Correspondence between the countess Palatine Elisabeth (1618-1680) and the René Descartes (1596-1650) - French philosopher, mathematician, scientist, and writer. Between the years 1643 and 1649, Elisabeth and Descartes exchanged fifty-eight letters. Their correspondence contains philosophical writings by Elisabeth, revealing her mastery of metaphysics, analytic geometry, and moral philosophy, as well as her interest in natural philosophy.