Imágenes de páginas
PDF
EPUB

The era of physical astronomy commences, 132. A theoretic
system proposed and discussed; a central sun and solitary planeta

Rapid survey of the system, 165. General characteristics of

the planets, 166. What phenomena gravitation must account for,

167. Stability not the sole object of the Creator, 168. Laws of

matter selected in wisdom, 170. By how much does the central

force diminish the primitive velocity of a planet ? 171. Changes

in the elements of the orbits of the planets, 174. The eccentri-

city, 175. Stability of the principal axes, 176. Motion of the

perihelion, 177. The inclinations, 180. The lines of nodes, 181.

The periodic times, 183. Stability of the great system, 185. Of

the system of the earth and moon, 186. Of Jupiter's system,

187. Of Saturn's system, 190.

LECTURE VII.

THE DISCOVERY OF THE NEW PLANETS.
Kepler's speculations, 194. Discovery of Uranus, 195. Bode's

law of interplanetary spaces, 196. The astronomical congress

of Lilienthal, in 1800, 198. Piazzi's discovery of a new planet,

Ceres ; íts loss and rediscovery, 200. The symmetry of the sys-

tem destroyed by the discovery of Pallas, 201. Olbers's theory of

the bursting of a planet, 202. Discovery of Juno and Vesta, 203.

Hencke discovers Astrea and Hebe, 204. Hind discovers Iris

and Flora, 204. Search for a planet beyond Uranus commenced,

206. Causes of this search, 207. Leverrier's researches on Mer-

cury, 209. Its transit in May, 1845,211. Leverrier presents his

computations to the French Academy, 212. Popular exhibition

of his reasoning, 215. The hypothetical planet found by Galle,

of Berlin, 216. Adams's computations, 217. The jew planet

detected by its disc, 218. Walker's computations, 219, Pierce's

views, 221. Leverrier claims Neptune to be the planet of

theory.

[ocr errors]

LECTURE VIII.

THE COMETARY WORLDS

Characteristics of comets, 223. Reduced to law by Newton,

225. The comet of 1680,226. Halley's comet of 1682,227. Its

return in 1759 predicted, 229. Its return in 1835, 231. Won-

derful changes in its magnitude, 233. Encke's comet, 235. Ap-

proaching the sun, 236. Resisting medium, 237. Biela’s comet,

238. Fears excited of collision with the earth, in 1832, 239. Its

nebulous character, 240. Its double character in 1846. Sepa-

ration of the comets, 242. Vast periods of some comets, 244.

Comets seen to transit the sun's disc, 246. Comets accounted for

by Laplace's nebular hypothesis, 247. Herschel's theory of the

physical condition of comets, 250. His theory accounts for the

diminishing period of Encke's comet, 251. Zodiacal light, 252.

LECTURE IX.

THE SCALE ON WHICH THE UNIVERSE IS BUILT.

Scale of the planetary system, 253. Radius of the earth's orbit

too small a unit, 254. The velocity of light determined from the

eclipses of Jupiter's satellites, and employed as a unit, 256.

Parallax of the fixed stars, 258. No parallax sensible to the
naked eye, 260. Great distance of the fixed stars inferred from
this fact, 261. Bradley's researches for parallax, 263. Discovery
of nutation and its value, 264. Discovery of aberration its
explanation, 266. Herschel's researches for parallax, 269. Dis.
covery of the revolving stars, 270. Power of modern telescopes,

271. Bessel discovers the parallax of 61 Cygni, 273.

LECTURE X.

THE MOTIONS AND REVOLUTIONS OF THE FIXED STARS.

Distances separating man from the stars, 290. Various diffi-

culties in the research for their motions, 291. Hipparchus dis-

covers a new and brilliant star, 292. The new star of 1572, 293.

The new star of 1604, 294. The disappearance of old stars, 295.

Changes of Algol, 295. Periodical stars, 296. Gravitation ex

tended to the sphere of the fixed stars, 297. Periods of some of

the binary systems, 298. Herschel sounds the depth of the Milky

Way, 299. Seeks the direction of the solar motion, 300. His

reasoning, 302. Argelander's research for the point towards

which the solar system is moving, 306. Struve's investigation

for the quantity of angular motion of the system, as seen from

stars of the first magnitude, 308. His father's research for the

relative distances of stars of different magnitudes, 310. Peters's

research for the parallax of stars of the second magnitude, 311.

Daedler's theory of the central sun, 319. The attributes of Goch

as displayed in the universe, 324.

THE

STRUCTURE OF THE UNIVERSE.

INTRODUCTORY LECTURE.

AN EXPOSITION OF THE PROBLEM WHICH THE HEAVENS

PRESENT FOR SOLUTION.

The subject to which your attention is invited claims no specific connexion with the every day struggle of human life. Far away from the earth on which we dwell, in the blue ocean of space,

thousands of bright orbs, in clusterings and configurations of exceeding beauty, invite the upward gaze of man, and tempt him to the examination of the wonderful sphere by which he is surrounded. The starry heavens do not display their glittering constellations in the glare of day, while the rush and turmoil of business incapacitate man for the enjoyment of their solemn grandeur. It is in the stillness of the midnight hour, when all nature is hushed in repose, when the hum of the world's on going is no longer heard, that the planets roll and shine, and the bright stars trooping through the deep heavens, speak to the wil. ling spirit that would learn their mysterious being.

Often have I swept backward in imagination six thousand years, and stood beside our Great Ances.

B 2

(17)

tor, as he gazed for the first time upon the goir.g down of the sun. What strange sensations must have swept through his bewildered mind, as he watch. ed the last departing ray of the sinking orb, unconscious whether he should ever behold its return Wrapt in a maze of thought, strange and startling, his eye long lingers about the point at which the sun had slowly faded from his view. A mysterious darkness, hitherto unexperienced, creeps over the face of nature. The beautiful scenes of earth, which through the swift hours of the first wonderful day of his existence, had so charmed his senses, are slowly fading one by one from his dimmed vision. A gloom deeper than that which covers earth, steals across the mind of earth's solitary inhabitant. He raises his inquiring gaze towards heaven, and lo! a silver crescent of light, clear and beautiful, hanging in the western sky, meets his astonished eye. The young moon charms his untutored vision, and leads him upward to her bright attendants, which are now stealing one by one, from out the deep blue sky. The solitary gazer bows, and wonders, and adores. The hours glide by—the silver moon is gone—the stars are rising-slowly ascending the heights of heaven-and solemnly sweeping downward in the stillness of the night. The first grand revolution to mortal vision is nearly completed. A faint streak of rosy light is seen in the east-it brightens—the stars fade—the planets are extinguished—the eye is fixed in mute astonishment on the growing splendor, till the first rays of the returning sun dart their radiance on the young earth and its solitary inhabitant. To him “ the evening and the morning were the first day.”

« AnteriorContinuar »