(Christian), one of the greatest mathematicians and astronomers of the 17th century, was the son of Constantine Huygens, lord of Zuylichem, who had served three successive princes of Orange in the quality of secretary; and was born at the Hague, in 1629. He discovered from his infancy an extraordinary fondness for the mathematics; in a little time made a great progress in them; and perfected himself in those studies under the famous professor Schooten, at Leyden. In 1649, he went to Holstein and Denmark, in the retinue of Henry count of Nassau; and was extremely desirous of going to Sweden, in order to see Des Cartes, but the count's short stay in Denmark would not permit him. He travelled into France and England; was, in 1663, made a member of the Royal Society; and, upon his return into France, M. Colbert, being informed of his merit, settled a considerable pension upon him to engage him to fix at Paris; to which Mr Huygens consented, and staid there from the year 1666 to 1681, where he was admitted a member of the Academy of Sciences. He loved a quiet and studious manner of life, and frequently retired into the country to avoid interruption, but did not contract that moroseness which is so frequently the effect of solitude and retirement. He was the first who discovered Saturn's ring, and a third satellite belonging to that planet, which had hitherto escaped the eyes of astronomers. He discovered the means of rendering clocks exact, by applying the pendulum, and rendering all its vibrations equal by the cycloid. He brought telescopes to perfection, made many other useful discoveries, and died at the Hague in 1695. He was the author of several excellent works. The principal of these are contained in two collections; the first of which was printed at Leyden in 1682, in quarto, under the title of Opera varia; and the second at Amsterdam in 1728, in two volumes quarto, intitled Opera reliqua.