Gilles de Roberval

Gilles Personne de Roberval, who lived from 1602 to 1675, was a French mathematician born at Roberval near Beauvais, whose name was originally Gilles Personne, with Roberval the place of his birth. Like René Descartes he was present at the siege of La Rochelle in 1627, went to Paris that year, was appointed to the philosophy chair at Gervais College in 1631, and in 1634 was made chair of mathematics at the Royal College of France, a chair whose holder had to propose problems and resign in favour of anyone who solved them better, yet he kept it until his death. Working just before the invention of the infinitesimal calculus, he treated the quadrature of surfaces and the cubature of solids by his Method of Indivisibles, but lost much of the credit because Bonaventura Cavalieri published a similar method he had found independently. He also devised a general method of drawing tangents by treating a curve as described by a moving point, and a method of deriving one curve from another that yields finite areas, curves that Evangelista Torricelli named Robervallian lines. He wrote a work on the system of the world that supports the Copernican system, invented the Roberval balance, and was on ill terms with Descartes.