Rotating disc machine, 1850-1900.
© Royal Institution / Science & Society Picture Library
This machine demonstrates one of the experiments performed by Michael Faraday (1791-1867) on using magnets to produce electric currents (electromagnetic induction). In 1831, Faraday had shown that moving one pole of a bar magnet into or out of a long coil of wire produced a pulse of electric current in the coil. Later, he rotated a copper disc between the poles of a powerful permanent magnet, and showed that a continuous current would flow in a wire connecting the centre of the disc to the edge of the disc.