54 6 THE POPULAR SCIENCE MONTHLY. 



pired. In the next year he was elected to a fellowship in Pem- 

 broke College. 



It was while still an undergraduate that Adams began the 

 investigation of the irregularities of Uranus, that culminated in 

 the discovery of the new, remote planet Neptune. The possibility 

 of the existence of such a planet, acting upon the motions of 

 Uranus, had been suggested by Bouvard in 1821. Mr. Adams's 

 attention was drawn to the subject, according to Prof. Glaisher, 

 by reading Airy's report upon recent progress in astronomy in 

 the British Association volume for 1832-33. On July 3, 1841, 

 at the beginning of his second long vacation, when he was in his 

 twenty-third year, he made the 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 Ura- 

 nus which are yet unaccounted for ; in order to find whether they 

 may be attributed to the action of an undiscovered planet be- 

 yond it; and, if possible, thence to determine the elements of 

 its orbit, etc., approximately, which would probably lead to its 

 discovery." 



Prof. Glaisher further relates the history of the calculations : 

 " In 1843, the year in which he took his 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 Prof. Challis, to the astronomer royal, for 

 the results of the Greenwich observations of Uranus. When they 

 were obtained, Adams 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 dis- 

 turbing planet, but retaining the same assumption as before with 

 respect to the mean distance. In September, 1845, he communi- 

 cated to Prof. Challis the values which he had obtained for the 

 mass, heliocentric longitude, and elements of the orbit of the 

 assumed planet. The same results, slightly corrected, he took 

 with him to the Royal Observatory, Greenwich, on October 21, 

 1845. The paper which he left at the observatory on this occa- 

 sion also contained a list of the residual errors of the mean longi- 

 tude of Uranus, after taking account of the disturbing effect of the 

 new planet, at dates extending from 1690 to 1840." Prof. Challis 

 began the search for the planet on July 29, 1846, three weeks be- 

 fore it was in opposition, and continued the observations for two 

 months. His plan was to sweep a zone covering the computed 

 place of the body, and extending over 30 of longitude and 10 of 

 latitude. et For the first few nights the telescope was directed to 



