14. Later Years

“There is a road that turning always
Cuts off the country of Again.
Archers stand there on every side
And as it runs time’s deer is slain
And lies where it has lain.”
– Edwin Muir, The Road.

Two weeks prior to their journey to Lund and Helsinki, Jim and Glen moved from their address in Lantree Crescent. Jim wasn’t confident about the house, there had recently been subsidence problems affecting some of the houses on the opposite side of the road, but that was the more tangible motive for the move. The room which Patrick had occupied was the first room at the head of the stairs and was still very much his room; to enter was to grieve, to pass by might provoke a feeling of guilt. The move was not such a difficult thing, being only a matter of about two miles across the southern outskirts of Cambridge.

The new house, on Almoners’ Avenue, was about the same distance from the city centre. Just ten minutes walk away, on Wort’s Causeway, one finds open countryside with a view over fields to the Gog Magog Hills. John C. Taylor recalls that he and his wife would often meet Jim and Glen going for a walk along Wort’s Causeway – the Taylors lived nearby and would call in for coffee from time to time.

A next-door neighbour, Thelma Miller, remembers : “We have happy memories of them as neighbours, as they were always very friendly…Jim was an extremely quiet and pleasant neighbour…we didn’t see much of them apart from when they went for their daily walk.” Jim attempted to get out for a walk each day and was unhappy if the weather prevented him. Even to the year before his death, aged 82, he would walk a fair distance.

An alternative to the walk along Wort’s Causeway was the short drive to Wandlebury, in the Gog Magogs, and a walk around the woods. Jim and Glen had responded to an appeal (through the Cambridge Preservation Society) for the Woodland Trust at Wandlebury and were interested to see how the funds were used. The walks at Wandlebury provided an opportunity to see birds other than the usual garden passerines : this was originally Glen’s interest, but Jim became absorbed by such topics as bird navigation. They would drive further afield, to the Fens, or to the north Norfolk coast, to observe the geese and migratory birds.

Jim sometimes used a bicycle for the journey into town, and this practice continued into the 1990s. The centre of Cambridge was still much the same as during the 1950s, although there were many fewer tourists at the earlier time. His time in Cambridge would be split between DAMTP, Christ’s College, the university library and book shops. Of his visits to Christ’s, Jim wrote : “I lunch once a week or so in Christ’s, and that is a pleasant activity – there are still quite a few fellows around from my time there.” Additionally he would meet old colleagues elsewhere; Richard Eden recalls Jim and Glen joining the Edens for lunch at Clare Hall.

Jens Lyng Petersen recalls his last encounters with Jim. It would have been in either 1992 or 1993. Jens had been working for a couple of weeks on a joint project with Anne Taormina at Durham, then they both visited Cambridge for a week and Jens delivered a seminar at DAMTP on their work. Jens knew that Jim would still regularly go into the department at that time and was keen on meeting up with him. He recalls : “Sure enough, one day he knocked on my office door and we had a wonderful conversation…I was struck as to how fit he looked. It was easy to forget how advanced in age he really was – he was almost like the man I had known so well 20 years earlier.” The next day they met again for tea in the lounge and chatted away “like old pals.” Having disagreed with Jim on some issues during the mid-1970s, Jens was very happy for these last encounters.

Located again in England, Jim could now more easily visit Ireland and Scotland; such opportunities had been rare during his time in Copenhagen. There were several visits to Scotland during the years 1987-95, on one occasion, in 1993, Jim and Glen travelled extensively around Scotland, even to the far north, revisiting Sutherland and Caithness. From 1986 they visited Ireland on two or three occasions, May 1994 was probably the last time. They spent a week over in the west, visiting Sligo and Donegal. Though their opportunities to meet were infrequent, Jim always kept in touch with Bertie Boyd, and would make a point of telephoning Bertie around New Year to give his greetings and best wishes. He was still very much concerned with Irish affairs and conversation at home would readily turn to Ireland, to what changes there had been in Donegal recently and the latest news from Bertie and his family, and other friends.

The writer was in the west of Ireland for extensive periods during 1995-6 and, on a subsequent visit to Cambridge, there was much to tell Jim about different people and places in the west. Jim would listen and listen, occasionally laughing or interposing a question or a short comment, but one had the feeling that he was prepared to listen all day. Many topics would be covered. How, out in the west, the turf was still being cut in the traditional way and neatly piled to dry, how many local people still kept the range burning even during a warm spell of weather, yet how the children walked what might be a good distance to school in the rain and sleet of winter, wearing nothing more than a thin jersey, and the wild weather would never seem to touch them, and of the rural pubs where conversation seemed not much more than a whisper. His son had taped some traditional music for Jim, on a whim that he might find it interesting. A couple of years later Glen commented that Jim had listened to the tape many times.

Winding back two years to December 1993, a letter from Glen to the writer stated : “Jim has received his article back from the editors of a scientific journal with a request that he expands it and includes more details.” Jim had become absorbed by systems which violate time reversal invariance and had written a paper about the Aharonov-Bohm effect. The editor had suggested that if the paper could be expanded, Springer might consider publishing it as a monograph. The managing editor of ‘Springer Tracts in Modern Physics’ was none other than Gerhard Höhler.

By March 1996 the work had indeed grown into the size of a small book. Jim would work away at an old PC : the word processor software satisfied all his requirements though he sometimes complained that the operation was unwieldy, requiring frequent removal and insertion of disks to access different character sets. In July 1996 Springer agreed to publish, but there was one more problem.

During 1996 Jim had been increasingly experiencing dimness of vision and checks revealed that he was suffering from glaucoma in both eyes. Immediately he turned in his driving licence. Glen could still drive him about, but it was uncomfortable for him to be reliant on others. Both eyes required corrective procedures and it was after one of these, in October 1996, that Bill Woolcock last met him. Bill was in Cambridge for a few days visiting some old friends and telephoned to see if it would be possible to meet up with Jim and Glen. As luck would have it, it was the day of the treatment and Jim was in Addenbrooke’s Hospital, though Bill was able to visit him there the next day.

Happily, the procedures were a complete success. In November Glen wrote : “…the eye has regained the correct pressure in unexpectedly short time and [Jim received] a diagnosis that the retina had returned to normal position.” By the summer of 1997 both eyes were okay again and Jim was working hard on correcting proofs of the book.

‘Aharonov-Bohm and other Cyclic Phenomena’ (Springer Tracts in Modern Physics, 139) was published in October. In 1959, Y. Aharonov and D. Bohm (Phys. Rev. 115, p.485) had proposed that a charged particle, in a region with no magnetic field present, could be affected by magnetic flux elsewhere. Given a zero magnetic field in the space accessible to the particle, if the associated vector potential is not zero, its effect on the particle would be an observable phase shift in the interference pattern. This effect became know as the Aharonov-Bohm effect, though Werner Ehrenberg and R.E. Siday had in 1949 (Proc. Phys. Soc. London, 62B, p.8) predicted a similar effect. In 1960, R.G. Chambers (Phys. Rev. Lett., 5, p.3) reported experimental verification of the effect. The Aharonov-Bohm theory was extended to include the effect of electric potential and this was observed experimentally in 1998 by van Oudenaarden et al (Nature, 391, p.768). Magnetic Aharonov-Bohm effects were also proposed for bound energies and scattering cross-sections, though these have not been confirmed experimentally.

The Aharonov-Bohm effect indicates that the behaviour of a charged particle in an electromagnetic field cannot be understood solely in terms of the classical mechanics interpretation of fields acting locally on the particle. The preface of Jim’s monograph begins : “The Aharonov-Bohm effect may seem to be strange. The interference pattern of an electron wave, in a region with no electromagnetic field present, depends on the value of a magnetic flux elsewhere. Moreover the effect cannot be detected for a single electron; it takes a number of electrons, or repeated experiments with one electron, to demonstrate it.”

The introduction allows some insight as to why Jim has developed such a close interest in this topic : “The purpose of this monograph is to discuss the nature of the Aharonov-Bohm effect and to consider also some other effects that are associated with the cyclic motion. The common feature is that the phenomena are all anholonomic. This means that the dynamical situation of a system depends not only on the general coordinates at the current position but also depends on the route by which the system reached the current position. Thus Foucault’s pendulum at noon today will, in general, move in a different plane than it did at noon yesterday. The systems that we consider, including the Aharonov-Bohm effect, have the property that they violate Wigner’s type of time reversal invariance. The part of the solution that arises from this violation is usually of particular interest.” Further into the introduction, Jim indicates that there has been “a fair amount of confusion about the nature of the AB effect. Much of the confusion can be traced to a misunderstanding of certain aspects of quantum theory…”

In the first half of the book, considerations of motion around a solenoid are discussed, followed by presentation of generalizations of the AB effect, including cyclotron motion. There is an account of some of the criticisms of the AB effect, and of the arguments about its dynamical origin. The measurements of its effect are studied, as well as its role in superconducting phenomena. There is a critical account of the basic quantum limitations on the accuracy of any flux measurement. The second half of the book broadens the subject matter further to discuss adiabatic theorems, and various other anholonomic phenomena such as Hannay’s angle, Foucault’s pendulum and Larmor procession, the Sagnac effect, and Berry’s phase. There is discussion of basic properties of particle accelerators for charged particles on circular tracks.

The writer recalls a wide-ranging conversation with Jim, late into the 1990s. ‘Aharonov-Bohm and other Cyclic Phenomena’ had been published and it seemed that he recognised that this probably constituted his last serious piece of work. When it was suggested that Jim’s career had been distinguished, Jim paused for a moment before answering. No, too much of his work had not produced what was hoped for. There was no particular sentiment expressed, it was a dispassionate self-appraisal, it was what it was.

Jim spoke to Glen about not feeling well around Easter time 1999. Other than his heart problem 20 years previously, it was rare for him to acknowledge illness. There seemed to be something of an improvement in his condition over the summer months of 1999, but by early autumn it was again clear that there was a problem. The writer recalls a visit to Cambridge from that time. Though Jim was by no means inhospitable, one felt that he was not keen for the rest of the family to visit him in this condition; he seemed to want to be left alone with Glen. There was some assistance from nurses who would call around, but it was Glen who mostly looked after him.

The writer’s last recollection of Jim, not long before he died, was of the same ready smile as always and a personal joke shared. His face was gaunt, his eyes deep-sunken and there was little strength left in his handshake – yet his welcome was still unmistakeable. The handshake was prolonged, neither party in any particular hurry for it to end. Jim died on 6th July 2000.