Pierre De Fermat, a French mathematician, born in southern France in August, 1601, died in Toulouse, Jan. 12, 1665. He studied law, and became in 1631 councillor at the parliament of Toulouse, devoting his leisure to mathematical studies. D'Alembert, Lagrange, and other French authorities claim for him the honor of having been the principal inventor of the differential calculus; and Laplace states that it was due to Fermat and his colaborer, Pascal. His theories are chiefly contained in his treatise De Maximis et Minimis, republished in 1679 with his miscellaneous scientific writings. Descartes combated his propositions concerning the calculus, and Fermat opposed Descartes's views in respect to geometry and optics.