We moved to Magdeburg, a big city in what is now East Germany, in 1930 and my father was mayor of Magdeburg which is an official position, not a part-time job and, of course, one could see the way things were going from about 1930-31 onwards. In 1933 in January, of course, when Hitler came to power, my father was almost immediately removed from office and taken into what they called protective custody, taken away by the police. Of course he was a socialist and had been mayor of Magdeburg for three years. He was then, after being held in protective custody by the police, put in a concentration camp ... he was in the concentration camp twice. He wasn't let out for very long after the first time and was then taken in again. One point was that he was very popular in Magdeburg and it was thought unwise by the Nazis to let him loose for too long. He was taken in again and particularly the second time had a very tough time indeed. He was ultimately released in early 1935 or perhaps late 1934 ... after a lot of communication from England particularly a Quaker Miss Howard who is now dead who went to a great deal of effort and trouble talking to people in Berlin, talking to people who are high up and also making the case known in England, they were finally persuaded somehow to release him. He then left Germany in March 1935 with a passport which was in fact out of date but we suspect when he crossed the frontier, he went to England straight away, they knew perfectly well, the frontier guards, that it was out of date but they let him through so he was lucky.

I had done two years of English at school [in Germany], which had been very well taught, and I could manage, not very fluently, but after I went to school [in Cambridge] it didn't take me very long to become reasonably fluent. Even before that I had no difficulty following lessons at school or talking to other schoolboys.

Harry and his colleagues (one was John Todd) brought off a great coup. They learned of the Mathematical Research Institute at Oberwolfach in the Black Forest, and decided to visit it despite the fact that it was in the French zone of occupation. When they found that it was destined to become an Officer's Club for the French Army, they protested vigorously and won the day - surely a famous victory, and one from which the whole mathematical world has benefited ever since.

One day at the beginning of May an English jeep drove up, manned by two soldiers: it was the mathematicians John Todd and G E H Reuter, a son of Ernst Reuter, who later became the Burgomeister of Berlin. ... The two gentlemen were sent by the English to inspect scientific institutes. They entered like friends and colleagues. Nothing had been as pleasant for them for a long time as a stay in a small castle in the country. So they asked to stay, Reuter drove his jeep back to Heidelberg in a hurry to get rations, and John Todd brought the authorization for some milk for our coffee table, where we all sat on the library terrace in the May sun. Suddenly a French officer appeared at the rose wall and asked for the director. He came back distraught: the institute had been confiscated, the house had to be cleared for the military ...

Ernst Reuter is best remembered now for his role as Burgomeister of West Berlin during the post-war confrontation with Stalin and the Berlin Air Lift of 1948-49; he is commemorated in the name of the Ernst Reuter Platz, the postal address of the Technical University of (formerly West) Berlin.

I should like to thank Miss M L Cartwright for suggesting this investigation to me, and for her advice during its progress.

The behaviour of an oscillatory system which is positively damped but in which the restoring force is unsymmetrical about the equilibrium position is investigated. It is shown that if a periodic external force whose period is approximately half the natural period is applied, the system may oscillate with twice the period of the external force (such oscillations are called subharmonics of order 2). The subharmonics only occur when the amplitude of the external force reaches a certain critical value; if the forcing period is slightly greater than half the natural period, there is a second critical amplitude beyond which the ordinary forced oscillation (with the same period as the external force) becomes unstable. In the range between the two critical amplitudes, therefore, the forced oscillation or the subharmonics may occur (which of them occurs will depend on the initial displacement and velocity of the system), whilst beyond the second critical amplitude only the subharmonics can occur. This gives rise to a 'hysteresis' effect when the amplitude of the external force is increased and then decreased again.

The enumerably infinite system of differential equations describing a temporally homogeneous birth and death process in a population is treated as the limiting case of one or the other of two finite systems of equations. Starting from the expansion of a finite matrix in terms of its associated idempotents, the solutions of the infinite system are displayed in spectral form which, in general, is written as a Stieltjes integral involving a spectral function. This method facilitates the investigation of asymptotic values and of the ergodic property of the system. When the birth- and death-rates satisfy certain conditions of regularity, the spectrum is discrete and the solution can be written down more explicitly. Concrete examples are given, where the system has two distinct solutions for any set of initial conditions. Finally, our method is applied to the known case of linear growth and to a problem in the theory of queues, confirming a result and a conjecture by D G Kendall.

This did much to interest pure mathematicians in the subject, and paved the way for a similar Conference on Algebraic Number Theory held in the University of Sussex in 1965, thus establishing what became a regular and valuable part of the London Mathematical Society programme. The choice of Durham as a venue in 1963 was a natural consequence of the fact that Harry was by now Professor there, and ever since there has been a close association between that University and the LMS.

Prof G E H Reuter has been appointed professor of mathematics in the Imperial College of Science and Technology from October 1965. For the past six years he has been professor of pure mathematics at the University of Durham. Educated at Trinity College, Cambridge, he took up his first appointment, in the Scientific Civil Service, in 1941. In 1946 he moved to the University of Manchester where he was made senior lecturer in 1955. His research has been chiefly concerned with the analytic theory of Markov chains. The development of a population of any kind may be viewed as a random process and a Markov chain may be thought of as a far-reaching generalisation of such a process. While Prof Reuter has, for example, made a study of competition between insect populations, his most, important work concerns the theory of general Markov chains. In the case of populations, one a assumes known the birth and death rates at the possible population sizes and attempts to deduce various aspects of the population behaviour from these. To solve the analogous problems in general is perhaps the main aim of Markov chain theory. Prof Reuter has shown that operator theory is a natural tool for tackling many of these problems and that it may be applied to solve some of them under wide conditions. One might single out his work on the Kolmogorov equations and his work with Dr D G Kendall (now professor of mathematical statistics at Cambridge) on ergodic theory and on 'pathological' Markov chains.

It was a wonderful change for me to have him living in the same city. At 47 Madingley Road, one was always sure of a warm welcome from Harry and Eileen, and equally sure to find support and wisdom, and a very gentle reproof if one had done something really outrageous. Indeed, I suspect that for many others besides myself, Harry had become a touchstone of integrity.

... it is for his personal qualities that those fortunate enough to have known Harry will best remember him. He had a first-rate mind; nothing that Harry did - research, teaching, administration - was hurried or skimped; he was a perfectionist, without being fussy. He had a delightful sense of humour, which he would deploy with a straight face and in his own inimitable tones (he spoke with no trace of his native German but utterly distinctively - in a Harry Reuter accent, as it were). He had wisdom and humanity, a light touch, and a wry and sceptical way ('les choses sont contre nous', he would say when I grumbled about the burdens of academia). And - supported always by his devoted wife Eileen - he bore his growing physical afflictions with a courage and dignity which impressed everyone who saw him. We will all miss him.