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The Cavendish in Wartime

Prof. A. P. French

The Cavendish during World War II became a place of greatly reduced activity. Many of its staff vanished into various defence research establishments - most notably, of course, in the development of radar. But at the time, everything was shrouded in secrecy, and all that the outsider could notice was the spiriting away of many of the laboratory's best known physicists. Those who remained worked heroically to maintain the teaching programmes, aided by an importation of evacuees from the University of London - and by the emergence from retirement of the white-bearded and still formidable figure of G.F.C. Searle. I vividly remember how Searle, who must have been about 80 at the time, returned (entirely at his own initiative) to dominate the first-year physics labs when I was an undergraduate. He was tireless in going the rounds of the students, beginning each encounter with a brusque "What are you doing?", and proceeding, in a sometimes rambling but usually instructive way, to explain the finer points of the experiments that he had devised over the years.

The head of the Cavendish at this time was, of course, Sir Lawrence Bragg, and much of the research that continued during the war years was in his own field of X-ray crystallography. The Mond, also, managed to keep active. But from direct knowledge I can speak only of nuclear physics, which from an early stage in the war went underground, so to speak, as it became focused completely on nuclear fission and the possibilities of constructing an atomic bomb. The whole project seemed at the time like something out of science fiction, but a slice of real-life drama was supplied by the presence of a group of European scientists who had fled from Paris at the fall of France, and had managed to get to England with a precious and irreplaceable stock of heavy water. This group concentrated on slow-neutron physics and the possibility of achieving a self-sustaining chain reaction. Another group, of which I was a very junior member, fresh from the Tripos, was concerned with measurements of fast neutron fission cross-sections as input to the design of an atomic bomb. To me, at the time, the whole business seemed wildly improbable. At the very least, our own thoroughly academic pattern of basic research seemed absurdly remote from the production of a super-bomb. And, indeed, it would probably have remained so if the whole effort had not been transferred in 1944 to the USA and Canada, where it became incorporated into the much larger Manhattan Project, with its seemingly limitless resources of people and materials.

As in so many laboratories, the war marked a turning point for the Cavendish. When it began, the frugal practices of research without government sponsorship still held sway; we would go to the scrap-box to hunt out the suitable piece of metal, or raid a disused chassis for a needed bit of circuitry. But by the end of the war, people were becoming used to obtaining and spending money on a far more lavish scale - though still trifling compared to the expansiveness of the two succeeding decades. And although the sealing-wax and string tradition encouraged an often praiseworthy ingenuity, there is no doubt in my mind that its continuance would have hobbled the Cavendish as a research institution. So I look back on the passing of those days, and all the excitement that they hold for me personally, with nostalgia but with no real regrets.