by T. G. Cowling, rev.
© Oxford University Press 2004 All rights reserved
Chapman, Sydney (1888-1970), mathematician and geophysicist, was born on 29 January 1888 in Eccles, Lancashire, the second son of Joseph Chapman, chief cashier at Rylands, a Manchester textiles firm, and his wife, Sarah Gray. He left elementary school at the age of fourteen and attended the Royal Technical Institute, Salford, for two years, intending to enter industry; there he was encouraged in a successful attempt for a county scholarship to Manchester University, which he entered, at the age of sixteen, to read engineering. After this course he spent a further year taking a mathematics degree, during which he won a sizarship to Trinity College, Cambridge (1908), being promoted to a full scholarship one year later.
Chapman gained a first class in part two of the mathematical tripos in 1910 and was starting research when the astronomer royal, Frank Dyson, offered him a post as senior assistant at the Greenwich observatory alongside A. S. Eddington, which he accepted. He was sent to work supervising the installation of instruments for a new magnetic observatory. He found that magneticians were unduly devoted to collecting data, spending too little time trying to interpret them. Encouraged by Dyson and Arthur Schuster he tried to rectify this, and thus began the study of the influences of the sun and moon on terrestrial phenomena which was to be a prime ingredient of his later work. In 1913 he won the first Smith's prize.
Chapman wished to complete work on gas theory begun earlier at the suggestion of Sir Joseph Larmor, so left Greenwich in 1914 and returned to Trinity as a college lecturer. His return coincided with the outbreak of the First World War, during which his religious principles made him a pacifist. He was granted exemption from military service but was asked in 1916 to return to Greenwich in an honorary capacity and remained there until December 1918. However, he felt the strain of maintaining unpopular views, and after the war he went through a period of agonized reappraisal.
Chapman's scientific achievements during the years 1912-19 were remarkable. In gas theory he, and independently David Enskog in Sweden, gave an exact solution to the problems of gas viscosity, heat conduction, and diffusion, posed much earlier by James Clerk Maxwell and Ludwig Boltzmann. Chapman and Enskog identified a hitherto overlooked phenomenon, thermal diffusion, which Clusius used in 1939 to develop a powerful method of separating gases in mixtures.
Furthermore, in four massive papers (1913-19) Chapman examined the regular variations in the geomagnetic field arising from tidal flows in the ionosphere, excited by the sun and moon. He estimated (following Schuster) the electrical conductivity of the ionosphere, and showed how it depends on the sun's radiation. In 1918 he identified a lunar atmospheric tide from sixty years of Greenwich barometer records, a remarkable achievement both because the effect detected was smaller than the limit of accuracy of an individual measurement, and because of the amount of computation which had to be done without mechanical aids. During the next thirty years he determined the lunar tide at numerous stations over the surface of the globe. Finally, in 1919 he made a first attempt at a theory of magnetic storms--sudden irregular changes in the geomagnetic field. Although this theory was soon abandoned as unsound, the accompanying analysis of storm morphology was to prove invaluable.
In 1919 Chapman's scientific achievements were recognized in his election as a fellow of the Royal Society and his appointment to succeed Horace Lamb as professor of natural philosophy at Manchester, where he met Katharine Nora (d. 1967), daughter of Alfred E. Steinthal, barrister and honorary treasurer of Manchester University. They were married in 1922 and had three sons and one daughter. His wife shared many of Chapman's later peregrinations.
Chapman remained in Manchester until 1924, when he became chief professor of mathematics at Imperial College, London. During the period up to 1928 he was much involved in reorganizing and modernizing student courses, though finding time to win the Adams prize from Cambridge for 1928 with an essay on geomagnetism, and to develop earlier ideas further, often in collaboration with younger men--for example, E. A. Milne. The years 1928-32 were another period of intense intellectual activity. He extended his gas-theory methods to cover Brownian motions and the electrical conductivity of plasmas (ionized gases). With a research student, V. C. A. Ferraro, he produced the first satisfactory explanation of the initial phase of magnetic storms as due to compression of the geomagnetic field by plasma streams emanating from the sun. The most significant feature of the Chapman-Ferraro theory was its recognition that plasma behaviour is essentially different from that of single charged particles, so that solar plasma streams can pen the geomagnetic field within a bounded 'magnetosphere'.
In the 1931 Royal Society Bakerian lecture Chapman gave a trail-breaking discussion of the effects of the sun's ultraviolet radiation on the earth's upper atmosphere. He provided a standard theory of layer formation in the lower ionosphere against which later experiments could be compared; he also gave an enlightening account of photochemical reactions in the upper atmosphere. Working in a period when experimental facts were at best only partially available, his achievement was to enable later observers to direct their efforts in the most profitable directions.
1932 to 1940 were years of expanding horizons. Always an internationalist, in 1934 Chapman spent three months in Cairo as visiting professor. He regularly attended international conferences, often cycling across Europe to do so. He made no secret of his distaste for Hitler. He did all he could, personally and through committees, to have refugee scientists settled in suitable posts. However, he maintained friendly relations with German scientists; from 1929 onwards he worked sporadically with Julius Bartels on a treatise, Geomagnetism, finally published in 1940 after the outbreak of war. He had a copy of this book transmitted via America to Adolf Schmidt in Germany, which led him into temporary trouble with officials concerned with stopping trade with the enemy.
A second book which Chapman had begun much earlier, The Mathematical Theory of non-Uniform Gases, was published in 1939 with T. G. Cowling as co-author. The war put an end to such pursuits. Chapman, no longer a pacifist, undertook civilian war work, finally, in 1943-5, working for the army council on problems of military operational research. His methodical nature and capacity for marshalling facts made him a valued leader in his group, whose members could rely on his firm support even against the wrath of generals.
In 1946, after the war, Chapman accepted an invitation to become Sedleian professor of natural philosophy at Oxford, and became a fellow of Queen's College. He appreciated the gracious living there, but not the relatively secondary status he found allotted to science. He tried to improve that status by giving general science lectures to non-scientists. He also supervised research students who were later to make their mark such as F. D. Kahn and K. C. Westfold. However, this time at Oxford was marked by no exciting new advance; his scientific role was becoming that of an elder statesman and counsellor.
In 1953, determined not to let himself be retired when he reached the official age, Chapman resigned his Oxford chair to take up a research post at the new Geophysical Institute at College, Alaska, helping to establish the research school there. In 1955 he added a similar post at the High Altitude Observatory, Boulder, Colorado, officially dividing his time between the two. In practice, however, the two were used as bases for sorties throughout the world. He was visiting professor at many places, among them Istanbul (1954) and Ibadan (1964). He made numerous visits to secure the co-operation of groups in many countries in the work of the International Geophysical Year (IGY) of 1957-8, of whose organizing committee he was president.
Soon after the IGY, Chapman was joined by Syun-Ichi Akasofu, a young geophysicist who had already begun good work in his native Japan. They worked together on the completion of the theory of magnetic storms and the explanation of aurorae in the light of recent discoveries about the van Allen belts, the magnetosphere, and the surrounding plasma from the sun. Another collaborator during this period was P. C. Kendall, with whom Chapman produced a theory of noctilucent clouds.
During the last years of his life Chapman tried, through review papers, to make generally available the wide knowledge he had accumulated over the years. Two of his longer papers were republished as books, Solar Plasma, Geomagnetism and Aurora (1964), and (with R. S. Lindzen) Atmospheric Tides (1970). In addition, at the time of his death he had largely completed the manuscript of a new and comprehensive book with Akasofu, entitled Solar-Terrestrial Physics; this was published posthumously in 1972. He was working hard on a variety of other projects up to the time of his death, which occurred at Boulder on 16 June 1970, after only a few days' illness.
Chapman's most distinctive personal characteristics were his kindliness, persistence, integrity, and simplicity. Those who saw through his surface reserves always found him ready to help. He was never afraid to tackle massive problems, though sometimes he surveyed them for years before the final assault; he tried to give complete solutions, often returning time and again to particular topics. His strength of principle was manifested both by his pacifism during the First World War and his war work in 1939-45; each was motivated by his opposition to violations of humanity. He had a strong sense of duty (including scientific duty) and encouraged high standards in others. If satisfied that a course of action was reasonable he would take it, even if it meant defying convention. When convinced of an error he was ready to acknowledge it. A simple directness pervaded both his writings and his way of life.
Chapman's distinctions and honours were many. He was in turn president of five British scientific societies, and of four international bodies, including the International Union of Geodesy and Geophysics (1951-4). He received royal and Copley medals from the Royal Society, and eight other medals and awards from societies in Britain and abroad, and was elected honorary member of six national academies. He was given honorary doctorates by ten universities, six British and four foreign.
T. G. COWLING, rev.
Sources
S.-I. Akasofu, B. Fogle, and B. Haurwitz, eds., Sydney Chapman, eighty; from his friends (1968)
T. G. Cowling, Memoirs FRS, 17 (1971), 53-89
personal knowledge (1981)
Archives
Bodl. Oxf., corresp. and papers
University of Alaska, Fairbanks, Rasmuson Library, papers | CAC Cam., corresp. with Sir Edward Bullard
Nuffield Oxf., corresp. with Lord Cherwell
Likenesses
photograph, 1913-1919, Trinity Cam.
Lafayette, photograph, 1929, NPG [see illus.]
photograph, 1954, RS
Russell & Sons, photograph, RS
photograph, repro. in Cowling, Memoirs FRS, facing p. 53
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