520 Prof. G. B. Airy on the History of the Discovery of 



series of tabular errors of Uranus. * * * The list you 

 have sent will give Mr. Adams the means of carrying on in 

 the most effective manner the inquiry in which he is engaged." 



The next letter shows that Mr. Adams had derived results 

 from these errors. 



No. 9. Professor Challis to G. B. Airy. / 



"Cambridge Observatory, Sept. 22, 1845. 

 " My friend Mr. Adams (who will probably deliver this 

 note to you) has completed his calculations respecting the 

 perturbation of the orbit of Uranus by a supposed ulterior 

 planet, and has arrived at results which he would be glad to 

 communicate to you personally, if you could spare him a few 

 moments of your valuable time. His calculations are founded 

 on the observations you were so good as to furnish him with 

 some time ago ; and from his character as a mathematician, 

 and his practice in calculation, I should consider the deduc- 

 tions from his premises to be made in a trustworthy manner. 

 If he should not have the good fortune to see you at Green- 

 wich, he hopes to be allowed to write to you on this subject." 



On the day on which this letter was dated, I was present at 

 a meeting of the French Institute. I acknowledged it by the 

 following letter : — 



No. 10. G. B. Airy to Professor Challis. 



" Royal Observatory, Greenwich, 1845. Sept. 29. 

 " I was, I suppose, on my way from France, when Mr. 

 Adams called here: at all events, I had not reached home, 

 and therefore, to my regret, I have not seen him. Would 

 you mention to Mr. Adams that I am very much interested 

 with the subject of his investigations, and that I should be de- 

 lighted to hear of them by letter from him?" 



On one of the last days of October, 184-5, Mr. Adams 

 called at the Royal Observatory, Greenwich, in my absence, 

 left the following important paper: — 



No. 11. J. C. Adams, Esq. to G. B. Airy. 

 " According to my calculations, the observed irregularities 

 in the motion of Uranus may be accounted for by supposing 

 the existence of an exterior planet, the mass and orbit of 

 which are as follows : — 



Mean distance (assumed nearly in accordance 



with Bode's law) 38'4 



Mean sidereal motion in 365-25 days l°30'-9 



Mean longitude, 1st October, 1845 323 34 



Longitude of perihelion 315 55 



Excentricity 0-1610 



Mass (that of the sun being unity) 00001656. 



