a sect of philosophers, who adhered to the system of Descartes, founded on two principles, the one metaphysical, the other physical. The metaphysical principle is, I think, therefore I am; the physical principle is, that nothing exists but substance. Descartes considered substances as of two kinds; the one a substance that thinks, the other a substance extended; and hence actual thought and actual extension are, according to him, the essence of substance. The essence of matter being thus fixed in extension, the Cartesians conclude that there is no vacuum, nor any possibility of one, in nature, and that the universe is absolutely full. Mere space is excluded by this principle, because extension being implied in the idea of space, matter is so too. Upon these principles the Cartesians endeavoured to explain mechanically the formation of the world, and to account for the celestial phenomena.