CROUSAZ, JEAN PIERRE DE, was born at Lausanne on the 13th of April 1663. He was one of the most prolific writers of the eighteenth century; but his works seldom rise above mediocrity, and are now but little read. He was a Protestant of noble extraction, and his father destined him for the profession of arms, but he 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 the 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 on the 22d of March 1750, at which time he was a member of the Academy of Bordeaux, and foreign associate of the Academy of Sciences at Paris. His principal works are, 1. Système des Réflexions qui peuvent contribuer à la netteté et à l'étude de nos Connoissances, ou nouvel Essai de Logique, Amsterdam, 1712, 2 vols. 8vo; 2. Traité de Beau, où l'on montre en quoi consiste ce qui l'on nomme ainsi, Amsterdam, 1713, 8vo, and 1724, 2 vols. 12mo; 3. De l'Education des Enfants, Hague, 1722, 2 vols. 12mo; 4. Examen du Traité de la Liberté de Penser d'Antoine Collins, Brussels, 1715, Amsterdam, 1718, 8vo; 5. Géométrie des Lignes et des Surfaces rectilignes et circulaires, Amsterdam, 1718, 2 vols. 8vo; 6. Examen du Pyrrhonisme ancien et moderne, Hague, 1733, fol.; 7. Œuvres diverses, 1737, 2 vols. 8vo; 8. Traité de l'Esprit Humain, against Wolff and Leibnitz, 1741; 9. Réflexions sur la belle Wolfienne, Lausanne, 1748, 8vo. In his Traité de Beau Crousaz maintains that, to constitute beauty, there must be a concurrence of five qualities or conditions, namely, unity, variety, order, proportion, and regularity. But this definition, it must be obvious, is far from having that character of simplicity which is suited to the nature of beauty; and a more refined analysis has since demonstrated that the only condition necessary to constitute beauty is association with certain feelings and emotions of an agreeable or a pleasurable kind. The most important of all his works, however, is the Examination of ancient and modern Pyrrhonism, which displays sound thinking, and no inconsiderable degree of philosophical learning. Besides the works above enumerated, Crousaz was the author of some sermons, an essay on metaphysics, reflections on gambling, remarks on the utility of physics and mathematics, an essay on rhetoric, another on motion, a treatise on algebra, observations on the logic of Horace, an examination of Pope's Essay on Man, a commentary on the analysis of quantities infinitely small, several dissertations crowned by the academy of Bordeaux, and other pieces. (See his Eloge by Fouchy in l'Histoire de l'Académie des Sciences, 1750, p. 779.)