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Joseph John Thomson (1856-1940) Photo
Photo A3; portrait. CREDIT: AIP Emilio Segrè Visual Archives, Physics Today Collection.
Photo Langmuir C4; Irving Langmuir, Thomson, and William David Coolidge during Thomson's 1923 visit to the G.E. Research Lab. CREDIT: General Electric Research & Development Center, courtesy AIP Emilio Segrè Visual Archives
Discovery of the Electron 

As professor at Cambridge, Thomson helped introduce laboratory demonstration work to the curriculum, which had been strictly mathematical. "We found many cases," he recalled, "where men  could solve the most complicated problems about lenses, yet when given a lens and asked to find the image of a candle flame, would not know on which side of the lens to look for the image. But perhaps the most interesting point was their intense surprise when any mathematical formula gave the right result."  (From Thomson's Recollections and Reflections) "J.J." (as he was called) had a boundless, infectious enthusiasm for any physical effect that turned up in the laboratory. He could not wait to start puzzling over it. Negatives of cloud chamber photographs had to be hidden from him when they were taken, for fear he would damage the image by handling the plate while it was still wet.
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