For demonstrating the conversion of electric energy into mechanical energy. Star-shaped copper disc 9 cm. Diameter rotatable vertically on pair of adjustable centers and dipping into mercury trough between the vertical limbs of a small horseshoe magnet on a wood base 15x 10 cm. Disc adjustable vertically on metal pillar which is connected to one of two terminals mounted on base. The other terminal is connected to the mercury trough. The apparatus will operates on 4 volts at which voltage it takes 1.8 amps., without battery.