate motion to the rule n, which slides between two tenons; the reciprocal
motion will take place if a performs the functions of a fly.
The extent of the alternate rectilinear course of the rod n
increases or diminishes in proportion as the point of rotation
m approaches or retires from the centre of the circle a.
we suppress the rule n, and cause the rule m to pass across
the circular opening, which we may suppose to be made in
the tenon, the rule m will have a compound alternate motion.

If
Fig. 1364. AB is a cylinder turning on its axis, and on its sur-
face are two grooves, like that of a screw, cut in opposite direc-
tions, and which tend to unite at the two extremities of the cylin-
der; C is a salient piece which exactly fits the groove, and
which surmounts a rod CD, traversing a groove cut in the cross
piece EF; the circular motion of the cylinder causes the
body C to go backwards and forwards by its alternate pas-
sage from one of the helices to the other; this motion is very
ingenious, and may be variously applied.
m
Fig. 1363.
D

E
100001
B
A
Fig. 1364.
CHAP. XI.
965
MECHANICS.
Fig. 1365. ab is a cross-piece pierced with a groove, in
which the axis of the toothed wheel e may move freely; c is
a bar furnished with teeth which engage a wheel, and
which is fixed to the rule to which the alternate motion in
a right line is to be given, sliding between the two tenons
d, d. When the toothed wheel e has arrived at the end of its
course, the obstacles n, n meet the springs to force it to return
and engage afresh.

Fig. 1366.
a is a crown wheel, whose interior is toothed;
b, a circle also toothed, whose diameter is equal to the radius
of the crown with which it engages. The crooked axis turns
in the centre of the crown, sustains on one side the centre
of the wheel b, and on the other a handle to the power
which communicates the motion of rotation to the wheel b.
Whilst this wheel turns round its centre, passing over the
contour of the crown, each of the points of its circumference
traces a diameter of the crown.
The two teethed wheels a and b produce an alternate
motion, the number of whose alternations, their extent and
velocity, may vary to infinity, either by the different ratios of
d
C
78
Fig. 1365.
Fig. 1366.
لمحي
(2
b
b
d
e
98




Fig. 1367.
Fig. 1368.
Fig. 1369.
their diameters, or by the different arrangement and proportions of their parts, but all
these movements may be exactly imitated by fig. 1349. Figs. 1368. and 1369. exhibit the
same motions.
Fig. 1370. is a circular crown furnished with teeth on both its concave and convex sides:
it is fixed to a large circular

pass
disc d, which turns on its axis,
leaving a part void, so that the
toothed wheel d can
freely; it is terminated by two
portions of arcs of circles also
furnished with teeth. The
toothed wheel d turns round
its axis, which has the facility
of moving in the groove mn.
The two springs leaning alter-
nately on the two stops de-
termine the alternate circular motion of the disc d.

Fig. 1370.
d
E
The alternate circular motion of the
disc d serves as an intermediary, communicating to the body another alternate rectilinear
motion by means of an endless cord, which envelopes the disc and passes through the two
pulleys s,t.
In this figure are united two well-known methods of
transforming circular continuous motion into alternate recti-
linear, either by employing a bent axle, or a circle
whose plane is inclined to its axis of rotation. The hydrau-
lic wheel causes the vertical axis to turn: this axis carries
a circle whose plane is inclined to it; the vertical rods of the
piston have catches or stops furnished with friction rollers,
and lean on the edge of the surface of the inclined circle;
thus the circular motion of the vertical axis of the hydraulic
wheel communicates an alternate rectilinear motion to the piston
rods; the rods of the piston are maintained in the vertical
position by grooves furnished also by friction rollers; a double
catch, viz. one which applies itself against the lower surface
of the circle serves to aid the piston in its descent, and renders the motion more uniform.

Fig. 1371.
3 Q 3
966
BOOK 11
THEORY AND PRACTICE OF ENGINEERING.
q
The great wheel r (fig. 1372.) turns round its axis; its surface is furnished with three
rollers, on which the roller q successively leans, at the end p of a lever pgh, whose arins make
a right angle; the other end tends
to turn by the action of a spring
or weight the lever p towards h; the
extremity h will have an alternate
circular motion, which will be
changed to alternate rectilinear by
means of the pulley f


s (fig. 1373.) is a fly-wheel fur-
nished with a pinion; p and r are
teethed wheels engaging each other;
p also engages the pinion: two
winches are fixed to the axis of the
wheels p, q: mf, mg, are two rods
whose ends turn freely and com-
municate to the rod pr an alternate
fa
Fig. 1372.
2
h
Fig 1373.
なれ
​m
h
9
rectilinear motion, while the fly s turns circularly in the same direction; reciprocal motion
is also obtained by this arrangement; it is applied to engines or pumps.

m
b
Fig. 1374.
m
Fig. 1375.
a is a toothed-wheel put in motion by the pinion b, which
obeys the immediate action of the mover; the weight is sus-
pended to the extremity of the cord d, which passes through
a pulley, and is rolled on the axle c of the wheel a; t is the
gudgeon of the same wheel. The brake consists of a lever
turning on the axle of rotation; it is furnished with a concave
piece p, which should apply itself to the axle c, and a counter-
poise h, which serves to raise it as shown in the figure; the
obstacle r maintains the break in this position: when it is re-
quired to discharge the weight suspended by the cord d, the
pinion b is drawn from the toothed-wheel a; the weight falls,
and when it is 3 or 4 feet from the pavement, where it would
be broken, the extremity m of the lever is heavily pressed,
and the piece p by its friction on the axle c immediately stops its velocity.
Let a be a drum fixed to the axle of the machine, furnished
with a ratchet-wheel turning in the direction indicated by the
arrow; m is the lever of the brake, c a catch suspended by a
cord at the extremity of the lever b which turns from the point,
and leans on the small pulley at the extremity of the brake m :
the piece e prevents the catch from mounting by means of a
salient point, while the spring tends to approach the ratchet-
wheel, and by its curvature sustains it when it is in motion;
when the motion becomes retrograde the catch is drawn back,
the brake acts, and the machine is stopped without shaking,
and consequently with the least possible inconvenience.
Wheels used at the Stone Quarries, Paris.
sustains on one side the wheel a, and
on the other a counterpoise p capable of
lifting the wheel a; the whole forms a
system similar to the Roman steelyard,
loaded with a weight whose place is here
supplied by the wheel a; and the run-
ning weight is replaced by the counter-
poise p, capable of lifting the wheela: be
is an upright, fe a beam which turns round
a point f, and which carries the brake q;
ed a rod of wood or metal turning round
the axes of rotation e and d; nn the cord
which serves to draw up the stones from
the quarry; pra ratchet-wheel fixed to
the axle-wheel a, with its catch v fixed to
the upright be; on the other side of the
wheel a should be another upright gh, to
sustain the other axle of rotation of the
lever q, which should have the form of
a fork in which the wheel a enters, and
whose sides should leave the space neces-
sary for giving it a free passage. The
stone to be drawn up is attached to one
d
h

A large beam 7 turns round a fixed point, and
e
C
Fig. 1376.
A

N
9
a d
h
n
p
CHAP. XI.
967
MECHANICS.
n
TEHE
m
m
a
a
of the extremities of the cord r, and the first efforts made to put the wheel a in motion
in the direction indicated by the arrow causes it to descend until the extremity leans against
a stop; the brake q then rises, and the workman experiences no difficulty; he can suspend
it at pleasure by the ratchet-wheel, and if the cord breaks at the moment the wheel rises by
the action of the counterpoise p, the brake q descends, and the force of the fall is broken.
Fig. 1377. Let a bean axle put in motion by the power n, that
which communicates with all the other parts of the machine: it
is required, that in the case where the resistance experienced by
the machine is greater than the limit assigned to it, it should
stop without the mover suspending its motion, and without
the communication being interrupted between the two axles
m and n: bb is the piece of iron fixed to the axle n; it is
composed of a circular plate whose surface on the side of n is
plane; that turned towards the axle m is furnished with two
circular crowns nn and mn: cc is another piece of iron formed
of a circular plate; its surface on the side of the piece b is
furnished with a circular crown which fits in the cavity of the
piece b, and of a tooth d in the opposite surface; there are two
salient pieces a, a, destined to meet the salient pieces s, s, of the
piece c, and a strong salient beak b, which is prolonged to-
wards the opposite surface, and enters the hollow which the
exterior of the ring or circular spring leaves; this embraces
the throat formed by the edges of the piece b, and its crown
mm; this ring or brake may be closed more or less by means of a key E, and consequently
the friction is increased or diminished at pleasure, in order that the axle n may stop, and the
axle m continue its motion; the latter will conduct the piece b, and the brake where the
communication shall be established, by means of the piece c which turns with it, and can
slide in the direction of its axle: the two salient teeth s,s, meet the obstacles a, a, of the
piece b when we bring c to b; by drawing them asunder, the action of the mover is sus-
pended, whatever be the resistance the axle n experiences: it is evident if we screw tightly
the key E, and establish the communication by bringing c to b, the two axles m and n
will turn as if they were one: if we release it entirely, the axle m will draw in its
motion the piece b, and the brake oo, but the axle n will remain at rest; we then screw
the key until n turns again. Belancourt has applied this to a machine for cleaning ports
at St. Petersburgh.
Fig. 1378. s is a fly, one of whose extremities of the axis is fur-
nished with two ratchet-wheels r, r; in the interval of these two
wheels there are two others toothed, which enter the axle of the
fly by gentle friction; both have a catch p placed in the same
direction in each of the opposite sides, and in such a manner
that they must turn in opposite directions, in order that the catch
may act on the ratchet-wheel which immediately touches it:
pQ is a great rod which slides between two tenons, and
being divided into two parts, forms a kind of frame furnished
with racks, f, g, h, i, which are not in the same plane: fg en-
gages the wheel n, and hi the wheel m; if we suppose that
the rod PQ moves from Q to P, the rack hi, acting on the
wheel m, by its catch p, will communicate to the fly a a motion
of rotation from right to left, whilst the wheel n will turn
without impressing any motion upon it. When the rod re-
turns from P to Q, the wheel n communicates to the fly a
circular motion in the same direction; we may suppress one
of the two wheels with its rack, the fly aa will not the less
continue by its inertia to move in the same direction.


bi
Fig 1377.
D
50
8

201
h
Fig. 1378.
i
Camus Pile Driver.-The ram a is attached to the ex-
tremity of the rope which passes over the pulleys b, c, and
envelopes the roller d, which with the lever i, is the principal
part of the machine, whose play depends on the manner in
which this roller is joined to the capstan; the capstan and
roller have the same diameter and the same axis; the roller
should be encircled with iron, with two or more pins of the
same material attached to the circle ef; the capstan g supports
the lever hi, which has a claw advancing on the roller, and
attached to the capstan by a hinge, in such a manner that it
may lower itself by leaning on the extremity i, and raise itself by means of a spring: this
machine is worked by men at the levers o, m, n, p, which turn the capstan and roller, fixed
to the capstan by the lever fi, applied to one of its pins; thus the cord is wound on the

i
m
gn p
Fig. 1379.
3Q 4
968
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
p
d
d
↑
roller, and the ram rises along the post vv; when the latter arrives at its greatest
height, a man placed at the end n of the bar leans on the end i of the lever, and lowers
it; then the point of the roller escapes the claw of the lever which retained it, and the ram
falls; the lever is then let go and raised by the spring, and lays hold of another pin, which
joins the roller to the capstan afresh. There is a great friction in this method.
Fig. 1380. is an iron axle, turning always in the same
direction, either by the action of men who act on the bar of a
capstan, or by the effect of any other mover; it traverses the
two wooden drums a and b which are attached to the axle
by gentle friction; the lower drum a rests on the plank, and
is furnished with two upright surfaces, one outer, the other
inner, each making one turn of its circumference spirally; these
surfaces are so situated that their extremities are at the two
ends of the same diameter; the same drum a is furnished with
a ratchet-wheel r, and a catch which prevents it from turning in
the direction of the mover; the upper drum b is hollow in its
inner part, and furnished with two vertical rods, which carry
Fig. 1380.
two rollers, the height of which is equal to that of the lower
drum; it is sustained by these two rollers on the inclined planes of the drum a, preserving
a horizontal position, it also carries a bar of iron t, terminated at the height of its lower
surface, and its convex surface is cut into a groove to receive the cord of the ram. When
the roller fixed on the rods is at the beginning of the inclined plane, the drum b is at its
maximum of descent, and if the latter is turned in a direction contrary to that of the
mover, the roller would meet the two heads of the upright surfaces, and would compel
the drum a to turn equally, but if b turns in the direction of the mover, a would remain
immovable, and b would elevate itself vertically, turning by means of the two rollers
to the height of the two surfaces on which it is situated. The iron axis p has a strong
iron cross piece i placed in such a manner that it touches nearly the upper part of the
cavity of the drum b when the latter is as low as possible. Supposing when the drum
b is at the maximum of its descent, the bar i in contact with, and ready to act on the point
t; the ram m on the head of the piles, and the cord d stretched, the axis p by its
motion will turn b, which will elevate the ram to a height equal to its circumference; then
the bar of iron t escapes the cross-piece i, and the drum b yielding to the action of the ram
m, turns in an opposite direction, and allows it to fall, consequently the drum b will have an
alternate circular motion, while the ram m will have an alternate rectilinear motion, and the
space which it goes over in this case is equal to the circumference of the drum b.
Fig. 1381. ab is an axis which the power
causes to turn always in the same direction;
the wheel c acting in a groove, enters into the
axis ab by gentle friction, but without being
able to slide along ab, and on one of its faces
a pin s is fixed: nm is an elastic bar fixed to
the axle; r is an inclined plane placed near
the circle e, and in the direction of its plane.
The cord ct has one of its extremities fixed in
the throat of the wheel e, and the other to the
flail which turns round its axis p. When
pq,
the axle ab turns, the elastic bar nm meets
the pin s, and obliges the circle e to turn also,
which lifts the flail pq. But the bar nm
meeting the inclined plane r retires from the
circle e, and allows the pin s to escape; the circle is then abandoned to the action of the
flail, which falls and goes on as before.


a
T
n
ల
b
m
q
Fig. 1381.
It is not possible to describe all the methods by which motion is
transformed or converted; to do so, it would be necessary to analyse
every species of machine that has been invented: to illustrate the more
simple means which have been resorted to, in connecting the first with the
second mover of a machine at the impelled point, and the last action
upon the working point, is all that we aim at describing; mechanists
have devised many ingenious contrivances for particular purposes, but
the whole of which it would be impossible to describe.
Fig. 1382. is applied to a machine for beating plaster, &c.
The piece
a is fixed to an axle turning always in the same direction, and the wheel
b is boxed on the same axle with gentle friction, in order that it may
turn in contrary directions; this wheel is furnished with a catch c to
which the piece a hooks, which thus causes the chain d to mount, to
which one of the pistons is attached.
p
n
S
Im
C
b
Fig. 1382.
q

CHAP. XI.
969
MECHANICS.
When the extremity of the catch has leaned against the pin or stop e, the piece a unhooks;
the piston suspended to the chain d descends by its own weight, causing the wheel b to turn.
To change motion at intervals, the Catch-Wheel b, mounted on an axle, receives the motion
of rotation by the assistance of a handle.
Fig. 1383. u is an axle which we suppose to be turning con-
stantly in the same direction by the action of any power: ca
circle or toothed wheel, which enters the axle a by gentle fric-
tion, and which has two mortices to receive the pins; dis
another circle which fits the portion q of the axle a, which, in-
stead of being cylindrical like the rest of the axle, is quadrangular.
In this circle are attached two small pins by means of a fork.

d
m
Fig. 1383.
a
The circle d may be made to advance and retreat at pleasure.
The machine being in the position represented in the figure, the
circle c may remain stationary, or may obey the action of the mover, which turns it in a
direction opposite to that of the axle a. We may regard it as absolutely independent of
the motion of this axle, except the slight friction which it experiences towards its centre.
But if by means of the fork we bring the circle d to the circle c, so that the mortices meet
the salient pins; the wheel c necessarily obeys the action of the axle a, until we are again
obliged to draw the wheel d away, and so on. The spring e tends to draw away the collar
d from the toothed wheel c, in order to remove it from the action of the mover; the catch
here shown in plan and section turns round the axle i; the obstacle b on the one hand, the
spring k on the other, determines the position and extent of its motions; if we turn the lever
so that the communication of motion takes place, the catch s will be arrested by the
spring e. When we wish to suspend the action of the mover on the machine, we must press
slightly on the extremity t of the catch; the spring e will act on the extremity of the lever,
and the collar d will retire from the wheel c, on which the mover has no more action.
this mechanism the motion of a machine may be stopped, first at any given hour, secondly,
in mills when the corn is ground, thirdly, in looms when the shuttle is stopped in its course.
The first case offers no difficulty; it suffices to make the weight of an alarum act on the
extremity t of the catch to render it perceptible.
By
In mills the motion may be stopped when the grain has run out, profiting by the same
mechanism as is employed in this case, to call the attention of the miller to remove the catch.
It often happens in looms for weaving that the shuttle is arrested by a thread breaking, or
some other cause, to prevent the disorder which would result in this case, it must be recol-
lected that when the batten is driven from the side of the weavers' beam, on which the warp
is rolled, the shuttle is driven by the blow which it receives from the shuttle driver;
the batten immediately returns towards the small working beam, to strike the woof, and
the batten whose section is given goes with an alternate circular motion over the arc ab,
whose centre or axis of rotation c traverses the sole of the weaver's frame. This motion
should not be uniform, but slackened towards the extremity a of the arc ab, which we sup-
pose to be that on the side of the great beam, to allow the shuttle time to pass from one
side to the other to the batten, whatever be the size of the loom, and it should be more
or less accelerated towards the extremity b of the same arc, to strike the woof.
We must
imagine an iron rod placed along the batten, and turning freely on the axle p, furnished
with a bent lever at each of its extremities, and tending by the action of a spring, placed
about the middle of its length, to turn in opposite directions, so that the levers resume
their original position.
It will be seen that if the shuttle was not arrested in its course, the lever would not
meet the obstacles a,c when the batten by its circular alternate motion passes over the arc
ab to strike the woof; but in the other case, viz. when it is stopped by any obstacle, the
lever will then meet the point a, which yielding to its action will descend, and acting
on the extremity t of the catch will separate the collar d from the wheel c, and in an instant
after it will meet the invincible obstacle b, the action of the mover will be suspended, and
the batten cannot strike the woof; the objects which were proposed will then be answered.
Fig. 1384. is a further modification of the preceding
movement. ab is the axle which turns in the same
direction with the action of the power; the wheel c transmits
the motion to the wheel d, which fits by gentle friction on
the axle ef; the wheel d is furnished with a pin, and the axle
ef with another g; the wheel d retires or approaches the
pivot q at pleasure, by means of the lever pq: it will thus be
immediately seen that we can stop or produce the motion of
the axle ef by bringing the wheel d near, or taking it away
from the pivot g.
Fig. 1385. Prony's machine: its mechanism only consists
of a very ingenious application of
Fig. 1383., by which we can suspend or communicate at

b
d
Fig. 1381.
a
970
THEORY AND PRACTICE OF ENGINEERING. BOOK II.
d
Q
a
b
g
m
$
N
pleasure to a wheel the action of the mover, which causes
the axle to turn on which the wheel fits; and reciprocally,
we can by this mechanism communicate to the axle, or sus-
pend at pleasure the action of the mover which drives the
wheel. Prony caused a great horizontal wheel, ab, to turn
by the immediate action of the mover; this wheel puts in
motion in contrary directions the two vertical wheels c and d,
which work into the horizontal axle ef, whose interior faces all
engage a ratchet-wheel at nm. At one of the extremities
of this axle is a pulley, g, round which a cord is wound, having
a bucket at each end; a piece, aa, formed by two iron bars,
which carry a ratchet-wheel, pg, at their extremities, slides
along the square axle ef by means of coupling boxes, also
cut square; it is evident that if the piece a a is pushed towards
the extremity e of the axle ef, the ratchet wheels g, n will en-
gage, and the axle ef will turn in the same direction as the
wheel d; if it be pushed towards the extremity f, the axle will
turn in the direction of the wheel c, and one of the buckets
will ascend while the other descends. Alternate motion is communicated to the piece a a,
in such a manner that it takes place immediately after the ascending bucket is emptied
into the trough, and the cord of the bucket itself determines its motion. For this
purpose under the axle ef another horizontal axis, ss, was placed in a direction perpen-
dicular to ef; this iron axle ss is furnished with a catch, x, which enters the sliding
boxes of the piece aa by a rod, h, terminating by a weight of lead, p, and by two claws,
s, t; two knots or forks are placed towards the extremity of the cord above the bucket, so
as to engage successively the two levers m, n. These levers act on the claws st, and raise
them, so that the rod h passes the vertical position at the moment when the ascending
bucket is emptied; then the weight p causes the axis ss to turn briskly, and its catch ☛
drives the piece aa towards the same side, and maintains its position, and makes the
ratchet-wheels act; the axle ef turns in a contrary direction, and so on, &c.

Fig. 1385.
3
3
6
6
6
5
4
Fig. 1386. shows Prony's method of unharnessing an animal employed to drive this
machine when the effort was increased by any cause. Three traces, 1, 1, 1, pass through
the openings 2, 2, made in the yoke 4 4, attached to the end of the lever 3; this lever
is fixed to the vertical axle, which gives motion to the machine; the openings 2, 2, are
furnished with pulleys to diminish friction: the extremity
of each trace terminates in an eye, which hooks on to a screw
ring, fixed in the axle 5, movable in gudgeons; round this
axle 5 is wound a cord, which ascends, passing through the
pulleys 6, 6, and attached to a weight along the vertical
axle; this weight, which may be varied at pleasure, determines
the resistance opposed to the effort of the animal. Sup-
posing the weight limited to 20 pounds, and a stick falls into
the teeth of a pinion, it would follow that by the effort of
the animal the machine would be broken; but, as the effort
will necessarily exceed the weight, which serves as a regu-
lator, the axle 5 will be obliged to describe a quarter circle.
The screw bolts having then quitted their vertical position,
the extremity of the traces hooked thereto escape, the animal
is freed, and the mechanism avoids injury.

v, v
Fig. 1387. ab is an axle turning on its axis by means
of a power applied at a; its pivot b rests on a piece of wood
e, furnished with two rollers, which enter a groove in
the cross piece nm. By this means the axle ab may easily
approach successively the toothed wheels o,o, to which the
endless screw h, with which it is furnished, engages.
are two cross pieces, which serve to sustain the axle, without
affecting the slight balancing motion which ought to be
communicated to it by the movable piece e, on which its
pivot rests. In this piece are two catches, which turn
round their two axes, which, as well as the two pins at
their extremities, are prolonged; this piece has an axle,
having two other branches cut in the form of a fork, to
allow the cord which carries the bucket to pass; near the
extremity g a rod rises, carrying a weight p. In the cross
piece nm are seen two screw rings, x and y, whose pro-
jection equals the thickness of the two catches ub, cd.
Two buckets are attached to the extremity of the cord,
1
2
1
1
Fig. 1386.

D
n
m
Fig. 1387.
CHAP. XI.
971
MECHANICS.
which passes over the cylinder of two toothed wheels 0,0.
making a turn round each. In the position represented by
the figure, the branch u, after having pushed the pin a'
towards the left, makes the endless screw h engage the
toothed wheel, and the catch a'b', falling by its own weight,
engages the pin x, and drives the axle against the toothed wheel.
When the button s, which is near the bucket
q, has engaged
the fork l, the piece u is obliged to turn on its axis, and the
arm n, touching the pin b, unhooks the catch, in order to
assume a horizontal position; but it has scarcely passed this
position when the counterpoise, p, falling on the other side,
the arm u pushes the pin, and causes the axle to pass to the
right, which engages the wheel o, while the catch cd by its
own weight engages the pin y. The two cylinders turn in
contrary directions, and the bucket q descends, while the other
mounts; the edges of the buckets are furnished with a piece
of iron, to oblige them to assume a situation proper for
emptying the water. This machine was the invention of M.
Belancourt.

e
h
b
m
Fig. 1388.
no
զ
२

Fig. 1389. — In proportion as the circular motion of the
axle ab increases or diminishes, the weights P and 9 retire
from or approach this same axle, by virtue of the centrifugal
force; and the crown r, which embraces the axle, descends or
ascends vertically. On this crown the motion of a valve m
depends, which prevents the steam from introducing itself
into the cylinders of steam-engines, or of escaping from
them to pass to the condenser, and by this means the machine
preserves an almost constant velocity, although the resistance may be variable.
seen it applied to a windmill to raise the revolving stone when the velocity was too great,
to prevent the flour from heating.
Fig. 1389.
m
a
We have

k
d e
The revolving stone a receives its motion at the upper part,
as is the case in all windmills; this stone is carried by
the axle, which rests on the sole plate fixed to the bearer.
In the axle is fixed the crown fg, which carries four arms
to receive the rods of the four iron balls, h, i, k, l, each 4
or 5 pounds weight; from the upper parts of these rods four
braces descend, which support the piece m, which slides
freely from the top to the bottom of the axle; in this piece a
groove is cut to receive the extremity of the lever de, of a
forked shape, whose other extremity o supports the bearer,
which turns on the centre n; it is evident that by the motion
of the revolving stone, the whole system of balls will revolve,
and that in proportion as the velocity of the wind increases that of the stone, the balls
will fly off from the axle, the piece m will descend, force the lever de into the part d, and
will lift the bearer, and consequently the upper millstone a.
Fig. 1390
Fig. 1391. Change of alternate rectilinear motion to continuous circular
a is the axle of the wheel turning on an iron pivot or
axis; bb are the wings of the wheel, a little inclined,
to allow the water to pass in a spiral direction; ce is
a drum or circular envelope, in which the wheel turns
in the least possible space between its sides and its floats
dd, dd. A second drum of a larger diameter is placed
above the wheel, and crowns the drum cc with which it
is combined; ee are movable doors which open on op-
posite sides; the first, on the side of the current, opens
when it is pressed by it, and is arrested by the post
f. The door on the opposite side will be pressed
by the current in the opposite direction, and will close
The inverse operation will take place when the water
which shall have mounted by the flux attempts to re-
tire at the instant of the reflux. The dotted lines also
indicate this contrary motion.
Suppose the surface of a river h, which at low water
is level with the cover of the upper drum, in order that
the same quantity may always act on the wheel; when
the surface of the water is above the circle of the
upper drum, the water which passes above will not pro-
d
C
k
e
रु
Fig. 1391.
Tide Mill.
h

α
i

b
972
Boos II
THEORY AND PRACTICE OF ENGINEERING.
ii
duce a greater effect by rising several feet, than when it was at the level of the cover.
shows the bottom of the river, and the water enters the drum by passing the door e until it
arrives against the post f; there it finds a passage, by means of which it arrives at the bottom
across the spiral floats, which yield to the impulse of the current, and give a motion of
rotation to the vertical axle. When it has arrived at the bottom, the water escapes by
the door k, producing motion when the tide is flowing out; when, on the contrary, it is
coming in, the two doors we have just mentioned close, and the two opposite ones open, by
means of which the water descends as before, and turns the wheel in the same direction by the
flux or reflux.
The advantages of this wheel over others of the same kind are, that if it be employed for
corn mills its velocity is more uniform, since the same quantity of water always acts on it;
secondly, it turns in the same direction by the flux or reflux, and in a more simple manner
than other tide-wheels; thirdly, as the wheel is horizontal, it is easy to adapt any gear to
its axle, since we can elevate this axle at pleasure above the surface of the water; fourthly,
the velocity of this wheel is greater with regard to the velocity of the tide, than for other
wheels, which dispenses with all the
contrivances used in the old wheels to
diminish friction; fifthly, it is more
economical.

A
d
h

Fig. 1392.
e
B
d
d
W
a
Fig. 1393
Fig. 1392. is a vertical axle, very
solidly fixed: it is terminated by a
toothed wheel, c. A hollow cylin-
der d fits this axle, and reposes in
a rebate practised on the lower part
of the same axle; four cross pieces
a,b,c,d, issue horizontally from this
cylinder, and at right angles with it; at the extremity of each cross piece is suspended
a car; on one of the cross pieces the axle of a small wheel i is fixed, which engages the
toothed wheel c. At the extremity of the small wheel i four cords are attached, each
passing through a fixed pulley to the extremity of the cross pieces. A person seated in
one of the four cars may easily communicate a continuous circular motion to the little
wheel i by means of the cord which passes through the pulley in front of it.
n
h
k l
A is a circle whose circumference is furnished with a crown ratchet-toothed; fc two
rules which turn freely round the axis of the wheel A; two other rules form an irregular
quadrilateral figure with the preceding, whose angles are nearly right angles: the extre-
mities of these four rules are united by axles, round which
they turn freely. hi is a rule united at h with the quadri-
lateral; an axis traverses at h the three rules; the rule hi
passes through the two tenons k and 1, and can only move
itself in the proper direction; two of the rules carry two
catches, placed, the one to the right and the other to the
left of the figure: these two catches are attached to the
rule by hinges, and enter the notches of the ratchet-wheel,
either by their weight or the action of a spring: let us
now suppose we can move the rule hi from h to i, the catch m will act on the crown,
and will turn the axle A in the direction indicated by the arrow, whilst the catch n
will slide on the teeth of the same crown: but if the rule return from i towards h,
the catch n will act, whilst the other, m, will slide; in both cases the wheel A will turn
in the same direction. The alternate rectilinear will then be transformed to circular con-

tinuous,
g
g
Fig. 1394.
D
b
6
k
a
4
Fig. 1395.
Let a be a wheel furnished with six pins; qp a horizontal plank sustained by the
rollers b and c, with a catch de, whose length is equal to the distance between the
plank and the half of the space which separates the two pins 1 and 2; fg and gh,
forming between them a right angle, this bent lever can turn freely round the axis
of rotation g: the length of the rod
the length of the rod g h is equal to the
radius of the circle g; the point g is in the line gk, 9
parallel to the rule or plank qp, and the rod hg tends
always to descend by its weight: ƒ is a pin which belongs to
the plank qp; the horizontal distance of this pin from the
vertical, which passes through the point g, is equal to the
distance Dd. If we make the wheel a turn in the direction
indicated by the arrow, the pin 1, acting on the catch de,
will draw the plank qp from q to p, while the pin 5 will restore the bent lever fg h. When
the pin 1 arrives at the point e it will cease to act on the catch de. The arm gf of the
bent lever fgh will be in a vertical position, and will commence to act on the pin f of the
plank hp, which will return in the direction qh; when the pin 5 of the wheel a arrives at
the point 6, it will quit the arm gh of the bent lever, and lean on the pin 4, which

CHAP. XI.
973
MECHANICS
will be found in the place of the pin 5; the pin 6 will occupy the place of the pin 1, and the
motion will continue in the same manner, so that at each revolution of the wheel a, the
plank qp will have made six alternate motions: such is the mechanism employed by Thiout
for polishing springs.
These two motions give the solution of the pro-
blem of the transformation of circular continuous to
rectilinear alternate, and have been applied to some
steam engines.
In the first, nm is the crank of an axle n, which
turns circularly by the action of the mover d a bar,
attached for example, to the extremity p of the piston-
rod of a pump, and which must go over the line bb,
equal to twice mn: any dimension may be given to the
two bars e and c, and the centre ƒ of rotation; c
must be placed in three positions, ft, fq, fr, which the
point p of the rod d must take up, at the extremities
and middle of its course. This will determine the
points q, r, and s, where the other extremity of the
bar e should be in the same line; through the three
points the circumference of a circle passes, the radius of
which and its centre will determine the length of the
bar a and its centre of rotation.


n
P
q
P
Fig. 1396.
a
n
In the second we must in like manner have the
dimensions of the bars e, i, and h, and the position of
the point of rotation f: we determine, as in the pre-
ceding case, the points m, n, and r; the radius and centre of the circle which passes through
these three points will give the length of the bar l, and the position k of its centre of
rotation.
Circular continuous motion with a uniform velocity, or which varies according to a given law,
may be changed into a circular continuous, with a velocity of the same nature as that of the motion
which produces it, constant or varying according to a given law, in the same plane or in different
planes.
The two teethed wheels a, b engage naturally; the circular
continuous motion of the one is communicated to the other in the
same plane, but in contrary directions; there must be a third
wheel c if the motion is to be continued in the same direction.
The ratio of velocities will be determined by that of diameters:
let m be the radius of the wheel n', and a that of the wheel b:
if m and n' are two integral numbers, the wheel a will make a
number n' of revolutions, whilst the wheel b will make a number
n of its own, in order that the same teeth of the two wheels
shall engage, that is to say, in order that the two wheels a and b
should resume the same relative position.
The same problem is resolved by means of a cord or endless
chain: the motion takes place in the same or different directions ac-
cording as the cord envelopes the two wheels without crossing, or
crosses in the interval which separates them. Physical causes con-
tinually tend to change the length of the chains or cords: to preserve
them always equally stretched, springs or counterpoises are employed,
but care must be taken to place them in such a manner that the tension
produced in the cord turns the wheel on which the mover acts, in
the same direction as the mover does the wheel: the counterpoise
then produces a very good effect, and may be applied with
success to all machines; but if the tension produced in the
cord by the action of the counterpoise acts in a direction
opposite to the motion communicated by the power, the effect
becomes null.
There are different means of communicating the motion of
one wheel to others employed in the arts, which are com-
bined in the annexed figure.

پیچھے
a
Fig. 1397.

Fig 1399.
Fig 1398.

When it is required to convert a continued circular motion
into another continued circular motion, two things are to be
considered, the axis round which the rotation is made, and the
velocity, or number of revolutions performed in a given time. If by a rotation round one axis
it be required to produce a rotation round another axis parallel to it, it may be accomplished
by placing two wheels on the two axes, so that they shall be in the same plane at right
angles to the given axes: these wheels may act one upon another, either by the friction of
974
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
their edges, or by a strap or chain, or finally by teeth: if they act either by friction or by
teeth, the rotation round the two axes will be in contrary directions; but if they act by a
strap or chain, the rotation will be in the same direction, if the strap be crossed, but
otherwise in opposite directions.
To
A
b'
S
ገራ
22
d
B
[2]
d
B
n
Pb3
ບາກນນັ
Fig. 1400. represents a watch escapement in-
vented by Breguet to prevent the spring from
being overwound or running down to its full ex-
tent. In these watches the fusee is suppressed;
the barrel A, which contains the spring, has a
toothed wheel which transmits the action of the
spring to the pinion of the first wheel of the watch
the spring is fixed by one of its extremities to the
axle rd, and by the other to the inner and concave
surface of the barrel. The length of the spring is
such that, supposing it entirely unwound, the axle
rd can make about twelve turns before it arrives
at its maximum of tension; in general the mean
tension of the spring is only employed, i. e. that
which results from four turns; the axle rd has a
ratchet-wheel which prevents the axle from turn-
ing in a direction contrary to that which the
spring tends to communicate to the barrel.
the axle rd a toothed wheel B is fixed, engaging
another C, which enters freely in a cylinder rising
from the upper part of the drum; a large-headed
screw keeps the wheel in its place; the diameter of
the wheels C and B are in the proportion of four to
five, the wheel B makes four turns, and C five
before the same teeth return to the same relative
position. Suppose that the spring contained in
the barrel A be entirely down, and that the axle
dr with the wheel B is turned eight times, it will produce the maximum of the action of
the spring, and prevent the axle rd from continuing to turn. If the distance de be
divided into two equal parts, and the semicircle dƒe be drawn, it is evident that the stops
to produce the desired effect in the most advantageous manner should be placed in one of
the points of this semicircle; another condition is moreover requisite, from the moment that
the wheel B is stopped, C turns, impelled by the barrel, and supposing that the proportion
of the diameter of the wheel C to the diameter of the wheel B is as n' to n, the wheel C
cannot return to the point where it is found after having made a number n' of revolutions
round the wheel B, because it previously meets the stops, whatever point of the semicircle
dfe be chosen for the point of contact; but they will meet under different angles, which does
not answer the end proposed. It is necessary that the stops should meet at right angles
before the wheel C terminates the nth revolution round the wheel B: let ƒ be the point
required, the length of the arc ab must be equal to the arc ac, for if the barrel be turned
in the wrong direction, the point b will meet and fall on the point c, and when the centre e
of the wheel c arrives at g, the angle def will be equal to the angle dgf, and all the con-
ditions will be fulfilled.


Fig. 1400.
A
In watches with turning barrels there is nothing to indicate the state of the spring, con-
sequently they stop or are wound up unnecessarily: M. Breguet, to obviate this, cuts the
part mn of the axis rd in a screw fitted with a nut st in form of a truncated cone; one or
two rods u rise above the surface of the barrel, and pass through the nut, without affecting
its motion, in the direction of the axis rd. When the watch is wound up, since the screw
turns without changing its place, and the nut cannot turn by reason of the rod u, it moves
in the direction of the screw or axle rd: while the watch is in motion the nut turns and
passes over the same space in the opposite direction; an alternate rectilinear motion is the
result, which is transformed to alternate circular by a bent lever a' b' c'd', whose lesser arm c' d'
rests on the conical surface of the nut, and the greater arm ab marks on the dial plate the
tension of the spring.
There can be no doubt that we are greatly indebted to the mechanists, who have applied
themselves to the improvement of machinery for the measurement of time: from the period
of Richard of Walingford, abbot of St. Alban's in 1326, we have continued to improve
in the manufacture of clocks, which perhaps had their origin in the time of Pope Syl-
vester II., who made one at Magdeburg as early as the year 996. Toothed-wheels were
certainly known 1300 years before, as we have them applied to the clepsydra: on
Trajan's column at Rome they are also represented, and we are not astonished that,
when observed by an intelligent mind, like Gerbert, afterwards Sylvester II., they should
be again brought into use. The history of clock-making would afford us the best method
CHAP. XI.
975
MECHANICS.
of judging of the progress of machinery; after the balance clock was used in France, about
1370, the most learned men applied themselves to its improvement.
The nature of all the wheels and pinions which are contained between the two brass
plates of a clock are highly curious as a machine, the first or great wheel of which in an
eight-day clock movement has concentric with it a cylindrical barrel with a spiral groove
cut on it to this cylinder is attached one end of a cord, wrapped round in the groove
for any determined number of turns, and to the other end of the cord is hung a weight
which constitutes a power or force to set the wheels in motion.
α
B
n
h
B
n
n
n
A
9
e
Ꮮ
C
C
A
B
A
B
A
B
n
e manu
b
с
f
C
A
A
A
u
d
b
n
e
f
D
C
h
G
Fig. 1401. represents a machine used in porcelain manufactories for grinding the materials.
The power communicates motion to four
or six lanterns whose axles descend verti-
cally into a circular tub A A A A at whose
bottom is a stone C, with another, D, laid
thereupon whose diameter is greater than
the radius of C: the stone D performs the
office of a muller, and is fixed to the lower
extremity of the axle ac by a cramp edbc.
The two stones G and D are often advan-
tageously replaced by porcelain plates, but
in this case the plate D is loaded with a
weight the materials are put into the tub,
which is filled with water; after some time
it is found that the stones C and D do not
wear equally, the parts farthest from the
centre of rotation c experiencing the greatest
loss, and the two surfaces do not touch at all
their points, fng m h remaining hollow. To
render these inconveniences less sensible, a
little liberty is allowed between the stone D
and the cramp edba, so that as the edges
wear it falls, but this only palliates the evil.
The stone D can only be made to wear equally
by causing each of its points to pass over
equal spaces in equal times: to obtain this
the following method is employed; the ver-
tical axle passing through the cross piece
B B, is supported by a rabbet nn, and is ter-
minated by a branch cỏ which forms a right
angle with ab; from the centre d of the
muller Da rod de rises, passing through a
circular hole in the branch cb, and carry-
ing the wheel e: the wheel h turns freely
round the rod fh, which rises from the
branch cb, and is supported by the rabbets
in the same rod fh: the wheel g is fixed to
the traverse B B, the axle ab passes freely through its centre: the diameters of the three
wheels e, h, and g are equal.

Fig. 1401.
d
C
The upper section in our figure represents a very simple method of obtaining the required
parallelism. From the centre d of the muller D a cylindrical rod de rises, passing freely
through a circular opening made in the horizontal branch rb of the vertical axle ab: from
another point f of the muller, at a distance df greater than c d, another rod ƒg rises, passing
freely through a circular opening in the horizontal branch ki of the vertical axle hi, which
is sustained by a cross piece B B; the two branches i k and rb should be equal. When the
axle a b turns, the point d will trace a circle round the centre
c, whose radius will be equal to de; the point ƒ will have
another circle, whose radius ƒh will be equal to cd; these two
radii will be continually parallel.
Fig. 1403. is a machine for polishing looking-glasses, con-
structed by M. Sureda at the imperial manufactory of
St Petersburgh. The polishers are worked by mechanism
precisely similar to that just described: a bed is an iron bar
supported by five bent bars of equal length, and disposed so
as to be always parallel to each other, while the centre one
turns round its axle by the action of the mover. By reason
of this motion each point of the bar traces a circle of a radius
equal to the length of the elbows, a property which allows
of its weight being diminished by sustaining it with cords,
8, s, attached to the ceiling.

Fig. 1402.
l'ig. 1403.
976
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
The endless screw, which transmits its circular motion to
a wheel; the motion of the mover is perpendicular to that of
the wheel; the application of this motion in the arts is innu-
merable.
The mill of Piedmont for twisting silk affords a practical
example of the application of the endless screw with a great
diameter, A B; the single worm of the screw which composes
it is divided into six equal parts, all comprised between two
parallel planes, represented by the
letters a, b. The wheel b turns by
means of six teeth, c, c, on its cir-
cumference.

A
a
Fig 1405.
B
The same problem may be re-
solved by employing a system of
wheels placed at right angles, re-
presented by the two truncated
cones a, b, which are furnished with
teeth. This mechanism is often
employed; the
the figure represents
one of its most common appli-
cations; it is the instrument known
under the denomination of wimble, much used by carpenters.
a and b (fig. 1407.) are two wheels, whose planes are per-
pendicular to each other, and which communicate their motion
by means of an endless cord wrapped round them, and passing
over the pulleys c, d. The pulley b moves from n to o, turning
on its axle: if an obstacle be opposed to the change of move-
ment of its axle, the pulley b will turn without changing its
position, and the motion will belong to the present class. This
motion is employed in mule jennies for spinning cotton.
12
Fig. 1404.
b


Fig 1406.
b
Fig. 1407.
a
a

d
0
The movements introduced into machinery for spinning
cotton, &c. are as numerous as curious: in 1767 Hargrave,
of Blackburn, in Lancashire, constructed a machine which
enabled him to spin twenty or thirty threads of cotton into yarn at one time, and in
1768 Mr. Arkwright introduced a new mode for spinning, and also a machine for the manu-
facture of stockings.
Let ab, cd be two axles, each furnished with three wheels,
e, f, g, h,i,k; the two wheels e, h, of equal diameter as well as
the two fi, and g, k, are disposed as shown in the figure; the
wheels which belong to the axle ab are fixed thereto, those
which belong to the axle cd fitted with gentle friction, but they
may all be fixed at pleasure to the axle by a mechanism before
described. It is evident that if we give to the axle cd the same
velocity as that of the axle a b, by making the wheel b act; its
velocity will be greater if we make the wheel a act; it will be
less in the same ratio if the wheel g, which forms a whole with
its axle, acts.
ab, cd, and ef are three parallel axes, each of which carries
two toothed wheels g,h; those of the wheels which belong to
the axle ab, to which we shall suppose the mover applied,
are fixed to the axle, the other fit their respective axles with
gentle friction, but may be fixed by methods before pointed d
out; we suppose the wheels g of equal diameter, as well
as the wheels h, but the diameter of the latter is double that b
of the former. We may combine this system in four different
manners: 1st, if we engage the two wheels b belonging to the
axles cd, ef, with the wheel a of the axle ab, the two axles
cd, ef, will turn in the same direction, contrary to that of the
mover, with the same velocity, which will be equal to half
the velocity of the axle ab.

f
d
口
​9
る
​У
Fig. 1408.

h g
9
Fig. 1409.
a
h
2nd. If the two wheels g of the axles cd and ef engage the wheel h of the axle ab, the two
first axles will turn in the same direction with equal velocities, and twice that of the mover.
3rd. If the wheel h of the axle cd acts on the wheel g of the axle ab, and the wheel h of
the axle ab on the wheel g of the axle ef, the two axles cd and ef will turn in the same
direction, and the velocities of ab, cd, and ef will be in the ratio of 2 to 1 and 1 to 4.
4th. If we make the wheel g of the axle cd act on the wheel h of the axle ab, and the
wheel g of the axle ab on the wheel n of the axle ef; the two axles cd and eƒ will turn in
the same direction, and the velocities ab, cd, and ef will be in the ratio of 2, 4, 1.
CHAP. XI.
977
MECHANICS.
To transform a circular, continuous, and uniform motion to a circular and variable
motion, whose velocity changes according to
a given law. This problem may be re-
solved in a general manner: if we require
that an axle D should make a number
n of revolutions, whilst another, C, makes
another of variable velocities, it is easy to
foresee that two points of the two axes
should return to the same position after
a number of revolutions of the axle D,
or one of the axle C. To simplify the
application we shall suppose that the two
axles turn in the same time; this case
being well understood, the others will not
offer the least difficulty.
n
n
d
D
M
a
C

Չ
p
1
m
7
e
2
f
$

q
C
D
α
Fig. 1410.
Let C Q, DM be the axles of two wheels
a,b; Ca,dD two segments, such that the
arc ab is equal to ad, both toothed and
placed at the height of the line 1 2; ďn,
m D two segments of equal radius, so
that the arc bef equals dum, both toothed and placed at the height of the line 22; qCp,
q Dr, two segments equal to the segments a DD and ab C, placed at the height of the
line 33. We see that by this arrangement the velocities may vary by finite intervals, and
in any manner we please, provided the condition is fulfilled of making the points a, a meet
at the end of n revolutions of the axles m, n.
The construction of this machine presents some difficulty, on account of the change of
gear when it passes from one rate of velocity to another; but this difficulty diminishes by
making the teeth very small. In case they cannot be rendered sufficiently short, we must
aid the passage by an exterior force, as that of a spring or weight.
G
m
n
E
We may resolve the same problem by means of two truncated cones, a and b, of equal
dimensions, placed as indicated in the figure, that is to say at some distance from each
other, their axes parallel, and the small base uppermost,
and at the same height as the great base b. A channel
is cut, in the form of a helix, in the convex surfaces of the
two truncated cones, and one of the extremities of a cord,
mn, is attached to the point where the spiral channel drawn
on the surface b begins at the great base, and after having
enveloped the whole of the same spiral, its other extremity is
attached to the corresponding point of the great base at a.
It is evident if the truncated cone a turns in its proper
direction with a uniform velocity, the other, b, will turn
also, but with a variable and decreasing velocity; at first
greater than that of a, afterwards equal, and at the end as much less as it was greater
at the commencement; the cord nm will then be found enveloping the spiral channel drawn
on the surface of a. The motion cannot continue longer in the same direction. If, instead of
cutting grooves in the forms of a helix on the convex surfaces of the two truncated cones a
and b, we leave these surfaces plain, and substitute instead of the cord nm another endless
cord which embraces both, it is evident that this cord may occupy any required place in
the height of the cones without its being necessary to change its length.

H
Fig. 1411.
F
Suppose, first, that the endless cord is placed at the lowest part of the cone; uniform
motion of rotation a will communicate to b another of the same kind, but whose velocity
will be greater than that of a in a known ratio, a motion which may be continued as long
as we please; according as we make the endless cord advance towards the upper part of the
cones, the ratio of velocities will diminish; will become equal to unity when the cord shall
have attained the middle of the height of the cones, and will follow an inverse course in
proportion as it approaches the upper bases.
This mechanism is used with the greatest success to modify the velocities of circular
continuous motion, particularly in the lathes used in the manufactures of earthenware
and porcelain; the endless cord is made to ascend or descend by means of a jack
placed in the midst of the interval
which separates the two cones; the
rack of the jack is placed parallel to
their axes, and directs the course of the

A
B

a
endless cord; the mechanism is very
simple, and gives instantly all the
changes of velocity which can be re-
quired.
Fig. 1412.
3 R
979
Book II.
THEORY AND PRACTICE OF ENGINEERING.
If we suppose that the motion of one of the two arcs mn, qp of the preceding figure is
uniform, we may render that of the other uniformly accelerated and retarded, as Roemer has
done in the construction of a wheel, proper for explaining the motions of the inequality
of the revolutions of the planets; this author supposes a conical pinion a cut in its whole
length, as in the figure; its iron teeth engage those of a wheel b, which is also conical ;
the teeth of the wheel b are placed on its surface in the form of a spiral: and it is useful to
observe that the form, the position, and the dimensions of each of
these teeth are determined by the form and position of the part of
the tooth of the pinion with which they are to engage.
Let a be a drum, b a truncated cone whose contour is
channelled into a hollow groove, drawn spirally from the base
to the summit, and e a cord whose extremity d is fixed to the
cone ; near its smallest base, this cord envelopes the chan-
nelled groove, and is attached to the surface of the drum. The
uniform rotation of the drum would produce a variable motion
of rotation in the truncated cone, and reciprocally if the truncated
cone turns with a uniform velocity, the motion of the rotation of
the drum will be variable. In watches we employ as a mover a
spring enclosed in the drum e, which is called the barrel: the
truncated cone g is known under the name fusee; round the
channelled groove the chain is wrapped, which goes from the fusee
to the barrel or drum, and it is by the inequality of the diameter
of the spiral that the fusee obtains the property of equalising the
unequal force of the spring.
a is a fixed plank: the axle of the toothed wheel c enters the
groove mn; the wheel c tends to approach a by means of a
spring; d is a surface, for example elliptical, whose edge is für-
nished with teeth; the uniform circular motion of the wheel c will
communicate to the surface d a circular motion which will change
its velocity; this method presents the same difficulty as the toothed
wheels, and only properly takes place supposing the teeth infi-
nitely small; but we may substitute for them a slightly elastic
endless cord, or one stretched by means of a weight spring, not
forgetting the observation made on the manner of placing this
weight or spring.
The universal joint, which serves to change the plane of
circular motion, is used in astronomical instruments, when the
observer, without changing his places, finds it necessary to com-
municate a circular motion to distant points which are in dif-
ferent planes.
a
A
Fig. 1413.
B

b
C

Fig. 1414.
Fig. 1415.
a

Lam
d
Let ab be an axle which is interrupted by another, which
obliges us to prefer this construction to that which we should
use if the axle were a single piece: it is required that these
two portions should turn as if the axis were continuous;
we fix to each part of the broken axle ab a wheel eƒ of equal
diameters; at the side of the axle ab we establish the axle mn
in a plane parallel to ab, and at an equal distance from the
wheel e and f; in this axle two grooves are cut, c and d,
whose planes are perpendicular to the axle mn. The distance
which separates them from each other should be equal to the
distance of the wheels e, f. Two endless cords embrace the
wheels e, ƒ and the throat cd; the two cords should be disposed
in the same manner, that is to say, that both should cross or
not in the interval of the two axes, in order that the axle mn
Fig. 1416.
may transmit its motion of rotation to the broken axle, as if it were entire.
of the endless cords crosses, and the other does not, as in the figure, one of the two parts
of the axle will turn in one direction, and the other will turn in the contrary direction.
Mechanicians often find themselves under the necessity of employing different means
either for regulating the inequalities induced by the moving power, or for guarding
machines and men from accidents, sometimes fatal, which take place from too rapid changes
of one of the powers acting on the machine. As an example we have fusees in ordinary
watches for rendering the unequal action of the spring uniform; the different means em-
ployed either for rendering the length of the pendulum constant, which tends continually
to vary by the action of the temperature, or for rendering the oscillations of a balance-
wheel isochronal. We also have the fly-wheel in bell towers for retarding, by the resistance
of its fans against the air, the too rapid motion communicated by the mover, a mechanism
also employed in other machines

But if one
CHAP. XI.
979
MECHANICS.

b
d
e
a and b are two wheels of different diameters,
as represented in the figure; they fit each other
on a common immovable axle, and are in different
planes: the circumference of the wheel a is cut
into a groove to receive an endless cord, and
the wheel b has also its circumference not only
cut in the same, but there is also on its surface
salient parts, which form a suite of wheels of
different diameters, and whose circumferences
are grooved: on an axle perpendicular to the
surfaces of the two wheels a and b are two
others, c. The diameters of these wheels are
equal to the difference of the radii of the two
z and b; they are placed on this axle in such a manner that the teeth of the one may engage
the teeth of the wheel a, and the teeth of the other those of the wheel b. The combination
and form of this gear is arbitrary, and depends on circumstances. The rod e is terminated
Fig. 1417.
Fig. 1418.
by two rings; the axle which belongs to the two wheels a and b fits one of these
rings, and that which belongs to the two wheels c fits the other, which obliges the latter
axle always to remain parallel, and at an equal distance from the first: d is a cylinder, to
which the mover communicates a circular continuous motion; two endless cords transmit
these motions in a contrary direction to the two wheels a and b.
es
*
*
n
Breguet invented a contrivance for regulating the variable action of the mover
in the different parts of a clock, by increasing the friction in proportion as the moving
power increases.
It was composed of three wheels, a, b, c, mounted on a plate, eeee, of
two pinions, and a lever d, whose centre of motion, variable at pleasure, was at e; this
lever carried at d a pivot of the wheel b, and rested on a round piece fixed at the axle at the
wheel c.
Supposing the wheel a moved in the direction of the arrow by a variable force,
as that of a spring, the greater the force acting on this wheel, the greater effect this wheel
would have on the pinion of the wheel b; but as this pinion was carried by the lever d, it
carried or drew it towards the point b, and caused its extremity to lean on the round part
of the wheel c, whose friction on the pivots was considerably augmented, which tended to
diminish the excess of force which the wheel c would have when the spring was unrolled.
Suppose the diameters of the
two wheels a and b equal, and we
substitute in the place of the two
wheels c one whose plane shall be
perpendicular to the surfaces of a
and b. The wheel c fits the axle
r; this axle is pierced with an
orifice through which passes the
axle de. The three wheels a, b, c
are retained in their respective
positions by collars made in their
axles d, e,r, which prevent them
from sliding. The wheel c has two
motions of rotation, one round its axle r, the other round the axle de.
angular velocities of rotation of the wheels a, b, and c. If we suppose that a and b turn
in a direction contrary to each other, we shall have v" = (v-v'). We may fix to the
1/2
axle r a ring rnem, whose plane shall be parallel to the wheels a and b, and whose outer
edge shall be circular, or of any other form which circumstances may dictate, and which
may be traced by the principles before developed; by this means we may transform a cir-
cular to alternate rectilinear motion, with any required modification of velocity and direction.
Circular continuous motion with a


uniform velocity, or variable according
to a given law, may be changed into al-
ternate circular, with a constant velocity,
or variable according to a given law, in
the same plane or in different planes.
Fig. 1420. a is a wheel whose sur-
face is furnished with wipers, and which
communicates a circular alternate
motion to the bent level
psr. Where
Fig. 1419.
ม
PLAN.
972
Let v, v', v" be the


there is only one wiper, on the sur-
face of a cylinder may be traced a
groove, and by introducing the extre-
Fig. 1420.
Fig. 1421.
mity of two levers, an alternate motion may be transmitted to four pumps at once, making
one upward and one downward motion.
3B 2
980
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

•
We may deduce the means of tracing a curve
amnp, cut in a groove, and fixed to a lever bb,
which may turn freely round an axle which traverses
its extremity b: if we suppose that the wheel m turns
uniformly round its centre, and the pin p, fixed to
a point at the surface of the wheel o, enters the groove
which forms the curve amnp:
this curve may be
such that the lever bb makes oscillations which fulfil
one of the following conditions.
N
K
m
"
b
Ꮳ
e
First, that the arcs described by any point of the
rule bb should be described with a uniform velocity.
Second, that the velocity varies according to a given law.
Third, that the arc should not be described but
its chord, which should be gone over with a uni-
form velocity, or variable according to a given law.
The curve drawn in this figure may be traced in such a manner as to satisfy the first
of these conditions.
Fig 1422.
Fig. 1423.
We may also fix the curve cdef to the surface of the wheel m, so that the circular uni-
form motion of the wheel m communicates to the lever a b a motion of oscillation which
may satisfy one of the three conditions just explained in the preceding motion, by means
of a pin, p, fixed to a lever which engages the groove. The curve drawn in this figure
answers to the first of these three conditions. The means indicated in this article and that
which precedes are capable of different applications useful in the arts. The circular alter-
nate motion of the lever belongs to this class; but if it is the chord of the arc drawn
on that on which we may fix a rule pierced by a groove, the intersection of this groove
by another longitudinal one made in the lever offers a vacant point in which we may
introduce a point, which may have an alternate rectilinear motion: the thing will happen if
it is the motion of a weight suspended at the extremity of a rule by means of a cord
passing through a pulley.
A cylinder, a, furnished with cams, raises the hammer b, which turns on its axle c;
this is a well-known motion, and requires no further explanation.
a is the extremity of an axle of


b
a great wheel or fly, furnished with
a ratchet-wheel b: cc is a wheel
which fits the axle of the fly; it
carries the catch d, which arrests
the ratchet-wheel by means of a
spring; the circular alternate mo-
tion of the wheel c will transmit
to the fly, whose axle is at a, a cir-
cular continuous motion in the same
direction, but the wheel c will only act during half its oscilla-
tions.
Fig 1424.
There is another application of the preceding motion; p q is
a balance beam with a circular alternate motion, which it com-
It is
municates to the wheel o by means of a cord abcd.
stretched by the weight e, or by a spring: the wheel o fits the
axle h of the fly; the extremity of the axle of the fly is
furnished with a ratchet-wheel, to which a catch g hooks, fixed
in the wheel o: the circular alternate motion of the wheel o
causes the fly to turn in the same direction.
b is a balance capable of an alternate circular motion round
the axle c: d is a rod which turns freely on its axle at c; at
its extremity is a toothed wheel, e, which engages another, ƒ,
fixed to the axle of the fly, n. In the opposite face of the two
toothed wheels e and ƒ is a rod, g, which forces the wheel e to
preserve this same distance from the centre of the axle of
the fly.
The alternate circular motion of the balance b
compels the wheel e to ascend and descend, but it can
only take place when the wheel ƒ turns on its centre; ac-
cording to the form of the machine the motion may be con-
tinuous or alternate, but the inertia of the fly necessarily
renders it continuous and nearly uniform; the reciprocal takes
place when the motion has begun in steam engines this
mechanism is employed, known by the name of the fly: it may
easily be conceived, that notwithstanding the two wheels e and
fare of the same diameter, the fly n should make two revolu-
2
a
C
Fig. 1425.

h
Fig. 1426.
Fig. 1427.
d
a
e

CHAP. XI.
981
MECHANICS.
tions for each oscillation of the balance, which enables us to dispense with such flies as the
ordinary winch would require to produce the same effect.
g
Fig. 1428.
We are indebted to Edmund Cartwright for a motion of rotation communicated
by steam, whose velocity may be increased at pleasure, without the necessity of
any gear-work. The upper part, a b, of the frame which embraces the furnace,
cylinder, fly, and all movable parts of the machine, are
traversed by an axle, on which a pulley, c, revolves, round
which a chain is wound, fixed to the top of the piston rod
t. The pulley, c, is put into alternate circular motion by
the piston and its counterpoise p; this axle is armed with a
winch, which, by means of a lengthened rod, communicates to
a lever ƒ, placed horizontally above, on the side of the furnace.
There is another axle, placed above or below, or at the side of
the first, which traverses the fly g, and which is terminated on
the other side by a winch, which communicates in the same
manner with the preceding by means of the rod, h, with the
horizontal lever, f, just mentioned of. It is evident that
when the pulley, c. is put into motion by the action of the piston, t, the winch which ter-
minates its axle will move that of the axle of the fly, g, because they are both attached to
the same lever, f. If then the pulley moves in the direction from a to b, and from 6 to a, by
the action of the piston and its counterpoise, and if the winch of the axle of the pulley
moves in the same direction, that of the axle of the fly will make the same movements,
unless its length be so determined that at the end of its course it cannot pass
beyond it; the motion of rotation will then take place. If the winch of the axle of the
pulley, c, is so disposed that when it moves in any space not exceeding a complete revolu-
tion, the winch will pass from e to a by f, or in the direction gone over by a given point of
the pulley; then the winch will cause the lever to make two vibrations at every stroke of
the piston, and at the same time the fly, g, will make two revolutions. If the diameter of
the pulley is so proportioned that at each stroke of the piston the pulley will make a revo-
lution and a half, and as much backwards, the lever will receive three vibrations by each
stroke of the piston. If the diameter of the pulley is so proportioned as to make two back-
ward and forward revolutions for each stroke of the piston, the lever will make four
vibrations, and the fly four revolutions.
Ordinary Pedal. If we suppose that the crank of the fly
communicates with the extremity of the lower lever or pedal
by an inflexible rod, the ratio between the constituent parts of
pedal and their play ceases to be indeterminate, as they are to a
certain point when we employ a flexible body. In fact, if we
suppose that we have given, first, the length of the lower lever,
secondly, its centre of rotation; thirdly, the value of the angle it
should pass over at each oscillation; fourthly, the position of the
centre of the fly relative to the centre of rotation of the lower
lever; the length of the crank, and that of the inflexible rod, are
determinate quantities. To find their value, place the pedal,
properly so called, viz. the lower lever, in its two positions, the
lowest and the highest, and draw two right lines from the centre
of the fly to the extremity of the pedal; the first of these two
distances is known, and it should be equal to the length of
the inflexible rod, minus the length of the crank. The second, also known, should be
equal to the sum of these two quantities; consequently the inflexible rod, which should
be greater than the crank, is equal to half the sum of the two distances between the
centre of rotation of the fly and the extremity of the pedal in its two extreme positions, and
the crank should be equal to half the difference of these same distances.


Fig. 1429.
If we suppose the angular velocity of the pedal uniform, that of the fly will be variable
in all its points: but these inequalities become less sensible in proportion as the angle gone
over by the pedal or lower lever is less, and the greater the distance between the centre of
the fly and that of the rotation of the pedal.
Quadrature of the Pendulum, which marks the true time,
invented by the Vicar of St. Cyr. The angular wheel o
carries a curve of equation bed; on the breadth of this curve is
cut a groove parallel to the edge of the curve; in this groove
a button i slides, adapted to the piece ef, movable at the
point e; this button also holds a second piece attached to the tube
which carries the minute hand g, in such a manner that it follows
the vibration of the curve over more than half the circumference
of the dial minutes, and is sufficient to mark the inequalities
which show the equation.

3 & 3
Fig. 1430.
982
Book 11
THEORY AND PRACTICE OF ENGINEERING.
a
a
g
g
to
a
m
n
d
Fig. 1431.
a
An invention of Breguet as applied to an equation clock,
is composed of two parts, one fixed, the other movable. The
fixed part is the plate o, held by four screws; it is cut out in
the form of an equation curve.
The movable part is composed
of a plate gg, having its centre of motion at c. It carries a
balancing rod, whose centre is at b; its two extremities c and
d lean, the one, c, against the edges of the curve, the other, d, on
the prolongation of an indicator or needle e, which has the same
centre of rotation as the plate gg. The prolongation of the needle
is maintained against the extremity d of the balance, by means
of a spring o screwed to the plate gg; the needle n is fixed, and is concentric to the
same plate; the movable system is carried by the plate gg, which makes a complete
revolution in a year. It may be conceived that the needle n, which is fixed to the plate,
may indicate the days of the year, provided it is placed on a dial divided into 365 parts.
The needle e, it appears, ought to go over the same space in the same time, which never-
theless is not the case: when the lever c leans on the part of the curve most distant from
the centre, the needle e should be behind n a certain number of divisions; when on the
contrary the arm leans on the part m, which is nearest the centre, the needle e will pre-
cede n by a certain number of divisions. This difference of motion of the needle n from
the needle e is produced by the lever cbd, which leans on the curve of the plate o, and
this curve is such that it causes the needle e to gain or lose on the needle n by a certain
number of divisions, equal to that of the minutes by which the true time differs from the
mean time at the date of the days which the needle n indicates.
Ratchet Lever, invented by Garousse. The
circular alternate motion is changed into
circular continuous without the reciprocal
taking place: the stirrups a,b,c,d, movable
on the points a,c, are so disposed that the
lever, by an alternate continuous motion, forces
one to draw the ratchet-wheel continually
towards it, whilst the other escapes the tooth
it had taken, and engages another.
author applies his lever to a machine for
driving four corn-mills at once.


The
Lever with a toothed Wheel, invented by
Garousse; a modification of the preceding.
b
a
Fig. 1432.
d
d
Fig. 1433.
The great lever a has its fulcrum at c; above and below are two claws or feet d, e,
movable round their pivots; each of these claws leans on one of the staves of the lantern
b. The circular alternate motion of the great lever will produce the circular continuous
motion of the wheel b; if the axle of the wheel b be enveloped with a cord, a con-
tinuous rectilinear motion will be produced.
b is a species of pendulum attached to
a horizontal cylinder, which serves to im-
press on it a circular alternate motion; the
two catches n,o are adapted to its surface
at its two extremities by hinges, and en-
gage the opposite teeth of the wheel st,
cut in a ratchet shape, by communicating
a continuous circular motion to it, when
the power acts without interruption: this
has been employed in the construction of a
machine for drawing loads: a modification
of Garousse's lever, but inferior to it because
the power does not act continually, is shown
in this diagram.

Fig. 1434.
a is a wheel toothed upon its edge, partly horizontal; b and
c are two toothed wheels fixed to the axle de; their distance
should be equal to the diameter of the wheel a. It is evident
that the toothed part of the wheel a, which is always less than half
the circumference, will engage alternately the wheels b and c, and
will communicate a circular alternate motion to the axle de.
Fig. 1435.

¿
d
a
In calculating the numbers for the movement of machinery, we
must remember that a wheel divided by its pinion shows how
many turns the pinion has to one turn of the wheel; and in that
of a watch, from the fusee to the balance, the wheels drive the
pinions, consequently these latter run faster, or make more revolutions than the wheel;
but the contrary is the case from the great wheel to the dial wheel.
Fig. 1436.
CHAP. XI.
989
MECHANICS
k
Recoil Escapement, invented in 1680 by Clement of London.
The escapement wheel bb receives from the mover a circular
continuous motion, which makes the sides of the teeth perpendi-
cular to the sides of the wheel advance, and transmits this mo-
tion to the lever or pallets carried by the vertical axle k, to which
the balance wheel is fixed. The alternate motion or vibration of the
balance wheel is here produced by the action of the wheel bb on the
pallets of the axle of the balance-wheel; they form together an angle of
about 90 degrees, in such a manner that when one tooth of the
wheel has escaped the pallet k, the other pallet presents itself to a tooth
diametrically opposite, which in its turn escapes, so that the wheel
always turning in the same direction gives vibrations which regu-
late and moderate the velocity of the wheel bb, and consequently of the system.
Dead-beat Escapement for Seconds Clocks, invented by Graham. The
piece which forms the escapement is like an anchor, but with this
difference, that the pallets of the anchor are so constructed, that
they do not cause any recoil, and in consequence this escapement
is a dead beat, by means of portions of circles formed on the pallets,
corresponding with the inclined planes which produce the impulse or
action which maintains the motion of the pendulum.
Graham's dead-beat escapement, employed in pendulum clocks, being
executed with required care and precision, is one of the most perfect
which can be used in these machines, especially by making the pallets
of rubies, as some have done.

Fig. 1437.

Fig. 1438
The following is the manner in which the escapement acts: suppose the part a just
escaped, b receives the shock of the ratchet tooth; the vibration being finished, the
pallet buries itself in the tooth without touching it, the vibration returning; the ratchet
wheel remains immovable, and only acts when the inclined plane presents itself to the point
of the tooth: for this purpose the tooth acting on the plane obliges the pallet to escape,
and in escaping the tooth c falls; it strikes the circular part of the pallet a, and is retained
until its inclined plane presents itself; the tooth of the ratchet then ceases to be immov-
able, but follows the inclined plane of the pallet, and in escaping restores motion to the
pendulum.
Cylindrical dead-beat Escapement for Watches, invented by Gra-
ham. a is an escapement-wheel furnished with an inclined plane b;
these inclined planes should be raised on the plane of the wheel; the
balance-wheel is carried by a cylindrical axis, one part of which is
hollowed, as at c; the inner diameter of this hollow cylinder is equal
to the length of a tooth, and can turn nearly one revolution round
it it will be seen by this description, that the balance-wheel coming
from a towards c, remains in repose; and when the point a arrives
at the extremity of the inclined plane b, the latter transmits the action
of the wheel to the balance-wheel, and leans against the inner part
c of the cylinder: the wheel still remains in repose; the balance-
wheel returns in an opposite direction, again receives the action of the same inclined plane
on its leaving c, and the following tooth leans on its outer part in the same manner as the
preceding, and so in succession.
Dead-beat Escapement with Pins, by Ament, Clockmaker at
Paris. This is composed of a plain wheel in which a row of
pins is fixed; the pin quitting the pallet a, that of b receives the
shock of the escapement: the vibration continuing, the pallet b
remains still, and the wheel rests immovable, which causes the
second hand not to recoil; the vibration returning, the pin
acting on the inclined plane restores the motion.
Escapement with free Vibrations, Arnold's Principle. c is the
escapement-wheel, d a cut piece fixed to the axle of the balance-
wheel, t a small salient point fixed also to the same axle, n a
spring whose centre of motion is at r; this spring tends con-
stantly to approach the wheel c, and stops its motion by
the salient part m: at its extremity a point p rises; the spring
nm is furnished with another, extremely delicate, s, whose centre
of rotation is at r.

•
t
Fig. 1439.

Fig. 1440.

Fig. 1441.
m
n r
Supposing the balance-wheel turning the point of its axle
will meet the extremity of the spring s, and will pass beyond,
only experiencing a very feeble resistance; but on the contrary
oscillation, the spring will meet the obstacle p, which is at a very slight distance from
its extremity, and instead of bending at r, it obliges the spring nm to turn round n, and
3 R 4
984
Book II.
THEORY AND PRACTICE OF ENGINEERING.
consequently it allows a tooth of c to escape; at the same moment another tooth of the
wheel c strikes the hollow of the piece d, and restores to the balance-wheel its lost force;
thus at each double vibration of the balance-wheel, the point of the spring nm allows a tooth
of c to pass, and the balance-wheel receives a new impulse.
e
b
Escapement with free Vibrations, by Berthond. a represents the
escapement-wheel, bc the catch; the pin of the catch suspends
the action of the wheel, whilst the balance-wheel oscillates freely :
the spring d serves to restore the catch as soon as the pallet c has
escaped the arm b: at this moment a tooth of the wheel a acts
on the roller carried by the regulator, and transmits its force to
maintain the motion of the balance-wheel; the latter having
finished its oscillation returns, and in returning the pallet c
meets the end b of the catch; but it yields in escaping this arm,
and approaching the centre of the circle most distant from b, the spring e restores it, to
engage it again when the balance-wheel has finished its oscillations, in such a manner that
in returning this pallet c presents itself afresh to the arms of the catch to disengage the
wheel, and give a new impulse to the balance-wheel.

Fig. 1442.
Breguet's ascending Escapement. a is a metal plate on which the whole of the escape-
ment is fixed; to understand its mechanism thoroughly, we must divide it into three parts,
of each of which we shall describe the
separate play, and then their reciprocal
action.

G
a
i
H
k
First part; this is composed, first, of the
wheel band of C, united together; the
wheel b is submitted to the action of the
primitive mover by a system of wheels
which tend to turn it in the direction bed.
Secondly, of a pinion g which engages the
stopping-wheel b, and which has a number
of teeth equal to those of the stopping-
wheel, which corresponds to the space be-
tween two consecutive teeth of the wheel
C; by this means the pinion can, at each
of its revolutions, be opposite one of the
teeth of the arming wheels: the axis of the
pinion carries a fly igh; the branch gi of
this fly is shorter than the other gh, at the
extremity of which a small piece of steel is
fixed. Thirdly, of a stopping spring rr F,
at right angles to the direction of the fly
fixed at its extremity rr, and in which at
about two-thirds of its length there is a ruby,
V, which may also be made of any precious
stone or of tempered steel. In the state of the machine represented in the figure, the ruby
leans against the extremity h of the fly; it there performs the office of a stop, which pre-
venting this fly from moving in the direction that the pinion g solicited, by the wheel BB
causes it to turn, thus suspending the revolutions of the wheel, and consequently the
action of the mover; but if any cause makes the spring rr F to bend on the side of the
pinion g, at the instant when the ruby V is opposite the notch, which is at the extremity h,
the fly will escape and make a revolution, and if at the end of this revolution the spring
rr F has assumed its first position hi, it will stop against the ruby V, and go no further.
Fig. 1443.
Second part is composed, first, of a spring G of impulse curved at its extremity;
this spring is the piece which serves to restore the power to the regulator at each
oscillation: it carries a catch or iatch m, in which is a small notch with a ruby p on its
exterior surface; this catch and the ruby serve, with the power we have just described, to
stop the pulsion-spring when it has been bent by the arming wheel C, which transmits
to it the action of the primitive mover. Secondly, of a grappling spring a H, fixed at its
extremity a, on which an extremely weak spring n is attached; the spring H carries a
ruby p, intended to enter the notch m of the catch m, and to fix this spring when it is on
the stretch: another ruby placed on its extremity s retains the spring n in such a manner,
that the end of this spring pressed from right to left opposes only a very feeble resistance,
and pressed from left to right gives back to the ruby s the whole effort which it experinces,
and making the spring H bend, disengages the ruby p from the notch of the catch m.
Third part consists of the pieces k, b, carried by the upper extremities of the axle of the
balance-wheel, and which are placed at a distance of a quarter of the circle from each other;
when the oscillation of the balance-wheel is from right to left, or in the direction bk, the
piece k makes the spring bend and passes beyond; and as the piece b is placed above the
CHAP. XI.
985
MECHANICS.
plane of the stopping-wheel band, below the spring H, the oscillation from right to left will
be easily accomplished, and without any other obstacle than the flexion of the spring n;
but when the balance-wheel makes an oscillation from left to right in the contrary direction,
the pin k drives the spring n against the ruby s, the spring H bends, the ruby p disengages
itself from the catch m, and the spring G, abandoned to itself, produces the effect which
we shall now describe.
It may easily be seen by the preceding description how the moving power is re-
stored, and the motion perpetuated: at the instant when the ruby p of the spring H is
disengaged from the notch of the catch m of the spring G, and when this spring G is free,
the straight part of the lever b is perpendicular to the direction of the motion of the
extremity q of the spring g which has struck it, and also restored to the balance-wheel the
force which is necessary to finish its oscillation; immediately after this first percussion the
same extremity q strikes the end F of the spring Frr, bends it, and drives the ruby against
the notch of the fly ih; the latter then becomes free, and the primitive moving power which
acts on the wheel BB, and by means thereof on the pinion, makes it describe a revolution,
at the end of which, finding the spring Frr at its first place, it again stops against the ruby
v; but during this revolution a tooth of the wheel DD has pressed on the tooth n, which
is near the extremity q of the spring G, and it has consequently forced it to return back-
wards: continuing to act according to the proportion established between the teeth of B
and D, until the ruby ƒ of the spring H is again disengaged in the catch m; all then
returns to the state represented in the figure.
da
h
ni
n
M p
g
D
Fig. 1444.
R
m
Another Escapement by Breguet: a is the movable part which tends to go from right
to left, in the direction of the arrow; b a wheel with six curved teeth, fixed on the
same axle with the wheel a, but placed at the opposite ex-
tremity of the axle; c a pinion which engages the wheel a, and
which should make six revolutions for one of the wheel a;
fly which fits the axle of the pinion, and which, by means of a
strong spring which presses it, allows it to continue its motion
when the pinion is suddenly stopped; e a wing or small cross-
piece of steel, fixed on the axle of the pinion c, and which leans
against the stopping-piece g, which can turn on the pivot v ;
is the axle, which carries three pieces essential for the escape-
ment: first, the piece i, which on one side is cut in the form of
the curved tooth k, and which on the opposite side has two
notches to form two ratchet teeth; the first of these two
notches serves to stop the motion of the axle, by means of the
stopping piece l, and the second to give impulse to the pen-
dulum when the axle is entirely free: secondly, a pin or small
roller, o, fixed in the piece i, to raise the stop g: thirdly, a little
weight, n, which by means of a screw may approach or retire
from the axle to regulate the force of impulsion which the
pendulum should receive, following the arc which it is required
to describe in its oscillation: 7 the stopping-piece, which may
turn freely on its centre, which is fixed to the frame of the
wheel-work: II a parabola of the pendulum suspended at its upper part: mm a piece
of copper fixed to the pendulum bob: M a small light lever, which on one side turns
on its pivot i, and on the other leans on a pivot l; it carries a small salient edge, m,
which serves to unhook the stopping piece l, and to leave the motion of the axle h free: n
is the edge on which the pendulum receives its impulsion; its elevation should be such
that it may easily pass behind the stopping-piece 7, and have a part engaged in the thick-
ness of the piece c; its height or lower part should in its motion graze the end of the tooth ƒ
without touching it. The mover tends to turn the wheel A; the cross-piece E is stopped
by the piece F; if we suppose that the bob makes its oscillation from right to left, the
salient edge, m, of the little lever, M, will touch the end of the stopping piece l, and
will unhook the tooth e, at the same time that the edge n presents itself to the im-
pulse tooth f. The axle G being entirely free, is driven by the weight of the tooth d, as
well as by the little weight h, to turn from right to left, as its motion is more rapid than
that of the pendulum, it arrives at the edge n, and gives it an impulse; the tooth
ƒ elevates itself in its motion: the axle G continuing its motion, the pin g touches the tail
of the stop F, and leaves the fly D free, at the same time that the tooth d presents itself
before the tooth p, while the fly makes a revolution; the tooth p acting on the tooth d, con-
ducts the axle D to its first position; the piece F presents itself to stop the fly, and the
stopping-piece H enters the notch e to stop the axle G; the pendulum going from left to
right, finds no other obstacle than the head of the stopping piece H, on which it touches
the edge m; but being both cut in inclined planes the lever m rises, and then falls into
its first situation. This is the most perfect manner of re-establishing the force which a
pendulum loses in its oscillations.

986
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Let de be the crank of the axis of rota-
tion d; this crank is equal to half the
chord of the arc abefg; an iron rod
suspended at f to another fh, which turns
round the point h, while the point e of
the crank goes from 1 to e, from e to m,
and from m to n; the point ƒ of the rod
hf goes from i to f, from ƒ to s, and from
s to k: consequently ki should be equal
to n l. The shuttle should pass over the
arc ab in the same interval of time; the
distance ai is divided into two parts, ir
and ra; the part fg of the rod eƒg equal
tori, and another rod gp, equal to ar,
which is placed as the figure indicates, in
such a manner that its extremities can
turn freely at g and p of the rod efg, and
of the radius cp of the shuttle; the latter
will pass over the arc ab with a velocity

b
q
p
d
a
Fig. 1445.
whose variations will depend on the ratio between ƒg and g p.
a
[1812MMAN
m
b
Let ab be an axis which receives from the mover an alternate circular motion ;
n and m two wheels fixed to the axle ab, both together,
but placed in opposite directions; c, d, and e are three
toothed wheels, the two first having two equal diame-
ters, which turn freely on the axle a b, and carry the two
catches p and q, engage the third e, whose axis is pro-
perly supported; the axis a b, by its circular alternate mo-
tion, will act successively on the two wheels c and d; they
will soon assume a circular continuous motion, and as this
takes place in opposite directions, the wheel e will
always turn in the same direction; thus the circular
alternate motion of an axle or wheel may be transformed into a continuous circular mo-
tion of another axle or wheel, the second being perpendicular to the direction of the first,
and the plane of the second also perpendicular to the plane of the first.

α
Fig. 1446
b
Let ab be the axis corresponding to one of the two cylinders, For G; c, the counter-
poise; no the axis of rotation of the vertical rod, which sustains the counterpoise; q a rod
perpendicular to the vertical rod and the axle; tsr the axle of the small machine: nothing
is easier, as we have said already, than to cause the rod rs
to make a single revolution round the axle de, whilst the axle
ab makes any number of revolutions we please: now sup-
pose that the axle rs elevates itself, the counterpoise c
would find itself in the vertical which passes through
no; an instant after it will fall to p; the motion of rotation
of the axle ab will change its direction; the axle sr will
also turn in a contrary direction, and meet the rod q above,
drawing it from above downwards, and make the counter-
poise c pass towards v

The
q
Fig. 1447.
Sep
A
P
E
M
Suppose the axle A B terminated by a square rod, gh, which fits freely an opening
made in the centre or the pulley G, sustained by a collar, provided its motion of rotation is
not affected; the movable screw m is furnished with a fork or lever, an endless cord
embraces the axles m, n, and the pulley
G, by means of the pulley H.
circular motion of the axle mn is then
communicated to the pulley G, and con-
sequently to the axle A B; this axle in
turning will mount or descend freely, if
we suppose that the screw m mounts;
the lower branch ml of the fork will
meet the lever og of the counterpoise
P, and will cause this counterpoise to
fall towards the right of the plane of
the figure. The axle mn will at the
instant take a motion in a contrary
direction; the screw m will descend,
and the upper branch ik of the fork will
meet the lever oq, and acting on it will


Fig. 1448.
ก
Fig. 1449.
conduct the counterpoise, and will make it fall on the other side in the time given.
B
CHAP. XI.
987
MECHANICS.
The mechanism may also be employed in the general
solution of the problem, without a counterpoise. Let ab
and cd be two axes, each furnished with a pulley and
a toothed wheel; an endless cord embraces the pulleys, and
communicates the circular motion from one to the other,
making them turn in contrary directions, because they cross
in the intervals which separate the pulleys. Let ef be another
axle furnished with a toothed wheel; this axle may approach
the axle ab or cd, because its gudgeons are enclosed in oblong
orifices. It will then suffice to bring it near sometimes to the
axle ab, so as to engage the wheel c with the wheel b; some-
times the axle CD, so as to engage the wheel c with the wheel
b, to render its motion circular alternate, supposing that of
its axle ab and cd circular continuous.

Fig. 1450.
e
Circular continuous motion with a uniform velocity, or vari-
able according to a given law, may be changed into a motion of
a given continuous curve re-entering in itself and closed, with a
velocity of the same nature as that of the motion which produces
it, constant or variable according to a given law, in the same plane or in different planes.
Let ƒ be a given curve: it is required that a point of a crayon
or any other tool may draw this curve on a surface pq by
means of the circular continuous motion of the wheel d
Take three toothed wheels a, b, c, of any convenient size:
place them as indicated in the figure, that they may receive
their motion from that of the wheel d: mm, p q are two rules
which move alternately, preserving their direction by means
of guides or bridges eee; they are terminated by two per-
pendicular rules, each pierced with a groove; the crayon or tool
which traces the given curve is placed at the intersection
of the two grooves.
On the given curve take any number of
points, which must be most numerous in the places where the
changes of the curve are most rapid.

Q
.b
a
Fig. 1451
P
Draw on the surfaces a and c the proper curves, which should
be such that the extremities of the rods lean on the curves, drawn in relief by means of
a spring or otherwise: the intersection of the grooves where the crayon is placed goes
over the points selected, which operation does not present any difficulty.
The object proposed by this problem is not to make a point,
such as the extremity of a tool, go over a certain curve, but to
trace this same curve on a given plane surface; for this effect
fix the surface a to the extremity of the rod b. By this means
the surface apparently immovable will receive an alternate rec-
tilinear motion; having fixed the crayon or tools to the end a of
the other rod, cd, draw convenient curves on the surfaces e and
f, and we shall have a machine susceptible of useful application in
the arts.
Second general Solution of the Problem. The points of a given
curve may also be subjected to angular co-ordinates: these curves
are of two kinds, first, those enclosed in the interior, in which we
can find such a point that all right lines passing through it can
only meet two points of the curve: secondly, curves closed in
the interior, in which we cannot find any point which has this pro-
perty; we can without any difficulty draw curves of the first kind
by circular continuous motion. We have in this simple ma-
chine an auxiliary wheel conveying its movement to two others
on the same axis; the rosette d is attached to the first wheel b,
which touches nn, fixed to the regular movement, resting on its
edge by means of a spring, b, which acts on the extremity of the
rule in the movable branch pq, and at the point q is a pencil,
which may be placed at pleasure on any point whatever of the
surface on a circle of paper placed on the surface c.

C
Fig. 1452.

You
n
We must always bear in mind that among the machines ap-
plied to useful purposes, there is scarcely one in which there is
not a deviation from a uniformity of action, either from the
nature of the impelling power, or the method by which it is ap-
plied, besides a desultory motion, which arises from the construc-
tion of the machinery; these peculiarities have been ably noticed by Desaguliers.
Let abd (fig. 1456.) be the given curve, and take in its interior any given point c for the
centre of the circular motion of the rule pq, which turns in the same direction, whilst the
Fig. 1453.
988
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
rule ef slides on pq; whilst the point f traces the given curve, the extremity e traces another.
abd, and the reciprocal takes place. The length of the rule ef being arbitrary, we may
substitute for it the rule d't', and we shall have another curve a'b'ď, which also satisfies the
condition of the problem: we see that it is capable of an infinity of solutions, all extremely
simple: we must take care not to place the centre c in the direction of any element
of the given line, to avoid too sudden motions of the rule ef.
The curves of the second kind offer some difficulties. Let a, b,d be the given curves; we
do not at first see the general means of satisfying this problem, whatever be the position



q
Չ
S
¿
d
m
T
ૐ
e
C
Fig. 1454.
P
Fig. 1455.
l
p
d
Fig. 1456.
we have chosen for the point c; the circular motion of the rule pq being continuous,
while the rule ot is in its direction, its solution becomes impossible; but a very simple
observation will enable us to solve it. Suppose OT, instead of being in the direction pq,
makes with it a constant angle cot, if whilst pq passes the position p'q' the point o ap-
proaches the centre, and places itself at o', the point t will pass to t', and have experienced
a retrograde motion relatively to that of pq.
A wheel a conveys its motion to two others, b, c, which in the lathe are on the same
axle; the rosette d is attached to the first wheel b, the tool nn is attached to the movable
rule pq, leans on its edge by means of a spring b, which acts on the extremity p of
the rule, in the movable branch pq, and at the point q is a pencil, which may be placed
at pleasure at any point of the surface of a circle of paper, placed on the surface c.
"
N
b
abc is a rule 3 inches long, pierced with a groove, throughout its whole length;
the port ab has several screw holes, in order to bring the point b nearer or further,
whose head is a screw; this rule is held by the tenons
e, g of a second rule; the first may slide on the second, which
carries a small barrel, the spring of which always draws the
lower rule towards it, which is attached with a pin or
fillet d. This same rule carries a second point n, which
always tends to approach the centre p; this centre is deter-
mined by a third point p, which traverses the two rules, and
is fixed to the upper eg, at any point with the screw z.

7
Fig. 1457.
It is required to find the most convenient rosette for the
contour of the head t. After having cut out this profile in
card, glue it to another card, rr; then take at pleasure any point t for the centre of the
contour of the head; pierce the two cards in this point, and attach them to a plane, by
driving the point p through; after having placed the point n on the contour of the head,
turn the whole machine with the hand, making the point n always touch the contour of
the head or turn the card on its centre, holding the machine fixed with the other hand,
taking care that the point n does not leave the edge of the contour.
In both cases the point b on the great card rr, draws the figure x, which is the
contour of the required rosette. The point n is always drawn towards the centre`p by the
effort of the spring, and driven back by the relief of the profile; it easily follows the
contour, while it does not leave the centre in a right line, which must be avoided as much
as possible, by selecting a centre within the contour for fixing the point p. If we can-
not prevent the point h from being arrested at some place, as for example below the nose,
and that the contour has the curve too stiff to drive back the point n, it must be aided
by the hand; but this inconvenience may be avoided by turning the card in the opposite
direction; in this manner the point, which cannot ascend without the assistance of the hand
from the nostril towards the nose, will slide without difficulty, and by the force of the spring
will be drawn from the point of the nose to the nostril; by changing the centre p, or by
taking the two points b and n further off, different contours may be made, the most flowing
and most practicable on the lathe, to serve the model for the rosette. Before cutting
it out, it is as well to verify it by cutting out in card the figure vr of the rosette, and
making the point go over the contour, to see if the other point n will describe exactly the
contour of the head t, which it is proposed to execute.
CHAP. XI.
989
MECHANICS.

Let an, bc be a system of toothed wheels, whose dia-
meters are in the ratio of the numbers 2 1, 2 4. Let
a'b' be a rule, whose extremity a is successively fixed at the
points 0, 1, and 2 of the wheel a, and subject at the same time
to touch one of the points ac of the wheel n, and O and 1 of
the line b. These points being placed in such a manner that
they may be found in the same direction in one position of
the system, each point of the rule a'b' will draw one curve in
space, and another on the surfaces of revolution, which are
below it.
To draw a cylindrical spiral in space, or what is the same
thing, to draw the helix of a screw. ab is a fixed axle to
which is attached the cylinder c, on the surface of
which a helix is to be drawn, and the toothed wheel d.
mlkn is a frame turning round the axle ab in its branches;
lmkn is an axle ƒg, which revolves on its own axis, and is
furnished with a toothed wheel e, which engages d, and a
cylinder, hi, cut into a screw with the nut p, which at one
end carries the rod op, whose extremity o enters a vertical g,
going from one side to the other of the frame, and the other
carries a pencil or tool.
a!
m
n
h
→
Fig. 1458.
е
C

เ
k
Fig. 1459.
n
Let a be the radius of the wheel e; b the radius of the wheel d, and d the thread of the
screw on the surface of the cylinder hi; if we make the frame lmkn perform a revolution
round the axis ab, the wheel e, and consequently the cylinder hi will have made a portion

b
of a revolution round their axes, and
-
a
the tool will have gone over a space
db
equal to which will be the thread
α
of the screw, drawn on the cylinder c.
To this quantity any value may be
given, by changing the ratio of a to b,
or that of d, by the substitution of
another guide hi.
d
e
a
h
e

i
Fig. 1460.
fg is the cylinder which directs the
rectilinear motion, and communicates
it to the tool, by means of its nut p. It
turns on its axle, and its position is de-
termined by the collars h and i; e is a
toothed wheel fixed to the directing
cylinder, c the cylinder required to be cut into a screw; it is
mounted on a lathe, and furnished with a toothed wheel a;
the two cylinders c and ƒg should be placed in such a manner
that their axes are quite parallel: a is a third wheel, which
serves as an intermediary to engage two wheels d and e; it
may be elevated and balanced in order to suit itself to all the
changes which circumstances may require in the wheel d to
change the ratio of the radii d and e. If the proportion is so
great that the invariable space of the machine between the
distance of the axes of the two cylinders does not permit us
to obtain it by the two wheels d and e, and that it is not possible
to change the directing cylinder, we may avoid this difficulty
by substituting for the wheel a another wheei and pinion.
We may substitute for the direction screw a rack whose
rectilinear motion may be engendered by that of the cylinder
which we wish to cut into a screw; the result will be the same,
but perhaps the machine does not combine the same advan-
tages as that just described.
A small machine for drawing an ellipsis. A circular
plate of wood a, and of a greater or less diameter, has its
surface ploughed by two grooves m, n; in these grooves move
easily two pieces b and c; in the middle of each of these
pieces a small cylinder or point rises; these points enter cir-
cular orifices pierced in the rule bd, one at its extremity b,
the other at a greater or less distance from it; we place the
pencil at any point of the rule cd, and turn it round its two
Fig. 1461.
Fig. 1462.
e
b
a
Fig. 1463.
P
η
es


990
Boor II.
THEORY AND PRACTICE OF ENGINEERING.
centres of rotation, which move in the same time; the pencil will have an ellipsis whose
dimensions and eccentricity we may vary at pleasure.
d
p
30
น
m
b
14
An Hygrometric Machine. Suppose that the hygrometric
effects act immediately on a rack ab, by communicating
a slight alternate rectilineal motion; the axle a is furnished
with a toothed wheel b, and a pinion c; it is placed in
such a manner that the pinion c engages the rack ab, conse-
quently the slight alternate rectilinear motion of the latter
will be transformed into alternate circular, whose effects will
be the more sensible, as the diameter of the wheel b is greater
than that of the pinion c: the axle nm carries the circle pq,
and the latter the index which should mark the degrees of the
humidity of the atmosphere, or the hour on a helix drawn on
the surface of the column, which should be properly divided:
the axle nm has two very distinct parts; one, nr, is cut in a
screw, and enters the fixed frame f; the other, rm, is a square rod which slides freely in an
opening of the same form, made in the toothed wheel in the centre; this latter engages
the wheel b; it is sustained by its edge xx, which rests on the cross piece de; the circular
alternate motion of the wheel b will be transmitted to the wheel tu; consequently the
axle nm, and the index, will have the alternate compound motion which the proposed
object requires.

Fig. 1464.

Fig. 1465.
k
The Geometric Pen is fixed to a table by means of sup-
ports, a,b, and c; the heads a, a, of two of these supports,
turn round a common axle, in order to be placed in the
same plane with the third, and for packing conveniently
in a box when the instrument is out of use. At the lower
part of the axle d, which is immovable and forms one body
with the support c, is fixed a toothed wheel i, which may
be changed, but which when it is in its place forms a part
of the axle d, and like it is irnmovable: eg is a metal rule
open throughout the greater part of its length, whose extremity
e is engaged between the piece k and the wheel i, in such a
manner as to turn freely round the axle d: a box b is disposed
to slide along the rule eg, and to fix itself in any place; this
box carries a second toothed wheel h, which may be changed
at pleasure, and which may, according to the place of the box
b, engage the wheel i immediately, or receive its motion by the intervention of another
toothed wheel, as in the figure: the axle of the toothed wheel h is fixed to a tube ¿, which
belongs to a lower box c; a rule de runs in this box, and carries at its extremity a pencil
k, which draws on the paper any required curve; this pencil approaches or retires from
the axle of the wheel h, by means of the facility of making the box c correspond to any
part of the rule de. It is clear if we turn the rule eg round the axle d, the toothed
wheel h will have a total motion of translation round the axle d, and a particular motion
of rotation round its own axle; the ratio of angular velocities which these two motions
bear will depend on the intermediary toothed wheels, and on the relation between the
respective number of their teeth: the box c and the pencil k will have, besides the total
motion of translation round the axle d, a special motion of rotation in common with the
wheel h, and the curve which the point k will describe will depend on the ratio of the
before mentioned angular velocities, and on the ratio between the radii db and bk. These
ratios may be varied at pleasure, either by employing different combinations of toothed
wheels, or by making the boxes correspond with different points of their respective rules.
a is a square plate, b a cylinder fixed to the plate a; its circumference
is grooved like that of a pulley: cde, fg, are two cords which enve-
lope the cylinder b in opposite directions, and are terminated on either
side; at a and d, where they are attached to pins in a fixed rule, and
on the other side at e and ƒ, where they are likewise attached to the pins of
another rule parallel to the first, which moves freely in the direction of its
length; if we communicate to the latter rule an alternate rectilinear
motion in the direction of its length, the square a will have a similar motion,
but will turn at the same time on the centre of the cylinder b; each point
of its surface except the centre will trace an epicycloid: it is applied to
polishing glass.

b
d
Fig. 1466.
In wheelwork, where the axis is immovable, and the body turns con-
tinually in the same direction, each point traverses a complete circle during
each revolution of the body round its axis; where this does not occur, the motion is either
alternate or reciprocating; where the former is constant and regular, it receives the term
of oscillation or vibration.
CHAP. XI.
991
MECHANICS.
k
2
h
n
Fig. 1467. aa is a fixed rule furnished with a row of pins, bb
is a bent axle, cd a rule whose extremity c is engaged between
two pins of the rule a, while its extremity d, terminated by a ring,
enters the bent part of the axle bb, in such a manner, that when
this axle turns, the rule cd has a motion composed at the same
time of rectilinear and of circular alternate: by this compound
motion each point of the rule cd draws a curve, which is more or
less of a long heart shape, whose point is always towards the
fixed rule aa: n is a square plate furnished with a ratchet-wheel ;
this piece may be fixed to any point of the rule cd, and ought to
turn freely round an axle which passes through the centre of the
ratchet-wheel: fg is a piece known by the name of wolf's
teeth; this wolf's tooth is terminated by a ring which fits the
bent axle b, traverses another ring ƒ fixed at the point of the rule
cd; and this ring being movable around its axle allows the wolf's
tooth to oscillate round the axle b in such a manner, that at each
turn the wolf's tooth makes a double oscillation, and is terminated
at ik by a curve constructed in such a inanner, that when the ex-
tremity d of the rule cd is in the point of its course most distant from the pins, between
which its other extremity c slides, the extremity k of the tooth will have given to
the wheel n a slightly circular motion round its centre; after having engaged one of the
teeth of its circumference, the same effect should be successively reproduced at each revo-
lution of the axle e, by the action of the wolf's teeth on the other teeth of the ratchet-
wheels. It is used for polishing glasses.

с
Fig. 1467.

Continuous motion according to a given curve with a uniform velocity, or
variable according to a given law, may be changed into a given curve, with
a velocity of the same nature as that of the motion which produces it, con-
stant or variable according to a given law, in the same plane or in different
planes.
Fig. 1468. Pantograph by Langlois. - By its means we draw all
kinds of similar figures, changing its size at pleasure with velocities
whose ratios are given.
M
G
Fig. 1468.
S
A
D
Р
L
T
K
Fig. 1469. Another method: let M G be a portion of the axle com-
prised between the two puppets c,p,
which it is required to cut; we sup-
pose that the part A G of its prolong-
ation is cut in a screw shape; this
prolongation of the axle M G is sus-
tained by the puppet q: the screw
MG enters the niche S, and cannot
turn the rule; AB is conducted by
the nut S, which turns freely round
the point a; it has a horizontal slit
mn, in which the fixed cylinder c
enters; the rule CD slides between
the openings practised in the three
puppets r, p, and qi it carries the
tool K, and the perpendicular branch
LG, from one of the points of
which a small cylinder a rises,
which enters the slit mn of the rule
AB: if we turn the axle a, the
nut s will proceed towards G, and will
draw with it the bar CD, consequently
the tool K will have a velocity which
may be varied at pleasure.
Fig. 1470. Machine for cutting
Screws. A, the cylinder to be cut
into a screw; it is sustained by two
puppets F and G; it is terminated
at A by a toothed wheel C, and the
power which turns it is applied at its
extremity A. The axle B is per-
pendicular to the cylinder A; it is
sustained by the two puppets H and
I, and carries a toothed wheel D, which
engages the wheel C; the part gh of

Fig. 1469.
T
G
B
a

b
H
α.
e
k
D'
L
с
9
B
C
Fig. 1470.
A
M
E
F
d
992
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
•
the axle B is cut in a screw shape: E is an iron bar, in which the cutter M slides
freely; this bar has the form of a square or triangular prism, it is sustained by two
puppets F and G: abcd is a large and deep mortice practised on the plane which
sustains the puppets F, G, H, I: efbd is a rule whose thickness is equal to the depth
of the mortice abcd; it enters into this mortice, and slides freely throughout its length;
from the surface of the rule ef, bd two puppets K and L rise; the first is terminated
by a cylinder pierced with a circular orifice, in which the axle B B enters, and the second by
the nut of the screw gh: at the extremity ef of the rule efbd is fixed the rule esi; the rule ik
turns on a hinge round the point i, it has a longitudinal slit 7m, in which a small cylinder
enters, which carries the tool M: p and g are two small spheres which are at the extremity
of the two cylinders which rise, the first from the rule ef bd, and the second from the rule
ik: these two cylinders turn freely round their axes; the part no of the rod np is
cylindrical and traverses the circular orifice of the little sphere p, it can turn freely but
cannot slide; the other part, or, of the same rod, nr, is cut in a screw shape, and enters the
nut cut in the little sphere g; if the cylinder A A turns, its circular motion will be
transmitted to the axle BB, the rule efbd will advance, and draw with it a rule ik; we may
vary at pleasure the inclination of the latter by means of the rod nr, consequently it will fulfil
the functions of an inclined plane, and will conduct the tool m with the required velocity.
Alternate rectilinear motion with a uniform velocity, or variable according to a given law,
may be changed to circular alternate with a velocity of the same nature as that of the motion
which produces it, constant or variable according to a given law, in the same plane or in different
planes.
Fig. 1471. ab is a lever turning on its axle; the centre
of the semicircle def fixed to the same lever, at d and ƒ are
the extremities of a chain dg,hkf fixed to two bolts, in such a
manner as to be shortened or lengthened at pleasure; the
chain passes round two pulleys g and k, and the alternate
circular motion of the lever ab produces an alternate recti-
linear motion at the point h of the chain. This motion has
been applied to a machine for cutting off the heads of piles
under water, and is one of the most simple and convenient for
this purpose.
Fig. 1472. The zigzag is a very well known motion re-
quently employed in toys: Du Vivier employed it in a
machine for drawing boats out of the water: the nippers for
raising heavy bodies from depths is a familiar illustration of it,
as is also the common reel or spindle.

k
g
h
Fig. 1471.
Fig. 1472.
b

Fig. 1473. is a double suction pump invented by Noble,
and first used on board the Windsor Castle, 74 guns, in 1790.
It consists of a lozenge formed by four rods a, b, c, d of iron,
united by a hinge at their extremities, in such a manner that
the angles may become acute or obtuse without increasing or
diminishing the perimeter of the figure. The plan of the
lozenge is here represented vertically, with one of its diagonals
in a horizontal position, and sustained by two pillars of
equal heights, in such a manner that the same bolt which
unites the contiguous sides attaches them to the corresponding
pillar; in this position it is clear that the other diameter of
the lozenge will be vertical; it should be in the same axis as
the pump barrel at the upper extremity of this diagonal two
rods of the lower piston of a pump are attached, and at its
other extremity that of the upper piston, and the same bolt
which unites the contiguous bars to this diagonal unites them
also to the piston rods; since the angles of the lozenge must vary, and with them the
length of the diagonals: the two pillars e, e cannot be fixed; they are consequently
placed between two cheeks c,r, to which they are united by a bolt, and thus have a motion
of rotation in the plane of the lozenge.

:
Fig. 1473.
Sometimes it is required to communicate an alternate circular motion, like that of a
pendulum, by means of an alternate motion in a straight line: this is done in a remarkable
manner in the steam-engine, where the moving force is the pressure of steam, which
impels a piston from one end to the other alternately in a cylinder; the power of this
piston is communicated to the working beam by a rod connected with one end of the
piston. The end of the beam, which has motion communicated to it when united with the
rod, draws it alternately to one side and the other, moving in the arc of a circle, the centre
of which is that of the beam: this being the case, it is necessary that the rod and the end
of the beam should be so connected that, while the one ascends in a straight line, the other
shall descend in like manner.
CHAP. XI.
.993
MECHANICS.


Fig. 1474. By means of two lengths
of chain attached in opposite direc-
tions to each of the rods m, n passing
through the tenons r, r, the circular
alternate motion of the balance b, to
which the ends of the chains are fixed,
communicates an alternate rectilinear
motion to these rods.
Fig. 1475. is the very well known
tool, the common drill: a is the
rod, b the cord, c the cross pieces, d
the fly, e the muffle or socket, which
together are called the stock, g the
cutting tool or drill.
Fig. 1476. is a motion applied
to pumps; ab is a rod sliding
between the guides c,d: the lever
ef turning on its axis g communi-
cates by means of a rod eh its
alternate circular motion to the
rod ab, which has an alternate recti-
linear motion.
m
Fig. 1474.
Fig. 1476.
و
n
9
Fig. 1475.
r
a
b
Fig. 1477. Parallelogram em-
ployed in double-acting steam en-
gines to transform the alternate
rectilinear motion of the inflexible
piston-rod to the circular alternate
motion of the balance beam: abc d
is the parallelogram attached to the
beam by the points a and c fixed to this beam, but the sides
of the parallelogram can change their inclination with regard
to each other by means of their hinged extremities, that is to
say, the boxes or collars embracing the horizontal axes: these
axes at a and c are in the same plane with the centre or axis
of rotation of the beam: the angle d of the parallelogram is
always kept at a constant distance from the point e, by means
of an iron rod with a box or collar at its extremity, which
embraces the axis passing through d.
Fig. 1478. The same problem has been resolved by Belan-
court without employing a parallelogram: two pieces of
wood, ab, do, turn round the points or centres a and o, their
extremities b and d are fixed to each other by the iron piece
bcd, with articulations at b and d; the lengths ab and do from
centre to centre of the gudgeons are equal.
The sum
ab+do of these lengths is equal to the distance from the
point a to the point o measured horizontally, so that when
ab and do are level, the right line passing through d and b is
vertical; and as the length of the piece bd, from centre to
centre of the gudgeons, is equal to the difference of level of the
points a and o, bd becomes vertical at the same time that
ab and do become horizontal.
Fig. 1479. The drill bow, too well known to require any
explanation.
Fig. 1480. If we cause a wheel a to turn in any direction,
the wheel b will turn in an opposite direction, and both will
act in corresponding racks, so as to communicate a rectilinear
motion to the rod cd.
Fig. 1481. is a modification of the preceding, adapted to
many useful applications. If on an axis we fix two toothed
wheels, and make two racks diametrically opposite engage
each of these wheels, the circular alternate motion of the axle
will communicate an alternate rectilinear motion to the racks,
and the extremities of these same racks will approach or
retire from the axle in a uniform manner: it is thus that
reels have been constructed, and that we may form a cylinder
whose diameter shall be variable as that of which we have
before spoken, by multiplying the number of wheels and racks
agreeable thereto.
a

d
b
Fig. 1477.

¿
α
Fig. 1478.
Fig. 1479.

Fig. 1480.

Fig. 1681.
3 S
994
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Fig. 1482. To transform alternate rectilinear to alternate circular motion. abcd is a rule
made to move in a groove, another rule, tvdkvt, is attached to the first by the hinger in
such a manner, that the system of two rules open
and shut round r, like the two limbs of a pocket
rule; a plate of metal lmhn, which moves paral-
lel to the line bd, carries two pins p, q, which
lodge in the grooves v't', vt, practised in the rule
tvdkvt. It will be perceived that in virtue of this
disposition of the piece lm, hn moves from the
side of e; the two rules being supposed open, they
ought first to close by the action of the pin q on
the curve t'v', and then to be drawn by the con-
tinuation of the motion of the piece Inhm. The
inverse of this takes place when the motion of this
piece is made in the opposite direction: such is
the mechanism employed by M. Droz to put under
the die the piece which is to be struck, and to
drive away that already struck.

b
m
Fig. 1482.
a
น
0
k
The alternate rectilinear motion of the alternate
hand is very slow towards the extremities of its
course, and accelerated towards the middle in order
to receive the pieces which fall from a hopper, and to
deposit them under the die without the least shaking;
this motion is communicated to it by means of a pin
fixed to the running piece Inhm, which enters an
oblong opening practised at the extremity of the lower arm dyd; the axis y is horizontal and
perpendicular to the plane, passing through the axis of the great screw of the die, in such a
manner that making this lever move in either direction, we push the pin A forwards or
backwards, and consequently the piece Inhm; the upper extremity of the lever dyd is sub-
jected to move between two curves of metal, constructed according to given rules; each of
these curves is attached by its extremity to the axle of the great screw, and they are
disposed in such a manner, that the pin A retires when the great screw lowers, and re-
ciprocally by this we see how the play of the mechanic hand is united with the motion of
the die, and what is the result of it; in fact, the circular alternate motion of the die being
supposed constant by means of the two horizontal curves which form a groove, in which the
upper extremity of the vertical lever dyd is transformed into circular alternate, very slow at
the extremity of the oscillations, and accelerated towards the
middle. The same result takes place for the lower extremity
8, but then we change the planes, and we preserve the same
length to the oscillations; if the axis y is the centre of the
lever dyd, we can render them greater or smaller by bringing
the upper point nearer or farther.
Fig. 1483. ab is the beam of a steam-engine, c the centre
of rotation, n a bar of iron which turns freely round an axis r,
placed at the extremity a of the beam, and which divides the
bar n into two equal parts; the bar of iron n is attached at one
of its extremities to the piston rod, o, and at the other extremity
to the iron bar de, which turns round a fixed axis.
Fig. 1484. Let c be a drum; a gorge or spiral goes from
one extremity a of this drum, and after a certain number of
revolutions terminates at the other extremity b; let fh be the
total course which the carriage must make; take hg equal to
the height ae of the drum A; fix a cord at f, and another at
g both should be of the length fg; the other extremity of the
first cord is fixed at a, and that of the second at b, after being
rolled in an opposite direction on the spiral gorge of the drum
A: these two cords ought always to touch at the same point of
the surface of the drum A; according to this arrangement we
see, first, if the drum A turns uniformly round its axis, its motion
of translation will vary, as the radii of the spiral; secondly, in
proportion as one of these two cords unwinds, the other
winds, consequently they are equally stretched; thirdly, the
drum A will have no tendency to move in the direction of its
axis ac.
This latter circular alternate inconstant motion is changed
into alternate rectilinear, following the law which the end of
the machine requires.

Fig. 1483.
Fig. 1484.
C

CHAP. XI
995
MECHANICS.
b
Fig. 1485.
Fig. 148.5. Camus describes
machines which he has invented
for making several sieves go at
once; that which the figure re-
presents reduces itself to a great
table a; above this table is a
plank bc, sustained by two iron
axles n, n, which turn on two sup-
ports of the same metal; these supports being fixed to the table
on the prolongation of one of the axles, or on a rod, which is
in their direction on the plank, is fixed the pendulum rs, and
consequently communicates also an alternate circular motion
to the plank bc; its edges strike against the table a at each
oscillation, and imitate the vibrations or strikes which workmen
give to sieves.
Fig. 1486. The cord abc is attached at a to the spring d,
turns round the cylinder e, and is fixed at the extremity c of
the pedal g.
The circular alternate motion of the pedal com-
municates another of the same nature to the cylinder e.
Fig. 1487. The circular alternate motion of the pedal d
produces circular continuous in the fly m, and circular alternate
in the cylinder a.
Fig. 1488. Nippers for cutting off the heads of piles: these
consist of two pieces of iron, abcd, efgh, which turn round the
axle i, the extremities ab, cf of these two pieces are cut into a
semicircular form, in order the better to attach themselves to
the pile to be cut off, and their whole forms the beak of the
nippers. The other extremities bcd, fgh of these same pieces
of iron are terminated in two portions of arcs of circles, dc, gh,
the first furnished with teeth in its convex, the other in its con-
cave part at the half of the interval which separates the two
arcs of circles, dc and gh, an axle s rises perpendicular to the
plane of the nippers; this axle carries two pinions, n, m, which
engage, the first with the teeth of the arc dc, and the second
with the teeth of the arc gh; the circular alternate motion of
the axles will open or shut at pleasure the beak of the nippers.
Fig. 1489. A long bar or beam ab is traversed in its centre
by an axle which is at the upper extremity of an upright post
cd. The circular alternate motion communicated to one of
the extremities of the bar ab by the action of a person seated
at this point, and who tends alternately, sometimes to elevate
himself by forcing his feet against the pavement, sometimes to
descend by his own weight, communicates the same motion to
another person seated at the opposite extremity.


9
α
d
9
Fig. 1486.

m
Fig. 1487.
Fig. 1488.
d
Fig. 1489.
α
d

ર

Circular alternate motion with a uniform velocity, or variable
according to a given law, may be transformed into alternate in a
given curve, with a velocity of the same nature as that of the
motion which produces it, constant or variable according to a given law in the same plane, or in
different planes.
مع
g
Fig. 1490. Lathe without an axle for making all sorts of screws, invented by Grandjean.
This lathe is composed like common ones of a bench and two puppets, p,o; these puppets
have, instead of points, two collars, s, t, to receive the axle fh, terminated in a point at its two
extremities; this axle carries the piece r required to be turned,
and the pulley g which receives the cord go attached to the
treadle o; the puppet a carries an iron support, i, to which is
attached at i an iron square hik, one extremity of which leans
on the point h of the axle, which it tends consequently to press
from h to f; the other extremity leans on a piece e, movable
on an axle d, at the extremity d of which the piece dc is d
mounted on a square, in the groove of which slides a box d, to
which is attached the cord no, which is fastened to the treadle
o; it is evident that by leaning the foot on the treadle we not
only shall turn the axle ƒh, but also lower the piece dc, which
causes the axle to advance from ƒ to h, by a quantity recipro-
cally proportionate to the distance dn of the box n to the centre
d of motion; and as the piece n is movable, we may place it

Fig 1490
q
3 s 2
996
Book II.
THEORY AND PRACTICE OF ENGINEERING.
wherever we judge fit; whence it follows that during a revolution the axle will advance any
quantity we require, and consequently, placing the tool at r, we can cut a screw of any size
we please. If we wish to turn a screw whose threads continue to contract, we may do it
easily by means of this machine; for this purpose we have only to take off the piece cd
and substitute dnc, whose circumference nvc, in the groove of which the cord at n
passes, is a curve whose radii dv, de increase in the same manner that we wish the
helix to diminish; for this purpose each point, c,v,n, of the curve will successively perform
the duty of making dn of a different length, which can only be done
by making the axle recoil unequally towards h, in order that the
threads of the screw should not be unequally cut in the portion of
the radii dcd,vdn.
Fig. 1491. Clairault has proposed the problem of finding the
curves m,o,n, round which, if we make the square men slide, its
summit ċ will always be in the curve ec. We give to the square
the motion that this problem requires by circular alternate motion,
which we may transform into alternate in the given curve ec.

a
m
Fig. 1491.
AH
d
d
Fig. 1492.
n
n
α
h
a
Fig 1492. a, a are two uprights, which rise from the beam b per-
pendicularly; the cross piece cc ties toge-
ther the two upper extremities of these
uprights; these four pieces form a frame,
whose vertical position is secured by the
other pieces d, and dg is a cylinder
furnished with a toothed wheel h; i is a
pinion which engages the wheel h; the
axle of the pinion carries a winch at the
extremity, to which the mover is applied;
a b c d is a carriage which slides down-
wards between the two uprights a, a;
two cords e, e fixed to the upper cross
piece of the carriage pass through two
pulleys which are attached to the head c,
and roll on the cylinder g; another cord f
is attached to the middle of the lower
cross piece of the carriage, passes through
a pulley fixed to the beam b, and rolls on the cylinder in a direction contrary to the two
preceding: the carriage abcd carries an iron cylinder; the extremity of this cylinder
rests on an iron cramp in the centre of the upper surface of the lower cross piece of the
carriage, passes through an orifice made in the middle of the upper cross piece, and is
terminated at h by a borer or other utensil. The cylinder of iron is furnished with a
pulley m, about the middle of the distance, which separates the two cross pieces of the
carriage; a cord nopq fixed to the head c at n passes through the pulley o, which is in the
middle of one of the vertical sides of the carriage, envelopes the pulley m, round which it
makes an entire turn, then passes through the pulley p, which is in front of the pulley o,
on the opposite side of the carriage, or which rises from the lower cross piece to a con-
venient height, and is terminated at q, where it sustains a weight h, which serves to keep
this cord in a degree of constant tension. If the mover acts by a circular alternate motion,
this motion will be transformed into rectilinear alternate by the means already indicated.
The iron cylinder gh will participate in the alternate rectilinear motion of the carriage
abcd, and at the same time will have a circular alternate motion produced by the constant
tension of the cord on pq. The combination of these two movements will make the utensil
perform a spiral; such is the mechanism employed in the royal manufactory of arms at
Versailles for rifling the bores of fire-arms.
The alternate motion according to a given curve, with a uniform velocity, or which varies
according to a given law, may be changed into alternate motion according to another given curve,
with a velocity of the same nature as that of the motion which produces it, constant or variable
according to a given law, in the same plane or in different planes.
We transform alternate given motion into circular continuous by the means indicated
already, and the latter into alternate.
So numerous are the contrivances for modifying motion, that we can scarcely define the
hundredth part of those introduced into our complex machines, many of which are as
conspicuous for their elegance as for their simplicity. The varieties which most commonly
present themselves are, however, divided into rectilinear or rotatory in the first we have
seen the several parts of the moving body proceed in parallel straight lines with the same
speed; in the latter, the several points revolve round an axis, each performing a complete
circle, or similar parts of a circle in the same time; each of these varieties are again
resolved into continued and reciprocating, so that we have four principal species of motion
in ordinary use for the transmitting motion.


CHAP. XII.
997
MACHINES, TOOLS, ETC.
CHAP. XII.
MACHINES, TOOLS, ETC., ETC., EMPLOYED IN CIVIL ENGINEERING.
MACHINES for raising weights, or removing them, are principally levers, capstans,
wheels, pulleys, inclined planes, screws, and their various combinations in the form of
cranes and derricks. Wheelwork is now employed in a variety of instances, its power in
all cases being derived from the same principles as the lever, each wheel and pinion being
considered as composed of a series of bent levers, of which the axis is the common fulcrum,
acting in succession on the teeth of the next wheel.
The Lever is the most simple and the most generally useful for raising weights to a
small height, but the extent of its action is still limited, although we are indebted to
Perrault for an invention which has greatly increased its power; two pins are fixed in the
lever at a short distance from each other, which slide in two pairs of vertical grooves pro-
vided with ratchets, so that when the long arm of the lever is pulled by means of a rope,
the nearer pin serves as a fulcrum, and the more distant one is elevated at the same time
with the weight, and detained in its place by the click; when the rope is slackened, the
weight sinks a little, and raises the pin, which first served as a fulcrum, to a higher place
in its groove.
A Winch with an axis is a bent lever, and often used as a power, to draw water from a
well; a vertical axis, with two or more levers inserted in it, constitutes the capstan; to
estimate their force all that is necessary is to add to their radius half the thickness of the
rope, and compare it with the arm of the lever.
The Gin for raising coals and other weights is an erect axis or drum, turned by the
force of horses working in a circle. The buckets are attached to the opposite ends of a
rope, passing round a drum, to which it is drawn by its property of adhesion: one
bucket descends empty, as the other rises full, and when the motion of the buckets is
required to be changed, the horses are turned, or the wheels are made to impel the axis in
a contrary direction, when any other moving power is employed.
The Capstan is not supposed to have been much employed in Britain previous to the
sixteenth century: at its first introduction it consisted of an upright barrel or drum,
turning on a vertical axle; at the upper part was the head, in which were holes or sockets
for the insertion of the eight levers or bars, which were from ten to twelve feet in length.
The action of the men employed to turn it round was necessarily constant, for if left an
instant, the weight would immediately run back or recoil.
An improvement in the method of pulling the capstan was first made in France by
Lalande, who contrived the palls, now attached to the lower parts of the barrel, which
turning on a pivot raise the
capstan, and press it forward over
any obstacle, when they fall by
their own weight into iron steps
made to receive them, which in
case of any recoil also check the
descent of the weight; when the
motion is to be reversed, the palls
are turned over on their pivots,
and they act in the other di-
rection.
There being some difficulty
in surging the rope on the plain
cylindrical barrel, it was fur-
nished with additional pieces
securely attached, and called
whelps; to which, as well as
to the barrel, the capstan head
is bolted down; they are slightly
conical, for the purpose of allow-



Fig. 1493.
CAPSTANS.
ing the rope to be received and delivered without rising or falling from its proper
place. The power of such capstans depends upon the length of the lever or bar, or the
distance of the centre of pressure on the bar, and on the radius of the barrel, including the
whelps, and half the thickness of the rope.
The power with which a man pushes when working a bar, multiplied by the distance
from the axis, expresses the effect of this power; when there are several, the power must
3 s 3
998
Book 11.
THEORY AND PRACTICE Of engineering.
be multiplied by the number, which is equal to the weight multiplied into the radius of
the barrel.
Power Capstan has a compound barrel, consisting of two cylinders of different radii; the
rope is fixed at the end of the largest, and after passing over the pulley, which is attached
by the hook to the load to be moved,

By
it is coiled round the other cylinder,
and fastened at its upper end.
means of the bar at the two ends, the
barrel is urged about its axis, so that
the rope may coil round the large
cylinder, whilst it unwinds itself from
the smaller. Supposing the diameter
of the one to be 21 inches, and the
other 20 inches, it will be evident that
one turn will gather 63 inches in one
cylinder, whilst 60 inches will be
uncoiled from the other; the quantity
of wound rope exceeds the quantity
unwound by 3 inches, the half of which
space will be the distance through
which the pulley moves by one turn
of the bar. By a common capstan
of the same dimensions the length of
rope coiled round the barrel by one
revolution of the bar would be 60
inches, and the space described by the
pulley or load half that amount.
Fig. 1494.
ECKART'S Power capstan.
The power of such a machine is
equal to the velocity of the impelled point, divided by the velocity of the working point;
or to the velocity of the power divided by the velocity of the weight.
The lever, then, on the two capstans of similar diameters will exert a power as 1 to 30,
30
that is, inversely as the velocity of their weights, and the power of one will be 20, or
11/
equivalent to twenty fold tackle of pulleys.
Such a
To double the power of the machine it is only necessary to cover the small cylinde
with a thickness of a quarter of an inch, making the difference between the radii of each
half what it was in the first instance; the power
of this capstan increasing as the difference between
the radii of the cylinder is diminished.
capstan is often used as a windlass for raising
weights, and a winch applied instead of a bar to
turn it; it has the advantage of not requiring a
ratchet-wheel and catch to stop it, as the two
parts of the rope pull on contrary sides of the
barrel; the rope which coils round the large
barrel acts with a larger lever and with greater
force than the other, but not sufficiently to over-
come the friction of the gudgeons, so that the
weight remains wherever it has arrived.
When the anchor of a ship is weighed, the
cable itself would be too large to bend round the
capstan; it is therefore connected to an endless
rope called a messenger, which, as it coils round
the lower part of the capstan, quits the upper, so
that its place becomes lower and lower, till it
has no longer room on the capstan; and it is
necessary to force it up from time to time, which
is called surging the messenger. This is done
by beating it; to add to the facility of the oper-
ation, the capstan is made conical, which enables
the rope by its tension, when guided by a pulley,
to bring the messenger into its proper place.

0 0
Fig. 1495.

Fig. 1496.
A
In the common windlass the power is applied by means of a winch, which is a rectangular
lever; in other cases no wheel is attached to the axle, but it is pierced with holes directed
towards its centre, in which long levers are introduced, and a continuous action produced
by several men working together, so that while some are changing the lever from one hole
to the other, the rest are turning the windlass.
CHAP. XII.
999
MACHINES, TOOLS, ETC.

A modification of the above capstan consists
in applying two cylinders in a vertical position,
around the larger of which the rope coils, as the
handspikes applied to the smaller made to work
in a frame turn it. When two cylinders of dif
ferent sizes revolve on the same axis, and the
weight is wound round the larger, its operation
is very powerful, as we have previously shown.
The capstan made use of on wharf walls or in
docks is usually of iron, with a shaft of consider-
able length, turning on a pivot at the bottom of
a brick or stone chamber constructed to receive
it: at the top of the chamber is a capping, which
guïdes the motion of the capstan as it is turned round by
a handspike or lever applied at the top.
The manner of applying the pulley to two cylinders
of different diameters on the same axis is very simple; the
rope is made to pass from the smaller one, over a pulley
connected with the weight, and returns again, to be wound
up by the larger one; a considerable length of rope is
required for a small extent of motion, but the action is
one of considerable power.
One of the most curious applications of the capstan was
made by the Count de
Carbury, when he moved
a mass of granite to St.
Petersburgh for the pe-
destal of the celebrated
statue of Peter the Great,
which was estimated to
weigh upwards of 1500
tons; its dimensions being
42 feet 6 inches long,
26 feet wide, and 23 feet
high. This immense block
was supported upon a
timber platform of great
Fig. 1498.
Fig. 1497.


Fig. 1499.
strength, beneath which were placed a series of axles with grooved ends that worked or
ran upon balls of copper 6 inches in diameter. The axles of the carriage were moved
T
Fig. 1500.
PLAN OF CARBURY'S Machine.
by the revolution of the balls, on a bed prepared to receive them, which was movable to the
fore part of the frame as the carriage progressed, forming a sort of continued railway; one
of these pieces of timber is shown under the side elevation.
The end or front of the stone mass was cut into steps, on the top of which the director
of the operation took his station; from whence he could make the various signals necessary
for the progress of the machine.
The capstans, firmly fixed, were worked by levers and pulleys; and as one set of workmen
became fatigued with turning them, they retired to mats attached by other ropes to the
flanks of the carriage and were drawn along, steadying the block at the same time, whilst
others who had previously rested took their places. This operation rivals that described
by Herodotus of the transport of the enormous rock, 240 feet in circumference, which was
brought from the quarry in the Isle of Philoe near the cataracts, for the shrine of the goddess
Latona, thousands of labourers being employed three years in taking it to its place of
་

3 s 4
1000
Book II.
THEORY AND PRACTICE OF ENGINEERING.
destination; he also informs us that the temple, consisting of one solid stone, was a cube,
the length of whose side was 40 cubits
We can scarcely imagine it possible to move so vast a block, the original weight of
which would be upwards of 100,000 tons; but supposing that four-fifths were cut away
previously to removal, to produce the cha-

racter of an Egyptian temple, there would
still remain 25,000 tons to transport by the aid
of levers, capstans, pulleys, and inclined planes.
The interposition of rollers or balls in the
above arrangement of Count Carbury bears
some resemblance to the application of fluids:
supposing surfaces to be flat and parallel, a
roller will move between them without much
friction; but it will have to overcome the re-

Fig. 1501.
END VIEW.
sistance occasioned by the depression which
it produces in the substance on which it moves,
and which is greater or less according to
its softness or want of elasticity: if perfectly
elastic, the depression would be productive of
little resistance, because the tendency to rise
Fig. 1502. The bed, balls, and axles.
behind the roller would be equivalent to the
force opposing its progress, the actual re-
sistance arising from a want of elasticity in the
materials made use of. In this case, by laying
down rails in front of the mass to be moved,
upon which the balls could turn, the objection
usually made to their introduction was ob-
viated; but had they been placed between
two cylinders, one convex and the other
concave, much of the friction would have been
avoided; it is always materially diminished
by lessening the velocity of the parts which
slide on each other, as is proved by reducing
the diameter of an axis on which a wheel turns.
Fig. 1503.
MOVING ROCK AT ST. PETERSBUrgh: side VIEW.

Combinations of wheels are generally used where heavy weights are to be moved, or
when, by the application of great power, a higher velocity is required: for the first the
power must be applied to the circumference of the first wheel, and its pinion must transmit
the motion to the teeth of the second wheel, and so on, in order that the weight may be
CHAP. XII.
1001
MACHINES, TOOLS, ETC.
:
raised by the axle of the last
wheel in the second case the
power must be applied to the
first pinion.
The Crab employed for raising
weights has a winch and barrel
worked by a wheel and pinion;
the whole is fixed in a strong
frame either of timber or iron,
and may be moved into any
situation where it is required.
A double handle enables two
men to lift considerable loads;
and the machine is furnished
with a brake, so that it may
be stopped at any time, whether
in raising or lowering a weight.
Two crabs worked by six men
each, at the London Docks,
raised a weight of 728,000 lbs.
to a height of 16 feet in 8
hours, equalling 2012 lbs. raised
1 foot high per minute by one

man.
Fig. 1504.
Fig. 1505.
CRAB.

The Gin usually accompanies
the crab in raising large stones;
it is composed of three long stout
legs, 12 or 14 feet in length and
6 inches in diameter, meeting
together at the top, and so placed
that two can be fixed at a certain
distance from each other by
means of two iron bars placed
horizontally, one being 12 inches
and the other 7 inches long: a
roller upon pivots turns be-
tween two cheeks attached to
two of the poles, 7 or 8 inches
in diameter and 6 feet in length,
20 inches of which
are left
square at each end, and holes are made in each to receive
handspikes, by which the roller is turned; the middle is
cylindrical, to wind up the rope. The transverse iron bars are
fixed at one end to one of the poles by a bolt, and at the other
to the other pole with a bolt and key, which enables the gin
to be separated and removed. Each cheek is fastened to the
pole by two iron bands and two iron bolts, between which the
cylinder revolves: the poles are usually hooped round at each
end, and to the upper are straps through which an iron bolt
passes to keep them together, and hold up the block through
which the rope or chain runs to the crab or windlass.
block contains two pulleys, and before the machine is mounted
for use, it is laid down flat on the ground, the lower end of the
single pole being turned over, for the purpose of fastening
the upper block, and when the rope is turned round both
the machine is raised.
The
The Jack or Hand-jack is a portable mechanical power for
elevating the end of a block of stone or piece of timber, to
allow of rollers or blocks being placed underneath; or to lift up
girders, brestsummers, or to hold up a wall that requires under-
pinning, and is one of the most useful mechanical contrivances
in the hands of the builder. The power of the common hand-
jack is obtained by a rack and pinion, placed in a block of
wood about 30 inches long, 10 inches broad, and 6 inches
wide: the rack has a double claw at its upper end, and a
small pinion which engages in the teeth; the axis of the pinion
is supported in two iron plates bolted to each side of the block,
CRAB.

Fig. 1506.
1002
Book II.
THEORY AND PRACTICE OF ENGINEERING.
and one axis passes through the side plate, to which is attached the winch or handle; this,
turning round, elevates the rack, and with it the claw which is applied to the load to be
raised: that the weight should not have the power of running the pinion back, the
handle is secured by a hook fastened to the outside of the block.
There are several modifications of the jack; one of the most powerful is that in which
the winch does not immediately act upon the rack, but first on a small pinion, then
a large toothed-wheel, which carries a pinion that elevates the load: supposing R to be
the length of the winch, R' the radius of the wheel, r that of the first pinion, and r' that of
the second, then
P: W' : : r: R
W': W: :r' : R'
P: W::rr': RR':
whence P:
=
you, yo'
R. R
W
•
W
50
Let rr'1 inch, R-10 inches, and R'-5 inches; then P= or 1 lb. power would be
a counterpoise to 50 pounds; and by exerting a force equal to an hundred weight, or
112 × 50=5600 lbs. might be raised.
A small power may
thus elevate a con-
siderable weight, but
in so doing, the to-
tal expenditure, in
raising the weight
through any height, is
never less than that
which would be ex-
pended if the power
were immediately ap-
plied to the weight,
without the interven-
tion of any machine:
this arises from the
universal property of
machines, by which the
velocity of the weight

Fig. 1507.
is always less that that of the power, in exactly the same proportion as it is less
than the weight, so that when a certain power is applied to raise a weight, the rate at which
it mounts is always slow, and in the same proportion as the weight is great; no machine,
therefore, can be said to have the property of totally diminishing the expenditure of power
necessary to raise the weight or to overcome its resistance; all that a machine can effect is
to enable the power to be expended at a slow rate, and more beneficially in its duration,
than if applied at once to the weight or its resistance; this common property refers to all
the mechanical powers, as the lever, the pulley, the inclined plane, screw, &c. &c.
The Screw is applied both to raise weights and press bodies
into a more compact state; and sometimes to set in motion
the sun and planet wheels; the worm of the screw working
into the teeth of that wheel which drives the gear, and by
its revolution compelling the wheel to move on its axis; it
is also preferred to the jack wherever a delicate movement is
required.
The working of the screw may be understood from the
observations made upon the inclined plane, and by con-
sidering that the weights rest on the inclined face of the
thread, whilst the power acts on the surface of the cylinder
parallel to the base of the screw: equilibrium is obtained
when the power, is to the resistance, as the distance between
the two threads of the screw, is to the circumference de-
scribed by the point to which the power is applied.

P: Wh: 2rw,
h
and P=
2 wr
W:
W being the weight or resistance to be overcome, h the
height or distance between the threads, and r the radius
of the screw. The space described by the power, is to
Fig. 1508.
CHAP. XII.
1003
MACHINES, TOOLS, ETC.

that described by the resistance, as the circumference of the
screw, is to the distance between two of the threads: in
some of its applications, these powers are multiplied by one
screw working within another; the larger, turning round
within a fixed nut, has a progressive motion, whilst the
smaller one is made to work within it.
For presses the application of the screw is very simple,
although the friction which accompanies it materially affects
its power; but it is of service in maintaining the press in
the position in which the force has brought it; it is always
turned by a lever, without which the friction would render
it useless. The double screw may be used with consider-
able advantage wherever a small extent of motion is required.
The screw of the printing press having to descend with
great momentum, it is made more open; and in all such
cases the handle must be loaded.
For raising weights, the screw has been substituted for
the rack and pinion of the common jack, and for many
purposes it is far better adapted; the mason requires the
use of such a machine for the elevating the massive stones
he has to work upon, and for ordinary purposes it is much
more convenient than the lever.
Fig. 1509.
100
Screw Jack. The block of wood has a hole bored through nearly its entire length for
the purpose of allowing the screw to move up and down without touching: at the top of
the block is firmly fixed a nut, through which the screw passes when turned round. The
claw fitted at the top and bottom of the screw has a round collar, which allows the screw
to revolve without turning it: at the bottom of the block are four points to prevent its
slipping when used. The motion is given to the screw by a worm wheel fitted upon the
square, the teeth of which are engaged by a worm on the axis of the winch; when this is
turned round, it causes the wheel to revolve by the action of the worm in its teeth, and as
the wheel is attached to the square part of the screw, it is compelled to turn with it,
permitting the screw to move up and down at the same time.


Fig. 1510.
SCREW JACK.
Fig. 1511.
SCREW JACK.
In another description of screw jack, not having so much friction, the screw does not
turn round, but only rises and falls; this is effected by the worm wheel being placed near
the top of the block, which has a nut cut in its centre, through which the screw passes,
and the nut is turned round instead of the screw. The axis of the worm is supported by
similar iron plates to that already described, and is also turned by a winch.
1004
Book II.
THEORY AND PRACTICE OF ENGINEERING.
The Crane is generally employed for raising or lowering heavy weights and large bodies,
for removing them from one situation to another, loading and unloading waggons and
ships, and for hoisting goods from the quay to the different warehouse floors: it consists
ordinarily of an upright post turning upon pivots; the gib
or arm which extends from the upper part is now generally
made of iron, or supported by a bracket of the same
material.
The wheels accompanying it are usually set in motion.
by turning a winch, a fly wheel being applied to the axis
to equalise the motion, as well as to prevent the rapid
descent of the load, should any accident occur. The powers
of the crane are adapted to its intended use, and the
weights to be raised: some have a variety of movements
introduced, with a train of several wheels, each turned by a
pinion smaller than itself. If the barrel or drum on which
the rope winds be 12 inches in diameter, with a cog-wheel
baving 96 teeth attached to the end of it, it may be turned
by a pinion of 12 leaves. On the same axis may be placed
a wheel of 32 teeth, moved by a pinion of 8 situated on a
third axis, which carries the fly wheel: a winch of a
foot radius applied to the gudgeon of the drum or barrel,
doubles the power of the labourer, as the circle it describes is double that of the
barrel on which the rope winds. If the winch is fixed on the axis which carries the pinion
of 12 and wheel of 32, it will have a power 16 times greater, and if attached to a pinion of
8, 64 times. The fly wheel being fixed upon the axis on which the pinion of eight is
attached, all danger from accidents is in a great degree prevented, and is much more
effective than the brake and ratchet-wheel. The spindles of all the wheels slide or push
endwise, so that they may be combined or disengaged at pleasure.

Fig. 1512.
The statical moments of the forces are inversely as the product of the radii of the axis, to
the product of the radii of the wheels in which they work; and as the number of teeth
which the wheels and leaves that the pinions carry must be as the peripheries of the wheels
and axles, their statical moments are also inversely as the product of the leaves of all the
pinions, to the product of the teeth of all the wheels.
At Ramsgate harbour a crane was made use of, designed by Mr. Peter Kier, by which
four men were enabled to hoist as many tons: the whole was mounted upon a frame of
cast-iron, 9 feet 7 inches square, weighing 2 tons; this was supported on four cast-iron
wheels, one pair of which on a common axle moved round on a centre, fixed to one side of
the frame: an arm projected from the axle to the opposite side beneath the framework,
where, by means of a rack or segment of a wheel fixed to it, a pinion moved by a winch
twisted the wheels round upon their centre, and allowed the whole crane to be moved in
any direction required.
The shaft of cast-iron weighing 23 cwt. was placed over the centre of the iron frame,
and supported by oak braces, stepped into boxes, cast in the angles of the frame, thus
forming a strong perpendicular shaft, round which axis the whole crane traversed: a steel
pivot or gudgeon at the top of the shaft sup-
ported the weight of the entire framing and
wheel-work. The former consisted of a long
beam, bearing the pulley at one extremity,
and the wheel-work or machinery at the other;
the whole was further strengthened by braces
and uprights, to which the platform was at-
tached, on which the workmen stood. This
crane has since been greatly improved, by
being made to balance itself perfectly when
hoisting a load, and to facilitate its turning on
its pivots, additional machinery is sometimes
applied.
At the West India Docks six men working
a crane raised 224,000 lbs. weight 15 feet high
in 8 hours, which is equal to 1166-6 raised
a foot high per minute by one man. The
friction of this crane was equal on an average
to one-twelfth of the absolute weight.
Wharf Cranes. Where cranes cannot con-
veniently be held by an upright post, they

Fig. 1513.
may be supported by a piece of framing, as in this example.
On the wharf is laid a sill
35 feet in length, and 12 inches square, under which at right angles is another piece of the
CHAP. XII.
1005
CRANES, ETC.
same scantling, 30 feet in length; into the ends of this are framed two inclined braces,
39 feet in length and 7 inches square, secured by three iron bolts to the head of the in-
clined timber, 39 feet in length, as shown to the left of the figure. The post of the crane,

Fig. 1514.
WHARF crane.
12 inches square, works on a gudgeon, both at top and bottom; the inclined piece holding
a metal box for the foremen, and the sill, that for the latter to work in. The gib, 12 feet in
length and 12 inches square, is braced by another piece, 6 inches by 4. This kind of
crane with a wheel 3 feet 4 inches diameter, and pinion 6 inches, is much used in
Scotland.
Another variety of wharf crane is shown in the accompanying figure, where the framing
is formed above, not lying immediately on the ground. The plan of the top is triangular,
´each side being 29 feet in length, and 12 inches square, secured at the angles by cast-iron

Fig. 1515.
boxes, and cross-braced.
WHARF CRANE.
The upright post, 12 inches square, works top and bottom on a
gudgeon, and the gib, 14 feet in length, and 12 inches square, is braced to it by a piece 6
inches square. By this crane ordinary weights are landed at the wharfs of many of the canals.
When the wheel and axle are applied to raise
a weight, the velocity with which the power
moves is as many times greater than that with
which the weight rises, as the weight itself is
greater than the power; hence it is that in the
elevation of the weight a quantity of power is
expended equal to that which is required to
elevate the weight, if the power were imme-
diately applied to it without using any machine.
When in one revolution of the machine the
length of rope uncoiled from the wheel is equal
to the circumference of the wheel, it is through
that space the power must move; and at the
same time we shall find
that the length of rope
coiled upon the axle is
equal to the circumferenee
of the axle, and through
this space the weight
must be raised; the
spaces, therefore, through

which
the power and
Fig. 1516.
WHARF CRANE.
weight move in the same time are in the proportion of the wheel and axle, and these cir-
1006
Book II.
THEORY AND PRACTICE OF ENGINEERING.
cumferences are in the same proportion as their diameters; therefore the velocity of the
power will bear to the velocity of the weight the same proportion as the diameter of the
wheel bears to the diameter of the axle, or as the weight is to the power.
When the upright post is secured by chains or ropes, the triangular timber frame is dis-
pensed with, which is sometimes necessary in building a quay wall. By means of blocks the
whole of such an arrangement

can be lightened at pleasure,
and made perfectly secure.
Double Crane, fixed on a
wharf or pier-head, is so
framed and braced that it ba-
lances exactly when turning
on a pivot at the bottom.
Such a crane was used at the
constructions on the Rochdale
Canal: the distance between
the ends of the gibs was 30
feet; they were held together
by a bar of iron, 14 inches
square: their scantling was 8
inches by 7 inches; the
length of each of the cross
braces was 27 feet 6 inches,
and their scantling 7 inches
by 6. The upright post was
a foot in diameter, and the
Fig. 1517.
DOUBLE crane.
The wheels were 3 feet
segmental piece which swung round upon its head, 12 inches by 9.
4 inches in diameter, the pinion 6 inches, and the rollers 12 inches, the latter being 2 feet
9 inches in length.

Iron Pit Crane composed of a
cast-iron frame shaft and gib, has
usually three different powers, each
power having a double purchase.
The height of the shaft is 20 feet,
11 of which is below the surface
of the ground; it rests on a gudgeon
about 6 inches in diameter, and
turns in a brass box. At the sur-
face of the ground two plates are
fixed to the shaft, 4 inches apart,
between which are five rollers ;
when the crane is turned, these
move round the inside of a cast-
iron circle. The gib and pro-
portions of a crane to carry eight
tons is 21 feet in length, and the
diameter of the winch is 3 feet;
that of the pinion taken at the
pitch line 54 inches with ten leaves :
the wheel in which it works is
3 feet 4 inches in diameter, with
eighty-four teeth: the second
pinion is 7 inches in diameter,
with fifteen leaves, and the wheel
3 feet 13 nches in diameter, with
eighty teeth the third pinion is
1 foot 33 inches in diameter, with
thirty-two leaves, and the wheels
2 feet 5 inches in diameter, with
sixty-two teeth. The pinion com-
mon to all the powers is 53 inches
in diameter with eleven leaves,
and the wheel 4 feet and of an
inch in diameter, with 100 teeth.
tion rollers for the chain 9 inches.
Fig. 1518.
WHARF CRANE.
The chain barrel is 16 inches in diameter, and the fric-
The Corvus or Raven of the ancients, according to Perrault, corresponded to our crane;
each comprised a strong arbor, or upright timber, firmly fixed in the ground, and sustained by
CHAP. XII.
1007
CRANES, ETC.


D
a number of arms, according to the strength
required: when the entire crane turned with
the load, it was originally called rat-tail, and
when only a portion moved, it was termed
the gibbet crane.
Double Crane, used for the construction
of breakwaters, is mounted upon a frame,
and by means of rollers, and a working gear,
can be readily moved forwards or back-
wards: when advanced to the edge of the
work one gib can be employed to lay a stone,
whilst the other lifts one from the carriage,
which is moved along a railway laid down
for the purpose. The gib has a sliding car-
riage for laying the stones either close to
the shaft, or as far out as it will reach: it
Fig. 1519.

Fig. 1520.
is worked by a sheeve and rope passing over the point of the gib, and down by the side
of the spindle.

Fig. 1521.
ABERDEEN: Double crane.
A gib crane with a shaft 40 feet in height and 12 inches square, turning upon a gudgeon
at the bottom, is frequently used in building lock walls, &r
At the top is a similar
1008
Book II.
THEORY AND PRACTICE OF ENGINEERING.
gudgeon, on which a plate with four arms and a hole in the centre is dropped:
to each of these arms is fixed a guy rope, which is carried to such a distance
from the shaft, that when the crane turns round, the gib may keep clear of it.
The lower end is thus connected with a pair of pulley blocks, previously
fastened to a pile driven in the ground, and then drawn tight and secured.
The gib, usually 26 feet long and 10 inches square, is fixed a little higher
than the middle of the shaft it is supported by a brace from below, and is
suspended from above by a wrought-iron bolt, and worked by a common
wheel and pinion.
The pincers or forceps, for holding the stone elevated by the crane, is made
of iron, and the pivots or rivets are of considerable strength: when the rope
is pulled, the points which attach to the stone are drawn or pressed together
in such a manner, that the heavier the weight the firmer it holds.

Fig. 1522.
The movable crane for lifting the timbers employed in the construction of the cones for
the breakwater at Cherbourgh was very simple, and was brought in mediately over
its work. The several pieces were pulled up, and lifted into their respective situations
by means of a pulley.


Fig. 1523.
MOVABLE Crane for building cones at CHERBOURgh.
Where the wheel and axle is used in cranes, the action of the power is liable to
occasional intermission, in which case a ratchet wheel is provided, which permits the
wheel to turn only in one direction, the catch which falls between the teeth of a fixed
wheel preventing its motion in the other direction. The power of the wheel and axle
being expressed by the number of times the diameter of the axle is contained in that of the
wheel, there are but two methods by which that power can be augmented; viz. by in-
*creasing the diameter of the axle, or lessening that of the wheel. Where great power is
required, each of these methods presents some difficulty as well as inconvenience; for if
the diameter of the wheel is enlarged, the power will work through an unmanageable
space; and if the other method is adopted, and the thickness of the axle is much reduced,
its strength will become insufficient for the purpose of supporting the weight: to combine,
therefore, strength with moderate dimensions, is sometimes accomplished by the methods
we have already described of giving different thicknesses to different parts of the axle,
carrying the rope which is coiled to the thinner part through a wheel attached to the
weight, and coiling it in the opposite direction on the thicker part.
In Eckart's power
capstan, fig. 1494., the weight is equally suspended by two parts of the rope; therefore each
part is stretched by a force equal to half the weight; consequently the power multiplied
by the radius of the wheel, is equal to half the weight multiplied by the difference of the
radii of the thicker and thinner parts of the axle; or, the power multiplied by the diameter
of the wheel, is equal to the weight multiplied by half the difference of the diameters of
the thinner and thicker parts of the axle: such a wheel and axle is equivalent to an ordi-
nary one, in which the wheel has the same diameter, and whose axle has a diameter equal
to half the difference of the diameters of the thicker and thinner parts. The power of such
a contrivance depends upon the proportion the diameter of the wheel bears to half the
difference of these diameters; therefore this power, when the diameter of the wheel is
given, does not depend on the smallness of the axle, but on the smallness of the difference
of the thinner and thicker parts of it.
CHAP. XII.
1009
CRANES, ETC.
The crane used by Perronet at the construction of the bridge at Neuilly was also exceed-
ingly simple; it was of timber, and worked by two wheels, one man at each wheel being

Fig. 1524.
0

PERRONET's crane used at neuilly.
ピコ
​sufficient to hoist the various stones used in laying the courses and placing the voussoirs
over the arches.
By means of two wheels mounted on a plane, the stones were lifted from the wheel

пе
C
Fig. 1525.
perronet's crane used at neuilLY.
3 T
1010
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
carriages, and placed upon the platforms, whence they were again moved to their several
places of destination.

T
Fig. 1526.
PERRONET's CRANES USed at neuilly bridge.
In wheel cranes we have an example in which the body receives an impulse in a direction
perpendicular to the axis, and where a uniform rotatory motion is produced, the velocity
of which depends on the force of the impulse, the distance of the
direction of the impulse from the axis, and the manner in which the
mass of the body is distributed round the axis: we must also con-
sider, that the whole force of the impulse is distributed amongst
the various parts of the mass, and is transmitted to them from
the point where the impulse is applied, in consequence of
the cohesion of the parts, and the impossibility of one
part yielding to a force, without carrying all the
other parts with it.
Another crane used by Perronet at the bridge
of Orleans, with a very simple framing, was
also worked by a wheel, as is still the
custom throughout France: at all the
quarries in the neighbourhood of Paris
wheels are made use of to hoist the
blocks of stone. This kind of crane
requires to be well balanced to
be effective, and in this example
great attention was paid to
this point.
Fig. 1527.
PERRONET'S CRANES Used at orleans bridge.
B
In some experiments made at the London Docks with a wheel crane worked by six
men, a weight of 787,920 pounds was raised 7 feet in 8 hours, equal to 1915 raised one
•

CHAP. XII.
1011
CRANES, ETC.
foot high per minute by one man. At another trial the six men raised a weight of
911,680 pounds 8 feet high in 11 hours, which was equal to 1841 pounds raised a foot
high per minute by one man.
The gib of a crane should always revolve wholly round its axis, and be able to deliver
the load at any point of the circle described by the axis of the gib: in the crane employed
by Perronet at the bridge of Orleans, the whole machinery was made to revolve, which
method answers admirably well, if the necessary space can be spared.
The gib apparently worked well in one particular, for as the rope by which the stones
were raised passed over the upper gudgeon, and then between two small vertical rollers,
when it was turned round, the rope always laid fair to the windlass, while in many
other cranes the contrary takes place; so that when the gib is turned on its axis, the rope is
so bent that it forms an angle more or less acute, which causes a great increase of friction,
and a continual effort to bring the arm of the gib into a parallel position with the inner
part of the rope: much inconvenience arises also from attempting to keep the gib in
its true position by guy ropes, or other contrivances where the crab or windlass is in a
fixed position, and not so attached to the crane as to revolve with it.
Perronet balanced this crane so equally, that when poised upon the post upon which it
turned, it worked freely in any direction.
The windlass or barrel on which the rope winds had two wheels fixed on the axis, at some
distance apart, which being united with boards formed a large hollow cylinder or drum,
and was worked by men walking upwards on the inside. But to this method there are
many objections: a wheel 16 or 18 feet diameter does not afford sufficient leverage for
men so placed to turn it with much effect, and they are often overpowered by the load,
when, if one makes a false step, or slips down, the wheel runs back with accelerated velocity,
and throws them against the sides and each other with tremendous violence, often occa-
sioning death.
It is indeed surprising that such cranes should have been used almost universally by the
engineers of the last century.
A walking wheel is, however, an advantageous method of employing the strength of a
labourer, but the requisite dimensions of such a machine render it sometimes inconvenient,
and unless large, it is not sufficiently powerful; if, however, it be worked on the outside
instead of the inside, this objection is obviated, but there should always be some means
provided to prevent the too rapid descent of the weight of the labourer, should he by any
accident be compelled to quit his position, and a catch is usually introduced, which coun-
teracts any retrograde motion, and in some instances a bar is suspended from the axis of
the wheel, on which he can support himself with his hands.
Other wheels of this description are made to incline a little from the horizon, and the
labourer walks on its flat surface, but these are not preferred, on account of the great loss
of power whenever the machine is stopped: when horses or other animals are used to
tread a wheel, the path within it should present as little elevation as possible, but their
power is always more advantageously employed in a circular mill-walk.
In the construction of piers it is often convenient to have a revolving crane that will
permit the stone not only to be lifted out of the lighter, but also passed round to the side
or position in which it is intended to be laid; and this can be easily effected by making

Fig. 1528.
SEA BANK of WESTON CANAL.
the gib or arms sufficiently long, and bracing them equally on each side; when thus
balanced properly the whole may be turned on its pivot, with the load suspended at one
extremity; and for the construction of sea-walls, such a crane has been found highly
useful.
3T2
1012
BOOK II,
THEORY AND PRACTICE OF ENGINEERING.
Derrick Crane used at Granton Pier, Edinburgh, was of a very superior kind, and was
executed by Mr. Wightman: it consisted of a vertical post, supported by two timber
back stays, and a long movable der-

rick or gib, hinged at the bottom of
the post; the top of this gib was held
by a chain, which passed from a barrel
over a pulley at the top of the post,
so that the gib could be raised or
lowered. This crane commanded a
circle of from ten feet to sixty radius
without being moved.
A similar machine was used by the
ancients, and is thus described by
Vitruvius: "Three pieces of timber
are prepared, suitable to the weight to
be raised, connected at the top by a
pin, but spreading extensively at the
feet; these are raised by means of
ropes made fast to the top, and when
raised are kept steady; to the top is
fixed a block, by some called rechamus,
in which two pulleys turn on axles.'
-(Vit. cap. ii. lib. 10.)
Tackle used by the East London
Waterworks Company in hoisting their
Stand Pipe. - A piece of timber
9 inches square was attached to the
upper flanch of the pipe, and held in
its place below by an iron hoop or
girdle. Guy ropes were fastened at
the top of this upright, which served
also to suspend the snatch blocks
through which the fall ropes passed
to the crab winches: attached to the
iron hoop were two pivots which tra-
versed the lower ends of two timber
gibs, connected at top by a cross timber, from the
centre of which were suspended the blocks and tackle
connected with the large crab. After each joint of
pipe had been elevated to its place, the gib frame
was drawn up vertically by the tackle from the
small crab, and the pipe was lowered to its place; the
pins were then passed through its flanches. This
operation was continued for each successive length of
pipe, until the whole had reached a height of upwards
of 130 feet.
Fig. 1529. DERRICK, GRANTON PIER, EDINBURGH,

The architects and engineers of the middle ages
were celebrated for moving and lifting great weights,
and probably the inscription at Pisa Cathedral, which
informs us that Buschettum in the eleventh century
raised the granite columns, each weighing upwards of
16 tons, by a machine so simple that children could
work it, refer to similar contrivances as those now
under our consideration: the inscription is curious,
as it exhibits the admiration which this engineer called
forth by his ingenuity.
QD VIX MILLE BOU POSSENT JUGA JUNTA MOVE
-
ET QUOD VIX POTUIT P MARE FERRE RATIS
BUSKETI NISU QD ERAT MIRABILE VISU
DENA PVELLARE TVRBA LEVABIT ONUS.
CUY ROP
FALL
SMALL
CRAB
LARCE
CRAB
FALL
CU
ROPE
Fig. 1530. EAST LONDON WATERWORKS.
Devonport Column is built of granite from Holman's Hill quarry, and is in height 101 feet
4 inches above the surface of the rock upon which it stands: the shaft is 11 feet in diameter,
and its height to the top of the capital 65 feet 4 inches; the abacus is formed of four
stones, each weighing between three and four tons. Mr. John Fulston raised the stones
CHAP. XII.
1013
CRANES, ETC.
which compose this column without the use of scaffolding, by means of a series of tall spars
joined together, like the mast of a ship; the lowest being fixed firmly in the ground,
and braced by diagonal pieces, as well as
lashed and strutted to the lower part of the
shaft. A gaff, with a jaw at the lower end,
was then slung in the throat by a strong
rope or chain, so as to work round the
upper spar in the jaw prepared for it; from
the ends of this gaff, blocks and a fall were
suspended, which, by raising or depressing
the point of the gaff, commanded every
portion of the work. The stones were raised
by means of crabs turned by winches, and
the whole work was terminated in a short
time.

Obelisk on the Whitaw Eskdale, erected
to the memory of Sir John Malcolm, is in
height 100 feet above the foundation; it is
built with a hollow space in the middle,
with whole courses occasionally passing
through; in these a large circular hole was
left, and the crane was raised after the com-
pletion of each course. It was thus
formed: In the lower hole was inserted
a pole 10 inches in diameter, and 40 feet
in length; the next hole above served as a
stay, whilst the upper one supported the
whole weight, a collar of hard wood being
firmly fixed arcund the pole. Beneath this
collar were introduced 17 metal balls about
3 inches in diameter, which running in
grooves prepared for them enabled the pole
easily to turn round. At the top of the
pole, and placed crossways, was mortised a
beam 12 inches square, and 12 feet in length,
strengthened by diagonal iron bars and
straps.
The stones were raised by a crab winch,
the rope passing over a pulley at each end
of the horizontal beam, and moved to their
situation by a traversing carriage, which
worked on the beam by means of a small crab and pulleys.
Fig. 1531.
DEVONPORT DERRICK.
We cannot perhaps better illustrate our present subject than by giving the account of
the manner in which the obelisk in front of St. Peter's at Rome was raised by the celebrated
Domenico Fontana; its weight was estimated by that architect as equal to 993,537
pounds; the height is 180 palms, but without the apex 77.2 English feet; the transverse
section at the middle contains an area of 76 superficial feet; the solid content may, there-
fore, be taken at upwards of 166 cubic yards, weighing about 332 tons; if to this be added
4 tons for the weight of the apex, the whole weight of the obelisk raised is upwards of 336
The length of each of the sides at bottom is 12 palms, and at top 8½ palms, the
palm being equal to 8.7 English inches: 46 cranes, 600 men, and 140 horses were
employed in removing it, and the timber, ropes, and iron made use of cost 20,000 crowns.
The operations for removing it, which were conducted with the greatest skill, were as
follows:
tons.
A scaffold, called a castellum or shears, was first constructed, 7 feet higher than
the top of the obelisk when mounted on the pedestal. The eight principal timbers, four on
each side, were 89 feet in height from the foundation; they were each built of oak and
walnut, four beams in thickness, and banded at every 9 feet with strong iron hoops, and
bolted together in several parts. The whole was so arranged that it could be easily put
up or taken down, to suit the several positions in which the obelisk might be placed:
wherever this castellum was to be used, 4 holes 3 feet square were prepared in a platform
of travertine stone, into which the four posts were dropped and secured.
The obelisk was cased over with double mats to protect it from injury; was then covered
with two-inch plank, and longitudinal iron bars, 4 inches in breadth, were attached to it,
three on each of the four sides; these, connected together by nine iron hoops, served to
attach the tackle; this coating of mat, wood, and iron was estimated to weigh as much as
one-twelfth of the obelisk. Thus entirely covered, the obelisk was lifted from the pedestal
3 T 3
1014
Book II.
THEORY AND PRACTICE OF ENGINEERING.
on which it stood by means of capstans and blocks attached to the iron hoops, and the
blocks hanging to the cross beams of the shears; after it was lifted up two feet perpen-
dicularly, a platform of timber was introduced beneath it, which rested on wooden rollers,
9 inches in diameter, their ends being secured by iron hoops. The ropes of the blocks
attached to the four lower angles of the obelisk being drawn, the platform which supported

XIX

Fig. 1532.
w
Fig. 1533.
the weight moved on the rollers, and the ropes of the blocks attached to the upper part
of the obelisk being slackened, the obelisk gradually descended, and was laid horizontally
on the platform prepared to receive it: during its descent it was found necessary to support
it in the middle by two shores, made movable on an axis attached to its centre, and which
prevented any great strain on the tackle.


Fig. 1534.
Fig. 1535.
The inclined plane along which it was moved to its destination was formed of a mound
of earth strengthened with timbers, and extended from the Circus of Caligula, afterwards
CHAP. XII.
1015
CRANES, ETC.
called that of Nero, to the position where the obelisk now stands; its former site is still
marked by a stone in the passage leading from sacristy to the choir of St. Peter's. After
the obelisk had been moved along this plane upon wooden rollers, the forty-six capstans
placed round the mound of earth were prepared for their work of raising: they were fixed
in the ground on each side, and each had four arms or handspikes; the first and third
arms were worked by a horse, and the other two each by from six to ten men: four of the


Fig. 1536.
Fig. 1537.
capstans acting upon as many blocks were used for drawing the foot of the obelisk for-
ward, one block to each angle; the other capstans were employed to raise the obelisk into
a vertical position. The whole operation is amply described in a work compiled by
Fontana, and in which are engravings of the entire machinery.
The foundations prepared to receive this enormous weight were carefully executed: an
excavation 43 feet square, and to the depth of 24 feet, was made, and the bottom being
found a clay, it was piled entirely over with oak and chestnut, with piles 18 feet in length
and 9 inches in diameter, the bark being previously removed from them: upon these was
laid a bed of concrete, composed of basalt broken into small fragments, and mortar com.
posed of lime and puzzolana. The total cost of the entire removal was about 9000l.
This obelisk, which now reposes on four pieces of metal, firmly run with lead into the
pedestal, is one of those which Herodotus mentions as having been erected by Phero, son
of Sesostris, when he recovered from his blindness, and which were in height 100 cubits,
and 8 wide. Pliny also mentions it: "ejusdem remanet et alius centum cubitorum,
quem post cæcitatem visu reddito ex oraculo Soli sacravit."
Caligula transported it to Rome, and dedicated it to Augustus (Ammian. Marcell.
lib. xvii.).
When Constantine removed an obelisk from Egypt, after floating it on a raft
down the Nile, and landing it at Alexandria, he put it on board another raft or ship
provided with 300 rowers: when it reached the Tiber, it was landed 3 miles from Rome,
and placed on rollers (cuniculis, or chamulcis impositum); then moved slowly to its
destination through the Porta Ostiensis: lofty beams, and a forest of machines or capstans
were then made use of; the latter, worked by many thousand men, lifted it bodily, and
placed it erect upon its pedestal.
The various machines for raising weights mentioned by Vitruvius were made of timber,
as were those called Scansoria, applied to the walls of a besieged town for the purpose of
scaling these were so contrived that, like a scaffold, they could be quickly put together.
The Tractoria were machines employed for raising those heavy masses with which the Romans
constructed their temples and public buildings; the same author also mentions the Rotæ,
Rhedæ, Cissiæ, Torni, &c., as in common use in his day; he also refers to the Charchesium,
which is supposed to have been an upright timber, with another lying horizontally across the
top, and movable upon a hinge upward and downward, as well as having a horizontal motion
around, by which stones could not only be raised from the ground, but conveyed to their
intended situation. The tympanum, or hollow cylindrical wheel, are also alluded to by
Vitruvius, but he does not inform us how the men who turned it were disposed; and we
know, too, that the ancients made use of powerful levers, wheels, and inclined planes for the
purpose of moving ponderous masses, or lifting heavy weights: but it cannot be denied
that since Fontana constructed his machinery for raising the obelisks at Rome great im-
provements have been made in this branch of mechanics; considerable attention has been
3 T 4
1016
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
paid to the arrangement and material employed for the tackle; ropes have yielded in some
instances to chains, and levers of great length have been applied, and sometimes a series,
turning on sockets at one end, have been used, where it has been necessary to multiply
power to any great extent: by the efforts of iron and timber judiciously combined in a
well-constructed machine, weights of any amount are now raised with apparent ease and
facility.
M. Lebas, an engineer of the Marine in France, was commissioned in 1831 to bring
from Luxor in Egypt one of the granite obelisks, and raise it on a pedestal to ornament
the city of Paris; it is 75 feet in height, containing about 3000 cube feet, and was estimated
to weigh nearly 258 tons.
The obelisk was cased with timber throughout its whole length; underneath its base, at
the lower side, was placed a wooden roll or cylinder, C, upon which the whole obelisk
turned as upon a hinge during its movement: there were five stays on each side, formed of
masts, one of which is shown at D; these were all united at their summit between two others
laid at right angles with them, the whole being bound round with ropes. The ten masts
rested on a level platform, and their ends being rounded, they worked in a hollow channel

E
D
I
Fig. 1538.
RAISING an obelisk.
prepared to receive them, and together could be moved upwards or downwards, in the
manner of a hinge, so that when the ends at E were pulled down by the ropes of the
windlass attached to them, the obelisk was advanced further into its perpendicular position;
480 artillerymen worked ten capstans, forty-eight being placed to each. Iron chains were
placed around the top, and four others passed to capstans at the extremity of the inclined
plane, for the purpose of holding the obelisk steady, and rendering its motion regular as it
advanced.
The whole of the operations were admirably conducted, and some improvements were
adopted which we do not find made use of by Fontana; the application of the lever, D,
is a decided advantage.
CHAP. XIII.
1017
CARRIAGES FOR TRANSPORTING WEIGHTS.

The erection of a vase or statue on
its pedestal is generally performed
by three movements, one vertical, to
raise the object to the required
height, another to move it horizon-
tally, and the third to fix it in its
place.
The most simple method is by the
use of tackle attached to the top of a
mast, or two poles lashed together
at a height sufficient to enable the
object to be lodged where required:
such a shear or support is represented
in the cut; its position on the ground
being established by pulling it up-
right, the base is hung directly over
the pedestal; after which it may
be lowered by means of pulleys at
pleasure. The term shear is ap-
plied to the arrangements made in
our dockyards by which the masts
are hoisted into ships: one at
Woolwich is an excellent example of
this kind of tackle. The polyspaston
of the Romans was no doubt a
similar machine in every parti-
cular.
Tractorial machines, as they are
termed by Vitruvius, consist of two
movements, different and dissimilar
from each other, but so agreeing
that the operation is perfected by
both; one is rectilinear, and the other
circular, but neither alone can be
made effectual for raising weights;
when stones were raised for building
purposes, the forfices or forcipes
were sometimes used: and Piranesi
in his "Antichità Romana” asserts
that he found, in some of the an-
cient buildings, stones with holes cut
in their upper faces, in such a form
Fig. 1539.
RAISING A VASE,
***********--------
as to suit the dovetail shape of the modern Lewis or Louis; there can be no doubt but
that this instrument was used by the Romans.
CHAP. XIII.
CARRIAGES FOR TRANSPORTING WEIGHTS, AND BOATS, ETC.
Carriages for transporting Weights and Boats, &c. The daily work of a horse has been
estimated as equal to that of five or six men; its immediate force may be somewhat greater,
but it cannot work profitably for more than 8 hours a day when pulling with a force of
200 pounds, or 6 hours when exerting that of 260 pounds, and walking 24 miles per hour:
when drawing up a hill the horse loses much of his power, as he does when the carriage to
which he is attached passes over a yielding or bad road. Whenever any large quantity of
earth or other material is to be carted away, it is found profitable to lay down a provisional
tram or railroad; but where this is not practicable, the carts or waggons should be well
adapted to the use for which they were intended. The waggons generally employed on
our railways whilst the works are in progress are without springs, and are now ordinarily
drawn by locomotives or fixed engines, at the rate of 8 or 10 miles an hour.
The dynamical effect of a horse employed for raising earth-work up an inclined plane,
the base of which was 60 feet, and the vertical height 40, was found only equal to a resis-
tance of 410 pounds when travelling through a space of 72 feet in 1 minute, which is equal
to 14,760 pounds raised 1 foot high per horse power per minute.
1018
Book II.
THEORY AND PRACTICE OF ENGINEERING.
For the removal of the earth necessary to construct the foundation of the bridges built
by Perronet, small carts were used having a triangular section in the line of their draught;
each was mounted on a pair of wheels, and two attached together would be drawn by one
horse: a part of the load rested below the axle, which passed through the middle of that

Fig. 1540.
PERRONET'S CARTS.
part of the cart which retained it; and as the whole was nicely balanced and swung
upon its centre of gravity, when it was to be discharged, a very small power only was
required to turn it over and empty it of its contents.
The shafts and frame were of timber, and the axle of iron; the wheels were of
considerable diameter, and placed wide apart, to prevent their being easily upset; the tem
porary or provisional roads being often far from level, this precaution was peculiarly

necessary.
Fig. 1541.
PLAN OF CARTS.
In the rear of each cart, and in the middle of the cross tie or brace, was an
iron ring and pin, which allowed of another cart, having a pole instead of shafts, to be
attached to it.
The transverse sections and end view of these convenient carts show the manner they
were suspended, and the diagram between them exhibits the difficulty of overturning a
figure so hung.



Fig. 1542.
SECTIONS AND ENDS OF CArts.
Two carts contained together about a cube yard, and were found extremely serviceable;
they could be easily disconnected in case of accident, and attached with facility, before or
after they were loaded.
The body of the waggons employed on the railroads for the conveyance of coals is made
like the frustum of a pyramid, although in some instances the square form is preferred:
about the middle of the last century iron wheels were introduced for the carriages em-
ployed at the coal mines near Newcastle, and they are now usually of cast-iron; the rim
is made cylindrical, with a projection on one side, called the flanch, which keeps it upon
the rail; the axles are of wrought-iron, and fixed in the centres of the wheels.
Waggons for conveying coals usually discharge their contents at the bottom, on which
account they are preferred of this shape; the framework consists of two side soles fastened
together by four cross sheths well bolted. The upright sheths and top framing are of
iron, and the ends and sides are clead with deals bolted to the upright sheths; sheet-iron
is sometimes preferred to the deals, when it is riveted on to iron uprights.
CHAP. XIII.
1019
CARRIAGES FOR TRANSPORTING WEIGHTS.


Fig. 1543.
WAGGON.
Fig. 1544.
WAGGON.
Each carriage is provided with a break fastened to the side frame by a cast-iron stud; a
wrought-iron pin is keyed into this stud, on which the break works, the pin acting as the
fulcrum: these breaks or brakes were formerly called convoys, and were made of wood.
Waggons of this description carry without heaping
55 cwt. of coals. The axles should always be made of
scrap or malleable iron of the best workmanship, of about
3 inches in thickness.
Trucks upon four wheels are sometimes used at the
collieries for the conveyance of heavy material; they
are of a simple form, and usually of timber; the main
framing consists of three longitudinal pieces bolted down
upon a timber axle, under which the wrought-iron axles
are secured, upon which the wheels are placed. The

+I
-


Fig. 1545.
TRUCKS.
Fig. 1546.
PLAN.
first cast-iron wheels had their rims case-hardened, wrought-iron tires were then adopted;
and some had cast-iron naves, and rims with hollow iron spikes. The wheel now generally
in use is made of wrought-iron entirely, though some have cast-iron rims hooped with
wrought-iron; cast-iron is not found sufficiently strong where great speed is required,
nor can they be considered safe against accidents.
On some of the northern railways the carriages are more simple in their form, and are so
framed that they can be easily taken to pieces: the longitudinal bearers are mortised to
receive the uprights, and the wheels run upon

axles secured to the under side of the trans-
verse timbers at the ends. In some cases, by

་་
Fig. 1547.
RAILWAY CARRIAGE.
turning a stop on each side, the bottom of the
carriage is made to open and deposit its load
without any additional labour. The flanch
Fig. 1548.
PLAN OF CARRIAGE.
1020
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
of the wheels is about 1 inch deep, slightly bevelled off from the inner side to the outer, so
that when the wheel is running in a straight direction, the edge of the flanch is kept about
an inch clear of the rail, or from coming in direct contact with it: this is effected by making
the tire, which is 4 inches broad, slightly conical, the inclination being about one part in
seven or eight. Where the flanches are not bevelled or are too shallow, the carriages are
very apt to run off the rails, and

should they come in contact with a
defective joint in a rail the same
evil is likely to occur.
Waggons 6 feet in length and
2 feet deep are found convenient on
railways for carrying earth and bal-
last, as well as the other materials
required whilst the works are in
progress. The plan shows the un-
der side of the framing, consisting of
two stout longitudinal timbers to
receive the iron axles, upon which
the wheels turn. The bottom of
the waggon is further strengthened
by iron plates, and a three quarter
round iron bar passes from one side
of the frame to the other, to hold
them together in the middle, and to
assist in supporting the load at the
bottom. The uprights at the sides
are mortised into the bearer at
bottom as well as the top rail, and
at each angle is an iron bolt that
screws the whole together in the
direction of its height. The ends
are movable, sometimes sliding in
grooves, at others merely pinned in
their place.
Fig. 1549.
Fig. 1550.
-
RAILWAY WAGGON.

0
J
០
D
PLAN OF WAGGON.
ם
ຕ
In the construction of all kinds of
railway carriages great attention
should be paid to the centre of
gravity of the load, for if too high their oscillation is considerably increased, which frequently
occasions them to be thrown off the rails, even where the wheels have the proper depth of
flanch: the revolving parts of the machinery in a carriage should be always so balanced
that a smooth and equable motion can always be maintained.
In Italy carts of a different character are used for ordinary purposes, mounted above four
cast-iron wheels, in such a manner that they can be tilted on one side, but the body being
above the top of the wheels is objectionable


Fig. 1551.
ပြား
CARTS IN ITALY.
Fig. 1552.
Another method is sometimes adopted where low wheels are used, which only requires a
stout block to be placed over one half the axle: the waggon or cart is hung upon the edge,
which allows of its being tilted sideways for unloading. The side is hung either upon pivots
or a strap hinge, so that it can be let down to accommodate the throwing out the earth or
ballast it may contain: when the carriage is level, it is maintained in that position by a
couple of irons, attached to the opposite side to that which inclines: these either hold within
an eye or fasten upon a loop by means of a pin.
CHAP. XIII.
1021
CARRIAGES FOR TRANSPORTING WEIGHTS.


1:
Fig. 1553.
CARTS IN ITALY.
Fig. 1554.
In Tuscany the conductor, seated behind the carriage, can, by a simple lever working in a
groove upon the axles, tilt the waggon forwards, and deposit the earth it conveys down a


Fig 1555.
END VIEW.
Fig. 1556.
PLAN OF cart.
steep bank or slope, without any inconvenience or danger to himself: an iron groove passes
obliquely from one axle to the other; in this the end of a crooked lever runs, which holds
the bottom bearer of the carriage by a ring ;
when this is pushed forward, with a slight
upheaving of the load, its action lifts the
hinder part and inclines the front forward
to shoot it out.

Railway Carriages. — Waggons for the
transport of coals, as they discharge their
load generally from the bottom, are made
larger at top, or shaped like a hopper;
they are sometimes of a more cubical shape,
but this is not found so convenient.
In the example given, which is that in use
at most of the northern collieries, the frame-
work is put together with iron bolts, into
which the uprights to receive the planks
that form the sides of the waggon are mor-
tised; the wheels are of cast-iron, and have
wooden brakes fastened by a cast-iron stud.
These waggons are about 9 feet in length
at top, 6 feet 4 at bottom, and 4 feet in
height, as much in width at the bottom, and
will carry nearly 3 tons of coals.
Fig. 1557.
mlllill
MOVEMENT OF CART.
The trucks used for the conveyance of
merchandise consist of a platform or longi-
tudinal frame, diagonally braced for greater strength, on which springs are placed, in order that
the carriage may be kept as low as possible: one check of the guides over the axles project
1022
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

Fig. 1558.
RAILWAY CARRIAGE.
upwards, and is on the inside of the frame, to which it is securely bolted. The dotted lines
represent the checks of the chair, within which the guides slide up and down.
These are
carefully fixed, to prevent any twisting or oscillation, to which the framework would be

Fig. 1559.
•
P
W
PLAN OF CARRIAGE.
>
subjected. These trucks on a railway 4 feet 8 inches in width have a superficial area of
platform equal to 75 square feet, and generally carry about 4 tons weight.
The second class passengers' carriages have the same kind
of frame, on which iron uprights support a curved top;
they are partly inclosed, and the seats are arranged between
the divisions. These carriages have sometimes a semicir-
cular bearing on the axle by means of a chair, which is
bolted to the framing of the carriage by two bolts, the
under side of which embraces the lever half of the axles
diameter, and is bolted to the chair above. Oil is poured
upon the axle through a cup and small tubular passage which is
sometimes made suf-

ficiently capacious to
contain a cotton wick
which drops the oil
upon the axle as it
is required.
In many carriages
the bearing is on the
outside of the wheels,
the end of the axle
being diminished gra-
dually towards its ter-
mination, where it is
again increased to
prevent its sliding.
The chair is an iron
box cast in two, se-
Fig 1560.
AXIES OF CARRIAGES, ETC.
Fig. 1561.
CHAP. XIII.
1023
CARRIAGES FOR TRANSPORTING WEIGHTS.
parated at the level of the diameter of the axle, or in the middle, where it is fastened
together by iron bolts. The brass which surrounds the axle and is contained within the
iron chair is nicely turned, and in the chamber above, which is cast in the chair, the oil
is put, which drops over the axle, to destroy the friction; an inclined lid resting against
the spring of the carriage allows it to be replenished as often as required.
The carriage spring has its bearing on the chairs, to which it is also attached by an iron
bolt passing quite through the chair, and secured at the bottom by a nut on the plan is
shown the grooves which allow the vertical guides to work, that are attached to the outside
of the carriage.
Thus the manner of fixing the wheels of railway carriages is the reverse of those in-
tended for the ordinary road, where the wheels revolve on the axle; in the former, they
are guided by the flanches, and as the carriage is not required to turn, it is securely
fixed to it.
The bearing of railway carriages, on which the axle turns, in common waggons is placed
within the wheels when they are outside the framework; in those constructed latterly upon
an improved plan, the bearings are on the outside of the wheels, so that a greater width of
framework is acquired, as well as elevation above the wheels, which raises the centre of
gravity. The springs, which are made long and straight, are all placed above the frame, so
that the platform, which receives the load, need not be elevated to an unnecessary height.
When the bearings in which the axle turns are placed outside the wheels, there is an
advantage over the plan of having the journal or bearing inside, as well as less friction
created; journals of wheels 3 feet in diameter may be reduced from 3 to 21 inches in
diameter, which presents considerably less surface in contact. The journal of the axle
requires to be turned with the greatest care, as any unevenness would produce considerable
mischief: at the outer end it should be made a trifle more in diameter, and be provided
with a collar, to prevent the axle from having any lateral movement.
In the nave of the wheel a square hole is bored to obtain a more perfect fit, and the
end of the axle is wedged firmly into it: in all the common carriages the bearings in which
the axle turns are placed inside the wheels when these are outside the framework, but in
those built upon the improved principle, the bearings are placed outside the wheels.
For lubricating the axle, there is a small box placed directly over the bearing, having a
small hole in the bottom through which palm oil or tallow may run upon the journal when
the angles become heated; as the contents melt away, fresh ointment, as the mixture is
termed, is supplied by lifting up the lid, which is kept closed by a spring whilst the
carriage is in motion.
Buffing Apparatus is composed of round blocks or discs of metal or wood, whch project
from the ends of the carriages, and are commonly covered with cushions of leather; they
are fixed to the ends of iron rods placed underneath the
framing of the carriage and have a free motion inwards, where
they press against an elliptical spring, when they touch or
come into contact with those of the adjoining carriage:
whatever may be the number of carriages in a train, the
buffers are all made to stand in a line with each other, so
that whenever any concussion takes place, the shock is con-
veyed throughout, and consequently materially lessened in its
effect: the buffers are also made so that the springs serve
either for pulling or pushing the carriages.
Several other kinds have been used, in which chain and
screw shackles keep the heads of the buffers constantly in
contact with each other; and some are furnished with spiral
springs, with an iron rod passing from one end of the carriage-
frame to the other, the buffer heads being connected by chains;
in such the rod of the buffer at each end passes through a
hollow tube, where it is surrounded by the spring, which
presses against the tube, but does not enter it.
Air, from its elasticity, has been found to diminish the
effects of concussion when confined in a cylinder, and acted
upon by pistons fixed in the place of buffers.
Boats for the Transport of Stone, to form Breakwaters, &c. &c.
- Suetonius (in Claud. c. 26.) informs us, that when Claudius
built the harbour at Ostia, by throwing out an arm right and
left, in order to form the pier which closed its entrance,
he ordered the ship to be sunk which had brought the
Fig. 1562. BUFFERS.
great obelisk from Egypt, and Pliny, lib. xvi. cap. 76.,
mentions that it was formed of immense timbers, one of which, a fir, was of prodigious size,
and that nothing ever appeared at sea more astonishing than this vessel, 120,000 bushels
of lentiles serving for its ballast. Granite columns of such dimensions as those which

1024
Book II.
THEORY AND PRACTICE OF ENGINEERING.
ornament the portico of the Pantheon, must have required vessels or rafts of considerable
size to have borne them across the Mediterranean: of their construction we have, however,
but vague accounts handed down to us, but we have descriptions of many employed in the
transport of the marble from Greece to Rome, and in some instances we learn that they
were not calculated for their destined purpose.
De Cessart's Machine for throwing large stones into the sea consisted of a pontoon
carrying an inclined plane made at an angle of 22°; this deck had a level platform, 6 feet
in width, to carry the stone, which was placed on three rollers 6 inches in diameter, and

Fig. 1563.
DE CESSART'S MACHINE.
which were hooped with iron: a gib moving on a pivot was furnished with pulleys, and
kept in its place by two iron rods: two wheels and axles worked the ropes, the wheels were
12 feet, the axles 1 foot in diameter.

Iron chains first lifted
the stone, brought by
lighters or other vessels;
the wheels were then
turned till the necessary
height was obtained, when
the hook was detached,
and the wheels worked,
fill the gib was in the
position indicated by the
dotted lines. It was then
slightly unrolled, and the
stones were placed on the
three rollers; two men
with levers pushed them
forwards to the inclined
plane, when they were
allowed to slide forwards
into the sea.

Fig. 1564.
de cessart's MACHINE,
The boats used for conveying the stone to the Plymouth breakwater were so arranged
that they could be easily unloaded by similar tackle, and their contents be thrown into the
places marked out to receive them. The transverse and longitudinal section through one
of these boats exhibit the manner in which the stones were placed; each mounted upon a
small carriage could be easily lowered by the inclined plane at the stern into the hold, out
of which they could, by means of a windlass, be drawn up upon deck and lowered.
The arrangement of the ballast and stores of a ship, or its stowage, is of the greatest
importance, as we know that the sailing of a vessel depends on the situation of the
centre of gravity, which is determined by the disposition of the movable weights on board;
to this subject Daniel Bernouilli, Euler, Bossuet, and others, directed their studies; they
have shown us the manner in which such weights affect the position of its centre
of gravity, the stability of which is increased or diminished according as it is lower
or higher in the ship; to place the weight, then, as low as possible is necessary; when the
CHAP. XIII.
1025
BOATS, ETC. FOR TRANSPORTING WEIGHTS.
stability is required to be increased, the nearer the stones are deposited to the middle of the
ship, in the full parts of the body, the more effectually will this be accomplished.

88
Fling
Fig. 1565.
BOATS FOR THE BREAKWATER.
Machines, &c. for proving the Strength of Materials, differ in their arrangement according
to the strains that are to be tested. We shall consider, first, what materials may be drawn
asunder by a force acting at the end; secondly, how they may be compressed by a force acting
in the same direction; thirdly, how they may be strained laterally, one part being supported,
and the strain immediately applied at the point of support; fourthly, how they may be
similarly affected transversely; fifthly, how they may be twisted; sixthly, how they may be
strained by any two or more of the above forces, and also how they may be strained by an
internal pressure, as is the case with hydraulic cylinders, water-pipes, &c.
First, with regard to the resistance to extension in length, arising from the direct cohe-
sion of the fibres or particles of matter; this kind of strain in timber requires some care to
be observed in ascertaining it, as the fibres are liable to be injured or destroyed when
roughly experimented upon: one of the best machines for the purposes here required is
described by Mr. Peter Barlow, in his Treatise on the Strength of Materials, and who made
experiments with it upon a piece of wood 12 inches in length, the square ends of which
were 3 inches, and the side of the square 1 inches; the intermediate part, 5 inches in
length, was by means of a lathe reduced to a third or a quarter of an inch in diameter, the
other cylindrical portions being left 3 inch in diameter; these pieces, so prepared, were
placed at the top of the frame, and passed partly through a circular hole in an iron frame,
laid horizontally upon two upright supports; the sides of this frame were then screwed
tightly together to prevent the piece of prepared wood being pulled through; a couple of iron
boxes were placed upon the lower square, and screwed tightly up; near the top they had
two semicircular holes, correctly fitted to the larger part of the cylinder; these were shut by
passing bolts through them, which perfectly secured the two shears; the head of the piece
of timber was placed above the collar, the upper large cylinder being retained in the hollow
iron chamber at top prepared to receive it; and the lower square end, inclosed in the two
iron boxes, the hook of the scale was passed through the circular hole, and the scale, being
wedged up from the ground, was loaded.
Among many experiments, the following results have been obtained, the smaller cylinders
being reduced to what they would have been on square inch bars, it being assumed that
the strength is proportional to the section of fracture:
Box
Ash
Teak
Fir
-
1
20,000 pounds per square inch.
17,000
15,000
-
12,000
15,500
10,000
9,000
8,000
Beach
Oak
Pear
Mahogany
Of the Stiffness of Beams supported at one end: as it is difficult to fix a piece of timber in
this manner, so that it will not be liable to extension beyond the point of support, there is a
great difference in the results of the several experiments that have been made on the subject.
3 U
1026
Book II.
THEORY AND PRACTICE OF ENGINEERING.
The beam which has one end placed in a wall and loaded at the other end will be
deflected from its horizontal position into an oblique direction, and Mr. Tredgold gives
for

Weight
Breadth
Specific Length in in
Gravity.
Feet.
Depth Deflexion
in
in
Inches. Inches. Inches.
produ- Value of
cing De- constant
flexion in Quantity:
Pounds.
Oak
Riga fir
•922
•537
44
2 2
2
1.176 112
1.34 112
•105
6
•12
2 2
The deflexion becomes greater as the distance A C is increased, and the equation given
when a beam is fixed in a horizontal position, (
*******
L x
b x W
0.6
D, and 0.6 D = B.
When the piece of timber is inclined, and c is the angle of inclination, (L x
To
bx cos. cx W³ {
0.6
A
B
D, and 0.6 D – B.
The value of b for oak being 105, and for fir 12; the deflexion calculated as inch
per foot in length. A beam fixed in the before-men-
tioned position has its fibre in the same state of tension
as when supported in the middle and loaded at each
end, its length being in one case double what it is in
the other : when resting on a fulcrum or support in the
middle, and acted upon by two weights at the end, it is
almost in the same condition as the force AB, excepting
that it has a double strain in contrary directions.
make the necessary experiment, Mr. Peter Barlow em-
ployed a block of hard wood, 18 inches long and 12 inches
square, which was cut through at about 5 inches from
each end for the convenience of forming a mortice or
hole 2 inches square, and as much in depth; the two parts of the block were then screw-
bolted together, and an iron socket 2 inches square on the inside, made to fit the holes,
was inserted in the mortice; the block was fixed by wedges into a wall, so that it was
quite firm and steady. The pieces of timber tested were reduced to a scantling of two inches
square, and made to fit tight into the iron socket, upon the other end of which the weight
was suspended.

Fig. 1566.
W
Of the Machines used to ascertain the Resistance of Materials to a crushing Force. — The
exciting force here acts directly in the reverse manner to that we have already described,
and we have also to take into consideration the state of the material acted upon, whether it
is too short to bend, as well as when its length is considerable with regard to its other
dimensions: in the first case, small pressure would crush it; in the other it might bend,
and afterwards alternately break, by a force somewhat similar to that exerted by a trans-
verse strain. Experiments were made upon the crushing force by Rondelet, which are
detailed in his Art de Batir; he states that a piece of oak whose base is an inch square
would require 5000 or 6000 pounds weight to crush it, and a similar piece of fir would
bear the additional pressure of another 1000 pounds.
Mr. Rennie found that a cube of English oak an inch square required only 3860 pounds
to crush it, which result materially differs from the other, and leaves us still in considerable
doubt upon this subject. Screw-presses and long levers have been made use of for testing
materials, and to ascertain the exact crushing force; both methods might possibly be em-
ployed with advantage, and the results calculated from the practical effects
The Hydrostatic Press is a machine by which prodigious force can be obtained, and is
frequently used to cut through bars of iron, as well as to press paper, cloths, and other
materials into a smaller bulk. A solid cross beam or piece of timber is fixed upon the
two upright posts A, which are either let into the ground or framed into a sill at the
bottom, and another, E, laid in an horizontal position, slides between the upright timbers;
between this and the top the articles to be compressed are laid. The horizontal timber is
supported on the under side by the piston D, which works in an air-tight cylinder F, at the
bottom of which is a small pipe or tube b of much smaller bore; the other end of this tube
enters at the bottom of a forcing pump L, and when the piston in the latter is pressed down,
the water in the cylinder is forced under the piston which carries the horizontal timber and
occasions it to rise. The difference of the size or area of the surface of the small tube,
compared with that of the rising piston, constitutes the power; for if the sectional area of
the tube be inch, and that of the rising piston 1 foot, as 576 to 1, or as 144 square inches
to inch and supposing a pressure of a ton weight to be exerted on the handle H of the
CHAP. XIII.
1027
MACHINES, ETC.
pump, the piston in the air-tight cylinder will press with a power equal to 576 tons: this
power has no limits, when materials can be found strong enough to make the machine.
Within the space or area of 100
inches and 1 foot in height, a
power equal to 500 or 600 tons
may be easily directed against
any substance that may require
pressing, tearing up, cutting, or
pulling asunder.

A
E
D
L
F
H
The operation of this press is
easily understood by supposing
the pump cylinder and connect-
ing pipe b to be filled with water,
and an adequate supply contained
in L: when the handle of the
lever H is raised, it lifts the piston
rod f, which would leave a va-
cuum beneath if the atmosphere
did not force the water through
the lower valve of the pump; the
lever being then pressed down,
the piston rod, by descending,
diminishes the capacity of the
pump, which causes the lower
valve to close, and forces the water through the pipe b into the cavity of the great cylinder
F, where it raises the piston D, together with the table E, a distance proportional to the
quantity of water which has been injected: on the rise of the piston in the pumps, the
descent of the upper valve prevents the return of the water, and consequently the fall of
the cylinder D. There is a discharge valve to relieve the action of the press, and which
permits the water that escapes to pass again into the cistern at L, when the table E again
descends.
Fig. 1567.
HYDROSTATIC PRESS.
We have only described the action of a single pump, but where great power is required,
a number worked by double handles are made use of; in which case particular caution is
required to insure accuracy and to prevent leakage.
Previous to the blocks and ropes being used at the Menai bridge for hoisting the several
parts, their strength was tested by a load of 50 tons placed in a square box: the frame was
made of timber, the posts of which

were 40 feet in length and 15
inches square, strongly framed
both at top and bottom: two
capstans placed at a distance
were attached to the main falls,
which passed through a pulley
at the bottom of the frame, by
which means the loaded box was
lifted off the ground, and every
portion effectually proved. The
tackle by which the main chains
of the bridge were hoisted to their
respective positions was first put
to the test of supporting 50 tons.
In the machines for proving
the iron work, the bar upon which
the experiment was to be made
was secured at its two ends, in
the same manner as the blade of
a pit saw: the power was obtained
by three cogged wheels working
in as many pinions; the radius of
the first was 1 foot 10 inches;
of the second, 2 feet 6 inches;
and the largest, 3 feet 6 inches: the diameter of the largest pinion was 134 inches; and
the other 10 inches.
Fig. 1568.
PROVING ropes, used AT MENAI.
The length of the bed of the machine was 12 feet 10 inches, and the diameter of the
axis of the largest wheel 8 inches: the levers and weights that measured the strength
were adjusted underneath the machine, the end view of which is shown at the top of the
figure; the diameter of the cylinder was 8 inches.
3 U 2
1028
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

wwwwww
CPIDE
១១៨២
Fig. 1569.
PROVING IRON WORK, USED AT MENAI,
Machine for bending Iron Plates is of the greatest service for the manufacture of boilers:
on the left of the figure are two riggers, one tight and the other loose, for driving the two
cylindrical rollers, the speed of which is regulated by the spur-wheel and pinions; on the
right is the fly-wheel placed on the driving shaft, which maintains a steady motion when
the machine is in use. The curvature to be given to the iron plate is regulated by a large
screw attached to each cylinder, which brings them nearer, or drives them farther from each
other, according to the required bend.

De
O
Fig. 1570.
1回
​O
O
BENDING IRON PLATES,
Fig. 1571.
SECTION.
Machine for making Screw Bolts. — A backward and forward motion is given to a hollow
shaft by three driving pulleys; when the strap is on that to the left, the spur-wheel and
pinion put the machine in motion, and communicate it to the chuck which holds the steel


B
wwwwww
B
C D E
Fig. 1672.
END VIEW.
Fig. 1573.
ELEVATION.
CHAP. XIII.
1029
TOOLS AND MACHINES.
In
cutters; and after the screw has been cut, by placing the strap on the other outside pulley,
the great internal wheel is made to revolve on the lower shaft, and draw the screw back to
its original position: when the strap is put over the loose pulley in the centre, the
machine does not produce any working effect, but is in the condition of perfect rest.
the section, the cutting of the screw is seen passing through the upper part of the chuck,
and these are removable when required. The bolts which are to be screwed are held by
a sliding frame, shown on the guide bolt, opposite the chuck in the elevation.
The two end views of the machine exhibit the iron frame as well as the gearing, and
when a screw is to be formed, all that is requisite is to place the bolt in the sliding frame,
and present it to the action of the die or cutter in the chuck, which, as it is turned round,
forms the thread.


В
C
Fig. 1574.
END VIEW.
A
CED
Fig. 1575.
SECTION.
B
The end view of the machine shows one of the two frames that support the works, as
well as the plummer blocks in which the two spindles marked A, A turn: the wheel marked
B reverses the motion when it is required by the application of the loose pulley shown at
E: Cis the pulley which communicates motion to the spur-wheel at B: F is the frame
into which the bolts are placed which are to have their ends made into screws.
The Lathe has of late years received so many improvements, that it bears no resemblance
to the long lath or pole which was fixed at one end to the ceiling or wall of the workshop,
and had the other moved by a cord passing over a pulley, and carrying the mandrell, which
was moved by a board or treddle: on raising the foot, the spring of the lath caused an
opposite rotation, which was again reversed by the pressure of the foot, causing the lathe
to work as a drill, the cutting taking place only during each direct rotation.

©!!
Fig. 1576.
FOOT LATHE.
The lathe now consists of a horizontal bed, formed of two parallel bars of wood or metal
firmly united together: to this are attached two puppets, one of which carries the mandrell
and pulley, which is fixed in its place, and the other the back centre, which slides between
the double bed, or along a single bar introduced for the purpose. The rest also slides on
the bed, which supports the cutting tool, and underneath is an axle with a crank; to the
former is attached a fly-wheel with a groove to carry the band, which passes over the pulley
to the mandrell; to the crank is attached the footboard by an iron bar, which produces the
motion to the fly-wheel and the other parts of the lathe.
Lathes are now generally made with cast-iron sides of a triangular form, bolted or
screwed together at the iron flanches at top: the puppet on the side next the end view of
the lathe is firmly secured by a bolt with a square head which passes through an iron
3 U 3
1030
BOOK II. '
THEORY AND PRACTICE OF ENGINEERING.
block under the bed of the lathe, where its end, with a screw cut upon it, receives a nut:
the rest may be turned in any direction, but is fixed in its place in a similar way to the
back puppet; the front puppet is also secured
by a screw and nut, and has a motion along the
bed when required: the chucks, formed of brass,
are tapped and screwed on to the mandrell, with
a hole in each to receive the wood to be turned.
Previous to the application of the slide rest
to the lathe, the tool was held by the work-
man and entirely guided by his skill, and in
turning the shaft of a column, it was scarcely
possible that his unaided efforts could bring the
whole into the true frustum of a cone, or that
he could set out the swell or entasis at a certain
portion of its height with the requisite precision:
but when the principle of sliding the rest which
held the tool for cutting was introduced, the
shaft could be turned with extraordinary correct-
ness: the cutting instrument in this new arrange-
ment is held firmly and securely, and made to
progress in a definite direction by means of a
slide, the motion being communicated by a
handle that turns a screw: two such slides pro-
duce a motion along as well as across the work,
and so nicely is this arranged by turning the
screw handles, that it is scarcely requisite to
look at the operation as it goes on.
Mr. Henry Maudsley contrived a self-acting
slide rest, which has produced great improve-
ments in every kind of machine: a piece of iron
is attached to the work at one end, and turns

Fig. 1577.
round a star wheel at the end of the screw that moves the rest, which at each revo
lution of the lathe turns the screw and moves forward the slide rest, which carries the

Fig. 1578.
SLIDE REST.
tool onwards by degrees until the whole is very accurately turned, without the constant
attendance of the workman. This ingenious contrivance has been applied, as we shall here-
after see, to a variety of other purposes.
Drilling machine is far more serviceable than the ordinary bore, and indispensable when
the heavier kinds of iron work are to be drilled. The winch or handle is carried by two
standards, and may be turned by three men; this, by means of a bevelled wheel, turns
another placed horizontally, through the centre of which the drill shaft passes freely, and
descends as the drilling proceeds. The drill at top, surrounded by a collar, is worked by
a rack and small pinions attached to another wheel, over which passes an endless
chain, which when pulled raises the rack and drill shaft; it is supported by a ratchet-wheel
CHAP. XIIL
1031
TOOLS AND MACHINES.

and spring fall. Two iron
standards passing from a pit
in the floor of the manu-
factory support a table at
any required height, on which
the iron work to be drilled
is laid; the drill is inserted
in a socket at the bottom of
the shaft, where it is secured
by a bolt.
The portable Hand Drill is
a similar machine, and found
very convenient for a va-
riety of purposes, particularly
where the work to be drilled
is difficult to move. A frame
supports the upright spindle
which carries the drill; on
the top is a screw, by which
it can be raised, and the re-
volving motion is given by
two small bevel wheels placed
at right angles with each
other; these are turned by
a small fly-wheel, to the rim
of which is affixed a handle
for working it; at the same
time, a slight revolving mo-
tion is given to the upper
handle, which causes the drill
to descend.
The Foot Drill differs only
in the mode by which the
upright drilling spindle rises
and falls; the examples al-
ready given are self-acting;
on this it is performed by
the pressure of the foot.
Fig 1579.
Fig. 1580.
பா
DRILL.

HAND DRILL.
Machines for boring or upright drilling were some years ago much employed in the pre-
paration of timber water pipes. In the work by Belidor before alluded to, the tree to be
bored is mounted upon a truck or wheel carriage, and well secured in its place: a water-
wheel gives motion to a vertical spindle, which by means of a trundle and face-wheel moves
round a horizontal bar that carries at one end the auger, by which the boring is effected:
as this revolves, motion is given to another wheel, around the shaft of which is attached a
rope that draws the carriage forward on which the tree is placed, as fast as the borer cuts
its way: when the whole is cut through, the carriage is drawn back, and the process is
repeated with a larger auger, and so on, until the whole is of a sufficient diameter.
In some machines the tree was made to revolve, and the cutter was fixed: the tree was
in a vertical position, and in other instances the core was cut out whole; this was per-
formed by employing a hollow cylinder, armed at the extremity with a circular saw, of the
trepanning form, the cylinder being made to rotate as the saw cuts its way: the core
entered the hollow of the cylinder as the latter advanced, and was thus preserved.
Stone
pipes were so cut that the block of stone was set nearly upright, and in the centre of the
intended pipe a block of wood was fixed, with a hole drilled in the middle to receive the
pivot of a perpendicular axis or spindle, considerably larger than the intended pipe, and of
a triangular or square form; this revolving, performed, by means of the cutter which was
attached to its end, the centre operation.
The horizontal boring Machine used for metal cylinders consists of a piece of iron callea
a cutter-head, which slides upon an axis, and has the knives or steelings which perform the
boring fixed into it. The cylinder to be bored is firmly secured upon a frame prepared to
receive it, and the cutters are advanced by means of a hollow cast-iron tube, on each side
of which is a longitudinal groove or aperture: the cutter-head consists of two parts, viz.
a tube fitted upon the axis with the greatest accuracy, and a cast-iron ring fixed upon four
wedges; on its circumference are eight notches, into which the cutters or steelings are held
by wedges; the slider or cast-iron ring is prevented from slipping round by two short iron
bars put through the axis, and passing into notches cut in the ends of the sliders. The
3 U4
1032
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

B
D
L
A
A. Sills.
B. Frame.
D. Cylindrical axis.
E. Iron supports.
Fig. 1581.
D
N
E
B
M
L. Cylinder to be bored,
M. A rack.
N. Pinion.
P. Weight.
BORING MACHINE.
rack is moved by the teeth of a small pinion, and maintained in its place by a roller under-
neath it, both axes of which are supported by the iron framing.
By means of a lever put upon the square end of the axis, which is loaded by a weight,
the pinion is turned round, giving to the cutter a constant tendency to draw through the
cylinder. The axis on which the cutter is placed revolves, and the accuracy of the machine,
depends upon its being truly turned, and on the centering of its pivots and gudgeons.
There are several varieties of boring machines, and other contrivances for drawing the
cutter through the cylinder: one consists of four wheels, one of which is fixed at the right-
hand extremity of the bar; another pinion takes the place of the rack, on which is a screw
working in a female screw fixed to the cutters below the second pinion is a third, fixed
on a horizontal axis parallel to the long bar, and having the same number of teeth; a
fourth pinion is placed at the other end of the axis, and is driven at the end of the hollow
axis. The first pinion has twenty-six teeth, the fourth thirty, and the second and third

K
D
K
K
J
K
N
M
K K. Cutter heads.
Fig. 1582.
L. Wedges.
CUTTER OF BORING MACHINE,
ff. The cutters.
the same number: as the axis revolves, the first pinion fixed on its extremity drives the
fourth, which by means of the third fixed on the same axis with it gives motion to the
second; the second pinion being fixed to an axis within the other unscrews the screw at
the other extremity, and advances the cutter along the cylinder: this screw has eight
threads in an inch; sixty turns are consequently required to cut an inch.
Some care is required in fitting the cutters, which are secured by wedges, and adjusted
by turning the axis round, to see whether they describe the same circle; the boring com-
mences by putting the axis in motion, and the machine then requires no further attention
than observing if the weight is lifted up as often as it descends by the motion of the cutters;
when the cylinder has been once passed through, they are again set to a large circum-
ference, and proved the second time, and so on until the boring and polishing is complete.
During the last few years great consideration has been paid to the manufacture of every
kind of tool that could perform the work of the mechanical engineers, with more imme-
diate effect and economy of time than could be produced by mere manual labour; all these
tools or rather powerful engines, used for the construction of others, are admirably described,
accompanied with engravings sufficiently large to explain all their parts and proportions,
in an edition of Buchanan's Millwork, edited by Mr. George Rennie: this elegant work,
containing also practical and very valuable observations on the sharpening of tools by
Mr. James Nasmyth, should be in the hands of every engineer; the latter writer, in an
essay in the appendix, shows us most clearly that in forming and setting a cutting tool, so
that it rightly performs its work, it is necessary that it be so placed that its end forms
the least possible angle with the surface to be cut; it must consequently be nearly parallel
with the face or plane it is to act upon
The workshop of the engineer at the present day contains machinery of the most costly
CHAP. XIII.
1033
TOOLS AND MACHINES.
kind, and the means now adopted to furnish that which the growing wants of our manu-
facturing and industrious population require, differ materially from those in use half a
century ago, when all work was performed by manual labour: an estimate of the value of
these leviathan tools, consisting of turnery lathes, planing, riveting, boring, screw cutting,
plate bending, punching machines, and others in a large establishment, would show the en-
terprise and skill which the demand for steam-engines and machinery employed in com-
merce and manufactures has called forth.

9
(0)
ť
k
m
Р
Fig. 1583.
CYLINDER BORER.
For boring the Cylinders of Steam-engines a powerful and very accurate machine is re-
quired: the cylinder is sometimes placed in a horizontal position, and when fixed the
cutters are made to revolve, and advance forward by the force of machinery; in boring
1034
Book II.
THEORY AND PRACTICE OF ENGINEERING.
9
guns, as the gun moves round, its exterior surface is turned quite true by means of a lathe...
Musket barrels are similarly bored and turned by
the several motions of the common turning lathe,
one machine finishing three barrels per hour.
The vertical boring machine, now generally
preferred, has the motion given to the upright
or drilling bar by three driving pulleys shown at
c, the speed of which is regulated by the spur-
wheels and pinions at d. When the drilling bar
is required to be lowered or raised, it is effected
by the spur gear at ƒ, immediately above the nut
in which the screw works.
The plan of the machine shows a slide at m,
which carries the work, and the table upon which
it rests is raised or lowered at pleasure by the racks
and pinions at n,n, worked by the handle at o,
which communicates with the spur-wheel and
pinion p: within this is a ratchet-wheel. In
the elevation at 1, is a small lever or handle,
for throwing the small clutch at k in and out of
gear, and the drilling bar is marked by e, t being
the boring part of the bar, which can be made to
bore a cylinder to the depth of 24 inches from
an inch up to 14 in diameter. In some machines
an alteration of speed is obtained by means of two
shafts, one of which has a wheel working in a
pinion, and the other a pinion on a wheel.
A boring machine may be defined as con-
trived for working a borer or tool, which, by a
rotary motion on its axis, cuts out a hollow cy-
linder in any substance it is applied to; the whim-
ble, the drill, the pulley, and the bow, are all of
this class, but we now only use the term to
an apparatus for boring large cylinders more
accurately, and in shorter time than can be per-
formed by manual labour. The method formerly
adopted for boring cylinders for pumps was
an horizontal axis turned slowly round by a
mill, at the end of which the borer was attached;
the cylinder fastened to a carriage, made to
slide in the direction parallel to its axis, was
drawn forwards by means of a weight that could
descend. The defect of this system was the
liability that the rectilineal motion of the carriage
would be transferred to the cylinder, and cause it
to be bored improperly. Smeaton remedied
these evils to a certain extent, by introducing a
steel-yard mounted upon a movable wheel car-
riage, which traversed with the cylinder, and by
suspending the weight of the cutter and boring
bar from it.

m
រ
t
-
yi
Հոդվ
Machines for punching Boiler Plates with the
greatest possible accuracy are now made use of,
instead of the ordinary punching machine, which
required the rivet holes to be marked out by a
template with white paint, and afterwards brought
under the punch: the plate is now affixed to the top of a movable table, and when it is
adjusted to the distance required between the rivets, the rest of the work is performed
by machinery. In the Royal Dockyard at Woolwich, several of these punching ma-
chines are at work in the shop where the steam boilers are wrought.
Fig. 1584. side ELEVATION
The plate to be punched being laid upon the movable table at k, and secured by clamps,
is brought over the die frame at i, where it is also directly under the influence of the
punch; the whole of the machinery is mounted within a strong iron frame, and motion is
conveyed to it by the tight and loose riggers at a, a, at the side of which is a fly-wheel for
regulating it; on the spur-wheel at m is a tappet or pin, which, coming in contact with a
small lever, as the spur-wheel turns round, advances by a connecting rod the table shown
at k, which runs along a railway provided for it by means of two carriages attached to the
CHAF. XIII.
1035
TOOLS AND MACHINES.
travelling table, and supported on the notched bar n: holes are now punched in plates of
sheet iron or copper with great accuracy and rapidity.

K
P
α
о
α α
Fig. 1585.
PUNCHING BOILER PLATES.
Punching Holes in plates of wrought-iron and copper: in experiments made with a cast-
iron lever 11 feet in length, when the strain was multiplied ten times by means of a screw
and counterpoise, the following results took place :
The sheets to be punched having been placed between two perforated steel plates, the
punch was introduced with a perfectly flat face, and then forced by the pressure of the
lever. The punch was inch in diameter, and through plates of iron 08 of an inch in
thickness, it required a power of 6025 pounds; through one of 17 inches in thickness,

10)
Fig. 1586.
PUNCHING holes.
11,950 pounds; and another of 24 inches in thickness 17,100 pounds: through a copper
plate 08 inches in thickness 3983 pounds, and 17 inches in thickness 7883 pounds.
The power required to punch holes of different diameters through metals of various
thickness is directly as the diameter of the holes and the thickness of the metal.
A plate 1 inch in thickness and having holes an inch in diameter being taken as unit
for a calculation, we shall have 150,000 as the constant number for wrought-iron plates, and
96,000 for those of copper. These constant numbers being multiplied by the given
diameter in inches, and then by the thickness in inches, the product will give the pressure
in pounds, which is required to punch the hole.
Riveting Machines now perform the work which usually required three men, the holder
on, or the one who placed the hammer against the head of the rivet, and two others, who
beat out the iron to the conical form given to its opposite end: the noise which ac-
companied this operation is now entirely prevented. The motion is given to the machine
by a leather strap, which communicates with both a tight and loose rigger; the speed is
prevented from being too rapid by a pinion and large spur-wheel; as the pinion makes six
revolutions, that on which the large wheel is hung, and also the cam, revolve but once.
The riveting lever rises and falls by the action of the cam, the face of which is steeled:
at the lower end of the lever is a steel roller, which is turned as often as the cam works
against it: this materially obviates the friction, which would otherwise be very considerable.
The riveting lever moves on a fulcrum, and is connected to the riveting tool by two short
links; this is kept at its work in a true and horizontal position by sliding backwards and
forwards in a socket bearing.
The riveting block, in the form of a frustum of a cone, is placed on the sole plate,
which receives the side framing: when the work is performed, the rivet is placed in the
hole prepared for it by the punching machine: the machine is then put in motion by
1036
THEORY AND PRACTICE OF ENGINEERING. BOOK. IL

၁ဝဝဝဝဝဝဝဝ
Fig. 1587.
RIVETING MACHINE,
F
HH
changing the position of the strap from the loose to the fixed pulley, which being com-
municated to the riveting tool gives the required shape to the rivet.
Eight rivets, inch in diameter, can be firmly fixed by this machine in a minute, by
the assistance only of two men and two boys. In the common process, three men and
a boy were required to rivet up forty in an hour; there is consequently a saving of more
than 10 per cent. in the labour.
A very ingenious machine was made use of for boring the eyes of the main chain links of
the Menai bridge; the side elevation and plan sufficiently indicate its form; the large

B
1
Fig. 1588.
BORING EYES OF MAIN CHAINS, MENAI.
19 18
D
CHAP. XIIL
1037
TOOLS AND MACHINES.
wheel was 5 teet 8 inches in diameter, and the small one 2 feet 8 inches: the transverse
part of the machine is shown below, as is the end of the spindle and cutter: the whole
was put in motion by means of two winches or handles and an endless chain.
Shears for cutting Iron or Copper either into square plates or lengths are formed in a
similar manner to those for punching the metals, except that the motion given to the cutting
part of the shears acts very gradually, by means of a circular eccentric. The lever has
a wheel at its extremity, which moves on its axle: on the edge is a groove in which the

Fig. 1589.
SHEARS Ffor cuttING IRON.
edge of a larger wheel works, which has the axle out of the centre; so that when the
rotary motion is communicated, the movable branch of the shears opens and shuts, the
weight of the lever keeping the small wheel at all times in contact with the eccentric; by
this means very stout iron bars are easily cut asunder.
Slotting or key-grooving Machine somewhat resembles one made use of by Messrs. Boulton
and Watt at Soho for

cutting the teeth of
wheels.
Slotting, paring, and
key-grooving, require
that the machine should
have an alternate or
reciprocating motion,
which is usually pro-
duced by a crank or
dog wheel. The ma-
chine a is made usually
of iron, and the power
applied to the driving
riggers b, which are re-
gulated by a fly-wheel
c: and the speed is
governed or changed
by the action of aspur-
wheel and pinion. The
tool fixed at i is kept
steady by screws at h, in
the sliding frame, and
the work to be operated
upon is placed in the
slide k.
There is a self-acting
apparatus, by which the
work is advanced at m,
m
d
m
Fig. 1590.
and a revolving table for circular work at 7.
a
a
n
2
777
SLOTTING machine.
h
Screw-cutting Machine is formed upon the principle of the lathe, its bed and puppets
being made of cast-iron; at one end two bevelled wheels fit on a part of an axle, which may
be thrown in or out of gear by means of another bevelled wheel at the side, which is put in
motion either by the power of a steam-engine or water-wheel.
The screw to be cut is shown in the middle of the machine; the slide-rests, which contain
the cutters of the threads, are moved forwards by the motion of the conical wheels at the
end; as these slide-rests pass from one end of the frame to the other, they enable the cutter
in its progress to form the thread in the revolving cylinder: when the frame has arrived
at the end of the bed, it presses against a stud, to which is attached a small lever that
throws the wheel out of gear; the cutting tool is again placed at the commencing end by
the workman, its motion is reversed, the tool is re-adjusted, a deeper cut is made, and this
is continued until the whole operation is performed.
1098
Book II.
THEORY AND PRACTICE OF ENGINEERING.

[3
Fig. 1591.
SCREW-CUTTING machine.
To cut a screw with a double thread, one is first cut, the driver is then applied to a hole
in an iron chuck, directly opposite its first position, by which a semi-rotation is given to
the new screw, without producing a motion in the cutting frame, the cutter being applied
to a point midway between two of the first formed threads: a third thread, or any number,

O
Fig. 1592.
SCREW-CUTTING.
may be cut in the same manner by this machine, by commencing at a third or two-thirds
or any other distance from the original position. The cutter is secured in its place by
plates fastened by nuts and screws.
Another process is generally adopted for large screws, which consists of moving the slide-
rest that contains the cutters, in the same way as performed by the lathe; the tool holder

Fig. 1593.
SCREW-CUTTING MACHINE.
CHAP. XIII.
1039
TOOLS AND MACHINES.
is moved onwards by the screw, as the cylinder to be cut revolves from the motion con-
veyed to it by the action of the lathe; this revolving motion also affects the small screws
in the rest, which yields to the point of the tool on sliding along a spiral action, which is
regulated by the proportion given to the diameters of the two cogged wheels; when the
diameter of that on the screw is twice that which acts in the slide, the pitch of the thread
will be double or twice that of the slide screw.
Cutting the Teeth of Wheels is a similar operation: the wheel to be cut is fixed on a spindle,
which forms a portion of the dividing wheel at the end, by fitting into a socket or chuck, so
that when this wheel is moved round, according to the required divisions made on its face,

Fig. 1594.
CUTTING THE TEETH OF WHEELS.
that to be cut presents its edge at the same time; the slide-rest, furnished with a revolving
cutter, works at right angles against the edge of the wheel on which the teeth are to be cut,
and the whole is speedily completed with great exactness. The dividing wheel is held fast
as each successive tooth is formed by an iron holder, which is removed to a fresh point every
time the cutter has perfected its work.
Planing Machine, here shown, has a strong vertical iron spindle, carrying the horizontal
wheel, in the rim or circumference of which thirty holes are pierced, into which are intro-
duced twenty-eight gouges or cutters and two planes; this perfectly level wheel, being well
braced by the aid of the machinery at top, revolves ninety times in a minute. The timber

Fig. 1595.
PLANING MACHINE.
1040
Book II.
THEORY AND PRACTICE OF ENGINEERING.
to be planed is placed upon a movable frame, which regularly brings it under the action of
the horizontal wheel, where the gouges and planes attached to it catch the surface in its
passage, and render it at one operation not only plane but perfectly smooth.
A similar machine was contrived at the Royal Arsenal at Woolwich, and the carriages
were moved backwards and forwards under the cutters by hydraulic pressure.
Machines for planing or smoothing Iron are of the greatest utility; the planing tool is fixed
in a frame in such a manner that it can be inclined, if necessary, to any angle; the frame
has a motion which allows it to rise up at the end of every stroke, and enables the carriage
which bears the iron to be planed to pass back free to the cutter: a single workman can
thus adjust the cutter at every stroke.

Fig. 1596.
PLANING IRON.
The machine generally consists of two parts, the bed on which the table slides backwards
and forwards, and a slide-rest made fast by two upright standards. The tool is held by
a transverse slide, and can be lowered and adjusted to cut what is required, by turning a
screw by a handle placed at the top; the whole slide traverses to any part of the width of
the plate by another handle that turns the screw, which passes from one standard to the
other.
There are many other applications of the slide-rest to machines and tools, and it has been
found of the greatest use in all our manufactories of machinery: since iron has been so
generally introduced for the construction of machines, it has been found necessary to obtain
a more perfect metallic surface on it than could be performed by chipping it with a cold
chisel and filing it; a process requiring also more time than could be allowed when the
lemand became great. The first substitutes for manual labour in smoothing iron were
revolving cutters, the plate of iron to be worked off by the aid of machinery being slowly
advanced under them by the ordinary rectilineal motion; in some instances the cutter or
plane passed over the iron, and in others the plane was fixed whilst the iron was placed
below, a method now generally adopted.
The planing tool is ordinarily fixed in a frame of iron, and can be advanced either
vertically or laterally to its work; it may also be inclined in any required position, as it can

h
Fig. 1597.
PLANING MACHINE.
b
CHAP. XIII.
1041
TOOLS AND MACHINES.
be graduated to work at any angle or bevel. A motion is given to the frame which holds
the cutter, by which, at the end of every stroke, it rises, to allow the carriage on which the
iron to be planed rests, to pass back free to the cutter, which a workman adjusts after every
stroke. The ease with which shaving after shaving is taken from the iron renders this in-
vention one of the greatest practical utility: in many manufactories there are now planing
machines which can at once smooth down a surface upwards of 15 feet in length with a
face of 10 inches, and for this purpose the chisel and the file are laid aside.
Most of these machines originated from im-
provements made by Mr. J. Bramah, who in 1802
obtained a patent for the purpose of producing
straight, smooth, and parallel, curvilinear surfaces,
in a more expeditious manner than could be
performed by axes, saws, planes, or other cutting
instruments used by hand.
The planing tool in some of the later machines
is fixed at j; b is the cylinder or work to be faced
or planed; motion is given to the drum h by the
spur-gear g g; i is a hollow cylindrical frame, on
which the slide works, and by means of levers
shown at m, the planing tool is made to come in
contact with the work it has to perform.
Forge Bellows, formerly much used on the con-
tinent, consisted of two pipes, which conducted
water from a stream about 10 or 15 feet in height,
into others placed vertically over a tub which was
sunk in the basement of the building where the
blast was to be conveyed: over the middle of
the top of the tub was raised a small pyramid,
having at its summit a pipe through which the
blast passed to the forge at A; the power was
obtained by the water falling from a height
sufficient to compress the air within the small
pyramid, and causing it to mount and force its
way out at the mouth of the pipe; this may
be considered an application of the hydrostatic
press for the purpose of obtaining a blast; the
plan represents a forge on the Isere, between
Ramand and Grenoble. The blower consists
of a tub, hi, of an oval form, 7 feet long,

回
​High
་་་་
and 3 or 4 feet wide. The edges are let into Fig. 1598. Forge worked BY A FALL OF WATter.
the ground 5 or 6 inches to prevent the air from entering; to the top of this cistern
or tub two wooden pipes B, C, 10 or 12 feet high, are attached. In the middle, between
these, is a kind

of pyramid, G,
having a tube D
at the top, which
conducts the air to
the forge. A small
trough, 1 foot wide
and 7 or 8 inches
deep, divided into
two branches E, F,
conducts the water
into the pipes B, C
in a greater or less
quantity, according
as we wish to in-
or diminish
crease
the quantity of wind,
by means of a sluice
in the trough. As
the pipes B, C have
several holes near
their summit in-
clined inwards, by
E
B
F
G
E
B
C
I
H
D
D)
TI
I
which air is ad-
mitted, the water in
Fig. 1599.
FORGE Bellows.
3 X
1042
BOOK II. :
THEORY AND PRACTICE OF ENGINEERING.
falling draws it down, and being compressed in the tub, without any other means of
escape, it rushes with violence through the pipe D: within the tub is a small stool H, on
which the air falling, more easily escapes from the water, which runs away by a trough,
always kept full, so that the air may not issue with it. A wheel driven by a stream
is shown at KQ on the plan: the hammer weighs about 300 lbs., and is stopped or set in
motion by means of a sluice at Q.
Forge Hammers are still used at many of the iron-works on the continent, which receive
their motion from a water-wheel, as shown at the side of the preceding figure, and at
Lanslebourg in Sa-

voy, in a manufactory
of iron hoes, the forge
is blown by means
of water descending
through two pipes
into a trunk, as de-
scribed above.
The wipers which
lift the cogs or cams of
these forge hammers
have their acting forces
on the involutes of a
circle, whose radius is
that of the wheel, upon
which they are fixed,
and they elevate the
hammer by acting
Fig. 1600.
FORGE HAMMER
upon a surface perpendicular to the vertical direction in which it rises, and a uniform
motion is obtained.
Block Machinery at Portsmouth, put up by Mr. Maudslay in 1802, after designs of
Mr. Mark Isambard Brunel, commenced working in 1804. This very complete and per-
fect system of machinery for the manufacture of every part of ship blocks consists of
44 separate machines, which operate upon 200 varieties required for the tackling of the
navy, together forming the finest example of practical machinery in the world: the 44
machines consist of 21 varieties, which form three sets of blocks of different sizes at one
time. The building that contains them has a steam-engine of 32 horse-power in the
middle; it is connected on one side with seven large machines for sawing the timber into
the proper sizes for the blocks, and on the other with the thirty-seven block-making
machines.
TF

ON
Fig. 1601.
SAW MILL OF THE PORTSMOUTH BLOCK MACHINERY.
The tree is first brought to the straight-cross cutting saw; secondly, submitted to the
circular-cross cutting saw; thirdly, to the reciprocating ripping saw, which cuts the elm
in the direction of the grain of the wood, and afterwards in a contrary direction; fourthly,
to the circular ripping saw, and the several parallelopipedons into which the timber has
been sawn are then taken, fifthly, to the boring machines, where they are fixed in a frame,
and two centre bits are applied; one bores a hole for the centre pin, and the other, perpen
CHAP. XIII.
1043
TOOLS AND MACHINES.

dicular to this, makes another, which is the commence-
ment of the mortice to contain the sheave. The sixth
machine is for mortising, and the cavities for the re-
ception of the sheaves are formed by chisels in two
blocks at the same time. In the seventh, a corner
saw cuts off the angles of the blocks. The eighth is
the shaping machine, which consists of a double wheel,
and contains the ten blocks at one time; when these
are put in motion, the external faces of the blocks
pass under the gouges, which cut them into the form
required.
The plan of the machine shows the two wheels fitted
on a common axis, which together form a chuck; the
blocks are retained by the screws; the compound wheels
or chuck, as it has been termed, receive a rapid circular
motion from an endless rope, which passes over the
pulley on the axis; and the blocks can be operated
upon in any way required, by presenting the gouge
or cutting-tool, which traverses a segmental bar by
means of a slide rest. The workmen guide the cutting
instrument to any part of the surface, as it revolves
by handles, and thus cut it into shape: after the edges
of the blocks have been taken off, the machine is
stopped, and they are turned round one quarter on
their respective axes, presenting another side as the
wheels revolve, and, in a similar way, they are again
and again turned until they receive their complete form.
The large bevelled wheel next the pulley wheel turns
two other bevelled cog-wheels fixed on a rod, at the
end of which is an endless screw, with the axis tending
to the centre of the chuck. On the large wheel is a Fig. 1602.
pin projecting from its circumference, which is detained
BLOCK-MAKING MACHINE.
by means of a stop that occasionally presses the pin, and turns the chuck round on a fork,
which stops the motion of the wheel; it is then that the attendant workman, by means of
the endless screws, places the blocks in a proper position to be cut by the gouge.

GREFERINT
Fig. 1603.
BLOCK-SHAPING MACHINE.
The ninth is the scoring engine, for cutting the groove round the largest diameter for the
reception of the strap of the block; thus the shells of the blocks are prepared, after which
they are trimmed, polished, and finished by hand.
The machines for making the sheaves are the next, and the tenth is the straight saw,
employed to cut the lignum vitæ.
The eleventh is a circular saw, employed when smaller sheaves are required
The twelfth is the crown saw, which works similarly to a trepan, having a centre bit on
its axis it is used for cutting out the circle, and at the same time the hole in the
centre.
:
The thirteenth is the coaking engine, which cuts the cavity in the centre of the sheave
for the reception of the coak or metal bush.
The fourteenth is the drilling machine, which is applied to perforate the three semicir-
cular projections of the coaks, at the same time drilling through both the coaks and the
wood of the sheave.
3 x 2
1044
Book II.
THEORY AND PRACTICE OF ENGINEERING.
The fifteenth are the hammers, put in rapid motion by the machinery, for riveting
the pins which hold the gun metal coaks into the cavity in the sheaves.
The sixteenth is the broaching engine, where the sheave is fixed to a vertical revolving
axis, and the borer is brought down into the hole in the centre of the coaked sheave, and
broached out to a perfect cylinder.
The seventeenth is the turning lathe, provided with a slide rest to support the turning
tool, by which the sheaves are faced. Thus the blocks, shells, and sheaves are com-
pleted.
The eighteenth is a turning lathe, with a slide rest to form the iron pins.
The nineteenth is a polishing engine, in which the pin is fixed into the lower end of a
vertical revolving axis, and forced down into a die immersed in oil, holding three pieces of
hard steel, Letween which the pin is pressed as it turns, and becomes completely
polished.
The twentieth apparatus is for boring large holes in any position, and is mostly used for
blocks that are 50 inches or more in length, and have four sheaves.
The twenty-first is the machine for making dead eyes.
By this machinery 1420 blocks are perfected in one day, and it is not too much to
observe that the entire contrivances seem to embrace all the useful purposes that are
required throughout the entire range of the mechanical arts. In the Edinburgh Encyclo-
pædia, conducted by Dr. David Brewster, are most perfect and beautiful representations of
these machines.
Saw Mills for cutting Marble: the frame is suspended by rods, in such a manner that a
free horizontal reciprocating motion is given to it; the saw frame is attached to a cast-iron

Fig. 1604.
PLAN OF MARBLE SAW MILL.
100
anya

H
101
КОН
H
Fig. 1605.
ELEVATION OF MARble saw MILL.
CHAP. XIII.
1045
MILLS.
box, which is movable upon a vertical post, from whence it receives its reciprocating
motion: it is made of wood, and the saws are tightened within it by several screws: any
number of saws may be introduced, and at any distance apart, according to the number of
slabs or thicknesses to be cut on the left of the plan are shown two sets of saws at work,
with four blades in each set. The saws are guided by upright iron bars, which also main-
tain them in a vertical position, and they are pressed upon their work by a cast-iron box,
suspended by a rope that passes over a pulley, and slides down upon the upright post of
the vibrating frame; a weight is attached to the other end of the rope, as shown in the
section. Water is introduced by a horizontal pipe under the ceiling of the manufactory,
and runs gently into the small inclined reservoir immediately above the block, which is
under the action of the saws: after the slabs have been cut, they are carried to the other
side of the machine, where they are laid flat and polished. The polisher is put in motion
by the action of the vertical post, which receives its vibration from the saw-frame by the
crank upon the main shaft: a continued supply of water is introduced with the various
substances made use of for polishing: sharp sand is first supplied, which produces a per-
fectly flat surface, then finer sand, and afterwards Tripoli red powder, which owes its cutting
quality to the oxide of iron that it contains; an oxide of tin, called putty, completes the
polish.
Hand-mills, for grindir g, are of very great antiquity, and had a variety of forms; one of
the most simple kind co: sists of a strong wooden frame, on which is mounted a face-wheel,
turned on proper bearings

by a winch or handle,
and which has its cogs en-
gaged in the staves of a
trundle or lantern, on the
spindle of which the re-
volving stone of the mill,
contained in the case be-
low, is fixed. The matter
to be ground is put into
the hopper at the side,
from whence it passes to
the space betwixt the
fixed and revolving stone,
after which it is carried
away, by means of the
lower spout or trough,
into a vessel prepared to
receive it: such mills are
much used for numerous
purposes, and are an im-
provement upon the Ro-
டாபாட
man hand-mill, which was
Fig. 1606.
HAND MILL.
an inverted hollow cone,
working round and upon a solid one below: when the stones are laid horizontally, there
is an equal bearing and friction over the whole.
Horse-mills are frequently used in manufactories in preference to the steam-engine, and
they are serviceable and convenient where the labour required is not constant.
The speed

Fig. 1607.
HORSE MILL.
with which a horse moves, so as to produce the maximum mechanical effect, is stated to be
two and a half miles per hour, or 220 feet per minute, or 32 feet per second; and the actual
3 x 3
1046
Book II.
THEORY AND PRACTICE OF ENGINEERING.
medium effect of a horse will raise each minute 22,000 pounds a foot high, although horse
power is defined to be competent to raise 33,000 pounds in the same time; but when em-
ployed in mills the action of the animal is perpetually restrained by the circular path in
which he walks, and the power is not so great as when pulling in a direct line; and in some

Fig. 1608.
HORSE-MILL.
measure to alleviate this impediment, it is an invariable rule never to make the diameter
of the horse-path less than 18 feet in diameter. Rotation is given to such mills either by
large cogged or bevelled wheels placed below or above the revolving shaft; the horses in
the one case walking on a level with the large cogged wheel.
If a steam-engine of 10 horse nominal power taken at 33,000 lbs. were to work day and
night, it would perform as much as 45 horses in the same time; and making every allow-
ance for casual and necessary stoppages, every nominal horse power in a steam-engine is
equivalent to four horses when working night and day, to two horses when working twelve
hours a-day, and to one and a half horses when working eight hours a day.
Mills for grinding Corn by the power of steam, were first used in 1783, on the Surrey
side of Blackfriars bridge, but in consequence of their being considered a monopoly in-
jurious to the public, they were destroyed by fire a few years afterwards.

E
Fig. 1609.
CORN MILL.
Since that period, Messrs. George and John Rennie have erected at the Royal William
victualling yard, Plymouth, one of the most perfect mills in the kingdom for grinding corn.
The building is 240 feet in length, and 70 feet in height: in the centre are two steam-
engines of forty-five horse power; on each side are twelve pair of stones 4 feet 3 inches in
CHAP XIII.
1047
MILLS.
diameter, each performing 123 revolutions in a minute, and grinding five bushels of corn
per hour, so that when the mill is in full work 120 bushels of corn are ground in that time,
as well as dressed by eight machines.
The fly-wheel that communicates the motion is on the left of the figure; the main shaft
has its bearings in plummer blocks bolted to cast-iron frames; on it are two bevelled
wheels 8 feet in diameter, which engage two others, 5 feet 4 inches in diameter, placed on
the main vertical shafts, which have their bearing at the lower end, on another cast-iron
frame, and on brasses and other plummer blocks attached to the floor of the mill. The
shafts are all placed in a well or circular mass of bulwark, and the large cog-wheels above,
10 feet in diameter, turn six toothed wheels set round their circumference, upon the
spindles of which the upper millstone is fixed, and revolves very rapidly.
The corn is laid on the upper floor, and then by spouts conducted first to screening ma-
chines or cylindrical sieves, arranged somewhat like an Archimedean screw; it is admitted
at one end, and in its course passes over a larger surface of wire; when cleaned of the sand
and dust, it falls into a hopper, from which it passes by spouts to the millstones.
On the second floor of the mill the dressing machine and bolting mills are arranged,
which are put in motion by a bevelled wheel on an horizontal shaft, which can be put in
or out of gear with the vertical shaft at pleasure. The machinery for raising the sacks is
suspended on the beams of the roof; it consists of a barrel and a system of wheel-work put
in motion by a bevelled wheel on the top of the vertical shaft.
The millstones are composed of a number of pieces attached together by a strong
cement, and further secured by iron hoops passing round their circumference: on the





Fig. 1610.
MILLSTONES.
O
upper and lower millstones are grooves or channels cut obliquely from the circumference,
to within an inch and a half of the centres: eight long channels divide the stone into as
inany portions, in each of which four others are usually cut; these furrows are sunk in
such a manner that one side is perpendicular, and the other oblique, and one being placed
upon the other, the sharp edges meet, and effectually cut the corn, which passes between
them. In bedding millstone, great care must be taken to have them perfectly level, and
firm on their bearing; they are sometimes supported by a timber frame, which is wedged
up from the floor, but more frequently an adjustment is effected with an iron frame and
screws.
The bed stone in the figure is fixed in an iron case, which can be raised or lowered by
turning the iron screws beneath, and at the side are other screws which move the stone
laterally when required: when the iron cross or damsel above revolves, it strikes the shoe
under the hopper, and gives it a tremulous motion, which causes the wheat to pass down
from it to the millstones, in proportion to the velocity of the motion. The upper mill-
3 x 4
1048
BOOK II
THEORY AND PRACTICE OF ENGINEERING,
stone is fixed upon the shaft by means of a cross with a segmental top, which is firmly at-
tached to it, and the octangular axle passes through the iron box on which this upper stone
hangs

L....j
Fig. 1611.
BEDDING MILLSTONES.
In the Victualling Yard at Deptford, the millstones, which are not quite 4 feet in
diameter, make 120 revolutions in a minute, and answer admirably well; though they
in`a
generally vary from 4 feet 6 inches to 5 feet in diameter, and make from 80 to 100 revo-
lutions in a minute.
The Dressing Machine is a hollow cylinder or frame, covered with wire cloth of different
degrees of fineness, that is, with 64, 60, 38, and 16 meshes to the inch, that which has
the smallest space being at the upper end: its axle is inclined to the same angle as the
bolting mill. Within the cylinder, which is stationary, is a reel, to the rails of which are
attached brushes, which, in their revolution, act against the interior wire surface of the
cylinder; the meal is conducted within it by a spout or hopper, and is thus rubbed through
the wire, the finest passing through the upper end, the second through the next division,

Fig. 1612.
DRESSING MACHINES.
Fig. 1613.
:
and the bran through the lower end the cylinder being enclosed in a tight case, the flour
cannot escape; there are usually four divisions within it, to collect the varieties of flour as
they are rubbed through: hence they are called, firsts, seconds, thirds, and pollard. The
pinion upon which the brushes move can be made to revolve either way, so that the motion
of the machine can be reversed to suit the brushes, when they become bent in one position.
The Bolting Mill consists of a reel fitted to an axle which revolves with great rapidity,
and is covered with a cloth called duck: in the box containing the reel are a number of
wooden bars called heaters, against which the cloth strikes with such violence that the
four is separated from the coarser parts or pollard.
CHAP. XIII.
1049
MILLS.
.


Fig. 1614.
Fig. 1615.
The reel has six bars fixed in an axle which works in a circle, and at the upper end is
22 inches in diameter, and diminishes gradually to 20 inches at the lower or tail end:
when at work it is turned with sufficient velocity to make the bolting cloth swell out to its
fullest extent, and occasion the beaters to force the flour through the meshes of the cloth in
a constant stream.
Some bolting machines have a contrivance applied to them containing a spring, which
facilitates the dressing of the flour: it consists of a cylindrical ring of iron, into which are
riveted six elastic arms: at the end of each is a hook, to receive a loop attached to the
tail leather of the bolting cloth, causing a more uniform action to be kept up.
The Mortar Mill is composed of a vertical shaft or spindle, to which the millstone is at-
tached, revolving on a bed upon which the limestone or chalk to be pounded is thrown:
curved pieces of iron, called rakes, are fixed to the shaft, and revolve round in a regular
manner to keep the iron bed free from any impediment to its regular motion: when the
lime is properly ground, it is passed into another mill, where it is mixed with its pro-
portion of sand, and triturated or compounded by the action of constantly revolving

Fig. 1616.
MILL FOR MIXING MORTAR.
rakes, attached to the arms of a horizontal wheel that moves round in a circular bed.
The pug mills are upon a similar construction, and have a post in the middle with a
long lever, to which the horse is applied The lime and sand thrown into the trough are
then mixed by the revolving rake fixed at the lower part of the upright shaft.
Mills for grinding Cement are formed like the corn mill, with the addition of two iron
rollers, shown under the right hand hopper, which receive motion from a spur-wheel
attached on the main shaft: by means of the rollers the cement stone is first broken down
into a powder or small fragments, after which it is hoisted to the top of the mill in sacks,
and then put into the hopper, whence it passes off to the millstones; the lower one being
fixed, and the upper put in motion by the machinery.
The millstones are grooved or channelled obliquely, from the circumference, as in the
flour mill, and make about 150 revolutions in a minute: when the cement is ground, it
passes out at the circumference of the stones into a spout, which conveys it to two sieves,
separating the fine powder from the coarse: the sieves placed beneath the large horizonta)
wheel have a rapid reciprocating motion by a rod and crank attached to the small spur-
wheel, which is turned by the larger wheel just mentioned.
To the right of the figure is a mortar mill, which works by means of the spur wheel,
and into which the cement powder is put, when prepared for use. At Sheerness dock-
yard a twelve horse-power steam engine was made use of to work a similar cement
mill.
1050
BOOK 11
THEORY AND PRACTICE OF ENGINEERING.

CEMENT MILL.
Fig. 1617.
Diving Bell. The earliest account we have of a machine similar to that now in use is
given by John Taisner, of Hainault, who was born in 1509, and went to Toledo with the
Emperor Charles V.: "he there saw two Greeks let themselves down under water, in a large
inverted cauldron, with a burning light, and rise to the surface again without being wet."
Lorini, in a work upon fortification, also describes a diving machine, consisting of a square
box bound round with iron, and furnished with windows; but no mention is made of such
a machine in England until Dr. Halley commenced his experiments; that ingenious
philosopher contrived means to supply the diving machine with air, and at the same time to
keep the water from rising in it; his description of the apparatus in the Philosophical
Transactions is as follows:-
"The bell I made use of was of wood, containing about 60 cubic feet in its concavity,
and of the form of a truncated cone, whose diameter at top was 3 feet and at bottom
5 feet; this I coated with lead, so heavy that it would sink empty, and I distributed its
weight about its bottom, so that it would go down in a perpendicular situation, and no
other; in the top I fixed a strong but clear glass, to let in the light from above, and like-
wise a cock to let out the hot air that had been breathed; and below, about a yard under
the bell, I placed a stage which hung by three ropes, each of which was charged with
1 cwt. to keep it steady. This machine I suspended from the mast of a ship by a spreit,
which was sufficiently secured by stays to the mast-head, and was directed by braces to
carry it over-board clear of the ship's side, and to bring it again within board.
"To supply air to this bell when under water, I caused a couple of barrels of about 36
gallons each to be cased with lead, so as to sink when empty, each having a bung-hole in
its lowest part, to let in water as the air in them condensed on their descent, and to let it
out again, when they were drawn up full of water from below, and to a hole in the upper-
most part of these barrels I fixed a leathern trunk or hose, well liquored with bees'-wax
and oil, and long enough to fall below the bung-hole, being kept down by a weight
appended, so that the air in the upper part of the barrels could not escape, unless the lower
ends of these hose were first lifted up: I fitted these air barrels with tackle proper to make
them rise and fall alternately, after the manner of two buckets in a well, which was done
with so much ease, that two men, with less than half their strength, could perform all the
labour; and in their descent they were directed by lines fastened to the under edge of the
bell, which passed through rings placed on both sides the leathern hose of each barrel, so
that, sliding down by those lines, they came readily to the hand of the man who stood on the
stage to receive them, and to take up the end of the hose into the bell. Through these
hose, as soon as the ends of the pipes came above the surface of the water in the barrels, all
the air that was included in the upper parts of them was blown with great force into the
bell, whilst the water entered at the bung-holes below and filled them as soon as the
air of one barrel had been thus received, upon a signal given it was drawn up, and at the
CHAP. XIII.
1051
DIVING BELL, ETC.
same time the other descended, thus by alternate succession furnishing air so quick and in
such plenty, that I myself have been one of five who have been together at the bottom in
nine or ten fathoms water, for above an hour and a balf at a time without any sort of ill
consequence; and I might have continued there as long as I pleased, for any thing that
appeared to the contrary. Besides, the whole cavity of the bell was kept entirely free
from water, so that I sat on a bench, which was diametrically placed near the bottom, with
all my clothes on; I only observed that it was necessary to be let down gradually at first,
or about 12 feet at a time, and then to stop and drive out the water that entered, by re-
ceiving three or four barrels of fresh air before descending any further, but being arrived
at the depth designed, I then let out as much hot air that had been breathed as each barrel
would replenish with fresh air, by means of the cock at the top of the bell, through whose
aperture, though very small, the air would rush with so great violence, as to make the
surface of the sea boil, and cover it with a white foam, notwithstanding the great weight of
water over us.'
Since Dr. Halley's invention, many improvements have been made in the diving bell,
particularly by Mr. Smeaton, who seems to have been the first engineer that used it for
sub-marine constructions.
When the diving bell is employed in still water, it is usually suspended between two
boats of 15 or 20 tons each, over the decks of which is laid a platform of timber, to keep
them at the proper distance from each other, and on which the tackle is worked for lowering
and raising the bell.
Smeaton employed the diving bell as early as 1778, in the constructions of the bridge at
Hexham in a letter which he addressed to Mr. Pickernell on the subject, we have the
method he adopted fully explained: he says, If the cases would have enabled us to
reduce the water so low, as to be even with the very bottoms of the caissoons of each pier,
I take it for granted, you would have thought it no difficulty with broken rubble, beton,
stones, and short blocks of wood, cut a little wedgeways, to have crammed and wedged
up the cavity washed under the wooden bottoms, so as to have been equally resisting,
and capable of bearing a weight with the original gravel, and particularly when this
new body of matter is supported, and even jammed tighter into its place by filling up
the vacancy between the pier and the base, a little above the wooden bottom, with rubble,
and then driving it tight down by a set with the ram. It therefore now remains that I
describe, and make you master of a piece of machinery, that will put you nearly into the
same condition, as if the water could have been reduced to the caissoon's bottoms as before
mentioned; and this is by means of an air-chest, or diving vessel, which being let down,
will exclude the water down to the very bottom of the diver if you please, and therefore as
low as the under side of the wooden bottom, which in the present case is as low as will be
necessary or useful, and the chest or vessel being large enough to give liberty for a man to
work therein, being furnished with a pair of boots, he will at mid leg deep in water do
his business with almost as much facility as if the water were pumped out to the same level.
The principal part of this machine will consist of a strong chest, suppose 3 feet 6 inches in
length, about 4 feet deep or height, and as wide as to give free leave for its going down
between the cases and the piers, which I suppose will be about 2 feet wide inside measure,
as the other measures are also supposed to be. Now you know very well that if you push
a drinking glass, or any other similar vessel, with its mouth downwards into the water, that
it will exclude the water, leaving the vessel full of air, as it was before it was thrust into
the water; in like manner, if this chest, being loaded with a sufficient weight, be let down
into the water, mouth downwards, the air will exclude the water to the bottom skirt of the
chest, and if let down, so as to rest upon the bottom of the river, a man may stand therein,
and do any kind of business, the same as he could do in the same space in the open air.
But to continue this for any length of time two things are obviously necessary, and those
are light and a circulation of fresh air. The former might on occasion be supplied by a
candle, but here we may have the advantage of day-light by putting two or three strong
round panes of glass into the bottom of the chest, which will in its inverted situation be the
top; a sufficiency of light will enter, this top of the chest being supposed above water.
Respecting air, you will conceive that any quantity might be forced in by a strong pair of
bellows; but those made of leather would be cumbersome and unhandy: I therefore sub-
stitute a kind of foreign air-pump, made of thin hammered copper, that will throw in a
gallon at a stroke, which will not only continually refresh the workmen within, but what-
ever air escapes through the joints or pores of the air-chest will be replenished, and the
overplus go out at the bottom or skirt of the chest, and boil up on the outside.
The quantity of weight that will sink it, mouth downwards, will be the same as placed
therein (bottom downward) would sink it the same depth; and as this chest I propose to
be suspended by a tackle, and to go down by its own weight, I compute that it will take
sixteen pigs of lead to sink it to the bottom of the river, and keep it steady. I propose
that the lead may be as much out of the way as possible, to place them upon the ends of
1052
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
the chest, endways upward, that is four in a row below and four above, and the same at the
other end, making in the whole 16 pigs, which are to be fastened on with screws, either by
At one end of the
cleats screwed on, or punching a hole through each end of each pig.
chest there is to be a board, fixed across for the man to sit upon, and a cleat nailed to each
side to set each of his feet upon, so that while the machine is being lowered or hoisted, he is
totally dry, and when let down enough, he stands upon the bottom of the river, without any
more water than the height between the skirt of the chest and the bottom of the river, which
may be more or less as is found convenient, I suppose never more than a foot deep, because
wherever the ground is taken out more than 1 foot below the underside of the caissoon's
bottom, I would propose to fill it up with rubble previously to that height or depth; nor
can it be of use to let down the skirt of the chest much below the caissoon's bottom, because
the side of the chest will then diminish the room you will have to get the matter for under-
pinning under the caissoon's bottom. The foregoing will, I believe, be sufficient for ex-
plaining the general principles and outlines of the method I mean to pursue in under-
pinning, and re-supplying what is underwashed from the bases of the piers, and which I
dare say you will now sce to be entirely practicable: what you are therefore immediately
to put in hand is the air-chest, of or about the inside dimensions before mentioned; I believe
the two flat sides will do very well, if of good red wood deal, shot clean of sap, the two
ends and bottom, (or in use its top); it would be well if they could be got of single planks
of elm, beech, or plane trees, as they would hold the nails better: I fancy 1 or 12 inches
thick for the sides, 21 or 21 for the ends and bottom, will be sufficient; they should be well
jointed, and put together with white lead and oil, as the effort will not be of the water to
enter, but of the air to escape from within. Were I with you, when it is put in use, I
should be the first to go down into it, as there is no more danger (all your tackle being
firmly fixed) than being let down into a coal-pit by a rope: and if it shall happen that all
your masons are too fine fingered, I fancy a couple of colliers to take turn and turn will
find it a very comfortable job. A particular encouragement, must, however, I expect be
given. I will give you more particular directions in my next as to the air-pump, all
that will be wanted from the coppersmith will be a cylindrical pipe of copper, 10 inches
diameter, and 12 inches high, wired at top, and a flanch at bottom of about 14 inches broad,
by which it is screwed down before the top of the air-chest: the copper to be about the
thickness of a halfpenny; if you have no
neat-handed coppersmith that can hammer
it straight and smooth inside, it may on oc-
casion be made of strong tin."

"A, the air-pump, B, sky-lights, 6 inches
in diameter, to be made of window glass
knobs, if plate glass cannot be had; C,
clamp plates of iron, to confine the top and
sides strongly together; D, D, pigs of lead,
end upwards; EE, the lever for working
the pump; G G, the axis and brace for steady-
ing the lever; H, H, two bows for hoisting
the chest; I, a strong hooked iron to lay
hold of the bows, to which the main rope or
tackle is to be fixed: MN, the opening from
the pump to the air-chest: op, the valve,
whereof o is leather, p wood, to be shut by
a wire spring qrs, a little more than suffi-
cient to overcome the weight of the valve."
The diving bell at Her Majesty's dockyard
at Plymouth is of cast-iron, and weighs 4
tons 2 cwt. It is 6 feet long, 4 feet broad,
and 5 feet in height; its cubical content
being 120 feet.
D
D
D
E
B
B
B
A
H
M
H
B
B
p
q
r
E
Twelve convex lenses, each 8 inches in
diameter, are placed at the top to admit the
light, which when sunk in clear water is
sufficient to enable the diver to read the
smallest print. In the centre of the top is a
hole for the admission of air, which is sup-
plied by a leathern hose long enough to
reach any moderate depth; at its upper end
is attached a forcing or air-pump, which is
worked by four men during the time the
bell is immersed, and the quantity of air supplied enables those in the bell to respire with
1
Fig. 1618. SECTION OF AIR-CHEST.
CHAP. XIII.
1053
DIVING BELL, ETC.
comfort. Inside the bell, and immediately over the hole, which admits the air, is screwed
a piece of stout leather, so that the air only enters through the spaces comprised between
the screws; this leather prevents the air, when once admitted, from returning to the hose;
and should it burst, the water
cannot enter through the air hole;
the divers are therefore secured
against any accident which might
arise from this cause, and the bell
contains a sufficient quantity of
air to support those within it,
without the assistance of the air-
pump, until it could be raised
up from almost any depth.

When the bell is overcharged
with air, it escapes under its edge,
and from its expansive nature,
agitates the water as it ascends
towards the surface; this has
been supposed to be the foul air
escaping, but that which has been
respired, being lightest, ascends
to the upper part of the bell, and
a continued current of air passing
from the top to the bottom pre-
vents any unpleasant effect.
There is a movable seat at
each end, and a narrow foot-board,
with several hooks and shelves
for the workmen's tools, and at
the top are two eye-bolts for the
purpose of securing any heavy
weights which may be required
to be raised with the bell.
O
G
о
B
о
H
No difficulty or danger attends
its use, provided the men are
sufficiently careful, and the bell
is properly suspended: when
immersed, and the divers require
its position to be changed, they
strike it with a hammer. Eight
signals are made: one strike in-
dicates that there is not sufficient
air, and that it is necessary to
work the pump faster: two an-
nuls a former signal: three, that
the bell is to be raised: four to
lower it: five, to move it to the right; six, to the left; seven, backwards, and eight, forward:
other methods are resorted to for holding a correspondence with those in the vessel, as
sending up small buoys, &c.
N
M
Fig. 1619. PLAN AND SECTION OF AIR-PUMP.
When any work is to be executed by the diving bell, it is important that the water
should be transparent, or at least sufficiently so that objects may be discerned when lying
two or three feet below the bell, that the machine may not touch them in its descent: with
artificial light it is impossible to distinguish objects in muddy water; but when clear, a
cloud passing over the sun is perceptible in deep water. The workmen employed usually
in the summer remain from 7 to 12 o'clock in the morning, and from 1 to 6 o'clock in the
evening, and in winter only as long as they can see.
It is necessary to observe that the greatest caution is required in lowering the bell: if it
descend with too great velocity, the air becomes so much compressed as to be injurious to
the lungs of the workmen, sometimes causing immediate death; when the descent is very
gradual, no evil consequences will arise.
The diving bell at Ramsgate harbour was a square chest of iron, weighing 50 cwt.; its
dimensions were 4 feet in height and length, and 3 feet in width: it was cast in one piece,
and sufficiently heavy to sink itself: by means of a forcing air-pump, worked in a boat
moored immediately over the bell, two men were supplied with fresh air in the crown
were eight round lenses, 4 inches in diameter, to admit the light. It was at first suspended
from shears, but Mr. Gott, the resident engineer, finding them inconvenient, adopted the
traversing crane, which enabled the masons to place the stone in any position required:
1054
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
I
another bell has been since cast, 6 feet long and 4 feet broad, which permits the workmen
to proceed with greater alacrity.
The Camel is a machine used in Holland for raising ships by the buoyant power of water;
it is a very ingenious contrivance, and consists of two similar hollow vessels, so constructed
that they can be applied on each side of the hull of a ship; these hollow vessels are
made water-tight, and on the deck of each windlasses are attached, by which ropes, which
are made to pass under the keel of the vessel to be raised, are worked. When the camel is
employed to raise a ship, the water is allowed to fill each half of it, and when the ropes
firmly unite the ship to the camel, the water is pumped out, and the buoyancy of the hollow
vessels raises the ship up.
The length of one of these camels employed to float vessels over the sands in Holland
was 127 feet, the breadth at one end 22 feet, and the other 13 feet: the hollow part
was divided into several compartments.
A vessel drawing 15 feet water could by this means be made to draw only 11 feet, and
the largest man-of-war in the Dutch service could be made to pass the sand banks of the
Zuyder Zee. Meuves Meindertszoon Bakker invented this curious machine at Amsterdam
about 1688: it has been used at Venice, on the Tiber, and elsewhere with success.
The camel is an excellent example to show that when a body is held beneath the surface
of a fluid, the force with which it will ascend, if it be lighter than the fluid, or with which
it will descend if it be heavier, is equal to the difference between its own weight and the
weight of an equal quantity of fluid. Ice by the same means can remove enormous masses
of rock, it being specifically lighter than water: when a river is frozen, and large stones
surrounded by ice, the upward pressure of lift exerted upon them so far exceeds that
exerted downwards, that they are brought to the surface, and then floated by the ice, and
often carried to a great distance.
DUBA
1
HIGH
WATER
33
3
4
5
6
16
LOW
WATER
The Pontoon, made either of timber or copper, acts somewhat upon the same principle:
when applied to close the mouth of a canal or entrance to a dock, they are sunk or raised
by either letting in or
pumping out the wa-
ter they contain, and
it is by an adjustment
of its contents that it
can be kept at any
height, shown by the
lines figured 1, 2, 3, 4,
5, 6, 7, 8, 9. If it be
required that water
should pass to or from
the canal or dock,
the pumps which are
within the pontoon are
worked sufficiently to
lighten it and allow
it to rise, or if it be
necessary to lower it,
this can be effected
by admitting the
water within it, by
means of a pipe and
turncock, shown in
the transverse section.
The letters A, B, C,
D, E, show the width

Fig. 1620.
PONTOONS.
C
of the corresponding parts of the plan and end elevation, as do the figures marked upon
it and the transverse section. Such a contrivance working in two grooves effects the
same purpose as lock-gates, but when it is required to allow the passage of any vessel, it is
necessary that the pontoon should be floated out of its position and be moored aside: such
pontoons or lighters are found serviceable at ferries and piers, where the height of the water
varies with the tides.
Raising Vessels when sunk at Sea: one of the most celebrated efforts of this kind was
recorded by the senator Zusto, by order of the Venetian government, after the ship of the
line of 74 guns, named the Phoenix, which had sunk in the year 1783 in the canal of
Spignon, near the entrance of the Lagune, was raised by the Chevalier Morelatto, a distin-
guished naval officer in the employ of the republic.
The Phoenix, sunk in a depth of 36 feet of water, and bedded several feet in the mud,
was considerably injured by the concussions it had experienced in its descent; it was
therefore necessary, not only that the weight of the vessel should be sustained, but that
CHAP. XIII.
1055
RAISING VESSELS, ETC.
:
also a power should be applied that should overcome the suction, as well as the mass of
mud with which it was filled: to effect this, a power equal to 3 millions of pounds
was required. Two methods were adopted, each of which was sufficient for the end pro-
posed, and the vessel would have been raised by the first, if a violent storm at the moment
it was lifted had not disengaged and deranged the apparatus, and allowed it again to
sink that first employed consisted of forming below a large and strong platform, with
eighteen pieces of timber, nearly 100 feet in length, bound together with five rows of other
timbers laid in a transverse direction; this frame was attached to the sunken vessel by
cables passed through its port-holes: four vessels were placed under the frame by filling
them with water, and when they were secured to it, a ship of the line was disposed at its
side, and five smaller vessels near the prow. On the first were ten capstans, which
worked a running tackle made fast to the sunken ship, and on the other five were placed
seventeen other capstans, which worked a tackle attached to the head; they emptied the
four vessels filled with water, and at the same time turned all the capstans together, and
by this process raised the vessel, which, as has been observed, again sunk in the second
attempt they made use of the capstans as before, but instead of the submerged vessel, they
employed sixty other capstans arranged upon a platform, placed over another seventy-four,
two smaller ships, and two enormous levers.
The seventy-four gun-ship which was employed had three strong shears or derricks
mounted on the deck, secured to the masts, and partly by arrangements made in the hold
below; besides these were eighteen others of a similar kind, but smaller in dimensions,
which rested on the upper deck, and provided with as many windlasses: a platform was
thrown out on the opposite side to that where the submerged vessel was level, with the
deck, and at the ends of the timbers, which projected as much as two-thirds the breadth of
the seventy-four gun-ship, were suspended casks and boats loaded with stone, for the
purpose of keeping the works steady, when the whole of the thirty capstans, which were
mounted on the platform and deck in three rows, were at full work; the three sets of great
and the eighteen lesser derricks served as the points of suspension to the tackle, which the
thirty capstans and eighteen windlasses worked.
Another apparatus of a similar kind was arranged upon a platform built over two
lesser vessels on the other side of the submerged ship, and, to render the whole suffi-
ciently buoyant, a number of large casks was attached in a circle: smaller platforms
were established at the head, and another at the stern, each of which carried an enormous
piece of timber, slung in a manner to act as a powerful lever; another served to moor a
part of these preparations, and rows of piles, wherever they could be driven, were made use
of; after every precaution had been taken to render the arrangements steady, 600 men
at one time applied their strength to the capstans and windlasses, and raised the Phoenix by
degrees; when it had been raised 15 feet, they moved the whole of the works, together
with the sunken ship, along the canal, and commenced its demolition: in preparing the
works, and accomplishing this mighty task, upwards of two years was consumed, besides an
enormous quantity of timber, iron, cordage, and labour.
In France, they have adopted several methods to raise vessels which have foundered or
sunk in situations where it was necessary for the purposes of the navigation that they
should be removed.
A vessel sunk at the mouth of the Loire was raised by Bonvaux after it had been in its
position twenty-four years: his method consisted in passing four cables, by means of an
iron bar, under it; the bars being formed in a manner to suit the curve of the ship's side,
which he had ascertained as well as he could; this curved iron bar was pointed at one end,
and provided with an eye at the other, through which the cables might be passed and
drawn under the keel. This bar, formed on an arc of a circle, resembled, when mounted,
a part of the felly of a wheel sustained by four of its spokes, whose central termination was
threaded by a stout bolt, which answered the purpose of the nave or axle round which the
wheel turned. The bolt passed into a vertical piece of timber, fixed at the lower end by
means of an iron fork in the ship's hull, and at the upper into some stout framing secured
to some strong piles, driven for the purpose.
When the point of the bar was introduced and partly driven into the ground, the first
spoke or radius of the wheel was released by removing a screw, and when the bar ex-
hibited its point on the other side, and it was sufficiently driven or forced through, they
employed a three-toothed fork, the prongs of which entered into holes previously prepared
in the iron bar, and then by main force pulled it through; a running tackle was then
applied, worked by a capstan placed on the deck of a small vessel moored near for the
purpose.
After four cables had been passed under the sunken ship, two barges were moored over
the hull of that bedded in the mud, on which four stout timbers or masts were laid; to these
were attached the ropes, firmly secured; when the tide rose the whole became buoyant,
and four or five tides enabled the sunken vessel to be towed on shore, where it was left at
low water, to be demolished or broken up.
1056
Book II.
THEORY AND PRACTICE OF ENGINEERING.
The method adopted by Goubert to raise a sunken vessel which had lain 42 years
in the roads of Renondelle was somewhat similar; its depth was 17 feet at low water ; the
bar made use of was the mast of a ship 33 or 34 feet in length, armed with four flat iron
bars, and pointed at the end with an iron rod 23 feet long; the two ropes which were to be
passed under the hull were attached to this point, and, previous to this being attempted,
Goubert dug small channels in the mud, one of which he made perpendicular to the
keel, and another he formed on the opposite side in an oblique direction: after intro-
ducing the mast into the first-mentioned hole, and placing it by means of tackle in an
oblique direction, with a pile-driving engine he forced it through the mud into the channel
cut to receive it on the opposite side, and then fastened a rope to the iron point; the
wooden mast was then separated from it, and, by means of three capstans, the ropes
were pulled through, and when all were passed under the vessel, they were made fast to two
rafts prepared to receive them, and, by means of the tide, the whole was worked into shallow
water, where it was demolished.
Another method adopted when the position of the vessel which has been sunk is thoroughly
ascertained, is to employ two vessels to pass a chain cable under or around her: these
are placed near the bow, with the cable suspended from one to the other in such a manner
that it sweeps along the ground; the chain is then moved backwards and forwards until
it comes under the sunken ship; the two vessels are then moved astern, and the ends of the
chains are brought together, and passed through an elliptical ring sunk close to the stern, the
ends of the chain being made fast when this main chain is in its required position,
others, called bridle chains, are fastened to it at various convenient distances, and also to
other vessels at the time of low water; then, as the tide flows, the vessel sunk is elevated,
and afterwards floated to the shore.
:
:
Hedgehog, in use for removing mud in rivers, or the accumulation on the land side
of sea-sluices: it is cylindrical in its form, like a garden roller; around the outside are
attached eight or more longitudinal ribs, each of which is
armed with as many spades or hoes fixed in them firmly by
bolts and screws. This cylinder revolves on pivots in gudgeons
in the side frame, which is made of oak, and diagonally
braced in front of the roller or the revolving cylinder. The
iron spades are in width 4 inches, and in length 7, and are
placed about 7 inches apart at each end of the shaft is
attached a strong chain, by which its motion is insured, and
when used it is attached to the stern of a barge, which in
Lincolnshire is usually drawn by horses; sometimes a barge
is moored at some distance from the mouth of the sluice to be
cleansed, and the hedgehog is moved backwards and forwards
by blocks and chains: such a machine made of oak, and well
bolted together, is most effective; as the cylinder revolves on
its axis, its sixty-four spades are all brought into work, and
in their progress disturb a vast quantity of mud, which the
stream through the sluice aids in carrying away. The timber
frame has its scantling 6 inches by 4, its cross-stays from one
side to the other being placed about 3 feet apart; and between
them are introduced diagonal braces, which are made fast to
the frame and stays by iron bolts. The stocks on the cylin-
drical drum or iron wheel are in length 6 feet, and made of oak
6 by 4 inches, into which pass the iron spades.

www
O
Floating Clough, for scouring out the channel of a river at
Great Grimsby, as well as other channels of the Humber.
A frame 12 feet in length, 9 feet in width, and 6 feet deep,
of timber 6 by 4 inches, covered with 2-inch plank; through
the middle is a culvert 2 feet 6 inches in width, made with
planks, with a small lifting door at one end. At the bottom
is secured two beams, which project in front, and which serve
as feelers to keep the machine in its right position: in the
front are placed frames of timber shod with iron, cut in a ser-
rated form, which, by means of a lever, can be raised at plea-
sure at the sides of the machine are wings, sloped to accom-
modate themselves to the fall of the banks, and when the water
is at high tide it is moored into the middle of the stream, with the wings extended by
means of ropes, and at half ebb the water is admitted by plugs, and the machine sinks to
the bottom; the plugs are then replaced, and it remains in this position till full ebb; the
iron shod frames, with teeth like a saw, are let down in front, and the whole machine
being forced along by the tide, scrapes up the bottom, and the mud disturbed is carried
along with the return tide for a distance of three miles or more in the space of two hours.
Fig. 1621.
CHAP. XIII.
1057
DREDGING.
Dredging forms a very important part of the work of the civil engineer, and is effected in
various ways; either by drags or scoops, or rakes, or machines. There are two sorts of
hand-drags, one for raising mud, the other sand; the first consists of an iron box pierced
with holes, open in front as well as at the top; to this is attached a slightly flexible handle,
of a length proportionate to the depth it is to work in: when this is made use of, the men
in a boat make the iron box enter the sand, sustaining the handle on the shoulder, and
when it is filled they raise it, and if there be any large stones they are disengaged by
means of hooks: a man will raise in this manner, where the depth is not more than 4 or
5 feet, a cube yard in the course of a day, and sometimes more.
The Drag for Mud is differently formed: it is an iron ring, to which a canvass bag is
attached, by passing a cord through holes made in the ring purposely to receive it: that
point of the iron rim which is intended to touch the ground and enter the mud must be
sufficiently strong: two men in a boat or punt are required to manœuvre it, and in
the course of a day they will raise from 12 to 14 cube yards, if the depth does not
exceed 6 feet: when the boat is made use of, it is first moored in such a manner that it
cannot drift, and in this way the canals at Venice are still dragged; such a drag allows the
water to flow out of it, and retains only the solid matter.
The Louchette, a kind of spade, or a collection of them, is used for cutting or extracting
turf under water, without the necessity of first pumping it dry: this consists of a light
iron frame, which is armed all round with a cutting blade, in length about 3 feet; the part
between it and the handle is open, being formed of four horizontal rods, and two vertical
ones; these receive the turf after it is cut and detached, and enable the workmen, by
means of a rope and windlass, to pull it up; these cutting instruments have a variety
of forms given them to adapt them to the peculiar work they may have to perform.
The Box Shovel consists of an open box fixed at the end of a long handle, usually made
of iron; the cutter traverses in a groove, and is worked by another handle; by this the
turf is cut and detached, and each successive piece falls into the box: as many as four turfs
may be thus drawn up at one time.
The machine at Venice probably first suggested our modern dredger; it consisted of
an oblong pontoon, covered in, on the deck of which the machine was worked; its
length was nearly 50 feet, and its breadth a little less than half; below the deck the space
was used by the workmen as a lodging place. The mechanism attached was a large
wooden beam, which moved on a pivot in its centre: this beam was formed of tapering
pieces, about 50 feet in length, and together 3 feet in thickness; there were five rows,
bound and hooped round with iron; this strongly constructed beam was furnished at one
end with two nuts, into which worked a perpendicular screw of beech, upwards of 30 feet
in height, and about 14 or 15 inches in diameter. This screw worked in a socket or plate,
fixed at the bottom of the pontoon, and this being provided with a windlass below the deck,
the screw was made to elevate or depress the huge wooden beam, which usually lay in a
horizontal position.
At the other end of the beam, a large iron spoon was worked, which had by means of
pulleys an alternate motion of rotation given to it by two vertical cylinders placed within
the pontoon: the iron spoons were opened and shut by ropes and pulleys, and the dredging
action was commenced by slightly depressing, then raising the beam; by the first move-
ment the cover was moved, by the second the spoon was opened; after it had filled, it was
again covered and lifted out of the water: such a heavy complicated apparatus consumed
much labour, and required to be moored very strongly to the place where it was worked,
and the manoeuvring of the perpendicular screw, which gave movement to the weighty
timber beam, was attended with painful and laborious exertions.
Eight men were required to work it, and they generally raised in a day about sixty cube
yards from a depth which did not exceed 14 or 15 feet: when a greater number of men
were employed, the quantity raised was proportionably greater, and twelve, which were
as many as well could work at one time, have been known to lift more than a hundred
cube yards. The spoon or drag contained two and a half cubic yards, and the mean time
for lifting it was a quarter of an hour; thus with forty extractions in a day considerable
space was cleared: such a machine was said to have cost upwards of 800 pounds.
The Chapelet was composed of three rollers, two of which touched the ground, and the
other was placed above a timber scaffold, on which the soil dredged was to be raised:
round these rollers worked an endless chain formed of large links, alternately flat and
square to this was attached four or more scoops or scuttles, placed at regular distances,
made of sheet-iron: these were pierced with holes, and provided with a strong, projecting
beak, which not only entered, but cut its way into the mud or earth below. The cylinders
were armed with iron spikes which entered the square links of the chain, and turned
round on pivots, working within a frame made for the purpose, of timbers sufficiently
strong to retain them, and put together so that they could be raised or lowered as the depth
to be dredged required. The whole was put in motion by a wheel and winch, placed
parallel to the cylinders, and by which they were turned; the axis of the winch working
3 Y
1058
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
in a lantern turned the cylinders, and they in their motion brought up the loaded scuttles
made fast to the endless chain when either of the scuttles had arrived above the upper
cylinders, it became inclined, and deposited its contents, which were immediately drawn
away by a vessel or trough, and in this manner the scuttles were kept in motion and dis-
charged.
When the depth was greater or less, the machine was made to accommodate itself by the
introduction or taking away of some of the links, and mounting higher the two lower
cylinders.
The winches being turned, moved the lantern fixed to their common axis; this engaging in
a toothed wheel fixed to the upper cylinder, in turning drew the chain and scuttle attached
to it, and also turning round, occasioned the descending scuttle to enter the ground, and to
elevate the loaded one to the top of the machine, where it was thrown over, and deposited
its contents upon a hinged trough, attended by a workman, who directed its further course.
Peyronnet describes a similar machine, and also furnishes the dimensions for its con-
struction, and the cost in his time: he makes the chain 17 inches in length, and places
upon it six scuttles. The cylinders were formed of elm, hooped with iron, and covered
with strips of plate iron: this machine, mounted on two boats, was employed with two others
at the bridge of Orleans, and each was worked by six men, who raised about twelve cube
yards per day, from a depth of upwards of 6 feet: such a machine was preferred to clear
out the cofferdams to the scoop previously used, which had, by means of a handle, the power
only of clearing the entire width between two rows of piles; it was drawn up and
down by a rope attached to it, worked by a capstan. The scuttles answered admi-
rably well, where the bottom was not stony, but great care is requisite in the manufacture
of the chains; the best were those made with bolts and screws, as they facilitated the
lengthening and shortening.
We find in many of the works published in the sixteenth century descriptions of dredging
machines, and at the commencement of the following century, Savery patented an invention
for raising ballast out of rivers by steam: and Cornelius Meyer, a Dutch engineer, about
the year 1680, contrived a machine, which strongly resembled the one in use, with this
exception, that boards were made to lift the ballast, and a horse wheel was employed.
Mortier and Hertel, Dutch engineers, also turned their attention to this subject, and Balme
made a vertical wheel, which worked between two boats armed with six buckets, which
lifted a vast deal of mud; these and many other inventions were brought over to Eng-
land, and used in the time of Charles I. for dredging the fens, both in Lincolnshire and
Yorkshire; and from them great improvements were afterwards made: from the evidence
of Mr. Watts, we find that in 1796 he manufactured an engine for dredging to be em-
ployed in the harbour at Sunderland.
The Bag and Spoon, which has succeeded the box-shovel, consists of a ring of malleable
iron, 2 feet in diameter, and 2 feet 4 inches deep, sharpened and steeled on the under side,
4 inches broad, for about one third of its circumference, and pierced on the inner edge with
holes for the lacing of the bag. The remainder of the ring is of round iron, 1½ inch in
diameter, and on the upper side, or that opposite to the mouth, a hose is welded to receive
the pole or handle, the length of which must be in proportion to the depth to be dredged :
on each side, about half way up the spoon, is fastened a chain 30 inches in length, which
is united by a ring at top, where the working rope is made fast: the bag is made of
strong tanned leather, about 31 feet in depth, laced with leather thongs to the spoon,
and a
sufficient number of holes is pierced through the bag to allow the water to escape.
flat-built barge, of thirty or forty tons burthen, is usually employed to work this machine,
and all that is required is a small projecting crane, so made that it can be readily thrown
out of
gear.
A
The Bucket dredging Machine, worked by steam, is now universally adopted to deepen
all navigable rivers, harbours, and docks, or wherever any accumulation of mud or sand
is required to be removed. The contrivances of Perronet, and other French engineers,
applied to the machine early used at Venice, no doubt gave rise to the introduction of this
very powerful one, now almost indispensable in all ports.
Mr. John Huges seems to have been the first who used it in clearing out the bed of the
Thames, about the year 1804; that originally contrived was apparently very defective,
but after expending a considerable sum of money, he brought the machine to such perfection,
that in one day he was enabled to raise, opposite to Woolwich, 2000 tons, where there
was a depth of water of more than 30 feet. On this occasion it was constructed in an old
bomb-vessel, and had a thirty-horse engine, the whole costing nearly 8000 pounds. In all
probability it was similar in plan to the first, made by Boulton and Watt, which was fixed
in a boat, and had four rollers, each of which had one spoon; the rollers were made to
move at the rate of 10 feet per minute, and each spoon could bring up 15 cwt. at a time.
The inachine employed by the Hull Dock Company in 1802 had eleven wooden scuttles
working on a ladder that passed over rollers, the motion given by a horse-wheel: those now
used in the harbours and navigable rivers, worked by powerful steam-engines, have a
CHAP. XIII.
1059
DREDGING.
series of iron or copper scuttles attached to a chain, which like a chapelet works round a
beam elevated at the side of the vessel, and brings up large quantities of ballast at each dip.
The fly-wheel of the dredging machine is turned by a large spur-wheel, fixed on the
shaft, acting in a pinion on the axis of the fly-wheel, to give it a greater velocity than the
crank, by which means a smaller fly-wheel is sufficient to regulate the motion of the engine.
The motion is conveyed from the steam-engine to the chain barrels by the inclined shaft,
shown in the section; at the lower end is a bevelled wheel, which receives its motion from
another fixed on the main shaft of the engine. At the upper end also of the inclined shaft
is another bevelled wheel, working in another fixed to the shaft, and situated in a line
with the centre of the two chain barrels: at the two extremities of this shaft are two
wheels, which communicate power to the chain barrels, and bring up the ballast; an
engine of 16 horse-power, dredging on a moderate depth, will raise 35 tons in an hour,
and consume about 343 pounds of Newcastle coal in that time.

Fig. 1622.
DREDGING MACHINE.
The upper rollers is a square barrel, as is that at the lower end, and around them passes
the double endless chain, each alternate link of which carries a bucket; these are pierced
full of holes, to allow the water to drain out as the sand or gravel is brought up.
mouths have a semicircular form, to prevent their sticking fast during the operation.
The


T
Fig. 1623.
DREDGING MACHINE.
Fig. 1624.
BUCKET.
Dredging machines of this kind are usually mounted in the hulk of an old sloop of 100
tons burthen, and no expense should be spared in making it strong and substantial; for
after the machinery is introduced, the smallest twisting of the vessel occasions fracture of
the wheels, or some other portion. The bucket frame is found to work best when at an
angle of 45 degrees.
Artesian Wells have been considered of great importance, since their introduction near
London in 1794, when one was sunk at Norland House, on the N. W. of the residence of
Lord Holland at Kensington, and which is described in the Philosophical Transactions
of 1797.
The water was derived from sandy strata, of the plastic clay formation, but so much sand
was brought up, that the pipes were constantly obstructed: it was therefore found necessary
to pass through the loose strata, and obtain the water from the chalk.
M. Hericart de Thury, M. Arago, and M. Von Bruckmann, have all drawn attention to
this subject, and shown that throughout Europe there are extensive districts where, under
certain conditions of geological structure, and at certain levels, water may be raised to the
3Y 2
1060
Book II.
THEORY AND PRACTICE OF ENGINEERING.
surface by boring, and that in many instances the supply will be sufficient, as in Artois in
France, to turn the wheels of corn-mills.
In the tertiary basin of Perpignan and the chalk of Tours there are subterranean rivers,
which have enormous upward pressure; the water rises near Rousillon in an artesian well
upwards of 40 feet above the surface, and M. Arago describes its force as sufficient to ele-
vate a cannon ball placed over the mouth of the pipe.
M. Von Bruckmann sank an artesian well at Heilbronn in
Wurtemberg, where the water was sufficiently warm to heat a
paper manufactory; similar wells are in use in Alsace, and
near Stutgardt.
In the Duchy of Modena are numerous artesian wells, as there
are also in America, Asia, and Africa: wherever impure water
is arrived at, it is necessary to continue the operation of boring
until that desired is attained: the supply of water in these wells
is generally referred to the same principles as the play of an ar-
tificial fountain, and their failure may be attributed to the rents
and faults which abound in rocks, or to the dip of beds, which
carry the fluid in another direction.
The well bored at Sheerness was continued through 300 feet
of clay, below which was a bed of sand and pebbles, which when
pierced, the water immediately arose in another situation this
water was obtained at a depth of 328 feet below the surface
clay.
În 1824 a well was bored at Fulham, 317 feet in depth, which,
after traversing the tertiary stata, was continued through 67 feet
of chalk, when the water arose, and was discharged at the rate of
50 gallons per minute.
In the gardens of the Horticultural Society at Chiswick, the
borings passed through 19 feet of gravel, 242 feet of clay and
loam, and 67 feet of chalk, after which the water arose to the
surface through the whole 329 feet. At Sion House, a short
distance beyond, the boring was continued to the depth of 620
feet, so as to enter the chalk, when the water rose in a considerable
volume, 4 feet above the surface.
In an artesian well sunk at Hammersmith water rose with a
considerable force from a depth of 360 feet, and at Tooting
another threw out sufficient to turn a water-wheel. By the
borer it was found that, at St. Ouen in France, there were
five distinct sheets of water, from each of which a supply was
obtained; in the third, which was at a depth of 150 feet, was
a cavity in which the borer suddenly sank a foot or more, and
the water rose immediately in a considerable volume.
In the older geological formations, it is useless to attempt the
construction of an artesian well, and among transition and se-
condary formations, there is seldom an abundant supply of good
water in France, it is in the tertiary formations where the
artesian wells succeed best, as that recently formed at Grenelle.
In some instances shafts have been sunk increasing in diameter,
lined with iron or masonry, and strengthened in their descent:
these have passed through sheets of water down to a solid
stratum, beneath which pure water has been found, and conveyed
by an upright pipe to the surface.
Boring. A well 6 feet in diameter is sunk to the depth of
8 or 10 feet, and one man above and two below are enabled
to carry on the operation: over the well, is laid a horizontal pole
made fast at one end, and the other is operated upon as the
man above gives it a slight up and down motion, to suit the
action of the two below, it having a chain around it, connected
with the cross-bar to which the boring instrument is attached.
This cross-bar or wooden handle passes through the socket of an
iron shank, which has a ring at top, and a female screw at
bottom; to this all the successive boring instruments are fas-
tened.

Fig. 1625.
BORING.
A chisel is first attached to the screw, and the two work-
men in the well press upon the cross-bar, and force it round like an auger at the same
time; this will continue to descend unless the ground is very hard or full of stones; when
it becomes necessary to drive it, and by changing its position occasionally, it is to revolve:
after the first hole has been well opened, the chisel is changed for a cylindrical auger,
CHAP. XIII.
1061
BORING, ETC.
which draws up the earth the chisel has separated; the earth entering at the bottom fills
the cavity of the auger, and, as it cannot escape, it is discharged at top, and finally drawn
up as occasion requires. When it is required to work the auger deeper, an iron rod is
attached, by screwing it on at the upper end, and using the chisel alternately with it
as before, the operation is continued: as the hole descends, additional rods are put on, and
these require to be well jointed, so that they work truly. To elevate a great length of
rod, it is necessary to have three poles over the wheel, secured at the top, and a pair of
pulley blocks: the rods are about 7 feet in length, and as this is the usual length of haul,
it must determine the position of the pulleys: a claw is used to gripe the rods to be drawn
up, attached to a chain, and a wrench to unscrew the rods as they rise; sometimes a
chisel 2 inches wide will descend 100 feet, and an auger of a little less diameter will
clear the way; a chisel 4 inches in width requires an auger of 33 inches.
There are varieties of instruments, all of which have a screw at the upper end, tapped
to one thread, and therefore easily fit into the various rods. A hollow conical instrument,
with a spiral worm around it, is useful in sandy soils; a cylindrical auger with a valve
in it in mud; as this is turned round, the fluid matter passes above the valve, and is se-
cured; another form is that of the bucket, which, when dropped into the hole, acts like a
pump in extracting any soft or watery matter: each of these are under the control of
guide pieces and stops: when a rod becomes broken in the hole, which often occurs in
rocky soils, it is drawn out by a pair of tongs which has at the lower end a cylindrical
tube, above which is a chisel-edged tongue, pressed down by a spring; when this is lowered,
the end of the broken rod passes into the cylinder, and pressing back the tongue, it is
held fast, and thus drawn out. Punches are also required to peck into hard stones, by re-
peated strokes, or to break them; these are of various forms, generally angular, with out-
side cutting edges: when the hole is formed it is usual to line it with a metal casing
about inch less in diameter than the bore; this tubing is either of tin or copper, in con-
14
venient lengths, and when sunk others are attached and soldered to it, to descend in their
turn; these are driven by means of a block of wood, with an iron rod attached, which is
made to traverse through a hole above; this is mounted like a pile-driver, and beats down
the tubes; sometimes this is effected by fastening at the end of one of the boring rods an
iron like an acorn, which enters the tube, and, by means of its projecting rim, presses it
downwards. It is, however, necessary, previously to inserting the pipe or tube, to pass
down the hole bored a diamond chisel, funnel-mouthed, with a triangular bit in its centre
to smooth the sides and form it into a true cylinder, by keeping the chisel turned as it
descends.
The well was
Well at Messrs. Truman, Hanbury, Buxton, & Co.'s Brewery in London.
commenced in the middle of another 16 feet in diameter, and the work as performed by the
miser instead of the usual methods adopted: after the land-spring in the old well had
been drained, another, 11 feet in diameter, was commenced, and carried down with brick
steening, the clear internal diameter being 8 feet 6 inches; after a depth of 115 feet 3 inches
had been by this means arrived at, a cast-iron cylinder was lowered, and others successively
were added; at a depth of 135 feet the yellow clay was reached: here the water over-
powered the excavations, and the miser was again made use of; an oyster bed was then
pierced 163 feet below; to drive the jumper or heavy chisel through the hard rocky crust of
this oyster bed occupied the workmen seven days; when this was done the iron cylinder
suddenly sank 5 feet 6 inches; the miser was again used, until the depth of 190 feet was
arrived at, and the cylinders became completely fixed soon after this, pumping was
resorted to, and then a blow of sand from the bottom filled the well for a depth of 28 feet:
the miser cleansed this, and the pumping again commenced, and soon after the iron cylinders
separated at a joint about 73 feet from the top; a portion of the cylinder was then cut
away, and, after removing the yellow clay, a dome was constructed with brick and cement
entirely around the exterior of the cylinder. An internal cylinder, 2 feet in diameter,
was lowered within the original cylinder, and this was continued until driven 4 feet into
the chalk; the space between the large and small cylinder was filled in with granite
paving-stones to a depth of 5 feet, then with broken stones, brick, and hydraulic cement for
another 25 feet, to prevent any future blow of sand from the bottom of the well. The well
was then drained, and 400 holes about inch in diameter were drilled in the cylinder
immediately below the level of the oyster bed: the bore was then resorted to, and continued
for a depth of 200 feet more, making the whole depth 400 feet, and then a supply of water
was obtained equal to 33 gallons per minute: after the work was complete, and the joints
of the cylinders picked out to admit the water, then, with all these sources combined, it was
found to yield 81 gallons per minute, or 135 barrels in an hour, viz. 55 from the chalk, and
Ɛ from the sand spring. The total cost of sinking this well was 44441., and the 12-horse
steam engine and pumps in addition 13517.
The tools vary in their form according to the material to be pierced, or in soft ground
the hole may be first opened with a chisel, and then a cylindrical auger, in which
the earth or broken stone passing through an aperture at the bottom, fills the cylinder, and
3 x 3
1062
Book II.
THEORY AND PRACTICE OF ENGINEERING.
is then drawn up to be discharged: as the work advances an additional rod is introduced,
by means of screws, which can be readily turned by a wrench, and taken to pieces as often
as is required.
The operation of boring is often resorted to when it is necessary to examine several beds
of earth, and to discover their nature. The engineer should on all occasions be careful to
make himself acquainted with the foundations previous to his operating in any way upon
the surface of the soil, and this is still more important when the constructions are under






000
Fig. 1626.
BORING INSTRUMENTS.
water: when the soil to be examined is so situated, a hollow cylindrical pile is driven
down, within which the boring rods can with facility turn; at the bridge at Moulins such
an operation was carried on to the depth of nearly 50 feet, and at Ambleteuse to 80 feet:
at the latter place a trough was used made of planks, in lengths of 6 or 7 feet, and placed
in succession one upon the other.
The borers used in France are of several kinds, and well adapted for every variety of
soil Hericart de Thury, who was inspector-general in 1810, contrived two very simple
methods of uniting the boring-rods; one, by means of a fork, the other by the screw :
forking was preferred, although it occupied a greater time to perform.
A more economical method of boring was practised by M. Sellow, near Saarbruck in
China, who used only a heavy bar of iron about 6 feet 4 inches in length, and 4 inches in
diameter, armed at its lower end with a cutting chisel, and surrounded with a hollow
chamber, to receive through-valves, and bring up the detritus of the perforated stratum; it
was suspended by a rope that passed over a pulley, and as the rope was pulled, the iron rod
in mounting received a circular motion, which was sufficient in its descent to turn round
19018






Fig. 1627.
BORING INSTRUMENTS.
the chisel. After the chamber was full the whole apparatus was lifted, and the earth
emptied out, when the chisel was again dropped, and the work continued: a thousand
feet have in this manner been bored by the Chinese, who perforate holes in the earth
18 inches in diameter, and several hundred feet in depth, to give ventilations to their
mines.
CHAP. XIII.
1063
BORING, ETC.
All the varieties of chisels that have been employed cannot be enumerated; those which
have been found most useful have been selected; they are of different dimensions, made
to suit the operations they are intended for: the chisels 2 inches diameter are cleared out
by a gouge 21 inches diameter, and when withdrawn, the hole is widened by another of
3 or 4 inches in diameter, and so on: where rocks or hard bodies are to be pierced, drills
of a conical form are used, and to bring up loose stones screw chisels; for clay, scoops or
gouges.

T
ค
K
wwww
Fig. 1628.
BORING INSTRUMENTS.
The tools employed by the miners consist of a pick, one side of which is used as a
hammer, and called a poll, the gad which has a steel wedge, and the shovel, which usually
has a pointed form, for the purpose of penetrating hard and coarse rubbish. The borer
is an iron bar tipped with steel, formed like a chisel, and is used by one man holding it
straight in the hole made to receive it, and giving it a constant rotation on its axis, whilst
another strikes the head with an iron mallet. This hole is kept constantly cleared out
by a scraper, which is a flat iron rod turned up at one end. The wheelbarrow for
under ground work differs from that here represented by not having any legs; when earth
is to be removed at the top, they are made generally of this form: scoops and shovels vary
in their form according to their application.
In sinking the Shaft of a Mine, it frequently occurs that water is met with in such
quantities, that cast-iron caissoons become necessary in some of the deepest at Newcastle
they are sunk 180 fathoms. The operation of sinking a shaft is extremely simple:
two or more workmen are employed digging, whilst others at the top, by means of a
windlass, hoist the soil; as the depth increases, so does the labour, and either a steam-




Fig. 1630.

MINERS' Tools.
Fig. 1631.
BARROWS.
Fig. 1629.
engine or horse-mill is applied, called a whim or whimsey, for that purpose. The sides
of the shaft are walled up or steined as it is sunk, and great care taken to prevent the
Um
3 x 4
1064
THEORY AND PRACTICE OF ENGINEERING. BOOK II.
MU
falling in of the earth; and where any
water is encountered, then attention must
be paid to the best method of preventing
its injury to the work.
After the shaft has been sunk to its re-
quisite depth, the several timber stages that
have served the uses of the workmen are
left, or others provided, to which all the
requisite pipes and machinery are attached
that serve to pump up the water or raise
the material. The two sections exhibit the
upper and lower portion of the shaft of one
of the deepest copper mines in Cornwall,
with the position of the ladders for the
workmen to descend, and the pumps for
raising the water, which with one lift and
one piston often raise it 150 feet. The
main rod gives motion to the pistons of
the different lifts of the pumps, and is
either impelled by a steam-engine or water-
wheel the pipes are of iron generally,
though wood is sometimes employed.
Machines for measuring the relative
strength of men and animals are usually
called Dynanometers; one invented by
Levoy, of the Academy of Sciences at
Paris, consisted of a metal tube about 12
inches long, which was placed vertically on
a stand: the tube contained a spiral spring,
having above it a graduated shank termi-
nating in a globe; when this was pressed
into the tube, the force used was measured
by a scale, which was graduated on the
shank.
Regnier's Dynanometer resembles a com-
mon graphometer, the principal part of
which instrument is a steel spring bent in
the form of an ellipsis; it should be pro-
perly tempered, and well welded, and
covered with leather, to prevent injury to
the hands when used. This spring is
represented by A A', BB', formed by two
equal plates united at the ends by rounded
half-rings. The dimensions of this spring
vary according to the tension required, or
the weight to which it is applied.

The dynanometer used to ascertain
human strength weighs little more than
two pounds, and serves to measure a thou-
sand times that weight; its total length
is about 12 or 13 inches, and its greatest
breadth, as measured in the middle of the
two arcs, is 2.2 inches, and the least breadth
at the extremity of these arcs is of an
inch. The thickness of the arcs at their
centres is nearly 2 inches, and its height,
which decreases from the centre towards
its ends, from to of an inch. the chords of the two arcs are 6·4 inches. This length,
added to that of the two demi-rings, gives for the total length of the dynamometer
12 or 13 inches. The distance between the parallel chords is about of an inch, and the
perpendicular of the arcs are each of an inch, giving about 2-2 inches for the total distance
between the centres of the arcs.
10
Fig. 1632.
SHAFT (F A MINE.
There are two methods of stretching the spring, by pressing it in the direction of the
perpendicular of the two arcs which form it, or by drawing it with the two rings at right
angles to that perpendicular: these two limits of tension are indicated by two scales
drawn on the same limb, called scales of pressure and tension: the first gives the pressure
of weight from zero to 264 pounds avoirdupois. The greatest pressure brings the centres
CHAP. XIII.
1065
DYNANOMETER.
within 4 of an inch of each other, each perpendicular, which is 7 of an inch when there
is no pressure, is reduced to 5 of an inch. The brass limbs on which the scales are drawn
is fixed on the centre of the arc A'B' of the spring, and the opposite arc A B carries a
counterpoise ab, 3.1 inches long; the extremity b of this counterpoise acts on a small
branch bH, 3 of an inch of a bent lever, bHc, whose other branch Hc is a needle, 2·4
inches long, from the centre, H, of rotation to the index, c. Below this index is a small
cylindrical thread, 1 of an inch, which is fixed to the needle Hc, and serves as a foot when
it turns on the centre H, parallel to the limb. This first needle by turning commu-
nicates a rotatory movement round the centre K to another needle K dd', which rolls on
the smooth portion of the screw K, and leans on the limb by a foot G furnished with a
washer to reduce friction. This second needle has two indices d and d', to mark the
pressure and traction; it is moved by the first needle Hc; the divisions of the arcs
described by the two indices are numbered in pounds, which indicate the weight brought
by the needle to these divisions: as long as the spring is not stretched, the needle Hc
preserves its primitive position, and the needle K dd' of the scales remains on the divisions

F
A
A
A
TO
A
d
M'
E
E/
t
L
Ba
H
M
L
B
B/
MI
??
K
HD
N
P
B/
B
Fig. 1633.
The
with
to which it is drawn by the tension of the spring; whence it is seen that the system of
two needles gives us the power of preserving the measure of a tension, when the force
which produced this tension no longer acts. The greatest arc which the needle He can
describe is determined by the course of the counterpoise ab, which is 39 of an inch.
points b and c of the bent lever G He describe arcs of the same number of degrees
regard to the positions of the two needles Hc, Kdd to the right line HKL of their
centres, the angle c K L, which the second needle makes with this right line, is equal to the
angle c H L of the first with the same right line, increased by the vertical angle HcK of the
two needles, for in the triangle Hc K, whose sides Hc and HK are constant, the angle
cKH is the supplement of the angle cK L, and of the sum of the two angles cK H and
HcK. The distance HK of the centres H and K is about 46 of an inch, and it results
that the total arc described by the needle K dd' is nearly one-third of the circumference.
To preserve from injury the system of these three pieces, viz. the counterpoise ab, the
bent lever b Hc, and the needle with two indices Kdd', the limb is covered by a plate
NNN, which rests on the three pillars, 39 of an inch high. If the axis of rotation of the
bent lever were prolonged, it would meet this plate in the point H', the centre of the arc
of a circle m' m' which terminates it, and whose radius is equal to the length of the needle
Hc.
The divisions of the arc m'm' are figured, and the figures indicate the same tensions
as those on the scale of traction.
1066
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
The dynanometer just described indicates on the scale of traction a tension of a ton
weight, which is greater than the most powerful effort of a horse, but nevertheless too
small to measure the ordinary effort of a power applied to a screw
M. Regnier constructed a dynanometer on the same principles, which measures a traction
of 6600 lbs. the spring was of the same power and length as the old one, but the two
arcs or plates of which it was composed were longer, thicker, and further apart in their
centres; their distance from each other was 4.5 inches; by the greatest traction it was only
diminished 4 of an inch; these arcs had in the middle a breadth of 18 inches and a thick-
ness of 2 of an inch; the total weight of the instrument was 5½ lbs.
By placing the machine between the two ends of a cord passing over two or more
pulleys, the ratio of the force which separates the extreme pulleys to the tension of the cord
will be known, and by this disposition we can measure a traction much more considerable
than that which is indicated by the scale of the dynanometer. Fig. 1633. shows the arrange-
ment with two pulleys.
Details of the Construction of the Dynanometer. Two supports D, D', of steel, are
adjusted solidly on the two opposite branches of the spring in the direction of the per-
pendicular of the axis. The first support D, cut in a fork, carries a screw on which
the extremity a of the counterpoise ab rolls; it is about 1·4 inches high, and 59 wide; it is
retained on the centre of the arc AB by a strong screw, whose head is marked T on the
convex part of the arc. The second support D is also retained by a screw, the extremity
of which, t, is seen on the concave part of the arc A'B; the upper face, E, E, of this support
is about 4 inches long on the opposite face, EF, which is of the same length, is a
brass plate, I L, fixed by a single screw g, which is level with EF in g: the plate, hardened
to make a spring, carries at its extremity a pivot I, which passes through the support and
the limb; this pivot, like that of a compass-needle, serves as a centre to the bent lever b Hc:
the limb is applied to the face EF, of the support D', and is fixed there by two screws e,f.
The plate IL being a spring, the pivot I yields to a pressure of the counterpoise, and pre-
vents any rupture of the mechanism which turns the needles of the scales.
The covering plate OPQ is voided at K' in a small circle of a diameter nearly equal to
that of the head of the screw K, round which the needle K dd works, with a slight friction
on the limb: if this friction be too slight, a turn-screw which passes through the circular
opening K' will tighten the pressure. The lower pivot of the bent lever b Hc rolls on the
pin I'; its upper pivot rolls on the side H', which is riveted to the covering plate OPQ.
Spring Balance and Eprouvette. The spring balance most used in commerce is formed
of two steel branches AC, CB, bent at an angle of 45°; each of the arcs DpqE, I Hrs G,
is fixed to one of the branches and traverses the other.
By drawing the rings E, G, which terminate the arcs in
opposite directions, we bring the branch A C near BC; a
circular scale figured from 5 to 40 indicates the respective
positions of these two branches. The branch AC pushes
before it a small cursor k of card or leather, which slides
easily on the metallic wire fg, attached to the branch CB
of the balance. To graduate the scale, suspend the balance
by a ring E fixed to the branch AC, and attach weights
to the ring G, which is at the extremity of the scale.
numbers on the scale indicate the tension of the spring.
Regnier has made an excellent instrument of this spring-
balance for trying the strength of powder.
The length

The
D
D
G
9
7
L
K
SI
Fig. 1634.
#
of the branches AC and CB is about 4·8 inches, and their
breadth about an inch; a small brass cannon, whose breech
H is on the branch CB of the balance, and whose mouth I
is closed by the fuse IL of the obturation DILE fixed on
the other branch A C of the balance, contains a given weight
of powder to be tried; it is primed by a little powder put in the pan F: the powder
within the cannon is fired and drives it away; after the ignition the two branches of the
balance approach, and the cursor k indicates on the scale the tension of the spring at the
moment of the explosion. The iron DE, and the brass arc GH on which the scale is
drawn, pass through openings pq, rs made in the middle of the plates CB and C A.
A dynanometer for measuring animal force was invented by Mr. Graham, and afterwards
improved by Desaguliers, but it was found to be inconvenient for the purpose, as it was
made of wood; Leroy afterwards formed one in a metal tube 10 or 12 inches in length,
with a spring within it placed vertically on a stand; this. however, was not found so useful
as Regnier's, where the sides of the spring are made to approach each other, and move an
index, which marks the degree of approximation on a semicircular scale; a man can ascer-
tain by it the mean force he exerts with either hand, or with both together; it was with this
kind of dynanometer that M. Quetelet, of Brussels, made his experiments upon the strength
of men of different statures and ages.
CHAP. XIII.
1067
DYNANOMETER.
A
G
B
Ω
10
с
This pinion and
Another kind of Spring Balance The spring of this balance is bent in a curve CKD,
terminated by two braces, CB, DE, one of which supports the pinion I, and the other
a rack DEGH, of which the toothed portion G H catches the pinion I.
the needle which marks the tension of the spring turn on the same axis.
The face is a circle whose
centre is on the axis of the
pinion I, and is fixed by two
screws t and t', on the plane
TV, which is soldered to the
upper brace A B, which carries
the pinion. To graduate the
scale, suspend the balance by
the ring A, and attach known
weights to F by the hook ô c.
The rack GH will work the
pinion I, and the needle fixed
on the axis of this pinion takes
up successively the positions
figured from 0 to 100; these
numbers express the force of
tension on the spring in pounds.
The index of the needle de-
scribes about g of the inch as
the maximum tension of the
spring, or for the greatest dis-
tance between the extremities
C and D of the spring, which
is about 1.1 inch.

as
2
B'
D
B
H
T
3
ε
O
t
ठ
D
B
Ꮄ
I
The plane of the balance
being supposed vertical,
in the projection, on another
vertical plane passing through
the axis of the pinion; the
face of the brace AB, per-
pendicular to the plane of
the limb, is drawn parallel
to itself in A'B'; we see on
this face in the parallelogram
1234, the projection of an
opening made in the thickness of the brace A B, to make way for the toothed part GH
of the rack; the breadth, 12 or 3 4, of this opening is 4 inches; LM is the projection of
the axis of the pinion I; the spring CKD is projected in CD; the plane on which the
face is screwed has for its projection TV. The spring is '11 of an inch thick, and 1.2
inches broad. To render this balance more convenient, a needle is added, which turns
freely on the face round
the axis of the pinion I,
and may be employed as
the dynanometer; it is
even preferable for mea-
suring the ordinary
strength of men.
Of the dynanometric
Machine, and the Mea-
surement of the tangential
Force of an Axletree.
Let AB, fig. 1636., be
the section of an axle
moved by water or any
other power; an un-
known but constant re-
sistance acts tangentially
to this axle, and we re-
quire to measure it. To
resolve this question,
suppose we fix on the
axle AB of a wheel
DEFGH, of any num-
a s
d
Fig. 1635.

Fig. 1636.
3
V
B
C
1068
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Another wheel having
ber of rays CD, CE, CF, &c.; this wheel turns with the axle.
the same number of spokes, Cd, Cc, Cf, turns freely on the same axle; springs Dd, Ee,
are attached to the couples of the spokes, CD, Cd, CE, Ce, of the two wheels, so
that the points of attachment D and d of the extremities of the springs are in a plane
perpendicular to the axis of rotation C of the axle A B, and at an equal distance from
this axle.
Having disposed the power or mover so that it shall turn the wheel freely in the direction
of the arrow X, it is evident that the extremities de,fg of the springs fixed to this wheel,
would swerve from the points of attachment D, E, F, &c.; that the equal angles Dc d,
Fce, Ecf, &c., whose sides pass through the extremity of the springs, considered in
their primitive position, would become other equal angles, Dcd, Ece, Ecf, &c., and all the
other springs would be stretched, if not equally, at least at the same angle: when the total
tension of the springs is equivalent to the resistance applied tangentially to the axle, the
system of the two wheels will turn on the axis A B as one and the same wheel. Now
suppose that the axis turns, and that we can measure one of the angles Dcd, at which all
the springs are stretched, we shall have in the triangle D Cď the angle C, the equal sides
CD, Cd, and consequently the perpendicular let fall from the centre C on the side Dd, or
the radius of the circle to which the force which stretches the spring is tangential. We
may, besides, observe the number of turns of an axis in a given time, whence we may
deduce the velocity of the point at which the force that stretches each spring is applied.
Multiply this velocity by the sum of the tension of the springs, the product will be the
dynamic effect of an axis in a unity of time, for example 1".
To measure the angle Dcd, which moves in a plane perpendicular to the axis of rotation
C of the axis AB, we fix on the lines Cd, CD, the middle of the radii, two small hammers
a, b, coupled by a spring Dd', which each move in a plane perpendicular to the axis of ro-
tation C, and at equal or unequal distances from this axis, but greater than the radii of the
wheels. These hammers strike two bells placed beyond on circles described through a and
b; this being arranged, we can with a seconds watch measure the time which elapses
between the two consecutive sounds resulting from the blow of each of the hammers on the
bells, and knowing besides the time of the entire revolution of the hammers, these two
portions of time will be in the ratio of the arc which measures the angle of the right lines
passing through the extremity of each spring to the entire circumference.
This angle
being known, we can easily measure the weight which stretches each spring at a known
angle, and the sum of these weights will be the total tension of the dynanometric
machine.
By this description it will be seen that simple springs without needles or scales, whose
force of tension for the same lengthening may be sensibly unequal, gives exactly the
measurement of a tangential force applied to axes: by taking springs capable only of a
tension of a ton, we may place eight on a circle of 39.37 inches radius, and eight others
on a concentric circle of 8 decimetres, supposing the axle makes four turns per minute; the
dynanometric machine, will show on this hypothesis that the dynamic effect produced by a
force applied to an axle is nearly equivalent to that obtained from 80 horses.
-
Portable Dynanometric Machine. The system of two wheels which composes the
dynanometric machine, being constructed at the same time as the axle AC B, we can
only measure the tangential force capable of overcoming the resistance applied to this
axle: but if this first construction did not exist, or if we would avoid the expense it would
occasion, we might make use of the portable dynanometric machine about to be described,
and which has for its object the measurement of a tangential force applied to any axle
A'C' B', provided we suppose, which is always the case, that this axle engages or disengages
at pleasure the wheel or pinion which communicates its movement to the resistance:

K
p
A
C TOT
B
L
Fig. 1637.
a frame of carpentry solidly bedded and fixed in the ground near the axle A'C'B', sus-
tains the axle A CB by its two gudgeons; the system of two wheels, one fixed on this axle,
CHAP. XIII.
1069
DYNANOMETER.
the other turning freely, is placed at the middle of its length: a factitious resistance is
applied on the length of the axle, which we may obtain in various ways: conceive for
example, that if the axle AC B. fig. 1637., is engaged between four blocks, p, q,r,s, fixed
to the beams K L, M N, and if we bring the second beam near the first by the screws M
and N, we shall increase the friction of the axle ACB on the blocks; and, by applying
other blocks and beams along the axle, we may indefinitely increase the factitious resistance
applied to the axle. Let us now explain the use of the dynanometric machine, fig. 1636.,
to measure the useful resistance applied to the axle A'B'C': when the axle is subjected
to this resistance its swiftness of rotation, or the number of turns which it makes in a
minute, for example, is known, in disengaging or communicating its movement to the
toothed-wheel R, or defgh of the dynanometric machine, we shall produce a factitious
resistance on the axle A CB of this machine, in the same manner as the axle ACB will
have the swiftness of rotation determined by the useful resistance. The springs, D,d, will
make known the factitious resistance applied tangentially to the toothed-wheel R, or axle
A CB, and consequently the useful resistance, which, by hypothesis, is equal thereto : if the
means of producing a factitious resistance equal to a real determined resistance were in-
sufficient, we shall now prove that, by a very simple calculation, one may deduce from the
measurement of one part of a resistance, the total value of this resistance.
Of the tangential Force applied to an Axle, deduced from the Measurement of one Part of
this Force. An axle communicates ordinarily its motion to a mechanical system of the
same kind, which can move at pleasure together or separately: suppose that by 'the instan-
taneous interruption of the communication of motion between some of these mechanical
arrangements and the axle by which the power is applied, we shall diminish the resistance
and increase the velocity of rotation of this axis: in this hypothesis, we may make it
catch the wheel R of the dynanometric machine, whose axle is submitted to a factitious
resistance, and by several trials we shall find the resistance which gives the primitive
velocity to the axle by which power is applied. Let us call X the total resistance applied
on this axle to the extremity of the radius I, and F the factitious resistance which com-
municates its primitive velocity: by diminishing the machinery moved by the axle by
which the power is applied, the total resistance X becomes of a mean value, which I call
X'; now these two resistances X and X' are evidently in the known relation to the
quantity of machinery turned by the axle; we shall then have X'=nX, n being a given
number.
Further, X = X' + F; then the axle by which power is applied submitted to the resis-
tance X, or the sum of the two resistances X and F, turns equally swiftly, whence it follows
F
that X=nX+F, which gives for the total resistance X the following value, X= 1 n
We comprise in the measured resistance F, the inertia and friction produced by the
communication of motion from the axle of power to the axle of the dynanometric machine,
and which adds to the factitious resistance.
The dynanometer invented by Sir David Brewster, to whom science is so considerably in-
debted, deserves to be mentioned: that celebrated philosopher has recommended that a vessel
containing water should have a cylinder, made of some heavier substance than the water,
suspended in it by a rope passing over a pulley: when the upper surface of the cylinder is
on a level with the surface of the water, the weight of the cylinder, or the force which it
exerts upon the rope, will be equal to the absolute weight of the cylinder in air diminished
by the weight of a quantity of water of the same magnitude as the cylinder: a horse
or a man pulling at the rope to raise the cylinder above the fluid surface, the weight of
the cylinder will gradually increase; and if the magnitude and specific gravity of the cy-
linder are duly adjusted to the force, there will be a particular position of the cylinder
at which its weight will exactly balance that applied. The forces in equilibrio, or those
required to be measured, will be equal to the absolute weight of the cylinder, diminished
by the weight of a quantity of water equal to the magnitude of the immersed part of the
cylinder a scale attached may be so set out, that it will accurately measure the force ap-
plied, and the cylinder can be increased to any length by diminishing its diameter, so that
a very lengthened division may be adopted.
:
Un
1070
Book II.
THEORY AND PRACTICE OF ENGINEERING.
CHAP. XIV.
ON PILES AND PILE-DRIVING, ETC.
BUILDING upon piles has been more practised by the moderns than by the ancients,
who only made use of them when it was not possible to attain a solid soil; it was not
their custom to lay upon them a platform of carpentry, but, after cutting off their heads
at the level, or a little below the soil, they covered them with charcoal to prevent decay,
on which they spread a bed of rubble or coarse concrete, which acquired strength with
age: the platforms of carpentry placed upon the heads of piles by modern engineers too
often are found to decay, and the filling in of the stones being disturbed, the waters are
allowed to filter through and endanger the foundation. Timber quickly perishes when
subject to alternate changes of wet and dry, but remains sound for a long time under
water, particularly in some soils: we have a remarkable example of such preservation
in one of the piles of the bridge built by Trajan over the Danube, which when examined
in the last century was found petrified; this, however, was not the case for more than
the thickness of of an inch, beyond which the timber was not in any way changed from
its ordinary character.
In Holland and other similar situations, planking and piling are adopted when the
soil is of that description that a more solid method cannot be used, and when there is great
facility of driving piles and covering them with planks fastened to their heads, after ram-
ming between them rough stones: on this is built a construction of freestone, the first
course being well cramped together. Timber and stone used together in foundations never
produce solidity and duration.
When it is absolutely necessary to pile, it is better to omit the floor of planking, and
to substitute a bed of concrete, which unites the masonry above with the filling in be-
tween the heads of the piles, the timber being first covered with powder of charcoal: on
this bed, well levelled and rendered solid, the first courses of squared masonry may be laid.
File-driving has for its object the consolidation of a soil when not sufficiently compact,
for piles driven close together tend in some degree to prevent that compression which might
manifest itself under a heavy construction: it is also resorted to when a solid stratum lies
at a depth too great to uncover, or when it is crossed by layers of soft earth difficult to
remove. The nature of the soil must guide us on all occasions in the selection of the
method to be adopted for work of this kind, and the qualities of the piles to be used;
they should be formed of the straightest timber, the fibres of which are not in any way
twisted, otherwise in driving they would bend and not arrive at the required depth;
they should not taper, or the difficulty will be increased: when, however, they are driven
to the greatest possible depth, in order to be certain that the soil is sufficiently consolidated,
they should be loaded with a weight equal to what they are intended to bear, and this
weight left a sufficient length of time to remove any doubts upon the subject.
In clay,
naturally firm, the pile sometimes becomes a conductor to the water, which insinuates itself
along the sides, softening and producing a settling, which would not have taken place had
piling not been introduced; and wherever such a soil occurs, the first piles should be
driven 5 or 6 feet apart, and before they arrive at their entire depth, others should be placed
in the intervals, greater resistance being experienced in proportion as the numbers are in-
creased; and it sometimes happens that, in order to drive the latter home, or until they
will drive no longer, it is necessary to place them so thick that they almost touch each
other.
When it is ascertained that there is a good substratum, of a solidity and consistence
capable of carrying the weight of the edifice to be put upon it, the piles may be regulated
with regard to their distances, and experience has proved that when placed about 4 feet
apart from centre to centre, they are capable of supporting the weight of the largest
bridges; they should be always driven to their greatest possible depth, and it is advisable
to commence with the middle row, as the soil then consolidates as the work is continued.
The only means of judging correctly of the resistance which a pile offers is to examine
the nature of the stratum on which it bears, the hold which it takes, and whether it has
penetrated a soil not susceptible of yielding under the weight of the construction, such as
rock or gravel, provided this latter cannot be washed away by the current; the refusal of a
pile to advance does not always insure it having arrived at a proper bed, the nature and
consistency of which should always be previously ascertained: many instances could be
adduced where piles have sunk under the weight placed upon them for want of these con-
siderations.
Piles are cut off nearly at the bottom of the river, and their intervals filled in with
CHAP. XIV.
1071
ON PILES AND PILE-DRIVING.
rubble work, in such a manner as to leave no fear of their bending under the weight; if
isolated at a certain height, it is necessary that their strength should be rightly calcu-
lated, and the power of their resistance made greater than the load they have to bear; their
height out of the ground should be considered in the nature of an upright piece of timber,
and the rules relative to its strength and power of support duly followed. The bending
and breaking of piles is not of so much consequence as their being driven out of a perpen-
dicular position: it often happens that when they have penetrated beds of slight consis-
tency, and have not a hold in firm soil, the foundation placed on them exerts a lateral
pressure, which acting as on the arm of a lever, greater in proportion to the length of the
pile, causes it to diverge; this may sometimes be prevented by inclining the external piles
outwards, and driving them in an oblique direction, or in the line of the thrust to which
they are subjected: with respect to the weight which piles are capable of sustaining, Per-
ronet thinks that one of 12 inches in diameter should not be loaded with more than 50
tons, and those of 9 inches in diameter with half that weight.
Piles for foundations are either of oak, elm, fir, or beech timber: those used at the New
London Bridge averaged 12 inches in diameter, were 20 feet long, shod with wrought-iron
shoes, weighing 30 pounds each, and had iron hoops of the same weight, to prevent them
from splitting whilst driving. The piles under the foundations of the abutments were driven
at right angles to the inclination of the foundations, those for the piers perpendicularly,
and the whole more than 18 inches below the under side of the platforms that were
placed upon them. They were placed at distances from 3 to 4 feet from centre to centre,
and when arrived at their proper depths, the heads were cut level and even, and the earth
between them taken out to the depth of 9 inches below, the space between being filled with
Kentish rag-stone well beat down, and racked in with sharp gravel and lime-screenings to
the level of the pile-heads, on which the sills of the timbers laid transversely were spiked:
when oak piles are used, their diameter is generally about the twentieth or twenty-fifth
part of their length; they should be very straight, and barked and dressed with care; the
head is cut at right angles to its length, and rounded to receive the movable hoop of iron;
the lower end is sharpened by cutting each side to the length of about 18 inches, in such
a manner as to bear upon the iron shoe, which is spiked or nailed to the end of the pile;
sometimes it is only necessary to sharpen the end of the pile, and char it in the fire; this
is sufficient for the scaffold pile, or for those which are for a temporary use: when sheet
piling is used for a cofferdam, or the facing of a wharf or jetty, it is generally from 4 to 6
inches in thickness, and the width about 12 inches, the length of the piles depending on
the nature of the soil they are to penetrate, and the depth to which the neighbouring piles
have been driven; the sheet piles do not generally descend so low, and they are often required
to be shod with iron; when they are to be exactly joined, there is on the side of each
pile a groove, into which the plank enters, though this adds to the difficulty of driving
for which as well as for the piles the beetle is sometimes made use of, but generally a ma
chine constructed for the purpose.
When it is necessary that either the points of the planks or piles should penetrate a hard
soil, holes may be pierced with an iron-shod piece of timber or rod of iron working perpen-
dicularly through a frame or hole cut in a large stone, which serves to guide the in-
strument, and the hole so formed may be sufficiently enlarged by an auger to admit them,
which ensures greater stability,
The timber now generally employed for piles is either Dantzic or Memel, and too great
caution cannot be used in the selection of it, to ascertain if it be perfectly sound; in
some works beech or Scotch fir are employed, and if kept always under water are found
equally durable: below London Bridge, on the Thames, and particularly where the water
is at all brackish, the ravages made by the Teredo navalis upon fir piles is so great that a
few years are sufficient entirely to destroy them above the level of low water; sheathing
with copper and iron is found of little use in protecting them, as the worm enters from
the mud, and pursues his ravages in a vertical direction, until the entire pile is com-
pletely hollowed out
The Three-hand Beetle is a large maul made of a block of hard wood, hooped with iron,
having two long handles radiating from its centre, put at such a distance that it can be
worked by two men, assisted by another in lifting it, who holds by a short handle opposite
to them: this has considerable power, and is used when the piles to be driven are not of so
great a length as to require the engine.
The Pile Engine varies in size and construction; when small, and the block which is let
fall does not exceed 2 or 3 cwt., it is worked by a single rope passing over a large pulley,
where it is divided into as many smaller ropes as may be required, at each of which a man
works, and when the weight is raised, the whole let go together. This kind of machine
can only be used for driving short piles, as the weight cannot be lifted beyond the height
to which the men's arms can reach, but it has the advantage of being easily and rapidly
worked.
For larger operations a ram of from 8 to 10 twt. is used, set in a frame of woodwork,
placed on a base formed by four timbers framed and bolted together at right angles, and to
Um
1072
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
which is screwed or securely attached a crab, with a cylindrical barrel and two handles,
worked by four or six men: on this framing is placed on one side two upright pieces
of timber, on the other an inclined ladder, the whole securely braced together: at the
top a wheel is fixed, over which the chain worked by the crab passes, and is attached
to the monkey, which has a plate in front and at the back, so that it is confined to work
a saw up and down the perpendicular pieces of timber, which are protected by plates
of iron.
The rope, fastened at the top, elevates the monkey, and the nippers
being applied at the bottom are enabled to hold the ram until
they are elevated to the inclined planes at top, where they are com-
pressed, by which means the bottom part, which holds the ram, is
opened, and it is suffered to fall the entire height of the machine
upon the pile head below. The monkey and nippers immediately
follow by their own weight; the latter open again, and admit the
hoop or ear of the ram to be ready to be lifted by the men at the
crab: the higher the ram is lifted, the greater will be the blow given
to the head of the pile; the time of raising it is increased, though
not in proportion to the advantages gained, but in a higher ratio,
the velocity being as the square root of the height, whereas the time
is as the height merely.
The rams are of oak, of a cylindrical form, strongly hooped round
for common purposes; but generally cast-iron is preferable, and is
more durable.
Coulomb valued the daily action of a man em-
ployed at the pile-engine as 75-2 kilogrammes, and capable of rais-
ing 1000 metres.
The pile is placed vertically in the spot where it is to be driven,
and is generally lowered by the chain of the engine being attached to
Fig. 1638.
it at about one-third of its length; it is then maintained in its
position, and allowed to descend until it has fixed itself in the soil; when the pile has
arrived below the frame of the engine, and the ram can no longer reach it, the driving is
continued by means of a false pile, or piece of timber bound with iron at the two extremi-
ties, and having a gudgeon of iron entering into a hole at the head of the pile; but grafting
the piles with others securely fastened and bound with iron hoops is perhaps the most
simple method, as well as efficacious, when they are to descend far into the soil.
Great care must be taken that the piles are driven in a vertical position: to insure this,
and prevent their swerving during the action of driving, they are passed through a piece
of framing attached firmly to the scaffold, which obliges them to descend perpendicularly;
sometimes a large stone will change the direction of the point; it should then be with-
drawn, and the stone be either crushed or removed; for if a pile takes a wrong direction,
it is better to pull it up and replace it, than persist in endeavouring to right it: in order
that the piles may each have its proper position, it is requisite to trace their places on the
platform, or to fix lines, which represent by their intersection their true positions; or,
where the situation will permit, stakes may be placed to indicate this, and these preliminary
operations are highly necessary when the engine is placed in boats or lighters.
The same means are adopted for driving the planks as for the piles; their use being
to enclose a certain space, it is highly important that their joints should be rendered as
close as possible; this is done by framing together two pieces of timber on the scaffold, in
the manner of a groove, between which the planks are driven.
Frames are formed by the rails, which are disposed on each side of the planks, and are
secured by a pin placed in a mortice horizontal in them and vertical in the plank, in order to
afford some play in the driving. The planks in the middle of the frame are driven first,
and when those at the extremities which carry the rail are arrived at, the peg must be removed
to the next plank, where a similar mortice has been made: a lower frame is used, when
necessary, to more perfectly regulate the driving: short planks may be carried to their
position, and placed vertically by the side of each other, and when made to enter a little
into the soil, a blow on their heads is sufficient to establish them; they may be held in
their places by a cramp or iron; driving planks as well as piles is often performed from
two boats coupled together, carrying a timber frame. The same force made use of to drive
the pile might be applied by machinery, but it would be difficult to construct it of suffi-
cient strength, and free from friction: a weight, for instance, of 500 pounds, falling through
a height of 50 feet, may drive a pile at each stroke 2 inches, and if the resistance be
considered uniform, the magnitude must be about 150,000 pounds; the same moving power,
with a mechanical advantage of 300 to 1, would perform the work in the same time;
but the strain upon some parts of such a machine would be equivalent to the draught of
600 horses.
The ends of the piles are variously cut, according to the soil they are intended to pene
trate being shod with iron they are prevented from splitting as they enter a hard stratum
or come in contact with stone.

CHAP. XIV.
1073
ON PILES AND PILE-DRIVING.
Fig. 1639.
Fig 1640.
Sheeting Piles are formed of thick plank, shot or jointed on the edges, so that they may
form a close joint, and not admit the water to pass between them: when their sides are
grooved and tongued, the passage of either air or water is prevented; the edge of one
plank is double, and the other single, rebated, so that about a third of the thickness of one
passes into the middle of the thickness of the other: to drive these piles the small or
ringing engine is generally made use of, and to bring the edges of the planks into close
contact with each other great care is necessary: the pointing of sheet piles should be
effected by cutting one side only of the plank.
Water and quicksands are often kept back by sheet piling, but it sometimes happens
that both rise so rapidly as to impede the workmen's progress; the pump or other
means is then adopted to drain off the water, and it becomes necessary, under such cir-
cumstances, to provide guides for driving, and afterwards retaining the planks or sheet-
piles in their proper position: square timbers, placed horizontally, as well as parallel with
cach other, are put as near the work as possible, and kept apart at each of their ends
by a short pile driven firmly into the ground, into which they are secured with screw
bolts. These horizontal timbers are not laid farther apart than just to allow of the thickness
of the sheet pile, which varies from 2 to 6 inches or more, according to the work it has to
perform. Piles introduced between guides can be very accurately driven, and easily
maintained in their position: when the resistance they offer is considerable, both the upper
and lower part of the guides may be made of whole timbers, and the lower stiffened by
bracing, or by short piles driven close behind them at small intervals: care must also be
taken to provide for the security of the sheet of piles when the whole is complete, for
during the progress of driving and fixing, the water and sand can rise to a common level
on both sides; but when these are cleared out on one side to form a dam, the accumulation
and consequent weight which exerts its influence on one side will break down, or force
out the work, unless strutted and braced with sufficient strength to prevent it.
It is necessary, when the water is perfectly clear, to stop all the joints, or to caulk them
with oakum, but generally the particles of clay or earth settle in the joints, and render
them water-tight.
In the formations of a cofferdam it is frequently requisite to drive two rows of vertical
piles and plank piles, and to fill in the intermediate space with well prepared clay : in other
cases main piles are driven, to which are fixed strong horizontal planks, and another mode
is to drive one row of gauged piles, and then fill the spaces between with pile planks driven
vertically.
In deep rivers the foundation of piers were previously made by driving piles all over the
space, so that their heads stood level with low water; the spaces between them were merely
filled with loose stones, and the masonry, as at old London Bridge, commenced at their top;
but the piers were immense masses, and required to be protected by sterlings, leaving a
very confined water-way, and created a head and velocity which ploughed up the entire
bed of the river below the piers: our old bridges appear to have been constructed without
cofferdams or caissoons, the engineers employed upon them probably considering that weight
and resistance were requisite to oppose the current of a river, and rather than yield to its
force they threw in sufficient material to almost draw it up: modern practice, on the con-
trary, endeavours not to abridge the width of water-way, and its advantages are universally
admitted, as are the employment of sheeting piles around the footings of the foundations.
The machine used by Perronet was worked by a number of ropes pulled by men; hence
it was named the ringing engine, and the pile was driven by a ram which descended per-
pendicularly the various parts of the framing were of stout timbers, put together with
round iron pins, which allowed of its being taken to pieces when necessary, and trans-
ported to some other situation: attached in the rear of the supporting frame was a windlass
for the purpose of hoisting the pile, or placing it into its position for driving, the rope
which wound it up passing over a pulley fixed in the projecting timber at the top of the
machine.
This celebrated Engineer, in the foundations of the piers of his bridges, made use of
piles of from 9 to 12 inches in diameter, placing them from 3 to 4 feet apart from centre
to centre, and driving them 6 feet into the bed of the river, when composed of soft mud,
·
3 Z
1074
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
clay, or gravel. The pile planks were from 9 to 12 inches in breadth, and 4 inches thick,
and one frame held 16 pile planks, which were driven at one time: the frames were
placed along, and embraced three of the main guide piles, and were composed of two
upright timbers of the same thickness as the pile planks, and were sharpened at the end:
these uprights were fastened together by two horizontal timbers, one above, the other below,
and separated from each other by the thickness of the uprights: when these frames were
fixed, they served the purpose of guides to the pile planks: the grooves at their sides
were 2 or 3 inches wide, and as much in depth.



ㅁ
​Fig. 1641.
PERRONET'S PILE-ENGINE.
Perronet used a similar engine at the
bridge of Orleans, and a ram for driving
the piles, which weighed 1200 pounds, and
another for the pile planks, of only half
that weight the windlass for elevating
the pile was conveniently placed in the
centre, and the pulling ropes were admir-
ably arranged.


:
At the bridge of Neuilly a large drum
wheel was made use of, round which a
rope was wound, worked by a horse, and
the weight of the rams employed varied
from 1000 to 2000 pounds weight; with
these the piles were driven, until they
did not sink more than of an inch
during 16 strokes: this method was not
found convenient, although tackle and
contrivances of various kinds were intro-
duced into the machine, to regulate its
action, and to prevent any accident oc-
curring from the breaking of the rope.
Fig. 1642
PERRONET'S PILE-ENGINE.
The dynamical effect of a horse power
applied to such an engine employed in
pile-driving, and worked by two horses,
was found to be equal to a weight of 42,536
lbs. raised 1 foot high in 35 seconds, or a weight of 36,459 lbs raised 1 foot high per
minute per horse.
When the ram is raised by horse instead of human power, the drum or cylinder upon
which the rope winds ought to be provided with a lever catch to lay hold of the arm by
which it is fixed or engaged, while the weight is rising, and which can be easily manoeuvred
when it is required to disengage, so that the rope may be allowed to run back, for re-
engaging the weight without the slow process of turning the direction of the horse.
Perronet's pile-engine placed upon a boat, worked by an armed wheel, has frequently
been found admirably adapted for its purpose; the end and side view of this machine at
CHAP. XIV.
1075
ON PILES AND PILE-DRIVING.

Fig. 1643.
PERRONET'S PILE-Engine.
once show how conveniently it may be moved to perform its operations. The platform
laid upon the deck of the boat being braced in all directions, the other timbers are fixed

Fig. 1644.
PERRONET'S PILE-DRIVING ENGINE.
upon it with facility, and may be taken down as readily when not required, and placed
under cover: by means of a ladder attached to the inclined braces at the back, the
upper parts of the engine could be approached, and the tackle adjusted. To keep
the ram steady, it was made to slide within a frame, so that its motion could always be
depended upon, and there was no danger of its falling into the water.
Pile-driver by De Cessart, used at the bridge of Saumur. The axis was 10 inches
diameter, furnished with a wheel, 12 feet in diameter, with trundles or round pins
on the periphery for turning it. Eight men employed at this wheel raised at three turns
a ram of 1500 pounds 6 feet high; a workman, by means of a cord, then unhooked the ram,
which suddenly fell; but to regulate the height of the fall and the price for driving,
it was determined that it should be limited to a stroke of 8 or 10 feet, giving the greatest
fall at the time the greatest force was required to be applied to it. The price was deter-
mined in this case at 20 shillings per pile, including the expenses of transport, and for the
scaffold piles 10 shillings.
3 z 2
1076
THEORY AND PRACTICE OF ENGINEERING. Book 11.

D
•
Fig. 1645.
DE CESSART'S PILE-ENGINE.
He
De Cessart found that when dri-
ving piles into the bed of the Loire
he could not make them enter more
than 28 or 29 feet below the height
of low water, after having received
8000 blows from a ram of from
1200 to 1400 pounds weight.
experienced some difficulty in pre-
venting the heads from splitting, as
the foundations were laid at 12 feet
below the surface, and the piles cut
off at 14 feet 1 inch; he imagined
that the longitudinal fracture was
not prolonged to this depth, being
compressed by the natural ground.

The
The plan of this machine is shown
as placed to drive the pile A.
cylinder is turned by the 10 feet
wheel, which has roundles 18 inches
apart on the circumference; the
rope which coils round the cylin-
der passes over a wheel at the top
of the machine, 4 feet in diameter,
and is then attached to the ram,
which weighed from 1200 to 1400
pounds; to release the ram when it
had arrived at its proper height, a
rope was attached to a hook, which,
when pulled, released the ram.
000
:
A
Fig. 1646. PLAN OF De cessart's pile.
Workmen, with the ordinary pile-engine, generally give 25 blows of the ram in a minute,
each time raising three feet, consequently 75 feet per minute, after which they rest 2
minutes, giving the same velocity to the wheel, with the same number of men; that
under consideration being 30 feet in circumference, it would make two turns and a half
CHAP. XIV.
1077
ON PILES AND PILE-DRIVING.
per minute; the circumference of the cylinders winding up 3 feet of rope at each turn, it
would raise the ram 7 feet 6 inches
per minute, and the blow given to
the pile would be equivalent to
200,000 pounds at least.

The pile-driving engine now in
use is upon a very superior prin-
ciple to those we have described;
instead of having the ram of oak
that was required to be hooped
round in various directions to pre-
vent its splitting, it is formed of
cast-iron or bronze; the latter me-
tal possessing greater elasticity is
supposed to contribute to the driv.
ing of the pile; after the ram has
been raised to its destined ele-
vation by means of a crab or wind-
lass, it is released by pulling a rope
that opens the nippers attached at
the top of it, when it falls with
considerable weight on the top of
the pile-head. The ram is main-
tained in its vertical position by a
frame at the back.
Pile-driving Machine used at
Montrose Harbour was attached
to the steam-engine, and of ingenious
construction. The ram weighed
12 cwt., and the clipper, with its
slider, was of the ordinary kind,
except that the upper part of the
clipper had its extremities made of
a sufficient length to allow the slider
to rise 15 inches after the ram had
been disengaged by the slips. The
ram chain, which was shackled to
the clipper, passed over one pulley
at the top of the guides, to another
part of the machine, by means of
another pulley placed at the base of
the guides.
As the ram may be supposed to
fall 16 feet in a second, we may
calculate its velocity in falling
through any given height, as pro-
portionate directly to the time of
descent; the velocity acquired at
Fig. 1647.
PILE-DRIVING ENGINE.
ง
the end of the first second is equal to 321 feet per second, upon which principle the follow-
ing table has been calculated, by which the force of the blow of any ram whatever

Force in Tons of
a Ram weighing
1 Ton.
10
1234567 · ✪ O
•25
⚫35
8.0 11
11.3 12
•43 13.9 13
⚫83
$86
•90
26.6 21 1.14 36.7 31
27.8 22 1.17
28.9 23
1.39
44.6
37.6 32
1.41
45.4
1.20
38.5 33
1.43
46.1
⚫50 16.0 14
⚫93
30.0 24
1.22
39.3 34
1.45
46.8
•56
17.6 15
.96
31.0 25
1.25
40.1 35
1.48
47.4
8
•70
•61 19.6 16 1.00 32.1 26
•66 21.2 17 1.03 33.1 27 1.29
22.7 18 1.05 34.0 28 1.32
1.27
40.9 36
1.50
48.1
41.7 37
1.52
48.8
42.4 38
1.54
49.4
9
·75
24.1 19 1.09 35.0
•79 25.3 20 1.11 35.9
3 z 3
285003
29 1.34
43.2 39 1.56
50.1
1.37
43.9 40 1.58
50.7
1078
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
may be ascertained, it being only necessary to multiply the force, in the last column, by
the weight of the ram; thus a ram weighing 12 cwt. falling 20 feet, will have a force thus,
12 × 35·9-430.8 cwt.
Withdrawing Piles. In harbours or tide rivers this is easily effected by attaching barges
at low water to the heads of the piles, and as the tide rises, the pile must either be pulled
out, or the barge pass under the water. In other cases Bramah's hydrostatic press has
been used, or a framework of timber inclined so as to work a chain by means of a crab,
to which blocks are attached, and draw them out: when piles have a slight hold, they
may be drawn out by a long lever, acting upon a chain attached to the head of a pile:
iron shod piles driven into gravel are sometimes difficult to withdraw, in consequence of
the great oxidising of the metal; this principally occurs in sea water; when, therefore, they
are to be withdrawn from such situations, it is advisable to omit the iron shoe, if at all
possible.
In drawing out piles, the operation is considerably assisted by striking them with heavy
blows near the head, in an oblique direction, by means of levers, and some ingenious

Fig. 1648.
methods have been adopted:
MACHINE for DRAWING PILES.
when the heads of the piles are out of the water, it is advis-
able to pierce a hole through them and pass a bolt, to which is attached the chain by
which they are to be raised up.
When the head is under the water, a square iron collar



Hit W
Fig. 1649.
MACHINE FOR DRAWING PILES.
is passed over the pile, and, having a greater diameter than the latter, is placed obliquely ;
when the chain is tightened, the edges of the collar embrace the wood, and from the great
pressure which takes place, all sliding

off is prevented.
When the piles are rounded and shod
with iron, they not only descend easier,
but may be more readily detached: an
improvement has been suggested upon
the last machine, which consists in
making the block attached to the screw
rise as it is turned round, and the head
of the pile being secured to each side
of it by a link of iron, it can be loosened
and drawn out with a more steady
motion, all disposition to swerve from
the perpendicular being prevented.
Fig. 1650.
10
SCREW FOr drawinG PILES.
Cutting off Piles. This operation is by no means difficult when the foundations are
―
CHAP. XIV.
1079
ON PILES AND PILE-DRIVING.
At
E
Ъ
B
B
AS
A
E
dry, but when under water a machine is requisite: this is composed of a horizontal
frame formed by the three pieces
A, A, A, 4 inches square, framed into
two cross pieces B, B, and a vertical
frame formed by the two uprights
C, C, each about 4 inches square.
At the foot of these is placed the
saw l, which is kept tightened by
screwing the iron at the other ex-
tremity of the upright timbers, so as
to bind or secure the blade. In
order to give motion to the saw, a
workman is placed to each of the
handles at E, and alternately pushes
them backwards and forwards in the
direction A A, whilst another on the
scaffold directs their labour, and hold-
ing a rope R, so places the saw that
it at once puts a kerf into the head
pile when required. This machine
.is usually mounted on wheels, and
enabled to traverse the scaffold freely.

•
A
A
B
B
Fig. 1651.
PILE
CUTTING off piles.
At the bridge of Choisy such a
machine was worked by a carpenter and six labourers, and who in 25 minutes sawed off a pile
10 to 12 inches diameter, placed at 3 feet 8 inches below the cross-pieces A, A, and thus cut
off about 22 in a day of ten hours, the rest of the time being employed in altering the
position of the machine and the scaffold. The saws cut with the most perfect correctness,
when the frames which guide them slide in such a manner that the cross pieces A, A are
allowed to remain in the same horizontal plane; but the upright pieces C, C cannot well
be made more than 9 or 10 feet in length below the cross-pieces A, A; therefore, when it
is necessary to cut piles at a greater depth, some other means must be resorted to.
Labelye, in building Westminster bridge, appears to have been the first who applied
such a machine, in 1738, to cutting off piles. This engineer published a brief report in
1751 upon the various systems he adopted. for the construction of this bridge, and it is to
be regretted that he did not complete the account which he announced as preparing: many
of Labelye's ingenious inventions have been copied without acknowledgment, and some
even patented since his time; this is evident by a reference to the account preserved by
the late Mr. Thomas Gayfere, who was senior apprentice to Mr. Jeff, the master mason
employed at Westminster bridge.
For cutting off piles at more than 'O feet, or up to 15 feet below the water, the in-
vention by Messrs. Voglie and Cesart at the bridge of Saumur may be considered ingenious,
and was very successful: it was a modification of the one already described, and with
four men to work the saw, and a fifth to adjust the saw against the pile, they were
enabled to cut off a pile in five or six minutes, and could in the course of 12 hours cut
off 22 piles, allowing for the moving and adjusting the machine.
De Cessart's Machine for cutting off the Heads of Piles under Water. The machine was
supported by a scaffolding, composed of three pieces of timber, 32 feet in length; each
carried at its extremity a roller, 18 inches long and 8 inches in diameter, which were run
on timber made perfectly smooth and level, placed equidistant along the length of the pier,
and supported on the tops of piles.
The object of this machine was first to cut off the piles at a uniform height, and that the
upper part of the pile should be cut truly level, that four men should work the saw with
ease; that the pressure of the saw against the head of the pile should be regulated by one
man, as the timber produced more or less resistance; that the operation should be performed
with as much facility when the head of the pile was absolutely out of sight, as when it ap-
peared above the water; that it should be practicable to cut another slice, if the first
did not effectually level the pile; that the machine should embrace the head by grappling
and taking a firm hold; that when necessary to clean or reset the saw blade, it should be
done with facility, and that the small rolling scaffold should advance by degrees along
the breadth of the pier, while the large scaffold carried it along to another row of piles.
For the first operation, the saw blade is drawn back by a regulator; the machine is
raised 6 inches by the four perpendicular rods, which work with racks and pinions at the
top, and is then advanced towards the pile; when it is lowered to the level of the intended
cutting, an iron sounding rod serves as a gauge to mark this, and having established the
level for the machine to work, the grapples are tightened by means of ropes, and the sawing
is commenced: this is performed by four men, moving alternately the iron rods, which
work in grooves at the top, and by means of other jointed rods give an oscillating motion
3 z 4
1080
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
resembling that of working a saw, to the bottom part of the machine, and which draws
backwards and forwards by means of other connecting arms the saw which is to operate
on the pile.
By a reference to the plan, we see the saw in its position after it has cut the head of the

Fig. 1652.
pile partly through; at the back of the semicircle which holds it is a straight rod, which
is made to slide along a straight groove; motion is given to this rod backwards and forwards

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Fig. 1653.
L
S
K
CA
B
CHAP. XIV.
1081
ON PILES AND PILE-DRIVING.
in the groove, in such manner as the saw is required to move, and this motion constitutes
the value of the machine.
A lever bent into three different directions, moving on a pivot at the first angle of its
bending, and having a movable roller at the other, conveys the motion from the bascule or
see-saw directly to the saw the dotted lines show the extent of this motion one way, and
the shaded part that of the other.

u
C
G
C
R
P
Fig. 1654.
de cessart's pile-cutter.
In the section we see the various positions of the bascule or jointed rods when the
sawing is in progress. The two wheels shown in the plan are worked by a rack and pinion
by means of a rod coming from the top, by turning which any required pressure is given
to the saw. The grapples, which clutch the head of the piles, are drawn back by means of
levers worked at the top, and they are kept from turning by a rope attached to a ring
fastened to one of the timbers of the upper platform: the time for cutting off the head of
a pile is from three to four minutes.
This complicated machine performed its work with great precision, although several
engineers continued to prefer that used by Labelye for cutting off the heads of the piles at
Westminster Bridge: there can be no doubt that De Cessart's machine, from the variety
of its movements and cost of construction, can only be adopted where very extensive works
are to be executed; the more simple the saw is set, as long as it can be maintained in a
truly level position, the better; for scaffolding, if not solidly put together, is very liable to
A saw
produce by its change of form very great inequalities in the work performed.
mounted on an iron frame, and made to traverse upon two rails of the same material, would
most correctly and efficiently execute the work, for there could be no difficulty by such an
1082
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
arrangement to maintain a perfectly horizontal action for the machinery, in whatever
situation it might be applied. In the "Traité complet de Mécanique appliquée aux
Arts," by M. J. A. Borgnis, some other machines for this purpose are described.

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Fig. 1655
DE CESSARt's pile-cutter.
Louis Alexander De Cessart, who executed the celebrated breakwater at the Port of
Cherbourg, described in a former part of this work, published an account of most of his
engineering works, among which is the detailed account of the dimensions and weight of
the several parts of his machine for cutting off the heads of piles under water: as it is a
curious document, and an example of the minute calculations entered into by French
engineers for the construction of such kind of machinery, we have thought right to insert
it; the dimensions are given in French feet, as the calculations in metres were not at that
time established.
CHAP. XIV.
1083
ON PILES AND PILE-DRIVING.
Details of De Cessart's Machine for cutting off the Heads of Piles, given in French
Measures.

Dimensions.
Cube quan-
tity of iron.
Dimensions.
Cube quan-
tity of iron.
First: Horizontal Move-
ments.

In. Lines.
In. Lines.
In. Lines.
Brought forward
In. Lines.
357 5
2 iron arms, G, G, I.
The semicircle, k, attached
Length
198 0
to the saw comprising the
mâchoires, &c.
Width
1 6
148 6
80 0
Thickness
0 6
Width
Thickness
2 0
0 8
106 8
Handle, I.
Length
54 0
The two branches, Y.
540
Length
30 0
Width
1
Thickness
Half circle, X.
0
996
22 6
Length
Diameter
Total cube of second
movement
Weight 186 lbs. 10 oz. 1 gr.
Great iron frame, A A.
Plates added together
Width
1 0
}
54 0
559 11
Width
Thickness
2 branches of ditto.
Length
Width
Thickness
Entretoise, Z,Z.
Length
Width
Thickness
Channel, U.
1
1
Length of two sides -
Width
Thickness
Supports, S, S.
Branches, M, M.
48 0
1 6
0 5
30
1
055
0 5
30 0
826 0
3 6
722 9
Thickness
0 3
Channels, R, for the regu-
6
18 9
lation of the triangle
Length of two sides
Height
-
144 O
0
1 6
108 0
44 0
1
0
064
Thickness
0 6
22 0
Iron plates cast for ditto.
Length
72 0
Width
2 3
40 6
122 0
09
0 9
Thickness
0 3
63 7 6
Supports of the channel.
The four
8 0
The two which sustain
The three wheels
50 0
the balance
42 0
The two uprights
60 0
Length
Width
Thickness
Buttress arches, V.
Length
1
120 0
0 6
0 6
Pieces attached
14 0
90 0
2 channels, Q, Q, which oc-
casion motion to the saw.
Length of two sides
108 0
88 0
Width
Thickness
Irons, J, J.
Length
Width
Thickness
1
0
034
Width
2 0
54 0
36 8
Thickness
0 3
Iron supports of first.
Length of the three
16
0
bands
66 0
1 3
6 8
Width
2 0
22 0
0 4
Thickness
0 2
2 entretoises, L, L, of the
The guide which envelopes
central movement.
the grappling irons
Length
48 0
The round
24 0
Width
1 6
24 0
Width
2 0
16 0
Thickness
0 4
Thickness
0 4
Entretoises, T, T.
Bands of iron, D, which
Length
66 0
maintain the
plate
Width
2 teethed-wheels
Thickness
I
1 3
0 4
27 6
against the pile.
Length of the 2 bands
64 0
and
Width
1 3
200
pinions.
Thickness
0 3
The two wheels
The two pinions
52 0
4 0
The two large levers, H, H.
Total iron-work of the
great plate
1107 3
Length of the two
236 0
Width
Thickness
2 0
0 8
314 O
Weight 369 lbs. 1 oz. 26 gr.
Irons which change the
Total cubical content of
the first movement
Weight in pounds of 16 oz.,
and taking 3 cube inches
as equal to 1 pound, 291
lbs. 5 oz. 44 grains.
Second: Vertical Move-
ments.
Equilateral triangle, P.
847
66
movement on the plate.
6 uprights, each 8 in.
high, and the pieces
attached
6 tail pieces
Channels.
Length
Height
Thickness
Total
Length
150 0
Width
6
93 9
Thickness
0 5
Entretien of the levers.
Length
50 0
Width
2 0
41 8
Thickness
0 5
The cover of the
Weight 22 lbs. 9 oz. 26 gr.
The griping pieces, F, F.
Length
Width
Thickness
Uprights, E, E.
Length
Thickness
angle
10 0
2 keys, b, b.
2 balances, G, G.
Length together
Width
Thickness
The two covers
Carried forward
192 0
Length
Thickness
2 0
192 0
0 6
Total
•
20 0
357 5
Weight
58 gr.
174 lbs.
10 oz.
48 0
6 0
44 0
1 3
13 9
0 3
67 9
40 0
1 6
1 0
J
60 0
288 0
1 2
}
392 0
72 0
1 0
72 0
524 0
1084
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Dimensions.
Cube
quân.
tity of iron.
Dimensions.
Cube quan-
tity of iron.
In. Lines.
In. Lines.
In. Lines.
Uprights, C, C.
Length
Width
Brought forward
In. Lines.
399 9
144 O
The four bands to hold the
Thickness
Side pieces for the spindles.
09
1 0
108 0
channels
48 0
447 9
Length
288 0
Platforms.
Width
2 0
144 0
Length of plates
160 0
Thickness
0 3
Thickness
1 6
60 0
108 spindles
54 0
Width
-
0 3
Stirrups at the end of the
Stirrup irons upon the
four uprights.
scaffold.
Length
Thickness
190 0
1 0
190 0
Total for the uprights
496 0
Length of the two
Height
Thickness
4 bolts and screws
86 0
2 0
43 0
0
3
28 0
5 ditto
14 0
For the whole four
1984 0
Pivots
36 0
628 9
Weight 661 lbs. 5 oz. 26 gr.
The four crics, ff.
Uprights
Thickness
Width
40 0
0 9
0 10
}
25 0
Four cross pieces.
Length
29 0
16 3 9
Thickness
0 9
Pinion contains
Wheel
Toothed ditto
Axle
2 0
8 0
12 0
*
1
6 0
Winch.
Length
4 bolts.
Length
Thickness
Thickness
26 0
0 9
}
4
14 7 6
Weight 209 lbs. 9 oz. 24 gr.
-
Sounding rod is in length
12 feet
Total weight of the ma-
chine 2082 lbs. 7 oz. 62 gr.,
which at 15 sols per lb.
amounts to 1561 livres
17 sous 3 den.
Copper employed: -
copper wheels which
carry the horizontal
levers of the saw
6 0
lbs. oz.
lbs.
-
7 10
40 0
6
40 0
1 0
copper wheels applied to
the bras de force
-
5 0
Total of one cric
For the four together
Weight 165 lbs. 4 oz.
Uprights, d, for regu-
lating the movement.
Length
Thicknesses
Key, a, for regulating
Length
Thickness
Iron arms, I.
123 11 3
495 9
-
4 smaller ditto
Rondelles or washers
4 copper plates on which
the large levers work
3 0
17 8
28
2 copper wheels upon the
plate
1 11
168 0
1 3
}
262 6
34 13
28
36 0
1 0
}
36 0
Length of the 4 arms
180 0
Thickness
0 9
}
101 3
Carried forward
399 9
Price of copper 1670 livres
1 sou 7 den.
Price of scaffold for the
machine 530 livres 18 sous
4 den.
Making the total cost of the
whole 2200 livres 19 sous
11 den.
Steam Pile-driving Machine, as used in America for the construction of railways, deserves
to be mentioned; it consists of two machines, similar to those used by hand, which are
placed 6 feet apart from centre to centre; these are firmly bolted and secured to a strong
horizontal framing, and further strengthened by two oblique ladders. The frame is 9 feet
wide, and 28 feet long, carries at one end a locomotive boiler 11 feet in length, and 30 inches
in diameter, which is calculated to bear 120 lbs. pressure per square inch, being worked
only at two-thirds that amount, making 100 strokes per minute: in the centre of the
framing, and on each side of the boiler, a pair of inclined cylinders, 5 inches bore, are
placed; these have solid pistons which work without packing, with a 14-inch stroke, acting
on right-angled cranks. The shaft centres are 1 foot 3 inches apart; the spur-wheel has
56 teeth, and pinion 19; the bevels 101 and 40 teeth; saw pulleys are 1 foot 9 inches and
10 inches in diameter: the ram is lifted from four to five times in a minute.
By this machine the piles are taken up by first securing the ram and then attaching the
dogs to the head of the pile, and then, by means of a rope attached, and which passes up-
wards through the small guide pulleys and over the outer pulley E, passes downwards, and
is coiled round the pulley F fixed on the shaft G, which, being made to revolve, raises the
pile to its place between the pile-engines, and is then secured by the stay H, and the hoop
or iron-work which guides it perpendicularly.
For driving the pile: the stop B being withdrawn from under the ram A, the ram is
raised by a rope, which being secured by a staple on the top journal, passes down under the
pulley I, then upwards over the pulley K, and again downwards to the drum L, upon
which the rope is coiled; the drum is then placed on the shaft G, which is made to revolve
by the spur-wheel N, working in the pinion O on the lower shaft P, which shaft revolves
by the action of the two cranks Q, placed on the ends of the shaft P; the cranks are set at
CHAP. XIV
1085
ON PILES AND PILE-DRIVING.
PILE
right angles to each other, and are worked by the connecting rods R, attached to the piston
rods, which are furnished with slide parallels. The slide valves of the piston are worked
by the eccentric V on the end of the shaft P.
The steam is supplied by the pipe S from the boiler T, which receives its water from the
cistern M by means of the pump W worked by the eccentric rod X fixed on the spur
nave at Y, by the handle at Z. The supply of steam is regulated by the handle a acting on
a valve in the steam pipe S.
The drum L consists of a fixed and loose cylinder, the latter revolving by the friction of
the former, and is brought into or out of contact by the hand lever Y, which has a fulcrum
attached to the standard.
The follower ƒ is furnished with a pair of clippers, which takes hold of a staple fixed in
the ram, and carries it to the top of the frame; and when the top of the tongs or clippers
are pressed closer together by coming between the contracted cheeks e, e, the lower part
opens and allows the ram to fall.

Fig. 1656.
PILE
PILF
STEAM PILE-DRIVING MACHINE.
h
For drawing a pile, chain tackle is secured to the pile and passed over the top pulley to
the drum L, and is then drawn by the drum of the apparatus turning round.
The saw apparatus has a saw 4 feet in diameter, which has teeth 3 inches apart, secured
to the beam c, which works on the upright shaft d for a centre, and slides laterally on the
iron arc e; when used the saw is adjusted to its proper height by the screw f, and a bar
having a hook in one end, and fitting into a staple in the beam's end, is used to press the
saw against the work; the bevel pinion g being raised into gear by the foot lever i, motion
1086
Book II.
THEORY AND PRACTICE OF ENGINEering.
is given to the pulley i and j and band k, which work the saw b, and which cut off the
head of a pile in less than a minute.

ΚΕ
A
A
KE
KE
Fig. 1657.
STEAM PILE-DRIVING MACHINE.
This machine has been very successfully employed on the railways in America, where the
gauge was 6 feet from centre to centre; two piles were driven at the same time, with a
ram weighing 16 cwt.; the number of men employed consisted of an engine tender, one
man for throwing each apparatus in and out of gear, and one man to attend to each pile,
making all together five men for driving two piles, which is about half the number of men
required to drive two piles by the ordinary crab engines. By the machine the ram was
lifted four or five times in a minute, and the cost of the whole engine and apparatus was
about 700%
CHAP. XV.
1087
ON MECHANICAL AGENTS.
CHAP. XV.
ON MECHANICAL AGENTS, OR THE FIRST MOVERS OF MACHINERY.
On the Strength of Men and Animals. — The animate moving powers most frequently em.
ployed are man, the horse, and the ox, the latter chiefly for agricultural labour: the
form and construction of the human body seems applicable in a peculiar degree to become
the first mover of machinery, particularly when aided by the skill and judgment which on
most occasions are called forth to direct it. There are two methods of employing men and
animals; one consists in making them walk with or without a load, the other in attaching
them to a part of the machine, where they are required either to push or to draw, and
hence communicate motion to the several parts.
By the term daily labour is meant the work performed during twenty-four hours, the
effective duration of which is only a portion of that time, the remainder being employed in
rest and taking meals. Animals of all kinds require that their work should be moderate
and regular, and the machine they put into motion should never call forth more exertion
than is natural for them: the limit of this action is indicated by the fatigue which the
mover evinces, and which we may term the daily fatigue. Daniel Bernouilli imagined that
the degree of fatigue was always proportionate to the action which produced it; so that
whether the man was employed in walking, carrying a load, drawing or pushing, working
at a windlass, or raising a weight, he always produced, with the same degree of fatigue, the
same quantity of action, and consequently the same effect; and that the daily labour of a
man may be estimated as raising 1,728,000 lbs. weight one foot high, or 60 pounds raised
that height every second, when his daily labour was eight hours only.
Since these calculations were made, the celebrated Coulomb and Hachette have fully in-
vestigated the subject, and in our description of their experiments, we prefer retaining the
French weights and measures, which cannot be so readily reduced to their proper quantities
in English without fractional quantities: the kilogramme may be taken as equal to 2lbs. 3 oz.
5 grs. avoirdupois, and the length of the metre, according to Captain Kater, is 39-37079
inches, and to M. Bailey, 39-3696786 inches.
The daily labour of man depends on the moving power, which results from the effort of
which this mover is capable at each instant, and from the duration of effective work during
a day of 24 hours, a deduction being made for rest, meals, &c. The moving power has for
its measure a mass M, multiplied by a space h, which each point of the mass passes over in
a unit of time: let us call T the time of effective work during a day; it is evident that the
daily labour of man has for its expression the product of the three quantities, MhT. But
keeping the product the same, can we vary the factors at pleasure? Daniel Bernouilli, who
has discussed this question, thought that we could, from an equal degree of fatigue, obtain
the same daily labour by changing the elements of this action. Desaguliers, differing
from Coulomb, gives his opinion, that there is always for each man and each kind of
labour to which he is habituated a maximum of action, which corresponds to the product
of the three factors, MhT. This observation destroys the opinion of Daniel Bernouilli,
who thought that a man or any other animated mover, in whatsoever manner he employed
his strength, whether in walking, drawing, or by a winch, or on the cord of a pulley or any
other machine, would produce with the same degree of fatigue the same quantity of action,
and consequently the same effect.
Nevertheless, if, knowing the value of the factors of the greatest daily action of man, we
give other values different from these, so that the product shall be constant, we shall be sure
not to pass beyond the limits of the natural strength of man, and the effort of which he is
capable, which will be conformable to the hypothesis of Daniel Bernouilli.
:
The expression of daily action of man or any other animated mover may be compared to
that of a weight multiplied by the height to which this weight is raised in effect, h being
the space which a mass M goes over in a unit of time, the moving power is expressed by
Mh; and because these masses are proportional to the weight, it has for its value the
quantity Ph, P being the weight of the mass M, that is to say, that it is capable of elevating
the mass P to a height h in a unit of time, and to the height Th in the time T: calling
this height H, the daily labour of man has for its expression the product PH of the weight
P elevated the height H.
Daniel Bernouilli estimates the daily labour of a rower as equal to 275 cube metres of
water elevated one metre, and he supposes that this action is the product of 8 hours' effective
labour out of the 24.
1088
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Sometimes the duration of effective work is confounded with the time which a man passes
at the shop or the machine which he moves; nevertheless these two periods of time are very
different; if a man walks and makes a halt of some minutes, we must regard the duration of
the halts as a part of the time of rest, and must be added to the time of sleep and food. It
is the same with all other work which requires an alternation of action and rest, only con-
sidering that the duration of action diminishes at the same time as the moving power or the
intensity of the momentary effort of the mover augments. It has been observed that a man
or horse developes the power of which he is capable, in a day of 24 hours, in a very variable
time, which is at least one hour, sometimes 1½ hours, and generally 8 to 12 hours.
When we can regulate the two elements of daily labour, the moving power and the time
of effective labour, it would be desirous that we should find the value of those elements
which determine the greatest effect of daily labour: by multiplying the experiments on a
great number of men, and for several years in succession, we shall ascertain exactly the
various daily labours, or at least the limits of these actions, having a regard at the same
time to the natural strength of the individual, to climate, and all the circumstances which
modify this force.
On the Velocity with which Man moves. This depends on various circumstances, for
when walking on a plain without a load, he moves at the rate of 13 or 16 decimetres per
second: according to the observations made by Bouvard during a review of the troops at
the Champ de Mars at Paris, 251 metres were passed over in 33 seconds, which is at
the rate of 7.7 metres per second. Soldiers when marching at ordinary time take 76 paces
per second, and pass over 50 metres: when this pace is accelerated 100 paces in the same
time, and they pass over 66 metres: when marching quick, 230 paces are made per second,
and 130 metres are passed over. This gives for the ordinary and accelerated time 0·66
metres, or 2 metres for 3 paces;
130
when accelerated, and
When a man is travelling without a
60
load, and on level ground, he performs from 40 to 50 kilometres per day during the 8
or 10 hours he is engaged out of the 24. The French soldier carries a load equal to 187%
kilogrammes in time of peace, and 25 in time of war.
66
60
50
60
and in 1 second of time of a metre at ordinary time,
when at quick time.
Daily Labour of a Man has for its measure the resistance expressed in weight, multiplied
by the road; and when he walks over a level road, the resistance he overcomes at each
instant is unknown: when he mounts a staircase. at each step he elevates the weight of
his body; the height of the riser and his weight we consider as the measure of resistance;
so that the daily labour has for its measure the product of the weight of the body,
multiplied by the height to which it is elevated during the effective labour of one day.
According to an experiment made at the Peak of Teneriffe, which is 3780 metres above
the level of the sea, 8 men loaded with 7 or 8 kilogrammes, who accompanied Borda, were
elevated the first day 7 hours' effective work, to the height of 2923 metres. Supposing the
resistance equal to the weight of a man, which is 70 kilogrammes, augmented by a load of
7 kilogrammes, we have for the measurement of the action in a day of each of the 8 men
225 cube metres of water elevated 1 metre; the ramp being 20 kilometres, the fall will
be 14 centimetres per metre. The man who mounts with two motions, one horizontal, and
the other vertical, each of which has a separate resistance, the sum of them must be taken,
which we suppose equal to 77 kilogrammes. In this experiment the height to which a
man is elevated in a day is not that to which he elevates himself by walking moderately,
for Coulomb offered to labourers the price of a day's ordinary work to mount 18 times
without burden on a ramp of 150 metres height, or, what is the same thing, once to a
height of 2700, and they constantly refused.
It is, therefore, probable that a man travelling in a mountainous country without a load,
and at a gentle elevation, would terminate his journey when he was elevated 2 kilometres,
after marching 8 hours, whilst he could at the same time, and without fatiguing himself,
move 40 or 50 kilometres on a level road: by only counting on a march the effort
necessary to elevate at each pace the entire body above the surface of the earth, and sup-
posing this elevation to be 3 centimetres, the total elevation will be the number of steps
multiplied by 3 centimetres; or, the number of paces is the quotient of the number of
metres gone over in a day, multiplied by the length of the steps, or 40000 metres divided by
0.66, which is 66666; multiply this by 0-3; the product is nearly 2000 metres, equal
to the height of the ramp. The act of walking consists in gliding over the earth,
and elevating the centre of gravity as little as possible; this first effect produced, he must
also give a horizontal velocity; this second effort of walking requires an effort which is
added to that which precedes for the elevation of the body, but which is evidently much
less. We know no experiment which determines the relation of these two efforts. Mul-
tiplying 2 kilometres by the weight of the man, 70 kilogrammes, we have for the measure-
ment of his daily labour during the length of his march in mountainous countries 140
units, each unit being a cube metre of water elevated 1 metre.
CHAP. XV.
1089
ON MECHANICAL AGENTS.
If a man mounts when loaded, this action will diminish, as we shall see by the following
experiment of Coulomb's: he observed that a man may carry in a day six loads of wood
to a height of 12 metres, each being 734 kilogrammes, carried in 11 journeys, or the
6 loads in 6 hours. Thus the man made 66 journeys, and elevated a weight of 6 × 734
kilogrammes of wood to a height of 12 metres, or 53 cube metres of water to a height
of 1 metre. He elevated himself 66 times to a height of 12 metres, and this work is
expressed by the number 56, the product of three numbers, 70 kilogrammes, 12 metres,
and 66 journeys. Adding this number to the preceding, we have for the measurement
of a man who mounts loaded, the number 109, less than the 140 found
of the daily labour
before.
TO
In the experiment made on the wood porter, each burden of 734, or 67 kilogrammes, were
mounted in 1 minute, so that the duration of the principal work in a day of 24 hours was
1 hour 12 minutes; this work was paid at the rate of 1 franc per load of wood mounted 12
metres. The time which elapsed between the two consecutive mountings was about
breathing time; it was employed in loading the crochets, log by log, in descending the
stairs, &c.; it appears that this method of dividing into short intervals of work and rest
the labour of men carrying great burdens, is that which agrees best with the animal
economy, and that men prefer a very fatiguing action of some moments, followed by the
time necessary for rest, to a less powerful exercise, but more continuous and of longer
duration.
The result of the experiment cited by Coulomb differs very little from that which Gue-
niveau relates in his Essay on Machines; this engineer observed the workmen who
mounted from coal mines by very steep and inconvenient stairs; their load varied from
35 to 40 kilogrammes, and the daily effect was 42 to 50 kilogrammes elevated 1 kilometre:
taking the weight of the man into consideration, 70 kilogrammes, the daily labour would
vary from 112 to 120 dynamic units.
Loads of equal weight fatigue much less in proportion as they are distributed equally
on all parts of the body; a man carrying a weight equal to his own, and mounting a ladder
of a given length, would fatigue himself more than if he mounted without a load by the
same ladder to double the height: although in these two cases he would produce the
same dynamic effect, the second height would produce much greater fatigue than the first.
Coulomb often proposed to different porters to carry furniture from one house to
another at a distance of 2 kilometres on a horizontal road, loading themselves at each journey
with a weight of 58 kilogrammes; they all told him that they could only make 6 journeys
per day, at 1 franc 50 cents per journey; they added that they could not sustain a similar
fatigue two days in succession.
Several hawkers were interrogated as to what was the greatest weight they could carry
in their journeys, and how far they could go with this weight; the strongest of them
answered that, loaded with 44 kilometres, they could not proceed farther than 18 to 20
kilometres in a day.
We conclude from these different experiments that the action of walking with or without
a load on a plain, or in a mountainous country, is bounded by limits which depend on the
development of the vital forces, which are very variable, and have no absolute measure.
The resistance surmounted at each instant by an animated mover is only to be determined
and measured when this resistance is without the mover: in this case the mover exercises
on a point which resists a pressure equivalent to that of a weight. The man who walks
either with or without a load exercises two kinds of pressure, one on the ground, the
other on himself; the latter is not known; whence it follows that there is no absolute
measure of the daily labour of a man walking, and it differs essentially from those labours
in which we only consider the pressure exercised on an exterior object of whatsoever kind
these labours may be, they are only to be compared to those when they produce the same
degree of fatigue, and when animated movers can sustain the daily labour which is an ob-
ject of comparison, without injuring their physical constitution.
:
Of the daily Labour of a Man moving a Load on a Wheelbarrow, or other small Carriage.—
Pascal was, it is said, the inventor of the wheelbarrow: this machine is a case longer
than it is wide, attached to a frame, whose arms are longer on one side than on the
other. The shortest side carries the gudgeons of the axle of a small wheel. The load
is placed in the case, and the man charged with transporting it seizes the handles of the
barrow at about 15 decimetres from the spindle. The total weight of the barrow is about
30 kilogrammes, and it is loaded with 70 kilogrammes when used for moving earth. Vauban,
whose name recals the epoch of the greatest earthworks, observed that a man in his daily
labour can make 500 journeys of 29 metres each, with a barrow loaded with 70 kilogrammes:
to compare this effect with that which we obtain from porters loaded with crochets, we shall
estimate the daily labour of the latter by the weight transported, and the distance passed
over. Thus, we have for the effect of the hawkers in a day 44 kilogrammes × 20 kilometres,
and for that of the workmen with a barrow 70 kilogrammes × 14.5 kilometres. These
two effects are in the relation of 880 to 1015; thus, if we only regard the weight of the
4 A
1090
Book II.
THEORY AND PRACTICE OF ENGINEERING.
masses transported, the wheelbarrow as a means of transport is preferable to the crochet;
but it must be remarked that the volume of the masses increases the difficulty of trans-
port, and it is probable that hawkers have more fatigue than men at the wheelbarrow.
Coulomb found that to sustain a loaded barrow by means of a dynanometer, fixed
at the point the man holds by, supported a weight of 18 to 20 kilogrammes, and
that the force necessary to drive the barrow loaded on dry firm ground was 2 to 3 kilo-
grammes. This weight measures the continuous effort of a man pushing the barrow ;
multiply this effort by the space, 14 kilometres, which he goes over in 500 journeys, and
we have 28 to 42 great dynamic units for the measure of the efforts which produce the
useful daily effect.
In mines sledges are sometimes used, which slide over an unequal and argillaceous soil;
those observed by Gueniveau were drawn by a single man, and loaded with 90 kilo-
grammes of coal.
The space passed over was 290 metres; the workman made 24 journeys
in the day, and returned with the sledge empty, which gives for the effect in a day 90
kilogrammes transported 6960 metres, or 626 kilogrammes transported 1 kilometre, an
effect less than that produced by the hawkers, and which was estimated in the preceding
article at 880.
The small waggons used in mines, says Gueniveau, are supported on 4 wheels, and
drawn by men distributed along the road at a distance of 100 metres: the waggon rolls
on planks, and the daily effect of each man is 900 to 1000 kilogrammes transported 1 kilo-
metre : when there are inequalities in the floor of the gallery, which are otherwise
supposed horizontal, this effect is reduced to 600 kilogrammes transported to the same
distance.
:
Of Men acting on Pulleys. — According to Coulomb, ordinary rams used for driving piles
weigh 350 to 450 kilogrammes: acord passing over a pulley sustains the ram on one side; at
the other extremity of the cord different strings are attached, which men seize with their
hands when the ram strikes the piles, the men hold the cord about the height of their
heads; bending at the same time as they apply an effort to the cord, they elevate the ram.
about 11 decimetres. They make nearly 20 strokes in a minute, and three or four minutes
in succession, after which they rest nearly as long as they have worked; notwithstanding
this repose they are obliged to be relieved every hour. Men cannot perform more than three
hours' effective work in a day; the remainder of the time is occupied in placing and dis-
placing the machines, dressing the piles, &c.; these works require slight effort, and afford
time for regaining the strength. In this experiment the number of men applied to the
machine is such that each man lifts 19 kilogrammes of the ram.
According to these data the daily action has for its measure the product of these three
numbers, 11 decimetres, 19 kilogrammes, and the number of strokes given in three
hours' effective work, at the rate of 20 per minute, which gives 75 dynamic units.
Coulomb has followed, fifteen months in succession, the labour of coining money at Paris.
These pieces are struck by means of a ram weighing 38 kilogrammes; two men are
employed, and consequently each elevated a weight of 19 kilogrammes: the elevation was 4
decimetres, and in one day 5200 pieces were struck, or, what is the same thing, the ram
was elevated 5200 times in a day, which gives for the daily labour 39 dynamic units. In
the preceding example, we have for the measure of this action 75; but it must be remarked
that the same men work in the Mint 15 hours in succession, instead of which, when driving
piles, the men pass from one kind of labour to another when they are fatigued.
An Experiment made at the Bridge of the Military School, under the Direction of M.
Lamandé, Chief Engineer of Bridges. For driving piles a ram was used weighing 587
kilogrammes, worked by 38 men; at each blow they elevated the ram 1·45 metre; after 30
blows they rested a time equal to that of the blows. They gave 12 series of blows in an
hour, or 12 strokes per minute, effective and continuous work: supposing they could have
sustained this work 6 hours a day at 12 series of blows an hour, the daily labour of each
587
38
man would be the product of or 15 44 kilogrammes multiplied by 1·45 metres, and by
72 series, 30 strokes, which gives 48 dynamic units.
Coulomb says,
"I have drawn water from a well 37 metres deep: a man worked by
means of a double bucket, attached to the extremity of a cord working over a pulley; he
drew up the first day 125 buckets; the second 119, at 25 centimes per 10 buckets: the
mean effort, measured by a dynamometer, was 16 kilogrammes. We have the daily labour
by multiplying the three numbers 16 kilogrammes, 37 metres, and 120, the number of
buckets mounted in a day, the product is 71 great dynamic units.
Men acting on Winches. According to Coulomb the pressure of a man in a continuous
labour exercised on the handle of a winch is about 7 kilogrammes; most frequently the
swiftness of the rotation of the handle is such, that each point describes in a minute 20 to
29 circles, each of 23 decimetres. The duration of effective work in a day is about 6 hours:
in this hypothesis the daily labour is the product of three numbers, 7 kilogrammes, 6 × 60
minutes, 20 × 2.3 metres, or 116 great dynamic units.
CHAP. XV.
1091
ON MECHANICAL AGENTS.
Of a Man pushing as he walks, or drawing harnessed. Mill-walk in the Wells of Bicêtre.-
The Bicêtre contains three establishments: the hospital for the mad people, the prison, and
the infirmary. Those who are least diseased, mostly the epilectic patients, receive a small
remuneration for drawing water from a well; 72 men are designed for this service; 24 only
work at once, for 1 hour 20 minutes in succession, and are replaced by others for the same
time.
The mill-walk is in an octagon tower, whose opposite faces are 11·69 metres distant; the
centres of the horizontal bars which the men push before them while walking are on a
circle 5.2 metres radius; these bars are directed towards the axis of the mill; 16 men walk
without the walk and 8 within; there are 8 couples of men, and each couple push the same
bar;
the distance between two men of the same couple is 8 decimetres; the height of the
bars above the ground is 9 decimetres; the distance between two consecutive bars is
1-3 metres; each man is placed between two bars, which he pushes alternately before him,
according as the wheel is to turn in one direction or the other.
The well is 52 metres deep from the surface of the water to the crochet which empties
the buckets; the interior diameter is 4.872 metres; the water constantly stands at 4·872
metres from the bottom.
A vast reservoir of a square form, well vaulted, contains more than 1000 cube metres of
water; the vault is supported by 16 columns, which serve as piers to 9 elliptical arches:
this reservoir, the tower, and the well, were executed in 1733-4, from the designs of
Boffrand, engineer of bridges and roads.
Of the Swiftness of Men pushing the Bars of the Mill.
The men make 8 turns in
5 minutes, the time necessary to elevate a bucket from the surface of the water to the bank,
taking the mean walk of 24 men as a circle of 10·4 metres diameter; the 8 turns correspond
to 278 metres, which gives 0·92 metre for the velocity in 1".
Useful Effect of the moving Power.— In a relay of 1 h. 20′, or 16 times 5′, they raise 16
buckets; a bucket contains 700 litres, weighing 700 kilogrammes: thus the useful effect
of 24 men is 700 kilogrammes x 16 x the height to which the water is elevated, or 52
metres, and for each man this number divided by 24, that is to say, 25 great dynamic
units of a cube metre of water elevated 1 metre. The remuneration of this work is 8 cen-
times a man.
The waters of Arcueil, and other sources more elevated than the Bicêtre, bring together
six months in the year a considerable quantity of water, and then four or six relays suffice
to draw from the well the water necessary for the service of the establishment; but in
summer the natural sources fail, and each labourer makes four relays, which causes his
daily labour to be 100 dynamic units; it is only one-half during six months of the year, so
that the mean daily labour is 75. The quantity of water drawn in 12 relays is expressed
by the product of the three numbers 700 litres x 16 x 12, or 134400 litres.
The popu-
lation of the Bicêtre being about 3000, we have nearly 45 litres for each individual;
it is generally supposed that 20 litres for each person would suffice for the wants of a great
town; on account of the baths watering the gardens of the Bicêtre, the consumption is
more than double.
The Force developed by the Mover.—It was intended to measure, by means of a spring, the
mean pressure of men on the bars of the mill at the Bicêtre; but this project was abandoned
on account of the great inequality of force in the individuals, more or less weakened by age
and infirmity. The resistance to be overcome is unequal, but it is at its maximum when
the buckets rise from the water, whilst the other begins to descend; the cables carrying
the buckets are 2 decimetres in circumference; each passes over a pulley 1.3 metres in
diameter, and coils round the drum of the machine, whose diameter is 19 metres; the part
of the cable comprised between the pulley and the level of the water in the well weighs
250 kilogrammes. The resistance which acts tangentially to the drum will be 700
kilogrammes, the weight of a full pail of water added to the weight of the cable
when the bucket begins to ascend, and subtracted from that of the cable when the
bucket is at the height of the hook, which is inclined to empty it; thus the resistance
varies from 850 to 550 kilogrammes. The buckets weigh, when full, iron and wood
comprised, 600 kilogrammes, but one always equalises the other, and we must only count
it as inertia: the distance of the axle of the machine to the vertical axis of the well is
about 13 metres: whatever is the weight of the cable, the mean resistance being 700
kilogrammes, acting on a radius of 3 feet, the power producing the equilibrium will be at
the extremity of the radius 16 feet; taking of 700 kilogrammes, gives 127 kilogrammes
for the total pressure on the bars. If we subtract the inertia and friction of the cable on
the pulleys and on the drum, the mean pressure of 24 men working the machine will be
kilogrammes, or 5 metres 3 kilogs. On account of the inertia, friction of the ropes
on the pulleys and drum, we suppose the mean pressure to be 7 kilogrammes, so that the
relation of the useful effect of the force developed to produce it is that of 5-3 to 7, or 0.8
to 1; that is to say, a fifth only of the force developed will be employed to overcome friction
127
24
3
16
4 A 2
1092
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
and inertia, which is probably the case in this machine, where the construction is simple and
carefully executed.
The Horse considered as a Mover. Of his Swiftness. — The greatest swiftness of a horse
in a course of 7 or 8 minutes is 12 to 15 metres per second. Bouvard observed that in
the Champ de Mars at Paris, a horse mounted by a cavalier on a smooth road winding in
the form of the figure of an eight, went over 2575 metres in 3′ 31″, or 211". In the
Newmarket races a horse has gone over 6784 metres in 7′ 30″: a horse harnessed in
a cart has gone over 1478 metres in 2' 13" on a road in the form of an eight, in the
Champ de Mars.
These three experiments gave for the swiftness of the horse in 1",
1st experiment
2
3
-
-
12-21 metres.
15.
11.11
We are assured that a harrier is capable of following the best English horse, and that
the reindeer attached to a sledge runs at the rate of 8 metres per second.
Cavalry makes in a minute,
at the common pace
trot
gallop
·
S
120 steps,
and goes over
-
-
. 180
100 metres.
- 200
200
320
which gives for the ordinary length of a horse's step 0.83 metres, for the velocity corre-
sponding to this pace 1·66 metres per second; for the velocity at a trot 3.3 metres; and at
a gallop 5.3.
It has been remarked that the pace of a man more or less accelerated is always nearly of
the same length: the inequality of a horse's step proves that he throws out his legs in
running, and clears a space which must be added to his ordinary step. Bosc saw in N.
America savages who leapt while walking, and he assures us that this manner of proceeding
was very favourable for an accelerated and continuous velocity, and also fatigues less than
any other.
A good horse loaded with about 80 kilogrammes, including the weight of the rider, can
daily go over 40 kilometres (25 miles English) in 7 or 8 hours, which gives from 1·4 metres
to 1.5 metres per second. The weight of a horse of mean strength is 225 to 250 kilo-
grammes.
The tractive Power and Load of a Horse.-In contracts for carting, we generally calculate
the load of the carts at 700 to 750 kilogrammes to a horse, without comprising the weight
of the cart: the tractive power of a good waggon horse is 140 kilogrammes; a team goes
over on a good horizontal road 38 to 40 kilometres in 8 or 9 hours; at 40 kilometres in 8
hours the velocity is 1·4 metres in a second.
Horses attached to diligences going at a trot, and making a post or 8 kilometres in an
hour, go over daily 34 to 38 kilometres: the tractive power of each is about 90 kilogrammes ;
their velocity is 2.2 metres in 1".
•
The daily action of the horse of a waggon being expressed by the product of two numbers,
90 kilogrammes and 38 kilometres, these two actions are in the relation of 5600 to 3420,
or 163 to 100. These experiments give 100 kilogrammes as the mean tractive power of
horses.
Of the Strength of the Horse taken as a dynamic Unit. The constructors of steam-engines
estimate the power of these machines in dynamic units, each of which measures the strength
of a horse when harnessed. Let us suppose that a horse is capable of moving a mass of
140 pounds with a velocity of 200 feet in a minute: this dynamic effect is 28000 pounds
elevated 1 foot, or 4149 kilogrammes 1 metre; according to this definition, the strength of a
horse working 24 hours continuously is equivalent to 5974 units, each the weight of 1 cube
metre of water elevated 1 metre; or, 5974 × 2208 pounds avoirdupois raised 3.281 feet
English.
Machine of Mr. Gonin Dyer, Rue Blanche Castile, Isle St. Louis. This machine has one
horse, which works 5 or 6 hours a day in three relays; in 1 hour he lifts by means of a pump
28 muids of water, each muid being 268 litres 13 metres high, or 97½ cube metres to a
height of 1 metre, which gives for the daily labour of 6 hours in the 24, 585 metres of
water elevated 1 metre.
Machine near Paris over a Plaster Quarry. — This machine has one horse which works
12 hours a day; the effect is to elevate by means of a drum 96 casks of plaster
from the bottom of the quarry to a height of 23-4 metres; each cask weighs about 375
kilogrammes, and the weight of the plaster elevated in a day is equal to 36 cube metres of
water, which gives 842 dynamic units for the daily action.
The horse harnessed to the extremity of a lever 3.575 metres long goes over in a minute
a circle of 22·4 metres, in a second an arc of 37 centimetres. and in 10 hours of labour
13.4 kilometres.
The cask is elevated in 7 minutes; at each ascension the horse stops to change the
direction of his rotatory movement; supposing the duration of effective labour to be 10
CHAP. XV.
1093
ON MECHANICAL AGENTS.
hours, and knowing by the dynamometer that the traction is 100 kilogrammes, we have
for the force developed in a minute 100 kilogrammes multiplied by 23-4 metres, or 23-4
dynamic units, and in 12 hours 1684 great dynamic units, which have produced the useful
effect expressed by the number 842, half the preceding. By only comparing the force
developed in a minute, and the corresponding useful effect, we have for its measurement the
weight of a tub, 375 kilogrammes, multiplied by the height, 23-4 metres, which product
must be divided by 7.5, although the barrel is only elevated in 7 minutes. The force
being 2.34, the useful effect is half, or 1·17.
Machine established in the Brewhouse called Bon Pasteur, 80 Rue Mouffetard. Three
horses harnessed to the same machine elevate by means of a pump 155 muids of water to
a height of 132 feet, and the duration of work corresponding to this effect varies between
4 and 5 hours, according as the pistons of the pump are in good or bad order: this action
of 3 horses is equivalent to 1784 great units, which gives 593 units for each horse.
The diameter of the circle described by the horses is 6 metres, and they make 13 turns
in 5'; each turn is 19 metres, which gives about 0-8 metres as the swiftness per second, the
length of the ordinary step of a horse. The traction of each horse being 100 kilogrammes,
the force developed in 4 hours is 1185, almost double the number of the useful action 595.
The machine communicates motion to the pumps, or to a mill for grinding malt: the
horses grind in an hour 5 sacks of malt weighing 100 kilogrammes each.
Machine established at the Hotel des Invalides to elevate Water from a Well by a system
of Pumps. — Eight horses perform the service from 6 in the morning to 6 at night: each
horse works 6 hours, in two relays of 3 hours each, separated by a rest of the same
duration: 4 horses are harnessed to the machine at once.
There are two reservoirs, one 6·02 metres high from the ground, the other 16.5 metres.
The distance from the ground to the level of the water in the well is 19.16 metres, so that
the height to which the water must be elevated in the first reservoir, which is the largest,
is 25.2 metres, the height for the small reservoir 35.6 metres. The quantity elevated in
12 hours in the two reservoirs are respectively 165 and 35 cube metres of water.
The useful effect corresponding to the daily action of the 8 horses will be expressed by
165 × 25.2 +35 × 35'6, or 5404 dynamic units, which gives for each day 675 units in 6 hours
of work, and 1·87 in a minute for each horse.
The radius of the machine is 4 metres; the horse makes 21 turns per minute, and goes
over 63 metres, which gives 12 metres for his swiftness in 1". The mean draught
of 4 harnessed horses, as observed by the dynanometer, is 130 kilogrammes for each, which
gives for the force developed in 12 hours four times 130 kilogrammes x 63 metres × 60′ × 12
hours, or 23586 dynamic units.
By comparing this number to the useful effect, expressed by 5404 dynamic units, we sec
that this effect is only 23 of the force developed.
Other Observations on the daily Labour of a Horse. Armallet, engineer of bridges and
roads, describes a machine with pulleys at work in the coal mines at Blanzy, near Creusot,
Canal du Charolais, moved by two horses, which elevated in 9 minutes coal weighing 450
kilogrammes to the height of 130 metres. He added that the effective labour was 8
hours out of the 24: according to these statements, the daily labour will be expressed
by 1560 great units. I agree to the first part of the observation, but has the second, rela-
tive to the duration of effective labour, been made several months in succession? It is
allowable to doubt this, when we arrive at a result double that which a great number of
experiments give.
Other Experiments on Transport by Water.—Perronet relates an experiment made on the
canal of Loing. A single man drew a boat loaded with 100 milliers, and in 10 days he
went over a space of 110 kilometres, so that his daily labour was 100 milliers transported
11 kilometres. Supposing the draught of a man 10 kilogrammes, the work would be
expressed by 110 dynamic units.
He has further observed that a single horse draws a boat of 300 milliers, and goes over
8 kilometres in a day: admitting that the draught is 100 kilogrammes, the labour of the
horse will be expressed by 800 units: it is very probable that the forces developed are
in fact in the relation of 100 to 800; nevertheless the useful effect produced in a day are
only in the relation of 11 to 24, or 1 to 2.2.
It would be important to repeat these experiments, and to measure the draught corre-
sponding to the velocity of men and horses, having relation to the form and swiftness of
the boat, and to the greater or less resistance of the fluid.
Summary of the Experiments on the daily Labour of Man; the dynamic unit being the
weight of a cube metre of water elevated to the height of 1 metre, or 2208 lbs. avoirdu-
pois raised 3.281 English feet.
We have, for a man walking 7 hours on a slope of 14 centimetres
in a metre with a burthen of 7 or 8 kilogrammes
A man walking in a mountainous country without a load
Dynamic units
225
140
4A 3
1094
Book Il
THEORY AND PRACTICE OF ENGINEERING.
A man carrying wood up a ladder, his own weight being 56, and that of his
load 53
A coal porter on a ladder, his own weight being taken into account
A man applying his strength to a rope over a pulley to raise a ram
The same another experiment
The same—another experiment
A man drawing water from a well by means of a cord
A man working the handle of a winch
A man drawing a boat with traces
Dynamic units.
109
112 to 120
75
40
48
71
116
110
A unit of transport being the weight of a cube metre of water transported 1 metre on a
level road, we have—
Dynamic units.
A man travelling over a level plain, his own weight being 70 kilogrammes
x 50 kilometres
9.500
A soldier loaded with 20 to 25 kilogrammes, and marching 20 kilometres f
a day
A Roman soldier making a forced march of 40 kilometres a day
Hawkers with crochets, the weight of the man not being taken into account
Men drawing sledges
A man drawing a boat on a canal 50,000 kilogrammes transported 11
kilometres
1800
1900
4400
4800
792
880
627
550,000
Summary of Experiments on the daily Labour of Horses: —
Daily Labour mea-
sured by the draught
and the road gone
Useful
Effect.
over.
Waggon horse
5600
Poste horse
3420
Mill horse
585
Ditto
1684
842
Ditto
1185
595
Ditto
2948
675
Ditto
1560
Barge horse
800
We see by the first summary that a man who mounts a ladder freely without any load
can furnish a quantity of action double that which he affords with crochets, cords, pulleys,
or winches.
In considering the useful effect of a wood porter in houses, it is expressed by the number
56, which is only the quarter of 225, the measure of the first daily action: it results that
if a man mounts a staircase freely, and lets himself fall by means attached to the extremity
of the cord of a pulley, he would elevate a weight equal to his own at the other extremity
of the cord; he would produce nearly the same useful effect as four men lifting the same
weight on their backs or with crochets.
It will be conceived that a man could elevate a load by a ladder greater in proportion as
the weight is equally distributed over all the active parts of his body, but the weight of
the man himself fulfils this condition to its greatest possible extent. This theory confirms
the result of experiment on the best employment of the greatest daily labour a man is
capable of.
Applying the same reasoning to a horse, it is easy to calculate the useful effect produced
by his mounting a slope. Let us suppose that he elevates himself in a day to 20 kilo-
metres, his weight being about 250 kilogrammes, he would elevate the same weight to the
same height by letting himself fall, and bis daily labour would be expressed by 5000, a
number six times greater than that which expresses the daily labour of a horse drawing a
boat, and which we generally regard as the mean action answering to a number
of horses. There would therefore be a great advantage in employing a horse as a weight
capable of lifting, even when we reduce the height to 10 kilometres, which he might mount
in a day.
The Measure of the greatest Effort of an animated Mover.
We have seen that the daily
labour of animated mover depends on three elements: the pressure which he exercises on
the resistance to be overcome; the velocity of the centre of application of the pressure;
and lastly, the duration of the pressure. There is such a relation between the two ele-
ments pressure and velocity, that if one attain its maximum the other becomes nothing.
The greatest velocities observed among men and horses are respectively 8 and 15 metres
per second; a man running with this velocity consumes in half a minute the labour he is
capable of in a day. The horse consumes the same in 7 or 8 minutes, and if he be
CHAP. XV.
1095
ON MECHANICAL AGENTS.
harnessed to a car, a course of 2′ 13″ suffices to exhaust his daily labour. The dynamometer
shows the pressure which a mover exercises on a fixed obstacle, and experiments on
individuals more or less strongly constituted prove that the greatest pressure which a
man exercises on a spring with his hands varies from 50 to 71 kilogrammes. The scale
of traction on the same dynamometer gives 140 to 150 kilogrammes as the greatest weight
which a man can lift with the aid of his hands and loins. It is generally believed that the
muscular strength of man in his savage state surpasses that of the workmen of civilised
countries. Experiments made on the New Hollanders by M. Peron, the naturalist, prove
that the English and French sailors have nearly the same strength as these savages in
pressing with their hands, and are far superior to them in the action of the loins: the
mean measure of this action being 100 kilogrammes for the former, and 128 for the latter.
To measure the greatest effort of a horse harnessed to a vehicle, we attach the dynano-
meter by one of its extremities, and the other to a large spring of wood which stretches
it gradually; or, if we have a row of continuous sledges heavily laden and fastened toge-
ther by pieces of chain of a certain length, the horse then draws the first sledges, and suc-
cessively those which are behind, until the resistance, increasing with the number of
sledges put in motion, equalises the greatest effort of the horse: by this procedure time
is allowed the horse to arrive at his maximum of effort. This maximum varies, according
to the scale of traction on the dynanometer, from 300 to 525 kilogrammes.
Whatever is the moving power there is always a certain relation between the quantities
which express the pressure and velocity at each instant of daily labour, and these two ele-
ments have their maximum. We find in the volumes of the Academie of Petersburg,
1750-1751, 1760-1761, two memoirs of Euler on this question. This geometrician has
in his second memoir considered an animated mover as a source of water falling from a de-
termined height, and the resistance as the effort capable of turning a water-wheel whose
float-boards receive the shock of the water. We call h the fall of water, a² the surface of
the float-board struck by the water, a2h is the expression of the maximum of the pressure
of the water on the float-board: calling A the maximum effort of the mover Euler supposes
A=a³h, calling & the velocity of the water at the end of its fall, and before the shock on the
float-board he makes it equal to the velocity of the mover walking freely without a load.
He designates by the letter u the velocity of the float-board after the shock of the water,
and makes it equal to the velocity of the mover which corresponds to the daily action :
he calls A' the pressure of the water on the float-board, which is equal to the pressure of the
mover corresponding to the velocity a: lastly, Euler admits, considering only the action
of the water on the float-board, that we have the equation A'=A (1–2).
5
To verify this formula as applied to animated movers, man for example, Schulze made
some experiments which are described in a memoir to the Academy of Berlin, 1783. He
selected seven men, differing from each other in weight and shape, he found that when he
made them draw horizontally from below the shoulder, a cord passing over a pulley to the
extremity of which weights were suspended, the men experimented upon stopped succes
sively at the 7 following weights:
95
105
110
100
105
100
115 livres.
The sum of these weights, 730 livres, is the measure of the maximum effort of the seven
men acting in concert: the velocity of these same men walking freely without a load was
found to be 5% Rhine feet per second. To find the velocity corresponding to their daily
action Schulze used a machine whose levers were fixed in a vertical axle, to which two
great cylinders of marble turning with the axle were attached; a horse was usually har→
nessed to this machine whose radius was 10 Rhenish feet.
Substituting for the daily labour of a horse that of 7 men working together, he observed
that the velocity of these men in the machine was 2.45 Rhenish feet per second: of the
four quantities A', A, v, u, three are known, for we have
A=730 livres ; v=5 feet; u=2·45 feet.
Substituting these numbers for the preceding formula, it gives A'=205 livres for the
pressure corresponding to the daily action.
Having fixed the extremity of the cord on the vertical axis, and having rolled it round the
axis, he passed it over a pulley whence it hung over the well; he then attached divers
weights to the other extremity of the cord: a weight of 215 livres gave a uniform velo-
city of 24 feet Rhenish per second, nearly equal to that of the men applied to the
machine: thus the pressure A', as found by the formula of Euler, was equivalent to a
weight of 205 livres, differing 10 livres or from the observed pressure, 215 livres.
20
In this experiment the mean value of the draught of a horse in the machine is 205 livres,
or about 100 kilogrammes: if we apply the formula of Euler to a horse harnessed to the
machine, taking the facts as given before, we have for the greatest mean effort of the horse
4A 4
1096
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
400 kilogrammes; his velocity at the ordinary pace without a load is 1·6 metres, his velocity
in the machine is 0·8 metres; we have then
A=400 kilogrammes; v=1·6 metres; u=0·8 metre.
The formula gives A'=400 (1—1), or 100 kilogrammes, which is confirmed by experi-
ment.
We must remark that the formula of Euler, which determines with sufficient precision
the pressure corresponding to the daily labour of animated movers as compared to water, is
not by any means satisfactory for the calculation of the effects of this fluid on the water-
wheel. When treating of this fluid as a moving power we shall give another formula, which
affords results approaching near to those observed.
7
CHAP. XVI.
HYDROSTATICS.
HYDROSTATICS which teaches of the equilibrium of fluids, and that a fluid is composed of
material particles, infinitely small, and move without friction on each other in every direction;
this property it is which occasions it to communicate pressure equally in all directions:
for the purpose of examining these qualities, it is necessary that we should leave out of
our consideration, all which relates either to their expansibility or compressibility, their
cohesion and capillary attraction. We must also view them as having a uniform density
throughout.
One of the first laws which is apparent is that the surface of such a fluid, when at rest,
assumes the horizontal: the face, however, always being perpendicular to the direction of all
the forces which act upon it, the power of gravitation having the effect upon the waters of
the ocean, of occasioning it to lie in parallel lines with the earth's curvature. We find also
that when any part of a fluid is raised above the surface, it will quickly return to its level,
from whence we learn that the pressure of a fluid on every particle of the vessel containing
it, or any other surface in contact with it, is equal to the weight of a column of the fluid of
which the base is equal to that particle, and the height to its depth below the surface of the
fluid: so that in a cistern 10 feet deep, each square foot will sustain the weight of 10 cube
feet of the liquid, or 10,000 ounces; in a vessel filled with mercury, an inch in depth, each
square foot will sustain a pressure of 1130 ounces; the atmosphere has a pressure upon
each square foot of the earth's surface of 34,000 ounces, which is equivalent to the weight
of a column of mercury 30 inches high. It is therefore obvious that the pressure on every
square foot of the bank of a river increases continually in descending towards the bottom.
Of the Level of Liquids and their Equilibrium. — Liquids, like other heavy bodies, tend
always towards the earth's centre, and descend as low as possible unless some obstacle pre-
vents them. Water poured into a vessel and left to itself always assumes its level, for if
there is at first one part of its surface more elevated than another, it will descend towards
the lower as on an inclined plane, or as along several contiguous inclined planes, if it make
a species of curve. If there be still some places higher than others, the same will happen
to each of them; the most elevated parts, if they can, will descend as low as possible, and
when there is no longer any agitation on the surface, it will be found level, since all its
points are equidistant from the earth's centre, and will always maintain themselves in this
state, if they are not put in motion.
When the surface of a liquid is level, all the columns of which this liquid is composed are in
equilibrio. — Suppose we pour water into the prismatic vessel B C, and that we suppose
this water divided into columns of equal bases, that the surface A E of the first column BE
should be level with the surface EF of the second; it is necessary that these two columns
should counterbalance each other, and tend mutually to raise each other by an equal effort
on their bases, otherwise if the first bore upon the second, the surface of this second, rising
above that of the first, could not maintain itself in this position, because, not being sustained
at the sides, it would fall on the first in order to assume its level. In like manner the
second column, EM, could not by its own weight bear upon the third, M G, without the
surface of the latter mounting, and the former descending, but these two columns being of
an equal weight, there is no reason why one should bear upon the other; in like manner
all those which follow sustain each other reciprocally in equilibrio.
Hence when we mix two liquids together, one of which is lighter than the other, as oil
and water, the heaviest compels the lightest to rise to the surface; nevertheless it appears
that it is the oil which separates itself from the water.
CHAP. XVI.
1097
HYDROSTATICS.
A
H
K
C
Although the columns EM, MG, GO, OI, IQ, QD, appear to unite themselves
against BE to surmount it, this latter is not in equilibrio with all the others, together or
separately, because they are divided among themselves, each tending to raise the other; that
is to say, the columns EM, MG, GO, OI, IQ, in like
manner unite with the first BE, against the single one
QD, because if each of these columns be opposed by all
the others, it is also supported by the others, and acts
against each in particular: whence it follows that the
column EL, CD, composed of several small ones, has no
more advantage over the single one BE than this has
over the preceding, which proves that a column of liquid,
however large it may be, balances the last thread of the
same liquid when both are level, because the larger
column is composed of threads similar to the first, which
oppose each other, and unite with the first against each
other as they all united against the first: all the
columns of the same liquid are then in equilibrio, their
surfaces are level, and as their surfaces are level, these
columns are in equilibrio.

b
L M
Q C
Fig. 1658.
If the vessel be of any other form than prismatic, it is only ne-
cessary to conceive it divided by horizontal sections from the
bottom X to the edge A C, in such a manner that each section
may be regarded as a small prism; pouring the liquid gently
along the edge of the vessel, it will level itself in the prism RXT;
then in the second, NP, having the first for its base; then in the
third, I O, which has the second for its base, and so on to the
last, A C.

A
D
N
R
A
Ꮐ
P
X
T
Fig. 1659.
E
H
M
N
L
If we have a siphon, whose branches A B, CD, EF, GH, we
suppose vertical, and of the same size, it cannot be doubted
that the liquid poured into the first branch, A C, to a certain
height, LM, will mount in another branch, EG, to a height
NO, equal to the preceding; for on account of
the pipe of communication CIK F, the co-
lumn LC will raise the column NG until it
is in equilibrio with it. These two columns
being equal in size, they must also be of the
same height, to weigh equally the two tubes
A C and E G being to be regarded as the scales
of a balance which contain equal weights, and
the pipe of communication as the beam round
which the two columns of water are in equi-
librio, and consequently their surfaces level.
With regard to the pipe of communication, it
is evident that its length does not affect the
equilibrium of the two columns: we may regard it as not existing, that is to say, as if the
two branches of the siphon were contiguous, separated only by a diaphragm, for as long as
the communication is horizontal, the water contained cannot increase in one branch to the
prejudice of the other.

B
K
F
Fig. 1660.
If the first column ABCD were less than the second EFPQ, the columns of the same
liquid, KC and MP, would not the less be in equilibrio; for if we cut off from the
second column another, M G, of the same size as the first, it is evident that the latter will
K
D
D
K
டாடா


F G
B C
Fig. 1661.
Fig.1662.
C
only have to oppose M G, which has the same base as itself: since the column MG
will be in equilibrio with the rest of the liquid of the branch EP, and also with the
column K C, the latter will be in equilibrio with the whole column M P.
1098
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Having a vessel, ABCD, filled with any fluid to the level IK, let us imagine that in
this vessel we form with the same liquid a glass siphon GEMNFHQPG, serving as a
diaphragm, it is evident that this liquid, which the siphon would contain, should be in the
same state as it was before its separation from what remains in the vessel; but as, before the
formation of the siphon, the parts of the liquid which it contains were in equilibrio, and
the surfaces GE and FH level, the same things would still subsist.
B
A
E
1
Fig. 1663.
D
F
H
K
C
B
A
G
E
Fig. 1664.
D


F
H
K
C
A
G
E
D
H
F
K
The liquid contained in the siphon having nothing in common with what remains in the
vessel, if we suppose the latter annihilated, and the glass siphon transformed into some
other material, as copper or tin, we shall see that water poured into a siphon of any figure
will assume its level in the two branches, and maintain its equilibrium, however unequal
the size of these branches may be: notwithstanding this law of nature, there are cases
in which liquids do not rise to their level, as will be noticed hereafter.
If we have a tube open at both ends, and we
plunge a part perpendicularly into the water, it
enters therein and maintains the level of the
surface of the water, since we may regard it as
a column which is in equilibrio with that
without, in the same manner as it was previous
to its inclosure in the tube; but what is sur-
prising, this does not happen in all tubes; and
in capillary tubes, or those of very small dia-
meter, the water mounts above the level of that
which is outside, and the higher in proportion
as the diameter is less.

I
B
Fig. 1665.
All columns of water tend by their weight to descend and raise each other, and it is the
equality of their force which keeps them level: if it should happen that one of these
columns were lighter than the others it would immediately rise above the others to the
height necessary for the equilibrium. When a capillary tube is placed on the surface of
the water, the drops of which are comprised in its opening attach themselves to the interior
of the small circle which forms it, are sustained by it in part, and consequently are so
much the lighter with regard to the water, which acts freely on the bottom of the vessel.
Then the column of water, which answers to the opening of the capillary tube, exercises its
weight less on the bottom of the vessel than the other columns, with which it is surrounded,
so these latter ought to elevate it in the capillary tube to a height at which it regains by a
greater quantity of water the weight by which it is deficient with regard to the bottom of
the vessel, to be in part sustained by the drops of water which adhere to the tube. It
follows that the smaller the diameter of the tube is, the more the water within would
elevate itself above the level of the other, as having more surface in proportion as a greater
number of drops of water are sustained by it; and those of the middle will have so many
the more leaning points in the part of the preceding, as the tube is narrow.
Another experiment which appears contrary to liquids always keeping in equilibrio.
Having a vessel A B in which water or any other liquid is placed to any height CD, if we
take a piece of cloth and dip it in the water, then placing
it on the edge of the vessel so that the part G H dips in the A
water, and the other EF is outside the vessel, and sufficiently
long for its extremity E to be below the surface CD of the
liquid, we shall see it mount along the band, drop from the
extremity E, and the vessel will be entirely emptied if the
extremity H reaches the bottom.

E
H
Gardeners adopt this method to water plants which require
to be kept moist, and chemists apply it in a way which
from its singularity requires mentioning. When they have
several liquids mixed which they desire to separate, they dip
cloth bands into each of the pure liquids; they then dis-
pose these bands on the edge of the vessel, and each distils the
liquid with which it was wetted, as well in a vacuum as in a plenum.
D
B
Fig. 1666.
CHAP. XVI.
1099
HYDROSTATICS.
B
G
!)
To compare the specific weights of different liquids an instrument
invented by Homberg is used, called an areometer, composed of a small
phial E, having two necks A B, DC, very narrow, but the second still
narrower than the first: through the opening A with a funnel F, the
liquid to be weighed is poured, which as it falls into E drives out the
air through the tube CD, and the place exactly marked at G on the neck
A B, to which the liquid reaches: having weighed the phial full of liquid
in a good balance, and the weight of the empty areometer subtracted, the
weight of the liquid poured in is obtained; the areometer is then emptied,
cleaned, and filled with another liquid to the same mark G, which is
weighed as before, to obtain the ratio of the specific weights of these two
liquids. As liquids are subject to dilate with heat and contract with cold,
Homberg reports his experiments on their weights, and remarks on their
difference in the greatest heat of summer and in the greatest cold of
winter, so as to ascertain very nearly the difference between these two extremities at the
times in which the areometer is used.

E
Fig. 1667.
On the vertical Action of Water against the Sides of the Vessel containing it.
One of the pro-
perties of liquids is the effort which they make in every direction against the sides of the
vessel containing them, caused by the motions of their parts, which being detached from each
other only seek to escape.
Having a right tube, A B CD, open at both ends fixed against a vertical
surface, if we introduce into this tube at the lower end a piston GHI to
serve as a bottom, and pour water to any height E F, the power applied to
this piston will sustain a weight equal to that of the column of water con-
tained in the tube. If we pay attention to the fact that liquids have this
property in common, that the motion of their parts in every direction, and
the effort they make sideways to discharge the pressure of those with
which they are loaded, diminshes nothing of the action of the weight
which causes them to tend towards the earth's centre like all other bodies,
we shall find that the power P being in the direction of the line KL
drawn through the centre of gravity of the column GEFH cannot
prevent this column from descending without sustaining the whole weight:
another proof that this power is in equilibrio with the weight of the
column of water which it sustains, is, that if we push the piston from below
upwards, to make it ascend, this column of water will have the same velocity,
and consequently the same quantity of motion.

B
A
P
K
Fig. 1668.
To estimate the effort which the power makes, suppose that the diameter
of the tube, or that of the piston, is 5 inches, and the height EG 18 inches;
the superficies of circles being as the squares of their diameters, we can, by using the weight
of the cylindrical foot of water, which was found to be 55 lbs., say, as the square of 12 is to
the
square of 5, or as 144 is to 25, so is 55 to the fourth term, which we shall find is
9 pounds 8 ounces, for the weight of a cylinder of water whose base is a circle 5 inches
diameter and whose height is a foot: but as the column is 1 foot 6 inches in height, its
weight will be 14 pounds 5 ounces.
It will be remarked that if the circle GH of the piston were less than
the bottom AD, the power P would only sustain the weight of a column
of water LIK M, which has for its base the circle of the piston, and for
its height the level of the water above the same piston, since it can only
sustain the column of water to which it is a base, all the others, which
make the difference of the columns A EFD and LIKM, resting on the
bottom A D. We may add that if the power works the piston so as to
elevate the column which it sustains, it would be easier than if this
column were enclosed in a tube, in which we must surmount the re-
sistance which causes the friction, or the friction of the water against its
sides.

E
A
L
G
H
Р
Fig. 1669.
C
Having a siphon consisting of two branches AB, CD of the same
diameter, place in the second a piston ILK at a determined height IK;
pour water into the first branch to the height EF; it cannot rise to this
level in the second, on account of the obstacle which the piston presents.
If we draw the horizontal line GK, the columns AH and M K, having
their surfaces level, would be in equilibrio if they made an equal effort on their
base to surmount each other; but as the first sustains all the weight of the column G F,
A F, which is composed of the two, will push with the weight of the part G F the latter
from below upwards, to make it rise to the level E Q. Thus subtracting the friction and
weight of the piston, we must, to prevent it from yielding to the effort which the column
MK makes to iift it, load it with a weight equal to that of the column G F, which is too
natural to need any further explanation.
1100
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Although the branches of a siphon were of
unequal thickness, the water in the lesser one,
QQ, as we have observed, was not the less in
equilibrio with that of the larger one, MK,
while their surfaces were level, because the
lesser one is in equilibrio with all those of
which the larger is composed. If water is
poured into the small tube R O, to the height
N, the column NO will make an effort to
raise all those of the branch MK to the level
EQ, which will push the piston IK from
below upwards, with as much force as the
column G F would; consequently, in order to
maintain the piston at the height IK, it must
be loaded with a weight equal to that of the
column. As the size of the branch NO is in-
different, we find that if it were reduced to
contain only a thread of water, this thread
would sustain in equilibrio the weight with
which the piston is loaded.

B
E
R
G
H
C
P
K
L
A
N
M
D
Fig. 1670.

R
E
B
C
L
H
L
K
Suppose that the superficies of the circle of
the thread NQ is of that of the diameter
GH or IK, the weight of this thread 1000 of
that of the column GF, or of the weight with
which the piston is loaded. If we also sup-
pose that the piston descends the height of one
line, this could not happen without 1000 small
columns, each a line in height, and of a dia-
meter equal N Q, passing into the tube Q R,
and without this column mounting in the
tube 1000 times as high as the piston de-
scended; whence it follows that the weight of
the fillet and that of the piston, being in the reciprocal ratio of their velocity, these two
weights are in equilibrio. It follows that if the thread N Q were 10 feet in height, and the
piston IK 1 foot in diameter, the weight loading the piston must be 550 pounds to be
in equilibrio with this fillet, although it would only contain 1 ounce weight of water.
A
M
Fig. 1671.
When a mass of fluid in a state of equilibrium is subjected to the action of any forces,
every particle is pressed equally in every direction, and vice versâ, if every particle of the
fluid mass be pressed equally in every direction the whole mass will be in equilibrio: for
since the parts of a fluid yield to the smallest pressure, any particle more pressed in one
direction than another would move to the side where the pressure was least, and conse-
quently the equilibrium would be destroyed; if the particles are equally pressed in every
direction, it is evident that the mass of which they are composed must be in equilibrio a
principle adopted by Euler, D'Alembert,
Bossut, and Prony: and the pressure exerted
by a fluid upon any given portion of the vessel
which contains it is equal to the column of
the fluid whose base is the area of the given
portion, and whose altitude is the depth of the
centre of gravity of the portion below the fluid
surface.
A single column of water may be in equili-
brio with an infinity of others, together or
separately. If we have a tube FM larger
below than above, to receive a number of
small tubes A B, ending in a cylinder DE
closed by a piston, if we pour water through
the orifice E, to fill all these tubes and their
cylinders, the single column G M being 10 feet
high, and each cylinder 1 foot in diameter; this
column alone would sustain as many times 550
pounds as this machine, which resembles a
lustre, had branches. Although the length
and thickness of the tube of communication
OM only contributes indirectly to the effect
which we have described in fig. 1671., we

G
F
Fig. 1672.
D
E
B
may suppress this tube, and show the same things with a machine yet simpler than the siphon
CHAP. XVI..
1101
HYDROSTATICS.
Let ABCD be a cylinder attached to a vertical surface, having for
its bottom the circle K L of a piston, and closed above with a plate of
metal soldered so as not to be detached by any effort made to raise it:
in the middle is a hole answering to the tube FE, which may be only
one line in diameter; if we fill the cylinder and tube to the respective
heights E, G, the power applied to the piston will sustain a weight equal
to that of the column KHIL, having for its base the circle of the piston,
and for its height that of the column GN.
To prove this we must remark that the column GN being higher
than all the others OR contained in the cylinder K BCL, these latter,
tending to rise to the level HI, will push the surface BC from below
upwards with a force equal to the weight of a column of water, BHIC,
minus the weight of the column G F.
H
B
K
F

N
L
A
D
Р
Fig. 1673.
If we have already remarked that a power of whatever nature it is
cannot make any effort by pushing or pressing a body without a fulcrum
which is always loaded with the effort which this power makes, we shall find
that all the fillets, as O R, having for their fulcrum the circle of the piston,
cannot push the surface BC from below upwards without pushing the
bottom KL with the same force downwards, consequently the power will have to sustain
the action of a force equal to the weight of a column of water, such as BHIC; and as
on the other hand, it actually sustains the weight of that which is contained in the cylinder,
KBCL, it will therefore sustain the action of a power equivalent to the weight of the
column K HIL.
F
As a second proof we may add that if the circle of the column G N were 1000 part of
that of the piston, the power could not make the piston descend one line without the level
G of the column G N descending 1000 times as much: and, as in
the state of equilibrium, the weight of this thread and the power
P should be in the reciprocal ratio of their velocities, or of the
spaces gone over in equal times; it follows that the power must
be equivalent to the weight of a column 1000 times greater than
GN, or to that of the column KHIL.
Suppose the cylinder ABCD similar in every respect to the
preceding, with this difference only, that the pipe, instead of being
adapted to the upper surface BC, is fitted to the side B A,
the same thing will happen. To prove this let us prolong the
horizontal line N M, and take the line MQ for a diaphragm, which
divides the cylinder K BCL into two parts. If we regard the
pipes FN and MBCQ as the branches of a siphon of which N M
is the communication, the column G N will cause all those of which
the branch MBC Q is composed to push the surface BC from
below upwards, with a force equal to the weight of a column
of water whose base is the circle BC, and its height GE or
H B.
But, as we have just seen, this cannot happen without
the bottom MQ being pressed from below upwards with a force
equivalent to the weight of the column MHIQ; if we suppress
the diaphragm M Q, the preceding pressure, having no other fulcrum
than the circle KL of the piston, which is also loaded with the
weight of water comprised in the part K MQL, the piston will sus-
tain a weight equal to that of the column of water K HIL.

M
H
G
E
N
Bi
C
A
}
A
P
Fig. 1674.
P
G
0
From the preceding example we learn that if we have a vessel AH well closed on all
sides, and that to one of the small faces EH we have adapted a curved tube KN F, and
if we pour water through the orifice F to fill the vessel
and tube, to the height G, the single column GN will
cause the bottom AR QE to be pressed by a weight
equivalent to that of the water which can be contained in
the parallelepiped A M PQ, which has this bottom for its
base, and the level G of the water in the tube above the
same bottom for its height, and that the upper surface is
pressed from below upwards by a force equal to the
weight of water which the parallelepiped CMOD can
contain.

B
A
C
R
D
K
N
E
Fig. 1675.
As the distance DE of the two opposite surfaces RE
and BH is indifferent to the action of the water which
presses the second from below upwards, we see that
they may approach each other as near as possible, pro-
vided they do not touch; the water of the tube will always have this effect, consequently
in this case, as in the preceding, it is not the quantity of water used which increases the
1102
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
effect, which only depends on its elevation in the tune, and the extent of the base over which
it is spread.
Supposing the surfaces CD and A Q, each 6 feet square, are so near each other that we
can still take something from the interval; if we give 24 feet to the height of the column
GN, each surface will be driven in the opposite direction by a force of 60480 pounds, and
produced by a weight of 3 or 4 ounces.
Belidor took two plates, each 1 foot square and 30 lines thick: having placed them
above each other, about 3 inches apart, he nailed a leather band all round, and formed a kind
of bellows, having the form of a parallelepiped. After having taken all proper precautions
to prevent the water with which it was filled from escaping, he attached the upper surfaces
in a firm manner horizontally to a beam supported by two uprights, so as to make the
bottom work upwards; at the four corners of this were iron rings answering to cords
attached to the arm of a balance; he then loaded the other arm as much as possible so
that the lower part of the machine was applied to the upper: this latter was pierced with
two holes, to one of which a vertical plug was adapted to be opened, solely for the escape
of the air when water was poured in: at the other was a copper tube, whose interior
diameter was 3 lines and 10 feet high, attached to a beam firmly fixed at both ends.
The question he wished to solve was, if by pouring water into the tube it would raise a
weight of a column of water 1 foot square at the base and 10 feet high; this happened when
about 3 pints of water were poured into it; he then remarked that the velocity of the
weight increased as it elevated, for, as by pouring the water in, he took care to keep a funnel
soldered to the summit of the tube full, the water with which the bellows was filled would
increase by its own weight the action of that of the tube.
B
C
As the gates of a canal often sustain 22 and 23 feet of water when the sea is low, it
happens that small threads pass under the sill, and insinuate themselves below the platform
and foundations; this water not finding means of escaping, pushes upwards everything
which could prevent it from mounting to the level of the canal, and causes the gates to
bend, notwithstanding their weight and solidity.
Having a cylindrical tube, ABCD, inclined
on its base AD, supposed horizontal, and filled
with water to a height EF, it would load the
bottom AD as much as if it were an upright
cylinder AGHD of the same base. Draw
through any point P of the height FI the
horizontal line LM, and consider that the water
enclosed in the space AEG is sustained by
the side EA; then all the threads K, L of which
it is composed have each a lean on the point L
of the inclined surface EA; consequently the
base A D is not charged therewith.

E
L
K G
FOH
M
N D
A
Fig. 1676.
It is not the same with that which comprises
the opposite space IFD, for as the thread FI
acts on the smaller MN, to elevate them to the height of the level EH, being prevented by
the surface FD, each of them will press all the points M of this surface from below
upwards, with a force equivalent to the weight of the thread FP, the difference of FI from
MN; and as the height FP is equal to KL, the point M will be as much pressed from
below upwards as the point L is from above downwards, which shows that the surfaces
EA and FD are driven in opposite directions with a force equivalent to the weight of
water enclosed in the space A E G, or what is equal to it, DF H. But as all the threads
whose action is sustained by the surface FD cannot press it from below upwards without
pressing as much the point ID of the bottom, which serves as a base, from above downwards,
we see that if we add to this latter pressure the weight of the threads which the space
IFD contains, each point of the bottom AD will be loaded with a weight equivalent
to that of the thread FI.
It follows that having a vessel BCDE similar to a reversed
truncated cone, to which the tube ABE F is fitted to receive a C
piston serving as a bottom; filling this vessel with water, the
power applied to the piston will only sustain the weight of the
column B G HE; then all the remainder of the water will rest
on the sides CB and DE. This consequence shows the error
of making the pipes of descent larger above than below, with
the intention of giving more elevation to a fountain in which the
pipe terminates, forgetting that the portion leaning on the sides
of the tube does not contribute to drive that which descends; this
practice, however, may be useful when the hole through which the
jet issues is too large.
If a piston answered to the great circle of the preceding
vessel, it would happen, on the contrary, that being filled with

B
P
Fig. 1677.
H
D
E
F
CHAP. XVI.
1103
HYDROSTATICS.
water, the power would sustain a weight equal to that of the
column AIK C: if we close the orifice È H, and hold a tube FB
filled with water to the height G, all the points of the base A C
being pressed with the same force as the fillet GN presses the
point N, the power would sustain a weight equal to that of the
water which the column ALMC would comprise, provided, as
already observed, that this vessel is attached to a fixed plan.
As a power cannot act in any direction without a fulcrum, it is
necessary, in order that the piston may press upwards with the
same force that the water presses downwards, that the machine
should be fixed, otherwise the action of the water would raise
the vessel, and leave the piston unmoved by the power: if the
water were to freeze, then, being without action, the fulcrum
would become useless, and the machine would only be charged
with the real weight of the water and the machine.

If we sup-
B
Fig. 1679. Suppose we take another pipe ABCD, where
none of the points of the level E F of the water answer to the
bottom AD, and we suppose that the column AEFD is
divided into several others, GF, IH, AK, by planes GH,IK,
parallel to the horizon: the base G H will be loaded with a weight
equal to that of the column GLMH, in fig. 1676.
press the diaphragm GH the column NO, having
no other base than the summit N of the column NI,
these two together will only make one, OI, which
communicates with all those enclosed in the space
ITK; these latter will each press the base IK with
as much force as the first OI: thus this base will be
loaded with a weight equal to that of the water which
the column I OPK comprises. In the same manner,
since the point Q of the base IK is pressed with a
force equal to the weight of the columns OI or R Q,
suppressing the diaphragm IK, the columns RQ
and QA only composing one, RA, which is in equi-
librio with all those comprised by the space AVD,
the bottom, AD, will be loaded with the water of the
oblique column AEFD, which would be the case if
the column were straight, A RSD.
Re-
L
C
E
H
M
C
N
Fig. 1678.

FOM R
E
T
K 0 :
г
ستا
G
Fig. 1679.
1
E
Fig. 1680.
H
-
P
V
K
M
N
Fig. 1680. If we have a tube whose parts, BD,
DF, FQ, were disposed in zigzag, and this tube,
which we suppose placed against one or more vertical
surfaces, were filled with water, the bottom B E would
be loaded with a weight equal to that of a column
of water BKO E, having the same base, and the line
BK, which expresses the elevation of the level HQ
of the water above the base BE, for its height.
garding the line FG as the bottom of the tube FQ,
the water of this tube will load the bottom as much
as that contained in the column FLIQ; suppressing
the diaphragm FG, the column L G, having no other
base than the film FG, will increase with its whole
weight that of the column FD, and the bottom CD
will be loaded with a weight equal to that of the
column CMND: we shall also find that the base
BE, being loaded with a weight of the right and in-
clined columns MD and DB, will be in the same case as if it served as the base of the
column BKOE. If the tube, instead of being zigzag, were serpentine, the same principle
would hold good, for, by dividing the water of the tube in horizontal sections, we divide it
into small right or inclined cylinders, which being contiguous may be regarded as the tracts
of a tube like the preceding: whatever be the size of a tube, whether it be uniform or not
through its whole extent, in whatever manner its parts are disposed, whether in a vertical or
inclined plane, the power applied to a piston of an equal, greater, or less diameter than the bot-
tom of the tube, it will always be loaded with the weight of a column having for its base the
circle of the piston, and for its height that of the level of the water above the same piston.
On the Action of Water against vertical and rectangular Surfaces. After having shown
the manner in which water acts to surmount the resistance of surfaces which prevent it
from descending towards the earth's centre, or from rising to its level, we shall proceed to
explain according to what law it presses the sides of the vessels containing it apart; but
first it must be observed that this pressure is always made in a horizontal direction: sup-

1:104
Book II.
THEORY AND PRACTICE OF ENGINEERING.
pose a cylinder of water suspended in the air without being enclosed in a tube, composed
of a great number of circles of an equal thickness, the highest circle pushing the second, so-
that it should always preserve the circular figure and the same thickness, which could not
happen without all the portions of water being driven forwards in the direction of the radii
to occupy a larger circle. If this latter, so increased, were to mix in like manner with the
third, the parcels of water would be still farther pressed in the direction of the radii, to oc-
cupy a larger circle than the second: in like manner, the course of all the circles of which
the cylinder is composed would be extended, and the circumference of the latter would be
as much increased as the number of circles was greater, or as the cylinder was higher.
If the cylinder be enclosed in a tube, all the circles of water, having the same tendency
to mix, will make an effort to spread out; but as this effort can only be exercised against
the sides of the tube, we see that they will be pressed from the centre to the circumference,
consequently, in horizontal directions, with a force which will always increase from the
top to the bottom of the tube.
Fig. 1681. Instead of
a cylinder, if we take a
prism A E, the water of
which is divided into an
infinity of films of an im-
perceptible thickness, the
upper will always make an
effort to mix with those
below; these latter tending
to extend will drive the
surface of the prism in a
horizontal direction: as we
suppose that these films
have an equal weight, the
second being loaded with
E


B
F
R\G
N
4
H
P
S
T
Y
V
19
:10
A
M
Ꭰ
A
M
D
Fig. 1681.
E
the first, will drive the rectangle 2, which sustains it, with a force twice that which will
press rectangle 1, whatever be its dimensions: in like manner, the third film, being
loaded with the weight of the first and second, will press the rectangle 3 with a force
triple that of the first, and so of the others, whose pressure will be proportioned to the
weight with which they are loaded. Now, as this weight increases in the order of
the terms of an arithmetical progression, the pressures also, increasing in the same order,
may be expressed by the elements of a triangle ALD whose height is that of the water:
thus we find that the pressures which answer to the elements NO and PQ of the surface
A B CD, are in the ratio of the elements FG and HI of the triangle ALD, or of the
height LR and SL of the water above the same elements; then FG: GI:: LR: LS.
It follows that the sum of all the pressures of the height LR, or the pressure which sus-
tains the surface NBCO, will be to the sum of all the pressures of the height LM, or
to the pressure which the surface ABCD sustains, as the superficies of the triangle
FLG is to that of the triangle ALD, or as the square of the perpendicular LR is to
that of the perpendicular LM; and when the surfaces have the same base, their pressures,
beginning from the level of the water, are in the proportion of the squares of the heights
of the water which sustain them. The pressure which answers to the height RS, and
which the surface PNOQ sustains, being to be expressed by the trapezium HFGI, the
difference of the triangles HLI and FLG, we see that it may also be expressed by the
difference of the squares of the heights of the water, LS and L R.
Fig. 1682. The line BC expressing the
level of the water, if we prolong it from C
to R, to serve as the axis to a demi-parabola
CLO, described at pleasure, drawing any
number of parallels to the line BR, as FH,
IL, A M, the pressures which the surfaces
BG, BK, BD, sustain will be to each other
in the ratio of the ordinates GH, KL, DM,
drawn from the tangent to the parabola, which
is very evident, since these ordinates are in the
ratio of the squares of the sections CG, G K,
CD, which mark the height of the water
which these surfaces sustain; consequently,
if from the points H and L we draw the
parallels H P and LQ to the tangent, the lines GH, PL, GM, which express the difference
of the ordinates, will be to each other in the ratio of the pressures which the corresponding
surfaces B G, F K, I D, sustain; and the pressure which the surface BD sustains, is to that
which the part ID sustains, as DM is to Q M, and so of the rest.
B
G
F
A
Fig. 1682.
E

X
L
R
M
D
Q
CHAP. XVI.
1105
HYDROSTATICS.
୮
The pressures of the films which the height LM comprises being in arithmetical pro-
gression, there will be a mean pressure between the greatest and the least, which being
multiplied by the weight which expresses the number of films will give a product equal to
the total pressure: now, as this mean is equal to half the greatest, we shall have
LM
2
AD
2
× L M
for this pressure, which being equal to × AD, we may suppose that all the films act
with equal pressure, and that this force is expressed by the mean height LZ, half L M.
C
1.1
E
G
Z
H
**
The pressure which the rectangle APQD sustains being expressed by the trapezium
AHLD, the mean element between HL and AD will express the mean pressure; and as
this element can only be the line TV, which passes through the middle of the height SM
of this trapezium, we may further express by the height LY the arithmetical mean between
LS and LM, supposing the pressure of each film which the surface AP QD sustains uni-
form. Supposing that the films which belong to the same surface act uniformly, it follows
that the pressures which two different surfaces sustain when rectangular will be in the
compound ratio of the extent of the same surfaces and the mean heights answering thereto :
thus, when the surfaces are equal, the pressures will be as the mean heights, and when the
mean heights are equal, the pressures will be in the ratio of the surfaces.
To show the method of calculating the
pressure of water against vertical surfaces
we use a siphon, fig. 1683., composed of
two right prismatic equal branches united
by a horizontal communication pipe, IADLM,
of the same figure and size as each of the
branches, separated into two parts by a
diaphragm NOPQ, parallel and equal to
the plane RSDT. If we pour water into
the first branch, to fill only the part of
the communication IA DPN, it will not
make any effort to mount above the level
A P, and its action will be reduced to press
the sides which sustain it, among the rest the
diaphragm NOPQ, in order to spread itself
on the other side: but if we fill the same
branch to the height V X, the column A V XD
will press the water of communication, which will be pressed from I to N in a horizontal
direction, and will tend to pass into the other branch, to rise to the level YZ, where it
would elevate itself, in fact, if it were always maintained at the same height VX, and were
not prevented by the surface NOPQ, which would sustain not only the pressure of the
water contained in the communication, but also all that which the column AVX D may
occasion, which is very evident. In fact, since no other force than the weight of this
column acts here to raise the water in the other branch, and to maintain it there at the
height YZ above the level AH, it is necessary that the superficies NOPQ should be
pressed in a horizontal direction by every effort of the power which prevents it from
acting. Since the length of the end of the tube RDOQ is indifferent to the effort which
the water makes to rise in the second branch, we may shorten it as
much as we please, and even place the surface NOPQ close to its
equal RSDT, which we may take for another diaphragm, in order to
detach the prism IBCT from the siphon: as this does not at all change
the action of the water contained in it, the surface RSDT will be
pressed with as much force as the diaphragm NOPQ.

R
N
Fig. 1683.
C
M
B
X
1

F
K
D
H
L
T
N
R
Fig. 1684. The pressure which the surface RSDT sustains from the
water enclosed in the space IADT, independently of that caused by
the column AVX D, being to be expressed by the product of this
surface and the mean height PQ, and the weight of this column by
the product of the base AD and the height OP, it follows that these
two products taken together equal that of the surface RD by the
height OQ, composed of the preceding OP and PQ; it will only
express that of the pressure which the surface RD sustains: as the
latter product is neither more nor less than the solidity of the prism
FVXL, we see that if the pressure caused by the column AVX D
against the surface RD should be expressed by its weight, all that
which the same surface sustains will be, by that of the column FVXL, which has for its
base the plane FHLG, equal to this surface, and for its height the line Q, the
arithmetical mean between OP and PN; which shows that if the surface RD was 4
feet, and the height OQ 10, this surface would be pressed by a force equivalent to the
weight of 2800 livres, =4 × 10 × 70 livres.
Fig. 1684.
4 B
1106
Book II.
THEORY AND PRACTICE OF ENGINEERING.
V
Z
H
Y
E
11
R
D
Fig. 1685.
A
I
M
N
K B
If of the two branches of a siphon we leave
the first as it is, and bring the opposite surfaces
IHXL and BGZM near together, to render
the prism IHZA much narrower than the
other; this will not prevent water poured into
one part of this new siphon from rising in the
other to the same level YY, or from that in the
second branch being in equilibrio with that in the
first, because the small column IE YA will never
have to oppose any other column than one of the
same base as itself, and as all the others contained
in the great branch are in equilibrio with the first.
As these columns make equal efforts on their bases
to surmount each other, the water of communication
will be pressed from & to B by the large column
with the same force as from B to & by the small
one; thus the diaphragm N O P Q will be pressed with equal forces in opposite directions.
If we suppose two other diaphragms, RSDT and KILC, and suppress the pipe of
communication, to detach the two branches, the surface RSDT will be pressed with the
same force as the surface KILC equal to the preceding, will be from B to K, both being
in the same case as the diaphragm NOPQ was previously, although the surface was
indifferent to the pressure it sustained. Although there is much less water in the second
prism than in the first, the surface KILC will sustain, like the other, a pressure equal to
the weight of the column having this surface for its base, and the arithmetical mean between
EI and E K for its height. The pressure of the water being in the compound ratio of the
surfaces which sustain them and the mean heights corresponding thereto, we find that, with-
out taking into account the dimension IR, by reason of the quantity of water which the
vessel IBCT contains, there will be the same ratio between the product of the surface
RSDT multiplied by the mean height CQ, and the product of the surface RZXT,
multiplied by the mean height O Y, as between the pressure which the first surface sustains
and that which the second sustains. Now, since the pressure which the first sustain is
equivalent to the weight of cube feet of water which the relative product gives, the pres-
sure which the second sustains will then be equivalent to the weight of the number of
cube feet of water which its relative product gives: - thus, supposing the base RT of
this surface to be 2 feet, and the height ON 12 feet, it will be 24 square feet, which
being multiplied by the mean height OY, 6 feet, and the product by 70 pounds, gives 10080
pounds for the weight equivalent to the pressure which it will sustain. If the vessel, instead
of being prismatic, be a tube or right cylinder, we must, to have the pressure which
the surface will sustain, multiply this surface by half the height of the water.
The difficulty of raising a flood-gate arises from several causes; suppose it 5 feet wide,
sustaining 8 feet height of water, the surface pressed will be 40 square feet, which being
multiplied by 4 feet, the mean height, we have 160 cube feet, or 11200 pounds, for the pressure
of the water, or the pressure of the vane against the grooves, of which we must take for
143
friction, which will be about 3733 pounds, which being added to the weight of the vane,
we have the resistance which the power must surmount at the first moment of its action.
In the following moments this resistance will continue to lessen, because the pressure or
friction diminishes in the ratio of the squares of the heights of the water which the vane
sustains. It must be remarked that the vane in mounting arrives at a point of elevation
at which its weight is in equilibrio with the friction, and that it is only when raised
above this point that it can acquire in descending a sufficient quantity of motion or power
to arrive at the sill of the gate: for as the friction will increase in the ratio of the squares
of the heights of the water, while this
force only increases in the ratio of the
square roots of the same heights, if the
gate does not fall from a point sufficiently
high, it will remain suspended in its road
without being able to descend except by
other assistance.

Fig. 1686. To render still more evi-
dent the action of water against a vertical
surface A B CD, we shall use the regular
parallelepiped ABCDEFLM, one of
whose dimensions AM will be either
greater or less than the height BA of
the water. We will suppose that we
have taken on the lines DI and AK
the parts DH and AG, each equal to
B
A
C
E

H
L
K
M
G
M
Fig. 1686.
CHAP. XVI.
HYDROSTATICS.
H
G
1107
the height BA of the water, and that we draw the lines CH, BG, to form the solid
ABCDHG, which will express a volume of water whose weight will be equivalent to
the pressure which the surface ABCD sustains; which is very evident, since to have the
If we
value of the solid we must multiply the same surface by the half of A G, or A B.
suppose the height B A divided into a great number of equal parts, and that through each
point of the division a plane parallel to the base AH passes, the solid ABCDHG will be
divided into a number of slices or prisms, and the surface ABCD into the same number
of rectangles equal to each other: then the weight of the water of each slice will express
the pressure which the small rectangle answering to it in surface will sustain, and these
slices or prisms having the same height B C, their weight, or the pressures which they mea-
sure, will be in the ratio of the trapeziums serving as bases to these prisms.
Since we can bring the surfaces KH XC and BGZM as near
each other as we please, provided only that they do not touch, we
see that with a very small quantity of water the plane KILC will
be pressed with as much force as if their distance was very great:
consequently if we have a prismatic vessel, two of whose parallel
and opposite faces are each 6 feet square, placed at the distance only
of one line from each other; filling this vessel with water, the two
surfaces will together sustain an effort of 15120 pounds. But what
appears still more extraordinary is, that if we close this vessel to
adapt a tube GF to it of any height, filling it with water, the sur-
faces will be pressed with the same force as if the vessel were filled
with water to the height HI; which is very evident, for each of the
columns contained in the vessel A E, and which would have for its
base that of the tube F G, being pressed downwards with the same
force as that of the tube presses the column FK, will make the
same efforts against the sides of the vessel, as the same column F K
would make against those sustaining it. Thus, supposing G F 10 feet;
the mean height CL will make 13, which being multiplied by 36 feet square, and the pro-
duct by 70, will make 65520 pounds for the effort which the water will make against the
two surfaces together, although its weight altogether will be near 18 pounds.

B
A
Fig. 1687.
E
F C
K
We may observe that the pressure of the water against a vertical surface does not depend
on the quantity which the vessel contains, but only on the extent of this surface and the mean
height of the water.
On the Action of Water against inclined Surfaces. Having considered the action of water
against vertical surfaces, we must now examine what is the pressure those which are inclined
sustain.
T
B E
VRF G
C
S
X
Р
N
K
Suppose that the trapezium ABCD
represents the profile of a vessel larger
above than below, composed of plane
surfaces, and filled with water to the
level B C, and that it is required to mea-
sure the pressure which the inclined
surface CD will sustain, not consider-
ing the breadth. From the point M
draw a perpendicular, D F, to the hori-
zontal line BC; take the part F E equal
to this perpendicular and draw the line
ED to have the right-angled isosceles
triangle E F D. We shall then find that
all the points H of the surface DC are pressed by columns of water, G, H, in two different
directions, one vertical, the other horizontal; that the first may be expressed by the su-
perficies of the triangle D F C, and the second by that of the triangle DFE; and as these
two triangles are in the ratio of their bases FC and FE, since they have the same height
FD, we may take their base in place of their superficies, then the vertical pressure will be
to the horizontal, as FC to FE, or as FC to FD, since EF=FD.

Fig. 1688.
M
Drawing from the point H the horizontal line H I, and the perpendicular HI to the side
DC, making the parallelogram KI, we shall have the similar triangles HIL and DFC,
which give DF: FC:: HI: IL. Thus we may take the side IL or HK to express the
power which sustains the vertical pressure in equilibrio, and the side HI to express that
which sustains the vertical pressure; then the diagonal HL will express the action of a third
power in equilibrio with the result of the assemblage of vertical and horizontal pressures.
It follows that the horizontal pressure will be to that which the surface DC sustains, as
HI to HL, or as DF to DC; consequently if we raise at the extremity D of the line CD,
the perpendicular DM equal to EF, and we draw the line CM, the triangles EFD and
CDM, having equal heights, will be in the ratio of their bases D F and DC, or as the hori-
zontal pressure is to the entire pressure which the surface DC sustains. Now as the first
4 B 2
1108
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
of these pressures is expressed by the superficies of the triangle DE F, the second will then
be so by that of the triangle D CM, or, if we wish, by a weight equivalent to that of a prism
of water having this triangle for its base and the breadth of the surface of its height.
Since we must, to have the value of the prism, multiply the surface DC by half DM or
its equal D F, we find that the rule for measuring the pressure of the water against inclined
surfaces is the same as that which we have described for the verticals, since it is reduced to
multiply the superficies of the surface by half the height of the water FD: thus all the
principles drawn from this rule may be applied to inclined surfaces; for example, if we
wish to know what is the pressure of water which acts on the part HD of the surface DC,
we must form the point H draw the horizontal line HN, and multiply this part by the
arithmetic mean between FD and FN.
If the vessel ST BA, contiguous to the preceding, were larger above than below the sur-
face, B A will be as much pressed upwards by all the columns which the triangle B X A
comprises, which tend to rise to the level TB, as the same surface will be downwards by all
the columns contained in the triangle BV A equal to the preceding.
It follows, that if the vessel STB A only contained water to the height YO, and the other,
A B C D, were full, the opposite pressures which the surface B A would sustain would be as
the squares BA and O A, if the surfaces of which these lines express the height have the
same base; and as the greatest pressure will be diminished by all the action of the least,
that of the water of the vessel ABCD will only be expressed by the difference of these
two squares, since it is with inclined surfaces as with vertical.
If the vessel ABCD had the figure of a truncated cone, we must, to have the pressure
which all its surface would sustain, multiply the arithmetical mean OP between BC and
AD by the side DC, and the product by half the height of the water, FD; if the cone be
entire, as BQ C, we must multiply half the circumference, BC, of its base by the side QC,
and the product by half its axis R Q.
It is of the utmost importance that we know how to calculate the pressure which water
exerts upon coffer-dams, gates or locks, dykes, banks, &c., in order to proportion the resist-
ance to the effort which they have to sustain relatively to the nature and quality of mate-
rials employed.
B
C
E
N
D
K
F
P
Having a vessel ABFG whose oppo-
site faces are equal, parallel, and vertical,
on filling it with water, all the small
columns having the same height will press
equally the bottom A D G H, which being
sustained by a horizontal fixed plane,
MNOQ, will prevent the vessel from
descending; on the other hand the opposite
surfaces A B CD, HEFG, being equally
pressed in a contrary direction by the
action of the water, one of these powers
not being able to overcome the other, there
is no reason why the vessel should be
moved to the right or left. The surfaces
DCFG and ABEH being in the same state, the vessel, not being able to be moved for-
wards or backwards, must necessarily remain at rest.
If we cut the vessel obliquely by a

t.
M
B
R
C
H
Fig. 1689.
E
F
N
Р
Q
plane AIDK, so as not to consider that
the water enclosed in the part A B CD,
FIKE, which we shall take for a new ves-
sel, placed freely on the inclined plane
LMNO, it will happen, independently
of the fall which all bodies have in des-
cending along inclined planes which sus-
tain them, that this vessel will have more
than if it were filled with a hard body of
the same weight, because the pressure
which the surface A B C D will sustain is as
much greater than that which its opposite
KEFI will sustain, as the square of the
height BA is greater than the square of
the height EK; thus the surface will be pressed in a horizontal direction, with a force which
may be expressed by the difference of the same squares; that is to say, for example, that
if BA were double EK, it would be pressed by a force equivalent to three-fourths of the
weight of the prism of water having this surface for its base, and half BA for its height.

L
Fig. 1690.
R
Regard being had only to the action of the weight, it will be indifferent to the power P,
which the vessel sustains in a horizontal direction, SP, whether it is filled with a liquid
CHAP. XVI.
1109
HYDROSTATICS.
or a heavy body, since the weight will always be to the power, as the base L R of the plane
is to its height RO. Now if we suppose the lines B A, B C, BE, equal to each other, the
volume of water which the vessel comprises will be of a cube of the height BA; thus we
3 RO
shall have, as LR, RO:: 2 × BA³, P, or × BA³=P, subtracting the weight of
4 LR
the vessel itself. But since the power must also sustain the difference of pressure against
the surfaces BD and E I, or a weight equivalent to the volume of water expressed by
3 RO
4 L R
BA
2
BA2 × =3B A³, we shall have
× BA³ + 3B A³= P.
As for the action of the water on the bottom, ADIK, of the vessel, we see that according
to a preceding article, it should be expressed by the product of the superficies of this bot-
tom and of the height TV, the arithmetic mean between BA and EK; but as we are here
only speaking of the absolute weight of the water which the same bottom sustains, the pre-
ceding product has no relation to the power P.
Resuming the vessel A B FG, which we shall suppose without a bottom, placed on the
horizontal plane M N O P Q, as highly polished as possible, so that the base A D G H should
be intimately united thereto; filling this vessel with water, the power which will draw it in
a horizontal direction will make no more effort to do so than if it were empty, for the ves-
sel having no bottom, this plane will be loaded with the whole weight of the water, whose
parts being extremely small will slide without perceptible friction, because all those which
might be stopped by the salient parts of the plan would not prevent the columns above from
moving horizontally on the surface of a film of water, which would smooth down all obstacles.
Thus the only resistance would be the pressure of the edges of the vessel on the plane, which
would cause an inexcitable friction, because the parts which would meet, not being fluid, could
not be in the same case as those of the water.
M
F
C
B
T
D
I
It follows that if the preceding vessel
were placed without a bottom on an in-
clined plane, and that the water rested
immediately on the plane, the power
would only have to sustain the difference
of the pressures of the same water against
the surfaces ABCD and HKIG in a
direction SP parallel to the plane. Thus
supposing that AD or H G are 30 inches,
AB 20, HK 12, and the height TA of
the water 18, we must, to have the power
P, begin by seeking the weight of the
volume of water which expresses the L
pressure which the surface ABCD sus-
tains, which will be 2183 pounds: square
the heights BA and K H of the surfaces, take the least square from the greater, say as 400,
the square of B A, is to 2183 pounds, so 256, the difference of the two squares, is to the dif-
ference of the pressures, which we shall find 140 pounds, to which we add what is necessary
to overcome the friction of the base of the vessel.

A
Fig. 1691.
H V
Y
e
The vessel ABFG having a bottom, or not being placed on an inclined plane, could not
contain so much water as if the plane were horizontal, and it would contain as much less
water as the inclination is greater; nevertheless, as we suppose that we have only given
this position to a power to procure greater facility for elevating water to a given height,
OR, the less the inclination of the plane, the greater length it will have, the more time the
power would take to draw the vessel from the foot of the ramp to the summit. We are at
present contriving to combine the greatest quantity of water which the vessel will contain
with the shortest road, so that it shall mount to the height RO of the plane in the least
possible time; because, if vessels like this chained together followed each other with a
uniform velocity, it would result that in a determined time, and with a determined velocity,
the power would draw from the receptacle, which would be at the foot of the plane, the
greatest possible quantity of water in the same time.
The line B K, which marks the level of the water, being parallel to the base LR, the
right-angled triangle BEK will always be similar to the triangle LOR. On one hand,
without regarding the breadth of the vessel, we may take the trapezium A B KH to express
the quantity of water which will be contained in the vessel; drawing the line AK, this
trapezium will be divided into two triangles, the first of which, A B K, will always have the
same superficies, at whatsoever point of the line EH its summit K abuts, instead of the
second À KH, which has for its base the constant line A H, increasing or diminishing in
the ratio of its height KH; thus the increase or diminution of the trapezium, or of the
water which the vessel will contain at the different inclinations of the plane, may be ex-
pressed by the line H K. On the other hand, the time which the power takes to draw the
4 Б 3
1110
Book II.
THEORY AND PRACTICE OF ENGINEERING.
vessel from L to O, will depend on the length of the road LO, or of the sine of the
angle OL R, for the less this sine is with regard to the total sine, the nearer the point K
will approach E, and the more water there will be in the vessel, but the road will also be
longer; on the other hand, the nearer this sine approaches the total sine, the less water it
will hold, but also the length LO approaching more nearly the height OR, the power will
take less time to draw it up. Now, since the greatest quantity of water depends on the line
K H and the shortest road of the sine of the angle OL R, we see that the product of these
two lines should be the greatest of all those which may be formed by the same lines.
Having made OV equal to OR, and drawn from the point V the line V Y parallel to
LR, OV may be taken for the total sine, V Y for that of the angle VOR, and OY for
that of the angle OVY or OL R. Then calling OR or OV, a, OY, x, VY will be Vaa-xx ;
as for the lines BE and EH, which we suppose equal, as the length is indifferent, we shall
express them by unity. Let us consider that the similar triangles VOY and BKE give
VY (√aa−xx), YO (x) : : BE, EK (aa-xx
;
whence we have EH-EK=KH
H (1
X
✔aa-xx
which being multiplied by OY (x) gives,
XX
x
√aa-xx
of which we must take the differential, and equal it to zero; we shall have
2xdx × √aa-xx-x³ dx x aa—xx-
dx-
0,
or, a adx
xxdx
2x dx xaa — xx —
x³ dx × aa— x x − 1 = 0;
from which effacing the dr we have
28
aa—xx × √aα-xx
Jaa
0,
√αa-xx
2αax+x 8
or, ɑɑ—x X
=0,
√aa-xx
3
x³-2ɑax
or,
=xx-αa;
α α — XX
which being squared gives,
26 -4aax¹+4a²x²
=x^—2ααxx+αª ;
whence we at last have 26-2a ax¹ + 2 α4x³- ½ a® = 0 ;
αα
-
and if we suppose 2,2 =ay, we shall have y³— ay³ + ½ a² y — } a³ = 0, for the simplest equation
to which this problem can be reduced.
Since we may suppose the line O R divided into as many equal parts as we please, taking the
number 10 to express the value of a, we shall find, according to the ordinary rules, y=17.
To convince ourselves, it is only necessary to multiply the values of a and y in the same
=
599913
1000
‚anday²+}a³
601150
1000
manner as in the preceding equation: we shall find y³ + a² y:
which showing that the sum of the plusses not differing much from that of the minuses, we
may regard them as equal.
x2
Having supposed x²=ay, or =y, and a= 10, we shall have ²=17, or ≈ =
:17, or ≈ =√17: now
α
=
if we multiply 17 by the square of 10000, which is 100000000, to extract the square root
more exactly, it is 41231: on the other hand, multiplying the value of a by 10000, we
shall have a=100000, which shows that OV (a) should be to OY(a) as 100000 is to
41231, or nearly as 5 to 2, which is the proportion that may be used in practice. Thus we
see that, for the greatest effect, it is necessary that the height OR of the inclined plane
should be g of its length, LO; then we shall find that the base, LR, of the same plane is to
ૐ
its height, OR, as 23 to 10, or as 43 to 2.
Taking the side OV (100000) for the total sine, OY (41231) will make that of the
angle OVY=OLR, which answers in the tables to 24º 21', which is the angie which the
inclined plane should make with the horizon.
On the Action of Water against circular, vertical, and inclined Surfaces. It remains to
show the action of water against circular surfaces, and in what manner we must calculate
its
pressure, since it is always equivalent to the weight of a volume of water expressed by the
parts of a cylinder cut under circumstances relative to the figure and situation of its surfaces.
CHAP. XVI.
1111
HYDROSTATICS.
Let ABCD be a right cylinder cut into two equal parts
by a plane E F G H passing through the axis IK, then by
another ROBM which forms an ellipsis, lastly by two
other planes parallel to the base, forming two circles, of
which the first, OLMN, passes through the small axis OM
of the ellipsis, and the second, OPVR, through the ex-
tremity R of the great axis.
Let us consider that all these sections produce several
solids: firstly, the frustum ROMNR, formed by the
semicircles OMN, the semi-ellipsis OM R, and a portion
of the surface of the cylinder MYNRTO.
Secondly; another frustum, OLB MO, equal and similar
to the preceding, since it is also formed by the semicircle
OLM, the semi-ellipsis O BM, and a portion of the surface
of the cylinder OLMB.
Thirdly; the solid RQOMVR, formed by the semi-
circle R QV, the rectangle QOMV, the semi-ellipsis
OM R, and the two portions VMVRV, QOTRA of the
surface of the cylinder: I shall call this solid the comple-
ment of the frustum ROM N, because it is the part which
is deficient to make the half cylinder QOMNRVA.
Fourthly; the solid BM ROQ PB, formed by the
circle PR, the ellipsis OMBR, and the portion of the
cylinder comprised between these two planes.
Fifthly; the solid A B M R DE OВ.
B
L
A
Sixthly; the two solids O E A B MHE and OEDRMHE.
If we examine each of these solids in particular, we may con-
sider the frustum OLBMO as composed of an infinity of
rectangles DEFC, which would have for their base the
double ordinate CF of the semicircle OLM, and for height
the corresponding element GH of the right-angled triangle
BLX; thus we shall find the sum of all these rectangles in the
same manner as we find the solidity of the frustum.
We may also imagine the frustum composed of an infinity of
right-angled triangles FHG of an infinitely small thickness,
having for base the ordinates FG of the semicircle, and for
height the corresponding element FH of the surface: to have
the sum of these triangles we shall call the radius DL or
DO, a; the height, LB, b; DG, x; GF,y; G,g; Kƒ,
by
dx; FK, dy, and FH,
α
byy
Multiplying the triangle FHG (2) by da, the product
by y dx
2a
a
will give
as the property of the demicircle gives a-xx-yy, substi-
tuting the value of yy in the preceding expression, we shall
abdx bxx dx
ab x bx 3
2
2 6 a
for the differential solid of the frustum; and
or
B
L
Ꮐ

I
C
F
M
Q
K
E
Fig. 1692.
Fig. 1693.
L
F
H
E
G
X
N
R
D

M

M
H
Fig. 1694.
When a becomes a we have for the solidity of half the solid, conse-
have
2 a
aab
aab
2
6
2aab
quently
3
the integral of which is
aab
3
2a3
3
for the entire solidity, or when ab, which shows that in this case the
frustum is equal to the third of the cube of the radius.
From what has gone before, we may regard the infinitely small superficies FHfh
as the differential rectangle of the surface of the frustum, of whose base we shall have
the expression by drawing the radius DF, and considering that the similar triangles
У
FDG and FƒK give FG (y) F D (a) : : ƒ K (dx) ƒ F (ada), of which the fourth term
being multiplied by FH (%) gives
a
by adx
ay
or simply bdx, whose integral is bx or ba
when x=a for half the surface of the frustum, consequently 2ab for the entire surface,
which is found equal to the rectangle comprised by the diameter MO and the height BL
of the frustum.
4 B 4
1112
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
M
C
Considering the complement RQO MV of the frustum as composed of an infinity of
rectangles A B C D, which have for their base the double or-
dinate AD, and for their height the corresponding element EF of
the right-angled triangle X YR, we shall find their sums by
subtracting the frustum, which makes the difference from the
demi-cylinder QOMNRVQ. Supposing then XY=YR=
a, and the half circumference QR V-b, we shall have for
aab

aab
2
X
D
2a3
the solidity of the demi-cylinder; consequently
3aab
4 a²
6
6
or
2
3
for the value of the complement of the frustum.
Thus the ratio of these two solids will be
4a
3b-4a
or
2 a
3b-2 a
2
4a3
3aab-4a³
which shows that the frustum is to its
or
A
Fig. 1695.
complement, as the diameter of the circle, is to the difference between the semi-diameter
and three-fourths of the circumference. It follows that if we could find the exact value of
the complement of the frustum, we should have the quadrature of the circle.
To have in figures the ratio of the frustum to its complement, supposing a=7 and b=22,
2 a 14
consequently
which shows that the frustum is to its complement as 14 to 19.
19'
α
3b
2
Considering also this solid as composed of an infinity of
planes E, F, G, H, comprised between the double ordinate
EH, and the element IK of the triangle PBR, we shall
have the sum of all these planes by multiplying the circle
PVQR by the mean element DC, serving as the axis of the
cylinder PLN R, because the frustums OLBM and
ROMN being equal, the solid we are speaking of will be
equal to the cylinder. Cutting this same solid into two
parts by the plane QOMV, which passes through the axis
DC, and whose base QV is perpendicular to the diameter
PR, the large piece OQPBMV will be to the lesser as

47 to 19.
L
P
B
M
A
X
Fig. 1696⚫
E
N
R
Supposing BP=PR, we shall have BL=LD, and DC
CR; consequently if the frustum OLBM is expressed
by 14, its complement OQ RVM will be so by 19; and as
these two solids together equal the half cylinder OQ PL MV,
it may be expressed by the sum of the preceding two
numbers, to which adding that of the frustum, we shall have 47 for the greater part
OQPR MV, and 19 for the lesser O QRVM.

G
A
B
M
Y
L
N
R
N
B
P
S
M
X
H
K
A
D
E
F
Fig. 1698.
B
M


A
R
D
N
Fig. 1697.
Fig. 1699.
To have the sum of all the planes CFHL comprised by the double ordinate CL, and
the element CI of the trapezium ABRD, we must, as in the preceding case, multiply the
superficies of the circle A D by the mean element X Y, serving as the axis of the cylinder
ALND, since this cylinder is equal to the solid of which we are speaking.
CHAP. XVI.
1113
HYDROSTATICS.
As for the solids, fig. 1698. and 1699., for the first we shall have the sum of all the
planes DING by bedding to the solidity of the demi-cylinder ALMHO that of the
frustum OLB M, and we shall have that of the second by taking from the cylinder
EOMNHD the value of the frustum MNRO.
It will be easy to calculate the pressure of water against all sorts of circular surfaces; for
example, if we wish to know that which the superficies of the demicircle ABC sustains,
whose diameter A C answers to the level RZ of the water, we remark that in making the
right-angled isosceles triangle DBE, all of whose elements represent the heights of films of
water, which answer to all the points of the height DB, we shall have the pressure which
acts against the double ordinate FG, by multiplying this line by the corresponding element
IH. Now as the sum of all these products will be equal to the solidity of a frustum,
which would have the demicircle A B C for its base, and the line BE equal to the radius
for its height, this pressure will then be expressed by a volume of water equal to two-
thirds the cube of the radius D B.
If the demicircle were situated in an opposite direction to the preceding, as KLM, we
shall see that since we must, to have the action of all the films of water against the double
ordinates OP, multiply each of these lines by the corresponding element Q R of the triangle
KLN, the pressure which this demicircle will sustain may be expressed by the comple-
ment of a frustum which would have this same demicircle for its base, and the radius for
2 LN
its height. Thus we shall find it by saying 14 is to 19, as is to 19 x L N³, which
3
shows that this pressure is equal to of the volume of water expressed by the cube of the
radius. It follows that if the two demicircles are equal, the pressure which the first will
sustain, is to that which the second will sustain as 14 to 19.

A
D
R
L
F
GO
P
E
B
K
N
M A
D
C
R
M
K
H
GP
F
H
L
Fig. 1700.
2
T
S
If the two demicircles were below the level RZ, as ABCD and HRS, the lines IB and OX
expressing the greatest height of the water, making the isosceles and right-angled triangles
IBN and OX L, we must multiply the double ordinates F G and QT by the correspond-
ing elements HE and PV of the trapezium NK DB and L MRX; then the sum of the
products for the demicircle A B C being expressed by a solid similar to that of fig. 1698.,
we must multiply its superficies by the line DK or DI, which marks the least height of
the water, to have the demi-cylinder, and add thereto that of the frustum, that is to say,
two-thirds the cube of the radius, we shall have the volume of water whose weight this
demicircle will sustain.
As for the other demicircle HRS, as the sum of the products we have been speaking of
will be expressed by a solid similar to that of fig. 1699., we see that to have the pressure
which it sustains, we must multiply its superficies by the line XL or XO to have the
solidity of the cylinder, from which we must subtract that of the frustum, that is to say,
two-thirds the cube of the radius.
Lastly, if we have two circles, one of
which answers to the level DL of the
water, and the other was lower, making the
isosceles and right-angled triangles CDB
and NL M, the sum of the products of the
double ordinates E F, by the corresponding
elements G H of the triangle CDB, may
be expressed by a solid similar to that of fig.
1696. We must, to have the pressure which
the first circle sustains, multiply its super-
ficies by the mean element IK, which is
the radius K D, and which marks the height
of the water above the centre K.
If we recal what has been said, we
shall see that the pressure which the lower

Z
T
G
D
F
R
E
Y
B
Fig. 101.
1114
Book II.
THEORY AND PRACTICE OF ENGINEERING,
demicircle IBZ sustains is to that which the
upper IDZ sustains, as 47 to 19
We shall see in like manner that the sum of
all the double ordinates QR by the correspond-
ing elements OP of the trapezium NSTM
may be expressed by a solid similar to fig. 1697.
To have the pressure which the second circle
sustains, we must multiply its superficies by
the mean element V X, or its equal X L, which
marks the height of the water above the centre
X.
It follows that having a tube AB curved
below to adapt thereto a species of funnel
GECDFH closed by a piston, pouring the
water in this tube to the height K, the power P
applied to the piston will sustain a pressure
equivalent to the weight of a column of water,
which should have the circle E F of the piston
for its base, and the line KB which marks the
elevation of the level of the water above the centre
I for its height, however small the diameter of
the tube may be; thus this power will be in
the same case as if it were applied to the piston
of fig. 1702.
If the preceding surfaces, instead of being
vertical, were inclined, all that we have just said
would still hold good, having shown that the
pressure against both must be measured in the

same manner.
A ST
K
B
It follows, that having an inclined tube ABCD
filled with water, and the bottom AD closed by a
piston, the power applied thereto will sustain a weight
equivalent to that of a column of water having the
circle of the piston for its base, and the perpendicular
EE, which marks the greatest elevation of the water
above the centre E for its height, of whatever form the
tube is, without considering its thickness.
The Centre of Pressure is that point of a surface ex-
posed to the action of a fluid, to which if a force equal
to the whole pressure upon a surface were applied, the
effect would be the same as when that pressure is dis-
tributed over the whole surface. The centre of pressure
coincides with the centre of percussion, which is two-
thirds the height of the body.
B
Since the action of all the films of water against a
surface ABCD may be expressed by the elements of
an isosceles triangle A E D, it is evident that there is a
point M in the perpendicular EF, where a power P G
being applied in the opposite direction, PM, will sus-
tain them all in equilibrio, and if we pay attention we
shall see that this point, which is called the centre of
impression, can only be the centre of gravity of the
triangle AED; whence it follows that the centre of
impression of a rectangular surface ABCD is placed
at two-thirds of the line EF, which divides it into
equal parts, and marks the height of the water.
A
K
D
C
E G
E
B
P
H
G
H
Fig. 1702.
C
Fig. 1703.
F
E
N
K
H
M
Fig. 1704.
Р


To
Regarding only the pressure which the rectangle AGHD sustains, which we may apply
to a lock gate, the water being always at the same height, EE, the centre of impression of
this surface will be the same as the centre of gravity, O, of the trapezium AIDK.
find it let us suppose that the point N marks that of the triangle IEK; then calling
EF, a, EL, b, EO, x, we shall have EM
2 a
3
EN
26
3
>
MN=
2 a 26
and MO
3
3
2 a
3
If, instead of the superficies of the similar triangles IEK and AED, we take the squares
of their perpendiculars, EL and EF, the difference of these two squares, or a a —
bb
CHAP. XVI.
1115
HYDROSTATICS.
will express the superficies of the trapezium AIKD; thus we shall have
aa-bb, bb ::
2a-2b
3
2 a
;
3
2
abb —bs
2 a
whence we have
X
or
a a
bb
3
2012
X
3
a a
abb - br
+ a
bb
Z.
2
abb — b³ + a³ — abb
X
X,
3
αα
A
b b
If we multiply the magnitude a by aa-bb, we shall have
2
or X
3 a² - bb
αα- bs
α
=x: whence we draw the following general rule.
To have exactly the interval from the Surface of the Water to the centre of Impression of u
Lock Gate. Measure the greatest and least height of the water; cube these two
heights; subtract the lesser cube from the greater; take two-thirds of the difference;
divide this quantity by the difference of the square of the greatest height of the water from
that of the least; the quotient will give the answer required.
L
F
F F F
G
B
G Ꮐ C
MA
P
If the height EF were 6 feet, and the lesser, EL, 4 feet, subtracting 64 (the cube of 4)
from 216 (the cube of 6), we shall have 152 for the difference, of which we must take two-
thirds, 101, which we must divide by the difference of the squares of 6 and 4, which is
20; the quotient will give 5, that is to say, 5 feet 10 inches nearly, for the interval E O.
As the centres of impression of circular surfaces are the same as the centres of gravity of
the solids which express these impressions, and
as we cannot have these last centres without
knowing that of the frustum, we must examine
this solid under a different aspect than before.
For this purpose we must consider the solidity
of a right cylinder, ABCD, as composed of
several surfaces E, F, G, H, of an infinitely small
thickness, which pass intersecting from the axis
IK to the great surface A B CD; if we imagine
that the circle which serves as the base to the
cylinder is composed of an infinity of concentric
circles, forming as many rings of an infinitely
small thickness, each of them will serve as base
for the corresponding element of the cylinder.
Following this idea, if we cut the cylinder by a
plane, MLNDOM, passing through the centre
I, and through the extremity, D, of the diameter
A D, this plane will detach a frustum, having for its base the semicircle MLC.
Now, as all the cylinders which pass from the axis to the surface A B C D, have been cut
in the same manner as the preceding, each of them furnishing also a frustum, it follows
that the largest may be considered as being composed of an infinity of other frustums,
similar to each other, all intersecting from the smallest, which answers to the centre, I, to
the largest, and similar to each other, because all the triangles IGP will mark their sec-
tions through the centre; consequently we may consider the frustum which answers to the
great triangle ICD as composed of an infinity of portions of cylindrical, similar, concentric
surfaces of an infinitely small thickness, each of which will be equal to the rectangle com-
prised by the diameter of the demicircle which serves as its base, and by the corresponding
element GP of the triangle ID C.

D
A
E
E
K
H
Fig. 1705.
R
To have the solidity of the frustum in this manner: let A B C be the semicircle which
serves for base: describe the semicircles F GE
and ƒge, near each other; call DB or BI,
a, DG or GP, x, Gg will be dr; thus we
shall have for the differential element of the
frustum FE× G P × Gg (2 x xdx), whose inte-
2x5 2 a³
gral gives
when x=a, for the solidity

or
>
3
>
3
of the frustum.
To have its centre of gravity, we must mul-
tiply the differential solidity 2x xdx by the
radius DG (x), which gives 2 x³ dx, whose inte-
2 x¹ x4 a¹
4
2» 0r
gral is
2a3
3
or
2'
which being divided by
3 a
4
Od
G
P
9
p
D
A
FJ
Fig. 1706.
E
the solidity of the frustum, gives which shows that the centre of gravity of the
frustum is distant of the radius from the centre of its semicircle.
To have the centre of gravity of the complement of the frustum, we only regard the
1116
THEORY AND PRACTICE OF ENGINEERING. · BOOK II.
V
K
E
H
Y
R
Ꭰ
B
semicircle VRQ common to these two solids, and the centre of gravity of the demi-cylinder
that of the frustum and that of its complement being in the
radius Y R, perpendicular to the diameter V Q. We shall sup-
pose that the first is at the point B, the second at the point C,
and the third at the point D; on which we must remark that the
position of the two first is known, for the semicircle V R Q is to
its diameter, V Q, as of the radius Y R is to the interval YB:
the demi-cylinder being composed of an infinity of semi-circles,
all of whose centres of gravity pass through the same line of
direction, we may regard all these circles, or the demi-cylinder
united in the weight P: on the other hand, as we have the posi-
tion of the centre of gravity of the frustum, by making YC equal
to of the radius Y R, we may also suppose its solidity united in
the weight T, and that of its complement in the weight S. Con-
sidering the point B as the fulcrum of a lever DC, round which
the weights S and T are in equilibrio, the first of which is to
the second as 19 to 14, we shall have 19: 14 :: BC; BD=
1 × BC.
If we make an angle YCK at pleasure, taking the
line CE of any length, it must be divided into 19 equal parts;
make E Fequal to 14 of these parts, draw the line E B, and through
the point F draw a parallel to it, ED, which will give the point
D, the centre of gravity of the complement of the frustum, since CE, EF: CB, B D.
Having a solid, as in fig. 1698., composed of a half cylinder, OE AL MH, and a frustum,
OLBM, we shall find in the radius A K the point through which the line of direction of
the centre of gravity of this solid should pass for taking the weight P, fig. 1707., for that
of the half cylinder, and the weight, T, for that of the frustum, we say, as the sum of the
two weights, which is the same as the solid, is to the interval B C, so is the weight T, or
the frustum, to the interval B G of the centre of gravity of the half cylinder to that which
we seek.

Q
'T
S
Fig. 1707.
To find it in the same manner, in the radius KD of the base of the solid of fig. 1699.,
the point through which the direction line of its centre of gravity should pass, we remark
that this solid being composed of the demi-cylinder EQVRDH and the complement
RQOMV of a frustum, we may, by taking in fig. 1707. the weight P for that of the
half cylinder, and the weight S for that of the complement, say, as the sum of these two
weights is to the interval D B, so the weight S, or the solidity of the complement of the
frustum, is to the interval B H, from the centre of gravity of the frustum, to that of the
entire solid.
If in fig. 1696. we take from the cylinder PLNR the equal frustums MN, RO, there
will remain the regular solid P OMVRQO, whose axis, DC, passing through its centre
of gravity, we may suppose this solid united in the weight Y: taking the line DA equal
to the radius DL, the centre of gravity of the equal frustums MBLO or MPLO,
being at the point A, we may also suppose it united in the weight X: we say, then, as the
sum of the weights X and Y, or the solidity of the cylinder PLNR, is to the interval
DA, so the weight X, or the sum of the two frustums, is to the interval D S from the
centre of gravity LN to the centre of gravity of the solid PB R.
Lastly, we may in the same manner find the centre of gravity of the solid represented in
fig. 1697., by subtracting the double frustum O G B M, and making' X Y equal to
3 the
radius, in order to say, as the cylinder ALND is to the interval X Y, so is the sum of the
two frustums to the interval X S from the centre of the semicircle to the required centre
of gravity S.
The
Specific Gravities of Bodies are determined on the principles of hydrostraties.
diminution of the apparent weight of a solid, upon immersion into fluid, affords us an easy
and ready method of comparing its density with that of the fluid: for the weight of the
solid being known previous to immersion, it is then ascertained what quantity it has
lost when plunged into a body of pure water, by measuring the bulk of water displaced:
thus we obtain the proportion of the specific gravity of the body to that of water, which is
the usual standard of comparison: for when a solid is weighed in water it will lose as
much of its weight as is equal to the quantity of fluid displaced; for bodies so plunged
are pressed upwards with a force equal to the weight of the fluid displaced; and as
this force acts in opposition to the natural gravity or absolute weight of the body, its
absolute weight must be diminished by a quantity equal to the weight of the fluid dis-
placed. The weight which the body loses is not destroyed, but is sustained by an equal
and opposite force.
When the specific gravity of a body is equal to that of the water, the part immersed is
equal to the whole body; or, it may be said, the solid will be completely immersed, and
remain wherever it is placed: when the specific gravity of the body is greater than that of
the fluid, it will sink to the bottom, and when the specific gravity of the fluid is greater
CHAP. XVI.
1117
TABLE OF SPECIFIC GRAVITIES.
than that of the body, then the part immersed is less than that of the whole solid, and the
body will float. The specific gravity of the solid is therefore to that of the fluid in which
it is weighed, as the absolute weight of the solid is to the loss of weight which it sustains.
In the following table all the measures are related to that of water, whose specific
gravity is 1.000. To ascertain the weight of either of the substances contained in the
following table, it is only necessary to compare it with the weight of a cubic foot of water,
which weighs nearly 1000 ounces avoirdupois, or more nearly 998. Thus a cubic foot of
native gold would weigh 170,000 ounces, or 1000 multiplied by 17, its specific gravity:
platina, which is one of the densest metals, is 23 times as heavy as distilled water; fine
gold 191; mercury 131; lead 111; silver 11; copper 9; iron and steel 73; stone 21; and
fir timber only half the weight.
This method of ascertaining the bulk of bodies was first discovered by Archimedes: but
in all experiments made it is necessary to consider that a considerable change of the joint
bulk of any two substances tried is often produced by their mixture, and generally their
dimensions are considerably contracted. 18 gallons of water, mixed with 18 gallons of
alcohol, will make only 35 gallons, and therefore the specific gravity of such a compound
is one-thirty-fifth greater than the mean of the specific gravities of the two ingredients:
iron also by an addition of one-eighth of its bulk of platina becomes contracted one-fortieth
of the whole bulk.
A Table of Specific Gravities.
METALS.
Copper, purple, from Bannat
4.956
4.300
Antimony, native
6.720
from Lorraine
4.983
fused
{
6.624
5.467
6.860
glass of
4.9464
grey
4.3
glance
pyrites
5.6
-{
sulphur of
4.9643
white
-
ore grey and foliated
4.368
radiated
4.440
grey
3.750
red
yellow
f4.080
-{
4.344
4.500
4.865
4.5
4·3
4.090
blue
5.670
{
3.2
3.4
Arsenic, native
5.600
foliated florid red
3.950
6.522
fused
8.310
azure radiated
-{
3.231
3.608
bloom
2.640
2.8.50
glass of
emerald
3.5942
pyrites
6.5
muriate of
Bismuth, native
9.570
arseniate, hexaedral
9.756
fused
9.822
9.070
sulphuretted
6.131
ochre
Brass, common cast
Cerite
wire drawn
cast, not hammered
Cobalt, fused
ore grey
-
earthy black indurated
vitreous oxide
Columbium
Copper native
-
from Siberia
from Hungary
4.371
partial arseniate
sulphate, solution sat. 42°
-
7.824
wire
8.544
Gold, native
-
8.395
-
4.5
[7.645
7.811
fused
-
Copper ores, ore compact vitreous
Cornish
}-
5.511
17.721
2.019
2.425
guinea George II. -
guinea George III.
Paris standard 22 carats
17.150
17.629
-
2.4405
5.918
[7.600
7.800
not hammered
same, hammered
-
17.486
17.589
Spanish coin
17.655
Holland ducats
19.352
8.5084
trinket standard 20 carats,
7.728
not hammered
15.709
7.788
same, hammered
-
15.775
8.895
Portuguese coin
17.9664
4.129
French money 213 carats,
·
5.452
fused -
17.4022
3.300
4.4
2.549
octoedral
2.88
trihedral
-
4.2
prismatic
4.2
3.4
1.150
8.878
£17.00
pure, fused, 24 carats fine
same, hammered
-
English standard, 22 carats
fine, fused, not hammered 18-888
19.00
19.2587
19.342
-
1118
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
-
17.6474
of Louis XIII.
-
17.5531
19.500
Iron, native meteoric
-
6.48
7.200
French money, coined
Iridium, ore of
fused, not hammered
Lead, muriate
sulphate
B
-
•
chromate
acetate
vitriol from Anglesea
6.00
6.3
6.00
2.3953
6.300
forged into bars
-{
7.600
glance
7.290
7.788
chromate from Var
4.0326
from Derbyshire
S 6.565
7.786
from Uralian mountains 4.0579
6.886
sulphate sat. solution 42° 1.157
-
7.444
arseniate
3.000
pyrites, dodecaedral
4.830
from Freyburg -
4.682
from Cornwall
4.789
cubic
4.702
4.698
radiated
4.775
compact
crystallised
radiated
-
from the Hartz
Kautenbach
Kirschwalder
4.319
5.052
7.587
-
5.500
7.448
6.140
5.820
magnetic
4.518
ore, corneous
-
6.065
white
4.
reniform
3.920
magnetic sand, Virginia
S 4.600
of black lead
6.745
7.800
4.200
blue
brown
-
5.461
6.974
magnetic
4.900
from Huguelgaet 6.600
4.793
black
-
5.770
5.139
specular ore
4.939
5.218
4.728
lock-head
micaceous
Ironstone, red ochry
5.070
2.952
compact
from Siberia
from Lancashire
3.423
3.760
{
3.573
white from Leadhills $7.236
phosphorated from Wan-
ditto from Zschappau
ditto from Brisgau
red lead spar
yellow molybdenated
-
6.559
6.560
-
6.270
=
6.941
5.750
6.027
-
5.092
3.863
Magnesium, sulphate, sat. solution
compact brown, Bayreuth 3.551
from Tyrol
3.753
42°
native hydrate
1.232
-
2.330
3.503
carbonate
-
2.200
cubic
3.477
5.005
Manganese
[6.850
red hematites
17.000
4.740
4.249
3.951
grey striated ore of
·
4.756
brown hematites
2.789
4.181
4.029
3.640
foliated
red from Kapnich
3.742
·
3.233
sparry or calcareous
3.810
2.0000
3.672
black oxide
3.0000
3.300
decomposed
3.7076
3.600
ditto, penetrated by
black compact
-
4.706
water
3.9039
clay reddle
-{
3.139
scaly
4.1165
3.931
sulphuret
3.95
clay lenticular
2.673
clay, common, from Ca-
white
phosphate
2.8
-
2.6
thina
-
2.936
Mercury, at 32°
-
13.619
ditto from Roscommon
3.471
at 60°
d
13.580
ditto from Carron in
3.205
Scotland
3.357
clay uniform iron ore
2.574
pea ore
5.207
Iron, native (Helenchen Mass)
www
6.723
ore lowland Sprottau
2.944
Lead
11.352
11·445
at 212º
at 3.42 cent.
in a solid state 40°
13.375
13.58597
below 0° Fahrenheit 15.612
in a fluid state 40°
above 0° Fahrenheit 13.545
native
corrosive muriate sat.
-
13.5681
5.00
solution
arseniate
-
6.40
natural calx
-
1.037
9.230
6.00
carbonate
1
17.20
precipitate per se
red
·
10.871
8.399
CHAP. XVI.
1119
TABLE OF SPECIFIC GRAVITIES.
Mercury, native Ethiops
2.233
Molybdena, saturated with water
7.500
Steel, soft
hammered
·
7.8331
7.8404
4.048
hardened in water
7.8103
native
4.667
hammered, and hardened in
4.7385
water
7.8180
Nickel, in a metallic state
57.421
Tantalium metal
·
5.61
·
8.500
9.3333
in large masses
in small pieces
6.291
6.208
6.6086
Tellurium, native
copper
-
6.6481
ƒ 5·700
6.10
7.560
graphic
Kupfernickel of Saxony
ditto of Bohemia
ditto, sulphuretted
Osmium and iridium, alloy of
6.648
yellow
5.7
10.6
6.607
black
-
8.9
·
6.620
-
19.5
Tin, pure from Cornwall, fused
7.170
·
7.291
Palladium
Platinum
wire
11.8
fused and hammered
·
7.291
-
20.722
of Malacca, fused
7.296
10
21.0417
same, hammered
7.306
-
W
a wedge sent by Ad-
miral Gravina to Mr.
Kirwan
a bar sent by the King of
Spain to the King of
Poland
in grains purified by f 17.500
boiling in nitrous acid
of Gallicia
7.063
of Ehrenfriedendsdorf
7.271
20.663
pyrites
ƒ 4.350
4.785
6.300
20.722
stone
6.989
6.750
18.500
black tin stone
6.901
15.601
6.9348
native
17.200
red
-
5.845
fused
14.626
6.970
purified and forged
- 20.336
7.000
milled and purified
-
· 20.98
fibrous
5.800
same, hammered
compressed by a flatting
mill.
Potassium at 150 cent.
Silver, glance
brittle
white
ruby
light red
sooty
native, common
antimonial
auriferous
ore, dark red
arseniated, ferruginous
same, penetrated with water
ore corneous, or horn ore -
virgin, 12 deniers fine 10.474
Paris standard, 11 deniers
10 grains fine, fused
6.450
22.069
new, fused-
7.3013
0.7223
hammered
7.3115
6.910
fine, fused -
7.4789
7.200
hammered
-
-
7.5194
7.208
common
7.9200
5.3
claire etoffe
8.4869
-
-{
5.564
5.5886
ore, Cornish
5.800
6.450
5.443
from Fahlun
6.55
5.592
stone, white
6·008
10.000
4.355
10.333
5.800
9.4406
6'028
10.000
Tungsten
6'066
-
10.600
6.015
[5.684
5.570
-
5.5637
Uranium
7.500
-
2.178
Wolfram
5.705
2.340
Zinc, pure and compressed
7.1908
S 4.7488
14.804
-
in its usual state
by sublimation
sulphate
6.862
-
5.918
-
1.9000
-
10.510
10.175
10.376
same, hammered
Alder
0·8000
-
10.784
Apple
0.7930
shilling George II.
10.000
Ash
0.8450
George III.
10.534
dry
0.800
French money, 10 deniers
Bay tree, Spanish
0.8220
21 grains fine, fused
10.048
Beech
0.8520
same, coined
-
10.408
Box-wood, French
0.9120
Sodium at 150 cent.
0.86507
Dutch
1.3280
Steel
-
7.67
dry.
1.030
saturated solution
1.386
WOODS.
11.20
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Brazil-wood, red
Campeachy or logwood
Cedar, American
wild
1-0310
Alabaster, semi-transparent
2.762
0.9130
stained, brown
2.744
0.5608
Malaga pink
2.8761
0.5608
Dalias
2-6110
Palestine
Indian
0 5960
3.119
1.3150
Allanite
4.001
-
Cherry-tree
0.7150
3.533
Citron
Cocoa-wood
0.7263
3.665
1.0403
Alumine, sulphate
1.7140
Cork
Cypress, Spanish
Ebony, Indian
0.2400
Amber, yellow transparent
1.0780
0.6440
opaque
1.0855
-
-
1.2090
red
1.034
American
1.3310
green
1.0829
Elder
Elm
0.6950
Amethyst
2.750
0.6710
Ammianthus, long
0.9088
Filbert
Fir, male
-
female
Hazel
Jasmin, Spanish
Juniper
Lemon
Lignum vitæ
Linden
Logwood
0.6000
penetrated with
0.5500
water
1.5662
0.4980
short
2.3134
0.606
penetrated with
0.7700
water
-
3.3803
0.5560
Ammianthinite, Raschian
-
2.584
0.7033
Bayreuth
2.916
1
·
1.3330
2.0
Analeime -
0.604
€3.0
0.9130
Andalusite
3.165
Mahogany
Maple
Mastic-tree
Medlar
-
1.0630
Anhydrite
2.95
-
0.7550
Anime, oriental
1.0284
0.8490
occidental
1.0426
0.9440
Anthophyllite
·
Mulberry, Spanish
-
0.8970
Oak, 60 years old, heart
-
1.1700
Aplome
Arcanson
Olive
0.9270
Areterite
-
Orange
0.7059
Pear-tree
Argillite
0.6610
Plum-tree
0.7850
Pomegranate
1.3540
Arragonite
Poplar
0.3830
white, Spanish
-
0.5294
Asbestirite
3.20
3.45
1.0857
3.606
ƒ 2.609
12.680
2.946
2.9267
2.94686
3.000
Quince
0.7050
3.310
Syringa
1·0989
0.6806
Asbestos
Walnut, French
0.6710
10.9933
Yew, Dutch
0.7880
1.2492
Spanish
penetrated with water
0.8070
1.3492
ripe
2.5779
penetrated with water
2.6994
EARTHS AND STONES.
starry
-
3.0733
2.950
Actinolite, glossy
penetrated with water
3.0808
3.903
unripe
2.9958
Agalmatolite
-
2.800
penetrated with water
3.0343
Agate, oriental
-
0.5901
onyx
speckled
cloudy
stained
veined
Icelandic
Havre
jasper
Mocha
iridescent
Alabaster, Valencia
veined
2.6375
Asphaltum, cohesive
1.450
-
2.060
2.607
1.070
2.6253
compact
·
1.165
2.6324
Aventurine, semi-transparent
2.6667
-
2.6667
opaque
-
2.6426
2.348
3.226
2.5881
Augite
3.471
2.6356
3.777
2.5891
Automalite
4.200
2.5535
4.690
2.638
3.213
Axinite or thumerstone
2.691
3.296
Piedmont
•
Malta
yellow
Spanish
2.693
3.250
2.699
Azure stone, lapis lazuli
[2.7675
2.699
2.896
-
2.713
Oriental
2.7714
Oriental white
-
2.730
Siberian
2.9454
CHAP. XVI.
1121
TABLE OF SPECIFIC GRAVITIES.
Barytes or baroselinite
-{
√ 4.400
2.252
Chalk
4.865
12.657
white
-
4-44300
Chrysolite, jeweller's -
2.782
grey
rhomboidal
octoedral
4.4909
2.692
4.4434
4.4712
in stalactites
-
4.2984
4.000
sulphate, native
4-460
Cimolete
4.48141
4.300
Chrysoprase
Brazilian-
Cinnabar, Deux Ponts
Almaden
3.340
3.410
-{
2.489
3.250
-
20
7.786
6.902
carbonate, native
4.338
crystallised
·
10.218
Basaltes
-
2.979
hepatic
-
8.000
Cinnamon stone
-
from Giant's Causeway 2.864
prismatic, from
Clinkstone
Au-
Bdellium
vergne
St. Tubery
Beryl, oriental
occidental
-
2.4215
Corundum, Indian
7.1
2-6
S2.575
2.620
ƒ 3.710
2.7948
1.1377
Chinese
3.5491
2.723
Cryolite
Cube iron ore
·
2.650
aquamarine
spar
-
3.875
3.981
2.957
3.000
2.964
12.759
Bitumen, Judæa
Black coal, pitch coal
slate coal, English
1.104
Cyanite
1.308
1.250
Cymaphane, Chrysoberyl
(3.517
3.622
3.600
11.370
Datolite
13.720
2.98
1.321
2:63
Bielschawitz
L 1.382
Cannel coal
Blende, yellow
1.270
[4.044
14.048
3.770
brown foliated
14.048
3.930
black
-
4.166
auriferous from Nagyog
5.398
Boracite
2.566
Borax
1.714
Bournonite
5.576
Bronzite
3.20
Calamine
[ 3.525
14.100
Carbon, of compact earth
1.3292
veined
transparent
reddish
common
-
2.84
3.5212
3.5310
3.5500
-
3.5238
3.5254
8·4444
yellow
orange
-
3.5185
3.55
2.800
2.673
2.683
2.600
2.723
of Brazil
pseudo
-
3.1555
Carnelian, stalactite
speckled
veined
onyx
2.5977 Euclase
2.6137
Felspar, fresh
2.6234
Adularia
2.6227
pale
2.6301
pointed
2.6120
arborised
2.6133
2.600
Labrador
glassy
-
2.701
3.0625
2.438
ƒ 2.500
2.600
2.607
12.704
-
Cat's-eye
2.625
Fettstein
-
grey
2.5675
yellow
2.6573
black
3.2593
Cerite
4.500
Flint,
Ceylanite -
[3.765
3.793
Chabasite
2.718
-
Chalcedony, bluish
2.5867
onyx
2.6151
1
2.6059
2.6640
2.6645
2.600
{2.655
Fish-eye-stone, ichthyophthalmite
olive
spotted
onyx
Rennes
England
Limosin
veined
Egyptian
Black
-
2.518
2.589
2.563
2.614
2.5782
2.467
2.594
2.6057
2.5867
2.6644
-
2.6538
2.6087
2.2431
2.6122
2.5648
2.582
Gabbronite
2.94
Dipyre
Diamond, oriental, colourless
-
rose-coloured
orange-coloured
green-coloured
blue-coloured
Brazilian
•
Dolomite -
Emerald
-
4 C
1:122
BOOK II.
THEORY AND PRACTICE OF ENGINEERING..
Flint, Gadolinite
-{
4.00
4.20
Hornblende, schistose
2.909
3.155
4.085
3.150
Garnet, precious, Bohemian
4.188
basaltic
3.220
4.230
3.333
4.352
volcanic
Syrian -
docaedral crystals
common
·
Hornstone, or Petrosilex
2.530
2.468
2.653
4.000
جن کے
Gehlenite
-
Girasol
Glance coal, slaty
Glauberite
Granite, red Egyptian
grey Egyptian
beautiful red
Girardmor
violet of Gyromagny
red of Dauphiny
4.0637
[3.576
3.688
2.78
4.000
1.300
{1-530
2.700
2.6541
ferruginous
veined
2.813
2.747
grey
-
2.654
blackish grey
2.744
yellowish white
2.563
bluish and yellowish
2.626
dark purplish
2.638
greenish white, from
Lorraine
2.532
iron shot brownish red
2.813
·
2.7279
Hyalite
2.110
2.7609
4.000
-
2.7163
Hyacinth
4.545
-
2.6852
4.620
-
2.6431
Hyposist
1.5263
green
-
2.6836
Jade, white
2.9592
radiated
red of Semur
grey of Bretagne
2.6678
gum
2.9660
2.6384
olive
2.9829
2.7378
from East Indies
2.977
yellowish
-
2.6136
[3.310
Switzerland
Corinthian blue
2.9564
3.389
Granitelle
3.0626
with boracic acid
2.566
Dauphiny
2.8465
Jasper, veined
2-6955
Graphic ore
5.723
red
-
2.6612
Gypsum, opaque
2.1679
brown
2.6911
compact, in Leskean mu-
yellow
2.7101
seum
2.939
violet
2.7111
f1.872
compact
2.288
grey
cloudy
2.7640
2.7354
impure
2.473
green
2.6274
foliated with limestone
-
2.725
bright green
2.3587
semi-transparent
2.3062
deep green
2.6258
fine
2.2741
brownish green
2-6814
opaque
2.2642
blackish
2.6719
rhomboidal
2.3114
blood-coloured
2.6277
10 faces
2.3117
ony x
2.8160
cuneiform, crystallised
striated, of France
-
2.3060
Jasper flowered, red and white
2.6228
2.3057
red and yellow
-
2.7500
China
2.3088
green and yel-
flowered
2.3059
low
2.6839
sparry opaque
2.2746
red, green, and
semi-transparent
3.3108
grey
2.7323
granular foliated (Les-
red, green, and
kean museum) -
2.900
yellow
2.7492
slaty, mixed with marl
2.473
universal
2.5630
Hauym
3.20
agate
2.6608
2.629
Heliotrope, blood-stone
Jenite
3.80
2.700
4.00
2.633
Jet
1.2590
Hollow spar, chiastolite
2-944.
Iolite
2.56
Hone, white razor
penetrated water
2.8763
Iserine, an oxide of titanium, from
2.8839
Iser
4.500
white and black razor
·
3.1271
Lapis nephriticus
2.894
Honeystone
1.586
hematites
4.360
1.666
judaicus
2.500
3.600
monatis
Hornblende, common
2.270
3.830
hepaticus
2.666
resplendent Labrador
3.350
Laumonite
2.20
-
3.434
Lenticular ore, arseniate of cop-
schiller spar
2.882
per
2.882
CHAP. XVI.
1123
TABLE OF SPECIFIC GRAVITIES.
2.816
Lepidolite
Leucite, or umphigene
12.854
Orpiment
-{
3·048
3.435
2.455
Pearl stone
2.34
| 2.490
Pearls, oriental
2.683
1.3864
Limestone, compact
Peridot, or olivine
2.7200
{
3.428
3.225
2.710
Pharmacolite, or
arseniate of
foliated
2.837
lime
2.6
2.700
granular
green
arenaceous
Lithomarge
Marl
Phosphorite or Sporgel stone,
12.800
without water
2.8249
-
3.182
with water
2.8648
2.742
greenish, from
2.50
Spain
3.098
2.9444
Saxon
3.218
sulphate
native hydrate
Magnesia, saturated solution of
Magnesite, carbonate of magnesia 2.200
new species from Baum-
Phosphorus
1.714
·
1.232
Stone of Volvic
2.320
2.330
Pinite
2.980
6.378
Pitch ore, or sulphuretted uranite 6.530
garten, Silesia
-
2.95
7.500
Malachite
3.572
Pitchstone, black
2.0499
3.641
yellow
2.0860
compact
3.994
red
2.6695
Marble, Carrara
2.716
brick red from Mis-
Pyrenæan
2.726
nia
2.720
block Biscayan
2.695
leek green or olive
2.298
Brocatelle
2.650
pearl grey
1.970
Castilian
2.700
blackish
2.3191
Valencian
2.710
olive
2.3145
Grenadian white
2.705
dark green
2.3149
Siennian
2.678
Roman violet
2.755
Plumbago
[1.987
12.267
African
2.708
Porcellanite
2.30
Italian violet
2.858
Porphyry, green
2.6760
Norwegian
2.728
red
2.7651
Siberian
2.728
French
2.649
Swiss
2.714
Egyptian green
2.668
from Dauphiny
from Cordova
green, from Cordova
hornblende or
2.7933
2.7542
-
2.7278
or-
Florentine yellow
2.516
Meionite
3.10
phites
pitchstone
2.9722
2.452
Melanite, or black garnet
[3.691
mullen
3.800
4.270
sandstone
Menochanite
4.427
Potash, carbonate
Mesotype
2.233
muriate
2.791
Mica
2.546
2.9342
tartrite, acidulous
antimonial
sulphate
{
2.600
* 12.728
2.564
1.4594
1.8365
1.900
Muricalcite, crystallised or rhomb
Potstone
A
spar
Natrolite, Swedish
Nepheline, or somnite
2.480
-{
[2.779
Prasium
2.790
3.2741
Nigrine, or calcareo-siliceous ti- 3-700
tanic ore
Nitre
Obsidian
quadrangular
Octoedrite
Prehnite, of the Cape
of France
Pumice stone, pu
4.445
-14.673
Pyenite, or shorlous beryl
1.9000
Pyrope
2.2460
-{
3.5145
3.718
3.941
2.348
Pyrophysalite
3.450
3.857
Quartz, crystallised brown and red
2.6468
Opal, precious
common
2.114
1.958
brittle
milky
2.6404
-
2.652
2.015
3.750
elastic
-
2.144
2.6240
semi-opal from Telkobanya 2.540
3.225
ligniform, or wood
Realgar, or red orpiment
-
2.600
3.338
2.2460
2.2980
$2.80
-{
3.00
2.5805
2.697
12.9423
2.610
3.9145
4 c 2
1124
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Rock crystal, from Madagascar
2.6530 Serpentine, fibrous, from Dau-
clove brown
2.605
phiny
2.6693
white from Marme-
spotted black and
rosh
2.888
white -
2.3767
European pure ge- ƒ 2·6548
black and
latinous
2.63717
grey
2.2645
Brazilian
2.6526
red and yel-
iridiscent
2.6497
low
-
2.6885
rose-coloured
2.6701
green from
yellow Bohemian
2.6542
Grenada
2.6849
blue
2.5818
deep green,
violet, or amethyst
2.6535
ditto
2.7097
Carthaginian ame-
black, from Daul-
thyst
2.6570
phiny
2.9883
Ruby, oriental
Rutile
pale violet
brown
black
Brazilian, or occidental
spinelle
ballas
Rutilite, or sphene
Sahlite
Sal gem
Sapphire, oriental white
of Puys
oriental
2.6513
green
2.8960
2.6534
yellow
2.7805
2.6536
violet
2.6424
4.2833
of Dauphiny
2.7913
·
3.5311
Shale
2.6
[3.7600
Siderocalcite
2.837
3.5700
Sinople
2.6913
3.6458
Slate, common
2.6718
f4·102
4.246
3.1
penetrated with water
2.6905
whet, or novaculite
0.722
2.609
·
3.5
Isabella yellow
2.955
3.234
stone
2.1861
2.143
fresh, polished
2.7664
3.991
adhesive
2.080
4.076
new
5.8535
3.994
3.1307
3.994
Brazilian
4.283
siliceous
horn, or schistose porphyry
S 2.596
2.641
2.512
12.700
4.000
Smalt
2.440
4.083
Smaragdite
3.00
Sardonyx, puce
pale
pointed
veined
onyx
2.6025
Sodalite
-
2.378
1
2.6060
Spar, white sparkling
2.5946
2.6215
red ditto
3.4378
2.5951
green ditto
2.7045
2.5949
blue ditto
2.6925
arborescent
2.5988
green and white ditto
3.1051
blackish
2.6284
transparent ditto
2.5644
Saussurite
3.260
adamantine
3.873
3.6800
fluor
-
3.1555
Scapolite
3.7000
fluor red, or false ruby
3.1911
Schorl, block, prismatic
3.3636
octoedral -
3.1815
octoedral
3.2265
yellow, or false topaz-
3.0967
enneaedral
3.0926
green, or false emerald
3.1817
black sparry
3.3852
octoedral
3.1838
amorphous, or basaltes
2.9225
blue, or false sapphire
3.1688
cruciform
3.2861
greenish blue or false aqua-
violet of Dauphiny
3.2956
marine -
3.1820
green
3.4529
violet, or false amethyst
3.1757
3.092
violet purple
3.1857
common
3.150
English
3.1796
3.212
Auvergne-
3.0943
Selenite, or broad foliated gypsum
Serpentine, opaque green Italian
penetrated by water
red and black veined
veined black
-
olive
semi-transparent
grain
fibrous
2.322
in stalactites
3.1688
2.4295
pearl or bitter (carbonate,
2.4729
2.6273
and
-
2.5939
lime, and magnesia)
calcareous rhomboidal
calcareous rhomboidal
tubes
of France
2.8378
·
2.7151
in
-
+
2.5859
2.9997
prismatic
2.71409
2.7146
2.7182
and pyramidal
-
2.7115
or flos ferri
CHAP. XVI.
Spar, pyramidal
puant gris
puant noir
TABLE OF SPECIFIC GRAVITIES.
Talc, black crayon
yellow
white
German
2.7141
2.7121
2.6207
2.6747
3.1923
Spodumene, or triphane
of mercury
3.218
black
Stalactite, transparent
2.3239
earthy
opaque
3.4783
penetrated with water
2.5462
Staurotide, staurolite or gnenatite
3.286
common Venetian
indurated-
Steatites, of Bareight -
2.6149
Tantalite
-
1
#
·
a
1125
2.080
2.246
2.655
2.704
2.7917
2.9004
·
penetrated with water
2.6657
Tartar
2.6325
2.700
- {2
- 12.800
2.90
7.953
1.8490
indurated
2.5834
Terra Japonica
1.3980
penetrated
2·6322
Stilbite
-
Strontian, sulphate
Titanite, rutulite or sphene
•
2.50
{
4.102
4.246
3.583
Topaz, oriental
4.0106
3.958
Brazilian
3.5365
carbonate -
Stone sand, paving
3.658
Saxon
3.5640
3.675
oriental pistachio
4.0615
2.4158
Saxon white
3.5535
grinding-
2.4129
cutlers'
2.1113
greenish blue -
red
-
3.5489
-
3.155
Fontainebleau glitter-
Tremolite-
ing
2.5616
[2.9
13.2
crystallised
·
2.6111
Turbeth, mineral
-
8.235
scythe of Auvergne,
mean-grained
2.5638
fine-grained -
2.6090
Ultramarine
coarse-grained
2.5686
Uran glimmer
Lorraine
2.5298
Liege
Mill
Stone, Bristol
Burford
Portland
Ray
Ratten
-
·
2.6356
Turquoise, ivory stained by blue 2.500
calx copper
Uranite, in a metallic state-
sulphuretted-
-
12.908
2.360
2.19
6.440
6.378
2.4835
3.150
Uranitic ochre, indurated
-
2.510
3.2438
2.049
Vermeille, or oriental ruby
4.2299
1
2.496
Vesuvian
S3.575
2.470
3.420
1.981
3.365
St. Cloud
2.201
Siberian
3.339
St. Maur
2.034
3.407
Notre Dame
2.378
Vitriol, Dantzic
1.715
Clicord, from Brochet
2.357
Wavellite, or hydrayellite
2.7000
Rock of Chatillon
2.122
Wolfs-eye, mineral
2.3507
hard paving
Siberian blue
touch
-
prismatic basaltes
quarry of Baurè
of Cherence
2.460
Woodstone
f 2.045
2.945
2.675
2.415
Yttrotantalite
5.130
-
2.722
Yttrocerite
3.447
-
1.3864
Zeolite, from Edelfors, red scintil-
·
2.4682
-
Sulphur, native -
2.0332
fused
1.9907
Sulphuret, triple, lead, antimony,
lant
white scintillant
compact
siliceous
-
2.4868
4.0739
2.1344
2.515
and copper
5.768
4.615
Sylvanite, or tellurite in a metal-
4.666
lic state, fused
6.343
Zinon, or jaryon
4.700
4.107
4.3858
Sylvan, native
5.723
4.4161
6.115
Zirconite
-
4.24
Sylvan ore, yellow
black
- 10.678
Zoizite
6.157
-{
3.26
3.31
4 c 3
8.919
1126
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
CHAP. XVII.
THE THEORY OF THE MOTION OF FLUIDS.
The Theory of the Motion of Fluids necessarily follows the consideration of the laws
which relate to their equilibrium: both Daniel Bernouilli and Huygens supposed that no
force is lost in the communication of motion between different bodies considered as belonging
to any system; and that they always acquire such velocity in descending through any
space, that the centre of gravity of the system is capable of ascending to a height equal to
that from which it descended, notwithstanding a mutual action between the bodies: an
elastic ball, for instance, weighing 10 ounces, descending from the height of a foot upon
another of 1 ounce, in such a manner as to lose the whole of its motion, the smaller ball
will acquire a velocity capable of carrying it to the height of 10 feet. These laws with
certain restrictions are applicable to the motion of fluids.
We are indebted to Archimedes for the first theory upon floating bodies; he established
the principles that the parts of a liquid least pressed are impelled by those which are more
so, and that each part is always pressed by the weight of its corresponding column; also,
that a body impelled by a fluid is driven in a vertical direction through its centre of
gravity: such were the established laws with regard to fluids upwards of two thousand
years ago, since which time a third principle has been discovered, viz. equality of pressure
in every direction, that is, if a pressure be applied to any point on the surface of a fluid, it
is equally transmitted to all other points in that liquid.
On the Measurement of Waters which flow through Tubes or Reservoirs. To establish the
principles which are the object of this proposition, we must remark that the portions of water
enclosed in the vessel press mutually in every direction with equal forces in each horizontal
bed; and that if any escape by an opening made in the bottom, all other portions with which
it is surrounded hasten to flow on this side with a certain gradation of velocity, dependent
Now as
on the force of those which follow, or on the weight with which they are loaded.
the force which presses on the surface of the water to make it descend may be regarded as
nothing, with respect to the pressure sustained by the film which serves as the base of a
column of water answering to the orifice, we cannot say that it is this column which escapes,
and is continually renewed by the surface, but that generally all contained in the vessel
rushes to the orifice.
B
C
To make this clear, suppose a vessel ABCD filled with water to the height IK, if we
plunge a tube EFGH open at both ends to the bottom, its surface will be pressed in
horizontal directions with equal and opposite
forces, intersecting according to the order of the
terms of an arithmetical progression. For
tracing on the sides EF, GH of the tube the
right-angled and isosceles triangles FES and
GHT, their elements will represent the action
of the water against the outer surface. As the
point X will be pressed with a force expressed by
the element VX, and the point Y opposite to the
preceding with a force expressed by the height
FY equal to VX; and it will be the same with
all the other points taken in the same horizontal
bed LM; we find that the water of the vessel will
make as much effort to enter the tube, as that in
the tube will to escape,
As the extent of the base AD is indifferent to
the pressure of which we have been speaking, it

L
A
XY
M
Fig. 1708.
D
E
HR
will be seen that if the vessel were itself a tube, O FQ R, a little larger than that in which
it is plunged, the surface of the latter will always be pressed with the same force, however
small the difference between the two circles OR and EH, provided their circumferences
do not join.
If the middle tube be suppressed, so as only to regard the column enclosed therein, the
surface will be pressed by the water with which it is surrounded with the same force as
that of the tube was to know the ratio of this force relatively to the action of the
weight of the column on the bottom of the vessel, let r be the radius, NH, of the circle
CHAP. XVII.
1127
THEORY OF THE MOTION OF FLUIDS.
hh c
for the pressure which the surface sustains, and
hhc rhc
2
EH, c its circumference, and h the height EF of the water. Thus we shall have
rhc
2
2
for its weight; whence we have
2
:h, r, which shows that the effort made by the water of the vessel to occupy
the place of the column, is to the inclination of this column to descend, as its height is to
the radius of its base. Hence we may conclude that when the height of the column
exceeds its semi-diameter, the portions of the water which compose it can never escape
altogether by an opening equal to its base, because the force with which it will tend to
descend will be less than that of the water which seeks to replace it: thus showing that
during the time of flowing the column will always have the same weight, since the parts
which escape will instantly be replaced by others.
It follows that when water in a vessel is continually maintained at the same level, that
which escapes by an orifice made in the bottom will always have the same velocity, since
it will be driven by the whole weight of the column, which presses it, and which we may
regard as a constant force acting uniformly on the whole extent of the orifice.
The same will not take place with water in a straight tube, which voids itself by an
opening equal to the base, because it falls in one piece, like a cylinder of glass, that is to
say, that in issuing it has at first a very slight velocity, which increases like that of heavy
bodies, from the instant of its fall. As the water of the column is not replaced either
from the top or sides, its surface answering immediately to that of the vessel, it is in the
position of all heavy bodies, and consequently follows the law of their accelerations, not
meeting any circumstance which can cause a change in its fall. The time which such a
tube would take to empty itself totally will be equal to that required by a body in
descending freely through the same space which the upper surface of the water goes over
in the tube.
Since we can always render a retarded or accelerated
velocity uniform, by taking half the great velocity, we
may apply the rule when we wish to compare the ex-
penditure of a tube such as the preceding with that of
another always maintained full.
Fig. 1709. If the surface of the water contained in
a tube or reservoir, after having remained during a
certain time at the same level BC, was then at the level
FG, notwithstanding the expenditure through the
orifice EH in the bottom of the vessel: its uniform
velocity in the first case would be to its uniform velocity
in the second, as the square root of the height I E is to
the square root of the height K E.
Fig. 1710. When in two reservoirs of different heights,
the orifices O, O are unequal in superficies; the small
prisms of water which issue therefrom in the same instant
may be expressed by OV and ou, because they can only
have for base that of the columns which impel them,
and for height the space which a film detached
from the same columns may go over with a
uniform motion in this instant. As these spaces
will be in the ratio of the velocities exercised
in the same instant, the velocities may hold
the place of spaces, since in this case the
question is only of the ratio of these prisms.
As the columns of water which the orifices
would expend in two different times T, t, will
contain as many times the small prisms OV,
ou, as the number of instants that elapse in
the duration of time T, t, we shall have

L
B
F
A
E
H
Fig. 1709.


F
K
M
-
T
ov,
m
M m
and
=ow; whence we have
: OV,ou,
t
T' t
Mou
T
m OV
t
or Motu =
B
G
D
which gives
m OTV, or a general formula comprising the
masses or quantities of water, their velocities,
the time of their flowing, and the size of the
orifices; that is to say, all the circumstances which enter into the measurement of the water.
Fig. 1710.
4 c 4
1128
BOOK II,
THEORY AND PRACTICE OF ENGINEERING.
E
To facilitate the calculations upon the ex- A
penditure of water, Belidor has furnished some
excellent tables relative to the uniform velocity of
the falls during a second of time, constructed in
arithmetical progression. The parabola A D C, the
axis of which, A B, is supposed to be 15 feet, and
its greatest ordinate, BC, 30 feet, was the figure
adopted: the ordinates E F, G H, &c., express the G
expenditure at the several heights.

B
Fig. 1711.
F
D
H
For the quantity of water discharged over a weir
Mr. Eytelwein represented the velocity, which
varies as the square root of the height, by the or-
dinates of a parabola, and the quantity of water
discharged by the area of a parabola two-thirds of
that of the circumscribing rectangle: hence the
quantity of water discharged may be found by
taking two-thirds of the velocity due to the mean
height, and allowing for the contraction of the vein.
On the Manner of estimating the Waste caused by the Edges of Orifices. As water flows
more swiftly towards the centre than at the edges of orifices, being retarded by the fric-
tion they occasion, less will issue from an orifice during a specified time, than would be
the case if all the threads had uniform velocity; consequently the expenditure stated
in the preceding calculations is greater than in actual experience, and this difference in-
creases as the orifices become less, because the circumferences of circles being to each other
as the diameters, while their superficies are as the square of these diameters, the small
orifices, having more circumference in proportion than large ones, the velocity of water with
relation to its quantity will be proportionably retarded.
(
To find this ratio, we must take the squares of the diameters for the superficies of the
orifices, and the sides of these squares as their circumferences: thus calling a the diameter
of the lesser, and b that of the greater, we shall have for the ratio of the circuit of the
α
αα
irst to its superficies, and the ratio of the circuit of the second to its superficies, which
b
bb
1
reduces it to
α
and };
1
ㅎ
​whence we have
1 1
a b
:b, a, since
a
a b
ō'
or ab=ab, which shows that
the ratio of the circuit of the first to its superficies, is to the ratio of the circuit of the second
to its superficies, as the diameter of the second, to the diameter of the first.
It follows that the ratio of the decrease of the first orifice to its natural expenditure will
be to the ratio of the decrease of the second to its natural expenditure, as the diameter of
the second is to the diameter of the first. By natural expenditure it must be understood
that which is found by rule, without considering accidental circumstances, and by waste,
the excess of the natural expenditure above the effective, found by experiment.
When the ratio of the waste to the natural expenditure of any orifice is determined by
experiment, we shall have the ratio for any other orifice thus: as the diameter of the given
orifice, is to the diameter of that of the experiment, so the ratio of the waste to the natural
expenditure found in the experiment, is to a fourth term, which will give that required.
M. Mariotte states in his "Traité du Mouvement des Eaux" that he has proved by a
number of experiments that from a horizontal orifice, three lines in diameter, 13 feet above
the surface of the water, 14 pints or 28 lbs. issued in one minute.
Let the circle AB represent an orifice, divide its diameter
at the point C in the ratio of the effective expenditure to the
waste: calling AB, a, and CB, b, the square DB (aa) will
express the natural expenditure, the rectangle FB (ab) the
decrease, and the rectangle DC (aabb) the effective ex-
penditure. In like manner, calling d the diameter of another
orifice, dd will express its natural expenditure, and as the
decreases are to each other in the ratio of the diameter, we
shall have a, d: ab, bd; whence we have dd-bd for the ex-
pression of the effective expense of the second orifice.
If we take a a-ab and dd-bd to express the ratio of the
two orifices, and Mm to express that of their expenditure, we
shall have M, maa-ab, dd-bd, when the times are
equal, and the reservoirs the same height. Calling V the
velocity of the water at the orifice, whose expenditure is ex-
pressed by M and T, the time of flowing, u the velocity of the
water of the second reservoir, whose expenditure is expressed

D
C
B
F
E
Fig. 1712,
CHAP. XVII.
1129
THEORY OF THE MOTION OF FLUIDS.
aa-ab × TV, dd-bd × tu,
orifices, the times, and the
by m, and t the time of flowing, we shall have M, m:
since the expenditures are in the compound ratio of the
velocities; whence we have aa-ab× TV m=dd-bd × tu M, which formula will give that
of the four required dimensions d,m,t, u.
If we wish to ascertain the diameter of the orifice of a reservoir whose height or velocity
is given, in order that it may effectually expend in a given time a determined quantity of
water, designated by m, taking the mean of all the other quantities comprised in the formula,
we shall substitute a for d, to have a a-abx TVm-xx-bxx tu M, which will be reduced
to 1 b +
bb TVm
+
4 tu M
×(aa−ab)=x.
If the diameter of the orifice, the height of the reservoir, or the velocity of the water,
and the time are given, and we require the effective expenditure, we must substitute x in
dd-bd tu M
place of m, to have a a-ab x TVx-dd-bdx tu M; whence we have x =
Xx
aa-ab TV
If the diameter of the orifice, the effective expenditure, and the times are given, and we
wish to know the velocity of the water per second, in order to deduce the height of the
aa-ab TVM
reservoir, we must put x in place of u, to have
dd-bd t M
X
—X.
When similar quantities have the same value, we must efface them from the formula,
which will render the calculation more easy. For example, it is required what diameter
should be given to the orifice of a reservoir, 13 feet high, in order that its effectual expendi-
ture per
M 4
יך
minute may be quadruple that of M. Mariotte; as we have T=t, V=u, and
m
14aa-4ab bb
1
b
9
+
-
+
4 2
x, having a=3 lines, b≈
and
10
the equation will be changed into
812
9
20
; making the calculation we shall find that the diameter required should be nearly
5 lines instead of 6, which appeared to be that required.
To show that the orifice just found will effectively expend quadruple that of the ex-
periment; as 9 (the square of the diameter of 3 lines), is to 304 (the square of the diameter
just found, 51 lines), so 4 lbs. of water (the natural expenditure of the first orifice), is to the
natural expenditure of the second, which will be 134 lbs. To subtract the waste, multiply
the denominator by the diameter 5½, we shall have for the ratio of the waste to the na-
tural expenditure: then, as 55 is to 46, so 1343, the natural expenditure of the second orifice,
is to its effective expenditure, which will be 1124 lbs., a number quadruple 28; that is to say,
the effective expenditure of the first orifice, neglecting the four ounces arising from the dia-
meter having been estimated at a little more than it ought, by supposing 4.
We shall have with geometrical precision the
required diameter by constructing the equation
✓
bb b
4 2
4aa-4ab+ + X.
For this purpose we must
draw the line AB equal to 2a; prolong it from B to
C, so that B C may be equal to 2b; describe on AC as a
diameter the semicircle A D C; elevate the perpendicular
BD, whose square will be 4ab; raise also on the ex-
tremity A the perpendicular A F equal to draw the
bb
4
ს
គួរំ
line FB, whose square will be 4aa+ ; describe on
this line the demicircle BHF; make BH equal to
49
Του

D
A
B
G
F
H
Fig. 1713.
BD; then draw the line FH, which must be prolonged from F to G by the length
FA; then the line GH will be exactly the diameter required, since we shall have
b
✓ FB (4aa+b). - BH² (4 ab) + G F
GF(2) =
-
GH (x).
Of whatever figure the orifices may be, whether similar or not, their natural expenditure
being always in the ratio of their superficies, and the wastes in the ratio of their circuit, it
follows that when the superficies are in the ratio of the circuits, the natural expenditure
will be as the decreases, and this happens when one of two orifices is a circle, and the other
cd
the square of its diameter; for calling d the diameter, and c the circumference, will be the
4
1130
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
cd
4
superficies of the circle, and 4d the circuit of its square; whence we have : dd C, 4d,
which shows that the ratio of the waste to the natural expenditure of a square orifice three
lines square may further be expressed by. Thus when we wish to know the proportion
for any square orifice, we must multiply the denominator of by the side of the square
reduced to lines: for example, for a square of an inch, we shall have
On the Measurement of the Water flowing through rectilinear and
9
or
3
10 x 12' 40°
vertical Orifices.

H
I
K
L
F
G
Fig. 1714.
It has been demonstrated that a prismatic vessel continually filled with water has each of
its faces pressed in a horizontal direction by the films of water which it sustains; conse-
quently, if this surface be pierced with several holes, H, K, &c. in the vertical E F, the water
in issuing will be driven in horizontal directions, with velocities which may be expressed
by the roots of the heights EH and EK, or by the corresponding ordinates HI and KL
of a parabola EIG, since the property of this curve gives √EH, √EK: HI, KL.
Supposing the perimeter of this parabola 60 feet, the ordinates HI and KL will express,
not only the ratio of the velocities of the water, but also the real velocities per second of
the threads which issue through the small holes H and K: then knowing the heights
EH and EK in feet, inches, and lines, we shall have, by the assistance of the first table,
the values in feet, inches, and lines of the ordinates HI and KL.
It follows, that if all the threads of water which issue through one of the orifices H or K
have the same velocity, the natural expenditure per second will be equal to a column which
would have for its base the plan of the orifice, and for height the ordinate which answers
to it.
If we suppose the axis E F of the parabola ELG divided into an infinity of equal parts,
they will compose an infinite arithmetical progression, or the smallest term of which will
be zero, and the greatest the height E F of the water, which will express at the same time
the number of terms of this progression. Drawing through each point of the division an
ordinate HI or KL, beginning from the summit E, all these ordinates being in the ratio
of the roots of their abscissæ, or those of the terms of the progression of the parts of the
axis, the sum of all these roots will be found in the same manner as those of the ordinates
which compose the superficies of the parabola, by multiplying the axis E F by two-thirds the
greater ordinate FG. We shall have also the sum of all the roots of the corresponding
abscissæ, or that of all the terms of the progression, by multiplying the axis E F by 3√EF,
2EF
or ✔EF by 3
E
M
N
17.
m
2 €
To demonstrate the same rule, independently of the parabola,
let us consider the right-angled isosceles triangle E F G, whose
height E F being taken for that of the water, all the elements MN
will compose the terms of the preceding progression, or all the
different heights of the water, taken from its level to the bottom
of the vessel. To have the sum of the roots of all these elements,
call E F, h; EM, x; thus Mm will be dx, which being multi-
plied by ✔r will give dx√x=xdx for the sum of the roots
comprised in the differential plane Mm Nn, the integral of which
gives x, or 3x × √x, or 3h × √h, when x becomes equal to h.
If a fluid, according to Mr. Vince, issues from a cylindrical or
prismatic vessel whose horizontal section is everywhere the same,
and in which the fluid is always maintained at the same height, the orifice will discharge
twice the quantity contained in the vessel, in the same time that the vessel would have
emptied itself. As the surface of the fluid is uniformly retarded, and as its velocity becomes
nothing at the bottom, the space which the descending surface would describe with the first
velocity, continued uniform during the time that the vessel takes to empty itself, is twice
the space that the surface really describes in the time in which the vessel empties itself: in
this time, therefore, the quantity of fluid discharged in the former case is twice that which

F
Fig. 1715.
CHAP. XVII.
1181
THEORY OF THE MOTION OF FLUIDS.
is discharged in the latter, as the quantity discharged when the vessel is kept full may be
measured by what would be the descent of the surface, if it could descend with the velocity
with which its descent commences.

When a vessel ABCD is pierced at the
bottom and the water is only maintained at
the height GH, it does not, in issuing out,
always entirely fill the hole D F, but leaves
a void in the middle, forming a funnel
MIQLOP, which gives place to a cir-
cular jet, whose total expenditure per second
is equal to a volume of water, comprised
by the hole EF, the height IK, and the
line which expresses the velocity acquired
by a fall of the height IK.
This jet only issues when the sum of
the velocities of the water tending to re-
place that of the column in the middle is
less than the uniform velocity of the same
column.
G
B
A
K
When a horizontal orifice NO is at the extremity of a
curved tube EPLM, the height IQ of the surface G H of
the water, with regard to the diameter of the orifice, is of no
consequence, because the curved part TPVM L of the tube
being filled, the air which answers to the level GH cannot
issue through the orifice; but although the water be main-
tained at the level GH, its velocity will not always be ex-
pressed by the root of the height IQ, because the diameter
of the orifice NO, that of the valve X Y, the height IQ,
and the height IK of the level of the water above the bot-
tom A D of the reservoir, may be such that the water may
not be sufficient for the orifice for whatever be the height
of the line I Q, the reservoir will not furnish more than can
issue by the hole XY; and for the jet to act fully it is ne-
cessary that the square of the diameter NO of the pipe,
and the root of the height IQ of the level of the reservoir
above this pipe, should be at least equal to the product of the
root of the height GA or IK of the water in the reservoir
multiplied by the square of the diameter XY; that is to
say, these four should be reciprocally proportionate.
:
F
E
G
A
R
N
P
Fig. 1716.
E
F
R
S
C
L
H

P
T
N
L
H
It is therefore not surprising that reservoirs considerably
elevated above the issue pipe frequently form jets of little
height, and very short of the proportion which they should
have; for the passage of the water on the grating being
always much less than the circle of the conduit pipe pre-
vents the tube from being always full, and keeps the water
at one height, RS, because the grating will only furnish a certain quantity which will cause
the expenditure of the orifice to be relative to ✅R P, and not to ✔IQ.
When the summit of a rectangular orifice is
above the level of the water, as MK LN, the
sum of all the velocities of the films of water
which issue from it may be expressed by the
elements of the parabolic segment FHIG, and
there will be a mean, OT, which being multi-
plied by the height HF will give a product
equal to the superficies of this segment. As
the portion of this element will determine the
mean height EO, the following method may be
adopted.
Calling E F, a; EH,b; HF, c, and the mean
height EO, x, the sum of all the velocities of
which the films in the height EF are capable
a, and the sum of all the veloci-
2 a
will be
3
ties of the height E A will be ✓b; consequently.
2b
3
V
Fig. 1717.

1
KH
R
G
T
D
F
M
Fig. 1718.
2 a
26
α
ō will give the sum of
3
3
all the velocities issuing from the orifice, which being equal to the product of the mean velocity,
1132
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
✅E O, (~), multiplied by the height HF, (c), we have 2/a-2
squared gives a³ − § × 2 ab √ ab+1 b³ = ccx, or 1 ×
3
α
3
✓b=c√x, which being
a³ + b³ — 2ab✅ab
Сс
=x; whence we have
a³ + b³ — 2 ab√ab
Сс
9, 4::
, x, or, 9 is to 4, as the sum of thecubes of the greatest and least
height of the water relatively to the orifice, minus twice the square root of the product of
these two cubes, the difference divided by the square of the height of the orifice, is to the
mean required.
If the height E F (a) be 8 feet, the height EH (b) 6, the height HF (c) will be 2 feet;
we shall then have 512 for the first cube, and 216 for the second, the product of which gives
110592, from which extracting the square root we have 332, twice which is 665, which
being subtracted from 728, the sum of the two cubes, there remains 62, which divided by 4,
the square of the height of the orifice, gives 1528 for the third term of the proportion: then
as 9 to 4, so is 1528 to the height required, which will be 6 feet 11 inches 10 lines.
Another and more simple method of finding the mean velocity of water from a rectan-
gular orifice is to seek the velocities which answer to the greatest and least height of the
water; multiply each of these velocities by its fall, subtract the second product from the
first, take the difference, and divide this quantity by the height of the orifice; the quotient
2383
will give the required velocity.
When the orifices are tra-
peziums whose sides BC, AD,
are parallel, having their sum-
mits at the level of the water,
the expenditure of the first will
be obtained by multiplying
two-thirds of the rectangle
EBCF, plus two-fifths the
sum of the triangles AEB,
FDC, by the greatest velocity
of the water; and the expen-

B
CA
D
E
F
G
H
A
E
بنا
D
B
C K C
A
Fig. 1719.
diture of the second by multiplying two-thirds the rectangle BEFC, plus four-fifths the
sum of the triangles A E B, FD C, by the greatest velocity.
If the two triangles CE A in figures 1719. and 1720. do not answer to the
level of the water, the summit of the first and the base of the second being below
the summit B of the parabola, multiply the elements of these triangles by the cor-
responding ordinates of the parabolic segment A E F D. Calling the perimeter of
the parabola p, A D, a, the base CA or CE, b, BE, c, EA, h, BA, n, E F, q, EH, x,
b x
HI, y, we shall have, on account of the similar triangles, h, b: x,
h
bxudx
h
GH, which
for the differential of the solid; and as we have
being multiplied by ydx gives
b x y d x
in
h
yy-pc
pc+px=yy, or x =
Ρ
2by dy-2pbeyydy
will give
pph
whose differential is dx
2 ydy
putting the values of x and dx
p
whose integral is
2 by5 2b cy³
5pph
3 ph
; and putting in

26
place of y5 and y³ their value will give
5 h
X C X X pc+px
2bc
3 h
x+
pc+px=
26
8
X
5h
(c+x)° /pc+px
2b c
xe+
3h
2 bcc
2bcc
5 h
pc-.
pc=
3 h
4 b c c q
15h
pc+px; and supposing x=0, there remains
which being added with the contrary sign gives
26
2 b c
5 h
xc+x²√pc+px - 3 h
xc+x
pc + px +
4 b c c q
15h
When a becomes equal to h, we shall have c+x=n, and√pc+px=a; therefore, by substi-
tuting these values, we shall, after reducing the terms to the same denomination, have
b
15h
× 6 ann + 4 ccq+10 acn, for the most simple expression of the solid; so that to have the
expenditure of a triangular orifice whose summit is below the level of the water, we must
first multiply the greater velocity, A D, by six times the square of the height BA of the
water; secondly, multiply the least velocity, E F, by four times the square of the height, BE
CHAP. XVII.
1133
THEORY OF THE MOTION OF FLUIDS.
of the level of the water above the summit of the orifice; add these two products together;
thirdly, multiply the greater velocity, A B, by ten times the rectangle comprised by the
whole height, BA, of the water, and by the part, BE, which marks its level above the sum-
mit of the orifice; subtract this latter product from the sum of the two preceding, mul-
tiply the difference by the base, C A, of the orifice, and divide this last product by five times
the height, EA, of the orifice.
On the Measurement of Water flowing through vertical and circular Orifices. The solid
under consideration must be regarded as formed by the sum of the products of the elements
of a semicircle, and by the corresponding ordinates of a parabola, because the diameter of
the semicircle being vertical, this solid will be exactly half that which expresses the dis-
charge of the entire circle: given a semicircle A E B, and a semi-parabola A FD, whose
axis is the diameter A B; re-
quired the solid formed by the
sum of all the planes comprised
by the elements, LP, of the
semicircle, considered as the
breadth of the planes of water,
and by the corresponding or-
dinates PM, which express the
velocity of these planes during
a determinate time; by calcu-
lation we find that the solid is

16
1g of the parallelepipedon com-
K
E
H
L
M
F
E
C
A
B
D
Fig. 1720.
prised by the square of the radius and the greater ordinate, or, which is the same thing, 13
of the parallelepipedon comprised by the square of the diameter and the greater ordinate :
therefore, to have the entire discharge per second through a circular orifice whose summit
is on a level with the water, take of the product of the square of the diameter, multiplied
by the velocity of which a body is capable per second, and which it has acquired by a fall
equal to the diameter of the orifice.
To have the discharge from an orifice in the form of a quarter circle, as A E C, multiply
the square of the diameter by four times the velocity, B D, answering to the extremity of
the same diameter; subtract from this product that of the square of the radius, multiplied
by 14 times the velocity of the centre, and part of the difference. The square B D being
twice CF, BD will be to CF as the diagonal of a square to its side, or nearly as 7 to 5;
wherefore the discharge of the upper quarter circle is the volume of water, which has the
square of the radius for its base, and the greatest velocity during the time of flowing for its
height, and the discharge from the lower circle is two-thirds the same volume; thus these
two are as 5 to 3.
To find the discharge from a quarter circle whose diameter is at the level of the water,
multiply the square of the radius by half the greatest velocity of the water during the time
of flowing, and by the entire velocity if that of a semicircle be required: in the first case
the fall is the radius, and in the second the diameter of a circle; thus the two velocities are
nearly as 7 to 5, or, by more accurate calculation, when two equal semicircles are disposed as
FKH and PLM, the expenditure of the first is to that of the second in equal times, as
25 to 28.
To find the discharge per second from a vertical and circular orifice above the level of
water, multiply the least height, EA, of the
water by 29, and divide the product by 37 for a
first quotient; multiply the diameter of the
orifice by 18, and divide the product by 85 for
a second quotient: cube the diameter of the
orifice, and divide the cube by the product of
72, multiplied by the square of the least height
of the water for a third quotient; square the
diameter of the orifice, and divide the product
by 28 times the least height of the water for a
fourth quotient: subtract the fourth from the
sum of the three other quotients; multiply
their difference by the product of the square
of the diameter of the orifice multiplied by
60; divide this product by the velocity ac-
quired by a body in a fall equal to the least height of the water; the quotient will be the
expenditure required.

Fig. 1721.
On Fluids flowing through Orifices under a constant Pressure. At the bottom of a vessel
abcd, is a horizontal orifice, gh, through which the liquid contained in the vase flows out :
required the quantity that will flow out under a constant given pressure em. To resolve
this question, adapt the given vessel to a reservoir A BDC, whose height, A C, is less than
1134
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
that of a column of liquid which measures the atmospheric
pressure. The reservoir is inclined on all sides, only com-
municating with the external air by the tube em, which is
open at the two ends, and whose lower extremity, e, is in a
horizontal plane drawn through a given point: the re-
servoir and the vase abcd being full, if the orifice gh be
opened, the liquid will flow through it, and sink below
the bottom, cd, of the reservoir; at the same time the
atmospheric air will enter by the tube em, and replace
the liquid: the point e of the bed, eƒ, of the liquid supports
the atmospheric pressure, each of the points of the same
bed supporting an equal pressure, there being two variable
pressures, owing one to the elastic force of the air, more or
less diluted, which presses the upper surface of the liquid,
the other to the height of the liquid above the same point;
whence it follows that the liquid contained in the reservoir will
flow through the orifice gh, under a constant pressure, em,
as long as the level of the liquid is above the bed lef.
C
A
m

n
D
B
a
Fig. 1722.
To refil the reservoir shut the orifice gh, open the top or stopper placed on the upper
part of the reservoir; after having filled it shut the stopcock, and again open the
orifice gh.
the
A
Ꭰ
ס
Z
R
B
V
H
Of the lateral Communication of Motion in Fluids when at rest.—Venturi, Professor of
Natural History at Modena in 1798, gave an account of his investigations on this subject,
and was almost the first of modern philosophers who turned his attention to it.
To prove
that the motion of a fluid is communicated to the lateral parts which are at rest, he intro-
duced the horizontal cylindrical pipe AC into the
vessel DEF B, filled with water as high as DB; op-
posite, and at a small interval from the aperture C,
was the commencement of a small rectangular channel
of tinned iron, SM BR, open at the top, SR, the
inclined bottom M B resting on the edge of the vessel
B. The breadth of the channel was 24 lines
diameter of the tube AC 14; it was inserted in a
reservoir, and the water kept at a certain height;
when the water of the reservoir was permitted to flow
through A C, the current rose along the channel M B,
and rushed out of the vessel, producing a current BV
in the vessel DEFB; the fluid was carried into the
channel SR, and issued at B along with the water in
the reservoir; in a few seconds the water, D B, fell to M H.
Light bodies placed near a stream of water issuing from a reservoir exhibit a similar
effect; they are impelled by the air which descends with the stream. The lateral parts
of a fluid by these experiments are proved to be carried along with any stream that flows
through it, and consequently the motion is communicated to the lateral parts, which
are at rest. This principle Venturi applied to explain the theory of the water-blowing
machine, and also to show that the eddies in rivers are caused by the motion communicated
from the more rapid parts of the current to the lateral and tranquil portions: he also
exhibited a method of draining a piece of ground on a lower level than the current, which
has been tried with some success, by means of a fall of water without the aid of
machinery when a vessel is filled with a fluid, and is at rest, or in equilibrio, all the
particles of the fluid are equally pressed in every direction; but when a small hole is made
at the bottom or in the side of the vessel, the fluid immediately over it will descend by the
force of its own gravity.

F
E
Fig. 1723.
In a vessel allowed to empty itself by a hole at the bottom, the surface of the fluid pre-
serves its level state until it comes to within half an inch of the bottom, when a funnel-
shaped cavity appears on the surface; when it issues from a hole in the side of the vessel,
it preserves its level until lowered to the upper edge of the hole, when it inclines a little,
and assumes a hollow form. The particles of a fluid move towards the hole in directions
which converge to a point outside the orifice, so that the column of fluid which
issues from the vessel must have a smaller diameter than the orifice itself; Sir Isaac
Newton, who first observed this effect, called it the vena contracta, or the contraction of the
fluid vein. The distance from the orifice, where the greatest contraction takes place, is
equal to half the diameter of the hole; and the area of the section of the vein at this place is
to the area of the orifice, as 10 to 14'14 according to Newton, or 10 to 16 according to
Bossut, who also noted that with a short cylindrical tube, applied instead of a mere aper
ture, the vena contracta was to that of the orifice as 10 to 12.3.
The pressure of the atmosphere increases the expenditure of water through a simple
CHAP. XVII.
1135
THEORY OF THE MOTION OF FLUIDS
cylindrical tube, when compared with that which issues through a hole in a thin plate,
whatever may be the direction of the tube; this Venturi has proved upon the principle of
vertical ascension combined with the pressure of the atmosphere, a heavy fluid moving in a
descending cylindrical pipe accelerating its motion: the lower particles have a tendency to
separate themselves from the upper, and thus cause the pressure of the atmosphere to
increase the velocity of the upper; this cannot take place in an ascending or horizontal pipe,
though the pressure of the atmosphere in such cases increases the velocity of the fluid
within the pipe. In descending cylindrical tubes, the upper ends of which have the form
of the vena contracta, the velocity of the effluent water corresponds with the height of the
fluid above the lower extremity of the tube. A descending tube applied to a reservoir
increases the expenditure, as was remarked by Frontinus, De Aquæduct, "Calix devexus
amplius rapit.”
F
Let B LKO be a conical tube having the form of the vena contracta, the cylindrical
tube LCQK having the same diameter as the contracted part LK; the fluid stratum LK
continuing to descend through the height LC, will have its
motion accelerated in the same manner as all other bodies falling
by the force of gravity: hence, when it passes from LK to LM
it tends to detach itself from the stratum immediately above it,
or, in other words, to produce a vacuum between L K and MN,
and the same effect is produced through the whole length, LC,
of the tube: the pressure of the atmosphere becomes active as far
as is necessary to prevent the vacuum, and its action is the same
both at A, the surface of the fluid, and at C, the lower extre-
mity of the tube; the atmospherical pressure at A increases the
velocity of the fluid, which issues at CQ, while at C it destroys
the sum of the accelerations, which would be produced along
LC, so that the fluid remains continuous in the tube.

A
B
M
CL...
Fig. 1724.
E
N
Let t represent the time in which the continuous column of
fluid LCQK passes through the tube LC, whatever be the
velocity at L, and the successive acceleration from L to C; if
we suppose this column to return upwards from D to E, it will
pass through the space DE, which is equal to LC in the same
time t, during which it will lose all the acceleration it ac-
quired in its descent from L to C: the pressure of the column ED continued during the
time t is therefore the force necessary to destroy the successive acceleration from L to C,
and to prevent the fluid from losing the continuity in the tube LC; hence it follows that
the pressure of the atmosphere, which is exerted at CQ to destroy the sum of the acceler-
ations along LC, is equal to the pressure of a column ED of a fluid of the same nature as
that of the reservoir from which the water flows; and since the same pressure must also be
exerted on the surface A of the reservoir, if we take FALC, the fluid at LK will
possess the velocity which is proper to the height FLAC, without considering the re-
tardation produced by the internal inequalities of the tube LCQK. It is supposed by
Hachette that the cause of this increased expenditure by tubes is the adhesion of the
fluid to the sides of the tubes, which results from capillary attraction.
On the Shock of Water against Plane Surfaces. The shock or impetus of a column of
water is in the compound ratio of the bases of the columns and the square of the velocity
of the water, or their falls: wherefore, when the bases of the columns are equal, the im-
pacts will be to each other as the squares of the velocities of the water, or as the heights of
falls capable of the same velocities. When the bases of the columns are equal, and they
strike equal surfaces, the water may be considered as a mass of small spheres whose
impact will depend on their velocity, and the number which strike at the same time: for a
portion of water flowing with twice the velocity of another portion, striking a surface
opposed to it not only with twice its force, but with twice its number of particles, its
impetus must increase in the double proportion, or as the square of its velocity, that is, if
the velocities are as 3 to 5, the shocks will be as 9 to 25. The shocks being to each other
as the product of the orifices multiplied by the heights of the water, or as the columns BR
and FS, in fig. 1725., which are the forces causing the impacts, it follows that the impacts
may be measured by the weight of the same columns, since the effect of a force acting simply
without modification may be taken for the force itself. As the pressure which the columns
BR and FS exercise on their base is nothing more than a tendency to motion whose effect
would be to produce a shock, which may be measured by the cause itself, it follows that the
weight which will express the pressure of water on a surface will express the impact also.
The difference produced by friction between the natural and the effective discharge from
the same orifice of a medium size will also be very great in the effect of impact, because
the impacts being in the double ratio of the velocities, the impression of the effective will
be as much less than that of the natural discharge, as the square of the velocity of the first
will be less than that of the velocity of the second.
1136
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
If the surface GH, in fig. 1726., be placed at a certain distance EI from the orifice E, the
water in escaping, acquiring a new degree of velocity in going through the space EI, will
B
Fig. 1725.
F
F
K P




TT
Fig. 1726.
give a greater shock than in the preceding case, because its velocity will then be expressed
by the root of its height FI; whence it has been imagined that the impact should be equal
to the weight of a column having the orifice E for its base, and the line FI for its height,
without remarking that, although the velocity of the water does really increase, yet the
quantity which would leave the reservoir would be always the same, at whatever distance
the surface might be situated; thus a greater force has been calculated on in working
machinery than really existed.
Another supposition was that, if the water were directed by a pipe IEFL, its impact
might be expressed by the weight of a column IK PL, but it is not possible that this
tube should fill perfectly, since, whatever its length, the velocity of the water at its
issue would always be greater than at its entrance; consequently a column could not be
formed without being increased by the acceleration, unless it were so narrow that its
velocity would be more retarded by friction than it could be increased by the acceleration;
for the water in the reservoir being alone capable of maintaining the column EKP F,
that in the tube not being replaced by the sides, its discharge could not be greater than
that of the orifice which fed it.
When the velocity of the impact of water is accelerated, it is equal to the weight of a
column having for its base the surface struck, and a mean proportional between the height
of the water in the reservoir and the line which expresses the elevation of its level above
the surface struck for its height; consequently the greater the interval between the surface
and bottom of the reservoir, the more power will be gained to work a machine, showing
that the only advantage to be drawn from the tube EL is to direct all the water towards
the surface, and prevent it from being dissipated in passing through the air.
If a prismatic reservoir BCDE be continually filled with water, and a rectangular
orifice FG HI be made in one face E C, serving as the entrance to a canal whose bottom
and sides are composed of

C
M
T
X
rectangles FIX S, I HVX,
FGTS, and a power R
sustaining a vertical surface
NOMQ equal to the rec-
tangular aperture, and this
be suddenly opened, the
immovable surface will be
struck by a force equal to
the pressure which sustained
the sluice when the aperture
was closed; that is to say,
the impact will be equal to
the weight of a prism of
water, having the surface
struck for its base, and the
mean height LK between
La and Lb for its height.
This is evident, for the
velocity of the water in the
canal being uniform, and
expressed by the root of the mean height LK, the impact will be equal to the product of
this surface multiplied by the square of LK, or, which is the same thing, by LK
itself: consequently, if the opposite surface contained 4 square feet, and the mean LK
10 feet, the impact would be equal to the weight of 40 cube feet of water, or about 3150
lbs., which is the force required by the power R to support in equilibrio the impulse of a
A
E
GK
Fig. 1727.
N
CHAP. XVII.
1137
THEORY OF THE MOTION OF FLUIDS.
current whose mean and uniform velocity per second will be equal to that which a body
would acquire in falling from the height LK.
As the threads of water of the current increase in velocity in approaching the bottom of
the canal, their impression on the surface will diminish as they approach the summit OM
in an arithmetical progression, since these impressions will be the same as those of the
pressure sustained by the sluice of the aperture when closed: if the surface in questica
be represented by the float-board of a wheel, it would be necessary to know its centre of
impression, because the arm of the lever which corresponds to the mover must always he
expressed by the distance from this centre to the axis of the wheel.
A body rolling or sliding on a
highly polished inclined plane BCDE
acquires in descending from the sum-
mit to the base the same velocity
which it would have acquired in falling
from the height BA of the same
plane. Hence, water at rest allowed
to run down an inclined plane would
acquire a velocity which may be ex-
pressed by the root of the height of
the plane. If a reservoir be placed at
the summit of an inclined plane, the
water which issues from F GHI,
having already a velocity expressed
by the root of the mean height L K, or
its equal MN, will acquire a greater,
expressed by MA, after having
gone over the inclined plane; but as
the volume of water which issues from the aperture each instant will always be expressed
by ✓ MN, whatsoever be the height of this plane, calling the aperture, the quantity
of motion, or the shock of the water, will be expressed by OMN× √MA =
© × √ M F × M A, which shows that if there be at the foot of the inclined plane a surface
equal to the aperture which receives the impression of the water directly, the power R,
which sustains this surface in equilibrio, will be equal to the weight of a prism of water
having a plane equal to the aperture for its base, and the mean proportional between MN
and MA for its height.

E
Fig. 1728.
P.
Q
A
0 X
Whatever may be the dimensions of a surface, to measure the impact or shock, the part
which receives the impression must alone be taken into the calculation: if the water in
issuing from the bottom or one of the faces of a reservoir flows over several contiguous
inclined planes, without meeting any other obstacle than the planes themselves, its direct
impulse against a surface, relatively to the height of the water in the reservoir, will be the
same as that of a solid body under similar circumstances.
When the direction of a current is not perpen- I
dicular to the opposing surface, it does not act
with its absolute force. Suppose, for example, that
the line NO represents the base of a vertical sur-
face placed obliquely to a current at the bottom of
a canal, and that PV expresses the velocity and
direction of the current; it is evident that if this
surface be impressed by a solid body, the im-
pression will be expressed by the perpendicular
PT. But as the object under consideration is a
fluid whose impression must be measured by the
square of the velocity, its absolute weight will bear the
same proportion to its respective force, as the square
of PV to the square of PT, that is, as the square
of the total sine, to the square of the sine of the
angle of incidence.

F
H
Fig. 1729.
P.
N
Q
V

N
Fig. 1730.
X
As the
Suppose the line NQ to represent the base of a surface directly opposed to the current,
as it will be perpendicular to the side IX of the canal, the parallels QO and PV will give
the similar triangles QNO, TPV; then calling NQ, a, NO,b, PV, m, PT, n, we
shall have aa, bb : nm, mm, which gives a amm=bbnn, and amm, bnn : b, a.
first term of this proportion expresses the product of the surface N Q, multiplied by the
square of the entire velocity of the current, and the second that of the surface NO by the
square of this modified velocity, the impulse which the direct surface sustains, is to the
impulse which the oblique surface sustains, reciprocally as the length NO is to the length
NQ.
If the surface NO be inclined, and have the same base as QN directly opposed to
4:4
the current, the line HV representing the level of the water, the impulse sustained by the
4 D
1133
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
vertical surface will be to that sustained by the inclined surface reciprocally as the breadth
NO to NQ.
When an immovable surface is directly opposed to a current, the power sustaining it
will be equivalent to the weight of a column of water having this surface for its base, and the
mean height of the reservoir for its height. Now if in the interval KY (fig. 1727.) a roller Z
be placed, which traversing the canal can turn freely on gudgeons, having two pulleys above, it
is evident that if a cord be attached to the centre Y, passing over the roller, and thence over
pulleys, with a weight P equal to the impulse of the current, this weight will take the place of
the power R, and sustain the surface NOM Q in equilibrio, as before; but if it be diminished,
the surface will be driven forwards with a velocity equal to that of the weight in ascending,
since there is no difference between the arms of the levers; the impulse of the current will
be diminished precisely by the same quantity as the weight was, since these two forces will
always be equal. When the weight P is diminished by a
certain quantity, the surface of the fluid acquires the greatest
velocity of which it is capable, and preserves it constantly
uniform while the weight mounts, and the impulse which
presses it will be expressed by the square of the excess of the
velocity of the current over that of the surface.
It
H
A
K
C

Since among all the elements of a rectangle there is always
one which can be divided by the diagonal AC, in such a man-
ner that the square of the greater part HK multiplied by the
lesser KI gives the greatest of all the products that can be
formed, it follows that the entire velocity of a current may be
divided into two parts, the smaller of which becoming that of
the surface, and the other that with which it is struck, this
surface will have the greatest possible quantity of motion.
is ascertained that the velocity of the surface should be one-
third that of the current for the greatest effect; that is to say,
that it may at the same time receive the greatest velocity and impression possible, the com-
bination of which answers to the greatest quantity of motion, the force of the shock being
equal to the weight of the column of water which measures the absolute force of the
current against the surface when it is immovable. In a state of equilibrium the quantity
of motion of the mover is always equal to that of the weight, and for the greatest effect
we can only count on of the moving power; it follows that it can only raise of the
weight with which it was in equilibrio when acting in full force.
Fig. 1731.
If the aperture FGHD be closed, in fig. 1727., and the water comprised in the space
FGMQ be at rest, leaving the weight P out of the question, the power which will drive
the surface NOMQ with a uniform velocity in the direction RY will be the same as
that which would be necessary to support this surface in equilibrio against the impact of
a current which would have the same velocity; for whether the water meets the surface,
or the surface the water, the impact will always be expressed by the square of their
respective velocities.
If the surface meet a current issuing from an aperture, the power having to support not
only the impulse of which the velocity of the current may be capable, but further that
which arises from its own velocity, the resistance resulting from their concussion must be
expressed by the square of the sum of the velocities of the surface and current; that is, if
the current have a velocity of 3 feet per second, and the surface in ascending passes over 2
feet in the same time, it would be the same as if it supported in equilibrio the impression
of a current whose velocity was 5 feet per second, or as if it were driven with this velocity
in still water; for if, when a surface retreats from a current, its velocity must be subtracted
from that of the current, to obtain the velocity with which it is struck, it is natural, when
the surface meets the current, to add the velocity of the former to that of the current: on
the other hand, when the same surface is moved in the natural direction of the current, with
a velocity greater than the impulse which the power sustains, it should be expressed by the
square of the difference between the velocity of the surface and that of the current, because
the surface is then relatively to the water which retires, what the current is when the surface
retires from its impact.
•
M. de la Hire first started the idea that the uniform velocity of running water may be
regarded as acquired by a fall, consequently as the mean velocity which the water from a
reservoir would acquire whose height would be equal to this fall; whence he concludes
that the direct impression of a current against a vertical surface should be measured by the
weight of a column of water having for its base the surface struck, and for its height the
fall relative to the velocity of the current.
If the surface retreat from the current, we shall, in like manner, find the impulse which
it sustains, by subtracting its velocity from that of the current, if the first is less than the
second, or by subtracting the velocity of the current from that of the surface, if it be the
contrary, and by dividing the square of the difference by 60, to have the height of the prism
CHAP. XVII.
1139
THEORY OF THE MOTION OF FLUIDS.
of water. But when the surface meets the current, we must add their velocities together,
and divide the square of the sum by 60.
When the force which moves the surface of water at rest is given, and it is required
to find what velocity that force will produce; first find the height of a prism of water
having the same surface for its base, and whose weight would be equal to the given force;
then seek the velocity relative to a fall equal to the height of the prism, which will be
that required.
If the force given move a surface against a current, first seek, as in the preceding case,
the velocity answering to the height of the prism of water, regarding it as the sum of the
velocities of the current and of the surface, from which subtracting that of the current, the
difference will be the velocity with which the surface will remount.
To find the Velocity of a Current, the rough method was
formerly adopted of throwing a piece of wood into the water,
and observing the space which it went over in a certain time;
to effect this more accurately, M. Pitot invented an instru-
ment consisting of two glass tubes open at the ends; the
first, A B, is straight, and the second, CD, has one extremity
curved and funnel-shaped, E FGD; the whole is enclosed in
a prism of wood to preserve it from accident. The tube is
divided into equal parts, like a barometer, expressed in inches
and lines, and is plunged perpendicularly into the water, so
that the entrance to the funnel may be opposed to the direc-
tion of the current, in order that it may enter the funnel ;
the water then rises in the two tubes, but at different heights.
The line HI represents its level: it can only rise in the first,
A B, to the height GB, which dips in the water, having only
its weight to compel its rise, while the water which enters the
curved tube CD will rise to a height MK proportionate to
the velocity of the current, which, being considered as ac-
quired by a fall of a certain height, the water will ascend to
the same height, and be sustained there by the impulse of this
velocity, which, acting on the entrance, DE, of the tube, will
be in equilibrio with the weight of a column M K. Care
must always be taken to direct the funnel in the most rapid
thread of the water, remarking the point where it rises
highest, without regarding whether this thread be straight
or oblique: if it sometimes happen that an eddy makes the
water rise above the level corresponding to its velocity,
after some little time it will assume its natural level: a still
day should also be selected, as the wind prevents it rising to
its proper height.

H
Fig. 1732.
R
M
E
F
Motion of Water in Conduit Pipes and open Canals.—M. Eytelwein observes that a head of
water may be divided into two parts, the one employed in producing velocity, the other
in overcoming friction, and that the latter height, employed in overcoming the friction
must be directly as the length of the pipe and the circumference of the section, or as the
diameter of the pipe, and inversely as the content of the section, or the square of the
diameter, viz. on the whole inversely as the diameter; this height must also vary, like the
friction, as the square of the velocity.
To determine the velocity of the discharge of a pipe, when the height of the water in the
reservoir above the point of discharge, and the length and diameter of the pipe, are given :
multiply 2500 times the diameter of the pipe in feet by the height in feet, and divide the
product by the length in feet, and add 50 times the diameter; the square 100t of the
quotient will be the velocity of the discharge in feet per second. Suppose the diameter of
the pipe to be 375 feet, the height of the water in the reservoir above the point of discharge
51.5 feet, and the length of pipe 14637 feet: then
2500 × 375 × 51·5 48281.25
14637 + 50 x 375 14655.75
= 3.3,
the square root of which is 1.816, the velocity in feet per second.
To determine the quantity of water a pipe will discharge when the height of the reser-
voir above the place of discharge, the length of the pipe, and the diameter are known,
multiply the area of the pipe in feet by the velocity in feet, as found by the above rule, and
the result will be the discharge in cubic feet per second.
If from these rules the equation for the quantity discharged be formed, and that quantity
1+30 d
་་
be called Q, we have Q (142
12
from whence the diameter of the pipe to supply a
given discharge may be found.
4 D 2
1140
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
On the Quantity of Water discharged by Crifices of different Forms from Vessels kept
constantly full. — In making these experiments M. Bossut employed very clear water
running through holes made in plates of copper half a line in thickness; the tempera-
ture of the water is not given; the time was exactly measured, as well as the quantity of
water discharged, and the result was, that the quantity of water discharged in equal times
by the same orifices, from the same head of water, is very nearly as the areas of the orifices;
and, that the quantities of water discharged in equal times by the same orifices, under
different heads of water, are nearly as the square roots of the corresponding heights of
the water in the reservoir above the centre of the orifices. If we call Q, q, the quantities
of water discharged in the same time from the two orifices A, A', under the same height
of water in the reservoir; q and Q', the quantities of water discharged during the same
time by the same aperture A, under the different heads of water h, h'; we have by the
first of the above results,
Q : q=A : A', and by the second q : Q=√/h: √h';
A' × Q
from which we obtain q
A
and q
Q'√h
√h'
:
then, since
A' × Q
A
Q'√h
✔h'
we have Q: Q'=A√h: A'√h.
The quantities of water discharged during the same time by different apertures, under
different heights of water in the reservoir, are to one another in the compound ratio of the
areas of the apertures, and of the square roots of the heights in the reservoirs.
M. Michelotti made on this subject a series of experiments on a great scale, and with
the utmost accuracy. The apertures extended to 3 inches both square and circular, and
at considerable altitudes: the reservoir was 20 feet high, and 3 feet square; the water
flowed from it into a cistern whose area was 289 square feet, and the results corresponded
nearly with the experiments by Du Buat on the quantity of water discharged over weirs:
the depth may be considered as the upper edge of a plank placed below the upper surface
of the water in the river or reservoir : one of the orifices was 18 inches English in
length.
Depth of the
Orifice in English
Discharge of
Water in cubic
Discharge
calculated by
the Formula.
feet.
1.778
3.199
4.665
6.753
feet.
506
1222
2153
3750
524
1218
2155
3772
Du Buat has given the following formula reduced to English inches, by which the third
column is calculated, and is very accurate. This formula, as altered by Dr. Robinson, is
D=1130.032 H³, or
D=11·41727H³:
where D is the quantity of water discharged in cubic feet, l the length of the waste-board,
and H its depth; that is, multiply the square root of the cube of the depth of the upper
edge of the waste board below the surface by 11, and by the length of the waste-board,
and the product will be the quantity discharged in English inches.
Dr. Robison found by his experiments that the discharge was one-sixteenth more than
that produced by Du Buat's formula.
For the Quantity of Water discharged over a Weir, we cannot do better than select a table,
drawn up and revised by Dr. Robison, from experiments made in Scotland, which showed
some slight variations from the formula given by Du Buat. The water from which the
discharge was made was perfectly quiet, but when it was suffered to reach the opening over
which it passed with any velocity, it was necessary that the area of the section should be
multiplied by the velocity of the stream.
Since the publication of "Traité théorique et experimental d'Hydronamique" by the
Abbé Bossut in 1771, this subject has been justly regarded as important, and has received
the attention of the most eminent philosophers. Bossut's experiments were made upon a
grand scale, and his formulæ are more to be relied on than those given by Michelotti;
and in order to determine the motion of the particles of a fluid which was in the act of
being discharged from an orifice, Bossut employed a glass cylinder, 8 inches in height and
6 inches in diameter, to the bottom of which he adapted several contrivances for the efflux
of the water.
Chevalier Buat, Colonel of Engineers, in 1779, adopted the theory of Bossut, and paid
particular attention to the motion of water in rivers and canals, and to him we are indebted
for the observation, that if water possessed perfect fluidity, and flowed in a channel infi-
nitely smooth, its motion would be constantly accelerated, like that of heavy bodies de-
ocending upon an inclined plane. But the velocity of a river is not accelerated ad
CHAP. XVII..
1141
THEORY OF THE MOTION OF FLUIDS.
infinitum, but soon arrives at a state of uniformity, which is not afterwards increased; new
degrees of velocity are not obtained in consequence of being retarded by the friction of its
channel,
Depth of the
upper edge of
the waste-board
below the sur-
face in English
inches.
Cubic feet of
water discharged
in a minute by
every inch of the
waste-board, ac-
cording to Du
Buat's formula.
Cubic feet of
water discharged
in a minute by
every inch of the
waste-board, ac-
cording to ex-
periment made in
Scotland.
133
0.403
0.428
2
1.140
1.211
2.095
2.226
4
3.225
3.427
5
4.507
4.789
6
5.925
6.295
7
7.466
7.933
8
9.122
9.692
9
10.884
11.564
10
12.748
13.535
11
14.707
15.632
12
16.758
17.805
13
18.895
20.076
14
21.117
22.437
15
23.419
24.883
16
25.800
27.413
17
28.258
30.024
18
30.786
32.710
When the quantity of water discharged over a weir is known, the depth of the edge of
the wasteboard, or H, may be found from the following formula,
D
H=(11·
H = (11·41721
Michelotti's experiments give 0·2703✓H for the number of cubical inches discharged
in a second over a weir, when the height H is one inch; and the real discharge to the theo-
retical discharge is 9536 to 1000. These numbers suppose the length of the weir to be
infinite; his formula includes only the contractions produced by the upper edge of the
waste-board.
M. Eytelwein, in calculating the discharge of rectangular orifices reaching to the surface
represents the velocity, which varies as the square root of the height, by the ordinates and
the quantity of water discharged by the area of a parabola, two-thirds that of the circum-
scribing rectangle. This may also be found by taking two-thirds of the velocity due to the
mean height, and allowing for the contraction of the vein. He purposes, for example, a
lake, in which there is a rectangular opening without any oblique lateral walls, 3 feet wide,
and extending 2 feet below the surface of the water: here the co-efficient of the velocity
corrected for contraction is 5'1, and the corrected mean velocity √2 × 5·14·8; therefore,
the area being 6, the discharge of water in a second is 28.8 cubic feet: C being the co-
efficient corrected for contraction, W the width of the aperture, and H its depth below
the surface, we have the general formula,
Q={√HxCx H x W,
for the quantity of water in cubic feet.
As the same co-efficient serves to determine the discharge over a weir of considerable
breadth, it is easy to deduce the depth or breadth requisite for the discharge of a given
quantity of water: for example, a lake has a weir 3 feet in breadth, and the surface of the
water stands at a height of 5 feet above it; it is required how much the weir must be
widened that the water may be a foot lower; we have the velocity 5 × 5·1, and the
quantity of water √5x5.1 × 3 × 5, but the velocity must be reduced to √4 x 5·1, and
then the section will be
} √ 5 × 5·1 × 3 × 5
√ 4 x 5.1
X
√ 4
√5 × 3 × 5
= 7.5 × √5,
7.5
4
5=4.19 feet.
and the height being 4 feet, the breadth must be
On the Motion of Water in Rivers. The theorem by which the velocity of a river is
determined, is one of the most valuable of M. Eytelwein's calculations: the friction is
nearly as the square of the velocity, not because a number of particles proportionate to the
velocity are torn asunder in a time proportionately short, (for according to the analogy of
solid bodies no more force is destroyed by friction when the motion is rapid than when
4 D 3
1142
Book II
THEORY AND PRACTICE OF ENGINEERING.
slow,) but because, when a body is moving in lines of a given curvature, the deflecting
forces are as the squares of the velocities, and the particles of water in contact with the
sides and bottom must be deflected in consequence of the minute irregularities of the
surfaces on which they slide, nearly into the same curvilinear path, whatever their velocity
may be.
The principal part of the friction is as the square of the velocity, and the friction
is nearly the same at all depths; it varies, however, according to the surface of the fluid in
contact with the solid, in proportion to the whole quantity of the fluid, viz. the friction for
any given quantity of water will be as the surface of the bottom and sides of a river directly,
and as the whole quantity of water in the river inversely; or, suppose the whole quantity of
water to be spread on a horizontal surface equal to the bottom and sides, the friction is
inversely as the height at which the river would then stand, which is called the hydraulic
mean depth.
When the river flows uniformly, and is neither accelerated nor retarded by the action of
gravitation, the whole weight of the water is employed in overcoming this friction, and if
the inclination vary, the relative weight, or the force which urges the particles along the
inclined plane, will vary as the height of the plane when the length is given, or as the fall
in a given distance: consequently the friction, equal to the relative weight, must vary as
the fall, and the velocity, which is as the square root of the friction, must be as the square
root of the fall; and supposing the hydraulic mean depth to be increased or diminished,
the inclination remaining the same, the friction would be diminished or increased in the
same ratio; therefore, in order to preserve its equality with the relative weight, it must be
proportionally increased or diminished, by increasing the square of the velocity, in the ratio
of the hydraulic mean depth, or the velocity in the ratio of the square root. The velocities
will, therefore, be conjointly as the square root of the hydraulic mean depth, and of the fall
in a given distance, or as a mean proportional between these two lines.
Taking two English miles for a length, we must find the mean proportional between the
hydraulic mean depth and the fall in two miles, and inquire what relation this bears to the
velocity in a particular case, and thence we may determine it in any other according to
Eytelwein's formula, this mean proportional is of the velocity in a second.
:
Mr. Watt found that in a canal 18 feet wide above, 7 feet below, and 4 feet deep, having
a fall of 4 inches in a mile, the velocity was 17 inches in a second at the surface, 14 inches
in the middle, and 10 inches at the bottom, the mean velocity being 14 inches in a second
or thereabouts; therefore, to find the hydraulic mean depth, we must divide the area of the
section 2 (18+7) ≈ 50, by the breadth of the bottom and length of the sloping sides added
50 feet
together, whence we have
or 29.13 inches; and the fall in two miles being 8 inches,
20.6
=
10
we have 8 × 29·13 = 15.26, for the mean proportional, of which, 19, is 13.9, agreeing
exactly with Mr. Watt's observation.
The Po falls 1 foot in two miles, where its mean depth is 29 feet, and its velocity is about
55 inches in a second; our rule gives 58, which is a sufficient approximation to show its
accuracy.
To find the velocity of a river from its fall, or the fall from its velocity, we have only to
recollect that the velocity in a second is of a mean proportional between the hydraulic
mean depth and the fall in two English miles.
For the Slope of the Banks of a River or Canal, Eytelwein recommends that the breadth at
the bottom should be two-thirds of the depth, and at the surface ten thirds; the banks will
then in general retain their form; the slope of the bank within the water making an angle
of 37 degrees with the horizon, or of 4 to 3. The area of such a section is twice the
square of the depth, and the hydraulic mean depth two-thirds the actual depth.
The superficial velocity of a river is nearly a mean proportional between the hydraulic
mean depth and the fall in two miles, and the mean velocity of the whole water is still
more, or nearly nine-tenths of this mean proportional.
The Ganges at 500 miles from the sea has its channel 30 feet deep when the river is at
the lowest, and it continues at least this depth to the sea: a section of the ground was
taken parallel to one of its branches, in length 60 miles, where the windings of the river
were so great as to reduce the declivity on which the water ran to less than 4 inches per
mile, its medium rate of motion being less than three miles an hour in the dry months.
Allowing a little for the banks, we may take 30 feet as the hydraulic mean depth; then if
the fall in two miles were precisely two-thirds, we should have 2 × 30=20, and √20=4·47
for the velocity of a second, or 3.05 miles in the hour.
This river when full has thrice the volume of water, and its motion is accelerated in the
proportion of 5 to 3; the hydraulic mean depth is then doubled, whence the velocity is
increased in the ratio of 7 to 5: the inclination of the surface is somewhat increased,
which increases the velocity from 14 to 1·7.
ABCD is the cistern for sup-
Smeaton's Experiments relative to undershot Water-wheels.
plying the water, DE the upper cistern or head, FG a small rod divided into inches, and
moving up and down as the water rises and falls; HI is a rod by which the sluice is drawn,
and stopped at any height required by the pin K, which is placed as a diagonal scale upon
CHAP. XVII.
1143
THEORY OF THE MOTION OF FLUIDS.
R
W
E
K
F
M
JI
the rod HI; GL is the upper part of the rod of the pump for drawing the water out of
the lower cistern to the head DE; MM the handle for working the pump, which is limited
in its stroke by N; O is the cylinder
upon which a cord winds, and pass-
ing over the pulleys P and Q raises
R, the scale into which the weights
are put for trying the power of the
waters; S, T, the two standards
which support the wheel, and made
to slide up and down to adjust the
wheel to the floor of the conduit;
W is the beam to support the scale
and pulleys; X X (fig. 1734.) is the
pump-barrel, 5 inches in diameter
and 11 inches long; Y is the piston,
and Z the fixed valve; GV is a wooden
cylinder fixed upon the pump rod,
reaching above the surface of the
water; its section is half the area
of that of the pump barrel, which
causes the surface of the water to
rise in the head as much while the
piston is descending as while it is
rising, and keeps the gauge rod more
equally to its height; aa is one of
the two wires which serve as direc-
tors to the float, so that the gauge
rod FG may be kept perpendicular;
b is the aperture of the sluice; cc is
a kant board for throwing the water
down the opening, cd, into the lower
cistern; ee is a sloping board for
bringing the water back that is
thrown up by the floats of the wheel.

B
C
Fig. 1733.
T
50
ELEVATION.
Fig. 1733. represents one end of the main axis, with a section of the cylinder marked
O. ABCD is the end
of the axis; B, D are
covered with hoops of
brass; E is a metal
cylinder; F the gud-
geon; aa is the section
of a brass ferrule, cc.
The section of the hol-
low cylinder of wood,
ee, is cut into teeth,
and oo a ratchet; G
is a pin fixed into the
axis, by means of which
the hollow cylinder
turns along with the
wheel and axle; when
drawn back by the
button gg, the hollow
cylinder is disengaged
from the pin G, and
ceases turning; the
weight on the scale is
prevented running back
by a catch that lays
hold of the ratchets 0,0;
the hollow cylinder is
by this contrivance put
in motion and dis-
charged while the wheel
is in motion.
The Power is the
exertion of strength,

A
B
Ge
A
C
g
H
Fig 1734.
K
h
ར
་་
F
E
M
a
N
S
V
X
D
Z
SECTION OF MACHINE.
M
4 D 4
1144
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
gravitation, impulse, or pressure, which produces motion. Raising a weight to a given
height in a given time is the measure of power; the weight raised, multiplied by the
height, gives a product which is the measure of the power that raised it: when velocity is
uniform, the space is as the velocity; then the power is proportionate either to the force
multiplied by the velocity, or the space described; it is unimportant whether the motion
be quick or slow if it be uniform. The original power is somewhat lessened by the
friction of the machinery and the resistance of the air, which, before the useful effect can
be obtained, must be calculated: from the velocity of the water at the instant it strikes the
wheel, the height of head productive of such velocity can be deduced; then, multiplying the
weight of water expended in any period of time by the height of the head, we have the
power of the water; the sum of the weight raised by the action of the water, and that
required to overcome the friction and resistance, multiplied by the height to which
the weight can be raised in a given time, the product will be the effect of the power: the
proportion of the two products is that of the proportion of the power to the effect.
To determine the Velocity of the Water striking the Wheel, according to Smeaton. When the
wheel of a machine is put in motion by the water without any weight in the scale, sup-
posing the number of turns in a minute to be 60, then 60 times the circumference of the
wheel will be the space through which the water would have moved in a minute if the
wheel were free from friction and resistance; the velocity is, however, greater than this,
as considerable deduction must be made for friction: suppose the cord wound round the
cylinder in a contrary direction to the usual method, and a weight put into the scale; this
weight will assist the wheel in turning; suppose it to be sufficient to cause the machine to
turn without any water somewhat faster than 60 turns a minute, as 63; let the water then
be applied, assisted by the weight, the wheel will now make 64 turns; hence we may sup-
pose that the water exerts some power in giving motion to the wheel; increase the weight,
so as to make 64 turns in a minute without water, and then try it with water as before.
and if it make the same number of turns with water as without, it must be evident that
the wheel makes the same number of turns in a minute as it would do if the wheel had no
friction, the weight being equivalent thereto; if this were too little, the water would acce-
lerate the wheel beyond the weight, and if too great, retard it; thus the water becomes the
regulator of the wheel motion of the wheel, and the velocity of its circumference becomes
a measure of the velocity of the water.
It
To find the greatest product, or maximum of effect, the weight which gives the greatest
product being known, multiply the weight in the scale by the number of turns of the
wheel; find what weight in the scale, when the cord is on the contrary side of the cylinder,
will cause the wheel to make the same number of turns in one direction without water.
is evident that the weight will be equal to all the friction and resistance taken together, and
consequently the weight of the scale added to the counterweight will be equal to the weight
that could have been raised if the machine had been without friction or resistance, which,
multiplied by the height to which it actually was raised, the product will be the greatest
effect of that power. This method, however, does not give the actual resistance when the
maximum power and load are upon the wheel, but only the friction from the weight of the
apparatus, when moving at a velocity corresponding to the maximum. The effect was
estimated by Smeaton at considerably less than its true value.
The pump was so well
Quantity of Water expended, or its Dynamic Effect on Wheels.
made, that it delivered the same quantity of water at each stroke, whether worked slowly
or quick, the length of the stroke being limited. The sluice by which the water was drawn
upon the wheel was stopped at a certain height by a peg; the aperture for the effluent
water was the same, so that the exact quantity of water expended was known; the sluice
being drawn to the first hole.
The water above the floor of the sluice
Strokes of the pump in a minute
The head raised by twelve strokes
The wheel raised the empty scale, and made
With a counterweight 11 lbs. 8 oz.
Ditto, tried with water
Inches.
30
391/
21
Turns in
a Minute.
-
80
85
86
4
6
♡¤IOU A UN
No.
1
2
Lbs
Oz.
Turns in a Min.
Product.
5
45678
45
180
0
42
210
0
361
217
0
3333
2361
0
30
240; maximum.
3
0
261
238
7
10
0
22
220
8
11
0
161
1811
9
12
0
ceased working.
CHAP. XVII.
1145
THEORY OF THE MOTION OF FLUIDS.
Counterweight for 30 turns, without water, 2 oz. in the scale; the area of the head was
105.8 square inches; weight of the empty scale and pulley 10 oz.; circumference of the
cylinder 9 inches; circumference of the water-wheel 75 inches.
The circumference of the wheel 75 inches, multiplied by 86 turns, gives 6450 inches for
the velocity of the water in a minute, of which will be the velocity per second, equal to
107.5 inches, or 8.96 feet, the head being 15 inches, and the vertical or effective head,
which differs from the real head by the velocity lost by the fluid in issuing through the
aperture of the sluice, and the friction of the channel. The area of the head being 105.8
inches, this multiplied by 579, the weight in avoirdupois ounces of a cubic inch of water,
gives 61.26 ounces for the weight of as much water as is contained in the head upon 1 inch
in depth, of which is 3.83 lbs. ; this multiplied by the depth, 21 inches, gives 80-43 lbs.
or the value of twelve strokes; and by proportion, 39, the number made in a minute will
give 264.7 lbs. as the weight of water expended in a minute: 264.7 lbs. of water, having
then ascended through a space of 15 inches in a minute, the product of these two numbers,
3970, will express the power of the water to produce mechanical effects, which upon this
wheel were as follows:
The velocity of the wheel at the maximum was thirty turns in a minute; this multiplied
by 9 inches, the circumference of the cylinder, makes 270 inches; but as the scale was
hung by pulley and double line, the weight was only raised 135 inches.
The weight in the scale at the maximum
Weight of the scale and pulley
-
Counterweight of the scale and pulley
Sum of the resistances
or 9.375 lbs.
lbs. oz.
8 0
0 10
0 12
9 6
Now, as 9.375 lbs. are raised 135 inches, these two numbers multiplied together produce
1266, the effect produced as a maximum; so that the proportion of the power to the effect
is as 3970: 1266, or as 10: 3.18. Though this is the greatest single effect by the impulse of
the water upon an undershot wheel, yet, as the whole power of the water is not exhausted
thereby, this will not be the true ratio between the power of the water and the sum of all
the effects producible therefrom; for as the water must necessarily leave the wheel with
a velocity equal to its circumference, it is clear that some part of the power of the water
must remain after quitting the wheel. The velocity of the wheel at the maximum is 30
turns in a minute, so that its circumference moves at the rate of 3·123 feet per second,
which answers to a head of 1·82 inches; this being multiplied by the expenditure of water
in a minute, viz. 264.7 lbs., produces 481 for the power remaining in the water after it
has passed the wheel; this being, therefore, deducted from the original power, 3970, leaves
3489, which is that portion of the power spent in producing the effect 1266, which is to
the greatest effect producible thereby, as
3489 : 1266 :: 10 : 3·62, or as 11 to 4.
The velocity of the water striking the wheel has been determined as equal to 86 circum
ferences of the wheel per minute, and the velocity of the wheel at the maximum to be 30;
the velocity of the water will, therefore, be to that of the wheel, as 86 to 30, or as 10 to 3·5,
or 20 to 7: the load of the maximum was equal to 9 lbs. 6 oz.; and the wheel ceased
moving with 12 lbs. in the scale, to which the weight of the scale was added, viz. 10 ounces;
the proportion, therefore, will be nearly as 3 to 4 between the load of the maximum, and
that by which the wheel is stopped. The velocity of the wheel in relation to the water is
proved to be greater than the velocity of the water; yet the impulse of the water, in the
13
case of a maximum, is more than double that assigned by theory, viz. instead of of the
column, it is nearly equal to the whole column: the power of the water is equal to the
velocity and pressure due to the effective head. The resistance reduced to the circum-
ference of the wheel is equal to the weight raised, added to the friction of the machine
when raising that weight, multiplied by the velocity of the wheel. The maximum of
useful effect takes place when the greatest weight is raised with the greatest velocity: in
the case experimented upon, to prove this, the wheel was not placed in an open river, where
the natural current, after it has communicated its impulse to the float, has room
sides to escape, as the theory supposes.
>
on all
After numerous experiments, Smeaton ascertained that the vertical or effective head
being the same, the effect will be nearly as the quantity of water expended; and that the
expense of water being the same, the effect will be nearly as the height of the vertical or
effective head, and the effect nearly as the square of its velocity: the aperture being the
same, the effect will be nearly as the cube of the velocity of the water.
Bossut's experiments on undershot water-wheels confirm many of Smeaton's results: he
tried their effect in a close canal, as well as in an open stream, varying in both cases the
1146
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
number of floats. In the close canal, he made use of a wheel the extreme diameter of
which was 3 feet 1·87 inches, 5 inches in breadth, and the depths of the float-boards from
4 to 5 inches: the axis of the wheel which received the cord was 2 inches in diameter; thẹ
diameter of the pulley 33 inches. The wheel was suspended on its axis within half a line
of the bottom of the canal: the sluice was raised 1 inch, and the velocity of the stream
was 300 feet in 33 seconds: in a close canal, the effect was with 48 floats on a wheel of
3 feet 1.87 inches diameter greater than that with a less number: the arc immersed was
about of the circumference of the wheel.
16
Water-wheels used in rivers have a less number of float-boards, and in the next experi-
ment the wheel was 3 feet diameter, breadth 6 inches, and the depth of the float-boards 6
inches, the whole weight of the moving parts of the apparatus being 44 lbs.
The stream was open, 12 or 13 feet wide, and 7 or 8 inches deep, and the float-boards
were immersed 4 inches: the wheels had a variety of float-boards, that with 48 producing
very little more effect than one with half that number; but there was considerable
difference between those with 24 and 12, the former being decidedly preferable: it was
apparent, when the wheel dipped of its circumference, less than 24 ought not to be
used.
In the close canal the sluice was raised 2 inches, the velocity of the current 300 feet in
27 seconds, and 48 float-boards to the wheel; and trials were made with the same wheels,
the maximum effect of which was 34½ lbs., raised by 20 turns of the wheel in 40 seconds,
thus making the product of the weight raised 7041 lbs. The velocity of the current was
to the velocity of the outer circumference of the wheel, as 10 is to 4-32 when the power is
a maximum.
In the open stream, where the velocity of the current was 68 inches per second, the
float-boards dipping 4 inches in the water, the wheel having 24 float-boards, the maximum
effect was 60 lbs. weight raised, 11 being the number of turns of the wheel in 40 seconds,
and 710 the product of the weight by the number of turns. The velocity of the current
was to the velocity of the outer edge of the float-boards at the maximum, as 10 is to 4.9
nearly. The velocity of the wheel in the stream and in the canal was nearly the saine.
The greatest effect, as it appears from Bossut's
trials, was obtained when the inclination of
the floats to the radius was from 15 to 30
degrees.
Construction of Undershot Wheels.-The wheel
here represented has twenty-four float-boards;
cd is that receiving the impulse of the water,
which, in consequence of falling from a height,
moves with great velocity down the inclined
mill-course MN, the construction of which
requires the greatest consideration, as does the
number, form, and position of the float-boards,
and the velocity of the wheel, in relation to
that of the water, when the effect is a max-
imum: it being important to have the height
of the fall as great as possible, the canal or
dam which conducts the water from the head
should not have more inclination than is abso-
lutely necessary; an inch in 200 yards is con-
sidered sufficient, care
being taken to make the
declivity for the first 50
yards about inch, that
the water may have suffi-
cient velocity to prevent
its running back into the
head.
The inclination of the
fall, shown by the angle
CG R, should be 25° 50′,
or CR; the radius should
be to CR, the tangent of
the angle, as 25 to 12; and
since the surface of the
water Sb is bent from ab
into ac before it is pre-
cipitated down the fall,
it will be necessary to

2
M
Fig. 1735.
UNDERSHOT WHEEL.
b a
W
W
n
K
M
L
H
N
Fig. 1736.
UNDERSHOT WHEEL.
F
G
R
P
B
N

B
A
E
5
CHAP. XVII.
1147
THEORY OF THE MOTION OF FLUIDS.
incurvate the upper part BCD of the course into BD, that the water at the bottom may
move parallel to that at the top of the stream. To effect this, take the points B, D, about a
foot distant from C, and raise the perpendiculars BE, DE; the point of intersection E will
be the centre from which the arc BD is to be described, the radius being about 10 inches.
That the water may act more advantageously upon the float-boards of the wheel W W, it
must assume a horizontal direction HK, with the same velocity that it would acquire when
it came to the point G ; but in falling from C to G, the water will dash upon the horizontal
part HG, and thus lose a great portion of its velocity; it will be necessary, therefore, to
make it move along FH, an arc of a circle to which D F and KH are tangents, in the
points F and H. For this purpose make GF and GH each equal to 3 feet, and raise
the perpendiculars FI, HI, which will intersect each other at the point I, distant about 4
feet 94 inches from the points F and H, and the centre of the arc FH will be
determined. The distance HK, through which the water runs, before it acts upon the
wheel, should not be less than 2 or 3 feet, in order that the different portions of the fluid
may obtain a horizontal direction, and if HK be much larger, the velocity of the
stream would be diminished by its friction on the bottom of the course. That no water
may escape between the bottom of the course K H, and the extremities of the float-boards,
K L should be about 3 inches, and the extremity O of the float-board, N O, should be beneath
the line HK K, sufficient room being left between O and M for the play of the wheel, or
KLM may be formed into the arc of a circle, KM, concentric with the wheel.
The line LMV, or the course of compulsion, should be prolonged, so as to support the
water as long as it can act upon the float-boards, and about 9 inches distant from O P, a
horizontal line passing through O, the lowest point of the fall; for if OL were much less
than 9 inches, the water, having spent the greater part of its force in impelling the float-
boards, would accumulate below the wheel and retard its action: for the same reason the
course of discharge should be connected with LMV by the curve VN, to preserve the re-
maining velocity of the water, which would otherwise be destroyed by falling perpen-
dicularly from V to N. The course of discharge is represented by VZ, sloping from the
point 0; it should be about 16 yards long, having an inch of declivity in every 2 yards.
The canal which conducts the water from the course of discharge to the river should
slope about 4 inches in the first 200 yards, 3 inches in the second 200 yards, decreasing
gradually till it terminates with the river. The diameters of undershot wheels must be in
accordance with the machinery on which they are to act; when a great velocity is required,
the wheel must be of a less diameter than is usually recommended; when this is not required,
the diameter of the wheel should be as large as possible.

பபபபலூ
Fig. 1737.
side ELEVATION OF AN UNDERSHOT WHEEL.
The number of float-boards, according to Pitot, should be equal to 360°, divided by the
arc of the circle plunged in the canal, and their depth equal to the versed sine of that
arc; but this number experience has proved to be too small, and some engineers have
€
1148
BOOK II.
THEORY AND PRACTICE OF ENGINEERING..

maintained that it is not possible
to have too many float-boards,
provided the wheel is not too
much loaded with them.
It may be readily understood,
that when water acts by its mo-
mentum only, the circumference
of the wheel, instead of requir-
ing buckets, as in the overshot
wheel, is furnished with float-
boards, which, exposed to the
action of running water, may
have its power increased by a
well regulated fall; such a wheel
may communicate its force to
any machinery. The figures
show the method that Smeaton
recommended for the construc-
tion of undershot wheels; the
sluice or penstock is raised
or depressed by a ratchet and
pinion; the spur-wheel to drive
the machinery is shown resting
on its bearings on the left of the
elevation.
On Overshot Wheels, by
Smeaton. We now proceed to
examine the power and applica-

Fig 1738. PLAN OF UNDERSHOT WHEEL.
tion of water, when acting by its weight: we might at first be led to suppose, that the same
quantity of water descending through the same perpendicular space would produce. equal
power, when the machinery is freed from friction, and that if the height of a column of
water be 30 inches, and its base or aperture 1 inch, every cubic inch that passes through the
aperture would acquire the same momentum, a column of uniform pressure being always
maintained, as one cubic inch let fall from the top will acquire in falling down to the level
of the aperture; but that this is not exactly the case, experiment has proved.
The alterations made in the machinery we have already described were as follows: the
sluice Ib (fig. 1733.) being shut down, the rod HI was unscrewed and taken off. The
undershot wheel was removed, and an overshot put in its place, of 2 inches in the depth of
the bucket, and the number of buckets was thirty-six: the standards S and T were raised
half an inch, so that the bottom of the wheel might be clear of dead water; a trunk for
bringing the water to the wheel was fixed according to the dotted lines f, s. The ratchet
oo not being of one piece of metal with the ferrule was with its catch turned to the con-
trary side the movable barrel acted by this means, although the water-wheel moved the
contrary way; the results were, head 6 inches; 14 strokes of the pump in a minute,
12 do. 80 lbs.; weight of the scale being wet, 10 oz. ; counterweight for twenty turns,
besides the scale, 3 oz. In the maximum experiment there were 203 turns in a minute,
each of which raised the weight 4 inches, or 93.37 inches in a minute; the weight in the
scale was 19 pounds; the weight of the scale 10 ounces; the counterweight three ounces
in the scale, making with the weight of the scale 20 pounds, and which was the whole
resistance or load; this multiplied by 93.37 inches, gives 1914 for the effect.
The ratio of the power and effect is 2900: 1914, or 10: 6'6, or as 3 to 2 nearly. If we,
however, compute the power from the height of the wheel only, we shall have 963 lbs.
multiplied by 24 inches, equal to 2320 for the power, and this will be to the effect as
2320: 1914, or as 10: 8.2, or as 5 to 4 nearly.
On the most proper Height of the Wheel in proportion to the whole Descent. We have
already observed that the effect of the same quantity of water descending through the same
perpendicular space is double, when acting by its gravity on an overshot wheel, to that pro-
duced by the same when acting by its impulse upon an undershot: it also appears, that
by increasing the head from 3 inches to 11, that is, the whole descent from 27 to 35 inches,
or in the ratio of 7 to 9 nearly, the effect is only in the ratio 8.1 to 8.4, that is as 7 to
7.26; consequently, the increase of effect is not a seventh of the increase of perpendicular
height; hence, the higher the wheel is in proportion to the descent, the greater will be the
effect, as it depends less upon the impulse of the head, and more upon the gravity of the
water in the buckets.
The Velocity of the Circumference of the Wheel which produces the greatest Effect. — If a
body be allowed to fall freely from the surface of the head to the bottom of the descent, it
will take a certain time in falling, and in that case the whole action of gravity is spent in
CHAP. XVII.
1149
THEORY OF THE MOTION OF FLUIDS.
giving the body a certain velocity, but if in falling, it be made to act upon some other, so as
to produce a mechanical effect, the falling body will be retarded, because a portion of the
action of gravity is then spent in producing that effect, and the remainder only will give
motion to the falling body; therefore the slower a body descends, the greater will be the
portion of the action of gravity applicable to producing a mechanical effect, consequently
the greater that effect will be. A stream of water falling into the bucket of an overshot
wheel is there retained until the rotary motion of the wheel discharges it; the slower the
wheel moves the more water each bucket receives, so that what is lost in speed is gained by
the pressure of a greater quantity of water acting on the buckets at once; thus the
mechanical power of an overshot wheel produces equal effects, whether it move quickly or
slowly when the wheel, according to the experiments, made 20 turns in a minute, the
effect was nearly the greatest; when 30 turns the effect was diminished one-twentieth; when
40 turns it was diminished one quarter; when less than 181 its motion was irregular, and
when loaded so as not to admit of its making 18 turns, it was overpowered. The velocity
most available in practice is that produced by a wheel making 30 turns in a minute, and
the velocity of the circumference is a little more than 3 feet in a second. Experience also
proves that the velocity is applicable to the highest overshot wheels, as well as the
lowest.
:
Smeaton, in the year 1796, put up an overshot wheel at Hull, some years after these ex-
periments were made, the diameter of which was 27 feet, and he directed that it should
move at the rate of 8 feet per second, remarking that its motion would not be equal and
regular if it moved at the rate of 3 feet per second.
The load for an overshot wheel that will produce a maximum effect is that which reduces the
circumference of the wheel to its proper velocity; and this will be ascertained by dividing
the effect it ought to produce in a given time by the space intended to be described by the
circumference of the wheel in the same time; the quotient will be the resistance over-
come at the circumference, and is equal to the load required, the friction of the machinery
included.
The greatest possible velocity of which the circumference of an overshot wheel is capable de-
pends jointly upon the height of the wheel and the velocity of falling bodies.
The greatest load that
an overshot wheel can
overcome is unlimited.—
According to Eytel-
wein the power which
operates upon overshot
water-wheels is divided
into two parts; one de-
rived from the weight
of the water in the
buckets, the other from
the impulse of the
water falling on it: the
effect of the first is
constant, that of the
second varies with the
velocity; the maximum
is said to be when the
velocity is half that of
the water received, but
the variable portion
being the smaller, the
rule is of little practical
importance, and the
velocity of the wheel is
generally greater than
this; by turning the
stream back upon the

Fig. 1739.
τυ
OVERSHOT WHEEL
Ло
nearer half of the wheel, we remove the resistance of the lower water, which runs off in the
same direction as that of the water-wheel. The iron overshot wheels have the same ar-
rangement of the pen.trough and shuttle for the supply of water as the other description
of wheels, and can be regulated in a similar manner.
On the Construction of Overshot Water-wheels. When the water is permitted to fall into the
bucket c, (fig. 1740.) from the horizontal mill-course E F, the weight of water in the bucket
acting at the end of the levers equal to m O puts the wheel in motion in the direction cd, and
all the buckets, which are filled in succession as the wheel turns round. When the bucket c
reaches the position d, its power to turn the wheel is increased, becoming equal to the
1150
Boox II.
THEORY AND PRACTICE OF ENGINEERING.
weight of water acting at the end of the lever n O, equal to the distance of its centre of
gravity, d, from a vertical line passing through the axis O. Thus the mechanical effect of
the water in the bucket in-
creases till it arrives at B,
after which in its progress
towards Cit diminishes. The
power of an overshot wheel
depends much upon the form
of the buckets, which should
always be the fullest when
at the point B, and should
retain the water as long as
possible.
E
F


A
M
C
Fig. 1740.
OVERSHOT wheel.
The form of bucket prefer-
red (fig.1741.) is composed of
three partitions; AB and G I,
called the start or shoulder,
which lies in the direction of
the radius of the wheel; BC
and I K the arm, inclined at
an obtuse angle to the radius;
and CD, KL the wrest, in-
clined to an angle less than
180°, to the arm BC or IK; the depth,
A G, of each bucket is about 11 of GH;
AB is half AM, and the angle ABC
is such that BC and GI prolonged would
pass through the same point H; it ends,
however, in C, so that FC is five-sixths
of GH, and CD is so placed that H D is
nearly a fifth of HM: hence, it follows
that the arc FABC is nearly equal to
DABC, so that the quantity of water
FABC will continue in the bucket
when AD is in a horizontal position,
which is the case when A B forms an
angle of about 35° with the vertical line.
There are several methods for sup-
plying overshot wheels with water ;
in
some instances it is let on a little below
the upper part, or is varied to different
heights, in which case the wheel must be adjusted to suit
the lowest head, which is a disadvantage.
2
K
D
G
H
B F
C
R
Fig. 1742.
PENTROUGH.
The Pentrough is made of cast-iron, and the water
runs over the upper side of the roller R, through barred
spaces into the buckets of the wheel.
Barker's Mill is supplied by water from a reservoir, and
conducted by an upright pipe into the horizontal trunk
O, which has arms of an equal length, and through the
ends of which the water runs out. The upright spindle
is fixed in the bottom of the trunk, to which it is screwed
by a nut, in such a manner that when the trunk or up-
right pipe is turned round, the spindle moves with it;
to this spindle the rynd of the upper millstone is at-
tached: when water is admitted from the constant reser-
voir into the cup at the top of the vertical pipe, and
suffered to run out by a continued stream from the ends
of the trunk, the upper millstone, together with the trunk
tube and spindle, turn round.
0
A
B
M
Fig. 1741.


0
The length of the axis in a mill of this kind must
always exceed the height of the fall, and therefore there
is some difficulty in introducing Barker's mill when the
fall is very high. M. Mathon de la Cour proposed that
the water should be introduced from the mill-stream into
the horizontal arms, which are fixed to the upright spin-
dle without having any tube; when the water would issue from the openings below in the
same manner as when introduced at the top of the tube as high as the fall.
Fig. 1743.
BARKER'S MILL.
There are
CHAP. XVII.
1151
THEORY OF THE MOTION OF FLUIDS.
several varieties of Barker's mill; one consists of a number of tubes arranged within the
circumference of a truncated cone, so that when the water is introduced into the upper ends
of these tubes, and allowed to flow out at the lower, a motion is produced around the axis of
the cone. Another contrivance introduces the water from
the mill-stream into an annular cavity of a fixed cylindri-
cal vessel, in the bottom of which are several inclined
apertures, for the purpose of making the water flow out
with a proper obliquity into an inferior vessel, which is
movable and of the form of an inverted frustum of a
cone; this latter moves about an axis which passes through
the centre of the fixed vessel; it has a number of tubes
contrived around its circumference, which do not extend
to the top, and are bent at the lower ends into right
angles. When the water is introduced into the upper
vessel, and delivered into the tubes of the lower as it issues
from their horizontal extremities, motion is conveyed to
the conical drum.
The theory of this engine is not thoroughly under-
stood, and Davies Gilbert, Esq., when President of the
Royal Society, decided against any mechanical advantage
being produced by it. In the Philosophical Transactions
for 1827 are several statements and calculations on the
subject.
Hachette has given us in his Cours de Géometrie
Descriptive the figure of a machine by which the power
of lateral pressure may be measured: as the water from
the constant reservoir pours into the cup and turns
round the spindle, it is made to raise a weight hung
over a pulley, which weight at once expresses its power.
Wind is produced by a fall of water, and Venturi has
shown that the air is dragged down upon the principle of
the lateral communication of motion in fluids; and he has
pointed out the best mode of constructing the machine,
so as to produce the greatest quantity of air.
According to the author just quoted, rain-water flows
out of gutters by a continued current; but during its fall
it separates into portions in the vertical direction, and
strikes the pavement with distinct blows; the air which
exists between the vertical and horizontal separations of
the water which falls is impelled and carried downwards;
other air succeeds laterally, and a current is produced
round the place struck by the water: blasts, or ventaroli,
are also produced by the difference of temperature be-
tween the air of a cavern and the external air.


Fig. 1744.
LATERAL PRESSURE.
The Tide Wheel is put in motion by the ebbing and flowing of the tide, and in con-
sequence of the variable head of water, the sluices are different to those of other wheels.
In the tide mill erected at East Greenwich, on the Thames, the water-wheel has its
axle parallel to the side of the river, or to the sluice-gates, through which it enters :
the length of the wheel is 26 feet, its diameter 11 feet, and its number of float-boards
thirty-two; the latter do not each run on one plane from one end of the wheel to the other,
but the whole length of the wheel is divided into four equal portions, and the parts of
the float-boards belonging to each fall gradually, one lower than another, each by
one-fourth of the distance from one board to the other, as measured on the circumference:
by this means all jerking is prevented, and the action of the water on the wheel equalised.
The wheel with its incumbent apparatus weighs 20 tons, the whole of which is raised
by the impulse of the flowing tide when admitted through the sluice-gates: it is placed in
the middle of the water-way, with a passage on each side 6 feet wide, through which the
water flows into the reservoir.
After the tide is mounted to its extreme height, which is 20 feet above low water-mark,
the water runs back from the reservoir into the Thames, when a contrary motion is given
to the tide wheel: the most ingenious part of the machinery is that by which the wheel
is raised and depressed.
Suppose A B to be the section of the water-wheels, and P the vertical shaft, which car-
ries two equal wallower wheels, E, F, so placed that either of them may, as occasion requires,
be driven by the first wheel D; and the first wheel acting upon the wallowers F and E at
points diametrically opposite, will, although its own motion is reversed, communicate the
rotary motion to the vertical shaft always in the same direction. In the figure, the wheel
1152
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
E is shown in gear, while F is clear of the cog-wheel D, and at the turn of the tide the
wheel F is let into gear, and E is thrown out; this is effected by the lever G whose fulcrum
is at H, the other end being suspended by the rack K, which holds the pinion on the same

W
*
P
MSI
B
A
R
T
S
y
Q
Fig. 1745.
SECTION OF WATER-WHEEL.
axle as the wheel M: into this wheel plays the pinion N, and the winch, O, on the other end
of the axle, enables the attendant to elevate or depress the wallower wheels as required.
When the tide is flowing, after the mill is stopped a sufficient time to gain a moderate
head of water, it is admitted upon the wheel through a sluice at Q, and the tail water runs
out at R. The hydrostatic pressure of the head of water acting against the bottom of the
wheel frame S, and at the same time between the folding gates T, W, which are thus con-
verted into very large hydrostatic bellows, buoys up the wheel and frame, and mounts
them higher and higher, so that the wheel is never drowned in the flowing water, which
cannot escape under the wheel frame, being prevented by the folding gates, which pass
from one end to the other of the wheel. The wheel and frame are thus buoyed up by a
head of 4 feet, and the mill works with a head of 5 feet, or a little more.
When the tide is ebbing, and the water is running from the reservoir into the Thames,
it might be supposed that the water-wheel would gradually lower with the subsiding of the
water; but to prevent this there are strong rack-works, of cast-iron, by which the wheel
frame can be either suspended at any height or let gradually down, so as to give the water
returning an advantageous head upon the wheel: the sluice R is then shut, and V opened
as well as X, the water entering

at X, to act upon the wheel,
and flowing out at R.
At each end of the water-wheel
is a vertical shaft with wallowers,
and a first cog-wheel, as F and
E, and each of the vertical shafts
turns a large horizontal wheel,
at a suitable distance above the
wallowers, while each horizontal
wheel drives four equal pinions
placed at equal or quadrantal
distances on its circumference,
each pinion having a vertical
spindle, on the upper part of
which the upper millstone of its
respective pair is fixed.
The vertical shaft at each end
of the water-wheel rises and falls
with it, but the large horizontal
wheel, which drives the ma-
chinery, remains always in the
same horizontal plane, and in
contact with the four pinions.
I
Fig. 1746.
DRYDEN'S 1IDE-WHEEL.
CHAP. XVII.
1153
THEORY OF THE MOTION OF FLUIDS.
In the tide-wheel contrived by Mr. Dryden, fig. 1746., the floats are all set at one and the
same angle with the respective radii of the wheel, and have an opening of an inch between
each float and the drum board or soling of the wheel: by this arrangement, the wheel is not
impeded by the tail water, and as the bucket rises out of the water, there can be no vacuum
formed in it, there being a full supply of air, in consequence of which the wheel is free.
Dr. Gregory in his Mechanics has given a clear description of the tide mill, to which we
must refer those readers who may be desirous of further information.
The Breast Wheel, now generally made of iron, differs from the undershot in requiring

10
- อาจารย
Fig. 1747.
ELEVATION OF IRON BREAST-WHEEL.
to be closely boarded, or, as it is called, closely sold round its circumference; the sides are
also close shrouded, or made so as to retain the

water, thus forming in effect a bucket-wheel.
The Pentrough, for conducting the water, has
a rack and pinion, which raises or lowers the
shuttle that regulates the supply.
Of Bodies plunged in Water.
When a body
is placed lightly on the surface of still water,
one of three things will happen, -
1st, If the specific gravity of the body be less
than that of water, it will swim, and only dis-
place a volume of water equal to its own.
Fig 1748.
PLAN OF BREAST-WHEEL.
2dly, If the specific gravity be equal to that of water, it will sink totally, and rest between
two waters.
3dly, If the specific gravity be greater than that of water, it will descend, and be driven
towards the bottom with a force expressed by the excess of its weight over that of the
volume of water the place of which it occupies.

To demonstrate the
first case, suppose a
vessel of a prismatic
form ABCD, placed
on the surface of
water, and that more
be gently poured into
it to the height EF,
which we shall consi-
der as an increase of
the column below
GADH, which being
heavier than the others
of the same base will
descend and cause
B
D
D
E
M
G
A
H
a
d
C
1750
1752
C
Fig. 1749.
H
Fig. 1751.
D
1753
4 E
1154
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
them to rise to its level; thus the first aefd (fig. 1750.) may be regarded as making a part of
the totality of the water: and as the weight of the water contained in the vessel abed was
the cause of its sinking, if a body of equal weight be substituted for it, the vessel will sink
to the same depth as before, that is, it will occupy the place of a volume of water of a
weight equal to that which it will contain. If the vessel abcd be a solid body of a
weight equal to the water which it can contain, it will sink to the same depth as before, to
occupy the place of a column of water in weight equal to its own: hence the specific gravity
of the prism abcd, considered as a solid, will be to that of the water reciprocally as the
height ae of the water in which the prism is sunk, is to the height ab of the prism itself:
when, also, a body lighter than the column it displaces is forced into water, it is driven
from below upwards by the surrounding columns, with a force equal to the excess of the
weight of this volume over that of the body.
In the second case, if water be continually poured into the vessel abcd (fig. 1751.) to fill
it, it will continue to sink until the surfaces of the two columns of water are at the same
level; the vessel being then entirely plunged in the reservoir will form a part of the
column gbch, which becoming in equilibrio with the others, the vessel will be so also. If
the height gb of the column gbch contain several times that of the vessel, this column will
be composed of several prisms abcd, and it being indifferent to the equilibrio whether
one be at the surface or bottom of the fluid, at whatever part the vessel be placed, it will be
in equilibrio with all that surrounds it. Since the volume which a body occupies in
water may be considered as forming a part of the totality of the water itself, it follows, that
when a body of a greater or less specific gravity than water is plunged therein, the bottom
of the vessel is more loaded than before, by the weight of the water, whose place this body
occupies, or by that of the body itself.
In the third case, (fig. 1752.) the body only maintaining itself between two waters as
long as it is kept in equilibrio by a force equal to the weight of the volume of water whose
place it occupies, it is evident, that when this body is heavier than that of the same
volume it must surmount the resistance opposed to it, and descend with all its remaining
force, i. e. with the excess of its weight over that of the volume whose place it occupies:
thus, bodies lose in water a part of their weight equal to that of a volume of water whose
place they occupy.
A heavy body whose specific gravity is greater than that of water swims, or is maintained
in equilibrio between two waters, if attached to another body whose specific gravity is
greatly less than that of water: for example, if the prism CEDH (fig. 1752.) be only
sunk in the water by the height CF, we may suppose all its weight united in the part
CFGH, and consider the other FEDG as without weight. If to the centre of gravity
of this prism a body D (fig. 1753.), of a specific gravity twice that of water, be suspended,
and the volume of this body be equal to CFGH, it will cause the prism to descend
to a depth Ck, twice CF, after which they will maintain each other at rest; because
the body D, weighing only half what it would in air, will be in equilibrio with the weight
of a volume of water occupying FkMG, which is only kept in equilibrio by the weight
D: the volume of the body D, and that of the part Fk M G of the prism, having raised
the surface of the water to the point which it would have reached if, instead of having
plunged the body D therein, a quantity of water had been substituted, of a weight equal
to that of the body, and the bottom of the vessel would be as much loaded with it
as if it supported it: if the thread be cut, the body will descend, and the prism CEDH
will rise to assume its natural position. If we suppose the vessel very deep, the bottom
during the time of the descent of the body will be less loaded than it was, by the excess of
the weight of the body over that of the volume of water whose place it occupies; for the
prism having remounted to the height Fk, the surface of the water will descend as much
as if a volume of water had been abstracted equal to that of the part Fk MG. It may then
be stated as a general principle, that as long as a foreign body is supported in water, it
forms a part of its total weight, and loads the bottom of the vessel with all its weight; but
from the moment when it begins to descend freely till it reaches the bottom, this latter is
relieved of the excess of the weight of the body over that of the volume of water whose
place it occupies.
On the Equilibrium of Floatation, or the position of a floating body when its centre of
gravity is in the same vertical line with the centre of gravity of the displaced fluid: when
a body is in equilibrio in a fluid, its weight is always equal to that of the fluid displaced :
from the equality between the weight of the body and that of the displaced fluid, the
upward pressure of the fluid is exactly capable of balancing the downward tendency of the
body; but unless these two forces are directly opposed to each other by passing through
the same point, the solid body will have a rotary motion instead of a position of perfect
equilibrium: all solids will not, however, permanently float in every case when their
centres of gravity are situated in the same vertical line, for a cylinder, whose specific
gravity is to that of the fluid on which it floats as 5 to 4, whose axis is to the diameter of
its base as 2 to 1, its length 2 feet, and diameter 1 foot at the base, when held in the fluid
with its axis in a vertical line, will sink in the fluid 18 inches; but when no longer sup
CHAP. XVII.
1155
EQUILIBRIUM OF FLOATATION.
ported, it will fall and float horizontally: a cylinder 6 inches in length, and of the same
diameter, will sink 4 inches, and in that position will float permanently: there are,
consequently, different kinds of equilibrium, as that of stability, instability, and of in-
difference.
The stability of bodies floating
on a fluid at any angle of in-
clination from a given position of
equilibrium may be thus deter-
mined: - suppose EDH F a ver-
tical section through the centre of
gravity G of a homogeneous solid,
whose figure is symmetrical with
regard to the axis of motion, and
that it floats on the surface HABL
of the fluid, O being the centre of
gravity of the part immersed: the
line GOC will be perpendicular
to AB: if, by an external force,
the solid is inclined through an
angle K GS, it will take the
position SRLMN, and the part
immersed will be WRMNP:

H
E
W
A
b
R
D
K
G
Z
X
F
B
-L
'P
tR
T
Y
N
E-
OQ F
H
M
Fig. 1754
hence, as the part X WI is raised out of the water, and the corresponding and equal part
X NP immersed, the centre of gravity, which would otherwise have been at E, will be
transferred to the point Q: by drawing QS parallel to GO and EY, and ZGz perpen-
dicular to SQ, it is obvious that the upward pressure of the fluid will be exerted in the
line QS, with a force equal to the weight of the body, or that of the fluid displaced, and
this force will have the same tendency to turn the body round its axis of motion, as if it
were applied at the point Z: to determine, then, the position which bodies assume on a
fluid surface, and the stability with which they float, it is only required to find the perpen-
dicular distances G, Z, between the two vertical lines which pass through the centre of
gravity of the solid and the part immersed: as the weight of the body continues the same,
the portion IX W elevated from the fluid, in consequence of the inclination, must be equal
to PXN, the portion immersed: supposing a to represent the centre of gravity IX W, and
f that of N XP, the centre of gravity Q will be at a distance from E corresponding to
the change produced by removing the fluid IW X to the position NX P. To determine
by a geometrical construction the line GZ, let fall the perpendicular ab, fc, and in the
line EY, drawn parallel to AB, take ET, so that ET: bc=volume I WK: volume
WRMP; through T draw FTS parallel to G O, the required centre of gravity will then
be somewhere in FS: and because ER: EG= sin. KGS : rad. ; the line GO-EG,
being supposed given, the line ER will be determined, and being taken from ET, already
found, will leave ET or GZ, the perpendicular distance required.
When the body of a system is removed from its place, the corresponding motion of the
common centre of gravity, estimated in any given direction, is to the motion of the body
moved, and estimated in the same direction, as the weight of that body is to the weight of
the whole system: considering, then, IRMN as a system of bodies, whose common centre
of gravity is E, and that the body IW X, whose centre of gravity is a, has moved, or been
transferred to NX P, whose centre of gravity is f, we shall have volume WRM P, or
ADHP: volume I W X, or W XP bc: ET, the motion of one body, and the centre
of gravity of the system.
Suppose, then, V= the volume of the immersed portion of the floating body,
A = the volume NX P, or the part immersed in consequence of the
inclination,
h = GO, the distance between the centre of gravity of the whole
solid, and that of the part immersed,
s = to the sine of the angle of inclination KGS,
b
---
bc, the space through which A has been transferred.
b x A
Then, b: E TV: A, and ET
;
V
but, ER: EG, or GO = s : 1, we have ER
8: ER=hs;
consequently, RT-ET-ER, or GE =
b A
hs.
V
When a solid body floats upon a fluid of greater specific gravity than itself, and has at-
tained a state of equilibrium, the magnitude of the body is to that of the part immersed
below the plane of floatation, as the simple specific gravity of the fluid is to that of
the floating body: therefore, to find the magnitude of any solid so floating, subtract the
4 E 2
1156
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
specific gravity of the solid from that of the fluid; multiply the remainder by the magnitude
of the solid, and divide the product by its specific gravity for the weight to be added: or
the same may be more practically expressed by multiplying the specific gravity of the
fluid by the height of the body above its surface, and dividing the product by the difference
between the specific gravity of the fluid and that of the solid; the quotient will give the side
of the cube required.
For example, if a cube piece of oak when floating with its sides vertical, stands above the
surface 12 inches, and we consider its specific gravity 8 when water is 1, we shall have
the length of side required
12 x 1
1-8
= 60 inches;
therefore the cubical content of the body is 60 × 60 × 60=216000 inches.
To determine how much of a Paraboloid will sink, when in a state of quiescence on the sur-
face of a fluid, we must divide the difference between the specific gravity of the fluid and
that of the solid by the specific gravity of the fluid; then from unity subtract the square
root of the quotient, multiply the remainder by the axis of the parabola, and we shall obtain
the height of the frustum that falls below the plane of floatation. Or, if we divide the
specific gravity of the solid by that of the fluid on which it floats, and multiply the square
root of the quotient by the axis of the body, the product will give the height of the part
below the plane of floatation.
Floating Bodies. If a body float on a fluid, it displaces, as we have shown, a quantity
of the fluid equal to itself in weight: for since the body is supposed to remain at rest, and
to retain the pressure of the fluid below it in equilibrio, it must exert by its weight a
pressure downwards equal to that of the quantity of fluid which would retain the same
pressure in equilibrio, or to the quantity displaced.
When the centre of gravity of the floating body is in the same vertical line with the
centre of gravity of the fluid displaced, the body remains in equilibrio: if the section of
a floating body made by the surface of the fluid be a parallelogram, its equilibrium will be
stable or tottering according as the height of its centre of gravity, above that of the portion
of the fluid displaced, is smaller or greater than one-twelfth of the cube of the breadth,
divided by the area of the transverse vertical section of the immersed part.
A
D
R
E
G
H
P
N
אס
K
MA
Let the body be inclined in a small degree from the
position of equilibrium, A B C, into the position DE F,
the triangles GH1 and KHL will be equal, since the
area of the section immersed must remain constant, and
GK and IL will ultimately bisect each other in H. Now
the centre of gravity of the section ILF is the common
centre of gravity of its parts, IHMF and LMH, making
KM GI; but N, the centre of gravity of IHM F, is in
the line H F bisecting it; and the common centre of gra-
vity may be found by making NO parallel to HK or
to HL, in the same ratio to the distance of the centre of
gravity of LMH from H, that LMH bears to IFL.
Now the distance of the centre of gravity of any triangle
from the vertex being two-thirds of the line which bisects
the base; in this case it is HK, and the area of the
triangle LHM is HK. KP; therefore NO: HK::
Fig 1755.
HKq. KP
HK. KP: LFI, NO=
; but drawing OQ vertically through O, NO:
IFL
NO.HK HK cub. I L cub.
KP
IFL

NQ:: KP: HK, and NQ=
=
ΤΣ
IFL
If therefore the centre of gravity be in Q, the body will remain in its position, or the in-
clination will be very small, since the result of the pressure of the fluid acts in the
direction OQ; if the centre of gravity be below Q, it will descend towards the line QO,
and the body will recover its situation; if above Q, it will be overset: hence the point Q
is sometimes called the centre of pressure.
Fountain of Hiero. The fountain of Hiero is a machine by which the motion of one
column of water is transmitted to another by the intervention of a bed of air separating the
two in generalising the principle on which the construction of this fountain is based, we
may consider it as a machine, transmitting the motion of a liquid, A, to any other liquid, B,
by the intervention of a compressible or incompressible fluid whose specific gravity is less
than that of the two liquids A and B.
Fig. 1756. represents the fountain of Hiero, composed of three bases, NPQI, DRSD,
PQË, also marked by the letters C, C', C". The C, C", are filled with water, and the vessel
C' with air; the water from the vessel C falls into C' by a tube, BD D', and transmits its
motion to a column of water, which is elevated from the vessel C by the tube KL; this
transmission is made by the intervention of the air, which fills the vessel C', and the tube
FEH.
CHAP. XVII.
1157
OF THE MOTION OF FLUIDS.
The bottom, PQ, of the vessel C forms a cover to the lower vessel, C", the two only
communicating by the opening A, which is closed by a plug when the vessel C" is full of

P
N
2+0=
CI
Q
Ꮮ
L
E
T
N
D
F
F
D
LJ
R
S
R
R
X
с
Fig. 1756.
HIERO'S FOUNTAIN.
Fig. 1757.
water: the vessel C" communicates with the external air by a tube, KL, which traverses
the bottom, PQ, of the vessel C, and is open at both ends,
To put this machine into play, the cock, Z, of the tube, BZ DD, is opened; the water
from the vessel C flows through D', fills the vessel C', and compresses the air contained in
it, which compression transmits itself by the tube FEH to the liquid in the vessel C', and
obliges it to rise by the tube, KL; the vessels C, C" are emptied, and C' is filled; NI, ni,
RS being the levels of the water in the three vessels; the air comprised between the levels
RS and ni is more compressed than the atmospheric air, and this increase of pressure, which
we may call p, is measured by a column of water whose vertical height is the distance between
the levels N 1 and R S, which is variable, the vertical distance being continually diminished.
The pressure at K, the extremity of the tube KL, open at both ends, is evidently the sum of
the two pressures, of which one is equal to p, and the other p' is measured by a column of
water of the variable height KK, KK, being the vertical distance from the extremity, K
of the tube to the level of the water, ni, in the vessel C"; therefore the pressure at K, which
elevates the water in the tube KL, is variable, because it depends on two other pressures p
and p' which decrease every moment. If the level ni descended to K, the water would
rise in the tube KL, to a height equal to the vertical distance of the two levels, NI and
R S, corresponding to the level ni, which we suppose has descended to K; but at the
moment when the machine is put into play, the water would elevate itself in the tube KL
to a height equal to the vertical distance of the extremity D' of the tube BD', from the
first level NÍ; then the force which elevates the water in the tube KL would decrease ·
4E 3
1158
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
and its limits are the minimum and maximum pressures which correspond to the two
heights to which the water can elevate itself in the tube KL, at the beginning and end of
the movement.
When the vessel C" is empty the cock Z is closed; the vessel C is then emptied by the
pipe VX, which is closed by a plug, X, removable at pleasure; the vessels C, C" are filled
as before stated, and the machine is ready to play again.
The tube BD', by which the water falls from C to C" might terminate at D; the pres-
sure of the air of the vessel C' would then only depend on the height of the level NI
above the point D; as long as the tube BD is prolonged to D, this pressure depends on the
distance between the two variable levels, NI and RS.
Supposing that instead of filling the vessels C and C" with water, some other liquid were
substituted, as mercury, and the air which the vessel C' and the tube FH contain replaced
by another incompressible fluid, such as water, the pressure of the water would replace that
of the air, and the mercury in the vessel C produce in falling a force capable of elevating
that in the vessel C" in the tube KL. The incompressibility of water transmits the moving
power, by increasing the effect for the power employed to compress the air which would
remain in the vessel C, and which is gained the instant that the tube K L no longer contains
water, as the air compressed in the vessel C' mixes with the atmospheric air by the tube
K L, and produces no useful effect.
The invention of this machine is attributed to Hiero, who lived 100 years B.C., and it
has been constructed on a large scale for emptying water from the mines at Schemnitz in
Hungary; its principle, modified by Gerard, has been applied to elevate the oil in
hydrostatic lamps. In the machine of Detranville, water is raised by the rarefaction of the
air; in the fountain of Hiero the same effect is produced by condensing it.
Gerard's bave this advantage over the ordinary Argand lamps, that the reservoir of oil
being below the focus of the lamp, it does not throw a shadow on the surrounding objects.
Fig. 1757. represents the new fountain of Hiero as applied to hydrostatic lamps: pq E
is a vessel filled with oil, which falls through a tube BDY in the vessel RDS, which is then
full of air; these two vessels correspond with those marked C and C' in fig. 1756.: they are
designated by the same letters in fig.1757.: the vessel C only communicates with the external
air by the tube UT, which traverses the cover pq ; the oil cannot escape from the vessel by
the tube BD Y, except when the air enters by the tube TU, so that the elastic force of the
air, pq
NI, and the pressure of the liquid, NIU, always equalise the pressure of the atmo-
spheric air which fills the tube UT.
Drinking glasses for birds and inkstands are constructed on this principle of equilibrium.
The tube BĎY is plunged below Y into a cylindrical vessel aßde filled with oil and open
above, while it is closed below by the plug Y; the height from which the oil of the vessel
C falls into C" is constant and equal, B Y, whatever may be the heights of the level NI and
RS in C and C'.
The vessel C' communicates with another, C", full of a liquid similar to that in C'; this
communication is established by means of a tube of any form FEe H, which passes through
the cover PQ of the vessel C", terminating at the bottom H of this vessel. The vessel C'
communicates with the external air by a tube L K, which is prolonged to the bottom of the
vessel; the orifices H and K of these two tubes are in the same line with the level H K.
If we suppose the vessel PpqQ or C" of a height Pp less than BY, the pressure of the
fluid PHQ on the orifice H cannot equalise the air contained in the vessel C' and in the
tube FeH; this air being compressed by the weight of the atmosphere and a column of
liquid of the height By, it will leave the tube FEH by the orifice H, and occupy a space
PQni in the upper part of the vessel Ppq Qor C"; the liquid which the air has replaced will
elevate itself in the tube KL.
When the air contained in the vessels C'; C" is in equilibrio, the height KL, to which
the liquid will elevate itself, will be equal to the constant keight By: the pressure on the
extremities K and H of the tubes RL and HcEF are equal; that at H results from the
pressure of the liquid ni H, and the elastic force of the air contained in the vessel C' and the
tube FeH; but this elastic force has for its measure the height BY of the liquid; the
pressure at the extremity of the tube L K is due to the same height B Y, and by giving to
KL a height less than BY, the liquid of the vessel C' would rise in the tube KL by a
constant force of pressure.
In the hypothesis of the ascensional movement of the air contained in the vessel C' and
the tube FH, the air of this tube is less compressed at H than at F, otherwise the
ascensional movement would be impossible; but to fulfil the object proposed it suffices
that the compression of the air at H be constant: by giving to the tube FH convenient
form and dimensions, the vessel C" may be placed in any position with regard to the ves-
sel C.
When the vessels C and C are empty, there are several methods of refilling them:
fig. 1757. indicates the following; the tube KL is composed of two parts, K 7, 7L, which
are screwed together at nl; when they are separated the oil is poured through the opening 1,
CHAP. XVII.
1159
OF THE MOTION OF FLUIDS.
and the air from the vessel C' or PpqQ escapes by the same opening: a tube A a traverses
the cover PQ, and the bottom pq of the vessel C"; oil is poured through the orifice A; it
flows through the other orifice a, and falls into the vessel C or pq U; the air of the vessel
escapes through the same orifice, u, of the tube A a, and as we suppose the cock Z closed, the
vessel C is filled.
It does not suffice to fill the two vessels C and C"; we must empty the vessel C', the
bottom of which communicates with a pipe VX closed by a plug; we remove the plug and
the liquid runs out; but at the same time the air must introduce itself, which it does in
two ways, for it may enter by the tube He F before we have filled the vessel C', or by the
cup aẞde, which is closed by a plug Y removable at pleasure.
Fig. 1757. is the form which Girard presented to the Polytechnic School. Of the three
levels NI, ni, RS, in the three vessels C, C', C", two being given, the third is found;
knowing the volumes of these vessels, we find by calculation the relation between the
quantities which determine the position of their level lines.
Description of the Hydraulic Ram. -The water from a source enters at A with an
acquired velocity due to the height of the fall, flows through the conduit-pipe AB, which

Fig. 1758.
B
H
I
G
HYDRAULIC RAM.
F
L
is exchanged at A, and inclined with a fall of at least 27 millimetres in 2 metres; it escapes
by an orifice C, which may be closed at pleasure by a valve. A reservoir of air, F, is
united by means of a cylindrical pipe, abcd, to the conduit pipe, BD; at the centre of the
bottom of the reservoir F is a circular orifice, to which a small cylindrical support is
adapted, whose extremity, E, is furnished with a valve; s is another valve destined to main-
tain the air in the reservoir F, and in the space m n, comprised between the pipe abcd, and
the small support E of the valve; GIH is an ascension pipe, which rises from G in the
air reservoir F. The pipe A B, B C, by which the water flows from the source, is called
the body of the ram; the tube GIH, through which the water elevates itself above the
source, the ascension pipe; of the two valves D and E, which close the orifices C and E,
the first is the flowing or stopping valve, and the second the ascension valve; these valves
are hollow balls, D and E, which are retained by muzzles, and they do not weigh more than
twice the volume of water they displace; the extremity of the body of the ram, which car-
ries the valves and reservoir of air, F, is termed the head.
This machine acts in the following manner: the water through the orifice C acquires a
velocity due to the height of the fall; it obliges the ball D to leave its muzzle, and elevate
itself to the orifice C, which is terminated by round pieces of leather, or tarred cloth, to
which the ball applies itself exactly; as soon as the efflux through this orifice stops, the
water raises the ball E, which closes the orifice E of the air reservoir F, and flows at the
same time into this reservoir and into the ascension pipe GIH, losing the velocity which
it had at the moment when the opening C was closed; the balls D and E then fall by their
own weight, one into its muzzle, the other into the orifice E; the water from the source
begins again to flow through the orifice C, the valve D again closes, and the same effects
are produced. The revolution of the ram commences when the stopping valve D ceases to
be applied to the orifice C; it ends when this valve returns to the same position: in this
revolution there are four distinct operations; in the first, the water, by flowing through the
orifice C, acquires a part of the velocity due to the height of the falls, and the stopping
valve D closes; in the second, the stopping and ascension valves are closed, and the elastic
bodies, whether metals or air, are compressed; in the third, the ascension valve opens the
air of the reservoir F, which is compressed; the water elevates itself in the ascension pipe
G, the ascension valve closes, and the stopping valve does not re-open; in the fourth, the
elastic bodies compressed in the second re-act, the ascension valve remains in its place, and
the stopping valve, no longer applied to the orifice C, falls into its muzzle.
With regard
to the duration of time occupied by these four operations, we may observe that in the first,
if the distance from the stopping valve D to the orifice C, and the weight of the valve, be
increased, the greater will be the velocity of the water which flows through the orifice C,
to raise the valve D and apply it to the orifice C: for each position of the valve, at the
4 E 4
1160
Book II
THEORY AND PRACTICE OF ENGINEERING.
bottom of its muzzle, the quantity of water elevated in a certain time is measured, taken
as unity through the ascending tube GIII; and by varying the distance from the valve D
to the orifice C, the water in the body of the ram receives the velocity which corresponds
to the maximum effect of the machine.
In the second operation, the air contained in the space MN is compressed by the force
developed in the first operation, which also drives the water through the orifice E, in the
reservoir of air F, and into the ascension pipe H, when the valve E immediately falls by
its own weight from its muzzle into the orifice E, and the stopping plug D again closes
the orifice C: the two valves being closed, the air compressed at mn reacts, and although
the time of this reaction is scarcely perceptible, the effects resulting from it have a great
influence on the play of the ram; the reaction obliging the water to return from the head
of the ram towards the source, which forms a void at the extremity of the head; the
atmosphere presses on the stopping valve D, the orifice C opens, and the water from the
source contained in the body of the ram ABC, in flowing through this orifice, reassumes
its primitive velocity: the water continues to elevate itself in the ascension pipe GH, by
the elasticity of the air compressed in the reservoir F, which acts on the water and forces
it to rise. The motion of the ascending column of water communicates itself to the air
of the reservoir F, which would soon be emptied if a fresh portion were not introduced
into it at each revolution of the ram: the little channel s, closed by a valve, conducts this
air; the valve opens from the exterior towards the interior of the ram, in consequence of
the void formed by the fourth operation, and a certain volume of atmospheric air enters
the little cylinder abcd, situate below the reservoir E, into which it is driven, a portion
being arrested in the space m n, and forming the elastic body we call a bed of air; it is
the reaction of this compressed air which causes the water contained in the body of the
ram to return to the source.
It results from this description of the hydraulic ram, that its principal parts are, 1st,
the body of the ram; 2dly, the head which comprises the stopping-valve, the ascension-
valve, the air-valve, the reservoir, and the bed of air; 3dly, the ascension-pipe. We do
not, as yet, know the dimensions which should be given to the different parts of the ram,
in order to ensure the greatest effect possible from a source of water. An experiment
was made at Marly, which showed the application of the hydraulic ram on a large scale;
the mean fall was 1.62 metres; this height is the mean difference between the levels above
and below the Seine: the body of the ram which was constructed was 33 centimetres internal
diameter; the vertical height to which it ought to have elevated water is 155.5 metres:
it is principally for these large rams that recourse must be had to experiment, and to
make a great number of observations on the form, dimensions, and general disposition of
the parts which compose them.
As for the lesser rams, experience has brought them to a great degree of perfection, and
those who use them praise them highly. A mechanic who should
A mechanic who should compare the quan-
tities of water expended to the quantity elevated would conclude that the ram was
the best hydraulic machine; it has, above most others, the advantage of being applicable to
the least abundant sources of water; the least fillet of water can move a ram by giving it
dimensions coincident with the moving power: with regard to economy there is no machine
which requires less expense for its first establishment and maintenance.
To give a precise idea of the dimensions of rams which have been employed, we must
refer to those which have been constructed, 1st, at Lyons, by Fay Sothonay, Mayor of
Lyons; 2nd, at the bleaching-ground of Turquet, near Senlis; 3rd, at Clermont Cisé,
under the sub-prefecture of Larochefoucauld.'
The source of Fay Sothonay gives 84 litres per minute; the fall of this source is 10-6
metres: by taking a cube diameter of water elevated 1 metre as the unit of force, the
power of the source during one minute will be expressed by 890. The body of the ram
is 54 millimetres diameter, and the length 32.5 metres. The ascension tube was 227 metres
long; it furnished 17 litres per minute. The water was elevated to a vertical height of
34.1 metres; thus the force transmitted by the ram during one minute is expressed by 579;
579 65
the relation of this number to the expenditure of power in one minute is
890 100
The body of Turquet's ram was cast-iron, 0203 metres in diameter, and the length
about 8 metres; it elevated water to a vertical height of 4:55 metres; the quantity so
elevated in one minute was expressed by 1224; the source furnished in the same time 1987
litres; its fall was 0.979 metres; its force in one minute was 1945. The relation of the
transmitted force to that expended was then 1224-635.
100
Delcassan, who executed Turquet's ram, has verified by experiment the importance of
giving to the tubes which form the body of the ram, as well as to the wood or stone
supports of the tubes, the greatest solidity; he conceived that the force employed to
move the body of the ram or its support is lost for the effect we wish to obtain. Having
remarked that, by increasing the head of the ram, the machine would elevate a greater
CHAP. XVII.
1161
THEORY OF THE MOTION OF FLUIDS.
quantity of water, he melted lead on the body of the machine, until the weight of the lead
seased to increase the product of the machine.
The body of the ram established near Clermont Oise is 27 millimetres diameter, and 33
metres long; it is on the side of a mountain with a fall of 7 metres in 33. The ascension
pipe is 14 millimetres in diameter, and 420 metres long; it furnishes 1400 litres of water
in 24 hours; the water is elevated to a vertical height of 60 metres; the force transmitted by
the ram in 24 hours is expressed by 84000.
;
The source furnishes in 24 hours 17,878 litres of water, or 19,200 pints; this water falls
7 metres in going through the whole length of the body of the ram, which is 33 metres
the force expended in 24 hours is 125146; the relation of the force transmitted to the force
expended is 84000
123146-100
67
Montgolfier, Junior, established at Mello, near Clermont, an hydraulic ram of cast-iron,
1450 kilogrammes in weight: the length of its body is 33 metres (100 feet), its diameter
11 centimetres (4 inches), and the thickness of each pipe 14 millimetres (6 lines); the head
of the ram separately weighs 200 kilogrammes. There were 7 balls or stopping valves,
each 4 centimetres diameter, disposed as is shown at N N', on 7 orifices pierced in a single
circular disc, as seen in the figures on page 1163; the ball or ascension valve is of the
same diameter; the ram makes 60 strokes per minute; the volume of the reservoir of air is
about 20 times that of the quantity of water elevated at every stroke. The source is 140
litres per minute, and its fall is 11.37 metres (35 feet): the water is elevated 59.44 metres
(183 feet) above the head of the ram, and the quantity of water raised is 17 litres per minute.
Taking the kilogramme elevated a metre as unity, the product and expenditure in a
minute are expressed by the numbers 1040 and 1592, whose nearest relation is 6.
100
100.
These examples prove that the force transmitted by the ram is at least of that em-
ployed to move it; we know of no other water-machine which transmits so considerable a
part of the action of the mover applied to it.
J
M
Siphon Ram. When water is made to pass by means of a siphon from one place to
another less elevated, the column of water fills the interior of the siphon; but if the summit
communicates by a small aperture with
the external air, the column separates
into two parts which flow through the
two branches of the siphon. There are
few machines more useful and simple
than the siphon: the cut represents one
executed for the Polytechnic School at
Paris.

ALCG is a siphon transporting
water from A to G ; on the long branch
GB is a ram's head with two valves
at C of flowing and ascension, and above
them a reservoir of air; a cock is placed
at G, and a valve at K, which opens and
shuts by means of a lever, the extremity
of which is fixed at L when this valve is
open.
£
B
D
K
To work the siphon, the cock G and
the valve K are shut; water is poured
through the pipe D; the air escapes by
the same pipe both out of the vertical
branch GB, and that inclined to the
horizon, DL; the pipe D being closed
by a plug, the cock G and the valve K
are opened; the water which flows
through the siphon from A to G shuts
the flowing valve C, opens the ascension
valve E, and escapes at M in a jet of water, or raises itself in the ascension pipe screwed
on the air reservoir above C.
Fig. 1759.
SIPHON RAM.
Suction Ram. A source of water flows through the tube A B DK, and it is proposed
to elevate by its means the water from the well M NG; in the interior of the branch PQ
of the tube is a ball valve C, to shut the orifice D of the same tube: near this orifice D is a
suction tube E, composed of two parts, EF, G G', united by an air reservoir HH,
and at this end of the tube is a valve opening from below upwards: the water from the
source, in flowing through the orifice K, acquires a velocity arising from the fall; the valve
C, sustained by the column of water produced by this velocity, closes the orifice D by
adhering to the round pieces of leather or cloth shaped into a hollow sphere; the column
DEK continues its movement towards K; the void formed in the tube DEK, and the
1162
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
atmospheric pressure elevates the water in the well by the suction pipe: the height to
which the water rises depends on the velocity with which it flows from the source through
the orifice K: the object of the dilated air reservoir H H is to maintain the motion of the
ascending column G'G.

P
H
H
·B-
Q
G'
M
N
HH
K
Fig. 1760.
SUCTION RAM.
We must now refer to what was before said on the return of the water, which the body of
the ram contained, towards its source, and we shall easily conceive how this may become a
suction ram: if the space mn, (fig. 1758.) of the bed of air communicates by a tube with
the reservoir of water placed below the body of the ram, at each re-action of the bed of air
the water of the reservoir would elevate itself, to equalise the elastic force of the air con-
tained in the space mn and the atmospheric air; and if the distance of the lower reservoir
from the body of the ram is not too considerable, the water of this reservoir would flow
with the water of the source which puts the ram in motion: when we estimate the total
effect of the ram, we must then have regard both to the water elevated by the ascension
pipe and that elevated by the return of the ram.
Example of this double Effect. Montgolfier had placed a ram's head at the extremity of
a cast-iron pipe 54 millimetres (2 inches) in diameter, and 19.5 metres (60 feet) in length;
this tube expended 65 litres of water per minute, falling from 3.25 metres (10 feet); taking
for unity a cube decimetre or litre of water elevated 1 decimetre, the power expended in a
minute by the body of the ram was 2212. At each pulsation of the active column of the
ram, which was followed by the return of the flowing valve to its orifice, 142-44 cube centi-
metres of water were elevated by the ascension tube 18.516 metres, the interval between
the two pulsations being 1 second; the ascension tube furnished 8·546 litres of water in a
minute to a vertical height of 18.516 metres; thus the force transmitted by the ascension
tube is expressed by the number 1582-37. To this first effect we must add that which we
obtained from the return of the ram; a suction tube which should arise from the space oc-
cupied by the bed of air, plunged in a reservoir distant 0·975 metres from this bed, all the
water in this ascension tube would be furnished by the suction tube; therefore at each
minute the return of the ram would elevate 8-546 litres of water to a vertical height of
0.975 metres. This effect is the measure of a force of 83-32, which being added to the first
effect, 1582.37, gives for the total effect of the ram in one minute 1665-65; but the force ex-
pended in the same time is 22·12; the relation 75% of these two numbers is still greater than
in the preceding examples.
100
Montgolfier projected at Marly a ram, which was at the same time a siphon and suction :
the siphon form appeared to him most preferable, because it placed the greater part of the
pipes of the body of the ram out of the water; the suction tube emptied the water filtered
by a chest placed on the bed of the river, and there was no fear of a deposit of sand on the
valves or their orifices.
Fig. 1761. shows, 1st, a system, N', of seven valves and seven orifices; 2d, a disc M',
pierced with holes, through which the water enters the air reservoir L, fig. 1762.: in
general the number and size of the flowing orifices determine the relation of the velocity
of the water in the body of the ram, and its issue through each orifice.
CHAP. XVII. THEORY OF THE MOTION OF fluids.
1163

E
N
12
નમ
@
E
Fig. 1761.
PLAN OF siphon and sucTION RAM.
Fig. 1762. KHB B is the branch of a siphon which leads the water from the source; it
flows through the apertures N, N, N, falls into the cistern PQSR, and joins the lower waters,

L
b
a
WA WA VIA
VA VA YA
M M M
T
B
Ρ
B
N
N
N
Q
H
H
K
X
Y
R
Fig. 1762.
SECTION OF SIPHON AND SUCTION RAM.
XY; H is a funnel, garnished with a stop-cock to feed the siphon; T is the suction tube,
which arises from above the ascension valves M, M, M ; below these same valves is a wooden
float, which is lowered by the action of the air-bed, and which rises by the action of the
water in the body of the ram against the ascension valves: the space in which the floater
moves is called the lift of the floater. O is the small canal through which the outer
air enters the reservoir L; ab is the ascension tube.
Fig. 1763. shows on a larger scale, 1st, the ascension valve; 2d, the air valve NO, which
serves to maintain the air in the reservoir L; 3d, the floater's lift, Z. In the ram executed
at Marly there is no suction tube, but the siphon form is preserved, as in the first
project; the inconveniences which result from this form for rams of a large size were
difficult to foresee: in small rams it is necessary to introduce the external air into the space
1164
THEORY AND PRACTICE OF ENGINEERING. Book II,

Plan
N
2
Fig. 1763.
SECTION OF SIPHON AND SUCTION RAM.
occupied by the bed and reservoir of air; the contrary takes place in the great ram siphon,
such as that established at Marly; the effect of the ram's return has a tendency to intro-
duce air through the joints of the tubes or cistern, and, as the junction cannot be per-
fectly exact, this air enters in so great a quantity that the whole force of the ram is required
to compress it.
In the first trials Montgolfier made with this machine he placed the ascension valve in
the interior of the ascension tube, at some distance from the body of the ram, and filled
the ascension tube with water, to put the ram more easily into motion; the atmospheric
air, however, retained between the ascension valve and the column of water in the body of
the ram, occupied so considerable a volume, as to destroy the useful effect of the ram, the
active column being employed to compress this air: an inconvenience of this sort presented
itself when the siphon ram at Marly was experimented on.
Great Siphon for drawing off Water, as employed at Metz in repairing a dyke constructed
on the Moselle: it raised the water from the head of the dyke, and discharged it into the

;
Fig. 1764
GREAT SIPHON EMPLOyed at mETZ.
M
K
CHAP. XVII
1165
THEORY OF THE MOTION OF FLUIDS.
river, the difference of level being 1 metre: the long branch of the siphon was 30 metres,
and the diameter 8 centimetres; the two extremities of the siphon were closed with wooden
plugs: the siphon was filled with water through the funnel I; the air escaped by the cock
M; when full of water this cock was closed, a cover LO was screwed on the funnel, and
the cock K was kept open; the velocity of the water in the siphon not being very
great, the air brought up by this water accumulated at the highest point of the siphon, and
lodged in the funnel I: to let it out, the cock K was closed, the cover LO taken off, the
funnel filled with water, after which the cock K was again opened, and the cover screwed on
the funnel; the part LO of the cover is a glass tube, which contains a needle supported
by a float to show when the funnel I must be filled with water.
Verra's Machine. This machine is a species of chain-pump or endless rope turning on
pulleys, and drawing a certain quantity of water with it; the pulleys, PP and P' P', are
traversed by parallel axes A, B, and united by endless ropes two and two: the pulleys
P, P', plunge into the water, which is to be elevated, and by turning the handle E F, the cord
which passes over the pulleys D, H, and C turns the axle A B, and the pulleys P, P'; the
endless rope that unites the pulleys acquires, by simple friction, a continuous motion, which
communicates itself to the water in the lower reservoir Z M, and forces it into the upper
reservoir NO. The play of this machine chiefly depends on the tension of the endless
ropes by which the required friction is obtained: if this be too great, the pulleys P, P',
cannot turn; if too slight, the pulleys slip on the ropes, and do not communicate any motion
to them. The adherence of the water to the cords favours
the transmission of their motion to the molecules of water.

A
R

Fig 1765.
A
P
Z
VERRA'S Machine.
C
B
H
E
C
Z
M
D
D

Fig. 1766.
HYDRAULIC CANE.
Hydraulic Cane. — This consists of a hollow tube ABCD furnished with a valve D in
the lower part; the extremity of the tube dips into water, and an alternate rectilinear
motion is given to it; the water is elevated, and issues through the upper extremity A; to
render the motion of the column continuous, an air reservoir, R, is added, which separates
the two parts of the tube A B, C D. The cane or tube is fixed by cords to the wooden
spring-blocks EF, GH, fixed to the wall of a well by a cross-piece Z M: aš a substitute
for these spring-blocks, a pole may be placed from an edifice at some distance from the
reservoir containing the water to be raised. The play of this machine depends principally
1166
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
on the velocity with which the tube CD mounts and descends, and it should be sufficient
to allow of the water preserving an upward motion in sliding on the sides of the tube,
although the tube continues to descend.
Machine of Vialon.-On a movable axis AB two helicoidal tubes are placed, whose
central lines are helices of the same number of turns drawn on the same cylinder, but
placed in an opposite direction; each extremity E, F, of the tubes is furnished with valves
which open from without inwards; by means of a lever CD fixed to the axle A B, an
alternate circular motion is given to the tubes; at each impulse of the water on one of the
valves it opens and allows the water to rise, at the same time the other valve closes, and
retains the water already elevated; the two helicoidal tubes unite in one, HKL, by which
the water, when elevated, flows out. This machine and the hydraulic cane are constructed
on the same principle; the tubes in both are terminated by a valve; they differ in the
manner of transmitting the motion to the tubes, the hydraulic cane having an alternate
rectilineal motion, and the machine of Vialon, which is composed of two hydraulic canes,
has an alternate circular motion.


L
K
A
E
D
C
D
M
Fig. 1767.
MACHINE OF VIALON.
Fig. 1768.
CENTRIFUGAL FORCE MACHINE.
Centrifugal Force Machine. — A B is a vertical axis movable on two gudgeons, and turned
by means of a winch A DE; hollow tubes are ranged round this axis like truncated cones,
the small base of which, lm, plunges into water; they are fixed on the circumferences of
circles Im, LM, and are curved at the upper part, so that the water which escapes at the
extremity of the tubes falls into a circular basin parallel to the circle LM: when the axis
A B is turned, the water, to escape from the small circle 7m, rises to the extremities of the
tubes, through which it falls into the vessel GH. Girard made a report to the Academy,
9th December, 1816, on a centrifugal pump, constructed on the same principle, by
Jorge: his pump, as first described in the collection of the Academy machines, 1732,
was composed of a vertical tube, and transversal branches fixed thereon, movable round
the same gudgeons. Jorge's modification consisted in fixing the suction pipe, and only
putting the transversal branches of the apparatus in motion above it: the inertia which
the moving power had to overcome was thus reduced to that of the portion of the machine
which it is indispensible to put in motion, and besides has the very great advantage of
allowing the suction pipe to be inclined at pleasure, or of giving it any form, and thus
enabling it to be used in localities which would not permit of vertical suction tubes.
Archimedean Screw. The newel and the barrel of the Archimedean screw are bounded
by right cylindrical surfaces with circular bases, having a common axis: the threads of the
screw are comprised between the newel and the barrel, and their threads are generated by
movable right lines always perpendicular to the axis of the screw; these right lines rest in
helices of the Same number of turns as are drawn on the internal cylinder of the barrel,
and which intersect the edges of the cylinder at an angle of 45°; the distance between the
two points of the circle at which the helices begin determines the thickness of the threads :
here are generally three or four rows of similar fillets on the same newel, at the upper
CHAP. XVII.
1167
THEORY OF THE MOTION OF FLUIDS.
extremity of which is a winch, and at the lower a gudgeon; the handle and gudgeon rest
on square wooden blocks. When the Archimedean screw is applied to emptying water, the
lower end is plunged into it by inclining the axle at a certain angle, the limit of which
must be determined geometrically; the winch is turned, taking care that its rotation is in
a contrary direction to that of the generating point of the helices, which are drawn on the
exterior, and serve as guides to the generating lines of the fillets. The barrel is formed of
staves strongly bound together by iron hoops, the staves sufficiently close to allow of no
water passing, but the atmospheric air penetrates the joints, so that the interior air between
the fillets of the screw is always of the same density as the outer: if the thickness of the
fillet be disregarded, we may consider it as composed of helices drawn on parallel cylinders,
having for their common axis that of the screw; these helices having the same number of
turns, their bases being the circles of the cylinders on which they are drawn, the com-
mon axis of these cylinders is inclined to the horizontal plane of the water level; the
limit of this inclination depends on the angle made by the tangents of each helix with
the same plane of the water level each helix may thus be considered as the element
of a fillet, or a small hollow channel whose origin is at the orifice at which the water in-
troduces itself: having drawn through this orifice a tangent to the helix, we may sup-
pose it prolonged to the lower part of the screw as a right tube, through which the water
may introduce itself into the helicial tube: if the screw be turned on its axis, the right
tube will engender an hyperboloid of revolution, the common point of the two tubes, of
which one is straight, and the other spiral, and the point placed at the extremity of the
straight tube would describe two circles; the right tube in all its positions would rest on
two points in these two circles, and it is on the position of these two points, with regard to

Fig. 1769.
ARCHIMEDEAN SCREW.
the level plane, that the introduction of water into the right tube depends; for it is necessary
that the extremity of this tube should be less elevated than the point in which it touches
the helicial tube, in order that the water may slide on the tangent to the helix as on an
inclined plane; there is, consequently, a necessary relation between the inclination of the
axis of the screw and the tangents to the helices of its threads, which induces the water to
rise this relation determines the limit of the inclination of the screw's axis with regard to
the level of the water. Suppose the orifice of the extreme helix, or the element of the
fillet farthest from the axis of the screw, constantly plunged in water, while the screw
turns on its axis, the right line, which touches the helix at its origin, will, in turning at
the same time as the screw, generate an hyperboloid of revolution; a parallel to this right
line, drawn through any point of the axis, would generate a right cone, the asymtote of
the hyperboloid of revolution; if through the summit of this right cone, a plane parallel to
the level of the water be drawn, either this plane would not touch the cone, or it would
cut it at the two edges, or be in a tangent thereto : supposing it a tangent, it would make
with the axis of the screw an angle which will be the limit of inclination of this axis with
the horizontal plane, for if this inclination were increased, there would be no position of the
extreme helix in which the water could introduce itself; the middle helices, that is to say,
those nearest the newel, whose orifices would turn in the water, could not, à fortiori, receive
any portion of this water, and no useful effect would be obtained from the motion of the
whole screw.
In Holland the screw is constructed without a barrel, and the fillets turn in a fixed por-
tion of the hollow cylinder, the lower extremity of which, as well as that of the screw
plunges in the water to be elevated, which fills the capacity of the hollow cylinder, and es-
capes at its upper extremity.
The Dutch screws are generally of large dimensions, the inner diameter of the hollow
zylinder being about seventeen decimetres: they are moved by the wind, and the same
windmill turns several.
1168
BOOK II
THEORY AND PRACTICE OF ENGINEERING.

Fig. 1770.
It has been proposed to employ a fall of water to turn the Archimedean screw, by adding
to the extremity of the barrel a second screw, having the barrel as its newel, and its
fillets inclined in a direction contrary to those of the first. This idea was suggested by the
Marquis of Worcester in his " Century of Inventions."
Calculation of the Effects of the Archimedean Screw. The first of the two following ex-
periments was made by Lamandé. The screw was 5.85 metres long, and 0.49 metres
diameter; it was turned by two relays of men, working alternately two hours in succession :
each relay consisted of 9 men; the winch made 40 turns per minute. The quantity of
water elevated in an hour was 45 cube metres, and the height was 3-3 metres: the 18 men
in two relays elevated in 10 hours' daily labour 450 cube metres of water 3.3 metres, or
1485 cube metres 1 metre, which gives for the measure of a man's daily work 82 units of a
cube metre of water elevated 1 metre, a power nearly equal to that of a man employed in
driving piles.
The following experiment gives 10 units more per man for the useful effect of the screw :
six men worked six hours a day; the screw made 35 turns per minute; they elevated in one
minute 765 litres to 2 metres, or 91·8 cube metres of water to 1 metre.
The
The motion given to the water beyond the screw consumed a great part of the moving
power ineffectually, and the less the screw plunges into the water, the more its useful
effect will increase with relation to the power employed in turning it. The external motion
is one cause of the loss of power, which increases with the dimensions of the screw.
same observation has been made with regard to screws for blowing. These machines have
externally the form of a short drum, whose diameter is very great in comparison with the
ordinary barrel of the screw; the part plunged in a reservoir of water impresses on it a
motion which has no effect in relation to the object required.
-
Suction Pump. The simple suction pump consists of two pipes A B, CD, (fig. 1771.) the
diameter of the second being much greater than that of the first, united by two flanges É, F,
cast with the pipes, pierced with four holes to admit the screws C, C, which are fitted with
nuts, to screw the flanges together, between which the two roundles of leather are placed.
The pipe AB, which dips in the water to be raised, YZ, is called the suction pipe; its lower
extremity is slightly widened, to admit the water more freely; at A A is a metal plate
pierced with several holes that the water may not carry any dirt with it. The pipe, CD,
generally of copper or brass, is called the barrel; it is well polished inside to enable the piston
to work easily, it being desirable that the friction should be diminished as much as possible.
The piston is an inverted truncated cone, OPLK, the base of which is surrounded by a
leather band fixed by one or two rows of tacks driven close together; this band should be
slightly funnel-shaped at the upper part, and fit the pump-barrel tightly where the piston
is introduced, the diameter of which should be two-twelfths of an inch less. These kinds
of pistons are generally of hornbeam or alder, being less subject to split than other wood;
iron rings are fitted to their two bases to give great durability. The piston has a hole
through its centre, M, closed with a valve, N, of leather, attached to the wood by a tail
serving as a hinge; the valve when closed should exceed by half an inch the circumference
of the hole, and to fit more exactly, it is loaded with a plate of lead; it has also a fork O QP,
to which an iron rod, R, is attached.
In the middle, E F, of the junction of the pump-barrel with the suction pipe is another
CHAP. XVII.
1169
PUMPS.
D
R
D
hole H closed by a second valve G, and cut in a copper plate which is united to the suction
pipe A B, and cast at the same time. The diameter E F exceeding the suction pipe forms
a flange, the breadth of which is the interval EG and IF between two concentric circles; or
this a leather roundle, N K L, is fitted, hollowed from N to L
to admit the tail of the valve, whose diameter is less than
G I, and greater than the hole H, in order that it may close
it more exactly. The figure shows that when the flanges
are fitted together, the tail of the valve N and the leather
roundle, O QP, will be between them, which are fastened
together by nuts and screws. The iron or copper plate R
with which the valve is loaded, that it may close more
quickly, is also circular, and its diameter should be rather
greater than that of the hole H, especially in forcing-
pumps, that the pressure which it must sustain may not
bend it.
When the piston is raised, a vacuum is produced in the
space IST G, or the air is more highly rarefied, and that
in the suction pipe being no longer in equilibrio with
that in the pump-barrel, forces open the valve G, which
closes the communication between the two pipes, expands
in the space ISTG, and becomes equally rarefied from
the surface of the water to the base ST of the piston.
The weight of the atmospheric air then pressing on the
surface of the water, YZ, forces it into the suction pipe to
a certain height, and having reduced the air contained
there to its natural density occupies its place. Thus the
water will ascend more rapidly at first, because as it drives
forward the air, it condenses it, and becomes its own obstacle
to further progress: for example, if it stop at 3 feet
above the water, and the weight of the atmosphere is
equivalent to a column of water 31 feet high, the elasticity
of the air remaining in the pump is capable of sustaining
a column of water 28 feet high, after the condensation
caused by the water which has ascended.

Y
N R
5
6
M
L
C
F
E
F
H
Β
B
Z
A
A
Fig. 1771. SUCTION PUMP.
K
If the piston be lowered, the valve G will close, the air
contained in the space IST G, being more and more com-
pressed as the piston descends, acquiring an elasticity su-
perior to the atmospheric pressure, and will raise the valve
N, and escape by the hole K L M. If the piston be again
raised, the valve N will. close, and the air in the pipe A B,
dilating in the space IT, the atmospheric weight will raise the water higher than at first;
continuing to work the piston, the water will rise in the pump-barrel to a certain height, 56,
and the space ISTG will be filled partly by water and partly by air, which will be com-
pressed into the space 5S T6. On lowering the piston, the valve C will close; the air
remaining in the pump-barrel will be forced through the piston with a part of the water,
which having once risen above the valve N, there will be no more air below, and the water
will accompany it to the height ST: on lowering the piston, the water will pass above
it, and when it is again raised will run into the cistern VX; thus the whole play of the
pump consists in the action of the external air, and the play of the two valves N and G,
which open and shut alternately.
Forcing Pumps have the same parts as suction pumps, but are differently placed, as shown
in the figure: the pump-barrel A BCD dips in the water to be raised, and is united to an
ascending pipe, ECHF, by flanges and screws; this pipe is composed of two pieces, the
first, CHEF, is bent in such a manner as to offer no obstacle to the motion of the frame
TX YV, which carries the rod N of the piston M; and the second EGHF, the diameter
of which is uniform, conducts the water to the height required. The piston of this pump
differs a little from the suction, being pierced with a hole L, covered by a valve K, which
opens from above downwards, its rod NO being attached to the cross piece RS and TV of
the frame, which is suspended to a piece, Z, attached to a crank or lever. The barrel is
sometimes in two pieces, to allow the water to ascend more freely: the upper part is
pierced with a hole covered with a valve I.
The piston being at the base of the pump-barrel, it will leave a vacuum or highly rarefied
air, arising from that between the valves I and K when first lowered. The water will then
be pressed upwards by collateral columns, aided by the atmospheric pressure; the valve K
will open; the water will pass through the piston, mount in the pump-barrel, and compress
the air remaining there, which will be reduced to its natural state; but as soon as the
piston remounts, the valve K will close, and the water above being driven upwards, will
4 F
1170
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

open the valve I, and pass with the air in the pump-barrel into the
ascending pipe: the piston then descending, the weight of the water
in the upper pipe will close; the upper valve and the vacuum formed
in the pump-barrel will be successively filled with water as the piston
descends, which it will the more freely do, as it meets with no obstacle
but the weight of the valve K, which is very small. When the piston
re-ascends, the water supported by it will again pass into the ascending
pipe, and the pumping being continued, will arrive at the height required.
The Suction and Forcing Pump, fig. 1773., consists of a barrel, A B C D,
a suction pipe, CDFE, and a branch GKNO made in three pieces;
the first, GK, is cast with the pump-barrel, the second, IKM L, forms
the elbow, and the third, LNOM, conducts the water to the reservoir.
At the junction I K is a clack valve, S, opening and shutting alternately
with the valve R, at the bottom of the pump-barrel; the first, S, retains
the water in the ascending branch, to prevent it from descending at the
time of suction.
The piston PQVT is solid, and traversed by an iron rod attached by
two keys; it consists of two equal truncated cones united at their sum-
mits; each cone has a slightly cup-shaped band of leather.
X
N
N
K
L
M
G
H
E
Y
C
Q
Fig. 1772.
FORCE-PUMP.
V
As the piston must not descend lower than TV, because it would
otherwise close the mouth GH of the ascending branch, there will
necessarily be condensed air in the space XTZ, which cannot be pre-
vented, although an essential defect. When the piston is first raised,
this air dilates in the pump-barrel and ceases to be in equilibrio with
that in the suction pipe, which forces open the valve R to expand also,
and allows the water to ascend some feet. The valve S remains closed,
and is with difficulty opened, because the air in the ascending branch, by R
which it is pressed, has more elasticity than that on the side of Z. But
when the piston descends, the valve R closes; the air contained in the T
pump-barrel being pressed acquires an elasticity superior to that which
presses the valve S, which it opens, and the air in the pump-barrel passes
into the ascending branch, as long as they are in equilibrio. On raising the piston the
valve S closes; the other, R, opens; the air in the suction-pipe again dilates, and is
forced up the ascending branch. Con-
tinuing to pump, the water reaches
the barrel, where it mixes with the
air that could not be expelled, which
is forced with part of the water by
the descent of the piston into the
ascending branch: that below pass-
ing without difficulty into the pump
barrel, whence it accompanies the
piston upwards, and the same action
is repeated.

A
Pumps of this kind may be vari-
ously constructed, and different po-
sitions given to the suction and©
ascending pipes, relatively to the
pump barrel.
p
N
O
B
L
M
T
γ G
Z
H
X
R
K
Fig. 1774. shows the suction pipe
CDE, separated from the barrel to
which it is united above, in order
that the piston, which differs in no
respect from the preceding, except
that the rod is carried by a frame,
may force the water from below up-
wards, while the other forces it from
above downwards. It is evident that,
when first lowered, it will form a
vacuum in which the natural air
enclosed in the space C B will dilate;
that in the ascending branch will then
open the valve C, and expand in the
pump-barrel. On raising the piston
the valve F will open, and the greater
part of the air will be driven up the Fig. 1773
ascending branch G: by continuing
E
F
SUCTION AND
FORCING pump.
B
E
Fig. 1774.
SUCTION AND
FORCING PUMP.
CHAP. XVII.
1171
PUMPS.

HARM
to pump, the water will rise to the barrel and ascend in
the pipe G.
A
B
The pumps of the third kind have sometimes two pistons,
one of which sucks while the other forces the water; those
of Notre Dame at Paris were of this description (fig. 1776.);
they consisted of a frame, CD, attached to the rods M
and N, which when raised, the water from the river passed
into the suction pipe, E F, by the pressure of the external
air, and raising the valve Y mounted in the barrel A B,
which the piston I left void; when the frame descended,
the valve X opened, the other Y closed, and all the water
from the pump-barrel, passing through the piston, discharged
itself into the cistern HG. On the other hand, the piston
O descending left a vacuum in the pump barrel PQ; the
air which pressed on the surface HW of the water in the
cistern raised the valve T, and the barrel was filled: on
the piston ascending, the
valve T closed, forced the
water to open the other,
V, and passed into the
pipe R S, which closed as
soon as the piston de-
scended. Thus the cis-
tern always remained full,
the piston I sucking as
much as the other forced;
the diameter of the lower
barrel should be rather
more than that of the
upper, in order that
there may always be
more water in the cistern
than can be raised, in
order to supply the loss
sustained.
ค
H
C
KE
R
K
M
A
D
G C
F
W
Р
Y
X
L
H
PUMP USED AT MARLY. ·
Fig. 1775.
R
Z
M
בחו
Q
E
F
B
D
W
Fig. 1776. PUMPS AT NOTRE
DAME BRidge.
HARK
P
2
Z C
B
B
I
F
F
C
Fig. 1775. is another pump of the same kind belonging to the Machine of Marly. It
has a communication pipe, HLM KIFDCE G, in one piece, one end of which, GH, is
joined to the suction pipe NO, which dips in the
water, the other, LMK, bent at a right angle, unites
with the branch KSM, which conducts the water to
the first reservoir. In the middle is a branch ECD F
joined to the pump-barrel A B C D, in which the piston
Q works, perfectly cylindrical and solid, traversed by
a rod YV, suspended as will be hereafter described.
When the piston ascends to I, the air in the part PX
dilates in the space YZ; that in the suction pipe NO
opens the valve P, mixes with the preceding, and the
valve R remains closed by the atmospheric weight:
but when the piston is lowered, the valve P closes,
the other R opens, and the air is forced in the pipe S:
when, after a certain number of strokes, the water ar-
rives in the barrel, it is forced into the ascending
branch S.
Fig. 1777. B is a suction and forcing-pump once used
at York Buildings, on the Thames. The suction pipe

copper
A B is united to the barrel CEFD, having a valve M
at the junction; the ascending branch F GLK has also
a valve N to close the aperture IH of the bent part
GI. The piston O P Q is a hollow cylinder of
filled with lead to give it sufficient weight to force
the water into the branch; and as the height of the
water might be so great that the weight of the piston
would not effect this, it is also loaded with plates of
lead, T, placed on the rod V; the head of the piston,
therefore, which does not enter the pump-barrel, has
a square form, sufficiently large to serve as a base to
the weight T.
Z
T
X
Y
P
Q
E
M
B
Y
K
L
H
Fig. 1778.
Fig. 1777. PUMP USED AT YORK BUILDINGS.
4 F 2
1172
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
To avoid the friction of the piston against the inner surface of the pump-barrel, which
would be considerable if it operated on its whole length, its diameter is a little less than
that of the pump-barrel, so as to leave a small interval between them: to prevent the
communication with the external air, which would be an obstacle to suction, and that the
water when forced may not issue through the mouth of the barrel C D (fig. 1778.), a very simple
and ingenious contrivance is used. The entrance LL of the barrel is provided with a flange
KL, which surrounds and is cast with it; on this are applied two or three roundles of
leather EFG, bent round the inner surface of the barrel, and then a copper ring whose
lesser diameter is a mean between that of the pump-barrel and that of the piston. Upon
this other roundles are placed, A BZ, bent like the preceding, but in an opposite direction,
the whole covered by a second copper ring, HH, whose lesser diameter, I I, is equal to that
of the barrel. This ring is united to the flange K L by screws, CD, fitted with nuts; thus
the middle ring serves as a guide to the piston, which only touches the leather ZG, with
which it is intimately united, for as there is always water in the cistern XY (fig. 1777), the
leather is continually swelled. This water, not being able to escape, prevents the external air
from entering the pump-barrel, and when necessary the leathers may be removed, and the
pump repaired without taking it to pieces. In order that the water from the pump may keep
the cistern always full, a small cock R is added, which communicates with the barrel and
is closed by a key S: when the piston plunges, the water mounts in the cock, and by
turning the key S is admitted into the cistern; as the violence with which it is pressed by
the piston would make it rush out impetuously, a plate of copper, Z, is opposed to it, sup-
ported on four branches. This cock also serves at the first moment to expel the air from
the barrel quicker than if it were driven out through the branch, it being opened and shut
alternately at each stroke of the piston. In all these pumps, the water only ascends the
branch at intervals, that is to say, when the piston plunges, consequently the time of suction
is lost. Large pumping machines, as that of the Samaritaine
at Paris, therefore have always at least two separate barrels, A, B,
fig. 1779., uniting in the same
branch C by the pipes D and E,
so that when the piston F sucks,
the other G forces, and the water
continually ascends. In this
manner, the pumps of the Sa-
maritaine, at Paris, were con-
structed.
Fig. 1780. shows a pump
having a pipe CAB divided into
two equal parts A B and A C,
forming two barrels uniting in
the same branch QDR, with
which they communicate by two
holes G and H. At this end the
branch is elliptic, as well as the
two holes G and H, which open
and shut alternately by means of
a valve common to both; below
is shown the valve in face, and
sideways, with a section through
the middle; this valve is entirely
of copper, either solid or hollow,
provided it be strong, and it
shows that it works on a hinge at
E, between the holes G and H,
which is its centre of motion.


C
D
E
G
A
B
Fig. 1779. Pump at the
SAMARITAINE.
-
T
2
K
F
B
V
G||F
K
LHE
R
O
X
E m
E
Fig. 1780.
E
The frame Z carries two
pistons, working in opposite di-
rections; for if we suppose the
machine plunged in water to the height TV, it will
be seen that when the frame ascends, the valve N
of the piston M opens, and the water enters the first
barrel AB; that in the second, A C, being forced by
the piston X passes through the hole H into the ascending branch, supports the
valve F in the situation represented, and while it slides along the face EK, the
other EI leans against the orifice G, which it keeps shut. But as soon as the frame
descends, the valve N closes, the other L opens, and that in the middle changes
position; the water in the pump-barrel A B passes through the hole G, to be forced in its
turn up the ascending branch, and the hole H is closed by the face EK. On the other
CHAP. XVII.
1173
PUMPS.
hand more water enters the barrel A C, occupying the vacuum left by the piston, to be
forced in its turn as before; it will thus alternately pass through the holes G and H, and
ascend without interruption into the reservoir: as it continually passes through the hole
P, the valve O is not necessary, but is convenient; for if
the play of one piston should he interrupted, the other
would raise the water, as in ordinary forcing-pumps.
Fig. 1781. raises water continuously, but in a more
simple manner than the preceding: the pump-barrel DB
is united to a recipient XYZ, of a cylindrical figure,
covered by a half sphere Y; these two pieces commu-
nicate by a hole G, opening and shutting with a copper
clack valve H: the suction pipe AD joins the pump-
barrel, and the ascending branch Z W the recipient; both
have their valves F and V as usual; the piston C is solid,
and worked by a frame.

D
Y
W
T
H
I
G
Z
When, after several strokes of the piston, the water rises
in the suction pipe above the valve F, it passes thence into
the barrel, and is forced upwards; it then enters the re-
'cipient, and reaches nearly the same level in the branch
IT above the hole I; the air in the recipient not being
able to escape, and the piston continuing to suck and force
more water, a part rushes into the branch and part remains
in the recipient, which increases the elasticity of the air, as
it is compressed to a less space; the hole G, by which the
water enters, being greater than I, by which it escapes, the
piston always forces more than can at the same time ascend
the branch as the valve H closes every time the piston
descends, when the air in the recipient acquires an elasticity
superior to the weight of a column of water having for
its base the circle of the recipient, and for its height that
of the ascending branch, the air would exert a pressure
on the surface of the water, and oblige it to descend;
and the diameter of the recipient being much greater than that of the ascending branch, if
the water descended only a few inches, it would furnish enough to pass into the reservoir
during the time of suction. It would in this manner ascend without interruption, since
the piston, at each stroke, drives twice as much
water as can in the same time escape through the
hole I.
In order that the air may always have the
proper elasticity, and not acquire more than ne-
cessary, it is convenient to have a small tube in
the recipient, fitted with a valve, which, being
loaded with a weight proportioned to the elas-
ticity of the air, maintains the equilibrium.
Hedderwick's Double-Piston Pump differs from
those which have rods attached to one side of the
pistons, and which produces an unequal pull
upon them: this inconvenience is remedied here,
by attaching the piston-rod to the centre of the
piston, the lower passing through the centre of
the upper.
When the long handle of this pump is de-
pressed, and the other raised, the two pistons
follow the same motion; which being reciprocal,
gives a double advantage in lifting the water;
for, when the one handle is pulled down, the
piston attached to that handle is raised; and
when the same handle is raised up, the other
piston is also raised, which belongs to the
opposite handle: such a contrivance would
raise twice as much water in the same time as
two others with pump-barrels of equal bore
with one piston each. It has been proved that
A
B
Fig. 1781. CONTINUOUS STREAM.

a pump with two pistons will actually raise Fig. 1782. HEDDERWICK'S DOUBLE-PISTON pump.
twice and a half as much water as another pump
with one piston only. It must be recollected also, that in the pump with a single
piston the water, after being put in motion, is suddenly stopped, during the descent of the
4 F S
1174
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
piston, and consequently the discharge of water through the pipe is not regular, whilst the
pump with two pistons causes it to flow in a continual stream: that part of the rod of
the lower piston is shown at the side of the figure.
In Taylor's Sucking Pump, the piston rods have racks at their upper parts, working on the
opposite sides of a pinion, and are kept to their proper position by friction rollers : a pump
of this description, with a bore of 7 inches, will lift a ton of water 24 feet high in a minute,
when worked by ten men,


five on each side. There
are three kinds of valves
employed; the first is a
spheric segment, which
slides up and down on the
piston-rod, and is carried
down by its own weight;
the second is a pendu-
lum valve; and the other
a globe which is raised
by the rising water, and
falls again by its own
weight.
Franklin's Double-Pis-
ton Pump, with a section
through the cylinder.
When the handle or lever
is raised, the upper piston
pressed down, the lower
piston elevated, and its
valves shut, the water is
forced through the upper
piston and the discharg-
ing pipe. When the
handle is pressed down,
the upper piston rises
with its valves closed, and
the water in its ascent is
forced through the dis-
charging pipe: at the Fig. 1783. TAYLOR'S Pump.
same time, the lower pis-
Fig. 1784
FRANKLIN'S DOUBLE-PISTON.

ton descends, by which action the valves are opened, and a fresh
supply of water is obtained: with a 6-inch stroke, a quantity
of water equal to twelve inches of the cylinder is discharged:
whatever the length of stroke, the quantity of water supplied is
doubled.
Stephen's Forcing Pump. To the handle is attached a wooden
rod of several lengths, united by iron joints, and capped with iron
forks firmly riveted. The bucket works a brass tube, and the
top of the barrel is covered with a metal lid, which has a stuffing-
box in the centre, to receive the metal cylindrical part of the pump-
rod, to the lower extremity of which the bucket is fixed. The
metal lid consists of a ring screwed to a wooden barrel by five
screw bolts.
The forcing pipe may be made of wood, or from
crooked timber.
The ordinary forcing-pump does not furnish an intermitting
stream of water, but this effect is very simply attained by the
addition of an air-vessel, fitted upon the side of the main or rising
pipe of the forcing-pump. The action of these air-vessels may be
thus explained: suppose the pump to have received water above
the valve, a part of which will get into the vessel and compress
the air within it, with a force proportional to the height of the
column in the main pipe; when, by the next stroke, the piston
draws up more water, and it stands higher in the main, the air-
vessel is more powerfully compressed. After the water is lifted
to the point at which it is discharged, the air in the vessel becomes
so much compressed, that it balances the whole height of the
column above it. If the opening through which the water flows
at the top of the main were sufficiently large to permit the water
to issue with the same velocity as that of the piston, it would flow
"
Fig. 1785. STEPHEN'S
FORCING-PUMP.
CHAP. XVII.
1175
PUMPS.
over, rising no higher by each successive stroke, and occasioning no
additional compression of the air in the vessel.
But if the aper-
ture of the main is diminished to half its size, the whole of the
water cannot pass during the stroke; consequently a portion goes
into the air-vessel, and increases the compression of the air included
within it.
Trevithick's Pressure Engine resembles one mentioned by
Belidor, although it may be considered more perfect in its ar-
rangement.
Chain Pumps.
As every ship of war is provided with a number
of chain and hand pumps, great attention has been paid to their
construction. Mr. Cole was the first to rectify their numerous
defects, adding a contrivance by which the chain could be easily
taken up and repaired. The old chain pumps required seven
men to raise a ton of water in seventy-six seconds, and Mr. Cole
was enabled to do the same work in forty-three seconds.

Fig. 1786. TREVITHICK'S
PRESSURE-ENGINE.
Mr. Smeaton contrived a hand-pump for the use of ships,
calculated to remedy the defect of delivering the water on the
main deck, which was the ordinary custom; thus lifting the water
considerably higher than was necessary to obviate this, he intro-
duced horizontal wooden pipes to carry off the water through the
ship's sides, at as low a level as possible: one end of these pipes.
proceeded from the upright trunk of the pump, and the other was
fitted into boxes, or short wooden tubes, let in through the ship's
side, and caulked above the low water line; these side pipes were
closely jointed with the boxes in the ship's sides at one end, and
at the other end into strong planks, which were bolted against the
sides of the pump, in order that the side pipes might be got out
and in without disturbing the pump, which was a sucking-pump with its bucket worked
by a lever upon the deck, over it. From the top of the pump a stand-pipe was carried
up to the main deck, or
as high as was thought
necessary to prevent the
water running back into
the ship, over the top, when
the sea rose above the ori-
fice of the side pipe. The
pump had three handles,
which four men worked at
a time; they effected 25
strokes per minute, and
moved the pump-rod 174
inches up and down each
stroke.

Kingston's Ship Pump con-
sists of 2 brass cylinders, 4
inches in diameter, at the bot-
tom of which is a pipe com-
municating with each. The
space around and between
the cylinders and the casing
of the pump serves as an
air-chamber, by which the
water is kept under com-
pression. The supply of
water is through a hose,
screwed on to the lower
pipe, and the action of the
solid piston is the same as
that of the force-pump:
water is thrown out by
this pump in a continued
stream through the eduction
pipe when used for ordinary
pumping, or through a
flexible hose when it is em-
ployed to extinguish fire.
Fig. 1787.
KINGSTON'S EXIP-PUMP.
4r 4
1176
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

The Chain Pump for
Ships is formed of a long
chain, with a number of pis-
tons or buckets fixed upon
it at regular distances, and
which pass over two wheels
called sproket wheels; by
turning the upper one, the
buckets are put in motion,
and working in a wooden
tube lined with brass, as
they mount they raise the
water on the ascending side,
which flows off by a trough
placed over the ship's side.
The links of the chain are
formed of two iron plates,
and the buckets or saucers
are two circular brass plates
with a piece of leather be-
tween them.
Double-acting Fire En-
gine is worked by a double
sector of iron, which has a
sufficient breadth of sole to
receive two chains, similar
to those used in a clock:
one chain is fastened to the
bottom of the arched head
and to the top of the piston.
rod, and the other chain is
fixed at one end of the top
of the arched head and the
lower part of the piston-rod,
so that when the sector de-
scends on one side, the chain
fixed at its lowest part
winds round, and pulls
down the piston on that side, while
in the opposite sector the chain
fixed on the upper part of its arched
head winds round and raises the
other piston: the reverse takes
place at the next stroke, so that a
continued action is maintained, the
water rushing at the same time
through the lower valve, from the
cistern, and fills the cylinder; and
when the piston descends, this valve
shuts by the pressure of the water,
and is forced through another
valve into the air-vessel, the upper
part of which is filled with air
compressed by thus forcing the
water in, and which, acting by its
elasticity on the surface, causes the
water to be thrown up with con-
siderable velocity. An iron handle
is attached to the air-vessel, which
sets the cock into a position either
to make a communication between
the cistern and barrels, or between
the feeding pipe and barrels, shut-
ting off the cistern, according as the
engine is supplied.
Let us suppose the air com-
pressed in the air-vessel to half its
Fig. 1788. CHAIN PUMP, USED IN THE NAVY.

:
Fig. 1789.
DOUBLE-ACTING FIRE ENGINE.
CHAP. XVII.
1177
PUMPS.
bulk by forcing in the water; if an additional quantity be thrown up, so as to compress
this half to one-third its original bulk, there will be the pressure of three atmospheres
internally to one externally, which will support a column of water 66 feet high.

Fig. 1790.
AIR-VESSEL.
Fig. 1791. SEction of fire-ENGINE.
Attached to the water-mains in many towns is a fire-plug of ingenious contrivance, which,
when the water is supplied from a high service, answers all the purposes of an engine, and
can be made available at a moment's notice.

The fire-engine now preferred has two
cylinders of 7 inches in diameter, and a stroke
of 8 inches: the whole weight of such an
engine, when strongly made and rendered
efficient for use, is about 17 cwt., without
taking into consideration that of the hose
and tools required, which may make an
addition of 4 or 5 cwt.; this, however, can be
easily drawn by two horses with five firemen
and a driver any short distance. There are
two pumps, both sucking and forcing, the
pistons of which are moved up and down by
a double lever : when one piston is up, the
water flows from the reservoir into the barrel,
and when the same piston is depressed, a valve
shuts, and the water of the barrel is forced into
an air-vessel into which is inserted a pipe
which reaches nearly to the bottom of the
vessel. The same effect is produced by the
other piston, only at a different moment, for
when one is rising and sucking water from
the reservoir, the other is forcing into the
air-vessel the water which it had raised into
the barrel by its previous ascent: when the
water has risen in the air-vessel to a certain
height, the air becomes more and more com-
pressed by every new quantity of water
forced into it, until the elasticity of the air,
acting like a spring on the surface of the
water, compels it to mount the hose which
is attached to the engine. The usual rate of
working such an engine is 40 strokes of each
cylinder per minute, which gives 88 gallons,
G
Fig. 1792.
FIRE-PLUG.
and it requires 26 men to keep it at work steadily for 3 or 4 hours. The lever is in the
proportion of 41 to 1, and with 40 feet of leather hose and a 7 inch jet, the pressure is
30 pounds on the square inch: this gives 10-4 pounds for each man to move 226 feet
per minute.
The friction must be added, which is equivalent to 21 per cent. for every ad-
ditional 40 feet of hose.
A variety of forms are adopted for the jet, but that generally used has the curve of
1178
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
:
the nozzle determined by its own size: of the difference between the jet to be made
and the end of the branch is set upon each side the diameter of the upper end of the
branch; a straight line is then drawn across, and an arc of a circle described on it, from the
extremity of each end of the diameter of the jet, until it meets the top of the branch: the
jet is then continued parallel, the length of its own diameter; the metal is carried of an
inch above this, which allows a hollow to be turned on its edge.
The size of the jet on the inside is proportioned by making its diameter of an inch for
every inch in the diameter of the cylinder, for each 8-inch stroke: when the water is to
be carried to a greater height, a jet whose area is less is made use of, with a branch from
4 to 5 feet in length. The following table will show how the water acts upon the surface
of the water in the air-vessel.



Height of Height of
Water in the the com-
Ratio of the
Air's Elas-
Height to
which the
Water will
Air-vessel. pressed Air.
ticity.
Height of
Water in the
Air-vessel.
Height of
the com-
pressed Air.
Ratio of the
Air's Elas-
Height to
which the
Water will
ticity.
spout.
spout.
-OEMS CONTRUKOR
2 3
2
33
3
66
4
99
788000
8
231
9
269
10
297
5
132
N
- 1
2
n
6
165
(a−1) 33
120
N
7
198
The common Garden Engine is made in a variety of forms, and with pipes, pistons, air-
chambers like that already described; in some the working barrel is placed on the outside,
and in others the wooden case is dispensed with.

Fig. 1793.
THE COMMON GARDEN ENGINE.
Another form of this engine will show the sort of pump sometimes adopted for throwing
up water from one level to another: but among machines employed for such purposes, pumps
are the most convenient,

as they can be made
readily to vary the height
to which the water can be
thrown, as well as to oc-
cupy the least space in the
interior of a cofferdam: the
body of such a pump is the
prolongation of an air-tube,
and the motion is usually
communicated by men act-
ing on a balance.
M. Boistard, who has re-
corded the useful effect of
the pump, observes that
one 27 centimetres in dia-
meter, (10.6 inches English)
worked by seven men for
eight hours, raised 508-52
cube metres of water 3.628
metres in height; the use-
ful product daily attained
Fig. 1794.
THE COMMON GARDEN ENGINE.
CHAP. XVII
1179
ON PISTONS.
is for each man 87.85 cube metres of water raised 1 metre: another pump 244 millimetres,
(or 96 inches English,) worked by the same number of men for the same time, raised 470′04
cube metres of water 3.573 metres in height, which gives for the useful effect furnished by
each man in 24 hours 79-97 cube metres of water raised a metre. The product of pumps
varies much in consequence of the manner in which the piston is connected with the
air-tube, but they are now brought to great perfection by the manufacturer, and it is
found that those of the greatest diameter are the most economical for raising water from
foundations.

Engine for raising
Water from Dykes is
contrived like a fire-
engine with a double
handle, working two
pistons in barrels at-
tached to an upright
pipe: after the water
is thrown up in the
trough above, it can
be poured out in any
direction required; the
mechanism and barrels
resemble some of
those already treated
on.
1
Q
Pistons and Valves.
-The pistons in
general use are of
two kinds, solid or
plungers, and pierced
or buckets; both are
commonly of wood:
the chief inconve-
nience of wooden
pistons is that when
pierced with holes
they are greatly
weakened, especially
if sufficiently large to
allow the water a free
passage, without which there is considerable resistance; and if a stroke of 6 feet be made in
two seconds, as in the machine at Frene near Condé, it is essential that the whole machinery
should work with the most perfect ease, otherwise the effort of the moving power tends to
the destruction of the machine. To avoid this, care must be taken that when the bucket
descends, its own weight should suffice to compel the water at the bottom of the barrel to
pass through the hole in the time necessary for its descent; and as this time is determined
by the velocity of the machine relatively to that of the moving power, it will be seen
that it depends on the quantity of water sucked by the bucket at each stroke, and the size
of the passage to be traversed.
Fig. 1795.
ENGINE FOR RAISING WATER from DYKES.
Suppose, fig. 1776., a pump-barrel, A B, 8 inches in diameter inside; that the stroke of
the piston is 6 feet, and that it is made in two seconds; it will raise at each stroke about
74 pints of water, which should pass through the hole Z in the time of the piston's descent:
with what weight ought it to be loaded in order to force the water, so that it may in two
seconds pass through the hole, which we suppose 3 inches in diameter, the greatest which
can be given to it without weakening the bucket too much? The quantity of water which
will pass through the piston in a given time will depend on the size of the hole and the
velocity communicated to it by the weight with which it will be loaded: the problem is
therefore to ascertain what height of water must be given to a reservoir pierced at the
bottom by a hole 3 inches in diameter, so that 74 pints may issue in two seconds.
If the piston weighed less than the column of water, the hole must be increased to make
up for the small velocity of the water arising from a want of sufficient pressure and the
superficies of the two holes, and the velocity of the water which must pass must form
four terms reciprocally proportional. But as the weight spoken of may be expressed by
columns of water whose base is the circle of the piston, and the square roots of the height
of these columns expresses the velocity of the water, we may substitute the square roots of
the weight with which the piston is loaded without fear of error.
As wooden pistons are not very convenient, since we cannot pierce them with a hole of
sufficient size without endangering their solidity, one of the description of the fig. repre-
1180
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
sented will be found infinitely preferable: it consists of a copper box forming the body of
the piston, in the form of a truncated cone, with a small flange, CC. The figs. 1799. 1802.

H
G C
C
C
с с
C
D
D
A
H
G
A
D D
A
R
B
X
X
B
B
B
B
Fig. 1797.
Fig. 1798
Fig. 1799.
Fig. 1796, p
P
H
H
HO
M
N
D
A
H
G
L
D
A
KA
T
B
R
X
B
X
Fig. 1801. P
M
D
Fig. 1800.
Fig. 1802.
show the section with the upper plan, where it is seen that this box is traversed by a bar
DD pierced by a mortice E: on the surface of the box is a leather band A A, confined
by an iron ring let into the leather, which is of an inch thick.
The piston is covered by a leather valve strengthened by iron or copper plates G, G,
(fig. 1800.), made in the segment of a circle: above the valve are similar plates, but of rather
less diameter, so that they may enter the piston, as indicated by the circle IK in fig. 1803.,
having only therein the leather and upper plates, which rest on the edge of the box; thus the
leather is screwed between the two by four nuts and screws, H: this valve is fitted to the box,
so that the centre F F is placed on the bar DD; to tie the whole together an iron cross is
used, L M N O P, in fig. 1801., which is a section through the bar DD of fig. 1796. The
part M N is placed, on the middle F F of the valve; then the tenon OP traverses the hole E,
and passes through an iron bar QR, whose extremities, X, X, are halved into the thickness
of the box, as well as the circle B B, which is sustained by this means, and secured to the
box by passing a key into the hole T, as shown in the section of the piston at right angles
with the preceding.
The rod LO is adjusted to an iron bar by a tenon at its summit, a mortice in the middle,
and two screws serving to tighten one against the other; this bar is suspended to a crank or
lever.
P
To remedy defects in the common plungers of wood, a much more solid one is now sub-
stituted, as shown in fig. 1803. The body of the piston consists of two copper cylinders
ABCD, EF GH, of a screw NO, and a ring
Z, all cast together; the diameter CD is rather
less than the barrel QRST, and the diameter
EF only half the preceding; the thickness A C
may be one-fourth the diameter A B, and EG
twice E F.


2
R
A
B
B
A
C
D
E
F
Y
G
H
K
ETTE TEAT
L
I
K
N
Fig. 1803.
PLUNGER.
Fig. 1804.
T
A number of leather roundles, whose dia-
meter is rather more than the pump-barrel,
pierced in their centre by an aperture of the
diameter GH, are fitted on the cylinder EFGH,
and beaten with a hammer to press them to-
gether; others are then added, supported by a
copperplate IK, the thickness of which should
be half A C, and being pierced in the centre is
fitted to the screw LM, after which the whole
is pressed together by the nut X. The piston
is then placed on a lathe to reduce the whole to the same diameter as the piston head, and
form a cylinder I A B K, having a uniform surface. The piston is then introduced into
the pump-barrel without difficulty, and water being poured above the leather it swells, and
all the roundles unite against the barrel, and form a new cylinder Y, whose diameter is
equal to that of the barrel, leaving no admission for air during suction, nor passage for the
water when forcing: in proportion as the surface of the cylinder Y wears by friction, the
leather swells, not having attained its maximum of dilatation in the first instance, especially
if it be of the best quality.
The ring Z serves to hook on the rod P, so that it may play freely, and enable the piston
CHAP. XVII.
1181
ON PISTONS, VALVES, ETC.
P
B
G
:
Q
H
in ascending and descending to work perpendicularly: it being impossible to make the rod
do this at all times, especially when worked by a crank, great freedom of action must be
allowed in forcing-pumps; therefore it is better to hook it to the piston than to attach it.
Although the preceding piston is one of the best, it must be acknowledged that after a
certain time, when the leather has successively swelled to compensate for the decrease
caused by friction, the adhesion will not be sufficient to prevent the passage of water when
forced, if the column be very high, for the resistance caused by its weight will always be
the same, while the adhesion of the piston will continue to diminish. To remedy this
there must be a power proportioning its adhesion to the pressure exerted in forcing this
has been effected by a copper cylinder gh, hollow and pierced
with several holes covered above by a plate ab of the same
material, both cast together with the flange IK, serving to
attach the cylinder to a second plate cd, similar to the first, with
this difference, that it has a hole of a diameter equal to the
interior of the cylinder, to which a cup valve is fitted, in such a
manner that the tail is retained between the flange I K and the
plate, the whole being secured with nuts and screws: on the
edge of each plate is a groove to receive the hem of a leather
purse of a cylindrical shape, for which the plates serve as
ends. Pitched twine is used to unite them, well tightened
round the leather, forming a drum, and having only an open-
ing at the bottom when the valve at K is raised; the piston
is attached to the rod H, having three or four branches I G,
united to the plate ab by nuts and screws.
Water being
poured into the pump-barrel until it is three-fourths full, the
piston is introduced, which will enter without difficulty; but
when it descends lower the air contained beneath, being com-
pressed, will raise the valve, pass into the cylinder gh, thence
into the drum, and, continuing to descend, the water will pass
also, until the piston arrives at the hole NO; the air and the
water then swelling the drum, the leather will begin to adhere
to the pump-barrel, feebly it is true, but sufficiently to prevent
the introduction of the external air when the piston is raised,
the valve instantly closing.

A
G
G
a
E
E
B
G
H
I
K
N
As the piston works and expels the air from the suction-pipe,
the water will rise in it, and enter the barrel: when arrived
there, the piston forcing it will itself receive a part, which will a
compress the air at each stroke into a still less volume, and the
action of the piston becoming stronger as the water is raised to
a greater height in the branch, the air in the drum will acquire
still more elasticity, and press the leather more and more against
the barrel, the water therein acting in the same manner as the
air. When the branch is full, the elasticity of the air will be in
equilibrio with the column of water, of whatever height it may
be, and whether the piston forces or sucks its adhesion will
always be the same: when the barrel is not sufficiently cylindrical, this defect, which
would be very great in any other case, will be of no account in this, since the surface of
the piston being flexible will adapt itself to whatever opposes it.
L
Fig. 1805.
M
The piston just described cannot lose water, its surface being perfectly applied to the
barrel; but as from this adhesion great friction results, the leather will not last long: it is
therefore necessary, in order to avoid its constant renewal, to place several, one over the
other, to strengthen the purse, which will not be the less flexible, but adapt itself to the
barrel; the friction in this case being very different from that occasioned by the contact of
two hard bodies, it is highly desirable to get rid of friction entirely, but in doing so, care
must be taken that other inconveniences are not produced, which may overbalance the one
advantage.
Messrs. Gosset and De la Deuille, while engaged on a very ingenious hydraulic machine,
invented a piston entirely free from friction, which may be used independently of the
machine: the piston may be of any size, even 3 feet in diameter; that described is 15 inches:
the barrel consists of two wooden plates 28 inches in diameter, and 5 thick; in the middle
of each is a cylindrical hole 15 inches in diameter and 21 deep, forming two boxes placed
against each other; their section is represented by the rectangles ABCD and E FH G.
The piston consists of a circular plate, YL, 1 inch thick, the diameter of which ought to be
rather less than the void TOQV, to facilitate the play: this plate is applied to a large
circle of leather, or to several, if one is not sufficiently strong, so as to project 6 or 7 inches
all round the edge; the plate is placed in the bottom of the box STV X, and the excess is
folded all round the edge ESX G; the other box, A B C D, is then applied to the preceding,
1182
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
A
R
T
N
W
Q
K
M
M
L
اعها
R
Ꮓ
X
and the leather fixed between them by means of several iron bolts fitted with screws: thus the
piston consists of a kind of purse,
which turns itself at every stroke of
the piston. At the bottom of this
purse is a hole, L, covered with a
valve, K, which, when raised, rests
against the handle MW M, to which a
rod, N, is attached, serving to raise
and lower the piston; for this rod
there is another hole in the bottom of B
the upper box, corresponding with the
pipe in which the rod N passes; this
hole is slished, to allow the plate to
touch the top OQ when the piston
ascends; the lower box has also a hole
corresponding with the suction pipe,
covered by a valve, I, as usual: when
the piston is raised the water opens
the valve I, and passes into the vacuum formed to the height of 4 inches, which is the
play the piston ought to have so as not to weaken the leather: when the piston descends
the valve I closes, the other, K, opens, and the water contained between the bottom, TV,
and the leather, passes through the hole L, enters the space OPYZ Q, and thence is forced
up the ascending pipe; thus the piston, always floating between two waters, will have no
friction: when the leather is good, it may be worked continually for three or four months
without any repair, as has been proved in the mines of Bretagne.

Fig. 1806.
Ι
GOSSET AND DE LA DEUILLE'S
HYDRAULIC MACHINE.
V
The sole defect in this piston is, that, whatever be the size of the discharge-pipe, the
power is always loaded with the weight of a column of water having for its base the circle
OQ, and for its height the elevation of the reservoir above its source: it is true the
diameter of the pipe may be increased, and that of the piston diminished, in order that these
being equal, the power may not be loaded with a greater weight than would naturally be
raised: the play of the piston being small, it will raise but little water at each stroke; the
strokes may, however, be more frequent. If the suction-pipe and the piston-rod are each
25 feet long, the water may be raised 50 feet above the source at a very small expense.
On Valves. The different valves in use may be classed under four kinds, the cup valve,
conical valve, spherical valve, and clack valve; the three first are of copper.
Fig. 1805. shows a cup valve E, at the bottom of a pump-barrel; the stalk, accompanied
by two leather roundles, is fixed between the flanges of the barrel and those of a cup IK,
to which the suction-pipe, LM, made of lead, is soldered: the valve E fits the cup BC,
and GH represents the support of the ring in which the rod F plays.
The upper fig. 1805. represents a section of the same valve, in order to show its defects,
which are decidedly great: the superficies of the great circle E diminishes the passage
of the water, as it can only escape through the space between the circumference of the circle
BC and the surface of the suction-pipe, whereas the water forced by the piston should have
a free passage equal to the circle of the barrel, in order that it may not pass more rapidly
into one part than another; otherwise the power will be forced to make a greater effort than
if the water were not confined.
To give more facility to the water in ascending, it is only necessary to diminish the circle
E; but this cannot be done without also diminishing its lower surface, or its equal
GH, consequently, without confining the passage of the water through the cup BC: all that
can be done is to regulate the upper and lower diameter of E, so that the water, in traversing
the cup and passing round the valve, should be as little confined as possible; therefore the
superficies of the circle G H must be equal to the ring causing the difference between the
superficies of the upper and lower surfaces of E. Of whatever size the barrel is, to proportion
the valve, we must divide the radius of the barrel into five equal parts, and take three for
that of the small circle of E, and four for that of the great circle: due consideration
having been given to the height which best suits the convex surface of the valve, it appears
that its side should be one-fourth the diameter of the upper circle, and the breadth of
the rest one-eighth; the angle which it makes with the side will then be of 60°, because the
section of the valve will form a trapezium drawn by an equilateral triangle, having the
upper diameter for its base.
The water forced from the barrel up the branch will be greatly confined in traversing
a very narrow passage; it will in its course meet the under part of the cup, and the
circle ND which causes it to rebound, and it will only be raised by an extraordinary
force, besides which it will be pressed in a direction obliquely to the surface of the
pipe. The power must be twelve times greater than if the water mounted with a uniform
velocity. This valve is not applicable to forcing-pumps, if placed at the bottom of the
branch, but may be used at the bottom of the barrel: for if the greatest height of the
n
H
CHAP XVII.
1188
ON PISTONS, VALVES, ETC
piston be 27 or 28 feet, the atmospheric weight will be sufficient to raise the water in the
barrel with a velocity much greater than the piston can have.
This valve sometimes fits the cup so tightly that it ceases to play: M. Amontons
having constructed a forcing-pump, dipping 6 feet in water, was surprised on observing
that the valves of cast-iron, and perfectly fitted, suddenly ceased to act; he several times
took the pump to pieces, but could not discover any sufficient cause for the defect. The
valves were placed horizontally in the barrel, and had they been pressed by the atmospheric
weight, they might have been imagined in the condition of two well-polished surfaces,
which can only be separated by a very great weight, but there being no air between the
valves and piston, they were only pressed from below upwards by the water which the piston
forced.
The only one cause to which the union of the valve and cup can be attached is their
being maintained by the water, whose particles attract each other so forcibly as to exclude
the air between them, and so require a great effort to detach them, which can only be
effected by evaporation or violent friction.
The conical valve, fig. 1807., consists of a truncated cone E resting in a cup B C, similar
to the preceding, except that it has no ring in the middle, the stalk being very short: at
its extremity is a plate R G, which prevents the valve from escaping; its great circle should
correspond with a convex head, whose edges should have sufficient projection to close the
aperture when the valve is down; for there being nothing to keep the axis of the cone in
the centre, it may, by moving right or left, leave a space through which the water in the
branch may escape into the barrel. This valve has the same disadvantages as the other,
that of contracting the passage of the water.
The spherical valve, fig. 1808., is much more simple, consisting only of a sphere E, which
falls into a cup B C when the piston sucks, and would certainly be superior to any other
if it did not contract the water-way, for, once placed at the base of the pipe, it would play a
number of years without needing any reparation: it is true the branch may be enlarged
above and below the valve, so that the whole of the cup, and the passage of the water
around the sphere, may be equal to the circle of the piston, and the water have a uniform
velocity, which would render this valve infinitely more perfect. Care must be taken not
to make it too light or too heavy; if too light, and the branch is of the same calibre with


E
R
G
Fig. 1807. CONICAL VALVE.
B
E
C
A
E

I
R
K
S C
Y
L
H
F
M
Fig. 1809.
CLACK Valve.
Fig. 1808. SPHERICAL VAlve.
the barrel, the impulse of the water would raise it to a great height, and the valve would
not close soon enough to prevent the water coming back: it might even happen that the
same water would pass continually from the barrel to the branch, and back again as the
piston forced or sucked, for if the passage be not closed at the moment the impulse ceases,
no fresh water will rise in the barrel nor in the reservoir: if, on the contrary, the valve be
too heavy, the power will have to raise it as well as the water. To obtain the proper mean
the specific weight of the valve must be regulated by the velocity of the piston, that it may
never go further from its cup than just sufficient to allow the water to pass, unless it be re-
tained by a chain.
The clack valve, fig. 1809., is the least imperfect, leaving a free passage for the water: the
valve A D consists of a piece of leather, CD, tightened between two copper plates, A B and
E F. The diameter of the first is two or three inches greater than that of the pipe LM ;
that of the second EF is rather less, in order to enter within it: these two plates are held
together by a screw SR and nut GH; the leather has a tail, DB, serving as a hinge, as
1184
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
usual. This valve, placed at the bottom of the branch, is lodged in a drum I K, so as not
to contract the passage of the water at that place; the lower part of the branch is swelled,
in order to have a ring, Y, all round the flange of the pipe L M for the valve to rest upon,
which is consequently horizontal, a situation preferable to the vertical, which do not close
well; it is true the void space is not so great.
E
B
D
A
Fig. 1810.
This valve must be made strong, otherwise the leather hinge will soon be injured; being
the weakest part, these kind of valves always give there, especially when much strained, and
being liable to frequent reparations are consequently not convenient for large pipes, as in
falling they often slip more on one side than another and do not close exactly; the leather
of the hinge becoming too flexible has not sufficient body
to keep the valve in its proper direction. To remedy this
inconvenience, when the branch is 8 or 10 inches diameter,
a valve may be formed of two clacks, consisting of a ring
of copper, as in the first piston described, whose lesser dia.
meter is equal to that of the ascending pipe, and its greater ▲
sufficient to admit of being held between the flanges of
the drum and those of the curved pipe. This ring should
have a bar, D, so as to make one piece of the whole, as
shown in section in fig. 1811., where L M represents this
ring with the bar A: a leather circle, 2 inches more in
diameter than the ascending branch, will form the two
clappers, E, I, strengthened above and below by copper plates
G, H. The circle of leather is laid on the cross piece, A;
a copper rule of the same length is then placed above it, and
they are united by two screws, as in fig. 1810., where the rule
BC has a knob DE to prevent the two claps both falling on
the same side. This valve is the most convenient, and
contracts the water-way so little as not to be of any importance.
Leather clappers not being very durable, those of copper are substituted in two semi-
circles, united by a hinge, as in figs. 1812, 1813, 1814, 1815.

hand, represents them
when closed; they are fitted
in a box BB, projecting
equally with them, and
moving on two hinges, G, G,
whose axis enters the two
uprights E: on the top of
each is a button F, to main- A
tain the clappers in the
situation shown by the two
upper figures, and oblige
each to fall towards its own
side, when the piston ceases
to force. The tongue A A
should be formed with
roundles of leather be-
tween the flanges, IK and
LM.
In selecting the best
form for valves, we must
always consider the pur-
pose to which they are to
be applied; the most im-
A
I
E
H
M
Fig. 1811.
The lower, on the right


E K
G
G
G
A A
A
I
V
K
I
Fig. 1812.
L
M
Fig. 1814.

B-
K
B
且
​B
A
A
A
G
L
M
B
portant considerations are,
that it should be perfectly
Fig. 1813.
Fig. 1815.
tight; that it have sufficient strength to resist the forces to which it is exposed; that it allow
the water to pass freely, and not permit it again to flow back, whilst it is in the act of closing.
The clack valve, which is the simplest, should be fixed in a box like a piston; its outer sur-
face should be a little conical, so as to fit a similar recess made for it in the tube; it should
have an iron ring or handle to enable it to be taken out by a hook whenever it is required to
be drawn up the top which the clack valve sustains, when opened, may be considered as
equal to one-half of the cylinder of water, whose height is equal to the diameter of the
valve. The spherical valve obstructs too much the passage of the water, and when made
very light there is the probability that it will not return to its place when required, without
allowing a quantity of water to flow back.
Another valve placed at the bottom of reservoirs or basins for the purpose of laying
them by or filling them, fig. 1816.; it consists of a copper box A B C D, having a rebate BC
CHAP. XVII.
1185
ON VALVES.
hollowed out, to admit the cover G, to which a rod H is attached for opening and shutting
the valve, working up and down through the cross bar E F.
Fig. 1818. is a pump used by Belidor to re-
place the old one in a machine at the Pont
Notre Dame, Paris; its chief advantage is in
the valves, which offer less resistance to the
passage of the water; the valve, fig. 1820.,
consists of a circular diaphragm movable on


E
B
A
1816
D
C
C

Fig. 1818.
F
Fig. 1823.
gudgeons, whose
axis does not pass
through the centre ;
that is to say, the
diameter being di-
vided into twelve
parts, A H com-
prises seven, and
HB five. The
centre, figs. 1825.,
1821., 1822., of the
axis EF is also
TZ
part of the diameter,
from the middle of
the thickness of the
diaphragm
A B,
which produces a
bent lever KIH,
whose lesser arm,
IK, corresponds to
the friction of the
gudgeons, and the
other IH sustains
at its extremity H
the weight of the
valve, which can
only remain open
when obliged by
some superior force.
The unequal seg-
ments of which this
valve is composed
Fig. 1817.


EC
A
Fig. 1819.
B
F
Fig. 1820.
F


E13
Fig. 1821.
G
(H)
ODLF
R
-B
H
Fig. 1822.
P
R
Q
P
Fig. 1824.

A
H
K
R
H
P
Ω
B
M
Fig. 1825.
are cut, fig. 1825., AL, BM, in opposite directions, so that when it is closed
the first, AL, which belongs to the greater segment, pressing downwards on the upper
4 G
1186
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
'T
Y
edge OP of its frame, and the other, B M, upwards against QR: when the piston
forces, the water presses the valve upwards, but with greater force, against the seg-
ment HA, fig. 1822., than against HB: the valve then assumes a vertical position,
and the water passes freely on each side the valve. On the other hand, the instant
the piston begins to descend, the valve ceasing to be supported by the ascending column,
closes by its own weight, and the column above pressing with much greater force
on the segment HA than on HB, it is impossible that it can open in order to give
greater superficies to the inner circle of the ring or plug than to the piston, the summit of
each pump-barrel is enlarged to make way for the valve when open, and not to oppose
any obstacle to the water; on which account the fork of the old pumps was suppressed,
and their place supplied by a large receiver, as in fig. 1818., cast with the barrels; thus
the water forced by the pumps unites in the receiver, and passes in a mass up the branch.
Manner of setting out the head of the Pump-
barrel. Divide the diameter A B into eight
equal parts or modules; on the centre raise the
perpendicular C D three modules high; through
the point D draw the line H G parallel to the
diameter A B, and from the point D as a centre,
with the radius D A or DB, describe the arcs
A E and B F. The rebates E H and F G must
be one module wider than the thickness of the
pump-barrel: to trace the profile of the head,
draw the rectangle IZLK, whose base IK
is eleven modules, and whose height IZ is
two; on the line IK draw another rectangle
MTX N, whose base MN is equal to the H
diameter A B of the pump-barrel, and whose
height M T is six modules. Divide the line Z L
into three equal parts, as at QR, and from
these points as a centre describe the arcs Z T
and L X; prolong the perpendiculars M T, N X
two and a half modules to the height TV, X Y.
Figs. 1827. 1828. 1829. represent the piston of this pump its construction is based upon
four principles; first, that it should have an aperture sufficiently large to allow water enough
to pass to fill the barrel at each stroke; secondly, that the valve in the piston should open
and allow the water to pass freely, and yet itself close firmly; thirdly, that the axis of the
piston should always be vertical, notwithstanding the obliquity given to the rod by the
motion of the crank or balance beams, so as to avoid any straining, and to prevent the
pistons wearing on one side more than on another; fourthly, that the leather which causes
the adhesion of the piston to the inner surface of the barrel should be so disposed as to last
a long time without requiring reparation.

E
A
L
Ω
R
M
D
Fig. 1826.
N K
G
F
B
This piston consists of a cast-iron box, ICD K, figs. 1827. 1828. 1829., serving as a nucleus
to a number of leather rings, G, H, pressed against one another, having a flange E F for
their base at the summit D is a screw furnished with a nut, A B, to bring the leather
rings together. To the piston a swing valve
is attached, similar to that previously de-
scribed. The base of the box has two ears,
I, K, traversed by a bolt, LM, which secures
them to the fork of the piston-rod.

The suction piston is entirely on the same
principle as the preceding, figs. 1830. 1831.
1833., only the flange AB must be at the
upper part as well as the ears C, D, which
attach the piston to the rod. The ring of the
valve is let into a rebate, and attached to
the flange with four screws.
The various methods of raising water by
means of pumps may all be classed under
three heads. The first, when water is raised
from a depth to the surface of the earth,
which may be performed by employing as
many suction pumps as may be necessary.
The second, when water is to be raised to a
great height above the surface, either verti
cally or on an inclined plane; in this case
forcing-pumps are employed. The third,
when the water is to be raised from a depth
A
E
BA
B
1827
1828
F
1829
F
I
K
M
K
E
B
A
K
F
1930
G
1831
1832
Fig. 1833,
CHAP. XVII.
1187
ON PUMPS.
M L
A
D
E
considerably below, to a height considerably above the surface of the earth; this case
comprising the two former, both suction and forcing-pumps must necessarily be employed.
Fig. 1834. represents a suction-pump adapted to raise water from a well or cistern: it
consists of a leaden pipe 2 inches in diameter, dipping into the water, having its extremity
curved and resting on a block of stone or wood. To this is fitted another leaden pipe, 5
inches in diameter, forming the pump-barrel; its
lower extremity takes off to adapt itself to the
suction pipe, and near their junction a wooden
plug D is fixed, perforated by a circular aper-
ture to which a clock or valve is fitted opening
upwards, to prevent the descent of the column
of water in the barrel. The piston is a similar
plug, E, furnished with a valve, also opening
upwards. To the upper part a band of leather
is nailed, which fits the barrel rather tightly;
the piston is attached to the rod by an iron
stirrup. The power applied to the handle K
works the bent lever M AI, whose arm LK is
30 inches,. and LM 5; thus the power is of
the weight, here expressed by that of a column
of water 5 inches in diameter, and in height
equal to that of the discharging pipe P above
the level of the water. The tools F and G serve
to draw up the lower valve, or to tighten it by
Το
striking it with the circular head of F.
draw it out, the valve O is first raised with the
hook G, and the whole is then drawn up with
the end H.

Fig. 1836. is a pump
with lever A working two
piston rods, B, C, one of
which is raised at the same
time that the other is de-
pressed, and may be used
when the water is too low
to be raised at a single
stroke. For example, if a
well were 40 feet deep, a
pump might be placed at
about half its depth, and
another at the surface of
the ground; the rod C
would then raise the water
to a height of 18 or 20 feet,
whence it would be brought
to the surface by B.
Fig. 1837. is a suction
pump worked by a balance
E; the power is applied to
a cord A, and raises the
weight B, which by sinking
raises the rod C. This
pump is well adapted to
serve two adjoining proper-
ties, by attaching a cord to
the arm D of the balance,
and passing it through
the party wall, but one
of the discharging pipes
must be closed when the
other is in use.
Fig. 1838. shows a
method of working two
suction pumps alter-
nately, so as to produce
a continuous stream; the
winch A, to which the
C
B
Fig. 1836.
A
K
F G
D
E
D
Fig. 1835.
Fig. 1834.
Fig. 1837.
E
D
E
4 G 2
1188
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
power is applied, has a fly-wheel B to produce uniformity of motion: on the axle is
a pinion C, engaging a wheel D, whose axle is a crank GLMKINOH, to which are
suspended the piston rods E, F. The crank A is 12 inches long; MN is 6, and wheel D is
6 inches in radius, and the pinion C 2, and the fly-wheel B 3 feet. Supposing the water
to be raised 28 feet by the power
of a man, equal to 25 pounds ap-
plied to the winch A, it is required
to find the diameter of the pistons
in order that the weight of the column
of water may be proportioned to the
power applied.
A
B

I N
G L
M
K
D
E
F
This machine may be considered as
consisting of a single pump barrel,
whose piston raises the water in an
uninterrupted stream, and the arm of
the lever which corresponds to the
weight as expressed by two-thirds of
the arm LM or NO of the winch.
Now as there are four arms of one
common lever united between the
power and the weight, namely the arm
LM reduced to 4 inches, the radius
of the wheel D to 6, that of the pinion
C to 2, and the arm of the winch A to 12; the power will be to the weight as 4 × 2 is to
6 × 12, or as 1 to 9, which may be stated thus, 1:9:: 25: 225 pounds, the weight of the
column of water which the power has to raise, and the volume will be obtained by stating,
as 70 pounds of water are to 728 cubic inches, so are 225 pounds to 5554 cubic inches, which
must be divided by 28 feet, or 336 inches, the height of the column of water; we shall then
have about 16½ inches for the superficies of the circle of the base, or a diameter of 4
6 inches.
Fig. 1838.
To calculate the Effect of this Machine. — The arm of the crank MN being 6 inches, the
stroke of the piston will be 12; thus in each revolution of the crank, the two pistons will
together discharge a column of water 2 feet high, 4 inches in diameter, weighing 15
pounds. The pinion C being one-third the radius of the wheel D, the power must make
three turns of the winch A to one of the crank MN; and as this power can make 1000
turns in an hour, the crank MN will make 333, which multiplied by 15 gives 5161 pounds,
or 184 inches of water per hour.

Fig. 1839. shows a very simple method for
working two pumps by means of a balance
beam, A B, loaded with a weight at each
extremity; it works on gudgeons at C. Two
foot-boards are attached to the beam at
I,I; on these a man is placed who gives it
motion: the whole is supported by four
posts. At 10 inches from each side of the
gudgeons the iron piston rods M, N are
attached, which draw the water in the
A
pump barrels O,P, and force it up the O
A
H
F
N
M
R
P
pipe LH to a height proportionate to
the diameter of the piston and the action
of the mover. It will be found useful
to place an iron roller carried by steel
springs, F, G, on each side, to assist the
action of the balance beam: M. Morel,
the inventor of this and several other
machines, having remarked that where
several men are required to ring large
bells, a single person could put them in
action by working a treadle, applied the
same cella to working two pumps.
Pumps with three barrels are sometimes used where the object is to keep up a con-
tinued current of water by the action of three pistons, one of which is at the bottom of its
working barrel, while the second is in the middle, and the third at the top of each respective
barrel. Mr. Smeaton made use of three pumps at the London Bridge water-works:
when the pumps are small, the barrels are made of brass, and sometimes iron: opposite to
the aperture of each barrel there is a short pipe, covered at the end by a door, through
which a workman can get access to repair the valves, which are of iron, and which shut
down upon hinges like a door, being covered with leather on the lower side.
Fig. 1839.
CHAP. XVII.
1189
ON PUMPS.

A, fig.
Suppose
1840., to be a weight
of 200lbs. suspended
to an axle traversed
by an iron bar which
carries
two pis-
ton-rods. A man
pressing with his
foot on the treadle
E would work
both pistons, for
when making an
effort of only 60
pounds, the lever
being 4 feet long,
and the rods sus-
pended to the centre
of the axle, the
weight may be four
times the power;
consequently, if we
suppose the pistons
2 inches in diameter,
they will force a
column of water 154
feet in height.
Fig. 1841. represents suction
and forcing pumps worked by
one or two men at a winch A,
on whose axle is a fly wheel
and a pinion which engages
two wheels C and D, to whose
axles two lesser, E and F, are
attached, having teeth on only
half their circumference: when the
winch is put in motion, it turns
the pinion B, and consequently
the wheels C and D; in like
manner the two others E and
F, which engage alternately in
the racks G and H attached to
the piston rods, one of which
forces the water into the discharg-
ing pipe O, while the other
raises it above the lower valve.
The teeth of the small wheels
being turned in opposite di-
rections, the first E raises the
rod G to the last tooth, after
which the weight I causes it to
descend, forcing the water to a
height proportionate to the size
of the pump-barrel and the weight
of I, which should be greater than
that of the column of water. On
the other hand when G ascends
and the piston sucks, the teeth of
the other wheel, F, engage the
rack H, making it descend to the
last tooth; the piston N by the
action of the moving power then
forces the water up the pipe 0;
when the last tooth is past, the
rod H is drawn up by the weight
K, which must be rather above
that of the column of water and
the piston and rod. The two rods
OM
Α
E
Fig. 1840.
H
K
OF
Fig. 1841.
N
A
G
1
4 G 3
1190
Book II.
THEORY AND PRACTICE OF ENGINEERING.
G and H should work in guides to maintain their vertical position. The arm of the winch
A should be 1 foot long, the fly-wheel 6 feet in diameter, the pinion B 4 inches, C and
D 16 inches, E and F 4 inches in radius from the centre to the middle of the teeth.
There being four levers between the power and the weight, viz. the arm of the winch
12 inches, the radius of the pinion 2, that of the wheels C and D 8, and E and F 4, the
power will be to the weight as 2 x 4 to 12 × 8, or 1 to 12; consequently a man with a force
of 25 pounds can raise a column of water of 300 pounds.
and
L
E
X
T
F
P
D
Fig. 1842. is a machine executed at Sources, a village of Alsace, on the road from
Strasburg to Landau, placed over a large square well, the water of which is used for
making salt. There are three floors, at 10 or 12 feet apart; the framework of carpentry, A,
is placed on the first at the edge of the well, the cylinder B on the second, and the chest C
on the lowest. A fall of water drives the wheel D, the axle of which, E, has 4 catches, X, Y,
or wipers, which successively depress the levers F, G, and move the cylinder B by means of
iron rods at the extremity of the
balance K. Another balance, N,
carries the piston rod, which
is alternately elevated
depressed. The suction-pump
H raises the water to the cistern
C about 24 feet; the forcing and
suction-pump I then drives it
up the tube L 60 feet higher
to the reservoir near the salt
works. The dimensions for a
similar machine will be nearly
as follows: the great water-
wheel 5 feet in radius; the
wipers X,Y 20 inches in length
from the centre of their axle
;
the lever FV 5 feet 10 inches
from its fulcrum to the point on
which the wipers lean; the
point T, to which the rod is
attached giving motion to the
balance K, is 5 distant from the
fulcrum V, and the pistons each
having a lift of 12 inches; the
extremity of the wiper X must
pass over a certain determinate
length SF of the lever VF, in
order that the point T. which
has the same movement as the
piston, may rise 12 inches and
descend as much, whilst the
wipers will act alternately on
the levers Fand G : if the wiper
does not escape the lever F at
the instant the piston reaches
its lowest point, the machine
ceasing to act may break some
portion, for the wheel D con-
tinuing to turn will tend to
surmount any obstacle which
may prevent it. If, on the
other hand, SF be too short,
the wiper will not make the
point T descend low enough,

C
I
B
K
H
Fig. 1842.
and the piston not having a lift of 12 inches, the effect of this machine cannot be
calculated on such data. The water-wheel must be considered as of 5 feet radius; the
wiper X 20 inches in length, the power l' will be to the effort made by the wiper on the
point S as 1 to 3, and reduced to the point S may be expressed by 3p, when the lever FV
and the wiper X are in the same line: now, as the lever is of the second order, the power
which will act on the point S will be to the effort which it will produce at the point T, to
divide the rod downwards, as Y T to Y S, or as 6 to 7; the effort at the point T may then be
expressed by p. To find the diameter of the pump barrels,-since H sucks while I
forces, they will together sustain the weight of a column of water 84 feet high. To find
the base of this column in square inches, reduce p into cubic inches, by saying as 70
CHAP. XVII.
1191
ON MACHINES FOR RAISING WATER.
6
33
pounds is to 1728 inches, so is p, to a fourth term, or 432 p; this divided by 84 feet or 1008
inches, gives p for the superficies of the pistons, which multiplied by gives the square
35
of the diameter, and being reduced gives p, the root of which will be the required diameter.
Supposing the force of the fall of water to be 110 pounds on each float-board of the wheel,
substituting this number for p, we shall have 12 square inches, whose root gives 333 inches
for the diameter of the pistons: although both the wipers X and Y are capable of
exerting a force expressed by 3p, those only which act on EV will exercise it entirely,
since those levers alone suck and force the water; the other wipers Y only exercise a
small portion of their force; the lever G not acting uniformly, the wheel turns more rapidly
at one moment than at another. A second defect in this machine is caused by the wiper
X not pressing equally on S F, because the direction in which it acts changes at every point
of its course, as well as the length of the lever VS, which continually increases: to rectify
this evil the wiper X, in place of being straight, should have the figure of an epicycloid.
Fig. 1843. is a more simple manner of arranging
the same machine, invented by M. Morel. The
wheel A is driven by a fall of water; its axle has two
half wheels B, C, placed on the same side and about
3 feet apart, to work the pumps, which is performed
by two racks attached to the piston rods, working in
guides D, E one of these is loaded with a weight
F, to make the rod of the suction pump H descend.
At the end of the other a cord is attached, passing A
over two pulleys, and carrying a weight G to raise the
rod of the forcing-pump I; each rod has a stop to limit
the stroke when it meets the guides. The wheel A,
by driving the half wheel B, raises the piston rod D,
and as soon as it escapes the rack, the weight F brings
it down. On the other hand the weight G keeping
the rod E at a proper height, when the half wheel
C engages the rack of this rod, it drives it down and
forces the water in the pump I up the discharging
pipe K; the weight G then again raises the rod; thus
the pistons suck and pump alternately. As the wheel
B will only allow a small power to raise the water
24 feet high, and surmount the resistance of the weight
F, plus that of the piston, whilst, on the contrary, the
wheel C acts with much greater force on the rod E
to overcome at the same time the resistance of the
weight G and that of the column of water which the
piston forces to the height of 60 feet, the wheel A
will turn unequally.

H
Fig. 1843.
E
Fig. 1844. is a machine executed at Nymphen-
bourg by Count Wahl, director of builders to the
Elector of Bavaria, to raise water to a height of 60 feet, for the fountains in the gardens
-of the electorate. A stream turns a large wheel, which carries two cranks, working two
*
K

N
3}
G
K
H
Fig. 1844.
NYMPHENBOURG MACHINE,
Fig. 1845.
4 G 4
1192
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
cylinders, C, by means of iron rods B, and these drive six piston rods, F, on each side the
wheel; each system of pumps is contained in a trough, and firmly secured by screws
to two joints pierced with holes to admit the water of the canal. The three branches of
each system unite in the forks O, O which convey the water to the discharging pipe P; the
pumps are tied together by interties, to which they are secured by iron bands; the
depth of water near the fall at Q is 2 feet, and it has that velocity per second, as it runs
along an inclined plane whose height is 10 feet: to find the absolute force of the current on
the float-board, find a mean proportional between 2 and 12, which is 4 feet 10 inches, cor-
responding to the tabular velocity of 17 feet 1. Thus the absolute power may be re-
garded as equivalent to the weight of a column of water having the superficies of the floats
for its base, and a height of 4 feet 10 inches; the diameter of the wheel is 24 feet, its
float-boards are 5 feet long by 1 high; consequently the absolute power is equivalent to a
weight of 1715 pounds.
ΤΣ
The cranks are 1 foot in diameter, and so arranged that when one is horizontal the other
is vertical by this means the pistons of one only of the four systems force at the same time,
by the action of a power which is only part of the weight of the three columns of water
sustained by these pistons, the radius of the crank being that of the wheel. The diameter
of the pump-barrels is 10 feet, and that of their branch 3; thus its circle will only be
expressed by 9, while that of the pistons will be 100, a defect common to all forcing-pumps,
and which is considerable in the present instance, on account of the bends in the branches,
which prevent the water from rising, and consequently require a greater amount of power
than is possessed by these pumps. As this increase cannot take place without augment-
ing the velocity of the current, and that of the wheel does not diminish in proportion, the
product of the machine will be much less than it naturally ought to be; in other respects
it is simple and well contrived.
B
T
0
V
T
Q
N
N
Fig. 1846. is a machine for working forcing-pumps, executed at Val St. Pierre, Chartreuse,
in Tiérache, 2 leagues from Vervins: it was formerly only supplied by drawing water from
a deep well, until 1720,
when the book of Che-
valier Morland having
fallen into the hands
of Don Fougeres, then
Prior, he seized the idea
of that author on the
subject of ellipses, which
he proposed to use in
place of the crank to work
pumps, and applied them
to a machine driven by
a horse to raise water
from a well to a height
of 150 feet. The ma-
chine consists of a turn-
ing post I, carrying a

lig. 1846.
cogwheel, which engages a lantern, whose axle carries three equal and similar
ellipses N, in whose circumference is a channel similar to that of a pulley; these ellipses
are so placed, that if brought together the extremities of their greater axes would
form the six angles of a regular hexagon. O is a post in whose suminit are three
slits, through which pass as many balance beams P, S, traversed by a bolt serving
as a common axis; to keep them in the same direction they are maintained by frames,
TV, attached to a joist: one of the extremities of each beam is held by two braces,
S, Q, between which are rollers R, which work in the channels of the ellipses; at the
other extremity X are suspended the rods XY, of three pump-barrels, placed in a
small vault, to which they are attached by iron cramps. The branches pass from the pump
barrels through the vault to the reservoir by an inclined plane of 1200 feet. To understand
the play of this machine, suppose the horse attached to the swing trees and having his
halter attached to the guide bar; when he advances, he turns the wheel and lantern M, and
consequently the ellipses which move the balance beams by the difference of their axis; for
when the great axis is vertical, the centre of the rollers is raised to a height equal to half the
difference between the greater and lesser axis; when this axis becomes horizontal, it descends
the same quantity: thus each roller goes over half the circumference of an ellipsis, and
during each revolution the piston sucks and forces twice, the rollers never quitting their
channel, because the part OQ of the balance beams bears by its length and weight on the
resistance of the other part PO: each ellipse may be regarded as the union of four
inclined and curvilinear planes turning round a fixed point, and at each revolution a
plane compels the weight to ascend from the foot to the summit; a second succeeds, down
which the weight descends by its own gravity; it then rises up the third, and falls down the
CHAP. XVII.
1193
HYDRAULIC MACHINES.
fourth. The three being never in the same situation, while one of the rollers mounts the
two others descend, after which one descends and two mount, the pistons sucking and
forcing accordingly six times during each revolution of the axle, whilst they would only
play three times during one revolution of a crank: thus ellipses have the advantage of
doubling the velocity of the pistons, and of rendering the action of the power more uniform,
because the angles formed by the axes of the ellipses are only 60°, or half those formed by
the simple crank.
The great wheel of this machine is 6 feet in radius from the centre to the teeth; the
teeth, 101 in number, are 16 inches long, project 4 inches, are 31 wide, 21 thick at the top,
and 21 at the base; the axle is 18 inches in diameter: in order that the horse in turning
may pass under the axle L'K of the lantern, the summit of the teeth of the wheel must be
raised 5 feet above the ground; the shaft or lever must be 14 feet long from the centre
of the turning shaft to the attachment of the swing-trees, and the horse should have a clear
way of 18 feet radius: the spindles of the lantern are 20 in number, and 2 inches in
diameter; their centres form a circle 2 feet 10 inches in diameter, and that of the hooping
round them 3 feet 8 inches, which is of timber 5 inches thick: the axle of the lantern
and ellipses is 16 inches in diameter; the ellipses are 6 inches apart and 7 thick; the
channel in their edge is 4 inches wide, and 11 thick: thus they have two edges forming no
part of the length of the axis, which is to be measured to the bottom of the channel, in
which is a band of iron to keep the timbers together; the greater axis of the ellipsis should
be 5 feet, and the lesser 3 feet; thus half the difference is 12 inches, which is the quantity of
alternate elevation and depression of the rollers: the length of the balance beams from the
centre of the rollers to the suspension point of the piston rods should be 25 feet, and their
scantling 5 inches by 9; their centre of motion should be 9 feet 6 inches above the ground:
the wooden rollers should be 1 foot in diameter, and 3 inches thick, with a ring of copper
on the edges: the centre of motion of the balance beams should be 15 feet from that of
the rollers, in order that the arm nearest the pistons, being of the other pistons, may rise
8 inches, or as much as the rollers. The pump-barrels are 24 inches inside diameter, and
DOT+


Fig. 1847.
Fig. 1848.
Fig. 1849.
Fig. 1850.
Fig. 1851.

12 inches high; they have four faces, each 31 inches wide, and
are united at the base by a pipe pierced with holes; to admit
the water between this pipe and the pump-barrel is a valve,
fig. 1847.; in one of the faces of the pump-barrel is an orifice
to which the branch is adapted; this branch is only 1 inch in
diameter, and comprises a valve similar to the preceding: the
pistons, fig. 1852. 1853. are cast-iron cylinders, with a plate of
the same metal attached to a double fork, to hold the piston
rod, which is a deal batten, 4 inches square. The pistons
are composed of two parts, one 8 inches high and 25
inches in diameter, and the other 4 inches high, and 14 in
diameter: at its extremity is a screw and nut serving to
tighten a number of roundles of leather: when the piston
sucks, the weight of the atmosphere forces the water to
enter the barrel by opening the valve which is at the
bottom; the moment the piston forces, the valve closing,
the water passes into the branch, opens the second valve,
and rises in the discharging pipe. The branches of the
pump-barrel being only 1 inch in diameter, while the
pistons are 2, the water is forced into a pipe, which is
only one-sixth the size of the piston; and thus the horse
employs a part of the force he exerts to overcome the
obstacles which are opposed to the water's progress.

0
To calculate the Product of this Machine.-The horse per-
forms two turns in a minute, or 120 per hour, and at each Fig. 1852.
turn goes over 88 feet; thus the velocity is 10560 feet
per hour the wheel having 101 teeth, and the lantern
1853.
PISTONS.
Fig. 1854.
PUMP
BARREL
20 staves, it will make 5 turns whilst the wheel makes 1; and as this latter performs
120 revolutions per hour, it follows that the lantern will make 606 in the same time, and
1194
Book II.
THEORY AND PRACTICE OF ENGINEERING.
as each piston forces twice at each turn of the lantern, the three together will make 3636
strokes per hour.
The pistons being 2 inches in diameter, and 8 inches lift, they force at each stroke a column
of water of 392 cube inches, which being multiplied by 3636 gives 142843 cube inches per
hour raised to a height of 150 feet: if it be required to raise water higher than 150 feet,
the piston must be diminished in superficies, otherwise the power of one horse would not
suffice; if, on the other hand, a less height be required, the superficies of the piston must
be increased, or the horse would not raise a quantity equal to his mean strength.
To pro-
portion the pump-barrels in either case, the following rule will be found useful: the
diameter of the pistons being 2 inches, its square will be 6 inches, which, multiplied by
150 feet, gives 937, and this may be taken for the weight of a column of water forced
by each piston; but as the diameter of these pistons might be greater if the pumps were not
to a certain extent defective, we may, supposing them to be perfect, take 1000 for the ex-
pression of a column of water instead of 937, and this will still be too low an estimate:
this number of feet is then divided by the height the water is to be raised, and the square
root of the quotient will give the number sought: for example, if the water is to be raised
60 feet, 1000÷60-163, whose square root is 4 inches.
The pumps may be placed at any convenient height above the water by using suction-
pipes to raise the water from a brook or river; the number 1000 must then be divided by
the height of the reservoir above the water, and not by its height above the pumps.
M. de la Hire, in his treatise on Epicycloids, has described a very simple method of
working pumps, as executed by M. Desargues at the chateau of Beaulieu, eight leagues
from Paris.
F
N
B
M
A
In fig. 1857., LMOI is a large wheel, placed horizontally, and composed of several
pieces of timber firmly united: the axle, AB, of this wheel turns on a pivot and socket,
and is kept in its place by a timber framework: the wheel has five wavy teeth on
its edge, at OI, which act on the rollers that turn on an axle, C; this axle is
carried by an arm, DC, also movable on an axle at D; the arm DC is attached to a
portion of a circle, DE F, in such a manner that one cannot move without the other.
On the thickness of the arc is a double flat chain, H G, attached at E: this chain has two
rings at its extremity, which support the iron stirrup of a forcing-pump. The lever or
arm, N, of this ma-
chine is let into the
axle at B, and may be
attached to the wheel
for greater strength.
There are two rollers
similar to the one
described diametri-
cally opposed to each
other under the wheel,
and which ought to
act alternately; for
when one is in the
hollow of the wheel
the other is on the
wave: but the wheel
turning from 0 to I,
the roller will descend
from the part O Q,
and remount on the
opposite side. The
part OQ is alone to
be considered, for it
is that which causes
the roller to descend,
and raises the piston
of the forcing-pump.


E
Ι
H
D
Fig. 1856.
G
Fig. 1855.
Fig. 1857.

K
Fig. 1858
H
F
ལ
C
D
The roller remounting on the other part of the wheel makes
no effort, but only follows the sinuosity of the tooth, being raised by the weight of the
piston as well as that of the triangle DE F, which fall by their own weight. The whole
effort of the wheel is due to its weight, so that if it be as heavy as the column of water
sustained by the piston, it is evident that there will not be any considerable friction on the
pivot P; it must, however, le heavier, so as not to be liable to lifting out of its socket,
otherwise it will work on both rollers at once: the number of teeth should be unequal,
in order that one roller may always work, and the power moving the lever N act equally
and not by jerks.
ChA. XVII.
MACHINES FOR RAISING WATER.
1195
Fig. 1855. represents a wheel somewhat similar to the preceding, but the faces A B and
CD are straight, being rounded at the summit and base alone: the rollers F are attached
to balance beams of a proper length in this case the pumps are reversed, the pistons
forcing upwards, but if a different arrangement be desired, the wheel may be made to work
as in fig. 1858; and this manner is preferable, as the balance beam may then be of any
required length without regard to its weight. After the position of the posts C and D is
fixed, in such a manner that the horse is not inconvenienced when turning, the length to
be given to E F is known, and the other arm must be two-thirds of this: the height of the
posts is so arranged that when the roller I arrives at the summit of a tooth K, the balance
beam G H may be horizontal. When the roller L is at the bottom N of the opposite tooth,
the angle M1.F formed by the vertical ML and the line LF, which joins the centres of
motion of the roller and balance-beam E F will be greater than a right angle; wherefore
the direction LF of the power, which sustains the weight L on an inclined plane, not being
horizontal, it is very nearly to the weight as the height of the plane is to its base: the
more the base of the inclined planes formed by the teeth exceeds their length, the less
resistance will there be to the rollers; but as the bases cannot be increased without ex-
tending the circumference on which they are placed, and so removing the weight further
from the centre of the wheel, which may be regarded as the fulcrum of the lever to which the
motive power is applied, the power will evidently gain nothing. The base should be twice
the height; the roller 8 inches in diameter, rising 12 inches, and the play of the piston 8
inches. The length of the base of the teeth is 4 feet 4 inches comprising the bottom in
which the roller rests; this multiplied by 5, gives 21 feet 8 inches for the circumference
of the wheel at the middle of its thickness, or 3 feet 10 inches for the external radius. The
wheel is constructed as in ordinary mill-work. The inclined planes are attached together
by a band of iron 4 inches wide, on which the roller works. Fig. 1856. shows the
manner in which the roller is attached to the balance-beam. The rule for finding the
proportion the motive power bears to the weight is thus expressed: the power is to the
weight raised by the teeth, as the product of the radius of the wheel multiplied by the
height of the inclined plane, is to the product of the length of the lever multiplied by the
base of the same plane. Supposing the lever AD to be 14 feet long, and the force of a
horse to be 180 lbs., we shall have 3 × 1: 14 × 2 :: 180 lbs., or 1: 8 :: 180 lbs., showing that
the power is one-eighth of the weight, which will consequently be 1440 lbs. Now, since in
a state of equilibrium, this weight should be to that of the column of water in the reciprocal
proportion of the arms of the lever, or as 2 to 3, the motive power will only be one-twelfth
part of the weight of the column which each piston forces, equal to the weight of 2160 lbs.
To find the diameter of the piston, multiply the weight of the column of water each can
force by 1728, as a constant number: multiply the height the water is to be raised in
inches by 55, another constant number: divide the first of these products by the second,
and extract the square root of the quotient, which will be the diameter required. Since a
horse can easily make 120 turns in an hour, and at each turn the pistons force ten times
with a stroke of 8 inches, they will raise 1200 columns of water 6 inches in diameter
8 inches high, in one hour. The cost of this machine is moderate, and it may be made
to draw water from a very

deep well, by using suction-
pumps at 25 feet apart.
Bascule used by Perronet
at the bridge of Orleans, was
worked by twenty men, ten
being placed at each end;
150 motions were given to it
each quarter of an hour, and
at each, 4 cubic feet of water
were raised 3 feet high, or 2400
cubic feet per hour.
The Chapelets employed at
the same bridge were placed
vertically, and from 12 to 18 feet
in length, and about 6 inches
in diameter: four men worked
the winches, and were relieved
every two hours; they made
20 to 30 turns in a minute,
according to the height to
which the water was to be
Fig. 1859.
BASCULE used at ORLEANS BRIDGE.
raised; 500 cubic feet of water, or 62 muids, were raised per hour, and at each turn
4 feet of the chain were wound round.
1196
Poor. II.
THEORY AND PRACTICE OF ENGINEERING.

Fig. 1860.
CHAPELET, ORLEANS Bridge.
The Persian Wheel is a double water-wheel, with float-boards on one side and a series of
buckets on the other, which are movable about an axis above their centre of gravity: the
wheel is placed in a stream, which puts it in motion by acting upon its float-boards: as
the wheel turns, the movable buckets dip in the water, and ascend filled with it: when
they reach the highest point their lower ends strike against a fixed obstacle, so as to oblige
them to empty themselves into a reservoir placed at the top of the wheel.
Drum or Persian Wheel, employed by Perronet, raised the water 8 feet, but its product
varied according to the different depths at which it worked: when at 1 foot, 12 men,
relieved every two hours, gave two turns in a minute, and at each turn 24 cells were
emptied, each containing 1 cubic feet, giving for the hour 4320 cubic feet, or 540 muids:

Fig. 1861.
Fig. 1862.
PERSIAN WHEEL, Orleans bridge.
Fig. 1863.
when at 9 inches of depth the same number of men made 150 turns in an hour, but raised
only 450 muids: when at 6 inches depth, they made 180 turns in an hour, and raised 405
muids: when at 3 inches in depth 180 turns were made in an hour, and raised 270 muids
in an hour.
The Scoop Wheel is intended to raise water through a height equal to its semi-diameter,
and consists of a number of semicircular partitions, which are open at both ends, viz. at
the circumference and at the centre of the machine: as the wheel turns round, the
scoops take up the water, which gradually descends during the rotation of the wheel,
till it runs into its hollow axle, which again discharges it into a spout.
Chain Pump, as the Spanish Noria, consists of an endless chain passing round a wheel,
and after entering the water to be raised, returns through a tube into a cistern: the chain
carries a number of flat cylindrical pistons, of nearly the same diameter as the tube, one
half of each piston being received into openings in the circumference of the wheel; when
the wheel is put in motion, the pistons enter the barrel, and pushing the water before them,
raise it into a reservoir; and if the wheel is made to go round rapidly, the barrel is generally
filled with water. Pumps of this description when put in an inclined position will raise
a considerable quantity of water; the inclination in which their power is the greatest is
CHAP. XVII.
1197
MACHINES FOR RAISING WATER.

that of an angle of
24º 21'. In Spain
the Noria is usu-
ally furnished with
earthen pitchers,
between two ropes
in place of a chain.
The Cellular Pumps
are of this kind,
and when stuffed
cushions are used
instead of pistons,
they are termed
Paternoster pumps.
Chapelet, worked
by Horses, at the
bridge of Orleans.
Twelve horses were
employed at one
time, making 140
turns per hour; but
as some allowance
is necessary
for
changing, we can
only calculate upon
120: the number
of cogs upon the
wheel was 115, that
of the great lantern
12, that of the small
8, making in all
9660 buckets of
water delivered per
Fig. 1864.
CHAPELET at the bridge of ORLEANS.
hour from each of the two chapelets: the heights of the buckets were 6 inches, their dis-
tance apart 6 inches, and the width of the trough 7½ inches.
Chapelet worked by a Water-wheel, at the bridge of Orleans. When the water was 18
inches above low water, the great wheel made 165 turns in an hour, which gives about 2

f
Fig. 1865.
PLAN OF CHAPELET
M
2000000000000
1198
BOOK. II.
THEORY AND PRACTICE OF ENGINEERING.

Fig. 1866.
section of INCLINED CHAPELET, WORKED BY WATER.
The
feet velocity per second, and 6 feet for the current: when the river was 2 feet above low
water, the wheel made 180 turns per hour: when it made 165 turns, the troughs were
plunged 30 inches; when from 216 to 240,
they were only in the water 15 inches.
great wheel had 124 cogs, and the lantern
which it turned 15 trundles: the other lantern
over which the chain of the inclined chapelet
worked, had eight trundles, each of which passed
one palette of the chapelet; giving 66 palettes
for each turn of the great wheel, 180 of which
it made in an hour, giving a total of 11,904
palettes, each of which brought up 290 cubic
inches of water; the whole producing in an
hour 19977 cubic feet raised 12 feet.
The vertical chain pumps employed at the
bridge of Orleans gave for the useful effect of
each man, during twenty-four hours, 139 cube
metres of water raised 1 metre: but many ex-
periments have been since made, and it has been
found that 128 cube metres of water raised a

Fig. 1867. ELEVATION OF INCLINED CHAPElet.

Ex
Fig. 1868.
END ELEVATION, ORLEANS BRIDge.
metre is nearer the result. The daily action of a man working at the winch being 155
cube metres of water raised the same height, the relation between the useful effect and the
force expended is 0.826. The vertical chain pump is, however, a very serviceable machine,
as there is not more than one-fifth part of its force lost: the chain-pump is easily taken up
and replaced, and can readily be repaired.
The great Bucket-wheel employed by Perronet at the construction of Neuilly Bridge
was 16 feet 6 inches in diameter, and 4 feet 6 inches in width, furnished with 16
buckets and 118 cogs. The wheel with float-boards was 18 feet in diameter, and had
128 cogs; the float-boards, 20 feet in length and 3 feet in width, made an angle of 15 de-
grees with the radius, to diminish the resistance of the water as they turned: generally the
lanterns of 4 feet in diameter had 30 trundles, and the tree was 12 inches in diameter; the
length was regulated according to circumstances; some were 38 feet, and from 54 to 108
CHAP. XVII.
1199
MACHINES FOR RAISING WATER.

3000
Fig. 1869.
ELEVATION OF GREAT BUCKET-WHEEL.
feet in length. The bucket-wheel was mounted on a strong frame, and the wheel with
float-boards had an axle 108 feet in length, 20 feet of which was appropriated to the float-
boards, which were 18 feet in diameter at the wheel.

M
Fig. 1870.
PLAN OF GREAT BUCKET-WHEEL, NEUILLY BRIDge,
Fig. 1871. shows the celebrated Machine de Marly, executed by Rannequin, a native of
Liege, by command of Louis XIV. it commenced work in 1682, and is said to have cost
320,000l. It was situated on the Seine, between Marly and Lachausseé, and consists of 14

W
Fig. 1871.
MACHINE AT MARLY.
HOMZIKI
1200
Book IL
THEORY AND PRACTICE OF ENGINEERING.
water-wheels, which first raised the water from the river to a cistern 150 feet high and 600
feet distant, then worked the balance-beams of the pumps, which raised the water to a
second cistern, 175 feet above the first, and 1944 feet from the river; from thence it was
lifted by other pumps to a strong tower or reservoir, 502 feet above the river and 3684 from
it; whence the water was conveyed by an aqueduct to the great reservoirs which supply the
gardens of Marly and Versailles.

Fig. 1871. is a longitudinal
view or section of one of the 14
wheels: on the bed of the river a
floor was laid on piles filled in with
masonry, and 14 feet above this
was the platform which sup-
ported the pumps. To the axle
of the great wheel a crank was
attached, which communicated
motion to the balance-beam, and
this worked the piston rods of four
pumps on each side, which sucked
and forced the water alternately.
To prevent the air from entering
the pump-barrels, a fifth suction-
pump raised water to a cistern
a little above the four others.
Fig. 1872. shows how these
pumps at the first and second
cisterns were worked: a crank
on the other end of the axle of
the great water-wheel communi-
cated motion to the two iron
chains, and these, by means of two
other cranks, alternately worked
the two iron frames to which
the piston rods of six pumps
were attached. All these pumps
worked independently of each
other, and each reservoir had six
pumps for the purpose of supply-
ing it when reparations were re-
quired. The whole system may
be drawn up by the crab shown
in the figure. The pulley in the
middle may be moved into any
position along the head of the
frame, by means of the winch at
the side.
Fig. 1872.
MACHINE AT MARLY.


A
C
B
Fig. 1875.
D
Fig. 1874. is one of the eight
suction and forcing-pumps put
in motion by the crank of the
great water-wheel; when the
piston ascended, the water from
the river rose in the suction pipe,
opened the first valve, filled the
whole of the horizontal pipe and
a part of the barrel: when it de-
scended, it forced the water in
the barrel, which by its pressures
closed the first valve, opened the
second, mounting in the branch;
when the piston remounted, the
second valve closed, and the first
reopened to admit more water;
B represents one of the suction-pumps, which supply the small cisterns to keep the eight
pump-barrels from leakage.
Fig. 1873.
Fig. 1874. Fig. 1876. VALVE.
Fig. 1873. is one of the pumps of the first and second cisterns: the barrels were carried
on iron bars, and the piston rod attached to an iron frame; at the upper part of this latter
are shown two small rollers to facilitate the operation of drawing the whole up. The manner
of working is the same in this example as previously explained, when on the description of
CHAP. XVII.
1201
MACHINES FOR RAISING WATER.
D is a
forcing and suction-pumps, and the valves operated precisely in the same manner.
valve at the bottom of each cistern to empty it, which was effected by simply turning the
handle at the end of the rod: when the machine was in full
work it threw up 168264 cube feet in 24 hours, and employed
60 workmen to keep it in condition.
Fig. 1877. is a machine invented by Belidor for raising
water by means of a fall. The water from the source is dis-
charged into the cistern C, at whose lower part is a pipe CD,
10 or 11 feet high, kept continually full. The water on issuing
from the pipe CD is divided into two unequal parts, of which
the lesser passes along the pipe GH, and up GL, into the
cistern M, and then down the pipe M N to the cistern of dis-
tribution; the space FE comprises the machine represented in
detail at fig. 1878. ABCD, EFGH, are two pump-barrels
united by a pipe, IKE G, open at LMNO to facilitate the
motion of the pin which passes through the piston rods R and
S, whose stroke is limited by ML and NO. I is the pipe
marked CD in the preceding figure, having two branches at
right angles to each other: the first, I Y, joins the communi-
cation pipe YV, which conducts water into the small pump-
barrel, and the second, TZ, is united to a cock, which admits it
to the large one. This cock has three conical branches; the
first is united to the pump-barrel, the second introduces the
water which gives impulse to the piston, the third facilitates
the escape of the same water: the tap of this cask acts at two
separate times, making a quarter of a revolution at each, to
the right and left, communicating alternately with the pump-
barrel and the discharge pipe, so that the water escapes from
the former while the supply pipe is closed by the solid part of
the tap P.

M
N
L
S
K
F P
D
B
Fig. 1879. represents this cock in detail: A is a plan of the
three conical branches; B is a section through the two opposite
branches; C a section at right angles to the preceding, and D is
the elevation behind; E is the plan of a jacket between the cock
and the branches to prevent leakage; G is a section, and H an
elevation of it, showing that its bottom is slightly convex, and
that the tap may not touch it, but turn on a pivot in its centre ;
F is a plan of the tap, I a section, and K an elevation of it; L is an elevation of the whole
put together, and M a plan and section of its head.
Fig. 1877.

K
B
W
N
RD
C
D
F
S
G
Н
Y
T
P
Fig. 1878.
BELIDOR'S MACHINE.
Fig. 1880. shows the pistons of this machine, B being an elevation, and M a section:
both rods consist of hollow cylinders, the less sliding in the greater, as to shorten the entire
length for the purpose of introducing them into the pump-barrels ; at each end is a screw;
A and C, to which the pistons are attached: the pistons themselves, DE F, IK L, consist
of a cylinder on which several leather rings are placed, and a washer and nut to tighten
them to diminish their friction, each is provided with a roller G and H.
The play of this machine will be understood by a reference to fig. 1877. The water in
the pipe CD having free communication by HG will rise as high as K: the valves shown
in fig. 1878. being pressed upwards, open to allow the water to pass; in doing this it will
also enter the small pump-barrel, and drive the piston R towards B D, and consequently S
towards the cock, supposed as at fig. 1877., where the pipe of admission closes and the dis-
charge pipe opens, the air or water in the great pump-barrel can escape: when the piston S
arrives at FH, the cock making suddenly a quarter of a revolution, and opening the sup-
ply pipe and closing the escape pipe, the water from the source will drive the piston
forward for if we suppose its circle six times that of the lesser, there will be six columns
of water equal to K F, acting together against and driving it towards N, the water in the
4 H
1202
BOOK II,
THEORY AND PRACTICE OF ENGINEERING.
K
B
Fig. 1879.
T
revolution in the opposite direction, closing the supply pipe and opening that of the dis-
charge; the water in the great pump-barrel will cease to act against the piston S, and at
E
F
H
Fig. 1880.
G
K
D
BELIDOR'S MACHINE IN DETAIL.
B
M
H
details OF THE ROBINET.
E
smal! pump-barrel, at the same time closing the lower and opening the upper valve in the
pipe GL. The axle Q having now arrived at ML, the cock will make a quarter of a


Х
M
L



CHAP. XVII.
1203
MACHINES FOR RAISING WATER.
the same time that in the pipe G L, being no longer forced, will close the upper valve; the
water in the pipe of communication Y V, driven by that from the cistern C, will open te
lower valve in GL, again drive the piston R towards BD, while the other S will in its
turn force that which had driven it forwards until the axle Q having arrived at N O,
will make a quarter revolution, closing the escape and opening the supply pipe: this will
again permit the water from C to drive the great piston, forcing that in the small barrel as
before, closing the lower valve, and opening the upper.
Thus the alternate motion of tho
cock will make the water rise to the cistern M, provided the product of the circle
of the small cistern, multiplied by the height of the column FL, be less than the product
of the circle of the great piston multiplied by the height of the fall CD.
Fig. 1881. shows how the cock is opened and shut alternately. The whole machine is
carried on stout timbers, to which are attached two uprights supporting an iron spindle CD:
on this as a centre an iron right angle OVHI revolves; the arms GH, KI, have claws at

E
U
V
Ba
H
Q
U
L
h
M
Z
N
m
F Y
A
A
E
T
B
F
D
X
N
C E Q
G
R
h
0
B
P
P
L
Fig. 1881.
their extremities, and the rod VO a weight, at O, of 9 or 10 pounds; this turns with the axle
CD. A stirrup QR plays on it, the axle being rounded at the rings Q and T.
The iron rods E A and Fƒ also move with the axle CD. The stirrup is traversed by two
bolts L and M, the second of which passes through the branch Z of an iron fork,
having a tail ZNP attached, the extremity of which works the key of the cock, which is
prevented from going too far by a brace O. The rod X traversing the two pistons has a
roller A B at each extremity, which alternately driving the two rods E A, Ff, before them
that move the axle CD, and consequently HIVO, but not the stirrup, which remains in
its position until moved by the action of the weight 0.
Suppose the stirrup in the situation represented by the upper figure, and that the supply
pipe be open, in order that the water may drive the great piston forward, the roller A
driving the rod E A will raise the weight O towards the right, and when arrived at the
point E, the weight having passed the perpendicular will suddenly fall; the claw IK
then meeting the bolt L, will oblige the stirrup to pass to the left, and drive the rod LNP
backwards, at the same time turning the key of the cock; thus directly the axle X
arrives at its extreme point to the left, the escape of the weight will shut off the supply
and open the escape-pipe. The rod Ff having performed the same operation will be
driven forwards by the roller B, in the same manner as the preceding, because the escape-
pipe being open, the small piston will be driven back, and the weight O raised to pass from
right to left when it is a little beyond the perpendicular, the claw IK will take up its
first position, meet the bolt L, drive the stirrup forward, thereby turning the cock, closing
the discharge and opening the supply pipe, the water from which will again drive the
great piston, and cause it to execute its first operation.
The axis CD should be placed at the middle of the open barrel, so that the three points
a, D, A may form an equilateral triangle in the same plane, whose base a A may be equal to
the course of the rollers between the points where they touch the rods E A, Fƒ when they
4 H 2
1204
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
arrive at the points which mark the stroke of the piston, in order that the distance from the
centre of the axle D to the centre of the bolt M may be equal to the course Mm or ki of
the bolts Mh.

Fig. 1882.
belidor's MACHINE.
The calculation of the dimensions and effect of this machine is based upon the following
data that the fall CD in fig. 1877. is 10 feet, the height FL of the pipe for raising the
water to the cistern M is 50 feet, the stroke of the piston 30 inches, and its velocity 1 foot
in a second of time; the resistance caused by the weight and friction of the machine must
be taken into account, or be considered as raising the water 60, instead of 50 feet. The
great piston is 10 inches in diameter, the lesser 31 inches, the discharge pipe 4 inches in
diameter: the product of this machine will be about 793 cubic feet per hour.
Machines made use of by the engineer for pumping out foundations require arrange-
ments to be provided, which are perfectly independent of raising the water, and the first
object when selecting a contrivance for such a purpose is to discover where the useful
effect is the greatest, with regard to the force expended by the moving power; sometimes,
however, it happens, that machines for pumping, apparently defective, may be used very
advantageously: men were employed with pails and scoops, at the bridge of Orleans, in the
first experiment made by Perronet, and it was found that each man raised with a pail 0034
cube metres of water per minute, at 1.79 metre of height, and in a second experiment
•0069 cube metres of water at 0.97 metres of height in the same time, which in the first
result amounts to 3.652, or the second 4·016, and mean 3.834 cube metres of water
raised per hour one metre high: the workmen laboured 12 hours, so that the useful
effect produced during the 24 was 46 cube metres of water raised 1 metre: the pail
contained 0018 cube metres, but as the workman filled it one-fifth was lost before it was
discharged out of the foundations; we must only estimate 55 111 cube metres of water
poured out of the pail 3062 times. The weight of the pail is equal to 004 metres cube
of water, and this raised 3062 times furnishes a quantity of action of 12,248 cube metres
of water, which added to the other gives 67,359 cube metres: a man using a wheel can
raise about 200 cube metres of water 1 metre in height in a day's work.
In the Chapelet at Rochfort, mentioned by Belidor, moved by 4 horses, 44·4 cube
metres of water were raised 7-8 metres high per hour, which makes the useful effect of
each horse 86.6 metres of water raised a metre in an hour; and supposing the horse to
work 8 hours, the daily useful effect would be 693 cube metres of water raised a metre:
but if we suppose that the machine consumed two-fifths of the moving force, the quantity
of daily action of each horse would be 1156 cube metres raised a metre.
Water Wheels moved by the stream have very variable effects: according to Smeaton two-
thirds of the force is generally consumed by the resistance of the wheel, and only therefore
one-third is transmitted to the shaft: the Archimedean screw only gives for the useful effect
a little more than half the force it consumes, and the French engineers assert that the roue
à tympan is one of the most advantageous powers that can be made use of for pumping.
Spiral pumps, as improved by Bernouilli, were introduced with considerable effect at
Moscow, where one raised a hogshead of water in a minute to the height of 74 feet, and
through a pipe 760 feet in length: among the variety of forms given to them, it has not
been yet sufficiently proved which is the best; some engineers giving the preference to the
cylindrical plane, others to the conical: at Florence the machine most used had its spiral
cylindrical; its diameter was 10 feet, and that of the pipe 6 inches. Eytelwein recom-
CHAP. XVII.
1205
MACHINES FOR RAISING WATER.
mended this machine to the attention of the engineer; its enlarged part occupied three-
fourths of its circumference, and was nearly 8 inches in diameter at the outer end; the
enlarged portion contained 6844 cube inches, and the spiral revolved six times in a minute,
raising in that time 22 cubic feet of water 10 feet high: when Dr. Young made his experi-
ments upon the Archimedean screw, he found that it required such a length of pipe, that
it became inconvenient when the water was to be raised to any very considerable height.
MM. Denisard and de la Dueille executed at Sevres, between Paris and Versailles, a
machine for raising water by a natural fall, shown in fig. 1885. it consists of a wooden
framework in which is a basin with two boards placed on each other, and hollowed out to
form the basin, which is lined with leather; in it is a piston of nearly the same diameter,
attached thereto by a piece of leather, in such a manner as to have a stroke of only 3 or 4
inches four pipes are adapted to this basin; the supply pipe IT, the branch Z Z, the
waste F, and the descending pipe G. The long screw with two nuts Y,N, raises and lowers
the balance-beam

consisting of two
basins O, Q, with
pipes of commu-
nication to allow
R
B
D
DR
Z
Fig. 1883.
Fig. 1884.
N
S
M
L
Ω
the water to pass
from one to the
other at the ex-
tremities of this
balance-beam are
rods which open
and shut valves in
the waste and sup-
ply pipes: these
are represented
in figures 1833.
1834. The valve
is enclosed in a
small coffer, A B,
in which is a trun-
cated cone, fitted
to the pipe. The
cover of this cone
is attached to an
axle C, and this
latter to the rod E,
which the balance-
beam works. The
part I of the valve
(fig. 1883.) being
stopped by the
cone, and the
whole valve being
immersed, the co-
lumn of water to
be raised is in
proportion to the
diameters of the
bases. When the
rod E descends, the solid cone, which has a contrary motion, will unstop the hollowed cone I,
and the water will without difficulty pass into the tubes D, R; if, on the contrary, the water raise
the rod E, the valve closes, and the pipe will be stopped. The source L being 10 feet high, the
water will introduce itself by the pipe ITV below the piston A, which being driven by this
water will naturally rise, at the same time driving out the water above at B, through the
waste pipe F; by this elevation the nut N raises the balance-beam, and the water passes from
the basin O to Q; the extremity O raises the rod R, which closes the valve H; the basin Q
resting on the rod S opens the valve X, in the descent pipe G, and the water from the
source, taken from below the great piston, rises by the branch ZZ. The pipe V being
stopped, the piston is loaded with the weight of water in the descent pipe G: by its
descent the balance-beam is drawn down, and the water returning from Q to O closes the
valve X and opens H: the water is thus raised in succession.
F
V
H
Fig. 1885.
B
A
D
Dueille's machine.
X
א
Z
ரு
T
Some alterations were afterwards made in this machine in order to raise the water in a
continuous stream; this disposition is shown in fig. 1886. The source A furnishes water
by the pipe A B C below the lower piston D; this source is supposed to be 10 feet high.
4 H 3
1208
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Y
W
M
E
The descent pipe EFG, 30 feet high, admits water below the upper piston H, and tends
to raise it the water compressed below the same piston H is forced up the pipe IL M.
The water below the lower piston D escapes by the waste N; the valve O is opened by
the rod P; the second acts in a similar
manner. The source V, supposed
10 feet high, admits water above the
upper piston H: the water in the
descent pipe Y Y, 30 feet high, presses
on the upper part of the lower piston
D, and forces the water up the pipe
ZW to a height of 40 feet: during
this operation the water contained
below the upper piston H escapes
through the waste K, the valve T
being closed. Thus the machine will

Z
P
NO
-D
H
force water alternately on each side.
The contrivance for opening and shut-
ting the valves is the same as that
described in the preceding machine.
The upright pipes are furnished with valves to prevent the return of the water.
Fig. 1886.
T
SIDE ELEVATION.
T
M
ะ
B
Fig. 1887. is a machine for raising water by means of two buckets; one of which, A, is
larger than the other B, so that both being full of water, the first in descending raises the
second, and the lesser B weighing more than the other, to oblige it to ascend when both
are empty. The bucket B has an iron hoop round its middle with an ear attached, and A
has a similar circle, Q, at the bottom : the water from
a source is conducted to a cistern E, and flows con-
stantly through the waste F; the two buckets are
attached to a cord or chain passing over a pulley R,
so that when the lesser bucket is in the cistern the
other may receive water from the waste F; when the
bucket A is full, it descends and raises the other B, as
much as its fall; it then catches the hook O, and empties
itself into the cistern; at the same moment the ear of
the bucket A catches another hook at the bottom of
its descent and empties itself; the lesser being heavier
than the greater will compel it to mount, and recom-
mence the same manœuvre. On the axle of the pulley
R is a toothed wheel S engaging a pinion T, which
carries a fly-wheel to preserve uniformity of motion:
if the fall CD be less than the height to which the
water is to be raised, the buckets K, L may be sus-
pended to two different wheels M, N, whose dia-
meters should be in the reciprocal proportion of the
fall and the height the water is to raised; these two
wheels must have a common axle, and turn with it.
For example, if the fall be 10 feet and the water is to
be raised 30, the radius of the lantern M of the lesser
bucket L must be triple that of the lantern N of the
greater bucket K; but the weight being in the reci-
procal ratio of the arms of the levers, the capacity of
the lesser bucket must only be one-third that of the
greater. Gironimo Finugio is said to have invented
this machine at Rome in 1616.

A
C
Q
D
E
P
Fig. 1887.
K
L
Fig. 1888. is a machine on the same principle invented
by Mr. Becket. BC is a fall 10 feet high, C is a well
receiving water from the cistern B, which is supplied
by a spring; H, I, K are three floors supporting the
machine; L M N is a timber frame; O is an axle 3
feet long, turning on gudgeons, and common to three wheels. The first, P, is 2 feet in
diameter and 5 inches thick, and has a groove in its circumference; the second, Q, is 6 feet
in diameter, with rebates in its circumference, forming a channel 14 inches wide, of a spiral
form, its greatest enlargement in a single revolution being 2 inches; the third, R, is 3 feet
10 inches in diameter; its circumference has also a circular rebate, enlargement at one
revolution being of an inch. To the wheel P a flat and flexible chain is attached, which,
after envoloping the circumference, is divided into two others P, S; to this chain is fixed an
iron rod carrying the greater bucket A; the wheel Q has a similar flat chain, so that when it
makes one revolution from left to right, its circumference winds up the chain from T to
CHAP. XVII.
1207
MACHINES FOR RAISING WATER.
ΜΕ
P
S
N
T'; the lower part of the chain, from T2 to T³, is crossed by small bars, which engage in
the rebates of the wheel Q, by which means this part of the chain is prevented from
touching that which envelopes the circumference, and an equilibrium is produced between the
chain and the rod SS, by the compensation of the arm of the levers produced by the spirals.
On the wheel R is a cord, whose other end surrounds
the wheel V, 2 feet in diameter; the axle of this
wheel is common to another W, 1 foot in diameter,
on whose circumference is a cord passing over a
pulley, and suspending a weight in a box X at the
extremity of the radius of the quarter circle Y, in
whose circumference are pulleys which receive the
cord from the wheel W; Z is a weight to counter-
balance that of the chains, and preserve a perfect
equilibrium. On the axle O is a cogged wheel
driving a fly to maintain uniformity of motion:
at the extremity of the chain is a copper bucket
F with a clasp valve in its bottom; the rod S
carries the bucket A, which contains three times
as much as the preceding; it has likewise a valve in
its bottom, opening by means of a catch, which
meets a pin in the cistern C; the buckets have
copper rollers at their sides which work on the
guides i, i; when the lesser bucket descends it meets
the pin A, which by means of a lever opens a valve
in the cistern B, allowing the water to flow into
the bucket A. When the smaller bucket F is full,
it runs over into the basin G, and thence through
B into the great bucket A, until this is suffi-
ciently full; the lesser bucket begins to ascend, and
ceasing to rest on the pin the valve in B closes,
and the water in the basin G, supplied from the
source, runs by a waste pipe into the bucket A,
continuing to precipitate its descent.
The great

:
same manœuvre.
T
F
H
B
I
A
wheel Q which carries the lesser bucket, being
6 feet in diameter, while P, which carries the greater
bucket, is only 2, and the fall being 10 feet, the
water will be raised 30; when the small bucket
arrives at the floor L it is arrested by a catch ƒ; at
the same time its valve is opened by a pivot at e,
and discharges its contents into a trough or cistern
of supply at the same time the greater bucket
meeting a pivot in the cistern C, which opens its
valve, discharges its water through the channel
D, both being empty and the lesser the heaviest, it
descends and raises the greater, again to perform the
The circumferences P and Q are
formed spirally, so that the weight of the chains
may always be in equilibrio, but this is more
particu arly effected by the quarter circle Y, and its
weight Z, which acts on the wheel Q when the
radius YZX is in an horizontal position, that is,
when the chain T is unrolled; for as this is effected,
the lever YX approaches a vertical position, and
the weight of the chain diminishing the action
of the weight X, diminishes also, until the weight
Z ceases to act on the wheel R, which happens when
the weight contained in X is at the bottom of its
box; thus the cord to which this weight is attached
is kept constantly stretched. When the lesser bucket
begins to descend, the movable weight in X remounts, before any motion is communicated
to the lever Y X; but as the chain T unrolls from the wheel Q. its weight increasing and
that of S diminishing by rolling on the wheel P, the lever Y X approaching a horizontal
position, the weight Z again acts on the wheel R, retarding its velocity and maintaining the
proper equilibrium in order to prevent the bucket F descending too fast. The fly-wheel
prevents the machine from receiving any shock when the buckets are emptying themselves:
this machine works very slowly, only raising the lesser bucket once in 5 minutes: it was
constructed in Buckinghamshire, to supply the house and gardens of Sir John Chester,
Fig. 1888.
D
C
4 н 4
1208
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
:
Bart. the original machine was put up by Mr. George Gervis, but the modification
described above is due to Mr. Becket.
Among the machines employed for drawing water from deep wells previous to the
general introduction of pumps and hydraulic engines, the following have been selected as
the most efficient, and

frequently of use to the
engineer for temporary
purposes.
Fig. 1889. is an appa-
ratus formerly existing at
Darés, near Dieppe; al-
though the well is exceed-
ingly deep, it drew a quan-
tity of water sufficient
for the consumption of
a large garrison in time
of war. It consists of
an upright axle, with a
pinion at its summit,
round which a rope was
passed twice, to which the
buckets were attached;
there were six levers to
the axle, each 71 feet long,
and as the radius of the
pinion was 14 inches, the
power was only one-sixth
of the weight; therefore
Fig. 1889,
A
MACHINE FOR DEEP WELLS.
13
six men applying their power to the six levers, assuming each to exert a force of 25 lbs.,
would raise 13 cube feet of water at once.
L
The weight A of
The cylinder B, 1
F
K
H
The machine represented in fig. 1890. was invented by M. Morel.
800 lbs. may be raised by means of the fixed pulley I which sustains it.
foot in diameter, has two toothed wheels C, I,
each 24 inches in diameter, the first of which
engages the lantern D, also of 24 inches, and the
axle of this lantern traverses another 3 feet in
diameter, which carries the chain of buckets.
The weight is raised by the winch F of 1 foot
radius, accompanied by a fly-wheel G and a
lantern H, 3 inches in diameter, which engages
the wheel I. As there are four lever arms
between the power and the weight, viz. the arm
of the winch 12 inches, the radius of the lantern
H 1 inch; that of the wheel I 12, and that of
the cylinder B 6, the weight will be to the power
as 16 to 1; consequently the action of the weight
being reduced to 400 lbs. the power will only
be 25 lbs., which is the force of a man applied
to the winch. While the power turns the winch
F and cylinder B, the chain of buckets remains
immovable, because the wheel C, which has a
spring or catch, is separated from the cylinder;
there being four levers between the weight and
the power of the respective lengths before men-
tioned, the weight is to the water in the buckets
as 4 to 1; thus the buckets in mounting will raise
100 lbs. of water, or rather less.
The net pro-

Fig. 1890.
A
B
MOREL'S MACHINE.
duct will depend on the height the water is to
be raised, the wheel C and lantern D being of the same diameter, the velocity of the
cylinder B will be to that of F, as the radius of the first is to that of the second, or as
1 to 3; consequently, when the cord has unrolled 1 foot, the chain of buckets will have gone
over 3: to maintain uniformity of motion, the wheel C engages the lantern K, on whose
axle is a small fly-wheel L.
Fig. 1891. is the plan of the cistern of distribution formerly existing at the fountain of St.
Catherine at Paris. The upright pipe A brought the water from the pumps of Notre Dame
to the circular cistern B C, in the middle of which is a rim D to calm the motion of the water,
which flowing through the gauges with which the circumference of the basin is pierced, runs
CHAP. XVII.
1209
MACHINES FOR RAISING WATER.
into the cistern EF, where its motion is further calmed by another rim G; from thence it
is distributed by gauges of different sizes into all the basins comprised between EF and
H1, having each a pipe at the bottom to conduct the water to its destination: each of

H
O
O
이
​о
O
O
O
B
G
A
D
Fig. 1891.
0
о
H
Fig. 1893.
T)
D
B
C
G
G
E
F
I
H
E
Fig. 1894.


C
D
B
Fig. 1892.
FOUNTAIN OF ST. CATHerine's.
Fig. 1895.
these descending pipes is closed by a valve A (Fg. 1893.), attached to a rod, whose extremity
terminates in a screw working in a nut C; the valve is raised and lowered by means of a
key E; to prevent extraneous matters from entering, each valve has a cover of metal
pierced with holes, and opening on a hinge.
Experiments have been made on the effects of flexures or bendings in the pipes which
conduct from the reservoirs of water-works: the pipes were perforated with small holes,
to allow the escape of the air, and at each end a tube, 2 inches in diameter, was soldered
on, which united with the reservoirs and it would seem that a curvilinear pipe, in which
the bendings lie horizontally, discharges less water than a rectilinear pipe of the same
length, and that a still greater diminution takes place when the flexures are placed in a
vertical plane. When there is a number of contrary flexures in a large pipe, the air some-
1210
Book II.
THEORY AND PRACTICE OF ENGINEERING.
times lodges in the upper portions, and stops the water's motion; air-holes and stop-cocks
may be used to prevent this, which can be shut when the water is in its proper condition




1896.
4P
1897.
1898.
The forms of cocks usually employed in water-
pipes are represented in the several figures, with three
branches at right angles to each other; the tube is
pierced in such a manner as to shut off or supply the
branches, together or alternately; the cocks must
always be proportioned to the size of their pipes, and
when too large to be turned by hand must be worked
by an iron key and lever.
1899.

Fig. 1900.
1901.
CHAP. XVIII.
SUPPLY OF TOWNS WITH WATER.
We have already described the methods practised by the Romans for the supply of their
towns with water, and also the attention paid to the subject at a very early period in our own
capital; but that much yet remains to be done to ensure cleanliness, and consequently
health, has been recently proved in the excellent report made "upon the State of Towns
and Populous Districts," by Her Majesty's Commissioners: with improved machinery
and the aid of the steam-engine, which enables us to raise water with perfect ease and at a
small cost to almost any height, we may hope ere long to see the object of the Com-
missioners fully carried out, in obtaining a plentiful supply of wholesome water for every
dwelling throughout the empire. The engineering works for such a purpose would be
neither difficult of execution, nor intricate in their arrangement.
The quantity of water given out by a pipe under pressure, when the aperture and head of
water are contiguous, is easily calculated; but when the water is to be delivered at a dis-
tance, the amount of friction and resistance of the fluid in its passage must be taken into
account: practical experience has established many rules to guide us on this subject, which
have been generally applied by most of the engineers of our water companies: when a town is
so situated that water can be brought from a higher source than where it is required to
be delivered, there is no difficulty whatever in regulating its descent; a reservoir must be con-
structed of sufficient dimensions to contain the ordinary supply, from which the mains are
laid, with their branch pipes to the houses or other situations where the water is to be
received.
The mains may be kept constantly full by the aid of a cock at the point of delivery:
where the water is to be shut off from one part of the town whilst it is running to another,
each house must have a separate cistern with a ball-cock, which shuts off the water when it
arrives at a certain height, and prevents any waste. To raise the water from a low level to
a higher, some additional works are requisite: a steam-engine is employed to throw it
to a reservoir upon some high ground, from whence sufficient pressure may be gained to
deliver the water to its destination; and when it is to be sent to any point above the level
of the highest reservoir, a simple and ingenious contrivance has been made use of, previously
to the introduction of which it was found that when the aperture leading to the reservoir
was closed, and the engine continued to force the water forward, the excess of pressure
burst the pipes. It consists of two upright standing pipes united at the top, and forming a
siphon, above which is another upright pipe open at the top, standing up twenty or thirty
feet above the reservoir: as this apparatus is connected with the upper supply, as soon as
the pressure exercised is greater than that arising from the head, the water will flow out of
the top of the pipe into the reservoir below, thus forming a safety-valve.
CHAP. XVIII.
1211
SUPPLY OF TOWNS WITH WATER.
Where the establishment is small, the forcing-pumps which raise the water are worked
either by horses, a water-wheel or steam-engine; but in large works the latter is usually
preferred.
It has been before observed that when pipes were first laid down they were bored out of
timber, and the taper end of one was inserted within the other, which method did not per-
mit of pressure being exercised. The introduction of cast-iron pipes, united by flanches at
each end, screwed tightly together, with lead and other stuffing, has enabled mains to be
formed perfectly water-tight: when inserted one within the other, or simply screwed toge-
ther, a variation in the temperature will in a length of 300 feet produce in winter a con-
traction sufficient to tear them asunder, some play being absolutely required at the joint.
The materials for closing the joints of the mains and pipes is now generally the best
Dantzic fir, cut into shocks of 9 inches in length; these are worked with an axe, or split into
pieces 2 inches wide, and 3 of an inch thick, worked into the proper shape by spoke-shaves,
so as to suit the curvature of the socket, as well as the convexity of the pipe to be inserted
within it a piece of fir, 9 inches in length, worked and cut into two, forms a pair of
wedges.
The joints are thus made: the wedges are first placed close to each other in the socket,
and by means of a set applied to the end of each they are driven tight, and cut off close:
should any escape of water take place, a wooden spile is driven in to stop the leak.
Another, though more costly method is that of introducing first some gasket, and driving
it tight, to prevent the melted lead from passing; then by means of a clay mould running it
with lead, and afterwards setting up the joints. Pipes of various bores with wood joints
are found to resist any pressure to which they are ordinarily subjected, and less likely to
require reparation.
Mr. Robert Thom stated to the Commissioners of Inquiry in 1843 that his plan for
supplying towns with water was first to obtain some natural basin, at a sufficient height,
either in itself containing a large quantity of water, or into which a great extent of sur-
rounding surface can be drained. This reservoir should be formed deep enough to main-
tain the water at a low temperature, and prevent the breeding of insects and the growth of
vegetables, and capacious enough to hold at least four months' supply: if it be not possible
to obtain a sufficient extent of drainage surface at one place, other basins must be sought
for to form auxiliary reservoirs, and the waters conducted into the main reservoir by
aqueducts furnished with sluices of a peculiarly simple contrivance. To facilitate the
collection of the water from the surfaces, catch-water drains must be made use of, and
advantage taken of any stream which may be accessible: from the main reservoir the
water is to be led by an aqueduct to some place near the town, where reservoirs can be
formed at such a height that from them it will rise considerably above the highest houses.
These two reservoirs or regulating basins are each to contain two days' supply, and from
them the water is carried into two or more self-cleaning filters, and from the filters into two
distributing basins; the regulating basins, filters, and distributing basins, being in juxta-
position, and so arranged that one of each may be connected together, to form a set of
apparatus, two of which are required, that the one may be in use, while the other is cleansing
or repairing. From the distributing basins, the water is carried through the streets by
supply pipes of iron, so placed that it shall always flow in one direction, entering at the
higher and wider end, and flowing to the lower: they are always kept full at high pressure,
so that there may be a supply for every emergency.
Self-cleaning Filters.-That constructed by Mr. Thom at Paisley, with the pure water
basins attached, is thus arranged: the stone pipe H brings the water from the regulating
basin to the filters, and iron pipes, p, communicate between the stone pipe or aqueduct and
the top and bottom of the filters.
A valve near the top of the iron pipe SP, at S, forces the water to enter on the top or
at the bottom of the filter at pleasure. The filter is 100 feet in length, and 60 feet in
breadth, divided into three compartments, which may either act together or separately, so
that when one compartment is being cleansed, the other two continue in operation. The site
of the filters is a piece of level ground, excavated to the depth of 6 or 8 feet, with retaining
walls all round, joined with cement, and puddled behind, so as to become water-tight.
The bottom is laid about a foot deep with strong stiff puddle, over which is a pavement
so cemented as to be impervious to water. The whole of this bottom is then divided
into drains or spaces, I foot wide, and 5 inches deep, by means of fire-brick laid on edge,
and covered with flat tiles, of the same material, perforated with small holes, like those
used in a kiln for drying oats. These holes are placed very near each other, and are
rather more than of an inch in diameter; there is also a space of of an inch left open
btween the ends of the bricks, which support the perforated tiles, and their upper edges
are little more than 1 inch broad, in order that there may be no space without holes, and
nothing to prevent the water spreading equally over every part of the bottom of these
drains. This is particularly necessary when the filters are being cleaned by the upward
motion of the water. The perforated tiles or plates are covered to the depth of 1 inch
1212
Book II.
THEORY AND PRACTICE OF ENGINEERING.
with clean gravel, about of an inch in diameter; this is followed by five other layers of
gravel, each of the same depth, and each succeeding layer a little finer than the previous
one, the last being coarse sand: over this is placed 2 feet depth of clean, sharp, fine sand,
similar to that used in hour-glasses, but a very little coarser; about
6 or 8 inches deep of the fine sand nearest the top is mixed with animal
charcoal, ground to the size of coarse meal, each particle about of an
inch in diameter. A longitudinal drain or pipe, N, runs between the
filter and the pure water basin, communicating with both; on each of

N
S
Fig. 1902.
FILTER AT PAISLEY.
the openings between the pipe and the filter is a stop-cock to close the communication
when necessary; there are also two drains, to carry off the foul water when the filters
are being cleaned, and another to prevent the water from rising too high: when the filter
is complete, its action is as follows: the sluice R and the valve S are opened, and the
water permitted to flow through the filter into the drain N below, until it becomes quite
clear. This will take two

or three days when first set
to work, unless very great
pains are taken to wash
the gravel and sand be-
fore they are put into the
filter, which will now flow
copiously for some weeks,
and when the quantity
passing begins to de-
crease, the stop-cocks are
shut, and the valves S
raised. The water then
enters below, filling all the
Fig. 1903.
S
Q
HI
FILTER AT PAISLEY.
drains, and having a head pressure of several feet it will force its way up through the
sand to the top, and in its passage raise the scales or particles of mud which have been

L
Fig. 1904.
FILTER AT PAISLEY: SECTION of SIDE.
deposited in the downward passage, and carry them into the foul water drain below. If the
sand of the surface be stirred by a fine-toothed rake, after the water has been raised above it
and a little additional water admitted on the top, through the conduit, it will facilitate the
operation of cleaning, as the mud is always deposited on the very surface of the sand.
CHAP XVIII.
1213
SUPPLY OF TOWNS WITH WATER.
By this means the sediment will be carried off, and the water pass through quite clear
again in a few hours: the valves, S, should then be lowered, the stop-cocks opened,
and the operation of filtering will again proceed as above described. The cost of this
filter was 600 pounds, and the quantity of pure water produced regularly every 24 hours
is on an average 106,632 cubic feet.
We have already described other methods which have been adopted by the several water
companies for the purification of water, to which we must refer.
Cost of raising Water, as given to the Commissioners of Inquiry into the State of Large
Towns by Thomas Wicksteed, the engineer to the East London Waterworks.
1st. A single pumping engine, made by Boulton and Watt in 1809, working 10 hours
per day, 6 days per week, mean power 29 horses: quantity of water raised per day equal to
612,360 gallons 100 feet high: the cost of coal 12 shillings per ton; in the estimate, all
charges, working the engine, coals, labour, and stores, are included, but none for interest
upon outlay, or repairs of machinery and buildings.
Cost of raising 1000 gallons 100 feet high
Or 22,099 gallons 100 feet high
This estimate is upon an average of two years' working.
8.
d.
0
0.543
1
0
2nd. Two single pumping engines, by Boulton and Watt in 1809, working 24 hours
per day, 7 days per week, mean power of each engine 301 horses; quantity of water
raised per day, 2,922,480 gallons 90 feet high; the cost of coals 12s. per ton. Labour,
horses, &c., taken as before. The estimate upon an average of 10 years' working.
Cost of raising 1000 gallons 100 feet high
Or of raising 33,519 gallons 100 feet high
s. d.
0 0.358
1
0
3rd. Two single pumping engines, made by Boulton and Watt, one in the year 1816,
and the other in 1828, working 12 hours per day, 7 days per week, mean power of each
engine 76 horses, quantity of water raised per day 3,601,116 gallons 100 feet high; cost
of coals 12s. per ton. Labour, horses, &c. as before. The estimate upon an average of 10
years' working.
Cost of raising 1000 gallons 100 feet high
Or of raising 36,036 gallons 100 feet high
S.
d.
0
0.333
1 0
4th. One single pumping engine made by Harvey and Co., upon the expansive principle,
in the year 1837, working 24 hours per day, and 7 days per week, mean power 951 horses;
quantity of water raised per day 4,107,816 gallons 110 feet high; cost of coals, 12s. per
ton; labour and stores as before; the estimate upon an average of four years' working.
Cost of raising 1000 gallons 100 feet high
Or, of raising 80,000 gallons 100 feet high
S. d.
0
1
0·150
0
The foregoing statements show a great variation in the cost of raising water with
different engines. The comparison, however, is favourable to those on the old plan, and of
the best make. The following table expresses the variation more clearly
To raise 160,000,000 gallons of water 100 feet high, it would cost,
according to the first statement,
second ditto
third ditto
fourth ditto
£.
362
238
222
100
A very great economy in the power employed in pumping water might be effected by
the use of the expansive engine and plunger pump, the advantages of which have been
acknowledged in the mines of Cornwall for more than thirty years: this principle, Mr. T.
Wicksteed observes, was first introduced into waterworks in the year 1837, when an engine
was set up at the East London Waterworks, and is now working most satisfactorily,
having from the time of its first starting continued to raise 225 barrels of water, with the
same quantity of coals required by the best engine on the works, made upon the old con-
struction, to raise 100 barrels; since that time another large engine of the same description
has been erected at the Southwark waterworks, which acts in an equally satisfactory manner.
There is also another advantage derived from the introduction of this new engine,
namely, that the same quantity of water may be raised from 24 to 5 times the height, by
the consumption of a given quantity of coals; and as the size of the pipes depends upon
the velocity of the water passing through them, and that velocity increases as the square
root of the head of water, so by increasing that four times, the dimensions of the pipes
may be reduced to one-half; the chief item in the expenditure in new works may conse-
quently be reduced one-half, and less capital be required
1214
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

Sluice Cocks, for letting off the water of a reservoir into
the mains, are of various kinds; the most ingenious are
those by which the valve can be opened and shut at
fl
.6.0….
AFELKLIEGEÆLIILLITHI: MILITAR
Fig. 1905.
SLUICE COCKS.
pleasure by means of levers.
The valve which covers the
mouth of the discharging
pipe has two arms secured
to an iron axle, at the ex-
tremities of which are two
levers; the chain fastened
to one passes under, and the
other over, a pulley, so that
by turning a windlass either
chain can be worked for the
purpose of opening or shut-
ting the valve.
The Screw is applied to
the same purpose, that of
shutting off the flow of water
in the mains.
Laying down the Mains.
The general rule according
to Mr. T. Wicksteed to be
followed, is "to take care that
the distances between the
mains shall not be too great,
for if it be so it will be neces-
sary to have services of larger
diameter than would other-
wise be required: to prevent
loss in pressure occasioned
by friction, the communi-
cations between the mains
and services must be kept
open for a longer time, to
give a supply to those houses
at the extremity of the ser-
vice; for when water is forced
through pipes, either by a
natural or artificial head, or
by steam or other power,
friction is created in pro-
portion to the velocity of
www.m
1907
廿
​Fig. 1906.
Fig. 1909.
SCREW COCK
1908
CHAP. XVIII.
1215
SUPPLY OF TOWNS WITH WATER.
the water and length of the line of pipes: as the distance increases, the power must either be
increased or the velocity reduced; the shorter the distance, the less the power required to
overcome the friction; if it be therefore necessary to exert a great power to force the water
to the extremities of an extensive district, that they may be properly supplied, it is very
evident that the power exerted near the source, not being required to overcome so great an
amount of friction as at the extremities, will increase the velocity of the water through the
orifices near the source; consequently, therefore, if some arrangement were not made to pre-
vent it, the houses so situated would have a superabundant supply, whilst those at a distance
would obtain a very small quantity, if any: when, however, those near the source have re-
ceived their supply, the cocks on the services are shut down, and the water in the mains
will pass on to supply the extremities: that each may have an equal supply, those near the
source have the communication opened with the main for a shorter time than those at a
distance, in proportion to the velocity with which the water is delivered. In addition to
this, on every line of mains and services, orifices about 2 inches in diameter are made at
certain distances, filled up with fire-plugs, which get the whole force of the water simply
by closing the service-cocks, in such a manner that in case of fire or other accident it may
be concentrated at the spot required.
Supposing, then, water to be required for 20,000 houses, and the height to which it must
be raised at the works is such that a 20-inch main would be sufficient to give the supply
according to the foregoing system; it could not be so, if the water were constantly on in
all the pipes, both mains and services; for if the size of the lead pipes to supply the houses
be upon an average ↓ inch in diameter, the aggregate areas of 20,000 half-inch pipes would
be equal to 27 square feet, and a main of 71 inches in diameter would be required at the
source to supply the town instead of 20 inches, and for side streets, containing 100 houses
each, pipes of 5 inches in diameter, instead of 3 or 4 inches: this is an extreme case, but
one that it may be necessary to provide against, because if the water is always on, the houses
may be all supplied at one time, and even, trusting to the chances of only one-half that
number, the main must be 48 inches in diameter at the source. In addition to the
necessity for this extraordinary outlay, in the first instance, the quantity of water used
would be enormous; and consequently, the expense of raising a sufficient supply be in-
creased in proportion, and the object souglit, that of having a strong pressure of water in the
mains, would be defeated by the very means proposed to insure it; for, as the water in the
pipes would be always on, so would the draught by the houses be constant, and the present
power of shutting off the supply from the side streets, and applying the full force to the
particular locality requiring it, would be destroyed: again, if separate mains were laid from
the works to be used as fire-mains only, the expense would be nearly the same as that of
the system of pipes for supplying the inhabitants, and this item, which is the most impor-
tant portion of the outlay in waterworks, would be nearly doubled.
=
Q³1
140d5
He
in
Mr. T. Hawkesley, in his evidence, taken before the Commissioners, states, that if the
water for the supply of the metropolis were taken from the Thames, in its full purity,
above Windsor, and filters or subsiding beds erected there, the transmission of 500 gallons
of water per second might be effected by two mains, each of 60 inches in diameter.
calculates the resistance from friction from this formula for long pipes, P
which P represents the horse-power necessary to overcome the friction, 7 the length of the
pipe in inches, Q the quantity of water to be delivered in one second, and d the diameter
of the pipe. Hence it appears that the resistance arising from friction in pipes of the
given size, and 25 miles long, would require less than 450 horse-power, beyond the force
employed to raise the water into an elevated reservoir: if this reservoir were situated at a
height of 220 feet, the steam power required to raise the water would be about 2000
nominal horses, and the total power in transmitting and raising 500 gallons per second
would amount to less than 2500 horses. The cost of the main pipes would be about
1,000,000%. sterling; of the engines and machinery, with some reserve of power, about
150,000l., and of the tanks and reservoirs probably 200,000%.
Height that a jet of water rose from the mains and services belonging to the Southwark
Water Company, under a fixed pressure of 120 feet. The first trial was made in Union
Street, between High Street and Gravel Lane, Borough, 31st January 1844, over an
extent of 800 yards of 7-inch main, and through the Fire Brigade stand-pipes, hose, and
jets.
This 7-inch main is connected to the 9-inch main in the High Street, Borough,
which, after a run of 500 yards, is joined to 200 yards of 12-inch main, and then continued
by 550 yards of 15-inch main to the great main, leading from the company's works at
Battersea, making a total distance of 5500 yards from the place where the experiment was
made.
One 2 inch stand-pipe, with 40 feet of hose, and 7 inch jet, rose 50 feet.
Two 2
Three 2
40
40
01478
45
40
'216
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Four 21 inch stand-pipe, with 40 feet of hose, and 7 inch jet, rose 35 feet.
Five 2
40
Six 21
40
7878780
30
27
All the fire-plugs on the main were then closed, except the first, and one 24-inch stand-
pipe with 160 feet of hose and 7-inch jet, rose 40 feet. The quantity of water delivered
from the same main, through one stand-pipe, and different lengths of hose, was as follows,
viz:-
One 21 inch pipe, 40 feet of hose, 7 inch jet, delivered 96 gallons in 59 seconds.
21/
2/1/
21/0
80
160
40
21
112
116
118
65
70
27
The second trial in Tooley Street, of a 9-inch main, 1400 yards in length, connected to
1000 yards of 15-inch, and 6650 yards from the works.
One 21 inch-stand pipe, 40 feet of hose, 7 inch jet, rose 60 feet.
Two 21/2
Four 2
Six 211
40
40
40
Quantity delivered from the same main trough.
77BTBIK
difference not perceptible.
rose
45 feet.
40
One 2 inch stand-pipe, 40 feet of hose, 7 inch jet, 114 gallons in 64 seconds.
Four 21
40
40
7
115
112
75
78
Six 2
Four-inch service in Tooley Street, 200 yards long, supplied through 200 yards of 5-Inch
pipe, from 9-inch main, one 24-inch stand-pipe fixed on the 4-inch service, near the 5-inch
pipe, with 40 feet of hose, 7-inch jet, rose 40 feet. Two 21-inch stand-pipes, 7-inch jets, rose
31 feet.
One 2½-inch stand-pipe fixed at the end of service, 200 yards from 5-inch pipe, 40 feet of
hose, 7-inch jet, rose 34 feet.
Quantity delivered from the plug near the 5-inch main, through
One 21 inch stand-pipe, 40 feet of hose, 7 inch jet, 112 gallons in 82 seconds.
Two 2
40
117
Quantity from end of plug of service 200 yards, from the 5-inch main.
103
One 2 inch stand-pipe, 40 feet of hose, 7 inch jet, 112 gallons in 90 seconds.
40
118
114
Two 2/1/2
It is also stated that water will rise higher from a hose attached to a fire-plug in the
street, at the extreme point of the delivery, in the night than in the day-time, and that
when water is in motion, there will be friction in the main pipes, by which the height to
which it rises is diminished. The higher the water is thrown on a pipe, or the higher the
nozzle of a hose-pipe is carried, the more the resistance of the atmosphere is avoided: if a jet
acting under a pressure of 100 feet attained an elevation of 50 feet when discharged from
the level of the pavement, and the hose pipe were elevated to the height of 50 feet, a jet
would be given probably from 20 to 25 feet in height: by this means, the water would
attain an elevation of 70 or 75 feet, instead of 50; hence the advantage of carrying a hose-
pipe up stairs or on a ladder, or as nearly as possible to the height of the story, when a
fire occurs.
CHAP. XIX.
ATMOSPHERE AS A MOVING POWER.
In the year 1667 Dr. Croune laid before the Royal Society the first instrument contrived
for measuring the force of the wind; consisting of a fan included within a cylindrical
vessel, which was divided into 32 equal parts, each having a narrow slit, through which the
air might pass: this imperfect machine was afterwards improved by Dr. Hooke, and others,
and several very ingenious anemometers are now made use of, by which both the force
and velocity of the wind may be ascertained. The weight or pressure of the atmosphere
is shown by the sucking pump, sustaining a column of water, or the barometer by a
column of mercury which is exactly equal in weight to a cylinder of air of equal diameter,
reaching to the top of the atmosphere. The mean height of the barometer at the level of
the sea is about 28.6 inches, and 1 cubic inch of mercury weighs 3425-92 grains, or 0.48956
pounds avoirdupois; so that a column of mercury whose base is a square inch, and having
the mean height of the barometer, weighs 0.48956 × 28.6=14.6 lbs. avoirdupois, which is
CHAP. XIX.
1217
ATMOSPHERE AS A MOVING POWER.
the weight of the atmosphere on every square inch of the earth's surface. The height of
the atmosphere has been estimated at 328,021 inches, or 5-17 miles.
The elasticity of the air having been ascertained by the experiments of Boyle, it was not
difficult to construct the air-pump, though the one used by this celebrated philosopher was
inconvenient for many purposes, in consequence of the neces-
sity of alternately opening and shutting the stop-cock and
valve, and the difficulty of making the piston descend when
the air within the pump was greatly rarefied.
Hawksbee and Smeaton both turned their attention to its
improvement: the latter found considerable difficulty in
opening the valves at the bottom of the barrels, and from
the pistons not fitting exactly when put close down to the
bottom, leaving a lodgment of air that could not be pumped
out of the barrel. The first of these defects arose from the
small orifice through which the air passed on raising the
bladder, which opposed a considerable resistance, from the
necessity of keeping it moist with oil. To remedy this Mr.
Smeaton resolved to expose a greater surface to the action
of the air; with this view, instead of one hole he used seven,
all of equal size and shape, one being in the centre, and the
other six round it, so that the valve was supported at proper
distances by a kind of grating formed by the solid parts
between these holes, which were hexagonal,
and the partitions filed almost to an edge;
the metal was made a little protuberant,
to prevent the piston from striking against
the bladder. To prevent any lodgment
of air in the lower part of the barrel, he
removed the external pressure from the
piston-valve, by making the piston move
through a collar of leather, and forced the
air out by a valve applied to the plate at
the top of the barrel, which opened out-
wards.
Cuthbertson, of Amsterdam, consider-
ably improved Smeaton's air-pump, by
allowing the air to escape by opening a
passage to it mechanically, without the
assistance of its elastic force.


Fig. 1910.
The construction of the air-pump is very simple,
the essential part consisting in the exhausting syringe,
a brass tube closed at one end, with the exception
of a small orifice, to which a valve opening inwards
is attached; an air-tight piston is worked up and
down on the barrel by a rack and pinion turned
by a a winch. The
piston has also an
orifice, with a valve,
which opens upwards,
or in the same di-
rection as the valve
of the tube. The
syringe communicates
by means of a small
pipe fitted into the
opening at its lower
extremity, with a
vessel called the re-
ceiver, from which the
air is to be pumped
out. The two
hausting barrels are
worked by a rack and
pinion, so that one
piston ascends while
the other descends, and
attached to the pump
ex-
Fig. 1912.
HAWKSBEE's air-pump.
Fig. 1911.

ARANANANANARI

SMEATON'S AIR-PUMP.
Fig. 1913,
4 I
1218
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
is a barometrical gauge or tube 6 or 8 inches in length, sealed at one end and filled with
mercury; as soon as the tension of the contained air becomes less than sufficient to support
the column of mercury, the liquid begins to fall, and the height at which it stands above
the level of that, on the basin into which it is plunged, is the measure of the tension of the
remaining air.
On the subject of the winds much has been written, but the various theories are involved in
considerable obscurity; its velocity varies from zero up to 100 miles an hour.
Post Windmills are much in use in many parts of England for grinding corn or cement,
but their size being limited, they are not generally applied to drive machinery for other
purposes. The mill is usu-

ally made on a rectangular
plan, and the narrow side
turned to the wind. The
wind-shaft bearing on a
beam at each end has a little
inclination, and on the out-
side is increased in di-
mension, forming a square
for the better mortising the
whips or arms of the sails,
which are wedged tightly
into it. The inclined wheel
attached to the wind-shaft
has on its circumference a
rim of wood, called the
brake, one end of which is
fixed to the side of the mill,
and the other, by an iron rod,
to a lever, which can be
pressed down, and made to
bind upon the circumference
of the wheel, with sufficient
power to stop the mill.
The whole mill revolves
round the upright post in
the centre, which is framed
at bottom into some long
horizontal timbers secured to
the ground, from which four
oblique braces are strutted,
to maintain it in its vertical
position. Where this up-
Fig. 1914.
POST MILL.
right post passes, the floor of the mill is a circular iron collar, and at the upper end of the
post is a pivot or gudgeon, entering a socket, let into one of the timbers, made of con-
siderable strength, as the entire weight of the mill rests upon it. The mill thus balanced
is turned by the ladder which serves as a lever; after the right position is obtained, it is
kept steady by dropping the ladder on the ground; this is readily performed by a rope and
pulley, or by manual labour.
The Tower or Smock Mill was formerly more common, but since the general introduction
of the steam-engine it has gone out of use in
has gone out of use in many districts. The body of the mill is
constructed either in brick or stone, and sometimes of timber; at the top of the building a
wooden curb is laid, or strong wall plate, on which the rollers of the cap revolve, and it is
essentially necessary that this portion of the work should be rendered very secure, or the
rattle and motion of the machinery will loosen and derange it, or cause great inconvenience.
In the outer end of the wind-shaft, which is commonly made of iron, are cast two sockets
for the insertion of the whips of the sails, which are tightened in their place by wooden
wedges. The pillows which bear the wind-shaft are of brass, and sometimes of hard stone.
The driving or brake wheel is bevelled, and furnished with two rows of teeth, which act
alternately upon those on the bevelled crown wheel, on the top of the upright shaft, and by
this arrangement a more regular motion is obtained: these hit and miss wheels, common
in many parts of England, are admirably adapted to windmills.
The brake wheel has a wooden rim, one end of which is attached to the framing of the
mill and the other to a lever: a rope passing over a pulley to the outside of the mill
enables the miller to raise the end of the lever, and engage it with a hook, which liberates
the brake, and allows the head of the mill to move freely round: when it is required to
stop the mill by pulling the rope, the end of the lever is disengaged from the hook, which
falling on the brake brings it down upon the wheel, and stops all motion even during the
CHAP. XIX.
1219
ATMOSPHERE AS A MOVING POWER.
highest winds.

The plan of the
head is extremely simple, and re-
quires to be merely balanced.
The self-adjusting Cap is turned
round by the force of the wind,
which acts upon a flyer or fan, so
contrived that it always presents
the sails in the proper direction,
by means of a smaller pair at-
tached to a gallery projecting from
the back of the cap; on the axle of
this fan is a pinion engaging in
another wheel attached to the in-
clined axis, at the other end of which
is fixed a bevelled pinion working
a wheel on the vertical spindle
of another pinion, which is en-
gaged in the cogs, arranged round
the outside of the fixed curb, so
that when the flyers are turned, the
head of the mill is slowly turned
round, the power depending upon
the ratio of the several radii.
Care
Fig. 1915.
SELF-ADJUSTING CAP.
must be taken that its action be sufficient to make a change when sudden gales arise, as

Fig. 1916.
SELF-ADJUSTING CAP.
it has frequently occurred, where these self-acting caps have been introduced, that if the
brake had not been made use of in time to turn the sails rapidly, the mill would have fired.
The sails of wind-

mills are of various
kinds, and the fixing
them requires great
skill on the part of
the millwright. When
the shafts are of cast-
iron, they have at
their extremities two
sockets to receive the
arms, also of the same
metal; these, after
being inserted, are
further secured by
two pieces of timber,
Fig. 1917.
PLAN OF SELF-ADJUSTING CAP.
41 ?
1220
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

I
which cross and continue up the back of each arm, to which they are
firmly screwed; by these timber horns, as they are called, the whole
is very much strengthened.
The whips are generally placed at right angles to each other, and
when 40 feet in length their scantling is about 10 inches by 8, or 10
inches square: at of the length of the arm from the centre of the wind-
shaft is the first bar, which is inserted to make an angle of 60 degrees
with the axis of the wind-shaft: 20 other bars are then placed at regular
and equal distances to the end, each making 1 degree of the angle less,
so that the last bar at the end has only an angle of 20 degrees ; the
bars are all of the same length, generally 5 feet.
The length of the sails of the Dutch mills is not more than 33 feet,
and their width about 6, 5 feet being covered with cloth, and the other

Fig. 1918.
Fig. 1919.
77
part boarded; where the board and cloth unite, a curve is formed,
which gradually diminishes towards the end, and the angles formed by
the tangents of this curve and the plane of their motion is called the
angle of weather, which at the foot bar is 30 degrees, gradually di-
minishing to 12 degrees.
In 1772 Mr. Andrew Mickle con-
trived a method by which the sails of
a windmill could adjust themselves;
but that patented in 1804 by Mr. John
Bywater, of Nottingham, was the most
efficient; it consisted in rolling or fold-
ing up the sails to the whip, by means

II

மய
IT
Fig. 1921.
Fig. 1920.
BYWATER'S SELF-ADJUSTING WINDMILL.
Fig. 1922.
CHAP. XIX.
1221
ATMOSPHERE AS A MOVING POWER.
of cylinders which extended the whole length of the sails, and were put in motion by a
system of wheelwork connected with the shaft in the following manner :- a ring of iron about
4 inches wide and 3 of an inch thick, was attached to the main shaft, and concentric with it, a
short distance behind the whip: a bevelled wheel without arms is made to revolve easily
upon the circumference of the ring, and a spur-wheel without arms turns upon four pins
in the back of the same. The whole machinery revolves with the shaft, and when the
quantity of canvas spread is too great, a lever fastened to the bracings, and weighed so
as to hang vertically, is brought into a horizontal position by means of a string attached to
the end within the mill; in this position it engages a stud upon the spur-wheel, and pre-
vents its motion: a bevelled wheel then gives motion to the four small pinions, and with
them the cylinders, which continue to wind up the cloth, until the miller from within lets
go the string, and the lever is disengaged from the stud.
On the relative Effects of Windmill Sails, according to Smeaton and Coulomb.
The velocity
of windmill sails, whether unloaded or loaded, producing a maximum effect, is nearly
as the velocity of the wind, their shape and position being similar. The load at the
maximum is somewhat less than as the square of the velocity of the wind, the shape and
position of the sails being the same. The effects of the same sails at a maximum are nearly,
but somewhat less than, as the cubes of the velocity of the wind. The load of the same
sails at the maximum is nearly as the squares, and their effects as the cubes of the numbers
of turns in a given time:
time: when sails are loaded, so as to produce a maximum effect
at a given velocity, and the velocity of the wind increases, the load continuing the same,
the increase of effect, when that of the velocity of the wind is small, will be nearly as the
squares of those velocities: when the velocity of the wind is double, the effects will be
nearly as 10 to 27: when the velocities compared are more than double that where the
given load produces a maximum, the effects increase nearly in the simple ratio of the
velocity of the wind. In sails where the figures and positions are similar, and the velocity
of the wind the same, the number of turns in a given time will be reciprocally as the
radius or length of the sail: the load at a maximum overcome by sails of a similar figure
and position, at a given distance from the centre of motion, will be as the cube of the
radius.
The effects of sails of similar figure and position are as the squares of the radius: the
velocities of the extremities of Dutch sails, as well as of the enlarged sails, in all their usual
positions when unloaded, or even loaded to a maximum, are considerably quicker than the
velocity of the wind.



Number of
Ale Gallons
delivered on
an Overshot
Wheel 10 ft.
in diameter
every minute.
Diameter of | Diameter of
the Cylinders the Cylinder
of the com- of the im-
mon Steam
Engine in
inches.
proved Steam
Engine in
inches.
Number of
Horses em-
ployed 9
working hrs.
per day, and
moving at the
rate of 2 miles
per hour.
Number
of men
working
12 hours
per day.
Radius of
Dutch Sails
in their com-
mon position
in feet.
Radius of
Dutch Sails in!
their best
position in
feet.
Radius of
Mr.Smeaton's
enlarged Sails
in feet.
Height to
which these
different
powers will
raise 1000 lbs.
avoirdupois
in a
minute.

230
8.
6.12
390
9.5
7.8
528
10.5
8.2
660
11.5
8.8
790
12.5
9.35
970
14.0
10.55
1170
15.4
11.75
1234567
5
21.24
17.89
15.65
13
10
30.04
25.30
22.13
26
15
36.80
30.98
27.11
39
20
42.48
35.78
31.30
52
25
47.50
40.00 35.00
65
30
52.03
43.82
38-34
78
35
56.90
47.33
41.41
90
1350
16.8
12.8
8
40
60.09
50.60
44.27
104
1445
17.3
13.6
9
45
63.73
53.66
46.96
117
1584
18.5
14.2
10
50
67.17
56.57 49.50
130
1740
19.4
14.8
11
55
70.46
59.33
51.91
143
1900
20.2
15.2
12
60
73.59
61.97
54.22
156
2100
21.0
16.2
13
65
76.59
64.5
56.43
169
2300
22.0
17.0
14
70
79.49
66.94
58.57
182
2500
23.1
17.8
15
75
82.27
69.28
60.62
195
2686
23.9
18.3
16
80
84.97
71.55 62.61
208
2870
24.7
19.0
17
85
87'07
73.32 64.16
221
3055
25.5
19.6
18
90
90.13
75.90 67.41
234
3240
26.2
20.1
19
95
92.60
77.98
68.23
247
3240
27.0 20.7
20
100
95.00 80.00
70.00
260
3750
28.5 22.2
22
110
99.64 83.90 73.42
286
4000
29.8
23.0
24
120
104.06
87.63 76.68
312
4460
31.1
23.9
26
130
108.32
91.22 79.81
338
4850
32.4
24.7
28
140
112.20
94.66
82.82
364
5250
33.6
25.5
30
150
116.35
97.98
85.73
390
413
1222
THEORY AND PRACTICE OF ENGINEERING. BOOK II.
Comparisons of the Effects of Mechanical Agents. A horse raising coals, by means of a
wheel and axle, moving at the rate of 2 miles per hour, and working 9 hours per day,
raised 1000 pounds avoirdupois to the height of 13 feet per minute: an overshot water-
wheel, 10 feet in diameter, and served by 230 ale gallons of water per minute, a steam-
engine with an 8-inch cylinder, and an improved one 6.12 inches in diameter, will do the
same work as a horse; upon which data the preceding table has been constructed.
Of Blowers and Ventilators. There are several kinds of blowers, differing from each
other principally in the flexibility or inflexibility of their sides: a sack of leather or
other substance, which is flexible and impermeable to the air, being filled with this fluid
and compressed, would experience a pressure from the interior to the exterior, and if a tube
open at both ends were attached to it, the air would be compressed in the tube, and would
rush out with a velocity due to its elastic force.
The regularity of the blast which maintains the combustion of furnaces is of the greatest
importance in the success of metallurgic operations, and to obtain this it is requisite that
the air-reservoir should be of such dimensions that the air which leaves the tube at each
stroke of the blower should be compressed into a very small volume with regard to the
capacity of the reservoir. The blower used at the Carron furnace is built of stone and
vaulted; its internal capacity is 445 cube metres; the air which rushes out at each stroke
of the piston is to the atmospheric pressure only as the 84th part of this capacity.
Whatever be the form of a blowing machine, the first points to be considered are the
pressure of the air in the reservoir, the volume which escapes through the pipe at each
stroke of the piston, and the number of strokes in a given time. The volume of the air
which passes in a unit of time, 1 second for example, from the pipe into the furnace being
determined, and divided by the area of the orifice of the tube, will give the velocity of the
blast at the orifice. The greatest pressure of the air in the reservoir rarely exceeds the
weight of a column of water 3 metres high, and may be measured by a column of
mercury 13 or 14 times less, the 3 metres of water answering to 22 centimetres of mercury:
if we multiply the number of cube metres of air in the reservoir, which escapes through the
tube in a given time, an hour for example, by the height of the column of mercury, and by
the density, 13-6, of this liquid, the product of the three quantities will express in units,
each of one cube metre of water raised 1 metre, the dynamic effect which the blowing machine
would produce in an hour. The moving power applied to the bellows will, at the same
time, be capable of a greater effect, since it will have to overcome the inertia and friction
of the movable parts of the blowing machine: if we measure the pressure of the air in
the reservoir by a column of water, the height of this column, and the volume of air
issuing from the reservoir, will be the two factors of the product which measures the
dynamic effect of the blower. The object of ventilators is to renew the air in a given
place, or rather to produce an artificial wind, by transporting the air from one space to
another. These two spaces communicate by a cylindrical tube, the extremity of which is
fixed in the centre of a drum, formed by two circular parallel plates, and united by supports
in the circumference of these plates. A fly with 6 or 8 vanes turns in the interior of
the drum; the air being driven from this is replaced by that in the cylinder, whence it
follows that it must be elevated from one extremity of the cylinder to the other, which
communicates with the drum: by placing a ventilator in a chest closed on all sides, and
divided into two compartments, the air in the chest receives such a motion that it
continually passes and repasses from one compartment to another; if, in the same chest,
such substances as sulphur, charcoal, and saltpetre are reduced to powder, the air will
carry with it the finer particles, and separate them from those not sufficiently pulverised.
The quantity of air to be raised from one place to another being given, the relation of the
dimensions of the parts composing the ventilator can be established, and the moving power
required estimated, Ventilators are used to renew the air in low close places, such as pits,
mines, cisterns, holds of ships, also in powder-mills to dry the powder in winter by currents
of warm air; it has also been proposed to employ them to assist the evaporation of the
water contained in various preparations made from sugar, as syrup, &c. In the south of
France, a single cube metre of air, placed in contact with water, will evaporate three
grammes: thus knowing the number of cube metres which a ventilator can put in contact
with water in a given time, the quantity vaporised in the same time can be estimated.
In coal-mines a portion of the small coal reduced to powder, and of little value in commerce,
is used to maintain fires in the upper part of vertical shafts, which communicate with
the galleries, where the warm air rises and is replaced by the lower air, which causes
a current in the interior of the galleries, towards the top of the shafts: if in the interior
of the shafts a horizontal axle were placed, carrying a fly, it is evident that the current of
hot air would turn the axle: by a similar method, in some kitchens, the hot air which
rises in the chimney serves as a mover to a smoke-jack.
We have considered air as a mover, and as a body to be moved:
of view in which we must regard it, as a resisting medium.
projected into the air soon loses its initial velocity: the air at rest,
there is another point
We know that a body
struck by a body, first is
CHAP. XX.
1223
WARMING AND LIGHTING.
compressed, and then passes into a more or less compounded state of motion. Birds using
their wings as oars in the water find in the air a fulcrum to raise themselves by; they
owe this faculty of flying to a muscular force which, compared to their mass, is superior
to that of all other animals.
Parachutes in unfolding embrace a large volume of air, compress it, and communicate
motion to it: the initial velocity due to weight decreases rapidly, and a mass of from 80
to 100 kilogrammes fixed to a parachute is soon reduced to that of a light body, such as a
feather, which floats by itself in calm air.
The vanes on the fly of a turnspit experience, when turning in the air, a resistance
which equalises the accelerating force of the moving weight, and by this means we regulate
the motion of the endless chain which supports the spit; this regulator is also used in
block-making. The effects of the air's resistance have been observed with care by phi-
losophers studying gunnery: we shall show the results of their experiments when treating
of gases employed as prime movers.
CHAP. XX.
WARMING AND LIGHTING.
Warming an Apartment. We have already seen that, among the Romans, air was heated
by passing over a small fire, and being then introduced into square earthenware tubes, which
were made to circulate around the walls of their houses; these tubes, after heating the walls,
by their radiating effect, raised the temperature of the rooms, or allowed the air so rarefied
to pass from apertures in the pipes into the apartments, thus diffusing a warmth throughout:
many of their villas discovered in England show the subterraneous furnaces, and we have
no instance of the open fireplace much earlier than in the keep of Coningburgh Castle,
built soon after the Conquest, the mantels of which are formed of flat arches, very inge-
niously built, and bearing some resemblance to others constructed at an earlier period in
the south of France.
:
Radiation, or the properties of heat, does not seem to have been understood, as applied to
furnaces, till the end of the last century, when Count Rumford drew attention to the
subject the open fire was preferred in Britain at a very early period, and has continued
to be so up, to the present day, notwithstanding the waste of fuel and expense attending it.
In the first cabins, and the halls of the Norman barons, the fire was made on a hearth in the
centre of the hut or place to be warmed, the smoke generally finding its way through a
hole in the roof, examples of which were remaining till lately at Penshurst Castle and
other ancient houses.
The blazing hearth, like our open fires, contributed its heat by radiation, and it is well
known that bodies will throw off heat when their temperature is far below that required
for ignition. Scheele, in a work published about 1777, observed that radiant heat passed
through air without communicating warmth to it, and that currents of air do not intercept
it: before heat can be radiated, it must be absorbed, and rough, unmetallic substances,
such as brick, are admirably adapted for this purpose: the heat which passes from an
open fire radiates from the burning coal, as well as from the surfaces surrounding it; this
traverses the air, and warms the bodies upon which it impinges; thus the contents of an
apartment, all the furniture, which can absorb heat, so receive it, and again radiate it upon
other bodies colder than themselves.
Various substances possess different powers of radiation, and those which are good
radiators when hot absorb it quickly when cold: from Mr. Leslie's experiments, taking
lampblack as equal to 100, crown glass is 90, plumbago 75, clean lead 19, and the
polished metals from 12 to 15, proving that polished metals are bad radiators, and not such
good recipients of heat as those surfaces which are not metallic. Sir Humphry Davy
says "that vessels intended to retain their heat should be metallic and highly polished
upon scientific principles, independently of elegance and delicacy. Steam or air-pipes for
warming houses should be polished in those parts where the heat is not required to be
communicated, and covered with some radiating substance, such as lampblack, wherever it
is to be diffused. Culinary implements should be blackened, and not polished, on those
parts which are to receive the heat: the surfaces of fireplaces or stoves should not be
metallic, but of stony or earthy materials, which will communicate much more heat by
radiation. The sun and an open fire both communicate heat upon this principle, and the
worst conductors, as lampblack, ground glass, &c. are often the best radiators.
Heat which radiates in right lines is also susceptible of being reflected: if a cannon
ball made red-hot be placed in the focus of one mirror, and an air thermometer in another,
41 4
1224
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
the rays of heat which impinge on one are reflected, consistently with the property of con-
cave mirrors, in parallel lines, so as to fall upon the opposed mirror, whence they converge
to its focus, in which is the thermometer, and which will be affected proportionably to
the heat of the original radiating body. As an experiment on the receptive and emissive
powers of surfaces, in regard to radiant heat, it has been proved, that when two vessels
filled with water are placed before a fire, the one clean and polished, the other coated with
lampblack, the former receives the heat more slowly, whilst the latter cools more quickly.
In an open fireplace the fuel should be arranged as near the hearth as possible, in order
that the air in the lower part of the room may become warmed; and the proportion given
to the length of the bars which contain the coal should be equal to the twelfth part of the
length of the room, if it be lofty and of good proportions; in their construction Stour-
bridge brick, or Welsh lumps, should be made use of in preference to metal, as they are
far better radiators of heat, and less liable to destruction by too rapid expansion or con-
traction. Whenever coke can be used, the heat produced is far more agreeable, and there is
no soot to lodge in the chimney: soft burnt coke, broken into small pieces, when all the
gases have been abstracted, is far preferable in point of economy, and when the method
of lighting and maintaining its combustion is acquired, coal is seldom again resorted to.
Attention is requisite to prevent too rapid a draught up the chimney, otherwise the greater
portion of heat will be drawn up it, and pass off without warming the room. The
chimney which is said to draw well, consumes well, and is by no means always the best;
that which draws sufficiently only, is the most economical in its consumption: all that
need be desired is to pass off the smoke, or prevent the cold air from descending down the
shaft, and disturbing the process of combustion, forcing the dust and smoke into the
apartment: different states of the atmosphere require different areas of flue; when the
air is very heavy, it often descends in our ordinary chimney more rapidly than it can
become rarefied; and the column of warm air, ascending cylindrically in a square flue, the
four angles are so many passages for the descent of cold airs; the less these disturbing
forces occur, the less chance is there of a smoky chimney.
Grates or Stoves, which have an open fire, and an apparatus for throwing out a stream
of warm air, are much used: this is effected by passing the air received by a pipe from
the outside of the building through a double casing, which surrounds the fuel in the
grate; in many parts of France, where wood is burnt upon the hearth, the back of the
fireplace is hollow, or has a chamber cast in it: by means of a pipe from the outside air
is introduced to be warmed, which by another pipe enters at the skirting, or some other
convenient part of the room.
The great quantity of hot air which passes up the chimney of an open fireplace has led
to the adoption of close stoves in this country, and necessarily to various methods for
insuring perfect ventilation; on the Continent they are universal, generally of earthen-
ware, either round or square, and so placed as to warm the air before it is admitted into
the apartment; in most of them the object seems to be, and a most judicious one, to
produce a large volume moderately heated, rather than a small quantity of very hot air,
the latter being apt to char or burn the organic dust which exists in the atmosphere of
our apartments, producing an unpleasant smell: an artificial hypocaustum is an arrange-
ment preferred in France; the small pillars which stand in the midst of the burning
embers, and support the oven or chamber above, are hollow; through these the cold air
from below ascends, and in its passage through the heated metallic supports becomes
warmed before it enters the chamber, where, on its arrival, it is heated, and then by its
expansion passes off by pipes, or ornamental apertures, where required.
Metallic Stoves, lined with fire-brick, are now generally substituted; they are found to
assist in radiating as well, care being taken so to dispose the lining that the outer case
shall never become red-hot, and only a sufficient quantity of air be admitted to feed com-
bustion, without exciting a rapid draught and a great consumption of fuel. All bodies
have the faculty of absorbing and emitting heat, so that radiation takes place, not only at
the surfaces, but also in the interior of solids and liquids, in the same manner as in air:
indeed the molecules of all bodies are regarded as so many foci radiating heat, and con-
tinuing to do so until the objects near them have arrived at the same degree of tempera-
ture: in solids as well as liquids the absorption takes place at very small distances, in air
and in gases at very considerable distances.
The low Temperature, or Dr. Arnott's Stove, by means of an ingenious contrivance,
economises fuel, and gives out a considerable degree of heat: it is a much more scientific
arrangement than that practised in the ordinary close stove: only sufficient air is admitted
to keep up a slow combustion, and the heat is communicated to the radiating surface of
the stove; the air is admitted by means of a self-acting valve, opened or shut by the rise
and fall of a thermometer, and the heat is prevented from passing into the chimney in con-
sequence of the very gentle motion imparted to it by the small draught maintained.
To determine the quantity of surface of steam-pipes, or vessel necessary to warm a room
in winter when the external temperature is 10° below freezing, and to make the apartment
CHAP. XX.
1225
WARMING AND LIGHTING.
of an agreeable temperature of 60°, there must be a surface of steam-pipe, or other
steam-vessel, heated to 200°, about a foot square for every 6 feet of glass, as much for
every 120 feet of wall, roof, or ceiling, and also for every 6 cubic feet of hot air escaping
per minute, as ventilation: an ordinary sized window permits about 80 cube feet of air
to pass through it in a minute, and there should be 3 feet of air per minute allowed for the
respiration of each person in the room. According to Dr. Arnott's view the quantity of
steam pipe for a room 16 feet square and 12 feet high, with 2 double windows, each 7
feet by 3, and with ventilation by them at the rate of 16 cubic feet per minute, would
require 20 superficial feet, or 20 feet of pipe 4 inches in diameter, or a box 18 inches
square and 2 feet high. A surface when heated, and exposed to colder air, gives out heat
with a rapidity nearly in proportion to the excess of its temperature above that of the
surrounding air, less than half the heat being given out by radiation, and more than half
by the contact of the air: a foot of pipe of 200° external temperature in the air of a
room at 60°, the difference being 140°, gives out nearly seven times as much heat in a
minute as when its temperature falls to 80°, reducing the excess to 20°, or a seventh of
what it was. The quantity of heat which changes the temperature of a cubic foot of water
produces the same effect on 2850 cubic feet of atmospheric air.
Hot-water Apparatus for warming manufactories or large buildings, &c., which keeps up
a circulation of hot water through iron pipes, the hot water having a tendency to rise, and
as it cools to descend.
In France the hydraulic calorifère was thus described some years ago: the boiler was said
to resemble the human heart, and the pipes which carried out and brought back the water,
the veins and arteries. In the early application of this method, the fireplace was made in
the middle of a large boiler, and from the top issued an ascending pipe, which mounted to
a large cistern filled with water, from the bottom of which was another pipe that took the
cold water into the bottom of the boiler. The rarefaction produced by the heat in the as-
cending pipe caused the cold water to descend from the pressure exercised upon it, and
thus a regular circulation was maintained.
Hot-water apparatus is now made in a variety of forms: the most simple are those where
one pipe, of 2 or 3 inches diameter, is made to surround a small room, or where two or
more of such pipes are made use of. There are other arrangements where a number of
small tubes are preferred; but in all the water is made to circulate through them upon
the same principle: one of its earliest applications in England was, perhaps, at Bromley,
in Kent, where the Marquis of Chabannes, in 1816, warmed the conservatory for Sir
Samuel Scott, Bart., though it has been asserted that Mr. Watt warmed buildings in this
manner as early as 1784.
M. Bonnemain, of Paris, who was decidedly the inventor, about 1777, had a calorifère,
by which hot water circulated, and a regulator being attached to it, he could maintain so
equable a temperature that he was enabled to hatch eggs, and produce a great many
chickens; the variation being scarcely ever more than half a degree of Reaumur's thermo-
meter. The regulator made use of depended on the unequal dilatation of different metals:
a rod of iron, screwed to another of brass, was enclosed within a tube of lead, termi-
nating at its upper end in a ring of brass: the leaden tube was plunged into the water
contained in the calorifère, by the side of one of the circulating tubes; the dilatation of
lead being greater than that of iron, at an equal degree of temperature, and the rod being
also enclosed within the tube, it was heated much less than the tube; when the temper-
ature was raised to the degree required, the lengthening of the tube brought the ring
into contact with a claw, at the short end of the bent lever, and when the slightest increase
of heat further lengthened the tube, the ring raised the claw of the lever, and allowed the
other to descend: by this contrivance a wire was made to open or shut a valve, through
which air was admitted to the fire, and the combustion either increased or lessened.
Various improvements have been made in the mode of warming by hot water: at first the
pipes were cylindrical, and laid horizontally, but it being found that its motion was accelerated
when placed in the two legs of a siphon, they are now laid in an inclined position, and flat

Fig. 1923.
SECTION SHOWING PIPES.
1226
Book II.
THEORY AND PRACTICE OF ENGINEERING.
iron pipes are substituted for the round, those giving out more heat: hermetically closed
tubes are found useful in conveying the warm water to a greater distance; and then a'
smaller diameter of tube may be adopted, as the water may be raised to a temperature
considerably above the boiling point: by the use of ascending and descending pipes, water
may be made to circulate to any height; and it is calculated that a fire-grate of about 12
superficial feet, with a properly constructed boiler, consuming a bushel of coals per hour,
is sufficient to heat a moderate dwelling; the boiler having a bottom surface, in this
instance, of 48 feet, or four times the area of the grate, and about 32 feet of side flue. The
quantity of pipe to be heated must regulate the size of the boiler, and as each cubic
foot of water evaporated per hour requires 4 superficial feet, we may ascertain the
requisite proportions for a boiler of a hot-water apparatus. Supposing the latent heat
of steam 1000°, we shall find that the size of a boiler which would evaporate a cube
foot of water, at the temperature of 52°, into steam, would supply sufficient heat to 232
feet of 4-inch pipe, and maintain its temperature 140° above that of the surrounding
atmosphere.
When the difference between the temperature of the pipe and the air is 125°, it has
been found that a foot of 4-inch pipe will heat 200 cubic feet of air 10 per minute; and
when the pipes are 146° hotter than the air around them, the water within them loses
1° of heat per minute.


80
Fig. 1925.
SECTION OF CALORIFERE,
ம்
Where many stories of a building are to be
warmed the boiler and furnace are placed on

Fig. 1924.
SECTION.
Fig. 1926.
VALVES.
the lower story or basement, from which rises a flow-pipe to a warm-water-box placed at
the top of the house; from this another pipe supplies a small calorifère or metal box con-
taining water, one of which is placed in every room intended to be warmed: and after
passing through all, the water returns to the boiler to be again heated; a regular circulation
is thus kept up; the cold water, being heavier than that warmed, falls to the bottom of the
pipe, and forces up the latter.
Each 100 feet of 4-inch pipe, containing 544 pounds of water, will require 14 pounds
༣
CHAP. XX.
1227.
WARMING AND LIGHTING.
of coal to raise its temperature throughout to 180°; and as the water loses only 60° of
heat per hour, this quantity of coal will serve for 3 hours; 200 cubic feet of air being
heated 1° per minute by every foot of 4-inch
pipe, we must cube the contents of the building
to be warmed, and divide it by 200, to obtain the
number of feet of 4-inch pipe that shall have a tem-
perature of from 55° to 56°; when greater heat is
required, the cubical quantity may be divided by a
less number; for example, in greenhouses, where
the temperature required is 60°, 30 should be
the divisor; for 75º, 20 will be sufficient.
In calculating the quantity of pipe due attention
must always be paid to the heat lost by ventilation,
as well as the power of glass in radiating cold,
1 square foot of which will cool down 14 cube feet
of air 1° per minute, when the external tem.
perature is 30°; in a greenhouse, therefore, we
ought to have sufficient power to warm 11 cube
feet of air at least for every square foot of glass con-
tained in the building.

same
Warming by Steam is attended with more expense
than by water heated to circulate through the same
extent; the boilers made use of are of various
shapes, and are generally either of wrought-iron or
copper. The tubes are generally of the
material as the boiler, though cast-iron is very
much used, and earthen pipes have been tried,
but with them there is some difficulty in making
a good joint.
ス
​Fig. 1927.
PIPES.
A mill at Watford in Hertfordshire, 106 feet in
length, and 33 in width, consisting of 4 stories, and
used for the manufacture of silk, was one of the
earliest warmed by steam. By this method it was
found that all smoke was avoided, as well as the danger of setting fire to the raw
material; there was also great economy, and an equable heat at all times maintained.
Outside the mill a small furnace was built, where, from the upper part of the boiler, rises a
main, from which the steam was conveyed by another pipe, suspended to the ceiling of each
floor in its progress towards the top: the upper story, which was 8 feet in height, had a pipe
of 3 inches in diameter; the next story downwards, being 8 inches higher, had one of 4 inches;
the next, which was 9 feet high, had one of the same diameter, and on the ground floor or
lower story the pipe was 5 inches in diameter; at the top of the mill was a cistern of water,
which feeds the boiler.
The pipes of each story are furnished with valves, which regulate the supply of steam,
and there are others ingeniously introduced to collect and discharge the condensed steam
into the boiler below, which is most important: the pipes are all laid with a slight inclina-
tion to accommodate this running off of the water immediately it is formed; for if the steam
meet with a great surface of cold water, it condenses so rapidly as to endanger the boiler
and pipes, should they not be strong enough to resist the external pressure: it has been
stated that the quantity of coal necessary per day to warm such a building as the one
described is about 1400 pounds.
Warming by Air has been preferred in many instances to either steam or hot water:
a stove or furnace is contrived in the basement, and the air from the outside is intro-
duced, passing under the same, and enters a chamber which surrounds the furnace, so
that in its passage it becomes heated, when it is afterwards conducted to the several
apartments required to be warmed: great attention should be paid to the closing of all
external doors and windows when this plan is adopted, and therefore it has been objected
to in manufactories, churches, and hospitals, or where any great number of persons are
assembled.
At the Reform Club House in Pall Mall the objections are obviated by the introduction
of a large fan, which revolves in a cylindrical case, by means of a small steam-engine
fixed in the basement, and by which 11,000 cube feet of air are forced every minute into a
tunnel, built to receive it, in the lower part of the building; the air then flows through
a series of cells formed in steam cases, where it cannot become scorched, but is heated to a
temperature of from 750 to 85° Fahrenheit, and from thence it enters a brick chamber, built
to contain it, and from which it is let off, in a variety of flues, into the several rooms
to be warmed: by the aid of dialled valves and registers, the quantity of air admitted is
nearly under control; there are three cast-iron chests, each of which is a cube of 3 feet;
1228
Book II.
THEORY AND PRACTICE OF ENGINEERING.
these have seven parallel cast-iron cases, 3 inches in depth; into these cases the steam
is conducted by proper pipes, and between them the air to be warmed passes.
steam-engine, of 5-horse power, which is on the expansive principle, serves other purposes
than that of turning the ventilator, and consumes about 2 cwt. of fuel in twelve hours.
The
This principle is the reverse of that already described as adopted at the New Model Pri-
son: here we have genial air thrown in by the fan, and its circulation insured by pressure
from below, and not by exhaustion from above; the pure cold air is obtained, and raised to
an agreeable state of temperature, after which it is dffused into all the halls, passages, and
rooms around them. When air is pumped out, and no abundant supply forced to succeed,
what remains in an apartment is likely to be so highly attenuated as to prove injurious to
health: when attention is paid to the ventilation and passing off the vitiated air, the pressure
system is preferable. Fans of sufficient size may be driven by means of steam power with
such velocity as to produce ventilation throughout the most extensive buildings: condensed
air has a much more agreeable and healthy effect upon individuals than can be obtained
from highly rarefied air: a person breathing condensed air does so with facility; he feels
the capacity of his lungs enlarged, and his respirations are less frequent; in rarefied air
the breathing is attended with difficulty, and in consequence of this, in some of the deep
mines in France, the men work in condensed air pumped down from a chamber above :
when these workmen are about to descend they shut the door over their heads, and then
turn a cock, which is in connection with the condensed air on the under shaft: an equili-
brium is established in an ante-room, by the entry of the dense air from below, and then
the man-hole can be opened for the men to descend: here they work in air maintained at
a pressure of three atmospheres by the action of pumps driven by an engine; in such
an atmosphere the miners gain additional strength, and work without fatigue.
fanner or blower is made in various forms; the most common is that with four arms or
blades, working in a box; the air entering in the centre is discharged at the circumference;
in some of the most powerful, the air is made to enter at the sides of the blades throughout
their whole extent, and to discharge it at its circumference; by unscrewing one side of
the cylindrical box, in which a fan works, it will be readily seen which way the air proceeds,
if a rapid motion be given to it; the external casing is generally made air-tight, and the
air is conducted by a pipe to the fanners, at the opposite side to which it is desired it should
be discharged.
The
The larger the fanner, the greater is the economy with which its supply of air can be had,
and they are less subject to noise; those making 2000 revolutions in a minute are exceedingly
disagreeable throughout the whole neighbourhood where they are used; quantity of air,
and not velocity, is the object to be attained, and for this purpose fanners of from 10 to 20
feet diameter, moving slowly, are to be preferred: powerful blasts of air are not required
for ventilation, and therefore rapid movement to the fanner can be dispensed with.
Ventilation probably was first attended to in the mining districts, but nothing on this
subject could be effected upon a proper basis until Priestley defined the composition of the
atmosphere; no definite meaning could be given to the word ventilation until the nature
of the air itself was known; to him, Scheele, Dalton, and Cavendish, are we indebted for our
knowledge upon these subjects.
Before the employment of many persons in a small space, particularly in mines, the ne-
cessity for ventilation was not rendered so apparent: and the practice first adopted there, to
throw in a succession of currents of wholesome air, has been latterly introduced to disturb
the vitiated atmosphere of our crowded halls and ordinary dwelling-houses. The archi-
tect and civil engineer have been roused to contrive and invent means by which life may not
only be supported but endured, when confined in rooms robbed of their fair proportion of
oxygen by the modern luxuries of warming and lighting by gas. A man making twenty
respirations in a minute is said to inhale at each 16 cubic inches of air, or 320 cubic inches
in a minute of this quantity 32 cubic inches of oxygen are consumed, and 25 inches of
carbonic acid gas are discharged; so that, if his life endured for 50 years, it has been esti-
mated he would inspire 166 tons of air, consume 18 tons of oxygen, and discharge nearly
20 tons of carbonic acid from his lungs, or, in other words, nearly 5½ tons of carbon, allow-
ing 10 cubic feet of air per minute to each individual, the consumption for 1000 persons
assembled in a theatre or church may in some degree be estimated: as may the necessary
quantity for any given number of persons in rooms of different dimensions.
Of the atmosphere 78 per cent. is nitrogen and 22 per cent. oxygen, and the quantity of
carbon and moisture evolved by a single individual in a minute is stated to be 3.27 grains
of carbon, and 3.2 of water: so that 1000 persons would evolve in an hour 28 pounds
of carbon, and nearly as much water.
It is not so easy to determine the quantity of air required for ventilation, as this is so
much affected by temperature: Dr. Arnott informs us that air expelled from the lungs
vitiates twelve times its bulk of pure air, so that a man vitiates every minute nearly 4 cube
feet, and agrees that 10 cubic feet of fresh air per minute is the smallest allowance that should
be made for each individual. To produce motion in the air, or, as it is termed, ventilation,
CHAP. XX.
1929
WARMING, LIGHTING, AND VENTILATION.
heat properly applied has been found most efficient. Air at an ordinary temperature ex-
pands ʊ part for the rise of every degree of the thermometer: thus it becomes, as it
advances in temperature, specifically lighter, and consequently has an inclination given to it
to mount higher, and give place to the colder air, which sinks on account of its greater
density this takes place in the common chimney, the draught of which depends on the
difference of temperature at the top and at the bottom; the air at the lower end, by being
heated, rises and passes off at the upper, its place being supplied by the pressure of the
surrounding air to fill up the vacuum. Supposing to denote the velocity in feet per se-
cond, g the accelerating force of gravity, (=32.2 feet per second,) a the rate of expansion
for 1° of the increased temperature, t' the temperature of the heated air as it enters the
chimney, and t, that of the external air, we shall have this formula,
v = √ [2gha (t'—t)],
the velocity of the draught being as the square root of the height of the chimney, and the
square root of the excess of temperature of the lower opening: and as the same quantity of
air passes through every section of the chimney in the same time, the velocity must be
inversely as the density, and therefore decrease from the bottom to the top.
Air forced into a chamber by mechanical means is often used for the purposes of ventila-
tion: at the Bank is a square box, furnished with a pump with a loose piston, which has
large-valved openings, and by it 11,000 cubic feet of air per minute are driven through the
various offices; at the Houses of Parliament a large shaft, with a fire made in it near
its summit, exhausts the air from the several apartments, in the same manner
coal mines, and other deep workings.
as in
The practice adopted in deep mines to obtain ventilation seems to have given rise to all
the modes now made use of in our buildings for the same purpose: suppose there are
two shafts, which descend to the bottom of the mine, one is called the downcast, the other
the upcast shaft; by the first the air descends, and by the other the vitiated air mounts
and is dispersed. This movement is effected by constantly keeping up a large fire at a
little distance from the bottom of the upcast shaft, and making use of it as a chimney: by
this simple contrivance, the descending air may be made to pass through and along every
working of the mine; in some instances, it travels at the rate of 30 miles per hour, driving
all the lighter gases before it; numerous doors are introduced to shut off the course as
well as to direct it; should any of these be left open, the whole system of ventilation will
be destroyed.
Theatres are frequently ventilated by means of a funnel placed in the ceiling of the
pit, and having its exit through the roof, upon the top of which is a movable cowl: by
placing the large chandelier, or a multi-
tude of gas-lights, immediately below
the opening in the ceiling, the air about
it becomes so rarefied, that it rapidly
mounts the funnel, and passes out
at the mouth generally this part of
the operation, viz. the exhausting or
pumping out, is tolerably well effected,
but not so the admission of a warm and
pure air to supply the wants of the
spectators, each of whom requires air
for 20 respirations per minute
Lighthouses may be classed among
the works of the greatest public utility
and importance to a maritime nation :
we have already described many erected
after the Eddystone; the form at present
usually adopted, when on land, is that
of Ramsgate Harbour, which is circular
on the plan throughout, the rooms for
the attendants being on the ground floor,
and a winding staircase conducting to the
lantern.
A Select Committee appointed by the
House of Commons made a report in
1834 upon the state and management
of lighthouses, floating lights, buoys,
and beacons, from which we gather the
most valuable information that could be
afforded to Joseph Hume, Esq., the
chairman of the committee, the com-

Fig. 1928.
RAMSGATE LIGHTHOUSE.
1230
THEORY AND PRACTICE OF ENGINEERING. Book II.
mercial world is infinitely
indebted for the mass of
evidence there brought
forward on this highly im-
portant subject, as the means
of preventing many of those
fatal accidents to which our
shipping is so constantly
exposed.
Till the date of the report,
the lighthouses which sur-
rounded our coast were
managed by a variety of
systems, and, instead of being
under the superintendence
of the Government, were,
many of them, in the hands
of private individuals: the
whole appear to have been
built at various times, by
slow degrees, and as the
naval and commercial inte-
rests required them.
There were belonging to,
and under the management
of, the Trinity House of
Deptford Strond in the year
1834, 108 lighthouses and 18
floating lights, and through-
out the United Kingdom
198 lighthouses and 21
floating lights. This fra-

Fig. 1929.
PLAN OF RAMSGATe lightHOUSE.
ternity, or college of seamen, seems to have existed prior to Henry VIII., but in the sixth
year of that monarch's reign they were incorporated by charter, as the Master, Wardens,
and Assistants of the Guild Fraternity of the Most Glorious and Undivided Trinity, and of
St. Clement's, in the Parish of Deptford Strond, in the County of Kent. Queen Elizabeth
afterwards gave them fresh powers, to erect and preserve beacons and signs for the sea,
but it does not appear that this fraternity erected any lighthouses till the year 1676.
The public lights of Scotland were under the Commissioners for Northern Light-
houses, incorporated by the 38 George 3. chap. 58.; there were 25 lighthouses under
their management: those of Ireland were under the superintendence of the Ballast Board,
a corporation consisting of the mayor and sheriffs of Dublin, three aldermen, and 17
other individuals, who had the control and management of 35 lights; there were several
other lighthouses held under lease from the Crown.
Lighting.. The first method employed for lighting these buildings was undoubtedly
coal fires, unaided by reflectors or any mechanical or optical arrangements: to this suc-
ceeded the use of candles, and till a late period we find them generally adopted: the
next improvement was the Argand burner, introduced on the focus of a parabolic
reflector: this instrument is made of silver, strengthened with copper; it is about 3 or
4 inches in focal length, and 21 inches in diameter; the number and arrangement of
reflectors in each house depend on the light being fixed or revolving, as well as upon
the situation and importance of the lighthouse: one of the methods much used in France
is to place a large Argand lamp, with four concentric wicks, giving a very powerful light,
in the centre of the lantern, surrounding it with a series of glass lenses, of a peculiar
construction, and using a refracting, instead of a reflecting instrument to collect the light,
and only one lamp instead of a number. The lens is a very beautiful instrument, about 30
inches square, plano-convex, and formed of separate rings or zones, whose common surfaces
preserve nearly the same curvature as if they constituted portions of one complete lens, the
interior and useless part of the glass being removed. To form a lens out of one piece of
glass of such a magnitude would be scarcely practicable, and if it were, the thickness of the
glass would materially obstruct the light: a lens so constructed gave as much light as nine
of the ordinary reflectors in common use, and the consumption of oil in the burner was as
great as in seventeen of the Argand lamps.
Lieutenant Thomas Drummond, who was employed on the Trigonometrical Survey of
England, had his attention directed to the subject of signal lights, in consequence of the
great difficulty he experienced in observing distant stations, particularly when it was required
to see Leith Hill, in Surrey, from Berkhampstead Tower, in Hertfordshire; and it
CHAP. XX.
1231
GAS LIGHTING.
appeared very desirable to procure a brilliant light, capable of penetrating the almost
constant haze which impeded his observations. He began his inquiries by repeating some
of Berzelius's experiments on the distinctive qualities of the different earths before the
blow-pipe; that assigned to lime was the property of emitting, when so heated, a peculiar
bright light, and which he found produced one so distinct that every particle of lime
could be seen with the naked eye. After this experiment, the idea presented itself, that
if an apparatus could be made, containing a ball sufficiently large, and kept in a state of
intense ignition, its effect, when placed in the focus of a reflector, would exceed that of any
light hitherto used.
After many experiments, the extraordinary intensity, as well as useful application of this
light was detailed in two papers published in the Philosophical Transactions for 1826 and
1831: it was afterwards fitted and adapted to the purposes of a lighthouse; the apparatus
consisting of a lamp, (fig. 1933.), which admitted at the same time through the apertures o
and the two gases, hydrogen and oxygen: they came from separate gasometers, and were
not suffered to mix until they arrived at the small chamber c, of which fig. 1931. is a
section; into this chamber the oxygen gas from the inner tube is projected horizontally,
through a series of very small apertures, and the hydrogen gas rises vertically through
similar apertures at d. The united gases then pass through two or three pieces of wire
gauze, placed at e, and being thus thoroughly mixed issue through the two jets against the
ball, b, fig. 1933. To prevent the wasting of the ball opposite the two jets, and at the
same time to diffuse the heat more equally, it is made to revolve once in a minute, by
means of a movement placed underneath the plate m, and with that the wire f, carrying
the ball and passing through the stem, is connected: notwithstanding this arrangement, the
effect of the heat is such as gradually to cut a deep groove in the ball, so that at the end
of about 45 minutes it becomes necessary to change it; to effect this a wire, ab, (fig. 1930.)
passes through the focus of the reflector, and upon it are placed a number of balls, at A,
required for any given time; these, by means of the shears, s, are admitted between the
plates, p, p, and hence are permitted to fall, in succession, to the focus. f represents the
focal ball, about two minutes before the change; the ball at g falls into the position i, where
it becomes gradually heated; at the end of that time the curved support, t, moving on a
pivot, is thrown into the position represented by the dotted line, by the momentary
descent of the ring r, which receiving an impulse from the weight W acts upon the
extremity u of the support; f falls, but it is prevented from descending more than its own

A
p
W
P
א
א
2
d
d
$
h
m:
Fig. 1931.
Fig. 1932.
Fig. 1933.
Fig. 1934
Fig. 1930.
DRUMMOND'S LIGHT.
diameter by the loop l, and i, following it, occupies the focus; the support t being imme-
diately released, returns by the action of a spring to its former position, retains i, and suffers
ƒto escape through the loop into the cistern. The wire ab, and the support t, revolve
together, and carry round the focal ball, which is ignited, as in fig. 1930. by the two jets,
These jets, which are movable round the joints d, d, enter through small apertures
cut in the sides of the reflector, and are easily adjusted to the proper distance from the
Z.Z.
1232
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
ball: should it be required to diffuse the light equally, the renewal of the lime may be
effected by using a cylinder instead of a ball, which, being gradually raised while revolving,
brings fresh portions in succession opposite the jets.
In a reflector, a cylinder occasions partial shadows at the top and bottom, but the sim.
plicity and certainty by which it may be renewed entitle it to be preferred: the apparatus
to supply the gas consists of two strong cylinders, 3 feet high, one to contain the
oxygen, the other the hydrogen; these gases are compressed, two or three times, the
latter by being generated under pressure, the former by being pumped in. To each
of these gas-holders is attached a governor, so that whatever be the variation of pressure
in the gas-holder, provided it exceed that of the governor, the gas issues with a uniform
and constant stream, in the present instance under a pressure of 30 inches of water:
all attempts made to apply the Drummond light and voltaic light have hitherto
failed, in consequence of the many great and practical difficulties with which these
modes of lighting are accompanied, and the usual methods adopted
are those of the lighthouse of Corduan, and others on the French

coast.
Mr. R. Stevenson, however, in his report upon the Drummond
light, observed that on several occasions during a dense haze
it had been seen, though not with brilliancy, while the reflected
and lens lights were totally eclipsed: this light was so intensely
brilliant, that the observers on the Leith road, in a favourable
state of the atmosphere, saw their shadows strongly marked at
full length across the road, at a distance of 13 miles from Gullan
hill, where the experiments were made. With regard to its appli-
cation to lighthouses, Mr. Stevenson was of opinion that with the
then state of the apparatus, it was not possible to maintain a steady
light; the heat of the united flames of these gases was so intense
that it destroyed platina, and all the substances applied to it; inde-
pendently of this, the very explosive nature of the oxy-hydrogen
gas was an objection, and great attention was necessary to keep up
a constant flame.
Fig. 1935. Drummond
LIGHT, GAS CYLINDERS.
Gas Lighting.-For gas manufactories it is necessary to have
premises of sufficient extent to contain buildings for the retorts, as
well as ample space for the gasometers, purifying apparatus, and stores of coal, pipes, &c.
employed in manufacturing, or in conveying the gas to the places required: the situation
usually chosen for these works is the lowest that can be obtained; coal gas being lighter
than air is sure to rise, and can only be made to descend by the application of pressure.
The plan given is that of some gas-works constructed by the writer for a town in Kent,
of 6000 inhabitants, about 30 years ago.
Retort-house is generally of brick, and sufficiently large to contain the requisite number
of retorts, which are of a cylindrical or elliptical form, of cast-iron; they are placed in rows

..
Fig. 1936.
PLAN OF GAS WORKS.
within a brick oven, where they are so surrounded with flues that the heat is distributed
equally.
CHAP. XX.
1233
GAS LIGHTING.

Some retorts are in the form shown in fig. 1941. and about
7 feet 6 inches in length, 18 inches in width, and 1 foot
high in the clear; such are said to yield in the shortest
time the greatest quantity of gas.
Those that are cylindrical vary from 8 to 6 feet in
length, and are about 12 inches in diameter; this form is
preferred as being the less expensive, but there are many
objections to it, particularly from its not allowing the coal
with which it is charged to lie equally thick throughout:
in the middle it must lie deeper than towards the sides; it
is important that every part of the coal should be equally
acted upon at the same time; this the cylindrical retorts do
not provide for in the same manner as those which have
flatter bottoms.
Whatever form is given to the retorts they are cast
closed at one end, and at the other they are fitted with
Fig. 1937.
SECTION OF RETORt-house.
mouth-pieces, also made of iron, into which is fixed the
conducting pipe, which carries away the gas as it rises from
the coal.
The cover or lid requires to be well closed: this is ac-
complished by an iron frame, through which a long screw
passes to the centre of the cover, where it enters; by this
means the retorts can be closed immediately they are
charged with coal: the joints round the cover are closed
more perfectly by the application of a lime-lute, which
prevents the gas as it is generated from making any escape.
These retorts are liable to accidents: they seldom last
more than six months, and often not so long; for they
indicate decay both on the out and inside, the former caused
by the heat, and the other by the action of the coal itself.
O
Fig. 1939.
ELEVATION OF RETORT-HOUSE.

The iron appears to increase in bulk,
and in time becomes soft, resembling
finely laminated black chalk. Par-
ticular attention is required for
their setting in large establishments :
several are set in one frame or oven,
with the fireplaces beneath them; the
flues are so contrived that there is not
only an equal distribution of heat, but
it is sufficient to decompose all
the coal put into them, which if not
properly done, all the volatile substances
will not be liberated, and a loss will
be proportionately sustained: each retort
is usually charged, after being pro-
perly heated, with a bushel of coal,
thrown into it by a long semicircular
iron shovel, or scoop, which spreads it
throughout into a thin layer; this remains
subjected to the action of the heat of the
Fig. 1939.
FRONT OF FURNACE.
4 K
1234
Book II.
THEORY AND PRACTICE OF ENGINEERING.
oven for 6 or 8 hours, when the plate which closes the mouth of the retort is withdrawn,
and a volume of flame pours out; after this the residue, which is coke, is drawn out by

Fig. 1940.
SECTION OF FURNACE AND RETORTS.
means of iron bars with crooked ends, and water thrown upon it, or it is allowed to
descend into a place prepared to receive it.
The quantity
of coke obtained
after distillation
varies, as coal
loses from 20 to
35 per cent.: it is
usually, however,
about half as
much more than
the bulk of coal
thrown into the
retorts, a bushel
yielding 11 bush-
els of coke. The
quantity of coal
required to heat
a retort is about
a fifth of the
quantity with
which they are
charged, and 1
cwt. yields from
300 to 500 feet

of gas.
or
Great attention
is required in so
carbonising
distilling pit coal,
that the carbu-
retted hydrogen
may be produced
in the largest
quantity; and
upon the eco-
nomy and care
carried into this
Fig. 1941.
福
​TRANSVERSE SECTION OF RETORTS.
operation depend the successful results of any establishment undertaking to light a
city. As soon as the retort into which the coals are put to undergo decomposition becomes
red-hot, atmospheric air and steam are given off, and the tar is distilled from it, together
with hydrogen and ammonia, in the state of gases, which continue to evolved as long as
the retort is kept up to this heat; when this is increased, the pyrites of the coal yields
sulphurous acid, which is found united with ammonia; the residuum after distillation is
carbonised coal or coke.
The first gas that comes off gives a very feeble light; that produced at a vivid red
heat consists of bicarburetted hydrogen or olefiant gas of the best quality, and affords the
brightest light in every 100 measures obtained from good coal, the products at the first
giving out are : —
:
CHAP. XX.
1235
GAS LIGHTING.
Olefiant gas
Bicarburetted hydrogen
Carbonic acid
Azote
82.5
13.
3.2
1.2
The whole combined having a specific gravity of 650: when the retort has been heated
5 hours, it may be thus stated :—
Bicarburetted hydrogen
Olefiant gas
Carbonic oxide
Hydrogen
Azote
-
The specific gravity of the compound being 5.
56.
7.
11.
21.3
4.7
At the end of 10 hours it contains 20 of carburetted hydrogen, 10 of carbonic oxide, 60
of hydrogen, 10 of azote, and the specific gravity is only 0.345.
In the first hour of distillation one-fifth of the whole quantity is given out, and the re-
mainder in tolerably equal quantities for each successive hour, until the whole, which
amounts to about fifty-four parts out of the hundred, is obtained: it is consequently advisable
to commence the operation by making the retort cherry-red; the best gas being then pro-
duced, when a portion of the tar is converted, instead of being distilled over. At the
commencement of gas-lighting it required half as much coal to heat a retort as it was
charged with; now five retorts are heated in one oven by a single furnace, and one-third
the contents of the retorts is sufficient for the purpose: 65 per cent. of coke remains in the
retort after distillation, and its volume is increased in the proportion of 4 to 3: it is now.
preferred for heating the retorts, and its power may be estimated at 65 per cent. of the
coals consumed. When the retorts have been some time in use, it is found that their
external capacity is diminished, in consequence of an incrustation of carbonaceous matter
within them: this has sometimes been removed by throwing in jets of heated atmospheric
air with considerable force, when the retort is heated to redness; it has been suggested
that this might be effected by common air, if applied in sufficient quantities, which would
burn away the extraneous matter.
The Hydraulic Main is a strong cast-iron pipe, usually about 12 inches in diameter, of a
sufficient length to receive all the perpendicular pipes that convey the gas generated in the
several retorts: this main is made perfectly horizontal, and supported on the brickwork
which covers the ovens. The gas leaves the retort by means of an upright conducting
iron pipe, about 3 inches in diameter, and 4 or 5 feet in length, fixed at one end into the
mouth-piece and mounting perpendicularly, curving at the top, before it is allowed to de-
scend and join the hydraulic main; through this pipe the impure gas passes.
The hydraulic main contains a certain quantity of cold water, for the purpose of con-
densing the several substances which constitute the first-formed gas; one end of the main is
firmly closed by means of a flange;
the other has a similar contrivance,
and a little above its diameter
is attached the pipe through which
the gas passes: at the end is a
semicircular piece of iron, which
maintains the water at a uniform
height.

The upright pipes, which are
bent at the top, and convey the gas
into the hydraulic main, dip 2 inches
or more into the water, obliging
the gas to flow through a portion
Fig 1942.
HYDRAULIC MAIN.
of it before it rises into the upper half of the main and passes off. The tar deposited
in the water from this process is drawn off by means of pipes, whilst the greater portion
of the ammonia, from its strong affinity for water, combines with it.
The Condenser, which receives the gas from the hydraulic main for the purpose of
cooling it, is a large cistern or tank constantly immersed in cold water; its form may be
either square or circular; but it must be so arranged, that when the gas has once entered
it may
be obliged to pass over a considerable cold surface before it can escape: it is usually
covered with wrought-iron plates pierced with holes, into which are inserted a number of
tubes; these are 4 inches in diameter, and attached by flanges and screws, connected in
pairs at top, by means of curved or saddle tubes. The chest or vessel which is so
covered is divided by vertical iron partitions, as many in number as there are pairs of
tubes; and as these vertical plates do not touch the bottom of the chest, the gas is obliged,
or rather made, to pass up and down this series of partitions and pipes, or from one
4 K 2
1236
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
薯
​compartment to another. In the passage of the gas it is at last cooled down to the tem
perature of the air, and made to deposit the whole of its tar and ammoniacal
liquor, which pass off into the tar cistern beneath, where the ammoniacal
liquor floats at the top, and is drawn

off by means of pipes placed there for
the
purpose; or there are two pumps,
one which passes to the bottom, to lift
up the tar, and the other enters only
the part containing the ammonia, where
it can be pumped out, without bring-
ing up the tar. A chaldron of coals
yields 1 cwt. of tar, and produces from
15 to 18 gallons of ammoniacal liquor.
Other condensers have been intro-
duced, which consist of a series of
ascending and descending bends of
pipes, where the tar, of two or three
qualities, may be drawn off, and the
ammoniacal liquor easily discharged:
it has been estimated that about 10
square feet of condenser is required to
cool 1 cube foot of gas per minute;
and that when 10 cubic feet of
gas are produced per minute, a
CISTERN
AMMONIACAL LIQUOR
The Purifier.
TAR
Fig. 1943.
CONDENSER.
cooling surface is required, equal to 100 square
feet; or in establishments where 100,000 cubic
feet of gas are produced every 24 hours the con-
densing surface must be from 800 to 900 square
feet.
As it is necessary to separate the sulphuretted hydrogen and carbonic
acid gases, which is not possible by mere cooling, and to clear the coal gas from other

kr226
| 223 16 17
ARGOLEK SZTUSU MARA
Fig. 1944.
Section of purifier.
impurities injurious to health, which also corrode the pipes, as it passes
through them to the burners, and injures the colour of the flame, it is sub-
jected to a chemical action, by passing through lime and water, mixed
together to the consistence of thick cream; hence called cream of lime. The
sulphuretted hydrogen and carbonic acid are taken up by the lime, and the water absorbs
any ammonia that may remain.
CHAP. XX.
1237
GAS LIGHTING.
When coal gas contains 5 per cent. of these gases, every 100 cube feet will require 1
pound of lime, or about in weight of the coal subjected to decomposition, with which as
much water must be mixed as will make it into 1 cubic foot of the cream. The purifier
should have a capacity sufficient to hold of a cubic foot for every 100 feet of gas that
passes through it in one operation, and the contents should be changed every 6 hours: 20,000
cubic feet would require 114 feet cube of cream of lime; so that a cylindrical vessel in
which it could stand to the height of 3 feet must be 7 feet in diameter.
#
The purifier is generally formed of three vessels within each other, air-tight, and of a
cylindrical form, with an upright shaft in the axis, to which is attached a number of arms or
paddles for the purpose of stirring up and agitating the mixture, and preventing the lime
from settling at the bottom: as the gas enters at the lower part of the vessel, it passes in air-
bubbles through a succession of plates around the edges, where a space is left for the pur-
pose, and in its passage becomes exposed to the action of the cream of lime: in this process
all the sulphuretted hydrogen is taken up; this is tested by allowing a portion to escape
through a cock, and pass over a piece of paper previously dipped in a solution of sugar
of lead, which will become brown if any sulphuretted hydrogen remain: when this is the
case, it must be again submitted to the cream of lime.
At large gasworks it has been found necessary to have three purifiers, so connected
together that the second is placed rather higher than the first, and the other a little above
it, so that the discharge-tube of the highest vessel, which is a little below the top, enters
into the upper portion of that which stands lower; by this means the milk of lime in
the uppermost vessel is made to rise above its ordinary level, flow over into the second,
and then into the third, from whence it is drawn off by the eduction-pipe; the gas is
introduced into the first vessel, and passed successively through the others into the
gasometer when the milk of lime is in sufficient quantity to allow the gas in its pro-
gression to pass over an entire new surface, it becomes thoroughly purified: its
purity may be tested, after it has passed through the vessel containing the lime, by means
of a siphon-tube with a stopcock; this, inserted in the cover of the purifier, may have one
end in contact with a solution of acetate of lead, which will become turbid, when it is
necessary to renew lime in the machine. It is very desirable that gas should be rendered
perfectly pure, and that no sulphuretted hydrogen should remain; it has been recom-
mended to make use of pyrolignite of lead for the purpose; the only objection is its
cost: coal-gas contains also sulphuret of carbon, which gives out sulphurous acid when
consumed, and which it is exceedingly difficult to prevent.
Various other methods have been tried to render gas pure: one was putting a small
quantity of water to the lime, and mixing it to such a consistence that it could be
spread into cakes over perforated iron plates, through which it was allowed to pass;
another was to pass it through red-hot pipes, in which was previously placed black oxide
of iron, iron filings, &c., or other matter capable of oxidation, which separated the sul-
phuretted hydrogen and carbonic acid from the carburetted hydrogen. By the former plan
the necessity of evaporating the waste liquor is avoided, and the product presumed to be
better, retaining the whole of its olefiant gas, from which the whiteness of the flame is said
to arise, whereas this latter, being slightly soluble in water, loses some of this quality in
its passage through the milk of lime: it is beneficial to submit the gas in the purifier
to the pressure of a column of water about 2 feet in height, and an Archimedean screw has
in some cases been used for the purpose.
Gasometers are now made of a cylindrical form, as this figure is the most capacious
for the quantity of metal used; its height ought to be equal to its radius, to comply with
this condition: sheet-iron is usually employed for its construction, and the cylindrical
form is strengthened by the introduction on the inside of cross iron rods, both at its top and
bottom; the top is like a very flat cone, the rods radiating from the centre to the outer
rim. The bottom rim is cast-iron, held to the upper by perpendicular rods bolted through
them; oblique and other rods are introduced in large gasometers, when additional strength
is required. The gas-holder has on the upper rim several rings, placed at the ends of
the perpendicular rods, to which rings the chains are fixed, which pass over the pulleys,
to balance it in its rise; this is aided and performed most effectually by attaching to
the other end of the chain a weight acting as a counterpoise.
:
Around the gasometer are three perpendicular iron columns, placed triangularly, over
which the chains pass, to mark the rising or falling of the gas-holder; a greater
number of columns are necessary when the diameter is considerable, to keep it steady.
The gas-holder is made to descend into a cistern of water, constructed either of brick
or cast-iron as the gas-holder sinks, it of course loses a proportion of its weight
equal to the quantity of water it displaces; so that when entirely immersed, as it is
when nearly empty, it exercises little or no pressure, but when entirely out of the tank
or water cistern its pressure is considerable; to render the escape of the gas equal, which
is important, it is necessary so to adjust the balance chain, that throughout its motion it
shall be equal to half the weight which the gas-holder loses by immersion.
4 K 3
1238
THEORY AND PRACTICE OF ENGINEERING. BOOK II.
The size of the gasometer depends upon the quantity it is required to contain: one
42 feet in diameter and 23 feet in height will contain 30,000 cubic feet, and the lower

GASOMETER
CONDENSER
PURIFIER
RETOKTS
*££
+DE+
Fig. 1945.
APPARATUS TO GAS MANUFACTORY.
vessel or cistern into which it plunges is made somewhat larger, as there is usually a pres-
sure allowed, which makes the water stand on the outside one or two inches higher than
within, which is necessary.
Before the gas is introduced into the gasometer, it is usual, after it has left the purifier,
to pass it through a large revolving meter, where its quantity and temperature are exactly
measured: some of these machines, in large works, are capable of measuring 30,000
or 40,000 cubic feet per hour, and by means of contrivances attached to them, register
the quantity as it is made, both by night and by day. Such is the gas-meter, now in
general use, and the section perpendicular to its axis shows its arrangement. The interior
consists of a hollow wheel or drum, divided into four compartments by as many thin
plates; this is made to revolve freely on its axis within an air-tight case, which as well as
the lower compartments of the wheel is filled with water to a level a little above the axis
on which it moves :


each
compartment
has two apertures,
one for admitting,
the other for dis-
charging the gas;
and these openings
are so placed, that
when it enters one
compartment, its
escape must be be-
neath the surface
of the water. The
gas is admitted by
the pipe, which is
bent upwards, so
that its mouth in-
ternally is raised a
trifle above the
water; it then flows
through into that
Fig. 1946.
GAS METER.
Fig. 1947.
SECTION.
compartment which is under water, its pressure on the surface of which causes this division to
rise, and the cylinder to revolve on its axis; another aperture then dips into the water, and the
gas is driven out as it enters, and so on in succession: the inner cylinder with its cog-
wheel attached continues to turn round, and the gas passes off: it is easy to fix upon the
machine a dial-plate, which indicates the quantity passed through it by one revolution or
move.
The inner cylinder is made to turn freely on the axis, passing partly through it; this
axis is fixed at one end to the revolving cylinder, and kept steady in its motion by the
cross bars; one end of the pivot is made to work in a hole drilled at the side of the pipe,
by which the gas is introduced; the other end projects beyond the inner cylinder, and
reaches through the hole in the outer cylinder to a cup placed over it, which contains
a hole, in which it turns; within this cup is a cog-wheel, which works by means of
others the hands of the dial-plate, in the same manner as a clock movement.
this machine water is poured into it by means of a pipe attached to the small outer cup,
which regulates its height within.
To use
The Gas Governor, which modifies the pressure of the gas-holders, consists of a small
gasometer, the interior of which is in direct communication with the pipe through which
CHAP. XX.
1239
GAS LIGHTING.
the gas enters from the gasometer it is distributed into the
mains, by means of the pressure exerted upon it, and
by the proper regulation of the valves, which command
the apertures connected with them. The pressure by
which motion is given to the gas in the mains is measured
by the outside height of water in the cistern, into which the
gas-holder is plunged; its velocity in its passage through
a main increases in the ratio of the square root of the press-
ing column of water upon the gasometer; so that by
adding to this it may be made to pass either more rapidly
or to a greater distance. In laying down the mains, that
they may distribute it as equally as possible, it is neces-
sary to take into consideration the velocity of discharge at
the several distances.

Fig. 1948. GAS GOVERNOR.
Laying down the Mains. All the pipes employed whose
diameter exceeds 1 inch in the interior, are made of
cast-iron, in lengths of from 6 to 8 feet; their ends
fit into a wide socket joint, the end of one pipe being
cast with a nozzle, inserted into a socket at the other:
after these are inserted, hemp soaked in tar is driven into the
joint around the nozzle, and over this is put a luting of clay, within which is poured hot
lead, which forms a ring in the socket; this is tightly driven with a blunt chisel, and
trimmed carefully. The pipes or tubes, for the distribution of the gas to the several
houses or manufactories, are of smaller diameter, though never less than inch, and made
either of tin, iron, copper, lead, pewter, or other compounds; they should, however, all
be subjected to proof before they are employed by means of a force-pump.
A pipe 1 inch in diameter and 250 feet in length is sufficient under ordinary circum-
stances to transmit 200 cubic feet of gas in an hour; and as the volume discharged
at the end of a pipe is directly proportionate to the square of its diameter, and inversely as
the square root of its length, other calculations may be founded upon it: it is highly
necessary that the engineer should, previously to his laying down the mains in a town or
city, correctly ascertain the difference of level of every part to be lighted, as well as the
quantity of gas to be distributed in the different quarters; whenever streets are wide, it
is preferable to lay down a main on each side, as it is far more convenient to attach the
service pipes as well as for their repair. The pipes should all be laid, if possible, in
a straight line, and with a gradual slope of about 1 inch to every 30 or 40 feet; this slope,
after it has continued for about 300 feet, may then, if it be on the ascent, descend the same
distance, so that the pipes alternately rise and fall, and are not laid level; otherwise
they will not drain off the water that may be condensed within them.
Where the mains are required to be laid at right angles, curved pipes cast for the purpose
are used for rounding the corners of the streets, as it is desirable to avoid any line or form
that may obstruct the free passage of the gas through them, which is so very subtile
that it is necessary to have the pipes cast internally as clean as possible, to prevent
friction. At the end of every fall of main, or where two descending lines meet, a
reservoir should be formed, to receive all that drains off by them; this reservoir, or siphon
as it is usually denominated, must be

proportionate to the duty it has to per-
form; it is made of cast-iron, of a
cylindrical form, its diameter being equal
to double that of the mains which fall
into it, and the depth is made twice or
more that of the diameter; the top is
provided with a cast-iron cover, into
which is fixed a wrought-iron pipe that
descends nearly to the bottom; on the
top of this pipe, which rises above the
cover some inches, is a screw for the
purpose of attaching a small pump, that
is applied whenever the condensed water
has accumulated, and requires to be
drawn out.
Sliding or Hydraulic Valves for passing
off the gas into the mains: this operation
is sometimes ingeniously performed by
means of a small gasometer or cast-iron
vessel, which has on one side a pipe communicating with the main, and on the other a com-
Fig. 1949.
SLIDING OR HYDRAULIC VALVE.
4 x 4
1240
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
t
munication with the gasometer with a similar pipe. The top cover, which is suspended over
pulleys by a balance weight, when raised, allows the gas freely to pass, but when let down,
the partition plate, sinking in the water which surrounds the ends of the two pipes, at once
prevents any gas from passing from one to the other: the water is maintained at a uniform
height by means of a small reservoir attached to the side, which is regularly supplied by a
ball-cock.
Pressure Indicator, which measures the pressure in the main and service pipes, is
used at most of the large establishments, and is a beautiful contrivance; by it is
ascertained the excess or deficiency of

supply: when
when a number of burners
are suddenly extinguished or lighted, the
indicator at the works immediately
makes it known; this is effected by the
small, but nicely-adjusted gasometer,
connected with the main service; its
rising and falling being the consequence
of diminished or increased pressure
within the main, the valves are either
opened or shut, to allow the gas to
pass or not from the gasometer. To
this is attached a regulating rod, which
has a pencil inserted in it, which in
its motion is made to trace a line upon a
ruled sheet of paper wrapped round a
small cylinder; this is kept in regular
rotation on its axis by means of ma-
chinery connected with the movement of
a clock; thus during the night as well
as day every change of pressure is indi-
cated.
Fig. 1950.
INDICATOR.
This invention of Mr. Crosley's for
registering the actual pressure at the
main outlet, and which indicates the
most minute variations, with the pre-
cise times when they occur, enables a
complete check to be kept against the
person employed to superintend and regulate the supply. In the interior of the small
gasometer is a small tube, which communicates with the main; an air-vessel within
the gasometer occasions it to float when immersed in the water, at which time it is in
a state of equilibrium with the external atmosphere; and as the gas in the main increases
ite pressure it rises, which rising is measured
off by a scale, 12 inches in height, being
equal to the pressure of a column of water
1 inch in height. The paper by the hori-
zontal lines shows every tenth of an inch
pressure, and by vertical lines the hours
when it occurs.
Sliding Valves are very simple, and are
placed in an upright position, within a
strong iron frame; they are perfectly
smooth, and the plate which slides up
and down is sometimes of brass, properly
ground, and made to fill up the groove, and
rendered completely air-tight: it is moved
up and down by a screw, which turns in a
socket formed on the upper part of the
frame; but where their dimensions are con-
siderable, a rack and pinion may be advan-
tageously employed.
A Quicksilver Valve is sometimes used,
formed by a square iron box, with a per-
pendicular division in it, which can be
made to dip into another iron box below it,
and in which a quantity of quicksilver
is placed into the sides of the upper box

:
Fig. 1951.
A
UHIDIHI
UHHIKI
QUICK SILVer valve.
19
are inserted the two pipes to allow of the passage of the gas, when it is required; it is
obvious that when the division of the upper box does not dip in the quicksilver, the
CHAP. XX.
1241
WARMING AND LIGHTING.
gas will freely pass under it, and proceed to the opposite pipe; when it is desired
to shut off the communication, all that is necessary is to turn the screw beneath the
bottom box, which works in a fixed female screw, and this so elevates the quicksilver that it
closes, by the dipping of the perpendicular partition into it, all communication between
the two horizontal pipes. The lower box has an iron rim round it, to preserve its regular
motion, and to prevent it from moving otherwise than in an upright position.
Construction of Burners, Length of Flame, &c. The burners are of several varieties. The
beak is perforated with one small hole, of an inch in diameter, made perfectly round and
smooth.
The Argand burner has the holes around a circle, and great care is required to
place them at equal distances, as well as make them all equal in diameter; for when
several jets issue from one burner, they should unite to form one flame. The distance
at which the holes should be bored should be from 16 to 18 hundredth parts of
an inch, or of an inch; and when the Argand burner has ten holes in the cir-
cumference and one in the middle, the central one should be made of an inch; and
when twenty-five holes, that in the middle must be 1 inch in diameter. If the holes
are too large, the gas will flow so rapidly that it will not mix proportionately with
the atmospheric air and render its combustion complete; this affects the brilliancy of
the light, and produces a quantity of smoke: when the holes are too small, the gas will
not flow in sufficient quantity to produce the necessary quantity of light; and it is
generally observed, that the burners which contain the greatest number of holes within a
certain space afford the most brilliant light.
The Argand burner being composed of a ring, the centre part is left open for the
admission of a supply of atmospheric air to the interior of the flame, and by means of a
glass chimney the combustion of the gas is rendered more complete, as well as more
active: those burners which have 10, 15, 20, or 25 holes, have their diameters, and
1 6,
95 of an inch; the breadth of the rim 12 of an inch, and the length of the burner
13 inch.
100
1800
2' 10'
The height to which flame may be raised without smoking is in this proportion: with
eight holes, 4 inches; ten holes, 3 inches; fifteen and twenty, 21; and twenty five, 2
inches; and it is a singular circumstance, that all these burners emit the same quantity of
light.
The most economical as well as the most brilliant light is afforded when the jet-
holes are very numerous, the air aperture small, and the chimney narrow: when several
jets are united, as in the Argand burner, the light increases in a greater ratio than the
expenditure of the gas. The glass chimneys for the burners mentioned should be 8, 12,
13, and 15 tenths of an inch in diameter, and 6 inches in height.
The luminous quality of gas depends upon the portion of carbon held in solution
by the hydrogen, and also upon the quantity of oxygen which each may require for
its perfect combustion, according to its volume, and the intensity or measure of the
light produced is ascertained by the faintness or blackness of the shadows, when an
opaque object is placed between the light and a sheet of white paper. Light always
moves in straight lines, and diverges in all directions, its intensity decreasing in proportion
with the square of the distance; thus at the distance of 1, 2, 3, or 4 yards, its
intensity will be diminished in proportion to the square of those numbers, or as 1, 4,
9, 16, so that at the distance of 2 yards the light will be only what it was at 1
yard distance, and when at 3 yards, 9 times less, and at four, 16. Dr. Priestley found
that when two lights shone upon the same surface at equal obliquities and an opaque
body was interposed, the two shadows produced differed in blackness or intensity in a
similar degree: the shadow produced by intercepting the greater light being illumined by
the lesser only, the other shadow would be less intense, and the strongest light would
have the deepest shadow. Thus when two lights are to be compared, they should be so
placed that a ray from each should fall with nearly the same angle of incidence upon the
middle of a sheet of paper; by interposing some opaque object the two shadows it
occasions may be made to lap over each other; then if the lights are removed or brought
nearer the paper, until all the shadows are of the same intensity, it will be found that the
quantity of light emitted by each will be as the squares of the distances from the paper.
Colour has something to do in the comparison of the intensity of two lights, that flame
which is nearest to a pure white being the most brilliant, and its lustre diminishes in its
approach to a brown hue, and this often affects the appearance of the shadows thrown for
the purpose of estimating the quantity of light.
To ascertain the purity of coal gas it is only necessary to pass it over a solution of
acetate of lead: this may be done by unscrewing the burner, and then in lieu of it screwing
on a bent tube, which, if allowed to dip its end into this solution, will at once indicate
whether there is any sulphuretted hydrogen remaining, by the solution becoming dusky or
a black precipitate, but if it do not change its colour you may be satisfied the gas is
perfectly pure.
1242
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Litmus paper dipped in water is a good test for sulphuretted hydrogen: the dark
purplish blue, if this gas be present, changes its colour to red; if carbonic acid be present,
by adding a little lime water to it, an effervescence will take place when a few drops of
muriatic acid are added. Hydrogen gas affects
both silver and mercury; on mercury it pro-
duces a black film, and it soon tarnishes the
other metal.
Six tallow mould-candles, weighing a pound,
will burn forty hours, if lighted in succession;
a gallon of sperm oil, burnt during the same
time, will give a light equal to 15 such candles;
500 cubic inches of coal gas give a light for
an hour equal to one of the above candles, so that
it would require 20,000 cubic inches to be
equivalent to the 6 mould candles, or between
11 and 12 cubic feet of gas; the cost of which
is estimated at about 14d. per cube foot, as de-
livered for burning.

:
Oil Gas is generally admitted to be more
pure than that made from coal, and the process
for its manufacture is very simple: a furnace
is provided to heat the retort red-hot, the
front of which is a cylindrical cast-iron vessel,
with a cover fitted to its mouth, so as to close
it completely the retort is partly filled with
coke and broken brick, so that the oil, which
falls by drops upon the heated substance, may
be exposed to as large a heated surface as
possible. The oil is contained in a copper
vessel, and permitted to drop regularly through
a pipe upon the heated matter in the retort,
where it is decomposed, after which the gases
ascend into the cistern or condenser above,
formed of two iron vessels, one within the other,
and the space between is filled with cold water,
for the purpose of condensing the products of
distillation.
Mr. Beale has contrived an apparatus for the
production of a powerful light, by the con-
sumption of the refuse tar of the gas-works:
it consists of an external copper case, at the
bottom of which is a cock to discharge the
fluid, should it rise above the required level.
The tar is placed in the cylinder, and allowed
to mount in the pipe attached, which it does
by the pressure of the atmosphere, on the prin-
ciple of the Argand lamp; at the bottom of
the pipe is another, connected with a vessel, in
which air is contained under a pressure of
1½ pound per square inch: this by means of a
small cock can be opened or shut at pleasure.
When the tar is lighted, a small lambent flame
is first obtained, and when the compressed air
is admitted, it burns with a strong vivid white
light.
Fig. 1952,
OIL GAS.
Fig. 1953.
BEALE's light.
GILEDLOGGEDE

CHAP. XXI.
STEAM CONSIDERED AS A MOVING POWER.
FROM the elasticity of steam, which arises from the latent heat it contains, very early
advantage was taken of its power, and it is now universally applied for the purpose of
moving and impelling machinery: like all gaseous fluids, if steam be separated from the
CHAP. XXI.
1243
STEAM CONSIDERED AS A MOVING POWER.
fluid which generates it, it does not possess a greater quantity of elastic force than the
same quantity of air. The latent heat of steam may be taken at about 950°; steam at the
temperature of 212° contains 900° of heat, which is not detected by the thermometer
in its gaseous state, so that the real quantity of heat may be taken at 950° added to 212º,
or 1162º. If a quantity of steam be mixed with 5 times its weight of water, at 32° of
temperature, the water will rise nearly to the boiling point: when water is boiled, its
temperature never rises above 212°, nor does the steam which is produced; the only
effect is in the more abundant supply of vapour, but if the water be confined in the
vessel in which it is boiled, it as well as the steam may be brought to almost any tem-
perature.
Steam Engine. The high-pressure and the low-pressure are the two kinds in ordinary
use; the first is simple and composed of few parts, and well adapted for locomotive
engines, and other purposes where economy and portability are a consideration: the low-
pressure engine is, however, not only more durable, but consumes less fuel, and is the most
efficient for all ordinary purposes. The high-pressure engine is sometimes called the
non-condensing, to distinguish it from the low-pressure engine, which is called the con-
densing; sometimes in one engine the properties of both are combined. The high-pressure
engine now in use, the principles of which are more elementary and simple, was not
brought into practice until long after Mr. Watt had perfected the other.
:
High-pressure steam is produced by confining it within the boiler and increasing its
temperature and strength to a greater degree. The force of such steam is thus estimated :
a pound weight is placed upon a hole on the top of the boiler, exactly an inch square;
when the steam is powerful enough to lift the weight off the aperture on which it rests,
its power is said to be one pound on the square inch by placing a greater weight, a
greater elastic pressure is produced, and 1000 pounds on an inch have been measured by
this means.
The ordinary pressure given to engines of this kind varies from 15 to 120
pounds per square inch: when 15 pounds is the pressure, it is called one atmosphere,
or high-pressure steam of the elastic force of one atmosphere: 6 pounds of coals, em-
ployed in converting 6 gallons of water into steam, is equal in power to the labour of a
man for an entire day.
One of the simplest forms of application of high-pressure steam for the raising of
weights is by conducting the steam through a cylindrical tube, into which is inserted
a movable piston, on the top of which is placed a weight: when the steam issues from the
boiler, and passing under the piston, is strong enough to overcome the weight, the piston
will rise to any required height; if the weight be equal to one atmosphere, and the area of
the piston equal to a square inch, any increase in the pressure of the steam beyond one
atmosphere of elastic force will raise the weight.
The Atmospheric Engine is not worked by the direct and immediate agency of steam,
but by the atmosphere: the steam is here used only to make way for the atmosphere,
and give effect to its pressure. Engines of this description are usually constructed to
condense the steam in their own cylinders, and are used for either raising water or coals:
in construction they are simple, but when their cylinders are less than 24 inches in
diameter, the consumption of fuel is considerably above the effect produced. In forming
the cylinder it is usual to make its diameter half its length, and the velocity should be
about 98 times the square root of the length of the stroke in feet per minute. The area of
the steam passages is, as 4800, is to the velocity in feet per minute, so is the area of the
cylinder, to the area of the steam passage. The number of cube feet of water required per
minute for steam is found by multiplying the number of feet contained in the area of the
cylinder, by half the velocity in feet, and that product by 1·23 added to 1·4, divided by
the diameter in feet, and that quotient again divided by 1480. Twelve times the quantity
of water required for the purposes of steam is necessary for its condensation, and the aper-
ture by which it is injected should admit that quantity at every stroke that is made. The
area of the jet aperture should be the 850th part of the area of the cylinder, and the con-
ducting pipe four times the diameter of the jet.
To ascertain the power of an atmospheric engine, multiply 5.9 times the square of
the diameter of the cylinder in inches, by half the velocity of the piston in feet per minute;
the product so obtained expresses the effective power, or the number of pounds elevated
a foot high per minute; the horse-power is found by dividing by 33000. In a cylinder
with a diameter 72 inches, length of stroke 9 feet, and making 9 strokes per minute, it will
be shown by 9 x9=81; then 5.9 × 72 × 72 × 81 = 2477433-6 lbs. raised a foot per minute,
or 75 horse-power.
In the ordinary atmospheric engine, when the condensation takes place in the cylin-
der, it is closed at the bottom and open at top, as represented at C: at S is a passage
for the steam at the bottom of the cylinder, with a valve or cock at V: at I is the
passage for the cold water, which condenses the steam, with a cock at D: at E is the
passage for the water which has been injected to run out; this passage has a valve
1244
Book II.
THEORY AND PRACTICE OF ENGINEERING
at F, which prevents its flowing back again: at G is
a valve for the air to escape. The engine beam has
attached to it mechanism which opens and closes the
valves; and water is supplied at the top of the piston to
make the packing around it steam-tight. When the beam
is in the proper position, steam is admitted below the
piston by the valve V: this valve is then, by the action of
the beam, shut off, and the injection cock at D opened;
water then flows through the pipe at I, and condenses the
steam within the cylinder, after which it passes off through
the pipe E; the atmosphere then acting on the piston, P,
it is forced down, the air contained in the cylinder, and
produced by the condensation of the water, being suffered
to escape at G: connected with the beam is a bar having
a vertical movement; in this is attached lappets, which
open the steam and injection cocks or valves: the steam-
valve closing, and the injection cock opening when the
up-stroke is completed, the steam-valve is made to open
with the rise of the piston.

F
G
F
C
D
This kind of engine may be regulated by turning
off the steam, and cutting off the injection: a hot well Fig. 1954. COMMON ATMOSPHERIC.
supplies the water for the boiler, and about 16 pounds of
coal per hour for each horse-power is the quantity
required to work it; the boiler, whatever its form,
should have the steam limited to 1 pound on the
circular inch.
When this kind of engine has a separate condenser,
it is constructed as shown in fig. 1955.; the steam is
admitted by the pipe S, through the slide B, into the
cylinder at D; A is a pump with a solid piston,
which expels the condensed steam, air, and water,
the injection being made into the pipe E; I is the
injection cock; Fis a cock to let out any air that
may accumulate when the engine is not at work,
below the piston P.

P
D
B
Q
Fig. 1955. ATMOSPHERIC ENGINE WITH
When it is required to set the engine to work, the
slide B is raised above S, and sufficient steam is admitted
to drive out the air at the valve Q, the pistons, both
of the cylinders and pump, being up: the steam is then
shut off by the slide B, and the injection opened,
when, in consequence of the condensation which takes
place, both pistons descend, during which the cock F
must be opened, and then closed: the injection being
stopped, the slide B closes the opening to the con-
denser, and by again admitting the steam, the pistons
rise, and the air and water are driven out at Q; by opening and closing these passages alter-
nately, the action is continued: by closing the valve B during the ascent, and the cock I
during the descent, the engine may be regulated: the power of the atmospheric engine,
when applied to raising water, should have its velocity in feet per minute 98 times the
square root of the length of the stroke, and the diameter of the cylinder should be
half its length. The area of the steam passages should be to the area of the cylinder,
as the velocity of feet per minute is to 4800: the stroke of the air-pump should be half
that of the piston, and its diameter three-eighths that of the cylinder.
SEPARATe condenser.
To ascertain the quantity of steam, multiply the number of feet contained in the area
of the cylinder by half the velocity in feet, with the addition of one-fifth of loss for cooling;
this result divided by 1480 gives the quantity of water requisite to supply the boiler; and
for injection, twenty-four times that quantity will be required. The aperture by which
the injection is made should have its diameter one-thirty-sixth that of the cylinder, and
the pipe one-ninth.
The power of the engine is found by multiplying 6.25 times the square of the diameter
of the piston by half the velocity in feet per minute, and the product is the effective power
in pounds raised one foot high per minute; this divided by 33,000 gives the horse-power.
The cylinder being 32 Inches in diameter, and the velocity 220 feet per minute, we have
6·25 × 32º × 110=704,000 pounds, or 21 horse-power; 29.4 feet of water is required
per hour, and 246 lbs. of caking coal, or 11.7 lbs. for each horse-power.
Steam Pressure Engines. Boulton and Watt's Single Engine, as applied to the raising of
water. The boiler is surrounded with brickwork, and the steam passes by the pipe b to
CHAP. XXI.
1245
STEAM CONSIDERED AS A MOVING POWER.
the cylinder, which is securely fixed to the floor; a lid at e covers the top; through this
slides the piston-rod in an air-tight stuffing-box; the beam moves on its gudgeons, the
bearings for which are properly sustained: a pump-rod carrying a counter-weight is
suspended at the end of the beam at g, and both it and the piston rod k are connected by
a parallel motion to the working beam, fg: at m is the condensing cistern, which con-

พ
20
b
k
THE
20
n
Em
y
C
Fig. 1956.
BOULTON AND WATT'S SINGLE-ACTING ENGINE.
tains the air-pump, n, the condenser and hot well, o. By the action of the cold water
pump, a continued supply is obtained, and all excess is carried away to the well by the
waste-pipe: r is the upper steam valve, s the lower one, t the exhausting valve; these
are all opened by the plug tree, v, and the lappets with which it is furnished. Water is
raised from the hot well, o, by the pump, to supply the boiler, and is carried by a pipe,
ww, into a small cistern, x, on the top of the feed-pipe, which has a valve, acted on
by a lever, attached to a wire passing through the stuffing-box to a stone float in the
boiler, which opens the valve by its descent, and permits an additional quantity of water to
flow in when required.
The Single-acting Engine differs from the double in the arrangement of its pipes and
valves, as shown in fig. 1959. the steam is condensed into the state of water: the moving
force equals the power of the steam: there are two cylinders; one admits the steam at
the top, and another, called the condenser, admits the steam at the bottom, from the
lower part of which is the passage to the air-pump. The cylinder in which the piston
works is shown at C, the condenser at B, and the air-pump at A: by the pipe S the
steam passes from the boiler through a valve at O, by which the piston, P, is forced down;
the steam which is beneath it passes into the condenser, the bucket, p, of the air-pump
descending at the same time: the rod O receives a motion when the piston has arrived at
the bottom of the cylinder, which opens the valve b, and shuts those of a and c.
pipe E has then a communication with both the bottom and top of the cylinder: the
jet is stopped, and the cylinder and condenser again filled with steam from the boiler;
the piston is raised by a counterweight to the top of the cylinder; this counterweight is
applied to the opposite end of the beam to that on which the piston-rod is fixed: when
the cock is open, which allows the steam to pass from the boiler into the cylinder, the
steam in the condenser, and below the piston of the cylinder, is, by the playing of the
jet of cold water into it, reduced to water; when the pressure on the top of the piston
being equal to the force of the steam in the boiler, and that below being small, the piston
is pressed down, and thus raises an equivalent weight at the opposite end of the beam.
The
The passage to the condenser is shut off when the piston reaches the bottom of the
cylinder; a valve in the piston then opens, and allows the steam to pass through it:
the piston rises by the action of the weight placed on the opposite end of the beam.
1246
THEORY AND PRACTICE OF ENGINEERING. BOOK II.

When the piston is
at the top this valve
closes, and that of
the condenser opens.
The air-pump
during this and the
succeeding opera-
tions is worked by
the beam, and at
each stroke of the
piston makes a
simultaneous move-
ment, and thus is
enabled to pump
out the air and water
which is the result
of each condensing
operation.
G is a

H
C
N
A
M
Fig. 1957. SINGLE CONDENSING ENGINE.
es
C
F
V
a
F
foot-valve between
the condenser and
the air-pump, M,
which has a dis-
charge valve at Q,
through which the
air and hot water
are forced into the
hot well, shown at
K: a pipe at N constantly supplies the cistern which
contains the condenser and air-pump with cold water.
The condenser has a flow valve at H: at the end of a
pipe is a rose, which admits the jet, through which the
cold water passes into B, and this is forced into it, and
made to spread through the steam as much as possible, for the purpose of speedily con-
densing it.
Fig. 1958.
D
The diameter of the cylinder should be half its height, and the velocity of the piston in
feet per minute ninety-eight times the square root of the length of the stroke: the
steam passages should be equal to the area of the cylinder multiplied by the velocity
of the piston per minute, and divided by 4800. The air-pump should have half the
diameter, and half the length of stroke of the cylinder, or should be one-eighth of the
dimensions of the cylinder, and the condenser should be equal to it. The quantity of
steam is ascertained by multiplying the number of feet contained in the area of the cylinder
by half the velocity in feet, adding one-tenth for waste; this, divided by the column of
steam of equal force to that contained in the boiler, gives the quantity of water required per
minute for the creation of steam, from whence the proportions given to the boiler are estab-
lished with the pressure of two pounds per circular inch on the valve, the divisor will be
1497. The water for the purposes of injection will be twenty-four times that required for
steam; consequently the diameter of the pipe used for this purpose must be about a
thirty-sixth of the diameter of the cylinder: usually the force of the steam in the boiler
equals 35 inches of mercury, that of the steam in an uncondensed state 3·7 inches.
find the effective power of such an engine, or the number of pounds raised a foot high per
minute, multiply 6.66 (which expresses the number of pounds of the mean effective
pressure on the piston) by the square of the diameter of the piston in inches, and by half
the velocity in feet per minute: the product is the effective power; this divided by 33000
gives the horse-power.
:
To
Double-acting Steam Engine. The steam cylinder is enclosed in a jacket or casing of
cast-iron, a trifle larger than the cylinder, and the space between them is supplied with
steam, to keep the temperature of the cylinder as near to that of the steam as possible.
The working beam is supported by a cast-iron column, and is connected to the piston-
rod by the parallel motion: the other end of the beam gives a rotary motion to the
crank shafts, by means of a connecting rod, the lower part of which is attached to the
crank. The steam enters at S, passes through the top valve, and acting on the piston
forces it down; before it arrives at the bottom of the cylinder, the plug on the rod R
comes in contact with a lever, shuts one valve, and opens another; the steam then
continues its course down the pipe S, acts on the bottom of the piston, and forces it up to
the top of the cylinder, while the steam, which forced it down, escapes into the condenser
B, where it meets with a jet of cold water, is condensed, and then cleared away by the
action of the air-pump A, which is worked by the rod R. The cistern is supplied with
CHAP. XXI.
1247
STEAM CONSIDERED AS A MOVING POWER.
cold water by the pump N; the governor, put in motion by bevelled wheels on the shaft
of the fly-wheel P, regulates the throttle-valve in the steam-pipe S: in the pumping
apparatus, the rod M is the pump-rod for raising water; when the rod descends, the water
will be forced through G into the upper air-vessel E, from whence it passes to the reservoir,

P
R
M
N
E
H
A
S
B
Fig. 1959.
DOUBLE-ACTING ENGINE.
at a distance and height proportionate to the power of the engine: the barrel of the pump
is refilled from the pipe F, which communicates with the lower air-vessel H.
The Double-acting Engine of Boulton and Watt (fig. 1962.) differs from that already described,
by having a passage from the boiler, both at the top and bottom of the cylinder, and similar
communications from both to the condenser: the counter-weight at the end of the beam
is not here required to raise the piston. The force of the steam impels the piston both
upwards and downwards, and a double power in the same space and time is obtained by
the use of a double quantity of steam: the steam enters the cylinder at S, passing by F
into the upper, and by D into the lower part: through D the steam escapes into the
condenser B, and during the ascending stroke, the uncondensed gases and water escape by
the valve G; when descending, they pass through the valve of the pump-bucket, and at
the ascending stroke are driven out at the valve Q into the hot well.
The steam passes
through F, down the pipe E, to the condenser, from the upper portion of the cylinder;
during the time the piston P is in the action of ascent, D slides open and closes the
passages at D and F, through the means of the rod O. The diameter of the cylinder
should be half its height; the velocity of the piston in feet per minute is found by
multiplying the square root of the length of the stroke by 103 for machinery, or by 98 for
raising water. The area of the cylinder multiplied by the velocity of the piston in feet
per minute, divided by 4800, gives the area of the steam passages. The air-pump should
have half the diameter of the cylinder, and half the length of stroke, or one-eighth
of the capacity of the cylinder, and the condenser should be equal to it.
The area
1248
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
0
of the cylinder in feet multiplied by the velocity in feet, with the addition of one-tenth for
waste, gives the quantity of steam; and this again divided by the volume of steam gives
the quantity of water required per minute for steam: the proportions of the boiler may
then be determined; at the common pressure of two pounds per circular inch on the
valve, the divisor will be 1497. The water for injection
must be 24 times that required for steam; and the dia-
meter of the injection-pipe made one-36th that of the
cylinder. The effective power of such an engine is found
by multiplying the effective pressure on the piston by the
square of its diameter in inches, and that product by the
velocity in feet per minute:

the quantity of pounds raised
one foot high per minute
being obtained, and divided
by 33000, gives the horse-
power, and each horse-power
requires a supply of 9-2 lbs.
of coal per hour; but when
the engine is less than ten
horse, the quantity required
is increased such an engine
is applicable to all purposes,
and when steam is made to
act expansively, the power is
obtained with less fuel; when
so applied, a fly-wheel equal-
ises its motion. Fig. 1961.
shows the steam shut off, and
the passage to the condenser
still open.
Fig. 1960. repre-
sents its state when steam is
let on at the bottom : the
letters refer to corresponding
portions of fig. 1962.
which
P
Fig 1962.
S
D
0
P
F
田
​Fig. 1960.
Fig. 1961.
DOUBLE-Acting conDENSING ENGINE.
One of the earliest engines
with a
double-action was
made by Mr. Watt, in 1782,
and some years afterwards
two of fifty-horse power each
were put up at the Albion
Mills, Blackfriars,
jointly drove 20 pair of mill-
stones, of which 12 or more,
with all the machinery for
dressing the flour, were generally kept at work. In this engine (fig. 1963.), A is
the cylinder, 34 inches in diameter; B, the piston, which has an 8-feet stroke; C, the
piston-rod; D, the stuffing-box, or cover of the cylinder; E, the steam-case or jacket
of the cylinder, from which a siphon empties the water, and which is supplied by
a pipe; G, the upper steam nozzle and valve or regulator box and regulator; H,
the upper exhaustion nozzle and valves; I, the perpendicular steam-pipe; J, the educ-
tion-pipe; K, the lower steam nozzle and valve; L, the lower exhaustion nozzle and
valves; M, the condenser, immersed in a cistern of cold water, the injection
cock being always open during the working of the engine; O, the blow-valve;
P, the air-pump; Q, the lower valve and air-pump; R, the bucket and rod of the
air-pump; S, the upper valve of the air-pump; T, the hot water pump, with the
bucket and rod; U, the cold water pump; V, the pump for supplying the boiler; W, the
governor, turned by a belt from the shaft of the fly-wheel; X, the lever and rod, which
connects the governor with the throttle valve t; Y, the working gear of the nozzle valves;
Z, the plug-tree which drives the working gear; a, the main lever or working beam; b,
its main gudgeon; c, the perpendicular links of the parallel motion; d, the parallel
bars; e, the regulating radii; ƒ, the small perpendicular links; g, the secondary parallel
motion for the air-pump; h, the connecting rod; i, the planet-wheel fixed to the con-
necting rod; j, the iron wheel; k, the shaft of the fly-wheel, on which the iron wheel is
fixed; 1, the connecting link, which retains the planet-wheel in its orbit; m, the fly-wheel;
n, the boiler; o, the tube through the boiler and the tube round it; p, the grate; q, the
feeding mouth; r, the damper; s, the chimney; t, the feed-pipe; u, the gauge pipes, with
the cocks; v, the safety-valve.
CHAP. XXI.
1249
STEAM CONSIDERED AS A MOVING POWER.
The boiler is generally made of iron, though formerly copper was used; and by means
of a pipe the steam passes from the boiler to the upper nozzle G, and by the perpen li

C
d
g
น
Y
W
n
E
A
Z
a
P
T
Fig. 1963.
ENGINE At the albION MILLS.
cular steam-pipe I, to the lower steam nozzle K: in the nozzle G there is a valve, which
when open admits steam into the cylinder above the piston B, through the horizontal
square pipe at the top of the cylinder, and in the lower steam nozzle K there is another
valve like that at D, which, when opened by the pin of the plug-tree, admits steam into
the cylinder below the piston. In the upper exhaustion nozzle, H, there is a similar valve,
which when open allows steam to pass from the cylinder above the piston into the educ-
tion-pipe J, which conveys it to the condensing vessel M, where it meets with the jet
of the injection from the cock N, and is reduced to water; and in the lower exhaustion
nozzle L, there is also a valve, which when open allows the steam to pass out of the
cylinder below the piston into the condenser M.
The engine being at rest, the cylinder quite cold, and the condenser cistern full of water,
when the water in the boiler begins to boil, steam will enter by the small pipe ƒ into the
space between the cylinder and the heating case E, which will expel the air contained in
that space, and between the two bottoms of the cylinder, at a cock fixed in the outer bottom,
which, when all the air is expelled and the cylinder thoroughly warmed, is to be shut, and
the water which may be formed in these spaces during the working of the engine will issue
by the inverted siphon e.
The first operation after this state is to open all the four valves, G, H, K, L; the in-
jection cock being shut, the steam will drive the air out of the pipes I and J, and out of
the condenser M, through the blow-pipe and its valve O, and as soon as this is succeeded
by a sharp crackling noise in the cistern O, the valves are to be shut, until it is thought
that the steam which has entered is entirely condensed; the same operation is to be
repeated, giving a longer time to cool between the times of blowing, until it is found upon
opening the injection cock some water will enter, and the barometer shows some degree of
exhaustion, after which the repetition of blowing will soon empty the cylinder of air. The
piston being then at the top of the stroke, the valves G and L are to be opened, and the
flywheel m turned by hand about of a revolution or more in the direction in which it
is intended to move; the steam which is then in the cylinder will pass by L into the
condenser, when, meeting with the jet of water from the injection cock, it will be converted
into water, and the cylinder thus becoming exhausted, the steam entering by the valve G will
press upon the piston, and cause it to descend, while by its action on the working beam,
through the piston rod, it pulls down the cylinder end of the beam, and raises up the
outer end, and the connecting rod h, which causes the planet-wheel i to tend to revolve
round the sun-wheel j: but the former of these wheels being fixed upon the connecting
rod, so that it cannot turn upon its own axis, and its teeth being engaged in those of the
4 L
1250
Book IL
THEORY AND PRACTICE OF ENGINEERING.
sun-wheel, the latter and the fly-wheel, upon whose axle and shaft it is fixed, are made to
revolve in the desired direction, and give motion to the mill-work.
As the piston descends, the plug-tree Z also descends, and a clamp or slider q, fixed
upon the slide of the plug-tree, presses upon the handle I, of the upper shaft or axis,
Y, and shuts the valves G and L; and by the same operation, by disengaging itself,
permits a weight suspended to the arm of the lower Y shaft to turn the shaft upon
its axis, and thereby to open the valves K and H. The moment previous to opening
these valves, the piston reaches the lowest part of its stroke, and the cylinder above
the piston is filled with steam; but as soon as H is opened, that steam rushes by the
eduction-pipe J into the condenser, and the cylinder above the piston becomes exhausted;
the steam from the boiler, entering by I and K, acts upon the lower side of the piston, and
forces it to return to the top of the cylinder; when the cylinder is very near the upper
termination of its stroke, another slider a raises the handle, and in so doing disengages
the catch, which permits the upper Y shaft to revolve upon its own axis, and open the
valves G and L, and the downward stroke recommences, as has been related.
When the piston descends, the buckets, R, S, of the air-pump and hot-water-pump T
also descend; the water which is contained in these pumps passes through the valves of
their buckets, and is drawn up and discharged by them through the trough t, by the next
descending stroke of the piston: part of the water is raised up by the pump V, for the
supply of the boiler, and the rest runs to waste. Engines of this kind, as described by
Mr. Watt, were employed in producing rotary motions, but they were also used to work
pumps by a reciprocating motion: for this purpose half of the pump-rods were sus-
pended by means of a sloping rod from the working beam near the cylinder, and the other
half were suspended directly from the outer end of that beam, so that the ascending motion
of the piston pulls up one-half of these rods, and works the pumps to which they belong,
while the descending motion of the pistons pulls up the other half of the rods, and works
their pumps such an engine was employed at Wheel Maid Mine in Cornwall; it had
a cylinder of 63 inches in diameter, and 9 feet stroke; but the stroke in the pumps, which
were 18 inches in diameter, was only 7 feet.
Mr. Watt gave the following account of the actual performance of one of his engines,
working in the Cornish mines : — "One bushel of good Newcastle or Swansea coal in the
reciprocating engine, working more or less expansively, was found to raise 24,000,000 to
32,000,000 pounds of water one foot high. In engines upon the rotative double construc-
tion, one having a cylinder of 31½ inches in diameter, and making seventeen strokes and a
half of 7 feet long per minute, called forty-horse power, consumed about four bushels of
Newcastle coal per hour, or four cwt. of Wednesbury coal. A rotative double engine with
a cylinder of 233 inches in diameter, making twenty-one and a half strokes of 5 feet long
per minute, was called twenty-horse power; and an engine with a cylinder of 17½ inches
diameter, making twenty-five strokes of 5 feet long per minute, was called ten-horse
power; and the consumption of coals was nearly proportionate to that of the forty-horse
power: a bushel of Newcastle coals, which is the quantity a ten-horse engine consumes
per hour, grinds and dresses about ten bushels of wheat.
Hornblower's Engine with two Cylinders, though it does not essentially differ from the one
already described, displays much ingenuity: the chief parts are two cylinders, A, B, the
largest of which is A; a piston moves in each, having their rods, C and D, moving
through collars at E and F: these cylinders are supplied with steam by means of the
square pipe G, which has a flanch to connect it with the rest of the steam-pipe; this square
part branches off to both cylinders; c and d are two cocks, worked by the plug W by
means of handles and tumblers: on the foreside of the cylinders is another communicating
pipe, whose section is square or rectangular, having also two cocks, a, b: the pipe Y, imme-
diately under the cock b, establishes a communication between the upper and lower parts
of the small cylinder, B, by opening the cock b: there is a similar pipe on the other side
of the cylinder, A, immediately under the cock d; when the cocks c and a are open, and
the cocks b and d are shut, the steam from the boiler has free admission into the upper
part of A, but the upper parts of each cylinder have no communication with their
lower parts from the bottom of the great cylinder proceeds the eduction pipe K,
having a valve at its opening into the cylinder, which bends downwards, and is connected
with the conical condenser, L. The condenser is fixed on a hollow box, M, on which
stand the pumps N and O for extracting the air and water, which last runs along the
trough T into the cistern U, from which it is raised by the pump V for recruiting the
boiler, being already nearly at a temperature of 212°; immediately under the condenser
is a spigot valve, at S, over which is a small jet pipe, reaching to the bend of the eduction
pipe.
The cistern of cold water, R, contains the whole of the condensing apparatus; a small
pipe P comes from the side of the condenser, and terminates at the bottom of the trough
T, and is there covered with a valve Q, which is kept tight by the water that is always
running over it; the pump-rods X "ause the outer end of the beam to preponderate, so
CHAP. XXI.
1251
STEAM CONSIDERED AS A MOVING POWER.
:
D
C
W
d_c G
E
F
that when the engine is at rest, it is as represented. The cocks being all open and
the steam issuing copiously from the boiler, and no condensation going on at L, the steam
must drive out all the air, and at last
follow it through the valve Q: on
shutting the valves b and d, and open-
ing the valve S of the condenser,
condensation will immediately take
place at this time there is no pres-
sure on the under side of the piston
at A, and it immediately descends.
The communication between the lower
part of B and the upper part of A
being open, the steam will go from
B into the space left by the pis-
ton of A it must therefore expand,
its elasticity diminishing, and will
no longer balance the pressure of
the steam above the piston of B.
This piston therefore, if not withheld
by the beam, will descend until it is in
equilibrio, having steam of equal den-
sity above and below it; but it cannot
descend so far, for the cylinder A is
wider than B: and the arm of the beam
at which the piston hangs is longer than
the arm which supports the piston of
B; therefore when the piston of B has
descended as far as the beam will
permit it, the steam between the
pistons occupies a larger space than it
did when both pistons were at the tops
of their cylinders; and its density
as well as its elasticity diminishing
as its bulk increases, it is no longer
a balance for the steam on the upper
side of B, which piston pulls at the beam with all the difference of their pressures:
as the pistons descend, the steam that is between them grows continually rarer and less
elastic, and both pistons pull the beam downwards.

X
V
K
Q
R
U
P
M
B
Y
A
Fig. 1964. HORNBLOWER'S DOUBLE CYLINDER.
When each has reached the bottom of the cylinder, if the cock a and the eduction cock at
the bottom of A be shut, and the cocks b and d be opened, the pistons will arrive at the top: the
cylinder B is now filled with steam of the ordinary density, and the cylinder A with an equal
absolute quantity of steam, but expanded into a larger space : on shutting the cocks b and d,
and opening the cock a, and the eduction cock at the bottom of A, condensation will again be
produced, and the pistons descend: thus the operation is continued. When both pistons are at
the top of their cylinders the active pressure on the piston at B is nothing, while that on the
piston of A is equal to the full pressure of the atmosphere on its area: this multiplied by
the length of the arm by which it is supported gives its mechanical energy :
as the pistons descend, the pressure on the piston of B increases, while
that on the piston A diminishes; when both are at the bottom, the pres-
sure on the piston of B is at its maximum.
Boilers.. Much yet appears to be wanting in practice to enable us to
construct a perfect boiler, and science has not succeeded in determining the
best form it should have: early in their application to the steam-engine, they
were of a spherical shape, in consequence of that figure having the largest
capacity with the least material; it was also fancied to be the strongest: a
boiler of this form, placed upon an open fire, required a large quantity of fuel
to raise a small quantity of steam, the heat being carried away by the sur-
rounding air, and one of the first improvements was setting it in brickwork,
or some non-conducting material that would bear the effect of the fire. The
flues were so constructed that the flame, after passing below the sphere,
wound round the sides in a spiral direction, and then passed off to the
chimney, a damper being introduced to regulate the draught: this gave
way to the cylindrical boiler, which was in a short time improved by
making the top hemispherical, and arching the bottom upwards in order
that a larger surface might be offered to the effects of the fire; the sides
were inclined in such a way that the flame acted in a slight degree upon
them.

4 L 2
Fig. 1965.
1252
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
The Waggon Boiler in its transverse section resembles that
already described, but its length is much greater in proportion,
and the sides are usually concave, that the flue constructed
at their side may have more effect upon them. This form is
in general use, and it is convenient, but not so strong, a
small pressure having been found adequately sufficient to
make these boilers bulge downwards and to press the sides out-
wards. To avoid these consequences strong iron stays are in-
troduced within; they are applied in various ways, and have
generally successfully resisted both compression and bulging.
The Cylindrical Boiler with hemispherical ends is one of
the best forms, where safety and cheapness are considered; the
flame is made to pass under it longitudinally, and heat its
whole length: when it has arrived at the farthest end, hot air
returns by means of a brick flue along one side, passes over
the front end, returns along the
other side, when it enters the
chimney, after having traversed
the whole length of the boiler
three times: when space is not
important, this form of boiler is
highly valuable.

Fig. 1967.
Fig. 1968.
-157
Fig. 1966.



Fig. 1969.
The power of a boiler de-
pends upon the extent of sur-
face exposed to the action of the
fire; heat passes through the boiler with a certain rapidity, and each square foot evapo-
rates three-fifths of a gallon of water per hour: to boil off a cubic foot of water in that
time will require 9 or 10 superficial feet of heating surface, and its quantity constitutes
the power of 1-horse in the steam-engine; so that a boiler with 100 superficial feet
exposed to the action of the flame will convert into steam 60 gallons of water in an hour,
which is called a 10-horse power; the extent of heating surface, and not the contents of
the boiler, measuring its power.
In the construction of a boiler regard must be had to the due adjustment and combina-
tion of all its parts, so that, while an extensive heating surface is obtained, any portion of it
becoming damaged may be readily repaired: and the flues must be so formed that they
can be readily got at and cleansed, and as much heat as possible obtained from the fuel,
without the draught up the chimney being materially interfered with.
Boilers must be so capacious that the quantity of water to be boiled does not entirely
fill them, but a sufficient space is left above its surface as a reservoir, for the steam as it
is generated; if this were not provided for, the cylinder to be filled with steam might
contain more than the volume of the boiler, so that it could not be regularly supplied, or
with the speed necessary: when the boiler is made to contain five or six times the volume of
the cylinder, one volume may pass off without any material change in the density of what
remains, and the speed of the machine can be kept up: the water in the boiler must
never rise above a certain level, and there should be sufficient quantity to produce steam,
and protect the boiler from any injury from the fire. According to some writers, it
should contain steam enough for eight or ten strokes of the engine, the quantity of water
required for which is usually admitted into the boiler by a pump regulated by a float-ball;
the temperature should be such that on its admission that of the steam is not reduced
more than one-thirtieth, which is the case when the temperature of the water is reduced but
two degrees; there ought to be in the boiler, then, about sixty-two times as much water as
is introduced at one feed, or the elastic force of the steam will be lowered more than one-
thirtieth: less water is required at a time, when the feeding apparatus acts frequently, and
this should be introduced as hot as possible into the boiler; when fed at every stroke,
5 cubic feet of water should be allowed for every one of steam that it boils off in an hour:
it is usual to allow 25 cubic feet of boiler for each horse-power, though this depends upon
its form and application. The form usually given to boilers is rectangular, with a top
consisting of the portion of a cylinder, the bottom a little concave, and the sides flat: in
large boilers a flue passes through the middle, which is surrounded by water; they should
always be constructed to consume as small a quantity of fuel as possible, and care should be
taken that the air which passes through the fire shall part with all its heat before it
escapes.
Rectangular Steam Boiler, with the top plate removed to show the internal arrange-
ment: A, is the boiler; fire-door B; bars G; back F: the flames pass over F, under the
bottom, rise at H and round I; then by another flue to the chimney at L, which is
regulated by a damper at K: C is the ashpit, the door of which is made perfectly close,
the air passing to the fire by the passage E, which enters by a grating at D: the pipe MN
CHAP. XXI. STEAM CONSIDERED AS A MOVING POWER.
1279

H
W
Fig. 1970.
K
M
N
A
D
S
F
G
B
RECTANGular steam boiler.
E
supplies the water; the steam passes to the engine by the
pipe S, and when not required goes off through the safety-
valve V, and through the pipes T, W.
To find the dimensions of a boiler without an internal flue,
we must divide the solid content of the water it contains by
the area of the bottom: we thus obtain the depth of water;
then multiply the bottom and side surface for fire and
flue, and divide the product by twice the capacity for
water, less the area of the bottom surface, and the result
will be one of the dimensions for the bottom; then divide
the bottom surface by the dimensions found, which gives
the other dimension. Cylindrical boilers, which are used
for the production of high-pressure steam, may have their
diameter and length found by adding their capacity for
water and steam together, and also the quantity of surface
for the action of the fire; then divide twice the capacity
by the quantity of fire-surface for the diameter: the capacity
multiplied by 1.27, and divided by the square of the
diameter, gives the length of the boiler.
The Materials of which Boilers are usually made are either
1973
1971
1972
100
00
1974
Fig. 1975. BOILER. 1976.
4 L 3
1954
Book II.
THEORY AND PRACTICE OF ENGINEERING.
iron or copper; cast-iron as well as wrought-iron plates are commonly applied; where fuel
is abundant, cast-iron boilers, with proper care, have been extensively and advantageously
employed. Copper, however, is decidedly the best of all substances for this purpose, cost
being the only objection; one copper boiler will, however, probably endure as long as
five or six iron ones, the uniformity of its texture at the same time insuring greater
security against bursting, though its strength to resist flexure at high temperatures is
not equal to that of iron; sheet-iron is liable to vary materially in its structure, although
manufactured by the same process. The pressure which occasions the bursting of a boiler
is proportional to the load on its safety-valve; that to crush it together is equal to the power
of the atmosphere: the boiler should always be of such a strength that when in a
working state, it will bear three times the pressure of what is on the valve; in low-
pressure this may be too much, but in high-pressure boilers it is insufficient.
Copper loses 5 per cent. of its strength between the temperature of freezing and boiling
water; at 550° a quarter of its strength; at 850° it loses one-half; and at 1330° it
is entirely lost, becoming an incohesive substance, although it does not totally melt till
it reaches 2000°. Iron plate, on the contrary, increases in strength, for at a temperature
of 550° it is 16 per cent. stronger than when cold: after this point its strength rapidly
diminishes, so that its maximum of strength does not certainly exceed 570°. The specific
gravity of iron boiler plates is said to be about 7-7344, and by repeated piling and welding
a great increase of strength may be obtained: the greatest practical strength is only to
be taken at one-sixth of the absolute cohesion; and to prevent explosion, we ought to have
four times the strength that any boiler is ordinarily worked at; 2500 pounds of extension
on each square inch of cohesive action is the safe working strain for those made of iron.
To ascertain the thickness of the boiler plates made of any of the ductile metals the
following rules are given: for the upper plates, when of iron, multiply the load in pounds
per circular inch on the safety-valve, by the greatest diagonal of the section in inches, and
divide the product by 120 times the cubic contents of the boiler per horse-power; the
result is the thickness in inches: when the plates are copper, divide by 72 instead of 120;
it is usual to increase the thickness of the bottom plates to about one and a half times
those of the upper.
For spherical boilers, of malleable iron, multiply the diameter in
inches by the pressure on the valve in pounds per circular inch, and divide by 240 times
the cubic contents of the boiler for each horse-power. For copper, divide by 144, instead
of 240. When cast-iron is used, its unequal expansion must be taken into account; and for
the strength of tubes exceeding 8 inches in diameter, multiply the square of the diameter
by the pressure on the safety-valve in pounds on a circular inch, and divide the product
by 150 times the cubic feet of space in the boiler per horse power, multiplied by the
difference between the diameter and 7.4 inches; the result is the thickness in inches that
should be given, together with some increase for wear and tear: thus, with a tube the in-
ternal diameter of which is 10 inches, the cubic feet of the boiler per horse-power being 10,
and the load on the safety-valve 36 pounds on the circular inch, its thickness will be found
to be '92 inches: when the thickness is greater, the risk from unequal expansion increases;
and when less, failure may result from the effect of pressure and inequalities in the iron itself.
The Piston Gauge is a small tube 2 inches in diameter; the cylinder has a solid plug
turned and ground, to set loosely in it, the pressure of the
steam bearing up the piston on the level, one end of which,
attached to the spring indicator, gives the pressure of the
piston.
Mercurial Gauges of various kinds are applied to the crowns


PISTON GAUGE.
1978.
Fig. 1979.
MERCURIAL GAUGE.
Fig. 1980
DYNAMOMETER.
Fig. 1977.
of boilers, which, by means of a graduated scale above, mark off the pressure at all times
exerted by the steam.
The Dynamometer, employed to measure the force of steam in the boiler, is a simple bent
tube, of glass or iron, in the form of the letter U, the two ends of which are curved; one
is applied to the boiler, and placed in communication with the steam: half the tube is
filled with mercury, which rises and falls according to the pressure exerted on it.
CHAP. XXI. STEAM CONSIDERED AS A MOVING POWER.
1255
Water Gauge is an instrument attached to the steam-engine boiler for the purpose of regu-
lating the quantity of water and fuel, as well as the combustion and elasticity of the steam.
The Glass Gauge attached to steam-engine boilers is either of flat or tubular glass:
the first description consists of a small


window, made of very thick glass, inserted
in the boiler, at the place up to which the
water should rise.
The Tubular Glass Gauge is a small pipe
of glass, about inch in diameter internally,
and 14 inches thick: it is placed outside
the boiler, and communicates at the top and
bottom by stopcocks with the interior of the
boiler: the higher stopcock enters where
the steam is a little above the surface of the
water, so that the water, standing in the glass Fig. 1981.
tube on the same level with the water in the
boiler, is shown to the attendant.
WINDOW
GLASS GAUGE
Fig.1982. TUBE GLASS
GAUGE.
Feeding Apparatus for Boilers is for the purpose of supplying it with water, in lieu of
that passing off continually as steam: a simple form, adapted to a low-pressure engine, may
have the water conducted into the reservoir of about 18 inches diameter, with a pipe
to conduct from it into the boiler: the top of this pipe may be closed by a conical plug,
hanging at the end of a rod Vr, from a lever supported at f,
and having two weights W and u; that of W rests on the
surface of the water in the boiler, which falls whenever the
water is below its proper level. The arm L is pulled down by

ENGL
1903
L

น
Fig. 1983.
FEEDING Apparatus.
the rod LW, which passes through a steam-tight stuffing-box;
by the same motion the lever L ascends and opens the valve
V, and allows the water to descend to replenish the boiler.
W
SELF-REGULATING
FEEDING APPARATUS.
This description of valve answers when the boiler is low-
pressure, or when the reservoir is more than 26 inches above Fig. 1984.
the surface of the water for every pound of pressure per square
inch of the boiler; for the height of the water in the cistern should be sufficient to balance
the strength of the steam, and if this height be too small, the water in the boiler will be
forced up the feed-pipe, and driven by the steam out of the valve. Water at a temperature
of 60°, 2.94 feet in height, is equivalent to one pound on the circular inch, but the water
in the feed-pipe is about 212°, so that 3 feet is required in height for every pound on
the circular inch: it is necessary that the stone float should be placed in that part of the
boiler where the steam will least affect it, and the feed-pipe should be as far away as possible
from where the greatest quantity of steam is produced.
In High-Pressure Engines, the water is supplied to the boiler by a forcing-pump, worked
by a lever connected with one of the reciprocating portions of the engine, and the water
supplied by a pipe that traverses the steam which escapes, so as to become raised
in temperature before it is admitted to the boiler: in order to proportion accurately the
quantity of water to be supplied, we must remember that there is exactly one cubic inch of
water for each cubic foot of atmospheric steam given to the engine, or one cubic foot
equal to six gallons per horse-power per hour: but as the evaporation does not proceed
uniformly, in consequence of variation in the intensity of the fire, which causes steam
of greater or less density to pass into the engine, the steam sometimes falling below the
standard and at others escaping through the valve, it is necessary to have some further
means of regulating its supply. In some engines this is effected by a float; a stop-cock
attached to the pipe of the feed pump will enable the attendant to regulate the
4 L 4
1 256
THEORY AND PRACTICE OF ENGINEERING. BOOK II.

supply this may be
effectually done by
having between the feed
pump and the boiler a
loaded escape-valve V,
its load W being so ad-
justed that whenever the
stopcock R is turned to
impede the passage of the
water towards the boiler,
the force of the feed-
pump pushes against the
loaded valve at V, and by it passes through the
return pipe into the reservoir of supply; this
adjustment requires the attention of an attendant.
:
Fig. 1985.
Safety-valves are of the utmost importance,
and the greatest care should be bestowed on
their construction; the earliest consisted simply
of a weight laid on a hole in the top of the
boiler but this plan cannot be adopted when
the pressure is high and the weight great, be-
cause it becomes unsteady: a valve is therefore
used, as in fig. 1989., carefully ground to its seat;
a spindle rising upwards carries a series of
weights which may be increased or diminished;
this being attended with inconvenience, a valve
with an internal weight (fig. 1990.) has been
contrived: but in all these modifications, when
the pressure is high the weight becomes cum-
brous. The lever safety-valve was introduced to
谁
​Fig. 1987. LEVER VALVE.
W
PIPE OF FEED-PUMP.

Fig. 1986. SAFETY-VAlve.

Fig. 1988. FRENCH SAFETY VALVE.
1990
Fig. 1989. COMMON SAFETY-VALVE.
五
​Fig. 1991. sOUTHERN'S Safety-valve.
Fig. 1992.
Fig. 1993. SPRING VALVE.
obviate this (fig. 1987.); a single weight hung on the longer arm of
a lever produces an effect proportional to its distance, and the lever
being graduated shows the amount of this effect. The form of fig.
1988. indicates still more correctly the point at which the pres-
sure of the steam becomes equal to that on the valve which is flat
or cylindrical, and acted on by a lever having equal arms with
weights on each; these rest on light rollers, so as to run down
from their places and release the steam entirely when the pressure
reaches the prescribed limit. Figs. 1991. and 1992. show the form
used by Mr. Southern in his experiments on high-pressure steam,
the first when closed, the second when open. Fig. 1993. is formed
of a series of bent springs placed alternately in opposite directions.
Fig. 1986. is similar in principle, but has a lever interposed Fig. 1994. NIMMO's VAL.VR
between the valve and the spring; both are employed in loco-
motives. Fig. 1994. was proposed by Mr. Nimmo for steamboat boilers.

CHAP. XXI. STEAM CONSIDERED AS A MOVING POWER.
1257
the
The most certain and safe method for low-pressure boilers is to balance the pressure
of the steam by a column of water, of a diameter sufficient to allow its escape:
height of the tube for different measures may be found readily, by considering that a
column of water equivalent. to one pound on a circular inch is for common temperature
3.1 feet; for pressure of 4 pounds on the circular inch it will be four times this, or
12.4 feet, which will be equal to a little more than 5 pounds per square inch: for
high-pressure boilers the most careful attention to security is necessary, and serious
accidents have occurred for the want of it, and it is obvious that the aperture by which the
steam is to escape ought to be of a size that it may freely have vent, as fast as it is
generated in the boiler: as 1 feet of fire-surface is sufficient to convert a cubic foot of
water into steam, it is necessary for the purposes of security to calculate upon only 1 foot
of surface being sufficient. If the density of the steam corresponding to the pressure be
found, multiplied by 7.5, and this product again multiplied by the square root of
the quantity, if the density is greater than 1, and the feet of fire-surface divided by the
product; the quotient will be the square of the diameter of the movement part of the
valve in inches.
Fusible metal plugs have been used as the means of forming safety-vents to steam boilers,
which, by melting at certain temperatures, suffer the steam to escape, and alloys which melt
from 2120 to 600° of heat have been applied, but this kind of plug cannot be relied upon
in practice.
The
Chimneys, and their Area for Steam-engine Boilers, form our next consideration.
fire-grate should have one superficial foot area for each horse-power; one-fifth of the area of
the fire-grate gradually diminishing to a chimney, which shall have one-tenth the area of
the fire-grate, is admitted to be an excellent proportion: the chimney should be of one
diameter throughout its height, and if 40 feet, and its area one-tenth that of the fire-grate,
its draught will be sufficient; when the height of the chimney exceeds this, the area may
be diminished as the square root of the height is increased. For a low-pressure engine
the area of the chimney, when above 10 horse-power, should be 112 times the horse-power,
divided by the square root of the height of the chimney: when less than 10 horse-power
its dimensions may be made less in proportion.
When engines are worked in the best manner, they require only 9 to 11 pounds of the
best coal per hour for each horse-power, when the power of the engine exceeds ten horse.
The flue must be proportionably increased when the smoke is the result of a consumption
of a greater quantity of coal; when wood is used, there is a larger quantity of smoke, but
as it is much lighter than that produced by coal, about one and half times the area
necessary for coals will be ample. When circular chimneys are used, they should not be
larger than is necessary to give effect to the fuel; this will be obtained when the square of
the diameter is equal to 90, multiplied by the horse-power, and divided by the square root
of the height in feet.
upon a
Piston Rods, their Strength. The height of a column of water at a temperature of 60°,
which presses with the force of one pound upon a square inch, is 2.31 feet, and
circular inch 2·94 feet; and in calculating the strength of the various parts of an engine, it
is not only necessary to bear this in mind, but also the power of the steam in the boiler, and
it will be perhaps safer always to take in our calculation double the pressure on the valve,
for it is not always in the same degree of action: when the load on the valve is 8 pounds
⚫ on the circular inch, call it double, and add this to the pressure of the atmosphere, which is
11-5 pounds; we then have 27.5 pounds for the strength of the steam acting on the
circular inch in steam-boats 39 pounds pressure per circular inch on the piston may
be allowed.
The stress which acts on any portion of an engine may be ascertained by considering it
inversely as the number of revolutions multiplied by the diameter of the circle, or the
chord of the arc described by the point where the force acts; thus a wheel 4 feet in
diameter, making three revolutions while the piston makes one stroke of 5 feet in length,
will give 4×3: 5:: pressure on the piston: the stress on the teeth of the wheel equal to
that of the pressure on the piston. The cohesive force being known, the strain the material
will bear is taken at about one-third.
Suppose D the diameter in inches of the piston, L the length of the stroke in feet, P the
double of the whole elastic force in pounds upon the circular inch; the length from the
centre of motion to the centre of stress in feet; d equal to the depth or diameter, and b
equal the breadth in inches; ƒ equal the cohesive force of a square inch at the point of
alteration; and R equal to the radius of the wheel. The force on the piston is then D'P
in pounds, or to find the diameter of the piston-rod in inches, multiply the diameter of the
steam-piston in inches by the square root of twice the elastic force of the steam in the
boiler in pounds per circular inch, and divide the product by 84. This rule applies
when the strain on the rods is tensile, but when they are alternately compressed as well as
extended, the diameter of the piston in inches should be multiplied by the square root of
twice the pressure of the steam on a circular inch, and the product divided by 45, which
1258
Book II.
THEORY AND PRACTICE OF ENGINEERING.
will give the diameter in inches for a piston-rod of wrought-iron: when cast-iron is used,
divide by 42, and when steel, divide by 72 for the result instead of 45: when rods of air-
pumps are to be considered, the pressure of the atmosphere and the diameter of the pump
must be taken instead of the force of the steam and the diameter of the cylinder.
Beams, their Strength. When of a uniform thickness it is not safe in cast-iron to make ·
it less than of its depth, when the velocity is the same as that of the piston: Dº Pl=
215bd2; and when 166 equals d, and 127 equals n D, it becomes
T6
D
1.34 Pn
212
18
-
=d;
16
D represents the diameter of the piston in inches; d the depth of the beam in inches, and
the breadth of that depth; n, the number of times the diameter is contained in the
length, from the point where the force is applied to the centre of motion; P, double the
force of the steam in the boiler, in pounds per circular inch: half the depth at the centre
of motion should be given to the depth at the end, keeping a uniform breadth: when
wrought-iron is employed, substitute 240 for 212, and for wood 64.
Cranks, their Strength. They should embrace the shaft, so that their depth should
be 1 times the diameter of the shaft; thus, if SD be the diameter of the shaft, the depth
of the crank will be 1·5 SD; hence D' PL=212bd²; we have
Pl
Pl
2.25 S² x 212 477 S2
= b.
Cylinders and Metal Pipes, their Strength.—To determine the thickness of a cast-iron
cylinder, the metal of which at an equal temperature is to bear a given stress; multiply
2.54 times the internal diameter of the cylinder by the greatest force of the steam on a
circular inch, divide by the tensile force the metal will bear without alteration, and you
have in the result its thickness in inches. The cylinder is supposed to have equal
resistance throughout its length, and the stress upon an inch of that length is equal to the
diameter in inches multiplied by the greatest possible force on a square inch, and the
resistance as twice the thickness of the cylinder, by one-fourth of the tensile strain of the
metal, the tension being unequal on the resisting part: thus, for a cast-iron cylinder of 60
inches internal diameter, for a pressure not exceeding 3-2 pounds per circular inch, in
addition to the atmospheric pressure; to determine its thickness
2·54 × 60 × 30
15000
0.305 inches:
twice the force is here taken, or 30 pounds on the circular inch, and the resistance of cast-
iron at 15,000 pounds the square inch. To determine the thickness of a working cylinder,
where wear and other causes of pressure exist, multiply four times the elastic force of
the steam in pounds per circular inch by the diameter in inches, and divide by 6000; this
result, multiplied by the quotient arising from dividing the diameter by the diameter less
2.2, is the thickness for strength, to which inch may be added for wear.
1-24
Pistons, their Construction.- It is most important that they should not admit of any
leakage, and Mr. Watt found that mutton tallow was the best adapted to keep the
piston tight; when cylinders were new and imperfectly bored, the grease soon was wanting
and the piston left dry; he afterwards mixed blacklead dust, but it was found that this
application wore away the cylinder, but they are now made so true as not to require.
it, or at least only for a short time. Pistons are usually of metal, and are formed so
as to have some elasticity: the common piston is a double cone of wood having
secured around it by strong nails a couple of bands of leather; when of metal, they are
usually turned out of brass, and made to fit the cylinder in which they are to move, so that
without much resistance they will slide to and fro; on this as well as below is a plate,
between which and the cylinder of brass is inserted two leathers cupped, with the edges
chamfered off to an angle of 45º.
The piston for the atmospheric engine is a plate of cast-
iron, about inch less in diameter than the cylinder, and
1 inch in thickness, with a rim about 4 inches from the
edge; beyond this a flat ring is fitted, and they are screwed
together, after hemp mixed with tallow has been inserted
between them to form the packing.
The hemp-packed Piston is that in general use: the bottom
is accurately fitted to the cylinder, and the upper part is
cut away to admit of gasket or unspun hemp or soft rope
being wound evenly round it, which forms the packing;
this is compressed by a plate by means of the screws: the
piston-rod is usually attached to the bottom of the piston, and

ע
it is secured by a screw-nut inserted between the top and Fig. 1995. Hemp-PACKED PISTON.
bottom: melted tallow is applied by a funnel on the top of the cylinder lid to the piston.
CHAP. XXI. STEAM CONSIDERED AS A MOVING POWER.
1259

The Wedge Metallic Piston is
formed of rings cut into a number
of parts, pressed upon the cylinder
by wedges, which again are kept
in their places by springs, and thus
a more perfect adaptation of the
ring to the cylinder is supposed to
be obtained.
In the Spring Metallic Piston,
fig. 1997. wedges are inserted behind

Fig. 1996. WEDGE
Fig. 1997.
Fig. 1998.
METALLIC PISTON.
SPRING Metallic PISTONS.
the rings, with springs behind them, forcing them outwards, and in fig. 1996. a single elastic
hoop is substituted for all these springs: springs without wedges are also in very common
use for metallic pistons with divided rings, double sets being used and the springs pressing
directly on the segments of the metallic rings, as in fig. 1998.
Wolf's Piston is so contrived as to enable the engine-man to tighten it without taking the
cover off the cylinder; the piston-rod forms part of a screw to which a toothed-wheel is
attached; this is turned by means of a pinion provided with a square head rising in a recess
in the cylinder surmounted by a cap.



עשי
Fig. 1999. Wolf's piston.
Fig. 2000. CARTWRIGHT'S PISTON.
Fig. 2001. JESSOP'S PISTON.
Cartwright's Piston is very similar to the wedge metallic piston, but has not been found
quite successful in practice, when the cylinders are not truly bored; the pieces forming
the piston having a determined curvature, and being too strong to be sensibly flexible,
cannot accommodate themselves to any irregularity, as is done by the elastic stuffing of hemp.
Jessop's Piston consists of an expanding coil of metal which binds round the piston body
in a spiral form, fig. 2001. : a bed of hemp packing is first prepared, which answers the double
purpose of preventing steam passing at the joints, and of supplying a means of pressing the
springs against the surface of the cylinder; their pressure and wear is more equable than
in other metallic pistons, and they have been successful in practice.
When a piston-rod is drawn as well as pushed, the proportion of its diameter to that of
the piston should be attended to, as the slightest inequality in the centering or in the fric-
tion will render it liable to stick and not move properly: in high-pressure engines the friction
and loss are estimated at two-tenths of the power. The piston-rod, collar, or stuffing-
box, is that which admits the smooth rod or plunger to pass into the cylinder or air-
tight vessel; the stuffing-box with the hemp packing surrounds the piston-rod; round it
is a collar, with a hole sufficient to allow the rod to pass, which is stuffed and screwed down
with similar stuffing to that already described.
The common Clack-valve is a piece of leather rather larger than the opening it is to close,
and is attached by a joint or hinge; it is strengthened by a metal plate on each side,
the lower one less and the upper larger than the aperture: an angle of 30° for it to open
allows a free passage.
A double Clack-valve is used for pump-buckets; they should also rise to an angle of
30°, and are decidedly preferable for large pistons.
Conical Steam-Valve is a metallic plate with bevelled edges, made exactly to fit into
a conical box, and is sometimes called a T valve; the valves of Watt's engine were
of this kind. The diameter of the box should be to that of the greater diameter of the
valve as 3 to 2, and should rise at least one-fourth of its greatest diameter when open :
they are usually of brass, and are turned so as to exactly fit, after which they are
further ground into each other with emery powder; the angle is 45°. When this valve
is to be self-acting, its weight must be equal to the square of the diameter multiplied
1260
Book 11
THEORY AND PRACTICE OF ENGINEERING.
·
by the pressure in pounds on a circular inch; it will then move as soon as its narrower
surface is exposed to a given pressure.
The Cup Valve is made with the seat a portion of a sphere, and the valve itself a sphere
or portion of it to fit it: they are occasionally used as safety-valves; a weight is sus-
pended below them to prevent sticking.
Sliding Valves are in general use, and consist of a box with a slider at right angles to the
passage, moved by a rod passing through a stuffing-box. The slider is accurately ground,
and is held by a spring; for small apertures it is moved by a handle, and for larger ones by
a rack and pinion.

S
Crown or Equilibrium Valve used in the
Cornish engines, and also in the rotative: it
requires little force to work it. The steam is
introduced through the pipe S, and the
aperture A is surrounded by an upright
ring or collar, rising a few inches into the
chamber, which ring is perforated by slits of
considerable size, but closed at the top. The
crown or cover of the valve is a ring at-
tached to a steel rod, by which it is raised
or depressed, care being taken that the collar and crown valve are both accurately ground
and made to fit each other.

When the valve is on its seat, it is closed
on all sides, so that no steam can enter:
when raised up from its seat, the steam
may enter freely from each of its sides:
this kind of valve is similarly arranged to
the conical valves, and work in the same
way, four of them being used in a single
engine. The conical valve was contrived by
Mr. Watt, and is shown when open in one
figure, and shut in the other.
S is the entrance for the steam, A the
port, V the conical valve, N the seat or
nozzle, which it covers: when the conical
cover V of the aperture N is up, the steam
has free admission; when it is closed, the
steam presses the valve down into its seat,
without escaping from the nozzle.
A
Fig. 2002.
Fig. 2003.
CROWN OR equilibrIUM VALVE.

Fig. 2004. Valve, shut.
Fig. 2005. VALVE OFEN.
A
Fig. 2006. WATT'S
CONICAL VAlve, open.
V
A
Fig. 2007. Ditto, shut
Murray's Sliding Valve.—All the apertures
terminate in a case that is steam-tight, and
within which a box slides up and down, which opens and closes the passages
alternately. The rod O,which passes through a stuffing-box, moves the sliding
part. The steam entering from the boiler at S passes through a to the top
of the cylinder when the slide is down, while the passage to the condenser
is open through the interior of the slide; when the slider is up, the pas-
sage b from the bottom of the cylinder is open, and the passage a from the
top to c, the condenser, is open to drive this slide a small reciprocating
motion is sufficient, and it has considerable friction from the pressure of
the steam against the box; they are generally of gun metal where salt-water
is used, and they act and wear well.
Rotary Valves are formed by a plate of metal moving on an axis, which
crosses the plate, and passes through an air-tight aperture to the outside :

a
Fig. 2008.
for throttle-valves, or where perfect tightness is not the object, they may Murray's slide,
be usefully employed.
Four-way Cock is used to open a communication alternately from the boiler and conden-
ser to the top and bottom of the cylinder: it is simple in its action, but steam is lost at
each stroke of the engine, and there is considerable
friction; it is of a cylindrical form, and when truly
ground the steam tends to keep it tight, but it soon
wears into an elliptical shape and requires re-grinding.
In a four-passaged cock made for the purpose of shut-
ting off the steam at any period of the stroke, without
closing the passage to the condenser, T shows the
passage to the top, B that to the bottom of the cylinder,
and C that to the condenser; the figures show its
position when the steam enters, and when shut off.


S
Fig. 2009. SHUT.
P
C
Fig. 2010. Open.
FOUR-WAY COCK.
To form the four-way cock, so that the steam can be cut off at any portion of the stroke,
it must be enlarged sufficiently to allow the breadth of two apertures between the middle
CHAP. XXI.
1261
STEAM CONSIDERED AS A MOVING POWER.
and each adjoining passage, increasing the diameter in the proportion of 10 to 8, the
rubbing surfaces remaining nearly the same, and the cone will be more equally pressed into
the socket. The most simple method in practice is to make use of two double-passaged cocks.
Plug Tree is a rod attached to the engine beam, and provided with tappets or projecting
pieces which strike levers or handles of valves for the purpose of shutting or opening them
at various intervals, as the rod descends or ascends. The handles turning on their axis act
as levers, and thus move the cocks, slides, or valves, to which they are attached.
Valves opened by Weights. — Fig. 2013. W is the weight, which acts upon an arm a on the
axis, and requires to be turned, that the valve may be moved: a spring-catch b, held by
the suspended weight, closes the valve, which opens when the catch is disengaged, and
the handle c is moved by the tappet d: direct action from the beam itself is now used to
open these valves, and the weights are in great measure dispensed with, though they are
said to open the valves more rapidly, which is important for working the engine, as the
opening and closing the passages at the proper time constitute its effect.
A weight opening a valve may descend into a vessel of water, while the aperture by
which the water escapes from under it may be increased or diminished at pleasure. The
weight uses its full force to open the valve, but when it be-
gins to move, it is stopped by the water: in the ascent, a
valve at the bottom of the vessel opens inwardly, and the
engine has only to raise the weight again. This method is
in constant use for opening valves of engines for the purpose
of raising water.
Eccentric Rollers, to raise the valve-rods, are ingenious,
though attended with some objections in their application.
Fig. 2012. shows a section of the steam pipes and valves of
Fenton and Murray's double engine, and fig. 2011. the com-
municating rods: by the pipe C the steam enters: at a is a
throttle-valve, which regulates its supply: a governor of two


E P
C
Fig. 2011.
E
h
अ
a
W
LOT
d
Fig. 2012.
FENTON'S STEAM-FIPE and valve.
Fig. 2013. Opening-valvES.
bent levers e, e, turning upon its axis at f, has a rotary motion communicated to it by means
of a band passing from a pulley to a similar pulley at d. The upper part of the spindle has a
slide n, which is connected by rods i,i, to the levers, which rises when the centrifugal force
of the governor is increased, and descends when it decreases; as the lever I is affected
by the rising or falling of the balls of the governor, so is the valve a attached to it.
1262
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
The arms k, k, serve as rests to the balls when the engine is not at work, and the rod
c is raised to such a height that the throttle-valve is in a horizontal position, and the
passage of the pipe open for the admission of steam: by the pipe DD the steam
passes either to the top or bottom of the cylinder through the throttle-valve a, and then
down to the condenser, through the pipes E, E: the valves n,o, have each a spindle passing
through the stuffing-boxes r,s. The rods of the valves p and q have also at t and u stuffing-
boxes to pass through, which rods open the eduction pipe E; thus the valves for the
admission or eduction of the steam are opened without any escape. The sliding rods,
which give motion to these valves, are kept in a perpendicular position by bands.
Modes of opening Valves, Cocks, and Slides, or the means by which the engine is rendered
automatic, or capable of performing its work without the assistance of manual attention to
open and shut them, is a matter of the greatest importance, and has partly been described;
but one of the most perfect is that of deriving the motion of the valves from a connecting

Fig. 2014.
ECCENTRIC STEAM VALVE.
rod, one end of which is made to move round in the circle of a crank, while the other end
performs a rectilineal or circular reciprocating motion: another method is by
The Eccentric, which is a circular disc or ring of metal, placed upon the shaft or axis,
turned by a crank. The distance from the centre of the disc to the centre of the axis
is called the eccentricity, and is equal to half the throw or range of the motion of
the valves to be moved by it; the rod is called the eccentric rod, and is attached to a
hoop that exactly fits the disc: this produces an easy change of motion, and being
constantly moving gives no stroke at the time of change. Suppose r to be the radius of
the eccentric circle, and d the distance of its centre; from the centre of motion then
r+d−(r−d) will be the extent of the movement, 2 d, or twice the eccentricity. At
of the stroke, counted from either end, a valve can only be opened half way; at part of
the stroke it may be calculated to be fully open: sometimes the valve rods are made
to branch out into four portions, and at their separation a flat brass plate is inserted, with
another at the summit to unite them: the eccentric works between the side forks of the
rod, and bears against its top and bottom plates, figs. 2015. 2017.: the other forks are
in width equal to the diameter of the axle, which prevents the rod deviating from the
vertical position, figs. 2016. 2018.; by adding a handle that can be worked by hand, the
reversing process may be performed.




Fig. 2015.
Fig. 2016.
Fig. 2017. PLAN.
Fig. 2018.
The Governor, or Centrifugal Power Regulator, is an ingenious contrivance for equalising
motion, in the steam-engine particularly; by its means the valves which suffer the
steam to pass from the boiler to the cylinder are opened or closed to the extent necessary,
and in such a manner as to allow a certain quantity of steam to pass through, and no
CHAP. XXI. STEAM CONSIDERED AS A MOVING POWER.
1263
more. When the action of the governor flags, the valves open more, and vice versâ,
so that it produces a motion free from vibration: this is effected by suspending two or
more balls from a revolving axis, and allowing them to revolve with it: when the velocity
is increased the balls


rise, and when it is
diminished
they
fall: by connecting
arms to the rods by
which the balls are
suspended, their
rising or falling
moves a lever, which
can be applied either
to open or close a
valve. The vertical
distance between
the point of sus-
pension and the
plane on which the
centre of the balls
revolve corresponds
with the length of
a pendulum, which
makes one vibra-
tion, forward and
back again, in the
time the balls make
revolution.
one
Fig, 2019.
T
H
Fig. 2020.
The common ve-
locity given to the
axis is about thirty revolutions in a second; consequently the height should be equal to the
length of the seconds' pendulum, which is 39.14 inches: to find the height for any other
number of revolutions, divide 35.226 by the square of the number, and the quotient will
be the height required. The balls usually weigh from 30 to 80 pounds, and the angle the
rods make with the axis is about 30° when they are at rest: the motion of the
governor is derived from the engine, by a cord or strap running round the axis of the
fly-wheel and communicating its motion to a pulley which is fixed upon the spindle
or upright rod: when the axis of the fly-wheel moves too rapidly, its increased motion
is communicated to the governor; its spindle then revolves more rapidly, and the balls
attached to it, from their increased centrifugal force, fly out farther from the spindle, and
depress the levers which act upon the throttle-valve so as to contract it.
B
E
Parallel Motion was the means of establishing a communication between the inflexible
rod of the piston, which oscillates in a straight line, and the beam which oscillates
circularly; this elegant arrangement is not perfect, and some allowance is requisite to be
made in the adoption of it upon a large scale, to prevent serious inconveniences to the
machinery to which it may be ap-
plied: three angles of a parallelo-
gram describe arcs of a circle, while
a fourth, which lowers and raises the
piston-rod, moves nearly in a straight
line; this will be shown by supposing
R the top of the piston, and B the
head of the beam, which describes
the segment of a circle whilst R
moves in a vertical direction; these
motions are made to suit each
other, by having a fixed point at F,
which is placed close to the line, in
which the piston-rod moves: on the
beam, at B and E, are hung the
inflexible bars BR and EH, which

F
k
R
K
Fig. 2021.
H
move freely on their pivots: the other extremities of these rods are connected at RH;
another rod passes from H to F: these several rods have free motion around their pivots.
The head of the piston being attached at R, the piston-rod will then have a vertical
motion; from the outward motion of the beam, during the first half of its descent
and the first half of its ascent, or from its inward motion, during the latter half of
its descent and the latter half of its ascent. When the beam is in an horizontal position,
as is shown by the dotted line ck, the rod B R will hang in a perpendicular direction, and
1264
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
that of FH will be horizontal, as shown by the line Fg: during the latter part of its
descent the point B will be bent inwards, and press with it the head R of the piston-rod;
the rod FH will then bend outwards, and thus resist the inward thrust of the beam; in
the ascent similar adjustments take place between the beam and the piston-rod, the latter
being always preserved in a vertical position, or nearly so, and the strain it is subjected to in
one direction neutralised by the opposite action of the rod RH. This motion may be further
understood by supposing it to be required that the top of the piston-rod P, fig. 2022., should
not be moved by the obliquity of

its connecting rod PR, which
may be prevented in this man-
ner : at s, s, are two fixed
points, at equal distances from
the piston-rod; there are two
parallel bars g, s, placed between
the piston-rod and these points,
which steady the motion, and
revolve freely on their points
s, the ends of the bars g,g
describing arcs of circles;
these rods being attached to
the piston-rod in the middle
of the two points g,g would
have the effect of always keep-
ing the point P in a straight
line; thus the piston-rod is not
attached to the ends of the
guide bars, but to the middle
of the link; the point P there-
fore is prevented from deviating
much from the straight line.

Fig. 2023.
9
g
Fig. 2022.
Fig. 2024.
P
P
The point P does, however, deviate from a straight line, and forms a double curve; and in
practice it is necessary to make some allowances for this, which may readily be shown by
tracing the point p during its motion: when gs, fig. 2024. comes into the straight line
with the link gg, the point p deviates from the straight line, by a quantity equal to p',
and this is reversed in the opposite extreme. When the link gg, fig. 2023. comes into
the same line with the bar gs, the deviation is much greater, and when the links have
returned to their original position, they have described the whole curve xpy. This deviation
increases more rapidly than the square of the length of the stroke; the greatest deviation
at the end of the stroke being ascertained, and also its amount, at one-eighth part of the
stroke from the middle, bring the centres s,s each nearer to the other, by a quantity equal
to the deviation at the eighth part, and the amount of its greatest deviation will be
reduced to less than one quarter of what it was in the first instance: the parallel motion
of one point may also be readily transferred to another by jointed parallelograms.
Fig. 2025. shows the simplest
kind of parallel motion, and is
usually employed to commu-
nicate the rectilinear movement
to the air-pump-rod of the steam
engine. Fig. 2026. is the ap-
parently more complicated case
in which three shorter bars are
added to the end of the beam,
so as to form a parallelogram,
to the lower angle of which the
piston-rod is attached. Fig.
2027. exhibits the parallel
motion used for steam-boat en-

Fig. 2025.
PARALLEL MOTION.
gines: the beam A F is below the cylinder; when AB is equal to DC, the point E is
in the middle of the length of the bar BD: the rod DG may be at any height, provided it
be parallel to A F, and B may be at any point in AF. Fig. 2028. shows how to arrange
three piston-rods to move parallel: as for Wolf's engine, the points of suspension must be
all in the line A G. Fig. 2029. shows another arrangement for three rods at one end and
two at the other end of the beam: when the proportions to obtain parallel motion have been
found by the following rules, the point for the air-pump-rod in the link D B is easily found
by drawing a line from G to A, and then the rod must be attached to the point of intersection.
In like manner, in any complex case, as in Wolf's engine with two cylinders, the points of con-
nection for the piston-rods must all be in the line AG. In these figures the corresponding
parts are marked by the same letters.
CHAP. XXI. STEAM CONSIDERED AS A MOVING POWER.
1265
-
To find the length which should be given to the radius bar, when the length of the beam
from the centre of motion is to half the length of the stroke as 3 is to 2: from three
times half the length of the stroke, subtract twice the length of the parallel bar, and


Fig. 2026.
PARALLEL MOTION.
B
2000
Fig. 2028.
PARALLEL MOTION.
B
E
D
C
D
G
D
E

b
G
F
Fig. 2027. PARALLEL MOTION FOR BOATS.

B
E
G
F
Fig. 2029.
PARALLEL MOTION.
multiply the difference by half the length of the stroke; this product divided by 343146
times the length of the parallel bar, and the quotient added to the length of the parallel
bar, gives the length of the radius bar. The radius bar and the parallel bar should be
of equal length, when twice the parallel bar is equal to three times half the length of the
stroke.
When there is no assigned proportion between the length of the stroke and the radius
of the beam, the length of the radius bar is thus found: first, from the length of the
radius of the beam, subtract twice the length of the parallel bar, and multiply the difference
by the square of half the length of the stroke; secondly, find the square root of the difference
between the square of the length of the radius of the beam and the square of the half
length of the stroke, and subtract this root from the length of the radius of the beam, and
multiply the difference by twice the length of the parallel bar. This product becomes
a divisor to the number found by the first part of the operation; the quotient obtained,
added to the length of the parallel bar, gives the length of the radius bar.
Cartwright's Parallel Motion, (figs. 2030, 2031.) consists of two toothed wheels, which work
in each other, and from corresponding points in their circumference two connecting
links unite at the extremity of a cross bar, to the middle of which is joined the piston-
4 M
1266
Book II
THEORY AND PRACTICE OF ENGINEERING.
rod. These wheels and connecting rods being always in similar positions, on opposite sides
ស
of the piston-rods, the obliquity of their
actions balances each other, and the rod is
made to describe a straight line; to make
this arrangement work accurately the greates's
nicety of execution is necessary.


Fig. 2030. CARTWRIGHT'S PARALLEL MOTION.

Fig. 2032.
CYCLOIDAL MOTION.
Fig. 2031. PARALLEL MOTION.
The Cycloidal Parallel Motion, which is exceedingly beautiful, depends on the prin-
ciple that an encycloidal curve, described by one circle rolling within another, approaches a
straight line, as the inner circle becomes more nearly equal in diameter to the radius of the
outer one. The large wheel, which has teeth on its inner circumference, is fixed on a frame
concentric with the axis and circle of the crank o: the small wheel, which has teeth
on its outer edge, is freely fixed on the crank-pin, and p is the point at which the piston-
rod is affixed. The small wheel is forced by the pressure of the piston-rod upwards, to
roll round the great circle, ascending on the one side and descending on the other; so that
the distance of the end of the piston-rod from the point of contact of the circles is always
equal to the distance of the circle from the diameter.


A
Fig. 2034.
Ρ
9
S
9
g
Ρ
Fig. 2033.
SUN AND PLANET WHEEL.
Fig. 2035.
PARALLEL MOTION.
The Sun and Planet- Wheel, (fig. 2033.) was contrived by Watt: a toothed wheel A is fixed
centrally with the large wheel to which the rotary motion is to be conveyed; B is another
toothed wheel fixed firmly to the end of a vertical rod C; a strong link connects the centres
of the two wheels. If the shaft D be turned, the wheel B will revolve in the same
direction, and elevate the rod C till it arrives at the top of the wheel A, when, by continuing
the motion of the large wheel, B must descend to its first position, and so on continually.
CHAP. XXI.
1257
STEAM CONSIDERED AS A MOVING POWER.
Another species of parallel motion has a joint at the bottom of the column, (fig. 2034.)
on which it and the beam and the crank rod perform a joggling motion backwards and for-
wards during each stroke, which may be better understood by supposing the point s (fig. 2035.)
on the plan fixed; s,g are movable bars. The point g describes a circle round s, so that p
describes also a curve round the same point: the oscillation of the moving mass of the engine
in alternate directions, with a sudden jerk at the end of the stroke, renders this kind of
movement injurious to engines on a large scale, particularly as the piston-rod also deviates
very considerably from a straight line.
e
Fig. 2036.
EPICYCLOIDAL MOTION.
Fig. 2036. shows another method of converting rectilinear to circular continuous motion
employed in steam engines, with its accompanying geometrical demonstration. Let aed
represent the fixed, and ac, b'e the interior revolving wheel in two positions, its first, being
at the extremity of the diameter ad; when it comes into any other, bc, the point a will
always be found in the diameter ad, since whatever be the position of the centres o, o, ba=b'a'
The Crank is one of the most important
appendages of the steam-engine, and is used
for converting a reciprocating into a rotary
motion. By the force of steam, motion is
produced upwards and downwards, in the
right line of the axis of the cylinder, and this d
can be rendered capable of producing a force
equally well in a circular direction: when an
engine is used for pumping only, a crank is
not necessary, but when applied to machinery,
its use is highly important; it increases the
velocity of the moving force, and in ordinary
construction this is in the ratio of the cir-
cumference of a circle to twice its diameter. The moving force of a crank may be uniform
and in a straight line; or it may be uniform in a curved line, or it may be variable in
either case :
on examining the action of the crank, it will be found neither to be con-
tinuous in direction nor in action: when the steam enters below the piston, it forces it to the
top of the cylinder; it is then cut off preparatory to its entering above the piston, and in the
interval it has no action, and this is the case after the steam has forced the piston to the
bottom of the cylinder: this double cessation of action between the impulses would pre-
vent the continuous revolution, were it not for the addition of a wheel, by which means is
obtained the power of continuing motion, by what is termed its momentum; such a wheel
attached to an axle is called a fly, and serves greatly to equalise motion; it is usually of
large dimensions, and its rim of considerable weight, in order that the action may be
regular and uniform. The fly-wheel, although partial and not quite perfect in its equalisa-
tion of motion, so far improves the action of the crank, as to make it applicable to all
ordinary purposes; the extreme delicacy which results from the motion of the water-wheel
is, however, superior where great nicety of movement is required.

:
The motion of the crank may be shown
by supposing E the extremity of the beam,
moving in the arc of a circle, and C the rod
or axis, to which a regular continuous
circular motion is to be given let a short
bar DB proceed from the rod to be turned,
and play upon the pivot B, to which is at-
tached, playing also freely upon it, a long
bar or rod E B, the other extremity of which
turns in a pivot E, at the other end of the
beam; the rod E B, descending as the beam
descends, and moving up with it, will turn
round the crank BD, the extremity B de-
scribing a circle C. There are, however, two
points in the revolution which are called
dead points; for when the end of the beam
is at its greatest elevation, the rod hangs
perpendicular, and the crank is in the same
line; the beam then depresses the crank and
axis, and will not turn either, and when the
end of the beam is at its lowest point, the
crank is also in a line with the rod. The
motion of the crank, which it acquires be-
fore it reaches these two dead points, carries
it beyond them, and the beam resumes its
natural action, and this is further aided by

마
​11
E
"1
•
D
B
Fig. 2037. CRANK AND FLY-WHEEL.
4 M 2
1268
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
the fly-wheel.
The crank moves more slowly when at these points, and more rapidly
in its other positions, from which there is inequality of motion in the axis.
The Fly-wheel is a necessary part of the machinery, where perfectly steady and uniform
motion is the object: it consists of a large wheel with a heavy rim, usually formed of iron,
is attached to the axis on which the crank turns, and revolves along with it; by its
weight it acts as a drag on the engine, and prevents its motion being too rapid, and the
impetus it acquires from its weight, it carries on the machinery with the usual or gradually
decreasing force, when the proportion of the resistance to the power becomes augmented,
and the engine has a tendency to move slowly; its heavy rim absorbs any surplus force
which it acquires, and yields it again when required; it is a reservoir which collects the
intermitting currents and sends forth a constant and regular stream.
To proportion the rim of the fly-wheel, multiply 40 times the pressure of the piston
in pounds, by the radius of the crank in feet, and divide this product by the cube of
the radius of the fly-wheel in feet, and by the number of its revolutions per minute; this
result will give the area of the rim of the fly-wheel in inches; the number of the horse-
power multiplied by 200 will be the greatest pressure on the piston. When the velocity of
the fly-wheel exceeds 12 feet at the rim per second, its arms should be of wrought-iron,
and a velocity of 33 feet per second at the rim is the extreme velocity that should be given
at any time; with cast-iron rims, the velocity should not exceed 18 feet per second, that
they may be perfectly safe. The proportions of the fly-wheel are derived from the laws of
rotary motion, and are found by adding the time, the radius corresponding to the angular
velocity of the exterior ring of the wheel; and comparing with the force of gravity to obtain
the co-efficient, it is,
32 P. drt
bx2
=nv.
P here is the mean quantity the moving force varies in its intensity in excess above the
resistance, and t the time in which that variation takes place; v, the velocity, and nv, the
greatest variation of velocity; d, the leverage the force P acts with; and r, the radius
corresponding to the velocity v; and b, the weight of the fly, acting at the distance x from
the axis the weight of the rim being always at the extremity of the radius; x=r, and
the equation becomes,
32 P. dt
br
:nv.
When the weight of the rim is great, it acquires a great momentum with little increase of
angular velocity, or it loses a considerable momentum with a small diminution of that
velocity; and the greater the angular velocity of the axis of the fly is, the greater will be
its equalising power, all other things being equal: variation of velocity is inversely as the
velocity of the rim.
To measure the useful Effect of an Engine. The most convenient method is by the means
of friction if the rim of a brake-wheel on the engine shaft of a given diameter, be pressed
with a force exactly equal to the effect of the engine at its working speed, then the friction
being ascertained, which this pressure produces, the power of the engine may be found by
multiplying the friction by the velocity of the rubbing surface.
Let A B be a lever, tightened by a friction strap, which passes round the shaft or wheel
C; the lever being stopped at the point D till the friction be equal to the power of the
engine when all other work is thrown
off; then, while the engine is in B
motion, place at E a weight sufficient
to retain the lever in its horizontal
position to obtain the power, mul-
tiply the length FC in feet, by the
weight placed at E in pounds, the
number of revolutions per minute
:
Fig. 2038.
lw
D

A
F
£
made by C, and 6·2832; the result will be the number of pounds raised in a minute one foot
high, which divided by 33,000 gives the horse-power. Suppose I be the leverage the
weight w acts with, r the radius of the wheel or shaft c, the friction f, the velocity o,
the revolution of c per minute n; then fv equals the power, and ƒ= and v=6.2832rn;
consequently, vf=6·2832lwn, the power in pounds raised one foot, when I is in feet and
w in pounds.
"
The portable Condensing Engine. The cylinder is supported by a cast-iron frame,
and two eccentric wheels on the crank-shaft give motion to the levers by connecting rods :
the lever works the cold-water pump by a rod, while the beam, by means of slings, works
the air and hot-water pumps. On the cross rail is a guide to confine the air-pump rod to
a vertical motion: the condenser surrounds the air-pump, and is again surrounded by
CHAP. XXI. STEAM CONSIDERED AS A MOVING POWER.
1269
one of the cold water cisterns; the two cisterns are connected by a pipe: the steam from
the cylinder passes by a pipe to the condenser, where the cold water is admitted by a cock:

IDE
Fig. 2039.
fortable condensiNG ENGINE.
4 M 3
1270
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
the air and condensed steam ascend through a foot-valve into the air-pump. The opening
and closing of the steam passages is performed by the eccentric, fixed on the crank shaft,
the action of which communicates a reciprocal motion to the rod, which, by a bent lever,
moves the connecting rod and lever fixed at one extremity of a spindle, having a bevelled
wheel at the other, which works into another spindle of the steam-cock, admitting the
steam into the cylinder: on the fly-wheel shaft is a pair of bevelled wheels, communicating
motion to the governor balls, which keep the valve on the steam pipes open a longer or
shorter time, according to the velocity of the engine.
Application of Steam Engines for raising Water. By means of an engine acting ex-
pansively, 280,000 cube feet of water may be raised by one bushel of coals a foot in
height, and when a pump is applied for this purpose, its stroke should not exceed 8 feet,
and the diameter of its cylinder 14 inches: the velocity of the piston should not exceed
98 times the square root of the length of the stroke. The quantity of water in cube feet
delivered at each stroke of the pump is 00518 lɗ² = the quantity in cube feet, l being the
length of the stroke, and d the diameter of the pump in inches. The power required to raise
water to a given height is found by taking the height in feet from the surface to the point of
discharge, and adding a foot and a half for each lift, for the force required to give the water
the velocity, and also add one-twentieth of the height for the friction of the piston, and call
this quantity in feet h; then 341 hd²=load in pounds, whence, if P=the mean effective
h\
force on the steam piston in pounds per circular inch, we have d=
meter of the steam piston in inches.
(341) * =D, the dia-
The quantity of work performed by one of the engines at Wheel Hope mine, Cornwall,
in 1826, was as follows:
Diameter of the cylinder
Load per square inch on the piston
Length of stroke in cylinder
Number of strokes per minute
-
Number of lifts, 1st, through 46 fathoms
2d,
3d,
Diameter of pump for 1st lift
11 fathoms
11 fathoms
60 inches.
8.37 pounds.
9 feet.
5 feet.
5 feet.
2 feet.
2d ditto
3d ditto
Consumption of coals
-
Number of strokes
Length of stroke in the pump
Number of pounds lifted one foot high by one bushel of coals
2 feet.
15 inches.
121 inches.
11 inches.
1242 bushels.
261,890
8 feet
46,838,246
Application of Steam Engines for raising Coals and Ores.—A double engine of from twenty
to thirty horse-power is used, the size of the cylinder being such that the power shall be
equal to the resistance when there is the greatest stress; consequently engines require mor
fuel to raise such bodies to the required height, as much is lost by the stoppages and changes
in motion: from 3 cwt. to 7 cwt. is usually raised at a time, and 1 pound of coal is cal-
culated to lift about 70,000 pounds of ore. The engine should work expansively, and
be equalised by a fly-wheel, and regulated by a governor.
Application to Corn Mills. The double expansive engine is usually employed, and with
low-pressure steam it will grind 14 bushels of wheat for each bushel of coals, when
working properly; but the average is perhaps about 11 only. To dress a bushel of
wheat, as well as grind it, per hour, is 31,000 pounds raised 1 foot per minute: the
velocity of the circumference of the millstone should be 23 feet per second, and with that
velocity a pair of 5 feet stones should grind 4 or 5 bushels per hour.
-
Application to Water Works. For this purpose, where fuel is expensive, double engines
with fly wheels are the most economical, and where it is cheap, single ones: in raising
water care must be taken that the air-vessel should be in the direction of the motion of the
fluid, for if placed on one side, the joints are liable to be torn asunder, the cranks broken,
and the machinery disarranged, from the concussion which take place.
Application to Threshing Machines. — Engines of from four to six horse-power are used :
the feeding rollers are 3 inches in diameter, and make from 35 to 37 revolutions per
minute: the straw rakes are 3½ inches in diameter, and make 30 revolutions per minute :
the diameter of the drum is 3 feet 6 inches, and makes 300 revolutions in a minute.
The quantity of wheat threshed by a machine with feeding rollers, 4 feet broad, varies
from 12 to 24 bushels per hour, according to its quality, and the quantity of oats from 16
to 30 bushels. The power required is 100,000 pounds raised 1 foot per minute for
threshing alone, and 133,000 when winnowing is applied; each inch of straw receives
three strokes of the beaters, and the stroke is made with a velocity of 55 feet per second, or
the beater should move 3300 feet per minute.
CHAP. XXI.
1271
STEAM CONSIDERED AS A MOVING POWER.
Application to Steam Boats.-The maritime engine is made more compact than that
usually employed in our manufactories, and, in order to diminish its height, the working
beams are placed below the cylinder on each side: in engines of 200 horse-power, the
cylinders are made 5 feet in height, and 53 inches in diameter, in order to save room; the
other portions of the engine do not materially differ from those we have already described.
The shaft, upon which the paddle-wheels are fixed, is made to revolve by cranks placed
upon it, in the same manner as the fly-wheel of a common engine: the paddle-wheels are
made like the common undershot, and bear on their rims flat paddle-boards: the marine
engine may be either condensing or high-pressure, but the low-pressure condensing is
generally used.
Locomotives. The general description of the locomotives on the London and Southampton
line is as follows: the engines have two horizontal cylinders, working to a double-cranked
axle in the driving-wheels: there are six wheels; the diameter of the driving wheels is 5 feet
6 inches, and the others 3 feet 6 inches, each of which have a nave of cast-iron, bound with
two hoops of malleable iron; the rims are also of the same metal, and well welded to the
rim, round which is a tire 1 inch in thickness and 5 inches wide, the flange of which pro-
jects 1 inch; these wheels are all turned very accurately, and have a conical inclination :
the cylinders are 13 inches in diameter, and have metallic spring pistons fitted into them,
which make an 18-inch stroke.
The Boilers are cylindrical, 3 feet 3 inches in diameter and 8 feet long, and contain about
120 tough rolled brass tubes, 18 inch in diameter at one end, and 13 at the other, drawn on
a mandrill; they are fastened to the boiler with steel hoops: the thickness of the tubes
is No. 15. wire gauze, and the holes in the ends of the boiler are all parallel.
The Fire-box is of copper, of an inch in thickness, but where the tubes are
fixed, the plate is of an inch in thickness: the width of the fire-box internally is 3
feet 6 inches; length 2 feet 6 inches, and depth from the roof to the top of the fire-bars 3
feet 4 inches; the water-spaces are 3 inches wide, and the roof and sides of the box are
stayed with copper bolts, tapped and riveted.
The Axles.—The cranked axles are made of the best Backbarrow iron, 51 inches in dia-
meter at the crank pin, and it is turned down to 34 inches for the outside bearings: the axles
for the fore wheels are. 33 inches, and for the hind wheels 34 inches in diameter; they are
turned throughout.
The Framing. The engine is provided with four inside stay and bearing frames of
wrought-iron, with brass bearings to fit to the main axle on both sides of each crank, the
axle being properly turned to suit these bearings, and the frames are connected with the
tire-box and cylinder beds, which form stays for their support. The outside frames are
made of well-seasoned ash plank, 3 inches thick and 7 inches deep, plated on both sides
with quarter-inch best Low Moor plates. These frames are 3 feet 2 inches clear above the
surface of the rails.
Feed Pumps.
There are two, made of brass, fixed at the side of the boiler, the water-
spaces of which have an area of 2 inches clear.
The Chimney is covered with a wire cap, and all its bearings and journals are case-
hardened, and its height is 13 feet from the rails.
The Engine is worked by eccentrics, with single slide valves and steel facings, and there
are two safety-valves, water-gauges, buffers, draw-bars, splash-boards, ash-pan, siphon cups,
safety-bars in front, wood sheathing, brass ball and socket, communication pipes, steel
springs, and all other requisites to complete their working order.
The Tenders have their frames made with well-seasoned ash timber, with transverse and
diagonal braces well bolted together: the tank is of a horse-shoe form, and contains 700
gallons of water; it is made of iron plates, of an inch thick, and provided with cocks
and pipes, to connect with the ball and socket feed-pipes of the engine: the wheels are of
wrought-iron, 3 feet 6 inches in diameter, with wrought-iron tires 1 inch thick.
5
32
The tenders are also provided with springs, break, buffers, long elliptical spring chains
to draw by, with a box of tools, oil-cans, shovel, and all other requisites to put it into a
working state.
Locomotive Engines differ from the ordinary steam-engine in their arrangement, and may
be said to consist of three several parts; the square box which contains the fire, the boiler
and its tubes, and the portion in front, where the cylinders and chimney are placed.
The usual construction is that with two horizontal cylinders, from 12 to 15 inches or more
in diameter, fitted with single slide-valves and metal spring pistons, having a length of
stroke from 16 to 18 inches. The fire-box is open only at the bottom, and placed at the
back part of the engine; it is made of copper, and has a door to admit the fuel; the general
dimensions may be said to be 30 inches in length, from back to front 40 inches in width,
and the height from the iron grate-bars at bottom to the top 39 or 40 inches: the fire-box
is entirely surrounded by water, except at the bottom, and where the opening is to admit
the putting on the fuel. The space for the water is about 3 inches in width, and where it
is in contact with the cylindrical portion of the boiler it is a little more.
4 M 4
...
Um
1272
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.

Fig. 2040.
HO
LOCOMOTIVE ENGINE:
WITHORA
O
CHAP. XXI.
1273
LOCOMOTIVE ENGINES.
The extreme width of the fire-box in such a case does not exceed 47 inches, and the iron
plates with which it is surrounded are in thickness about of an inch: the covering or

CENORIALE
:
O
O
O
O
O
о
O
•
•
O
O
C
Fig. 2041.
LOCOMOTIVe engine, longitudinal section.
O
1
O
O
•
•
O
•
O
O
O
D
0
top, however, where greater strength is required, has four wrought-iron rods riveted
to the upper surface, and the sides are held more firmly together by means of copper bolts,
which are tapped and riveted. The aperture to admit the coals is usually formed by a ring
of copper, and the iron plates of the casing are gathered in, and firmly riveted to it with
copper rivets.
The boilers are of a cylindrical form, about 8 feet in length, and 3 feet or more in diameter;
the ends are closed by circular iron plates, the lower half drilled with holes, in which from
70 to 140 longitudinal tubes of tough rolled brass are inserted by means of hoops of steel;
the thickness of the brass out of which they are formed is that called No. 15 wire gauge;
they are made truly cylindrical by drawing them through a mould: one end of these
Un
1274
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
tubes is open towards the fire-box,
and the other towards the chamber
in front, where the chimney is placed;
there is another door which allows
of the tubes being cleaned out when
requisite. The iron used for the
construction of the boiler is mostly
Yorkshire plate, g of an inch in thick-
386
ness, or, where more strength is re-
quired, inch, as at the back, and
at other parts only in thickness;
f
the fire-boxes are lapped and riveted
together as well as the boilers, care
being taken that the action of the
fire does not come too strong against
the parts where the welding is made.
Since the introduction of the tubular
boilers few accidents have occurred
from bursting; they were the in-
vention of M. Seguin, an engineer
at Annonay in France, who patented
them early in the year 1828 The
steam occupies the upper part of
the boiler, from which it passes into
a chamber by two pipes, each of
which has three openings or apertures,
to admit it before and behind the
piston, as well as to escape up the
chimney. The evaporation in the
boiler is effected partly by radiant
heat communicated to the water
which encompasses the fire-box, and
partly by means of the hot air trans-
mitted through the tubes. It has
been ascertained that 1 superficial
foot exposed to the action of heated
air, as that passing through the tubes,
has no more than a third of the
effect when the same area is ex-
posed to radiant heat, or has the
direct action of the fire: a locomotive
in action, proceeding at the rate of
nearly 19 miles an hour, was found
to evaporate 55-82 cubic feet
water during that time, where the
surface exposed to radiation was 43·12
superficial feet, and that to heated
air 288-35 superficial feet: when a
number of tubes of small diameter
are made use of, the temperature of
the air passing through them should
be as nearly as possible that of the
water in the boiler; there would then
be little loss in that which passes
off by the way of the chimney: but
the heated air is much higher in
temperature, which is partly rendered
necessary, in the present locomotive, to maintain sufficient draught to carry on com-
bustion.

of
Fig. 2042.
PLAN OF LOCOMOTIVE.
The Regulator Box (fig. 2044.) was first constructed by Mr. Watt; a spindle passes through
one side of the box, on which a toothed sector moves as a centre, working a rack fixed to
a brass valve accurately ground to its seat; the plug tree, part of which is shown under the
valve box, alternately opens and shuts the valve by means of a pin acting on the bent lever,
the upper arm of which works the toothed sector: this is the form usually applied to
stationary double-acting engines, but for locomotives the contrivance shown in fig. 2045. is
adopted; the steam is carried up into a hemispherically crowned cylinder, whence it descends
to the regulator, where the communication is made with the two pipes connected with the
CHAP. XXI.
1275
LOCOMOTIVE ENGINES.
chambers above the cylinders, in which
the pistons work; the uppermost rod,
which passes longitudinally through the
chamber of the boiler, where the steam
is confined, has a handle at the end,
which, when turned by the conductor
or engine-man, moves the two discs
alternately backwards and forwards,
which cover the aperture of the two
steam pipes; and this can be easily
effected. The discs being fixed upon
a horizontal rod, the cylinders can be
either opened or closed at pleasure:
it is important that these discs should
press against the mouth of the pipes,
which is partly effected by the steam
and partly by spiral springs.
Safety-Valves. The boiler has two
safety-valves: their forms vary; the
mitre valve, when shut, prevents the
steam from escaping, and it remains
closed as long as the steam is above the
common pressure of the atmosphere,
during which time it cannot escape:
above the spiral spring is a plate at-
tached to a perpendicular spindle, which
passes through the top of the valve,
where it has a screw-thread and nut;
when this is turned it presses against
the spring, and by forcing it downwards
opens the valve, and allows the steam
to pass off; any pressure may be put
upon this valve, and when the steam is
below that pressure, the attendant upon
the engine observes the steam escape, and
is then assured that it has not the re-
quisite elasticity.
The Water Gauge, attached to the
boiler, is for the purpose of ascertaining

Fig. 2013.
END OF LOCOMOTIVE.
the height at which the water stands; but generally a small cock is placed at various heights
on the side of the boilers, which when turned indicates the level of the water. A glass


RIZZLA
Fig. 2044.
REGULATOR BOX.
Fig. 2015.
REGULATOR.
Um
1276
Book II.
THEORY AND PRACTICE OF ENGINEERING.
tube fixed in brass rims is attached to the boiler, having at the top a brass cock turned by
a handle, and at the bottom another for letting off the water in the glass tube, after the level
has been ascertained.

ar
The Cylinders, which are placed in front, are attached to the framework of the boiler;
they are surrounded by heated air, as they are within the front chamber, through which
is the escape from the tubes to the passage of the chimney: in order effectually to
prevent any water passing off with the steam from the boiler into the cylinders, the steam.
pipe is carried up, as has been described, into a hemispherically crowned cylinder, and
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О
O
whatever water boils or bubbles up cannot reach the funnel mouth, intended only for
the passage of steam; before the steam is admitted by the regulator to the pipes,
which conduct it to the cylinders, it enters a small chamber, which is an admirable con-
trivance, and perhaps one of the most important parts of the whole machine. These
chambers are placed above the cylinders, and within them is a movable box or slide, which,
as its motion is either backwards or forwards, effects a communication with the steam-
O
Fig. 2047.
SECTION OF LOCOMOTIVE.
Un
Fig. 2046.
SECTION OF LOCOMOTIVE.

CHAP. XXI.
1277
LOCOMOTIVE ENGINES.
chambers, and with one or other of the openings which lead to the front or back of the
piston, giving the first impulse to the moving powers. When the steam is admitted
through the regulator into the pipes which conduct to the steam-chamber or valve-box, it
there presses the sliding valve lightly upon its horizontal plane; this, however, is moved
backwards and forwards by means of a rod, having four sheaves or rings fixed upon the
axles of the driving-wheels, upon false centres or eccentrics, so that at each revolution of
the axle the slide is moved backwards and forwards, admitting the steam both before and


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Fig. 2048
WATER GAUGE.
Fig. 2049
MITRE VALVE.
behind the piston. Thus an alternate motion is kept up by the slide passing, first, over one
opening, then the other; the steam passes by the third aperture into the chimney, where it
causes an additional draught to the fire. The motion given to the slide, however, is a
little in advance of the required stroke of the piston, it being necessary that the steam should
be admitted before the piston commences moving, so that it may exert its full power
upon it; and this is effected by giving a lead to the slide The eccentric attached to the

Fig. 2050.
SLIDE VALVE AND ECCENTRIO.
Un
1278
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
axle of the wheel, which as it turns pushes and draws the rod of the slide, does the duty of
a crank, converting the circular to alternate motion, as far as the slide is concerned, and
alternate into circular, as regards the axle of the engine. The slide, however, not being
exactly in the same plane with the axle, the motion is not directly communicated to the

Fig. 2051.
ECCENTRIC SLIDE Valve, side vIEW.
rod by the eccentric, but by a cross axle, and the two arms affixed to it; so that when the
eccentric goes back, the slide rod is made to advance: there is an instant during the time
the slide is in progress that all the passages are shut, and this is whilst the piston is
changing its direction; to obtain a maximum effect, the steam requires to be shut off before
the piston has reached the extremity of the cylinder, and the aperture on its other side
should be partly opened before its change of motion takes place.
The Drivers are those portions of the engine which serve to change its movement: this
is performed by disengaging the eccentric from one, and carrying it to the other; so that
the director of the locomotive can at pleasure cause it to advance or retire. The drivers
are fixed on the axles on opposite sides of the eccentrics, which being pushed by means
of a lever can be thrown either into or out of gear; so that to change the motion it is only

HI-
Fig. 2052.
DRIVERS.
requisite to lift one set of forked arms from off one set of weight bars, and replace them on
the other, which is performed by a handle, working on a fulcrum, and moving the arm attached
to it: this also works a small pin fitting into the oblong groove of another lever, and
moves the forked arms upwards; at the same time the lever is depressed by the pin,
and with it the forked arms below. The piston-rods slide on guides, and preserve a
regular horizontal motion, and from them is communicated a rotary movement to the axles
of the hind wheels, the alternate being transformed into circular motion by means of a
crank on the axle.
There is great danger in cranked axles from their breaking, which with four-wheeled
engines might occasion considerable damage; this has repeatedly happened, generally from
bad welding: in one instance, on the London and Birmingham Railway, an engine was
discovered to have been running for some time with a broken axle, arising from the eccen-
trics being keyed on to the weakest part of the axle, and only two-thirds of its section
being soundly welded.
CHAP. XXI.
1279
LOCOMOTIVE ENGINES.
Pumps for the supply of water to the boiler are usually two in number, placed beneath
the piston-rod of the cylinders; they suck a portion from the tender, and then force it into
the boiler: these pumps have spherical valves, made of metal, which rise within a cylinder
having four apertures for the passage of the water.
To fill the boiler a square pit should be sunk, large enough to admit a pair of 3 feet
wheels, fixed on an axle similar to the carriage wheels; they should have no flanges, and
their circumference should come up through the rails, and be made to lock at pleasure.
When it is required to pump water into the boiler, the engine must be brought with its
driving wheels directly over those in the pit, and these latter being unlocked, the steam
is let gradually on, and the pumps worked as long as is necessary for filling the boiler,
without the engine advancing from where it was placed.
The Steam Whistle is fixed to the boiler; by turning the handle, the cock placed in
the pipe is moved round; the steam issues with such
violence that when it enters the brass hemispherical cup
at the top, it strikes in its passage the thin edges of a
horizontal brass plate, producing a shrill and loud whistle
as it escapes.
We shall now give the dimensions of some of the most
approved locomotives: those used upon the Liverpool and
Manchester line have cylinders 10 inches in diameter, and
a length of stroke of 16 inches; their boilers are 3 feet in
diameter, and 6 feet in length, within which are inserted
90 tubes, 2 inches in diameter: the fire-box is 24 inches
in length, and 36 in width, with a similar height. The
area exposed to radiant caloric is 25 feet 6 inches super-
ficial, whilst the area of the fire-grate is 6 feet: the
superficial area of the tubes in contact with the heated
air is 283 feet.
In an engine where the diameter of the cylinder is 11
inches, and the length of stroke 16 inches, the boiler is 3
feet in diameter, 61 feet in length, and contains 132 tubes,
1 inches in diameter; the length of the fire-box is 22
inches, the width 40 inches, and the height 34 inches.
The area exposed to the radiant heat is 323 feet; that
of the fire-grate nearly 7 feet, and the area of the tubes
exposed to the contact of the heated air is 379 feet.
An engine with 12-inch cylinders, and with the same
length of stroke, has a boiler 3 feet in diameter, and 7
feet 9 inches in length, with 104 tubes, 1½ in diameter :
the fire-box is 24 inches in length, 43 inches in width,
and 37 inches in height above the fire-bars.
The area
exposed to the radiant heat is 393 square feet; that of the
fire-grate is 7 feet, and the total area of the tubes 354
feet.

Fig. 2053.
STEAM WHISTLE.
An engine of 14-inch cylinders on the Leicester Rail-
way, and 18-inch stroke, has a boiler 42 inches in dia-
meter, 90 inches in length; 97 tubes 2 inches in diameter; the length of the fire-box
is 26 inches, the width 41, and the height 44 inches: the area exposed is 46 superficial
feet, and that of the fire-grate nearly 7 feet. The area of the tubes in this engine is
420 feet the total weight, when in working trim, 10 tons 8 cwt.; the dimensions of
the steam-way to the cylinder are in length 7 inches, and width 1 inches.
An engine on the Newcastle and Carlisle line, with 15-inch cylinders, and a length of
stroke of 16 inches, has its boiler 45 inches in diameter, 8 feet 6 inches in length, and 145
tubes, 1 inches in diameter. The fire-box nearly 39 inches in length, 41 in width, and
444 inches in height: the area exposed to radiant heat 60 feet 4 inches, and that of the
fire-grate 111 feet superficial. The area of the tubes in contact with the heated air nearly
547 feet.
An engine on the Great Western, with 16-inch cylinders, and a stroke of 16 inches,
has its boiler 4 feet in diameter, and 8 feet 6 inches in length; the number of tubes 167,
all 1½ inches in diameter. The fire-box in length 413 inches, in width 47, and in height
above the bars of the grate 453 inches. The area exposed to radiant heat 70 superficial
feet, and the area of the fire-grate 136 feet. The area of the tubes exposed to the heated
air was 543 square feet.
The above engines were constructed by R. Stevenson and Co., at Newcastle-upon-Tyne;
the following were made by Messrs. R. & W. Hawthorn of the same place. An engine
with 12-inch cylinders, and a length of stroke of 16 inches, had the diameter of the boiler
1280
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
36 inches, and length 89; in this were 64 tubes, 2 inches in diameter. The length of the fire-
box 21½ inches, width 41, and height above the bars 38 inches. The area of the fire-box
exposed to radiant heat 37 square feet, and the area of the fire-grate 6 feet 1 inch, and that
of the tubes 262 feet 6 inches. The weight of this engine without water in the boiler was 145
cwt., and when filled 170 cwt.; the length of steam-way to cylinder 6 inches, and width
11 inch.
A 12-inch cylinder, with an 18-inch stroke, made for the Paris and Versailles Railroad, had
a boiler 39 inches in diameter, and a length of 8 feet, with 121 tubes, 15 inches in diameter.
The length of the fire-box 30 inches, width 411, and height above the bars 403 inches; the
area of the fire-box exposed to the heat 46 superficial feet, and that of the fire-grate 8 feet
7 inches. The area of the tubes in contact with the heated air was 428 feet 3 inches; its
weight, without water, 172 cwt. and with, 200 cwt.
A 13-inch cylinder, made for the Grand Junction, with an 18-inch stroke, had the boiler
39 inches in diameter, and 8 feet in length: there were 130 tubes, 18 inches in diameter :
the length of the fire-box 32 inches, width 41, height above the bars 421; the area of the
fire-box 491 superficial feet, and that of the fire-grate 9 feet 2 inches; the area of the sur-
face of the tubes 460¦ feet. The weight of this engine without water, 175 cwt., and 203
cwt. when filled.
A 14-inch cylinder, and 18-inch stroke, on the Newcastle and Carlisle line, had its
boiler 42 inches in diameter, and 8 feet 6 inches in length, which contained 115 tubes 2
inches in diameter. The length of the fire-box 36, the width 414, and the height above
the bars 44 inches; the area of the fire-box 54 feet, and that of the fire-grate 10 feet 4
inches. The area of the tubes 532 feet, and the weight of the entire engine, without water
in the boiler, 205 cwt., and with, 235.
A 16-inch cylinder, on the Great Western, with a length of stroke of 20 inches, has
its boiler 44 inches in diameter, and 8 feet 8 inches in length: there are 135 tubes, 15
inches in diameter. The length of the fire-box 44 inches, width 60, and height 47; the
area of the fire-box 108 feet, and that of the fire-grate 17 feet 2 inches; the area of
the tubes exposed 516 feet.
The locomotives constructed for the Southamptom Railway by the Messrs. Rennie, of
Holland Street, London, combined all the improvements that had been made up to that
period. The diameters of the cylinders were 13 inches, the length of the stroke 18 inches,
and the area of each of the cylinders was 1323 inches; there were 118 brass tubes, and
the heating surface 493 feet: the area of the fire-grate 9 feet 4 inches, containing 14 cube
feet of fuel: the water in the boilers was a little more than 36 cube feet, and the space
for the steam was 32 cube feet. The water evaporated in an hour, with steam equal
to 50 pounds pressure on the safety-valve, was 631 cube feet. The following table will
show the other proportions:
Water supplied by each pump, per stroke
Diameter of the driving wheels
of the small
Cubic content of water in tender tank
Weight of ditto when full
Time which the water in tender will supply engine
Coke fuel necessary to evaporate all the water in the tank
Number of revolutions of driving-wheel per minute, at 30
miles per hour
56.5 cube inches.
5 feet 6 inches.
3 feet 6 inches.
118.8 cube feet.
3.3 tons.
1.87 hours.
Velocity of each piston in feet per minute, at the average
speed of 3 miles per hour
Area of steam pipe
of steam ports
of eduction pipes
of blast pipe mouth
of chimney
of radiating surface
91 cwt.
152.76
458.28
9.62 square inches
9.56
14.87
7.06
159.
-
6696.
-
70960⚫
77650.
of communicating surface
of total heating surface
Total resistance to the motion of the pistons per square inch
on its surface
Volume which the whole steam produced per hour will occupy
at the reduced pressure of the preceding resistance
Ratio of the preceding volume to that expended in effecting a
single stroke of one piston, number of strokes per hour
Corresponding number of revolutions of driving-wheel,
Distance travelled per hour
Weight of the engine without water
Ditto of tender
38.4 pounds.
46695 cube feet.
32427
8106-75 per hour.
261 miles.
11 tons.
51
CHAP. XXI. STEAM CONSIDERED AS A MOVING POWER.
1281
The velocities of these engines have frequently exceeded 41 miles per hour, and the
safety-valve is so constructed as to liberate the steam in an admirable manner, the principle
being to diminish the resistance in proportion to the opening of the valve, contrary to that
practice where springs and levers are used, the improved valve being made capable of
regulation for any intensity of resistance.
the
A locomotive engine and tender made by Messrs. Hawthorne for the Versailles line has
Diameter of cylinders
Steam way to cylinder
Length of stroke of piston
-
Boiler 8 feet long, 39 inches in diameter, contains 121 tubes 1
length of tubes 8 feet, and presenting a surface exposed
428.40 square feet
Fire-box
Height above the bars
Area of fire-grate
presenting a surface exposed to radiant caloric of
Quantity of fuel contained in fire-box to the height of the
lowest row of tubes
Diameter of chimney
The wrought-iron driving wheels
supporting wheels
Weight of engine, without water, in boiler
with water,
12 inches.
length 6, width 11 inches.
18 inches.
inches in diameter, exterior
to contact with heated air of
- length 30, width 41 inches.
40 inches.
8.59 square feet.
46.16 square feet.
1360 cube feet.
14 inches.
5 feet diameter.
3 feet diameter.
8 tons 12 cwt.
10 tons.
Consumption of Fuel. When coals are used the same quantity is required as of good
coke, which varies with different engines from half a pound to a pound per mile for every
ton of load: the latter is perhaps nearest the truth upon level lines.
In locomotive engines the power does not depend altogether upon the diameter of the
cylinders, a certain quantity of steam being produced each moment; if the diameter of the
cylinder be increased, the number of strokes will be diminished, or the steam will have less
elasticity; and if the diameter be less, then a greater elasticity or pressure per square inch is
obtained, or an increased number of strokes: the quantity of steam being limited, the power
of the engine depends entirely upon the number of times the cylinders can be filled during
a minute, or the quantity of steam that can be generated or water evaporated in a given
time. The elastic force of the steam is also partly diminished before it reaches the cylin-
ders, by being obliged to pass through the small apertures of the pipes: and the pressure
upon the piston is less than against the steam-valve in the boiler, which is still further dimi-
nished when the engine increases in velocity.
The Killingworth engine had a boiler 9 feet 2 inches in length, and 4 feet in diameter;
within it was an elliptical tube which contained the fire, 2 feet 4 inches broad, 2 feet high,
and 4 feet 8 inches long. The area of the fire-grate was nearly 13 square feet; the number
of tubes 43, the radiant surface 221 square feet, and that of the communicative surface 101
feet 6 inches. The volume of heated air which passed through the tubes was equal to 135
square inches; the load 60 tons, exclusive of the tender, and the velocity upon a level road
9 miles per hour. The quantity of water evaporated per hour in this instance was 279
gallons, and of coal consumed 14 pounds for every cube foot of water converted into steam.
By another experiment it was found that the same engine with a load of 40 tons,
travelling at the rate of 9 miles per hour, evaporated 40 cube feet of water, or 247 gallons
per hour, with about 13 pounds of fuel for each cube foot evaporated: in one of the early
experiments made at Liverpool, the Rocket engine, whose fire-grate contained an area of
6 superficial feet, a radiant surface of 20, a communicative surface of 118 square feet, with
a load of 40 tons, going a velocity of 13 miles an hour, evaporated during that time only
30 cube feet of water, which shows the improvements that have been made since that
time. By Mr. Watt's experiments, it required 8 feet of surface to be exposed to the
direct action of the fire to evaporate a cube foot of water in an hour, and 10 cubic feet were
converted into steam with 84 pounds of coal; in many locomotive enginės, it requires
upon an average 19 pounds of coal to convert a cube foot of water into steam, which is
more than 24 times Mr. Watt's estimate; there is therefore at present in some instances a
very great loss in the application of fuel to locomotives: upon the Killingworth railway
the average of several years' consumption for the engines employed was 2-12 pounds per
ton per mile; on the Darlington railway, 2-16 pounds; upon the Bolton and Leigh
railway 2.03 pounds per ton per mile.
1
Railway Hydraulic Traversing Frames, used at the Bristol terminus of the Great Western, for
moving the railway carriages from one line of railway to the other, without the use of the
turntable. This machine is a wrought-iron frame, strongly braced and tied together
laterally and diagonally; at each of the four corners is placed a cast-iron hydraulic press,
4 N
1282
BOOK IT.
THEORY AND PRACTICE OF ENGINEERING.
connected with two force-pumps by means of copper pipes and gun metal nozzles:
upon the plungers of the four presses rest two additional frames, which are attached
to the one below by four sets of parallel motion bars, so that they rise truly perpendicular.
When it is required to move a carriage from one line of rails to another, the apparatus
is pushed under it, and when the carriage is in a position directly over the frame, the
large pump which acts upon the four hydraulic presses raises the frames until they
arrive under the axles of the carriage wheels; after this the smaller pump is worked,
which raises the flanges of the wheels clear of the rails: when the carriage is moved, a
stopper is unscrewed, which permits the water to flow from the presses back again into the
cistern, and the carriage is lowered to the rails; the apparatus is then drawn out and ready
to be again made use of; the cost of this machine is about 2207., and was designed by Arthur
John Dodson.
Locomotive Engines on the London and Birmingham railway are all constructed with
four wheels and in one uniform pattern; the passengers' engines have 12-inch cylinders,
and the pistons an 18-inch stroke; the driving wheels are in diameter 5 feet, and the
carrying wheels 4 feet: the engines employed for the transport of goods have 13-inch
cylinders, and a stroke of 18 inches also, but in these all the wheels are 5 feet in diameter;
a passenger engine with its coke and water in the fire-box and boiler weighs 9 tons 13 cwt.
1 qr., and the other 11 tons 13 cwt. 1 qr.
The framing of these engines is fixed inside the wheels, which allows of its being better
attached to the boiler; the whole is of wrought-iron; the cylinders are also made fast
to this frame by strong wrought-iron bars, as are the cranks and fore axles: when the
engine is either advanced or made to retrograde, the motion is conveyed through the
framing alone, and no strain whatever is produced upon other parts. There are two
bearings inside the wheels alone on the axles; and the bushes in which the axles run are
so fitted to the frame that the springs have a vertical movement and no lateral action;
they are so arranged with a flange at their sides, that if an axle were to break, they would
support the engine for a time.
1000
Two of these Engines, made by Edward Bury, in the year 1839, performed a journey
of 700,000 miles at the following cost: for the first six months the cost of conveyance of
passengers was 353 of a penny per ton per mile; and for the second 6 months 380; and for
the first six months of the other engine carrying goods, the total cost per ton per mile was
2003 of a penny, and for the second six months 237 of a penny: this calculation included
the cost of coke, oil, tools, wages, repairs, and general charges.
1000
1000
Locomotive Engines, manufactured by Mr. Norris, of Philadelphia, and sent by him to
the Grand Junction Railway: the construction of these engines was simple; their boilers
were horizontal; each contained 78 2-inch copper tubes, 8 feet long each, with an iron
fire-box the cylinders were 10 inches in diameter, and were slightly inclined downwards,
and the piston-rods were made to work outside the wheels, so that cranked axles were not
required: six wheels supported the frame, and the two driving-wheels were 4 feet in
diameter, placed close before the fire-box: the other four wheels were 30 inches in
diameter, and attached to a truck, on which rested the front end of the boiler: this
truck, by means of a centre-pin, was connected with the frame, which was made to turn
freely, and with very little stress, along any curve in the rails.
The weight of one of these engines, when the boiler and fire-box were full, was 9 tons
11cwt.; that of the tender, with 21 cwt. of coke and 520 gallons of water, was 6 tons
4 cwt.; when empty it weighed only 8 tons: 62 pounds per square inch was the
limits of working pressure of the steam on the boiler, and when the engine passed a
plane with a rise of 1 in 330, with a load of upwards of 100 tons, the speed varied from 14
to 22 miles in an hour, and on a plane of 1 in 177, from 10 to 14 miles per hour. The
rise of the gradients from Liverpool to Birmingham is 620 feet: and from Birmingham to
Liverpool 380 feet, exclusive of those in the Liverpool and Manchester Railway. In seven
journeys of 596 miles up to Birmingham, the engine conveyed 682 tons, evaporating
12,705 gallons of water, and consuming 265 cwt. of coke: in seven journeys the other
way, or returning, the same engine conveyed 629 tons gross, evaporating 12,379 gallons of
water, and consumed the same quantity of coke.
The price of these engines complete, including the duty, was about 1600/: they were so
well adapted to travel over a curved line, that they have gone at a speed of 20 miles
per hour round one of 10 chains radius; when on a straight line they travelled often 40
miles per hour, and appeared less likely to be thrown off the rails than the ordinary loco-
motives.
CHAP. XXII.
1283
TIMBER AND ITS PROPERTIES.
CHAP. XXII.
TIMBER AND ITS PROPERTIES.
By the civil engineer this production is required to be sound and properly seasoned;
its durability depends upon the absence of those natural juices which possess a saccharine
quality, undergo the process of fermentation, and destroy the substance as well as strength
of the timber.
The various trees of the forest are composed of bark, wood, and pith, and spring from
the acorns or seed which each bears: early in the spring a tender shoot breaks the
ground, which by the end of the year has extended, enlarged, and hardened into a ligneous
substance, terminated by a bud, which in the following year throws out a second shoot,
but of greater strength and larger than that of the preceding year; this process continuing
year after year enables the tree to acquire its full growth.
A cylindrical ring encloses the pith in its early stage, which is surrounded by the bark,
and if a longitudinal section of the plant be made, we perceive medullary rays traversing
the wood; the bark and the alburnum or woody matter have each a layer deposited every
year, whilst the tree is in a growing state; these layers are both formed from a secretion
called Cambium, deposited by the succulent vessels of the bark, and the medullary rays
between the wood and the bark, which secretion is prepared by the leaves and transmitted
through the bark; the new liber and alburnum formed by this gelatinous fluid are by
a process of nature transformed into cells and layers, the diverging as well as concentric
being produced simultaneously; these layers of wood obtain in a few years greater density,
from a deposition of woody matter in the cells, which increases until the tree has arrived at
maturity: each succeeding year of growth a hollow elongated cone may be imagined to
cover the ligneous productions of the former years; the circles, which are distinguishable
when the tree is cut down at its base, exhibit the number of these cones, as well as the
increase of growth each year
The pith and the bark in young shoots are in contact; and the former, composed
entirely of cellular tissue, is at first filled with a watery fluid, and afterwards with air,
becoming dry before the first layer of wood is perfected: the form of its cells is usually
hexagonal; but as the age of the plant increases, they undergo some change; a horizontal
communication of the most perfect kind continues to be maintained between the pith and
the bark, although their separation is annually increased by the succession of concentric
rings deposited. Medullary rays, or the silver grain, which are flattened masses of cellular
tissue, consisting of oblong cells horizontally arranged, effect this by separating into
wedge-shaped vertical plates the rings of zones of wood as they form, and thus keep up a
connection between the pith and the woody tissue and vessels they are combined with on
the outside.
The bark, or outer cuticle, is a thin membrane extending over the entire surface of the
plant, spreading its members like a net, the form of which varies in different plants; this is
divided into four distinct parts: the epidermis, the cutis, the cellular, and the liber
or inner bark; the cutis consists of two layers, the outer of which is the epidermis, and
the inner a composition of transverse cells, of a varied structure. The longitudinal
fibres of the bark vary, but are formed of hollow tubes, which convey the sap downwards,
for the purpose of increasing the solid contents of the tree. The bark itself is annually
reproduced, and the old layers pushed outwards: there are no annular or spiral vessels,
the cells contain occasionally a secreted fluid, which, in some instances, is useful to the arts.
Elasticity, extensibility, contractibility, permeability to fluids and gaseous matters, are
the chief elementary organs of trees; which, by their cellular tissue, transmit their food in
all directions by it the sap is circulated, and the medullary rays formed, which convey
the juices from the bark to the centre of the stem; the bark itself is composed of it, as
well as the leaf, which exposes to evaporation, light, and atmospheric action the parenchyma
in which the sap is diffused. The woody tissue, destined to convey the fluids upwards and
downwards, gives firmness and elasticity to the various parts: and the sap-wood next the
bark, containing all the nutritive matter to be converted into leaves, buds, and heartwood,
may easily be supposed to be acted upon by a variety of causes, and be most subject to
decay when its vessels have lost their juices, and it is compressed into heartwood, its use
is then to give support to the tree.
:
:
Wood is formed, according to Linnæus, from the pith, and by other naturalists it is
supposed to be produced by a change of the liber of the previous season by Du
Hainel, that it is deposited by the secretion called Cambium, which is found between
4 N 2
1284
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
the bark and the wood, and in process of time converted into cellular and woody tissue, and
that the alburnum derives its origin from the bark, and not from the wood; whilst others
imagine that wood and bark are independent formations out of cambium. The central part
of the tree is the best timber, for the last layers or rings have their vessels larger and less
compressed, being full of juices, and consequently of less density.
Different Species of Timber used in Construction. — Acacia, (Robinia pseudo-Acacia, or
Locust Tree,) forms heartwood at an early stage; when it arrives at maturity it measures
nearly 2 feet in diameter; in the pleasure-ground it is a very ornamental tree, and of rapid
growth. When used for construction it is durable, and well adapted for sills and wall-
plates, its lateral strength being greater than that of oak, in the proportion of 1 to 75: it
is heavier, harder, and tougher than the best oak, and more elastic, not readily breaking to
any strain for posts placed in the ground it will endure sound a long time; it is valuable
for fences and treenails for ship-building. The weight of acacia is one-sixth greater than
that of oak.
It weighs when newly cut
half dry
quite dry
lbs. oz.
63 3 per cube foot.
56 4
48 4
Its strength is as, compared to oak, 1427 to 820, and its elasticity as 21 to 9: its lateral
strength has perhaps been too highly rated.
Alder (Alnus). This tree has the property of enduring a long time under water, which
renders it valuable for piles and water-pipes: it has a fine and close texture, is of a
beautiful colour, works easily and well, and has been much used by the joiner and cabinet-
maker.
It weighs when green
half dry
quite dry
lbs. oz.
62 4 per cube foot.
48 8
39 4
The charcoal obtained from it is valuable for gunpowder, and 1000 lbs. of its ashes
yield 65 lbs. of potash.
Ash (Fraxinus excelsior) grows to a large size, with a straight trunk; its wood is very
elastic, and joists cut out of it bear before breaking a greater weight than almost any other
variety of British timber. The wood when young is very flexible, and easy to work; but
after it has undergone the process of seasoning, it is both tough and hard, and is then
more used by the wheelwright than the carpenter. When subject to alternate dryness and
moisture it is not durable, and if cut down when full of sap the worm soon attacks it: its
quality is much altered in different soils.
When green it weighs
dry it weighs.
lbs oz.
64 9 per cube foot.
49 8
Beech (Fagus sylvatica) is described by Pliny as one of the thirteen species of trees
bearing mast or acorns; on a chalky soil it acquires a prodigious size, and is the finest
tree of the forest: its timber is smooth and hard, its transverse fibres very obvious, some-
times forming distinct and dark lines, and it is highly useful for various purposes. The
worm attacks it speedily, if not freed from sap, which is often done by steeping it in water,
and then exposing it to smoke: when beech is constantly under water, it is very lasting,
and therefore well adapted for piles; in a dry state and much exposed, it will split and
crack.
When green it weighs
half dry
quite dry
lbs. 02.
-
65 13 per cube foot.
56 6
50 3
Its ashes are productive of potash, 100 lbs. of green wood producing 1 lb. 10 oz.
Birch (Betula alba) has its wood tinged with red, and a moderately fine grain; when
the tree has acquired its full growth, the timber is exceedingly hard, but not very durable;
it works better in a green state than when perfectly seasoned and dry.
When green it weighs
half dry
dry
lbs oz.
65 4 per cube foot.
56 6
45 1
In a tree 60 years old, perfectly dry, a cube foot only weighed 36 lbs. 13 oz.: 1000 lbs.
weight of this wood burnt in a green state yields 1 lb. 4 oz. of potash, which is most abun-
dant in the bark and spray.
Box (Buxus sempervirens) is a valuable wood, of a yellowish colour, close grained, very
hard and heavy; it cuts better than most others, is susceptible of a fine polish, and is very
durable; it is much used by turners and mathematical instrument-makers, and by the wood-
engraver almost exclusively.
CHAP. XXII.
1285
TIMBER AND ITS PROPERTIES.
Cedar (Cedrus pinus) grows to a great size; the timber is resinous, of a reddish white
colour, light and spongy in its texture, easily worked, but apt to shrink and warp, if great
attention be not paid to the seasoning; the annual rings are distinctly marked, and appa-
rently consist of two layers, one narrow and hard, the other three or four times its thick-
ness, and softer: it was exceedingly valued by the ancients for its durability and other
properties.
Pliny asserts that the beams of the Temple of Apollo at Utica, which were of Numidian
cedar, had endured 1178 years: its resin or gum was considered to possess the quality of
preserving any matter from decay that had been steeped in it; the leaves of the papyrus,
rubbed with it, Vitruvius says, were never attacked by insects. The wood is odoriferous,
and admirably adapted for joiners' work: it is the lightest of resinous woods, and con-
taining but a small quantity of resin: its weight is said to be 29 lbs. 4 oz. per cube foot,
according to one authority; 42 lbs. 14 oz., and 57 lbs. by others: as a mean, it may,
perhaps, be taken in a dry state at 42 lbs., or a little more.
Cedar, Indian (C. Deodara), a native of the Indo-Tartaric mountains, grows to a very
large size, and is a very compact wood, strongly impregnated with resin: the hardness and
the fineness of its grain occasion it to be much used by the Hindoos for the purposes of
building, and when constantly exposed to the weather, its durability is considerable :
bridges constructed of it, though occasionally exposed to the action of the torrent, have
endured for 500 years.
Chestnut (Castanea).— This timber, when found in old buildings, has been frequently
mistaken for oak, but the pores in the alburnum of the latter are generally much larger,
more numerous, and very distinguishable, whilst those of the chestnut are irregular, and
scarcely discernible to the naked eye; there is also an absence of the tranverse septa, which
distinguishes the oak: there is, however, a species of oak, much used in the middle ages
for the carpentry and roofs of halls and chapter-houses, which in colour and texture bear
a close resemblance to chestnut; this species has a smooth bark, large leaves, and its wood
rather softer than that of the ordinary oak, which might occasion it to be preferred for
carved work, or where delicacy of execution was required; but whichever material was
selected, great care was taken to admit the air freely, as well as to protect it from the
weather, precautions as important as the proper selection and requisite seasoning of the
timber. The cohesive force of the chestnut varies from 9670 to 12,000 lbs. per square
inch when dry.
The weight of the chestnut when
Ditto
-
green
dry
is
-
·
lbs. oz.
68
9 per cube foot.
41 2
Horse Chestnut is a soft wood, and not applicable to any purposes where strength is
required; in the open air it has little. durability: it has been employed for water-pipes,
when it can constantly be covered with earth.
The wood, when newly cut, weighs
Ditto dry
lbs. oz.
60 4 per cube foot.
37 7
Cypress is remarkable for its fine grain and durability, and by some is supposed to be the
Gopher wood used in the construction of the ark: this evergreen tree grows with a straight
trunk, and its wood is harder than that of the pine, the colour partaking of a yellowish
red with dark veins in consequence of its not being subject to injuries from the worm,
it was said to be incorruptible, and was much employed by the ancients for statues,
in the construction of temples, and the gates of their public buildings: those removed from
St. Peter's, when the bronze gates were introduced, had previously served to adorn the
basilica of Constantine. In Egypt this wood was used for mummy cases; it is less
affected by exposure to the atmosphere than cedar.
Elder. The wood of this tree, when old, is very hard and adhesive, of a fine yellow
colour, and susceptible of a high polish; in a dry state a cubic foot weighs 42 lbs. 3 oz.
Elm (Ulmus). The campestris is the most durable and the hardest of the five
English species; the suberosa not so valuable; the montana, or broad-leaved, is that most
commonly produced in Europe; the glabra, or wych elm, is used by wheelwrights; and
the major, or Dutch elm, is of an inferior quality. The elm, either in a perfectly wet or
dry state, is very durable, and is admirably suited for planking or piling under water,
enduring six or seven centuries. The wood is porous, cross-grained, has no large septa,
shrinks in drying, both in length and breadth, is difficult to work, but will not readily
split when nails or bolts are driven into it.
The wood of the campestris, when green, weighs
ditto
dry
lbs.
70 per cube foot.
481
The cohesive force of a square inch varies from 6070 to 13,200 pounds: it is rich in alkaline
salts, occupying a tenth place out of 73 woods experimented upon.
4 N 3
1286
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Sweden
Fir (Pinus sylvestris). — Of all the species this is the most valuable for its timber; it is
produced in most parts of Europe, and its quality varies according to the soil on which it
is grown on a stiff cold earth, the wood has a red tinge, and acquires a solidity which it
does not attain on sandy or light lands, where it becomes in colour nearly white.
and Norway, as well as Prussia, Poland, and Russia, supply the English market from their
extensive forests with both timber and deals cut out of this tree; the timber is floated
on the Gotha to Gottenburgh, being divested of its bark, and on the Glomm to
Christiana: but that most esteemed from the Baltic is the Riga, which is preferred for
masts by the navy; the Russian timber is said to take so long a time in reaching
Cornstadt, the port from whence it is exported, as to lose much of its quality.
In Scotland this species of fir, on favourable soils, attains considerable size, and forms
most excellent timber; one tree at Duninore contained 300 cube feet; and its durability,
particularly the red, is equal to that of the oak: there are instances of its being found in
the roof of a castle, after 300 years, as full of resin and as fresh as any newly imported from
Memel.
'The appearance of fir timber differs materially in the best, the concentric rings are
seldom so much as inch in thickness, whilst they increase in the inferior kinds; the
colour is of a reddish yellow, and it has no large transverse septa: when spongy, and
presenting a woolly texture, it is improper for the purposes of construction.
lbs. lbs.
A cubic foot of this tree in a green state weighs from 54 to 74
Ditto
dry
m
31 to 41
Pinus Strobus.-The white or Weymouth pine is brought into the English market from
Canada or North America: its annular rings are not very distinct, nor is its durability
remarkable, being subject to dry rot; a cubic foot when dry weighs 29 lbs.
Pinus, Mitis, or yellow pine, called in England the New York, is very full of turpentine,
and more durable and of greater strength than the white pine above mentioned: it does not
attain so large a size, but is a more valuable timber.
Pinus Abies, or Norway Spruce, is another variety of white deal, and considerable
quantities are annually imported from Christiana, which are highly esteemed for their
quality: a cubic foot weighs 34 lbs. when dry.
Holly.. The veins of this wood are scarcely perceptible, but it is valuable for many
purposes, to the joiner, cabinet-maker, engineer and turner, as well as to the wood
engraver: when dyed black it is a substitute for ebony.
When perfectly dry it weighs
lbs Oz.
47 7 per cube foot.
Hornbeam. — A hard, heavy, tenacious wood, very close-grained, is diminished much in
drying, and consequently loses weight: the cogs of wheels are usually made of it, for
which purpose it is well adapted.
When green it weighs
half dry
quite dry
lbs.
64 per cubic foot.
57
51
Laburnum is in use amongst turners: pulleys and blocks are ma f it, being a hard
and compact wood; it is capable of endurance when exposed to the weather, and for various
purposes is extremely valuable.
When perfectly dry a cube foot weighs
lbs. Oz.
52 11
Larch (Larix). This valuable timber comes to perfection in a good soil in about 40
years the colour of its wood is a yellowish white; on some soils, particularly if on an
elevated situation, it is of a reddish brown and very hard, so much so that it is difficult to
season, as it warps and twists in every direction; this wood not being so knotty as that of
the fir, is excellent for all sorts of carpenter's work, being from its strength well adapted
for girders and principal timbers. Scammozzi thinks it the most useful of all woods
for the purposes of construction; it is not attacked by worms; he also mentions the
enormous size of some of the trees growing in the Venetian Alps, many of which he
employed in the public buildings at Venice. The Romans used this timber, and procured
it from Rhetia and Switzerland, floating it down the Po, then by the Adriatic, the Ionian
and Tyrrhenian Seas, and finally by the Tiber to the Capitol : no wood endures so long
under water: in France and Switzerland it is much used for pipes to conduct water for
the irrigation of the lands, particularly in Provence; by the Swiss it is universally
preferred; they cover their houses with shingles made of it, and from its taking a high
polish after planing it gives an agreeable finish to the interior: the closeness of its grain,
and the strength of its fibres, enable it to resist twisting; it is not subject to crack,
from which cause it was selected, according to Pliny, by the painters of old, as it
was by Raphael in later times. The knots are never in a state of decay, and it is much
CHAP. XXII.
1287
TIMBER AND ITS PROPERTIES.
less liable to shrink than the other kinds of deal, nor will it split with the grain to any
considerable length, from the crossing of its fibres.
Lignum Vitæ, is a hard wood much used by millwrights; its specific gravity is 1·333, and
the weight of a cubic foot is 83-31 pounds avoirdupois.
Lime is a beautiful ornamental tree, and grows to a prodigious size, acquiring a
diameter of 15 or 16 feet: the wood is of a pale yellow colour, close-grained, soft, light,
and smooth in its texture, admirably adapted for the purposes of fine carving and cabinet-
work.
Maple (Acer Pseudo-platanus) is found growing in mountain districts, and valuable for
its lightness, and not being subject to warp or split it will take any colour and a fine
polish.
When green, it weighs
dry,
lbs. oz.
- 61
9 per cubic foot.
51 15
Sugar Maple, (Acer saccharinum). The bird's-eye maple, from the beauty of its grain
and the shades of its spots, is much employed for veneering; by sawing the timber nearly
parallel with the concentric rings, the effect of its marking or pencilling is much improved:
in America wheelwrights employ it, after giving it a seasoning for three years, and when
constantly under water it will not readily perish.
Mahogany (Swietenia Mahogani) is the produce of America and the West Indies, and it
is principally imported from Honduras and Campeachy: that imported from the islands
is called Spanish mahogany; the annular rings are not very distinct, it has no large septa,
and warps less than most other woods: that brought from Honduras is the production of
low marshy ground, and is coarse, soft, and spongy, whilst the most beautiful mottled and
veined is grown upon high ground, and is often very valuable, being cut into veneers
eight or ten to an inch: worms will not attack it when properly seasoned, but exposure to
our climate soon destroys it; it is much used in parts of machinery, furniture, and por-
tions of joiners' work, where ornament is studied. The weight of a cube foot is from 35 to
53 lbs.
Oak, ( Robur Quercus, or pendiculata). The common English Oak acquires considerable
size, but does not grow so tall as some of the other species; its wood from its hardness is
difficult to work, though preferred, where solidity is required: the Greeks call this
species drys; the leaves have short footstalks, and the acorns long ones; the grain of the
wood is fine, of a reddish tinge, free from knots, and will cleave easily into pales or lathes;
where stiffness is an object, as in guiders or joists, it is very useful, as it will not bend
readily.
When green it weighs
half dry
perfectly dry
lbs.
Oz.
·
76
13 per cube foot.
65 9
-
52 13
Oak (Quercus sessiliflora). — In this variety of oak, the wood is of a softer quality,
and consequently yields more readily to the tools of the workman; the leaves are
attached by long footstalks, and the acorns set close to the branches, differing in this
particular from the specimen above described: the timber is subject to warp and split, but
in consequence of its elastic qualities, it is highly prized for ship-building, its toughness
and strength recommending it for that purpose; its hardness is sufficient for all ordinary
purposes where oak is required. The grain of this variety bearing a strong resemblance
to that of the chestnut, it is often mistaken for it, and it will last a long time, when
preserved either entirely dry or under water.
When green it weighs
half dry
perfectly dry
lbs. oz.
80 5 per cube foot.
67 12
51 10
Among the other varieties of the oak is the Etumodrys, which grows more lofty than
the robur; the Esculus, or holm oak, mentioned by Vitruvius as having "its elements
composed of earth, air, fire and water, in more equal proportions than others, is of great use
in building, but damp soon destroys it; and its air and fire being driven off, it soon rots."
The Quercus Ilex, or holm oak, is probably the Cerrus of Vitruvius; it produces acorns
similar to that of the Esculus, which are also edible; the leaves continue during the winter,
and the tree lives to a great age; its bark is very thick; the wood takes a fine polish;
like other hard specimens it splits and warps in drying, though it possesses considerable
flexibility; it weighs 70 lbs. the cube foot.
Oak (Quercus alba), or American oak, and the Quercus rubra of Canada, are of quick
growth, but not so durable as the British oak: wainscot is obtained from the Riga oak,
which is very clean and free from knots, and much in request by the joiner, forming good
floors and wainscoting.
4 N 4
1288
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Olive. This wood, when covered with mortar, endures a long time, and was much
employed by the ancients to tie their walls together, as well as to form their roofs, when
these were covered with stucco, and for all sorts of carpenters' work.
Plane (Platanus orientalis) is a native of the Levant, and its wood much resembles the
beech; the trunk of the tree grows very lofty and straight before it throws out branches.
Pliny mentions one at Lycia the circumference of which was 81 feet; in its cavity
eighteen persons were entertained at dinner. The wood is applied to many useful
purposes by the joiner and cabinet-maker.
Plane (Planus occidentalis) is produced in North America, and is of a more hardy quality
than that just described: its diameter on the borders of the Ohio and Mississippi is
sometimes as much as 12 feet; it will last a considerable time under water, and is used for
the construction of quays, &c.; when dry it weighs from 40 to 46 lbs.
Poplar (Populus). The different kinds are useful in building; one is especially preferred
in Lombardy, which, when cut into planks, has considerable durability; Vitruvius says,
where great strength is not required, it may be used, and certainly if maintained in a
dry state will last a long time: when applied for flooring boards, two or three years'
seasoning is required, as it loses much of its bulk in drying; it does not easily split by
driving nails into it, and it has an advantage over many other timbers in not catching
fire easily.
When green it weighs
in dry state
Populus tremula, (trembling poplar,) is another variety,
weighing when green
half dry
quite dry
lbs. oz.
58 3 per cube foot.
38 7
lbs. oz.
54 6 per cube foot.
40 8
34 1
Populus nigra, the black poplar; its wood is more soft and fibrous, splitting with more
facility, and shrinking in its drying nearly one-sixth of its bulk; it is easy to work, does
not splinter, and is useful to wheelwrights and turners.
In a green state it weighs
half dry
dry state
lbs. oz.
60 9 per cube foot.
42 13
29 O
Populus fastigiata (Lombardy Poplar) is much used for the linings and fitting-up of
store-rooms, as it is said mice will not attack it, and is well suited for the joiners' work
of a cottage: the weight of a cube foot in a dry state is 24 lbs.
Sycamore, or Great Maple: when in a dry state the wood is durable, but the worm soon
attacks it; it is susceptible of a polish, and will not easily warp.
When green a cube foot weighs -
half dry
dry
Losing a twelfth part of its bulk in drying.
64 lbs.
56
48
Walnut (Juglans regia) The wood is solid, compact, easy to work, will neither warp
nor crack, has a beautiful vein, and is rightly esteemed one of the choicest of English woods.
Hilly and poor calcareous soils produce the finest timber; when used in building it will
bend under ordinary weights, but will not crack without giving due notice: rooms wains-
coted with it have a good effect, and it was formerly much employed by cabinet-makers ;
screws of presses and gun-stocks are generally made of it.
When green it weighs
dried
lbs. oz.
58 8 per cube foot.
46 8
Juglans alba grows to a large size; its wood is very tough and flexible.
Juglans nigra has a more beautiful vein, and takes a higher polish, and is esteemed supe-
rior to all other varieties for cabinet-work.
Willow (Salix): this wood is soft, smooth, and light, which occasioned it to be made into
shields by the Romans; if kept from wet, it will last a long time in rafters or other light
timbers.
Salix caprea, a cube foot when dry weighs
Salix alba
lbs. oz.
41 6
27 6
The first losing a twelfth and the latter a sixth part of its bulk in drying.
In Scotland the red willow (S. fragilis) is used for building small vessels in conse-
quence of its lightness, pliability, elasticity and toughness; the wood is of a salmon colour,
CHAP. XXII.
1289
TIMBER AND ITS PROPERTIES.
and before wheels were ring with iron, this sort of willow was employed for the fellies,
enduring under friction and exposure a longer time than most other woods.
Felling Timber. -To the timber-grower the object aimed at should be that of obtaining
the largest quantity of hard and durable wood, as free from sap as possible: no tree should
be severed from its stool until it has arrived at a state of maturity, and previous to its being
thrown down, the natural juices which pervade it should be discharged and allowed to run
out, that the wood may be freed from what would bring about premature decay, and
prevent its becoming dry and hard.
Barking the tree whilst in a growing state, and cutting through the sop or sap-wood, so
as to allow the juices to be discharged, are practices of high antiquity. Vitruvius observes
that both the density and the strength of timber are much improved by causing the tree to die
standing: and most persons have agreed that barking the timber, previous to felling, greatly
improved its quality. "When a tree has an incision made through the sap-wood at
its trunk it soon dies, and no further change takes place; and the barking of trees, when
in full growth and vigour, and letting them stand a twelvemonth after the operation, is
admitted not only to improve the quality, but to increase the quantity, at the same time
that it seasons the wood: time, however, is the best seasoner, and no artificial method can
equal the natural process, which is that of getting rid of all juices in so regular a manner,
that dissipating them does not too rapidly shrink and crack the timber. Trees may be
suffered to stand too long before they are cut down; but this is not a usual fault, for often
when they can measure to a load, which in half a century is sometimes the case, they are
marked for felling, the heartwood not having either acquired its hardness or its full
quantity."
Seasoning Timber. Nothing more effectually contributes to this purpose than suffering
it to lie for a time in fresh water; and our fir timber on its arrival is usually formed into
floats on the Thames, where it remains for some time; thus the natural juices of the tree
are removed by the water penetrating throughout its pores; this not containing any
quality to produce fermentation, and being afterwards easily evaporated, tends to improve
it for building purposes. Salt water, on the contrary, would require a considerable time
to evaporate from the wood, in consequence of its deliquescence, and would render it unfit
for use when taken out of the water, it should be suffered to become thoroughly dry before
it is carried to the pit to be sawn; and the usual method adopted is to block it up from the
ground, and suffer a free circulation of air around it. When the tree is cut into scantlings,
a further seasoning should be permitted by a free exposure to air, guarding against too
violent an effect of wind or the sun's rays, and if it be cut into boards, they should be piled
one on the other, with fillets or small pieces of wood between them, or laid in a triangular
form, with their ends alternating, so as to permit the air to pass freely about them.
Gradual drying should always be resorted to, as it invariably produces the most durable
timber, the object of seasoning being chiefly to drive off the water, and not to disturb any
portion of the carbon, which would certainly be the consequence of elevating the tempera-
ture of the wood, or exposing it to great heat. Timber dried too quickly loses its tough-
ness as well as its pliability; the outer pores become rapidly contracted, and do not permit
the moisture from within to pass off freely.
Experiment has proved that oak, when seasoned properly, has lost nearly two-fifths of its
weight, showing the necessity of allowing a sufficient time for the juices to be thoroughly
driven off, which time must vary in proportion to the scantling of the timber; if cut into
thin planks the operation of seasoning would be perfected in quicker time than that
which would be necessary for the entire tree. All timber should be permitted to arrive at
this dry state before it is cut into smaller scantlings or planks, great shrinking being the con-
sequence of their suddenly drying by exposure to the air, which, by disturbing the fibres of
the wood, affect its durability: to avoid this it was formerly the practice, after the planks
were cut out by the sawyer, to prevent their exposure to the air, by laying them imme-
diately in a running stream, and after some time to dry them very gradually, care being
taken that the planks, when immersed, were removed from atmospheric influence; but,
like steaming or boiling, this injured the strength of the wood, though it prevented its
warping, and rendered it easier to work. The changes produced by these artificial processes
undoubtedly injure the fabric of the wood; when a piece of thoroughly seasoned timber is
immersed in water, and afterwards subjected to the heat of a stove, it will weigh less than
previously; consequently a portion of its carbon must have passed off.
Where posts or piles are to be driven or plunged into the earth, it has been from the
earliest time customary to char the surface to be placed underground: but to apply this
practice to green timber is injurious, as it confines within, rather than expels these
juices, which by fermenting cause its decay; it may be serviceable in destroying any
fungi or worms that may attach themselves, or prevent their preying upon the fibres of the
wood.
Decay of Timber, its Causes. As woods were supposed to differ in the proportions of
their ultimate elements, various experiments have been made upon them. Dr. Prout has
shown satisfactorily that their composition is similar, and that they consist of equal weights
1290
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
of carbon and water: moist woody fibre in a state of decay evolves one volume of carbonic
acid for every volume of oxygen absorbed; woody fibre containing carbon and the elements
of water, the result of the action of oxygen upon it is the same as if pure charcoal had
combined with oxygen; the elements of water are not, however, contained in the woody
fibre in the form of water, but in their separate states.
When wood in water, therefore, putrefies or rots, carbon and oxygen are separated from
it in the form of carbonic acid, and hydrogen in the form of carburetted hydrogen; when this
decay takes place in the air its hydrogen does not combine with carbon but with oxygen,
for which it has a much greater affinity at common temperatures, and being converted
into vegetable mould, and in a state to be acted upon, is taken up by the plants which
grow within its influence, whilst the oxygen which it contained is gradually given out
to the atmosphere as its decomposition is carried on.
This decomposition may proceed, whether the air has free access or is excluded
from it; under water or in dry air timber will endure for ages without much apparent
change, but when it has been immersed, if the air be admitted freely, the oxygen sur-
rounding it is converted at once into carbonic acid, and the woody fibre is decomposed :
240 parts of dry oak sawdust would convert 10 cubic inches of oxygen into as many
of carbonic acid, which contains 3 parts by weight of carbon, whilst the weight of the saw-
dust is diminished by 15 parts, and 12 parts by weight of water are separated from the
wood.
The decay of wood bears a strong resemblance to the slow combustion of those bodies
containing a quantity of hydrogen, which is oxidised at the expense of the oxygen of the
air, while carbonic acid is produced from the elements of the wood: carbonic acid is not,
however, formed at a common temperature.
Wood in a state of decay sets free two atoms of oxygen and one of carbon for every two
equivalents of hydrogen oxidised; this decay is not effected in a short space of time at
common temperatures, or when humidity is not present: when timber not in a perfectly
dry state is in contact with any of the alkaline earths, its decay is accelerated, the presence
of an alkali enabling it to absorb oxygen, which alone it has not the power to do, whilst
an acid would produce a different effect and retard decay. In a loamy soil timber will
endure some time, because it is kept from contact with air but if this earth contain much
water, then decay will be produced: in moist situations, where the soil is composed of sand
and carbonate of lime, decay is very rapid, the alkaline lime assisting much to hasten it.
When woody fibre or sawdust is moistened with water and excluded from the air for
any time carbonic acid gas is evolved in the same manner as when the air is admitted, and
a putrefaction takes place, converting it into a rotten state; when exposed to a certain
degree of moisture and a temperature not sufficiently high to evaporate the water, decom-
position takes place suddenly, and as this increases, carbonic acid and hydrogen are given
out. Sapwood is consequently more perishable than the heartwood, as it contains those
juices which more readily ferment; hence it must be cbvious that unless they are abstracted
by seasoning, mischief arises from confiuing them in the wood, by covering the surface with
paint or pitch, or even bedding their ends solidly in newly constructed walls; when timber
is quite immersed in water, and kept so, it is by no means so liable to perish as when exposed
to moisture only, aided by a slight degree of warmth.
The well-seasoned timber employed by the carpenters of the middle ages, in the old halls
particularly, as well as in our churches and chapter-houses, needed neither paint nor dressing
of any kind to preserve them; and in many instances they are found sound after four or
five centuries. The weather-boarding of our English barns, which in many instances is of
undressed elm timber, owes its duration to a hard external surface, which it acquires by
time, and which resists almost the edge of a sharp tool, or the point of a nail, apparently a
coating of silica, quite impervious to water, or even the action of moisture; this silica may
be derived from the decomposition of the wheat straw with which the barns are usually
thatched.
When the engineer or the carpenter selects timber for the purposes of construction due
regard must be paid to its firmness, density, and strength, without which qualities no
solid or durable works can be executed. The great weight with which timber is sometimes
loaded, placed vertically or horizontally, shows at once the caution which should be used
in its selection, and when it is exposed to the action of the air, the necessity of having it so
seasoned and protected that it should not be subject to decay: when employed in the
formation of centres to the arch of a bridge, durability for a time only is required, but in
permanent roofs and floors it should be capable of resisting all efforts which may destroy
its utility or strength; its warping and shrinking in edifices entirely formed of it lead some-
times to the greatest inconveniences, as the strength of a truss may be entirely destroyed by
this cause.
The oak and the fir are the species most in use, and are the best for the purposes of con-
struction: the first has the advantage of duration over the other, and will bear either to
be exposed to the action of the air, the water, or to be buried in the earth; in water it will
endure to a time unknown, and it has the advantages also of strength over all other timber.
CHAP. XXII.
1291
TIMBER AND ITS PROPERTIES.
The oak varies in its specific gravity according to the soil which produces it; its
strength is in proportion to its density, and that timber is the most durable which has
this quality in the highest degree: density is mainly owing to the length of time occupied
in the production of the wood; that which grows fast, as it will do on light soils, is not so
heavy, or so hard and compact, as that produced on cold soils, and of consequence slower
growth.
From all the experiments made upon the strength of oak timber it has been found that
this is in proportion to its weight and density, and invariably the heaviest is the strongest :
in the trunk of a tree the most dense wood is found in the lower parts; this quality de-
creases in those branches and portions farther removed from the base. Trees which are
suffered to complete their growth have their heartwood throughout of the same weight
and strength, whilst those cut down prematurely are found to possess these requisites only
in their centre wood, which is considerably harder than that formed by the outer concentric
rings; it may be said to decrease in hardness in arithmetical proportion as it approaches
the sap-wood.
When a tree, however, is suffered to stand too long, and its decay has commenced, the
outer wood is in many instances the hardest: the specific gravity of the oak when cut down
varies from 1000 to 1054, and its weight per cube foot from 70 to 74 lbs.; this weight by
seasoning is reduced to 60 or 63 lbs., and it has been shown that the greatest degree of dry-
ness that can be acquired is when it has lost about one-third
of its original weight; but in this state it is not so durable,
and more apt to break when exposed to a strain, or when a
weight is imposed upon it. That preferred for carpentry
is when only one-sixth of its weight has been lost, as a
certain portion of sap is necessary for the fibres of the
wood to preserve their union; in a perfectly dry state
they have less adherence, lose their stiffness, and split
and break more readily; oak seasoned so as to reduce it
to the weight of about 60 lbs. per cube foot is the most
preferable.
The fir in common use is imported generally from the ports
which surround the Baltic Sea, or from the coast of Norway
or Sweden, and the best deals come chiefly from Christiana
or other ports of Sweden, Prussia, or Petersburgh. The
lightness and stiffness of this timber render it preferable for
girders and framing in general; it is less expensive to convert,
and, although not quite so durable as oak, has the ad-
vantage of cheapness. The timber of the best quality has its
annular rings much thinner than that of the inferior kinds
and when the saw is put in it does not cut so as to leave a
rough or woolly surface, nor is it in the least of a spongy
quality.
White deal is obtained from the spruce fir, the best from
timber of 70 or 80 years' growth; in seasoning it will lose
about one-seventieth part: deals are usually 3 inches in
thickness, and 9 inches wide, and are sold by the hundred,
which consists of 120; whatever may be their thickness
they are reduced to a standard; one of 1½ inches in thickness,
11 inches wide, and 12 feet long, contains 1 foot 4 inches
cube.
The Teredo navalis is most destructive to timber used in
the supports of a bridge or other purposes by the water-
side this pile-worm, as it is sometimes called, is particu-
larly active in destroying timber in contact with the mud
of rivers like the Thames; and wherever the water is

;
A
B
B
...A
B
B
B
DED
E
brackish its ravages are certain. On the left of the figure
the worm is represented on its belly, about half its natural
size, and to the right on its back; A a, at the top of the
figure, is the shell; ABCDE is the form of the hinge
Fig. 2054.
by which the shell is united; A C, BC, the two defences of the tail; ABD and ADC
are its moving fibres; A A, the circular membrane covering the head; and the bottom
figure, A A A A, is the same membrane turned back: this animal, so well described
in the 41st voluine of the Philosophical Transactions, No. 455., is very small when first
exuded from the egg, but soon acquires a considerable size; its head is provided with
a hard substance which resembles an auger, by which it penetrates the hardest wood; the
fir and alder are the woods it most readily destroys.
The carpenter, before he commences any work, should thoroughly comprehend that im-
portant proposition in mechanics, which shows the composition and resolution of forces
1292
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
he should study well the nature of every strain, and its
direction in the timber he is about to apply.
A

Suppose, for instance, an upright beam pushed in the
direction of its length by a load at B, and abutting on
the ends of two beams A C, A D, which are firmly sup-
ported at C and D; and as they cannot move, the pres-
sures they sustain from the post BA are in the direction
A C and AD: to ascertain what each of these timbers
sustain, we must produce A E to B, taking A E from a
scale of equal parts, to represent the number of tons or
pounds by which BA is pressed: draw F F and EG
parallel to A D and A C; then A F, measured on the same
scale, will give the number of pounds by which A C is
strained, and A G will give the strain A D.
Where two pieces of timber, as AC and AD, are
pressed or drawn down by a weight at B, the same
rule will apply, and the nature of the strain produced
must always be observed; in general, if the straining
piece be within the angle formed by the pieces strained,
the strains which they sustain are of the opposite kind
to that which it exerts; if it be pushing, they are
drawing, but if it be within the angle formed by
their directions, the strains which they sustain are of
the same kind; all the three are either drawing or
pressing.
Fig 2055.
F
Fig. 2056.
B
A
G
E
D
Ᏼ

G
E
D
Resistance of Timber to a transverse Strain. The
weight that will break a piece of timber must be
ascertained before we can find the load that it will per-
manently bear; the stiffness of a beam is the proportion
that exists between its deflection and its length, and the deflection, is what it sinks when
loaded below a horizontal line: the deflection of beams of the same timber similarly
loaded varies as the weight applied, and the cube of the length directly, and as the breadth
and cube of the depth inversely, and this deflection should never be permitted to extend
beyond part of the length, or part of an inch to the foot.
The lateral strength of a beam is less than its absolute longitudinal strength, either
against extension or compression; timber will bear a considerable weight if suspended to
it perpendicularly, or when pressing in the direction of its length, provided the timber is
prevented from bending; and in using timber, a lateral strain should always be avoided,
where a longitudinal one can be substituted.
Rectangular pieces of timber have their centres of gravity in the centre of their
dimensions: a piece of timber 12 inches by 12 contains 144 square inches, and its centre
of gravity will be 6 inches from each side; if the piece be broken by any load its fracture
will terminate at the upper surface, or 6 inches above the centre of gravity. The area 144
multiplied by 6, gives 864 as the lateral strength, which may be applied in comparison
with any other scantling of different dimensions on wood of the same quality: saw this
piece of timber down the middle; the centre of gravity remains the same; if the sides are in
the same vertical position, the area of the section of each is 72, and this multiplied by 6,
the distance of the centre of gravity from the upper surface, makes half the product
obtained before the timber was sawn; it is apparent, then, that, the depth remaining the
same, the strength varies as the thickness: should the position of these latter timbers be
reversed, that is, placed flat instead of on edge, the centre of gravity then is only 3 inches
below the upper surface: the area of the end 72 being multiplied by 3, we obtain only 216
as the product, which is only half the strength which it had placed edgeways. The
scantling which has the greatest strength is not all square, but that with the same area,
which has its centre of gravity farthest from the top; a piece of timber 14 by 10 inches
squares to 140 inches, and contains less than a piece 12 × 12, or 144 square inches: but the
centre of gravity of the first is 7 inches from the top, and 140 multiplied by 7 produces
980, which exceeds 144 × 6=864. This is further illustrated by a plank 10 inches in
depth and 1 inch in thickness; the sectional area, 10 inches, multiplied by 5, the distance in
inches of the centre of gravity from the upper edge, the product is 50: the same piece
placed flatwise must only be multiplied by inch; the product then is only 5, conse-
quently the plank when placed on edge is ten times stronger than when placed flatwise.
A beam or piece of timber whose section is that of an equilateral triangle, when
subjected to lateral pressure, is twice as strong, when resting on its broad base, as when
placed on edge, the centre of gravity of this figure being at of its height measured from
the base, or from its apex: the lateral strength of square beams is as the cubes of their
breadth or depth; the lateral strength of any beams whose sections are similar are as the
cubes of similar sides of the section. In cylindrical beams, the lateral strengths are as the
CHAP. XXII.
1299
TIMBER AND ITS PROPERTIES.
cubes of their diameters in rectangular beams, the lateral strengths are to each other as
the breadths and squares of the depths, the strength varying as the breadth multiplied into
the square of the depth.
A piece of timber of the greatest strength that can be cut out from a round tree is
obtained by dividing the diameter of the circle into three equal parts, raising perpen-
diculars upon it, and prolonging them till they cut
the circumference; a rectangle uniting these points
shows the form of the strongest beam that can be
obtained. The comparative strength of beams, but not
their actual strength, may be calculated by the fore-
going rules the value of actual strength must be
converted into relative on account of the length and
other dimensions being relative; thrice the length of
a beam, is to its depth, as its absolute cohesion is to
its relative strength, to which must be added the
weight of the timber.
The strains upon a beam fixed at one end in a wall
and loaded at the other is four times greater than
when the same weight is hung upon the middle of the
same beam, and the latter supported at the two ex-
tremities: when a beam is fixed at both its extremities
and loaded in the middle, its strength is to that when

Fig. 2057.
only supported at its two ends as 3 to 2: when a weight is uniformly distributed over a
beam, its mechanical action to produce fracture is only one-half of what it is when collected
in the middle.
Let the length in inches:
=
b=the breadth in inches:
d=the depth in inches:
W=the weight in pounds that would break it:
S=the weight requisite to break a piece of similar timber, whose
length, breadth, and depth are each 1 inch: then,
bd2
IW
bd2
as : 1 :: W: = S,
which S will be a constant number of reference for computing the strength of any piece of
timber of the same kind, under all variety of dimensions and modes of fixing and loading.
For a beam fixed at one end, and loaded at the other,
:
W=
Sbd2
For a beam fixed at one end, and loaded uniformly throughout,
2 Sb d³
W
7
For a beam supported at each end, and loaded in the middle,
4 Sb d2
W
For a beam supported as above, and loaded uniformly,
8 S b d2
W =
7
For a beam fixed at one end, and loaded in the middle,
6 S bds
W
1
For a beam fixed as above, and loaded uniformly,
12 Sbd2
W=
The value of has been deduced from a variety of experiments, and in the following
table is shown the experimental strength of different timbers, when exposed to a transverse
strain.
Alder
Ash
Acacia
Beech
Chestnut
Elm
Fir, Riga
Memel
Value of Cohesive Strength of a Rod an Inch Square.
-
-
1590 | Fir, Norway
Scotch
New England
Spruce
2355
1866
1556
1350 Larch
1620
very young
1590 Mahogany, Spanish
1635
Honduras
1
1
1
2376
1746
1102
1395
-
1896
966
1275
191!
1294
THEORY AND PRACTICE OF ENGINEERING. BOOK II.
Oak
Canadian
Dantzic
Pine, pitch
red
-
1766
1672 | Poplar
Plane
-
1457
Sycamore
-
1632 Teak
1341
981
1821
1608
2151
By the above table, to find the weight which will produce fracture, on a rectangular
beam, supported at the two ends, when it is loaded in the centre, we must multiply the
breadth by the square of the depth, and again by four times the constant value S: then
this product, divided by the length in inches, will give the weight required. For example,
it is required to know what weight would break a beam of English oak, 10 inches deep,
4 × 6 × 102 × 1672
6 inches in breadth, and 20 feet long:
240
16720 lbs.
When the beam is fixed at one end, and loaded at the other, then the co-efficient 4 is
omitted, and the weight is thus found,
6 x 102 x 1672
240
4180 lbs.
When the beam is uniformly loaded throughout, and supported at both ends,
4 × 6 × 102 × 1672
240
× 2=33440 lbs.
The application of the numbers given in the table to the preceding formula will afford
the means of finding the weight that will produce fracture, and this weight diminished one-
tenth, by cutting off one figure on the right hand, will give the weight in pounds that
it ought to carry, and the timber should never be subjected to more; indeed it is never
safe to put timber to the utmost of its efforts; a fourth of the breaking weight is in many
cases considered sufficient.
To ascertain the weight or load any timber will bear when laid horizontally, the length and
scantling being given, we must seek in the table for the breaking weight which corresponds
to the length and scantling, and find the primitive horizontal strength of the timber in the
second table. Thus, for a piece of oak 12.792 by 18.122, and 27.18 feet long, we find the
breaking weight to be 85461: when fir is to be substituted, look into the second table for
its primitive horizontal strength, which is 918. Then as 1000: 918 :: 85461: 78453, which
expresses in pounds avoirdupois the weight that would break the piece of fir; diminish
this weight one-tenth, and then 7845 lbs. is the weight it should be subjected to, or be made
to carry.
Resistance to Compression in the Direction of its Length, or its Vertical Bearing Strength.
This power is as great as that which would tear it asunder, though, under some circum-
stances, it exerts a greater strength when used as a tie than as a strut; in the latter case,
it is sometimes apt to bend, which it cannot do when pulled in the direction of its length.
The resistance to compression is increased according to the position in which the strut
or support is placed: when the weight applied begins to overpower it, the centre
fibres swell, and the outer ones in consequence burst or lose their cohesion, and yield to
the strain resistance to such an effect depends on the lateral adhesion of the fibres,
which may be resembled to a bundle of rods, which would not yield if bound round
firmly together. Timber which has its fibre cross-grained offers still less resistance;
therefore it is that a fir-post is capable of carrying three times as much as one of oak,
although for a tie the oak is the strongest. The relative strength of timber against com-
pression is as the cube of their diameters directly, and inversely as the square of its length ;
but the area of its section may be modified to produce greater strength; for a post in some
places 9 by 4 is stronger than another 6 by 6; the stiffest post is that which has its sides in
the proportion of 10 to 6.
Rondelet found the most simple method of ascertaining the absolute strength of oak, or
its proportion for different lengths when lying between two points of support, was to
multiply the area of the section by half the absolute strength, and to divide the product
by the number of times its depth is contained in the length between the points of support,
wherever beams are placed horizontally, and have a bearing at the two ends; those of
equal depth diminish in strength, in proportion to the distance given between their supports :
where the lengths are equal, their relative strengths are as their widths and square of
their depths.
The following tables, taken from Rondelet, and converted by Mr. Gwilt into English
dimensions and weights, are of the greatest value in estimating the results of the various
experiments made by Buffon upon timber. The first column gives the proportion that
the depth has to the length; the second the length of each piece in English feet; the
third the greatest strength of each piece in rounds avoirdupois.
CHAP. XXII.
1295
STRENGTH OF OAK TIMBER.

Proportion
of Depth
to Length.
in Pounds.
Length of each Breaking Weight|| Length of each
Piece in Feet.
Piece in Feet.
Breaking Weight|| Length of each
in Pounds.
Piece in Feet.
TABLES showing the greatest Strength of Oak Timber, laid horizontally, in Pounds Avoirdupois.
Breaking Weight|
in Pounds.
Breaking Weight||
in Pounds.
Length of each
Piece in Feet.
Breadth
Depth
3.198 inches.
- 3.198 inches.
Breadth
Depth
-
3.198 inches.
-
Breadth 3.198 inches.
Breadth
3.198 inches.
4.264 inches.
Depth
5.330 inches.
Depth
6'396 inches.
6
1.599
12,245
2.132
16,326
2.664
20,418
3.198
24,489
8
2.132
8,747
2.842
12,090
3.553
15,109
4.264
18,136
10
2.664
7,163
3.553
9,547
4.441
11,934
5.330
14,321
12
3.198
5,889
4.264
7,852
5.330
9,815
6.396
11,778
14
8.730
4,980
4.974
6,642
6.218
8,303
7.462
9,963
16
4.264
4,290
5.685
5,724
7.106
7,167
8.528
8,761
18
4.796
3,771
6.396
5,027
7.994
6,283
9.594
7,540
20
5.330
3,247
7.106
4,462
8.883
5,578
10.660
6,694
22
5.862
3,000
7.817
4,000
9.771
5,010
11.726
6,001
24
6.396
2,711
8.528
3,615
10.660
4,519
12.792
5,422
26
6.928
2,447
9.238
3,289
11.548
4,111
13.858
4,934
888
28
7.462
2,257
9.949
3,010
12.436
3,758
14.294
4,514
Length of each
Piece in Feet.
Breaking Weight
in Pounds.
30
7.994
2,076
10.660
2,767
13.324
3,459
15.990
4,150
Breadth
Depth
·
4.264 inches.
Breadth
- 4.264 inches.
·
Breadth 4.264 inches.
Breadth 14.264 inches.
-
Breadth 4.264 inches.
4.264 inches.
Depth
5.330 inches.
Depth
6.396 inches.
Depth
7.462 inches.
Depth
8.528 inches.
8
2.842
16,224
3.553
16,224
4.264
20,152
4.974
28,244
5.685
22,242
10
3.553
12,728
4.441
12,730
5.330
16,913
6.218
22,277
7·106
25,460
12
4.264
10,469
5.330
10,469
6.396
13,086
7.462
18,321
8.528
21,942
14
4.974
8,696
6.218
8,856
7.462
11,071
8.705
15,499
9.949
17,713
16
5.685
7,645
7.106
7,645
8.528
9,557
9.949
13,379
11.37
15,291
18
6.396
6,702
7.994
6,702
9.594
8,379
11.19
11,730
12.79
13,410
20
7.106
5,951
8.883
5,951
10.66
7,438
12.44
10,413
14.21
11,902
22
7.817
5,333
9.771
5,333
11.73
6,668
13.68
9,334
15.63
10,6'77
24
8.528
4,820
10.66
4,820
12.79
6,023
14.92
8,427
17.06
9,562
26
9.238
4,386
11.55
4,396
13.86
5,482
16.17
7,675
18.48
8,772
28
9.949
4,014
12.44
4,013
14.92
5,017
17.41
7,022
19.90
8,026
30
10.666
3,686
13.32
3,766
15.99
4,613
18.65
6,457
21 32
7,480
1296
Book II.
THEORY AND PRACTICE OF ENGINEERING..´
Pounds.
|| || ||
Proportion Length of Breaking Length of Breaking Length of Breaking Length of Breaking
of Depth each Piece Weight in each Piece Weight in each Piece Weight in each Piece Weight in
to Length. in Feet.
Pounds. in Feet.
Pounds. in Feet.
in Feet.
Pounds.
Length of
each Piece
in Feet.
Breaking Length of
Weight in || each_Piece
Pounds. in Feet.
Breaking
Weight in
Pounds.
Breadth, 5.330 in. || Breadth, 5.330 in. || Breadth, 5·330 in. || Breadth, 5.330 in. || Breadth, 5.330 in. || Breadth, 5.330 in.
Depth, 5.330 in. Depth, 6.396 in. || Depth, 7-462 in. Depth, 8-528 in. || Depth, 9.594 in. | Depth, 10.660 in.
10
12
14
4.441 19,890
5.330 16,359
6.218 13,839
5.330
• 6.396
7.462
16,374 8.705
18,373
16
7.106
11,946
8.528
14,294 9.949
16,724
18
7.994
10,473
9.594
12,568 11.19
14,663 12.79
20
8.863
9,298 10.66
11,157 12.44
13,017 14.21
23,869 6.218 27,847 7.106 32,225 7.994 35,803 8.883 39,782
19,630 7.462 22,901 8.528 26,174 9.594 29,445 10.66
9.949 22,141 11.19
11.37 19,106 12.79
16,757 14.39
14,877
39,717
24,919 12.44
27,677
21,493
14.21
23,888
18,853
15.99
20,648
15.99
16,737
17.77
18,595
22
9.771
24
10.66
8,334 11.73
7,531
10,001 13.68.
11,667 15.63
13,338 17.59
15,002
19.54
16,669
12.79
9,037 14.92
10,544 17.06
12,057 19.19
13,556 21.32
15,063
26
11.55
6,863 13.86
8,223 16.17
28
888888
12.44
30
13.32
6,270 14.92
5,765 15.99
7,524 17.41
6,918 18.65
9,595 18.48
8,778 19.90
8,072 21.32
10,965
10,053 22.39
9,225 23.98
20.78
12,336 23.10
13,706
Length of
11,287 24.87
10,378 26.65
12,551
each Piece
11,531
in Feet.
Breaking
Weight in
Pounds.
Breadth, 6.396 in. || Breadth, 6.396 in.
Depth, 6.396 in. Depth, 7.462 in.
Breadth, 6.396 in. || Breadth, 6.396 in. ||
Depth, 8.528 in. || Depth, 9.594 in.
Breadth 6.396 in. || Breadth, 6.396 in.
Depth, 1066 in. || Depth, 11·726 in.
Breadth, 6.396 in.
Depth, 12.792 in.
10
5.330
12
6.396
14
7.462
16
8.528
28,643 5.218 33,400
23,556 7.462 27,482
19,927 8.705
17,191 9.949
23,244
9.949
27,341
20,067
11.37
18
9.594 15,082 11.19
17,596 12.79
20
10.66
13,389 12.44
15,321 14.21
11.19
22,936 12.79
20,110 14.39
17,852 15.99
7.106 38,158 7.994 42,964
8.528 31,407 9.594 35,334 10.66
29,891 12.44
8.883 47,738
9.771 52,512
10.66
57,285
39,261
11.72
43,176
12.79
47,083
33,212
13.68 36,533
14.92
37,854
25,791 14.21
22,623
20,084 17.77
28,670 15.63
31,537
17.06
34,404
15.99
25,135 17.59
27,631
19.19
30,164
22,315 19.54
24,546
21.32
26,719
22
11.73
12,001 13.68
13,986 15.63
16,001 17.59
18,002 19.54
19,973 21.50
22,003
23.45*
24,003
24
12.79
10,844 14·92.
12,652
17.06
14,460
19.19
16,267 21.32
18,075 23.45
19,883
25.58
21,689
26
13.86
9,857 16.17
11,572
18.48
13 158
20.79
14,802 23.10
16,447 25.41
18,092
27.72
19,377
28
14.92
8,710 17.41
10,534 19.90
12,425
22.39
13,444 24.87
15,050 27.36
16,554
29.85
18,060
30
15.99
8,302 18.65
9,668 21.32
11,070
23.93
12,453
26.65
13,638 29.31
15,221
31.98
16,000

CHAP. XXII.
1297
STRENGTH OF OAK TIMBER.

Length of Breaking
each Piece Weight in
in Feet.
Pounds.
Length of Breaking
each Piece Weight in
in Feet. Pounds.
Length of
each Piece
in Feet.
Breaking
Weight in
Pounds.
Length of
Breaking
each _Piece Weight in
in Feet. Pounds.
Length of
each Piece
Breaking
Weight in
in Feet.
Pounds.
Length of
each Piece
in Feet.
Breaking
Weight in
Pounds.
Breadth, 7.462 in. || Breadth, 7 462 in. || Breadth, 7.462 in. || Breadth, 7-462 in.
Depth, 7.462 in. Depth, 8.528 in. || Depth, 9.594 in. || Depth, 10.66 in.
Breadth, 7-462 in. Breadth, 7·462 in.
||
Depth, 11-726 in. Depth, 12.792 in.
Breadth, 7.462 in.
Depth, 13.858 in.
10
6.218
12
7 462
14
16
35,746 7.106 44,577
31,911 8.528 36,643 9.594
8.705 27,123 9.949 29,806 11.19
9.949 23,413 11.37 26,746
7.994
50,125
8.983 55,738
41,221
35,644
10.66
12.44
9.771 60,264 10.66
45,804 11.73
38,757 13.68
66,832
12.61
72,403
49,384
12.79
55,964
13.86
59,5+6
42,622
14.92
46,497
16.17
*50,371
18
11.19
20,530 12.79
12.79
24,060 14.39
20
12.44
18,224 14.21
21,838 15.99
30,103 14.21
26,394
23,432 17.77
33,449 15.63
36,792 17.06
40,138
18.48
43,483
15.99
29,226 17.59
31,808 19.19
34,992
19.72
38,124
26,142 19.54
28,637 21.32
31,241
22
13.68
16,335 15.63
18,667 17.59
21,003 19.54
23,325 21.50
24,719 23.45
28,003
24
14.92 14,761 17.06
16,870 19.19
26
16.17
13,436 18.48
15,418 20.79
18,979 21.32
17,270 23.10
28
17.41
12,637 19.90
14,046 22.39
30
18.65
10,940 21.32
12,915 23.98
15,802 24.97
14,530 26.65
21,807 23.45
19,139
17,557 27.36
16,144 29.31
23,196 25.58
25,305
25.40
21,307 27.72
23,068
18,928 29.85
21,070
17,758 31.98
18,373
Proportion Length of Breaking
of Depth each Piece Weight in
to Length. in Feet.
Pounds.
|| ||
Breadth, 8.528 in. || Breadth, 8.528 in. | Breadth, 8.528 in. Breadth, 8.528 in. | Breadth, 8.528 in. | Breadth, 8 528 in.
Depth,
||
8.528 in. || Depth, 9.594 in. | Depth, 10.66 in. || Depth, 11·726 in. || Depth, 12.792 in. Depth, 13.858 in.
Breadth, 8.528 in.
Depth, 14.924 in.
10
12
14
7.106 50,921
8.528 41,878
9.949 35,426
16
11.37
30,581
7.944 57,285 8.883
9.594 47,093 10.66
11.19 39,854 12.44
12.79
62,651
9.771
69,975 10.66
76,381 11.55
82,746
12.44
89,111
52,348 11.73
57,582 12.79
62,817 13.86
68,052
14.92
73,279
44,283 13.67
48,711 14.92
53,139 16.17
57,576
17·41
61,996
34,403 14.21
38,227 15.63
42,049 17.06
45,872 18.48
49,627
19.90
53,517
18
12.79
26,812 14.39
30,170 15.99
20
14.21
23,803 15·99
26,773 17.77
22
15.63
21,342 17.59
24,003 19.54
33,516 17.59
29,754 19.54
26,669 21.50
36,668 19.19
32,729 21.32
40,219 20.79
43,628
22.39
46,923
35,715
29,337 23.45
32,004
24
17.06
19,280 19.19
21,690 21.32
24,100 23.45
26,017 25.58
28,920
26
18.48
17,345 21.95
19,737 23.10
21,930 25.40
24,124 27.72
26,356
28
19.90
16,051 23.45
17,960 24.87
30
21.32
14,760 25.05
16,605 26.65
20,066 27.36
18,444 30.20
22,073 29.85
20,295
24,851
31.98
22.149
4 0
1298
Book IL
THEORY AND PRACTICE OF ENGINEERING.
Proportion
Length of
Feet.
of Depth each piece in
to Length.
Breaking
Weight in
Pounds.
Length of
each Piece in
Feet.
Breaking
Weight in
Length of
Breaking
Pounds.
each Piece in
Feet.
Weight in
Pounds.
Length of
each Piece in
Feet.
Breaking
Weight in
Pounds.
Length of
each Piece in
Feet.
Breaking
Weight in
Pounds.
each Piece in
Length of
Feet.
Breaking
Weight in
Pounds.
Breadth, 9.594 inches.
Depth,
9.594 inches.
Breadth, 9.594 inches.
Depth, 10.66 inches.
Breadth, 9.594 inches.
Depth, 11.726 inches.
Breadth, 9-594 inches.
Depth, 12.792 inches.
Breadth, 9.594 inches.
Depth, 13.858 inches.
Breadth, 9.594 inches.
Depth, 14.924 inches.
10
7.994
64,447
8.983
71,607
9.771
78,848
10.66
85,929
11.55
93,089
12.44
100,250
12
9.594
52,992
10.66
58,891
11.73
64,780
12.79
70,670
13.86
76,458
14.92
82,447
14
11.19
45,402
12.44
49,818
13.68
54,800
14.92
59,782
16.17
64,763
17.41
69,745
16
12.79
38,704
14.21
43,010
15.63
47,305
17.06
51,406
18.48
55,906
19.90
60,207
18
14.39
33,935
15.99
37,705
17.59
41,476
19.19
45,247
20.79
49,117
22.39
52,771
20
15.99
30,125
17.77
33,473
19.59
36,820
21.32
40,167
22
17.59
27,003
19.54
30,003
21.50
33,004
23.45
36,004
24
19.19
24,401
21.32
27,112
23.45
29,825
25.58
32,535
26
20.79
22,205
23.10
24,671
25.40
27,138
27.72
29,606
28
22.39
20,317
24.87
22,574
27.36
24,830
29.85
27,090
30
23.98
18,681
26.65
20,756
29.21
22,832
31.98
24,908
Breadth, 10.66 inches.
Depth, 10.66 inches.
Breadth, 10.66 inches.
Depth, 11.726 inches.
Breadth, 10.66 inches.
Depth, 12.792 inches.
Breadth, 10.66 inches.
Depth, 13.858 inches.
Breadth, 10.66 inches.
Depth, 14.924 inches.
Breadth, 10.66 inches.
Depth, 15.990 inches.
10
8.883
79,564
9.771
87,520
10.66
95,476
11.55
103,633
12.44
111,389
13.32
119,345
12
10.66
65,435
11.73
71,978
12.79
78,521
13.86
85,065
14.92
91,609
15.99
98,152
14
12.44
55,453
13.67
60,889
14.92
64,424
16.17
72,037
17.41
77,495
18.65
83,030
16
14.21
47,783
15.63
52,548
17.06
57,340
18.48
62,118
19.90
66,896
21.32
71,675
18
15.99
41,895
17.59
45,985
19.19
50,274
20.79
54,463
22.39
58,653
29.98
62,841
20
17.77
37,192
19.54
40,911
21.32
44,631
22
19.54
33,337
21.50
36,671
23.45
40,005
24
21.32
30,125
23.45
33,138
25.58
36,151
26
23.10
27,412
25.40
30,155
27.72
32,896
28
24.87
24,083
27.36
27,491
29.85
30,100
30
26.65
23,061
29.21
25,369
31.98
27,676
•


CHAP. XXII.
1299
STRENGTH OF OAK TIMBER

Length
of each
Piece in
Breaking
Weight in
Pounds.
Length
of each
Piece in
Breaking
Weight in
Pounds.
Length
of each
Feet.
Feet.
Piece in
Feet.
Breaking
Weight in
Pounds.
Length
of each
Piece in
Feet.
Breaking
Weight in
Pounds.
Length
Piece in
of each Weight in
Breaking
Pounds.
Feet.
Length
of each
Piece in
Feet.
Breaking
Weight in
Pounds.
Inches
Inches.
Inches.
Inches.
Inches.
Inches.
Breadth, 11.726|| Breadth, 11·726 || Breadth, 11.726 || Breadth, 11·726|| Breadth, 11.726 || Breadth, 11-726
Depth, 11.726 Depth, 12-792|| Depth, 13.858|| Depth, 14.924 Depth, 15.99 Depth, 17.056
Inches
Breadth, 11.726
Depth, 18.122
Proportion
Length
of each
of Depth Piece in
Feet.
to Length.
Breaking
Weight in
Pounds.
10
12
14
16
18
17.59
20
19.54
51,493 19.19
45,002 21.32
22
21.50
40,338 23.45
9.771 96,272 10.66 105,023 11.55 113,776
11.73 79,174 12.79 86,374 13.86 93,572
13.67 66,978 14.92 73,067 16.17 79,155
15.63 57,818 17.06 63,074 18.48 68,328
55,301 20.79 60,910
49,093
44,006
12.44 | 122,528 13·32 | 131,280
14.92 100,769 15.99 107,968
17.41 85,244 18.65 91,333
19.90 73,576 21.32 78,842
22.39 64,518 23.98 69 126
14.21 148,784
17.06 122,362
15.10 157,537
18.12 129,561
19.90 103,511 21.14 109,600
22.74 89,355 24.16 94,611
25.58 78,344 27.18 82,350
24 23.45 36,407 25.58 38,765
10
26
25.40 33,087 27.72
36,185
28
30
27.36 30,350 29.85 33,109
29.21 27,906 31.98 30,443
Length of
each Piece
in Feet.
Breaking
Weight in
Pounds.
Inches.
Inches.
Inches.
Inches.
Inches.
Inches.
Inches.
Inches.
||
Breadth, 12.792 Breadth, 12.792
Depth, 12.792|| Depth, 13-858
Breadth, 12.792 Breadth, 12.792 Breadth, 12.792
Breadth, 12.792|| Breadth, 12-792 || Breadth, 12-792 || Breadth, 12.792|| Breadth, 12.792
Depth, 14.924|| Depth, 15.99 Depth, 17.056|| Depth, 18.122 Depth, 19.188
Breadth, 12.792
Depth, 20-254
00
10
12
14
16
|
10.66 115,572 11:55 124,119
12.79 89,826
13.86 | 102,078
14.92 79,709 16.17 86,351
17.06 68,708 18.48 74,542
19.90
18
19.19 60,329 20.79 65,356 22.39
12.44 133,667 13.32 | 143,214
14.92 | 110,930 15.99 117,783 17.06 125,634 18.12 123,487
17.41 92,994 18.65 99,636 19.90 106,279 21·14 | 112,921
80,275 21.32 86,010 22.74 91,744 24.16 97,479
70,384 23.98 75,411 25.58 76,238 27.18 85,461
14.21 152,762 15.10 162,310 15.99 171,857
16.88 181,405
19.19 141,340
22.37 119,565
25.58 103,212 27.00
28.78 88,894 29.38
20.2.5
149,191
23.63
126,207
108,946
95,521
20
21.32 53,557
22
23.45 48,006
24
25.58 43,380
26
27.72 39,475
28
28.85 36,119
80
31.98 33,211
40 2
1300
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Proportion
of Depth
to Length.
Length of
each Piece
in Feet.
Breaking
Weight in
Pounds.
Breadth, 13.858 in.
Length of
each Piece
in Feet.
Breaking
Weight in
Pounds.
Breadth, 13.858 in.
Length of
each Piece
in Feet.
Breaking
Weight in
Pounds.
Length of
each Piece
in Feet.
Breaking
Weight in
Pounds.
Length of
each Piece
in Feet.
Breaking
Weight in
Pounds.
in Feet.
Breadth, 13.858 in.
Breadth, 13.858 in.
Breadth, 13-858 in.
Depth, 13.858 in.
Depth, 14.924 in.
Depth, 15.99 in.
Depth, 17.056 in.
Depth, 18.122 in.
10
11.55
134,463
12.44
144,806
13.32
154,825
14.21
164,426
15.10
175,836
15.99
Length of
each Piece
Breaking
Weight in
Pounds.
Breadth, 13.858 in.
Depth, 19.188 in.
141,179
12
13.86
110,584
14.92
119,092
15.99
127,598
17.06
136,153
18.12
144,61ì
19.19
133,115
14
16.17
93,547
17.41
100,813
18.68
107,939
19.90
114,364
21.14
121,332
22.37
129,528
16
18.48
80,754
19.90
86,966
21.32
93,177
22.74
99,396
24.16
105,601
25.58
18
20.79
70,802
22.39
76,249
23.98
81,755
25.58
91,941
27.18
92,588
28.78
111,813
98,935
Breadth, 13.858 in.
Breadth, 13.858 in.
Breadth, 13.858 in.
Depth, 20-254 in.
Depth, 21.326 in.
Depth, 22.326 in.
|
10
16.88
196,522
17.77
205,531
18.65
217,210
12
20.25
161,624
21.32
170,130
22.38
178,637
14
23.63
136,724
24.87
144,920
26.12
151,115
16
27.00
118,026
28.43
124,237
29.85
130,049
18
29.38
103,481
31.98
108,951
33.58
114,374
Breadth, 14.924 in.
Breadth, 14.924 in.
Breadth, 14.924 in.
Breadth, 14.924 in.
Depth, 14.924 in.
Depth, 15.990 in.
Depth, 17.056 in.
Depth, 18.122 in.
Breadth, 14.924 in.
Depth, 19.188 in.
Breadth, 14.924 in.
Depth, 20-254 in.
10
12.44
155,944
13.32
167,083
14.21
178,223
15.10
189,362
15.99
200,501
16.88
212,547
12
14.92
128,092
15.99
137,213
17.06
146,674
18.12
155,735
19.19
164,895
20.25
174,057
14
17.41
108,493
18.65
116,242
19.90
123,993
21.14
131,741
22.37
139,492
23.63
147,331
16
19.90
93,655
21.32
100,354
22.74
107,034
24.16
113,764
25.58
120,415
27.00
127,104
18
22.39
82,114
23.98
87,980
25.58
934845
27.18
99,711
28.78
105,575
29.38
111,441

Breadth, 14.924 in.
Breadth, 14.924 in.
Breadth, 14.924 in.
Depth, 21-326 in.
Depth, 22.386 in.
Depth, 23-452 in.
10
17.77
212,776
18.65
233,917
19.54
246,136
12
21.32
173,218
22.38
192,378
23.45
201,540
14
24.87
150,991
26.12
162,737
27.36
170,490
16
28.43
133,733
29.85
140,483
31.27
147,173
18
31.98
117,306
33.58
112,372
35.18
129,037
CHAP. XXII.
1301
STRENGTH OF OAK TIMBER.

Breadth, 15.99 in. Breadth,
||
Depth, 15.99 in. Depth,
Proportion Length of
of Depth each Piece
to Length. | in Feet.
Breaking
Weight in
Pounds.
Length of Breaking
each Piece Weight in
in Feet. Pounds.
Length of Breaking
each Piece Weight in
in Feet.
15.99 in. Breadth,
17.056 in. Depth,
17-056 in. Depth,
Pounds.
Length of Breaking
eachPiece Weight in
in Feet. Pounds.
15.99 in.Breadth, 15-99 in. Breadth,
18-122 in. |Depth,
18-122 in. Depth,
Length of
each Piece
in Feet.
Breaking
Weight in
Pounds.
Length of
Breaking
each Piece Weight in
in Feet.
Length of
each Piece
Pounds.
in Feet.
Breaking
Weight in
Pounds.
Length of
each Piece
in Feet.
Breaking
Weight in
Pounds.
19.188 in.||Depth,
19.188 in. Depth,
15.99 in. Breadth, 15.99 in.
20-254 in.||Depth,
20-254 in. Depth,
Breadth, 15 99 in.
21-326 in. Depth,
Length of
Breaking
eachPiece Weight in
in Feet.
Breadth, 15.99 in. Breadth, 15.99 in
22-386 in. Depth, 23-452 in. Depth,
Pounds.
24-518 in.
10
12
14
16
18
13.32 179,009 14.21
15.99 147,229 17.06
18.65 124,547 19.90
21.32 107,513 22.74
23.98 94,164 25.58
Breadth, 17.056 n. Breadth,
Depth, 17.056 in. Depth,
190,953 15.10 202,888
15.99
160,244 18.12 166,859 19.19
132,849 21.14 141,153 22.37
114,680 24.16 121,848 25.58
100,548 27.18 106,832 28.78
17.056 in. Breadth,
18.122 in. Depth,
17.056 in. Breadth,
19.188 in. Depth,
214,823 16 88
238,692 18.65
176,584 20.25 186,490 21.32 196,365 22.38
149,456 23.63 157,759 24.87 166,062 26.12
129,015 27.00 136,183 28.43 143,350 29.85
113,118 29.38 119,401 31.98 125,686 33.58
17.056 in. Breadth, 17-056 in. Breadth,
20-254 in. Depth, 21-326 in.||Depth,
226,757 17.77
250,626
206,127
17-056 in. Breadth, 17.056 in. Breadth,
22.386 in. Depth, 23-452 in. Depth,
19.54 262,561 20.43
23.45 215,935
174,365 27.36 182,668
150,517 31.27 157,685 32.69
131,770 35.18 138,254 36.78
17.056 inBreadth, 17-056 in.
24-518 in. Depth, 25.584 in.
274,495
24.52
225.750
28.60
190,751
164,852
144,538
10
12
14
16
18
02468
216,412
15.99 229,144 16.88
177,983 19.19 188,456 20.25 197,322 21.32
150,563 22.37 158,439 23.63 168,276 24.87
129,970 25.58 137,617 27.00 145,261 28.43
113,954 28.78 120,659 29.38 127,341 31.98
10
12
14
21.14 159.973
16
24.16 142,094
18
27.18 121,077
25 58
28.78
Breadth, 19-188 in. Breadth,
Depth, 19.188 in. Depth,
14.21 203,684 15.10
254,605 18.65 267,334 19.54
17.06 167,513 18.12
209,391 22.38 219,861 23.45
19.90 141,706 21.14
177,132 26.12 184.989 27.36
22.74 122,967 24.16
152,807 29.85 160,552 31.27
25.58 107,251 27.18
134,112 33.58 140,768 35.18
Breadth, 18-122 in. Breadth, 18-122 in. Breadth, 18-122 in. Breadth, 18-122 in. Breadth, 18-122 in. Breadth,
Depth, 18 122 in. Depth, 19-188 in. Depth, 20-254 in. Depth, 21-326 in Depth, 22-386 in.||Depth,
15.10 229,907 15.99 243,465 16.88 257,091 17.77
270,317 18.65 284,043 19.54 297,569 20.43
18.12 187,107 19.19 200,131 20.25 211,356 21.32 222,479 22.38 233,603 23.45 244,727 24.52
22.37
169,383
23.63 178,793 24.87 188,203 26.12 197,611 27.36 207,023 28.60
146,217 27.10 154,340 28.43 162,463 29.85 170,275 31.27 188,710 32.69
128,199 29.38 135,261 31.98 142,443 33.58 149,266 35.18 156,688 36.78
19.188 in. Breadth, 19.188 in.||Breadth, 19-188 in. Breadth,
20-254 in. Depth, 21-326 in.||Depth, 22:386 in. Depth,
241,875 17.77
280,064 21.32
292,795
21.32
305,525
230,330 25.58
190,846
240,800
25.58
251,360
29.85
203,702
29.85
212 559
168,772
147,471
34.11
175,842
34.11
183,421
38.37
154,174
38.37
160,277
18-122 in. Breadth, 18-122 in
23-452 in.||Depth,
Breadth, 18·122 in
24-518 in. Depth,
25-584 in.
310,771 21.32
324,621
255,851
25.58
256,975
216,434
29' 5
225,844
186,833
34.11
194.956
163,810
38.37
170.933
19-188 in. Breadth,
23-452 in. Depth,
19-188 in. Breadth, 19.188 in. Breadth, 19.188 in.
24-518 in. Depth,
25.584 in. Depth, 26.65 in.
10
15.99
12
19.19
14
257,787 16.88 272,108 17.77
212,107 20.25 223,788 21.32
22.37 179,347 23.63 189,310 24.87
286,430 18.65
235,565 22.38
300,763 19.54
315,073
247,344 23.45
259,122
196,074 26.12
209,238 27.36
219,101
20.43 329,395 21.32
24.52 270,901 25.58
28.60 229,165 29.85
343,716 22.21
258,037
286,679
26.65
294,458
140,130
31.09
24',092
16
25.58 150,818 27.00
163,419 28.43
171,010
29.85
180,261 31.27
189,222
32.69
197,824 34.11
207,092
35.53
216.026
18
28.78 135,741 29.38
143,281
31.98
150,823
33.58
158,364 35.18
165,905
36.78
173,446 38.37
180,987
39 97
188,529
Breadth, 20-254 in Breadth,
Depth, 20-254 in.||Depth,
20·254 in.
21.320 in.
10
16.88 287,226 17.77
292,343
12
20.25 236.220 21.32
248,653
14
23.63 199,827 24.87
200-345
16
27.10 172,498 28.43
181.577
19
29.38
151,242 31.98
159,202
4 0 3
1302
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
In the foregoing tables the primitive horizontal strength of oak is considered as 1000,
its vertical strength at 807, and its cohesive or absolute strength at 1821: for its appli-
cation to the other species of timber the following table has been calculated :
Primitive or,
Horizontal
Primitive
Vertical
Strength.
Strength.
Absolute
Strength.
Apricot
Acacia, yellow
1096
1255
2040
780
1228
1560
Arbutus
857
1062
1620
Alder
644
780
2080
Ash
1072
1112
1800
Apple
976
903
1187
Aspen
624
717
1293
Birch
853
861
1980
Box
1160
1444
2324
Beech
1032
986
2480
Cedar
627
720
1740
Cherry
961
986
1912
Chestnut
957
950
1944
horse
931
689
1231
Citron
1192
871
1460
Cypress
682
869
1880
Ebony
1155
1062
2321
Elder
1072
789
1500
Elm
Fir
Lemon
Larch
1077
1075
1980
918
851
1250
1087
858
1400
843
902
1460
Lignum vitæ
Lime
Maple, foreign
Mulberry
707
741
1113
B
750
717
1407
1094
843
2094
-
I
981
1031
1050
Oak
1000
807
1821
Orange
Pine tree
Plane
?
Poplar
Plum
Pear
Oriental
Occidental
1180
843
2340
882
804
1041
728
830
1916
776
874
931
853
941
1031
586
680
940
950
843
1770
850
816
1680
Sycamore
Service
Tulip tree
Walnut
-, American
Yew
900
968
1564
955
981
1642
563
682
981
900
733
1120
864
701
1020
•
1037
1375
2287
This is deduced from pieces 19-188 lines English square.
When a piece of timber is put in an upright position, it seems at first that it will carry
the same weight, whatever may be its length; but experience shows us that when a post
is more than seven or eight times the width of its base in height, it bends under the
weight, previous to crushing or giving way. When a post is 100 times its diameter, it is
incapable of maintaining an upright position, and then we find its strength diminishes in
relation to the height: to crush a piece of oak which is too short to bend, it requires 49-72
pounds avoirdupois for every 888 area of an inch at its base, and for fir timber 56·16 pounds.
Rondelet used cubes of oak and fir in the experiments he made, and found they diminished
in height by compression previous to disuniting, the first more than a third, the latter a
half: when either of these timbers are of a length to bend under the weight imposed
upon them, they immediately have their strength diminished, and he found the mean
strength of oak to be 47.52 pounds avoirdupois for a cube of 888 of an inch, which is
reduced to 2.16 pounds, when the height is as much as 72 times the width of the base;
for a cube whose height was 1, the strength was taken as 1; for a post equal to 12
times its base, the strength was five-sixths; for 24 times, a half only; for 36 times, a third;
1000
CHAP. XXII.
1303
STRENGTH OF TIMBER.
48 times, a sixth; 60 times, a twelfth; and at 72 times the height of its base, its strength
is only a 24th part. It results from the above experiments that we ought never to make
a post in height more than ten times its diameter or width at the base; and in calculating
its strength, at the rate of 10·80 pounds for every 1·066 line superficial of base, which is
not a quarter of the weight that would crush it, we find that a post whose sides are
1.066 feet, and containing 22104-576 lines English, would sustain a weight of 238729
pounds avoirdupois, or 106 tons. When a post is made in height equal to ten times its
width of base, it should never have in practice a weight of more than 5 pounds per 1.066
line imposed upon it: and when the height is 15 times the base, 4 pounds; and when
20 times, not more than 3 pounds for the same proportion: all posts should have
their bases extended, or their area made proportionate to the weight they have to sustain :
they ought also to have a stability given them, in reference to their situation and
isolation; this stability is in proportion to the base, the diameter of which, as compared
with the height, may vary as 7 to 10.
For Timbers placed vertically, as Posts, &c.— To find the vertical strength of an oak post
9.594 inches square and 9.594 feet high, seek in the preceding table for the primitive
vertical strength of oak, which is 807 for 19.188 lines superficial of base; but as this strength
should diminish in a ratio of the number of times that the width of the base is contained in
the width of the post, which in the present case is 12, only of 807 must be taken,
or 672. This post, which is 9.594 inches, or 115.128 lines square, has an area of 13254-756
square lines, which being divided by 19.188 will give 692-34; and for the greatest weight
it can bear before breaking, 692·34 × 672·5=465,000 lbs., and this divided by 10 gives
46,500 pounds as the weight the post may be loaded with: when the post is of fir, the
primitive vertical strength of which is as 851 to 807, to have its greatest strength, it is only
necessary to make the proportions, as 807: 465000:: 851: 490980, which divided by 10
gives 49,098 pounds as the utmost weight it should be loaded with.
To find the absolute or cohesive Strength. This strength by which timber resists when
drawn at the two ends is ascertained by multiplying the area of the section, reduced to
lines, by 1821 for oak, which is its tabular number, and dividing the product by 19·188,
and the quotient will indicate the greatest weight that it ought to bear.
For oak, 9.594 inches square,
13254·75 × 1821
19.188
1,260,700, which divided by 10 gives
126,070 pounds for the greatest weight it should be subjected to.
We find by the table that beech has the greatest absolute strength, so that a
piece of timber of the same dimensions as the preceding would have a strength by
13254·75 × 12480
=1,363,850, which will give 136,385, as the greatest weight to which it
19.188
ought to be subject.
To find the Strength of Timber when in an inclined Position.— If it be supposed that a
piece of vertical timber, as A B, be inclined on its base, experience proves that its strength
to support a vertical effort diminishes in proportion to its inclination,
so that if from its upper extremity a vertical Dƒ be lowered, and
from the points of the base B a horizontal line BC be drawn, the
strength of the piece will be less in proportion as Bƒ is larger: whence
it results that the strength of a piece of vertical timber is to that of an
inclined piece of the same scantling, as the length A B is to Bf, or as
the radius to the size of the inclination of the timber.

A
B
F
Secondly, the vertical pieces have the greater power to support a
weight, and the horizontal the less; the first of these results gives an
easy method by means of the preceding table, to find the strength of a
piece of timber, the length and inclination of which are known: for ex-
ample; a piece of oak 9.594 feet long, inclined 4.692 feet, its dimen-
sions being 8.528 by 9.594 inches, whose area therefore is 11781·74 lines; this must be
divided by the tabular number, 19.188, and the quotient will be 614.
0
Fig. 2058.
In the preceding table 807 is the primitive vertical strength of oak for 19-188 lines
superficial of section; but as the length of this piece is more than twelve times the width of
the base, we must only take of 807, viz. 672, which multiplied by 614 gives 412915.
Then 9.594 : 4·692 :: 412915: 843400; this divided by 10 gives 84,340 for the utmost
load to which the inclined piece should be loaded.
Joints and Joining Timbers. As timber cannot always be obtained
of sufficient length for tie-beams or bridges, it is necessary to show
the method usually employed to unite two or more pieces together
by their ends, which is called scarfing, and is differently performed
by carpenters: the most common means is lapping or halving, or
as it is sometimes called ship-lapping. This is nothing more than
cutting away a part of the thickness of one piece, and an equal quan-
Fig. 2059.
404
1304
Book II.
THEORY AND PRACTICE OF ENGINEERING.
tity of the other, which is to be joined to it, so as to suffer the diminished end of one piece
to overlap that of the other, and then uniting them by nails or wooden pins, which are called
tree-nails. This method is applied to plates, bond timbers and others, where there is not
much longitudinal compression or extension: where this kind of effect is to be provided
for, the upper as well as the lower timbers should be cut and let into each other; the
under piece having a tenon formed at its extreme end, with a corresponding cutting
to receive it in the upper piece; that these tenons may be enabled to pass each other,
it is necessary to cut away a part of the timbers in the middle of the length of the joint,
equal to the length of the two tenons, so as to form a square hole, through the middle of
the timbers to be joined together, and this is afterwards closed up by driving an oak key
into it; this also helps to drive the tenons to their respective mortises, and prevents the
timbers from being pulled asunder: the thickness of the key, in order that it may not be
compressed, should be equal to a third of that of the piece into which it is inserted: another
principle is here shown, which is more simple, the joint being cut obliquely; to make these
two pieces stiff, the ends of both should be cut in an angular form. To strengthen these
scarfs, iron straps and screw-bolts are added, but no joining can be made so strong as the
timber itself.
In making joints, it must be remembered that all timber is liable to shrink when dry,
and when wet to expand; on this account dovetail joints should be avoided as much as
possible, as they are liable to draw out, and all joints should be made with reference to
their contraction and expansion, which sometimes tends to split off portions of the framing :
where iron bolts or straps are introduced care must be taken that their effect is not lost by
the changes that the timber undergoes; the areas of the former should never be less than
two-tenths of the area of the section of the beam; it must also be recollected in making a
joint, that when force is applied to any portion, the
fibres of the timber will slide upon each other.
Fishing a Beam is merely placing a piece of
the same scantling to one side of the timber to be
united, and bolting them or hooping them toge-
ther separate pieces of timber
are united either by scarfing,
notching, cogging, pinning,
wedging, tenoning, &c.
Scarfing consists in cutting
away equally from the ends, but
on the opposite sides, of two
pieces of timber for the purpose
of connecting them lengthwise :
the usual method of scarfing
bond and wall plates is by
cutting about through each
piece on the upper face of the
one, and the under face of the
other, about 6 or 8 inches
from the end transversely,
making what is termed a kerf ;
and longitudinally from the
end, from ? down, on the same
side, so that the pieces lap to-
gether like a half dovetail.
Notching is either square or
dovetailed, and is made use of
for connecting the ends of wall
plates and bond timbers at the
angles, in letting joists down on
girders, binders, purlins or prin-
cipal rafters.

Fig. 2060.
SCARFING A BEAM.

Fig. 2061.
Fig. 2062.

Fig. 2063.
Cogging or Cocking is a species of notch extending on
one side, and having a narrow cog alone in the bearing
piece, flush with its upper face; it is principally made use
of in tailing joists on wall plates.
Pinning consists in inserting cylindrical pieces of wood
or iron through a tenon.
Wedging is the insertion of triangular prisms, whose
converging sides are under an extremely acute angle, into
or by the end of a tenon, to make it fill the mortise so
completely as to prevent its being withdrawn.
Fig. 2064.

Fig. 2065.
CHAP. XXII.
1305
CARPENTRY.

Tenon and Mortaise or Mortise of
the most simple kind, in which
the two timbers united are at
right angles with each other; the
tenon is on that which appears
horizontal, whilst the mortise is cut
in the upright timber; the tenon
is left one-third of the thickness of
the timber, as shown in the upper
part of the figure.
The greatest strain upon the
fibres of a girder is at the upper
and lower parts, decreasing gra-
dually towards the middle of the
depth, which is the best situation to
make the mortise. The form to be
given to the tenon requires consi-
deration; some carpenters introduce
it at the lowest part of the girder,
which in a great degree destroys its
Fig. 2066.
TENONS AND MORTISES.
stiffness; being a sixth of the depth, it should be placed at one-third of the depth from
the lowest side. Horizontal timbers intended to bear great weights should be always
notched on their supports, in preference

to being framed in between them, and
this rule is applicable to inclined tim-
bers, as common rafters and braces; all
the pressures to which they are sub-
jected should be brought to act in the
direction of their lengths, and the form
of the joint should be such as to convey
the pressure as much as possible into
the axes of the timber; when subjected
to a strain, a partial bearing is liable
to very serious disadvantages, parti-
cularly in bridges.
Where the mortise is to be made
in the upright timber, and the tenon
to be cut on another inclined, as
in a brace to a partition, a bevelled
shoulder is cut on the inclined piece,
and a sinking made in the upright post
to receive it, the pin which secures it in
its mortise passing through the tenon.
Fig. 2067.
TENONS.
The bevelled shoulder adds greatly to the strength of a mortise and tenon joint, and
should never be dispensed with; it renders the junction of the two pieces of timber more
exact, and makes the abutments of all the fibres stronger and more capable of resistance.

Fig. 2068.
BEVELLED shouldeR JOINTS.
1306
BOOK II
THEORY AND PRACTICE OF ENGINEERING.

The common method of effecting
such a junction does not occupy so
much time or labour, but is not so
effective; it is usual to drive one or
two wooden pins through holes bored
for the purpose at right angles through
the timber, in which the mortise is
made as well as through that which
has the tenon.
Boring the hole for the pin requires
to be nicely performed, in order that it
may draw the tenon tight into the
mortise prepared to receive it, and
make the shoulder butt close into the
joint, without running the risk of
tearing out a portion of the tenon
beyond the pin: square holes and
square pins are preferred to round,
as they bring more of the wood into
action, and there is less liability to split.
Fig. 2069.
SHOULDER JOINTS.
Fox Tail Wedging, adopted by ship carpenters, is made with long wooden bolts, which do
not pass completely through
the timbers, but take a very
fast hold; they are subject to
be crippled in drawing, if they
are too nicely fitted; this is
remedied by placing a thin
wedge into the hole previous
to the insertion of the wooden
bolt, which, when driven, is
split by the wedge, and thus
squeezed tight to the sides of
the hole.
Bond Timbers and Wall
Plates require to be carefully
notched together at every angle
and return, and scarfed at every
longitudinal joint.

Fig. 2070.
HALVING.


Fig. 2071.
HALVING.
To make a good tie joint requires great attention on the part of the carpenter, and for
uniting wall plates the dovetail joint is sometimes adopted: if the effects that shrinking
may produce be taken into consideration, the more usual system of halving is decidedly pre-
ferable; whenever this joint is employed, a stout pin of
tough oak, or an iron bolt, should be driven through to
render it secure, and, where there is the slightest tendency
for one piece to slide from the other, iron straps must be
used.
Timbers which are laid
upon the Plates, and in-
tended to act as ties,
should be cut with a
dovetail, and let into the
timber it is to secure;
generally, where they
cross at right angles,
halving or cutting away
the moiety of each is
adopted, and one is let
into the channel cut in
the other.
Cauking, or dovetailing
a cross, as used for fitting
down tie-beams or other
timbers upon wall plates,
should never be made too
large, nor too near the
Fig. 2073.
Fig. 2072.
DOVETAIL JOINT.

CAUKING JOINTS.
Fig. 2074.
ends of the plates, the grain of the wood, if cut across, being very liable to split off; it may
be observed that the dovetail joint so frequently referred to is not so termed on the Continent,
but is universally known as the swallow-tail, queue d'hirondelle.
CHAP. XXII.
1307
CARPENTRY.
For joining two pieces of tim-
ber together notching is the most
common and simple method;
for, when four angles are to be
formed, the surfaces of one
piece are both parallel and per-
pendicular to those of the other;
a notch may be cut out of one
piece (fig. 2071.), the breadth of


Fig. 2075.
Fig. 2076.
the other, which may be let down on the first, or the two pieces may be both notched
to each other, and then secured by an oak pin: this is the best practice when each of the
timbers is equally exposed to a strain in any direction. When one piece has to support
the other transversely, the upper may have a notch cut across it, to the breadth of two-
thirds the thickness of the one below, which must also have a similar notch cut out on each
upper edge, leaving two-thirds of the breadth of the middle entire, by which means the
strength of the supporting or lower piece is less diminished than if a notch of less depth
were cut the whole breadth: such joints are particularly adapted for purlins, when let
down upon the principal rafters.
Lupping is performed in a variety of ways, either by simply halving the end of each tim-
ber, or by halving and dovetailing; in the latter case the timbers act as a tie, and cannot
be readily pulled asunder.
In these joints the greatest attention is required to make the several parts abut com-
pletely on each other, as the least play or liability to motion at once destroys their
efficacy; the butting joints, being slightly tapered to one side of the beam, require very
moderate blows with a hammer to force them into their place; if driven too hard, the parts
will be liable to strain, and the abutments to split off; it is better sometimes to leave the
abutments open, and afterwards drive in a small
wedge, which, if made of hard wood and not likely to
compress, is an excellent substitute; iron has been
said to injure the fibres of the timber, from its too
great hardness, otherwise it is well adapted for the
joggles and wedges.
Two pieces of timber may be united in such
a manner that they preserve the same breadth and
depth throughout, which is of great importance
in the construction of beams for bridges or roofs of
considerable span: the length to be given to the
scarf must depend upon the force that will cause
the fibres of the timber to slide upon each other,
and that for oak, ash, or elm should be 6 times
the depth of the timber, in fir 12 times; but where
bolts are used so much is not required in either
case: the simplest method for uniting the ends of
two timbers is by cutting away an equal portion of
each, and letting one down upon the other.
Timbers united together by
a number of such cuttings,
afterwards united and bolted
through or hooped round with
iron, are capable of sustaining
great resistance: a stirrup-iron
at each end holds the timbers in
their places, and one or more
bolts is sufficient to prevent
their being drawn asunder.
The carpenter frequently ex-
ercises great ingenuity in join-
ing timbers of considerable
scantling, and, by the introduc-
tion of iron or small cubes of
harder wood into the joints, can
prevent their being thrust or
drawn out of their position
either longitudinally or late-
rally.
The Starfing of Girders and
Beams, which the French en-
gineers term Traits de Jupiter,


Fig. 2079.
।।
·
Fig. 2080.
SCARFING.
Fig. 2077.

Fig. 2078.


1308
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
from their resemblance to forked lightning, have a great variety of forms given them,
and are sometimes bolted through, at others strapped round with strong hoops of iron :
where bolts are dispensed with, it is perfectly clear that the joint cannot have half the
strength of an entire piece: where the stress is longitudinal, two irons put on each side

Fig. 2081.
will prevent the scarf
that is merely in-
dented from pulling
asunder; but such
a provision will not
maintain the con-
stant horizontal po-
sition of the timber.
When a scarf is
forced to its bearings
by the introduction of
keys or wedges driven
tight, they sometimes
receive an additional
strain, and it is often
found advisable to
omit them, and to
SCARFING.


Fig. 2082. Scarfing.
Fig. 2083.
bring the joints to a bearing by some other means before the bolts are inserted: when
keys are made use of they should be of very
hard wood, having a curled grain, which re-
sists the insertion of the fibres opposed to it.
To prevent lateral movement cogging is
adopted, in addition to the ordinary method,
and a small tenon or cog is left upon a por-
tion of the scarf, which enters into a notch
prepared in the piece which is to cover it:
beams intended to resist cross strains require
to be lengthened more frequently than any
others, and from the nature of the strain a
different form of scarf must be made use of
to that which is required for a strain in the
direction of its length: when timber is sub-
jected to both strains, the cross strain is that
which demands the greatest attention: where
a floor is supported, the scarfing requires to be
further secured by iron bolts made to pass
through a longitudinal piece, laid to cover the
under side of the joint.

#

M:
"

Bearing Posts, when used to support the
floors of a magazine or warehouse, are ge-
nerally formed exactly square: to obtain their
dimensions, we must refer to what has been
already stated in reference to the weight the
several timbers will bear in the direction of their
length, or the weight they will carry previous
to the compression of their fibres: some
timber will support, whilst that of another quality will suspend the most; therefore in the
selection of story-posts, we must pay attention to these peculiarities. Iron, however, is
generally used for these purposes, in consequence of its horizontal sec-
Fig. 2084.
SCARFING.

tional area occupying less space than timber of the same strength.
When a tie-beam is mortised through to receive a king or queen-
post, and it is necessary to provide for the means of holding it up, the
tenon should not be pinned through, as it is not advisable to depend
entirely on the pins for the support: the tenon should be cut like a
half dovetail, or in a sloping direction, on one side, and left straight
on the other: the mortise-hole should be so cut that the lower end
Fig 2085.
CHAP. XXII.
1309
CARPENTRY.
can just pass; when it is in its place, a wooden key or wedge is driven tightly on the
straight side, which forces the tenon against one side of the mortise-hole, and prevents
it effectually from being drawn out: oak or iron may be added, or an iron strap may be
applied.
Tenons may be wedged at the end, but to do
this they must be made long enough to pass en-
tirely through the mortise: two saw cuts are then
made across it, and the wedges are driven home:
the tenon sometimes splits, but not sufficiently to
injure its strength. When in machinery it is not
practicable to cut the mortise through, the fox-tail
wedging is adopted; the tenon is made to fit the
mortise exactly; the wedges are loosely put into
the saw-cuts, as before, and the whole is driven
to its place: when the wedges touch the bottom
of the mortise, they cause it to spread, and thus
hold the tenon firmly in its place.
Dovetailing in some degree resembles mortising
and tenoning, and is more adapted to uniting toge-
ther the angles of framework: the feet of the rafters
require the mortise and tenon to be carefully made,
and the thrust is destroyed to a certain extent to
obtain greater strength: a portion of the rafter is
tenoned into the tie-beam, and another small part is
let into the upper part of it; both rafter and tenon
are cut at right angles with the inclination of the
roof: in one example the rafter has two bearing
shoulders in its depth, one behind the other, in
addition to the tenon which unites them. Struts
and braces which are loaded require but little
mortising to keep them from sliding out of their
places; the more flat their ends can be cut, the
more efficient will they be the shrinking of tim-
bers sometimes occasions them to become loose,
particularly where there is not much stress upon

them.
King-posts, queens, and principal rafters, which
are subject to great strains, should have iron straps or
ties, when they unite with the tie-beam, and an iron
strap should embrace the head of the kings and queens,
and unite with the principal rafters, the feet of which
in large buildings sometimes
have their abutment in a cast-
iron shoe, which prevents the
splitting off the end of the
tie-beam.
The ends of king or queen
posts may have a screw-bolt
passed into them, which
allows the nut to be turned
at pleasure, and thus the
framing may be tightened
again, when shrinking of the
timbers renders it necessary :
this in many instances is
preferable to the iron strap,
and keys or screws put in
the ordinary way.
Whatever form we adopt
for the butting joint, we must
be careful that all parts bear
alike, for in the general com-
pression the greater surfaces Fig. 2089.
KING-POSTS.
Fig 2086. PRINCIPAL RAFTERS

Fig. 2087.

Fig. 2088.


Fig. 2090.
QUEEN-POSTS.
will be less affected and the smaller undergo the greatest change; when all have come
to their bearing they should exhibit an equally close joint, and as large timbers are moved
with some difficulty, the joint cannot be often put to the test of trying whether it fits
nicely; it must therefore be set out with great precision, and worked with regard to its
1310
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
When
lines with exactness; a very small portion of a tie-beam left at the end is sufficient to
withstand the horizontal thrust of a principal rafter, and blocks may be used at the ends
where the rafters abut to give additional strength.
Scarfing a Timber in a perpendicular Direction.
the top surface is divided into nine squares, if four are cut
down, the other five serve as tenons to enter into as many
vacant spaces left in the piece of timber placed upon it; or
two may be cut away, as in the side figure, to receive a
tenon left on the upper piece.
Partitions and Framing for the outside of Buildings, &c.,
are a species of timber walls, usually covered with lath and
plaster, and formed of upright posts, mortised into a
head and sill, braced in different directions, and filled in
with quarters: the posts are placed at the extremities, as
well as at the sides of all doors and openings. When a
partition dividing two or more rooms has a bearing which
is perfectly solid throughout, it is better without braces;
the posts or quarters have only then to be maintained in an
upright position, which is effected by driving pieces between
them horizontally, so as to strut them, and prevent their
bending. Where they rest upon joists, which are liable to
shrink, and yield to a weight placed upon them, the par-
tition should be trussed in a manner to throw its load on the
parts able to sustain it in most houses we find great
neglect upon this subject, which occasions cracking in the
cornice, inability to open and shut the doors, and many other
inconveniences.



คา
Fig. 2091.
The thickness given to partitions which do not exceed 20 feet in length is 4 inches:
the posts are then 4 inches square, and the other timbers 4 by 3: when they are of greater
extent, they should be increased in thickness: when it is required to make a doorway in the
middle, the truss may be formed by the braces, the inclination of which should be at
an angle of about 40° with the horizon. When the doors are at the sides, the truss may
be formed over the heads; the posts should all be strapped to the truss, and the braces
halved into the upright posts.

Fig. 2092.
PARTITION.
The weight of a square of quartered partition may be estimated at from 12 cwt. to 18
cwt., and every precaution should be taken to discharge its weight from the floor on which
it is placed, to the walls, which are its best points of support: in ancient timber houses,
mills, &c., the fronts or external sides are formed of upright posts, placed at a distance
equal to their scantling; these are mortised and tenoned into a top and bottom plate,
which serves also to carry the floors: the posts at the angles are of a larger scantling, and
into these, which form openings for doors and windows, are framed horizontal pieces, which
serve for heads and sills: braces are then introduced, crossing each other, like a St. An-
drew's cross: above the lintholes, and beneath the sills, short quarters or punchions
fill in the space, and the whole are mortised, tenoned, and pinned together. The framing
should be placed on brickwork, or a wall of masonry, so as to be kept quite clear of the
ground.
Floors. When the bearings are equal, if joists of the same width, but of different
depths or thicknesses, are used, their strength is increased in proportion to the squares of
their vertical thickness: when the joists are but 6 inches deep, they are in strength to
those of 8 inches in depth, as 36 to 64, the square of 6 being 36, and that of 8, 64. The
CHAP. XXII.
1311
CARPENTRY
quantity of timber in the one case to that of the other is as 4 to 3, so that one-third more
timber gives a strength double that of the other.
Where square oak joists are used, and the bearing 12 feet, their scantlings should be 6
inches, and laid at a similar distance apart: such a floor contains the same quantity of
timber as if entirely formed of 3-inch plank: the strength of timber being as the
square of its vertical thickness, it results that the strength in these two instances is
2 to 1: the floor composed of 3-inch plank is only half the strength of the other; but
had the whole been formed 6 inches thick, instead of with joists 6 inches apart, it would
have been four times as strong, the square of 3 being 9, and the square of 6, 36.
Naked Floors are divided into single-joisted, double, and framed, floors; and it must be
remarked that unsawn timbers are considerably stronger than planks or scantlings cut out
of a round tree: when a tree is cut longitudinally, and formed into two pieces, these will
support less than they would do when united in the original tree, arising from the circular
concentric rings which compose the tree being cut through, which renders the timber more
compressible on one side than on the other; and as the texture is less close where it has
been sawn, it is also more susceptible of change from humidity on alternation of temperature.
Joists, whose width is less than half their vertical thickness, are subject to twist and
bend, if not strutted; and for this reason squared timber was usually employed by the
builders in the middle ages; and we have numerous examples, four or five hundred years
old, where the timber selected has the pith in the centre, and the concentric rings
nearly entire, being in a sound and perfect condition: experience also teaches us that
timber, whether sawn or unsawn, used for a floor of 16 feet bearing, composed of 12 joists,
8 inches square, placed at a distance of a foot apart, is much stronger than another of 24
joists, 8 by 4, placed edgeways, at a distance of 6 inches apart, although there is the
same quantity of timber in both cases.
Single-joisted Floors consist of one series of joists, which ought to be let down or halved
on to wall plates of a sufficient strength and scantling to form a tie, as well as a support to
the floors; each joist should be spiked or pinned to the
timbers on which it lies: wherever fireplaces occur, and
the joists cannot get a bearing on the wall, they are let into a
trimmer or piece of timber framed into the two nearest
joists that have a bearing; into this the other joists are
mortised. As the trimming joists support a greater weight,
they must be made stronger than the others, and should
have inch additional thickness given to them for every
joist they carry. When the bearing exceeds 8 or 9 feet
the joists should be strutted, or they will have an inclination
to turn sideways: the joists in use, being generally thin and
deep, require strutting on all occasions, and a rod of iron
is often passed through them, which, being screwed up after
the strutting pieces are placed, gives the entire floor great
solidity and firmness. The weight of a square of single-
joisted floor varies from 10 cwt. to 1 ton, and the joists should never extend to a greater
bearing than 20 feet in ordinary cases.

Fig. 2093.
To find the Depth of a Joist, when the length of bearing and breadth in inches is
given: divide the square of the length in feet be-
tween the supports by the breadth of the joist in
inches, and the cube root of the quotient multiplied
by 2.2 for fir and 2-3 for oak, gives the depth in
inches: a single-joisted floor, which has the same
quantity of timber as a double floor, is considerably
stronger, particularly if properly strutted, than the
latter. The plates, bedded on the walls, upon which
the joists are to be tailed down, should have their
depth equal to half that of the joists, and their width
half as much more; in many instances the plates are
not bedded entirely in the wall, but have one half
resting beyond the face on corbels let into the wall,
at a distance of 6 feet apart. To form the entaille
or dovetail great care should be used, to prevent the
joist from drawing out of its place, when once pinned
down.

Fig. 2094.
Double Floors are formed of Joists, Binders, and Ceiling Joists: the binders rest upon the
plates bedded on the walls, and serve the purpose of supports to the joists which are bridged
on them, as well as to the ceiling joists, which are pulleys mortised into their sides
when the depth of a binding joist is required, the length and breadth being given, divide
the square of the length in feet by the breadth in inches, and the cube root of the quotient,
:
1312
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
multiplied by 3:42 for fir, and 3.53 for oak, will give the depth in inches: when the length
and depth are given, and the breadth is required, divide the square of the length in feet by
the cube of the depth in inches, and multiply the quotient by 40 for fir and 44 for oak,
which will give the breadth. The above rules suppose the binders to be placed at a
distance of 6 feet from each other.
Binding joists must be framed into the girders, and care must be taken that the bearing
parts fit the mortise made for them very accurately: the tenon should be one-sixth of the
depth, and placed at one-third of the depth, measured from
the lower side. When binding joists only are employed to
carry the ceiling, their scantlings may be found in the same
manner as those of ceiling joists, which are small timbers,
and only of a sufficient thickness to nail the laths to;
when their length and bearing are given, their depth may
be found by dividing the length in feet by the cube root
of the breadth in inches, and multiplying the quotient by
0.64 for fir, or 0.67 for oak, which will give their depth in
inches. Ceiling joists are usually notched to the under
sides of the binding joists, and nailed to them; this is better
than mortising, which weakens the binder, and gives more
labour.

CIRDERS,
Fig. 2095. BINDING JOIST.
Double-framed Floors depend entirely on the girders for their strength; their vertical
thickness should be not less than one-eighteenth part of their length: the practice of halving
them down, and reversing their sides, is only beneficial for the purpose of ascertaining the
soundness of the interior of the timber used; whenever the concentric rings are cut through,
and the series of inclosed cones destroyed, the timber loses a portion of its natural strength:
a girder or piece of timber that has its breadth equal to double its thickness, when placed
edgeways, will carry considerably more; for with pieces of equal length, the strength is in
a compound ratio to the squares of their depth or vertical thickness and their width; thus,
a piece of timber 16 inches by 8, placed on edge, is to the strength of the same piece placed
flat, as the square of 16 multiplied by 8, is to the square of 8 multiplied by 16, or, as 2048
is to 1024, or as 2 is to 1; but this piece of 8 by 16 inches would not carry the half of
what a piece 16 inches square would do.
To find the Depth of a Girdler, when its length of bearing and breadth are given. Square
the length in feet, and divide this product by the breadth in inches; the cube root of the
quotient, multiplied by 4·2 for fir and 4.34 for oak, will give the depth in inches. To find
the breadth, when the length and depth are given, divide the square of the length in feet by
the cube of the depth in inches, and the quotient multiplied by 74 for fir, or by 82 for oak,
will give the depth in inches: in giving the above rules it has been supposed that the
girders are not placed more than 10 feet apart; when that distance is exceeded, they must
be increased in proportion.
The Strength of Girders, or any other piece of timber of the same length and thickness,
are in proportion to the squares of their depth; but when the thickness and depth are
both to be taken into consideration, then their relative strengths are in proportion to the
square of the depth multiplied into the thickness: when the length, breadth, and thick-
ness are taken together, the weights that will break each will be in proportion to the
square of the depth multiplied into the thickness, and divided by the length: and if we
multiply the square of the depth of each piece into its thickness, and divide each product
by its length, each quotient will give the proportionate strength of each piece of timber.
When it is required to have girders of greater length than 20 feet, it being difficult
to obtain timbers of that scantling, it is usual to form them of two pieces trussed
and bolted together: the core of such trusses must not be let close into the grooves
of the side beams, but must be well secured both at the ends and middle, or a
weight laid upon the girders should not bend the braces, which would render them
of no use; to prevent this effect, they should not be fitted in close; then the girder can
never bend materially, as the side beams cannot do so without shortening their length, and
in the act of bending, the braces force against the ends, and act on an opposite direction to
the side beams. When the truss is tightened, it is necessary to grease the head of the
king-bolt, in order that it may slide freely by the ends of the trusses; and when the
workman by a smart blow drives the head of the king-bolt, another should be ready to
turn the nut at the same time, so that the girders may be made to camber about an
inch in a length of 20 feet: all the stiffness obtained on trussing a girder is by
forcing the abutments, or cambering it; but this to a certain extent injures the natural
elasticity of the timber, and in the course of a short time the truss becomes a load and
useless this has caused the introduction of an iron truss, with an iron tie as an abutment,
and thus the compression which took place on the abutments is in a great degree
removed.
The common method of trussing girders is very defective, and where the depth is
CHAP. XXII.
1313
TIMBER ROOFS.
limited iron must be employed; a cast-iron girder is much more simple, and less expensive,
than iron framing introduced into timber as the means of strengthening it; but as this
cannot always be readily obtained, it will be necessary to describe other methods that have
been adopted in trussing girders: one of the most simple and best methods is by cutting
the girder, for a considerable distance, in the direction of its length, and wedging the
upper portions upon the middle, and then hooping it round with iron straps.
Another method is to place two pieces of timber like rafters on the upper part of the
girder, and which has abutments cut to receive their ends; a stirrup iron passes over the
centre, or one is placed on each side at a little distance from it, and these ties are placed
square with the rafters: another method is a kind of queen truss; two rafters abut against
a straining piece, and are let in, as well as hooped round by stirrup irons; this plan is
varied by omitting the straining piece, and introducing an oak block to form the upper
abutment.
As timber resists more when pressed longitudinally, or in the direction of its fibre, than
when it is acted upon laterally, it is advisable to substitute for the piece of oak a plate of
iron or lead, or some other incompressible metal; the rafters can then be adjusted, to form
a common joint in the middle, and a complete truss; the girder should be suspended in
the middle, whilst the iron ties at the extremities are tightened by this means: the girder
may then be made to acquire greater stiffness, by having a curvature given it, fitted up
with other pieces of timber cut to the camber, and made to fill up the voids between
the rafters and the girder. It has been satisfactorily proved that a piece of timber curved
on its upper side, and its extremities secured, to prevent its springing, when placed on two
supports, and loaded in the middle with a weight sufficient to make it bend one-third
of its thickness, if strengthened by another piece of timber, so as to preserve its curve
and form an arc, will sustain a weight more than double without yielding. Forming
floors with joists of small thickness, where camber timbers are united with straight,
so that they are not permitted to spring, is perhaps the most simple method of making
them strong; thus for floors where the joists have a bearing of 24 feet in the clear, the
depths are made in two, the lower 7 inches in thickness, and the upper, 13 inches, are made
up, after cutting the superior surface in a curved form, by laying on them others bent to
the curve, by means of iron straps 3 or 4 feet apart, taking care to give to this
curve half the difference between 7 and 13, viz. 3 inches, so that the lower joists will be in
depth 7 inches in the middle and 4 at each end; we shall thus have joists sufficiently strong
to bear any ordinary weight that can be put upon them. Girders may be formed in this
way, by uniting several such joists side by side, so that for a bearing of 24 feet, where they
ought to have a depth given to them of an eighteenth of this width, or 16 inches, it may
be
thus done: supposing the under joists to be 7 inches in depth, 9 inches more is required,
the half of which is 4 inches, which is the amount of curvature to be given to the upper
joists; instead of cutting away any portion of the lower joists, the curved top may be
given by furring out the 4 inches in the middle and letting it fall off to nothing at the
extremities: on these joists so prepared, with a curvature on the upper sides, the upper
joists are laid, and then bent to the lower ones, and secured by means of iron straps: a
series of such joists bound together or united forms a guider.
Some builders have taken advantage of the difficulty of crushing timber in the direction
of its length, and applied it very ingeniously for obtaining strength in a girder: a saw
cut is made across the middle of the girder to the depth of one-third its vertical thickness;
it is then bent upwards, and when the cut has opened sufficiently, a wedge is introduced
into it, thus making it camber, and consequently stiffer, whence it can bear a greater weight;
Parent has proved that joists so cut and prepared are one-sixth stronger than those of
the same scantling unsawn.
Another method of building up a girder, or strengthening a beam, was adopted by
Smeaton, which was by bending a piece into a curve, and securing it from bending back
by straps and bolts; the additional stiffness so obtained is considerable, particularly if the
pieces are properly bolted, or prevented from sliding on each other; the thickness of the
bent pieces should be made about the fiftieth part of the bearing, and as many should
be added as will increase them to the depth required; when the whole depth of the
curved pieces exceeds half the depth of the guider, then straight pieces must be added
to the under side, so as to make the entire depth of the straight part exceed that of the
curved part: care must be taken, when pieces cannot be found of sufficient length, that the
joints do not come in the middle of the length of the lower half of the girder.
Roofs, or the Coverings of Buildings, which protect them from the weather, serve also to
bind them more firmly together, and a knowledge of the strains to which the various
timbers are subjected, as well as what should constitute their relative strength, is one of
the most important studies of mechanical carpentry: the various inclinations that have been
given to them is perhaps dependent upon the nature of the climate where they are used.
In northern latitudes, where there is more rain, and the cold is greater, the pitch is made
higher; this decreases as we approach warm and dry climates; in Egypt, the covering of
4 P
1314
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
their houses is almost flat, and forms a terrace, and this is the case in some parts of Italy.
The inhabitants of the north have pitched their roofs very steep, for the purpose of more
easily throwing off the water; for though it rains more frequently in temperate than in
warm climates, the rains are heavier in the latter, and consequently require less inclination
in the roofs to carry them off; and the temperature is so elevated, that they become dry
immediately the rain is over. Where the rain is more frequent and less heavy, the air is
more humid, the water has more difficulty to run off, and the roof takes longer time to
dry; consequently a greater inclination in some degree compensates for this. The incli-
nation of the roof depends also upon the material that forms its covering: pan tiles require
less inclination than flat or plain ones, as the water collects in the hollow, and more easily runs
away, and is not so much subject to be driven by the wind under them, as where flat tiles
or slate is employed: in very rainy weather, and when fine rain is falling, the under parts
of slates and other coverings which have a trifling inclination is almost as wet as the upper,
as the water is induced to flow up by capillary attraction: when snow is melting, this is
often found to be the case, and the more so, the more smooth and compact the materials
which form the covering are, even between two panes of glass, the water will remount
between the lapping surfaces, and it. becomes necessary that a sufficient inclination should
be given to counteract this effect.
As the inclination to be given to roofs, then, should increase with the latitude, we must
commence, after quitting the tropical regions, with something like a fall; we find, for the
latitude of Athens, which is 38° 5', if we subtract 23° 28', which is that of the Tropics,
there will remain 14° 37′ as the inclination to be given to roofs in that city: and upon
examining the roof of the Propyleon, we find its inclination to be 1410; that of the
Parthenon 151, and that of the Erechtheum 15°. Rome is situated in 41° 54′ north latitude,
and deducting that of the Tropics, we have 18° 26′ remaining, which affords us the incli-
nation indicated by the term tertiarium, as used by Vitruvius: speaking of Tuscan
temples, he observes, "stillicidium tecti absoluti tertiario respondeat," which makes the
entire height of the roof, from the gutter, one-third of the length of the horizontal line
this system gives precisely an inclination of 18° 26'. The porticoes at Rome do not agree
with this inclination, for they vary between 23° and 25°, and which was owing probably
to the material with which they were covered being different, in order that the pro-
portions of the façade should not be made subservient to necessity: when we give to the
height of a roof the fifth part of its span, we have an inclination of 21° 48', which is suffi-
cient for flat tiles or slates, and in our latitude we usually make the pitch for pan tiles
27° 24', for slates 33° 24′, and for plain tiles 25° 24'.
The simplest construction
employed is undoubtedly that
which roofs in an excavation
made out of the solid rock or
earth. Trees pitched one against
the other in a triangular form,
and well secured at the base,
would serve for rafters, which
would support either branches,
shingles, or cleft pieces laid one
over the other, to keep out the
weather; upright boarding or
palisades to close the gables or
ends would then constitute it a
rude dwelling.
An improvement upon the
above method would be that of
raising the roof sufficiently
above the ground to enable the
inhabitants to walk erect be-
neath it without sinking a hole
in the earth, and which in many
situations would be damp, and
perhaps occasionally filled with
water.
Roofs, Vitruvius informs us,
were covered with reeds, and
sometimes with clay mixed
with straw; and Pliny observes
Fig. 2096.
;


that the ancients made use of
Fig. 2097.
the shells of tortaises for the same purpose. In Switzerland and in Germany shingles
split out of oak and fir are, on account of their lightness, preferred to any other covering.
CHAP. XXII.
1315
TIMBER ROOFS.

In some of the ancient works on
carpentry we have designs for pri-
mitive huts, with the principals
curved or set out like the pointed
arch, or with the ribs of a whale so
placed that they are made to carry
the weight of the roof.
;
The roof is that portion of a build-
ing which requires the greatest degree
of skill, and where the aid of science
is more essential than in any other
in our primitive timber houses we ob-
serve that much of their construction
bears the impress of the labour of the
ship-builder rather than that of the
carpenter; in the Weald of Kent and
Sussex many fine timber structures
are still remaining, in which the skill
of the carpenter seems borrowed
from the mason, for the mouldings
and forms introduced are evidently
Fig. 2098.
imitations of those executed in stone: oak is the material generally employed, and in some
instances the corner posts are 24 inches square, and in a perfectly sound state; the roofs
are generally highly decorated, the barge boards and pendants which accompany them
delicately carved, and present an

endless variety of design.
Buildings are sometimes found
rudely braced by such curved ribs,
and which bear a resemblance to a
boat turned upwards: these ribs
are occasionally made by nailing or
pinning together short lengths of
thin deal, and securing the plate on
which the roof pitches to their
sides: rafters laid with a slight pro-
jection to throw off the water, and
a number of purlins resting on them
in a longitudinal direction, require
nothing more than the tile, slate, or
metal covering to complete the
roof.
When two or more stories
are required, the same con-
struction may be made use
of; the upright posts and
partitions contribute much
to the strength of the build-
ing, and the curvilinear
braces extending from the
ground to the ridge of the
roof, where they do not in-
terfere with the convenience
of the apartments, are of
considerable service.
(-
The timber houses in
Switzerland, which gene-
rally consist of two stories,
are fine examples of cheap
construction, and when
placed upon a basement of
masonry, and preserved
from the heavy rains, are
as durable as if built en-
tirely of stone. The roofs
are flat, covered with
shingles, laid with a good
lap one over the other, and
24
Fig 2099.

Fig. 2100.
4 P 2
1316
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

sometimes the fronts of the house
are cased with courses of wooden
tiles with ornamental edges, placed
over each other like plates of
mail.
Circular Chambers are obtained
in a roof by keeping up the tie-
beams, but at the expense of their
utility in such cases the external
walls should be of sufficient thick-
ness to resist the outward pressure
of the feet of the rafters, which can-
not be sufficiently held in by the ribs
of the curves, or the braces attached
to them.
Where semicircular ribs are in-
troduced, with their lower ends
framed into the girders of the floor
below, a part of this objection may
be removed, and a very convenient
apartment obtained: the outer walls
should only be carried up to such a
height that they can have their
crowning-plate affixed or tied to the
braces, which are framed into the
collar above: this kind of roof is
very common on the Continent,
and is evidently derived from an-
cient examples; to light these
apartments a dormer window is
constructed, which has its top a
little below the collar, or hammer-
beam, as it is sometimes termed ;
the chambers being appropriated
for rest were called dormitories,
from whence these windows pro-
bably derived their name.
In many of our parish churches
we find roofs whose length of rafter
is equal to the entire width of the
building; at about half their height
is thrown in a collar, on which
stands a tree-post, strutting up the
principals: beneath the collar are
usually thrown in two braces, which are framed
into it and the rafters; such a roof, with a
tie-beam to hold in the plates which receive
the rafters, endures for ages.
Where the tie-beam is omitted, for the
purpose of giving a polygonal character
to the ceiling, it is necessary to have the
walls of considerable strength: over their
entire width is a capping of timber, on which
the principals rest, and to which they are
firmly pinned.
The walls of our churches where these roofs
are introduced are generally 3 feet in thickness,
but if the width of the span be great, buttresses
are required at every 10 or 12 feet, to resist the
thrust which it occasions: by spreading the
feet of the rafters the weight of the roof bears
upon the entire thickness of the masonry, and
further strength and protection are obtained by
an additional short rafter, which projects to the
outer face of the wall, and carries the eaves out
sufficiently to throw off the water, and prevent
its doing injury to the construction.
Fig 2:01.

.
Fig. 2102.

Fig. 2103.
CHAP. XXII.
1317
TIMBER ROOFS.

Semicircular ribs, formed by three
thicknesses of deal or other timber, and
others of the figure of the pointed arch,
are occasionally met with, where timber
of large scantling cannot be readily ob-
tained; and when well put together
and pinned carefully, such a roof has
remarkable strength, and will endure
for ages.
23
The timber roofs of the middle ages
are of high pitch, and formed without
any horizontal ties; they are supported
by the walls on which they rest, and the
thrust of the ends of the principal rafters
is counteracted by buttresses of sufficient
strength to resist it; indeed the in-
troduction of a tie-beam would have
destroyed the effect of carpentry framed
upon the principles adopted in masonry.
The roofs of our churches are usually
formed of pairs of rafters, the feet of which are framed into a piece of timber laid across
the thickness of the wall, into which at the other extremity is framed an upright quarter,
fair with the inner face of the wall; at about two-thirds of its height a collar is framed, in
which is supported the tree or post which carries the ridge: beneath the collar two braces
are introduced, which give the contour for the ceiling a half-decagon or semicircular form.
The plates are usually made of considerable thickness, and the pitch given the roof is as
much as their span: some
of the roofs constructed
in the fourteenth century
are of surprising beauty,
both for their construction
and workmanship: that
over Westminster Hall,
finished about 1399, is in
extent equal to any; its
clear span is 68 feet, and
its total length 238 feet
8 inches, and its width 66
feet 6 inches, divided into 13
bays. The skilful arrange-
ment of its timber combines
lightness, strength, and
beauty, and its pitch is such
that the length of the rafters
is about three-fourths of
the entire span.
This roof
exhibits perfectly the con-
struction in use before the
introduction of tie-beams;
and the lateral thrust is
prevented by placing at the
foot of each pair of prin-
cipals flying or arched
buttresses, of sufficient
strength; these principals
are placed at about 18 feet
apart, and run throughout
the whole length of the
building, forming 13 se-
vereys or bays of roofing:
each pair of principals
comprehends one large
arch, resting on stone
corbels, which project
from the wall at a dis-
tance of about 21 feet
from the base line of the
Fig. 2105.
Fig. 2104.

ELTHAM HALL.
4P 3
•
BOOK 11.
· 1918
THEORY AND PRACTICE OF ENGINEERING.
roof. The ribs that form this arch are framed into a beam, which connects the rafters in
the middle of their length: within this large arch is introduced another, which has its
springing on a level with the base line of the roof, and this is supported by two brackets, or
half arches, issuing from the springers of the main arch; each of the trusses acts like an arch,
and by placing their springing below the tops of the walls, a better abutment is obtained.
Eltham Hall is internally 101

feet 4 inches in length, and 36 feet
in width, and is divided into 6
compartments or bays; the length
of the rafters is about four-fifths of
the span, so that it has not so great
a pitch as that of Westminster
Hall. In this example the arches
are obtusely pointed, and struck
from four centres. The trusses
at Eltham have a greater quantity
of timber in proportion to their
breadth than those of Westminster,
but the walls and buttresses are
much lighter.
Crosby Hall, finished about
1470, is internally 69 feet by 27,
and is another fine example of these
admirable works in oak timber :
three ranges of pendants form the
chief ornament and variety.
Hampton Court Great Hall was
completed about 1537; its di-
mensions internally are 106 feet
by 40 feet; the flattened pitch
at the top is a novelty in this
kind of construction.
The Hall of Christ Church,
Oxford, is 115 feet by 40 feet; that
of Trinity College, Cambridge, 100
feet by 40 feet; the New Hall at
Boreham, 90 feet by 40 feet; that
of the Middle Temple, London,
100 feet by 44 feet; Lambeth
Palace, 93 feet by 38 feet; Guild-
hall, London, 153 feet by 48 feet.
Fig. 2106.
HAMPTON court.
In examining the principles of
the beautiful roofs, of which we have so many remaining in England, we find that
the pressure against the walls is sometimes too oblique, and that the buttresses have
yielded after the strong plates, laid upon the walls, had given way, as is the case at
Eltham. These timber roofs originated in the reign of Edward III., and were common
to all large halls: they were executed with the best quality of well-seasoned oak timber,
admirably put together with oak pins; the mouldings all cut out of the solid, and set
out upon simple principles; the halving, mortising, tenoning, and framing, performed
with the greatest nicety, and no iron work of any kind, not even a nail, used; their pitch
varies in most examples, but the loftiest were the earliest built. The greater portion were
originally covered with lead, of a weight equivalent to 10 pounds to the foot superficial.
The roofs of some of the early buildings in Brittany, where timber is not abundantly
produced, are exceedingly simple in their construction; the principals have the form of a
pointed arch, or inverted boat, and are formed on masonry or rubble work: the walls are car-
ried up upon them to the necessary height, and then cut to the rake of the roof. The walls
of the houses are brought up to a level, and then quarter circles described determine
the commencement of the roof. In many parts of Germany, barns are erected upon
this principle, using timbers instead of masonry: fir planks are united in the form of a
pointed arch, into which a piece of timber is framed resting upon the top of a plate,
mortised on to the head of an upright post: upon this is laid a rafter, which carries
a number of purlins to receive the boarded covering. The same system is adopted in
Holland to houses of two or more stories; the principals are formed of solid timber, and
placed about 12 feet apart; the outer walls are framed together, and the spaces between
the timbers filled in with brick; the timbers are painted yellow, the rooms admirably
arranged within, forming convenient houses at a moderate cost for people of the working
classes.
CHAP. XXII.
1319
TIMBER ROOFS.
Tie-beams, at their introduction, com-
pletely altered the principles of framing
roofs; the ends of the rafters were now
held together at the feet, by framing them
into a horizontal piece of timber which
acted like a rope, and resisted their being
pulled asunder, in the direction of its
length. When a heavy body is supported
by two pieces of timber, A C and BC, its
effects depend upon their position; the far-
ther the ends of the timbers are apart,
the greater is the strain upon them: the
weight resolves itself into two forces, one
in the direction of each beam.
The weight W might be sup-
ported upon an upright post in the
direction of Cc, where its vertical
force is equal to the weight: this
may be resolved again into two
forces, acting in the direction of the
beams, that would produce the same
effect as the vertical force Cc.
If the vertical line Cc be drawn
through the centre of the weight,
and ac be drawn parallel to the
rafter or beam A C, also be parallel
to BC; then the weight and pres-
sures exerted will be found thus:
b
10

C
Fig. 2107.

с
Fig. 2108.
W
E
as the line Cc, is to the line Cb, so is the weight W, to the pressure in the direction of the
beam Ac: and as the line Cc, is to the line Ca, so is the weight W, to the pressure in the
direction of the beam C B.
If the position of the beam were that shown by the dotted lines CE the magnitude of
the strain would be considerably increased on both beams: by drawing lines parallel to
them in this position, expressing the weight by the line Cc, then the pressure on the beam,
in the position CE, is expressed by the line Cd, instead of Ca, and the strain on CA by
the line Ce; we find that considerable strains are often the result of comparatively trifling
weights, when a change is made in the position of the supports A, B, and E. By drawing
out a variety of diagrams we are enabled to form some idea of the changes which posi-
tion can effect, and to judge of the alterations in the duties which the several timbers com-
bined into a truss or piece of framing have to perform; the object of the carpenter ought
always to be that of not relieving one piece at the expense of another, but of so arranging
the whole that the burden may be equally distributed.

B
E
An easy method of ascertaining how much each sus-
tains is, by passing a string over two pulleys, as B and
C, and tying another to any point at A, which has a
weight attached to it at W: if the sum of the weights
b and c be greater than the single weight W, it is a
position in which they may be placed, and will allow
the three weights to be at rest, or in equilibrio.
When the whole is in this state of equilibrium, draw the
figure on paper, and from a scale of equal parts make
A F equal to the number of pounds contained in the
weight W, and continue the line BA to E, and draw
the line EF parallel to AC: then FE measured on
the scale will express the number of pounds on the
weight at c; and the length of A E by the same scale
will show the number of pounds in the weight b.
When the three weights are equal, the three lines
A F, FE, and AE will be equal, and all the angles
round the point A, where the perpendicular string is
tied, will be equal. When these three forces are in the
same plane, and meet in a point, they are always in
equilibrio, and the forces are represented by the three
sides of a triangle drawn parallel to the directions of the
forces. When a weight is kept at rest by three forces, and any two are represented in
magnitude and direction by the two sides of a triangle, the third side, taken in order, will
show the magnitude and direction of the other force.
F
W
Fig. 2109.
4 P 4
1320
BOOK II,
THEORY AND PRACTICE OF ENGINEERING.
The sides of triangles are as the sines of the opposite
angles, and when three forces keep a body in equilibrio,
each is proportional to the sine of the angle made
by the other two: the weight W, for instance, is as the
sine of the angle A E F, the weight b as the sine of the
angle AFE, &c. &c. When the framing of a roof, or a
pair of principals, are drawn upon paper to a scale, the
proportion of the forces may be correctly ascertained in
this manner, without further calculation, at least suffi-
ciently near for all practical purposes.
Tie-beams con-
R

C
F
C
W
о
necting two rafters at the feet prevent their spreading;
and the horizontal strain given to the tie-beam is depo-
sited with the entire weight, and without any thrust upon
the walls. The triangle is the strongest form that can be
given to framing; suppose three pieces of timber
united by pins, such a triangle will not alter its form;
but if the top pin be drawn out, the two inclined sides
will revolve round the other two pins; but as long as the
three pieces of timber are of the same length the figure
will retain its form. The pins, upon which any pair
are held together, are free to revolve in circles, before the third is put in, but this makes
no difference to its strength or its form: from this very simple principle two important
rules are elicited for framing timbers, and which show that all framing should have the
figure of a triangle, with the largest or most obtuse angle that can be obtained, or that
the application will admit of, care being taken to prevent the sides from bending.
Fig. 2110.
To properly brace a piece of carpentry, so as to resist any force that may be applied to
it, and to give it the necessary stability, requires careful arrangement, and considerable
knowledge in the art; but the chief object to be attended to in framing a roof is to provide
against any alteration in the form of the triangle made by its principals, or the sagging or
bending of the tie-beam, which is the longest side of it. In determining the scantlings of
the various timbers, it must be borne in mind that the load the roof has to support is equally
distributed over their whole surface, and which never need be calculated at more than a
floor has to carry.
The timbers are, however, more apt to shrink, and alter their form
by change of temperature, and oak is more subject to this than fir. The principals of a
roof may be regarded as the girders of a floor, the common rafters as the bridging joists,
but there is the advantage of giving the principals additional strength by framing and
trussing them, which cannot be done so readily with the girder; and the more at right
angles to the rafters the strutting pieces are placed, the firmer and stronger the roof
becomes.
The most advantageous method of employing a piece of timber, so as to have its entire
strength, is to place it perpendicularly, as in a king-post, which not only holds up the tie-
beam where it is the weakest and inclined to sag most, but, when properly strutted,
forms with the principal rafters a complete truss. A collar in addition to the tie-beam
placed half-way up the principals, and acting as a coupling, has not the stability of the king-
post with its braces, which transport the weight of the purlin to a point or points which
contribute to its strength.
Some of the roofs used between the fifteenth and seventeeth centuries had their principals
set out in the form of an equilateral triangle; a collar was framed into them, and on this
rested a king-post, into the head of which the tops of the principals were framed and
pinned; two short struts were placed above the collar, from the king to the rafters, and
two others below the collar were also framed into the principals: on the principals were
pinned blocks, to support the purlins without cutting into them, and the common rafters
had their feet framed into a small plate, which laid fair with the outside of the wall;
they were also securely pinned to the purlins and the ridge piece, which rested on the
top of the king-post or tree-post in the middle.
This formed altogether a very solid roof, but required a quantity of timber, and of
course a considerable expense: the tie-beams generally, for roofs from 25 to 30 feet span,
were in depth equal to an eighteenth part of the width between the walls, and all the rest
of the timbers in proportion.
In some early buildings, where it was required to improve the rooms obtained in the
roof, the tie-beams, on which the floor rests, are placed two or three feet below the level of
the pole-plate, upon which the common rafters pitch: by forming a semicircle over the tie-
beam, composed of crooked or cut timbers, and introducing above it another tie framed
into the principals, and again strutted on to the ends of the lower tie-beam, a convenient
arrangement for a room is obtained: above the upper tie was introduced the tree-post,
with a collar and struts, which deposited the weight of the upper portion of the roof on to
the tie-beam, supported partly by the middle of the arch.
CHAP. XXII.
1321
TIMBER ROOFS.

Mansard's Roof, as it is termed, is curbed,
for the purpose of keeping down the height
of a building, or obtaining a more capa-
cious apartment within it; the whole is usu-
ally arranged within a semicircle, but its
system may be said to consist of four pieces
or rafters hung together in such a manner
that, if inverted, they would naturally assume
the form given to them.
·
AW
MANSARD'S ROof.
The tie-beam in this case, which holds the
wall plates together, are the common joists of
the building, and the principals and struts
above the collar, which hold in the curb-plates, are proportioned to their uses.
F g. 2111
Many granaries and storehouses of considerable extent are constructed in a very simple
manner, and have their roofs in a single span the entire width is divided into four parts,
two of which are given to
the middle. Upright posts
with braces framed into the
joists, which extend through
the entire width, support the
middle of the rafters: as they
are equally balanced, they
have but little
outward thrust.
It is the ge-
neral practice in
England, where
the span of the
roof exceeds 25 feet, to adopt
the king-post and tie-beam,
and not omit the struts.
Where it is required that the
backs of the common should
lie even with those of the
principal rafters, the purlins
must be framed
into the side of
the latter, or
strapped up with
iron. When
the tie-beam is

Fig. 2112.
SECTION OF A WAREHOUSE.
placed at a height above the level of the plates on which the rafters pitch, it is called a
collar: the chief object in framing a roof should be to make it neither too heavy nor
too light, though the former
is often preferred to the
latter, from the idea that
weight upon
the walls
adds to their stability, so
long as it is not sufficient
to crush them.

P
Fig. 2113.
ROOF With tie-bram.
1322
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
When the upright posts are omitted, for the sake of obtaining a spacious room, it is
necessary to hold up the tie-beams, so that they are prevented from sagging; and where
two or more stories are required in a roof, as in theatres, every means must be taken to
render them secure.
At the Palais Royal, in Paris, is a remarkable roof of considerable span, with two
floors within it: the tie-beams are scarfed together, and hung up to the rafters by strong
stirrup-irons.
The roofs of the houses in Flanders are frequently contrived to contain three or more
floors, and examples exist of more than double that number: when the building is of a
considerable span, and the roof true pitch, it is important that the space it contains should
not be entirely useless; upright posts and partition walls generally sustain a portion of the
load that such an arrangement must produce. In theatres and large assembly rooms,
where the whole weight of the roof is laid upon the outer walls, difficulties often occur that
require considerable skill on the part of the constructor, to avoid the danger which ac-
companies them. The first study should be directed to securing the feet of the principal
rafters to the ends of the tie-beams, and

wherever a joint occurs in the length of the
latter to hold it up, and prevent it from
sagging; the more securely the timbers are
framed together and made to resemble an
entire truss, the less is their liability to dis-
arrangement, which often occurs through
hanging additional weight to the several
floors contrived within it, or the bending or
pushing out of the walls of the building.
Fig. 2114.
ROOF AT THE PALAIS ROYAL.
In some instances, as at Louvois, the great weight of the roof is deposited below the
tie-beam by an angular brace, at the foot of which is a tie-beam hung up to pendentives

D
Fig. 2115.
ROOF AT LOUVOIS.
attached to the principal rafters, where the collar that supports the king-post is framed in:
another iron strap secures the collar to the post, and binds all firmly together.
:
Several methods have been adopted to brace the rafters together where tie-beams have
not the king-post to hold them up in some examples, on one side is a stirrup-iron, and on
the other a brace; the latter is rather calculated to deposit weight than to uphold it,
whilst the foriner, which performs both services, is to be preferred
CHAP. XXII.
1323
TIMBER ROOFS.
The carpenter should avoid as
much as possible the effect of all
cross strains, or those which are
transverse; and in the ar-
rangement of the timbers of
a roof, he should never em-
ploy a very open angle at
a point where a load is to
be supported, the obli-
quity of the two pieces
forming the an-
gle

requiring
them to exert a
great force, in
order to oppose
a much smaller
one.
If the two braces forming the ob-
tuse angle in the present figure con-
sisted of wood cut across the grain,
and the piece joining their
extremities were cut in the
usual manner, the oblique
pieces would contract more
than the others in drying,
and the angle would be-
come more obtuse, so that
the strain would
be increased
considerably be-
yond what it was
at first.
Fig. 2116.
ROOFS WITH TIE-BEAMS SUSPENDED.
At the Theatre of St. Martin, at Paris, which is of considerable span, the timbers are
arranged for the convenience of the scenes, which are in many instances suspended from it;
shores or supports are consequently necessary to discharge or bear the great weight to which
the several floors are subject, and they are admirably placed for the purpose.
The angle of inclination of a roof varies much,
and is dependent in a great degree upon the nature
of the material with which it is covered.

A steep
roof is absolutely necessary in climates where there
are considerable falls of snow, and we must always
bear in mind, that the horizontal force exerted by
roofs of all kinds is proportionate to the length of
a line perpendicular to the
rafter, descending from its ex-
tremity till it meets another
similar line drawn from the
opposite rafter.
ד
N
The transverse strain which a roof is required to
bear, and which tends to break the rafters, is better
provided against in one of low than in a high pitch,
supposing the number of posts and braces equal in
each for when a weight is to be borne by a rafter,
whether it be placed in the middle or equally dis-
tributed throughout the entire length, the rafter
neither gains nor loses force by being lengthened or
raised higher, while the horizontal span continues
the same.
Fig. 2117.
THEATRE OF ST. MARTIN.
In the Palais Royal, at Paris, over the larger apartments the several floors are all hung
by irons to the principal rafters, which are so strutted and braced that they effectually
1324
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
resist the strain to which they are subjected: the feet of the main timbers are secured
by iron straps, and from the outer walls are projecting corbels, to afford a firm rest to the
joists and braces which are framed into them.
The obliquity given to a rafter lessens the
effect of the weight which it bears, precisely in
the same ratio that its length diminishes its
strength: for in all beams, when lengthened,
there is an additional weight to be supported,
which diminishes their strength, and in calcu-
lating that of rafters, we must remember that the
slight flexure produced by the transverse strain
diminishes their strength
by resisting a longitu-
dinal force.

Fig. 2118.
M
U U A U
ROOF AT THE PALAIS ROY.
ROYAL.
In framing the feet of the principals into the tie-beam, care should be taken to place
them at some little distance from its extremities, at the same time not allowing them to be
projected a long way within the walls, which might occasion the bending of the tie-beam, an
evil which often occurs when the slant of the roof is very flat; in many of our churches
covered with lead, this portion of the construction is very faulty. Every roof, however
well put together, must undergo some change from its original form, from the shrinking of
the timbers, but a scientific knowledge of this fact will sometimes prevent any great evil
from arising; to know how much a piece of timber will yield when compressed will enable
us to give it such dimensions that its form will be retained, and its efficiency continued :
when any part of a roof assists in suspending the floors below, it becomes important to
consider the nature of this new strain, and to provide properly for it. In the present
example, the upper floor forms a portion of a trussed arch, which assists in carrying the
principal rafter at the point where the suspension rods are attached, and as long as the
feet of the rafters are maintained in their place, there is perfect security, provided also that
the tie-beams are not drawn asunder, which hold in the wall plates and corbel timbers
beneath them. A truss of this description will bear great weight, as it forms but one
piece of framing, the timbers of which cannot pull out, each being acted upon in the manner
of a strut, and if of a dimension to resist bending, there is no danger of the whole retaining
its strength and usefulness.
Iron rods are now often substituted for king-posts, and all other situations where beams
perform the office of ties, and it is advisable to introduce iron sockets whenever it is possible,
to receive the ends of all braces and struts, so that the principal timbers may not be weak-
ened by cutting mortises or notches to receive them. The principal rafters may be set in
an iron shoe, which may be bolted down upon the tie-beam, and every purpose of a mortise
answered without the labour of cutting it or destroying the strength of tie-beam. Although
iron is twelve times heavier than fir timber, it is more than twelve times stronger, therefore
CHAP. XXII.
1325
TIMBER ROOFS.
both equal in weight and strength, when properly proportioned. Roofs which are de-
pendent upon the principle of a truss and straight tie-beam should have all their tim-
bers proportioned to the duties they perform, and few subjects deserve more attention,
as it seldom happens, that in large buildings we can place the several timbers exactly where
the strength of the roof requires them.
The Theatre at Bordeaux has a fine example of roof, which is adapted to all the purposes
required for the arrangement of the scenes: the whole, strutted and braced in a judicious
manner, is partly curbed, and the plate, where the bend is made, is secured by a piece of
timber bolted to the tie-beam.
A curb roof is sometimes preferred,
both on account of a greater space
being contained within it than a plain
roof of the same height, and of its
exerting less strain on the tie-beam or
abutments: the carpenters of the
middle ages thoroughly understood
the mechanical prin-
ciples by which the
equilibrium of a roof
could be maintained,
and the examples they
have left us are de-
serving of our
particular

tention and
study.
at-
•
:.
#IL
| #[113
Fig. 2119.
THEATRE AT BORDEAUX.
Roofs of theatres, or any building where the opening is too wide to be spanned with one
or even two pieces of timber, are generally framed by a combination of pieces, which in some
degree assume the property of an arch constructed in masonry, but their principles of sta-
bility differ: all carpenter's work is dependent upon the strength of the material and manner
in which it is framed or put together. When timber is strained by a force that destroys the
balance existing throughout its parts, that strain should be examined, and it should be
decided whether it is produced by stretching or compressing: in all framing there will be
one point in a neutral state, as in a solid piece of timber.
1326
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
At the Palais of Versailles is a roof of novel construc-
tion, which has two collars, resting upon two upright
posts on each side, to allow of a passage between
them.
Theatres admit of such an arrangement, the space be-
tween the two upright posts on each side the roof being
usually devoted to the passage which conducts to
the several boxes in front of the interior part. The
ceiling of the pit is suspended to a king-post,
strengthened on each side by

a long strut that braces the
whole together.
At the Italian Theatre at
Paris, the roof was formed
by a double arrangement
of principal rafters,
SO
strutted and braced as
to have strength enough to
hold up the floor by means
of iron rods, which covered
the entire width of the
theatre.
Fig. 2120.
PALAIS AT VERSAILLFS.
When roofs are constructed
in this manner additional
strength would be obtained by
the introduction of a St. An-
drew's cross between each pair of upright struts, framed
between the upper and lower principal rafter; these
bolted together would form a strong truss, and support or
hold up a considerable weight; the abutments require
to be held firmly in their position, and in
the present example the lower strut was
introduced to discharge a
portion of the weight upon
the floor below, where the
outer walls are tied together.
The collar or beam under the
king-post also

acts as a strut,
to prevent the
sagging of the
truss
into
which it is
framed.
Fig. 2121.
THEATRE Des italiens, at paris.
Roofs without tie-beams are frequently used where height is required in the building
they cover, but, with all the care possible, it is difficult to frame them so that they will

Fig. 2122.
ST. MARTIN'S, PARIS.
CHAP. XXII.
1327
TIMBER ROOFS.
resist depression, or to hold their form sufficiently to maintain the outer walls erect; the
shrinking of the timbers is another cause of change.
Over an assembly room at Brussels, the coved ceiling was carried up to the under
side of the rafters, and scarcely any space was lost; the abutments were produced by
the aisle formed by the columns on each side,

which were strutted above, so as to insure
perfect stability.
In roofs of this description the framing
might be so equally balanced upon the up-
right post, that there would be little or no
disposition to thrust out the external walls:
such construction has been adopted by the
builders of small
houses in the neigh-
bourhood of London,
who have balanced
their rafters
upon the
two internal partitions
of the house, which
Fig. 2123
ROOF AT THE BALL ROOM AT BRUSSELS.
have enabled them to carry up the outer walls a few feet in height above the upper floor,
and thus gain more head-way in the attic than could be obtained if the rafters were
framed into a tie-beam in the ordinary manner: but the construction is faulty, and ought
not to be adopted, as it is liable to push out the outer walls, if not very accurately executed.
A similar principle to that in fig. 2123. was adopted by Sir Christopher Wren, and has
been followed by several architects since his time: buildings divided into four equal parts,
two of which are given to the centre, may have this roof applied with great advantage; the
coved ceiling being extended to the very summit, every part of the space comprised
beneath the rafters is available. The circular ribs, formed of several thicknesses of plank,
are strapped to the principal rafter, and abut against the upright posts, which carry the
weight of the roof.
The Roof over the Pantheon, or St. Genevieve, at Paris, is contrived to permit the cur-
vature of the vault to rise above its springing: another roof in the same building is diffe-

Fig. 2124.
ROOF AT ST. GENEVIEVE, PARIS.
rent.y framed, and has a considerable quantity of timber bestowed upon its arrangement,
which is remarkable for its strength.
The two side walls are tied together by strong oak plates; over that on the inside is an
upright post, strutted on each side to the principal rafter: a collar framed above the struts
prevents the posts from being forced out of their perpendicular position, and an iron bolt
1328
Book II
THEORY AND PRACTICE OF ENGINEERING.

holds up the collar, in the middle of its
length, to the king-post; a brace parallel to
the principal rafters unites the several portions
of the framing together: three purlins on
each side support the common
rafters, forming a roof that could
be lifted off in one entire piece.
A
Fig. 2125.
ROOF AT ST. GENEVIEve, paris.
At the Opera des Arts, at Paris, over the proscenium, it was necessary to have a lofty and
spacious room for the purpose of mounting the scenes and other useful purposes; this is
admirably contrived, and the principal timbers of the roof are so framed as to resist any
effects they might be subject to when heavy weights were suspended from them.

-
א.
Fig. 2126.
ROOF AT THE OPERA DES ARTS, PARIS
Roofs framed with pieces of timber which act as struts as well as braces are both simple
and strong in their arrangement.
CHAP. XXII.
1329
TIMBER ROOFS

យុ
a
Fig. 2127.
Pfeiffer executed several roofs
in Germany, which derive con-
siderable strength from the intro-
duction of inclined timbers, which
serve the double purpose of hold-
ing up the tie-beam to the prin-
cipal rafter, and strutting them :
where timbers act as struts and
ties an iron bolt is almost indis-
pensable to secure the joints; but
as the carpenters of the middle
PFEIFFER • CONSTRUCTION of roof.

Fig. 2128. roof at st. PAUL, ROME,

ages seldom introduced iron into their framing, they were obliged to form
their joints in such a manner as to answer the same purpose; the shoulders
of the timbers were accurately cut, to fit both the principal
and tie-beam, into which they were framed and secured by
an oak pin; as long as the latter resisted fracture or draw-
ing down, the framing remained entire,
and from the observations made upon
several ancient roofs so constructed we
rarely find that any
injury has taken place.
어머
​Fig. 2129.
roof at RIDING-SCHOOL, MOSCOW, AS IT IS at present.
The celebrated roof of St. Paul's-out-of-the-walls at Rome exhibited an admirable con-
struction, and was perhaps one of the earliest where the upholding the tie-beams by iron
rods was introduced.
The riding-house at Moscow, which at present exists, covers a considerable area; it is
framed in an admirable manner, upon the same principles; a series of ties and struts in
succession are united into one simple and complete truss.
King Post Roofs, or their principle, we find adopted very early in Italy, and particularly
in the basilicas at Rome: in the church of St. Paul-without-the-walls, where the span is
nearly 79 feet, was a finely constructed roof destroyed by fire a few years ago: it was con-
structed of fir timber, and consisted of pairs of trusses, placed 15 inches apart, and each pair
rested on the walls, with a distance of 10 feet 6 inches between them. The manner in which
the trusses were framed together was as simple as it was ingenious, and a remarkably strong
roof was formed by it: a king-post received the upper ends of the principal rafters, which
were about 22 inches by 15; a collar or straining piece 15 by 12 abutted against the heads
of two queen-posts, the position of which was maintained by additional timbers, placed under
the principals, and forming a double thickness where the greatest strength was required.
The Tie-beams were formed by scarfing two lengths of timber together, and securely
strapping them with three stout irons; their scantling was 23 inches by 15.
The Collar, or upper tie-beam, was placed at two-thirds the height of the king-post, and
by the introduction of the pairs of queens the tie-beam was hung up in three places to pre-
vent its sagging; such a suspension of the tie-beam by the middle, and again at 14 feet on
each side of it, exhibits a thorough knowledge of the true rules which should direct the car-
penters: no tie-beam should exceed the length of 15 feet, without some precautions
similar to these being adopted, to prevent it from drawing in the wall plates and crippling
the truss. In this example we have an early instance of suspending the tie by means of the
heads of a king and a pair of queens, and which is now universally adopted, though the
irons which have been used for the purpose have been variously formed; sometimes bolts
and at others stirrup-irons secured by keys have served the purpose.
4 Q
1330
Book II.
THEORY AND PRACTICE OF ENGINEERING.
The simple King-post Truss is usually adopted in buildings where the span does not
exceed 30 feet, and the rise given to it varies as the inclination of the rafters are formed to
receive different kinds of covering: for thatched buildings the height is made equal to
half the span; for pantiles two-ninths; plain tiles two-sevenths, and for slate one quarter, a
quarter of the span forming an inclination of angle of 2610.
The king-post suspends as well as supports, and must be proportioned according to the
span; its scantling may be found by multiplying the length of the post in feet by the span

Fig. 2130.
KING-POST roof.
in feet, and again their product by 0.12 for fir and by 0·13 for oak, which latter product
will be the sectional area of the king-post in inches; by dividing this area by the breadth, or
by the thickness, either may be obtained; the area divided by breadth gives thickness, and
divided by thickness gives breadth.
Tie-beams have two strains, one in the direction of their length, and the other from the
weight of the ceiling, or whatever is suspended from it: the thrust of the rafters is never
so great as to pull the beam asunder, and the chief strain which the tie-beam is subjected
to, and which is to be guarded against, is the weight of the ceiling, or any thing which
induces it to sag in the middle, or any other part of its length. The weight it carries will
be proportional to the length which is unsupported: where a ceiling has to be supported,
the scantling of the tie-beams is found by dividing the length of the longest unsupported
part, by the cube root of the breadth, and then multiplying the quotient by 1·47 for the depth
of fir in inches, and by 1.52 for that of oak: where rooms or warehouse floors are held up or
supported, then their strength must be provided for in the same way as for girders. To
find the scantling for the principal rafters, where the king-post is in the middle, multiply
the
square of its length by the span in feet, and divide the product by the cube of the thick-
ness in inches: for fir, multiply the quotient by 0-96, which will give the depth in inches.
Struts and Braces must be proportioned to the effect they have depending upon them, or
upon the load they are to carry; when they are placed at the back of the principal, in a
right angle, or perpendicular to its inclination, the strain upon them is the least, and when
the same inclination is given them as to the roof, the same strain is thrown on the principal
as is borne by the strut. By multiplying the square root of the length supported in feet, by
the length of the strut in feet, and then multiplying the square root of the product by 0.8 for
fir, the depth may be obtained, which multiplied by 0-6 will give its breadth in inches.
Common Rafters, being uniformly loaded, they are usually made 2 or 24 inches in thickness,
and their depth is found by dividing the length of bearing in feet by the cube root of the
breadth in inches, and multiplying the quotient by 0.72 for fir or 0.74 for oak, to obtain
the depth in inches.
Purlins must have their scantling proportioned to the distance the principals are apart,
and as the weight diffused over them is uniform, the stiffness is reciprocally as the cube of
the length. By multiplying the cube of their length in feet, by their length of bearing in
feet, the fourth root of the product will be the depth in inches for fir; or, multi-
plying by 1.04, will give the depth for oak: this multiplied by 0-6 will give the breadth.
Purlins should never be framed into the principal rafters, which are weakened by having
mortises cut into them; it is better to lay them on the principals, and simply notch down
and secure them; when the purlins are weak, the roof is materially damaged, proper strength
being of the highest importance to them.
When king-post roofs are adopted, the following scantlings for the chief timbers may be
adopted.

Span.
Tie-beam.
King-posts.
Principals,
Struts.
Feet.
in.
in.
in.
in.
in.
in.
in.
in.
20
9 by 4
4 by 4
4 by 4
4 by 3
25
10 by 5
5 by 5
5 by 4
5 by 3
30
11 by 6
6 by 6
6 by 4
6 by 3
CHAP. XXII.
1331
TIMBER ROOFS.
Queen Post Trusses have two suspending pieces, and are used when the span is above
30 feet up to 45 feet; there is an advantage in this species of framing which is not obtained
where the king-post is introduced, viz. a passage or space available for many useful
purposes: where queen-posts are used each is so placed that it bears one-half the span:
to find the scantling of one of these suspending pieces of timber, multiply its length in
feet by the length of the tie-beam it holds up in feet; and then multiply the product so
found by 0.7 for fir and 0.32 for oak, to obtain the sectional area in inches of the post:

Fig. 2131.
QUEEN POST ROOF.
dividing this area by the thickness in inches, the breadth will be obtained: these rules
apply to the smaller portions of the posts; the heads must be made as small in addition as
possible, as there is then less inconvenience from their shrinking. Carpenters are generally
not disposed to use much iron for their trusses, and to dispense as much as possible with
straps and stirrup-irons: the most ancient method adopted was to wedge them up, and
where oak was employed, and that well seasoned, it seems fully to have answered the
purpose. The straining pieces between the heads of the queens, in order that its strength
may be as great as possible, its depth should be to its thickness as 10 to 7: by mul-

Fig. 2132.
QUEEN POST ROOF WITH STRUTS.
tiplying the square root of the span in feet by the length of the straining piece in feet, and
then extracting the square root of the product, and multiplying it by 0-9 for fir, the depth
in inches may be found: to find the thickness, multiply the depth by 0.7.
The Roof of the Teatro Argentino, at Rome, has a span of about 80 feet, and its slope is
about 24°: a short king-post without any side braces receives the upper ends of the
principals, and by means of an iron suspends or holds up a collar beneath it, which abuts
and frames into the heads of two queens: by this arrangement the tie-beam, which is
formed of three pieces of timber, is held up at four places. The whole roof is of fir, and
admirably executed. The heads of the queens are strutted on to the ends of the tie-beams,
which rest on other timbers laid like corbels on the walls; the whole is sufficiently strong
to hold up any scenes that are required to be suspended to them: there are twelve purlins,
which carry the common rafters on each side, and the covering is tile, of considerable weight.
The Roof of the Odeon is of oak, and similar in design to the above: its span is about
78 feet, and its angle about 34°, so that the stirrup-irons which hold up the tie-beams
are considerably longer.
The scantling for the principal timbers of queen-post roofs may be thus stated : —

Span.
Tie-beams.
Queens.
Principals.
Struts.
Straining piece.
Feet.
in.
in.
in.
in
in.
in.
in. in.
in. in.
35
11 by 4
4 by 4
5 by 4
4 by 2
7 by 4
40
12 by
5
5 by 5
5 by 5
5 by 21/
7 by 5
45
13 by 6
6 by 6
6 by 5
5 by 3
7 by 6
50
13 by
8
8 by 8
8 by 6
5 by 3
9 by 9
55
14 by 9
9 by 8
8 by 7
5 by 3
10 by 6
60
15 by 10
10 by 8
8 by 8
6 by 3
11 by 6
4Q 2
1332
BOOK II,
THEORY AND PRACTICE OF ENGINEERING.
Purlins of 6 feet bearing may be 6 inches by 4; of 8 feet, 7 inches by 8; of 10 feet,
8 inches by 6; and of 12 feet, 9 inches by 7: where the common rafters have a bearing of
8 feet, they may be made 4 inches by 2; 10 feet, 5 inches by 21; 12 feet, 10 inches by 21
Roof of St. James's Church, Piccadilly, is admirably contrived, and is one of Sir Christopher
Wren's best designs for a covering to a church or large building where tie-beams cannot be
introduced. The breadth of the church is 63 feet, which is divided into five equal parts,
three of which are given to the nave, the others to the side aisles. The principal rafters
are framed into a plate which rests on the outer wall, and on the capitals of the columns an
upright post, immediately over the capitals, supports the principal at about one-third of
its length, and a semicircular arch simply cradled is placed between these upright posts, and
abuts against them: above this arch the principal rafters are held together by stout collars;
the timber framing or the principals is prevented sliding by the St. Andrew's cross intro-
duced over the side aisles. Sir Christopher Wren describes this roof as the cheapest he
could invent; it is both convenient and beautiful in its application and arrangement, and it
is astonishing that it is not more generally adopted: over the side aisle galleries between every
pair of principals are semicircular arches at right angles with the main arch, which rest
upon the returned entablatures, so that no portion of this roof is hidden or unemployed.
The length of this church is 84 feet, the breadth 63, and height at the centre of the vaulting
42: with its galleries it will contain upwards of 2000 persons.
Roofs trussed with Iron Rods. Over the passengers' shed at the Croydon railway station,
London Bridge, is an ingeniously constructed roof, 54 feet span, formed by a series of struts
and iron rods, placed 4 feet apart: the tie-beams camber about 6 inches, and are 12 by 6
inches; the principals are 9 by 6; the struts 6 by 4, and the p r.ins, which have a 12 feet

T
Fig. 2133.
CROYDON RAILWAY Roof.
bearing, are 8 by 3; 14 inch boarding with a zinc covering lays upon the purlins without
the aid of common rafters: the iron rods or bolts are 1 inch in diameter; that which
forms the centre or king passes through the ridge piece, against which the two principals
abut; there is great stiffness and economy in this system of construction, and the whole has
a light effect, and it is evident that the more at right angles to the inclination of the prin-
cipals the wooden struts are placed, the greater will be the strength.
The Roof of the Hall of Christ's Hospital, London, constructed by Mr. Shaw out of
Baltic timber, possesses considerable strength: the walls, 3 feet 6 inches thick, are
15 feet apart in the clear; the rise of the roof in the centre, from the under side of the tie-
beam to the top of the principals, is 9 feet 4 inches; it is queen-post trussed, and the tie-
beams are held up at five different points, or at every 8 feet 6 inches; the principals are
distant from each other 17 feet; the length of the hall is 187 feet, and the breadth 51:
every precaution has here been taken to unite the feet of the principals with the ends of the
tie-beam, and their weight at the ends is partly borne by iron standards, which rest on
shoes worked into the wall below. The principals taper, and are 12 inches by 9 inches at
the feet, and 9 inches by 9 inches at the top; the tie-beams are 14 inches by 14 inches;
the straining piece between the heads of the queens, 12 inches by 9 inches; the struts
6 inches by 6 inches: between each pair of principals is a pair of main rafters, supported
by five longitudinal trusses, and which are also made to carry the ceiling-joists These lon-
gitudinal trusses bear upon the principal tie-beams, which are 17 feet apart from centre
to centre; the middle longitudinal truss comes under the ridge, and is very strongly
braced; the lower beam is 12 inches by 7 inches, the king-post 6 inches by 6 inches, and
head 12 inches by 6 inches; the struts 6 inches by 6 inches: into the head of the kings are
lodged the main rafters, which are 7 inches by 5 inches; on these are laid the common
rafters longitudinally to receive the boarding, which is laid in the direction of the slope of
the roof; so that the lead which covers it is not so subject to derangement as when the
CHAP. XXII.
1999
TIMBER ROOFS.

I
Fig. 2134.
Fig. 2135.
Fig. 2136.
CHRIST'S HOSPITAL, LONDON.
boarding is laid the reverse way. The two other trusses on each side are similarly framed,
the heights being varied to suit the top of the roof: that of the pairs on each side of the
centre is 5 feet from the under side beam to the under side the main rafter; the outside
pair are only 2 feet 9 inches in height from the same points.
Pantheon, Oxford Street, constructed from the designs of Mr. Sidney Smirke, exhibits some
novelty in the roof, which is admirably adapted for its purpose; it is formed of teak and fir:
the centre opening, or the width between the pillars, is 37 feet 3 inches; the pillars are in
thickness 2 feet 1 inch, and the side rooms in the clear 23 feet 5 inches, so that the clear
space between the walls is 88 feet 3 inches: a semicircular rib, formed of three thicknesses
bolted together, and having iron abutments, spans the centre⚫ the middle rib is of teak, 5

Fig. 2137.
PANTHEON, LONDON.
inches thick; the other or side flitches are fir, each 2 inches thick, and their depth in the
smallest part 16 inches: the under side of these is scribed to the curve of the roof; the top
is left polygonally, so that the abutting ends of each piece is broader than in the middle;
cast-iron shoes receive the feet of each rib, and the three thicknesses are bolted together at
the ends.
These nine semicircular ribs, when they rest on the pillars, are framed into upright tim-
bers, which form king-posts to half trusses; these half trusses assist in opposing the lateral
thrust of the semicircular ribs, as well as carry the roofs and ceilings of the side galleries.
The tie-beams are 14 inches by 6 inches; the principals taper, being at bottom 13 inches
by 6½ inches, and at top 11 inches by 6 inches; the large strut is 11 inches by 6 inches,
and the smaller 9 inches by 6 inches, and 7 inches by 6 inches: a cast-iron shoe,
resting on a stone template, receives their ends where they rest upon the wall, which
it is calculated would be of service, should the ends of the timbers at any time decay. At
the other end, where the king-post unites with the tie-beam, is a cast-iron shoe, with
sockets and flanges, made to unite by means of a longitudinal iron plate, at the head
of the main pillars, which are also of iron: the lateral compression of the timbers is
provided for by the introduction of iron shoes.
4 Q 3
1334
Book II.
THEORY AND PRACTICE OF ENGINEERING.
The intermediate ribs, between the iron pillars, rest also on iron shoes, fitted on to the
heads of upright pieces, which rest on the centre of the longitudinal plate, which is in
two thicknesses, 12 inches by 12 inches, and has a bearing of 22 feet. The principals
which form the truss are 12 inches by 9 inches, and they rise 7 feet 8 inches: thus the
entire weight of these intermediate ribs is thrown by means of this simple truss on to
the main pillars. The roofs over the galleries are covered with slate, the other part with cop-
per, laid on diagonal boarding supported by longitudinal rafters notched on the great ribs.
For roofs of considerable span an arrangement of horizontal and vertical iron ties has
been successfully employed; and timber, as in the present example, when framed with care

Fig. 2138.
Fig. 2139.


E
ゴ
​
Fig. 2140.
ROOFS WITH HORIZONTAL TIES.
answers the same purpose, and is not so costly; each horizontal timber becomes a strut and
a tie, and should be placed perpendicularly to perform the same office.
Roofs with iron ties are now commonly preferred for manufactories: at the Butterley

+
Fig. 2141.
BUTTERLEY IRON WORKS.
CHAP. XXII.
1335
TIMBER ROOFS.
iron works, they are executed with great strength, lightness, and economy of metal: the
small vertical and horizontal rods acting as ties are made of wrought-iron, and the principal
rafters and struts, which incline at the same angle, are of cast-iron; such a series of triangles
may be extended over roofs of almost any span, if due allowance be always made for the ex-
pansion and contraction of the metal.
Fig. 2142. is a design for a roof, in which iron and timber are combined: the vertical rods
suspend the tie-beam, and when tightly screwed up bring the ends of the struts home against

Fig. 2142.
the principals and tie-beam, forming a very strong truss; the purlins may be supported
by a truss similar to that in the under side of the figure, by which means the entire roof will
be braced in every direction.
Roof of the old Riding-house at Moscow. The Emperor Paul, whilst travelling through
Europe in the year 1781, saw at Darmstadt an extensive riding-house, and on his arrival at
Moscow he commissioned his engineers to construct a similar building. Rondelet, upɔn

Fig. 2143.
ROOF OF OLD RIDING-House at moscow, as it was formerly.
the authority of Kraft, has given the design for a building 1800 feet in length and 290 feet
in width, the interior being 220 feet, which has been copied and often described in
works on carpentry, but it never existed except on paper. M. Betancour has furnished in
Bruyère's work the design for the building erected at Moscow, which was commenced
under his direction in June, 1827, and completed in the short space of five months:
this riding-house is 531 feet in length, and 160 feet in width in the clear. The foundations
were dug 13 feet deep, the bricks were made on the spot, and the timber used in its
construction was brought from the neighbouring forest. The walls were built up to the
level of the ground, 14 feet thick, and above were 8 feet 6 inches.
A scaffolding composed of 1500 posts was raised level with the tops of the walls, for
the purpose of supporting the chief timbers of the roofs. The principals were at first 19 feet
• Q 4
1336
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
D.
D
apart, one over each pier, and one against each pediment, making altogether 32 pairs: after
they were raised, and the supports taken away, it was found that the tie-beams deflected 2
inches more than was calculated upon, and at the end of four months the deflection increased
to nearly 5 inches; this occasioned the whole to be reconstructed, and the principals were
then placed only 13 feet apart.
The tie-beams were formed of two thicknesses of timber scarfed together, each 12 inches
square, one laid upon the top of the other, forming an entire beam 24 inches deep and 12
inches wide; at every 3 feet of its length were introduced iron bolts, 1 inch in diameter;
double keys of oak, driven into

notches formed at equal distances
between the two beams, assisted in
resisting the horizontal drawing
of the two extremities; the middle
of the tie-beams was drawn up
Fig. 2144.
13 inches by the middle or centre post, which is 34 feet in length, or of the total span,
forming an angle of 21° 48′; above the chief tie-beam are three others placed horizontally
at equal distances, which are tied together in a similar manner: a number of designs have
been given by the most celebrated engineers of Europe for roofs of this kind, in which
iron and timber are used to the best advantage.




Fig. 2145.
roof of the original rIDING-HƆUSE, Moscow.
The rafters, if formed of several stout timbers, are capable of supporting considerable
weight, when held firmly at their abutments, and the tie-beams strongly bound together,
to prevent any drawing out, may be suspended to the principals: a series of iron straps or
bands passed round the feet of the principal rafters, and secured to the tie-beams, will

Fig. 2146.
ROOF OF THE _Riding-HOUSE, MOSCOW.
effectually prevent any rising or spreading of the main timbers; but for still greater
security the introduction of an iron rod has been suggested in lieu of a timber tie-beam:
CHAP. XXII.
1337
TIMBER ROOFS.
such an arrangement would no doubt retain the curved or bent timbers in their original
position.

Fig. 2147.
RIDING-HOUSE, MOSCOW.
E
In making the joints where struts and ties unite, great attention is requisite, particularly
when they are intended to hold up a suspending rod or timber: the joint should always be
at right angles with the timbers, and the head of the piece they
are to sustain cut to fit that arrangement, in order to prevent
it being pulled through; the irons or stirrups for holding up
the tie-beams or other large timbers are attached to a pin made
to pass through them, but there is no better method than that
which allows the iron to strap entirely around the timber it is to
hold up.


M
園
​AWY
{
Fig. 2148.
3
RIDING-HOUSE, MOSCOW.
Fig. 2149.
Philibert Delorme, in a work published in 1561, describes a method of constructing roofs
and domes with timbers, or rather planks, of short lengths, and which is only objectiona le
on account of the labour necessary in putting them together: one of these roofs covered
the stables of the Tuilleries, at Paris, and after remaining perfectly sound and secure for
234 years was demolished to make way for some improvements in the palace: the arches
were formed of two planks, about 9 inches in width, cut into convenient lengths for
the required form; this seldom exceeded 4 feet, and when applied to each other to
form the rib, they were so laid that the ends of one set came in the middle of the length
of the others: mortises in length double their width were then made in them, through
which were longitudinal ties, and these had a small wooden pin passed through them,
on each side of the circular ribs, to keep them in their upright position, or prevent
their twisting. In some of the buildings executed by this celebrated architect, the span
of the roof exceeded 60 or 70 feet; two ribs were then used, so put together that they
partook of the character of hollow voussoirs, and were very strong; indeed there is scarcely
any span where, if properly proportioned, they might not be applied. *
Designs are also shown for the construction of girders to carry floors upon this principle,
which are well adapted for lofty rooms intended to have coved ceilings, and by placing the
ribs in pairs the whole might be covered in a very regular way: when this system is
applied to domes, we must commence by tracing out the true curve to be executed, and
laying on this mould the first range of planks; when it is intended for a simple roof,
the under side of which is not to be formed into an arch, the planks must be placed below
the curve line traced; if for a vault, above it, but always in such a manner that the lines
may be traced upon them; when the ribs are to be curved above and below, then the
I SAA
Book IL
THEORY AND PRACTICE OF ENGINEERING.

Fig. 2150.
planks must cover the
two lines of the curve
or mould, that the
true sweep may be
obtained throughout.
Philibert Delorme
fixes the length of
these planks for every
kind of curve at not
more than 4 feet, but
this rule may be oc-
casionally departed
from, when we have
to follow a curve
which is irregular ;
it is perhaps better to
take such lengths as
shall enable us to
divide the curve into
an equal number of
parts, the length of
which may vary in
each division. When
these lengths are de-
termined upon, draw
lines perpendicular to
the curves, which will
indicate the direction
to be given to the
joints of the boards;
after these are cut
and adjusted, a se-
cond row is so dis-
posed that its joints
will fall over the
middle of the planks
O
Fig. 2151. philibert Delorme's SYSTEM OF Rroof.

LU
Fig. 2152.
PHILIBERT Delorme's SYSTEM Of roof.
CHAP. XXII.
1339
TIMBER ROOFS.
of the first row, it being requisite that the planks at the ends should either be half or
once and a half the length of the others. When the two planks are properly adjusted,
they are then to be united, by first cutting the mortises, through which the ties are to be
threaded, which are to unite the principal ribs with each other; these ties are to be of the
same thickness as the two planks, and their width four times as much; they are also
mortised on each side the ribs, into which are introduced the wooden keys or pegs, the size
of which are proportioned to the ties.

Fig. 2153.
SHED ROOF.
As some objection has been made to this construction, on account of the labour required
in cutting the number of mortises, making the longitudinal ties, and introducing the pins,
that the whole may be firmly united, it may be well to consider if much of this labour
might not be dispensed with, and

the construction not be weakened:
it might no doubt be effected
by securing the ties either to the
upper or lower parts of the ribs, or
both; the boarded covering pinned
on to them, or properly spiked
down, would almost serve the pur-
pose, and thus avoid an expense
of labour, which is rather calculated
to weaken the ribs, by so frequently
cutting mortises into them. When
the ribs can be cut out of 8-inch
plank their thickness is to be 1 inch,
and this is sufficient for a roof of
25 feet span; for one of 38 feet
the width of the planks must be 10
inches, and their thickness 14 inch;
for a span of 60 feet they are
to be 13 inches, and their thickness
2 inches; for 90 feet 2 inches, and
for 100 feet 3 inches.
*
X
哥
​At Libourne, in the department
of the Gironde in France, is a
riding-house with a roof, erected
in 1826, under the direction of
A. R. Emy, colonel of engineers, which is an improvement upon the principles of
Philibert Delorme. The internal diameter at the springing is 68 feet, the clear width
between the walls a foot more, and the roof springs 25 feet above the floor.
The system
adopted for the construction of the ribs was first suggested in 1811 by M. de Saint
Phar, who proposed to make the arches of a bridge of bent planks: in the riding-house
roof neither mortise nor tenon is used in the arrangement of the bent timbers: and
Fig. 2154. ROOF OF HOTEL DE SALM Kersbourg, paris.
1340
Book II.
THEORY AND PRACTICE OF ENGINEERING.

the construction is so
simple that few work-
men were required to
raise it. There are
fourteen main arches
or principals, and the
walls, though exceed-
ingly thick, are
further strengthened
with buttresses: each
principal is composed
of five thicknesses of
timber throughout;
these were bent to
their form on the
floor, and then raised
in a body to their
situation.
Marac, near Ba-
yonne. This roof,
constructed also by
M. Emy, in 1826, is
65 feet 6 inches span,
and 187 feet in length;
each principal is a
Fig. 2155.
LIBOURNE.
semicircle, composed of deals 2 inches in thickness, 5 inches in width,
and about 40 feet in length; they are about 10 feet apart: 21-inch
planks placed end to end form one arch: none of the bent timbers
have more than three joints, ordinarily two, and there are never more
than ten or twelve to a principal. The principals are held at every 10
feet distance by pendant binding pieces which have a horizontal con-
nection under the soffite;
these passing over the prin-
cipal rafter form a strong
and irresistible piece of
framing.
Where eight or more
timbers or thin planks are
bent one over the other
and bolted through at short
distances, the shape of the
arch is not likely to be much
varied; but with all the pre-
cautions that have been
hitherto taken this cannot
be insured.
The difference between
this system of construction
and that of Philibert De-
lorme chiefly consists in
the planks being employed
in the reverse manner to
each other: the method
practised by the latter
architect would at first ap-
pear the strongest, as the
depth of the deals or planks
is greater than their width,
from their being placed
edgeways: in the other
system, thin boards are bent
upon a cylindrical mould;
then united firmly together,
being rendered strong by
their inability to spring;
should this, however, occur
Fig. 2156.
MARAC, NEAR BAYONNE,
CHAP. XXII.
1341
TIMBER ROOFS.
in any layer, the whole truss loses its continuity, and becomes weak, and liable to fracture
in that part where iron bolts are passed through, not only do the holes bored to receive
them produce mischief by weakening the series of planks, but the bolts prevent that neces-
sary play between each layer which is conducive to its strength: the manner in which the
side-pieces are attached contributes very much to the stiffness of the whole, as, being united
above and below, there is no fear of the planks starting or changing their position: where
tangential timbers can be laid on the extrados of these arches, and united to the pendant
side-pieces, a further security against any change of form is insured. The solid content
of an arch constructed of bent timber being ascertained, an estimate may be readily made
of its cost, and the contrast between it and the ordinarily framed roof easily made: a series
of rafters laid longitudinally may carry the slate
or tarred paper covering, and all expensive fram-
ing be dispensed with.


1
O
O
ם
a
Fig. 2157.
Fig. 2158.
SECTION OF PRINCIPALS.
Other roofs of far greater span have been
constructed by the same engineer, who after
many experiments suggested the employment
of a double curved rib having different radii :
these, held in at the springing, were in the spandrill space braced by timbers arranged like
St. Andrew's crosses; iron bolts or timber binding-pieces pinned at the sides hold the
masses together, and form a most effectual support to either tiles or slates that may be laid
upon them.
Roofs of bent timbers may be formed in the same manner as adopted for the construction
of bridges by M. Wiebeking, who employed pieces of as great a length as he could
obtain, and then bent them to the form of the required curve: joints should, if possible, be
entirely dispensed with; nothing should be introduced which in any way can weaken
the strength of the ribs, or render any part of them liable to decay. As timber shrinks
but little in the direction of its length, there is no inconvenience arising from this
circumstance, when planks are bent one over the other whatever change takes place is
either in the width or thickness of each layer, and this may occur to a considerable
extent without disturbing the strength of the entire rib but when the timber is not
:
:
1342
THEORY AND PRACTICE OF ENGINEERING.
BOOK II.

thoroughly seasoned, by paying
attention to the work some time
after its execution, the ligatures
which strap or hold the several
pieces together may be tightened,
or wedges introduced, so that
each plank may be brought to its
bearing.
Fig. 2159.
RIDING-HOUSE ROUP.
Where brick or stone can be readily
obtained, it is often far less expensive to
construct a series of arches in one or
other of these materials, and to lay the
purlins on them to support the common
rafters many custom-houses in France,
and buildings destined to receive mer-
chandise, are so formed; semicircular
brick or stone arches, 100 feet in diameter
or more, span the entire building at every
15 or 20 feet of its length, and these alone
support and carry the roof. There is
in such an arrangement far less labour
required, and as great durability, and
the centres used for their construc-
tion are of a very simple kind, one
serving for each successive arch; run-
ning on wheels upon strut timbers or
two iron rails they can be readily
moved; and as the first course is con-
tinued through or over its entire surface,
the rib is wedged up, and the weight
taken off the rollers beneath it.
form a covering with a flat arch upon
this principle, three curved ribs have
been employed, which strutted and
bolted together have the strength of a
solid timber. Bent timbers are made
use of for a variety of purposes, and
care should always be taken, when heat
is applied, to give them the necessary
curvature, that it is general and equal
throughout.
Το
m
Fig. 2160.
LIBOURNE.
O
CHAP. XXII.
1343
TIMBER ROOFS

Fig. 2161.
RIDING-HOuse, libourne.
Sheds for Ship Building are of various kinds : those constructed at Rosieres in Francs
are very simple, resting upon posts placed upon a solid mass of masonry: a series of such
spans must be rendered secure at their commencement, and the two outer need some
additional security at the feet of the rafters to prevent their spreading. At the ship-

yards of L'Orient, the roof,
composed of iron and bent
timbers, is supported by arches
and columns of masonry; light
being admitted to the ship-
wrights by dormers constructed
along the sides at the springing
of the roof: occasional ties are
here requisite, which are
above the vessel when it is let
off the blocks to be launched.
Fig. 2162.
SHEDS FOR SHIP-BUILDING.
Fig. 2163 LONGITUDINAL SECTION.
The walls of masonry and post above are well adapted for the struts and braces intro-
duced to receive the middle gutters placed between the several roofs in succession; and
the water is ingeniously led from them by pipes into a drain formed within the wall below,
and conducted into the ocean without injuring the inclosure: when the timber is well
seasoned properly framed together, and all injurious effects from the rain prevented, roofs
formed in that manner will endure for a length of time: it is always necessary to provide
against the action of strong winds by bracing the sides in every possible position.
1544
THEORY AND PRACTICE OF ENGINEERING.
Book II.

Where timber cannot be
obtained of sufficient scant-
ling for the principal rafters,
they may be made in two
thicknesses, or be placed
side by side, and the
hanging-post, which is sus-
pended from the apex of
the roof, may be secured
by an iron head cast to
receive the principals, and
to admit of the introduction
of a screw-bolt or iron tie,
against which the lower
struts may abut.
Roofs of large span where
Tie-beams are omitted.— As
ships are now built under
cover, and the dock is pro-
tected from the weather,
the most convenient as
well as economical con-
struction is that of the roof
of equilibrium: many of
these roofs are upwards of
100 feet span, formed of a
combination of trusses, so
Fig. 2164.
SHED FOR Ships at l'orient.
}
с
supported that they perfectly balance, in the same way as the principals of a Mansard roof.
To balance a roof or a pair of principals, framed alike on both sides and loaded equally,
so that it does not fracture, requires some little knowledge of the various strains to which
its parts are subject, and also care in the
direction given to the posts that support it:
for as these posts constitute the main
strength, every cross strain by which they
can be affected tends to weaken them as sup-
ports.

The centre of gravity of one-half the fram-
ing, which is easily found, we will suppose at
C, fig. 2165. and 2166.; a vertical line car-
ried through this point from g will cut the
horizontal line, cb, drawn through the
middle of C, at b: a line drawn from this
point b, through B, will give the proper
direction for the post; this, however, is some-
times, for the sake of convenience, placed
perpendicularly; the weight of the roofs has
then been found to cause fracture at BC,
or to yield at the points A, B, C, c.
من
A
Fig. 2165.
Timber roofs are supplanted by others constructed entirely of iron, partly cast and
partly wrought: some of wrought-iron, lately erected at the Woolwich Dockyard, are
b

B
a
A
Fig. 2166
SHEDS FOR SHIP-BUILDING.
B
CHAP. XXII.
1845
TIMBER DOMES.
noveities of their kind, and admirably fitted for their purpose: although their first construc
tion may be far more costly, they will in all probability supersede timber structures, on
account of their greater security against fire.
It has been suggested to form roofs of bent timber for the purpose of covering the
building docks in our shipyards: when the depth of a piece of timber does not exceed
120
of its length, it may be curved easily, and its elastic force not be destroyed, if its versed
sine is not more than an eighth of its span: two pieces may be so bent and laid one over
the other, by first securing one end by a cord or iron strap, and then pulling down the
second piece to the back of the other; a number of layers may be thus brought down
upon each other, and secured by bolts or ties.
Domes and Cupolas. To construct these in timber it is usual either to frame trusses
entirely across the opening, or, where the ties cannot be allowed, to form the ribs, which
carry the covering like a series of centres, thus dispensing with the ties. The dome of the
Val de Grace at Paris is an example of the first kind; it is composed of four principal
trusses, two of which cross the others at right angles, leaving an opening to the cupola
in the centre: sixteen half trusses converging to the centre, arranged at equal distances
around the dome, carry the rafters, which support the covering: such constructions

22
M
27/2
$222
Fig. 2167.
DOME AT val de Grace AT PARIS.
as the above admit of application where the exterior effect is alone considered, or where it
is merely required to cover in and protect a hemispherical dome of masonry: it is evident
that the interior cannot be made available either for use or decoration, in consequence of
the timbers which are introduced.
Dome of the Invalids, at Paris, whose external diameter is 90 feet, is another example,
compised of two principal trusses, which cross in the middle at right angles, and unite in a
double upright post; each quarter of the dome, or the space between these principal
4 R
1846
THEORY AND PRACTICE OF ENGINEERING. BOOK II.
trusses, is filled in with two half trusses of the same kind, and four smaller ones, which
are sustained by great braces in their proper position.

Fig. 2168.
dome of the INVALIDES AT PARIS.
Dome of the Assumption, at Paris, designed by Errard, is an example where the interior
may be rendered available to effect, and to the purposes of decoration; its principles are laid
down by M. Stierme, in Krafft's work on carpentry: two trusses cross each other at right
angles in the middle, and these, with twelve others arranged intermediately around the
dome, all converge to the centre, and carry the lantern. The principle adopted in the
setting out was to form first a square, the side of which was determined by the height
to the under side of the lantern: where the diagonals of the square so set out cross
each other a point was established, determining the radius of the inner dome, which is
perfectly hemispherical: this point is found by elongating the line of face of the inner wall,
until it intersects the diagonal, establishing the height at which the horizontal tie is
to be placed. The inclined posts, which carry the chief weight, are tangents to the curve
of the inner dome, and are each framed into two struts, that support the outer rib of the
dome, which carries the covering: five horizontal and concentric ties, at regular and
parallel distances, maintain these four principal ribs in their true position, and, being
framed into them, bind them together.
The Church of St. Mark, at Venice, exhibits a dome of very early construction, its date
being assigned to the year 1085; after its erection some additional timbers were intro-
duced by Giacomo Sansovino, in 1530, which act as inclined shores to bear up the
cupola: the outer diameter is about 51 feet, and its height 60: it forms a covering
to a brick vault beneath it. The lower portion is cylindrical, and is framed throughout
its circumference with upright posts, set at a distance of about 2 feet from centre to centre;
they are united at the top and bottom by circular plates. The hemispherical portion of
the dome is composed of stout double planks, so put together that each forms a sort of rib;
these are united by four horizontal ties placed at regular distances: the exterior is
covered with planking bent round to receive the lead.
CHAP. XXII.
1947
TIMBER DOMES.

88
Fig. 2169.
STIERME'S SYSTEM FOR A DOME.
In the example given of Stierme's construction of a dome, we have a horizontal tie intro-
Juced above the curve, into which are framed two upright posts that form the sides of the
lantern above: on the drum wall or cylinder that carries the timber dome two circular
plates or curbs are first laid, generally formed of two thicknesses well bolted together:
considering the dome to consist of four such trusses, as shown in the figure, they may be
placed to cross at right angles, each pair being parallel to the other, and situated at a dis-
tance apart that suits the framing of the lantern.
The Church of the Salutation, at Venice, has a timber dome, the outer diameter of which
is 80 feet; it covers an interior brick hemispherical vault, which has an opening of nearly
13 feet diameter. The exterior is formed of planks, in four thicknesses, laid one
over the other, united together by nails: ninety-six of these ribs, each about 6 inches
in thickness, have their lower ends let into a circular plate, formed of four thicknesses
of plank, which lie over the attic cornice: at the top they are framed into a curb or
plate which bears upon eight columns, placed round the opening of the brick dome: the
lantern and its balustrade externally is partly supported by this arrangement; eight
additional posts are introduced to carry the weight of the obelisks, which surround the
base of the lantern. To keep the ribs which form the outer dome from spreading, they are
hooped round with iron at about one-third of their height, the hoop being 5 inches wide,
4 R 2
1348
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.

Fig. 2170.
DOME OF The church of the SALUTATION AT VENICE.
and half an inch thick, secured by an iron pin to each rib: stout laths are nailed on the
backs of the ninety-six ribs to carry the lead covering; and where the joints are formea,
additional wooden rolls are fixed to dress the lead round.
CHAP. XXIII.
TIMBER BRIDGES. SWING BRIDGES. - DRAWBRIDGES. -ROPE BRIDGES.
CENTERING. - SCAFFOLDING.
TIMBER bridges are general in all countries where timber abounds, and where cheap-
ness and expedition are important; it has its objections in being less durable than either
brick or stone, but, if covered and protected from the weather, may be made to last
a considerable time. Bridges constructed of timber, so that they may be easily repaired
when decay takes place, have also their inconveniences, as the traffic across them must be
stopped whilst the workmen are employed: they are undoubtedly of very early invention,
and may be considered as strong platforms crossing rivers, and preserving an uninter-
rupted communication. Among those built by the Romans, we have the description left
CHAP. XXIII.
1949
TIMBER BRIDGES.
us by Julius Cæsar of one over the Rhine: Alberti, Palladio, and Scammozzi, have each
attempted to design its form; but their ideas upon the subject differ materially.

路
​Fig. 2171.
CÆSAR'S BRIDGE,
Cæsar tells us that two pieces of timber 18 inches square, after being pointed at their
lower ends, were sunk into the river, and afterwards driven 2 feet distance from each other
by means of machines; these piles were inclined a little; two others were driven at a dis
tance of 40 feet opposite them, inclining in the contrary direction; these two pairs of piles

Q
Fig. 2172.
Cæsar's bridge.
were united by a transverse beam at the top, which was in thickness 2 feet, and properly
secured: on these were laid joists in the direction of the breadth of the river, which were
covered with hurdles to sustain the road. On the side below the stream inclined piles
were driven, which supported the bridge against the force of the current, and above the
bridge were others, to protect it from injury against floating masses, as trees or boats: it
was completed, and the troops were enabled to pass over it in ten days.
Alberti fastens the girders to the heads of the piles by ropes instead of two bolts
(binis fibulis), as perhaps the text implies: Palladio has introduced two pieces of timber
for their supports, halved and bolted into the sides of the inclined piles: Scammozzi
gives a double tie of cordage: Perrot d'Ablincourt attaches these cross-beams or girders
by means of several enterties, which seems justified by the text.
4 R 3
1350
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Trajan's Bridge over the Danube is shown in bas-relief upon the triumphal column erected
to that emperor in Rome: its construction was timber resting on stone piers, and so framed
that it was both solid and durable; three rows of concentric arches united by binding
pieces formed each division; these

abutted upon timbers radiating
with the curve, which were
framed into heads and sills,
again strengthened by braces
and struts; the joists which car-
ried the floor traversed the bridge,
and rested on strong plates which
were laid on the backs of the
timber arches. The parapets were
formed of perpendicular pieces
with a St. Andrew's cross between
them, united at the top and bottom
by a longitudinal sill and head.
Fig. 2173
TRAJAN'S BRIDGB.
This construction is admirable, though more strength might have been introduced in the
carpentry, which rests on the piers and forms the abutments to the concentric arches which
span the river; they would then have resisted more perfectly the thrust to which they are sub-
jected; horizontal timbers driven between the struts, particularly between the heads of the
shorter, would have added materially to the strength, and given those timber abutments
greater power of resistance to compression.
The Pontus Sublicius at Rome was an earlier wooden bridge, and constructed 500 years
before the Christian æra, under the reign of Ancus Marcius, one of the first kings: all
that we know of it is that it could be taken to pieces, and that neither iron nor nails were
used in its construction; the timber was united by solidly framing it together, using
wooden pins to secure it.
Sublicius is derived from sublica, a pile, which indicates that the platform or roadway was
supported by them, driven at regular distances from each other: this bridge is mentioned
as that so valiantly defended by Horatius Cocles. Most of the timber bridges that have
been constructed since the fall of the Roman empire exhibit in their design one or other of
the twelve principles which we are about to describe.
The first principle that we can adopt is that of a single beam, or one composed of many
thicknesses: if the lower, which spans from A to B, is laid flat, the others, as P', C', P, C,

m
a
ཁྱཻ༤
AT
Fig. 2174.
C
P
C'
P
FIRST PRINCIPLE.
IB
may be cut tapering, and as they are laid upon each other either bolted or strapped together
to make one entire mass: by this means the requisite increase of depth towards the centre
inay be given, to support any weight for which it is destined.
The second principle, as adopted at the bridges of Schaffhausen, Zurick, Landsberg, Wit-
tingen, &c., has the tie-beam to constitute the abutments for the compressed timbers; con-

Fig. 2175.
SECOND PRINCIPLE.
sequently there is no thrust exerted against the walls, as the entire timber-work may be re-
garded as a trussed frame.
The third principle was introduced at the Kandel Bridge by Joseph Ritters, but here it
is requisite that the abutments should be made sufficiently strong to resist the entire thrust :
sometimes the tie cannot be made use of; then we are obliged to adopt some such method
as here shown.
The fourth principle exhibits a different arrangement for beams that are compressed;
CHAP. XXIII.
1351
TIMBER BRIDGES.

Fig. 2176.
THIRD PRINCIPLE.
instead of abutting against the pendant timbers, as in the third example, they are laid over
each other, and constitute in effect but one beam.

Fig. 2177.
FOURTH PRINCIPLE.
The fifth principle is a modification of the preceding, and is particularly adapted to a bridge
where long pieces of timber cannot be obtained: the bridge of St. Clair, over the Rhone,

Fig. 2178.
FIFTH PRINCIPLE.
at Lyons, is so constructed, as it was not found possible to obtain timber of sufficient
depth and breadth.
The sixth principle was adopted at the bridge of the Mulatière at Lyons, over the Saone;
such were the bridges constructed over the Thames formerly at Kingston and Walton:

Fig. 2179.
SIXTH PRINCIPLE.
there is no advantage gained by shortening the beams, because the angles of junction being
more obtuse, the strain in the direction of the length is considerably increased.
The seventh principle exhibits a framed rib, but it must be remarked that the weight to

Fig. 2180.
SEVENTH PRINCIPLE.
be applied in the middle must proportion its depth: a number of curved ribs may be so
put together that they will resist either extension or compression.
4 R 4
1352
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
The eighth principle shows a different combination of bent timbers, where the framed
voussoirs are dispensed with, which sometimes are found objectionable, from the diffi-
culty of making all the joints fit properly, and their liability to decay.

Fig. 2181.
THE EIGHTH PRINciple.
The ninth principle does not materially differ from the last; the pendant binding pieces
are placed perpendicular, and do not diverge to the centre, from whence the bent timbers
are curved.

Fig. 2182.
THE NINTH PRINCIPLE.
The tenth principle is a continual lattice, or open beam, so proportioned that it has been
made to span very wide rivers in America.


Fig. 2183.
LATTICE bridges.
Fig. 2184.

The eleventh principle, called Long's, does not consume so much timber or labour, and has
been much employed in America: it consists of a series of St. Andrew's crosses between
Fig. 2183
long's ameRICAN BRIDGE
CHAP. XXIII.
1359
TIMBER BRIDGES.

upright posts, the head and sill into which they are
framed being bolted well together by iron rods: the
depth or height of the framing is proportioned to the
span; the string pieces are formed of three timbers,
the posts and braces of two, and the counter beams
of one.
The twelfth principle is that of suspension, and
is admirably adapted to spans of almost any re-
quired extent: the platform is supported by hang-
ing up the under transverse timbers by iron rods,
which pass over a saddle, also of iron, placed at the
top of two long piles, driven in with the requisite
inclination to support them. The chains, which are
suspended from pier to pier, are sometimes placed
beneath the platform, as in fig. 2189., upon the prin-
ciple now generally used for trussing longitudinal
timbers, which system is far more economical.
A combination of these principles is sometimes
found adapted to bridges of different span: Bruyere
has given us the method by which we may form
foot and other timber bridges in a firm and solid
manner.
Kraft, in his work on carpentry, has suggested
for foot-bridges the hexagonal struts and binding-
pieces, as shown in fig. 2190, 2191.: and the same
author prefers for bridges, over which loaded
carriages are to pass, that the timbers should be
arranged polygonally, and held together at their
Fig. 2186. ONE DIVISION OF LONG'S
AMERICAN bridge.

joints by binding-pieces: over the piles a St. Andrew's Fig. 2187. SECTION OF LONG'S AMERICAN

BRIDGE.
Fig. 2188.
SUSPENSION BRIDGE.

Fig. 2189.
SUSPENSION BRIDGE.
1354
BOOK II.
THEORY AND PRACTICE OF ENGINEERING

cross is constructed,
upon which the timbers
that carry the road are
laid. Another form for
bridges of considerable
span is that in which a
Fig. 2190.
BRUYERE'S SYSTEM.
Fig. 2191.
BRUYERE'S SYSTEM.
series of polygonal timbers cross over the junctions of the ends of each other, and are
then bound together by the pendant or inclined binding-pieces.
In the system adopted by Bruyere the pendant binding-pieces are placed parallel with
the sides of a square, the diagonal of the square, in bridges of small span, being a per-
pendicular let fall from the centre of the bay, (fig. 2190.) When the distance between the
piers is increased,
the timbers that sup-
port the platform
have an hexagonal
form, as in fig. 2191.,
the struts which
spring from the
heads of the piers
being placed paral-
lel with the sides
of the square: the
several thrusts and
pressures are all ad-
mirably provided for
in these designs.
When the stream
is tranquil, and not
subject to floods,
piers may be intro-
duced, so as not to
interfere with the
navigation;

and
their number may
be lessened, where
Fig. 2192.
SYSTEM OF POLYGONAL TIMBERS.
long pieces of fir timber can be obtained; where oak is used the pieces should be as short
and of as small a scantling as possible, to avoid expense: but whenever piers of masonry can
be adopted, they should be

preferred, as the ice in
its descent cannot injure
them, if properly con-
structed and protected.
The system of poly-
gonal timbers offers con-
siderable facility for the
employment of short
lengths, and is adopted
for small bridges, where
economy is an object; but
a number of joints in-
creases the liability of
movement in the parts,
and it is necessary to in-
Fig. 2193.
Another SYSTEM With polyGONAL TIMBERS.
CHAP. XXIII.
1355
TIMBER BRIDGES.
troduce struts and binding-pieces in the position, where such a change in the arrangement
is likely to occur.
The timber employed in the construction of a bridge requires to be considered in
a different manner to that in ordinary buildings: besides the weight of the framing and
roadway, there is a constant vibration, from the movement of carriages and passengers over
it, and the timbers so acted on affect one portion at a time. As the load passes over, the
timber immediately bearing it bends, and recovers itself when the weight is removed:
experience, however, proves that we must not permit any portion of the structure to bend
beyond its powers of elasticity or its ability to recover the original form; constant action
upon timber in the course of time destroys its flexibility, and experiment teaches us that
the elasticity of timber decreases with time, and particularly when subjected to the effects of
a momentary action by a load passing over it. But the momentary load is less dangerous
to its strength than that which acts continually, so that in valuing the strength of a piece
of timber to support the heaviest weight to which it may be subjected when immovable,
there will be no danger in applying it to a bridge. Timber of good quality and properly
seasoned endures a great length of time, particularly if protected from moisture and the
worm: the alternations of humidity and dryness occasion a constant change in the movement
of the fibres, and in the course of a few years an entire disorganisation.
When trees are growing, that portion of the wood nearest the heart is the strongest, but
when their growth ceases, the other portions acquire the same strength, and when on the
decline, the change commences at the heart, so that the outer parts, or those nearest the
bark, are the most to be depended upon: when decay has commenced at the pith or
heart, it extends by degrees until the whole timber perishes; too much care cannot be
taken in the selection of timber, and it is well to observe the dimensions of the trees in the
forests, that afford the supply, and to choose only those which are beneath the average
diameter, so as to be certain that decay has not already commenced. Timber is often cut
down the middle for the purpose of ascertaining if the heart be sound; when the concentric
rings are destroyed there is less resistance offered to pressure than before.
Where timber is free from attacks by the worm, and no change has taken place at
the heart, humidity and alternate dryness are the only effects we have to guard against:
the fibres on the exterior become more saturated with moisture, which they take in from the
atmosphere, and again readily yield when the air is heated, and the surface being that portion
more exposed to frequent alterations, its disorganisation will commence first, the fibres lose
their elasticity, and, no longer exerting any resistance, a diminished scantling is the result.
Timbers employed in bridges may be considered as losing a portion of their scantling
every year, and consequently their strength: the bridge in the course of time, no longer able
to support its load, must fall, and this ruin is delayed so long as the proportion given
to the timbers admits of the annual loss, without reducing its scantling below the minimum
that would bear the weight imposed upon it: in consequence of the cost increasing with
the extra scantling of the timbers, we are restrained from making them perhaps so large as
they ought to be in the first instance; true economy, however, consists in using the
quantity of timber sufficient to bear the required weight.
There can be no difficulty in ascertaining the weight or load to which any piece of
timber is subjected, after the rules already given: these may be applied to timber either
singly or collectively, but they must be carefully analysed and calculated.
Of Piers. These are usually composed of one, and sometimes of several rows of
piles, driven in the direction of the current; but the best plan is to drive the first
so that their heads may be cut off immediately below the water, and on them to construct
a platform of timber, into which the posts which carry it may be framed: this construction
has a considerable advantage, as the parts above water, which more frequently go to decay,
can be easily repaired, whilst that constantly immerged endures for a greater length of time.
There are various methods of uniting these timbers together; one is by iron pins, about
3 feet in length, passed through the horizontal timbers into both the upper and lower piles;



PLAN OF CROSS TIMBERS.
Fig. 2195.
PIERS.
Fig. 2194.
Fig. 2196.
the horizontal timbers are also strapped to them by alternate horizontal and vertical iron
bars, the upper timbers of the pier being level with the surface of the water.
1356
Book II.
THEORY AND PRACTICE OF ENGINEERING.
The head of each pile should be well bolted and secured to the timbers with which it
is capped, or which holds it to the others in the same row: the bridging-piece, or bearer,
is laid transversely upon the capping, as fig. 2196., and should be strapped securely down,
and where other perpendicular posts rest upon them they should bear upon a plate, con-
tinued through the entire length of the pier mortises and tenons should be avoided as
much as possible in the framing of all wooden bridges, and where any junction of the
timbers is to be made, it should be formed by iron bolts or straps.
When the river has a considerable depth, a double row of piles is requisite, for it would
be hazardous to depend upon a single one: the lower range is driven about 3 feet apart,
or from centre to centre, and a capping piece, extending the whole breadth of the bridge, is
laid upon the heads of each row; an intertie crosses these, and on it is placed a third
timber, extending the breadth of the bridge, into which is framed the post, which carries
the platform; these timbers are all well framed and bolted together. Timber 12 inches
square has sufficient strength to bear any weight to which an ordinary wooden bridge is
subject, though double rows of piles are often used: where many rows are requisite, they
must be protected by sterlings so contrived as to prevent ice or other floating bodies from
injuring them, and the best method of effecting this is

2
to drive two rows of piles tending to a point, in front
of the pier to be protected, and plank them so as
to resemble a wedge; upon the top of this, which
is level with the surface of the stream, is laid an
inclined piece of timber against the pile, which may
be strutted on to the heads of the piles forming the
wedge, and, by putting an iron edge to resist the ice,
be made very efficient. The posts composing the
upper part of the piers are always terminated with
a capping, and if their height be considerable they
should be supported towards the middle by one
or several courses of horizontal binding-pieces, the
effect of which is to support the posts in a parallel position: to
out, there must be inclined or discharging pieces; one of the best examples of their
application is at the
the
bridge of Fresingen.
Experience has proved
that piers of this kind,
which resist perfectly
the shock of the ice,
and are preserved from
injury by the fascines
which surround
foot, are suffi-
ciently solid to
carry the largest
arches of carpen-
try: but notwith-
standing all the
precautions pos-
sible, the timbers
of which they are
formed must be
destroyed before
those of the arches
which they carry,
and it is prefer-
able to establish
these arches on
piers of masonry,
whenever
the
do
L
Fig. 2197.
FLAN OF TIMBERS.
prevent their going

foundations
not render it to-
tally impractica-
ble: if, however,
Fig. 2198.
FRESINGEN BRIDGE: TRANSverse seCTION.
this difficulty
does occur, and timber can be procured sufficiently long to form the large piles necessary
for the construction of the piers, the arrangement adopted by M. Wiebeking may be em-
ployed with advantage. In many cases also the piers may be constructed with cylinders of
cast-iron, traversed by a piece of timber, which would give them the greatest solidity.
CHAP. XXIII.
1357
TIMBER BRIDGES.


Fig. 2199.
BAYS.
Bays and Arches. When the opening of a bay is
not more than 10 or 12 feet, a floor is formed on
girders, bearing on the cappings with which the piers
are crowned; the piles as well as the girders are then
from 12 to 13 inches square: when the distance of
the piers is from 17 to 26 feet, pieces of 13 inches
square have sufficient strength to carry the weight of
the floor, as well as that of carriages; it is, however,
always prudent to support them by inclined braces,
without which such bays could not last a long time.
When the opening of the bays becomes more con-
siderable, the middle of the girders must be sustained
by under-girders, supported by braces; this arrangement may be adopted for bays from 26 to
30 feet span, and they may be equally used when they are from 30 to 36 feet, but the girder
must then be composed of two pieces framed in the middle, and another under-girder must
be placed over the capping, which
crowns the piers; a great part of
the weight of the bay is then
carried by struts, and care is taken
to prevent these pieces from yield-
ing by means of one and some-
times two binding-pieces.
A
XXI
Fig. 2200. FRESINGEN Bridge.

IXIX
It is rare that the system of
under-girders and struts is used
for large bays; but in countries
where timber from 12 to 14
inches square is easily procured,
and not very expensive, this prin-
ciple may be applied to bays of from
40 to 52 feet span; in which case
it is necessary to use two struts,
one of which carries the under-
girder in the middle of the prin-
cipal, and the other the extremity
of that placed on the capping of
the piers: these struts are main-
tained by two binding-pieces; the
under-girders are united to the
upper, the extremities of which
are screwed together very tightly.
If the opening of the bay were as
much as 65 or 82 feet, another
arrangement might be used by making the under-girders and struts of double or triple
pieces; but timbers applied in this manner are far from resisting so advantageously as
they might do, the pressures to which they are exposed acting perpendicularly to the
length of the pieces, whilst the system might be so disposed that the weight should be
distributed in the direction of the length: in this kind of construction the principals must
Fig. 2201.
SECTION of bay.
1358
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
be multiplied, and very large
timbers used, which involves
a considerable and needless
expense. It is now generally
acknowledged that the best
method of applying timber
in bridges is to form arches
with courses of curved tim-
bers bent over each other:
this arrangement has been
preferred, after several others
have been tried, which have
proved entirely defective,
and the result of long ex-
perience is justified by an
analysis of the different
systems of carpentry in large
arches.

Fig. 2202.
BAYS AND ARCHES.
Let A and B, fig. 2174. be two points of support, united by a large principal of carpentry,
which principal, besides its own weight, is to carry that of the floor, which may be con-
sidered as distributed uniformly throughout its length. The first idea which would present
itself is to establish on the two points of support a solid bearing in timber, the form
of which shall be such that it resists this double effort equally in all its points, and if
we recal the notions which have been given on solids of equal resistance, we shall
imagine that this should present nearly the form of a C b, indicated in the figure: let us
then observe that if this solid should yield, the fibres situated on the upper surface would
be compressed, whilst those situated on the lower would be extended, so that we can trace
in the interior of the solid two lines Ca and Cb, which shall separate the compressed from
the extended fibres, and that the resistance of the solid exerts itself by means of the pressure
directed in the lines Pm, Pn, and of the tensions directed in the lines P'm', P'n', efforts in
which this resistance consists solely, and which are the more considerable following each
of the lines Pm, Pn, P'm', P'n', as these lines are nearer the surface of the solid, and further
removed from the line a Cb.
It is easy to draw conclusions from such an example: first, the pieces of which the
solids should be formed must be disposed in the direction of the lines, according to which
the pressure and the tensions are exerted, for of all the applications of timber, the most
advantageous is that where it is pressed or drawn in the direction of its length; it must
be observed also, that there is advantage in using the same quantity of pieces, in removing
them from each other, in not making the solid full, and in augmenting its height; in short,
the effort of the weight which the solid supports may be assimilated to that of a certain
weight suspended at the point C, and which decomposes itself into two forces, directed
from this point towards the points of support A and B; when the point C is higher
with relation to the points A and B, the two components of weight, making a less angle,
have a less considerable value, and produce pressures less strong. We are led by these
considerations to a system of carpentry represented in fig. 2175., which is that of the
bridge of Schaffhausen and Wittingen: the principals of these bridges have the form
which would suit a solid of equal resistance, and the timbers are disposed exactly in the
direction of the pressures and tensions which they would exert in the solid; but the
pieces which would be found in connection with a Cb (fig. 2174.) are suppressed, because,
having scarcely any effort to make, they would increase the weight without having any
utility: we may remark that the pieces which resist the pressures are in much greater
number than those which resist the tensions, which arises from the timber being drawn
in the direction of its fibres, and consequently having much more strength than that
which is compressed in the same direction. The carpentry of these bridges bears on the
abutments, but does not exercise against them any effort which tends to overthrow them;
the thrusts being retained by the tensions of the inferior girder, in rendering the abutments
capable of resisting the thrusts, we may then, without changing the nature of the system,
suppress the girder; this idea leads to the arrangement represented fig. 2176., which is
that of the bridge of Kandel. A slight modification in this arrangement gives the com-
bination represented in fig. 2178., which is that of the bridge projected for Lyons;
this latter has an advantage over the preceding, because the braces united and subjected
to each other form a rafter, and resist much better than when they are isolated, above
all, if each of them were to be only of one piece; but this advantage has its inconvenience,
for the effort of the weight of the bridge may be considered as that of several weights
attached to pendant binding-pieces; in the systems, figs. 2175, 2176. the efforts of the
weights suspended to each binding-piece is carried back towards the points of support,
and maintained almost entirely by the inclined piece, which abuts at the upper extremity
CHAP. XXIII.
1359
TIMBER BRIDGES.
of the binding-piece, for this weight separates at this extremity into two forces, the one
acting in the direction of this piece, and the other in the direction of the beam, and does
not tend to make the other struts, which are held by the binding-pieces, yield; all these
struts then support only longitudinal pressures, whilst in the system fig. 2176., besides the
longitudinal pressures, which are the same as in fig. 2174., the inclined timbers have also to
support transversal pressures, since the weight carried by the binding-piece then decomposes
into two forces, the one acting in the direction of the great rafter, and the other perpen-
dicular to it. This observation leads to a new modification: as the timbers yield less
easily as they are shorter, there must be an advantage of substituting for two inclined timbers
a system of three pieces, and although these pieces, making more obtuse angles, cause the
weight to be decomposed in stronger longitudinal pressures, more must be gained by the
diminution of their length than is lost by the effect of the augmentation of their pressures;
thus we obtain the system fig. 2177., which is that of the bridge built by Palladio over
the Cismone: in placing, as in fig. 2178., four inclined timbers instead of three, their
strength would be augmented, and by thus multiplying their number and diminishing
their length, we should have pieces too short to bend, as seen in fig. 2179., and
which could only yield by crushing; this is the arrangement for the arches projected by
Perronet for the bridge of the Salpetriere, and for those executed at Lyons in that of the
Mulatière. In order clearly to show where these last systems are wrong, we shall make
some observations on the nature of constructions in carpentry, which naturally find place
here.
Whatever may be the combination, in constructions of carpentry the object should always
be the transmitting of certain efforts to points of support, by means of a system of levers,
subjected one to the other: now we can distinguish in such a system two different equi-
libriums, which we shall designate as Equilibrium of Position, and the Equilibrium of
Resistance. The first takes place when the efforts exercised on each lever are so combined
with their respective situations that the system does not tend to produce any move-
ment: it is that which forms the objects of statics, of which science teaches us to regulate the
conditions. The equilibrium of resistance consists in making each lever, which in statics
is considered as an inflexible line, have the necessary force for the resistance of the
pressures exercised in it; the conditions of this latter equilibrium are the object of the
theory of the resistance of solids, and, according to what we have already described, we can
always express these conditions with sufficient exactness in constructions of oak.
A system of levers may be maintained in repose by two different means; first, it may be
disposed in such a manner that the conditions of the equilibrium of position should be
exactly satisfied; secondly, the levers should be so subjected to each other by framing, or
by auxiliary pieces, as binding pieces or braces, that it should be impossible for them to
change situations with regard to each other as long as the resistance of this framework is
superior to the efforts which tend to make the form of the system vary in this latter case
we are not required to satisfy the conditions of the equilibrium of position; the system must
be regarded as formed by one single piece, and the equilibrium of resistance should alone
be taken into consideration. If these ideas be applied to wooden bridges, and the system
represented in fig. 2179. be taken, having only regard to the weight of the carpentry and
the pavement, the levers may be placed in the situation which suits the equilibrium of
position, so that they do not tend to any change of form under the load: but we must
remark, that the equilibrium will often be found deranged by the passage of carriages ;
and secondly, that this not being stable, the slightest derangement would involve the
falling of the bridge, whence we may conclude that in the system of levers which compose
the principals of a bridge, the equilibrium of position can never be exactly attained: it is
then necessary that these levers should be subjected and framed to each other, and that at
each articulation the framing should be opposed to their various angles with a force equal
to that which produces the variation, according to the effect of the weight; thus the system
of the carpentry of a bridge must necessarily be in the second of the two cases already
stated. The consideration of the equilibrium of position can never be employed, but to
assure ourselves that the framing of the articulations has the force necessary to oppose
every change of form; this indispensible condition fulfilled, the system changes its nature;
it should be regarded as forming only a single piece, and its resistance valued in conse-
quence.
In examining the principles of figs. 2174, 2175, 2176., we see that in whatever manner
the load is distributed, it does not tend to make any change of form, and among the
different framings of carpentry, that which has the figure of a triangle is the only one
which can have this property; we ought, then, to carry every other system to this, by properly
fortifying the articulations, with the exception of that of the summit, so that, whatever may
be the arrangement of a principal, its two halves may be considered as two rafters made of a
single piece, which at the summit abut against each other; it is an indispensable condition
in order that the system should have stability, and no bridge can subsist if this condition
be not fulfilled.
1960
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
In the system of two inclined timbers abutting against each other, it is easy to imagine
that the load will separate in pressures in the direction of their length, following two lines
drawn from each side of the summit of the principal to the springing; the resistance of
these timbers must make an equilibrium to these pressures, and in order to appreciate this
resistance, we must consider the timbers as placed upright, and loaded vertically with a
weight equal to the pressures. According to this consideration, it is evident how disad-
vantageous it is that the two halves of a principal should be divided into a great number
of articulations, forming so many points of rupture, leaving them no resistance but that
which arises from the strength of the framing; it may be easy to give to the framings at each
articulation sufficient force to render the system invariable in form, but, as experience has
proved, it is very difficult, and even impossible, when the number of levers is considerable, to
fortify them sufficiently to procure for each half of the centre a resistance capable of making
equilibrium to the pressure which it exercises in the direction of the length: it is for this
reason that the systems figs. 2178, 2179. become more disadvantageous as the number of
the timbers augments, and terminates by being entirely impossible of execution.
A more solid combination is obtained by disposing inclined timbers, as seen in fig.
2180., in polygons, some of the angles of which answer to the middles of the sides of
the others, because if each half of the arch yielded to the pressures which exert themselves
from the summit to the springings, not only the framing of the articulations would bend,
but the timbers would break in the middle of their length: we must observe that the
courses of the inclined timbers not being solidly framed, touch by a very small number of
points; a certain flexion may therefore be produced in the whole without each piece sensibly
bending; this may happen, should each binding-piece diverge a little from its position,
so that the pieces of the polygon situated on the side of the concave face are not shortened,
and those of the polygon situated on the convex face are not lengthened, as they would be,
on account of the flexion, if they were perfectly united. It is impossible to execute
the notches of the binding-pieces with the perfection necessary to prevent this diverging
from taking place: thus the system fig. 2180., although very preferable to that of fig. 2179.,
is far from perfect; the system fig. 2180. was that which Perronet used for the centres of
stone bridges. But if, instead of forming the timbers with straight pieces, which can
only touch each other at their extremities and in the middle of their length, the whole
of which may yield together without each piece in particular being obliged to bend, we
use, as in fig. 2181., curved pieces in juxta-position, united and tightened by binding-pieces
and bolts, the joints of the extremities of which do not unite opposite to each other, the
nature of the system will be found totally changed, and it will receive a very great im-
provement, for the centre (fig. 2181.) cannot bend without all the pieces of which it is
formed yielding: the strength of the framework of the extremities of these pieces no longer

-
EN
-88-
Fig. 2203.
BRIDGE FORMED OF CURVED TIMBERS.
opposes itself alone, to the flexion of each half of the centre; the resistance presented by the
timbers is a second obstacle to the flexion, more powerful than the first, rendering all
bending impossible, if this resistance be sufficient, even if we discard all consideration of
the manner in which the framework of the ends is executed.
Arches formed of bent timbers have been adopted for some of the viaducts constructed
on our railways, and where sufficient caution has been taken to prevent too much motion
from their elasticity, are found to answer very well: the reparation of such bridges is
difficult, should any of the timbers exhibit decay; but this disadvantage has been over-
come in some instances by making the bolts and straps that hold the curved timbers
movable, so that one timber can be taken out without disturbing the others, which lie
above or below it.
The disposition fig. 2181. offers, with regard to the force with which each half of the
centre resists the longitudinal pressure exerted upon it, the same resistance as the system
fig. 2176.; it is equally invariable in form with the latter, and much more advantageous,
CHAP. XXIII.
1361
TIMBER BRIDGES.
as the curve given to each rafter leaves nothing to fear from the transverse pressure to
which it is submitted, and there is even no necessity to consider these pressures.
Fig. 2203. represents an arch projected according to these principles for an opening of
132 feet; the principals are at a distance of 6 feet 6 inches from centre to centre; the
arch is composed of four courses of curves, tightened by bolts, and so placed that
their joints do not meet, some being opposite the others; it carries the floor by means
of pendant binding-pieces, which it appears more proper to place vertically than per-
pendicularly to the curve, and it may be admitted as a general principle, that each piece
should always be placed exactly in the centre of what it supports; these pendant binding-
pieces are held by horizontal binding-pieces placed on centres, which prevent the spreading
out of the principals; courses of vertical and horizontal binding-pieces should never be at
more than 16 feet apart.
When the opening of the arch is considerable, the movement of carriages, and sometimes
even the action of the wind alone, occasions oscillations in the horizontal direction, which
injure the carpentry, and might become very dangerous; the greatest care should be taken
to prevent this. If an arch bend in the direction of its width, the horizontal binding-
pieces, which were at first parallel between each other, would become normal to the curve
which the arch would have taken; they will then have changed position with relation to
each other; thus the flexion of the arch will be prevented, if pieces are so disposed as to
maintain these binding-pieces in their respective positions; in the half-plan represented in
fig. 2203., braces are placed for this purpose in the interval of the courses of binding-pieces.
In the oscillations of an arch, the entire system of its carpentry may participate in the
movement, or it may only be partial; for example, the floor may to a certain point move
independently of the arch; still it is very important to oppose these effects; there are
therefore placed between the first course of pendant binding-pieces, near the springing,
inclined struts which secure the union of the floor and the arch, and it appears
that this disposition would give to the arch all the solidity and stability which could be
desired; it is scarcely necessary to observe that the framing of all these pieces should be
secured by bolts, without which the union could not be obtained.
It is requisite to allude to the manner in which the thrust of the arches in carpentry
of the kind we have just indicated, should be considered, and on the settling, of which
they are susceptible. If timber did not suffer any compression, and if the execution of the
work could be sufficiently perfect for no voids to remain in the framing, and all the pieces
could bear exactly one against the other, there could be no settlement; and the force of
the timbers being regarded capable of resisting the load, no flexion would be produced;
the centre would then be as a single piece placed upon two supports, and would have
no thrust; this perfection in the quality of the materials, and in the execution of the
work, not existing, it happens that the moment an arch is placed and left to itself it has
a tendency to settle: if this movement could operate freely, and the chord of the arch
elongate without obstacle, until the framework was tightened, the settling would stop,
and the arch would then have no more thrust; but it is always retained by obstacles,
which do not permit the chord to be thus elongated, which obstacles necessarily experience
a certain pressure; the most simple manner of valuing this pressure is to assimilate the
arch of carpentry to a wall of stone, and to examine the horizontal thrust which it would
produce, according to its weight and the relation of the yielding at the opening; we
shall thus have, not the true value of the thrust of the centre, but a limit below which
this thrust always remains, and according to which the dimensions of the piers and
the abutments may be regulated. Although the arches of carpentry be confined at their
springing, and their chord not being able to lengthen itself the summit cannot sink,
they experience a slight settlement, analogous to that of a vault in stone, and to which
regard must be had in construction. According to the observations of M. Wiebeking,
by representing c as the opening of an arch, and ƒ as its fleche or settlement, the lowering
f
at the middle, expressed in inches, is given by the formula 0·02 but we must remark that
these observations were made on bridges of fir timber; for centres in oak the settlement
should be less considerable. This formula gives the settlement immediately after building,
but it increases from the effect of the alteration of the timber.
C
Floors and Parapets. Floors of wooden bridges are constructed in various ways;
formerly they were almost always covered with a pavement placed on a bed of sand; but it
has been ascertained that a very considerable weight was the result, and that the damp
produced on the planks tended to make them rapidly perish, as well as the girders on
which they were carried; it is therefore preferable to cover them with a false floor, which
also prevents them from being injured by the wheels of carriages, and can be renewed as
often as necessary.
Fig. 2204. represents the section of a floor disposed to receive a pavement; it is formed
by timbers, from 7 to 8 inches square, slightly notched at the meeting of the main timbers,
4 S
1362
BOOK II,
THEORY AND PRACTICE OF ENGINEERING.
to which they are attached by iron pins, and the spreading out of which they prevent;
the intervals between are filled up by planks, of from 3 to 4 inches in thickness, which

You
Fig. 2204.
are also nailed; these intervals are generally 6 feet 6 inches, and care has been taken to
prolong the pieces, and to place at their extremity a tenon, on which a brace is framed,
which consolidates the posts of the parapet, and is prolonged a little further, to prevent
the water from remaining in the framework; the posts are also strengthened by another
brace, also frained into the main timbers; they are kept together in the length of
the bridge by two courses of horizontal rails, one of which, placed on their heads, is
laid so as to cap them: within and against the foot of the parapet are planks called
guards, which keep in the pavement and sand. It may be remarked that in this floor
the main timbers are entirely covered either with joists or planks: there is therefore a
constant dampness, and in demolishing ancient bridges, it is constantly observed that the
upper parts and the interior of the main timbers are entirely perished, whilst at their

Fig. 2205.
exterior extremities they appear quite sound: this essential defect has been avoided in
fig. 2205.
The platform of boards is carried on joists from 9 to 10 inches square, at
about 3 feet apart: the planks should then be placed lengthwise on the bridge, but the
linings with which they are covered are laid transversely, for the purpose of preventing the
feet of the horses from sliding on the wood: not only has this latter floor the advan-
tage of allowing the air to circulate round the principal bearers, but it also permits of the
principals being removed further apart. Sometimes it is usual to substitute iron balus-
trades for the wooden parapets on timber bridges; they are composed of upright standards,
which should traverse the joists of the floor, and the brestsummers of the principal, on
which they bear by means of shoulders secured by screws; these uprights are stiffened by
consoles, and their intervals filled up either by rails which traverse them in the middle, or
by irons diagonally placed.
It has been proposed, in order to preserve the floors of wooden bridges, to cover the
planks with plates of lead and copper, and it appears that the greater duration produced
by this precaution will compensate for the expense, or the wooden floors might be
entirely omitted, and the main timbers covered with a plate of lead, the edges of which
should be lapped one over the other.
During the middle ages throughout Europe, as aas been already stated, numerous timber
bridges were constructed, generally supported by one or two rows of piles, forming a
pier, united by several horizontal binding-pieces, and strengthened by inclined struts: such
piers were placed from 15 to 25 feet apart, and protected by sterlings covered with planks,
the intervals between the piles being filled in with stone or chalk, and a capping of tim-
ber placed on them, on which the girders which carried the platform rested.
Considerable improvements have since been made in constructing wooden bridges, and
almost every country has had its peculiar system: the abutments, and often the piers,
are formed of stone or brick where the streams are narrow, a simple platform laid on
timbers of the requisite scantling for the bearing is sufficient; for an increased width
struts are added, and trusses of various descriptions.
:
:
Foot Bridges of the simplest construction have the beams laid across the opening
without any struts; for a span of 15 or 16 feet, a depth may be given to the principal
bearers of 15 inches and a breadth of 8 inches; these may be laid about 2 feet apart, and
covered with plank or two piles may be driven, inclining inwards, coupled at the
head by transverse beams mortised and pinned into them; they may be further
strengthened by horizontal pieces at different portions of the height; on the transverse
beams may be laid as many joists as are required for the width of the bridge, for which, if
of an ordinary kind, two will be sufficient; the parapets may be strutted on to the pro-
CHAP. XXIII.
1363
TIMBER BRIDGES.
jecting parts of the transverse beams, which are mortised on to the piles, and thus be firmly
supported.
Foot Bridge over the Clyde at Glasgow. The nine bays are carried on pairs of piles,
distant about 42 feet apart, and under each longitudinal beam is a second, over the
heads of the piles, which extends 10 or 12 feet on each side, and acts as a corbel; this
being firmly bolted through gives considerable strength to the main timbers, which are
further strengthened by a truss formed in the parapets of the bridge.
Timber Bridges with longitudinal timbers laid across the stream, and supported at
every 15 or 20 feet by a row of piles driven into the bed of the river, have the capping
placed upon the heads, and supported by side braces; additional strength is given by

Fig. 2206.

O
་་
0+ 20

Fig. 2207.
bolts passing through the longitudinal timbers; cross-planking forms the road or foot-
way, over the ends of which another longitudinal timber is laid, and iron bolts are
passed through the whole to unite them together.
In narrow foot-bridges the piles may be driven slanting, and united at the top by a cap-
ping, which, projecting considerably on each side, serves for the introduction of a strut to
strengthen the side fence or railing.

Fig. 2208.
The piles may be driven further apart when the struts are used to discharge the weight
of the platform; a horizontal timber is bolted from one pile to the other, which serves
as an abutment to the struts, and unites the piles which form the piers more firmly.
4 s 2
1364
Book II.
THEORY AND PRACTICE OF ENGINEERING.

Fig. 2209.
Fig. 2210.
Such a bridge as the last may be made of very considerable strength by introducing under
the longitudinal timbers an additional thickness, against which the two struts abut; and

Fig. 2211.
bridge over the DANUBE, NEAR ULM.
taking the precaution of having a hard material between the ends of the timbers, where their
fibres are likely to penetrate, and iron bolts to secure the whole together: abutments of
brick or stone are always preferable when they can be constructed.
Where the bearing is upwards of 40 feet, additional strength is obtained by the intro-
duction of stout pieces of timber under each beam; these may be secured by iron pins; so
strutted, they are capable of sustaining considerable weight.

Fig. 2212.
DIEPPE.
In many instances it is found that the construction of a timber bridge is renaered less
difficult when the piles that support the platform are in two lengths, or that the first are
driven into the bed of the stream, and cut off a little below the level of the water upon
the heads of these lower piles rests a plate, laid in the direction of the current, and on
which the piles that form the piers are secured: should these require any reparation, it can
be readily effected without the aid of the pile-driving machine.
CHAP. XXIII.
1965
TIMBER BRIDGES.
A bridge for carriages of 30 feet distance between the piers may be constructed upon
this principle; but as greater stability is required, ano ther strong piece of timber may be
put under the principal bearers, and strutted as shown: the clear width is 15 feet between
the parapets.

Fig. 2213.
VRACH IN WURTEMBERG.
Horse Bridge at Vrach in Wurtemberg exhibits a simple form of truss, which answers for
the parapets of the bridge; the distance between the piers is about 35 feet, and the clear
width between the parapets is 7 feet 6 inches.
There is considerable
ability displayed in the
arrangement of the timbers
of the several bridges over
the arm of the Necker,
which are so disposed as
to form the railing or
parapet; a kind of con-
struction productive of the
greatest economy, at the
same time allowing the
entire space beneath the
platform of the bridge to
be open for the passage
of boats, and unimpeded
by the torrent, which may
occasionally require the
entire opening of the
bridge for its passage:

Fig. 2214.
DETAILS of the bridge at Vrach.
where timber is floated down a stream from the forest to a port for its embarkation, there
should not be the slightest impediment presented, which would be the case if the framing
of a bridge were continued down to the water's edge.

NA
Fig. 2215.
NECKER.
That over an arm of the Necker, built by M. Ezel, is of the
same character; the distance between the piles is not less than
38 feet, and the clear width between the parapets is 17 feet.
Fig. 2216.
St. Clair, over the Rhone at Lyons, constructed by M. Morand
in the year 1775, shows great skill in the application of
the timbers: it has 17 bays, varying in width; that in the
centre is 45 feet, and they proportionably decrease on each side, the extreme openings being
only 33 feet. The first piles that were driven to form the piers were cut off level with low
water, and on their tops was laid a timber platform, into which the posts which sup-
ported the bridge were framed the bridge was 36 feet in width, and the piers con-
sisted of 13 posts in a row, each composed of two pieces of timber strengthened and
4 s 3
1366
Book II
THEORY AND PRACTICE OF ENGINEERING.
protected by horizontal pieces, one under the braces, and the other immediately above the
level of the river, through which passed iron bolts that tied and secured the whole pier
together: the 13 double posts, which formed the pier, were capped, and on them were laid
as many longitudinal timbers, which formed the supports to the floor of the bridge, and
an additional piece or two was bolted to them, in the middle of their span, with struts
and pendant braces.


Fig. 2217
Fig. 2218.

Palladio's Bridge over the Cismone.
This was executed over a river at
the foot of the Alps, between Trent
and Bassano; its length is about 108
feet; it is divided into six equal
openings. The river being rapid and
subject to floods, bringing down trees
and stones, it was not thought advi-
sable to fix any piles in the current:
the timbers mutually support each other, and the whole system is strongly framed
together.
Fig. 2219.
LYONS, BY NEAngrez.

Fig. 2220.
PALLADIO'S bridge at BASSANO.
Five girders, 12 or 13 inches square, disposed at equal distances, are laid at right
angles to the length of the bridge, or about 18 feet from centre to centre: these appear
to have no support; the girders being a little longer than the width of the bridge, carry
the principal timbers or joists which cross the river, on which the planks are laid which
form the floor. The five girders do not lie level; the three in the middle are elevated
a little above the

other two, so that the
sill which lies upon
them, and into which
the king- and queen-
posts are framed,
is also out of a level
;
the part at which the
two outer sills abut
against that in the
middle being ele-
vated, the whole takes
the form of a seg-
ment; the upright
posts or colonelli,
which are framed
into them, are also
bolted through and
secured on the under
side: all the struts,
Fig. 2221.
Fig. 2222.
PALLADIO'S BRIDGE,
CHAP. XXIII.
}
TIMBER BRIDGES.
1367
straining-pieces, and other portions of the trusses on each side are out of timber 12 inches
by 9; these trusses form the parapets, and are secured by iron straps and bolts at the
extremities; they are capable of supporting a considerable weight without any sensible
deflection; their height is about 16 feet, and the principle seems to have been that of
a series of triangles, which are not liable to any change of form. The abutments
are of stone, and the
height of the para-
pets or trusses are
nearly of the entire

span.
Fig. 2223. is an-
other of Palladio's
bridges, supported
like the preceding
by a truss on each
side; its length is
divided into eight
bays by transverse
girders, suspended
Fig. 2223.
PALLADIO'S bridge.
by stirrup-irons and bolts from the posts framed into the head and sill of the truss; these
posts are braced strongly, but their strength is not equal to those of fig. 2222.; the centre
bays are liable to drop, as the bearing is too great: in this construction the first bays
from the abutments should have four depths of sill, the second three, and the third two,
leaving the two centre bays with only one; thus the ends of the bridge would appear
to rest on corbels gathered over from the abutments, or these additional timbers might
be laid side by side; this would require the transverse girders to vary in length, that they
might comprise and tie them together. The height of the trusses is about one-tenth of the
span.
Fig. 2223. is a portion of a polygon of five sides, with four king-posts and braces,
like a St. Andrew's cross; the outer heads are doubled, and struts are added to throw the
weight of the first bay on the abutments: the transverse girders are carried by the king-
posts, to which strong stirrup-irons and bolts are attached: the side trusses of this design,
which form the parapets of the bridge, are about one-ninth of the span in height.
the
The parapets in fig. 2224. may be considered as consisting of eleven voussoirs, each
formed of posts, strongly braced by diagonal timbers like a St. Andrew's cross:
transverse girders are held up by iron straps, as in the other examples, and the height
of the framing of the parapets is not more than one-twelfth of the span.
Of the four designs left us by Palladio the first combines the best arrangement of the
timbers with the greatest solidity: in the last there is an appearance of great strength, but
when we take into account

the shrinking to which the
timber is liable, it is evident
that the voussoirs would
be subject to great change
from the compression they
must undergo when heavy
loads passed over: motion
destroys in the course of
time the tightness first
given to the framing, and
subsequently the nice ba-
Fig. 2224.
PALLADIO's bridge.
lance of such a timber construction: that design braced like a St. Andrew's cross, and
which partakes of the arc of a circle, would not so readily alter its form, and would
preserve its firmness and solidity for a length of time.
Bridges of Palladio's construction could not be adopted where a greater width of
carriage-way than 14 or 15 feet was required; the transverse girders would require
upholding by additional longitudinal trusses, if the width were increased.
Bridge at Bassano, at the foot of the Alps, over the Brentar, was also erected by
Palladio: the river is 180 feet in width, and there were five bays of equal widths.
Palladio gives the following directions for the construction of the bridge fig. 2241.:
"The banks must be first fortified with pilasters; then one of the beams that forms the
breadth of the bridge must be placed at some distance from them, and the beams that form
the sides be disposed upon it, which, with one of their heads, must lie upon the bank, and
be fastened to it; upon these, directly plumb with the beams for the breadth, the colonelli
are fixed, fastened with cramps of iron, and supported by braces secured to the heads of
the bridge; the other beams are then placed, leaving as much space between each as there
is between the first and the bank: in the middle of the breadth of the river there must be
4 s 4
1368
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
a colonello or post, in which the centre braces meet, and on the upper part of which must
be fixed other braces, uniting with the next colonello, tying all together, and forming with
the braces in the head of the bridge a portion of a circle less than a semicircle.
Foot Bridge, over the canal of Gooda, in Holland, 45 feet span, is of very simple
construction; it is formed of curved timber, framed to resemble the segment of an
arch. There are two sets of ribs, on which rest the longitudinal bearers that carry a
planked floor, 4 feet 6 inches clear width between the parapets or railing: the posts into
which the horizontal rails are mortised, by an additional length unite and hold together the
curved and straight timbers, on which the platform rests.

Fig 2225.
GOODA IN HOLLAND.
Another Foot Bridge in Holland, over the canal at Utrecht, of the same span, shows
greater strength; its clear width between the railing is 5 feet 6 inches: struts are in-
troduced, held in their positions by couples or pendant binding-pieces.

Fig. 2226.
UTRECHT CANAL.
Fig. 2227.
Mulatière Bridge at Lyons, over the Saone, has eleven openings; the centre is 57 feet
6 inches, and the others gradually diminish to 49 feet span. The piers are each formed
of two rows of piles, driven parallel to each other: three horizontal pieces of timber
bolt them together above the water: on the tops are framed abutments like those of
Trajan's bridge, receiving the thrust of the principal timbers: each opening has an

Fig. 2228.
MULATIERE AT LYONS.
arch, formed of four sides of a polygon; each of these sides consists of two pieces of
timber, framed or scarfed together, one being cut like the teeth of a saw, and the other
indented to receive it: after these are fitted they are securely bolted together. Where
the ends of these pairs of timbers unite and abut against each other are pendant
binding-pieces, to hold up and secure them to the principal longitudinal timbers which
carry the platform: the error of this kind of construction arises in part from the
pendant pieces maintaining a constant humidity, which is communicated in time to the
polygonal pairs of timbers and the framed abutments, when a partial decay takes place,
and a settlement follows.
и
The timber bridges at Kingston-upon-Thames, Walton, and many others in England,
cre constructed upon this principle, and were constantly requiring repairs.
CHAP. XXIJI.
1369
TIMBER BRIDGES.
Bridge over an arm of the Necker, at Wurtemberg, has a width of carriage-way of 14 feet,
and a clear span of 53 feet; it is queen-post trussed, and strongly strutted against stone
abutments.

Fig. 2229.
Bridge of NECKER, AT WURTEMBErg.

This kind of bridge does not require much
skill in framing the timbers, nor any other ap-
plication of mechanical principles beyond that
of strength; the squared timbers are placed
across the stream or canal parallel to each other
on these are laid stout planks or transverse
pieces to carry the roadway, which is made
either with earth or gravel, and kept in its place
by stout planking at the sides. The princi-
pal timbers are prevented from sagging by the
introduction of the two upright posts in the
railing, which hold up that portion of the plat-
form most liable to drop by means of struts and
a stretching-piece put together in the manner
of a queen-post truss; and if the abutments are
maintained in their position and prevented from
Fig 2230. BRIDGE OF NECKER.

Fig. 2231.
bridge of loiret, near ORLEANS.
sliding, and the ends of the timbers protected from decay, such a bridge will endure for a
considerable length of time. As timber of a uniform scantling and of the proper quality

Fig. 2232.
SCHONENBerg canal.

for bridge-building is difficult to obtain be-
yond the length of 50 feet, these constructions
must be limited to that span.
A horse bridge, 6 feet 6 inches wide, over
the Loiret, near Orleans, with a span of 60
feet, has its longitudinal timbers bearing on a
very strong truss.
Över the canal of Schonenberg, near Brussels,
is an occupation or horse bridge, 8 feet wide
and 70 feet span, formed of pendant binding-
pieces which diverge from a centre, against
which timbers are strutted polygonally, in three
rows at a distance from each other, all held
Fig 2233. Schonenberg CANAL.
1370
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
in their places by transverse ties; the parapets are formed by the introduction of a St.

Fig. 2234.
BRIDGE OVER THE BRUSSELS Canal.

Andrew's cross between the pendant binding-pieces,
and making a very strong truss, by uniting the whole
together like an arch, which cannot materially alter
its form as long as the stone abutments maintain
their solidity.
Over the canal at Brussels is a horse bridge, 83 feet span,
of very simple construction, and which would have
been much more solid, if perpendicular posts or blocks
had been introduced into the triangular space formed
by the inclined timbers which support the platform of
the bridge.
Fig. 2235. BRUSSELS CANAL.
Over an arm of the Necker, which is 93 feet wide, is a light horse bridge 8 feet span;
two sets of king-post trusses in the parapet strengthen the main longitudinal timbers,

Fig. 2236.
horse bridge, necker.

but from the disconnection of the middle pieces of framing, this
arrangement of the timbers must be very defective.
Notre Dame at Cahors, built by Sganzin, has a clear width of
carriage-way of 17 feet, and a span of 95 feet, formed of one
polygonal arch, the versed sine of which is between a fourth
and a fifth of the span; its composition is defective, from being
composed of too many pieces, which must be subject to a
considerable shrinking, and seriously derange the whole
8
Fig. 2237. NECKER.

Fig. 2238.
Notre Dame at cahors.`
framing; when the timbers are thus shortened, the angles of their junction necessarily
become more obtuse, and in consequence are likely to open, particularly when heavy loads
pass over them. This cannot be considered any great improvement in construction over
the bridge of Mulatière at Lyons.
CHAP. XXIII.
1971
TIMBER BRIDGES.
Bridge of three Arches over the Loire, each 92 feet span, with a clear width of car
riage-way of 27 feet, and a versed sine of 8 feet 6 inches; they are well framed

XE
Fig. 2239.
together; nine pendant
binding pieces radi-
ating to a centre main-
tain the polygonal tim-
bers that form the arch
in their position; and
where these pendant
timbers increase in
length towards
abutments, they are
again strutted securely.
the
Over another arm of
the Necker is a horse
bridge 90 feet span, and
a clear width of way of
10 feet, in which the
pendant pieces are the
posts that form the
parapet.
The king-posts in
this bridge are placed
perfectly perpendicular,
and the side braces ap-
BRIDGE OVER THE loire.


TTTTTTTT
Fig. 2240.
Fig. 2241.
LOIRE.

Fig. 2242.
bridge of VRACH IN WURTEMBERG, over an ARM OF THE NECKER.
plied to their sides spread to the full extent of the opening, having their abutments against
each other on the piers: a nail is introduced between the tops of the several king-posts,
which serves as a straining piece, and prevents them from approaching each other. The
floor is carried in the middle of the span upon a stout transverse bearer, suspended to the
ends of the king-posts by means of iron straps and bolts. So long as decay is prevented, and
main timbers preserve their form, this construction is durable and economical; but if the
heads of the piers are suffered to break the tie by which they are held in their perpendi-
1372
Book II.
THEORY AND PRACTICE OF ENGINEERING.

cular position, the struts will lose their abut-
ments, and the balance between the timbers
which constitutes the entire strength of the
bridge will be destroyed; an iron tie would
insure greater stability, and might be intro-
duced across the stream, under each side of the
platform, without changing the disposition of
any of the timbers.

Fig. 2243.
Fig. 2244.
In some of the timber bridges on the con-
tinent, where the oak platform that sustains the
road has been in a state of decay, and re-
quiring constant repair, stone pavement has
been substituted, laid from bearer to bearer,
and in some instances iron plates perforated with holes, to allow the water to pass through;
but the additional weight produced by either of these is so considerable, that it is a
question whether any benefit has been obtained.
Bridge at Tête in Picardy, erected by M. Coffinet; its span is nearly 126 feet, and its
versed sine scarcely an eighth of the span.

Fig. 2245.
BRIDGE AT TETE IN PICARDY.



Fig. 2247.
Fig. 2246.
bridge at TETE IN PICARDY.
Fig. 2248.
Perronet's Timber Bridges were upon the principle of the polygonal arch ; the spans of
the arches were equal; the framing of the timbers that carried the roadway extended

Fig. 2249.
PERRONET'S TIMBER BRIDGES,
through the parapet or railing on each side of the bridge, by which means the form of a

LH
Fig. 2250.
perronet's TIMBER BRIDGES,
CHAP. XXIII.
1373
TIMBER BRIDGES.
polygon was given to the several struts and supports: regarding each side of the polygon
that abutted on the piers as a simple truss, and proportioning the timbers to the
duty they had to perform, there perhaps could not be a more simple arrangement, or
one that offered, with the same amount of material, greater strength; but the quantity of
framed work and the liability to decay in the several joints have occasioned this system to
be abandoned.
Bridge of St. Clement, over the Durance, with a span of 115 feet, was an early instance of
the application of the suspension principle. The length was divided into nearly three equal
parts; in the middle
division an addition-
al timber was placed
under the main lon-
gitudinal beam, to
which it was firmly
bolted, and the di-
vision was held up
by four radiating
posts, which were
kept in their position
by strong straining

Fig. 2251.
BRIDGE OF ST. CLEMENT.
pieces introduced between their heads, and by a St. Andrew's cross framed in between them;
the centre framing formed almost a single mass, and was kept from sinking by diagonal
struts resting on the abutments; the lower of the two, from their inclination being so flat,
could not be very effective, and the principal stress in consequence must have been thrown
upon the others, which abutted against the top of the suspendant posts; these diagonal
struts had also two pendant binding-pieces and cross struts, to assist in carrying the
platform of the bridge, and prevent their springing. After the timbers had shrunk,
the whole weight of the bridge must have been thrown upon the upper pair of struts,
which abut against the pendant binding-pieces.
Bridge at Savines has a clear width of way of 10 feet, and a span of 75 feet; it is also
upon the suspension principle, but the timbers are more simply arranged; the abutments

Fig. 2252.
BRIDGE AT SAVINES.
on each
are of timber. In the centre is a post 16 feet in height above the platform of the bridge,
into the head of which are framed two diagonal struts or principals, one
side, for the purpose of suspending it; this post is strutted
to the principals, and holds up the middle of the longi-
tudinal timbers of the bridges, as a king-post sustains the
tie-beam of a roof; other pendant pieces are attached to
the inclined principals, and shorten the bearing, by holding
up the longitudinal timbers at regular distances: all those
bridges formed of braces diversely inclined are defective in
strength, and consequently in duration.
Bridge of Schaffhausen was constructed in the year
1757, by John Ulrich Grubenmann, a village carpenter
of Tuffen. It was formed of two arches, one spanning
172 feet, the other 193 feet
193 feet: this bridge, so cele-
brated for its beautiful carpentry, was destroyed by the
French troops in the year 1799. The abutments as well as
the middle pier were of stone; the longitudinal timbers or
plates were formed by uniting two strong pieces together,
en cremaillere, which were supported underneath by four
inclined struts on each side: above the platform six other inclined struts on each
side supported another longitudinal series of beams; double binding pieces hanging
perpendicularly from the upper longitudinal beams, under the eaves of the roof, held
these struts in their proper position, and prevented their springing. The transverse

Fig. 2253. SAvines.
1374
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
girders or beams which supported the floor of the bridge were suspended to the per-
pendicular binding-pieces, at a point immediately under the lowest longitudinal beams;
the top longitudinal beams were composed of five thicknesses throughout the five middle
divisions of each set of framing, and four at the two outer. Every precaution was taken
to prevent the framing from yielding in the centre or middle of the arches; the whole of
the timbers were judiciously applied, and perfectly succeeded; the platform or floor
was made with a double thickness of planks, the lowest being nailed to joists, and the
others crossing them at right angles. This bridge was not constructed in a straight line;

ወ
Fig. 2254.
BRIDGE OF SCHAUFFHAUSEN.
the middle pier being placed about 13 feet up the stream, which it was supposed would give
the structure greater strength and stability, but it trembled considerably, even from the
weight of one passenger passing over it. It was only once repaired during the 42 years
that it stood, though the oak timbers which rested immediately on the abutments and
pier, from not being thoroughly seasoned and sufficient air allowed to circulate around
them, went early to decay; to replace these defective timbers, screw-jacks were employed
upon scaffolding supported on piles, to raise this ponderous piece of carpentry in a mass,
when others were introduced.
Bridge over the Limmat, near the Abbey of Wittingen, was also erected by the same
carpenter, assisted by his brother John Grubenmann, and burnt soon after that of
Schaffhausen. It consisted of one opening, 390 feet span, with a rise of 43 feet, and was
a more solid and even superior piece of carpentry, all the timbers being well proportioned

Fig. 2255.
BRIDGE OVER THE LIMMAT, ONE-HALF.
to the great opening. The floor was sustained by two longitudinal beams on each side,
put together one over the other en cremaillere, and supported at each abutment by
inclined struts, the lowest of which were doubled: level with the plate of the roof was a
second longitudinal timber, which formed the principal support to the whole structure;
this consisted of a single thickness at the parts nearest the abutments, but increased
in number as it approached the middle, where it was composed of four thicknesses. Struts
of various inclinations were placed between these longitudinal timbers, and the whole
CHAP. XXIII.
1375
TIMBER BRIDGES.
maintained in their places by twenty-four pendant vertical binding-pieces, put at a distance
of about 16 feet from centre to centre. The ridge of the roof of this bridge, as well as that
of Schauffhausen, was supported in the centre by inclined struts, which carried the weight

Fig. 2256.
nearly to the extremities.
BRIDGE OVER THE LIMMAT.
This is the greatest span ever executed with timber, and its
radius of curvature, or curve of equilibrium, was about 600 feet.
Bridge at Zurich has a bearing of 128 feet, and is extremely simple in its construction;
the floor or platform of the bridge is sustained upon longitudinal timbers which increase in

100
Fig. 2257.
BRIDGE AT ZURICH.
thickness towards the abutments; they are sustained in a level position by eight pendant
binding-pieces, attached to another longitudinal series of beams, which are strutted on
to the abutments by eight variously inclined struts on each side.
Bridge at Ceslingen, over the Necker, upwards of 210 feet between the abutments, is another
fine example of similar construction.

F
IN
Fig. 2258.
BRIDGE AT CESLINGEN,
Fig. 2259.
1376
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Bridge at Berne, over the Kandel, was constructed by Joseph Ritter, in the year
1764; the distance between the abutments is 166 feet; their height has allowed

Fig. 2260.
BRIDGE AT BERNE.
the struts to be placed in a more judicious position, and to be inclined almost parallel
with each other; there are five on each side, of fir timbers about 11 inches square;
the longest are about 75 feet. The lon-

gitudinal timbers which carry the floor
are highest in the middle, where they are
strengthened with an additional thickness,
bolted to the upper one from below: into
the longitudinal timbers are framed trans-
verse girders at every 13 feet, which are
again diagonally braced; over them are
placed the joists and timber platform.
11
Fig. 2263.
Fig. 2261.
Fig. 2262.
Bridge over the Saone at Lyons, designed by
M. Gauthey for an opening of 164 feet, was
upon the foregoing principles: it was in-
tended that this bridge should have had three
sets of longitudinal timbers, one passing through the middle, which would have permitted
of two independent thoroughfares. Bridges constructed upon a different plan have now

Fig. 2264.
Bridge over the Saone.
succeeded to the celebrated examples just described: the art of construction had at one
time attained, it was thought, the greatest possible perfection, and Schaffhausen, Wittingen,
and others were named as works of carpentry not to be surpassed; but, renowned as
they were, the binding of timbers into arched forms has been found not only stronger, but
more economical and durable.
In the "British Carpenter," by Price, published in 1765, a method is described for
forming curved ribs to support the roadway of a bridge. He proposes that they
should rise as much as one-sixth of the intended span, and be divided into convenient
lengths, suitable to the timber to be employed: for an arch or opening of 36 feet he
makes the ribs of oak in five lengths, and 3 inches in thickness, each rib to consist of
two thicknesses, and 12 inches deep, the joints alternating in the middle of each
length, and the two thicknesses keyed together with oak keys, and he states that two
perfect ribs, so formed, would be strong enough to support the roadway.
Chazey on the Ain has a bridge of four arches, each 63 feet 6 inches span, supported by
stone piers and abutments, and this is said to be the first erected in France upon
the new principle. The platform or floor is supported by several ribs, each of two
thicknesses of timber, united by forming the sides in contact, like the teeth of a saw, one
entering the other; these ribs are the arc of a circle, and are so secured by iron bolts
that they cannot easily spring: pendant binding-pieces, radiating from the centre of the
circle, of which the arc is a portion, are attached to the longitudinal timbers which
cross the stream, and the spandrills of the arches or spaces between the curved and longitu-
dinal timbers are each filled in with two additional struts bearing upon the abutments.
CHAP. XXIII.
1377
TIMBER BRIDGES.
Bridge of Mellingen, constructed by Ritter, a carpenter of Lucerne, in the year 1794, has an
arch of 157 feet span. The two principal timber arches are arcs, equal to the sixteenth of
the entire circumference of the circle of which they are portions; they are formed

Fig. 2265.
BRIDGE OF MELLINGEN.
of six pieces of fir, each 10 inches square: twelve vertical binding-pieces are suspended
to them, extending from the plate that carries the roof to the longitudinal timbers which
support the platform or roadway of the bridge, and down to another timber arch, of a flatter
segment than those already described, formed of single timbers, and, though apparently
intended to assist in supporting the roadway, adds very little to its strength, but materially
to its weight.
Bridge of Tournous, constructed over the Saone in the year 1801, has five equal arches of 89
feet span, carried on stone piers, 16 feet 6 inches in thickness: they are arcs of circles, one-
sixth of the circumference, and each is formed of six ribs composed of three pieces of bent
timber, 9 inches in height, and 11 inches in width; the ribs are 4 feet 8 inches from
centre to centre; twelve radiating pendant binding-pieces, about 6 feet 6 inches apart,
support the longitudinal timbers that carry the platform or road; in the intervals between
these is an iron bolt, which passes through the three thicknesses of bent timbers, screws
them firmly together, and prevents their springing.
Bridge over the Seine, in Paris, erected in the year 1802, has two arches, each 104 feet
span, with a versed sine of 6 feet 6 inches: the two main arches consist of four

Fig. 2266.
thicknesses of timber, 10 inches
square, bolted together with great
care; there are no intermediate prin-
cipals, although the bridge is 32 feet
wide. An arch is thrown across
the space between them, continuing
the whole length of the bridge, and
abutting against the two principal
longitudinal arches, which
prevented from yielding to
thrust by a number of iron ties
above and below the arch, and
crossing from one side of the bridge
to the other.
are
the
The Timber Bridge at Grenelle was
an excellent specimen of an arch of
bent timbers supporting the plat-
form: there was another of this kind
constructed over the Seine at Ivry,
in 1828, by M. Emmery, who pub-
lished a description of it a few years
BRIDGE Over the skine.

目
​Fig. 2267.
TIMBER Bridge AT GRENELLE.
4 T
1378
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
:
afterwards the span of the arches was about 75 feet, and their rise about; they were
composed of three bent timbers, the lowest being of a greater depth than the others, and
were kept together by the binding-pieces which sustained the timbers on which the plat-
form for the road rested.
The Bridge over the Meuse is 60 feet span, and consists of four arches, a section of
two of which is shown in the diagram below, having the longitudinal timbers and springing

SECTION.
Fig. 2268.
bridge ovER THE Meuse.
plates placed above and below the three bent timbers: the entire width of the bridge being
about 28 feet, the distance between the arches was scarcely 8 feet.
Bridge over the Rhone is another example of supporting the roadway on timber arches
held firmly by transverse timbers bolted together above and below, into which are framed
radiating binding-pieces that abut against the under side of the longitudinal timbers.

Fig. 2269.
BRIDGE OVER THE Rhone.


ㅠ
​Fig. 2270.
田田
​Fig. 2271.
The plans of the piers and section are shown, as well as the contrivance above the piers
or protecting them against ice or trees that may be carried down by the river.
Bridge built over an arm of the Necker, at Wurtemberg, about 63 feet span, has the roadway
CHAP. XXIII.
1379
TIMBER BRIDGES.
suspended to the timber arch: this kind of hang werck, as it is termed in Germany, is the
same as that employed at Feldkirch and Mellingen.

Whee
Fig. 2272.
WURTEMBERG BRIDGE, on the necker.

Before the principle was adopted of jagging or notching the
three timbers which form the ribs, to enable them more firmly to
lock into and abut against each other, it was the custom to build
up the arches with courses of solid logs of oak, in length from 12
to 15 feet, and about 16 inches square; those were selected from
the forest which had a curve most suitable to the arch to which
they were to be applied; and in producing the requisite form
the timbers were never cut across the natural grain; they were
so laid that their abutting joints did not come over each other,
and were afterwards secured together by straps or hoops, which
surrounded them at every 5 feet distance. Much inconvenience
resulted from this method, and an arch constructed with three
bent timbers notched into each other is a rash improvement upon
it: in one instance the platform of the bridge was supported by
the sides of the polygon, and in the other by the arc of a
Fig. 2273.
circle; both required that the abutments should not yield, but
the strength of an arch formed with bent timbers is far less likely to be interfered with than
that consisting of a number of timbers arranged along the portion of a polygon; for some
of the sides lying horizontally, and others perpendicularly, it is not possible to make them
all bear equally, and resist the effort occasioned by a load placed on the centre of the
bridge.
The Bridge of Feldkirch, on the Rhine, is perhaps one of the earliest constructed upon the
principle of suspending the roadway to one or more timber centres or arches; the span is
about 65 feet 6 inches: each centre is formed of two timbers, cut and indented so as

Fig. 2274.
BRIDGE OF FELDKIRCH, switzerlaND.
4 T 2
1380
BOOK II
THEORY AND PRACTICE OF ENGINEERING.

to unite closely and firmly together; the carpentry
was well executed, all the mortises and tenons cut
with great precision, and the whole protected from
the weather by a light timber roof.
Bridge at Seurre, on the Saone, is supported upon
the ancient stone piers: the arches are 95 feet span,
and are formed of five principal ribs, placed 4 feet
9 inches from centre to centre, each composed of
three pieces, bent one over the other, each piece
being about 10 inches in width and 16 inches deep;
the versed sine is 11 feet 6 inches. The timbers
which carry the floor are 12 inches by 10, and
are supported by inclined pieces, which are not of
much utility: the eight pendant binding-pieces are
formed out of timbers 9 inches square, and iron bolts
and straps are frequently introduced to add to its
strength.
Fig. 2275.
FELDKIRCH.
The Bridge at Choisy has five arches supported on
stone piers and abutments, the span of which is 67 feet, and their versed sine 8 feet
9 inches: each of the three timbers which form them is 10 inches in width and 12
inches in height; pendant binding-pieces with iron bolts are introduced in the intervals,
to secure the bent timbers. The longitudinal timbers that carry the parapets and platform
have a double thickness over the piers; on these lie the transverse timbers that support
the planking of the floor, which is formed of two thicknesses: this bridge was completed
in the year 1811.
M. Wiebeking, director-general of the bridges and roads in Bavaria, has published many
designs of bridges executed under his direction since the year 1807, and by him the con-
struction with curved ribs has been greatly improved: instead of using short pieces of tim-
ber he employs those of considerable length,

and bends them one over the other to suit
the curve required; the number of joints is
lessened as much as possible, which renders
the ribs stronger, and less liable to decay.
The Bridge of Neucettringen, over the Inn,
was one of M. Wiebeking's first works
where curved ribs were used: it is com-
posed of five arches with stone abutments,
the span of which are 102 feet 6 inches,
and the versed sine about of their
span. The breadth of the bridge is 24 feet
6 inches, and there are but two principals to
each arch, each formed of three courses of
timbers, one over the other; the courses are
13 inches in height and width: five trans-
verse girders rest on the curved ribs, and
occupy the depth between their top
and the horizontal timbers that support the
floor; those in the spandrills have an extra
XXXX
HHHHHH
depth: between the transverse girders, which Fig. 2276. BRIDGE OF NEUCETTRINGĒN.
cross the principal ribs, are struts laid hori-
:
XXXX-CH
zontally, and the whole is pinned securely and bolted with iron into the projecting
ends of the transverse girders are framed upright posts, which are strutted and form the
parapets.
In the spandrills, or the space between the curved ribs and the longitudinal timbers
which carry the floor, are vertical timbers, called piers of tension; from these issue struts,
which are more or less inclined as they are placed farther from the abutments. The abut-
ments of the arches are 10 feet within the face of the masonry; the piers consist of a
row of nine piles, the ones inclined, to give the greater stability. Starlings are formed
above bridge: all the timbers were well pitched, and the whole was covered with planks
externally, which are removed in the fig., to show the construction.
Freysingen Bridge, over the Isar, in Bavaria, was constructed by M. Wiebeking in the
year 1808, and consisted of two arches, 152 feet span, with a rise of 11 feet 6 inches, the
radius of curvature being 246 feet: the width of the bridge is 24 feet 6 inches; there
were three sets of curved ribs in the section transversely; each arch of these sets had three
curved ribs, united at seven points by as many pendant binding-pieces, which supported
seven ranges of beams laid in the direction of the length of the bridge, with diagonal braces
between them, the joists that supported the road being laid across them. The ribs that
CHAP. XXIII.
1381
TIMBER BRIDGES.
carried the road were varied in their curve; the lowest, having the greatest, was formed
of three courses of timber, from 13 to 14 inches in thickness, and about 45 feet in length:
these timbers were bent by screws made for the purpose, and when curved sufficiently
were bolted together.

Fig. 2277.
FREYSINGEN BRIDge.
The upper arch or rib was formed of two courses of timber about 15 inches square each;
sixty-eight piles, from 30 to 40 feet in length, and 15 inches square, were driven by a ram,
the force of which was equal to 1450 pounds, 17 or 18 feet into the ground, to form each
of the abutments. The middle pier consisted of nine vertical and two inclined piles, about
17 inches square, and 45 feet in length; on the heads of these was laid a horizontal
capping, which sustained the vertical posts, against which the ends of the ribs abutted;
the posts were lined with strong oak planking, and the spandrills filled in with beton.
The exterior was cased with planks, and by jointing made to resemble a stone bridge;
to preserve the timbers every mortise and tenon was well saturated with hot oil previous
to uniting, and small channels for the water were cut in the curved ribs and inclined struts
and braces; pitch and tar were applied in abundance to all the principal timbers. After
the bridge was completed, one arch settled about 3½, and the other nearly 12 inches, which
probably arose from the difference of workmanship; this bridge was destroyed about
1809, since which it has been re-constructed on the same plan.
Bridge of Bamberg, over the Regnitz, constructed by the same engineer, in the year 1809,
has one arch, the span of which is 206 feet, and the versed sine 16 feet 6 inches, with a
width of roadway of 32 feet: the radius of curvature is 422 feet. The ribs and joists
are all of fir timber, and the cross ties and plates of oak: there are three sets of
main ribs, one placed in the middle of the width, and the other on each exterior side; that
in the centre has three ribs side by side, the middle having at the abutments five beams
in depth, and at the crown three; the two other or outer main ribs have but three courses

Fig. 2278.
BRIDGE OF BAMBERG.
of timber throughout their whole extent: the dimensions of the timbers which form these
courses vary from 13 to 15 inches square; as in the bridge of Freysingen, cross ties are
introduced between the main ribs, and the roadway is similarly constructed.
This celebrated engineer and bridge-builder erected in Bavaria many others, upon
the same principle to those already described: that at Sharding has a width of roadway of
25 feet, the span of its arches 194 feet, with a rise of 19 feet; another at Augsbourg has
its span 114 feet, and the rise of its arch 10½ inches, the radius of curvature being 158 feet;
that at Ettringen, over the Wertach, has a span of 139 feet, with a rise of 8 feet, and the
radius of curvature 305 feet; that at Irsingen, over the Wertach, 126 feet span, with a rise
of 7 feet, and a radius of 285 feet; that of Oettingen, over the Inn, 103 feet span, 6 feet
9 inches rise, and a radius of curvature of about 200 feet; that at Vilshoven, 179 feet span,
and 11 feet rise, the radius of curvature being 378 feet; that at Altenmarkt, on the Alz,
140 feet span, 13 feet rise, and 203 feet radius of curvature.
M. Wiebeking has usually given 25 feet for the ordinary width of his bridges, which is
sometimes increased to 32, and the rise of roadway is 1 in 24, which is by no means
inconvenient; he found that timber bridges would settle, when constructed upon his
principle, about 1 foot in 72, so that, to have a rise of 1 in 24 when finished, it must be
framed for a rise of 1 in 18. The proportions he gives for the rise of different spans
are valuable, as they are entirely the result of his practical observations, unmixed with any
theory; he states generally, that a tenth rise is the best proportion, but that for convenience
it is better to keep them lower: from 100 to 155 feet span, he makes the rise; for 200
feet, 1; 300 feet, ; 400 feet, ; 500; and 600 feet span, the greater the span, the
greater must be the rise.
13
12
4 T 3
1382
THEORY AND PRACTICE OF ENGINEERING. Book 11.
Bridge over the Delaware, at Trenton, in New Jersey, in America, built by Mr. Burr, in
1804, consists of five arches of different span, and crosses the river where its width is

Fig. 2279.
·160 ft-
DELAWARE BRIDGE.
--200 ft
∙180 ft.
1100 feet. The arches rise from their chord line, in the proportion of 13 to 100 feet,
and they are all segments of circles: there are in the width of the bridge five parallel

Fig. 2280.
DELAWARE at TRENTON.
rows of these arches; one traverses the middle, two are placed at a distance of 11 feet, and
admit carriages between them; the outer are at a further distance of 4 feet 6 inches,
forming two carriage and two footways.

Fig. 2281.
PLAN.
The ribs are cut from planks of white pine from 35 to 50 feet in length, 12 inches
wide, and 4 inches thick; these planks are laid close together, the joints being broken, and
having an equal depth throughout of 3 feet; they are all held firmly together by iron
straps: thus a rib is made as strong as one of whole timber, and, to prevent them from

Fig. 2282.
SECTION.
Fig. 2283.
ABUTMENTS.
springing, horizontal tie-beams are introduced, from one pier to the other, connected
by diagonal timbers with the ribs; these are carried above the spandrills of the arches,
which are filled in with diagonal braces; thus the ribs are so strengthened above and below
that they cannot easily change their form.
CHAP. XXIII.
1383
TIMBER BRIDGES.

The platform that carries the road is suspended from these five arches by perpendicular
iron rods, which hook into eyes fixed on the arches, at a distance of 8 feet apart in the
B
B
B
NII
Fig. 2284.
ARCH OF Delaware bridge.
three middle, and 16 in the two outer arches; stirrup-irons at the lower ends of these
rods receive the joists; diagonal braces unite the platform with the tie-beams, and prevent
any motion to which it would be subjected; stone piers and abutments carry this
ingenious piece of carpentry, and the whole is roofed, to protect it from the weather.
Three arches on one side are each 200 feet opening, the fourth 180, the fifth 160 feet, and
the versed sine of the largest 27 feet.
The Bridge over the Susquehanna, in Columbia, constructed in a similar manner, was com-
pleted in 1834; there are twenty-nine timber arches, each of 200 feet span, supported on
two abutments and twenty-eight stone piers. The water-way of this magnificent bridge
is 5800 feet, and its whole length, including piers and the abutments, 11 mile.
There are
three sets of timber arches, which allow of two passage ways for road and railway carriages,
the whole breadth being 30 feet.
The Timber Bridge over the Portsmouth rivers in America, built after the designs of Mr.
Bludget, has but one arch, with a span of 250 feet. The timbers are placed at a
distance apart equal to twice their own depth: there are three concentric ribs; the middle
carries the floor of the bridge; they were selected from crooked timbers, so that the fibre
might run nearly in the direction of the curves, and are connected together by pieces
of hard and incompressible wood, with wedges driven between, the ribs being mortised
to receive them; thus the three ribs are kept at a regular and parallel distance from
each other. Each rib is formed of two pieces, laid side by side, about 15 feet in length;
they are all disposed in such a manner as to break joint, the end of one piece of timber
coming in the middle of the length of the other, which is near it; their ends all abut
with a square joint against each other, and are neither scarfed nor mortised, the two
pieces of timber being held together by transverse dovetail keys and joints: all the
timbers are admirably united, and freely exposed to the action of the air; any piece may
also be removed, in case of its requiring reparation, without injury to the rest of the
structure.
The only defect in its construction is that of mortising through the principal ribs so fre-
quently for the purpose of admitting the wedges, which renders them not so strong, and
more susceptible of injury by compression; the keys and wedges effectually fill up the holes
cut to receive them, therefore it is supposed that the strength is not so much impaired. This
bridge would receive additional strength by the introduction of braces, which would
connect the three ribs together, and if of iron more firmness would be given to it.
Richmond Bridge, in America, is a fine example of lattice-work, as adapted by Mr. Town
to a span of 78 feet up to 150 feet; and as there is no lateral thrust, and materials of
small scantling are required, this system has been much adopted on the railroads: the
lattice framing is composed of fir planks, about 3 inches in thickness and 12 inches wide,
arranged so as to lie across each other at right angles; at the points of intersection they
are united by oak treenails 1½ inch in diameter, which pass entirely through them. The
depth of the lattice-work is proportioned to the span, and is about 9 feet 6 inches when the
former is 78 feet.
In the bridges constructed upon this system there are but two ribs, one under each side
of the roadway, connected together at every 12 feet by cross timbers, between which are
diagonal braces. The lattice frames are usually placed in recesses prepared for them in
stone abutments: at Philadelphia a lattice bridge was constructed, which extended 1100
feet, resting on ten stone piers; and on the New York and Haerlem railway another, 736
feet in length, with only four stone piers.
One of the chief points to be considered in the construction of large timber arches is the
lightness and elasticity of the material; for when a heavy load is placed near one of the
4 T 4
1384
Boox 11.
THEORY AND PRACTICE OF ENGINEERING.

Fig. 2285.
RICHMOND BRIDGE, IN america.
Fig. 2286.



Fig. 2287.
TRANSVERSE SECTION, RICHMOND
BRIDGE, America.
abutments, it causes a depression at one part
and an elevation at the other, which, although
apparently trifling, disturbs the equilibrium,
and racks the framing in such a manner
as to be highly detrimental to its stability.
Cross-framing, by halving scantlings together,
and attaching them strongly to a top and
bottom beam, has long been practised, and
found to constitute a very effectual truss :
but wherever they are used, they should be
covered by a roof, or protected from the
effects of the weather; for a framing com-
posed of a great number of pieces would have
its form greatly changed by any trifling con-
traction or shrinking of the several parts.
The horizontal timbers are more subject to
such an effect than those which are placed
vertically, or that receive their pressure in the
direction of their length; consequently, in
lattice bridges, great care is requisite to have
that portion of the timbers well seasoned
upon which the abutments of the several
struts are secured.
Fig. 2288.
RICHMOND BRIDGE, America.
CHAP. XXIII.
1385
TIMBER BRIDGES.

Fig. 2289.
PLAN OF RICHMOND BRIDGE.
Fig. 2290.
PLAN UNDER platform.
E


Fig. 2291.
PLAN OF RICHMOND bridge.
Bridge over the Schuylkill, at Fairmount, near Philadelphia, was designed by Louis
Wernwag, and destroyed by fire in 1838: it was a beautiful piece of carpentry, composed
of a single arch, the span of which was 340 feet, and it had no other support than that of

Fig. 2292,
BRIDGE OVER THE SCHUYLKILL.
the two abutments; the versed sine was 38 feet, and the breadth of the carriage-way 30 feet.
The principal timbers, which were of large dimension, were all sawn down the middle, for
the purpose of ascertaining whether they were perfectly sound; and when applied to the
bridge they were placed at a sufficient distance apart to allow the tenons of 29 king-posts,
1386
Book II.
THEORY AND PRACTICE OF ENGINEERING.
which radiated to the centre, to pass, without any mortises being cut to receive them;
by this means the air circulated freely round all the timbers, and dry rot was prevented:
the main ribs consisted of three double rows of timbers, laid three deep, or one above the
other, the whole bound together strongly with wrought-iron. Between the tops of the
king-posts straining beams were introduced, which kept the heads from approaching each
other, and in addition two other timbers, placed diagonally, like St. Andrew's cross, were
inserted in each of the divisions, strutting the king-posts more firmly and preventing the
arch from springing. The abutments, against which the timber arch pressed, were
of solid masonry, and carried up considerably higher than the top of the arch. The
floor of the bridge was upon girders, laid upon shoulders formed in the sides of
the king-posts, to which they were firmly bolted: on the tops of the kings, and in the
direction of the transverse girders, were the tie-beams of the roof; these latter not
only served to maintain the roof securely, but also the heads of the kings in their perpen-
dicular and proper position. The roof was lightly formed, and the sides of the bridge
were close boarded, so that the timbers, or the principles of their construction, could not be
seen.
Bridge across the Tees, with an arch of 150 feet span, and a versed sine of 16 feet, is a
bold piece of construction: the arch is formed by an upper and lower circular rib, with
vertical or rather radiating timbers between them; and the bracing or St. Andrew's cross,
inserted between each pair, gives at first the character of 28 hollow voussoirs: each
circular rib is formed of two thicknesses of timber 12 inches by 6, bolted together
with 7 round bolts, and the heading joints are broken every 10 feet in length; vertical
timbers are placed upon these ribs, 12 inches by 10, which support the longitudinal pieces
that carry the road: these are also of a similar scantling to the main ribs, and are halved
and bolted to the transverse bearers upon which the roadway is formed, which has a
clear width of 13 feet.
The abutments at each side are of red sandstone quarried out of the bed of the
river, and laid in courses with a face tooled, and a cast seating plate separates the stone
from the timber arch: the latter was placed by means of a stage formed on piles driven 15
feet apart; and when the two ribs with their radiating timbers and diagonal braces were
fixed, the wedges were drawn, and the weight of the ribs thrown upon the iron seating
at the abutments, and upon the head joints of the framing, which were protected by two
plates of lead, 7 pounds to the foot: after this the piles and stage were removed: in this
bridge there was employed 4240 cubic feet of Memel timber, and the total cost was 1200l.
Swing Bridges of Iron are now so generally adopted at docks and canals that those of
timber are scarcely to be met with: they revolve easily upon a circle, and can be moved
with the greatest facility.

ושרונר
Fig. 2293.
SWING BRIDGE of iron.
Swing Bridges over canals are simply framed and loaded at the turning end, where an
iron circle and wheel facilitate their motion in either direction: where the bridge

Fig. 2294.
SWING BRIDGE.
CHAP. XXIIÏ.
1387
SWING BRIDGES.
extends over the abutments to a sufficient distance to counterpoise its weight over the
canal a pivot, or small wheel, enables it to be turned readily. Swing bridges may be

Fig. 2295.
UTRECHT SWING BRIDGE.
constructed on the suspension principle, and made to revolve on rollers working in a
groove or iron rail: at Havre they are suspended by chains which are fixed

Fig. 2296.
SWING BRIDGE.
Fig. 2298.
HAVRE SWING BRIDGE.
Fig. 2297.
SECTION.

1388
Book II.
THEORY AND PRACTICE OF ENGINEERING.
at the two extremities of the principal timbers, and pass over an iron standard, placed over
the revolving point; in this arrangement there is considerable strength: at Honfleur the

Fig. 2299.
HONFLEUR SWING" BRIDGE.
swing bridge is suspended over a lofty standard of timber, round which it revolves :
those at Helvoetsluys swing around a pole or iron standard, being counterpoised on the

•
סם
Fig. 2300.
HELVOETSLUYS SWING BRIDGE.
banks sufficiently to prevent any inclination from taking place when the bridge is in motion.
Double turning bridges may be made upon either of the principles already described.

Fig. 2301.
DOUBLE TURNING bridge.
CHAP. XXIII.
1389
DRAWBRIDGES.
Drawbridges are another description of shifting bridges, and consist of a wooden platform,
wide enough to allow of the passage of horses and wheel carriages, and extending in length
from one side of the watercourse to the other, or from a jetty to a projecting pier on
the opposite side: whenever such bridges are adopted, the passage of the water is con-
tracted as much as possible, and only sufficient room left for vessels to pass through; by
this means, the platform is rendered as small and light as possible, without sacrificing the.
necessary strength: it is secured by pivots or large hinges at one of its ends to the jetty,
so that it can be raised from its horizontal to a vertical position, which is easily effected
by chains attached to each of the corners of the side that is unhinged, and afterwards passed
over pulleys, or hung to the ends of long levers, balanced on the top of stout posts, fixed
firmly, and braced in that position. Those formerly existing at Brussels were balanced
by weights attached to chains passing over standards that stood immediately over the
walls of the canals: they were strongly braced, and firmly kept in their vertical position

Fig. 2302.
•
DRAWBRIDGe, brussels.
by means of iron ties. That contrived by Perronet opened in the middle, to allow the
masts to pass through; by a windlass mounted in a frame it was easily manœuvred, and
raised or let down promptly.

Fig. 2303.
PERRONET'S DRAWBRIDGE, BRUSSELS.
Balancing Bridges at Brussels, to work in a quadrant of iron: when in a position
to permit a passage over them, they are supported by struts, which have a bearing on
a set-off in the masonry; when tilted up, they are maintained in that position by a rack
and pinion; at Neuf Brisack the bridge is lifted by a weight over a pulley.
1990
THEORY AND PRACTICE OF ENGINEERING. Book II.

Fig. 2304.
&
-ព..
BALANCING bridge, bruSSELS.
Fig. 2305.
The platforms of all draw-
bridges should have a pre-
ponderance, to render them
steady, when in their le-
vel position; counterpoising
weights are, however, ex-
ceedingly useful, in affording
facility in moving them when
required, and for lowering
them into their place. Draw-
bridges of considerable extent
should be formed out of
curved timbers, or slightly
cambered. Provision must
be made for the load to which
such bridges may be subject, from the possi-
bility of their being crowded with human
beings, such a load amounting to one
hundredweight at least for every super-
ficial foot, independent of the weight of the
materials with which the bridge is con-
structed: if therefore it be calculated for
three times that weight, there will not be
more than the requisite strength; and the
levers, chains, and pivots must be propor-
tioned to the duties they have to perform.
Where drawbridges were used to cross
a ditch or moat around a fortified house
or castle, they were hung so that when
drawn up they covered the face of the

D-0-0-
portcullis, and constituted a double
protection: the under side of the
platform should be cased with iron,
or rendered secure against the at-
tempts of the enemy either suddenly
to burn or cut it away. The weight
of the bridge thus increased requires
greater power to hoist it than was
ordinarily obtained by the levers and
chains manœuvred by the soldiers
stationed within the gate-house ;
Fig. 2306.
DRAWBRIDGE, NEUF BRISACE.
!
CHAP XXIII.
DRAWBRIDGES.
1391
several of the loopholes through which these levers passed may yet be traced round the
ruins of our castles.
Rolling Bridges are sometimes substituted for those which swing, the pulleys and wheels
being so contrived that a considerable length may be operated upon without danger.

Fig. 2307.
ROLLING BRIDGE,
Drawbridge, with a platform composed of three principal timbers, is made to rise by
pulling up a lever on each side, which has a pivot that works against the under side of each
bearer when it is re-

quired to be let down
and form a defence, the
frame in which the plat-
form turns upon its pivots
is first drawn up by
chains; the platform is
then swung round, and
hangs upright upon the
pivots, the longest end
descending into the ditch.
The dotted circle indi-
cates the various positions
of the platform.
The bridge called pons
subductarius was hung
at one end by a hinge,
whilst the other was ele-
vated by some such simple
contrivance as the ba-
lance or plyers; when
raised or elevated, it pre-
vented the passage
of any
one across the ditch or
moat it crossed. In many
parts of the continent the
bridges are still made to
Fig. 2308.
draw backwards and forwards, so as to prevent or afford a passage across the water,
whenever it is desired. The flying-bridge, or pons ductarius, was generally formed in a
different manner, leather boats, casks, or metal pontoons, being laid on the river and
covered with a platform of timber: they are sometimes made by attaching or hanging
several platforms to boats, then dropping them one to the other, the boats being pre-
viously anchored or moored in the middle of the river: flying-bridges are occasionally made
by laying one platform over another, in such a manner that they can be pushed forwards
upon wheels or rollers.
1392
THEORY AND PRACTICE OF ENGINEERING Book. II.

Another Draw-
bridge, by which the
platform may be first
raised from its level
and afterwards turned
up in a perpendicular
direction, consists of
two simple levers
united by a cylin-
drical shaft at the
lowest end, mo-
ving on a pivot or
hinge below, and
above is another, which lifts up the platform from
the recess into which it is laid when the bridge is level;
when so lifted it is drawn back, as shown by the dotted
lines, and turning on the upper pivot assumes an upright
position, dropping into the ditch, where it is lodged in
a recess of the masonry prepared to receive it.
Spherical Rollers for bridges of this description unite
Fig. 2309.
many advantages over the pivots, as they produce less friction and can be more easily
turned.


งบ
IDE
Fig. 2310.
Fig. 2311.
Rope Bridges are of very simple construction: upon a number of cords stretched across a
ravine or river may be placed a timber tripod framed together in a triangular shape, upon
which timber bearers may be laid, to sustain the planks that are to constitute the road-way:
the weight to be transported must guide the engineer in the number and strength of the
ropes employed, which are to be secured by piles driven firmly on each bank.

Fig. 2312.
ROPE BRIDGES.
Or a Mast may be used to sustain the ropes, when the breadth of the river is too great to
admit of the ropes being carried over in one length; the height must be governed by the
width of the stream. After ropes are secured to the shores and mast, others are suspended

Fig. 2313.
ROPE BRIDGES.
CHAP. XXIII
1393
ROPE BRIDGES.
by blocks and pulleys to carry the timber platform: such an arrangement in all probability
gave the idea of the several wire suspension bridges that have been constructed for rivers

Fig 2314.
ROPE BRidge.

H
Fig. 2315.
PLATFORM of a rope bridge.
of considerable breadth, it is often necessary to erect a framing of carpentry on each shore,
to which the several ropes which are to carry the platform are suspended.

Fig. 2316.
ROPE Bridge.
Bridges of Boats were of very general use during the middle ages, and are still found
convenient over the Rhine, and in many parts of Germany: one at Strasbourg yet remains,
upwards of 1300 feet in length, and another at Cologne: they are frequently described
by ancient authors, and we have already alluded to them. That over the Seine at
Rouen was constructed in 1700 by an Augustine monk, named Nicolas: various forms
are given to the boats, which are flat-bottomed, and placed at a distance from centre to
centre, equal to their length, or a trifle more; they are loaded with stone or ballast, so
as to enable them always to remain at the same height above the water, and are secured
together by the longitudinal timbers that pass over them, or by chains that cross diagonally
from one to the other.
Anchors dropped in the stream, to which the boats are moored, enable them to maintain
their position, and, when it is required to make an opening to let the vessels pass, two of
the boats with the platform upon them are floated on one side, and held in their new
position by anchors laid down for the purpose. The bearers on which the platform is laid
may be formed of three or more longitudinal timbers, over which are short joists to receive
the planking, or by at once laying the planks transversely on a greater number of long
timbers; the nature of the stream and the strength requisite for the bridge must determine
which method is preferable.
Floating Bridge across the Hamoaze, between Torpoint and Devonport, consists of a flat-
bottomed vessel, 65 feet in length, and in width at midships 45 feet; it is further lengthened
by a drawbridge at each end, where its width is only 38 feet 6 inches: when freighted, its
draught of water is 30 inches, and the clear depth of the hold is 4 feet 3 inches; it has its
sides curved vertically, in order that the spray may not so readily mount, and to prevent
4 U
1394
THEORY AND PRACTICE OF ENGINEERING. BOOK II.

•
D
+
1
·
口
​Fig. 2317.
BRIDGE OF BOATS.

שן
Fig. 2318.
BRIDGE Of boats.
the effect of the waves breaking over. The roadway is cross-battened, to prevent the cattle
from slipping, and the sides are fenced in the drawbridges are suspended by two three-
quarter-inch chains, one of which forms a guard-rail, and the other passes through the
engine-house, where it is connected with a small purchase machine. This bridge at the
time of low-water is passed in 7 minutes, and at high-water in 8, at a spot where the
Hamoaze is 2550 feet wide at high-water, and 2110 at low, the greatest depth being 96
feet, and at low-water 18. The current at the ordinary spring-tides runs from 260 feet per
CHAP. XXIII.
1395
CENTERING.
minute to 330, which is considerably increased when the wind is north-west and there are
heavy land floods. Two chains which pass through the bridge over two cast-iron wheels
are laid across the river, and fastened at the opposite banks; they are of inch-iron,
and each link is made to a gauge to fit the wheels and prevent its slipping off: the chaius
sink to the bed of the river when the bridge is alongside either shore, and as it is put in
motion, they form arcs of a circle, the ends on shore, to which weights are attached, rising
and falling from 5 to 8 feet in the shafts made to receive them.
Two steam-engines, each with a cylinder of 19 inches diameter, and 2 feet 6 inches stroke,
working at a pressure of 3 pounds per inch, and at an average speed of 35 strokes per
minute, is the moving power; these turn a shaft, at each end of which is a large cast-iron
wheel, whereon the guide chains rest. To prevent the chains which cross the Hamoaze
from becoming tight and impeding the navigation, their ends have heavy weights attached
to them, in shafts 25 feet deep and 16 feet square, at the head of each landing-place, the
weights being of cast-iron, each loaded with 5 tons; these enter the shafts over cast-iron
sheaves, 2 feet in diameter, so that when there is a strain upon the chains the weights
rise and fall. The feeding water, which supplies the one boiler common to the two
engines, is obtained on the eastern shore, and the waste steam is made to pass into the tank,
where it assists in raising the temperature of the water contained in it.
Centres. The systems laid down for the construction of roofs, particularly those having
a convex form, as domes and cupolas, apply also to that of centres: a pair of principals
may equally serve for the construction of an ordinary roof, as for the formation of a centre,
care being taken to give it strength in the parts where the greatest weight is deposited;
this strength varies according to the nature of the material to be supported: brick, rubble,
and freestone, differing in weight, require different degrees of support.
Timber Centres, formed of a series of principals or trusses, are always adopted when the
arches are of freestone and strength is required; in constructing the arches of a bridge of
any considerable diameter, where the form is that of a semicircle, or semi-ellipsis, after the
voussoirs are laid to a certain height, the timbers of the centre are compressed, occa-
sioning the crown or upper portion, which is not loaded, to spring, producing a con-
siderable change of form; this inconvenience is only to be obviated by loading the summit
as the process of laying the voussoirs advances; but this precaution will not prevent the
centre from altering towards the haunches: whenever a tie-beam is omitted in that part
where the greatest pressure occurs, compression and change of form are the consequence.
Centres with tie-beams are always to be preferred to those formed by parts of polygons
inscribed within each other; when constructed without horizontal timbers, in the direction
of the greatest compression, they must yield very considerably, occasioning great de-
rangement and inconvenience: various principles have been acted upon in later times for
setting out centres, and for the disposal of the principal timbers.
M. Lorgna, of Verona, in a work
entitled Saggi di Statica e Mecanica
applicate alle Arti, gives the dia-
gram here introduced: but the tim-
bers C, D are too much inclined,
as are those at E,G, to have the
requisite effect; the pendant timbers
AZ, BT, are not well placed, and
the small struts h,i, are not calcu-
lated to discharge the several weights
F,A,B, I, resting on the centre, which
are expressed by the balls a,b,c,d.

•
о
B
T
о
b
с
d
Fig. 2319.
The art of disposing various lengths of timber, so as to form a perfect centre, capable,
without undergoing any change in its form, of carrying the weights of the voussoir throughout,
until the key-stone which locks the whole is placed, and to determine the scantling for
the various pieces composing it, requires greater knowledge than is usually possessed
by the ordinary builder. Rondelet observes that mathematicians, who have written
largely on the subject, have not entered sufficiently into detail to make their labours
practically useful; their theory is so general that it cannot be applied to particular cases;
and when it is considered that their formula does not embrace every quality that the
materials may possess, or comprise the kind of workmanship adopted in putting the pieces
together, it is not surprising that the results are so much removed from truth, and that there
should be such material differences between those who practise the art of construction.
After examining with the greatest attention all that Pitot, Couplet, Freziers, and
Lorgna of Verona had written, Rondelet found that their theories simply proved, that
all the pieces of timber composing a centre ought to be so combined as to support
in the most advantageous manner possible all the stones or voussoirs, which were supposed
to slide in their joints, more or less, according to their inclination as the surfaces of stones
:
4 U 2
1396
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
are not sufficiently smooth to slide, unless the plane on which they are placed ceases to be
horizontal, experiments have been made to ascertain at what inclination they can support
themselves; and it has been found that hard stone, which slides most easily, does not begin
to do so until inclined about 300. The same experiments made with stone bedded in
fresh mortar give for hard stone from 34° to 36°, and for soft, which by absorbing the
moisture of the mortar forms itself into a body almost immediately, up to 45°, when
the centre of gravity of the stone does not fall out of its base. Thus by taking 30° for
the point where the voussoirs begin to slide, we are sure of results above those which
experience would give; whence it would appear that the centre ought only to begin
at that height. In several constructions of ancient bridges, such as the Pont du Garde
and Ponte Sisto at Rome, we still sec
the projecting stones on which the bases
of the centres were placed; they are
from 25° to 28° above the springing;
nevertheless for centres of vaults of great
diameter, the tie-beam of which is re-
quired to be supported at a certain
distance, it is better to begin the centre
at the springing, so as to strengthen the
tie-beam underneath. The weight on
the centres is not material until above
30°; it then goes on augmenting with
the voussoirs, until the key is placed
which supports the vault and relieves
the centre of its weight.
In order to find a combination of
pieces of timber which shall resist the
efforts of the voussoirs, we must first
determine the position of the tie-beam.
For this purpose, whatever may be the
centre of the arch, whether lofty,
a semicircle, or an ellipsis, draw from
the points A and D, figs. 2320, 2321,
2322, 2323., two indefinite tangents
which meet at the point F, through
which draw a perpendicular to the curve;
the point K, where it intersects, will
determine the position of the tie-beam :
having then divided the part KD into
two or three parts, in proportion to
its developed length, draw through the
points of division E and G other per-
pendiculars to the curve, which will
indicate the position of two intermediate
king-posts. From the point I, where
the direction of the first will meet the
tie-beam, draw the line HIL, which
K
D

E
L'
K
H
R
T
Fig. 2320.

D
T
H
Fig. 2321.
will indicate below the position of an inclined piece to support the bearing of the tie-beam,
and above, that of a brace to sustain the top of the king-post LT, supported on the other
side by the brace LH, which abuts against the king-post of the centre.
below the tie-beam will be divided into two, three, or four parts in proportion to
its length, through which must
The part
D

E
be passed the binding pieces R, S, F
to support the inclined pieces,
posts and braces which unite
these, as well as to prevent their
yielding in the direction of their
length.
The scantlings of the various
timbers must be found in the
manner before indicated, taking
care to observe which are pressed
in the direction of their ends,
and which in their width, and
it is important to consider that
it is not only requisite that each
of these pieces should have
A
H
Fig. 2322.
ન
T
CHAP. XXIII.
1397
CENTERING.
strength sufficient to resist a
portion of the weight which
is applied to it, but also to resist
any effect arising from partial
movement, or from imper-
fections in the timber or in the
workmanship of their framing.
Timbers, which have great
weights to support, and which
are pressed in the direction of
their length, should be as many
inches square as they are long
in feet, or from a twelfth to a
tenth of their thickness in length:
when drawn in the direction of R
their length, from a thirtieth to
a twenty-fourth: and bearers,
loaded at right angles, or per- ▲
pendicular to their length, from
a twenty-fourth to an eighteenth.
A centre for a semicircular arch
with a tie-beam may be determined
according to the rules before given :
for an ellipsis the same rule is
applicable: for an elongated ellipsis,
the timbers may be similarly ar-
ranged.
H
R
S
S
גז
12
D
F

T
Fig. 2323.
D
F

Fig. 2324.
N
D
Κ
F
In examining the stiffness of cen-
tres, the chief point for our consider-
ation is, where do the arch-stones
first begin to press upon them,
and what is the pressure exerted
by the several voussoirs? We have
seen that stone placed upon an in-
clined plane does not begin to slide,
unless it slope a little more than
30° from the horizontal plane; con-
sequently any stone which did not slide
upon its bed would not bear at all upon
the centre. Hard stone laid in mortar
slides when the angle is beyond 34°, and
one of a soft nature will remain firm
when the angle which its joint makes
is as much as 45°; this point has been
termed the angle of repose, and if we
suppose the pressure to be represented
by the radius, the tangent of the angle
will represent the friction; hence if we
call the pressure unity, the friction will
be 0.625, or according to Perronet 0.8.
The next course of voussoirs after the
angle of repose will press upon the centre, as will every succeeding course, with an in-
creased weight. The relation between the weight of a vcussoir and its pressure upon the
centre in a direction perpendicular to the curve of the centre may be determined by the
following equation, W (sin. a - ƒ cos. a) = P; where W is the weight of the arch-stone,
P the pressure upon the centre, ƒ the friction, and a the angle which the plane of the lower
joint of the arch-stone makes with the horizon.

H
When the angle which the joint makes with the horizon is
Fig. 2325.
34°
36
38
40
42
44
46
1
P = '04 W
48°
P = 33 W
P
= '08 W
50
P
= ·37 W
P
- •12 W
52
P
་་
•40 W
P
= ·17 W
54
P
P
= '21 W
56
P
P
***
•25 W
58
P
=
= '44 W
- '48 W
52 W
P
= 29 W
60
P
=
·54 W
413
1398
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
When the plane of the joint becomes so much inclined that a vertical line passing
through the centre of gravity of the voussoir does not fall within the lower bed of the
stone, the whole weight of the voussoir may be said to rest upon the centre. If it be
required to determine the weight of any voussoir, we must take from the table the
decimals opposite the degrees at which it is laid; for example, to obtain the pressure
upon the centre of the twenty degrees which commence at the joint: making an angle of
32° with the horizon, or from 32° to 52°, we must add them together, and multiply this
sum by the weight of that portion of the voussoirs comprehended between 2°, and the pro-
duct will be the pressure of 20° of the arch upon the centre. Supposing the frames of the
centre to be 5 feet apart from the middle of each, the depth of the voussoirs 4 feet, and the
space comprehended between 2° of the arch, measured at the middle of the depth of the
stone, 1.5 feet, the solid content of which is 30 cube feet, the weight of 1 foot being 150
pounds; the weight of 2° will be 30 x 150=4500 pounds: adding the decimals together
from 32° to 52°, the sum is 2.26, which multiplied by 4500, gives 10·170 pounds for the
pressure of 20 degrees.
The two middle arches of the Bridge of Cher, near Tours, one 62 feet, the other 59 feet,
has centres formed upon this construction.

•
Fig. 2326.
BRIDGE of cher.
At the Bridge of the Assise, near Tours, where the arches had 64 feet span, and the thickness
of the arch was 3 feet 2 inches, this sort of centre was also used: the stone employed was
of the ordinary weight, and the principals which formed the centering were placed 6 feet
apart.

Fig. 2327.
·
BRIDGE OF L'ASSISE, NEAR tours.
•
CHAP. XXIII.
1399
CENTERING.
Perronet's system of forming Centres was to omit the tie-beam, and from his elegant work
on bridge-building a few examples are selected: this engineer imagined that when the

*
Fig. 2328.
CENTRE, 76 feet span.
timbers were prolonged they found a portion of their support in the opposite sides of the
arch; a centre so contrived may be regarded as composed of a number of trusses or framed
voussoirs, and are subject, as he found, to great disarrangement, if not loaded very carefully.

-----------
Fig. 2329.
CENTRE, 64 feet span.

The centres used by Labelye for the
construction of the arches of Westminster
Bridge were an improvement upon those
of Perronet, and calculated to bear more
equally the weight that was placed upon
them, see fig. 429. p. 424. The centres
for Blackfriars Bridge were contrived partly
upon Labelye's and partly upon Perronet's
principles, but they were supported upon in-
clined timbers, which greatly assisted the
wedging up and gradual lowering of them
after the last voussoir was placed; see fig.
432. p. 428.
That of Cravant, situated on the River Yonne,
had a span of 64 feet and a rise of : there
Fig 2330.
were five trusses or sets of principals, placed 5 feet 6 inches from middle to middle; each
was composed of three triangles, the larger timbers of which were from 16 to 19 feet in
length and 10 inches square; the pendant binding-pieces were nearly 8 feet in length, and
of the same scantling. The thickness of the arch at the key was 4 feet 3 inches: the
4 U4
1400
THEORY AND PRACTICE OF ENGINEERING.
BOOK II.
stone employed in its construction was of the ordinary weight; this centre was found teo
weak for the purpose.

$
Fig. 2331.
CENTRE, 64 FEET SPAN.
The Arches of St. Edme were 95 feet 6 inches span, and rose 27 feet 8 inches: the
principals forming the centres were five in number, and placed 7 feet apart. The tim-
bers used in their construction varied from 19 to 24 feet in length, were from 15 to
16 inches square, and sufficiently strong for the purpose; the thickness of the arch at
the key was 4 feet 10 inches.
The Centres of the Bridge at Mantes, contrived by Perronet, show the care and attention
he bestowed upon this portion of his constructions, and the ability he evinced in forming

•
8 8 8 8 8 8
仁
​क.
Fig. 2332.
BRIDGE at mantES.
the temporary bridge and scaffolding for the purpose of hoisting them was equally
admirable. The thickness of the arch at the key was 4 feet 4 inches, and it continued
CHAP. XXIII.
1401
CENTERING.

Fig. 2333.
ות
או
IL
BRIDGE AT MANTES.

45
ита
Fig. 2334.
רא
XI
LX
I
BRIDGE AT MANTES.
IM
LIX
*
the same throughout to its abutments; as there were six principals or ribs to each centre, it
required considerable power to raise them into their places, which was well accomplished
by strong tackle attached to lofty poles.

We have evidence that this system
of Perronet's was previously adopted
by Hardouin Mansard, when the
bridge at Moulins was constructed
under his direction, and it would
appear at first sight that the timber
was placed in a manner to be sus-
ceptible of the greatest resistance:
but it has not always succeeded
well where it has been applied; the
multiplicity of timbers occasions
too much play about their joints,
and centres so formed are very
liable to change their figure. The
centres of the bridge at Mantes, the
ribs of which were 6 feet 6 inches
apart, were formed of four courses
of rafters or inclined pieces 18 inches
square, and their settling was found

Fig. 23.5.
CENTRES Of arches.
Fig. 2336.
to be very considerable; when the voussoirs were placed at the haunches, the centres bent
under the weight, and rose at the summit, which it was necessary to load considerably,
to keep the centres in their true form.
1402
THEORY AND PRACTICE OF ENGINEERING.
BOOK II.
The Centres of the Bridge at Neuilly were similar to those at Mantes, and the span of the
arches was equal to that of the great arch of the latter: but this is not so flat, and although
the thickness of the arch be less than that at Neuilly, and the principals only 6 feet 6 inches
distant from each other, they were found to be too weak: each principal had seven or

Fig. 2337.
•
BRIDGE OF NEUILLY.
•
eight timbers split
throughout
their
length, others were
bent, and their extre-
mities penetrated into
the faces of the binding
pieces the settling of
the arches being very
considerable, it was ne-
cessary to load the
centres with a weight
nearly equal to 600
tons: when the arches
were ready to be closed,
and only seven courses
of voussoirs remained
to be placed, the gene-
ral settlement of the
centre was more than
an inch in 24 hours,
and it would have
been still greater, but
for the celerity with
which the work was carried
on, and the precaution taken
to strengthen it by braces ex-
tending from one principal
timber to the other, and by
placing struts between the
courses of the opposite
voussoirs. The openings
in the framing were caused
by the timbers not bearing
equally against the binding-
pieces throughout the whole
surface of their extremities,
and an attempt was made to
correct this defect by cutting
Fig. 2339.
each extremity in the form of an arc of a circle: this disposition, which was adopted
at the bridges of St. Maxence and of Concord at Paris, was successful in preventing the
inclined timbers from splitting, but they continued to penetrate into the binding-pieces;
it also increased the play of the framework, and rendered the centres more susceptible


Fig. 2338.
BRIDGE OF NEUILLY.
CHAP. XXIII.
1403
CENTERING.
of changing their form. The ends of the two inclined timbers in the upper part might be
framed with bevelled shoulders, thus making them bear upon each other; the binding-
pieces would continue to embrace them, and the whole being consolidated by bolts would
be more firm.
In forming the centre of a bridge, the weight should be equally borne throughout, and
the parts should be made sufficiently strong to support any portion or the whole of the
pressure to which it is submitted; wherever the timbers abut end to end, a socket of iron
should be used, as was done in the centre of Waterloo Bridge, London. The timbers should
intersect one another as little as possible, and should never be halved or cut into, as either
practice causes a great loss of strength.
The Centres used at the Bridge of Orleans were not sufficiently strong as originally
projected, and some braces were added to it in the course of the construction, extending
from one principal to another. The scantling of the timbers was about 15 inches square,

R
Fig. 2340.
CENTRES OF BRIDGe of orleans.
that of the braces 9 inches, and that of the needles 16 inches: these centres were successful,
and proved of sufficient resistance, although not very much loaded with timber: they were
composed of fewer pieces, which rendered them less liable to change form, which a weight
of 100 tons was sufficient, when placed on their summit, to prevent.
Fig. 2341.
a
8
h
CENTRE OF THE BRIDGE AT NEMOURS.
Fig. 2341. represents the centre used at the bridge of Nemours on the Loing: in an arc
so flattened, the whole arch bears equally on the centre, and removing the wedges
becomes very difficult: striking the centre
was in this instance effected by destroying
by degrees the extremities of the second and
third rows of inclined timbers, at the point
where they framed into the side timbers;
the centre, being no longer sustained except
by the upper row, sunk a little, after which it
was easily taken down. The centres employed
in the construction of the bridges of Neuilly
and Mantes have but little strength, notwith-
standing the quantity of timber employed
in them, each course of which may be con-
sidered in such centres as an assemblage of several levers, united at their extremities by
hinges or turning joints, and loaded with different weights; we know that the equilibrium
of such a system depends on certain conditions, which are the same as in the polygon, so
that the length of the levers being given, their respective inclination depends on the weights
which they support, and are functions determined by those weights: before the centre is
loaded by the voussoirs, it is in a state of equilibrium; but it is no longer so when the
first voussoirs are laid, and the centre would crush if no attempt were made to establish
the equilibrium, by loading the upper parts provisionally; by the advancement of the work,
the equilibrium is again broken, and fresh settlements arise, which would become dangerous
if the weight on the top were not increased, and the arch completed as quickly as possible:
thus at different periods the equilibrium is alternately broken and re-established, and the
centre is in a continual movement during the whole time of the construction.
Several engineers have believed that this movement of the centre during the placing of
the voussoirs, far from injuring the construction of large arches, serves on the contrary to
ensure it.
A distinction has been made between fixed and movable centres, and the pre-
ference has often been given to the latter; the only reason for this preference must arise from
the idea that a movable centre yields to the settlement of the arch, which, with the com-

1404
Book II.
THEORY AND PRACTICE OF ENGINEERING.
pression of the joints, begins before the striking of the centre, and even before the arch is
closed; by the time the centre is struck, the mortar has already acquired much con-
sistency, and no sensible change can happen in the figure of the arch: but it is very
easy to imagine that a centre composed so as to remain fixed during construction should
have the same properties; for whatever may be the system of the carpentry of a centre, in
gradually destroying the points of support on which it is placed, its resistance may always
be insensibly diminished, leaving it the necessary strength for supplying that which the
arch has not yet acquired; which resistance should continue until after the joints having
been compressed as much as possible, the arch can sustain itself, and is no longer susceptible
of any movement. The only precaution to be used is not conducting this operation with too
great rapidity.
The question of fixed and movable centres was examined by the engineers of the Ponts
et Chaussées in France, on the occasion of the construction of the arch of the bridge of
Jena, and they decided in favour of the first; the success attending the execution of these
arches confirmed the propriety of this decision. With respect to the system of carpentry
to be employed for fixed centres, it appears that, in order to have requisite solidity, they
should be composed of three parts at most, the two inferior ones immediately resting on
corbels placed at the springings, to carry the upper parts; by such an arrangement there
will be no tendency to a change of form, at any epoch of the construction of the arch;
for it is evident that the only condition necessary for the equilibrium is, that the number
of the voussoirs at the springing should be the same at each side.
Fig. 2342. represents a centre formed after these principles, for the construction of
the arches of the bridge of

Moulins, which was built on a
general radius, on which was
established a centre, on points
of support taken on the same
radius, evidently producing
the greatest solidity: the prin-
cipals were distanced at 7 feet
from centre to centre, and main-
tained by horizontal binding-
pieces, and by St. Andrew's
crosses; the timbers were
inches square.
The centres of West-
minster Bridge, constructed
by Mr. King, were an im-
provement upon those de-
signed by Perronet. Two
timbers resting on the
abutments incline, and
meet at the top of the arch,
forming a large triangle;
this is crossed and braced
again in various directions,
forming as it were seven
large voussoirs: there is
considerable strength in
13
Fig. 2342.
CENTRE AT MOULINS.

10000000
Fig. 2343.
CENTRE AT WESTMINSTER.
such an arrangement, and it combines a portion of the principles afterwards adopted with
so much success.
Centres of 130 feet span have been formed by vertical and horizontal timbers braced
by others in a diagonal position: they are exceedingly simple, and are easily put
together and taken down: the upper portion is contrived to rest on wedges, and can be
lowered without disturbing the rest; and by striking the inclined supports at bottom, their
position can be altered when required.

Fig. 2344.
CENTRES OF 130 FEET SPAN
CHAP. XXIII.
1405
CENTERING.
The Coldstream Bridge
had a frame with a tie
and a series of braces
united; this truss sup-
ported on each side a
portion of the centre, or
the ribs, on which were
laid the planks for turn-
ing the arch; this was de-
signed by Mr. Smeaton.
The Centering used by
Mr. Telford at the bridge
of Cartland Crags pos-
sessed considerable no-
ANNONS - - - ~ - ~~JARAN SAODINGNANAMNJAJANAM NARASANNONNNNNAANAN

Fig. 2345.
CENTRE OF COLDSTREAM BRIDGE.
velty, and was well adapted for its purpose: as the piers were built, care was taken to
provide for a lodgment of the inclined timbers which were to support the second platform,
on which the centre was to be constructed to carry the whole of the arch above it.
The

temporary platform on which the materials were
brought, previously to lowering to their place, rested
upon the centre, and by its weight assisted in steadying
the work.
VA
0
Fig. 2346. CENTRE OF CARTLAND CRAG BRIDGE.
Centres made use of for Tunnelling
do not require to be always timbered
throughout; although as much or
greater care is necessary for their
Fig. 2347. CENTRE FOR A TUNNEL.
1406
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
formation as for those employed in the construction of the arch of a bridge. When the
width of the tunnel and the earth which is to be removed will permit, a way may be
driven on each side, and a portion of the earth or rock left in the middle, or at the two
sides, upon which the timber centre may rest until the entire arch it is intended to sup.
port is completed. many tunnels have been cut through the chalk hills, with a parabolic
curve given to their centres, two masses of chalk having been left to support their lower
timbers.
In the former portion of the work, we have given the design and description of the
centres used at many of the bridges erected during the last century, and to them we
must refer the reader; those used for the construction of the bridges of London and
Waterloo are particularly worthy of observation.
On Pitot's manner of
determining the Strength
and Power of Centres.
One of the first consider-
ations he gives this sub-
ject is to determine the
effort which the centre
will have to make, in
resisting the pressure at its
various parts; or what it
will have to bear, at dif-
ferent portions of time,
whilst the voussoirs are
fixing; the centre not
being at all times equally
loaded, the dimensions of
the timbers must be pro-
portioned to the burdens
placed upon them, and this
often before the load is
equally distributed.

Fig. 2348.
CENTRE FOR A TUNNEL.
M. Pitot has calculated the scantlings of the timber ribs for a semicircular arch
60 feet span, the stone ring that formed the first row of voussoirs being 7 feet in
thickness. The timber was oak, and he states that a square inch will carry 8640 pounds
weight with perfect security and for any length of time: but as knots and shakes may
occur, in order to be on the safe side, he only calculates upon 7200 pounds as the
measure of absolute strength. The entire weight resting on each rib or principal was
707,520 pounds, the weight of a cube foot of stone being 160 pounds. M. Pitot has
in this case assumed a much more considerable weight than could occur in practice, as no
arch of such a span could ever require a depth of voussoirs equal to what he has given.
In a semicircular arch the voussoirs would not deposit much or any weight upon the
centre, until the joints began to form a greater angle than 30°, as before observed;
consequently the pressure on each rib would be diminished at least three-fourths of the
entire load, and 555,908 pounds of stone would be the quantity resting on one rib, or eleven
parts out of the entire fourteen.
The dimensions of the timber forming one of the ribs were as follow: the exterior
curved rib, cut to the form of the intrados, was in several lengths, no part less than a
foot in width, and the whole 6 inches thick, all framed and bolted together; the main
stretching piece or horizontal tie-beam, as well as the under one, were each 12 inches square :
the king-post 12 inches square; the upper struts 10 inches by 6, and the lower 10 inches
by 8; each rib has to carry 555,908 pounds, or of the entire weight of the stone ring,
and as the lower portions of the arch on each side were nearly perpendicular, the curved
outer rib would have to bear 7200 pounds weight on every square inch of sectional area.
The scantling being 12 inches by 6, the area is 72 square inches, and this multiplied by
7200 gives 518,400 pounds as the quantity of support that each end of this timber will
afford the lower struts will, after the same calculation, sustain 576,000 pounds; their
inclination has not been considered, as it does not materially affect them.
We shall find that the strength of the outer rib, or timber ring of this centre, will
have a power of sustaining 1,036,800 pounds; and if we add to this 576,000 pounds
for each of the four lower struts, we shall obtain 3,340,800 pounds strength to support
a load of 555,908 pounds. But as this load does not press perpendicularly on the
supports, it is necessary to carry the investigation further, and to determine the value
of the oblique forces, by reducing them to a parallelogram, with sides proportionate
to each force, and thus acquire the exact result. To do this a scale of equal parts may
be set out, from which may be taken the lengths of such sides as are proportionate to the
existing forces, and then measure the results by the same scale; the scale should be divided
CHAP. XXIII.
1407
CENTERING.
into parts representing 576,000; this must be set off upon each of the lower struts, to
express their sustaining force, which is shown by the dotted lines at, as; and as the
exterior strut receives some assistance from the outer arched rib, to the extent of 518,400
pounds, we must set off this quantity in continuation of these lines from t to e, which will
form one side of the parallelogram ae; the other side will be as. The parallelogram is to

m
k
A
Fig. 2349.
PITOT'S SYSTEM.
be completed by drawing sx and ex, equal
in length and parallel to their opposing
sides. A line drawn diagonally, as ax, will
then express the supporting strength of all
the pieces, supposing the pressure had been
in the direction of the diagonal, and as the
maximum of the weight is in the perpen-
dicular direction, and not obliquely, we
must let fall a perpendicular from the point
z, and let this line cut the base line of
the arch; then the distance ac must be
set off upon it at b, so that ac shall be
equal to cb.
From the point b, draw a
right line parallel to ax, of the same
length, which will cut the perpendicular
y; join xb, and draw ay parallel to it;
the parallelogram axby will be
at
com-
pleted, and xcy is a vertical diagonal, the proportionate length of which will express
the strength of the rib; this upon the scale will be found to be 2,850,000 pounds,
making the centre equal in strength to more than four times that required for the
load it has to support.
All the timbers in the upper part of the centre may have their
strength calculated in the same manner as we should proceed for a pair of principals
with a king-post, making due allowance for the extra support given to a centre by the
outer arched rib, which does not exist in a roof. The force of each strut being taken at
432,000 pounds, and that of the curve at 518,400, we must draw two lines from the
middle of the top of the king-post, viz. mv, parallel to the lower strut c, making its length
equal to 432,000, and the second line, upon the upper strut ms, must also have a similar
length added to 518,000, or 950,000 pounds given to it. Complete the parallelogram
msrv, and draw the horizontal line rk, from the lowest point of the parallelogram, cutting
the line mq in k, and make kq equal to km; then mq will represent the weight that can be
carried by the upper portion of the centre, which will be found equal to 1,160,000 pounds,
greatly exceeding the strength required. The chief part of the load is sustained on the
upper portion of the centre, therefore it requires that the struts should have had a greater
scantling than the lower, although there is abundant strength throughout. The strain
of the stretching-piece A A is denoted by rk and mg, which is the actual load sustained
by the upper portion of the centre; one-sixth part or less of the strength of the cohesion
of this stretching-piece is sufficient for the horizontal thrust to which it is exposed.
1408
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
These researches were made in the year 1726, and inserted by Pitot in the memoir of
the Academy; they are founded on the hypothesis that the voussoirs are very numerous,
and capable of sliding without any friction; consequently Pitot has valued the weight,
therefore, which rests on the centre as too high.
Couplet has also examined the weight supported by centres, in his memoir of 1729 :
referring to arches composed of polished voussoirs, he remarks, and with reason, that on
each side, starting with the springing, there is a certain number of voussoirs, which do
not bear any weight upon the centre; and seeking the length of the arc embraced by these
voussoirs in the semicircular vault, he finds it equal to the third of a quarter of a circle,
a result which, being independent of the thickness of the arch, could only be exact in a
particular case. With regard to the relation between the load which the upper part of
the arch makes the centre support and its absolute weight, Couplet arrives at a result
different from that of Pitot, and points out the error into which this latter had fallen :
we will not enter further into these details, the inaccuracy of which is generally ac-
knowledged.
U
M
T
It is known that in an arch extradossed the first courses support each other, without
the assistance of a centre, so that it does not receive any load from it, until the
plane of the joint makes with the horizon an
angle, the trigonometrical tangent of which is
equal to the relation of the friction to the
pressure. It appears that when the voussoirs
are placed on wedges, and laid dry over each
other, this relation should be equally valued
nearly as O is to 8, whence it results that the
voussoir which begins to make the centre ex-
perience a certain pressure should have the
plane of its joint inclined about 42° to the
horizon as to the value of this pressure, which
acts perpendicularly to the surface of the centre,
calling a the angle of inclination of the plane of
the inferior joint, m the weight of the voussoir, ƒ the relation of the friction to the pressure,
it will be expressed thus,

S
m ( sin. a - -ƒ cos. a)
D
R
A
Fig. 2350.
The weight of the centre may be valued by calculating the value of this expression, for the
different courses which shall be successively placed, until we arrive at a voussoir, M, so
inclined that the vertical passing by its centre of gravity falls on the edge, R, of the voussoir
immediately beneath it. There then happens one of two things, if the angle TRD, formed
by the surface of the centre with a horizontal line DR, be less than 42 degrees, the
voussoir M will sustain itself on the centre, without leaning on the inferior voussoirs; but if
that angle be greater, the inferior voussoirs will carry a part of the weight of the voussoir
M. It is easy to convince ourselves that the latter of these two cases hardly ever occurs,
and that the first is the only one necessary to take into consideration. Starting from the
voussoir M, the load of the centre may be estimated by the entire weight of the voussoirs :
the position of the voussoir M depends moreover on the curve of the vault, and on the
relation of the dimensions of the voussoirs.
Let us suppose that the head of the voussoir M be a rectangle, U R will be the vertical
passing by the centre of gravity, and the triangles URT and TRD being similar, we
RT
shall have tang. TRD= but if the angle TRD be the angle of friction, the tangent
TU
ᎡᎢ
TU
of this angle will be =0·8; then we shall have also, 0-8, that is to say, that the width
of the youssoir will be of its length. Now the width of a voussoir, in large arches, is
at the most only or of its length; consequently the angle TRD will be less than the
angle of the friction; but if in the first moment the voussoir M, and those which follow
it, do not exert any action on the inferior voussoirs, it is not the case when the settling
of the centre takes place. As this settling cannot continue without obliging the arc A Š
(fig. 2351.) to become shorter, this arc resists, as a portion of the arch, the pressure which
exerts itself at its superior extremity; as long as that pressure is not strong enough, it pre-
serves its form and position; it is the voussoirs situated above M which yield by spreading,
but as soon as there is placed above M a sufficient number of courses for their stability
to be superior to the resistance of the portion of the arch A S, this latter breaks in two
parts, which tears the centre asunder; two points of rupture are the result, at the extre-
mities A B and RS, and a third at a certain point, such as KL, the position of which
latter joint is determined by the condition that the momentum of stability of the two
parts A L and LR, taken with relation to the point B, be equal.
When an arch is constructed at the moment the rupture takes place, and the arc A S re-
CHAP. XXIII
1409
CENTERING.
I
M
R
* U
moves itself from the centre, the first joints of the extrados
towards the point I are seen to open, and this effect con-
tinually augments with the settlement of the centre, until the
placing of the keystone; then the effects change their nature,
because the voussoirs of the upper part being able to sustain
themselves, without the assistance of the centre, the equi-
librium tends to establish itself in the entire arch, and no
longer in the portion A S. The point of rupture is then no
longer situated in KL; it rises higher, and therefore at this
period the first joints, which had opened at the extrados, are
closed, and others open at joints farther removed from the
springing. It is now evident that the lower part AR of the
centre will find itself entirely disengaged, but that the part
RC, besides the weight of the voussoirs R, X, will still sup-
port a certain pressure, resulting from the thrust of the rampant arch AS: it will be
easy, knowing the weight of the portion KS, to have the value of that pressure which
will be directed, following the line SF perpendicular to the joint SR, which will meet
the vertical in F, passing by the common centre of gravity RX; then, supposing the
pressure which exerts itself according to SF, and the weight of the voussoir RX, ap-
plied at the point of meeting, F, of their directions we should take the result of these
two forces, which will be directed, following a line such as FH, and will represent the
total burden supported by the centre: an equal force will be furnished by the other half
of the arch.

A
B.
Fig. 2351.
The effects alluded to are equally evident in a semicircle, or the segment of any kind,
unless the latter is so flat that the first voussoir from the springing leans entirely on the
centre; in this case the weight of the centre is due solely to the weight of the voussoirs, and
the calculation of this weight becomes simple, and may be readily continued for every
period of the construction; thus the first part of the study is resolved by considerations,
exactly agreeing with the observations and experiments that have been made, and form a
necessary addition to our knowledge on the theory of arches.
The forces which act on the centre at the different epochs of the construction being
known, it will be very easy to determine the loads supported by the different pieces of
carpentry, whether parallel or perpendicular to their length, and it would only remain to
proportion their dimensions to these loads. Gauthey has given an example of this kind of
calculation, which he has applied to the bridge at Nemours. The effort of the weight
of the arch is transmitted first to the first row of inclined timbers, but the pieces of which
it is composed, slanting very little towards each other, can scarcely offer any resistance; the
slightest settlement carries back the weight on the second and third rows, so that the first
must be considered as destined only to receive the voussoirs, and to transmit their weight
to the pendant binding-pieces: by observing that the principals of the centres support
2.05 metres of length of arch, that the specific weight of masonry is 2·6, and having regard
to the different heights of the section of the voussoirs carried by each binding-piece, it is
found that the weight of the binding-piece ab is 18,789 kilogrammes, and that of the
binding-piece gh is 14,696 kilogrammes.
We must remark that each of these binding-pieces bears on the meeting of two pieces
of one of the lower rows of inclined timbers, and on the middle one in the other row:
now if the pressure acting on the binding-piece ab, (fig: 2341.) for example, cannot fail to
make the piece cd bend, and greater strength would be obtained than by augmenting the
angle of the two pieces be and bf, though it is not possible to know precisely what part of
the weight carried by the binding-pieces is supported on one side by the piece cd and on the
other by the pieces be and bƒ, because this in part depends on the settlement of the centre
and the goodness of the framing: it is evident that these two last pieces will carry almost
the whole, and in the impossibility of regulating exactly the manner in which the weight is
distributed, the most natural and the nearest to the truth consists in supposing it is
supported entirely at the point b, that the piece cd does not carry any weight, and that it
has no other effort to sustain but the pressure which it exercises in the direction of its
length: it is always easy to render the work conformable to this supposition, by leaving
little play in the notch of the binding-piece at the meeting of this piece. Naming P the
weight supported by ab, p its composante following be, p' its composante following bf, a
the angle ebf, C and Y the angles formed by each of the pieces be and bf with the vertical,
we shall have
p=P
sin. Y
; p' = P
sin. a
sin. C
sin. a
making in these equations P=18,789 kilogrammes, and putting for the angles a CY the
4 X
1410
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
values which suit them, according to a formula given by Boistard for this centre, and
which makes a=191·09°, C=75·37°, Y=115°, we shall find p=128,730 kilogrammes,
p' = 124,730 kilogrammes. In the same design the length of the piece bc is 3.41 metres,
that of the piece bƒ is 4.28 metres, and their square is 35 centimetres: making then in the
equation
Q=(20336845+21017476 bc)
abs
C2
a=b=0·35 and c=3·41, we shall find for the weight which would begin to make the
piece be bend, Q=16·7480 kilogrammes and making in the same equation C=4·28, we
shall find for the weight which would begin to make the piece bƒ bend, Q=121,400
kilogrammes: thus the first of these two pieces is a little stronger than is necessary, and
the second would be too weak, if, as we have supposed, the pressure transmitted by the
binding-piece ab were entirely carried on be and bf.
In seeking in the same manner what portion of the load transmitted by the hinding-
piece gh is supported by the pieces cd and di, we shall find that the pressure exercised
according to di is equal to 4149 kilogrammes, and that the pressure which exerts itself
according to cd is equal to 44,020 kilogrammes: thus the load of di is scarcely the third of
that of bƒ, and as the length of the two pieces is the same, the square of di might be less
than 35 centimetres; cd is also much less loaded than be, but its length, which is 5.85 metres,
is more considerable. In making in the preceding equation a=b=0·35, and c−5·85, we shall
find Q=79,380 kilogrammes: notwithstanding, then, its greater length the piece cd is
stronger than is necessary: thus we may conclude that of all the inclined timbers, regard
being taken to the pressure compared with the length, bf is that which supports the greatest
effort; that 35 centimetres square is rather small for this piece, but a little too large for
all the others.
Scaffolding requires as much care in the selection of the timber employed, as for that
which is to constitute a part of the edifice: generally a scaffold is composed of upright
poles, and ledgers laid horizontally and secured by strong cords; on the latter
is laid the ends of shorter poles or putlocks, which have a bearing on the wall of the
building in holes left in the masonry purposely to receive them: for churches and public
buildings a double scaffold is employed, which is braced in several directions, and, where
round poles are not obtained of sufficient strength, squared timber is made use of.
The example given was erected by M. Dubrin, master carpenter, before the façade of Saint
Gervais at Paris, and was found to answer its purpose admirably: where the walls are to be
carried up to a considerable height, it is requisite to spread the base of the scaffold, and to
introduce additional braces.
Scaffolding used in the erection of the Monument, by Sir Christopher Wren, occupied a
square, the side of which was 60 feet, and as there was a double row of poles, it left an
interior square, the side of which was 35 feet, in the middle of which the Monument was
constructed. The entire width of the scaffold was therefore 12 feet 6 inches all around it,
and at each angle of the inner and outer square was placed two poles, pitched upon the
diagonals of the square: between these, in the middle of the length of the outside, were three
poles, and between them and the angle two others; each side of the inner square was divided
into two, by two upright poles, so that there were 36 standard poles on the outside, and 16
on the inside, in all 52, which were continued up, with a slight inclination, to the height of
120 feet, after which single poles were found sufficient to construct the remainder of the
scaffolding to the top: 28 ranges of ledgers were fastened to these upright standards, at
distances of 8 feet; those continued round the interior and exterior, forming as many stories,
and supported the putlocks or cross timbers, on which the planks were laid; diagonal braces,
each of which crossed four stories, were secured firmly on all sides, to the ledgers, from the
foundation to the summit, to which a well-contrived wooden stairs enabled the workmen
to mount and descend.
The Scaffolding for the Nelson Column in Trafalgar Square was designed and executed
under the direction of Mr. Allen. The whole was composed of unsawn timber, and the
total height was 180 feet; 154 loads of timber, or 7700 cubic feet, were made use of, and
the cost of its erection was 240Z. The upright timbers were slightly tenoned into the
horizontal, and where the joint was made, iron dogs were driven into the timbers in a
diagonal direction across the joints; these afterwards were easily withdrawn, and the timber
but little injured: the base of the scaffold was 96 feet square, without measuring in the
raking braces; there were in all seven stories, which diminished in height from 48
feet to 21: the whole was strengthened by flying wind-braces, which were supported by
cross transoms, which projected outwards about 6 feet from the perpendicular of the scaffold
at each stage: at the summit worked a travelling machine, by which one mason could set
as much work in a day as was formerly done in three.
At the London and Birmingham Railway Station, Euston Square, Messrs. Cubitt contrived
CHAP XXIII.
1411
SCAFFOLDING.

Fig. 2352.
SCAFFOLDING.
Fig.2353.
Fig. 2354. SECTION.
a scaffold, with two parallel rows of standards, 50 feet in height, and about 17 feet apart,
which were all diagonally braced: after the building had advanced to this height, another
4 x 2
1412
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
similar arrangement was
made, and the whole was
raised to 90 feet; the ma-
terials were all hoisted by
travelling trucks mounted
on tram-ways laid down
for the purpose. Square
timber is decidedly prefer-
able to round poles for the
purposes of scaffolding, as
there is comparatively little
waste incurred; and the
timber, being thoroughly
seasoned by exposure, is
benefited rather than in-
jured by its application to
The travel-
this purpose.
ling winch on a frame
is now universally adopted;
where 10 or 15 tons are to
be hoisted at a time there
would be great economy
in the employment of steam-power.

Fig 2355.
When poles or squared timbers
are employed in an upright position,
as they are in a scaffold, the force
that would bend them when acting
in that direction must be exactly
calculated, for if bent in the slightest
degree, any additional effort will
cause fracture. The strain is always
directly as the weight or pressure,
and inversely as the strength, which
is also inversely as the cube of the
diameter: it is also directly as the
deflexion, which will be directly as
the quantity of angular motion, and
as the number of parts strained;
that is, directly as the square of the
length, and inversely as the diameter.
The stiffest rectangular post is
that in which the greatest side is to
the less as 10 is to 6, but this
will bend in two directions, and
braces and struts must be introduced
in a position to prevent any change
of form: the ledgers of our ordinary
scaffolds being secured by cords to
the upright standards, at distances of
5 feet or more apart, prevents any
bending of the latter, the cord passing
round both the horizontal and ver-
tical pieces, so that it secures the
two firmly together, supporting them
against each other in those parts
where they would most probably
yield to the weight they have to
sustain. The expert scaffold-builder
makes his knots so that the hori-
zontal poles or ledgers form a series
SCAFFOLDINg of euston square station.

n
D
SCAFFOLD used at turin.
Fig. 2356.

O
E
Fig. 2357.
C
נ'
PLAN OF scaffold.
다​.
of struts or straining pieces, and prevent the standards from yielding under any weight.
The Scaffold made use of at a chapel at Turin in Piedmont, for cutting the caissoons
in the vault, which was cylindrical, was well adapted for its purpose, and by means of
wheels, the position of which are shown in the plan, it could be moved either forwards or
backwards.
A similar scaffold was contrived by M. Mandar, the architect, at Paris, for the construction
of a roof erected under his direction, on the principles of Philibert Delorme; it was com-
CHAF. XXIII.
1413
SCAFFOLDING.

t-
+
+
ים.
+
Fig. 2358.
SCAFFOLD DESIGNED BY MANDAR.
posed of three frames or floors, supported upon braces and portions of St. Andrew's
crosses: it was so light that it could be moved with facility by means of copper wheels.
A suspended scaffold for a single
workman is easily contrived by ropes
and pulleys, and is frequently used
by painters: where the cornice has
sufficient projections, as at St. Peter's at
Rome, a pole may be suspended, into
which a brace may be pinned with
its end lodged on the architrave below
such a pendant scaffold requires to be
well secured at top, either by loading it
or pinning it down.

;
SUSPENDED SCAFFOLD.
Fig. 2359.
In all suspended scaffolds, we must
regard the timber employed as pulled in
the direction of its length, and the quan-
tity of space through which it extends is directly proportional
to the number of parts extended, and to the weight.
Emerson says that a piece of oak 1 inch square, and 1 foot
long, supported at both ends, bears 315 pounds before it
breaks, and the same will bear, when drawn in the direction
of its length, 2835 pounds, or 14 tons. We have not sufficient
data to enable us yet to decide upon the strength of the
timbers in the situation we are now considering, when drawn
in the direction of their length; but the extension to which
they are subjected is inversely proportional to the area of
the section, or inversely as the breadth and thickness.
Suppose L the length in feet, W the weight in pounds, B the breadth in inches, and T the
L x W
thickness in inches, then
is the extension; or, when the extension is given,
BxT
B x T
Fig. 2360.
SUSPENDED
SCAFFOLD.
L×W: B× T. Where a is a quantity derived from experiment, then a = L x W®
4 x 3
1414
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.

To Nicholas Zabaglia,
who was born at Rome
in 1674, we are indebted
for designs of some of the
best scaffolds that have
been erected. This ce-
lebrated mechanic, first
employed at the Vatican
as a carpenter, afterwards
became the chief director
of the works at St.
Peter's: Jean Bottari,
the librarian of the Va-
tican, collected several
of his designs for scaffold-
ing, which are published
under the title of " Castelli
e Ponti di Nic. Zabaglia, con alcune
ingegnose pratiche, e con la Descri-
zione del Trasporto del Oblelisco
Vaticano e di altri del Dom Fontana,
1743." In one of the plates
the scaffold-builder is represented
in his workshop examining the
force of a pulley, and of the fifty-
four, thirty-six are designs of
various machines to assist in con-
struction; they are exceedingly in-
teresting, and should be in the
possession of every civil engineer.
Caylus considered the talents of
Zabaglia as of a very superior
kind, and Passeroni commemorated
them in his poem called "Il Ci-
cerone." In the construction of
the scaffolding at St. Peter's, he
made use of the holes left in the
vaulting, for the purpose of sus-
pending, by means of iron rods,
platforms, upon which the work-
men stand to clean or re-colour
the soffites.
Turning Scaffolds may be attached
to a revolving pole with two arms,
acting like the radii of a circle, which
may be raised or lowered at pleasure:
these arms carry a platform attached
by iron hooks, on which stand the
workmen; by means of ropes and pulleys
Fig. 2361. SCAFFOLD DESIGNED BY ZABAGLIA.

-------
Fig. 2362.
TURNING scaffold.

YA
[42]
Fig. 2363.
TURNING scaffold.
Fig. 2364.
TURNING scaffold.
CHAP. XXIII.
1415
SCAFFOLDING.

it can be placed in any required part
of the vault. Turning scaffolds are
rendered more steady when the lever
which supports the workman is
elevated at the side of a quad-
rant, to which it may
be secured at the height
required.
Some scaf-
folds are made
with a num-
ber of floors;
་་་
Fig 2365.
SCAFFOLD used at sT. PETER'S.
the most simple are those suspended from holes
in the vault.
The scaffold used at St. Peter's at Rome
in 1773, when the great vault was repaired and
re-decorated, was of a novel and ingenious character. It
was composed of two sets of principals united together by
braces and intermediate ties, upon which the planks for the
workmen were laid: this scaffold traversed from one end of
the vault to the other; it was raised in one mass by ropes
and pulleys, and lowered to the pavement by the same
VA
D. M
ト
​Fig. 2366. SCAFFOLD USED AT THE DOME OF ST. PETER's.
means when the work for which it was destined
was completed, the ropes were passed through the
holes left in the vaulting for the purpose.
The
editor cannot omit the opportunity of bearing his
testimony to the skill and ingenuity of the Italians
in making scaffolds for the most temporary pur-
poses: when engaged in taking the casts and
measurements of various remains in the Imperial
city, the ladders and scaffolds prepared by the
workmen for his use were of the most perfect kind :
although light, and apparently fragile, he often
mounted upwards of 100 feet, and remained the
whole of the day at his work, without the slightest
risk of accident.
The scaffold for the dome of the same church
was contrived by Pietro Albertini at the same time:
the diameter of this beautiful piece of carpentry
was 133 feet, and the height nearly 80 feet: it was
formed of three frames, the vertical timbers of which
were suspended by iron rings that passed over hooks
inserted in the masonry of the vault to receive
them. When a portion of the dome was repaired
4 x 4
1416
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
the position of one of the sets of principals was transferred to the other side, without
•
deranging the two, which served to make the alteration in the scaffold without danger.

The scaffold contrived by
Campanarino for the re-
storation of the dome of the
Pantheon at Rome rivalled
all others in the beauty of
its design and delicacy of
its execution: it was com-
posed of two principals, an
elevation of which with the
braces is shown below.
At the summit, through
which the only light is
admitted into this mag-
nificent rotunda, a stout
timber curb was fixed, in
the centre of which was
the pivot upon which the
upper part of the scaffold
revolved: the lower end
rested on the bold project-
ing cornice beneath the
coffered dome, and by means
of pulleys a small power
could advance the entire
scaffold; these were also at-
tached to various parts for
the purpose of hoisting the
materials to their required
situations: iron ties and
braces were introduced to
prevent any springing, ren-
dering the whole perfectly
steady, and admirably
adapted for its purpose.
This noble building
is internally 143 feet in
diameter, and 148 feet 4
inches in height from the
pavement; the dome which
covers it may have been
constructed on several such
ribs, supported from below
by a forest of upright tim-
bers.
Fig. 2367.
SCAFFOLDING AT THE PANTHEON.

WW
W
Fig. 2368.
SECTION OF THE Aperture AT THE TOP OF THE DOME.
CHAP. XXIII.
1417
SCAFFOLDING.

L.J
Fig. 2369.
PLAN OF SCaffolding AT THE Aperture at THE TOP OF the dome.
To the scaffold builder a knowledge of the variety of knots is important, and as ropes
are used in several machines, it is

necessary that every mechanic should
understand how they can be secured
and tied together.
280


An ordinary knot is simply made
by twisting a rope twice round, and
passing the ends in opposite directions.
Loop knots for joining pieces of
rope together are passed through a
loop in such a manner that, when
pulled tight, they are firmly united
they may cross each other, or sim-
ply pass through each rope when
doubled.
The wall knot is made with the lays of a rope, and cannot
slip; the bow-line knot is so firm that when fastened it is
perfectly secure.
:
Fig. 2370.
The sheep-shank knot, which shortens a rope without
cutting it, is so arranged that it can be readily loosened
again: most knots are for the purpose of fastening one
rope to another, which is effected by means of a small cord
attached to the neck of the knot, and firmly tied about both
ropes.
The fibres of a rope seldom exceed in length 3 feet;
they must therefore be well twisted together before they
are applied: large ropes are either cable-laid or hawser-laid;
the former are composed of nine strands, the latter of three,
and each of a number of primitive yarns: a rope 8 inches
in circumference may have 414 yarns equally divided among
three strands.
The greater the obliquity of the fibres that compose a
rope, the greater will be their adhesion, but the greater also
will be their immediate tension, in consequence of the action
of a given force in the direction of the rope; but the relative
Fig. 2371.
Fig. 2372.


Fig. 2373.
Fig 2374.
1418
Book II.
THEORY AND PRACTICE OF ENGINEERING.
position and comparative tension of all the fibres employed can scarcely be estimated, and
it must depend in an essential degree upon the quality of the hemp or material employed.




Fig. 2375.
Fig. 2376.
Fig. 2377.
Fig. 2378.
Ropes passing through Rings may be variously secured, either by taking one end through
a series of loops, or by a triple twisting through a single one. Emerson found that a good
hempen rope, of 1 inch in circum-

·
ference, would bear 1000 pounds
weight suspended to it, whilst a rod
of iron of the same dimension would
support 3 tons, and another of yellow
fir, 2 inches in diameter, would carry
7 tons.
The rigidity of ropes or cords, and
the difficulty of bending them into
any given curve, prevents the form-
ation of a close knot, particularly
where they are of large diameter: the
resistance arising from this stiffness
is as the weights which stretch the
cords, multiplied by their thickness,
and divided by the radii of curvature
of the surfaces over which they pass.
The Scaffold Builder must form his
knots or make fast his ropes in the
way best adapted for his purpose:
when a St. Andrew's cross is formed
by two poles, to be tied tightly toge-
ther, two or more ropes are lashed
around them, drawn tight and made
fast; a single or double loop may be
passed around the head of a post
according to the security required.
Mariners make use of a great
variety of knots which have been
adopted by engineers, to secure the
heads of piles or attach horizontal
timbers laid against them; a double
loop, or thrice twisting round, and
afterwards passing the rope through
a double loop, is an effectual fasten-
ing, and prevents the knot from slip-
ping in any direction.


Fig. 2379.
Fig. 2380.
Fig. 2381.

Fig. 2382.

Fig. 2383.

# Ay

Fig. 2385.
Fig. 2384.
CHAP. XXIV.
1419
MASONRY.
The double loop is always to be preferred, and made by doubly twisting the rope round
the pole, passing it by the loops, and drawing them tight.



Fig. 2386.
Fig. 2387.
Fig. 2388.

Chains made of
iron
are often
found more con-
venient in their ap-
plication to ma-
chinery, consisting
of a series of links
riveted in the man-
ner of a watch
chain, or hooked
posed by M. Vau-
together, as pro- Fig. 2389 WATCH-CHAIN.
ভ

IIII
Fig. 2390.
VAUCANSON.
canson: each system, however, has its advantages and peculiar application.
CHAP. XXIV.
:
MASONRY.
BUILDING with stone is of the greatest antiquity, and it is extremely difficult to trace
its origin the Egyptians were perfect masters in the art of stone-cutting, and the Greeks
exhibit such perfection in their works, that it is almost impossible to equal them; to the
mason's art they added that of the sculptor, and the buildings executed in marble, still
remaining, are monuments of their taste and skill. The Romans have also left much that
is worthy our admiration, particularly those structures in which arches and domes of con-
siderable dimension form the striking features: to the freemasons of the middle ages we
are also indebted for many wonderful examples of their ingenuity and knowledge, of which
we have ample proofs in the well-executed groined vaults they introduced, and which are
unequalled for design in the structures which preceded them: they lessened the area of
the points of support, balanced the thrust of their stone roofs by judiciously conceived
buttresses, and evinced great skill in their adaptation.
For facing the stone our masons now make use of the point, the inch tool, the broad
tool, and the boaster; the first is to form a series of narrow furrows, with rough ridges
between them, afterwards to be cut away by the inch tool. The boaster is 2 inches in
width, and the broad tool 3½ inches at the cutting edge. Stone axes, jedding axes, cavil or
scabbling hammers are employed to bring rough stones into shape: mallets and chisels,
levels, plumb-rules, bevels and squares, are also required by

the mason.
The Opus incertum, formed of small stones of irregular
shape, touching only at certain points, was preferred by
Vitruvius to the opus reticulatum, not on account of its
appearance, but for its superior strength; if the mortar be
well composed for the materials with which the inner part
of the work is filled, and the angles are protected with
squared or hewn stone, a solid mass will be the result.
The Emplecton had the faces of the stones smooth; the
other sides were left as taken from the quarry. Walls
are often built with flint or round stones from the sea-
beach; it is then necessary to protect the quoins with square
masses, and to carry up the outer faces by means of frames
formed of planks, as has been described for pisé work; we
have many castle and city walls so built, that have acquired
Fig. 2391.
OPUS INCERTUM,
1420
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
considerable hardness, and if occasionally bonded through with flat tiles, as at Richborough
Castle, Kent, are difficult of demolition: such walls consist of three thicknesses, two forming
the outer faces, and one the rubble core in the middle.
When the opus incertum is made with large polygonal facing stones, and piers of tile or
brick are occasionally introduced, the effect is greatly improved, and the strength of the
wall considerably increased; they are frequently met with in Italy, built with great care,
and filled in with rubble composed of excellent mortar. This kind of masonry bears a
strong resemblance to the cyclopean walls that are scattered over the country inhabited by
the early Greeks; but the latter construction was executed with large blocks, and generally
without mortar, its strength depending upon the locking of the several stones together, and
the weight superimposed to keep them in their places.


00
Fig. 2392
EMPLEOTON.
Fig. 2393.
OPUS INCERTUM.
The Opus reticulatum is considered by Vitruvius the most beautiful species of construction;
the term applied to it originated in its net-like arrangement, and we have an example
in a part of the west front of Rochester Cathedral, supposed to have been built before

I
=
Fig. 2394.
OPUS RETICULATUM WITH STONE.
the Norman Conquest: it is, however, liable to split, from the bed of the stones being
unstable, and its deficiency in respect to bond; there are several varieties of this kind of
work remaining in Italy, and some examples are attributed to the time of the Etruscans.
CHAP. XXIV.
1421
MASONRY.

In Volscinium, the capital of the Volscii,
are several remains: this style of masonry,
found also at Tivoli, Præneste, Terracina,
Fondi, Pompeii, &c., continued in use
to the time of the emperors of Rome.
It is generally formed of tufa, or small
stones found in the neighbourhood of the
constructions; the angles, as well as other
portions of the wall, are carried up with
tiles laid in regular courses; there are several
varieties of opus reticulatum besides the two
specimens given.
Walls formed with triangular tiles are
found in the Coliseum and baths, &c.,
of the imperial city; other tiles of a square
or oblong shape pass through the entire
thickness, at every third or fourth course,
and the interior is filled with rubble. In
the ruins of Pompeii are walls built of
tufa, rough stone, and brick, executed in a
very careless and inefficient manner; some-
times only one course of brick alternates
with one of stone, at others three courses
of tile or brick intervene between one
of tufa or squared stone.
Whatever may be the character of the Fig. 2395.
Opus RETICULATUM WITH BRICK.

MM
ㄷ
​I
Fig. 2396.
TRIANGULAR TILES.

masonry, one of the first considerations
is the arrangement of the footings, which
should be constructed of stones as large
as can be obtained; they should all be
squared, brought to an equal thickness
in the same course, and laid upon their
natural bed: the foundations should
consist of several courses, each decreasing
in breadth as they rise, in proportion to
the thickness and height of the intended
wall; this decrease of breadth should
take place equally on both sides: ashlar
facing backed with brick or rubble work
is often substituted for brick and tile;
but in those districts where stone is not
easily obtained, there can be no better
method than following the practice of
the Romans.
In some ancient walls the bond-stones
pass through the entire thickness, and
Fig. 2397.
STONE AND TILES.
I
have a filling-in between the stretchers, composed of rubble or small stones bedded in mortar,
the excellence of which has rendered them remarkably durable; such walls are classed
under those called Pseudisodomon, from the courses varying in height.
Walls constructed partly of squared stone and rubble should have every second stone in
the same course to run entirely through the whole wall, so that the work may be prevented
from splitting in the direction of its width; the filling-in should be cautiously performed,
and due regard paid to the shrinking of the mortar : the stone facing is sometimes rubbed
1422
Book II
THEORY AND PRACTICE OF ENGINEERING.

Fig. 2398.
I
perfectly smooth by
means of a sand or grit-
stone; at others it is
either drove, broached, or
striped; the former me-
thod is the least costly, is
usually adopted, and ge-
nerally known in London
as random-tooling or boast-
ing.
The tomb of Cecilia
Metella at Rome is
cased on the outside with
stone in courses, laid very
regular, filled in behind
with rubble work, which
seems to have been done
at the same time with the
courses, as there are indi-
cations where the levels have been left and again commenced.
Fig. 2399.
Wherever ashlar facing is adopted, the stones of each course should be placed on their
natural bed, otherwise they will be liable to flush off at their joints; and where piers are
required, unless they are of large dimensions, this kind of work must be abandoned; for
there cannot be the requisite strength without the courses passing entirely through: in
several churches constructed in the tenth and following centuries, we find the polygonal
and cylindrical shafts of columns

faced with ashlar, and hearted or
filled in with rubble or chalk, run
together with a durable mortar ;
where the latter has lost its te-
nacity, the columns have in several
instances split asunder.
Pseudisodomum had the courses
unequal in height: in other respects
it resembled the isodomum. There
are many remains of Roman walls
where the stones of each course are
of the same form as well as dimen-
sion throughout, ordinarily 3 feet
long, 18 inches wide, and 9 inches
in thickness; in some instances one
course is laid flat, and the others
are placed on their edges, so that
the first reaches to the middle of
the wall, which is filled in with
rubble.
Diatonous was a term given by
Fig 2400
PSEUDISODOMON.
CHAP. XXIV.
MASONRY.
1423
the Greeks to that species of masonry in
which the stones were of the same form
and dimensions, but placed in courses of
unequal height; such stones had their
length equal to double their width.
At Athens there are several walls
which have the courses of masonry of
two different heights alternating with
each other; the small course is only two-
thirds that of the other; consequently
three stones form the entire thickness in
the one course, and two in the other or
larger one, which doubly ties the entire
thickness of the wall.

Fig. 2401.
DIATONOUS.

Fig. 2402.
PSEUDISODOMON.
Another variety of masonry often met with in Italy bears some resemblance to those
already described, but instead of presenting in the same course one header and one
stretcher alternating, there is a course of headers and one of stretchers, like the old
English bond in brickwork: as the headers pass entirely through the wall, the work is
rendered very solid.

Fig. 2403.
Isodomum: the courses are all of equal height, producing both durability and solidity;
first, because the stones are hard and solid, and therefore unable to absorb the moisture
of the mortar, which is thus preserved to the longest period; and secondly, because
the beds being smooth and level, the mortar does not escape, and the wall is bonded
throughout the entire thickness.
To the admirers of solid construction we cannot do better than refer to the various methods
employed in the amphitheatre of Vespasian at Rome: amidst the ruins of that stupendous
pile, we yet observe specimens of almost every style of masonry, and a judicious application
of stones of different degrees of hardness: brick and tile, with every kind of backing or
filling in, was made use of where economy was desirable, or could be practised without
sacrificing stability and strength; the large stones are wrought on all their faces. to suit
their position around an oval plan, or circular on the elevation. The Coliseum is not only
1424
THEORY AND PRACTICE OF ENGINEERING.
Book II.

a model for construction,
but a school for the study
of the mason's art; its
general arrangement, and
the proportion of its piers
and walls, were no doubt
most useful guides to the
builders of the middle
ages. There is scarcely a
peculiarity in masons'
work of which an example
may not be found admi-
rably effected amidst the
corridors or vaultings of
this edifice; and the test
to which its stability has
been subjected during nearly 2000 years is a
convincing proof that every point in its construc-
tion was well considered, and must impress upon
us the rather humiliating conviction that masonry
has not progressed beyond the knowledge ac-
quired by the
ancients.
Fig. 2404.
Fig. 2405.
Cramps of metal, either iron
or bronze, were much used by
the ancients for uniting one
stone with another, and were
sometimes run with lead. The
holes in the walls of the Co-
liseum and other monuments
at Rome were drilled or cut
for the purpose of extracting
cramps of bronze that united
the courses of masonry toge-
ther in the Parthenon at
Athens the writer found oak
dovetails applied for the
same purpose.
An excellent
method of uniting a course of
stone is by forming a triple
range, notching one into the
ISODOMON.

Fig. 2407.
ISODOMON.

Fig. 2406.

CHAP. XXIV.
1425
MASONRY.
other; this has in modern times been applied to circular walls, and found inefficient, on
account of its cost and difficulty of execution, from the effects of unequal settlements in the
building.
In the theatre of Marcellus at Rome the stones of the piers are prevented from sliding
off their beds by sinking a portion of one into the other: the bed of each stone is divided
into four parts by two right lines
which cross in the centre at right
angles, and abut against each other
in the middle of their faces; the
stones are placed upon each other,
so that every one is united to two
others, by means of the projecting
parts of the upper stone, which keys
into the sinking or mortise of the
two lower, to which it is adapted.

Placing, and the Form to be
given to wrought Stone, for Walls,
Abutments, Piers, &c.-As every
solid body has a tendency to de-
scend in a vertical or perpendicular
direction, it is evident that it can
only be perfectly supported on a
horizontal or level plan; thus the
form best adapted to wrought
stone, when applied to walls or
piers, is that of a parallele-
piped or perpendicular prism, or
a solid placed on a horizontal
plane, and terminated by vertical
surfaces. The stones being laid
on each other in union and level

Fig. 2408.
courses, the whole effort of the weight will fall on their base, and tend to consolidate
them, so that the pressure of each stone on the other will increase their stability, and if the
whole be well constructed, it will be almost as solid as if in one piece. As it is the effect
of weight which unites the stones together, it is evident that the larger they are, the
greater will be their stability, and the more solid their union; but their beds must be well
dressed, and brought to a level, that they may have an equal bearing; for if of considerable
dimensions they are more subject to break in parts where they have no bearing. The effect
which causes the rupture produces also a general derangement of the construction,
which renders it defective, certain points bearing a considerable weight, under which they
break, whilst others are not in contact; the solidity and perfection of construction in
wrought stone, which should be independent of any mortar or cement, consists in the
stones being placed immediately over each other, so that they touch throughout their
whole surface, both in their beds and joints, as was done by the ancients, and it is in the
precision with which irregular constructions in large stones are executed, that their solidity
depends, the joints being so well keyed, that their stability is often greater than that of
squared stones. It must be observed that in construction of wrought squared stones the
perpendicular joints do not add to the stability, whilst in those with irregular stones,
being inclined in an opposite direction, the stability is increased by the manner in which
the stones are keyed one into the other.
Of the Dimensions of Stones. In many edifices, both ancient and modern, it has been
observed that the stones used were too thin, viz. that they had not sufficient thickness in
proportion to their length, and that in consequence they broke under the weight. These
accidents arose from the stones not resting equally throughout the whole surface of their
beds, either because these surfaces were not exactly dressed or levelled, or because some
unequal settlement took place, which deranged the lower stones; the greater the thickness
given to stones relative to their length, the greater is the power of resisting this effect,
which it is often very difficult to foresee or prevent. For works which have very great
weights to carry, such as walls and points of support, cubes are the strongest, but they
have less stability, and do not form sufficient bond; those in which the length is much
greater than the height have more bond, but less strength to carry the weight; according
to the experiments made on stone, the length may be fixed at from twice to thrice their
height, and their width from once to twice, supposing the stone of a moderate hardness.
When stones are very hard, more than a foot thick, and wrought on all sides, their length
may be from four to five times their height, and their width from two to three times;
larger dimensions increase the expense without adding to the utility.
4 Y
1426
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
in
D
G
In ancient structures wrought stone was laid without mortar, or the small quantity
used was so clear and fine that it only served to fill up the inequality of the bed, and
did not prevent the parts between
these inequalities from bearing on
each other. The Romans observed
that walls constructed of soft stone,
or inferior brick, were subject to be
affected by the changes of the atmo-
sphere and driving rains; to obviate
which Vitruvius advises that
apartments on the ground floor at a
height of 3 feet from the pavement,
the first coat of stucco be of potsherds
instead of sand, and that a thin
wall be built on the inside, leaving
a cavity between for the air to
circulate. Where there was
sufficient space for this second wall,
tiles 2 feet square were placed, one
over the other, in front of a flue
left in the wall; G shows the position
of the tiles up the face of the wall,
D its effect when plastered over or
stuccoed: A is a channel or drain,
contrived to receive any moisture
that may run down the flue, or hol-
low part of the wall.

not
For cottages the same arrange-
ment might be adopted with great
economy, and in several parts of
England walls are constructed in a
somewhat similar manner, by setting
the bricks on edge, both on the inner
and outer face, so that in a 9-inch
wall, there is a space of 4 inches
between them. To produce the
requisite strength, each header passes
through the entire wall, and by care-
fully excluding the mortar or dust
from occupying the vacuum between
the two faces of the brick, a dry wall
is secured, and a much less quantity
of material consumed than is re-
quired for a solid 9-inch wall. Stone
walls might be so constructed, and
it has been suggested to work with-
in thin walls vertical plates of sheet
iron, pitched previously to insertion,
to keep out moisture.
The Romans formed the floors of
their rooms very carefully; after
excavating the earth to the depth
of 2 feet, they well ramined the bot-
tom, and laid over it a layer of broken
stone or potsherd prepared for the
purpose; on this was spread a com-
position of pounded charcoal,
lime, sand and ashes, 6 inches
in thickness, which was ren-
dered perfectly smooth by first
rubbing it with stone and then
polishing it. Rakes, rollers,
scrapers, and trowels, were
A
Fig. 2409
PLAN OF wall.

Fig. 2410.
A
ELEVATION OF WALL.
made use of during the processes, and several of these floors remain at Pompeii, which attest
their strength and durability.
It was the practice of the Romans to construct the upper portion of their walls with tes-
taceous materials, forming a projecting cornice to carry off the water. When mouldings
CHAP. XXIV.
1427
MASONRY.

are made in cement or plaster,
for the sake of economy, they
are run either upon projections
of rough stone or tile; the tools
required are trowels of different
forms, and chisels and hammers
to cut away the masses which
may obstruct the working of the
running mould, which is cut out
to the form intended, and passed
along the face of the cement,
spread over the cornice.
2411.
2412.
2413.
2417.
2419.
2418.
Fig. 2414.
Fig. 2415.
Fig. 2416.

2422.
2423.
Fig. 2420.
Fig. 2421.
Fig. 2424.

Stone Pipes are in many parts of the continent made
use of for conducting water, and are sometimes laid in
the thickness of the walls, to bring down that which
falls upon the roofs: they are bored by simple means,
setting the block of stone upright, and in the centre
of the intended pipe or cylinder placing a wooden plug
having a hole through which the axis of the spindle
passes; the cutter is attached to this, and rotary mo-
tion is obtained by means of a pulley; the action of
this borer is that of the common drill.
Arches composed of four voussoirs cannot sustain
themselves, whatever be the resistance of the piers, if
their thickness be less than the seventeenth part of their Fig. 2425.
span; but they sustain themselves with a less thickness
BORING STONE PIPEs.
when the arch is extradossed equally over 3 of its extent, the surplus being comprised in the
piers, as shown in fig. 2427.: when the thickness of the arch is increased, it may be made
only part of the span.


Fig. 2427.
Fig. 2426.
Arches of Equilibrium, being calculated to stand by themselves, must necessarily be better
4Y2
1428
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
adapted to sustain any additional weight, which will be opposed by the whole resistance of
the cohesion of their parts; but where the arch does not equilibrate, a portion of the
cohesion is employed in resisting the inequality in the actions of its own parts. "Equi-
libration," observes Mr. Samuel Ware, in his very admirable treatise on the properties of
arches and their abutment piers, "is as important as the construction of the arch." All
arches which support themselves, whatever their form, include a catenarian curve in their
thickness, upon the principle of a line formed of a perfectly flexible chain, suspended at its
two extremities, which is an arch of equipollence.
In semicircular arches all the joints prolonged intersect at the centre; consequently if
a horizontal line be drawn at such a distance from the centre that the parts comprised between
the joints of the key are equal to the thickness to be given to the arch at the centre
of the key, the other parts of this line, intercepted by the joints, will express the differences
of the tangents, and the thicknesses to be given to each correspondent voussoir. Το


1
Fig. 2428.
Fig. 2429.
determine the point where the horizontal line should be drawn, draw a parallel to the axis,
at a distance equal to half the thickness of the centre of the key of the arch, which will
cut the joint of the key prolonged in a point, and is that required. By measuring the


Fig. 2430.
POINTED.
Fig. 2431.
widths on the straight line, we have the thickness to be given to each of the voussoirs
comprised by the two radiating lines; and when the thickness of the keystone is determined,
we must set out half this depth on the intrados from the axis of the arch, drop a per-


Fig. 2432.
Fig. 2433.
pendicular from that point, and when it cuts the radiating line that represents the side
of the keystone, draw a horizontal line, as shown in the various figures, upon which we
obtain the depths to be given to the respective voussoirs comprised between the lines:
by this means the extrados of every kind of arch, parabolic, hyperbolic, or elliptical, can be
traced.
CHAP. XXIV.
1429
MASONRY.



Fig. 2434.
•
-

Fig. 2435,
Cylindrical Vaults have their
voussoirs always parallel to their
axis, whatever their curvature or
situation : oblique or inclined
vaults of this description should
have their courses of voussoirs
similarly arranged.
Conical Vaults have their courses
inclined towards the point of the
cone, whether they form a part of
an entire, or the frustum of a
cone; taking care in the former
case to avoid the too great acute-
ness of the voussoirs by making the
point or trompillon of a single stone.
When the conical vault is of a
size which renders the lower vous-
soirs too thin, its length must be
divided into several parts; so that
if the great circle be divided into
8 voussoirs, and the length of the
arch into 4 parts, the second part
Fig. 2436. CYLINDRICAL VAULT.
Fig. 2437. CONICAL VAULT.


VAULT.
should be divided into 5 voussoirs, Fig. 2438. OBLIQUE CONICAL
the third into 3, and the fourth be
constructed of a single piece :
these slices must be comprised
between surfaces perpendicular
with that of the cone, by cutting off
any irregularity in the first row.
Spherical Vaults consist of hori-
zontal courses of concentric rings
placed upon each other: when the
rows of voussoirs form squares on
the plan, or other plane figures,
as triangles, pentagons, &c., they
are difficult of construction and
not so solid, especially at the angles
of the polygons; nor does this ar-
rangement effect so firm a tie as
when the voussoirs are arranged in
horizontal rows.
When the vaults are composed
of several parts the rows of vous-
soirs should be disposed as they
would be in the vaults originating
Fig. 2440.
Fig. 2439. SPHEROIDAL VAULT.

Fig. 2441.
them; thus in the figures composed of parts of cylindrical vaults uniting in the centre, the
rows of voussoirs are parallel to those axes.
4 x 3
1430
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Diagonals drawn from one angle of the hexagon to the other, and passing through the
centre, form salient angles in the voute d'arète, and re-entering angles in the route de cloitre.

Fig. 2442. Voute d'arete.
Fig. 2443. Arc de cloitre.
Fig. 2444. ARC DE Cloitre.
In the Voute d'arète, composed of triangular voussoirs, these parts have no other supports
than the angles of their plan: whilst in the vaults termed arc de cloitre they are sup-
ported on their side, which is carried on the wall throughout its whole length: hence the
latter are much more solid, and have less pressure than the voute d'arète.
Flat Arches are constructed by making each course of voussoirs run parallel with the
faces of the walls which support them.

In all arches stability being

the object,
cohesion and
friction are necessary: the
larger the voussoirs, or, in
other words, the fewer the
joints introduced, the less
liability there is to derange-
ment, as the cohesion is in-
creased: but we must always
regard the nature of the ma-
terial employed, and its dis-
position to fracture. The
mason as well as the brick-
layer should avoid the im-
propriety of making his skew
backs to flat arches too great;
1
for an arch composed of stones
with parallel beds and slightly
inclined joints cannot yield
until some one of them slides
out, or becomes crushed. At
page 410. (fig. 410.) is shown
a flat arch at Coningsburg
Castle, where the voussoirs
are held up by an indented
joint: similar arches are
found among the buildings of
the Romans, over the great
western door of the cathedral
at Rochester, and elsewhere.
Flat Vaults over a square plan are comprised between four walls which support them:
the rows of voussoirs form concentric squares; those of the angles are common to two of
the sides; the key is square, and locks the whole together. The lines traced on the
plan show the position of each stone; the dark line is the lower joint, and the lighter line
the upper.
Vaults of such a description are rarely to be met with in England, and require
great skill for their execution: wherever they are introduced, an iron tie or a strong abut-
ment is requisite to prevent the yielding which takes place at the joints of the stone.
Fig. 2445. FLAT ARCHES.
Fig. 2446.
FLAT ARCHES COM-
PRISED BETWEEN FOUR WALLS.
CHAP. XXIV.
1431
MASONRY.

A flat Vault on a circular plan has
its voussoirs arranged concentrically,
and locked by a conical key.
Flat Vaults supported upon four
pillars require a different arrangement;
the rows of voussoirs are parallel to the


Fig 2447.
FLAT VAULT ON A CIRCULAR plan. Fig. 2448. FLAT VAULTS SUPPORTED ON FOUR PIERS.
inner faces, and intersect at right angles on the diagonals, on which are placed voussoirs
common to the two sides: the last row on each side is cut to receive the diagonal voussoirs.
To trace the Caissoons in spherical and spheroidal Vaults is the most difficult portion of
a mason's work: after the circumference of the dome is divided into the number of intended
caissoons, from the centre of each perpendiculars are raised, united in the key of the dome;
these lines may be considered as the circumferences of several vertical semicircles which
intersect at the axis of the vault: whence it results, that if a cord be stretched, to represent
the diameter of one of these circles, the points of the circumference will be found by
elevating with a plumb-line several corresponding points on the surface of the vault, a line
passed through which will be the circumference of the circle. To draw them, a template
or mould cut to the curvature of the vault is employed, which should not be more than
3 feet in length. The points raised upon the diameter represented by the cord should be
not less than 18 inches apart, so as to have always three points to fix the mould: instead of
raising these points perpendicular to each diameter, we may effect this in a far more
expeditious and simple manner, by means of a plumb-line suspended from the centre
of the key; if at night, a light may be placed at each division opposite to that suc-
cessively, through which a vertical circle is to be drawn, which will be indicated in its
whole extent by the shadow of the thread of the plumb-line, serving to place the wooden
mould as before described. After having thus drawn the centre of the caissoons,
their height may be thus determined: circles are inscribed, one above each other in the
divisions or parts of the development, comprised between the vertical arcs which pass
through the middle of the sides, as is shown in the figure B. In order that the first row
of caissoons may experience less foreshortening, the first may be raised above the
4 Y 4
1432
BOOK II:
THEORY AND PRACTICE OF ENGINEERING.
springing, as at C. To determine the lower circle of the first row, a semicircle is first
described, through which the summit of a spherical triangle is traced; having then divided
the angle formed by this circle, we must proceed as shown in the figure, drawing the
spherical angles upon each caissoon, which is a tedious process. For octagonal and lozenge-
C
B


Fig. 2449.
CAISSOONS IN SPHERICAL VAULTS.
D
•
"
"
Fig. 2450.
shaped coffers a similar system must be adopted, taking care to project the several lines
upon the spherical diagonals.
In setting out the caissoons of a dome, like that of the Pantheon at Rome, after having
decided the number, we must commence with the plan, and set out the lower tiers, with all
their sinkings and ribs between: perpendicular lines drawn up from these divisions to the
base line of the elevation of the dome will determine the commencement of the several
curved lines that are to bound the caissoons in their vertical position: to mark out their
direction, an inner circle, of the diameter of the dome, must be drawn on the plan, at the
height of the first caissoon, divided in a similar manner, and then the perpendicular lines
be proceeded with as before.
Domes that are elliptical on their plan must, in order that the caissoons may not produce
a disagreeable effect, have their rows comprised between horizontal ellipses similar to that
of the base. The projection of the sides should also form right lines meeting at the centre;
these lines, which vary in length, are the great axes of vertical semi-ellipses, which give
different measure, and curves to the developed width of each row of caissoons, and even for
the upright edges of each.
CHAF. XXIV.
1433
MASONRY

D
Fig. 2451.
↓
1
OVAL.
Fig. 2452.
To trace the Stones forming an Arch with parallel Faces.—Fig. 2453. is the elevation
of the arch, showing the forms of the voussoirs, under which is the plan of the arch


2453.
19
20
m
L
B
f
71
2/
id'
10/5 11/
12/
B'
h'
2454.
D
n'
a!
p
qimi ri
18
Fig. 2455.
17
α
K∞
K
2458.
18
ARCH WITH PARALLEL FACES,
Fig. 2459.
M
2456.
2457.
n น

y
1484
THEORY AND PRACTICE OF ENGINEERING. BOOK IL

Ι
T
Fig. 2460.
Fig. 2463.
2462.
L
Fig. 2461.
I
L////
Fig. 2464.
Fig. 2465.
2166.
2467.
Fig 2468.
Fig. 2469.
reversed; the lines indicate the joints of the soffite, and those dotted the projection
of the interior section; these are formed by means of the profile, on which is taken,
according to the vertical

or perpendicular face, the
thickness corresponding to
each joint of the soffite,
thus: fig. 2455. shows the
section and its corre-
sponding lines. A mould
must first be formed
for each of the voussoirs,
I, K, L, M. for the purpose
of accurately tracing them;
one is shown in fig. 2459.
marked K, and in the
voussoirs drawn in per-
spective. The manner of
working it is thus per-
2472.
Fig. 2470.
Fig. 2473.


formed (fig. 2459.): the
upper bed is first cut, and
Fig. 2471.
Fig. 2474.
the two parallel lines 17t and an are to be drawn, at a distance corresponding to the thick.
ness to be given to the arch; then the two faces, 17tex, and auy, at right angles
CHAP. XXIV.
1435
MASONRY.
or square with the bed first obtained. When the perpendicular faces are formed apply
the mould, and trace out the figure to be given to the voussoirs; the stone is then
reduced by cutting away all extending beyond the outline of the mould, and between the
dotted lines. For oblique and circular arches the stones may be traced in a similar manner;
their developement and profile are shown by the figs. from 2462. to 2474. By observing
the letters on each there will be no difficulty in applying the several stones to their respective
positions.
E
C
D
10
9
8
11
F
2 3
12
1
TIR
E
K
H
2476.
H
G
F
The Development of Arches, either perpendicular, oblique, or circular, on the Plan.
ABCD is a half cylinder, on which are placed arches extradossed, of an equal thickness,
and to which it acts as a newel. Fig. 2475. represents them geometrically; fig. 2476. the
profile, and in fig. 2477. the whole is shown in perspective at an angle of 45º. The develop.
ment of these several arches is expressed in figs 2478, 2479, 2480, and 2481.; the voussoirs
are shown lying on their extrados, so that the joints appear open at their intrados, where
they form angles that separate their soffites. The development of the straight arch E F is
shown by fig. 2478.; that composed of
two parts forming an angle GHI, by fig.
2479.; the circular L M N by fig. 2480.;
and that which is circular on the plan
O P Q, but situated obliquely with regard
to the axis of the cylinder, by fig. 2481.
To set out these developments, take from
the profile (fig. 2476.) the width of the
faces of the extrados, which carry on a
right line df, supposed perpendicular to
the axis in d, 7, 8, 9, 10, 11, 12, and f. 0
For the straight arch E F, it will be
sufficient to draw a parallel at df, at a
distance equal to the thickness of this
arch: having then divided each face of the
extrados into two equal parts, carry on each side half the width of the internal face, and as
it is narrower than that of the extrados, the lines drawn by the points a, 1, 2, 2, 3, 3, 4, 4, 5,
5, 6,6, 6, and b, will leave on each side spaces which will represent the joints foreshortened,
as shown by fig. 2478.

L
K
K
M
M
N
R
P
P
N
A
B
Fig. 2475.
Q
Fig. 2477.
For the other arches, G HI, LMN, OPQ, the faces of which are oblique or circular,
it will be necessary on the horizontal projection, fig. 2475. to draw the lines K R, perpen-
d
a
7
8
9
10
11
12

2
3
3
4
4
5
5
6
6
b
Fig. 2478.
dicular to the axis, which may pass at pleasure through one of the projecting extremities,
as the point H for the arch GHI, M, for L M N, and R, for OPQ.
α
a
1
1 g
1 ½ 1 1 1 H 1 k 1

1 1
1 π. 1
1
K
1
4
1
•
+
1
R
#
1
1
t
10
4
G
2
5
3
H
3
9/1
10
8"
1
1
13
11
12h
Fig. 2479.
Then prolong the lines from the points of the extrados and intrados until they meet the
directing line KR: for the arch GHI, for example, make the development for the faces
of the extrados, by carrying, as already stated, their width taken on fig. 2475., on the
line developed, an, fig. 2479., from a through g,h,i,k,l,m, and n; having drawn indefinite
perpendiculars through all these points, carry on each the distance of their extremities to
the directing line K R on fig. 2475.; then carry the distances cd, g7, h8, i9, k10, 71l, m 12,
1436
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
and nƒ, through ad, g7, h8, i9, k 10, 711, m 12, and nƒ', on the developinent, fig. 2479.: then
apply the thicknesses d' d", 77, 88, &c. &c., to the development fig. 2479 from d' through
d", from 7 through 7, from 8 through 8, &c. &c., and tracing through these points the curves
d', H', f', and d", H", and ƒ", we shall have the faces of the extrados.
For those of the intrados, take on the profile fig. 2475. half the difference of the internal
and external faces, which will be found by making two parallels to the lines, which pass
through the middle of each voussoir, as 3r and 4s, with relation to the key.
له
ณ
al
2
4

3
3
4
2
2
Q
•
3
5 5
6 6
10
5
6
6
b
11
b
12
7
1 g
1
1 kl
1 1 1
1 m 1
Fig. 2480.
The arch in question being extradossed in equal thickness, the differences 9r and s 10
are throughout the same, and rs always gives the width of the inferior face: thus to have
the position of the latter, draw 9r through s 10, on the line dn of the development, fig. 2479.
through a, a, lg, g 1, 1h, &c. &c., and after having drawn by the points a, and all the points

@
al
A
5
6
6
10
3
12
t
d
h
g
Fig. 2481.
m
"
1, indefinite parallels, carry on each the width of the corresponding lines traced on the
cylinder, that is to say, au, 11, 22, 33, &c. &c., of the fig. 2475., through a, a, a', 1,2,1,
3, 1, 4, &c., fig. 2479.
As the lines which terminate each of these faces are in this direction curved, it will be
necessary, for greater precision, to take for each a measure in the centre of the face, which
will give the curve of the opposite sides, by carrying throughout an equal distance dd
To bring together these two faces, and to give them the appearance of reversed voussoirs,
draw the lines a 1, d, ad", 2,7; 7,2; 3,8; 8,3; 4,9; 9,4; which will represent the joints fore-
shortened: the developments of the two other arches, fig. 2480. and 2481. LMN, and
OPQ, may be found in a similar manner, the same numbers and letters being used for
the developments of each.
For Skew Arches, inclined in walls circular on the plan. Fig. 2482. is the elevation;

2484,
E
F
G
"
+
2482.
E/
G/
2485.
Fig. 2483.
Fig. 2486
Fig. 2487.
Fig. 2488.
CHAP. XXIV.
MASONRY.
1437

Fig. 3489.
Fig. 2491.
·
fig. 2483. the plan of the
same; fig. 2484. is the
profile or section, and fig.
2485. its development;
fig. 2489. is the plan of
an arch where the faces
are not parallel; fig. 2490.
is the profile, and fig.
2491. the development;
fig. 2494. is a skew arch,
with the wall battering;
fig. 2496. its profile, and
fig. 2498. its development.
The voussoirs fig. 2486.,
2488., and 2487., shown in
perspective, belong to the
arch, the plan of which
is at fig. 2483.: the
voussoirs fig. 2493.,
2492., show those of the
arch fig. 2489., and
2495., 2497., those
of the inclined arch fig.
2489.: these voussoirs
need no further descrip-
tion than that they are
to be cut first, as if for
arches in walls, with
their faces perpendi-
cular, and then by the
means of the mould the
projecting parts to be cut
off are determined, for the
purpose of forming the
curve of the respective
faces: to prevent the
voussoirs from sliding on
their joints the ancient
masons used holes and
notches; in others mor-
tises and tenons, which
fitted into each other,
an example of which is
seen in the Coliseum,
Fig 2496.
1
E
G
Fig. 2490.
Fig. 2494.
2493.
2492.
2495.
G”
Fig. 2498,
E
Fig. 2437.
1438
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
To facilitate the opening of a door or casement inwards, the arch is constructed in the
manner shown in the accompanying diagram: in France this method was first practised at
Marseilles; these voussoirs or vault headings are formed by right lines intersecting three
arcs of circles: the first is shown on the plan at E K, in the elevation at ESP, and on the
profile or section at PE; the second is the arc RTE, and the third the arc RO:
from the point R on the elevation draw the line R V, perpendicular to the arch ESP;

Fig. 2499.
h
Fig. 2500.

G
R
T
N
s\v
m
A
B
G
n
Fig. 2501.
T
D C
C
E
the
Fig. 2502.
M
T
e
n
d
Marseilles
fg
h
JOINTS.
2.
9
N
Fig. 2506.
R
S
E
Fig. 2509,
2508.
P
P
R
O
Р
C
E
B
H
K
ནབ
R
co
Σ
R
Fig. 2503.
Fig. 2504.
F
Fig. 2505.
Fig.2507.
T
E
Montpellier
2510.
Fig. 2511.
Fig. 2512.
T
Fond
C
m




CHAP. XXIV.
1439
MASONRY.
the right lines, which form the upper part of the vault, are to be drawn from the arc RO
To deter-
to the arc SP, and that of the lower part from the arc EV to the arc RTE.
mine the position of these lines, divide RO and VP into the same number of equal
parts, and draw them from one point of division to the other, and do the same on the arcs
RTE and EV.
The plan, elevation, and section are more fully comprehended by the development of
the first, second, and third stones, in isometrical perspective; the mould by which
they are set out is also shown: the letters sufficiently indicate their position, as the corre-
sponding parts are similarly lettered in the plan, elevation, section, voussoirs, and mould
by which they are cut. Another method practised at Montpellier shows a difference at
the head, which instead of being circular is straight.
Clement Metezeau adopted this arch to decorate the internal face of the gate of St. An-
toine, at Paris: it has a semicircle at the back, and resembles a portion of an hemi-
spherical niche; the springing of the head, being from a straight lintel, is gathered over
Divide the circle FO
very ingeniously to meet the curved line which bounds the recess.
and the right line IH into equal parts, observing that the latter must contain two divisions
less than the circle; the entire semicircle would contain seven, and the horizontal line five.

G
G
Fig. 2513.
1
h
H
m
n
Saint Antoine
·
B
NN
H
Sł
"
t
F
Fig. 2515.
K
Fig. 2514.
P
દેશ ત
Fig. 2517.
9
h
a
b
Fig. 2516.
Fig. 2518.
To find the centres of the curvatures of the joints, draw the right lines hi, fn, bm; from
their centres raise perpendiculars, as 1, 2, and 3; where they intersect IH prolonged will
be the centres required.
The curvature in this vault is represented by a quarter ellipsis, whose two semi-axes are
FO and FH; they may be drawn by means of ordinates to a quarter of a circle of which
F H will be the radius; or by means of foci or points, which is the most simple. Having
developed the arcs hti, fsn, brm, they are taken for the great axis of quarter ellipses, which
indicate its curvature, and then drawn on a flexible mould.
In cutting the stone commence with the face nf, fh, hi, and in. The voussoirs in
isometrical perspective show the two intermediate stones defined by the corresponding
letters.
Intersecting semicircular Vaults. Where one semicircular arch intersects another, a void
or opening is formed, its figure varying with the angle of intersection, and the diameter of
1440
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
the vault in the accompanying diagram a semicircular vault is penetrated at right angles
by one of a less diameter. A HB is the form of the void or opening determined by the
intersection of perpendiculars dropped from the joints of both the arches. The develop-
ment of the soffite or intrados of the lesser arch is of that portion of the arch comprised
between the right line pq on the plan, and the curved line AH B forming the arris of the
void or opening. the upper stone, in isometrical perspective, shows the key of the arch

ก
g
Fig. 2519.
с
d
97
B
A
G
q
9
H
n
H
Fig. 2521.
C
d
h
B
B
P
A
9
18
ง
Fig. 2520.
h
9
n
d
m
Fig. 2522.
Fig. 2523.
where the smaller arch intersects; the voussoir underneath is the next in succession, and the
lower one that of the springing: it is apparent by tracing the various lines, which parts
correspond in plan and section, and the letters also indicate the position of the stones, as
well as their development.
The same method of
A similar Vault intersected by another in an oblique Direction.
setting out is applied to this kind; the stone in isometrical perspective is the springing
stone at MTN. The development shows the portion of the arch comprised between the
corresponding letters on the plan.
CHAP. XXIV.
1441
MASONRY.
The acute angles are objectionable in this arrangement; greater strength is obtained by
adopting the form laid down in the small figure ABCD.

B
C
Fig. 2524.
D
B
4
M
R
T
Fig. 2525.
MT
x
2526.
R
H
Fig 2527. Vaults of different diameters connecting obliquELY.
Descending Vaults, intersecting at right Angles. These are adopted to support the steps
of a staircase, as well as to form its ceiling: by a reference to the letters on the plan
and sections, as well as to the several stones shown in isometrical perspective, its construction
may be understood. The springing stone, fig. 2531., the third voussoir, fig. 2529., the counter
key, fig. 2530., and the key, fig. 2528., may have their several places found in the arch, by
observing the letters on the plan and sections corresponding with them.
It has always been the practice with masons, when greater strength and security were
required than could be obtained by the stone itself, to use metal cramps of different forms,
adapted for the purpose to which they were applied: dowel, dovetail, and cauked or
cogged are severally used to secure the joints both vertically and horizontally that are
likely to be acted upon by the sliding or moving of any of the stones after they are
bedded.
The Dowel Cramp is generally a piece of round iron, varying from inch to 3 inches in
124
diameter, and from 1 to 9 inches in length, according to the dimensions of the stones; two
holes are drilled into the contiguous faces of the work, exactly opposite to each other, and
a little larger than the dowells to be inserted, which are either fixed in soft fluid plaster
of Paris and water, or run with very hot molten lead: when the latter method is adopted,
a small channel is cut out between the faces of the contiguous stones to introduce the lead,
and a small cup or funnel is formed at the end of the channel with damp clay, into which
the lead is poured from a ladle: care must be taken to cut this channel in a perpendicular
direction, or obliquely to the back of the work, so that it may not be seen after its
completion.
Dovetail Cramps are made of flat pieces of cast or wrought-iron, with the ends spreading
out like the tail of a dove or swallow; a cavity of the same form is sunk half into one
stone and half into the other, so that the cramp may be sunk rather more than its thickness
into both, after which it is run with lead.
Descending Vault, intersecting obliquely. — In this example we are required to make
another section to indicate the length of the joints, and obtain the development of the
soffites; the great vault being oblique to this projection, the section through its centre is
expressed by portions of ellipses, determined by perpendiculars raised from all the points
4 2
1442.
BOOK FI.
THEORY AND PRACTICE OF ENGINEERING.
where the projections from joints on the plan cut with the horizontal line AB, and
continued to the intersections of the joints of the new section. The three first voussoirs are

Fig. 2528.
d
b
B
a
Fig. 2529.
G
B
a
B
IM
I M
B
a
P
N
d
C
a
Fig. 2530.
с
b
a
Fig. 2531.
α
b
C
d
d
d
e
g
h
Fig 2532. Descending vauLTS INTERSECTING AT RIGHT ANGLES.
shown in isometrical perspective: the acute angles resulting from the double obliquity of
the lesser vault, and the irregularity of the arris formed by the intersection requires the
acute angle to be changed, as in a former example.
To construct a vault where both the extrados and intrados are conic surfaces having a
common vertical axis, the solid being equally thick between the conic surfaces, so that in
the joint lines those of the beds are horizontal, and those of the headings in vertical planes
passing along the axis, the beds must be so formed that they will unite in horizontal
planes, and the headings in vertical planes. As the sides of the joints of the courses of all
vaults terminate upon the intrados in a horizontal plane perpendicular to it, if the intrados
be cylindrical, the sides are straight lines parallel to the horizon, those of the coursing
joints will be in planes intersecting the intrados perpendicularly in straight lines, and the
course will form one solid prism; the sections will consequently all be equal and similar
figures, and in vertical planes.
Groined Arches. When on a rectangular plan, and formed by two vaults of the same
height, but differing in diameter, the smaller arch being set out, and perpendiculars
dropped to the diagonal or line of intersection, by drawing others at right angles to
them, and setting off the heights of the several voussoirs of the smaller arch, we have
several points, which traced through by hand give the curvature of the greater arch.
To
CHAP. XXIV.
1443
MASONRY.

h
D
Fig. 2533.
A
Fig. 2534.
h
Fig. 2535.
9
Fig. 2536.
Fig
.
→
III
2537. Descending vault INTERSECTING OBLIQUELY.
Fig. 2538.
{
$
Fig. 2540.
Fig. 2539. GROINED ARCHES ON A RECTangular plan,
-
14


4 z 2
1441.
BOOK II:
THEORY AND PRACTICE OF ENGINEERING.
indicate the proper curve of the groin over the diagonal line, at the points of intersection
of the two perpendiculars already mentioned, draw others at right angles to the diagonal,
on which if the heights are set, a line may be drawn through them, which will express
its curvature. This latter method may serve to set out the stones of the greater arch, and
less stone is used or wasted than by the first.
Groined Vault, on an irregular Plan. The primitive form is a semicircle, drawn on the
shortest side; on this is marked all the voussoirs, after which the others are set out,
having an elliptical form. The diagonal line on the plan shows the position of the groins;
each side is then divided into two equal parts, and lines drawn from them through the centre:
from the primitive semicircle perpendicular lines are dropped from each joint, until they
intersect the diagonals; at these points of intersection, lines parallel to the centre line on
the plan are drawn, until they intersect its several sides; perpendiculars are then raised

2541.
A
K
L
L
2512.
B
2543.
Fig. 2544. GRound arches on an irregular plan,
from these points, on which is set out the various heights; a line traced through them
indicates the form of the respective vaults. The several voussoirs on the diagonal C I are
shown to the left, and those on the diagonal DI to the right of the plan; the figure
in isometrical perspective shows the stone K L.
In vaults of this description there are no groins or diagonal ribs, as was the practice of
the Romans: in the concrete vaults which remain of their construction, as the Pantheon,
Minerva Medica, and the Coliseum, a course of tiles or stone is generally introduced
at the groin, which performs the office of ribs, and it was probably discovered at a very
early period that there was a necessity for strengthening this part, and providing more
security than could be attained by the arris joint.
Before we can construct vaults composed of stones, where each is to be cut into a
particular form, we must be thoroughly acquainted with the rules by which figures may
be projected, or with the principles termed by the French engineers descriptive geometry,
by which every point in space is represented, and perpendiculars drawn from them to
each of the planes of projection, the point where any perpendicular falls being the prü-
CHAP. XXIV.
1445
MASONRY.
jection of that point: as a series of points in succession represent lines, the boundary of
any figure may be arrived at and accurately defined in every position; by dropping
perpendicular lines from the sections of an arch, the position of the several voussoirs on the
plan are perceived, and their form may be traced according to their several positions, which
vary as the stones approach or recede from each other.
Groined Vault, on an hexagonal Plan. The primitive centre, from whence the rest is
derived, is here a semicircle composed of seven voussoirs: after drawing the six diagonals
from the opposite angles, and perpendiculars dropped from the arches to intersect with
them, on either of the diagonal lines may be raised others at right angles, upon which
by setting out the heights the curvature of the groin may be traced through. The
central stone or key is set out on the plan, and its sides are perpendicularly cut, after
which the mould of curvature is applied to mark out on its section the intrados and
extrados: B is the central key, C represents the form of the other voussoirs.

2517.
A
B
Fig. 2545.
Fig. 2546.
2548.
Fig. 2549 GROINED Arches on an hexagonal plan.
In vaults of this description the pressures are reduced to six points of support,
consequently buttresses or walls of considerable depth are required in the direction of that
pressure, between which a very thin wall may enclose the building; this was the practice
of the freemasons, who did not require their external walls to have one uniform thick-
ness throughout, but applied the greater portion to resist the external pressure where
it was most needed, and by this system of construction they greatly economised their
material.
In the plan the position of every stone is laid down by dropping perpendiculars from
the joints drawn in the section above, after which their dimensions can be obtained, and the
mould taken, by which they can be accurately cut. To ascertain the form of all the plane
4 z 3
1446
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
•
faces or surfaces by which stones are circumscribed at their junction edges or arrises, the
method of projecting right lines in every possible position must be thoroughly understood
and no better study can be suggested for the mason than laying down upon paper the
representation of the solids in various positions, by which he will acquire facility in com-
prehending this most difficult part of his art.
;
Hexagonal groined Vaults, with pointed Arches or Ribs. These are composed of parts of
circles less than 90°, so arranged as to form different compartments; the intervals are filled
in with small stones bedded in plaster or mortar. To cut the ribs two moulds only are
required, one taken from the plan, which gives the upper and lower surfaces, and the other
on the section for the profile of the height comprised between the intrados and extrados.
The key is a truncated reversed pyramid, whose base is a hexagon inscribed in a circle, as in
the right hand figure: we commence by cutting a surface, on which is set out the
polygon, or base of the pyramid; its inclined sides are set out by taking the bevel; on
each of these surfaces are drawn parallel lines, the first marking the contour of the joint at
the extrados, and the other that of the intrados. The first stone of the ribs is shown at the
bottom of the figure, and its section above: A is the keystone, and its plan is shown at B.

A
B
2553.
1
2555.
2550.
Fig. 2554.
Fig. 2552.
2551.
Fig. 2556. HEXAGONAL VAULTING WITH RIBS.
A great improvement was effected by the masons of the middle ages in the construction
of polygonal vaults: the groins are always covered, as well as supported by ornamental
mouldings, and the ribs so formed carry the vault above them; we may imagine the ribs,
after they were built up, to constitute a centre or support, upon which the covering was to
be laid, and a beautiful result is produced from the expression given to the construction,
differing so materially from the former practice of concealing the ribs, or covering them up
in the mass of concrete which constituted the vault.
We have several examples of light stone or chalk filling up the spaces between the ribs,
sometimes laid to constitute an arch from one to the other, forming a groin in the
centre of each compartment, or pitching against a smaller rib in the middle, producing
CHAP. XXIV.
1447
MASONRY.
every imaginable diversity of figure: there can be no doubt that the Romans practised
the various methods of groining in concrete adopted after the introduction of pointed
architecture, with the omission of the rib, although there are several instances of it
concealed in the thickness of their vaults; the flat tile is found built up in ribs, of which
there are several remains in the springing of the vaults in the Temple of Peace at Rome.
Circular Vaults, with double Groining. The primitive vault, from whence we commence
setting out the voussoirs, is a semicircle; the others are ellipses formed from its ordinates:
lines are let fall until they meet the diagonals, as is described in a former diagram; others
are then drawn at right angles to them, to enable the setting out of the greater vault.
The double groin is then drawn to the points of the right lines which cross the centre of
the figure on the plan, at pleasure; where the perpendiculars are crossed by these groins,
they are united at their points by other lines; these show the joints of the stones at the
double groins. The four first voussoirs are at the side, and above is the vault, and on
the right is the third voussoir, both in perspective.
an
Fig. 2557.
The stones which compose
vaults of this description are
terminated by both plane and
curved surfaces: some exhibit
merely a point and two surfaces;
others, one curved and one flat,
the junction or meeting of which
produces either a circular or
elliptical arris common to both :
such figures are very difficult
to project, and must be con-
sidered as cones, which require
several points to be laid down
for the curvature forming their
bases. A pyramid with
elliptic or circular base may
serve to facilitate the projection
of a polygon, and advantage
will always be derived from a
knowledge of the regular solids,
when there is a necessity for
setting out any curved lines,
whether vertically or hori-
zontally placed. In the work
of Le Croix, the "Complément
des Elemens de Géométrie," the
best method for projecting
figures of this kind is laid
down; and their careful study
cannot be too strongly recom-
mended to those desirous of
arriving at excellence in the
art of stone-cutting, which is
decidedly much better under-
stood on the Continent than in
this country.
When vaults of large dimensions are to be constructed, there is a considerable saving of
materials as well as expense by the engineer making his contract with the proprietors of
the stone quarry for the delivery of blocks of certain forms and dimensions, for which
purpose a sketch of the forms of the stones will be required, with the several dimensions ;
and after the quarryman has roughed them out, he puts numbers upon them corresponding
with those of the drawing; each stone being thus dressed somewhat to its intended shape is
reduced in weight, and expense of transport is considerably lessened: the numbering upon
the stones should commence with those to be first used, and be regularly proceeded with
to the last. Where a series of arches is to be constructed, the voussoirs may all be got
out of the quarry in the same manner, and much of the after labour be dispensed with: no
general rule can be given for the dimensions of the various stones to be used, but the
blocks should be as large as possible, as the strength of all masonry depends as much upon
the weight as upon the quality of stone; large and heavy stones with few mortar joints
constitute the best construction. We have already observed that the Egyptians and
Phoenicians used stones of greater size than are to be found in any modern buildings, and
our astonishment is naturally excited to the manner in which they were enabled to move
them to the situations in which they are placed: whenever great strength is required, solid

Fig. 2558.
Fig. 2559. CIRCULAR VAULTS.
4 z 4
1448
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
masonry should be employed; the piers of bridges and vaults which have to resist
considerable pressure should be formed of carefully selected stone, and of a quality free
from all fissures and cracks, and care should be taken that when placed the under sides of
all the beds are perfectly smooth and level, which is not always done, less attention being
paid to them than to the upper bed, which is always in sight, and more easily worked:
the engineer who is desirous of having his work solid should observe that every stone is
bedded perfectly flat, and placed at right angles to the side that is to form its external face
throughout the whole depth, and not merely for a few inches within the joint, as is often
permitted; there should be perfect contact between the several stones in every direction
and on every plane, and no vacuity or space allowed to be filled in with cement or mortar :
for the vaults of buildings used as warehouses where heavy weights are deposited, the
masonry should be constructed with the greatest care and solidity; but for the covering of
a nave or side aisles of a cathedral or church, where no extraordinary additional weight is
to be supported, this solidity may partly be dispensed with.
Gothic Vault, with three Ribs in each Compartment, uniting at several Keys.
The centres
of these ribs are always in a horizontal plane, which passes through the springing.
The plan of the ribs being given, we first set out the centre GH, passing through the
middle of the sides which form the plan; after having drawn the chord G H, draw a
perpendicular through its centre to the point L. This point is the centre from which the
are GH is to be struck. To obtain the rib 1N, prolong their centre to 0; then set off
FO from the plan on the elevation from P to b; through the point b, draw a parallel to
the axis RP, which will cut the arc G H in d, and give the height bd for the arc IO.
To have the curve of

this arc, take for base the
diagonal E F on the plan;
set off IO from E to q,
and after having raised the
perpendicular qg, equal
to bd, draw the chord Eg,
on the middle of which
raise another perpendi-
cular, which will cut the
base E F prolonged in h;
this will be the centre of
the arc Eg raised perpen-
dicularly on Eq, and
equal to IO: but as it
must stop at N, we shall
obtain its true length by
setting off O N from qton,
and drawing through the
point n a parallel to qg,
which will cut the arc
Egati, and Ei will be the
arch represented by IN.
P
m
For the parts of the ribs
which intersect the others,
as FN on the same base
EF, describe the pointed
arch EH, whose height
FH is given; then set off
FN from F top: having
drawn through p a paral-
lel at FH, set off from
to k the height ni of the
intersecting ribs, and
having drawn the chord
k H, raise on its middle
a perpendicular cutting
the base EF in t; this
point will be the centre
of the arch forming the
intersecting rib, whose
length is expressed by
k H. The arc forming
the other rib ND is
obtained by setting off
>
k
H
R
Hi
G
R
D
(N)
n
q
P
C
B
Fig. 2560. GOTHIC VAULTS WITH RIBS.
CHAP. XXIV.
1449
MASONRY.
ND from p to s, and by raising through this last point a parallel pk, on which is set off
the height CG, taken on the section from s to m; and having drawn the chord km, raise
on its centre a perpendicular cutting the base E F in a point, which is found as p; it will
be the centre of the arc mk, answering to D N.
To facilitate the drawing of ribs of this kind of vault, the diagram may be referred to,
where their various forms are divided into voussoirs. The keys being the parts which
require the most care should be set
out with reference to all their projec-
tions.
Hanging Keys.-The last voussoir
of arches of this kind, having their
abutments against the principai key,
form together one independent of
that which constitutes the centre; this
has given the idea of suspending
keys, as well as those hollowed out,
found in many vaults of the middle
ages, which have excited astonishment
in all who have beheld them.
The filling in between the ribs
forms surfaces of double curvature,
which would be very difficult to
execute, if not sufficiently small to be
supported by plaster or mortar, and
to follow the curvature of the arcs
without its being necessary to cut
them expressly.
Gothic Vaults, formed of four
quadrants of an inverted concave
parabolic conoid with a central key,
are the perfection of the mason's art,
and we have examples of them
of great beauty in buildings con-
structed during the fifteenth century
in England. If a cone of this form
be constructed upon its broad base,
with rings of voussoirs, in the same
manner as for a

dome, their ver-
tical joints di-
verging to a ver-
tical line drawn
through its cen-
tre, it will stand
in a similar man-
ner; when the
conoid is so con-
structed, if it be
stood upon its
apex, and the
base prevented
from spreading,
the vousscirs will
retain their po-
sition. We may
imagine such a
figure cut into
four parts, each
having one flat
side against the
wall of the build-
ing and the open-
ing formed by the
four quadrants of
outer voussoirs,
which consti-
tuted its original
base, filled in with
Fig. 2561.
2562.
Fig. 2563.
11
RIBS OF GOTHIC VAULTS

Fig. 2566.
KEYSTONE AND TTS MOULDINGS.
Fig. 2564.
Fig. 2565.
1450
Book II.
THEORY AND PRACTICE OF ENGINEERING.
a large block of stone or a central key, to keep them in their place, and to lock them
together, which would form a very solid vault, and is the principle of keyed ribs.
When four arches raised on the sides of a square, as in the compartments of a cloister,
traverse each other, and unite over the centre, they are called
The Voute d'Arete and Arc de Cloitre, and are composed of triangular portions of a semicir-
cular vault: in the first, each of these parts only rests on two of their angles, as A, while in that
of the arc de cloitre each triangular part, E DC, has for its base one of the sides, which rest


E
;
D
C
B
A
Fig. 2567.
Fig. 2571. VOUSSOIR AT B.

Fig. 2568,
C
B
ARC DE CLOITRE ON A SQUARE PLAN,
E
Fig. 2572. FIRST VOUSEOIB,

B
C
D
C
A

Fig. 2573.
A
D
Fig. 2569. voute d'arete.
Fig 2570. Arc de cloitre.
E
Fig. 2574.
KEYSTONE.
on the wall throughout its whole extent: each part of the vault in the arc de cloitre is
formed by portions cut from two intersecting semicircular vaults of the corresponding
voute d'arète, that is to say, agree in figure and dimension.
Arc de Cloitre, on a square plan, having its primitive centre a semicircle, shows the
joints of the several voussoirs; the drawn lines indicate the intrados, and the dotted the
extrados.
The rows of voussoirs inscribed on each other form hollow squares, subdivided by joints
perpendicular to their sides. this projection serves to find the base of the prisms in
which each voussoir is contained. The section indicates the form of the several stones.
The four examples of development at the sides show the intrados of the voussoirs forming
the re-entering angles which characterise this kind of vault; the voussoirs are indicated on
the plan and section by the several letters, A, B, C, D, and E. The upper figure in perspec-
tive is the voussoir marked B, the other is that marked A.
Vault of Arc de Cloitre with an Octangular Plan. The general setting out is the same as in
the previous figure The primitive centre is a semicircle, as seen on the section, which when
CHAP. XXIV
1451
MASONRY.
lengthened out forms the ellipsis on the plan. The voussoirs of the angle, instead of being
comprised in parallelepipeds with a square base, are contained in a prism with a pentagonal
base; the key is a portion of a truncated octagonal pyramid, whose bases are formed by an
assemblage of triangular portions of curved surfaces, concave below and convex above.
The Arc de Cloitre on an irregular Plan has a less solid form than others, and ought
never to be used; when adopted, the operation of constructing it is tedious, but not
difficult. The rows of voussoirs should be always parallel to the walls, so that the
key has the same form as the plan; the projections on the plan give for regular vaults the
bases of the prisms in which the voussoirs are comprised; the sections perpendicular to each
side, through the centre, give the profile of the moulds at the several joints; the only dif-
ference is, that in regular vaults it is sufficient to draw out a single side, the others being
similar, while in irregular we must draw each, as they are all different in form, and as
the distance from the centre of the key to the walls is unequal, different curves result,
but they are only prolongations of that which
has the least radius, considering it as the pri

mitive centre.
N
B
Fig. 2576.
A
B
C
D
2575.
E
M
A
C
D
B
2577.
K
E
D
L
Fig.2578.
D
M
N
K
Ar
=
T
D
ი
N
Fig. 2579. ARC DE CLOITRE WITH AN OCTANGULAR PLAN. Fig. 2580. Arc de cloitre on an oblong plan.
Vaults of Arc de Cloitre, on an Oblong Plan. — On the section the form of the several
stones L, M, N, O, D is shown, and the plan of their intrados below; K is the second
stone at the angle, in perspective. In this example the re-entering angles correspond
to the diagonals of the rectangular plan, which makes the centre over the lesser side
of greater length, when drawn out, than that over the greater, which does not produce
a good effect; therefore it is preferable, when an oblong square is to be vaulted, to make
the middle portion semicircular, and the angles 45°, which gives an equal curvature to all
the sides.
1452
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

2582.
(1
10
J.
S
Fig. 2581.
Q
R
ARC DE Cloitre.
Fig. 2583.
Fig. 2585.
H
Fig. 2584.
M
L
K
I
M
K
H
H
K
Fig. 2586.
Fig. 2587. ARC DE CLO¡TRE WITH A FLAT TOP.
Vault of Arc de Cloitre, with a flat top, called by the Italians Volta a Concha, is used in large
rooms; the form which has the best effect is that which results from dividing the breadth
into three equal parts, giving two to the vaulting, and the other to the middle platform: to
give this vault all the strength possible, it is necessary to pay particular attention to the di-
rection of the joints of the level part in the centre; setting out the width of the platform on
the base of the section, and then forming upon it an equilateral triangle, we obtain the point
G, to which all the joints of the centre compartment tend.
All that has been previously described will apply to this vault; the re-entering angles
being all similar, it is sufficient to make the mould for one, as indicated by H, I, K, L, M,
which show the form of the intrados of the several stones marked on the plan. H is the
springing voussoir, and I the one resting on it.
Where vaults are constructed entirely for ornamental purposes, the thickness of the
voussoirs may be very small in some instances: at the Chapter House at Wells, they are
not more than 3 or 4 inches; particularly in the panels between the several ribs, tufa,
chalk, and stone of light weight is selected, to prevent any pressure or thrust against the
outer walls or their abutments, which in several buildings is entirely resisted by the weight
thrown vertically upon them. The masons of the middle ages knew well how to calculate
these vertical and lateral thrusts in all their constructions, and seldom used more material
than was absolutely necessary to produce the effect they aimed at; the spandrills of their
arches were kept from springing by a mass of rubble; in some cases we find the whole
spandrill formed of one large stone tailed into the wall, and maintained in its position
by the weight of several courses of masonry placed upon it; in the construction therefore
of vaults like that of the arc de cloitre, centering is only required for the voussoirs marked
C, D, and E, in fig. 2567., or NOD, in fig. 2580., where the plan is an oblong: by a
CHAP. XXIV.
14.53
MASONRY.
judicious extradossing, vaults of this kind may be made almost to balance themselves, and
to exert but little thrust, certainly not more than can be overcome by a weight put upon
the external walls, or that deposited by the timber roof, which usually covers the entire
building.
Conical Vaults have their interior surfaces
parts of cones; the most simple are those
constructed on two walls, forming an angle,
so that the centre of the face represents the
base of the cone.
All the joints tend to the apex of the
cone, diminishing in breadth; but if
continued throughout, they would be-
come too weak, therefore a single stone
is adopted, called a trompillion, A. To form
the voussoirs we must first set out their
horizontal projections, their vertical and
their profile or section, which are shown in
the elevation, plan, and the development
of the diagram.
To transfer the moulds of the intrados,
joints, and beds, with the bevels of the
angles formed by the union of the sur-
faces to which these moulds are to be
applied; the workman should take care to
select the greatest face as a base from which
to set out the others: thus in trompes he
commences with the intrados of the vous-
soirs, and dresses a face preparatory to
applying the mould.
;
In the example given the develop-
ment is a semi-cone or sector of a circle,
whose radius is equal to BC on the plan,
and whose arc is equal to the development
of the semicircle which forms the face
whence it results that each intrados is re-
presented by a small sector or isosceles
triangle, whose base is formed by the arc,
or by the corresponding chord of each
voussoir, and by two radii or sides equal to
CB.
If from the entire development, or from
that of each intrados, we cut off the part
answering to the trompillion, the surplus
will be the entire intrados, or each part
of the intrados; thus the intrados of the
trompe is expressed in the development by
C, a,b,c,d, E, n 43210, for one half, the
other being perfectly similar.
The moulds for the joints are supposed
to be laid flat on the development of the
intrados, and attached to the side to which
they have reference; thus the mould (fig.
2591.) 5, 6, 7, 4, d h is that indicated by the
line hd 4, shown on the elevation, and gc3,
10, 98, answers to the line g c 3: fb 2, 11,
has reference to fb 2 on the elevation, and
eal v to e, a, 1. This result being formed
of a right cone, hollow, and of equal thick-
ness, the angles of all the joints taken per-
pendicularly to the intrados are all equal.
C
Fig. 2588.
5
1
Fig. 2589.
8
Fig. 2591.
C
2
d
u
♡
e
r

3
(
3
h
2
0
A
L2 3 4
Fig. 2590.
d
PLAN.
E
1
E
id
b
a
DEVELOPMENT.
P
CONICAL VAULTS.
To find these angles, observe that the
voussoirs are supposed to be divided on
a circle, whose radius is perpendicular to the inclination of the inner surface of the
cone, and drawn from a centre placed on the axis; by a reference to the figures and
letters on the elevation, plan, and development, the whole setting out may be understood,
difficult as it may appear.
W
1454
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
To construct a Trompe in an Angle raking with a salient Angle. — This is a prolongation of
the preceding problem, cut by two vertical planes forming a right angle. The word
G
24
1
H
H
2592.
trompe, which has been so frequently made
use of, is a peculiar feature in French archi-
tecture of the time of Philibert Delorme,
who describes it as signifying a projecting
vault supported in the air, and derived from
the shell called the sea-trumpet; or because
it is deceptive, its construction being
hidden. It is variously used, both on ex-
terior and interior angles, in niches, or in
round towers projected to contain a staircase :

E
g
h
it
A
d
1
19 20 C
17
0
18
C
b
L
14
C
E
22
K
5
d
10
6
7.
4
-
p
M
b
k
Fig. 2 94.
32 1
G
Fig. 2593.
TROMPE ON AN Angle.
that called the Trompe de Montpellier was one of the most celebrated. Having divided
the voussoirs on the quarter circle, E C, of the elevation, whose projection is seen on the plan
at EC, and transformed to this line the divisions of the quarter circle, by others parallel to the
axis GL, we must draw through the points a, b, c, d the point L, representing the apex of the
cone on the plan, right lines from no, which indicate the projection of the circle, forming
the trompillion to GC, indicating the projection of one of the faces of the angle. These
lines will show on the plan the joints of the several voussoirs which form the trompe, and
the face of their intrados: to obtain their elevation, draw from the point L indefinite lines,
passing through the points of division of the circle dcba. To determine their extre-
mity and height, observe that this trompe being formed by a right cone, whose axis GL
is level, if we prolong the side LC to the intersection of the perpendicular G M, with the
axis LG, the angle of the trompe raised perpendicularly above G will be in the middle
of a semicircle, whose radius will be G M, and which will be the base of a cone prolonged
to the line GM: thus the height of the angle G should be equal to the radius; whence it
results, that to have the extremities of the joints of the intrados, which terminates at the
edge of the trompe, we must draw through the points d,c,b,a of the plan, lines parallel to
GM, which will indicate the radii of the semicircles in which the extremities of these
joints are found. Then from the point I at the summit of the cone, on the elevation, with a
radius equal to 5 d6 of the plan of projection, make the section, which will cut the
joint 4d, prolonged in d: from the same point, I, with a radius equal to 7 c, make another
section, which will cut the joint 3c prolonged in c. the points b and a may be obtained
CHAP. XXIV.
1455
MASONRY.
in the same manner with the radii 9b, 10, 11, a 12 of the plan. Through the points G,
d, c, b, a, C, draw a curve, which will express the edge of the trompe foreshortened to
have this curve without foreshortening, take the breadth of the line GC on the plan;
being the result of a plane cutting a cone parallel to the opposite sides, it will be a
parabola.
To draw the profile represented in the development, which indicates the section of the
trompe taken on the axis LG, on the plan: first make the base line, L F, equal to L.G;
then from the point F raise a perpendicular, FG, equal to IG on the elevation, and
draw the oblique line LG, which gives the inclination and real length of the line
passing through the middle of the key: then set off Ln from the plan from L to 0,
raise the perpendicular on, which gives the vertical projection of the circle terminating
the trompillion. In like manner set off LE from the plan from L to C, and raise the
perpendicular CE, representing the projection of the quarter circle, E C, on the elevation :
having then set off on this line the heights 17d, 18c, 196, and 20a, from C to d,c,b,
and a, draw these points to L, the summit of the cone; the indefinite lines will represent
the joints of the intrados, to terminate which, and to indicate the curve at the edge
of the trompe, set off the points E, 11, 9, 7, 5, from the plan, from C to 13, 14, 15, and 16,
through which raise the perpendiculars, cutting the joints of the intrados in the points
a,b,c,d, through which and the point CG draw a curve which terminates these joints,
and shows the edge foreshortened.
Development of the Moulds for the Intrados and Joints. The intrados of the trompe
being oblique in two directions, cannot be wholly expressed either on the plan, elevation,
or section: to find their elongation, it must be remembered, that the length of a line in-
clined to the plane of projection depends on the difference of the perpendicular distance
from its two extremities to this plane, which gives in every case a right-angled triangle,
whose vertical and horizontal projections give the two sides forming the right angle; so
that the hypotenuse of this triangle always presents the real length of the foreshortened
line.
In the figures which represent this trompe, the projection of the joints of the intrados
of the plan, and the heights given by the elevation or the profile, express the sides of
triangles which answer to each joint, represented as foreshortened; thus, to have their real
length, we raise, from the points d,c, b, and a of the joints shown on the plan, perpendiculars
to each of the lines which represent them: the corresponding heights are set off at d,p, c,
q,b,r,a,s; then through the points p, q, r, s lines are drawn to L, which give the true length
of the joints of the intrados prolonged to the point of the cone: knowing these lengths and
the chords Gd, dc, cb, ba, and a C of the centre of the developed face forming the edge
of the trompe, we obtain the three sides of the triangles forming the moulds of the intrados
prolonged to the summit of the cone, and they are united in the development, where they
are indicated by the letters L, d, G for the half key, and Lcd, Leb, Lab, L Ca.
•
The moulds of the joint are placed on the corresponding lines of the intrados to obtain
a greater solidity: they are of equal width, and their lower angle is a right angle, that is
to say, perpendicular to the slopes of the intrados, so that it only remains to find the
elongation produced by the obliquity of the joint of the intrados with the face. To obtain
this elongation, take on the plan the length of the line Lg, which represents the projection
of the diagonal of the joint mould of the key, indicated on the elevation by dg; set off this
length from G to 21 on the horizontal line passing through g, and take the distance in
a right line from I to 21, which gives the length of the diagonal required with this
length, from the point I describe an indefinite arc, intersecting another, described from
the point d with a radius equal to dg, taken on the development of the curve forming
one of the two edges of the trompe, on the elevation; having then drawn a parallel to
Ld, to mark the width of the joint, till it intersects dg prolonged, cut off by a line drawn
from g the point of the mould intercepted by the level joint. To have the direction of ·
this line, take the length Ld on the plan, with which, from the point I of the develop-
ment, describe the arc of a circle, intersected at the point 23 by another described from
the point d, with a radius equal to the perpendicular height of the point d above the
horizontal line IC on the elevation.
:
To have the mould of the joint, indicated on the plan by Lc, and on the elevation by ch,
take, as in the preceding, the length Lh, which indicates the projection of the diagonal
of this joint; set it off from 24 to 25 on a horizontal line of the elevation passing
through h, to have the distance I, 25, which will be the length of the prolongation of the
diagonal with this length as a radius, from the point L of the development describe an
indefinite arc, intersected by another, described from the point c, with a radius equal to
the joint of the head, ch, of the centre of the face prolonged: from the point of intersection,
h, draw a parallel to Lc, to determine the breadth of the joint, terminated by a perpen-
dicular raised from the point 3, which forms the section of the base. The two other
moulds of the joints are found in the same manner: it is sufficient to draw on the
stones which form the voussoirs the bevels which give the angles of the intrados with
1456
Book II.
THEORY AND PRACTICE OF ENGINEERING.
the joints; to these may be united the moulds of the head, taken from the centre of the
elongated face, Gc C, of the elevation. The figure in perspective is one of the voussoirs
adjoining the key.
Trompe under a Round Tower, in a re-entering Angle. — This is a cone cut by a circular
plane, shown on the plan by G dba C; the voussoirs are divided on the elevation in the
quarter circle, B dcba C, which presents a section of the cone, through the line B C on the
plan.

b
几
​в
A
У
Fig. 2595.
d
G
d
d
G
B
a
A
•
A
B
a
Fig. 2596. Trompe under a round tower.
Fig. 2597.
The projection of the joints of these voussoirs being prolonged on the plan to that
part of the circle forming the round tower, and indefinitely on the elevation, to deter-
mine the extremity of these joints in the double curve which forms the edge of the centre
of the face, draw, as in the preceding, from the points a, b, c, d, lines perpendicular to the axis,
till they meet the side A C prolonged. It is evident that those lines are the radii of circles
which pass through these points: with these radii, describe from the centre A of the ele-
vation, sections deba, which cut the corresponding joints in the perpendicular on the plan,
indicating the extremities of the joints of the intrados, and those of the curve of the
centre of the face. Knowing the heights and projections, it will be easy to draw the
profile indicated by the development, and the moulds of the intrados and joints, by
operating as in the preceding example.
It must be observed that, whatever be the contour of the trompe on the plan, that is to
say, straight, angular, round, polygonal, or undulated, as in the example at the Chateau
of Anet in France, the heights projections, and elongations of the lines and surfaces are
found in the same manner, by supposing sections parallel to the primitive centre, per-
pendicular to the axis of the cone, whatever be the curve of this centre: the operation
becomes longer and more complicated as the contour is more or less regular, or as the cone
is more or less oblique. The stone in perspective is one of the voussoirs adjoining the
key.
CHAP XXIV.
1457
MASONRY.
Trompe Circular, on plan erected on a straight wall. —This may be taken as an example of
roussoirs sustaining a round tower. The utmost projection which may be given to the
part of the tower it sustains must not be greater than two-thirds the radius of its
outer circumference, and
the centre of the voussoir
must have a greater height
than the projection.
To find the curve of
the voussoir or vault, the
primitive centre is shown
on the elevation, as the
base of a horizontal half
cylinder, cutting another
of greater diameter placed
vertically, and which
serves to represent the
tower; the curve formed
by the intersection of
these two cylinders is the
arris of the voussoir.
This curve being sym-
metrical and double, if
right lines are drawn.
from all the points of
one half to the other,
they will indicate the
surface of the voussoir
which sustains the tower;
we shall have the profile
of this voussoir by draw-
ing from the division
points a, b, c, of the primi-
tive centre, lines parallel
to the vertical on the
plan, and other horizontal
aa, bb, cc, on the sec-
tion. The distances are
set off at 1c, 2b, 3a, on
the plan at C1, C2, C3
on the section; through
these points raise per-
pendiculars, which will
cut the parallels drawn
from the elevation in the
points a, b, c.
E
G
h
a
h

m
Fig. 2598.
d
2
ig
4
Fig. 2602.
+
B
H B
ల
Fig. 2599.
b
a
α
3
2601.
7
6
b
Fig. 2600.
a
m
k
Fig 2603.
CIRCULAR ON A STRAIGHT WALL.
a
C
These points of intersection will indicate the curve of the section of the
voussoir, and more exactly as the division points are multiplied.
To draw the voussoirs which form the trompe, begin by cutting on each its largest face;
then for the second voussoir, which we suppose to form the thickness of the wall, get out
the square mass 1230 in the elevation, and 4567 on the plan. Take the mould mionkp,
expressing the contour which it will form on the surface of the wall, indicated on the plan
by GH, and the mould 486, B 95, of its projection on the plan; having cut the two
straight surfaces at a right angle, apply the mould mionkp to one of them, and 486, B95
to the others.
After having cut the joints mi and nk, apply the mould hefibe to trace their contour :
according to which and that drawn on the upper bed io, the stone is cut to form the convex
surface of the part corresponding to the tower, which should be square with the bed above.
The surface mb ne is formed with a curve taken from the section, placed always vertically,
as the lines bs, tv, cx indicate: the curved joint mn is hollowed perpendicularly to the
inner face of the wall; this voussoir is shown in perspective.
Skewed and inclined Arch in an inclined Wall. The interior of a round window or
bull's-eye presents the surface of an oblique cone with a circular base; the joints of the in-
trados of the voussoirs with which it is formed all tend to the summit of the cone, and the
joints of the face to the axis; from the double obliquity of this cone, the vertical face
alone, and the two horizontal beds, E F, GH, give the real size of the moulds and
the joints; the development of the intrados is performed in a similar manner to that of
oblique cones.
To trace the voussoirs, for example, of the bull's-eye or the key K, we must apply the
5 A
1458
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
E
mould 17 de and 18, of the vertical face, which will give its greatest height, and that of its
horizontal bed 12 13, 17 18, representing the extrados on the plan, which gives its greatest
length. Having then faced the stone, square with the bed, the mould is placed on it, to
draw the head of the voussoir and that of the extrados; on this tracing we may cut the two
joints, these moulds giving their double obliquity; it is only necessary to find the two other
lines, which should terminate them at the intrados, and on the side of the sloping face; this is
done by cutting the second face with the bevel of the obtuse angle, which the surface of the
extrados forms with the talus of the wall; the head mould, 12, 13, ed is then applied to
finish the tracing of the voussoir; this process may be applied to the others. The deve
lopment is seen below, as well as the key in perspective.

G
G
E
15
14!
131
BULL'S-EYE.
Fig. 2605.
Fig. 2606.
8
7
12
K
3
13
6
H

2604.
10
ELEVATION.
Fig. 2609.
d
e
18
H
MOULD OY VERTICAL FACE.
e
5/
d
15
DEVELOPMENT.
#
a
Fig. 2607.
h
9
F
MOULD.
Fig. 2610.
PLAN.
Fig. 2611.
8
10
DEVELOPMENT.
14
11
13
12

Fig. 2613.
CONICAL VAULT DOUBLY SKEWED
Fig. 2608. Key.
CHAP. XXIV.
1459
MASONRY.
Conical Vault doubly skewed, and splayed in a Wall having an Inclination. The voussoirs
may be traced in a similar manner, as in the preceding example. The voussoir in perspec-
tive is formed by dressing the vertical face at right angles with the extrados; the mould is
then applied, and the mould of the extrados on the horizontal plan; then with a bevel the
second face is cut, on which the mould of the sloping head is applied, and the stone dressed
accordingly.
Spherical Domes are formed on the plan and elevation by semicircles; the interior sur-
face of this kind of vault presents the effect of a reversed bowl, which has given them the
term cupola, when of large diameter, as those which terminate as domes. The best method
for setting them out is by horizontal courses, forming concentric crowns. Fig. 2617. shows
the plan of the soffites of the courses of voussoirs of the vault above; it is set out in the
same manner as it would be for a sphere. Supposing the interior surface of each course of
voussoirs to be formed of a portion of a truncated cone, the sides of which are represented

2616.
b
6
Cli
5'
Fig. 2614.
2617
Spherical
Vault.
d
bl
ds
Fig. 2615.
by the cords A a, ab, bc, cd of fig. 2617.
Thus to
find the radius of the arc of a circle, showing the
development of each of these parts of a cone, the chords
which answer to the courses of the voussoirs are pro-
longed until they meet the axis.
A
Fig. 2618.
DEVELOPMENT.
The interior surfaces of spherical vaults being circular on the plan, as well as on the sec-
tion, the moulds for the soffite can only be calculated by approximation, and they also re-
quire preparatory surfaces, which are not those on which should be traced the arrises of the
joints of the voussoirs.
To form these voussoirs more accurately, commence by cutting a prism which has for
base its projection on the plan: from this will result a portion of a hollow cylinder, the
surfaces of which will be terminated by the extreme arcs of this projection; thus the vous-
soir represented by fig. 2617. is comprised in a portion of a hollow cylinder, indicated on
the plan by c'l 5′ 5′ clll. The profile of the mass of this portion of the cylinder is indicated
in the section. It will be found that if the several horizontal lines be traced by a bending
rod on the curved surfaces, they will show the exact position of the arrises which pass
by these joints. There must then be exactly traced on the straight surfaces the arrises in-
Be
a?
k
5 A 2
1460
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
dicated by the angles made with the arcs taken on projection. If, according to these lines
and those traced on the two straight joints with the mould 5b, c6, the stone which is
without be levelled, using the rule, for the joints 6 c, 5 b, and cutting out the convex
parts for the arcs 5, 6, and b,c of the profile, the voussoir will be indicated with correctness.
Fig. 2619.
Fig. 2620.
D
Fig. 2619. represents the section and
horizontal projection of a spherical vault,
the courses of voussoirs of which form
in elevation vertical arches, and on the
plans open squares inscribed in each
other, like the vault of an arc de cloitre
on a square plan; this arrangement
presents at the bottom four niches form-
ing together a square.
This is appropriate for niches in
straight walls, but objectionable when ap-
plied to a spherical vault, on account of the triangular voussoirs
required by the union of the four vaulted parts of niches;
those parts which rest on acute and fragile angles are
more difficult in execution, and less solid, than where the
courses are arranged horizontally, because the parts are not
so well bonded together, and occasion a thrust which tends
to spread outwards.
In fig. 2619., B, C, D, show the moulds for the stones of
the soffite which are applicable to this arrangement, it being
understood that the surface of each course is formed by a
portion of a truncated cone, the axes of which are perpen-
dicular to the centre of the lines, expressing in plan the
projection of these slices of a cone; whence it
results that each of the hollow squares consists

C
B
of four parts of
similar cones, the
axes of which cross
in the centre, and
meet at the diagonals
of these squares. As
the direction of these
surfaces in a right
line is to the summit
of each cone, that of
the parts which unite
on the diagonal tend-
ing to two different
points should form an angle, which
prevents the development of the
soffites, corresponding to the angle of
a single piece, that is to say, those
triangular parts which are at the com-
mencement in the angles.
---
A, fig. 2619., represents the voussoir
joining the key in perspective: the joints answering to the lines of the plan, which are
vertical, may be traced on the contiguous face of the prism with a square base, in which
this voussoir is comprised, with the mould taken from the section.
For the voussoirs of the lower angles a stone must be selected large enough to hollow
out a segment of a sphere, capable of containing the soffite of the voussoir, and something
more, for the projection, as shown in fig. 2620.; it is then only required to cut out the
stone, according to the figure of the soffite traced with curves, and to form the joints with
bevels, which give the angles of the soffites, with the sections, and which should all tend to
the centre of the sphere: this method consumes more stone, but it is more simple and
accurate.
Vaults formed of a portion of an hemisphere, where the Plan is a Square, constructed in hori-
zontal Courses, agreeing with the preceding examples in every other particular, excepting
in the addition of the pendentives; it is the portion of a sphere whose diameter is the
diagonal of a square; the parts cut off by the walls form semicircles on their interior
surfaces, whose diameter is equal to the inner length of the walls; the section of a sphere
by any plane is always a circle.
CE.
In the section the arc NI is a portion of a semicircle described with the semi-diagonal
The quarter circle A D indicates the re-entering arris formed by the intersection of
CHAP. XXIV.
1461
MASONRY.
one of the walls. The voussoirs are divided on the quarter circle, E NI, prolonged from N
to E, representing the section on the diagonal of the vault.
The joints of the stones are only prolonged until they intersect the vertical PE, which
indicates the re-entering angles of the walls,. prolonged in the part occupied by the vault;
those of the pendentives form an arris, also at the intersection of the interior surface of the
walls to which they belong. To draw one of these stones, as shown in perspective, for
the beds, we use arcs marked on the plan bb and aa; and for the elevation, those distin-
guished by similar letters on the section: to form the surface of the stone, instead of a rule
a pair of callipers is applied to the great circle, directed perpendicularly to the arcs a,b.

H
P
L
E
a
L
A
a
E
N
b
D
Fig. 2621.
b
Fig.2622.
Fig. 2623.
VAULTS FORMED ON THE PORTION OF
AN HEMISPHERE.
h
A
Fig. 2624.
18
16
17
k
1
9
B
13
k
k
Fig. 2625.
g h
VAULTS ON A square plAN, WITH SPHerical headS
LAID IN VERTICAL COURSES.·
m
n
m
13
Vaults on a square Plan, with sphe
rical Heads laid in vertical Courses.
The rows of voussoirs are shown on
the plan by right lines, which are
drawn perpendicularly to the dia-
gonal; these lines form on the ele-
vation arcs of circles, shown in the
section as foreshortened, but deve-
loped outside the plan, and having
for radii other lines which are
the projection lines of the rows of
voussoirs prolonged to the great
circle passing through the diagonal
GE, and expressing the projection of
the springing of the entire vault.
To draw the voussoirs, we must form
a horizontal and perpendicular plane
corresponding to the line of projection on the plan; upon it is traced the curve of ele-

k
k
Fig. 2626.
p
5 A 3
1462
Book II,
THEORY AND PRACTICE OF ENGINEERING.
vation, which should form the arris of the section, and the remainder of the operation is
performed as in the preceding example, that is to say, with the arcs taken from the
section, and on the great circle whose diameter is the diagonal. The voussoir in per-
spective is marked with letters corresponding with its position on the plan and elevation.
The most convenient method of constructing either entire or segmental spherical vaults
is in horizontal courses: we have only described those constructed in vertical courses, to
notice the difficulties which they produce, as an assistance to those who prefer some
exercise for their ingenuity.
Hemispherical Niches are so formed that they may be cut into two equal parts by a vertical
plane passing through the centre, which would support themselves independently of each
other, or into four by vertical planes crossing each other at the centre, and each will support
itself. Hemispherical niches may be set out by three different methods: by horizontal
courses forming half circles or courses; by vertical courses, or in the form of a trompe.
The niche has the trompillion, indicated by H; it is shown in front in fig. 2627., on plan,
fig. 2628., and profile, fig. 2629. The joints of the voussoir above, tending to the centre
of the niche, are indicated by straight lines in fig. 2627., and by curved lines in figs. 2628.
and 2629.
To find the curved projection of these joints, divide the thickness of the wall in fig. 2628.,
in which they are comprised, into two or three unequal portions, by lines qr, st, parallel
to the face AC;

these lines are ra-
dii of the quarters
У
α
Fig. 2627.
L
M
of a circle, which
divide the surface
of the niche in
elevation
into
parts proportion-
ate to those of the
plan; thus for the
first joint ai of
the elevation,
lower the points
1 and 2, where
these quarters of
circles cut the
joints of the pa-
rallels, to the axis
DC, common to
the two figures;
these cut the lines
of the plan qr,st,
at the points 1', 2',
which will be two
of those of the
projection curve of
this joint in plan,
and should ter-
minate at the
points a, i, giving
four points by A
which it may be
traced, and so on
for the others. To
trace the voussoirs
of this niche,
moulds may be
used for all the
a
1
H
H
F
E
1 ig. 2629.
D
b
a
m
b
k
i
M
a
b
C
Fig. 2628.
0
Fig. 263^.
HEMISPHERICAL NICHES.
C
B
d
H
k i
Fig. 2631
faces and joints, viz. one for the elevation, fig. 2627., which may serve for the two sides
by turning it from right to left; two for the joints, and one for the trompillion. The
moulds for the joints are shown at fig. 2631., placed one over the other, so that the line
indicating the arrises of the returns of the quoins, and the arris of the extrados of the
key, are common to all. As the hollow surface of this niche is supposed to be exactly
spherical, the curves cl, bk, ai, are equal arcs of circles described with the radius A C.
Fig. 2630. represents the key, in perspective; its arrises and principal angles are indicated
by letters corresponding in figs. 2627, 2628, and 2629.
A Niche situated in an Angle. Figs. 2636. and 2637. show the plan and elevation; the
divisions of the voussoirs which tend to the centre I are made on the semicircle abcdefgh
of the elevation, the projection of which on the plan is shown by a straight line, with
CHAP. XXIV.
1463
MASONRY.
the corresponding divisions marked with the same letters. The divisions on the front
centres are determined by prolonging the joints until they meet the vertical planes of
the projecting angle; the curved arrises which they form with the soffites are, on account
of the property of the sphere, quarters of a circle of which ABCDEFGH in the
elevation only indicate that the ellipsis formed with the ordinates B1, C2, D3, K4, is of
a quarter of a circle, of which A K is radius. One of the two faces developed is shown at
fig. 2635., with its divisions of joints to serve as moulds. Fig. 2636. shows the section
R
Fig. 2634.
K
D
16
P
15
N
B
E
B
Fig. 2632
L
R
Ρ

Fig. 2635.
K
D
E
Q
M
n
12
C
F
A
H
A
I
2636.
R
L
A!
M
H
11
12
1
C
K
M
D
D
D
L
21
B
Fig. 2633.
A
N
#1
"
R
K
L
P
D
y
NICHE SITUATED in an angle.
11
Fig. 2637.
12
taken on the common axis, RIK, of the projection in plan and elevation. As this niche
is supposed to be of such dimensions that the voussoirs cannot be made in one single
stone, the profile of the joint which divides the key into two parts, and that of the trom-
pillion, is indicated in the part shaded; the lines formed by the joints of the other voussoirs
on the concave surface are also indicated in the plan and elevation, and in the part of
the profile which is not shaded. The upper part of the key, the profile of which in
fig. 2634. is represented by fig. 2637.: to form this part of the voussoir, begin with the upper
horizontal bed, which is the largest face, indicated in fig. 2636. by K, L, x, y, P; after
having applied a mould with the same form to trace its contour, cut the two faces LR DK
and RKEP square with the upper part; apply to each the mould R L K D,
taken on the fig. 2633. on the return, in order that the side R K should fall on the
arris KR for the two sides. These moulds, with the angular bevel RLD, will form
the surfaces, on which should be applied the moulds of the joints, which will give the
curves and arrises of the soffites: according to these curves, and those of the faces DK
and K E, formed by tracing with the aid of points on K 16 of the profile, the curved
surface of this soffite may be set out, on which having traced the line 11 12 terminate this
part of the voussoir by forming the back section with a bevel, producing the angle
K 16 15 on fig. 2634.
Fig. 2632. is another portion of the voussoir, uniting with the level courses; this may
be traced, like the preceding, by commencing with the upper horizontal bed, for which
apply the mould to the plan, make the large joint on the side of the key by means
of bevels taken on the elevation; then the facing, and the part of the joint forming a rebate,
which should be square with the upper bed; having prepared the face of the other
joint, trace with the moulds the straight and curved arrises which are to terminate them:
for the soffite, use points taken on the profile, as for the preceding voussoir.
Spheroidal Vaults upon a circular and elliptical Plan. Fig. 2640. shows one quarter of a
spheroidal vault on a circular plan, the half of which is an elevation or half ellipse.
Fig. 2639. is divided into three courses of voussoirs to the key; the first, the section of
5 A 4
1464
BOOK II
THEORY AND PRACTICE OF ENGINEERING.

The 91
which is expressed by E, da A G.
curve of the extrados gives at the centre
of the key a thickness equal to the

b
d
D
u
Fig. 2639.
d
E
b
A
ق
r
d
d
Fig. 2638.
half of what it is where detached from
the wall. Fig. 2638. shows in perspective
one of the voussoirs of the second course,
developed in a portion of the hollow
cylinder, the base of which is taken on the
plan, where it is marked by the letters
h, i, k,m, comprehending the projection of
the lower section: on the straight joints
of this species of prism apply the mould
dabe taken on the section, fig. 2639., which
must be turned to trace the other side.
Spheroidal Vault on an oval or elliptical
Plan, the inner surface of which is
produced by the ellipsis or oval of the plan,
which turns round its greatest axis or
greatest diameter, so that all its vertical
sections made in the direction of its length,
parallel to the lesser axis, will be semi-
circles.
B
i
a
D
m
~.
Fig. 2640.
K
لا
d
b
b
SPHEROIDS ON A Circular PLAN,
The primitive centre for dividing the
voussoirs is the qua-
drant of a circle,
whose radius AC is
equal to half the lesser
axis of the ellipsis on
the plan. The rows
of voussoirs being
horizontal, the curve
of the greater axis
being more elongated
than that of the lesser,
the intradosses are
not of equal breadth,
but increase from the
lesser to the greater
axis. The projection
on the plan of the
horizontal joints form
similar ellipses, that
is to say, their two
the
preserve
same proportion, but
they are not equi-
distant.
axes
The execution of
this kind of vault is
attended with many
difficulties, and re-
quires more opera-
tions than that for
spherical vaults with
a circular base, be-
cause, by reason of
2642.
a
a
2641.

A
SPHEROID ON AN ELLIPTICAL PLAN.
с
¿
A
k
እ
m
9
B
PLAN.
h
Fig. 2643.
CHAP. XXIV.
1465
MASONRY.
the inequalities of the diameter of the elliptic base, each upright joint requires to be elon-
gated. A simple method of obtaining these elongations, for example, that of the upright
joint whose projection is expressed by the right line b4 on the plan, is first to let fall from
the primitive centre corresponding to this joint, the perpendicular c 4, and the horizontal
64; secondly, after having divided b 4 into four equal parts, draw through these points
lines parallel to c 4, till they intersect the curve; likewise divide the projection line b 4, on
the plan, into four equal parts, and having raised perpendiculars through these points, set
off on each the height corresponding to that on the section, and through all these points
draw with a flexible rule the curve be, which will be that of the joint indicated by the
right line 64; the curves for the intrados and extrados may be found in a similar manner
for each joint. The joints in the thickness da, eb, cf, do not form surfaces of concentric
cones, whose summits are in the axis of the vault, as in spheroidal vaults with a circular
base, but a doubly curved surface.
A more simple and easy method is represented by the rows of voussoirs shown on the
plan by right lines drawn parallel to the lesser axis, and on the section by concentric
circles, whose diameters are the corresponding lines on the plan; the joints of these circles
form surfaces of truncated cones, whose summit is the point where the joint prolonged
would meet the great axis; the other joints will be plane surfaces tending to the axis; by
this arrangement we draw the voussoirs, by taking the concentric arcs to form the circular
arrisses, and the joint moulds from the section, which will be the same for all the voussoirs
of the same row. To form the intrados and extrados, take the convex and concave curves
from the section, and divide the joints into the same number of equal parts.
Conoidal Vaults, as in the interior of the Dome of the Pantheon at Paris. — The curve of
its centre, as well as that of the open arches, are Catenarian. To execute this kind
of vault it is sufficient to have the section and the plan, because each voussoir is cut

I
1
•
1
+
Fig. 2645.
Fig. 2644.
1
1
0
1
0
Fig. 2646.
Fig. 2€47.
CONOIDAL VAULTS.
1466
Book II.
theory and PRACTICE OF ENGINEERING.
as before explained for the spherical vaults, forming first the parts of a cylinder in which
they are comprised, in order to trace them by means of moulds of the curves taken on the
section and plan; the voussoirs, where the open parts or lunettes intersect with the other,
should be obtained out of portions of cylinders, comprising their greatest height, length, and
width: besides the moulds of the section and plan we must have others of the intrados and
extrados, made of flexible material; this method would suit every variety of conoidal
vault, whatever be the curve of its centre, hyperbolic, parabolic, or any other, and even
whatever the form of base, circular, oval, or elliptic.
Pendentives that support domes are portions either of spherical or spheroidal vaults,
resulting from the section of several parts of these vaults by vertical and horizontal
planes: they are made use of in gathering over a square or polygonal figure into that
of a circle or ellipsis. The domes at the intersection of the naves and transepts of a church
are so constructed.
19
B
17
Ο

C
191816 14 12
10
13
5
a
D
6
Fig. 2618.
k
เ
D
9
e
h
d
Fig. 2349.
10
12
14
15 JPG
11
13
15
A
Fig. 2651.
Fig. 2650.
A
PENDENTIVES.
When the plan upon which the dome is to be placed is square, the faces of the four
great arches that are to support it may be considered as four vertical planes cutting a
spherical dome into as many segments, and the base of the cupola usually constructed on
it, as a fifth horizontal plane which cuts off the upper portion of the sphere, so that four
spherical triangles alone remain; but as the effect of these resting on a point is unpleasant
to the eye, various arrangements have been made to overcome this defect. The faces of
the pendentives are not always portions of spherical vaults, but irregular surfaces, the
plan and elevation of which are shown.
Where rows of horizontal voussoirs are introduced, their execution and arrangement will
be found extremely simple; the projection of the rows is shown on the plan by lines of
concentric circles. To obtain these curves suppose between G and C as many vertical
arcs as there are points of each curve; to unite them on the section, so that they
have a common point B, set off AG, abcd, BC, projections on the plan of these arcs
from O to C, db G, and draw the chords BG, Bd, Bb, Bc, on the middle of which raise
perpendiculars cutting the horizontal line BI in 1, 2, and 3, which will be the centres of
each of these arcs.
CHAP. XXIV.
1467
MASONRY.
On the section is shown the position of the various arcs numbered on the plan, which
tend to the centre of the sphere, of which the triangle D A G is a portion. The figure in
perspective is a voussoir of the fourth bed.
Another method by Voussoirs in the manner already described for the Construction of a Trompe.
-The surface of these pendentives are portions of arcs of circles, but instead of being com-
prised in planes tending to the axis of the dome, they are contained in those which unite
in the interior of each pillar, at a vertical line whose projection is the point K: in order
that this should produce a good effect, the joints are not divided on the entire arc CD of
the plan, but on the part between C and M, to avoid the too great thinness of the edges
of the row of voussoirs joining AD; the part M D may be a fourth or fifth of the are CD;
in the present instance it is rather less than the fourth.

C
5
17
20
20
19
2
21
7 8
D
4
3
2 1
N
Is
5
8
Fig. 2652.
3
2
G
C
B
K
Fig. 2655.
22
Fig. 2653.
M
P
21
D
18
Fig. 2654.
17
PENDENTIVES.
To draw the projection of these joints commence by dividing CM into nine equal parts,
one of which is given to half the key, and two to each of the other voussoirs: then having
prolonged AD, till it cuts CB prolonged in K, draw through these points to 1, 2, 3, 4,
right lines which cut AB in the points 5,6,7,8. The lines 15,26, 37, 48, express the
projection of the chords of the arcs which form the upright joints of the voussoirs: by setting
off these on the elevation, draw the chords in a similar manner, but neither those
on the plan nor on the elevation give their true length, by reason of their double obliquity;
to have this, after having drawn the horizontal line CD, raise a perpendicular to it, O B,
equal to B C, and set off on CD the distances 01, 02, 03, 04, 0 D, equal to B C, 51,
62, 73, 84, 8 D on the plan; then draw the lines BC, B1, B2, &c. &c., which will be the
chords of the arcs required: these centres may be found by raising on the middle of each
perpendiculars which will cut BN in 5,6,7, and 8, which will be the centres of the arcs
corresponding to each of these chords. Then having prolonged the lines 17, 18, 19, &c. &c.
from the horizontal joints of each voussoir in the section, in such a manner that they cut the
arcs just traced, these intersections will serve to find the projection of the plan of the hori-
1468
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
zontal joints, by setting off their distance from the line O B on the lines 1 5, 26, 37, and 48.
of the plan; thus for the joint P21 of the section set off Pa on the plan from B to g,
Pb from 5 to i, Pe from 6 to m, and Pd from 7 too: through the points g, i,m,o draw a curve,
which will be the projection of the joints situate on the line P 21.
The projection of the plan of these joints and the intersections of those represented by
the lines 15, 26, 37, 48, furnish an easy method of drawing the foreshortening of the joints
on the elevation, by setting off the distances of the intersections from the line BC on the
plan on the right lines, which indicate the horizontal joints of this elevation on the vertical
B. C The stone in perspective exhibits one cut to suit this arrangement.
Groined Vault over a circular Plan consists of two semicircular vaults, differing in dia-
meter, crossing each other; the principal, AHDE, is comprised between two circular
concentric walls, and traversed by an irregular conical vault, IGQS, whose heights agree.
Ο
N

i
k
22
A
D
h
NO
α
b
d G
g
C
b
S
Q
b
C
b
d G
1
B
m
B
H
a
P
d
d
d
L
E
a
d
Y
a
9
B
g
h
h
d
ય
C
C
h
d
Q
a
፩
Fig. 2657.
9
е
F
d
S
b
α
h
C
C
T
α
16
Fig. 2656.
Fig. 2658.
CIRCULAR GRoined vault,
Fig. 2659.
If we take as a primitive centre the quadrant MS, having for
its radius the least width, QS, it results that the curvature,
starting from this line, is formed by different quarter ellipses,
whose greater axes increase from QS to IG, while the lesser
remain the same. The only difficulty in this kind of vault is
to form the voussoirs at the arris properly.
After having projected them on the plan, the mould is taken from them, by the
assistance of which prisms are cut, having a mixtilinear base; on the faces of this solid
moulds are applied, taken from the centres on the sections. To form the hollow parts re-
gularly curved rules are made use of. The development and the voussoirs are also
indicated.
Constructions for a Circular Staircase round a newel, called Vis Saint Gilles, first
practised at the priory of that name, situated about four leagues from Nismes, has the
reputation of being the most difficult operation that could be performed by a mason; all the
surfaces of the voussoirs are irregular, and the arrises formed of double curves.
CHAP. XXIV.
1469
MASONRY.


-------------------
M
K
5
Fig. 2660.
ი
Fig. 2661.
m
n
}.
с
m
d
n
m
A
Fig. 2603.
E
hi
Aa
५
Fig 2665.
d
n
e
e ft
C
a
y
m
m
•
CIRCULAR staircase.
•
•
Fig. 2662.
n

b
Fig. 2664.
α
D

G
D
1470
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
The hollow AabcdefE is the primitive centre of the vault; the easiest method of
constructing such a stair is first to set out that part of the hollow cylinder, army,
in which each voussoir is comprised, according to its projection mm, nn, on the plan,
in order to trace on their curved surfaces their ramp and arrises, as well as the heights and
widths of the steps to which they correspond. In regular staircases like the present,
the steps being equally divided, give for the developments of the concentric circles bdb,
right lines more or less inclined, which may be drawn on the curved surfaces corre-
sponding to them with pliable rules. This operation being performed for the arrises
mm,nn, of the thickest voussoirs, we may afterwards cut away the rampant part
and form the smooth soffite and extrados. To trace the voussoir, apply at each end
the mould medn of the primitive centre: the curve of the intrados and joints being set
out, draw on the intrados two lines parallel to the curved edges of the smooth soffite;
then to form these joints cut away the stone beyond the lines, applying the rule
always vertically from one curve to the other, and hollow the intrados according to the
curves traced at the two ends, by means of compasses, taking care to keep perpendicular
to the side on which is the curve; the voussoir is terminated by cutting the two ends n 3
and 64 at right angles to the extrados.
Commence by
Another method to perform this Operation, and to economise Stone.
making the horizontal projection mm, nn, of the voussoirs X, proposed to be executed, and
draw the geometrical elevation in order; to find the section of an oblique cylinder in which
it may be comprised, indicated by the lines mn and ba, representing two parallel planes,
which pass through the highest points, m, n, and the lowest points, a, b, of the voussoir when
in its place. To have the inner curve, which produces this section, divide the chord nn
of the arc, expressed in the horizontal projection, into equal parts, through which draw
the ordinates of the curve; then divide the inclined chord nn into the same number
of equal parts, through which raise other perpendiculars, and set off on each the
height of that which corresponds to it in the horizontal plane. This effected for the
two curves will give the mould mmnn, for the section of the oblique cylinders in
which the voussoir should be comprised, and which may be formed with a stone, whose
thickness will be equal to the distance between the oblique lines mm and ba, pr
and qs.
This stone should have a face at right angles with the two parallel surfaces,
answering to the chord nn of the inner curve, for the purpose of tracing from the elevation
the vertical lines nb, nb, which serve to fix the position of the mould, mmnn, with
which the contours are traced, to form the oblique section of the cylinder in which the
voussoir is comprised: this section being made on the inner and exterior curved sur-
faces, draw the ramp lines in proportion to their heights 56,n7, and the breadths n6,
57, of the steps to which they correspond, proceeding as in the preceding method for the
ramps, the joints, and the extremities of the voussoirs, which should be perpendicular to
the lines of ramp.
Vis Saint Gilles, on a square Plan. - This example is composed of jointed vaults, and
skewed as well as rampant arc de cloitre; its execution is attended with some difficulty.
The centres corresponding to the arrises of the steps, perpendicular to the middle of the
faces, can alone be right lines, all the others being oblique, and forming more or less elongated
ellipses, according to the steps to which they appertain. The plan of the vault shows one
half the arrangement: the primitive centre is a semicircle IK L, raised perpendicular on
IL as a diameter; on this semicircle the voussoirs are set out through the points a, b, c, d, e, f,
through which lines parallel to the faces BC and FG of the wall are drawn, till they
intersect the diagonals FB, GC; these lines, which indicate the projections of the rows of
voussoirs, would form on the plan of the entire vault squares inscribed in each other, as in
the projection of an arc de cloitre; the two halves of the primitive centre are represented
on the section, with the thickness of the vault, extradossed in a right line, and in the
direction of the steps it is to sustain; this figure is a section of the rampant part of the
vault, forming an arc de cloitre along the wall B C, and of the portion returned, CD, with
the projection of the joints corresponding to those indicated on the plan by aa,bb, c c.
Half the section is shown on the side of the newel, forming an arris vault, with
the direction of the joints corresponding to ff, ee, dd, on the plan. To trace the voussoirs
commence by drawing on the plan and elevation the particular voussoir to be executed,
in order to form the mould, which comprises its greatest length, breadth, and height; having
then cut a prism, whose base is the plan of the voussoir, trace on its vertical surfaces
curved or right lines with the moulds taken from the corresponding section.
To draw the rampant vault forming the joint gh, divide the arc ab of the primitive
centres into equal parts, and draw through these points lines cutting gh, which may
be regarded as the profile of a vertical plane passing through this joint; the inter-
sections give the heights, which, starting from the point h, correspond to the projec-
tions shown on the plan by parallels drawn from the division points of the primitive arc
ab on the projection of the same joint, indicated on the plan by gh, where this line repro-
CHAP. XXIV.
1471
MASONRY.
sents the projection of the vertical plane forming this joint. To draw the curve corre-
sponding to gh on the plan, set off on the parallels which indicate the projections the

fon
100
8
9
9
e
k
B
α
d
e
F
Fig. 2666.
L
1
d
9
h
G
D
k
d
a
C
A u b
d
Fig. 2667.
E
f e
H
VIS SAINT GILLES, ON A SQUARE plan.
b
a D
heights h3, hh, and gh, of the joint gh on the elevation from 3 to 3, from 4 to 4, and from
g to g on the plan, and draw with a flexible rule through the points h3, 4g, a curve which
will express that part of the arc rampant of the joint, indicated by hg on the plan and ele-
vation. The same method is adopted to find the curvature of the other joints: we must
observe that those which are perpendicular to the middle of the faces of the walls and of
the newel are portions of the primitive centre: the centres on the direction of the steps
are half-ellipses, whose lesser semi-axis, indicating the height of the centre, is always the
same, while the greater axis, which is level, is represented by a line tending to the centre of
which it is a part: these ellipses may easily be drawn by means of foci, serving to form
curves for the adjustment, when the vault is completed.. The second voussoir in the angle
is in horizontal projection, and serves as the mould for the base of the prism from which the
voussoir is to be cut: above this plan is the prism, seen at the angles, in which the vous-
soir is developed by means of the joint moulds B and C, represented fig. 2668.
The horizontal and vertical projections of the key, marked N on the plan, are also shown;
the former is the base of the prism in which the key is comprised; on the sides of the
upper figure are the joint moulds E and F.
The horizontal and vertical projections of the second voussoir from the newel is marked
O on the plan; the lower is the base of the prism from which it is to be cut, and H and
I are the mould joints.
As for the joint moulds, shown on the plan and elevation by the right lines g, h, all their
breadths and heights are set out on these lines; thus for the second voussoir, M, com-
1472
THEORY AND PRACTICE OF ENGINEERING. Book II.
mence by raising from all the points of the lines pg and gp on the plan perpendiculars,
and one from the point b, on which take a point a to represent the lower re-entering
angle of this voussoir; having set off above r, and below k, the height of the slope of

B
M
Fig. 2668.


α
6
n
C
d
H
་
Fig. 2669.
Fig. 2670.
the ascending and descending parts, draw through the two points r and k horizontal lines,
which determine the points h and h on the elevation, by their intersection with perpendicu-
lars raised from the corresponding points on the plan: then draw the inclined line hah,
to represent the apparent arris of the lower joints of the voussoir.
To obtain the curvature of the descending branch of this voussoir from the point a, take
the heights h, 2, 3, 4, g, n, indicated on the perpendicular joint gh of the centre; set them off
on the perpendiculars raised through the corresponding points of M, beginning from the
horizontal line of the base, passing through the point h.
For the ascending branch take the heights on the upright joints g,h of the centre, which
will be found similar to those indicated by the letters h, 8,9,g,n of the section, which were
set off in the same manner on the perpendiculars raised on figure M, commencing from the
upper horizontal line passing through rh.
Find the divisions on the perpendicular lines gh, gh, which mark the joints, by drawing
arrises, 7a, 12, from the profile of the second voussoir, to those corresponding to the
upper centre, 2a, b6, of the lines which cut the vertical projection of these joints.
This
operation is founded on the idea that the arrises of the rows of voussoirs on the plan form
right lines from the centre of the diagonal B F to that of the diagonal G C. We must
observe that the elongated centres of these diagonals are represented on the elevation by
semicircles, because the plane of projection on which they are expressed is parallel to the
planes of the semicircles from which they originate, and which form the primitive centre of
rampant vaults.
CHAP. XXIV.
1473
MASONRY.
Staircase with Quarter Spaces supported by rampant Vaults and Trompes on the Angles, or
by the Vault called the Arc de Cloitre. ABCD is a square plan in which the staircase is
placed: commence by drawing the parallels EH, IM, NP, at a distance corresponding
with the length to be given to the steps; these lines by intersecting form two squares,
AEFN, IKP B, and a rectangle EFKI: it is evident that in the entire plan a square
should be formed at each angle, indicating the quarter landings, and four rectangles similar
to EFKI for the steps: the well-hole will be expressed by a square or rectangle,
FHMK, and NFHC and KMDP will indicate the halves of the ascending and de-
scending ramps.

10
L
11
13
12
15
Fig. 2671.
14
Fig. 2672.
C
SECTION.
2
M
K L
H
3
E
D
2673.
5 6
7
8
B m
p q r
S
t
2
3
14
12
F
13
H
•
Fig. 2674. PLAN.
K
M
ہے
715
16
ఎ
m
n
D
To make the projection, having drawn the diagonal IP, and described a semicircle or
semi-ellipsis upon it for the primitive centre of the trompe, divide the voussoirs upon it,
which set off on the diameter I P, and draw mn parallel to IP, to indicate the trompil-
lion; then draw from the point B to all the points of the diameter a, b, c, d, e, f,h lines pro-
longed until they meet the sides KI and KP, which lines will be the projection on the
plan of the joints of the trompe.
The cone with a circular or elliptic base which forms this trompe, being cut by two
vertical planes KI, KP parallel to its sides, their section is a parabola; and this curve
forms the profile of the vault to the right of the lines KI, KP, and not an arc of a circle,
as some have supposed.
The figure in perspective shows the voussoir at the junction of the two vaults; after
having drawn on the plan and sections to indicate its greatest height and projection, cut
prisms, on the faces of which the moulds taken from the sections are applied, showing
5 B
1474
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
the ellipses which pass through the upper extremities of the joints of the trompes, and
which determine their elevation; they are drawn by sections described from their foci.
The semi-greater axis of each quarter ellipsis is found by drawing on the plan parallels
to IP, through the extremities I, 1, 2, 3, 4, and K, of the joints: the semi-lesser axes
are obtained by setting off on the section the distances Bi, B5, B6, B7, B8, B9, BK;
from each of these points perpendiculars are raised to the intersections of the line BK,
which represents the profile of the cone in its centre, and the height Kk is made equal
to the breadth IK of the ramps.
Another Method, with an Arc de Cloitre under the Quarter Space, whose Springing is level.
The centre of the voussoirs is formed of portions of an ellipsis: to obtain them, describe on
NA prolonged an arc of a circle A G, whose semi-chord G N is twice the width of the
ramp IH; this semi-chord is divided into seven equal parts, through which ordinates
are drawn parallel to NA: having then drawn the lines AN, NG, which form a right
angle, both equal to NA, fig. 2677., divide N G into the same number of parts, as NG;
and after having drawn parallels to AN, set off the length of the ordinates on fig. 2677.,
as on fig. 2678., by means of which describe a quarter ellipsis corresponding to the
arc GA.
The perspective figure is the voussoir I of the section.

Р
16
15
14
7
2675.
A
∞
Fig. 2676
ELEVATION,
G
13
F
囯
​E.
F
A
d
K
P
D
H
M
G
6
5
4
d
3
2
፩
b
2678.
2677.
N
N
A
+
H
པ
8
ico
9 10
7
F
17
I
12
13
A
G
Fig. 2679. PLAN,
18
K
D
CHAP. XXIV.
1475
MASONRY.
An oper. Staircase, sustained by the steps themselves, without an arch under them, called
geometric. There are two principal considerations for the construction of one of these
staircases, the steps, and the limon or string. The steps, which are supported independently
of the string, should be formed at their soffites by a smooth uniform ramping surface,
terminated at one side by a notch or rebate, hcd, and on the other by a face perpendicular
to the soffite: by means of these faces, and the steps resting on each other, the stairs are
pinned into a wall, and by abutting against the quarter spaces, may be sustained inde-
pendently of the string. In staircases of this kind, it is necessary to proportion the bearing
to the quality of the stone; it is usual to make the section or the height of the step,
and the part which bears upon it double; a string at the outer end of the steps prevents
the possibility of their turning, when not well pinned at the other end; this is its only
advantage, and it is now generally dispensed with: to form the steps, it is only
required to have one mould taken from the plan, and another from the elevation.

Fig. 2683.
Fig. 2684.
2
Fig. 2680.
Fig. 2682
Fig. 2681.
Fig. 2f85
An example of a similar stairs with winders and quarter space may be constructed
either with or without a string on the outer edge; those with a string, as in the former
example, form portions of cylinders, on the faces of which, by means of the height and
breadth of the steps, the ramps are set out. After having drawn on the elevations, taken
from the horizontal projections, parallel lines A B, CD, to indicate the oblique sections
of the cylinder in which the portions of the curved strings are comprised, form the
elongated moulds from the projections, fig. 2687. and 2691., by raising from all the points
k,b,o,s,p, of these projections perpendiculars till they meet the line bm, parallel to AB;
then draw through these points other perpendiculars, on which set off the distances
or corresponding widths, taken from fig. 2687. and 2691.: the moulds being found, select
a stone whose thickness is equal to the distance comprised between the parallels, and after
having dressed these two surfaces, and a face at right angles to them, fix the angle
5 B 2
1476
THEORY AND PRACTICE OF ENGINEERING. · BOOK II.
bm of the mould, and trace its contour for the cylindrical section in which the string
is comprised: the upper and lower arrises are drawn by means of plumb-lines, and a leve

k
A
k
B
m
Fig. 2ʊ 8
Fig. 2687.
D
Fig. 2686.
4
Fir. 2689
D
Fig. 2690.
corresponding with the section of the steps at fig. 2687. and 2691.
receive the ends of the steps within it.
Fig. 2691.
The string is sunk to
Geometrical staircases are now usually formed without a string, each step being partly
supported by tightly wedging its end into the wall, and it is further assisted by resting
upon the step below it. The outward end of such steps have the nosing returned on them:
the under joint, where two steps unite, is made perpendicular to the soffite of the staircase,
and the depth of the step, perpendicularly through the middle, must depend upon the
quality of the stone; when of a hard quality, like the Cragleith, the following equation may
be applied. Suppose w = the greatest uniform load on a square foot, including the weight
of the stone itself 300 pounds: the length of the flight of stairs, measured on its soffite,
and which we will call CD=10 feet, and the length of the step 6 feet, represented by BD;
wx CD³ x D Bº
then,
55 feet will be the depth of the
ƒ (C D² + D B²)
step, from the middle of the tread to the soffite, in a perpendicular direction. Where the
step is inserted in the wall, from 4 inches to 8 may be the depth of the indent; but
this must depend upon the length the steps project from the face: in staircases where
there are windows, considerable care is required to work the soffite in a regular and easy
=d²or
300 x 100 x 36
26000 × (100+36)
=
CHAP. XXV.
1477
ON STONE BRIDGES.
⚫manner; and all abrupt changes from one form to another should be guarded against, as
they produce an unsightly and disagreeable effect.
Staircase of the same Construction, on a circular Plan, may be executed either with

Fig. 2692.
Fig. 2696.
Fig. 2697.
Fig. 2695,
Fig. 2693.
Fig. 2698.
Fig. 2694
or without a string at the outer end of the steps: the forms of the steps and their
construction are sufficiently indicated by the figures which accompany.
CHAP. XXV.
ON STONE BRIDGES.
HAVING already described several bridges, we shall now proceed to give some account of
the theory and practice by which the engineer has been enabled to erect those useful, and,
in some instances, magnificent structures, which rank among the greatest efforts of his
science and skill.
On the Situation of Bridges. This must depend on local circumstances, as the leading
streets in a city, or the direction of the public roads; but wherever possible, it should
be selected at the point where the width of the river is contracted below, and continues
in a straight course for a considerable distance below, and its position should be at right
angles with the river. Skew bridges, on account of the difficulties attending their con-
struction, should be avoided as much as possible.
5 B 3
1478
Book II.
THEORY AND PRACTICE of ENGINEERING.
The quantity of Water-way to be given may be determined by the condition of other"
bridges, both above or below the situation of that to be constructed, taking care to make
the measurement at the time of the highest and lowest state of the river, and to observe
the force and rapidity with which it moves.
The Number and Span of the Arches must depend upon these circumstances, as well as
upon the nature of the foundations, the height of the banks, and the material to be em-
ployed in their construction.
The greater portion of the following observations on the construction of bridges is
selected from the " Traité de la Construction des Pons, par M. Gauthey," as edited by
M. Naviers, a work deservedly celebrated throughout Europe for its research and practical
utility.
To estimate the Quantity of Water to which the Bridge must allow a Pussage. This is
not the same at all seasons; not only is it generally less considerable in summer than ir
winter, but all rivers are subject to temporary increase, produced by abundant rains, or
the thawing of snow or ice; and the span of a bridge should be wide enough to allow the
mean quantity which the bed contains to flow through, and also afford room for the super-
abundant quantity arising from floods: it will be found that this quantity of water bears
some proportion to the surface of the land which is drained off at that point of the
course of the river where the bridge is to be erected; and it is very important to observe
carefully the time which the superabundant quantity of water takes to flow through, or
its velocity.
Gauthey's Instrument for measuring the Velocity of running Water, consists of a pallet 6.3
inches wide and 3.1 inches high, made of tin plates; a rod 3 feet 3.3 inches long is attached,
flattened at its lower extremity, as well as

10
at its upper, but in opposite directions, and
having a round hole, of an inch in diameter,
through its centre: two holes are bored in
the upper part, one oblong, the other circular,
of an inch above the first; the whole is so
constructed that the rod is in equilibrio about
the centre hole. The second part of this in-
strument is an iron handle about 2 feet 3 inches
long, whose lower end is split and pierced so as
to clasp the rod of the pallet about the middle,
nearly in the same manner as the beam of a
balance, by means of a gudgeon turning freely:
to the upper extremity of this handle an arc of
a circle is attached, having the lower gudgeon
for its centre, also a brass wire, likewise curved
in the arc of a circle. These arcs should be
placed opposite the holes in the extremity of
the pallet-rod, and pass freely therein: this
flat arc is graduated, to show the different
degrees of pressure acting on the pallet; to
retain this latter, a spring is secured to the
lower end of the handle, and it is attached to
the pallet-rod a little below the hole of the
arc, by means of a movable ring in the third
hole of the rod. To graduate the arc a table
of impacts compared to velocities must be
formed, in which the first column indicates the
current's velocity per second, and the other
the impact produced by this velocity. The
pallet-rod is then placed horizontally, the handle
being firmly fixed; a light bag is fixed to the
centre of the pallet, and all the weights shown
in the table are successively placed in it, and the
spots on the arc where the pallet-rod becomes
stationary is carefully marked and engraved.
Fig. 2699. Fig. 2700.
Fig. 2701.
To use this instrument a small piece of wood
is placed in the arc of brass; the upper extremity
of the handle is held by one hand, and the lower part of the rod by the other: the pallet
is then placed in a current of river water, and the rod allowed to leave the hand by
degrees, inclining the handle, so that the pallet-rod is always vertical. The current by
its pressure compresses the spring, and advances the small piece of cloth; it is then taken
out of the water, and, by pressing the rod till it touches the cloth, the degree to which the
spring was compressed may be read off, and hence the velocity of the current: this instru-
CHAP. XXV
1479
ON STONE BRIDGES.
then serve.
ment will measure a velocity of 6 feet 4 inches in a second; but great velocities are too
much for the instrument, and very slight are not sensible enough to be perceived; but in
rapid currents the pallet may be reduced, and in slow, enlarged; the same graduation will
We know that this velocity depends in a great measure on the fall, and as
this commonly diminishes in proportion to its distance from the source, it follows that
the same mass of water which would flow very rapidly amidst the mountains where the
river takes its rise, and where it is only a torrent, would flow considerably diminished in
velocity as it approached near the sea, or the channel into which it emptied itself: thus,
admitting that it receives no considerable increase, and that the bed has always an equal
consistency, if two bridges were to be constructed over the same river, the greatest span
must be given to that nearest the source, although a passage is to be afforded to the same
flood, but which will flow through the first in two days, whilst it will take eight to flow
through the second. To value the quantity of water, we must multiply the surface of the
section by the mean velocity: the first of these two elements of the calculation it is easy to
ascertain, but not so with the second, which must be deduced by more or less approximation
from the measure of the velocity of the threads of water of which the river is composed,
and particularly from those at the surface and middle of the current.
Dubuat, in his experiments upon the motion of fluids, had for his object the determining
the relations between the velocity of the surface and that at the bottom of the river, as well
as to discover its mean velocity. He also deduced from his observations the following
formula: calling V the velocity of the surface, and U the mean velocity, he found,
U=(V}-{W)²+W,
W being a constant number =0.02707 metres and to express the relation between the
velocity of the surface and that of the bottom, calling this last W, we have
W=(V*—W )º
On these two formulæ he calculated a table, which gives the value of the velocities of the
bottom and the mean velocity, relatively to that of the surface, from V=0·027 metres to
V=2·707 metres.
On this subject M. Prony has remarked that the above formulæ do not correspond with
experience, for supposing the second Vo, we have W=w, whence it follows that the
velocity of the surface being null, that of the bottom would be equal to 0·027 metres, a
result which could not be admitted. If in the first formula, we make V=0, we must
deduct for U a finite value, which does not agree with what we find in nature: the relation
established between U and V must necessarily give at the same time U=0 and V=0, or
V (V+a)
V+b
U= ∞ and V= ∞. M. Prony therefore adopted another equation, U=
; and the
value of the constant numbers a and b having been determined, after seventeen experiments
by Dubuat upon the values of AV, which varied from V=0·15 metres to V=1·30 metres :
he found also a=2·37187, and b=3·15312, the metre being the unit of the measure, which
gives for the preceding formula
U
V(V+2 37187)
V+3.15312
This formula has the advantage of representing more faithfully than that of Dubuat the
results of his own experiments, and of agreeing likewise with the phenomena in question,
confined within their proper limits. M. de Prony remarks that from Vo to V=3
V+2-37187
metres the relation
is evidently equal to 0·82, and as practical cases are
V+3·15312
commonly within these limits, this formula will be sufficiently exact:
U=0.82 V, or even U=V.
Neither practice nor theory has hitherto afforded any closer method of deducing the
value of the mean velocity of a current of water from that at the surface and middle; but
some observations may be made upon the manner of applying the results just explained.
The experiments of Dubuat were made in artificial canals, in which the section was a rect-
angle or trapezium, and where the depth of the water varied from 54 millimetres to
27 centimetres: some reservations must therefore be made in considering the results de-
duced, and the nature of the motions of fluids is not yet sufficiently well-known to allow of
an absolute decision, by comparing great things with small: moreover, the experiments
upon which the preceding formula is established have appeared to indicate that the
relations existing between the three velocities, V, U, and W, are independent of the size
and figure of the bed of the river, and these relations did not appear to change sensibly
when the breadth of the bed was six or seven times greater than the depth.
"It is thus,"
observes M. de Pronv" difficult to persuade oneself that the different elements have no
5 B 4
1430
Book II..
THEORY AND PRACTICE OF ENGINEERING.
influence on the relative values of V, U, and W: and experiments made on a larger scale
would possibly prove that too much deduction has already been made.
In the sixth volume of the Memoirs of the Academy of Sciences are some researches on
the motion of fluids, applied principally to what is called linear motion, that is to say, to
the case in which the molecules of the fluid move in a rectilinear bed, following right lines
parallel to the axis of this bed; and the results relative to the question now under conside-
ration are, that, whatever be the figure of the transverse section, the mean and greatest velo-
cities at the surface and middle of the current tend to become equal as the dimensions of
the bed decrease the relation between these two velocities is independent of their absolute
value: if in a rectangular bed the horizontal breadth be supposed very great, and the
vertical depth of the water very small, the mean velocity will be about 0.64 of the greatest
velocity. If the two dimensions of the rectangular bed are supposed to be very large, the
relation between them will be about 0.41, which formulæ give the means of calculating the
relation for different beds, of which the transverse sections are semicircles or rectangles.
:
Experience proves that the true laws of the motion of waters in the beds of rivers or in
pipes differ from those of the linear motion: the only case in which nature realises these
latter laws is that in which fluids flow in rectilinear pipes of very small dimensions, and
the results deduced immediately from this observation are those alone to which we can pay
any consideration in the case before us.
At the time of great floods, which is that for taking the elements of a calculation on the
quantity of water, it is generally overflowing the banks and extending on both sides over a
large surface, where it flows slowly, whilst there is a considerable velocity in the midst of the
current, and it is very probable that gross errors would occur if the rules for calculation
just cited were applied to these cases. If possible, a part of the river should be selected
where the water is so confined that during floods it does not overflow to any great extent;
and the section of the velocity should be taken at a bridge, if any exist near the site of that
projected.
It must be acknowledged that the means we at present possess for obtaining the direct
value of the mean velocity of a river are very limited, and subject to more or less error.
As a certain relation must exist between the section, the fall, and the velocity of the cur-
rent, and as it is always possible to measure these, the value of the velocity would naturally
be deduced from it, if its relation were well known; M. de Prony in the work before cited
has deduced it from the best experiments he could collect, and has arrived at the equation,
U : = −0·0719 + √/0·005163+3232·96 R I,
in which U being always the mean velocity of the current, R represents the mean radius,
that is to say, the area of the section divided by the part of the perimeter of that section
which belongs to the solid side in which the fluid flows, and I, the fall in a metre.
Since the researches of M. de Prony, M. Eytelwein has published in the memoirs of
the Academy of Berlin some experiments, on the means by which he has established a
formula similar to the preceding, but of which the coefficients have somewhat different
values: this formula, taking the metre for the linear unity, is,
U — —·003319+ √0·0011016 +2735·66 R I.
The experiments which have determined the coefficients comprise the values from two to
three metres for the velocity, whilst the experiments which M. de Prony has made do
not exceed 0 m. 88 c.. the formula of M. de Prony agrees, as well as that of M. Eytelwein,
with experience, as regards small velocities, but they appear to give very feeble results for
large ones. M. de Prony has given for the motion of water in pipes this expression,
U – 0·02488 + √/0·0006192 +2871·43 R I,
which agrees better than that mentioned above with those experiments in which the value
of the velocity is above one metre. The first equation will give the value of the mean
velocity with sufficient practical exactness; but it must be observed, that it supposes the
size of the section of the river, and the value of the fall, to be the same in a sufficient length
for the mean velocity to be regarded as constant; and it is necessary to take this into consi-
deration when the formula is used.
The dimensions of the beds of rivers are generally sufficiently constant, with the ex-
ception of particular cases in which their course is through sandy lands, which yield with
so much facility to the action of water that the current may at each increase be carried
into different parts: at each point of the course of the river a certain equilibrium is
established between the action exercised by the waters on the cavities, and the tenacities
of the matters of which the bed is composed; and in virtue of this equilibrium remarkable
changes seldom occur either in the size or form of the bed, which nearly always preserves
the same rule. But if, from any cause whatever, the force with which the water tends
to corrode and destroy the bottom and shores of its bed be augmented, the bed will be
enlarged until a new equilibrium is established, unless the side walls are so composed
CHAP. XXV.
1481
ON STONE BRIDGES.
·
as to present a resistance more considerable than the force with which they are attacked.
If the rapidity of the river has, on the contrary, undergone a diminution, the bed will
increase from the effect of the successive deposits, until the size of the section becomes
equal to what had been taken away, according to the relation marked out by nature
for the stability of rivers.
It results from these principles, that if the width of the river be diminished by works
going on in its bed, the rapidity being increased, a shoal or island will be formed, and such
a fall that the bed will be deepened until the increase of the section combined with that of
the velocity will compensate for the diminution in the width of the river, and the velocity
be again in equilibrio with the resistance of the bottom. If, on the contrary, the width
of the bed be augmented, the rapidity being diminished, it will have a tendency to fill up.
It is very essential in constructing a bridge to pay attention to the velocity with which
the water will move under the arches, and which must not be allowed so to augment as
to force the current to attack the bed of the river and injure the foundations of the piers
and abutments; it must not either be sensibly diminished, because in that case a con-
siderable additional length would be required for the bridge, and the deposits which would
take place might become dangerous. The nature of the ground of which the bottom of the
river is composed must be considered: if excessively compact and tenacious, and approach-
ing to rock, it will not yield sensibly to the action of the water, and whatever then may
be its velocity, there is nothing to fear for the safety of the bridge; but as the waters
cannot acquire a great velocity, an eddy more or less considerable will be formed above the
bridge, which, in the case of the mouth being extremely narrow, might produce inundations
in the upper part of the river, and render the navigation difficult. If the bottom be
composed of matter which can easily be acted on by the water, care must be taken to
prevent the usual velocity from being sensibly augmented: if the ground yield to the
action with such a facility that there is reason to fear the increase of the current
will be carried under some arches and hollow out the bottom, whilst it would deposit,
at the same time, sand under others; this would be a case for constructing a general frame-
work of ground timber, by which the bottom, presenting uniformly the same resistance to
the action of the current, would oblige it to distribute itself equally through the whole
width of the river; and so long as this framework should subsist, there would be no
reason to fear that any of the piers would be injured. From the preceding observations
it is evident, that the velocity with which the water will flow under the bridge should be
in all cases determined before-hand, either from the nature of the ground which composes
the bed of the river, or by the height of the eddy formed above bridge, and which depends
on the value of the velocity; and as the quantity of water which the river discharges
is also known, the surface of water-way which the bridge should leave can be easily es-
tablished. The question then resolves itself into the following problem: the section of the
bed of the river, and the velocity of the water being given, to determine the new velocity
which the current will take, and the height of the eddy which will be formed, supposing
that the bed is narrowed by the construction of the piers and abutments of a bridge.
This problem cannot be very rigorously solved, but we
shall, neglecting some circumstances, the effects of which
are not very sensible, and which compensate for them-
selves in a great degree, give after Dubuat an approxi-
mate solution, which can be usefully applied.
C

D
}
H
K
I
F
E
A
B
Let us suppose AC, DB to represent the lateral
face of a pier, and GE F the natural inclination or fall
of the river before the bridge is constructed; the cur-
rent being confined in the interval E F, the velocity, and
consequently the fall, will be there more considerable;
and the surface of the water, making allowance for the
particular resistances produced by the starlings, will take an inclination represented by the
line IF; the surface above bridge will necessarily rise above the point I, represented by
the line HK, which for a small length is horizontal.
Let us call
the area of the section natural to the river ;
Fig. 2702.
w, the area of the section after the bridge is constructed, or the area of the
surface of the water-way;
V, the medium velocity of the river;
v, the mean velocity of the water under the arches, after the construction of
the bridge;
I, the fall by metre of the river;
s, the length of the piers and abutments = A B, or EF;
H, the height of the eddy - EK;
=
g, the accelerated force of the weight=9·809 metres.
Ω
We shall have v=
since in a river the velocities are in an inverse ratio to the area
W
1482
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
of the corresponding sections, and the heights due to the rapidities V and will be
represented by
Vº
and
2 g
w2g
The part IK of the height of the eddy corresponding to the increase of the rapidity
will be then
IK=
(-1);
and as, on account of the contraction which the current will undergo in general at the
passage of the bridge, the section w is diminished, we must substitute in this expression
the area w by mw, designating by m a coefficient, the value of which depends principally
on the width of the piers, as well as the form of the starlings and springing of the arches.
We shall have then
IK=
V2 Q2
2
29
g m² we
−1).
We must now seek the value of the fall, which will form itself on the length of the piers:
before the construction of the bridge this fall was equal to sI; and as the falls increase
nearly in the relation of the heights due to the correspondent velocities, we shall have for
the value of the new fall,
s I
Ω
m² wa
Thus the part of the height of the eddy which arises from the increase of the fall under
the arches of the bridge will be represented by
and we shall have
EI=sI (23-
(1900-1);
リ
​EI+IK=H=
2
g
(+1)(31)
2
m²
for the height to which the waters of the river rise above bridge, since their level must
remain the same below bridge. To apply this result it will be sufficient to put in the
m w
Ω
place of V the expression v and to give afterwards to v the value which will have
been fixed before, according to the principles referred to, for the velocity which the waters
take under the bridge. As to the value of the coefficient m, we are unable to fix it very
exactly; the experiments relative to this subject have been made on orifices pierced in
walls of different thicknesses, to which pipes have sometimes been adapted, and through
which the water flowed under weights more or less considerable; independently of the
circumstance that the dimensions of these orifices, even in experiments made on the greatest
scale, are not to be compared with those of the arches of bridges, it must be remembered
that the flowing is different from that now under consideration.
The form given to the starlings of the piers of bridges has a sensible influence, as well
as the thickness of the piers, on the manner in which the contraction operates, by
which the natural flow of the river is modified on meeting the bridge. The value of the
coefficient m, as we have seen, depends principally on the form of the starlings and
the springing of the arches, when they are plunged in the water. We have not fixed with
exactness that which it would take in different cases; but we should not be far from
the truth in supposing m=0·95, when the piers are terminated in a half circle, or by acute
angles; m=0·90, when terminated by obtuse angles; m= -85, when terminated square,
supposing the arches to be large: in the most disadvantageous cases, that is to say, for
small arches, and when their springing is under water, the value of the coefficient m
may be about 0.7.
In putting in the preceding equation for H and v the values which
we have given, according to the nature of the bed and other local circumstances, we shall
easily deduce from it that of the relations of the two sections w and 2.
To determine the height of the eddy which may be formed above bridge, we must
consider the changes it will occasion in the height of the river, and the inundations which
may hence result on the banks. According to Dubuat, it is generally admitted that
the surface of the waters, which, before the construction of the bridge and in the hypo-
thesis of a uniform fall, was an inclined plane, becomes after the construction a concave
surface, touching the primitive surface at the point where the exhaustion of the water
ceases. This author has also given rules for the calculation of the eddy, on the suppo-
sition of the profile of this surface being the arc of a circle of great amplitude; but
much confidence cannot be placed in them. When the bed of a river is irregular,
and presents considerable variations in the fall and in the width,—when, in the case of an
CHAP. XXV.
1483
ON STONE BRIDGES.
increase, a part of the waters flow slowly over inundated banks, the exact figure of the
surface of the fluid cannot be obtained, but it may by a sufficient approximation when
the bed is uniform and the movement of the waters permanently established. M. Belanger,
engineer of the Ponts et Chaussées, has given for this purpose the following calculation :-Let
us calls a length taken on the bottom of the bed, in the direction of the stream; h, the
vertical height of the transverse section of the current; w, the area of this section
corresponding to the height h; x, the width of the section w taken on the surface of the
water; R, the mean radius; i, the fall of the bottom of the bed in metres, which is supposed
to be constant; Q, the volume of water which the river discharges in a second; we have the
equation
8:
-fah + (0000
gw
Q
ω
1
Q
0-00002427+0-0003655);
in which the metre and the second sexagesimal are taken as units of length and time,
g representing the velocity 9.809 metres, which the gravity may impress on the body in a
may be valued as the function of the
height h of the section. In calculating the value of the integral indicated by this sign,
setting off from the greatest value of h, which takes place at the point of elevation, that is
to say, immediately above bridge, to a second value intermediate between the preceding
and natural value of the section, the result will give the length comprised between above
bridge and the section to which belongs this second value of h. We may thus ascertain
the relations between the given heights of the sections and the distances from the bridge to
which these heights extend, and consequently the figure of the surface of the fluid through
the whole extent of the eddy, which is generally prolonged to an infinite distance, but the
increased or greatest height at a limited distance ceases to be evident. The formation of
an eddy above bridge producing great inconveniences, both in relation to the solidity of an
edifice and the difficulties to which it subjects navigation, every effort should be made to
diminish it as much as possible.
second; all the quantities comprised under the sign fr
It has been observed that it was dangerous to give too great an opening to the water-
way, for the reason that under some arches alluvial deposits might be formed, which,
acquiring by time sufficient hardness to resist the action of the current, would, in a flood,
oblige the waters to flow under the arches which had remained free, and thus expose the
piers to injury by attrition. For a similar reason building a bridge of two parts, separated
by an island, should be avoided: it might happen that one portion becoming encumbered,
the whole current would be obliged to pass under the other, and occasion its destruction:
the bridges of Chazey and Roanne were carried away from this cause, and the fall of most
bridges may be attributed to some error in the water-way producing too great a
diminution of the section, from too little or too great a length having been given.
All the
elements for the calculation of the area of the water-way should be taken at the time of
the greatest floods; and according to the quantity which flows at this period, the area
must be determined. It is essential in rivers which will admit of them, so to dispose the
arches that at low water there should be under some at least a metre in depth, in order that
the navigation be not interrupted: it will always be possible to combine the different
conditions between the size and the form of the arches used, and in each particular case,
by making different experiments, to arrive at the best solution of the problem.
Gauthey applies the preceding ideas to the bridge over the Durance at Bonpas, which is
constructed in wood between two banks, distant from each other 534 metres. The width
of the river at low water is only 110 metres, and the mean depth 1.30 metres: but the
flow of the river rises 3 metres, and the surface of the water-way is then 1530 square metres.
The bed of the river not being confined, and the width being considerable in reference to
its depth, it was difficult to ascertain the mean velocity with exactness; but at about 4 my-
riametres above Bonpas, near to Mirabeau, the Durance passes between two precipitous
rocks, distant from each other only 180 metres. At this point, the height and velocity of the
water were ascertained during the floods, more or less considerable, and the result was,
1st, That the river being 2·44 metres reduced depth, the mean velocity was 1.95 metres
for a second:
2nd, That when the river was 2.92 metres reduced depth, the mean velocity was 244
metres per second:
3rd, That at the moment of the greatest floods, the depth of the waters being 4.87 metres,
the mean velocity was 4·12 metres. Thus, in this latter case, which must be particularly
considered, the expenditure of the river is 180 x 4.87 metres x 4.12 metres =3612 cube
metres per second.
The distance from Mirabeau to Bonpas not being considerable, and the river only re-
ceiving between these two points some rivulets or unimportant streams, there cannot be a
1484
Book II:
THEORY AND PRACTICE OF ENGINEERING.
very great difference between the quantity of water which flows at either place: we may
value by approximation this difference, by comparing the superficies of the basins, which
supply the water at Mirabeau and Bonpas, and we find the latter surpasses the other about
one-sixteenth; hence there must flow at Bonpas in a second a volume of water equal to 3838
cube metres, which for a section of 1530 square metres gives a mean rapidity of 2.51 metres.
The construction of the bridge in wood diminishes a very little from the superficies of
the water-way, and we may remark that the rapidity of 2.51 metres per second, which cor-
responds to a height of water of more than 3 metres in the bed of the river, scarcely
surpasses 2.44 metres of rapidity, which the river takes naturally at Mirabeau, for a
height of water of 2.92 metres. Thus the mean rapidity at Bonpas is less considerable
than in other parts of the course of the river, and the waters have there an easy discharge.
The discharge of the Rhone at the bridge of St. Esprit is about 3580 square metres; that
is to say, a little more than double that of the Durance at Bonpas, whilst the superficies of the
basins, the waters of which flow to the Rhone at St. Esprit, is more than five times greater
than that of the basins which flow into the Durance at Bonpas: thus, although the rapidity of
the Rhone is very considerable under the arches of the bridge of St. Esprit, it would ap-
pear that the discharge given to the Durance is much too great. But we must observe
that this river at Bonpas, being only 25 myriametres from its source, is still a torrent, whilst
the Rhone at St. Esprit is no longer such.
It is then very essential in regulating the water-way of bridges to distinguish the torrents
of rivers, and to have regard, in comparing the superficies of the basins, to the nature of the
soil, and to the time which the waters take to flow: it may happen, as we have said above,
to be necessary to construct over a river a bridge larger at a little distance from the source,
than at a place farther distant, although it may have received in the interval several tribu-
tary streams.
Of the Form of Arches used in Bridges. The arches of bridges are divided relatively to
their form into three principal kinds: semicircular; those generally described by several arcs
of a circle of different radii, and the form of which approaches to a demi-ellipsis; and arches
which form the part of a circle, more or less. Semicircular arches are the most ancient; there
is scarcely any ancient bridge in which this form is not employed, and during a long time it
was generally adopted in Europe; it has the advantage of greater solidity and more facility
in construction, but the inconvenience of considerably obstructing the passage of the water.
Flat arches were not introduced until the end of the seventeenth century, and their adoption
arose from the necessity of giving as much water-way as could be obtained without con-
siderably increasing the height of the arch: this it effects admirably, and presents besides,
when the two diameters are not very unequal, almost as much solidity and facility in the
construction as the semicircular.
Of arches forming a part of a circle there are two varieties: the first is that where the
springings are under water, as is the case in the first great bridge built in France, as the
St. Esprit, and the ancient bridge at Avignon; but this form has the disadvantage of
giving less water-way than the flattened one, and of requiring very massive tympanums.
This latter defect appears to have been recognised by the first builders, for the backs of the
arches are almost always simply filled with earth, or discharged by means of a number of
small arches. In the second case the springing of the arches are raised on piers nearly the
height of the greatest rise of the river, as at the Pont Louis XVI. at Paris, which generally
requires the arch to be much flattened; hence it results that the lateral pressure of the
voussoirs is very considerable, and great care is required in the construction, in order that
the arch should not sink after the striking of the centre, which has sometimes occurred.
The manner in which the thrust of arches of this kind exerts itself is different from that in
which it acts in others; they do not generally tend to overthrow their abutments, but to
make them slide horizontally; we shall indicate hereafter the means for resisting this thrust
without incurring any considerable expense. We shall also find that the resistance
opposed by the springing of the arches to the current when they are plunged in it, is one
of the principal causes of the wearing away that takes place at the foot of the piers :
bridges with circular arches have in this particular a great advantage over others, when
their springing is not reached by the waters of the river.
It is not possible to give general rules for the selection of these different kinds of arches ;
the decision must be made in each particular case according to local circumstances, as
the width of the water-way, the height with regard to either high or low water, the height
at which the surface of the pavement of the bridge may be placed, the obligation which
sometimes occurs of destroying one arch, and consequently making the piers perform the
functions of abutments, are the principal considerations: due regard must also be paid to
the nature of the materials and the degree of resistance they may offer.
To the three species of arches mentioned, which are those now in use, we may add the
forms employed by the Arabs, and above all the Gothic, composed of two arcs of a circle,
and known under the name of OG: this latter has the inconvenience of considerably
diminishing the water-way; but this defect is easily remedied by making openings in the
CHAP. XXV.
1485
ON STONE BRIDGES.
tympanums, as in one of the bridges of Pavia, and there may be cases in which they may
be used with advantage: taste should proscribe none, for each has its merit when properly
applied.
On the Width of Arches of Bridges. Although the width of the arches depends generally
on the particular circumstances of the place where the bridge is to be built, a few obser-
vations may assist us relative to this point. Small arches principally suit tranquil rivers,
whose waters do not rise to a great height, whence it is generally easy to lay the foundations,
and no fears need arise with regard to multiplying the points of support: great arches on
the contrary are adapted for torrents, in which it is generally difficult to obtain foundations,
and which, carrying down rocks and trees, damage the piers and springing of the arches,
which in such cases consequently should be placed above the surface of the waters. In
great rivers large arches are preferable, above all where strong eddies frequently occur; but
the cost which the foundation of the piers would entail must greatly influence the decision
on this subject: due consideration must also be given to the nature of the materials
employed, which require to be of greater solidity for large than for small bridges, also to
the size of the craft navigating the river, for which a commodious passage must be left.
With regard to the relative openings of the arches, these two plans may be adopted, either
to make them equal to each other, or to diminish them progressively from the centre to
the abutments. If all the arches be equal, a level line may be preserved and the same
centres used; but then the height of the approaches must be augmented, and consequently
it is necessary to enlarge the embankments, thereby raising them above the houses in the
vicinity another inconvenience arises from the want of fall to drain off the rain water,
which, if allowed to remain long on the bridge, penetrates by degrees down to the covering
of the extrados, and injures it: much inclination cannot be given to the channels which
convey the water to the gullies by which it is ejected into the river, whether the waters
flow off at the extremities of the bridge, or by the openings practised through the arches
themselves. If the diameters of the arches are unequal, these latter inconveniences dis-
appear; each side of the pavement of the bridge may then have a fall, which, however,
must not exceed 3 in 100: the difficulties occasioned by lofty embankments are at the
same time overcome. It is possible, however, to unite the advantages of these two
methods, by giving to all the arches the same opening, but placing the springing at
levels decreasing from the middle to the extremities of the bridge: it is necessary to leave
the arches of a sufficient height that in floods, trees, &c., which the river carries down, may
pass freely under them.
:
Of the Breadth of Bridges.-The breadth which should be given to bridges depends
solely on their situation, and must be regulated by the importance of the road on which
they have been constructed, or the population of the town to which they belong; and it is
essential not to make the breadth too considerable, because it uselessly increases the
expense. If the bridge be constructed in the country for a road in its vicinity, it will
be sufficient to give it a width of from 12 to 15 feet, if not very long; for a road of the
second class, the width should be from 18 to 22 feet, which will be sufficient for the passage
at one time of two carriages and foot passengers: for a road of the first class it should be from
25 to 35 feet in width. In the interior of cities the width may vary from 30 to 60 feet,
with relation to the population and commercial activity, but it should seldom exceed this
latter limit, though the Pont Neuf at Paris, which is without doubt one of the most
frequented bridges in existence, is 72 feet in width between the parapets.
Arches used in the Construction of Bridges, when semicircular, should have their centre at
the level of the top of the foundations, or that of low water; circumstances sometimes
require it to be elevated above when it is raised on piers.
Flat Arches with three Centres, or two. The form of these arches is not entirely deter-
mined either by the span or the height; it is possible to describe on two given diameters
an infinity of different curves; the sole condition to which the curve of flat arches is
subject is, that the tangent at the summit be horizontal, and those at the springing be
vertical. As a semi-ellipsis satisfies these two conditions, it appears natural to select this
curve, which, decreasing regularly from the springing to the summit, is peculiarly agree-
able to the eye: but it has the inconvenience of requiring a different template for each
voussoir composing the arch; neither does it allow so much water-way as the curves of
which we are about to treat, unless the difference in the two diameters of the arch be made
very considerable.
Instead of the semi-ellipsis, curves are generally employed, formed by arcs of a circle,
since they enable the engineer to determine with ease the length and the radii of these
arcs, and thus to give the most convenient form to the arch: two conditions must, how-
ever, be fulfilled:
1st, That the outline of the first arc of the curve, setting out from the springing, should
contain that of an ellipsis, constructed on the two diameters of the flat arch, in order to
obtain for the latter greater water-way than it would have if the ellipsis were employed.
2nd, That the radius of the arc at the summit should not surpass a certain limit; for the
1486
Book II.
THEORY AND PRACTICE OF ENGINEERING.
value of this no general rule can be given, but it must scarcely exceed the width of the
arch; and if particular circumstances require a greater radius, the joints of the voussoirs
must not be directed to the centre of the arch, but towards a nearer point.
These two first conditions fulfilled, the number of arcs of a circle of which the arch
shall be composed must be determined; it must not be less than 3, nor exceed 11. The
following rules for describing these arches are usually adopted by engineers.
Flat Arches described with three Arcs of a Circle. The length of the radii of the three arcs
composing the flat arch not being determined, when the two diameters of the curve are
fixed, another element must be introduced. We will suppose first that the three ares
are all of 60°; that is to say, each equal to the sixth part of the circumference.
The half of the span of the arch A C is equal to a, and its height CD=b; the centres of the
two arches described at the springing will necessarily be situated in the two points F, G, in
the line A B, and the centre of the third arch in a point E in the line DC prolonged;
one of these centres being found, the two others will be also.
Call the distance from the point C, in the
middle of AB, to the centre G. The triangle
FGE being equilateral, we have EG equal FG,
and, consequently,
or
CE+CD=FG+GB;
√3.x+b=x+a;
and by resolving this equation,
I=
a-b √3+1
/3-1
(a—b).
2
This value is constructed by setting off from the
point C the line CK-a-b, and after having
formed on it the equilateral triangle CHK, carry-
ing from L to G the height LH of the triangle.
The position of the centres of the three arches
may also be obtained by tracing the quarter of the
circle AIH (fig 2704.) and the equilateral triangle
ACI; then drawing DM parallel to HI, and
MFE parallel to IC.
Let us now suppose that one of our conditions is
that the greater and lesser arc differ from each
other as little as possible. Call the half of the
span of the arch AC-a, and its height C D=b;
the radius AF of the arc of the springing y, and
x that of the arc of the summit, the centre of
which is in E; we shall have by reason of the rec-
tangular triangle CFE,
(x-y)=(x-b)² + (a—y)³.
In resolving this equation with relation to x, we
find
D

H
A
B
F
C
LK/G
M
E
Fig. 2703.
H

D
Fig. 2704.
ח
G
B

ļ (b³ + a³) — ay
b-y
We shall then have for the expression of the re-
lation of the two radii,
§ (b² + a²) — y
Y by — y³
By making its differential equal zero, and find-
ing the value of y, we find, after abridging, b² + a³ =c³,
bc
y=
c+(a−b) '
putting this value in that of x, we deduce from it,
ac
I=
-(a-b)
G
H
F
C
E
Fig. 2705
These two expressions are formed by cutting off from the line A D (fig. 2705.) the distance
DG, equal to a-b, and raising on the middle of the remaining part AG the perpendicular
HE; the points E, F, where it meets the two diameters of the curve, will be the centres
sought. This method gives a greater difference between the lengths of the two arcs than
the preceding, which appears preferable. When the relation of the two diameters is not
less than one-third, the difference of the radii of the arcs of which the flat arch is composed
is not sufficient for the passage from one to the other to be marked, and produces a dis-
agreeable effect, and it must be described with three arcs of a circle; but when the arch
is flatter, a greater number inust be employed.
CHLAP. XXV.
1487
ON STONE BRIDGES.
The forms which are here described for the arches of bridges are given without any
reference to their equilibrium, a subject which has been found one of the most difficult the
mathematician has had to consider, and perhaps of little value to the practical engineer, if
it could be rightly solved; for the latter must ever be guided by those rules which expe-
rience dictates; if he follow implicitly in the path theory points out, he may fail, from
observing the nice and too often close deductions made in her calculations: when, however,
theory is borne out by practice, we are warranted in submitting to all that is propounded.
Emerson's Fluxions and Hutton's Principles of Bridges may be consulted by the reader
who is desirous of becoming acquainted with these delicate but important applications of
mathematical science. The practical method of hanging up a semicircular polygon, with
weights at the joints of each link or side, will afford the student data for calculating the
form that should be given to the extradossing of an arch of any figure, as the weights which
would pull it into any given curve would, if placed upon an arch, maintain it in the same
position, or cause it to be in a state of equilibrium.
Of flat Arches described with more than three Arcs of a Circle. — Different methods have
been employed to determine the positions of the centre, and the length of the radii of the
arcs of which these curves should be composed; the following was that adopted for
the arches of the bridge at Neuilly.
After having fixed the radius F B of the
first arc at the springing, on the pro-
longation of the lesser diameter CD, a
distance is taken, CE, which is arbi-
trarily made triple C F, and which might
bear any other proportion to that line:
having then divided CE into five equal
parts, CF into five parts, which are to
each other in the proportion of the num-
bers 1, 2, 3, 4, and 5, join the points of
division by the lines LF, MG, NH, OI,
EK; take for centres of the different
arcs which compose the arch the points
E, P, Q, R, S, F, which are found at the
respective intersection of these lines.
A
D

C
K
I
B
F
M
R
In the curve described in this manner,
the relation of the height CD to the
span AB depends on the data from
which we started, that is to say, on the
length CF, and of its proportion to CE.
But when a flat arch is to be described,
the two diameters are generally fixed
beforehand, so that after having con-
structed a curve by the preceding method,
that curve must be so modified that the
height CD becomes precisely equal to
that which is assumed. Call a half the
span of the arch required, and bits
height, the dimension CF, and y that
of CE. Suppose, moreover, that the primitive and arbitrary values which shall have been
given to C F and CE be represented by n and m; and that by the development of the
portion of the polygon EPQRSFB, a length =s results, whilst that in the flat arch
described on the diameters a and b this length will be =z. We have the relation,
z+a x = y +b;
Fig. 2706.
and if we suppose the figure that will be constructed on the lines x and y to be similar to
the figure ECF, constructed on the lines C F = n, and CE =m, we shall have
m x
SX
y=
2
n
n
substituting these values in the preceding equation and taking that of x, we find
I =
n (α-b)
m + n S
which is the value to be given to CF, in order that the opening and the height of the
arch may be precisely equal to the lines represented by a and b.
This method is applied to the flat arch, composed of any number of arcs whatever: by
means of the same centres, parallel curves may be described, in which the proportions of
the diameters shall vary; and if the ratio between CF and CE be correctly determined,
curves will be obtained, which, although having the same axis, will assume different forms,
1488
Book II.
THEORY AND PRACTICE OF ENGINEERING.
and afford more or less passage for the water. The tediousness of the preceding method is its
only objection; but in the case in which the arch would be lowered, it is useless to
compose the flat arch of so large a number of arcs of a circle; five will generally be found
a sufficient number, and the process be much simplified.
Suppose, for example, (fig. 2706.) that
the length AF and DE of the radii of the
arc at the springing and the summit be
determined, and represented by r R: call p
the radius of the intermediate arc, which
may be determined by the condition of its
being a mean proportional between r and
R: then we shall have
p =
= √ Rr.
From the point F as a centre, and with a
radius equal to pr, describe an arc;
and from the point E, with a radius equal
to R p, a second, which shall cut the
first in G; the point G will be the centre
of an arc uniting that at the springing
and that of the summit.
If a flat arch described from seven
centres is required, we must determine
two mean proportionals, p and p', between
the radii of the extreme arcs r and R,
which would give
p=3Rrs, and p' 3 Rºr:
=
from the point F as a centre, (fig. 2707.),
and with the radius equal to pr, de-
scribe an arc which should contain the centre
of the arcs, the radius of which is
P; and
from the point E, and with the radius
ע

F
C
F
G
G
Fig. 2707.
H
EH=R-p', a second arc, which should contain the centre of the arc of which p' is
the radius. To fix on each of these arcs the respective position of the two centres, draw
a line H G, the length of which must be equal to p' —p, between the two arcs; but as the
position of this line is not determined by this single condition, we must imagine it to be
so fixed, that the length of the arcs of which the arch is composed decreases uniformly
from the summit to the springing. This method may be extended to flat arches composed
of a greater number of arcs, but it is useless to use more than five.
In constructing moulds for the arches of bridges, it is not possible, except for the part
near the springing, to use beam compasses for tracing the arcs of which they are composed;
the engineer commences, therefore, by fixing the extremities of each of these arcs, of which
the data have been calculated beforehand; and they are described by means of two rules
firmly united, so as to form an angle the supplement of which is equal to half of the
arc. This angle is made to move so that the sides always pass through the extreme points
of the arc: the summit gives the intermediate points.
Flat Arches not formed by Arcs of a Circle. The difficulty of exactly tracing the
projected curve, when composed of several arcs of a circle, has given rise to different
methods for describing the flat arch.
Carpenters generally use, for the purpose of uniting
two sides of an angle AED a curve, the form of
which may be obtained by dividing the two sides of
the angle into the same number of equal parts, and
by joining the points of division by lines regarded
as tangents to the curve, and which, supposing them
infinitely near, determine each of these points by
their successive intersections; in performing this
operation for an angle, a portion of the curve equal
to the first will be obtained, which will complete
the description of the arch A D C.
It has long been remarked, that the curve traced
by the preceding method was a portion of a para-
bola, the summit of which is situated between the
points A and D; it gives more water-way than a
flat arch composed of three arcs of a circle, or a
semicircle which could be constructed on the same
E 1 2 3 4 5 6 7 8 9 10 D
1
2
3
5
6
7
8
9
10
A
·

Fig. 2708.
CHAP. XXV.
1489
ON STONE BRIDGES.
axis; it has this advantage over the preceding form, and is more easily described, but it
is attended with an inconvenience common to most of these curves, viz. its disagreeable
appearance to the eye: in the parabola the value of the radius of the curve is a minimum
to the summit of the curve, and from the position of the summit, the curve does not
diminish progressively from the springing to the highest point of the arch.
It has also been proposed to form flat arches with two arcs of a circle, setting off from
the springing and united at the summit of the vault by a portion of the catenary.
Curves
of this kind have a greater water-way than the ordinary segmental arches, and are certainly
to be preferred on this account. The ellipsis whose curvature diminishes progressively
from the springing to the summit is decidedly the most elegant figure that can be adopted
for the intrados of flat arches: it may be readily drawn by the following simple method,
which is recommended by M. de Prony.

Given half the great arch CA,
and the lesser semi-axis CB of the
ellipsis, describe from the point C,
with CA for a radius, a circle; then
move a square so that one of its sides
n F, passing continually through the
focus F, the summit n of the right
angle shall always follow this circle;
the other side nt of the square will
be a tangent to the ellipsis: by tra-
cing thus a number of tangents, the
curve may be obtained with the
greatest accuracy, and we shall have
Fig 2709.
B
at the same time the direction of the tangents and the normals.
m
n
L
F
μ
The same method may be applied to the hyperbola: for the parabola, the circle becomes
a right line tangent to the summit of the curve. This process possesses the advantage of
not requiring an area greater than the rectangle circumscribing the curve.
M. de Prony
has also given a very simple formula for determining the direction of the tangent tT, when
the point t is given, as well as the position of the point m, by means of its co-ordinates
Ap,mp.
Calling A the major
semi-axis A C;
B the minor semi-axis
BC;
x and y the co-ordi-
nates Ap,mp;
a the distance At;
b the distance AT;
k the distance Dt;
and for conciseness mak-
Α

B
C
b
a
a
ing,
B
=X, we have
α
A
√2 Ax − x².
y=B √2
α
2 A
-
Bx
2
x² + 1'
b:
2
2 A
Χ
x² - 1'
√2Ax-x.
2 Bx
y=
x² + 1°
2 A
A
Fig. 2710.
k=
+1
C
C
B
C
These formulæ, the calculation of which is very easy, may be used with advantage. When
the curve of great arches is formed by the arc of a circle, the direction of the tangents, and
the position of a great number of points, should be fixed by a method analogous to the
preceding.
A very simple process, and not requiring any instrument, may be found useful to the
engineer having the major and minor semi-axis, set off their respective lengths from the
same point on a slip of card, (or a rod, if a large ellipsis be required); then commencing
from one extremity of the minor semi-axis, as A, turn the slip of card in the direction of
a to A, observing always to keep the point B continually touching the major semi-axis,
and C the minor; the card or rod will then assume the positions marked a,b,c, and by
keeping a pencil at a, the curve is drawn at once: a, b, c, will be the joints of an elliptical
arch.
5 C
1.490
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
C
The Bridge of Saumur, on the Loire, of which we have given some account at page 258.,
was executed by De Cessart, who published a series of tables on Chezy's principles for setting
out arches, approaching the elliptical form, from 24 feet to 100 feet span: the diagram
was drawn for an arch of 60 feet opening, and by a reference to the table the distance
from one letter to the other will be found; the radiating lines from F, N, O, G,

•
E
A
B
---------
Fig. 2711.
For a consider-
There are several
&c., being set off upon arcs of from 10, 20, 30, 40, 50 degrees.
calculations which accompany these tables which it is unnecessary to dilate upon: the
dimensions are all in French feet and inches, which are here retained.
able time this system of setting out arches was adopted in France, and the bridges so con-
structed have been very much admired.
24 Feet Opening.
AF-20 feet 9 inches 11 lines 113 points.
36 Feet Opening.
AF-31 feet 2 inches 11 lines 82 points.
ft. in. 1.
p.
ft. in. 1.
p.
AB
= 8
4 10 9 EC = 7
2
4 9
BG
40
3
7 EL
1
1
0 93
BG= 6
GO
ON
=
=
1 10
1
4 9
9
7
LK
LK = 0
9
7 61
4 93 KI
2 3
7 93
ft. in. 1.
AB=12 7 3 104 E C
= 6 0 5 4 EL
1
GO= 2
ON 2 9 7 22 KI = 3
p.
ft. in. 1. p.
10
9
7 23
1
7
7 22
2 44 LK
= 1
2
5 1/
5
7 23
NM
= 2
4 0
OIH
= 3
11
0 0
MF= 2
9 7 22 HF:
AF=20 9 11 11 Idem. 20
30 Feet Opening.
A F=26 feet 0 inches 5 lines 9 points.
= 5
5
6
20
NM= 3
MF = 4
6
0 0
IH
5 10
6
0
2
4 93
H F:
8 3
3 0
9 11 119
A F=31
2 11 8
83
Idem. 31
Idem. 31 2 11 83
ft. in. 1.
AB=10 6 1 3
BG 5 O
CO
4 6
1
9 0
2000
p.
-
ft. in. 1.
EC 0 0 0 0
EL 1 4 4
p.
ft. in. 1.
p.
AB=14
0
BG:
= 7
LK
=
1
0 0
3
GO:
= 2
1 4 9 11
ON
= 2
4 0
= 2 10 8 0
NM 2 11 0
I H
0
= 4 10 9 0
MF= 3
HF
3 6 0 0
= 6 10 8 6
AF=26 0 5 9
ΚΙ
ON = 3
3
2
NM
MF
-
9 7
4층
​42 KI = 4 0 6
ΙΗ
= 4 1 0 0
6 10 3
4 10 9
HF
9 7 9 6
Idem. 26 0 5 9
A F =36 5 5 7
Idem. 36 5 5 7
ools.
42 Feet Opening.
A F-36 feet 5 inches 5 lines 7 points.
805
ft. in. 1.
p.
6 63 EC
6 33 EL: 1 10 10 4
LK
4 9
:12 7 2 2 44
-
CHAP. XXV.
1491
ON STONE BRIDGES.
48 Feet Opening.
72 Feet Opening.
AF 41 feet 7 inches 11 lines 63 points.
ft. in. 1.
p.
ft. in. 1. p.
AB=16 9
9
2
EC=14
BG= 8
0
7
7
22
EL
= 2
G() =
2
9
7
4
LK
= 1
ON =
3 8
9
8
KI = 4
4277
9 7
1 73
B G=12
0 10 9
9
A F-62 feet 5 inches 11 lines 2 points.
ft. in. 1. p.
AF-25 2 7 9
ft. in. 1. p.
EC=21 7 2 43
EL 3
= 3 2
2 9
GO= 4
2 4
9
LK 2
= 2 4 10
5 7
ON = 5
= 5 7
2
4
NM= 4 11 10
0IH = 7 10 0 0
NM = 7
0 0
MF = 5
3 4
4
HF=11
0 4 0
MF = 8
= 8
4 9
KI = 6 11 2
0IH=11 9 0 0
7 HF
HF=16 6 6
422204
AF =41
7 11
62 Idem. 41
7 11 62/
A F=62
5 11 23
Idem. 62 5 11
2층
​54 Feet Opening.
A F 46 feet 10 inches 5 lines 52 points.
90 Feet Opening.
A F=78 feet 1 inch 5 lines 3 points.
--
ft. in. 1. p
A B 18 10 11 10
ft.
in. 1. p.
EC = 16
2 4 9
94/
AB=31
ft. in. 1. p.
6.3
-
BG=
<= 9
O 7 0
EL 2
=
5
4
4
992
BG=15
1 1
GO= 3 1
ON = 4 2
8 0
LK
= 1
9
7 7
GO= 5 3 0
0
ft. in. 1.
9 EC 27
27 0 0
6 EL = 4 1 0
OLK
p.
0
0
= 3 0 O
7
8 43
KI
= 5
2
4
9
ON = 7
0
0
OKI 8 8
0
NM:
= 5
3
0
ΙΗ 8
9 9 0
NM = 8
9
0
0 I H
-
14 8
3
0
MF: = 6
3
6 6
22 HF=12
4 10 6
MF=10
6
0
0
0HF-20
20 8
1
8
5 52
A F 78
1
5 3
A F46 10 5
5 53 Idem. 46 10
60 Feet Opening.
AF=52 feet 0 inches 11 lines 6 points.
Idem. 78 1 5 3
95 Feet Opening.
A F=82 feet 5 inches 6 lines 23 points.
ft. in 1. p.
3 113 EC=28
=28 6 0 O
2 3 EL = 4 3 8 8
OLK 3 2 0 93
KI = 9 1 9 4
ΙΗ 15 6 0 6
HF=21
21 9 10 11
ft. in. 1. p.
AB =
=21 0 2
6
EC
18
ft. in. 1. p.
000
ft. in. 1. p.
AB=33 3
BG = 10
0 9
0
EL
= 2
8 8 0
GO: 3
6
0 0
LK = 2
006
ON = 4
8 0
0
KI = 5
9 4 0
MF
NM 5 10 0
7
0
7 0 0 0
IH = 9 9 6 0
HF=13 9 5 0
BG =15 11
GO= 5 6 6
ON = 7 4 8 0
NM = 9 2 10 0
M F=11 1 0 0
A F=52 0 11 6
Idem. 52 0 11 6
AF=82
5 6
Idem. 82 5 6 23
66 Feet Opening.
AF 57 feet 3 inches 5 lines 23 points.
6 23 Idem. 82
100 Feet Opening.
A F=86 feet 9 inches 7 lines 2 points.
ft. in. 1. p.
A B = 35 O 4
2
9
3
O
EL= 4 6
5 10
0
ft. in. 1. p.
EC = 30 0 O 0
5 4
0 10
4
BG=16
GO=
LK
0
3
ON= = 7 9 4 0 ΚΙ = 9 7 6 8
NM 9 8 8
IH=16
0
3 10 O
MF=11 8 0 0 HF=22 11 8 4
AB=23 1
ft. in. 1. p.
5 1
=
BG=11 0
9 10
=
GO 3 10
2 42
ft. in. 1.
p.
EC 19 9 7 2
EL = 2 11 11 11
LK =
2515
= 2 2 5 4
ON = 5 1
NM:
MF=
7
2
= 6 5
7 8
A F = 57 3 5
KI = 6 4 3 2
0 0 IH=10 9 30
4 9 HF=15 1 11 5
5 23 Idem. 57
3 5 23
AF=86 9 7 2
Idem. 86 9 7 2
-
Rondelet gives in his "L'Art de Batir," the following methods for drawing arches
formed of several circular arcs. For that represented in fig. 2709., after having deter-
mined the semi-diameter AC at 60 feet, and the length of the radius Ad of the arcs
at the springing at one-third of A C, divide d C into fifteen equal parts; give one to di,
two to ik, three to kl, four to lm, and five to m C: having then fixed CH at twice A C,
divide it into five equal parts, and from the points of division D, E, F, G, H, draw
lines through the divisions on the horizontal line dC, and prolong them sufficiently to de-
termine the form of the arc which results from their intersection, as DdI, EiK, Fk L,
G/M, and HmN, whose points of intersection, e, f, g, h, give the centres of the intermediate
thus d is the centre of the arc AI, e that of the arc IK, f that of the arc K L,
g that of the arc LM, h that of MN, and H that of N B. The intersections marked
x, x,v, indicate the curvature of a regular ellipsis, and is here introduced in order to show
the difference of the two curves.
arcs;
Fig. 2710. is an arch composed of six arcs of a circle, which increase in arithmetical
progression from the centre of the key to the springing. After having drawn the diagonal
PC, and described the quarter circle A Q, the angle A Pn is made equal to the angle o PQ,
and the prolongation of the line Pn gives the point d on the semi-diameter AC, and the
5 c 2
1492
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
point H on the axis BC prolonged; the two points D, H are the centres of two extreme
arcs: to have

those of the four
(
M:
L
B

t R
intermediate
arcs, draw ID
parallel to PC,
which gives the
first arc AI of
27 degrees: by
calculation
we
find IK will be
22 degrees 12
minutes, KL 17 degrees 24
minutes, LM 12 degrees 36
minutes, MN 7 degrees 48
minutes, and NB 3 degrees, mak-
ing up 90 degrees for the whole.
From C as a centre, and with
CA as a radius, describe the
quarter circle AR; make VR
equal to one-fifth, or 18 degrees:
this arc, divided into six, gives
tR 3 degrees, forming the first
term of the arithmetical progres-
sion: to have the difference, the
arc AV is divided into fifteen,
which gives s V for this value;
DH being then divided into ten
parts, four are given to DE,
three to EF, two to FG, and
one to GH. From the point H
with radius equal to CR, having
described an arc, tR is set off
from 1 to 2; draw H2N,
which forms an angle of 3 de-
grees with HB.
From the point
N
B
m
C
M
Fig. 2712.
G
D
A
---
Fig. 2713.
ابي
7
C
5
D
1
E
F
G, with CR for a radius, de-
scribe a second arc, on which set
off from 3 to 4 the measure of
the two arcs BN and NM taken together, equal to twice tr and s V, and draw G4M,
which forms with HB an angle of 10 degrees 48 minutes, and with G N one of 7 degrees
48 minutes.
From the point F, with the same radius, a third arc is described, on which measure off
the three arcs BN, NM, and ML, which is equal to three times t R and three times s V,
from 5 to 6, and draw F6L, forming with H B an angle of 23 degrees 24 minutes, and
with M G an angle of 12 degrees 36 minutes.
From the point E a fourth arc is described, as are other arcs, from F and G: the points
h,g, f,e, where the lines intersect, are the centres of the four intermediate arcs.
Fig. 2711. is formed of eleven equal arcs, to draw which the centres d, H, are determined
as in the preceding figures: after drawing the diagonal PC, the angle A Pd is made equal
to o PQ, and Pd is prolonged to H: from the point C, with the radius AC, draw the
quarter circle A R, and divide it into six equal parts: from the point d raise a perpendi-
cular to the intersection q, on the radius C 1, drawn from the first division of the quarter
circle: from the point g draw qr parallel to AC, which cut the radii drawn from the
divisions 2, 3, 4, 5, in the points 6, 7, 8, 9. After setting out the parts q6, 67, 78, 89,
and 9r, from C to m, m to 7, l to k, k to i, and i to d, from these points d, i, k, l, m,
radius equal to CA, draw the arcs of circles, on which set off the arc A1 of 15 degrees,
once from 10 to D, twice from 11 to E, thrice from 12 to F, four times from 13 to G, and
five times from 14 to 15, through the points Dd, Ei, Fk, Gl, Hm, draw the lines whose
prolongation makes the arcs AI, IK, KL, LM, MN, and NB, of the same number of
degrees; the intersection of these lines gives the centres d, e, f, g, h, and H, to describe the
several arcs.
with a
Fig. 2712. An arch of the same diameter and height as the preceding may have the
quarter circle AR divided into six equal parts at 1, 2, 3, 4, 5, through which lines are
drawn parallel to RC: from the point C, with CB as a radius, another quarter circle is
described, also divided into six equal parts, in the points 6, 7, 8, 9, 0, through which lines
CHAP. XXV.
1493
ON STONE bridgES.

B
R
m
C
10 11 12 13
14
A
15
D
3
द
M
10
L
8
K
m
C
h
11
Fig. 2714.
H
Fig. 2715.
are drawn parallel to A C, intersecting the first in the points I, K, L, M, N, through which
other lines are drawn forming a polygon: on the middle of each of the sides of this polygon
perpendiculars are raised, some of which intersect the semi-diameters A C and BC in the
points d, H, and the others intersect one another at e, f, g, h, which are the centres of the
arcs answering to each side of the polygon; this curve approaches the nearest to the
ellipsis.
The arches of the bridge at Neuilly were composed of eleven portions of the arcs
of circles, each of which had their respective centres, as shown in fig. 2709.; and in fig.
2720. we have Perronet's manner of tracing the curve for the formation of the centres;
the small figures at the sides exhibit portions of the operation of constructing the
curve. Fig. 2721. shows how the piers were placed, and 2716, 2717, 2718, 2719, the
manner in which the joints of the pendentives were set out. Fig. 2713. exhibits one of
the arches after the centre was removed; and fig. 2731. the joints of half one of the arches.
Fig. 2716.
BRIDGE OF NEUILLY.
旷
​Fig. 2717
It is unnecessary to enter into the minute calculations made by Perronet, which are
contained in his " Description de la Courbure et des Epures des Arches du Pont de
R


5 c 3
1494
THEORY AND PRACTICE OF ENGINEERING.
BOOK II.
Neuilly:" it is sufficient to observe, that the engineers of that period attempted to obtain
the elegance of an elliptic arch by an assimilation of several curves, taken from as many

K
Fig. 2718.
A
Fig. 2719.
----
•
Fig. 2721.
Fig. 2720.
circles: by a reference to
their calculations, it will be
seen how nearly they ac-
complished the object they
had in view.
The ellipsis was supposed
to have no portions of its
curvature alike, but that
it varied throughout. Per-
ronet, in the bridge at
Mantes, employed the me-
thod which had been pre-
viously adopted by M.
Hupeau, to render portions
of a number of circles alike
in form with the ellipsis.
In fig. 2724. we have his
manner of tracing the
arch with three centres;
in fig. 2725. it is com-
posed of five arcs of a
circle, with the portion of
an oval above; in fig. 2731.
is represented the simple
method of describing an
arch with three centres;
fig. 2732. shows one of the
small arches of the bridge
at Mantes, with its upper
and lower starlings; fig.
Fig. 2722.
lig 2723.

Fig. 2724.
Fig. 2726.
2725.
2726. and 2727. the mouldings of the parapets; fig. 2731. the sort of wooden com-
passes made to strike the several arcs; fig. 2729. the courses as laid in the arch, as does
fig. 2730. on a different level.
CHAP. XXV.
1495
ON STONE BRIDGES.

Fig. 2727.
Fig. 2728.
Fig. 2729.
Fig. 2730.
Fig. 2732.
Fig. 2733.
Fig. 2731.
Thickness to be given to the Key-stones of the Arch. Having determined the form of
the curve, the thickness of the key must next be considered, as upon it depends the
dimensions of the abutments. Alberti, Palladio, and Serlio, have allowed the twelfth,
the fifteenth, and seventeenth parts of the span of the arch, without regarding the nature
or quality of the stone employed. Perronet asserts that the twenty-fourth of the opening
of the arch should be the depth of the key-stone, and Gauthey thinks thirteen inches
a proper dimension for all arches which have a less span than 6 feet 6 inches: for those
above that, up to 52 feet, he makes the key-stone the twenty-eighth part of their

Fig. 2734.
Fig. 2735.
ба 4
1496
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
span, in addition to the 13 inches, and for arches exceeding these the twenty-fourth part
for the first 104 feet, and the forty-eighth for the remainder.
In the segmental arch of Wide Bargate Bridge, at Boston, in Lincolnshire, whose span
is 50 feet, the height of the key-stone is 2 feet; at Conan Bridge, in Ross-shire, whose
span is 65 feet, the key is 2 feet 6 inches; at Kelso Bridge, the span of which is 72 feet, it is
3 feet 3 inches; Darlinton on the Trent, which has a span of 80 feet, the key-stone is 3
feet; Hobhole, near Boston, whose arch is 90 feet span, the key is 3 feet 9 inches; Wel-
lington Bridge, over the Aire, where the span is 100 feet, the depth of the key is 4 feet.
The arches of Waterloo Bridge, London, are 120 feet span, and the key-stone is 4 feet 6
inches. At Vieille Brioude Bridge, erected in 1454, over the Allier, where the span was
183 feet 3 inches, the height of the key was 5 feet 3 inches; the chord of this arch was
the largest known, but failing in the haunches it was taken down, and replaced by the pre-
sent bridge.
Nothing is more important than the right proportioning of the key-stone, and by a
reference to the several accounts already given of bridges, it will be seen how this has been
regulated by practice; a twenty-sixth of the span is generally given for its depth where
granite is employed.
Whatever the form given to the arch, the walls or piers that support it may either
be brought up in horizontal courses, or depressed in such a manner that they gradually
incline, following out the curve: a semi-circle, or semi-ellipse, requires level abutments
to spring from, whilst the others should be made to incline, and have their joints and
foundations radiating, or vertical to the intrados, so that the pressure they produce may be
carried in a direction as nearly as possible at right angles to it: after the arch-stones are pre-
pared and their two beds cut to their proper inclination and numbered, they are laid in their
situation, so that their joints radiate vertically to the intrados; after which the curve under
it, which is a portion of the arch, must be examined and worked out to its proper form,
or when the centering is removed, the whole will have a crippled appearance. The exact
curvature of the intrados, already drawn out at large, must be constantly referred to during
the progress of setting the voussoirs, to ascertain if each is not only in its due position,
but has its proportion of curvature, and its joints properly directed. Mould boards, fitted
exactly to the large curve, and numbered, enable the mason to effect this portion of his
work with great accuracy: when the voussoirs are not composed of single stones, the
same or greater care must be taken to fit in that which is to complete the one the length
of which is not sufficient. The lewis-hole, cut in the upper part of each stone, is so placed
with relation to its centre of gravity, that it can be raised and lowered in its intended
position without turning or twisting it round. Without this attention, it is useless for the
engineer to occupy himself with the form of the curvature of an arch, for the flowing line
of an ellipsis would be destroyed and rendered unsightly, if either of its numerous voussoirs
were otherwise placed than in its right position: instead of a continued and regular sweep,
either a polygon or broken outline would be the result; to remedy such neglect, and
bring the soffite of an entire arch, of any curvature, into the state required to please the
eye and satisfy it that its strength is not impaired, would oblige, after the centre was
struck, the erection of a scaffold and the employment of many workmen, and after all the
beautiful form first aimed at would not be produced.
The Thickness to the Abutments of Bridges. - Parent and Lahire were the first to turn
their attention to the form of arches, but the nature of the thrust, and the manner in
which the rupture of an arch takes place, had not been at that time sufficiently ob-
served, and consequently they employed an hypothesis which does not agree with
practice they supposed that the joints of the voussoirs were perfectly polished, from
whence it results that for the arch to support itself in equilibrio, it is necessary that the
reciprocal pressures exerted by the voussoirs perpendicularly to their beds should mutually
destroy each other; if such were the case, it would be easy, when the thickness of the
arch at the key is given with the curve of the intrados, to determine that of the extrados,
and it must be observed, that in the case where the intrados is a semicircle, we have for
the extrados a curve, which is infinitely prolonged, and to which the horizontal diameter
of this semicircle serves as a symptote. Hence it results that the semicircular arch could
not support itself unless the first voussoir, setting off from the springing, had an infinite
length; these arches then would not have any thrust, and would tend on the contrary
to add to the stability of their piers. If the arch were extradossed of equal thickness, or
if the voussoirs had all the same length, the equilibrium could not subsist, unless there
were given to the curve of the intrados a particular form: when the thickness of the arch
is very small, this form must be a reversed catenarian curve, since the arch being then
considered an assemblage of heavy spheres infinitely small in contact with each other,
the conditions of equilibrium are the same as those of a heavy and inextensible cord,
which results are deemed of little practical utility. The first writers on this subject,
wishing to prove that they were applicable, endeavoured to determine the thick-
CHAP. XXV.
1497
ON STONE BRIDGES.
E
ness of the abutments, and Bernoulli gave a solution of the problem. In the hypothesis
of the perfectly polished joints, the arches where the tangent at the springing is not vertical
are those only which can have a thrust; but experience proving that other arches also
have one, we must recur to a supposition to determine its value. In a memoir published
in 1712, in the History of the Academy of Sciences, Lahire supposes that a semicircular
arch tends to disjoint at Dd, and that the upper part DEd acts as a wedge to overthrow
the inferior parts, sliding down on the joints of rup-
ture, and making the lower parts turn on Kk.
According to this hypothesis, we can easily deter-
mine the effort produced by the weight of the
superior part of the arch, following a direction DV
perpendicular to the joint of rupture; and in ex-
pressing that this force is in equilibrio round the
point K with that which results from the stability
of the inferior part of the arch, we obtain an equa-
tion which gives K B, or the thickness which the
pier should have to resist the thrust. It was sup-
posed in the calculation that the arc BD was equal
to half the quarter of the circle, because it was thought that the rupture of semicircular
arches usually took place at an angle of 45°; but it has since been observed that the
calculation of Lahire makes the thicknesses of the piers greater as they approached the
joints of rupture of the summit F of the vault.

F
D
d
K
B
C
Fig. 2736.
k
This method of determining the thickness of the abutments of arches has been admitted
by all engineers who have paid attention to this subject. Belidor has applied it to arches
of different kinds, and tables have been calculated, which have appeared in the " Cours
d'Architecture de Blondel," and it was supposed that in the arches described with three arcs
of a circle, the joints of rupture would be at the junction of the arcs, in the "Memoires
de l'Academie des Sciences" for the year 1729. Couplet adopted the same theory, and
resolved, always upon the hypothesis of the joints being perfectly polished, the principal
questions relative to arches: he examined also the pressure which they exercised on their
centres, a subject which Pitot had already treated upon in 1726. In a second memoir
printed in the year following, Couplet endeavoured to establish a theory on arches, on an
entirely contrary hypothesis to that which he had previously adopted: supposing that in the
fall of an arch the rubbing of the joints of the voussoirs was such that they could never slide
on their beds, and that to separate themselves from each other it was necessary that their
joints should open and turn round upon the edge, he made moreover an abstraction for the
resistance which the adhesion of the mortar might oppose to this movement. Although
this supposition, as well as the preceding, is not conformable to truth, it conducted the
author to a theory approaching it: the observations and experiments which have been
made since the epoch at which he wrote have taught us that, in almost all cases, the consi-
deration of the friction was nothing in the nature of the movements of the arch, and that in
these different movements, the voussoirs turned in certain places round their edges, whilst
the joints tended to open and shut; but the expressions to which Couplet arrived are so
complicated, and of so little value in practice, that no one has used them; the supposition
on which they were established being also false, no confidence could be given to them.
A little time after the publication of the two memoirs of Couplet, Danisy repeated
before the Academy at Montpellier experiments on models of arches in plaster divided into
a certain number of voussoirs, and pointed out the effect of the weights with which he
loaded them, and the manner in which they produced the rupture: these experiments are
indicated in the "Coupe des Pierres," by Frazier, which also contains a rule the author
deduced from them, and in which he attended less to exactness, than to the convenience
of the workman, as, in determining the thickness of the abutment, he neglected to take into
consideration the height of the piers, which nevertheless materially influences it. These
experiments are the first indications of the true theory of arches; but they were made upon
too small a scale, and the calculations do not appear to have been properly applied to
them.
We find in the "Recueil des Savants Etrangers," for the year 1773, a memoir by Coulomb,
where there is a question on the equilibrium of arches: this celebrated natural philosopher
considers them successively in the hypothesis of the joints perfectly polished, and in that
where the friction and adherence produced by the mortar would oppose this disjunction of
the voussoirs in the latter case, he regards first the half D E of the upper part of the arch
as a body carried on an inclined plane, and, having regard to the effect of the friction and
of the cohesion, gives the limits between which are found comprised the value of a hori-
zontal force acting in the sense Ei, which opposes itself to the sliding of the body, and
supports it in the inclined plane DF. He afterwards observes that the result of the two
forces which act on the portion of the arch DF must necessarily meet DF, between the
1498
THEORY AND PRACTICE OF ENGINEERING. ·´ BOOK II.
points D and F, and
the second condition
furnishes two new li.
mits between which
the value of the
horizontal thrust
should be com-
prised after that, if
we suppose that the
friction of the joints
be sufficiently con-
siderable for the
upper part not to
slide on DF, the K
second condition of
the equilibrium will
F
Fig. 2737.
2
༡

p
be the only one necessary to take into consideration, and the value of the horizontal force
will be found comprehended between the maximum of the expression :
B=0
Dp
Di
and the minimum of the expression:
B=-
lq
FI'
in which B represents that force, o the weight of the portion of the vault DE, and Dp
and lg the horizontal distances of its centre of gravity, to the points D and F, round which
it tends to turn; these maximum and minimum being taken by varying the angle formed
by the joints F, D with the vertical. This analysis leaves nothing to desire, and to make it
coincide with that to which we are conducted by recent experiments on the stability of
arches, it is sufficient to express that the horizontal thrust of the arch, such as has been just
determined, cannot displace the piers D, K, whether it tend to turn round the external
edge K, or to slide horizontally on its base.
Bossut published in 1774, in the "Memoires de l'Academie des Sciences," some researches
on the equilibrium of arches, in which he took up the hypothesis of the infinitely polished
joints, and developed it to determine the conditions of the equilibrium of semicircular
arches and of domes. He endeavoured to ascertain, after admitting the hypothesis of
Lahire, the manner in which the rupture of the arch is made, and by what means its
thrust is exercised against the piers; also to establish the form to be given to the ex-
ternal face of the pier, that it may offer equal resistance in all parts of its height.
M. de Prony in the first volume of his Hydraulic Architecture, published in 1790, after
having given the different equations for establishing the thickness of the abutments, the
length of the joints of the voussoirs, the form of an extradossed arch, which in the received
hypothesis should be that of a catenarian curve, that the voussoirs should be in equili-
brio, he introduced into the question the condition of the friction of the joints, and
showed that, on account of the modification which results from this in the equation of
equilibrium, it is not necessary to attribute to the horizontal joint an infinite length, as
required by the first hypothesis. M. de Prony also insists on the necessity of giving to
the key of an arch a sufficient thickness for it to resist the pressure it supports, and in-
dicates the manner of determining this thickness: with a view of enabling builders to judge
of the boldness of their works, he establishes a relation between the opening of an arch, and
the smallest length which can be given to the key.
A memoir entitled "Dissertations sur les Degradations du Panthéon Français," published
by Gauthey, contained researches on spherical vaults, in which are indicated the true
methods by which the thrust of cylindrical vaults may be estimated, deduced from known
observations.
M. Boistard, chief engineer of the Ponts et Chaussées, has since repeated at large, and
with all the care and exactness possible, the experiments on the stability of arches, the
description of which is given in a memoir placed in the school of the Ponts et Chaussées,
to which is subjoined a theoretical essay on the most important conclusions to which they
may lead.
Such are the principal researches which have been made on the theory of semi-
circular arches. Several experiments upon this subject were made by M. Lecreulx, on a
model of the Pont Fouchard, which was on a scale of about a sixtieth of the original, and
the material employed was freestone.
Fig. 2738. shows the abutments formed of a single stone; one was 24 feet thick, the
other 18 feet 6 inches: after striking the centre the equilibrium was maintained, but when
a weight equal to one-twentieth part of that of the arch was added, it fell: when both
CHAP. XXV.
1499
ON STONE BRIDGES.


Fig. 2738.
Fig. 2739.
abutments were 24 feet, and the weight was increased upon the arch, they each slid upon
the platform, as shown in fig. 2739., and the three voussoirs altered their position.
Fig. 2740. shows one similar abutment to the last, and the other replaced by one 36 feet
thick, formed by three stones; on striking the centre, the abutments, which was of one


Fig. 2740.
Fig. 2741.
stone, did not move; the upper portion of the other slided horizontally, whilst the lower
remained stable, as in fig. 2741.
Fig. 2742., one abutment being substituted, 32 feet thick, of a single piece; the second
of the same thickness, composed of four pieces, three of which were cut, with joints radiating


Fig. 2742.
Fig. 2743.
to the centre of the arch: the abutments resisted until one-seventh of the weight of the
arch was added, when it assumed the form shown in fig. 2743.
Fig. 2744. shows one abutment of a single stone, 36 feet thick, and others of 65 feet, com-
posed of four pieces: when the centre was struck, the key sunk, and the joints opened at

Fig. 2744.
Fig 2745.
the intrados, and it remained in this position; but a trifling weight added gave it the
character shown in fig. 2745.
Fig. 2746., two abutments of 36 feet, one divided into five pieces: in this case the arch
supported one-fifth of its weight; it then gave way, as seen in fig. 2747. : if a resistance be


୮
Fig. 2746.
placed beyond the abutment, composed of several
pieces, the arch will support more than three-
fourths of its weight without yielding, as seen in
fig. 2748.
Fig. 2749., with two arches and one pier, the
first abutment
formed of five
pieces, 36 feet in
thickness, and the
other six pieces,
and 72 feet thick:
on adding a slight
weight to the
arches, the
upper part of
the latter slipt,
and the other
resisted, as in
fig. 2750.
Fig. 2749.
Fig. 2750.
Fig. 2747.

Fig. 2748.


1500
BOOK II.
THEORY AND PRACTICE OF ENGINEERING
23
Perronet has given in his works a description of the movements which have taken
place in great arches which he constructed, both whilst their voussoirs were carried by
their centres, and after the keys were placed and the centres removed; he has indicated
the means of striking these centres, so as not to expose the curve of the arches to any
change, and the precautions which are necessary to be taken in placing the voussoirs: the
observations he has published form a complete system, and are of considerable value.
It is generally remarked, he says, that the first course of the voussoirs may be placed
without the assistance of the wooden centre, which only becomes necessary as they begin
to slide one over the other, which happens when the bed of the joints makes an angle of
40° with the horizon: the centre then begins to carry a portion of the weight of the
voussoirs; it sinks in its lower part, and when the centres are forced up, it would rise at
the summit, if an opposition were not used to resist this movement, by making it support a
weight more or less considerable. In the arch of Saint Edmé, at Nogent-sur-Seine (see
page 265.) these effects were observed and described with the greatest care; it was
struck from three centres, its span being 96 feet, and 29 feet 9 inches from the springing
to the key; its thickness at the summit is 4 feet 3 inches; each half of the arch is com-
posed of forty-seven courses of voussoirs, not comprising the key.
The first twenty
courses of voussoirs having been placed, the five last separated, on account of the sinking
of the centre on which they rested, the joint opened 2 inch at the extrados above the fifteenth
course, and a vertical disjunction took place between the arch and the horizontal beds of
the abutments, the effect of which was evident to the seventh course: in continuing the
masonry, the joints closed, and the point of separation of the acting and resisting parts
being carried higher by the effect of the addition of a greater number of voussoirs, the
joints opened at the extrados about 2 inch from the twenty-sixth to the thirty-first course.
At the bridge of Neuilly (see page 268.), in the arches adjacent to the abutments, the
half of which is composed of fifty-six courses of voussoirs, not including the key, the joints
opened successively at the extrados, on account of the advancement of the laying of the
voussoirs, from to inch from the eleventh to the thirty-sixth course; analogous effects
have been observed in other bridges. After the placing of the key these effects produced
by the weight of the voussoirs manifest themselves in a different manner, the centres,
which at first had been loaded in the lower part, inducing the summit to rise, were now
charged in the middle, tending on the contrary to rise at the haunches: at the arches of
the bridge at Neuilly the last joints opened at the extrados, and on each side other joints
opened at the intrados, starting from the key. At the bridge of Nogent the vertical
disjunction which took place between the voussoirs and the laying of the abutments almost
entirely disappeared, and the last joints opened at the extrados, in the upper part of the
arches, again closed. Before the striking of the centres, there had been traced on the heads
of this latter bridge three right lines, one horizontal, at the summit of the arch, from above
the twenty-eighth course on one side to the corresponding one on the other, and the others
inclined, traced on the haunches from the extremity of the first line to the point where the
joint of the seventh course meets the tangent vertical at the springing: the position of the
extremities of these lines had been made with relation to fixed points, and the object was
to know by the changes which should show themselves in their position and form, what
would be the play of the voussoirs during the sinking. The curve of the upper line
indicated a vertical sinking, which diminished uniformly from its centre to its extremities:
as for the other two lines there was formed in their curve a point of inflexion at the meeting
of the joint of the sixteenth and seventeenth course, which indicated, besides the vertical
sinking and the closing of the joints in the upper courses down to and including the seven-
teenth, a closing also of the joints of the lower part, which was even carried down to the
joints of the abutments.
It may be concluded from these observations, which may be repeated in all constructions
of a similar kind, that the upper part does not tend to push out the lower by sliding on
the joints of rupture, as was supposed by Lahire, and consequently that the result of the
calculations made upon this hypothesis is erroneous: to form a just idea of the nature of
the thrust, we must consider successively the two principal epochs of the construction of
an arch. When the greatest number of voussoirs is placed, and we are near arriving at the
key, the centre becomes considerably loaded in its upper part, because it entirely supports
the weight of the arch, and it consequently undergoes a sinking, the effect of which is most
sensible towards the summit: each voussoir descends in proportion to its proximity to the
key, and it is evident that that cannot take place but as it turns round its inferior edge,
which obliges the joint to open at its extrados; this opening is above all evident at the
point where, on account of the inclination of the planes of the joints, compared to the
direction of the weight, the vertical sinking is distributed more unequally in the consecutive
voussoirs, and therefore in the bridge of Nogent the most open joint was found towards
the twenty-sixth course.
When the key is placed and the centre is struck, the upper parts of the arch DE,ɗE,
are no longer supported by their reciprocal pressure, on account of the sinking hence
CHAP. XXV.
1501
ON STONE BRIDGES.
produced; their common point of support is necessarily carried in E to the extrados;
the joints then tend to close, as is constantly observed, and some builders add to this
effect by removing wedges, which augment the solidity of the arch, at the same time
that the energy of the pressure which these two parts exert upon each other is the means
by which they are mutually supported. The efforts of this pressure is necessarily carried
towards the abutments and the inferior parts of the arch, which it tends to overthrow, by
E

U
G
N
1
1
D
M
K
S
R
C
Fig. 2751.
F
m
Q
n
K
making them turn round their exterior edges K,k; each half of the arch separates itself
into two parts, D,d, which serve as points of support to the upper parts, by means of which
their effort is transmitted to the abutments. These points of support are necessarily
placed at the intrados: if the abutments have not sufficient stability to resist the efforts of
the arch, the four parts fall down, turning round the points K, D, E, and d,k: if they are
capable of supporting it, the effect of the sinking is limited to closing the joints at the
extrados near the point E, to the intrados near the points d, D, and to make them open at
the intrados near the point E, and the extrados near the points D, d. The position of the
points D,d, which are called points of rupture, which it is extremely important to ascertain
exactly, depends on the form of the arch, and the disposition of the weights which it
supports. At the bridge of Nogent the position of the joints of rupture was indicated
between the sixteenth and seventeenth course of voussoirs, by the points of inflexion of the
two lower lines traced on their heads. At the bridge of Neuilly it was not possible to
discover it by the same means, on account of their form, which is an arc of a circle; but it
was discovered that the joints of rupture were placed between the twenty-sixth and twenty-
seventh course, as it was in this place that the joint opened on the extrados.
It is seen that arches cannot fall but in proportion as the voussoirs are placed near the
key, the points of rupture and the base of the abutments separating from each other by
turning round their edges: the tenacity of the mortar is opposed to this effect, and this
may be sufficiently great for the arch to support itself, as happens sometimes in ancient
constructions, although the abutments have not their proper thickness; we cannot, however,
rely on the adhesion of mortar, because its effect is only produced at the end of a certain
time, and although, on leaving the arches on their centres, time may be given for the
masonry to become solid, it is better not to regard the increased solidity obtained by this
means, and which it would be difficult to value exactly. These observations are found
to be confirmed by several arches which were in danger of falling, as well as in those
which have been demolished: with regard to the latter, horizontal cuts were made in
their piers, and it has been remarked that the first disjunctions appeared at the intrados
towards the key; that others afterwards took place towards the haunches, where their
greatest width was at the extrados, and that, in short, the upper part lowered, dividing
itself into two principal parts, each overthrowing the piers opposed to it.
This theory is equally in agreement with the direct experiments made by Gauthey on this
subject, who constructed semicircular arches and others for the purpose; their openings
were 25½ inches; the voussoirs, 1 inch in width at the intrados, were made in wood, and
worked with great exactness; he endeavoured to break the equilibrium between the thrusts
of the upper parts and the stability of the lower parts, by diminishing the thickness of the
abutments, or by loading the summit of the arch, and he constantly remarked that the
rupture tended to operate with the circumstances already explained.
These same
experiments were repeated on a larger scale by M. Boistard, in arches which he constructed
with much exactness in voussoirs of brick rubbed to a face, the thickness and the height
of the section of which were 44 inches; the arches were 2.274 metres (7.458 feet) of opening.
1502
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
0.22 metres (0.72 feet) in length. With these materials arches were constructed semicircularly
with three centres, and others flattened a third and a fourth in the arc of a circle, the versed
sine of which was the fourth, the eighth, and the seventeenth of the opening: they were
constructed on a wooden centre, and their rupture took place on lowering it vertically,
either when loaded at the top or when the thickness of the abutments was diminished.
Each of the arches was submitted to three principal trials; in the first they were extra-
dossed 4 inches of thickness, and as that thickness was not sufficient for them to support
themselves when the centres were lowered, a certain number of voussoirs of the upper part
descended vertically with it, and were carried on its summit; the two inferior parts of the
arch then had the effect of two ramping arches, and divided into two parts; the last joint
of each part opened at the intrados, near the upper extremity and near the springing, and
the rupture appeared towards the middle, where the voussoirs did not touch the centre, and
where the joints opened at the extrados.
In the second trial, where the arches were again extradossed, on each side a certain num-
ber of voussoirs of the lower part were embraced by a cord which leant on their extrados,
and was extended by a weight: the pressure which this cord produced on the last voussoir
opposed their separation, which the upper parts of the arch tended to produce; and it was
constantly observed that if the weight occasioned by the tension of the two cords was not
sufficient for the equilibrium, the arch broke by opening at the intrados, near the key and
near the springing, where the last voussoir tended to swing round its external edge, and
at the extrados on the haunches. Secondly, that where the weight was sufficient to main-
tain the equilibrium, the joints opened in the same manner, on account of the inevitable
sinking, but that the action of the weights tending to tighten them, they opened and shut
alternately by an oscillating movement, in which the parts of the arch turned alternately
round the points of support which the edges of the consecutive voussoirs presented to
them. Thirdly, that when the tension of the cord was sufficiently considerable for the
pressure which it exerted over the inferior parts of the arch to be capable of raising up the
upper parts, the same effects were manifested in a contrary sense, that is to say, that the
arch broke at the key, opening at the extrados, and at the haunches it opened at the
intrados, and at the springing the last voussoir turned round the interior edge. When
the arches were raised on piers, the effects were exactly similar, except that the piers
became a body with the inferior parts of the arch, which in falling over tended to turn
round the external edge of the base of the piers, instead of that of the voussoir placed at
the springing.
In the third trial abutments were established, and the haunches of the arch filled in
with masonry, levelled at the summit, where this vault was 4 inches in thickness. When
the stability of the abutments was sufficient to resist the thrust, the arch preserved its primi-
tive figure after striking the centre; when the weight of the upper part was increased, the
arch broke as usual, and the position of the joints of rupture in the haunches was de-
termined by the value of the weight, by the manner in which it was distributed on the
summit of the arch, and by the height of piers on which this arch was sometimes raised ;
it has generally been observed that when the arches were not raised on piers, the rupture
tended towards the angle of 30° of the half circle described by the semicircle, or towards
the angle of 50° of the little arc described in the arch struck with three arcs of a circle:
the point of rupture tended to rise when the height of the piers was augmented, and when
the summit of the arch was more loaded.
All these experiments confirm the principle already established on the nature of the
movement of arches, from whence it results that in the research for the conditions of their
equilibrium, we may without sensible error consider them as a system of four levers, KD,
DE, Ed, d K, each loaded with the respective weights of the parts of arches which cor-
respond with them (see fig. 2737.), and being able to turn round the points of support
K, D, E, d, k, where they form turning joints; the position of the points d, D depend
for each particular case on the figure of the arch, and the distribution of the weights with
which it is loaded.
The same conclusion is applicable to the arcs of a circle, and to the flat arch, where the
arch and its piers form a system, the nature of which is similar: we must here remark with
regard to the figure of this arch, that the position of the joints of rupture is found naturally
fixed at the springings, unless it be very slightly extradossed, or the versed sine of the arc
of the circle according to which it is described be almost equal to the radius. The ex-
periments of M. Boistard proved that an arc, the versed sine of which is the quarter of
the chord, has its joints of rupture at the springing, when the haunches are filled with
masonry.
The application of the calculation to the preceding theory presents no difficulty: the
points N, M, m, n, being those where the levers are met by the verticals which pass by the
centres of gravity of the parts corresponding to the arch, we may suppose that these levers
are loaded in these points with four weights equal to those of the masonry, and we must
CHAP. XXV.
1503
ON STONE BRIDGES.
determine the relation which ought to exist between the weights and the direction
of the levers, in order that the equilibrium may be maintained. Let us consider the
half of the arch divided into two symmetrical parts by the axis E C, and let us
suppose, first, that the point D is fixed: call μ the weight applied in M.
The system
will not be changed in substituting for it two other weights, the one applied in E,
FQ
EF
the other applied in D, and represented by The point E
EQ
and there will result from it in the
FQ ED
and represented by μEQ'
will then be loaded with a weight equal to 2μ.
FQ
2μEQ'
sense of the lever ED a pressure represented by "EQEQ '
and which, if the point D
were really fixed, would be destroyed by its resistance, as well as the effect of the vertical
EF
force, μ "EQ'
which is applied at the same point: but this point D being situated at the ex-
tremity of another lever, the point of support of which is in K, and which is loaded at the
point N with a new weight, represented by y, we must for the equilibrium take the mo-
mentum of these different forces with relation to the point K as null, which will give the
equation,
FQ ED
"EQEQ
EF
KV: =
μ E Q
KR+V KS,
K V being a perpendicular lowered from the point K on the line ED prolonged, and
KS and KR being the horizontal distances from the point K to the point N and to the
point D.
We have,
KV
KU.DQ-DU.EQ,
ED
and in substituting this value in the preceding equation it becomes,
FQ DQ
"EQ EQ
KU=uKR+KS;
and if we desire that the system have stability we must have,
FQ DQ
EQEQ
KU<µKR+ v K S.
The value of the thrust, and consequently the thickness to be given to the abutments,
augments with the value of F Q, that is to say, when the centre of gravity of the upper
parts of the vault approaches the summit; it is the same with the horizontal pressure which
the two parts of the arch exert on each other, in the case of the equilibrium, as is indi-
cated by the form of its expression, which is
FQ DQ
"EQ EQ
It is to be remarked, with M. Boistard, that there has been a mistake hitherto, in
endeavouring to make the sinking of an arch depend on the diminution of the length of the
curve of the intrados: this sinking evidently depends on the shortening of the curve D Ed,
fig. 2737., which unites the points by which the voussoirs carry each other near the
joints of rupture, and which may also be considered as the place of the points of support
of the intermediate voussoirs: the nature of this curve is not easy to be determined, but we
may in the application regard it, without any great error, as being of the same kind with
the curve of the intrados.
Application of the Theory to the determining of the Thickness of the Abutments.
equation
FQ DQ
"EQEQ
ku=µ KR+vKS
This
contains all that is necessary to resolve this question; and it is now only required to find a
value of BK which shall satisfy this equation, or rather which shall render the second
member a little larger than the first, in order that the arch should have the necessary sta-
bility this is supposing that the positions of the points of rupture D,d is known à priori,
which is not generally the case; we must then begin by determining it. And we shall ob-
serve that these points must be so placed that the momentum of the force which tends to
overthrow the lower part be the greatest possible with regard to that of the forces which
tend to retain it in its position. We must then seek the value of the arc BD, which corre-
sponds to the maximum of the expression
!
μ
FQ DQ
´EQEQk u
μ KR+vKS
1504
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
The calculation is almost impracticable for semicircular arches, on account of the
various quantities which the nature of the circle introduces in this formula, and it becomes
totally so, for the arch composed of several arcs; we must therefore have recourse to an in-
direct method, which consists in making different hypotheses on the position of the point D,
and in determining for each the corresponding value of B K, from examples of known bridges,
whose form approaches that of the one projected; it is evident, moreover, that the greatest
value which we could find for BK will be that which we must take into consideration,
and that the positions of the joints of rupture will be determined by the correspondent
value of the arc BD.
The following table contains the result of this calculation for those vaults most frequently
used; we have supposed that the opening of these vaults was 20 metres, that the thickness at
the key was 1 metre, that the upper part was extradossed level.
Thickness of the
Abutments.
Metres
Position of the
Points of Rupture.
Semicircular arches
Arches struck from three centres depressed one-third
depressed one quarter of the span
Arch of a circle of 60 degrees raised upon piers 5 me-
tres high
Degrees.
0.45
27
·
· 0.66
45
-
0.82
54
-
2.95
0
The calculation has given for the arches of the three centres flattened a quarter a joint
of rupture placed differently to that which experiment has indicated for the bridge of
Neuilly; this joint of rupture will be here found at the 16th and 17th course of vous-
soirs, and we have before observed that it was above the 26th course; this difference de-
pends on the supposition in the calculation that the masonry of the haunches was raised,
which was not the case with the bridge at Neuilly at the moment of striking the centres,
and in which the position of the joint of rupture was decided.
The addition of this masonry necessarily changes the position, and the joints of rupture,
as shown in the experiments of M. Boistard, are the more elevated, as the summit of
the arch is more loaded with relation to the haunches. The results of the calculation agree
exactly with the observations made at the bridge of Nogent, where the masonry of the
haunches was constructed when the centres were struck.
The results comprised in the table are below the ordinary dimensions, and the theory
indicates thicknesses less considerable than those which have hitherto been thought neces-
sary for the abutments of bridges.
The preceding calculations suppose that the different portions of the arch form solid
masses, the parts of which are perfectly united together, and cannot undergo any sinking; it
supposes also that the abutments are established on a base entirely incompressible, and that
in the fall of the arch these abutments would turn, without disjointing, round their exterior
edge; these suppositions are in general far removed from the truth. The fall of a bridge
could scarcely happen without some disjunction taking place on the abutments, however
great the care with which they may have been constructed; and even should there be none,
these abutments could not turn round their external edge, where the stones would neces-
sarily be crushed under the effort they would have to support, an effort which should be on
that account spread over a sufficiently great surface: as for the incompressibility of the
foundations, this condition is very difficult to obtain exactly, above all when the masonry of
the walls is not established on a platform placed on piles; and we cannot doubt that the
fall of the greater number of bridges must be attributed to the movements which have
manifested themselves in the points of support on which they were carried; but as the foun-
dation approaches to incompressibility, in proportion as the effort which it supports is
distributed on a greater surface, the constructor is obliged, in order to unite physical
circumstances to analytical hypothesis, to increase the dimensions of the points of support.
The difference existing between the methods adopted by practice and theory may be thus
accounted for, and it is easy to conclude that we must augment the points of support: it
is not easy to determine the value of this augmentation; it depends evidently on the nature
of the materials and the kind of construction used, on the nature and solidity, more or less
great, of the foundation, and of the other particular circumstances relative to the projected
bridge. It is prudent to adopt greater thicknesses than those indicated in the preceding table,
or than can be calculated by means of the same theory; but as this theory in its application
to very flattened arches gives very considerable thicknesses, we have sought and succeeded
by different means, as will be seen below, to reduce this enormous mass of masonry without
any loss of its resisting force. The arches may be raised on piers, and then the positions
of the points of rupture change, as well as the thickness of the abutments, which becomes
more considerable; it is indispensable to determine its value in each particular case. We
suppose then, conformably to the results of the experiments already alluded to, that the
piers form only one single body with the inferior part of the arch, and that in the rupture
it turns round its external edge: some have thought that a rupture might take place in
CHAP. XXV.
1505
ON STONE BRIDGES.
some point of the height of the pier, and they have in consequence endeavoured to deter-
mine what form it ought to have to present everywhere an equal resistance; the solution of
this problem is difficult, on account of the calculations to which it would lead; it is
besides of no practical value.
We have hitherto supposed that the rupture of arches could not take place unless the
abutments should turn round their exterior edge; there might, however, happen a horizontal
disjunction, when the upper part would slide over the lower. The resistance which the
abutment opposes to this movement depends on the weight of the upper parts, and on the
manner in which the beds are united to each other; the friction and the adhesion of the
mortars being here the two principal means of solidity, the value of which effect has been
calculated.
M. Boistard published in 1804 some experiments on this subject, the results of which
were that the adhesion of the mortar is proportioned to the surface; that the time after
which the stones are detached has little influence on the value of this adhesion, which
is almost as great after the first month as after years. It may be valued as 6960 kilo-
grammes for a square metre for mortar composed of lime and sand, and 3700 for mortar
of lime and cement; these values only being considered as proximate results because
they necessarily vary, on account of the quality of the material of which the mortar is com.
posed. The great superiority of mortar made with sand over that of cement, which at the
end of a year is increased, does not exist when employed under water; in this latter case
the cement contracts quickly into a strong consistence, which is not the same with the
other.
With regard to the friction, M. Boistard has equally endeavoured to discover its effects,
and found that its relation to the pressure is constant, and that in taking the least value given
by these experiments, this relation for a stone indented or picked, gliding on a similar
stone, or what is the same, on a surface of mortar hardened by the air, was equal to 0·76,
or about 4.
Considering the equilibrium of arches in this point of view, we find for the abut-
ments thicknesses different to those which are indicated in the preceding table; the equation
of equilibrium is then
μ
FQ DQ
EQ EQ
(−0·76 ( µ + v)+6960 K R.
The following table contains these new results applied to arches extradossed to the level, the
opening of which is 20 metres, and the thickness of the key one metre: we have supposed
that the disjunction always took place at the level of the springing, and no account has
been taken of the vertical pressure resulting from the weight of the upper part of the vaults,
which reduces the preceding equation to
FQ DQ
"EQEQ
=0·76 + 6960 K R.
The masonry is supposed to be 2600 kilogrammes per cube metre.
Semicircular arches
Arches struck from three centres as before
depressed one-fourth
Arc of a circle of 60 degrees
Thickness of the
Abutments.
Metres.
1.32
1.62
2.24
3.09
Position of the
Points of Rupture.
Degrees.
14
32
41
0
These last results are again below the dimensions which engineers have generally adopted,
but they, however, approach nearer to them than those of the former table. According
to this manner of calculating the equilibrium of arches, there is less of hypothesis than in the
first, and if it be observed that the values of the second table suppose that the arches have
remained long enough on their centres for the mortar to have acquired a tenacity similar
to that which it presented in the experiments just given, which scarcely ever happens, as
it dries very slowly in the interior of the masses of masonry, we shall be convinced of the
necessity of increasing them still more, and of thus approaching nearer to the results of
practice.
We have allowed a little more thickness to arches than is generally given, which tends
to favour the acting power: no account is taken of the beds of sand or earth, or of the
pavement with which the arches are generally charged, nor of the difference of specific
weights of the various kinds of masonry; it would be easy to introduce these objects in
detail in the calculations, but we are convinced we should not then obtain for the thick-
ness of the abutments values sensibly different from those which have been given.
The arches of the arc of a circle require the thickness of the abutments much more
considerable than others, and these thicknesses would be still greater, if the arch, which
we have supposed described by an arc of 60 degrees, was more flattened, as in many
bridges. The first engineers who raised arches of this form opposed to their great thrust
5 D
1506
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
very thick abutments, but it is evident that very flattened arches tend principally not to over-
throw their abutments, but to produce a horizontal disjunction in their piers, and cause
their upper parts to slide. It results from hence that the mass of the abutments situated
below the point where this disjunction would take place is scarcely of any utility to
the solidity of the arch, and only serves to support the upper part, which alone resists the
thrust efficiently; consequently means have been sought to avoid the construction of this
mass, which occasions a useless expense. Among the plans proposed for this object are
the two following: in the first the abutment is only an ordinary wall, behind which the
arch is prolonged, and abuts against a platform supported by inclined piers; in the
second, there is substituted for the mass of the abutment, walls constructed in the prolonging
of the heads, which support an arch, the summit of which is placed a little below the level
of the springing of the main arch; this latter method appears to unite all the advantages
which can be obtained in such constructions.
It has also been the practice to incline the platform of the foundations, as well as the
beds of the masonry, to the side of the arch to be supported; and there is no doubt that
by means of this arrangement, the mass of the abutment is considerably diminished :
it would also be very advantageous to distribute in the interior of the masonry rough
stones placed upright, which should bind the beds together, and contribute effectually to
prevent disjunctions.
In all that has preceded, we have supposed that the haunches of the arches were filled
in with masonry, levelled even with the summit of the curve of the intrados, or following
a slight inclination from this summit; it does not appear necessary to fill the haunches
of an arch entirely in this manner, which augments the expense, as well as the load
it must support: if the haunches be filled with earth or gravel, besides the load
being very little less, the arch would be exposed to dangerous actions when these
matters should be penetrated and diluted by the water which would filter through
them. To prevent these inconveniences, it is advantageous, conformable to a custom
generally practised, after having levelled the masonry of the haunches to an inclination
towards the piers and the abutments, to a height sufficient to ensure the equilibrium of the
arch, to raise on this masonry vertical walls parallel with the heads, to which from 18
inches to 3 feet in thickness may be given, placing them 2 feet 3 inches apart: the
intervals of these walls remain void, and are covered with landings of stone or small
arches, in order that they may have little thrust, and on which the pavement rests: care
is moreover taken to contrive at the foot of the walls, or in the masonry which supports
them, small openings, by means of which the water which would penetrate the haunches
may be conducted to a single point, whence it runs away by a pipe placed across the
voussoirs. In adopting an arrangement of this kind, passages may be reserved for the
convenience of viewing the construction, and making the necessary reparations, to prevent
the changes which time might produce in the masonry of the arch: where, however, void
spaces exist in the haunches of the arches of a bridge, provision must be made for an
accident which might take place, by a total immersion of these arches in the water.
Bridges constructed in mountainous countries, on rivers or torrents subject to great floods,
or near the sea, where the tide rises to a great height, are exposed to the chance of the
level of the water surmounting the summit of the bridge, or even rising above the
pavement; in this case it might happen, that on account of the voids left in the haunches,
the weight of the construction would become inferior to that of the volume of water
it would displace, and would then be exposed to be vertically raised and thrown down
by the current, if the difference of the two weights were sufficiently great to surmount
the forces of adhesion which would be opposed to this movement.
The loss of weight undergone by masonry plunged in the water should always be
taken into consideration; regard should above all be paid to it when the dimensions of
the piers of a bridge are regulated, with the intention of rendering them capable of serving
as abutments, and of resisting the thrust of the arches they support.
Thickness of Piers. The piers of bridges may be considered under two principal points
of view; as destined to carry the weight of the arches, or to serve as abutments to resist
their thrust. In ancient works they are always of a considerable thickness, and the
bridges of Vicenza and Padua are almost the only exceptions from this practice.
Bridges of the middle ages, like the ancient, are constructed on piers thicker than would
be necessary for the uses of an abutment: when the engineers submitted the thrusts of
arches to calculation, and determined according to the hypothesis of Lahire the thickness
necessary for the abutments, they thought that the piers should have the same thickness;
and it was on this principle that the greater number of large bridges were constructed
in the last century, whether in France or the other countries of Europe. The piers
of the bridges of Blois, Saumur, Orleans, Moulins, Tours, Westminster, &c., were thick
enough to serve as abutments, and the vaults were always centred one after the other :
it would, without doubt, have been imprudent to expose bridges, composed of so great a
number of arches, to be entirely overthrown by the failing of one of the piers.
CHAP. XXV.
1507
ON STONE BRIDGES.
But when, at the end of the last century, it became the custom to erect large arches
struck from three or more centres, or those of the arc of a circle of one great radius,
the practice of giving a thickness to the piers sufficient to resist the thrust of the arches
was abandoned: for had it been adhered to, it would have been necessary to construct
enormous piers, which, with the inconvenience of giving to the bridge an exceedingly
heavy appearance, would have added the more important one of considerable expense,
and much obstruction to the passage of the water. This latter is the principal ob-
jection against the piers being thick; the resistance which they oppose to the current,
and the contraction which they cause, depending in great measure on their width.
Supposing all other things equal, a bridge in which the piers are very thick would have
a greater inclination to fall than one in which they are small; and for this reason, that it is
necessary to augment the surface of the water-way, and consequently the length of the
bridge: but the importance of this objection is diminished by observing, that when
the dimensions of a pier are considerable, it is difficult for it to be carried away
by a single flood, and it is generally possible to arrest the progress of the damage:
a narrow pier does not present the same properties, unless it is carried on large
footings, and the advantage in the point of economy is almost nothing, as the saving
in the masonry is of little consequence, either in the piers or in the foundation, on account
of the wide sets-off on which it is necessary to place them; but there is a considerable
increase in the expense of the centres, as all the arches must be centred at the same time,
instead of the timber employed in the two first arches serving for all the others;
this inconvenience is always important, and it will become more so, as the scarcity of
timber is more felt. In cases in which there is no danger in carrying the arches on very
thin piers, as when established on a rock, and there can be no fear of either being carried
away, the increase of the price of the centres may oblige a total rejection of the use of
piers, and a proscription consequently of very flattened arches, which absolutely require
them. Arches composed of the arcs of a circle flattened very much should always be
carried on piers of little thickness, and one of these arrangements necessarily induces
the other. The inconvenience resulting from the use of piers is thus united to the other
reasons opposed to the general adoption of very flat arches for the construction of bridges.
When we cannot give to all the piers the thickness they should have for the office of abut-
ments, and when the great length of the bridge and the nature of the ground create
some alarm for the solidity of the edifice, an arrangement may be adopted which would
diminish the dangers resulting from the use of thin piers.
Bridges are divided into several parts, by constructing at intervals piers capable of sup-
porting the thrust of the arches; then, if an intermediate pier be carried away, it will
certainly induce the fall of some arches, but there will not be a necessity for reconstructing
the whole bridge: if the bridge were established on one general platform, there would be
no danger of accident; nevertheless as it may happen that some part of the platform may
be carried away, it is proper to place the resistance of the piers in equilibrio with the
thrust.
When the piers serve as abutments, their thickness is determined after the prin-
ciples already shown; when their object is only to carry the weight of the arches, the
resistance of the stone with which they are constructed is the principal consideration to
which attention must be paid, and the only one which can be submitted to calculation; it
leads to dimensions much below those in use. M. Perronet has remarked that the
piers of the bridge at Neuilly would support the mass with which they are charged, if
their thickness were reduced to 13 inches: he admitted certainly that the stone would then
carry a weight under which it was crushed in a previous experiment; these piers
are about 14 feet in thickness. According to this example, we must not determine the
thickness of a pier with relation only to the strength of the stone, but also to various
circumstances which it is not possible to submit to calculation, such as the nature of the
construction, which may be entirely in freestone, or some part in moellon or rubble
(rough stone); the force of the shocks to which the pier is exposed either from the ice,
from trees, or other bodies which the river may carry down, and above all in the manner
in which the pier has its foundations laid. There is no doubt that when the con-
siderable weight which a pier has to support is spread over a great surface, more
confidence should be felt in its foundation, whether in relation to the accidents, which
are less dangerous and more easy to repair, or to the unequal settlements which may be
manifested in it; and for that reason we cannot dispense with a large base for a pier the
body of which is not of great thickness.
The form of piers, and above all that of their starlings, is important, and when
the piers are very large, have great influence on the solidity and duration of a bridge;
when their form is imperfect, it is one of the causes of the destruction which mani-
fests itself, and always increases that which may arise from others. It appears from the
first view, that if the water-way of a bridge is regulated in such a manner that the relation
between the resistance of the soil and the mean velocity of the current be not sensibly
5 D 2
1508
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
altered, it is impossible that any damage can take place, and this would be true if
the mean velocity were distributed uniformly throughout the mass of the waters to which
the bridge gives passage. But the obstacles which the piers and the springing of the
arches oppose to the current injure that equal partition of the velocity, and whilst very
rapid currents are formed, in other places the water turns and returns on itself; it is
then important to give to piers the form the most proper to prevent these effects, the con-
sequences of which are often dangerous.
In the piers of ancient bridges the starlings are generally half a circle, or a rectilineal
triangle, but modern engineers have rounded the angles formed by the faces of the star-
lings and the body of the pier. There are some bridges built in the middle ages where
the starlings have been entirely suppressed, and the piers terminated parallelly at the heads;
this latter arrangement is most effective: when the current strikes against the starling
of a pier, the water rises to meet it, the dash which tends to shake the starling is obliged
to divide, and produces two oblique currents, which turn aside from the lateral faces of
the pier, against which there only remains a dead water; these two currents narrow the
principal run, by forming with those produced by the neighbouring piers little shoals,
where the water flows less quick towards the edges than in the centre, because it has lost
some of its rapidity against the obstacle which it meets with, and although the rapidity
of the current be generally greater in the middle of the arch than at the shoulder of
the pier, that part is not less exposed to it, on account of the falls and eddies which are
formed there, and which attack the ground and cause the wearing away: all these
effects, which are produced whatever be the form of the pier, are more evident as the faces
struck by the current are more directly opposed to it. When water is introduced into a
canal narrower than that where it first ran, the rapidity must augment by the effect of
the diminution of the section, if the entrance into the narrow canal be not widened; and
if the section diminish suddenly there is necessarily a contraction, which obliges the
current to take a velocity greater than the diminution of the section requires: it is then
important to render this contraction as small as possible, and this is the more essential as
by it may be avoided the fall which it occasions to the shoulder of the pier, and which is
the cause of the undermining: with this view we have endeavoured to compare the effects
of the contraction for piers of different forms, in the experiments of which we are about
to give an account, after having referred to some researches made on the subject.
We find in "Recherches sur la Construction la plus avantageuse des Digues,” by MM,
Bossut and Viallet, that problem resolved which has for its object to determine the
proper form for the head of a jetty, and the starling of a pier subject to the same
conditions; it is equally necessary to defend these structures against the action of the
Huid which continually strikes against them, and it appears that the form proper to the one
is equally so to the other. M. Bossut supposes that each face of the head of the jetty is
struck by threads of the fluid (small currents), the directions of which are parallel, and
the rapidity equal; he then seeks, according to a general theory of the shock of fluids,
the form for the base of each face, in order that this shock may be the least possible; he
finds that the right line resolves the problem, and that if the base be a triangle, it should
be an isosceles, the two equal angles of which would be 45°. This solution is subject
to many difficulties, as it appears unnecessary that the head of a jetty or the starling of
a pier should receive any shock from the current, because there is no fear that it would
displace the mass entirely: this must be taken into consideration if the subject were the
prow of a vessel, but when the facing of the head of a jetty is well constructed, unless
the water undermines it, it never can be carried away, and it is only essential to guard
against this latter effect.
M. Garipuy, in a manuscript preserved in the Ecole des Ponts et Chaussées, has
endeavoured to modify the triangular form generally given to starlings, so as to obtain
from the fluid an equal pressure over the whole length of their faces; as the fluid
accelerates its movement a little, going round the length of the starling, it follows
from the ordinary theory on the resistance of fluids, that each face should be slightly
convex; the form which is obtained in this manner differs very little from the triangle,
and it is not under that point of view we must consider the question. We will pass
over similar theories, to arrive at that which M. Dubuat has given in his Principles of
Hydraulics: he thought that the essential object was to prevent the contraction and the
undermining which is its consequence, and which always manifests itself when a current
undergoes a sudden change in its section.
Call V the primitive mean rapidity of the current, v the mean rapidity resulting
from the diminution of the section, A and a the corresponding widths of the bed, I the
inclination by metre of the river, if no contraction be formed, we shall evidently have
=AV.
V2
The height due to the rapidity V is ; and if the water had acquired this
2 g
rapidity in flowing over an inclined plane, where it had not met with any obstacle, it
α
CHAP. XXV.
1609
ON STONE BRIDGES.
should have flowed over a space equal to
V2
2 g I; if we suppose that it continues in the
same manner to accelerate its movement, it must, to require the rapidity v, flow over a
A2 V2
space equal to
V2 A
291 (4-1)
α
•
a²*2g I
The length of the narrowing will then be represented by
; and to have the intermediate widths between A and a, it will be sufficient
to remark that the point where the width of the section is equal to x should be situated at
V2 A²
a distance
2
2gI X
-1)
from the point where that width is equal to A.
The preceding analysis gives the means of enabling a current to pass from a greater
section into a smaller, without the inclination being altered, or without any fall or contrac-
tion being formed; and although no account is here taken of the resistance produced by
friction, this want of exactness cannot produce any sensible errors, when the section is
considerable but these results cannot be applied to the form of the starlings of piers,
because in the more ordinary cases it is necessary to give them an excessive length,
and to render their angle very acute; the projection of a starling being limited, we
cannot avoid the change of the section being made more rapidly than should be for the
fall to remain the same, and all that can be done is to give to the faces of the starlings the
least disadvantageous forms possible. To obtain this it will be sufficient to bring
together the ordinates of the curve, previously determined for the form of the narrowing,
V2 A º
so as that the distance
between the points, where the width of the sections
29 I (4
is A and a, is equal to the portion of the length of the pier to which a curvilinear form is
to be given. The principle of the solution is not satisfactory, as we may remark,
according to the construction which results from it, that the curve of the starling will
not be tangent to the direction of the flanks of the pier; nevertheless it appears that to
prevent as much as possible all contraction in the current to the passage of the arches, it
is necessary that the surface of the starling should not form an angle with the lateral face
of the pier, but should be, on the contrary, traced in the prolongation of that face. The
condition here proposed is that the velocity of the water should only augment in insensible
degrees, and that from the effect of the figure of the starlings, the small threads of
the stream should be conducted, so that they enter under the arches, in directions
parallel to the flanks of the pier, and not flow from the flanks in such a manner as
to increase that contraction of the current which results from the pier. This condition
would be satisfied by giving to the sides of the starling a convex curve tangent to the sides
of the pier, by which the starling will be prolonged, and the sides rendered more acute;
the nature of the curve does not appear to be of great importance.
៖
When determining the best form to be given to piers, we must always bear in mind that
when they are totally immersed in water they will lose of their weight; and when we are
obliged to place the bridge with a considerable obliquity to the current of the stream, we
produce an obstruction which varies with the cosine of the angle of obliquity, and, conse-
quently, the additional head is as the versed sine of that angle: but if the banks of the
river are parallel lines, the water-way under the bridge will increase as the secant of the
angle of obliquity, or inversely as the cosine.
The effect of the gyration at the shoulders of piers deserves also some notice, as it often
causes their entire destruction; and the beds of rivers being all porous, the springs work
through them, with a force equal to a pressure of the whole depth of the river: wherever
there is a void or means for the escape of such a spring or source, its force or pressure
upwards will act against any construction that comes within its influence, and wherever
such a void extends to the depth of 4 or 5 feet, it is capable of lifting up an enormous
weight: such a force was exerted upon the floor of the dock constructed by Smeaton at
Ramsgate harbour: that celebrated engineer found that the natural springs rose in the chalk
bed, and issued with such violence as to break the paving-stone with which the area was
covered. Stones weighing a ton and a half, laid down at Plymouth, with a wall 100 feet
in length, were hoisted up and overthrown by a similar force.
However necessary it may be to give to the piers the most proper form to prevent too
great a contraction, this condition is not the only one to which regard must be paid: we
must endeavour to protect them from the shocks of ice, from floats of timber and boats,
and this can only be effected by giving great solidity to the starlings, taking care to
make their projecting angle not too acute, which would subject it to wearing away, or
blunt the angle too much, which would render it less capable of opposing the masses of
ice: to avoid the contraction, it is indispensable to make the starlings very long and ter-
minating in a point; it is thus impossible to satisfy at the same time the two con-
ditions; and as, according to peculiar circumstances, it may be essential to have regard
5 D 3
1510
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Lo one or the other condition, that form must be selected which is most proper to produce
the result required: the following experiments will enable engineers to make this choice
with a sufficient knowledge of the subject.
A
These were made by means of a rectangular canal between boards of 50 centi-
metres in length, in which were placed models of piers, 15 centimetres in thickness,
and where the water flowed about 40 millimetres in height. By means of a fall, velocity
was given to the fluid of about 3 metres 9 centimetres per second, which is about that of
great rivers in floods: care was taken to observe all the circumstances of the contraction,
and the eddies and currents formed were accurately measured. The first experi-
ment (fig. 2752.) was made on a pier, the
starling of which was rectangular; the
eddy formed before the pier presented a
species of band, A, nearly circular, which was
raised 34 millimetres above the level of the
water, falling at the angle of the shoulder
almost vertical. The length of the faces of
the sides of the pier exhibited two other
currents, B, C, uniformly inclined, and which
were only real at the surface; below, the
water, from the rapidity due to the fall of
the eddy, formed a stream both rapid and
dangerous: when two abutments were sub-
stituted for the pier, two similar bands
were produced, which met each other in the
centre of the arch, where they reciprocally
crossed: below the figure the profile of
the water taken in different parts is traced,
which the letters indicate.

e
B
C
b
d
с
9
h
Fig. 2752. RECTANGULAR Starling.
In the second experiment, fig. 2753., the
starling of the pier was a triangle, the pro-
jecting angle being a right one; it did not
form so great an obstacle as the rectangle,
nevertheless the eddy rose as high: the two
currents established against the flanks of the pier were much less strong, but the fall formed
at the side of the shoulder was as deep, and more dangerous; the current before the eddy
became a species of sheet where the water fell, returning on itself, as seen by the section.
The third experiment, fig. 2754., was made on a pier the starling of which was a half-
circle: the eddy rose nearly the same height as in the preceding, but it was not so
wide; it formed two currents, the first, A, followed in gentle inclination along the faces
of the pier; the second, B, appeared to be produced by the opposition of the first, and
a.
-------P
neither of the two formed a fall against
the pier; the water rose before the pier
above bridge, but in the middle of the

f

222
Fig. 2753.
TRIANGULAR PIER,
d
Fig. 2754.
b
g
h
SEMICIRCULAR STARLING.
arch it evidently preserved its level, and only increased in rapidity in proportion as the
principal current was narrowed by the two currents resulting from the eddy.
CHAP. XXV.
1511
ON STONE BRIDGES.
The fourth experiment, fig. 2755., was made on a starling, the base of which was an
equilateral triangle; the same effects were remarked as in the two first, but they were not
so evident; the height of the eddy was not so much, and the lateral currents diverged
less; the fall, although less, still subsisted at the shoulder; the small letters on the several
diagrams show the situation where the sections below were taken.


e
a
a
d
b
d
h
b
เ
2
d

1
BENDRAAL TE Men
h
e
g
h

Fig. 2756.
ARCS OF A CIRCLE.
Fig. 2755. STarling of an equilateral triangle.
The two sides of the base of the starling were formed in the fifth experiment, fig. 2756.,
by two arcs of a circle equal to a sixth of the circumference, described on the sides of an
equilateral triangle; no cataract was formed at the shoulder: along the faces of the pier
the current took an inclination which extended below bridge; there was produced on each
side, as in the semicircular starling, a second current, which did not commence so soon, nor
rise at first to so great a height, but which was as considerable on leaving the arch; the
eddy did not rise quite so much, but the water equally fell in a sheet.
In the sixth experiment, fig. 2757., the form of the pier was that of an ellipsis, the
small diameter of which was the fourth of the large one; the water rose much less before
the pier than in the preceding experiments, and the lateral currents had a uniform
inclination along its faces; the second current was relatively more considerable, and even
became higher than the first, with which it was confounded on leaving the arch: both ex-
tended to a less width.


f
b
a
ď
h
9
ĥ
א
9
h
d
¿
C
d
g
h
e
Fig. 2757.
ELLIPTICal pier.
Fig. 2758.
CONCAVE TERMINATION.
The seventh experiment, fig. 2758. was made on a pier, the base of the starling of which
was a concave mixtilinear triangle. Starlings of this form are not generally applied to piers,
5 D 4
1512
Book II.
THEORY AND PRACTICE OF ENGINEERING.
but use has sometimes been made of them to bind together the abutments with the walls of
the shoulder. It is doubtless the most dangerous of all: setting off from the starling, the
water rose considerably as far as the angle of the shoulder, where it formed a fall stronger
than in all the other experiments, and the bottom of which was lower than the general level
of the current: the lateral current, obliged to turn itself, was accompanied on each side
by two others; the one joining the pier was weak, the other, but little elevated at first, soon
acquired more volume, because it was raised by the principal current, and was not lowered
but at a considerable distance down the river.
The eighth experiment, fig. 2759. The starling of the pier had the same form as fig. 2758.,
but we have supposed here the springing of the arches surmounted by the current; the
eddy was also very considerable, and the currents which resulted from it diverged almost as
much as in the first experiment; the

fall was very strong and very wide,
and of the three separate currents
which were formed on each side,
those which joined the pier were
the least elevated; they were all con-
founded together at some conside-
rable distance.
We see by these experiments that
whenever the faces of the starling
are united to those of the pier by a
curve which is tangent to them, and
that the water does not surmount the
springing of the arches, the fall is not
formed at the shoulder, but two other
currents are produced by the side of
those which envelope the pier, which
are not very rapid. The under-
mining then is not much to be feared
in this case, the less so as the most
rapid currents are those which are
most removed from the pier : we may
also remark that the elliptical form
has great advantages over all the
others, and occasions contraction
b
b
a
d
C
Fig. 2759.
9
h
much less considerable, because the lateral currents diverge at much less distances.
With regard to starlings the plan of which is triangular, the equilateral triangle is
much to be preferred to the rectangular, which presents an obstacle almost as great as
the rectangular pier, and is perhaps still more dangerous, the greatest fall taking
place at the angle of the shoulder, whilst in the rectangular pier it is a little removed
from it; if right faces are used, the equilateral triangle must be preferred, with the
precaution of rounding the angle opposed to the current, if there be any fear for its solidity:
the most preferable of all is the equilateral triangle mixtilinear; it unites the advantages
of producing the least contraction and the least undermining possible, with that of presenting
sufficient solidity to the projecting angle, since this angle is measured by the third of its
circumference; the oval pier is the only one which occasions a less considerable contraction,
and which may be preferred on this account.
The above experiments were made on a current where the rapidity was 3 metres
9 centimetres per second: as rivers have still greater in their overflows, two other
experiments with a velocity of 4 metres 87 centimetres were made.
In the first (fig. 2760.) the base of the starling was formed by two arcs equal to the sixth
of the circumference. The eddy produced at the meeting of the pier rose to a height
nearly twice as great as that which had taken place for the rapidity of 3 metres 9 cen-
timetres, and although there was no fall, the inclination formed along the faces of the piers
was much more rapid: it did not, however, extend beyond the extremity of the square
body, as may be judged by the profile eagf; this singular effect, which is observed in all
similar circumstances, arises from the water being forced to flow, first with a considerable in-
clination, in virtue of which it can attain a velocity relative to the diminution of the section
which the body of the pier causes it to experience, and when, on arriving below the bridge,
the section widens, the velocity becomes what it was, and the water remounts almost to
the level it had at first, so that for each point the inclination of the fluid has precisely the
value which agrees with the corresponding velocity.
This experiment agrees with an observation made at the Bridge de la Drome by M.
Montluisant, engineer of the Ponts et Chaussées. He marked the trace left by the waters on
the surface of the piers on the starlings on each side after a flood, and found that the water,
which had risen to nearly the same height on both starlings, was lowered about 1 metre 5
centimetres, at the angle of the shoulder of the one against the stream, and along the square
CHAP. XXV.
1513
ON STONE BRIDGES.
body; this effect is analogous to that just described, and, though it may appear extraordinary,
necessarily takes place in all cases, but it is only evident where the rapidity is great.


d
d
b
b
e
Fig. 2760.
Fig. 2761.
The second experiment made with a velocity of 4 metres 87 centimetres per second, on
a pier of an elliptical base. Fig. 2761. presented the same effects as that where the
current had a velocity of 3 metres 9 centimetres, but they were more marked: hence we
may conclude that the elliptical piers have the property of occasioning the least contraction.
The following table contains the principal dimensions of the currents observed in the pre-
ceding experiments.
Height of the Water.
Form of the Base of the Starlings.
Starlings.
Middle of
the Pier.
Distance of the Side
Current.

Opposite
the Angle
of the
Shoulder.
Opposite
the Middle
of the Pier.
Rapidity 3.9 Metres per Second.
Metres.
Metres.
Metres.
Metres.
1.
Rectangle
0.041
0.018
0.099
0.203
2.
Triangle rectangle
0.036
0.014
0.081
0.126
3.
equilateral
0.034
0.016
0.036
0.072
4.
Half circle
0.038
0.023
0.023
0.095
5.
Triangle mixtilinear
0.036
0.016
0.027
0 077
6.
Ellipsis
0.032
0.011
0.018
0.061
7.
Triangle mixtilinear concave
0.036
0.009
0.036
0.104
8.
0.045
0.009
0.041
0.189
4.87 Metres per Second.
1.
2.
Triangle mixtilinear
Ellipse
0.032
0.090
0.072
0.131
0.059 0.045 0.045 0.081
These experiments and observations will enable us to appreciate the advantages and in-
conveniences of the different kinds of starlings, with relation to the size of the contraction
which they cause the current to undergo; but we must not forget that the starlings are
also useful in breaking the ice, and preventing any floating mass from stopping against the
piers of a bridge, and diminishing the section, which would necessarily tend to produce an
undermining.
Ice in places where the temperature is the same is more dangerous, as the course of the
river is slower; in this case the rivers freeze more quickly, and the ice, which has time to
acquire a considerable thickness, detaches itself in larger masses; it is essential then, in
such cases, to take precautions in relation to the effect they may produce, and to make
the projecting angle of the starlings more acute; if any fears are entertained for its solidity,
it may be protected by bands of iron, or with a bar of iron placed in the masonry.
One of the best methods proposed for remedying the inconveniences resulting from ice
in rivers is that which Perronet had adopted for the bridge projected over the Neva
at St. Petersburgh; it consists in inclining forward the projecting edge of the starling; by
1514
Book II.
THEORY AND PRACTICE OF ENGINEERING.
means of this arrangement the masses of ice which strike the pier tend to mount a little
along this edge; their weight then acts on each side so as to break them, when each part is
easily carried away by the current.
The form of the starlings down stream is not so important as those above: there are
even a great number of ancient bridges in which they are omitted; in this case the
space which they would have occupied is filled by stagnant water or a whirlpool, which
it is necessary to prevent: it is therefore more advantageous to place them on both sides.
When a river has been narrowed by an obstacle, such as a pier, the effect of which is to
diminish the width of its bed, the two currents formed along its faces unite, describing
a species of curvilinear triangle, and are then prolonged on each side the faces of
the starling below bridge; hence result underminings, which are scarcely less frequent
below than above; this should induce builders never to omit the starlings below bridge,
but even to give them greater length than is customary. When the waters rise much
above the springing of the arches, the form of the starlings has little influence on the
nature of the contraction, which then depends principally on that of the arch, and the
manner in which the intrados of the vault is united with the face of the starlings: one of
the best methods of diminishing the contraction in this case is that adopted at the bridge
of Neuilly to effect it, the two faces of the starlings may be terminated by a curved
surface agreeing with that of the vault; examples may be found at the bridge of Gignac,
and at that of Navilly on the Doubs. In a design projected by Gauthey for a bridge at
Auxonne, the starlings had the form of the prow of a vessel; when they are destined to
divide the waters and break the ice, they should rise to the height of the greatest floods,
or at least to that where the breaking-up of the ice takes place. We must observe that
in semicircular arches the starlings diminish the contraction but little when the waters
rise much above the springing, because the tympanum of the arch then presents a great
surface, which is directly opposed to the current; and the starlings serve only to receive
the first shock of the ice. In the last century much attention was paid to their decoration,
which is not so important as the solidity of their construction: the crowning easily
decomposes, and plants grow in the joints, which increase this effect, which might be
prevented by forming them with great stones.
:
In fig. 2762. is the elevation and plan of one of the piers of the bridge of
Moulins: both starlings above and below are triangular, with the angle projecting and
rounded, which gives greater solidity, a precaution from whence no inconvenience can
result, and which it is proper always to take; it is preferable to the use of a bar of
iron in the masonry, which latter method should not be resorted to
unless the bad quality of the stone obliges its use: the crowning has
the form of a triangular pyramid; in the stones of which it is con-
structed, a vertical part has been preserved, which should have from 8
to 10 centimetres in height: starlings of a triangular base have some-


Fig. 2762.
PIER OF Moulins' bridge.
Fig. 2763. PONT AU CHANGE.
times been crowned with a cap formed by the prolonging of their faces cut by an inclined
plane coming forward, as in the Pont au Change at Paris, fig. 2763.
Figs. 2764. and 2765. represent one of the piers of the bridge
at Orleans. The base of the starling is terminated by two arcs
equal to the sixth of the circumference; that of down stream is a half
circle; the projecting angle of the upper starling is not sufficiently
acute to require any


rounding, and the form
of the pier is that per-
haps which best answers
all the conditions re-
quired. The crowning of
both the terminations
of the starlings has a
height which might be
Fig. 2764. PIER OF ORLEANS' bridge.
diminished; they are formed by a conical surface.
Fig. 2765.
Figs. 2766. and 2767. represent one of the piers of the bridge of St. Maxence: in some
foreign works are examples of piers divided into two parts, the interval of which is covered
CHAP. XXV.
1515
ON STONE BRIDGES.
by a vault; these piers are very massive, and the bridge referred to is the only one in which
it has been attempted to carry arches on so feeble and isolated points
of support: but this construction has no particular utility, since it
diminishes the expense but little: the crowning of the starlings is


Fig. 2766.
PIER OF bridge oF ST. MAXENCE.
formed by a conical surface of moderate height, and the pier being
thin is constructed of a single stone.
Figs. 2768. and 2769. represent one of the piers of the bridge
of Louis XVI., at Paris; the starling is formed by a column set in
the square body of the pier, about 4 of its diameter, and surmounted
by a capital, above which is placed a short architrave, over which
----------
-------
Fig. 2767.



Fig. 2768.
PIER OF BRIDGE OF LOUIS XVI.
runs a cornice with which the whole of the bridge is crowned,
and which carries a square socle.
Figs. 2770. and 2771. represent a pier of the bridge of
Neuilly; the plan of both ends of the starlings is a half oval,
which commences under the vault itself, at the inferior origin
of the corne de vaches; the crowning is terminated by a
conical surface of little height. Sometimes the starlings of
piers have been raised to the level of the upper parts of the
bridge, making them carry columns, obelisks, figures, or even
small shops, as in the Pont Neuf, at Paris: sometimes also
the starlings form a space surrounded by a parapet, which
towers above the bridge, serving as a shelter for passengers,
and is serviceable when bridges are used as a promenade.
Fig. 2769.

Fig. 2770.


Fig. 2771.
PIER OF NEUILLY BRIDGE.
That portion of the pier that carries the arch always preserves its oblong form, with its
sides right lined and parallel; and under low water, this is increased in breadth downwards
to the foundation, at the rate of from 1 to 9 inches for every foot in height, and the platform
extending from 2 to 6 inches beyond the masonry; the rate of this increase of breadth
must be governed by the nature of the bed of the river. At Neuilly, the thickness of the
piers being at the springing of the arches only one-ninth of the span, it was necessary to
spread the base very considerably.
1516
Book II
THEORY AND PRACTICE OF ENGINEERING.

Figs. 2772. and 2773. re-
present a pier of the bridge
of Toledo, at Madrid, which
is in this latter style; the
base of the starlings is a
semicircle.
Quay Walls of Bridges.
In general, when the bed of
the river is permanent and
not liable to change, a wall
AB is built on each side ;
the part B C unites the
breadth of the bridge with

Fig. 2772.
B
Fig. 2773. Bridge of toledo.
that of the roadway, which is usually more considerable: the parapet of the bridge
should be continued round this part. AC supports the earth at the abutments; the

B

Fig. 2774. ABUTMENTS.
D
C
G
G
Fig. 2777.
C
E
Fig. 2776.
+
E
F
Fig. 2775.
PLAN.
B
B
QUAY-WALLS at the bridge at NEUILLY,
B

E


CHAP. XXV.
1517
ON STONE BRIDGES.
upper portion of the wall is terminated by the talus of the slope, which is generally faced
with masonry for some distance: its lower extremity is cut vertically at A, that it may
have the requisite solidity at this part.
Fig. 2778. shows the wing-walls, as set out perpendicularly to the axis of the bridge.
This arrangement does not allow so free a passage for floods, and ought only to be adopted
when the natural banks of the river are not subject to injury from the running of the water.
When the river flows through a soil easy to be washed away, it is necessary to confine
the bed where the bridge is situated. To do this we must construct embankments at the
quays paved with stone, and continue them to such a distance above and below the
bridge as may be necessary: the quays of several bridges, as that at Moulins, on the Allier,
C
B
A

Fig. 2778.

C
B
Fig. 2779.
BRIDGE at MOULINS.
A
are so arranged: AB is a splay joining the bridge with the road, BC is a return wall
parallel to the axis of the bridge, D, D show the paved slope at the abutments, the toe of
which is strengthened by two rows of piles, between which rubble-work is laid.
In cities, bridges are usually accompanied with quay-walls; the angle formed by their
intersection with the bridge obstructs the passage of carriages, and is generally cut off
by a straight or curved line, as at A; the angle formed by the quay-wall AB and the
bridge is curved, and the projection occasioned by such an arrangement supported by a
gathering over of the masonry.
At the bridge of Neuilly, the portion of the quay-wall A B unites the width of the bridge
with that of the road, and the return wall BC is in the line with the edge of the footway,
the interval between the two pedestals C and D answering to its width, and the quay-
walls C,D are prolonged to a considerable distance, sustaining the road GG. To
allow the passage for the towing-horses a tunnel and a road EE is constructed beyond
the abutment.
1518
THEORY AND PRACTICE OF ENGINEERING. Book II.


1
:
ט
B


Fig. 2780. QUAY-WALLS AND PLAN.
When the width of the quay and breadth of
the bridge is small, and the passage over much
used, the quay-walls must be set out, as at the
bridge of the Tuilleries at Paris, where by means
of a gathering over of the courses at A, B, C a
splay is formed, uniting the bridge with the
roadway, at the middle of the first arch; at
the Pont au Change in the same city this splay
is extended still farther, but it is supported
differently.
1
J
Fig. 2781. quAY-WALL AT the tuilleries.
Foundations. The establishment of proper foundations for a bridge, where the points
of support carry all the weight, is of the greatest importance: rock is almost the only
unexceptionable foundation for hydraulic constructions, and even in that case it is necessary
to ascertain whether the thickness is sufficient to be entrusted with the weight intended to
be put upon it.
A soil composed of clay and gravel often forms a very compact bed, upon which the
masonry may be placed without pilings; but sand, peat, and compressible earths require
piles to render them sufficiently compact and solid. In deep rivers piles have been driven
over their entire beds, so that their heads stood level with the low water, and the spaces
between filled with loose stones; but this method, though formerly much practised, has
been long discontinued.
Cofferdams are now generally made use of for laying in the foundations of the piers
and abutments of a bridge, constructed to suit the particular position of their locality:
they are commenced by driving two rows of vertical and plank piles, between which
CHAP. XXV.
1519
ON STONE BRIDGES.

a mass of clay is
thrown, or by driving
main piles and lay-
ing strong planking
across them in a hori-
zontal position, or by
driving one row of
gauging piles, and fill-
ing the spaces between
with pile planks
driven vertically: at
page 445. is a de-
scription of one of the
largest cofferdams re-
quired; it is therefore
unnecessary to en-
large upon it, or to
mention others, the one
referred to having per-
formed its duties ad-
mirably.
Sounding the Soil to
ascertain its nature is
the next work, which
Fig. 2782.
:
COFFERDAM.
is done by an iron rod driven in by the pile-engine, or by an auger that will bring
up the soil, as in sinking an artesian well. Soundings have been taken to the depth
of 80 feet by using a strong chest made of planks, about 18 inches square, the bottom of
which was shod with iron,
that it might more easily
force its way through the
soil: and M. Fauvelle, of
Perpignan, has described an
easy method of boring to
any depth, either for the
examination of the soil or
for obtaining water. He ob-
serves, “if through a hollow
boring-rod water be sent
down into the bore-hole as
it is sunk, the water in
coming up again must bring
with it all the drilled par-
ticles:" he had therefore an
apparatus made composed
of a hollow boring-rod of
wrought-iron tubes screwed
end to end, the lower end
being furnished with a per-

Fig. 2783.
A
S
COFFERDAM.
forating tool suited to the strata in which it had to work; the diameter of the tool was
larger than that of the tubular rod, in order to form an annular space around it, through
which the water and the excavated material might rise up. The upper end of the hollow
rod was connected with a force-pump by jointed or flexible tubes, which followed the
descending movement of the boring-tube for an extent of some yards; this tube may be
worked in the ordinary way, with a turning handle or a jumper: the pump must be first
put in motion; a column of water is sent down to the bottom of the bore-holes through
the interior of the tube, which, rising in the annular space between the exterior of the
hollow rod and the sides of the bore-hole, creates an ascending current, which carries up
the triturated soil; the boring-tube is then worked like an ordinary boring-rod, and as the
matter is acted upon by the tool at the lower end, it is immediately carried up to the top
of the bore-hole by the ascending current of water: the usual necessity of drawing up the
boring-tube to clear it is therefore avoided, and a great portion of time is economised.
bore of 6 inches in diameter has been made to the depth of 560 feet in 140 hours at
Perpignan, and this system is now universally adopted in France.
A
Cofferdam for building the River Wall of the new Houses of Parliament. The excavations
for the works were commenced on the 1st of January, 1839. The mud on the shore varied
in thickness, and beneath was a bed of gravel 14 feet in depth; under this was a stratum of
stiff clay, into which the piles were driven 2 feet, a trench being first dredged in the line
1.520
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
of the dam, 8 feet in depth and 27 feet wide; the piles were of Memel timber, 12 inches
square and 36 feet in length; these were all driven till their tops stood 4 feet 6 inches
above Trinity high-water mark of ordinary spring tides; to these were attached the waling-
pieces; and the outer sheet piles, formed of whole timber 13 inches square, and of similar
length to the others, sawn perfectly square, were driven close together and firmly bolted to
the waling-pieces. The inner sheet piles were of half timber, of the same length, and
driven to the same depth: between these rows of piles, the space above them was occupied
with horizontal pieces, bedded down to them, and made fast with bolts to furring pieces,
inserted above the waling of each gauge pile. Throughout the whole length of 920 feet
the dam was secured by diagonal braces, extending back to the old river wall, against which
they had an abutment: the outer and inner rows of piles were held together by three rows
of 21 inch wrought-iron bolts: when all the piles were driven, the whole space between
was cleared down to the clay, and then filled up with stiff clay, mixed with a small
quantity of gravel.
The foundations of the river wall were got out in lengths of 50 feet, and the footings
laid on a bed of concrete varying in thickness from 1 to 6 feet; this was composed of six
parts of gravel and sand to one of ground lime, made from the lower stratum of the chalk
formation. Along the face of the wall was a row of elm sheet piles, 8 inches in thickness,
and from 10 feet to 12 feet in length; after being driven close to each other they were
spiked to an oak waling-piece, and further secured by inch wrought-iron bolts at every 4
feet distance, which passed 6 feet into the wall, where they were held by cast-iron washers
bedded between the courses.
The two lower courses of the wall were formed of York landings, 11 feet in width, and
6 inches in thickness; on these were laid two courses, 15 inches thick, of Bramley fall-
stone, and above the stone facing of the wall, Aberdeen or Cornish granite was laid in
courses varying in thickness from 26 inches to 19 inches at top; the front had a curve
of 100 feet radius, and the whole filled in at the back with brickwork; the total thickness
at bottom was 7 feet 6 inches, and at top 5 feet; at every 20 feet was a counterfort, 3 feet
9 inches in width, projecting 3 feet 4 inches; the height above the footing is 25 feet 6 inches.
The face of the foundation of the main building is 28 feet 9 inches behind this river wall,
and the space between the two was entirely filled up with concrete, formed of ten parts of
gravel and one of ground lime: the cost of the excavation, cofferdam, and river wall was
74,3731.
Excavations are usually performed by a class of men called navigators, who also level
down the bed to receive the foundation: to assist the labour of wheeling out the soil, it is

I
ނ
A
Fig. 2784.
E
Fig. 2785.
DRAG EMPLOYED AT ORLEANS BRIDGE.
often necessary to lay down temporary bridges, and to construct different heights of
scaffolding; the method of loading and unloading the boats employed for this purpose
has already been described.
Dragging is generally resorted to for removing the soil which lies below the level of
the water, which is done with an iron shovel or scoop with a long flexible handle, or with
the dredging-machine. The drag used at the bridge of Orleans was moved by a windlass,
and could be lifted at pleasure.
CHAP. XXV.
1521
ON STONE BRIDGES.
Of the Construction of the Piers and Abutments.-The material of which these are formed is
granite or hard stone cut into headers and stretchers, the length, breadth, and depth varying
according to circumstances; excess of length should be avoided in either, which would
render them liable to fracture. Each course of stone around the outside should be laid
header and stretcher alternately; the latter should be from 18 inches to 2 feet in breadth,
and the header should occupy one-third of the whole fact, and be 3 feet or 4 feet in length;
their upright joints should be perfectly square, at least 1 foot in from the face, and in no
part more than 1 inch in width. The interior or filling-in stones should be of equal height
to those on the outside, their upright joints not more than 1 inch in width, and they
should break joint at least 12 inches; the bed and upright joints of all the courses should
be flushed in with proper mortar, as they are laid, and the outer joint, when compressed, not
show more than of an inch: the whole should be run with grout.
180
In many places it was
formerly the custom to fill in the interior of the piers with rubble-work, a practice that
cannot be too much reprobated, as such constructions can never be depended on.
Raising the Centres is the next operation after the abutments and piers are terminated,
and is usually performed from a scaffold or temporary wooden bridge, constructed for the
purpose. The centres rest on wedges placed upon the bearing timbers, by which they can
be eased at any time; the wedges are in separate pairs, crossing each other under each
frame, or are fixed upon a piece of timber, extending across the whole width of the soffite
of the intended arch, and passing between all the centre frames and the supporting frames
or beams; the wedges are sometimes formed or fixed upon the timber, which is placed
longitudinally under the foot of each rib of the centre, resting on the supporting frame:
when it is requisite to ease the centre, either the wedges or the timbers on which they are
fixed are driven along each other, by which the wedges are made to take up a new position,
and the centre descends very gradually. Beams mounted like a battering-ram are used to
effect this purpose.
The Construction of the Arches is commenced after the centres are fixed, and the masonry
of the piers and abutments is carefully adjusted. When the voussoirs begin to bear upon
the centres, the latter are liable to a partial change of form, which must be provided for
by loading them in various parts as the works proceed.. Great care should be taken to
make each course of arch-stones point in the direction of the radius, and to do this effec-
tually their thickness should be marked upon the outer ribs, and their line of direction
upon the lower part of the beams: the courses should be laid equally on each side of
the centre, an excess of weight on either side being likely to produce an alteration
in the form, and the top must be loaded until the arch is complete: the key-stone
should occupy its proper place, but not be driven home until the whole is finished; all the
back and end joints of the entire arch are then wedged up with slate, run with mortar,
and left some time to dry. The masonry of the spandrills are brought up to about
one quarter of the height of the arch, after which the centre may be removed. The soffites
of the arch and all its joints are then pared, cleaned, and pointed with mortar; for this
purpose Perronet contrived a hanging scaffold at the bridge of Orleans, which could

Fig. 2786.
SCAFFOLD FOR THE bridge of ORLEANS.
Fig. 2787.
5 E
1522
Book II.
THEORY AND PRACTICE OF ENGINEERING.
be made to roll along the parapet, and by means of a windlass be raised or lowered as
required.
The Spandrills and Wing-walls should progress as soon as the centres are struck, and we
cannot do better than refer to the construction of London Bridge for the manner in which
they are to be carried up.
CHAP. XXVI.
ON THE CONSTRUCTION OF FASCINES AND BASKET-WORK FOR JETTIES.
-RIVER, SEA, AND DOCK WALLS.
In many parts of Italy gabions made of twigs and branches, in the manner of
basket-work, are filled with stones laid one on the other, to form rivers and sea walls: this
method is both expeditious and convenient, and when laid down and covered with
sand or mud, it is several years before the basket-work is destroyed, and the stones become
consolidated and require

little further adjustment:
such osier-work may be
made where it is to be
used, and as the manufac-
ture advances, the baskets
can be filled with stones or
other hard material.
The cylindrical
cylindrical form
gathered in at the top is
given by placing eight up-
right rods on the ground,
with a hoop to hold them
in at the top; the osiers are
then woven in alternately
up to the hoop; the eight
rods are then united at
the summit, and the whole
finished to the required
form.
There are several varieties
of this work, which is ad-
mirably adapted to the
purpose for which it is em-
ployed; sometimes a breach
in a river wall is stopped
by laying in several rows
of these gabions, which
serve the purpose of sand-
bags. When shell-fish,
muscles, &c. attach them-
selves to works of this kind,
they should not be removed,
as they contribute very
much to their consolidation;
Fig. 2783.
Fig. 2789
Fig. 2790.
to protect banks so formed from injury from boats, fender piles are driven in at convenient
distances.
Rods 15 or 16 feet in length, interlaced round the heads of several piles driven either in
rows or around a circle, form a very efficient barrier to ordinary streams, and when several
rows are repeated, filled in with chalk or stones, will last a considerable time: such was the
practice on the banks of the Thames, but the wash now produced by the steam-boats has
occasioned this practice to be abandoned, and a more efficient one to be introduced, which
consists of dressing the slope of the banks and laying on them a pavement of heavy stone.
Wherever sand is deposited by the waters on a coast, and it is desirable to retain it for
the purpose of forming a sea-wall: that which is furthest distant from low water is first
secured by small bands of osier or basket-work; the winds not having any power to scatter
it, in the course of a short time it becomes consolidated; should any clayey or earthy
CHAP. XXVI.
1523
FASCINES AND BASKET-WORK FOR JETTIES
matter be held in suspension, by allowing it to deposit itself over twigs of trees or fascines
firmly pegged down, a considerable quantity will be obtained after filtration, and on the

Fig. 2791.
Fig. 2792,
Fig. 2793.
GABIONS.
Fig. 2794.
whole becoming bound together, a fresh layer of fascines may be pegged down, upon which
another course of earthy matter will be deposited, and the work advanced till a certain height

Fig. 2795.
is attained above the level of the salt water; after which, by exposure to the sun and air, the
surface will be rendered fit for vegetation, producing first grass or rushes, which mixing
with more earthy matter continue to rise above the water altogether, and at last become
fit for agricultural purposes. By means of basket-work an island may be formed in
shallow water, the mud being deposited within it at the time of high water; when the tide
retires, the whole will settle, and the water draining off, become more and more consolidated
at every fresh deposit, the wicker-work being admirably adapted to allow the surplus
water to pass away, and the more solid matter to be retained. When such operations were
conducted upon a large scale in Holland, the islands were at first of no very considerable
5 E 2
1524
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
extent; these were by degrees united, until large tracts of very valuable land were obtained:
Spanish broom and twigs of various trees, as the alder and willow, are well adapted for
this purpose.
The general plan in Tuscany for forming sea or river walls is to lay down a framework for
round timbers, which being well secured, bundles of faggots or branches of trees in one
direction are laid upon them, and another layer or several in a contrary direction; this is
repeated several times, and where the water deposits any earthy matter, it is effectually
retained.
An earth bank covered with fascines formed in this manner is generally sufficiently pro-
tected, and will continue sound for several years.

Fig. 2796.
Jetties at the entrance of small harbours are frequently for the sake of economy formed with
fascines, and the same kind of work is sometimes adopted as a temporary expedient, to facilitate
the construction of others more solid: the height to be given to jetties of this description
should be always proportionate to their extent of base, which generally is as 1 to 3;
so that a jetty 24 feet in height, where the summit is to be left 5 or 6 feet in width, should
be at least 78 feet in width at its base. In setting out the work due regard must be had
to the increasing depth of the water and to the necessary spreading of the base.
To prevent the fascines from being displaced after they are laid, they may be covered

Fig. 2797.
Fi¿. 2798.
AM

Fig. 2799
with a framework of rough timber, over which rods, planks, or boarding may be nailed or
tied down timber 4 or 5 inches in diameter laid with the proper inclination, and secured
to the heads of inclined piles driven for the purpose, may be covered with smaller timber
laid in squares, and the interstices filled either with stone, chalk, or gravel; where there is
a deposit from the water, land may be gained by allowing filtration through such em-
bankments, taking care to retain the solid matter, for which purpose baskets closely woven
are well adapted; the foot of such jetties should be well protected at the toe by a row of
piles.
CHAP XXVI
1525
RIVER AND SEA WALLS.
Triangular baskets filled with stones are sometimes laid in rivers subject to floods, to
protect the starlings of the bridges.

the
Fig. 2800.
Fig. 2801.
Groins used on the coast for preventing encroachments of the sea are made of timber and
constructed across a beach, between high and low water, perpendicular to its general line:
they are for the purpose of retaining the shingle or accumulating more, and are formed of
piles, planking, land ties, blocks, tail piles, keys, and screw bolts. Their length depends
on the nature of the beach upon which they are to be formed; those on the Sussex coast
vary from 150 to 250 feet, and have oak or beech piles from 12 to 25 feet long, shod with
iron, their scantling being 8 inches by 61. The planking is 2 inches thick; the land ties
are about 25 feet in length of rough timber, and the bars which secure them at the ends
are 13 feet 6 inches in length, and 12 inches by 5; the land tie bar blocks are 2 feet in length,
and the tail blocks 2 feet 6 inches, their scantling 6 by 3: the screw-bolts are of inch-
round iron, 2 feet 9 inches long. Every 16 feet in length of these groins contains four
piles, one land tie, with tail piles and keys, one land tie bar with two blocks 2 feet long,
and two short bolts, 180 superficial feet of planking, and 140 6-inch spikes, the cost of
which is about 30 pounds.
To accumulate more shingle, the first pile is driven at the high water mark of neap tides,
leaving its top level with that of spring tides; the next is driven at the point on the sands,
beyond the bottom of the shingle to which the groin extends, leaving about 4 feet out of
the beach; the tops of these two piles formed the general slope of the groin, unless where
the beach is curved, when it was slightly modified to meet the curvature.
From the high water mark of neap tides the piles are carried back nearly level to that of
spring tides, or further if necessary, and driven 4 feet apart from centre to centre, so as to
adınit the planking to pass alternately between them; the land ties are placed about one-third
from the top of the planking, and usually on one side, so as to resist the action of the most
prevailing winds. The groins are placed from 50 to 100 feet apart, and are raised as the
shingle mounts.
Of River and Sea Walls. Before walls of masonry are commenced for this purpose,
the soil must be carefully examined, and the foundations laid in at sufficient depths
below the current or flowing in of the tide; the footings must also be protected by
internal and external rows of planking and piling; another matter for consideration is
the escape of the water from the land, which sometimes, if not properly drained off, will
either wash away the soil on which the foundations are laid, or thrust the whole out of a
perpendicular direction; and when river walls are built upon the heads of piles not
properly secured, they will often press the latter out of the position in which they were
driven, and destroy the strength of the work. Sea walls, from being exposed to a great
force, must be so set out that the necessary resistance is obtained, and the slope next the
ocean should always be as flat as possible, that the waves may break easily upon it: in
those instances where a slope of 1 in 30 has been given, and the surface paved with stone,

Fig. 2802.
SEA WALLS.
there has been less expenditure to keep it in repair than in others made more steep.
Dock walls require that the interior should be puddled with clay, as it is found that at low
5 E 3
1526
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
water the pressure from the interior sometimes forces the water through the banks, unless
this precaution is taken.
Walls constructed of earth to hold water in a reservoir or filter are set out in the same
manner, but as the pressure to which they are subjected is only on one side, the inclination
of their slopes is varied according to circumstances. Puddling a wall in the centre is always

C
Fig 2803.
advisable, and before the work is commenced, it is usual to lay in the main or pipe,
through which the contents of the reservoir are to be admitted or discharged; if this
main be required of considerable size, a brick tunnel may be substituted, which permits
of attention to the hydraulic works, and gives facility for their repair.
Sea Wall at Brighton is constructed with sand and shingle taken from the beach, and
cemented together by an hydraulic lime made in the vicinity; salt water was used
at first, and answered the purpose well. The wall is at the top 2 feet 6 inches in
thickness; the back is built perfectly perpendicular, and the front has a talus equal to one-
third of the height; its base is on the chalk; its height varies from 40 to 70 feet. The
lime was obtained at Bycombe, where chalk marl lies under the lower chalk formation,
and is of the same quality as the Dorking and Halling limes; it is found generally
in the north escarpment of the South Downs, and in the southern of the North Downs.
After being properly burnt it was not ground but slaked at once, and at the same time
mixed with three parts sand; it was then put into a pug-mill, and combined with
three parts of shingle, wheeled away and thrown down upon the wall, into a case made of
boards lodged together; the rear lodges were strutted against the face of the chalk, and
the front was held to them by iron ties, which were afterwards drawn by taking out the
pins, and again used as the work advanced. The whole was executed at a price equal to
3s. 4d. per cube yard.
The Humber Dock Wall is in perpendicular height 32 feet; at top it recedes 6 feet 8
inches from the perpendicular line; the thickness of the wall is 6 feet; the projection and

Z
Fig. 2804. HUmber dock wall.
E a
V VA
#
Fig. 2805. DOCK WALL.
肉
​N
AY
N
•
צו
N
22
13
Z
א
N
ES
"
width of the counterforts, which are 15 feet apart, is 3 feet 9 inches.
Oak fenders 12
inches
square are placed along the walls to protect them; these project 8 inches before the
face; there are also two horizontal rows of fir fenders, 7 inches square, let into the uprights
by short tenons with angle pieces, to prevent vessels catching underneath or riding upon them
as the tide rises or falls.
The Humber Dock Wall has the foundations all piled, with a row of 6-inch grooved
sheeting piles in front; those upon which the wall is founded are 9 inches square, and
the counterforts 8 inches in diameter, all driven with a ringing engine, and a ram of
9 cwt. worked by fifteen men: longitudinal sleepers of half timber were bolted down upon
CHAP. XXVI.
1527
SEA AND DOCK WALLS

the heads of the bearing piles; the sheeting piles
were spiked to an inner waling of the same
size, and the whole was covered with 4-inch
close planking, on which the walls, which were
of brick, rested: their thickness at bot-
tom is 10 feet, at top 4 feet 6 inches; the
height is 24 feet 6 inches, and it batters 5 feet.
The counterfort at the back is 9 feet thick, and
projects at bottom 8 feet, and at top 3 feet
6 inches from the back face of the wall.
Retaining walls built of stone in some of
our tidal harbours are 12 feet in thickness at
the base and half that width at the top; in
many instances the face is curved with a radius
of 80 feet, to allow the nearer approach of the
vessels to be loaded and unloaded: and the
fenders of oak, which are placed perpendicularly,
are secured by iron ties.
It is important to carry the foundations of all
retaining walls to the depth of 6 or 7 feet below
the bed of the harbour or basin where they are
constructed, and to protect them at the toe by
rows of piles; in many places the oak fenders
are capped with iron, and lewis iron eye-bolts
are introduced to secure vessels.
Where the soil of the foundations is soft, a
timber platform is generally laid below the
footings, the toe of which is protected by sheet-
piling.
Fig. 2807.
The Brunswick Wharf
at Blackwall, wholly of
iron, was constructed in
1834. A trench 6 feet
in depth was dug along
the intended line, and the
timber guide-piles after-
wards driven: the iron
piles, which are in two
heights, with a socket-
joint secured by a screw-
bolt, were then driven at
intervals of 7 feet, and
the intermediate spaces
filled in: each sheet-pile
is secured at the top by
two bolts to the upper-
most wall of the wood-L
work behind: the iron
Fig. 2808.
10
Fig. 2806.





Fig. 2809. BRUNSWICK WHARP.
5 Б 4
1528
Book II
THEORY AND PRACTICE OF ENGINEERING.

·
plates filling up the spaces over the sheet piling are bolted
to the main piles and to each other, and the joints stopped
with iron cement: the plates that receive the mooring
rings are cast concave; the whole of the work is backed
by a wall of concrete, and the coping is granite. The
sheet-piles are 14 inch thick, and the weight of each pile
17 cwt. The length of the wharf is 720 feet, and the
quantity of iron used was upwards of
900 tons: the height of the sheet-piling
is 22 feet, and that of the plates above
14 feet: the average rise of the tide is
about 18 feet.
Dykes of Timber filled in with Stone
were formerly much adopted, and at
many of our ports, as well as on the
continent, we find them ex-
ecuted in oak: in some
instances their form is cur-
vilinear, to suit the bulge
of the vessel that is to be
secured to the quay; and
by spreading out the base
to obtain this, additional
strength is acquired: the
whole is braced horizontally
by a succession of St. Andrew's
crosses, and being afterwards filled
in with stone and planked on both
sides, is rendered tolerably secure.
Fig. 2810.
At the Quay of Rouen the sides
were made to incline gradually,
and a filling in with courses of ma-
sonry contributed to its strength :
but this mixture of timber with
masonry is not durable; it fre-
quently requires repair, and is only
adopted where timber is abundant
or of little cost.
In another variety of dyke the
thickness is obtained by slant-
ing one side only, or giving
it a greater inclination than the
other the base is in width half
as much more as the height, and
DYKE IN CARPENTRY.

Fig. 2811.
strongly braced and tied together by horizontal
timbers, laid throughout from one side to the other,
and further strengthened by inclined struts, abutting
against perpendicular timbers which pass entirely
through its height.
The quays at Rouen are admirable pieces of con-
struction, notwithstanding the objection just referred
to: in some instances the walls rest
on sleepers, filled in between with
beton or rubble and mortar, guarded
on the waterside by rows of sheet-
piling secured to timbers laid in the
wall; and where the ground was in
a soft state, and could not be de-
pended upon, piles of
considerable length were
driven and braced,
shown in the figure; they
excited for years the ad-
miration of engineers,
and are allowed to be
peculiarly well adapted
for their situation.
as
QUAY AT rouen.

Fig. 2812.
DYKE,
CHAP. XXVI.
ŠEA AND DOCK WALLS.
1529


In facing the sides of a
pier or dock wall with
timber, series of land-ties
are requisite to prevent the
pressure outwards, as well
as to act as struts against
its action inwards: a strong
capping of timber framed
to the heads of the piles, a
brace secured by iron straps,
and a horizontal tie halved
on to the sides and heads
of the piles, may be so put
together as to endure for
Fig. 2813.
ROCHELLE.


40
Fig. 2814.
QUAY AT rouen.
Fig. 2815

a length of time, if secure from
the ravages
ravages of
of the
the teredo
navalis.
The Piers of the Humber
Basin are 18 feet across their
top; the main piles are 14
inches square; those of the
outer wall of the same dimen-
sions; those of the inner wall
12 inches by 6 inches; the cap
sill 12 inches by 10 inches; the
joists 7 inches by 4 inches; the
ties 12 inches by 6 inches
sheet-pilling 6 inches thick,
and the planking 3 inches.
;
In the construction of piers
of this kind great attention
should be paid, so that they
have sufficient strength to
resist the force which is often
exerted during storms against
them. Up to a certain height
P
Fig. 2816.
HULL.
Fig. 2817.
1530
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

they require to be loaded with
stone, or filled in solid; and
where this is done, planking
and sheet-piling are required
to keep the materials so de-
posited within the framework
from washing away.
The foundations of walls con-
structed in the sea or in deep
rivers require the greatest at-
tention on the part of the en-
gineer: where the soil is soft,
and cannot be depended upon,
it is necessary not only to pile
it closely all over, but to lay
on the heads of the
piles a piece of whole
timber, and then fill
up level with rubble;
another series of tim-
bers of the same
scantling should be
laid in a transverse
direction, and when
brought level by
another filling-in of
rubble
masonry,
the wall is built
upon it: such was
the system adopted

the
by Perronet when
constructing
bridge at Neuilly.
At Rochelle similar
were
precautions
adopted for the walls
of the docks, which
were faced with free-
stone and backed
in with brick: a row
of sheet-piling was
driven along the
Fig. 2818. NEUILLY FOUNDATIONS.

W
Fig. 2819.
NEUILLY FOUNDATIONS.

ם
ם
Fig. 2820.
D
。
.
ROCHELLE.
whole length of the footing, to prevent the water from acting upon any portion of the foundation.
Another system of holding in the upright fenders is by irons worked into the solid wall,
or they may be made to pass round a row of horizontal timbers, halved into the upright at
the levels of high and low water.

카
​THE
E
Fig. 2821.
Fig. 2822.
Stone facings backed with brick, when made to batter, afford the best protection to the
sides of a dock or pier that can be devised: upright fenders of oak or fir secured by iron
CHAP. XXVI.
1381
SEA AND DOCK WALLS.
ties may be placed at regular distances, for protection against the vessels, and rings may
be inserted to make them fast. Sheet-piling should never be omitted to protect the foun-
dations.

HHH
Fig. 2823.
Where the foundations are chiefly composed of sand. or of an earth liable to slip, it is
absolutely necessary to continue a row of sheet-piling to the stratum beneath it: to drive
the piles a crab engine with a ram of 10 cwt. may be made use of, with a fall varying
from 8 feet to 18 feet, or 12 feet on an average, which will generally drive an inch at each
stroke.

Fig. 2824.
Platforms of carpentry, when laid upon the heads of piles, should be perfectly level, and
boarded through in the longitudinal, as well as transverse, direction; taking proper care▾
first to drag between the heads of the piles, and render the intervals solid, by throwing in
loose stones or a mass of concrete.
When foundations are upon gravel, it is very necessary that they should be consolidated,
cither by dropping in large stones, or by piling, and afterwards laying over the whole a
timber platform, at such depth below low water that it cannot be affected by the tide.
1532
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
In some instances, in forming sea walls, timber and stone may be introduced together,
and particularly when the banks are loose and subject to slip, or are acted upon by the
land-springs. A stone wall carried up in front of the work, supported at the back by
strong wooden piles¸strutted and braced, and afterwards filled in with concrete, or puddled


Fig. 2825.
Fig. 2826.
with clay in the manner of a cofferdam, will have great strength, and resist any force to
which it may be opposed: a row of sheet piles round the face of such walls, as well as the
buttresses, prevent any irruption, and planking the whole foundations over binds them into
one entire mass. It is sometimes advisable in face of a cliff to form a temporary defence.
by driving in double rows of piles, and filling up the space between with clay or earth im-

0
Fig. 2827.
pervious to water: the weight acting against such a dam should be always resisted by a
timber framing on the opposite side. When a length has been put together and secured
by iron bolts, they may be drawn, and the same framing advanced another length, and so
continued until the entire shore is out of danger.
CHAP XXVII.
1533
CANALS AND RIVER LOCKS.
CHAP. XXVII.
CANALS AND RIVER LOCKS.
CANALS are to the inhabitants of a country what seas are to nations; they equally serve to
assist the wants of society and benefit commerce. The great navigations extend over the
whole globe, and transport the products of all nations and climates where they are in excess
to where they are most needed, which, by means of the internal canals, are distributed to
the various districts in smaller craft, enabling these latter at the same time to maintain
a continual and economical interchange of whatever may be required either for food or
manufacturing purposes. But the formation of a canal is frequently attended with great
difficulties; and all the talent of the engineer is called forth in overcoming obstacles ap-
parently insurmountable, but which by a careful survey and patient investigation will gene-
rally be vanquished.
In commencing a canal the first consideration should be directed to the quantity of
water that will be required, and from whence it is to be supplied, the means of keeping
the bottom clear, the construction of the sluices, and the distribution of the slopes of its
bed.
The water is usually collected from springs or rain, or derived from some neighbouring
river; and in whatever way the supply may be received, it is incumbent on the engineer
carefully to examine not only the nature of this supply, but also to ascertain the quantity
lost by evaporation and absorption: should it be drawn from a river, it is commonly
effected by constructing a weir across it, and after damming up the stream, admitting
a portion into the canal, and, if a continuance of a navigation be not practicable in the
bed of the river itself, the stream must be traversed by other dykes or weirs, the height
of which, as well as the depth of water required, will demand great consideration. The
smallest possible quantity consistent with the purposes of navigation should be ad-
mitted, in order to keep down the height of the sluices, banks, and dykes, all of which
are affected by the pressure of an increased body of water; and it is highly necessary to
make such arrangements that no injurious consequences shall arise from the floods, which
occasionally swell the waters in the rivers of supply. Another important precaution
is preventing any deposit of gravel or other matters held in suspension by the water,
whilst it is permitted to move rapidly forward: could it be freed from these before their
introduction into the canal, much manual labour would be saved, and the fatal effects arising
from the miasma produced by throwing out the mud on the banks be prevented.
The common method adopted in Italy for cleansing the canals is by sluicing: bottom or
ground sluices are constructed in the banks nearest to the river of supply, having their sills
laid at a considerable depth below the bottom of the canal, over which the water being
occasionally allowed to fall, acquires sufficient velocity for a considerable distance beyond
the opening of the sluice to detach any substances that may have lodged at the bottom of the
bed: numerous sluices distributed throughout the whole length, placed at distances
where they can be made to operate after the action of those below has ceased, have suc-
cessfully moved large quantities of gravel deposit.
When the supply is first accumulated in a large reservoir, the deposit may be made to
take place before the water is used for the purposes of navigation: the expense attend-
ing this method has been its great objection: wherever gravel and coarse substances are
brought down by the river that feeds the canal, their diffusion should be as much as pos-
sible prevented; this is sometimes done by opening an ample bottom gate immediately
above the sluice, and making the platform slope considerably towards the mouth of the
outlet; by keeping up the sill of the first gates, a little above the level of the outer
platform, when they were opened the gravel would be prevented from entering; but this
must be guided by circumstances, as no obstruction must be allowed to the navigation
when the waters are low in the canal.
Level Cutting. This term is applied to an excavation when the banks are made of the
earth taken out; it is the most economical method, and consequently the most generally
practised, the breadth and depth of the bank being of course dependent on the strength re-
quired. It often occurs that a canal is cut on a hill, and a bank is made only on one
side: the work is then exceedingly simple, and called side or oblique cutting.
The Centre of Cutting is that point in a transverse section through which, if a line be
drawn representing the surface of the ground, the part for excavation will be found equal
to that of embankment. To apply this to a canal on the side of a hill with parallel slopes,
where one bank only is required, let A B C D be the section of the intended canal, CDEGF
that of the bank; to find the centre of cutting, continue the lines BC and DE to G and
1534
BOOK 11.
THEORY AND PRACTICE OF ENGINEERING.
!
A; draw the perpendiculars Cm, Dn, and the diagonals A G,mn, intersecting at p: through
p draw the parallel spt, and bisect it in o, which is the centre of the cutting, through

H
A
B
m u
E
น
F
Fig. 2828.
which, if any line HoF be drawn cutting the slopes AB and EG produced, HBCw
will always be equal to wDEF; for mn D-CDn, therefore mnGÊ=CDEG. But
mn GE=sBGt=CDEG, and taking away Cut G, we have s B Cv=v DEt, and the
triangles Hso and ot F are equal, having equal angles, and the side so ou; therefore the
sum Hso+sBCv=ot F÷vDEt, and taking away the part owv, there remains H B C w
=wDEF; therefore, as the total breadth of the canal and bank is to the breadth of the
bank added to the base of one slope, so is the depth of the canal from its surface to the
depth below the centre of cutting, which is also the centre of cut and cover, for a line
staked out at the level of the centre of cutting will show the middle of the land required
for the canal.
A canal with a bench or towing-path on the upper side. Let a ABCDEG be the
profile of the canal and bank; take Dd=a A, and draw ab and cd parallel to the slopes;

A
q
₫ D
F
M
t
G
b
B
C
20
ቀ N
Fig. 2829.
the section a ABCDE is converted into abcd E, which comprises the towing-path: draw
the lines a G, cd, and st, and the middle o will be the centre of cutting. The distance from
centre of canal is equal to uq+DE—a A.
Eq: Em: 1mc: oz; that is, as a E: ED: ED+Dd+dm :: mc: oz.
To reduce the section ABCDEF with a second bench or path E F, to the equivalent
section ABIK F, with one bank only, but wider and shallower, the banking cut down, and

H
F
E
M
K
G
D
L
B
A
Fig. 2830.
filled in to the bottom.
Produce BC and HF to Z, and CD to G; make DN to equal
DG; draw the parallel NL; on FL describe the semicircle LMF; make ZK and ZI
equal to Z M, and draw the parallel K I, and the figure is complete.
To find the Lines of Level Cutting, when the section of a canal has two banks, and the
slopes are made all equal. The section ABCD must first be reduced into AH KE, and
CHAP. XXVI.
1535
CANALS AND RIVER LOCKS.
the centre of the cutting must be found; each slope must be prolonged to meet in V:
draw the perpendicular NV; with the radius NV and N as a centre, cut EA in p,
make Va equal pQ; then through a, parallel to E A, draw ML, which is the line of
level cutting.

A
M
B
D
E
Q
IN
K
Fig. 2831.
To find any Line of Oblique Cutting. Find the line of level cutting, produce the slopes to
meet in V; draw the perpendicular VI; from L draw LN with the given slope of the
V

L
K
p
Fig. 2832
N
R
12
ground, cutting VI in N, making Np and p Q equal to V I, and V R equal to pI: through
R draw KRH, which is the line of oblique cutting sought for.
Theory of Locks. Locks with gates for the purposes of navigation are of modern
invention; those of the Canal of Martezana, in Italy, already mentioned at p. 186., were
the first executed: their date is not more than 386 years since; they were the model from
whence all others have been taken, nor does it appear that any great improvements have
been made, nor have any rules been given for their proportion: the only difference in
the various locks hitherto constructed consists in the greater or less width and height, for
the purpose of containing one or more boats, isolating or uniting several chambers, and
making the side walls either straight or curved. Belidor has treated on this matter, and
given an account of various works; he has, however, only mentioned the proper pro-
jection for the pointed sills, and the strength of the timber necessary for the gates, and
endeavoured to show that no advantage is derived from a curvature in their plan.
The least Length that can be allowed between the Locks should be such that 12 inches of depth,
over and above what a loaded boat will draw, will only lower the water 6 inches without the
navigation being interrupted; and if it be required to draw the contents of each lock from
the interval above, the distance for the locks must be so regulated that the quantity of
water expended by one should not lower that of the upper interval more than 6 inches at
most; thus the distance should be greater in proportion to the contents of the chamber
of the locks and the width of the canal; that is to say, when the chambers are large and
the canal is narrow, the distance between the locks should be greater. Chambers 110 feet
in length between the gates by 17 feet in width, as those of the canal of Briare, contain
1870 superficial feet; therefore 11,843 cubic feet when the fall is 6 feet 4 inches, 15,859
cubic feet when it is 8 feet 6 inches, and 19,635 cubic feet when 10 feet 6 inches. If the
canal be 48 feet in width, at 3 feet below the ordinary level of the water, the length of the
interval should be 446 feet, in order that the expenditure of locks of 6 feet 4 inches of fall
should not lower the water more than 6 inches; this length should be 607 feet when the
locks are 8 feet 6 inches of fall, and 755 feet when they are 10 feet 6 inches: the distance
then between the lower gate of one lock and the upper gate of the other should be always
about 624 feet for ordinary canals. If two locks of 8 feet 6 inches fall were only distant
1536
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
160 feet, the water drawn from the interval, for the purpose of mounting the boat, would
lower it nearly 26 inches, and there would not remain sufficient to keep it afloat; conse-
quently, it would be necessary to draw a lockful from the upper interval, and then a second
to cause it to rise, whilst only one would be required if the locks were at a sufficient distance.
This example will show the inconvenience of having locks too near each other, which is
still further increased when they are contiguous: it frequently happens that several boats
arrive together in the same interval, particularly where the bargemen stop or sleep, and that
no water may be lost, the interval where they stop should be sufficiently long to admit
more than one; if circumstances will not permit this, a greater width must be given,
that the lockfull which the rising boats draw from the interval should not cause the water
to lower so considerably as to prevent their floating, or the descending boats force in
such a quantity as to make it run over the gates: if the interval has only the ordinary
width of 48 feet, it should be 6398 feet in length, so that ten rising boats could stop, if
one were descending at the same time, otherwise a part of the water must be drawn from
the other intervals to keep them afloat if there were as many ascending as descending
boats, this need not be so great; but this observation proves that in forming a canal it is
necessary to have basins at those situations where boats are required to stop any length of
time.
·
Quantity of Water expended by Boats in traversing a Canal. It was the opinion of
MM. Gabriel and Abeille, that the passage of a boat through the whole length of a canal
always cost twice the quantity of water necessary to fill a lock: Belidor thought the same,
and it is still the common opinion. M. Thommason has nevertheless maintained that this
idea is erroneous, and that when one boat passes several locks one after another, the second
boat only expends two locksfull in its whole passage; but when they pass alternately, one
up and the other down, that it costs as many locksfull as there are locks in the ascension
of each boat. He founds this assertion on two statements, one of M. Caligny, the other of
M. Regemorte, asserting that the expenditure of the water is the same, whether contiguous
or separated; but this distinction not having been sufficiently examined, a second error has
been committed; but it is undoubted that when locks are contiguous, they often expend
more than two locksfull; and it has not been remarked that when the locks are more than
640 feet apart, they often expend only a single lockfull for the whole journey. When
locks are distant from each other, and the boats pass alternately, one up and the other
down, the boat which passes after the first frequently finds in mounting all the locks
empty, and to fill them it must draw a lockfull from each interval and one from the
starting point; in descending, as it finds the locks full, it does not draw any from the starting
point, consequently it will only expend a single lockfull in its whole voyage.
When the locks are distant from each other, and the boats follow, the second boat will
find all the locks full going up, and to ascend it must first empty all, and then fill them
with water drawn from the intervals, and the highest from the starting point: in de-
scending, all the locks will be empty, and the first lock will be filled with water from the
starting point, which will serve to fill all the others, so that this boat will expend two
locksfull in its journey.
When the locks are so near each other that the water of one taken into the interval
between the two diminishes the depth of this interval sufficiently to impede the navigation,
or when the locks are contiguous and the boats pass alternately, the second boat in
ascending finds all the locks empty, and as it cannot draw water from the intermediate
intervals from the contiguity of the locks, all are filled with water from the starting point.
Thus in ascending each boat expends as many locksfull as there are contiguous chambers;
in descending, all the locks being full, no water need be drawn from the starting point,
consequently in a whole journey as many locksfull will be expended as there are
contiguous locks in ascending. When the locks are contiguous, and the boats pass each
other in succession, the second in ascending will find all the locks full, and to enable it to
enter the intervals, it must empty them successively to fill them with the water from the
intervals, except the last, which it fills with water from the starting point; in descending,
another lockfull is taken from the starting point, so that in this case two locksfull are
taken from the latter.
Although the four above cases contain the whole theory of the working of locks, it may
be remarked that if two boats meet at the starting point, and two others before or after
the starting point, the four will expend five locksfull; if two boats meet at the starting
point, and the two following meet there also, the four will only expend four locksfull; if the
two last boats that have passed meet before or after the starting point, and the two succeeding
meet also before or after the starting point, then they will only expend four locksfull,
nad the first come in an opposite direction to that which had passed previously, and five it
it had come in the same direction; and it has been generally observed, that a boat always
takes a lockfull from the starting point to ascend but that it often does not take any to
descend on the other side, consequently, when there are no contiguous locks, the boats will
only expend a lockfull for their whole journey, when they pass the starting point al-
CHAP XXVII.
1537
CANALS AND RIVER LOCKS.
ternately, one going up, the other down in like manner, where there are contiguous locks,
the boats will expend in their journey as many locksfull as there are contiguous locks in
ascending; when one boat follows another, it will expend two locksfull, whether the locks
are contiguous or isolated. It must be remarked that the passage of those boats only can
be considered relatively to the locks which join the starting point: when the locks are not
contiguous, and their fall is equal, which happens in the lower intervals, it has no influence
on the expenditure of water, especially when the boats do not stop any length of time; in
giving 640 feet length to each interval, it is evident, when two boats follow each other,
they will never be together in the same interval, since whilst the second passes the lock, the
first will have time to pass the interval and enter the following lock; thus two boats cannot
meet in the smaller intervals, except when one ascends and the other descends, and in this
case, as one takes a lockfull from the interval, whilst a second pours one into it, consequently
the water does not diminish or increase in it. It must be observed that we can never have
above a lockfull, more or less, in an interval, unless several boats remain in them together,
which should be avoided when they are small; further, when the contiguous locks are distant
from the starting point, it often happens that the lockfull is not immediately taken
; but
when there is no second quantity of water before the contiguous locks, it is always the
starting point which furnishes that of the canal above them.
Locks to contain several boats are successfully employed where water is abundant. In form-
ing them the side walls may be dispensed with, the sides of the chambers only being laid with
stone to a proper talus; some of those chambers may contain four boats, others a large and a
small one; at the ingress and egress there usually are two pairs of gates, one small and the
other large locks to contain two boats are either double the length or the width of the
chamber. The second plan is the least expensive, the length of the chamber walls in this
case not being greater than for the more simple locks; but the first has the advantage of
receiving a third pair of gates in the middle of its length, so that one or two boats can pass
at pleasure; the length of the chamber is also varied, by placing more than two pairs of
large gates, enabling boats of different dimensions to pass together or separately, without
expending a greater quantity of water than would be necessary for each boat. To make
the chamber of a sufficient length for two ordinary-sized boats, a gate is placed in the
middle of its length, and another at the necessary distance for the larger boats; the
rest of the length is then available for smaller it is, however, seldom necessary to
make provision for the passage of boats of various sizes, as there is no advantage
in two boats passing at once; when the chamber is constructed of masonry, twice
as much water is expended for the passage of two boats as for one, consequently twice as
much time is employed in filling a lock for two boats as for a single one; there is therefore
no gain either in time or the quantity of water, and the expense of construction is con-
siderably augmented.
The chambers of this kind of locks are sometimes formed by a slope of earth only, without
a facing of masonry; but they expend much more water, consequently take a longer time
to fill, and are less advantageous on account of the time lost by the boats having to wait for
each other should one arrive alone it must remain until a second comes up before it can
pass the lock, or as much water must be expended for the one as would be required for
two, and of course this inconvenience is increased when the chamber is made to contain
four boats.
:
The
Form to be given to the Chambers of Locks. The most convenient is the parallelogram, a
little wider than the boats that require to pass, and sufficiently long to admit of the gates
being moved with facility. The chambers of the canal of Languedoc are of an oval form,
to give greater strength in resisting the banks contiguous to them; but as this causes an
increase of expense in construction as well as in the quantity of water necessary to fill it, it
will be useful to enquire if, in avoiding one inconvenience, a greater is not produced.
oval chambers of the canal of Languedoc contain an area of 3636 feet, whilst if the side
walls were parallel, they would only be 2248 superficial feet: thus the expenditure of water
in the oval chamber exceeds more than a third that of the parallelogram, the proportion
being about 5 to 3: the inconvenience is considerably increased by want of water, which
frequently occurs. Another result of the oval form is that the passage of the lock is also
longer than in the rectangular; in the same proportion the expense of the timber platform
is also increased: it is, however, certain that a curved wall is stronger against a pressure of
earth than a straight one, and if the cost of masonry requisite to give the same strength to a
straight wall is greater, the expense is compensated for by the diminution of the cost of the
timber platform, which is two-fifths stronger. It is very essential to prevent the filtration
of water through the side walls, and the best method to effect this is to place on their thick-
ness a lining of beton, or of brick laid in cement, which will be impervious to water; but
as this will destroy the bond, a greater thickness of wall is requisite; thus there are many
circumstances where it might be necessary to give to curved walls as great a thickness as
to straight. The thickness of straight walls which support earth should be a third of their
height, whilst those which resist the thrust of water should be one-half; if the wails of the
5 F
1538
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
1
chambers of locks have a thickness relative only to the thrust of the earth, they may give
way when the earth is put in motion, which often occurs from a slight filtration behind the
wall. Gauthey has a rule for finding the thickness to be given to the wall of a basin in-
tended to support water throughout its whole height, and in the chambers of locks it must
be remembered that the thrust of the water against the vertical surface is equal to the product
of these surfaces by half the height of the water: call h the height of the wall, x=its thickness,
supposing its length to be 1 metre, the acting power will be 1000 × 1h: supposing the
cube metre of water to weigh 1000 kilogrammes, and the centre of impression of this thrust

Fig. 2833.
LONGITUDINAL SECTION.

E
A
B
D
Fig. 2834.
PLAN OF LOCK.
being at a third of the height of the wall, the arm of the lever of the acting power will be
equal to h.
3
The resisting power will be the wall itself -hx × 2000, supposing that the cube metre
of masonry generally weighs 2000 kilogrammes. The arm of the lever will be half the
thickness of the wall =1, consequently the momentum of the acting power will be 1000
× 1½³ × 1h, and that of the resisting power 2000 × 1hr²; and as in the state of equilibrium
these two powers should be equal, we shall have 167 h³= 1000h x³, from whence we have
x= √/0·167 h³=0·41h: but, as something should always be allowed above the equilibrium,
by adding, we shall have x = -h nearly: hence it is evident that the thickness of a wall
intended to support water should be equal to half the height of the water which acts
against it.
The length and width of chambers of locks must necessarily be regulated in conformity
with the boats used on the canal; these are generally longer and narrower than those on
rivers, where the shallows which occasionally occur require flatter bottoms to be given
them: the letters A B, CD, EF, refer to the sections through the several parts of the
lock chambers. With regard to the length of the chambers, it should be such as to enable
the gates at the lowest ends to open and shut easily; if the rudder of the boat cannot be
unshipped, or occupies any portion of the length of the chamber, then the chambers must
be made sufficiently long to prevent them from interfering with the opening of the gate, on
which account the most proper rudders for navigable canals are those like broad oars,
which can be taken out whilst passing through the locks. The height of the water in the
intervals is regulated by the mean height of the waters of the river which communicate
with the canals: it is, however, customary to allow the latter a sufficient height of water
to receive boats of the same tonnage as those which navigate the river; another advantage

E
Fig. 2836.
TRANSVERSE SECTIONS.
Fig. 2836
D
CHAP. XXVII.
1589
CANALS AND RIVER LOCKS.
in giving an extra depth of water to canals is the greater ease with which the boats can be
drawn, the weeds at the bottom causing less inconvenience, and the evaporation being of
course less than in a shallower body of water; in summer also, when the boats can only
carry half a load, two loads may be put into one boat, and the transport rendered less
expensive.
The quantity of water expended by locks is found to be in direct proportion to the
height of the fall, and the time employed in going through them, and the expense of con
struction nearly in the same proportion; this is greater as the locks are least elevated,
because they are more in number, but the increase is not in proportion to the number.

A
FO
B
A

©
Fig. 2837.
TRANSVERSE SECTION.
To render these relations evident, trace the curves AB, A C,
and the line DC on the axis EF; the ordinates of the first mark
the relation of the time employed in going through the total of
the locks of different falls: those of the second mark the relation
of the expense of construction, and those of the line DC mark
the quantity of water which they will expend.
E
Fig. 2838.
It may be concluded that when there is a great deal of water in a canal, the locks may
be high, because the saving in the expense is a great consideration, less time being required
to go through them, and the wages of the lock-men reduced.
The Talus. It is by no means advisable to make the walls of the lock chamber strictly
perpendicular: some inclination, or talus, is always preferable, particularly at the back,
whence resistance is required against

the thrust of water; and as its filtration
is another point of importance to be
guarded against, a greater thickness is
necessary at the bottom than at the
top of the wall, that filtration being
greater in proportion to its height.
The walls should, however, be per-
pendicular towards the interior of the
lock, at least in that part where the
boats mount and descend; the lower
part may have the same talus as that
usually given to the boats. The least
thickness for the walls at the level of
the water is 4 feet 3 inches, in order
to allow for a course of beton in cement
or of brick, as a protection against the
Fig. 2839.
filtration of water: as a general rule, the thickness should be equal to half their height,
and as the walls become more lofty, their foundations must be spread out in proportion.
Inverted arches have been introduced with considerable advantage to form the profile of the
wall of lock-chambers; where there is a good foundation they may commence with a
considerable batter or inclination, rising gradually in a curved form, finishing at the top with
a perpendicular face; such a wall resembles an arch, from its having the joints and beds of
the several stones made perpendicular to their face, which also prevents them from sliding
on each other: the triangle of earth, supported by the back of the upright retaining wall,
may be regarded as a wedge, of which its own gravity is the acting power, and it is only
supported by the re-action of the inclined plane of earth, and the back of the wall, each of
which acts perpendicularly to its plane. The breadth of such retaining wall must be
always proportionate to the height, and to be of equal specific gravity with the earth, its
breadth should be more than of its height. The specific gravity of walls built of brick
or stone is a trifle more than that of the earth they support, therefore the dimensions may
be slightly diminished.
5 F 2
1540
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Dimensions of the other parts of the Locks. — The chambers have also walls above streams,
called shoulders of defence, shoulders below stream, or discharging walls, wing-walls
above and below, and return walls. The thickness of the shoulders of defence should be
less than those of the sides of
the lock; 3 feet 2 inches will
be sufficient, or half the height
of the water; but on account
of the foundations, and above
all, of the beton to be placed
in the centre, it is better to
make them, as well as the
wing-walls above stream, 4 feet
3 inches their length should
be at least equal to the width
of the gates; an additional
1 foot 8 inches will form the
necessary projection for the
recess, into which they will
fall when opened.
The return walls of the wings
are necessary, to prevent the
water from working behind the

Fig. 2840.
body of the lock, but as the back walls are furnished with a lining laid very low, it will 1.
sufficient to give 25 inches of thickness to the return walls; their length must be pro-
portionate to the quality of the soil with relation to its permeability to water or otherwise.
The lining may be continued further than the length of the walls; this portion cannot be too
well protected both before and behind, nor can the wing, the shoulder wall, and the back of
the fall.
The shoulders of discharge must not be regulated by the height of the water, as it seldom
rises to half that of the walls, which should be regulated by the thrust of the earth, and
consequently the thickness may be equal to one-third their total height, if they are
perpendicular on both sides; but it is better to make a retreat or set-off of 12 inches at the
back, level with the water, and to give the lower part an increased thickness: it is not
absolutely necessary to use any beton, but it would be unquestionably advantageous. The
length of the shoulders of discharge should be relative to the height of the water in the
chamber of the lock, the gates down the canal supporting all the weight of water, which is
sent back against the heel-posts, which in their turn rest entirely on the shoulders; con-
sequently their length must depend on the resistance necessary for opposing this thrust.
To ascertain this resistance it must be remembered first, that if instead of gates a wall were
substituted, it must have the same thickness as the longitudinal walls of the chamber of the
locks, that is to say, a third of the total height of the gates, for although the water of the
lower interval resists the thrust of the upper, it must not be taken into account, the
resistance being small with regard to the thrust, not only from the weight of water being
much less, but from the centre of impression being very near the point of support; there is,
therefore, but little action to resist the centre of impression of the water on the chamber,
which is much higher.
Secondly, the two gates may be regarded as a single inflexible sluice, resting against the
heel-posts and the sills.
Thirdly, as the thrust is considerable, it is to be presumed that if the masses constructed
behind the heel-posts of the gates were not sufficiently strong to be in equilibrio with it, a
disjunction would take place in the masonry, the tenacity of which alone is not capable of
very great resistance, particularly if the masonry be lately constructed.
Fourthly, this disjunction will take place in the line of an angle more or less open,
according as the stones are shorter or longer in the direction of the headers; if they were
about as long again as wide, the angle would be one of 50°, and its base would be one-half
smaller; if the lengths were equal to the widths, it might be even less, as the masons
usually bed the stone in the direction of the face of the wall; the filling-in being almost
always of small stones, so that the facing only would forin a resistance.
Fifthly, in order to place the resistance above the equilibrium, the tenacity of the mortar
must not be taken into account, and the base of the angle of rupture must be considered as
equal to half its height. When the weight of water, instead of acting against the gates,
acts against the wall, it has been already shown that the thickness of this wall should be
equal to half the height of the water. Let / be the width between the hanging-posts, h
the height of the water, the cube of this wall will be lh²; the arm of the lever will be
h, thus its energy or momentum lh³. Let the shoulder wal be AHDC; draw A E in
such a manner that E B shall be equal to A B, naming BEa, BA will be equal to 2a;
let a be the length B C sought for. It is evident that the mass A EDC, and that which
CHAP. XXVII.
1541
CANALS AND RIVER LOCKS.

is opposite, must form a resisting power, the energy
of which should be equal to that of the wall, which
has been supposed in the place of the gates. Each
of these masses is composed of a triangular prism,
the base of which is A B E, and of a parallelepiped,
the base of which is BCDE; the cube of the tri-
angular prism is a²h; its arm of lever is a+x,
thus its energy will be a³h+a³hx. The cube of
the parallelepiped is ahr, its arm of lever is x, thus
its energy is ahx2, so that the energy of this re-
sisting mass is a³h+a²hx+ahx²: the other mass
being the same, the total energy will be a³h+
2a²hx+ahx², and as that energy should be equal
to that of the wall, which we have supposed in the
place of the gates, which is h³, we shall have the
equation, a³h +2a² hx+ah x² = {lh³, or x² + 2a x =
lh² 4a2
8 a
3
1=5.2 metres, we shall have x +α=0·65
3
; whence we have x+a=
A
B
D
Ih2
a 2
8 a
3
and as
A
B
a
a 3
ن
G
H
E
D
Fig. 2841.
E
If the thickness of the wall is equal to a third of
its height, or a=}h, we shall have x+h=√1·95h
+27h², or x + 3 h = } h + √ 1·95h+h: if the thick-
ness of the wall be made equal to half of its height,
we should have a=1h, and the equation would become x+h=√1·30h+h², or x + h
= { h + √ 1·30 h +12. By means of these two equations, tables have been calculated
by Gauthey for the length of the shoulders.

ப
Fig. 2842.
CHAMBER WALLS.
Fig. 2843.
It may be remarked, that on giving to the thickness of walls half their height, their
length need only be one-third, in order to have the requisite resistance, although their cube
is one-third greater. Supposing the rupture to take place from A in H, the length
would be less, but not considerably so; allowance must be made for the set-off of 12
inches below the water, which increases the resistance of the wall, and puts it above
the equilibrium. These shoulder walls are generally terminated by expanded wings, with
an angle of 50°, on which it must be observed that, if the shoulders were shorter, the wing-
walls would not be of much service in assisting the former to support the thrust of the
water, because the fracture would take place on the facing of the wing-walls, and there
would only be a small mass of masonry, AB C, to resist the thrust, whilst when the shoulder
pieces A, D are long, the wing-walls may entirely resist the thrust, since the direction of the
rupture A E abuts at their extremity. The length of these walls should be equal to the
radius of the gate, that they may open entirely and with facility, as the lockmen must walk
on them to perform their operations.
The Wing-walls to the lower Gates should have a thickness equal to one-third of their
height, on account of their supporting the earth; steps may be added to them when they
support a talus, giving convenient access from the platform of the lock to the upper part :
these walls generally terminate in the banks of the canal, and perpendicular return walls
may be formed following their direction; but they are not so essential as in the upper
part, because the filtration of the waters from the lower interval is not so dangerous as that
from the upper, or from the chamber of the lock.
Masses are generally constructed behind and below the hanging-posts, to receive the
anchors which retain the collars, and to make them enter deeply into the masonry, in order
that they may have a firm hold; but they are also essential in preventing the water from
insinuating itself at the back of the side walls, and forming a disjunction between the earth
and the masonry, where a void would allow the water from a chamber to percolate, and
ultimately cause the walls to give way: to prevent this alone a great thickness would not
be requisite; but it must be increased on account of the anchors, two being attached to
5 F 3
1542
THEORY AND PRACTICE OF ENGINEERING. Book II

each collar forming an angle, generally in a line with
the pointing sills; but it is better that one should be
pointed up, and the other down the stream, to resist
the thrust of the water on one side when the gates are
closed, and on the other to check the weight of the
gate when in movement.
Counterforts are sometimes introduced in the length
of the chamber to resist the thrust of the water, in
which case the thickness of the side walls might be
diminished, which would be a considerable saving of
masonry; but on account of the filtration, which
cannot be too carefully guarded against, it is better to
make the walls of sufficient thickness, and to dispense
with the counterfarts.
The wall which constitutes the fall in the lock is
usually perpendicular, though a talus may be given
without any inconvenience to the boats: when the
canal is dry, and requires to be filled, the water
flows from the top of this fall on to the platform, and
tends to injure it; to remedy this as much as possible,
the fall of the lock should have a curye of uniform
descent; the direction of the running water then be-
Fig. 2844.
GATE ANCHOR.

1
Fig. 2845.
coming horizontal at the end of its fall,
it has much less action against the plat-
form than when its direction is inclined.
Fig. 2846. SCOURING SLUICE Platform.
When the pointed sills are of stone, it is
advisable to make the fall of the lock
concave on the plan, in order that the
key of the sill may have a sufficient section
to be solidly based. The thickness of the walls which form the fall is usually considerable,
but this is unnecessary; the same as that of the side walls is quite sufficient.,
The Platform. · This construction is of the greatest importance, being that part of the
lock most difficult to keep in repair, and most often requiring it; they were formerly
made of timber, but this is to be avoided as much as possible, timber never uniting well
with masonry, and a film of water almost invariably insinuating itself between the planks and
the masonry, between the heads of the piles, the force of which in relation to its weight is
considerable, making the platform yield, disuniting the framework, and preventing the
easy working of the gates: the shock of water from the upper interval is, however, less
injurious to timber than to stone, and if good stone cannot be procured, to resist this
effect, a platform of

cross planks over that
of rubble might be
formed on pieces of
timber encased in the
walls, but only in that
part where the shock´
takes place, Where
it is possible to obtain
them, large flagstones
are preferable for the
surface of the plat-
form; and in order that
L
K
D
D
D
D
they may be solidly
row
bedded, each
Fig. 2847.
SECTION Through plaTFORM.
D. Piles.
K, Planking.
G, Stone.
H, Sleepers.
L, Heel-post. Y, Planking.
should be worked with dovetails into a course of freestone placed upright, which would
CHAP. XXVII.
1543
CANALS AND RIVER LOCKS.
comprise the whole thickness of the masonry, and be very difficult to displace. When only
large rubble stone can be obtained, the platform should be concave, like an inverted
vault: if the lock is on a solid foundation, it will be only necessary to give it a thickness
of 27 inches to 3 feet 3 inches: when the ground is of a doubtful quality, it is better to
make a wide platform of from 4 feet 3 inches to 5 feet 3 inches in thickness, on which the
walls of the lock and platform are constructed: if the ground have no consistence, piling
must be adopted.
Down stream there should be a guard platform as deep as is practicable, and as this
part of the lock is most subject to injury, it must be made perfectly solid, for which pur-
pose the plan of the masonry of the platform should be concave, tangential to the direction
of the wing-walls, forming a species of arch with them as abutments. The last course
should be cut in a double section, making a hollow arc above; the key-stones will then
be perfectly closed, and, independently of the cramps, this course, which holds together all
those of the platform, will be as solid as it is possible to make it.
The Projection of the pointed Sills. - M. Belidor has given dimensions for this part
of a lock, but they are too small for general purposes. He remarks first, that if the gates
form a right angle, the projection should be equal to half the opening, the greatest
that could naturally be given them, and this angle would be the most advantageous
for shutting the gates against each other, because the thrust of the water acting perpen-
dicularly against them, each gate would push the other at right angles to the length of

<


Fig. 2848.
POINTED 'SILL.
the timber, in which direction they have the greatest strength; but, on the other hand, by
giving them an obtuse angle, there is the advantage of having the leaves narrower, and
consequently stronger. If this angle be extremely obtuse, that is to say, if the gates
merely formed a straight line, they would certainly have the least width that could be
given them, but they would not support themselves, a very essential defect; a mean
should be adopted either between the pointed sill having the greatest projection and
that which has the least, or between the greatest width of gate and the least, or between
the greatest angle the gate forms with the lock and the least. In the first case the pro-
jection of the pointed sill would be a quarter of the width, in the second nearly the third,
and in the third about the fifth. M. Belidor has determined upon the latter, but the
angle is not sufficiently projecting, as it prevents the timbers from resting against each
other, and giving it a greater projection, increases the width of the gates, the solidity of
which may be maintained by additional strength; thus it appears a selection must be
made between the other two methods, and possibly the most judicious would be a mean,
that is to say, to give to the projection of the pointed sill between a third and a quarter
of the width of the lock: either might be adopted without any inconvenience.
Pointed sills are sometimes made of timber, and frequently of stone; the latter is very
5 F 4
1544
Book II.
THEORY AND PRACTICE OF ENGINEERING.
liable to chip, the joints wear away, and allow the water to pass through, which it is exceedingly
difficult to prevent. These inconveniences may be in great measure avoided by placing
in front of the stone sills two pieces of timber, to receive the gates when closed, which can
be much more easily cut than the stone, and consequently the gates, &c., be made to fit
exactly; by bolting the pieces of timber to the stones beneath them, and securing them in
the wall, and filling the joints with moss, all filtration between the timber and the stone may
be effectually stopped.
In locks of rivers whose course is over stones or gravel, there is considerable inconvenience
with regard to the pointed sills, pebbles often lodging between them and the gates, prevent-
ing their close shutting, and

causing a loss of water,
which it is very difficult
entirely to prevent, but
which is in some degree
obviated by a space of a few
inches being left between
the gate and the bottom of
the platform; the sill and
the lower rail might also
be chamfered, so that the
gate in shutting should
drive the pebbles before it.
Sluices to gates are about
25 inches square, and are
raised above the lower rail
of the frame, so that the
water which comes out
makes over the gate down
stream a fall over the plat-
form, which wears away,
and in the course of time
materially injures it. It
would therefore be more
advantageous to make the
water flow out under the
gates, and throughout their
whole width: there would
then be only a film, which
acting horizontally would
be less injurious than when
flowing in a direction in-
clined to the horizon,
The lower rail should
RuiumwWWWE
Fig. 2819.
SLUICES TO LOCK-GATES.
also be placed at 12½ inches above the bottom of the posts; the sluice should only be a
simple plank, equal in length to the entire width of the gates, with its ends attached to two
small posts raised by means of a lever. The
pointed sill, against which this rests, should have
but little height, and the bottom of this sluice-
board should be cut in a bevel form, to throw off
the stones and gravel that might be driven towards
the sill, which it is sufficient to make more elevated
in the centre to receive the chamfered or bevelled
planks forming the sluice.
This construction has another great advantage,
that of producing a current under the gates,
carrying away whatever might stop there, and is
particularly calculated for river gates.
It is generally admitted that the portion of the
platform where the gates move should not be in an
inverted arch, but extremely solid, and so constructed
that the water cannot filtrate through or flow out at
the platform between the discharging shoulders: if
attached to the pointed sill, which must be always
on a level, the form of an inverted arch may be
given to it.
The Gates of Locks are composed of two posts
placed vertically, and several horizontal rails; the


-t
良
​C
О
Fig. 2850.
DOUBLE VALVE FOR TIDE.
0
O
CHAP. XXVII.
1545
CANAL AND RIVER LOCKS.
Z
former, being supported throughout their height, are not subject to much wear, although
they are of larger scantling than the other timbers of the gate, which is necessary.
as they sustain the entire framework: the
horizontal rails resist the weight, and as
that weight is greater where the rails are
placed below the level of the water, it would
seem natural that their dimensions should
vary in proportion to the weight. To
determine these dimensions it must be re-
collected that the thrust of water against
vertical surfaces is equal to the weight of a
prism of water having its surfaces as a base,
and its height half that of the water. It must
next be considered that the rails of the gate
are at least 26 inches apart, and 38 inches
from centre to centre, so that, on account of
the casing of plank in the first instance,
12 inches of height support 26 inches of
water, and in the second 38 inches. The
weight supported by each rail will be found
by multiplying their length, the interval from
one to the other, the height of the water
above the centre of the rail, and the whole
by 62 pounds, the weight of a cube foot of
water; the product of these measures will be
the number of pounds which the rails ought
to support throughout their whole
length.

Timbers from 4 to 5 inches
square would be sufficient for
small gates, and for larger from
8 feet 6 inches to 10 feet 6 inches
of fall, with a width of 17 feet
between the hanging-posts, the
rails would be sufficiently strong
if from 7 to 8 inches square, putting
six rails in the height. They are
generally from 9 to 10 inches at
least, which is double the strength
required; it is true that the gates
are more durable, but the weight
is greater, which is sometimes
injurious to the collar and the
masonry to which it is attached,
requiring more reparations than
lighter gates.
.
Fig. 2851.

The frames or styles of gates
should be at least 5 inches in
thickness more than the rails,
and the joint covered by a fillet,
as well as the edge of the planks,
which are affixed perpendicularly
to the rails, and mortised into the
styles, increasing the strength of the rails and the framework by their greater thickness.
Braces are also introduced between the rails. which aid materially in strengthening
them, and by their inclined position transfer the stress to the hanging-post.
Fig. 2852.
Great gates should always have a line of braces placed diagonally, and making an angle
with the lower rail; all the braces above should have the same effect, and consequently
the same inclination: those below resting on the lower rail tend to depress it, and, even
when properly framed and pinned into the rails, their inclination towards the hanging-post
renders them insufficient to sustain the lower rail; but they inay be made useful by
giving them an inclination in a contrary direction, and uniting them by pins to the rails,
producing the effect of a St. Andrew's cross, without which no framework of carpentry is
perfectly solid.
Instead of inclining the braces below the diagonals on the side of the strutting-post, a bar
of iron is sometimes placed diagonally from the collar to the lower end of the strutting-post,
which is an excellent contrivance; or the planks may be placed diagonally, inclining them
1546
Βουκ ΙΙ
THEORY AND PRACTICE OF ENGINEERING.

from the side of the hang-
ing-post, and crossing them
solidly, especially that of the
diagonal above the hanging-
post, and at the extremity
of the lower cross-piece ; or
instead of a plank, a piece
may be let in in an opposite
direction to the cross-pieces,
which must not be mortised
into, or very little, that
it may not be in any way
weakened; this piece united
carefully to the lower cross-
piece would tie it to the
post, and give more solidity
to the framework; the dia-
gonal position of the planks
gives them more strength
to resist the pressure: there
is a little loss of material,
but, on the other hand,
plank of different kinds may
be used after cutting out
the knotty or defective
portions.
Gates are
by
opened
means of large
timbers fixed
above the posts,
forming a coun-
terpoise to the
gate, and pre-
venting it from
Fig. 2854.
grinding the collars and racking
the framework; for this purpose
the tail of the balance-beam must
be very large: trees are some-
times used with their butt ends
not cut off, to which it is easy to
add any additional weight; this
balance-beam should be united
to the upper rail by a St. An-
drew's cross, which serves also
to maintain the entire frame-
work. The hanging-posts often
allow much water to be lost, in
consequence of being obliged to
give them sufficient play, and
this could scarcely be prevented
if the pivot had not a little
motion, and the collar fitted
exactly; but the weight of water
occasions the gate to unite by
pressing it considerably against
the hanging-post; still as this
is cut circularly, it only leans
against a small portion of its
surface, and the water easily
passes, notwithstanding the great
pressure. To remedy these de-
fects, the posts should be partly
cut in a circular form, and partly
bevelled; the latter leaning along
E
Fig. 2853.
Fig. 2855. TIDE GATE WITH ITS APPARATUS.
I


its whole length upon the rebate made to receive it, which having a corresponding
bevel interrupts any filtration; the circular part should not touch the masonry, but have
CHAP. XXVII.
1547
CANAL AND RIVER LOCKS.
sufficient play without affecting the ease of the motion; it is also advisable to attach
pieces of timber to the hanging-posts, which may be bolted and cramped to the masonry,
and by caulking the joints the water is prevented from passing between them and the

2856.
2857.
Fig. 2858.
2859.
Fig. 2860.
masonry. The strutting-posts also allow a considerable quantity of water to escape,
because, if not very exactly fitted, they only touch on one of their edges, and consequently
it is scarcely possible but that the water should find a passage: to make them touch
throughout their whole length, they should be cut in a circular form, one concave and the
other convex, so that if the gates had even a play of some inches, they would always touch
very nicely; the curvature of the posts should form part of a great circle of from 10 to 13
feet radius.
The gates of locks of navigable canals are generally made in a right line, but in great sea-
locks they are curved: Belidor has demonstrated, that these latter are not more solid than
the former, but this must only be understood when the curved timbers are made out of
straight pieces; for it is undoubted that, if naturally curved, they are much stronger, and
will resist more pressure than straight pieces, especially when resting on their two ex-
tremities. The collars embrace the whole heel-post, which being generally 12 inches in
diameter produces considerable friction, especially when the balance-beam does not act as
a counterpoise: a large bolt may be placed in the axis of the post, and a smaller collar be
substituted to confine it; but this method can only be applied to chamfered posts; round
posts must have a motion in their collar to lean against the hanging-posts, which could
not be effected by an axis; the collars must be attached to iron anchors strongly bedded
into massive masonry. The pivots

often get deranged, the posts, as.
generally made, causing consider.
able play; if these were bevelled,
the pivots might be fixed and
bedded in large stones cramped to
those adjoining, or united with
anchors to the surrounding ma-
sonry. Formerly the pivots were
made of copper, but cast-iron is
equally efficient; they should be
the same size as the ends of the
posts, and terminated at the lower
end in a spherical form. The
other iron work of the gates con-
sists of squares laid on at right
angles, which must be very strong;
it is also well to lay on the rails of
each sluice a band or two of iron
to bolt them securely together.
Lock Gates measuring 8 feet
from the centre of one heel-post
to that of the other are in some
canals on a segment of a circle,
the chord of which is about the

E
Fig. 2861.
크림
​1548
BOOK II
THEORY AND PRACTICE OF ENGINEERING.

sixth of the span, or a little more :
these proportions not only allow
of the gates being smaller, lighter,
and stronger, but also increase
the pressure of the heel-post against
the hollow quoins, which renders
them quite water-tight. Where
canals are narrow, the paddles of
both the upper and lower gates are
usually kept open by an iron pin
inserted between the teeth of a
rack and pinion which raises them :
when the paddle is required to be
shut, the pin is withdrawn, and the
paddle falls by its own weight.
Hollow Quoins, or upright circular
grooves, are formed in the side
walls, at the ends of the timber
sills, serving as the hinge for the
gates; the upright post that turns
within them is called the heel of
the gate, and the other the head.
The former are retained in their
position by a gudgeon or pivot
turning in a cup let into the found-
ation stones for the purpose; some-
times the pivot is fixed, and the
cup revolves upon it.
The upper part of the
post is retained by an
iron ring or strap let
into the side wall, and
made very secure; the
hollow quoins should
be worked with great
attention; they are
usually of stone or
brick, though cast-iron
has been found well
suited for the purpose.
Lock Gates of large
Dimensions are now
usually opened and shut
by machinery, and the
boom or spar attached
to
the head-post en-
tirely dispensed with:
on many canals a rack-
bar of wrought-iron is
connected with the
gates, which are fur-
nished with rollers to
run in a groove fitted
into the sill, and by
working a wheel and
pinion, they
they can
can be
opened and shut at
Fig. 2862.
FRESHWATER LOCK.

Fig. 2863.
pleasure. We ought not to omit mention of several gates formed like boats, upon the
principle of the camel, which rise and fall in deep recesses prepared to receive them as
water is pumped out or admitted into them: such boat-gates are sometimes constructed
with three parallel keels, which fit into as many grooves in the side walls of the lock; they
are maintained in their position by admitting the water, and raised by pumping out their
contents, after which they are floated away; for the stop-gates of docks such a contrivance
is well adapted, but where the navigation is regular, as on a canal, they are not found to
answer, from the time requisite to open and replace them.
The Boom or Spar attached to the head-posts is brought over a windlass, placed on the
lock walls a little above the gate; a rope is made fast to the end of the spar, and by two or
CHAP. XXVII.
1549
CANAL AND RIVER LOCKS.
three turns on the windlass, the gate is either open or shut; a rack bar is occasionally em-
When the gates are very heavy, a roller or truck wheel is
ployed for the same purpose.
placed under the foot of
the head-post, and made
to run in a quadrant
groove, which assists the
motion.
The Angle to be given
to Double Lock Gates has
long occupied the at-
tention of engineers, and
the view now taken of
the subject may be thus
defined: - the pressure of
the water on one of the
gates, which we will call
BC, is in proportion to
its breadth the strength
of the gate being in-
versely as its breadth, the
effect of the pressure
upon it is as the square
of BC. The support
afforded by one gate to
the other, which we will
designate as CA, is as
a perpendicular raised
at the end of a line
BC at E, represented by
AE: the strength of
the gate is therefore as
AE directly and in-
versely as B C²; but A E
is the sine of ABC; the
radius A B-BC is the
secant of the same angle
to half the radius BD.
The strength of the gate
is therefore,
A E 2 sin. A B C

BC2
sec.
2 ABC'
Fig. 2864
Fig. 2865.
PLAN AND ELEVATION OF DOUBLE LOCK-GATES.
2
or, as the cosine is the reciprocal of the secant, as sin. x cos. of A B C, the angle at the base.
The maximum value of this expression is when the tangent of ABC= √, or =0·7071,

Fig. 2866.
ST. KATHERINE'S LOCK-GATES.
I
中
​1550
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
or when the angle at the base is 35° 16' nearly, and the sally of the gate is, or a trifle
more than one-third of the breadth of the lock.
The Gates of large Locks, or those at the entrances of docks, as at St. Katherine's in the
port of London, are framed with whole timbers, the uprights and horizontal rails being
secured to each other by

strong wrought-iron straps.
The planking which covers
the face of the framework
is placed perpendicularly,
and the paddles are worked
by a rack and pinion. The
turning or heel-posts are
held in their position by
iron ties let into the stone-
work.
have
Some lock-gates
their paddles made to open
and shut by the movement
of a lever, the lower end of
which being loaded keeps
it always over the aperture
in the lower part of the
gate when it is required
to be moved, the upper part
or handle of the lever is
pulled back, and the water
forcing its passage through,
keeps it open until its weight
overcomes the power, and it
is balanced back into its
original position.
Fig. 2867.
PLAN OF GATES.


1 2 3 4 $•
Fig. 2868. HEEL-POST.
$ 10 15 30
Fig. 2869. SECTION.


Fig. 2870. ELEVATION.
Fig. 2871. SECTION.
The crank and pinion working in a toothed rack are now generally applied to raise the
paddle.
Screws are sometimes used for this purpose, formed of wood, sliding up and down in
a rebated frame, fixed in the stone mouth of the conduit or paddle-hole; the lateral
pressure of the water, occasions it to adhere closely to the frame, so that it is not only
necessary to make it run with the grain of the wood, but also to have considerable power
to move it; this is occasionally effected by means of a long iron lever, with an eye at one
end that spans the square end of the screw and allows a sufficient force to be applied to
raise the paddle.
There are several applications of the screw, one of which, as used at the gates of Dunkirk, is
very simple, and was for a long time adopted throughout Europe. To overcome the hydro-
static pressure and friction, at the mouth of the paddle-hole was a horizontal circular opening,
within which was inserted an open cylinder of wood or iron ground to fit it, which could be
CHAP. XXVII.
1551
CANAL AND RIVER LOCKS.



Fig. 2872
ם
Fig. 2873.
ต
ㅁ
​U
Fig. 2874.
ם
raised by a lever; the waste water of the canal could then escape over the upper lip of the
cylinder, and afterwards pass out by the paddle-holes, in the same manner as the waste water
of a cistern.
At the Caledonian Canal the head
rails, and well secured by iron straps.
and heel-posts of the gates are connected by cross
The weight of the capstan-head employed to open




wwwwww
回
​2877.

2
2878.
Fig. 2875, DUNKIRK.
Fig. 2876.
Fig. 2879.
Pig. 2880
1552
BOOK JI.
THEORY AND PRACTICE OF ENGINEERING.
them is 2cwt. 1qr. 14lbs. and that of the wheel and pinion, 3 cwt. Oqrs. 26 lbs. ; the bottom
ring is shown in the lower figure, with its footsteps or gudgeon, round which it works.
The capstan works the chains, which

lead to the middle of the head post on
either side, and is admirably well adapted
for its purpose.
The covering plate of the capstan-hole
is made very solid, and prevented from
turning round by six projections on its
outer edge.
The bridge and conical roller which
turn the capstan is also of iron, the
weight of the former being 2 cwt. 6 lbs.
The pivot working in a recess is some-
times so arranged that the cup which
receives it is let into the stone sill,
and prevented from turning by two

Fig. 2881.
283
O
2883.



Fig. 2884 PIVOT.
Fig. 2885. PRofile.
Fig. 2886. PLAN.

dovetail pieces at the sides; to attach the
pivot to the turning-post, four vertical
projections or dovetails are placed at equal
distances round its upper edge, as shown in
the figure.
The collars to the turning-posts are usually
of iron, the interior radius of which is shown
by the dotted line, and its elevation at the
side. The iron rollers under the other post
of the gate, which runs on an iron plate, are
so fixed that they clear themselves in the
grooves cut to receive them; they are usually
from 5 to 6 inches in diameter, and run on
an iron axle fixed into a frame that receives
the end of the gate. Where the wheels run
upon timbers, the sill is formed of several
pieces, altogether 4 inches in width: the
radius of the gates determines their curve,
and they are secured by iron cramps to the
Around the
ground timbers or stone sills.
heel-posts of some gates is a collar, to which
a rod of iron is attached that passes through
the entire width of the lock-walls, where it is
secured in blocks of masonry, or by forming
an eye it may be linked on to another joint,
and made fast to an upright post.
Fig. 2887.



B 8
Fig. 2889.
In attaching the iron-work to lock-gates
we must be cautious not to weaken the
framing, or in any way to obstruct their
motion; for as they are of course very heavy,
and the lower rails nearly in contact with the bottom or floor of the
lock, should they lose their form, the mitre posts by sinking would
impede their opening and shutting: as the gates are sometimes covered
by water and at others left dry, the material of which they are formed
should be carefully selected, and all the metal work applied to them
Fig. 2890
protected from the effects of these alternate changes. To balance the gates and support
them properly is the best method of preventing their tendency to sink and drag; and if
every precaution is not taken to make them move easily and readily, they will be a constant
trouble and expense, which can only be remedied by their total removal.
Chap. XXVII.
1553
CANAL AND RIVER LOCKS.

The capstan used at the basin of Dunkirk will
give some idea of a simple arrangement for the
purpose of hauling the boats from the reservoir
into the stream of the canal: upon a platform of
timber on the quay, an upright post is turned by
handspikes, which coils the rope around it.
The profile of a capstan executed at Cherbourg
shows a nut pierced to receive an iron rod 4 inches
square, set 5 feet in the side of the lock-walls,
where it is held firm by two long arms termi-
nating in the form of a T; this arrangement is the
most simple, and not so likely to decay as the
timber framework. The upper portion of the lock
or fore bay is the usual position for the capstan;
the tail bay of locks sometimes also requires one
where the canal communicates with the ocean.
Iron Lock Gates at the Wet Dock at Montrose.
The frames are of cast-iron, and entirely covered
on both sides with wrought-iron boiler-plate :
where they are placed the entrance is 55 feet wide
in the clear, and the centre of the heel-post is 1 foot
within the face of the wall, the distance between
their centres being 57 feet: the height of the gates
is 22 feet 6 inches; they point 10 feet, and their ribs
have a curvature on the hollow side of 18 inches.
The heel-posts are 21 inches in diameter, and in
form a little more than a semicircle; after casting
they were turned in a lathe: the thickness of the
metal is 1½inch; they each fit into a cast-iron
socket, and work on an iron gudgeon 10
inches in diameter, cast on a sole-plate 4 feet
6 inches long, 21 inches wide, and 2 inches
thick; this is dovetailed and riveted firmly
into the stone, and afterwards so keyed as
to press the heel-posts into the quoins,
which are of Kingoodie stone, polished as
nearly to the circle as possible, and the
stone and iron are in such close contact, that
the water is effectually prevented from pass-
ing throughout any portion of their height.
The mitre posts are 18 inches in breadth,
inch thick: holes are cast in them for
the introduction of the iron bars, of which
there are eleven to each leaf, 2 inches thick,
D
Fig. 2890.

D
Fig. 2891.
CAPSTAN,

Fig. 2892.
5 G
1554
Book II.
THEORY AND PRACTICE OF ENGINEERING.
16 inches broad at the ends, and 18 in the middle; their cross ends are 18 inches in height
and 2 in thickness, with 4 inch screw-bolts to each, which pass through the heel and mitre
posts. The clap sill was cast in two pieces for each leaf; it is 8 inches in depth and 1½ inch
thick; the height of the sill above the platform is 15 inches. The bottom bar is of oak
12 inches thick, 17 inches broad at the ends, and 19 in the middle; this is bedded on felt
to the lowermost cast-iron bar, and securely fixed by 14-inch bolts. The boiler plates
which line both sides of the gates are so arranged that they break joint; for 6 feet in
height their thickness is of an inch, above only, they overlap each other about 21 inches,
and were riveted on while hot, that the rivets might completely fill up the holes. The
collars of the heel-posts are of wrought-iron, 4 inches by 2 inches, keyed through the anchors,
which are of cast-iron, 3½ inches square; they are dovetailed into the quoins, and run with lead.
The roller segments or railways are 10 inches in breadth by 14 inch, 4 inches in thickness;
they are sunk into the stone, and securely bolted, and bedded with felt and white lead.
The rollers are of cast-iron and conical, 18 inches in diameter, and 5 inches in thickness,
with turned steel axles; the roller boxes are of cast-iron, 14 inch thick, moulded to the
bevel of the gates, and fastened by screw-bolts through the flanks of the horizontal bars :
cast-iron covers confine the roller blocks, which slide up and down withinside the boxes by
the action of the top screws; the roller bars are of wrought-iron. 3 inches in diameter,
keyed into the blocks at the bottom, each being steadied by three plummer blocks; each
bar near the top has a coupling, with a square threaded screw, and a brass nut at the top,
working in a cast-iron bracket, which bears the whole weight of the outer end of the gate,
and is fastened by three screw-bolts through the flanges of the horizontal bars. Each
leaf has a sluice, 3 feet by 2, the frames of which are 7 inches broad and 1 inch thick ;
the sluice valves are also 1 inch thick; all the screwed bolts have zinc nuts, to prevent
the iron from rusting: the sluice-rods are 2 inches in diameter, and have a square
threaded screw, and a brass nut at the top; these are worked by a wheel and pinion,
and bevelled gear, with a crank handle, nearly level with the hand-rail.
The gangway is 42 inches in width, and is supported on cast-iron brackets for each leaf;
cast-iron ballusters and a wrought rail is attached to the convex side of the gates, with
movable iron stanchions and chains on the other: in each heel-post is a pump with a
brass chamber and boxes, 24 inches in diameter, with a lead pipe down to the bottom.
The gates are worked by four double-purchase capstans, and gearing with seven 8-inch
chains.
Their weight is as follows,--
Cast-iron work in the gates
Wrought-iron
Brass
Zinc
Cast-iron in segments and other fittings
1
Tons. Cwt.
64
14
22 15
0
5
0
1
19
0
107
0

---------------
These gates were made
by Mr. Stirling of Dun-
dee.
At Woolwich the clear
opening of the dock-
gates is 65 feet, and the
weight of each of the two
iron gates is 150 tons.
Fig. 2893.
1
PRINCE'S DOCK, LIVERPOOL.
T
Fig. 2894.
Inclined Planes and Lifts, mentioned by Mr. Smeaton as early as 1774, are adopted at
many of our canals to raise and lower the boats from one level to another, and by some
CHAP. XXVII.
1555
CANAL AND RIVER LOCKS.
engineers are deemed preferable to locks: in the neighbourhood of Taunton are examples
of both systems, which, by the aid of machinery, enable the boats to pass from one canal
to the other, from a height of above 80 feet. At the summit of the inclined planes is a
steam-engine, of sufficient power to pull up a sledge, which receives the loaded boat; the
chains pass over a cylinder of large diameter, but are frequently out of order, and some-
times break, to the destruction of the vessel to be hauled up.
The Lifts are inore easily worked, as a single attendant can raise or lower a boat from
one level to the other. There are two lock chambers, at the summit level of which,
working in a lofty frame, are three or more large wheels; the outer circumference, or
rather their radii, are exactly over the middle of each lock-chamber; around their peri-
phery chains are suspended, and at the end of each is a fork or iron attached to the two
sides of a sledge or boat, large enough to receive the one freighted, passing either up or
down the canal. When a boat is to be raised, the sledge which receives it is at the bottom,
and the other on a level with the upper water of the canal, which the attendant allows to
run into it, and when the weight is sufficient, it descends in the lock-chamber, and in
falling raises the other which contains the freight; the end of the sledge opens, and it is
then admitted through a pair of gates into the upper channel: when it is required to
descend, the sledge receives the boat, after that at the bottom has been filled with water;
and when it has acquired nearly its balance by letting off a portion, it mounts and the
loaded boat descends.
Means of making the Water enter and leave the Locks. One of the greatest inconveniences,
and causing great injury to locks, arises from the velocity with which the water from the
upper interval rushes into the chamber, or from the chamber into the lower interval;
the great difference in the level of the water and the space requisite for the opening, in order
to avoid loss of time in filling or emptying a lock, causes a considerable rush of water,
which, falling from the upper interval on to the platform nearly perpendicularly, seriously
injures it, as does also another volume of water issuing from the lower gates, although its
effort is nearly horizontal, and consequently less injurious: the weight is, however, more
than double that of the upper part, the rapidity of the water and its consequent effect
greater; false platforms are therefore constructed some distance below the locks, to protect
the edges of the canal in this part, but, notwithstanding every precaution, frequent repara-
tions are required. The gates being inclined towards each other cause the current
through the sluices not to be parallel to the sides of the canal, and to strike the edges
at a certain distance, whence they rebound from side to side, producing considerable
damage. If the two sluices were opened at once with equal velocity, the two currents meeting
with equal force, a mean current would be the result, taking the direction of the lock, but
there is frequently only one lock-keeper to open the sluices, and if there are two, they do
not act together; the current is therefore almost always directed to one side, especially
when the sluices are first opened, at which time the rapidity is the greatest
C
A great inconvenience arising from the rapidity of the water is modified by making it
flow from the bottom of the platform in several smaller streams, which prevent its force from
being more directed to one side than to the other. For this purpose, on the upper side
under the lower pointing sill, and in the thickness of the wall which constitutes the fall of
the lock, an arch is turned, having the top perforated by two holes 2 feet 2 inches in
diameter; in the upper shoulder walls, behind the gates, are also two conical recesses, 3 feet
2 inches square, forming an entrance for the water, the bottoms being paved with a large
stone pierced by a hole 2 feet 2 inches in diameter; these openings communicate by
means of bent tubes worked into the masonry, either of cast-iron or stone; if of the
latter material, semicircular gargoulles are cut,
cramped together, and the joints united with
moss and mastic; or they may be made of several
flat stones properly cramped, forming a square
trough, the joints being stuffed carefully, and the
whole confined within a mass of well-executed
masonry. The openings are closed with conical
plugs of the shape of the holes in the stone,
furnished with a handle acted upon by a lever
on the platform of the lock, and by the action of
which the water passes from the upper interval
into the chamber: to close the pipe the plug is
let fall, and a blow is given to the handle with a
mallet; this method is more expeditious than
racks or screws, and the most efficacious for
closing an opening.
The water passes from the chamber of the lock
into the lower interval by a nearly similar ar-
rangement in the platform behind the gates, and

D
Fig. 2895. 1.OCK CHAMBER.
5 G 2
1556
BOOK II
THEORY AND PRACTICE OF ENGINEERING.


Fig. 2896. SECTION AT A B.
Fig. 2897. SECTION AT CD.
in the middle of the shoulder walls for its issue: perhaps there would be a greater
advantage in making the tube in the side walls of the chamber, above and below, the
recesses of issue being higher than under the wall of fall: there is no fear that the striking
of the water against the lower part of the wall of fall will in any way injure it.
In the pipes through which the water issues it rushes violently, but does not rise very
hign, as its expenditure at the mouth is greater than the quantity which enters at the same
moment, and it may be rendered less rapid by making the tube larger at its exit than at
its entrance. The recesses at the exit should be much larger than those of its entrance,
and should be formed of large stones well cramped together, so as not to be easily
deranged; the platform should also be well cramped, as well as the stones of the arch
under the wall, and the wall at the bottom of this recess should be tied in with that of the
upper guard platform.
Bridges and Towing-paths.— The former may be made either above or below the lock-
gates; by placing them above, on the shoulder walls, the whole lock is free; and if the
boats are loaded high, they meet with no impediment, but in this case, the balance beams
must be dispensed with, but if the collars are well fitted, the gates will manœuvre
sufficiently well; the shoulder walls must also be of an additional length, which increases
the expense.
By placing the bridges over the gates, and on the upper parts when opened,
the expense is diminished; and as the load of the boats is seldom placed at the ends, which
are left free for working, them, this cannot in any way affect their passage; the only
objection is that the lock-keeper has to pass over the roadway to shut or open the lower
gates, which is, however, avoided by making a small vaulted passage behind or under the
abutments of the bridge.
The Towing-path may be made at the side of the lock in two ways, one by commencing
the ramp after the lower shoulder walls, in order to have a great platform at the side of the
lock, and the other by making this ramp along the lock itself. The first method has the
best effect, but is objectionable, as the height of the wall of fall requires the talus to be
very steep, and covered with masonry. The second method is the most convenient ;
the banks of the canal being always at the same height, there is great economy in the
excavation as well as in the masonry; the towing-path in both cases forms a right line, but
the platform of the lock is not so wide in the second as in the first.
Stop-gates and Lets-off. Between Corpach and Loch Lochy, at Sirone, on the
Caledonian Canal, is an outfall of three sluices, which prevents any injury occurring to the
canal banks from acci-
dental breaches; they are
in such a position at the
end of the embankment
that the water in the
canal can be discharged
when required for the
purpose of repair. The
open fan or trough is 80
feet at the widest end;
that of the channel 18 feet,
and the diameter of the
semicircular pool about
82 feet: the three sluices
shown in the elevation are
each in width 4 feet, and
in height 3 feet; their
sills are on a level with
the bottom of the canal,
and the water falls 9 feet
before reaching the bed

Fig. 2898.
1000
PLAN.
LONGITUDINAL SECTION.
SLUICE AT SIRONE.
POOL.
2
ELEVATION.
חחח
CHAF. XXVIII.
1557
DRAINING AND EMBANKING.
of the pool that receives it; the frames and sluice-doors are of iron; the latter are worked
by rack and pinion-wheels within a copper groove.
In forming the channels for these lets-off, it is necessary to guard against the tearing
up of the beds by the rush of water, by conducting it over a watercourse lined with



O
Fig. 2899.
masonry:
Fig. 2900.
Fig. 2901.
a platform of timber is laid on piles over soft ground to receive stone; the
section given to it varies according to the nature of the situation, or quantity of water to be
discharged.
Stop Gates are sometimes placed at the bottom of the canal, lying partially afloat, so that
any motion in the canal water makes them rise and shut against a vertical frame in the
masonry of the abutments on each side: others are so contrived that they can be drawn
across the canal from a recess, and so made to run in a groove, but the most simple
method is the common lock-gate, or the sluices made in the sides of the canal, connected
with drains as first described.
Reservoirs for supplying the Canal with Water must be placed sufficiently low to collect
all the flood waters that may be required, and at the same time high enough to enable all
the water they contain to be drawn into the summit of the canal: the basin should be
made narrower towards its lower extremity, in order to contract the base of the embank-
ment as much as possible, and the bottom and sides must be impervious to water. The
dimensions of the embankment depend upon its height and the materials to be used; in
general, the top is 3 or 4 yards higher than that of the water when the reservoir is full, and
the breadth of the top is then about 5 yards; the outside slopes at the rate of three hori-
zontal to one perpendicular, and the inside two to one. It is not only highly important
for the engineer to take into consideration the best position for the reservoir, but also to
be assured that he has the means of a regular as well as abundant supply of water on all
occasions
Aqueducts are of course requisite where rivers are to be crossed, as are weirs where the
waste water is to be discharged; several of these have already been described in the history
of canals.
CHAP. XXVIII.
DRAINING AND EMBANKING.
WHEN a level is to be drained, or the water carried off from the surface of a swamp or
fenny district, the first point for the engineer to ascertain is the situation of the lowest
outfall, in discovering which nature frequently affords him considerable assistance: the
runs of water in flood times may be noticed, as well as the direction in which the several
aquatic plants lie, these always pointing down the stream, and inclining with the currents, and
when the flood waters are draining off, their motion and progress may be accurately measured.
After the surfaces have been levelled, and the most available outlet decided upon, a main
drain should be set out, from which oblique branches should be cut, pointing in the direc-
tion of the current; into these all the minor cuts and ditches are to be collected, so that,
by intersecting the whole watery waste in an equal and regular manner, it may be effectu-
ally drained.
The fall should be greatest at the most remote part, diminishing as the
quantity of water increases; large and deep rivers run sufficiently fast when the fall is one
foot per mile; for smaller rivers double that is requisite; ditches and ordinary drains re-
quire 8 feet per mile.
When water is drained from the surface, it should be made to pass away gradually, so
that the sides and bottoms of the drains are not injured by friction: it should be in con-
stant motion, that the channel may be kept clear and increase in velocity as it proceeds.
When the surface is a dead level, the fall must be obtained by cutting the drain at the
lower end deep enough to obtain one, which is always preferable to increasing the width;
if there be a large body of water, less fall is needed, for, as above observed, the small drain
requires a fall eight times as great as that of a large river, and the water flows over straight
and smooth beds with greater rapidity than when the channel winds and rocks and
shallows intervene to obstruct it.
5 G 3
1558
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
After the quantity of water has been ascertained by meteorological and other surveys,
the proportions and dimensions of all the drains must be considered, and care must be
taken that their sectional areas and velocities are rightly calculated, so that the main drain
which, like a great artery, is to receive them all, should not be overcharged, or in danger
of overflowing. To facilitate the current, the slope of the sides of the drains or water-
courses should have one and a quarter of base to one of perpendicular height, and their
breadth at the bottom should be equal to two-thirds the depth of the water they con-
tain.
When drains are cut through bogs, they may have a greater slope than when loose sand
or gravel is to be operated upon, the fibres of the plants that constitute the peat or bog
resisting considerably the action of running water.
When rivers which pass through low grounds are to be embanked or confined, that the
floods they bring down may not inundate the adjoining lands, care must be taken to make
the banks sufficiently strong, as the force increasing as the embankment is raised, in conse-
quence of the stream not being able to expand itself in proportion to the increase of water,
the more it is allowed to spread, the less occasion is there for strong barriers. The slope
of such embankments should not be less than twice their height, and three times is neces-
sary when the rivers they confine are affected by the tide, or subject to the force of the sea
wave: the thickness at top should not be less than 5 or 6 feet, and the inside slope
should be one perpendicular to one of base: for sea-banks, where the waves do not rise
higher than 4 feet, the thickness at the top may be 6 feet, the slope on the land side 1½
feet for every 1 foot in height, and on the sea-side 4 feet to 1 foot in height. The slope on
the land side must vary with the height of the waves, and should be increased to two and
a half base to one of perpendicular height: the slope on the water side should be still
more in proportion to the rise of the tide; for every increase of a foot in height the slope
must be greater, so that when the waves mount to 10 feet in height on the water-side, it
should be 10 feet for every foot in height.
When the earth with which the embankments are formed is of a gravelly or loose
nature, it is requisite to carry up in the middle a wall of clay, or some impervious material;
the system of puddling is now generally adopted, by which the percolation of the waters
is prevented: there are several methods of protecting the face of banks towards the sea;
in some parts of Holland, straw is used for this purpose, twisted first into ropes about 2
inches in diameter, and then laid on the face of the bank, and pinned down with hooked
sticks, the whole surface of the dyke being covered with a regular mat of straw; in the
course of time vegetation commences under it, blades of grass make way through the straw
ropes, and the whole becomes a compact mass.
On the banks of the Thames and other large rivers, piling is generally adopted, which
is expensive, maintains the soil very imperfectly, and is far from durable or holding:
rows of piles are driven parallel to the river at 2 or 3 feet apart, raking with the slope of
the bank, one standing in its retreat from the water higher than the other; these are
secured by either working rods or wattling twigs between them, or by spiking horizontal
pieces to them: the spaces between the rows are filled with chalk or stone, and brought as
nearly as possible to a regular slope; this is called breach piling, and is now nearly
abandoned. Kentish rag or other hard stone is infinitely preferable, and less costly, for
maintaining a wall subject to the action of a river on which steam-boats are constantly
passing; this, laid with a gentle slope from a little below the level of the lowest state of
the tide, up to the summit of the wall, and the interstices run with fine gravel, has been
proved to answer admirably well. The sea walls at Dimchurch and elsewhere, which have
a slope of one in thirty or more, appear to have little or no disarrangement throughout
any part of them: fascines and brushwood are used where expense is a matter of consideration,
and when laid in the direction of the force, and pegged down with living willows, succeed
well; but with materials of this kind the slope should be brought to one regular inclined
line, and turfed over as far as possible; where a sea-wall is formed of sand, the interior is
puddled with clay, and along with the sand Spanish broom or twigs of trees are strewed in
layers, which bind the whole together. Within these walls provision must always be made
to let off the land waters, and as the marshes bordering on the Thames and other great
tidal rivers are considerably lower than the level of high water, it is important that the
openings for their discharge should resist the entry of the water when at its highest
state. The simplest form is a clapper or valve hung at the top, and falling over the
opening of the pipe or trunk of discharge, which is kept closed, as the tidal water rises and
presses against it.
Sluices are at other times used, which slide up and down in a frame, and the ordinary
lock-gate either made to revolve on a pivot or to shut like folding-doors against a fixed
frame. The passage through the wall consists of either a mass of masonry or a pipe of
cast-iron; for culverts the latter is generally preferred.
When the passage of the fresh water is over a low beach or sandy flat, it is necessary to
CHAP. XXVIII.
1559
DRAINING AND EMBANKING.

Fig. 2902.
HARTLEPOOL.

protect its course by building jetties, or so
effectually to cover it that no obstructions can
occur.
After the main drain in a level has been cut,
the rivers which run into it are embanked, and
catch-water drains are formed to collect the
water flowing from a higher level; the several
channels must be kept open by dredging, scour-
ing, and cutting down the aquatic plants and
weeds. Attention must then be turned to the
subsoil draining, that the surface may be rendered
valuable for the purposes of agriculture.
l'ig. 2903.
HARTLEPOOL.
Subsoil Draining. Geology has assisted this
operation very materially by rendering us ac-
quainted with the quality and nature, as well as
succession of the soils beneath the surface to
be drained. The soils which are impervious
are usually the most heavy, and the porous are
those of a lighter quality. Clays, when they
receive water, will only part with it by evapo-
ration when left in a natural state, and there-
fore to make such a surface fit for agriculture,
or to render it dry for any useful purpose, or to
improve the atmosphere above it, requires con-
siderable ingenuity and a great expenditure. Such a soil is fertile when drained, and
it is only necessary to prevent the waters from the neighbouring lands overspreading
it, or to contrive means to carry off what falls in rain, and is not required to nourish
the crops it is not rendered wet by the action of the underground springs, and may
be effectually drained by penetrating through the clay, and letting off the water into
the under-stratum where this is of a porous quality, as chalk or such material. The surface
of clay is often cut into drains, which are taken in a diagonal direction across the piece of
land operated upon; these are made at about 15 or 20 feet apart, and usually about 2 or
3 feet in depth; they are often filled in with loose stones, and again covered up. Drain
tiles are admirably adapted for grass land, as well as that under the plough; they are
about 13 or 14 inches in length, 4 inches in width at bottom, and a little more in height;
they have an arched channel for the passage of the water, 3 inches in width at bottom, and
4 inches in depth: the drains are cut just large enough for their insertion, and not deeper
than is required to prevent their being disturbed in the ordinary process of cultivating the
soil above. When the tiles are put into the channels, and laid with a proper current to
discharge into the drain prepared at their lower extremity, some straw is laid over them to
prevent any loose earth from falling in or choking them up: in general, 1000 tiles are put
to an acre, and the cost of draining that quantity of land varies from 37. to 4l.
Another common practice is for the drainer to take out a spit of clay with a wedge-
formed spade or too!, and then to deepen it by another of the same form but smaller, after
which he uses a scoop to remove any crumbs that may have fallen down: the drain when
finished presents the section of a wedge 30 inches deep, 1 foot wide at top, and only 2 or
3 inches at bottom, and indeed the narrower it is the stronger it is. It is then filled in with
brushwood to the height of 10 inches, and covered with long wheat-straw twisted into
bands, which are carefully laid in by hand; after this the earth is thrown on, and the
5 G 4
1560
Book 11.
THEORY AND PRACTICE OF ENGINEERING.
first portions trod gently down, the remainder spread and levelled over it. Where there
is an impervious bottom, the drains are often cut 4 feet or more in depth; they are then
made proportionately wider, and filled up within 12 or 14 inches of the surface; where
the depth does not exceed 5 feet, a width of 2 feet at top is amply sufficient; the width
should, however, be increased 4 inches for every foot in depth, and that at the bottom be
20 inches. A great variety of tiles are now used for the purpose of draining; some are
cylindrical, the upper half being perforated with small holes to allow the water to pass
into the channel formed by laying one-half of the pipe over the other; they are very
durable and effective when properly laid down.
When the land abounds with springs, or is subject to the oozing out of subterraneous
waters, the draining must be effected by a different method. Springs have their origin from
the accumulation of the rain water, which, falling upon the earth, after passing through
soils of a porous nature, descends to a bed of clay, close gravel, or some other water-bearing
stratum, upon which it glides or runs down the sloping bed, until it crops out at the surface
of the ground, generally in some valley, where it forms a run of water. In the chalk dis-
tricts, the water rises to the slant line of its drainage, or rather stands at the level at which
it can drain off; and where a considerable detritus has been deposited upon its bed, the
natural oozing out of the water from these springs is prevented, and being penned back, they
are forced to find an opening elsewhere.
Wherever a ditch is cut on the slope of a hill at a level, to tap the strata in which the
water stands, there it will flow out and effectually drain the soil above it, as has been proved
by constant experience; in sinking a shaft or tunnel in the chalk districts, below the
ordinary standing of water in the neighbouring wells, the whole has been drained dry for
many miles therefore, to drain a valley which suffers from floods or inundations produced
from such causes, it is only necessary to have a catch-water drain made at the foot of the
hills which skirts it, and cut sufficiently deep to receive the water which will pour into it.
Descending waters are readily got rid of, by collecting them into a stream before
they injuriously overspread the plains below; there are many instances of a valuable level
being ruined by the filling of the ditches with water, producing weeds and vegetable matter,
which in decaying give out gases of the worst kind, in consequence of the natural drain or
river being raised or penned up, which elevates the level of the springs by forcing them
backwards; whenever this occurs a new catch-water drain should be sunk, and a free dis-
charge for all the waters which descend from the high ground kept open. If this drain
passes through sand or a porous soil, it must be puddled at the sides and bottom.
It is not uncommon in many parts of Kent, where the chalk is capped with a stiff clay
and flints, to drain the surface by sinking wells through the clay, and filling them up with
stones the water which falls upon the surface is directed
into these artificial cavities, and led off to the chalk, where it
sinks to the level of the water-bearing stratum, or to the
height of its slant line, which finds an outlet or natural dis-
charge at the toe of the hills, or in some fissures of the chalk.
This clay is supposed to be the alumina held by the chalk
before its decomposition, or rather before it was dissolved,
and carried away by the waters which acted upon it· that a
great height has been reduced from both the North and South
Downs is evident from the quantity of flints which remain on
the surface, and the loftiest parts of these ranges, which are
most exposed to the action of the weather, abound with
them. Wherever pits can be sunk to arrive at the chalk or
the limestone, there is no difficulty in obtaining a free and
perfect drainage.
When a morass or a peaty ground is to be drained, the
several strata which it reposes upon should be examined by
boring, and if, as is often the case, a layer of clay intervenes
between the limestone and the mossy surface which holds the
water, by tapping the clay in various places well selected, the
whole of the water will be discharged and sink away.
Tunnelling under rivers presents very considerable difficulty,
as has been experienced in that under the Thames, and it
could not have been effected, but for the shield contrived by
Mr. Brunel, which consisted of twelve frames, each having
three cells that could be opened and shut at pleasure.
Each of the twelve frames, one of which is shown in the
cut, had boards 3 feet in length and 4 inches in thickness,
called polling-boards; these were supported and maintained
in their position by screws, to the number of fifty-four in
each frame. When it was required to take out the earth,
one of these boards only was removed at a time by the

Fig. 2904.
CHAP. XXIX. ON THE CONSTRUCTION OF MACHINERY.
1561
workmen employed; by this means a firm buttress was formed, which resisted the inward
pressure of the earth, as progress was made in the tunnel: for a further description of the
application of this shield, we must refer to p. 522. The brickwork which lined the bottom,
sides, and arches of the tunnel, were completed up to the shield before it was pushed
farther along.
Wherever large sewers or drains are required to be made under the beds of navigable
rivers, no better nor safer method can be adopted than that of the shield; the workmen are
protected by it, and a great irruption cannot take place suddenly, nor without giving ample
warning to allow them to escape.
CHAP. XXIX.
ON THE CONSTRUCTION OF MACHINERY.

WHEN machines were formed of wood, the art of the millwright
was required to put together the various movements, and other
portions of his work, in such a manner that they resisted every strain
to which they were subjected: since the universal introduction of
iron for this purpose, he is now only required to prepare moulds for
casting them; still there are occasions when it is necessary for the
civil engineer to have his machinery constructed as formerly, and it
is then important that the work be properly performed.
It is necessary that the ram of a pile-engine should be suspended



H
0
Fig. 2905. Ram.
Fig. 2906. Ram.
Fig. 2907. RAM
Fig. 2908. Screw.
so that it falls perpendicularly in the groove prepared to direct its motion, and this has
been admirably and simply effected by attaching to the back of the ram two frames in the
form of a H, the arms of which serve as a guide when rising or falling. Our limits will


О
Fig. 2909,
Fig. 2910.
1562
Book Il.
THEORY AND PRACTICE OF ENGINEERING.
not permit us to detail the construction of many portions of those machines, the principles
of which have been already described: we can only allude to the movements of a few of
those most generally in use.
In forming a screw the hardest wood should be selected, as that of the box tree, or
any other of equal strength, which is not likely to warp or get out of form. As the
power of the screw depends upon the correctness with which the thread is turned, the
primitive cylinder, which the inclined plane is to surround, should be worked very accu-
rately before it is offered to the lathe or cutting machine.
When the screw is mounted to serve the purposes of a press, the standards which confine
its action must be braced and firmly held together; the braces at the sides may be made to
serve as supports and ties.

Where two screws are required
to lift the same plane, great at-
tention must be paid to the cutting
of the spiral threads around them,
or they will work unequally, and
Te
Fig. 2911.
时
​H

throw greater stress upon one thread than the other.
Fig. 2912.
The framework upon which the spindles of wheels are mounted, as well as the axles,
should be wrought with the greatest nicety, and the staves of the trundles and the cogs of
the wheels made either of hornbeam wood or lignum vitæ : in mounting a trundle Per-
ronet used two triangularly framed stands, into the heads of the upright posts of which
the gudgeons worked.

I
Fig. 2914.
Fig. 2913.
When a beam is to be lifted perpendicularly, the wipers
require to be fixed firmly, otherwise the cams on the
turning wheels, which produce its motion, and occasion it
to rise and fall successively, will not act with that precision
which is required for stamping or pounding, to which this
motion is particularly applicable. After passing the wipers
through a mortise made to receive them, they require
firmly wedging from the opposite side.
Tread Wheels are of very simple construction, and
serviceable in moving pumps or other machines; they
have a long iron shaft, with four or six wheels about 40
inches in diameter, 24 spurs or starts, like those of an un-
dershot water-wheel, being fixed upon it; these spurs are
8 or 9 inches in length, with footboards attached by
strong screws: the useful effect of a tread mill has been
calculated upon the supposition that a man can lift his own
weight 12,000 feet high in a day; supposing him to weigh
150 pounds, the total weight lifted would be equal to
1,800,000 pounds raised a foot in the course of a day's
work of 8 hours; walking wheels are variously made, and
there are several with footboards attached to the levers
that move the spindle round.
3
Fig. 2915.

Fig. 2016. WIPERS-
CHAP. XXIX. ON THE CONSTRUCTION OF MACHINERY.
1563

The cams are set out at the required distances on the
turning wheel or cylinder, and are repeated as often as
motion is considered necessary; the three stampers shown
are raised alternately, by attending to the several positions
in which the cams are placed.
M. Camus, to whose valuable treatise on the Teeth of
Wheels we have so frequently referred, considered the best
form that could be given was that which placed them
always in such positions that they equally favoured the
action of each other; the smaller wheels of a machine are
sometimes made out of a single piece of hard wood, with
the teeth cut out of the solid.
A crown wheel and
pinion,
construc-
ted of timber, must
be so framed, that
every portion of its
rim or periphery is
strongly held and
braced together:
this cannot be more
effectually done
than by crossing
two timbers at right
angles; through the
opening in the mid-
dle, the shaft may
be secured to the
frame, and when
it revolves motion
is conveyed to the
machinery in
easy and steady
manner.
in an
Additional strength
may be given to the
arms on the under
side of the large, and
upper side of the
small wheels; the cogs
are formed of horn-
beam, mortised and
tenoned into the pe-
riphery of both
wheels, the propor-
•
tion of which has already been described.
A A A A A
Fig. 2918.
Fig. 2919.
To secure the wheel on the shaft which turns is easily effected by
wedging all these operations require attention to the strength of the
several materials employed: they should be well seasoned, and not likely
to shrink from their original dimensions.
Where a spur-wheel is to work in a crown-
wheel below, its spindle may pass into the
same timber that the gudgeon of the upright
shaft works in, if it be securely framed and
braced to resist any lateral movement. The
rims of these wheels may be further strength-
ened by inner circles made fast to the outer,
and the upright shaft left
square where it
it passes
through the frame of the
wheel.
Wheels which engage
each other should be braced
in proportion to the stress
and action they are sub-
jected to: where the dia-
Fig. 2920.
D
Fig. 2917.

வ
•


1564
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
meters are small, the arms at right angles may be sufficient; but in those of greater dia-
meter, the arms will often require diagonal braces from one to the other, and these again
strutted to the outer rim; the more solid the framing, the more exact the movement;
great attention is required to effect this
In the construction of a chapelet it is necessary to consider the power that is to be
employed; it has been shown that at the building of the bridge of Orleans one put in
motion by twelve horses made 140 turns in an hour: the number of cogs upon the
great wheel was 115, and of trundles upon the lantern 12: the height as well as width


O
ს
·
•
•
•
n
O
Fig. 2921.
o


A
O
•

ה

•
O
Fig. 2922.
Fig. 2923. Chapelet.
of the buckets was 6 inches. As the chain passes over the staves of the lantern, it is raised
with its load by the turning of the latter: the outer frame is generally made of wood, the
sides braced together at convenient distances, and trapped with iron.
The Archimedean screw is surrounded by a cylinder made generally of wood; the spindle,
round which the screw traverses, may either be made of the same material or of iron this
ancient and very useful power has already been described.
:

Fig. 2974.
ARCHIMEdean scrEW.
Pumps are often made of timber, when there is a difficulty of obtaining those of metal :
but the trough or pipe in which the plunger works can rarely be made sufficiently water-
CHAP. XXIX. ON THE CONSTRUCTION OF MACHINERY.
1565
and air-tight to prove very effective.
In pumping

water out of foundations or trenches, the bottom of
the pipe should be pierced with holes, to prevent the
mud and soil from entering: the buckets and plungers
may be formed out of elm or beech, and the handle
connected by a wooden rod, the strength of which is
considerable, particularly when made of deal.
The Construction of a Vessel belongs to the ship-
builder rather than the civil engineer, although it is of
the utmost importance that the latter should be ac-
quainted with the principles upon which it is set
out: plans, elevations, and sections through every part
are required, before any of the timbers can be rightly
proportioned. The safety of a ship requires that the
timbers should uniformly cross the keel, and that the
frame be filled up so as to form one compact body
of timber; to trace the changes which have been
made in the sections of ships by different nations,
and at different periods, is of the highest value, and
still occupies great attention.
The Displacement of a Vessel, or the cubical contents
of that part which is below the water's surface, may
be calculated from the principle that a body speci-
fically lighter than water
will sink until it has dis-
placed a portion of the fluid
equal in weight to the
entire body itself: in de-
signing a boat or vessel,
the frst object is to form
as accurate an estimate
of this weight as possi-
ble.
The universal joint may
be formed out of any hard
wood, and the action of
the concave upon the con-
vex ball guided in any
direction required; the
strength of the globe is
sufficient in itself to resist
fracture; but the casing
which works upon it re-
quires to be braced or
strengthened by a metal
rim, into which the mov-
able arm may be let.
ANE ZAMAN WAZI VINJE
Fig. 2925. PUMPS.
Fig. 2926. SECTION OF A VESSEL.
II
Fig. 2929.
0

•


Fig. 2927. UNIVERSAL JOINT.
Fig. 2929. ROpe ladder.
Rope ladders are frequently in request by the mechanic, and are easily made by passing
the staves through a slip-knot, and fastening them in their position.
1566
THEORY AND PRACTICE OF ENGINEERING. Book II.
CHAP. XXX.
RAILROADS.
THE steam-engine being the means by which carriages are propelled on a railway, it would
be natural that the first men consulted upon the best method of laying out a line should
be those most acquainted with the uses of the new motive power; but time and experience
have extended this knowledge, and created many practical civil engineers, whose added
stores of information, skill, and ingenuity, will, it may be fairly hoped, very considerably
lessen the expenditure for all future railroads. The first operation in these new national
works is an accurate survey of the country to be passed through, which should extend to a
considerable distance on each side of the intended line: there should be scope enough left
either way for the engineer to benefit from the levels of the land he is desirous of crossing.
The land-surveying and the levelling should progress together, one party mapping while
the other lays down the rise and fall; the cuttings and embankments must next be calculated
and made to balance as nearly as possible, care being taken that sufficient land is mapped
to extend the base of the embankments, and, where deep cuttings are necessary, that a
width at top is provided, to allow for the talus or slope, as well as for any casual
slips or shrinking to which the various earths may be subject. Should the embankments
not require all the earth from the cuttings, proper situations must be secured for the deposit
of the surplus; and, if the cuttings do not afford sufficient for the embankments, the earth
must be obtained at the nearest and most convenient spot: these and various other points
dependent on locality must be well considered at the time of laying down the map, that,
when the period of execution arrives, there may be no obstacle to the pre-arranged plans.
Before the engineer can finally determine the width of the respective cuttings, it will be
necessary to examine into the nature of the various earths through which his operations
are to be carried, as upon this must depend the quantity to be removed, and consequently
the widths to be set out. When a cutting is made through clay, the slope in some in-
stances is only required to be 1 to 1; but if in a constantly wet state, it will slip, even
if 3 to 1 is given; soapy shale will slide when at a much greater slope than 5 to 1:
chalk will stand nearly vertical, and the more it approaches that position, the less it will
be affected by the weather. Sand has been found to stand with a slope of 1 to 1:
on the Newcastle and Carlisle Railway, where the depth of cutting is upwards of
100 feet, it stood well with the talus of 1 to 1. Gravel and dry soils stand well
with a slope of 1½ horizontal to 1 perpendicular, when the height does not exceed 40
feet; but in wet seasons the greatest caution is required to make most of the soils stand,
whatever slope be given them: 81 feet in width requires for each mile in length an acre of
ground; 16 feet 6 inches, or a rod in width, requires two acres, there being 320 rods to a
lineal mile, and 160 square rods to an acre. Thus there is no difficulty in ascertaining the
quantity contained in the cutting for a general estimate; when the slope and the depths
have been determined on, the mean width multiplied by the depth will give the cubical
content. Where the embankments should cease, and the construction of a viaduct begin,
or where the open cutting should give way to the tunnel, are points of great importance
for the decision of the engineer.
As it is usual to estimate all earth-works by the cubic yard, it is advisable, wherever
practicable, to take all the dimensions in yards, and their decimal parts; and, by calculating
4840 square yards as making an acre, and 1760 yards in length a mile, there would be a
great facility afforded in arriving at the desired quantity. Numerous tables are, however,
constructed, by which the quantities are ascertained, without the trouble of calculation.
must be remembered that clay, as well as some other earths, will require a larger quantity
of cutting to form the embankments than they cube to; whilst with some common earths
there is an increase of at least ten per cent. in the quantity, when first used, and before it
has time to become consolidated.
It
When the railroad is made, it must be entirely free from water: drains must be cut
on each side, and conducted to watercourses constructed so as readily to receive all that
passes by them in soils like that of the Chatmoss, varying in depth from 10 to 34 feet,
and resting on a substratum of clay and sand, considerable difficulty is experienced in
forming the embankments as well as the cutting In that instance the operations of the
engineer extended over a length of 4 miles; drains were cut at every 5 yards, and as soon
as the water had passed off, and the moss become dry, it was removed, and the embank-
ments formed of it, four times as much being required in the dry state to fill up the same
CHAP. XXX.
1567
RAILROADS.
quantity of yards as when wet; other drains were then cut on each side the embankments,
2 feet deep, and when the water had drained out of the moss under the intended roadway,
double layers of hurdles, covered with heath, were laid upon it, and on these a stratum of
ballast. The drains were entirely effectual; 670,000 cubic yards of moss in its natural
state when dry were required to make 277,000 cubic yards of embankments, so great
is its capacity for water.
When the fall is 10 feet in a mile, the gradient is 1 in 528; when 20 feet, 1 in 264 feet; and
when 30 feet per mile, a third, or 1 in 176; when the gradients are established, allowance can
be made in the calculations of quantities, and the average depths and heights determined on.
The plans and sections of the intended line being prepared, the quantities of earthwork
may be accurately ascertained, and contracts made for the cuttings and embankments, and
the centre of the line being marked out, the operations of cutting may immediately
commence. The first contractor usually provides engines, rails, waggons, and whatever
is required for the transport of the earth, and sublets the work to gangs of navigators.
Horse-power has been abandoned, the locomotive or stationary engine, drawing the waggons
at the rate of 8 or 10 miles an hour when loaded, being much more convenient. Much
judgment is required in establishing the situations for the waggons to tip or shoot their
load: where the depth of cutting is considerable, inclined lines may be formed, along
which very little labour is required to move the carriages. One man will throw into a
waggon in the course of a day 15 cube yards of stiff clay, or 25 of sand, and, according to
the nature of the ground, from 60 to 90 men can throw up and load 1000 cubic yards in
that time.
Ashley Cutting, on the Great Western Railway, about 5 miles on the London side of
Bath, at the base of Kingsdown Hill, is 23 feet above the level of Box Brook, which runs in
one of the two valleys separating the parallel ridge of the upper oolite that caps the hills in
this district, and upwards of 800 feet above the level of the sea. The top of Kingsdown
Hill, behind the cutting, is above Box Hill, where the tunnel passes, and the land slopes
down to the railway at the rate of 1 in 11, exposing an inclined plane of at least 4000 feet in
length to the action of the atmosphere. The cutting was made through a drift from the
high lands, and not through the original stratification: and after its completion, the upper
portion of this deposit slipped, producing considerable inconvenience: this arose from its
tendency to absorb water, from which it had no means of clearing itself, the lower portion
of the bed, on which it rested and abutted, being removed. To remedy this the whole was
cut to a slope of 4 to 1, and shafts were sunk until they pierced the water-bearing strata;
these were connected with several headings, driven on the surface of the marl, parallel to the
railway, which most effectually decreased the quantity of water; but 1500 yards of shafts
and headings were driven at a cost of 30s per yard run before this was entirely accom-
plished, or the drift could be made to stand at a slope of 2 to 1.
Equalising the Excavations and Embankments, so that the parts excavated will furnish earth
sufficient to fill up the valleys or low ground to be crossed: to effect this we must resort
to a system of successive approximations, by assuming different slopes, and shifting the line
to one side or the other till we arrive at the proper result. The solid contents of both
excavations and embankments must be calculated, bearing in mind that the earth in its
natural state occupies less than when broken up, and that an artificial embankment settles
considerably: this allowance must depend upon the nature of the soils. The axis of the
road is then set out by piquets, and its width with stakes, on which is marked either the
height to be filled in, or the cutting to be made.
The removal of the earth by the most economical method is the next consideration, and
then the inclination to be given to the side slopes: when the earth is a mixture of clay and
sand, 2 of base to 1 of perpendicular, and where the latter material predominates, a greater
slope is necessary: in solid rock the sides may be left nearly or quite perpendicular; but
it must also be remembered that slaty rocks disintegrate very rapidly when exposed to the
action of the frost, and it is better to cut them into steps and cover their surfaces with
vegetable mould, on which grass seeds should be sown.
The stratified rocks, which dip towards the horizon, being liable to slip when cut
through, require great attention; where clay and sand alternate, they must be effectually
drained, all the surface water collected, and the springs working in them conducted away,
for which purpose deep trenches must be cut, and filled in with gravel or loose stones with
an easy fall.
Drainage of the subsoil is also necessary, and this is often performed by making a
longitudinal drain under the roadway, or by side-cuttings in the manner of catch-water
drains on the slopes, running them obliquely along the surface, and then allowing them
to empty into the cross drains or natural watercourses.
In marshy soils it is often requisite to make an entirely new artificial bed to receive the
roadway, and this is best done by taking out the spongy elastic earth, and substituting a
harder material.
Gradients, or the proportionate ascent or descent of the several planes constructed on the
1568
BOOK II
THEORY AND PRACTICE OF ENGINEERING.
railway, demand from the civil engineer very considerable attention. In the Treatise on
Locomotive Engines by Chevalier F. M. G. De Pambour, the author, after stating that
inclined planes are a great obstacle to the motion on railways, supposes if a train of 100
tons be drawn by an engine on a level, the friction of the carriages will produce a resistance
of 8 lbs. per ton, and consequently the power required of the engine will be 800 lbs. He
then supposes the same train ascending an inclined plane at ; on that plane, besides the
resistance owing to the friction of the waggons, a fresh resistance occurs, which is the gravity
of the total mass in motion on the plane that gravity is the force by virtue of which the
train would roll back if it were not retained, and is equal to the weight of the mass, divided
by the number indicating the inclination of the plane. If therefore, in this case, the load of
100 tons be drawn by an engine weighing ten tons, the total mass placed on the inclined
plane will be 110 tons, or 246-400 pounds; thus its gravity on the inclined plane at
246-400
100
100
will
be
lbs. 2.464 lbs. The surplus of traction required of the engine on account of
that circumstance is therefore 2.464 lbs.; and as on a level one ton load is represented by
eight pounds traction, 2·464 lbs. represents the resistance that would be offered by a load
of 308 tons on a level. The engine which before drew 100 tons must now draw 408 tons,
or must exert the same effort as if it drew 408 tons on a level: upon this data the author
above quoted has calculated the resistance on inclined planes; some writers have given the
angle of repose as 1 in 280; and the Irish Railway Commissioners have stated that at the
angle of 1 in 140 a velocity is acquired which has a useful practical effect.
On the London and Birmingham line of railway, where the plane for a considerable
length was 1 in 75, the trains attained a velocity of thirty miles an hour. A gradient of
1 foot per mile is equal to a rise of 1 in 5280; of 10 feet, to 1 in 528: of 20 feet, to 1 in
264, and tables are calculated showing the inclination up to 60 feet, or 1 in 88; and other
tables have been drawn up, to show the lengths of equivalent horizontal lines to gradients,
from 1 in 90 to 1 in 1500

Gradient.
Ascending. Descending.
Mean.
Gradient. Ascending. Descending.
Mean.
1 in 90 2.66
1.00
1.83
1 in 200
1.75
.83
1.29
95
2.58
1.00
1.79
250
1.60
⚫83
1.21
100
2.50
1.00
1.75
300
1.50
⚫83
1.16
110
2.36
1.00
1.68
350
1.43
⚫83
1.13
120
2.25
1.00
1.62
400
1.37
.83
1.10
130
2.15
1.00
1.57
500
1.30
.83
1.06
140
2.07
1.00
1.53
750
1.20
.83
1.01
160
1.94
⚫83
1.43
1000
1.15
.85
1.00
180
1.83
⚫83
1.33
1500
1.10
•90
1.00
To calculate the resistance of the trains on an inclined plane, we have in the work before
alluded to a very useful table for engines weighing from 8 to 12 tons, with the load they
draw. Where the engine weighs 8 tons, the following table may apply.
Equivalent Load on a Level, the inclination of the Plane being

· Load in Tons.
300
400
300
200
150
100
25
44
48
56
71
87
117
50
83
91
105
191
158
212
75
122
133
153
191
230
307
100
161
176
201
251
302
402
125
200
218
249
311
373
497
150
239
261
298
371
445
592
By such a table we can observe the resistance of the trains on inclined planes.
Width between the Rails. On the first establishment of railways, the clear width between
the rails was fixed by parliament at 4 feet 8 inches, which is that of the Liverpool and
Manchester line; but since the year 1836 this has been optional with the engineer, and
the Great Western is 7 feet between the rails. The width between the two lines of railway
is ordinarily the same as that between the rails; but upon the London and Birmingham
line it is 6 feet, though, for all practical purposes. 4 feet 8 inches has been found sufficient.
A proper width outside the rails is, however, exceedingly important, in order to obtain the
requisite stability or firmness in the embankments for fixing the blocks and rails.
Whether the broad or narrow gauge will eventually prevail, it is difficult to decide; but
certainly the latter is the most economical in construction, and, if equally answering the
CHAP XXX.
1569
RAILROADS
purpose with the other, it should on that account be preferred. When the distance between
the rails is increased, every additional inch in width adds to the expense, not only for the
land on which it is set out, but also from requiring stouter sleepers and rails of a greater
weight; the length of the axles of both the locomotives and the carriages they draw must
also be prolonged, and consequently rendered more likely to fracture, if their strength be
not greatly increased; the draught is more immediate from the middle of the narrow than
from that of the broad gauge.
Foundation for the Stone Blocks and Sleepers. The surface of the way transversely
should be convex, with a rise of about 3 or 4 inches in the middle, to throw the water into
the lateral drains, and previously to placing or bedding the blocks, a stratum of broken
stones should be spread over the whole to the depth of a foot, through which the water can
penetrate into the brick drains previously constructed beneath it: another stratum of finer
stone with sand is laid, and after being well rammed is levelled to form a firm foundation.
The blocks are of a hard and compact stone, often of granite; they are drilled for the
reception of the trenails and made level to receive the chairs; but if great care is not taken
in setting them they will sink and require to be reset: they are now usually bedded by
means of a machine containing a lever, about 20 feet in length, with its fulcrum at a suffi-
cient distance from the end to raise the block intended to be set about a foot high from
the ground; and while one man is manœuvring it, another, as often as it is lifted up,
throws under the block a layer of sand or fine gravel, until it is not only level transversely,
but ranges with the others along the line, and when once placed it should not again be
moved. Where the ground is not very firm, wooden sleepers are laid across the way, from
one side to the other, made of larch or other durable timber, and of a scantling not less than
12 inches by 6: they were at first cut out of round timbers or Scotch fir, 12 or 13 inches in
diameter, and after one cut was made in them, they were laid with their flat side downwards
across the road, at a distance of 3 feet from centre to centre. Transverse with longitudinal
sleepers over them, extending the whole length under the rails, make the most stable
arrangement, and are now generally adopted: it is highly important to prevent any sinking
of the rails after they are once set, and it is a false economy that dispenses with the timber
substructions, which form an extended base to receive the weight passing over the rails.
When, however, stone blocks are used in preference to timber sleepers, they should be
made perfectly level before the chairs are set upon them: two holes, about 2 inches in
diameter, are then drilled into them, for the purpose of inserting plugs of heart of oak
which, when firmly driven in, are bored with an
auger, to receive the iron pins which fasten down
the chairs. In many instances the former have
been dispensed with, and a piece of tarred felt
inserted between the bottom of the chair and the
top of the block: oak pins engine-turned have
also been used, and if well driven, they are found
to render the chair tight and firm; if tarred over
after their heads are cut off level, they will last
many years in a sound state.

Fig. 2930.
Triangular sleepers, laid longitudinally upon
others which cross the railway, are in some instances
preferred: as in the fixing the iron rails chairs can be dispensed with, and greater strength
can be obtained from the same quantity of timber; for there is no better form to resist
compression than a triangle placed upon a broad base.
In the construction of the Great Western Railway stone blocks were dispensed with,
longitudinal rails of American pine being substituted for them; they were 14 inches in
breadth, from 6 to 7 inches in thickness, and laid on alternate double and single transverse
ties.
The double ties were each 6 inches in breadth and 7 inches in depth; the single
were 6 inches in breadth and 9 inches in depth: two beech piles, 10 inches in diameter,
were driven between each double pair, and two others by the side of each single tie, the
rows being about 8 feet 6 inches apart. In cuttings the piles were driven 8 or 10 feet.
but on the embankments, or where the earth was made, they were usually driven through
into the subsoil.
The heads of the piles were secured to the double and single rows of transverse cross
ties or sleepers by iron bolts with screws and washers. The longitudinal timbers, 14 inches
in width, were laid down upon the cross ties, and then firmly bolted to them with screw
bolts and washers; the head of the bolt and washer, being counter-sunk in the longitudinal
rail, and passing through the transverse ties, were secured below: two bolts were used
when the timbers were double, and one at each point of intersection of the single timbers.
The longitudinal timbers being bolted securely to the transverse ties, the latter were again
secured by bolts passing through the head of the piles.
After the cross ties and longitudinal timbers were all securely placed, finely screened
5 H
1570
¸
THEORY AND PRACTICE OF ENGINEERING
Book II.
sand or gravel was driven or packed under them by means of pointed beaters, which was
continued until the tim-

bers were strained up-
wards of half an inch or
more in the middle and
made to curve; they were
then adzed down to a
level, and a plank of hard
American oak, 8 inches
broad and 1 inch in
1/1/2
thickness, was laid upon
a bed of tar, the whole
length of the longitudinal
timbers, and nailed down
in two rows with 2-shil-
ling nails, their heads
being well punched in.
The oak plank was
then planed to a surface
throughout, and the iron
rails laid on it with great
care, each joint being
fitted very nicely, with
due allowance for ex-
pansion and contraction;
the iron rails were fastened
down by screw-bolts pass-
ing through a piece of felt,
the American oak, and
then into the longitudinal
timber: the screws on the
outside of the rails had
square heads, but those
on the inside were counter-
sunk, so as to avoid
any interruption to the
flanges of the wheels as
they passed along. When
the outside screw had
been so tightened as to
draw the rail close down
to the oak plank, and the
inner screws also made as
tight as possible, a heavy
roller, weighing 10 tons,
was moved several times
over the rails, and as it
passed the screws were
again turned until per-
fectly tight. The gauge
of these rails is, from
centre to centre, 7 feet
2 inches, and the width
Fig. 2331.
D
Fig. 2932.
V
Fig. 2933.
between each pair of rails in the middle 6 feet;
so that from the centre of the outside rails,
where the double line is complete, is 20 feet
5 inches.
The piles are for the purpose of holding down
the sleepers, and the packing under the timbers
which cross the railway is to give them a pres-
sure upwards, to enable them in some degree
to resist the weight of the carriages; it has
been stated that this springing of the timbers adds
considerably to their stability; and, undoubtedly,
the pressure upon a curved timber would throw
the weight towards the ends, and deposit it
against its abutment, which would be the sec-
U
Q
Fig. 2935.
ព





V
Fig. 2934.

CHAP. XXX.
1571
RAILROADS.
tional end of the adjoining one, as long as the pile maintained its retentive power. This
timber foundation required for every mile of double line 420 loads of American pine,
40 loads of oak, 6 tons of wrought-iron bolts, and 30,000 screws.
84
Rails, when of cast-iron, are more brittle than when of malleable metal, and consequently
require an increased area in their section to be equal in strength to the latter they are
durable, resist for a long time the action of the wheels, and, from the hardness of the metal,
oppose little or no obstruction to them: but the malleable iron, from not being so subject
to fracture, is now usually preferred. The width of the rail at top is about 2 inches,
which is that now given to most wheels, and considered sufficient for all purposes. It has
been estimated that the wear and tear or waste of the rails is about of a pound per yard
per annum, or that inch in depth is annually worn away; but this must in a great
degree depend upon the quality of the iron, and many other attendant circumstances: their
length is about 15 feet, and the expansion and contraction in our temperature is estimated at
equal to 20 of that length, or inch. In comparing the strength of rails great differences are
observable from the various kinds of iron used; when diversities of metal in proper pro-
portions are employed, the rail is stronger, with the same weight of iron, than when com-
posed of one metal. It is admitted that those of malleable iron are easier kept in order;
that, extending over several chairs or blocks, there are fewer joints; that they present to
the wheels of the carriages a smoother surface, and are also more regular in their decay;
that their elasticity being great, they are not so subject to fracture, and will bear considerable
change of form without the cohesive power being affected; and that pressure which would
crumble down the crystalline texture of the cast-iron flattens the malleable, and renders its
powers of resistance greater.
2000
With regard to the best form for the section of a rail, there have been various opinions;
it has been ascertained that a malleable iron bar of any length is extended 100000 of that
length by the direct strain of a ton for every inch of its sectional area, and when
strained by ten tons per inch, or stretched of its length, it does not regain its form or
elasticity.
The Plate Rail, first used about the year 1767 in a colliery near Sheffield, was a flat
bar of cast-iron with an upright ledge; it was in 6 feet lengths, and the upright and flat
part measured in width 2 inches; they were secured by nails to transverse timber sleepers;
they were placed on square wooden blocks, and it was not until the year 1800 that stone
blocks were used on the railway at Little Eton, in Derbyshire: some flat rails are cast
with a square hole at every joint; through this an iron pin is driven, which enters a wooden
plug previously introduced into the stone block; one-half of the pin thus secures the end
of each rail, which is in lengths of from 3 to 4 feet. In some cases a return is cast on the
edge of the flat part of the rail, which enters a groove cut into the stone, and adds consider ·
rably to its steadiness. Wrought-iron rails were first used about 1824; they are now all so
manufactured, and rolled out to the form required.
The first Edge Rail was of cast-iron, and used at Loughborough about the year 1789: its
upper surface was level, and that below elliptical: a flange on the wheel guided it along the
rail; it consisted of a bar of cast-iron, about 3 inches thick, increasing towards the top to a
breadth of 21 inches, in which the wheel ran: they were either fixed to wooden sleepers or
stone blocks, and this description of rail, when its section was that of a parallelogram, was
calculated to bear the greatest strain.
Iron chairs, of which there are now many varieties, were a most useful introduction: the
first were made with a flat base, of about 7 inches in length, 4 inches in width, and 2 of an
inch thick, gradually diminishing towards the edge to inch: the upper part, which
received the rail, had two uprights cast on it, at a distance sufficient to allow the rail to enter
between them, when fixed pins were passed through the cheeks or uprights, as well as
through the holes in the ends of the rails, which prevented them from moving; they were
placed either on stone blocks, 18 inches square and 9 inches in depth, or on wood 3 feet
long, 10 inches wide, and from 6 to 8 inches in depth. The chair was fastened down by
driving an oak pin or plug through a hole cast on each side, and another drilled into the
blocks.
I
In the year 1816 Loch and Stephenson obtained the first patent for an improved rail and
chair: the ends of the rails united in a half lap, a pin passed through the two ends as well
as the chair, and kept them
together. The object of this
patent was to fix both the ends
of the rails, or separate pieces
of which the ways are made,
immovably in or upon the
chairs or props that support
them, and so to place the rails
that neither of the ends should

Fig. 2936.
5 н 2
1572
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

project above, or fall below, the
corresponding one of that with
which it is in contact, and so to
form the union of the rail and
chairs, that they should always
remain perpendicular: this con-
trivance relieved the carriages
from the sudden jerks to which
they were previously subject,
and diminished the resistance
offered to the wheels in their
transits over the rail.
Brunton and Shield's Railway.

Fig. 2937. Loch and stephenson's chair.
The rail is fastened to the
chair, which has only one cheek,*
by a screw-bolt, which draws a
concave nutt tightly against a
convex protuberance on the rail,
holding it firmly against the up-
right cheek of the chair: the
thread of the screw, however,
being exposed to the action of
the weather, is, in the course of time, apt to break,
when turned for the purpose of tightening the joints.

Fig. 2938. Loch's chair.

Loch obtained a patent for another chair, in which
the pin was dispensed with the rails were united at
the ends by means of a half lap passing each other,
when they were set on edge 3 inches: upon the outer
side of each rail was a circular projecting knob, and
on one of the inner sides a similar knob, which
entered a cavity cast to receive it, and prevented the
rails from being drawn out in the direction of their
length: the rails maintained their proper position,
and were prevented from
by their own
rising by
weight. Other means
have been adopted to
maintain the rails on their
chairs without a pin;
some have round knobs
cast on their ends, which
enter cavities answering
to them, and are kept
in their places, thus ob-
taining a level surface
throughout, which is the
chief result to be arrived at.
Fig. 2940.
Fig. 2939.

One of the first malleable rails formed by rolling-bars was made
effected a great change in all that were afterwards manufactured.
passing bars of iron heated red-hot between two rollers so grooved
quired form; the under side of the rail is
sometimes made elliptical, by fixing it on a
false centre. This kind is usually rolled
out into 15 feet lengths, and laid on 3 feet
bearings, with their ends formed with half
laps.
Fig. 2942.
Fig. 2941.
in the year 1820, which
The process consists of
that they give the re-

Fig. 2943.
The Liverpool and Manchester line had
rails of this description, weighing 35 pounds
per lineal yard with square ends, and a square
projection on one side, which, by driving an
iron key into a hole on the other, force it into
a recess cast in the side of the chair to receive
it. The key was in form of a wedge, and driven longitudinally.
The chairs were secured to stone blocks, 2 feet square and 12 inches thick, by iron pins
driven into wooden plugs, previously inserted in the stone. In Loch's patent the key is
driven on each side above the projection at the bottom of the rail, so that it is kept from
rising, which became necessary when the rails were made in 15 feet lengths, the alterations
CHAP. XXX.
1573
RAILROADS.
arising from the variations of temperature rendering it difficult to pass the pins through them
and the sides of the chairs, as had been done with those of shorter lengths. The joints are
liable to become loose from the constant action of the carriages, and the most effectual way
of tightening them is to drive wedges of iron along the sides of the rail.
London and Birmingham Railway has a joint or double chair, and a single or interme-
diate, made of strong grey cast-iron. of the No. 1. quality. The double chair has 2 wrought


Fig. 2944. SINgle chair.
Fig. 2945. PLAN
iron pins, 2 wrought-iron wedge bolts, and 2 wrought-iron keys: the single or intermediate
chairs have 2 wrought-iron pins, and 1 wrought-iron key, which are of the best malleable
iron.
By a reference to the plan it will be seen that the seat of the rail is convex on the one, and
double convex in the other; the side of the chair next to the flanges of the wheels is in
contact with the rail at only two points: on the other side, the rail is secured by a cast-iron


Fig. 2946. Double chair.
Fig. 2947.
chock of a spheroidal form where it touches the rail; this chock has a step or foot by which
it rests on the bottom of the chair, and is wedged into its place by means of a wrought-iron
key, which passes perpendicu-


larly into a mortise, one-half of
which is cut through the chock,
and the other half on the chair.
The chairs were pinned
down to the blocks with iron
spikes 7 inches long, and
inch in diameter, their heads
being 14 inch in diameter.
Some of the fish-bellied rails
were laid down upon this rail-
way
with chairs, for which Fig. 2948. STEPHENSON'S patent.
Fig. 2949.
A key
Mr. Robert Stephenson took out a patent; the weight of the rail was 50 pounds per yard
in length, and it fitted exactly into the chair, with no space for lateral movement.
acts directly against the side of the rail through a
mortise-hole passing into the sides of the chair; through
these holes is driven a tapering key, which, acting upon
the pin, forces it against the sides of the rail.
has a sharp point, and therefore, when tightly driven, in-
dents itself into the rail.

The pin
On the London and Croydon Railway chairs are dis-
pensed with altogether, and the rail is screwed down to
longitudinal sleepers, laid on transverse timbers through-
out. The base of the rail is in width 41 inches, producing
great steadiness: in every yard in length are two sleepers,
and over them four rows of longitudinal sleepers; 16,672
cubic feet of timber were used for every mile.
The cross
or transverse sleepers are 8 feet in length, and 9 by 41
inches: the longitudinal timbers 9 by 41 also.
The iron rails were in weight per lineal yard 48
pounds, and that per mile was 337,930 pounds; there
Fig. 2950.
are 7040 trenails, as many bolts, and 16 screws to every yard, making 28,160 screws,
5 н 3
1574
Book II.
THEORY AND PRACTICE OF ENGINEERING.
weighing 4692 pounds. These materials, including the labour of fixing them, and the
ballast over an average breadth of 26 feet to a depth of 18 inches, cost 5211l. 4s. per mile.
An iron rail of this form, resting on a continued sleeper, is considerably stronger than
when placed on chairs; a 48-pound rail, so applied, is as strong as one of 75 pounds when
resting on points of support 3 feet distant. The sleepers were all of Memel, and the
screw-bolts, which secure the rails, were 18 inches apart.
Helton Rail has a half lap joint; the bottom of the chair is let into the stone and se-
cured by two wooden pins; a convex boss is cast in the bottom of the chair, upon which the


Fig. 2951.
Fig. 2952.
O
Fig. 2953.
ends of the rails are halved, and a pin, passing through a hole cast in them, secures them to the
chairs.
The Southampton Railway bars are of a parallel form, and weigh 75 pounds per lineal
yard: they were placed in two varieties of chairs, the weights of which were 26 and 22
pounds. The rails are in lengths of 15 feet, their depth is 5 inches, the width of the tops
and bottoms 23 inches, and the thickness of the middle 13 of an inch.
London and Greenwich Rails are laid to a gauge of 4 feet 8½ inches, and are of the edge
form, 21 inches wide at top, 41 inches in depth, and 1 inch in thickness at bottom: they are
supported in cast-iron chairs placed at distances of 3 feet. The chairs are fixed in rough
blocks of granite or Bramley Fall stone, each containing about 4 cube feet.
Railway Curves. When circumstances oblige a departure from the straight line, the
curvature to be given to the rails is a point of the highest importance; if it be struck from
a radius of a mile only, the inclination of the rail rises but 16 feet in the mile, and the speed
of the locomotive engine is reduced nearly one-half; but when the rails are perfectly level,
the curvature does not materially impede the progress of the carriages. The flanges of the
wheels on the outside rails of the curve, acting against the rails, prevent the carriages
being thrown off; but to make them travel along the curve without friction, the wheels
have the outside of their rims made conical, or their diameter is increased on the side next
the flange. When the carriages move around a curve the wheels eing connected together
form conical rollers, moving upon the rails with different radii, the smallest being that of
the inner curve, and the increase of that diameter of the wheel which runs on the outer
curve makes up to a certain degree for its increased length. The diameter of the wheels
next the flange is generally 1 inch more than on the outside of the tire: the breadth is 3
inches; when moving in a straight line, they are usually placed upon the axle, so that they
work at about 1 inch from the rail, but some latitude is allowed for their changing into a
curved direction; and it is found that for 3 feet wheels, this kind of tire is quite efficient in
preventing their rubbing against the inside of the rails at all ordinary curves.
When a carriage moves round a curve, its tendency will be to move in the direction of a
tangent to that curve, which is altered by the force or velocity, as well as by the radius of
curvature. By raising the outside rail, an inclination may be given to the axles, which
will produce upon the carriages a gravitating force towards the centre of the curve, equal
to the outward centrifugal force, and there will consequently be no extra pressure against
the rail, nor any chance of the carriages being thrown off.
Turn- Tables only admit of one or two carriages being turned at the same time, and
consequently are not generally useful; there is some trouble attending their manage-
ment, and they require great attention. The length of the locomotives employed on the
line determines their diameter: those on the London and Birmingham Railway are 12
feet, those on the Leeds and Selby 8 feet; they are made of cast-iron, and turn on a pivot
in the centre; on the outer rim are rollers, which facilitate the rotary motion: that on
the London and Birmingham line has 8 cast-iron rollers, 10 inches in diameter, working
upon iron arms, which radiate from a wrought-iron hoop that works round the centre pivot.
A circular ring of cast-iron, 12 feet 7 inches in diameter, surrounds the turning-table,
and is in depth 1 foot 9 inches; at the bottom is a circular iron plate, 12 inches wide,
CHAP. XXX
1575
RAILROADS.


Fig. 2954.
and 1½ inch in thickness, upon which the rollers
work.
The table rests upon four iron bearers at
right angles with each other: they are 9 inches
in depth at the middle, and 63 at the ends; their
intersection leaves a square in the middle, the
sides of which are 4 feet; from the angles of
this square are four other arms serving as radii,
which unite with the iron hoop that works
round the centre pivot; they are 8 inches in
depth at their junction with the hoop. The
bearers are at the same distance apart as the
rails on the line, and have holes inch in
diameter cast in them, for the purpose of at-
taching the rails to the table; at their ex-
tremity is a circular cast-iron plate, which works
round upon eight rollers; its width is 2 inches,
and the distance from its middle to the centre
5 feet 13 inch.
Fig. 2955. TURN-RAIL.

Fig. 2956. TURN-Table,
The rollers work between two wrought-iron hoops, 2 inches deep and § thick, and upon
58
the ends of eight wrought-iron rods, inch in diameter, which are screwed into the hoop
that surrounds and traverses the centre pivot. The hoop is also of wrought-iron, 1 inch in
thickness, 2 inches in depth, and 5 inches in diameter, and is accurately turned, so as to
work round the collar of the centre pedestal, which is also turned, and of cast-iron, with a
hole 3 inches in diameter and 5 inches in depth, at the bottom of which is a brass step 2
inches thick, for the pivot to work upon. The pedestal is fastened to the stone block by
four pins, and a hole is left for the necessary supply of oil to the pivot: to this pivot the
table is attached by four screw-bolts, 14 inch diameter, so adjusted that by turning them
may be eased off, or lowered on the rollers. On the surface of the table two lines of
railways are fixed at right angles, the rails being of wrought-iron, 3 inches broad and 2
inches thick, bolted to the principal arms with -inch screw-bolts, their heads being
counter-sunk into the rails. At the intersection of the rails are four sets of wrought-iron
inclined planes, for the flanges of the wheels to run upon when passing the openings; and
on the outer rim is a latch to hold the table in its desired position. Cast-iron gratings,
3 inch in thickness, are made for the separate compartments, and put into rebates formed to
it
receive them.
Passing from one Line of Railway to another.-Where double lines of railway are laid
down, and carriages of equal speed run upon them in opposite directions, the neces-
sity for turning out, or for sidings to allow them to pass, is avoided: but where there are
Fig. 2957.
Fig. 2958.
5 μ 4
1576.
THEORY AND PRACTICE OF ENGINEERING. BOOK II.

two classes of carriages, one
for passengers, and the other
for goods, varying in speed,
means must be provided to
allow of their occasionally
passing each other, with-
out which the passengers'
carriage would be subject
to delay and obstruction
from the one more heavily
laden.
:
As there is always some
risk in passing in and out
of a line, it is advisable
to have as few sidings as
possible in the best con-
trived crossings, trains ra-
pidly passing may meet with
accidents, if there be the
slightest want of care and
attention on the part of the
attendants. Where there is
a single line of railroad,
either of the three methods
shown may be adopted, as
the carriages, travelling in
either direction, can pass by
the sidings without incon-
venience to those going in an
opposite direction. The first
is generally applied when the
carriages are all proceeding
in the same direction, but
Fig. 2959.
Fig. 2960.

Fig. 2961.


Fig. 2962.




Fig. 2963.
:
with a difference in the speed, a movable rail is alone required to divert them into the
siding, or a switch which is restored to its first position by the servant whose business it
is to attend it should carriages require to pass in an opposite direction, the switches are
moved so as to enable them to digress, and again enter the main line. Loaded carriages
invariably keep the line, and the empty ones take the sidings, the movable rail being on
the side towards which they pass.
In the second example, the movable switch is dispensed with, as the carriages can pass each
other without changing the rail: this arrangement is usually adopted in mines. The third
example allows the carriages both going and coming to diverge, and the main line to be
gained by both. Wherever the sidings are adopted, the oblique lines of rails should be laid
at an angle that will prevent the carriages passing by them from having their wheels thrown
off the rails by the sudden change of direction, which angle must in some degree be
determined by the speed: when this is not more than 8 miles an hour, it may be made at
that number of degrees; but when at 20 or 30 miles 1° or 2º should be the extent of the
angle from the straight line.
Switches and their Movements.—The point and switch rails are most commonly used
for sidings, and when worked by hand, they always remain open, so that if the trains are
required to be moved into the siding place, this is effected by moving the switches: they
are sometimes kept shut by the application of a weight, which the loaded carriages can push
open, but the empty ones cannot, so that they are obliged to pass by the siding. The
ends of the point rails do not touch the continued line, and the space left between them is
CHAP. XXX.
1577
RAILROADS.
a great objection to rapid movement, carriages passing over it being subject to a shock, to
remedy which inconvenience the rail is sometimes made to turn on a joint, so that the
carriages can pass in a straight line, those coming in an opposite direction opening the
inner rail on one side, and shutting the other by their own pressure.
For the switches on the Liverpool and Manchester Railway, about 9 feet of the rail on
each side are moved on a cast-iron framing, securely bedded in the ground, or placed on
chairs made to re-

ceive it: the move-
able rails are united
by an iron rod, and
work upon a joint
at one end. A hori-
zontal sheave is fixed
on a false centre,
with an iron ring
working round it in
the manner of an
eccentric, so that
when the handle at-
tached to the verti-
cal rod is turned it
will either open or
shut the rail.
are
In another system
practised on this rail-
way the rails
placed upon a frame
of cast-iron; two short
rails move on joints
at their ends, and
work to either side
upon it; they are
united by a bar of
iron, and when in one
position the carriages
pass by the continued
rails; when in the
Fig. 2964.
O
wwwww
KILLINGWORTH RAILWAY.
[9]
Fig. 2965.
other they are di-
verted: these switches are moved in a similar manner to those already described on the same
railway.
The most usual plan is the crossing-rail: to prevent the wheels running off, the top of
the rails is sunk below the surface, but the openings, where they cross, subject the
wheels to a shock in their passage; the flanges are on the inside of the rails, and where
narrowed out to a mere point, they are liable to change of form and to get out of order.


Fig. 2966.
Fig. 2967.
Engine for a double Plane The shaft which turns the machinery, fig. 2968., may be
moved by manual labour; but where a steam-engine is employed, a crank will be neces-
sary, or the shaft may be attached to a water-wheel. The cylinders upon which the rope
1578
BOOK II.
THEORY AND PRACTICE of engineerING

A
Fig. 2968.
RAILWAY PLANES.
coils can be put out of gear by couplings, or by the ordinary methods of disengaging
machinery; one end of the small levers in turning touches the cylinders, which drives them
into the clutches fixed at the other end, and throws them out of gear. The fly-wheel
which regulates the motion is made proportionate to the cylinder.
When there are a succession of planes throughout a railway, as is the case in some situa-
tions, it is necessary at the top of each pair of planes to have two rollers on which the
rope coils, worked by a stationary steam-engine. Ropes attached to the carriages draw
them up and let them down the inclined plane: each station must be provided with two
rope rolls, one uncoiling at each end of the train. When it is required that the carriages
should descend, the action must be reversed, enabling them to proceed in the opposite direc-
tion, or towards the roll at the further end of the train; thus, by an endless rope working
alternately round a cylinder at each end of the railway, a regular transit is maintained. The
ropes must always be placed in a line with their work, or the middle of the cylinders must
be opposite the division of the rails.
Where a line of railway is to be worked by stationary engines, they are placed at regular
distances, each engine drawing the carriage to it from the opposite end, unwinding at the
same time a rope from the roll of the next engine, which in its turn pulls a carriage or
train in the opposite direction, by re-winding the rope on its former cylinder.
When engines of great power are made use of, four trains of carriages may be drawn
towards them by four rope rolls at the same time: on the Liverpool and Manchester line
a fixed engine is employed to drag the waggons loaded with merchandise up an inclined
plane of 1 in 22, for a length of 2250 yards: this is effected by an endless rope; at the
summit of the plane is a horizontal wheel worked by a pair of engines, one on each side;
the waggons always mounting by one road and descending by the other, so that they
are in a right position for the locomotives which bring them, or are to continue them on
their journey. In some instances a horizontal shaft extends across the whole width of the
railway, upon which, in the middle of each pair of rails, is a wheel 20 feet in diameter with
a groove on its vertical edge. The rope which ascends the plane is passed over the upper
edge of the wheel, round the under side, and then nearly to the top a second time, by the
aid of a sheeve 4 feet in diameter in front. The rope nearly surrounds the 20 feet wheel,
and the adhesion is powerful enough to pull up 80 or 90 tons on a plane with a rise of 1
in 100.
Self-acting Planes. —It has not been determined at what angle a plane should be laid, that
would give to a carriage passing it a regular and uniform motion: to produce this the
motion should be greatest at the starting point, so that the body should descend by the law
of gravity with accelerated force at first, and afterwards gradually lessen, The cycloidal
curve has been adopted for this purpose, as giving a diminution of force at the termination
proportionate to the gravity at starting; were the inclined plane regular in its descent, the
force would accumulate with the body that descended it, and carriages placed upon it would
increase their velocity when they were required to be at rest. At many of the mines the
loaded carriages draw up the unloaded, and then two inclined planes are necessary; but it is
exceedingly difficult to decide on the angle at which they should be laid, as it must greatly
depend on its uses and the weights to be drawn, as well as time allowed for the transit.
CHAP. XXXI.
1579
PRINCIPLES OF PROPORTION.
CHAP. XXXI.
PRINCIPLES OF PROPORTION.
For a full and comprehensive view of architecture, we must refer the reader to the
Encyclopædia on that subject so ably written and illustrated by my friend Mr. Joseph
Gwilt, and confine our attention to the principles and science of building, the more
immediate province of the civil engineer. "Architecture," says Vitruvius, "has for its
parents practice and theory; the first is the result of the frequent and continued contem-
plation of the mode of executing any given work, or the operation of the hands for the
conversion of the material in the readiest way: theory is the reasoning produced by.
that contemplation, demonstrating and explaining that the material wrought answers the
end proposed, and on him alone who is familiar with both branches of the art can the title
of architect be justly bestowed; the theory, however, may be studied by all, but the results
of practice can only be fully appreciated by the practitioner; and the civil engineer should
not only be acquainted with all the sciences, of which an epitome has now been presented to
him, but have a thorough knowledge of the principles of architecture, and the character of
each particular style; but that branch which is most intimately connected with his
practice, the proportioning of masses, or the arrangements for the supports of an edifice,
must be the objects of his unwearied study and attention.
We shall therefore endeavour to point out, as briefly as possible, the general features
which in this respect belong to the three great divisions, viz. the Greek, the Roman, and
the architecture of the middle ages. That part of Greece which lies to the south of
Thessaly, near the foot of Mount Othrys, is supposed to have contained the capital of
Hellen, who left his kingdom to his three sons Æolus, Dorus, and Xuthus, the second son
becoming the founder of the Dorian race, and the youngest that of the Ionian.
Architecture can hardly be said to have existed as a science until the Dorians perfected
that style, which we find in the temples and other buildings scattered throughout those
islands and countries in the Mediterranean Sea which received Doric colonies. The
dwellings of these early civilisers of mankind were plain and simple; the laws of Lycurgus
forbade the use of any carving or decoration, their doors being fashioned only with the saw,
and their roofs by the axe; but in their temples and public edifices, they were encouraged
to bestow more labour and superior workmanship : the Dorian architecture appears
never to have undergone any great change; the same style, and almost the same proportions,
are found in most of the examples that have been spared us.
These people spread a knowledge of the arts of construction wherever they settled; and
we find them at a very early period in the northern districts of Greece, under the Olympian
chain of mountains, in the island of Crete, on the eastern side of the northern coast, on which
is situated the town of Cnossus with its harbours, Heracleum and Apollonia, at which
latter places their religious rites were celebrated. After having overrun Thessaly, they sent
from thence a colony to the district of Driopis, called the Doric Tripolis, between Eta
and Parnassus, from the union of the three cities Bæum, Cytinium, and Erineus, and,
subsequently, when Acyphas was added, Tetrapolis.
The country next occupied by the Doric tribes extended from the river Sperchius
beyond Eta to Parnassus and Thermopylæ, but the most important of their migrations
was that called the Return of the Heraclidæ. After this period they were for a short time
driven into Attica, where they received protection from Theseus, and when again settled in
the Peloponnesus, they sent out colonies to Rhodes, Cnidus, and Cos, led by princes of the
Heraclidæ from Argos and Epidaurus. Another colony from Trozen was established at
Halicarnassus. The towns which composed the Tripolis of Rhodes, together with Cnidus,
Cos, and Halicarnassus, formed the Doric league called Hexapolis, but after the separation
of the latter place, Pentapolis: this league met on the Triapian promontory to celebrate the
rites of Apollo and Ceres. A colony was sent from Lindos to Telos; others from Cos,
Nisyrus and Calydna; from Argos to Carpathus, now the island of Scapanta; from
Cnidus to Syme, a town of Asia Minor; from Megara a migration took place, which
settled at Astypalea, one of the Cyclades; and others to Anaphe, Thera, Phalegandros,
Melos, Myndus, Mylasa, Cryassa, Synnada, and Noricum in Phrygia.
The Rhodians founded Gagæ, and Corydalla in Lycia, on the shores of Asia Minor;
Phaselis on the confines of that country; Pamphylia; and Soli in Cilicia. According to
Thucydides, about 713 years before Christ, Antiphemus led a colony from Lindus, and
founded the town of Gela in Sicily.
1580
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Corinth sent out numerous colonies from Lechæum in the Cresæan Gulf, which founded
Syracuse about 760 years before Christ; Molycrion, Chalcis, towns of Æolia; Salicum in
Acarnania; Ambracia and Anactorium in Epirus; Leucadia, now the island of St.
Maura, which was formerly joined to the continent by a narrow isthmus; Corcyra, on the
coast of Epirus; Epidamnus in Macedonia; Apollonia Potidea, with several others.
Issa, an island in the Adriatic, was peopled from Syracuse. Megara, situated between
Corinth and Athens on the Sinus Saronicus, after it became a part of the territory of the
Heraclidæ, sent colonies to Astacus in Bithynia and Chalcedon, another city in that pro-
vince opposite to Byzantium, Selymbria in Thrace, and Heraclea in Pontus, celebrated
for its naval power.
Megara also colonised Hybla in Sicily, famous for its wild thyme and honey, which
people founded Selnus. Sparta founded Tarentum about 700 years before Christ, which
at one time comprised thirteen tributary cities within its government, and could muster
100,000 foot and 3000 horse.
From Gela, which was colonised from Lindus in the Island of Rhodes, originated
Agrigentum, a place of considerable importance at the time the Cretan Phalaris obtained
the sovereignty; indeed Crete and Rhodes jointly may be said to be the founders of
Agrigentum.
In following the progress of the Heraclidæ along the shores of the Mediterranean to the
Pillars of Hercules, we find wherever they settled those beautiful examples of construction
in masonry which we can never be weary of admiring and studying. The temples in the
Doric style in Sicily are of great beauty, and they may be some years anterior to those now
remaining in Greece, but the difference cannot be very great: those at Syracuse and
Agrigentum were constructed from the spoils obtained when Hiero defeated the Carthaginian
general Hamilcar at Himera, and those at Athens were not built till some time after the
defeat of Xerxes; but by some of the historians it is said that both battles were fought on the
same day, that whilst Hiero was obtaining his independence, the Persians were overthrown
at Salamis. Some time, however, elapsed after these victories before the Athenians and other
states of Greece which had been engaged in the war recovered their prosperous condition ;
and it was not until the time of Pericles, which is nearly 50 years after the building of the
temples at Agrigentum and Syracuse, that the restoration of the Parthenon and other
public buildings throughout Greece was undertaken. The temples at Selinus are said to
have been built when the city was founded, 620 years before Christ, and it is asserted they
were entirely destroyed when the inhabitants deserted the city 250 years after its foun-
dation could this be proved, they would rank among the first erected.
The Propylea at Athens was built by Mnesicles in the 85th Olympiad; and a few years
afterwards, when Pericles governed, Ictinus completed the Parthenon, and probably the
temple of Theseus. The temples at Sunium and Phygalia were also the work of that
renowned architect, and are deservedly ranked for their proportions and execution among
the most graceful productions of Greek architecture. The temple of Jupiter Panhellenius
in the Island of Egina was founded by Eacus before the Trojan war, but the ruins we
now admire no doubt may be referred to the time of Pericles.
The source of those beautiful effects which have received the almost instinctive admi-
ration of every age and country can only be traced by correct measurement, and a careful
observation of the proportions of the masses, which will almost irresistibly convince us that in
temples and fronts of porticoes one general law prevailed, and was applied to all tetrastyle,
hexastyle, and octastyle arrangements, based upon the proportion of a cube. This is found
to govern most of the designs executed from the time of Pericles to the death of Alex-
ander, the golden age of Greek art, when sculptors, painters, architects, and engineers were
called forth to vie with each other in their several branches, and workmen of skill and in-
genuity were found to embody the suggestions of their imagination; and the results would
lead us to suppose that the acmé of perfection was attained, for since that period none of
the productions either in sculpture or architecture have equalled those of the Greeks in the
simple elegance of their design, or the excellence of their execution.
Tetrastyle Porticoes with four columns exhibit the simplest, and perhaps the earliest,
application of the Doric order; the entire façade is comprised within a square, the height
being divided into three portions, the upper constituting the entablature, and the
other two-thirds being divided equally between the supports and their three intercolumnia-
tions, making the latter a little more than a diameter. We may imagine the square divided
in its height and width by 8, making altogether 64 compartments of equal area ; the upper
8 devoted to the pediment will have, when the inclined sides are set out, a diminution of one-
half their area, four whole squares being rejected in those parts above the pediment, the
area of the tympanum being only equal to four. The entire mass is thus reduced to the
area of 60 of these squares, which are thus disposed of; 20 are given to the supports,
5 cubes to each column, 20 are divided between the three intercolumniations,
and the remaining 20 constitute the load supported; the columns are 5 diameters in
height, and bear no more than their own weight, a due harmony being obtained through-
or
CHAP XXXI..
1581
PRINCIPLES OF PROPORTION.
>>
out; the eye is satisfied that the load cannot distress its supports, and the spaces between
the supporting masses are again proportioned and made equal to either, so that we have a
triple division,
the
one, per-
pendicular arrangements of the
supports, another their just
distribution or equal distances,
and the third, the entablature
proportioned to the strength
that is to carry it, all of which
are comprised within the boun-
dary of a square. The tetra-
style porticoes that remain are
not numerous, and none are
perfect; three have been se-
lected, which will enable us to
test the idea we have attempted
to define. First, that at Eleusis,
the entire width of which is
20 feet 6 inches, the height
21 feet 6 inches; and if we
reject half the height of the
pediment we
we shall have a
square: the united dia-
meter of the columns only
varies 5 inches in width
from those of the intercolum-
niations.

Fig. 2969.
TETRASTYLE PORTICOES.
If we divide the height into three, rejecting, as already observed, half the pediment, which
in this case is 1 foot 1 inch, we have for the height of the square 20 feet 4 inches, whilst
the entire width is 20 feet 6 inches, a difference not very great: this divided into three, and
giving two-thirds to the height of the columns, would make them only 13 feet 6 inches and
8 seconds, whilst they really are 14 feet 2 inches in height. In this example the entire
height, which we may call 21 feet 5 inches, is divided into three, two parts of which
constitute the height of the columns.
In the Temple of Themis at Rhamnus, the width is 20 feet 11 inches, and the height
the same, the diameters of the columns being in excess 3 inches only above the width of
the intercolumniations.
In the Doric Portico at Athens, the entire height equals nearly the width.
Hexastyle Porticoes. The practice of the Dorian architects, in setting out a temple
with six columns in front, appears sometimes to have been to divide the width into twelve
parts, the height without the pediment being made equal to eight of them; thus forming
a façade within a parallelogram or a square and a half: as the ninth division in height cuts
the pediment in half, we have thirty-six squares for the entablature or mass supported,
being the same quantity found in the six columns and the five intercolumniations; at other
times we find the entire width divided into nine parts, and six given to the height, one of
which indicates the pediment, thus rising a ninth : if a circle be described in the tympanum,
and a horizontal line drawn through the centre, cutting off a twelfth of the height, the
remaining being divided into three equal parts, the upper third, or entablature, being
the part supported, the remaining are divided between the columns and their interspaces;
thus making the columns equal to of the height comprised between the centre of the
tympanum and the platform upon which they were placed.
If we take each of these nine parts as 5 feet, we have 45 feet for the width, 30 for the
height, including the 5 feet for the rise of the pediment, which if we divide by the horizontal
line, to obtain its true area or quantity, we shall have 2 feet 6 inches for its mean height,
and 6 feet 8 inches for that of the level entablature: for as we have observed, these two
dimensions, which make 9 feet 2 inches, must be equal to half the height of the columns, or
the whole will not be divided into three parts; or, which is the same thing, the height from
the centre of the pediment must be divided into three parts, and the upper division taken
for the entablature. These proportions are exceedingly simple in their application; if it
were intended that the columns and the spaces between them should be equal, half the width
of the façade, or 22 feet 6 inches, should be distributed among the intercolumniations,
and the other half divided among the columns.
The Temple of Theseus at Athens is one of the best preserved as well as the most admired,
and was probably erected soon after the Parthenon; it is of Pentelican marble, adorned
with admirable sculptures. The total width of its hexastyle portico is 45 feet, and its height,
instead of 30, is 31 feet; the extra foot, which prevents it being an exact square and a half, is
given to the pediment, which probably has undergone some change, as it rises inuch more
than the ninth of its whole extent.
1582
THEORY AND PRACTICE OF ENGINEERING. BOOK IL

brwaved
Fig. 2970.
The height of the pediment is
HEXASTYLE PORTICOes.
Fert.
In.
5 9.75
level cornice
1
0.45
frieze
architrave
"
columns
1
I
18
220
8.55
8.9
8.8
and of the entire façade
31
0.45
Feet.
In.
half the pediment
2
10.875
the level entablature
6
5.9
making together a dimension nearly equal to half the height of the
columns.
the
}
9
4.775
The outer
The façade of this beautiful temple is divided equally into three parts; is given to the
entablature, and the other two to the columns and their intercolumniations.
columns are 3 feet 4.85 inches in diameter, and all the others 3 feet 3·4 inches. The middle
intercolumniation is 5 feet 3.95 inches, the next two each 5 feet 4.05 inches, and those
towards the angles 4 feet 6.35 inches. The diameters taken together are 20 feet, and the
intercolumniations 25 feet, so that the columns and their spaces are not in equal proportions:
the former would have required a diameter of 3 feet 9 inches, which would have made
them nearly five diameters in height, instead of what they are; they would have been heavier,
it is true, but more in accordance with the early examples.
The Hexastyle Temples at Rhamnus, Sunium, Egina, Eleusis, and Phygalia, are not suffi-
ciently perfect to enable us to decide whether our principles would apply to them: but
from the judgment we can form from their remains, they appear to have been all comprised
in a square and a half, and their entablatures and pediments in the proportion of a third
of the whole.
The Hexastyle Temple at Segesta in Sicily is sufficiently perfect to enable us to judge of
its entire proportions.
Its total length is
and height
or the whole façade is bounded by a square and a half.
The height of the columns is
entablature
pediment
Feet. In.
-
76 0
50 8
Feet. In.
-
31 Q
11 4
8 4
Total 50 8
CHAP. XXXI.
1 589
PRINCIPLES OF PROPORTION.
Half the height of the pediment is
entablature
Total height of superincumbent mass
Feet. In
4
2
11 4
15 6
which is exactly one-half of 31 feet, the height of the columns; so that we have, as far as
height is concerned, for the superincumbent mass or entablature, and for the columns
and their intercolumniations.
13
The columns have their united diameters
The intercolumniations ditto
·
Feet.
37
39
so that they are not in exact equality, although the difference is not considerable.
At Agrigentum are the remains of four Hexastyle Temples.-That of Juno Lucina is without
its cornice and pediment: the diameter of the columns is 4 feet 6 inches, and the entire
width is 55 feet. The united diameter of the six columns is 26, and of the five intercolum-
niations 29 feet.
The Temple of Concord is in width 57 feet, and in height 38; or it is comprised within
a square and a half.
The height of the columns is
entablature
pediment
Half the height of the pediment is
The height of the entablature
which is equal to half the height of the column
Feet. In.
-
23 0
8 O
7 0
38 0
Feet In
3 6
8 0
-
11 6
Thus one-third of the entire height is given to the entablature or mass supported. The
united diameter of the columns is 28 feet, and that of the intercolumniations 29 feet, the
latter being a little in excess.
Temple of Hercules. The total width is 84 feet, and height 56, which is a square and a
half.
The height of the columns is
entablature
pediment
1
11
Feet. In.
33 6
13 0
9 6
Making a total height of
·
56 0
The united diameter of the columns is 43 feet, and that of the intercolumniations 41 feet.
The height of the entablature and half pediment is in this case 17 feet 9 inches, instead of
16 feet 9 inches, as it should have been to have equalled half the height of the columns.
Temple of Castor and Pollux is imperfect, but the total width is 45 feet, of which the
diameters of the six columns occupy 24 feet, and the intercolumniations 21. The height of
the columns is about 20 feet, and that of the entablature 8 feet, as measured on the flank.
This temple nearly agrees in width with the temple of Theseus at Athens, but its pro-
portions vary; there is not sufficient remaining to judge of its entire form.
At Selinus are the remains of five hexastyle temples. In one the total extent is 51 feet,
of which the united diameters of the columns occupy 24, and that of the five inter-
columniations 27 feet. The height of the entablature is about 11 feet, but that of the
columns and pediments has not been yet ascertained.
The second temple is in width 77 feet 6 inches, the diameters of the columns occupying
37 feet, and the five intercolumniations 40 feet 6 inches; the height is 50 feet 8 inches, so
that the whole façade is included in a parallelogram, having a height not quite equal to
two-thirds its extent, or a square and a half.
The height of the columns is
entablature
pediment
In all
which is a foot less than the required height.
Ft. In.
29 4
13 4
8 0
50 8
In this example there is not an exact correspondence between the columns and what they
support: the entablature and pediment occupy 13, the intercolumniation 12, and the
1584
BOOK JI.
THEORY AND PRACTICE OF ENGINEERING.
columns 11 parts out of the whole number, 36, into which the parallelogram may be sup-
posed to be divided.
The third temple is not sufficiently measured to enable us to examine into its propor-
tions; the total width is 79 feet, of which the united diameters of the six columns occupy
36 feet, and the five intercolumniations 43 feet.
The fourth temple is in width 84 feet 9 inches, and in height 56 feet 6 inches or a square
and a half.
The height of the columns being
entablature
pediment
In all the height is
The height of half the pediment is
the level entablature
Feet. In.
·
34 O
11 6
11 O
56 6
Ft. In.
5 6
11 6
17 O
Making a height equal to half that of the columns, viz.
Thus the heights are in just proportion, one-third being given to the entablature and
pediment, and the other two-thirds to the columns and their intermediate spaces, which
are in the proportions of 44 feet 9 inches for the columns, and 40 feet for the five inter-
columniations.
The fifth temple is 81 feet in front, the six columns occupying 37 feet 8 inches, and the five
intercolumniations 43 feet 4 inches. The height of the column is 31 feet, and the entabla-
ture 15 feet 6 inches, or one-half the height of the column, so that, without the pediment,
the entablature in this example would constitute a third; and if the pediment had only risen
7 feet 6 inches, to make the general proportion a square and a half, these columns would
have had more to sustain than any other example we have yet referred to.
Octastyle Temples.- We will now apply these principles to a façade with eight columns,
and endeavour to follow the same system. We have already had a square, ana a square
and a half, as the form or figure within which the design was comprised; the portico of
four columns being circumscribed by the one, and that of six by the other; and as in the
octastyle there are double the number of columns contained in the first, a double square is
required to comprise it, that the same relative proportions may be obtained.

Fig. 2971.
OCTASTYLE PORTICOes.
After the width of the façade is determined, it is divided into sixteen parts, and ten are set
out for the height to the top of the tympanum of the pediment; which generally rising a
ninth of the extent, two divisions will serve to denote it, and if a circle be inscribed in the
tympanum, and a horizontal line drawn through the centre, we shall have a parallelogram
16 squares in width, and 9 in height.
Six squares in height will determine the under side of the entablature, which, if divided
equally between the columns and their intercolumniations, would give 48 squares to each,
which are precisely the proportions of the example we are about to examine.
CHAP. XXXI.
1585
PRINCIPLES OF PROPORTION.
The Parthenon or Temple of Minerva at Athens is admitted to have the most beautiful
proportions of all octastyle Greek examples; its entire width, measured in the front of the
columns at the base, is 100 feet 9 inches, and its height to the centre of the tympanum, from
the level of the platform on which the columns are placed, 51 feet 2 inches, 20 inches only
beyond what it should be to accord with the rules laid down. Dividing this height into
three parts, we have in round numbers 17 feet 1 inch for each the height of the
entablature and half pediment is 17 feet, and that of the columns 34 feet 2 inches, precisely
one-third of the height being devoted to the entablature, the lower two-thirds being divided
between these and their intercolumniations; adding all the diameters together, we have
49 feet 6 inches; the intercolumniations being 51 feet 3 inches, or only 1 foot 9 inches in
excess for the latter: hence if a parallelogram or double square be divided into 40 squares,
and 13½ be given to tle columns, the same quantities to the intercolumniations, the en-
tablature and its pediment, we should have the general proportions of the Parthenon, the
difference before alluded to being too slight to produce any effect on the eye in so large a mass.
The height to the centre of the pediment is 51 feet 2 inches, consequently the width to make
it an exact double square should have been 102 feet 5 inches, instead of 100 feet 9 inches;
and this difference may have been occasioned by the difficulty of setting out the triglyphs,
or from the idea that the width, as measured along the corona, should have some con-
sideration, and a mean be established.
As we have before observed that the Parthenon is considered perfect both in its design
and execution, a more detailed account of its construction and mouldings will be the best
illustration that can be offered on the subject of Greek masonry, premising that in the pre-
sent instance it is all of the finest marble from Pentelicus.
The Doric Column varies considerably in its proportions, some not being more than four
diameters in height, whilst in other examples they are from that to six and a half: those
we are now considering are formed of twelve blocks; on the upper and lower bed of each
are described two circles, the circumference of the outer being 9 inches from the edge,
whilst the inner circle is only 20 inches in diameter. The space between these is not
polished, but left rough as from the chisel, and a little sunk for the purpose of retaining



M
Fig. 2972.
Fig. 2972.
Fig. 2974.
DORIC CAPITALS.
a fine mortar or cement. In the centre of each block is a square hole, measuring 5 inches
on each side, sunk 3 inches in depth; in these were inserted pieces of hard wood, 6 inches
in length, to steady the blocks, and keep them from being displaced, particularly at the
time the flutes were worked, or the exterior was undergoing the process of polishing.
The outer columns are 6 feet 3 inches in diameter at bottom, and the others 6 feet
1 inch, the upper diameter of the latter being 4 feet 9 inches: their total height is 34
feet 2 inches, or nearly five diameters and a half; the diminution is not regular, there
being at a certain height a swelling or entasis, which improves the outline, and destroys
that meagreness which is the result of a straight line. The angular column is a little more
in diameter, that it may not appear less than the others, which are not so surrounded
by air.
10
The shafts have generally twenty flutes, uniting in an arris, and not with a square fillet
between them, as in the other orders; they are elliptical in some examples, as at Pæstum,
where their number is 16 and 24; the heads are variously finished. The capital of this
order varies in its height from to of the lower diameter of the columns, and the
5 I
1586
Booz II.
THEORY AND PRACTICE OF ENGINEERING.
abacus is sometimes more than longer than that width, all these proportions depending
more upon the height of the column than upon its lower diameter.


Fig. 2975.
Fig. 2976.
Under the abacus is the echinus or ovolo, which is beautifully turned, or cut like the
bell or profile of a flat cup, under which are usually from 3 to 5 annulets. The contour


Fig. 2977. DORIC CAPITALS. Fig. 2978. ANNULETS.
Fig. 2979. DORIC CAPITALS.
or profile of the echinus is a portion of a curve formed by the section of a cone. Where
the capital is placed on the column is another sinking, and sometimes three; and the true and
delicate manner in which these lines are cut gives a charm that more elaborate sculpture fails
in attaining.
The architrave of the Parthenon, which extends from the centre of one column to that
of the other, is in three thicknesses, showing two joints on the soffite. The frieze is admirably
contrived not to overload the architrave: the triglyphs are each in a single block, 3 feet
wide and 2 feet 3 inches in thickness. On each side is a perpendicular groove 1½ inch
deep, into which the sculptured metopes are slipped, the clear width between the triglyphs
being 4 feet 315 inches, and the angular one 3 inches less: at the back of the metopes, and
between the triglyphs, is a hollow space, from 8 to 14 inches deep. The metope is held to
the back of the frieze by a metal cramp in the form of an H, 2 feet long, and attached on
each side to the adjoining triglyph by others 17 inches in length. The cornice is in one
thickness; the angular block covers two mutules, each of the others one space and a
mutule. For further particulars of the construction of the Parthenon, and for several
dimensions omitted by Stuart, the writer must refer to some notes he added a few years
after his return from Athens to his wife's translation of "The Lives of celebrated Architects,
ancient and modern, by Francesco Milizia.”
In the Doric Order we may trace a reason for the direction given to the several lines,
whether perpendicular or horizontal; and although there is great variety in the form of
the members, yet when examined in detail, nothing will be found to disturb the unity
CHAP. XXXI.
1387
PRINCIPLES OF PROPORTION.
of the design. The voids are nicely adjusted to the solids, and all those parts, as the
columns and triglyphs, intended as supports, are striated perpendicularly, whilst those sup
ported are decorated with members and mouldings running horizontally, and indicating
rest or repose.
The inclined lines of the pediment are the only exception to this rule, and
they are composed of longitudinal members, placed consistently with their use, viz. that of
throwing off the water from the roof: so well-combined a whole, consisting of parts all
expressing their utility, deserves our admiration: even the annulets under the echinus
of the capital indicate so many cinctures to bind the tops of the perpendicular flutes
together, before the elegant tazza or cup-like vase is placed between the shaft and the abacus.

Fig. 2980.
IONIC CAPITAL.
Ionic Proportions. This style seems very nearly coeval with the Doric: it is supposed by
some commentators to be of Achaic origin, by others of Persian; both Greeks and
Persians may have contributed to its formation; the term Ionic was applied to it by Vitru-
vius, from its being first used by the inhabitants of Ionia; the few perfect examples re-
maining are of the greatest beauty, both in design and execution.
The shores of Asia Minor, in the reign of Medon, the son of Codrus, were taken pos-
session of by a number of Greeks, who commenced their migration about a thousand years
before Christ; after they had passed from Attica, they first mixed with the inhabitants of
Caria and the Leleges. Helen the son of Deucalion, who reigned in Phthia, situated be-
tween the rivers Peneus and Asopus, having left his kingdom to his eldest son, the others
sought for settlements elsewhere: Dorus established himself in the neighbourhood of
Parnassus and Xuthus in Attica, where he married the daughter of Erechtheus, the sove-
reign of Athens, and had by her two sons Achæus and Io.
Io with a number of followers from Athens went into the Peloponnesus and established
himself at Ægialus, a place on the sea-shore lying between Elis and Sicyonia; here he
married the daughter of Selinuntus, king of that district, at whose death he succeeded to
his dominions; Io built Helice, and called the inhabitants Ionians. Some time after Io
was recalled to Athens to command the troops in a war against the Thracians, over whom
he obtained a victory: the Athenians in consequence designated themselves Ionians. Attica
was divided by Io among four tribes, the Geleontes, the Argades, the Ægicores, and the
Hopletes, the names of his four sons, or according to Strabo, labourers, artisans, priests, and
guards.
When Erechtheus died, Cecrops, his eldest son, succeeded, and Xuthus, his other son,
was driven out of Attica; in the country he afterwards inhabited he built four towns,
Enoe, Marathon, Probalinthus, and Tricorythus, after which he died at Ægialus; his son
Achæus then passed into Laconia and Thessaly, when he recovered his father's dominions;
his two sons Archandar and Architeles went into Argos, where they married two daughters
of Danaus, one of the royal family of Argos. The Lacedæmonians and Egeans were
called after Achæus Achæans, until the return of the Heraclidæ, when they were driven out,
and obliged to flee to Ægialus and into Attica, where the Ionians again received them on
account of their common origin.
At the death of Codrus, his youngest son Nileus embarked with all the Ionians into
Asia, where they occupied eight of the Ionian cities, viz. Miletus, Ephesus, Myus, Teos,
Priene, Lebedos, Erythræ, and Clazomene; the other four founded by the Ionians were
Colophon, Phocæa, Samos, and Chios. The Ionians formed themselves into twelve states,
because, according to Herodotus, they were previously so divided in the Peloponnesus; the
names of the cities from whence they were ejected were Pellene near Sicyon, Ægira and
Ægæ, Bura, Helice, Ægium, Rypæ, Patræ, Pharæ, Olenus, Dyme and Tritæa, the last
being an island.
The inhabitants of Athens who migrated from the Prytaneum were the most noble
51 2
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BOOK II
THEORY AND PRACTICE OF ENGINEERING.
among the Ionians, though all who celebrated the Aplurian festival, from which alone the
Ephesian and Colophonians were excluded, were afterwards called Ionians.
The appellations Doric, Ionic, and Corinthian are derived from Vitruvius: but it ap-
pears doubtful whether these terms were current among the Greeks: that author
asserts that the first is the most ancient; "for Dorus, the son of Hellen, and the nymph
Orseis, built the temple of Juno at Argos of this order when he reigned over the whole c
Achaia and Peloponnesus: that many temples afterwards erected throughout Greece were
of the Doric order, but by command of the Delphic oracle in a general assembly of the
different states of Greece, thirteen colonies were sent into Asia, who built the cities
before mentioned, and erected temples; among the first they dedicated was one to Apollo
Panionios, having Doric proportions, and another to Diana, in which some variations was
made. The first was of a masculine proportion, the other feminine, and the latter was the
invention of the Ionian settlers, and afterwards called from them Ionic.
But if it be difficult to trace the Ionic order to its origin, we may analyse its proportions,
and compare them with that order which prevailed so universally in Greece, which will
lead us to remark that a very great change took place when the rules that guided the
Doric builders were laid aside: at no other period were such material alterations made in
the proportions of the masses, the columns, entablatures, and intercolumniations; to the
Corinthian, so universally used in later times by the Romans, the feminine proportions
were applied which are stated by Vitruvius to have commenced with the Ionians.
There is of course much fable in all the accounts that have reached us upon these impor-
tant changes, but among them is one which seems to carry with it some semblance of truth,
and which is as follows:- "when Hermogenes was employed to erect the temple of
Bacchus at Teos, according to Vitruvius, the marble was prepared for one in the Doric
style; but the architect changed his mind, from the idea that other proportions, afterwards
called Ionic, were more suitable for the purpose, almost inducing the inference that Hermo-
genes was the inventor of those delicate proportions; he appears unquestionably to have dis-
played great skill and ingenuity in all his designs, and to have entertained the opinion that
sacred buildings should not be constructed with Doric proportions, as they obliged the
adoption of false and incongruous arrangements."
To obtain more delicate proportions, without sacrificing the great principle of making the
weight supported equal to its supports, would seem at first difficult: in the example of
the Doric order we have seen this practice universally adopted, and it is equally evident
in the Ionic, though not exactly after the same method; the columns and their entablatures,
or what they carry, agree in quantity, but their distribution is different.
The square or
figure which bounds the Ionic façade is divided into four parts, one of which is given to the
entablature, a second to the columns, and the other two, or one half, are distributed among
the intercolumniations.
In the quantity of material for constructing the two varieties of temples there is a con-
siderable difference, the Doric requiring one-third more than the Ionic; for example, in a
Doric tetrastyle portico where the area was 12, four parts would be given to the entablature,
four to the columns, and four to the intercolumniations. In the Ionic three parts would be
required for the entablatures, and three for the columns, six being allowed for the inter-
columniations; thus one temple would have eight, and the other six parts solid out of
twelve, consequently, with a given quantity of materials, two very different porticoes
might be built, without making any change in the proportions which the columns
bear to their entablatures. Hermogenes could construct with the same material a much
larger temple in the Ionic style than in the Doric; and supposing the dimensions already
decided upon, there would be a saving of labour and material: from the imperfect
state of the Ionic temples remaining, it is scarcely possible to enter into a thorough exami-
nation of their proportions; that on the Ilissus at Athens, measured by Stuart, no longer
exists, but its dimensions, given by that very accurate delineator, may serve our purpose
as an example of a tetrastyle portico. Its entire width was 18 feet 7 inches, and height
to the top of the level cornice in front 18 feet 4 inches, to which must be added that of
the tympanum of the pediment: multiplying the width by the height of the entablature and
half the pediment, which together is 5 feet 7 inches and 10 parts, we have for the area of
the portions supported 105 feet 4 inches and 9 parts: the quantity contained in the four
columns is found by multiplying their united diameters, 7 feet 1 inch and 7 parts, with
their height, 14 feet 9 inches and 4 parts, giving a product of 105 feet 4 inches and 9 parts
as their area. The united intercolumniations in this example are 11 feet 6 inches and 2
parts, which multiplied by the height of the columns is 170 feet 1 inch and 9 parts for the
area; 40 feet 7 inches and 9 parts less than it would have been had it equalled the quantity
contained in the columns and their entablature, or been one-half the entire area of the façade.
The portico of this elegant example of Ionic was nearly a square without the pediment,
and the supports and supported are in exact accordance as to quantity, whilst the inter-
columniations are about 12 times the quantity contained in the columns, instead of
double. Departing a little from the proportions before us, let us endeavour to set out a
CHAP. XXXI.
1589
PRINCIPLES OF PROPORTION
:

Fig. 2981.
IONIC TETRASTYLE temples.
portico, as already done for the Doric order, having the same number of columns, and like
the tetrastyle eustyle of Vitruvius, divide each side of the square which circumscribes it
into 11 parts, premising that the pediment rises a ninth and one side of the square passes
through its centre. The side of the square being divided into 11 parts, 1 is given to the
diameter of the columns, 3 parts to the middle intercolumniation, and 2 to each of the
others; thus the sites for the columns are obtained: dividing the upright sides of the
square into the same number of parts, 8 are given to the height of the column, and the
remaining 3 to the entablature and half pediment.
Multiplying 11 by the same, we have for the entire area 132, which if divided into 4 is
33 and a fraction for the columns, the same for the entablatures, and double that for
the intercolumniations: the columns being four in number and 8 diameters in height,
their area will be 34 parts; the intercolumniations being 7 in their united width, that
multiplied by 81, their height, gives 633 for their area, and the entablature, being 3 high
and 11 in width, we have for its contents 341 parts, giving a result of nearly a fourth
for the entablature as well as for the columns, and a half for the intercolumniations. By
making some allowance for the diminution of the columns, an exact agreement between
the quantities might be obtained; those in the intercolumniations would then be found
equal to those in the entablature and its supports, or half the entire square devoted to solid
and the other half to voids: had the columns of the temple on the Ilissus been about 1 inch less
in diameter, its proportions would have been in close accordance with those of the figure,
where the 4 columns occupy 38 squares, the entablature the same number, and the inter-
columniations 76.
Ionic Hexastyle. Temple of Erechtheus at Athens.—This highly-enriched example, executed
in the finest marble, is in height without the pediment 26 feet 63 inches, and in width,
measured along the front of the corona, 40 feet 6 inches, so that this portion is comprised
within a square and a half or nearly so the lower diameter of the columns is 2 feet 38
inches, and the upper 1 foot 11 inches, giving a mean of 2 feet 1 inches; their collected
diameters are 12 feet 9 inches, whilst that of the intercolumniations at the same level is 23
feet 1 inches, nearly double the space occupied by the columns. The height of the en-
tablature without the pediment is 4 feet 11 inches, and its superficial content on the face
190 feet, and adding 85 feet for the area of the tympanum, we have altogether 275 feet,
513
1590
Book II.
THEORY AND PRACTICE OF ENGINEERING.

Fig 2982
IONIC HExaStyle TEMPLES.
supposing the tympanum to rise a ninth of its base; the height of the columns is 21 feet
7½ inches, and their united mean diameter 12 feet 9 inches, which being multiplied together
produce 275 feet 8 inches, or nearly equivalent to the area of the mass they support. To
obtain the exact quantity of mass and void, the mean diameters of the columns as well
as of the intercolumniations should be taken; the greater the probable delicacy of ex-
ecution, the greater is the necessity for the architect to balance his quantities exactly. In
the subject now under consideration the whole is comprised within a square and a half; the
supports and the entablature are equal, and the intercolumniations as much as the two to-
gether or one-half the whole. The height of the architrave is 2 feet 11 inches; that
of the frieze 1 foot 11 inches, and the level part of the cornice 10.5 inches.
45
Roman Tetrastyle. Ionic Temple of Fortuna Virilis.-The width is 33 feet 6 inches, and
height, including half the pediment, 37 feet 1 inch, comprising an area of 1242 feet 4 inches,
one quarter of which, 313 feet 1 inch, nearly agrees with the quantity contained in the
entablature as well as in the columns which support it; their height is 27 feet, and their
united diameters 12 feet 4 inches, which multiplied together produce 333 feet for the area of
the supports. The height of the entablature with half the pediment is 10 feet 1 inch this
multiplied by its width, 33 feet 6 inches, gives 337 feet 10 inches for the area of that supported:
the intercolumniations are together 21 feet 2 inches, which multiplied by their height, 27 feet,
gives 571 feet 6 inches for their area, about 100 feet less than the quantity comprised in
the columns and entablature.
:
Without the pediment this façade is nearly square; its proportions rank very high in
the estimation of all admirers of Roman architecture; it has, however, undergone many re-
parations before the stucco was put upon the columns; they were lighter, as was the entab-
lature, the upper members of the cornice being somewhat heavier than is usual in the
early examples of this order; if divested of these additions, and giving a trifle more to the
intercolumniations, we shall obtain half the area for the columns, and a quarter for each of
the other divisions; at present the columns equal in quantity the mass they carry.
If it be required to draw a tetrastyle portico in exact accordance with the rules laid
down, after forming the square each side should be divided into 12 parts, or 144 squares,
arranged like those of an abacus: one of these divisions on the base would become the dia-
meter of the column, and nine their height, the other eight on the base would be devoted to
the intercolumniations, and the upper three of the height to the entablature. The columns, 9
diameters in height, would thus comprise 36 squares, the intercolumniations 72, and the
entablature and half pediment 36; consequently the columns and entablature would be
equal in quantity, and the intercolumniations half the whole, or equal to the contents of
the supports and supported.
Roman Hexastyle. Corinthian, Maison Carrée at Nismes. This beautiful temple has
undergone several restorations; its entire width and height to the apex of the pediment is
43 feet 8 inches, from whence it has derived its name. The height of the columns, includ-
CHAP. XXXI.
1591
PRINCIPLES OF PROPORTION.
ing base and capital, is 29 feet 6 inches, that of the entablature 6 feet 9 inches, and of the
pediment 7 feet 5 inches; taking away half the height of the pediment, we have 39 feet
11 inches and 6 parts, which may be considered as 40 feet; this multiplied by the width
produces for the entire area 1746 feet 8 inches. The superficial content of pediment and
entablature, 456 feet 8 inches, is obtained by multiplying the entire width by 10 feet 51
inches, the height of the entablature and half the pediment, which superficies is only 20 feet
2 inches more than a quarter of the whole. The united diameter of the six columns is
17 feet 6 inches, and that of the intercolumniations 26 feet 2 inches, so that they are in
the proportions to each other of 2 and 3, the whole being 5, one having an area of
515 feet 9 inches, the other 772 feet; when added together they are nearly three times the
area of the part supported.
The proportion between the columns and intercolumniations of the temple at Assissi is
also similar, the height of the columns is 32 feet 10 inches, and the total width of the six
52 feet, which dimensions multiplied together produce 1707 feet 4 inches, one-fifth being
341 feet 6 inches nearly.
The area of the columns is 684 feet, and that of the intercolumniations 1023 feet 4 inches,
giving a proportion of two-fifths and three-fifths. The entablature, pediment, and pedestals
upon which the columns are placed seem to have undergone a change since their erection.
If the whole extent of an hexastyle portico be divided into 18 parts, and one be called the
diameter, to obtain the same proportions as those laid down for a tetrastyle portico, the height
up to the centre of the pediment must include 12 only of those parts, which would give a
portico of a square and a half, comprising 216 squares; the 6 columns, each 9 diameters
in height, would require 54; the 5 intercolumniations, double that number, or 108, and the
entablature and half pediment 54.
Roman Octastyle. The Pantheon at Rome, which has a portico of 8 columns, is one of
the best examples that can be selected for examination. The total width is 109 feet 10
inches; the diameters of the eight columns 39 feet 5 inches, and the seven intercolumnia-
tions 70 feet 5 inches, or nearly in the proportion of 1 to 2. The height of the columns is
46 feet 5 inches, and that of the entablature and half pediment 23 feet 2 inches, together
69 feet 7 inches, nearly a square and a half, the area of which is 7647 feet 2 inches.

Fig. 2983.
OCTASTYLE PORTICO of the PantheonN,
The united diameter of the columns, 39 feet 5 inches, multiplied by their height, gives
1829 feet 7 inches, and the collected intercolumniations multiplied by the same height will
be 3268 feet 6 inches: multiplying 109 feet 10 inches by 23 feet 2 inches, we obtain for
the area of the entablature and pediment 2549 feet, which, rejecting parts of an inch, will,
when added to the two other calculations, make up a sum agreeing with the entire area.
The supported is
The area of columns
Feet.
2549
1829.7
3268.6
}
5098
Together
7647
of intercolumniations
1592
Book II.
THEORY AND PRACTICE OF ENGINEERING.
A line drawn through the centre of the pediment, another at half the height of
the columns, and a third under the entablature, would divide the height into three
equal portions, proving that, in this example, the Romans made the part supported one-
third of the whole, and divided the other two between the columns and their intercolumni-
ations. The shaft of each column is cut out of a single block of granite; they are not
sufficiently delicate to be exactly in the proportion of half the quantity contained in the
intercolumniations; but if allowance be made for their diminution, the difference is not
very great. The whole width being 109 feet 10 inches, the third, 36 feet 7 inches and 4
parts, is nearly a mean between the collected diameters of the top and bottom of the shaft,
making the intercolumniations double the quantity contained in the supports, or equal to
that of the supports added to the mass they carry.
The whole would then be divided into
four, as in the previous examples of the Ionic, and two portions given to the intercolumniations.
The Pantheon Portico is a double square without the pediment, or nearly so, the length
of the level cornice, which crowns the entablature, being double the height of the order:
this, no doubt, was the outline of the proportions before the heavy pediment was placed
upon it, which in all probability was heightened beyond the ordinary rise of a ninth, for
the purpose of concealing the wall behind it. The Roman proportions are frequently
made independently of the pediment; the tetrastyle porticoes are a square, the hexastyle a
square and a half, and the octastyle, as in this instance, a double square without it.
To set out an octastyle portico, in which half the pediment should be comprised within
the double square, after dividing the width into 24 and the height into 12, which multi-
plied produce 288 squares, 72 are given to the column, the same to the entablature and
half pediment, and double that, or 144, to the intercolumnations, or proportions similar to
those laid down for the tetrastyle and hexastyle porticoes. The columns in such a case
would be nine diameters in height, the entablature and half pediment three: supposing the
latter to rise a ninth of the span, the remainder would be distributed among architrave,
frieze, and cornice.
We have endeavoured to show the proportions required in a tetrastyle, hexastyle, and
octastyle portico among the Dorians, the Ionians, and their followers the Romans: the
square and a half, or the double square, were the outlines or boundary figures from whence
the other proportions were deduced.
The great difference of character in the Doric and Ionic designs arises from the distance
at which the columns are placed, which affects the proportions of the entablature laid
upon them, as well as that of the columns themselves; where these are six diameters in
height or consist of six cubes, they are made to carry the same quantity, whatever may be
their distance apart, and where drawn out to nine diameters, they have only their own
weight to support; but the form given to this weight, or the proportions of architrave, frieze,
and cornice, vary, as the intercolumniations are of one or more diameters.
It has been too generally considered that the orders derived their proportions from the
lower diameter of the columns, without reference to their application: this has produced a
variety of design, but at the same time occasioned a great departure from the true principles,
and led to very important errors. The Tuscan, the Doric, the Ionic, the Corinthian, and
Composite orders have been laid down in modules or measures of various kinds, which the
young architect has adopted as mere isolations, regardless of the many other considerations
which have stamped beauty on his model; hence we have imitations, but soul is wanting.
The Doric order is treated of as so many diameters in height according to its age, and the
entablature is said to be heavy or light, as it was of early or late execution; the other
orders have been chronicled in a similar manner, and architecture has been fettered, and its
great principles lost, or at least neglected: it is true that the outline which bounds the
figure has undergone but few changes, but the subordinate parts or the filling-in are sus-
ceptible of interminable variety. An object inscribed within a circle is perhaps the
most easily compassed by the eye, next that within the square, and when a building
is vast, and distance is necessary to comprise a view of the whole, the double square;
beyond this the ancients seem seldom to have gone for the proportions of their façades, or
of a portico intended to be seen in front. After the masses were proportioned, their de-
corations were more various than the buildings themselves; no two are perfectly alike,
but the great difference is in their ornaments and enrichments, or in the number of diameters
contained in the height of the columns.
The Parthenon and Pantheon porticoes are both octastyle, each admitted to be as beau-
tiful as they can be—one the perfection of sober grandeur, the other of cheerful lightness;
one Greek Doric, the other Corinthian, both comprised within a double square, and having
their columns equal in quantity to the mass of entablature they support: where, then, is the
difference between the two examples? It results, as we have already seen, from the mate-
rial in the one occupying two-thirds, and in the other only half the entire area. In
the façade of the Parthenon the eye has one-third void only to contrast with the solid
matter, and in the Pantheon half, which proportions seem to have been established by the
Ionians, and usually adopted by the Romans.
CHAP. XXXI.
1 593
PRINCIPLES OF PROPORTION.
In proportioning the architrave, frieze, and cornice, care must be taken that no more
is laid upon the columns than their own bulk: when the latter are one diameter apart,
this quantity will be greater in height than when they are further distant; so that
the greater the intercolumniation, the lighter in appearance will be the entablature, the
columns still bearing the same weight, nor need they be increased after it is ascertained
that they are competent to their duty: to do so would be to employ material in excess,
which it should be the aim of an architect to avoid.
If we now examine the portico of the Pantheon, we cannot fail to perceive the agreement
existing between the parts supported and their supports.
The mean diameter of the columns is
Their height, including capital and base
The solid content of each
Consequently the cube of the whole 8 is
The mean width of the architrave and frieze is
Their height
The solid contents of the entire length, 110 feet, is
-
ft.
· 4
in.
7
- 46
5
76.5
10.6
6027
0
ft.
in.
4
3
6
8.3
3125
11
0
The mean width of the cornice is 7 feet, length 114 feet, height 3.6 feet, 2793
and its cubical contents
The solid content of entablature 5918 11
which leaves little more than 100 cubical feet of difference between one and the other;
and if the crown moulding returned on the flank be comprised, the quantity contained in
the entablature would equal that of the eight columns.
The pediment is omitted altogether in this calculation, it being in reality, though not
in appearance, an additional load for the eight columns beyond their regular entablature,
which is of marble, and weighs probably 452 tons; the granite columns with their marble
bases and capitals are something more than that quantity, and these, including the entabla-
ture and pediment, probably contain upwards of 1000 tons of material.
The Capitals of the Columns of the Pantheon are admitted to rank among the best examples
found in Rome: though not so highly and elaborately worked as those which decorate the
columns of the temple of Jupiter Stator, yet they are remarkable for the elegant

Fig. 2184.
CAPITALS or ter PANTHEON
1594
Book 11
THEORY AND PRACTICE OF ENGINEERING.
arrangement of the ornaments: further details will be found in the Architectural Antiquities
of Rome, whence this has been selected.

Fig. 2935.
Fig. 2986.
Fig. 2987.
ས་
クリリ
​CAPITALS OF PANTHEON.
Fig. 2988.
Fig. 2989.
Although the Romans did not improve the arts which the Greeks had spread among
them, by the introduction of the arch they materially altered the character of the archi-
tecture practised before the time of the Republic: this feature alone produced entirely
CHAP. XXXI.
1595
PRINCIPLES OF PROPORTION.
different construction, and the several changes it has since undergone in form have served
to establish a variety of styles, as we shall afterwards find.
Sewers, aqueducts, bridges, theatres, amphitheatres, baths and triumphal arches, all
exhibit the arch in its most useful application, and as did the halls of the baths vaulting
of stupendous span; the dome of the Pantheon being 142 feet 6 inches in diameter in-
ternally, covered by a hemispherical dome.
Symmetry, as understood by Vitruvius, seems to relate more to the proportions of the
façade than to those of the detail; but he doubtless intended it to be understood that

--------------
-----------
Fig. 2990.
ARCH OF polipheLE.
perfect harmony should subsist between them as well as between each particular member,
however subordinate; as in the well-formed human figure, all the limbs being in due pro-
portion, the whole when combined produces true symmetry: and the same author insists very
strenuously on a careful study of the rules upon which this is founded, proving that the
effect desired cannot be produced by a mere effort of fancy, or what is commonly called
taste.
1596
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
A building, though entirely devoid of ornament, may be rendered beautiful by the
justness of its proportion, and the richest edifice wanting in this never can excite admira-
tior façades having but height and breadth, these two dimensions must be equal to each
other, if we adopt the symmetrical proportions prescribed by Vitruvius, for he observes
"the square includes the human figure either lying down or standing in an erect posture,
the arms being stretched out." Temples, triumphal arches, and other buildings left us by
the Greeks and Romans were decidedly designed upon this principle, as were most of the
façades of the religious structures erected since the fall of the Roman empire.
In the "Songe de Poliphele," originally published in Italian by Aldus in the year 1499,
are some observations on setting out a façade, which convey some idea of the principles
adopted for the formation of a perfect and harmonious design on the revival of Roman
architecture.
"Draw a square figure, divided by three perpendicular and three horizontal lines, at
equal distances from each other, forming sixteen squares; on the top of the square add a
half square, which, similarly divided, makes altogether twenty-four squares: in the lower
square draw two diagonals, crossing eight squares in the same manner; then form a lozenge
above the great square, tracing within it four lines on the four principal points that separate
the four sides of the void."
After understanding this figure, I thought within myself what can modern architects do,
who esteem themselves so learned without letters or principles? They neither know rules
nor dimensions, and therefore corrupt and deform all sorts of buildings, both public and
private, despising nature, who teaches them to do well if they would imitate her:
good workmen, besides their science, may enrich their work either by adding to or diminishing
therefrom, the better to please the eye, but the mass should remain entire, with which all
should be made to harmonise. By the mass is understood the body of the edifice, which,
without any ornament, shows the knowledge and spirit of the master, for it is easy to
embellish after any invention; the distribution and arrangement of the parts is also a matter
of consideration; hence we may conclude that any workmen or their apprentices know
how to ornament a work, but to invent lies only in the heads of the wise.
Taking from the square and a half, the lozenge and the diagonal lines leaves the three
perpendicular and the three horizontal, except that in the middle, which terminates in the
centre of the perpendicular, cutting it into four parts or portions; by this rule will be found
two perfect squares, one above and one below, each containing four small squares, which
form the opening or doorway; now if you take the diagonal of the lower square, it will show
you what thickness must be given to the centre of the portico; if you carry it straight, the
line will serve to denote the architrave: and the point of the centre of the upper square
will show you the centre of the arch or curve to be given to the door; turning a semicircle
it will rest on the transverse line, which cuts the square and a half into two equal parts; but
if done by any other means I do not esteem it perfect. This method was invented by an-
cient and expert masons, and observed in their arches and vaults, to give them both grace
and solidity; the pedestal on which the columns rest commences at the level of the pave-
ment by a plinth, and the whole is a foot high, furnished with mouldings; one portion
is divided into architrave, frieze, and cornice, the latter being something more than the
others; that is to say, if the architrave and frieze contained five parts, the cornice should
be six. The whole twenty-four squares form a square and a half; then divide the upper
half into six parts by five horizontal and five perpendicular lines, and draw a line from the
centre of the fifth transverse to the corner of the great perfect square, where the architrave
commences; then draw it perpendicular on the key of the archivolt, and it will show you
the height to be given to the frontispiece above, the extremities of which should unite and
relate to the projection of the cymatium and its mouldings.
General Principles.—It would appear that all the principal Roman triumphal arches with
single openings were a square, either comprising or excluding their attics: that the centre
from whence the archivolt was struck was the centre of the square, or if the façade was
more than a square, as the arch of Trajan at Ancona, then where the two diagonals crossed
the centre was fixed. The width of the opening is generally half the entire extent, some-
times three parts out of seven.
These triumphal arches were generally surmounted by a group of figures, or the car and
horses of the conqueror, accompanied by his companions in arms and the trophies obtained
from the enemy; these, as shown on several medals, appear to be equal in height to } of
the entire edifice upon which they are placed, the attic and entablature representing, and
the columns and pedestals the other; and as the former are nearly equal in their height, it
follows that the horse and his rider, or the car and its triumphant hero, were double the
height of the pedestal on which they were placed, for so we may consider the attic
which contained the inscription, the body of the arch being a perfect square, and in correct
proportion, without the attic. The depths of these arches varied; that of Constantine at
Rome is nearly the same as the width of the great centre opening; many of the
others are less than that proportion; but it seems that the cube was the measure that
CHAP. XXXI.
· 1597
PRINCIPLES OF PROPORTION.

are
bounded the propor-
tions, as shown in fig.
2995. The several
Roman examples se-
lected differ in ar-
rangement, but not
in principle, from the
description given by
Poliphele: take away
the pedestals on which
the columns
placed, and then four
squares in height in-
clude half the tym-
panuin, and eighteen
squares the entire
figure, 6 of which
may be considered as
devoted to the arch,
and the other 12 to
supports: or, if we
comprise the whole
façade in 20 squares,
and abstract the 8
which belong to the
opening between the
pedestals, we have 4
for each pier or sup-
port, and 4 for the en-
tablature, the supported being only the quantity contained in the two supports: resistance
to the arch, or its thrust, requires a different arrangement from that of a portico, but we
nevertheless find definite proportions made use of, and a double quantity given to masses
which have to bear weight as well as resist thrust.
Fig. 2991.
142
ARCH OF AUGOSTUS AT RIMINI.
The Arch of Augustus ut Rimini has the height of its order determined by the length
of the frieze.
The Arch of Augustus at Aosta resembles that of Titus in arrangement; it is a perfect
square comprising the attic.

Fig. 2992.
ARCH OF AUGUSTUS AT AOSTA.
1598
THEORY AND PRACTICE OF ENGINEERING. BOOK IL

The Arch of Sergius at
Pola is a perfect square,
without attic, like that of
Titus.
The Arch of Titus at
Rome, raised by the senate
and Roman people to com..
memorate the conquest of
Judæa, is one of the best
examples of proportion that
remain : built of white
marble, it is a monument
of constructive art, some
of the blocks being 9 feet
square, and 2 feet thick; the
arch is composed of eleven
voussoirs 16 feet deep.
For a detailed account
of its construction and or-
nament the reader is re-
ferred to the "Architectural
Antiquities of Rome
>>
The proportions are a
square, as is the opening
of the archway, up to the
springing; and not a double
square, as described by
Serlio. The pedestals are
in height nearly half the
opening of the archway,
which Palladio observes
was the ordinary proportion
Fig. 2993.
ARCH OF SERGIUS AT POLA.
given by the ancients. The entire length of the upper member of the cornice in this
example is 48 feet, which dimension corresponds with the entire height, almost to a fraction:
the width of the opening is 17 feet 6 inches, a trifle more than one-third of the entire width:
bounding the façade by a parallelogram, excluding the attic, and drawing two diagonals,
we obtain the centre from which the arch is struck, which rule will apply to the other

Fig. 2994.
ARCH OF TITUS AT ROME,
CHAP. XXXI.
1599
PRINCIPLES OF PROPORTION.
triumphal arches with a single opening, though varying materially from the principles
laid down by Poliphele, and adopted by Serlio and other architects at the revival of Italian

architecture. The Arch
of Titus is a square com-
prising its entire façade ;
that of Poliphele a square
up to the under side of
the entablature; conse-
quently, the opening of
the triumphal way is in
width half the height
to the top of the impost
upon which the archivolt
rests, while in the more
ancient the entire aper-
ture without the arch is
a square.
In the Arch of Poli-
phele the entablature and
pediments are nearly
equal in quantity to each
of the piers upon which
they are carried; and the
piers themselves are in
width only one quarter of
the whole breadth of the
façade it will be found,
however, that nearly the
same proportions exist be-
tween supports and sup-
ported in both examples.
The Arch of Augustus
at Susu has a single
arch: proportion a square
to the top of the entabla-
Fig. 2995.
ARCH OF AUGUSTUS AT SUSA.
ture, opening a square to the springing: width divided into four, two given to the opening
and one to each pier, which has a three-quarter column at the angle: attic as high as piers
are wide.
In arches with three openings, as those of Septimus Severus and Constantine, these

Fig. 2996.
ARCH OF SÉPTIMUS EVERUS AT ROME.
1600
Book II.
THEORY AND PRACTICE OF ENGINEERING.
occupy one-half the width, and the piers the other: where the diagonals of the figure
cross is the centre, from which the principal arch is struck.
The Arch of Trajan at Beneventum.― Circle struck from the centre which describes the
archivolt; comprises all within it except the attic: division of width into seven, two for each
pier, three for centre; attic half the height of the order.

Fig. 2997.
ARCH OF TRAJAN AT RENEVENTUM.
In the foregoing examples, we have attempted to show that the beauty which belongs
to form in architecture rests upon one principle based on the laws of nature, and that the
first element in a good design is the proportion of the parts as well as the whole: nothing
has more misled the critics upon this subject, as well as architects themselves, than im-
plicitly following the rules laid down for drawing the orders. In treating upon the
antique, they have frequently been right as far as regards the letter, but essentially wrong
in the spirit. The laws of nature do not vary, nor do our organs of sense or perception,
and what was apparently fit and proper in the opinions of the Greeks is equally so at the
present day in their sculptures we never find a man represented carrying more than his
own weight, and such laws ought to be our guide.
:
After the destruction of the Roman empire, the character impressed upon architecture
by the Greeks was lost: other styles arose in succession, which have been designated as
Byzantine, Romanesque, Lombardic, Saxon, Norman, Saracenic, and Pointed. The five
first retained the semicircular arch, and only differed in the quantity of material em-
ployed: for examples of the three first-mentioned we must refer to a work entitled
"Architecture of the Middle Ages at Pisa," by Edward Cresy and G. L. Taylor, containing
measurements made in 1817, in which is an engraving of the monument of the architect
who executed all the work in the pointed style introduced in the celebrated baptistery,
supposed to have been the work of the twelfth century; the discovery of this monument
satisfactorily proved the date when that building was altered from the original Romanesque
character.
In England the Saxon style prevailed to the time of the Conquest (1066), and the Norman,
which succeeded, varied but little from it. The pointed arch is found as early as 1180;
after which the Lancet style became general, and continued to be used till about 1272; to
this succeeded the decorated or geometric, which was practised till 1326, when the perpen-
dicular style was universally adopted, and continued till the early part of the sixteenth
century, when classic architecture was again revived. Our attention must not, however, be
directed to the decorative portions of either style, but to the construction, from the study of
which some valuable lessons may be deduced.
CHAP. XXXI.
1601
PRINCIPLES OF PROPORTION.
The Saxon manner of Building. A division of the transept of the cathedral at Win-
chester has been selected as the best authenticated example of the style in use previous to
the Norman Conquest. In a paper read before the British Archæological Association at
their second annual congress, held at Winchester in August, 1845, the author gave his
reasons for supposing it to be the work of St. Athelwold, for which the reader is referred to
its "Transactions," recently published.

Arches upon arches enabled the Saxons
to continue their walls to a considerable
height, the openings between the piers being
proportioned as those of the Roman build-
ings in the time of the emperors.
The
plans of the piers differ from those pre-
vious to the introduction of Christianity:
in Britain both the Greek cross and the
circle are applied to them.
At Winchester Cathedral the columns
of the triforium recede within the pier, and
are set round a circle, (fig. 2999.); the
passage in the walls of the clerestory is
shown at the side; in another portion of
the same building is a similar arrangement
in less massive piers. (fig. 3000.)
The Saxon churches were generally di-
vided into three tiers or stories, viz.
viz. a
lower arcade, a triforium, and clere-story
above; and such was the solidity and thick-
ness of the walls, that buttresses were alto-
gether omitted, the outer face of their build-
ings in this particular bearing a closer
resemblance to the Roman than the Nor-
man, although the workmanship was rude,
and the decoration scanty.
The proportions found in Saxon buildings
are the same as in the Roman, which,
without doubt, they took for their models.
The circular temple of the Pantheon at
Rome, 142 feet 6 inches diameter internally,
and 183 feet 8 inches externally, contains
the proportions of two-fifths wall and three-
fifths void; the area of the latter being
15,948 superficial feet, and of the former
26,493 superficial feet; the difference of
these areas giving 10,545 feet for the area
of the walls.
We have already seen that in the Coli-
seum at Rome the points of support are
about one-sixth of the entire area of the
plan; and the proportions of both these
buildings have been adinired for nearly 2000
years, the one vaulted, the other uncovered.
Generally the walls and piers of our
Saxon cathedrals occupy from one-third to
two-fifths of the entire area; in their sections
one-third is devoted to walls and piers, and
the remainder divided between the nave and
side aisles.
The division of the cathedral at Win-
chester exhibits very perfectly
the
Saxon manner of building; the piers that
support the lower arches are 10 feet wide,
and the clear openings between them 12 feet
1 inch. The nave and transepts retain
their original construction; in the former
under the casing executed by William of
Wykeham, and in the latter it is seen in its
full purity. The choir stands over the
crypts built by St. Athelwold, and though
Fig. 2998. WINCHESTER CATHEDRAL,
5 K
1602
BOOR IL
THEORY AND PRACTICE OF ENGINEERING.

GALLERY
OF
CLERE-
STORY.
8-9
3.0
2.0
-8---
2-9
1-5--
1..8 ---->
-2-8
--71
1--5--->
Fig. 2999.
PIER IN NAVE AT WINCHESTEr cathedral.

somewhat changed by the Nor-
mans, it yet retains the di-
mensions given to it by its
celebrated Saxon constructor.
The small piers, one of
which, in the south transept,
is nearly perfect, are set out
with great regularity, and
measure 9 feet 8 inches from
west to east, and 8 feet 2
inches from north to south;
their form is that of the Greek
cross, composed of five cubes,
each 2 feet 7 inches in width,
with large and small columns
placed around them to receive
the mouldings that decorate
the arches: six of these co-
lumns have their centres on
the same circle: it is evident
that the hexagon, or the du-
plication of the equilateral
triangle, was applied, and
that the whole was set
out by one conversant in
geometry, and acquainted
with the proportions of the
cube. The Greek cross, which
defines the solid mass, is con-
tinued through the triforium
and clerestory up to the timber
roof.
Fig. 3000.
PIER AT TRANSEPT AT WINCHESTER CATHEDRAL.
The columns of the triforium, set round the inner circle, are partly cut into
the lateral arms of the Greek cross, but the face of the shafts of the columns are in a line
CHAP. XXXI.
· 1603
PRINCIPLES OF PROPORTION.
with its outer side. The centre of the pier is preserved throughout, and so placed as
always to balance the masses around it equally. The circular shafts at Gloucester
Cathedral, Tewkesbury Abbey Church, and several others, were probably of earlier date
than pillars formed of several shafts; those in the church of Saint Germain des Prez, at
Paris, are delicate examples of the former style.
That aisles, galleries, and passages, belonged to the construction of a Saxon church,
we have sufficient evidence in the accounts left us by contemporary historians; but the
present subject is almost conclusive on this point, there being a preparation for a wall
6 feet 8 inches in thickness, containing the passage 2 feet in width, indicated by the plan
of the pier at fig. 2999. The arrangement of the columns shows that there was no
intention of vaulting the side aisles, for the two which carry the cross springers appear
to have been added some time after the original construction, as were also those in the pier,
fig. 3000.
Athelwold is supposed to have executed the whole of this work before the year 980:
the mouldings throughout are rudely cut, the capitals of the main pillars being the only
portions which are at all enriched by sculpture, and they are very simply carved.
The Norman manner of Building can scarcely be said to differ from the Saxon, though the
masons employed after the Conquest certainly acquired a superior knowledge in their art.
The ornaments which we find in Norman buildings had all been previously used by
the Saxons; hence the difficulty of distinguishing the works of one from the other: where
written authority is not handed down to us, we can only judge by the difference of the
workmanship; it cannot be denied that there were many very able masons among
the Saxons, who were qualified to raise buildings and enrich them with sculptured
ornament.

The finest examples of Norman
work may be seen at Caen and its
neighbourhood, and have been en-
graved from measurements taken by
the late Mr. Pugin.
In England the same style pre-
vailed throughout our religious
structures; there is a great similarity
of arrangement, and little variety of
ornament. The Norman style was
generally adopted after the Conquest,
but that named by the monkish
historians the "Opus Romanum " was
continued in many of our parish
churches, as well as in some larger
buildings. The Norman pillar was
sometimes composed of a cylinder
with four small half columns at-
tached, as at Amiens, which is 7 feet 2
inches diameter.
For the Saracenic or Arabian Styles
we must refer to the beautiful work
recently published by Mr. Owen
Jones, where the decorative parts of
this curious and highly ornamented
architecture are admirably given, and proceed to the description of the principles which
guided the constructors of pointed architecture.
Fig. 3001.
PIER AT AMIENS.
The Lancet Style succeeded the Norman, and we find it well defined in many churches
and cathedrals as early as the year 1180; in it decoration was sparingly introduced,
and throughout every part of the design there was simple uniformity, and a display of
a considerable knowledge of geometry: the heads of the windows and doors were formed of
a pointed arch, constructed upon an equilateral triangle; all the mouldings which sur-
rounded those apertures were delicately formed, and had both capitals and bases; this style
was practised till 1230, when it was followed by another, which by some writers has been
termed
The Early English or the Geometric Style, from the manner in which the several portions
of a building were set out; and we find it adopted generally up to the year 1280.
Salisbury Cathedral, founded by Bishop Richard Poore, in the year 1220, was finished
in 1260. Its plan is that of a Greek or patriarchal cross, the extreme length being 480
feet, that of the great transept from north to south 232 feet, and that of the lesser transept
172 feet: the stone used for the external walls and buttresses was brought from the quar-
ries at Chelmark, which lies about 12 miles distance, westward from the city. The middle
5 x 2
1604
Book II.
THEORY AND PRACTICE OF ENGINEERING.
of the walls is filled in with rubble, and the shafts of the columns are of marble, from the
Purbeck quarries. At the intersection of the nave with the great transept rises a noble
stone tower and octagonal spire, the total height of which is 400 feet; the stone of the
spire is in thickness about 2 feet to the height of 20 feet above the tower, after which it is
only 9 inches in thickness to the summit: this spire, though braced and strengthened
throughout by timbers and ironwork, has declined from the perpendicular 22½ inches;
but since 1681, when the observation was made, there has been no further declination.
The walls, after they were carried up to the floor of the triforium, appear to have beer.
increased by corbelling, as if it had been doubted whether, as originally set out, there would
be sufficient strength to carry the cross springers of the vaulted nave; the total width
is exactly 100 feet. The clear width of the nave, as measured on a level with the triforium,
is 33 feet 3 inches, and that of each side aisle half that dimension, or 16 feet 9 inches ;
had this last been 16 feet 7 inches only, the proportions shown by a section would
have been exactly one-third for walls and two-thirds for voids; after appropriating the
third of the 100 feet to the walls, half the remainder is given to one side, and half
to the other; we also find that each of these dimensions of 16 feet 8 inches is divided
into three, two parts of which are given to the outer wall and buttress, and the other to
the main pillar that divides the nave and side aisles, or nearly so.
The inclination of the arched buttresses is not such as to resist the spreading of the
vault at its base, the knowledge of their use not having then been attained. The height
of the vaulting of the nave from the pavement is 81 feet.
Wells Cathedral has some peculiarities in its construction, particularly in the application of
its arched buttresses: they pitch against a stone corbel inserted below the springing of the

Fig. 3002.
PLAN OF CLERESTORY.
Fig. 3003. PLAN OF TRIYORIUM.
Fig. 3004.
SECTION Of wells CATHEDRAL,
middle vault, and a tangent drawn at the back of the vault and elongated determines the
inclination of the top of the flying buttress: here some improvement is shown upon those
CHAP. XXXI.
1605
PRINCIPLES OF PROPORTION.

at Salisbury. The masonry of the arches is admi-
rably constructed, and the joints all radiate to a com-
mon centre.
The total width of this cathedral from face to face
of the buttress is 86 feet 5 inches, and that of
the nave 31 feet 10 inches, instead of 28 feet 91
inches, as it would have been if a third had been
adopted; the side aisles are also diminished in conse-
quence, being only 13 feet 7 inches in the clear;
they are, however, equal to the buttress, outer
wall, and main pillar added together, the first pro-
jecting 2 feet 8 inches, the second or outer wall
being 6 feet in thickness, and the piers 5 feet diame-
ter; whilst the width of the side aisle measures 13
feet 7 inches, an approximation sufficiently near to
suppose that the proportions of thirds was still adopted
in practice. The nave has been increased at the
expense of the side aisles, and its height is 68 feet
9 inches to the top of the vaulting from the pave-
ment.

Fig. 3005. TRIFORIUM, INSIDE.
Chapter House at
Wells, erected between
the years 1293 and
1302, is an octangular
building of great
beauty. A section
through the but-
tresses shows that
two equilateral tri-
angles crossing each
other have determined
the mass and void,
which are in the pro-
portion of one to two,
or the thickness of the
two walls is equal to
one-third the entire
diameter: the base
line of the triangle,
on which the supports
of the crypt are placed,
clearly indicates this
arrangement. Of the
twelve equilateral tri-
angles comprised in the
parallelogram formed
by uniting the bases
of the two larger, each
outer wall and buttress
Occupy two, or the
two walls and their
buttresses four of the
twelve divisions,
leaving eight for the
space between them.
Fig. 3007.
Fig. 3006. DIVISION OF WELLS cathedral.

CHAPTER-House at wELLS.
5 K 3
1606
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
$
Where it is determined that the walls shall occupy one-third of the section of a building,
no figure is so well calculated for such a distribution as the equilateral triangle; it enables
the architect at once to limit and fix the proportions of his design; hence its universal
application: and the mysterious qualities attached to it by the freemasons no doubt arose
What
from the extraordinary facility it afforded them in setting out their several works.
can be more simple or more beautiful than the distribution of this edifice? Within a circle
a hexagon is set out, the perpendicular sides of which mark the outer faces of the buttresses;
the junctions of the angles, by forming a base to every two sides, produce the two
equilateral triangles, which sub-divided not only enable us to arrange the other portions
The
accurately, but also to measure with the greatest nicety their relative dimensions.
quantities of material employed in construction can be estimated by such means much
more easily than by measuring each portion separately, cubing it, and adding the numerous
dimensions so obtained together; there is decidedly more simplicity in the former than in
the latter system: the area of one triangle being found, we at once know that of all the rest.

美
​Fig. 3008.
CHAPTER-house, wELLS: PLAN.
or of any portion. In the subject before us the distance from the middle of one buttress to
that of the other is 31 feet 6 inches, and the diameter taken through them at this level is
92 feet; omitting the buttresses, the outer side measures 26 feet, and the inner 21 feet
6 inches, the respective radii of the circles which comprise the octangular outer walls and
the void being 38 feet and 31 feet 5 inches. Hence we find that the entire area of the
building without the buttress is
The area of the void
And of the walls or points of support
· 3264 feet.
2176 feet.
1088 feet.
At the level of the crypt, above the outer plinth, we have these regular proportions, two-
thirds void and one-third walls.
The height of the entire building, from the pavement to the top of the parapet, is 72 feet
6 inches, and to the top of the pinnacles 92 feet, the total height being equal to the extreme
diameter taken above the plinth moulding on the outside. The interior of this chapter-
1
CHAF. XXXI.
1607
PRINCIPLES OF PROPORTION.
•
house exhibits the most perfect proportions as well as appropriate decorations; the eight
windows, divided into four days, have their heads filled in with circles set out upon
equilateral triangles; the vaulted stone roof rests partly upon the octangular central pillars,
3 feet in diameter, surrounded by sixteen small columns, one at each angle and another
between; the height of the pillar is 22 feet 8 inches.
Thoroughly to comprehend the expression, as well as use of the various members found
in the architecture of the middle ages, we must trace the progress made in vaulting, and
observe the changes it underwent, from the simple cylindrical to the more complex and
difficult display of fan tracery or conoidal arches. The ridge ribs, or liernes, as they are
termed, in the crypt of the Chapter-house at Wells, pass from the centre of the building to
the middle of each buttress; the diagonals, or croissées, mitre into them as well as into the
formerets or ribs against the outer walls.
In the vaulting of the Chapter-room, we have evidence of greater refinement, and an

BEGO ZETOOD
Fig. 3009.
CHAPTER-HOUSE AT WELLS: SECTION.
improvement in the decoration, by the addition of a number of intermediate ribs
terminating against the octangular one in the middle.
At a later period we find transverse ribs made use of, then others between; but
although the design may seem complicated, yet when laid down the plan will as-
sume the greatest simplicity, as shown in the division representing the groining of the
crypt.
When this system had been carried out to a considerable extent, the fan tracery was
introduced, and although apparently more difficult of execution, it is far more scientific in
its application and arrangement, evincing a higher knowledge of mathematical principles
and geometry, and is another evidence of the gradual progress of the mind towards
perfection in this style of architecture.
5 K 4
1608
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
Westminster Abbey, commenced in the year 1245, is in that style which for many years
prevailed in France: the fine church at St. Denys, near Paris, is exactly similar in all its
detail. The windows are wide, divided by mullions,
and have their heads filled in with plain circles, the
origin of the cusp, or that kind of decoration which
every pointed arch afterwards received. This style,
which succeeded the Lancet, is found throughout
England, and many of the parish churches exhibit
fine examples of it. Stone Church, in Kent, of
which the writer has published an account, may be
cited as one of the best; its ornament shows the
skill and taste that prevailed among the free-
masons at that period, Salisbury, Wells, and York
Cathedrals abound with rich foliage and sculptures
of the highest merit executed at the same time, and
it is wonderful to observe to what a state of perfec-
tion the artists of this country had arrived. The
effects of the chisel of the Pisan school were dis-
played upon marble, but our sculptors worked upon
an inferior material; yet the draperies of their
figures, as seen in the front at Wells, and else-
where, are quite equal to those wrought by
the pupils of Italian masters at the same time.
The circle and its intersections at this period were
alone employed for the plans of piers, sections of
mouldings, and the filling in of windows and
doorways: from them we trace the origin of the
style which immediately succeeded.
The cathedrals of Cologne, Amiens, Beauvais, the
Sainte Chapelle at Paris, and numerous other ex-
amples on the continent, exhibit the same propor-
tions and style with that of Westminster; the lofty
pointed arches, which rest upon the main cluster, are
decorated with numerous small mouldings; the tri-
forium, in some instances glazed, have their pointed
arches filled in with trefoils, cinquefoils, or sexfoils,
and the clerestory, carried up to the very apex of
the vaulting, is similarly adorned. Westminster
Abbey is one of the finest examples of building
executed in the thirteenth century.
Tracery and Geometric Forms.-To comprehend
thoroughly the principles which directed the free-
masons of the middle ages in the execution of
all their works would require far greater illustra-
tion than can be bestowed upon the subject in
the present volume: it must be sufficient if we
point out a few which influenced the design of
some of their best examples, and show that it is a
perfectly erroneous opinion to suppose they were
executed without a thorough knowledge of certain
rules, originating with themselves, and perfected by
a constant study of what was not only useful, but
productive of the best effect. Those who inquire
into this subject must collect the data upon which
an opinion can be formed, for it is scarcely possible,
without positive measurement, to arrive at any con-
clusion upon the matter: the admirer of the Greek,
or the commentator upon Vitruvius, alone can
scarcely hope to be successful: it is true that in
one of the early printed Italian editions of the
valuable author quoted, there are several dia-
grams which seem to point to the subject, but
the student will find only the nucleus around
which the lovers of geometry in the middle ages
arranged their varying and beautiful forms; this is the equilateral triangle, and by
inclosing the plan, section, or elevation of a building within it, the several proportions
can be accurately measured, and if sub-divided into a number, either of the triangles.
would show the proportion it bore to the whole area.

Fig. 3010. WESTMINster abbEY.
CHAP. XXXI.
1609
PRINCIPLES OF PROPORTION.

In one of the tracery heads of
the windows in the cloister at West-
minster, the date of which is about
1348, we have two figures that re-
semble the plans given to clustered
pillars, indicating at once that the
same principles were applied to
the setting out of both windows
and points of support.
When
the circumference of a circle is
divided into twelve equal parts,
the points which divide them form
the termination of four equilateral
triangles, and we have at their
intersections, not only the centres
of the circles that constitute the
filling in, but also the several
mitres and other portions of the
figure.
Fig. 3011.
These rules were evidently ap-
plied to windows, and to tracery of
every description, executed at
the end of the thirteenth and
commencement of the fourteenth
centuries; also to the plans of the
main cluster of pillars in many
cathedrals and churches. For
nearly a century, circles and their
intersections formed the ornamen-
tal portions of every kind of panel
and window head; they were
afterwards blended into other
figures, and apparently set out
upon different principles; but the
hexagon and equilateral triangles
were necessary to produce the flow-
ing lines which succeeded. The
change which took place in design
no doubt arose from the facility
which had been attained by the
practice of this method, and if it
were possible to exhibit each
variety in England alone, there
would be ample evidence of the
inventive power of the freemasons,
and the progressive improvement
in their school for depicting form.
The quatrefoil in fig. 3011. is met
with in the panels of several altar
tombs, in the spandrills of the arches of door-
ways, and it is worthy of observation that
all the mitres, where the figures change their
form, are perfect for each: had these con-
siderations been neglected, we should not
have had the graceful flowing lines found
in these designs: no other triangles crossing
are so universally applicable, or require less
skill in their adoption. The student of the
present day might occupy a life in the col-
lection of these subjects, and they are most
excellent models for the application of the
rules of theoretical geometry to practice.
Fig. 3012.
Windows of three Days or Divisions are
met with, having heads of singular beauty,
inclosed within an equilateral triangle, and
SO numerous are the designs, that it is
rare to meet with two exactly similar. In
CLOISTERS AT WESTMINSTER ABBEY.

CLOISTERS at westminster abBEY.

Fig. 3013.
1610
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
the more simple of three days or lower divisions, the head is occupied by three circles,
each of which contains a trefoil constructed upon the crossing of either three or four equi-
lateral triangles.
A very extraordinary design, composed of intersecting circles, is to be seen at the east
end of the chancel of the church at Sutton, at Hone, in Kent; although much dilapidated,
it still preserves many of its original flowing lines, all struck from the same radius, through
points previously determined by crossing the primitive circle by four equilateral triangles.
At half the height of the head

of the window a horizontal line
may be supposed to be drawn
from one side to the other, on
which are three circles: the two
outer touching, are crossed by
the third, struck from the point
of their junction; with the same
radius several spherical triangles
are struck from the points of
intersections, producing the
lines, which unite and divide
the window head into several
compartments, differing in pat-
tern and dimension. After the
circles were struck, the lines that
did not play into each other
were left out, and those only re-
tained which flowed on grace-
fully; by these nice consider-
ations and just application of
principles, the masons were cer-
tain of producing a perfect ef-
fect, without rigidly adhering to
any particular form.
Fig. 3014.
SECTION AT HONE, KENT.
Windows of four Days or Divisions. — Among the heads of a more simple character
are those which contain one large circle, subdivided by three equilateral triangles, each


Fig. 3015.
Fig. 3016.
inclosing a trefoil. Others contain, in addition to the one great equilateral triangle,
two smaller, constructed upon the points of its base, and dropping into the space comprised
between the heads of the divisions below.
CHAP. XXXI.
1611
PRINCIPLES OF PROPORTION.
Windows of Six Divisions are far more complicated, and, though exhibiting greater skill
in geometry, are set out precisely upon the same principle. The two equilateral triangles
inclosed within the great circle mark out the prominent features of the design, and their
terminations are the centres of as

many spherical triangles, which,
by their crossing, constitute the
elaborate filling in.
In some examples,
above
the two main lower divisions
is a circle divided by several
others, the twelve which are
indicated in the figure serving to
proportion the tracery of this
compartment.
At the latter end of the four-
teenth century, these designs
were so multiplied that almost
every cathedral and church had
its peculiar windows: in Amiens
cathedral, the chapels constructed
at this same time receive their
light from windows, the heads of
which are filled in with tracery
exceedingly varied, but the
general principles of setting out
the work are preserved; the
circle and the equilateral
triangle were subdivided
almost to infinity, and at no
period of the arts do
the inventive facul-
ties appear so fertile as
in that we are now
considering.
The
great west window of
York Cathedral is the
finest example of the
improvement made in
this mode of deco-
ration; the geometric
forms are there so con-
cealed by the blending
of the several curves,
as to produce con-
tinued flowing lines,
which is partly shown
in fig. 3014.: they are,
however, all set out
in the same manner,
and the centres upon
which they are struck
are established by
the crossing of equi-
lateral triangles.
During the epis-
copacy of John Gran-
disson, from the year
1327 to 1369, Exeter
Cathedral was under-
going an entire change
in
its architecture.
Fig. 3018.
Fig. 3017.

To this bishop we are indebted for the great west window, of nine days, and several smaller
of four and five, in which are introduced tracery showing a great variety of design: some
are composed of equilateral triangles, each containing a trefoil, some of circles with six
turns, others have four and three; but the heads of all, varied as they are, belong to the
same school as fig. 3017.
The great east window at Bristol Cathedral is another fine example of nine days;
1612
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
executed about the middle of the fourteenth century; the centre of the head of the window,
or rather the nucleus to the tracery, is an octagon, six sides of which are retained, the other
two being suppressed, to allow of a better combination with the three centre divisions of
the lower part.

Th equilateral triangle also defined
the form and magnitude of the several
mullions, as shown by the d agram,
constructed upon measurement of the
windows of the clerestory of the nave
at Winchester: a line drawn from
the apex of one mullion to the other
is the base of the triangle, and
the space inclosed by the two is
divided into ten other equilateral
triangles, two of which agree in
dimensions and form with each mul-
lion. Of the twelve equilateral tri-
angles embracing two half mullions,
ten are given to the day or space to
admit the light, and two, or one-
sixth of the whole, is comprised by
the mullion; such appears to have
been the manner of proportioning the
parts of windows in the middle ages.
Fig. 3019.
Rose Windows in the West Transept of the Church of St. Ouen at Rouen is 29 feet 6 inches
in diameter, and composed of seven equal circles, one of which occupies the centre: each of
those, which surround it, are again subdivided by others; two only of the outer six are pre-
served in the figure, and form the quatrefoils, whilst the intersections of the others serve as
centres to the rest of the design.

Fig. 3020.
8t. ouen at ROUEN.
Rose Window of the South Transept of the Cathedral at Rouen is 23 feet in diameter,
measured to the centre of the large bead, which comprises the figure. A portion only of
CHAP. XXXI.
1613
PRINCIPLES OF PROPORTION.
this beautiful example is given, for the purpose of exhibiting the principle upon which it is
set out: it will be evident that the nucleus of the design is composed of two equilateral
triangles, and the sides of each continued, constitute the alternate divisions.

Fig. 3021.
8+
哈
​of
Fig. 3022.
て
​ROUEN CATHEDRAL: SOUTH TRANSEPT.
The internal hexagon has its parallel sides prolonged, to mark the position of the four
divisions that have their pointed heads attached to the small circle, which forms the eye of
the pattern; and the length of these prolonged lines is limited to the extent of the sides of
an equilateral triangle, which is again divided regularly, the triangular spaces between
being filled in with trefoils. The small mullions are in width 24 inches, the next size
3 inches, and those which mark out the figure and have a bead for their termination are
4 inches: another bead and bold projecting label, or rim, circumscribe the whole rose window,
the hollow around which is enriched with a curved leaf. On each side of the internal
hexagon an equilateral triangle is constructed, around which a circle is struck, uniting
elegantly with the next, and forming the six turns which characterise the filling in of
1614
Book II.
THEORY AND PRACTICE OF ENGINEERING.
circles at this period; these were the principal decorations after the Lancet style was aban-
noned, and were continued until succeeded by more flowing and varied designs.
Rose Window of the South Transept at Beauvais, 34 feet 4 inches in diameter, is composed
of six large circles and their intersections.
To set out this win-

the
dow the great circle
expressed by the outer
bead is divided into
twelve parts, each
being equal to half the
radius; twelve equi-
lateral triangles are
then inscribed,
points of which touch
each of the divisions,
and where they cross
nearest to the outer
circle, the twelve
pointed arches
arches that
surround the figure
are struck; the other
points of intersection
of the triangles are
centres, from which
the other curves are
drawn. It must at once
be evident, that in a
circle so divided, or by
any other equal num-
ber of equilateral tri-
angles, the portions
contained between the
smaller angles must
be equal to each other;
the six circles around
the centre have their
curves blended into
the outer, and if it be
required to fix centres
for each of these flow-
ing lines, they can only
be obtained by cover-
ing the entire rose
window with lines in
the manner already
described. The radius
being equal to the
side of a hexagon, and
that figure being com-
posed of two equi-
lateral triangles, was
probably the chief
reason of its first pre-
ference over all others;
it certainly affords the
most
extraordinary
powers of combination,
Fig. 3023
BEAUVAIS CATHEDRAL: SOUth transEPT.
and there is carcely a moulding or form in the architecture of this period but is set out
from it. The mullions that bound the divisions are all portions of this figure, as are the
mouldings, which sweep round the arches of the buildings themselves. Nothing can sur-
pass the brilliant effect of these marigold windows when glazed with rich colours, and
exposed to either a rising or setting sun; in the example now described, this effect is still
further heightened by making nearly the whole end of the southern transept a continuation
of the same design, the glass descending almost to the tops of the doors which afford access
to the cathedral. The construction of such works must excite our highest admiration, for
it appears scarcely possible to excel the perfect manner in which the parts are put
together and worked off, the execution being in every particular worthy the design.
CHAP. XXXI.
1615
PRINCIPLES OF PROPORTION.
The Rose Window in the South Transept at Amiens, 29 feet 6 inches in diameter, is set out
upon two squares, which cross each other diagonally.

Fig. 3024.
AMIENS CATHEDRAL : SOUTH TRANSEPT.
Sixteen divisions are employed in this figure, and by crossing as many squares, we arrive
at the method by which it is set out; each side of the square is equal to the radius by
which the master line on the outer bead or circle is struck: where the squares cross each
other are the divisions of the pattern, and their several points are the centres upon which
the pointed arches are struck, which surround the outer portion of the rose.
Where the lines of the squares cross, in the interior of the figure, the smaller divisions
are established, and their points of intersection serve for centres to strike the lesser curves;
to show this clearly the whole must be set out, and drawn to a large scale.
The architecture of France underwent a material change after the thirteenth century;
the heads of the windows were no longer filled with tracery composed of six foils, generally
three in each window, but branched out into a more running pattern, as practised in
several parts of England. The fourteenth century not only exhibits windows of more
difficult design, but an apparent absence of the principles by which the several parts were
proportioned to each other. Before the Perpendicular style appeared, great progress had
been made in the groining of the spacious vaults of the naves, as well as those of the side
aisles. After the fan tracery was substituted in England, the windows had straight
mullions ascending till they intersected the arch; and we have no further display of the
varied figures that everywhere prevailed before: geometry was now exercised upon the
intricacies which their surprising vaults exhibited. It is somewhat singular that we never
find the beauties of a previous era retained, and blended with that which succeeded.
For the 300 years during which the Pointed style continued to flourish, each half century
gave to it a new character; hence we have seldom any difficulty in establishing its date:
all these changes resulted from an improved knowledge in the art of construction. The
lodges of freemasons were gradually approaching the principles which directed the efforts
of the architects of the Byzantine school, and which were found too refined and delicate to
be practised out of Italy after the eleventh century.
1616
Book II.
THEORY AND PRACTICE OF ENGINEERING,
The Rose Window in the Northern Transept of the Church of St. Ouen at Rouen, 28 feet
6 inches in diameter, is an example of the pentagonal setting out.

Fig. 3025.
ST. OUEN AT ROUEN.
:
When the sides of a pentagon are prolonged, they unite and form five isosceles triangles,
each having for its base a side of the original pentagon. The equilateral triangle, the
square, and the pentagon may have been adopted by different confraternities of freemasons;
the first can be formed into hexagons, duodecagons and their multiples; the squares, by
crossing diagonally, into octagons; they may be also tripled and quadrupled the
mitre of the equilateral triangle is in the direction of its centre of gravity, as is that
of the square and the isosceles triangles; consequently to unite the mouldings around
either, the plummet would indicate the direction of the line, when dropped from the
angles and suffered to cross, the point of intersection being the centre of gravity
common to the several lines.
In the chapel of St. Cecile is the monument of Alexander Berneval, the master mason of
the works at St. Ouen, at the time the rose window was executed by his pupil, whom it is
reported he murdered from jealousy: such an application of triangles was then called
the pentalpha.
The foundations of this church were laid by Mardargent, about 1318, by whom it was
built as far as the transept; but probably the rose window of the northern transept was
not inserted till many years after, for the memorial of Berneval bears the date of 1440:
this monumental stone is 8 feet 6 inches in length, and 4 feet in width, and in it is
represented the architect and his pupil, each employed tracing with his compasses his
respective design; these beautiful brasses with their rich tabernacle work were in the
highest state of perfection when the writer was last at Rouen, and around the master figure
was inscribed in German letters: ---
Cy gist Maistre Ulerandre de Berneval, Maistre des oeuvres de Maconnerie du Roy,
notre Sire, du Baillage de Rouen, et de ceste Eglise, qui trespaya, l'an de grace
mil ccccpl. le v jour de Jaunier.
Prie's Dieu pour l'ame de luy.
The date of the pupil's death is not commemorated, which has led some to imagine the
tale of his murder untrue, and that he erected the monument to his master with the
intention of being buried by his side.
CHAP. XXXI.
1617
PRINCIPLES OF PROPORTION.
The North Rose Window at Amiens, 37 feet 8 inches in diameter, is a magnificent example
of the application of the pentagon, with 5 isosceles triangles around it.
This window, probably

executed in the fourteenth
century, has a great resein-
blance to the last described;
the fan tracery, of which
we have early specimens in
the cloisters at Gloucester,
required the same know-
ledge of geometry to perfect
their design. In 1482
Euclid was first printed at
Venice from the Greek
text; but geometry had been
studied in England from the
time that Adhelard, in 1130,
had introduced a transla-
tion of that author from
the Arabic versions which
he met with during his tra-
vels in Spain. In 1256
Campanus of Navarre
translated Euclid, who
seems to have been com-
mented upon by several
eminent writers, and no
doubt it was the text-book
of the freemasons, who dili-
gently applied the problems
it contained to every pur-
pose of their art. In 1486
the Editio Princeps of
Vitruvius appeared, and
the commentaries of Cæsare
Cæsariano followed in
1521; the latter author
published three plates of
the Cathedral at Milan,
covered with equilateral
triangles, which have not
been described so as to be
useful or understood.
The compartments which
Fig. 3026.
AMIENS: Rose window.
have the flat sides of the original pentagon for their base, and parallel sides throughout till
they terminate in the pointed arch, have their mullions proportioned to their opening, the
larger being double the size or the smaller, whilst the latter are equal to half the open space
between them: the mullions in these examples, which divide two spaces, 6 inches in
width, are usually 3 inches in thickness, and the others are in the same proportion. The
next sized mullion is 44 inches, with a bead of 14 inch diameter, which runs round the
whole pattern of the figure, the centre of which may be called the master line, by which
all the rest are set out; the several mullions are all twice as much in depth as in width.
Baptistery of Pisa. — The internal diameter of this circular building is 100 feet, and the
thickness of its outer walls and columns 10 feet 6 inches; its external diameter is 121 feet,
the area of which is 11,499 superficial feet, that of the interior being 7854; if we
deduct from it what is occupied by the four piers and eight columns, or 188 fect, we
have 7666 feet for the void, exactly two-thirds of the entire area. To find these pro-
portions in an edifice commenced about the middle of the twelfth century in Italy, is a
curious corroboration of the opinions already advanced, the same rules as those described
for the Chapter House at Wells being apparently followed: the conical brick dome was the
work of an after period, and may have been the prototype for that of St. Paul's at London;
the pointed architecture belonging to the exterior of this edifice, of the same character as
that which adorns the crosses of Queen Eleanor in England, was added in the fourteenth
century.
The section shows how the equilateral triangle governs the proportions of this celebrated
building; the extreme diameter is the base, and its apex the level on which the
5 L
1618
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
more recent conical and hemispherical domes are placed: the intersection of the two
great triangles fixes the diameter to be given to the internal void, around which the side
aisle, its walls and pillars should be formed. The circle which has its diameter com-
prised between the apex of the two equilaterals determines the clear width between the

BAPTISTERY OF PISA.
Fig. 3027.
outer walls. That the architects of those days delighted in the forms produced by the
several intersections of the circle in combination with the equilateral triangle, we are
assured by viewing the several designs they have left us in mosaic upon the walls of the
Duomo, and at the cathedrals of Florence, Sienna, and elsewhere.
Roslyn Chapel, Scotland, commenced about the year 1446, has its, buttresses well
suited to give aid to the walls, and to enable them to resist the thrust of its nearly semi-
circular vault, which they receive below the springing. The extreme width from face
to face of the buttresses is 48 feet 4 inches; the span of the nave is 15 feet 8 inches,
being 5 inches less than the proportion of a third; the two side aisles together
CHAP. XXXI.
1619
PRINCIPLES OF PROPORTION.


are 15 feet, or within a few
inches of the width of the
nave; consequently the walls
and piers in this beautiful
example are 17 feet 8 inches,
or 15 inches more in extent
than they would have been
if the proportion of one-third
had been adopted. The
height from the pavement
to the under side of vault is
41 feet 10 inches.
After the examples de-
scribed, we cannot doubt of
the great proficiency that had
been made in the application
of the rules of geometry to
architecture; every feature,
whether the simple moulding
or the most elaborate tracery,
was set out either upon the
equilateral triangle, square,
or pentagon, and these regu-
lar figures seem to have been
chosen on account of the
facility by which they are
subdivided. From the in-
troduction of the style each
fifty years that succeeded
brought with them new and
improved principles, and at
the very commencement of
the fourteenth century, we
see the clustered pillar and
Fig. 3030
Fig. 3028.
ROSLYN CHAPEL.
Fig. 3029.

SECTION OF ROSLYN CHAPEL.
5 L 2
1620
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.

its many moulded arches yielding to a
style that combined greater simplicity
with a more thorough knowledge of con-
struction, which will be evident upon an
examination of St. Stephen's Chapel, West-
ininster, (now destroyed,) begun in 1348,
the nave of Canterbury and Winchester
Cathedrals, and several others. In these
examples we have elegantly formed arches
resting on well-proportioned piers, the
mouldings of which so combine that they
form a perfect figure, and show that the
points of support were designed to carry
all that is placed above them; the same
contour of moulding that surrounds the
pier performs its useful part in the upper
portions of the building, constituting one
entire whole. This style, simple as well
as elegant, was executed by masons fully
qualified to advance it to the greatest per-
fection, and deserves both our study and
admiration.
Canterbury Cathedral exhibits every
variety of style found in mediæval
architecture; its history has been
published by Mr. Britton: to that
work, to which the writer contributed
some measurements in 1820, he must
refer for a detailed and elaborate
account of the several changes made
in the decoration of the edifice.
It is only to the pillars of the nave
we are desirous of drawing the at-
tention, and that merely to show their
simple form, and the manner of setting
them out: four squares are so placed that
their diagonals and sides are united in
the centre, thus con-
stituting a form
capable of the great-
est resistance at the
four points of the en-
tire pier, where the
several thrusts and
re-
pressures are
ceived: the OG
mouldings of the
piers run round the
arches, whilst the co-
lumnar mouldings
towards the aisle and
nave support the ribs
of their respective
vaults. Greater sim-
plicity can hardly be
obtained, and every
line and indentation
of the plan has its use
and appropriation :
there is no profusion,
or member for the
sole purpose of deco-
ration; in this ar-
rangement we have
the commencement of
good taste, and the
indication of a more
harmonious and per-
fect style.
Fig. 3031. CANTERBURY CATHEDRAL.

Fig. 3032. CANTERBURY CATHedral.

Fig. 3033.
ST. OUEN AT ROUEN.
CHAP. XXXI.
1621
PRINCIPLES OF PROPORTION.
In the Church at St. Ouen at Rouen, we have a very different arrangement, and
by no means so solid a form.
Winchester Cathedral. — One division of the nave has been selected to show the peculiar
style practised at the latter end of the fourteenth century, and also the skill exhibited in
changing the form of a Saxon edifice, and giving it its present character.
fig.3035., is that of the pillar, as well as
of the mouldings and walls of the tri-
forium and clerestory above. When
William of Wykeham effected the changes
in the nave of this cathedral, he pre-
served all above the arches of the trifo-
rium, cutting away only the masonry of
each division below that level which in-
tervened between the main pillars; he
then caused the whole to be cased with
an ashlar, so that the original Saxon
masonry and proportions of the mass
remain within the casing. The dotted
semicircular arch is the same as that in
fig. 2998., and in the roofs above the
groining the Saxon walls are traceable,—
another proof that when any alteration
was made in a building by our me-
diæval masons, they did not think it
necessary entirely to demolish it.
We
have in this example the decorative
character which belongs to the architec-
ture of the latter end of the fourteenth
century, though somewhat heavy in its
proportions, which arises from the mass
constituting the original fabric being
preserved, or having undergone so little
change. The thickness of these pillars
from north to south is 10 feet 8 inches,
and from east to west 10 feet, whilst the
width of the opening from east to west
is only 14 feet.
If we examine the area of one severy
of the nave, as left by Wykeham, and
calculate the points of support, we shall
see that the proportions are not those
found in the nave at Canterbury, or
in other cotemporary buildings; com-
prising the space between the buttresses,
the entire area of the parallelogram con-
tained between lines drawn through the
middle of the piers from north to south
is 2228 feet; while the points of support
within that area are 557 feet, or one-
quarter of the whole.
On the section, shown at fig. 3036., the
buttresses on the north side project
6 feet; the north wall is 5 feet 6 inches
in thickness, the half piers attached
project internally 2 feet 1 inch; the
north aisle is in width 13 feet 1 inch,
the pier 10 feet 8 inches; the clear
width of the nave 32 feet 5 inches;
the pier 10 feet 8 inches; the south
aisle 13 feet 1 inch, the half-pier which
projects from the south wall 2 feet 1 inch,
and the thickness of the south wall 7 feet
2 inches; there are no buttresses, as the
cloister, now removed, served their pur-
The width from east to west,
pose.
measured from the centres of the piers,
being 22 feet 1 inch, and the width of
The plan,

100101011110111111E
:
Fig. 3034. NAVE of Winchester cathedral.
5 L 3
1622
THEORY AND PRACTICE OF ENGINEERING Book II.

buttresses outside 3 feet 2 inches.
The cathedral or duomo at Pisa
presents a very different result;
the total width of the nave is
113 feet 6 inches, and the width
of a severy 17 feet 1 inch, the
area of which is nearly 1930 feet,
the points of support being only a
twelfth of that quantity on the
plan, and one-sixth as regarded
upon the section. Hence we see
the necessity of ascertaining the
proportions of mass and void in a
building, before we can accurately
judge of its merits as a style, each
having its peculiar quantity, which
marks its character.
The section or rather plan of
the walls, on the level with the
gallery of the triforium, shows
the method adopted to proportion
the openings to the mass. The
thickness of the clerestory walls is
included within the eight equila-
teral triangles, and where their
sides cross, the position of the
mullions is established. In fig.
3019. the circle which comprises
the two that divide the window
into three days shows their pro-
portion and their size, which
.in
this example is one-third
of the opening: in a window
of three days we have six triangles
for space, and three for mullions :
the splays at the sides of these
windows, uniting them with
the faces of the wall, are cut
parallel with the sides of the
several triangles. The main pier
is set out by uniting the bases of
two equilateral triangles with
perpendicular lines, or forming
the whole into the figure of a
hexagon. By a comparison of
this plan with that of fig. 2999.,
the additions made by William of
Wykeham to the original Saxon
pillar will be readily perceived.
AA
XX
19 ft. 1 in.
The width of one of the di-
visions of the nave at Winehester,
measured from the centres of the
piers from west to east, is 22 feet
1 inch, and the same dimension
taken in the nave at Canterbury
is 20 feet only. In the former
example the opening between the
piers is 12 feet 1 inch, and in the
latter 14 feet; there is conse-
quently no comparison, with re-
gard to lightness, in these two
works of the same period; the
pier being comprised 23 times in the entire division at Winchester, and 3 times at Can-
terbury, or on the pavement the plinths around the base seem to fall within one-third of the
entire width. It would almost appear that in setting out the pillars of several cathedrals,
the same system was practised as shown for the mullions of windows at fig. 3019.: but the
plinths, and not the cluster of columns and mouldings, must be regarded as occupying the
third. Bath Abbey church is 20 feet 2 inches from centre to centre of pier from east to
Fig. 3035. PIER, AND WINDOWS OF CLERESTORY.
CHAP. XXXI.
1623
PRINCIPLES OF PROPORTION.
west, and the clear width between the plinths about two-thirds of that dimension, and this
is the case with many examples.
The Section through the Nave of Winchester Cathedral is highly deserving of our attention:
the clear width of the side aisles is 13 feet 1 inch, and that of the nave 32 feet 5 inches; the
clear width of the building between the outer walls is 80 feet, the thickness of the walls
16 feet 10 inches, the projection of the buttress 6 feet, and the thickness of the piers 10
feet 8 inches, making for the entire width from north to south 102 feet 8 inches.
The width between the walls forms the base of an equilateral triangle, the apex of which
determines the height of the vaulting of the nave; a semicircle struck upon this base, with
a radius of 52 feet, determines the intrados of the arches of the flying buttresses on each side,
which are admirably placed to resist the thrust opposed to them.
On this section we have endeavoured to apply the principles of Cæsare Cesariano, before
referred to, to the measurement of mass and void by a method far more simple than that
usually adopted.
By covering the design with equilateral triangles we see the number occupied by the
solids, and can draw a comparison with those that cover the voids to prevent confusion in
the diagram a portion only of three of the triangles has been subdivided, to show with what
facility the quantities of the entire figure might be measured, if the several large equi-
laterals were subdivided throughout in a similar manner. The band which extends

Fig. 3036.
SECTION OF WINCHESter cathedral.
from the face of the outer buttress to the centre of the section contains 36 small equilateral
triangles, six of which cover the pier; consequently it occupies on the section one-sixth of
that quantity; no further calculation is requisite to find the proportion it bears to the
whole in like manner the other parts of the section may be compared. Such was the use
of equilateral triangles in the middle ages for ascertaining quantity.
The two equilateral triangles which occupy the nave and a portion of the piers are
comprised within the figure called a Vesica Piscis; if the horizontal line drawn at half the
height, uniting the base of the upper and lower triangles, be taken as a radius, and its
extremities as centres, it will be evident that parts of circles may be struck, comprising the
two triangles within them. Euclid has shown that a perpendicular may be raised or let fall
from a given line by a similar method, the space between the segments being called afterwards
a nimbus; and there can be no doubt that from time immemorial all builders have used
it: the bee adopts for its honied cell a figure composed of six equilateral triangles, and
this is proved to be the most economical method of construction; the sides of each hexagon
are all common to two cells, and no space is lost by their junction. The nearer the
boundary line of a figure approaches the circle, the more it will contain in proportion to it,
5 L 4
1624
Book II.
TIIEORY AND PRACTICE OF ENGINEERING.
but circles could not be placed above and under each other, or side by side, without
interstices occurring, and the equilateral triangle, or a figure compounded of it, is the only
form that will admit of it being so arranged.
The interior and exterior division of the choir at Winchester exhibits two styles; the
latter is a fine example of the decorated elegance to which architecture had arrived at the
commencement of the sixteenth century.

X
HI
Fig. 3007,
WINCHESTER CATHEDRAL: CHOIR,
Fig. 3038.
CHAP XXXI.
1625
PRINCIPLES OF PROPORTION.
King's College Chapel, Cambridge, has no side aisles, but in lieu of them are small
chapels between the buttresses, which are not interrupted in their depth, their whole
strength being requisite to maintain in

equilibrio the highly wrought stone
vault; this they have hitherto perfectly
done, to the admiration of all who have
studied its principles of construction.
The chapel is divided in its length
into twelve equal divisions or severies,
each of which is formed of four quad-
rants of a concave parabolic conoid
standing on their apex, and is bounded
by a main rib or arch of masonry
which has its abutments secured by the
weighty buttresses added to the outer
walls. The width of each severy from
centre to centre is 24 feet, the thickness
of the buttresses being 3 feet 7 inches,
and the length of the chapel between
them 20 feet 6 inches; their depth is
13 feet 6 inches in the clear.
The transverse section shows more
particularly the proportion of mass and
void, which are here equal: the total ex-
tent or width from the face of one but-
tress to that of the other is 84 feet,
and the clear width 42 feet; the height
from the pavement to the top of the
stone vault is 80 feet 1 inch, though this
varies from the pavement being out of the
level; the thickness of the walls at top
is 5 feet 7 inches; in it is a gallery
2 feet 1 inch wide, and 7 feet high, com-
municating entirely around the building.
The height of the cluster column,
whose capital receives the points of the
inverted cones, is 59 feet 3 inches, so
that the arch, which is struck from four
centres, does not rise more than 18
feet 6 inches, and the intersections take
place at one quarter of the span when
the height is 15 feet 6 inches: this arch
or stone rib is 2 feet in depth and 18
inches in breadth, formed of twelve vous-
soirs on each side, the joints radiating
to the centres respectively; it abuts
at its extremities against the ponderous
buttresses, and remains steadfast and
immovable, dividing, as before stated,
the vault into several severies.
The plan of the main piers shows that
there has been no after-thought grafted
upon the original design, which, in all
probability, was commenced soon after
the year 1446, as we find that a stone
quarry at Haselwode, and another at
Huddlestone, in Yorkshire, were granted,
for the works to be carried on here. The
stone roof does not appear to have been
commenced till about 1512, the inden-
ture concerning it bearing date the fourth
Fig. 3039. KING'S COLLEGE CHAPEL.
year of King Henry VIII.; in this document Thomas Larke is called the " surveyor,"
John Wastell the "master mason," and Henry Semerk one of the "wardens," the two
latter agreeing to set up a sufficient vawte, according to a plat signed; the stone to be from the
Weldon quarries: the contracting parties were also to provide "lyme, scaffoldyng, cinctores,
moles, ordinaunces," and "every other thyng required for the same vawting: the timbers
1626
BOOK IL
THEORY AND PRACTICE OF ENGINEERING.
of two severies of the "great scaffolding" were given them for the removal of the whole;
and they were to have the uses of all "gynnes, whels, cables, hobynatts, saws, &c. ;" they
were to pay for the stone, and to have 1007. for each severy, or 1200% for the whole, money
being advanced for wages as the works proceeded: the "chare roff," as the vault is called,
was to be sufficiently buttressed, and the whole performed in a perfect manner.

Fig. 3C40.
SECTION OF king's college chapel.
The extreme width, measured from the face of one buttress to that of the other, is
84 feet, and from north to south, from the centre of one pier to that of the other, 24
feet; thus the area comprised in a severy, or space between two lines drawn through the centres
of the buttresses on the plan, is 2016 feet, exactly double the area of one of the severies of
St. George's Chapel, Windsor: the extreme width is the same, but the difference arises
from the divisions in the one being double that of the other, as ineasured from east to
west.
The area of the nave, 42 × 24
of the chapel on one side
ditto
on the other
of the walls on one side
ditto on the other
Feet.
1008
336
336
168
168
Hence we have for the areas of the space or void on the plan 1680 feet, and for the walls
and pier 336 feet, or one-sixth of the whole 2016 feet, similar proportions to those which we
CHAP. XXXI.
1627
PRINCIPLES OF PROPORTION.
ļ
shall afterwards find in St. George's
Chapel, Windsor. In King's College
the nave comprises half the entire
area of a severy, and the remaining
half is divided into three, one of
which is given to each of the chapels,
and the other divided between the
points of support: in this beautiful
building, with its majestically con-
trived roof of stone, the lightest
construction is adopted. The cate-
narian curve exhibits the direction of
the thrust of the vault, which falls
within the base.
The stone roof we are now ex-
amining differs somewhat from that
of Henry VII.'s chapel at West-
minster; the area of the points of
support is only one-half of those in
the latter elegant example; in no
instance have we so much effect pro-
duced by the mason's art, with so
small a quantity of material: it is
evident that the gradual changes
made in the architecture of the me-
diæval period led at last to the
greatest perfection, beyond which
it seems impossible for us to advance.
In selecting a style of any one
period, it may be fairly asked whether
the principles found in the latter, or
the economy adopted in the con-
structions of the 15th century, might
not be applied to it, and the same
effect produced,—the section of the
chapter-house at Wells, for instance,
lightened of half its material: un-
doubtedly it might, for the lofty
pointed arch, not having the thrust
which the latter, struck from four
centres, had, would exert less thrust,
and be in favour of such a change.
But at the present day, when copies
are rigidly made of the finest ex-
amples of each style, it would seem a
bold innovation to suggest such an
adoption; still it might be introduced,
and probably would have been, had
the freemasons continued an operative
fraternity, and been required to build
in the Lancet or other style, which su-
perseded it. The same decorations and
form of arch may be used in the later

2
6
7
8
10
Fig 3041, VAULTING of king's college chapel.
styles as in the earlier, as far as construction is concerned, and we have evidence of
sufficient strength in the example before us; the principles are the same in each, though
they may differ in form; there would be no more difficulty in transforming one style to
that of another, than was experienced by William of Wykeham, when he changed the
Saxon nave of Winchester to the Perpendicular.
On the section shown at fig. 3040. a line is drawn exhibiting the catenarian curve, for the
purpose of showing that the abutment piers are set out in correspondence with its
principles; it is not contended that a knowledge of this curve guided the freemasons in
proportioning their piers, or that their flying buttresses were always placed within it;
but it is singular that in those structures where their true position seems to have been
decided, the catenarian passes through them.
Bath Abbey section (fig. 3051.) is an example which exhibits this most perfectly; and by
a comparison of its section with that at Wells, (fig. 3004.) it will be perceived that the struts
are differently placed, and that the earlier example is defective: fig. 3930. represents Roslyn
1628
Book II.
THEORY AND PRACTICE OF ENGINEERING.
Chapel, in which there is evidently some improvement; but at the time of its construction
perfect knowledge on this subject had not been attained. In a catenarian chain formed of
links of equal length, every side is a tangent to the curve, and the direction of each link is
at right angles to it, acting in a direction perpendicular to the line it forms in the cate-
naria; and hence its useful application to the science of construction. It is quite clear that
wherever the curve passes through the section of a building, stability is obtained; and
where it does not, it is doubtful: certainly the best application of flying buttresses is
that which can be tested by this principle.
The main arches of the
roof abut against the outer
buttresses, and spring from a
cluster of mouldings set round
a circular pier; the situation
of the small columns and hol-
lows which decorate it being
determined by the crossing
of equilateral triangles. The
ribs of each severy abut in
the centre upon a circle 3 feet
6 inches in diameter, formed
of two stones, and indicated
by No. 1.: in the middle is a
mortise-hole 9 inches square;
No. 2. is in width 17 inches
in the widest part; No. 3. is
2 feet 2 inches; No. 4., 3 feet
8 inches; No. 5., the same;
No. 6., 3 feet 3 inches; No. 7.
4 feet 3 inches; No. 8., the
same; No. 9., 3 feet 2 inches,
and No. 10., which abuts
against the outer wall, 4 feet.
By a reference to the plan
on fig. 3044., it will be un-
derstood how the several
rings of voussoirs which com-
pose the quarter of the para-
bolic conoid abut and are
locked one into the other: the
construction of this vault is
somewhat similar to that
adopted by Soufflet at the
Church of St. Geneviève at
Paris, although his manner
of applying it materially
differs.


6
2
10
ツ
​7
10
Fig. 3043.
Fig. 3042. King's collegE CHAPEL: Ribs of vault.
5
·
•
•
The buttress in the present
example has an area of 56 feet,
equal to that of the piers, to which it is attached; or the two piers and buttresses together
have an area of 224 feet: it is curious to find that of the 336 feet before given to the
points of support, one-sixth should be applied to the piers, one-sixth to the buttresses,
and the other portion to the walls between; for 55 ft. 6 in. x 6=336 feet-the area of the
points of support taken on both sides; so equally are the parts even distributed.
When the Normans first used flying buttresses, as at the Cathedral at Chartres, the
Abbaye aux Hommes at Caen, and several other buildings, they abutted them against the
ordinary outside wall; but it was soon discovered that a greater resistance was necessary to
oppose the thrust, and prevent the abutments from yielding. Salisbury Cathedral was
probably one of the earliest where flying buttresses were used; and the opinion of Sir
Christopher Wren is worthy of quoting upon this subject, as it applies more particularly
to the first constructed, and not so immediately to those erected in the fourteenth or
fifteenth centuries. "Almost all the cathedrals of the Gothic form are weak and defective
in the poise of the vault of the aisles; as for the vaults of the nave, they are on both sides
equally supported and propped up from spreading by the bowes or flying buttresses, which
rise from the outward walls of the aisles: but for the vaults of the aisles, they are indeed
supported on the outside by the buttresses; but inwardly, they have no other stay but the
pillars themselves, which, as they are usually proportioned, if they stood alone, without the
weight above, could not resist the spreading of the aisles one minute: true, indeed, the
great load above of the walls and vaulting of the nave should seem to confine the pillars
CHAP. XXXI.
1629
PRINCIPLES OF PROPORTION.
in their perpendicular station, that there should be no need of butment inwards, but
experience hath shown the contrary, and there is scarce any Gothic cathedral, that I have

کہو
The man w
Fig. 3044.
KING'S COLlege chapel: piers.
seen at home or abroad, wherein I have not observed the pillars to yield and bend inwards
from the weight of the vault of the aisle; but this defect is the most conspicuous upon the
angular pillars of the cross, for there not only the vault wants butment, but also the

20 0
13 5
5 01
6 3
21
9
15 6
!
J
Fig. 3045.
KING'S COLLEGE CHAPEL: BUTTRESSES, ETC.
angular arches that rest upon that pillar, and therefore both conspire to thrust it inwards
towards the centre of the cross.
19
At King's College chapel, flying buttresses are dispensed with, and happily the
knowledge of construction had arrived at such perfection, when its astonishing vault was
projected, that we have no evidence whatever of its yielding in any part.
It may seem extraordinary that the Pointed style made so little progress in Italy, the
Byzantine being always preferred: the architects of that country were probably unwilling
to relinquish a mode of construction so economical, half only of the material employed in
the lightest, and a quarter in the earliest of the Gothic style, being required for the basilica :
for example, where 100 rods of stonework would be used in the latter, 200 would be
necessary for the style practised at King's College, St. George's Chapel, and Bath Abbey
Church, and 400 for that of the Chapter-house at Wells; this result would lead to the
conclusion, that no style is so well adapted for the wants of the present day as the Byzantine.
1630
THEORY AND PRACTICE OF ENGINEERING. BOOK II.

St. George's Chapel, Windsor.—If we sup-
pose a line on the plan to pass through the
centre of the buttresses and piers, and one
severy of the nave to be defined, we shall
have a width of 12 feet, and a length of
84 feet, the area of which is 1008 feet: after
this we shall find the area of the walls and
piers comprised within this severy to be
168 feet, or one-sixth of the whole; such are
the proportions of mass and void found in
this chapel. The clear width of the side
aisles between the columns is 11 feet 9 inches;
that of the nave 34 feet 10 inches, and be-
tween the outer walls 69 feet 2 inches: the
height of the top of the vaulting of the nave
is 54 feet 2 inches. The height up to the
springing line of the great vault over the
nave being equal to half the entire width,
it is evident that two squares must comprise
within them the entire building beneath this
line; upon setting them out we find the nave
and its pillars occupy one, whilst the other
is given to the side aisles, external walls, and
buttresses.
The Rev. John Milner, in his admirable
treatise on the Ecclesiastical Architecture
of England, which has been the text-book
for all modern writers, states that "its rise,
progress, and decline, occupy little more
than four centuries in the chronology. of the
world as its characteristic perfection con-
sisted in the due elevation of the arch, so its
decline commenced by an undue depression
of it. This took place in the latter part of
the 15th century, and is to be seen, amongst
other instances, in parts of St. George's Chapel,
Windsor, commenced by Edward IV. in 1482;
in King's College Chapel, Cambridge, and in
the Chapel of Henry VII. at Westminster.
It is undoubtedly true that the architects of
these splendid and justly admired erections,
Bishop Cloose, Sir Reginald de Bray, &c.
displayed more art and more professional
science than their predecessors had done; but
they did this at the expense of the character-
istic excellence of the style itself which they
built in."
"In St. George's Chapel we have the
work covered with tracery and carvings of
the most exquisite design and execution, but
which fatigue the eye, and cloy the mind by
their redundancy:" but
but we have also a
building constructed with one-half the ma-
terials that would have been employed had
the style practised in the chapter-house of
Wells been adopted: The admirers of the
Pointed style have not sought for the true
principles which mark its several changes;
they have not examined into its constructive
arrangements; had they done so, they would
have perceived that, as the skill of the free-
masons advanced, and their workmanship im-
proved, they economised material, con-
structed more solidly, and produced a richer
and more harmonious effect, without sacri-
ficing any of the principles which governed
their practice; the improvements they made
were as great as those noticed when the
AAAAAA
Fig. 3046.
ST. GEORGE'S CHAPEL, Windsor.
CHAP. XXXI.
1631
PRINCIPLES OF PROPORTION.
Doric proportions were changed to the Ionic. In the Doric we had two-thirds mass, one-
third void; in the Ionic half mass, half void; at Wells Chapter-house one-third mass,
two-thirds void; in St. George's Chapel, one-sixth mass and five-sixths void.

Fig. 3047.
ST. GEORGE'S CHAPEL, WINDSOR.
The plan of the pillars is that of a double square, or parallelogram, the diagonals of
which latter figure become the sides of equilateral triangles that serve for the setting out

Fig. 3048.
PIER OF ST. GEORGE'S CHAPEL, WINDsor.
the splays, upon which the several mouldings are cut: from east to west these piers are 3 feet
1 inch, from north to south 3 feet 6 inches, not comprising in this last dimension the three
1632
BOOK II.
THEORY AND PRACTICE OF ENGINEERING.
small columns on the fall towards the nave, or the single column on that towards the side
aisles, the first of which projects 6½ inches, and the latter 4 inches.
The mouldings around the windows and their mullions are shown at the side of the-
pier in their proper position.
Division of the Nave of St. George's Chapel.—The mouldings set around the plan of
the pier are continued up to the vaulting of the roof, without any other interruption
except where they are mitred round the arches.
Bath Abbey Church is 89 feet 5 inches in width from cut to cut measured across the nave,
and the clear width of the nave is 29 feet 10 inches, or one-third of the whole, and each of
the side aisles is a trifle more than the half of the width of the nave, being 15 feet 8 inches;
the walls and piers added together are not quite equal to a third, as they amount only to 14
feet 2 inches on each side, or together to 28 feet 4 inches, the difference being given to
increase the side aisles.
The section of this beautiful building presents
to us all the improvements made in vaulting, and the
right proportions as well as directions to be given
to the flying buttresses: in the first application of
those supports, as at Salisbury, they are evidently
misapplied, but in the example before us we find
that the constructors had arrived at a knowledge
of the principles of the catenarian curve, which
is traceable through the solid masses of the section :
it was by slow degrees that the freemasons arrived
at a knowledge of the peculiar properties of this
figure; had it been known at the first commence-
ment of the introduction of flying buttresses, we
should have had a better application of them; in
several instances we find them adopted where no
advantage, or very little, could be derived from
them.
Division in Bath Abbey Church differs from all
other examples of this period, by the height given
to the clerestory and the omission of the triforium :
the judicious and excellent arrangement of the
flying buttresses permits of the greater display
of glass, which in the sixteenth century had arrived
at its most gorgeous state, rich in every colour, and
beautiful from the drawing of the patterns, and
figures with which it was covered.
Bishop King commenced this building about the
year 1500, on an entirely new site, near the old
church from the centre of one pier to that of the
other is 20 feet 1 inch; the thickness of the outer
buttresses 3 feet, and their projection 4 feet; one
severy of building contains 1650 feet, and the area
of the points of support is 275 feet, or one-sixth.
The pillars are square, though set diagonally, their
width from north to south and from east to west
being 5 feet, and the opening of the arches between them 15 feet 1 inch; half their plan
and base is shown at fig. 3052.: the height from the pavement to the top of the capitals,
where the sculptured angel is placed, is 56 feet 3 inches, and to the top of the vaulting
73 feet 6 inches, within 7 feet as much as the clear width between the outer walls.

Fig. 3049. BATH ABBEY CHURCH.
Fig. 3053. shows the plan of the stone vaulting, which is perfectly geometrical in its
setting out; the cloisters at Gloucester, the aisle at the east end of Peterborough cathedral,
and St. George's Chapel, Windsor, have vaults of a similar kind,
The thickness of the stone which comprises the vaults of fan tracery varies according to
its position, but in no instance is it considerable, or more than absolutely necessary to resist
crushing. The spire of Salisbury, 180 feet in height, of an octangular form, ineasures from
east to west internally 33 feet 2 inches, and from north to south 6 inches more; the
thickness of the spire at bottom is only 2 feet, or the area of its base is half that of the
void, the void containing two parts, and the solid around it one; this spire diminishes in
thickness for the first 20 feet, after which it is 9 inches in thickness throughout; at about
30 feet from the summit is a hole, by which an exit from the interior may be made, and
by means of the crockets and irons on the outside the top of the spire may be attained: in
1816 the writer examined the position of the vane, and the manner in which the capping
stone was placed, and descended astonished at the perfection of the masonry, and the
thinness of the stone with which it was constructed,
CHAP. XXXI.
1633
PRINCIPLES of proPORTION.

Fig. 3050.
Fig. 3051.
SECTION OF BATH Abbey church.


Fig. 3052.
PIER.
Fig, 3053,
GROINING.
Caudebeck Sacristy, near Rouen, in Normandy, exhibits the manner of suspending a key-
stone by locking it between the voussoirs of a strong semicircular arch. The length of this
5 M
1634
Book IL
THEORY AND PRACTICE OF ENGINEERING.

pendent stone is 17 feet
6 inches, and its thick-
ness at the top, where
locked, is 30 inches: the
voussoirs are 3 feet in
depth; the small pointed
arches or ribs that form
the groining of the hexa-
gonal vault spring from
the side walls and the
ornamental knob of the
pendentive, and are per-
fectly independent. The
abutments of the semi-
circular arch, which has
a radius of 12 feet, are
formed by solid walls
continued for some
length in the direction
of its diameter. This
sacristy is hexagonal;
each side internally
measures 12 feet, and the
height from the pave-
ment to the springing
of the ribs is 18 feet.
Seventh's
Henry the
Chapel, Westminster.
The first appearance of
the pointed arch was
probably a little before
the termination of the
twelfth century; the pil-
Fig. 3054.
CAUDEBECK SACRISTY.
lars and mouldings which then accompanied it were of Saxon origin: to its acute form was

Ад
Fig. 3055.
FIER OF HENRY VII.'s chapel.
afterwards added the slender Purbeck columns and simple groining, producing that unadorned
majesty which reigns throughout the cathedral of Salisbury. This style underwent
several changes, and was succeeded at the latter end of the thirteenth century by another, in
GHAP. XXXI.
1695
PRINCIPLES OF PROPORTION.

which the arch was struck from more than two
centres: the naves of York, Canterbury, and
Winchester Cathedrals have been cited as
among the best examples. But we have now
to describe the principles of a style founded
upon the others, and applied to all buildings
in England from the middle of the fifteenth
to the middle of the sixteenth century; it is
not met with on the continent, the Italian
or revived classic architecture having there
been generally introduced and preferred.
The variety exhibited in groined vaults,
progressing from simple ribs to those of an
in.ricate and net-like arrangement, no doubt
led the masons of the time to the construction
of the cloisters at Gloucester, King's College,
and Henry the Seventh's Chapel at Westmin-
ster, which works are the best evidences that
can be adduced of the improvements made in
professional science, and which could only
result from a continued perseverance in the
study of the subject: an examination of the
several styles will prove that they must have
been produced by the same school or fraternity,
and that neither Sir Reginald Bray nor Wil-
liam of Wykeham could have become ac
quainted with the mysteries of the craft, unless
they had been instructed by the freemasons;
and that to them, and not to any individual,
nor to the clergy as a body, ought we to
attribute the construction of these scientific
and highly decorated works.
The Division of Henry the Seventh's Chapel
bears a strong resemblance in its general pro-
portions to that of St. George's at Windsor,
although it is rendered more ornamental by
the multitude of figures enshrined in delicate
tabernacle-work, which covers almost the entire
walls. The mouldings of the main piers (fig.
3055.) that separate the middle from the side
aisles are enclosed within a circle divided
into a pentagon—a form the best adapted to
receive the weight of the ribs, and the flying
buttresses that were to resist their force.
The Rev. James Dallaway, whose dis-
courses upon the architecture of England,
created so many admirers of this interesting
subject. observes, that "here the expiring
Gothic seems to have been exhausted by every
effort. The pendentive roofs, never before
attempted on so large a scale, are prodigies
of art." But it is not to the profusion of
sculptured angels, statues, royal heraldic de-
vices, &c., that we are desirous of drawing
the attention, so much as to the extraordinary
construction that prevails throughout this
master-piece, in which we have the strongest
evidence that theory and practice went hand
in hand; that the knowledge of geometry
had advanced to its highest pitch in the con-
structive arts, and that not only were the
principles of the arch thoroughly understood,
but considerable advance made in the appli-
cation of the properties belonging to the cone.
The section of this beautiful chapel is 78 feet
in width; the buttresses and outer walls
together are 6 feet 9 inches, the side aisles 11 feet
3 inches; the piers from north to south 4 feet
5 м 2
A
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pa papa papa papa
Fig. 3056.
HENRY VII.'s Chapel.
KOM DIYIMKONIKUININUSHTADIALIT (
1636
THEORY AND PRACTICE OF ENGINEERING, BOOK II.

Shannar
པའི་ཐུན་མ
t
www
Fig. 3057.
SECTION OF henry vii's. chapel.
6 inches, and the clear width of the nave 33 feet. The entire width, at the basement or level
of the pavement of the crypt, is 79 feet: 261 feet, or §, is devoted to points of support, and
523 feet, or, to the side aisles and nave; the area of a severy shows applied to walls
and piers, and to the void, which proportions accord with the early rather than with the
៖
late examples; the great weight of the vaulting, which is 62 feet high from the pavement
of the chapel, requiring additional strength, the proportions of St. George's Chapel at
Windsor would not have been equal to the necessary resistance.
Our limits will not permit a more extended inquiry into the principles of proportion,
the study of which is calculated to produce an important improvement in the noble art,
for the practice of which the young architect must prepare himself by careful measure-
ment, not only of the ruins of the Acropolis and of the Capitol, but of all that remains of
mediæval architecture: he must be a pilgrim seeking after truth, not bowing before any.
favourite shrine, but returning with a devotion as enlarged as his subject. The stupendous
works which antiquity has transmitted to us, it is hoped, may excite the attention of the
general reader, nor will his interest be diminished by the contemplation of the astonishing
development of modern industry. The writer cannot but feel the importance and variety
of his subject, and, while he is conscious of his own imperfections, he must often accuse the
deficiency of his materials: but the results of his labour, however inadequate to his own
wishes, he finally delivers to the candour of the public.
SUPPLEMENT.
WATER SUPPLY.
THE quality of this important element supplied to the Metropolis by various Companies
has of late years become a subject of serious consideration, both publicly and privately,
The still increasing area covered with habitations naturally suggested the idea that the
two principa sources of supply, the Thames and Lea rivers, could not retain that purity
so necessary to health if still made the recipients of so enormous a drainage. The
quantity of water supplied from the Thames is stated to be about 20,000,000 of gallons,
from the Lea 26,000,000, daily; and it was asked, does not this quantity return tainted
with all the impurities incident to so large a population? and, if so, is there not a constant
exchange of discharge and supply injurious to health. Amidst much discussion, this view
of the case has been denied, on the principles of evaporation, the soluble quality of water,
&c. &c. Into these discussions it is not requisite here to enter; but there can be no question
that to be under the necessity of using water, for any purpose, supposed to be charged with
all sorts of abominations, would be repulsive in the extreme to even the least fastidious;
while to the refined mind, it must be a source of regret, that so many of our rivers, whose
pure streams would delight the eye and gladden the heart of the beholder, should now only
produce feelings of disgust, or so accustom the dwellers around them to the sight of every
species of pollution that a positive moral injury is produced by the continual blunting
of the external senses.
To satisfy the public mind upon this important question, at the commencement of the
year 1851 Sir George Grey, then principal Secretary of State for the Home Department,
commissioned Thomas Graham, W. A. Miller, and A. W. Hofmann, Esquires, eminent
chemists and medical men, after proper inquiry and analysis, to report to him, for the in-
formation of Government, their opinion upon the waters delivered and proposed to be
delivered by the several water companies.
In June, 1851, the report was completed, and contained not only the analysis of all the
actual sources of supply, but that of several others, proposed to be taken from the chalk
districts about Watford and along the side of the North Kent Railway, and also of the
Farnham and Surrey waters, which flow from the green sand in the neighbourhood of
Farnham.
The analysis was given in two forms: first, the acids and bases separately; and, secondly,
the same acids and bases arranged in the forms of salts, or chemically combined, as they
are believed to exist in the waters.
5 a 3
1638
[ SUFF.
THEORY AND PRACTICE OF ENGINEERING.
First, the analysis of the New River, East London, Kent and Hampstead waters:

Lime
Magnesia
Potassium
Sodium
1
Iron, Alumina and Phosphates
Sulphuric acid (S. O.)
Chlorine
Carbonic Acid
Silica
Nitric Acid
Ammonia
The second analysis was as follows: -
Grains in an Imperial Gallon.
New River East
Water. London.
Kent.
Hamp-
stead.
-
5.7192 6.9034 8-4931 2.9160
0.5280 0.7336 1.6537 1.7098
0.4972 0.5600 0.4586 1.6471
1.1634 0.9989 1.3790 7.5761
trace. 0.4760 trace. trace.
3.2550 2.5830 6.8180 9.1702
1.0500 1.0682 2.3387 4.1230
11.1020 11.4527
0.5005 0.6216 0.7679 0.0728
0.0150 0.4800 0.0470 0.0500
trace
trace. trace. trace
9.828010·9823

Grains in an Imperial Gallou.
New River East
Water. London.
Hamp-
Kent.
stead.
Carbonate of Lime
Sulphate of Lime
Nitrate of Lime -
Carbonate of Magnesia
Chloride of Sodium
Sulphate of Soda
Chloride of Potassium
Sulphate of Potassa
Carbonate of Potassa
Silica
-
1
Iron, Alumina and Phosphates
Ammonia
W
}
7.82
10.16
7.02
4.95
}
3.23
2.33
11.03
0.02
0.72
0.07
0.07
1.09
1.51
3.42
3.53
1.73
1.76
3.50
6.79
1.49
0.94
15.14
0.44
1.11
1.25
0.70
1.40
1.80
0.50
0.62
0.76
0.07
trace,
0.47
trace.
trace.
trace.
trace.
trace.
Organic matter
2.79
4.12
2.61
1.84
Total
19.78
23.88
29.55 35.59
Solid residue obtained on evaporation
-
19.50
23.51
29.71
35.41
Free Carbonic Acid in cubic inches 44° F.
14.49
12.38
10.15 13.30
"
grains in a gallon
7.24
6.19
5.07
6.67
Suspended matter
1.49
1.07
0.52
Degree of hardness, Clark's scale
14.90
15.00
16.00
9.80
The first analysis of the Thames water: —

Grains in an Imperial Gallon.
Southwark
Thames
Ditton.
Grand
Junction,
at Kew.
West Mid-Chelsea,
dlesex,
Barnes.
Red House,
Battersea
and
Vauxhall, Lambeth.
Red House.
Lambeth,at
Lime
Magnesia
Potassium
Sodium
8.0046 7.4522 7.5390
0.6070 0.5544 0.5628
0.4261 0.2769 0.2185
0.4330 0.6127 0.7387
7.5117 7.2751 6.7970
0.5527 0.6020 0-7011
0.2821 0.6048 0.4291
0.5784
0.7861
0.7805
Iron, Alumina, Phosphates
0.0940 0.7630 0.7630 0.2912
0.3430
0.8505
Sulphuric Acid
Chlorine-
Carbonic Acid.
Silica
Nitric Acid
Ammonia
1.8782 2.6460 3'0380 3.3005
2.4150
2.2015
0.9890 0.8512 1.1424
1.2229 1.1725
1.1746
14-2170|11·9826 10.6260
0.6290 0'4466 1·0013
10.647012∙1100 | 12·8520
07189 0.7679
1·0451
0.0180
trace.
trace.
trace.
0.2960
trace.
+
trace.
trace.
trace.
trace.
0.0309
trace.
SUPP.]
1639
WATER SUPPLY.
The second analysis of the Thames water:

Grains in an Imperial Gallon.
Southwark
Thames
Ditton.
Grand
Junction
West
Chelsea,
and
at Kew.
Middlesex, Red House,
Barnes. Battersea.
Lambeth,at
Vauxhall,
Lambeth.
Red House.
Carbonate of Lime
·
11.79
10.90
9.94
9.28
10.57
8.99
Sulphate of do.
3.06
3.26
4.78
5.61
3.05
2.99
Nitrate of do.
-
0.27
trace.
trace.
trace.
0.35
trace.
Carbonate of Magnesia
1.27
1.17
1.16
1.08
1.29
1.44
Chloride of Sodium-
1.10
1·40
1.88
1.47
1.99
1.95
Sulphate of Soda
0.18
Chloride of Potassium
0.67
0.55
Sulphate of Potassa
0.17
0.61
0.48
1.34
0.95
Silica
0.62
0.44
1.00
0.71
0.76
1.04
Iron, Alumina, Phosphates
0.09
0.67
0.76
0.29
0.34
0.85
Ammonia
trace.
trace.
trace.
trace.
0.03
trace.
Organic matters
2.29
3.07
2.75
2.38
1.51
2.59
Total
21.33
21.70
22.75
21.37
21.23
20.80
Solid residue after evapo-
ration.
-
20.78
21.72
22.07
21.28
21.08
20.40
Free Carbonic Acid in cubic
inches, at 44° F.
16.89
13.46
11.56
12.30
13.57
16.64
Free Carbonic Acid, grains
in gallon
8.25
6.73
5.78
6.15
6.78
8.32
Suspended matter
0.01
0.02
1.92
1.15
Degree of hardness, Clark's
scale
-
14.22
14.00
14.60
14.44
15.00
14.16
The soluble organic matter from some of the Thames water, upon a further examination,
was found to give 0.105 grain of nitrogen, and 0.031 grain. The existence of nitrogen is
supposed to imply the animal origin of organic matter; but it has been observed by Dr.
Clark, that nitrogen, which gives the offensive smell to animal matter, becomes oxydized,
forms nitric acid, and is convertible into nitre; and indeed we can hardly suppose that
animal matter of any kind can be long subjected to the action of the river water without
undergoing a complete change, for the exposure of the water in its course to the free action
of the air, would naturally increase chemical action, which would be again greatly aided
by the alkaline substances found in it. We can scarcely meet with any water, collected
upon the earth's surface, perfectly free from organic and mineral matter; but the quality
of the water is not by these means rendered unfit for use, unless the substances dissolved
within it are of a noxious or unwholesome kind.
The hardness of water does not affect its salubrious qualities; for perfectly pure or soft
water, when in contact with chalk or carbonate of lime, will dissolve but a very small
quantity: a gallon of water, the weight of which is 70,000 grains, will only take up two
grains of carbonate of lime, which will impart two degrees of hardness. When we find
twenty grains, or as many degrees of hardness, in a gallon of water, it is owing to the pre-
sence of carbonic acid gas, found abundantly in some waters. Sulphate of lime has not
carbonic acid gas for its solvent; on this account it differs from carbonate of lime, as it
cannot be got rid of by boiling, but remains in solution, and renders the water permanently
hard.
There can be no doubt that water taken directly from the chalk strata, contains abso-
lutely nothing of organic origin, that it has a brilliancy and clearness superior to any
other, is completely free from any suspended matter, and, under mean temperature, is
remarkable for its freshness.
Pumping Establishments in the Metropolis, &c.— Considerable improvements have been
made during the last seven years by the water companies. Thus, instead of pumping the
water at once into the various reservoirs, stand pipes have been erected close to the
pumping engines, which not only give increased impulse to the water in the pipes of
supply, but contribute considerably to the even and regular working of the engine; many
more miles of iron main have been laid down; and filters have been very generally
introduced.
The engine power possessed by the nine companies that supply the metropolis with
water may be estimated at about 4000 horses; the quantity of water delivered daily is 90
5 м 4
1640
[Supp.
THEORY AND PRACTICE OF ENGINEERING.
gallons per house, and annually for all uses about 17,000,000,000 imperial gallons. The
engine power absolutely required to raise that quantity is that of 2000 horses only, or
half the whole power; so that about 8,500,000 gallons are raised by each horse power in
the course of the year, to heights varying from 60 to 190 feet,
The stand pipes of New River, being from 84 to 145 feet high
""
""
""
Chelsea
West Middlesex
>>
85 to 135
""
122 to 188
""
Grand Junction
100 to 151
""
Lambeth
135
""
""
East London
60 to 107
99
The mean height of all the water delivered being probably 100 feet, we have the mean
daily lift to that height of each horse power 25,000 gallons; for 25,000 × 2000 (horse
power) × 365 (days)=18,250,000,000 gallons, an amount somewhat exceeding the year's
supply.
At page 1213 of Encyclopædia, it is stated that an engine of 29 horse mean power, made
by Boulton and Watt in 1809, working 10 hours per day for six days a week, raised 612,360
gallons 100 feet high, or 9720 gallons per hour; which divided by 29 (horse power,) gives
32.2 gallons as the quantity raised by one-horse power per hour. At that rate we should
only require 780 horse power, or about one-fifth the 4000 as stated, to raise daily the
amount of 25,000 gallons; so that a great allowance must be made, evidently, for
minimum, mean, and maximum working of steam engines under these circumstances.
NEW RIVER Waterworks receive their supply from several sources :-
The Chadwell spring, which affords
The water from the river Lea
The Amwell well
Hill well
The Cheshunt well
The Tottenham Court Road well
Cubic feet.
·
""
per minute 500
1340
""
196
285
""
*
50
""
70
2441
Cubic feet per minute
At the
Engine Power. At the Amwell End well, the engine works two 17-inch pumps
with a 6-feet 3-inch stroke, 10 strokes per minute, and lifts 30 feet at a stroke.
At the Amwell Hill well are two 20-inch pumps, with a 6-feet 3-inch stroke, making
10 strokes a minute and 50 feet lift.
At the Cheshunt well is one 12-inch pump, with a 6-feet stroke, making 10 strokes per
minute, 105 feet lift in two heights.
At the Tottenham Court Road well is one 14-inch pump, with a 6-feet stroke, making
11 strokes per minute, 203 to 204 feet lift in two heights.
In addition there are other engines for the distribution of the water at Newington, and
at the New River head.
The total amount of engine power altogether may be estimated at 720 horses, one-half
of which only is in use during the summer months, and probably about one-third in the
winter months. 2000 tons of coal are annually consumed.
The sources from whence this company draw their supply, are chiefly from the chalk
district, and 1340 cube feet per minute is at present permitted to be drawn from the
river Lea : the manner in which this was measured is described in a report made to the
New River Company by Mr. Bryan Donkin, in October, 1836:
"After several ineffectual attempts to obtain a tolerably correct estimate of the
quantity of water flowing from the river Lea into the New River, through the gate of
their balance engine near Ware, without stopping the supply of the New River, I was
obliged to resort to the only expedient remaining, namely, that of allowing the whole of
the water obtained from the river Lea, to flow over the tumbling bay, near to the marble
guage, and thus for some hours, to divert it from the New River, back again into the
Lea. With Mr. Mylne's assistance, this was effected on the 19th of August last, when the
sluice or gate near the marble guage was shut down, by which means the whole of the
water coming from the river Lea, through the balance engine, was made to flow over the
tumbling bay.
"This experiment was continued until the depth of water flowing over the bay was
taken, every five minutes; and corresponding observations were made by several stationed
at the balance engine, at the same intervals of time, of the height of the water in the river
above the sill of the sluice gate, and also of the opening under the gate through which
the water passed from the river Lea into the manifold ditch. The last-mentioned obser-
vations were necessary, from the constant variations which took place in the height of
the water in the river Lea, and also in the consequent alteration in the opening under
SUPP.]
1641
WATER SUPPLY.
the gate, through the agency of the balance engine, lessening the opening as the water
in the river Lea rises, and again increasing it as the river becomes lower. I believe that
the distance from the balance engine to the tumbling bay, measured by the serpentine
course of the manifold ditch, by which the water passes from one to the other, would be
found to be somewhat more than a mile. These changes in the height of the river,
and in the opening under the gate, although they did not perceptibly affect the depth
of the water flowing over the tumbling bay, must necessarily have had some effect on
the whole quantity discharged through the opening during the period of observation.
I have therefore for the last hour, during which the depth of water running over the
tumbling bay appeared to be quite uniform, reduced the various heights of water in the
river and the various openings under the gate, which occurred during that time, to the
hydraulic mean depth and opening, which would have occasioned the same quantity to be
discharged through the gate of the balance engine as was found to run over the tumbling
bay.
·
Estimating the whole quantity of water flowing through the gate of the balance engine
by the depth of water flowing over the tumbling bay, which I have found to be a very
correct method, it amounts to 1020 cubic feet per minute, and I find that the mean height
of water in the river Lea, above the bottom of the opening under the gate of the balance
engine, and the opening itself, if uniformly the same, would have been 408,913 inches and
5.1823 inches. From Mr. Mylne I learn that henceforward the greatest quantity of
water to be taken from the river Lea is to be at the rate of 1340 cubic feet
per minute,
and that he considers the mean height of the surface of the water in the river Lea to be
42 inches above the sill of the balance-engine gate. Under this head or height of water,
I find that the opening under the gate should be 6.67 in order to admit this discharge
of 1340 cubic feet per minute. Hence I have found the openings which are required
for other heights of the water in the river Lea, within certain limits, so as that the same
quantity of water may uniformly flow through the gate of the balance engine.
"But it is obvious that the balance engine, as at present constructed, cannot produce the
discharge of a quantity of water under the gate which shall be uniformly the same at all
the various heights at which the water in the river Lea is liable to be. I do not know
the extreme height to which the greatest flood in the river may occasionally rise; but I
have presumed it may do so as far as 60 inches above the sill of the balance-engine gate;
that is 18 inches above its ordinary or mean height. I have therefore calculated the
openings to the same height; and in order more distinctly to show the difference of
quantities of water which would be discharged through different openings, as they are
determined by the balance engine, and the quantity required to this end, I assume that
the balance engine is so adjusted as that when the water in the river is at 42 inches, the
mean height, the opening under the gates is such as will allow of the required quantity
of water to pass, namely 1340 cubic feet per minute.. I have also assumed that the river
may occasionally vary its height from six inches below to twelve inches above the mean
height, which would be from 36 inches to 54 inches, above the sill of the balance-engine
gate. Now under a 42-inch head the table gives an opening of 6'674, and at 54 inches
head, it gives an opening of 7.298, whereas at the 54 inches head the balance engine
would make the opening of 5·174 inches, and for 36 inches head the opening would
be 7.424. So that with a head of 54 inches, and an opening of 4.304, the quantity of
water would be 985 cubic feet per minute; with 42 inches head, and an opening of 6.674,
the quantity would be 1340 feet; and with a 36-inch head, and an opening of 7·424, the
quantity would be 1556 cnbic feet per minute.
“Thus, whenever the river sinks below 42 inches, the balance engine permits too great
a quantity to flow through the gate; and, on the contrary, whenever the river rises above 42
inches, the quantity is too small.
+6
Presuming that it will be an object of great importance to make such a change, in the
construction of the balance engine, as that it may effect uniformity in the quantity of
water flowing from the river Lea into the New River, under every variety of height to
which the water in the river may rise, I have turned my attention to this subject; and
out of a variety of expedients I have selected one which appears to me certain in its
operation, simple in its construction, and, from its nature, very durable and little liable to
derangement, and which will also still bear, very appropriately, the name of balance engine,”.
The contrivance alluded to was adopted by the New River Company, and the exact
quantity of water meted out by means of the machinery; it elevates and depresses the gate
either to enlarge or diminish the aperture by which the water passes, and this under any
rise or fall to which the river Lea is subject.
Reservoirs. — The two at Cheshunt contain
(Subsiding)
">
وو
at Stoke Newington
one at the New River head
1 1
a
Acres. R. P.
18 2 0
42 2 0
5 0 0
66 0 0
1512
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
The reservoir at Tottenham Court Road is of considerable dimensions, and built of brick.
it is 200 feet in diameter.
The Stoke Newington subsiding reservoirs are 24 feet deep in the middle, and upon an
average 12 feet, and contain 130,000,000 gallons.
Quantity of Water now annually delivered by the company, is 5,634,000,000 imperial
gallons. Average annual expenditure, about 45,8181. or twopence for every 1000 gallons
delivered.
The New River Company supplies upon the intermittent principle nearly one-third of the
metropolis with water, that is 86,000 houses with a population of about 700,000, at the rate
of 40 gallons daily per head.
This company'supplies a considerable district with water by gravitation alone, which
allows a supply without the necessity of pumping; and consequently some advantages are
obtained by this facility.
The total capital of the New River Company was estimated in 1851 as amounting to
1,455,6341. And the average per-centage was 5l. 48. 9d.
The yearly expenses for coals, engine, stores, repairs
Wages
Paving, plumbing, repairing pipes
Wages
Salary to the Secretary
to the Engineer
Rent
Rates and taxes
-
£ S. d.
2,737 0 0
688 O 0
8,894 O 0
4,533 O
800 0
830 O
nil.
6,699 O O
The annual water rents, not deducting commission, in 1850 –
amounted to 128,660l.
Arrears
1,108
}
Receipts from other sources
Rents from houses, &c.
The total expenditure for the same year
Collector's commission
Cost of management
Directors
Officers and servants
Rent of offices, and office expenses
Working expenses
Street work, paving, plumbing &c.
Wages
Pumping establishment
Coals, engine stores, repairs
Wages
Annual rent charges
Miscellaneous disbursements
Outlay for new works
•
-
25,181 0 0
£ 3. d.
129,768 0 0
3,346 0 0
10,165 0 0
143,279 0 0
F
S. d.
5,218 O O
2,254 O 0
5,013 O 0
815 O O
8,272 0 0
4,597 0 0
5,648 0 0
1,273 O O
12,596 O 0
15,460 0 0
61,146 0 0
17,010 0 0
78,156 0 0
To the north of the Regent's Canal the supply is four days a week, and the high service
three days a week; on the south the high and low service is given daily. To convert this
intermittent into constant supply would in some instances occasion expense and be of
difficult execution.
The company do not supply any filtered water, the only cleansing being performed in the
reservoirs, and in the conduits, by depuration, fully two-thirds of the New River supply
is served by gravitation, the remaining portion being pumped; the cost of the former being
double that of the latter for the same quantities of water. This is accounted for partly by
the original outlay for forming the aqueduct, and the annual expenses incident on the
maintenance of its banks and numerous bridges.
The CHELSEA Waterworks were established in 1722; the Millbank works were purchased
in 1729. From a recent investigation, the district supplied by this company contains
10,000 houses with water-closets, 500 houses with baths, supplied by direct pipes. In
SUPP.]
1543
WATER SUPPLY.
}
1849, the company supplied 20,996 houses and 248 cottages from stand-cocks, besides the
necessary quantity for watering the roads, and cleansing the sewers.
The whole supply
pumped into the mains during this year, was 1,438,458,000 imperial gallons.
The average quantity delivered to each house per day, including trade and other purposes,
was 219 gallons; excluding trade and other purposes, 187 gallons, and to large consumers
from 200,000 to 300,000 gallons per day.
The successive improvements that have taken place during the last 120 years, are a
curious illustration of the increasing requirements of the community to be supplied, as
well as that of the numbers. In 1743, the first steam engine at these works was erected;
in 1746, iron mains were adopted for those of wood; in 1747, a second steam engine was
erected; and in 1779, a third, and the water-wheel and wind-engine, which served to in-
crease the supply, were improved. The metropolis continued to increase its buildings to
that extent that in 1805 a fourth steam engine was required; in 1812 a fifth, of 70-horse
power, was put up; in 1823, a sixth, of 80-horse power; in 1838, an eighth engine, of 120-
horse power; and in 1850 two 20-horse power engines were added.
Street Watering. In the year 1849, 36,000,000 gallons were supplied for this purpose,
at the following charges: -under 10,000 superficial yards of road watered, 8s. 4d. per 100
yards; from 10,000 to 20,000 superficial yards, 78. for 100 yards; from 20,000 to 100,000,
6s. 3d. per 100; above 100,000 superficial yards, 5s. 9d. per 100 superficial yards: 15,000
to 20,000 gallons per mile per day is about the quantity used.
For Fires, in the same year, this company afforded 5,000,000 gallons, which was less
than the average quantity.
For flushing and cleansing the sewers, the quantity was estimated at 15,000,000 gallons.
Iron mains are in length about 134 miles; and the largest are 18 inches in diameter, 12
inches, and 10 inches; the auxiliary mains are 7 inches and 6 inches; the services are 3,
4, and 5 inches in diameter; but the exact quantity of each cannot be accurately ascertained.
The beds for depuration cover an area, at present, of 90,000 superficial feet.
The highest service afforded to the houses of this district, is 157 feet above high-water
mark.
Pumping Establishments in 1851.—An increase is continually making in the engine power;
and it appears that, for every pound of Newcastle coal, we have 7 to 8 pounds of water
evaporated by the boilers.

Diameter of
Horse
Engine.
the Cylinders
Length of
Stroke in
Strokes per
Minute.
in inches.
feet.
Maximum
height of Ser
vice, in feet.
120
65
81
131
157
65
50
8
14
157
Ditto.
36
31
6
13
106
Single power. Pumps fil-
tered water.
Double power. Do.
Ditto.
75
54
8
18
32
Single do.
Pumps river
water.
24
27
4
27
32
20
20
3
30
180
Double do. Do.
Double power.
20
20
3
30
180
Do.
180
50
8
14
157
Do. (not finished).
540
The Total Capital in 1851 of the Chelsea Company was 428,2431., the average per-cent-
age of which was 3l. 5s.
The yearly expenses for coals, engines, stores, repairs of works
Wages
One years expense's for street work, viz., paving, plumbing, repair-
ing pipes
Wages
Salary to Secretary
Engineer
£ S. d.
3919 7 0
2616 2 10
608 13
5
2386 12
8
800 0 0
100
830 0 0
Rent annually paid by the Company
Rates and taxes -
Annual expenses
342 15
0
-
1111 10 10
-
12615 1 9
The nett annual water rents from 10th October, 1849, to the 10th October, 1850,
amounted to 36,8187. 13s. Od.
1644
[SUPP
THEORY AND PRACTICE OF ENGINEERING.
And the Total Expenditure for the same period is thus stateď :
Collector's commission
Directors, officers, and servants
Rent of office, taxes and other disbursements
Working expenses :
Street work
Paving and plumbing
Pumping establishment :-
1
£ 8. d.
1311 16 4
754 17 8
1740 0 0
610 6
2472 1
20
Coals, engine stores, repairs
·
Wages, total
Reservoir expenses
Rates and taxes on pipes and works, rent on leasehold, law charges,
annuities, charities, &c.
5051 4 10
2807 17 5
2462 4 10
2614 3 6
£20997 19 4
WEST MIDDLESEX Waterworks, which are established near Barnes Terrace, draw their
supply from the Thames; the pumping establishment is at Hammersmith. The company
have four reservoirs; viz., two at Barnes, one at Kensington, and one at Barrow Hill
the two first contain about 16 acres area; that at Kensington has an elevation of 111 feet
above the Trinity standard, is lined with brick, and will contain 16,000 tuns. That at
Barrow Hill is 177 feet 6 inches above the same standard, holds 22,000 tuns, each of 54
gallons. These reservoirs were constructed at a considerable expense in 1838, and
answer their purpose admirably, the water which is admitted being rendered more pure
by depuration and subsidence.
Mains and Pipes. There are about 150 miles of iron main and pipe, varying from 30,
23, 21, 19, 13, 15, 12, 10, 9, 8, and 7 inches in diameter, the service pipes being from 6
to 3 inches in diameter.
The number of houses supplied is 24,480; and within the district are 3000 fire plugs.
Out of the above number of houses, 7,500 are considered to have water-closets, as they are
supplied by the high service, which is 207 feet 6 inches above the Trinity high-water
standard.
The total quantity of water pumped in the year 1849 was 1,216,929,812 imperial
gallons.
Charge for watering the roads is 757. per mile; and for this the water cart is used twice
a day.
The West Middlesex Water Company has now an iron main 36 inches in diameter
and 14,500 yards in length, laid down near the village of Hampton, to supply the works
at Hammersmith. This main passes through Mortlake to the reservoirs of deposit and
filtration at Barne Elms, on the Surrey side of the Thames, opposite to and connected
with the present main, which passes under the river at Hammersmith; which works were
done in conformity with the parliamentary inquiry of 1852.
This company united with the Southwark and Vauxhall Company in laying two
parallel lines of pipes, 36 inches in diameter, from Hampton Wick, 19 miles above
London Bridge, to the existing pumping engines and filtering beds of their respective
establishments at Battersea and Hammersmith.
Where these 36-inch pipes cross the Thames, two others, 21 inches in diameter, are laid
between the Twickenham and Richmond banks, at a short distance below Richmond
Bridge, where the direction across the river is 463 feet.
These pipes were laid in at a depth of 16 feet below the Trinity datum, or about 9 feet
below the bed of the river, that the navigation might not be impeded.
Three coffer dams were made, of the several lengths of 185 feet, 136 feet, and 175 feet;
they were of an elongated oval form, and 40 feet in width in the centre; the sides were
curved, and the form such that the timber and iron works for the first served for the use
of the whole. After driving whole-timber piles, 6 feet apart, and bolting on two half.
timber waling pieces (in height), half-timber guide sheeting piles were driven, to correspond
with the main piles, and two tiers of outside walings were fixed, and the spaces filled in
with half-timber sheeting piles.
The bed of the river was then dredged, through 4 feet 6 inches of gravel, to a tenacious
clay; puddle was filled in against the piles up to one foot above low water, the gravel ex-
cavated being piled upon the puddle of the first, forming a backing. The joints of the
piles were then caulked with oakum from without; after this the trench for receiving the
pipes was excavated, the dams being drained by Gwynne's centrifugal punıp, worked by
engine power. The whole was completed on the 20th June, 1854.
Pumping Establishment at Hammersmith has three engines; the dimensions and power of
which, when working at full speed 22 hours out of the 24, allowing on an average two
hours each engine for repairs, was as follows, in 1850:—
SUPP.]
:1645
WATER SUPPLY.

Cylinders.
Number
of the
Diameter
Engine. in inches.
No. 1.
2.
54
54
3.
64
Pumps.
Nominal
Gallons per
Gallons per
Horse
Twenty-two
Stroke
Diameter
Stroke
Annnm.
in feet.
in inches. in feet.
Power.
Hours.
∞ ∞ ∞
8
20
8
8
20
23
∞ ∞ ∞
8
70
1,912,680
698,128,200
70
1,912,680
698,128,200
8
105
2.530,440
923,610,600
245
6,355,800 |2,319,867,000
The total Capital of the West Middlesex in 1851 was stated to be 830,000l., the average
per-centage upon which was 41. 5s.
F
8. d.
The annual cost for coals, engine, stores, and repairs of works
Wages -
Paving, plumbing, repairing pipes
Wages -
Salary to Secretary
1,111 4 11
919 19 4
478 19 7
1,982 5 4
800 0 0
Engineer
Rent
Rates and taxes
#
1
L
600 0 0
337 19 8
-
2,176 4 7
8,406 13 5
One year's water rates for the year 1850, 64,920l. 2s. Id., not deducting commission.
The total expenditure for the year 1850 was thus stated:
Collector's commission
-
Cost of management, directors, auditors, &c.
Officers and servants
Office charges, including rent, taxes of do., &c.
Working expenses, cost of paving
£ 8. d.
1,840 4 0
-
1,161 6 0
2,986 5 0
928 16
9
157 1
7
""
plumbing
54 15
pipes, plugs, &c.
Total
wages
201 6
2,003 1
ગ૭
5
1
Pumping establishment, cost of coal
-
1,606 11 0
"9
engine stores
repairs
116 2 3
113 4 6
930 6 2
""
43
wages
Disbursements, parliamentary and law
Superannuation
Interest
-
Repairs of turncocks' houses
Rents
Rates, taxes
New works
330 0 2
71 0 0
10
3 10
69 2 10
366 14 6
2,186 7 5
15,132 8 9
- 2,803 18 9
17,936 7 6
GRAND JUNCTION Waterworks are on the Surrey side of the Thames, three hundred and
sixty yards above Kew Bridge and extending nearly half a mile in length. They have
six engines on the north side of the Brentford turnpike road, and one engine at
Paddington, near the Great Western Railway terminus. At Kew Bridge is a depositing
reservoir and filter bed, and a storage reservoir at Campden Hill, and another at the
Paddington works.
The contents of the depositing reservoir at Kew Bridge is
That of the filter bed ditto
Store reservoir, Campden hill
19
Paddington
Imperial Gallons.
5,000,000
3,500,000
6,000,000
3,400,000
17,900,000
These reservoirs are partly excavated and partly embanked, the sloped bank being
formed of earth and puddled clay, the inside slopes lined with concrete, and the bottom
1646
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
paved with bricks and concrete.
the bottom is coated with gravel.
Mains and Pipes.
The Paddington reservoir is formed of brick-work; and
1 trunk main, 30 inches diameter internally
271
24
}
Total length of trunk
Branch main 12 inches diameter internally
1
-
Yards in length.
12,991
3,069
-
16,060
"9
9
99
8
""
""
7
"
""
6
1
7,869
4,860
484
8,267
4,614
Side services
""
Total length of branch main
6 inches diameter internally
5
""
4
3
"
""
79
Total length of side service
26,095
-
17,878
•
87,910
48,747
10,347
98,882
The Grand Junction Water Company has laid down an iron main 33 inches in diameter,
and 13,500 yards in length, from the north bank of the Thames, immediately above the
village of Hampton, 22 miles above Vauxhall Bridge as the river winds: this main at
Twickenham diverges through Isleworth and Brentford to the Company's works near
Kew Bridge.
Pumping Establishment.— There are seven Cornish boilers 33 feet 3 inches long, 6 feet
6 inches in diameter internally, with an internal tube 4 feet in diameter.
The chimney is circular, and 3 feet 8 inches in diameter inside at the top, 7 feet at the
bottom; its height is 131 feet above the surface of the ground; and 143 feet 8 inches
above high-water mark.
There are three air vessels: that attached to the Maudslay engine is 5 feet in diameter,
14 feet above the delivery pipe of the pump, and usually contains from 10 to 12 feet of
compressed air during the working of the engine.
The air vessel attached to the Boulton and Watt engines, is 5 feet in diameter, 13 feet
6 inches above the delivery pipe of the pump, and usually contains from 8 to 10 feet of
compressed air when the engines are working.
The air vessel to the Grand Junction engine is 5 feet 2 inches in diameter, 14 feet
8 inches above the delivery pipe of the pump, and usually contains from 8 to 10 feet of
compressed air when the engine is at work.
All the air vessels are supplied with air by means of small pumps attached to and
worked by the different engines.
The Stand Pipe. The top is 218 feet above Trinity high-water mark, the cistern or
reservoir at the summit being 4 feet 6 inches diameter, and 11 feet deep.
After the water has been pumped up to the top through the large stand pipe to the
cistern, it descends by 4 other pipes, each 12 inches in diameter; 9 feet being the square
of the diameter of the rising main, and that of each of the four descending being only
1 foot.
The engine power may be thus stated : —
Grand Junction engine
Maudslays' engine
East Cornish engine
West Cornish engine
Paddington engine
North filter engine
South filter engine
Total horse power
Horse power.
300
130
130
130
70
40
40
840
Three thousand seven hundred and ten tons of coal are annually consumed; the cost
per annum, on an average for the last seven years, has been 2,285l. 4s. 11d.: and the
quantity of water daily evaporated amounts to about 20,160 gallons.
The quantity of water pumped up and delivered in the year October 1848 to October
1849, was 1,289,184,950 imperial gallons, the gross supply of which is equivalent to 252
imperial gallons per house per day, after deducting for street watering, large consumers, &c.
SUPP.]
1647
WATER SUPPLY.
The quantity of water supplied for street watering, during the same year, was about
54,960,000 imperial gallons; the charge is at the rate of one penny per superficial yard,
for an unlimited supply given twice a day during the season it is required.
To water a mile of road of an average width of 30 feet twice a day, would probably
require 14,000 imperial gallons per day.
For the extinguishing fires the supply is gratuitous; and there are within the district of
the company 2,117 fire plugs.
The total capital of the Grand Junction Waterworks in 1851 was 523,7357.; the
average per centage, 31. 19s. 6d.
The yearly expenses for coals, engine, stores, repairs
Wages
Paving, plumbing, repairing pipes
Wages
Salary of Secretary
Rent
of Engineer
Rates and taxes
•
£ S. d.
3,089 8 0
-
1,135 15
6
982 4 3
845 8 6
600 0 O
400 0 0
315 19 11
673 15 8
Gross amount of year's water rates for 1850, 46,740l. 19s. Ild.
8,042 11 7
The total expenditure by the company for one year, to Michaelmas 1850, is thus
stated:
Collectors' commission
Cost of management : Directors and Auditors
Salaries
Rates and taxes
Office disbursements
Law charges
Working expenses: iron main and pipe repairs
Stopcocks and plug-boxes do..
Paving repairs
Lead pipe repairs
-
-
£ S. ď.
1,196 17 1
521
0 0
1,395 0 0
969 10 6
423 1 9
379 19
7
102 8 0
107 12 11
224 15 4
9 13 6
102 6 10
61 3 2
General street work
Tools, &c.
Offices and premises' repairs
Repairs of reservoirs and filters
Total wages
Pumping establishment: repairs of engines and houses
Coals
Engine stores
Reservoir and filter charges
Total Wages
64 11 1
912 11 0
211 13
+
9 15 8
2,478 0 1
345 6 4
564 18 11
1,143 7 0
11,193 12 1
SOUTHWARK AND VAUXHALL Water Company has 24 acres of land on the banks of the
river Thames, near the Red House at Battersea; and the source of supply is in the bed
of the river, considerably below low-water mark, on the southern side. The water is
taken in through a 4-feet culvert pipe, by a lifting engine, which is worked between four
and five hours of each falling tide, commencing to pump two hours and a half after ebb.
Reservoirs. There are two depositing, and two for filtering. The first depositing has
an area of 120,000 superficial feet, is capable of containing 11,000,000 gallons; the second,
21,000,000 gallons, the area of which is 250,000 superficial feet, the first depositing reser-
voir being usually filled to 9,360,000 gallons, and the second to 19,500,000 gallons. The
first filtering reservoir has 33,000 superficial feet of surface, and contains 3,000,000 gallons;
the second has 88,000 superficial feet in area, and a capacity of 8,000,000 gallons.
The filter medium is composed of five strata: first, at the top, two feet thick, is a layer
of clean, sharp, river sand; then a layer, 1 foot thick, of hoggin or fine gravel, under
which is a 9-inch layer of fine screened gravel; below that another, of the same thickness,
of rough screened gravel; and the fifth, or lowest layer, is 1 foot thick, composed of
coarse gravel.
After the water has percolated these five media, it is received into brick tunnels, formed
with open joints in cement, which communicate with a main tunnel leading to the pump
wells of the engines.
The Southwark and Vauxhall Company has laid down a 36-inch main, 23,000 yards in
3648
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
length, from the north bank of the Thames above Hampton. This main, after it arrives at
Twickenham, continues through Putney and Wandsworth to the side of the company's
works in the New Park at Battersea.
The Waterworks Clauses Act, which passed in 1847, indicates the future source whence
water for the supply of the metropolis may be taken; and a limit was given of three years.
only from the passing of the Act, for the change to be adopted by the West Middlesex,
the Grand Junction, and the Southwark and Vauxhall Companies.
The pumping establishment has four engines.
Diameter of
Cylinders
in inches.
Length of Stroke
in feet.
ft. in.
17
No. 1. engine
Pump
64
10
6
32
10 4
50-horse power by Boulton and Watt.
No. 2. engine
Pump
64
11 8
Cornish engine, 130-horse power.
331
10 6
No. 3. engine
Pump
31
6 3
211
3 7/2/2
Do., 145-horse power.
24
No. 4. engine
and combined
8
0
Sims' patent lifting, 30-horse power.
40
Pump
60
8
Eight boilers supply steam to the four engines, and burn, on an average, daily 8 tons of
coal, the average price of which, during the last seven years, has been 13s. 3d.
The Stand Pipes are 185 feet above the Trinity standard, and vary in their diameter, the
six being each made proportionate to their duty. Those by which the water rises are
48 inches, 30 inches, and 18 inches in diameter; and those by which the water descends
are 30 and two of 24 inches. The 27-inch main, and 20-inch, conduct the water from the
engines.
Mains and pipes:
2,000 yards of 27-inch pipe, internal diameter.
1,050
24
do.
4,250
20
do.
1,100
15
do.
"
12,000
12
do.
29,500
9
do.
Branch mains:
45,500
26,000
65,500
Side services:
49,500
16,500
765
49
do.
do.
do.
do.
3
do.
Services for small streets:
408,000
4, 3 and 2-inch, do.
Making altogether a total of 380 miles of iron pipe, &c.
There are 34,864 houses of various kinds supplied with water; about 2000 have
not the water laid on; but their inhabitants receive it from the stand pipes.
There are 243 common stand-cocks, 1060 stopcocks, and 3500 fire-plugs.
The quantity of water delivered during the year 1849 was 2,195,006,370 gallons.
The Street Watering. Every mile has cost upon an average 50l. to 60%, according to
their state; and probably 43,200,000 gallons of water have been required in the season.
The total capital of the Southwark and Vauxhall Water Company in 1851 was 439,662). ;
aid the average per-centage 4l. 15s. 2 d.
Annual cost for coals, engine stores, repairs
Wages
Paving, plumbing, repairing pipes, &c-
Wages
Salary to Secretary
Engineer
Rent
Rates and taxes
•
£
4.
8.
2336 4 2
1415 14 (
700 11 (
1156 17 10
400 0 0
400 0 0
815 19 11
1455 12
6
2180 19
શ
5
SUPP.]
1649
WATER SUPPLY.
One year's water rates due ending Michaelmas 1848, amounted to 38,362. 1s. 5d.
The total expenditure for the year ending Michaelmas 1850 amounted as follows: —
Collector's commission
Cost of management:-Directors and Auditors
Officers and servants
Rent, taxes, and rates
Office disbursements
Working expenses:
Plumbing ditto
Paving repairs
Iron pipes, cocks, &c.
Plug and cock box repairs
Tools
Wages
Pumping establishment, coals
Oil, tallow &c.
Reservoir charges
Engine and boiler repairs
Tools
Wages
Repairs of works
Office premises
Parliamentary charges and law expenses
-
£ 8. d.
1,313 4 2
599 8
2200
1,491 0 0
1,309 19 7
406 3 3
378 11 9
66 3 2
390 16 8
56 1 6
-
39 18 5
1,279 10 0
1,640 17 5
·
708 8 10
-
1,022 19 5
899 9 6
40 0 0
0
1,415 14
69 8 7
9 5 5
204 15 0
13,341 12 8
LAMBETH Waterworks, originally established near Waterloo Bridge, have recently been
removed to Seething Wells, Ditton, above Kingston-on-Thames. The districts comprised
in the Lambeth Waterworks Act (1848) include the parish of St. Mary, Lambeth, as
well as the parishes and hamlets of Newington, Christ Church, St. George the Martyr,
Camberwell, Dulwich, Norwood, Westow Hill, Sydenham, Penge, Beckenham, Lewisham,
Streatham, Croydon, Clapham, Wandsworth, Battersea, Putney, Tooting, Mitcham, Mer-
ton, Wimbledon, Maldon, Morden, Kingston-on-Thames, Surbiton or New Kingston,
Long Ditton, Esher, and Thames Ditton; and the number of houses at present supplied
with water by this company amounts to 26,000.
The volume of water flowing, in ordinary seasons, down the river Thames past Seething
Wells, is 1,200,000,000 gallons per day, and in the dryest period of the year does not fall
below two thirds of that quantity.
The site of the new establishment is a mile and a half above Kingston-on-Thames,
23 miles by the course of the river above London Bridge, and upwards of three miles
above the range of the tide.
The clearness and purity of the water was the chief cause of the selection of this part of
the river for the supply, which is seldom disturbed except during floods; to avoid this in-
convenience, there are a series of sunk reservoirs, containing layers of sand, shell, and
gravel, through which the water descends constantly, and filters into subterranean culverts
and receiving wells.
There are four filterers, each having two compartments 75 feet in length, 45 feet wide,
with segmental ends, making a total length of 90 feet. These are 30 feet in depth; but 13 feet
of the upper portion was constructed to keep out the flood waters.
The water is obtained from the river through two vertical cast-iron gratings lined on
the inside with screens of copper wire; a 36-inch culvert passes between each of the two
filters, which has a branch on each side furnished with 30-inch sluice valves, and the water
passes by them into a semicircular chamber, from whence it is carried to the top of the
filtering media.
A concrete foundation a foot thick, covered with brick-on-edge paving, forms the bottom
of these filters; a space of 4 feet for stowage of filtered water is then formed by a layer of
4-inch slate slabs, with open joints, upon which is laid coarse Thames ballast, coarse sand,
and fine Thames sand, in equal thicknesses, making altogether 5 feet of filtering material.
On this the water lies in depth equal to that of the filtering media, through which it
percolates to the stowage below, and then, by 30-inch culverts furnished with valves, into
the well under the engine house.
7800 feet is the computed area of each of these filters, or the four 31,200 superficial feet;
and in the course of twenty-four hours they will filter nearly 3,000,000 gallons.
The four steam engines are so contrived, that any two of them can be linked together
and worked as one engine of 300-horse power. The smallest cylinder is 24 inches in
diameter, and 5 feet 6 inches stroke, and receives the steam at a pressure of 30 pounds; it
then passes into the larger cylinder, 48 inches in diameter, and 8 feet stroke, and by ex-
pansion is reduced down to five-pound steam, when it passes into the condenser. The bean
5 N
1650
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
of each engine is 28 feet in length, and the connecting rod 24 feet, the cranks are 4-feet
radius, fixed to a rotatory shaft, with a large fly-wheel to each pair of engines.
The works already established are capable of extension; and engines of 600-horse
power, calculated to pump 10,000,000 gallons per day, are now in operation.
These steam
engines are on the double or compound cylinder high-pressure expansive principle, of the
most improved and substantial construction.
The aqueduct or main iron pipe contains, when filled, 1,667,822 imperial gallons, is
30 inches in diameter, and 10 miles 3 furlongs in length; it passes through Surbiton
(Kingston New Town), proceeding two miles by the South-Western Railway, and
thence along the roads through Merton, Tooting, Balham and Clapham Park, to the
reservoirs originally constructed at Brixton Rise and Streatham Hill; the former being
105 feet above high-water mark.
At the Brixton reservoir there is an engine which can raise the water an additional
height of 187 feet, making a total of 372 feet above Trinity high-water mark. This iron
main is provided with several stop valves, to prevent any back flow, and with all necessary
venters. The reservoirs originally constructed have been greatly improved; and all the dis-
tributing mains and pipes have been retained, and rendered, as far as practicable, subservient
to the new works.
The 30-inch iron main which conducts the water from the works to the Brixton reservoirs,
weighing 8000 tons, rises about 10 feet per mile; and the velocity of the water passing
through it is calculated at something more than 3 feet 6 inches in a second, delivering in
that time 17 cubic feet of water.
The engines are so contrived that they can be kept at work constantly with a minimum,
medium, or maximum speed, according to the quantity of water required for the supply,
by which means a very great economy of fuel is obtained, as well as less injury incurred,
and consequently less repairs required to the engines.
The pumps are double-acting, with bucket and plunger, requiring but two valves, instead
of the ordinary number of four. The outer cylinder is 233 inches in diameter, and 7-feet 8-
inch stroke, the plunger on the inside being 16 inches in diameter.
When any two of these pumps are required to be worked at the same time, they are so
connected with the engines that a regular and constant flow of water is maintained through
the great supply pipe; thus the water passes through these pump barrels directly into the
main, without incurring the stoppage and concussion found to take place in the four-
valved double-acting pump. There appears to be no necessity for any stand pipe, as the
steadiness of motion in the working of the engines testify; and the main has an equable and
regular flow, without any oscillation of pressure during the action of pumping, which is
usually produced by the expensive addenda of a lofty stand pipe.
There are nine boilers of a cylindrical form, each 31 feet 6 inches long, and 5 feet 6 inches
in diameter, with an internal furnace-tube continued through its whole length. These boilers
are furnished and arranged in such a manner that any of them may remain at rest. A chimney
100 feet in height, concealed in a square tower, carries off the smoke from the furnaces.
The reservoirs at Brixton are two in number, and occupy an area of three acres, with an
available capacity of 12,150,000 gallons. These are constructed of brick, with a paved
bottom. Another reservoir, 14 acre in area, containing 3,750,000 gallons, has also brick
side walls, with an earthen bottom.
Mains and Service, as laid down previous to the removal of the works to Ditton,
amounted to a length of 135 miles, consisting of principal mains, of 23 inches, 20 inches,
18 inches, 12 inches, and 10 inches in diameter.
The secondary mains are 9 inches, 7 inches, and 5 inches in diameter.
The service pipes are 2 inches, 3 inches, 4 inches, 5 inches, and 7 inches in diameter.
Two thousand two hundred and forty-six fire plugs are placed throughout the district.
The quantity of water delivered by this company in 1849 is stated to be 1,123,200,000
imperial gallons.
The quantity allowed for street watering was 28,600,000 gallons, the charges for which
amounted to 5 to 8 of a penny per superficial yard.
For flushing sewers 10,500,000 gallons, and for fire-extinguishing 7,000,000 gallons.
The Lambeth waterworks now possess considerable advantages, drawing water from
that portion of the river where there is uniformly an abundant quantity, partly derived
from the spongy chalk strata, in which are reservoirs of great capacity, which during the
summer months, afford an extraordinary supply, compensating for more than the ordinary
effects of evaporation The bed of the Thames in London covers 2,245 acres; and it
has been estimated that 4,170,000 gallons of water are carried off by evaporation in the
course of the day. This may account for the great diminution of the contents of several
streams during the summer months, when each acre of water loses per day upwards of 1800
gallons by evaporation alone.
In April 1850, the buildings of the old Lambeth Waterworks contained three engines;
the works at Brixton Hill, one; and another at Streatham.
SUPP.]
1651
WATER SUPPLY

Maximum
120 horse engine
90
12
>>
""
At Brixton, high pressure
20 horse power
At Streatham, high pressure
10 horse power
G
Strokes per Height of Ser
Diameter of
Cylinders.
Length of
Stroke.
Minute.
vice above
Trinity Mark.
Inches.
Feet.
Feet.
643900
8
14
140
46
81/12
12
140
20
3
22
100
16
CO
3
33
200
11
233
38
350
In August, 1851, the total capital of the Lambeth Company was stated to be 368,1911
and the average per-centage 2l. 16s. 5½d.
The annual cost of coals, engines, stores, repairs
Wages
Paving, plumbing, repairing pipes
Wages
Salary to secretary
Engineer
Rent
Rates and taxes
1
£ s. d.
2,475 5 1
585 9 6
565 12 4
1,595 18
8
500 0 0
200 0
O
60 0
0
-
1,616 2
0
7,598 7 7
One year's water rents for the year 1850
Receipts from other sources
The gross rentals being 25,910l. 18s.
S. d.
23,462 13 8
216 8 2
23,679 1 10
The total expenditure for one year ending Michaelmas 1850 is thus stated :—
Collector's commission
Cost of management,
Directors
Officers and servants
Rent of offices, taxes
Working expenses,
Plumbing
paving
-
Repairs of pipes, cocks, &c.
Pumping establishment,
coals
Engine stores, repairs, &c.
Wages
Reservoir charges
Rates and taxes
Law charges
Premiums to former officers
·
£
8, d.
909 18
4
600
0
O
1,000
0
O
572
13
6
51 12
2
135
19 3
700 Ο 0
1,705 2 8
1,102 19 11
642 11 6
480 4 11
7
10 2 5
1,605
12
Interest
Addition to plant, iron pipes, &c.
J
220
0
2,707
7
04
14,299
13
4,8.50
13
૦૦
8
**
4
19,150
7 0
·
Already expended at Ditton up to this period, 104,6821 8s. 5d.
EAST LONDON Waterworks, receive their supply from the river Lea, which is pumped
into reservoirs two of which, at the old Ford works, were made in 1809, and are lined with
brickwork. On the eastern side of the river Lea are two others, made in 1826, which, by
means of an iron tunnel laid under the bed of the river, communicate with those pre-
viously mentioned. These are lined partly with brick, and partly with Kentish rag stone.
Another reservoir at Lea Bridge, lined with Kentish rag and gravel, and another at
Stamford Hill lined with brickwork. These six reservoirs, and canal uniting them, contain
35,000,000 gallons, and the water is cleansed by deposition.
The mains extend over a distance of 88 miles, varying in diameter from 42 inches to 5
inches, and are always charged with water under pressure.
5 N 2
1652
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
Service pipes throughout the district measure 140 miles, and vary in diameter from
4 inches to 3 inches.
At Christmas 1849, there were 56,673 tenements supplied with water; the inhabitants
of 3,297 houses received water from 389 stand cocks, and 516 from common cisterns.
The quantity of water delivered in the year ended 25th January 1849, amounted to
3,222,753,876 gallons.
Dimensions and power of engines and water wheels belonging to East London Water-
works Company, when working at full speed for twenty-four hours round:

Cylinders.
Pumps.
Diame
Diame.
Horse
Power.
Gallons per
24 Hours.
Gallons per
Annum.
Stroke
ter in
inches.
in feet.
ter in
inches.
Stroke
in feet.
The Wicksted engine
90
11
44
11
170
Cornish engine -
80
10
41
9
120
Ajax
60
8
27
Hercules.
60
Twins
36
∞ ∞
8
27
8
1724
∞ ∞ ∞
8
80
7,954,330 2,903,330,450
6,345,216 2,316,003,840
3,723,149 1,358,949,385
8
80
8
73
3,723,149 1,358,949,385
3,454,616 1,260,934,840
Lea Bridge, large wa-
ter-wheel, double-
acting pump
Small do., three pumps
Stratford water-wheel,
201
7
1,001,184 365,432,160
40
11
3
11
3
LO
5
443,232 161,779,680
89,250 32,576,250
do.
-
9
3
Total
568 26,734,126 9,757,955,990
The total quantity of water, delivered in the year by the nine companies, was about 163
thousand millions of gallons, not double the quantity that could be raised by this com-
pany alone, if they worked their whole engine power for the entire 24 hours throughout
the year, and raised the water to a similar elevation.
The capital of the East London, August 1851, was stated at 752,1281., and the average
per centage 4l. 14s. Ild.
The yearly expenses for coals, engines, stores, and repairs
Wages
Paving, plumbing, repairing pipes
Wages
Allowance to Secretary
Rent
99
Engineer
Rates and taxes
The gross amount of the water rates for the year ending Christmas
1850 amounted to
From other sources
Total revenue
The total expenditure for the year ending Christmas 1850:
Collector's commission
Director's attendance
Officers' salaries
Rents
Rates and taxes
-
Office expenses
-
£ S. d.
4
1,849 15
1,074 0 9
963 6 6
2,607 5 9
700 O 0
500 0 0
1,005 6 4
3,798 13 10
12,498 8 6
£ S. d.
70,161 7 6
495 16 4
70,657
3 10
£ S. d.
2,439 15
2
-
1,575 0 0
·
2,265 19 10
-
1,228 11 4
Street work: Wages
Paving
Plumbing
Pipes, cocks, branches, plug box
Sundry materials
·
Carried forward
1
D
4,082 2 8
614 12 10
766
7 3
248 17 7
14 10 1
391 16 5
58 10 9
13,686 3 11
Supp. 1
1653
WATER SUPPLY.
Brought forward
Pumping and water wheels:
Wages
Coals
Stores
Repairs of engines
Reservoirs and canal:
Wages
Repairs
Sundries
·
£
S.
d.
13,686 3 11
1,087 3 3
1,516 6 10
376 18 6
920 11 10
477 8 1
470 17 10
30 12 2
211 4 6
Turncocks
Yard, wages to fireman, gate keeper, &c. &c.
Sundries -
Stable, including wages of carmen
Smiths' and carpenters' wages
Insurance
Law and parliamentary expens: s
Pensions
General disbursements
Repairs to engines damaged by fire
1,673 19 0
679 13 7
38 1 3
99 3 8
4
Expenses for extending the works
Total expenditure
17 6 6
2,204 17
184 1 6
297 1 11
1,389 18 10
25,361 10 6
4,364 19 5
£29,726 9 11
The KENT Waterworks, established in 1809, the celebrated Mr. Smeaton being employed
as their first engineer, and the parishes supplied by them with water include St. Nicholas
and St. Paul, Deptford, Greenwich, Lee, Lewisham, Hatcham, part of Rotherhithe, Wool-
wich, Charlton, Plumstead, St. Mary, Bermondsey, Peckham, and Peckham Rye.
The water is partly drawn from the river Ravensbourn, and the small river Pool.
Reservoirs, of which there are two, are capable of holding 6,319,410 imperial gallons,
and the water is cleansed by deposition.
There are also two filtering beds of 14 acres, of sand service.
Three Reservoirs for filtered water, 2 at Woolwich and 1 at Deptford, holding 3,865,344
gallons.
The height of service is 220 feet above high-water mark, and the pressure of high service
at the works is equal to a head of water of from 280 to 300 feet.
Mains and pipes extend in length about 100 miles, and are of various diameters, and
the quantity of water delivered in 1850, was 493,392,858 gallons, or 108 gallons to each
house supplied, the number of houses being 11,481, which includes 408 supplied by 48
stand cocks.
Three Steam Engines, viz. one Cornish, two Boulton and Watt. Gross amount of water
rents in 1850, was 16,100l. 8s. 7d.
The total capital, August 1851, was stated to be 221,3771., and the average per-centage.
31. 1s. 4d,
The yearly expenses for coals, engine stores, repairs
Wages on ditto
Paving, plumbing, repairing pipes
Wages
Secretary
Engineer
Rent
F
8.
d.
1,076 12 7
395 4 0
220 16 11
751 11 2
500 0 0
400 0 0
121 7 2
724 17
Rates and Taxes
The total expenditure for the year ending 1850 is thus stated
Collectors' commission
The directors
Officers and servants
Rent, taxes, and other office disbursements
4
£4,190 9 2
£ 3. d.
605 11 1
521 17 0
900 0 0
184 5 4
Carried forward
- £2,211 13 5
5 N 3
1654
[SUPP
THEORY AND PRACTICE OF ENGINEERING.
Street work: plumbing
Pipe laying
Brought forward
£ s. d.
2,211 13 5
10 6 4
83 19 8
Pumping establishment:
Coals
704 15
Oil, tallow, &c. for engines, and repairs of ditto
Rent of reservoir
Ditto springs
Repairs of river banks, &c.
364 9
19 8
624
101 18 10
232 8 9
113 17 1
149 18 7
Filter bed
Repairs of premises
Law charges
General expenses
Insurance
Rates and Taxes
Interest on loans, &c.
Water wheel
Wages
29 14 8
16 7 3
14 19 0
791 19 1
928 9 5
9 5
1,260 9
8
1
£7,043 19 8
HAMPSTEAD Waterworks derive their supply from the springs at Hampstead, Ken Wood,
and two Artesian wells, and occasionally from the New River.
The Reservoirs are formed by embankments across the valley between Highgate and
Hampstead, and have a total area of about 35 acres ; with depths varying according to the
flow.
The mains and pipes are of the length and diameters as under :-
12 inch main
7
453 yards.
9,878
6
543
""
"
""
340
3,306
28,221
3,913
The engine power consists of one high-pressure condensing engine of 12 horse power,
one Cornish pumping engine with a 44 inch cylinder and ten feet stroke, equal to 60 horse
power.
The quantity of coal used in the year 1849 was 234 tons, delivered at the rate of 28s.
per ton.
The total number of houses supplied with water in 1849 was 4490, and within the dis-
trict 460 fire plugs.
The total capital of the Hampstead Water Company was stated to be, in 1851, 86,195l.,
and the average per-centage, 41. Os. 8d.
One year's water rates for the year ending 31st March 1851, not
deducting commission, amounted to
Receipts derived from other sources
£ S. d.
7,903
2 3
56 5 0
7,959 7 3
The total expenditure for the year during the same period:
Collector's commission
Cost of management: Directors
Officers and servants
Rent and expenses of office
Working expenses: Paving, plumbing, repairs
Wages
Pumping establishment : Coals, engine stores, pump
Reservoir charges: Repairs
Wages
Wages
-
Sundry disbursements: as, New-River Company rent
City of London
Earl Mansfield
Yard
-
Carried forward
-
U
S. d.
395 3 5
75 0 0
258 16 0
91 2 6
178 12
5
387 8 0
673 14 10
328 7 0
62 18 11
54 12 0
1,208
7 11
80 0 0
104 10 0
50 0 0
£3,948 13
SUPP.]
1655
WATER SUPPLY.
Brought forward
Mr. Pricket
Rates and taxes
Sundries -
Extension of mains and services
-
New works for procuring further supply -
Total -
£
S.
3,948 12
d.
0
23 O 0
222 1
0
104 11
2
4,298 5
2
620 19
0
1,115 6 5
£6, 34 10 7
CONSTANT SUPPLY.-The difficulties of obtaining for the public this desirable boon have
been overcome by Mr. Simpson, president of the Institute of Civil Engineers, in the water
works at Bristol, the most complete of any that have been established, upon the principle
of natural pressure.
The great desiderata in works of this nature which are the subsidence of any earthy
particles carried by the water, the maintenance of such velocities in the current as will
prevent all ordinary accumulations and deposits, and the easy means of periodically cleans-
ing the water conduits of any accumulations, are in this instance admirably obtained; and
may be considered to imitate, and perhaps excel, the system, practised by the Romans in
the days of Frontinus. The use of iron pipes, and tubular channels made of the same ma-
terial, have facilitated the labours of the British Engineer and enabled him to accomplish
works at a cheaper rate than could have been effected by the ancients; the iron age gives us the
power of forming tunnels in the air and avoiding the multitude of lofty piers necessary
for arches of stone or brick.
The water is selected from the springs at Barrow-Gurney, Litton, and Chewton
Mendip, the first being about 5 miles and the last 16 miles, as measured along the line
which the nature of the country pointed out as the best for the direction and construction
of the works.
Mr. Herepath's analysis of the water selected gives but 2·316 grains for the total salts
contained in an imperial pint of 8750 troy grains. These salts are chlorides of calcium
and sodium, sulphates of soda, magnesia, and lime, and the carbonates of lime; and,
according to Dr. Playfair, the waters at the springs vary from 18 to 21 degrees of hardness.
The springs at Chewton and Litton are collected below the ground level, by means of
opeu-jointed drains, or culverts, and conveyed by the several branches to the principal aque-
duct at East Harptree, a distance of 24 miles, where it joins the tunnel driven through the
high land above Harptree village, The inclination given to this aqueduct, which is
constructed of masonry, is 5 feet per mile.
•
The Harptree tunnel is 1 mile in length, driven through a hard magnesian limestone
conglomerate: this, like the former, is lined with masonry throughout, and corresponds
also in section with the other, as well as in the fall given to the current of the water.
At Harptree Coombe, a tributary aqueduct from Coombe unites with the main works.
The waters, now collected, are conveyed across a ravine by means of a wrought iron
tube, 350 feet in length, supported on piers of masonry at intervals of 50 feet. The in-
ternal dimensions of the tube accord with the stone aqueduct, and the ends are connected
by means of stone tanks and collars of clay puddling.
The iron tube is placed on cast iron saddles, fixed to the piers and abutments, friction
rollers or balls being introduced under the tube, to allow any expansion or contraction
produced by the changes of temperature which might affect its stability or injure the stone
piers.
250 yards beyond the iron tube, and near to West Harptree, the stone aqueduct is dis-
continued, and a line of cast-iron pipes, 30 inches in diameter and 44 miles in length, is
laid as an inverted syphon- rivalling the aqueduct at Lyons (see page 179.) across the
valley, near Compton Martin, and nearly on the summit of the watershed between the
River Yeo, and the westerly branches of the Chew, and thence over Breach Hill to the
tunnel through North Hill.
The line of pipes undulates with the contour of the land, and has a fall of 42 feet 6 inches,
so arranged that the escape of the air from the pipes, while they are being charged
with water, takes place at each extremity, and at a high point on Breach Hill, where there
is a venter or open upright pipe, clevated sufficiently to allow of any overflow of water,
round which a stone obelisk, 50 feet in height, has been built, which steadies and
strengthens it.
The remainder of the line, from the 30-inch pipes, to the stone reservoir at Barrow,
consists of a tunnel through North Hill, of a mile in length. Then a stone aqueduct,
with two wrought iron tubes across the valleys on Leigh and Windford Downs, each 834
feet in length, and similar to that already described at Harptree Coombe of 350 feet;
lastly the Winford tunnel, 1 mile in length.
5 N 4
1656
[Supp.
THEORY AND PRACTICE OF ENGINEERING.
Each of the wrought-iron tubes, described as 834 feet in length, rest upon abutments
distant from each other 800 feet, with piers between, placed at intervals of 50 feet, the
greatest height being 60 feet.
The sectional area of the iron tubes is 13 superficial feet, the water area 10, and the fall
per mile 5 feet.
The weight of wrought-iron work 84 tons, and cast-iron work 26 tons;
the cost of the iron work being 2617., and that of the masonry 2000l.
Each of the two iron tubes in the stone aqueduct already described are oval, their con-
jugate diameter being 4 feet 8 inches, and their transverse 3 feet 6 inches in the clear
inside.
Throughout the entire line of aqueduct, there are no paddles or gates for stopping or
shutting off the water. The mode adopted is to place sunk tanks at various points on the
line, at about a mile distant from one another, with which large bottom sluices are con-
nected, for the purpose of letting off the water, and intercepting the entire flow through
the aqueduct; and these are taken advantage of, as the means of cleansing the
whole work, from end to end. Wide weirs or overflows are connected with each of the
tanks, so as to prevent the aqueduct being overgorged with water; and thus the works are
protected from injury by floods, the carelessness of workmen, or otherwise, which would
probably have resulted from any system in which stop-gates, or paddles were adopted.
The total length of the aqueducts, tunnels, and tubes from Chewton Mendip to the stone
reservoir at Barrow is 11 miles; and the springs at Chewton are 400 feet above the level
of the high water line of the float or docks at Bristol the reservoir at Barrow being 300
feet above the same level. The whole of the water for the use of the city is thus conveyed
direct from the springs, and the rivulets and streams throughout the district, over which it
is passed, are left undisturbed, and remain the natural courses to carry off the rain
water. The stone reservoir at Barrow, 25 acres in area, is 5 miles from Bristol, and
from hence the water is conveyed to the city by two lines of main pipes, one 20 inches, the
other 10 inches in diameter; the former convey the Chewton water, the other that from
the Barrow springs. Three service reservoirs have been formed, one on the Bedminster
Down for the supply of that district, the second at White Ladies near Clifton, and a third
on Durdham Down, which has an elevation of 300 feet above the high water of the float.
The water is conveyed from Barrow, through the 20-inch pipe into the reservoir at
White Ladies; and here the quantity required for the higher service is pumped, by means
of steam-machinery, into the reservoir on Durdham Down; two engines, each of 30-horse
power, being employed.
From 60 to 70 miles of main and service pipe have been already laid down, of various
diameters, and upwards of 2,000,000 gallons of water per day are distributed: the Company
could supply daily double that quantity, which would be at the rate of 20 gallons for a
population of 200,000; and means are now afforded to the poorer inhabitants of Bristol of
having water delivered to their houses at a charge of less than 1d. per week.
Constant Supply(at Wolverhampton), by Wicksted at Tettenhall works, 2 miles from
Wolverhampton; the water is drawn from the new red sandstone, 820 feet below the
surface, and then forced up over a stand pipe 180 feet in height, the top of which is about
100 feet above the highest part of the town.
These works were originally constructed in 1845 for carrying out the principles of the
intermittent supply. Sandstone water generally ranges from 16° to 21° of hardness. The
intermittent system, after being two years in practice, was changed; and the supply is now on
the constant principle, the inhabitants finding they could not erect tanks or cisterns, and
therefore had no means of storing their supplies. To introduce the constant system, it
became necessary to construct an elevated reservoir, instead of passing the water over the
stand pipe, any stoppage of the pumps rendering it difficult to give the adequate and
constant supply. The stand-pipe system is also very expensive, the engines being required
to be worked both day and night; and, in case of fire, the pressure should always be on the
mains.
The stand-pipe system at these works required that the engine should be of sufficient
power to raise the whole supply of a week's consumption in 30 hours; and in conse-
quence of having no other elevated storage room than that contained in the stand pipe,
the engine was obliged to be worked 168 hours to deliver this quantity.
With a stand pipe only, the speed of the engine has to be altered, and regulated with
every variation of the draught on the mains: thus, although the mains are constructed to
deliver a very much larger quantity than the engine can pump at any one time, the parties
supplied can derive no advantage, as they can never draw the water faster than it is pumped.
Thus the variation of draught that can take place in the mains is limited to the speed of
the engine, instead of the velocity due to the head to which the water is actually raised.
The expense and inconvenience attending this system was found so great that it was
determined to construct a reservoir.
Very little alteration was required in the distributory works or arrangements: the sub-
mains were all proportioned to deliver the day's supply in the very small period of 24 hours.
SUPP.]
1657
DRAINAGE OF TOWNS.
The dead ends of the pipes were united to keep up a free circulation, which occasioned less
oxidation.
With the constant supply, it is necessary to have several guard cocks on the submains
and services; these are placed at an average distance of not more than 50 yards apart.
All the cocks are double-faced, so as to shut off the water either way. This is necessary
in case of repairs, or laying on the water to a single house. Upon the constant system, the
pressure on the mains is imperceptible, and there are no jerks.
The common bib tap produces a recoil; therefore the "screw down" is the best to pre-
vent this, where high pressure is introduced; and each house service has a stopcock, to
prevent any inconvenience from this cause, or to regulate it by partially turning.
Cost per house, for lead services, stopcocks, bib taps, and laying on, 16s. 6d., if tanks had
been used, the extra cost to each house would be 22s. 6d.
The intermittent system costs 136 per cent. more on this head than the constant supply
requires.
Cost where there is a front supply: -
Mains
Service pipes
Tenants branch
e--
£
S.
d
1
6 0
1
1
0
16
6
£3
3 6
6 per house.
Cost where there is a back supply:
Mains
Services
Tenants branches
en
8.
d.
}
6
0
14 0
7 0
£2
7
O per house.
DRAINAGE OF TOWNS.
'The next important requisite to a good supply of water is the means to be relieved
from it, when the uses to which it has been applied have destroyed its purity and loaded
it with all the adulterations that it must incur in its passage to its final discharge. That
sufficient power to effect this is at our command, is evident, when we remember that in the
metropolis alone engine power equal to 3500 horses is already used in the supply of water :
the question for us to consider is, how can a similar power be efficaciously applied for
the removal of that which is daily becoming a serious evil; and this involves a variety of
considerations, both retrospective as well as future.
All towns on the banks of rivers have now become difficult of drainage, in consequence
of the elevation of the beds of those rivers, arising chiefly from the deposits constantly accu-
mulating at their months, and increased by the establishment of mills, when, to obtain
greater power, the banks have been so raised that the pluvial waters can no longer enter
the main current, no attention having been paid to connect the ditches with the mill tails.
Many instances might be brought forward of the ill effects produced from the above
causes. In the town of Dartford the basements of houses, which a century ago were
perfectly drained, are now much below the beds of the rivers; and in several instances where
the bed of the Cranford, which stream discharges into the Darenth, has been sought for, the
remains of drains have been discovered considerably below those more recently constructed;
and layers of sand, of various colours, for many feet in depth, indicate the gradual rising
of its bed.
Wherever land is below the level to be thoroughly drained naturally, it becomes neces-
sary to institute some artificial means, to carry off all the water which, after due allowances
for evaporation, may remain in the soil, and which, if in too great a quantity, causes a
constant diminution of temperature in the atmosphere above it and produces disease among
the inhabitants.
The nine water companies annually supply 9 gallons of water to each superficial fcot
of the 65 square miles comprised within the whole of these respective districts, or a cube
nearly of 12 inches by 18 inches of water upon each superficial foot, which is something less
than half the quantity of rain which annually falls, viz.: 1,812,096,000 superficial feet
contained in 65 square miles, multiplied by 9 gallons, gives us 16,308,864,000 gallons,
which nearly corresponds with 16,755,430,362, annually delivered from the nine water
establishments that supply the metropolis and its suburbs. Taking 27 gallons of water
for each superficial foot, viz., 9 gallons delivered by the companies and 18 gallons rain-
fall, we have then to remove 48,926,592,000 annually by the sewers; or daily, upon an
1658
[Supp.
THEORY AND PRACTICE OF ENGINEERING.
average, 134,046,005, that is 44,682,002 gallons sent by the nine companies, and
89,364,004 supposed daily rainfall. We calculate that 272,000 houses are scattered over
the 65 square miles, and each provided with a pipe of discharge 4 inches in diameter, the
sectional area of which is 12:56 superficial inches, and supposing 12 such pipes to contain
the sectional area of a foot, we shall have upwards of 22,000 superficial feet as the amount
of discharging area. Comparing this with the sectional area of the Thames at London
Bridge, which is 19,586 superficial feet (see page 443.), we have nearly one-sixth more
in the area of the mouths of the 4-inch pipes than in that of the Thames.
The 9-inch barrel drain, so much in use, has a sectional area of 63.6 inches; and if
each house were provided with one of that dimension, their area of discharge would be
more than five times the sectional area of the Thaines. The evils that have been brought upon
the metropolis and most of our cities and large towns by converting the river into a main
trunk sewer, have to be remedied; and no cost should be spared to effect such a change as
shall restore the main as well as tributary streams to their pristine purity. After the con-
struction of sewers, the waters were rendered positively noxious, and the vapours or
gases arising from them injurious to the health of the inhabitants for whose use they were
contrived. This being now a received maxim, we must repair the evil done, and provide
some other outlet, as well as means of discharge for our sewers. Whether the chemist
decides that the contents of the sewage be useful or not, or the farmer hesitates to acknow-
ledge their beneficial qualities, the rivers must no longer be polluted.
London has upwards of 1000 miles of sewer, the cost of which has not been less than
5,000,000l. sterling, laid with various inclinations to discharge the entire volume of con-
tents into the Thames,- portions of which are by the tide carried up and down the river
to a certain distance. These sewers receive the discharge of the drains connected with the
numerous dwellings, stables, and manufactories; and in any arrangement for improving the
drainage of this vast city, it is important to interfere as little as possible with what has
already been executed at so vast an expense; the only apparent manner by which the system
can be improved is by collecting, at the points of discharge into the river, all the outpour-
ing, and, by other deeply laid sewers, conducting it to a distance, where it may be so dealt
with as not to be injurious to any portion of the community.
It is presumed that the pipes and drains, which connect the houses, &c., with the sewers
the length of which cannot be much less than 20,000,000 of feet, are in a complete condi-
tion. These drains, varying in diameter from 4 to 18 inches, are formed of tubular earthen-
ware pipes, or of brick laid in mortar or cement, usually with a fall of 14 inch in every 10 feet,
- a fall found sufficient to discharge freely whatever enters them, and are, or ought to
be, always provided with a trap at the mouth, or wherever they receive a fresh supply of
liquid of any kind.
kind. Where earthenware pipes are adopted, too much care cannot be taken
in securing the joints; for if the water is suffered to trikle through any crevice, it loses
its carrying power, deposits the solid matter as a sediment, and the pipe becomes ob-
structed. The water, also, escaping softens the soil upon which the pipe is laid, occa-
sions it to sink, ruptures the joint, and it no longer acts as a drain.
A pipe 30 inches in diameter, with a sectional area of 4·9 superficial feet, will deliver with a
velocity 3 feet 6 inches per second, about 10,000,000 gallons in the space of 24 hours; and all
the water supplied by the nine companies would require not more than five such pipes, with
a sectional area united of 24 feet 6 inches, or a cylindrical pipe the diameter of which was
not more than 5 feet 8 inches. We may therefore presume, that if a pipe of that diameter,
or five of 30 inches diameter, is sufficient to supply London with water at various heights
ranging from 100 to 200 feet, that the same would carry away with a very moderate fall
the water so delivered. A pipe 5 feet 8 inches in diameter, of the length of 9 miles or
47,520 feet, with a total fall of 72 feet, or 8 feet in a mile, would have a velocity of 4
feet 6 inches per second, and, by gravitation alone, would discharge upwards of 61,000,000
of gallons in the space of 24 hours.
Three such cylindrical pipes, or one 24 feet in diameter, with an area of 452.4 feet would
therefore theoretically carry away, not only the present water supply of the metropolis,
but also the 36 inches of rainfall or 18 gallons per superficial foot: a large estimate,
allowing none to be either evaporated or absorbed, discharged into the Thames.
The great sewer of Rome, the Cloaca Maxima, which drained the whole of that city as
well as the Campagna, was 14 feet in width and 32 feet high, where it discharged itself into
the Tiber, its sectional area being 448 feet, about 4 or 5 feet less than we have calcu-
lated as necessary to drain the district of London supplied by the water companies. The
height of the Cloaca Maxima being more than twice and a half its breadth, indicated con
siderable knowledge of the power of deep water for scouring the bottom of a sewer or re-
moving the accumulations left by deposition.
An elliptical sewer, 30 feet in height and 20 feet for its transverse diameter, with a sec-
tional area of 471 feet 3 inches, would be perhaps preferable in point of form to the Cloaca
Maxima. The circumference internally of such an ellipse would be about 78 feet 6 inches.
And if the sides were constructed of brickwork 18 inches in thickness, the outer circumfe-
SUPP.J
1659
DRAINAGE OF 10WNS.
rence would be about 88 feet. A mile, or 5280 feet × 83 feet, the mean circumference,
gives 440,880 superficial feet of work; and if this be two bricks in thickness throughout,
we have 587,840 superficial feet of reduced brickwork, or about 2161 rods ; if cement
were used for its construction, the cost of the brickwork might be estimated at about
25,000l. a mile : adding 5000l. per mile for the excavation and accidental expenses, 30,0001,
per mile would be the estimate for the sewer.
Such a sewer would be ample for the whole of London; but if 9 miles were constructed
on each side of the Thames, the total cost, with all the connections with the old sewers
might be performed for less than 600,000Z. There would then be two sewers adequate to
the discharge of the entire area, or of sufficient dimensions to do double the duty required,
supposing the two districts to be drained by them were equally divided in area, or that 32½
square miles drained into each sewer of 9 miles in length.
These sewers must be constructed beneath those which at present discharge into the
Thames, at the most convenient distance from their openings into the river, and made to
receive all their contents, carrying the latter away to a reservoir at the extremity, where
pumping would either lift it in into the river or pass it to lands which would be benefited
by its manuring properties. The lift required would not exceed altogether 100 feet, and
the mouths of the present sewers could be left open, to carry any surplus waters into the
Thames as a safeguard against torrents during storms.
Instead of one lift for the whole of the fall, several might be adopted, at convenient
distances, or one established at the termination of each mile, by which arrangement some
expense might be saved in deep digging, though perhaps not adequate to the additional
outlay for constructing separate engines and houses for the managing department.
If the pluvial water were suffered to be discharged into the Thames, carrying with it
the partial contents of the sewers only during storms or heavy rains, then the dimensions
of the 18 miles of new sewer might be diminished to one. quarter each of the two
main discharges, 9 miles in length, if made elliptical. would require that their inter-
nal diameters should be 7 feet for the vertical, and 4 feet 4 inches for the transverse,
diameters, the outer circumference of which would be one quarter only of that already
estimated as 30 feet by 20 feet.
We should then have a sewer on each side the river, equal in power to the pipes
necessary to the discharge of all that is delivered by the water companies, or double the
capacity requisite for the removal of the sewage under ordinary occasions; and only
during very heavy rains, would anything pass through the mouths of the old sewers into
the river.
120,000l. would suffice for the construction of two such sewers, which would be found
ample for collecting all that is brought down by the 1000 miles of sewers, and conduct-
ing it beyond the limits of the metropolis. If we add another 20,000l. for the shafts and
mechanical contrivances to nuite the ends of the present with the proposed sewers, we
shall then require 140,000l. for the two new sewers, which would benefit materially the
drainage of so vast an area as that comprised within the limits of supply of the nine
water companies. A rate of 6d. annually upon each house would pay the interest of the
outlay; or an average of that amount might be distributed according to the rates of houses.
The great advantages to be derived from sewer water would not long permit of its being
pumped into the Thames. Whenever the water is thoroughly drained from the marshes,
they would be immensely benefited by such a supply; those on the Kentish side of the
river would require that the springs from the chalk should be collected and conducted
away, so that their flow under the surface of the soil should no longer be allowed: this
partially done, would then render the application of sewage water so beneficial that, for the
growth of vegetables, the land would become as productive as any in the world. But
before any calculation can be formed of their value, we must estimate the cost per acre of
thoroughly draining them; for, without that, irrigation by sewage water would be highly
injurious, the vegetable mould resting generally on a bed of clay, under which is a peat
bog of some depth. Should the chalk water be ever esteemed for domestic purposes, the
collection of it along the line of the North Kent Railway would be of the greatest possible
value, to supply the neighbouring villages and towns, or add to that of the metropolis. A
catchwater drain would prevent the flow of the chalk water under the staple of the richest
land in Kent; the whole extent of Plumstead and the marshes eastward would be greatly
enhanced in value for all the purposes of agriculture and horticulture, and, by draining and
improved cultivation, rendered salubrious instead of being, as at present, the seat of
and intermittent fever, and the producer of mephitic air, which seriously affects the health
of the inhabitants of the metropolis whenever the wind blows from the east. Building
might then spread over this district; quays might be formed along the Thames, and one of
the finest rivers in the world have habitations constructed on its banks, whose inmates
would enjoy as healthy an atmosphere as that of the neighbouring hills.
agues
The draining of 125,000 acres of land in the fen districts of Lincolnshire has employed
engines varying in their power from 20 to 8 horses.
1660
[Supp.
THEORY AND PRACTICE OF ENGINEERING.
The proportion of horse power being about 10 for every 1000 acres drained, and the
annual fall of rain about 26 inches after allowing for evaporation and the quantity taken
up by vegetation, probably not more than 1 cubic foot of water per square yard
remains, or 7260 cubic feet to the acre, in any one month during the year, to be pumped up
and discharged. 33,000 pounds raised one foot high in a minute, or 3300 pounds raised 10
feet in the same time, is here considered the measure of a horse's power; and as a cubic foot
of water weighs 62 lbs. and a gallon of water 10 pounds, so a horse power will raise and
discharge, at a height of 10 feet, 330 gallons, or 52.8 cubic feet, of water in a minute: 2
hours and 10 minutes, will therefore, be sufficient time to raise 10 feet high the 7260
cubic feet supposed to cover an acre. Upon this calculation, a steam engine of 10-horse
power will in 232 hours, or something less than 20 days, working 12 hours a day, lift
the cubic feet upon 1000 acres. The rainfall occasionally may exceed the quantity
per acre in some months; and the quantity to be pumped may be greater than that we
have assumed; it may then be necessary to work the engine 20 hours out of the 24; but this
rarely happens.
The drains in the fen districts are cut about 7 feet 6 inches in depth, and of a width to
give them the required capacity to receive the rain water as it falls and bring it down to
the engine. Where the districts extend over a considerable length, the drains require
to be made deeper than the above average, and the usual fall given to them is about
3 inches in a mile.
The Scoop Wheel, which resembles in some degree the undershot wheel of a water-
mill, is used to raise the water; but this wheel or scoop, instead of being turned by the
impulse of the water, is moved by steam power, and the wheel only used to lift the water
to the height required for its discharge.
The float boards, or ladle boards, of the wheels are of wood, and fitted to work in a
trough or track of brickwork or masonry; these are 5 feet in length, and immersed about
5 feet in the water; their width, or horizontal dimension, varying according to the head
of water to be overcome, and the power of the engines employed.
The wheel track at the lower end communicates with the main drain, and the higher
end with the river, the water in the river being kept out by a pair of pointing doors,
resembling those of the lock of a canal; and these are kept closed when the engine ceases
from working.
The wheels are made of cast iron, formed in parts for the convenience of transport; the
float boards are connected with the cast-iron parts of the wheel, by oak starts, which are
slipped into sockets cast into the circumference of the wheel to receive them.
There are
cast-iron toothed segments fitted to the wheel, into which works a pinion upon the crank
shaft of the engine.
When the head of water in the delivering drain does not undergo much variation, one
speed for the wheel will be sufficient; but when the tide rises it is necessary to have two
speeds or powers of wheel-work, the one to be used at low water, and the other more
powerful combinations to act against the rising tide. In most instances 3 or 4 feet above
the level of the land is all that is sufficient to raise the water, and even that height is
only required after floods. The drainage by natural outfalls can take place only during
the ebb of the tide.
If we suppose the wheel to dip 5 feet below the surface of the water in the main drain,
and that the water in the river into which the former must be raised and discharged has
its level 5 feet above that of the drain, the wheel in such a case will have 10 feet head
and dip, and ought to be 30 feet in diameter; where the head and dip are 15 feet, the wheel
should be 35 feet or 40 feet in diameter. A wheel of this description, driven by an 80-
horse engine, is situated near Littleport, in the Isle of Ely.
Two steam engines of the joint power of 140 horses drain 25,000 acres at Deeping
Fen. The largest of these engines, of 80 horse power, drives a scoop wheel of 28 feet in
diameter, with float boards or ladles, measuring 5 feet 6 inches by 5 feet, and moving
with a mean velocity of 6 feet per second; so that the section of the stream, when the
engine has its full dip, is 27 feet 6 inches, and the quantity discharged per second is 165
cubic feet, or 16,200 tons, per hour.
20,000 acres of land on each side of the Thames might be greatly improved by draining
them, as has been so successfully adopted in the Lincolnshire and neighbouring fens, and
at so very moderate charge per acre that it seems extraordinary that the attempt has not
been made. But now, when there is a possibility of using the sewage water, it becomes
more imperative that the owners of these valuable lands should endeavour to unite the
two advantages of drainage and supply of manure in one scheme.
A conduit for the manure might be laid with a proper height and fall throughout the
middle of the district, or at an equal distance from the Thames and the sloping lands on
the opposite side, with branches on each side for distribution; or where the marshes are of
the greatest width, a number of conduits might be introduced, to render the flow of the
smaller pipes more equal.
SUPP.]
1661
RAILWAYS.
Fach proprietor might have his own reservoir or store; or large reservoirs might be
established along the main conduit, to regulate the daily supply to each acre, at times
or constantly.
There are, however, many holders of the lands adjoining the banks of the Thames that
object to the application of sewer water, and who state that, to render them more productive,
it is only necessary to find an outlet for the water, which saturates the vegetable
mould on the surface, and which cannot pass through the thick capping of clay that
intervenes between it and the peat mass below and it is very true that a great portion
of the Plumstead Level, converted into arable land, producing abundant cereal and grass-root
crops, has never required any manure whatever to maintain its productive quality. The
farmers generally object to the idea of improving the marshes by making them the recep-
tacles of the drainage of the metropolis, but they do not for a moment doubt that the
uplands which rise from them would receive incalculable benefit by highly manuring.
The sandy and gravelly beds which cap the chalk, the greatest height of which probably
is 100 feet above the marshes, would be greatly enhanced in value, if reservoirs could be
established to allow of a regular irrigation, under such control that, at seasonable times,
the cultivators of the soil could apply to their crops a beneficial dressing of sewage water.
The lifting the sewer water to a sufficient height into reservoirs to allow of its
distribution over the poor lands which run along to the south and north sides of the Thames
marshes presents no engineering difficulties; the cost of machinery and pipes for the purpose
is easily calculated; and the only question which arises is that of whether the cultivators
of the land would pay an additional annual rent, equivalent to the cost of distribution.
RAILWAYS in the United Kingdom have been greatly augmented since the account given
of them at page 597.
In the year 1851, the capital and loans authorised by the Acts of Parliament amounted
to 361,428,4841., which in the following year was increased by the two sums 4,333,8341.
and 1,792,3871., making a total of 367,554,6691., the sun raised by shares and loans being
264,165,680l., and up to the end of December 1851, 247,776,6871., amounting to
16,398,9934. raised for railways in the year 1852; in which year the railway companies
retained the power to raise 92,624,9781., which, added to the above, forms a total of
356,790,6581., which was in excess of the powers granted by Parliament of 180,2027.
The length in miles, in December 1852, opened for railway traffic, was 7336, of
which 1458 were single lines. The length of line in course of construction was 735
miles, leaving 3806 miles authorised, but not commenced at that date; making the total
length authorised 11,878 miles. The amount of capital to be raised for the construction
of 22483 miles of railway allowed to expire and not taken up was 42,289,3251.
4
In 1854, as appears from an elaborate statement of the capital, dividends, rents, and loans,
the total length of the 135 railways in the United Kingdom was 7736 miles, and that
their share capital was 203,211,907., upon which the half-year's dividends and rents
amounted to 3,613,9267., or at the rate of 31. 11s. 1d. per cent. per annum. The loan
capital and mortgages amounted to 68,970,1807., and the half-year's interest to 1,406,6961.,
or 41. 1s. 6d. per cent. per annum, making the total capital invested in those lines
272,182,0871., averaging a rate of 31. 13s. 6d. per cent. per annum, after paying all the working
expenses, including rates, taxes, and duty on passengers. The ordinary share capital re-
ceiving no dividend was 21,719,8621., of which sum 15,390,580l. is in respect to 895 miles
of railway in England and Wales, 5,346,6991. to 383 miles in Scotland, and 982,5831. for
1643 miles of railway in Ireland.
The capital per mile on the railways of England and Wales is 38,9697., in Scotland
29,2697., and in Ireland 15,3251.
Three or four years have elapsed since the following statement was drawn up, by which
it would appear that the cost of the railways then under traffic for construction and equip-
ment was as follows:
United Kingdom
Germany
United States
France
Belgium
Russia
Italy
Total Expenditure.
£250,000,000
66,775,000
Miles.
7,000
5,342
10,289
66,654,600
1,818
48,781,000
532
9,576,000
200
3,000,000
170
3,000,000
Total Miles 25,351 and £447,786,000
Supposing 20 years employed in the accomplishment of these vast enterprises, more than
an average of 20,000,000l. sterling must have been expended, and the comparative cost of
1662
[SUPP
THEORY AND PRACTICE OF ENGINEERING.
construction and plant per mile in the United Kingdom was
France
Belgium
Germanic States
United States
£35,700
26,800
18,000
12,500
6,500
The average cost of railways per mile of the United Kingdom has been one third more
than those in France, twice that in Belgium, three times those of the Germanic States, and
six times those of the United States; this may in some degree be accounted for by the high
price of land in the United Kingdom, and the parliamentary costs of obtaining the Acts,
these two excessive charges not being so heavy in other countries.
At the end of 1854, in the United States, the number of miles of railway had reached to
19,440, and those of France, Belgium, and Germany have been greatly augmented, though
not in the same proportion.
At the British Association for the Advancement of Science held at Hull in September
1853, Mr. F. G. P. Neison gave an analytical view of the railway accidents in England
in the 12 years from 1840 to 1852. In the period of 1840 to 1851, the number of railway
passengers was 478,488,607, of whom 237 were killed and 1406 injured, showing a ratio
of 1 killed in 2,018,939, and 1 injured in 337,916, and it was also calculated that 1 passenger
was killed for every 40,025,395 miles travelled.
The several railways in England and Wales contributed towards the poor rates
187,6147. in the year 1851, and 186,5397. in 1852, while the total amount collected in the
several parishes through which they passed amounted to 3,189,1357. in the year ending Lady
Day 1851, and 3,113,9261., ending the same period in 1852.
The total acreage of the parishes is 9,177,190, and the acreage of the land occupied by
the railways is 65,047, or 0·71 per cent., while the amount of poor rates collected in the
parishes in the year ending Lady Day 1852 was 3,113,9267., and the amount paid by the
railway companies 186,5397., being nearly 61. per cent. of the whole of the rates. The average
amount paid by the parishes per acre for the poor rates is 678 shillings, while that paid
by the railway companies for the land they occupy was upwards of 47s. per acre.
The average quantity of land occupied per mile of railway appears to be between 11 and
12 acres, and the average sum paid per mile to the different parishes about 331,
337.
The form of rail now adopted is called the double-headed, as it can after use on one
side be easily reversed in the chair; its weight per yard varies, according to the quality of
the iron rolled out, and the care used in its manufacture, from 65 to 80 pounds.
These rails, laid on longitudinal timbers, thoroughly creosoted, and properly put together,
are found to be the most economical, from their duration being the longest, the repairs less
frequent, and their being less injured by the rolling stock.
The railway bars are fastened in their chairs by wooden keys manufactured for the purpose,
which are easily applied to the double-headed rail, and are therefore preferred to those of
metal; more especially those of oak, which are subjected to compression before they are
applied, at the cost of 107. per 1000; the quantity required for a mile of railway per annum
not amounting to more than 51.
Great attention has been given to drainage, ballasting the lines, and also to the laying
of the rails. The sleepers, of Baltic timber laid transversely, have now generally given
place to others formed of half timber laid longitudinally; in some instances a triangular
piece, laid with its base upwards, has been adopted, as it was supposed to be one third stronger
than any other form containing the same sectional area. When longitudinal timbers 12
inches by 6 inches support the rails, and these are firmly bedded, or rest upon a hard
foundation, there is little compression by the rolling effect of the train, and when braced
transversely, or tied by iron rods to prevent lateral movement, they may be considered to
constitute a permanent way.
The locomotive engines are made of much larger dimensions, and of greater weight
than when the first rails were laid down, which were not more than a third of the weight
and strength of those now in use.
One of the ordinary class of engines, constructed for the Great Western Railway Com-
pany, is capable of taking a passenger train of 120 tons, at an average speed of 60 miles per
hour, upon easy gradients. The evaporation of the boiler, when in full work, is equal to
1000 horse power, of 33,000 lbs. per horse, the effective power being equal to 743 horse
as measured by the dynamometer. The weight of the engine empty is 31 tons; coke
and water, 4 tons. Engine in working order, 35 tons. Tender empty, 9 tons; water,
1600 gallons, 7 tous 3 cwts. ; coke 1 ton 10 cwts.: total, 17 tons 13 cwts. The heating sur-
faces and fire box are 156 feet, and 305 tubes of 1759 feet.
Diameter of the cylinder 18 inches, length of stroke 24 inches, diameter of driving wheels
8 feet, maximum pressure of steam 120 lbs.
The average consumption of fuel with a load of 90 tons and a speed of 29 miles per hour
is 20 8 pounds of coke per mile.
SUPP.]
1663
CUBICAL PROPORTION.
The Liverpool express locomotive, belonging to the London and North Western Railway
Company, weighs, when in working order, 32 tons; coke and water, 4 tons. The diameter
of the cylinders is 18 inches, length of stroke 24 inches, diameter of driving wheels 8 feet;
heating surface in tubes 2136 feet, and in fire box 154 feet. The evaporation of the boiler,
when in full work, is equal to 1140 horse power. Pressure of steam 120 pounds per
square inch. The engine has a very low boiler, and the greatest weight is in the extreme
wheels. The patentee was Mr. T. R. Crampton, the power of whose locomotive engine is
ascertained by taking the area of the piston which works in the cylinder, and the pressure of
the steam acting upon it. When steam can be rapidly increased in the boiler, additional
speed of the engine is the result. The high pressure which produces the power, and the
rapid evaporation which maintains it, is entirely owing to the method adopted to heat the
water in the boiler. The diameter of the cylinder, the length of the stroke and the driving-
wheels of a locomotive act and react upon each other. Some of the engines constructed
to run light express trains have six solid wrought-iron wheels, the pair of driving-wheels
being 6 feet in diameter, and the other four 3 feet 6 inches only. The cylinders are 11
inches in diameter, and the length of stroke 22 inches; these light engines will run 50 miles
without a tender, as they are provided with two water tanks beneath the boiler, and a suf-
ficient space for the coke.
THE FIGURE OF THE CUBE has from time immemorial been selected by the architect and
engineer as best suited for every variety of edifice; and it is remarkable that the multi-
plying of the cube constitutes the design of the Greek temple, the Gothic cathedral,
and the modern iron structure at Sydenham, the variety of effect depending upon the
mode of its application. Reviewing the temples of the ancients, we find that those
composed of a portico of four columns, and six intercolumniations on the flank, or
seven columns; that the whole constituted a double cube, or two cubes side by side.
cube of 32 feet 4 inches in height, breadth, and length, placed behind another of the same
dimensions, would represent the entire mass of the Temple of Fortuna Virilis at Rome.
The temple of six columns, or the Hexastyle, is composed of nine half cubes, or three
entire, placed one behind the other, with the addition of three half cubes against the sides of
the first, making altogether four cubes and a half.
A
The Octastyle temple is composed of nine whole cubes, or four cubes and a half in depth,
repeated twice, placed side by side. The Parthenon is thus formed of cubes, whose sides
each measure 50 feet 6 inches; two occupy the front, of 101 feet; the depth of the four and
half cubes are a trifle more than 227 feet, the true extent heing 227 feet 7 inches.
Six cubes, placed one above the other, form the design of the Campanile, erected at
Florence by the celebrated Giotto in the year 1833; and on the breaking up of these cubes
into ornament, the perpendicular lines are lengthened out, whilst in the Greek temple
the horizontal are made to preponderate; repose in the latter, and lofty aspiration in the
former, marks the distinction between them.
The Tower of Rochester Castle, usually supposed to be of Norman construction, has
decided evidence of having been erected by the Romans. To the military and civil engineer
this strong keep affords a study of peculiar interest; and if, as we suppose it to be, the
work of Frontinus or his contemporaries, we are not at a loss to comprehend why it so
perfectly resembles the far-famed Coliseum at Rome, in the manner in which the spiral
vaults are executed, or indeed in the general method adopted in carrying up the massive
walls. The cement employed was evidently manufactured on the spot, as it is entirely
composed of the materials found close at hand, and the stone such as could be brought
down the Medway, and quarried on its shores.
If this enduring structure was the work of Gundulph in the twelfth century, we have
the strongest evidence that the Roman arts of construction were continued without any
change either in the art or mystery of building up to that period at least.
The building is a cube and a half nearly, being about 74 feet square without the en-
trance porch, and its height to the top of the angular turrets 112 ft. A square divided into
twenty five equal squares exhibits its plan; the sixteen outer squares represent the thick-
ness of the walls, in which are galleries, recesses, and contrivances necessary for its pro-
tection against an enemy; the nine inner squares of the plan are divided into two spa-
cious rooms, one being 45 feet by 19, the other 45 feet by 21 feet; the wall that divides
them is 5 feet 6 inches in thickness. The height comprises a basement story and three
others beneath its roof, which has been vaulted, and which is 90 feet to the top of the bat-
tlement, and 112 feet to the top of the turrets.
Rules adopted by the Free Masons in setting out their Buildings, from the Tenth to the
Fifteenth Century : —
In the Chapter on Proportion in the Encyclopædia some general rules have been suggested
as to mass and void, and more particularly the principles of setting out the windows and
tracery of the English and French cathedrals. On referring again to this interesting
subject, the writer was led to inquire why the structures of the latter country should be
1664
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
so uniformly larger than those of the former, from which they differed but little in style,
preserving the same relative proportions, though differing in dimensions. Guided by the
fact that those erected in the above period of time were the works of the fraternities of
free masons, it seemed conclusive that they should have some standard of measurement,
either of their own or peculiar to each country; and, on testing the measurements with
that view, it resulted that those of England were set out with the English perch of 16 feet
6 inches, and no doubt by an English lodge; while in those of France the French perch
royal, of 22 pieds du roi, equal to 23:452 English feet, was employed; the few exceptions
at Bayeaux, Caen, St. George Bocherville, and some others with round arches, and the
elegant church of St. Ouen at Rouen, in the flamboyant style, are set out with the English
perch of 16 feet 6 inches, and are universally attributed to English constructors; they
certainly most curiously agree in proportion and dimension with the English cathedrals,
which have two cubes given to the nave, producing on the plan a Latin cross, instead
of the Greek so usually found in France.
To illustrate this subject fully is not within our present narrow limits; a very few
examples must suffice, out of the numbers which might be adduced in support of the
proposition; and it is earnestly hoped that the young engineer may be sufficiently
interested to test the theory practically, that while he admires their picturesque beauties,
he will examine by measurement their plans and sections.
It would seem that the standard measures referred to were well and wisely chosen, as
if intended to apply to all times and all varieties of structure; for it is singular how nearly
the dimensions of the cubes of the fairy palace at Sydenham, 24 feet, correspond to 23 feet
6 inches of the royal French perch.
Of the French Cathedrals, we must be content to refer to Chartres, Rheims, and Amiens
as those most admired, and which serve as examples of the application of the French perch
in setting out their various parts as well as the whole.
Chartres Cathedral, in which the pointed arch first appears, is a structure of the eleventh
century, and one of the most remarkable as well as beautiful, erected after the first intro-
duction of the pointed style by those free masons who had journeyed with the Crusaders, and
had an oportunity of studying their craft in the East.
The proportions are simple in the extreme. A cube is devoted to the nave, two to the
transept, one to the choir; in addition to which, at the eastern extremity, is a semicircular
termination with six polygonal chapels attached, forming on the plan a Greek cross of ad-
mirable design.
The nave, comprising six divisions of pointed arches on each side, is in its length and
width six royal perches, the distribution of which will enable the reader to comprehend the
setting out of the entire plan, which he can refer to in several publications.
The clear width of the nave is two royal perches between the clerc story walls; each
side aisle is one royal perch, and the distance from the middle of one pier to that of the
other, from west to east, is also a royal perch.
The entire width of the nave from out to out, that is to say, from the face of the exterior
buttresses, is six royal perches, four perches being given to the two side aisles and nave for
their clear widths, and the other two to the projection of the buttresses, thickness of the
two outer walls, and those of the clerc story of the nave.
The royal perch divided into three, one part constitutes the diameter given to the pillars,
another to the thickness of each of the walls of the side aisles.
The internal height of the nave is the same as its clear internal width with side aisles;
so justly is all proportioned that the perch royal, and its division into three, enables us
to comprehend the dimensions of the parts, as well as that of the entire mass of construction.
Rheims Cathedral was similarly set out. The clear width of the nave is two royal
perches, and each of the side aisles one. The extreme width of the nave, comprising the
projection of the buttresses, is six royal perches; the diameter of the piers, one third of a
royal perch, as in the example of Chartres.
It must be observed that the dimensions do not apply to the clear distances between
the pillars, but to the space between the walls, which in the clerc story are peculiar
for the contrivances of a gallery, which usually continues around the entire cathedral, and
which will be better understood when we treat upon Amiens cathedral, reserved for a fuller
description. And that the perch was the standard of measurement there can be no doubt;
for in the smaller churches of England, as that of Rosylin, for example, the nave is a single
perch in width, and the side aisles half a perch; the proportions of the parts being also
those of the third of an English perch.
Salisbury Cathedral, a contemporary structure with Amiens, is set out with the English
perch, and affords us the best commentary upon the two standard measures made use of in
the same century by the French and English free masons.
The Nave of Amiens Cathedral is usually admired for its elegant proportions, and by
several eminent critics has been cited as the beau ideal of that style of architecture
so universally practised during the middle ages, or after the Roman had been discon.
SUPP.]
1665
CUBICAL PROPORTION.
tinued. It is one of the most simple in its arrangement, though at first sight, removing
all idea of simplicity, and appearing so complicated from its variety of parts, as to defy the
application of any ordinary rules; the numerous arcades, the narrow and lofty compartments,
the vaulted divisions, the diagonal and curved lines, blending one into the other, and ap-
parently without limit, it is some time before the eye can acquiesce in the idea that such an
edifice can be brought under the same laws as a Greek temple, or that the cube could be
the measure of its parts or its whole. In taking the measurements, however, of this rare
example, the dimension of 23 feet 6 inches so frequently occurred that it seemed to denote
a standard by which to arrive at the length, breadth, and height of the whole, and that, if
considered after the manner of Sebastian Serlio, where he describes Bramante's plan of St.
Peter's, we might arrive at something like a clue to the whole design.
It is curious to note, in the work of the above mentioned architect, several allusions to
the cube, in the defining the parts as well as the whole of a design, and there can be little
doubt that this simple figure served as the means of measuring the quantities, of either
solid or void, in every period of the constructive arts; certainly none presents to the archi-
tect a better means of comprehending or of measuring quantity, and none is more readily
subdivided, or rendered subservient to the taste of the designer, whatever may be the architec-
ture he is anxious to imitate.
Within an isometrical cube may be placed the entire nave of Amiens Cathedral; and the
better to understand its proportions, we must suppose each square or cube into which it is
divided to measure 23 feet 6 inches each side, or the isometrical figure to contain 216
such cubes; the total height, width, and length being 141 feet, or six times the 23 feet 6
inches.

Fig. 3058. NAVE OF AMIENS CATHEDRAL,
On the plan are six divisions in length and width, or altogether 36 squares; each
measure 23 feet 6 inches on each of their sides. The six outer divisions of the principal
figure are devoted to walls and buttresses; the adjoining six on each side show the situation
50
1666
[SUPP.
THEORY AND PRACTICE OF ENGINEERING
of the side aisles; and the two middle divisions that of the nave. The two side aisles
occupy together 12 squares, as does the nave; the remaining 12 being devoted to outer
walls and their buttresses.
The entire area, therefore, has 24 squares to re-
present its interior distribution, and half that
number its external walls; or one third walls, two
thirds void. Such are the general arrangements
of its plan, and its extreme simplicity has enabled
the constructors to execute the vaulting of the side
aisles and that of the centre nave by diagonal
ribs, which in the former extend over one square,
and in the latter two, thus giving to the nave its
due proportion of height, without changing the
principle of its construction.
The free masons of the middle ages were so per-
fectly acquainted with geometry that there is sel-
dom any defect in their vaulting; it is evident that
they laid down their plans for its execution before
they decided upon the form of their main piers
in their setting out, every part had its due function;
and the column, which was intended to be con-
nected with the vaulting, either of nave or side aisle,
was peculiarly adapted by its position for its use.
The master mason Robert de Luzarche com-
menced the building of this nave about the year
1220, the founder being Bishop Evrard. The pillars
of the nave were raised to the height of their
capitals in 1223, but it was not till 1236 that the
vaulting was completed; and about eight or nine
years afterwards the lateral chapels were added.
To the top of the battlement of the nave there
is not quite so much height as the outer wall of
the Coliseum at Rome, which is 157 feet; but it
is curious to observe that one division of this re-
nowned building does not differ very materially
in its proportions from that at Amiens; the divi-
sion of the amphitheatre being seven cubes in
height; the piers occupy one third of the width of
a compartment, as is usual in Roman structures of
the same period. The masonry of Amiens Cathe-
dral is executed after the Roman models, con-
sequently the pointed arch makes the chief differ-
ence between the two styles.
To render the application of the theory of the
cube to the nave of Amiens Cathedral more evi-
dent, or how the 216 cubes which the isometrical
figure contains are placed, somewhat more of detail
must be entered into.
The six main divisions shown in the figure, with
the side aisle behind them, have their points of
support at the four angles of each of the six
squares; then each square, with its 23 feet 6 inches
sides, show the position of the lowest cube of the
six placed one above the other, forming the entire
height of each division or severy.
At the top of the second cube is the level upon
which the main arches spring, and that upon which
the ribs of the vaulting of the side aisles rest.
The top of the third cube indicates the level
upon which the triforium is based, and conse-
quently contains the vaulting of the side aisle.
The fourth cube is the triforium, and the fifth
and the sixth the clerc story.
On examining the section, the side aisles are
three cubes in height, including the vaulting, and
the nave six; the entire open space of the interior
has 18 cubes for each aisle, or 36 for the two side

Fig. 3059.
ELEVATION OF NAVE DIVISION.
SUPP.]
1667
CUBICAL PROPORTION.
aisles, and 72 for the nave; in all 108 cubes, or exactly one half the entire number contained
in the isometrical cube.
It must be remarked that considerable alterations have been made since the building was
constructed; between the buttresses, chapels have been formed, and the original windows,
which lighted the side aisles, removed to the extent, or somewhat beyond the outer face of
buttresses, as represented.
The interior is therefore increased materially in width, and its effect greatly improved,
making the entire internal width and height more in conformity with each other, or each
141 feet.
In the elevation of the divisions the boundary of each of the six cubes is more clearly
marked; the width from centre to centre of each pillar, indicated by the seven circles, is
23 feet 6 inches; to the top of the capitals from the pavement the height is twice that
dimension; to the bottom of the bases of the column of the triforium, the same; thence to
the bottom of the glass of the clerc story windows, 23 feet 6 inches; to the tops of the ca-
pitals or spring of the arches, the same; and above that line to the underside the vaulting
again, 23 feet 6 inches; thus, six times 23 feet 6 inches, or 141 feet, is the total height
from the pavement of the division represented.
As the groined vaults of the side aisles are set out upon a square, and the width from the
centres of piers is the same as those towards the nave, we have three perfect cubes of
24 feet in each severy up to the bottom of the triforium story, and the same number from
thence to the top of the vaulting of the nave.
The seven circles on the top line of the lowest cube of this division show the propor-
tion each pier bears to the opening or distance between two; in the proportion of two
sevenths for piers, and five sevenths between them. The dimensions vary a little as taken
throughout the six severies; in some instances the diameter of the piers are as much as
7 feet 2 inches; in others they agree with what has been stated.
It may be remarked that the contour of the mouldings are, in this example, Byzantine.
The Torus and Scotia, around the base, are not sections of cylinders or their portions; the
circular form which develops the Roman detail here partakes of the elliptical, and is more
in accordance with what we see in Athens, belonging to the best days of Grecian architec-
All the mouldings below are contoured differently to those above the eye, and con-
sideration is given to their position, to produce proper effect.
ture.
The main pillars are 7 feet, and 7 feet
2 inches in diameter, composed of a large
cylindrical column, with others attached
for the support of the vaulting. Towards
the nave there are three columns which
are carried up to the height of about the
middle of that of the clerc story windows;
on the capitals which terminate them
rest the cross springers and diagonal ribs
of the vaulting. The arches of each di-
vision are 4 feet 9 inches in thickness,
and rest on the side columns, of 18 inches
diameter; a faint line on the plan repre-
sents the pier and mullions of the divi-
sion of the clerc story window.
The base and capital of the main pil-
lars, as seen at the side with their di-
mensions, is the same as the front view
towards the nave, with the exception that
the two 7-inch columns at the side of
that in the middle are omitted.
The piers that divide the side cha-
pels, and the original outer buttresses,
have been changed probably from their
original design; they are now 8 feet
wide.

Fig. 3060.
11
72
PLAN OF CLERC STOBY.
The clerc story window with its piers
and mullions being already given, it
remains to show the plan of the piers
and mullions of the triforium, and its
gallery or passage, which has a clear
width of 20 inches between the main
pier and the outer wall, which is about
10 inches in thickness. The middle mullion, or that which divides the triforium into two
Fig. 3061.
PLAN OF COLUMNS.
50 2
1668
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
principal arches, is 2 feet 6 inches in width, and composed of seven small columns, as
shown attached to the main pillar, which has a depth of 6 feet 8 inches.


10
BASE OF
Fig. 3063.
6T
1.7€.
36+
7.2--
16 -->
Fig. 3062
4
2″
3.
COLUMN.
8"
5.62

Fig. 3064. PIERS IN SIDEe aisles.

The ordinary decoration in this ca-
thedral is very simple, consisting of a
circle, comprising either three, four, five,
six, or eight others; the centres of which
and their portions may be understood
by reference to the five diagrams in the
margin. Sculptured foliage occurs in
the capitals and along the string mould-
ings; figures, however, of the most elabo-
rate execution and design decorate the
exterior, and particularly around the
chief entrances; perhaps few buildings
excel the Cathedral of Amiens in the
richness of these portions, or the magni-
ficence of its porches.

-- 2:6
.8
1.6."
Fig. 3065. PLAN OF TRIFORIUM.
In a former part of the work an at-
tempt was made to convey an idea of the
geometrical style of its tracery in the
rose windows, as well as those of the side
chapels. And we cannot quit this part
of our subject without regretting that
we are not allowed more ample space for the treatment of this very interesting reference
to the arts as displayed by the builders of this period, particularly as the principles
upon which they practised are so little known. Simple as they were, their system seems
to have been forgotten after the lodges of the free masons were broken up, and the new
era appeared. The renaissance, or the return to the Greek models, at once set aside all
knowledge of that architecture which had attained such perfection in Europe for four
centuries.
The Crystal Palace in Hyde Park was a remarkable example of the manner in which
most of our institutions have been founded by the people, who, when the requirement is
evident, raise funds to carry them into execution. Suggested to the Society of Arts in
June 1845 by his Royal Highness Prince Albert, the plan for its adoption was not
long ere it was developed; at a banquet given by Mr. Farncomb, the Lord Mayor of
London, to the municipal authorities of the United Kingdom, his Royal Highness explained
the wishes of the promoters, by stating:
"It must be most gratifying to me to find that a suggestion which I had thrown out,
as appearing to me of importance at this time, should have met with such universal con-
SUPP. ¡
1669
CUBICAL PROPORTION.



Fig. 3066.
Fig. 3067.
Fig 3068.


Fig. 3069.
Fig. 3070.
currence and approbation; for this has proved to me that the view I took of the peculiar
character and requirements of our age was in accordance with the feelings and opinions
of the country.
I conceive it to be the duty of every educated person closely to watch and
study the time in which he lives, and, as far as in him lies, to add his humble mite of in-
dividual exertion to further the accomplishment of what he believes Providence to have
ordained. Nobody, however, who has paid any attention to the peculiar features of our
present era, will doubt for a moment that we are living at a period of most wonderful
transition, which tends rapidly to the accomplishment of that great end to which indeed
all history points, the realisation of the unity of mankind; not a unity which breaks
down the limits and levels the peculiar characteristics of the different nations of the
earth, but rather a unity the result and product of those very national varieties and antago-
nistic qualities. The distances which separated the different nations and parts of the
globe are gradually vanishing before the achievements of modern invention, and we can
traverse them with incredible ease; the languages of all nations are known, and their ac-
quirements placed within the reach of everybody; thought is communicated with the ra-
pidity, and even by the power of lightning. On the other hand, the great principle of the
division of labour, which may be called the moving power of civilisation, is being extended
to all branches of science, industry, and art. Whilst formerly the greatest mental ener-
gies strove at universal knowledge, and that knowledge was confined to the few, now they
are directed to specialties, and on these again, even to the minutest points; but the knowledge
acquired becomes at once the property of the community at large. Whilst formerly dis-
covery was wrapt in secresy, the publicity of the present day causes that no sooner is a
discovery or invention made, than it is already improved upon and surpassed by competing
efforts; the products of all parts of the globe are placed at our disposal, and we have only
to choose which is the best and cheapest for our purposes, and the powers of production
are intrusted to the stimulus of competition and capital. So man is approaching a more
complete fulfilment of that great and sacred inission which he has to perform in this world.
His reason being created after the image of God, he has to use it to discover the laws by
which the Almighty governs his creation, and, by making these laws his standard of action,
to conquer Nature to his use— himself a divine instrument. Science discovers these laws
of
power, motion, and transformation; industry applies them to the raw matter which the
earth yields us in abundance, but which becomes valuable only by knowledge; art teaches
us the immutable law of beauty and symmetry, and gives to our productions forms in ac-
cordance with them.
"The Exhibition of 1851 is to give us a true test and a living picture of the point of de-
velopment at which the whole of mankind has arrived in this great task, and a new starting
point, from which all nations will be able to direct their further exertions. I confidently
hope the first impression which a view of this vast collection will produce upon the spec-
tator will be that of deep thankfulness to the Almighty for the blessings he has bestowed
5 0 3
1670
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
upon us already here below; and the second the conviction, that they can only be realised in
proportion to the help which we are prepared to render to each other, therefore only by
peace, love, and ready assistance, not only between individuals, but between the nations of
the earth."
After this eloquent appeal, the public quickly responded by subscribing 75,000l., to enable
the commissioners to erect a suitable building, to be completed by the 1st of May 1851;
the site being granted by Her Majesty, on the south side of Hyde Park; and all that was
required of the exhibitors was, to deliver their various specimens of art and manufacture at
the building which would be provided for them.
Two hundred and forty-five designs and specifications were submitted to the Building
Committee appointed to conduct the operation; but they having reported that there was
not "a single plan so accordant with the peculiar objects in view, either in the principle or
detail of its arrangement, as to warrant them in recommending it for adoption," Mr. Paxton
submitted a novel design, composed chiefly of glass and iron, which Messrs. Fox, Henderson,
& Co. tendered to construct for 79,800l. This was immediately carried into effect.
The site for the building contained about 26 acres, being 2300 feet in length, and 500
feet in breadth; the principal front extending from west to east. The total area of the
ground-floor was 772,784 superficial feet, and that of the galleries 217,100 square feet.
The length of these galleries extended nearly a mile. The cubical contents of the building
were estimated at 33,000,000 feet.
There were used in its construction 2300 cast-iron girders, 358 wrought-iron trusses for
supporting the galleries and roof, 30 miles of gutters for carrying water to the columns,
202 miles of sash bars, and 900,000 superficial feet of glass.
On the ground-floor, 1106 columns of cast-iron, rested on cast-iron plates, based upon
concrete; these columns were 8 inches in diameter, and 18 feet 5 inches in height; they
were cast hollow, the thickness of the metal varying from 3 to 1 in., according to the
weights they were destined to support.
The principal entrance was in the centre of the south side; passing through a vestibule
72 feet by 48, the transept was entered, which was covered by a semi-cylindrical vault 72
feet in diameter, springing from a height of 68 feet from the floor; and this vault of iron
and glass was in length 408 feet from north to south. On each side of the transept was an
aisle 24 feet wide.
Standing in the middle of the transept, the vista or nave, at right angles, extended east
and west 900 feet in each direction; the total length being 1848 feet. This nave was
72 feet wide, and 64 feet high; and on each side was an aisle 24 feet in width; and above,
at a height of 24 feet from the floor, were galleries which surrounded the whole of the nave
and transept.
Beyond these side aisles and parallel with them, at a distance of 48 feet, were second
side aisles, of an equal width to those already mentioned, and also covered with galleries on
a similar level to the others. Bridges of communication were male at convenient distances,
to allow of an unbroken promenade, and from which a view of the several courts might be
obtained. These courts were roofed in, at the height of 2 stories, and were 48 feet in
width; and 10 double staircases 8 feet wide gave access to the several galleries.
After the transept and nave were marked out, the general arrangement consisted of a
series of compartments 24 feet square, and as much in height; these bays or cubes were
each formed of 4 columns, supporting girders put together very ingeniously, as we shall
hereafter more minutely describe in the construction at Sydenham, to where they were
all removed, and re-adapted to a much more extensive building.
One of these bays or gallery-floors, 24 feet square, containing 576 superficial feet, were
calculated to support as many cwts., or 30 tons.
The symmetry and strength of this vast building depended upon the accuracy with which
the simple plan was drawn out, and much credit is due to Mr. Brounger, who superin-
tended this portion of the work; he had to establish a series of squares of 24 feet, and this
was admirably effected by rods of well-seasoned pine, fitted with gun-metal cheeks.
Stakes were driven into the ground to mark the position of the columns, their precise
centres being afterwards found by the theodolite, and marked by a nail on the top of the
stake or pile; and when the digging commenced for the foundations, and there was a ne-
cessity to move the pile, a right-angled triangle was formed in deal, and previous to the re-
moval of a stake, a nail indicating the position of the column was placed at the apex of the
triangle; two other stakes were driven in, and the first withdrawn. The entire ground plan
may be considered as composed of 1453 squares, each containing 576 superficial feet.
south front occupied 77, the east and west fronts each 17, so that the entire parallelogram
contained 1309 of these squares; on the north side were 48 others, 3 divisions in depth,
making an addition 144, thus completing the number stated. The nave, transept, and
courts were formed by the omission of the columns, where their width required to be
either 48 or 72 feet, and girders of sufficient strength were substituted to span the space
The
SUPP.]
1671
CUBICAL PROPORTION.
where the columns were omitted. Had each of the 1387 squares of which the plan con-
sists had its complement of columns, to have perfected each cube, 1502 would have


Fig. 3071. GRound plan.
Fig. 3072.
UPPER PLAN
504
1672
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
been required; but the formation of the wider openings occasioned only 1106 to be em-
ployed, so that, by the omission of a third, the courts, nave, and transepts acquired their
admired proportions.
The columns being 8 inches in diameter, the area of the section of the whole 1106 is
380 superficial feet, or the points of support part of the entire area.
2
The plan, which has 1106 columns, is composed of 1387 squares, each of 576 superficial
feet, or 798,912 superficial feet.
The points of support, being 380 superficial feet, is a trifle more than a 2000th of the
entire area, for 798912 - 2102.
380
When we compare the Crystal Palace with one of the lightest constructed basilicas of
ancient Rome, we are astonished at the difference in the proportions; for instance, the
total area of the basilica of St. Paul, without the walls of Rome, was 108,000 superficial
feet; while the points of support were 12,000, or one ninth. The Crystal Palace, which
was seven times the area of the basilica of St. Paul, had it been constructed in a similar
manner, would have required 84,000 superficial feet for the points of support, instead of
380 superficial feet.
In the Saxon cathedrals, one third of the entire area was employed for walls and piers;
in the Pantheon at Rome, one quarter; in St. Paul's, London, one sixth; and in most of
the cathedrals constructed from the twelfth to the fifteenth century, the same proportions
are practised; but we have never hitherto seen any attempt to lessen the proportions of
the supports beyond a twentieth of the entire area, when the ordinary building materials, as
brick or stone, have been employed, whilst in this instance iron columns are found suf-
ficiently strong, when they have the proportion of a 2000th part of the whole, or are
one hundred times less in section than their points of support, estimated as a twentieth
of the whole, and which we have considered as the lightest of the constructions hitherto
practised; the round Temple of Claudius at Rome being the example. At page 691. we
find in the table, calculated by Mr. Tredgold, that an iron column of cast-iron 8 inches
in diameter, and 24 feet high, will carry nearly 50 tons, or 1106, 55,300 tons; so that, if
each of 1387 squares had to sustain 30 tons, there would be ample strength, this not
amounting to more than 41,610 tons.
In preparing the foundations for the columns, great care was taken to arrive at the
gravel, upon which a bed of concrete was thrown; and it was estimated that a pressure per
superficial foot of 2 tons should be provided for. The concrete varied in depth from
3 to 4 feet, and was finished by covering the top with a surface of fine mortar, worked even
and with a level face. On this was laid a base plate for each column, the lower part
consisting of a horizontal plate having attached to it a vertical tube of the form of the
column it was to carry. The length of these base plates was from north to south, so
that the water brought down by the columns from the roof might run in the direction
from east to west. Into the sockets, cast iron pipes 6 inches in diameter were inserted,
for the purpose of conveying the water into the cisterns and tanks provided to receive it.
At the upper portion of the base plate four holes were cast, in as many projections,
which answered to others at the foot of the column to be placed upon it, which, when
fixed, was secured by nuts. Between the shaft and its base, pieces of canvass dipped in
white lead were introduced before the joints were secured, which were thus rendered
water-tight.
The columns are 8 inches in diameter, and those on the ground floor 18 feet 5 inches
in height, being cast hollow to allow of a current for the rain water; the strength of these
columns is increased by the four projecting ribs, and the form of the angular additions made
to receive the nuts and screws.
The columns were elevated to their positions by a pair of shear legs, consisting of two
poles lashed together at their heads, and maintained in a steady position by ropes extending
from the apex of the triang] (formed by the base line of the ground and the inclination of
the poles towards one anothe, to piles driven in the ground at a considerable distance.
From the apex of the triangle a series of ropes passing over pullies were suspended
perpendicularly; and by means of this fall, not only the column, but the girders and other
heavy portions of ironwork, were lifted.
The Crystal Palace at Sydenham had the simple Cube as the nucleus of which this vast
edifice was composed ; and the simplicity of its form enabled the constructors, by a small
variety of castings, to execute the whole.
The perfection of the work, as it was delivered to the artificer to be put together, abridged
much of his labours, and enabled him to perform an apparent quantity of work in a very
small space of time.
Three of these cubes, placed one on the other, formed the side galleries, as seen in the
section; and the omission of six such cubes measures the width and height of the nave to
the level of the springing of the arched covering; such are the proportions of which this vast
structure is composed.
SUPP.1
CUBICAL PROPORTION.
1673
The foundation generally was gravel, on
which was laid a bed of concrete varying
in thickness, according to the nature of the
ground; and it was so formed, that it was
estimated that a load of 2 tons might be
placed upon a superficial foot.
Iron base-plates were bedded in mortar
upon the concrete; they were laid at right
angles to the vertical lines of the building,
strengthened by shoulders which united the
base-plate, on which rested the columns.
The height from the concrete to the junc-
tion of the column was so well calculated,
and the casting of the base-plate so uni-
formly accurate, that the snugs of the one
corresponded exactly with the other, so that
the joints required no packing to make
them perfect.
Under the hollow columns which con-
veyed the water from the roofs were
socket branches that carried it into the
transverse drains; and thus the water which

Fig. 3074.
.42.
.62.
SPRINGING
·7210-
Fig. 3073.

SECTION.
fell upon the various roofs, whose superficial area may be estimated at nearly 18 acres, was
conveyed to six rows of cast-iron pipes, each 6 inches in diameter; these communicate


Fig. 3075
CONCRETE FOUNDATION
FLOOR
3.
Fig.3076, PLAN.
1671
[SUPP
THEORY AND PRACTICE OF ENGINEERING.
with sewers on the outside of the building, and eventually into an egg-shaped culvert
whose sectional area is 4 feet 8 inches.
The columns and connecting
pieces are well put together.
The section of the former is a
ring, the external diameter of
which is 8 inches, and the thick-
ness of the metal varies ac-
cording to the area of the duty
it has to perform. The mini-
mum thickness is half an inch,
and the maxium, 1 inch. The
sectional area is further increas-
ed by four fillets 3 inches in
width, and a little more than a
sixth of an inch in thickness.

•
Four snugs are cast on the
top, and the same on the bottom
of the columns, between these
fillets; and corresponding with
them, others are cast on the
connecting pieces, to help to sup-
port the girders. Bolt holes are
pierced in the snugs and con-
ㅁ
​Fig. 3077.
necting pieces, by which four bolts secure the whole together, by means of nuts.
Connecting plates may thus be attached to columns, and columns may be attached also when
required and the whole made steady by the girders placed at right angles with one another,
as seen in the following diagram,
On the ground-floor is laid boarding 1 inch in thickness,
joists 7 by 24 inches, which rest upon sleepers 13 inches by 3
apart.
an inch apart, upon
inches placed 8 feet
The four girders in places that required them, are connected with the plates over the
columns, as the two here represented.

op
Fig. 3078.
The horizontal planes in the three-story portion of the building consist of base-plates,
the upper bearing surface of which rises 3 inches from the ground-floor; the columns,
18 feet 5 inches long, rest upon the base-plate; above are the connecting pieces,
3 feet 4 inches in depth, to which are attached the cast iron girders, 24 feet in length,
and which support the gallery floor at the height of 23 feet from the ground-floor.
The second tier of columns are 16 feet 7 inches long, with connecting pieces 3 feet
4 inches deep, and similar girders to those below; and the third tier of columns and con-
necting pieces in every case are the same as the second.
Supp.]
1675
CUBICAL PROPORTION.

The two-story portion of the building
and the one-story differ but little in the
dimensions of the columns, connecting pieces,
or arrangement of the girders.
The galleries are floored with 14 inch deal,
iron-tongued, laid on joists of 7 feet 9 inches
in length; the latter resting upon binders,
which are under trussed by means of cast-
iron shoes, rods of wrought iron, and struts,
so as to deposit the bearing upon four, instead
of upon two girders.
The shoes and struts, with the wrought-
iron rod, are admirably contrived, to assist in
preventing any vibration that might, from
any number of persons walking over the
floor, be conveyed to the extremities of the
girders, and in lieu spreads it over the whole
bay.
The longitudinal and sectional positions
Fig. 3079.
of these trusses may be better understood by the accompanying figures.


Fig. 3080.


Fig. 3081.
"
7×22/2
Fig. 3082.
The 24 feet truss, as well as all the others double or treble the length, have their sub-
divisions crossed with similar diagonals, and thus preserve a uniform character throughout.

Fig. 3083.
1676
L SUPP,
THEORY AND PRACTICE OF ENGINEERING.
The 48 feet trusses consist of cast-iron standards and vertical struts, an upper portion
formed of two portions of angle iron set 1 inch apart, a bottom portion of two bars,
increasing in sectional area as they approach the centre of bearing, and tye bars, which,
passing diagonally between the two pieces of angle iron in the upper portion, and the two
bars in the lower, are riveted to them, and form a complete suspension truss. The other
diagonals in the opposite direction are constructed of wood,
Fig. 3084.
-.24.. 0

The 24-feet girders are 3 feet in depth, and their vertical lines are placed 8 feet apart.
The sectional area of the upper rail is 8.31 inches, and the lower 7.64 inches.
The sectional area of the diagonals, 3.50 inches.
Upon trial, the breaking weight was 30 tons, and their strength wascalculated to bear
22 tons.
Fig. 3085.
Fig. 3086.
Fig. 3087.
SAYSAMAS SMAGUROSŤ
-24.0


-3.0"

-30%..
->
These girders were cast in one piece, and weighed 11 cwt. 3 qrs. each, and which are
similar in all respects to the 24 feet roof girders, but 2 cwt. 1 qr. heavier, bore 30 tons, and
broke down with 30 tons.
The extra strong trusses, 72 feet in length, which support the lead flats, cover two
bays 72 feet by 24 feet, are made twice the depth of the others; the vertical struts are
8 feet apart from centre to centre, and the tension bars the same as those set in the
angles of the other girders.

6′0″.
6'.6%
I
6.07
Fig. 3088.
14.2
>


Supr.]
1677
IRON CONSTRUCTION.
The diamonds are double in depth, the intersecting diagonal bars passing through slots
cast for them in the middle of the cast-iron struts.
The side, front, and back elevation of the end standard, with their dimensions, and the
front and side elevation of the cast-iron vertical struts, or intermediate standards, being
shown below.
The sectional area of the top rail is 5.71 inches, of the bottom 675, the diagonal tyes
3.38 inches, and the weight 35 cwt.

6"->
V
主
​
HI
.5.0.
Fig. 3089. SECTIONS.
The semicircular ribs of the roof are made in three thicknesses of timber, each 9 feet
6 inches long, cut into segments of a circle 74 feet extreme diameter; the central thickness
being 13 inches by 4 inches, and the outer flitches breaking joint, with the centre, are
13 inches by 2 inches.

The flitches are nailed to
the centre, and further
secured by th-inch iron
bolts every 4 feet apart,
thus binding the three
thicknesses into one.
On the extrados of the
timber arch is placed two
thicknesses of gutter boards,
each 11 inches wide and
1 inch in thickness, and an
iron bar 2 inches wide, and
gths of an inch in thickness,
bent to the curve. On the
intrados a piece of timber
7 inches by 2 inches, made
to correspond to the form
of the columns, and a bar
of iron 3 inches wide and
3ths of an inch in thickness,
is bent round and bolted as
that on the outside.
The gutters which col-
lect the water from the
roofs extend over the en-
tire building, and are placed
24 feet apart; altogether
their length is computed at
24 miles. These gutters are
WOOD
WOOD
18
LEAD FLAT
BARS
Fig. 3090. MAIN TRUSSES.
ARCHED RIB
OF TRANSEPT
cut in timber, and attached to the upper flange of the main trusses; they are 5 inches by
6 inches before cutting by the machine, which at one operation scoops from the middle of
the upper surface, and throughout its whole length a semicircular groove about 14 inch
radius; at the same time the machine cuts two smaller grooves downwards, at an oblique
angle to its sides.
1678
[SUPP
THEORY AND PRACTICE OF Engineering.
To give this gutter a proper current for the water, and to add to its strength, it was
trussed into a curve, by means of an inch iron bolt, threaded at both ends, and bent so as
-8--.0"..

Fig. 3091.
K------8--0%.
Fig. 3092. GUTTER bearer.
to pass under and press up the underside of the wood gutter, by 2 cast-iron struts 9 inches
long, giving it a camber of 24 inches.
Smithfield Market, Manchester, is covered with an iron roof of simple construction, extending
over a length of 440 feet, and a width of 244 feet, consisting of 2 central spans, each of
72 feet, and two others at the sides, each of 50 feet.

14′, 6″ GLASS
Fig. 3093.
GLASS
The material is chiefly of wrought iron, and rests upon columns 25 feet in height, which
carry cast-iron gutter girders, of an average length of 23 feet each. At the point of the
roof is a skylight on each side the ridge, 15 feet in width, supported on louvre framing,
which is continued through the entire length; and the glazing comprises about 60,000
superficial feet, thus affording ample light and ventilation. The rain-water is conducted
down the middle of each column into drains constructed to lead it away.
The columns were so cast that at the top there is an adjustment to allow of expansion
and contraction, in order to prevent the joints of the guttering laid upon them becoming
leaky, or being in any way rendered faulty, and cast-iron shields placed against the ends
of the gutters over the columns assist in giving additional strength to this part of the
work.
SUPP.]
1679
IRON CONSTRUCTION.
Fig. 3094. shows the manner in which the foot of the principal rafter is in connection
with the cast-iron gutter resting on the top of the column.
Fig. 3095. exhibits the louvre boarding with its wood roll above the glass skylight, and
also the top of the queen bolt and strut attached to the rafter.
Fig. 3096. shows the bottom portion of the tye rod, the queen bolt, and the strut.


Fig. 3094.
SLATE
1. BOARDING
RAFTER
SHOE FOR
RAFTER
TIE ROD 13″
WOOD ROLL
Fig. 3095.
FF
Fig. 3096.
GUTTER-PLate.

Fig. 3097. is the middle standard that supports the skylight.
Fig. 3098. is the ridge standard, and head of the king bolt.
Fig. 3099. represents the sash bar and wood roll.
WOOD
I I
Fig. 3097. MIDDLE STANDARD,
Fig. 3098. RIDGE STANDARD.
Fig. 3100. represents the section of the rafter.
· LOUVRE.


GLASS
Fig. 3099. SASH BAR.
Fig. 3101. shows the bottom arrangement of the king bolt and struts, with the tye rods,
and the manner in which the latter are connected

T
A

Fig. 3100. SECTION OF THe rafter.
Fig. 3101. ELEVATION OF King bolt and struts,
1680
[Surp.
THEORY AND PRACTICE OF ENGINEERING.
Faris Providence Magazine.
The iron roof which spans this building is 87 feet in width,
and is another example of light construction, which has been erected on the Quai Jemappes,
the banks of the Seine, for the stowage of iron.
In France iron has been tested as to its strength, in every case where it
has been employed in the arts of construction, and malleable irun-
plates have been experimented upon with reference to their di-
rect tensile strain upon the fibre of the metal in every direc-
tion; and the breaking weight per square inch, when
drawn in the direction of the fibre has been given
as 22 tons, and when drawn across the fibre

23 tons.
Rafters of wrought iron are now
universally made use of and
©
Q
24
-87′.0-----
Fig. 3102. TRansverse section.
preferred to cast-iron on account of the saving in weight, where equal
strength is required, of one half at least: by this means the loads
upon the walls, or points of support, are greatly diminished, and the
duty of the tension rods is also lessened. There is no doubt great
economy in the use of wrought over cast iron; and wherever the T
form of section can be given by the rolling mill, the difference of cost
will be so considerable in the first instance, that it must be preferred
on that account independently of the load of metal in the case of roof-
ing being diminished a half or two thirds. The cost of iron in France
being so much greater than in England, has occasioned the engineers
to adopt every economical system that science has suggested. Occa-
sionally this has been carried too far; and structures which have evinced
considerable skill in execution, have needed additional strength to
their construction.
In cast iron a fracture may occur without any warning; but with
ම
wrought iron there is generally some indi-
cation of danger previous to a rupture
taking place.
The length of the building is 173 feet;
and eleven principals, including the two ga-
bles, carry the entire roof, the total cost
of which was 1600l.
Each principal consists of two main
beams formed of double T-iron, connected
together by tye bars, which are secured to
the principals and crown plates by cast-iron
pillars and diagonal rods.
These principals each weigh
-
Kilog.
1676 00
And the intermediate parts of the
construction
2982.50
4658.50
Fig. 3103.
The total weight is 64,290 kilog,, which
includes the glass and every other ma-
terial employed to complete it.
For every 103 superficial feet or a metre of
horizontal surface we have
a weight of 42 kilog, or
95 lbs. avoirdupoise, at
the rate of about 9 lbs.
per superficial foot only.
SUFF.]
1681
IRON CONSTRUCTION,

Fig. 3104.
+
B..
Fig. 3105. Top ridge of sKYLIGHT.
IT
Fig. 3106. SUPPORT OF SKYLIGHT.
Т
Fig. 3107. RIDGge.


Fig. 3108. SECTION THROUGH PURLINS.
Fig. 3109. ELEVATION OF shoe.
PART OF SHACKLE.
Fig. 3110. Shoe.
Iron roof, Lime Street, Liverpool, over the railway station, covers an area of 6000 super-
ficial yards, and was constructed at a cost of 15,000l., about 27. per superficial yard.
The roof is in length 374 feet, and its span is 153 feet 6 inches.
It consists of a series of principals placed at a distance of 21 feet 6 inches apart, which
are in some instances supported by side walls, and in others by a box beam made of wrought
iron, resting on iron columns.
These principals are vertically trussed by struts which radiate to the centre of the
segmental curve given to the roof, and these struts are maintained in their position by tye
and diagonal rods. Laterally they are trussed by the purlins, which are placed over the
radiating struts, and intermediately between them, as well as by diagonal bracing.
The wrought iron deck beam which forms each principal is 9 inches in depth, with a
plate of iron 10 inches wide and 4 inch in thickness riveted on the top. The lower flange is
3 inches wide and 1 inch thick; the web is about 7 inch in thickness. Each of the curved
principals or ribs is formed of seven pieces connected with each other, at the points where
the radiating struts are attached, by riveted plates 6 feet in length placed on each side.
At the haunches the beam has some additional strength given to it for a distance of
27 feet from the springing, by plates 7 inches in width and 7 inch thick, strongly riveted
together.
5 P
1682
[ SUPP.
THEORY AND PRACTICE OF ENGINEERING.

Λ
-55′0″--
153.6" WHOLE.SPAN.
Fig. 3111.
V
T
∙25.0"
WATER DRAIN

Fig. 3112. Half plan.
The 6 radiating struts to each rib vary in length from 6 to 12 feet, but all are 7 inches
in depth, and attached to the tye rods with wrought iron linking plates.
The tye rods are composed of three lines between the two extreme radiating struts, and
from these struts to the extremities of the principals they are in two lines; the sectional
area of both arrangements is 6½ inches.


о
Fig. 3113. IRON COLUMN and chair.
о
O
Fig. 3114. Struts.
The ends of the tye rods are prepared with eyes to receive the bolts, placed side by side
etween the linking plates attached to the struts, and through them is passed a bolt.
SUPP.]
1683
IRON CONSTRUCTION.
The wrought-iron box girder is 63 feet 4 inches in length, 3 feet 2 inches in depth
at the ends, and 2 feet 6 inches in the centre, being cambered on the under side 8 inches.
The upper chamber is 1 foot 8 inches wide, and 8 inches deep, and the body 133 inches wide
and 1 foot 10 inches deep; the bottom, 193 inches wide, is formed of two rows of plates
T6 of an inch in thickness in the middle, and inch at each end; the thickness of all the other
plates are of an inch.
The cast iron columns, placed at intervals of 21 feet 6 inches, are in height 19 feet; they
are securely based upon stones each weighing 5 tons.
The roof is covered with galvanized corrugated wrought iron and rough plate glass; the
iron is No. 16. wire gauge, in sheets 7 feet in length and 2 feet 8 inches in breadth, secured
with galvanised rivets and washers.
The glass is inch thick, in plates 12 feet 4 inches in length and 3 feet 6 inches in
width, bedded upon iron sash bars.
The gutters which collect the water are of cast iron, 20 inches in width, and rest upon
the columns and intermediate arches, and the water is made to pass through the columns
into the drains.
Iron roof at the Liverpool terminus of the Lancashire and Yorkshire Railway covers
five lines of rails. Three platforms, and a roadway for carriages 36 feet in width; the total
area covered in 83,457 superficial feet.
This roof is very light in its construction, and in one span extends 132 feet, having no
columns or supports between the outside walls. The principals are distant from each other
11 feet from centre to centre; each of these principals have two cast-iron plates bedded in
the masonry to receive their ends; the shoes are 132 feet 8 inches apart.
Each pair of principals has eleven king bolts or rods placed at equal distances,
which, by means of screw ends, are attached to the joints of the tye rods, which have a
curved line.
The principal rafters
are of wrought iron plate,
with two pieces of angle
iron riveted along the
top, and two along the
bottom, with one on
each side forming in its
section a figure of the
letter.

E
Fig. 3115. BOTTOM OF THE CENTRE KING ROD.
The struts, which are ten in number to each pair of principals, are all of T iron of large
dimensions; these are secured at the upper ends of the principal rafters by wrought iron

6
о
-I
о
O
O
о
O
Fig. 3116. SIDE VIEW OF KING ROD.
Fig. 3117. JOINTS OF RAFters, strut, AND KING ROD.
knees, firmly riveted and bolted to the principal rafter, and at their lower end are fixed
into cast-iron shoes, which fit upon the tye rod, and are attached to the suspension rods.
The main tye rods are of round iron, screwed into wrought iron sockets under each
queen rod which passes through it, where it is secured by a nut below.
The upper ends of the principal rafters enter a cast-iron king head formed of two castings
bolted together, and above is placed the louvre standard, which carries a cast-iron ridge,
5 P 2
1634
[SUPP
THEORY AND PRACTICE OF ENGINEERING.
upon which the sash bars of the skylight are fixed. These two skylights are 20 feet in width,
and, with two others at the eaves 10 feet wide, make a total width of 42 feet, and their
length being 616 feet, form nearly

an area equal to one third of the
entire roof.
The ventilation is completed by
means of fixed louvres placed under
the ridge skylights; they are formed
of galvanized iron blades fixed into
cast-iron standards.
The covering of the other por-
tions of the roof is corrugated, gal-
vanized iron plate, on purlins, with-
out the aid of any other support;
the struts are riveted together, and
further secured to the purlins by
bolts and nuts.
Fig. 3:18.
BOTTOM JOINT OF KING ROD, AND TYE ROD AND SHOES.
Catenarian Curve was the form adopted by Jacques-Germain Soufflot for the middle
dome that was destined to support the lantern at the church of Sainte Geneviève at Paris ;
this far-famed Catenarian dome is 70 feet diameter at the base, and 50 feet in perpendicular
height; the stone of Conflans was employed for its construction.
Among the writer's earliest constructive works, he imitated this curve in the formation
of a roof with courses of plane tiles, laid in cement in three thicknesses, breaking the joints
as much as possible; the strength of this form induced him to employ it for the covering
of stables, and less important structures. The four-roomed labourer's cottage is submitted
to the reader as an example for the employment of brick and iron without any wood,


PUMP
UNDER STAIRS
STORE FOR COALS
SINK
OPP
KITCHEN
LIVING ROOM
--15.0″.
OVEN
PANTRY
DRESSER
DRESSER
RECESS
BED
t
RECESS
6--
12%.3″.
ia: 3
BED
·
>
BED
1.9
RECESS
RECESS
-25.0%
-16.
n
Fig. 3119. GROUND PLAN.
Fig. 3120.
· 13′′ 0″----
CHAMBER floor.
except for the doors of the several rooms, thus constituting a cheap fire-proof building, the
cost of which would not exceed 100%. when materials can be had at the ordinary prices of
the present day.
Each of the two rooms on the ground floor is 15 feet by 10 feet; the
stack of chimneys dividing them one from the other, with a door of communication on
one side. The back room has a staircase to the chamber floor, underneath which is
another to the cave below, in which is placed the cistern or tank that collects the rain-
water that falls upon the outer covering of the cottage; and beneath is a floor or
pavement, upon which a water-closet apparatus is fixed, discharging into a drain that leads
away to lower ground, where its outlet is placed. From the tank, a jigger pump near the
1
SUFP]
168.5
BRICK AND IRON CONSTRUCTION.
sink supplies the water for the family use; and in the opposite angle of the kitchen is a
pantry of a triangular form. An oven is constructed at one side of the fire place, and a
small copper on the other, the flues of which communicate with those of the fire places.
The upper rooms are only 12 feet 3 inches in width; but the smallest is sufficiently
large to contain two small beds. Each of the two chambers have fire places, and the com-
munication between them is by a doorway in the middle of the chimney stack.
By a reference to the figures, and particularly that drawn isometrically, the general ar-
rangement may be understood without any further description. The sections of the cottage
are bounded by a catenarian curve, over which, at the height of every foot, two horizontal
lines are drawn as a scale, and between the perpendicular lines only 1 foot is defined; so
that, by a reference to these lines, the approximate width of the catenarian curve at every
6 inches in height may be ascertained.
The true form of the curve is obtained by hanging a chain upon two points, expressing
the width at the foundations, and suffering it to drop round another as much below as it as
it is intended to make the height. In the example before us, two nails placed upon a level

♡
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20 FT
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17
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10
12 13 14
Fig 3121. SECTION.
Fig. 3122. ISOMETRICAL VIEW.
line 15 feet apart, and another 20 feet below, exactly on the middle of the space between the
other two, and then a flexible chain attached at the two upper nails, and drawn up till it
passes over the lower point, will represent the catenarian figure, to which a mould is to be
cut.
With this mould to the two end and middle walls, the proper curvature may be given as
they are carried up in 9-inch brickwork; and at the height of 9 feet may be laid, from back
to front, five iron railway bars, to serve as girders to carry the arches, which, when rendered
level on the top, may receive an asphalte flooring.
By building the external wall 9 inches thick, or one brick, laid in cement, no other pre-
caution is required than to strain the line, when each course is bedded, over the three
sectional walls previously carried up in advance, occasionally applying the mould to the
inner face of the outer covering. Where cement is not employed, it may be necessary to
have some support in the middle of the length of each 10 feet between the end and middle
walls, to prevent the work from sagging; but good cement does not require this precaution,
for when the height has attained the chamber floor, the series of arches which constitute it
acts as an abutment, and serves as a scaffold to carry up the remainder of the external and
internal walls. The stack of chimneys must be set out very accurately, as they contain four
flues, and these cannot be obtained in a shaft less than 23 bricks in thickness and 6½ in
width; and it is important to the stability of the structure, that it should be placed in the
5 3
1626
[SUPF
THEORY AND PRACTICE OF ENGINEERING.
F
middle of the building. The bricks should be worked in alternate courses of headers
and stretchers; and where impervious bricks cannot be obtained, the exterior may be ren-
dered with a coat of Roman cement. Three courses of plain tiles in cement, and rendered
at the back, would be equally durable with the 9-inch wall we have described; and where
tiles can be had at a more reasonable rate than bricks, they may be preferred.
As all the windows are of similar form and dimensions, the six may be easily cast in
iron, of one pattern, one half their area, made to open upon pivots, and secured when shut
by a latch or pin.

Much has unquestionably been done
within the last few years towards im-
proving the dwellings of the working
classes; but the experiments have been
generally made on large piles of build-
ing, where numbers could be accommo-
dated under one roof, thereby diminish-
ing the amount of rent to the occupiers,
and in several instances affording a rea-
sonable return for the capital employed:
and in proportion as such establishments
become known, they will be more and
more estimated, and their comfort in-
creased at less cost; but we have yet to
wish that the blessings of warmth, sup-
ply of water, and drainage, with all their
attendant advantages, could be as easily
applied to the isolated cottage of the la-
bourer, on a principle which would enable
the small owner to afford them without
positive loss. Every appliance of science
is now put forth to warm and ventilate
our-garden structures; and if the same
skill could be applied to our catenarian
cottage, one furnace with one flue, in-
stead of four, might heat the boiler and
oven, and, by means of
iron pipes, each of the
rooms above and below;
hot water could be made
to circulate, without the
expenditure of much fuel;
and the inmates of such a
cottage would then have an
advantage which is rarc-
ly enjoyed, viz. that of re-
turning to well warmed
and ventilated rooms after
the labours of the day.
EARTH
STONE SLAB
RAIN
WATER
CISTERN
U
M
A.
120 FT
19
18
17
(6
15
14
ก
13
12
2:6
1-6
SO
1618
Fig. 3123. SECTION OF HOUse.
10
9
:
18
+6
h
The supply of water, with tanks of suf-
ficient capacity for all the uses of a small
family could be provided for without.
Eyes may be bedded in the external surface of the catenarian walls, through which
horizontal wires may be passed, for the training of creeping plants or roses; and such a
building, so covered, would assume a picturesque character. The front and back walls
should be carried up so that their outer faces are 4 inches behind the covering, that
projection being necessary to the roof, to make a perfect joint, and to keep out the driving
rain.
The rain water, falling down the sloping sides into an iron gutter resting on a plinth,
and led into the tank by 4-inch pipes, would provide an average supply of 10 gallons of
water per day. Windows might be perforated through the longitudinal sides, if required,
upon the same principle as the openings are made in the dome of St. Généviève, and
dormers of an ornamental character attached, the outline of which might also be catenarian,
though placed at right angles with the main curve, to which they unite, thus breaking
the side length. Where a continued line of cottages is built under such a formed roof,
then such openings must be made in the longitudinal sides; but the cost of construction
would be much enhanced.
There would be no necessity to insure such fire-proof structures; and the ordinary re-
pairs would be but trifling in the course of several years.
Iron Beams and their Supports.-The British Association for the Advancement of Science
in their Seventh Report, have given some experiments made upon the strength of cast-iron
bars; and Mr. Hodgkinson, in a general summary of his experiments on rectangular bars
SUPP.]
1687
BRICK AND IRON CONSTRUCTION.
an inch square, has given their breaking weight, and the transverse strength of such bars,
when placed 4 feet 6 inches between their supports,-the modulus of elasticity being
taken from the deflection caused by 1 cwt. on those bars.
The breaking weight of several qualities of cast iron varied in fifty experiments from
350 lbs. to 550 lbs. Mr. Hodgkinson has given a formula representing the breaking
weight-
4.5 bď² S
in pounds avoirdupoise. The length in feet, multiplied by the breadth in inches, by the
depth in inches squared, and by the mean breaking weight in pounds,—this product divided
by the length in feet, gives the breaking weight in pounds. For example,-
A bar of cast iron 4.5 feet long between the supports, 2 inches in breadth, and 3 inches
in depth, taking a tabular number of 450, which we will assume as a mean breaking weight,
would be thus represented.
4·5 × 2 × 32 × 450
4.5
= 8100 lbs. avoirdupoise as the breaking weight;
consequently not more than half that amount should constitute its load when used in
construction. (See page 690.)
The form of beam admitted to be of the greatest strength is that of the letter reversed.
Ꮮ
Such a beam + feet 6 inches in length between the supports, and in depth 51 inches, the
weight of the casting 40 lbs., broke with a weight of 8270 lbs. avoirdupoise.
Whenever cast iron is employed for construction, we must guard it against exposure to
wet or intense frost, as sudden contraction or expansion often disturbs the crystalline tex-
ture of the metal, and occasions fracture. The transverse strength has been usually estimated
by considering that perfect elasticity existed in the iron beam up to one third of the break
ing weight, and therefore we ought not to load it more than up to that point, and some
experiments have proved that it is better not to trust to more than a sixth of the
breaking weight, and then not without previously testing the iron before it enters into the
constructive portions of a building.
.
For warehouses of several stories in height, cast-iron hollow columns are placed
one over the other, with rolled-iron girders, 8 inches deep, resting on the lower capitals;
upon which, in an opposite direction, are laid rolled-iron joists 5 inches deep, with
flanges 2 inches wide both at top and

bottom.
When cast-iron girders of large dimen-
sion are required, it is important to notice
that in cooling a very irregular contrac-
tion takes place, often creating a strain in
some parts of the metal, producing fracture.
This contraction is more equal when the
form of the girder in its section exhibits
uniformity of thickness throughout its se-
veral parts; in a T shape the arms con-
stituting it, if made of one width, will
have less tendency to an unequal cooling,
and consequently a greater dependence
upon its strength. Another caution for
the founder is, that the angles should be
rounded off, and not left too sharp or recti-
linear. The builder will find that the same
weight of metal applied to several small
castings, will be of equal strength, and
more to be depended upon than one large
girder, which is also more difficult to
move, and to secure in its place, than a
number. The tensile strength of cast-iron
hoving been considered as equal to 6½ tons
per square inch, we may use that calcula-
tion to proportion any beams, and make
them of a size that the builder may de-
pend upon their strength and be able to
move them into the places destined, without
the labour required for hoisting at one time
a very considerable weight, not always practi-
ASPHALTE
CONCRETE
7
Fig. 3124.
5 P 4
1688
[Surp.
THEORY AND PRACTICE OF ENGINEERING.

cable where a small number
of workmen are engaged;
and smaller weights may
be also more equally dis-
tributed over the walls that
are to carry them.
Wrought iron being
crushed when 16 tons are
applied to each square inch,
this weight should not be
hazarded upon a column of
any height. The heights
of columns must be made
proportionate; for we find
that their strength varies
inversely as the square of
their length. Square co-
lumns have their strength
as the fourth powers of their
diameters, their breaking
weights being proportional
to their width and to the
cube of their thickness di-
rectly, and to the square
of their length inversely.
Where the metals are pre-
ferred for construction to
CONCRETE
JOISTS OF
ROLLED IRON
Fig. 3125,
timber on account of its inflammability, the cost is perhaps not so much taken into
account; but the power of Baltic timber to resist a strain is greater than is usually sup-
posed. Rods of that material will bear a tensile strain of five tons per square inch; the
tension rod of wrought iron of the same strength, would be one fourth only of its sectional
area, but nearly three times its weight; wrought iron will bear a strain of 10 tons per
square inch, and Baltic timber one fourth only of that weight.
The cylindrical rod of wrought iron an inch in diameter, and weighing about 8 lbs. per
yard, will bear tensilely 16 tons. To serve the purposes of calculation, the square of the
diameter, taken in quarter inches, is
the breaking weight in tons, and half
this quantity is the weight in pounds
per yard; as a rod 6 inches in dia-
meter contains 24 quarter inches, that
number squared gives 574 tons for
the breaking weight, one third of
which should be allowed in practice.

A layer of concrete, with a surface
of asphalte, forms a secure floor, and
fire proof.
The figure shows the manner of pass-
ing the iron girder through the iron
upright shaft, above the capital, by
which means the columns are braced
in every direction.
The rolled girder rests sometimes
on the moulded capital of the column;
and the joists of rolled iron rest at
right angles upon it, passing through
holes left in the column above the
girders; a concrete pavement spread
with asphalte constituting the floor,
flat tiles being laid in courses between
the joists for its support.
ASPHALTE
CONCRETE
GIRDER
Fig. 3126.
0
<...
Where brick and iron are made use of, the girders of rolled iron rest immediately over
the capitals of the columns, upon which are placed, at regular distances, rolled-iron joists;
between them is turned a flat brick arch, on which is laid the concrete and upper floor or
asphalte.
Fireproof floors are made with the ordinary rolled iron; in some instances forming
joists, in others girders. On the lower flange is laid stout laths, to receive the plaster
SUPP.]
1689
BRICK AND IRON CONSTRUCTION.
ceiling; over the upper face of the laths a layer of course mortar, on which rests the
concrete which sustains the floor, which will be better understood by reference to the lon-
gitudinal and transverse sections.

Fig. 3127.
I
CONCRETE
LAYER OF COARSE MORTAR
STRIPS OF WOOD
PLASTER CEILING

BOARD
SPACE
IRON GIRDER
Fig. 3128.
CONCRETE
PLASTER CEILING
The fire-proof floors at Guy's hospital have girders of wrought iron, which carry cast-
iron joists, over which is a bed of concrete, strips of fir being embedded in the upper surface,
on which a deal floor is laid.

CONCRETE
Fig. 3129.
BOARD
SPACE
IRON JOISTS WITH
FLANGE FOR CEILING JOISTS

CONCRETE
Fig. 3130.
CAST IRON JOISTS
FLANGE FOR JOISTS
The Bermuda cast iron Lighthouse was erected by Mr. Alexander Gordon, after the
model of one he had previously constructed in Jamaica.
The base upon which it is placed is 250 feet above the level of the sea; the structure
itself is 105 feet 9 inches in height, and the lower diameter 24 feet. It is composed of
135 concentric cast-iron plates, moulded to be readily adapted to the conoidal figure of the
lighthouse.
These plates vary in thickness from 1 inch to of an inch, and are cast with flanges on
1690
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
the inside, 4 inches broad, including the thickness of the plate, and are farther strengthened
at intervals of 12 inches by angular feathers, an inch thick. Holes are drilled in all the
vertical and horizontal flanges, 6 inches apart, into which are passed square-headed screw
bolts, of an inch in diameter, with nuts and washers,


D
Fig. 3135. SECTION.
Fig. 3136. ELEVATION.
0
SUFF.]
1691
BRICK AND IRON CONSTRUCTION.
In the centre of the light-house is a column from bottom to top of cast iron, 18 inches
in diameter in the inside, the thickness of the metal being of an inch, This supports the
optical arrangements introduced by M. Fresnel; and the weight of the revolving apparatus
descends in the hollow shaft. This column was cast in 9 lengths, each terminating with
circular flanges, to which the floor plates are bolted. At the height of 2 feet above each
floor, there is a man hole or opening into the hollow shaft, 26 inches high and 15


Fig. 3131. GROUND PLAN.
Fig. 3132. UPPER PLAN.


Fig. 3133.
MIDDLE PLAN.
Fig. 3134. ROOF.
inches wide, to which are fitted wooden doors, opened when any stores are lifted to the se-
veral floors. The waste-water pipe is also enclosed in it.
By reference to the section, it will be seen that
the lower part of the tower, to the height of 20 feet,
is filled with concrete, leaving a well in the middle
8 fet in diameter, steined with brickwork.
The seven floors are each 12 feet in height; and
the first and second are cased with brickwork, and
used as store-rooms: the five upper are lined with
sheet iron, of No. 16 gauge, disposed in panels
with oak pilasters, cornices and skirtings.
On the first floor is a cast-iron curb, 10 inches
wide and 1 inch thick, on which a cast-iron floor-
plate, of an inch thick, is fixed by bolts of an
inch in diameter. The inner edges, as well of this
as all the other floor-plates in the lighthouse, are
bolted between the flanges.
The second floor consists of ten radiating cast-
iron plates, of an inch thick, resting on brick-
work, the other five floors are similar, but rest upon
the upper flanges of the outer plates that form the
lighthouse. The eighth floor consists of sixteen ra-
diating plates of cast iron, of an inch in thickness
connectea with 3-inch bolts.

ת
Fig. 3137.
There are five windows on each floor, one in the centre of every alternate plate in the
circle. They are 18 inches square, fitted with. plate-glass in strong wooden frames 9½ inches
square. Windows are introduced into the sides of the circular well, making altogether 36
windows.
1692
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
7
The staircase is formed spirally with two wrought-iron strings 1 inch thick, the risers
and supports being inch thick; upon these are oak treads 1 inch thick. On each step
is an iron baluster, of an inch in diameter, which supports a wrought-iron handrail.
Around the outside of the upper platform is a gallery railing; and from the gallery to the
centre of the light is 11 feet, from thence to the top of the vane 17 feet, making the
total height of the lighthouse 378 feet 9 inches above the level of high water, so that
it has been supposed that the light could be seen from the deck of a vessel at a distance of
26 miles.
The cost of this building after its completion was nearly 8000%.
Screw Piles and Moorings, so extensively used by the inventor, Mr. Mitchell, for construct-
ing sub-marine foundations, have also been employed for lighthouses, beacons, piers, jetties,
and breakwaters, in situations where the civil engineer found a soil composed of loose and
unstable sand, incapable of supporting any kind of structure, or where the waves of the sea
had the power of undermining any work within its influence.
Upon the Goodwin sands (in 1851) a hollow pile, 6 inches in diameter, was screwed down
with ease to a depth of more than 50 feet, passing through a fine and compact sand. Since
that period the use of screw piles has been adopted for construction in situations where
a solid foundation could not be otherwise obtained.
To obtain a firm hold in sand or soft ground, nothing was found to succeed so well as the
insertion of a bar of iron to a considerable distance beneath the surface, having at the
lower end a broad plate or disc of metal, either of a spiral or helical form, resembling the
screw. This form could be made to penetrate sand with facility without materially disturbing
its solidity; and when an extended base was presented, it would resist any upward strain as
well as downward pressure. The disc or area of the plate must be decided upon after the
stratum it is to enter has been examined by boring; and in few cases has it been required
to extend this diameter more than 4 feet.
Among the earliest lighthouses constructed upon screw piles, was that at Maplin sand,
where 9 malleable-iron piles were used, 5 inches in diameter and 26 feet in length, with a
cast-iron screw 4 feet in diameter screwed to the foot of each. Eight of these piles were
placed at the angles of an octagon, and one in the centre, screwed into the bank to the depth
of 22 feet, leaving 4 feet above the surface.
Fleetwood Lighthouse, the cost of which, including the dioptric apparatus, was 3,350l., is
constructed on a sand bank two miles from the shore, and required seven wrought-iron piles
16 feet in length, with cast-iron screws 3 feet in diameter, one being placed at each angle of a
hexagon, and one in the centre. On these were erected seven pieces of Baltic timber, 14 inches
square, the six on the exterior 48 feet in length, and that in the centre 57 feet, to admit of
its rising through the house to support the base of the lantern. In the foot of each of these
supports a hole 5 inches in diameter was bored to the depth of 7 feet, to receive the
end of the pile upon which it was shipped; and over this arrangement iron hoops were
driven, hot.
A small spiral flange was fixed on the end of each, to draw it into the sand. The dia-
meter of the hexagonal base is 50 feet; that of the platform on which the house stands, 27
feet, the exterior piles having an inclination of 1 in 5. The floor of the house is 45
feet above the surface of the bank; and the tide rises 32 feet on the supports at equinoctial
springs.
Belfast Lighthouse, erected on the tail of the Hollywood bank, about a mile from the
coast of Down, is of a similar description. The cast-iron screws were 2 feet 6 inches in dia-
meter, attached to malleable-iron piles 5 inches in diameter and 26 feet in length, sunk in
the bank 16 feet.
Dundalk Lighthouse, is supported on nine malleable-iron piles, arranged octagonally, one
at each angle, and one in the centre.
The centre pile is 60 feet in length, the outer 52 feet; their diameters, 8 inches at the
surface of the ground, diminishing upwards to 5 inches at the platform, and downwards to
6 inches at the level of the cast-iron screws, which are 2 feet in diameter, screwed 17 feet
into the ground.
The piles have an inclination inwards of 1 in 5; the diameter across the octagon
at the base of the screws being 50 feet, and at the platform 30 feet. Each pile is in two
parts, connected by a strong screw coupling. A strong iron framing of malleable-iron bars
is placed 18 feet below the floor of the house, radiating from the centre pile to all the
outer ones, and connecting the outer piles with those adjacent; these bars are 5 inches in
diameter at the centre of their length, and are reduced to 4 inches at their extremities; they
are secured to the piles by iron bands placed between collars forged on the piles; diagonal
braces or tension rods of cable iron 2 inches in diameter are fixed between the centre and
each of the outer piles, commencing at the horizontal bracing, and terminating below the
platform, each pair being bound together at their crossing, and fitted, near the upper ex-
tremity, with a screw and shackle for accurate adjustment, so that all the parts are bound
together.
SUPP.]
1693
IRON SCREW PILES.
A cast-iron cap is ftted on the head of each pile, each resting on a forged collar, and
form bed plates on which the main timbers of the platform are bolted. They are all secured
to the piles by strong screws chased in the upper extremity, the nuts resting on a broad
iron plate above the platform.
The timber used is oak, and that only for the framing of the platform, the corner posts,
the studs of the walls, and the rafters. The side walls are plate iron, and the covering sheet
lead, 10 lbs. to the superficial foot.
Chapman Sand Lighthouse, on a sandbank in the estuary of the Thames, is founded
upon seven wrought-iron screw piles, one placed in the centre, and six at the angles of a hex-
agon at an inclination inwards of 1 in 5; the piles are 7 inches in diameter, and 42 feet
in length, with cast-iron screws 4 feet in diameter. Each pile weighs 3 tons, and is
screwed down, 39 feet below the surface of the bank, into sand. Upon the heads of these
piles are fixed strong cast-iron cylinders, connected by wrought-iron braces, to support
the superstructure, which is of wrought iron with the exception of the interior fittings
of the house.
The foundations were laid in 1850, and the whole completed in 1851.
F
For ordinary uses piles are made extremely light, their discs varying from 1 to 2 feet,
the latter being found sufficient for an ordinary mooring chain.
At the Portland breakwater these screws were employed, entering very deep into the soil.

<..... 1 .3. ... >
--B!
<<<<--- 2.0%
Fig. 3138.
5.0"
Fig. 3141.
Screws for fencing-posts on the
sands or the sea shore have been
employed.
Varieties of hollow iron piles,
with screw ends,, have been used
as supports for lighthouses, their
lengths being made proportionate
to their use. One used at the
"
<--8"..>
ה
4'.0"-
Fig. 3139.
2:6.
Fig. 3140.
<--1.0-->
3.0%
<----- 2′.0"
Fig. 3142.
1.2
foundation of the aqueduct at Well Creek weighed 33 cwts., was 2 feet in diameter; and
another of the same diameter weighed 3 cwt., with a hexagon-formed shaft.
A screw 3 feet in diameter, with a hollow shaft, is capable of great retension.
1694
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
For bridges, screws with hollow cast-iron piles, and the auger screws employed on rocks,
are of several forms; their weights according to the services required.


·8.2-
# 1 1

2.0%
Fig. 3143.
<--...... 2.0'.......>
Buoys may be fixed by such screws, and, when made 8 feet in length, weigh about
13 cwt. For the attachment of guy ropes, or for any temporary use, this form is admi-
rably adapted.


<------ 1'. 6″------
Fig. 3144.
Fig. 3145.
A mooring for very hard ground re-
quires conside able strength; and the
weight of a sufficient screw for such a
purpose would be 9 cwts.
For mooring-chains 14 inches dia-
meter, the diameter of the disc or screw
extends 4 feet, and the weight of such is
about 111 cwts.
The screw mooring employed at
the Portland breakwater is shown in
fig. 3146.
Rochester new Bridge
Bridge across the
Medway.-Nearly over the site of the
old wooden bridge, mentioned in a
former part of this work (page 414), a
new one is in the course of erection,
to consist of three openings for ves-
sels, which are to be spanned with
cast-iron segmental girders, — the cen-
tral opening 170 feet, and the two
1
4.0%-
Fig. 3146.
2.6.


SUPP ]
1695
ROCHESTER NEW BRIDGE.
others each 140 feet; but the works already performed deserve particularly to be noticed,
as they are of a novel character in engineering, and reflect the highest commendation upon
Mr. John Hughes, who was the first to adopt them. The old diving bell, contrived by

ROCHESTER,
ABUTMENTĮ,
ROCHESTER PIER
STROOD
PIER

200
800 FT
100
EXTREME HIGH WATER
LEVEL
EXTREME LOW WATER LEVEL
000000
STROOD
BUTMENT
oooooo
00000
0000 00

Fig. 3147.
Dr. Halley, and improved by Smeaton, has been by Mr. Hughes's application entirely
superseded for foundations in deep water. Compressed air is made to free a cast-iron hollow
pile from the water within it after it has been placed in its situation on the bed of the
river where it is to be fixed; and afterwards this diving bell is to perform, without again
being drawn up, a part of the permanent structure.
The first application of this principle is mentioned by Dr. Ure, in his Dictionary
of Arts and Manufactures, as having been tried on the banks of the Loire, in France, by
M. Triger in sinking a shaft through a quicksand 65 feet thick, to arrive at a stratum
of coal. In the Comptes rendus, de l'Académie des Sciences, Mr. Hughes found a complete
account of the system adopted by the French engineer, which was as follows: A pipe of
wrought iron, 3 feet 4 inches in diameter, inch in thickness, and 65 feet in length, was
made in several lengths of from 15 to 20 feet, which were connected together, as they were
driven into the sand by an engine stationed near, in the same manner as usually adopted
in the sinking of artesian wells. The sand was withdrawn from the wrought-iron cylinder
by an auger, and the cylinder descended to the depth of 50 feet without much difficulty;
but afterwards, when a stratum of coarse sand was arrived at, 200 blows of a ram weighing
2 tons, and falling through 5 feet, were required to force the hollow pipe a few inches.
is stated that the two last yards of the descent consumed labour and time equal to more than
double what was required for the previous part of the operation. (See page 1228)
It
The pneumatic aparatus used by M. Triger raised the water 82 feet by compressing the
air two atmospheres including the natural atmosphere; and this was performed, by making
an opening in the outlet pipe, at about 20 feet above the bottom, for the purpose of admit-
ting a current of compressed air upon the column of water, thus bringing the tension of
the air to act upon two points, so that, if it was not powerful enough to raise the entire
column, it would partially effect it. The jet of water mingled with air rose 82 feet when
the pressure exercised was not more than equal to 12 atmosphere.
The apparatus altogether, on this occasion, only consisted of a steam engine, two air pumps,
and an air vessel with a stuffing-box fixed at the lower part, intended to connect it with the
wrought-iron pipe in a manner to enable the communication with the atmosphere to be
at any time cut off. To this was added, to complete the apparatus, a supply pipe for the
conveyance of the compressed air from the pumps to the shaft, and an outlet pipe for the
discharge of water, two man-hole valves, for the passage of men and materials into and
out of the air vessel, two cocks to be used for the same purpose, a pressure gauge, and safety
valve.
The air which passed from the pumps through the supply pipe, was compressed below
the air vessel in the shaft, whenever the man-hole valve, which communicated between the
two, was closed; and whenever the shaft became filled with water, the water, yielding to
the pressure of the air, made its escape by the outlet pipe. Thus a constant supply of com-
pressed air kept the shaft dry.
The manner in which the above principle was applied to sinking the piles at Rochester
Bridge, reflects as much credit upon Mr. Hughes as the invention upon M. Triger; as
firmly fixing 70 hollow cylindrical piles in the bed of a tidal river was attended with far
greater difficulties than sinking a single shaft upon terra firma.
Each of the two river piers of the new bridge at Rochester covers an area of 1118 super-
1696
[Surf.
THEORY AND PRACTICE OF ENGINEERING.
ficial feet; their length being 70 feet, and width 17 feet 8 inches. Fourteen cylindrical
piles, at distances of 9 feet longitudinally and 10 feet transversely, are employed in each
of these two piers.
In the Strood abutment, 30 of these piles, and on the Rochester side 12, are employed,
each pile consisting of two, three, or more cylinders 9 feet in length and 7 feet in diameter,
bolted together through stout flanges, the bottom length having a bevelled edge, to render it
better able to enter the soil.
To facilitate the fixing of the piles, Mr. Cubit, the engineer-in-chief, who designed the
bridge, erected over the site of each pier a substantial timber stage, which aided the workmen
to place the piles in such positions that they might be accurately dropped; and other tem-
porary wooden platforms were adopted, to receive the materials as well as machinery required
for the operation. The bed of the river was found, by boring, to consist of strata of soft
clay, sand, and gravel overlying the chalk, which appeared at a depth of 44 feet below the
average high-water line. On the side of the river where the Strood pier was placed, there
was a hard mass of stone difficult of penetration. As it was found necessary that worknien
should descend to the bed of the river to level the site of each cylinder, and to assist its
descent, it was important to make the piles perform the duty of diving-bells, and conse-
quently that the water should be kept out until the cylinder pile should be sunk 30 feet
into the bottom of the river, and the workmen enabled to excavate and remove the earth
in the interior, and fill up the void with brickwork and concrete instead.
To effect this, one of the cylinders 7 feet in diameter and 9 feet in length, was converted
into a diving-bell, with a wrought-iron cover securely bolted to it; through this cover,
projecting 2 feet 6 inches above the top of the cylinder, and 3 feet 9 inches below the
cover, were two cast-iron chambers or air locks of the form of the letter D. on the plan,
with a sectional area of 6 superficial feet. The tops of these air locks, were provided with
a circular opening 2 feet in diameter, and with a flap working on a horizontal hinge,
which, when closed, enabled the chamber to be filled with compressed air.
The communication from these air locks or chambers to the inside of the cylinder was
made by an opening 3 feet 4 inches long and 2 feet wide, on the flat side of the chamber;
this opening was closed by an iron door working on vertical hinges, rendering it air-tight
when required. These air locks were placed upon opposite ends of the same diameter of
the cylinder; and the lock doors opened so as to communicate with opposite semi-cylinders.
Within the cylinder was fixed two wrought-iron cranes, their jibs sweeping over the space
between the air locks, extending into the chamber when the doors opened, so that a loaded
bucket suspended from the crane could be lodged in the chamber.
A loaded and empty bucket, at the opposite ends of these cranes, were worked by a two-
handled windlass, from the barrel of which the chain passed over the sheaves of the
two cranes.
Cocks were attached to the air locks, allowing a communication between them and the
interior of the cylinder, and also from the chamber to the atmosphere. Each air lock had
two sets of cocks,-one, accessible from the inside of the chamber, for the use of the workmen
passing either from or into the cylinder, the other for passing buckets of materials
through the air locks. One cock was placed under the charge of a workman inside the
cylinder, communicating between the chamber and the atmosphere in such a manner
that he could, after the door was closed, let off the compressed air, and pass a bucket from
the inside to the out.
Another cock, communicating from the chamber to the interior of the cylinder, worked
by a man outside, enabled him on closing the flap to fill the chamber with compressed
air, and to pass a bucket from the out to the inside.
The cylinder which contained the cranes was provided with two glass lenses, 9 inches in
diameter, inserted in the cover; and two similar admitted light to the chambers of the air
locks.
A removable platform was provided for the workmen, so that in working the winch they
might always be placed at a convenient height.
Steam engines, and air pumps for the supply of compressed air, were conveniently placed;
and the cylinder pile received the latter by a double-barrelled pump 12 inches in diameter
and 18-inch stroke, with double action, driven by a 6-horse power non-condensing steam
engine. The pipe through which the air was supplied was 24 inches in diameter, formed
of iron lap-welded tubes, with hose pipes at the ends, so as to suit its various applications.
Within the cylinder, the air pipe was terminated by a valve opening inwards, which ob-
viated any accident that might occur by the bursting of the pipe.
When the works were commenced, the water in the cylindrical pile was first expelled, be-
neath the lower edge of the pile, into the river; but after it had descended sufficiently into
the earth to oppose a resistance to this expulsion, a siphon pipe was introduced, the longer
leg of which depended on the bottom of the pile, and the outlet for the water provided in
the uppermost cylinder. The pressure of the condensed air was thus made to act on the
SUPP.]
1697
CAST-IRON PILES.
surface of the water within; whilst the shortest leg, leading into the river, had the effect of
relieving the amount of compression for nearly the difference, as a column of water between
the summit of the siphon and the surface of the river outside, by the action of the ex-
ternal atmosphere, provided a vacuum was once obtained in the body of the siphon; and
this was produced by connecting the summit with the exhausted side of the air pumps by
a pipe which could be opened and shut at pleasure. Another cock, placed on the internal
leg of the siphon, enabled the workmen to dissipate the fog which would occasionally arise
within the cylinder, caused by too sudden an expansion of the compressed air.
This siphon also acted as a safety valve, as well as an outlet for the continual change
of air; when the cock was closed, the air locks were worked at regular intervals, so as to
abstract a portion of the air contained in the pile, and to replace it by fresh air through
the pumps.
When the works were proceeding under the weight of a column of water of 30 or 40 feet,
it was found that the escape of the air, suddenly, caused a depression of 2 or 3 pounds on
the square inch, as the pressure gauge attached indicated; but by the continued action of
the air pumps and the flow of water from the outside, this action was rapidly reversed.
After this siphon was adopted, the escape of the air within the pile caused a dense fog,
which obscured the lights and chilled the workmen, and the rush of water out of the river
rising to the same height in the pile, was prevented.
To insure the downward action of each pile in its proper vertical position, it was neces-
sary to load it sufficiently to counteract the upward pressure; and this was done by laying
on the top of the cylinder two stout trussed beams of Dantzic timber, in such a position as
to bring the adjacent piles into action as counterbalance weights, which was effected by
passing four chains connected with them over cast-iron sheaves.
One end of each chain was attached to the flange of the adjoining pile; and the other was
secured to one of the 6-feet cylinders suspended inside the 7-feet cylinders, and freely
worked up and down within it; by this means an additional weight of 40 tons could
be added.
The bottom of the Medway is dry at extreme ebbs, and has from 24 to 26 feet depth of
water at extreme high tide.
The apparatus here attempted to be described, is most admirably shown on a large
scale, with all its important details, in a work published by Mr. John Hughes, to which
we must refer the reader who requires its use or application. The method of working it
commenced by setting the pumps in motion, the flap of one of the air locks and the door
of the other being closed. a few strokes compressing the air within the pile sufficiently to
seal the joints; and every subsequent stroke delivered an additional quantity, until the
density was sufficient to expel the water, and leave the bottom dry. Fifteen feet of water
was cleared out in five minutes; and whilst the pumping continued, the workmen passed
through the air locks to their respective stations; and as the excavations proceeded, the
material, sent up in buckets, was discharged into lighters placed alongside. During the
time of shallow water, the pile descended as rapidly as the excavation below would
permit it; but when the water was deep, and the weight of the pile and elasticity of com-
pressed air contained in it were nearly in equilibrio, the excavation was carried down 14
inches below the edge of the pile, when it would at once descend through the whole space,
as soon as the pressure was eased off.
Our woodcut ought to have comprised seven cylinders in height, the lowest of which
rested upon hard chalk; the next above was surrounded by soft chalk; and the third from
the bottom by Kentish rag stone, the bed of the river being about the middle of the
fourth cylinder from the top as well as from the bottom.
The cast-iron pile a is 7 feet in diameter; and the adjacent piles, b, b, are pitched on the
bottom of the river, and supposed to be erected to the height to receive the lock cylinder.
c, c, c, c, are cylinders 9 feet in length, added in succession as the pile enters the ground
below the bottom of the river.
d is the the level of the bed of the river.
e, e, e, e, are the flanges through which the cylinders are bolted together, the joints being
made air-tight with cement.
f, the lock cylinder fitted up with apparatus for passing men and materials into and
out of the pile. After the pile was sunk 9 feet, this cylinder was lifted off, and an ordinary
cylinder was then bolted on to the pile, and the lock cylinder again placed on the upper
end of it, leaving it ready for the exclusion of the water by the air pumps.
g, a wrought-iron cover, bolted to the upper flange of the lock cylinder, having an air-
tight joint.
h, h, cages or air locks, two in number, each having an opening 3 feet 4 inches by
2 feet, closed by a door below the cover, and a circular hole at top 2 feet in diameter,
with a flap which when open hangs down inside, and when closed is retained in its place
by the pressure of the condensed air underneath it.
k, l, are the two flaps, the latter represented open, the other shut,
5 Q
1698
[Surr.
THEORY AND PRACTICE OF ENGINEERING.

28
8
#
q
V
f
M
b
Fig. 3148.
30330CVIBUIVYTÍVAAVOLVALETTIENTS MORTUAAAAAAAADA TESUMEUNANUS MUST TAI YUKLE
Ꮽ
Л
2
ย
W
o, the interior windlass, and chain.
q, q, the full and empty buckets.
p, the cranes.
r, r, ladders and their stages pitched alternately right and left.
SUPP.]
CAST-IRON PILES.
1699
s, the interior stage for the working the windlass.
t, t, the beams, with the sheave timbers across at each end.
u, u, cast-iron sheaves, and wrought-iron chains carrying the counter weights.
v, v, apparatus for controlling the counter weights.
w, w, the counter weights.
x, the outside windlass.
z, z, z, the interior leg of the siphon.
b, b, are the adjacent piles.
c, c, the cylinders added in succession.
e, e, the flanges by which they are connected.

f, the lock cylinder.
g, the wrought-iron cover.
h, the cages or air locks.
1, the flap, shut.
m, m, doors.
o, interior windlass.
p, the cranes.
q, the buckets.
r, r, the ladders.
s, the stage.
t, t, the beams.
u, u, cast-iron sheaves.
v, v, apparatus for weights.
w, w, the counterweights.
x, the outside windlass.
z, z, the leg of siphon.
z', the exterior ditto.
1, 1, the atmospheric cocks for the escape of the
compressed air out of the cages, after closing the doors,
when passing the buckets.
2, 2, pressure cocks, for the admission of compressed
air into the cages after closing the flaps for the pur-
pose of passing the buckets to the inside of the pile,
worked by a man on the outside.
3, 3, atmospheric cocks, for the escape of compressed
air, which are worked from the interior.
A
h
A
B
B
m
The cylinder pile, which is being sunk, is shown in plan.
Fig. 3149.

W
པ་
t
D
h
g
18
கு
Fig. 3150.
Fig. 3151.
向
​.O
魚
​B
向
​W
W



D
5 Q 2
1700
[Supp.
THEORY AND PRACTICE OF ENGINEERING.

W
1
t
אי
a
a
O
3
b
Fig. 3152.
4, 4, pressure cocks used for a similar purpose.

5, 5, siphon cock
6, 6, the bucket-ways through the stage s.
7, 7, glass lenses in the flaps of cages.
8, 8, glass lenses in the cover of the lock cylinder.
a, the cylinder pile which is being sunk.
b, b, the adjacent piles, shown in section.
e, e, the flanges, through which the cylinders are bolted.
f, the lock cylinder in elevation.
h, cages or air locks.
t, t, the beams, with sheave timbers across each end.
u, u, cast-iron sheaves and chains, for carrying the counter-
weights.
v, v, apparatus for regulating them.
w, w, the counter weights, for the spare cylinder,6 feet in
diameter, inside the adjacent piles, which is floored at the
bottom, to carry a load of bricks.
x, the outside windlass.
z, outside leg of siphon.
9, air-supply pipe connecting the lock cylinder with the
air pump and fitted with a safety valve inside the former.
10, pipe leading to the pressure gauge.
We have endeavoured to convey an idea of the manner
in which these iron supports were placed in the middle of a
tidal river, and to show the working of the apparatus which
pumped out the water, and introduced the material within
the piles which was required to render hem solid enough to
bear the bridge to be placed upon them. The use of hollow
cylindrical piles has here been improved upon, by making
them serve the purposes of a diving bell, and this at the least
possible cost; wherever iron cylinders had been used on former
occasions, there was considerable difficulty in sinking them to
the depth required. In this instance the labour was abridged,
and the dangers attendant upon it overcome.
h
W
FIG. 3153.
SUPP.
1701
CRANE FOR HOISTING.
Dundee Hurbour.-At Earl Grey's Dock has been erected a crane, capable of lifting as
much as 30 tons, the total weight of which does not exceed 60 tons; and the cost of the
materials and construction was about 20007.
The crane is moved easily; its radius is 35 feet to the centre of the jib sheave, giving a
sweep of 28 feet beyond the face of the wall when using a double purchase, and a foot more
with a single purchase: for the former the chain is hooked up to the eye under the jib,
and the weight suspended from a sheave in the bight.
The jib is of oak, 24 inches in diameter in the largest part, and 21 inches in lesser ;
from the platform the height to the centre of the jib sheave is 34 feet. It is worked by
eight men when 30 tons is required to be lifted; and one man can move it round by
the application of the horizontal gearing.

LEVEL OF QUAY
Fig. 3154.
side elevVATION AND SECTION OF MASONRY.
GUINDELARIO
豚
​Fig, 3155.
BACK BLEVATION
5 Q 3
1702
[SUPP
THEORY AND PRACTICE OF ENGINEERING.
The weights of the cast-iron employed are as follows:-
Footstep
Cylinder
Ring
Washers
Cwt.
47
qrs. lbs.
3 15
303
1
10
30
3 25
5 0 0
$87
0 22
Fixed cast iron
#
Movable cast iron: -
Lower part of post
Cwt.
181
qrs. lbs.
0 14
Top do.
147
0
24
Cheeks
68 0 14
Bottom socket for jib
20
1
19
Top do.
33
1 18
Barrel
13
1 11
Cylinder cover
16
0 13
Various parts
77
3 12
557
2 13
Malleable iron employed in the
Cwt. qrs. lbs.
Masonry
In the crane -
Chain
68
0 9
148 1 10
19
2
0
235
3 19
About 2 cwt. of brass was employed, which added to the above weight of metal amounts
to 1183½ cwt. or thereabouts.

DHE
433
Fig. 3156. PLAN OF GEARING.
Fig. 3157. SIDE Elevation of framing.
Figs. 3154, 3155. show the side transverse and back elevations of the crane.
Fig. 3156. Plan of gearing.
Fig. 3157. Side elevation of framing.
Fig. 3158. Plan of footsteps.
Fig. 3159. Plan of cylinder and crane post, together with the plan of foot of crane
post.
SUPP.]
CRANE FOR HOISTING
1703
回
​Fig. 3159. PLan of cylin))er and crane post.
回
​回
​Fig. 3158. PLAN OF FOOTSTEPS.

回
​O
回
​D
A
10
回
​回
​PLAN OF FOOT of crane post.
2X6
回
​回
​Fig. 3160. Plan of friction rollers.
Fig. 3161. Plan of cylinder cover.
Fig. 3162. Sections of the several parts.
The iron plate worked in at the bottom of the shaft is 6 feet 6 inches in diameter; and
the turning part is 24 feet 8 inches in height from the bottom to the level on which the
gearing is placed. The diameter of the cast-iron cylinder in which the crane turns is
5 feet 3 inches; the cylinder is lined with cast iron, and the crane is placed upon a stone
platform raised 6 feet above the level of the quays.
That portion which moves round is 27 feet in depth, and nearly reaches the bottom of
the dock, working in the cast-iron water-tight cylinder, 5 feet 3 inches in diameter at bot-
tom, and 6 feet 4 inches at the top, where it forms a collar for the friction rollers.
The masonry is secured by sixteen 24-inch round bolts, with four others of the same size
placed diagonally.
The jib stays are well wrought, 24 inches in diameter; and the chain is formed of
iron 14-inch diameter.
The side elevation of the framing stands 11 feet 8 inches in height above the level of
the masonry.


O
C
D4x″
O
O

O
回
​O
Ο
O
ព
#25

J
J
Fig. 3160. PLAN OF FRICTION ROLLERS.
Fig. 3162. SECTIONS OF Parts,
7

ESTAMINASAISE.
5 Q 4
1704
[SUPP.
THEORY AND PRACTICE OF ENGINEERING,

.9%.0%..
B
同
​E
回
​12.
a a
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回
​Fig. 3161. PLAN OF THE Cylinder cover.
The Hydraulic Ram, in-
vented by J. L. Gatchell, in
America, differs somewhat
from those described in a
former part of this work.
Between the air vessel, C,
and the body of the ram, A,
is placed a flexible diaphragm,
H, depressed by a spiral
spring, G, but also capable of
a recoil, thus communicating
the momentum of the water
passing through the body of
the instrument to that which
is contained in the air vessel.
The ram is by this means
made double-acting, as the
water in the air vessel is kept
separate from that which
drives the instrument. This
effect has in some degree been
produced by sliding pistons
and by interposed columns of
air; but the flexible dia-
phragm enables the water to
be lifted into the chamber by
atmospheric pressure, and
also assists tne discharge valve
in its action.

K
D
୯
J
M
B
F
E
L
G
H
A
Fig. 3163. THE HYDRAULIO RAM,
SUPP.]
1705
CONICAL FLOUR MILL.
When the water in the feeding pipe is in motion, its momentum closes the impetus
valve at L, and exerts an influence upon the diaphragm, H; and at the same the spring valve
opens and lets in the water to the air vessel, C, the compressed air at D gradually forces
the water up the rising pipe K. A weight placed over the diaphragm at the moment the
water reacts in the body of the ram, the falling of the diaphragm will produce a vacuum
in the chamber B, admitting a portion of the water up the pipe J, through the valve F, from
By admitting the water from the reservoir
into the diaphragm chamber through the pipe J, it will not require that the weight before
alluded to should be placed on the diaphragm.
a well or reservoir below the level of the ram.
In putting this ram together, screw bolts were avoided, as they were found to corrode ;
the joints are, instead, secured by small keys, which can be drawn by an ordinary hammer.
These rams are of several sizes, some being capable of throwing up 10 gallons per minute.
Conical Flour Mills, invented by Mr. Westrup, have been erected in several parts of the
kingdom, and differ materially from the ordinary method of grinding corn, where the
lower circular stone was fixed, and the upper revolved, the wheat being introduced by an
opening, and ground between the revolving and fixed dressed surfaces. These stones were
about 4 feet 6 inches in diameter,
and weighed about 14 cwt., and
that which revolved made about
120 revolutions in a minute, a
single pair of stones requiring the
power of a 4-horse engine to main-
tain the necessary speed.

The new conical mill has the
upper stone fixed; and that which
runs is beneath and reduced in
weight to 1 cwt. ; the two stones are
made in the form of a frustum of
a cone. E is the upper fixed mill-
stone, and F the upper runner; Gis
the lower top stone, stationary, and
H the lower runner.
Both pairs of stones are mounted
upon the same spindle, and are im-
pelled by the same gearing.
The reduction of the weight of
the running stone from 14 cwt. to
1 cwt., the placing it below, instead
of above, giving it the same number
of revolutions per minute neces-
sarily requires much less power,
In the old mills about 192 lbs.
of flour were delivered per hour;
in the one described the quantity
is asserted to be 462 lbs. per
hour.
The feed pipe, through which the
wheat passes to be ground, is shown
at A, first entering a chamber at B ;
and the quantity to be passed is
regulated by the rod C. At Dis
a chamber over the eye of the stones,
which receives the corn from the
regulator.
Between the upper and lower
mill-stones is placed an upright
wire cylinder with side brushes
acting upon the wires.
L
B
K
D
K
Fig. 3164. CONICAL MILL.
P
I
K
K is a level wheel and driving shaft, which turns the spindle I, upon which the runners
are hung. L is the iron frame in which the entire machine is placed. O is a regulator
for adjusting the upper pair of stones, and P that of the lower.
THE CONWAY AND BRITANNIA TUBULAR BRIDGES.
The Conway and Britannia Tubular Bridges, designed and carried into effect, by Mr.
Robert Stephenson, constitute the most remarkable engineering works of the period, since
the publication of our first edition of the Encyclopædia. The latter bridge is only a mile
1706
[ Sufp.
THEORY AND PRACTICE OF ENGINEERING.
distant from the suspension bridge erected by Mr. Telford in 1820 (described at page
509), and equally deserving of admiration for the boldness of the undertaking and from
the careful manner in which the several portions of the work have been carried out.
This highly talented engineer, tho-
roughly acquainted with the vast re-
sources and various improvements which
had grown out of the thousands of miles
of railway already constructed, called to
his aid the ablest among the practical
men who had tested by experience the
employment of iron in every variety of
construction. With this aid he ventured
to carry out his gigantic project of con-
structing hollow iron beams 470 feet in
length, each weighing 2000 tons, floating
them on rafts through the contracted
channels of the Strait, where the force
of the tide is eight miles per hour, and
from the surface of which they were
to be lifted into their permanent position
100 feet; without the aid also of ex-
perienced contractors as well as of men
of ability and experimental inquiry, it
would have been dangerous to risk the
crossing of the Menai Strait, which sepa-
rates the Isle of Anglesey from Carnarvon.
Models upon a large scale, of various
forms and dimensions, of every variety
of material to be employed, were tested
as to their strength before their ulti-
mate proportions were decided upon.
The machinery for the lifting and con.
struction of the tubes, which were the
characteristic feature of the design, un-
derwent the most diligent observations;
and nothing was done towards carrying
out this stupendous work before all was
satisfactorily inquired into, and the effi-
ciency proved beyond a shadow of
doubt.
The Britannia and Conway bridges
together cost nearly 750,0007.
The Chester and Holyhead Railway
Company, desiring to facilitate the com-
munication between England and Ire-
land, extended their north-western line
through the mountains of North Wales
to the intended Harbour of Refuge at
Holyhead, which, completed, will con-
tain at low water an area of 316 acres.
The distance from Chester to Holy-
head Island is 84 miles; and through-
out, the engineering difficulties that
occurred were most admirably sur-
mounted by Mr. Robert Stephenson.
At the commencement is a tunnel 405
yards in length through the red sand-
stone; a viaduct of forty-five arches lead-
ing to the bridge that crosses the Dee; a
pile and swing bridge which crosses the
river Foryd; a tunnel 530 yards in
length through the limestone of Pen-
maen Rhos. At Conway, 45 miles
from Chester, the river close to the castle
is crossed by the tubular bridge, a
tunnel 90 yards in length; and before
the railway reaches the Snowdon moun-

Fig. 3165. VIEW OF THE CONWAY TUBULAR BRIDGE.
SUPP.]
1707
TUBULAR BRIDGES.
tains there are two others 680 and 220 yards in length, after which it is carried over a
cast-iron girder viaduct. The Ogwen river and valley are crossed by a stone aqueduct
246 yards in length. Three tunnels, 440, 920, and 726 yards in length, through slate,
greenstone, and primary sandstone; a viaduct 132 yards in length, and 57 yards above
the river Cegid, conducts to the last tunnel, 550 yards in length, where the Stanley-sands
embankment leads to the Island of Holyhead.
The Conway Bridge (Fig. 3165.) is situated over the river where it forms the eastern
watershed of the Snowdon mountains. Eight miles above, the river is navigable; and as
it approaches the castle it widens to three quarters of a mile or more; but where the
castle is situated the channel is interrupted by a small island 120 yards from the castle,
on which site Mr. Telford erected an elegant suspension bridge at the time he was
building that over the Menai Strait.
This bridge, commenced in 1847, was so far advanced in March 1848, as to be floated
to its place, and raised to its ultimate destination in the month following, the range of the
tide at Conway being 21 feet. The suspension bridge is 50 feet at the Chester end, and
63 feet at the Conway end, from the tubular bridge erected by Robert Stephenson.
The span of Mr. Telford's suspension bridge is 315 feet; but in consequence of the
shelving suddenly of the rock beneath the castle walls, an abutment could not be ob-
tained for the tubular bridge without making it 400 feet in length, the height above the
water being 18 feet, which corresponds with that of the suspension bridge.
The foundations of the towers on both shores were obtained by cutting the rocks into
steps, wherever it was possible, and forming a platform 2 feet below high water, resting
on piles, where the silt occurred, 4800 cube feet of Memel timber being employed for that
purpose.
The masonry is faced throughout with stone from the Anglesey and Great Orme's
Head quarries, the courses varying in thickness from 18 inches to 3 feet, and the stones in
weight from 5 to 8 tons, the total quantity employed being 161,450 cubic feet.
The external face up to the level of the iron tubes is quarry faced, with the angles
boasted or smooth. Above this level the exterior is of dressed Ashlar, backed throughout
with Runcorn stone, and occasional brick-work. All the beds and joints of the stone are
dressed fair, and set in mortar made of Aberthaw limestone. The Runcorn stone em-
ployed amounted to 191,255 cubic feet.
The walls were backed with Buckley fire-brick set in Roman cement, with its due pro-
portion of sand. (Fig. 3166.)

HIGH
WATER
Fig. 3166. TOWERS OF THE conway bridge.
The contract for the masonry was 38,500%, and this part of the work was completed by
February, 1849; the scaffolding was of the ordinary kind, and the hoisting the material
was effected by travelling cranes.
Construction of the First Tube.After a platform of timber had been erected, 420 feet in
length, and 40 feet in breadth, 21 feet above the tide, upon a convenient part of the beach,
the construction of the tube commenced upon seven longitudinal sleepers, so placed that
the joints of the tube could be easily riveted.
Workshops, with a 20-horse steam engine, were placed alongside the platform; and three
punching and shearing machines, a vertical drill and lathe, a fan blower for the rivet fur-
naces, and a powerful punching machine were all worked by the shafting connected with the
engine. Square wooden tubing conducted from the fan blower blasts for all the furnaces
and forges throughout the work. These works had a crane for unloading the iron plates,
and a riveting machine erected in front of the sheds.
Afrer the wrought-iron plates were sheared to the uniform dimensions, and pro-
1708
THEORY AND PRACTICE OF ENGINEERING.
[Supr.
perly flattened, which, from their thickness being 3 inches, was not very easily accom-
plished; they were marked out for punching by the application of a wooden template,

CORRUGATED IRON ROOFING
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Half Section at End, showing the lifting beams.
Half Section at Centre.
Fig. 3167. CONWAY TUBE.
25′.5"
SUPP.]
1709
CONWAY TUBULAR BRIDGE.
in which the requisite holes were bored; and a stick dipped in whiting, passing through
them, marked the position where the rivet holes were to be punched.
The angle and T-iron were straight-
ened by hammering, and the ends care-
fully forged to obtain good butt joints,
after which they were also marked with a
template for riveting.
The bent T-iron was forged into a
curved shape for the knees, upon a cast-
iron pattern; and the angle iron was
cranked for passing over the covers by the
smiths at the forge.
The punching press was worked by a
crank with a fly-wheel, the plates being
moved by hand, so as to bring the
whitened spots beneath the punch; in
some instances two holes or more were
punched at once through the 2-inch
plates.
The power of this machine may be esti-
mated when it is understood that 46 tons
pressure is required to punch a 1-inch
hole through a plate inch in thickness,
and about 8500 holes may be made in
three days with a good punch; one ma-
chine with a double punch made in one
day, 5670 holes.
After the iron had been thus far pre-
pared, it underwent the operation of plat-
ing, the bars and plates being secured into
their position by cotter pins and bolts,
preparatory to riveting.
The rivets were made of 2-inch iron
rod, which was cut up, in a cold state, into
lengths of 4 inches by a pair of shears.
These were made red hot on the floor
of a reverberatory furnace, and in this
state dropped into a mould, with their tops
protruding 1 inch, which, by the blows
of a heavy hammer, was flattened into a
head; a man and boy in the course of an
hour, by the aid of a machine, making
from 300 to 450 rivets.
These rivets were fixed by several sets
of riveters, a set consisting of two riveters,
one holder up, and two boys; one of the
latter, at the furnace, attended to the heat-
ing of the rivets, and cast them to the
other boy, who with the pincers placed
them, when red hot, into the holes de-
stined for their reception. The holder up
then, with a large hammer, maintained a
pressure behind the rivet, whilst the two
other riveters in front struck it alternately,
and formed the head by the assistance of
a snap of a cup shape held over the rivet,
which being struck gave it the hemisphe-
rical form. This was performed rapidly,
or in the space of half a minute.
The steam riveting machine chiefly
made use of for the Conway tube con-
sisted of a steam cylinder, with a piston
of large diameter, with a 9-inch stroke,
working horizontally.
As the work brought to this machine
weighed several tons, a travelling crane,
moving on rails laid on two stone walls


DIXZ1
12 x 6
12×7
12x6
12X8
12X7
BX21
12X8
4.6
E
宅
​TIL
Fig. 3168. PONTOONS.

1710
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
for the purpose, gave a parallel motion in a vertical direction to the masses of iron to be
riveted.
The steam employed was at a pressure of 40 pounds per inch; consequently a pressure of
32 tons was exerted upon the rivet. Plates riveted in long strips by this machine were finally
united in their places by hand-riveting.
By August 1847 the tube was far advanced, and in the following January completed.
It was 424 feet in length, allowing at each end a 12-foot bearing on the tower. At the
bottom it had a camber of 6.49 inches in the centre.
The six Pontoons (fig. 3168. p. 1709).— Each contained 5461 cubic feet of timber, and
6 tons 4 cwt. of iron, and cost about 15007.
The length was 98 feet, breadth 25 feet, and depth 8 feet. The sides were perpen-
dicular, with their ends sloped. They were formed of 4-inch deal, upon four longitu-
dinal braced timbers, held by iron ties, and provided with pumps and brass valves to
admit water when required to be sunk to accommodate the loading or unloading.
As the tide rose and fell, the valves at the bottom were left open, so that they were
entirely under command, and could be made to bear up the tube, or be released from it, at
pleasure, by alternately filling and emptying the pontoons. When the tube was laid upon
the pontoons, struts were placed within it, to prevent any change taking place in its
form.
The floating the Conway tube was commenced on the 6th of March 1848; after it had
been placed upon the pontoons, it was with some difficulty moored into its position by
the 11th, the weather proving unfavourable.
On the 8th of April the raising of the tube commenced; and the rate of lifting was
about 2 inches per minute; a 6-feet stroke occupied 34 minutes, the engine making
60 strokes per minute. By the 10th the tube was raised 6 feet; the packing underneath
was effected by timber struts. On the following day it was raised, and suspended from
the clams attached to the presses 3 feet above the level destined for its ultimate position,
when the end pieces, with the bed plates under them, were finally arranged.
On the 16th the tube was lowered and properly secured on its permanant bed; by the
18th the rails were placed throughout its entire length, and the engineer was enabled to
pass through with the first locomotive.
The second tube was floated afterwards, and finally lowered to its bed by the 2nd
January 1849, and the two tubes, secured upon their permanent beds, were painted with
stone colour, having previously had two coats of red lead as the work was put together,
the joints being all carefully fitted with red and white lead; the tops of the tubes were
covered with corrugated galvanised iron plates.

T
P
T
ច
T
D
·

T
T
P
Fig. 3169. STeam ExGINE
SUPP.1
1711
CONWAY TUBULAR BRIDGE.
To float these tubes, it was necessary to make use of two heavy chain cables, which were
attached to moorings near the suspension bridge, and made tight at the other end by
strong crabs.
These cables were passed over the decks of the two outer pontoons, through
hawse pipes in the timber of the boats, in each of which were crabs worked by twenty-
four men.
A capstan, fixed beneath the first tube near the castle, and another near the Chester
point, each worked by fifty men, constituted the moving power employed upon the transit
of the second tube. These two capstans were each 3 feet in diameter; and the ropes
were 10-inch white Manilla hemp, untarred. Other cables were employed as guides to
this difficult operation, and for the purpose of securing the pontoons in their positions.
The tide on the occasion of raising the first tube rose 17 feet, the level at which the
permanent rail was fixed being 21 feet 6 inches. To hasten the placing of the tube on
its bed as the tide was running out, the valves of the pontoons were opened, and 18 inches
of water admitted, so that in about 20 minutes the operation was completed, and the pon-
toons, being freed from their burtben, were allowed to drift from beneath it, and were then
towed away.
The Cost of the Conway Bridge:
-
Cast iron
Wrought iron
Hydraulic presses
Chains
Proportion of experiments
Construction, floating, and raising
Masonry
Total
-
F
S. d.
6,887 19 3
28,239 18 3
983 0 0
203 0 6
1,306 0 0
69.071 0 0
106,690 18 0
- 38,500 0 0
£145,190 18 0

Steam Engine employed to work the Hydraulic
Presses. It was at first intended to work force pumps
by hand in the interior of the tube, for the purpose of
raising it; but it was afterwards found more economical
to apply steam.
The steam cylinder, C, rested on an horizontal frame
of cast iron, secured on wooden framing.
The two pumps were worked by the direct action of
the piston of the steam cylinder, which passed through
stuffing boxes at each end of the cylinder.
The two fly-wheels were put in motion by a cross beam
on the piston rod.
The engine and boiler were placed with the presses on
the lower level.
The steam cylinder was 17 inches in diameter, or
227 inches in area, and the length of the stroke 16 inches.
The piston of the force pump was 1 inch in diameter,
and the length of its stroke 16 inches, 36 124 cylindrical
inches of water being required for each stroke.
As
Hydraulic Press for raising the Tubes at Conway.
we have, at page 1026, given an idea of this machine, it is
not necessary to repeat it; we here see it worked by steam,
and an enormous weight lifted to a considerable height.
By this simple power the tubes were raised from the
level of the water to their permanent position.
Had this been performed by a simple lever, it would
have been requisite for one arm to have been 448,000
times longer than the other; to enable the force of
1 pound to raise the weight 100 feet, it would have been
necessary to continue that pressure through a space of
83,522 miles. H (fig. 3170.), cross head; P A', are
iron beams, supported in the masonry of the piers to re-
ceive the press, which was placed in the cast-iron jacket
J, bedded on a sheet of lead.
رح
M
K
H
R
X
J
K
P
P
Fig. 3170. HYDRAULIC PRESS.
Y
The power used to elevate the tubes was the pressure
of steam on the piston of the steam engine, which at every 16-inch stroke raised the
cross head, H (fig. 3174.), parts of an inch; the pressure of 1 pound on the steam
piston through any space is represented in the cross head by a pressure of 2 cwt. through
1712
[ SUPP.
THEORY AND PRACTICE OF ENGINEERing.

P
P
K
K
J
K
Fig. 3171.
SECTION AT X Y OF FIG. 3170.
Cross Head.
:8-
H
9'. 1ő
K
3.8-
P
P
Fig. 3172. H, the cross HEAD OF FIG. 3174.
Fig. 3173. Vertical section AT E F
of Fig. 3175.
a proportionably less space; a continued pressure of of a ton, therefore, was sufficient
to elevate the 2000 tons.
In the hydrostatic press, where air instead of water is used, to obtain the necessary
power considerable attention is required to make the lid or piston air-tight; in the
hydraulic press there is the same necessity of attention to make them water-tight.
The cast-iron jackets were made of great strength, to resist the pressure; the piston
rods worked in packing round the ram of the hydraulic press, which was effected by a
curved leather collar, maintained in close contact, both with the ram and the cylinder,
by the pressure of the water in the inside of the curve.
The internal diameter of the press was 20 inches; that of the ram 18 inches; the ex-
ternal diameter of the press 3 feet 1½ inch; the thickness of the metal 83 inches.
The water was forced into the cylinder through the aperture shown near the top at T,
by a wrought-iron supply pipe, nearly half an inch in diameter, and a quarter of an
inch in thickness.
The ram was guided vertically by two wrought-iron 6-inch guide rods, fitted into a
socket at the top of the press, and keyed above into a cast-iron girder built into the
masonry.
The lifting-chains were bored and slotted with great attention; each link alternately
consisted of eight and nine plates, was in length 6 feet from centre to centre of the pin-
holes.
The thickness of these plates was 11 inch, and that of the nine plates 1 inch, their
width being 7 inches.
The sectional area of the eight-plates was 70 inches, and that of the nine-plates 69
square inches.
The weight of the eight-plate link 16 cwt. 2 qrs. 16 lbs., that of the nine-plate link
16 cwt. 2 qrs. 6 lbs.
The area of the four chains was 276 square inches.
There were two sorts of clams: that placed on the cross head rose with it and lifted
the chain and tube: that on the under side was fixed to the cast-iron girders which sup-
ported the press, and was used for securing the chain at the end of each lift while the press
was lowered and the upper set of links removed.
The wrought-iron clamping cheeks were so slotted as to closely fit beneath the slotted
shoulder in the head of each link; these were withdrawn or closed by right and left-
handed screws, by turning of which the cheeks were brought into close contact with
the chain.
The Britannia Bridge, as we learn from an inscription on the frieze of the abutment
towers, was "Erected Anno Domini MDCCCL., Robert Stephenson, Engineer;" and
SUFP.]
1713
CONWAY TUBULAR BRIDGE.
it is remarkable that only a mile from the suspension bridge has this work been executed,
which rivals that daring undertaking by Mr. Telford in 1820. The Menai Strait has
Top of Girder Plan.

O
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A
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R
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X
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P
P
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Fig. 3174. FRONT ÉLEVATION.
P, iron additional girder, with half-inch deal plank between.
A¹, large girders, of 12 tons weight each.
J
E
C
K
H
K
K
1
Fig. 3175. SEction at a B.
Y
B

5 R
1714
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
been crossed by the two novelties of engineering boldness, which are the boast of the
present century. The Island of Anglesey has been united to the main-land by iron con-
structions of the most novel character, differing in
great principles one from the other, and both calling
forth a knowledge of the tensile qualities of the
metal employed.
The Island of Anglesey (Fig. 3176.) has between
it and the mainland a channel which runs from
Carnarvon Bay to that of Beaumaris, its direction
being from south west to north-west, its length be-
tween 11 and 12 miles, the width of its tortuous water
way varying from 1000 feet to three quarters of a
mile.
The tides of this rocky and dangerous strait are
peculiar, as they advance up the Irish Sea, branch
off over the sandbanks of the bay at Carnarvon, and
reach the Beaumaris Bay some time before the main
tidal wave has passed round the Island of Anglesey.
Immediately the tidal wave reaches Beaumaris
Bay, the current that has set in from Carnarvon is
opposed, and the tide flows in opposite directions into
the strait. This conflict of the two forces occasions
it to be high water at the site of the Britannia
Bridge at least 20 minutes before the proper high
water arrives, and the tide continues to flow 20
minutes after the current is changed; and this current
in both directions resembles the rapids of a river,
and runs at the rate of 8 miles an hour.
The Britannia tubular bridge crosses the Menai
Strait where it is contracted by the rock desig-
nated the Britannia, dividing it by two equal
water ways.
The Carnarvon shore is steep; and it also rapidly
rises on the Anglesey coast. In the middle of the
strait, the rocks rise about 11 feet above the level of
low water; these rocks, in length 350 feet, and
120 in breadth, are formed of chlorite schist. On
the Carnarvon side the depth of high water is 47 feet,
and in the Anglesey Channel 56 feet.
The masonry employed for the construction is
composed of various stone its general surface is
left with a rough or quarry face, the angles are alone
dressed smooth. The external walls are faced with
Anglesey limestone; and the internal work is Run-
corn sandstone and brickwork.
The Britannia tower was based upon the rock,
after steps had been formed by blasting it into pro-
per beds. Two rectangular walls 10 feet 6 inches in
thickness, placed in the direction of the tubes, are
made to batter regularly until they reach the bottom
of the tubes, where they are only 8 feet in thickness.
The internal wall is 8 feet 4 inches in thickness
throughout. Those walls which are at right angles
with the tubes are 6 feet in thickness from the top
to the foundations.
IN3W10BY
NOA
This tower is 221 feet 3 inches in height, and
batters 1 in 36 on each of its sides, its base being
in length 60 feet, and in width 50 feet 5 inches; the
plinth rises 25 feet 6 inches above the foundations,
the top being 8 feet above the level of the highest
tides. To give additional security to this tower,
the lower portions or recesses are filled with rubble
masonry as high as the top of the plinth.
Immediately under the tube, wall boxes of cast-
iron were built into the masonry, beneath the string
course, for the purpose of inserting the cast-iron
beams that now support the tubes, and to strengthen
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Fig. 3176.
SITE OF THE BRITANNIA TUBULAR BRIDGE.


the angles of support. Cast-iron beams 15 feet in length were introduced into the masonry.
SUPT.]
1715
BRITANNIA TUBULAR BRIDGE.
*
458-1
HDIH
LOW
WATER
Fig. 3177. PIERS OF THE BRITANNIA TUBULAR ERIDGE.
WATER
One hundred and fifty-one thousand one hundred and fifty-eight cubic feet of Anglesey
limestone, 127,000 cubic feet of Runcorn sandstone, and 68,411 cubic feet of brickwork, al-
together weighing 24,700 tons, were employed for its construction. Including the bed
plates of iron, 479 tons of cast-iron were employed

5 B 2
1716
| Supp
THEORY AND PRACTICE OF ENGINEERING.
C..
E
BRITANNIA Town.

.H
A..
B
.D
.-15.4..
15.4
RUBBLE
IN MORTARS
RUBBLE
IN MORTAR
k7-6
25'.
97.0"
221.3″.
30
Fig. 3178. END ELEVATION.
Fig. 3179. TRANSVERSE SECTION.
The Scaffolding was composed of timber varying from 12 to 16 inches square, and from
40 to 60 feet in length; these were connected by iron bolts with butt bearings; and the
scaffolding required for the masonry contained 175,000 cubic feet.
The platform upon which the large tubes were constructed required 110,105 cubical
feet, and for the construction of the land tubes 118,230 cubic feet.
Feet. In.
Spans :
From the Carnarvon abutment to the first pier
Pier
230 0
32 0
Pier
Span to Britannia Pier
Span of third opening
458 8
45 3
459
3
Pier
To the Anglesey abutment
Clear between abutments
Length of Carnarvon abutment
Anglesey
do.
Total length
32 O
230
O
1487 2
172 8
172 10
1832
345 6
8
Surr 1
1717
BRITANNIA TUBULAR BRIDGE.

HIND. FREMTIES
ДИЛИМИН
WW
Fig. 3180.
The bottom of the tube is 103 feet 9 inches above average high water of spring
tides.
The side and abutment towers were also based upon the rock; and their construction
was similar to that of the tower, their height being 177 feet 6 inches above the plinth.
5R3
1718
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
_INSIDE_➡
The side towers are 62 feet in length by 39 feet in breadth, or, above the plinth, 60 feet
by 37 feet; at the level of the tubes the battering of the faces of the masonry reduces their
dimensions to 59 feet 6 inches by 36 feet 6 inches. The height of the campaniles above
the top of the tubes is 53 feet, which was necessary for the placing of the presses used for
lifting the tubes.
Each tower contains 120,000 cubic feet of limestone, 100,000 cubic feet of sandstone,
35,000 cubic feet of brickwork, and 382 tons of cast-iron; the whole weight of each
tower is therefore 18,000 tons. The plan of the two abutments is similar; and the height of
that on the Carnarvon side is 88 feet, and of that on the Anglesey side 143 feet; the face
walls are in thickness 10 feet 6 inches, and batter from the foundations to the under side of
the tubes, where their thickness agrees with the other walls.
A longitudinal wall of arches with 22-feet openings, is carried up in the middle of the
abutment, from which springs waggon-headed vaults, resting on the two external walls.
Upon these vaults brick arches are built transversely for the support of the permanent
way. Over the tubes are placed lintels of a single stone 20 feet in length; 80,792 cubic
feet of limestone, 59,896 cubic feet of sandstone, 30,931 cubic feet of brickwork, and 12,837
cubic feet of rubble, were employed in the Carnarvon abutment; besides, 3569 cubic feet of
Penmaen limestone, of which the two lions were formed, were used for the Carnarvon abut-
ment, the whole weight of which was 13,425 tons.
The Anglesey abutment contained 145,906 cubic feet of limestone, 148,998 cubic feet of
sandstone, 126,982 cubic feet of brick-work, 35,177 cubic feet of rubble, besides 3569 cubic


14.10.
OUTSIDEj……25, 62
19′0″ CLEAB. WIDTH--
i 15´O FROM OUT TO QUI
O
O
281.0
Fig. 3181.
SLEEPERS
II
TRANSVERSE SECTION THROUGH THE
MIDDLE OF THE TUBE.
feet of limestone for the two lions, alto-
gether constituting a weight of 31,084 tons.
The masonry of the Britannia bridge, in
Sept. 1848, had so far advanced that it was
in a state to receive the tubes. The vessels
employed for the transport of material dis-
charged upwards of 2000 cargoes: to raise
it, three steam engines and twenty six tra-
velling cranes were made use of.
The Tubes were so constructed as to be-
come beams of 1511 feet in length, sup -
ported at each extremity as well as at three
intermediate points. The weight of one
of these continuous tubes, of wrought and
TOP LEVEL OF
RAILS
cast iron, together with that of the perma- Fig. 3182. TRANSVERSE SECTion of a PART OF THE
nent way,
is 5270 tons.
TUBE, SHOWING ONE Side or its CONSTRUCTION.
SUPP.]
1719
BRITANNIA TUBULAR BRIDGE.
Where the tubes pass through the towers, cast iron is employed.
The side towers are 230 feet from the abutments, and from them on either side to the
Britannia Tower 463 feet, making 1380 feet clear openings, the remainder of the tube,
or 131 feet, having a bearing upon the solid masonry.
The tubes were made in four lengths, the two land portions being formed on timber
platforms; and the two main lengths were put together on the beach, and afterwards
floated on eight pontoons to their destination, where they were raised by hydraulic presses
placed upon the tops of the towers,
The two tubes, as completed, together contain 9360 tons of wrought iron, 1015 tons of
cast iron, and 160 tons of permanent way: they are formed of 186,000 pieces of iron,
pierced by 7,000,000 of holes, and united by 2.000,000 of rivets; they contain 435,700 feet
run of angle iron, the total weight being 10,540 tons.
Consequently, the weight of the iron work of the Britannia Bridge is about 74 tons per
foot run.
Comparing it with the quantity of iron used by Mr. Telford for his suspen-
sion bridge across the Menai Strait, where the span was 570 feet between the towers, we find
3.8359 tons per foot run (see page 517). In the Southwark iron bridge (see page 498) the
width of the river between the abutments is 708 feet, and the total quantity of iron em-
ployed was 7·887 tons for each foot run.
The Southwark Bridge and the Britannia tube Bridge have in them nearly the same
weight of iron per foot run, and the suspension bridge not more than half the quantity per
foot run that was used in either of them. The width of the soffite of the former is 43 feet
4 inches; the Telford suspension bridge, although more economical in its use of material,
probably shows as much hardiesse as can be discovered in iron structures, although there
remains for us a comparison with a suspension bridge erected in America.
The sides of the tubes may be regarded as a continued trellis, with vertical pillars con-
necting the top and bottom cells of plates. The side plates are two feet in breadth, and
vary in length from 6 feet 6 inches to 8 feet 8 inches; the rows in which they are placed
consist alternately of three short and four long plates, with a longer or shorter plate at the
top.
The thickness of these plates in the centre are half an inch, increasing towards the ends,

Fig. 3183.

Fig. 3184
Fig. 3185,

CH STRIP
..3 ½
Fig. 3187.
6 ½
Fig. 3188.
Fig. 3186.
Fig. 3189.
5 R 4
1720
[SUPP.
THEORY AND PRACTICE OF ENGINEERING.
0
where the whole weight of the tubes is supported; their increase being to eight, nine, and
ten sixteenths.
The sides are connected with the top and bottom cells by stout angle irons, riveted at
every 3 inches, the rivets passing through the plates and covers of the platforms, as well
as through the angle irons of the bottom cells; here the rivets traverse six layers of iron,
and are 3 inches in length, and 13 in diameter.

CINE
Fig. 3190.
Q
O
•
O
a
C
•
•
a
O
"
SUPP.]
1721
BRITANNIA TUBULAR BRIDGE.
The top cells are connected with the sides more simply, the T-iron pillars being cranked
over the angle irons, and then riveted together.
The vertical pillars, or ribs, consist of two sheets of iron plate, varying in thickness from
an inch to inch; these are considerably stiffened by angle and T-irons and gussets.
The weight of the sides of one


-
- 938 in
line of tubes is 1727 tons,
plates, 607 in angle irons, 113 in
rivets, and 68 tons of covering
plates.
IRON
RAIL

TIMBER SLEEPER
Fig. 3191.
Where the two platforms at the
bottom of the tube are united with
the vertical plates, great care was
taken to rivet them well together,
breaking the joints in such a man-
ner that they never occurred with Fig. 3192.
those of the horizonal plates.
The plates which cover the joints
are 2 feet 3 inches in length, but
vary in their breadth : those within
the cells, on the upper side of the
platform and on the under side of
the cell, are 2 feet 4 inches in
width, the edges being cranked
over the angle iron placed on each
side, the rivets passing through the
whole.
The cells throughout the tubes
are all strengthened by angle irons,
which unite the plates more firmly
together.
The side plates, 2 feet in width
and 10ths of an inch in thickness,
with their edges butted against each
other, and additionally secured by
the T vertical pieces placed against
each face, are shown in the cut
(fig. 3190). The pillars, which are
in height from 19 to 26 feet, and
which occur every 2 feet, are fur-
ther strengthened by short lengths
of angle iron riveted over the
joints.
On the outside of the tube, the
T iron is cranked over the angle
iron which unites the sides to the
top and bottom, the ends butting
upon the floor plates; but on the
inside the T iron is curved round
to make a right angle, and is con-
tinued horizontally across the tube,
on the floor 32 inches, and at the
top 42 inches, both securely riveted.
The angle is filled with triangular
gusset plates riveted on both sides
of the rib.
88
SLEEPER
15′ 0″
HORIZONTAL SECTION TO SHOW THE BOTTOM OF THE
..1..6...
"
RAIL
TUBE.

ด
.0.
LONGITUDINAL JOIST OR SLEEPER
-3...g.
SLEEPER
Fig. 3193. LONGITUDINAL SECTION SHOWING THE BOTTOM OF
THE TUBE.
1722
[SUPP
THEORY AND PRACTICE OF ENGINEERING.
The top and bottom of the tube are each formed of square cells at the top are eight,
each 1 foot 9 inches in height and breadth; at the bottom there are six cells, 2 feet 4 inches
in width and 1 foot 9 inches in height, these cells all being large enough for the work-
men to enter.
The sides are plain sheets of plate iron, stiffened by vertical pillars of T iron within and
without, and further strengthened by corner pieces of the same metal.
The bottom of the tube is composed of two platforms of plates connected by seven vertical
plates.
The upper and lower platforms of plates are arranged in six parallel rows, the four inner
rows being each 2 feet 4 inches in width.
The outer rows are 4 inches more in width, for the purpose of better attaching them to
the sides.
All the plates are 12 feet in length.
The vertical plates are also 12 feet in length, and 21 inches in height. Their thickness
varies from ths to ths of an inch.

Fig. 3194.
The longitudinal bottom plates are lapped over by those above them 6 feet, so that
the joint is over the middle of the plate beneath. Over the joint a short plate is riveted,
the rivets passing through the three plates. The six rows of double plates thus longitu-
dinally connected, are arranged side by side, to allow the joint of each to be 3 feet in
advance of the three neighbouring layers.
The bottom of the tube forms a chain of 31 plates united by 21 angle irons: the floor
plates are 12 feet in length, 2 feet 4 inches and 2 feet 8 inches in breadth, varying in
thickness from ths to ths of an inch.
The vertical plates are the same length, 21 inches in depth, and vary in thickness from
ths to 18ths of an inch.
The angle iron is of the same dimensions throughout the tubes, having a sectional area
of 2.7 superficial inches, weighing about 9 pounds per lineal foot.
The weight of wrought iron in the bottom of one entire line of tube is 1472 tons,
965 tons of which are in plates, and 217 tons in angle iron, 237 in covers for the joints.
The Permanent Way is continued through the tubes upon transverse bearers placed
6 feet apart; the longitudinal timbers are 14 inches by 7 inches.
The bridge rail has been preferred which at bottom is in width 7 inches and at top
23 inches, its total height being 34 inches; these rails are secured to the sleepers by fang
bolts passing through them.
Single Hydraulic Press, used on the land towers of the Britannia tube, was of unusual
dimensions, the internal diameter being 1 foot 10 inches, the diameter of the ram 20 inches,
the cylinder 6 inches in thickness, the length externally 9 feet 1 inch, the length of
stroke 6 feet.
The weight of the press, 13 tons 16 cwt.
The area of this press was 314 16 inches, and its capacity, with a six-feet stroke,
22,169.5 cubic inches; the quantity of water employed for a lift was 81.57 gallons, or
815.7 lbs.
The pressure of 3 tons per circular inch, equal to 3.819 tons per square inch, would be
SUPP.J
1723
BRITANNIA TUBULAR BRIDGE.

sufficient to raise a column of water 5.41
miles in height. The ratio of the area of
the pump to that of the cylinder was 1 to
354.
The hydraulic press is therefore a most
powerful machine, and useful where great
pressure is required, and of infinite use
in the lifting of heavy weights, the steady
character of its action making it applicable
to such purposes.
Floating the First Tube.-The distance it
had to float was 1600 feet; and four cap-
stans erected on platforms on the beach,
were worked by eleven superintendents,
under whom were placed 450 labourers, 65
sailors, and 12 carpenters.
Each capstan was worked by 48 men;
in each set of the pontoons 105 men were
employed; and in addition six boats with
their crews accompanied the floating tube.
The butt end of the tube, after much
difficulty, was brought to its position under
the Anglesey tower, on which, as upon a
centre, the tube was to be moved round
into its position across the opening.
The Britannia end was then drawn round
into the recess of the masonry; and after it
was securely placed at both ends on the
temporary beds prepared to receive it, the
rafts which transported it were removed,
and the pontoons were liberated from be-
neath.
The raising the tube to its permanent bed
followed as soon as the machinery could be
adapted. This consisted of the two presses
used at Conway, which were placed in the
Britannia tower, and one new single press
in the Anglesey tower.
The chains were raised in separate por-
tions by capstans and suspended from the
cross-heads.
On the 11th of July, the Britannia end
was raised 6 feet with the double press,
and the under-pinning proceeded as the
tube was elevated. which was performed
by building up brickwork in cement in the
space between the buttresses, left for the
mounting of the tube.
о
∙1.3".
о
Fig. 3195. FORCE PUMP.

Fig. 3196. SECTION OF THE VALVE POx.
Some accident occurring to the ram, it
was not until the 1st of October that the lifting of the tube was again undertaken, when
it was raised 6 feet daily. On the 6th it was 58 feet high; and by the 13th the tube was
in its ultimate position It was then raised 18 inches above the upper bed plate, and
secured by packings beneath the cross head, and also upon the cast-iron beams inserted
through the wall boxes.
The bed plates were then moved forward into their position beneath the tube, and the
whole finally secured.
About a fortnight afterwards, the presses were lowered and again raised by capstans,
with an 8-inch rope, for the purpose of raising the second tube, which was ready to be
floated by the 2nd of December, 650 men being this time employed; twelve days after the
floating, the raising the tube was commenced; and by the 7th of January 1850 it had, by
regularly lifting 6 feet per day, attained its final elevation.
The uniting the ends of the tubes followed. This was completed by the 6th of February;
and by Tuesday, the 5th of March, the engineer and a large party, in a train of 945 feet
in length, consisting of three engines, 45 coal waggons, and carriages containing 700 per-
sons, weighing altogether 700 tons, passed through the tube to Holyhead.
The third tube was floated 10th of June 1850, and the fourth on July 25th, soon after
which the Britannia Bridge received its completion.
:
1724
1
THEORY AND PRACTICE OF ENGINEERING.
D.
H
о
Fig. 3197. Cross head, section at D E, FIG. 3198.
F
H
RAM
-1.10%
H
Fig. 3198. SEction at F &, FIG. 3200.
i.......3'
-3′0
Ꭻ
C
·3'.11" 2-
5'. 4"
RAM
∙1.10
E
N° 2
N: 3
Fig. 3199. CYLINDERS BY Which the raising was completed.
- 1 A - - 1 1 1 1
12.10
5′.2″.
Fig. 3200.
PLAN OF TOP.
G
[SUPP




Thus the first stone of the Britannia tower was laid September 21st, 1846; the Carnar-
von and Anglesey towers completed February 22nd, 1849; the first tube floated June
20th, 1849, the second deposited in its bed February 7th, 1850; the third floated July
11th, and the last tube floated 25th July.
Mr. Edwin Clark, the resident engineer whilst these works were in the course of execu-
tion, has given to the world an admirable account of the progress made in the construction of
the Britannia and Conway tubular bridges, accompanied with folio plates of the highest
value; and to these the writer must refer those readers who are desirous of becoming
SUPP.]
1725
BRITANNIA TUBULAR BRIDGE.

J
J
acquainted with the minutest details of construc-
tion and the principles which influenced the designs
of Mr. Robert Stephenson, so masterly carried
out.
The Cost of the Britannia Bridge :
Carnarvon wing walls, pedestals,
£
&c.
tower
Britannia tower
17,459
28,626
·
38,671
Fig. 3201. PLlan of casing.
Anglesey tower
Anglesey wing walls, pedestals,
&c.
31,430

·
40,470
Lions
2,048
158,704
Wrought iron used in tubes
Cast iron in tubes and towers
Construction of tubes
118,946
30,619
-
226,234
Pontoons, ropes,
capstans,
painting materials
-
28,096
Raising machinery -
9,728
Carpentry and labour, floating,
raising, &c.
25.498
Experiments, proportiona. part
3,986
Total
443,161
£601,865
Ꮣ .
Fig. 3202. SECTION at L M, of fig 3199.
H
3. 1½
IRON, having received so many improvements in
its manufacture. is now employed very generally
in Naval construction: the Crystal Palace and
the gigantic tubular bridges are almost eclipsed
by what has been effected in ship building, by the
Messrs. Napier on the Clyde. The Cunard
Company's ship "Persia ", which has lately made
its trial trip, is in length, from the figure head to
the taffrail, 390 feet, and its length on the water
360 feet; breadth of the hull, 45 feet; breadth over
all, 71 feet; depth, 32 feet; tonnage, 3600 tons, with
paddle wheels 40 feet in diameter and steam power,
equal to 1200 horses, though she is expected to
work up to the pitch of 4000 horse power.
This mighty vessel is composed of innumer-
able pieces of metal, welded, jointed, and riveted
together, and secured to powerful ribs of iron, ten
inches deep, and placed at that distance apart.
The plates on the outside are laid alternately over
each other, so that one adds strength to the other.
The keel plates are ths of an inch in thickness; the bottom plates of the ship are ths
of an inch in thickness; and above to the level of the load water line, ths of an inch,
above this line ths of an inch; and the plates around the gunwale 7ths of an inch.

Fig. 3203. END VIEW.
The weight of iron in the "Persia," when launched, was 2200 tons; with the engines
and a full load, she will be equal to 5400 tons, and will draw 23 feet of water. In her
trial trip, she ran 175 knots or 203 miles in 10 hours and 43 minutes, or 19 miles per
hour.
The total weight of iron employed in the Britannia Bridge for the two tubes, was
10,540 tons, or nearly five times as much as was used for the construction of the “Persia,”
which in length and breadth nearly equals the dimensions of one of our cathedrals, which it
also greatly resembles in plan, taking the position of the paddle-wheels for that of transepts.
The Niagara Suspension Railway Bridge, lately erected by Mr. John A. Roebling,
Civil Engineer to the Niagara Falls Suspension and International Bridge Companies in
America, is a work which does honour to the present age. From a report made by the
engineer in May 1855, its span is 821 feet 4 inches from centre to centre of the towers; it
forms a slightly curved hollow beam or box of a depth of 18 feet, width at bottom of 24 feet,
and at the top of 25 feet, the lower floor of which is used for common traffic, whilst the
upper is devoted to the railway. The two floors are connected by two trusses of simple
construction, so arranged that their resisting action operates both ways, up as well as
1726
[SUPP
THEORY AND PRACTICE OF ENGINEERING.
down. The suspenders are 5 feet apart. The beams of the upper and lower floor are
connected by posts arranged in pairs, leaving a space between for the admission of truss
rods. The ends of the posts are secured between the beams, in a manner that no part is
weakened, and that any amount of strain can be thrown upon them without injuring or
loosening their connections. There are no joints to work loose; and if the timber should
shrink, the truss rods simply require tightening. The depressing action of any loads is
by these posts transmitted from one floor to the other.
From the end of each pair of posts a truss rod extends each way to the fourth pair of
posts, at an angle of 45 degrees. The rods therefore cross each other, and form a diamond
figure; they are 1 inch in diameter, with screw ends of an inch and an eighth; by these
rods the pressure upon any pair of posts is'spread 40 feet apart. All the nuts work on cast-
iron plates placed above or below the posts.
Without adding much to the weight of the structure, a considerable degree of
stiffness has been obtained by this simple construction. The pressure of an engine and
whole train of cars is so much distributed that the depression caused by a light freight
or ordinary passenger train is scarcely perceptible A freight train of twelve loaded cars,
with a 25-tons engine, covers about half the length of the floor; and its effect is
more noticeable than either a smaller or larger train. When in the centre, the camber is a
little flattened; but when near the towers, where the grade forms nearly a straight line, the
depression is from 3 to 4 inches. A longer train, of greater weight in proportion, disturbs
the equilibrium less, as it covers a greater extent. Passenger trains of fifteen long cars,
which frequently cross the bridge, make so little impression that the eye can scarcely
detect it.
The height of the railway track above the middle stage of the river, is 245 feet.
The tubular or box form of the bridge adds much to its stiffness, vertically as well as
horizontally, there being an entire freedom from all lateral motion during the passage of
a train; and half a dozen heavy teams on the lower floor produce a more perceptible hori.
zontal motion, and a much greater jar and trembling than is caused by a train of cars
moving at the stipulated speed of five miles an hour, the smoothness, evenness, and per-
fectly level condition of the railroad tracks contributing to that effect. While teams on the
lower floor move forward outside the centre of the bridge, the trains are exactly poised
in the centre.
The horizontal stability is maintained by the lateral bracing of the upper cables, which
are suspended with a considerable inclination. Stays above and below the floors add to
the stiffness; these, as well as the suspenders, are made of wire rope manufactured at the
engineer's works at Trenton, N. J.
There are above the floors sixty-four diagonal stays of 18 inch diameter, equally distri-
buted among the four cables. These are fastened to the suspenders by small wrappings,
so as to form straight lines.
Each of these stays represents the hypothenuse of a rectangular triangle, of which the
two cadets are formed by the towers and the floors. These being solid and rigid in the
direction of the lines they represent, by preserving the straight lines of the stays, and not
allowing them to sag or deflect, as many triangles are formed as there are stays.
The triangle, preserving its form, maintains these stays by tension, and not only stiffens
them, but adds much to the strength of the cables.
The friction of the cables in the saddles is about equal to 166 tons, one third of the pres-
sure, which upon each tower is estimated at 500 tons.
The ordinary tension of each stay is 4 tons; the united horizontal force of sixteen stavs
upon the two saddles is about 56 tons, to which a resistance of 166 tons is opposed, with-
out taking into account the curvature of the cables in the saddles, which nearly doubles it.
To the underside of the lower floor fifty-six stays are attached, which are anchored in
the rocks below, and prevent either vertical or horizontal motion, and preserve an equili-
brium at the tiine the trains are passing over the bridge; their usual tension is about 2 or
3 tons; their aggregate force, exerted upon the lower floor in a vertical direction, is less
than 100 tons.
The Anchorage was commenced in September 1852, and was formed by sinking eight
shafts into the solid limestone rock. Those on the New York side are 25 feet in depth; the
fourth, on the south-east, is 18 feet; all the others on both sides the river were sunk to an
equal depth of 54 feet below the railroad track.
The surface of the rock on the Canada side being 10 feet higher than on the New York
side, the depth of the shafts was increased that much, and the height of the masonry above
reduced in proportion.
Each shaft is 3 feet by 7 feet, which is enlarged at the bottom to a chamber 8 feet
square.
The Anchor chains are composed of nine links, which are all 7 feet in length except the
uppermost, which is 10 feet in length. The first or lower link is composed of seven bars,
7 inches by 1 inch, and is secured to a cast-iron anchor plate, by a pin 3 inches
SUPP.J
1727
THE NIAGARA SUSPENSION BRIDGE.
in diameter ground upon its seat.
and two half bars on the outside.
From the fourth link on, the chain
perficial inches.
The next link is composed of six bars of the same size,
The aggregate section of each is 69 superficial inches.
curves, and the section is gradually increased to 93 su-
These chains were manufactured with great care out of the best quality of Pennsylvania
charcoal blooms, and Salisbury pig iron puddled in wood fire, and can be depended upon
for a strength of 32 tons or 2000 lbs. per square inch.
All the sockets attached to the ends of the wire-rope suspenders and stays were made of
the best Napannock iron.
The tension of the different links composing each chain diminishes as they descend,
the strain upon the vertical links being more than one third reduced in consequence of
position, friction, and hold in the masonry.
The lowest link is secured to a cast-iron plate 6 feet 6 inches square, and 24 inches in
thickness at the edges, with eight heavy ribs on the lowest side. The central part,
through which the bars are admitted, has a depth of metal of 12 inches
Great care was
used to solidly bed this plate and chain, after which the whole shaft was filled up with ma-
sonry laid in cement, and well grouted; the bars were first well dressed with linseed oil,
and twice painted with zinc paint and Spanish brown.
The masonry above the plate was made to press upon the roof of the chamber like a
wedge: large stones were placed upon the knuckles, so that every joint has a hold in the
masonry above as well as below the surface of the rock.
Above the rock where the chain curves, each knuckle rests upon a cast-iron plate, bedded
upon a large cut stone; this again rests upon one still larger, or upon two flat stones,
which distribute the pressure upon the masonry below. These iron anchor plates were cast
of very strong cold-blast charcoal metal at the foundry of Chippewa.
The aggregate section of the upper links of the four chains is 372 square inches, and
their ultimate strength, at 32 tons per square inch, equal to 11,904 tons.
The strain upon
the lowest link being diminished a third, there remains 7936 tons; this pressure, on the
New York side, is resisted by a surface of solid rock 100 feet in length, 70 feet wide, and
20 feet in depth, weighing 160 pounds per cube foot.
The sudden changes of temperature rendered it necessary to enclose the whole length
of the chains in masonry; but as the strength of the wire is not affected by similar causes,
the cables, which were made of it, required no particular protection.
Masonry.— The base of the lower floor level is 60 feet by 20 feet, with an arch 19 feet
in width, forming the entrance to the lower bridge. Each of the four towers is 15 feet
square at the base, 60 feet high above the arch, and 8 feet square at the top, making a surface
of 64 superficial feet to each at the top.
The limestone used in their construction is sufficiently solid to bear 500 tons per super-
ficial foot without crushing. The base and towers on the New York side contain 1350
cubic yards, or about 3000 tons; and if we add the weight of 1000 tons for the superstructure,
the whole amounts to 4000 tons.
The inclination of the tangents of the suspension cables, nearly coincides with the
angle of the land cables; consequently the vertical pressure is brought over the axis of each
tower.
The base of the towers presents a rock face; the stones are large, well bonded and bedded.
The beds of the backing course are all cut true; and all the stones were laid in cement mortar
well grouted.
In the towers above, a regular bond is preserved, and all the stones are of a uniform
dimension, with the backing very carefully performed.
The upper courses were rendered more secure by dowellng their joints.
The Saddles on the Towers.-On the top course of each tower, a cast iron plate 24 inches
thick was laid, 8 feet square, well bedded in cement, and strengthened by three parallel
flanges for the reception of two independent saddles, each of which rests on ten cast-iron
rollers 5 inches in diameter, 25 inches in length, placed close together.
The pressure
upon each tower being 500 tons, that upon each roller is therefore about 25 tons; the
rollers were all cast from a close-grained, dense, and uniform metal.
Cables.-There are four of 10 inches in diameter, each composed of 3640 wires, of No. 9
gauge, 60 of them forming 1 square inch of solid section, making the entire solid section
of each cable 60·40 square inches, wrapping not included.
The construction of such massive cables, to make each individual wire perform its duty,
required more than ordinary care, and was thus performed. Each of the four large cables
was composed of seven smaller ones or strands. Each strand contained 520 wires; one of
these formed the centre, and the six others were placed around it. The ends of the strands
were passed around, and confined in cast-iron shoes, which also receive the wrought-iron
pins, that form the connection with the anchor chains.
The strands were manufactured in the same position as they are actually placed, in
order that the tension of the wires should not undergo any change.
1728
SUPP.
THEORY AND PRACTICE OF ENGINEERING.,
The splicing of the ends of the wire as it was unreeled from fourteen reels, was carefully
performed; and the machinery for plying the wires across the river was worked by horse
power. The adjustment of the wires in the centre of the span was performed by two men
stationed on a platform, suspended by four wire ropes about 40 feet above the upper
floor.
The tension of one complete strand was 50 tons, or 200 pounds per single wire. Two
strands were made at the same time, one for each of the two cables under construction.
On the completion of one set, temporary wire bands were laid on, about 9 inches apart, for
the purpose of keeping the wires closely united, and securing their relative position; they
were then lowered to occupy their permanent position in the cables.
On completion of the seven pairs of strands, two platform carriages were mounted upon
the cables, for laying on a continuous wrapping, which was performed by the engineer's
patent machines; whilst the work was progressing, the wire was constantly dressed with
oil and colour, to prevent its oxidation.
The wire, when suspended between two posts 400 feet apart, did not break at a greater
deflection than 9 inches; and 20 feet of it weighed 1 pound. Each wire had a tension power
of 1300 lbs., or 20 wires constituting a sectional area of an inch, 90,000 lbs. Five hundred
tons of this wire were obtained from Messrs. Richard Johnson and Brother of Manchester in
Great Britain, where it was manufactured.
The 14,560 wires composing the four cables, it is calculated, are equal to the strength of
supporting 23,878,400 lbs. ; another calculation assumes the aggregate ultimate strength at
12,000 tons, or 2000 lbs. each.
The Niagara suspension bridge, of 821 feet 4 inches span, appears to have cost only 1007.
sterling per foot run; for we are informed by the engineer that the whole money expended
upon the structure was less than 400,000 dollars. The mixed application of timber, iron,
and wire, seems to have been most judicious, and all the requirements of strength, effects of
change
of temperature, high winds, the moving of the rolling stock, the motion of men and
cattle admirably provided for.
Various suspended aqueducts constructed by the same engineer, five of which are
considerable, and two of great extent, bear evidence of as great strength as any con-
structed of stone or cast iron; he has in every instance, by means of weight, girders, trusses,
and stays, obtained such a degree of stiffness as to be proof against the effects of violent
winds or even hurricanes; and all his suspension bridges are well provided with stays below,
secured to the land in so admirable a manner that they cannot be swayed upwards or down-
wards sufficiently to produce any injurious consequences. The omission of such stays has
been found detrimental to the stability of many such bridges, and has caused their destruc-
tion by the momentum acquired by their own dead weight. The weight of a suspension
bridge should always be proportionate to the transient loads it has to bear; the smaller
the transient weight is in proportion to the weight of the bridge, the less will its equili-
brium be interfered with.
The Niagara suspension bridge only cambers 10 inches at the time a freight train weighing
about 326 tons is passing over it; and immediately it has passed, the platform assumes its
former level. There can be no doubt that the suspension principle of construction is the
most economic over large spans, and, wherever the smallest quantity of material is required
to be adopted, must have the preference over every other. The flexible condition, in oppo-
sition to the rigid ought to be no objection to it, particularly as the proper equilibrium
can be so well maintained by the introduction of timber girders, which support the track-
way, and which, by the judicious connection with four lines of rails, distribute the pressure
uniformly; without these girders the trusses could not have resisted the action of the
trains.
The hollow trough or beam, 24 feet wide and 20 feet deep, having the railway traffic on
its top and the ordinary traffic below, is well contrived for its purpose: the solid girders are
5 feet in depth; and the trusses are so arranged that they contribute a stiffness to counter-
act the effect of any gale of wind; but in addition there are 56 wire-rope stays attached to
the lower floor, and anchored to the solid rocks, capable to resist the force of 1680 tons.
The surface of the upper floor is 20,000 superficial feet, and that of the lower 18,000 super-
ficial feet; therefore a pressure of 50 lbs. upon the square foot does not amount to more
than 950 tons.
The length of the floor between the towers is 800 feet; there are four wire cables, each
10 inches in diameter; the solid wire section of each cable is 60 square inches, the aggre-
gate of the four cables 241 square inches.
The aggregate section of the anchor chains: lowest links, 276 square inches, and of the
upper links 372.
There are 14,560 wires used in the four cables, the strength of each cal-
culated to bear 1648 lbs. weight, thus enabling the four cables to bear 12,000 tons.
The length of the anchor chains is 66 feet, of the upper cables 1261 feet, of the lower
1193 feet.
SUPP.]
1729
THE NIAGARA SUSPENSION BRIDGE.
The number of suspenders are 624, the aggregate ultimate strength of which is equal to
bear 18,720 tons weight.
There are 64 over-floor stays, of sufficient strength to bear 1920 tons, and 56 river stay
of an aggregate strength of 1680 tons.
This suspension bridge of 800 feet clear span, placed at a height of 245 feet above a
flood that no man has been able to ferry, must be ranked among the foremost of the works
of the engineers of this or any other century. Delicate as lace work, it hangs between the
clouds and the boiling flood below, a bold and apparently well executed combination of the
principles and uses of the tubular and suspension structures, carried out with all the fresh-
ness and originality which so singularly distinguish our younger brethren of the New
World.
5 S
INDEX.
INDEX.
Page
Page
Page
Abattoirs in Paris
Absolute strength of
•
286
Amphitheatres
Castrensis
Anchor of ships,
·
108
weighing of
998
timber
-
1303
Catania
108
Anemometers
-
1216
Acacia, timber
-
1284
Constantium
108
Angles
738. 859. 868
Acherusia Palus
140
Cuma
139
to be given to
Acres, the quantity
Die in Dauphine
108
lock-gates
1549
of, in England and
Doue
108
Antarctic Ocean
635
Wales
759
Drenaul
108
Antimony
655
Acridina, city of
57
Drevant
-
108
Ants, turret-building
725
Acrita
621
El Jemm
119
Apodyterium
-
128, 131
Actus, single carriage
Fedena
-
108
Apollonius, the geo-
road
149
Fesole
108
meter
782
Adrian, villa of
93
Florence
108
Appian Way
·
148, 149
Agetor
75
Agonalis, circus of
-
119
Frejus
Hispalis
108
Apulia
·
183
108
Air, compressed
Air-pumps
-
1695
Istria
-
108
Aqua, Alsietina 175, 176
Anienne nuovo- 176
1217
Jerusalem
108
vetus
•
175
Alabaster
Alban Lake
stone
Alber timber
-
704
Lucca
108
Appia
97. 170. 175
-
192
Lyons
108
Claudia
·
174, 175
tunnels at
193
Melos
108
Julia
97
Metz
108
Tepula
-
175
169
J
101. 1284
Minturno
108
Virgo
170. 175
Alburnus
Alexandria, city of
ter
Aluminum
Alberti, Leon Battista 212
reservoirs of wa-
Allatri, city of
Alveum
Amiens, Cathedral of 1664
rose window
Narbonne
-
108
Aqueductibus Urbis
6.5
Neri
108
Romæ
169
-
32
Nice
108
Aqueducts of iron
-
597
Nismes
108
of timber
549
34
Orange
108
Aqueducts
70
Otricoli
·
108
Buc
286
S
653
131
Pæstum
Palermo
65. 108
108
Carpentras
Carthage
266
184
Parentium
108
Civita Castellana
158
-
1615
Paris
108
Constantinople
·
185
1617
Perigeaux
108
Croton
299
Ammanati
163
Placentia
108
Evora
184
Amphitheatres
Pola
108. 119
Frejus
182
Adria
108
Pompeii
108
Jouy
183
Adrian
108
Pozzuoli
140
Lisbon
185
Ægeda
·
108
Puteoli
108
Lyons
179
Agrigentum
108
Saguntum
108
Marcia
175
Alba
-
108
Saintes
108
Maintenon
285
Arezzo
108
Sardis
108
Marly
286
Argos
108
Smyrna
108
Metz
182
Arles
109. 118
Syracuse
60. 108
Montpellier
264
Autun
-
108
Tarragona
-
108
Nicomedia
185
Beneventum
108
Tergeste
108
Nismes
177
Besançon
Bordeaux
Bruieres
·
108
Toulouse
108
Pont-y-Cysyllte
567
108
Udena
108
Segovia
184
108
Valonges
·
108
Spoleto
158
Cahers
108
Capua
108
Verona
Vespasian
48. 108
Tarentum
147
108
Volsci
179
Cassano
108
Vienne
1
108
Udena
184
5 s 3
1734
INDEX.
1505
-
1430
Aradus, city of
Arc de Cloitre
Page
5
·
1450
Arch, antiquity of 22. 32.
>
70, 73. 194
-
-
Aristotle, death of
Arithmetical propor-
tion
Arnold's escapement
Arsenals
Arsenic
410
of Coningsburg
Castle
construction of 1521
development of 1435
equilibrium of 1427.
flat
of bridges 1486
formed of flex-
ible timber 419
-
J
Arsinoe, city of
Artemisia, Queen
Artesian wells
Articulata in Geology 621
Artificers' work, value
-
Fage
Page
47
Aulis, mole of
47
Aurelian, walls of
86
766
Autun, city of
92
982
Avernus, lake of
139, 140
138. 238
Axis, horizontal
957
656
of rotation
939
51
Axles
1271
196
Azimuth circle
809
291, 292
Bacciali, Giovanni
206
of-
Backwater, its effects
Bag and spoon
322
1058
Beton
909
Balance-bridge of iron 326
Binding-pieces,
Ballast machine
-
1058
groined -
·
1442
labour
902
Balneum
→
121. 131
hexagonal
1455
Brickwork
908
Baltic Sea
635
pointed, at Ar-
Carpenters' work 897
Banks, slope of
1142
peno
semi
skew
-
triumphal
·
70
Cofferdams
900
to resist inunda-
-
1428
Dredging
897
tions
324
1436. 1457
their
proportions - 1596
three arcs of a
w
circle
wedges which
Earth, removal of 896
Baptistery at Pisa, sec-
145
-, levelling
897
tion of
1617
Entretoises
901
Barium
651
Fascines
898
Barnabeta
206
Fences
898
Barometer
207. 845
P
- 1487
Foundations, car-
—, to measure
pentry of
902
heights
845
form
-
-
152
Groined work
896
Bars, Bootham
404
to
-
Aosta -
1597
weights applied
triumphal, of
Augustus at Pola 1598
of Augustus at
Planks
Platforms
Iron work
910
Micklegate
406
421
Joists, labour on
904
Monk,
405
Piling
899
Walmgate
407
Planking
899
Barton, Spanish
931
904
Bascule for pumping 1195
902
Basilica of Constantine 93-
of Augustus at
Stonework
908
100
Susa
-
-
1599
Timber, latour
at Fano
·
104
of Poliphele
of Septimus
-
1595
on
-
903
of Paulus Emi-
Timber, carriage
lius
-
100
Severus
•
1599
of
904
Basin of Hull Docks
326
of Sergius at
Timber, raising
903
Bath Abbey Church 1632
Pola
-
1598
of Titus at
Rome -
of Trajan at Be-
neventum
proportions
given to
Architecture
cubical propor-
Turf, laying
down
Baths, manner of heat-
897
ing
-
125
·
1598
Artificial globes
756
of Agrippa
120
islands
136
Badenweiller 130
1
-
1600
stone
-
724
of Caracalla
93
Ash, wood of
-
100. 1284
at Chester
128
- 1596
Asphaltum
728
of Constantine
-
93
-
1579
Astrolabe
825
of Dioclesian
-
93
to measure dis-
Greek
122
tion in
Cyclopean
Gothic
Greek
hydraulic
-
1663
tances
827
of Hippias
122
67
to measure
of Julius Cæsar
120
1602
heights
825
of Livia
-
94
79
to measure
of Nismes
131
205
depths -
828
of Paulus Emi-
Roman
-
1590
to measure
lius
120
Saxon
1601
widths
827
Roman
120
Archimedes
58
Athens, city of
41
of Scipio
125
screw of
-
1567
Atlantic Ocean
635
of Stura
130
Arctic Ocean
635
Atmosphere, density
of Titus
94
Area of land, how
of
207
Wroxeter
128
computed
848
as a moving
Battering engines at
Areas of a sphere
876
power-
1216
Rhodes
47
Argand
fountain
Atomic weight
643
Beach, sea
642
lamps
244
Argives
68
Argos, city of
72. 75
Argosies, or ships
144
Atwood, experiments
on falling bodies
Augusta Prætoria
Augustus, house of
Beams, strength of
1258
-
921
fishing
-
1304
89
motion of steam-
-
93
engine
-
994
INDEX.
1735
Page
Bearings of carriages 1023
Beauvais Cathedral · 1614
Beech, wood of 101. 1284
Page
Page
Bricks, machine for
Bridges
making
-
711
Chester
461
Bridges-
Choisy
1380
Beetle, three-hand
Guy
1071
Aberaven
426
Civita Castellana
158
Belfast
Belidor's machine
398
Albias
265
Clair, St., on the
1204
Alexandrié
163
Rhone
-
1365
Belisarius, miles of
-
203
Alford
M
468
Claix
253
Bellows for forging
1041
Allier
161.251
Bends of rivers, to
Allness
-
468
measure
837
Beneventum, city of
148
Bernareggi, Isidoro
206
Ambrussum
Angelo, St.
Assise,
-
159
154. 157
Clement's, St. 1373
Clyde at Glasgow 1363
Coldstream 433. 1405
Colebrook Dale
·
near
Collingen -
Blue
regular
Bevelled gear
Birch, wood of
Birds, in geology
Bismuth
Bitumen
Blast furnaces
Block machinery
Blouett's baths
Blowers of iron forges 1041
Boats for transport
for bridges
Bodies, action of
-
Bogs, drainage of 1558
Boilers, steam - 1251.1271
942
Tours
-
1398
Compiegne
-
1284
Avignon
250
Conan
621
Avon, cast-iron
497.
Concorde
-
655
506
Conway
493
-
1375
256
468
251
517
728
Bachiglione
157
682
Baiæ
139
Corvo,
1042
Ballater
-
468
Aquino-
-
130
Bamberg
Bassano
1381
·
1367
Cravant
Conway tubular 1707
Craig Ellachie
163
- 503
256. 1399
near
104
Bellecour
274
Cremera
-
158
· 1023
Berghette -
157
Croyland
•
416
66, 67
Berne
1376
Cyrus
67
923
Bettwys
426
Danube,
near
890
Bewdley
·
463
Ulm
1364
-
Bishops Auck-
Darius, over Ister
66
land
414
Delaware
•
1382
'
cylindrical
materials for
1252
Blackfriars
427
Dieppe
-
1364
Blois
251
Diez, St.
274
making
-
1252
Boisseron
-
158
Dole
264
rectangular
1252
Bonar
498
Drone
266
waggon head
-
1252
Bord
265
Dryburgh-
508
ing
Bolting machines
Boiler plates, punch-
-, apparatus for
feeding
Bond in brickwork
plates and tim-
Bordeaux
·
280
Dunkeld
·
468
·
1036
Bosphorus
Boucherie
66
Durance
250
•
215
1255
Brighton
-
518
Edinburgh
Edme, St.
468
-
1400
- 1049
Bristol
430
710
Britannia tubular
1705. 1712
bers
-
1306
Brives
266
Elbe
Esprit, St.
Exchange
Fabricius
-
214
252
255
-
154. 156
Boning lines
805
Broughton
520
Fairness
-
468
Boom chains
334
Brunoi
·
273
Feldkirch.
-
1379
Booming
805
Brussels
-
1370
Felice
163
Boring instruments
·
694
1060. 1062
Boring,
machines
for
·
Boron
- 1031
649
Buildwas
Cæsar's
Caligula
Capo Dorso
Carbonne
-
461.494
Ferrato
156
-
-
1349
Fochabers
468
95
Fouchard
251. 269
-
158
Freysingen 1356. 1380
-
266
Boundaries of lands 759
Carlisle
473
Frouart
Galashiel
274
-
507
Bourse at Paris
290
Carraja
-
163
Gignac
273
Bouse ore
663
Cartland Crags
Ga
1405
Box, wood of
-
101. 1284
Castellane
253
shovel
1057
Cephissus -
66
Glasbury
Glasgow
Gloucester
-
426
·
463
462
Brass
Brakes of carriages
Breakwater,
1019
Ceret
253
Goldsmiths
162
610
Cestius
156
Gooda
-
1368
Ply-
Chalons
251. 270
Grenelle
#
1377
mouth
366
Chamas, St.
159
Guillatière
-
2502
Bresica, red
100
Change Au
251
Hammersmith
-
509
Bricks
-
93, 94. 709
Charmes
256
Hamoaze
·
D
1393
used in the py-
ramids -
Chateau Thierry
272
Havre
-
1387
28
Chatellereau 251. 254
Helmsdale
468
kilns
709
Chavannes
!!!
fire-bricks
floating
retorts
710
Chazey
710
Chenonceaux
710
Cher, near Tours 1398
272
·
-
1376
Herault
-
250
Hexam
Homps
Helvoetsluys
-
1388
·
273
433
272
5 s 4
1736
INDEX.
Bridges
Honfleur
Page
Page
Bridges-
Bridges-
·
1388
Horbourg
Hotel Dieu
- 269
1493. 1515. 1516.
Nemours 274. 1403
Serriere
Page
278
Seurre
-
1380
251. 255
Neucettringen
-
1380
Hutcheson
470
Neuville
269
Hyde Park
460
Newhaven
518
Sevres
Simplon
Sisteron
276
274
253
Ingersheim
266
Newton Stewart
435
Sisto Ponte
-
156
Isere
-
253
Niagara suspen-
Sommieres
159
Janiculum
154. 156
Ge
Jardin du Roi 283
sion
Nogent
·
1725
Sorges
2€ 5
265
Southwark
498
Juvisi
Kelso
Kosen
Arles
Lary
•
255
Nomentano
155
Spoleto
-
158
434, 508
Norfolk
-
520
Stanies
458
-
215
Notre Dame, Ca-
Stoneleigh
-
436
La Crau, near
hors
1370
Sublicius
254. 284
Paris 251.
Sunderland
506
254.
Lavaur
Laythorpe
Lempde
Libourne
Limmat
Llanwast
Loire
270
Nottingham
471
Taaf
-
415
Nurembourg
215
Tees
154. 1350
Susquehanna 1383
426
1386
·
495
·
·
-
272
Orleans
254. 1403.
Terni
·
158
•
-
281
1514
Têtes
256.1372
-
d
•
1374
417
Ouse
472
Teviott
-
468
Palatine,or Ponte
Tewkesbury
504
-
Loiret
London
412. 441
Londonderry 426
-
251. 1371
1369
Rotto
-
154
Toledo
1516
Palladios
1366
Tongueland
463
Pavia
Peas
162
Toul
256
468
Toulouse
251. 254
Louis XVI. 273. 1515
Peebles
507
Tournelle
251.255
Louvre
Lovat
Lyons
281
Perth
430
Tournou
-
253
468
1366
Pesmes
Pelantio
•
251. 266
Tournous
-
158
Tours
1377
251.263
Macon
251
Pisa
163
Maestricht
-
255
Pontilieu
-
266
Trajan's
Trilport
158. 1350
·
257
Maligny
274
Mammea
157
Manchester
504
Port de Pile
Portsmouth
Portumna
-
257
Trinity
163
-
1383
Triumphalis
154
506
Tuilleries
255
Mantes
·
264, 1400
Potarch
-
468
Utrecht
1368. 1386
Marachia
Marche Palu
-
165
Prague
214
Vaison
161
254
Quatro Capi
>
156
Vecchio, Ponte -
163
Marie
-
251.255
Queen's, Ireland
473
Verona
-
165
Marlow
Maxence, St. 251. 270.
-
520
Ratisbon
·
215
Vicenza
-
157.163
Ravinnes
274
Vieille Brioude
253
Mazeres
•
-
Meuse
Michel, St.
Micklewood
Mediolanum
Mellingen -
Menai
1377
509. 513
1378
251, 255
Roanne
Rochester-
1551
Rhone
272
Rialto
-
161
Richmond
Rimini
1378
Villeneuve
253
163
Vizille
272
-
1383
Vrach
·
1365
Rieucross
274
Waterloo
436
-
157
Wellesley -
473
274
Wellington
436
414
Westminster 422. 429.
-
520
Rochester, new
-
1694
1404
Military School - 279
Rosoi
273
Witham
497
Milvius
Mireppis
-
153
Rotto Ponte
-
154
Wurtzburg
215
274
Rouen
276
Wychbree
426
Monnou
Montelimart
413
Rumilly
272
Xerxes, over Hel-
274
Saintes
161
lespont
-
66
Montignac
266
Salara
155
York, over the
Montilun
274
Salarius,
-
153
Ouse
-
415
Montrose
518
Saone
1376
Zurich
-
1375
Mossen
215
Sarah
-
475
Zwettau
215
Moulins 251.263.1404.
1514. 1517.
Saumur 251.258. 1490.
Saut du Rhone 250
Bridges built by Ge-
Mulatière -
1368
Musselburgh
435
Naville
270
Necker1365.1369.1378
Neuf Pont 251.254
Neuilly 251. 268. 1402.
Schuylkill
Seine
Savinnes
-
1373
Schaffhausen
d
1373
Schonnenberg
-
1369
1385
phyræans
abutments of,
66
thickness
1496
abutments at
Orleans
-
1521
Semur
- 1377
270
arches, their
form
1357. 1484
INDEX.
1787
Page
Page
Page
Bridges, arches, ex-
periments upon 1498
arches, con-
·
struction of 1521
balance
-
·
·
329
boats of - 661. 1393
Campbell's tomb in
Egypt -
Cams in machinery - 980.
Camu's pile-engine
Canals-
Crooked Lane
21
Dearne Deve
Delaware -
·
565
296
1566
Derby
565
-
967
Dora Batea
187
breadth of
·
1485
Canals
1551. 1560
Dorset and So-
-
centres of
-, drawbridges
floating
first built over
the Tiber
form of piers
foot
foundations of- 1518
Nicias at Delos
piers of
-
, quay-walls of
rolling
of ropes
starlings of
-
, suspension 518.520
-, prin-
·
1402
Canals
merset
565
-
1389
Aberdare -
556
Droitwich
565
-
1393
Aberdeenshire
556
Drusiana Fossa - 185
Abiato
187
Dudley
565
·
85
Adige
188
Edin burgh
and
1507
Aire and Calder.
G
556
Glasgow
-
565
-
1362
Albana, Val d'
-
188
Ellesmere
and
Albany
·
295
Chester
·
565
52
Albania
187
Erewash
-
568
J
1506
Alford
556
Erie
295
-
1516
Ancholme-
555
Exeter
568
1391
Andover
557
Forth and Clyde 568
·
1392
Arun
552
Foss Navigation 569
. 1514
Ashby de
la
George, St.
187
ciples of
, swing
timber
·
1350
1386
1346
tubular
turning iron
-, waterway of
Broadstairs
Bronze seats
Brothers
-
- 1705
Zouche -
Ashton-under-
Lyne
Avon
Barnsley, -
Basingstoke
557
Geresee valley
295
Glamorganshire
569
-
557
Glasgow
and
557
Paisley -
569
557
Glenkenns
569
•
557
Gloucester and
335
Basanallo
188
Berkeley
569
-
1478
Baybridge
557
Grantham -
571
396
Beverley Beck
557
Gresley
571
·
129
Bianco di
-
188
Harecastle
575
of
the
Birmingham and
Bridge
250
Liverpool 557,558
Hereford
Hartlepool
-
571
571
Buffing apparatus
within cities
Brundusium
Brunswick wharf
Bruschetti, Giuseppe
Buckets, brazen 203. 1206
Building, strength of 104
Bulk of bodies,
bodies, to
-
148
Blyth
560
Horncastle
57 1
-
1527
Black river
295
Huddersfield
57 1
206
Bologna
-
187
Hull and Leven
571
Borrowstounness
560
Ivelchester
-
57 1
·
1023
Bradford
560
Brecknock
560
Junction, Grand
Kennet
570
·
571
92
Brenta novella
188
Kidmelly-
571
Briare
249
Lancaster
571
ascertain
1117
Bride
561
Languedoc
248
Burners, construction
Bridgewater
560
Leeds and Liver-
of
1241
and Taun-
pool
·
571
Argand
-
1241
ton
561
Leghorn
188
Burning bodies
-
196
Britton
561
Leicester
572
Buoys fixed with iron
Brondo
188
Leominster
572
screws
1694
Bure
561
Leven
572
Burgundy
249
Liskeard and Loe 572
Cadmus
Cables and capstans
Caissoons, to trace 238. 1431
231
Bury
561
Lledi
561
81
Caistor
561
Loing
249
Cajuga & Seneca 295
London and Cam-
for bridge build-
Calder and Heb-
bridge
572
ing
259
bel
561
Loughor
561
used at Toulon
238
Caledonian
561
Louth
572
at Westminster
423
Carbonania Fossa 185
Macclesfield
572
"
Calcareous gritstone
628
Carlisle
-
564
Maestra Fossa
·
187
Calcium
-
6.52
Champlain
295
Malshum
249
Caligula, bridge of
139
Charolais
245
Manchester and
Callais, or mountain
Chemung -
295
Bolton
-
572
road
149
Chesterfield
565
Marduck
-
222
Cambrian system
632
Chinango -
295
Mariana Fossa -
·
185
lower do-
633
Corbulonis Fossa 185
Market Weigh-
Camel for raising ships 1054
Coventry
565
ton
572
Caminus, or chimney
131
Crinan
565
Campanile at Florence 1663
Cromford -
566
Martenaro
Martesana
187
196
1738
INDEX.
Page
Page
Canals
Canals
Page
Cement for aqueducts 176.
Medicina -
182
Weaver
577
181
Monkland
577
Western, Grand 578
Centre of cutting on
Monmouthshire-
572
Wey and Arun
577
Montgomery-
Wilts and Berks
577
shire
·
572
Wilts, North
-
573
canals
Centres of timber
Perronet's
·
G
1533
-
1395
-
· 1399
Morris
296
Wisbeach
578
Mosolino
187
Witham
-
573
at Chester Bridge 461
at Gloucester
Muzza
187
Worcestershire
578
Bridge
462
Narbonne -
248
Wyrley and Es-
Cephalopoda
621
Naviglio della
·
137
sington -
578
Cessart, Louis Alex-
Neath
-
572
Yare
561
andre de
227
Newcastle
573
Canals and river locks
1533
Cetras
75
Norwich
and
-
573
-
573
573
296
187
•
250
295
Newport Pagnell 573
Northampton 572
Lowestoft
Nottingham
Nulbrook -
Ohio
Ollegio
Orleans
Oswego
Cane, hydraulic
Canterbury cathedral
Canusium
-
1165
Chain and offset staff 846
1620
Gunter's
846
-
148
Chains of iron
157
Caps of windmills
-
1219
endless
955
Capstan, varieties of
997
for lifting stone
1024
Caracalla, circus of
-
119
for
measuring
Caravelli, Don Vito
147
land
846
Carbon
649
pumps
1176
Carboniferous system
630
-, suspension
514
Oxford
573
Carbury, Count de
Carpentry
-
999
Chalcis, mole of
47
-
· 1305
Chapels on bridges
-
415
Padua
188
Carriages for boats
Peak Forest
573
for railways
297
1020
Chalk
626
, green
103
Phillistina Fossa
185
for ships -
347
marl
710
Picardy
249
Piedmont -
187
of timber, how
valued
904
Westminster
Pocklington
-
573
for weights
1017
Chapelets
Ponfilio
188
Carts in Italy -
-
1020
Portsmouth and
Arundel
-
573
Puzzola, Fossa di
Rangone Fossa -
187
187
used by Perronet
for railways
Cartwright's steam-
engine.
1018
Chapel of Henry VII.,
worked by water 1197
Chartres cathedral 1664
1634
1057. 1195
-
1019
Chelsea Waterworks
1642
Chesnut timber 101. 1285
981
Chimneys, their origin 131
Regent's
Rochdale
Rye
Salisbury
Sankey
575
Carybdis, Pool of
64
-, area for
-
1257
·
573
Carystos, or
Castel
Chlorine -
646
-
573
Rosso
-
100
Choras, the engineer
75
and
Southampton
Schuylkill
Casks for floating bo-
Chorabates
·
166
573
-
573
dies
Castelli, Benedetto 207
230. 352. 385
Chords and arcs
820
-
Chromium
655
297
Castles
139. 409. 411
Secchio
Sheffield
-
187
Catacombs
60
Churches, roofs of
Cippolino marble
1316
704
.
573
Catch piers
345. 401
Circei
75
Shrewsbury
Shropshire
Somersetshire
Staffordshire
Stainforth
Stourbridge
Stratford-upon-
573
Catch-water drains
-
540
573
"
573
-
574
Catenarian arches 419. 1684.
Cathedrals, cubical
proportion in
Circeum
Circles
88
·
-
741
area
-
874
1664
circumference of 746
574
Amiens
-
-
1667
874
574
Chartres-
-
· 1664
diameter of,
874
Rheims
Avon
574
Salisbury
-
1664
1664
proportions of
746
to reduce to a
>
Swansea
Tavistock-
Tesino
Tetney haven
-
574
Caudebeck sacristy - 1636
square
880
-
574
Cauking -
-
1306
to reduce to an
-
187
Causeways
10. 541
oval
-
881
-
575
Cedar, wood of
-
1285
to reduce several
Thames
Medway
and
Celestial arc, measure-
to one
-
·
888
-
574
ment of
-
758
and Severn 574
Trent and Mer-
sey
Ulverstone
Cella Solearis
·
123
Cellular pumps
1197
to triple and
Circumferenter
double
884
862
575
Celsus on rain water
165
Circular staircases
1468
577
Cement
721
Circular alternate mo-
Union, Grand
-
571
kilns for burn-
tion changed to con-
Walsham
Warwick
Waveney
573
577
ing
mills for grind-
717. 721
tinous
960
Circus
119
561
ing
-
1049
Cirrhopoda
621
INDEX.
1739
·
Cissiæ, machines
Page
· 1015
Cisterns for water 168. 544
Clay, Kimmeridge
Convex mirrors
Copper
Page
Page
244
Demetrius, Poliorcetes 44
51. 670
Denudation
-
623
628
adit of mine
675
Derrick cranes 1012, 1013
London
Oxford
-
624
alloys of
671
Desarque's pump
-
1194
628
crushing-mills
Devonport column
1012
Wealden-
for brick-making 709
627
for
676
Dilatability
·
915
oxides of
670
Dimchurch wall
1558
Cleavage
Clepsydra
Cloaca Maxima
of
-
633
riddling of
677
Dinocrates
32
35
sampling of
678
Divisibility
-
916
1658
sulphates of
670
Delorme, Philibert
1377
Clock-making, history
Clutch or gland
Copying plans
870
Delos, Isle of
-
69
-
974
Coral rag.
628
Diaclos, or drawing
950
Corlina
-
99
plan
44
, bayonet
-
950
Cornbrach limestone
628
Diades
75
friction
·
950
Corneil wood
-
101
Diagonal lines
736
Coaking engine
1043
Corvus or raven
-
1006
Coal
630
fields
694
Cos, Island of
-
54
fields in Scotland 694
77
mines, how
lighted
-
976
Coryceum, apartment 122
Cosa, walls at
Cotton spinning
Diallage, or serpentine 635
Diameters of circles -
874
Diatonous
-
1423
Diognetus
46
Dioptera
166
-
696
Cobalt
656
Couplet on centres
Couplings
►
1408
Diverticulum road
149
949
Diving bells
1050, 1051
rock
-
walls
fourway -
sluice
Cogs
Cobb composed of
Cocking or cogging - 1304
Cocks, stop and metal 167
Cofferdams 269. 430. 446.
465. 468. 1518. 1519.
Cohesive strength
friction
-
950
Docks at Antwerp 214
-
385
727
Crab for raising
weights
Commercial
310
-
1001
Catherine's, St.
308
Cradle for hoisting
-
239
Chatham
318
Cramping of stone
379
Cumberland
-
363
-
1260
1214
Cramps, dowel and
dovetail
-
1441
Deptford
Goole
314
324
-
1566
-
Colechurch, Peter
1293
412
Cranes 1004. 1006. 1011
for hoisting 1701
movable -
Perronet's
Hull
-
1008
-
1009
Crank
1267, 1268
-
India, East
India, West
London
Ramsgate
325. 327
-
312
313
310
396
Coliseum
23. 96
Crapone, Adam
Colossus
48
Crayon, Port
-
245
868, 869
Sheerness
318
how cleansed
329
of Claudius
133
Cretaceous system
626
Dock-gates at Mon-
Colours used by the
Cross staff for measur-
trose
1553
Romans
103
ing
870
at Wool-
Column of Antoni-
applied to angles
871
wich
·
1554
nus
-
198
polygons
873
Dodecaedron
755. 779.
of Trajan
198
rhomboids
872
889
Comitium
85
Crystal Palace in Hyde
Dolabella, arch of
97
Compressibility
917
Park
-
1668
Dolamite
702
Conches or locks
186
at Sydenham
1672
Domenico's invention
Couchifera
621
Ctenoidans
621
of locks
187
25. 309. 724
172. 1139.
1226
for heating
127
758
to construct
>
781
to find their su-
weeds
perficies
their solidity
877
-
877
Cyclops
Cylinders
-
Conic sections -
782
Contectis Piscinis
Continuous rectilinear
motion changed 954, 955
Contour lines on maps 802
Contract for London
Bridge
·
455
Danaide -
De rius's Bridge over
Hellespont
Degrees
122
890
Dædalus -
-
169
Daily labour of men
Dams, double
Concrete
Conduit pipes of clay 94.
——, of metal
Cones
Conical flour mills 1705
-
Conisterium, apart-
ment
Conoid, parabolic
Ctesibius's pump
Ctesiphon's method of
75. 201
·
raising weights
Cubical proportion 1663
Current, to find the
velocity of 636. 1139
Cutting knife for
-
751, 781. 877.
, strength of metal 1258
Cypress, wood of, 108. 1285
-
Assumption at
Paris
Invalides at Paris 1 348
St. Mark at
Venice
Salutation
Church
-, spherical
Val de Grace
Domitian, villa of
Dorians
Doric temples
Doron
Dovetailing stone
Downs or dunes
for mud
•
· 188. 1562
Belgium pro-
-
204
Domes
-
1345
-
-
1346
-
191
$67
955. 1275.
80
1087
-
128
Dragging
959
Drainage
67
748. 811
-
1361
1347
1459
-
1345
93
158
1580
708
379
-
642
1520
-
1057
vinces
214
1740
INDEX.
-
-
theatres
112, 113
Drainage, Fens
Hontsdam
Nene outfall
Pontine Marshes 188
Purmer Lake - 212
Romney Marshes 532
of towns 543. 1657
Witham Marshes 537
Drain pipes
Draining and embank-
ing
2
Drains in the amphi-
Drawing circles and
Germany
Greece
Page
Page
Page
541
Engineering, history
Figures, triangles, to
214
of, in England
306
reduce to
879
539
France
215
213
unequal, to di-
vide
888
40
Filters for cleansing
Holland
213
water
1211
Phoenician
1
>
Mauras's system 553
Roman States
83
Fir, wood of, varieties 1286
468
Engines, steam
955
Fire basket for light-
for boring
1033
houses
332
1557
fire
·
1196
Fishes in geology
621
high pressure
locomotive
-
1255
Flashes for canals
-
568
-
127]
Flats in canals
618
raising water
-
202
Flint glass
-
731
ovals
773
steam-boat
583
Floatation of bodies
►
1156
9
parabolas
polygons
piles
773
England and Wales,
Floating
207. 229
·
773
area of
759
equilibrium of 1154
- 1078
Eocene in geology
624
Flora, circus of
-
119
Drawbridges
1392
Ephebium, apartment
122
Flood-gates, to raise
-
1106
1057
-
1031
carriages
·
-
213. 1528
213
Dredging machines 229.
bucket machines 347.
1058
value of work - 897
Drilling machines 1030
hand and foot
machines
Drivers to railway
-
Equilateral triangles
Equilibrium
Etruria
1278
Drummond's light 1230
Dykes, their construc-
tion
of Holland
Dynamometers 1064. 1254
-
Epicycloid
940
Floors
-
1310
Epures or drawings
Equation clock
·
781
fire-proof
1688
982
double-framed 1312
-
768
naked
-
1311
934.938.
Roman
-
1426
1505
Escapements, recoil
-, ascending
Breguet's
·
983
·
984
974
single joists
Flour mills, conical
Fluids, pressure of
Fluorine
-
·
1311
-
1705
1133
-
647
•
78
Foccaci, Francesco
206
roads, &c.
83
Foculare
9
Euripus,
wooden
Focus or hearth
131
bridge at
47
Fontana, Carlo
1015
Evangelus
751
Excavations
-
1520
Force, measure of
developed by
-
916
for piers of
the mover
1091
bridges
432
value of work
896
Hegnier's
1066
various, applied
water
-
to machines
Ear of Dionysius
Earthen pipes for
East London Water-
1068
60
915
166
Fall of water-wheels
1146
works
-
-
1651
Exchange at Antwerp 214
Extension
Eyes, boring in metal 1036
given to water - 178
equilibrium of 917
mechanical la-
-
, parallelogram of 919
Flashing for supply of
water
Foreshores, how pre-
bour
917
544
Eau Branch cut
539
Faraday's lamps
361
served -
Forging of iron
3.3
34
Ebony, wood of
101
Fascines for jetties -
231.
Formæ, town of
44
Eckart's power cap-
898. 1522
Fortifications of the
stań
1008
Faults in mines
623
Greeks
74, 75
Edifices of Rome,
Felspar, analysis of
705
Forum
105
materials used in
Fenders of oak
327
Appii
152
construction
92
Fengite, marble of
99
Fossombroni Vittorio
206
Edwards, William
-
426
Fens
541
Foundations
225. 238
Egeria, fountain of
-
94
Ferrari
206
of bridges
1518
Egnatiam
148
Ferries over rivers
412
of sea locks
225
Elasticity
915
Field book for sur-
of sluices
218
Eleusis
43
veying -
847
Elder, wood of
1285
Figures, regular
866
Ellipse
74
equiangular
744
Elm, wood of
100. 1285
equilateral
.
744
cavating
Emissarium
Emplecton
of, in America
Embanking and ex-
and draining
Engineering, history
Egypt
-
1567
1558
194
"
121
>
293
irregular
isoperimetrical
multilateral
plane, to reduce 878
quadrilateral, to
-
divide
rectilinear
877
745
·
887
-
1310
886
ing by
Fresnel, Augustus
750. 1663
244
884
Friction
951
of London
Bridge
Fountain of Hero
Fowey Consols mine 674
Frames for building 180
Framing in carpentry 1310
partitions
Freemasons, measur-
-
447
1156
•
7
INDEX.
1741
Page
Page
Page
121
206
·
169
127. 709
95
Frigidarium, apart-
ment
-
-
Frisio, Paolo
Frontinus, Sextus Ju-
lius
Fucinus, lake of 140. 195
Fuel, consumption of 1281
Fuller's-earth beds 629
Furnaces, construc-
tion of
Gabina, stone of
-
Gabions, construction
proportions
Goubert's apparatus
for raising ships
Governor or centri-
fugal power
Gradients on railways
Graham's dead beat
Grandi, Guido
Goldsmith, arch of
96
Hexaedron
755.889
Gortyna, city of
Gothic windows, their
51
Hexagon-
-
887
Hexastyle temples
1582
-
1608
1663
-
1056
a
1262
tus
1567
several
>
-
983
proportions
Hiero, palace of
Hippodamus of Mile-
Hippodrome of Con-
1582
57
46
148
206
stantine
95
Granite, Aberdeen
634
Hoisting tackle
1012
graphite
383. 634
crane
·
1701
of
G
1522
-, porphyritic 348. 634
for the Menai
Gadsdon, Isaac
- 417
Gravatt's level
-
797
Bridge
1027
Galeasses
144
Graving docks
-
294
Holly, wood of 101. 1286
Galileo Galilei
207
Galleys built by the
Rhodians
46
cut in
the
rock
72
Ganoidans
621
Gravity, specific, of
bodies, tables of
centre of
, earth's
force of
metals
Hooke's universal
1116
joint
950
921
Hooke, Dr., on the
- 1120
Catenarian
417
-
920
Horizontal line
-
735
-
1117
Hornbeam wood 101. 1286
Gargouille
Gas lighting
-, condenser
, gasometers for
, governors
history of
hydraulic mains 1235
113
woods
1119
Horse, power of
· 1092
·
1214
of a circle
921
observations on 1093
·
1235
of a cone
921
daily work of
-
1237
of a paraboloid - 921
Hot-blast iron
1017
683
- 1238
of a sphere
921
Hounslow
Heath,
-
1230
of a segment
-
921
base line on
-
of a sector
921
Humber dock wall
853
1526
mains
1239
of a trapezium
921
basin piers
1529
purifiers
M
1236
of a triangle
921
Hulls, Jonathan
583
retorts, &c.
1232
Greece
40
Hydraulics
34
Garousse's lever
982
Greenstone
634
Hydraulic traversing
Gates turning on pivots 219
or entrances to
cities
69
of
of Augustus
91
Grilliage of timber
Groins, construction
Groundwork, value of 896
221
frames
-
1281
docks
294
=
1525
lime
721
press
1711. 1722
Circeium
88
Gudgeons
948, 949
ram
-
1704
of the Lions at
Guglielmini,
Domi-
Mycenæ
71
nico
The
207
Hydrometry
of canals
-
1102
engines
bular
Gear, bevelled
Geometry
Gauges for steam.
water and tu-
Gaunus, Mount
Gunter's chain
Gymnasium
846, 847
Hydrogen
Hydrostatic balance - 207
644
207
120
Hydruntum
1954
Hadrian, circus of
119
chine
1255
Halley's diving bell
Gu
1051
148
Hammers for forg-
Hygrometric ma-
Hymettus, marble of 99
Hypersthene rock
-
148
-
990. 999
-
942
ing
-
1042
Hypocaustum
-
733. 835
Hampstead Waterworks
Windsor
ble
George's, St., Chapel,
Gephyræans
Giallo Ontico mar-
Gin for lifting
Girders, strength of 1312
1654
1630
66. 81
Harbours, see Ports.
Harmonical propor-
tion
water
766
-
703
957. 959
Harry Grace de Dieu
Heat, radiation of
314
•
1223
Girgenti, town of
•
63
Glass, its manufacture
machine for
781
•
polishing
Globe
Gneiss system
-
975
701
conduit pipes
Hedgehog for rivers
Heights
Helepolis
Heliogabalus, circus of 119
Hellespont, bridge
127
Icosaedron
Impact, or shock of
Impenetrability
Impression, centre of 1115
Inclined plane 296. 924
planes on canals 1554
634
121. 131
779. 889
-
1197
-
915
-
1059
Indian Ocean
G
**
635
736
Inertia
-
916
47
Invertebrata in geo-
logy
621
Iodine
647
Globular projection
its composition 654
Gnomonic, or central
·
747
over
66
633
Henry VII.'s Chapel,
proportions
Westminster -
Iron
Heptagon
879
projection
Gold
746
Hepteres -
137
650
Herodes Atticus
50
Ionic temples, their
· 1587
620, 621. 657
and brick con-
struction
its cohesion
-
-
1684
693
1742
INDEX.
Iron, alloys of
~, assay of
construction
Page
Page
Page
-
681
Kent Waterworks
1653
Levelling, compound 799.
·
679
Key, grooving -
1037
802
1676
Kilns for cement
721
Levers used by the
corrugated
-
693
King's
College
Romans 201.928.982.
cylinders
307
Chapel
1625
997
cylindrical co-
Knolles, Sir Robert- 614
with toothed
lumns -
691
wheels
*
-
982
Į Į Į Į Į Į Į Į Į Į Į
Duleau's expe-
Labelye, Charles
422
Lias formation
629
riments on
forging
furnaces
galvanised
•
498
Labour, mechanical
918
Libra aquaria
166
685
measure of
Lichens which grow
682
value of
918
694
Laburnum wood
-
1286
on stone
Lifts on canals
-
384
·
1555
hand used by
Laconicum
121. 131
Light, Beale's
*
1242
Archimedes
58
Ladders in mines
675
reflected
684
670
•
· 1048
moulding
native
piles 313. 315. 549
, planing
plate bending - 1028
, power of sus-
pension
, proving
making
Land reclaimed from
the sea
Lapping in carpentry 1307
Lagunes
211
Lambeth Waterworks 1648
Lamp black
-, apparatus
·
103. 728
for
730
-
320
Lighthouses
Belfast
WA
Bell rock
Bermuda
Cape de la Heve
Chapman sand
Cordouan-
Dundalk
Eddystone
Fleetwood
-
Isle of Man
Lowestoft -
·
784
61
-
1692
·
-
341
1689
232
-
1693
240
507
ma
1692
chine
puddling
-, revolving shafts - 693
507
685
Larch, wood of 101. 1286
Larnica, gulf of
367
51
-
1692
Lateran, baptistery of 100
-
342
, rolling, forg-
Lathe for turning
1
1029
319
ing, &c.
685
ships
-
1725
Latitude -
-, strength of 690. 693
without an axle
Latomiæ, or quarries
995
Menai
360
757
Northern
342
60
Pentland Skerries
342
sulphate of
680
Latrina
128
Ramsgate
-
1229
sulphuret of
680
Laurel, wood of
1
101
Spurn Point
329
swivel bridges
328
Laurentinum
of
Sunderland
335
teeth of wheels
946
Pliny
122
lamps
361
-, tenacity of
-
514
Lavacrum
126
Lignum vitæ wood
-
1287
tension of
693
Lazaretto
209
Limaria
168
valuation of
work done in 910
weight, tables of 690
Ancona
105
Lime
-
71. 78. 94. 717
Genoa
209
-
wood of 100. 1287
Leghorn
210
Lime-kilns
-
719, 720
wrought
685
Varignano
210
manufacture of 720
Ischia
139
Lead mines
-
659. 661
Limestone
701
limestone of
-
95
Lea River
-
1639
-, aymestry
632
Isodomum
-
1423
Isosceles triangles
·
768
casting
hushing
667
carboniferous
·
631
662
·, magnesian
639
Iter, or bridle way
Jack for lifting
149
milled
667
mountain
630
pipes, forming of 100
primary
633
166. 667, 668
scar
631
weights
Jacob's staff
-
1001
red
-
103
Lines, perpendicu-
832
reducing
667
lar
734
Jessop, William
Jet
height
for measuring
heights, &c. . 834, 835
of water, its
Jetties 217. 220. 226. 236.
refining
666
inclined
C
735
roasting
668
variety of 734, 735,
363
sludge
668
736
smelting
665
Links of Gunter's
-
1215
smiddum
-
664
chain
·
846
washing .
663
Liquids, level of
· 1096
1522
Lecchi, Antonio
206
Lithium
-
-
651
Joas Johnson
-
320
Let-off for water
564
Llandello flags
632
-
1306
of arches
-
-
1428
socket
549
Joints in carpentry
Joists, to proportion - 1303
Levels, variety of
-, gunners
instruments for 793
Leupold Theatrum
962
Loam, Windsor
710
Level
cutting
on
Locomotive engines 301
canals
1534
1272. 1282
796
Locks on canals 217. 222,
Journals
949
Junction,
Grand,
Waterworks
1645
Juniper, wood of
-
101
lines
to rectify
-
736
795
used by the
Kaminus or chimney
131
Romans
166
མ
736
223. 1537
bridges
at Cherbourg
cast-iron
centres of im-
pression 1115. 1540
·
· 225
-
1559
-
566
INDEX.
1743
Page
Page
Locks, chambers of 1537
dimensions of
-
·
, gates of 232. 247.
gates of iron 1553
Mahogany, wood of
1287
Mica schist
1540
water
326. 328
on the Humber
327
Mains for supply of
Malton's perspective -
Mammalia in geology 620
Mammertine prison
Micænas, mole of
Page
633
142
1214
Mickle'swindmill sails 1220
789
Middleton, Sir Tho-
mas
545
97
Middlesex, West,
scourer of sluice 1542
Man, daily labour of 1093
Waterworks
1644
sections of
1538
drawing
and
, stop gates
1557
pushing
1091
terns
talus to be given
moving a load
-
1089
to walls of
-
1539
moving winches 1090
, theory of
1535
Manfredi Eustachio
to admit several
-
boats
towing paths
water enter
water ex-
pended
-, Zendrini's
count of
-
1537
Manganese
206.
208
655
cement
dams
mortar
-
1556
Maple, wood of 100. 1287
Miliaria, or lead cis-
Mills, hand and horse 1045
grinding corn 1045
saw for marble
129
-
1029
639
-
·
1049
204
-
1558
Marble
99
water
203
>
Alracian
100
Millstone grit
632
1539
Barsenite
100
ac-
Carrara
99
Millstones
Minerals, their com-
-
1047
187
, Chios
100
position
643
Logarithms
860
forest
628
Mine, sinking shaft of 1063
Lombardy, stone of
95
Lacedæmonian
100
Miners
-
675
tract for
Longitude
London Bridge, con-
Looms for weaving 969
Lydian
-
100
Mines
659.661. 671
455
mills for sawing 1044
Mining instruments 1063
757
statuary
-
703
Miocene in geology - 624
-
Markots
287
Mirrors, how made
732
Lorenzo, St., gate
of 93
Givars, St.
288
Mole, constructed at
Lorgna's centres
-
1395
Germain, St.
289
Euboea
67
Marco
•
206
Martin, St.
-
289
Louchette
Lough Swilly and
Foyle
Loutron or cold bath
Lubricating axles
Lucrinus, lake of
Lugdunum
1057
Marls, variegated
629
542
Pontine
Marshes, Linturna 148
152
·
Mollusca
122
-
· 1023
Masonry
-
140
-
180
Luna, town of ·
marble
143
Masetto, Giovanbatista 206
Eddystone light-
house
of London
Morice, Peter
·
-
at Misenus, 141. 142.
Montanari, Genunano 206
Morelatto raising ships 1054
-
-
544
Morland, Sir Samuel 582
455. 717. 1049
147
621
-
99
1419
371
Mortar
value of
906
Bridge
·
450
Morton's mechanical
Luxor obelis at Paris 1016
valuation of the
slips
-
347
Lycia
76, 77. 82
Machines used by the
Romans
of Ctesibius
for measuring
several kinds -
Materials, strength of 1025
MausoleumofAdrian 99.198
907
Motion of fluids
·
1126
Motions of machines,
conversion of
953
200
Augustus
197
alternate recti-
-
204
Mausolus, palace of 54
-
linear
992
Mean proportional
766
circular alter-
distances
, Cagnarel
tour's
205
Measurement of depths,
La-
&c.
815
959
Measures, ancient and
nuous
-
, Carberry's
centrifugal force 1166
999
modern
911
Mechanical agents
-
1087
cycloidal
Cessart's, de,
•
1024
-, power, equili
nate 973. 995, 996
circular conti-
parallel motion 1263
Mouldings of Greek
979.987
1266
Verra's
Morel's 1191. 1280
Vialon's -
brick-making
construction of 1565
disengagement
of
dressing flour
effects of
elementary
parts of
proving strength
of materials - 1025
for punching
Maggiore, lake of
brium of
939
temples
758
1165
Mechanics
915
Moulds of arches, de-
1166
Mechelini, Famiano
206
velopment of
1455
-
711
Mediterranean Sea 635
-
Movements of machi-
Meltuno, town of
Menander crossed by
-
146
nery
how calculated
982
Mud boats
329
950
Cyrus
67
Mulberry, wood of
-
101
1048
Mengotti, Francesco
206
Multilateral figures -
771
·
1188
Mensuration
863
Mural circles
809
Mercury
656
Muriatic acid
-
647
939
Meridian, to deter-
Muro Torto at Rome
87
mine
855
Messene, city of
72
vibrations
·
1035
Metagenes
75
Musical strings, their
Mycenæ
-
766
67
186
Mica, analysis of
·
715
--, treasury of
79
1744
INDEX.
Page
Page
Page
Naples, Bay of
138
Octares, boats
137
Pephasmenos
75
Narcissus,
employ-
Octaedron
889
Pepperino stone
95
ment of
195
to construct
778
Perea, Carli
206
Narducci, Tommaso
206
Octastyle proportions 1582
Perelli, Tommaso
206
Nasmyth, James, on
1663
Perronet, Jean Ro-
tools
1033
Oil gas
-
1242
dolphe -
266
Neapaphos
51
Olive, wood of
101. 1288
Perspective
789
Neapolis
57
Onctuarium
121
isometrical
791
Nero, circus of
119
Oolite
627. 701
Perugia, gate of
90
antico marble
100
Newcomen, Thomas 582
railway bridge
Nickel
-
New River Company 1642
Niagara suspension
Niches, hemispherical 1462
at an angle 1462
Nicholson, Peter
Nippers for cutting
, Bath
inferior
middle
628
Perry, Captain John
398
-
628, 629
Pertuis or sluices
188
628
Phalasarina, city of
51
Portland
627
Phalerum
43
·
1725
Optical square
843
Pharos
133. 146
Opus incertum -
98
Philopater, ship of
-
137
·
reticulatum 98. 1420
Phosphorus
648
777
Orchomenos
79
Phrygian marble
100
656
Ordinates
735
*
Organic remains
620
piles
995
Ostia, Basilica at
-
100
Nisida, Isle of
139. 142
Ovals
-
749. 876
Nismes, walls of
90
to reduce to a
Nitrogen or azote
644
circle
·
88
Noble's suction pump
992
Oxygen
644
Nonagon
744
Norma
-
72
Pacey, Whin
348
Norman architecture 1603
Paddles
188. 218. 1550
Notching in carpen-
try
Nymphenburgh ma-
chine
Pæonius
75
1304, 1307
Paddle wheels, Ro-
man
205
Piers 132. 314. 320. 397,
of bridges
of cathedrals,
their form
Pile-driving 327, 328. 423.
465. 967. 1070
drawing - · 1078
, cutting off
Pila, or moles -
Pile worm
navalis)
Pinchbeck
-
398. 434, 557
1506
1624
-
-
1080
140
(Teredo
1291
671
·
1191
Painters' work, pieces
Pincian gate
-
87
of
910
Palæozoic in geology 623
Pine, yellow, 101. 729.1286
Pinning in carpentry 1304
Oak, wood of
100. 1287
Palæstra -
130
strength of 1295
Obelisks, manner of
Palladio -
211
del
Palling the capstan
M
206
conveying
38
Palm
101
&c.
of elevating
1013
Pantheon, roof of
-
1332
single blocks
39
portico of
-
1591
, at Alexandria
Arles
Axum
39
Pantograph
991
39
Paoli, Pietro
206
39
Parabola
750. 758
Piombino, Stephano
Pipes of earthenware,
stone
for baths
Piquets
Pisa cathedral
baptistery
805, 806
1012
163
167
-
1427
123
-
· 1618
Cavallo
-
40
Paraboloid
-
757
Piscina, remains of
-
63
Cœlian Hill
40
Parallel lines
-
-
735
limaria, &c.
-
168
Citorio Monte
40
Parallelogram
760. 880
mirabile
142
Constantinople
39
*
919
Flaminio del
888
Popolo
39
99
Jebel Barkal
39
Luxor
39
gazine
-
1680
Maria Maggiore 39
Parthenon,
Medinet
el
tions of
Faioum
39
Minerveo della
of forces
Parallelepipedon
Parian marble
Paris Providence ma-
propor-
1584. 1663
Partitions, framed 1310
-
Pavements, Roman 101, 102
Pit cranes
Pitch tree
manner of mak-
Pisé, manner of build-
ing
725
Pistons, their con-
struction
1258
, strength of
varieties of
·
1257
1259
-
1006
·
101
Minerva
40
Pedal
981
ing
729
, Navona, Piazza
Pelasgi
-
68
lines of wheels
941
of
40
Pen, geometric
990
prices of pitch-
, Pantheon
40
Penara, gates of
76
ing
911
Pincio, Monte
40
Pendentives of vaults 1466
Pitot's centres -
1406
Sallustiano della
Pendulum
-
981
Placoidans
621
Trinita
40
Penstock, ancient
194
Plane, epicycloid
940
Vatican
39
Pentadoron
-
708
table
835
Whitaw Esk-
Pentagon
43, 879. 886
to measure with
836
dale
-
1013
Pentaspastos
200
to
map
with
840
Ocha, quarries at
..100
Ochre, red
103
Pentelican marble
Pentrougn
99
Planeometry
733
-
· 1150
Planing, machine for 1039
INDEX.
1745
Page
Page
Page
Planking and piling,
value of
Plans, to draw
to copy
ichnographic
-, orthographic
-, scenographic
Plants, fossil
Ports and harbours
Ports and harbours
-
899
Boston, America 293
Harwich
319
737.864
Boston
224
Hastings
387
870
Bridgewater
363
Havre de Grace
232
760
Bridlington
332
Holyhead
361
-
760
Bristol
363
Howth
-
399
•
761
Brundusium
147
Ilfracombe
363
622
Burghhead
349
Isere
48
Plaster, machine for
Byrsa
6
Ive's, St.
-
363
beating
-
968
Caernarvon
360
Jersey
401
Plate glass
731
Cardiff
362
Jura, small isles
356
Platform of timber for
Carlisle
369
Kingston
upon
sluices
·
219
Carthage
5
Hull
325
of locks
-
1542
Centocellæ
133
Kingstown
460
Platinum
Platonic bodies
Pliocene in geology
Plungers of wood
Poikilitic formation
Points of support
varieties of
Poleni Giovanni
658
Charlestown
296
Kirkwall
-
353
889
Chios
50
624
Civita Vecchia
-
137
Kyle
Lancaster
353
-
359
G
1180
Claudius
-
134
629
Cnidus
32
Leghorn
Leith
142
-
338
-
118
Cordouan
240
Liverpool
359
733
Corinth
44
Lyme Regis
385
208
Cork
401
Lynn, King's
322
Poleri Giovanni
206
Corran
367
Mabomac -
352
Poliphele, arch of
·
1595
Cothon
6
Margate
396
Polygons 743, 744. 755.
Cromarty
352
Marseilles
237
879
Cullen
351
Megara
6
Polyhedrons
754
Cuma
139
Messina
64
Polyspaston
201
Cherbourg
223
Milford Haven
-
362
Pomærium
85
Christchurch
-
385
Miseno
139
Pontoons 231.1054. 1710
Crete
51
Misenus
-
142
Pontou Gephura
66
Cuxmere haven
387
Montreal
293
Ponts et Chausées
215
Cyprus
51
Montrose
342
Poplar wood
-
100.1288
Dartmouth
385
Munychia
41
Porosity
-
915
Delos
51
Myndus
55
Porcelain, grinding
Dieppe
235
Naples
198
for
975
Douglas
396
Newhaven
387
Portes busquées
218
Dover
389
Orford
$19
Ports and harbours
Dublin
398
Orkney isles
353
Aberconway
360
Dunbar
337
Orleans, New
-
294
Aberdeen -
343
Dundee
339. 1701
Ostia
133
Aberystwith
·
362
Dunkirk
218
Adria
Agrigentum
Alexandria
Ancona
Androssan
138
Egina
45
Padstow
Palermo
363
56
60
Eleusis
43
Paros
51
32
Ephesus
51
Penzance
364
145
Exmouth
385
Peterhead
358
-
367
Eyemouth
337
Phalerium
41
Antium
-
-
145
Falmouth
364
Philadelphia
296
Arbroath
Aubin's, St.
Avoch
Axmouth
342
Feoline
356
Piræius
41
402
Findhorn
349
Plymouth
364
-
350
Folkestone
389
Poole
385
385
Fortrose
351
Port Patrick
397
Ayr
358
Fowey
364
Portsmouth
386
Baiæ
139
Frazerburgh
-
349
Posidonia
65
Baltimore
294
Genoa
143
Pozzuoli
139
Banff
350
Glasgow
357
Pulteney town
-
352
Bangor
360
Goole
324
Quebec
293
Barnstaple
363
Barton on Hum-
Gourdron
Gravelines
-
342
Ramsgate
392
-
322
ber
324
Greenock
357
Beaumaris
360
Grimsby
324
Ravenglass
Ravenna
Rethymna
359
•
138
51
Berwick on
Halicarnassus
53
Rhea
354
Tweed
33
Halifax
་
293
Rhodes
45
Bideford
-
363
Hampton (Little) 386
Rimini
138
Birkenhead
860
Hartland
363
Rochefort
238
Bordeaux
237
Hartlepool
332
Rouen
239
5 T
1746
INDEX.
Page
Page
Page
Ports and harbours-
Projection of globes
783
Quadrant
749
Rye
387
Prony's machine
969
Salamis
44
Property,
how to
Salines
51
value
-
891
Hadley's
Quadrilateral figure
Quadriremis boats
845
-
742
-
137
Samos
49
houses
893
Quarries in Egypt 36, 37, 38
Sandwich
592
mills
894
-, Baruthel
-
116
Scarborough
332
soils
892
of granite
348
Selinus
63
Shoreham
386
Proportions belong-
Sidmouth
385
Sidon
2
ture
Smyrna
50
Propylons
Southampton
·
386
Proportionals various 766
ing to architec-
Protraction of lines
-, marble
143
Quartz
·
Southwold
319
Protractor
Spezzia
143
Pseudisodomum
Stonehaven
243
Pug mills
S
1579
30
-
839
748
-
1422
709
Roquemaillere
Quay walls 223. 238, 239.
116
704
Sunderland
335
Swansea
-
362
Syracuse
Tabermory
57
355
Tain
Tarbut, East
352
-
355
Tarentum
146
Pumice-stone
Pump-barrels
cellular
chain
Tenedos
49
Teos
50
Terracina
137
Pumps 207. 1169. 1279
forcing 1169. 1174
foundations to
·
1197
·
1196
Pulleys, 201. 930. 936, 937
Quirium, city of
Quoins of lock gates 1548
Radiata in geology
accidents on
1518
of earth and
timber
293
Quinqueremes boats
137
-
85
Toulon
238
clear
Trajan, port of
-
133
Franklin's
Treport
-
233
-
Tripoli
5
ship
Troas
49
Hedderwick's 1173
suction 207. 1170.
curves given to 1574
cutting
edge rails
embankments - 1667
999
95
1186
621
Radii of wheels
943
Railroads
· 1566
capital and loans
1662
1661
chairs
-
1572
1639
cost of
·
1661
*
1204
- 1174
*
1567
1571
-
1175
engines
excavations
-
-
1662
-
1567
Troon
350
1174
Tynemouth
336
Pterepoda
621
Tyre
2
Punching machines
·
1034
Venice
144
-, press
1709
Watchet
363
Purbeck marble
627
foundations for
sleepers
gradients
-, length in miles
passing rails
1569
-
1568
1661
·
1576
Wells
320
Purifying apparatus
552
.
planes on
-
1578
Weymouth
385
Purple colour
-
100
plate rails
1571
Whitby
-
382
Whitehaven
359
Wich
352
Pyramids of Egypt
Abou Roash
Abou Seir
9
23
rails, various
rails, their form
·
1571
1662
28
1871
Wisbeach
·
324
Biahhmoo
29
-,
sleepers 1569. 1662
Workington
359
Dashoor
27
stone blocks
1569
Yarmouth
320
El Koofa
29
switches
-
1577
>
York, New
296
Ethiopian
29
Populunia
77
Geezeh
9
Port crayons
868
Gibel el Birkel
31
rails
Posilippo, grotto of
-
139
Howara
29
turn tables
width between
Railroads in America
-
1575
-
1568
300
Posts, king and queen 1309
Ilahoon
29
Belgium
-
292
bearing
1308
Lisht
28
England
584
Potassium
649
Meroe
#
29
France
292
Power, mechanical
919
-, producing mo.
tion
1143
Moydoom
Mycerinus
Nouri
28
Germany
292
14
Allegany
and
$1
Portage
་
304
Pozzolana
92. 95
Pozzuoli, note of
95
camp
Prænestine roadway - 149
Press, hydraulic 1711. 1722
, hydrostatic
punching
Pressure on vaults
centres of
Reegah
Saccara
Zowyet el Arrian
23
Altona
292
24
Atlantic, Great
-
301
23
Ballochney
588
-
93
Pyramid, great, solid
Baltimore
and
contents of
-
10
Wheeling
301
1026
- 1708
-
706
1114
-, passages and
galleries
second, dimen-
Berlin and Pots-
13
dam
292
Berwick
and
sions of
14
Kelso
586
Prisms
Prisons
Procida
·
755.888
601, 602, 609
third,
dimen-
Bolton and Leigh 589
sions of
139
inclined passages
14
15
Bolton
and
Buffalo-
800
INDEX.
1747
Page
Page
Page
Railroads
Railroads
Railroads
Boston
and
Hay
-
586
Plymouth
and
Lowell
301
Heck and Went-
Dartmouth
587
Boston and Pro-
bridge
589
Portland
-
580
vidence-
302
Hull and Selby
592
Portsmouth and
Braine la Compte
Jersey, New
303
Pensacola
300
to Namur
292
Johnstan and
Preston
and
Brandling Junc-
Androssan
589
Wyre
592
tion
592
Junction, Grand
589
Breslau and Fri-
Kiel
-
292
burg
292
Kilmarnock
·
586
Bridgend
-
589
Kingston
587
Bristol and Glou-
cestershire
*
589
Yorkshire
Brunswick and
Lancashire and
Leeds and Selby
1683
589
Providence and
Stonington 302
Redruth and
Chasewater
Richmond and
Covington
Rouen and Havre 292
-
587
301
However
292
Leicester and
Rumney
-
-
587
Brussels
and
Swannington -
589
Severn and Wye
586
Antwerp
292
Leipsic and
Sirhowey
586
Brussels
and
France
•
292
Dresden
Liverpool and
292
Stevens, St., and
Lyons
292
Budweis
-
292
Manchester
-
589.
Stockton
and
Bullo Pill or Fo-
1681
Darlington 587
•
rest of Dean
Caermarthen-
shire
·
586
Llanelly
-
589
Strasburgh
292
Llanfihangel
586
Stratford
and
586
London and Bir-
Moreton
587
Camben
and
mingham 590. 1663
Surrey
586
Amboy -
302
London
and
Union, North
592
Canterbury and
Croydon
592
Versailles
-
292
Whitstable
-
589
London
and
Vienna
and
Carlsruhe
292
Greenwich
589
Gloggnitz
292
Charlestown and
Long Island
302
Warrington and
Ohio
301
Lothian, West 587
-
Newton
589
Clarence
·
589
Magdeburg
292
Western, Great
591
Cologne and Aix
Malines to Os-
la Chapelle
-
292
tend
22
Wishaw
Western, South-
and
591
Cologne
and
Malines
to
Coltness
-
589
Bonn
Columbia and
-
Philadelphia 303
Cromford and
High Peak 587
Croydon, Mers-
·
292
Prussia
292
Mamhilad
587
Manchester and
York and Albany 302
Ramming earth
Rams, hydraulic 1109. 1704
897
Birmingham 591
Manheim -
292
at Marly
Montgolfier's
1162
20
954
Mansfield and
tham, &c.
586
Pinxton
587
siphon
suction
-
1161
-
1161, 1566
Dublin
and
Monkland and
Ratchet lever
982
Kingstown 589
Kirkintillock -
587
Ravenna
206
Duffryn Llynvi
588
Monmouth
586
Receptaculum
for
Dulais
588
Montpellier and
water
-
-
172
Dundee
and
Cette
292
Recipiangle
864
Newtyle
588
Mulhausen and
Durham and
Tham
-
292
Recoil escapements
Rectangle reduced to
-
989
Sunderland
587
Nantle
588
triangles
878
Dusseldorf and
Newcastle and
Rectilinear
figures
Elberfeld
292
Edinburgh and
Carlisle
Newcastle and
590
and motion 202. 880. 889
Reflected light
243
Dalkeith
588
Frankfort and
Darlington 590
Norwich and
-
-, circle
809
Regemont, M.
246
Wisbaden
292
Garnkirk and
Glasgow
588
Furth
Gemunden
292
Worcester
Nurembourg and
Oystermouth 586
302
Regular solids
778
Regulator box
1274
-
292
Rennie's, George, ex-
periments
sim
102€
Germains, St.
292
Paris and Or-
Buchanan
-
1002
Ghent to France
292
leans
292
Repeating circle
810
Gloucester and
Paris and Rouen
292
Repose
916
Cheltenham
-
587
Penrhynmaur
587
Reptiles
621
Grossmont
587
Philadelphia and
Reservoirs
60. 1664
Harlem
302
Erie
300
for baths
-
123
1748
INDEX.
Page
Page
Page
Reservoirs for baths
123
of loc
1557
Roof of Pantheon, Paris 1327
Paul, St., Rome 1329
Scale, manner of di-
viding -
-
7337
Resin
728
Riding house,
Scarfing timber 1304. 1307
Resistance of materials 1026
Rhedæ
Rheims cathedral
1015
Moscow 1329. 1335
Theatre of Bor-
Schist, chlorite
634
hornblende
632
1664
Ridge and hip tiles
-
711
deaux
Theatre, Italian,
1324
talcose
633
Sciography
785
Riding-house
at
Paris
-
1326
Scipio Africanus, bath
Moscow
1335
St. Martin
1323
of
-
125
Right and oblique
Roofs trussed with iron 1332
Scouring sluice
234. 1559
cylinders
-
780
tie-beams, expe-
Screw
1214. 1566
Rimini
206
riments on
1319
Archimedian - 1167
Ring, circular
875
with horizontal
bolts, machines
, cylindrical 749. 890
Risban at Dunkerque
Rivers, Alabama, &c. 293
origin of
ties
1334
for
1028
217
Rope ladders
1569
docks
294
—, rigidity of
1418
endless or per-
·
638
Roslyn Chapel, pro-
petual
-
927
method
crossing
of
portions
1618
jacks
1002
66, 67
Rosso antico
703
mill and press
-
955
walls
the Rhone, &c.
Riveting -
Rocks, Kelloway
642
Rotæ machines
-
1015
piles and moor-
-
1625
Rouen, quay wall at
1528
ings
1692
1035. 1709
Cathedral win-
628
Ludlow -
632
dows, propor-
tions of
1612,
Plutonic
684
1613
•
-, Quartz
Yaredale
653
St. Ouen at
1616
631
Roads in France
-
216
Rubble work, value of 907
Roughton Gill mine 664
Screw-cutting machine 991.
lock at Dun-
wall at Brighton 1526
at Dim-
Sea banks
kerque
-
1037
542
-
217
wall
Roman
149. 523
Rudder Roman
202
church
-
laid out
by
Rudyard, John
368
water
Perronet
267
Rules, parallel -
-
763
materials
for
Running water, ex-
making
names of
-
150
periments on - 1138
151
waves
Seasoning timber
Seats in amphitheatres 114
Secants of an angle
- 1558
636
-
636
-
1289
856
parish
524
Sabbadino
Christo-
Sectants
844
, specifications for
pher
209
Sectors -
749
making
-
526
Sabinum
83
-, uses of
-
819
-, timber
516
Sacbuts used at Syra-
to find the area
friction
Rochester castle
Rollers, eccentric
spherical for
-
1663
cuse
58
of
875
-
1261
Sails of windmills
1219
to
measure
952
Salisbury cathedral
-
1603.
heights with
825
1664
bridges -
1392
Sallust, circus of
-
119
ceous
Roman cities and
gardens of
93
towns, walls,
Salopians
84
Sediments, argilla-
Segments,to find area of 875
of spheres
624
876
Brussels
towers. &c. 84, 85
wall at Hartle-
pool
Rondelet's table of
the strength of oak 1294
Roof of ball room,
Christ Church
Samaritaine
255
Selce, stone for pave-
Samnites
83
ments
95
333
Samos ware
49
Selenium
648
Sand used by Romans
94
Self-acting slide rest -
-
1030
banks
642
Semicircles
748
, green
626
Semita, or foot-road-
149
-
1327
for mortar
723
Sandstone
-
629. 631. 698
-
Hall
Crosby Hall
"
1318
Savo, river of
-
-
1318
Saxon architecture
·
148
1601
Roman
Eltham Hall
1317
Scæan gate,
with
Sepulchres cut out of
rocks
Seradifalco, Duca di
Serpentine, its compo-
82
196
80
Hampton Court 1318
James's, St.,
mole
Scaffolding
72
1410
sition
-
635
Servius, wall of-
86
church
-
1332
made of spars -
1013
Louvais
L
1322
Mandar's design 1413
Setting out lines
Sewers
793
Mansard's
1319
of Britannia
Odeon
1331
tubular bridge 1716
- 83. 192. 1658
commission of
Roman
543
←
191
of large span
of timber
Opera des Arts
Palais Royal
-
1344
of Pantheon
-
1416
1332
1328
1322
value of
Zabaglia's
Scalding houses
900
Shackles, chain and
screw
- 1023
1414
Shadows
<
286
Shafts, or axles
784
945
INDEX
1749
Page
Page
Shafts of cast-iron,
-
strength of 945
sunk for tun-
Smoothing iron, ma-
chine for
1040
Sodium
650
nelling- 184. 194
Soldering the metals
167
Shales, limestone
upper lias
630
Solids, how to con-
629
struct
776
Steam-engines, loco-
motiv>
-, pumping
-
Page
single-acting 1245
used for pile-
-
1271
327, 328
iron
-,
Shears for cutting
Sheds for ship-build-
mensuration of
888
driving
1084
·
1037
Sophia, St., at Con-
used for bridge-
ing
Sheeting-piles
·
1343
stantinople
Sopwith's levelling
-
100
building
437
Steel
686, 687. 689
-
1075
staves
·
799
yards
729
Sheets of iron, punch-
ing
Shield for tunnelling
Ships, Roman
-
1035
Sounding the soil 1519
lines
Stereometry
733
850
Stevenson, Robert
-
470
1560
Sources, machine at
-
1190
137
Southwark and Vaux-
-, loaded, manner
hall
water com-
of lifting
294
pany
1647
loading and un-
Space
•
916
loading
201
Spandrill and wing
sunken to raise 1054
walls
-
1522
Stierme's domes
Stone, 92. 95. 1020. 1425
-blocks and sleepers1572
laid without
cement
machine
throwing, into
·
1346
178
for
Sdes of triangles, how
Spar, calcareous
700
sea
-
1024
to calculate
854
Specifications 445. 465. 468.
Stone pipes
· 1427
Sieves, machine to
526
polygonal
move
•
995
Spello, gate at
·
88
blocks
68
Sight, point of, in per-
Speluncas
148
quarries
697
spective
790
Sphere
·
756.876, 890
quarries, wheels
Signals
854
surfaces of
747
used at
966
Siliceous
698
Spherical valves
1183
Stone, resistance of, to
Silicium
654
Silk-twisting machine 976
Silurian in geology
-
622
Silver
657
-
Sines
761.793.
856
lipse
Spiral, to find area of
trigonometry
Spheristerium 122. 130
Spheroid, or solid el-
, transport
boats
Stoves and grates
Dr. Arnott's
778
the crush
-
705
on
367
890
1224
875
-
1221
to find areas of
857
>
cylindrical, to
metallic
1224
Sinuessa on the Do-
mitian road
Siphon for draining - 1098.
Siphon for extinguish-
draw
789
Strade at Hastings
·
387
-
-
148
Spirit levels
794
Stratification
623
Spoliatorium
131
Strike in geology 619. 623
1164
Spring balances and
Strontium
652
of water
ing fire
167
165. 1067
Square, to draw 880.881.
Stucco, tempering
102
Skew back of arches
-
1430
883
in damp places
Sublimation
103
-
916
bridges -
Skins inflated to cross
rivers
Slate, Stonesfield
Slips, inclined planes
-
471
, geometric, use of 817
to double
Subsoil, drainage of - 1559.
-
67
to reduce
883
880, 881
1563
Sulinis Minerva, altar
628
Stadium
<
122
to
130
619
for ships
in geology
advantages
Sluices of cast-iron
-
239
619
Staircases 111, 112. 1469.
Stamping-mills for ore
Sulphur
647
1475
Sunderland
light-
664
Sloping beaches, their
Slotting, machines for 1037
Stand pipes,hoisting of 1012
house, removal of
Superficies
-
335
759.877
345
Stateræ, Roman
Station pointer
•
326
-
218
Bergue's
-
219
Sluices, 217, 218, 219, 220.
223, 1558
for scouring
harbours
391. 394
side walls of
at Turner's and
Smeaton, John, me-
Statutes of Romney
Marsh
Staves for levelling 799
Steam as a moving
power -
Steam-engines,history
of
Supply of water in
France
America -
Surveying, cross
-, maritime
-, parish
subterranean
Suspension bridges
202
808.850
285
229
532. 1242
843
-
847
848
-
1260
-
832.
849
-
581
507.
moir of
-
429
diving bell of
·
1051
,application to
mills
atmospheric
Albion mills
1725
-
1270
1243
Suspensura floors 122. 127
Swape
331
-
1248
Swing bridges of iron
521
hand pump of -
Smelting and refining
Smithfield market,
1175
double-acting
-
1247
Sydma, gate of
76
34
employed at the
Syenite, composition
London docks
311
of
634
Manchester
-
1678
Hornblower's - 1250
Symmetry
1595
1750
INDEX.
Tabularum
Tandini, Antonio
Page
96, 97
Page
Page
Thermæ, Pompeii
128
Travertine stone
95
206
Titus
120
Treasuries of Greece
79
chine
Tar, how obtained
Tangential force ma-
Tangents -
Taorminum
Tatian marble -
Trajan
120
Trenches cut
by
·
1067
Thermolousia
131
Greeks
66
8.57
Thermometer
dis-
Tres Taburnæ
148
64
covered
207
Trevithick, Richard
-
583
-
728
Thomasin
246
engine
-
1175
99
Threads, double cut-
Triangles
741
Teeth of wheels, their
ting of-
1038
sides of
854
curve
940
pitch line
-, strength -
thickness
Telegraph, electric
Tide gauges
849
to divide
884
-
941
•
942
currents
mill
636
to form
769
971
to measure
872
944
Tiles
94. 711, 712, 713
to reduce
878
599
Timber, varieties of 100.
-
Triangulations
for
Telescope
Telford, Thomas
207
1285
surveying
812
-
469
Temples, façade of 1581
Antoninus, &c.
•
cohesive
strength of
to draw one simi-
-
1293
lar to another
769
96
decay of
- 1289
Ægesta
Castor
Pollux
64
felling of
and
-
Fortuna Virilis
Hercules
·
Jupiter Capito-
linus
Jupiter Olympus, 61,
258 870
1303
-
100. 1289
resistance of 1294
, strength placed
vertically
strength, inclined 1303
transverse
Trigonometry
-, surveying
Triremes or Roman
boats
Trispastos for raising
Triumphal arches,
proportions
Trompe, to construct 1454.
Troughton's improved
<
733. 803
-
852
137
weights
200
·
- 1596
strains
1292
waste of
904
"
62
Tides, their effect
322
1464
Jupiter
Pan-
of the sea
636
hellenius
45
their force
229
level
-
796
Minerva
61
of the atmo-
Trucks with wheels
-
1019
Romulus
98
sphere
637
Trypho
75
Vesta
98
Tile-kiln
730
Tubes of Britannia
Tenons and mortises- 1305
Tiles, draining with
-
1564
Tepidarium
121. 131
Teredo navalis
-
1291
Terracina
138. 148
Tertiary series
in
ornamental
Timber bridges
principles of
platform
-
713
bridge
Tubular bridges
-
1718
1705
-
1350
1350
Tubuli fictiles
·
167
Tufa stone
95
for
Tumuli
197
geology
Testudines used
622. 628
sluices -
219
Tunicata -
621
at
value of -
902
Tunnel, Thames
522
Rhodes
Tetradoron
Tetraedron
dity
47
Tin
670
708. 755
Tomb of Archimedes
777
centres for
for cleaning har-
-
· 1405
-
889
at Agrigentum
80
bours
840
temples
mans
to find soli-
Tetrastyle proportions 1580
Thames river
Ti:eatres
of the
of Marcellus
Theodolite
Thermæ, Adrian's
Alexander
verus
Antoninus
Caracalla
Antoninus
Aurelian
Commodus
Constantine
Decius
and
of Alexander
in chalk
574
889
Severus
-
200
for
scouring
of Cecilia Me-
docks
359
·
-
1581
tella
97
Tunnelling by Romans 166.
·
307 1639
of Romans
199
193
107
of Scipios
93
Ro-
of Telmessus
77
-
Turning gates of
Turf, laying down 897
106
of Theodoric
-
206
sluices
220. 232. 234
-
107
Tools used in lead
Turn tables
1577
840.842
mines
661
Turpentine
729, 730
-
120
of miners
675
Tusculum
77
Se-
Torni, machines
1015
Tympanum, Roman -
202
-
120
Torricelli, Evangelista 207
Tour de Corduan
-
237
Umbria
83
-
120
Towers of Roman
94
walls
87
120
Tracery of
Gothic
-
120
-
1608
120
120
762
Diocletian
120
-
Domitian
120
Trajan's Column
Nero
Philip
·
120
Trapezium
198
743. 878
windows
Tracing lines on the
ground
Tractoria, machine 1015
Unharnessing an ani-
mal, machine for
Unit of labouring force 918
Universal joint
Val St. Pierre, ma-
chine at
·
970
windmill
·
1569
958
-
1192
Valves 1179. 1182. 1259
-
120
Trapezoid
-
743
crown, rotary &c. 1260
INDEX.
1751
Valves, cocks
eccentric
•, opened
weights
safety
sliding
Vanvitelli
Vauban's works
Vauloüé, James
Vaults, conical
conoidal
cylindrical 753. 1429
, descending and
intersecting 1441
flat
·
Gothic, their
construction
Gothic with ribs 1448
·
Page
1260
Page
Page
Visual
1262
rays in per-
spective
Water on inclined
by
Vitruvius
789
83. 166
surfaces
1107
pipes, wooden
-
549
1261
-
1256. 1275
Volterra, walls at
-
77
-
1239, 1240
Voute d'Arete 1430. 1450
-
145
217
422
-
1429
-
1465
Walls, Aurelian's
Waggons used 011
railways
used in mines
built by the
Greeks around
-
1020
1018
·
88
Vivarium, remains of 97
pumping of, in
the Metropolis 1639.
1643, 1644. 1646.
quantity of,
supplied by
London com-
panies
, quantity
charged by
rivers
reservoirs of,
1648.
-
1642
dis-
1228
their cities
75
642
1430
of cities
67.83
of crude brick -
36
1641. 1645. 1647.
-
1448
, double, of Greek
1653
cities
76
screw
203
groined
-
1444
Chester
and
hexago-
Winchester
·
407
nal
-
1445
London and
supply of 139. 297,
298, 299
towns supplied 544.
hemispherical - 1460.
hexagonal - 1446
keys of ditto 1449
skewed
splayed
spheroidal
-, spherical
Veins in geology
Velarium or covering
Velocity of a river,
how ascertained
of a current
Venice, city of
Vent pipes for aque-
ducts
-
1139
Ventilation 181, 612. 675.
York
403
1210
1461
Rhine to Da-
vertical action
nube
86
of
·
1099
Servius Tullius
86
waste through
Southampton
and Roches-
ter
1525, 1526
and
-་
1459
·
1464
1459
618
117
sea
Walnut, wood of 1288
·
Warming and lighting 1223
apartments in
for sup-
ply of London 548.
550. 1637
works at Lon-
J
640
Paris
by air
-
132
don Bridge
·
211
by hot water
by steam
1227
1225
Watt's
·
1227
on canals
181
new prison
615
Persian method
Roman method 131
132
experiments
Waves in a storm,
force of
Weardale mines
orifices
-
1128
wheels
1142
408
works
estab-
lished for
-
442.
545
1142
·
229
660
Ventilators
and
Water
blowers
-
1222
Verd and Bonne Es-
165, 166. 552. 635
analysis of
bodies plunged
1637
Weather tiles
Wedge, use of
•
711
925
Wedging in carpen-
perance forts
217
in
1153
try
1304
Verdigris
104
circular
and
fox-tail
1306
Verzy's steam-engine
958
vertical
·
1110
Weights, tables of
914
Vermillion
-
103
closets
intro-
Vermuyden, Cornelius
duced
-
549
536. 539
companies
1655
water
-
Vessels, sunken, rais-
ing of
constant supply
1054
of
1655
Vestini, country of
Via, or common road
83
149
Appia
Domitiana
151
-
148
Flaminian
·
149
Prænestine
152
Sacra
-
85
Ulpian or un.
paved
151
Viaducts
303
Victualling yard, Dept-
ford
314
View, point of, in per-
spective
790
Vis St. Gilles stair-
Į Į Į Į Į │↓ ↓ ↓ ↓
conducting
cost of raising
166
1213
at Sheerness
engines
for
raising
-
1179
filters 550, 551, 552
Wenlock formation
gauges
533
-, raising of
Weirs, discharge of
Wells Cathedral
Wells, Artesian, 1059, 1060
sunk by Romans 167
for supply of
water
Westminster Abbey - 1608
928. 999
1140
-
1604
-
318
553
632
machines for
Wharf cranes
·
1005
raising
measurement
-
1201
Wharfing of boards
-
323
Wheel and axle
938
through tubes 1126
method of find-
Wheels, construc-
tion of 944, 945
ing
165
breast water
case
1470
motion of, in
pipes
motion of, in
rivers
1139
bucket water
drum water
fly
1141
overshot
1153
1198
-
1196
-
1268
·
1148
1752
INDEX.
Wheels, Persian
Page
Page
Page
, scoop
1196
1196. 1660
White lead
-
104
Workmen's
tools,
Winchester Cathedral 1621
their power
927
tide
1151
Windlass used by
undershot
·
1142
Romans
201
Wheelwork
Wheel, sun and planet 1266
machines for
cutting teeth 1039
velocity of 1148
rotating round
two parallel
axes
Winstanley, Henry
368
Xerxes'
bridge of
Willow, wood of
101.
boats
66
1288
Wind produced by a
-
1566
fall of water -
1151
Zanotti, Eustachio
Windmills
956, 957
Zendrini, Bernardo
horizontal
956
Zinc
939
sails, effects of, 1221
Zones
Whistle, steam
1279
White's pulley -
933
Wipers applied to
wheels
Zuliani, Pietro
979
Zureda's machine
206
208
669
-
760
·
206
-
962
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INDEX.
Abbey & Overton's English Church History 14
Atelier (The) du Lys
Atherstone Priory...
ΙΟ
Acton's Modern Cookery…..
20
Alpine Club Map of Switzerland
17
Autumn Holidays of a Country Parson
Ayre's Treasury of Bible Knowledge
...
18
18
อง
7
20
Guide (The)
17
Amos's Jurisprudence
5
Primer of the Constitution…………………..
5
Bacon's Essays, by Whately
5
50 Years of English Constitution
5
• Gada
Anderson's Strength of Materials
ΙΟ
Life and Letters, by Spedding
Works
5
5
Armstrong's Organic Chemistry
ΙΟ
Bagchot's Biographical Studies
4
Arnold's (Dr.) Lectures on Modern History
Miscellaneous Works
Sermons
(T.) English Literature
Poetry and Prose
Arnott's Elements of Physics……………………..
26
2
6
15
ac
6
6
...
9
Economic Studies
Literary Studies
Bailey's Festus, a Poem
Bain's James Mill and J. S. Mill
Mental and Moral Science
on the Senses and Intellect
18
21
6
455
22
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Bingham's Bonaparte Marriages
Blackley's German-English Dictionary.
Bloxam's Metals
Bolland and Lang's Aristotle's Politics......
Boultbee on 39 Articles.....
5
15
14
14
19
18
18
II
Bain's Emotions and Will........
Baker's Two Works on Ceylon.
Ball's Alpine Guides
Ball's Elements of Astronomy
Barry on Railway Appliances
5
Critical Essays of a Country Parson.........
7
...
17
Culley's Handbook of Telegraphy
13
17
Curteis's Macedonian Empire
3
ΙΟ
ΙΟ
Davidson's New Testament
14
19
& Bramwell on Railways, &c....... 13
Bauerman's Mineralogy
....
ΙΟ
Beaconsfield's (Lord) Novels and Tales 17 & 18
Speeches
Wit and Wisdom..
Becker's Charicles and Gallus......
Beesly's Gracchi, Marius, and Sulla
Black's Treatise on Brewing
I
673 +
4
20
7
ΙΟ
տ տ
-'s History of the English Church...
Bourne's Works on the Steam Engine......
Bowdler's Family Shakespeare
Brabourne's Fairy-Land
Higgledy-Piggledy
Bramley-Moore's Six Sisters of the Valleys. 18
Brande's Dict. of Science, Literature, & Art
Dead Shot (The)
De Caisne and Le Maout's Botany
De Tocqueville's Democracy in America...
Dewes's Life and Letters of St. Paul
Dixon's Rural Bird Life
Dun's American Farming and Food
Irish Land Tenure
II
4
15
...
.11 & 19
21
D
21
Eastlake's Hints on Household Taste...... 13
Edmonds's Elementary Botany
Ellicott's Scripture Commentaries ..........
Lectures on Life of Christ
Elsa and her Vulture
Epochs of Ancient History..……………………………..
English History
Modern History
....
II
HHHHH
15
15
18
MH IN I∞ MMM IN LO
3
3
3
15
H H
Ewald's History of Israel
Antiquities of Israel.........
15
Brassey's British Navy......
13
Sunshine and Storm in the East.
Voyage in the 'Sunbeam'..
17
Fairbairn's Applications of Iron
13
17
Bray's Elements of Morality
16
Information for Engineers...... 13
Mills and Millwork
13
Browne's Exposition of the 39 Articles......
Browning's Modern England
15
Farrar's Language and Languages
7
3
Fitzwygram on Horses
19
Buckle's History of Civilisation...............
Buckton's Food and Home Cookery......
Health in the House ............12 & 21
Bull's Hints to Mothers
Maternal Management of Children.
2
Francis's Fishing Book
19
21
Freeman's Historical Geography
Froude's Cæsar....
2
4
21
-English in Ireland
I
21
Burgomaster's Family (The)
Cabinet Lawyer....
18
Calvert's Wife's Manual
Capes's Age of the Antonines...………………………………………
Early Roman Empire
Carlyle's Reminiscences
Cates's Biographical Dictionary
Cayley's Iliad of Homer
Changed Aspects of Unchanged Truths
Chesney's Waterloo Campaign
Christ our Ideal
Church's Beginning of the Middle Ages...
367
Colenso's Pentateuch and Book of Joshua. 16
Commonplace Philosopher........
Comte's Positive Polity
2
Outline of English History
...
2
3
Thirty Years' War
3
3
Struggle against Absolute
Monarchy
4
Goethe's Faust, by Birds
Conder's Handbook to the Bible
15
by Selss
Conington's Translation of Virgil's Æneid
19
by Webb
Ho Ho How
18
18
Prose Translation of Virgil's
Goodeve's Mechanics...
IO
Poems.....
18
Mechanism
Contanseau's Two French Dictionaries
13
7
Conybeare and Howson's St. Paul....
Gore's Electro-Metallurgy
ΙΟ
15
Cotta on Rocks, by Lawrence
Counsel and Comfort from a City Pulpit...
Cox's (G. W.) Athenian Empire
Crusades
Greeks and Persians.....
Creighton's Age of Elizabeth
England a Continental Power
Papacy during the Reformation
Shilling History of England
Tudors and the Reformation
Cresy's Encyclopædia of Civil Engineering
II
Gospel (The) for the Nineteenth Century. 16
Grant's Ethics of Aristotle ......
5
7333MM
14
3
3
14
Graver Thoughts of a Country Parson......
Greville's Journal
Griffin's Algebra and Trigonometry......... 10
Grove on Correlation of Physical Forces...
Gwilt's Encyclopædia of Architecture......
Hale's Fall of the Stuarts.......
Halliwell-Phillipps's Outlines of Shake-
speare's Life
7
I
ΙΟ
9
13
3
4
History of England
Short Studies.......
Thomas Carlyle...........
Gairdner's Houses of Lancaster and York
Natural Philosophy
Gardiner's Buckingham and Charles I.
20
16
3
Ganot's Elementary Physics
3
4
4
19
...
7
2
16
-Personal Government of Charles I. 2
Fall of ditto
Puritan Resolution
(Mrs.) French Revolution
3962 ~ ~ ~ ~M M
I
6
4
WORKS published by LONGMANS & CO.
23
Hartwig's Works on Natural History,
&c.
...Io & II
Macalister's Vertebrate Animals
Macaulay's (Lord) Essays
17
ΙΟ
6
Hassall's Climate of San Remo...............
Haughton's Physical Geography
Hayward's Selected Essays
Heer's Primeval World of Switzerland..
II
Helmholtz's Scientific Lectures
Herschel's Outlines of Astronomy
Hopkins's Christ the Consoler
Horses and Roads
9
8
16
19
Howitt's Visits to Remarkable Places
Hullah's History of Modern Music
Transition Period
19
I I
II
I
H H
I
...
History of England
Lays, Illus. Edits. ... 12 & 18
Cheap Edition...
Life and Letters........
Miscellaneous Writings
Speeches
Works
....
18
I
466T6 amo
Writings, Selections from 6
MacCullagh's Tracts
McCarthy's Epoch of Reform
McCulloch's Dictionary of Commerce
Hume's Essays
6
Macfarren on Musical Harmony
Treatise on Human Nature.....
6
Macleod's Economical Philosophy...
Economics for Beginners
ΙΟ
9
3
8
......
12
5
21
Ihne's Rome to its Capture by the Gauls...
History of Rome
Ingelow's Poems
18
320
Elements of Banking....
Elements of Economics...
21
21
Theory and Practice of Banking 21
Macnamara's Himalayan Districts
Mademoiselle Mori
17
18
Jago's Inorganic Chemistry
12
Mahaffy's Classical Greek Literature
Marshman's Life of Havelock
3
Jameson's Sacred and Legendary Art…………..
·
4
12
Jenkin's Electricity and Magnetism.......
ΙΟ
Ferrold's Life of Napoleon
I
Johnson's Normans in Europe
3
Second Death
Patentee's Manual
Johnston's Geographical Dictionary....
Jukes's New Man....
Types of Genesis
21
Maunder's Popular Treasuries.
15
Kalisch's Bible Studies
15
Commentary on the Bible
15
Path and Goal.......
Keary's Outlines of Primitive Belief.......
Keller's Lake Dwellings of Switzerland..
Kerl's Metallurgy, by Crookes and Röhrig. 14
II
Landscapes, Churches, &c.......
Latham's English Dictionaries
Handbook of English Language
7
Lecky's History of England......
European Morals.........
Rationalism
Lessons of Middle Age
^^ ^H @ 2 + 76 720∞
7
7
I
2
HHH
56 15
асчеты
8
15
16
Martineau's Christian Life..........
Hours of Thought………..
Hymns....
Maxwell's Theory of Heat
May's History of Democracy
History of England
Melville's (Whyte) Novels and Tales
Mendelssohn's Letters
Merivale's Fall of the Roman Republic
General History of Rome
16
16
16
20
ΙΟ
I
I
18
4
2
2
Roman Triumvirates.........
Romans under the Empire
3
2
Leaders of Public Opinion.........
Leisure Hours in Town
Leslie's Political and Moral Philosophy
.....
Lewes's History of Philosophy
Lewis on Authority
Liddell and Scott's Greek-English Lexicons
Lindley and Moore's Treasury of Botany
Lloyd's Magnetism
Wave-Theory of Light…………………..
Longman's (F. W.) Chess Openings.........
Frederic the Great.....
German Dictionary
(W.) Edward the Third......
Lectures on History of England
St. Paul's Cathedral......
Loudon's Encyclopædia of Agriculture
...
4
a
3722
Monsell's Spiritual Songs......
7
12
1
.10 & 12
HHHH
17
II
14
18
16
12
12
7
16
6
aäväνww 552 2.
2 Moore's Irish Melodies, Iliustrated Edition
12
14
Gardening...11 & 14
Plants........
Lubbock's Origin of Civilisation
Ludlow's American War of Independence
Lyra Germanica
II
II
3
16
Lalla Rookh, Illustrated Edition..
Morris's Age of Anne
Mozley's Reminiscences of Oriel College...
Müller's Chips from a German Workshop.
Hibbert Lectures on Religion
Science of Language
Science of Religion
Selected Essays
...
Merrifield's Arithmetic and Mensuration...
Miles on Horse's Foot and Horse Shoeing
on Horse's Teeth and Stables………………..
Mill (J.) on the Mind
Mill's J. S.) Autobiography
Dissertations & Discussions
Essays on Religion ........
Hamilton's Philosophy
Liberty
Political Economy
Representative Government
Subjection of Women.........
System of Logic
Unsettled Questions
Utilitarianism
Millard's Grammar of Elocution..
Inorganic Chemistry ......
Wintering in the Riviera............
6
Miller's Elements of Chemistry
8
...
20
9
Milner's Country Pleasures
Mitchell's Manual of Assaying
20
Modern Novelist's Library
Monck's Logic
ΙΟ
19
19
4
4
+20 2020 2020 +20 2020 201
4
24
WORKS published by LONGMANS & CO.
Neison on the Moon......
Nevile's Horses and Riding
New Testament (The) Illustrated..
Newman's Apologia pro Vitâ Suâ….
Nicols's Puzzle of Life
Northcott's Lathes & Turning
Oliphant's In Trust
Orsi's Fifty Years' Recollections
Our Little Life, by A. K. H. B.
Overton's Life, &c. of Law.........
Owen's (R.) Comparative Anatomy and
Physiology of Vertebrate Animals....
Experimental Physiology
(J.) Evenings with the Skeptics
Perry's Greek and Roman Sculpture
Payen's Industrial Chemistry.....
Pewtner's Comprehensive Specifier
Piesse's Art of Perfumery
Pole's Game of Whist
Powell's Early England
Preece & Sivewright's Telegraphy.
Present-Day Thoughts...
Proctor's Astronomical Works ........
Scientific Essays
Public Schools Atlases
.....
8
19
12
3
II
13
17
4
7
4
ΙΟ
ΙΟ
6
Southey's Poetical Works
& Bowles's Correspondence
Stanley's Familiar History of Birds
Steel on Diseases of the Ox
Stephen's Ecclesiastical Biography.....
Stonehenge, Dog and Greyhound
Stubbs's Early Plantagenets
19
4
....
II
19
4
...
19
3
7
16
5
Sunday Afternoons, by A. K. H.B.
Supernatural Religion
Swinburne's Picture Logic
Tancock's England during the Wars,
1765-1820
Taylor's History of India
Ancient and Modern History
•
(Jeremy) Works, edited by Eden
Text-Books of Science...
Thomson's Laws of Thought
Thorpe and Muir's Qualitative Analysis
Three in Norway
••
12
Thome's Botany
13
.20
Thorpe's Quantitative Analysis
14
20
3
10
7
...8&9
II
8
22 7
20
Rawlinson's Ancient Egypt
Sassanians
Recreations of a Country Parson
Recve's Cookery and Housekeeping
Reynolds's Experimental Chemistry
Rich's Dictionary of Antiquities
Rivers's Orchard House
Rose Amateur's Guide.......
Rogers's Eclipse of Faith and its Defence 15
Thudichum's Annals of Chemical Medicine
Tilden's Chemical Philosophy
Practical Chemistry
Todd on Parliamentary Government..
Trench's Realities of Irish Life
Trevelyan's Life of Fox
....
ma ma
16
ΙΟ
ΙΟ
6
ΙΟ
ΙΟ
16
12
ΙΟ
12.
2
6
I
Trollope's Warden and Barchester Towers 18
Twiss's Law of Nations
....
5
Tyndall's (Professor) Scientific Works... 9 & 10
Unawares
Unwin's Machine Design
18
12
ΙΟ
7
Ure's Arts, Manufactures, and Mines
14
II
II
Ville on Artificial Manures.......
14
Roget's English Thesaurus
7
Ronalds' Fly-Fisher's Entomology
19
Rowley's Rise of the People
Settlement of the Constitution
...
Rutley's Study of Rocks
ΙΟ
mma
Walker on Whist......
20
3
Walpole's History of England
I
Warburton's Edward the Third
Watson's Geometery
3
10
Watts's Dictionary of Chemistry
12
Samuelson's Roumania
16
Webb's Celestial Objects.
8
Sandars's Justinian's Institutes
5
Weld's Sacred Palmlands
17
Sankey's Sparta and Thebes
3
Wellington's Life, by Gleig
4
Seaside Musings
....
7
Whately's English Synonymes
7
Scott's Farm Valuer
Rents and Purchases
Seebohm's Oxford Reformers of 1498....
Protestant Revolution
Sennett's Marine Steam Engine
Sewell's Passing Thoughts on Religion
Preparation for Communion
Private Devotions
Stories and Tales
Shelley's Workshop Appliances
21
Logic and Rhetoric
5
21
2 3
White's Four Gospels in Greek.....
and Riddle's Latin Dictionaries
Wilcocks's Sea-Fisherman
15
noo
8
19
13
Williams's Aristotle's Ethics.............
5
16
...
Willich's Popular Tables
21
16
16
18
Wilson's Studies of Modern Mind
Wood's Works on Natural History
Woodward's Geology
6
IO
II
IO
Short's Church History
14
Smith's (Sydney) Wit and Wisdom
6
Yonge's English-Greek Lexicons
8
(Dr. R. A.) Air and Rain
8
Youatt on the Dog and Horse
19
(R. B.)Carthage & the Carthaginians
2
Rome and Carthage
3
(J.) Shipwreck of St. Paul
15
Zeller's Greek Philosophy
3
Spottiswoode & Co. Printers, New-street Square, London.
AUG 21 1919

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