Jean Pierre de, an eminent mathematician, was born at Lausanne April 13, 1663. He was a Protestant of noble extraction, and was destined by his father for the profession of arms, but preferred the more tranquil pursuit of letters. He applied himself particularly to the study of the mathematics, and became a warm partisan of the Cartesian philosophy. After some time spent in travelling, he returned to his native place, where he was successively appointed pastor, professor of philosophy, and rector of the academy. In 1724, he was called to Groningen to teach mathematics, and appointed governor to the young prince Frederick of Hesse-Cassel. The king of Sweden also conferred upon him the title of counsellor of embassies. Crousaz died March 22, 1750, at which time he was a member of the Academy of Bordeaux, and foreign associate of the Academy of Sciences at Paris.

His works are exceedingly voluminous, but seldom rise above mediocrity. The most important are Système des Réflexions qui peuvent contribuer à la netteté et à l'étude de nos Connaissances, ou nouvel Essai de Logique, Amsterdam, 1712, 2 vols. 8vo; Traité de Beau, où l'on montre en quoi consiste ce qui l'on nomme ainsi, Amsterdam, 1715, 8vo; De l'Éducation des Enfans, Hague, 1722, 2 vols. 12mo; Examen du Traité de la Liberté de Penser d'Antoine Collins, Brussels, 1715, Amsterdam, 1718, 8vo; Géométrie des Lignes et des Surfaces rectilignes et circulaires, Amsterdam, 1718, 2 vols. 8vo; Examen du Pyrrhonisme ancien et moderne, Hague, 1733, fol.; Œuvres diverses, 1737, 2 vols. 8vo; Traits de l'Esprit Humain, against Wolff and Leibnitz, 1741; Réflexions sur la belle Wolfienne, Lausanne, 1743, 8vo.