88 Things not generally Known. 



of the earth would thereby be heated ll^OO 3 ; it would therefore be quite 

 fused, and for the most part reduced to vapour. Tf, then, the earth, 

 after having been thus brought to rest, should fall into the sun, which 

 of course would be the case, the quantity of heat developed by the shock 

 would be 400 times greater. 



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 five- 

 fold. With the exception of Neptune, the discovery of new 

 planets is confined to the class called Asteroids. These all 

 revolve in eliptic 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 accord- 

 ing 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 Her- 

 schel 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 hypo- 

 thesis, this conclusion has been verified to a considerable extent as a 

 matter of fact by subsequent discovery, the I'esult of a careful and mi- 

 nute 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 



