Huygens, Christian (1629-95), mathematician, mechanician, astronomer, and physicist, the Newton of Holland, was born at The Hague. His education was begun by his father Constantijn Huygens, the celebrated poet and diplomatist, continued at Leyden, under Vinnius and Schooten, and completed in the Juridical school at Breda. In 1649 he took part in the mission of Henry, Count of Nassau, to Denmark; but he soon gave up law and diplomacy for physical science, and gained distinction by attacking the unsound system of quadratures then in vogue. In 1654 he surpassed all approximations to the evaluation of the ratio of the circumference of a circle to its diameter. In co-operation with his brother, he made great improvement in the grinding and polishing of telescopes, and invented the achromatic eye-piece. The result was the discovery of one of Saturn's satellites (announced 1656), and of the ring (announced 1659). He invented the pendulum clock in 1656. From 1666 to 1681 he resided in France, where he produced his great work Horologium Oscillatorium (1673). On his second visit to England (1669) he was elected a fellow of the Royal Society, which still possesses three of his lenses of very long focal distance, which he made for aerial telescopes (1681-87). Among his achievements are the establishment of Hooke's wave theory of light, the resolution of the main undulation, and the explanation of the polarisation of light.