Sir Harold Jeffreys

(1891–1989; b. Durham, England; d. Cambridge, England) English astronomer, geophysicist, and mathematician. Jeffreys studied at Cambridge U, being made a Fellow of St John's College in 1914 and holding this title for a record 75 years. From 1946 to 1958 he was Plumian Professor of Astronomy and Experimental Philosophy. He was interested in scientific method and developed Bayesian inference. He was elected FRS in 1925 and was awarded the Society's Royal Medal in 1948 and its Copley Medal in 1960. He was elected to membership of the NAS in 1945 and was elected FRSE in 1953. In 1953 he was knighted. He was awarded the Guy Medal in Gold of the RSS in 1962.

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British astronomer and geophysicist (1891–1989)

Jeffreys was born in Birtley in the northeast of England and educated in Newcastle upon Tyne and at Cambridge University. After graduating in 1913 he was made a fellow of his college. He was reader in geophysics from 1931 to 1946 before being elected to the Plumian Professorship of Astronomy and Experimental Philosophy where he remained until his retirement in 1958.

In 1924 Jeffreys produced one of the fundamental works in geophysics of the first half of the 20th century, The Earth: Its Origin, History, and Physical Constitution. In this he argued forcibly against Alfred Wegener's proposed theory of continental drift. He demonstrated that the forces proposed by Wegener were inadequate. This did much to inhibit interest and research into drift theory for a while but much new evidence in its favor has since been uncovered.

Jeffreys was also joint author, with Keith Bullen, of the Seismological Tables (1935). These, more frequently known as the JB Tables, were revised in 1940 and are the present standard tables of travel times of earthquake waves. They allow observers to determine from the elapsed time between the arrival of the primary (P) waves and the secondary (S) waves the distance between the observer and the earthquake.

Jeffreys's work in astronomy included studies on the origins of the universe. He developed James Jeans's theory of tidal evolution. He also devised models for the planetary structure of Jupiter, Saturn, Uranus, and Neptune.

He was knighted in 1953.

British mathematician, astronomer, geophysicist, and philosopher Sir Harold Jeffreys (1891-1989) was one of the great original applied-mathematical thinkers of the 20th century. He is noted for his wide variety of scientific contributions.

Harold Jeffreys was born on April 22, 1891, in Durham, England. He graduated from Durham University and then carried out research in chemistry and photography. He won major prizes at the University of Cambridge, from which he graduated in 1917, in mathematics, astronomy, and geophysics. At Cambridge he was a lecturer in mathematics, reader in geophysics, and Plumian professor of astronomy and experimental philosophy from 1946 to his retirement in 1958. In 1940 he married Bertha Swirles, a talented mathematician and a fellow of Girton College, Cambridge.

Scientific Contributions

The contributions for which Jeffreys is noted cover a wide range of fields. Much of his interest centered on the solar system and the theory of geophysics, fields in which progress demands the use of evidence and techniques from a variety of other fields, for example, statistical techniques and mathematical methods. It was characteristic of Jeffreys that when he found it necessary to refer to fields outside of astronomy and geophysics, he usually made important contributions to those fields as well. Noted examples are to be found in his books on the theory of probability, scientific inference, operational calculus, Cartesian tensors, and asymptotic approximations, as well as in a large treatise on the methods of mathematical physics written jointly with his wife. All of these works contain much original material inspired by the needs of his work in astronomy and geophysics. Additionally, he made significant contributions to the general theory of dynamics, aerodynamics, meteorology, relativity theory, and plant ecology.

To Jeffreys's credit are a number of outstanding achievements in astronomy and geophysics. In 1923, Jeffries calculated the surface temperatures of the four large outer planets - Jupiter, Saturn, Uranus, and Neptune - to be more than 100° below zero Centigrade. This was in sharp conflict with the then-prevailing view that these outer planets were red-hot. His findings were later verified by direct observation and led to a complete revision of theories on the composition and structure of the outer planets.

Using observations on the earth's bodily tides, Jeffreys, in 1926, gave the first quantitative estimate of the rigidity of the earth's core and established that most of the core is probably molten. He was the senior author of tables produced during 1930-1940, giving the travel times of earthquake waves through the interior of the earth. Since 1940 these tables have been used as the standard in calculating the epicenters and origin times of the world's earthquakes for the International Seismological Summary. Jeffreys also contributed notably to theories of seismic wave propagation, of mutations of the earth's axis, on mountain building, on convection currents inside the earth, on tidal problems, on the figure of the earth and the moon, and a theory on the internal structures of other terrestrial planets.

Knighted for his outstanding contributions to the scientific community in 1953, Jeffreys spent his career at Cambridge until his retirement in 1958. He died in Durham on March 18, 1989.

Further Reading

For references to Jeffreys and for background see Ruth Moore, The Earth We Live On (1956).