Sir Harold Jeffreys

Sir Harold Jeffreys (1891-1989), English geophysicist and astronomer who authored or co-authored several new hypotheses in his fields. Born in Fatfield, Durham, Jeffreys was educated at Armstrong College at Newcastle-on-Tyne, and Saint John's College, Cambridge. After a brilliant scholastic career he became a fellow of Saint John's in 1914, and from 1946 to 1958 was Plumian professor of astronomy and experimental philosophy at Cambridge University.

Jeffreys was one of the world's leading authorities on geophysics and wrote many papers on cosmogony, the study of the origin of the universe. With the Dutch astronomer Willem de Sitter he used precession methods to determine the oblateness (slightly flattened shape) of the earth. He made a precise measurement of the moon's shape, calculated the energy of tidal friction exerted upon the earth's shores, and made extended researches on George Darwin's tidal evolution theory of the earth-moon system. With Sir James Jeans, Jeffreys authored the now-discounted tidal hypothesis of the origin of the solar system, which proposed that planetary systems are formed by the close passing of two stars. He later modified the hypothesis with the collision theory, which held that an actual collision of the sun and a star created the solar system. His book The Earth: Its Origin, History, and Physical Constitution (6th edition, 1976) was regarded an authoritative statement of geophysics. Jeffreys also wrote on mathematics and mathematical physics, and was knighted in 1953.