THE PLANET NEPTUNE. 15 



vibrates around this curve as in the dotted line, a curve 

 which is not reproduced at every revolution, but will 

 pass through an indefinite number of variations. To 

 compute the exact orbit which a planet will describe, 

 subject to the attractions of all the members of the solar 

 system, is one of the grandest problems in astronomy. 



Hitherto mathematicians had only aspired to compute 

 the disturbing influence of one body upon another, when 

 the magnitude and position of both bodies were known. 

 But, in the case of Uranus, it was necessary to solve the 

 inverse problem which Professor Airy had pronounced 

 hopeless, viz., from the observed disturbances of one 

 body, to compute the place of the disturbing body. 



After taking his degree of Bachelor of Arts in Jan- 

 uary, 1843, with the honor of Senior "Wrangler, Mr. 

 Adams ventured to attack this problem, and obtained 

 an approximate solution by supposing the disturbing 

 body to move in a circle at twice the distance of 

 Uranus from the sun. His results were so far satis- 

 factory, as to encourage him to attempt a more complete 

 solution. Accordingly, in February, 1844, having ob- 

 tained through Professor Airy a* complete copy of the 

 Greenwich observations of Uranus, from 1754 to 1830, 

 he renewed his computations, which he continued dur- 

 ing that and the subsequent years. In September, 1845, 

 he had obtained the approximate orbit of the disturbing 

 planet, which he showed to Professor Challis, the director 

 of the observatory at Cambridge ; and near the close of 

 the next month, he communicated his results to the 



