Today, 142 years ago, on May 13, 1883 (April 7, 1883), Edison discovered that in a vacuum glass bubble, metal plates transmitted electricity to the heat lights. On May 13, 1883, the famous American inventor Edison discovered that in a vacuum glass bubble, electricity can be transmitted from metal plates to the heat lights, but not vice versa. This is the earliest discovery of the phenomenon of thermal electrode emission, and essentially the first discovery of the function of the diode vacuum tubes.