A high-voltage direct current is applied to a glass tube that is close to a vacuum inside and sealed with metal electrodes at both ends, and the cathode will emit cathode rays at one end. The fluorescent screen can display the direction of this kind of rays. If a uniform electric field is applied, the cathode rays will be biased towards the anode; and if a wheel is installed in the glass tube, the rays can make the wheel rotate. It was later confirmed that the cathode rays are a group of high-speed particles with negative charges, that is, a stream of electrons. Electrons were discovered here.
The electron is the first subatomic particle discovered. So far, the electron is the lightest of all particles, only 9.11×10⁻³¹kg, which is a hydrogen atom [1/1836.152701(37)], which was passed by Millikan around 1910 The famous "oil drop experiment" was made. An electron has a negative charge of one unit, that is, 4.8×10⁻¹⁹ electrostatic unit or 1.6×10⁻¹⁹ coulomb. Its volume is too small to measure with existing technology.
Modern physics believes that one of the electrons belonging to the leptons is one of the basic units of matter (the other is the quark).