How was the electron discovered?

Thomson’s experience consisted of studying beams of cathode rays passing through a system of parallel metal plates that created an electric field, and systems of coils that created a magnetic field. It was found that the beams were deflected under the action of both fields separately, and at a certain ratio between them, the beams did not change their straight trajectory. This field ratio depended on the particle velocity. Through a series of measurements, Thomson found that the speed of particles is much lower than the speed of light – thus, it was shown that particles must have mass. Further, an assumption was made about the presence of these particles in atoms and a model of the atom was proposed, which was later developed in the experiments of Rutherford.