LEVERRIER, URBAIN JEAN JOSEPH (1811-1877), one of the greatest astronomers of modern times, was born at St LO in Normandy, March 11, 1811. His father, who held a small post under Government, made great efforts to send him to Paris, where a brilliant examination gained him, in 1831, admittance to the Ecole Polytechnique. The distinction of his career there was rewarded with a free choice amongst the departments of the public service open to pupils of the school. He selected the administration of tobaccos, addressing himself especially to chemical researches under the guidance of Gay-Lussac, and gave striking proof of ability in two papers on the combinations of phosphorus with hydrogen and oxygen, published in Annales de Chinzie et de Physique (1835 and 1837). His astronomical vocation, like that of Kepler, came from without. The place of teacher of that science at the Ecole Polytechnique falling vacant in 1837, it was offered to and accepted by Leverrier, who, "docile to circumstance," instantly abandoned chemistry, and directed the whole of his powers to celestial mechanics. The first fruits of his arduous labours were contained in two memoirs presented to the Academy, September 16 and October 14, 1839. Pursuing the investigations of Laplace, he demonstrated with greater rigour the stability of the solar system, and calculated the limits within which the eccentricities and inclinations of the planetary orbits vary. This remarkable debut excited much attention, and, on the recommendation of Arago, he took in hand the theory of Mercury, producing, in 1843, tables of that planet far superior in accuracy to those hitherto available. The perturbations of the comets discovered, the one by Faye in November 1843, the other by De Vico a year later, were minutely investigated by Leverrier, with the result of disproving the supposed identity of the first with Lexell's lost comet of 1770, and of the other with Tycho's of 1585. On the other hand, he made it appear all but certain that Vico's cornet was the same with one seen by Lahire in 1678.

He was once more, by the summons of Arago, recalled to planetary studies, and this time it was to Uranus that his attention was directed. Step by step, with sagacious and patient accuracy, he advanced to the great discovery which has immortalized his name. Carefully sifting all the known causes of disturbance, he showed that one hitherto unknown must be added to their number, and on the 23d of September 1846 the planet Neptune was discerned by Calle at Berlin, within one degree of the spot indicated by Leverrier. See ASTRONOMY, p. 813.





This memorable achievement was greeted with an outburst of public enthusiasm, and requited with a shower of public distinctions. Academies vied with each other in enrolling Leverrier among their members ; the Royal Society awarded him the Copley medal; the king of Denmark sent him the order of the Thinnebrog ; he was named officer in the Legion of Honour, and preceptor to the Comte de Paris ; a chair of astronomy was created for his benefit at the Faculty of Sciences ; he was appointed adjunct astronomer to the Bureau of Longitudes. Returned to the Legislative Assembly in 1849 by his native department of Manche, he voted with the anti-republican party, but devoted his principal attention to subjects connected with science and education. After the coup d'etat he became a senator and inspector-general of superior instruction, sat upon the commission for the reform of the Ecole Polytechnique (1854), and, on January 30, 1854, succeeded Arago as director of the Paris observatory. His official work in the latter capacity would alone have strained the energies of an ordinary man. The institution had fallen into a state of lamentable inefficiency. Leverrier placed it on a totally new footing, freed it from the control of the Bureau of Longitudes, and raised it to its due rank among the observatories of Europe. He did not, however, escape the common lot of reformers. His uncompromising measures and unconciliatory manner of enforcing them raised a storm only appeased by his removal, February 5, 1870. Three years later, on the death of his successor Delaunay, he was reinstated by M. Thiers, but with authority restricted by the supervision of a council. In the midst of these disquietudes, he executed with unflinching resolution a task the gigantic proportions of which cannot be contemplated without amazement. This was nothing less than the complete revision of the planetary theories, together with a laborious comparison of results with the most authentic observations, and the construction of tables representing the movements thus corrected. It required all his indomitable perseverance to carry through to the end a purpose which failing health continually menaced with frustration. He had, however, the happiness of living long enough to perfect his work. Three weeks after he had affixed his signature to the printed sheets of the theory of Neptune he died at Paris, in his sixty-seventh year, September 23, 1877. By his marriage with Mademoiselle Choquet, who survived him little more than a month, he left a son and daughter.

The dkcovery with which the memory of this great man is popularly i.lentified was only an incident in his career. The elaboration of the scheme of the heavens traced out by Laplace in the Mecanique Cel.s.le was it; larger aim, for the accomplishment of which forty years of unremitting industry barely sufficed. The work once done, however, may almost be said to have been done for all time, from the extraordinary care with which errors were guarded against, and imperfections in the data allowed for. The organization of the meteorological service in France is entirely due to Leverrier, and the present system of international weather-warnings is the realization of a design which lie warmly promoted. Ile founded the Association Scientifique, and was active in introducing a practical scientific element into public education. His inference of the existence, between Mercury and the emu, of an appreciable quantity of circulating matter (Comptes 1819, ii. p. 379), though unquestionably sound, has not yet been satisfactorily verified by observation. lie was twice, in 1868 and 1876, the recipient of the gold medal of the Royal Astronomical Society, London, and the university of Cambridge conferred upon him, in 3875, the honorary degree of LL.D. All his planetary tables have been adopted by the Nautical Almanac, as well as by the Connaissance des Temps.

The Annales de l'Obserratoire de Paris, the publication of which was set on foot by Leverrier, contain, in vole. i. - vi. (Memolics), 1855-61, and x. - xiv., 1874-77, his theories and tables of the several planets. In vol. i. will be found, besides his masterly report on the observatory, a general theory of secular inequalities, in which the development of the disturbing function is carried to a point hitherto unattempted. The memoirs and papers communicated by him to the Academy have been summarized in Comptes Rendus, 1839-76, and the more important published in full either separately, or in the Come. des Temps and the Journal des Mathematiyucs. That entitled Developpemens sur differents points de la Theo?* des perturbations, 1841, has been translated in part xviii. of Taylor's Scientific Memoirs, For his scientific work see Professor Adams's address, Monthly Notices, vol. xxxri. p. 232, and M. Tisserand's review in Ann. de l'Obs., torn. xv., 1880 ; for a notice of his life, RI. Bertrand's " loge Histo•ique," Mean. de l'Ac. dcs Sciences, torn. xli., 2me senie. (A. M. C.)