Rene Descartes (1596-1650), French mathematician and philosopher, also known as Renatus Cartesius. Descartes most important scientific works were in mathematics. Descartes created analytical or co- ordinate geometry, known as Cartesian geometry, in which geometrical problems are converted into algebraic forms so that algebraic techniques may be applied to their solution. He attempted to explain planetary motions in terms of vortices surrounding the Sun, but this theory was later refuted. He is also considered the father of modern philosophy, and stated, I think, therefore I am". Engraving from Vies des Savants Illustres (1876)."