Biela's comet, 219. Fears excited of collision with the earth, in 1832, 220. Its nebulous character, 221. Its double character in 1846, 222. Separation of the comets, 224. Vast periods of some comets, 225. Comets seen to transit Scale of the planetary system, 233. Radius of the earth's orbit too small a unit, 234. The velocity of light determined from the eclipses of Jupiter's satellites, and employed as a unit, 236. Parallax of the fixed stars, 237. No parallax sen- sible to the naked eye. Great distance of the fixed stars, inferred from this fact, 240. Bradley's researches for paral- lax, 244. Discovery of nutation and its value, 245. Discovery of aberration—its explanation,. 246. Herschell's researches for parallax, 247. Discovery of the revolving stars, 249. Power of modern telescopes, 250. Bessel discovers the paral- Distances separating man from the stars, 268. Hipparchus discovers a new and brilliant star, 270. The new star of 1572, 271. The new star of 1604, ib. The disappearance of old stars, 272. Changes of Algol, 273. Periodical stars, 274. Gravitation extended to the sphere of the fixed stars, ib. Periods of some of the binary systems, 275. Herschel sounds the depth of the Milky Way, 277. Seeks the direction of the solar motion, 277. His reasoning, 279. Argelander's research for the point towards which the solar system is moving, 280. Struve's investigation for the quantity of angu- lar motion of the system, as seen from stars of the first mag- nitude, 284. His father's research for the relative distances of stars of different magnitudes, 285. Peters's research for the parallax of stars of the second magnitude, 287. Maedler's THE STRUCTURE OF THE UNIVERSE. INTRODUCTORY CHAPTER. AN EXPOSITION OF THE PROBLEM WHICH THE HEAVENS PRESENT FOR SOLUTION. THE subject to which your attention is invited, claims no specific connection 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 the 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 B millions of six thousand years, and stood beside our Great Ancestor 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 watched 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 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 splendour, 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 mysteries 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 down 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 develope the means by which the deep foundations of the rock-built pyramid of science have been laid, and to follow it as it slowly rears its stately form from age to age, until its vertex pierces the very heavens-these are the objects proposed for accomplishment, and these are the topics to which I would invite your earnest attention. The task is one of no ordinary difficulty. It is no feast of fancy, with music and poetry, with eloquence and art, to enchain the mind. Music is here-but it is the deep and solemn harmony of the spheres. Poetry is here-but it must be read in the characters of light, written on the sable garments of night. Architecture is here-but it is the colossal structure of sun and system, of cluster and universe. Eloquence is here" but there is neither speech nor language. Its voice is not heard," yet its resistless sweep comes over us in the mighty periods of revolving worlds. Shall we not listen to this music, because it is deep and solemn? Shall we not read this poetry, because its letters are the stars of heaven? Shall we refuse to contemplate this architecture, because "its architraves, its archways, seem ghostly from infinitude?" Shall we turn away from this surging eloquence, because its utterance is made through sweeping worlds? No-the mind is ever inquisitive, ever ready to attempt to scale the most rugged steeps. Wake up its enthusiasm— fling the light of hope on its pathway, and no matter how rough, and steep, and rocky it may prove, onward! is the word which charms its willing powers. It is not my wish or design to introduce you to the dark technicalities of science, neither do I propose to rest satisfied with the barren statement of the results which have been reached by the efforts of genius. While on the one hand I shall endeavour to shun all attempt at critical scientific demonstration, which could only be intelligible to the professed student of astronomy, I shall on the other hand, fearlessly attempt such an exposition of the processes and trains of reasoning by which great truths have been elicited, as to show to every intelligent mind that the problem is not impos |