Huygens
CHRISTIAN (hoi'gens), an eminent Dutch mathematician and astronomer; born in The Hague, April 14, 1629. He settled in Paris in 1663, at the invitation of Colbert, who bestowed on him a handsome pension, but returned to the Netherlands in 1681. In pure geometry, Huygens gave the reasons for the quadrature of the hyperbola, the ellipsis, and the circle; in mechanics, he laid down the theory of the pendulum, and its application to the clock; he discerned the synchronism of the cycloid, lutes of curves, and explored the doctrine of centers of oscillation; most important of all, he announced the law of the motion of bodies revolving in circles, thereby "grazing" the law of gravitation. In astronomy, we owe him an improvement of the telescope and the memorable discovery of Saturn's ring. In optics he laid the foundation of the theory of undulations. He died in The Hague, June 8, 1695. invented the theory of involutes and evo-