Joseph John (J.J.) Thomson was born on December 18, 1856 near Manchester, England. In 1876, he entered Trinity College, Cambridge. He spent the rest of his career at Trinity College, becoming Lecturer in 1883 and Master in 1918. He was Cavendish Professor of Experimental Physics at Cambridge from 1884 to 1918 and Honorary Professor of Physics, Cambridge and Royal Institution, London.
In 1897, Thomson discovered the electron. At a lecture to the Royal Institution, he announced that cathode rays were negatively charged particles which he called "corpuscles." He also announced that they had a mass about 1000 times smaller than a hydrogen atom, and he claimed that these corpuscles were the things from which atoms were built up. He later discovered a method for separating different kinds of atoms and molecules by the use of positive rays, an idea developed by Aston, Dempster, and others towards the discovery of many isotopes.
Information as of 1922