Lagrange, Joseph Louis (1736–1813)

Italian-born French mathematician. His Mécanique analytique (1788) applied mathematical analysis, using principles established by Isaac Newton, to such problems as the movements of planets when affected by each other's gravitational force. He presided over the commission that introduced the metric system in 1793.

Lagrange was born in Turin and appointed professor of mathematics at the Royal Artillery School there when he was just 19. In 1766 Frederick the Great of Prussia invited him to become director of the Berlin Academy of Sciences, and in 1787, on the invitation of Louis XVI, Lagrange moved to Paris as a member of the French Royal Academy. He was professor at the Ecole Polytechnique from 1797.

In 1755, advancing beyond Newton's theory of sound, Lagrange settled a dispute on the nature of a vibrating string. Later he proved some of Pierre de Fermat's theorems, which had remained unproven for a century.

In Mécanique analytique, Lagrange succeeded in reducing the theory of solid and fluid mechanics to an analytical principle, explaining it without the aid of a single diagram or construction. His lectures at the Ecole Polytechnique were published as Théorie des fonctions analytiques (1797) and Leçons sur le calcul des fonctions (1806).