Invented by Michael Faraday in 1831, his Faraday disk showed the connection between electricity and magnetism by producing an electric current between the center of the disk and its rim as the disk is rotated by a hand crank. The disk center and rim are connected to the terminals, the rim via a mercury bath on the base. The copper rim passes through the bath. This Faraday disk is a demonstration motor. With a battery or DC power supply connected to the terminals, the disk rotates due to the force on the moving charges produced by the magnetic field from the horseshoe magnet. We no longer use this demonstration to avoid possible mercury vapor emission due to electrical sparks at the copper-mercury connection.