Working for the Edison Electrical Light Company of England, Sir John Fleming invented the diode, a vacuum tube at the heart of all early electronics. Radios, television, telephones, computers – virtually every electronic we’re familiar with today – was first built with diodes.
Diodes are typically vacuum tubes, though some have specialized gasses in them. They conduct electricity, moving it from the cathode to the anode.
Early diodes evolved from lightbulbs. Electrons flow free in lightbulbs. Their purpose is to emit light and there is no need to shepherd the energy. Diodes enable the controlled flow of electrons. This enables all sorts of nifty tricks when tied together into circuits.
Compared to modern electronics, Diodes were enormous and also enormously power-hungry. Since they were tubes that typically operate at high heat they also tend to burn out, like old-fashioned pre-LED lightbulbs. Diodes often consumed as much as 100 volts. An iPhone, with billions of more circuits, consumes five volts.
Diodes typically contained additional electrodes, called grids, to control the flow of electricity and form circuits. Diodes with one grid are called a triode, because electricity flows from the cathode to the anode but can be diverted by the grid. Tetrode’s are four-grid diodes, etc…
Despite that Fleming was a physicist he was an avid anti-evolutionist. He profited from the invention of his diode, and subsequent discoveries, and left the bulk of his fortune to Christian charities serving the poor.
Transistors eventually replaced the vacuum tube.