Chapter VI: The Variation of Latitude (2)

Secondly, there is the modifying influence of this new phenomenon on other phenomena already known, such, for instance, as that of "aberration." We saw in the third chapter how Bradley discovered this effect of the velocity of light, and how the measure of it is obtained by comparing the velocity of light with that of the earth. This comparison can be effected in a variety of ways, and we should expect all the results to agree within certain limits; but this agreement was not obtained, and Chandler has been able to show one reason why, and to remove some of the more troublesome differences. It is impossible to give here an idea of the far-reaching consequences which such work as this may have; so long as there are differences of this kind we cannot trust any part of the chain of evidence, and there is in prospect the enormous labour of examining each separate link until the error is found. The velocity of light, for instance, may be measured by a terrestrial experiment; was there anything wrong in the apparatus? The velocity of the earth in its journey round the sun depends directly upon the distance of the sun: have we measured this distance wrongly, and if so what was the error in the observations made? These are some of the questions which may arise so long as the values for the _Constant of Aberration_ are still conflicting; but it requires considerable knowledge of astronomy to appreciate them fully.

[Sidenote: Latitude Variation Tide.]

[Sidenote: Earthquakes.]

Another example will, perhaps, be of more general interest. If the axis of the earth is executing small oscillations of this kind, there should be an effect upon the tides; the liquid ocean should feel the wobble of the earth's axis in some way; and an examination of tidal registers showed that there was in fact a distinct effect. It may cause some amusement when I say that the rise and fall are only a few inches in any case; but they are unmistakable evidences that the earth is not spinning smoothly, but has this kind of unbalanced vibration, which I have compared to the vibrations felt by passengers on an imperfectly engineered twin-screw steamer. A more sensational effect is that apparently earthquakes are more numerous at the time when the vibration is greatest. We remarked that the vibration waxes and wanes, much as that of the steamer waxes and wanes if the twin-screws are not running quite together. Now the passengers on the steamer would be prepared to find that breakages would be more numerous during the times of vigorous oscillation; and it seems probable that in a similar way the little cracks of the earth's skin which we call great earthquakes are more numerous when these unbalanced vibrations are at their maximum; that is to say, about once every seven years. This result is scarcely yet worthy of complete confidence, for our observations of earthquakes have only very recently been reduced to proper order; but if it should turn out to be true, it is scarcely necessary to add any words of mine to demonstrate the importance of this rather unexpected result of the Latitude Variation.

[Sidenote: The Kimura phenomenon.]

Finally I will mention another phenomenon which seems to be at present more of a curiosity than anything else, but which may lead to some future great discovery. It is the outcome of observations which have been recently made to watch these motions of the Pole; for although there seems good reason to accept Mr. Chandler's laws of variation as accurate, it is necessary to establish their accuracy and complete the details by making observations for some time yet to come; and there could be no better proof of this necessity than the discovery recently made by Mr. Kimura, one of those engaged in this watch of the Pole in Japan. Perhaps I can give the best idea of it by mentioning one possible explanation, which, however, I must caution you may not be by any means the right one. We are accustomed to think of this great earth as being sufficiently constant in shape; if asked, for instance, whether its centre of gravity remains constantly in the same place inside it, we should almost certainly answer in the affirmative, just as only twenty years ago we thought that the North Pole remained in the same place. But it seems possible that the centre of gravity moves a few feet backwards and forwards each year--this would at any rate explain certain curious features in the observations to which Mr. Kimura has drawn attention. Whatever the explanation of them may be, or to settle whether this explanation is correct, we want more observations, especially observations in the Southern Hemisphere; and it is a project under consideration by astronomers at the present moment whether three stations can be established in the Southern Hemisphere for the further observation of this curious phenomenon. The question resolves itself chiefly into a question of money; indeed, most astronomical projects do ultimately resolve themselves into questions of money; and I fear the world looks upon scientific men as insatiable in this respect. One can only hope that on the whole the money is expended so as to give a satisfactory return. In this instance I have no hesitation in saying that an immediate return of value for a comparatively modest expenditure is practically certain, if only in some way we can get the means of making the observations.

It would be natural, at the conclusion of this brief review of some types of astronomical discovery, to summarise the lessons indicated: but there is the important difficulty that there appear to be none. It has been pointed out as we proceeded that what seemed to be a safe deduction from one piece of history has been flatly contradicted by another; no sooner have we learnt that important results may be obtained by pursuing steadily a line of work in spite of the fact that it seems to have become tedious and unprofitable (as in the search for minor planets) than we are confronted with the possibility that by such simple devotion to the day's work we may be losing a great opportunity, as Challis did. We can scarcely go wrong in following up the study of residual phenomena in the wake of Bradley; but there is the important difficulty that we may be wholly unable to find a clue for the arrangement of our residuals, as is at present largely the case in meteorology. And, in general, human expectations are likely to be quite misleading, as has been shown in the last two chapters; the discoveries we desire may lie in the direction precisely opposite to that indicated by the best opinion at present available. There is no royal road to discovery, and though this statement may meet with such ready acceptance that it seems scarcely worth making, it is hoped that there may be sufficient of interest in the illustrations of its truth.

The one positive conclusion which we may derive from the examples studied is that discoveries are seldom made without both hard work and conspicuous ability. A new planet, even as large as Uranus, does not reveal itself to a passive observer: thirteen times it may appear to such a one without fear of detection, until at last it encounters an alert Herschel, who suspects, tests, and verifies, and even then announces a comet--so little did he realise the whole truth. Fifteen years of unrequited labour before Astraea was found, nineteen years of observation before the discovery of nutation could be announced: how seldom do these years of toil present themselves to our imaginations when we glibly say that "Bradley discovered nutation," or "Hencke discovered Astraea"! That the necessary labour is so often forgotten must be my excuse for recalling attention to it somewhat persistently in these examples.

But beyond the fact that he must work hard, it would seem as though there were little of value to tell the would-be discoverer. The situation has been well summarised by Jevons in his chapter on Induction in the "Principles of Science;" and his words will form a fitting conclusion to these chapters:--

"It would seem as if the mind of the great discoverer must combine
contradictory attributes. He must be fertile in theories and
hypotheses, and yet full of facts and precise results of experience.
He must entertain the feeblest analogies, and the merest guesses at
truth, and yet he must hold them as worthless till they are verified
in experiment. When there are any grounds of probability he must hold
tenaciously to an old opinion, and yet he must be prepared at any
moment to relinquish it when a clearly contradictory fact is
encountered."

INDEX

Aberration, 105-109, 111, 112, 117, 118, 185, 188, 192, 214, 215

Accidental discovery, 15, 73, 121-154

Adams, 12, 45-85;
resolution, 55

Airy, 32, 40-85, 214

Algiers, 130

Alleghenia, 26

Almucantar, 180, 181

Alphabet used for planets, 27

Anderson, Dr. T. C., 8, 142, 143, 144, 146

Anthelm, 142

Apollo, 9

Argon, 109

Ascension, 34

Assumption, forgotten, 196

Astraea, 22, 23, 219

Astrographic chart, 122, 125, 130

_Astronomical Journal_, 177-217

_Astronomische Nachrichten_, 52, 158

Astrophil, 143

Auwers, 142

Ball, Sir R., 24

Balliol College, 87

Banks, Sir J., 9

Barnard, E. E., 146, 220

Berlin, 181, 183, 184, 188, 193

Berlin star-map, 45, 66, 83, 124

Bessel, 192

Bettina, 26, 27

Birmingham, 142

"Black Drop" (in transit of Venus), 30

Bliss, 114

Board of Visitors of Greenwich Observatory, 63

Bode, 11, 14, 15, 22

Bode's Law, 12, 13, 38, 43, 45, 52, 72, 76, 77, 84

Bourdeaux, 130

Bouvard, 39, 40, 42, 48, 49, 50, 61

Bradley, 39, 86-120, 188-192, 213, 214, 218, 219

Bradley, John, 115

Bremen, 20

Bridstow, 87, 88, 94

Briggs, 119

Brinkley, 192

British Association, 63

Bruennow, 193

California, 26

Cambridge (Mass.), 180, 184, 188

Cambridge Observatory, 23, 42, 49, 52, 63, 65, 66, 135, 193

Cambridge University, 68-71, 114

Cape Observatory, 123, 124, 130

Cards, 11

Cassini II., 156

Catania, 130

Ceres, 14-22

Chacornac, 124

Challis, 49-54, 63-68, 71, 85, 218

Chandler, S. C., 118, 177-217

Chapman's "Homer," 2

Chicago, 157

Chromosphere, 170

Clarke, C. C., 2

Coelostat, 94

Columbus, 63

Comet, 4-8, 88, 108, 117, 123, 125

Commission, planetary, 27

Common, A. A., 124, 127

_Compte Rendu_, 62

Comstock, 202

Conference, Astrographic, 125-136

Copernicus, 79, 95

Cordoba, 130, 199

Cornu, 210-213

Corona, 170-175

_Cosmos_ (Humboldt's), 160

Delambre, 157

Deviation of Pole, 187

Disc of Neptune, 44, 64, 79

Disc of Uranus, 4-7

Dorpat, 192

Doublet (photographic), 127-129

Draconis, [gamma], 96-104

Draconis, [beta], 193

Driessen, 23

Dry plate, 122

Dublin, 192

Earthquakes, 215

Earth's Pole, 177-217

Eccentricity, 41, 83

Eclipses, 170-176

Edinburgh, 143

Eduarda, 26

Egeria, 22

Endymion, 25

Eriphyla, 26

Eros, 25, 26, 28, 35, 37, 68

Eulerian, 200, 209

Evelyn, 26

Exposure, times of, 122, 131

Faculae, 170

Faraday, 201

Flamsteed, 39, 53, 115

Fleming, Mrs., 142

Flora, 22

Foulkes, Martin, 94

French Academy, 43, 51, 62

Galileo, 95, 163

Galle, 44, 45, 47, 66, 67, 83

Gasparis, 22

Gauge (railways), 56

Gauss, 17-20

Geminorum, H., 4

George III., 8, 10

"Georgian," 11

_Georgium Sidus_, 8, 10, 11

Gill, Sir D., 32, 34, 35, 123

Gilliss, 32

Gotha, 20

Gould, 32

Graham, 22, 23

Gravitation, law of, 38, 45, 59, 84, 105

Greaves, 119

Greenwich Observatory, 48-64, 88, 89, 114-117, 130, 160-169,
182, 192, 193, 206, 213

Gregory, 93, 119

Hale, G. E., 170, 171

Hall, A., 184, 185

Halley, 88-92, 108, 112-116, 119

Hansen, 41, 59

Harkness, 184

Hartwig, 142

Harvard College Observatory, 128, 142, 144, 145

Hebe, 22

Hegel, 15

Heidelberg, 145

Heliometer, 32, 34

Helium, 109

Helsingfors, 130

Hencke, 22, 23, 64, 153, 219

Henry brothers, 124-129

Herschel, Sir John, 63, 75, 83

Herschel, Sir William, 2-11, 39, 44, 82, 219

Herschel (Uranus), 11, 12

Hind, 22, 23, 25, 142

Hooke, 96, 97

Hubbard, 184

Humboldt, 160

Hussey, Rev. T. J., 40, 42

Hygeia, 22

Ilmata, 26

Industria, 26

Ingeborg, 26

Instruments at Greenwich, 114-116

Iris, 22, 23, 32, 35

Janson, 142

Jevons, 219

Johnson, M., 156, 160

Juno, 9, 21, 22

Jupiter, 9, 28, 43, 49, 50, 61;
satellites, 92, 117

Keats, 1-3, 7, 8

Keill, 94, 112, 119, 156

Kelvin, Lord, 196, 197

Kepler, 95, 142

Kew, 95, 96, 188, 190

Kiel, 141

Kimura, 216

Koenigsberg, 192

Kuestner, 118, 181, 183

Lalande, 7, 11, 107, 157

Lameia, 26

Laplace, 61

La Plata, 130

Latitude variation, 99, 100, 117, 118, 177-217

Lemonnier, 39, 53, 157

Le Verrier, 12, 43-85

Libussa, 26

Lick Observatory, 152

_Liouville's Journal_, 73

Lisbon, longitude of, 92

London, 23, 25, 96

Long, 157

Longitude, 92, 117

Lowth, Bishop, 119

Lyrae, [alpha], 184, 196

Macclesfield, Earl of, 94, 113

Maedler, 192

Magnetic observations, 161, 164, 174

Magnitude equation, 135

Markree, 23

Mars, 9, 28, 32, 34, 35, 91

Mayer, 39

Measurement of plates, 132-135

_Mecanique Celeste_, 61

Melbourne, 130, 193

Memorandum (Adams), 55

Mercury, 9

Messier, 7

Meteorites, 59

Meteors (November), 60

Metis, 22, 23

Micrometer, 5, 133

Milky Way, 125

Minerva, 9

Minor planets, 13-28

Minor planets tables, 22, 24, 26

Mistakes, 71-83

Molyneux, Samuel, 94-96, 101, 104

Monte Video, 130

Moon, tables of, 117

Names of minor planets, 22-28

Nasmyth, 162

"Nautical Almanac," 11

Nebula, 124, 146-152

Neptune, 11, 12, 38-85, 124

New College Lane, 112

Newcomb, Simon, 81, 183, 184, 195-202, 207, 208

New stars, 121, 140-154

Newton, 38, 84, 90-95, 105, 113

New York, longitude, 92

Ninina, 26

Northleach, 87

Northumberland, 65

Nova Geminorum, 141, 145, 146

Nova Persei, 143, 146-152

Nutation, 99, 100, 110, 115, 117, 118, 188, 219

_Observatory_ (magazine), 26

Ocllo, 26

Olbers, 20-22

Olympic games, 119

Oriani, 15

Ornamenta, 26

Oxford University, 87-89, 94, 105-119

Oxford University Observatory, 121, 130, 132, 136, 142, 145, 154

Palermo, Observatory of, 18

Palisa, 26

Pallas, 9, 21, 22

Parallax, 34, 91, 95-98, 109, 185

Paris, 130

Parkhurst, J. A., 145

Parthenope, 22

Peirce, 73, 80-83

Pendulum, 117

Perseus, 8, 143

Personal equation, 31, 134, 135, 185

Perth, 130

Perturbations of Uranus, 12, 42, 51, 54, 55, 61, 75

Peters, 188, 192

Phaetusa, 26

Philosopher, 201, 219

_Philosophical Transactions_, 3, 4, 9

Photographica, 26

Photographic methods, 24, 33, 36, 121-139;
lenses, 125, 126

Photographs of sun, 163, 170-173

Piazzi, 13-18, 22

Pickering, E. C., 128, 144

Pittsburghia, 26

Plana, 61

Planetary distances, 13;
commission, 27;
numbering, 27

Planets by photography, 24

Pole Star (_Polaris_), 177, 178, 192, 193

Pond, 192, 213

Potsdam, 130, 181

Pound, Mrs., 104, 110-112

Pound, Rev. James, 89-94, 104, 115

Prague, 181

Precession, 96, 178

Prymno, 26

Puiseux, 32

Pulfrich, 154

Pulkowa, 181-188, 213

Quadrants at Greenwich, 116

Radium, 175

Radius vector, 52-58, 60-62, 79, 83

Rayleigh, Lord, 109

Records before discovery, 144

Reflector, 93, 127, 128

Reflex zenith tube, 192, 214

Refraction, 96, 101-103, 117

Refractor, 93, 128

Reseau, 133

Residual phenomena, 108-110, 118, 120, 218

Rigaud, S. P., 87, 115, 119

Rome, 130

Rothschild, 27

Royal Astronomical Society, 40, 47, 68, 74, 124, 155, 157

Royal Society, 4, 9, 10, 92, 94

Sampson, R. A., 74-76, 84

San Fernando, 130

Santiago, 130

Sappho, 32, 35

Saturn, 9, 43, 61, 149, 150

Savile, Sir H., 119

Savilian professorship, 87-94, 108-119

Schmidt, Julius, 142, 160

Schuster, A., 169

Schwabe, 155-163, 176, 177

Sheldonian Theatre, 119

Sherbourn, 87

Solar eclipse, 26, 170-176

Spectro-heliograph, 170, 171

Star-maps, 45, 65, 83, 124

"Star-trap," 24

Stereo-comparator, 154

Stone, E. J., 32

Struve, 184, 188, 192

Sun's distance, 28-37

Sun-spots, 155-176

Sydney Observatory, 130

Tacubaya Observatory, 130

Telescopes, 92, 124-129

Thames River, 105

Themistocles, 119

_Theoria Motus_, 17

Theory and observation, 208

Thomson, Sir W., 196, 197

Tides, 215

Titius, 13

Toulouse Observatory, 130

Tycho Brahe, 95, 140, 142

Uranus, 2-14, 25, 38-85, 144, 219

Variable stars, 140

Variation of latitude, 99, 100, 117, 118, 177-217

Venus, 9, 79;
diameter of, 92;
transit of, 28-32, 34

Vesta, 21, 22

Victoria, 22, 25, 32, 35

Von Zach, 20

Wallace, 119

Wansted, 88-94, 104, 110, 115, 188, 190

Ward, 119

Washington Observatory, 184-188, 193, 196, 213

Weather and sun-spots, 161, 167-169

Weyer, 193

Whiteside, 112

Williams, Mrs. E., 110, 111

Wind-vane, revolutions, 167-169

Winnecke, 32

Wolf, Dr. Max, 145

Wolf, Rudolf, 163

Wren, Sir C., 119

Yerkes Observatory, 145, 146, 152, 157, 170, 176

Zeiss, 154

Zodiac, 64, 124, 137

THE END

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Footnotes:

[1] The inferior planet Venus comes closer, but is not visible throughout the night.

[2] The facts were collected with great care and ability by S. P. Rigaud, and published by the Oxford University Press in 1832 as "Miscellaneous Works and Correspondence of the Rev. James Bradley."

[3] Since the light must travel from the sun to Saturn _and back again to the earth_, the interval would be more nearly 150 minutes.

[4] Monthly Notices of the Royal Astronomical Society, vol. xvii. p. 126.

[5] This should be Cambridge, _Mass._

[6] The distances do not represent the _total_ displacement, but only the displacement towards Washington in one case and towards Pulkowa in the other.

Transcriber's Notes:

Passages in italics are indicated by _italics_.

Passages in bold are indicated by =bold=.

Subscripted letters are indicated by {subscript}.

The original text includes the Greek a, b, and g. For this text version these letters are presented as [alpha], [beta], and [gamma].

All side notes belonging to a single paragraph have been moved to the beginning of the paragraph.

Sidenotes split across pages have been joined together.

Punctuation has been corrected without note.

Corrections in the "Errata" have been made in this text version.

The following misprints have been corrected:
"Hencke'" corrected to "Hencke's" (page 23 sidenote)
"annouced" corrected to "announced" (page 45 sidenote)
"are are" corrected to "are" (page 119)
"Konigsberg" corrected to "Koenigsberg" (Index)

Other than the corrections listed above, inconsistencies in spelling and hyphenation have been retained from the original.

End of Project Gutenberg's Astronomical Discovery, by Herbert Hall Turner