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SEPARABIT
MDCCLXXXIII
Elton Hall
6
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#314
1768
;
:
J. J. Borby
1
The GREAT ORRERY
Four Feet in Diameter. Made by
THO: WRIGHT Mathematical Inftru=
-ment-maker TO HIS MAJESTY
For the Royal Academy at
PORTSMOUTH
Now & Cofe;
at the Same Shop.
atthey
OPIS 20
M 301, H, 1OP.
PTE20
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TARCH
20
10
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Who makes Orrery's of different forts
be seen at his Shop in
as
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FLEET-STREET
ARCTIC
.
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MOVE ABLE
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Where is Sold a Large Print of the Orrery with the Explanation on a Sheet of Imperial Paper, Price. 2:
1
A
1
Harris, Johns
THE
Deſcription and Use
OF THE
GLOBES,
[
AND THE
ORRERY, Un
To which is prefix'd,
By Way of INTRODUCTION,
A brief Account of the SOLAR SYSTEM.
By 70 SEPH HARRIS,
TEACHER of the MATHEMATICS.
The NINTH EDITION.
LONDON:
:
Printed for B. COLE, at the Orrery, near the
Globe Tavern in Fleet-Street, late the Shop of Mr.
THOMAS WRIGHT, Inftrument-Maker to His
MAJESTY; and E. CUSHEE, near St. Dunstan's
Church, Fleet-freet. MDCCLXIII.
J
170
}
#
!
Advertiſement.
}
}
T
HE great Encouragement Mr,
Wright has had for many Years
paſt in making large Orreries, with the
Motions of all the Planets and Satellites,
and the true Motion of Saturn's Ring,
has made him fo ready and perfect, that
Gentlemen may depend on having them
made reaſonable and found, not liable
to be out of Order.
As may be ſeen
be ſeen by one he made for
Mr. Watts's Academy in Tower-Street.
Another for his Majefty at Kenfigton.
Another for the New Royal Academy
at Portſmouth.
Another for his Grace the Duke of
Argyle (late Lord Ila.)
And ſeveral other large ones for No-
blemen and Gentlemen.
The above, and all other Mathemati
cal, Philoſophical, and Optical Inſtru-
ments, are now made in the most com-
plete Manner, by B. Cole, Servant to
Mr. Wright at the Time of the above
being made, and Succeffor to him in
the fame Trade and Bufinefs.
11:
•
1
3
Hist. of Sei,
Halliday
5-19-20²
11738
THE
CONTENTS:
The INTRODUCTION: Containing a brief Account of the
Solar Syftem and of the fixed Stars.
SECT. I.
F the Order and Periods of the Primary
Planets revolving about the sun; and of
the Secondary Planets round their respective Primaries
Of the Primary Planets
nets
Of the Secondary Planets
1.
5
Of the Annual and Diurnal Motion of the Pla-
That the Planets are Opaque and Globular
7
That the Earth is Placed betwixt the Orbits of
Mars and Venus
That the Planets tûrn round the Sun
That the Earth alſo turns round the Sun
ibid.
15
How the Annual and Diurnal Motion of the Planets
are computed
ibid.
How the relative Distance of the Planets from the
Sun are determined
puted.
mined
18
How their abfolute Distances from the Sun are com-
23
How the Magnitudes of the Planets are deter
nets
26
Why the Moon appears bigger than any of the Pla-
A Table. of the Distances, Magnitudes, Periodical
ana Diurnal Revolutions of the Planets
27.
28
Of Comets
SECT. II. Of the Fixed Stars
29
Diftances from us
That the fixed Stars are luminous Bodies, at immenfe
32
ibid.
Of Telescopical Stars
The Stars digefted into Conftellations
Of the Galaxy, or Milky Way
A 2
35
36
8
TH
The CONTENTS
6161666161616161006)
The DESCRIPTION and USE of the
CELESTIAL and TERRESTRIAL
GLOBES.
>
་
響
​THE Geomètrical Definition of a Globe, and of the
principal Ufe of the Artificial Globes
42
45
That there will be the fame Prafpect of the fixed Stars,
whether the Spectator be placed in the Sun, or on the
Earth
SECT. I. An Explanation of the Circles of the Sphere, and
of fome Aftronomical Terms arifing therefrom
Of the Divifion of Time
Of the Atmosphère
SECT. II. Geographical Definitions
Of the Situation of Places upon the Earth
Of Zones and Climates
47
69
81
84
ibid.
مو
Of the Poetical Rifing and Setting of the Stars
Of the Surface of the Earth, confidered as it
pofed of Land and Water
Of the appurtenances of the Globe
96
is com-
ibid.
1of
SECT. III: The Ufe of the Globes
PROBLEM I. To find the Latitude and Longitude of any
given Place upon the Globe; and in the contrary, the
Latitude and Longitnde being given to find the Place 104
PROB. II. To find the Difference of Latitude betwixt any
two given Places
106
ibid.
PROB. III. To find the Difference of Longitude betwixt any
two given Places
PROB. IV. Any Place being given; to find all thofe
Places that are in the fame Latitude with the fain
Place
107
PROB. V. The Day of the Month being given; to find the
Sun's Place in the Ecliptic, and his Declination Fos
PROB. VI. To rectify the Globe for the Latitude, Zenith,
and Sun's Place
109
PROB
1
The CONTENTS.
V
110
PROB. VII. To find the Distance between any troo givin
Places upon the Globe, and to find all thofe Places
upon the Globe that are at the fame Difrance from a
given Place
PROB. VIII. To find the Angle of Pofition of Places;
or the Angle form'd by the Meridian of one Place,
and a great Girele paſſing through both the Places
Pròs, IX. To find the Antoci, Pericci, and Antipodes
to any given Place
113
PROB. X. The Hour of the Day at one Place being given;
to find the correfpondent Hour (or what o'Clock it is
✯ that Time) at any other Place
114
PROB. XI. The Day of the Month being given; to find
thofe Places on the Globe where the Sun will be Vertical,
or in the Zenith, that Day
115
PROB. XII. A place being given in the Torrid Zone; to
find thofe tavo Days in which the Sun fhall be Vertical to
the fame
116
PROB. XIII. To find where the Sun is Vertical at any
given Time affigned; or, the Day of the Month and
the Hour at any Place (Suppofe London) being given
`to find in what Place the Sun is Vertical at that very
Time
´PROB. XIV. The Day and the Hour of the Day at one
Place being given; to find all thofe Places upon the
Earth where the San is then Rifing, Setting, Culmi-
nating (or on the Meridian), alſo where it is Daylight,
Twilight, Dark Night, Midnight; where the Twilight
then begins, and where it ends; the Height of the Sun
in any Part of the illuminated Hemisphere; alfo his De-
ſcription in the obfcure Hemiſphere
117
PROB. XV. The Day of the Month being given, to fhew,
at one View, the Length of Day and Night in all
Places upon the Earth at that Time; aud to explain
bow the Viciffitudes of Day and Night are really made
by the Motion of the Earth round her Axis, in 24 Hours,
the Sun ftanding ftill
ibid.
119
PROB. XVI. To explain in general the Alteration of Sea-
fons, or Length of the Days and Nights, made in all
Places of the World, by the Sun's, or the Earth's annual
Motion in the Ecliptic
121
PROB. XVII. To fhew by the Globe, at one View, the
Length of the Days and Nights in any particular Place,
at all Times of the Year
128
PROE:
vi
The CONTENTS.
1
PRÓB. XVIII. The Latitude of any Place, not Exceeding
69 Degrees, and the Day of the Month being given;
to find the Time of Sun-rifing and Setting, and the
Length of the Day and Night-
136
PROB. XIX. To find the Length of the longest and shortest
Day and Night in any given Place, not exceeding
66 ½ Degrees of Latitude`.
137
PROB. XX. To find in what Latitude the longest Day
is, of any given Length less than 24 Hours
139
PROB. XXI. A Place being given in one of the Frigid
Zones (Suppose the Northern) to find what Number of
Days (of 24 Hours each) the Sun doth conftantly shine
upon the fame, how long he is abfent, and alfo the firft
and laft Day of his Appearance
PROB. XXII. To find in what Latitude the longest
Day is, of any given Length less then 182 Natural
Days
PROB. XXIII. The Day of the Month being given; to
find when the Morning and Evening Twilight begins
and ends, in any Place upon the Globe
140
141
144
142
PROB. XXIV. To find the Time when total Darkneſs
ceaſes, or when the Twilight continues from Sun-fetting
to Sun-rifing, in any given Place
PROB. XXV. The Day of the Month being given to find
thofe Places of the Frigid Zones, where the Sun begins
to fhine conftantly without fetting; and alfo thofe Places
where he begins to be totally abfent
1
146
Day and
149.
Day, and
PROB. XXVI. The Latitude, the Sun's Place, and his
Altitude being given; to find the Hour of the
the Sun's Azimuth from the Meridián
PROB. XXVII. The Latitude, Hour of the
the Sun's Place being given; to find the Sun's Alti-
tude
150
PROB. XXVIII. The Latitude of the Place, and the
Day of the Month being given; to find the Depreffion
of the Sun below the Horizon, and his Azimuth at any
Hour of the Night
151
PROB. XXIX. The Latitude of the Sun's Place and his
Azimuth being given, to find his Altitude and the Hour
152
PROD. XXX. The Latitude, the Sun's Altitude, and his
Azimuth being given ; to find his Place in the Ecliptic,
and the Hour
ibid.
PROT!
The CONTENTS.
vii
{
PROB. XXXI. The Declination and Meridian, Altitude
of the Sun, or of any Star being given; to find the
Latitude of the Place
153
PROB. XXXII. The Day and Hour of a Lunar Ecliple
being known; to find all thofe Places upon the Globe in
which the fame will be visible
154
PROB. XXXIII. The Day of the Month, and Hour of the
Day, according to our Way of reckoning in England,
being given; to find thereby the Babylonifh, Italick,
and the Jewish or Judaical Hour
155
PROB. XXXIV. To find the Right Afcenfion and Decli-
nation of the Sun, or any Fixed Star.
156
PROB. XXXV. To find the Longitude and Latitude of a
given Star
158
PROB. XXXVI. The Latitude of the Place, the Day of
the Month, and the Hour being given; to find what Stars
are then rifing and fetting, what Stars are culminating,
or on the Meridian, and the Altitude and Azimuth of any
Star above the Horizon and alfo how to diftinguish the
Stars in the Heavens one from the other, and to know
them by their proper Names
PROB. XXXVII. The Latitude of the Place being given;
to find the Amplitude, Oblique, Afcenfion and Defcenfion,
Afcenfional Difference, Semi-diurnal Arch, and the Time
of Continuance above the Horizon, of any given Point
in the Heavens
159
162
PROB. XXXVIII. The Latitude and the Day of the
Month being given; to find the Hour when any known
Star will be on the Meridian, and also the Time of its
rifing and Setting
165
PROB. XXXIX. To find at what Time of the Year a
given Star will be upon the Meridian, at a given Hour
of the Night
166
PROB. XL. The Day of the Month, and the Azimuth of
any known Star being given; to find the Hour of the
Night
167
PROB. XLI. Two known Stars, having the fame Azi-
muth, or the fame Height, being given; to find the
Hour of the Night
168
PROB. XLII. The Latitude, Day of the Month, and the
Altitude of any known Star being given; to find the
Hour of the Night
2
165
PROB.
·
Viu
The CONTENTS,
PROB. XLIII. Having the Latitude of the Plage to find
the Degree of the Ecliptic, which rifes or fets with a
given Stars and from thence to determine the Time of
its Coſmical and Achronical Riſing and Setting 171
PROB. XLIV. Having the Latitude of the Places to find
the Time when a Star riſes and ſets Heliacally 172
PROB. XLV. To find the Place of any Planet upon the
Globe, fo by that Means to find its Place in the Hea-
vens; alſo to find at what Hour any Planet will riſe
or fet, or be on the Meridian, at any Day in the Year
173
Prob. XLVI. To find all that Space upon the Earth
where an Eclipfe of one of the Satellites of Jupiter quill
be visible
The DESCRIPTION of the ORRERY.
175
377
Of the Motions of the Planets in general -- po 183
Of the Stations and Retrogradations of the Planets
Of the Annual and Diurnal Motion of the Earth
186
194
Of the Phafes of the Moon, and of her Motion in her
Orbit
201
Of the Eclipfes of the Sun and Moon
Of the Eclipfes of Jupiter's Satellites
208
A12
{
1
THE
*******
*
THE
INTRODUCTION,
*
CONTAINING
A Brief Account of the SOLAR
SYSTEM, and of the FIXED
STARS.
SECT. I.
Of the Order and Periods of the Primary
Planets revolving about the Sun; and
of the Secondary Planets round their re-
Spective Primaries.
**** HE Sun is placed in the Midft
T of an immenſe Space, wherein
fix opaque ſpherical Bodies re-
volve about him as their Center.
Thefe wandring Globes are called the
Planets, who, at Different Distances, Planets,
B
and
2
The INTRODUCTION.
and in different Periods, perform their
Revolutions from Weft to Eaft, in the
following Order:
1.
Mercury is neareſt to the Sun of
all the Planets, and performs its Courſe
in about three Months. 2. ? Venus in
about ſeven Months and a half.
half. 3. →
The Earth in a Year. 4. 3 Mars in
about two Years. 5. 4 Jupiter in twelve.
And lastly, ↳ Saturn, whofe * Orbit in-
cludes all the reſt, ſpends almoſt 30 Years
in one Revolution round the Sun. The
Diſtances of the Planets from the Sun
are nearly in the fame proportion, as
they are repreſented in Plate 1. viz.
Suppofing the Diſtance of the Earth
from the Sun to be divided into 10
equal Parts; that of Mercury will be
about 4 of theſe Parts
of theſe Parts; of Venus 7; of
Mars 15; of Jupiter 52; and that of
Saturn 95.
The
The Characters placed before the Names of the Pla-
nets, are for Brevity's Sake commonly made uſe of by
Aftronomers, inſtead of the Words at length, as o̟ for
Venus, &c.
By the Orbit of a Planet is commonly underſtood
the Tract or Ring, deſcribed by its Center round the
Sun, but by the Plane of the Orbit is meant a flat Sur-
face extended every Way thro' the Orbit infinitely.
}
+
Plate 1.
!
i
Page 2
THE SOLAR SYSTEM or the Orbits of the Planets
-according to their mean
1
}
2
C
3
+
1
I
14
h
}
}
distances from the Sun
MB. The Orbits of the
greater in
Secondary
Planets are
here 50
times
e diftances of the Primary
proportion than the
Planets from the Suni
Saturn
Jupiter
Magnitudes
Mars
theEarth
Venus
Mercury
• the Moon
the Sun Inches Diameter
according to this proportion
R. Cafhce foulp.
Sect. I.
Of the SOLAR SYSTEM.
The Orbits of the Planets are not all
in the fame Plane, but variouſly inclined
to one another; fo that fuppofing one
of them to coincide with the above
Scheme, the others will have one half
above, and the other half below it; in-
terfecting one another in a Line paffing
through the Sun. The Plane of the
Earth's Orbit is called the Ecliptic; and
this the Aftronomers made the Stand-
ard to which the Planes of the other
Orbits are judged to incline. The
right Line paffing thro' the Sun, and
the common Interfection of the Plane
of the Orbit of any Planet and the E-
cliptic, is called the Line of the Nodes Nodes
of that Planet; and the Points them-
felves, wherein the Orbit cuts the Eclip-
tic, are called the Nodes:
3
The Inclinations of the Orbits of the
Planets to the Plane of the Ecliptic
are as follows, viz. the Orbit of Mercury
maks an Angle with it of almoft 7 De-
grees; that of Venus fomething above
3
Degrees; of Mars, a little lefs then 2
Degrees; of Jupiter, 1 Degree; and
of Saturn, about 2 Degrees. The
Orbits of the Planets are not Circles, but
Ellipfes or Ovals. What an Ellipfis is,
may be eaſily understood from the
following
B 2
2
I
उ
}
The INTRODUCTION.
following Deſcription. Imagine two
fmall Pegs fixed upright on any Plane,
and ſuppoſe them tied with the Ends of
a Thread fomewhat longer than their
Diſtance from one another: Now if a
Pin be placed in the double of the Thread
and turned quite round, (always ſtretch-
ing the thread with the fame Force) the
Curve defcribed by this Motion is an
Ellipfis. The two Points where the
Pegs ftood, (about which the Thread
was turned) are called the Foci of that
Ellipfis; and if, without changing the
Length of the Thread, we alter the
Pofition of the Pegs, we fhall then have
an Ellipfis of a different kind from the
former; and the nearer the Focus's are
together, the nearer will the Curve de-
fcribed be to a Circle; until at laft the
two Focus's coincide, and then the Pin in
the doubling of the Thread will defcribe
a perfect Circle. The Orbits of all the
Planets have the Sun in one of their
Focus's and half the Diſtance between
Excentri- the two Focus's is called the Excentri-
city of the Orbits. This Excentricity
is different in all the Planets, but in
moſt of them fo fmall, that in little
Schemes or Inftruments, made to repre-
fent the Planetary Orbits, it need not be
confidered.
city.
1
The
Sect. 1. Of the SOLAR SYSTEM.
5
Thefe Secondary
Planets.
The Six Planets above-mentioned, Primary
are called Primaries, or Primary Pla- Planets.
nets; but befides thefe, there are ten
other leffer Planets, which are called
Secondaries, Moons, or Satellites. Theſe
Moons always accompany their re-
fpective Primaries, and perform their
Revolutions round them, whilſt both
together are alſo carried round the Sun.
Of the Six Primary Planets, there are
but three, as far as Obfervation can
affure us, that have theſe Attendants,
viz. the Earth, Jupiter, and Saturn. -
I
27 3/3/3
The Earthis attended by the Moon, who
performs her Revolution in about 27
Days, at the Diſtance of about 30 Dia-
meters of the Earth from it; and once
a Year is carried round the Sun along
with the Earth.
3
Moons,
Jupiter has four Moons, or Satellites ; Jupiter's
the firft, or innermoft, performs its
its four
Revolution in about one Day and 184
Hours, at the Diſtance of 5 Semidia-
meters of Jupiter from his Center ;
the ſecond revolves about Jupiter in 3
Days 13 Hours, at the Diſtance of
9
of his Semidiameters; the third in 7
Days and 4 Hours, at the Diſtance of
14 Semidiameters; the fourth and out-
ermoft
3
B 3
The INTRODUCTION.
1
Saturn
Moons.
1
ermoſt performs its Courſe in the Space
of 16 Days 17 Hours; and is diftant
from Jupiter's Center, 25 of his Semi-
diameters.
ड
3
उ
}
Saturn has no lefs than five Satellites;
has five the first, or innermoft, revolves about
him in 1 Day and 21 Hours, at the Dif-
tance of 4 Semidiameters of from
3 ↳
3/
his Center; the fecond compleats his
Period in 2 Days, at the Diſtance of
5 of his Semidiameters; the third, in
about 4 Days, at the Diſtance of 8
4/2/
Semidiameters; the fourth, performs its
Courſe in about 16 Days, at the Diſt-
ance of 18 Semidiameters; the fifth and
outermoft takes 79 Days to finiſh his
Courſe, and is 54 Semidiameters of Sa-
turn diftant from his Center. The Sa-
tellites, as well as their Primaries, per-
form their Revolutions from Weft to
Eaft: The Planes of the Orbits of the
Satellites of the fame Planet are vari-
ouſly inclined to one another, and con-
fequently are inclined to the Plane of
the Orbits of their Primary.
Saturn's
Ring.
I
उ
Befides theſe Attendants, Saturn is en-
compaffed with a thin plain Ring, that
does no where touch his Body: The Di-
ameter of this Ring is to the Diameter
of
Sect. 1. Of the SOLAR SYSTEM.
7
of Saturn as 9 to 4; and the void Space
between the Ring and the Body of Saturn
is equal to the breadth of the Ring it-
felf; fo that in fome Situations the Hea-
vens may be feen between the Ring and
his Body. This furprizing Phænomenon
of Saturn's Ring is a modern Diſcovery;
neither were the Satellites of Jupiter
and Saturn known to the Ancients.
The Jovial Planets were firſt diſcovered
by the famous Italian Phoilofopher Ga-
lilæus, by a Teleſcope which he firſt
Invented; and the celebrated Caffini,
the French King's Aftronomer, was the
firit that faw all the Satellites of Saturn;
which, by Reaſon of their great Diſtan-
ces from the Sun, and the Smallneſs of
their own Bodies, cannot be ſeen by us,
but by the Help of
very good Glaffes.
The Motion of the primary Planets Annual
round the Sun (as alfo of the Satellites Motion.
round their reſpective Primaries) is cal-
led their Annual Motion; becauſe they
have one Year or alteration of Seafons
compleat in one of theſe Revolutions.
Beſides this Annual motion, four of the
Planets, viz. Venus, the Earth, Mars, and
Jupiter revolve about their own Axis,from
Weft to Eaft; and this is called their Di- Diurnal
urnal Motion. For by this Rotation each Motion.
Point -
B 4
The INTRODUCTION.
Diurnal
Motion of
the,f,
Point of their Surfaces is carried fuccef
fively towards or from the Sun, who al-
ways Illuminates the Hemiſphere which
is next to him, the other remaining ob-
ſcure; and while any Place is in the
Hemiſphere, illuminated by the Sun, it
is Day, but when it is carried to the
obfcure Hemiſphere, it becomes Night;
and fo continues, until by this Rotation
the faid Place is again enlightened by
the Sun.
The Earth performs its Revolution
and 24. round its Axis in 23 Hours 56 Minutes,
* Venus in 24 Days 8 Hours; Mars in
24 Hours and 40 Minutes; and Jupiter
and moves round his own Axis in 9 Hours
likewife and 56 Minutes. The Sun alfo is found
turn to turn round his Axis from the Weft to
Eaft in 27 Days: And the Moon which
is neareſt to us of all the Planets, re-
volves about her Axis in a Month, or in
the fame ſpace of Time that fhe turns
round
their
Axis.
1
I
round
*N..B. According to Biachini's Obfervations, Venus's
Axis inclines 75 Degrees from the Perpendicular to the
Plane, the Ecliptic (which is 514 Deg. more than the
Axis of our Earth) her Tropics are onl, 15 Deg. from
her Poles; and her Polar Circles at the fame Diſtance
from her Equator; fo that the Sun's greateſt Declination
on each Side of her Equator is 75 Deg. by which fhe
muft undergo a much greater Variety of Seafons then
we do on our Earth.
** .
ነ
}
Sect, 1. Of the SOLAR SYSTEM,
round the Earth; fo that the Lunarians
have but I Day throughout the Year.
I. The Planets are all Opaque Bodies, The Pla-
having no Light but what they borrow nets are
from the Sun: For that Side of them and Glo
Opaque
which is next towards the Sun, has al-bular.
ways been obferved to be illuminated,
in what Pofition foever they be; but the
Oppofite Side, which the Solar Rays do
not reach, remains dark and obſcure;
whence it is evident that they have no
Light but what proceeds from the Sun;
for if they had, all Parts of them would,
be lucid without any Darkneſs or Sha-
dow. The Planets are likewife proved
to be Globular; becauſe, let what part
foever of them be turned towards the
Sun, its Boundary, or the Line feparat-
ing that Part from the Oppofite, always
appears to be Circular; which could not
happen if they were not Globular.
round the
II. That the Earth is placed betwixt The Pla-
the Orbs of Mars and Venus, and that nets turn
☀,,, 4, and ½, do all turn round Sun.
f,
the Sun, is proved from Obſervations as
follow:
1. Whenever Venus is in Conjunction
with the Sun, that is, when ſhe is in the
fame
10
The INTRODUCTION.
fame Direction from the Earth, or to-
wards the fame Part of the Heavens the
Sun is in; fhe either appears with a
bright and round Face like a Full Moon,
or elſe diſappears: Or if the is viſible,
the appears horned like a new Moon;
which Phænomena could never happen
if
did not turn round the Sun, and
was not betwixt him and the Earth :
For fince all the Planets borrow their
Light from the Sun, it is neceſſary that
g's lucid Face fhould be towards the
Sun; and when the appears fully illu-
minated, fhe fhews the fame Face to the
Sun and Earth; and at that Time ſhe
muſt be above or beyond the Sun; for
in no other Pofition could her illumi-
nated Face be ſeen from the Earth.
Farther, when ſhe diſappears, or if vifible,
appears horned; that Face of her's which
is towards the Sun is either wholly turn-
ed from the Earth, or only a ſmall Part
of it can be ſeen by the Earth ; and in
this Cafe fhe muft of Neceffity be betwixt
us and the Sun. Let S be the Sun, T
Fig. 1. 1. the Earth, and V Venus, having the fame
Façe prefented both towards the Sun
and Earth; here it is plain that the Sun
is is betwixt us and Venus, and therefore
we muſt either place Venus in an Orbit
round the Sun, and likewife betwixt him
Plate 2.
and
Sect. I Of the SOLAR SYSTEM.
11
•
>
and us, as in Fig. 1. or elſe we muſt
make the Sun to move round the Earth
in an Orbit within that of Venus, as in
Fig. 2. Again, after Venus diſappears,
or becomes horned at her * 6 with the
o, fhe then muſt be betwixt us and the
Sun, and muſt move either in an Orbit
round the Sun, and betwixt us and him,
as in Fig. 1. or elſe round the Earth,
and betwixt us and the Sun, as in Fig. 2.
But Venus cannot move fometimes within
the Sun's Orbit, and ſometimes without
it, as we muſt ſuppoſe if ſhe moves
round the Earth; therefore it is plain
that her Motion is round the Sun.
Befides the foregoing, there is another
Argument to prove that Venus turns round
the Sun in an Orbit that is within the
Earth's, becauſe ſhe is always obferved
to keep near the Sun, and in the fame
Quarter of the Heavens that he is in,
never receding from him more than
about of a whole Circle; and there-
fore ſhe can never come in Oppoſition
to him; which would neceffarily hap-
pen, did the perform her Courſe round
the Earth either in a longer or ſhorter
Time than a Year. And this is the
Reaſon
I
8
6 is a Mark commonly uſed for Conjunction: thus
with the O, is to be read Conjunction with the Sun.
!
$2
The INTRODUCTION.
nus is al-
Why Ve- Reaſon why Venus is never to be ſeen
ways ei- near Midnight, but always either in the
ther our Morning or Evening, and at moſt not
Morning above three or four Hours before Sun-
ing Star. rifing or after Sun-fetting. From the
or Even-
The Or-
Time of's fuperior Conjunction (or
when ſhe is above the Sun) fhe is more
Eafterly than the Sun, and therefore
fets later, and is feen after Sun-fetting;
and then ſhe is commonly called the
Evening Star. But from the Time of
her inferior Conjunction, till fhe comes
again to the fuperior, fhe then appears
more Wefterly than the Sun, and is
only to be ſeen in the Morning before
Sun-rifing, and is then called the Morn-
ing Star.
After the fame Manner we prove
that Mercury turns round the Sun, for
he always keeps in the Sun's Neigh-
bourhood, and never recedes from him
fo far as Venus does, and therefore the
Orbit of muft lie within that of ;
and on the Account of his Nearnefs to
the Sun, he can feldom be feen without
a Teleſcope.
Mars is obferved to come in Oppoſi-
bit of tion, and likewife to have all other Af-
cludes the pects with the Sun; he always preferves
Mans in-
Earth's.
a round
Sect. 1. Of the SOLAR SYSTEM.
13
a round, full, and bright Face, except
when he is near his Quadrate Afpect,
when he appears fomewhat gibbous,
like the Moon three or four Days before
or after the full: Therefore the Orbit
of a muſt include the Earth within it,
and alſo the Sun; for if he was betwixt
the Sun and us at the Time of his
inferior Conjunction, he would either
quite difappear, or appear horned, as
Venus and the Moon do in that Pofition.
Let S be the Sun, T the Earth, and Fig. 3,
A P Mars, both in his Conjunction
and Oppofition to the Sun, and in both
Pofitions full; and BC Mars at his
Quadratures, when he appears fome-
what gibbous from the Earth at T.
"Tis plain hence, that the Orbit of Mars
does include the Earth, otherwife he
could not come in Oppofition to the
Sun; and that it likewife includes the
Sun, elſe he could not appear full at his
Conjunction.
Mars, when he is in Oppofition to
the Sun, looks almoft feven Times
larger in Diameter than when he is in
Conjunction with him, and therefore
muſt needs be almoſt ſeven times nearer
to us in one Pofition than in the other;
for the apparent Magnitudes of far
diftant
14
The INTRODUCTION
}
rior Pla-
mets.
diſtant Objects increaſe or decreaſe in
Proportion to their Diſtances from us.
But Mars keeps always nearly at the
fame Diſtance from the Sun; therefore
it is plain that it is not the Earth but
the Sun that is the Center of his Mo-
tion.
It is proved in the fame Way, that
Jupiter and Saturn have both the Sup
and the Earth within their Orbits, and
that the Sun, and not the Earth is the
Center of their Motions; altho' the
Difproportion of the Diſtances from the
Earth is not fo great in Jupiter as it is
in Mars, nor fo great in Saturn as it is
in Jupiter, by Reaſon that they are at a
much greater Diſtance from the Sun.
Inferior We have now fhewn that all the Pla-
and Supe-nets turn round the Sun, and that Mer-
cury and Venus are included between
him and the Earth, whence they are
called the Inferior Planets, and that the
Earth is placed between the Orbits of
Mars and Venus, and therefore included
within the Orbits of Mars, Jupiter and
Saturn, whence they are called the Su
perior Planets: And fince the Earth is
in the Middle of theſe moveable Bodies,
and is of the fame Nature' with them,
We
Sect. I. Of the SOLAR SYSTEM.
15
f
we may conclude that ſhe has the fame
fort of Motions; but that ſhe turns
round the Sun is proved thus:
9
ſtand ſtill
Sun.
All the Planets feen from the Earth TheEarth
appear to move very unequally, as does not
fometimes to go fafter, at other times but turns
flower ; ſometimes to go backwards, round the
and fometimes to be ſtationary, or not to
move at all; which could not happen
if the Earth ftood still. Let S be theFig. 4.
Sun, T the Earth, the great Circle
ABCD the Orbit of Mars, and the
Numbers 1, 2, 3, &c. its equable Mo-
tion round the Sun; the correfpondent
Numbers 1, 2, 3, &c. in the Ĉircle a,
b, c, d, the Motion of Mars, as it would
be ſeen from the Earth. It is plain
from this Figure, that if the Earth
ftood still, the Motion of Mars will be
always progreffive, (tho' fometimes very
unequal;) but fince Obfervations prove
the contrary, it neceffarily follows, that
the Earth turns round the Sun.
Diurnal
The annual Periods of the Planets The An-
round the Sun are determined by care-nual and
fully obſerving the Length of Time Motions
fince their Departure from a certain of the
Point in the Heavens, (or from a fix'dhow com-
Star) until they arrive to the fame again.puted.
By
Planets
1
$6
The INTRODUCTION.
}
By theſe Sorts of Obfervations the An-
cients determined the periodical Revo-
lutions of the Planets round the Sun,
and were ſo exact in their Computations,
as to be capable of predicting Eclipfes
of the Sun and Moon. But fince the
invention of Teleſcopes, Aftronomical
Obfervations are made with greater Ac-
curacy, and of Confequence our Tables
are far more perfect than thofe of the
Ancients. And in order to be as exact
as poffible, Aftronomers compare Ob-
fervations made at a great Diſtance of
Time from one another, including fe-
veral Periods; by which means, the
Error that might be in the whole is in
each Period fubdivided into fuch little
Parts as to be very inconfiderable. Thus
the mean Length of a Solar Year is
known even to Seconds.
The Diurnal Rotation of the Planets
round their Axis, was diſcovered by
certain Spots which appear on the Sur-
faces. Theſe Spots appear firft in the
Margin of the Planets Disks, (or the
Edge of their Surfaces) and feem by
Degrees to creep toward their Middle,
and ſo on, going ftill forward, till they
come to the oppofite Side or Edge of
the Disk, where they fet or diſappear;
and
Sect. I,
Of the SOLAR SYSTEM
1
and after they have been hid for the
fame Space of Time, that they were vi-
fible, they again appear to rife in or
near the fame Place, as they did at firſt,
then to creep on progreffively, taking
the fame Courfe as they did before.
Theſe Spots have been obferved on the
Surfaces of the Sun, Venus, Mars, and
Jupiter; by which means it has been
found that theſe Bodies turn round their
own Axis in the Times before-menti-
oned. It is very probable that Mercury.
and Saturn have likewiſe a Motion round
their Axis, that all the Parts of their
Surface may alternately enjoy the Light
and Heat of the Sun, and receive fuch
Changes as are proper and convenient
for their Nature. But by Reaſon of
the Nearness of to the Sun, and 4's
X
immenſe Diſtance from him, no Obſer-
vations have hitherto been made where-
by their Spots, (if they have any) could
be difcovered, and therefore their diur-
nal Motions could not be determined.
The diurnal Motion of the Earth is
Computed from the apparent Revoluti-
on of the Heavens, and of all the Stars
round it, in the Space of a Natural Day.
The Solar Spots do not always remain
the fame, but fometimes old ones vaniſh,
and afterwards others fucceed in their
Room;
C
>
Co
The INTRODUCTION.
How the
Relative
Diſtances
Room; fometimes ſeveral ſmall ones ga-
ther together and make one large Spot,
and fometimes a large Spot is feen to be
divided into many ſmall ones. But not
withſtanding thefe Changes, they all turn
round with the Sun in the fame Time.
The relative Diſtances of the Planets
from the Sun, and likewife from each
of the other, are determined by the following
Planets Methods: Firft, the Diſtance of the
two inferior Planets & and from the
Sun, in reſpect of the Earth's Diſtance
from him, is had by obferving their
grea eft Elongation from the Sun as they
are ſeen from the Earth.
from the
Sun are
deter-
mined.
Elonga-
tion.
?
The greateſt Elongation of Venus is
Fig. 5. found by Obfervation to be about 48
Degrees, which is the Anglè S T ? ;
whence, by the known Rules of Trigo-
nometry, the Proportion of S, the
mean Diſtance of Venus from the Sun
to S T, the mean Diſtance of the Earth
from him may be eafily found. After
the fame Manner, in the right-angled
Triangle S Tg, may be found the
Diſtance Sy of Mercury from the Sun.
And if the mean Diſtance of the Earth
from the Sun S T be made 1000, the
mean Diſtance of Venus Sg from the
Sun
Sect. I. Of the SOLAR SYSTEM,
19
Sun will be 723; and of Mercury S ☀
387: And if the Planets moved round
the Sun in Circles, having him for their
Center, the Diſtances here found would
be always their true Diſtances: But as
they move in Ellipfes, their Diſtances
from the Sun will be fometimes greater,
and ſometimes lefs. Their Excentricities
are computed to be as follows; viz,
10
Excent. of Venus
S Mercury 80
of the Parts
5
above-men-
Earth 169
tioned.
The Diſtances of the fuperior Planets
viz, ♂ '4, and, are found by com-
paring their true Places, as they are
feen from the Sun, with their apparent
Places, as they are feen from the Earth.
Let S be the Sun, the Circle ABC the Fig. 6.
Earth's Orbit, AG a Line touching the
Earth's Orbit, in which we'll fuppofe
the fuperior Planets are feen from the
Earth in the Points of their Orbitș ♂
>
>
24, h; and let DEFGH be a Portion
of a great Circle in the Heavens, at an
infinite Diftance: Then the Place of
Mars feen from the Sun is D, which is
called his true or Heliocentric Place; Heliocen
but from the Earth he will be feen in Geocentric
G, which is called his apparent, or Places,
G;
C 2
tric and
Geo what,
20
The INTRODUCTION.
1
Geocentric Place. So likewife Jupiter
and Saturn will be feen from the Sun
in the Points E and F, their Heliocen-
tric Places; but a Spectator from the
Earth will fee them in the Point of the
Heavens G, which is their Geocentric
Place. The Arches DG, EG, FG, the
Differences between the true and appa-
rent Places of the fuperior Planets, are
called the Parallaxes of the Earth's an-
nual Orb, as feen from theſe planets.
If thro' the Sun we draw SH parallel to
AG, the Angles A & S, AS, A ½ S,
will be reſpectively equal to the Angles
DSH, ESH, and FSH; and the
Angle AGS, is equal to the Angle
GSH, whofe Meaſure is the Arch GH ;
which therefore will be the Meaſure of
the Angle AGS, the Angle under which
the Semidiameter AS of the Earth's
Orbit, is feen from the Starry Heavens.
But this Semidiameter is nothing in re-
ſpect of the immenſe Diſtance of the
Heavens or Fixed Stars; for from thence
it would appear under no fenfible An-
gle, but look like a Point. And there-
fore in the Heavens the Angle GSH,
or the Arch GH vanishes; and the
Points G and H coincide; and the
Arches DH, EH, FH, may be con-
fidered as being of the fame Bignefs
with
Sect. 1. Of the SOLAR SYSTEM.
zí
with the Arches DG, EG, and FG,
which are the Meafures of the Angles
·
A ¿S, A 4 S, AS; which Angles
are nearly the greateſt Elongation of
the Earth from the Sun, if the Earth
be obferved from the refpective Planets,
when the Line GA, touches the
Earth's Orbit in A. The nearer any of
the fuperior Planets is to the Sun, the
greater is the Parallax of the Annual
Orb, or the Angle under which the
Semidiameter of the Earth's Orbit is
feen from that Planet. In Mars the
Angle A & S (which is the viſible Elon-
gation of the Earth feen from Mars, or
the Parallax of the Annual Orb feen
from that Planet) is about 42 Degrees,
and therefore the Earth is always to the
Inhabitants of Mars either their Morn-
ing or Evening Star, and is never feen
by them ſo far diftant from the Sun as we
fee Venus. The greateſt Elongation of
the Earth feen from Jupiter, being near-
ly equal to the Angle A 4 S, is about 11
Degrees. In Saturn the Angle AS is
but 6 Degrees, which is not much above
I
4
Part of the greateſt Elongation we ob-
ferve in Mercury, And fince Mercury is
fo rarely feen by us, probably the Aſtro-
nomers of Saturn(except they have bet-
ter Opticks than we have) have not yet
dif-
C3
22
·
The INTRODUCTION..
>
}
diſcovered, that there is fuch a Body as
our Earth in the Univerſe.
The Parallax of the Annual Orb or
the greateſt Elongation of the Earth's
Orbit ſeen from any of the fuperior Pla-
nets, being given; the Diſtance of that
Planet from the Sun, in refpect of the
Earth's Diſtance from him, may bé
found by the fame Methods as thẻ Diſt-
ances of the inferior Planets were. Thus
to find the Diſtance of Mars from the
Sun, it will be as the Sine of the Angle
Sa A is to the Radius, fo is the Diſtance
AS(the Diſtance of the Earth from the
Sun)to S, the Diſtance from the Sun
to Mars. After the fame Manner the
Diſtances of Jupiter and Saturn are alſo
found. The mean Diſtance of the Earth
from the Sun being made a 1000, the
mean Diſtances of the fuperior Planets
from the Sun are, viz. the mean Diſt-
ance from the Sun of
♂ 1524
141
45201 and the Excentricity 250
k9538.
547
To which, if you add or fubtract their
mean Diſtances, we fhall have the great-
eft or leaſt Diſtances of thofe Planets
from the Sun.
There
1
Sect. I Of the SOLAR SYSTEM.
23
There are other Methods by which
the relative Diſtances of the Planets
might be found; but that which hath
been here illuftrated, is fufficient to e-
vince the Certainty of that Problem.
abfolute
nets from
the Sun
Hitherto we have only confidered the How the
Diſtances of the Planets in relation to Distances
one another, without determining them of the Pla-
by any known Meafure; but in order to t
find their abfolute Diſtances in fome de- are com-
terminate Meaſure, there must be fome-puted.
thing given, whofe Meaſure is known.
Now the Circumference of the Earth is
divided into 360 Degrees, and each of
theſe Degrees into 60 Geographical
Miles, fo that the whole Circumference
contains 21600; and by the known Pro-
portion for finding the Diameter of a Cir-
cle from its Circumference, the Earth's
Diameter will be found to be 6872
Miles, and its Semidiameter 3436 Miles.
The Parallax of the Earth's Semidia- Earth's
meter, or the Angle under which it is Semidia-
ſeen from a certain Planet, may be found
by comparing the true Place of the Pla-
net, as it would be feen from the Center
of the Earth, (which is known by Com-
putation) with its apparent Place, as it
is feen from fome Point on the Earth's
Surface. Let CZA be the Earth, ZC its Fig. 7.
Semi-
C 4
Parallax
of the
meter.
24
The INTRODUCTION.
Semidiameter, fome Planet, and BHT
Arch of a great Circle in the Heavens,
at an infinite Diftance. Now the Pla-
net will appear from the Earth's Cen-
ter C, in the Point of the Heavens H;
but a ſpectator from the Point Z upon
the Earth's Surface, will fee the fame
Object in the Point of the Heavens B;
and the Arch BH the Difference, is e-
qual to the Angle B✪ H=Z→ C, the
Parallax; which being known, the Side
Ce the Diſtance of the Planet from the
Center of the Earth, at that Time, may
be eaſily found. Now if this Diſtance
of the Planet from the Earth be deter-
mined, when the Centers of the Sun, the
faid Planet, and of the Earth, are in the
fame right Line, we have the abfolute
Diſtance of the Planet's Orbit from the
Earth's in known Meaſure; then it will
be, as the relative Diſtance betwixt the
Earth's Orbit and that of the Planet is
to the relative Diftance of the faid Planet
from the Sun; fo is the Diſtance of the
Planet's Orbit from the Earth's in known
Meaſure to the Diſtance of the faid Pla-
net from the Sun in the fame Meaſure:
Which being known, the Diſtance of
all the other Planets from the Sun may
be found. For it will be as the relative
Diſtance of any Planet from the Sun, is
!
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1
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¡ Plate 2.
Fig. 1.
}
1
&
Fig. IV
6
8 A.
R
T
C←
A
Fig.VI
Fig. VIII
A-
b
d
A
3
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་
Fig.
T
Fig.v
orbit of the Earth
orbit of Venus
orbit
of
Mercury
+
E
T
20+
E
Page 24
Fig.I
A
H
Fig.
A
B
E
h
B
D
FG H
Sect. I. Of the SOLAR SYSTEM,
25
to its Diſtance from him in a known
Meaſure; fo is the relative Diſtance of
any other Planet from him to its Dift-
ance in the fame Meaſure. This may
be done by finding the Diſtance of the
Planet Mars, when he is in Oppofition
to the Sun, after the fame Manner as
we find the Diftance of a Tree, or the
like, by two Stations.
}
Let a be Mars, D the Point on the
Earth's Superficies, where Mars is verti-
cal when he is in Oppofition to the Sun,
which may be exactly enough found by
Calculation, at which Time let an Ob-
ferver, at the Point Z (whofe Situation
from D muſt be known) take the Alti-
tude of Mars, whofe Complement will
be the Angle & ZR; then in the Trian-
gle ZC will be given the Angle Z ♂ C,
the Angle C (whofe Meaſure is the Arch
DZ) and confequently the Angle Z & C
the Parallax, and alfo the Side Z C the
Semidiameter of the Earth; by which we
may find C & the Diſtance of Mars from
the Earth. The extreme Nicety requi-
red in this Obfervation, makes it very
difficult to determine the exact Diſtances
of the Planets from the Sun; but the
celebrated Dr. Halley has in the Philo-
ſophical Tranſactions, fhewed us a more
cer-
ཟ
26
The INTRODUCTION. -
How the
tudes of
termin'd.
certain Method for finding the Diſtances
of the Planets; which is by obſerving
the Tranfit of Venus over the Sun.
;
The Eye judgeth of the Magnitudes
Magni- of far diftant Objects, according to the
the Plan- Quantities of the Angles under which
ets are de- they are feen (which are called their ap-
parent Magnitudes; ) and thefe Angles
appear greater or leſs in a certain Pro-
portion to their Diſtances, Wherefore
the Diſtances of the Planets from the
Earth, and their apparent Diameters
being given, their true Diameters (and
from thence their Magnitudes) may be
found. How the Diſtances of the Planets
may be found has been already fhewn
their apparent Diameters are found by a
Teleſcope, having a Machine fix'd to it
for meaſuring of Angles, called a Mi-
Fig. 8. crometer. Let BD, or the Angle BAD
be the apparent Diameter of any Planet,
and AB, or AD, (which by reaſon of the
great Diſtance of the Planets in reſpect
of their Magnitudes) may be confidered
as being the Diſtance of the faid Planet
from the Obferver. Now in the Trian-
gle ABD, having the Sides AB, AD,
given, and the Angle A, we have alfo
the other Angles B and D, (becauſe the
£ides AB, AD, are equal) whence the
Side
Sect. I.
27
Of the SOLAR SYSTEM.
Side BD the Diameter of the Planet may
be eafily found by Trigonometry.
•
+
From hence it appears, that the fame
Body at different Diſtances, will ſeem to
have very different Magnitudes. Thus
the Diameter BD will appear from the
Point E, to be twice as large as from the
Point A. It alfo follows, that a ſmall
Body, when at no great Diſtance from us,
may appear to be equal, or even to ex-
ceed another at a great Diſtance, tho'
immenfely bigger. Thus bd appears
under the fame Angle, and confequent-
ly of the fame Bignels from the Point A,
that the Line BD doth, tho' one vaftly
exceeds the other. And this is the Rea- why the
fon, why the Moon, which is much leſs Moon ap-
then any of the Planets, appears to us pears big-
vaftly bigger then either of them, and any of the
even to equal the Sun himſelf, which is Planets.
many Thouſand Times greater in Mag-
nitude.
The Diſtances of the Planets, and
Periods round the Sun, their Diameters
and Velocities round their own Axis,
according to modern Computations, are
as follow:
Saturn
ger then
*
28
The INTRODUCTION.
戚
​Saturn 1
Jupiter
Mars
Earth
Revolves about the
Sun in the Space of
Diſtance in
Y. D. H. Miles
29: 167: 22777.000.000
11: 314: 12424.000.000
1:321:23 123.000.000
0: 365: 6 81.000.000
0: 224: 16 59.060.000
0: 87:23 32.000.000
Venus
Mercury
S
Moon Earth.
Periods round Diameters
|240:000
?Round the SD.H.M. 240:000
27:7:43
their own Axis in Miles.
D. H. M.
Sun
Saturn
25: 6:
6: 0763.000
61.000
Jupiter
0: 9: 56
81.000
Mars
I : O: 40
4.440
Earth
Venus
24: 8:
Mercury
7.900
4.240
0:23: 56 7.970
Moon 27: 7: 43 2.170
The Caufe of Eclipfes and Phafes of
the Moon, and fome other Phænome-
na not here explained, fhall be fhewen
when we come to give a Deſcription of
the Orrery.
}
Befides
£.
}
Sect. 1. Of the SOLAR SYSTEM.
29
Beſides the Planets already mention-
ed, there are other great Bodies that
fometimes viſit our Syftem, which are
a Sort of Temporary Planets; for they
come and abide with us for a while,
and afterwards withdraw from us, for a
certain Space of Time, after which
they again return. Theſe wandering
Bodies are called Comets.
The Motion of Comets in the Hea-Of Come
vens, according to the beſt Obfervations
hitherto made, feem to be regulated by
the fame immutable Law that rules the
Planets; for their Orbits are Elliptical,
like thofe of the Planets, but vaſtly nar-
rower, or more Excentric. Yet they
have not all the fame Direction with
the Planets, who move from Weft to
Eaſt, for fome of the Comets move from
Eaft to Weft; and their Orbits have
different Inclinations to the Earth's Or-
bit; fome inclining Northwardly, others
Southwardly, much more than any of
the Planetary Orbits do.
Altho' both the Comets and the Pla-
`nets move in Elliptic Orbits, yet their
Motions ſeem to be vastly different : For
the Excentricities of the Planets Orbits
are fo ſmall, that they differ but little
from
}
30
The INTRODUCTION.
from Circles; but the Excentricities of
the Comets are fo very great, that the
Motions of fome of them feem to be al-
moſt in right Lines, tending directly to-
wards the Sun,
Now, fince the Orbits of the Comets
are fo extremely Excentric, their Moti-
ons, when they are in their Perihelia, or
neareſt Diſtance from the Sun, muſt be
much fwifter than when they are in
their Aphelia, or fartheft Diſtance from
him; which is the Reaſon why the Co-
mets make fo fhort a Stay in our Syf
tem; and when they diſappear are ſo
long in returning.
The Figures of the Comets are ob-
ferved to be very different; fome of them
fend forth fmall Beams like Hair every
Way round them; others are feen with
a long fiery Tail, which is always oppo-
fite to the Sun. Their Magnitudes are
alfo very different, but in what Propor-
tion they exceed each other, it is as yet
uncertain. Nor is it probable, that their
Numbers are yet known, for they have
not been obferved with due Care, nor
their Theories difcovered, but of late
Years. The Ancients were divided in
their Opinions concerning them; fome
imagined
Sect. 1. Of the SOLAR SYSTEM.
3 1
imagined that they were only a Kind of
Meteors kindled in our Atmoſphere, and
were there again diffipated; others took
them to be fomé ominous Prodigies:
But modern Diſcoveries prove, that they
are Worlds fubject to the fame Laws of
Motion as the Planets are; and they
muſt be very hard and durable Bodies,
elſe they could not bear the yaft Heat
which fome of them, when they are in
their Peribelia, receive from the Sun,
without being utterly confumed. The
great comet which appear'd in the Year
1680, was within Part of the Sun's
Diameter from his Surface; and there-
fore its heat muſt be prodigiouſly in-
tenſe beyond Imagination. And when
it is at its greateſt Diſtance from the
Sun, the Cold muſt be as rigid.
I
ठ
SECT.
32
The INTRODUCTION.
T'
F
SECT II.
Of the FIXED STARS,
HE fixed Stars are thofe bright
and fhining Bodies, which in a
clear Night appear to us every where
difperfed through the boundleſs Regions
of Space. They are term'd fixed, becauſe
they are found to keep the fame immu-
table Diſtance one from another in all
Ages, without having any of the Mo-
tions obferved in the Planets. The
Starsareat fixed Stars are all placed at fuch im-
immenſe menſe Diſtance from us, that the beſt
of Teleſcopes repreſent them no bigger
than Points, without having any ap-
parent Diameters.
The fixed
Diſtance
from us.
The fixed
Stars are
It is evident from hence, that all the
luminous Stars are luminous Bodies, and fhine
Bodies with their own proper and native Light,
like the elfe they could not be feen at fuch a
great Diſtance, For the Satellites of
Jupiter and Saturn, tho' they appear
under confiderable Angles through good
Sun.
Tele-
1
Sect. 2. Of the FIXED Stars:
33
Teleſcopes, yet are altogether inviſible
to the naked Eye.
us to the
Compari-
the fixed
Although the Diſtance betwixt us The Dif
and the Sun is vaftly large, when com-tancefrom
pared to the Diameter of the Earth, yet sun is no-
it is nothing when compared with the thing in
prodigious Diſtance of the fixed Stars; fon of the
for the whole Diameter of the Earth's vaft Dift-
Annual Orbit, appears from the neareſt tance of
fixed Star no bigger than a Point, and Stars.
the fixed Stars are at leaſt 100,000
times farther from us than we are from
the Sun; as may be demonftrated from
the Obfervation of thofe who have en-
deavoured to find the Parallax of the
Earths Annual Orb, or the Angle un-
der which the Earth's Orbit appears
from the fixed Stars.
theCenter
Hence it follows, that tho' we ap-As to Ap-
proach nearer to fome fixed Stars at pearance,
one Time of the Year than we do at the the Earth
may be
oppofite, and that by the whole Length confider'd
of the Diameter of the Earth's Orbit; as being
yet this Diſtance being fo fmall in com- of the
parifon with the Diſtance of the fixed Heavens.
Stars, their Magnitudes or Pofitions
cannot thereby be fenfibly altered; there-
fore we may always, without Error, fup-
pofe ourſelves to be in the fame Center
D
of
34
The INTRODUCTION
The fixed
Stars are
Suns.
The fixed
of the Heavens, fince we always have
the fame vifible Profpect of the Stars
without any Alteration.
If a Spectator was placed as near to
any fixed Star, as we are to the Sun, he
would there obſerve a Body as big, and
every way like, as the Sun appears to
us: and our Sun would appear to him
no bigger than a fixed Star: and un-
doubtedly he would reckon the Sun as
one of them in numbering the Stars.
Wherefore fince the Sun differeth no-
thing from a fixed Star, the fixed Stars
may be reckoned ſo many Suns.
It is not reaſonable to fuppofe that
all the fixed Stars are placed at the ſame
Difiance from us: but it is more pro-
Stars are bable that they are every where inter-
al vaft fperfed thro' the vaft indefinite. Space of
from each the Univerſe; and that there may be as
Diſtance
other.
great a Distance betwixt any two of
them, as there is betwixt our Sun and
the nearest fixed Star. Hence it follows
why they appear to us of different Mag-
nitudes, not becauſe they really are ſo,
but becaufe they are at different Diſtan-
ces from us; thofe that are neareſt ex-
celling in Brightnefs and Luftre thofe
that are moſt remote who give a fain-
ter
蟊
​P.35
10 20
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2
+
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10
20 30
Meridian
40
50
60
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8
Hour
ME
Trobe of Canker
OCEAN.
Equinoctial Line
ATRICA
orizar
Cizele
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We do I do 1 3/6 | slo | 40 | 5
10 20
130 130
NEW and CORRECT GLOBES according to the lateſt Obſervations
Made and Sold by RICHARD CUSHEE at the Globe and Sun between SDunstans Church & Chancery Lane
and Tho:Wright Inftrument-maker to His Majefty at the Orrery and Globe near Salisbury Court
FLEETSTREET LONDON
VGRAVD
ESTATES Survey'd MAPS DRAW and ENGRAV
ALSO
R. Cafnec pulp.
'
Sect. 2. Of the FIXED STARS.
35
ter Light, and appear fmaller to the
Eye.
The Aftronomers diftribute the
into ſeveral Orders or Claffes;
Stars The Dif
of the
theſe tribution
that are neareſt to us and appear Stars into
brighteſt to the Eye, are called Stars of 6 Claffes,
the firſt Magnitude; thoſe that are near-
eft to them in Brightnefs and Luftre,
are called Stars of the ſecond Magni-
tude;
thoſe of the third Clafs, are
ftiled Stars of the third Magnitude;
and ſo on, until we come to the Stars
of the fixth Magnitude, which are the
ſmalleſt that can be difcerned by the
naked Eye. There are infinite Num-
bers of finaller Stars, that can be ſeen
through Teleſcopes; but theſe are not
reduced to any of the fix Orders, and
are only called Teleſcopical Stars. It of Telef
may be here obſerved, that tho' the copical
Aftronomers have reduced all the Stars
that are viſible to the naked Eye, into
ſome one or other of theſe Claffes, yet
we are not to conclude from thence
that all the Stars anfwer exactly to fome
or other of theſe Orders; but there may
be in Reality as many Orders of the
Stars, as they are in Number, few of
them appearing exactly of the fame
Bignefs and Luftre.
D 2
The
Stars.
36
The INTRODUCTION.
}
1
The ancient Aftronomers, that the
might diſtinguiſh the Stars, in regard to
their Situation and Pofition to each o-
ther, divide the whole ftarry Firma-
ment into feveral Afterifms, or Syſtems of
Stars, confifting of thoſe that are nearer
to one another. Thefe Afterims are
The Stars called Conftellations and are digefted into
digeſted the Forms of fome Animals
as Men,
telations Lions, Bears, Serpents, &c. or to the
Images of fome known Things; as, of
a Crown, a Harp, a Triangle, &c.
1
into Con-
Zodiac.
Conftel-
within the
}
The Starry Firmament was divided by
the Ancients into 48 Images or Con-
ſtellations; twelve of which they placed
in that Part of the Heavens wherein
are the Planes of the Planetary Orbits;
which Part is Called the Zodiac, becauſe
moft of the Conftellations placed there-
in refumble fome living Creature. The
two Regions of the Heavens that are on
each Side of the Zodiac, are called the
North and South Parts of the Heavens.
The Conftellations within the Zodiac
tations are, 1. Aries, the Ram; 2. Taurus, the
Zodiac. Bull; 3. Gemini, the Twins; 4. Can-
cer, the Crab 5. Leo, the Lion; 6.
Virgo, the Virgin; 7. Libra, the Ba-
lance; 8. Scorpio, the Scorpion; 9. Sa-
1
gitta-
Sect. I Of the FIXED STARS.
37
gitarius, the Archer; 10. Capricornus,
the Goat; 11. Aquarius, the Water-
Bearer; and 12. Pifces, the Fishes.
;
3
Northern
Conftella-
The Conſtellations on the North Side
of the Zodiac are Twenty-one, viz. tions.
the Little Bear; the Great Bear the
Dragon; Cepheus, a King of Ethiopia;
Bootes, the Keeper of the Bear,; the
Northern Crown; Hercules with his Club
watching the Dragon; the Harp; the
Swan; Caffiopeia; Perfius; Andromeda ;
the Triangle; Auriga; Pegaſus, or the
Flying Horfe; Equuleus; the Dolphin ;
the Arrow; the Eagle; Serpentarius ;
and the Serpent.
The Conſtellations noted by the An- Southern.
cients on the South Side of the Zodiac; Conftella-
were fifteen, viz. the Whale; the Ri-tions.
ver Eridanus; the Hare; Orion; the
Great Dog; Little Dog; the Ship Ar-
go; Hydra; the Ceutaur; the Cup'; the
Crow; the Wolf; the Altar,; the South-
ern Crown; and the Southern Fifh. To
theſe have been lately added the follow-
ing, viz. The Phanix; the Crane
the Peacock, the Indian; the Bird of
Paradife; the Southern Triangle; the
Fly; Cameleon; the Flying Fish; Toucan,
or the American Goofe; the Water Ser-
pent!
D´3
;
38
INTRODUCTION.
The
1
pent, and the Sword Fish. The Anci
ents placed thoſe particular Conftella-
tions or Figures in the Heavens, either
to commemorate the Deeds of fome
great Man, or fome notable Exploit
or Action; or elfe took them from the
Fables of their Religion, &c. And the
Modern Aftronomers do ftill retain
them, to avoid the Confufion that would
arife by making new ones, when they
compare the modern Obfervation with
the old ones.
❤
Some of the principal Stars have par-
ticular Names given them, as Syrius,
Arcturus, &c. There are alfo feveral
Stars that are not reduced into Conftel-
Unformed lations, and theſe are called Unformed
Stars.
Stars.
The Ga-
laxy or
Milky
Way.
Pefides the Stars vifible to the naked
Eye there is a very remarkable Space
in the Heavens, called he Galaxy, or
Milky Way. This is a broad Circle of a
whitiſh Hue, like Milk, going quite
round the whole Heavens, and confift-
ing of an infinite Number of fmall Stars,
viſible thro' a Teleſcope, tho' not dif-
cernible by the naked Eye, by reaſon
of their exceeding Faintnefs; yet with
their Light they combine to illuftrate
that
Sect. 2.
39
Of the FIXED STARS.
that Part of the Heavens where they are;
and to cauſe that ſhining Whiteneſs.
The Place of the fixed Stars, or their
relative Situations one from another,
have been carefully obferved by Aſtro-
nomers, and digeſted into Catalogues.
The firft among the Greeks, who redu-
çed the Stars into a Catalogue, was Hyp-
parchus, who, from his own Obfervati-
ons, and of thoſe who lived before him,
inferted 1022 Stars into his Catalogue,
above 120 Years before the Chriftian
Era: This Catalogue has been fince en-
larged and improved by feveral learned
Men, to the Number of 3000, of which
there are a great many Teleſcopical, and
not to be diſcerned by the naked Eye;
and theſe are all ranked in the Catalogue
as the Stars of the feventh Magnitude.
:
It may ſeem ſtrange to fome, that.
there are no more then this Number of
Stars viſible to the naked Eye; for ſome-
times in a clear, Night they feem to be
innumerable but this is only a Decep-
tion of our Sight. arifing from their ve-
hement ſparkling. while we look upon
them confuſedly, without reducing them
into any Order; for there can feldom
be ſeen above 1000 Stars in the whole
Hea
D 4
40
The INTRODUCTION.
1
An Idea
Heavens with the naked Eye at the fame
Time; and if we ſhould diftinctly view
them, we ſhall not find many but what
are inferted upon a good Celeſtial Globë.
Altho' the Number of Stars that can
be diſcerned by the naked Eye are ſo
few, yet it is probable there are many
more which are beyond the Reach of our
Opticks, for thro' Teleſcopes they ap
pear in vaft Multitudes, every where
difperfed throughout the whole Hea
vens; and the better our Glaffes are,
the more of them we ftill difcover. The
ingenious Dr. Hook has obſerved 78 Stars
in the Pleiades, of which the naked Eye
is never able to diſcern above 7; and in
Orion, which has but 80 Stars in the
British Catalogue, (and fome of them
Teleſcopical) there has been numbered
2000 Stars.
Thoſe who think that all thefe glo-
of the Urious Bodies were created for no other
niverſe.
Purpoſe, than to give us a little dim
Light, muſt entertain a very flender Idea
of the Divine Wiſdom; for we receive
more Light from the Moon itſelf, than
from all the Stars put together. And
fince the Planets are fubject to the ſame
Laws of Motion with our Earth, and ſome
1
of
Ject. 2. Of the FIXED STARS.
41
of them not only equal, but vaftly ex-
ceed it in Magnitude, it is not unreafon-
able to fuppofe, that they are all habitable
Worlds. And fince the Fixed Stars are
no ways behind our Sun, either in Big-
nefs or Luftre, is it not probable, that
each of them have à Syftem of Planet-
ary Worlds turning round them, as we
do round our Sun? And if we aſcend
as far as the ſmalleſt Star we can ſee,
fhall we not then difcover innumerable
more of theſe glorious Bodies, which
now are altogether invifible to us? And
foad infinitum, thro' the boundleſs Space
of the Univerſe. What a magnificent
Idea muſt this raiſe in us of the Divine
Being! Who is every where, and at all
Times prefent, difplaying his Divine
Power, Wifdom and Goodnefs amongſt
all his Creatures!
The
ご
​f. 42..
13
**********
史
​The DESCRIPTION and
USE of the CELESTIAL and
TERRESTRIAL GLOBES.
Sphere or
Globe.
A
Globe or Sphere is a round folid
Body, having every Part of its
Surface equally diſtant from a
Point within it, called its Cen-
ter; and it may be conceived to be for-
med by the Revolution of a Semicircle
round its. Diameter.
{
}
Any Circle paffing through the Cen-
ter of the Sphere, thereby dividing into
two equal Parts or Segments, is called
Great Cir- a Great Circle; and the Segments of
the Sphere fo divided are called Hemi-
Spheres.
cle.
Hemi-
Iperes
Poles.
Every Great Circle has its Poles and
Axis.
The Poles of a Great Circle are two
Points on the Surface of the Sphere di-
ametrically oppofite to one another,
and
}
Of the GLOBE S.
43
and every where equally diſtant from the
faid Circle.
The Axis of a Circle is a right Line Axis.
paffing through the Center of the
Sphere, and through the Poles of the
faid Circle, and is therefore perpendi-
cular to the Plane: Therefore
All Circles paffing through the Poles
of any great Circle, interfect it in two
Places diametrically oppofite, and alſo
at right Angles; and with refpect to the
faid Great Circle, they may be called its
Secundaries.
Secunda-
ries.
Leffer
All Circles dividing the Sphere into
to unequal Parts, are called leffer or pa- Parallel
rallel Circles, and are ufually denomina- or leer
ted by that Great Circle to which they
are parallel.
The Earth being globular, its out-
ward Parts, as the feveral Countries,
Seas, &c. are beſt, and moſt natural-
ly reprefented upon the Surfaces of a
Globe; and when fuch a Body has the
outward Parts of the Earth and Sea de-
lineated upon its Surface, and placed in
their natural Order and Situation, it is
called a Terreſtrial Globe.
The
Circles.
Terrestrial
Globe.
44
The Defeription and Uſe
;
The Celeſtial Bodies appear to us as
if they were all placed in the fame Con
cave Sphere, therefore Aftronomers
place the Stars according to their re-
Ipective Situations and Magnitudes, and
alio the Images of the Conftellations,
upon the external Surface of a Globe
for it anfwers the fame Purpoſes as if
they were placed within a Concave
Sphere, if we fuppofe the Globe to be
tranſparent, and the Eye placed in the
Center. A Globe having the Stars pla-
ced upon its Surface, as above defcribed,
Celestial is called a Celestial Globe. Theſe Globes
are both placed in Frames, with other
Appurtenances, as fhall be defcribed in
a proper Place.
Globe.
The prin-
The principal Uſe of thefe Globes
cipal Ufe (befides their ferving as Maps, to dif-
of the tinguiſh the outward Parts of the Earth,
Globes. and the Situations of the fixed Stars)
is to explain and refolve the Phænome-.
na arifing from the diurnal Motion of
the Earth round its Axis.
It has been ſhewed in the Introduc-
tion, that the Diſtance of the Earth
from the Sun is no more than a Point,
when compared with the immenfe Dif-
tance of the fixed Stars; therefore let
the
器
​45
Of the GLOBE Ș,
will be
of the Fix-
tator be
Sun.
the Earth be in what Point foever of There
her Orbit, there will be the fame Prof-the fame
pect of the Heavens, as a Spectator Profpect
would obferve did he refide in the Sun: ed ſtars,
And if feveral Circles be imagined to whether
paſs thro' the Center of the Earth, and the Spec-
others, parallel to them, be conceived to placed on
paſs thro' the Center of the Sun, theſe the Earth,
Circles in the Heavens will feem to coin- or in the
cide, and to paſs exactly thro' the fame
Stars. Wherefore as to the Appear-
ances of the Fixed Stars, it is indifferent
whether the Earth or the Sun be made
the Center of the Univerſe. But becauſe
it is from the Earth that we always ob-
ferve the Celeſtial Bodies, and their ap-
parent Motions feem to us to be really
made in the Heavens, it is more natural
in explaining the Phænomena arifing
from theſe Motions, to place the Earth
in the Center. And again, becauſe the
Semidiameter. of the Earth, when com-
pared to her Diſtance from the Sun, is
of no fenfible Magnitude, any Point up-
on the Earth's Surface, let her be in
what Part foever of the Orbit, may be
confidered as being the Center of the
Univerſe. Upon thefe Principles, the
different Phænomena arifing from the
diurnal Motion of the Earth, and the
dif-
46
The Defcription and Ufe
different Situation of a Spectator upon
its Surface, are very naturally illuftrated
and explained by the Globes.
As to the Alterations of Seafons, &c.
arifing from the annual Motion of the
Earth round the Sun, it is indifferent
which we fuppofe to move, the Earth,
or the Sun; for in both Cafes the Ef-
fect will be the fame: Wherefore be-
cauſe it is the Sun that appears to us to
move we ſay the Sun is in fuch a Part
of the Ecliptic, without attributing any
Motion to the Earth, any more than
if ſhe had actually been at Reft. For
the fame Reaſon we fay the Sun rifes,
or the Sun fets; by which we mean,
that he begins to appear or diſappear,
without confidering in the leaft how
thefe Effects are produced. Thefe
Things are here mentioned, to obviate
the Objections that might be made by
Beginners, after they had been told that
the Sun ftands ftill.
1
SECT.
Sect. I. Of the GLOBE S.
47
}
*
SECT. I.
An Explanation of the Circles
of the Sphere, and of Jeme
Aftronomical Terms arifing
therefrom.
IN
N Order to determine the relative
Situations of Places upon the Earth,
as well as the Pofitions of the fixed Stars,
and other Celeſtial Phænomena, the
Globe of the Earth is fuppofed to be
inviron'd by ſeveral imaginary Circles,
and theſe are called the Circles of the
Sphere. Theſe imaginary Circles are The Cir-
either fixed, and always obtain the fame cles of the
Pofition in the Heavens, or moveable, Sphere.
according to the Pofition of the Obfer-
ver,
Thofe Circles that are fixed, owe
their Origin to the two-fold Motion of
the Earth, and are the Equator, and the
Ecliptic, with their Secundaries and
Parallels
> 1
The Defcription and Uſe
The E-
Parallels. Thefe fixed Circles are ufu-
ally delineated upon the Surface of the
Globes.
The moveable Circles are only the
Horizon, its Secundaries and Parallels:
Theſe are reperefented by the Wooden
Frame, and the Brafs Ring, wherein
the Globe is hung, and a thin Plate of
Brafs to be ſcrewed in a proper Place
upon the faid Ring, as Occafion re-
quires.
I. Of the Equinoctial.
I. The Equator or the Equinoctial, is
quator or that great Circle in the Heavens, in
Equinoc whofe Plane the Earth peforms her di-
rial
urnal Motion round her Axis; or it is
that Great Circle, parallel to which the
whole Heavens ſeem to turn round the
Earth from Eaſt to Weft in 24 Hours.
Note, The Equator and the Equinoć-
tial are generally fynonymous. Terms;
but fometimes the Equator particularly
fignifies that Great Circle upon the Sur-
face of the Earth, which coincides with
the Equinoctial in the Heavens. This
Circle is alfo by Mariners commonly
called the Line.
The
Sect. 1. Of the GLOBE $.
49.
World or
The Equinoctial divides the Globe of
the Earth, and alfo the whole Heavens Northern,
into two equal Parts, North and South and South-
which are called the Northern and Sou-ern Hemi-
thern Hemispheres. The Axis of thispheres,
Circle is called the Axis of the World, or The Axis
the Earth's Axis, because the Earth re- of the
volves above it (from Weft to Eaft) in
24 Hours. The Extremes of this Axis
are called the Poles of the World, whereof Poles of the
that which lies in the Northern Hemi-of the E-
fphere, is called the North Pole, and the quater.
other is called the South Pole. The E-
quinoctial Circle is always delineated
upon the Surface of each Globe, with
its Name at length expreffed; the Axis
of this Circle or the Earth's Axis, is on-
ly an imaginary Line in the Heavens,
but on the Globes it is expreffed by the
Wires about which they really turn. The
Poles of the World are the two Points
upon the Surface of the Globe through
which thefe Wires pafs: the North Pole
is that which hath the little Braſs Circle
with a moveable. Index placed around
ît; and the other oppofite to it is the
South Pole. The Northern Hémi-
fphere is that wherein the North Pole
is placed, and the oppofite one is the
Southern Hemiſphere.
E
LI
The
50
The Defcription and Ufe
1
་
>
The Aftronomers divide all Circles
into 360 equal Parts, called Degrees, each
Degree into 60 équal Parts, called Mi-
nutes, each Minute into 60 Seconds, &c.
But befides this Divifion into Degrees,
the Equinoctial is alfo divided into 24
equal Parts or Hours, each Hour into
60 Minutes, each Minute into 60 Se-
conds, &c. So that one Hour is equal
to 15 Degrees, each Minute of Time is
equal to 15 Minutes of a Degree, &c.
2. All Circles conceived to pafs
through the Poles of the World, inter-
fecting the Equinoctial at right Angles,
are with refpect to any Point in the.
Hour Cir-Heavens called Hour Circles; and alfo
cles of 4-Circles of Afcenfion, becauſe the Afcen-
fcenfion, al- fion of the heavenly Bodies, from a cer-
Meridians, tain Point, are by them determined.
cies or Cir
fo called
Theſe Circles are alſo, with regard to
Places upon Earth, call'd Meridians.
The Meridians are commonly drawn
upon the Terreſtrial Globe thro' every
15 Degrees of the Equinoctial, thereby
making an Hour difference betwixt the
Flace through which they pafs. On
the Celestial Globe there are commonly
drawn but two of thefe Meridians, croffing
..
the
Sect. 1:
Of the GLOBE S.
A
the Equinoctial in four Points equidift-
ant from one another, thereby divi
ding it into four Quadrants; but the in-,
termediate ones are here fupplied, and
alfo upon the Terreſtrial Globe, by the
Brafs Circle on which they are hung,
which is therefore called the Brass Me- The Braf
ridian, and fometimes only the Meridi- Meridian.
an, it ferving for this Purpoſe to all the
Points upon either Globe.
There is alfo a little Brafs Circle fixed
upon this Meridian, divided into 24
Hours, having an Index moveable round
the Axis of the Globe to be. turned to
any particular Hour. The Ufe..of this
Circle is to show the Difference of Time
-betwixt any two Meridians, and is there- The Hour
fore called the Hour-Circle:
7
Circle
3. All Circles parallel to the Equi-
noctial are with refpect to any Point in Parallels:
the Heavens, called Parallels of Decli-
nations. So that.
4. The Declination of any Point
in the Heavens. (as of the Sun, a fix-
ed Star, or the like) is an Arch of
the Meridian paffing through that
Point, and intercepted betwixt it and
the Equator; and if the faid Point be
E 2
10
of Declixa-
52
The Deſcription and Ùſe
Declina-
to the Northward ofthe Equator, it is
tion North Called
or South
Southward
North
South Declination.
itis
Of the Parallels of Declination, four
are eminently diſtinguiſhed by particu-
Trepics lar Names, viz. The two Tropics, and
Circles. the two Polar Circles.
and Polar
The Tropics are on different Sides of
the Equator, each 23 Degrees and 29
Minutes diftant from it, that which lies
in the Northern Hemifphere, is called
Tropic of
Concer; the Tropic of Cancer; and the Southern
of Capri- one, the Tropic of Capricorn.
Forn.
Arctic
Circle.
}
Theſe Circles are the Limits of the
Sun's greateſt Declination, and are cal-
led Tropics, becauſe whenever the Sun
arrives to them he ſeems to return back
again towards the Equator.
6. The Polar Circles are each of
them at the fame Diftance from the
Poles of the World, that the Tropics
are from the Equator, viz. 2.3 ° 29'.
That which lies near the North Pole,
is called the Arctic Circle, from Arctes,
a Conftellation fituated in the Heavens
near that Place; whence alfo this Pole
is
Sect. I Of the GLOBE S.
53
Pole.
is fometimes called the Arctic Pole. The&ic
other Polar Circle, which is ſituated near
the South Pole; is called the Antarctic Antarctic
Circle, becauſe its Pofition is contrary Circle.
to the other; and the South Pole is fome-
times called the Antarctic Pole.
The Tropics and the Polar Circles
having each their Names expreffed upon
the Globes.
II. Of the Ecliptic.
Antarctic
Pole.
7. The Ecliptic is that Great Circle Ecliptic.
in whofe Place the Earth performs its
annual Motion round the Sun; or, in
which the Sun feems to move round the
Earth once in a Year. This Circle
maks an Angle with the Equinoctial
of 23 Degrees 29 Minutes, and interfects
it in two oppofite Points which are cal-
led the Equinoctial Points; and the two Einac-
Points in the Ecliptic that are at thetal
greateſt Diſtance from the Equinoctial-
Points, are called the Solftitial Points. So!tial
The two Meridians paffing through
thofe Points are, by Way of Eminence,
called Colures; whereof that which paf-Colures.
feth thro' the Equinoctial Points is cal-
led the Equinoctial Colure; and that Equinocti
which is at Right Angles to it, paffing
E 3
through
Points
al
54
The Defcription and Ufe
through the Solftitial Points, is called
Solftitial the Solftitial Colure.
Colure.
The E-
}
•
The Ecliptic is divided into 12 equal
cliptic Parts, called Signs, each Sign being 30
digided
Into Signs Degrees, beginning from one of the E-
quinoctial Foints, and numbred from
Weft to Eaft; the Names and Charac-
ters of the twelve. Signs are as follows:
viz.
Signs.
Aries, Taurus, Gemini, Cancer, Leo, Virgo,
I. N 2. 8 3. - II 4:00 5.2 6.1m
Libra, Scorpio, Sagittarius, Capricornus, Aquarius, Pifces,
10. h IL.
6.
8. m
9. t
>
*
INN
12. H
The firft fix of theſe are called the
Northern Northern Signs, and poffefs that half
of the Ecliptic which is to the North-
ward of, the Equator; begining with
the firſt Point of r, and ending with
the laſt Point of "
Southern
Signs.
The latter fix are call'd Southern
Signs,, becauſe they poffefs the Southern
Half of the Ecliptic, beginning at the
firſt Point of, and ending with the
laft Point of *.
1
21
A
The Divifion of the Ecliptic into
Signs, and the Names of the Colures,
are particularly expreffed upon the
Globes.
•
}
The
•
Sect. 55
I.
1
of the GLOBES.
The figns of the Ecliptic took their
Names from 12 Conftellations mentio
ned in the Introduction to be fituated
in the Heavens near thofe Places. It
is to be obſerved, that the Signs are not
to be confounded with the Conſtellati-
ons of the fame Name: For the Sign of
Aries is not the fame with the Conftella-
tion Aries; the latter is a Syftem of
Stars digefted into the Figure of a Ram;
but the Sign of Aries is only 30 Degrees
of the Ecliptic counted from the Equi-
noctial Point, (which is reckon'd the
firſt Point in the Ecliptic) to the begin-
ning of Taurus : Or, it is ſometimes ta-
ken for all that Space upon the Celeſtial
Globe contained between the two Cir-
cles paffing through the first Points of
Y and 8. What has been here ſaid of
Aries, is to be noted of all the reſt of
the Signs.
*
The Conftellations above-mentioned
were formerly fituated within the Signs
which now bear their Names; but by a
flow Motion of the Equinoctial Points,
being one Degree in 72 Years, the Con-
ſtellation Aries has now got into the
Sign: 8, and fo of the reft. So that Pif
ces is now got into the Sign of v; this
flow Motion in the Heavens is called the
Preceffion of the Equinoctial Points.
E 4
r;
The
56
*
The Defcription ana Uſe
Poles of the The Poles of the Ecliptic are both fi-
Ecliptic tuated in the Solftitial:Coture, at 23
SA
Degrees 29 Minutes Distance from the
Pole of the World; and they take their
Denomination from the Hemifphere
wherein they are plac'd, big that which
lies in the Northern
Southern
+
called the
S
Hemiſphere, is
{ North Poleof the Eclip-
South
tie. The Arctic and Antarctic-Circles are
defcribed by the Poles of the Ecliptic in
the Diurnal Motion of the Earth round
its Axis, whence it feems thefe two
Circles are called Polar, · ·
"
$
8. All great Circles paffing through
the Poles of the Ecliptic, and conte-
quently interfecting it at right Angles,
Circles of are called Circles of Longitude: So that,
Longitude
in the Hea
vens.
یش
?
Longitude 2. The Longitude of any Point in
of any Point the Heavens, (aš a Star or Planet &c.)
is an Arch of the Ecliptic contained be-
tween the Circle of. Longitude paffing
thro' that Point, and the Equinoctial
Point r. And that Degree of any Sign
which l'es under the Circle of Longi-
tude paffing thro any Star or Planet, is
Place of a
Star. called the Place of that Star or Planet.
?
Note
Sect. I. Of the GLOBES,
57.
- Note, the Sun never goes out of the
Ecliptic, and it is not uſual to ſay the
Sun's Longitude, but we commonly ex-
prefs it the Sun's Place, which is that
Sign, Degree, Minute, &c of the E-
cliptic, which he at any Time poffeffes.
To. All Circles conceived to be drawn
parallel to the Ecliptic, are called
rallels of Latitude: So that,
pa-
1. The Latitude of any Point in the Latitude of
aStar, c.
Heavens, (as a Fixed Star, &c.) is an
Arch of the Circle of Longitude, in
paffing thro' that Point, and intercepted
betwixt it and the Ecliptic; or, the La-
titude is the Diſtance from the Ecliptic;
and if the faid Point be to the North-
ward of the Ecliptic, it is called North-
Latitude; but if it be to the South-
ward, it is called South Latitude.
Upon the Terreftrial Globes none of
the Circles of Longitude are deſcribed;
and upon the Celestial, they are com-
monly drawn thro' the Beginning of
every Sign; but they are all fupplied
upon both Globes, by faftening a thin
Plate of Braſs over one of the Poles of
the Ecliptic, and fo as to be moved to
any Degree thereof at Pleaſure. The
Pa-
$8
The Deſcription and Ufe
1
Florison..
senfible
Parallels of Latitude are alfo fupplied
by the Graduations upon the faid Plate
as ſhall be ſhewn in a proper Place,
i'
We have now done with all thofe
Circles that are fixed and fuch as are
diawn upon the Globes themſelves; we
next proceed to the moveable Circles.
III. Of the Horizon.
12, The Horizon is that great Cir-
cle which divides the upper or viſible
Hemiſphere of the World, from the
lower or invifible: This Circle is diftin-
guiſhed into two Sorts, the Senfible, and
the Rational...
>
3
*
The Senfible, or Apparent Horizon, is
Horizon. that Circle which limits of determinates
our Profpect, whether we are at Land
or Sea, reaching as far as we can ſee; or
it is that Circle where the Sky and the
Earth or Water ſeem to meet. When
we are on Terra Firma, this Circle com
monly feems rugged and irregular, oc-
cafioned by the Unevennefs of the Ground
terminating our Profpect; but at Sea
there are no fuch Irregularities; the Se-
midiameter of this Circle varieth accor-
ding to the Height of the Eye of the
1
ob-
!
Sect.
59
I
Of the GLOBE 8.
1
Obferver; if a Man of fix Feet high
ftood upon a large Plain, or the furface
of the Sea, he could not fee above three
Miles around.
This Circle determines the Rifing and
Setting of Heavenly Bodies, and dif
tinguiſhes Day and Night.
The Rational or true Horizon is a Rational
great Circle paffing thro' the Center of Horizon.
the Earth parallel to the fenfible Hori-
zon, being diftant from it by the Earth's
Semidiameter, which is about 3980
Miles This Diſtance is nothing in
Compariſon of the immenſe Diſtance of
the Sun and the fixed Stars, therefore
Aftronomers make no Diftinction be-
tween theſe two Circles, but confider
the apparent Horizon, or that wherein
the Sun appears to riſe and ſet, as paf-
fing thro' the Center of the Earth.
This Circle is divided by Aftronomers
in to four Quadrants, and each of the
Quadrants into 90 Degrees, &c. The
four Points quartering this Circle are
called the Cardinal Points, and are term-Cardinal
ed the East, Weft, North, and South. Points of
The Eaft is that Point of the Horizon.
where the Sun rifes when he is in the
Equi-
the Hori-
The Deſcription and Use
>
Equinoctial, or on that Day when he
afcends above the Horizon exactly at
fix o'clock; and the Weft is that Point
of the Horizon which is directly oppo-
fite to the Eaft, or where the Sun fets
when he is in the Equinoctial. The
South is 90 Degrees diftant from the
Eaſt and Weſt, and is towards that Part
of the Haevens wherein the Sun always
appears to us in Great Britain at Noon
and the North is that Part of the Hea
vens which is directly oppofite to the
South: Or the North and South Points
of the Heavens may be found by turning
yourſelf either directly towards the Eaft
or the Weft: If you look towards the
F Eaft South
*
Weft the North willbe to the Right
S
Hand, and the
{
South
North to the Left.
Befide's the aforementioned Divifion
of the Horizon into Degrees, Mariners
divide it into 32 equal Parts, which they
Points of call the Points of the Compass; to each of
the Com- which Points they give a particular
Name, compounded of the four Ca: di-
nals, according to what Quarter of the
Compass is intended.
paſs.
The Center of the Horizon is the
Place
Sect. I
61
Of the G L OBES.
Place of Obfervation, and the Poles of
it are, one exactly over our Heads, called
the Zenib; and the other exactly under Zenith.
our Feet, called the Nadir.
Nadir.
Circles
13. All Circles conceived to paſs
thro' the Zenith and Nadir, are called
Vertical Circles, or Azimuths. Of thefe Vertical
Circles, that which paffeth thro' the
North and South Points of the Horizon
is called the Meridian: fo that when any Meridiane
Object is upon the Meridian, it then
bears either due South or due North
from us; and the Azimuth of any Ob- Azimuth.
ject is an Arch of the Horizon intercep-
ted between the Vertical Circle paffing
through it, and either the North or
South Part of the Meridian; which Part
is commonly ſpecified.
The Meridian paffes thro' the Poles
of the World as well as through the
Zenith and Nadir; and therefore is a
Secundary both of the Equinoctial and
the Horizon: This Circle divides the
Globe into the Eastern and Western He-
mifpheres, and the Points of it are the
East and West Poles of the Horizon.
All the Heavenly Objects are, during
one Half of their Continuance above
the Horizon, in the Eastern Hemi-
Sphere
t
62
The Defeription and Ufe
tical,
;
fphere, and for the other Half in the
Weſtern ſo that whenever the Suri
arrives upon the upper Part of the Me-
ridian, it is then Noon or Mid-day,
which is the Reaſon why this Circle is
called the Meridian; and when he comes
to the lower Part, it is then Mid-night.
The Vertical Circle paffing thro' the
-Eaft and Weft Points of the Horizon,
Prime Ver-is called the Prime Vertical, or Circle of
East and Weft; fo that when any Ob-
ject is upon this Circle in the Eaftern
Hemiſphere, it appears due Eaft; and
if it be in the Weſtern Hemiſphere, it
appears due Weſt.
That Degree in the Horizon wherein
any Object riſes or fets from the Eaft or
Amplitude. Weſt Points, is called the Amplitude
which for Rifing is called Amplituae Or-
tive, and Occafive for fetting; which
muſt be alfo denominated whether it be
Northerly or Southerly.
It may be obferv'd, that the Am-
plitude and Azimuth are much the fame;
the Amplitude fhewing the Bearing of
any Object when he rifes or fets, from
the Eaft or Weft Points of the Hori
zon; and the Azimuth the Bearing of
any
Sect. I. Of the GLOBE S.
b3
any Object when it is above the Hori-
zon, either from the North or South
Foint thereof. As for Example, if
an Object riſes or fets within 10 Degrees
of the Eaft or Weft, fuppofe towards
the South, we accordingly fay, its Am-
plitude is 10 Degrees Southerly; but if
an Object, that is of any Height above
the Horizon, fhould be in the Vertical
Circle, paffing thro' the before menti-
oned Point, we then fay, its Azimuth
is Ɛo Degrees from the South, or 100
Degrees from the North, both which
Expreffions fignify the fame.
thers
14. All Circles drawn parallel to the
Horizon, in the upper Hemiſphere, are
called Almacanthers, or Parallels of Al- Almacan
titude: So that the Altitude of any Altitudes
Point in the Heavens is an Arch of the
Vertical Circle paffing thro' that Point,
and intercepted betwixt it and the Ho-
rizon; and if the Object be upon the
Meridian, it is commonly called the Me-
ridian Altitude. The Complement of
the Altitude, or what it wants of 90 Zenith
Degrees, is called the Zenith Diſtance. Distance.
The Horizon (by which we mean
the Rational) is reprefented by the upper
Surface of the Wooden Frame, wherein
the
Meridian
Altitudes
GA
The Defcription and Ufe
the Globes are placed, upon this Hori-
zon are deſcribed feveral Concentrick
Circles, the Innermoft of which is divi-
ded into Degrees which ought to be
numbred both Ways from the Eaft and
the Weft, until they end at 90 Degrees
in the North and South Points. The
Uſe of theſe Divifions is to fhew the
Amplitude of the Sun and Stars, at
their rifing and Setting: Alfo in fome
convenient Place upon this Horizon,
there is commonly noted the Points of
the Compafs. Without the before-men-
tioned Circle there is drawn the Ecliptic
with its Divifions into Signs and De-
grees, and a Circle of Months and Days:
The Uſe of theſe two Circles is to ferve
as a Kalendar to fhew the Sun's Place at
any Time of the Year, and by that
Means to find his Place in the Ecliptic
drawn upon the Globe itſelf.
The Vertical Circles, and the Paral-
lels of Altitude, are ſupplied by a thin
Plate of Braſs, having a Nut and Screw
`at one End to faften it to the Brafs Me-
ridian in the Zenith Point; which be-
ing done, the lower End of it may be.
put between the Globe it felf and the
inner Edge of the Horizon, and fo tur-
ned round about to any Point' required.
The
Sect. 1. Of the GLOBES.
65
The fiducial Edge thereof reprefenting
the Vertical Circles, and the Degrees
upon it, defcribing the Parallels of Al-
titude. This thin Plate is called the Quadrant
Quadrant of Altitude.
The Center of the Horizon being
the Place of Obfervation, it is evident
that this Circle, and all the others be-
longing to it, are continually changed,
which Way foever we move; wherefore
we may ſuppoſe the Horizon, with its
Secundaries and Parallels, to inveſt the
Globe like a Rete or Net; and to be
moveable every Way round. This is
very naturally illuftrated by the Globes;
if we move directly North or directly
South, the Change made in the Horizon
is repreſented by moving the Brafs Me-
ridian (keeping the Globe from turning
about its Axis) in the Notches made in
the Wooden Horizon, juft fo much as
we travelled. If our Courfe fhould be
due Eaft or due Weft, the Alterations
made thereby are reprefented by turning
the Globe accordingly about its Axis,
the Brafs Meridian being kept fixed; and
if we ſteer betwixt the Meridian and the
Eaſt or Weſt Points, then we are to
turn the Brafs Meridian, and alfo the
Globe about its Axis accordingly, the
F
Súm
of Alti-
tude.
66
The Defcription and Uje
1
Sum of which is, let the Spectator be in
what Point foever of the Earth's Surface
he'll there gravitate or tend exactly to-
wards its Center, and imagine himſelf
to be on the higheſt Part thereof, (the
Unevenneſs of the Ground not being
here confidered) wherefore if we turn the
Globe in fuch a Manner as to bring the
feveral progreffive Steps of a Traveller
fucceffively to the Zenith, we fhall then
have the fucceffive Alterations made in
the Horizon, in every Part of his Jour-
ney. This Explication being well con-
fidered, will be of Help to young Begin-
ners, to conceive how the Earth is every
where habitable, and how Paffengers
çan travel quite round it; for fince every
Thing tends towards the Center of the
Earth, we are to conceive that Point as
being the loweſt, and not to carry our
Idea of downwards any farther: Thoſe
that are diametrically oppoſite to us be-
ing as much upon the upper Part of the
Earth as we are, there being no fuch
Thing in Nature as one Place being
higher then another, but as it is at a
greater Diſtance from the Center of the
Earth, let it be in what Country foever.
We have now done with all the Cir-
cles of the sphere, and it may be ob
ferved
Sect. 1. Of the GLOBE'S.
87
{
ferved, that the Equinoctial, the Ecliptic,
and the Horizon, with their Secundaries
and Paraliels, are all alike; and altering
their Pofition, may be made to ferve for
one another. Thus, if the Foles of the
World be brought into the Zenith and
Nadir, the Equinoctial will coincide with
the Horizon, the Meridians will be the
fame with the Vertical Circles, and the
Parallels of Declination will be the Pa-
rallels of Altitude. After the fame Man-
ner, if ſhifting the Pofition we bring the
Ecliptic to coincide with the Horizon, the
Circles of Longitude will be the Vertical
Circles, and the Parallels of Latitude and
Altitude will coincide.
The Horizon and the Equator may
be either parallel, perpendicular, or o-
blique to each other.
15. A Parallel Sphere is that Pofition Parallel
where the Equator coincides with the Sphere.
Horizon, and confequently the Poles of
the World are in the Zenith and Nadir:
The Inhabitants of this Sphere (if there
be any) are thoſe who live under the
Poles of the World.
16. A Right or Direct Sphere is that Right
Pofition where the Equator is perpen-Sphere.
F 2
dicular
68
The Defcription and Ufe
dicular to the Horizon, the Inhabitants
whereof are thofe who live under the
Equinoctial.
Oblique 17. An Oblique Sphere is when the
Sphere. Equinoctial and the Horizon make o-
blique Angles with each other, which
every where happens but under the
Equator and the Poles.
The Arch of any Parallel of Declina-
tion, which ſtands above the Horizon is
Diurnal called the Diurnal Arch; and the re-
maining Part of it, which is below the
Horizon, is called the Nocturnal Arch.
and Noc
turnal
Arch.
Right
That Point of the Equinoctial which
Eaftern Part of the Ho-
{ Baftern
comes to the Western
rizon with any Point of the Heavens, is
called the
SAfcenfion
Defcenfion S
}
of that Point,
counted from the Beginning of; andif
it be in a right Sphere, the Afcenfion or
Defcenfion is called Right; but if it bẹ
an oblique Sphere, it is called an oblique
Afcenfion or Defcenfion. So that,
18. The Right Afcenfion of the Sun,
Afcenfion Moon, or any Star, &c. is an Arch of
the Equator contained betwixt the Be-
1
gin-
Sect. I. Of the GLOBES.
69
ginning of v, and that Point of the
Equinoctial which riſes with them in a
Right Sphere, or which comes to the
Meridian with them in an oblique Sphere.
19. Oblique Afcenfion, or Defcenfion,
is an Arch of the Equinoctial intercep-
ted between the Beginning of, and
that Point of the Equator which riſes or
fets with any Point in the Heavens in
an oblique Sphere.
Afcenfion,
20. Afcenfional Difference, is the Aſcenfional
Difference betwixt the right and oblique Difference.
Afcenfion or Defcenfion, and fhews how
long the Sun rifes or fets before or after
the Hour of Six.
IV. Of the Divifion of Time,
The Parts that Time is diftinguiſhed
into, are Days, Hours, Weeks, Months and
Years.
A Day is either Natural or Artificial.
any
A Natural Day is the Space of Time Natural
elapſed while the Sun goes from and Arti-
Meridian or Horary Circle, till he arrives ficial Day.
to the fame again; or, it is the Time
contain'd from Noon, or any particular
Hour,
F. 3
79
The Defcription and Ufe.
Hours,&c.
Hour, to the next Noon, or the fame
Hour again; An Artificial Day is the
Time betwixt the Sun's Rifing and Set-
ting; to which is oppofed the Night
that is, the Time the Sun is hid under
the Horizon.
The Natural Day is divided into 24
Hours, cach Hour into 60 Minutes, each
Minute into 60 Seconds, &c. The Ar-
tificial Days are always unequal to all
the Inhabitants that are not under the-
Equator except when the Sun is in the
Equinoctial Points and, which
happens (according to our Way of reck-
oning) about the 21ft of March and
23d of September; at thofe Times the
Sun rifes at fix and fets at fix, to all the
Inhabitants of the Earth. Thele Days
Equinoxes are called the Equinoxes, or Equinoctial
Days; the first of which, or when the
Sun is in the firft Point of Aries, is cal-
led the Vernal Equinox, and the latter is
Autumnal called the Autumnal Equinox. In all
Equinox Places where the Sun decends below the
Vernal and
Horizon, excepting under the Equator,
the Days continually lengthen or fhorten
and that fafter or flower, according as
the Sun is nearer to, or further from
the Equinoctial, untill he arrives to ei-
ther of the Soiftitial Points or . At
thofe
1
Sect. I Of the G L O BE S.
75
thoſe Times the Sun feems to ftand ftill
for a few Days, and then he begins to
return with a flow Motion towards the
Equinoctial, ftill haftening his Pace as
Le comes nearer to it: The sun enters
the Tropics of and, about the 21ft
of June, and the 22d of December, which
Days are fometimes called the Solstices; Solftices.
the firft of which we call the Summer Summer
Solstice, and the latter the Winter Solstice.Solstice.
All Nations do not begin their Day The Dif-
and reckon their Hours alike. In Great-ferent Be-
Britain, France and Spain, and in noftging of
the Day
Places in Europe, the Day is reckoned to
begin at Midnight, from whenceis coun-
ted 12 Hours till Noon, then twelve
Hours more till next Midnight, which
makes a compleat Day; yet the Afirono-
mers (in thefe Countries) commonly be-
gin their Day at Noon, and ſo reckon
24 Hours till next Noon, and not twice.
twelve according to the vulgar Compu-
tation.
The Babylonians began their Day at
Sun-rifing, and reckoned 24 Hours till
he roſe again! This Way of Computa-
tion we call the Babylonish Hours. In Babylonifo
ſeveral Parts of Germany they count their Hours.
Hours from Sun-fetting, calling the firſt
1
F 4
Hour
72
The Defcription and Uſe
'
Hour after the Sun has fet the fi ft Hour,
&c. till he fets the next Day, which
24
they call the 24th Hour: Thefe are com-
Italian monly called the Italian Hours. Accord
Hours. ing to both thefe Ways of Computation,
their Hours are commonly either a
little greater or lefs than the Part of
a natural Day, in Proportion as the Sun
rifes or fets fooner or later in the fucced-
ing Days. They have alſo this Incon-
venience, that their Mid-day and Mid-
night happen on different Hours, ac-
cording to the Seaſons of the Year.
Hours.
The Jews and the Romans formerly di-
vided the artificial Days and Nights each
into 12 equal Parts; these are termed
wish the Jewish Hours, and are of differ-
ent Lengths according to the Seaſons
of the Year; a Jewish Hour in Summer
being longer than one in Winter, and a
Night-Hour fhorter. This Method of
Computation is now in Ufe among the
Turks, and the Hours are ftiled the first
Hour, Jecond Hour, &c. of the Day or
Night; fo that Mid-day always falls up-
Planetary on the fixth Hour of the Day. Theſe
Hours.
Hours are alfo called Planetary Hours,
becauſe in every Hour one of the ſeven
Planets were fuppofed to prefide over
the World and fo take it by Turns. The
first
*
Sect. 1. Of the GLOBES.
73
firſt Hour after Sun-rifing on Sunday
was allotted to the Sun; the next to Ve
nus; the third to Mercury; and the reſt
in Order to the Moon, Saturn, Jupiter,
and Mars. By this Means on the firſt
Hour of the next Day the Moon prefided
and fo gave the Name to that Day;
and fo feven Days by this Method had
Names given them from the Planets
that were ſuppoſed to govern on the firſt
Hour.
A Week is a Syſtem of ſeven Days, in A Week,
which each Day is diftinguiſhed by a
different Name. In moft Countries theſe
Days are called after the Names of the
feven Planets, as above noted. All Na-
tions that have any Notion of Religion,
lay apart one Day in feven for public
Worſhip the Day folemniz'd by Chrif-
tians is Sunday, or the fift Day of the
Week, being that on which our Saviour
rofe from the Grave, on which the Apo-
ftles afterwards uſed more particularly
to aſſemble together to perform Divine
Worship. The Jews obferved Saturday
pr the feventh Day of the Week, for
their Sabbath, or Day of Reft, being that
appointed in the fourth Commandment
under the Law. The Turks perform
their Religious Ceremonies on Friday.
A
3
74
The Defcription and Ufe
4 Monih
dical
A Month is properly a certain Space
of Time meaſured by the Moon in its
Courſe round the Earth. A Lunar Month
is either Periodical or Synodical. A Pe-
Periodical riodical Month is that Space of Time the
and Sync-
Moon taks to perform her Courſe from
Months. one Point of the Ecliptic till the arrives
to the fame again, which is 27 Days
and fome odd Hours; and a Synodical
Month is the Time betwixt one New
Moon, and the next New Moon, which
is commonly about 29 Days. But a
Civil Month is different from thefe, and
confifts of a certain Number of Days,
fewer or more, according to the Laws
and Cuſtoms of the Country where they
are obſerved.
de. eal and
र
The compleateſt Period of Time is a
Year, in which all the variety of Seafons
return, and afterwards being a-new. A
Year is either Aftronomical or Civil. An
A Year Sy- Aftronomical Year is either a Sydereal,
Tropical. wherein the Sun departing from a fixed
Star, returns to it again; or Tropical,
which is the Space of Time the Sun
takes to perform his Courfe from any
Point of the Ecliptic till he returns to it
again.
A.
Sect. I Of the GLOBE Ş.
75
}
5
A Tropical Year confifts of 365 Days,
Hours and 49 Minutes; this is the
Time in which all the Seaſons com-
pleatly return, which is a ſmall matter
leſs then a Sydereal Year.
The Civil Year is the fame with the
Political eſtabliſhed by the Laws of a
Country; and is either moveable or im-
moveable. The moveable Year confifts
of 365 Days, being lefs then the Tro-
pical Year by almoft fix Hours, and is
called the Egyptian Year, becauſe ob-Egyptian
ferved in that Country.
The Romans divided the Year into 12
Kalender Months, to which they gave
particular Names, and are ſtill retained
by moſt of the European Nations, viz.
January, February, March, April, May,
June, July, August, September, October,
November, and December. The Number
of Days in each Month may be known
by the following Verſes
Thirty Days bath September,
April, June, and November;
February hath Twenty-eight alone,
And all the reft have Thirty-one.
Thẹ
Itar.
76
The Defcription and Ufe
The Year is alfo divided into four
Quarters or Seaſons, viz. Spring, Sum-
mer, Autumn, and Winter. Thefe Quar-
ters are properly made when the Sun
enters into the Equinoctial and Solftitial
Points of the Ecliptic; but in Civil Ufes
they are differently reckoned according
to the Cuftoms of feveral Countries.
In England we commonly reckon the
first Day of January to be the firſt in
the Year, which is therefore vulgarly
called New-Year's-Day; but in Politi-
cal and Ecclefiaftical Affairs, the Year
is reckoned to commence on Lady-Day,
which is the 25th of March; and from
thence to Midfummer-Day, which is the
24th of June, is reckoned the fi ft Quar-
ter; from Midſummer-Day to Michael-
mas-Day, which is the 29th of September,
is the ſecond Quarter; the third Quar-
ter is reckoned from Michaelmas-Day to
Christmas-Day, which is the 25th of
December; and from Christmas-Day to
Lady-Day, is reckoned the laſt Quarter
in the Year. In common Affairs, a
Quarter is reckoned from a certain Day
to the fame in the fourth Month follow-
ing. Sometimes a Month is reckoned
four Weeks, or 28 Days, and fo a Quar-
ter 12 Weeks. To all the Inhabitants
in
Sect. I Of the Ĝ L O BE S.
77
་ཝཱ
SNorthern?
in the Southern S Hemiſphere, their
Midfummer is properly when the Sun
is in the Tropic of
of Cancer. 2
Capricorn S
and
their Midwinter at the oppofite Time
of the Year; but thofe who live under
the Equinoctial have two Winters, &c.
when the Sun is in either Tropic; tho
indeed properly, there is no Seafon that
may be called Winter in thoſe Parts
of the World.
The Egyptian Year of 365 Days be-
ing lefs then the true Solar Year by al-
moft fix Hours, it follows, that four fuch
Years are lefs then four Solar Years by
a whole Day; and therefore in 365
Times four Years, that is, in 1460 Years,
the Beginning of the Years move through
all the Seaſons. To remedy this In-
conveniency, Julius Cæfar (confidering
that the fix Hours, which remain at the
end of every Year will in four Years
make a natural Day) ordered that every
fourth Year ſhould have an intercalary
Day, which therefore confifts of 366
Days; the Day added was put in the
Month of February, by poftponing St.
Matthias's Day, which in common Years
fall on the 24th, to the 25th of the faid
Month,
酆
​78
The Deſcription and Ufe
Month, all the fixed Feafts in the Year
from thence forwards falling a Week-day
+
later then otherwife they would, VAc-
Biflextile, cording to the Roman Way of reckon-
or Leap ing, the 24th of February was the fixth
Year.
of the Kalends of March, and it was
ordered that for this Year the e fhould
be two fixths, or that the fixth of the
Kalends of March ſhould be twice re-
peated; upon which account the Year
was called Biffextile, which we now call
the Leap-Year.
+
+
To find whether the Year of our
Lord be Leap-Year, or the firft, fecond,
or third after; divide it by four, and
the remainder, if there be any, fhews
how
many Years it is after Leap Year ;
but if there be no Remainder, then that
Year is Leap-Year: Or you may omit
the Hundreds and Scores, and divide the
Refidue by 4, Examp. 1757, omitting
the Hundreds and the Twenties, I di-
vide the Refidue 17 by 4, and the Re-
mainder fhews it to be the firſt after
Leap-Year.
This Method of reckoning the Year,
viz. making the common Year to con-
fift of 365 Days, and every fourth Year
to have 366 Days, is now uſed in Great-
Britain
}
Séct. I Of the GLOBES.
79
$
↑
Britain and Ireland, and fome of the
Northern Parts of Europe, and is called
the Julian Account, or the Old Style.Julian Ac-
But the Time appointed by Julius Caefar count or be
Old Style.
for the Length of a Solar Year is too
much; for the Sun finishes his Courfe
in the Ecliptic in 365 Days, 5 Hours
and 49 Minutes, which is 11 Minutes
lefs then the Civil Year; and therefore
he again begins his Circuit 11 Minutes
before the Civil Year is ended; and fo
much being gained every Year, amounts
in 131 Years, to a whole Day. So that
if the Sun in any Year entered the Equi-
nox upon the 20th of March at Noon,
after the Space of 131 Years, he'll enter
the fame Point on the fame Hour on
the 19th of March. And therefore the
Equinoxes will not always fall on the
fame Day of the Month, but by Degrees
will move towards the Beginning of the
Year.co
At the Time of the Council of Nice,
(when the Terms were fettled for ob-
ferving of Eaſter) the Vernal Equinox fell
upon the 21st of March; but by its
falling backwards II Minutes every Year,
is was found that in Anno 1582, when
the Kalender was corrected, the Sun en-
tered the Equinoctial Circle on the 11th
of
80
The Defcription and Uſe
of March, having departed ten whole
Days from its former lace in the Year;
and therefore Pope Gregory the XI:1th,
defigning to place the Equinoxes in their
Situation with refpect to the Year, took
thefe ten Days out of the Kalender, and
ordered that the 11th of March fhould
be reckoned as the Twenty-firft: And
to prevent the Seafons of the Year from
going backwards for the future, he or
dered every hundredth Year, which in the
Julian Form was to bea Biffextile, fhould
be a common Year, and confift only of
365 Days; but that being too much,
every fourth Hundred was to remain
Bifextile This Form of reckoning be-
ing eſtabliſhed by the Authority of Pope"
Account, or Gregory XIII. is called the Gregorian
New Style Account, or the New Style; and is ob-
ſerved in all the Countries where the
Authority of the Pope is acknowledged
and likewiſe by feveral Nations of the
reformed Religion. There being now
above an hundred Years paft, fince this
Reformation was made in the Kalender.
the Gregorian Account has accordingly
got before the Julian one Day more
then it was in the Time of its Inftitu-
tion, the Difference between theſe two
Accounts being now eleven Days; fo that
the firft Day of any Month, according
Gregorian
to
Sect. 2:
81
Of the GLOBE s.
to that Way of reckoning, is the 12th
of the fame Month according to the
New Style.
I fhall conclude this Section with a
brief Account of the Atmoſphere.
The Atmosphere is that thin Body of Atmo
Airwhich furrounds the Earth, in which Sphere.
the Clouds hover, and by which in their
Deſcent they are broke into Drops of
Rain; which fometimes according to
the Warmth or Coldneſs of Air, are
froze into Snow, or Hailftones. Thunder
and Lightning are alſo made in the At-
mosphere, and Wind is nothing elſe but
a Percuffion of the Air, occafioned by
its different Denſity in different Places.
The Benefits we receive from the Atmo-
ſphere are innumerable; without Air no
earthly Creature could live, as is plainly
proved by Experiments made by the
Air-Pump; and the wholfomeneſs of
a Climate chiefly depends upon that of
its Air: If there was no Atmoſphere to
reflect the Rays of the Sun, no Part of
the Heavens would be lucid and bright,
but that wherein the Sun was placed;
and if a Spectator fhould turn his Back
towards the Sun, he would immediately
perceive it to be quite dark, and the
leaft™
G
82
The Deſcription and Uſe
}
A
leaſt Stars would be ſeen ſhining as they
do in the cleareſt Night; and the Sun
immediately before his fetting would
fhine as brisk as at Noon, but in a
Moment as foon as he got below the
Horizon, the whole Hemiſphere of the
Earth would be involved in as great a
Darkneſs as if it were Midnight.
But by means of the Atmoſphere it
happens, that while the Sun is above
the Horizon, the whole Face of the Hea-
vens is ſtrongly illuminated by its Rays,
ſo as to obfcure the faint Light of the
Stars, and render them invifible; and
after Sun-ſetting, though we receive no
direct Light from him, yet we enjoy its
reflected Light for fome Time: For the
Atmoſphere being higher than we are,
is a longer Time before it is with drawn
from the Sun (as if a Man was to run
to the Top of a Steeple, he might ſee the
Sun after it had been fet to thoſe at the
Bottom.) The Rays which the Atmo-
fphere receives from the Sun, after he is
withdrawn from our Sight, are by Re-
fraction faintly tranfmitted to us; untill
the Sun having got about 18 Degrees
below the Horizon, he no longer en-
lightens our Atmoſphere, and then all
that Part thereof which is over us be-
' comes
JJ
Sect. I.
83
Of the GLOBĖ S.
}
>
comes dark. After the fame Manner in
the Morning, when the Sun comes with-
in 18 Degrees of our Horizon, he again
begins to enlighten the Atmoſphere, and
fo more and more by Degrees, untill he
rifes and makes full Day.
This fmall Illumination of the Atmo-
fphere, and the State of the Heavens Twilight,
between Day and Night is called the or Crepuf-
Twilight, or the Crepufculum.
The Duration of Twilight is different
in different Climates, and in the fame
Place at different Times of the Year.
The beginning or ending of Twilight
being accurately given, we may from
thence eaſily find the Height of the At-
moſphere, which is not always the fame.
The mean Height of the Atmoſphere is
computed to be about 40 Miles; but
it is probable, the Air may extend itſelf
a great deal further, there being pro-
perly no other Limits to it, as we can
conceive, but as it continually decreaſes
in Denſity the farther remote it is from
the Earth, in a certain Ratio; which at
laft, as to our Conception, muft in a
Manner terminate.
culum.
G z
SECT
}
84
The Defcription and Uſe.
惠​券
​惠
​+
Latitude.
*}*<}&********************
茶茶
​SECT. II.
GEOGRAPHICAL DEFINITIONS.
Of the Situations of Places
upon the Earth; of the dif-
ferent Situations of its Inha-
bitants of Zones and Cli-
mates.
T
;
HE Situations of Places upon the
Earth are determined by their
Latitude and Longitude.
1. The Latitude of any Place (upon ·
the Earth) is its neareſt Diſtance, either
North or South, from the Equator; and
if the Place be in the SNorthern?
Southern
ſphere, it is accordingly called
Hemi-
North?
South
Latitude; and is meaſured by an Arch
of the Meridian intercepted betwixt the
Zenith of the faid Place and the Equator.
And all Places that lie on the fame Side,
and at the fame Distance from the Equa-
tor,
Sect. 2.
85
Of the GLOBES.
tor, are faid to be in the fame Parallel
of Latitude: the Parallels in Geography
being the fame with the Parallels of De-
clination in Aftronomy.
From this Definition ariſe the follow-
ing Corollaries.
(1.) That no Place can have above 90
Degrees of Latitude, either North or South.
2.) Thofe Places that lie under the
Equinoctial (or thro' which the Equator
paſſes) have no Latitude, it being from
thence that the Calculation of Latitudes is
counted; and thofe Places that lie under
the Poles have the greatest Latitude, thofe
Points being at the greateſt Diſtance from
the Equator.
(3.) The Latitude of any Place is al-
ways equal to the Elevation of the Pole in
the fame Place above the Horizon ; and is
therefore often expressed by the Pole's
Height, or Elevation of the Pole; the
Reafon of which is, becaufe from the Equator
to the Pole there is always the Diſtance of
90 Degrees, and from the Zenith to the Ho-
rizon the fame Number of Degrees, each
of thefe including the Distance from the
Zenith to the Pole: That Distance there-
fore
86
The Defcription and Uſe
fore being taken away from both, will leave.
the Distance from the Zenith to the Equa-
tor, (which is the Latitude) equal to the
Distance from the Pole to the Horizon.
(4) The Elevation of the Equator in any
Place is always equal to the Complement of
the Latitude of the fame Place.
(5.) A Ship failed directly
}
towards?
from
the Equator Lements ber Latitude,
}
the Pole) juſt ſo much
(or Raifes
Depreſſes
as is ber Diſtance failed,
Difference 2. Difference of Latitude is the neareſt
of Lati-
Sude.
Diſtance betwixt any two Parallels of
Latitude, fhewing how far the one is to
the Northward or Southward of the o-
ther, which can never exceed 180 Degrees.
And when the two Places are in the
fame Hemiſphere (or on the fame fide
of the Equator) the leffer Latitude ſub-
ftracted from the greater, and when
they are on different Sides of the Equa-
ror, the two Latitudes added, gives the
Difference of Latitude.
3. The
Sect. 2: of the GLOBES.
87
3. The Longitude of any Place (upon Longitude.
the Earth) is an Arch of the Equator,
contained betwixt the Meridian of the
given Place, and fome fixed or known
Meridian; or, it is equal to the Angle
formed by the two Meridians, which
properly can never exceed 180 Degrees,
tho' ſometimes the Longitude is counted
Eaſterly quite round the Globe.
Since the Meridians are all moveable,
and not one that can be fixed in the
Heavens, (as the Equinoctial Circle is
fixed, from whence the Latitudes of all
Places are determined to be fo much
either North or South) the Longitudes
of Places cannot fo well be fixed from
any other Meridian, but every Geogra-
pher is at his Liberty to make which he
pleaſes his firſt Meridian, from whence
to calculate the Longitudes of other
Places. Hence it is that Geographers
of different Nations reckon their Lon-
gitudes from different Meridians, com-
monly chufing the Meridian paffing
through the Metropolis of their own
Country for their firft: Thus, the En-
glish Geograghers generally make the
Meridian of London to be their first, the
French that of Paris, and the Dutch
that of Amfterdam, &c. and Mariners
gene-
+
88
The Defcription and Ufe
generally reckon the Longitude from
the laſt known Land they faw. This
arbitrary Way of reckoning the Longi-
tude from different Places, makes it ne-
ceffary, whenever we expreſs the Lon-
gitude of any Place, that the Place from
whence it is counted be alfo expreffed.
From the preceding Definitions ariſe
the following Corollaries-:
1. If a Body ſhould ſteer directly North,
or directly South, quite round the Globe,
he'll continually change his Latitude; and
paſs through the two Poles of the World,
without deviating the least from the Me-
ridian of the Place he departed from ; and
confequently on his Return will not differ
in his Account of Time from the People
refiding in the faid Place.
2. If a Body fhould fteer round the Globe,
either due Eaft or due Weft, he'll continu-
ally change his Longitude, but will go quite
round without altering his Latitude; and
if his Courfe fhould be due Eaft, he'll gain
a Day compleatly in his Reckoning, or
reekon one Day more than the Inhabitants
of the Place from whence he departed; and
if his Courfe had been Weft, he would have
loft one Day, or reckon one lefs.
The
}
Sect. 2. Of the GLOBE S.
89
The Reaſon of which is evident; for
admitting our Traveller fteers due Eaſt
fo many Miles in one Day as to make
his Difference of Longitude equivalent
to a Quarter of an Hour of Time, it is
evident that the next Day the Sun will
rife to him a Quarter of an Hour foon-
er than to the Inhabitants of the Place
from whence he departed; and fo daily,
in Proportion to the Rate he travels,
which in going quite round will make
up one natural Day. In like Manner,
if he ſteers due Weft after the fame Rate,
he'll lengthen each Day a Quarter of an
Hour, and confequently the Sun will
riſe to him ſo much later every Day; by
which Means, in going quite round,
he'll loſe one Day compleat in his Reck-
oning. From whence it follows,
3. If two Bodies fhould fet out from the
fame Place, one fteering East, and the other
Weft, and fo continue their Courfes quite
round, untill they arrive at the Place from
whence they fet out, they'll differ two Days
in their Reckoning at the Time of their
Return.
4. If a Body ſhould ſteer upon an Oblique
Courfe (or any where betwixt the Meridi-
an and the Eaft or Weft Points), he'll
con-
90
The Deſcription and Uſe
continually change both Latitude and Lon-
gitude, and that more or less, according to
the Courſe be fteers; and if he should go
quite round the Globe, he'll differ in his
Account of Time, as by the Jecond Corol.
1
5. The People refiding in the Eafter-
most of any two Places will reckon their
Time fo much the fooner than those who live
in the other Place, according to the Dif
ference of Longitude betwixt the two Pla-
ces, allowing one Hour for every 15 De-
grees, &c. and the contrary.
II. Of Zones and Climates, &c.
4. Zones are large Tracts of the Sur-
face of the Earth, diftinguiſhed by the
Tropics and Polar Circles, being five in
rid,Tempe- Number; viz. one Torrid, two Tempe-
rate, and rate, and two Frigid.
Zones Tor-
Frigid.
The Torrid or Burning Zone is all the
Space comprehended between the two
Tropics, the Antients imagined this
Tract of the Earth to be uninhabitable,
becauſe of the exceffive Heat, it being fo
near the Sun. All the Inhabitants of
the Torrid Zone have the Sun in their
Zenith, or exactly over their Heads twice
in every Year; excepting thoſe who live
}
ex-
}
1
1
{
Sect. 1.
Of the GLOBES.
exactly under the two Tropics, where
the Sun comes to their Zenith only once
in a Year.
The two Temperate Zones lie on ei-
ther Side of the Globe, between the
Tropics and the Polar Circles.
The two Frigid Zones are thofe Spa-
ces upon the Globe that are included
within the two Polar Circles.
ans.
91
The Inhabitants of the Earth are alſo
diſtinguiſhed by the Diverſity of their
Shadows. Thoſe who live in the Torrid
Zone are called Amphifcians, becauſe Amphifci-
their Noon-Shadow is caft different
Ways, according as the Sun is to the
Northward or Southward of their Ze-
nith; but when the Sun is in their Ze-
nith, they are called Afcians.
Afcians.
The Inhabitants of the Temperate
Zones are called Heterofcians, becauſe Heterfei
their Noon-Shadow is always caft the ans.
fame Way: But thoſe who live under
the Tropics are called Afcians Heterofci- Afcians He-
ans; thoſe who live in the Frigid Zones ferocians.
are called Perifcians, becauſe fometimes
their Shadow is caft round about them.
Theſe
Perifcians.
92
The Defeription and Uſe
>
Periæci.
Antoeci.
글
​Theſe hard Names are only Greek
Words, importing how the Sun cafts
the Shadow of the feveral Inhabitants
of the Earth; which would be a too tri-
fling Diſtinction to be made here, was
it not for the fake of complying with
Cuftom.
The Inhabitants of the Earth are alfo
diſtinguiſhed into three Sorts, in refpect
to their relative Situation to one another,
and theſe are called the Periæci, Antæci,
and Antipodes.
5. The Periaci are thoſe who live
under oppofite Points of the fame Paral-
lel of Latitude. They have their Sea-
fons of the Year at the fame Time, and
their Days and Nights always of the fame
Length with one another, but the one's
Noon is the other's Midnight; and when
the Sun is in the Equinoctial, he riſeth
with the one when he fets with the
other. Thoſe who live under the Poles
have no Periæci,
6. The Antæci live under the fame
Meridian, and in the fame Latitude,
but on different Sides of the Equator;
their Seaſons of the Year are contrary,
and the Days of the one are equal to
the
Sect. 2. Of the GLOBE S.
93
the Nights of the other, but the Hour
of the Day and Night is the fame with
both; and when the Sun is in the Equi-
noctial, he riſes and fets to both exactly
at the fame Time. Thoſe who live un-
der the Equator have no Anteci.
7 The Antipodes are thoſe who live Antipodes.
diametrically oppofite to one another,
ſtanding, as it were, exactly Feet to
Feet: Their Days and Nights, Summer
and Winter, are at direct contrary
Times.
The Surface of the Earth is by fome
diſtinguiſhed into Climates.
8. A Climate is a Tract of the Sur-Climates.
face of the Earth, included between two
fuch Parallels of Latitude, that the
Length of the longeſt Day in the one ex-
ceeds that in the other by half an Hour.
The whole Surface of the Earth is
confidered, as being divided into 60 Cli-
mates, viz. from the Equator to each
of the Polar Circles 24, arifing from the
Difference of Hour in the Length of
their longeſt Days; and from the Polar
Circles to the Poles themſelves are fix,
arifing from the Difference of an entire
I
2
Month,
94
The Deſcription and Ufe.
1
Month, the Sun being feen in the firſt
of theſe a whole Month without fetting;
in the ſecond two; and in the third,
three Months, &c. Thefe Climates
continually decreaſe in Breadth, the
farther they are from the Equator. How
they are framed, viz. the Parallel of
Latitude in which they end (that being
likewiſe the Beginning of the next) with
the reſpective Breadth of each of them,
is fhewed in the following Table :
1
J
$
Á TÁ≤
Sect. 1.
95
Of the GLOBE s.
A
ATABLE of the CLIMATES.
cı
AT
CLIMATES between the Equator and the Polar
童
​Circles.
Cli-Longeft Latitude. Breadth
Day. D. M. \D. M.
mates Day.
~
2
W N
HIN
Cli- Longeft Latitude. Breadth
mutes. Day. D. M. D. M.
1859 58
61 18
I
12 /
8 25
8 25
13
1 29
13
16 25
8 00
14
19
I 20
3
13 /
2350
7 25
4
14
30 25
6 30
16
1962 25
20 63 22
I 7
• 57
56 200
14
KIN
4556
36 28
6 8
17
15
7 15
8 16
9 16 / 51 58
54 27
10 17
41 22
4 54
18
78
20 64 6
• 44
21
64 49
0 43
45 29
4 7
19
49 I
3 32
20
2165 21 0 32
22 65 47
O 26
2 57
21
22
66 6
o 19
2 29
22
23
66 20
0 14
11
17
12
18
HIN
56 37
2 10 23
236628
8
58 29
1 52 24
24
66 31 0 3
CLIMATES between the Polar Circles and the
Poles.
Length of Days.
Latitude.
Length of Days.
Latitude.
Months.
I
W N Mot
3
D. M.
67 21
Months.
2
69 48
73 37
456
D. M.
78 30
84
5
00 Oo
1
III. Of
26
The Defcription and Ufe
Acronical.
III. Of the Poetical Rifing and Setting of
the Stars.
The Ancient Poets make frequent
Cofmical, Mention of the Stars Rifing and Setting,
and Helia- either Cofmically, Acronically, or Helia-
cal Rifing cally; whence theſe Diſtinctions are cal
and Set- led Poetical.
ting.
A Star is faid to rife or fet Cofmically,
when it riſes or fets at Sunrifing; and
when it rifes or fets at Sun-fetting, it is
faid to riſe or ſet Acronically. A Star riſes
Heliacally, when firft it becomes vifible,
after it had been fo near the Sun as to be
hid by the Splendor of his Rays: And
a Star is faid to fet Heliacally, when it is
firft immerfed, or hid by the Sun's Rays.
}
The Fixed Stars, and the three fupe-
rior Planets, Mars, Jupiter, and Saturn;
rife Heliacally in the Morning; but the
Moon rifes Heliacally in the Evening,
becauſe the Sun is fwifter than the fupe-
rior Planets, and flower than the Moon.
IV. Of the Surface of the Earth, confide-
red as it is compofed of Land and Water.
The Earth confifts naturally of two
Parts, Land and Water, and therefore
Sect. 2. Of the GLÓ BE´S.
97
}
it is called the Terraqueous Globe. Each
of thefe Elements is fubdivided into
various Forms and Parts, which ac-
cordingly are diftinguiſhed by different
Names
*
1
I. Of the Land.
The Land is diftinguiſhed into Con-
tinents, Ilands, Peninfuld's, Ifthmus's,
Promontories, Mountains, or Coafts.
9. A Continent is a large Quantity Continents
of Land, in which many great Countries
are joined together, without being fe-
perated from each other by the Sea :
Such are Europe, Asia, Africa, and thệ
vaſt continent of America; which foùr
are the principal Divifions of the Earth.
A Continent is ſometimes called the
Main Land.
•
MainLand
10. An Iſland is a Country, or Por-Iland,
tion of Land, environ'd round with
Water Such are Great-Britain and
Ireland; Sardinia, Sicily, &c. in the Me-
diterranean Sea; the Iſles of Wight, An-
glefey, &c. near England. Alfo a fmall
Part of dry Land, in the Midſt of a
River, is called an Iſland, when compa-
red to a leffer, is called the Continent;
H
1
a's
98
The Defcription and Ufe
[
Peninfula.
Ifthmus.
Promon.
tory
as if we compare the Isle of Wight to
England, the latter may be properly cal-
led the Continent.
II. A Peninfula is a Part of Land
almoſt environ'd with Water, ſave one
narrow Neck adjoining it to the Conti-
nent; or which is almoſt an Ifſland: Such
is Denmark joining to Germany; alfo
Africa is properly a large Peninſula join-
ing to Afia.
12. An Ifthmus is a narrow Neck of
Land joining a Peninſula to the Con-
tinent; as the Ifthmus of Sues, which
joins Africa to Afia; that of Panama
joining North and South America, &c.
+
13. A Promontory is a high Part of
Land ftretching out into the Sea, and
is often call'd a Cape, or Headland: Such
is the Cape of Good Hope in the South
of Africa; Cape Finiftre on the Weſt
of Spain; alfo the Lizard Point, and
the Land's End, are two Capes or Head-
Mountain. lands on the Weft of England. A Moun-
tain is a high Part of Land in the
Midſt of a Country, over topping the,
adjacent Parts.
4 14.
Sect. 2.
99
Of the GLOBE S.
14.
A Coaft or Shore is that Part of 4 Coast of
Land which borders upon the Sea, whe- Shore.
ther it be in Iſlands or a Continent: And
that Part of the Land which is far dif-
tant from the Sea, is called the Inland Inland.
Country. Theſe are the ufual Diftinc-
tions of the Land.
The Water is diftinguiſhed into O-
ceans, Seas, Lakes, Gulfs, Straits, and
Rivers.
15.
TheOcean,
or Main
The Ocean, or Main Sea, is a
vaſt ſpreading Collection of Water, not Sea.
divided or ſeparated by Lands running
between: Such is the Atlantic or Western
Ocean, between Europe and America,
the Pacific Ocean, or South-Sea, &c.
Note, Thofe Parts of the Ocean
which border upon the Land, are called
by various Names, according to thoſe
of the adjacent Countries; as, the Brit-
ish Sea, the Irish Sea, the French and
Spaniſh Sea.
16: A Lake is a Collection of deep A Lake:
tanding Water, incloſed all round with
Land, and not having any vifible and
open Communication with the Sea: But
When this Lake is very large, it is com-
H 2
monly
ioo
The Deſcription and Uſe
A Gulf.
monly called a Sea; as, the Cafpian Sea
in Afia, &c.
}
17. A Gulf is a Part of the Sea al-
moft encompaffed with Land, or that
which runs up a great Way into the
Land; as, the Gulf of Venice, &c. But if
it be very large, 'tis rather called an In-
tand Sea; as the Baltick Sea, the Medi-
terranean Sea, the Red Sea, or the Ara-
bian Gulf, &c. And a ſmall Part of the
Sea thus environed with Land is uſually
called a Bay. If it be but a very fmall
Part, or, as it were, a fmall Arm of the
Sea, that runs but a few Miles between
Haven. the Land, it is called a Creek or Haven.
Creek or
A Strait.
18. A Strait is a narrow Paffage ly-
ing between two Shores, whereby two
Seas are joined together; as, the Straits
of Dover, between the British Channel
and the German Sea; the Straits of Gib-
raltar, between the Atlantick and the
Mediterranean Sea. The Mediterranean ·
itſelf is alſo ſometimes called the Straits.
Theſe are all the neceffary Terms
commonly uſed in Geography. The
Names of the feveral Countries and Seas,
and all the Principal Divifions of the
Earth, the Reader will find exprefled
upon
·Sect⋅ 2. Of the GLOBE S.
IQI
upon the Terreftrial Globes. To give
a tolerable Account of the Produce of
each country, the Genius of the People,
their political Inſtitutions, &c. is pro-
perly a particular Subject of itſelf, and
quite foreign to our Defign. We fhall
next proceed to the Uſe of the Globes;
but firſt it may not be amiſs to take a
fhort Review of their Appurtenances.
Thoſe Circles of the Sphere that are
fixed, are (as has been already ſaid )
drawn upon the Globes themſelves; thofe
that are moveable, are fupplied by the
Brafs Meridian, the Wooden Horizon,
and the Quadrant of Altitude.
1. That Side of the Brazen Meridian, Brass Me-
which is divided into Degrees, repre-ridian.
ſents the true Meridian; this Side is com-
monly turned towards the Eaſt, and 'tis
ufual to place the Globe fo before you,
that the North be to the Right-hand,
and the South to the Left. The Meri-
dian is divided into 4 Quadrants, each
being 90 Degrees, two of which are
numbered from that Part of the Equi-
noctial, which is above the Horizon, to-
wards each of the Poles; the other two
Quadrants are numbered from the Poles
towards the Equator. The Reaſon why
H 3
two
102
The Defcription and Ufe
Horizon.
two Quadrants of the Meridian are
numbered from the Equator, and the
other two from the Poles, is, becauſe the
former of theſe two ferve to fhew the
Diſtance of any Point on the Globe from
the Equator, and the other to elevate
the Globe to the Latitude of the Place.
2. The upper Side of the Wooden
Wooden Frame called the Wooden Horizon, re-
preſents the true Horizon; the Circles
drawn upon this Plane have been alrea-
dy deſcribed; we may obferve, that the
firſt Point of is the Eaft, and the op-
pofite being the firft Point of is the
Weft, the Meridian paffing through the
North and South Points.
Quadrant
3. The Quadrant of Altitude is a
of Altitude. flexible Plate of thin Braſs, having a Nut
¿les:
and Screw at one End, to be faſtened to
the Meridian of either Globe, as occafion
requires. The Edge of this Quadrant,
which has the Graduations upon it,
called the fiducial Edge, is that which is
always meant whenever we make men-
tion of the Quadrant of Altitude.
Hour-Cir 4. The Horary or Hour-Circle is
divided into twice twelve Hours, the two
XII's coinciding with the Meridian; the
upper
Sect. 2. Of the GLOBE S.
103
uppermost XII is that at Noon, and the
lower-moft towards the Horizon is XII
at Night. The Hours on the East Side
of the Meridian are the Morning Hours,
and thoſe on the Weft Side the Hours af-
ter Noon. The Axis of the Globe car-
ries round the Hand or Index which
points the Hour, and paſſes through the
Center of the Hour Circle.
The Things above deſcribed are com-
mon to both Globes; but there are fome
others which are peculiar or proper to
one Sort of Globe. The two Colures, and
the Circles of Latitude, from the Eclip-
tic, belong only to the Celestial Globes;
alfo the Ecliptic itſelf does properly be-
long only to this Globe tho'it is always,
drawn on the Terreſtrial, for the fake of
thoſe that might not have the other Globe
by them. The Equinoctial on the Celeſtial
Globe is always numbered into 360 De-
grees, beginning at the Equinoctial Point
r; but on the Terreftrial, it is arbitary
where theſe Numbers commence, accord-
ing to the Meridian of what Place you
intend for your firft; and the Degrees
may be counted either quite round to 360
or both Ways, till they meet in the op-
pofite Part of the Meridian at 180.
H 4
SECT.
104
The Ufe of
SECT. III.
The USE of the GLOBES.
PROBLEM I, To find the Latitude and
Longitude of any given Place upon the
Globe; and on the contrary, the Latitude
and Longitude being given, to find the
Place.
I.
TU
URN the Globe round its Ax-
is, till the given Place lies ex-
actly under the (Eaſtern Side of the
Brafs) Meridian, then that Degree up-
on the Meridian, which is directly over
it, is the Latitude; which is accordingly
North or South, as it lies in the Nor-
thern or Southern Hemiſphere, the
Globe remaining in the fame Pofition.
That Degree upon the Equator,
which is cut by the Brazen Meridian, is
the Longitude required from the firſt
Meridian upon the Globe. If the Lon-
gitude is counted both Ways from the
firſt
Sect. 3.
195
the GLOBE S.
firſt Meridian upon the Globe, then we
are to confider, whether the given place
lies Eaſterly or Wefterly from the firſt
Meridian, and the Longitude muſt be
expreffed accordingly.
The Latitudes of the following Places:
and upon a Globe where the Longitude
is reckon'd both Ways from the Meri-
dian of London, their Longitudes will be
found as follow:
}
Latitude.
Deg.
41 North. 13
Longitude.
Deg.
Rome
Paris
3
Eaft.
48
2
E.
Mexico
20
N.
102
W.
Cape Horn - -
58
S.
80 W.
N.
2. The Latitude and Longitude being gi-
ven to find the Place,
Seek for the given Longitude in the
Equator, and bring that Point to the
Meridian; then count from the Equa-
tor on the Meridian the Degree of La-
titude given, towards the Arctic and An-
tarctic Pole, according as the Latitude
is Northerly or Southerly, and under
that Degeee of Latitude lies the Place
required.
t
}
PROB.
106
The Ufe of
}
PROB. II. To find the Difference of Lati-
tude betwixt any two given Places.
Bring each of the Places propofed
fucceffively to the Meridian, and obferve
where they interfect it, then the Number
of Degrees upon the Meridian, contained
between the two interfections will be the
Difference of Latitude required. Or, if
the Places propoſed are on the fame Side
of the Equator, having firſt found their
Latitudes, fubftract the leffer from the
greater; but if they are on contrary
Sides of the Equator, add them both
together, and the Difference in the firſt
Cafe, and the Sum in the latter, will be
the Difference of Latitude required.
Thus the Difference of Latitude be-
twixt London and Rome will be found to
be 9 Degrees; betwixt Paris and Cape
Bona Esperance 83 Degrees.
3
4
PROB. III. To find the Difference of Lon-
gitude betwixt any two given Places.
Bring each of the given Places fuc-
ceffively to the Meridian, and ſee where
the Meridian cuts the Equator each
Time; the Number of Degrees con-
tained betwixt thoſe two Points, if it be
lefs
Sect. 3.
107
the GLOBE S.
lefs than 180 Degrees, otherwiſe the
Remainder to 360 Degrees will be the
Difference of Longitude required. Or,
Having brought one of the given
Places to the Meridian, bring the Index
of the Hour-Circle to 12 o'clock; then
having brought the other Place to the
Meridian, the Number of Hours con-
tained beween the Place the Index was
firſt fet at, and the Place where it now
points, is the Difference of Longitude
in Time betwixt the two Places.
Thus the Difference of Longitude be-
twixt Rome and Conftantinople will be
found to be 19 Degrees, or i Hour and
a Quarter; betwixt Mexico and Pekin in
China, 240 Degrees, or 9 Hours.
I
3
PROB. IV. Any Place being given to find
all thofe Places that are in the fame
Latitude with the faid Place.
The Latitude of any given Place be-
ing marked upon the Meridian, turn
the Globe round its Axis, and all thoſe
Places that paſs under the fame Mark
are in the fame Latitude with the given
Place, and have their Days and Nights
of equal Lengths. And when any Place
is
ย
108
· The Ufe of
is brought to the Meridian, all the In-
habitants that lie under the
upper Semi-
circle of it, have their Noon or Mid-
day at the fame Point of abfolute Time
exactly.
PROB. V. The Day of the Month being
given; to find the Sun's Place in the
Ecliptic, and his Declination.
1. To find the Sun's Place: Look for
the Day of the Month given in the Ka-
lender of Months upon the Horizon, and
right againſt it you'll find that Sign and
Degree of the Ecliptic which the Sun
is in. The Sun's Place being thus found,
look for the fame in the Ecliptic Line
which is drawn upon the Globe, and
bring that Point to the Meridian, then
that Degree of the Meirdian, which is
directly over the Sun's Place, is the De-
clination required; which is accordingly
either North or South, as the Sun is in
the Northern or Southern Signs. Thus,
April 23
July 31
October 26
January 20
Sun's Place
Deg. Min.
Declination.
Deg. Min.
3 00
12
32 N.
7 51
18
20 N.
m
2.49
12
28 S.
49
20
07 S.
PROB,
Sect. 3.
1óg
the GLOBE S.
PROB VI. To rectify the Globe for the
Latitude, Zenith, and the Sun's Place.
1. For the Latitude: If the Place be
in the Northern Hemiſphere, raiſe the
Artic Pole above the Horizon; but for
the South Latitude you muſt raife the
Antarctic; then move the Meridian up
and down in the Notches, untill the De-
grees of the Latitude counted upon the
Meridian below the Pole, cuts the Ho-
rizon, and the Globe is adjuſted to the
Latitude.
2. To rectify the Globe for the Zenith:
Having elevated the Globe according to
the Latitude, count the Degrees thereof
upon the Meridian from the Equator
towards the elevated Pole, and that
Point will be the Zenith or the Vertex
of the Place; to this Point of the Meri-
dian faften the Quadrant of Altitude, fo
that the graduated Edge thereof may be
joined to the faid Point.
3. Bring the Sun's Place in the Eclip-
tic to the Meridian, and then fet the
Hour Index to XII at Noon, and the
Globe will be rectified to the Sun's Place.
If
you have a little Mariner's Compaſs,
the Meridian of the Globe may be eafily
fet to the Meridian of the Place.
1
1
110
The Ufe of
PROB. VII. To find the Distance between
any two given Places upon the Globe,
and to find all thofe Places upon the
Globe that are at the fame Distance
from a given Place.
Lay the Quadrant of Altitude over
both the Places, and the Number of De-
grees intercepted between them being re-
duced into Miles, will be the Diſtance
required: Or, you may take the Diſtance
betwixt the two Places with a Pair of
Compaffes, and applying that Extent to
the Equator, you'll have the Degrees of
Diſtance as before.
Note, A Geographical Mile is the th
Part of a Degree; whereof if
you mul-
tiply the Number of Degrees by 60, the
Product will be the Number of Geogra-
phical Miles, of Diſtance fought; but to
reduce the fame into English Miles, you
muſt multiply by 70, becauſe about 70
English Miles make a Degree of a great
Circle upon the Superficies of the Earth.
Thus, the Diſtance betwixt London
and Rome will be found to be about 13
Degrees, which is 780 Geographical
Miles!
{
Sect. 3..
III
the GLOBE S.
If you rectify the Globe for the Lati-
tude and Zenith of any given Place, and
bring the faid Place to the Meridian ;
then turning the Quadrant of Altitude
about, all thoſe Places that are cut by
the fame Point of it are at the fame
Diſtance from the given Place.
PROB. VIII. To find the Angle of Pofition
of Places, or the Angle formed by the
Meridian of one Place, and a great
Circle paffing through both the Places.
Having rectified the Globe for the
Latitude and Zenith of one of the given
Places, bring the faid Place to the Me
ridian, then turn the Quadrant of Alti-
tude about, untill the fiducial Edge
thereof cuts the other Place, and the
Number of Degrees upon the Horizon,
contained between the faid Edge and the
Meridian, will be the Angle of Poſition
fought.
1
Thus, the Angle of Pofition at the
Lizard, between the Meridian of the
Lizard and the Great Circle, paffing
from thence to Barbadoes is 69 Degrees
South-Wefterly; but the Angle of Po-
fition between the fame Places at Barba-
does, is but 38 Degrees North-Eaſterly.
SHO
¡ enx
}
The Ufe of
SCHOLIU M. D
་
The Angle of Pofition between two
Places is a different Thing from what is
meant by the Bearings of Places; othe
Bearings of two Places is determined by
a Sort of Spiral Line, called a Rhumb
Line, paffing between them in fuch a
Manner, as to make the fame or equal
Angles with all the Meridians through
which it paffeth; but the Angle or Po-
fition is the very fame Thing with what
we call the Azimuth in Aftronomy,
both being formed by the Meridian and
a great Circle paffing thro' the Zenith
of a given Place in the Heavens, then
called the Azimuth, or upon the Earth,
then called the Angle of Pofition.
}
If
From hence may be fhewed the Error
of that Geographical Paradox, viz.
a Place A bears from another B due
Weſt, B ſhall not bear from A due Eaſt:
I find this Paradox vindicated by an
Author, who at the fame Time gives a
true Definition of á Rhumb Line: But
his Arguments are ungeometrical; for
if it be admitted that the Eaft and
Weſt Lines make the fame Angles with
all the Meridians through which they
pafs, it will follow that theſe Lines are
the
1
Sect 3.
fig
the GLOBESI
Pa
the Parallels of Latitude: For any
rallel of Latitude is the Continuation of
the Surface of a Cone, whofe Sides are the
Radii of the Sphere, and Circumference
of its Baſe the faid Parallel; and it is evi-
dent, that all the Meridians cut the
faid Surface at right (and therefore at
equal) Angles; whence it follows, that
the Rhumbs of Eaft and Weft are the
Parallels of Latitude, though the Cafe
may ſeem different, when we draw
inclining Lines (like Meridians) upon
Paper, without carrying our Ideas any
farther.
PROB. IX. To find the Antœci, Perioci,
and Antipodes to any given Place.
Bring the given Pläce to the Meridian,
and having found its Latitude, count the
fame Number of Degrees on the Meri-
dian from the Equator towards the con-
trary Pole, and that will give the Place
of the Antæci.. The Globe being ftill
in the fame Pofition, fet the Hour Index
to XII at Noon, then turn the Globe a-
bout till the Index points to the lower
XII; the Place which then lies under the
Meridian, having the fame Latitude
with the given Place, is the Periaci re-
quired. As the Globe now ftands, the
I
An
114
The Use of
1
I
.2
Antipodes of the given Place are under
the fame Point of the Meridian, that its
Antaci ftood before: Or, if you reckon
180 Degrees upon the Meridian from
the given Place, that Point will be the
Antipodes. Let the given Place be Lon-
don in the Latitude of 1 Degrees
North, that place which lies under the
fame Meridian and the Latitude 514
Degrees South, is the Antaci; that which
lies in the fame Parallel with London, and
i80 Degrees of Longitude from it, is the
Periæci, and the Antipodes is the Place
whofe Longitude from London is 180
Degrees, and Latitude 51. Degrees
South.
I
2
PROB. X. The Hour of the Day at one
Place being given; to find the correfpon-
dent Hour (or what o'Clock it is at that
Time) in any other Place.
The Difference of Time betwixt two
Places is the fame with their Difference
of Longitude; wherefore having found
their Difference of Longitude, reduce it
into Time, (by allowing one Hour for
every 15 Degrees, &c.) and if the
Place where the Hour is required lies
S Eafterly, ? from the Place where the
Wefterly, S
Hour'
}
sect: 3.
itš
the GLOBE S.
Hour is given,
en,
Add
the Differ-
Subtract
ence of Longitude reduced into Time
Sto the Hour given; and the Sum
From}
or remainder will accordingly be the
Hour required. Or,
Having brought the Place at which
the Hour is given to the Meridian, ſet
the Hour Index to the given Hour;
then turn the Globe about until the
Place where the Hour is required comes
to the Meridian, and the Index will point
out the Hour at the faid Place.
Thus when it is Noon at London, it is
Rome
Conftantinople
H. M.
O
52 P. M.
2 07 P. M.
Vera Cruz
5-
30 A. M.
Pequin in China
7
50 P. M.
PROB. XI. The day of the Month being
given, to find thofe Places on the Globe
where the Sun will be Vertical, or in the
Zenith, that Day.
•
Having found the Sun's Place in the
Ecliptic, bring the fame to the Meridian,
and note the Degree over it; then
turning
H 2
116
The Ufe of
turning the Globe round, all Places that
paſs under that Degree will have the Sun
vertical that Day.
>
PROB. XII. A Place being given in the
Torrid Zone, to find thofe two Days
in which the Sun fhall be Vertical to the
fame.
Bring the given Place to the Meridian,
and mark what Degree of Latitude is
exactly over it; then turning the Globe
about its Axis, thoſe two Points of the
Ecliptic, which pafs exactly under the
faid Mark, are the Sun's Place; againſt
which, upon the Wooden Horizon,
you'll have the Days required.
PROB. XIII. To find where the Sun is
Vertical at any given Time affign'd; or.
the Day of the Month and the Hour at
any Place (fuppofe London) being
given, to find in what Place the Sun is
Vertical at that very Time.
Having found the Sun's Declination,
and brought the firſt Place (London) to
the Meridian, fet the Index to the given
Hour, then turn the Globe about until
the Index points to XII at Noon; which
being done, that Place upon the Globe
which
Sect. 3.
117
the GLOBE S.
.
which ſtands under the Point of the Sun's
Declination upon the Meridian, has the
Sun that Moment in the Zenith.
PROB. XIV. The Day, and the Hour of
the Day at one Place, being given; to
find all thofe Places upon the Earth,
where the Sun is then Rifing, Setting,
Culminating (or on the Meridian) alfo
where it is Day-light, Twilight, Dark
Night, Midnight; where the Twilight
then begins, and where it ends; the
Height of the Sun in any Part of the
illuminated Hemifphere; alfo his De-
preffion in the obfcure Hemisphere.
Having found the Place where the
Sun is Vertical at the given Hour, rectify
the Globe for that Latitude, and bring
the faid Place to the Meridian.
Then all thofe Places that are in the
Weſtern Semicircle of the Horizon, have
the Sun rifing at that Time.
Thoſe in the Eaſtern Semicircle have
it ſetting.
To thoſe who live under the upper
Semicircle of the Meridian, it is 12 o'
Clock at Noon.
And,
I 3
Thoſe
118
The Ufe of
Thofe who live under the lower
Semicircle of the Meridian have it at
Midnight.
All thofe Places that are above the
Horizon, have the Sun above them, juſt
fo much as the Places themſelves are
diftant from the Horizon; which Height
may be known by fixing the Quadrant
of Altitude in the Zenith, and laying it
over any particular Place.
In all thoſe Places that are 18 Degrees
below the Weſtern Side of the Horizon,
the Twilight is just beginning in the
Morning, or the Day breaks. And in
all thofe Places that are 18 Degrees be-
low the Eaſtern Side of the Horizon, the
Twilight is ending, and the total Dark-
nefs beginning.
The Twilight is in all thofe Places
whoſe Depreffion below the Horizon
does not exceed 18 Degrees. And
All thofe Places that are lower than
18 Degrees have dark Night.
The Depreffion of any Place below
the Horizon is equal to the Altitude of
its Antipodes, which may be eaſily found
by the Quadrant of Altitude.
เ
Sect. 3.
119
the GLOBE S.
PROB. XV. The Day of the Month being
given; to fhow, at one View, the Length
of Days and Nights in all Places upon
the Earth at that Time; and to explain
How the Viciffitudes of Day and Night
are really made by the Motion of the
Earth round her Axis in 24 Hours,
the Sun ftanding fill.
The Sun always illuminates one half
of the Globe, or that Hemiſphere which
is next towards him, while the other
remains in Darkneſs: And if (as by the
laft Problem) we elevate the Globe ac-
cording to the Sun's Place in the Ecliptic
it is evident, that the Sun (he being at
an immenſe Diſtance from the Earth)
illuminates all that Hemiſphere, which
is above the Horizon; the Wooden
Horizon itſelf will be the Circle termi-
nating Light and Darkneſs; and all
thofe Places that are below it, are wholly
deprived of the Solar Light.
The Globe ſtanding in this Pofition,
thoſe Arches of the Parallels of Latitude
which ſtand above the Horizon, are the
Diurnal Arches, or the Length of the
Day in all thofe Latitudes at that Time
of the Year; and the remaining Parts of
thofe Parallels, which are below the
I 4
Hori-
\
1
120
The Use of
Horizon, are the Nocturnal Arches, or
the Length of the Night in thofe Places.
The Length of the Diurnal Arches may
be found by counting how many Hours
are contained between the two Meri-
dians, cutting any Parallel of Latitude,
in the Eaſtern and Weftern Parts of
the Horizon.
In all thoſe Places that are in the
Weſtern Semicircle of the Horizon, the
Sun appears rifing: For the Sun,
ftanding ftill in the Vertex, (or above
the Brafs Meridian) appears Eafterly,
and 90 Degrees diftant from all thofe
Places that are in the Weſtern Semicircle
of the Horizon; and therefore in thoſe
Places he is then rifing. Now, if we
pitch upon any particular Place upon
the Globe, and bring it to the Meridian,
and then bring the Hour Index to the
lower 12, which in this Cafe we'll fup-
pofe to be 12 at Noon; (becauſe other-
wife the Numbers upon the Hour Circle
will not anfwer our Purpoſe) and after-
wards turn the Globe about, until the
aforefaid Place be brought to the
Weſtern Side of the Horizon; the In-
dex will then' fhew the Time of the
Sun rifing in that Place. Then turn
the Globe gradually about from Weſt
fact
to
←
Sect. 3.
the GLOBE S.
"121
7
to Eaft, and minding the Hour-Index,
we ſhall ſee the Progreſs made in the
Day every Hour, in all Latitudes upon
the Globe, by the real Motion of the
Earth round its Axis; until, by their
continual Approach to the Brafs Meri-
dian (over which the Sun ftands ſtill all
the while) they at laſt have Noon Day,
and the Sun appears at the higheſt; and
then by Degrees, as they move Eaſterly,
the Sun feems to decline Weftward,
until, as the Places fucceffively arrive in
the Eaſtern Part of the Horizon, the Sun
appears to ſet in the Weſtern: For the
Places that are in the Horizon, are 90
Degrees diftant from the Sun. We may
obferve, that all Places upon the Earth,
that differ in Latitude have their Days of
different Length (except when the Sun
is in the Equinoctial) being longer or
fhorter, in proportion to what Part of
the Parallels ftand above the Horizon.
Thoſe that are in the fame Latitude,
have their Days of the fame Length; but
have them commence fooner or later, ac-
cording as the Places differ in Longitude.
PROB. XVI. To explain in general the
Alteration of Seaſons, or Length of the
Days and Nights, made in all Places of
the World, by the Sun's (or the Earth's).
annual Motion in the Ecliptic.
122
The Ufe of
It has been fhewed in the laft Pro-
blem, how to place the Globe in fuch a
Pofition, as to exhibit the length of the
Diurnal and Nocturnal Arches in all
Places of the Earth, at a particular
Time: If the Globe be continually recti-
fied, according as the Sun alters his
Declination (which may be known by
bringing each Degree of the Ecliptic
fucceffively to the Merdian) you'll fee
the gradual Increafe or Decreaſe made in
the Days in all Places of the World, ac-
cording as a greater or leffer Portion of
the Parallels of Latitude ftands above
the Horizon. We fhall illuftrate this
Problem by Examples taken at different
Times of the Year.
2
-/-/-
1. Let the Sun be in the firſt Point of
(which happens on the 21st of June)
that Point being brought to the Meri-
dian, will fhew the Sun's Declination to
be 23 Degrees North; then the Globe
muſt be rectified to the Latitude of 23
Degrees; and for the better Illuftration
of the Problem, let the firft Meridian
upon the Globe be brought under the
Brafs Meridian. The Globe being in
this Pofition you'll fee at one View the
Length of the Days in all Latitudes, by
counting the Number of Hours contained
between
t
Sect. 3.
the GLOBE S.
123
between the two extreme Meridians,
cutting any particular Parallel you pitch
upon, in the Eaſtern and Weſtern Part
of the Horizon. And you may obſerve
that the lower Part of the Arctic Circle
juft touches the Horizon, and confe-
quently all the People who live in that
Latitude have the Sun above their Hori-
zon for the ſpace of 24 Hours, without
fetting; only when he is in the lower
Part of the Meridian (which they would
call 12 at Night) he just touches the
Horizon.
To all thoſe who live between the
Arctic Circle and the Pole, the fun does
not fet, and its Height above the Hori-
zon, when he is in the lower Part of the
Meridian, is equal to their Diſtance from
the Arctic Circle: For Example, Thofe
who live in the 83d Parallel have the
Sun when he is loweft at this Time
13 Degrees high.
2
If we caft our Eye Southward, to-
wards the Equator, we fhall find, that
the Diurnal Arches, or the Length of
Days in the ſeveral Latitudes, gradually
leffen: The Diurnal Arch of the Parallel
of London at this Time is 16 Hours;
that of the Equator (is always) 12 Hours;
I
and
2
124
The Use of
and fo continually lefs, till we come to
the Antarctic Circle, the upper Part of
which juſt touches the Horizon; and
thoſe who live in this Latitude have
juſt one Sight of the Sun, peeping as it
were in the Horizon: And all that
Space between the Antarctic Circle and
the South Pole, lies in total Darkneſs.
If from this Pofition we gradually
move the Meridian of the Globe accord-
ing to the progreffive Alterations made
in the Sun's Declination, by his Motion
in the Ecliptic, we ſhall find the Diurnal
Arches of all thofe Parallels, that are on
the Northern Side of the Equator, con-
tinually decreaſe; and thofe on the
Southern Side continually increaſe, in the
fame Manner as the Days in thofe Places
fhorten and lengthen. Let us again ob-
ſerve the Globe when the Sun has got
within 10 Degrees of the Equinoctial;
now the lower Part of the 80th Parallel
of North Latitude juſt touches the Hori-
zon, and all the Space betwixt this and
the Pole, falls in the illuminated He-
miſphere but all thofe Parallels that
lie betwixt this and the Arctic Circle,
which before were wholly above the
Horizon, do now interfect it, and the
Sun appears to them to rife and fet.
From
Sect. 3.
125
the GLOBE S.
墨
​}
From hence to the Equator, we fhall
find that the Days have gradually ſhort-
ned, and from the Equator Southward,
they have gradually lengthened, until we
come to the 80th Parallel of the South
Latitude; the upper Part of which juſt
touches the Horizon, and all Places be-
twixt this and the South Pole are in total
Darkneſs; but thoſe Parallels betwixt
this and the Antarctic Circle, which be-
fore were wholly upon the Horizon, are
now partly above it; the Length of their
Days being exactly equal to that of the
Nights in the fame Latitude in the con-
trary Hemiſphere. This also holds
univerfally, that the Length of the Day
in one Latitude North, is exactly equal
to the Length of the Night in the fame
Latitude South; and vice verfa.
Let us again follow the Motion of
the Sun, until he has got into the
Equinoctial, and take a View of the
Globe while it is in this Pofition. Now
all the Parallels of Latitude are cut into
two equal Parts by the Horizon, and
confequently the Days and Nights are
of equal Lengths, viz. 12 Hours each
in all Places of the World; the Sun
rifing and fetting at Six o'clock, except-
ing under the two Poles, which now lie
exactly
'
126
The Use of
exactly in the Horizon: Here the Sun
feems to ſtand ſtill in the fame Point of
the Heavens for fome Time, until by
Degrees, by his Motion in the Ecliptič,
he afcends higher to ofte and diſappears
to the other, there being properly no
Days and Nights under the Poles; for
there the Motion of the Earth round its
Axis can't be obſerved.
1
If we follow the Motion of the Sun
towards the Southern Tropic we fhall
fee the Diurnal Arches of the Northern
Parallels continually decreafe, and the
Southern ones increafe in the fame Pro-
portion according to their refpective
Latitudes; the North Pole continually
defcending, and the South Pole afcend-
ing, above the Horizon; until the Sur
arrives into, at which Time all the
Space within the Antarctic Circle is a-
bove the Horizon; while the Space be
tween the Arctic Circle, and its neigh-
bouring Pole, is in total Darkneſs. And
we ſhall now find all other Circumftances
quite reverſe to what they were when
the Sun' was in ; the Nights now all
over the World being of the fame Length
that the Days were of before.
V
{
We
Sect⋅ 3.
127
the GLOBES.
We have how got to the Extremity
of the Sun's Declination; and if we fol-
low him through the other half of the
Ecliptic, and rectify the Globe accord-
ingly, we fhall find the Seaſons return in
their Order, until at length we bring the
Globe into its firſt Pofition.
The two foregoing Problems were
not, as I know of, publiſhed in any Book
on this Subject before; and I have dwelt
the longer upon them, becauſe they very
well illuftrate how the Viciffitudes
of Days and Nights are made all over
the World by the Motion of the Earth
round her Axis; the Horizon of the
Globe being made the Circle, feparating
Light and Darkneſs, and fo the Sun to
ſtand ſtill in the Vertex. And if we
really could move the Meridian, accord-
ing to the Change of the Sun's Decli-
nation, we ſhould fee at one View the
continual Change made in the Length
of Days and Nights, in all Places on the
Earth; but as Globes are fitted up, this
cannot be done; neither are they adapt-
ed for the common Purpoſes, in Places
near the Equator, or any where in the
Southern Hemiſphere. But this Incon-
venience is now remedied ( at a ſmall
additional Expence) by the Hour Circle
being
128
The Life of
>
being made to shift to either Pole; and
fome Globes are now made with an
Hour Circle fixt to the Globe at each
Pole, between the Globe and Meridian,
fo as to have none without Side to `in-
terrupt the Meridian from moving quite
round the Wooden Horizon.
PROB. XVII. To fhew by the Globes at
one View, the Longest of the Days and
Nights in any particular Places, at all
Times of the Year:
+
Becauſe the Sun, by his Motion in
the Ecliptic, alters his Declination a
fmall Matter every Day; if we ſuppoſe
all the Torrid Zone to be filled up with
a fpiral Line, having fo many turnings;
or a Screw having fo many Threads, as
the Sun is Days in going from one
Tropic to the other: And theſe Threads
at the fame Diſtance from one another
in all Places, as the Sun alters his De-
clination in one Day in all thofe Places
refpectively: This Spiral Line or Screw
will repreſent the apparent Paths de-
fcribed by the Sun round the Earth every
Day; and by following the Thread
from one Tropic to the other, and back
again, we fhall have the Path the Sun
feems to deſcribe round the Earth in a
Year
•
•
1
Sect. 3.
129
the GLOBE S.
1
!
Year. But becauſe the Inclinations of
thefe Threads to one another are but
fmall, we may ſuppoſe each Diurnal
Path to be one of the Parallels of Lati-
tude drawn, or fuppofed to be drawn.
upon the Globe. Thus much being pre-
miſed, we ſhall explain this Problem, by
placing the Globe according to ſome of
the moſt remarkable Pofitions of it, as
before we did for the moſt remarkable
Seaſons of the Year.
In the preceding Problem, the Globe
being rectified according to the Sun's
Declination, the upper Parts of the
Parallels of Latitude, reprefented the
Diurnal Arches, or the Length of the Days
all over the World at that particular
Time: Here we are to rectify the Globe
according to the Latitude of the Place,
and then the upper Parts of the Parallelš
of Declination are the Diurnal Arches ;
and the Length of the Days at all Times
of the Year, may be here determined by
finding the Number of Hours contained
between the two extreme Meridians,
which cut any Parallel of Declination;
in the Eaſtern and Weſtern Points of
the Horizon; after the fame Manner,
as before we found the Length of the
Day in the feveral Latitudes at a particu-
lar Time of the Year.
K
1. Let
130
1
,
The Use of
1. Let the Place propofed be under
the Equinoctial, and let the Globe be
accordingly rectified for oo Degrees of
Latitude, which is called a direct Pofition
of the Sphere. Here all the Parallels of
Latitude, which in this Cafe we'll call
the Parallels of Declination, are cut by
the Horizon into two equal Parts; and
confequently thoſe who live under the
Equinoctial, have the Days and Nights
of the fame Length at all Times of the
Year; and alfo in this Part of the Earth,
all the Stars rife and fet, and their con-
tinuance above the Horizon, is equal to
their Stay below it, viz. 12 Hours.
If from this Pofition we gradually
move the Globe according to the feveral
Alterations of Latitudes, which we will
fuppofe to be Northerly; the Lengths
of the Diurnal Arches will continually
increaſe, until we come to a Parallel of
Declination, as far diftant from the E-
quinoctial, as the Place itfelf is from the
Pole. This Parallel will juſt touch the
Horizon, and all the Heavenly Bodies
that are betwixt it and the Pole never
defcend below the Horizon. In the
mean time, while we are moving the
Globe, the Lengths of the Diurnal Arches
of the Southern Parallels of Declination,
- cont
sect. 3.
131
the GLOBES.
continually diminiſh in the fame Pro-
portion that the Northern ones increaf-
ed; until we come to that Parallel of
Declination which is ſo far diſtant from
the Equinoctial Southerly, as the Place
itſelf is from the North Pole. The up-
per Part of this Parallel juft touches the
Horizon, and all the Stars that are be-
twixt it and the South Pole never appear
above the Horizon. All the Nocturnal
Arches of the Southern Parallels of De-
clination, are exactly of the fame Length
with the Diurnal Arches of the corref
pondent Parallels of North Declination.
I
2
2. Let us take a View of the Globe,
when it is rectified for the Latitude of
London, or 51 Degrees North. When
the Sun is in the Tropic of, the Day
is about 16 Hours; as he recedes from
this Tropic, the Days proportionably
ſhorten, until he arrives into, and
then the Days are at the ſhorteſt, being
now of the fame Length with the Night
when the Sun was in, viz. 7 Hours.
The lower Part of that Parallel of De-
clination, which is 38 Degrees from
the Equinoctial Northerly, juſt touches
the Horizon; and the Stars that are
betwixt this Parallel and the North Pole,
never fet to us at London. In like Man-
K 2
2
2
ner
13.2
The Uſe of
ner the upper Part of the Southern Pa-
rallel of 38 Degrees just touches the
Horizon, and the Stars that lie be-
twixt this Parallel and the South Pole
are never viſible in this Latitude.
'
Again, let us rectify the Globe for the
Latitude of the Arctic Circle, we ſhall
then find, that when the Sun is in he
touches the Horizon on that Day with-
out fetting, being 24 Hours compleat
above the Horizon; and when he is in
Capricorn, he once appears in the Hori-
zon, but does not rife in the Space of
24 Hours: When he is in any other
Point of the Ecliptic, the Days are
longer or ſhorter according to his Diſ-
tance from the Tropics. All the Stars
that lie between the Tropic of Cancer,
and the North Pole, never fet in this
Latitude; and thofe that are between
the Tropic of Capricorn, and the South
Pole, are always hid below the Horizon.
/
If we elevate the Globe ftill higher,
the Circle of perpetual Apparition will
be nearer the Equator, as will that of
perpetual Occultation on the other Side.
For Example, Let us rectify the Globe
for the Latitude of 80 Degrees North;
when the Sun's Declination is 10 De-
grees
Sect. 3.
133
the GLOBES.
4
grees North; he begins to turn above
the Horizon without ſetting; and all the
while he is making his Progreſs from
this Point to the Tropic of, and back
again, he never fets. After the fame
Manner, when his Declination is 10 De-
grees South, he is juſt ſeen at Noon in
the Horizon; and all the while he is
going Southward, and back again, he
diſappears, being hid juſt ſo long as be-
fore, at the oppofite Time of the Year
he appeared viſible.
Let us now bring the North Pole in-
to the Zenith, then will the Equinoctial
coincide with the Horizon; and conſe-
quently all the Northern Parallels are
above the Horizon, and the Southern
ones below it. Here is but one Day and
one Night throughout the Year, it be-
ing Day all the while the Sun is to the
Northward of the Equinoctial, and
Night for the other half Year. All the
Stars that have North Declination, al-
ways appear above the Horizon, and at
the fame height; and all thoſe that are
on the other Sidė, are never ſeen.
What has been here faid of rectify-
ing the Globe to North Latitude, holds
for the fame Latitude South; only that
K 3
before
134
The Uſe of
:
;
before the Longeſt Days were, when the
Sun was in, the fame happening now
when the Sun is in ; and fo of the reft
of the Parallels, the Seafons being di-
rectly oppofite to thoſe who live in dif-
ferent Hemiſpheres.
I ſhall again explain fome Things de-
livered above in general Terms, by par-
- ticular Problems.
But from what has been already ſaid,
we may firſt make the following Obfer-
vations:
1. All Places of the Earth do equally
enjoy the Benefit of the Sun, in respect of
Time, and are equally deprived of it, the
Days at one Time of the Year being exactly
equal to the Nights at the oppofite Seafon.
2. In all Places of the Earth, fave ex-
actly under the Poles, the Days and Nights
are of equal Length (viz. 12 Hours each)
when the Sun is in the Equinoctial.
3. Thofe who live under the Equinoctial
have the Days and Nights of equal Lengths
at all Times of the Year.
4. In all Places between the Equinoctial
and the Poles, the Days and Nights are
never
Sect. 3. the GLOBE S.
135
1
never equal, but when the Sun is in the
Equinoctial Points and .
5. The nearer any Place is to the Equa-
tor, the lefs is the Difference between the
Length of the Artificial Days and Nights
in the faid Place; and the more remote
the greater.
6. To all the Inhabitants lying under the
fame Parallel of Latitude, the Days and
Nights are of equal Lengths, and that at
all Times of the Year.
7. The Sun is Vertical twice a Year to
all Places between the Tropics; to thoſe un-
der the Tropics, once a Year, but never any
where elſe.
8. In all Places between the Polar Cir-
cles, and the Poles, the Sun appears fome
Number of Days without fetting; and at
the oppofite Time of the Year he is for the
the fame Length of Time without Rifing ;
and the nearer unto, or further remote
from the Pole, thofe Places are, the longer
or Shorter is the Sun's continued Pre-
fence or Abfence from the fame:
9. In all Places lying exactly under
the Polar Circles, the Sun, when he is in
K 4
the
136
The Ufe of
the nearest Tropic, appears 24 Hours with.
out fetting; and when he is in the contra-
ry Tropic, he is for the fame Length of
Time without rifing; but at all other Times
of the Year he rifes and fets there, as in
other Places.
{
S Northern
10. In all Places lying in the
the Southern
Hemisphere, the Longest Day and Short-
eſt Night, is when the Sun is in the
Northern
Tropic; and the contrary.
Southern S
PRÓB. XVIII. The Latitude of any
· Place, not exceeding 66 Degrees, and
the Day of the Month being given; to
find the Time of Sun-rifing and fetting,
and the Length of the Day and Night:
Having rectified the Globe according
to the Latitude, bring the Sun's Place
to the Meridian, and put the Hour-In-
dex to 12 at Noon; then bring the Sun's
Place to the Eaftern Part of the Ho-
rizon, and the Index will fhew the Time
when the Sun rifes. Again, turn the
Globe until the Sun's Place be brought
to the Weſtern Side of the Horizon,
and the Index will fhew the Time of
Sun-fetting.
1
The
1
fect. 3.
137
the GLOBES.
The Hour of Sun-fetting doubled,
gives the Length of the Day; and the
Hour of Sun-rifing doubled, gives the
Length of the Night.
3
4
Let it be required to find when the
Sun rifes and fets at London on the 20th
of April. Rectify the Globe for the
Latitude of London, and having found
the Sun's Place correfponding to May
the ift. vix. 8 10 Degrees, bring &
10 Degrees to the Meridian, and fet the
Index at 12 at Noon; then turn the
Globe about till 8 10 Degrees be
brought to the Eaſtern Part of the Ho-
rizon, and you'll find the Index point
4 Hours; this being doubled, gives the
Length of the Night 9 Hours. Again
bring the Sun's Place to the Weſtern
Part of the Horizon, and the Index will
point 7 Hours, which is the Time of
Sun-fetting; this being doubled, gives
the Length of the Day 14 Hours,
3
I
PROB. XIX. To find the Length of the
Longeſt and Shortest Day and Night in
any given Place, not exceeding 661 De-
grees of Latitude.
Note, The Longeſt Day at all Places on
the {North Side of the Equator, is when
the
138
The Ufe of
the Sun is in the firſt Point of
Cancer
Capricorn S
Wherefore having, rectified the Globe for
the Latitude, find the Time of Sun-
rifing and ſetting, and thence the Length
of the Day and Night, as in the laft Pro-
blem, according to the Place of the Sun:
Or having rectified the Globe for the
Latitude, bring the Solftitial Point of
that Hemiſphere to the Eaft Part of the
Horizon, and fet the Index 12 at Noon;
then turning the Globe about till the
faid Solftitial Point touches the Weftern
Side of the Horizon, the Number of
Hours from Noon to the Place where
the Index points (being counted accord-
ing to the Motion of the Index) is the
Length of the Longeft Day; the Com-
plement whereof to 24 Hours, is the
Length of the Shorteſt Night, and the
Reverſe gives the Shorteſt Day and the
Longeſt Night.
Longest Day
Short N.
Deg.
Hours. Hours.
45
15 1/1/0
81
Thus in Lat. 251.
16
7/2/
260
18/1/2
5 2
If from the Length of the Longeft Day
you fubftract 12 Hours, the Number of
half
Sect
139
3.
the GLOBE S.
་
I
21
half Hours remaining will be the Cli-
mate: Thus that Place where the long-
eft Day is 16 Hours, lies in the 9th
Climate. And by the Reverſe, having
the Climate, you have thereby the
Length of the Longeſt Day.
ક્
PROB. XX. To find in what Latitude the
Longeft Day is, of any given Length
lefs than 24 Hours.
Bring the Solftitial Point to the Me-
ridian, and fet the Index to 12 at Noon;
then turn the Globe Weftward till the
Index points at half the Number of
Hours given; which being done, keep
the Globe from turning round its Axis,
and flide the Meridian up or down in
the Notches, till the Solftitial Point
comes to the Horizon, then that Eleva-
tion of the Pole will be the Latitude.
If the Hours given be 16, the Lati-
tude is 49 Degrees; if 20 Hours, the
Latitude is 63 Degrees.
PROB.
The Uſe of
PROB. XXI. A Place being given in owe
of the Frigid Zones (Suppose the Nor-
thern) to find what Number of Days
(of 24 Hours each) the Sun doth con-
ftantly ſhine upon the fame, how long be
is abfent, and alſo the firſt and laſt Day
of his appearance.
Having rectified the Globe according
to the Latitude, turn it about until fome
Point in the firſt Quadrant of the Eclip-
tic (becauſe the Latitude is North) in-
terfects the Meridian in the North Point
of the Horizon; and right againſt that
Point of the Ecliptic on the Horizon,
ftands the Day of the Month when the
Longeſt Day begins.
And if the Globe be turned about till
fome Point in the fecond Quadrant of
the Ecliptic cuts the Meridian in the
fame Point of the Horizon, it will fhew
the Sun's Place when the Longeſt Day
ends, whence the Day of the Month may
be found as before: Then the Number
of Natural Days contained between the
Times the Longeſt Day begins and
ends, is the Length of the Longeſt Day
·required.
1
Again
}
Sect. 3.
141
the GLOBES.
Again, turn the Globe about, until
fome Point in the third Quadrant of the
Ecliptic cuts the Meridian in the South
Part of the Horizon; that Point of the
Ecliptic will give the Time when the
Longeft Night begins. Laftly, turn the
Globe about untill fome Point in the
fourth Quadrant of the Ecliptic cuts the
Meridian in the South Point of the Ho-
rizon; and that Point of the Ecliptic
will be the Place of the Sun when the
Longeſt Night ends.
Or, the Time when the Longeſt Day
or Night begins, being known, their
End may be found by counting the
Number of Days from that Time to
the fucceeding Solftice; then counting
the fame Number of Days from the
Solſtitial Day, will give the Time when
it ends.
PROB. XXII. To find in what Latitude
the Longest Day is of any given Length
lefs than 182 Natural Days.
Find a Point in the Ecliptic half fo
many Degrees diftant from the Solſtitial
Point, as there are Days given, and bring
that Point to the Meridian; then keep
the Globe from turning round its Axis,
and
142
The Use of
and move the Meridian up or down.un-
til the aforefaid Point of the Ecliptic
comes to the Horizon; that Elevation
of the Pole will be the Latitude required.
If the Days given were 78, the Lati-
tude is 71 Degrees.
2
This method is not accurate, becauſe
the Degrees in the Ecliptic do not correſ-
pond to Natural Days; and alſo becauſe
the Sun does not always move in the
Ecliptic at the fame Rate; however, fuch
Problems as theſe may ſerve for Amuſe-
ments.
PROB. XXIII. The Day of the Month be-
ing given, to find when the Morning and
Evening Twilight begins and ends, in
any Place upon the Globe.
In the foregoing Problem, by the
Length of the Day, we mean the Time
from Sun-rifing to Sun-fet; and the
Night we reckoned from Sun-fet, till he
rofe next Morning. But it is found by
Experience, that Total Darkness does
not commence in the Evening, till the
Sun has got 18 Degrees below the Ho-
rizon; and when he comes within the
fame Diſtance of the Horizon next Morn-
ing
7
Sect. 3.
143
the GLOBES.
ing, we have the firft Dawn of Day.
This faint Light which we have in the
Morning and Evening, before and after
the Sun's rifing and fetting, is what we
call the Twilight.
* Having rectified the Globe for the *Prob. VỊ
Latitude, the Zenith, and the Sun's
Place, turn the Globe and the Quadrant
of Altitude until the Sun's Place cuts
18 Degrees below the Horizon (if
the Quadrant reaches fo far) then the
Index upon the Hour-Circle will fhew
the Beginning or Ending of Twilight
after the fame Manner as before we
found the Time of the Sun-rifing and
fetting, in Prob. 18. But by reaſon of
the Thickneſs of the Wooden Horizon,
we can't conveniently fee, or compute
when the Sun's Place is brought to the
Point aforefaid. Wherefore the Globe
being rectified as above directed, turn
the Globe and alfo the Quadrant of
Altitude Weftward, unti 1that Point in
the Ecliptic, which is oppofite to the
Sun's Place, cuts the Quadrant in the
18th Degree above the Horizon; then
the Hour Index will fhew the Time
when Day breaks in the Morning. And
if
you turn the Globe and the Quadrant
of Altitude, until the Point oppofite to
the
144
The Ufe of
the Sun's Place cuts the Quadrant in
the Eaſtern Hemisphere, the Hour-Hand
will fhew when Twilight ends in the
Evening. Or, having found the Time
from Midnight when the Morning
Twilight begins, if you reckon fo many
Hours before Midnight, it will give the
Time when the Evening Twilight ends.
Having found the Time when Twilight
begins in the Morning, find the Time
of Sun-rifing, by Prob. 18. and the Dif-
ference will be the Duration of Twilight.
Thus at London on the 12th of May;
Twilight begins at three Quarters paſt
One O'Clock: the Sun rifes at about
half an hour paft Four: Whence the
Duration of Twilight now is 23 Hours,
both in the Morning and Evening. On
the 12 of November, the Twilight be
gins at. Half an Hour paſt Six, being
fome what above an Hour before Sun-
rifing.
PROB. XXIV. To find the Time when to
tal Darkness ceafes, or when the Twi
light continues from Sun-ſetting to Sun-
rifing, in any given Place.
Let the Place be in the Northern He-
mifphere; then if the Complement of
the
Sect. 3.
145
the GLOBE S.
2
the Latitude be greater than (the De-
preffion) 18 Degrees, fubtract 18 De-
grèes from it, and the Remainder will
be the Sun's Declination North when
total Darkneſs ceafes. But if the Com-
plement of the Latitude is lefs than 18
Degrees, their Difference will be the
Sun's Declination South, when the Twi-
light begins to continue all Night. If
the Latitude is South, the only Differ-
ence will be, that the Sun's Declination
will be on the contrary Side.
༧་
Thus at London, when the Sun's De-
clination North is greater than 20 De-
grees, there is no total Darkneſs, but
conftant Twilight, which happens from
the 26th of May to the 18th of July, be-
ing near two Months. Under the North
Pole the Twilight ceafes, when the Sun's
Declination is greater than 18 Degrees
South, which is from the 13th of No-
vember, till the 29th of January: So
that notwithſtanding the Sun is abfent
in this Part of the World for Half a
Year together yet total Darkneſs does
not continue above 11 Weeks; and be-
fides, the Moon is above the Horizon
for a whole Fortnight of every Month
throughout the Year.
PROB:
146
The Use of
}
PROB. XXV. The Day of the Month be-
ing given; to find thofe Places of the
Frigid Zones, where the Sun begins to
Shine continually without fetting; and
alfo thofe Places where he begins to be
totally abfent.
Bring the Sun's Place to the Meridian,
and mark the Number of Degrees con-
tained betwixt that Point and the Equa-
tor; then count the fame Number of
Degrees from the neareſt Pole (viz. the
North Pole, if the Sun's Declination is
Northerly, otherwiſe the South Pole) to-
wards the Equator, and note that Point
upon the Meridian; then turn the Globe
about, and all the Places which paſs un-
der the faid Point, are thoſe where the
Sun begins to fhine conſtantly, without
fetting on the given Day. If you lay
the fame Diſtance from the oppofite
Pole towards the Equator, and turn the
Globe about, all the Places which pafs
under that Point, will be thoſe where
the longeſt Night begins.
The Latitude of the Place being given, to
find the Hour of the Day when the Sun
Shines.
If
1
Sect. 3.
f
1
the GLOBE S.
If it be in the Summer, elevate the Pole
according to the Latitude; and ſet the
Meridian due North and South; then
the Shadow of the Axis will cut the
Hour on the Dial-Plate: For the Globe
being rectified in this Manner, the Hour
Circle is a true Equinoctial Dial; the
Axis of the Globe being the Gnomon:
This holds true in Theory, but it might
not be very accurate in Practice, becauſe
of the Difficulty in placing the Horizon
of the Globe truly horizontal, and its
Meridian due North and South.
F.
If it be in the Winter Half Year, ele
vate the South Pole according to the
Latitude North, and let the North Part
of the Horizon be in the South Part of
the Meridian; then the Shade of the
Axis will fhow the Hour of the Day as
before, But this cannot be fo con-
veniently performed, tho' the Reaſon is
the fame as in the former Cafe.
}
To find the Sun's Altitude, when it shines,
by the Globe.
Having fet the Frame of the Globe
truly horizontal or level, turn the North
Pole towards the Sun, and move the
Meridian up or down in the Notches,
L 2
fill
1
147
+
148
The Uſe of
till the Axis cafts no Shadow, then the
Arch of the Meridian, contain'd betwixt
the Pole and the Horizon, is the Sun's
Altitude.
Note, The beſt Way to find the Sun's
Altitude, is by a little Quadrant gra-
duated into Degrees, and having Sights
and a Plummet to it: Thus, hold the
Quadrant in your Hand, fo as the Rays
of the Sun may paſs through both the
Sights, the Plummet then hanging free-
ly by the Side of the Inftrument, will
cut in the Limb the Altitude required.
Theſe Quadrants are to be had at the
Inſtrument-Makers, with Lines drawn
upon them, for finding the Hour of the
Day and the Azimuth, with feveral
other pretty Conclufions, very entertain-
ing for Beginners.
The Latitude and the Day of the Month
being given, to find the Hour of the
Day when the Sun fhines.
Having placed the Wooden Frame up-
on a Level, and the Meridian due Northr
and South, rectify the Globe for the La-
titude, and fix a Needle perpendicularly
over the Sun's Place: The Sun's Place
being brought to the Meridian, ſet the
Hour
Se&t. 3.
the GLOBE S.
149
Hour-Index at 12 at Noon, then turn
the Globe about until the Needle points
exactly to the Sun, and cafts no Shadow,
and then the Index will fhew the Hour
of the Day.
༄
PROB. XXVI. The Latitude, the Sun's
Place and his Altitude, being given;
to find the Hour of the Day, and the
Sun's Azimuth from the Meridian.
Having rectified the Globe for the
Latitude, the Zenith, and the Sun's
Place, turn the Globe and the Quadrant
of Altitude, ſo that the Sun's Place may
cut the given Degree of Altitude: then
the Index will fhow the Hour, and the
Quadrant will cut the Azimuth in the
Horizon. Thus, if at London, on the
21st of Auguft, the Sun's Altitude be
36 Degrees in the Forenoon, the Hour
of the Day will be IX, and the Sun's
Azimuth about 58 Degrees from the
South Part of the Meridian.
C
The Sun's Azimuth being given, to place
the Meridian of the Globe due North
and South, or to find a Meridian Line
when the Sun fhines.
Let
I 3
159
The Uſe of
T
Let the Sun's Azimuth be 30 De-
grees South-Eaſterly, fet the Horizon
of the Globe upon a Level, and bring
the North Pole into the Zenith; then
turn the Horizon about until the Shade
of the Axis cuts as many Hours as is
équivalent to the Azimuth (allowing I
Degrees to an Hour) in the North-
Weft Part of the Hour-Circle, viz. X at
Night, which being done, the Meridian
of the Globe ftands in the true Merdian
of the place. The Globe ftanding in
this Poſition, if you hang two Plummets
at the North and South Points of the
Wooden Horizon, and draw a Line
betwixt them, you'll have a Meridian
Line; which if it be on a fixed Plane (as
a Floor or Window) it will be a Guide
for placing the Globe due North and
South at any other Time.
PROB. XXVII. The Latitude, Hour of
the Day, and the Sun's Place being
given, to find the Sun's Altitude and
Azimuth.
*
Rectify the Globe for the Latitude,
the Zenith, and the Sun's Place, then the
Number of Degrees contained betwixt
the Sun's Place and the Vertex, is the
Sun's Meridional Zenith Diſtance; the
Com-
Se&t. 3.
151
the GLOBE S.
Complement of which, to 90 Degrees,
is the Sun's Meridan Altitude. If you
turn the Globe about until the Index
points to any other given Hour, then
bringing the Quadrant of Altitude to
cut the Sun's Place, you'll have the Sun's
Altitude at that Hour; and where the
Quadrant cuts the Horizon, is the Sun's
Azimuth at the fame Time. Thus
May the 31ft at London, the Sun's
Meridian Altitude will be 61 Degrees;
and at 10 O'Clock in the Morning, the
Sun's Altitude will be 52 Degrees, and
his Azimuth about 50 Degrees from the
South Part of the Meridian.
•
I
2
PROB. XXVIII. The Latitude of the Place,
and the Day of the Month being given ;
to find the Depreffion of the Sun below
the Horizon, and the Azimuth at any
Hour of the Night.
Having rectified the Globe for the
Latitude, the Zenith and the Sun's Place,
take a Point in the Ecliptic, exactly
oppofite to the Sun's Place, and find
the Sun's Altitude and Azimuth, as by
the laſt Problem, and theſe will be the
Depreffion and the Altitude required,
Thus, if the Time given be the ift of
December, at 10 o'Clock at Night, the
L 4
De-
152
The Ufe of
Depreffion and Azimuth will be the
fame as was found in the laft Problem.
+
PROB. XXIX. The Latitude, the Sun's
Place, and bis Azimuth being given;
to find bis Altitude, and the Hour.
Rectify the Globe for the Latitude,
the Zenith, and the Sun's Place, then
put the Quadrant of Altitude to the
Sun's Azimuth in the Horizon, and turn
the Globe 'till the Sun's Place meet the
Edge of the Quadrant, then the faid
Edge will fhew the Altitude, and the
Index point to the Hour. Thus, May
the 21ft at London, when the Sun is due
Eaft, his Altitude will be about 24 De-
grees, and the Hour about VII in the
Morning; and when his Azimuth is 60
Degrees South-Wefterly, the Altitude
will be about 44 Degrees, and the
Hour about 2 in the Afternoon.
3
2
Thus, the Latitude and the Day be-
ing known, and having befides either
the Altitude, the Azimuth, or the Hour;
the other two may be eaſily found.
:
61
PROB. XXX. The Latitude, the Sun's Al-
titude, and his Azimuth being given ; to
find his Place in the Ecliptic and the
Hour.
Rectify
Sect. 3.
153
the GLOBE S.
Rectify the Globe for the Latitude
and Zenith, and fet the Edge of the
Quadrant to the given Azimuth; then
turning the Globe about, that Point of
the Ecliptic which cuts the Altitude will
be the Sun's Place. Keep the Quadrant
of the Altitude in the fame Poſition, and
having brought the Sun's Place to the
Meridian, and the Hour Index to 12 at
Noon, turn the Globe about till the
Sun's Place cuts the Quadrant of Alti-
tude, and then the Index will point the
Hour of the Dạy.
PROB. XXXI. The Declination and Me-
ridian Altitude of the Sun, or of any
Star being given; to find the Latitude
of the Place.
Mark the Point of Declination upon
the Meridian, according as it is either
North or South from the Equator; then,
flide the Meridian up or down in the
Notches, till the Point of Declination be
fo far diftant from the Horizon, as is the
given Meridian Altitude; that Elevation
of the Pole will be the Latitude.
Thus, if the Sun's, or any Star's Me
ridian Altitude be 50 Degrees, and its
De-
i
$54
The Use of
* Prob.
XIII.
Declination 11 Degrees North, the La-
titude will be 514 Degrees North.
PROB. XXXII. The Day and Hour of a
Lunar Eclipfe being known; to find all
thofe Places upon the Globe in which the
fame will be vifible.
L
* Find where the Sun is vertical at
the given Hour, and bring that Point to
the Zenith; then the Eclipſe will be vi-
fible in all thofe Places that are under
the Horizon: Or, if you bring the An-
tipodes to the Place where the Sun is
vertical, into the Zenith, you will have
the Places where the Eclipfe will be vi-
fible above the Horizon.
Note, Becauſe Lunar Eclipfes continue
fometimes for a long while together,
they may be ſeen in more Places than
one Hemifphere of the Earth; for by
the Earth's Motion round its Axis, dú-
ing the Time of the Eclipfe, the Moon
will rife in feveral Places after the E-
clipfe began.
Note, When an Eclipfe of the Sun is
central, if you bring the Place where the
Sun is vertical at that Time, into the
Zenith, fome Part of the Eclipfe will be
vifible
}
Sect. 3.
155
the GLOBES.
viſible tin moft Places within the upper
Hemiſphere; but by Reaſon of the fhort
Duration of Solar Eclipfes, and the La-
titude which the Moon commonly has
at that Time, (tho' but ſmall) there is
no Certainty in determining the Places
where thofe Eclipfes will be viſible by
the Globe: but Recourfe muſt be had
to Calculations.
PROB. XXXIII. The Day of the Month,
and Hour of the Day, acccording to our
Way of reckoning in England, being gi-
ven; to find thereby the Babylonic, Ita-
lic, and the Jewish or Judaical Hour.
1. To find the Babylonic Hour (which
is the Number of Hours from Sun-ri-
fing.) Having found the Time of Sun-
rifing in the given Place, the Difference
betwixt this and the Hour given is the
Babylonic Hour.
2. To find the Italic Hour (which is
the Number of Hours from Sun-fet-
ting.) Subtract the Hour of Sun-fetting
from the given Hour, and the Remain-
der will be the Italic Hour required.
+
3. To find the Jewish Hour (which is
Part of an Artificial Day.) Find how
many
1
456
The Use of
many Hours the Day confifts of; ther
fay, as the Number of Hours the Day
conſiſts of is to 12 Hours, fo is the Hour
fince Sun-rifing to the Judaical Hour
required.
Thus, if the Sun rifes at 4 o'Clock
(confequently fets at 8) and the Hour gi-
ven be 5 in the Evening, the Babylonic
Hour will be the 13th, the Italic the 21ft,
and the Jewish Hour will be Nine and
Three Quarters.
The Converſe being given, the Hour of
the Day, according to our Way of reckon-
ing in England, may be eaſily found.
The following Problems are peculiar
to the Celestial Globe.
PROB. XXXIV. To find the Right Aſcen-
cenfion and Declination of the Sun or any
Fixed Star.
Bring the Sun's Place in the Ecliptic
to the Meridian; then that Degree of
the Equator, which is cut by the Meri-
dian, will be the Sun's Right Afcenfion;
and that Degree of the Meridian, which
is exactly over the Sun's Place, is the
Sun's Declination.
1
After
Sect. 3.
*57
the GLOBE S.
After the fame Manner, bring the
Place of any Fixed Star to the Meridian,
and you'll find its Right Afcenfion in the
Equinoctial, and Declination of the
Meridian.
Thus, the Right Afcenfion and Decli-
nation is found, after the fame Manner
as the Longitude and Latitude of a Place
the Terrestrial Globe.
upon
Note, The Right Afcenfion and De-
clination of the Sun vary every Day; but
the Right Afcenfion, &c. of the Fixed
Stars is the fame throughout the Year +.
The Sun's Right Afcenfion. Declin
Deg. Deg.
January 31
Thus on<
April 5
July 21 -
314 17 S.
14 6 N.
12020 N.
November 26
242 21 S.
R. Afc. Decl.
Aldebaran
Spica Virginis
Capella
Syrius, or the Dog-Star
Deg. Deg.
65 16 N.
3
1979/ 9 5.
74
981
453 N.
16 S.
+ The infenfible Change in the Longitude, Right-
Afcenfion, and Declination of the Fixed Stars, made by
their flow Motion, Parallel to the Ecliptic (being but i
Degree in 72 Years) is not worth Notice in this Place.
Note
158
The... Uſe of
(
1
Note, The Declination of the Sun
may be found after the fame Manner,
by the Terrestrial Globe, and alſo his
Right Afcenfion, when the Equinoctial
is numbered into 360 Degrees, com-
mencing at the Equinoctial Point :
But as the Equinoctial is not always
numbered ſo, and this being properly a
Problem in Aftromony, we chufe rather
to place it here.
By the Converſe of this Problem, hav-
ing the Right Afcenfion and Declination
of any Point given, that Point itſelf may
be eaſily found upon the Globe.
Bl 201
PROB. XXXV. To find the Longitude and
Latitude of a given Star.
3
Having brought the Solftitial Colure
to the Meridian, fix the Quadrant of Al-
titude over the proper Pole of the Eclip-
tic, whether it be North or South; then
turn the Quadrant over the given Star,
and the Arch contain'd betwixt the Star
and the Ecliptic will be the Latitude;
and the Degree cut on the Ecliptic will
will be the Star's Longitude.
Thus the Latitude of Arcturus will be
found to be 31 Degrees North, and the
Lons
Sect. 3.
159
the GLOBES.
of 20
Longitude 200 Degrees: fram
•
2
•
L,
Z
Degrees from The Latitude: of
Fomalbaut in the Southern Fifh, 21-De-
grees South, and Longitude 299 De-
grees, or 29 Degrees. By the Con-
verſe of this Method, having the Lati-
tude and Longitude of a Star given, it
will be eafy to find the Star upon the
Globe.
i
The Distance betwixt two Stars, or
the Number of Degrees contained be-
twixt them, may be found by laying the
Quadrant of Altitude over each of them;
and counting the Number of Degrees
intercepted; after the fame Manner as
we found the Diſtance betwixt two
Places on the Terreftrial Globe, in Prob.
VII.
PROB. XXXVI. The Latitude of the
Place, the Day of the Month, and the
Hour being given; to find what Stars
are then rifing or fetting, what Stars
are culminating or on the Meridian, and
the Altitude and Azimuth of any Star
above the Horizon; and alſo how to
diftinguish the Stars in the Heavens one
from the other, and to know them by
their proper Names:
1
Having
160
The Ufe of
Having rectified the Globe for the
Latitude, the Zenith, and the Sun's
Place, turn the Globe about until the
Index points to the given Hour, the
Globe being kept in this Pofition.
All thofe Stars that are in the
Side of the Horizon, are then
་
Eaftern
Weftern
Rifing.
Setting. S
All thofe Stars that are under the
Meridian are then culminating. And
if the Quadrant of Altitude be laid
over the Center of any particular Star,
it will ſhow that Star's Altitude at that
Time; and where it cuts the Horizon,
will be the Star's Azimuth from the
North or South Part of the Meridian.
The Globe being kept in the fame
Elevation, and from turning round its
Axis, move the wooden Frame about
until the North and South Points of the
Horizon lie exactly in the Meridian;
then right Lines imagined to pafs from
the Center thro' each Star upon the Sur-
face of the Globe, will point out the real
Star in the Heavens, which thofe on the
Globe are made to repréfent. And if
you are by the Side of fome Wall whoſe
Bearing
Sect. 3.
i6t
the GLOBE S.
Bearing you know, lay the Quadrant of
Altitude to that Bearing in the Horizon,
and it will cut all thofe Stars, which at
that very Time are to be feen in the fame
Direction, or clofe by the Side of the ſaid
Wall. Thus knowing fome of the re-
markable Stars in any Part of the Hea-
vens, the Neighbouring Stars may be
diſtinguiſhed by obferving their Situati-
ons with refpect to thoſe that are already
known, and comparing them with the
Stars drawn upon the Globe.
Thus, if you turn your Face towards
the North, you will find the North Pole
of the Globe points to the Pole-Star
then you may obferve two Stars fome-
what leſs bright than the Pole-Star,
almoſt in a right Line with it, and four
more which form a Sort of a Quadrangles
theſe feven Stars make the Conftellation
called the Little-Bear; the Pole Star
being in the Tip of the Tail. In this
Neighbourhood you'll obferve feven
bright Stars, which are commonly called
Charles's Wane; theſe are the bright Stars
in the Great Bear, and do form much
fuch another Figure with thofe before-
mentioned in the Little Bear: The two
foremoſt of the Square lie almoſt in a
right Line with the Pole Star, and are
called the Pointers ; fo that knowing the
M
Pointers,
162
The Uſe of
•
Pointers, you may eafily find the Pole-
Star. Thus the reft of the Stars in this
Conſtellation, and all the Stars in the
neighbouring Conftellations, may be
eafily found, by obferving how the un-
known Stars lie either in Quadrangles,
Triangles, or ftrait Lines, from thoſe that
are already known upon the Globe.
After the fame Manner the Globe be-
ing rectified, you may diftinguiſh thoſe
Stars that are to the Southward of you,
and be ſoon acquainted with all the Stars
that are viſible in our Hemiſphere.
SCHOL IU M.
The Globe being rectified to the Lati-
tude of any Place, if you turn it round
its Axis, all thofe Stars that do not go
below the Horizon during a whole Re-
volution of the Globe, never fet in that
Place; and thoſe that do not come above
the Horizon never riſe.
PROB. XXXVII. The Latitude of the Place
being given; to find the Amplitude, O-
blique Afcenfion and Defcenfion, Afcenfio-
nal Difference, Semi-Diurnal Arch, and
the Time of Continuance above the Ho-
rizon, of any given Point in the Heavens.
Having
Sect. 3.
163 ·
the GLOBE Ś.
Having rectified the Globe for the
Latitude, and brought the given Point
to the Meridian, fet the Index to the
Hour of 12; then turn the Globe until
the given Point be brought to the Eaſt-
ern Side of the Horizon, and that Degree
of the Equinoctial which is cut by the
Horizon at that Time, will be the Oblique
Afcenfion; and where the given Point cuts
the Horizon, is the Amplitude Qrtive:
If the Globe be turned about until the
given Point be brought to the Weſtern
Side of the Horizon; it will there ſhow
the Amplitude Occafive; and where the
Horizon cuts the Equinoctial at that
Time is the Oblique Defcenfion.
The Time between the Index at either
of theſe two Pofitions, and the Hour of
6; or Half the Difference between the
Oblique Afcenfion and Defcenfion is the
Afcenfional Difference,
If the Place be in North Latitude and the
North
Declination of the given point be) South
}
the Afcenfional Difference reduced into
Time, and added to
fubtracted from
}6 o'clock,
gives the Semi-Diurnal Arch; the Com-
plement whereof to a Semicircle, is the
M 2
Semi-
164
The Use of
Semi-Nocturnal Arch. If the Place be
in South Latitude, then the contrary
is to be obferved with refpect to the De-
clination.
Diurnal
The Semi- Nocturnal Arch being
S
doubled, gives the Time of Continance
above
the Horizon. Or the Time of
> below
Continuance above the Horizon, may
be found by counting the Number of
Hours contained in the upper Part of
the Horary Circle, betwixt the Place
where the Index pointed when the given
Point was in the Eaſtern and Weſtern
Parts of the Horizon. If the given Point
was the Sun's Place, the Index pointed
the Time of his Rifing and Setting,
when the faid Place was in the Eaftern
and Weſtern Parts of the Horizon, as in
Prob. 18. Or the Time of Sun-rifing
may be found by adding or fubtracting
his Afcenfional Difference, to or from
the Hour of Six, according as the Lati-
tude and Declination are either contrary
or the fame Way.
Thus, at London, on the 31st of May,
the Sun's
Amplitude is 24 Degrees Northerly,
Oblique Afcenfion, 20.
+
Obli-
Sect. 3.
165
The GLOBE S.
}
Į
>
2
Oblique Defcenfion,' 58.
Afcenfional Difference, 19.
Semidiurnal Arch, 109.
His Continuance above the Horizon,
141 Hours.
A
2
Sun riſes at three Quarters paft Four.
Sun fets at a Quarter paft Seven.
Theſe Things for the Sun vary every
Day; but for a fixed Star the Day of
the Month need not be given, for they
the fame all the Year round.
are
In the Latitude of 51 North Syrius's
Amplitude is about 28 Degrees Southerly.
Oblique Afcenfion, 121.
Oblique Defcenfion, 75.
Afcenfional Difference, 23.
Semidiurnal Arch, 67.
↓
Continuance above the Horizon, 9
Hours.
PROB. XXXVIII. The Latitude and the
Day of the Month being given; to find
the Hour when any known Star will be
on the Meridian, and alfo the Time af its
Rifing and Setting.
Having rectified the Globe for the La-
titude of the Sun's Place bring the given
Star to the Meridian, and alſo to the Eaſt
M 3
or
1
166
The Ufe of
+
or Weft Side of the Horizon, and the
Index will ſhew accordingly when the
Star culminates, or the Time of the Rifing
or Setting.
"
Thus at London, on the 21ft of Janu-
ary, Syrius will be upon the Meridian,
at a Quarter paft Ten in the Evening,
rifes at 54 Hours, and ſets at three Quar-
ters paft Two in the Morning.
By the Converſe of this Problem,
knowing the Time when any Star is
upon
the Meridian, you may eafily find
the Sun's Place. Thus, bring the given
Star to the Meridian, and fet the Index to
the given Hour; then turn the Globe till
the Index points to 12 at Noon, and the
Meridian will cut the Sun's Place in the
Ecliptic. Thus when Syrius comes to
the Meridian at 10 Hours after Noon,
the Sun's Place will be Deg.
I
2
~
PROB. XXXIX. To find at what Time
of the Year a given Star will be up-
on the Meridian, at a given Hour of
the Night.
Bring the Star to the Meridian, and
fet the Index to the given Hour, then
turn the Globe till the Index points to
-
12
1
Sect. 3.
167
the GLOBE S.
12 at Noon, and the Meridian will cut
the Ecliptic in the Sun's Place; whence
the Day of the Month may be eafily
found in the Calendar upon the Horizon.
PROB. XL. The Day of the Month, and
the Azimuth of any known Star being
given; to find the Hour of the Night.
Having rectified the Globe for the
Latitude and the Sun's Place, if the given
Star be due North or South, bring it to
the Meridian, and the Index will ſhow
the Hour of the Night. If the Star be
in any other Direction, fix the Quadrant
of Altitude in the Zenith, and fet it to
the Star's Azimuth in the Horizon; then
turn the Globe about until the Quadrant
cuts the Center of the Star, and the In-
dex will ſhew the Hour of the Night.
The Bearing of any Point in the
Heavens may be found by the following
Methods.
Having a Meridian Line drawn in two
Windows, that are oppofite to one an-
other, you may croſs it at right Angles
with another Line repreſenting the Eaſt
and Weft; from the Point of Inter-
fection deſcribe a Circle, and divide each
Qua-
M 4
168
The Uſe of
3
4
Quadrant into 90 Degrees; then get a
fmooth Board, of about 2 Feet long, and
Foot broad, (more or less, as you
judge convenient) and on the back Part
of it fix another ſmall Board croffways,
fo that it may ſerve as a Foot to ſupport
the biggeſt Board upright, when it is fet
upon a Level, or an Horizontal Plain.
The Board being thus prepared, fet the
lower Edge of the fmooth, or fore fide
of it, clofe to the Center of the Circle,
then turn it about to the Meridian, or
to any Azimuth Point required (keeping
the Edge of it always clofe to the Cen-
ter) and cafting your Eye along the flat
Side of it, you'll eafily perceive what
Stars are upon the Meridian, or any
other Bearing that the Board is fết to.
PROB. XLI. Two known Stars having the
fame Azimuth, or the fame Height, be-
ing given ; to find the Hour of the Night,
Rectify the Globe for the Latitude,
the Zenith, and the Sun's Place.
I. When the two Stars are in the
fame Azimuth, turn the Globe, and alſo
the Quadrant about, until both Stars co-
incide with the Edge thereof; then will
the Index fhew the Hour of the Night;
}
•
and
¿
12
Sect. 3.
169
the GLOBE S.
and where the Quadrant cuts the Hori-
zon, is the common Azimuth of both
Stars.
to
12. If the two Stars are of the fame Al-
titude, move the Globe ſo that the fame
Degree on the Quadrant will cut both
Stars, then the Index will fhew the Hour.
量
​1
This Problem is uſeful when the Quan-
tity of the Azimuth of the two Stars in
the firſt Cafe, or of their Altitude in the
latter Cafe, is not known.
If two Stars were given, one on the Meri-
dian, and the other in the Eaft or West
part of the Horizon; to find the Lati-
tude..
Bring that Star which was obferved
on the Meridian, to the Meridian of the
Globe, and keep the Globe from turning
round its Axis; then flide the Meridian
up or down in the Notches, till the other
Star is brought to the Eaft or Weſt Part
of the Horizon, and that Elevation of
the Pole will be the Latitude fought.
PROB. XLII. The Latitude, Day of the
Month, and the Altitude of any known
Star being given; to find the Hour of
the Night.
Rec
170
The Uſe of
1
Rectify the Globe for the Latitude,
Zenith, and Sun's Place: Turn the Globe,
and the Quadrant of Altitude, backward
or forward, till the Center of that Star
meets the Quadrant in the Degree of Al-
titude given; then the Index will point
the true Hour of the Night; and alfo
where the Quadrant cuts the Horizon,
will be the Azimuth of the Star at that
Time.
If the Latitude, the Sun's Altitude, and his
Declination (instead of his Place in the
Ecliptic) are given; to find the Hour
of the Day and Azimuth.
Rectify the Globe for the Latitude
and Zenith, and having brought the E-
quinoctial Colure to the Meridian, ſet the
Index to 12 at Noon; which being done,
turn the Globe and the Quadrant, until
the given Declination in the Equinoctial
Colure cuts the Altitude on the Qua-
drant; then the Index will fhew the Hour
of the Day, and the Quadrant cut the
Azimuth in the Horizon.
If the Altitude of two Stars on the fame
Azimuth, were given; to find the Lati-
tude of the Place.
Set
Sect. 3.
17!
the GLOBE S.
Set the Quadrant over both Stars at
the obferved Degrees of Altitude, and
keep it faſt upon the Globe with your
Fingers; then flide the Meridian up or
down in the Notches, till the Quadrant
cuts the given Azimuth in the Horizon;
that Elevation of the Pole will be the
Latitude required.
}
PROB. XLIII. Having the Latitude of
the Place, to find the Degree of the
Ecliptic, which rifes or fets with a given
Star; and from thence to determine the
Time of its Cofmical and Achronicaļ
Rifing and Setting.
Having rectified the Globe for the
Latitude, bring the Given Star to the
Eaſtern Side of the Horizon, and mark
what Degree of the Ecliptic rifes with
it: Look for that Degree in the Wooden
Horizon, and right againſt it, in the
Calendar, you'll find the month and Day
when the Star rifes Cofmicaly. If you
bring the Star to the Weſtern Side of the
Horizon, that Degree of the Ecliptic
which riſes at that Time, will give the
Day of the Month when the ſaid Star, fets
Cofmically. So likewiſe againſt the De-
gree which fets with the Star, you'll find
the Day of the Month of the Achronical
Setting
172
The Uſe of
Setting; and if you bring it to the
Eaſtern Part of the Horizon, that De-
gree
which fets at that Time will be the
Sun's Place when the Star rifes Achro-
nically.
Thus, in the Latitude of London, Sy-
rius, or the Dog-Star, rifes Cofmically the
10th of August, and fets Cofmically the
10th of October. Aldebaran, or the Bull's
Eye, rifes Achronically on the 22d of May,
and fets Achronically on the 19th of
December.
PROB. XLIV. Having the Latitude of
the Place, to find the Time when a Star
rifes and fets Heliacally.
Having rectified the Globe for the
Latitude, bring the Star to the Eaftern
Side of the Horizon, and turn the Qua-
drant round to the Weſtern Side, till it
cuts the Ecliptic in twelve Degrees of Al-
titude above the Horizon, if the Star be
of the firſt Magnitude; then that Point
of the Ecliptic which is cut by the
Quadrant, is 12 Degrees high above the
Weſtern Part of the Horizon, when the
Star riſes; but at the fame Time the op-
pofite Point in the Ecliptic is 12 Degrees
below the Eaftern Part of the Horizon,
which
Plate 4
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Page 172
·
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;
R. Cophee jinip,
Sect. 3.
173
the GLOBE S.
which is the Depreffion of a Star of the
firft Magnitude, when the rifes Heliacally;
or has got fo far from the Sun's Beams,
that ſhe may be ſeen in the Morning be-
fore Sun-rifing. Wherefore look for the
faid Point of the Ecliptic on the Horizon,
and right againſt it will be the Day of
the Month when the Star rifes Heliacally.
To find the Heliacal Setting, bring the
Star to the Weft Side of the Horizon,
and turn the Quadrant about to the
Eaſtern Side, till the 12th. Degree of it
above the Horizon, cuts the Ecliptic;
then that Degree of the Ecliptic which
is oppofite to this Point, is the Sun's
Place when the Star fets Heliacally.
Thus you'll find that Arcturus riſes
Heliacally the 28th. of September, and
fets Heliacally December the 2d.
PROB. XLV. To find the Place of any
Planet upon the Globe; and fo by that
Means, to find its Place in the Heavens :
Alfo to find at what Hour any Planet
will rife or fet, or be on the Meridian at
any one Day in the Year.
You muſt firſt ſeek in an Ephemeris,
(White's Ephemeris will do well enough)
for the Place of the Planet propoſed on
that
174
The Use of
that Day; then mark that Point of the
Ecliptic, either with Chalk, or by ſticking
on a little black Patch; and then for that
Night you may perform any Problem, as
before, by a Fixed Star.
Let it be required to find the Situation
of Jupiter among the Fixed Stars in the
Heavens, and alfo whenabouts it rifes
and fets, and comes to the Meridian on
the 19th of May, 1757, N. S. at London.
Looking for the 19th of May, 1757;
in White's Ephemeris, I find that Jupiter's
Place at that Time is in about 12 De-
grees of m; Latitude about 1 Degree
North. Then looking for that Point
upon the Celeſtial Globe, I find that 4
is then nearly in Conjunction with the
bright Star in the Southern Balance, and
about 1 Degree North of it.
To find when he rifes and fets, and
comes to the Meridian: Having put a
little black Patch on the Place of Jupiter,
elevate the Globe according to the La-
titude, and having brought the Sun's
Place to the Meridian, fet the Hour-
Index to 12 at Noon; then turn the
Mark which was made for Jupiter, to
the Eaſtern Part of the Horizon, I find
4 will rife fomewhat more than Half
arr
Sect. 3.
the GLOBE S.
175
an Hour after Three in the Afternoon;
and turning the Globe about, I find it
comes to the Meridian a little before
Eleven at Night; and fets almoſt a
Quarter paſt Six next Morning.
This Example being underſtood, it will
be eaſy to find when either of the other
two fuperior Planets, viz. Mars and Sa-
turn, rife, fet and come to the Meridian.
I fhall conclude this Subject about the
Globes with the following Problem.
PROB. XLVI. To find all that Space upon
the Earth, where an Eclipfe of one of the
Satellites of Jupiter will be viſible.
Having found that Place upon the
Earth, in which the Sun is Vertical, at
the Time of the Eclipfe, by Prob. 13.
clevate the Globe according to the Lati-
tude of the faid Place; then bring the
Place to the Meridian, and fet the Hour
Index to 12 at Noon. If Jupiter be in
Conſequence of the Sun, draw a Line
with Black-Lead, or the like, along the
Eaſtern Side of the Horizon, which Line
will pafs over all thoſe Places where the
Sun is ſetting at that Time; then count
the Difference betwixt the Right Aſcen-
fion of the Sun, and that of Jupiter, and
turn the Globe Weftward, till the Hour-
Index
176
The Uſe of
Index points to this Difference; then
keep the Globe from turning round its
Axis, and elevate the Meridian, accord-
ing to the Declination of Jupiter. The
Globe being in this Pofition, draw a Line
along the Eaſtern Side of the Horizon;
then the Space between this Line, and
the Line before drawn, will comprehend
all thofe Places of the Earth where Jupi-
ter will be viſible, from the ſetting of the
Sun, to the ſetting of Jupiter:
But if Jupiter be in Antecedence of
the Sun (i.e. rifes before him) having
brought the Place where the Sun is Ver-
tical, to the Zenith, and put the Hour
Index to 12 at Noon, draw a Line on
the Weſtern Side of the Horizon; then
elevate the Globe according to the De-
elination of Jupiter, and turn it about
Eaſtward, until the Index points to fo
many Hours diftant from Noon, as is
the Difference of Right Afcenfion of the
Sun and Jupiter. The Globe being in
this Pofition, Draw a Line along the
Weſtern Side of the Horizon; then the
Space contained between this Line, and
the other laft drawn, will comprehend
all thofe Places upon the Earth where
the Eclipfe is viſible, between the rifing
of the Sun and that of Jupiter.
The
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( 177 )
The DESCRIPTION of the
Great ORRERY, lately made
by Mr. THOMAS WRIGHT,
Mathematical Inftrument Ma-
ker to His late MAJESTY, and
now by BENJAMEN COLE,
his Succeffor.
T
XXX HE ORRERY is an Aftrono-
mical Machine, made to re-
preſent the Motions of the
Planets. Thefe Machines are
made of various Sizes, fome having more
Planets than others; but I fhall here
confine myſelf to the Defcription of that
above mentioned.
In the Introduction we gave a fhort
Account of the Order, Periods, Distances,
and Magnitudes of the Primary Planets;
and of the Diſtances and Periodical Re-
volutions of the Secondary Planets round
their reſpective Primaries. We ſhall here
explain their Stations, Retrogradations;
N
Eclips
178
The Deſcription of
The De-
Eclipfes, and Phafes, &c. but firſt let
us take a general View of the Orrery.
The Frame which contains the Wheel-
fcription Work, &c. that regulates the whole Ma-
of the Or- chine, is made of fine Ebony, and is near
very.
Vide
piece.
:
four Feet in Diameter; the Outfide
thereof is adorned with twelve Pilafters,
curiouſly wrought and gilt: Between
theſe Pilafters the twelve Signs of the
Zodiac are neatly painted, with gilded
Frames. Above the Frame is a broad
Frontif Ring, Supported with twelve Pillars
This Ring repreſents the Plane of the
Ecliptic, upon which there are two Scales
of Degrees, and between thoſe the Names
and Characters of the 12 Signs. Near the
Outfide is a Scale of Months and Days, '
exactly correfponding to the Sun's Place
at Noon, each Day throughout the
Year.
Above the Ecliptic ftands fome of the
principal Circles of the Sphere, accord-
ing to their refpective Situations in the
Heavens, viz. N° 10, are the two Colures,
divided into Degrees and Half Degrees:
N° 11, is one Half of the Equinoctial
Circle, making an Angle with the Eclip-
tic of 23 Degrees. The Tropic of Can-
cer, and the Arctic Circle, are each fixed-
2
parallel
the ORRERY.
179
1
1
parallel, and at their proper diſtance
from the Equinoctial. On the Northern
Half of the Ecliptic is a Brafs Semi-
circle, moveable upon two Points fixed
in and; This Semicircle ferves as a
moveable Horizon, to be put to any De-
gree of Latitude upon the North Part of
the Meridian. The whole Machine is
alſo ſo contrived, as to be fet to any La-
titude, without in the leaſt affecting any
of the infide Motions: For this Purpofe
there are two ftrong Hinges (Nº. 13.
fixed to the Bottom Frame, upon which
the Inftrument moves, and a ſtrong Braſs
Arch, having Holes at every Degree,
thro' which a ſtrong Pin is to be put,
according to the Elevation. This Arch
and the two Hinges fupport the whole
Machine, when it is lifted up according
to any Latitude; and the Arch at other
Times lies conveniently under the Bot-
tom Frame:
?
When the Machine is fet to any La-
titude, (which is eaſily done by two Men,
each taking hold of two Handles con-
veniently fixt for the Purpoſe) ſet the
moveable Horizon to the fame Degree
upon the Meridian, and you may form
an Idea of the refpective Altitude, or
Depreffions of the the Planets, above or
N 2
below
180
The Deſcription of
7
below the Horizon, according to their
reſpective Poſitions, with Regard to the
Meridian.
Within the Ecliptic, and nearly in the
fame Place thereof, ftands the Sun, and
all the Planets, both Primary and Se-
condary. The Sun (No 1.) ftands in
the Middle of the whole Syftem upon
a Wire, making an Angle with the
Plane of the Ecliptic, of about 82 De-
grees; which is the Inclination of the
Sun's Axis, to the Axis of the Ecliptic.
Next to the Sun is a ſmall Ball (No 2.)
repreſenting Mercury: Next to Mercury
is Venus (No 3.) reprefented by a larger
Ball, (and both theſe ſtand upon Wires,
ſo that the Balls themſelves may be more
vifibly perceived by the Eye.)
Earth is repreſented (No 4.) by an Ivo-
ry Ball, having fome of the principal
Meridians and Parallels, and a little
Sketch of a Map deſcribed upon it. The
Wire which fupports the Earth makes
an Angle with the Plane of the Ecliptic
66 Degrees, which is the Inclination
of the Earth's Axis to that of the Eclip-
tic. Near the Bottom of the Earth's
Axis is a Dial-Plate (No 9.) having an
Index pointing to the Hours of the Day,
as the Earth turns round its Axis.
I
2
The
Round
the ORRERY.
181
Round the Earth is a Ring, ſupport-
ed by two fmall Pillars, which Ring re-
preſents the Orbit of the Moon, and the
Diviſion upon it a fwers to the Moon's
Latitude; the Motion of this Ring repre-
fents the Motion of the Moon's Orbit,
according to that of the Nodes. With
in this Ring is the Moon (No 5.) hav-
ing a black Cap or Cafe, which by its
Motion, repreſents the Phafes of the
Moon according to her Age. Without
the Orbits of the Earth and Moon is
Mars (N° 6.) The next in Order to
Mars is Jupiter, and his four Moons,
(No 7); each of thefe Moons is fupport-
ed by a crooked Wire fixed in a Socket,
which turns about the Pillar that fup-
ports Jupiter. Theſe Satellites
may be
turned by the Hand to any Pofition;
and yet when the Machine is put in
Motion, they'll all move in their pro-
per Times. The outermoft of all is
Saturn, and his five Moons (No 8.) Thefe
Moons are fupported and contrived after
the fame Manner with thofe of Jupiter.
The whole Machine is put into Motion
by turning a ſmall Winch, (like the Key
of a Clock, Nº 14); and all the infide
Work is fo truly wrought, that it re-
quires but very ſmall Strength to put the
Whole in Motion.
N 3
Above
182
The Defcription of
Above the Handle there is a Cylin-
drical Pin, which may be drawn a little
out, or puſhed in at Pleaſure: when it
is puſhed in, all the Planets, both Pri-
mary and Secondary, will move accord-
ing to their reſpective Periods, by turn-
ing the Handle: When it is drawn out,
the Motions of the Satellites of Jupiter
and Saturn will be ſtopped, while all the
reft move without Interruption. This is
à very good Contrivance to preferve the
Inftrument from being clogged by the
fwift Motions of the Wheels belonging
to the Satellites of Jupiter and Saturn;
when the Motions of the rest of the Pla-
nets are only confidered.
There is alſo a Brafs Lamp having
two Convex Glaffes, to be put in the
Room of the Sun; and alſo a ſmaller
Earth and Moon, made fomewhat in
Proportion to their Diſtance from each
other, which may be put on at Pleaſure.
The Lamp turns round in the ſame
Time with the Earth, and by means of
the Glaffes cafts a ſtrong Light upon
her; and when the ſmaller Earth and
Moon are placed on, it will be eafy to
fhew when either of them may be eclip-
fed.
Having
the ORRERY.
183
1
Having thus given a brief Deſcription
of the outward Part of this Machine, I
fhall next give an Account of the Pha-
nomena x ained by it when it is put
x:
into Motion.
1. Of the Motions of the Planets in ge-
ရာ
neral.
Having put on the Handle, puſh in
the Pin which is juſt above it, and place
a ſmall black Patch (or Bit of Wafer)
upon the Middle of the Sun (for In-
ftance) right againſt the firſt Degree of
r; you may alfo place Patches upon
Venus, Mars, and Jupiter, right againſt
fome noted Point in the Ecliptic. If you
lay a Thread from the Sun to the firft
Degree of r, you may fet a Mark where
it interfects the Orbit of each Planet,
and that will be a Help to note the
Time of their Revolutions.
One entire turn of the Handle anſwers
to the Diurnal Motion of the Earth
round her Axis, as may be ſeen by the
Motion of the Hour-Index which is pla-
ced at the Foot of the Wire on which
the Terella is fixed. When the Index
has moved the Space of ten Hours, you
may obſerve that Jupiter has made one
N4
Revo-
4
184
The Defcription of
Revolution compleat round its Axis;
the Handle being turned until the Hour
Index has paffed over 24 Days 8 Hours,
will bring the Patch upon Venus to its
former Situation with refpect to the E-
cliptic, which fhews that has made
one entire Revolution round her Axis.
Mars makes one compleat Revolution
round his Axis in 24 Hours and about
40 Minutes. When the Handle is turn-
ed 251 Times round, the Spot upon the
Sun will point to the fame Degree of
the Ecliptic, as it did when the Inftru-
ment was firſt put into Motion. By
obferving the Motions of the Spots up-
on the Surface of the Sun, and of the
Planets in the Heavens, their Diurnal
Motion was difcover'd, after the fame
Manner as we do here obſerve the Mo-
tions of their Repreſentatives, by that
of the Marks placed upon them.
If while you turn the Handle you ob-
ſerve the Planets, you will fee them per-
form their Motions in the fame relative
Times as they really do in the Heavens,
each making its Period in the Times
mentioned in the Tables, Page, 28;
27 Turns of the Handle will bring
the Moon round the Earth, which is
called a Periodic Month, and all the
4
while
→
'
f
1.
1
*
芥
​3
Plate 5
Fig. I
Fig.II
I'
B
B
C
B
T
K
1
T
B
R
Fig.III
[C
Fig. IV Fig.
I
Fig. V
E
B
Fig. VII
H
D
C
i
T
G
A
F
C
OE
Page 184
H
G
R. Cafhee feuiir.
*
the ORRERY.
185
while fhe keeps the fame Face towards
the Earth; for the Moon's Annual and
Diurnal Motion are perform'd both in
the fame Time nearly, fo that we al-
way's fee the fame Face or Side of the
Moon.
²
T
I
If before the Inftrument is put into
Motion, the Satellites of Jupiter and
Saturn be brought into the fame right
Line from their reſpective Primaries,
you'll fee them as you turn the Handle,
immediately difpers'd from one another,
according to their different Celerities.
Thus one Turn of the Handle will
bring the firft of Jupiter's Moons about
Part round Jupiter, while the fecond
has deſcribed but Part, the third but
above, and the fourth not quite
Part, each of its refpective Orbits. If you
turn the Handle until the Hour-Index
has moved 18 Hours more, the firſt
Satellite will then be brought into its
former Pofition, and fo has made one
entire Revolution; the ſecond at the fame
Time will be almoſt diametrically op-
pofite to the firſt, and fo has made a lit-
tle more then Half of one Revolution;
the others will be in different Afpects,
according to the Length of their Periods,
as will be plainly exhibited by the In-
Ι
2
ſtrument.
386
The Defcription of
ftrument. The fame Obfervations may
be made with refpect to the Satellites
of Saturn.
•
$
The Machine is fo contrived, that
the Handle may be turned either Way;
and if before you put it into Motion,
you obferve the Afpect (or Situation
with refpect to each other) of the Pla-
nets, and then turn the Handle round
any Number of Times; the fame Num-
ber of Revolutions being made back-
wards, will bring all the Planets to their
former Situations: I fhall next proceed
to Particulars.
ነ
Of the Stations, and Retrogradations of
the Planets.
*
The Primary Planets, as they all turn
round the Sun, at different Diſtances,
and in different Times, appear to us
from the Earth to have different Moti-
ons; as fometimes they appear to move
from West to Eaft according to the Or-
der of the Signs, which is called their
direct Motion, then by Degrees they
flacken their Pace, until at laſt they lofe
Stationary all their Motion and become Stationary,
or not to move at all; that is, they ap-
pear in the fame Place with refpect to
the
the ORRERY.
187
Motion of
the fixed Stars for fome Time together;
after which they again begin to move,
but with a contrary Direction, as from
Eaft to Weft, which is called their re-Retrograde
trograde Motion; then again they be- the Planets
come Stationary, and afterwards reaf-
fume their direct Motion. The Reaſon
of all theſe Appearances is very evident-
ly fhewn by the Orrery.
Of the Stations, &c. of the inferior
Planets.
་
t
We fhall inſtance in the Planet Mer-
cury, becauſe his Motion round the Sun
differs more from the Earth's than that
of Venus does.
When Mercury is in his fuperior Con-
junction (or when he is in a direct Line
from the Earth beyond the Sun) faſten
a String about the Axis of the Earth,
and extend it over Mercury to the Eclip-
tic; then turning the Handle, keep the
Thread all the while extended over g
and you'll find it move with a direct
Motion in the Ecliptic, but continually
flower, until Mercury has the greateſt
Elongation fron the Earth. Near this
Pofition, the Thread for fome Time will
lay over Mercury without being mov'd
+
$
in
188
The Defcription of
cury
in the Ecliptic, tho' the Earth and Mer-
both continue their progreffive Mo-
tion in their respective Orbits. When
Mercury has got a little paft this Place,
you'll find the Thread muſt be moved
backward in the Ecliptic, beginning firſt
with a flow Motion, and then fafter by
Degrees, until Mercury is in his inferior
Conjunction, or directly betwixt the
Earth and the Sun. Next this Fofition
of, his retrograde Motion will be the
fwifteft; but he ſtill moves the fame way,
tho' continually flower, till he has again
come to his greateſt Elongation, where
he will appear the fecond Time to be
ſtationary; after which he begins to
move forward, and that fafter by De-
grecs, .until he is come to the fame Po-
fition with refpect to the Earth, that
he was in at firft. The fame Obfèrva-
tions may be made relating to the Mo
tions of Venus. In like Manner the dif-
ferent Motions obferved in the fuperior
Planets may be alfo explained by the
Orrery. If you extend the Thread over
Jupiter, and proceed after the fame
Manner as before we did in regard to
Mercury, you'll find that from the Time.
Jupiter is in Conjunction with the Sun,
his Motion is direct, but continually
lower, until the Earth is nearly in a
Qua-
the ORRERY.
189
Quadrate Afpect with Jupiter, near
which Pofition Jupiter ſeems to be ſtati-
onary: After which he begins to move,
and continually mends his Pace, until
he comes in Oppofition to the Sun, at
which Time his retrograde Motion is
fwifteft. He ftill feems to go back-
ward, but with a flower Pace, till the
Earth and he are again in a Quadrate
Afpect, where Jupiter feems to have loſt
all his Motion; after which he again re-
fumes his direct Motion, and fo proceeds
fafter by Degrees, till the Earth and he
are again in Oppofition to each other.
Theſe different Motions obferved in Plate 3
the Planets, are eaſily illuftrated, ás fol-Fig. 1.
loweth: The leffer Circle round the Sun
is the Orbit of Mercury, in which he
performs his Revolution round the Sun
in about three Months, or while the
Earth is going thro' Part of her Orbit,
44
or from A to N. The Numbers 1, 2,
3, &c. in the Orbit of Mercury ſhow
the Spaces he defcribes in a Week near-
ly, and the Diſtance AB, BC, CD, &c.
in the Earth's Orbit, do likewife ſhow
her Motion in the fame Time. The
Letters A, B, C, &c. in the great Orb,
are the Motions of Mercury in the
Heavens, as they appear from the Earth.
Now
190
The Deſcription of
Now if the Earth be fuppofed in A,
and Mercury in 12, near his fuperior
Conjunction with the Sun; a Spectator
on the Earth will fee x, as if he were in
the Point of the Heavens A ;-and while
is moving from 12 to 1, and from 1
to 2, &c. the Earth in the fame Time
alfo moves from A to B, and from B to
C, &c. All which Time appears in
I
the Heavens to move in a direct Motion
from A to B, and from B. to C, &c. but
gradually flower, until he arrives near
the Point G; near which Place he ap
pears ſtationary, or to ftand ftill; and
afterwards (tho' he ftill continues to
move uniformly in his own Orbit, with
a progreffive Motion) yet in the Sphere
of the fix'd Stars he'll appear to be re-
trograde, or to go backwards as from G
to H, from H to I, &c. until he has ar-
rived near the Point L, where again
he'll appear to be ſtationary; and after-
wards to move in a direct Motion from
L to M, and from M to N, &c.
What has been here fhewed concern-
ing the Motions of Mercury, is alſo to
be underſtood of the Motions of Venus;
but the Conjunctions of Venus with the
Sun do not happen fo often as in Mer÷
cury; for Venus moving in a larger Orbit,'
1
and
the ORRERY:
idi
and much flower than Mercury, does not
fo often overtake the Earth. But the
Retrogradations are much greater in Ve-
nus than they are in Mercury, for the Fig. 2:
fame Reaſons::
**
I
I 2
The innermoft Circle repreſents the
Earth's Orbit, divided into 12 Parts, an-
fwering to her monthly Motion; the
greateſt Circle is in the Orbit of Jupiter,
which he deſcribes in about 12 Years;
and therefore the thereof, from A to
N, defines his Motion. In one of our
Years nearly, and the intermediate
Divifions, A, B, C, &c. his monthly
Motion. Let us ſuppoſe the Earth to
be in the Point of her Orbit 12, and
Jupiter in A,in his Conjunction with the
Sun; it is evident that from the Earth
Jupiter will be ſeen in the great Orb,
or in the Point of the Heavens A, and
while the Earth is moving from 12 to 1,
2, &c. 4 alío moves from A to B, &c.
all which Time he appears in the Hea-
vens to move with a direct Motion
from A to B, C, &c. until he comes in
Oppofition to the Earth near the Point
of the Heavens E. where he appears to
be ſtationary; after which 4 again
begins to move (tho' at firft with a flow
Pace) from E through F, H, I, to K,
where
192
The Defcription of
where again he appears to ſtand ſtill,
but afterwards he reaffumes his direct
Motion from I thro' K, to M,&c..
From the Conftruction of the preceed-
ing Figure it appears, that when the
fuperior Planets are in Conjunction with
the Sun, their direct Motion is much
quicker than at other Times; and that
becauſe they really move from Weſt to
Eaft, while the Earth in the oppofite
Part of the Heavens is carried the fame
Way, and round the fame Center. This
Motion afterwards continually flackens,
until the Planet comes almoſt in Op-
pofition to the Sun, when the Line
joining the Earth and Planet, will con-
tinue for fome Time nearly parallel
to itfelf, and fo the Planet feems from
the Earth to ſtand ftill; after which, it
begins to move with a flow Motion
backward, until it comes into a Quartile
Afpect with the Sun, when again it will
appear to be ſtationary for the above
Reaſons; after that it will refume its di-
rect Motion, until it comes into a Con-
junction with the Sun, then it will pro-
ceed as above explained. Hence it alſo
appears, that the Retrogradations of the
fuperior Planets are much flower than
their direct Motions, and their Conti-
nuance
7
the QRRERY.
193
+
·
·
ง
nuance much fhorter; for the Planet,
from its laft Quarter, until, it comes in
Oppofition to the Sun, appears to move
the fame Way with the Earth, by whom
it is then overtaken: After which it
begins to go backwards, but with a flow
Motion, becauſe the Earth being in the
fame Part of the Heavens, and moving
the fame Way that the Planet really
does, the apparent Motion of the Planet
backwards muſt thereby be leffened.
-
What has been here faid concerning
the Motions of Jupiter, is alſo to be un-
ftood of Mars and Saturn. But the Re-
trogradations of Saturn do oftner happen
than thofe of Jupiter, becauſe the Earth
oftner overtakes Saturn; and for the
fame Reaſon, the Regreffions of Jupiter
do oftner happen than thoſe of Mars.
But the Retrogradations of Mars are
much greater than thofe of Jupiter;
whoſe are alſo much greater than thoſe
of Saturn.
In either of the Satellites of Jupiter
or Saturn, thefe different Appearances
in the neighbouring Worlds are much
oftner feen than they are by us in the
Primary Planets.
O
We
194
The Defcription of
}
}
We never obferve theſe different Mo-
tions in the Moon, becauſe ſhe turns
round the Earth as her Centre; neither
do we obferve them in the Sun, becauſe
he is the Centre of the Earth's Motion
whence the apparent Motion of the Sun
always appears the fame Way round the
Earth.
Of the Annual and Diurnal Motion of the
Earth, and of the Increafe and Decreaſe
of Days and Nights.
;
The Earth, in her Annual Motion
round the Sun, has her Axis always in
the fame Direction, or parallel to itſelf;
that is, if a Line be drawn Parallel to the
Axis, while the Earth is in any Point of
her Orbit, the Axis in all other Pofitions
of the Earth will be parallel to the faid
Line. This Parallelifm of the Axis, and
the fimple Motion of the Earth in the
Ecliptic, folves all the Phænomena of
different Seaſons. Thefe Things are ve-
ry well illuftrated by the Orrery.
If
you put on the Lamp in the Place
of the Sun, you will ſee how one Half of
our Globe is always illuminated by the
Sun, while the other Hemifphere re-
nains in Darkneſs; how Day and Night-
are
the ORRERÝ.
195
are form'd by the Revolution of the
Earth round her Axis; for as the turns
from Weft to Eaft, the Sun appears to
move from Eaſt to Weſt. And while
the Earth turns in her Orbit, you may
obferve that her Axis always points the
fame Way, and the ſeveral Seaſons of the
Year continually change.
To make theſe Things plainer, we will
take a View of the Earth in different
Parts of her Orbit.
A
·
When the Earth is in the firſt Point
of Libra (which is found by extending a
Thread from the Sun, and over the
Earth, to the Ecliptic) we have the
Vernal Equinox, and the Sun at that
Time appears in the firſt Point of v
In this Pofition of the Earth, two Poles
of the World are in the Line feparating
Light and Darkneſs; and as the Earth
turns round her Axis, juſt one Half of
the Equator, and all its Parallels, will be
in the Light, and the other Half in the
Dark;
and therefore the Days and
Nights muſt be every where equal.
As the Earth moves along in her Or-
bit, you'll perceive the North Pole ad-
vances by Degrees into the illuminated
02
Hemi-
196
The Deſcription of
Hemiſphere, and at the fame Time the
South Pole recedes into Darkness; and
in all Places to the Northward of the
Equator, the Days continually lengthen
while the contrary happens in the South-
ern Parts, until at length the Earth is ar-
rived in Capricorn. In this Pofition of
the Earth all the Space included within
the Arctic Circle falls wholly within the
Light, and all the oppofite Part, lying
within the Antarctic Circle, is quite in-
volved in Darkneſs. In all Places be-
tween the Equator and the Arctic Circle,
the Days are now at the Longeſt, and
are gradually longer as the Places are
more remotefrom the Equator. In the
Southern Hemiſphere there is a contrary
Effect. All the while the Earth is travel-
ling from Capricorn towards Aries, the
North Pole gradually recedes from the
Light, and the South Pole approaches
nearer to it; the Days in the Northern
Hemiſphere gradually decreaſe, and in
the Southern Hemisphere they increaſe
in the fame Proportion, until the Earth
be arrived in ; then the two Poles of
the World lie exactly in the Line fepa-
rating Light and Darkneſs, and the Days
are equal to the Nights in all Places of
the World. As the Earth advances to-
wards Cancer, the North Pole gradually
recedes
the ORRERY.
197.
recedes from the Light, while the South-
ern one advances into it, at the fame Rate.
In the Northern Hemifphere the Days
decreaſe, and in the Southern one they
gradually lengthen, until the Earth being
arrived in Cancer, the North Frigid Zone
is all involved in Darkneſs, and the South
Frigid Zone falls intirely within the
Light; the Days every where in the Nor-
thern Hemiſphere are now at the ſhorteſt,
and to the Southward they are at the
longeft. As theEarth moves from hence
towards Libra, the North Pole gradually
approaches the Light and the other re-
cedes from from it; and in all Places to
the Northward of the Equator the Days
now lengthen, while in the oppofite He-
miſphere they gradually fhorten, until
the Earth has gotten into ; in which
Poſition the Days and Nights will again be.
of equal Length in all Parts of the World.
You might have obſerved that in all
Pofitions of the Earth, one Half of the
Equator was in the Light, and the
other Half in Darknefs; whence under
the Equator, the Days and Nights are
always of the fame Length: And all
the while the Earth was going from ~
towards, the North Pole was conftant-
ly illuminated, and the South Pole all
03
the
198
The Defcription of
1
Plate 4.
the while in Darkneſs; and for the other
Half Year the contrary. Sometimes
there is a Semicircle exactly facing the
Sun, fixed over the Middle of the Earth,
which may be called the Horizon of the
Disk: This will do inſtead of the Lamp
if that Half of the Earth which is next
the Sun be confider'd, as being the illu-
minated Hemiſphere, and the other Half,
to be that which lies in Darkneſs.
-
'
The great Circle 8, п, &c, repre-
fent the Earth's annual Orbit; and the
four leffer Circles ESQC, the Ecliptic
upon the Surface of the Earth, coincid-
ing with the great Ecliptic in the Hea-
vens. Theſe four leffer Figures repre-
fent the Earth in the four Cardinal Points
of the Ecliptic, P being the North Pole
of the Equator, and p the North Pole of
the Ecliptic; SPC the Solftitial Colure
which is always parallel to the great Sol-
ftitial Colure in the Heavens
EPQ the Equinoctial Colure. The o-
ther Circles paffing thro' P, are Meridians
at two Hours Diſtance from one ano-
ther; the Semicircle EQ is, the North-
ern Half of the Equator; the parallel
Circle touching the Ecliptic in S, is the
Tropic of Cancer; the dotted Circle
the Parallel of London, and the fmall Cir-
cle,
the ORRERY.
199
cle, touching the Pole of the Ecliptic,
is the Arctic Circle. The fhaded Part,
which is always oppofite to the Sun,
is the obfcure Hemisphere, or that
which lies in Darkneſs; and that which
is next the Sun, is the illuminated Hemi-
ſphere.
1
If we fuppofe the Earth in ^, fhe'll
then fee the Sun in r, (which makes our
vernal Equinox) and in this Poſition the
Circle, bounding Light and Darkneſs,
which here is SC, paſſes thro' the Poles
of the World, and bifects all the Paral-
lels of the Equator; and therefore the
Diurnal and Noctural Arches, or the
Lengths of the Days and Nights, are
-equal in all Places of the World.
But while the Earth, in her annual
Courſe. moves through m, 4, to w, the
Line SC, keeping ſtill parallel to itſelf,
or to the Place where it was at firſt,
the Pole P will, by this Motion, gradu-
ally advance into the illuminated Hemi-
fphere; and alſo the Diurnal Arches of
the Parallels gradually increaſe, and con-
ſequently the Nocturnal ones decreaſe in
the fame Proportion, until the Earth
has arrived into ; in which Pofition
the Pole P, and all the Space within the
Artic
0 4
200
The Deſcription of
Arctic Circle, fall wholly within the illu
minated Hemifphere, and the Diurnal
Arches of all the Parallels that are with-
out this Circle; will exceed the Nocturnal
Arches more or lefs, as the Places are
nearer to, or farther off from it, until-
the Diſtance from the Pole is as far as
the Equator, where both theſe Arches
are always equal.
Again, while the Earth is moving from
, through, x, tor, the Pole P begins
to incline to the Line, diftinguiſhing
Light and Darkness in the fame Pro-
portion that before it receded from it;
and confèquently the Diurnal Arches
gradually leffen, untill the Earth has
arrived into r, where the Pole P will a-
gain fall on the Horizon, and ſo cauſe
the Days and Nights to be every-where
equal. But when the Earth has paffed
r, while fhe is going thro' 8, and I, &c.
the Pole P will begin to fall in the ob-
fcure Hemiſphere, and fo recede gradu-
ally from the Light, untill the Earth is
arrived in; in which Pofition not
only the Pole, but all the Space within
the Arctic Circle, are involved in Dark-
nefs, and the Diurnal Arches of all the
Parallels, without the Arctic Circle, are
equal to the Nocturnal Arches of the
>
fame
1
the ORRERY.
201
<
fame Parallels; when the Earth was in
the oppofite Point ; and it is evident
that the Days are now at the ſhorteſt,
and the Nights the longeft. But when
the Earth has paft this Point, while ſhe
is going through and m, the Pole P
will again gradually approach the Light,
and fo the Diurnal Arches of the Paral-
lels gradually lengthen, until the Earth
is arrived in; at which Time the Days
and Nights will again be equal in all
Places of the World, and the Pole itſelf
juſt ſee the Sun.
Here we only confidered the Phæno-
mena belonging to the Northern Paral-
lels; but if the Pole P be made the South.
Pole, then all the Parallels of Latitude
will be Parallels of South Latitude, and
the Days, every where, in any Pofition
of the Earth, will be equal to the Nights
of thoſe who liv'd in the oppofite Hemi-
ſphere, under the fame Parallels,
Of the Phafes of the Moon, and of her
Motion in her Orbit,
The Orbit of the Moon makes an
Angle with the Plane of the Ecliptic, of
above 5 Degrees, and cuts it into two
Points, diametrically oppofite (after the
I
fame
202
The Defcription of
Nodes.
Head.
fame Manner as the Equtor and the E-
cliptic cut each other upon the Globe,
in and) which Points are called the
Nodes; and a right Line joining theſe
Points, and paffing through the Center
of the Earth, is called the Line of the
Nodes. That Node where the Moon
begins to afcend Northward above the
Plane of the Ecliptic, is called the Aſ-
Dragon's cending Node, and the Head of the Dra-
gon, and is thus commonly marked & .
The other Node, from whence the Moon
deſcends to the Southward of the Eclip-
tic is called the Defcending Node, and the
Dragon's Dragon's Tail, and is thus mark'd 8.
The Line of Nodes continually ſhifts
itſelf from Eaſt to. Weft, contrary to the
Order of the Signs; and with this Re-
Retrograde trograde Motion, makes one Revolution
Motion of round the Earth, in the Space of about
19 Years.
Tail.
the Nodes.
Month.
The Moon defcribes its Orbit round
the Earth in the Space of 27 Days and
7 Hours, which Space of Time is called
Periodical a Periodical Month; yet from one Con-
junction to the next, the Moon ſpends
29 Days and a Half, which is called
Synodical a Synodical Month; becauſe, while the
Moon in her proper Orbit finiſhes her
Courfe, the Earth advances near a whole
Month
Sign
the ORRERY,
203
Sign in the Ecliptic; which Space the
Moon has ſtill to defcribe, before fhe will
be ſeen in Conjunction with the Sun.
When the Moon is in Conjunction
with the Sun, note her Place in the E-
cliptic; then turning the Handle, you'll
find that 27 Days and 7 Hours will bring
the Moon to the fame Place; and after
you have made 2 Revolutions more,
the Moon will be exactly betwixt the
Sun and the Earth.
the Moon,
The Moon all the while keeps in her
Orbit, and fo the Wire that fupports
her continually rifes or falls in a Socket,
as the changes her Latitude; the black
Cap ſhifts itfelf, and fo fhews the Pha-Phafes of
fes of the Moon, according to her Age,
or how much of her enlighten'd Part is
ſeen from the Earth. In one Synodical
Month, the Line of the Nodes moves a-
bout 1 Degree from Weft to Eaſt, and
fo makes one entire Revolution in 19
Years.
I
2
Let AB be an Arch of the Earth's Or-
bit, and when the Earth is in T, let the
Moon be in N, in Conjunction with the
Sun in S, while the Moon is defcribing
her Orbit NAFD, the Earth will de-
fcribe
204
The Deſcription of
fèribe the Arch of her Orbit T ; and
when the Earth has got into the Point t
the Moon will be in the Point of her
Orbit n, having made one compleat Re-
volution round the Earth. But the
Moon, before ſhe comes in Conjunction
with the Sun, muft again defcribe the
Arch no; which Arch is fimilar to Tt,
becauſe the Lines FN, fn, are parallel ;
and becaufe, while the Moon deferibes
the Arch no, the Earth advances forward
in the Ecliptic; the Arch deferibed by the
Moon, after ſhe has finiſhed her perio-
dical Month, before the makes a Syno-
dical Month, muſt be ſomewhat greater
than no. To determine the mean Length
of a Synodical Month, find the Diurnal
Motion of the Moon (or the Space fhe
deſcribes round the Earth in one Day)
and likewife the Diurnal Motion of the
Earth; then the Difference betwixt thefe
two Motions is the apparent Motion of
the Moon round the Earth in one Day;
then it will be, as this differential Arch
is to a whole Circle; fo is one Day to
that Space of Time wherein the Moon
appears to deſcribe a compleat Circle
round the Earth which is about 29
Days. But this is not always a true
Lunation, for the Motion of the Moon
is fometimes fafter, and ſometimes flow-
·
2
er,
the ORRERY.
205
er, according to the Pofition of the Earth
in her Orbit.
In one Synodical Month the Moon
has all Manner of Afpects with the Sun
and Earth, and becauſe ſhe is opaque,
that Face of hers will only appear bright
which is towards the Sun, while the op-
pofite remains in Darkneſs. But the
Inhabitants of the Earth can only fee
that Face of the Moon which is turned
towards the Earth; and therefore, ac-
cording to the various Pofitions of the
Moon, in refpect of the Sun and Earth,
we obferve different Portions of her illu-
minated Face, and fo a continual Change
in her + Phafes.
Let S be the Sun, RTV an Arch of
the Earth's Orbit, T the Earth, and the
Circle ABCD, &c. the Moon's Orbit, in
which the turns round the Earth in the
Space of a Month; and let A, B, C, &c.
be the Centers of the Moon in different
Parts of her Orbit.
Now if with the Lines.S A, SB, &c. Fig. zi
we join the Centers of the Sun and
+ Phafes of the Moon are thofe different Appearances
we obferve in her, according to her Pofition in reſpect
of the Sun and Earth.
Moon
+
200
The Defcription of
1
Full Moon.
Moon, and at right Angles to thefe draw
the Lines HO; the faid Lines HO will
be the Circles that feparate the illumi-
nated Part of the Moon from the dark
and obfcure. Again, if we conceive a-
nother Line IL to be drawn at right
Angles to the Lines TA, TB, &c. paff-
ing from the Center of the Earth to the
Moon, the faid Line IL will divide the
viſible Hemiſphere of the Moon, or that
which is turned toward us, from the in-
viſible, or that which is turned from us;
and this Circle may be called the Circle of
Viſion.
Now it is manifeft, that whenever the
Moon is in the Pofition A, or in that
Point of her Orbit which is oppofite to
the Sun, the Circle of Viſion, and the
Circle bounding Light and Darkneſs, do
coincide, and all the illuminated Face of
the Moon is turned towards the Earth,
and is viſible to us; and in this Pofition
the Moon is faid to be full. But when
the Moon arrives to B, all her illumi-
nated Face is then not towards the Earth,
there being a Part of it, HBI, not to be
feen by us; and then her viſible Face is
deficient from a Circle, and appears of
à gibbous Form, as in B. Fig. 3. Again
when the arrives to C, the two fore-
men-
3
the ORRERY.
207
mentioned Circles cut each other at right
1
Moon.
Angles, and then we obſerve a Half Half
Moon, as in C, Fig. 3. And again the
illuminated Face of the Moon is more
and more turned from the Earth, until
fhe comes to the Point E, where the
Circle of Vifion, and that bounding
Light and Darkneſs, do again coincide.
Here the Moon diſappears, the illumina-
ted Part being wholly turned from the
Earth; and ſhe is now faid to be in Con-
junction with the Sun, becauſe ſhe is in
the fame Direction from the Earth that
the Sun is in, which Pofition we call a
New Moon. When the Moon is arrived New
to F, fhe again refumes a horned Figure,
but her Horns (which before the Change
were turned Weftward) have now chan-
ged their Pofition, and look Eaſtward.
When ſhe has arrived to a Quadrate
Aſpect at G, ſhe'll appear biffected, like
a Half Moon, afterwards fhe'll ſtill
grow
bigger until at laſt ſhe comes to A, where
again ſhe'll appear in her full Splendor.
The fame Appearances which we ob-
ferve in the Moon are likewife obferved
by the Lunarians in the Earth, our Earth
being a Moon to them, as their Moon is
to us; and we are obſerved by them to
be carried round in the Space of Time
that
Moon.
208
The Defcription of
Eclipfe.
Fig. 4
1
>
that they are really carried round the
Earth. But the fame: Phafes of the
Earth and Moon happen when they are
in contrary Pofition; for when the Moon
is in Conjunction to us, the Earth is then
in Oppofition to the Moon, and the Lu-
narians have then a full Earth, as we in
a fimilar Pofition have a full Moon.
When the Moon comes in Oppoſition to
the Sun, the Earth, feen from the Moon,
will appear in Conjunction with her,
and in that Pofition the Earth will dif-
appear; afterwards ſhe'll affume a hom-
ed Figure, and fo fhew the fame Phaſes
to the Inhabitants of the Moon as the
does to us.
Of the Eclipfes of the Sun and Moon.
An Eclipfe is that Deprivation of
Light in a Planet, when another is in-
terpoſed betwixt it and the Sun. Thus,
an Eclipſe of the Sun is made by the In-
terpofition of the Moon at her: Con-
junction, and an Eclipfe of the Moon is
occafioned by the Shadow of the Earth'
falling upon the Moon, when ſhe is in
Oppoſition to the Sun.
Let S be the Sun, T the Earth, and
ABC its Shadow; now if the Moon,
when
the ORRERY.
200
}
when ſhe is in Oppofition to the Sun,
fhould come into the conical Space AB
C, fhe'll then be deprived of the Solar
Light, and ſo undergo an Eclipfe.
Lunar
Eclipfe.
In the fame Manner, when the Sha-
dow of the Moon falls upon the Earth
which can never happen but when the
Moon is in Conjunction with the Sun)
that Part upon which the Shadow falls
will be involved in Darkneſs, and the solar
Sun eclipfed. But becauſe the Moon is Eclipfe.
is much leſs than the Earth, the Shadow
of the cannot cover the whole Earth,
but only a Part of it. Let S be the Sun, Fig. 5.
T the Earth, ABC the Moon's Orbit,
and L the Moon in Conjunction with
the Sun: Here the Shadow of the Moon
falls only upon the Part D E of the
Earth's Surface, and there only the Sun
is intirely hid; but there are other Parts,
EF, DG, on each Side of the Shadow,
where the Inhabitants are deprived of
Part of the Solar Rays, and that more
or leſs according to their Diſtance from
the Shadow. Thoſe who live at H and I
will fee Half of the Sun eclipſed, but in
the Spaces FM, GN, all the Sun's Body
will be vifible without any Eclipfe.
From the preceding Figure it appears,
that an Eclipſe of the Sun does not reach
P
a
210
The Defcription of
Fig. 6.
}
a great Way upon the Superficies of the
Earth; but the whole Body of the Moon
may ſometimes be involved in the Earth's
Shadow.
Although the Moon feen from the
Earth, and the Earth feen from the
Moon, are each alternately, once a
Month, in Conjunction with the Sun ;
yet, by Reafon of the Inclination of the
Moon's Orbit to the Ecliptic, the Sun is
not eclipſed every New Moon, nor the
Moon at every Full. Let T be the
Earth, DTE an Arch of the Ecliptic, A
LBF the Moon's Orbit, having the
Earth T in its Center; and let AGBC
be another Circle coinciding with the E-
cliptic, and A, B, the Nodes, or the two
Points where the Moon's Orbit and the
Ecliptic cut each other; A the aſcend-
ing Node, and B the defcending Node.
The Angle GAL equal to GBL is the
Inclination of the Moon's Orbit to the
Ecliptic, being about 5+ Degrees. Now
a Spectator from the Earth at T, will
obferve the Sun to move in the Circle A
GBC, and the Moon in her Orbit ALB
F; whence it is evident, that the Sun and
Moon can never be ſeen in a direct Line
from the Center of the Earth, but when
the Moon is in one of the Nodes A or B ;-
W
}
and
the ORRERY.
211
and then only will the Sun appear
centrally eclipfed. But if the Conjunc-
tion of the Moon happens when ſhe is
any where within the Diſtance A c of the
Nodes, either North or South, the Sun
will be then eclipfed, more or lefs, ac-
cording to the Diſtance from the Node
A, or B. If the Conjunction happens
when the Moon is in b, the Sun will be
then one half eclipfed; and if it happens
when ſhe is in c, the Moon's Limb will
juſt touch the Sun's Disk without hid-
ing any Part of it.
The Shadow of the Earth at the Place
where the Moon's Orbit interfects it, is
three times as large as the Moon's Di-
ameter, as in Fig. 4. and therefore it of-
ten happens that Eclipfes of the Moon
are Total, when they are not Central:
And for the fame Reaſon the Moon may
fometimes be totally eclipfed for three
Hours together; whereas Total Eclipfes
of the Sun can ſcarcely ever exceed four
Minutes.
The Eclipfes of the Sun and Moon are
very well explained by the Orrery: Thus
having put the Lamp in the Place of
the Sun, and the little Earth and the
little Moon in their proper Places, in-
ftead
P 2
I
The Defcription of
}
ftead of the larger ones, let the Room
wherein the Inftrument ftands be dark-
ned; then turning the Handle about,
you'll fee when the Conjunction of the
Moon happens. When the is in or near
one of the Nodes, her Shadow will fall
upon the Earth, and fo deprive that Part
upon which it falls of the Light of the
Sun: If the Conjunction happens when
the Moon is not near one of the Nodes,
the Light of the Lamp will fall upon
the Earth, either above or below the
Moon, according to her Latitude at that
Time. In like Manner, when the full
Moon happens near one of the Nodes,
the Shadow of the Earth will fall upon
the Moon; and if the Moon's Latitude
be but ſmall, her whole Face will be in-
volved in Darknefs. At other Times,
when the Full Moon happens when the
is not near one of her Nodes, the Sha-
dow of the Earth will pafs either above
or below the Moon, and fo by that
Means the Moon will eſcape being e-
clipfed.
go and
Of the Eclipfes of the Satellites of Jupiter.
The apparent Diameters of the Infe-
rior Planets are fo fmall, that when they
pafs betwixt us and the Sun, they only
appear
the ORRERY.
213
appear like fmall Spots upon the Sun's
Surface, without depriving us of any
fenfible Quantity of his Light, The
Shadow of the Earth likewiſe terminates
before it reaches any of the fuperior
Planets, fo that they are never eclipfed
by us; and the Earth, when ſhe is in
Conjunction with the Sun, only appears
like a black Spot upon his Surface.
But Jupiter and his Moons mutually
eclipfe each other, as our Earth and
Moon do; ás alfo doth Saturn and his
Moons: The Satellites of Jupiter be-
come twice hid from us, in one Circu-
lation found 4; viz. once behind the
Body of Jupiter, i. e. when they are in
the Right Line joining the Centers of
the Earth and 2; and again they be-
come invifible when they enter the Sha-
dow of Jupiter, which happens when
they are at their Full as feen from 4,
at which Times they alfo fuffer Eclipfes;
which Eclipfes happen to them after the
fame Manner as they do to our Moon..
by the Interpofition of the Earth betwixt
her and the Sun.
Let S be the Sun, ABT the Earth's Fig. 7-
Orbit; and C & D an Arch of Jupiter's
Orbit, in which let Jupiter be in the
P 3
Point
214
The Defcription of
Point ; and let CFDH be the Orbit
of one of Jupiter's Satellites, which we'll
here fuppofe to be the fartheft from him.
Theſe Satellites, while they move thro' the
Inferior Parts of their Orbs, viz. from
D thro' H, I, to C, feem from the Earth
and the Sun to have a retrograde Mo-
tion; but when they are in the fuperior
Part of their Orbit, they are then ſeen to
move from Weft to Eaft according to
their true Motion. Now while they.de-
ſcribe the fuperior Part of their Orbits,
they will be twice hid from the Earth,
once in the Shadow of 2, and once be-
hind his Body. If Jupiter be more
Wefterly than the Sun, that is, when
the Earth is in A, they'll be firff hid in
the Shadow F, and afterwards behind
the Body of 4 in G: But when the
Earth is in B, then they are firſt hid be-
hind 4's Body in E, and afterwards fall
into the Shadow F. While theſe Satel-
lites deſcribe the inferior Parts of their
Orbits, they only once difappear, which
may
be either in I or H, according to
the Pofition of the Earth, in which Pla--
ces they cannot be diftinguiſhed from
the Body of Jupiter.
When the Satellites feen from 4 are
in Conjunction with the Sun, their Sha
dow's
{
the ORRERY.
255
dows will then fall upon 2, and fome
Part of his Body be involved in Darkneſs,
to which Part the Sun will be totally e-
clipfed.
By obferving the Eclipfes of Jupiter's
Satellites, it was firft difcover'd that Light
is not propagated inftantaneouſly,
though it moves with an incredible
Swiftnefs: For if Light came to us in
an Inftant, an Obſerver in T will fee an
Eclipfe of one of theſe Satellites, at the
fame Time that another in K would. But
it has been found by Obfervations, that
when the Earth is in K at her neareſt
Diſtance from Jupiter, thefe Eclipfes
happen much fooner than when the is
in T. Now having the Difference of
Time betwixt thefe Appearances in K
and T, we may find the Length of Time
the Light takes in paffing from K to T,
which Space is equal to the Diameter of
the Earth's Annual Orb. By thefe
Kinds of Obfervations it has been found,
that Light reaches from the Sun to us
in the Space of eleven Minutes of Time,
which is at leaft at the Rate of 100,000
Miles in a Second.
FINIS.
冰
​**
* G MDX
SR
oooooooooocoooooooooooooo000000000000
A N
INDE EX
OF THE
Aftronomical TERMS
Made Ufe of in this BOOK.
A
Chronical Rifing and Setting of
the Stars
Almacanthers
Page 96
63
Altitudes
ib.
Meridian Altitude
63
Amplitude
62
Amphifcians
Annual Motion
91
7
Antaci
92
Antarctic Circle
53
Pole
ib.
Antipodes
Arctic Circle
93
52
Aretie
£
The IN DE X.
217
Arctic Pole
Page $3
Afcenfion
68
-- Right
ib.
Oblique
69
Afcenfional Difference
ib.
Alcians
Hetreofcians
91
ib.
Afteriſms
36
Atmosphere
81
Axis
43
of the World
49
Azimuth
61
Babylonifh Hours
71
Biſſextile
78
Circle
42
Great Circles
ib.
Parallel, or lefler Circles
43
Secundary Circles
ib.
Circles of the Sphere
47
Climates
93
Colures
53
-----
Equinoctial Colure
ib.
Solftitial Colure
54
Comet's
29
Conjunction
II, 207
Conftellations
36
Crepufculum
Cofmical Rifing and Setting of the Stars 96
Day, Natural and Artificial
83
69
Declination
52
Diurnal Motion
7
Diurnal
218
The INDEX
Diurnal Arch
Eclipfes
Solar
Lunar
1
Page 68
208
...ib.
ib.
212
53
75
Ecliptic
Egyptian Year
Elongation
Eclipfes of Jupiter's Satellites
Equator, or Equinoctial
Equinoctial Points
Preceffion of
Vernal and Autumnal
Excentricity
Galaxy, or Milky Way
Geocentric Place
Globe
Terrestrial
Cleftial
Gregorian Account
&
18
48
53.
-55
'coming too
70
19
42
43
44
89
Heliacal Rifing and Setting of the Stars 96
Heliocentric Place
Northern and Southern
Hemisphere
Heterofcians
Horizon
Senfible
Rational
19
42
· 49
91
5.8
ib.
59
Hour Circles
50
Italian Hours
72
Jewish Hours
ib.
Julian Account
79
Latitude
The IN/DE.X.
219
Latitude; in Aftronomy
in Geography
Longitude, in Aftronomy
in Geography
Meridian
Nadir
Nodes
Nocturnal Arch
Orbit
56
56
.87
50, 61
61
31202
68
3
Parallel of the Earth's Semi-diameter 23
•
of the Earth's, Annual Orb · ·20
Periæci
Perifcians
Periodical Month
Phafes of the Moon
Planets
!
Inferior and Superior-
Planetary Hours
Poles
of the World
92
91
74, 202
201
I
14
72
42
49
of the Ecliptic
Polar Circles
56
Points of the Compas
Primary Planets
52
60
Cardinal Points
Retrograde Motion of the Planets
of the Nodes
59
5
187
202
Secondry Planets
5
Sidereal Year
74
Signs of the Zodiac
54
Northern and Southern
ib.
Solftices
220
The INDEX.
Solstices
M
Summer and Winter Solstices ib.
71
Solftitial Points
1
53
Sphere
42
Parallel and Right
Oblique
68
Stationary
186
Style Old
79
New Style
80
Synodical Month
Tropics (of Cancer and Capricorn)
174 202
Twilights
Vertical Circles
61
Prime Vertical` .
62
Zenith
61
Zenith Distance
63
Zones, Torrid, Temperate and Frigid 90
THE EN D.
甘
​1
*
}
:
Directions to the Binder.
The great Orrery to face the title.
Plate I
Plate II.
The Globes,
Plate III.
Plate IV.
Plate Vi
1
i
1
J
>
>
1
1
*
$
Y
Page
28
35
<
1
194
200
214
****
**
COLE, Sen and Jun"
Mathematical, Philofophical, and Optical
Inftrument Makers (Succeffors to Mr.
WRIGHT, Mathematical Inftrument-
Maker to His MAJESTY) at the Or-
rery next the Globe Tavern in Fleet-
street, LONDON,
M
A
"AKES all Sorts of Mathematical, Philofo-
phical, and Optical Inftruments, according
to the lateſt and beft Improvements in Sil-
ver, Brafs, Ivory, or Wood, neatly and
compleatly fitted for all their different Ufes in the fe-
veral Branches of the Mathematics and Philofophy;
where Gentlemen by fignifying the Plate and Figure of
any Inftrument in Gravefend, Defaguliers, or other Au-
thors, may be punctually ferved therewith, or any o-
ther Model or Machine made according to their own
Contrivance; COLE, Sen. having had for many
Years paft great Practice and Experience in making fe-
veral large and curious ORRERIES and SPHERES,
of different Sizes; Foot-Meaſuring Wheels, Way-wi-
fers for Coach or Chaiſe, within fide or without; The-
odolites, and Levels of various Kinds; Hadley's new-
invented Sea-Quadrant, mounted either in Brafs or
Wood (which for its Excellency far exceeds all Inftru-
ments yet contrived for that Üfe; but for fuch who
till retain a Defire for Davis's Quadrant, or are un-
willing
{
willing to be at the Expence of Hadley's; COLE, Sen.
has contrived one on the Principle of Davis's; which
for its eafy Application, and Correctneſs in Ufe, may
juftly be, allow'd greatly preferable thereto :) Alſo,
Smith's Quadrant, Davis's Quadrant, Azimuth, Am-
plitude, or other Compaffes of all Sorts, either for Ca-
bin, Steerage, or Pocket.
Artificial Magnets, made according tothe Improve-
ments lately communicated by Dr. KNIGHT to the
ROYAL SOCIETY; and likewife his new-contrived Ap-
paratus, for touching of Needles for the Mariners Com-
paffes; very uſeful for Maſters of Ships, eſpecially fuch
as make long Voyages.
Curious Cafes of Inftruments for drawing, in Silver,
Brafs, &c. neatly fitted for the Pocket; alfo Magazine
Cafes, with Variety of uſeful Inſtruments, fit for Gen-
tlemen who travel, or live too remote from any Place
to be readily furniſh'd with fuch Things.
Large Horizontal Dials for Gentlemen's Gardens,
in any Latitude; and other Sorts, of new Contrivance.
Gunners Quadrants and Callipers; and all other
Inftruments uſed in Fortification.
Elliptical Compaffes, Compaffes of Proportion, and
Variety of other Sorts,
Gauging Inftruments of all Sorts.
Reflecting Teleſcopes, either after the Newtonian or
Gregorian Manner, accurately and neatly compleated:
Refracting Teleſcopes of all Sorts, either for Sea or
Land; Microſcopes of all Sorts, with the beft and latest
Improvements.
The Camera Obscura (very uſeful for drawing the
Perſpective of any Seat or Building) wherein the ex-
ternal Objects are fhewn in their Proportion and Co-
lour.
Reading
1
Reading Glaffes and Spectacles, ground on Brafe
Fools, as approved by the ROYAL SOCIETY, fitted in
Variety of Frames, and adapted to each Perfon's Sight;
Hikewife Spectacles of the true Venetian Green Glafs;
magnifying Glaffes in Frames, for Watch-makers and
other Artificers; multiplying Glaffes, Opera Glaffes,
and Priſms for demonftrating the Theory of Light and
Colours.
Barometers of all Sorts; Thermometers, either the
framed Mercurial or Spirit Ones, nicely adjuſted.
With Variety of other Inftruments, made and fold at the a-
bove Place; where any Gentleman, by Letter or other
Directions, may depend on being as faithfully fer'd as
if preſent,
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