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THE CENTURY'S PROGRESS IN ASTRONOMY 



Ceres, happened on another tiny moving star, similarly 

 }} located, which soon revealed itself as planetary. Thus 

 two planets were found where only one was expected* 



The existence of the supernumerary was a puzzle, but 

 Olbers solved it for the moment by suggesting that 

 Ceres and Pallas, as he called his captive, might be frag- 

 ments of a quondam planet, shattered by internal ex- 

 plosion, or by the impact of a comet. Other similar 

 fragments, he ventured to predict, would be found when 

 searched for. William Herschel sanctioned this theory, 

 and suggested the name asteroids for the tiny planets. 

 The explosion theory was supported by the discovery of 

 another asteroid, by Harding, of Lilienthal, in 1804, and 

 it seemed clinched when Olbers himself found a fourth 

 in 1807. The new-comers were named Juno and Yesta. 

 respectively. 



There the case rested till 1845, when a Prussian 

 amateur astronomer named Hencke found another aste- 

 roid, after long searching, and opened a new epoch of 

 discovery. From then on the finding of asteroids be- 

 came a commonplace. Latterly, with the aid of pho- 

 tography, the list has been extended to above four hun- 

 dred, and as yet there seems no dearth in the supply, 

 though doubtless all the larger members have been re- 

 vealed. Even these are but a few hundreds of miles in 

 diameter, while the smaller ones are too tiny for meas- 

 urement. The combined bulk of these minor planets is 

 believed to be but a fraction of that of the earth. 



Olbers's explosion theory, long accepted by astrono- 

 mers, has been proven open to fatal objections. The 

 minor planets are now believed to represent a ring of 

 cosmical matter, cast off from the solar nebula like the 

 rings that went to form the major planets, but prevented 



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