126 Britain's Heritage of Science 



and we may here confine oursel ves to its salient features . When 

 the path of Uranus, the planet discovered by William 

 Herschel in 1781, was carefully examined by Alexis Bouvard 

 of Paris, it was found that it showed irregularities which could 

 not be accounted for by the gravitational action of the other 

 planets known at the time. Bouvard himself entertained 

 the idea that the discrepancies might be due to the attraction 

 of an ultra-Uranian planet, and an English amateur 

 astronomer, the Rev. J. T. Hussey, wrote in 1834 to Airy, 

 who was then Astronomer Royal, offering to make a search 

 for this planet, if some idea of the position could be given 

 him. Adams heard of and became interested in these 

 discussions as an undergraduate, and the following memo- 

 randum, in his own handwriting, dated 3rd July, 1841, is 

 still preserved : " Formed a design, in the beginnuig 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, etc., approximately, which would probably lead to its 

 discovery." 



Having graduated in 1843, he at once set to work on the 

 problem. His first solution was communicated to James 

 Challis, the head of the Cambridge Observatory, in September 

 1845, and about the 1st of November of the same year he sent 

 his calculations to Airy, indicating the position at which the 

 new planet might be looked for. Although, according to the 

 American astronomer Newcomb, two or three evenings 

 devoted to the search could not have failed to make the planet 

 known, Airy was not satisfied, but sent a further enquiry to 

 Adams, which, apparently, was left unanswered. Mean- 

 while. Leverrier, a young French astronomer, had, at the 

 suggestion of Arago, taken up the same subject, and made 

 an independent calculation, which led to a position of the 

 unknown planet agreeing so closely with Adams', that Airy's 

 interest became seriously engaged, and he suggested to 

 Chalhs, on the 9th of July, 1846, to make a search for the 

 planet. Three weeks later Chain's started work in a leisurely 

 way, but was hampered by the want of a good star map. 



