LAGRANGE, JOSEPH Louis, Comte. one of the greatest of mathematicians, was b. at Turin in 1736. He was of French extraction, andwas the grandson of Descartes. When still a youth he solved the isoperimetrical problem of Euler, and when scarcely 19 years of age was appointed professor of mathematics in the artillery school in Tut in. Frederick the great appointed him to be Euler's successor, as director of the academy at Berlin, in 1750. After Frederick's death, Naples, Sardinia, Tuscany, and France strove for the honor of offering Lagrange a better position. He accepted the offer of France, and took up his quarters in the Louvre in 1787, obtaining a pension of 0,000 francs (S238). In 1791 he was chosen a foreign member of•the royal society of London, and the same year the national assembly confirmed to him his pension, and he was appointed one of the directors of the mint. He was in great danger during the reign of terror, but escaped, and was afterwards professor in the normal and polyteehni schools. Napoleon made him a member of the senate, bestowed on him the grand cross of the legion of honor, the title of count, and many other favors. He died April 10, 1813, and was interred in the Pantheon. His principal works are: Memoirs "ou the Motion of Fluids" and "the Propagation of Sound;" another memoir refuted D'Alembert's views regarding the theory of the earth's formation. When only 24 years
of age, he published his New Method, subsequently known as the Calculus of Variations, thus adding a new and powerful weapon to the philosophical armory. In 1704 his memoir on the " Libration of the Moon" carried off the first prize at the academy. It was in this treatise that he showed the extent and fruitfulness of the principle of " virtual velocities" which he afterwards so successfully applied to mechanics. Next appeared his works on the solution of "numerical" and "algebraic" equations; and in 1787 his Micanique Analytique, a work in which mechanics is reduced to a mere question of cal culation. His last important works were: Caleut des Fonetions Analytiques; Trate des Fonctions; and Igsolution des Equations Numeriques. Lagrange made many other impor tant investigations in pure and mixed mathematics, and particularly in astronomy—the chief subjects of which are: the problem of three bodies, the long inequality of Jupiter and Saturn, the moon's secular inequality, attraction of ellipsoids, perturbations of Jupiter's satellites, diminution of the eelifAic, variation of the elements of the planetary orbits, etc.