2.1 - The Fleming diode
The Fleming tube image


The British phycisist John A. Fleming discovered that the Edison effect could be used for the detection of the Hertzian waves.  Basically Fleming used an electric lamp whose filament was surrounded by a cilindrical plate.  Since such device could control the flow of current in a circuit, in analogy to a valve in a water pipe system it was named also as a valve.
Unfortunately the Fleming valve later known as a diode was still unable to amplify the feable electric signals detected by the aerial.