(born July 18, 1635, Freshwater, Isle of Wight, Eng.—died March 3, 1703, London) English physicist. From 1665 he taught at Oxford University. His achievements and theories were bewilderingly diverse. His important law of elasticity, known as Hooke's law (1660), states that the stretching of a solid is proportional to the force applied to it. He was one of the first to build and use a reflecting telescope. He suggested that Jupiter rotates on its axis, and his detailed sketches of Mars were later used to determine its rate of rotation. He suggested that a pendulum could be used to measure gravitation, and he attempted to show that the Earth and Moon follow an elliptical orbit around the Sun. He discovered diffraction and proposed the wave theory of light to explain it. He was one of the first proponents of the theory of evolution. He was the first to state in general that all matter expands when heated and that air is made up of particles separated from each other by relatively large distances. He invented a marine barometer, contributed improvements to clocks, the quadrant, and the universal joint, and anticipated the steam engine.

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