In 1898 Thonson was working on an experiment which would lead to the discovery of the electron. USing a cathode
ray tube and added a electric charge to both ends. The plates in the middle of the the tube would gain opposite charges.
He would then shine a beam of charged particles through the tube.
Thomson was interested when the beam proved to be negativly charged. After several monthes he conclueded that all
atoms contained these electrons.
He then came up with the model of the atom called the plum pudding model of the atom consisting of small negative spots
in a large circle of positive mass.