Michael Faraday found the principle of electromagnetic induction on October 17, 1831, in his laboratory at the Royal Institution in London, and he wrote the experiment down in his notebook the same day. He had wound a coil of wire around an iron ring and found that when the current in another coil was switched on or off, a current appeared for a moment in the first. A changing magnetic field makes an electric current. That one sentence is the foundation of the electrical age.
The idea had been in the air for years. It was known that a current could make a magnet. Faraday had set out to find the reverse, whether a magnet could make a current, and he had been trying, on and off, since the 1820s. The answer, when he found it, was not what anyone expected: the current appears only while the field is changing, not while it sits still, and the motion, or the change, is the point.
From that came the machines. The generator makes current. The transformer steps it. The transformer steps it up or down. The electric motor turns current back into motion. They are the same principle in different arrangements, and they are the reason electricity could be made in one place and used in another, which is the whole shape of the modern world.
Faraday was no mathematician. He could not write the equations, and that work was left to James Clerk Maxwell, who turned Faraday's lines of force into the theory that still stands. Faraday himself was the son of a blacksmith, self-taught, and the Royal Institution where he worked kept his notebook, and the entry for October 17, 1831, with its sketch of the ring, is one of the most reproduced pages in the history of science.