Thomson

On the evening of Friday the thirtieth of April 1897, in the Royal Institution lecture theatre at 21 Albemarle Street in Mayfair, Sir Joseph John (J.J.) Thomson, forty years old, the Cavendish Professor of Experimental Physics at the University of Cambridge, gave the Friday Evening Discourse on the experimental investigation of the so-called cathode rays. Across the hour of the discourse he set out the results of fifteen months of experimental work at the Cavendish Laboratory in which he had measured the deflection of cathode rays by both magnetic and electric fields, calculated the ratio of charge to mass of the rays, and concluded that the rays were composed of particles substantially smaller than any known atom. The particles (which Thomson called corpuscles and which were renamed electrons within a decade on the prior coinage of the Dublin physicist George Johnstone Stoney) were the first sub-atomic particles ever identified, and the discovery was the foundational result of modern atomic physics. The hundred-and-fifty-year-old Daltonian conception of the atom as the indivisible smallest unit of matter ended on the Royal Institution platform that evening. Thomson was awarded the Nobel Prize in Physics in 1906 for the discovery, and the body of physics work he founded at the Cavendish across the next forty years produced seven Nobel Laureates among his direct research-pupils (Rutherford, Aston, the elder Bragg, the younger Bragg, Richardson, Wilson and Born), the largest single research-school production in the history of the prize.

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