Portraits of science. "The most versatile physicist of his generation"

P. M. S. Blackett (1897-1974) entered Cambridge University and the Cavendish Laboratory as a young veteran of the first world war. His innovative research with the Wilson cloud chamber resulted in photographic evidence of nuclear transformation and the existence of the positron. In the 1950s and 1960s, he helped to pioneer the use of paleomagnetic evidence in support of the theory of continental drift. A leader of operational research during the second world war, Blackett became an outspoken critic in the postwar period of American atomic policy and British development of nuclear weapons, taking on a public role for which he was sometimes criticized.