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Huygens, Christiaan

light pendulum theory wave

[hoy khenz] (1629–95) Dutch physicist and astronomer: proposed wave theory of light; discovered Saturn’s rings; introduced the pendulum clock; worked on the theory of dynamics and the compound pendulum.

Well educated as a member of a wealthy family in The Hague, Huygens studied law before turning to science and mathematics. He was, after , the most influential physical scientist of the late 17th-c. In 1655, using an improved home-made telescope, he was the first to describe correctly Saturn’s ring system, also discovering Titan, its largest moon. He announced the discovery and observation of Saturn’s rings in the form of a cypher. The following year he obtained the first solution to the problem of the dynamics of colliding elastic bodies had discovered the constancy of a simple pendulum’s period; and Huygens showed that for small swings T =2p( l / g ) ½ where T = period, l = length, g = acceleration due to gravity. He designed a pendulum clock and later invented the more accurate compound pendulum (which moves in a cycloidal arc). Physics could not have moved on without accurate time measurement.

Huygens’s greatest achievement, however, was his wave theory of light, first expounded in 1678. He described light as a vibration spreading through an all-pervading ‘ether’ consisting of microscopic particles, and he considered every point on the wave-front to be the source of a series of secondary spherical wavelets, the envelope of which defined the wave-front at the next instant (known as Huygens’s construction). He was thus able to give a simple explanation for the laws of reflection and refraction of light, and for the double refraction of some minerals. He correctly predicted that light travelled slower in denser media. Newton preferred a particle theory of light. The present view that each concept can be appropriate, depending on the experimental situation, came only in the 20th-c.

Huygens found a value for the distance of a star (Sirius) by assuming that it had the same actual brightness as the Sun, and making a hole in an opaque plate so small that the Sun’s light seen through it matched Sirius. Simple calculation then gave a distance of 27 664 AU, about one-18th of the correct value and the best then obtained. He also convinced himself that the planets were populated and wrote in detail about shipbuilding and other engineering on Jupiter and Saturn.

Hyman, Paula E. (1946–) - Jewish History [next] [back] Huxley, Thomas Henry

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