emissions of vapor from hot surfaces see Thermionic emission.
The ABC, ENIAC and Colossus all used Thermionic valves(vacuum tubes).
A Thermionic tube having two electrodes; used as a rectifier.
Relays and vacuum tubes(Thermionic tubes) were commonly used as switching elements;
The Atanasoff-Berry Computer(ABC), ENIAC, and Colossus all used Thermionic valves vacuum tubes.
Owen Willans Richardson,"for his work on the Thermionic phenomenon and especially for the discovery of the law named after him.".
Relays and vacuum tubes(Thermionic tubes) were commonly used as switching elements;
a useful computer requires thousands or tens of thousands of switching devices.
The central electrode is usually the one designed to eject the electrons(the cathode, i.e. negative polarity relative to the engine block) because it is the hottest(normally) part of the plug; it is easier to emit electrons from a hot surface, because of the same physical laws that increase
emissions of vapor from hot surfaces see Thermionic emission.