happily supplied by the discovery of the numerous star-form planets, occupying the very space where the unexplained vacancy presented a strong objection to his theory. According to Bode, the distances of the planets may be expressed nearly as follows: the Earth's distance from the Sun being 10. Comparing these values with the actual mean distances of the planets from the Sun, cannot but remark the near agreement, and can scarcely hesitate to pronounce that the respective distances of the planets from the Sun, were assigned according to a law, Although we are entirely ignorant of the exact law, and of the reason for that law.Brinkley's Elements, p. 89. 471. The Asteroids are much smaller in size than the older planets-they all revolve at nearly the same distances from the Sun, and perform their revolutions in nearly the same periodsSheir orbits are much more eccentric, and have a much greater incli vation to the ecliptic-and what is altogether singular, except iu the case of comets-some of their orbits cross each other; so that here is even a possibility that two of these bodies may, some time, in the course of their revolutions, come into collision. The orbit of Vesta is so eccentric, that she is sometimes farther from the Sun than either Ceres, Pallas, or Juno, although her mean distance is many millions of miles less than theirs. The orbit of Vesta crosses the orbits of several other asteroids, in two opposite points. The student should here refer to the Figures, Map I. of the Atlas, and verify such of these particulars as are there represented. It would be well for the teacher t. require him to observe particularly the positions of their orbits, and to state their different degrees of inclination to the plane of the ecliptic. 472. From these and other circumstances, many eminent astronomers are of opinion, that these telescopic planets are the fragments of a large celestial body which once revolved between Mars and Jupiter, and which burst asunder by some tremendous convulsion, or some external violence. The discovery of Ceres, by Piazzi, on the first day of the present century, drew the attention of all the astronomers of the age to that region of the sky, and every inch of it was minutely explored The consequence was, that in the year following, Dr. Olbers, of Bremen, announced to the world the discovery of Pallas, situated not many degrees from Ceres, and very much resembling it in size. What How substantially jurified? 471. Size of the asteroids? Distance from the Sun? Periodic time? Forms of their orbits? Position with respect to the eliptic other singularity in their orbits? What remarkable facts respecting the orbit o. Vester $72. What conclusion has been drawn from these facts? Progress of discovery? 473. From this discovery, Dr. Olbers first conceived the idea that these bodies might be the fragments of a former world; and if so, that other portions of it might be found either in the same neighborhood, or else, having diverged from the same point, "they ought to have two common points of reunion, or two nodes in opposite regions of the heavens through which all the planetary fragments must sooner or later pass." 474. One of these nodes he found to be in the constellation Virgo, and the opposite one in the Whale; and it is a renark able coincidence that it was in the neighborhood of the latter constellation that Mr. Harding discovered the planet Juno. In order, therefore, to detect the remaining fragments, if any existed, Dr. Olbers examined, three times every year, all the small stars in Virgo and the Whale; and it was actually in the constellation Virgo, that he discovered the planet Vesta. Since that time, very many additional asteroids have been discovered, and it is not unlikely that still additional fragments of a similar description will hereafter be discovered. Dr. Brewster attributes the fall of meteoric stones to the smaller fragments of these bodies happening to come within the sphere of the Earth's attraction. Meteoric stones, or what are generally termed aerolites, are stones which sometimes fall from the upper regions of the atmosphere upon the Earth. The substance of which they are composed, is, for the most part, metallic; but the ore of which it consists is not to be found in the same constituent proportions in any krown substance upon the Earth. Their fall is generally preceded by a luminous appearance, a hissing noise, and a loud explosion; and when found immediately after their descent, they are always hot, and usually covered with a black crust, indicating a state of exterior fusion. Their size varies from that of small fragments of inconsiderable weight to that of the most ponderous masses. They have been found to weigh from 300 pounds to several tons; and they have descended to the earth with a force sufficient to bury them many feet under the surface. Some have supposed that they are projected from volcanoes in the Moon; others that they proceed from volcanoes on the Earth; while others imagine that they are generated in the regions of the atmosphere; but the truth probably is not yet ascertained. Ir some instances, these stones have penetrated through the roofs of houses, and proved destructive to the inhabitants. If we carefully compute the force of gravity in the Moon, we shall find that if a body were projected from her surface with a momentum that would cause it to move at the rate of 8200 feet in the first second of time, and in the direction of a line joining the centers of the Earth and Moon, it would not fall again to the surface of the Moon; but would become a satellite to the Earth. Such an impulse might, ir deed, cause it, even after many revolutions, to fall to the earth. The fall, therefore, of these stones, from the air, may be accounted for in this manner. Mr. Harte calculates, that even a velocity of 6000 feet in a second, would be sufficient to carry a body projected from the surface of the Moon beyond the power of her attraction. If so, a projectile force three times greater than that of a cannon, would carry a a body from the Moon, beyond the point of equal attraction, and cause it to reach the Earth. A force equal to this is often exerted by our volcanoes, and by subterrar.ean stenin. Hecce, there is no impossibility in the supposition of their coming from the Moon. 478. Theory of Dr. Olbers? 474. Where did he find these nodes? What remarkable coincidence? Dr. Olbers' efforts? Discoveries since? Dr. Brewster's idea respecting meteoric stones? What are meteoric stones? Circumstances of their fall? Size and weight? Supposed origin? Could they have fallen from the Moon? What computations f 475. Vesta is the only asteroid that can be seen with the ked eye. 476. The largest of the asteroids is probably about 220 miles in diameter; the smallest is less than 20 miles. 477. The following table comprises their names, &c. : 240,194,177 1,555 Dec. 15, Ilind London. 24. Themis... 287,371,205 2,035 April 5, 1853 De Gasparis. Naples. 25. Phocæa... 219,507,125 1,359 April 6, Chacornac... Marseilles. 27. Euterpe. 214,561,317 1,313 Nov. 8, 26. Proserpine.. 242,841,895 1,581 May 5, 28. Bellona. 254,036,415 1,692 March 1, 1854 Luther... ... 216,275,879 1,329 July 22, 31. Euphrosyne. 288,251,117 2,045 Sept. 1, 32. Pomona... 236,556,455 1,520 Oct. 26, 33. Polyhymnia. 261,863,473 1,770 Oct. 28, 34. Circe... 215,615,324 1,608 April 15, 1855 Chacornac.. Paris. Luther.... Bilk. Hind... London. Bilk. Ferguson..... Washington, D.C Goldschmidt. Paris. Chacernac... Paris. 35. Leucothea.. 274,897,315 1,904 April 19, Luther.... Bilk. 36. Atalanta. 251,079,425 1,662 Oct. 5, Goldschmidt. Paris. 37. Fides.. Luther....... Bilk. .Leda... 89. Lætitia. 40 Harmonia... 207,295,315 1,247 March 1, " Goldschmidt. Paris. 41 Daphne. 253,183,175 1,683 May 23, Goldschmidt. Paris. 42 Isis. 223,095,367 1,392 May 23, 44 Nysa...... 43 Ariadne..... 201,445.216 1,195 April 15. 1857 Pogson...... Oxford. 221,441,119 1,377 May 27, 45 Eugenia.... 248,801,071 1,640 June 27, 46 Hestia....... 230,994,315 1,467 Aug. 16, 47. Aglaia....... 263,432,471 1.786 Sept. 15, 48. Doris ....... 284,293,510 2.003 Sept. 19, 49. Pales.... 281,833,015 1,977 Sept. 19, 50. Virginia.... 242,203,713 1,575 Oct. 4, 51. Nemausa... 216,296,571 1,329 Jan. 22, 1858 Laurent...... Nismes. 52. Europa..... 263,431,110 1,994 Feb. 4, 53. Calypso Goldschmidt. Paris. 239,521,473 1,549 April 4, 54. Alexandra. 247.986.795 1,632 Sept. 11, 55. Pandora. 252,262,491 1,674 Sept. 11, 56 Melote.... 237.347,157 1.528 Sept. 9, 1859 50 Echo.. 218,796,250 1,352 Sept. 15, 81. Danaë 272,898,017 1.883 Sept. 19, Ferguson..... Washington. D.O 62. Erato.. 286,145,013 2,022 Oct. 10, 33. Ansonia.... 218,971,905 1,354 Feb. 10, 1861 De Gasparis Naples. 73. Clytie.... 243,806,171 1,590 April 7, 1862 Tuttle Cambridge, Mass Marseilles. Clinton, N. Y. 309,736,915 2.277 Oct. 21, 92. Undina 291,844,560 2,081 July 26, 1367 Peters.. Clinton, N. Y. 77. Frigga. 244,294,717 1,595 Nov. 12, 81. Terpsichore 261,151,257 1,763 Sept. 30, 1864 Watson...... Copenhagen. Clinton, N. Y. Bilk. Ann Arbor, Mich Marseilles. Luther.... Bilk. 83. Beatrix... 222,061,135 1,383 April 26, 1865 De Gasparis. Naples. Bilk. Clinton, N. Y. Madras. Clinton, N. Y. D'Arrest. Peters.. Luther... 66 Pogson. Since the discovery of Felicitas, nineteen other asteroids have been announ:AN Alaking the whole Lumber, up to 1873, one hundred and twenty-eight. CHAPTER VII. PRIMARY PLANETS-JUPITER AND SATURN. 473. JUPITER is the largest of all the planets belonging to the Bolar system. It may be readily distinguished from the fixed wars, by its peculiar splendor and magnitude; appearing to the aked eye almost as resplendent as Venus, although it is more than seven times her distance from the Sun. When his right ascension is less than that of the Sun, he is our morning star, and appears in the eastern hemisphere before the Sun rises; when greater, he is our evening star, and lingers in the western hemisphere after the Sun sets. Nothing can be easier than to trace Jupiter among the constellations of the zodiac; for in whatever constellation he is seen to-day, one year hence he will be seen equally advanced in the next constellation; two years hence, in the next; three years hence, in the next, and so on; being just a year, at a mean rate, in passing over one constellation. The exact mean motion of Jupiter in its orbit, is about one-twelfth of a degree in a day; which amounts to only 30° 20' 32" in a year. For 12 years to come, he will, at a mean rate, pass through the constellations of the zodiac, as follows: 479. Jupiter is the next planet in the solar system above the asteroids, and performs his annual revolution around the Sun in nearly 12 of our years, at the mean distance of 475,000,000 of miles; moving in his orbit at the rate of 29,000 miles an hour. The exact period of Jupiter's sidereal revolution is 11 years, 10 months, 17 days. 14 hours, 21 minutes, 25 seconds. His exact mean distance from the Sun is 475,693,000 miles; consequently, the exact rate of his inotion in his orbit is 28,744 miles per hour 480. He revolves on an axis, which is nearly perpendicular to the plane of his orbit, in 9 hours, 55 minutes, and 50 seconds; so that his year contains 10,471 days and nights; each about 2 hours long. His form is that of an oblate spheroid, whose polar diameter 478. Comparative size of Jupiter? How distinguished from the fixed stars? When morning star, &c.? Is he easily traced? 479. His position in the system? His pori raic time? Distance from the Sun? Rate of motion? 480. Time of diurna. revcin tion? Position of axis? Length of his days? Number in his year? His forra וי ais oblateness? Difference of equatorial and polar diameters? The Earth? Cator |