We have yet *another* French mathematician from the 1600s to thank for our system of plotting coordinates on a graph. (Can you believe how many good mathematicians there were in France back then?) René Descartes (1596–1650) published his treatise, *La géométrie*, in 1637, as an appendix to his scientific and philosophical masterpiece, *Discours de la methodé* ("Discourse on the Method"). *La géométrie* was the only mathematical work Descartes ever published, but it changed mathematics forever by inventing a way of linking algebra and geometry. Today, when we use coordinates to define the points in a plane, we're using the Cartesian Coordinate System, named after Descartes. |