20 HISTORY OF ASTEONOMY. 



different parts of the ecliptic. He finds that when he 

 locates the supposed disturbing planet in one part of the 

 ecliptic, the discrepancies between the observed and 

 computed effects are enormous. By varying the place 

 of the planet, the discrepancies become smaller, until at 

 a certain point they nearly disappear. Hence he con- 

 cludes that there is but one point of the ecliptic where 

 the planet can be placed, so as to satisfy the observations 

 of Uranus. Having thus determined its approximate 

 place, he proceeds to compute more rigorously its effects ; 

 and on the first of June, 1846, he announces as the 

 result of his investigations, that the longitude of the 

 disturbing planet for the beginning of 1847, must be 

 about 325. 



The result thus obtained by Le Terrier, differed but 

 one degree from that communicated by Mr. Adams 

 to Professor Airy, more than seven months previous. 

 Upon receiving this intelligence, Professor Airy ex- 

 pressed himself satisfied with regard to the general ac- 

 curacy of both computations, and immediately wrote to 

 Le Verrier, inquiring, as he had done before of Mr. 

 Adams, whether his theory explained the error of the 

 tables in respect to the distance of Uranus from the sun. 

 Le Verrier answered that the errors of radius- vector must 

 be accounted for, inasmuch as the equations of condition 

 depended on observations at the quadratures as well as at 

 the oppositions. Professor Airy was now so well con- 

 vinced of the existence of a planet yet undiscovered, that 

 he was anxious to have a systematic search for it forth- 



