Chapter XXXII: Letter XXXII: Recent Discoveries

"All are but parts of one stupendous whole."--_Pope._

WITHIN a few years, astronomy has been enriched with a number of valuable discoveries, of which I will endeavor to give you a summary account in this letter. The heavens have been explored with far more powerful telescopes than before; instrumental measurements have been carried to an astonishing degree of accuracy; numerous additions have been made to the list of small planets or asteroids; a comet has appeared of extraordinary splendor, remarkable, above all others, for its near approach to the sun; the distances of several of the fixed stars, an element long sought for in vain, have been determined; a large planet, composing in itself a magnificent world, has been added to the solar system, at such a distance from the central luminary as nearly to double the supposed dimensions of that system; various nebulæ, before held to be irresolvable, have been resolved into stars; and a new satellite has been added to Saturn.

IMPROVEMENTS IN THE TELESCOPE.--Herschel's forty-feet telescope, of which I gave an account in my fourth letter (see page 36), remained for half a century unequalled in magnitude and power; but in 1842, Lord Rosse, an Irish nobleman, commenced a telescope on a scale still more gigantic. Like Herschel's, it was a _reflector_, the image being formed by a concave mirror. This was six feet in diameter, and weighed three tons; and the tube was fifty feet in length. The entire cost of the instrument was sixty thousand dollars. Its reflecting surface is nearly twice as great as the great Herschelian, and consequently it greatly exceeds all instruments hitherto constructed in the _amount of light_ which it collects and transmits to the eye; and this adapts it peculiarly to viewing those objects, as nebulæ, whose light is exceedingly faint. Accordingly, it has revealed to us new wonders in this curious department of astronomy. Some idea of the great dimensions of the _Leviathan_ telescope (as this instrument has been called) may be formed when it is said that the Dean of Ely, a full-sized man, walked through the tube from one end to the other, with an umbrella over his head.

But still greater advances have been made in refracting than in reflecting telescopes. Such was the difficulty of obtaining large pieces of glass which are free from impurities, and such the liability of large lenses to form obscure and colored images, that it was formerly supposed impossible to make a refracting telescope larger in diameter than five or six inches; but their size has been increased from one step to another, until they are now made more than fifteen inches in diameter; and so completely have all the difficulties arising from the imperfections of glass, and from optical defects inherent in lenses, been surmounted, that the great telescopes of Pulkova, at St. Petersburgh, and of Harvard University (the two finest refractors in the world) are considered among the most perfect productions of the arts. A lens of only 15 inches in diameter seems, indeed, diminutive when compared with a concave reflector of six feet; but for most purposes of the astronomer, the Pulkova and Cambridge instruments are more useful than such great reflectors as those of Herschel and Rosse. If there is any particular in which these are more effective, it is in observations on the faintest nebulæ, where it is necessary to collect and convey to the eye the greatest possible beam of light.

INSTRUMENTAL MEASUREMENTS.--When astronomical instruments were first employed to measure the angular distance between two points on the celestial sphere, it was not attempted to measure spaces smaller than ten minutes--a space equal to the third part of the breadth of the full moon. Tycho Brahe, however, carried his measures to sixty times that degree of minuteness, having devised means of determining angles no larger than ten seconds, or the one hundred and eightieth part of the breadth of the lunar disk. For many years past, astronomers have carried these measures to single seconds, or have determined spaces no greater than the eighteen hundredth part of the diameter of the moon. This is considered the smallest arc which can be accurately measured directly on the limb of an instrument; but _differences_ between spaces may be estimated to a far greater degree of accuracy than this, even to the hundredth part of a second--a space less than that intercepted by a spider's web held before the eye.

DISCOVERY OF NEW PLANETS.--In my twenty-third letter (see page 286), I gave an account of the small planets called asteroids, which lie between the orbits of Mars and Jupiter. When that letter was written, no longer ago than 1840, only four of those bodies had been discovered, namely, Ceres, Pallas, Juno, and Vesta. Within a few years past, nineteen more have been added, making the number of the asteroids known at present twenty-three, and every year adds one or more to the list.[17] The idea first suggested by Olbers, one of the earliest discoverers of asteroids, that they are fragments of a large single planet once revolving between Mars and Jupiter, has gained credit since the discovery of so many additional bodies of the same class, all, like the former, exceedingly small and irregular in their motions, although there are still great difficulties in tracing them to a common origin.

GREAT COMET OF 1843.--This is the most wonderful body that has appeared in the heavens in modern times; first, on account of its appearing, when first seen, in the broad light of noonday; and, secondly, on account of its approaching so near the sun as almost to graze his surface. It was first discovered, in New England, on the 28th of February, a little eastward of the sun, shining like a white cloud illuminated by the solar rays. It arrested the attention of many individuals from half past seven in the morning until three o'clock in the afternoon, when the sky became obscured by clouds. In Mexico, it was observed from nine in the morning until sunset. At a single station in South America, it was said to have been seen on the 27th of February, almost in contact with the sun. Early in March, it had receded so far to the eastward of that body as to be visible in the southwest after sunset, throwing upward a long train, which increased in length from night to night until it covered a space of 40 degrees. Its position may be seen on a celestial globe adjusted to the latitude of New Haven (41° 18´) for the 20th of March, by tracing a line, or, rather, a broad band proceeding from the place of the sun towards the bright star Sirius, in the south, between the ears of the Hare and the feet of Orion.

The comet passed its perihelion on the 27th of February, at which time it almost came in contact with the sun. To prevent its falling into the sun it was endued with a prodigious velocity; a velocity so great that, had it continued at the same rate as at the instant of perihelion passage, it would have whirled round the sun in two hours and a half. It did, in fact, complete more than half its revolution around the sun in that short period, and it made more than three quarters of its circuit around the sun in one day. Its velocity, when nearest the sun, exceeded a million of miles per hour, and its tail, at its greatest elongation, was one hundred and eight millions of miles; a length more than sufficient to have reached from the sun to the earth. Its heat was estimated to be 47,000 times greater than that received by the earth from a vertical sun, and consequently it was more intense than that produced by the most powerful blowpipes, and sufficient to melt like wax the most infusible bodies. No doubt, when in the vicinity of the sun, the solid matter of the comet was first melted and then converted into vapor, which itself became red hot, or, more properly speaking, _white hot_. Much discussion has arisen among astronomers respecting the periodic time of this comet. Its most probable period is about 175 years.

DISTANCES OF THE STARS.--I have already mentioned (page 389) that the distance of at least one of the fixed stars has at length been determined, although at so great a distance that its annual parallax is only about one third of a second, implying a distance from the sun of nearly sixty millions of millions of miles. Of a distance so immense the mind can form no adequate conception. The most successful effort towards it is made by gradual and successive approximations. Let us, therefore, take the motion of a rail-way car as the most rapid with which we are familiar, and apply it first to the planetary spaces, and then to the vast interval that separates these nether worlds from the fixed stars. A rail-way car, travelling constantly night and day at the rate of twenty miles per hour, would make 480 miles per day. At this rate, to travel around the earth on a great circle would require about 50 days, and 500 days to reach the moon. If we took our departure from the sun, and journeyed night and day, we should reach Mercury in a little more than 200 years, Venus in nearly 400, and the Earth in 547 years; but to reach Neptune, the outermost planet, would require 16,000 years. Great as appear the dimensions of the solar system, when we imagine ourselves thus borne along from world to world, yet this space is small compared with that which separates us from the fixed stars; for to reach 61 Cygni it would take 324,000,000 years. But this is believed, for certain satisfactory reasons, to be one of the nearest of the stars. Several other stars whose parallax has been determined are at a much greater distance than 61 Cygni. The pole star is five times as far off; and the greater part of the stars are at distances inconceivably more remote. Such, especially, are those which compose the faintest nebulæ.

DISCOVERY OF THE PLANET NEPTUNE.--From the earliest ages down to the year 1781, the solar system was supposed to terminate with the planet Saturn, at the distance of nine hundred millions of miles from the sun; but the discovery of Uranus added another world, and doubled the dimensions of the solar system. It seemed improbable that any more planets should exist at a distance still more remote, since such a body could hardly receive any of the vivifying influences of the central luminary. Still, certain irregularities to which the Uranus was subject, led to the suspicion that there exists a planet beyond it, which, by its attractions, caused these irregularities. Impressed with this belief, two young astronomers of great genius, Le Verrier, of France, and Adams, of England, applied themselves to the task of finding the hidden planet. The direction in which the disturbed body was moved afforded some clue to the part of the heavens where the disturbing body lay concealed; the kind of action it excited at different times indicated that it was beyond Uranus, and not this side of that planet; and the magnitude of the forces it exerted gave some intimation of its size and mass. The law of distances from the sun which the superior planets observe (Saturn being nearly twice the distance of Jupiter, and Uranus twice that of Saturn), led both these astronomers to assume that the body sought was nearly double the distance of Uranus from the sun. With these few and imperfect data, as so many leading-strings proceeding from the planet Uranus, they felt their way into the abysses of space by the aid of two sure guides--the law of gravitation and the higher geometry. Both astronomers arrived at nearly the same results, although they wrought independently of each other, and each, indeed, without the knowledge of the other. Le Verrier was the first to make public his conclusions, which he communicated to the French Academy at their sitting, August 31, 1846. They saw that there existed, at nearly double the distance of Uranus from the sun, a planet larger than that body; that it lay near a certain star seen at that season in the southwest, in the evening sky; that, on account of its immense distance, it was invisible to the naked eye, and could be distinctly seen with a perceptible disk only by the most powerful telescopes; being no brighter than a star of the ninth magnitude, and subtending an angle of only three seconds. Le Verrier communicated these results to Dr. Galle, of Berlin, with the request that he would search for the stranger with his powerful telescope, pointing out the exact spot in the heavens where it would be found. On the same evening, Dr. Galle directed his instrument to that part of the heavens, and immediately the planet presented itself to view, within one degree of the very spot assigned to it by Le Verrier. Subsequent investigations have shown that its apparent size is within half a second of that which the same sagacious mind foresaw, and that its diameter is nearly equal to that of Uranus, being 31,000, while Uranus is 35,000 miles.[18] The distance from the sun is less than was predicted, being only about 3000, instead of 3600 millions of miles; and its periodic time is 164-1/2, instead of 217 years, as was supposed by Le Verrier. One satellite only has yet been discovered, and this was first seen by Professor Bond with the great telescope of Harvard University.

RECENT TELESCOPIC DISCOVERIES.--The great reflecting telescope of Lord Rosse, and the powerful refracting telescopes of Pulkova and Cambridge, have opened new fields of discovery to the delighted astronomer. A new satellite has been added to Saturn, first revealed to the Cambridge instrument, making the entire number of moons that adorn the nocturnal sky of that remarkable planet no less than eight. Still more wonderful things have been disclosed among the remotest _Nebulæ_. A number of these objects before placed among the irresolvable nebulæ, and supposed to consist not of stars, but of mere nebulous matter, have been resolved into stars; others, of which we before saw only a part, have revealed themselves under new and strange forms, one resembling an animal with huge branching arms, and hence called the _crab_ nebula; another imitating a scroll or vortex, and called the _whirlpool_ nebula; and other figures, which to ordinary telescopes appear only as dim specks on the confines of creation, are presented to these wonderful instruments as glorious firmaments of stars.

In the year 1833, Sir John Herschel left England for the Cape of Good Hope, furnished with powerful instruments for observing the stars and nebulæ of the southern hemisphere, which had never been examined in a manner suited to disclose their full glories. This great astronomer and benefactor to science devoted five years of the most assiduous toil in observing and delineating the astronomical objects of that portion of the heavens. He had before extended the catalogue of nebulæ begun by his illustrious father, Sir William Herschel, to the number of 2307; and beginning at that point, he swelled the number, by his labors at the Cape of Good Hope, to 4015. He extended also the list of double stars from 3346 to 5449, and showed that the luminous spots near the South Pole, known to sailors by the name of the "Magellan Clouds," consist of an assemblage of several hundred brilliant nebulæ.

The United States have contributed their full share to the recent progress of astronomy. Powerful telescopes have been imported, made by the first European artists, and numerous others, of scarcely inferior workmanship and power, have been produced by artists of our own. The American astronomers have also been the first to bring the electric telegraph into use in astronomical observations; electric clocks have been so constructed as to beat simultaneously at places distant many hundred miles from each other, and thus to furnish means of determining the difference of longitude between places with an astonishing degree of accuracy; and facilities for recording observations on the stars have been devised which render the work vastly more rapid as well as more accurate than before. Indeed, the inventive genius for which Americans have been distinguished in all the useful arts seems now destined to be equally conspicuous in promoting the researches of science.

FOOTNOTES:

[17] The names of all the asteroids known at present are as follows:

1. Ceres. 9. Metis. 17. Psyche.
2. Pallas. 10. Hygeia. 18. Melpomene.
3. Juno. 11. Parthenope. 19. Fortuna.
4. Vesta. 12. Victoria. 20. Massalia.
5. Astræa. 13. Egeria. 21. Lutetia.
6. Hebe. 14. Irene. 22. Calliope.
7. Iris. 15. Eunomia. 23. Un-named.
8. Flora. 16. Thetis.

[18] Sir John Herschel, however, states its diameter at 41,500 miles

INDEX.

A.

Alamak, 371

Aldebaran, 369

Alexandrian school, 394

Algenib, 371

Algol, 371

Alioth, 374

Almagest, 14

Altair, 373

Altitude, 20

Amplitude, 20

Anaxagoras, 395

Anaximander, 395

Andromeda, 371

Antares, 370

Antinous, 373

Apogee, 187

Apsides, 188

Aquarius, 371

Aquila, 373

Archimedes, 136

Arcturus, 372

Aries, 369

Aristotle, 136

Astrology, 393

Astronomers royal, 48, 404

Astronomical clock, 51

Astronomical tables, 190

Astronomy, 17
history of, 14, 392

Atmosphere, 100, 410

Attraction, 135

Auriga, 371

Axis of the Earth, 21

Azimuth, 20

B.

Bacon, 16, 136

Base line, 76

Base of verification, 79

Bellatrix, 375

Betalgeus, 375

Bissextile, 64

Bootes, 372

Bouguer, 74

Bowditch, 148

Brahean system, 403

C.

Cæsar, Julius, 64

Calendar, Grecian, 67
Gregorian, 65

Cancer, 369

Canis Major, 375

Canis Minor, 375

Capella, 372

Capricorn, 370

Cassiopeia, 374

Catalogues of the stars, 367

Central forces, 130

Cepheus, 374

Ceres, 287

Cetus, 374

Chronology, 157

Chronometers, 210

Circles, great and small, 19
of diurnal revolution, 81
of perpetual apparition, 85
of perpetual occultation, 85
vertical, 20

Clusters, 376

Colures, 23

Coma Berenices, 372

Comet, Biela's, 339
Encke's, 340
Halley's, 323

Comets, 313
brightness of, 315

Comets, distances of, 317
light of, 317
magnitude of, 315
mass of, 318
motions of, 320
number of, 315
periods of, 316
perturbations of, 319
structure of, 314
tails of, 317

Complement, 18

Conjunction, 200

Constellations, 366

Copernican system, 256, 401

Copernicus, 14, 255

Cor Caroli, 372

Cor Hydræ, 375

Corona Borealis, 372

Corvus, 375

Crotona, 394

Crystalline spheres, 397

Cygnus, 374

D.

Day, astronomical, 61
sidereal, 60
solar, 60

Days of the week, 68

Declination, 24

Deferents, 400

Denebola, 370

Distances of the heavenly bodies, how measured, 94

Distances of the stars, 387

Dolphin, 373

Double stars, 381

Draco, 374

E.

Earth, diameter of the, 78
ellipticity of the, 78
figure of the, 69
motion of the, 126
orbit of the, 149

Eclipses, annular, 204
calculation of, 201
of the moon, 195
of the sun, 203

Ecliptic, 22

Epicycles, 400

Equation of time, 61

Equations, periodical, 193
secular, 193
tabular, 190

Equator, 21

Equinoxes, 22
precession of the, 154

Eudoxus, 397

F.

Fomalhaut, 371

Fraunhofer, 37

G.

Galaxy, 379

Galileo, 15
abjuration of, 272
condemnation of, 266
life of, 258
persecutions of, 265

Gemini, 369

Gemma, 372

Globes, artificial, 25

Gravitation, universal, 145

Gravity, terrestrial, 134

H.

Hercules, 372

Herschel, Sir Wm., 36, 105, 383

Hesperus, 397

Hipparchus, 398

Horizon, rational, 20
sensible, 20

Hour-circles, 21

Huyghens, 72

I.

Inductive system, 137

Inquisition, 138

Instruments, astronomical, 29

J.

Juno, 288

Jupiter, 247
belts of, 248
diameter of, 247
distance of, 247
eclipses of, 250
magnitude of, 247
satellites of, 250
scenery of, 247
telescopic view of, 247

K.

Kepler, 300

Kepler's laws, 296

L.

Latitude, 22
how found, 210

Laws of motion, 126
terrestrial gravity, 139

Leap year, 64

Leo, 370

Leo Minor, 372

Libra, 370

Librations of the moon, 179

Light, velocity of, how measured, 252

Longitude, celestial, 24
terrestrial, 22
its importance, 208
how found, 210
by chronometers, 210
by eclipses, 212
by Jupiter's satellites, 251
by lunar method, 213

Lucifer, 397

Lynx, 372

M.

Magnitudes, how measured, 94

Magellan clouds, 378

Mars, 245
changes of, 245
distance of, 245
revolutions of, 246

Mecanique Celeste, 148

Mercury, 230
conjunctions of, 231
diurnal revolution of, 235
phases of, 234
sidereal revolut'n of, 231
synodical revolut'n of, 231
transits of, 237

Meridian, 20

Meteoric showers, 346
origin of, 350

Meteoric stones, 290

Metonic cycle, 192

Miletus, school of, 394

Milky Way, 379

Mira, 375

Mirach, 371

Mizar, 374

Month, sidereal, 173
synodical, 173

Moon, 157
atmosphere of the, 167
cusps of the, 174
diameter of the, 158
distance of the, 158
eclipses of the, 195
harvest, 177
irregularities of the, 186
librations of the, 179
light of the, 158
mountains in the, 159
nodes of the, 173
phases of the, 174
revolutions of the, 178-182
scenery of the, 163
telescopic appearance of the, 158
volcanoes in the, 166
volume of the, 158

Motion, laws of, 126

Motions of the planets, 291

Mural circle, 54

N.

Nadir, 20

Nature of the stars, 390

Nebulæ, 377

New planets, 286
distances of, 288
origin of, 289
periods of, 288
size of, 289

New style, 66

Newton, 16, 143

O.

Oblique sphere, 84

Obliquity of the ecliptic, 115
effect of, on the Seasons, 123
how found, 117

Observatory, 42
Greenwich, 42-48
Tycho's, 42

Old style, 66

Ophiucus, 372

Opposition, 200

Orion, 375

Orreries, 112, 292

P.

Pallas, 287

Parallactic arc, 91

Parallax, 90, 389
annual, 387
horizontal, 93
how found, 94

Parallel sphere, 84

Parallels of latitude, 24

Pegasus, 373

Pendulum, 79

Perigee, 187

Periodical inequalities, 193

Perseus, 371

Pisces, 371

Piscis Australis, 371

Planets, 225
distances of, 228
inferior, 227
magnitudes of, 229
periods, 229
superior, 243

Pleiades, 369

Pointers, 374

Polar distance, 22

Polaris, 373

Pole, 19
of the earth, 21

Pollux, 369

Power of the Deity, 408

Præsepe, 369

Precession, 155

Prime vertical, 20

Primum mobile, 398

Principia, 147

Procyon, 375

Projection of the sphere, 27

Proper motions of the stars, 384

Ptolemaic system, 399

Ptolemy, 398

Pythagoras, 394

Q.

Quadrant, 18

R.

Radius, 17

Refraction, 95

Regulus, 370

Resolution of motion, 132

Resultant, 132

Revolution, annual, 111
diurnal, 111

Rigel, 375

Right ascension, 23

Right sphere, 83

S.

Sagittarius, 370

Saros, 192

Saturn, 274
diameter of, 274
ring of, 275
satellites of, 282
scenery of, 283

Scorpio, 370

Seasons, 119

Secondary, 19

Secular inequalities, 193

Serpent, 373

Sextant, 57

Sidereal day, 81
month, 173

Signs, 23

Sirius, 375

Solstices, 23

Sphere, celestial, 19
doctrine of the, 16
oblique, 84
parallel, 84
right, 83
terrestrial, 19

Spica, 370

Spots on the sun, 104
cause of, 106
dimensions of, 105
number of, 104

Stability of the universe, 410

Stars, fixed, 365

Stylus, 63

Sun, 101
attraction of the, 110
density of the, 103
diameter of the, 102
distance of the, 101
mass of the, 103
nature and constitution of the, 107
revolutions of the, 104

Sun, spots on the, 104
volume of the, 103

Supplement, 18

System of the world, 392-406
Brahean, 403
Copernican, 401
Ptolemaic, 399

T.

Tangent, 129

Taurus, 369

Telescope, the, 31
achromatic, 34
directions for using, 39
Dorpat, 37 Herschelian, 36
history of, 33
reflecting, 34

Temperature, changes of, 124

Temporary stars, 380

Terminator, 119, 159

Thales, 394

Tides, 216
cause of, 216
spring and neap, 219

Time, 59
apparent, 61
equation of, 61
mean, 61
sidereal, 60

Transits, 237

Triangulation, 75

Tropic, 117

Twilight, 98

U.

Unity of the Deity, 407

Uranus, 283
diameter of, 283
distance of, 284
history of, 284
period of, 284
satellites of, 284
scenery of, 285

Ursa Major, 373

Ursa Minor, 373

V.

Variable stars, 379

Venus, 230
conjunctions of, 231
mountains of, 237
phases of, 234
revolutions of, 232
transits of, 239

Vesta, 288

Vindemiatrix, 370

Virgo, 370

Y.

Year, astronomical, 63
tropical, 156

Z.

Zenith, 20

Zenith distance, 21

Zodiac, 25

Zodiacal light, 363

Zones, 25

RECENT DISCOVERIES.

Improvements in the Telescope, 414

Rosse's Leviathan Telescope, 415

Pulkova and Cambridge Telescopes, 415

Improvements in instrumental Measurements, 416

New Planets and Asteroids, 416

Great Comet of 1843, 417

Distances of the Stars, 418

Discovery of Neptune, 419

Recent telescopic discoveries, 420

Longitude by the Electric Telegraph, 422

* * * * *

Transcriber's Notes

Obvious punctuation and spelling errors repaired.

Greek transliterations are inclosed by equals signs.

Inconsistent hyphenation has been repaired.

Characters that could not be fully expressed are "unpacked" and shown within braces, e.g. {oblong symbol}.

In ambiguous cases, the text has been left as it appears in the original book. In particular many mismatched quotation marks, have not been changed.

Page 26, "knittingneedle" changed to "knitting needle".
Page 241, "trignometry" changed to "trigonometry".
Page 303, "dedecaedron" changed to "dodecaedron".
Page 392, "generrally" changed to "generally".