In railroading a switch diverts a train from one track to another. In plumbing, a valve can redirect the flow of water between pipes. In early electronics, directing electrons along a certain path was controlled by what North American scientists called a tube, while British scientists referred to it as a valve. That device controlled the current flow in a high vacuum between electrodes to which a difference in electrical potential had been applied.
The simplest vacuum tube was the diode. It acted much like a check valve that prevents water from flowing in the wrong direction. The electronic check valve featured a heated, electron-emitting cathode and an anode. Electrons could only flow in one direction, from the cathode to the anode. Electronic control grids within the bottle could exert more precise control by varying the voltage on the grid.
“Transistor” was a term coined by John Robinson Pierce of Bell Laboratories. He borrowed parts of two relevant words because it selectively transfers an electrical current across a resistor. Its function is still best understood in that transference and resistance context. Most, but not all, of the vacuum tube’s early functions are now performed by transistors. Audiophiles still prefer what they sometimes call “little tone bottles.”