HUYGENS VAN ZUYLIOHEM, CHRISTIAN, one of the great philosophers of the 17th c., was b. at the Hague, April 14, 1629, and was the second son of Constantine Huygens, secretary and counselor to the princes of Orange. Huygens studied at Leyden and Breda. His first work, Theoremata de Quadratura Hyperboles, Ellipsis, et Circuli, ex Dato Portionum Gravitatis Centro (Leyden, 1651), is an example of that powerful geome trical talent which lay at the foundation of all his scientific achievements. Soon after this, he constructed the pendulum-clock, following out the idea first suggested by Galileo (q.v.). A complete description of Huygens's instrument is contained in his great work, Horelogium Oscsllatorium, sine de Motu Pendulorum (Hague, 1658).
This work contains expositions of many of the cases of constrained motion, especially those applicable to the construction of time-keepers. Huygens has also developed and given precision to the investigations of Galileo upon accelerated motion under the action of gravity; and there is no doubt that to the clearness of his demonstrations, his great successor, Newton, in preparing his magnificent development of the principle of accele rating force, was largely indebted. Newton was a student and admirer of his works, and assigns to him, along with sir C. Wren and Wallis, the distinguished epithet of Wits atatis geometwruin facile principes.
By means of an improved telescope of his own construction, Huygens, in 1655, discovered the ring of Saturn and the fourth satellite of that planet. In 1659 he pub lished an account of these discoveries in a work entitled Systema Saturnium, sine de Calais Mirandorum Batumi Phenomenon, et Comite this Planets Novo. In the end of
this work is described an invention of great importance in astronomy—namely, the micrometer (q.v.), by which small angle& between objects viewed by a telescope are accurately measured. In 1660 IIuygens visited England, where he was admitted a member of the royal society. He discovered the laws of collision of elastic bodies about the same time with Wallis and Wren, and also made a material improvement in the air-pump.
In 1666 Huygens received an invitation to settle in France, with the promise of a pension from Colbert, then all-powerful in that country. He repaired to Paris, where he remained till 1681, having been admitted to the membership of the royal academy of sciences; but alarmed at the danger which seemed impending over the Protestants, he returned to his own country. After his return he still continued his favorite pursuits till his death at the Hague, June 8, 1693.
The optical works of Huygens lastly claim our attention. They are chiefly remark able for his maintaining a theory of light, which opposed as it was to the then more popular theory of Newton, is substantially the same with that which is now called the undulatory theory. By means of his theory, he explained the ordinary phenomena of reflection and refraction, and further succeeded in a satisfactory explanation of the phe nomenon of double refraction, which Newton's theory failed to account for.