AN ASTRONOMER’S DREAM VERIFIED.
The most fertile region in astronomical discovery during the last quarter of a century has been the planetary members of the solar system. In 1833, Sir John Herschel enumerated ten planets as visible from the earth, either by the unaided eye or by the telescope; the number is now increased more than fivefold. With the exception of Neptune, the discovery of new planets is confined to the class called Asteroids. These all revolve in elliptic orbits between those of Jupiter and Mars. Zitius of Wittemberg discovered an empirical law, which seemed to govern the distances of the planets from the sun; but there was a remarkable interruption in the law, according to which a planet ought to have been placed between Mars and Jupiter. Professor Bode of Berlin directed the attention of astronomers to the possibility of such a planet existing; and in seven years’ observations from the commencement of the present century, not one but four planets were found, differing widely from one another in the elements of their orbits, but agreeing very nearly at their mean distances from the sun with that of the supposed planet. This curious coincidence of the mean distances of these four asteroids with the planet according to Bode’s law, as it is generally called, led to the conjecture that these four planets were but fragments of the missing planet, blown to atoms by some internal explosion, and that many more fragments might exist, and be possibly discovered by diligent search.
Concerning this apparently wild hypothesis, Sir John Herschel offered the following remarkable apology: “This may serve as a specimen of the dreams in which astronomers, like other speculators, occasionally and harmlessly indulge.”
The dream, wild as it appeared, has been realised now. Sir John, in the fifth edition of his Outlines of Astronomy, published in 1858, tells us:
Whatever may be thought of such a speculation as a physical hypothesis, this conclusion has been verified to a considerable extent as a matter of fact by subsequent discovery, the result of a careful and minute examination and mapping down of the smaller stars in and near the zodiac, undertaken with that express object. Zodiacal charts of this kind, the product of the zeal and industry of many astronomers, have been constructed, in which every star down to the ninth, tenth, or even lower magnitudes, is inserted; and these stars being compared with the actual stars of the heavens, the intrusion of any stranger within their limits cannot fail to be noticed when the comparison is systematically conducted. The discovery of Astræa and Hebe by Professor Hencke, in 1845 and 1847, revived the flagging spirit of inquiry in this direction; with what success, the list of fifty-two asteroids, with their names and the dates of their discovery, will best show. The labours of our indefatigable countryman, Mr. Hind, have been rewarded by the discovery of no less than eight of them.