History of the Discovery of the Planet Neptune. 189 
posing the disturbing body to move in a circle, at twice the dis- 
tance of Uranus from the sun. His results were so far satisfac- 
tory, as to encourage him to attempt a more complete solution. 
Accordingly in February, 1844, having obtained through Profes- 
sor Airy, a complete copy of the Greenwich observations of Ura- 
nus, he renewed his computations, which he continued during 
that and the subsequent years. In September, 1845, he had ob- 
tained 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 communi- 
cated his results to the Astronomer Royal, together with a com- 
parison of his theory with the observations. ‘The discrepancies 
were quite small, except for the single observation of 1690. Pro- 
fessor Airy, in acknowledging the receipt of this letter, pronoun- 
ced the results extremely satisfactory, and enquired of Mr. Ad- 
ams whether his theory would explain the error of the tables in 
regard to the distance of Uranus from the sun, which error he 
had shewn to be very great. ‘T'o this enquiry Mr. Adams return- 
ed 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 pub- 
lished. In the summer of 1845, M. Arago of Paris, requested M. 
Verrier, a young mathematician who had already distinguish- 
ed himself by his improved tables of Mercury, to attempt the 
solution of this problem. This he accordingly did, and his sue- 
cess astonished all Europe. He commenced his investigations by 
enquiring whether the observations of Uranus could be reconciled 
with the supposition, that this body is subject to no other attrac- 
tion than that of the sun and the known planets, acting accord- 
ing to the Newtonian law of gravitation. He carefully compu- 
ted the effects due to the action of Jupiter and Saturn, neglecting 
ed with the Astronomer Royal at Greenwich, a 
the elements of the supposed disturbing planet, 
