Thomson, Joseph John
The Englishman Sir Joseph John Thomson (1856 - 1940), son to an antiquarian bookshop keeper, was a physicist.
He explored the properties of cathode rays, streams of electrons in a discharge tube. He concluded that they were composed of very light, negatively charged particles, which were a universal building block of atoms.
He showed that the mass of these particles was around 1800 times smaller than hydrogen, suggesting the subatomic particle now known as the electron. He also showed they were identical with particles given off by the photoelectric effect and by radioactive materials.
See also
Last modified:10 January 2026 2.23 p.m.