Electronic rectifier

A British engineer discovered that a hot filament and cold plate in a glass vessel can rectify current, creating a device that lets electricity flow in only one direction. Fleming called it a valve, but they came to be known as radio tubes. Today, because they contain two electrodes, they are called diodes.
 John Ambrose Fleming England 1904 Electronic rectifier

A British engineer discovered that a hot filament and cold plate in a glass vessel can rectify current, creating a device that lets electricity flow in only one direction. Fleming called it a valve, but they came to be known as radio tubes. Today, because they contain two electrodes, they are called diodes.