BIOGRAPHICAL NOTICE. xxv 



reply to it, and applied himself to his second calculation with a different mean distance. 

 With respect to Challis, he has explained in his report to the Cambridge Observatory 

 Syndicate 1 that it might reasonably be supposed that the position of the planet was only 

 roughly determined, and that a search for it must necessarily be long and laborious. In 

 1845, when Adams had completed his calculations, the planet was considerably past opposition, 

 and Challis had no thought of commencing the search then. The succeeding interval 

 until June 1846 was occupied with observations of the planet Astraea, Biela's double comet, 

 and several other comets, and during this period he had little communication with Adams 

 respecting the new planet. Attention was again called to the matter by Le Verrier's 

 paper of June 1, and, as has been stated, the search was commenced on July 29. 



From the Astronomer Royal's "Account &c." we learn that he attached great importance 

 to the explanation of the error in radius vector. After giving the letter which he addressed 

 to Adams on this subject he states that he considered the establishment of the error of 

 the radius vector of Uranus to be a very important determination and proceeds, " I 

 therefore considered that the trial, whether the error of radius vector would be explained 

 by the same theory which explained the error of longitude, would be truly an experimentum 

 crucis. And I waited with much anxiety for Mr Adams's answer to my query. Had it 

 been in the affirmative I should have exerted all the influence which I might possess, 

 either directly, or indirectly through my friend Professor Challis, to procure the publication 

 of Mr Adams's theory. From some cause with which I am unacquainted, probably an 

 accidental one, I received no immediate answer to this enquiry. I regret this deeply for 

 many reasons. While I was expecting more complete information on Mr Adams's theory, 

 the results of a new and most important investigation reached me from another quarter." 

 This refers to Le Verrier's paper of June 1, 1846, after giving an account of which, the 

 Astronomer Royal proceeds : " This memoir reached me about the 23rd or 24th of June. 

 I cannot sufficiently express the feeling of delight and satisfaction which I received from 

 it. The place which it assigned to the disturbing planet was the same, to one degree, 

 as that given by Mr Adams's calculations which I had perused seven months earlier. 

 To this time I had considered that there was still room for doubt of the accuracy of 

 Mr Adams's investigations... But now I felt no doubt of the accuracy of both calculations, 

 as applied to the perturbation in longitude. I was however still desirous, as before, of 

 learning whether the perturbation in radius vector was fully explained." 



Le Verrier replied to this enquiry in a letter from which some passages have already been 

 quoted. With reference to Le Verrier's explanations regarding the error of radius vector 

 the Astronomer Royal writes : " It is impossible, I think, to read this letter without being 

 struck with its clearness of explanation, with the writer's extraordinary command, not 

 only of the physical theories of perturbation, but also of the geometrical theories of the 

 deduction of orbits from observation, and with his perception that his theory ought to 

 explain all the phenomena, and his firm belief that it had done so. I had no longer 

 any doubt upon the reality and general exactness of the prediction of the planet's place." 

 After describing the contents of Le Verrier's third paper, of August 31, 1846, the 

 Astronomer Royal proceeds: "My analysis of this paper has necessarily been exceedingly 

 imperfect, as regards the astronomical and mathematical parts of it; but I am sensible 

 that in regard to another part it fails totally. I cannot attempt to convey to you the 

 1 This report, on account of its importance, is reprinted in extenso on pp. xlix liv. 



