# Gerd Edzard Harry Reuter

### Quick Info

Berlin, Germany

Cambridge, England

**Harry Reuter**was born in Germany but came to England as a refugee in 1935. His career was at the University of Manchester, the University of Durham and Imperial College, London. He contributed to a wide range of topics but is best know for outstanding contributions to probability, particularly to Markov processes.

### Biography

**Harry Reuter**was always known by this name but he published under the name

**G E H Reuter**. He was the son of Ernst Rudolf Johannes Reuter (1889-1953) and Charlotte Gertrud Herta Scholz (1901-1977). Ernst Reuter, the son of Karl Georg Wilhelm Reuter and his wife Auguste Elise Wilhelmine Karoline, married Charlotte Gertrud Herta Scholz on 7 January 1920, the day she became nineteen years old. Charlotte was the daughter of Oskar Scholz and his wife Klara Friederike Dorothee. When Ernst and Charlotte's two children were born Ernst was First Secretary of the Berlin section of the German Communist Party. The children were Hella, born 1920, and Harry, the subject of this biography, born the following year. Ernst was expelled from the Communist Party in 1922, and then had a political career as a member of the SDP, the Social Democratic Party of Germany. The marriage of Ernst and Charlotte, however, was short-lived and they were divorced in 1925. Harry was brought up by his father and his sister Hella by her mother.

Ernst Reuter was a member of the Berlin Government from 1926, responsible for transportation. He married Johanna Margarete Kleinert (26 December 1899-1974) on 15 July 1927 and from then on, Johanna became Harry's mother. The family moved to Magdeburg in 1930 when Ernst became mayor of the city. In the interview he gave to Margaret A Brooks on 28 September 1979 he said [16]:-

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.After Ernst was arrested Harry and his step-mother stayed in Magdeburg for a while, then moved to Hannover where his step-mother came from and they stayed there. Ernst Reuter was held in Dachau Concentration Camp but after his release he travelled to England and went to Cambridge. Not long after he arrived, he went to see some friends and they told him that a free place had just been announced in Leys School, Cambridge, for the children of refugees. This had been arranged by the school in collaboration with the Quaker's 'Germany Emergency Committee'. Ernst applied for Harry to have the place and by April 1935 it was agreed. Harry's step-mother accompanied him to England, and then she returned to Germany. We should note here that Harry Reuter was not a typical refugee fleeing Germany at that time since most of the refugees had fled because they were Jewish, but the Reuter family were persecuted for their political views.

Ernst Reuter looked for a job in England but nothing came up and he then went to Ankara in Turkey where he was offered a job. Ernst's wife joined him in Ankara but Harry remained in Cambridge. He was a boarder at Leys School, Cambridge, but was looked after by Charles Burkill and his wife Greta who took him and another refugee into their home and treated them like their own children. Greta had been born in Germany to a German father and Russian mother and after Hitler came to power the Burkills did amazing work supporting refugee children. Greta Burkill helped to bring many hundreds of refugee children out of Germany and to settle in England. The Burkills assumed legal responsibility for Harry and for that of another refugee boy from Austria. It was the Burkills who gave Reuter his love of mathematics for in their home "mathematics was in the air."

At Leys School, Reuter had little difficulty with English [16]:-

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.In late 1938 he acquired British nationality and went to visit his family in Ankara, Turkey; they were a bit appalled at the way his German sounded. While in Ankara he got the news that he had been successful in winning a scholarship to the University of Cambridge. He matriculated at Trinity College in 1939 where he studied the Mathematical Tripos. In 1941 he took the examinations of Part II of the Tripos and graduated with a B.Sc.

After leaving Cambridge, Reuter joined the Royal Naval Scientific Service as a Scientific Officer. There was one story that he enjoyed relating which involved a trip he had to make to a naval base in the north of Scotland. On his journey he had to pass through a control point and he gave them his Admiralty Pass as identification. The guards asked also to see his personal passport which he handed over. Examining the passport sent the guards into great consternation when they saw "Place of Birth: Berlin." After the war ended in 1945, Reuter was sent on a mission to debrief German scientists [11]:-

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.Wilhelm Süss was the director of the Mathematical Research Institute at Oberwolfach and his wife wrote about the arrival of Reuter and John Todd at the Institute [1]:-

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 ...Süss need not have worried since Reuter and John Todd said they could avert that, and continued drinking their coffee. Since Reuter's father is mentioned in this quote we should note that Ernst Reuter became somewhat of a hero in this period. Leaving Turkey, he had returned to Berlin at the end of the war becoming the Burgomeister of West Berlin [2]:-

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.His war service at an end, Reuter returned to Cambridge to continue his studies aiming for a doctorate. He worked with Frank Smithies, who was assigned as his official advisor, and also with John Littlewood and Mary Cartwright.

In 1945 Reuter married Eileen Grace Legard (1921-2012), the second daughter of the leather merchant Hubert Ronald Legard and his wife Amy Key. Eileen had been born on 19 December 1921 in Barnsley, Yorkshire, and it was in Barnsley that the marriage took place. Harry and Eileen Reuter had four children: Timothy Reuter (1947-2002), Penelope Reuter (1949-2017), Stella Reuter and Elizabeth Reuter.

In 1946 Max Newman approached Reuter with an offer of a position at the University of Manchester. Reuter decided to accept the offer from Manchester and left Cambridge without finishing his doctorate. The first papers he published were, however, related to research he had been undertaking at the University of Cambridge before going to Manchester. These first papers were

*An inequality for integrals of subharmonic functions over convex surfaces*(1948), (with A B Pippard and E H Sondheimer)

*The conductivity of metals at microwave frequencies*(1948), (with E H Sondheimer)

*The theory of the anomalous skin effect*(1948), (with I J Good)

*Bounded integral transforms*(1948),

*On the boundedness of the Hermite orthogonal system*(1949),

*Subharmonics in a nonlinear system with unsymmetrical restoring force*(1949).

The first thing to note here is that right from the beginning of his research career, Reuter was working on topics in pure mathematics, applied mathematics and physics. We should also explain briefly about Reuter's three collaborators on the above papers. Alfred Brian Pippard (1920-2008) had been appointed as a Demonstrator in Physics at the University of Cambridge in 1946. Ernest Helmut Sondheimer (1923-2019) had been born in Stuttgart but came to England in 1936. In early December 1941 he was accepted to study Chemistry and Physics in Cambridge. He continued to work for a Ph.D. at Cambridge before becoming a lecturer in applied mathematics at Imperial College in London in 1951. Irving John Good did research under G H Hardy and Besicovitch at the University of Cambridge before moving to Bletchley Park in 1941 on completing his doctorate. At Bletchley Park he worked with Alan Turing and in 1947 he was recruited to the University of Manchester by Max Newman.

The last of the five papers listed above contains the acknowledgement:-

I should like to thank Miss M L Cartwright for suggesting this investigation to me, and for her advice during its progress.It begins as follows:-

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.At the University of Manchester, Reuter was a colleague of Walter Ledermann. In 1952 the two began working on problems related to probability. Their interest had come from conversations with Maurice Bartlett who was the Professor of Mathematical Statistics at the University of Manchester. Their two papers on discrete-state Markov processes in continuous time

*On the Differential Equations for the Transition Probabilities of Markov Processes with Enumerably Many States*(1953) and

*Spectral theory for the differential equations of simple birth and death processes*(1954) were described by D G Kendall as "path-breaking." The second of these papers has the following abstract:-

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.David Kendall met Reuter at the British Mathematical Colloquium held in Durham in September 1953. They quickly began a collaboration which led to them presenting the paper

*Some pathological Markov processes with a denumerable infinity of states and the associated semigroups of operators on l*to the International Congress of Mathematicians held in Amsterdam in September 1954.

Reuter spent sabbatical leave at Yale in the United States in 1958 where he was able to work with William Feller. He left Manchester in 1959 when he was appointed as Professor of Pure Mathematics at the University of Durham, taking up the appointment on 1 January. His research interests were now mostly on Markov processes with the paper

*Denumerable Markov processes III*being published in 1962 but he was still involved in applied mathematical work such as

*A nonexistence theorem in magneto-fluid dynamics*(1961) written jointly with Keith Stewartson. Along with David Kendall, he set up the 'Stochastic Analysis Group' with the aim of having a base for probabilists and also to increase contacts between the London Mathematical Society and the Royal Statistical Society. Part of this project involved running the 'Instructional Conference on Mathematical Probability' in Durham in March and April 1963. David Kendall writes [11]:-

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.In 1965 Reuter moved from Durham to London when he was appointed to the chair of Pure Mathematics at Imperial College. This appointment was announced in

*Nature*[12]:-

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.In 1983 Reuter retired from his chair at Imperial College and went to live in Cambridge. David Kendall writes [11]:-

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.Reuter served the London Mathematical Society as editor of the

*Journal*and Secretary of the Society in 1966-69. He also served as Vice-President of the Society.

Finally, we quote from Nicholas Bingham [2]:-

... 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.

### References (show)

- H Bauer, 50 Jahre Mathematisches Forschungsinstitut Oberwolfach: Verantwortung und Herausforderung,
*Mitteilungen der Deutschen Mathematiker-Vereinigung***3**(2) (1995), 10-14. - N H Bingham, Obituary: G E H Reuter,
*Journal of Applied Probability***29**(1992). 754-757. - N H Bingham, A Conversation with David Kendall,
*Statistical Science***11**(3) (1996), 159-188. - Charlotte Gertrud Herta Scholz,
*ancestry.com*. - Ernst Rudolf Johannes Reuter,
*ancestry.com*. - G E H Reuter,
*The Times*(18 May 1992). - Gerd Edzard Harry Reuter,
*ancestry.com*. - Johanna Margarete Kleinert,
*ancestry.com*. - D G Kendall, Reuter, (Gerd Edzard) Harry (1921-1992), mathematician,
*Oxford Dictionary of National Biography*(Oxford University Press, Oxford, 2004). - D G Kendall, Harry Reuter: An appreciation,
*Advances in Applied Probability***18**(1986), 1-7. - D G Kendall, N H Bingham and E H Sondheimer, Obituary: Gerd Edzard Harry Reuter,
*Bulletin of the London Mathematical Society***27**(2) (1995), 177-188. - Mathematics in the Imperial College of Science and Technology: Prof G E H Reuter,
*Nature***207**(4993) (1965), 130-131. - Probability at Durham. Some historical notes,
*University of Durham*.

https://www.maths.dur.ac.uk/PiNE/PaD/history.html - Obituary: G E H Reuter,
*The Times*(9 May 1992). - Obituary: G E H Reuter,
*Daily Telegraph*(25 June 1992). - Reuter, Gerd Edzard Harry (Oral History),
*Imperial War Museum*.

https://www.iwm.org.uk/collections/item/object/80004441

### Additional Resources (show)

Other websites about Harry Reuter:

Written by J J O'Connor and E F Robertson

Last Update June 2021

Last Update June 2021