Christiaan Huygens
1629-1695
Dutch Physicist
Christiaan Huygens is famous for establishing the wave theory of light. He formulated the conservation law for elastic collisions, produced the first theorems of centripetal force, and developed the dynamical theory of oscillating systems. He also made improvements to the telescope, discovered Saturn's moon Titan, and invented the pendulum clock.
Huygens was born on April 14, 1629, in The Hague, Netherlands. His father Constantijn (1596-1687) was a diplomat and well-known Renaissance poet. The Huygens household received frequent visits from French intellectuals including René Descartes (1596-1650), who greatly influenced young Christiaan. Huygens was educated at home before entering the University of Leiden to study law and mathematics (1645-47). From 1647 to 1649 he studied law at the Collegium Arausiacum in Breda. Rejecting the idea of a diplomatic career, he returned home in 1650 to devote himself to science.
Although an outstanding mathematician, Huygens's only original mathematical contributions were his theory of evolutes, developed in connection with his work on the pendulum clock, and his probability theory, in which he introduced the concept of the expectation of a stochastic variable. His importance as a mathematician lies in his improvement and application of existing techniques to the analysis of physical problems.
In 1652 Huygens began his study of colliding bodies and by 1656 arrived at a correct solution for the case of elastic collisions. The Royal Society asked John Wallis (1616-1703) and Christopher Wren (1632-1723) to examine the theoretical aspects of this problem in 1666, and Huygens was solicited for a report of his discovery. The results of all three, obtained independently and published together in the Philosophical Transactions (1669), established the law of conservation of momentum.
With his brother Constantijn, Huygens developed lens-grinding techniques that reduced spherical aberration. After incorporating these lenses into their telescopes, Huygens discovered Saturn's satellite Titan (1655), correctly described Saturn's ring (1656), and first observed Martian surface markings (1659). Huygens also invented a two-lens eyepiece—the Huygens ocular—and an improved micrometer.
Huygens rendered astronomy a greater service in 1657 with his invention of the pendulum clock, which made possible accurate time measurements. Huygens demonstrated that the period of pendulum swings will not be equal unless the arc of the swing is a cycloid. He devised fulcrum attachments to produce the appropriate arc and patented his device.
When the Académie des Sciences was established in 1666, Huygens became its most prominent member and continued his research on oscillatory systems in Paris. These culminated in the publication of Horologium Oscillatorium (1673), which includes a mathematical analysis of the compound pendulum and derivation of the relationship between pendulum length and period of oscillation. He also included the laws of centrifugal force for uniform circular motion and an early formulation of Isaac Newton's (1642-1727) first law of motion.
In 1678 Huygens completed work on Traité de la lumière, which was his response to Newton's corpuscular theory of light. Publication was delayed until 1690. Huygens presented a wave construction capable of explaining light's rectilinear propagation, reflection, refraction, and certain properties of double refraction in Iceland spar. He also predicted, in opposition to Newton, that light travels slower in denser media. Newton's theory dominated eighteenth-century optical thinking but was eclipsed by Huygens's theory in the early nineteenth century. The two views were later synthesized in quantum theory during the early years of the twentieth century.
Huygens's fifteen-year residence in Paris was interrupted by two extended periods of convalescence at The Hague. When illness brought him home once again in 1681, he decided not to return to France due to the climate of growing intolerance towards Protestants. Huygens died in The Hague on July 8, 1695.
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