The french physicist **Joseph Louis Lagrange** He was born on January 25, 1736 and died on April 10, 1813. He was one of the most important mathematical and physical scientists of the late 18th century. He invented and brought to maturity the calculus of variations and then applied the new discipline to CELESTIAL MECHANICS. , especially to find improved solutions to the THREE-BODY PROBLEM.

Lagrange also contributed significantly to the numerical and algebraic solution of equations and to number theory. In your classic *mecanique analytique* (Analytical Mechanics, 1788), he transformed mechanics into a branch of mathematical analysis. The treatise summarized the main results known in mechanics in the 18th century, and it is notable for this to use the theory of differential equations. Another of Lagrange's central concerns was the foundations of calculus. In a 1797 book he stressed the importance of Taylor's series and the concept of function. His search for rigorous foundations and generalizations has set the stage for Augustin Cauchy, Niels Henrik Abel, and Karl Weierstrass in the next century.

Lagrange served as a professor of geometry at the Royal Artillery School in Turin (1755-66) and there he helped found the Royal Academy of Science in 1757. Because of overwork and low pay, he suffered from his health, leaving him with weakened constitution for life. When Leonhard Euler left the Berlin Academy of Science, Lagrange succeeded him as director of the mathematical section in 1766. In 1787 he left Berlin to become a member of the Paris Academy of Science, where he remained for the rest of his career. A mild and diplomatic man, Lagrange survived the French Revolution. In the 1990s (1790), he worked on the metric system and defended a decimal basis. He also taught at the Polytechnic School, which he helped found. Napoleon appointed him to the Legion of Honor and Empire Account in 1808.

Abbott, David, ed., The Biographical Dictionary of Scientists and Mathematicians (1985); Boyer, Carl B., A History of Mathematics (1968); Burzio, F., Lagrange (1942)