Obituary: Heinrich Kuhn

Heinrich Gerhard Kuhn, physicist: born Breslau, Poland 10 March 1904; Lecturer in Physics, Gottingen University 1931-33; researcher, Clarendon Laboratory, Oxford 1933-71; Lecturer, University College, Oxford 1938-45; University Demonstrator, Oxford 1945-55; Fellow, Balliol College, Oxford 1950-71 (Emeritus); FRS 1953; Reader in Physics, Oxford University 1955-71 (Emeritus); Holweck Prize 1967; married 1931 Marie Nohl (two sons); died Oxford 26 August 1994.

IN 1933 Frederick Lindemann (later Viscount Cherwell) brought to the Clarendon Laboratory in Oxford from the horrors of Europe four outstandingly gifted physicists: Heinrich Kuhn, Nicholas Kurti, Kurt Mendelssohn and Franz (later Sir Francis) Simon. Their impact on Oxford physics was both immediate and long-

lasting, and is still reflected in today's Physics Department. Kuhn developed at Oxford a world centre for innovative high-resolution spectroscopy and laid the foundations for the present Atomic and Laser Department.

Kuhn was born and brought up in Silesia (now in Poland). His father was a lawyer and he had a comfortable and protected childhood. He showed an early interest in science and his first university studies were in chemistry at Greifswald University on the Baltic. But the subject lacked the precision which he found so satisfying and for his doctorate he changed field and university, studying physics under the Nobel Laureate James Franck at

Gottingen.

He continued at Gottingen for a further seven years, building up a substantial reputation in atomic and molecular spectroscopy. During this time he wrote a highly regarded text, Atomspektren (1934). In 1931 he married Mariela Nohl; theirs was an ideal partnership which triumphed over the difficulties to come.

Although Kuhn had a Christian upbringing, two of his grandparents were Jewish and in 1933 this required dismissal from his university post. Shortly thereafter, Lindemann invited him to come to Oxford under the scheme organised with support from ICI to bring emigres from Europe to work in England.

It was presumably Lindemann's inspired idea that Kuhn would form an excellent partner for the wealthy but eccentric spectroscopist Derek Jackson. At first sight they were an unlikely pair, differing completely in background and lifestyle. But united by a common enthusiasm for their subject they struck up a most productive partnership, pioneering work on the use of atomic beams to reduce the line width of spectral lines and so make possible more accurate spectroscopic measurements. During this period, he also published important work of his own on the formation of spectral profiles. He was naturalised in 1939.

At the outbreak of the Second World War, 'peacetime research' at the Clarendon was replaced by work on radar. However the policy was not to employ ex-aliens, especially ex-enemy-aliens, on sensitive work. So when atomic bomb work took off in 1940, a majority of those available to work on it were not British-born, and Kuhn was among them. He made important contributions to the work on diffusion, developing reliable instruments to characterise the diffusion membranes.

After the war, he continued to work in the field of high-resolution optical spectroscopy, developing techniques based on the Fabry-Perot interferometer and applying them mainly to the study of atomic hydrogen, nuclear effects in atomic spectra and atomic collisions. The ingenuity and insight he brought to this programme kept the Clarendon in the forefront of the field for many years.

With his students and visitors, he developed optical coating technology, successfully excited spectra from minute quantities of separated isotopes, and worked on scanning interferometry. This last was particularly well-adapted to the study of spectral profiles, one of Kuhn's early interests, and was later to allow his group to exploit the power of digital methods of recording and analysis. These greatly increased the scope and accuracy of all the group's high-resolution work.

This mastery of experimental techniques, combined with Kuhn's instinct for an interesting problem, led to a series of critical studies of nuclear sizes and tests of collision theory. His style of supervision was to lead by example. He inspired admiration, respect and affection in his graduate students. He encouraged independence, but was ready with help and advice.

His book Atomic Spectra (1962), originally intended as an English version of his earlier publication, is quite remarkable in that it is a wide-ranging work of reference but written in a pedagogical style. Because of its emphasis on principles, it is still after 25 years widely used and quoted.

Kuhn always believed strongly that laboratory work must be central to the teaching of physics. Over the years, with his colleague George Series, he built up the Oxford atomic practical laboratory. Their philosophy of well-thought- out experiments supported by knowledgeable and caring demonstrators continues to underpin today's very different course.

As early as 1938, Kuhn was appointed a College Lecturer at University College. In 1950, Balliol were looking for a physics tutor and elected him to a Fellowship. He started in a small way, though in charge of both physics and engineering. But Balliol were then expanding in science and over the years he established the engineering school in its own right and built up physics to the strong position which it has maintained to the present. He was an excellent tutor, conscientious and caring. His teaching was individual, without any concept of the modern production-line approach. In the early days he covered a large part of the syllabus. For a keen student, a tutorial was on occasion a marvellous opportunity to see a great physicist approach an unfamiliar problem. One learnt by example how to think about physics. Apart from losing one of his books, the only real crime was not to do one's best. His sorrowful reproach was almost unbearable.

'Heini' Kuhn retired in 1971 and initially remained very active, writing and keeping in touch with developments in the laboratory and in spectroscopy. Alas, over the years this became less and less possible and he suffered a long and difficult illness through which he was supported by his close and devoted family.

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