The induced reactions caused by the line wires on each other are not the only ones which may be observed on a telephonic circuit: every manifestation of electricity near a telephone may produce sounds of greater or less force. Of this we have already given a proof in M. d’Arsonval’s experiments, and others by M. Demoget demonstrate the fact still more clearly. In fact, if a small bar magnet provided with a vibrator be placed before one of the telephones of a telephonic circuit, and the vibrating plate of the telephone be removed, in order to draw away the sound produced by the vibrator, its humming noise may be distinctly heard on the second telephone of the circuit; a noise which attains its maximum when the two extremities of the electro-magnet are at their nearest point to the telephone without a diaphragm, and it is at its minimum when this electro-magnet is presented to it along its neutral line. M. Demoget supposes that the action which is exerted in this instance is that of a magnet exerting two inducing actions which are opposite and symmetrical, with a field limited by a double paraboloid and with an axis, according to his experiments, which extended 55 centimètres beyond the magnetic core, and a vertical diameter of 60 centimètres. He believes that in this way it would be easy to telegraph on the Morse system, and that, in order to do so, it would only be necessary to apply a key to the inducing electro-magnet. Mr. Preece points out three ways of overcoming the difficulty presented by the induced reactions caused by the wires on each other. 1. By increasing the intensity of the transmitted currents, so as to make them decidedly stronger than the induced currents, and to reduce the sensitiveness of the receiving telephone. 2. To place the telephonic wire beyond the range of induction. 3. To neutralise the effects of induction. The first mode may be effected by Edison’s battery system, and we have seen that it is very successful.