Heinrich Hertz

Maxwell’s equations predicted that a changing electric field makes a magnetic one and back again, travelling as a wave at the speed of light. Nobody had made one on purpose.

Hertz built a spark gap on one side of his laboratory and a loop of wire with a tiny gap on the other. When the transmitter sparked, a smaller spark jumped the receiver’s gap across the room, with nothing between them. He measured the waves’ wavelength and speed and showed they reflected and refracted like light.

Asked what use it was, he is reported to have said it was of no use at all — just an experiment proving Maxwell right. He died at thirty-six, before radio existed.

Anything that oscillates is doing a tamer version of his spark: a circuit that will not sit still, flipping back and forth on its own. The one on this board is two transistors taking turns.