When originally published in 1952, this book filled a gap in the history of philosophy and science and remains an important work today, because it puts the main mathematical and physical discoveries of Descartes in an accessible form, for the benefit of English readers. Descartes is acknowledged to be the founder of modern mathematics, through his invention of analytical geometry and this volume charts Descartes' role in bringing a unity into algebra and geometry and the development of mathematics into a discipline which could be properly analysed. Carefully paraphrasing the Géométrie, this volume retains much of Descartes' original notation as well as the original diagrams. The volume also discusses the considerable contribution that Descartes made to the physical sciences which involved accurate work in optics, light, sight and colour.