BIOGRAPHICAL NOTICE. xvii 



ciation for 1831-32 1 , and on July 3, 1841, he made the following memorandum: 

 "Formed a design at the beginning of this week of investigating, as soon as possible after 

 taking my degree, the irregularities in the motion of Uranus which are yet unaccounted 

 for, in order to find whether they may be attributed to the action of an undiscovered 

 planet beyond it ; and, if possible, thence to determine the elements of its orbit &c. 

 approximately, which would probably lead to its discovery." This memorandum was made 

 at the beginning of his second long vacation, when he had just entered upon his 

 twenty-third year 2 . 



In 1843, the year in which he took his B.A. degree, he attempted a first rough 

 solution of the problem on the assumption that the orbit was a circle with a radius 

 equal to twice the mean distance of Uranus from the Sun. The result showed that 

 a good general agreement between theory and observation might be obtained. In order 

 to make the data employed more complete, application was made through Professor 

 Challis, to Mr Airy, the Astronomer Royal, in February 1844, for the errors of the tabular 

 geocentric longitudes of Uranus for 1818 1826, with the factors for reducing them to 

 errors of heliocentric longitude. The Astronomer Royal at once supplied all the results 

 of the Greenwich observations of Uranus from 1754 to 1830. Adams now undertook a 

 new solution of the problem, taking into account the most important terms depending 

 on the first power of the eccentricity of the orbit of the supposed disturbing planet, but 

 retaining the same assumption as before with respect to the mean distance. In September, 

 1845, he gave to Professor Challis a paper containing numerical values of the mean longitude 

 at a given epoch, longitude of perihelion, eccentricity of orbit, mass, and geocentric longi- 

 tude for September 30, of the assumed planet. On September 22, 1845, Challis wrote 

 a letter of introduction to the Astronomer Royal beginning, " 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 ho would be glad to communicate to you, if you could spare him a few 

 moments of your valuable time." Adams called at the Royal Observatory, Greenwich, 

 in September, but the Astronomer Royal was absent in France. In the following month, 

 on October 21, 1845, Adams called again at the Royal Observatory, and not being suc- 

 cessful in seeing the Astronomer Royal, left a paper giving the following values of 

 the mass and orbit of the new planet : 



Mean distance (assumed nearly in accordance with JBode's law) 38'4 

 Mean sidereal motion in 365'25 days 1 30' 9" 



Mean longitude, 1st October, 1845 323 34' 



Longitude of perihelion 315 55' 



Eccentricity 0'1610 



Mass (that of the Sun being unity) 0'0001656 



The paper which he left on this occasion also contained a list of the residual 



1 This report does not contain any reference to the elliptic orbit, and that Bouvard was therefore obliged 



possibility of the irregularities being due to an undis- to reject the ancient observations entirely (Keport, p. 154). 

 covered exterior planet. It is merely mentioned that it " The original memorandum, written by itself on a 



seems impossible to unite all the observations in one slip of paper, is reproduced in facsimile facing p. liv. 



c2 



