Girard Desargues

Girard Desargues (1591 to 1661) was a French mathematician and engineer from Lyon, regarded as a founder of projective geometry. Born into a wealthy family of lawyers and officials, he spent much of his working life in Paris as part of the circle around Marin Mersenne, which included Descartes and the Pascals. His work centred on conic sections and perspective, and he invented a non-Greek way of doing geometry that treated points at infinity as ordinary points. His famous perspective theorem, that when two triangles are in perspective the meets of corresponding sides are collinear, was first published in 1648 in a work on perspective by Abraham Bosse. He also proposed practical devices such as a Seine water-raising machine and a stone-cutting method, and his writing was often obscure, so his ideas were long neglected.