The magneto-electric machine advertised in 1832 by the French instrument-maker Hippolyte Pixii is the ancestor of all the machines for converting mechanical energy into electricity.
A crank-operated gear system is used to rotate a large magnet placed under a pair of coils mounted on an iron yoke. The magnet's movement induces an alternating current in the coils. The direction of the current varies at periodic intervals. The current can, however, be rectified by means of a special commutator connected to the wires extending from the coils. The commutator is composed of a series of mobile rods that alternately touch a set of contacts consisting of copper strips. The rods are made to oscillate by means of a small bar actuated by a cam on the axis of the rotating magnet.
The Pixii machine system was long used for small generators employed in laboratory experiments and electrotherapy.
Hippolyte Pixii, Paris, ca. 1832