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Thomson, J. J.

Thomson, J. J. (1856–1940). Discoverer of the electron. After study in Manchester, Thomson gained a scholarship to Trinity College, Cambridge. In 1884 he became Cavendish professor, working on electricity and gases. Michael Faraday and then William Crookes had thought that the rays coming from the negative pole, or cathode, were charged particles, but with Wilhelm Röntgen's discovery of X-rays, most Germans supposed that cathode rays were similar, radiation akin to light. Thomson, with better vacuum pumps, devised an experiment in which the rays were deflected by a magnetic field, and then deflected back again by an electric field. This proved they were negatively charged particles, or corpuscles as he called them following Robert Boyle, and he calculated their ratio of charge to mass, showing how much smaller they were than atoms. Thomson was knighted in 1908, served as president of the Royal Society 1915–20, and was master of Trinity College, Cambridge, from 1918 to his death.

David Knight

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