The question whether Leverrier should receive the sole credit of the discovery was warmly discussed. Arago took the extreme ground that actual publication alone should be considered, reject ing Adams's communications to Airy and Challis as quite un worthy of consideration. He also suggested that the name of Leverrier should be given to the planet, but this proposal was received with so little favour outside of France that he speedily withdrew it, proposing that of Neptune instead.
The observations at the first opposition showed that the planet was moving in a nearly circular orbit, and was at a mean distance from the sun much less than that set by Leverrier as the smallest possible. The latter had in fact committed the error of deter mining the limits by considering the variations of the elements one at a time, assuming in the case of each that while it varied the others remained constant. But a simultaneous variation of all the elements would have shown that the representation of the observations of Uranus would be improved by a simultaneous diminution of both the eccentricity and the mean distance, the orbit becoming more nearly circular and the planet being brought nearer to the sun. But this was not at first clearly seen, and Benjamin Peirce of Harvard University went so far as to main tain that there was a discontinuity between the solution of Adams and Leverrier and the solution offered by the planet itself, and that the coincidence in direction of the actual and computed planet was an accident. But this view was not well founded, and the only explanation needed was to be found in Leverrier's faulty method of determining the limits within which the planet must be situated. As a matter of fact the actual motion of the planet during the century preceding, as derived from Leverrier's ele ments, was much nearer the truth than the elements themselves were. This arose from the fact that his very elliptic orbit, by its large eccentricity, brought the planet near to the sun, and there fore near to its true position, during the period from 1780 to 1845, when the action on Uranus was at its greatest.
The observations of the first opposition enabled Sears Cook Walker of the National Observatory, Washington, in February 1847 to compute the past positions of the planet, and identify it with a star observed by Lalande at Paris in May 1795. This
being communicated to the Paris observatory, an examination. of Lalande's manuscript showed that he had made two observa tions of the planet, on the 8th and loth of May and finding them discordant had rejected one as probably in error, and marked the other as questionable. A mere re-examination of the region to see which observation was in error would have led him to the dis covery of the planet more than half a century bef ore it was actually recognized. The identity of Lalande's star with Neptune was also independently shown by Petersen of Altona.
BIBLIOGRAPHY.-The principal sources for the history of the discovery of Neptune are the Astronomische Nachrichten, vols. xxv., xxvi., xxviii., and Lindenau's paper in the Ergtinzungsheft to this publication, pp. 1-31 (Altona, 1849). In the Memoirs of the Royal Astronomical Society, vol. xvi., Airy gave a detailed history of the circumstances connected with the discovery, so far as he was cog nizant of them. Documents pertaining to the subject are found in the Monthly Notices of the Royal Astron. Society. B. A. Gould, Report to the Smithsonian Institution on the History of the Discovery of Neptune, published by the Smithsonian Institution (Washington, 185o), is the most complete and detailed history of all the circum stances connected with the discovery, and with the early investiga tions on the orbit of the planet, that has been published. Leverrier's investigation was published in extenso as an addition to the Con naissance des temps, and Adams's as an appendix to the Nautical Almanac for 1851. Peirce's discussions, so far as published at all, are found in the Proceedings of the American Academy of Arts and Sciences. The first computations of the orbit after the discovery were made by Sears Cook Walker, and published by the Smithsonian Institution (1848-185o). General tables of the motion of Neptune are in Kowalski's Tables du mouvement de la planate Neptune; Newcomb's Investigation of the Orbit of Neptune, Washington, Smithsonian In stitution (1866) ; Leverrier's Annales de l'Observatoire de Paris; Memoirs, vol. xiv. (1877), and lastly Newcomb's "Tables" in Astron. Papers of the American Ephemeris, vol. vii., part iv. Tables of the satellite are found in Newcomb, The Uranian and Neptunian Systems; appendix to the Washington observations for 1873.