THE DOUBLE-STAR DEPARTMENT
The foregoing chapters will have shown that though the original
purpose of the Observatory has always been kept in view, yet the
progress of science has caused many researches to be undertaken
which overstep its boundaries. Thus in the present transit room,
beside the successive transit instruments we find upon the wall two
long thin tubes, labelled respectively Alpha Aquilæ and Alpha Cygni.
These were two telescopes set up by Pond for a special purpose.
Dr. Brinkley, Royal Astronomer for Ireland, had announced that he
had found that several stars shifted their apparent place in the
sky in the course of a year, due to the change in the position of
the earth from which we view them, by an amount which would show
that they were only about six to nine billions of miles distant
from us; or, in other words, they showed a parallax of from two to
three seconds of arc. Pond was not able to confirm these parallaxes
from his observations, and to decide the point he set up these two
telescopes, the Alpha Aquilæ telescope being rigidly fixed on the
west side of the pier of Troughton's mural circles; the Alpha Cygni
telescope on another pier, the one which now forms the base of the
pier of the astrographic telescope. Pond's method was to compare
the position of these two stars with that of a star almost exactly
the same distance from the pole, but at a great distance from it in
time of crossing the meridian; in other words, of almost the same
declination, but widely different right ascension. The result proved
that Brinkley was wrong, and vindicated the delicacy and accuracy of
Pond's observations.
These two telescopes, therefore, had their day and ceased to be.
Others have followed them. An ingenious telescope was set up by
Sir George Airy in order to ascertain if the speed of light were
different when passing through water than when passing through
air. Or, in other words, if the aberration of light would give the
same value as at present if we observed through water. The water
telescope, as it was called, is kept on the ground floor of the
central octagon of the new observatory. The observations obtained
with it were hardly quite satisfactory, but gave on the whole a
negative result.
Turning back to the transit room, and leaving it by the south-west
door, we come into the little passage which leads at the back of
Bradley's transit room into the lower computing room. Just inside
this passage, on the left-hand side, there is a little room of
a most curious shape, the 'reflex zenith room.' Here is fixed a
telescope pointing straight upwards, the eye-piece being fixed
by the side of the object-glass. The light from a star--the star
Gamma Draconis--which passes exactly over the zenith of Greenwich,
enters the object-glass, passes downwards to a basin of mercury, and
is reflected upwards from the surface of the mercury to a little
prism placed over the centre of the object-glass, from which it
is reflected again into the eye-piece. By means of this telescope
the distance of the star Gamma Draconis from the zenith could
be measured very exactly, and, consequently, the changes in the
apparent position of the star due to aberration, parallax, and other
causes could be very exactly followed, and the corrections to be
applied on account of these causes precisely determined.
This particular telescope was devised by Airy, and the observations
with it were continued to the end of his reign. The germ of the idea
may be traced back, however, to the time of Flamsteed, who would
seem to have occasionally observed Gamma Draconis from the bottom
of a deep well; the precise position of the well is not, however,
now known. Later, Bradley set up his celebrated 12-1/2-foot zenith
sector, still preserved in the transit room, first at Wanstead
and then at Greenwich, for the determination of the amount of
aberration. Later, a zenith tube by Troughton, of 25 feet focus, was
used by Pond in conjunction with the mural circle for observations
of Gamma Draconis in order to determine the zenith point of the
latter instrument.
These telescopes for special purposes have passed out of use.
Observations with the spectroscope have been suspended for some
years. The work of the Astrographic Department will come to an end,
in the ordinary course of events, when the programme assigned to
Greenwich in the International Scheme is completed.
Within the last few years a new department has come into being at
Greenwich--a department which has been steadily worked at many
foreign public observatories, but only recently here.
This is the Department of Double-Star Observation. The first double
star, Zeta Ursæ Majoris, was discovered 250 years ago. Bradley
discovered two exceedingly famous double stars whilst still a young
man observing with his uncle at Wanstead--Gamma Virginis and Castor.
Bradley made also other discoveries of double stars after his
appointment to Greenwich, and Maskelyne succeeded him in the same
line, but the great foundation of double-star astronomy was laid by
Sir William Herschel.
At first it was supposed that double stars were double only in
appearance; one star comparatively near us 'happened' to lie in
almost exactly the same direction as another star much further
off. It was, indeed, in the very expectation that this would
prove to be the case, that the elder Herschel first took up their
study. But he was soon convinced that many of the objects were
true double stars--members of the same system of which the smaller
revolved round the larger--not merely apparently double, one star
appearing by chance to be close to another with which it had no
connection--but real double stars. The discovery of these has led to
the establishment of a new department of astronomy, again scientific
rather than utilitarian.
[Illustration: DOUBLE-STAR OBSERVATION WITH THE SOUTH-EAST
EQUATORIAL.
(_From a photograph by Mr. Edney._)]
As mentioned above, it is only recently that Greenwich has
taken any appreciable part in this work. Under Airy, the largest
equatorial of the time had been furnished with a good micrometer,
and observations of one or two double stars been made now and
again; but Airy's programme of work was far too rigid, and kept the
staff too closely engaged for such observations to be anything but
extremely rare. And, indeed, when the micrometers of the equatorials
were brought into use, they were far more generally devoted to the
satellites of Saturn than to the companions of stars. In the main,
double-star astronomy has been in the hands of amateurs, at least
in England. But the discovery in recent years of many pairs so
close that a telescope of the largest size is required for their
successful observation, has put an important section of double stars
beyond the reach of most private observers, and therefore the great
telescope at Greenwich is now mainly devoted to their study. The
Astronomer Royal, therefore, soon after the completion of the great
equatorial of 28-inches aperture placed in the south-east dome,
added this work to the Observatory programme.
The 28-inch equatorial is a remarkable-looking instrument, its
mounting being of an entirely different kind to that of the other
equatorials in the Observatory, with the solitary exception of the
Shuckburgh, which is set up in a little dome over the chronograph
room. The Shuckburgh was presented to the Observatory in the year
1811, by Sir G. Shuckburgh. It was first intended to be mounted as
an altazimuth, but proved to be unsteady in that position, and was
then converted into an equatorial without clockwork, and mounted in
its present position. The position is about as hopelessly bad a one
as a telescope could well have, completely overshadowed as it is by
the trees and buildings close at hand. The dome is a small one, and
the arrangements for the shutters and for turning the dome are as
bad as they could possibly be. It has practically been useless for
the last forty years.
Its only interest is that the method of mounting employed is a small
scale model of that of the great telescope in the S.-E. dome. In the
German or Fraunhofer form of mounting for an equatorial there is but
a single pillar, which carries a comparatively short polar axis. At
the upper end of the polar axis we find the declination axis, and
at one end of the declination axis is the telescope, whilst at the
other end is a heavy weight to counterpoise it. The German mounting
has the advantage that the telescope can easily point to the pole
of the heavens; its drawbacks are that, except in certain special
forms, the telescope cannot travel very far when it is on the
same side of the meridian as the star to which it is pointed, the
end of the telescope coming into contact under such circumstances
with the central pier, whilst the introduction of mere deadweight
as the necessary counterpoise, is not economical. It has been
already pointed out that the present Astronomer Royal has not only
considerably modified the German mounting in the great collection of
telescopes in the Thompson dome, but has used a powerful reflector
as a counterpoise to the sheaf of refractors at the other end of the
declination axis.
The English equatorial requires two piers. Between these two piers
is a long polar axis. Both in the little Shuckburgh and in the
great 28-inch equatorial the frame of the polar axis consists of
six parallel rods disposed in two equilateral triangles, with their
bases parallel to each other, the telescope swinging in the space
between the two bases. The construction of this form of equatorial,
therefore, is expensive, as it requires two piers. It takes much
more room than the German form, and the telescope cannot be directed
precisely to the pole. But the instrument is symmetrical, there is
no deadweight, and the telescope can follow a star from rising to
setting without having to be reversed on crossing the meridian.
The great stability of the English form of mounting, therefore,
commended it very highly to Airy, and he designed the great
Northumberland equatorial of the Cambridge Observatory on that plan,
as well as one for the Liverpool Observatory at Bidston, and in 1858
the S.-E. equatorial at Greenwich.
The telescope at first mounted upon it had an object-glass of 12-3/4
inches' aperture, and 18 feet focal length. That was dismounted
in 1891, and is now used as the guiding telescope of the Thompson
26-inch photographic refractor. Its place was taken by an immensely
heavier instrument, the present refractor of 28 inches' aperture,
and 28 feet focal length; and that this change was effected safely
was an eloquent testimony to the solidity of the original mounting.
The clock that drives this great instrument, so that it can follow
a star or other celestial object in its apparent daily motion
across the sky, is in the basement of the S.-E. tower. It is a very
simple looking instrument, a conical pendulum in a glass case. The
pendulum makes a complete revolution once in two seconds. Below
it in a closed case is a water turbine. A cistern on the roof of
the staircase supplies this turbine with water, having a fall of
about thirty feet. The water rushing out of the arms of the turbine
forces it backward, and the turbine spins rapidly round, driving a
spindle which runs up into the dome, and gears through one or two
intermediate wheels with the great circle of the telescope; the
extremely rapid rotation of the spindle, four times in a second,
being converted by these intermediate wheels into the exceedingly
slow one of once in twenty-four hours. Just above the centre of
motion of the turbine is a set of three small wheels, all of exactly
the same size, and of the same number of teeth. Of these the bottom
wheel is horizontal, and is turned by the turbine. The top wheel
is also horizontal, and is turned by the pendulum. The third wheel
gears into both these, and is vertical. If the top and bottom wheels
are moving exactly at the same rate, the intermediate wheel simply
turns on its axis, but does not travel; but if the turbine and
pendulum are moving at different rates, then the vertical wheel is
forced to run in one direction or the other, and, doing so, it opens
or closes a throttle valve, which controls the supply of water to
the turbine, and so speedily brings the turbine into accord with
the pendulum. The control of the motion of the great telescope is
therefore almost as perfect as that of the astrographic and Thompson
equatorials, though the principle employed is very different. And
the control needs to be perfect, for, as said above, the great
telescope is mostly devoted to the observation of double stars, and
there can be no greater hindrance to this work than a telescope
which does not move accurately with the star.
There is a striking contrast between the great telescope and all the
massive machinery for its direction and movement, and the objects
on which it is directed--two little points of light separated by a
delicate hair of darkness.
The observation is very unlike those of which we have hitherto
spoken. The object is not to ascertain the actual position in the
sky of the two stars, but their relative position to each other.
A spider's thread of the finest strands is moved from one star to
the other by turning an exquisitely fine screw; this enables us
to measure their distance apart. Another spider thread at right
angles to the first is laid through the centres of both stars, and
a divided circle enables us to read the angle which this line makes
to the true east and west direction. Such observations repeated
year after year on many stars have enabled the orbits of not a few
to be laid down with remarkable precision; and we find that their
movements are completely consistent with the law of gravitation.
Further, just as Neptune was pre-recognized and discovered
from noting the irregularities in the motion of Uranus, so the
discordances in the place of Sirius led to the belief that it was
attracted by a then unseen companion, whose position with respect to
the brighter star was predicted and afterwards seen.
[Illustration: THE SOUTH-EAST DOME WITH THE SHUTTER OPEN.]
Gravitation thus appears, indeed, to be the Bond of the Universe,
yet it leaves us with several weighty problems. The observation of
the positions of stars shows that though we call them fixed they
really have motions of their own. Of these motions, a great part
consists of a drift away from one portion of the heavens towards a
point diametrically opposite to it, a drift such as must be due, not
to a true motion of the individual stars, but to a motion through
space of our sun and its attendant system. The elder Herschel was
the first to discover this mysterious solar motion. Sir George Airy
and Mr. Edwin Dunkin, for forty-six years a member of the Greenwich
staff, and from 1881-1884 the Chief Assistant, contributed important
determinations of its direction.
What is the cause of this motion, what is the law of this motion,
is at present beyond our power to find out. Many years ago a
German astronomer made the random suggestion that possibly we were
revolving in an orbit round the Pleiades as a centre. The suggestion
was entirely baseless, but unfortunately has found its way into many
popular works, and still sometimes is brought forward as if it were
one of the established truths of astronomy. We can at present only
say that this solar motion is a mystery.
There is a greater mystery still. The stars have their own
individual motions, and in the case of a few these are of the most
amazing swiftness. The earth in its motion round the sun travels
nearly nineteen miles in a second, say one thousand times faster
than the quickest rush of an express train. The sun's rate of motion
is probably not quite so swift, but Arcturus, a sun far larger than
our own, has a pace some twenty times as swift as the orbital motion
of the earth. This is not a motion that we can conceive of as being
brought about by gravitation, for if there were some unseen body so
vast as to draw Arcturus with this swiftness, other stars too would
be hurtling across the sky as quickly. Such 'runaway stars' afford a
problem to which we have as yet no key, and, like Job of old, we are
speechless when the question comes to us from heaven, 'Canst thou
guide Arcturus and his sons?'
It will be seen then that, fundamentally, Greenwich Observatory was
founded and has been maintained for distinctly practical purposes,
chiefly for the improvement of the eminently practical science
of navigation. Other inquiries relating to navigation, as, for
instance, terrestrial magnetism and meteorology, have been added
since. The pursuit of these objects has of necessity meant that the
Observatory was equipped with powerful and accurate instruments, and
the possession of these again has led to their use in fields which
lay outside the domain of the purely utilitarian, fields from which
the only harvest that could be reaped was that of the increase of
our knowledge. So we have been led step by step from the mere desire
to help the mariner to find his way across the trackless ocean, to
the establishment of the secret law which rules the movements of
every body of the universe, till at length we stand face to face
with the mysteries of vast systems in the making, with the intimate
structure of the stellar universe, with the apparently aimless,
causeless wanderings of vast suns in lightning flight; with problems
that we cannot solve, nor hope to solve, yet cannot cease from
attempting, problems to which the only answer we can give is the
confession of the magicians of Egypt--'This is the finger of God.'
INDEX
Aberration of light, 79
Adams, John C., his discovery of Neptune, 217
Adhara, 183
Airy, George Biddell, seventh Astronomer Royal, his early
life, 102;
his work at Cambridge, 105;
comes to Greenwich, 105;
his relations with the Visitors, 106;
his autobiography, 108;
his character, 111;
his labours, 113;
attacks on, 114;
his distinctions, 118;
his resignation, 119;
his death, 120;
anecdote of, 142;
his conduct _re_ Adams, 217;
his water telescope, 304
Alderamin, 183
_Almagest_, 185
Almanac making, 29
Alpha Aquilæ, telescope for, 303
---- Cygni, telescope for, 303
Altazimuth the, 114;
description and work of, 207, _et seq._
Altazimuth Department, 205, _et seq._
American time, 153
Andromeda nebula, 301
Anemometer, use of, 238;
trace of, 242
Angström, 268
Anson, Commodore, 17
Apparent time, 152
Arcturus, motion of, 315
Argelander, star catalogue of, 287
_Art of Dialling_, the, 28
Assistants, position of the, 98, 100, 117, 137
Astrographic chart, 128
---- Department, 284, _et seq._
---- dome, 128
---- telescope, 289, _et seq._
Astronomers Royal, the, 25
Astrophysical researches, 282
Auroræ, 281
Automatic register, 241
Axis of the earth, precession of, 184
Ball, Time, 162
Barometer, use of the, 192, 233
Battery basement, 161
Beaufort, Captain, 107
Bessel quoted, 266
Betelgeuse, 184
Birkenhead, wreck of the, 180
Bliss, Nathaniel, fourth Astronomer Royal, history of, 82
Bradley, James, third Astronomer Royal, his life, 73;
his ordination, 74;
Vicar of Bridstow, 74;
Savilian Professor of Astronomy, 75;
discovers Aberration of Light, 75, _et seq._;
becomes Astronomer Royal, 79;
labours of, 80;
character of, 81
Bradley's transit room, 128
Brinkley, Dr., 303
_British Mariner's Guide_, the, 90
Bunsen, 268
Buys Ballot's law, 237
Canadian time, 153
Castor, 74, 306
Catalogues, star, 182, 185, _et seq._, 198, 284
Cepheus, 183
Charles II., warrants of, 39, 40
Christie, W. H. M., eighth Astronomer Royal, work of, 120
Chromosphere of the sun, 268
Chronograph, the, 157
---- room, 126
Chronometer business, 101, 107
Chronometers, Harrison's improvements in, 165, _et seq._;
tests of, 169;
'runs' of, 173;
romance of, 178
Circle Department, 181, _et seq._
Clock, Astrographic driving, 290;
driving 28-inch telescope, 312
Clocks, standard, 160
Columbus, aim of voyage of, 18
Comet, appearance of a, 28
---- Wells, 280
Comets, observation of, 224;
spectra of, 280
Commutator, the, 162
Comte, assertion of, 267
Constant of Aberration, 79
Cook, Captain, work of, 170
Copper, use of in Observatory, 245
Corona of the sun, 264
Crabtree, James, 31
Crosthwait, Joseph, 57
Dallmeyer telescope, 252
Declination, 186, _et seq._
Denebola, 184
Distances of planets, 223;
of sun, 224
Double-Star Department, 303, _et seq._
Double Stars, 306
Dublin time, 155
Dunkin, Edwin, 315
Earth, the, movements of, 201
Eclipses of the moon, 216;
of the sun, July 25, 1748...85;
other eclipses of the sun, 263, _et seq._
Electric Railway, influence of, 249
Equation of Time, the, 29, 151
Equatorial, Shuckburgh's, 101
----, the great 28-inch, 221
----, the Merz, 12-3/4-inch, 114
----, 28-inch, driving clock of, 309;
use of, 313
----, clock-driven, 74
Eros, discovery of, 223;
photographs of, 298
Errors in observations, noting of, 199, _et seq._
Evaporation, 241
Faculæ of the sun, 257
Flamsteed, John, his report on Saint-Pierre's proposal, 23, 32;
appointed first Astronomer Royal, 23, 34;
his autobiography, 26;
his studies, 29;
his almanac, 29;
sent to London, 30;
enters Jesus College, Cambridge, 31;
completes his observatory, 31;
acquaintance with Newton, 31;
takes his degree, 32;
his work, 34;
warrant for his salary, 39;
position of, 42;
his ordination, 45;
his pupils, 45;
his trouble with Newton, 46, _et seq._;
his catalogue, 53;
his letter to Sharp, 54;
his death, 56;
his labours, 57
Flamsteed House, 126
Fraunhofer mounting, 310
French time, 155
Galileo, his discovery of Jupiter's satellites, 19
Gamma Draconis, 75, 304
---- Virginis, 306
Gascoigne, William, 31
Gemma Frisius, plan of, 22
George of Denmark, Prince, 50
German mounting, 276, 310
Gould, Dr., 287
Graham, 166
Gravitation, the bond of the universe, 313
Great comet of 1882, the, 280, 288
Greatrackes, Valentine, 29
Green, Charles, 91
Greenwich time, 153;
distribution of, 163
Halley, Edmund, his life, 60;
his early work, 60;
his catalogue of stars, 63;
elected F.R.S., 63;
his work on Kepler's laws, 64;
becomes captain, 65;
Savilian Professor of Geometry, 66;
Astronomer Royal, 66;
observations on saros of the moon, 67;
pressed by Newton, 68;
his death, 68;
his services to science, 68;
his pay, 70;
nominates his successor, 73;
his transit instrument, 73
Halley's comet, 225
Harrison, James, timekeepers of, 86, 91, 93, 165
Heineken, Rev. N. S., 59
Heineken quadrant, 59
Heliographic Department, 251, _et seq._
Herschel, Caroline, 57
Hipparchus, catalogue of, 185
Hodgson, Mr., 50
Hooke, Robert, 75, 206
Horrox, Jeremiah, 31
Huggins, Sir W., his use of spectroscope, 268
Inscription, an, 126
International Photographic Survey, 296
Ireis, 224
Iron quadrant, 73
Isobars, 237
Jupiter, satellites of, 19, 296;
atmosphere of, 279
Keill, John, 74
Kendall, Larcum, 166
Kepler, laws of, 64
Kew, photo-heliograph, the, 252
Kinnebrook, David, 176
Kirchhoff's use of spectroscope, 267
Latitude, finding the, 18
Ledgers, chronometer, romance of, 176
Leverrier, his discovery of Neptune, 217
Libraries, 132
Linacre, G., 28
Lindsay, Thomas, quoted, 204
Litchford, W., 28
Local apparent time, 22
Longitude, finding the, 18;
at sea, problem of, 86;
determination of, 173
Longitude nought, 148
Lower computing room, 128
Lunars, method of, 86
Magnetic Department, work of, 133;
description of, 228, _et seq._
Magnetic inclination and declination, 246
---- needles, movements of, 247, 262
---- observatory, 132
---- pavilion, 245
---- storms, 248, 262
Mars, distance of, 223;
atmosphere of, 279;
satellites of, 296
Maskelyne, Nevil, fifth Astronomer Royal, 85;
practical work of, 86;
Astronomer Royal, 91;
his work, 92;
his publications, 92;
his observations and work, 92, _et seq._;
his death, 94;
his character, 97;
recommends his successor, 97;
his mural circle, 101
Mean solar clock, 160
Mean time, 152
Meldrum, Dr., on sun spots, 263
Meridian, the, 149
Merz telescope, 279
Meteorological Department, work of, 133;
description of, 228, _et seq._
Micrometers, use of, 309
Microscopes, use of, 188
Milky Way, 288
Miller, Professor, 268
Milne, Professor, on earth movements, 201
Minor planets, 222
Molyneux, Samuel, 75
Moon, observation of the, 212, _et seq._;
eclipses of, 266
Moore, Sir Jonas, 30;
death of, 42
Morin, 33
Mounting telescopes, modes of, 310
Mudge, Thomas, 94
Mural arc, 7-feet, 46
Mural circles, 101, 196
Names of stars, origin of, 183
Nares, Sir George, 170
_Nautical Almanac_, the, 22, 23, 92
Navigation, state of primitive, 17
Neptune, discovery of, 217;
atmosphere of, 280;
satellite of, 298
New altazimuth, the, 132, 210
New Observatory, the, 136, 275
New stars, 268
Newcomb, Professor, on growth of Observatory, 124;
on Greenwich observations, 207
Newton, Sir I., his absent-mindedness, 31;
his trouble with Flamsteed, 46, _et seq._;
on Kepler's laws, 65;
his _Principia_, 65;
his pressure on Halley, 68;
his discovery of gravitation, 206
North terrace, the, 126
Northumberland equatorial, 218
Nutation of the earth, 80
Observation, modes of, 156, 176, 188;
by reflection, 196;
of comets, 224
Observatory, Greenwich, work of, 13;
foundation of, 23;
warrant for building, 40;
position of, 41;
foundation stone laid, 42;
condition of, 79;
enlargement of, 112;
recent extensions of, 120;
description of, 124, _et seq._;
staff of, 137;
work of, 139, _et seq._;
visitors to, 175;
new altazimuth building, 211;
magnet house, 228;
magnetic pavilion, 245;
new Observatory, 275;
future of, 283;
reflex zenith room, 304;
objects of, 316
Occultations by the moon, 212, _et seq._
Octagon room, 125, 238, 242
Oldenburg, Mr., 30
Orion nebula, 268, 301
Parallax of stars, 303
Paramour, the, 65
Paris, conference at, 288
----, noon at, 151
Philip III., offer of, 19
Photographic registration, 244, 247, 252, 255;
refractors, 288
Photographs, star, 290
Photo-heliographs, 252, _et seq._, 279
Piazzi, discovery of, 222
Pleiades, the, 301
Polar plumes of the corona, 264
Polaris, 188
Pole-star, variation of, 184
Pond, John, sixth Astronomer Royal, his life, 97;
his reign, 98;
his salary, 98;
his assistants, 98;
his observations, 99;
censured by Visitors, 99;
his observations of stars, 303
Pound, James, 73
Precession of earth's axis, 184
_Principia_, publication of, 65
Proctor, R. A., attack of, 116
Ptolemy, Claudius, catalogue of, 185
Publication, the problem of, 48, 92
Quadrant, Heineken, 59
----, the iron, 73
Railway time, 152
Rain gauge, 238
Record rooms, 132
Reflection, observation by, 196
Reflex zenith room, 304
---- ---- tube, 131
Refraction, effects of, 194
Right ascension, 186, _et seq._
Roberts, Dr. Isaac, 301
Römer, discovery of, 78
Rosse, Lord, 268
Royal Society and Flamsteed, 46, _et seq._
Saint-Pierre, Le Sieur de, proposal of, 23, 32
Sappho, 224
Saros of the moon, 67
Satellites, discovery of, 296
Saturn, atmosphere of, 279;
satellites of, 296
Schaeberle's comet, 280
Schedar, 184
Schiehallion, attraction of, 94
Schönfeld, 287
Scotchmen, anecdote of, 146
Sharp, Abraham, 46
Sheepshanks, Rev. James, on Airy, 107
Shuckburgh equatorial, 309
Sidereal clock, 160
Sirius, 287
Sloane, Dr., 50
'Smith, Mr.,' his chronometer, 179
Solar photographs, 257
---- storms, 261, 282
Sound waves, 271
South, Sir James, 105, 114
South-east equatorial, the, 132, 221
Spectroscope, use of, 267
Spectroscopic Department, 266, _et seq._
Spots, sun, 251, _et seq._, 281
Staff of Observatory, 137;
work of, 139, _et seq._
Standard time, 21
Stars, observations of, 156, 176, 188;
origin of names of, 183;
movements of, 187;
catalogues of, 198, 284, _et seq._;
composition of, 268, _et seq._;
colour of, 271;
classes of, 287;
census of, 287;
photographs of, 288, _et seq._;
motions of, 303, 315
Story, Mr. A. M., 97
Sun, distance of the, 74, 224;
spots on, 251, _et seq._, 281;
eclipses of, 263, _et seq._;
chromosphere of, 268;
motions of, 315
Sunshine recorder, 238
Swiss time, 155
Tebb, Mr. W., 58
Tebbutt's comet, 280
Telescope, the great transit, 156
----, 28-inch, 275
----, astrographic, 289
----, Shuckburgh, 309
----, Thompson, 256, 279, 296
Thalèn, 268
Thermometer, use of, 192, 234
Thome, Dr., 287
Thompson photo-heliograph, 256, 279, 296
Time ball, 162
---- Department, the, 146, _et seq._
---- desk, 161
----, foreign, 153
---- signals, 162
---- standard, 21
Transit, Halley's, 73
Transit circle, the, 114;
mode of observation with, 188, _et seq._
Transit circle, Troughton's, 98
---- Department, 181, _et seq._
---- observations, number of, 140
---- pavilion, 126, 175
---- room, 128, 147
Troughton's transit circle, 98
Uranus, discovery of, 217;
atmosphere of, 279;
satellites of, 296
Vanes, use of, 238
Venus, distance of, 223
Victoria, 224
Visitors, the Board of, 53;
censures Pond, 99;
work of, 106;
constitution of, 144
Visitors to Observatory, 175
Warrant for Flamsteed's salary, 39
Water telescope, 304
Weather predictions, 229, _et seq._
Winds, study of, 237
Witt, Herr, discovery of, 223
Working Catalogue, the, 142
Zenith sector, 82, 305
---- tube, 75, 305
Zeta Ursæ Majoris, 306
Zubeneschamal, 184
THE END
LONDON: PRINTED BY WILLIAM CLOWES AND SONS, LIMITED,
STAMFORD STREET AND CHARING CROSS.
* * * * *
Transcriber's note:
Minor typographical errors have been corrected without note.
Irregularities and inconsistencies in the text have been retained as
printed.
The illustrations have been moved so that they do not break up
paragraphs.
Mismatched quotation marks were not corrected if it was not clear
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