THEORIES FOR THE EXPLANATION OF THE MOTIONS OF THE
HEAVENLY BODIES.
The names of early discoverers lost, 70. Chaldean period
found among many nations; the days of the week, and their names,
place of the vernal equinox, 71. Precession of the equinoxes, 73.
Astronomy of the primitive ages, and condition of the mind at the
beginning of the era reached by history, 75. Causes retarding
the progress of astronomy, 77. The confounding of true and
apparent motion; immobility of the earth and its central position,
78. The Greek astronomers, Pythagoras, Nicetas, Hipparchus,
Ptolemy, 80. System of Ptolemy, 82. Astronomy cultivated by
the Arabs, 82. The era of modern science commences, 84. Co-
pernicus and his discoveries, 86. His system promulged with
great caution, 87. Kepler, the character of his mind, his mode
of research, 91. His great discoveries; he finds the orbits of the
planets, 92. Detects his second law, 93. His efforts to find the
third law successful, 98. Importance of these laws, 99.
The philosophy of Aristotle-its hold on the mind, 101. Cha.
racteristics of Galileo's mind, 102. He detects the errors of Aris
totle, 103. Attacks his theories, and demonstrates their falsehood
by experiment, 104. Driven from Pisa by his enemies, 105.
Discovers the law of falling bodies, 106. Adopts the Copernican
theory, 107. Constructs a telescope, 108. His discoveries in the
moon, and among the planets and fixed stars, 110.
Venus, 111. Questions relating to the planetary motions, 113.
Laws of motion; the centrifugal force, 114. Problem presented
for solution to Newton, 116. Discoveries of Descartes; conjec
tures of Kepler, 117. Measure of the moon's distance and of the
earth's circumference, 118. The law of gravitation-Newton's
first effort to demonstrate the truth of this law, 121. He finally
shows that the moon is ever falling towards the earth, and proves
the law, 124. Enunciation of his great law, 125. Discovers
that the planets may revolve in conic sections, 126. Contrast
between Kepler's and Newton's methods of research, 128.
UNIVERSAL GRAVITATION APPLIED TO THE EXPLANATION OF
THE PHENOMENA OF THE SOLAR SYSTEM.
The era of physical astronomy commences, 132. A theoretic
system proposed and discussed, a central sun and solitary planet
133. Planets and satellites added and their effects considered
136. How the imagined system may be made the system of na
ture, 137. Discussion of the relative motions of the sun, moon
and earth, under the action of their mutual influences, 139. The
moon's acceleration; motion of her apsides, nodes, &c., and the
discovery of the change in the figure of the earth's orbit, 146.
Perplexity occasioned by the seeming discrepancy between the
observed and computed motion of the moon's perigee, 149. Fi-
nally removed by Clairault, 150. Changes in the earth's figure
occasioned by its rotation, 153. The form of equilibrium reached,
155. The precession of the equinoxes caused by the protuberant
matter at the earth's equator, 157. Moon affected by the re-
dundant matter at the earth's equator, 160. Wonderful questions
answered by an examination of the moon, 161.
THE STABILITY OF THE PLANETARY SYSTEM.
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; its 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 new planet
detected by its disc, 218. Walker's computations, 219. Pierce's
views, 221. Leverrier claims Neptune to be the planet of
theory.
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.
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.
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.
Maedler's theory of the central sun, 319. The attributes of God
as displayed in the universe, 324.
STRUCTURE OF THE UNIVERSE.
AN EXPOSITION OF THE PROBLEM WHICH THE HFAVENS 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 willing spirit that would learn their mysterious being. Often have I swept backward in imagination six thousand years, and stood beside our Great Ances
tor, as he gazed for the first time upon the going 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."
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