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Christiaan Huygens, FRS (, ; 14 April 1629 – 8 July 1695) was a prominent Dutch mathematician, astronomer, physicist, horologist, and writer of early science fiction. His work included early telescopic studies elucidating the nature of the rings of Saturn and the discovery of its moon Titan, investigations and inventions related to time keeping and the pendulum clock, and studies of both optics and the centrifugal force.

Huygens achieved note for his argument that light consists of waves,, now known as the Huygens–Fresnel principle, which became instrumental in the understanding of wave-particle duality. He generally receives credit for his discovery of the centrifugal force, the laws for collision of bodies, for his role in the development of modern calculus and his original observations on sound perception (see repetition pitch). Huygens is seen as the first theoretical physicist as he was the first to use formulae in physics.

Life


Christiaan Huygens was born in April 1629 at The Hague, the second son of Constantijn Huygens, (1596–1687), a friend of mathematician and philosopher René Descartes, and of Suzanna van Baerle (deceased 1637), whom Constantijn had married on 6 April 1627. Christiaan studied law and mathematics at the University of Leiden and the College of Orange in Breda. After a stint as a diplomat, Huygens turned to science.

French Academy of Sciences and Royal Society
The Royal Society elected Huygens a member in 1663. In the year 1666 Huygens moved to Paris where he held a position at the French Academy of Sciences under the patronage of Louis XIV. Using the Paris Observatory (completed in 1672) he made further astronomical observations. In 1684 he published "Astroscopia Compendiaria" which presented his new aerial (tubeless) telescope.

Death
Huygens moved back to The Hague in 1681 after suffering serious illness. He attempted to return to France in 1685 but the revocation of the Edict of Nantes precluded this move. Huygens died in The Hague on 8 July 1695, and was buried in the Grote Kerk.

Probability theory
After Blaise Pascal encouraged him to do so, Huygens wrote the first book on probability theory, De ratiociniis in ludo aleae ("On Reasoning in Games of Chance"), which he had published in 1657.

Mechanics
Huygens formulated what is now known as the second law of motion of Isaac Newton in a quadratic form. Newton reformulated and generalized that law. In 1659 Huygens derived the now well-known formula for the centrifugal force, exerted by an object describing a circular motion, for instance on the string to which it is attached, in modern notation:


 * $$F_{cf}=\frac{m\ v^2}{r}$$

with m the mass of the object, v the velocity and r the radius. Furthermore, Huygens concluded that Descartes' laws for the elastic collision of two bodies must be wrong and formulated the correct laws.

Wave theory
Huygens is remembered especially for his wave theory of light, expounded in his Traité de la lumière (see also Huygens-Fresnel principle). The later theory of light by Isaac Newton in his Opticks proposed a different explanation for reflection, refraction and interference of light assuming the existence of light particles. The interference experiments of Thomas Young vindicated Huygens' wave theory in 1801, as the results could no longer be explained with light particles (see however wave-particle duality).

Optics
Huygens experimented with double refraction (birefringence) in Icelandic crystal (calcite) and explained it with his wavetheory and polarised light.

Clocks
He also worked on the construction of accurate clocks, suitable for naval navigation. In 1658 he published a book on this topic called Horologium. His invention of the pendulum clock, patented in 1657, was a breakthrough in timekeeping.

Devices known as escapements regulate the rate of a watch or clock, and the anchor escapement represented a major step in the development of accurate watches. Subsequent to this publication, Huygens discovered that the cycloid was an isochronous curve and, applied to pendulum clocks in the form of cycloidal cheeks guiding a flexible pendulum suspension, would ensure a regular (i.e isochronous) swing of the pendulum irrespective of its amplitude, i.e. irrespective of how it moved side to side. The mathematical and practical details of this finding were published in "Horologium Oscillatorium" of 1673. Huygens was the first to derive the formula for the period of the mathematical pendulum (with massless rod or cable), in modern notation:


 * $$T_{slinger}= 2 \pi \sqrt{\frac{l}{g}}$$

with T the period, l the length of the pendulum and g the gravitational acceleration.

Huygens also observed that two pendulums mounted on the same beam will come to swing in perfectly opposite directions, an observation he referred to as odd sympathy which in modern times is known as resonance. Contrary to sometimes expressed popular belief, Huygens was not a clockmaker, and is not known to have ever made any clock himself; he was a scholar, scientist and inventor, and the oldest known pendulum clocks were made by Salomon Coster in The Hague, under a license from Huygens.

The oldest known Huygens style pendulum clock is dated 1657 and can be seen at the Museum Boerhaave in Leiden  , which also shows an important astronomical clock owned and used by Huygens.

Huygens also developed a balance spring clock more or less contemporaneously with, though separately from, Robert Hooke, and controversy over whose invention was the earlier persisted for centuries. In February 2006, a long-lost copy of Hooke's handwritten notes from several decades' Royal Society meetings was discovered in a cupboard in Hampshire, and the balance-spring controversy appears by evidence contained in those notes to be settled in favor of Hooke's claim.

Internal combustion and other inventions
In 1673, Huygens carried out experiments with internal combustion. Although he designed a basic form of internal combustion engine, fueled by gunpowder, he never successfully built one.

In 1675, Christiaan Huygens patented a pocket watch. He also invented numerous other devices, including a 31 tone to the octave keyboard instrument which made use of his discovery of 31 equal temperament.

Saturn's rings and Titan
In 1655, Huygens proposed that Saturn was surrounded by a solid ring, "a thin, flat ring, nowhere touching, and inclined to the ecliptic." Using a 50 power refracting telescope that he designed himself, Huygens also discovered the first of Saturn's moons, Titan. In the same year he observed and sketched the Orion Nebula. His drawing, the first such known of the Orion nebula, was published in Systema Saturnium in 1659. Using his modern telescope he succeeded in subdividing the nebula into different stars. (The brighter interior of the Orion Nebula bears the name of the Huygens Region in his honour.) He also discovered several interstellar nebulae and some double stars.

Transit of Mercury
On May 3, 1661, he observed planet Mercury transit over the Sun, using the telescope of telescope maker Richard Reeves in London together with astronomer Thomas Streete and Richard Reeves.

Extraterrestrial Life
Christiaan Huygens believed in existence of extraterrestrial life. Prior to his death in 1695, he completed a book entitled Cosmotheoras in which he discussed his notions on extraterrestrial life. Huygens was of the opinion that life on other planets is pretty much similar to that on Earth. He thought that availability of water in liquid form was essential for existence of life and therefore the properties of water should vary from planet to planet, since the kind of water that is found on Earth would instantly freeze on Jupiter and vaporize on Venus. He even reported observing dark and bright spots on the surface of planet Mars and Jupiter. This he explained could only be justified by existence of water and ice on those planets.

Works

 * 1649 - De iis quae liquido supernatant (About the parts above the warer, unpublished)
 * 1651 - Cyclometriae
 * 1651 - Theoremata de quadratura hyperboles, ellipsis et circuli (theorems concerning the quadrature of the hyperbola, ellipse and circle, Huygens' first publication)
 * 1654 - De circuli magnitudine inventa
 * 1656 - De Saturni Luna observatio nova (About the new observation of the moon of Saturn - discovery of Titan)
 * 1656 - De motu corporum ex percussione, published only in 1703
 * 1657 - De ratiociniis in ludo aleae = Van reeckening in spelen van geluck (translated by Frans van Schooten)
 * 1659 - Systema saturnium
 * 1673 - Horologium oscillatorium sive de motu pendularium (theory and design of the pendulum clock, dedicated to Louis XIV of France)
 * 1673 - De vi centrifuga (Concerning the centrifugal force)
 * 1684 - Astroscopia Compendiaria tubi optici molimine liberata (compound telescopes without a tube)
 * 1685 - Memoriën aengaende het slijpen van glasen tot verrekijckers (How to grind telescope lenses)
 * 1686 - Kort onderwijs aengaende het gebruijck der horologiën tot het vinden der lenghten van Oost en West (How to use clocks to establish the longitude
 * 1690 - Traité de la lumière
 * 1690 - Discours de la cause de la pesanteur (Discourse about gravity, from 1669?)
 * 1691 - Lettre touchant le cycle harmonique (Rotterdam, concerning the 31-tone system)
 * 1698 - Cosmotheoros, sciencefiction
 * 1703 - Opuscula posthuma including
 * De motu corporum ex percussione (Concerning the motions of colliding bodies - contains the first correct laws for collision, dating from 1656).
 * Descriptio automati planetarii (description and design of a planetarium)
 * 1724 - Novus cyclus harmonicus (Leiden, after Huygens' death)
 * 1728 - Christiani Hugenii Zuilichemii, dum viveret Zelhemii toparchae, opuscula posthuma ... (pub. 1728) Alternate title: Opera reliqua, concerning optics and physics


 * 1888-1950 - Huygens, Christiaan. Oeuvres complètes. The Hague Complete work, editors D. Bierens de Haan (tome=deel 1-5), J. Bosscha (6-10), D.J. Korteweg (11-15), A.A. Nijland (15), J.A. Vollgraf (16-22).
 * Tome I: Correspondance 1638-1656 (1888). Tome II: Correspondance 1657-1659 (1889). Tome III: Correspondance 1660-1661 (1890). Tome IV: Correspondance 1662-1663 (1891). Tome V: Correspondance 1664-1665 (1893). Tome VI: Correspondance 1666-1669 (1895). Tome VII: Correspondance 1670-1675 (1897). Tome VIII: Correspondance 1676-1684 (1899). Tome IX: Correspondance 1685-1690 (1901). Tome X: Correspondance 1691-1695 (1905).


 * Tome XI: Travaux mathématiques 1645-1651 (1908). Tome XII: Travaux mathématiques pures 1652-1656 (1910). 


 * Tome XIII, Fasc. I: Dioptrique 1653, 1666 (1916). Tome XIII, Fasc. II: Dioptrique 1685-1692 (1916). 


 * Tome XIV: Calcul des probabilités. Travaux de mathématiques pures 1655-1666 (1920). 


 * Tome XV: Observations astronomiques. Système de Saturne. Travaux astronomiques 1658-1666 (1925). 


 * Tome XVI: Mécanique jusqu’à 1666. Percussion. Question de l’existence et de la perceptibilité du mouvement absolu. Force centrifuge (1929). Tome XVII: L’horloge à pendule de 1651 à 1666. Travaux divers de physique, de mécanique et de technique de 1650 à 1666. Traité des couronnes et des parhélies (1662 ou 1663) (1932). Tome XVIII: L'horloge à pendule ou à balancier de 1666 à 1695. Anecdota (1934). Tome XIX: Mécanique théorique et physique de 1666 à 1695. Huygens à l’Académie royale des sciences (1937). 


 * Tome XX: Musique et mathématique. Musique. Mathématiques de 1666 à 1695 (1940). 


 * Tome XXI: Cosmologie (1944). 


 * Tome XXII: Supplément à la correspondance. Varia. Biographie de Chr. Huygens. Catalogue de la vente des livres de Chr. Huygens (1950).

During his lifetime

 * 1639 - His father Constantijn Huygens in the midst of his five children by Adriaen Hanneman, painting with medaillons, Mauritshuis, The Hague
 * 1671 - Portrait by Caspar Netscher, Museum Boerhaave, Leiden, loan from Haags Historisch Museum
 * ~1675 - Possible depiction of Huygens on l'Établissement de l'Académie des Sciences et fondation de l'observatoire, 1666 by Henri Testelin. Colbert presents the members of the newly founded Académie des Sciences to king Louis XIV of France. Musée National du Château et des Trianons de Versailles, Versailles
 * 1679 - Medaillon portrait in relief by the French sculptor Jean-Jacques Clérion
 * 1686 - Portrait in pastel by Bernard Vaillant, Museum Hofwijck, Voorburg
 * bewteen 1684 and 1687 - Engraving by G. Edelinck after the painting by Netscher
 * 1688 - Portrait by Pierre Bourguignon, Koninklijke Nederlandse Akademie van Wetenschappen, Amsterdam

Science

 * The Huygens probe: The lander for the Saturnian moon Titan, part of the Cassini-Huygens Mission to Saturn
 * Asteroid 2801 Huygens
 * A crater on Mars
 * Mons Huygens, a mountain on the Moon
 * Huygens Software, a microscope image processing package.
 * Achromatic two element eyepiece designed by him.
 * The Huygens–Fresnel principle, a simple model to understand disturbances in wave propagation.
 * Huygens wavelets, the fundamental mathematical basis for scalar diffraction theory
 * W.I.S.V. Christiaan Huygens: Dutch study guild for the studies Mathematics and Computer Science at the Delft University of Technology
 * Huygens Laboratory: Home of the Physics department at Leiden University, The Netherlands
 * Huygens Supercomputer: National Supercomputer facility of The Netherlands, located at SARA in Amsterdam
 * The Huygens-building in Noordwijk, The Netherlands, first building on the Space Business park opposite Estec (ESA)
 * The Huygens-building at the Radboud University, Nijmegen, The Netherlands. One of the major buildings of the science department at the university of Nijmegen.

Other

 * Christiaan Huygens College, High School located in Eindhoven, The Netherlands.
 * The Christiaan Huygens, a ship of the Nederland Line.
 * Huygens Scholarship Programme for international students and Dutch students

Primary sources, translations

 * Treatise on Light translated into English by Silvanus P. Thompson, Project Gutenberg etext.
 * De Ratiociniis in Ludo Aleae or The Value of all Chances in Games of Fortune, 1657Christiaan Huygens' book on probability theory. An English translation published in 1714. Text pdf file.
 * Horologium oscillatorium (German translation, pub. 1913) on the pendulum clock
 * ΚΟΣΜΟΘΕΩΡΟΣ (Cosmotheoros). (English translation of Latin, pub. 1698; subtitled The celestial worlds discover'd: or, Conjectures concerning the inhabitants, plants and productions of the worlds in the planets.)
 * Traité de la lumière or Treatise on light (English translation, pub. 1912 and again in 1962)
 * Systema Saturnium 1659 text a digital edition of Smithsonian Libraries
 * On Centrifugal Force (1703)
 * Huygens' work at WorldCat
 * | Christiaan Huygens biography and achievements
 * | Christiaan Huygens biography and achievements

Museums

 * Huygensmuseum Hofwijck in Voorburg, The Netherlands, where Huygens lived and worked.
 * Huygens Clocks exhibition from the Science Museum, London
 * Exhibition on Huygens in University Library Leiden (in Dutch)

Other

 * Huygens and music theory Huygens–Fokker Foundation &mdash;on Huygens' 31 equal temperament and how it has been used
 * Christiaan Huygens on the 25 Dutch Guilder banknote of the 1950s.
 * Christiaan Huygens on the 25 Dutch Guilder banknote of the 1950s.

Christiaan Huygens كريستيان هوغنس Xristian Hüygens খ্রিস্টিয়ান হাওখেন্স Christiaan Huygens Christiaan Huygens Кристиан Хюйгенс Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens Κρίστιαν Χόυχενς Christiaan Huygens Christiaan Huygens Christiaan Huygens fa:کریستین هویگنس Christian Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens 크리스티안 하위헌스 क्रिस्टियन हुगेन्स Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens כריסטיאן הויגנס Christiaan Huygens Christiaan Huygens Christianus Hugenius Kristiāns Heigenss Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens クリスティアーン・ホイヘンス Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens Гюйгенс, Христиан Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens Christiaan Huygens Кристијан Хајгенс Christian Huygens Christiaan Huygens Christiaan Huygens கிறிஸ்டியான் ஹைஜன்ஸ் คริสเตียน ฮอยเกนส์ Christiaan Huygens Хрістіан Гюйгенс Christiaan Huygens 克里斯蒂安·惠更斯