It was Mr. Varley’s aim to make his telephone work in conjunction with instruments with ordinary currents, by the addition of rapid electric waves, incapable of making any practical change in the mechanical or chemical capacity of the currents which serve for the ordinary signals, yet able to make distinct signals, perceptible to the ear and even to the eye. He says: ‘An electro-magnet offers at first a great resistance to the passage of an electric current, and may consequently be regarded as a partially opaque body with respect to the transmission of very rapid inverse currents or of electric waves. Therefore, if a tuning-fork, or an instrument with a vibrating plate, tuned to a given note, be placed at the sending station, and so arranged as to be kept in constant vibration by magnetic influence, the current which acts upon it must be passed into two helices placed one above the other so as to constitute the primary helix of an induction coil: in this way it will be possible to obtain in two distinct circuits two series of rapidly broken currents, which will correspond to the two directions of the vibrations of the tuning-fork, and we shall also have the induced currents produced in the secondary helix by these currents, which may act on a third circuit. This third circuit may be placed in connection with a telegraphic line previously used by an ordinary telegraphic system, if a condenser is applied to it, and in this way two different transmissions may be obtained simultaneously.’ [Illustration: FIG. 65.] Fig. 65 represents the arrangement of this system. D is the vibrating plate of the tuning-fork designed to produce the electric contacts necessary to maintain it in motion. These contacts are at S and S′, and the electro-magnets which affect it are at M and M′. The induction coil is at I′, and the three helices of which it is composed are indicated by the circular lines which surround it. There is a Morse manipulator at A, another at A′, and the two batteries which work the system are at P and P′. The condenser is at C, and the telephone is at the end of the line L.