Obituary: Sir Charles Frank

CHARLES FRANK was remarkable for the sheer breadth of his contributions to science. Though his main work was in dislocation theory, he also made major contributions to our understanding of cold fusion, liquid crystals, alloy structures, polymers, earthquakes and continental drift.

Part of his strength as a theoretical physicist lay in the breadth of his background. He grew up on his father's farm in Suffolk, and always retained a love of the country. (He had in fact been born in South Africa, but the family returned to Britain when he was only a few weeks old.) After schooling in Thetford and Ipswich, he won a scholarship to Lincoln College, Oxford, and began his academic career as a chemist, taking his first degree in 1933.

He then became nominally an engineer, earning a DPhil in 1937 for work on insulators carried out in the Oxford Engineering Laboratory. From 1936 to 1940, he worked successively as a physicist in Berlin, as a colloid chemist in Cambridge, and (in the early days of the war) as a chemist at Porton, before finding his wartime metier with R.V. Jones in Air Ministry Intelligence.

He had met Jones at Oxford, and they became lifelong friends. The story of their wartime collaboration is well told in Jones's book Most Secret War (1978), which includes many stories of the characteristic inspired common-sense with which Frank managed to interpret the confused scraps of information brought back by various means from occupied Europe. For this work he was appointed OBE in 1946.

In the same year he came to the physics department in Bristol University, where he worked until (and long past) his retirement in 1976, becoming a professor in 1954 and Head of Department in 1969. Soon after his arrival, Cecil Powell and his group there discovered the pi-meson (one of the fundamental particles of physics), and this led Frank to look for other possible explanations of what Powell had found, and to his brilliant realisation that a mu-meson (or muon: another and different fundamental particle) might catalyse nuclear fusion by enabling two nuclei to approach very close to each other. (A year or so later, Sakharov made the same suggestion independently.) Fifty years later, muon-induced fusion continues to be an active field of study, and Charles Frank's original paper continues to be widely quoted.

But this was by way of a digression for Frank: his main field of work for many years was the study of dislocations, those imperfections in crystal structure which profoundly influence the mechanical strength of metals and other materials, and which are therefore of great technological importance. There, his contributions were manifold and of fundamental significance: they included the laws governing dislocation branching, the existence and properties of dislocation networks, and the Frank-Read mechanism for the generation of dislocations.

The idea for this mechanism came simultaneously and independently in 1950 to Frank and to W.T. Read, working at General Electricity in the United States, as they discovered when they met at a conference where they were both going to report it. In consequence, they were happy to report it jointly.

A year earlier, Frank had shown that accepted theories failed by an enormous factor to account for the observed growth rates of crystals, but that these could readily be explained if the growth face contained a screw dislocation, and that this mechanism would produce "growth spirals" on the growth face. This theory was dramatically confirmed when he presented it at a conference: a member of the audience rose to say that he had recently observed just such spiral features, and produced photographs of them illustrating exactly what Frank had predicted. Theorists seldom have such immediate, unexpected and gratifying confirmation of their ideas.

From all the other fields in which Charles Frank made significant contributions, it is perhaps enough to pick out here just two characteristically short, incisive and seminal papers: one on liquid crystals and the other on island arcs. His paper on liquid crystals - substances now familiar in the ubiquitous form of liquid crystal displays - was a classic, and has stimulated a vast amount of subsequent work on these materials. His paper on island arcs - those curved chains of islands which occur particularly in the Pacific - is delightful for the simple analogy he draws between the earth's crust and a ping-pong ball. If one pushes one point on a ping-pong ball inwards, it will form a circular dimple with a sharp rim, and he suggested that island arcs are formed by a similar deformation of the earth's crust.

In his retirement, he continued to publish until well into his eighties. In particular, he undertook the substantial task of editing the Farm Hall transcripts: the secretly made recordings of the conversations of a group of eminent German physicists who were detained at Farm Hall in Cambridgeshire between June and December 1945. He had himself visited and talked with them in November 1945; now, almost 50 years later, he was able to correct errors in the transcripts, and to elucidate their contents, which make a fascinating story.

In recent years, sadly, he became increasingly infirm physically, though his clarity of mind and his phenomenal memory remained unimpaired, and he bore his infirmities with stoic patience.

In all his work, Charles Frank showed deep physical insight, an easy mastery of the relevant mathematics, great originality and an incisive clarity of presentation. For his many scientific achievements, he was elected FRS in 1954, and was awarded the Copley Medal, the Royal Society's highest honour, in 1994. He was knighted in 1977.

For over 60 years, he contributed notably to our understanding of nature, not only through his own publications but also through endless conversations with all the colleagues who came to seek his help and advice in understanding their work. He contributed greatly, too, to the intellectual life of Bristol University, and not only as a scientist: on almost any issue worthy of debate, he could be counted on to express lively, stimulating and well- argued views. Equally lively, equally stimulating and equally a contributor to the life of the university during all that time has been his wife Maita, who survives him.

Frederick Charles Frank, physicist: born 6 March 1911; OBE 1946; Reader in Physics, Bristol University 1951-54, Professor in Physics 1954-69, Henry Overton Wills Professor of Physics and Director, H.H. Wills Physics Laboratory 1969-76 (Emeritus); FRS 1954; Kt 1977; Raman Professor, Raman Research Institute, Bangalore 1979-80; Copley Medal 1994; married 1940 Maita Asche; died Bristol 5 April 1998.