HUYGENS, CHRISTIAN, a celebrated mathematician and natural philosopher, was born at the Hague on the 14th April 1629. He was the son of Constantine Huygens, Lord of Zelem and Zuylichem, who had acted as secreta ry and counsellor to three successive princes of the house of Orange. Constantine Huygens was not only a poet, but a good mathematician, and took particular pleasure in the instruction of his son, who, at the early age of thirteen, ex hibited an ardent passion for mathematical learning, and was constantly occupied in examining all the machines and pieces of mechanism that accident threw in his way. In the sixteenth year of his age he went to the university of Leyden, to study law, under Professor Vinnius ; but he still pursued his mathematical studies, in which he was assist ed by the learned Professor Sehooten, the commentator of Descartes. After remaining a year at Leyden, he prosecut ed his studies at the university of Breda, which had been newly established, and placed under the direction of his father. In the year 1649, he travelled into Holstein and Denmark, in the suit of Henry, Count of Nassau ; but on account of the short stay which that prince wus to make in Denmark, he was prevented from visiting Descartes in Sweden, an object which he was very anxious to accom plish.
In the year 1651, he began his career as an author, by publishing a refutation of the famous work of Gregory St Vincent, entitled Opus Geometricum quadraturte circuli et sectionum Coni. Huygens' reply, which is considered as a model of distinctness and precision, was entitled Exetasis guadraturte circuli P. Greg. a saneto Vincentio, 4to. He published, in the same year, his Theoremata de circuli et hyperbole Quadratura; and in 1654 appeared his ingenious work, entitled De circuli magnitudine inventanovti,aceedunt ,roblematunt quorundam illustrium constructiones. In 1656, he travelled into France, and took out his degree of Doctor of Laws at the university of Angers. The new subject of the calculation of probabilities, which had been successful ly begun by Pascal and Fermat, and which has recently been so much advanced by La Place, now occupied the attention of Huygens, who developed the principles of the science in his treatise De Ratiociniis in Ludo 441e r, which appear ed in 1657. In the same year he printed his Brevis insti tutio de Usu Horologiorum ad inveniendas Longitudines, in which he described the model of a newly invented pendu lum. In 1659, Huygens published his Systenia Saturni num, sive de causis mirandorum Saturni phenomenon, et comite ejus Planeta novo, which contains the various important discoveries relative to the planet Saturn, of 'which Nye have already given a full account. See ASTRO
NOMY.
In the year 1660, Huygens travelled into France ; and in the following year he came to England, where he made known his method of grinding the lenses of telescopes. In the year 1663, he paid a second visit to this country, and was one of the hundred individuals who were declared members of the Royal Society at a meeting of the council held on the 20th May 1663. At this time the Royal Society had requested its members to apply themselves to the consi deration of the laws of motion, and Huygens resolved se veral of the cases which were proposed to him. On the 15th November 1668, Dr Wallis communicated to the So ciety his principle of the collision of bodies. Doctor, after wards Sir Christopher, Wren made a similar communica tion on the 17th of December ; and on the 5th January 1669, Huygens wrote a letter to Mr Oldenburgh, containing his first four rules, with their demonstration, concerning the motion of bodies after impact. The method of \Vallis was the most direct, but related only to bodies absolutely hard. Wren's method was founded on the same principle, but related only to elastic bodies ; and the method of Huy gens was the very same as that of Wren.
Huygens had now acquired such a reputation, that, in the year 1663, he was invited by Colbert to settle in France. He accepted of the honourable and advantageous conditions which were offered to him, and took up his residence in Paris in 1666, when he was admitted into the Academy of Sciences. In 1668, he published, in the Journal des Sp vans, and also in the Memoirs of the Academy, a paper en titled Examen du livre intitule Vera Circuli et Hyperboles quadratura a Jacobo Gregorio, which led to the dispute of which we have already given some account in our life of GREGORY. In the year 1673, he published his great work, entitled Horologium oscillatorium ; sive de nzotu pEndulorum ad horologia aptato in which he published his great discovery of applying pendulums to clocks, and rendering all their vibrations isochronous, by causing them to vibrate between cycloidal cheeks. This discovery was made about the year 1656 ; and about the middle of 1657, he presented to the States of Holland a clock constructed on this new prienciple. In our article HOROLOGY, we have given a description and a draw ing of this machine. The contrivance of cycloidal cheeks, however, though exceedingly beautiful in theory, was found in practice to be of no advantage.