Lagrange, Joseph Louis, Comte
Joseph Louis Lagrange, Comte (zhôzĕf´ lwē kôNt lägräNzh´), 1736–1813, French mathematician and astronomer, b. Turin, of French and Italian descent. Before the age of 20 he was professor of geometry at the royal artillery school at Turin. With his pupils he organized (1759) a society from which the Turin Academy of Sciences developed. Among his early successes were his method of solving isoperimetrical problems, on which the calculus of variations is based in part; his researches on the nature and propagation of sound and on the vibration of strings; and his studies on the libration of the moon and on the satellites of Jupiter. On the recommendation of Euler and D'Alembert, Frederick the Great invited him (1766) to succeed Euler as director of mathematics at the Berlin Academy of Sciences. The memoirs of the academy were enriched by his distinguished treatises, and during this time he wrote his chief work, Mécanique analytique, a treatment of mechanics based solely on algebra and the calculus and containing not a single diagram or geometric explanation. This was published (1788) in Paris, where he had been called by Louis XVI in 1787. In 1793 he became president of the commission on weights and measures; he was influential in causing the adoption of the decimal base for the metric system. A professor at the École polytechnique from 1797, he developed the use in teaching of the analytic method that he so skillfully employed in his research. He wrote Théorie des fonctions analytiques (1797) and Leçons sur le calcul des fonctions (1806), both based on his lectures. Under Napoleon, Lagrange was made senator and count; he is buried in the Panthéon. His contributions to the development of mathematics also include the application of differential calculus to the theory of probabilities and notable work on the solution of equations. In astronomy he is known for his calculations of the motions of planets.