Urbain Jean Joseph Leverrier, a French astronomer, born in St. Lo, March 11, 1811. He studied successively at the college of St. L6, at Caen, and at the college of Louis le Grand in Paris, and graduated at the polytechnic school. He then obtained a place in the tobacco bureau, and as his new occupation required some knowledge of chemistry, he pursued that science at leisure, and published in 1837 two memoirs on the combinations of phosphorus with hydrogen and oxygen. He devoted himself, however, principally to mathematics, and soon obtained a minor appointment in the polytechnic school. From this time he studied continually the highest problems in speculative astronomy, investigating especially the irregularities manifested in the course of the heavenly bodies. Two memoirs on this subject, supporting the observations of Lagrange, and asserting that the masses of the planets Jupiter, Saturn, and Uranus were sufficient to insure the stability of the solar system, were submitted in 1839 to the academy of sciences. These and some other writings attracted the friendship of Arago, who induced him to study closely the orbit of Mercury and its perturbations.

In 1844 he presented to the academy a theory of the periodical comet of 1770, and a paper on that of 1843. These contributions to science obtained for him admission to the academy of sciences, to the astronomical section of which he was elected, Jan. 19, 1846. The success which had attended his calculations of the course of Mercury induced him to revise the still more imperfect tables of Uranus. His studies on this subject convinced him that the movements of this planet could not be explained by the attraction of any known bodies, and he accordingly sought further for the cause of its perturbations. Finally, on June 1, 1846, he indicated to the academy of sciences within 10° the place where a new planet might be seen on Jan. 1, 1847. This was in fact done by the German astronomer Galle, who discovered it, however, Sept. 23, 1846. Leverrier had made an error, but only of 2°. The sensation excited by this discovery was immense, and Leverrier received abundant honor. The king of Denmark sent him the order of the Danebrog; most of the academies of Europe inscribed his name on their lists; Salvandy, the minister of public instruction in France, had his bust erected in public with great ceremony; Arago declared that the new planet should be called Leverrier; a chair of mathematical astronomy was created for him in the faculty of sciences; the royal society of England sent him the Copley gold medal, and the grand duke of Tus'cany a splendidly bound copy of the works of Galileo. It is true that the planet only bore for a time the name of Leverrier, that of Neptune being subsequently given to it, but even this honor could hardly have added much to the renown of one whose name is so closely identified with it.

The priority of discovery was however contested in favor of a distinguished young English geometrician at St. John's college, Cambridge, Mr. Adams, who had arrived at the same conclusion about the same time, but who was less fortunate than his French rival in making it known to the world. (See Adams, John Couch.) In 1848 Leverrier made some ineffectual efforts to distinguish himself as a democratic leader, but it was not till 1849 that he was elected from La Manche to the legislative assembly, He modified his liberal views, took his place among the counter-revolutionary members, and occupied himself principally with questions of public instruction and with laws relative to scientific discoveries. He was in consequence appointed to prepare several important reports relative to the construction of electric telegraphs, the organization of the polytechnic school, and recruiting for the corps of engineers. When a decided division into parties took place in the assembly, Leverrier joined the imperialists. After the coup d'etat of Dec. 2, 1851, he was appointed senator, and some time after inspector general of public instruction. He exerted a decided influence on public instruction in France, particularly with regard to the polytechnic school.

In 1849-50 he read to the academy of sciences an account of new investigations into the movements of the planets, and in 1853 presented to it tables of the sun's rotation, with the complete system of the small planets situated between Mars and Jupiter. In 1853, on the death of Arago, Leverrier succeeded to the title and authority of director of the observatory. During his tenure of this office he was much occupied in urging upon government a reform of the old method of observations, which caused much dispute between himself and his colleagues. In September, 1859, he communicated to the academy of sciences a movement of the perihelion of Mercury, which could be accounted for only by the supposition of another planet, or perhaps a series of small bodies, moving between it and the sun. This communication called forth Dr. Lescarbault's revelation of a discovery which he asserted that he had made at Orgeres as early as March 25, 1859, of a new planet, which received the name of Vulcan, and which was announced through Leverrier to the academy of sciences in the beginning of 1860. But subsequent researches have failed to establish the existence of such a planet.

On June 3, 1861, Leverrier communicated to the academy of sciences a letter on the constitution of the planetary system, and on the theory and tables of Mars. The following are the results presented in this paper: 1. There is between Mars and the sun a ring of asteroids whose united mass is comparable to that of. Mercury. 2. At the distance of the earth from the sun there is a second ring of asteroids, whose mass is nearly equal to the 10th part of that of the earth. 3. The united masses of the asteroids between Mars and Jupiter is nearly equal to the third part of the mass of the earth. 4. The masses of the last two groups are complementary to each other. Ten times the mass of the group at the earth's distance added to three times the united mass of the zone between Mars and Jupiter is nearly equal to twice the mass of the earth. In 1870 Leverrier found it desirable to withdraw from the office of director of the observatory, differences having arisen between himself and other eminent astronomers. Delaunay succeeded to the post, which he retained till his death by drowning, Aug. 5, 1872, soon after which Leverrier was reappointed. Shortly before this he had published an important memoir on the theories of the four exterior planets.

This is noteworthy as in part withdrawing the ideas promulgated in the paper of 1861, above mentioned. "It has been proved," says Leverrier, "that the matter of which no account had hitherto been taken in the theory of Mars ought to have been added to the earth itself, the estimate of the mass of our planet being one eighth too small." This of course relates to the recognition of the fact that the sun's distance is not so great as has been supposed. For the diminution of the sun's distance and of all the distances within the solar system (save the moon's alone), in the proportion of about 143 to 149, corresponds to the reduction of the relative masses of the sun and all the planets as compared with the earth in the proportion of (143)3 to (149)3, or roughly as 137 to 155; which is the same as saying that the earth's mass is increased relatively in the proportion of 155 to 137, or by about an eighth part. " With regard to Mercury," Leverrier proceeds, "this confirmation is not yet complete. Several astronomers have placed on record the passage over the sun's disk of various small bodies, which could be nothing else but very small planets, but it has not been possible to determine the orbit of any one of them.

Whether we have to deal with the action of a certain number of small masses, or with that of matter distributed in the neighborhood of the sun, the theory of Mercury has been determined with considerable care, and the transits of the planet over the sun's disk furnish us with observations too precise to admit of any doubt of the accuracy of our results, especially as they have been obtained in the same manner as for Mars; and for this latter planet the confirmation which the theory has received leaves nothing more to be desired." He then recommends corresponding researches into the theory of the four large planets, as they would furnish us with data concerning any matter still unknown to us that may be situated in those regions. It is probable that the greater part of Leverrier's time will hereafter be given to this important subject.