In 1820 it had been found that a current in a wire deflects a nearby compass needle: electricity created magnetism. Michael Faraday wondered about the reverse — could magnetism create electricity? Finding the answer took him ten years.

Faraday was an unusual scientist: born to a poor family, self-taught by reading books while apprenticed to a bookbinder, an experimenter who knew almost no mathematics. He made up for that lack with an extraordinary physical intuition. In 1831 he performed the critical experiment: with two separate coils wound on either side of an iron ring, when he connected a battery to one and opened or closed the circuit, a momentary current appeared in the other — with no connection between them. What produced the current was not a steady magnetic field but its *change*. The same happened when he pushed a magnet in and out of a coil.

This principle of "electromagnetic induction" was no laboratory curiosity; it was a lever that changed civilisation. Generating electricity continuously by rotating a wire within a magnetic field — the generator — rests on this principle; today nearly every power station, whether coal, wind, or nuclear, ultimately produces current by rotating a magnet relative to a coil. The reverse process is the electric motor.

Faraday wrote no mathematical theory; he thought of the field intuitively as invisible "lines of force." It was James Clerk Maxwell, a generation later, who cast that intuition into equations; Maxwell's electromagnetic theory was built directly on Faraday's experiments. Einstein kept portraits of three scientists on his study wall: Newton, Maxwell, and Faraday. The whole electrical world, from lighting to motors, from communication to computers, was born from that momentary current in 1831.