Joseph Bertrand

Joseph Louis François Bertrand (11 March 1822 to 5 April 1900) was a French mathematician and historian of science whose work emphasized number theory, differential geometry, probability theory, economics and thermodynamics. He lends his name to various paradoxes in mathematics and economics, known as Bertrand's paradoxes, and to Bertrand's theorem on the stability of celestial orbits. He was a professor at the École polytechnique and the Collège de France and a member of the Paris Academy of Sciences, of which he was the permanent secretary for twenty-six years. In 1849 he was the first to define real numbers using what is now called a Dedekind cut.