12. Copenhagen 1964-73

“Do not enfeeble your spirit with half wishes and half thoughts… for only the truth that builds up is truth for you.” – Søren Kierkegaard, Either/Or.

Jim, Glen and younger son, Patrick, arrived in Copenhagen in September 1964. The elder two children remained in England at boarding schools and would visit the rest of the family out of term time. The family’s first address in Copenhagen was near Hellerup, a rented property on Ellemosevej. It was a fairly quiet residential road; there was an S-tog suburban railway close by which was Jim’s transport to work for his first few months at Nordita. Jim, at age 46, had already lost much of the hair on his head and what remained was greying; he arrived at Nordita with something of a distinguished profile.

The Nordita organization differed from the British Universities which Jim had worked at hitherto and the differences are perhaps best described by a brief summary of the Nordita hierarchy. The highest authority is the Nordic Council of Ministers who have granting authority over Nordita‘s budget and who appoint the national representatives to the Nordita board (up to 3 representatives from each Scandinavian country).

The Nordita board, being comprised of the national representatives plus the Nordita director, one Nordita professor, one Nordita fellow and one representative from the Nordita administration staff, typically meets twice a year and appoints the director, professors, fellows and administrative staff at Nordita. Otherwise, the board is mostly concerned with budget and administrative matters. There is a subset of the board, the executive committee, which meets more frequently.

The permanent Nordita professors constitute a Professor collegium which is advisory to the board in scientific matters and in the matter of appointment of professors and fellows. Formally, a Nordita professor would report to the Nordita director.

For many years, particularly at Nordita’s inception, there was also a less formal, but nevertheless perceptible influence from their next-door neighbours at the University Institute of Theoretical Physics : the two institutes shared adjacent premises on Blegdamsvej (in the interest of clarity the writer henceforth refers to the University Institute as NBI, the Niels Bohr Institute, although this was not the official name until 1965). In 1957 Niels Bohr (the NBI director) became the first chairman of the Nordita board. Still in 1957-8, the first Nordita director was Christian Møller (Nordita director, but professor extraordinarius at Copenhagen University), and the first permanent Nordita professors were Gunnar Källén, Ben Mottelson and Léon Rosenfeld. Stefan Rozental was appointed lecturer.

Møller and Rosenfeld had been with Niels Bohr for many years. Møller had been at NBI since 1929 and remained there until 1975. He had also been director of the CERN Theoretical Study Group from 1954 until 1957 and was therefore a natural choice for the equivalent position at Nordita. Møller and Rosenfeld’s modification of the meson theory was one of the models Jim had referred to back in the early 1940s. Rosenfeld had been at NBI from 1930, a close collaborator and assistant of Niels Bohr’s, until taking a professorship at Manchester in 1947. Rosenfeld knew Jim well from that earlier time.

Mottelson had held a travelling fellowship at NBI from 1950 (from 1953 he was also involved in CERN research). At NBI he had been in collaboration with Aage Bohr, son of Niels, their project being the modernizing of Niels Bohr’s ’liquid drop’ nuclear concept by unifying it with the other current concept of the nucleus, that of particles arranged in shells. Källén had been in Copenhagen with the CERN theoretical group until 1957 and then switched to Nordita for one year prior to taking up a professorship at Lund. His fields were quantum electrodynamics and elementary particle physics.

Jim’s appointment in 1964 was recommended by the existing permanent professors (the faculty : since 1957-8 Gunnar Källén had left, and Gerry Brown had arrived), and by the chairman of the board. The Nordita board, including Christian Møller, authorised the appointment and one might assume that the appointment had the tacit approval of NBI, in particular Aage Bohr. Next door, at NBI, there were several faces that Jim would have recognised from his 1947 visit : Torben Huus, Niels O. Lassen, O.B. Nielsen and J.K. Bøggild were all still at NBI in 1964, though the most significant of all was missing. Niels Bohr had died in 1962, his directorship at NBI had been taken up by Aage, and Torsten Gustafson had become chairman of the Nordita board.1

Gerry Brown had been at Nordita since 1960. From 1964 he would also hold a professorship at Princeton and, from 1968, Stony Brook, New York. Nordita was keen to attract distinguished theoretical physicists and developed an arrangement known as an ’adjunct’ professorship to allow Gerry to split his time between Copenhagen and America. Gerry had gone on from his work with Ravenhall in 1951 to become one of the world’s leading nuclear theorists and would from the 1970s (often in collaboration with Hans Bethe) make very significant contributions to the understanding of black holes, star collapse and supernovae.

Jim was the only particle physics professor at Nordita, however NBI also appointed a new associate professor in particle physics at this time, Zirô Koba. As a graduate student at Tokyo University, Koba had worked after the war with Sin-itirô (variously spelt Sin-ichirô, Shinichiro) Tomonaga’s research group at Tokyo Bunrika. From 1950 Koba had worked on various topics of Quantum Field Theory at the universities of Osaka and Kyoto, then had worked at the Warsaw Institute for Nuclear Research until his move to Copenhagen.

There is a prior link between Koba and NBI. Tomonaga had graduated from Kyoto University in 1929 (together with Hideki Yukawa) and subsequently, in 1932, joined Yoshio Nishina’s group at Riken. Nishina had spent six years at the Bohr Institute during the 1920s.

On their arrival in Copenhagen Jim and Glen were determined to learn the Danish language at least to a point sufficient for everyday use, if not for technical conversation. One of Jim’s early non-technical contributions in Copenhagen was to assist in the translation of Stefan Rozental’s tribute ’Niels Bohr’, which appeared originally in Danish during the autumn of 1964. His assistance is acknowledged in the English edition of 1967. Within a year Jim was able to follow most of the TV news and he would read the Danish newspaper ‘Politiken‘. The pronunciation of the Danish language is more difficult, and neither Jim nor Glen would become completely fluent. Nevertheless, by the mid-1970s, Jim’s grasp of spoken and written Danish was sufficient for him to undertake a evening-class course in navigation and seamanship and to obtain his Master’s certificate. The course and examination were conducted entirely in Danish.

Though Gerry Brown and Jim might both be described as ’non-dynasty’, Gerry had the advantage over Jim of 4 years more experience in the Nordita setup. He recalls that Jim did not know well how to get along with the Danish administration. Gerry’s office was “kitty-korner” to Jim’s and they had become very good friends since their original meeting back in 1952. There were times when Jim walked into Gerry’s office and vented his frustration. Gerry would wait patiently for the storm to blow over. In the early days this frustration with administration may have been caused simply by the language barrier. Another factor may have been that the Nordita Director was also head of administration, there was no hierarchical link between professor and admin. Jim’s experience of departmental administration at English universities was likely very different.

Two of the three senior Nordita secretaries in 1964 were the Abrahamsen sisters, who were said to be formidable, but it seems unlikely that the difficulties Jim experienced were with the secretariat. Anyway, from 1965 another secretary, Helle Kiilerich, joined Nordita. Helle would have held a junior position at first, but soon became an extremely helpful assistant to Jim. After Jim’s death, Helle also helped Glen with some important issues, and even at the time of writing she has contributed much assistance with research for this project.

In addition to the scientific staff (the director and professors) and the administration there were about ten Nordic fellows, young physicists from around Scandinavia, supported by Nordita on one- or two-year grants. There were also other young physicists who would visit for short periods. This was the main purpose of Nordita, to provide a centre of excellence from which to promote scientific collaboration between Nordic physicists.

Jim arrived at Nordita a world-leading expert in elementary particle physics, particularly in the use of dispersion relations in the analysis of the strong interaction. At the time of Nordita’s founding, elementary particle physics had not yet developed into a separate field within theoretical physics but was considered to be a sub-field of nuclear theory. Though Christian Møller had interests close to particle theory, much of the emphasis of Nordita’s research until 1964 had been on the nuclear physics side. Jim was the first Nordita professor expert in particle physics.

He immediately started delivering his first major course of lectures, ‘Elementary Introduction to Elementary Particle Physics’, which was attended not only by Nordita fellows but also by students from the University of Copenhagen. Jens Lyng Petersen was one of those from the university who attended these lectures and he recalls the excitement of the time. Jim would have been only too pleased that external students were attending his lectures and it would be customary for a Nordita professor to provide further guidance to the external students, if advice was sought. Lyng Petersen approached a couple of people (one was Jim) to advise on a topic for his upcoming Master’s thesis. He readily opted in favour of Jim’s recommendation but did not confer much with him during work on his thesis : “I must admit at the time he seemed to me a formidable person to approach.” Lyng Petersen goes on to say “During that work I had occasion to study some of Jim’s papers and I could not help admiring the grace and elegance by which he employed dispersion relations to analyze experimental data and thereby obtain valuable information from quantum amplitudes, partial wave amplitudes in particular.“

During the spring of 1965 Jim and Glen had found a suitable permanent address and had moved in by June. This was a comfortable terrace house on Soldalen, in the district of Svanemølle. From here it was a straightforward journey to work, down the broad Østerbrogade to Trianglen and nearby Blegdamsvej, and it became the regular custom for Jim to cycle to and from Nordita. There was a good tram service besides, and in snowy or rainy conditions he was happy to use this option.

Maybe 600 metres to the east of Soldalen is Svanemølle Bugt, a bay of the Øresund. Along the shore a promenade stretched for more than a kilometre, from the rear of Tuborg brewery at its north end to the Svanemølle power station at the south, and allowed a good view of the strait dividing Denmark from Sweden. On a good day Sweden was clearly visible from the promendade. Svanemølle power station was one of the coal-burning generation, but something quite clever had been done. The steam generated by the cooling process was then circulated in a piped network in order to heat many homes in the Svanemølle district, at reasonable cost.

At home, in the evenings and at weekends or during vacation, Jim would dress simply, in grey trousers and white or cream shirt, the shirt open at the collar and without a tie. The shirt sleeves would be loosely rolled up. In colder weather it would be the same except a jumper would go over the shirt. On hot summer days a straw hat might be donned outside. This was an Irish trait, ordinary people in the west of Ireland often dressed like this.

Jim had become a smoker, probably during the war. Into the 1950s, he switched to a pipe. Having lit the pipe, he had the habit of, for the sake of tidiness, returning the spent match to the same box still occupied by live matches, and then returning the match box to his trouser pocket. On one occasion the match box subsequently exploded in Jim’s pocket, causing quite a stir for a few moments. Jim escaped without serious burns. Patrick, maybe aged 6 at the time, had witnessed the whole thing and was crying with mirth as he related the story to his older brother. Fair play to Jim, he didn’t begrudge the amusement at his expense.

Additional to his work at Nordita, Jim took on an editorship for ‘Physics Letters’, the foremost journal for nuclear and particle physics, in 1965. Gerry Brown and Dirk ter Haar had started the journal in the 1950s and after Jim’s arrival in Copenhagen, Gerry asked Jim to take over the editing for particle physics, leaving himself just the nuclear physics editing. When ‘Physics Letters’ was sectionalised in 1967, Jim went on to edit for ’Physics Letters B’ for a further five years. The 1967 editorial board comprised Gerry Brown and Jim from Copenhagen, P.M. Endt and M. Veltman from Utrecht, D. ter Haar from Oxford, and J. Volger from Eindhoven. Jim was conscientious with this work, spending many hours poring over the submitted articles.

After Lyng Petersen had presented his Master’s thesis, Jim encouraged him to keep working, asking him to go over the hand-written lecture notes for Jim’s second and third major lecture courses at Nordita ‘The Dynamics of Elementary Particles and the Pion-Nucleon Interaction‘ (Course A and Course B), not only to proof read but to check calculations and suggest alterations. This was quite a lot of work and Jim allowed Lyng Petersen two months to complete it. A hard task-master, he then enquired whether Lyng Petersen had any vacation plans. Lyng Petersen, who had been married just over two years, said that he was expected to become a father. This caused considerable laughter between the two of them. Jens goes on : “All in all the years 1967 to 1970 were extremely happy ones for me…and I thrived under the warm and friendly support from Jim…I can say that I became a friend of Jim’s as well, I think, even though our relationship was more like a father-son relationship, given the age difference and Jim’s rather formal attitude. But I really did feel very comfortable with him at a human level as well.”

On ‘The Dynamics of Elementary Particles and the Pion-Nucleon Interaction‘, Gerry Brown comments : “…on this topic, theoretical physics has gone further. However important aspects are being dug up and used in the theoretical work on relativistic heavy ion reactions that followed from the Mandelstam Representation and the dispersion theory that described the distributed mass mesons, especially sigma and rho.” Gerry recalls “We were very good friends and I learned a lot from him. I went to all his lectures and I am still (actually again) using in my research mathematics I learned from him…The mathematics in the dispersion theory are pretty tough, mostly analytical continuations…”.

Gerry also refers to a visit to Nordita around this time from a very clever Rumanian, Sorin Ciulli, whom Jim had invited. Ciulli was expert in dispersion relations and had developed a technique similar to Cutkosky’s (whose work was being used at the time by the young members of Jim’s group) for carrying out analytical continuations of phenomenological amplitudes. Such visits were common at Nordita and were usually highly beneficial for all parties.

Jim’s elementary particle research group at Nordita, which would loosely become known as the ‘Nordic Dispersion Relations Group‘, was beginning to take shape. Jens Lyng Petersen (who was awarded a Nordita fellowship in 1967), Henry Nielsen (also Danish), and Esko Pietarinen from Finland were early members. In addition to Brian Martin, two other members of Jim’s high energy physics group at UCL, Geoff Oades and Andrew Lea, joined Jim in 1965. At meetings of this group in Copenhagen there would also often be visiting researchers. Another member of Jim’s UCL high energy physics group, Bill Woolcock, recalls visiting Jim at Nordita on two occasions to give seminars, once in the spring of 1968 and again in the winter of 1973-4. His opinion was that Jim was happy at Nordita, that it was a well-deserved appointment and he served Nordita well.

A little later Jim introduced a scheme whereby Nordita financed meetings to bring together people from around Scandinavia on a regular basis – perhaps four times a year – and the group expanded further, with Gösta Gustafson from Sweden; Ingjald Øverbø and Sigmund Waldenstrøm from Norway; and Bjarne Tromborg and Finn Elvekjaer from Denmark. Jim’s innovative scheme for an extended research group, forming a coherent research effort, would later be copied in various forms by others. Lyng Petersen notes that Jim’s pan-Scandinavian initiative “brought out his deep care and feeling of responsibility for the people surrounding him.” It also completely fulfilled Nordita’s stated purposes, to run a research institute in Copenhagen and to promote scientific collaboration between Nordic physicists. Jim took this matter very seriously and throughout his time at Nordita made many short visits to the universities of Aarhus, Helsinki, Lund, Odense, Stockholm and Trondheim. The writer would often receive a postcard from Jim with “just here for a day to give a lecture”, or something similar written.

Jim encouraged yet further widening of the collaborative effort. He had attended the Black Forest meeting of 1963 (possibly he had visited Karlsruhe earlier even than this) and was again in Karlsruhe during October 1965. Certainly he had met Gerhard Höhler (of the University of Karlsruhe) previously : Höhler was one of the organizers of the Black Forest meetings (Hans-Martin Staudenmaier was another). Höhler was very interested in using dispersion relations to study pion-nucleon scattering. It seemed only natural that the two should join forces; Jim’s Nordita group would meet intermittently with Höhler’s group, either in Copenhagen or near Karlsruhe.

Three years younger than Jim, Höhler’s career had followed quite a similar pattern to Jim’s. He had started to study physics at the excellent Technische Hochschule Berlin in 1939, but in 1941 had been called up (despite his considerable myopia) and posted to the advance on Moscow. He recalls winter temperatures around -40° (C or F) in which machinery and weapons did not work. In 1942 his division had been transferred to Tunisia where he was captured, together with over 100,000 others, in May 1943. The allied forces in Tunisia comprised British, American and French troops and it was the Americans, operating in the Bizerta area, who took Höhler prisoner. After the war he had completed his doctorate at Berlin and during the 1950s had held positions at Göttingen and Munich Universities prior to obtaining his professorship at Karlsruhe in 1960.

Whilst at Munich, Höhler had become interested in the theoretical aspect of work carried out at the experimental Deutsches Elektronen Synchrotron (DESY) research centre near Hamburg and together with one of the directors of DESY had initiated the Black Forest meetings in order to give opportunities for discussions between experimenters and theorists. Höhler recalls that for some of the Black Forest meetings they had chosen a hotel near Freiburg from which one could walk to the highest summit, Feldberg (at nearly 1500m), and remembers that Jim enjoyed the altitude walks.

After the summer, and with funding at Copenhagen University for the then Danish equivalent of Ph.D. study, Lyng Petersen again approached Jim to advise on a topic for his research. Jim suggested a possible topic and Lyng Petersen embarked on the work. At some point Lyng Petersen concluded that the only way to proceed was to use the N/D method, the method for solving partial-wave dispersion relations which Jim and Sandy Donnachie had in 1964 found to contain certain disadvantages and had avoided by using a variational method (‘Semi-phenomenological Solutions of Pion-Nucleon Partial-Wave Dispersion Relations’, Phys. Rev. 133, p.B1053). Lyng Petersen was cautious in case Jim should disapprove, but tried the N/D method anyway and got good results. Some time later Jim called Lyng Petersen in for a routine progress report (although Lyng Petersen was at the University, he was de facto Jim’s research student) and Jens confessed to having used the N/D method. He recalls that Jim was rather gloomy, but that on seeing the promising results he was immediately delighted.

Jim’s 1966 publication, ‘Pion-Nucleon Scattering and Conservation Laws’ (Phys. Letters 20, p.687), deals with various recent suggestions that pion-nucleon scattering showed violations of certain rules. The paper addresses the suggestion by K.J. Foley et al. in 1965 (Phys. Rev. Letters 14, p.862) that causality might be violated and the suggestion by Samaranayake and Woolcock, also in 1965 (Phys. Rev. Letters 15, p.936) that time reversal invariance might be violated, and provides explanations for these difficulties. A suggested violation of charge independence, which was the conclusion of work by Donald et al. published in 1966 (Proc. Phys. Soc. 87, p.445), was not easily answered. Jim recommends further examination of this problem. This conclusion echoes the abstract of Jim’s 1958 paper ’Pion Scattering and Dispersion Relations’ (Phys. Rev. 110, p.1134) which had concluded “The discrepancy cannot be removed without contradicting one of the several apparently accurate experimental results. A relation to check charge independence is suggested”.

‘Dynamics of the Pion-N System’ (Acta Physica Austriaca, Supplement III, p.229) comprised the text of a lecture delivered by Jim at Schladming during the 5th International Conference for Nuclear Physics in 1966. The lecture ends with a section titled ‘Outlook’ :

“1. We have analysed the S-waves at low-energy, but it would be desirable to have some understanding of the origin of the very strong short range repulsion. This might turn out to be a profound question…

4. …Phase shift predictions should be extended above 500 – 600 MeV, and inelasticity predictions should be made. Again we have two- or many-channel problems and since we believe N/D is not adequate we require new techniques.”

For Glen it was a time of adjustment. Many miles away from all the friends she had made in Cambridge and London, she needed to establish some sort of social network for herself. She was warmly welcomed by Aage Bohr’s wife, Henrietta, and they visited each other quite a number of times. There were social engagements involving the staff and wives of both NBI and Nordita, and there were also some social engagements with the Copenhagen diplomatic circle. After two or three years in Copenhagen, maybe in 1966, Glen got herself work at the World Health Organisation offices which were conveniently close to Soldalen – only ten minutes walk – just beside the Tuborg Brewery in fact. This was beneficial for her, not just financially, since she also made some good friends at work. Nevertheless, maybe into the 1970s, she would from time to time say that she’d prefer to be living back in England. Throughout her life, Glen maintained an active commitment to the Anglican church. There were periods when she wouldn’t attend church every Sunday, but she would probably attend more often than not. Jim remained firmly unreligious, yet was entirely comfortable with others exercising their choice. He would drive Glen and Patrick to and from St. Alban’s Church, spending the intervening time on pressing business, such as a quiet stroll to Langelinie and the docks.

At the house in Soldalen there was a large cellar, with one of the rooms spacious enough to allow Jim to set up a table tennis table for the play room and the whole family would enjoy the use of this. He was a steady backhand player, preferring to keep his eye behind the flight of the ball, and would only rarely open up his forehand. Against his older son, his shots were consistently low over the net, and many of his points were won through the impatience and rash errors of his opponent. Jim‘s tactics with Patrick were different, giving the ball more height and encouraging the younger boy to develop his game.

One day, after Jim had returned from work, there was discussion with Glen about one or two of the fellows/students (at either Nordita or NBI). There had been much rudeness. and Jim questioned whether this was appropriate at a scientific institute. He also suggested that their behaviour was foolish, because they might be exempting themselves from receiving any assistance from him in the future.

In April 1967 Jim was elected a Foreign Member of the Royal Danish Academy of Sciences and Letters. At the time of writing, the academy has approximately 250 national and 260 foreign members of which some 40% of the members are from humanities fields. Among Jim’s contemporaries, Aage Bohr had been inducted in 1955, Gerry Brown was inducted the same year as Jim, and Ben Mottelson was inducted in 1974. Jim’s feet remained on the ground; he was not inclined to become pompous about such honours.

‘High Energy Physics’ Vol 1 (Ed. E.H.S. Burhop, Academic Press 1967) carried a 147-page article by Jim titled ’Pion-Nucleon Interactions’. This comprehensive article covers basic properties of the pion, analysis of P- and S-wave pion-nucleon scattering and prediction of pion-nucleon scattering. Some of the same material was presented in ‘The Dynamics of Elementary Particles and the Pion-Nucleon Interaction‘, Course B of Jim’s Nordita lecture notes series.

Also in 1967 Jim’s paper ‘On Zero Mass Pions’ (Nucl. Phys. B1, p.449) was published. The introduction describes how pions of zero mass, like other particles of zero mass, will be subject to a gauge principle : “this leads immediately to special properties for the pion-nucleon scattering amplitude at zero energy.“ Lyng Petersen recalls that Jim told him of his idea as to how the pion-nucleon S-wave amplitude might be changed if hypothetically the pion mass was allowed to change, in particular downward towards zero. “Such a change of the pion mass was (and still is) very fashionable to consider in connection with what was called current algebra theory and Weinberg’s soft pion theorems. Based on Jim’s idea I soon did an extremely simple calculation, and lo and behold the results were exactly as Jim had anticipated.” Though Lyng Petersen considered his results fortuitous, he showed them to Jim by way of a simple plot. Jim was “thrilled beyond belief” and the next day the plot was pinned on the wall of Jim‘s office, where it stayed for several years. The work associated with this publication also became the basis for Jim’s fourth course of lectures at Nordita.

It should be added that the idea of particles with zero mass dated back quite a few years. In 1954 Ron Shaw had been hesitant about his ideas on non-abelian gauge fields (there is more about these in the next section), “since I did not doubt at that stage that the new non-abelian gauge fields would require particles to have zero mass, and such particles did not appear to exist in nature.” Similar work was published independently the same year by Chen Ning Yang and Robert Mills.

Two weeks of May 1967 were spent in Italy. There are slides from Como, Bergamo, Verona, Venice and Trieste. Abdus Salam had founded the International Centre for Theoretical Physics at Trieste just three years previously (the centre had opened in 1965) “to foster advanced studies and research, especially in developing countries.” The idea of the Trieste Centre had really started in June 1960 when the University of Trieste had organized a seminar on elementary particle physics. “Scientific thought is the common heritage of mankind” was a notion often expressed by Salam.

During the first week of October 1967, Jim attended the 14th Solvay Conference in Brussels. At the time Jim played it down in his usual way : the impression at home being that this was just another conference. Ernest Solvay, a Belgian chemist, had established the first Conseil de Physique Solvay in 1911 as a forum for twenty to thirty leading international physicists to discuss one of the important areas of the subject. The first Conseil had comprised 24 members, including Madame Curie, Einstein, Lorentz, Nernst, Planck, Rutherford and Sommerfeld. A photograph from the 14th Solvay Conference shows Jim flanked by Regge, Michel and Chew on one side, and by Speiser and Wightman on the other. Seated at the front are Prigogine, Marshak, Wigner, Schwinger, Heisenberg, C. Møller, Amaldi, Perrin and Geheniau. Léon Rosenfeld is also present. Just another conference ? The third week of the following May saw Jim at the 1968 Nobel Symposium on Elementary Particle Theory in Göteborg. Again there was nothing much said at home about this.

Gösta Gustafson recalls the tragic death (in an air crash) of Gunnar Källén in 1968. Källén had been his supervisor at Lund University at the time, and suddenly Gustafson was one of a large number of students left without a supervisor. Gustafson applied for, and received, a Nordita fellowship in order to continue his doctoral studies. He tells : “I contacted Jim Hamilton who was very helpful and accepted me as a student…It implied a change in the direction of my work, which I think suited me very well…Jim introduced me to the field of dispersion relations, and gave me a problem to work on. He always had time for discussions, and besides Jim I also got a lot of help from the other members of the dispersion theory group, in particular from Henry Nielsen and Jens Lyng Petersen.”

“Jim’s influence was very important not only for me, but also for other students from Lund, for example Nils Johannesson and Mats Lyberg. During the difficult times after Källén’s death he also helped the department at Lund in many ways. In particular he acted as a referee at doctoral dissertations. He functioned as a guarantee that the thesis met international standards, and he also always participated, asking questions, at the aural defence and in the discussions of the evaluation committee. This help was the reason why he was conferred an honorary doctorate at Lund University in 1986.”

The writer recalls that Jim was highly complimentary of Gustafson, who had needed to familiarise with Nordita, change the direction of his work, and learn to use a computer, all in a short time. Though Gustafson would return to Lund in 1972, he retained close contact with Nordita over several years. Into the late 1970s and 1980s he played a leading role in developing what would in time become the world famous ’Lund String Model’, a phenomenological model of hadronization (1983, Phys. Rep. 97(2&3), p.31).

After the evening meal Jim often went to work in his study for an hour or two. There would be long periods of concentration, punctuated only by the occasional scraping of his chair on the hard floor as he retrieved a reference, or by the sound of him blowing his nose. Typically, after an hour or two of work, his desk would be covered with many sheets of A4 paper, each full of hand-written calculations which largely employed the Greek alphabet. Completely indecipherable to the rest of the family. Occasionally a letter would be received from Jim with the intended message on one side but a mass of hieroglyphics on the reverse.

He liked to spend at least part of the evening reading. Perhaps a good novel but generally non-fiction – he was particularly interested by European history, also the history of the various religions and sects, of which he was very knowledgeable. In the 1960s and early 1970s, Sunday afternoons were often times when Jim could relax and read a copy of the ‘Irish Times‘. His father, Joe, sent the papers on to Jim, and after Joe‘s death in 1969, Jim arranged with an Irish newsagent to continue sending them. The newspapers were especially important to him whilst he was in Copenhagen, his homeland must have seemed far away; on the other hand there were times during the ‘Troubles’ when he expressed that he was best off out of it.

In early autumn 1966 Jim had visited to his father Joe in Donegal. Joe had sold up the last of his businesses in Larne at the end of 1965 and moved back to the bungalow in Tullaghcullion. Looking through his letters to Jim, there is a sense that he had been perfectly content with the move. Tullaghcullion was where he had been born, he still felt that he belonged, and aside from two visits to see the family in Copenhagen, he was content to live out his last years in Donegal.

Around this time Jim had investigated the possibility of obtaining an Irish passport. The British embassy in Copenhagen invited Jim and Glen to various social occasions and it was at such an event in about 1965 that Jim had first met Peter Kinsella, who worked for the Irish embassy. Jim very much enjoyed Peter’s company and the Kinsellas would frequently visit and the conversation at one point turned to Jim’s nationality. A person born in what is now Eire but prior to the partition, as Jim was, had the right to claim either or both nationalities. By the time of partition Jim was living in Belfast and had only ever held a British passport. Peter Kinsella cleared the way for Jim to apply for an Irish passport, which he duly did.

In 1969 Jim was involved with the international conference at Lund. He chaired one of the parallel sessions and had arranged for a few of the Nordita fellows to present their work. Jens Lyng Petersen was one of these and he recalls that Jim thought the conference went very well. Lyng Petersen was at that time working on his second paper : ‘Calculating Partial Wave Amplitudes on the Left Hand-Cut’ which would be published in 1970 (Nucl. Phys. B15, p.549). Jim would later say in ‘On Mesons and Methods‘ : “A few years after I moved to Nordita, some of my younger colleagues set out to improve the derivation of the pion-nucleon discrepancies…and helicity amplitudes” and refers to this piece of work by Lyng Petersen, using a method related to finite energy sum rules. Jim also later refers to further refinements by Henry Nielsen, Jens Lyng Petersen and Esko Pietarinen (1970, Nucl. Phys. B22, p.525).

But Jim’s father, Joe, had been in deteriorating health. Jim delivered the 1969 Donegall Lecture at Trinity College, Dublin, which gave him the opportunity to visit Joe in Donegal. Most of July was spent at AERE Harwell and there may have been an opportunity for Jim to see Joe during this time also. Joe died, aged 85, at the start of September.

A significant addition to Nordita’s fellowship (although not to Jim’s ‘Nordic Dispersion Relations Group‘) at this time was Holger Bech Nielsen, who was a Nordita fellow from 1969-71. H.B. Nielsen had started his physics studies at NBI in 1961 and during the mid-1960s he was another who had found Jim‘s lectures very useful. While at Nordita he worked mainly under Zirô Koba (next door, at NBI) and was soon to achieve a very high profile for such work as ‘Scaling of Multiplicity Distributions in High Energy Hadron Collisions’ (1972, Nucl. Phys. B40, p.317) and ‘Vortex-line Models for Dual Strings’ (1973, Nucl. Phys. B61, p.45). These pieces of work became known respectively as ’KNO-Scaling’ and ‘Nielsen-Olesen Vortex Lines’ and were followed a few years later by the ’Froggatt-Nielsen Mechanism‘, a framework to explain the flavour hierarchy of quarks and charged leptons (1979, Nucl. Phys. B147, p.277), the ‘FNNS (Förster, Nielsen, Ninomaya, Shenker) Mechanism’ (1980, Phys. Letters B94, p.135) and the Nielsen-Ninomaya (‘no-go‘) theorem (1981, Phys. Letters B105, p.219).

Perhaps the best known piece of work by Holger Bech Nielsen dates from 1970. The work, titled ‘An Almost Physical Interpretation of the Dual N Point Function’, an interpretation of the Veneziano Model, was never published (it was photocopied a good many times). It has been suggested that Jim played a part in the ‘censorship‘, by refusing to allow the manuscript to be issued as a Nordita preprint. On the other hand, it has been indicated that the manuscript was not submitted in the proper manner. This seems to have been the basis for some distrust between Jim and one or more of the younger people who were following new theories.

In June 1970 Jim again visited Les Houches for the French International Summer School, then travelled on to Geneva, where he spent three weeks at the CERN Theoretical Studies Division. Much of his time at CERN was spent writing up two papers, ‘Prediction of S-wave Pion-Nucleon Scattering (I)’ and ‘Prediction of S-wave Pion-Nucleon Scattering (II)’, both collaborations with J.L. Petersen, which were published together in 1971 (Nucl. Phys. B29, p.29 and p.51). The papers use the earlier calculation by Lyng Petersen (which had resulted in the plot on Jim’s wall) and explore various ideas for mass extrapolation of a pion-nucleon partial wave to predict S-wave scattering. The summary of the first of the papers states “We are of course well aware that our basic assumptions may be regarded as risky or crude.“ Lyng Petersen recalls that he had reservations about the way the pion was taken “off the shelf” in the calculations.

Also written during his stay at CERN was the article ‘New methods in the Analysis of Pion-N Scattering’ which was published in 1971 (‘Springer Tracts in Modern Physics, vol. 57, p.41). The article acknowledges the Theoretical Studies Division of CERN for facilities and hospitality, and Sorin Ciulli “for numerous discussions”. The work focuses on modern methods which use analytic continuation and reviews partial wave amplitudes in new regions, the discrepancy method and analytic continuation, improvements in the backward pion-nucleon method and examination of the sigma meson.

Immediately on completion of his work at CERN, Jim travelled to Karlsruhe to take part in one of the expanded pion-nucleon meetings between his Nordita research group and Gerhard Höhler’s group and from there he made a brief visit to the University of Heidelberg (a beautiful city, one of the few large German cities not to have been destroyed by allied bombing). The writer recalls meeting Jim at Mannheim to share the journey back to Copenhagen. It was a pleasant time, Jim was in very relaxed mood; he seemed to particularly enjoy his visits to Germany.

Family holidays since 1965 had involved the renting of summerhouses in Sweden for a week in August. Once near Halmstad; once near Västervik, on the east coast; and twice at the same place near Ronneby, a town about halfway between Karlskrona and Karlshamn. The summerhouse near Ronneby had been much enjoyed by all the family, being situated right by the water on an inlet of the Baltic. If memory serves correctly, it had its own jetty with a rowing boat and the shallow waters of the inlet were good for swimming. Glen had attempted to book this place again for 1970, but this time had not been lucky – somebody else had got there first. It seemed hard luck, but through this disappointment the family discovered Gilleleje, a quiet fishing village on the north coast of Sjaelland.

August 1970 family holiday was spent in a rented summerhouse at Gilleleje, not far from the strand. It seemed to suit everyone. Jim enjoyed swimming from the strand and watching fish being unloaded at the harbour, also in the evenings he would walk down to the coast and observe the lights away to the northeast, on the Swedish coast. After a while he knew, by the pattern and timing of the flashes, all the different static lights. And Gilleleje was very convenient, being little more than an hour’s drive from Copenhagen.

Christian Møller retired in 1971 and Bengt Strömgren was appointed the new director of Nordita. Bengt, whose father had been director of Copenhagen University Observatory, had been a student and then lecturer at Copenhagen in the 1920s and 1930s. From 1951 he had pursued his career in America but had returned from Princeton to Copenhagen University in 1967. He was probably best known for his theory of ionized gas clouds surrounding hot stars. Judged to be the most distinguished living Danish scientist, Strömgren was granted residence at the Carlsberg Honorary Mansion, a privilege previously enjoyed for a great many years by Niels Bohr. The palatial ‘House of Honour’ had been built by Carl Jacobsen, the founder of Carlsberg brewery. Lyng Petersen recalls that once a year Strömgren would entertain the combined Nordita staff, visitors and fellows at this grand residence.

In 1971 Jim attended the ten day CERN/SIN Spring School on ‘Pion Interactions at Low and Medium Energies‘. From Jim’s lectures, ‘Pion-Nucleon Scattering Theory’ (CERN 71-14, p.101) was published in 1971. The same material was also presented in Nordita Publications no.419. The location of the Spring School meeting was the Lyceum Alpinum in Zuoz, a small town in Engadin, valley of the river Inn. The valley is about 100 km in length and contains ski resorts San Moritz and Samedan, though Zuoz is comfortably 10km away from the nearest of these, tucked under 3000m mountains and facing the 4052m Bernina. Jim travelled to Zuoz with Glen and Patrick and had invited his older son to join them for the week. In early April 1971, Zuoz was a peaceful place.

The writer recalls the occasion of a mealtime at Zuoz. There were in the order of 100 people at the Lyceum and for meals this number divided onto several long tables. Late arrivals would sit wherever there was space. For Jim’s son this meant that he might find himself at a table where nobody knew him. It was usual, and perfectly understandable, for these men to make introductions and some polite casual conversation before engaging in more serious physics discussion amongst themselves. However on one occasion a young physicist approached the table and enquired of one of his seated colleagues who the stranger was. When it was explained that this was Jim’s son, the enquirer appeared to snort and went away. The polite man across the table apologised for the Snorter’s behaviour. The Snorter wasn’t old enough to have been engaging in research for more than two or three years, yet he’d shown disrespect for a man who’d been at the forefront of meson research for 30 years. Not long after this, the writer learned that similar disrespect was shown to one or two of the senior figures at NBI.

In 1968, out of the idea that there is a consistent expansion starting from stable particles on straight-line Regge trajectories, Gabriele Veneziano had formulated the first string theory, catching the attention of many young high-energy physicists. It is true to say that Jim had not immediately put his own ideas to one side – perhaps he was concerned that some of this early dual resonance work was very speculative. Yet of Jim’s 12 publications from 1961 to 1967, references are made in 7 to work by Regge, Mandelstam or Gell-Mann : Jim was most definitely still taking notice of contemporary work in the field. Indeed, from Zuoz, Jim travelled directly to Bologna for the International Conference on Meson Resonance.

As for the dual resonance models, a number of disastrous properties were gradually proven about them which eventually convinced everybody that they could not possibly form the foundations for the strong interactions as had been originally hoped, and by 1974 study of dual resonance models had fallen out of favour (though more recently the ‘new string theory’ validates some of the old string interpretations). Jim was not the sort of man to take pleasure from such a failure, yet it may well have reinforced his tendency to stand back from work which appeared so speculative.

Jim, Glen and Patrick were in Zürich for eleven days during June 1971. Günther Rasche was then at Zürich and he recalls that this was one of two visits Jim made to the Institute of Theoretical Physics at the University of Zürich. Walter Heitler had been appointed director of the Institute in 1949. It must have been a pleasure for Jim to meet up with each of them again.

Following Jim’s 1971 visit to Zürich, Günther Rasche was at Nordita for 2 months in 1972, at Jim’s invitation. He recalls that a British naval ship was docked for a fortnight in the harbour at Copenhagen, and open for the public to visit. By coincidence the dentist on this ship was a family friend of the Rasches, a man named John. Günther and his wife invited John for dinner, together with Jim and Glen. “It was one of the most pleasant dinners I ever had. Jim and John understood each other at once. It turned out that Jim knew the ship from wartime and expressed his surprise that it could still be used. He considered it to be unsafe and dangerous. Both J’s had the same humour.”

The older son visited Jim and the family in Copenhagen over Christmas 1971. There was a lengthy conversation about Jim’s work. Jim had just completed the process of preparing a paper for publication, this would be only the third paper he had submitted since early 1967 (the other two having been the ‘Prediction of S-wave Pion-Nucleon Scattering’ papers with J.L. Petersen). “Why was this ?” the son enquired. Well, there had been a lot of work preparing and delivering the four major courses of lectures at Nordita and he was putting a good deal of time and energy into ensuring that Nordita was fulfilling its prime purpose – to promote scientific collaboration between Nordic physicists. There were also lectures he was expected to give at various conferences and summer schools each year. He had been preparing a book together with Bjarne Tromborg and then there was his editorial work for ’Physics Letters B’. The writer knew that this was all true. The ’Physics Letters B’ work would often stretch into the evenings and at weekends too, if there were no prior family commitments.

Then, unusually, for Jim knew that his son had little knowledge of physics, he described a little of the paper he had just readied for submission, ‘Effective Range Formulae for N*33‘ with A.T. Lea (1972, Nucl. Phys. B42, p.518). Jim described it as tidying up some loose ends which had been left for some time : Andrew Lea had been one of Jim’s students at UCL but had recently visited Nordita. “We look for an effective range formula because the exact prediction method (based on N/D) is subject to considerable uncertainties due to the small short range interactions at high energies not being accurately known.” The paper explores an alternate method of using almost unitary functions.

As Jim was explaining the problem of CDD arbitrariness (in analysing the data on resonances, Leonardo Castillejo, Richard Dalitz and Freeman Dyson had recently co-discovered what became known as CDD poles : each pole giving rise to an ambiguity in the solution to the N/D equations), his listener drifted into opacity and was idly leafing through the manuscript. At the end of the paper there is comment about disagreement with previous results, one set of which were from Jim’s 1964 publication with Sandy Donnachie ‘Semi-phenomenological Solutions of Pion-Nucleon Partial-Wave Dispersion Relations’ (Phys. Rev. 133, p.B1053), the paper which had proposed a variational method of solving pion-nucleon dispersion relations (the authors had warned about this method : “…it is not obvious why the variational method should give such a good result“).

His son’s eyes were drawn to the footnote : “Unfortunately we were unable to recover the computer tapes for the DH [Donnachie & Hamilton] calculation to determine what actually went on”. Jim’s response was essentially “Yes, it was a pity that the tapes could not be located, but given that the work had been done more than eight years previously, not altogether surprising.” Jim’s stance was that the current paper was probably still worth submitting, though he wasn‘t pretending that it was ground-breaking either.

At UCL, Harrie Massey had preferred to appoint people with whom he was personally acquainted and Jim appears at times to have favoured this approach too. There is the aspect of wanting to help a friend, but there is also an obvious security in this : the candidate’s work, work habits and personality are all known in advance. Jens Lyng Petersen returned to Copenhagen in 1972 (after completing two years work at CERN); he had already been a Nordita fellow, so that was an option no longer available, but Jim had persuaded the Nordita board to offer him a position as an Assistant Professor. This was a non-trivial achievement, being one of the first arrangements of its kind at Nordita.

Jim’s article with Gösta Gustafson, ‘The Dynamics of Some Pion-N Resonances’ (Springer Tracts Mod. Phys. 61, p.49) was published in 1972 (also as Nordita Publications no. 420). The publication was dedicated to Gerhard Höhler on his 50th birthday. The introduction reads “Some understanding of the relations between sets of elementary particle resonances can be obtained by combining Regge trajectories with concepts which arise from finite energy sum rules. Degeneracy properties and the relation to symmetry schemes can be understood in this way. Nevertheless it remains of interest to ask what do we know about the dynamical forces which produce individual resonances. Such an enquiry can be fruitful in various ways; it can test the extent and accuracy of our knowledge of simple interactions, it can raise speculations about such problems as straight line trajectories and it can also suggest quite new phenomena, such as the pN processes…”

Gerhard Höhler recalls that he visited Jim several times in Copenhagen. On one of these visits, in the early 1970s, Jim talked to Höhler about Esko Pietarinen, the young physicist from Helsinki who was one of Jim’s elementary particle research group at Nordita.

The Finnish language is markedly different from other Nordic languages, and translation to or from English is considerably more difficult. To effectively use the Danish language as an intermediary would require both parties to have a good level of fluency. Jim remarked to Höhler that in general, though Pietarinen was always very polite, he would talk only a little, and that what he did say was not easy for Jim to understand. This discussion concluded with Jim asking Höhler to talk to Pietarinen, and Höhler was soon very impressed with the young Finn. It seems that most of the difficulty with communication had been on Jim’s side. Pietarinen recalls : “I shall always remember [Jim] as a very kind and pleasant teacher and collaborator…he provided great guidance in pion nucleon physics for many, including me, at Nordita.”

Pietarinen was very much involved in analysis of experimental data to provide information on the quantum amplitudes. He was strong in mathematics and computing and in the 1970s his work attracted a good deal of attention. After some years Höhler provided a position for him at Karlsruhe where Pietarinen made a major contribution to the ‘Karlsruhe-Helsinki Partial Wave Analysis’. In ‘On Mesons and Methods‘, Jim is complimentary about Höhler, Pietarinen and their colleagues and highlights some of their work : (1972) Nuovo Cimento 12A, p.522; (1972) Nucl. Phys. B49, p.315; (1975) Nucl. Phys. B95, p.210; ZAED Phys. Data, Vol. 12-1 (1979, Handbook of Pion-Nucleon Scattering). Some further references for the Karlsruhe-Helsinki work are ’Handbook of Pion-Nucleon Scattering’ by Höhler, Kaiser, Koch and Pietarinen (Fachinformationszentrum, Karlsruhe, 1979), R. Koch in ‘Proceedings of IV International Conference on Baryon Resonances’ (ed. N. Isgur, University of Toronto, Canada, 1980) and ’Pion-Nucleon Scattering’ by G. Höhler (Springer, 1983).

Jim’s monograph with Bjarne Tromborg ’Partial Wave Amplitudes and Resonance Poles’ (Oxford Clarendon Press) was published in 1972, a summary of the efforts to understand the structure of resonances and scattering amplitudes. The book had grown from an article they had intended to write “in order to clear our own minds on some of the more mathematical aspects of the partial wave amplitudes used for the binary collisions of elementary particles. This origin explains why we have not attempted to give a complete treatment of partial wave amplitudes. For physicists, we can say that we have assumed about the average knowledge of partial wave amplitudes which an elementary particle physicist would have. On the other hand, we feel that a mathematician might well consider that the book is self-contained, at least as far as the elementary material is concerned.”

In ‘On Mesons and Methods’ Jim says : “Bjarne Tromborg and I studied the movement of the resonance pole of a partial wave amplitude in the complex plane, as the strength of the interaction was increased from zero to large values. Not much seemed to be known about this topic…” Early in the monograph there is considerable focus on the arbitrariness of solutions of partial wave dispersion relations : “The problem is whether the partial wave amplitude is uniquely determined by the discontinuity across the left-hand cut and by the unitary relation on the physical cut. The problem of the uniqueness of solutions of partial wave dispersion relations has been known for a long time in connection with CDD poles, and it is usually discussed in terms of the N/D method…Such treatments are apt to look complicated, and we shall here give a simple and direct approach to the uniqueness problem.” There is acknowledgement of contributions from Jens Lyng Petersen and Gösta Gustafson.

Bjarne Tromborg had been granted a two-year Nordita fellowship in 1969 and then a fellowship at NBI until 1977. Of the work for ’Partial Wave Amplitudes and Resonance Poles’, Tromborg comments : “At the start of my time at Nordita, Jim had written some notes on the analytic properties of partial wave amplitudes and he asked me to read the notes for corrections and comments. The main purpose was to introduce me to the field of dispersion theory. This started a process where the ever expanding set of notes was handed back and forth between us until Jim finally submitted our very long manuscript, I believe to Nuclear Physics B. It came back from the editor with the suggestion that, if we could add an introductory chapter, Oxford University Press might consider publishing the manuscript as a research monograph. As I remember the process, my role was to do the detailed mathematics and to present it in modern form. A typical example is Section 2.2 [Arbitrariness of Solutions of Partial Wave Dispersion Relations – Simple Method : One Bound State] which was first formulated by Jim, while I did the detailed analysis presented in Section 2.3 [Improved Method : No Bound State]…”

Tromborg goes on : “For me this period of collaboration was a very happy time. I admired Jim immensely and I considered him as a fatherly figure, although my relation to him was always rather formal and respectful. I do not think that I ever called him ’Jim’ except when Henry Nielsen and I sent him a bottle of wine at his 60th birthday [January 1978]. I spent many hours sitting next to him at his office table going through the manuscripts. He did not always agree on my suggestions from the start, but he listened carefully and most often he accepted my version when I presented it in writing…I do not remember any cases where I was dissatisfied with the final result. This was a learning period for me, and I cannot imagine that I could have had a more conscientious supervisor than Jim.”

By 1972, Glen had been working at WHO for maybe six years. She’d continued to quietly bank her earnings until one day she announced that she was going to buy the family their own summerhouse in Gilleleje – there need no longer be a concern over availability for renting, and this would now give Jim, Patrick and herself the option of short weekend breaks whenever they wanted. In September 1972 Glen purchased a place not far from the one they’d rented, which would prove a valuable retreat over the years.

Glen’s work at WHO exposed her to a mass of statistics on disease caused by smoking and from time to time she would lecture Jim. Jim put up with this for a few years, but then on one occasion when he went off to a conference on his own for a week, he stopped smoking. It was neatly done – some people at the conference may have suffered as a result, but by the time Jim returned home he was over the worst of the withdrawal. This was in about 1971 or 1972. No longer a smoker, Jim still habitually cycled into the Institute at Blegdamsvej, this was about a fifteen minute ride down Strandvejen and Østerbrogade. He continued this practice until he moved from the house in Soldalen in 1978, when he was 60.

Jim’s collaboration with Ingjald Øverbø and Bjarne Tromborg, ‘Coulomb Corrections in Non-Relativistic Scattering‘ (Nucl. Phys. B60, p.443), published in 1973, became a much-cited piece of research. Jim later said “The nonlinear relation between interaction and scattering amplitude means that it is difficult to remove electromagnetic effects from the results of meson-baryon scattering experiments if you want an accuracy of 1% or better. Woolcock and I (‘Determination of Pion-Nucleon Parameters and Phase Shifts by Dispersion Relations’, Rev. Mod. Phys. 35, p.737, published in 1963), did early primitive work on Coulomb corrections, and Tromborg, Øverbø and I solved the non-relativistic problem by applying Gorskov’s theorem to deal with the infinite range difficulty. We later used Yennie’s factorisation device (D.R. Yennie, S.C. Frautschi and H. Suura; 1961, Ann. Phys. 13, p.379) to obtain a dispersion relation which gives the full electromagnetic corrections to meson-baryon scattering. This was applied by Tromborg, Waldenstrøm and Øverbø to pion-nucleon scattering.”

In dealing with scattering amplitudes, the term ‘hadronic’ is used. Hadron is a term for any elementary particle susceptible to the strong interaction. There are two classes of hadrons; mesons (particles with integer spin), and baryons (particles with half-integer spin).

Baryons are fermions and as such are subject to the Pauli exclusion principle – only one fermion can occupy a quantum state at a given time – the term baryon implying an heavy subatomic particle and may be applied to a proton or neutron, but also many other unstable particles. It should be added that not all fermions are baryons (e.g. electrons are not susceptible to the strong interaction). All hadrons are composed of quarks.

The first attempt to find the Coulomb correction had been by van Hove in 1952 : he had assumed the minimum of information about the hadronic interaction, namely that it was of short range. Jim’s 1959 text ’The Theory of Elementary Particles’ (Oxford Clarendon Press) had advised “For a careful calculation of the low-energy cross-sections including Coulomb effects, see L. van Hove (Phys. Rev. 88, p.1358)”, and in his 1960 paper with Bill Woolcock, ‘Low Energy Pion Phenomena’ (Phys. Rev. 118, p.291), Jim had looked in some detail at Coulomb corrections.

On ‘Coulomb Corrections in Non-Relativistic Scattering‘, Bjarne Tromborg comments : “Jim’s collaborators, Günther Rasche and Geoff Oades, had already done some studies of the problem, and Jim had also started a project on determining the corrections to partial wave amplitudes for potential scattering where the potential is the sum of a Coulomb potential and a short-range potential, the latter simulating strong interactions between the particles.” Tromborg recalls that he was much involved in this work, including the example of analytic calculations for a Yukawa potential : “The work was very satisfying for me, and I think also for Jim. The problem was well defined and we solved it in a very elegant way.” Tromborg recollects that Jim’s contribution was mainly in the initial key steps. Øverbø, then a Nordita research associate, joined the project at a later stage and carried out some of the numerical calculations.

1 On the Nordita website there is a ‘Brief History of Nordita’ https://www.nordita.org/aboutus/history/index.php  which itself links to further articles by Helle Kiilerich, Chris Pethick, Ben Mottelson and Einar Gudmundsson. For the benefit of anyone who has navigated in the opposite direction, there is information here about the founding of Nordita, and its early days, in the preceding section, ‘London’. Additionally, in the section ‘Manchester’, relating to Jim’s visit in 1947, there is information about Copenhagen University Institute of Theoretical Physics (renamed ‘The Niels Bohr Institute’ in 1965), Niels Bohr himself, and some of the other people who were there in 1947.