MERSENNE, MARIN. - French scientist and theologian, born at Oizé (Sarthe) on 8 Sept. 1588, died in Paris on 1 Sept. 1648. After completing his studies at the College of La Flèche, he entered the Order of Minims. His name is still unjustly associated almost exclusively with his friendship with Descartes (q.v.). It should be noted in this regard that when Mersenne left the College of La Flèche, Descartes was only 13 years old, and many of Descartes’ principal works predate the *Discours de la méthode* (1637). M., “the general secretary of learned Europe” of his century, as Haureau writes, is much more than “Descartes’ man” and occupies a place in the great scientific and intellectual revolution of the 17th century. In contact with all the most renowned scientists and philosophers of the time, he served as a point of connection, meeting place, and understanding, often succeeding in overcoming personal rivalries and disagreements, not always of a doctrinal nature, among his friends and correspondents. From a group of scientists whom he gathered around himself (Étienne Pascal, Mydorge, Hardy, Roberval, the Abbé Chambon, Pailleur, Montholon) there arose the *Academia Parisiensis*, the first nucleus of what would become the *Académie des Sciences*. His ideal remained always to found an international Academy (under the patronage of the pope and Christian princes) that would bring together theologians, philosophers, jurists, physicists, chemists, and so on. His name belongs more to the history of science and music than to that of philosophy, having also been a distinguished musicologist.
He dealt in fact with ancient and modern music in its various aspects: the nature of sound, the art of singing, harmony, composition (*Les préludes de l’harmonie universelle*, Paris 1634; *L’harmonie universelle, contenant la théorie et la pratique de la musique*, 2 vols., ibid. 1636–37, where, among other things, he adopts the theory of the subjectivity of sensible qualities). He conducted research on musical instruments, designing portable organs; and his experiments on vibrating strings and pipes enabled him to discover and announce precise laws that for about three centuries have borne his name.
The *Quaestiones celebérrimae in Genesim* (Paris 1623) treat questions of philosophy, astronomy, cosmology, and music. In *L’impieté des déistes et des plus subtils libertins découverte et réfutée par raison de philosophie et de théologie* (2 vols., ibid. 1624) he refutes intellectual “libertinage,” especially that of Bruno (“a bad author,” p. 364) and Charron (q.v.), and combats skepticism in *La vérité des sciences contre les sceptiques ou Pyrrhoniens* (ibid. 1635), where, before Descartes, he appeals to immediate evidence, demonstrating that the skeptic’s doubt destroys itself, since whoever doubts everything at least knows with certainty that he doubts (p. 204). He collected and re-edited the principal works of ancient mathematicians in the *Synopsis mathematica* (ibid. 1626; reprinted in 1644 under the title *Universae geometriae mixtaeque mathematicae synopsis*). Among his other writings should be mentioned his translation of Galileo’s mechanics (*Les méchaniques de Galilée*, ibid. 1634; with the great Italian scientist, whom he admired, Mersenne maintained an active correspondence [A. Favaro, *Amici e corrispondenti di Galileo*, XXXVIII, Florence 1917; P. Tannery, *Correspondance de M.*, so far 3 vols., Paris 1933, 1936, 1949, passim] and contributed greatly to spreading and having his doctrines accepted in France).
**MERSENNE, MARIN** — MERTEL, TEODOLFO