René Descartes (1596-1650), French mathematician, physicist, and philosopher, who made valuable contributions to mathematics, physics, and philosophy. Descartes was a pioneer and major figure in 17th century rationalism. He represents a major break with the Aristotelianism and Scholasticism of the Medieval period. René Descartes is regarded as the father of modern philosophy. → Descartes ray, → Cartesian coordinates, → Cartesian vortex theory.
Fr.: rayon de Descartes
Same as → rainbow ray.
Fr.: formule de Descartes
A formula that gives the position of an image formed by highly → paraxial rays from a → spherical mirror. It is quite accurately given by: 1/xo + 1/xi = 2/xC, where xo is the distance along the → principal axis from the mirror to the object, xi is the distance from mirror to image, and xC is the distance from the mirror to its center of curvature. Any distance measured on the same side of the mirror as the reflecting surface is positive; on the other side, negative. Thus for a → concave mirror xC is positive; for a → convex mirror, negative.