Sir Harold Jeffreys, FRS (1891-1989) was a mathematician, statistician, geophysicist, and astronomer. His book Theory of Probability, which first appeared in 1939, played an important role in the revival of the Bayesian view of probability.
Jeffreys was born in Fatfield, Washington, County Durham, England. He studied at Armstrong College in Newcastle upon Tyne, then part of the University of Durham, and with the University of London External Programme. Jeffreys became a fellow of St John's College, Cambridge in 1914. At the University of Cambridge he taught mathematics, then geophysics and became the Plumian Professor of Astronomy.
One of his major contributions was on the Bayesian approach to probability, as well as the idea that the Earth's planetary core was liquid. He was knighted in 1953.
Jeffreys received the Gold Medal of the Royal Astronomical Society in 1937, the Royal Society's Copley Medal in 1960, and the Royal Statistical Society's Guy Medal in Gold in 1962. In 1948, Jeffreys received the Prix Charles Lagrange from the Academie royale des Sciences, des Lettres et des Beaux-Arts de Belgique.
From 1939 to 1952 he was established as Director of the International Seismological Summary later known as International Seismological Centre.