16 HISTORY OF ASTRONOMY. 



Astronomer Koyal, together with a comparison of his 

 theory with the observations. The discrepancies were 

 quite small, except for the single observation of 1690, 

 which differed by 44"; this observation not having been 

 used in the equations of condition. Professor Airy, 

 in acknowledging the receipt of this letter, pronounced 

 the results extremely satisfactory, and inquired of Mr. 

 Adams whether his theory would explain the error of 

 the tables in regard to the distance of Uranus from the 

 sun, which error he had shown to be very great. To 

 this inquiry Mr. Adams returned no answer for nearly 

 a year ; probably because he was not able to answer the 

 question entirely to his own satisfaction. 



Meanwhile, this grand problem was undertaken by 

 another mathematician who was entirely ignorant of the 

 progress which Mr. Adams had made ; for none of his 

 results had yet been published. In the summer of 1845, 

 M. Arago, of Paris, requested M. Le Yerrier, a young 

 mathematician, who had already distinguished himself 

 by his improved tables of Mercury, to attempt the solu- 

 tion of this problem. This he accordingly did, and his 

 success astonished all -Europe. He commenced his in- 

 vestigations by inquiring whether the observations of 

 Uranus could be reconciled with the supposition, that 

 this body is subject to no other attraction than that of 

 the sun and the known planets, acting according to the 

 Newtonian law of gravitation. He carefully computed 

 the effects due to the action of Jupiter and Saturn, 

 neglecting no quantities until he had proved that their 



