SECOND EDITION. xiii 



first he had not taken into account the earlier 

 Greenwich observations; but these were supplied 

 to him by the Astronomer Royal, in 1844. In Sep- 

 tember, 1845, Mr. Adams communicated to Prof. 

 Challis values of the elements of the supposed 

 disturbing body ; namely, its mean distance, mean 

 longitude at a given epoch, longitude of perihelion, 

 eccentricity of orbit, and mass. In the next month, 

 he communicated to the Astronomer Royal values 

 of the same elements, somewhat corrected. The 

 note, p. 306, vol. n., of the present work, in which 

 the names of MM. Le Verrier and Adams are men- 

 tioned in conjunction, was in the press in August, 

 1846, a month before the planet* was seen. As I 

 have stated in the text, Mr. Adams and M. Le Ver- 

 rier assigned to the unseen planet nearly the same 

 position; they also assigned to it nearly the same 

 mass ; namely, 2^ times the mass of Uranus. And 

 hence, supposing the density to be not greater than 

 that of Uranus, it followed that the visible diameter 



memorandum his design of examining its effect : but deferred the 

 calculation till he had completed his preparation for his exami- 

 ntion in January 1843. He was the Senior Wrangler on that 

 occasion. The conjecture of an exterior planet was not quite 

 new. It had occurred to Mr. Hussey, M. Alexis Bouvard, and 

 and M. Hansen, as early as 1834. See Mr. Airy's Account read 

 to the Royal Astronomical Society, Nov. 13, 1846. 



