Baron Augustin Louis Cauchy, French mathematician, c 1820.

FRANCE - MAY 31: Etching of Cauchy (1789-1857) who was employed as a military engineer before ill health forced him to retire and teach mathematics at the Ecole Polytechnique, Paris. His contribution to mathematics is considerable, notably on partial differential equations, the mathematics of elasticity, algebra and calculus. Along with Karl Friedrich Gauss, he founded the modern form of complex analysis, which was to have a profound effect on mathematics for the rest of the 19th century. (Photo by SSPL/Getty Images)