by Alan Cook, rev.

© Oxford University Press 2004 All rights reserved

**Jeffreys, Sir Harold** (1891-1989), geophysicist, was born on 22 April 1891 in Fatfield, co. Durham, the only child of Robert Hall Jeffreys, headmaster of the village school at Fatfield, and his wife, Elizabeth Mary, schoolteacher, daughter of William Sharpe. His parents both came from families living near Morpeth, Northumberland. Jeffreys was educated at Rutherford College and Armstrong College (both in Newcastle upon Tyne) and at St John's College, Cambridge, of which he was a scholar. He obtained a first class in part one (1911) and was a wrangler in part two (1913) of the mathematical tripos. He was awarded the Smith's prize in 1915. Inspired by the work of Sir George Darwin on tides he began research in celestial mechanics. He was elected a fellow of St John's in 1914, retaining his fellowship until his death. He obtained a Durham DSc in 1917.

During the First World War Jeffreys worked in the Cavendish Laboratory, Cambridge, on wartime problems, from 1915 to 1917. He then went to the Meteorological Office from 1917 to 1922, returning to Cambridge as lecturer in mathematics in 1922. He won the Adams prize in 1927. He became reader in geophysics in 1931 and was elected Plumian professor of astronomy and experimental philosophy in 1946, retiring in 1958. On 6 September 1940 he married Bertha Swirles, mathematician *[see below].* There were no children of the marriage.

Jeffreys worked in five branches of mathematics: hydrodynamics, celestial mechanics, seismology and the physics of the interior of the earth, probability, and pure mathematics. His wartime work led him to study fluid dynamics. He demonstrated the importance of eddy viscosity, identified by G. I. Taylor, in geophysical fluid motions, classified winds by their dynamical origins, and established the essential role of cyclones in the general circulation of the atmosphere. He was the first to identify the importance of viscosity in boundary conditions. He studied the mechanism for the generation of surface waves on water and developed the work of J. W. Strutt (third Baron Rayleigh) on the initiation of convection.

Jeffreys had early realized the importance of seismology, which occupied him from 1921 to the end of his life, for investigating the interior of the earth, for which he established three major structural features. In 1921, with Dorothy Wrinch, he showed from records of an explosion in the Rhineland that the crust of the earth had at least two layers above the mantle; the study also demonstrated the value of explosions as seismic sources. In 1927 Jeffreys showed that the earth must have a dense core which must be effectively liquid, and this was amply confirmed subsequently. His third major discovery was the division between the upper and lower mantle of the earth, which he attributed to a change of crystal structure of olivine to a denser form at high pressure. He spent many years on calculations of travel times of seismic waves over the earth, and produced the Jeffreys-Bullen tables, first published in 1940, and still used in routine identification of earthquake epicentres and as reference times for both comparison with observations and calculations of models of the interior of the earth. Jeffreys also made many contributions to the theory of elastic waves.

Working mostly by himself and with few research students, Jeffreys wrote extensively on the dynamics of the earth and the solar system. In the years before artificial satellites were launched he analysed observations of gravity on the surface of the earth, another very laborious numerical project, and derived a consistent set of dynamical parameters of the earth and the moon. He studied the variations in the rotation of the earth and showed that the slowing down of the earth's rotation, found astronomically, was probably due to eddy viscosity in shallow seas, another result that later seemed fully confirmed. Those studies, and his theoretical work on the effect of the liquid core on the earth's rotation, dominated the subject.

Jeffreys's book *The Earth* (1924) was the first systematic account of the physical state of the earth as a whole and had a profound influence on generations of geophysicists through its many successive editions. Jeffreys was not uncontroversial, and indeed he was involved in a number of major debates which seem to have called forth his tersest writing. In particular he always opposed the ideas of continental drift and plate tectonics, although it was he who first pointed out that the earth's crust was just the upper layer of a rigid lithosphere about 100 km thick, and he was a keen advocate (1936) of systematic studies of the floor of the oceans. Although his most significant work in geophysics was completed before the technical revolutions of artificial satellites, marine geophysics, and new methods of seismology changed the face of geophysics in the middle of the twentieth century, his major results were the foundation of subsequent developments. He showed, above all, how rigorous methods of classical mechanics should be applied to the study of the structure of the earth and the planets.

He had an early interest in scientific inference and, later, prompted by statistical problems arising from his work on seismic travel times, he constructed a comprehensive corpus of methods for estimation and tests of significance according to Bayesian principles. His *Theory of Probability* (1939), which presented a formal algebra of probability on an axiomatic basis, with many applications in various branches of physics, became very influential. Much of his original work in pure mathematics was incorporated in *Methods of Mathematical Physics* (1946, with his wife). His most important contributions were to the study of operational methods for the solution of differential equations and to asymptotic methods.

Jeffreys was elected a fellow of the Royal Society in 1925 and was president of the Royal Astronomical Society in 1955-7. He was a foreign member of a number of academies, among them the US Academy of Science, the Accademia Nazionale dei Lincei (Rome), and the royal academies of Sweden and Belgium. He was awarded, besides other prizes, the gold medal of the Royal Astronomical Society (1937), a royal medal (1948) and the Copley medal (1960) of the Royal Society, the Vetlesen prize of Columbia University (1962), the Guy medal of the Royal Statistical Society (1963), and the Wollaston medal of the Geological Society (1964). He received five honorary degrees and was knighted in 1953.

Jeffreys had wide interests within and beyond science. Besides some prophetic papers on physics and stellar structure, he wrote on the ecology of co. Durham and the Breckland and on psychology. He was a skilled photographer; a large collection of his negatives was given to St John's College. He was for many years active in national and international astronomical and geophysical societies. Undoubtedly one of the distinctive personalities of Cambridge in his time, he was difficult to talk to and was known for his intensive smoking and for his bicycling everywhere. Yet he was very sociable, dined regularly in his college, sang tenor for many years in the Cambridge Philharmonic choir, and greatly enjoyed the dinners of the Royal Astronomical Society Club. He was somewhat over medium height and spare of frame. He wore glasses, had a small moustache, and was usually dressed informally, often wearing shorts in hot weather. Jeffreys died in Cambridge on 18 March 1989.

Jeffreys's wife, **Bertha Jeffreys,** Lady Jeffreys (1903-1999), mathematician, was born on 22 May 1903 at 22 St Michael's Mount, Northampton, the daughter of William Alexander Swirles, a commercial traveller in leather, and his wife, Harriet, *née* Blaxley, later a primary school teacher. She was a cousin of Michael Stewart, Baron Stewart of Fulham. She was educated at Northampton School for Girls and, from 1921, read mathematics at Girton College, Cambridge, where she graduated with first-class honours. Her postgraduate research on quantum theory, partly under R. H. Fowler, and partly at Göttingen under Max Born and Werner Heisenberg, gained her a PhD in 1929. A series of teaching posts at Manchester, Bristol, London, and again Manchester preceded her return in 1938 to Girton, where she was fellow and lecturer in mathematics, and from 1949 director of studies in mathematics. After her marriage to Jeffreys in 1940 she continued to publish on quantum theory, but expanded her interests to include seismology. She took an active role in the life of Girton, where she was vice-mistress from 1966 to 1969, and, although never one to suffer fools gladly, always offered a warm welcome at her house to her and her husband's pupils and former students--friendships repaid when about 140 people attended her ninetieth birthday party. Music was an important element in her life (she was a talented pianist and cellist), as was women's education generally. She died at 160 Huntingdon Road, Cambridge, on 18 December 1999, following a stroke.

ALAN COOK, *rev.*

**Sources **

A. Cook, *Memoirs FRS,* 36 (1990), 303-33

H. Jeffreys and B. Swirles, eds., *Collected papers of Sir Harold Jeffreys on geophysics and other sciences,* 6 vols. (1973-7)

M. A. K. and D. H. G., 'Sir Harold Jeffreys', *Annual Report* [Geological Society of London] (1989), 34-5

J. A. Hudson, *Astronomy and Geophysics,* 41 (2000), 3.36-3.37

*The Independent* (22 Dec 1999)

m. cert.

b. cert. [Bertha Swirles]

d. cert. [Bertha Jeffreys]

**Archives **

St John Cam., papers | CAC Cam., corresp. with Sir Edward Bullard

**Likenesses **

photograph, repro. in *Memoirs FRS*

portrait, St John Cam.

**Wealth at death **

£635,235: probate, 2 Aug 1989, *CGPLA Eng. & Wales*

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