The “new electrical machine” was an exceedingly simple contrivance. A disc of copper, twelve inches in diameter (Fig. 6), and about one-fifth of an inch in thickness, fixed upon a brass axle, was mounted in frames, so as to allow of revolution, its edge being at the same time introduced between the magnetic poles of a large compound permanent magnet, the poles being about half an inch apart.[29] The magnet first used was the historical magnet of Gowin Knight. The edge of the plate was well amalgamated, for the purpose of obtaining a good but movable contact, and a part round the axle was also prepared in a similar manner. Conducting strips of copper and lead, to serve as electric collectors, were prepared, so as to be placed in contact with the edge of the copper disc; one of these was held by hand to touch the edge of the disc between the magnet poles. The wires from a galvanometer were connected, the one to the collecting-strip, the other to the brass axle; then on revolving the disc a deflexion of the galvanometer was obtained, which was reversed in direction when the direction of the rotation was reversed. “Here, therefore, was demonstrated the production of a permanent current of electricity by ordinary magnets.” These effects were also obtained from the poles of electro-magnets, and from copper helices without iron cores. Several other forms of magneto-electric machines were tried by Faraday. [Sidenote: NEW FORMS OF APPARATUS.] [Illustration: FIG. 7.] In one,[30] a flat ring of twelve inches’ external diameter, and one inch broad, was cut from a thick copper plate, and mounted to revolve between the poles of the magnet, two conductors being applied to make rubbing contact at the inner and outer edge at the part which passed between the magnetic poles. In another,[31] a disc of copper, one-fifth of an inch thick and only 1½ inch in diameter (Fig. 7), was amalgamated at the edge, and mounted on a copper axle. A square piece of sheet metal had a circular hole cut in it, into which the disc fitted loosely; a little mercury completed communication between the disc and its surrounding ring. The latter was connected by wire to a galvanometer; the other wire being connected from the instrument to the end of the axle. Upon rotating the disc in a horizontal plane, currents were obtained, though the earth was the only magnet employed. [Illustration: FIG. 8.]