RENE DES, descended of an ancient family in Touraine in France, was one of the most eminent philosophers and mathematicians in the 17th century. At the Jesuit College at La Flèche, he made a very great progress in the learned languages and polite literature, and became acquainted with Father Marfenne. His father designed him for the army; but his tender constitution then not permitting him to expose himself to such fatigues, he was sent to Paris, where he launched into gaming, in which he had prodigious success. Here Marfenne persuaded him to return to study; which he pursued till he went to Holland, in May 1616, where he engaged as a volunteer among the Prince of Orange's troops. While he lay in garrison at Breda, he wrote a treatise on music, and laid the foundation of several of his works. He was at the siege of Rochelle in 1628; returned to Paris; and, a few days after his return, at an assembly of men of learning in the house of Montigny Bagni, the pope's nuncio, was prevailed upon to explain his sentiments with regard to philosophy, when the nuncio urged him to publish his system. Upon this he went to Amsterdam, and from thence to Franeker, where he began his metaphysical meditations, and drew up his discourse on meteors. He made a short tour to England; and not far from London, made some observations concerning the declination of the magnet. He returned to Holland, where he finished his treatise on the world.

His books made a great noise in France; and Holland thought of nothing but discarding the old philosophy, and following his. Voetius being chosen rector of the university of Utrecht, procured his philosophy to be prohibited, and wrote against him; but he immediately published a vindication of himself. In 1647, he took a journey into France, where the king settled a pension of 300 livres upon him. Christine, queen of Sweden, having invited him into that kingdom, he went thither, where he was received with the greatest civility by her majesty, who engaged him to attend her every morning at five o'clock, to instruct her in philosophy, and desired him to revile and digest all his writings which were unpublished, and to form a complete body of philosophy from them. She likewise proposed to allow him a revenue, and to form an academy, of which he was to be the director. But these designs were broken off by his death in 1650. His body was interred at Stockholm, and 17 years afterwards removed to Paris, where a magnificent monument was erected to him in the church of St Genevieve du Mont. The great Dr Halley, in a paper concerning optics, observes, that though some of the ancients mention refraction as an effect of transparent mediums, Des Cartes was the first who discovered the laws of refraction, and reduced dioptries to a science. As to his philosophy, Dr Keill, in his introduction to his examination of Dr Burnet's theory of the earth, says, that Des Cartes was so far from applying geometry to natural philosophy, that his whole system is one continued blunder on account of his negligence in that point; the laws observed by the planets in their revolutions round the sun not agreeing with his theory of vortices. His philosophy has accordingly given way to the more accurate discoveries and demonstrations of the Newtonian system.