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 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. 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 Characteristics of comets, 223. Reduced to law by Newton, Halley's comet of 1682, 227. Its return in 1759 predicted, 229. 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, 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. 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 THE STRUCTURE OF THE UNIVERSE. INTRODUCTORY LECTURE. 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 B2 (17) 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." The curiosity excited on this first solemn night-the consciousness that in the heavens God had declared his glory-the eager desire to comprehend the mys teries that dwell in these bright orbs, have clung to the descendants of him who first watched and wondered, through the long lapse of six thousand years. In this boundless field of investigation, human genius has won its most signal victories.-Generation after generation has rolled away, age after age has swept silently by, but each has swelled by its contribution the stream of discovery.-One barrier after another has given way to the force of intellect-mysterious movements have been unravelled-mighty laws have been revealed-ponderous orbs have been weighed, their reciprocal influences computed, their complex wanderings made clear, until the mind, majestic in its strength, has mounted step by step up the rocky height of its self-built pyramid, from whose starcrowned summit it looks out upon the grandeur of the universe, self-clothed with the prescience of a God. With resistless energy it rolls back the tide of time, and lives in the configuration of rolling. worlds a thousand years ago, or more wonderful, it sweeps away the dark curtain from the future, and beholds those celestial scenes which shall greet the vision of generations when a thousand years shall have rolled away, breaking their noiseless waves on the dim shores of eternity. To trace the efforts of the human mind in this long and ardent struggle, to reveal its hopes and fears, its long years of patient watching, its moments of despair and hours of triumph-to develop the means by which the deep foundations of the rock-built pyra |