French mathematician who wrote 789 papers, a quantity exceeded only by Euler and Cayley, which brought precision and rigor to mathematics. He invented the name for the determinant and systematized its study and gave nearly modern definitions of limit, continuity, and convergence. Cauchy founded complex analysis by discovering the Cauchy-Riemann equations (although these had been previously discovered by d'Alembert).

Cauchy also presented a mathematical treatment of optics, hypothesized that ether had the mechanical properties of an elasticity medium, and published classical papers on wave propagation in liquids and elastic media. After generalizing Navier's equations for isotropic media, he formulated one for anisotropic media. Cauchy published his first elasticity theory in 1830 and his second in 1836. Both were rather ad hoc and were riddled with problems, and Cauchy proposed a third theory in 1839. Cauchy also studied the reflection from metals and dispersion relationships.

Cauchy extended the polyhedral formula in a paper which was criticized by Malus. His theory of substitutions led to the theory of finite groups. He proved that the order of any subgroup is a divisor of the order of the group. He also proved Fermat's three triangle theorem. He refereed a long paper by Le Verrier on the asteroid Pallas and invented techniques which allowed him to redo Le Verrier's calculations at record speed. He was a man of strong convictions, and a devout Catholic. He refused to take an oath of loyalty, but also refused to leave the French Academy of Science.

Additional biographies: MacTutor (St. Andrews), Bonn