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Dick's life with physics, page 4 |
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Dick was frequently called upon to give talks to non-specialist audiences - senior schoolchildren, the students' Physical Society, members of the IOP. Perhaps the most memorable was about Maskelyne's experiment on Schiehallion in 1774 to 'weigh the earth', a topic of interest in the International Geophysical Year, 1957, revisited in the early 60s and again in 1990. That 1990 text can be seen on the internet, illustrated with photographs taken by Michael Smyth in 1962. Michael had initially come to Edinburgh in 1950 when Astronomer Royal W M H Greaves was professor of the new university department of Astronomy. In 1957 Michael went to Dunsink Observatory, which Hermann Brück had just left to come to Edinburgh following the death of Greaves. A few years later Michael returned to Edinburgh. In 1959 Dick gave an address as past Chairman (Arthur Brown was now Chairman) of the Scottish branch of the Institute of Physics. This was published in 1960 in the Institute's Bulletin under the title Light waves, radio waves and photons. In it Dick discussed two remarkable experiments of the mid 1950s - one by Hanbury Brown and Twiss, working at Jodrell Bank; and the other by Forrester, Gudmundsen and Johnson, in USA. Both could be interpreted, up to a point, in terms of coherence, but attempts to understand them in terms of the crude popular model of a beam of light - as a stream of discrete indivisible corpuscular photons - generated vigorous controversy. The use of fast photo-electric detectors was crucial to both experiments, and Dick had contributed to the discussion with a short paper which happened to attract the attention of a refugee from Hungary, Peter Farago. Later that year, 1957, Peter was appointed to a senior lectureship in the department. At last Dick had a colleague, five years his senior, with similar interests. Peter has written Soon after I had settled down to my job, I moved in to share Mr. Sillitto's office. It was only a few years later that we acquired 'private' offices next door to one another and we continued to live in an 'entangled state' of co-operation both in teaching and in research, activities which were very closely coupled. To return to the paper in question: it was about a very 'hot' topic of the time: correlation between events in photon detectors... The phenomenon usually referred to as the 'Hanbury Twiss effect' had recently been experimentally established, but was somewhat controversial (apparently at variance with a dictum of Dirac's) and understood by only a few. Dick understood it, and I was taught about it by him. About the same time, the illness and death of 61-year-old Bernard Childs in July 1956 precipitated Dick into a stint as Director of Studies. He was somewhat surprised to discover that some of his 'clients' were doing physics only because of parental pressure and had no heart for it. After his interview with Dick, one of them left and joined the Black Watch band. Francis Barnes, Richard Dougal and David Vass, later to be members of staff, were among the more enthusiastic first-year students. Routine white blood cell counts for those who worked with the Cockcroft-Walton machine during these years were causing concern about Dick. He was examined frequently in the respiratory diseases clinic because beryllium poisoning was suspected. However, there were no other symptoms apart from intermittent fatigue, and the diagnosis seems to have been based simply on the fact that beryllium was being used in Bob Galloway's PhD project. Dick was diagnosed with diabetes in 1964, a period when the relevant dietary advice included (unfortunately) "butter and cream -- as much as you like". Shortly afterwards he flew to New York to attend a conference in Rochester, where Emil was now established, and was bewildered when his emergency snack, an orange, was confiscated at Kennedy airport. By 1961 Dick was a Fellow of the Institute of Physics and of the Royal Society of Edinburgh. He was granted his first and last sabbatical leave, for one term, with a view to spending more time on the new problems in optics. He continued in charge of the HT lab until 1963 and to supervise nuclear physics students until 1966 when George Bradford and David Vass had completed their PhDs. He used his leave to visit, with Peter Farago and Peter Kennedy, various university and government laboratories, making contacts in the establishment in Malvern which had developed radar during the war and whose name has changed many times since. Back in Edinburgh he applied methods used in the mathematical analysis of random noise to show that, with the then available circuit techniques, it should be possible to observe interference between beams of incoherent light from sources whose line widths are comparable with those of the Hg-198 electrodeless discharge. In 1962 he was promoted to Senior Lecturer, and Feather encouraged him to proceed with such an experiment, an extension of the Hanbury Brown Twiss classic. Farago's former colleague suggested using a Fresnel biprism (a prism whose vertex angle is nearly 180 degrees) to create two closely spaced virtual replicas of each of the two incoherent sources. No interference fringes would be visible, but coincidence rates should show a periodic variation as one photodetector is moved relative to another across the uniformly illuminated field. Nigel Haig, who graduated in 1963, tackled this as part of his PhD studies. Although a sufficiently accurate biprism could not be obtained, a modified experiment was begun in July 1967 using instead a second double slit. Complete success would have required observing times of 369,000 seconds, but by September fluctuations in the ambient temperature of the laboratory forced an early conclusion with only 102,000 seconds at each position. Statistically significant results had however been obtained and further counting would not have improved the statistics. The multitude of practical problems associated with stabilising and optimising this equipment and the fast (for the time) coincidence circuitry provided a training which stood Nigel in good stead in his subsequent inventive career at RARDE. Of Dick he writes it was his great gift of thinking logically and with clarity about 'ordinary Physics', the tuning fork, for example, that drew my admiration more than his remarkable facility with the theory of quantum mechanics. . . . Dick's approach to physical problems impressed me enormously, and has helped me by teaching me to challenge the apparently obvious, and showing that things may not be quite so obvious after all. It is the way of thinking, rather than the straightforward data manipulation, that I found so useful in my later research. In 1966 Dick had published a paper in American Journal of Physics showing that the intensity variation in sound from a rotated tuning fork was due to quadrupole, not dipole, radiation. Another topic he tackled was the treatment of the children's swing as a parametric oscillator - very relevant to topics in optics which had arisen since the invention of the laser in 1960. Lasers were objects of great interest in those days. In January 1964 Dick used one when he talked on Waves in the fortnightly series of illustrated evening lectures at the Royal Scottish Museum in Chambers Street. That afternoon he had given the Christmas Lecture for senior schoolchildren there, repeated in Paisley the following week. In a letter two days later Dick wrote: Dear Mr Chilcott, |
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