« PreviousContinue »
effect produced on the fixed stars, its disk widened, Watching it for several nights, he detected its motion in space, and, mistaking its true character, announced the discovery of a new comet A few months5 examination revealed the error, and the new body was universally admitted to be a member of the solar system—new to us, but older perhaps than our own world. It is now known that Uranus had been previously observed by other astronomers. Indeed, Le Monier at Paris had watched it for twelve successive nights, but pronounced it a fixed star. Since he had also seen it on previous occasions, had he been an orderly observer, he would doubtless have detected its planetary character; but he was extremely careless, as may be inferred from the fact related by Arago, that he had been shown one of Le Monier's observations of this planet written on a paper bag which originally contained hairpowder purchased at a perfumer's. Uranus may be seen by a person of strong eyesight in a perfectly dark sky, if he previously knows its exact position among the stars. Its faintness is due to its great distance from the earth. Were it as near as the sun, it would appear twice as large as Jupiter.
Motion In Space.—Uranus revolves about the sun at a mean distance of 1,754,000,000 miles. Its year exceeds eighty-four of ours.
Dimensions.—Its diameter is about 33,000 miles. It is lighter than water, having a density about equal to that of ice.
Seasons.—We know little of the seasons of Uranus, Since its axis lies in tlie plane of its orbit, the stm winds in a spiral form around the whole planet. The light and heat are only T^ws- of that which we receive; the light is about the quantity which would be afforded by three hundred full moons. The inhabitants of Uranus can see Saturn, and perhaps Jupiter, but none of the planets within the orbit of the latter.
Telescopic Features.—No spots or belts have been discovered with any telescope yet made. The time of rotation and other features so familiar to us in the nearer planets, are unknown with regard to Uranus.
Satellites.—Uranus has four moons, of which little is known except the curious fact that their orbits are nearly perpendicular to the plane of the planet's orbit, and that their movements are retrograde—-i. e.9 in the same direction as the hands of a watch.
The god of the sea. Sign j>, his trident.
Description.—Neptune is the far-off sentinel at the very outposts of the solar system, being the most distant planet of which we have any knowledge. It is invisible to the naked eye, and appears in the tel' escope as a star of the eighth magnitude.
Discovery.—For many years the motions of Uranus were such as to baffle the most perfect calcula* tions. While far-distant Saturn came around to his place true to the minute and second, even after his journey of nearly thirty years, "Uranus defied arithmetic, and refused to conform to the time set down for him on the heavenly dial.
At length it was suggested by several astronomers that there was another planet outside of its orbit, whose attraction produced these perturbations. So marked was this impression with Herschel, that he writes: ""We see it as Columbus saw America from the shores of Spain. Its movements have been felt trembling along the far-reaching line of our analysis with a certainty not far inferior to ocular demonstration." Finally, two young mathematicians, Leverrier of Paris, and Adams of Cambridge, England, each unknown to the other, set themselves about the task of finding the place of this new planet. The problem was this: Given the disturbances produced by the attraction of the unknown planet, to find its orbit and its place in the orbit Adams, after assiduous labor for nearly two years, completed his calculations and submitted them to Prof. Airy, the Astronomer Royal, in October, 1845. In the summer of 1846, Leverrier laid a paper before the Academy of Sciences in Paris, announcing the position of the unknown planet. Prof. Airy, hearing of this, was so impressed with the value of Adams's calculations, that he wrote to Prof. Challis, of Cambridge, to use his large telescope to search that quarter of the heavens. Prof. Challis did as requested, and saw a star wliich afterward proved to be tlie planet so anxiously sought for, although at that time he failed to ascertain its true character. On September 23d, of the same year, Leverrier wrote to Berlin, asking for assistance in searching for the planet. Dr. Galle, that same evening, turned the large telescope of the Observatory to the place indicated, and almost immediately detected a bright star not laid down in the maps. This proved to be the predicted planet, found within less than a degree of the spot described by Leverrier. Such is the history of one of the grandest achievements of the human mind. It stands as an ever fresh and assuring proof of the exactness of astronomical calculations, and the power of the intellect to understand the laws of the God of Nature.
Motion In Space.—Neptune revolves about the sun at a mean distance of about 2,750,000,000 of miles. The Neptunian year is equal to nearly 165 terrestrial ones. Its motion in its orbit is the slowest of any of the planets, since it is the most remote from the sun. The velocity decreases from Mercury, which moves at the rate of 105,000 miles per hour, to Neptune, whose rate is only 12,000 miles.
Dimensions.—Its diameter is about 37,000 miles. Its volume is nearly 100 times that of the earth. Its density is about that of Uranus, a little less than that of water.
Seasons.—As the inclination of its axis is unknown, nothing can be ascertained concerning its seasons. The sun gives to Neptune but y^Vo the light and heat which we receive.
Though at the extreme of the solar system, 2,650 millions of miles beyond us, the same heavens bend above, the same starry sky is seen by night—the Milky Way is no nearer to the eye, the fixed stars shine no more brightly. The planets, however, are all too near the sun to be seen, except Saturn and Uranus. The Neptunian astronomers, if there be any, are well situated for observing the orbits of comets, and for measuring the annual parallax of the stars, since they have an orbit of 5,500 million miles in diameter, and hence the angle must be 30 times as great as that which the terrestrial orbit affords.
Telescopic Features.—On account of the recentness of the discovery of this planet and its immense distance, nothing is known of its rotation or physical features.
Satellites.—Neptune has one moon, at nearly the same distance from it as our own moon is from the earth. The revolution of this about the planet, which is accomplished in about six days, has furnished the materials for calculating the mass of Neptune.
METEOES AND SHOOTING STAES.
Description.—All are familiar with those luminous bodies that flash through our atmosphere as if