îiurtlîaipaiprn lîtiiofratig iCthrarg
Enanainn, 3Uinma
ZENOGRAPHICAL FRAGMENTS.
ZENOGRAPHICÂL FRAGMENTS.
I.
THE MOTIONS AND CHANGES
OF THE
MARKINGS ON JUPITER
IN THE
APPARITION OF 188^-87.
BY
A. STANLEY WILLIAMS, F.R.A.S.
LONDON:
MITCHELL AND HUGHES, 140 WARDOUR STREET, W.
1889.
€o tíje JHemcirg
OF
JOHANN HIERONYMUS SCHROETER,
TO WHOSE LABOURS WE ARE SO MUCH INDEBTED FOR OUR
KNOWLEDGE OF THE PHYSICAL CONDITIONS OF
THE MOON AND PLANETS,
Wiizst fragments
ARE RESPECTFULLY INSCRIBED
BY
®iie ^utljor.
íntríiliucttíin.
♦
D URING recent years much has been accomplished towards
the systematic study of some of the varied details pre¬
sented hy the planet Jupiter^ the " Giant Planet/^ as it has been
termed, of the Solar System. So far as I am aware, however,
no attempt has hitherto been made to subject all the visible
markings of JupitePs surface of any degree of plainness to such
a systematic examination, as to bring out the details of their
relative motions, and the changes which they from time to time
undergo ; and to present in fact a complete record of all the
alterations that may have taken place in the aspect of the
planet and of the different features with which its surface is
variegated. The present Volume contains a first instalment
of the results derived from such a systematic examination,
which, it is hoped, will assist in filling up this void, by present¬
ing for the Apjjarition of 1886-87 ^ fairly complete and compre¬
hensive record of the motions and changes of all the markings
of sufficient plainness, that were visible on the face of the planet
during that period, and by which, with the help of similar, but
more complete records in subsequent years, we may come to a
better knowledge of the true physical conditions of this planet
considered as a harmonious whole.
The outline of the present Volume is very sinijile. After
describing the instrument with which the observations were
viii INTRODUCTION.
made, the methods of observation, the nature and construction
of the Chart of the Jovian markings prefixed to these Frag¬
ments, and which is believed to be the first satisfactory delinea¬
tion of its kind that has yet appeared, there follows a short
general outline or description of the various kinds of markings,
and the nomenclature employed for the purpose of designating
the different features. This is succeeded by detailed observa¬
tions and descriptions of fifty-one different markings, with their
periods of rotation, and accompanied by short discussions of
the results derived therefrom. After these, which form the body
of the work, will be found a summary, or table, exhibiting tbe
periods of rotation of all the various markings, followed by a
few notes upon tbe relative altitudes of some of the Jovian
markings, and on the repelling influence apparently exerted by
the Red Spot.
In conclusion, it is necessary to express my great indebted¬
ness to the valuable " Ephemeris for Physical Observations
of Jupiter" of Mr. Marth, without which indeed this work
would probably never have been commenced. It is also hoped
that any defects and deficiencies in the present Volume may be
ascribed, partly at least, to the circumstance that the whole of
the work connected with the observations, reductions, calcula¬
tions, and discussions had to be accomplished in such spare
intervals as were permitted by arduous professional duties.
Contents«
page
Section I.—The instrument : Methods of Observation,
Delineation, and Reduction - - - - i
Section II.—Construction of the Chart of the Markings of
Jupiter .... 8
Section III.—General Arrangement of the Jovian Belts and
Markings in the Apparition of 1886-87, and the
Nomenclature employed in the present Work - 10
Section IV.—Observations of Individual Markings, with
Remarks on their Motions and Changes - - - 16
(1) The North Temperate White and Dark Spots 17
(2) The North Equatorial Dark Spots - - 38
(3) The South Equatorial White and Dark Spots 47
(4) The Red Spot - - 95
(5) The Southern White and Dark Spots - - loj
(6) Miscellaneous Observations 108
Section V.—Summary of Rotation Periods ; Mean Motion
of Matter in different Zenographical Latitudes in
1887 - - - iii
Section VI.—On the Relative Altitudes of different Jovian
Markings - - 112
Section VII.—On the Repellent Influence apparently exerted
by the Red Spot - 116
Plate I.
CHAET OP THE MAEKINGS ON JIJPITEE
IN THE APPARITION OF 1886-87.
fyi»iíamíl.ii ii>ii^iiiííifaí'piilitfiiiytsdtt¡l^tm''fc ii lg üái
ils'ô.iî^-î'ot-î
JSÍor'tK
BY A. 8. WILLIAMS.
TO THE DATE OF THE OPPOSITION (APRIL 2Ist, 1887).
ZENOGRAPHICAL FRAGMENTS.
SECTION I.
The Instrument ; Methods of Observation,
Delineation, and Reduction.
The instrument, with which the observations contained in this
volume were made, was a silver-on-glass reflector by Calver,
6^ inches in aperture, and equatorially mounted. With this there
was almost invariably employed an eyeglass formed of a single
plano-convex lens, giving a magnifying power of about 170
times. With the planet situated in considerable south declina¬
tion, it seldom happened that a higher power than this could be
used with much advantage, and no lower power gave such good
results, however bad and confused might be the state of the
definition.
The observations were principally designed to effect two
objects : firstly, to fix the zenographical longitudes of the dif¬
ferent spots ; secondly, to record the magnitude, intensity, and
appearance of the various markings diversifying the disc of
Jupiter. For the first of these purposes three methods were
employed, which may be described as follows : (i) By direct
transits. In these, the time at which a spot was observed to
be on the central meridian of the planetas disc, or to transit
over that meridian, was carefully noted, generally to the nearest
minute of time, though in the case of very definite or conspicu¬
ous objects greater exactitude was observed as to this. (2) By
double transits. In this method, the time being noted at which
any two spots of the same kind and in the same latitude
were at equal distances on either side of the central meridian,
and likewise the time of transit over the same of either of these
two spots, the time at which the transit of the other spot
B
a
ZENOGRAPHICAL FRAGMENTS.
occurred can easily be ascertained. (3) 'Qy estimated transits ;
where a spot being a short time before, or past, transit over the
central meridian, the time at which such transit occurred was
estimated from that knowledge of the apparent motions of the
Jovian markings, due to the rotation of the planet, which an
observer speedily acquires.
Of these three methods, the first, or that of direct transits,
is the most exact, and was the one almost universally employed
in the present series of observations. Under favourable cireum-
stances it is susceptible of considerable exactness, for the
rotational motion of markings situated near the equator of
Jupiter is so rapid that, provided the object observed be a con¬
spicuous and definite one, an interval of only a single minute
is sufficient for it to produce a marked displacement in the
apparent position of the marking on the planet's disc. The
principal element of accuracy consists, in fact, in the degree of
definiteness or plainness of the feature observed. A plain and
very definite marking can be observed to transit over the cen¬
tral meridian with great accuracy, even in very confused states
of the definition, whilst a faint or diffuse and ill-defined spot
cannot be satisfactorily observed, notwithstanding that the
conditions as regards seeing may be very favourable, and in
such cases the time assigned to the transit may be five minutes,
or even more, in error. As before stated, this method was the
one almost universally made use of, and in the tables of observa¬
tions which follow afterwards the times of transit were always
obtained in this manner, except where otherwise mentioned.
The observations were weighted according to a definite scale, in
which I equals the poorest quality or least degree of satisfac-
toriness, and 5 the highest quality. These weights are often
of great assistance in selecting the best observations, with the
view of ascertaining the periods of rotation of markings, and
should not be omitted in observations of this kind.
The method of double transits was only employed in a few
cases, generally when the direct transit of an object was missed
on account of cloud or other causes. It is capable of giving
fairly accurate results, though not equal to those obtained by
direct transits. Care should of course be taken that the objects
selected are in very nearly the same latitude, or serious errors
METHOD OF OBSERVATION. 3
will creep in. The two spots observed ought also to be of the
same kind—i.e., both white spots^ or both dark ones as
otherwise errors might be introduced should the white spots be
situated at a higher level in the atmosphere of the planet than
the dark ones, or vice versâ. This of course may be the case
in two spots of the same kind, but there is more likelihood
then of uniformity in this respect than where the two objects
are dissimilar. No weights were assigned to the results ob¬
tained according to this method.
Much dependence cannot of course be placed upon the
passages obtained according to the third method, or simple
estimation, though, provided the object be not distant more
than about 10™ from the transit, this method is more satisfac¬
tory than might have been expected. It was only employed in
a few cases where, on account of cloud or other causes, the
direct transit could not be obtained. Weights were likewise
not assigned to observations of this nature.
Simple eye-estimations of the times of transit over the
central meridian of the planet's disc, though not equal in point
of accuracy to carefully-made micrometrical measures, are yet in
most cases of ample exactness for all practical purposes. It
appears from a careful consideration of the observations of this
kind, made both in this and past years, that the discordances
arising from changes in the forms and intensities of markings, or
from variations in their rate of motion, causing real displacements
of position, are much greater, generally speaking, than any that
could be ascribed to the unavoidable errors of observation.
This is a point of considerable importance, because an outlay
of £20 or .^30 will thus enable a careful observer to do work
which, in point of practical accuracy, will vie w ith that accom¬
plished by the most costly and elaborately-fitted equatorial,
driven by clockwork and provided with the most delicate micro-
metrical appliances. The total number of transits obtained in
the period to which the present observations relate was 339,
made up as under :
Direct transits 312
Double transits 7
Estimated transits 10
Total 3 29
4
ZEN06RAPHICAL FRAGMENTS.
In observing the transits^ two precautions were taken which
it might be desirable generally to adopt in observations of this
kind. These are : (i) To always employ the same eye.
(z) To hold the head so that the direction of the eyes is
parallel to that of the belts. These precautions are mentioned
because it has happened that a spot, which to my right eye
seemed to be exactly on the central meridian, when observed
with the left eye, appeared distinctly removed from that situa¬
tion ; and the same thing has heen noticed if the eyes were not
kept parallel to the direction of the belts.
With regard to the second branch of the investigations to
which the observations were mainly devoted, namely, to record¬
ing the magnitudes, intensities, and appearances of the various
markings visible upon Jupiter, two ways were adopted to accom¬
plish the end in view. Firstly, a careful description of each
marking was made when near the central meridian of the disc,
and consequently it was in the best position to enable its true
form and appearance to be made out. Reference to the tables of
observations which follow will shew better than any explanation
the nature of these descriptions. The chief points to which
attention was directed were the size, or magnitude, of each spot,
together with its shape ; its position with regard to a neighbouring
belt, etc. ; its degree of definiteness, colour, and intensity ; and,
finally, any peculiarities of structure or appearance which seemed
worthy of being recorded ; and, as far as possible, a similar
meaning was always attributed to the same word. Thus, the
expressions, " large," " very large," " bright," " very bright,"
etc., are always employed so as to indicate the dimensions and
brightness of a spot as far as possible according to a fixed and
definite scale; so that these designations and descriptions are
thus strictly comparable inter se ; in the same manner as are de¬
scriptions of nebulse according to the manner of recording the
same at present in vogue. The term " intensity " is a convenient
one to use in referring either to the brightness of a bright spot,
or the darkness of a dark one.
The second method by which it was attempted to record the
appearance of each marking consisted of a series of sketches ;
and as the manner of making these sketches is somewhat
peculiar and different from that usually employed, it may be well
METHOD OF OBSERVATION.
5
to enlarge a little upon the subject. The best time for dis¬
tinguishing the true form and appearance of a marking is
obviously when it is in course of transit over the central meridian
of the discj since then the effect of foreshortening is reduced to
a minimum ; and in the case of objects situated near the equator
of the planetj with which we have chiefly to deal, it may be said,
for all practical purposes to vanish altogether. As the object is
removed farther and farther from the central meridian, foreshort¬
ening has more and more influence upon its form and appearance.
This of course is well known to all observers and interpreters of
observations of Jovian phenomena, but it does not seem to be
appreciated at its true value, and the occasional existence of
regularly shaped features, such as the great Red Spot, is apt to
cause erroneous ideas to be formed upon the subject. From a
study of this planet extending over a period of ten years, it
appears that in the case of irregularly shaped markings, or
those of non-uniform intensity, the true form and appearance
can he made out with distinctness and certainty only when the
object is within half an hour of its transit over the central meri¬
dian of the planetas disc, or even less in some cases. It must
be borne in mind that the question is not one purely of fore¬
shortening, as it chiefly is in the case of a planet like Mars ;
but that an important factor, modifying the comparatively simple
laws due to this cause, exists in the circumstance, which may
now be considered as established, that the markings visible
upon Jupiter are at various and greatly different altitudes above
the surface of that planet, and moreover situated within a very
dense and vapour-laden atmosphere.
Accordingly, in the present series of observations, each
marking was delineated at about the time of its transit, when it
was in the most favourable position for being seen; and the
manner of making the observations was as follows. When a
marking was perceived to be approaching the central meridian,
it was carefully scrutinized until it arrived at that point, when
the time was noted down. It was then generally watched for a
few minutes longer, until it was seen that the transit was clearly
past ; after which the appearance of the spot was noted and a
sketch made rapidly, but with as much accuracy as possible, of
the marking and its immediate surroundings as resulting from
6
ZENOGRAPHICAL FRAGMENTS.
the whole of the examination. By this time another spot was
generally to be seen approaching transit, and it would be
treated in exactly the same manner, and inserted in the same
sketch, in its proper position relative to the first one ; and so
the work would be continued for each succeeding marking, until
the approaching dawn, the declining altitude of the planet, or
other causes, put an end to the work for the night. It was in this
way that the sketches reproduced in Plates II. to VIII. were
made. Each individual spot is represented as it appeared near
the time of its transit, and when most favourably placed for its
true form and appearance to be made out. In general the dif¬
ferent markings are exhibited fairly well in their relative positions
in these sketches, but great exactness was not aimed at in this
respect, because the exact relative situations were almost always
indicated and controlled by the observed times of the transits
over the central meridian. This remark applies chiefly to the
positions east and west, as greater care was taken over the rela¬
tive situations of markings in a north and south direction. It
will be clear from what has been said, that the representations
of individual markings are all strictly comparable inter se, and
these sketches should therefore have a peculiar value, greater in
some respects than usually attributed to ordinary delineations
of this planet. Altogether seventy sketches were obtained
during the apparition of Jupiter.
In the earlier observations no attempt was made to predict
the times of transit of the different markings, and in consequence
a number of observations, especially when the same were in a
faint and inconspicuous condition, must have been lost. In May
and June, however, nightly ephemerides were constructed of the
approximate times at which all the markings, which had been
previously observed, should be on the central meridian, and the
advantage of this was found to be so great, that it should never
be omitted in undertaking a series of observations similar to the
one now in question ; notwithstanding the considerable labour
involved in the preparation of the nightly ephemerides for fifty,
or more, markings ; though this work is rendered comparatively
simple and expeditious by the valuable Ephemeris for Physical
Observations of Jupiter of Mr. Marth. It is of course essential
to have a knowledge of the motions of the various features
METHOD OF OBSERVATION.
7
situated in different latitudes, before the construction of such
ephemerides can be safely resorted to.
In the reduction of the observations and calculation of
rotation periods, the first step taken was to ascertain the zeno-
graphical longitudes corresponding to the observed times of
transit. This was expeditiously accomplished by means of
Mr. Marthas ephemeris already alluded to, the work being fur¬
ther facilitated by the construction of simple tables, by which
the degrees and fractions of a degree of longitude corresponding
to any given interval of time could be taken out at sight. The
observations were then all carefully plotted upon a spot chart,
similar in its construction to one which has been described by
Mr. F. C. Dennett in the English Mechanic, vol. xxx., p. 555,
and lines were drawn through all the observations of the same
spots.
The next step was to collect the observations relating to each
spot into tables, similar to those given in Section IV. of this
work. By means of these tables, and with the assistance of the
above-mentioned spot chart, and the various sketches, the pecu¬
liarities of the motions and appearances of the different features
became manifest.
The computation of the periods of rotation of the spots was
effected by comparing the observations with Mr. Marthas ephe¬
meris, and then obtaining the necessary corrections to be applied
to the rotation period, upon which the ephemeris is based.
Generally two or three observations were selected at the com¬
mencement of a series of observations of a spot and also at the
end of the series, these giving from four to nine sets of com¬
parisons; and in the selection of the observations, preference was
given to those to which the highest weights had been attached ;
though of course the insufficiencies in the observations obliged
this plan to be more or less modified in the case of many of the
spots. Except in the case of a few spots, where the observa¬
tions were insufficient to furnish a reliable result, the rotation
periods given in this work will be found to be very close approxi¬
mations to the truth.
SECTION II.
Construction of the Chart of the Markings of
Jupiter.
Plate I., at the commencement of this volume, contains a map
of the markings on Jupiter observed in the season of 1886-87,
accompanied by a key-plan shewing the designations of the
various features, according to the system of nomenclature enun¬
ciated in Section III. There is nothing new in the idea of
constructing a map of the principal markings seen on Jupiter
during the observations of any particular season, as such have
indeed been constructed before now, hut, so far as I am aware,
no attempt has hitherto been made to employ the principles
embodied in the present chart of the features of this planet.
The most important of these principles consists in the reduction
of the places of all the various spots and markings observed to
a specified date or epoch. In this case the date of opposition of
the planet (21st April) has been selected as the most convenient
and natural epoch. It must therefore be understood that, with
the few exceptions hereafter mentioned, the positions of all the
spots or markings shewn upon the chart are such as they would
have been on the aist April 1887, the date of opposition;
allowance having been made for their known proper motions, or
various periods of rotation. The only exceptions to this rule
occur in the case of the two dark equatorial spots 3 and 3, and
of course the few unnamed markings shewn in the map. The
two first-named spots have been made an exception to the rule,
in order that their remarkable connection with dark spots on the
opposite side of the equator might be preserved, which otherwise
would not have been the case on account of the more sluggish
motion of these two objects. The unnamed spots were only
observed on a single night, and therefore their rates of motion
did not admit of being ascertained, but it seemed desirable
that they should be inserted in the map.
CHART OF JUPITER.
9
Generally the individual markings have been shewn in the
form in which they more usually appeared; though this rule has
not been strictly adhered to, and the duplicity of a spot, or its
visibility in the rift of a belt, has always been indicated, even
though it may but rarely have appeared under that form.
The latitudes of the different belts cannot be regarded as
satisfactory. They depend upon measures made of a limited
number of drawings of the entire disc of Jupiter. In reducing
the resulting measures into zenographical latitudes, use has been
made of the table given by Dr. O. Lohse in Vol. III. of the
Publications of the Potsdam Observatory, p. 7. The corrections
due to the elevation of the earth above the plane of Jupiter's
equator have of course been applied, but the measurement of
drawings cannot be expected to give satisfactory results.*
The actual number and positions of the fainter and more
delicate belts in latitudes greater than 30° remain open to doubt,
as, owing to the considerable southern declination of Jupiter, it
was seldom found possible to make satisfactory observations of
these more delicate features.
It must be borne in mind that the relative positions of many
of the markings would be quite different if some other date had
been selected for the epoch of the map. Thus it is well known
that the equatorial spots, such as I., II., III., etc., make a com¬
plete rotation of the planet relatively to the Red Spot in an
interval of about 45 days. If, therefore, the date of opposition
in 1887 had chanced to fall about three weeks earlier or later,
the dark spot I. would have changed its longitude by nearly
180°; so that instead of being north of the following end of the
Red Spot in longitude 11°, it would have been in about longitude
190°, and similar differences would occur in the case of other
markings. A little consideration of this interesting peculiarity
sufficiently shews why all the previous maps of Jupiter are so
unsatisfactory and comparatively useless, save for indicating the
arrangement and positions of the different belts that encircle the
planet.
* In 1888 a number of microraetrical measures of the positions of the
principal belts were obtained, which will enable their latitudes in that year
to be ascertained with more satisfaction.
SECTION III.
General Arrangement of the Jovian Belts and
Markings in the Apparition of 1886-87, -^^d the
Nomenclature employed in the present Work.
The object of the present Section is two-fold, being, firstly,
to give a brief general account of the arrangement of the various
belts and other features as they appeared in the season of
1886-87, and, secondly, to enunciate the system of nomenclature
adopted throughout the present work for the purpose of desig¬
nating the different markings. This latter subject is an im¬
portant one, as it is desirable that some simple and uniform
system should he employed, and one moreover that, in the case
of the spots at least, should he capable of indefinite expansion.
The subject of nomenclature naturally divides itself into two
heads, namely: (i) That used for indicating the different belts
usually visible upon Jupiter's disc, (a) That employed for
designating the various light and dark spots diversifying the
visible surface of the planet. These will be considered in their
proper order.
(i) Nomenclature of the Belts.—For the fainter belts the
numerical system has been adopted, it seeming on the whole
the most convenient for use, and suited to the circum¬
stances of the case. For the great equatorial system of belts,
however, it seemed to he very desirable that the customary verbal
designations should he retained, since these expressions convey
much clearer impressions than do mere bald numerical symbols ;
and the individual members of this great system of hands are of
sufficient importance to deserve proper names. The following
is the arrangement of the principal belts visible in the year 1887,
with their adopted designations.
Commencing at the north, we find, after a dusky polar cap
composed in the main of faint, narrow, delicate, dusky streaks,
perhaps generally represented in drawings of Jupiter of too
NOMENCLATURE OF JOVIAN MARKINGS. II
decided a character, two narrow dark belts in north latitudes
40° and 32° respectively :* these are belts i and 2. Farther
south, in latitude 23°, there comes a more conspicuous and
altogether more important dark band, which is belt No. 3.
Under favourable conditions as regards definition, it was seen
actually to be composed of two narrow, dark, parallel bands
running close together, and separated from each other by a
narrow lighter interval or rift ; which duplex character has
existed ever since the year 1881. Some tendency towards a
spotty character was noticed about this belt in 1887, but the low
altitude of Jupiter, and consequent want of sharpness in the
definition, prevented any systematic observation of the details of
the more delicate bands.
We then come, after a bright and generally white interval,
to the great equatorial system of belts. This system, as will he
seen by reference to Plate I., or to the sketches of the equatorial
region of the planet reproduced in the subsequent plates, consists
of a great dark belt having its northern edge in latitude 11° N.,
and a still darker, broader, and more conspicuous belt with its
southern edge in latitude 19° S. Each of these two great bands
is moreover double, being composed of two dark parallel belts
separated by a narrow lighter interval. This duplex nature of the
belts is a very characteristic feature of the bands of Jupiter, and
one which is not confined exclusively to this planet, since it is
likewise found in some of the belts of the planet Saturn.f It will
also be noticed, in part at least, in the dark belt No. 6 ; whilst, as
already stated, it was present in belt No. 3. The most northern
of the two primary bands forming the great equatorial system
has been uniformly designated the "North Equatorial Belt;"
the southern one being called the " South Equatorial Belt."
Between the two was a lighter region, evidently in a highly
* See Plate I.
f In the winter of 1886-7 duplicity was well shewn in one of the belts
of Saturn. Immediately south of the bright equatorial zone there was a rather
narrow dark belt, separated by a cloudy interval from a broader but fainter dark
band. The first-mentioned belt is probably shewn in all the drawings of the
period, and when examined in good air with high powers it was distinctly double,
being formed of two very narrow dark parallel streaks, separated by a minute
bright interval or rift. The duplicity of this belt does not, however, seem to
have been noticed elsewhere.
12
ZENOGRAPHICAL FRAGMENTS.
disturbed condition, which may be conveniently termed the
" Equatorial Zone."
The two equatorial belts of late years have been by far the
most prominent markings of the kind visible, and have been no
less distinguished for their remarkable colour. This colour, in
1887, a very fine, intense, though rather dull, brick-red.
The component bands of the North Equatorial Belt were of
about equal breadth and intensity, subject, of course, to minor
variations ; and the brighter rift separating the two was a fairly
broad and conspicuous feature. The two bands making up the
South Equatorial Belt were likewise of about equal breadth and
intensity through the greater part of their extent, but here the
rift was a narrow and, consequently, more difficult feature,
though it was always visible more or less continuously, except
in the worst observing weather. The duplicity of this belt seems
to have escaped the notice of some observers during the last two
or three years. It is nevertheless an important peculiarity,
since the formation of the southern component of the belt in
1883 has been described as a southerly drift of what, at that
time, constituted the whole of the South Equatorial Belt, instead
of its being due to the very different phenomenon of the forma¬
tion of a new and entirely distinct band immediately south of,
and parallel to, the old South Equatorial Belt. This is a point
of considerable importance, and the continued existence up to
the present time of the separating rift shews that the duplex
character of the belt has been maintained ever since without
coalescence of the component bands, so that there has been no
extension or drift southwards, in the proper sense of the word,
of the pre-existing belt ; and this distinction it is necessary to
bear in mind in considering the actual physical nature of the
changes which have taken place in the appearance of the South
Equatorial Belt.
Just following the Red Spot the southern component of
the South Equatorial Belt made an abrupt bend northwards, so
as to form a remarkable and very prominent kind of shoulder.
This diversion would appear very probably to be due to some
repulsive action manifested by tbe Red Spot. East of longitude
265°, the southern component rapidly faded away, so that it
could barely be traced just up to the preceding end of the Red
NOMENCLATURE OF JOVIAN MARKINGS. I3
Spot. The transition from a dark to a faint band generally
took place in a rather gradual manner, hut on the ;î4th March
the point of change was sharply marked.
It will be noticed that the equatorial system of belts was
somewhat eccentrically placed with respect to the equator of
Jupiter, so as to be more largely situated in the southern than
in the northern hemisphere of the planet. This peculiarity has
existed for several years past, and in connection with the fact
that the spots have been more considerable, more numerous,
and more changeable in the southern than in the northern
hemisphere, it would appear to indicate that the chief seat of
disturbance was situated slightly to the south of the centre of
the planet.
The Equatorial Zone was evidently in a very disturbed con¬
dition, and presented considerable varieties of colour. The
general ground was whitish or pale yellow, many of the bright
spots being intensely white, whilst the dark spots and streaks
with which it was diversified were of a dusky, greyish, and in
some cases blackish appearance.
South of the great equatorial system of belts we find first
the great Red Spot, and then a series of fainter and com¬
paratively inconsiderable dark belts, which from time to time
undergo considerable variations in number and position. The
three most important of these streaks are here numbered 6, 7,
and 8, the last named being in about latitude 50° S., compared
with the 40° N. latitude of the most northern belt, so that
with the finer bands occupying the higher latitudes, as with the
equatorial belts, there is an evident displacement towards the
south with regard to the equator of the planet.
(3) Nomenclature of the Spots.—It is desirable that some
simple, efficient, and uniform system should be employed for
the purpose of designating the different light and dark mark¬
ings, and one moreover that should be capable of indefinite
expansion. Many of the spots continue visible for the space of
years, and it is obviously of importance that the same marking
should continue to bear the same designation, wherever possible,
throughout the whole period of its visibility, and that such
designation should not be used for the purpose of naming more
than one object. The spots of Jupiter are so numerous that it
H
ZENOGRAPHICAL FRAGMENTS.
is evident that the system to be adopted must be to a great
extent a numerical one. A purely numerical system is, how¬
ever, insufficient, because the spots are arranged in the form of
great streams, situated in different parts of the planet ; the indi¬
vidual markings composing a stream occupying nearly the
same latitude and partaking of a nearly similar motion, which
may be, and generally is, widely different from that of neigh¬
bouring streams ; so that it is obviously desirable that the stream
should be indicated, as well as the separate spots of which the
same is made up. The following, therefore, is the nomen¬
clature devised for the purpose of designating the different spots
and the streams to which they belong.
On the south side of the Equatorial Zone, and the north
side of the South Equatorial Belt, will be noticed a row or
stream of numerous light and dark spots. These spots, 2,^ in
number, composed the most important of the streams of mark¬
ings visible on the surface of Jupiter in 1887. They were all
indued with nearly the same motion, or rate of rotation, the
mean period of rotation of matter forming this stream being
qt ^0°'22®*4, and are termed "South Equatorial Spots," and
bear the Roman numerals I., II., III., etc. In naming them
the full description has sometimes been given, such as " The
white south equatorial spot IX.," but it is obvious that the
same thing would be signified by using the shorter designation
of " The white spot IX. ;" for as these numerals are only
employed for the purpose of indicating spots belonging to this
particular stream, it is clear that there would be no possibility
of confounding them with other white spots in a different
latitude.
On the north side of the Equatorial Zone, and on the south
side of the North Equatorial Belt, was an inconsiderable stream,
the separate spots composing which were few in number and
inconspicuous in character. These spots have been called
" North Equatorial Spots," and are numbered i, 2, 3, etc.
Immediately to the north of this row of north equatorial
spots, we come to an important stream of numerous and con¬
spicuous white and dark spots. These were situated chiefly on
the north side of the North Equatorial Belt, and have been
termed "North Temperate Spots," and are indicated by the
NOMENCLATURE OF JOVIAN MARKINGS. 15
capital letters etc. ; the nomenclature for these mark¬
ings being rendered capable of an indefinite degree of expansion
by the addition of numbers to these letters.
Proceeding now to the southern part of the planet, we come
to the Red Spot, which of course has always been referred to
by this name. We also find various dark spots and one white
one, and these have been called " Southern Spots," and bear
the letters of the Greek alphabet a, ß, y, etc.
In conclusion, it may be mentioned that designations have
only been attached to those spots which were observed on more
than one night.
SECTION IV.
Observations of Individual Markings, with Remarks
on their Motions and Changes.
This Section constitutes the bulk of the present work, con¬
taining as it does details of the observations of fifty-one different
markings which were visible on Jupiter during the apparition of
1886-87, with their periods of rotation, and exhibiting the
changes of form and intensity which they underwent from time
to time. It also contains notices of some other markings, but
which could not be followed for a sufficiently long interval to
enable their rotational rates to be ascertained. This Section may
therefore be considered as giving in a fairly comprehensive
manner the history of the visible surface of Jupiter, and of the
different markings variegating the same, for the period com¬
prised within the observations ; and it is believed that very few
markings, and certainly none of any great degree of magnitude
and permanence, could have been visible within the period in
question, and yet have escaped observation.
The arrangement of the following sub-sections i, a, 3, and 5
is in all cases the same. We have first of all, at the commence¬
ment of each sub-division, a general description and short study
of the principal results and points of interest relating to the
class of objects, considered chiefly as a whole, to which such
division is expressly devoted. Then follow tables of observa¬
tions and remarks and discussions relative to the individual
markings. In the tables of observations, the first column con¬
tains the date. The second, the Greenwich mean time of the
transit of the marking over the central meridian of the planeTs
disc. The third column contains the weight attributed to the
observed time, expressed according to a scale ranging from i—5,
where i signifies the least, and 5 the greatest degree of satis-
factoriness or goodness of the observation. In column 4 will
be found the zenographical longitudes corresponding to the
NORTH TEMPERATE SPOTS.
17
observed times of transit. These longitudes are derived from
the ephemeris of Mr. Marth, and for sub-sections i, 4, and 5,
are expressed according to his " system II. and for sub¬
sections 2 and 3 according to " system I." of such ephemeris.
The daily rotation according to system II. being 8^0°'2^, cor¬
responding to a rotation period of 55"^ 40®'63j that of
system I. being 878°'25, corresponding to a rotation period of
9h 15^*88. Finally, in the last column will be found the
notes descriptive of the appearance of the markings. The
remaining sub-sections are necessarily arranged somewhat dif¬
ferently from the rest, but no difficulty will be experienced in
comprehending the details of the arrangement employed in
these cases.
(i) The North Temperate IVhite and Dark Spots.
These spots were grouped along the north edge of the North
Equatorial Belt, and are designated by the capital letters of the
Roman alphabet, A, B, C, etc. Seventeen of these markings
were followed for greater or lesser periods of time in 1887, nine
of them being white spots, and eight dark ones. The white
spots were oval-shaped markings situate on the north side, but
occasionally extending sufficiently far south to become visible in
the rift, of the North Equatorial Belt, whilst, no doubt partly
from their brightness and intensity, they sometimes appeared to
eat, or penetrate, into the belt. These objects were remarkable
in general for their whiteness, but above all for their durability
and permanence of form and appearance. This permanence of
aspect, whilst in itself of great importance, tended to render them
features of comparatively little interest, and in this respect they
contrast strongly with the south equatorial markings, which were
characterized by great, and often rapid, changes in their appearance.
As an instance of the great permanence and durability of these
first-named features, the white spot C may be mentioned. This
marking was first seen by Mr. W. F. Denning on the 27th January
1885, and since that date up to the end of the observations of
1887 it has apparently preserved almost unaltered the same mag¬
nitude, form, and brightness; and its rate of motion was also
remarkably uniform. The spot was likewise seen again in 1888,
of the same general appearance and brightness as before, so that
c
i8
ZENOGRAPHICAL FRAGMENTS.
it has now preserved without material alteration the same aspeet
for a period of four consecutive apparitions of Jupiter, a degree
of permanency almost rivalling that of the great Red Spot.
The dark spots had the appearance of dusky or blackish
condensations of the most northern of the two bands composing
the North Equatorial Belt, and they usually projected to a con¬
siderable extent north of the northern edge of this feature.
They were very generally accompanied by similar but less con¬
spicuous condensations on the southern band of the same belt.
This duplicity of form, which, as has already been pointed out,
is so characteristic of the belts of Jupiter, is thus no less marked
in the case of the spots ; such duplicity being well indicated in
the present series of observations by these dark north temperate
spots, and by the dark south equatorial spots. In one of these
latter a tendency to triplicity was even observed. The dark north
temperate spots exhibited a permanency of aspect similar to the
white ones, though perhaps the peculiarity was not quite so
marked.
The mean period of rotation of the north temperate spots in
1887 was 55™ 36®'5, somewhat shorter than that of the Red
Spot (q** 55"^ 40®"5) ; but with reference to this a remarkable
and highly interesting phenomenon presents itself, consisting,
namely, in there being a distinct difference in the periods of
rotation of these markings in two opposite hemispheres of
Jupiter. Thus the nine spots A to H, extending over longitudes
45° to 160°,* had rotational periods amounting in the mean to
9^* 55™ 32^*2 ; whilst the mean period of rotation of the eight
remaining spots, comprised within longitudes 170° to 330°,
amounted to q'' 55™ 4i®'3, or q' longer; a difference which is
much too great to be ascribed to errors of observation. So that
here we have the curious phenomenon of a different rate of motion
in markings of the same kind, and situate in the same north
latitude, in opposite hemispheres of the planet. When we come
to the consideration of the equatorial spots, we shall find that
here also there is evidence of somewhat similar differences in the
rotational rates of markings situate in the same latitude, but in
different zenographical longitudes. It is obvious that should such
rotational differences continue unaltered, the more swiftly moving
* These longitudes refer to the chart of the markings of Jupiter in Plate I.
NORTH TEMPERATE SPOTS.
19
spots must in time overtake the more sluggish oneS; and either
pass above or below them, or else come into collision with them.
The observations of 1888 shew that the motions of the swifter
spots have actually received a check, so as to bring them into
conformity with those of the more sluggish ones. The longitudes
in the following tables are expressed according to "system II."
of Mr. Marthas ephemeris (daily rotation =870°'a7).
White North Temperate Spot A.
G.M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
H. M.
0
April 18
II 21
2
43'6
Spot not very conspicuous nor well de¬
fined, but much misty cloud about, so
that it was only seen with difficulty.
30
II 18
3
46'S
Small, pretty bright, not very well defined,
altogether rather inconspicuous. Plate
III., fig. II ; Plate VIII., fig. 50.
Shewn in fig. 41, Plate VII., as an oval-
shaped white spot.
June 10
—
.. 17
10 38
3
36-6
Pretty bright, very white, only moderately
well defined, though a fairly definite
object. Plate IV., fig. 19.
29
10 34-5
2
36-8
Moderately large, not very bright, white,
not well defined.
This white spot was observed for a period of 7a days, during
which it performed 174 rotations, but it was rather an incon¬
spicuous object. It preserved throughout that permanency and
monotony of aspect as regards magnitude, shape, and brightness,
which is so eminently the attribute of the white spots situate on
the north side of the North Equatorial Belt, and which consti¬
tutes one of the chief points of difference between them and the
similar, but very changeable, markings ori the north side of the
South Equatorial Belt. The mean period of rotation of this
spot was 9'' 55™ 34®"y-
Dark North Temperate Spot B.
Date.
G. M.T.
of
Transit.
Wt.
Long.
Description.
1887.
April 18
h. m.
II 45
0
58-1
An instant's glimpse through cloud shewed
a dark spot on the N. Equat. Belt and
projecting N. of the belt a little past
transit, and it was estimated to have
been on the C. M. at the time given.
C %
20 ZENOGRAPHICAL FRAGMENTS.
Dark North Temperate Spot B {continued).
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1
co
00
h. m.
0
April 25
12 20
3
52-0
A rather small elongated marking lying
obliquely on the N. component of the
N. Equat. Belt, and with one corner
projecting N. of that belt. It was dark
and altogether an easy and rather
striking object. Plate V., fig. 29.
» 27
13 S7
3
Si'4
Rather dark, pretty big, and a fairly con¬
spicuous object, though not very well
defined. It appeared to project a little
N. of the belt. In a sketch of this date
it is shewn as filling the whole space
between the two components of the
belt.
May 10
Shewn in fig. 34, Plate VI., and described
as a dark spot on the N. component of
the N. Equat. Belt, projecting N. of the
same, with apparently a feebler dupli¬
cation of the spot on the S. component
of the belt.
» 14
13 ii
2
S9'8
It seemed to consist of a dark spot not
very small, nor very dark or well de¬
fined, which projected considerably to
the N. of the belt. It was by no means
inconspicuous. Weather unfavourable.
June 17
II S
2
S2'9
A rather ill-defined, diffused, darker
patch on the N. component of the N.
Equat. Belt, and perhaps bulging to
the N. of the belt. It was not a con¬
spicuous feature. Plate IV., fig. 19.
,, 29
10 SS"S
i
49'5
Time very unsatisfactory. The spot was
on the N. component of the belt, and
appeared to be fairly dark and definite.
A similar object strongly suspected on
the S. component of the belt, and pro¬
jecting S. of the same.
Although some changes were observed in this spot, yet on
the whole it possessed considerable permanenee of aspect and
intensity. The spot proper was situated on the northernmost
of the two bands composing the North Equatorial Belt, but, as
will be seen from the above descriptions, a feebler companion
was sometimes noticed on the southern component band just
opposite to it.
The mean period of rotation in 1887 from the observations
is 55™ 408-4, but the exact value of this period is not well ascer¬
tained, because there have evidently been slight variations in the
place, or motion, of the object. I was at first inclined to ascribe
NORTH TEMPERATE SPOTS.
21
these small variations of position to errors of observation, but
recent observations bave shewn that there can be no doubt of the
actual occurrence of minor changes of this kind. Should one
of them have occurred towards the commencement or termina¬
tion of the series of observations, an alteration amounting to
several seconds might be caused in the corresponding mean
rotation period. The drawings in this case also support the
reality of the small apparent changes of position.
White North Temperate Spot C.
Date.
G. M. T.
of
Transit.
Wt.
Long.
1887.
Feb. 26
h. m.
IS 45
3
0
93'2
Mar. 18
—
—
—
April 8
14 9
3
8ri
„ 16
10 46
—
817
„ 18
—
—
—
„ 20
13 51
3
75'I
25
13 0
3
76" 2
>, 27
—
—
—
30
12 6
5
75'5
May 7
12 45
—
7i"6
„ id
10 19-5
4
74*8
Description.
Bright, considerably elongated, mode¬
rately defined. Shewn in a sketch of
this date as oval-shaped and indenting
the N. Equat. Belt.
Moderately large, bright, very white,
pretty well defined. The time of tran¬
sit was not observed. Plate II., fig. 2.
Exceedingly bright, large, well defined,
considerably elongated E. and W., very
white. In a drawing it is shewn as an
oval-shaped spot, eating well into the
N. component of the belt, and at times
it seemed as if it extended into the
rift beyond.
Large, much extended E. and W., very
bright, very white, with a nearly circular
much brighter condensation (near the
middle). An estimated transit.
Following B a little way was a large,
very bright, white spot, lying on the
N. side of the N. Equat. Belt.
Large, bright, fairly well defined. The
spot was considerably elongated, and
seemed to curve into the N. component
of the belt. Plate V., fig. 27.
Very bright, pretty large, very white,
fairly well defined. Plate V., fig. 29.
Shewn in a drawing of this date of the
usual appearance.
Not very large, well defined, extremely
brilliant, very white, altogether a very
neat and striking object. Plate III.,
fig. IX.
Transit observed by Mr. W. F. Denning
with 10 in. With-Browning reñector.
The spot was described as " a brilliant
spot on the N. edge of the N. belt."
Large, white, extremely brilliant, well
defined, though fading somewhat on
the edges. It was a very conspicuous
feature. Plate VL, fig. 34.
22 ZENOGRAPHICAL FRAGMENTS.
White North Temperate Spot C {continued).
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
May 14
13 39
3
767
Large, very bright, very white, well de¬
fined, altogether a very conspicuous
June 10
object.
10 45
3
69'3
Rather small, but bright and pretty well
defined. It was very white. Drawn as
a very neat oval, indenting the belt,
in fig. 17, Plate IV.
>. 15
10 0
73"3
Rather small, but bright, very white, well
defined, a pretty regular oval. The
spot was 8 or lo™ past the C. M. when
observed, and was estimated to have
transited at the time given. Fig. i8.
» 17
ii 36
4
717
Small, bright, pretty well defined, very
white, nearly round, and, notwithstand¬
ing Jupiter's low altitude, it was well
seen, and the observed time of transit
was satisfactory. Fig. 19.
„ 22
id 36
3
66-4
Rather small, but very bright, very white,
very well defined, a very regularly
shaped oval, not far from round. Plate
VIIL, fig. 48.
The white spot C was observed in 1887 for a period of 116
days^ during which it performed 380 rotations, the mean period
of rotation being 9'' 55™ 33®"6 + 0*4®. The spot possessed
a remarkable permanency of aspect, the slight differences in
the descriptions of the marking being only such as would
naturally be expected from the different circumstances under
which the observations were made, with the exception perhaps
of those relating to the magnitude of the object. The differences
as to this last are probably partly due to there being a small,
bright, central condensation, or nucleus, surrounded by white
radiations of a less degree of brilliancy, as is well indicated by
the observation of the i6th April, so that the effect caused by the
object resembled that produced by what have been termed the
inner and outer coronae of the sun. This spot has therefore
maintained unaltered for a period of nearly four months, ex¬
cepting perhaps as to some minor details, its appearance of a
well-defined oval spot of great brilliancy and whiteness indenting
the North Equatorial Belt, at least to appearance, and formdng
an object of a striking and conspicuous nature.
Actually, however, it has been possessed of a much greater
NORTH TEMPERATE SPOTS.
«3
degree of permanency^ since it has been visible for a long time
prior to this apparition of Jupiter. In the ^ Journal ' of the
Liverpool Astronomical Society, vol. v., p. 65, will be found
some observations by Mr. Denning of two of tbe white spots
lying on tbe north side of tbe North Equatorial Belt made by
him in 1884-5 1886, and one of tbese, tbere designated
as [h], is tbe same object as tbe present marking C. It
was also seen again in 1888, so that this feature has therefore
been visible as a conspicuous object during four consecutive
apparitions of tbe planet, or for tbe space of nearly four years.
Tbe motion of tbe spot up to tbe end of tbe observations of
1887 bas been very uniform. It is interesting to find such a
degree of permanency, comparable to tbat of tbe great Red
Spot, in an object so completely different from tbe latter in
appearance, and probably also in constitution.
On the 8tb April C, or tbe white radiations around it,
seemed to extend so far south as to be visible in tbe rift between
tbe two component bands of tbe North Equatorial Belt, but
this was not noticed on any subsequent occasion. Tbe fol¬
lowing appear to be all tbe observed transits of tbe spot prior
to 1887.* They were all made at Bristol by Mr. Denning
with a lo-incb reflector, with the exception of tbe two marked
by a L which were made by Mr. E. E. Barnard at Nashville,
Tennessee.
G. M.T.
G. M. T.
1885.
of Transit.
1885.
of Transit.
h. m.
h. m.
Jan. 27 . .
April 23 . . .
. . II 23
Mar. 4 . .
. . 10 11
» ^5 • • •
• • 12 55'2t
„ 7 ■ •
■ ■ 7 34
May I . . .
„ II . .
. . II 4
June I . . .
• ■ 8 33
„ 12 . .
• • 6 57
J} 3 • • •
. . 10 18
14 • ■
« 13 • • •
„ 28 . .
. . 10 3
„ 20 . . .
. . 9 II
April 2 . .
..98
1886.
» 4 • •
• • 10 45
April 6 . . .
. . 7 27
„ 12 . .
. . 7 19
„ 13 • • •
„ 18 . .
25 • • •
..84
„ 19 . .
. . . 87
„ 27 . . .
■ • 9 42
„ 20 . .
• • 13 49'7t
>y 3® •
• • 7 13
* See ' Observatory,' 1885, p. 304 ; L. A. S. 'Journal,' vol. v., p. 65.
34 ZENOGRAPHICAL FRAGMENTS.
Dark North Temperate Spot D.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
H. M.
0
April 20
14 11
3
87-2
Small, moderately dark, not very sharply
defined. See Plate V., fig. 27.
.. 25
The N. component of the N. Equat. Belt
was described as being somewhat
darker and broader just following C.
The transit was not observed.
June 15
—
—
—
Careful search was made for this spot on
this date at the time when it should
have been near the C. M. ; but, with all
attention, no sign of it could be seen.
Definition was pretty good, though
sometimes rather confused.
„ 22
3
2
827
A pretty obvious dark patch on the N.
component of the N. Equat. Belt, and
projecting considerably to the N. of
the belt. It was pretty well defined.
Near it was the shadow of satellite II.
Plate VIII., fig. 48.
But little can be said concerning this spot, because the
observations of it are so few in number, but as it was invisible
on the 15th June, under rather favourable conditions, whilst
on the zznd of the same month it was a pretty obvious feature,
it is evident that some considerable changes must have occurred
in its intensity. The period of rotation was 55"" 37^*7, but
this result is probably too long, since the spot was seen in
nearly the same position with respect to C all through the ap¬
parition of 1888.
White North Temperate Spot D^.
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
1887.
h. m.
0
Feb. 26
16 r8
2
1131
Pretty bright, rather extended, mode¬
rately well defined. In a sketch of
this date it resembles C, but is smaller.
April 20
14 40+
—
1047+
On this night there seemed to be a small
white spot north of the N. Equat. Belt,
opposite the white spot VI. Its tran¬
sit was not observed; but, judging
from its position in fig. 27, Plate V.,
with reference to VI., this must have
occurred at about the time given.
NORTH TEMPERATE SPOTS.
25
The rotation period of from the above observations comes
out as 9** 55® 34®'I. Perhaps the spot did not actually fade
away, or become invisible, but very likely its outlines became
so indefinite and ill marked that it lost all appearance of a
definite object.
Dark North Temperate Spot E.
G. M, T.
Date.
of
Transit.
Wt.
Long.
Description.
1887.
h. m.
0
April 16
12 9
3
131-8
Small, but dark and well defined, situate
on the N. component of the belt, and
projecting N. of the same. Opposite
to it, on the S. band of the belt, was
a corresponding but less conspicuous
spot. See Plate V., fig. 25.
May 10
ii 41
2
124-0
Very faint, ill-defined and inconspicuous,
projecting scarcely at all N. of the
belt. In fig. 35, Plate VI., a corre¬
sponding spot of about the same inten¬
sity and magnitude is shewn on the S.
band of the belt.
As only the two observations given above were obtained,
little can be said concerning this marking beyond calling atten¬
tion to the duplicity of the object. The period of rotation was
9I1 27®'3, but it is obvious that this period cannot be
determined with any great degree of exactness, owing to the
paucity of observations and the short space of time over which
they extend.
White North Temperate Spot F.
Date.
G. M. T.
of
Transit.
Wt.
Long.
Description.
1887.
Mar. 6
h. m.
—
0
Shewn in fig. i, Plate IL, and described
as a brighter spot, but the definition
was too confused to do anything with
it.
Moderately large, considerably elongated,
very white, moderately bright, at times
it gave the impression of penetrating
partly into the space between the two
components of the N. Equat. Belt.
Plate IV., fig. 20.
>, 23
Ï2 53
2
148-7
20 ZENOGRAPHICAL FRAGMENTS.
White North Temperate Spot F {continued).
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
April 14
10 54
4
1457
Rather small, nearly round, it being only
a little oval E. and W., very bright,
rather well defined. It was visible in
the rift of the belt, and was connected
with the S. Equat. spot VI. by a bright
train from the latter. See fig. 24,
Plate V.
„ 16
12 31
2
i4S'i
Rather faint and ill-defined, and by no
May 8
means conspicuous. Fig. 25.
A long white spot is shewn in fig. 31,
Plate VI., cut almost in half by the
dark spot G. The part W. of G is F,
and the part east of the same H.
The long white double spot con¬
sidered as one object was noted on the
C. M. at 10'' 4i'"'5.
,, 10
Appearance same as on the 8th. The
long white double spot was observed
to transit at 12'' is". Fig. 35.
IS
II 5
4
134-0
Rather small, well defined, very white.
very bright, bounded sharply on the
east by spot G. Fig. 37.
June i
10 10
—
i3S"9
Rather small, not very bright, not well
defined, white. When observed it was
8" or 10™ past transit, which was esti¬
mated to have occurred at the time
given. Plate III., fig. 15.
This was a somewhat more interesting object than most of
the similar features situate in the same north latitude. A
rather important peculiarity was its visibility in the rift of the
great double Nortb Equatorial Belt, the two portions of the
spot being separated from each other by the northern com¬
ponent of this belt. This circumstance would indicate that, as
in the case of the equatorial white spots, it was situated at a
lower level in the atmosphere of Jupiter than the neighbouring
dark belt, under which it is probable that it extended. The
connection observed between F and the white equatorial spot
VI. on the 14th April, in the form of a white streak, was pro¬
bably more apparent than real, since it seems unlikely that
there could be any actual physical connection existing between
two spots possessed of such différent properties ; the former
having great permanency of aspect, and a period of rotation
approximating to that of the Red Spot, and the latter possess-
NORTH TEMPERATE SPOTS.
27
ing great fickleness or changeability of appearance, and a motion
very much swifter than that of the last-mentioned object. It
is, however, by no means impossible that, in spite of these dif¬
ferences, a physical connection of some kind may exist between
the white north temperate spots and the white equatorial spots,
and it would be hasty, considering our present knowledge of
the physical conditions of Jupiter, to confidently affirm, or
assume, that there is no such connection.
From the descriptions of the appearance of the marking on
the 8th and loth May, it would seem as though we had here
one large very much elongated spot, separated into two by the
projecting dark spot G; though the appearances would be met
equally well by two distinct bright condensations or spots con¬
nected by the bright radiations, which are so frequently met
with in connection with these features of the planet. Either
of these cases would indicate that the dark spot G, like the
North Equatorial Belt on which it is placed, was situate at a
higher level in the atmosphere of the planet than the adjacent
white spots. The rotation of the spot F was performed in a
period of 9'' 55™ 3o'''o.
Dark North Temperate Spot G.
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
00
00
H. M.
0
Mar. 23
13 i6'S
4
i62"g
Pretty large, fairly well defined, rather
dark. The greater part of the spot
appeared to lie N. of the belt, but
there seemed to be a fainter continua¬
tion of it southwards, which formed a
fainter, nearly similar, spot on the
southern component of the belt. The
spot seemed to be darker and more
distinct before transit than when
actually on the C.M. Plate PV., fig. 20.
„ 30
13 SS
4
158-9
Dark, fairly well defined, much extended.
It was partly on theN. component of the
belt, but also projected considerably N.
of that band. The companion spot
apparently was not seen.
April 14
II II
3
155-9
A small elongated dark patch on the N.
component of the belt, and projecting
a little N. of the same, with a corre¬
sponding but not so pronounced spot
opposite to it on the S. component.
It was not very conspicuous. Plate-V.,
fig. 24.
28 ZENOGRAPHICAL FRAGMENTS.
Dark North Temperate Spot G {continued).
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
May 8
10 3i'S
3
i4i'3
Fairly large, pretty dark, projecting well
N. of the belt. See fig. 31, Plate VL,
where it is shewn extending over the
S. band of the belt, and also covering
the rift.
,, 10
12 is
3
144-6
Small, dark, well defined, projecting con¬
siderably N. of the belt. The com¬
panion spot on the S. component of
the belt does not seem to have been
seen. Fig. 35.
>, IS
ii 21
4
1437
Rather small, dark, well defined, project¬
ing considerably N. of the belt. The
June 13
companion spot not noticed. Fig. 37.
The spot H was observed ; but, with all
attention, no sign of G could certainly
be seen. Definition very fair.
„ 20
—
—
—
Not seen for certain when it should have
been near transit ; at most only a sus¬
picion of a fragment of a dark spot.
Definition pretty fair.
This was rather a conspicuous object at one time, and was
rendered more than naturally so from its contiguity to the two
very white spots F and H. Its duplex constitution was also
clearly and strikingly marked, a pretty evident companion spot
having been seen opposite to it on the southern component of
the double North Equatorial Belt. On one occasion also, at
least, the two spots were connected by dark material, which
covered the light rift in the belt, and from which it would
appear that the spot was at a higher level than the rift, and
that the latter was really a break in the dark belt, permitting
the lower, and lighter, surface to be seen (see Fig. 31, Plate VI.).*
The dark material composing the spot would thus be at a com¬
paratively considerable altitude in the Jovian atmosphere, and
this is indicated also by the obvious and remarkable manner in
which this object projected north of the belt, and concealed
* In this figure the dark spot is shewn extending S. of the belt a little way.
This extension is probably due to the presence of a dark north equatorial spot,
similar in its nature and motion to spots i, 2, 3, etc. A similar observation to
the one just mentioned was made by Dr. L. de Ball at Liège on the 28th March
1884, from which this observer also inferred nearly the same thing. There
are many other similar observations relating to the south equatorial belt and
spots.
NORTH TEMPERATE SPOTS.
^9
from viewj to all appearance^ a large part of the white radiations
connecting the two spots F and H. The subject of the relative
heights of different Jovian markings will be found more fully
considered in Section VI.
The dark spot G would seem to have gradually diminished
in magnitude and plainness with the progress of time, so that
in the month of June it disappeared altogether from view, though
it is probable that the marking could have been followed con¬
siderably longer, had Jupiter been more favourably placed. It is
also by no means certain that G may not again become visible.
Many of the Jovian markings are subject to temporary fluctua¬
tions in visibility, and the apparent disappearance of the spot
in June may have been due to one of such temporary varia¬
tions, aided by the increasing unfavourableness of Jupiter's
position. The rotation period of this spot was 9" 55™ 26^*0.
White North Temperate Spot H.
Date.
G. M. T.
of
Transit.
Wt.
Long.
18b7.
Mar. 23
h. m.
13 30
3
0
171*0
May 8
10 50-5
3
152-8
„ 10
—
—
—
,> IS
—
—
—
June 13
id 17
2
143" I
„ 20
—
—
—
Description.
Rather small, very bright, very white,
rather diffuse on the edges, the brighter
(interior) part being nearly circular.
Plate IV., fig. 20.
The appearance of this spot in conjunc¬
tion with F was that of a single much
elongated spot, divided almost into two
portions, or two separate spots, by the
dark spot G. Plate VI., fig. 31.
Appearance same as on the 8th. The
transit was not observed, but F and H,
considered as one spot, were estimated
on the C. M. at 12'' 15™. Fig. 35.
Shewn in fig. 37, and described as a feeble,
ill-defined, whitish patch.
Rather small, not bright, not well defined,
white. It was by no means a con¬
spicuous object. In fig. 43, Plate VII.,
it is shewn extending largely into the
rift of the N. Equat. Belt.
Looked for when it should have been
near the C. M., but it could not be seen
for certain. At most there were only
a few white ill-defined traces of it.
Definition pretty fair.
The observations available for the purpose of ascertaining
the rotation period cover a period of nearly 82 days, during
3°
ZENOGRAPHICAL FRAGMENTS.
which the spot performed 198 rotations, the mean period being
9'' 55"" 26®'8, a result which is practically the same as that
obtained for the dark spot G immediately preceding, and very
nearly the same as the mean period of spot F ; so that very pro¬
bably these three closely adjacent markings were either phy¬
sically connected with each other, or else independent bodies
carried along in the same great atmospherical current, which
at this place must have had sufficient depth and uniformity of
motion to affect the three markings to nearly the same extent.
The observation of the 13th June is interesting as throwing
light upon the question of the relative altitudes of the white
spot and the dark North Equatorial Belt, the circumstance of
the former being so clearly visible in the rift of the belt, appear¬
ing to indicate that the white spot was situate at a lower level
than the dark belt. The observations of this and the white
spot F in May point to a probable connection between the two
objects, since on two occasions they were considered to form
one very elongated spot almost divided into two by the inter¬
vening dark spot G.* Too much stress must not be laid upon
the fact of the invisibility of the object on the 20th June,
because the position of Jupiter was very unfavourable at that time.
Dark North Temperate Spot H^.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
May 8
ii 16-5
3
168-5
Small, not very dark, not very well de¬
fined, but still at times a fairly definite
object. It projected distinctly N. of
the belt. Plate -VT, fig. 31.
„ 10
13 0
3
1718
Not very large, faint, not well defined. It
projected a little N. of the belt. Fig. 35.
„ 18
Shewn in fig. 39, Plate "VII., but the
transit was not observed. It seemed
actually to consist of two faint dark
spots, one on each component of the
N. Equat. Belt, but the weather was
not very favourable, and it was difficult
to make out the precise character of
the object.
June 13
ii 2
i
170-3
Very faint, projecting to a small extent
N. of the belt. Fig. 43.
» 30
—
—
—
Shewn in fig. 49, Plate -VIII. It was
pretty dark, well defined, and projected
considerably N. of the belt.
* See also p. 27.
NORTH TEMPERATE SPOTS.
31
An inconsiderable object, chiefly interesting from its duplex
character, and from the circumstance of its being the first of a
number of spots having a motion rather more sluggish than
that of the markings in this latitude which have hitherto been
considered. The mean rotation period of this spot was
9^ 55" 40®"7i or 14^ longer than that of the spots G and H, a
short distance preceding it.
White North Temperate Spot K.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
April 19
ii 17
2
191*6
Bright, much extended E. and W., not
well defined. Plate V., fig. 26.
May 8
II 55*5
1
192-1
Very faint, ill-defined, extremely incon¬
spicuous, definition poor. Plate VI.,
fig. 31-,
>. 13
10 59
1897
Rather faint and very ill-defined, so that
it was not readily observed and was
generally inconspicuous.
IS
12 42
3
192*6
Faint, extending very far E. and W., ill-
defined, fading off almost imperceptibly
at the edges. Fig. 38.
„ 18
10 9
i
191*1
Pretty bright, very white, but very narrow,
and much extended E. and W. Plate
VII., fig. 39.
June 18
10 37
i
186-3
A faint very indefinite marking, which, in
the confused state of the definition,
could only be dimly seen. Fig. 45.
M 30
10 41
i
190-9
A bright, pretty large, and pretty well
defined object, though definition was
very confused. Plate VIII., fig. 49.
The period of rotation of spot K was 9^ 55™ 38®'6. The
object was neither an important nor conspicuous one. Its
chief peculiarities consisted in an unusual extension in an east
and west direction, and in its variations in brightness, which
appear to have been independent of the different atmospherical
conditions under which the observations were made. The indi¬
vidual determinations of the zenographical longitude of the
spot are remarkably accordant, considering the frequent faint-
ness and indefiniteness of the object.
32 ZENOGRAPHICAL FRAGMENTS.
Dark North Temperate Spot K'.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
May 20
12 13
3
2067
It appeared to consist of a small darkish
spot on the N. component of the belt,
projecting a little N. of the same, and
a corresponding spot opposite to it on
the southern component. It was fairly
though not very conspicuous. Plate
VIL, fig. 40.
June 30
11 S±
—
205-5 ±
Dark and well defined, projecting con¬
siderably N. of the belt. The com¬
panion spot does not seem to have
been seen. The time given is estimated
from the position of the spot in fig. 49,
Plate VIII.
Only these two observations were obtained, giving a rotation
period of 9'' 55"^ 39®"4} a result which is probably very near the
truth, notwithstanding the insufficieneies of the observations.
The duplicity of the spot on the 20th May is worthy of notice.
White North Temperate Spot L.
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
00
co
h. m.
0
April 10
ii 8
2
272-5
Large, much extended E. and W., con¬
siderably bright, pretty -well defined.
Plate IL, fig. 6.
„ 12
12 47
2
273-1
Moderately large, extremely bright and
white, rather well defined. It extended
S. of the N. component of the N.
Equat. Belt, so as to be visible in the
rift. The white equat. spot XVII. ex¬
tended northwards to the N. Equat.
Belt by L.
.. 14
14 24
5
272-6
Moderately large, exceedingly bright,
well defined, very white, a little oval E.
and W., but not much. In fig. 7 it is
shewn indenting the belt.
„ 16
Seen very brightly when about midway
between the centre and the f limb. Its
transit was not observed. Plate III.,
fig. 8.
» 17
II S3
i
272-5
Pretty large, very bright and white, well
defined, a conspicuous object, which
appeared to indent the N. Equat. Belt
a little.
.. 19
13 29
3
271-4
Large, very bright, very white, well defined.
and altogether a most conspicuous ob¬
ject. It is drawn indenting the belt.
NORTH TEMPERATE SPOTS.
33
White North Temperate Spot L {continued).
Date.
G. M. T.
of
Transit.
Wt.
Long.
1887.
h. m.
0
April 24
12 35'S
4
27 i'd
m 29
II 42-5
5
270'9
May 8
op
2
272-5
» 9
9 55
4
269-6
„ 28
10 40
3
272-8
June 9
10 29-5
4
269-7
„ II
—
—
—
14
—
—
—
» 16
ii 16
2
269-4
>, 21
10 24
2
269-0
Description.
Rather small, exceedingly brilliant, very
white, well defined, not far from round,
a very conspicuous object. It was
visible in the space between the com¬
ponents of the N. Equat. Belt, or, at
least, that space was lighter opposite
the spot. Plate V., fig. 28.
Moderately large, extremely bright, very
white, well defined, a most conspicuous
object. So quick is the apparent ro¬
tational motion of Jupiter at the place
of this spot that, on looking at it two
minutes later, it had moved considerably
past the centre. It is drawn as a very
regular oval, almost round.
Pretty large, extremely brilliant, very
white, well defined.
Pretty large, nearly round, excessively
brilliant, very white, extremely well
defined,a most definite and conspicuous
feature. See fig. 33, Plate VI., where
it is drawn indenting the belt.
Pretty large, nearly round, well defined,
, very bright, very white, more sharply
defined on the / than on the p side,
apparently from the presence of the
dark spot M. Plate III., fig. 14.
Pretty large, a little oval, very white, ex¬
tremely brilliant, very well defined. A
slightly brighter and whiter radiation
from it extended into the rift of the
N. Equat. Belt.
Seen and drawn as a brilliant slightly
oval white spot.
Shewn in fig. 44, Plate VII.
The spot was not so conspicuous as was
expected, but the circumstances were
unfavourable.
Pretty large, bright, white, well defined.
In fig. 47, Plate VIII., it is shewn in¬
denting the belt and bounded sharply
on the/side by the dark spot M.
This spot was a very brilliant^ well-defined, and extremely
conspicuous object. Of all the white spots on the north side
of the North Equatorial Belt visible in 1887 it was indeed
perhaps the most striking. The notes attached to the observa¬
tions shew the remarkable permanency of aspect presented by
the feature, which aspect was rendered more peculiar from the
D
34
ZENOGRAPHICAL FRAGMENTS.
great whiteness of its appearance, and the whole marking was
brought still more strikingly into prominence through its
proximity to the prominent dark spot M immediately following it.
Such a brilliant and well-defined marking was of course particu¬
larly suited for exact observations, and its motion having been
unusually uniform, the longitudes given above are remarkably
accordant inter se; whilst on one occasion it was noted that
an interval of only two minutes of time was sufficient to cause
a marked displacement in the position of the spot from the
rotational motion of Jupiter, which in this latitude of course is
nearly at its greatest. Notwithstanding that the observations are
in such close agreement, it would appear that the slight dis¬
cordances in the same were actually due in part to small real
changes in the position, or motion, of the spot itself, and not to
errors of observation. The mean period of rotation of the
white spot in 1887 was 9'^ 55" 38^*5 + '057®-
This white spot L generally appeared as if indenting, or
eating into, the North Equatorial Belt, and was several times
noticed to extend so far southwards that a portion of the object,
or the white radiations from it, became visible in the rift of
this belt, from which it may be inferred, as in the case of other
white spots, that it was situate at a lower level in the atmosphere
of the planet than the dark belt; and that the material of which
the latter was composed did not, at least, extend everywhere
downwards so as to reach the crust or solid shell of the planet,
if indeed there be such a thing.
Dark North Temperate Spot M.
Date.
G. M. T.
of
Transit.
Wt.
Long.
1887.
April 24
h. m.
12 48-5
3
0
2789
„ 29
—
—
—
May 9
—
—
—
Description.
An oval dark spot, not well defined, lying
nearly wholly on the N. component of
the N. Equat. Belt, and projecting
north of the same. Plate V., fig. 28.
The white spot L just preceding was well
seen, but although definition was good,
M was not noticed.
Following the white spot L the N. Equat.
Belt was darker and broader in both
component bands. Plate VI., fig. 33.
NORTH TEMPERATE SPOTS. 35
Dark North Temperate Spot M (continued).
G. M. T.
Date.
of
Wt,
Long.
Description.
Transit.
1887.
h, m.
0
The region of the N. Equat. Belt just/
May 28
ii 0
2
284'9
L was considerably darker and broader
than p, and especially immediately /
that spot it was still darker and pro] ected
more north, so as to appear as a darker,
ill-defined spot. Plate III., fig. 14.
June 9
10 49*5
3
281-8
A rather small though dark and pretty
conspicuous spot and projection. In
instants of best definition the more
northern part of it appeared to be
quite detached from the belt as a small,
dark, isolated spot, but generally it
looked like a rather ill-defined patch
and projection of the belt.
,> II
Seen and drawn. Described as a con¬
spicuous and pretty large object. The
appearance as drawn is nearly the same
as on May 28th.
.. 14
9 55
280-0
Pretty dark and obvious. In fig. 44,
Plate VII., it is shewn as an oval spot
projecting N. of the belt.
„ 21
10 50
2
284-7
Pretty large, dark, well defined, projecting
considerably N. of the belt, so as to
be a conspicuous object. Plate VIII.,
fig- 47-
In somewhat striking contrast to the white spot L lastly
described was the dark marking immediately following it, and
designated M. This object was followed for the space of 58
days, in which time it performed 140 rotations, of the average
duration of g'' 55™ 43®"i. It is probable, however, that this
determination is actually slightly too long, since at the last
observation on June 31st the spot still maintained its position
immediately following L, which it had occupied on the 34th April.
During most of the time it was under observation, the spot, which
was sometimes a more than usually definite and conspicuous
feature, must manifestly have experienced considerable variations
in intensity, as is indicated by the observations, and it would
be difficult otherwise to account for its not having been noticed
on the 39th April, on which date the conditions as regards the
quality of the seeing were favourable. Spot M was rendered a
more than usually striking object, from its position just following
the very brilliant and very white spot L. Although the spot
D 3
3^
ZEN06RAPHICAL FRAGMENTS.
itself was not actually seen as a double one^ traces of duplicity
were probably present, as in the observation of the 9th May
both of the two dark bands making up the North Equatorial
Belt were darker and broader at the place of the spot.
White North Temperate Spot N.
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
1887.
h. m.
0
May 14
10 10
2
310-4
Small, faint, ill-defined, especially on the
N., though the colour was very white.
It was an inconspicuous object. Plate
III., fig. 13.
June 9
ii 42-5
i
00
co
White, much extended E. and W., not
bright, very ill-defined, and altogether
an inconspicuous feature.
„ 14
—
—
Faint traces could be seen of the white
spot about the dark spot shewn in
fig. 44, Plate VIL, and which latter
appeared to partially hide N. This
dark spot was observed on the C. M.
at lo*" 40™, and there are no other
observations of it.
This was an insignificant and inconspicuous marking, of
which only three observations were secured. Its rotation
period was 9'' 55"" 46^*0, rather longer than that of other objects
in the same north latitude, but this determination is obviously
not a very reliable one. The observation of the 14th June is
rather interesting, suggesting as it does that the preceding
portion of N was at that time partly hidden by the northern
component of the little dark double spot shewn in fig. 44,
Plate VIL, the transit of which occurred at 10'' 40™; and it thus
furnishes an additional piece of evidence to shew that the dark
spots are at a higher level in the Jovian atmosphere than the
white spots. It is to be regretted that further observations
were not obtained of these apparently insignificant, though
interesting, little spots, with the planet in a more favourable
position.
NORTH TEMPERATE SPOTS. 37
Dark North Temperate Spot O.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
Very small, extremely dark, very well
May 14
10 31
4
323'I
defined. It was on the northern com¬
ponent of the belt and projecting
northwards, and on the S. component
there was a corresponding spot, but
this was not so dark nor so well defined.
Plate III., fig. 13.
II 28
II 57
i
3i9'4
Weather so bad that nothing could be
made out beyond the existence of the
spot.
June 14
II 105
4
32S'6
A fairly large, pretty dark spot, pro¬
jecting considerably to the N. of the
belt. It was rather a conspicuous
object. In fig. 44, Plate VIL, a similar
but less conspicuous spot is shewn on
the south component of the belt.
>, 19
10 14-5
—
322-9
Shewn in fig. 46, and described as a slight
bulge and darkening of the belt. The
companion spot on the S. component
of the belt does not seem to have been
seen. Transit estimated, the spot being
5 or 6™ past when observed.
The rotation of this spot O was performed in a period of
çh 55™ 44®"0, and this result seems to be deserving of some
confidence, because the two observations of the 14th May and
the 14th June, on which it is based, were both highly weighted.
The spot was a fairly conspicuous one, and interesting from its
duplicity, a corresponding but rather less conspicuous com¬
panion spot having been visible opposite to it, on tbe southern¬
most of the two bands forming tbe Nortb Equatorial Belt.
White North Temperate Spot P.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
April 3
12 i
3
33I"6
Moderately large, pretty well defined, a
little elongated E. and W., rather
bright and very white. Plate IV., fig. 21.
May 14
10 45
3
33T5
Very bright, very white, not very large,
pretty well defined. Plate III., fig. 13.
June 19
10 24+
328s±
Shewn in fig. 46, Plate VIL, as a rather
indefinite elongated patch. The time
given is estimated from the drawing.
38
ZENOGRAPHICAL FRAGMENTS.
Only three observations were obtained of this spot, perhaps
owing to the attention having been chiefly concentrated upon
the Red Spot, the preceding end of which was almost in
the same longitude. These give a rotation period of 9*^ 55™
40®"4, nearly exactly the same as that of the Red Spot itself
(9" 55" 4o'-5)-
(2) The North Equatorial Dark Spots.
Leaving the north temperate markings and proceeding
southwards, we come to two groups, or streams, of spots
situated in the region bordering on the equator, which differ
widely from those that have just been considered. One of
these groups, situate on the north side of the South Equatorial
Belt, was the seat of the greatest visible disturbance in 1887,
and forms the subject of the succeeding sub-section. The
other one lies on the north side of the equator, and immediately
on the south side of the North Equatorial Belt, and was rather
feebly represented in the present series of observations by a few,
generally inconspicuous, dark spots only, no white ones having
been seen, although in some years these latter are largely
represented. It is with these dark spots that we have to do at
present.
It will be seen from an inspection of Plate I., or the
sketches reproduced in the following plates, that these dark
spots, which have been termed north equatorial spots, and are
designated by the numbers i, 2, 3, etc., lie immediately on the
south side of the North Equatorial Belt, and so close in fact to
this feature, as usually to appear in contact with it ; and perhaps
the most remarkable thing known in connection with them
is the vastly different velocity with which they moved compared
with the north temperate spots, several of which extended
as far south as the southern boundary of the belt, or, in other
words, as far as the north equatorial spots themselves. The
mean period of rotation of the north temperate spots was,
as already stated, q'' 55™ 36»'49, whilst the mean rotation period
of the five north equatorial spots, which were all that were
observed sufficiently to enable this element to be ascertained,
was 9** 50™ 40®'o6, or very nearly 5™ shorter. This difference will
NORTH EaUATORIAL SPOTS.
39
be better comprehended when it is stated that the north
equatorial spots were flying past the immediately adjacent north
temperate ones with the velocity of 244 miles per hour ! It
must be recollected too that this great difference in the velocity
of matter situated in what are evidently great, closely contiguous,
aeriform currents, was not due merely to the transient passage
of some temporary cyclonic or atmospheric disturbance, but
continues practically unaltered in quantity certainly for years,
and in the case of the south equatorial spots, where the difference
in velocity is even greater, there is every reason to believe that
it has existed for centuries 1
The north equatorial spots in 1887 were seldom conspicuous
or very permanent features, and in consequence they were
difficult to follow for any length of time, and in fact only five of
them can be identified with certainty, so as to enable their
periods of rotation to be ascertained. In appearance they
much resembled the dark south equatorial spots situate on
the opposite side of the equator, at least when these belonged
to that type of appearance which has been included in class II.
(see sub-sec. 3, p. 54). Their chief points of difference from
these last-mentioned objects consisted in their comparatively
feeble intensity, small size, from their never (except in one
doubtful case) having appeared upon the North Equatorial Belt,
in the same manner that the other spots have so often appeared
upon the South Equatorial Belt, and from the fact that they
seldom departed from the type of spots characteristic of class IE,
and never assumed completely that of class I. Dark spots, it
is true, were frequently observed upon the North Equatorial
Belt, but these were all north temperate spots, and were
evidently of a diflFerent nature from the more southern ones ;
and besides, as has already been mentioned, their period of
rotation was about 5" longer than that of the equatorial
markings.
A very peculiar circumstance observed in connection with
these features consists in their having frequently been seen
connected by dark streaks or trains with neighbouring dark
equatorial spots on the south side of the equator. This peculiarity,
which would indicate a real physical connection between objects
situated rather widely distant from each other, has been con-
40
ZENOGRAPHICAL FRAGMENTS.
sidered in sub-section 3, when dealing with the more numerous
and more important south equatorial markings, so that it will
be unnecessary here to do more than just to mention the
circumstance. The presence of these connecting streaks, it
may he observed, has been of material assistance in identifying
the diflferent north equatorial spots, and without their help
it is probable that even the small number of the spots which
have been now identified would have been diminished.
As regards tint the northern equatorial spots were dusky or
blackish, and this was also the case with the dark trains or
streaks observed in connection with them, though these were
seldom so dark as the spots. The dark spot 3 was more than
usually interesting, from its having a considerably slower
motion than the others, and from its having been followed
in its consequent change of place by a dark streak connecting
it with spot X. on the other side of the equator. It is possible
that this slower motion, which was also incident, though to
a less extent, in spots 2 and 4, may have been due to its
proximity to the comparatively sluggish north temperate
current, which may have acted somewhat in the manner of
a drag upon it.
It is necessary to hear in mind that the longitudes given in
the tables of observations, which now follow, are derived from
" system I." of Mr. Marthas ephemeris, corresponding to a
rotation period of 50°' I5®'88, ora daily rotation of 878°"25.
Dark North Equatorial Spot i.
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
00
00
h. m.
0
June 10
—
—
—
Shewn in fig. 41, Plate VII., and described
as a very plain, dark, and defined spot,
from which a dark train ran s p to the
S. Equat. Belt. It was the darkest and
plainest feature of its kind seen during
this apparition of Jupiter. It was some
way past transit when observed.
12
10 50
2
i9S'5
A fairly-defined spot, shewn in fig. 42,
with a dark train extending s p from it
to the S. Equat. Belt. When some
way past the C. M. the spot was more
notable than when in transit, which
perhaps indicates a high altitude in the
atmosphere of the planet.
NORTH EaUATORIAL SPOTS. 4I
Dark North Equatorial Spot i {continued).
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
1887.
h. m.
0
June 19
Ï0 S
—
I95'6
When seen the spot was about 15'" past
the C. M. and estimated to have tran¬
sited about the time given. Though
rather small, it was described as dark
andfairly distinct. A dark train is shewn
in fig. 46 extending i p towards the
S. Equat. Belt.
The rotational period of this object was 9" 50'" \6^'6, but
this can obviously only be regarded as an approximate deter¬
mination. It is unfortunate that the spot only became visible,
or noticeable, towards the close of the observations, since, as it
was then the most conspicuous object of the kind which had
been up to that time observed, it would have been interesting to
have followed it longer. In all the three observations given
above, the marking was substantially the same in appearance.
In none of the drawings prior to the loth June shewing the
region of Jupiter in which i made its appearance, is there any
spot shewn which can be identified with this one, so that in all
probability it first became visible in the month of June, or at
least must then have received a substantial increase in intensity.
If the drawings shewing this spot are inverted, it will be
noticed what a marked resemblance exists between this
marking and the dark equatorial spots south of the equator,
at least when the latter possess the appearance typical of
class II.
Dark North Equatorial Spot 2.
Date.
G. M. T.
of
Transit.
Wt.
Long.
Description.
1887.
May 9
h. m.
0
In fig. 33, Plate VI., a dark train is shewn
extending from the dark spot V. to the
North Equat. Belt N. of VIL The
point of junction of the train with
the belt is about in the position of
spot 2, though no actual spot appears
in the figure.
42
ZENOGRAPHICAL FRAGMENTS.
Dark North Equatorial Spot 2 {continued).
Date.
1887.
May 20
June
„ 17
„ 19
G. M. T.
of
Transit.
h. m.
12 59
id 37
10 15
II 32
Wt.
Long.
234'3
247-0
24s "I
248-7
Description.
The spot was actually at the point of
junction of the oblique streak from V.
with the N. Equat. Belt, and was a
darkish and perfectly definite object,
which seemed connected with the N.
Equat. Belt. Another dark streak
connected the spot with VIL, which
on this date was slightly following 2.
Plate VIL, fig. 40.
The spot appeared substantially as in
fig. 15, Plate III. A dark train extended
from VIL to it, but the spot itself was
entirely distinct from the streak,
though it was rather small, not very
well defined, and only pretty dark.
This spot now slightly followed VIL,
though on May 20th it was slightly
preceding that object, and the dark
streak extending from 2 to V. seems to
have disappeared.
In fig. 16, Kate IV., the dark streak
extending from VII. to the N. Equat.
Belt is shewn as on the ist June, but
no actual spot appears to have been
noticed at the point of junction.
In fig. 42, Plate VIL, a dark train is
shewn extending from the place of V.
to the N. Equat. Belt, at a point some¬
what/ VL, though no spot appears at
the point of junction. Observations,
however, had to be discontinued before
2 had arrived on the central meridian.
The spot is shewn in fig. 19, Plate IV.,
and was an object of some size and
definiteness and pretty dark. From it
a dark streak extended to spot VIL,
which now considerably preceded 2,
owing to the more sluggish motion of
the latter object.
A pretty dark and definite object, though
not large. A rather dark and definite
streak joined it to VIL, which latter
considerably preceded 2. Plate VIL,
fig. 46.
The mean period of rotation was 50"^ 33®'35 and between
Mav 20th and June 19th, 73 of these rotations were performed.
The spot can also be traced up to the 9th May^ and uncertainly
perhaps farther, so that it has been under observation for a longer
period than the remainder of these objects. One of the principal
NORTH EaUATORlAL SPOTS.
43
features of interest in connection with it was its slower motion,
its rotation being performed in a period i3®'6 greater than that
of the dark spot VII. nearly opposite to it on the other side of
the equator. The result of this more sluggish motion is made
manifest by an alteration in the relative positions of the two
markings. Thus, on the 20th May spot 2 was slightly preceding
VIL, but on the 17th and 19th June the former was considerably
following the latter. This is well shewn also by the different
sketches referred to in the observations, where it will likewise be
seen that the angle made by the dark streak connecting these
two objects with the line of the belts, has been greatly altered by
their change of relative position. It is important and interesting
to note, that notwithstanding this alteration in relative position,
the dark connecting streak always extended in a straight line
from one spot to the other, thus affording strong evidence of the
existence of an actual physical connection between the two
objects. This spot 2 was also remarkable from there having
been two dark streaks seen in connection with it at the same
time, a second one joining it to the dark spot V., some distance
preceding on the south side of the equator.
Dark North Equatorial Spot 3.
G. M. T.
Date. of Wt. Long.
Transit.
Description.
1887. h. m.
Mar. 20 12 o
3 2s8'2 Small, faint, not well defined, apparently
O
lying partly on the S. component of
the N. Equat. Belt. No dark train
appears to have been noticed in con¬
nection with the spot, which then pre¬
ceded the dark spot X.by 24™. Plate II.,
%• 3-
Shewn in fig. 4, and described as a dark
spot just south of the N. Equat. Belt
opposite to X. It is drawn due north
of that spot. No dark streak seems to
have been noticed in connection with
3, the transit of which was not observed.
i )
29
A dark train extended from X. to the N.
Equat. Belt, and there might be a trace
of a dark spot at the point of junction.
In fig. 5 the spot is drawn some dis¬
tance/oWoraiMg' X.
April 3 10 52
274'I A small dark spot on the S. side of the
belt. It was not very conspicuous.
In fig. 21, Plate IV., it is shewn as an
isolated object with no train in con¬
nection with it. An estimated transit.
44 ZENOGRAPHICAL FRAGMENTS.
Dark North Equatorial Spot 3 {continued).
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
00
00
h. m.
0
April 14
13 S
3
2974
Small, not very dark, not very well
defined, altogether inconspicuous. The
spot now followed X. by 44™. Plate II.,
fig- 7-
„ 16
14 20
3
299-9
Small, not very dark, moderately defined.
A faint dark streak ran S. from it to
the place of XII., and another dark
streak obliquely to X., in a slight curve.
See fig. 8, Plate III. The spot followed
X, by 49™.
The spot itself was not seen again,
though its position might be traced for
some time longer by means of the
dark trains from the dark spots S. of
the equator, but identification becomes
difficult owing to the rapid motion of 3,
relative to the last-mentioned objects.
The rotation of this spot was performed in a period of 51""
which is nearly a minute longer than the average rotational
rate of the equatorial markings, and longer than that of the
dark south equatorial spot X., nearly opposite to it ; and since
it was followed for 37 days, in which time it made 66 rotations,
and the observations upon which the period depends were
all assigned a weight of 3, it is probable that this result is a fairly
reliable one. That the marking in question was actually endowed
with a large proper motion relative to the equatorial spots south
of the equator, and to the other objects in its own latitude, there
can be no doubt, and there likewise can be no possibility of any
mis-identification. The observations and drawings shew well,
and in a connected manner, the rapid change of position of this
spot with respect to the dark spot X., and the other markings in
its vicinity.
The spot was frequently seen connected by means of a dark
train with the dark equatorial spots on the opposite side of the
equator, especially with X. In most cases these connecting
streaks were seen to extend in a perfectly straight line from
one spot to the other, but the dark streak connecting 3 with X,
proved an exception to this rule, it having been observed upon at
least one occasion to be slightly curved, and that in such a man-
NORTH EaUATORIAL SPOTS.
45
ner as to suggest the idea^ that^ owing to the rapid motion of one
spot with respect to the other, the connecting streak was not
quite able to keep up with the former object. As to the cause
of the slower motion of spot 3, it may not improbably have arisen
in the same manner as was suggested for the slower motion
of the preceding spot %, namely, by the proximity of the object
to the North Equatorial Belt and the markings upon the same,
which moved with approximately the same velocity as the Red
Spot. In the observation of the 20th March, the spot seemed
in fact to lie partly on the belt, and it is quite possible that its
motion may have been retarded somewhat in this way, and
more so than in the case of the other north equatorial spots,
because the observation just alluded to would indicate that it
was situate rather far north, and so be more liable to be affected
by the sluggish north temperate current.
Dark North Equatorial Spot 4.
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
1887.
h. m.
0
Mar. 18
II 57
3
299'6
Small, moderately dark, pretty well de¬
fined. In best definition it appeared
just detached from the N. Equat. Belt.
No dark streak is shewn in connection
with the spot. Plate 11., fig. 2.
„ 20
13 II
4
301-5
Pretty large, oblong, well defined, hut a
little hazy at the edges, very dark.
Two minutes produced a perceptible
displacement of the spot through the
rotation of the planet. In fig. 3 the
spot is shewn just detached from the
belt and without any dark streak in
connection with it.
„ 27
12 33
2
307-0
Small, rather faint and inconspicuous, but
definition so disturbed that actually
nothing certain as to its shape, etc.,
could be made out. No dark train was
seen in connection with the spot. Fig. 4.
April 3
II 51
3
310-1
Dark, much elongated, pretty well defined.
It looked like a short, slightly curved,
dark streak lying on the [S. side of]
the belt. From it a dark well defined
streak ran to the dark spot XII., and
another streak, fainter, broader, and
not so well defined, proceeded to XVI.
Plate IV., fig. 21.
46
ZENOGRAPHICAL FRAGMENTS.
The observations of this marking accord closely, so that,
although it did not remain under observation for any great length
of time, the rotation period of 50™ 44^*9 given by them is
probably a fairly reliable determination. The accordance of the
observations is probably due in great measure to the fact that
the spot was usually a rather definite object, and moreover
situate farther south than usual, so as to lie very close to the
equator, where of course the apparent motion of objects arising
from the rotation of the the planet is most rapid. Thus on one
night the apparent motion of the spot due to this cause was so
evident, that an interval of no more than two minutes sufficed
to produce a marked displacement in its position. In appearance
spot 4 varied from a small isolated dark marking to a dark spot
with two dark streaks connecting it with dark spots on the south
side of the equator. It is possible that these two appearances
are of the same kind, only less clearly marked, as the two typical
aspects of the dark south equatorial spots which have been
referred to classes I. and II.
Dark North Equatorial Spot 5.
G. M. T.
Date.
of
T ransit.
Wt.
Long.
Description.
1887.
H. M.
0
Mar. 6
16 24
4
2*1
A rather small, elongated streak, pretty
dark, not well defined. It was perhaps
continued farther E. and W. as a fainter
streak. No dark train was observed
in connection with the spot.
April 3
13 3i±
—
iii±
A dark train is shewn in fig. 21, Plate IV.,
extending from XVIII. to the N. Equat.
Belt. Assuming the point of junction
of the train with the belt to be the
place of the spot, it would have tran¬
sited at about the time given.
„ 8
II 33±
—
II "0+
A narrow dark streak was seen extending
from XVIII. to the N. Equat. Belt,
and at its junction with it, it seemed
to expand into a sort of dark spot.
This would have been about on the
C. M. at the time given. Fig. 23.
„ 10
12 42+
—
9"9±
In fig. 6, Plate II., a dark train is shewn
extending from XVIII. to the N. Equat.
Belt; the point of junction would have
transited at about the time given.
The observations are but few in number, and since in only
one case was the spot observed in transit over the central
SOUTH EaUATORIAL SPOTS.
47
meridian of the planet's disc, it follows that the resulting rotation
period of may be considerably in error. The times of
transit in the three last observations were merely derived from the
sketches with the assistance of the observed times of transit
of adjacent spots, but notwithstanding this, and that the deter¬
minations were made quite independently of each other, the
estimations are remarkably accordant. The spot itself was an
unimportant one, and no other trace of it appears to have been
noticed beyond the results recorded above.
(3) The South Equatorial White and Dark Spots.
We now come to the numerous markings which have been
termed south equatorial spots. These were situate chiefly in the
Equatorial Zone and immediately to the north of the South
Equatorial Belt, but they also at times extended as far south as
the southern edge of that belt, and were of two kinds—white
spots and dark spots. Since the phenomena observed in con¬
nection with these markings were numerous, important, and
complex in character, it will be convenient firstly to allude briefly
to the more important peculiarities affecting the south equatorial
spots as a whole, and then to refer in like manner to those
relating severally to the light and the dark markings.
The region of Jupiter with which we are now dealing has
been during several recent years the seat of the greatest visible
disturbance on the surface of the planet, and we find accordingly
that, in the present series of obervations, the markings occupying
it have been numerous, often very conspicuous, and subject to
great and frequently rapid variations in magnitude and intensity.
Notwithstanding, however, the disturbed state of this portion of
the ])lanet, the arrangement of the spots is, in some respects, a
rather regular one, since we almost invariably find that a white
spot is followed by a dark one, which in its turn is succeeded by
another white spot, and so on. Although their arrangement,
however, is thus regular as regards the succession of white and
dark spots we find that their grouping, or massing, partakes
rather of an irregular character, and that the individual markings
were by no means uniformly scattered round the circumference
of the planet, but exhibited a marked tendency to congregate in
48
ZENOGRAPHICAL FRAGMENTS.
one hemisphere, leaving the other hemisphere comparatively void
of spots. A glance at Plate I. will shew this clearly, 15 out of
the 26 south equatorial spots shewn in the chart being comprised
within the hemisphere of Jupiter extending from longitude 10° to
longitude 190°, whilst in the other hemisphere there are only the
remaining spots, eleven in number. The chart also exhibits the
marked manner in which the spots crowd together between
longitudes 80° and 190°; this crowded aggregation of markings
having in its midst the remarkably brilliant white spot IX. and
the no less conspicuous dark spot X. The region adjacent to,
and including these two markings formed then in 1887 the most
spotty, and, to all appearance, the most disturbed portion of the
most disturbed zone of the surface of Jupiter.
The mean period of rotation of matter in the zone of the
south equatorial markings, as determined from 21 spots,* was
50™ 22®"4, being thus more than five minutes shorter than that
of the Red Spot, or than the mean period of the north temperate
spots. It will be seen from the summary of rotation periods
contained in Section V. that the periods of none of the individual
markings differ very much from this mean result. There are,
however, some minor variations, and these perhaps exhibit a
tendency to form groups, so that we find, for instance, the spots
V. and VI., and to a less extent also IV. and VII., forming a
group of objects possessed of a swifter motion, or shorter period
of rotation, than the average. This phenomenon appears to be
analogous in its character to that which has been described in
the case of the north temperate spots, where there was a perfectly
distinct difference, amounting to 9®, in the mean rotational
periods of the markings of two opposite hemispheres.
The phenomenon now about to be described is one of great
interest and of much importance in connection with the eluci¬
dation of the real physical conditions of Jupiter. In observing
one of the more marked groups of spots, such for instance as
that in the neighbourhood of IX. and X., it sometimes happens
that one or more of the separate spots situate near the eastern, or
following, extremity of the group, undergo a rapid increase in
* Spots VIII., XL, XII., and XIX. were rejected in this determination, as
their rotational periods are not capable of being ascertained with sufficient
accuracy.
SOUTH EaUATORIAL SPOTS.
49
intensity^ so as to become much more conspicuous than the
remaining objects of which such a group may he composed.
Observing the same region a few days later, the observer is some¬
what surprised to find that, whilst the spot, or spots, which
suffered this increase have, if anything, experienced a diminution
in intensity, the immediately adjacent markings to the west¬
ward exhibit a similar increase of energy and are objects
of unusual prominence ; and as time goes on the different
spots to the westward each in turn suffer this increase in
importance, whilst the easternmost ones, in which it was first
observed, shew on the contrary a very marked decline of energy.
After a further lapse of time, the westernmost spots would in
turn undergo a decrease, and the whole group for a time perhaps
subside into quiescence ; hut presently to again suffer similar
extraordinary vicissitudes. These remarkable modifications
would appear to indicate the passage of vast waves of energy at
or under the surface, or in the atmosphere, of the planet; and for
this reason they may perhaps not inaptly he termed waves of
translation of energy. The passage of these waves would seem
to have been first remarked, at least in the case of the equatorial
markings, in the year 1882. In that year attention was drawn
by Dr. F. Terby to the fact that the region of the South Equa¬
torial Belt for some distance following the then position of the
well-known white equatorial spot was persistently darker than
the average,* and the same circumstance was also remarked by
Mr. Denning. This darker region was actually composed of a
number of closely contiguous, distinctly marked, dark spots,
forming in fact a group of markings resembling the one situate
in the neighbourhood of IX. and X. in 1887, and the passage of
more than one of these waves in a westerly direction seems to
have been distinctly observed in the same manner as has been
above described.
One result of the progress of a wave of energy is to give the
impression of a single abnormally conspicuous marking carried
onwards with greater velocity than usual, and such was the view
which the writer at the time, perhaps not unnaturally, took of
the matter. The more numerous and carefully made observa-
* ' Observatory,' 1882, p. 85.
E
5°
ZENOGRAPHICAL FRAGMENTS.
tions now available negative, however, any such abnormal rapidity
of motion, and sbew tbat the whole phenomenon is explainable
by the passage in a westerly direction of one of these waves.
It is nearly always rather a difficult matter to follow the
progress in a satisfactory manner of a wave of energy, par¬
ticularly for any length of time, on account of the gaps in the
observations arising from bad weather and other causes. The
following six cases (or rather five, since two of them relate to
the same wave) in 1X87, however, seem more or less clearly to
indicate the phenomenon in question :—
(i.) On the 3rd April, the dark spot XX. was evidently near
a maximum of intensity, it being described as " large, very dark,
well defined," and tbe spots farther west being comparatively
inconspicuous. This was also the case on the 8th, though the
observations on that night are incomplete ; and the next date on
which this region was completely observed was April loth, wben
XX. bad suffered a diminution both in magnitude and intensity,
whilst the dark spots XVIII., XII., and X. were all ata distinctly
marked maximum of plainness. Four days later, the formerly
very prominent marking XX. had diminished so much that it
was not even noticed; XVIII. had greatly decreased in plainness;
XII. was at the last degree of visibility; and X. was very incon¬
spicuous, at least for that object. But, on the other hand, spot
VII. was at a maximum, and V. a fairly plain object. Spot
XVI., for some reason or other, was not observed on the
loth April nor on the 8th of the same month, so that the change
cannot be followed in tbe case of this spot, though what little we
do know about it supports tbe evidence furnished by the other
spots. On the i6th April, the progress of the wave westwards
was continued : on that date XVI. had suffered a diminution in
magnitude and intensity; XII. was absolutely invisible; X.
shewed perhaps a slight increase in intensity, though a diminu¬
tion in magnitude; VIL had begun to decline; but now V. in
its turn was at a clearly marked maximum.
(ii.) The white spot XIX. was at a well-defined maximum
both in size and brightness from the 3rd to the 8th April, the
other spots west of it being very inconspicuous (at least on tbe 3rd,
no observations of it having been secured on the 8th). The
progress of the wave westwards seems then to have affected the
SOUTH EaUATORIAL SPOTS.
51
three spots XVII., XV., and XI. nearly to the same extent,
since all three markings indicate a conspicuous maximum from
the loth to the 14th of the same month, whilst XIX. had
greatly declined. Two days later, on the i6th April, XVII. was
in a rapid decline; XV. was not noticed; and XI. was very
inconspicuous; but now VI. was at a well-defined maximum.
It would appear therefore, from this and the preceding case, that
the passage of this considerable wave of energy must have affected
both the white and dark markings occupying this region of the
planet, about the same time, and nearly to the same extent—
a rather uiilooked for circumstance.
(iii.) The present instance relates to a minimum of energy,
apparently that following the passage of the preceding maximum.
Thus, the dark spot XII. was invisible on the i6th April and
therefore at or near a minimum, whilst VIL was near, and V. at
a maximum. On the 27th of that month, XII. had greatly
increased in importance, but now VII. was invisible, and V.
comparatively inconspicuous. By the 2nd May, the minimum of
energy had extended to V., which in its turn had become invisible.
(iv.) Spot XI. shews a maximum about the 25th April, after
which there was a falling off. Spot IX. to the westward does
not seem, however, to have attained its maximum until some
days later. This wave is badly marked, probably chiefly on
account of the paucity of observations about this time.
(v.) The white spot IX. seems to have been near a maximum
of intensity on the ist June: on that date VI., the next succeeding
white spot to the west, was extremely brilliant. On the 3rd June
the latter had increased in magnitude, though it had undergone a
slight decrease in intensity, whilst IX. had decreased both in size
and brightness. Jupiter was then a considerable time past
opposition, so that only a comparatively small extent of his sur¬
face could be observed on any one night, and the consequently
disconnected state and small number of the observations prevent
the progress of this wave from being satisfactorily traced; and the
same drawback applies to the subsequent wave. However, we find
that XV. was a conspicuous object on the 28th May, which might
indicate the position of the wave at a date prior to the above
observations. The great brightness of XXV. between the 8th and
15th May may also be due to the passage of the same wave.
E 2
52
ZENOGRAPHICAL FRAGMENTS.
(vi.) The dark spot XXVI. must evidently have heen near
a maximum on the 9th June; XVI. indicates a maximum some¬
where near the 15th June ; spot X. near the 17th June; spot
VII. near the 19th June ; and spot V. near the 21st of the same
month. Here there would seem to have been a passage of a rather
well-defined wave^ though, for the reasons above stated, it is not
possible to trace its course or velocity in a perfectly satisfactory
manner, nor to determine with any accuracy the times of maxi¬
mum plainness of the different markings apparently affected by
its passage.
The white south equatorial spots were situate mainly on the
equatorial side of the South Equatorial Belt, and were generally
apparently bounded more or less sharply by that feature. Many
of them, however, must actually have extended farther to the
south, since, after disappearing for a space, to all appearance
behind the northern component, they again became visible in the
rift, or lighter space, separating the two component bands of the
South Equatorial Belt. When at their utmost intensity, these
spots appeared as rather small, nearly circular, excessively bril¬
liant, neatly defined discs, sometimes surrounded by fainter
radiations, and having much resemblance to the satellites when
just entering upon the disc of the planet. Spot IX. as it
appeared on the 25th and 27th April may be cited as an instance
of this extreme brilliancy and definiteness. Most of the spots,
however, at least as observed in 1887, never attained to this
phase at all, but more generally appeared as rather larger, but less
brilliant and more or less irregularly shaped and ill-defined
objects. In shape they usually more or less approximated to an
oval form, with the major axis directed east and west, though
there were occasional exceptions to this rule. Several spots
were remarkable for the extreme whiteness of their colour, and
a few had an appendage in the shape of a white train or
streak extending in a northerly direction as far as the North
Equatorial Belt—the precursor of a remarkable change in the
aspect of the Equatorial Zone which occurred in the season
of 1888.
The white spots which have just been described have long
attracted the attention of observers. They were seen by the first
Cassini as far back as the end of the seventeenth century, and
south eauatorial spots.
53
it is an interesting circumstance that the periods of rotation of the
equatorial spots as ascertained by this keen-sighted and diligent
observer, do not differ very much from those that they now
have.* The observations of Herschel and Schroeter shew
that this was also the case at the end of the eighteenth century,
and as the numerous determinations made since then are likewise
in accordance upon this point, we seem constrained to conclude
that during the last two hundred years, at least, a vast equatorial
current has been blowing without cessation with the velocity of
something like 250 miles per hour, as compared with the imme¬
diately adjacent extra-equatorial markings. That there have
been minor variations in the velocity of this current is certain,
but this does not alter the remarkable fact of its continued
existence for the space of centuries.
The dark south equatorial spots, like the white ones, have
long attracted attention, since they also were observed by Cassini
towards the end of the seventeenth, and by Herschel and Shroeter
near the termination of the eighteenth, century. Some of these
markings indeed as delineated by the last-named observer were
of very minute size. As observed in 1887, these spots were
remarkable for the magnitude and rapidity of the changes which
they underwent, during the course of which they were sometimes
completely transformed in appearance. Two of the appearances
presented by the markings in question are so marked and
characteristic, that it seems desirable to form them into two
distinct classes, namely :—
Class I.—The typical appearance appertaining to this class
is that of a small, round, very dark or blackish, very well-defined
spot, generally situated chiefly uponthenorthern component of the
double South Equatorial Belt, and frequently accompanied by a
companion spotof a similar butsomewhat less conspicuous nature
on tbe southern component of the belt, whilst occasionally even a
third companion may be present. This typical appearance is well
illustrated by spot X., as observed on the 25th, 27th, and 30th
April, and the ist and 17th June (Figs. 9, 10, 11, 15, and 19);
and by spot XII. on the 30th April and the 9th May. Spot X.
* See Cassini's ' Elements d'Astronomie,' pp. 404-408, for an account of
the early observations of the equatorial spots, and their periods of rotation.
54
ZENOGRAPHICAL FRAGMENTS.
is an especially good instance, and at times indeed this object has
resembled the shadows of the satellites in dimensions, blackness,
roundness, and definiteness of form.
Class II.—The characteristic appearance of this class is that
of a darkish, frequently faint, ill-defined patch of indefinite shape
and outline, generally lying on the north side of the South
Equatorial Belt, not itpon that, feature, as in the case of class I.,
and being often of considerable dimensions. Spot V. as observed
on April 20 and 25, and spot XXIV. as seen on the 8th May
(Figs. 27, 29, and 31), are good instances of this class in
appearance.
Besides these two typical appearances, the spots had also
almost every kind of intermediate form j and in the course of their
changes, many of the markings assumed at some time or other
the appearances characteristic of both classes. Spot X. may
be instanced as an example of this.
Most of the dark south equatorial spots had, at some period
of their existence, somewhat curious appendages in the shape of
narrow dark trains or streaks extending, usually in an oblique
direction, to the North Equatorial Belt. These streaks in 1887
were chiefly observed in connection with spots of the form of
class II., but they are by no means confined only to objects
possessing this type of appearance.
It will be remarked that all the dark north equatorial spots
were joined to south equatorial ones by these dark streaks, and it
would seem probable in the other cases, where similar streaks were
seen extending to the North Equatorial Belt, that the presence of a
dark north equatorial spot is indicated at the point of junction of
the streak with the belt, though such spot may have been too
faint, small, or inconspicuous to attract attention. This is
rendered more probable from the circumstance that a known
spot was sometimes not observed, although the streak extending
to the same still remained visible.
The presence of these dark trains or streaks clearly indicates
the existence of some actual physical connection between the
dark equatorial markings situate on opposite sides of the equator,
though what the nature of that connection may be is by no
means clear at the present time. The impression has sometimes
been conveyed of a stream of dark matter flowing away from
SOUTH EaUATORIAL SPOTS.
55
the south equatorial spots to those lying on the north side of the
equator, but such a hypothesis does not seem to explain all the
observed phenomena. The remarkable manner in which the
dark train from spot X. was observed to follow the dark spot
3 on the other side of the equator, and the tendency of this streak
to lag behind on account of the much slower motion of the latter
object, have already been alluded to (see p. 44), and this peculi¬
arity is strongly confirmatory of some real physical connection
having existed between the two spots. It must be left to future
observation, however, to explain satisfactorily the observed
appearances, and the nature of such a connection.
Besides the above-mentioned particulars relating to the south
equatorial spots, there were of course many minor peculiarities
observed in connection with these markings. Most of these
of any importance are noticed in the remarks appended to
the observations of the individual markings, so that it is
unnecessary to refer to them here. As in the last sub-section,
the longitudes in the following tables are all expressed according
to "system I." of Mr. Marthas ephemeris.
Dark South Equatorial Spot I.
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
1887.
h. m.
0
April 8
IS 5
2
140-3
A dark mass on the N. side of the S.
Equat. Belt, with the customary dark
streak running obliquely to the N.
Equat. Belt. It appeared to be rather
small and inconspicuous.
June 14
10 49
4
151-3
Rather small, very dark, well defined,
altogether a conspicuous object. A
narrow dark train shewn in fig. 44,
Plate VII., extending from it obliquely
to the N. Equat. Belt.
„ 21
10 S
3
151-7
Rather inconspicuous, the spot being
diffuse and chiefly situate upon the S.
Equat. Belt, not extending much to
the N. of the belt. No dark train was
noticed. Plate VIII., fig. 47.
The mean period of rotation was g'' 50™ 22®"3, and as the
spot was followed for a period of 74 days, during which it per¬
formed 180 rotations, this result should be a reliable one. There
5^
ZENOGRAPHICAL FRAGMENTS.
does not seem to be any likelihood of a misidentification, not¬
withstanding the considerable interval^ from the 8th April to the
I4tb JunCj during which no observations were obtained.
White South Equatorial Spot 11.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
Feb. 26
15 45
3
151-6
Bright, much elongated east and west,
April 8
moderately defined.
IS 33
i
iS7"4
Large, bright, pretty well defined.
May 13
II 38
3
156-8
The spot was rather small, pretty bright,
fairly well defined, and ate well into
the S. Equat. Belt. Plate VL, fig. 36.
.. IS
12 S4
3
1598
Pretty bright, pretty large, fairly well
defined, eating into the S. Equat. Belt,
and also visible brightly in the rift
between the component bands of this
belt. Fig 38.
„ 18
9 SO
3
162-5
The spot is rather curious, inasmuch as
much of it lies in the space between
the two component bands of the S.
Equat. Belt. The northern component
band seemed much narrowed at this
point, an effect perhaps partly due to
irradiation. The spot was fairly well
defined, the portion within the rift
being on the whole rather the most
prominent. Plate VIL, fig. 39.
„ 20
II 3
i
163-6
The spot did not appear to be very bright
nor well defined, but only the most
unsatisfactory glimpse could be ob¬
tained through thin cloud which did
not permit of anything certain as to its
structure being made out.
June 14
II 9
2
163-5
Bright, not well defined. In fig. 44 it is
not shewn in the rift of the S. Equat.
Belt.
„ 21
In fig. 47, Plate VIIL, it is shewn as a
rather small inconspicuous white spot,
with no portion of it appearing in the
rift of the S. Equat. Belt.
This spot was followed for a period of 115 days, and between
February 26th and June 14th 263 rotations were performed by
it, the mean period of rotation being 50™ 20®'4. Generally
speaking, it was not an object of any specially great interest, but
there was one peculiarity observed in connection with it, which
is important as throwing light upon the question of the relative
altitudes of this marking and the great South Equatorial Belt in
SOUTH EaUATORIAL SPOTS.
57
the atmosphere of Jupiter, and also upon the nature and density
of the latter belt itself. This peculiarity consists in the visi¬
bility of the spot in the rift separating the two component bands
ofthe South Equatorial Belt; and on the i8th May, so much of the
white spot appeared within the rift in question, that this portion
seemed on the whole rather more prominent than the part north
of the belt (see fig. 39, Plate VIE), though the latter was per¬
haps the larger. The considerable narrowing of the northern
component of the belt on that night is doubtless in great
measure an effect of irradiation, but it seems to be too great to
be ascribed wholly to this cause, and it would therefore indicate
also that the edges of the belt are less dense tban the central
part, and probably ragged, thus permitting the brilliant spot to be
traced farther and through denser material than the fainter
regions lying on either side of that object.
Dark South Equatorial Spot III.
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
1887.
h. m.
0
May 13
12 0
3
170*2
The spot described as rather small, not
very dark, not well defined. It had
sometimes a tendency to assume a
double character. Plate VI., fig. 36.
IS
13 i3'5
3
1717
Large, very dark, well defined. Definition
confused and details not easily made
out, but the general shape appeared to
be triangular. Fig. 38.
„ 18
id 7
3
172^8
Pretty large, not very dark, fairly well
defined. Its exact details could not be
distinctly made out, but it had the
appearance somewhat of two spots in
contact with each other, one situate on
either component band of the S. Equat.
Belt. At any rate the spot extended
far south, and occasionally even ap¬
peared to extend southward of the S.
component of the belt. Plate VIL,
fig- 39-
June 14
ii 32
4
i77'5
Rather small, dark, well defined. In
fig. 44 it is only shewn on the N. com¬
ponent of the belt.
,, 21
id 43
2
i74'9
Inconspicuous, being chiefly situate on
the S. Equat. Belt (N. component) and
rather diffuse. Plate VllL, fig. 47.
Three things are worthy of notice concerning this spot :—
(i) The absence of any dark train extending to the North Equa-
58
ZENOGRAPHICAL FRAGMENTS.
torial Belt, and which has so generally been noted in connection
with these features ; (2) The situation of the object chiefly on,
or over, the South Equatorial Belt ; (3) The tendency of the
spot to assume a duplex appearance, with one component on
each of the two bands forming the South Equatorial Belt.
From the iact that in cases of this kind the two component
spots travel together with the same velocity, it would seem
that either the matter composing the two bands of the belt is
carried along with the same velocity, or else that there is
an upper atmospherical current which extends over both
the component bands of the belt, and possessing a much
swifter motion carries the spots along with it. The motion
of the matej-ial of the South Equatorial Belt has been con¬
sidered to be the same as that of the Red Spot, chiefly
because of tbe constant position of the great hollow or bay
in the belt opposite the latter object; and this is rendered more
probable from a certain dark spot having been seen thereon, of
the same colour as the belt, which also maintained nearly the
same relative position. The latter hypothesis is therefore probably
the correct one. The mean rotational period of spot III. was
9I1 50™ 21""].
White South Equatorial Spot IV.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
r-
00
00
h. m.
0
May 13
12 32
2
b^
00
A very curious spot, the greater part of
it being comprised between the two
component bands of the S. Equat.
Belt. The N. component band was
very narrow by the spot, and bright
radiations extended a little way to the
N. of the belt. Plate VI., fig. 36.
„ 20
Described as a whitish patch. In fig. 40,
Plate VIL, no portion of it is shewn in
the rift of the belt. The spot, however,
was past transit when observed.
June 12
10 46
3
193-0
Moderately bright, not well defined, not
very large, nor a very conspicuous
object. The spot was just opposite
the sharp bend of the S. component of
the S. Equat. Belt / the Red Spot, so
that it could not be seen S. of tbe N.
component of tbe belt, if indeed it
extended S. of this feature at the time.
Fig. 42.
SOUTH EaUATORlAL SPOTS. 59
White South Equatorial Spot IV. {continued).
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
June ig
—
—
The spot appeared as in fig. 46, and was
described as large and bright, eating
well into the S. Equat. Belt. It was
opposite the Red Spot, and is not
shewn in the light space between the
belt and that object.
21
II 5
4
188-3
Not very large, but extremely brilliant
and very well defined, so as to form a
conspicuous object. It was largely
situate in the space between the two
components of the S. Equat. Belt, the
N. component at this part being very
narrow. Plate VIII., fig. 47.
The period of rotation of the white spot IV. was 50" i7®'4,
which is somewhat shorter than the periods of the south
equatorial markings hitherto considered, and the proximity of
this object to the two following spots V. and VI., which have
considerably shorter periods than the generality of these features,
renders it probable that the greater rapidity of its motion may
have been due to that proximity. The effect of the swifter
motion of this object is shewn also by the drawings: in the
last sketch in which it appears (Plate VIII., fig. 47) it is
absolutely in contact with the preceding dark spot III., though
in fig. 36, Plate VI., it is separated therefrom by a considerable
interval.
The spot altogether was a remarkable one, and it is a pity that
more observations of it were not obtained, since some of the
phenomena observed in connection with it are of much interest
and importance, and appear capable of throwing considerable light
upon the somewhat vexed question of the relative heights of some
of the markings in the atmosphere of Jupiter. Thus, in the first
observation of the 13th May, the spot was traversed almost
centrally by the most northern of the two dark bands forming
the South Equatorial Belt, the greater portion being comprised
between these two bands. This in itself affords strong pre¬
sumption that the white spot was actually situate beneath the
dark belt, which latter, floating at a higher level, was pro-
6o ZENOGRAPHICAL FRAGMENTS.
jectecl upon the former object. This presumption is strengthened
by the observation of June 12th, when no portion of the white
spot was seen south of the northern component of the belt.
At the time of this observation, however, the spot was just
opposite the sharp bend northwards made by the southern
component of the belt immediately following the Red Spot (see
fig. 42), and this bend, in the event of the belt being at a higher
level than the spot, would necessarily conceal from view any part
of the latter at that time projecting south of the northern band
of the belt. On the 19th June again no part of the spot was
seen south of the belt, but it was then situate opposite
the Red Spot, and was probably under the influence of the
mysterious repelling power apparently exercised by this feature,
and which is seemingly sufficiently strong to force the whole
southern component band of the belt bodily northwards, so as
to make it, to all appearance, commingle with the northern
component. Kven at this observation the white spot was de¬
scribed as " eating well into the S. Equat. Belt," which would
indicate that at this time it must still have been situated rather
far south. Finally, when last observed on the 2xst June, the
white spot had passed beyond the sphere of influence exerted by
the Red Spot, and it was then again seen largely in the rift
separating the two bands which form the South Equatorial
Belt.
This spot seems throughout to have been situate farther
south than usual, though in the observation of the 20th May
it does not appear to have been noticed south of the northern
component of the belt, notwithstanding that it was then free
from any disturbing effects of the Red Spot; but this observation
is not conclusive, since when observed the spot was already a
considerable distance past the central meridian of the planet's
disc, and as other markings were visible near transit at the
same time, which required attending to, it is probable that
only a casual glance was given to the white spot in question.
SOUTH EaUATORIAL SPOTS. 6l
Dark South Equatorial Spot V.
Date.
G. M. T.
of
Transit.
Wt.
Long.
Description.
1887.
April 14
h. m.
10 50
—
0
215-1
Moderately large, pretty dark, well de¬
fined. Plate v., fig. 24. Time by
double transits.
„ 16
12 0
S
214-6
Moderately large, very well defined, very
dark, altogether forming a rather un¬
usually definite object. It was not far
from circular and was less dark on the
edges. Fig. 25.
„ 20
14 24
2
2i5'9
Pretty large, but very little darker than
the S. Equat. Belt, and not prominent
at all. A faint dark train was seen
extending obliquely from it to the N.
Equat. Belt. Fig. 27.
n 25
12 12
3
207-3
The spot a mere vestige of what it had
been. It was small, very faint, not well
defined, and projected only a little way
north of the belt. It had a slight
extension in the shape of a dark train
running obliquely to the N. Equat.
Belt. Fig. 29.
„ 27
13 25
i
2086
Spot pretty large, not very dark, had a
dark train extending to the N. Equat.
Belt in a K/direction.
May 2
The spot was looked for at about the
time it should have been on the C. M.,
but nothing of it could be seen for
certain. A fair view of Jupiter was
obtained for some time, when mist
interrupted.
.. 9
10 30
3
202-2
Very small, not very dark, pretty well
defined, very inconspicuous, a mere
shadow of its former self. But for the
presence of a slight oblique train joining
the N. and S. Equat. Belts, it would
probably have been overlooked alto¬
gether. Plate VI., fig. 33.
„ 20
12 23
i
212-4
Very inconspicuous. So far as could be
made out in bad definition it was a small
faint spot just N. of the S. Equat Belt,
with a dark streak preceding joining it
to the belt. A plain dark pretty broad
streak extended from it obliquely to
the N. Equat. Belt. The observed
time ef transit was very unsatisfactory.
Plate VII., fig. 40.
June 10
10 4
2
211-0
Very small, excessively faint and incon¬
spicuous. It had an exceedingly feeble
dark train running obliquely to the N.
Equat. Belt. Fig. 41.
6%
ZENOGRAPHICAL FRAGMENTS.
Dark South Equatorial Spot V. {continued).
G. M. T.
Date. of Wt. Long.
Transit.
Description.
1887. H. M.
June 12 117
205"8 No spot actually visible, but there was,
o
however, a very faint dark oblique
streak joining the N. and S. Equat.
Belts, the s p end of which probably
occupied the place of the dark spot.
This end was on the C. M. at the time
given. There might also be a little
diffuse shading about the place of the
junction of the streak with the S.
Equat. Belt. " Fig. 42.
„ 19 10 207 3 205-2
205-2 Dark, not very large, rather well defined.
It was rendered conspicuous from the
presence of two white equat. spots
(IV. and VI.), one on either side of it.
No dark train seems to have been
noticed on this night. Fig. 46.
21 II 25 3
200-5 Moderately large, very dark, well defined.
No dark train is shewn in fig. 47,
Plate VIII.
This feature moved wdth somewhat greater rapidity than the
generality of the markings in its latitude, its rotation being per¬
formed in a period of only 9'' 50" 9®'5, and it was also accom¬
panied in its more rapid progress by the succeeding white spot
VI. The rate of progress of the equatorial spots has been
gradually becoming more and more sluggish for several years past,
and these two spots would seem to have possessed a last remnant
of the former swifter motion. The dark spot V. would appear to
be at a lower altitude in the atmosphere of the planet than the
generality of the dark south equatorial markings, as is indicated
by the following observations, and this may have had something
to do with its swifter motion. On the 14th April at ii'^ zo™,
when the dark spot VII. was on the central meridian, and the
dark spot V. consequently only 30" past transit, the following
note was made :—" The preceding dark spot V. is already almost
completely lost to view, having a very dim appearance, and has
every appearance of being deeply situated in the atmosphere of
Jupiter.-"-" This note, it should be observed, was made long before
it was known that the spot V. moved more rapidly than the rest
of the similar objects in the same latitude. Generally speaking,
an equatorial dark spot, if at all conspicuous, becomes well visible
SOUTH EaUATORIAL SPOTS.
63
about an hour before transit, and of course does not become
indistinct until about the same time following that event. An
observation made on the i6th April of the succeeding dark spot
VII. well illustrates this, and differs greatly from the above note,
since on that date this feature when 53™ past transit was
described as being "still clearly visible near the W. limb." It
should be remembered that this spot VII. had a mean rotation
period of 9I' 50™ 19^7, so that it cannot have accompanied V. in
its more rapid progress, and this fact, considered with reference
to the above two observations, renders it highly probable that
the two markings w.ere actually situate at considerably different
altitudes in the atmosphere of the planet, and that V. was pro¬
bably at a lower level than VII.
The motion of the dark spot V. appears to have been far
from perfectly uniform, the discordances in the observations
being too great to be attributed entirely to the nature of the
marking and the changes which it underwent in appearance
and intensity. There seems especially to have been a retro¬
grade movement of a temporary character about the end of
May and early part of June, but the object was then so faint
and inconspicuous that this is not certain.
The changes in appearance and intensity were very consider¬
able. The spot usually appeared to be situate well on the north
side of the South Equatorial Belt, and on the 14th and i6th
April was a very conspicuous feature. Four days later it had
much faded, and a dark train extending obliquely to the North
Equatorial Belt had made its appearance j whilst after the lapse
of five days more the object was described as being a mere vestige
of what it had been ; and on the 2nd May it was absolutely in¬
visible. On the 9th May it was seen again, though only as an
inconspicuous object. It was next observed on the 20th of the
same month, when some changes must have taken place, since it
then appeared as a small faint spot situate just north of the
South Equatorial Belt, with a dark streak preceding, joining it to
that belt (Fig. 40), and with a plain, dark, pretty broad train
extending obliquely from the spot to the North Equatorial Belt.
By the loth June the streak preceding had disappeared, and the
spot itself had become excessively inconspicuous ; whilst two days
later it had again disappeared from view, though the dark train
64
ZENOGRAPHICAL FRAGMENTS.
from it still remained visible. Finally, on the 19th and 21st
June, the spot seems to have regained most of its former
consequence, but the dark train extending to the North Equa¬
torial Belt was no longer visible. The observations point to a
great outburst of matter, forming the dark spot, about the middle
of April, and another one towards the end of June, whilst between
these two great outbursts, this region of the planet, subject to
minor variations, gradually subsided to quiescence. The relation
perhaps existing between the outbursts of material forming the
spot and the appearance of the dark train extending to the North
Equatorial Belt, in the case of this and some other spots, requires
careful consideration.
White South Equatorial Spot VI.
G. M.T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
April 14
II S
4
224-3
Large, very bright, pretty well defined,
distinctly visible in the space between
the two components of the S. Equat.
Belt. A white train extended N. from
it to the white spot F on the N. side
of the N. Equat. Belt, this latter spot
being also visible most clearly in the
space between the two component
bands of the N. Equat. Belt. Plate V.,
fig. 24.
„ 16
12 17
S
224-9
Excessively bright, large, very well de¬
fined, and a m.ost conspicuous object.
It had a yellowish colour, not intensely
white, like many of these spots. Fig. 25.
„ 20
14 44
3
228-1
Large, bright, pretty well defined, rather
a conspicuous object. Fig. 27.
„ 25
12 37
i
222-5
Small, not bright, and rather incon¬
spicuous. Fig. 29.
» 27
13 43 5
3
219-9
Bright, rather small, well defined.
May 9
10 50
2
214-2
Rather small, pretty bright, pretty well
defined. Plate VL, fig. 33.
„ 20
12 46
2
226-4
Moderately large, bright, pretty well de¬
fined, a pretty definite object. Plate
VIL, fig. 40.
June i
10 8
—
229-3
Moderately large, a very well defined oval
disc, intensely brilliant, eating well
into the S. Equat. Belt, very white,
reminding me much of the old white
equat. spot which had been visible
during the preceding six years. In
fig. 15, Plate III., a feebler white train
is shewn extending northwards to the
N. Equat. Belt opposite the white
spot F. Compare this observation
with that of April 14th, when the white
equatorial spot was also nearly oppo¬
site the white spot F. Time by double
transits.
SOUTH EOUATORIAL SPOTS. 65
White South Equatorial Spot VI. {continued).
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
00
00
h. m.
0
June 3
II 15
1
2267
Rather large, extremely bright, well de¬
fined. Too cloudy for any details to be
made out. In fig. 16, Plate IV., it is
shewn eating well into the S. Equat.
Belt.
12
II 30
i
219-9
Not very bright or well defined. Defini¬
tion confused. Plate VIL, fig. 42.
.. 19 .
10 4S7
3
220-4
Large, bright, moderately defined, eating
well into the S. Equat. Belt. A less
bright extension extended nearly, if
not quite, to the N. Equat. Belt, nearly
opposite to the white spot P. Fig. 46.
The mean period of rotation of this spot in 1887 was p'' 50™
which is 2®'5 longer than that of spot Nbut io®"4 shorter
than the average period for this region, so that there is every
reason to believe that this marking accompanied the preceding
dark spot V. in its swifter motion, albeit its rate of progress may
have been a little slower than that of the last mentioned object.
The observations, however, shew clearly that the motion of the
white spot in question was not perfectly uniform, there being a
distinct retardation in the same about the end of May and
beginning of June, so that at that time the spot lagged consider¬
ably behind its mean position. This is the more interesting
from The circumstance that the dark spot V. likewise gives
signs of a retardation in its motion at about the same time -,
and this increases the probability of some relationship existing
between the two objects.
The white spot VI., during the time over which the obser¬
vations extended, was almost invariably a brilliant and con¬
spicuous object, and on one or two occasions had considerable
resemblance to the quasi-permanent white equatorial spot of
1880 and subsequent years, though there is little probability of
its being the same object. The yellowish colour noted on April
i6th is rather interesting, especially as on the ist June the spot
was described as very white. There was one other peculiarity
of interest about this spot, in addition to the fact of its having
been visible in the rift of the South Equatorial Belt, which
was the existence of a white train extending northwards to the
North Equatorial Belt.
F
66
ZENOGRAPHICAL FRAGMENTS.
Dark South Equatorial Spot VII.
G. M. T.
of
Transit.
Wt.
Description.
h. m.
II 20
12 38
2334
2377
11 9
9 36
13 3
(10 29)
225-8
240-6
236-8
(242-1)
Shewn in fig. 5, Plate II., and described
as being a similar but less conspicuous
marking than X., which latter was
large, dark, and well defined.
Moderately large, very dark, well defined,
and a conspicuous object. In fig. 24,
Plate v., the spot is drawn of a tri¬
angular shape on the N. side of the
belt, with its apex downwards.
Not very large, dark, well defined, forming
a very definite object, in which two or
three minutes produced a marked dis¬
placement from the rotation of Jupiter.
In fig. 25 it appears as a nearly round
spot on the N. side of the belt.
Shewn in fig. 27 as a pronounced bulge
northwards of the belt, and described
as being a little more distinct than V.,
which latter was pretty large but very
little darker than the S. Equat. Belt,
and not at all prominent.
Looked for carefully at the time when it
should have been near the C. M., but
no trace of it could be certainly made
out. Definition very fair.
Not seen.
Very small, very faint, extremely incon¬
spicuous. It had a narrow dark train
of extreme faintness running obliquely
to the N. Equat. Belt.
Dark, well defined, not very large. A
very feeble dark train is shewn in fig. 13,
Plate III., extending obliquely to the N.
Equat. Belt. Time by double transits.
Fairly large, pretty well defined, not very
dark. It seemed at times to have a
faint dark streak running to the dark
spot 2, and another one extending
more obliquely to the N. Equat. Belt.
Plate VII., fig. 40.
Large, pretty dark, much extended E.
and W., moderately well defined. At
times it seemed to give an impression
of being diffusely double E. and W.
A pretty broad dark train is shewn in
fig. 15, Plate III., extending from the
p side of the spot to the dark equat.
spot 2. [This double appearance was
undoubtedly due to the two spots VIL
and VIII. being seen together, and as
the time given is that when the spot as
a whole was on the C. M. it is evident
that this time must be too late for VIL
and too early for VIIL]
SOUTH EaUATORIAL SPOTS. 67
Dark South Equatorial Spot VII. (continued).
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
go
00
h. m.
0
June 3
(1143)
3
(243'8)
Rather a remarkable object. It had the
appearance of two dark spots connected
by dark material, and divided from
each other more particularly by a lighter
space in the rift between the two com¬
ponent bands of the S. Equat. Belt.
It was rather dark, particularly in the
individual spots. In the observed time
the two spots were considered as one.
[The same remark therefore applies as
in the preceding observation.] In fig.
16, Plate IV., a broad dark train is
shewn extending from the preceding
of the two spots to the place of the
dark spot 2.
„ 10
(11 10)
4
(251-2)
See obs. of VIII. of this date.
>. 17
Shewn in fig. 19 as a rather large dark
spot, with a dark train extending from
it to the dark spot 2. In this fig. it is
shewn widely separated from VIII.,
and with a small white equat. spot
intervening between. It was some way
past the C. M. when observed.
19
ii22
2
242-6
Large, very dark, well defined, and alto¬
gether a very prominent object. In
fig. 46, Plate VIL, a broad dark train
is shewn extending to the dark spot 2.
The mean rotation period of spot VII. was 9" 50™ I9''7,
slightly shorter than the average period of the markings in this
latitude. It is, however, sufficiently clear that this object did
not accompany the two preceding spots V. and VII. in their
more rapid motion westwards, though it may have been
slightly affected by its proximity to these features.
The spot was situate nearly opposite to the dark spot 2 on
the other side of the equator. This latter object had a some¬
what longer period (g*" 50™ 33®'3) than the former, and in
consequence of this a considerable alteration occurred in the
relative situations of the two markings, which is well demon¬
strated by the observations and sketches. It is worthy of note
that, notwithstanding this alteration, whenever a dark streak
was visible stretching from one spot to the other, it invari¬
ably extended in a perfectly straight line between the two
objects, thus conveying the impression, as has been already
pointed out, that the two markings had an actual physical
connection of some kind with each other.
F 2
68
ZENOGRAPHICAL FRAGMENTS.
Perhaps the most interesting phenomena observed in con¬
nection with the dark equatorial spot VII. relate to its apparent
subdivision into two distinct spots, a peculiarity which is
unique in the history of these markings, at least in the
apparition of 1886-7, ^-nd which may ultimately prove of value
in investigations respecting the physical nature and origin of
these interesting features. Prior to the ist June there was not
the least suspicion of any tendency on the part of VII. to
separate into two portions, though the elongation of the object
on the 20th May, as shewn in fig. 40, may perhaps indicate an
early stage of the change, but on that night it seemed to give
an impression of being diffusely double east and west. When
next observed, only two days later, considerable changes had
taken place, since it had then assumed the remarkable appearance
depicted in fig. 16, namely, of two closely adjacent dark spots
connected by dark material. A week later, on the loth June,
still further changes must have occurred, as on that date a
single large dark spot projecting a considerable distance north
of the belt was observed, which was probably VII. and VIII.
seen as one object without the duplicity having been noticed,
and from the north part of this spot a dark streak proceeded in
a preceding direction, and ultimately joined the South Equatorial
Belt (see fig. 17, Plate IV.). On the 17th June, however, both
VII. and VIII. were seen, and a further alteration had taken
place, since they were then widely separated from each other,
and with a white spot intervening between, as will be seen by
reference to fig. 19. Finally, when this portion of the planet's
disc was observed for the last time on the 19th June, the
altitude of Jupiter was very low, and the seeing very confused,
so that VII. alone was seen, just at the termination of the
observations.
It has already been remarked that the dark south equatorial
spots alternate with the white ones in a remarkably uniform
manner, so that it would seem altogether abnormal for two of
these dark spots to be seen close together without the usual
white spot in between. The spots VII. and VIII. formed no
exception to the general rule in this respect, as a small white
spot was actually seen between them on the 17th June, the
transit of which occurred at io'> 24™.
SOUTH EOUATGRIAL SPOTS.
69
It has been assumed that the origina] spot VII., after
dispartition, continued in existence as the preceding of the two
resulting spots. The observations, however, are not sufficiently
numerous to prove conclusively that this was actually so, though
altogether it appears probable that it was really the case.
Dark South Equatorial Spot VIII.
G. M.T.
Date.
of
Transit.
Wt.
Long.
Description.
1887.
H.
M.
0
Tune I
(10
20)
3
(242-1)
See observations of VII. on this date.
3
(II
43)
3
(243-8)
Ditto.
„ 10
(II
10)
4
(251-2)
Very dark, well defined, somewhat elon¬
gated. Probably VII. and VIII. seen
together. A dark streak ran from its
p end and connected it with the S.
Equat. Belt. A faint dark train pro¬
ceeded obliquely to the N. Equat. Belt.
Plate IV., fig. 17.
-, 17
10
40
2
260-4
Small, fairly well defined, very little
darker than the S. Equat. Belt. It
only projected a very little to the north
of the belt and was rather incon¬
spicuous. In fig. 19 it is drawn a con¬
siderable distance from VIL, and with
a small white equatorial spot inter¬
vening.
The details connected with the appearance of this spot and
its apparent separation from VII. have been considered under
the remarks concerning that spot. The observations are not
sufficiently numerous or extended to enable the period of rota¬
tion to be even approximately ascertained.
White South Equatorial Spot IX.
Date.
G. M. T.
of
Transit.
Wt.
Long.
Description.
1887.
Mar. 29
April 25
h. m.
13 33
S
0
256-7
Shewn in fig. 5, Plate II., and described
as a bright equatorial spot.
Rather small, but intensely brilliant and
very well defined, and being nearly
circular it had much resemblance to a
satellite when just entering upon the
disc. In appearance it exactly resembled
the principal white equatorial spot of
1880 and subsequent years, when that
object was at its greatest brilliancy.
Plate III., fig. 9.
70
ZENOGRAPHICAL FRAGMENTS.
White South Equatorial Spot IX. {continued).
Date.
G. M. T.
of
Transit.
Wt.
Description.
1887.
April 27
30
June i
"10
IS
» 17
h. m.
14 44'S
II 34
May 14 9 51-5 2
10 58
12 11
II 30
10 58
257'I
2SS'9
250-1
259-8
260-8
263-4
271-3
Intensely brilliant, very white, very well
defined. In fig. 10 it is shewn a little
oval east and west, and eating into the
S. Equat. Belt.
Pretty large, intensely bright, very white,
well defined. It was not, however,
quite so disc-like as it had been a few
days before. In fig. 11 the spot is
drawn nearly round and eating well
into the S. Equat. Belt.
Pretty large, very bright, pretty well
defined, very white, eating well into
the S. Equat. Belt. In fig. 13 the spot
is a little oval E. and W.
Large, very white, intensely bright, very
well defined. It was plainly visible in
the space between the two component
bands of the S. Equat. Belt, though
the part visible there was not so broad
nor quite so bright as the part N. of
the belt. The north component of the
belt was very narrow just where it
crossed the white spot. Fig. 15.
Very bright and well defined, and a very
conspicuous object. In fig. 16, Plate IV.,
part of it is shewn in the rift of the
belt, the northern component band
being very narrow just by the white
spot. Time by double transits.
Pretty large, extremely brilliant, well
defined. It is not shewn in the rift of
the S. Equat. Belt. Fig. 17.
Shewn in fig. 18 as a rather small, slightly
oval, white spot. It is not shewn in
the rift of the S. Equat. Belt, but when
observed it must have been 12™ or 13™
past transit.
Small, very bright, very well defined.
It was slightly oval, with the major
axis directed nearly N. and S., a rather
unusual circumstance, the major axis
being almost invariably directed E. and
W. It does not appear in the rift of
the S. Equat. Belt. Fig. 19.
This spot was remarkable for its extreme brilliancy, its rather
small but disc-like appearance when at its brightest, the white¬
ness of its colour, and for its frequently having been seen to eat
well into the South Equatorial Belt, and even to appear in the
lighter space between the two component bands of the belt, a
SOOTH EaOATORlAL SPOTS.
71
circumstance which would indicate a position rather farther south
than many of the similar objects in the same region. When at
its brightest, this marking strikingly resembled the principal
white equatorial spot visible in 1880, though there is little
likelihood of its being the same object. The observations
and drawings are strongly confirmatory of the view that the white
spots are situated at a lower level in the atmosphere of the planet
than the South Equatorial Belt. Altogether this marking was
the most brilliant and generally the most conspicuous object of
its kind visible throughout the whole apparition.
Owing to the extremely brilliant and conspicuous character
of the spot, its transits over the central meridian of the planet's
disc could be observed with much exactness. The observations,
however, are only fairly accordant inter sc. The mean period of
rotation was q'' 50™ 24^*9 + o®"85.
Dark South Equatorial Spot X.
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
oc
00
h. m.
0
Mar. 6
13 34
4
258-4
The spot was a -very dark short elongated
streak, and was well defined, though
fading off a little at the edges. Some¬
times there seemed to be a fainter spot
south, just east of it, on the S. com¬
ponent of the S. Equat. Belt, but this
was not certain. Plate II., fig. i.
„ 18
ii 9
4
270-3
Very dark and somewhat of a pear-
shaped form, as represented in fig. 2,
where are indications of a dark train
extending in a « /direction.
„ 20
12 24
4
272*8
A pretty regular dark oval on the N. side of
the S. Equat. Belt, and joined to that belt
by an inclined dark streak preceding.
The spot seemed detached and distinct
from the S. Equat. Belt. In fig. 3 a
narrow dark streak is shewn extending
in a/ direction from the spot. [N.B.—
The dark streak p would partly occupy
the place of the bright spot IX., per¬
haps thus accounting for its not being
seen.]
27
—
—
—
Seen when past transit and described as
a large, dark equat. spot. In fig. 4 it
appears as a nearly round dark spot,
partly on the S. Equat. Belt and pro¬
jecting considerably north of the same,
with a fainter dark train extending in a
f direction.
72
ZENOGRAPHICAL FRAGMENTS.
Dark South Equatorial Spot X. {continued).
Date.
G. M. T.
of
Transit.
1887.
Mar. 29
h. m.
12 40
April 10
10 S
„ 12
14
„ ic
II 7
13 3'
m 25
13 48
27
14 58-5
Wt.
268'o
274-1
268-7
2706
270-1
265-9
265-6
Description.
Large, dark, and apparently well defined,
somewhat as represented in fig. 5, but
its exact characteristics were not certain
owing to bad definition. However, it
had a long train extending n f to the
N. Equat. Belt at the dark spot 3.
The spot is drawn nearly entirely north
of the belt.
Large, very dark, well defined, and sub¬
stantially as drawn in fig. 6, where a
dark streak appears p, joining it to the
S. Equat. Belt, much as on 20th March.
The spot is drawn on the N. side of
the belt, with its S. edge in contact
with the same.
Apparently large, dark, and well defined,
but definition so bad that all detail was
obliterated. However, it had a dark
train extending obliquely to the N.
Equat. Belt.
Large, not at all dark, very ill-defined.
There was a faint extension of it m/to
the N. Equat. Belt in the form of an
ill-defined train. Fig. 7.
Pretty large, moderately dark, not very
well defined. It was still a fairly con¬
spicuous object, though nothing like
what it had been. A dark train is
shewn extending very obliquely to the
N. Equat. Belt at the dark spot 3 in
Plate III., fig. 8.
Rather small, but intensely dark, quite
blackish, and extremely well defined.
This and the preceding spot IX. might
well be taken for a satellite and its
shadow, only there was no shadow or
satellite on the disc, nor, if there were,
could they then have occupied the
positions of these spots. This dark
spot was the very antithesis of the
white spot IX. preceding it. No dark
train is shewn in the drawing, fig. 9.
The lapse of a single minute sufficed to
produce a visible alteration of its posi¬
tion on the disc through the rotation
of the planet.
Small, nearly round, extremely dark, and
very well defined. So blackish was it
that it very nearly resembled the shadow
of a satellite. The shadow of satellite I.
was actually on the disc, and was but
little superior in blackness to the spot.
No dark train shewn in fig. 10.
Dark
SOUTH EaUATORIAL SPOTS.
South Equatorial Spot X. {continued).
73
Date.
G. M. T.
of
Transit.
Wt.
Long.
Description.
1887.
April 30
h. m.
II 53
267-5
May 9
14
June i
10 15
ii 12
264-4
268-4
,, 10
„ 15
II 51
10 5
276-2
282-6
.. 17
II 16
282-3
At first sight the spot seemed much
extended in a n p, sf direction, but
on closer scrutiny it was found to con¬
sist of two spots almost in contact.
One, the p one, was placed quite clear
on the N. of the S. Equat. Belt, the
other was on the north component
of the belt itself. The northern one,
which was observed on the C. M. at
the time indicated, was nearly round,
extremely well defined, intensely dark,
looking almost black in fact. The other
spot, which was observed on the C. M.
at II*" 58™, was also well defined and
intensely dark, but was not quite so
striking as the preceding spot. A
third smaller spot was suspected on
the S. component of the S. Equat.
Belt, in a line with the other two, but
cloud interrupted. Fig. 11. See also
fig. 50, Plate VIII.
Shewn in fig. 12, and described as a
much fainter and more diffuse spot
than XII.
Large, very dark, well defined, though
somewhat diffuse on the edges. It had
a dark train running obliquely to the
N. Equat. Belt. Fig. 13.
Rather small, nearly round, extremely
dark and black, very well defined, so
as to have much resemblance to the
shadow of a satellite. Traces were per¬
haps apparent of another fainter darker
spot in nearly the same latitude and
immediately f this spot, but mist
interrupted. No dark train shewn in
fig- IS-.
Small, faint, and inconspicuous. Plate
IV., fig. 17. No dark train shewn.
Rather small, fairly dark and well defined.
It was on the north component of the
S. Equat. Belt, and there also seemed
to be a slight darkening of the S. com¬
ponent opposite to it. An estimated
transit, the spot when observed being
about 7™ past transit and estimated to
have been on the C. M. at the time
given. No dark train. Fig 18.
Dark, pretty large, well defined. It was
apparently double, a companion lying
just s/, chiefly on the S. component of
the belt. Fig. 19.
74
ZENOGRAPHICAL FRAGMENTS.
This spot was observed more frequently than any other
marking, with the exception of the Red Spot, it having been seen
on 18 nights between the 6th March and 17th June; an interval
of 103 days, during which the spot performed 251 rotations.
The observations do not, however, shew that accordance inter se
which might have been expected in the case of such a conspicuous
and definite feature, and it is evident that the apparent
motion of the spot has not been uniform. The variations
in the motion were doubtless in part only apparent, and
due to the great changes which were observed in the appearance
of the object, but they must have been chiefly caused by real
changes in the velocity with which it moved. The observations
point to a series of small jumps in the motion, or changes in the
position of the spot. One of these jumps would seem to have
occurred in the early part of March, for the observations here
shew a considerable slackening of the motion. After the iSth
of that month, the spot, subject to minor variations, moved with
a tolerably uniform motion, conformable nearly to that corre¬
sponding to the ephemeris, until the commencement of June.
There then occurred, however, another distinctly marked retro¬
grade, or easterly, movement of the spot. It may be mentioned
that during the apparition of 1888, several of these mysterious
jumps of a decided and indubitable character were observed,
affecting sometimes at the same time several adjacent markings.
The changes in the appearance of this spot were so remarkable,
and appear so likely to prove of value hereafter in considerations
relating to the physical nature and conditions of these interesting
features, that not only have the descriptive notes been given very
fully, but also all the more important of the drawings of the
region including the object in question have been reproduced in
their order of date in Plates IL, III., and IV., in order to render
the history of the marking as complete as possible.
The descriptions given are so full and comprehensive, that it
is unnecessary to refer more particularly to the details of the
changes which occurred in the appearance of the spot. At one
time or the other it clearly assumed both the two typical ap¬
pearances that have been ascribed to classes I. and II. The
relations of the dark train running to the North Equatorial Belt
to the spot are also interesting and appear worthy of careful
SOÖTH EaUATORIAL SPOTS.
75
consideration. The tendency of the spot to assume a double,
and even triple, form is likewise an interesting peculiarity,
though one hy no means confined only to this spot. It would
be premature, however, and to a great extent wasted labour, to
attempt to theorise at present upon the nature of the processes
which could have produced this marking, and caused such
extensive alterations in its appearance, though when we have
more and better materials at command, it is to be hoped that
it may he done with some degree of success. Our present
knowledge of what may be termed, the birth, life, and death
of Jovian markings is so limited, that we cannot do better
than confine ourselves at present chiefly to the recording of
facts. The interesting relationship of the dark train with the
dark north equatorial spot 3 has already been referred to on
p. 44.
This dark spot X. was perhaps the most conspicuous, and
certainly was the darkest, most definite, and blackest looking,
of all the markings observed upon Jupiter in this apparition.
The apparent blackness of the spot was extreme, so that at
times there was little to choose as regards depth of colour between
it and the shadows of the satellites, and the resemblance to these
latter was greatly increased by its regular form and size. There
is no reason to suppose, however, that the object was in reality
necessarily so very obscure, for reasoning from the carefully
conducted experiments made recently by Dr. E. J. Spitta upon
the cause of, what have been termed, the dark transits of the
satellites,* it is not improbable that this spot X., even when
near its darkest, would have shone with much the same intensity
as the fourth satellite, if it could have been seen on the dark sky,
or, in other words, that its albedo was not greatly different
from that of the satellite in question.
The motion of spot X., on account of its variations and the
importance of the object, has been rather carefully investigated,
and the mean period of rotation was found to be q*" 50™ I9®'2,
with a probable error of + o'*8o.
* See ' Monthly Notices,' vol. xlviii., p. 32.
7^ ZENOGRAPHICAL FRAGMENTS.
White South Equatorial Spot XI.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
00
00
h. m.
0
Mar. 18
11 29
4
282-5
Very large, much extended E. and W.,
very bright and white, bordered on the
N. in part by a narrow dark ray from X.
Plate II., fig. 2.
„ 20
12 42
3
283-8
Large, considerably extended, roughly
oval, bright and white, bordered partly
on the N. by a dark streak from X.
Fig. 3-
27
—
Seen when past transit, and described as
a bright equat. spot. Fig. 4.
„ 29
12 53
i
2759
Spot bright, pretty large, well defined,
but it could not be seen well owing to
bad definition. Fig. 5.
April 3
Seen and drawn as a small white spot,
and described as inconspicuous. Plate
IV., fig. 21.
„ 10
10 28
3
288-1
Large, extremely bright, very white, fairly
well defined. Fig. 6, Plate IL
„ 12
11 40
2
288-8
Large, extremely bright, well defined. It
apparently extended under and beyond
the N. component of the S. Equat.
Belt, for a small light patch corre¬
sponding with the white spot was visible
in the space between the two com¬
ponent streaks of the belt.
,> 14
12 52
2
289-5
Large, exceedingly bright, pretty well
defined. Fig. 7.
„ 16
14 6
1
291-4
Small, faint, extremely ill-defined. Plate
III., fig. 8.
>. 25
14 3'S
3
275'3
Not very large, very bright, pretty well
defined, not nearly so conspicuous as IX.
Fig. 9.
>, 27
—
—
—
Shewn in fig. 10 as a rather small, pretty
well defined, white spot.
30
—
—
—
Shewn in fig. 11 as a rather small white
spot, rather elongated east and west.
May 14
10 35
3
276-6
Very bright, pretty large, fairly well de¬
fined, rather diffuse on the N., eating
well into the S. Equat. Belt. Fig. 13.
The rotation period of this marking was about 50™ 15^%
but its apparent motion was so far from being uniform that
this determination is clearly not to be relied upon. The varia¬
tions in the motion were probably due in part to the great
alterations in the magnitude of the spot from time to time, but
the apparent changes of position were too great to be ascribed
altogether to this cause, since they extended to over i5°ofzeno-
graphical longitude, corresponding to a difference of 25™ in the
SOUTH EaUATORIAL SPOTS.
77
times of the transits over the central meridian. The spot was
usually a large, bright, and conspicuous one, though there were
great variations both in magnitude and intensity. It was also
noteworthy for its whiteness, and for its visibility in the rift of
the double South Equatorial Belt, by which it would seem that
it was situated at a lower level in the Jovian atmosphere than
the belt.
Dark South Equatorial Spot XII.
G. M. T.
Date.
of
Wt.
Long.
Transit.
00
00
h. m.
0
Mar. 18
ii 50
3
29S"3
„ 20
13 g
2
294-8
>, 27
il 56
3
284-4
29
13 S
3
283-2
April 3
II 32-5
3
298-8
„ 10
10 54
i
304-0
,, 14
„ 16
13 5
2
297-4
„ 25
14 28
3
290-3
m 27
—
—
—
Description.
Rather small, faint, not well defined,
elongated rather in a N.E., S.W. direc¬
tion. Traces of a dark train are shewn
in fig. 2, Plate II.
Small rather faint and ill-defined, incon¬
spicuous, apparently joined to the belt
on the S. Fig. 3.
Rather small, not very dark. Fig. 4.
Rather small, well defined, pretty dark.
Fig- S-
Small, pretty dark, not very well defined,
and not at all conspicuous. A dark
streak ran from it in a n f direction to
the N. Equat. Belt at the small dark
spot 4. XII. is almost detached from
the S. Equat. Belt in fig. 21, Plate IV.
Rather small, dark, pretty well defined,
but definition very confused. In fig. 6
a considerable amount of fainter dark
material is shewn, particularly on the
f side, with traces of a dark train run¬
ning obliquely to the N. Equat. Belt.
Very small, very faint, extremely incon¬
spicuous. No dark train shewn in fig. 7.
The time was recorded as 12'' 5™, but
this is evidently a slip for 13'' 5".
In fig. 8, Plate III., a dark train is shewn
extending due south from the dark
spot 3 to the S. Equat Belt. The point
where this streak touches the belt is in
the position of XII., but no distinct
spot seems to have been visible.
Large, dark, pretty well defined. A dark
train extended in a «/direction to the
N. Equat. Belt. In fig. 9 the spot is
shewn chiefly on the N. side of the S.
Equat. Belt.
Shewn in fig. 10 as a moderately big, not
very dark, oval shaped spot on the N.
of the belt.
ZENOGRAPHICAL FRAGMENTS.
Dark South Equatorial Spot XII. {continued).
Date.
G. M. T.
of
Transit.
Wt.
Long.
Description.
1887.
April 30
h. m.
12 32
May g
12 47
291-3
285-6
14
(10 57)
28
(290-1)
The spot evidently double like the preced¬
ing one [X.], only on a comparatively
inconspicuous scale. It was dark and
fairly well defined. In fig. 11 the N.
component of the double spot is shewn
almost completely N. of the belt, the
S. one being situate on the northern
component band of the belt, and ex¬
tending a little S. of the same.
The northern component of a large
double spot observed on the C. M. at
the time given, the transit of the
southern component having been noted
at 12'' 53™. At first sight there appeared
to be a large dark oval spot, but with
more attention feeble signs could be
seen of a duplex constitution. The
« p component was large, round, ex¬
cessively dark, extremely well defined.
The sf spot was large, plain, very dark,
well defined. The peculiar position of
this double spot with regard to the Red
Spot and the hollow of the S. Equat.
Belt will be seen by reference to fig. 12,
and it is evident that the most southern
spot would over, or under, lie the N.
part of the Red Spot, or else come into
collision with the same, if it should
continue its course westwards in a
straight line. In the drawing a dark
train is shewn extending from the n p
spot in a n/direction to the N. Equat.
Belt.
The appearance was that of a very dark
spot much elongated E. and W., and
lying wholly on the N. component of
the S. Equat. Belt, the major axis
being in fact nearly in a line with the
direction of the belts. At times there
were slight indications of duplicity.
It would seem from this observation
compared with the previous one, that
the s/ of the two spots had been
forced northwards by the action of the
Red Spot (see fig. 13), a circumstance
of extreme interest and importance.
A dark train is shewn in the drawing
extending obliquely from the p of the
two spots to the N. Equat. Belt. The
time given is that at which the double
spot considered as one object was on
the C. M.
Shewn in fig. 14, and described as a dark
equatorial spot or bulge, which had a
faint dark train extending «/to the
N. Equat. Belt.
SOUTH EOUATORIAL SPOTS.
79
The motion of the present marking was remarkable for its
want of uniformity, and it is singular that the variations in the
rate of this motion occurred synchronously with similar varia¬
tions in the velocity of the white spot XI. immediately preceding
it. The changes in the position of the spot consequent on such
variations will be apparent from the column of longitudes in the
above table, and indeed these are so considerable as at one time
to have induced the suspicion that there must have been two
distinct spots instead of one ; and similarly that there were two
separate white spots in place of the single one denominated XI.
The drawings, however, give no indications in support of this
hypothesis; and the observation in the apparition of 1888 of
well-marked and indubitable variations of a similar character
renders it quite unnecessary to have recourse to any such
explanation. That the observed changes might be due to
accidental errors of observation is perfectly inadmissible, because
every instance of the change of position of this feature is sup¬
ported by two or more accordant observations ; and such
changes are moreover of too great a magnitude to be ascribed
either to systematic errors of observation, or to changes in the
shape and magnitude of the object. There are therefore very
strong reasons for believing that there were changes of a real
and palpable nature in the rate of motion of this dark spot,
these changes moreover occurring at the same time in the case
of the white spot XI. preceding it, and from which it would
appear that the cause of such variations was capable of affecting,
either directly or indirectly, a considerable region of the planet,
and at the same time both the white and the dark markings.
A comparison of the observations of the two spots XI. and XII.
will shew how the change in the position of one marking was
always accompanied at the same time by a similar change in the
place of the other. One result of these singular variations in
the rate of motion of the spot is that the period of rotation can
only be approximately ascertained. The rotation seems to have
been performed in a period of about 9*" 50® 19'.
The dark spot XII. was interesting also for the curious changes
which took place in its appearance, and which resembled in
character those which occurred in the case of the preceding dark
spot X., but above all from the remarkable evidence afforded by
8o
ZENOGRAPHICAL FRAGMENTS.
it of the probable existence of some repelling influence exercised
by the great Red Spot upon certain features in its neighbour¬
hood ; an influence indeed of which the existence has before
now been suspected, but of which no direct proof bearing upon
the subject has hitherto been obtained. The former of these
peculiarities will abundantly appear from the observations and
drawings; the latter has been made the subject of consideration
in Section VII. of the present work, and therefore need not be
referred to further in this place.
White South Equatorial Spot XV.
Date.
G. M. T.
of
Transit.
Wt.
Long.
1887.
Mar. 18
h. m.
12 5
—
0
304"5
,, 20
13 ii
2
30i'5
„ 27
12 id
1
292-9
April 3
ii 46
i
3070
„ id
,, 14
13 26
2
310-3
19
ii 10
2
299-2
Description.
Rather small, faint, not well defined,
apparently bordered on the N. by a
narrow dark band joining the dark
spots XII. and XVI. The spot was
observed on the C. M., but no weight
was recorded. Plate II., fig. 2.
Spot not conspicuous or well defined.
It seemed bordered on the N. by a
dark streak running from XVI. towards
XII. Fig. 3.
Spot apparently pretty bright, moderately
large and probably well defined, but
definition very bad. Fig. 4.
Small, faint, not well defined, altogether
inconspicuous. It occupied the space
between XII. and XVI., the most
distinct portion being near the pre¬
ceding of these two spots. Plate IV.,
fig. 21.
This region of the planet is shewn in
fig. 6, Plate II., but the spot is not
shewn. Probably it was concealed by
the dark extension eastwards of spot
XII. shewn in that sketch.
Pretty large, pretty bright, not well de¬
fined. It was situate north of and close
to XVI. (instead of to XII., as on the
3rd), and looked as if a considerable
portion of it was concealed by this spot.
Fig. 7.
Rather small, not well defined nor con¬
spicuous. It appeared to extend beyond
the belt, so as to be visible in the rift
between the two component bands of
this belt. At any rate the rift was
broader and brighter opposite the spot
than elsewhere. Plate V., fig. 26.
SOUTH EaUATORIAL SPOTS. 8l
White South Equatorial Spot XV. {continued).
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
Large, very bright, not very well defined,
May 14
II 24
.8
306-5
particularly on the N. side. Plate III.,
fig- 13-
» 28
10 13
.8
3i9'3
Pretty large, bright, fairly well defined.
white. A fainter extension of the spot
extended northwards to the N. Equat.
Belt, and was traversed by the dark
train from XIL, which would therefore
seem to be at a higher level than the
white spot. Fig. 14.
Followed for the space of 71 days^ during which 173 rota¬
tions were performed^ the motion of spot XV. was not quite
uniform, and it is interesting that the variations in the motion
seem, partially at least, to have occurred at the same time as
those of the two preceding markings. At any rate the remark¬
able change in the position of the object on the March
was absolutely synchronous with a similar alteration in the
places of both XI. and XII. The spot did not apparently
accompany the latter objects exactly in their variations towards
the end of the observations, however, so that at most it would
seem to have been only partially subjected to the influences
which determined the changes in the motions of the two
former spots. The mean period of rotation of the white
spot XV. was 9*" 50™ 2i®'9, and this is probably a fairly reliable
determination, notwithstanding the variations in the velocity of
rotation.
Although usually an inconspicuous feature, on two occasions
observations of interest were obtained in connection with the
relative altitudes of the equatorial light and dark markings.
Thus on the 19th April, a portion of the spot appeared in the
rift of the South Equatorial Belt ; and on the aSth of the same
month, a somewhat fainter light radiation extended northwards
from the spot proper to the North Equatorial Belt, and this
fainter radiation was crossed by a dark train from the dark
spot XII.
G
82
ZENOGRAPHICAL FRAGMENTS.
Dark South Equatorial Spot XVI.
Date.
„ 12
14
„ 16
19
May 14
„ 28
June 13
» IS
G. M. T.
of
Transit.
1887.
Mar. 18
20
April 3
h. m.
12 ig
12 16
13 33
14 52
ii 42
II 48
10 29
II 32
Wt.
313'°
3i9'2
3108
3i4'S
3i9'S
3187
321-2
329-1
329*3
33S'7
Description.
Rather small, dark, fairly well defined.
In fig. 2, Plate II., a narrow dark streak
is shewn connecting XVI. to XII. on
the N. side of the intervening white
spot XV.
Shewn in fig. 3 as a rather small dark
spot on the N. of the belt, and with a
dark streak projecting towards XII.,
north of XV.
Pretty dark, fairly well defined, though
rather diffuse on the N. In figs. 21, 22,
Plate IV., a fairly broad though faint
dark streak is shewn extending from
it in a N. a little p direction to the
dark spot 4, a direction rather unusual
in these streaks, at least in 1887.
Large, dark, pretty well defined, had a
dark train extending obliquely to the
N. Equat. Belt.
Large, dark, well defined, a conspicuous
object. It had a faint narrow dark
train running obliquely to the N. Equat.
Belt. Plate IL, fig. 7.
The spot extremely indefinite and incon¬
spicuous, appearing generally merely as
a slight bulge of the belt with a slightly
darker condensation. A dark train
appears in fig. 8, Plate III.
Rather small, dark, pretty well defined.
It seemed situated in great measure on
the N. component of the S. Equat.
Belt, with perhaps a trace of a similar
object on the S. component opposite
to it. No dark train seen. Plate V.,
fig. 26.
Dark, not very large, pretty well defined,
a fairly conspicuous feature. Traces
of a dark train are perhaps indicated
in fig. 13, Plate III.
Extremely faint and ill-defined, so as to
be very inconspicuous. Faint traces
were visible of the usual train nf to
the N. Equat. Belt. The spot is drawn
almost completely on the N. com¬
ponent of the belt. Fig. 14.
Small, not dark, not well defined. A
pretty dark train ran from it obliquely
to the N. Equat. Belt. In fig. 43,
Plate VIL, the spot is shewn north of
the belt.
Moderately big, pretty dark, pretty well
defined, a fairly prominent object. In
fig. 18, Plate IV., it is drawn N. of the
belt, and with a dark train extending n f.
SOUTH EaUATORIAL SPOTS. 83
Dark South Equatorial Spot XVI. {continued).
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
00
00
h. m.
0
June 22
10 51
i
338'o
It appeared as a rather large, dark patch
on the N. component of the belt,
bulging a little northwards. As it was
diffuse and ill-defined on the edges,
with nothing definite much north of
the belt, it was not easy to observe its
exact position, and the obs. was con¬
sequently unsatisfactory. No dark
train was seen. Plate VIII., fig. 48.
Spot XVI. was followed for a period of 96 days, in which
time it performed 234 rotations, the mean period of rotation
afforded by the observations being ç*" 50™ 34®'o. The changes
which the spot underwent in its appearance are indicated by
the observations given above. They are of rather an interest¬
ing character, and in some respects bear considerable resem¬
blance to those manifested by the conspicuous dark spot X.,
though the present marking was greatly inferior to this latter
object in definiteness and prominence. It will be noticed that
the spot assumed at one time or the other the appearances
which are typical of both class I. and II.
White South Equatorial Spot XVII.
Date.
G. M. T.
of
Transit.
Wt.
Long.
Description.
1887.
Mar. 27
h. m.
13 19
2
0
335*0
Spot very large, very bright, much ex¬
tended E. and W., and bounded both
E. and W. by dark equatorial spots
or projections from the belt.
April 3
12 28
3
3326
Bright, pretty large, moderately well
defined, fading off on the N. edge,
much extended E. and W. Plate IV.,
figs. 21 and 22.
,, 10
II 35
3
329-0
Large, extremely brilliant, very white,
well defined, a very conspicuous object.
Plate 11., fig. 6.
G 2
84
ZENOGRAPHICAL FRAGMENTS,
White South Equatorial Spot XVII. {coniinued).
G. M. T.
Date.
of
Wt.
Long.
Transit.
1887.
h. m.
0
April 12
12 52
3
332'8
>. 14
14 0
4
331 "0
„ 16
is 21
2
337" I
.. 17
10 5S
i
333"3
May 14
—
—
—
June 13
id 40
2
347'6
„ 22
ii 13
351 "4
Description.
Large, extremely brilliant, well defined,
a most conspicuous object. It extended
very far N., almost, if not quite, reach¬
ing the N. Equat. Belt, and in the
then confused state of definition it ap¬
peared as if actually one with the white
spot L N. of the N. Equat. Belt, an ap¬
pearance which was intensified by the
fact of this more northern spot being
visible in the rift of the N. Equat. Belt.
A short glimpse in better air at 13''
shewed clearly that XVII. extended
quite to the N. Equat. Belt, though
not in its full intensity, and also shewed
L clearly visible in the rift of the belt.
Very large, exceedingly bright, well de¬
fined, altogether an extremely con¬
spicuous object. Fig. 7.
Large, pretty bright, fairly well defined.
Definition fair. Plate III., fig. 8.
Small, extended E. and W., narrow, not
bright nor well defined. Altogether
very inconspicuous. Definition pretty
good.
Shewn in fig. 13, and described as a " not
very conspicuous white equat. spot."
The transit was not observed.
Small, faint, ill-defined. Plate VIL, fig. 43.
The place of the spot was examined, and
faint traces of a white spot of indefinite
character were seen. The observed
time very precarious, and must be
assigned no -weight. Plate VIIL, fig. 48.
The rotational period of this marking was 9*^ 50°* 25^*4,
which is probably very near the truth, notwithstanding the
faintness of the object in June, and the poorness of the
observations during this month, sinee in the interval covered by
the observations as many as 212 rotations were performed by
it. The changes in its appearance were of great magnitude and
extremely rapid, and may he put forward as typical of the great
and rapid changes which the white equatorial markings at
times undergo. Thus on the 14th April, the spot was very
large and of great brilliancy, so as to be an extremely con¬
spicuous object; on the i6th of the same month it had under¬
gone a considerable diminution both in size and brightness;
SOUTH EaUATORIAL SPOTS.
85
whilst on the following day it had dwindled away so much as
to be described as " small, not bright nor well defined, altogether
very inconspicuous.'" So that in the course of three days only,
the spot had diminished from a very large and exceedingly
bright object to a small and faint one !
Dark South Equatorial Spot X'VIII.
G. M. T.
Date.
of
Transit.
Wt.
Long.
Description.
1887.
h. m.
0
Mar. 27
—
—
Spot XVII. is described as being bounded
both E. and ^W. by dark spots or pro¬
jections from the S. Equat. Belt. The
one on the E. must have been XVIII.
April 3
57
2
350-3
Spot large, dark, pretty well defined.
It was darkest on the preceding side
and more diffuse on the following. A
narrow dark streak ran from it obliquely
to the N. Equat. Belt. The spot was
chiefly N. of the belt. Plate IV.,
figs. 21 and 22.
„ 8
Shewn in fig. 23 as a not very large spot
on the N. side of the belt, with a dark
train extending to the dark spot 5 on
the opposite side of the equator.
„ 10
12 5
3
347'3
Not very large, very dark, well defined,
extended E. and W. Traces of the
usual dark train are shewn in fig. 6,
Plate II.
„ 12
13 18
i
348-6
Moderately large, pretty dark, pretty well
defined, but definition so bad and con¬
fused that nothing certain could be
said about it.
» 14
14 33
3
3S1-I
Large, moderately dark only, not well
defined. It was not a very conspicuous
object. In fig. 7 it appears diffuse on
the edges, with no certain traces of
any dark train.
This spot was an unimportant and rather uninteresting
object, and since the available observations only extend over
an interval of 11 days, the rotation period of 9'' 50™
derived from them cannot be relied upon, though, all things
considered, it is probably not very far wrong. The appear¬
ance throughout the observations was that characteristic of
class II.
86 ZENOGRAPHICAL FRAGMENTS.
White South Equatorial Spot XIX.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
April 3
13 20
2
4'4
Very large, pretty well defined, fading
off at the edges, very bright. Plate IV.,
fig. 21.
„ 8
ii 29
2
8-6
Very large, very bright, not well defined.
Fig. 23.
„ 10
12 31
2
3'2
Bright, moderately large, not very well
defined, not very conspicuous. Plate II.,
fig. 6.
24
II 85
3
I0"2
Small, very bright, well defined, clearly
visible in the space between the two
component bands of the belt. At any
rate there was a light patch in the
rift exactly opposite the spot. Plate V.,
fig. 28.
The period of rotation of spot XIX. was 9'' 50™ 18% but
this determination, like that of the preceding spot, is entitled to
but little weight on account of the short period during which
the marking was followed, and the paucity of observations.
The changes in size and brightness were considerable, and are
perhaps interesting chiefly as indicating the connection between
the white undefined cloudy patches of large area, and the small
very definite white spots, such as IX. generally appeared.
According to Mr. Marthas ephemeris, this spot XIX. should
be very near the position of the old white spot of 1880 and sub¬
sequent years, but therè appear to be no reasons for believing
it to be that object. It may be remarked that the marking
was visible in the rift of the vSouth Equatorial Belt, and hence
would seem to lie at a lower level than the belt itself.
Dark South Equatorial Spot XX.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
Mar. 27
—
—
Spot XXL is described on this date as
being preceded by a dark projecting
spot from the S. Equat. Belt. This
must be XX.
April 3
13 42
4
17-8
Large, very dark, well defined, with a
dark train running obliquely to the N.
Equat. Belt. Plate IV., fig. 21.
SOUTH EaUATORIAL SPOTS.
87
Dark South Equatorial Spot XX. {continued).
Date.
G. M. T.
of
Transit.
Wt.
Description.
1887.
April 8
h. m.
II 52
22'6
» 24
12 58
II 30'5
I9'6
237
26
12 18 ?
9"3 ^
May 8
June 18
Large, very dark, well defined. From it
a dark train, broad and rather diffuse,
ran in a slightly oblique direction to
the N. Equat. Belt, and another feebler
and narrower streak ran more obliquely
to the same feature, there being small
dark spots at the junction of both these
streaks with the belt. Fig. 23.
Resembled XII. and XVIII. as seen on
this night. A dark streak extended
obliquely to the N. Equat. Belt.
Small, dark, well defined, nearly round.
It was on the N. component of the
belt and seemed to extend its full
width. On the S. component was
a corresponding spot, not quite so
distinct. A line joining the two spots
was not quite at right angles to the
direction of the belt, and the time
given is that of the transit of the
northern spot. No dark train appears
to have been seen. Plate V., fig. 28.
The spot was almost wholly on the N.
component of the S. Equat. Belt,
scarcely projecting at all N. of the
belt. It was elongated in as/, n p
direction and perhaps double, a fainter
spot lying on the S. component of the
belt. The spot was not dark, was
rather small, not well defined. In a
sketch of this date it is drawn almost
exactly as on the 24th April. No dark
train was seen. The time of transit
relates to the northernmost component
of the double spot.
In fig. 31, Plate VI., a dark train is shewn
extending from about the place of this
spot obliquely to the N. Equat. Belt,
but no spot, properly so called, is
shewn.
The spot was looked for at the time
when it should have been near the
C.M., but nothing for certain could be
seen of any dark spot. Only at times
faint traces of an oblique streak
extending from the South to the
North Equatorial Belt were to be
seen, perhaps appertaining to this spot.
Fig- 35-
Shewn in fig. 45, Plate VIL, as a con¬
siderable bulge of the belt. No dark
train shewn.
88 ZENOGRAPHICAL FRAGMENTS.
Dark South Equatorial Spot XX. (continued).
Date.
G. M. T.
of
T ransit.
Wt.
Long.
Description.
1887.
June 20
July 16
h. m.
ii 14
1
0
35'6
Spot large, pretty dark, but very diffuse
and ill-defined. It was almost entirely
situate on the S. Equat. Belt.
Shewn in a sketch m.ade by Mr. Denning
and reproduced in 'l'Astronomie,' 1887,
331 ; being the westernmost equatorial
marking there figured. A dark train
is drawn extending obliquely towards
the North Equatorial Belt.
The rotation period was 9'' 50"" 24?'^. Notwithstanding the
long interval separating the observations in June from those in
April, it is unlikely that any misidentification has occurred.
The considerable changes in appearance experienced by the
spot resemble those which occurred in the very prominent
marking X. In May the spot must have disappeared from
view altogether for a time.
White South Equatorial Spot XXI.
Date.
G. M. T.
of
Transit.
Wt.
Long.
Description.
1887.
Mar. 23
>, 27
April 8
.. "4
June 18
July 16
h. m.
12 36
Ï4 SI
12 ii
15 58
10 32
3S"3
31-2
34'2
43"o
537
Small, bright, well defined, nearly circular,
appearing to project a little into the
S. Equat. Belt. Plate IV., fig. 20.
Pretty large, elongated E. and W., very
bright and very white.
Spot pretty bright, pretty large, ill-de¬
fined. Fig. 23.
Not large, rather faint, not well defined.
In Plate II., fig. 7, the spot is drawn
immediately following XVIII. Either
the sketch must be wrong, or there
must be a mistake of an hour in the
time. In the latter case the observa¬
tion would refer to spot XIX.
Moderately large, very bright, very white,
very well defined, eating well into the
S. Equat. Belt. A fainter white radi¬
ance extended from it northwards,
almost, if not quite, reaching the N.
Equat. Belt opposite the white spot K.
Plate VII., fig. 45-
Shewn in a sketch made by Mr. Denning.
See ' l'Astronomie,' 1887, 331, where it
is the westernmost white equat. spot
figured.
SOUTH EaUATORIAL SPOTS.
89
The period of rotation of spot XXI. was 9** 50® a5'*2> and
as the effeetive observations extended over 87 days, in which
time it performed 212 rotations, this period is probably reliable.
A considerable break in the continuity of the observations
occurred between the 14th April and the i8th June, but it does
not seem likely that any mistake in identification could have
been made. Little of importance was noted with reference
to the appearance of the spot, though its extension northwards
on the 18th June is perhaps worthy of notice.
Dark South Equatorial Spot XXII.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
Mar. 27
IS 9
3
42-1
Appearance similar to that of other dark
spots about this time \i.e. that of a
rather indefinite dark patch on the N.
side of the S. Equatorial Belt].
June 18
10 SI
3
6S"3
Pretty large, nearly round, very dark.
very well defined. In best seeing it
gave somewhat the impression of being
double. It was a conspicuous object.
Plate yil., fig. 45.
July 16
—
—
—
Shewn in a sketch of Mr. Denning's.
See 'l'Astronomie,' 1887, 331, where it
is shewn a little W. of the centre, and
with a dark train extending obliquely
from it.
Only two transits of this spot were obtained, and as they
are separated by an interval of nearly 83 days, identification
necessarily becomes rather precarious. All things considered,
however, it appears pretty certain that the two observations refer
to the same object; and the rotation period of 9'' 50" 27®'2
derived therefrom agrees well with the periods of other markings
in the neighbourhood.
9°
ZENOGRAPHICAL FRAGMENTS.
White South Equatorial Spot XXIII.
Date.
G. M. T.
of
Transit.
Wt.
Long.
1887.
H. M.
0
Mar. 16
13 34
2
42'I
,, 18
14 45
2
42-1
>. 23
13 0
2
49'9
July 16
8 12
763
Description.
Moderately large and bright, not very
well defined. Obs. unsatisfactory, the
night being very clear, so that with a
power of 170, the highest that could be
used, the image was too bright and
dazzling to be seen well.
Pretty large, not well defined, not very
bright. It was situate just N. of the
South Equat. Belt.
Small, nearly round, pretty well defined,
moderately bright. Not by any means
a conspicuous object. Plate IV., fig. 20.
Obs. made at Bristol by Mr. Denning
with 10 in. reflector. Described as
"an intensely bright equatorial spot."
See sketch by the same observer in
'l'Astronomie,' 1887, 331, where the
spot is drawn near the centre of the
disc.
Between March i6th and July i6th, the spot performed 397
rotations^ of the average duration of 9h 50™ 26^-6. On account
of the large hiatus between the observations of March and the
one made by Mr. Denning in July, identification, as in the
case of the preceding spot, necessarily is rather precarious,
but the different markings were so regularly arranged in this
region that it is unlikely that any misidentification has really
occurred. After March the spot must either have been con¬
cealed by overlying vapours or else have faded away, since
it does not appear to have been seen, although this region of
the planet was subsequently several times examined. The
subsequent intense brilliancy in July is thoroughly characteristic
of the changes which not infrequently occur in these white
equatorial spots. There is some probability that the present
spot XXIII. is identical with a white spot observed by
Mr. Denning in 1886,* and which was identified by him with
the well-known white equatorial spot of 1880 and subsequent
years. The period of rotation of the equatorial spots has, how¬
ever, of late years much increased in duration, rendering any
attempts to establish the identity of the markings difficult
and uncertain.
* 'Journal' of the Liv. Ast. Soc., vol. v., p. 65.
SOUTH EaUATORIAL SPOTS.
Dark South Equatorial Spot XXIV.
91
Date.
G. M. T.
of
Transit.
Wt.
Long.
Description.
1887.
April 17
h. m.
13 32
69'I
24
„ 26
May 8
12 44'5
13 56-5
11 9'5
12 25
68-8
69-4
67-8
70s
15
10 33
73'8
July 16
Small, dark, well defined, and seemed to
be situate partly on the N. component
of the S. Equat. Belt. It was alto¬
gether an insignificant object, of which
the exact nature could not well be
made out owing to rather confused
definition.
Rather small, very dark, well defined, a
little oval, and seemed situated almost
entirely upon the N. component of the
belt, projecting but very slightly north¬
ward of the same. Plate V., fig. 28.
Large, dark, well defined. On this night
it was much larger than on the 24th,
and extended much farther north.
Very large, dark, moderately well defined,
a very conspicuous object. It had a
dark train running nf to the N. Equat.
Belt. Plate VL, fig. 31.
Not very large, very dark, nearly round,
well defined. It is drawn partly on
the N. component of the S. Equat.
Belt, and was actually double, a less
conspicuous companion spot appearing
on the S. band of the belt. The time
given is that when the northernmost
of the two spots was on the C. M.;
from this a broad plain dark train is
shewn extending obliquely to the N.
Equat. Belt. Fig. 35.
Rather small, dark, pretty well defined,
considerably elongated E. and W.
Preceding it was a bulge of the S.
Equat. Belt, the N. edge of which was
darker, so as to form a separate streak.
Both the spot and this streak partook
of the reddish colour of the belt, but
in their case the colour was much
deeper and blacker. Fig. 37.
Shewn in Mr. Denning's sketch in
'l'Astronomie,' 1887, 331, where it is
drawn a little E. of the centre and
with a dark train nf.
Spot XXIV. is interesting from the magnitude and rapidity
of the changes of aspect which it underwent during the period
of its visibility, and particularly from the short space of time in
which it changed from the appearance typical of class II. to
that represented by class I. Thus on the 8th May it was a
9»
ZENOGRAPHICAL FRAGMENTS.
very large and conspicuous marking, extending half way from
the South to the North Equatorial Belt, and thoroughly
representative of class II. ; whilst only two days later, on the
loth May, it had assumed the appearance of a not very large,
nearly round, well defined, and very dark spot, in great measure
situate on the South Equatorial Belt, and with a less conspicuous
companion spot closely south following itj an appearance
which, it is scarcely necessary to say, is characteristic of class I.
The reddish colour observed on the 15th May is also interesting.
The rotation of the spot was performed in a period of
9I1 50™ 18'" 7.
White South Equatorial Spot XXV.
Date.
G. M. T.
of
Transit.
Wt.
Long.
Description.
1887.
April 17
h. m.
13 42
3
0
75'2
Spot small but bright and well defined.
There was something peculiar about it
which could not be clearly made out
owing to rather confused definition.
The spot appeared to extend south of
the South Equat. Belt, which at this
part [almost opposite the p end of the
Red Spot] was of course single.
May 8
II 32-5
3
8r8
Very large, very bright, pretty well de¬
fined. Plate VI., fig. 31.
„ 10
12 45
2
827
Large, bright, pretty well defined, not
very white but rather yellowish. Fig. 35.
15
10 53
3
86-0
Large, very bright, much elongated E.
and W., not well defined. Its S. edge
was bounded in a very regular curve
by the S. Equat. Belt. Fig. 37.
July 16
Shewn in Mr. Denning's sketch in
'l'Astronomie,' 1887, 331, following
the centre of the disc.
Little of interest was noticed about this spot, with the ex¬
ception of the unsatisfactory note on the 17th April, when it
apparently extended south of the South Equatorial Belt almost
opposite the preceding end of the Red Spot. Its rotation was
performed in a period of q'* 50™
SOUTH EaUATORlAL SPOTS.
93
Dark South Equatorial Spot XXVI.
Date.
G. M. T.
of
Transit.
Wt.
Long.
Description.
1887.
May 8
„ 10
13
15
June 9
14
16
„ 30
July 16
h. m.
II 58-5
977
13 18
102-8
10 S
ii 12
II 49'5
100* i
97-6
iiy'i
9 SI
1159
Rather large, rather dark, fairly well
defined. It had a dark train running
obliquely to the N. Equat. Belt. This
train was dark and well defined, and
for some distance was nearly as broad
and dark as the spot itself, thus ren¬
dering the exact time of transit not
quite so certain, it being difficult to say
exactly where the centre of the spot
was. In fig. 31, Plate VI., the spot is
drawn N. of the belt.
Pretty large, pretty dark, fairly well
defined. It seemed to extend to the
S. component of the belt, so as to be
roughly triangular with the base to the
south. A narrow dark train is shewn
in fig. 35, where there is also a slight
appearance of duplicity in the spotitself.
Small rather, nearly round, pretty well
defined. A great part of it was on the
S. Equat. Belt, only a somewhat small
part projecting N. A faint dark train
of the usual character extended ob¬
liquely to the N. Equat. Belt seen.
Small, not very dark, ill-defined and
generally very inconspicuous. A pretty
evident dark train extended obliquely
to the N. Equat. Belt. Fig. 37.
Moderately large, very well defined, ex¬
ceedingly dark, slightly oval in a direc¬
tion inclined 45° to that of the belts,
altogether a very definite and con¬
spicuous object. It was mostly situate
on the N. component of the S. Equat.
Belt.
A nearly round dark spot, principally
situate on the N. component of the S.
Equat. Belt. Plate VII., fig. 44. Time
by double transits.
In a drawing of this date an ill-defined
spot is shewn projecting N. of the belt
at the place of XXVI. with a dark
streak extending obliquely to the N.
Equat. Belt.
Seen on this night when about f" past
transit, and described as a not very
dark spot with a pretty dark and
distinct streak extending from it to the
N. Equat. Belt. Plate VIII., fig. 49.
Shewn in Mr. Denning's sketch in
'l'Astronomie,' 1887, 331, opposite the
/ end of the Red Spot with a dark
train extending n f from it.
94
ZENOGRAPHICAL FRAGMENTS.
The mean period of rotation of spot XXVI. was
9I1 36^-5, which shews a somewhat slower motion than the
rest of the markings in the same zenographical latitude. Besides
the unusually slow rate of its motion, the spot is interesting for
the magnitude of the changes of aspect which it underwent, and
for the rapidity with which such changes took place, as will be
seen from the descriptions given fully in the preceding table.
The observations of the 8th, loth, and 13th May are specially
interesting as shewing the course of the change from the appear¬
ance typical of class II. to that characteristic of class I. On
the first and last of these dates the spot had the aspect of
classes II. and I. respectively, whilst on May loth it was inter¬
mediate between the two.
White South Equatorial Spot XXVII.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
H. M.
0
April 8
14 42
I
126-3
Large, moderately bright, very ill-defined.
„ 24
14 9'5
4
120-6
Rather small, bright, pretty well defined.
extending rather far south, seeming to
be visible in the space between the two
component bands of the S. Equat.
Belt. It had a fainter light train ex¬
tending n f.
.. 29
12 12
3
120-8
Not very large, pretty well defined, bright.
seeming to extend very far south so as
to penetrate considerably into the belt.
Oval shaped in a sketch of this date.
June 14
10 IS
I
i30'S
Spot indefinite and not very bright. Part
of it was visible between the two com¬
ponent bands of the S. Equat. Belt.
Plate VIL, fig. 44.
,, 21
Shewn in fig. 47, Plate VIIL, and de¬
scribed as a pretty bright white equat.
spot. It was considerably past transit
when observed.
„ 30
ID 0
—
132-2
Very bright, well defined, eating well
into the S. Equat. Belt, and perhaps
visible also in the rift of the belt.
Fig. 49. An estimated transit, the
spot being about J*" past the C. M.
when observed.
This marking was observed for 83 days, during which it
performed 20Z rotations of the average duration of 9*^ 50™ 24®'i.
Like so many of its predecessors, the spot seems to afford
THE RED SPOT.
95
evidence as to the relative altitudes of the white and dark
markings in this region of the planet. The observation made
on the 14th June and the accompanying drawing (Fig. 44),
produce an irresistible impression that the white spot was at
a lower level than the dark belt, so that the latter appeared pro¬
jected upon the former.
(4) The Red Spot.
Although under favourable conditions the Red Spot was a
fairly conspicuous object in 1887 with an aperture of 6| inches,
yet the considerable southern declination of Jupiter, and his
consequently low altitude, even when on the meridian, proved a
great hindrance to the satisfactory observation of the details of
this remarkable feature. This was particularly the case in the
earlier part of the apparition, when the planet's meridian altitude
was several degrees less than it was later on. Enough, however,
was done to obtain a fairly satisfactory record of tbe physical
peculiarities and the motion of rotation of the marking. The
results of the season's operations naturally divide themselves
under two heads ; namely, the motion of rotation, and the
physical appearance of the object.
The Motion of Rotation of the Red Spot,
The following table contains all the observed transits of the
spot over the central meridian of the planet's disc obtained
during the apparition of 1886-7, and which have come to my
knowledge. The différent columns of the table explain them¬
selves sufficiently : the longitudes are of course those corre¬
sponding to system II. of Mr. Marth's ephemeris. Observers :
D.=Mr. W. F. Denning; W.=A. S. Williams.
Date.
G. M. T. of Transit.
Corresponding Long.
Obs.
Free.
End.
Wt.
Centre.
Wt.
Foil.
End.
Wt.
Free.
End.
Centre.
Foil.
End.
1886.
Nov. 23
Dec. 17
„ 20
H. M.
—
H. M.
19 34
19 25
16 49
I
H. M.
17 24
I
0
0
358-4
357-0
353"3
0
14-5
D.
W.
<}
Ol = /'i'
9^ ZENOORAPHICAL FRAGMENTS.
G. M. T. of Transit.
Corresponding Long.
Date.
Obs.
Free.
End.
Wt.
Centre.
Wt.
Foil.
End.
Wt.
Free.
End.
Centre.
Foil.
End.
CO
00
H. M.
H. M.
H. M.
0
0
0
Jan. I
—
16 50
I
—
—
—
356-4
W.
Feb. 26
—
13 6
I
13 35
2
—
357'I
14*6
t)
Mar. 20
—
II 14
—
—
—
357-6
)f
.. 27
—
II 56
12 22
I
—
355-8
11*5
i)
.1 29
—
—
13 25
I
—
—
—
350-4
—
» 0
April 3
12 II
I
12 38
2
13 6
2
3377
354-0
10*9
,< 0-3
)) ^
—
—
—
—
12 II
2
—
9*8
,. 10
—
—
13 II
I
—
—
—
346-8
—
0
.. 17
13 31
I
14 5
2
14 31
3
331 "S
352-3
80
0.- 3
J)
„ 20
II 4
I
II 33
3
12 I
3
334*1
3517
8-6
.. 24
14 I9'S
I
14 47'5
2
—
—
333'9
350-8
—
» .
„ 27
II 45
I
12 17
I
12 45
2
331*6
351-0
7'9
,1 I'M
>. 29
13 26
I
13 52
I
14 20
I
333*5
349-2
6'i
» 0-6
May 2
—
II 23-5
I
II 53
I
—
350-6
8-4
»
.. 7
—
10 31
—
—
—
—
350-6
—
D.
9
—
12 9
—
12 38
2
—
350-6
8"2
D.-W.
„ 10
—
8 2
—
—
—
—
351-7
—
D.
.. 14
10 48
I
II 17
3
IX 48
3
333'3
350-9
9*6
W. o-S'
„ 26
—
—
II II
—
—
—
—
351-0
—
D."
June 10
—
—
8 39
—
—
—
—
353-2
—
„ 12
—
—
—
—
ID 41
3
—
—
7*3
W.
„ 19
—
—
10 55
I
II 25
I
—
347-3
5*4
„ 22
—
—
8 40
—
—
—
—
356-3
—
D.
July 16
—
—
8 34
—
—
—
—
356-5
—
»
Aug. 2
7 43
357"5
M
It will be gathered from the above table that the individual
determinations of longitude occasionally differ considerably
amongst themselves, and this must he ascribed partly to the
general faintness of the spot, partly to the unfavourable posi¬
tion of Jupiter and the usually more or less confused state of
the definition resulting therefrom, and partly to the fact that
the preceding portion of the spot was fainter and less distinct
than the following part; so that in confused definition, at least,
there would he a tendency for the apparent centre of the spot
to shift itself towards the following end.
According to the observations, the motion of the spot must
have been slightly irregular. Thus the mean period of rotation
from observation between the end of November .n^86 and the
middle of May 1887 was 3^^'^ ! whilst from the com¬
mencement of May to the termination of the observations it
was as long as 9^ 55"" 44®'o. A stationary period, with respect
to the adopted zero meridian, àeems to have occurred for a
3 5 '3 o
^If-
XyxH % ^ o
. 6"' 5 :.- 3rv; 6'- S Sr-S Ts/
TH u
+ 4 0^*,',, •^"'7 37VÍ'V,7 S7.,rv/
'L
t-X
-í- 4 '
VI
-h ^
ti
^ 1, 8
/<»
- X O
-t í ^
_
_ / -3.
Illinois Alphci Chapter
OF THE
^FHI BETA KAFFA^ss^^
Northwestern University,
Evanston, June , 1891.
DEAR
You have been elected a member of the
0 Ii h Chapter of Northwestern University.
In order to complete your membership,
it is necessary that you signify your accept¬
ance now, and that you be present for in¬
itiation, at your earliest convenience, at
some annual meeting.
The annual meeting is held in Room 2,
University Hall, at 9 a. m. on Wednesday
preceding Commencement.
Secy.
THE RED SPOT.
97
time about the end of April and the early part of May.
It is curiouSj however^ that the maximum of the westerly
motion, with respect to the zero meridian, occurred near the
time of opposition of the planet, and this circumstance induces
the suspicion that the apparent irregularities in the motion
of the spot may have been fictitious, and perhaps dependent
in some way upon the different positions of the planet
before, at, and after opposition. It may be remarked that the
observations of the following end of the spot (the plainest
and most definite part of the object throughout the apparition)
likewise confirm, so far as they go, the variations in the motion
of the spot.
Making use only of the observations obtained near the
commencement and the termination of the series, the resulting
mean period of rotation of the Red Spot is 55" with
a probable error of + *049®; and this result has been adopted
as the mean period of rotation of the spot for the apparition of
1886-7. Somewhat curiously this determination is practically
identical with that found by Mr. Denning for the same period
probably the same observations were employed for the purpose
in either case.
The following list of the various determinations of the rotation
period of the Red Spot during the different apparitions of the
planet, was given by Mr. Denning in the 'Journal' of the
Liverpool Astronomical Society, vol. v., p. 64, with the exception
of the result for 1886-7 above mentioned.
Dates of Limiting Observations.
1879, July 10—1880, Feb. 7
1880, Sept. 27—1881, Mar. 17
1881, July 8—1882, Mar. 30
1882, July 29—1883, Mar. 4
1883, Aug. 23—1884, June 12
1884, Sept. 21—1885, July 8
1885, Oct. 24—1886, July 24
1886, Nov. 23—1887, Aug. 2
No.of
Rotations
• 512
• 413
. 640
. 674
. 710
. 700
• 659
. 609
Period.
H. M.
9 55
s.
34'2
Ï5 35'6
55 38-2
55 39'Ï
55 39" I
55 39"2
55 4I-I
55 40-5
The observations on which the period for 1879-80 was based,
were made by Professor Pritchett at the Morrison Observatory,
* See ' Journal ' of the Liv. Ast. Society, vol. vi., p. 5.
H
98
ZENOGRAPHICAL FRAGMENTS.
Glasgow, Missouri. The rest were made by Mr. Denning
himself at Bristol. It will be seen from the above list that the
long-continued retardation in the motion of the spot has at
length ceased, and a slight acceleration taken place.
From the observed times of transit of the preceding and
following ends, and the centre of the Red Spot respectively, an
estimate may be formed of the length of the object. Thus the
average time required in 1887 for a complete transit of the spot
past the central meridian of the disc of the planet was 57'°'4,
equal to 34-7 degrees of zenographical longitude. It is in¬
teresting to compare this with the mean result obtained by Mr.
Denning for the length of the spot from 252 observations made
by seven different observers in the years 1879—8a, namely
33°'7* = 55"'7* These results accord so closely that it is
evident that the length of the spot in 1887 was practically the
same as it was in 1879—8a.
The Physical Appearance of the Red Spot,
The preceding portion of the Red Spot throughout the obser¬
vations was rather markedly less conspicuous than the following
part. The ring-shaped form observed in previous oppositions
was also present in 1886-7, and on the following, and especially
the south following, edge the darker border had a very consider¬
able degree of intensity and definiteness. On the preceding
portion of the spot, however, at least as observed at Brighton,
the darker border was scarcely to be distinguished, it partici¬
pating here in the greater feebleness characterizing the whole
of this part of the marking. An interesting little detail
consisted in the continued visibility of a minute dark spot
exactly on the following tip of the Red Spot, a peculiarity which
has been very generally noticed in past years. A corresponding
spot has also been seen sometimes at the preceding extremity
of the marking, but nothing of the kind was noticed in 1887.
Perhaps, however, the most important partieulars in connec¬
tion with the Red Spot have reference to a remarkable dusky
streak, which was seen to connect the following end of the spot
with the conspicuous and sharply marked bend of the South
* ' Observatory,' 1885, p. 339.
THE RED SPOT.
99
Equatorial Belt immediately following. The details respecting
this feature are given fully in the notes on the appearance
of the spot, but it may be mentioned that this connecting
streak was not of long continuance. A feature of a similar
character was noticed by several observers in 1883-4 not
only at the following, but also at the preceding end of the spot.
A good drawing made by Mr. T. G. Elger at Bedford exhibiting
this curious feature will be found in the 'English Mechanic,'
vol. xxxix., p. 99. It has been somewhat strenuously insisted
that on no occasion has the Red Spot been in actual or visible
contact with any of the outlying markings, but the evidence
now in existence, accumulated by a numerous body of observers,
provided with reflectors ranging up to 18 inches and refractors
up to 23 inches in aperture, seems to be overwhelmingly
strong in favour of such contact, whether the same be only
apparent or otherwise.
As regards colour, the spot was described by Dr. Terby as
having lost its characteristic tint, but as observed here, a distinct
reddish or pinkish tinge was always apparent, except perhaps
when the atmospherical conditions were very unfavourable; so
that the marking did not altogether belie its name in 1887.
In the following pages all the notes made at Brighton
upon the physical appearance of the spot which seem likely
to prove of any interest or value are given. Such observa¬
tions made by others as have come to my knowledge, have
likewise been inserted in their proper chronological positions,
for the purpose of comparison, and to render the record more
complete. In these cases the names of the observers and
the instruments employed are included in brackets at the
end of the observations. The state of the definition has
generally been recorded according to a definite and uniform
scale, in which 10 indicates the finest possible definition, and i
the worst imaginable definition.
Physical Observations of the Red Spot,
1886, Dec. 20, lyii 24". The reddish tint of the spot could
be faintly discerned at times.
1887, Jan. I, löii 50™. Definition = 2. Spot fairly distinct,
at times its reddish tint was fairly apparent.
H 2
lOO
ZENOGRAPHICAL FRAGMENTS.
Feb. 26, 13'' 6™. Definition = 5. The spot was very faint,
and could only at times be distinctly made out. The f tip
seemed darker than the rest, and the spot was not uniform in
plainness. Its red colour was still faintly apparent. A con¬
siderable clear interval separated the southern margin from the
dark belt farther to the south.
13'' 35™- Def. = 5. A better view obtained of the spot,
and it was by no means a difficult object. The interior part
seemed to be a little paler than the rest.
Mar. 20, 12^ o™. Def. = 6. The Red Spot seen quite
plain and defined near the p limit. Its outline could be traced
with perfect distinctness, and on the south a narrow light space
separated it from the dusky belt on the south, at least from the
centre to the f end, the p half of the spot being too near the
limb to be clearly made out. The red colour of the marking
was apparent, and the /"tip was a little darker. The sf edge
also seemed to be a little darker than the rest.
Mar. 27, 11** 54". Def. = 2. Spot pretty clear at times, and
its reddish colour was evident. In best seeing it seemed quite
distinct from the belt on the south. Plate II., fig. 4.
20". Definition = 2. The spot was distinct and well
defined in the following part, but the detail of the /'tip could
not be distinctly made out owing to the disturbed definition. It
looked as if the shoulder of the South Equatorial Belt just
following were almost or quite connected with the tip of the
spot. Red colour of spot distinct.
Mar. 29,15^^ 25"". The Red Spot would not have been difficult
but for bad definition. It was fainter on the preceding than on
the following half. From the dark shoulder of the South Equa¬
torial Belt a narrow dark streak extended to the following end
of the spot, and was continued for some distance along the
i/"edge of the spot. (See fig. 5.) This feature was tolerably
eertain, though a satisfactory view of it could not be obtained.
A narrow lighter space separated the spot from the dark belt on
the south.
April 3, 12'' IT™. Definition pretty good. The spot was
visible in its entirety, but the preceding portion was the most
difficult part to see well. Altogether it was easy enough and
pretty uniform in tint up to the following end. The red colour
THE RED SPOT.
ICI
was plain. The p end was not pointed, but nearly rounded
off. Plate IV., fig. 2%.
13I1 5111. The drawing. Fig. 2%, was thought to represent
with fair accuracy the actual appearance of the object and its
surroundings. A narrow dark streak started from the dark
shoulder of the South Equatorial Belt, and eurved round slightly
so as to follow the edge of the Red Spot on its s f side, and then
gradually faded away. Unfortunately, owing to the generally
very confused state of the definition at this time, a really
satisfactory view of this interesting feature could never be
obtained.
April 8, 11^ 4a™. Def. = 3. Outline clear at times and
reddish colour distinct. Fig. 33.
12h iim_ Def. = 4. Outline distinct at times. A narrow
dark streak extended from the dark shoulder of the belt to the
f end of the spot, and a little way beyond along the s f edge.
The shoulder itself was intensely dark. A considerable lighter
interval separated the spot from faint dark markings on the
south. Fig. 23.
April 17, 14'' 5™. Definition pretty good at times. Spot
perfectly defined and the reddish tint apparent. It was nearly
uniform in intensity. The south margin was divided from dark
markings on the south by a considerable lighter interval.
14" 31"". Definition fair. The following end was very easy
and well defined, with the narrow dark streak starting from the
belt and curving round into the s f end of the spot quite
distinct.
April 30, 11'' 4™. Def. = 6. The preceding part of the
spot was not easily seen quite distinctly, although definition was
very fair indeed.
ii'^ 15'". "Dark belt seen on s. p. edge of N. polar
shading; also at the E. shoulder of the depression in S. equa¬
torial belt near middle of disc. Streak to red spot, which was
at limit of vision. Dark belt above red spot, then lighter region
and darker polar cap." [Mr. G. T. Davis at Theale, with
3I in. refractor.]
11'' 33°>. Def. = 7. The interior part of the spot near the
following end gave the impression of being a little lighter than
the rest at times.
loa
ZENOGRAPHICAL FRAGMENTS.
12,^ I™. Def. =6. The following half of the spot was
rather clearer than the preceding half, and was perfectly distinct,
the outline being quite sharp. The dark streak from the
shoulder of the belt could be seen extending to the y tip of the
spot, and from thence it followed the border of that marking a
little way round on the south, but it was not then a very
distinct feature, not so pronounced as it had been. The interior
near the following end was certainly a little lighter. The spot
was clearly separated from all dark markings on the south.
April 24, iq*" 19°'. Definition poor. It was difficult at this
time to see the preceding end well defined, but about 10™ earlier
it was seen with perfeet distinctness, and there was then a
very noticeable reddish tinge about the spot.
141» 47m. Red Spot central. Notwithstanding the low alti¬
tude and consequently disturbed definition, the spot was quite
distinct at times and well seen in outline. There was a distinct
light space between the S. side of the spot and dark markings
on the south. The narrow dark line running from the shoulder
of the belt to the f end of the spot was well seen on one
occasion.
April 27. " The red spot appeared to me to be more circular
in shape than last year, and its f end was joined to a dusky belt,
which curved away into the equatorial belt ; the 'hollow' in this
was very conspicuous and very dark, while the light central
region of the spot was almost white. There appeared to be a
very faint belt remaining parallel with and just south of the
great equatorial belt, and this apparently joined the spot at the
p end, but definition was not steady enough to be certain of the
more delicate detail. The/> side of the 'hollow' is quite gone,
and I did not see the little dark speck that was so plain last year
at the / extremity of the red spot." [This observation was
made by Mr. K. J. Tarrant with a power of 250 on a lOç in.
reflector, and it confirms in a satisfactory manner the existence
of the dark streak connecting the following end of the Red Spot
with the South Equatorial Belt.J
J 2h 17m. Red Spot central. Definition very confused,
= 2-3. The spot was free from any dark markings on the
south, and was rather more easily seen on the f than on the p
part. There was a faint reddish colour about it.
THE RED SPOT.
12^45™. Def. =3. The spot was very distinct and easy
in best definition, and had a rather strong reddish tint. The
outline was distinct, and on the S. quite free from any markings.
The dark streak connecting the f tip of the spot with the belt
seemed much the same as it had been lately.
April 29, 13'' 52". Definition generally very confused.
Spot plain and well defined, with a distinct reddish colour.
14"^ 20"°. Definition very bad and confused, notwithstanding
which the spot was pretty distinct at times, and its reddish
colour was readily noticeable. As far as could be ascertained, the
narrow dark streak connecting the f end with the belt was the
same as it had been recently.
May 2, 11'' 23™. Red Spot central. Definition fair. It
was pretty distinct and plainer on the following than on the
preceding half. Reddish colour evident. Outline easy to see
defined except near the preceding end. The narrow dark streak
joining the /"end to the belt still visible, but it was not so plain
as it had been. The spot was perfectly free on the south from
any dusky streaks or other markings, being separated therefrom
by a considerable lighter interval.
11'' 53°>. An unsatisfactory glimpse obtained through dense
mist. The dark streak from the shoulder of the belt to the f
end of the spot was more pronounced than in the last observa¬
tion.
May 7, lo"! 31°'. The Red Spot seen central by Mr.
Denning at Bristol with 105 in. reflector, when its following end
appeared perfectly free from belts.
May 9, 12'» 38™. Def. =4. The /end of the spot was on
the C. M. The spot was darker and more distinctly and easily
visible than it had hitherto been in this apparition. It was very
distinct. No mention is made of the dark streak joining the J
end to the belt, and no trace of it appears in fig. 12, Plate III.
May 10. " Hier soir, 10 Mai, à j'ai observé la tache
rouge de Jupiter avec le grossissement de 280 fois de mon
equatorial de Grubb ; la tache a perdu sa teinte caractéristique
et apparait comme un nuage ovale blanc, limité par une bordure
grise elliptique ; cette bordure est moins marquée a l'ouest.
L'extrémité orientale de la tache a passé an méridien central
vers 9'^, t. m. de Bruxelles. Le ciel légèrement nebuleux a
ZENOGRAPHICAL FRAGMENTS.
empêché d'utiliser toute la puissance du réfracteur, mais l'image
offrait néanmoins une grande richesse de détails très délicats."
[Observation of Dr. F. Terby at Louvain, with an 8^ in.
refractor.]
May 14, lo'* 48"^. Def. = 5-6. The p end (at this time
central) was difficult to see nicely defined.
j;ih jym £)gf_ _ Spot vcry nicely defined and per¬
fectly easy, with a fairly pronounced reddish colour. It was
quite distinct from any dark markings on the S., though these
approached rather near to it a little preceding the centre of the
spot. Plate III., fig. 13.
ii''48'". Following end central. Def. = 5. This end of
the spot was very clearly defined. At the following tip was a
small dark spot, and the s f border was delicately edged by a
narrow dark line. No connection, however, could be seen for
certain between the end of the spot and the South Equatorial
Belt, though the bend of the latter terminated rather sharply.
The faint dark band south of the S. Equat. Belt was distinctly
visible, though it was a somewhat delicate feature. It appeared
to start from the/^ end of the Red Spot, at least no space could
be seen between the two objects, though it was separated from the
South Equatorial Belt by a narrow lighter interval. See fig. 13.
June 10, 10'' 4™. Red Spot visible very plainly near p limb.
Its reddish colour was obvious. Plate VIL, fig. 41.
June 12, io'>4i™. Following end central. Def. = 5. The
^ half of the spot was visible with perfect distinctness, thejS half
not being quite so clear, though the outline could be traced
sharply all round. The reddish, or pinkish, colour was very
obvious. The spot was nearly uniform in intensity, but increased
imperceptibly in density from the p end. The s f border was
edged by a darker band. The f end usually looked as if joined
to the shoulder of the South Equatorial Belt, but in best defini¬
tion a clear interval could be seen between, though the shoulder
itself is drawn sharply pointed in Plate VIL, fig. 42.
June 19, 10'' 55™. Def. = 5, but generally confused. The
f part of the spot was dark, plain, and well defined, but the p
end was faint and difficult to see in confused definition. The
spot seemed surrounded nearly completely by a white aureole..
Fig. 46.
SOUTHERN SPOTS.
June 22, 9'* lo"^. The little dark spot on the f tip seen hy
Mr. Denning at Bristol with 10^ in. reflector. See drawing by
this observer in L.A.S. ' Journal/ vi., 10.
June 39, 9^ 15". "Red spot appeared very distinct as a
long ovalj no apparent joining to S. equatorial belt^ and doubtful
whether touching lighter belt S. of the red spot." [Mr. G. T.
DaviS; with 3I in. refractor.J
July 16, S"* 30". See drawing by Mr. Denning in
' PAstronomie/ 1887, p. 331.
(5) The Southern White and Dark Spots.
The markings now about to be considered were situated in the
region south of the South Equatorial Belt^ and nearly in the
latitude of the southern portion of the Red Spot; but it is pro¬
posed that the term "southern spots" should include all
markings south of the great equatorial system of belts, as the
different groups or streams of markings seem only in a state of
partial development in this region of the planet. Properly
speaking, the Red Spot itself should be included in this sub¬
division, but on account of its importance this object has been
considered by itself, and moreover its different rate of motion
shews it to have had no connection with the other markings
south of the equatorial belts. Only three of these southern
spots were followed for any length of time in 1887. One of
them was a white spot of great brilliancy and definiteness of
outline ; the other two were small, dark, nearly round objects
with considerable resemblance to the shadows of the satellites.
Other markings were of course seen, but being delicate, the
generally confused state of the definition prevented their being
kept in view. The mean period of rotation of the southern
spots was 9*^ 55™ 17®'I, and this period, which accords closely with
former determinations of this element from objects situated in
nearly the same south latitude, indicates a motion somewhat
swifter than that of the Red Spot.
Io6 ZENOGRAPHICAL FRAGMENTS.
White Southern Spot a.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
00
CO
H. M.
0
April 17
II 3
3
242-3
Very white, a little oval, with the major
axis lying a little obliquely to the
direction of the belts. It was situate on
the first dark belt S. of the equatorial
bands, apparently severing that belt.
19
12 40
3
241-8
Rather small, pretty bright, fairly well
defined, a tolerably conspicuous object.
Sometimes it looked as if a bright
streak extended N. from it to the S.
Equat. Belt, but this was not certain.
The spot was oval, and in a sketch
of this date is drawn severing the belt.
» 24
II 4i'5
3
238-4
Pretty large, well defined, very brilliant, a
very conspicuous object, which was
thought to be larger than when pre¬
viously observed. It was actually on
the S. side of the narrow dark belt, but
it seemed to force this belt a little
northwards, as shewn in fig. 28, Plate V.
Sometimes it appeared actually to
divide the belt, but in best seeing it
looked as drawn. The space between
it and the S. Equat. Belt was rather
lighter than the rest, which increased
the deceptive appearance of the spot
cutting through the belt.
„ 26
13 22
i
2399
Unsatisfactory obs. owing to confused
definition. The spot still had a light
trail extending northwards to the S.
Equat. Belt.
May 8
12 58-5
2
230-2
Rather small, a little oval, very well
defined, extremely white. It was situate
on the S. side of the belt, the region
N. of the belt being also lighter and
whiter than the average. In best de¬
finition the spot was a very well defined
and conspicuous object. Plate VI.,
fig- 32.
.. 13
12 2
3
227-8
Not large, slightly oval, very white, very
well defined ; a lighter patch also ex¬
tended N. from it to the S. Equat.
Belt. The spot did not quite divide
the belt, but the latter could be seen
faintly on the N. edge of the former.
Fig- 36-
„ 20
12 40
2
223-0
Pretty small, regularly oval, well defined.
bright. It had a bright patch also on the
N. side of the belt. Plate VIL, fig. 40.
June 18
II 22
i
213-5
The spot seemed much the same as when
last observed, and had the usual bright
streak between it and the S. Equat.
Belt. Once or twice the spot seemed
well defined and bright, but definition
was very confused.
SOUTHERN SPOTS.
The mean period of rotation of this spot was 9'' 55*"
In appearance it was of a conspicuous and definite character,
more so in fact than is generally the case with objects in the
same latitude. The two observations of the 17th and 19th May
would seem on a hasty consideration to indicate that the white
spot was situate above the belt, so that it concealed part of the
belt from view, but the evidence is not conclusive on this
point, because in later observations, made under more favour¬
able conditions, the belt was seen feebly bounding the northern
side of the white spot. Thus seen, the marking somewhat
recalls a curious bright partial break in a belt in the same latitude
observed by Mr. J. Gledhill in the year 1870,* differing chiefly
from it in having the portion of the belt bounding the northern,
instead of the southern, side of the white patch. The white
train extending northwards to the South Equatorial Belt
observed in connection with the present object is rather an
interesting feature. In the preceding table, and also in the two
following ones, the longitudes are expressed of course according
to ' system 11.^ of the ephemeris.
Dark Southern Spot ß.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1
00
00
h. m.
0
April 17
ii 23
2
254'4
Very small, moderately dark, pretty well
defined, immediately / spot o.
19
12 57
1
252'i
Spot small and dilficult. Weather un¬
favourable.
24
12 5
3
252-6
Small, very dark, well defined. In shape
it appeared a little triangular with the
base to the E., and it sometimes then
looked as if it consisted of a larger
spot with a smaller one to the W., and
sometimes as if it were a single spot
with a small lighter interior. Plate V.,
fig. 28.
.. 29
11 6-5
249-2
Small, dark, well defined, nearly round,
like the shadow of a satellite. In
diameter it was thought not to exceed
ij". Time by double transits.
May 8
13 18-5
2
242-3
Small, nearly round, dark, well defined.
Plate VI., fig. 32.
13
12 17
2
236-8
Dark and well defined, but very small.
Fig. 36.
* See ' Astronomical Register,' vol. viii., p. 209.
io8
ZENOGRAPHICAL FRAGMENTS.
A small and rather inconspicuous dark spot^ situate on the
narrow dark helt just south of the equatorial bands, and imme¬
diately following the preceding spot a. Owing to its insignifi¬
cant character, the observations were not numerous, nor was
the object kept in view for any great length of time, and in
consequence the rotation period of 9I1 55™ 11®*8 indicated by
observation is not a satisfactory determination.
Dark Southern Spot 7.
G. M. T.
Date.
of
Wt.
Long.
Description.
Transit.
1887.
h. m.
0
April 17
—
—
—
Seen and shewn in a sketch of this date
as a similar object to ß.
24
12 41-5
3
274-6
Small, very dark, well defined. Plate V.,
fig. 28.
.. 29
IÏ 44'S
3
272-1
Very small, nearly round, not very dark,
pretty well defined, by no means a
conspicuous object.
May 28
10 12
—
2SS'9 ]
Small, not very dark, pretty well defined.
„ 28
10 16
258-3 )
Plate III., fig. 14. Times by double
transits and estimated transit re¬
spectively.
An insignificant object, the rotation of which was performed
in a period of q'' 55"" 17^*8. It should he mentioned that the
relative positions of the three southern spots in fig. 28, Plate V.,
are altogether wrong.
(6) Miscellaneous Observations.
In addition to the observations recorded in the preceding
pages, a few isolated transits of different markings were
observed, and are given in the following table. As only
single observations were obtained, there is of course no possi¬
bility of determining even roughly the periods of rotation of
these objects, though they may generally he inferred by
analogy. This is especially to he regretted in the case of the
large dusky spot observed on the 2¡th April in latitude 45° S.,
since it is comparatively rare to find objects of such magnitude
and definiteness in these higher latitudes. Many eiforts were
made to re-observe this spot, but without success. In the
following table the longitudes of equatorial spots are expressed
according to " system I." and those of extra-equatorial markings
according to "system II." of Mr. Marth's ephemeris.
MISCELLANEOUS OBSERVATIONS.
109
Miscellaneous Observations of Spots.
Date.
G. M. T.
of
Transit.
Wt.
Long
1887.
Feb. 26
h. m.
IS 49
2
0
i54'o
Mar. 6
16 17
3
235'4
April 8
12 2
?
287
8
12 33
1
47-6
2S
12 i6
4
49-6
30
n 32
4
25 47
May 28
10 52
i
280" i
June 14
id 40
3
307-2
.. 17
10 24
i
250-6
Description.
A dark north equatorial streak on the S.
side of the N. Equat. Belt. Not very
large, nor very dark.
North Temperate white spot. Pretty
large, moderately bright, not well de¬
fined.
A dark N. equatorial spot. Feeble and
undefined. Plate IV., fig. 23.
A feeble dark N. equatorial spot. Plate
IV., fig. 23.
A pretty large, moderately dark, not
extremely well defined spot, situate in
about lat. 45° S. The spot was rather
more diffuse on the S. Plate V., fig. 30.
A dark N. equatorial spot. Small, dark,
well defined, with a faint dusky streak
s p. Plate III., fig. II.
A small dark southern spot, similar to y
and in the same lat. Small, not very
dark, not well defined. Plate III.,
fig. 14.
A dark N. Temperate spot. Small, faint,
inconspicuous, projecting a little N. of
the belt. About it faint traces could
be seen of the white spot N, occupying
nearly the same position. Plate Vll.,
fig- 44- . ,
A small, faint, ill-defined, white S. equat.
spot. Plate IV., fig. 19.
Notes relating to the Belts ; their Colours, etc.
1887, Feb. 26, 13'' 35™. Both components of the S. Equat.
Belt following the Red Spot were broad^ not very dark, of a
pronounced red colour. The two components of the N. Equat.
Belt were somewhat narrower than the southern ones, and were
also of a red colour—a kind of dull brick-red.
Mar. 24, 12" 8™. The South Equatorial Belt was rather
peculiar. The p half of the southern component was extremely
dark and broad, but just west of the central meridian it
faded off considerably both in darkness and width. The north
component also seemed here a little less dense and broad, so as
to leave a whitish elongated patch between the two component
bands. The point where the fading off took place was sharply
defined, and its transit was estimated to have occurred at
no
ZENOGRAPHICAL FRAGMENTS.
11'* 58"", SO that its longitude would be about 265°. On no
subsequent occasion was the fading off of a sufficiently definite
character for its transit to be observed.
April 3, ii'' 32™*5. The south component of the S. Equat.
Belt at this time was very faintly visible.
12'' 6". The southern component was seen to stop just p
the p end of the Red Spot. It was also thought to bend
northwards to join the northern component, but this was not
certain. Plate IV., figs. 21 and 22.
April 24, 12'* 5™. Definition being good, the positions of
the more conspicuous of the fainter belts were delineated as in
Plate v., fig. 28. Belt 6 was dark and well defined; 7 not so
dark, but broader; Belt 3 was closely double; north of it was
a feeble band ; and north of this extended the north polar cap,
itself evidently a series of streaks.
i/
April 30, ii'* 34™. Fig. 50, Plate VIII., shews the arrange¬
ment of the belts. Belt 2 narrow and delicate ; 3 a delicate
double belt ; N. Equat. Belt composed of two dark bands of
about equal intensity and of a reddish colour; S. component of
S. Equat. Belt not quite so conspicuous as the N. one. Both
components reddish ; just S. of the S. Equat. Belt was a feeble
dark band of about uniform intensity and breadth extending up
to the f end of the Red Spot ; 6 fairly broad and conspicuous ;
7 narrow and delicate. Between 3 and the North Equatorial
Belt was a rather bright zone. Definition fair, = 5.
May 13, II*" 20™. N. Equatorial Belt brownish in colour,
both components alike ; S. Equat. Belt reddish, also both
components alike ; Belt 6 seemed at times to have a slightly
warm tinge. It was double in part. Belt 3 was also double.
May 14, loii 48™. The south component of the S. Equat.
Belt was visible faintly though with perfect distinctness just up to
the p end of the Red Spot, but the bend northwards to the north
component observed in former years could not certainly be seen.
June 9, 11'' 49™. The N. component of the S. Equat. Belt
was not uniform either in width or intensity ; the S. component
was here faint and inconspicuous, though distinctly visible.
June 17, 11'' 16™- The light rift between the two component
bands of the South Equatorial Belt was distinctly visible, nearly
all along.
( I" )
SECTION V.
Summary of Rotation Periods ; Mean Motion of
Matter in different Zenographical Latitudes in 1887.
North Temperate Spots.
Mean Period
Spot. of Rotation.
h. m. s.
White Spot A .
9 55 347
Dark ,,
B .
9 55 40-4
White „
C .
9 55 32-6
Dark ,,
D .
9 55 377
White „
D2 .
9 55 34" I
Dark
E
9 55 27 3
White „
F .
9 55 30-0
Dark ,,
G .
9 55 26-0
White „
H .
9 55 26-8
Dark
HL
9 55 407
White „
K .
9 55 38'6
Dark „
K2 .
9 55 39'4
White „
L .
9 55 38-5
Dark „
M .
9 55 43" I
White „
N .
9 55 46-0
Dark ,,
0 .
9 55 44'o
White ,,
P .
9 55 40-4
North Equatorial
Spots.
h. m. s.
Dark Spot
i
9 50 i6'6
D D
2
9 50 33'3
)» }>
3 •
9 51 187
)f '>
4 •
9 50 44'9
)» >J
5 ■
9 50 26 8
South Equatorial Spots.
Mean Period
Spot. of Rotation.
h. m. s.
Dark Spot
1.
. . 9 50 22-3
White „
IL
. . 9 50 20'4
Dark „
III.
. . 9 SO 217
White „
IV.
. . 9 50 17-4
Dark „
V.
■ • 9 50 9*5
White „
VI.
. . 9 so I2"0
Dark ,,
VIL
• • 9 50 197
Dark ,,
VIH.
?
White ,,
IX.
. . 9 SO 24-9
Dark ,,
X.
. . 9 SO i9'2
White „
XL
• ■ 9 50 iSà*
Dark
XII.
. . 9 so 19 *
White „
XV.
. . 9 SO 21-9
Dark ,,
XVI.
. . 9 SO 24-0
White „
XVII.
• . 9 50 2S-4
Dark „
XVIII.
. . 9 50 197
White „
XIX.
. . 9 so 18 *
Dark „
XX.
• ■ 9 50 24-3
White „
XXL
. . 9 SO 2S'2
Dark ,,
XXIl.
. . 9 SO 27-2
White „
XXIII.
. . 9 so 2&6
Dark ,,
XXIV.
. . 9 50 187
White ,,
XXV.
. . 9 50 2g-7
Dark „
XXVI.
• • 9 50 36-S
White „
XXVII.
. . 9 SO 24T
Southern
Spots.
h. m. s.
Red Spot .
■ • 9 55 40-5
White Spot
«
. . 9 55 21-6
Dark „
ß . .
■ ■ 9 55 ii"8
7 • •
■ • 9 55 I7'8
Mean Period of Rotation of Matter (from 17 North! ,,
Temperate Spots) in Latitude j '""9 55 30 49'
Mean Period of Rotation of Matter (from S North ) *t
Equatorial Spots) in Latitude \ • — 9 50 4° 00.
Mean Period of Rotation of Matter (from 21 South ! o o
Equatorial Spots) in Latitude 3 0 b. —9 50 22 4.
Mean Period of Rotation of Matter (from q Southern ) „
Spots) in Latitude J 30 S. =9 55 lyi.
* Spots thus marked have been rejected in ascertaining the mean motion of
matter in about latitude 8° S., their periods of rotation not being known with
sufficient accuracy.
( 112 )
SECTION VI.
On the Relative Altitudes of different Jovian
Markings.
The subject of the relative altitudes of different Jovian
markings in the atmosphere of that planet is a very important
one, but one nevertheless about which it is, unfortunately,
difficult to obtain decisive evidence of any kind. This difficulty
arises principally from the circumstance that most of the
observations that have from time to time been brought forward
in support of any particular theory are vitiated by being capable
of a double interpretation. The whole subject is a comprehen¬
sive one, requiring a great deal of consideration, and more
exact and numerous observations are necessary before it will be
practicable to thoroughly investigate the matter in a satisfactory
manner. In the course of the last ten years, however, I have
observed various circumstances which would seem to shew that
the commonly received opinion, that the dark markings are
situate at a lower level than the light ones, is untenable, at least
for some regions of the planet, and speaking generally; and
that in reality the contrary is the case.
In the present series of observations, a number of
peculiarities were noticed bearing upon the subject in question.
Most of them consist in the visibility of the white equatorial
spots in the light rift separating the two component bands of
the double South Equatorial Belt, and it seems extremely
difficult to account for them upon any other hypothesis than
that the dark belt was situate at a higher level in the atmo¬
sphere of the planet than the white spots, so that it appeared
projected upon, and concealed from view portions of the latter
objects, though when these extended sufficiently far to the
south, they again became visible in the comparatively clear rift
of the belt. Many instances of the phenomenon above
indicated will be found in the various drawings reproduced in
the plates at the end of this volume. Spot XXVII. as
ALTITUDES OF JOVIAN MARKINGS.
"3
shewn in fig. 44 may be specified as a good example. We have
here an oval-shaped white spot traversed almost centrally by the
northern component of the South Equatorial Belt, and it seems
impossible to avoid the conclusion that the belt was really
uppermost. Spot IV. as seen on the 13th May (fig. 36) is
another good instance. It will be seen from Plate I., that
most of the white south equatorial spots have, at one time or
other of their existence, been visible in the rift of the belt.
That they were not always so seen must of course be ascribed
to the frequent and extensive alterations in magnitude and
brightness undergone by the markings in question.
Two principal objections may be urged against this
evidence in favour of the hypothesis just indicated ; firstly, that
in many cases the white spots appeared to eat or penetrate into
the belt, which might be construed to mean that the former
overlapped to a small extent the latter feature ; and, secondly,
that the white patches in the rift opposite to the spots were
generally broader than the rift itself, and therefore that a
similar overlapping of the belt by the white spots might be
indicated. Both these appearances, however, are capable of
a satisfactory explanation on other grounds. The peculiarities
in question must be largely due to apparent projection caused
by the well known phenomenon of irradiation, which would
cause the white spots to appear larger than they actually are,
so as to seemingly encroach upon the adjacent dark belt.
There is also another circumstance which would considerably
intensify this appearance of encroachment. The edges of the
belt, it must be observed, are not sharply defined, but have
numerous small irregularities, and the belt does not come up to
its full intensity, or depth of tint, at once, but the edges are
clearly of less density than the middle portions. Hence bright
objects, such as the white spots, would necessarily, if situated
beneath the belt, be traced to some extent through the less
dense outer edges of that feature, and would thus appear to
encroach upon or indent the same. This peculiarity in con¬
junction with irradiation seems quite capable of affording a
satisfactory explanation of all the observed appearances in
connection with the encroachment upon the dark belt by the
white equatorial spots.
I
114
ZENOGRAPHICAL FRAGMENTS.
Like considerations apply of course to the similar appear¬
ances sometimes presented by the white north temperate spots
and the adjacent North Equatorial Belt. Several good instances
occur in the different drawings, and fig. 43, Plate VII., may
be referred to as a rather good example, as here again is a
white spot traversed almost centrally by a dark belt. One of
the neatest and most striking cases I have noticed is depicted
in fig. 51, Plate VIII., and was observed on the 9th December
1882. Here there was a nearly circular, definite, pretty bright,
white spot, cut almost exactly into two equal portions by one
of the narrow dark bands at that time composing the North
Equatorial Belt. This example is particularly valuable and in¬
structive, because in tbis case the dark band was so narrow as
to bear but a small proportion to the breadth of the spot, so
that the latter remained visible almost in its entirety, and its
sbape was scarcely affected by being partly concealed behind
the belt. A similar observation was made on the aßrd December
1882, at 9'' 59", but in this case the spot was large, very bright,
and well defined, so that the peculiarity in question was still
more striking.
Sometimes the dark streaks so frequently seen extending
from one of the equatorial belts to the other, across the Equa¬
torial Zone, are capable of throwing light upon this obscure
subject of the relative heights of Jovian markings. Thus, in
fig. 14, Plate III., a bright extension of the white spot XV. is
shewn reaching the North Equatorial Belt. A dark train from
the dark spot XII. to the same belt was seen extending right
across this bright extension, and remained to all appearance
completely unaffected thereby. Here then it seems imperative
to conclude that the dark train was at a higher level than the
bright extension, so as to appear projected upon it.
Further, on the 14th June, a small dark spot on the northern
component of the North Equatorial Belt was seen projecting
northwards in such a manner as, to all appearance, to partially
conceal the white spot N. (See fig. 44, Plate VH.) The two
spots F and H more than once gave the impression of really
forming one long white spot, divided almost into two by the
projecting and overlying dark spot G. The usually very brilliant
white spot IX. on the 2Qth March was invisible, or at least so
ALTITUDES OF JOVIAN MARKINGS. II5
inconspicuous as to have escaped notice, whilst a dark extension
from the neighbouring dark spot X. occupied its place, and if it
was at a higher altitude must have concealed it, in great measure
at least, from view (fig. 3, Plate IL). Again in fig. 40, Plate VIL,
the white spot IV. is partially concealed hy a dark streak pro¬
ceeding from the adjoining dark spot V. These observations
are of course hy no means conclusive in themselves, but they
all tend to the same conclusion.
These, and other reasons, which it is unnecessary to set
forth here, constrain us to believe that, in the equatorial regions
of the planet at least, the dark markings are found floating
in the atmosphere at a higher level than the light ones,
though it is of course not impossible that the contrary may not
occasionally happen, and that the dark markings may not some¬
times extend down to the surface of the planet, or at any rate
below the level of the white spots. Since the dark south
equatorial spots are, for evident reasons, certainly situated at a
higher level than the dark belts, on which they often appear to
be projected, the following would be the probable order of suc¬
cession in altitude. First, and lowest, the white equatorial and
north temperate spots ; second, the dark equatorial belts ;
third, and highest, the dark south equatorial spots and dark
north temperate spots. As to the altitude of the dark north
equatorial spots, we have nothing definite at present to
guide us.
( ii6 )
SECTION VIL
On the Repellent Influence apparently exerted by
the Red Spot.
There is nothing new in the supposition of a repelling force
exerted by the Red Spot upon matter in its immediate vicinity,
but, so far at least as I am aware, no observations tending
directly to establish the existence of any such power have been
hitherto described, it having been inferred chiefly from the
presence of the remarkable bay in the South Equatorial Belt
immediately opposite the spot. In the course of the operations
of 1887, however, some observations were obtained which would
seem to go far towards confirming the reality of this
phenomenon. These observations relate to the behaviour of the
dark equatorial spot XII. in the course of its passage past the
Red Spot, by reason of the greater rapidity of its motion in a
westerly direction, and are as follow :—
On the 9th May, the dark spot XII. was situate just
following the Red Spot, and, as will be seen by reference to
fig. i a, Plate III., it then had the appearance of a large and well-
developed double spot, one component being situated on the
northern band of the double South Equatorial Belt, projecting
also considerably north of the same, and the other component
lying upon the southern band of the belt, and also covering the
light rift between the two bands. Now it will appear evident from
the drawing, that should the dark spot continue to sweep on
unchanged in a straight line from right to left, or east to west, a
portion of the most southern component of the double spot
must inevitably do one of three things ; namely—(i) partially
occult the Red Spot; (2) be partially occulted by this feature;
or (3) come into collision with it. There consequently seemed
to be here a grand opportunity for obtaining some definite
information upon the subject of the relative altitudes of the
Red and dark spots, and it was with much eagerness that I
waited for an opportunity of re-examining this part of the planet
REPELLING POWER OF RED SPOT.
117
when it should again be favourably placed for. observation.
The weather at first proved unfavourable, but the I4tb May
fortunately turned out fine, accompanied too by very fair defini¬
tion. What the appearances and relative positions of the Red
and dark spots were at this time can be best gathered from fig.
13, where it will be seen that the latter object bad moved almost
to the preceding end of the Red Spot, and that whilst the most
preceding component of the double spot remained almost
unaltered, the southern component had apparently been forced
northwards, so as almost directly to follow what formerly was
the northern component. It would seem then, from these
observations, that the same influence, presumably to be attri¬
buted to the Red Spot, which has apparently forced the southern¬
most band of the double South Equatorial Belt to bend abruptly
northwards, so as to mingle with the northernmost band of the
same belt, thus producing the singular deep hollow in the belt
opposite the Red Spot, has likewise affected this dark equa¬
torial spot, so that what was formerly the more southern of its
two components has been also forced northwards, as well as
pressed closer to the northern component, as appears from the
somewhat greater difficulty experienced on the 14th May in
detecting the duplicity of the object. Although therefore the
observations failed to tbrow any light upon the somewhat vexed
question of the altitude of the Red Spot in the atmosphere of
the planet compared with other objects, yet they have furnished
results scarcely less interesting in another direction, by demon¬
strating the great probability of the existence of a real repulsive
influence exercised upon neighbouring objects by this remark¬
able formation.
In connection with this subject, it is interesting to recall
that in the early years of its existence, the spot was sometimes
seen surrounded by a bright aureola, as it was indeed on the
19th June 1887, and though this has been ascribed to con¬
trast, there seems actually no valid reason for doubting the
objective character of the appearance, and it is perhaps per¬
missible to infer that this aureola may have indicated the extent
of the repulsive action in question.
That all neighbouring objects have not been influenced by
this repelling power seems certain from the fact that, besides
Il8 ZENOGRAPHICAL FRAGMENTS.
the dark streaks seen joining the p and ^ ends to the South
Equatorial ßelt^ dusky markings have been observed in apparent
contact with the southern portion of the spot. There was
indeed one observation in 1887 which indicates, perhaps, the
same thing. Thus on the 17th April, the white spot XXV.
was almost opposite the preceding end of the Red Spot, and was
thought to extend south of the South Equatorial Belt, and if so,
it must have been nearly, if not quite, in contact with the
former object. This observation, however, was very uncertain
owing to the confused state of the definition, and the object,
like the dusky markings on the south, may very likely have
been at a considerably different altitude than the Red Spot,
so as in this way to escape being affected by its repelling
influence.
It must not be overlooked that the alterations in the
appearance of spot XII. above narrated may have been caused
by real changes in it, but as none of the other double spots ever
underwent similar alterations, this does not appear to be likely.
It is also possible that in place of a repelling power, the Red
Spot may be surrounded by an outer, and usually invisible,
envelope composed of some material substance, and which
would be capable of producing the observed appearances. There
is at any rate nothing in the published observations adverse to
such a solution of the question.
London: Mitchell and Hughes, Printers, 140 Wardour Street, W.
Jupiter, i887.
plate ii.
X. XI. XII. XV. XVI.
'«»wiasnçipïÂ-
F
e
Fig. 1. Mar. 6.
Fig. 2. Mar. 18.
X. XI. XII. XV. XVI.
3 4
3 4
Fig. 3. Mar. 20.
Fig. 4. Mar. 27.
X. XI. XII. XVII. xvm. XIX,
3
Fig. 5. Mar. 29.
Fig. 6. April 10.
X. XI. XII. XV. xvi. XVII. xvm. xxi.
3 . "
■-• ."in'.j ;'.' ■•.■ • ■ " ' ' -c
..•, ^■"■•.•. :. \'.,,ui>i«.rr.-.'r V:—. ..■ .
h ' '
Fig. 7.
April 34.
JUPITER, 1887.
PLATE III.
Pig. 10. April 27.
Pig. 11. April 30.
A.S.W,
Pig. 14. May 28.
Pig. 15. June 1.
Pig. 8. April 16.
Pig. 12. May 9.
Pig. 9. April 25.
Pig. 13. May 14.
JUPITER, 1887.
PLATE IV.
TI. VII. Till. IX.
Fig. 16. June 3.
VII.VIII. IX. X.
immmm.
Fig. 17. June 10.
IX. X.
XTI.
TU. Till. IX. X.
Fig. 18. June 15.
XXI. XXIII.
A 13-0
Fig. 19. June 17.
ï' © H
Fig. 20. Mar. 23.
Fig. 21. April 3.
AS-Vy. pjg 22. April 3.
Fig. 23. April 8.
JUPITER, 1887.
PLATE V.
y. VI. VII.
V. VI. VII.
•■•••' "•
Fig. 24. April 14.
m F
Fig. 25. April 16.
XT. XTI.
ŒÛSî
V. TI. TU.
Fig. 26. April 19.
- '■■ D-./jLsir:.
Fig. 27. April 20.
Limb.
T. TI.
■ ■ xxiy.
Fig. 29. April 25.
... -
Limb.
Fig. 28. April 24.
Fig. 30. April 25.
JUPITER, 1887. PLATE VI.
Fig. 33. May 9.
Fig. 34. May 10.
Fig. 35. May 10.
Fig. 36. May 13.
Fig. 37. May 15.
Fig. 38. May 15.
Fig. 33. May 8.
Fig. 31. May 8.
JUPITER, 1887.
PLATE VII.
"ría:?"
II. m.
IV. V. yi, yji.
;-î 7; TE , •■ -; T
K2 2
Fig. 39. May 18.
Fig. 40. May 20.
' rv*C^# " '
■' ' ' ^
Fig. 41. June 10.
Fig. 42. June 12.
XVI. XVII.
XXVI. XXVII. I. II. III.
-■•-,■ ------ ■;• -' r^iaf^.-' -■ "^l£
",- .'i " ;.' --'T^^-- • - •' "^
j... H H3
..\0: '■-, ';:;:-v7:7ft:-;f
'-=■ .;-"■ ■ ■7.. ■ ' J^-^<
Fig. 43. June 13.
Fig. 44. June 14.
XX. XXI. XXII.
^,"■7'^'^*-, " - v7 V
%jyy-' T>f^ÎTî?3
0 P .
il .TV,: Kg. 45. Junéis.
Fig. 46. June 19.
JUPITER, 1887.
PLATE VIII.
XXVII. I. II. III. IT. V.
. -'.ff. V- H
L - M
' ' - .zimg^m»
Fig. 47. June 21.
xvr. XVII.
C
T)
Fig. 48. June 22.
N
Fig. 50. April 30. 11h. 34in.
E
XXVI. XXVII.
,, H2 K l£2
Fig. 49. June SO.
SMIHH
' 'th ™U ,
Fig. 51. 1882. Dec. 9.