The correspondence between Descartes and Fermat (Q2714848)

All correspondence between Descartes and Fermat in 1637-1639, excluded one letter, was addressed to Mersenne, highly confided and respected by both of them. The letters of Sept.-Dec. 1637, directly after publication of Descartes' \textit{Discours de la Méthode}, cited here from \textit{Œuvres de Fermat} (ed. P. Tannery and Ch. Henry), Paris, 1841 and R. Descartes, \textit{Œuvres} (ed. Ch. Adam and P. Tannery), v. 1-12, Paris, 1897-1913, concerned the problem of refraction. Descartes re-established the polemics in Jan. 1638, when he had obtained through Mersenne a little essay by Fermat \textit{Methodus ad disquirendam maximam et minimam}. (Before that Mersenne had asked Fermat to give his opinion about Descartes' algebraic method to find the tangent of a curve, and Fermat had demanded to compare this method with his own.) In this and some further letters to Mersenne (March--June 1638) Descartes was rather critical to Fermat's method, but in a letter of July 1638, sent directly to Fermat, he concluded finally that this is \textit{très bonne}. The author compares also the manners of expression of both Fermat and Descartes. NEWLINENEWLINENEWLINEFor more details of this last correspondence he indicates to his paper in Mnémosyne 2, 29-57 (1992).