THE OUTER PLANETS 121 �in the midst of his labors Flemming died, and shortly after Bessel himself, who had taken up the matter after Flemming's death. �Somewhat later Arago, then head of the Paris observ- atory, who had also been impressed with the existence of such a planet, requested one of his assistants, a re- markable young mathematician named Leverrier, to un- dertake its investigation. Leverrier, who had already evidenced his marked ability in celestial mechanics, pro- ceeded to grapple with the problem in the most thor- ough manner. He began by looking into the pertur- bations of Uranus by Jupiter and Saturn. He started with Bouvard's work, with the result of finding it very much the reverse of good. The farther he went, the more errors he found, until he was obliged to cast it aside entirely and recompute these perturbations himself. The catalogue of Bouvard's errors he gave must have been an eye-opener generally, and it speaks for the ability and precision with which Leverrier conducted his investigation that neither Airy, Bessel, nor Adams had detected these errors, with the exception of one term noticed by Bessel and subsequently by Adams.* The result of this recalculation of his was to show the more clearly that the irregularities in the motion of Uranus could not be explained except by the existence of an- other planet exterior to him. He next set himself to �* Adams, "Explanation of the Motion of Uranus," 1846. ��� �
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