Christiaan Huygens
![Huygens by [[Caspar Netscher]] (1671), [[Museum Boerhaave]], [[Leiden]]<ref>Wybe Kuitert "Japanese Robes, Sharawadgi, and the landscape discourse of Sir William Temple and Constantijn Huygens' ''Garden History'', 41, 2: (2013) pp.157–176, Plates II-VI and ''Garden History'', 42, 1: (2014) p.130 ISSN 0307-1243 [https://www.researchgate.net/publication/313059385_Japanese_robes_sharawadgi_and_the_landscape_discourse_of_Sir_William_Temple_and_Constantijn_Huygens Online as PDF] {{Webarchive|url=https://web.archive.org/web/20210809203016/https://www.researchgate.net/publication/313059385_Japanese_robes_sharawadgi_and_the_landscape_discourse_of_Sir_William_Temple_and_Constantijn_Huygens |date=9 August 2021 }}</ref>](https://upload.wikimedia.org/wikipedia/commons/a/a4/Christiaan_Huygens-painting.jpeg)
Huygens first identified the correct laws of elastic collision in his work ''De Motu Corporum ex Percussione'', completed in 1656 but published posthumously in 1703. In 1659, Huygens derived geometrically the formula in classical mechanics for the centrifugal force in his work ''De vi Centrifuga'', a decade before Newton. In optics, he is best known for his wave theory of light, which he described in his ''Traité de la Lumière'' (1690). His theory of light was initially rejected in favour of Newton's corpuscular theory of light, until Augustin-Jean Fresnel adapted Huygens's principle to give a complete explanation of the rectilinear propagation and diffraction effects of light in 1821. Today this principle is known as the Huygens–Fresnel principle.
Huygens invented the pendulum clock in 1657, which he patented the same year. His horological research resulted in an extensive analysis of the pendulum in ''Horologium Oscillatorium'' (1673), regarded as one of the most important 17th century works on mechanics. While it contains descriptions of clock designs, most of the book is an analysis of pendular motion and a theory of curves. In 1655, Huygens began grinding lenses with his brother Constantijn to build refracting telescopes. He discovered Saturn's biggest moon, Titan, and was the first to explain Saturn's strange appearance as due to "a thin, flat ring, nowhere touching, and inclined to the ecliptic." In 1662 Huygens developed what is now called the Huygenian eyepiece, a telescope with two lenses to diminish the amount of dispersion.
As a mathematician, Huygens developed the theory of evolutes and wrote on games of chance and the problem of points in ''Van Rekeningh in Spelen van Gluck'', which Frans van Schooten translated and published as ''De Ratiociniis in Ludo Aleae'' (1657). The use of expected values by Huygens and others would later inspire Jacob Bernoulli's work on probability theory. Provided by Wikipedia
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