Faraday also proposed a multiple machine[32] having several discs, metallically connected alternately at the edges and centres by means of mercury, which were then to be revolved alternately in opposite directions, In another apparatus,[33] a copper cylinder (Fig. 8), closed at one extremity, was put over a magnet, one half of which it enclosed like a cap, and to which it was attached without making metallic contact. The arrangement was then floated upright in a narrow jar of mercury, so that the lower edge of the copper cap touched the fluid. On rotating the magnet and its attached cap, a current was sent through wires from the mercury to the top of the copper cap. In another apparatus,[34] still preserved at the Royal Institution, a cylindrical bar magnet, half immersed in mercury, was made to rotate, and generated a current, its own metal serving as a conductor. In another form,[35] the cylindrical magnet was rotated horizontally about its own axis, and was found to generate currents which flowed from the middle to the ends, or _vice versâ_, according to the rotation. The description of these new electrical machines is concluded with the following pregnant words:-- [Sidenote: AN EARTH-INDUCTOR.] I have rather, however, been desirous of discovering new facts and relations dependent on magneto-electric induction, than of exalting the force of those already obtained; being assured that the latter would find their full development hereafter. [Illustration: FIG. 9.] In yet another machine (Fig. 9), constructed by Faraday some time later,[36] a simple rectangle of copper wire _w_, attached to a frame, was rotated about a horizontal axis placed east and west, and generated alternate currents, which could be collected by a simple commutator _c_. Within a few months machines on the principle of magneto-induction had been devised by Dal Negro, and by Pixii. In the latter’s apparatus a steel horseshoe magnet, with its poles upwards, was caused to rotate about a vertical shaft, inducing alternating currents in a pair of bobbins fixed above it, and provided with a horseshoe core of soft iron. Later, in 1832, Pixii produced, at the suggestion of Ampère,[37] a second machine, provided with mercury cup connections to rectify the alternations of the current. One of these machines was shown at the British Association meeting at Oxford in the same year (p. 64). The idea developed in the third part of this research was intensely original and suggestive. Faraday’s own statement is as follows:-- [Sidenote: THE ELECTROTONIC STATE.]