Lagrange, Joseph-Louis

later count de L'Empire

born Jan. 25, 1736, Turin, Sardinia-Piedmont

died April 10, 1813, Paris, France

Italian-born French mathematician who made important contributions to number theory and to classical and celestial mechanics.

By age 25 he was recognized as one of the greatest living mathematicians because of his papers on wave propagation (see wave motion) and maxima and minima (see maximum; minimum) of curves. His prodigious output included his textbook Mécanique analytique (1788), the basis for all later work in this field. His remarkable discoveries included the Lagrangian, a differential operator characterizing a system's physical state, and the Lagrangian points, points in space where a small body in the gravitational fields of two large ones remains relatively stable.

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