Sir Harold Jeffreys

Harold Jeffreys was born on 22 April 1891 at Fatfield, a colliery village in County Durham where his father was headmaster of the village school. He received his school education at Fatfield and Rutherford College, Newcastle, proceeding in 1907 to Armstrong College, Newcastle, the forerunner of Newcastle University but then part of Durham University. Here he took courses in mathematics, physics, chemistry and geology, graduating in June 1910 with first class marks and a distinction in mathematics. Encouraged by his mathematics teacher C.M. Jessop he applied for a Cambridge award and in December 1909 he was elected to an entrance scholarship at St John's College as one of four mathematics scholars. Although there were financial difficulties and the problem of adjusting to a standard of mathematics much harder than that of Armstrong College, his performance in the third year of the Mathematical Tripos (1913) was a distinguished one. He was awarded one of the two Hughes Prizes for undergraduates who had done best in the college in any subject, his college scholarship was extended for a fourth year, and he began research.

Jeffreys was elected a fellow of St John's College in November 1914 and remained one for the rest of his life. He held the Isaac Newton Studentship, 1914-1917, worked part-time at the Cavendish Laboratory on war-time problems 1915-1917, moving to the Meteorological Office in London in 1917 where he first employed his mathematical skills to 'certain difficult questions in gunnery which came to us from the services' and then to 'problems of the atmosphere'. In 1922 he returned to Cambridge as College lecturer in mathematics and was appointed to a university lectureship in 1926. He was Reader in Geophysics in 1931 and Plumian Professor of Astronomy and Experimental Philosophy in 1946, retiring in 1958.

Jeffreys was one of the small international group of scientists who founded modern geophysics. He applied classical mechanics to investigate the interior of the earth, showing that the core of the Earth was liquid and that there is a substantial difference between the upper and lower mantle. His analyses of travel times of seismic waves with K.E. Bullen became standards of reference. Generations of students learned their geophysics from his book The Earth (first published 1924, sixth edition 1976). Jeffreys was also distinguished as a statistician, developing a theory of probability on Bayesian principles and in a form suitable for use in the physical sciences. His key books in statistics were Scientific Inference (1931) and Theory of Probability (1939). He also made significant contributions early in his career in fluid dynamics and dynamical meteorology and, although primarily an applied mathematician, in pure mathematics. His use and development of mathematical techniques led him to write, jointly with his wife, Bertha Swirles Jeffreys, the treatise Methods of Mathematical Physics (1946), which went through several editions. His first published paper (1910) was on photography and his early interest in natural history is reflected in papers on plant ecology.

Amongst his professional affiliations were the Royal Astronomical Society where he was active in supporting and developing geophysics over many years (President, 1955-1957), the British Association for the Advancement of Science, the National Committee for Geodesy and Geophysics (chairman of the Seismology SubCommittee), the International Union of Geodesy and Geophysics (President of the International Association of Seismology 1957-1960) and the International Astronomical Union.

His scientific distinction was recognised by many honours. He was elected FRS in 1925 (Royal Medal 1948, Copley Medal 1960; Bakerian Lecture, 1952); at the time of his death he was Senior Fellow. Other scientific awards included the Gold Medal of the Royal Astronomical Society 1937, the Vetlesen Prize of Columbia University 1962 and the Wollaston Medal of the Geological Society 1964. He was made a knight bachelor in 1953.

He married Bertha Swirles in 1940. She was a student at Girton College, Cambridge where she took a Ph.D in atomic physics under the supervision of R.H. Fowler and D.R. Hartree. After periods at Manchester, Bristol and Imperial College London she returned to Girton in 1938 as Fellow and Lecturer in Mathematics. She was Director of Studies in Mathematics, 1949-1969 and Vice-Mistress, 1966-1969. Her great support for Jeffreys, especially in his last decades, is very evident in his archives. Her role in preserving and identifying materials is acknowledged below.

Jeffreys died on 18 March 1989.

For a fuller account of Jeffreys's life and work see the memoir by Sir Alan Cook for the Royal Society, Biographical memoirs of Fellows of the Royal Society, 36 (1990), 303-333.

From the guide to the Papers and correspondence of Sir Harold Jeffreys, 1891-1989, 1886-1999, (St John's College, Cambridge)