John Fleming was an English electrical engineer who invented the thermionic electron tube (valve). Fleming's tube was a rectifier, or diode. It consisted of two electrodes in an evacuated glass envelope resembling an electric light bulb. The diode permitted current to flow in one direction only. It could detect radio signals but could not amplify them. He is also remembered for Fleming's rules, which he devised.

 

Fleming's rules

 

Fleming's rules

 

Fleming's rules are aids for remembering the relationships between the directions of the current, field, and motion in electric motors, generators, and related applications.

 

In the left-hand rule (for motors), the forefinger represents field, the second finger current, and the thumb, motion; when the digits are extended at right-angles to each other, the appropriate directions are indicated. The right-hand rule applies the same principles for generators.