Obituary: Professor Arthur Wilson

Arthur James Cochran Wilson, crystallographer: born Springhill, Nova Scotia 28 November 1914; research assistant, Cavendish Laboratory, Cambridge 1940-45; Lecturer in Physics, University College, Cardiff 1945, Senior Lecturer 1946, Professor of Physics 1954-65; Editor, Structure Reports 1948-59; Editor, Acta Crystallographica 1960-77; FRS 1963; Professor of Crystallography, Department of Physics, Birmingham University 1965- 82 (Emeritus); married 1946 Harriett Friedeberg (two sons, one daughter); died Cambridge 1 July 1995.

Arthur Wilson ranked amongst the world's leading crystallographers for almost half a century.

Crystallography embraces most fields of scientific endeavour; a knowledge of the structure of materials on an atomic scale is of fundamental importance in all branches of the physical, chemical and earth sciences, in metallurgy and medical research. Wilson made outstanding contributions to the theory and practice of the subject throughout his career, through more than 300 publications, and was actively involved in the affairs of the International Union of Crystal- lography from its inception in 1946. (The IUCR is the body responsible for promoting international co-operation in the field, for encouraging publication of research and other works, for the standardisation of methods and units and for providing a focus for the relations of crystallography to other sciences.)

Born in Springhill, Nova Scotia, in 1914, Wilson was educated at King's Collegiate School, in Windsor, Nova Scotia. He received his BSc in 1934 and MSc in 1936 from Dalhousie University, Halifax, and proceeded to the Massachusetts Institute of Technology, where he received his first PhD in 1938.

Although he was not then contemplating a career in crystallography - his thesis was concerned with the anomalous thermal behaviour of the ferro- electric Rochelle salt - he worked with Bertram E. Warren, a pioneer in the study of imperfect crystals. Awarded an 1851 Exhibition Scholarship in 1937, he left MIT for St John's College and the Cavendish Laboratory, Cambridge, in 1938. This was the year in which Sir Lawrence Bragg succeeded Lord Rutherford as the Cavendish Professor of Experimental Physics at Cambridge University. During the remaining two years of his scholarship, Wilson made accurate measurements of the thermal expansion of aluminium and lead, which led to the award of his second PhD in 1942.

It was through this work at the Cavendish Laboratory, and the influence of Bragg and Henry Lipson that Wilson acquired a lifelong interest in X-ray crystallography.

Wilson's crystallographic activities were diverse, but one remained constant throughout. When asked to review a paper submitted to Nature in 1942, on deriving absolute from relative intensities of X-ray diffraction data, he first became aware of the analytic power of crystallographic statistics. The complex method described in the paper stimulated a simpler, and more direct, approach to the problem which was published alongside the original contribution.

The practical importance of this work was not realised for a while, but the 1942 paper in Nature eventually became one of the most frequently cited papers in crystallography. This work was concerned with determining the atomic structure of materials from single-crystal data, but Wilson also made important contributions to the diffraction physics of imperfect structures encountered in polycrystalline materials. His book X-ray Optics (1949; second edition 1962) has been the starting-point for much subsequent research in this field and is still a definitive work on the subject.

Wilson left Cambridge in 1945 to take up an appointment as lecturer in the Department of Physics at University College, Cardiff. In 1946 he became a senior lecturer and in 1954 was appointed Professor of Physics and Director of the Viriamu Jones Laboratory, a post he held until 1965. At Cardiff he founded a school of organic crystal chemistry which achieved world- wide recognition for its work on alkaloids and other organic substances. In the late 1940s he demonstrated, from statistical considerations, that the symmetry elements of a crystal structure can be deduced from observed diffraction data.

These elements include a centre of symmetry, which had previously been thought impossible to detect by X-ray methods. Sir Lawrence Bragg said of this discovery, "Like all brilliantly original ideas, it seems obvious when pointed out!"

The introduction of commercial X-ray powder diffractometers about 1950 resulted in a dramatic improvement in the quality of powder diffraction data and a second group at Cardiff was formed to exploit the new device. Wilson again introduced statistical concepts to analyse the data, as a means of characterising polycrystalline materials, and this contribution to diffraction physics was published in Mathematical Theory of X-ray Powder Diffraction (1963).

Together with H.S. Peiser and H.P. Rooksby, he was editor of X-ray Diffraction by Polycrystalline Materials (1955; revised 1960), and lecture courses he delivered at Cardiff formed the basis of Elements of X-ray Crystallography (1970). He was also a co-author of X-ray Diffraction (1974). In 1963 he was elected a Fellow of the Royal Society.

In addition to pursuing the research activities engendered at Cambridge, Wilson had a lifelong interest in editorial work and his contribution to presenting and disseminating scientific information is incalculable. In 1948 he became editor of Structure Reports, the systematic and critical compilation of crystal-structure determinations. This initiated an important leadership role in the publication activities of the IUCR which continued without interruption throughout his life.

In 1960 Wilson succeeded Paul Ewald as Editor of Acta Crystallographica, a post he held until 1977. Acta, then the principal publication of the IUCR, thrived under his editorship, expanding to two volumes, with a five- fold increase in publications. As editor of Acta, Wilson was also Chairman of the Commission on Acta Crystallographica from 1960 to 1967 and, following the launching of the Journal of Applied Crystallography in 1968, Chairman of the Commission on Journals. From 1960 to 1977 he was the first Chairman of the Commission on Crystallographic Nomenclature and was subsequently an active ex officio member.

In addition to these editorial duties for the IUCR, he was Associate Editor of the Proceedings of the Royal Society from 1978 to 1983. He became associated with the ICSU/Unesco Committee on Physics Abstracting in 1948 and actively represented the interests of the IUCR on its successor organisation, the Abstracting Board of the International Council of Scientific Unions (ICSU) from 1951 to 1984. This became the International Council for Scientific and Technical Information (ICSTI), on which Wilson served until 1990, as Vice-President from 1980 to 1986.

In 1965 Wilson was appointed Professor of Crystallography in the Department of Physics at Birmingham University, where he continued to pursue his research interests and editorial activities. Shortly before his retirement in 1982, he was involved in the formation of the British Crystallographic Association.

On retirement from his post at Birmingham, he returned to Cambridge, where he took on the chairmanship of the IUC's Commission on International Tables. The two series of crystallographic tables published previously had been widely distributed, but were in need of revision. At the time of his death, he had just completed editing the revision of Volume C of the Tables, Volumes A (third edition) and B having appeared in 1992 and 1993.

Arthur Wilson was a member of the Society of Friends and during his "retirement" was Clerk of the Jesus Lane Meeting, Cambridge. Despite his crystallographic commitments, he also found time to become actively involved in the University of the Third Age, an extramural body in Cambridge that stages meetings and discussions for older people, an interest he shared with his wife, Harriett. An enthusiast for mountain walking, he was a life member of the Rambling Club and a member of the Alpine Club and the Sierra Club (San Francisco).