Willem Jakob Van's Gravesande, a Dutch philosopher, born in Bois-le-Duc, Sept. 27,1688, died in Leyden, Feb. 28, 1742. He published at the age of 18 an essay on perspective, and a philosophical thesis on suicide. After completing his studies in the university of Leipsic in 1707, he was admitted to the bar at the Hague, where he wrote for the Journal Litteraire an examination of Fontenelle's "Geometry of the Infinite," a dissertation on the construction of the air pump, one concerning the force of bodies, in which ho embraced the opinion of Leibnitz against that of Newton, and dissertations upon the motion of the earth, etc. In 1717 he was appointed professor of mathematics and astronomy in the university of Leyden, and exchanged his chair in 1734 for that of philosophy, which he held till his death. His philosophical writings are eclectic in character, combining portions of the doctrines of Locke, Descartes, and Leibnitz. His principal works are: Physices Element a Mathematica (2 vols. 4to, the Hague, 1720-'23); Matheseos Universalis Elementa (8vo, Leyden, 1727); and Introductio ad Philosophiam, Metaphysi-cam et Logicam (Leyden, 1736-'7).