Page:Popular Science Monthly Volume 41.djvu/562

546. In the next year he was elected to a fellowship in Pembroke 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 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."

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 disturbing planet, but retaining the same assumption as before with respect to the mean distance. In September, 1845, he communicated 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 occasion also contained a list of the residual errors of the mean longitude 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 before 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. "For the first few nights the telescope was directed to