260 ELEMENTS OF GENERAL SCIENCE 



plane of the planet's orbit. Like Jupiter and Saturn it is 

 of low density, is in an early stage of its development, and 

 cannot possibly be the abode of life. 



263. The discovery of Neptune. The discovery of Neptune 

 was one of the most striking things in the history of science, 

 and proves the high accuracy of astronomical methods. 



After a planet has been observed a few weeks, its orbit 

 can be computed and the position it will occupy at any 

 future time can be determined. Its motion depends not 

 only upon the attraction of the sun but, to some slight 

 extent, upon the attraction of other planets for it. 



After Uranus had been discovered, its orbit was computed 

 and the place it would occupy at future dates was predicted. 

 In 1820, or about forty years after its discovery, it was found 

 to be deviating very slightly from its predicted position. 

 Between 1830 and 1840 the deviation had become still 

 greater. The cause was a question of the greatest interest 

 to astronomers. 



The problem of finding the position of a more remote 

 planet which might have disturbed Uranus from its posi- 

 tion by the observed amount in these forty or sixty years 

 was one of such great difficulty that the foremost mathema- 

 ticians of the world did not even attempt to solve it. It was, 

 however, boldly attacked by two young men who had just 

 graduated from college Mr. J. C. Adams, of Cambridge, 

 England, and Mr. Joseph Leverrier, of Paris. Each worked 

 independently of the other and, in fact, without announcing 

 that he was attempting to solve the problem. Adams com- 

 pleted his work first, and found that if there were in a certain 

 part of the sky another planet farther out from the sun than 

 Uranus, it would have produced the deviations in the motions 

 of Uranus which had been observed. He attempted, without 

 success, to have it sought for both at Cambridge and at the 

 Royal Observatory in Greenwich. In the meantime Leverrier, 

 who had finished his computations by a method entirely 



