Cathode ray

Cathode ray, stream of electrons that flows from a cathode (negative electrode) to an anode (positive electrode) in a vacuum tube when a potential of 4,000–10,000 volts is applied across them. Cathode rays were first detected when a glowing light was seen to emanate from a cathode; this is a secondary effect the rays produce only when traces of certain gases are present.

See also: Electrolysis; Electronics; Vacuum tube.