In this instrument, the magnet N S (fig. 57) is snail-shaped, like others we have mentioned, but the core of soft iron S, to which the coil E is fastened, can produce two different effects on its two extremities. On the one side, it reacts on a small armature which is fastened to the end of a vibrating disk C, fig. 58; the armature is placed against a contact fastened to the bridge B, and constitutes an electro-magnetic vibrator. For this purpose the bridge is in metallic communication with the coil wire, of which the other end corresponds with the line wire, and the spring C is mounted on an upright A, which also supports another spring D G acting on two contacts, one placed at G, and corresponding to the earth wire, the other at H, and connected with the positive pole of the battery. A small moveable button, which passes through a hole in the lid of the box, and projects beyond it, is fixed at G, and all this part of the instrument faces the bottom of the box. The upper part consists of the vibrating disk and the mouthpiece, so that the mechanism we have described is all mounted on an inner partition forming a false bottom to the box. When the box rests upon its base, on the side shown in fig. 58, the button at G presses on the spring D G, and raises it so as to break the connection with the battery; the coil of the instrument is then united to the circuit, and consequently receives the transmitted currents, which follow this route: line wire, coil E, bridge B, spring C, spring D G, earth contact. If these currents are transmitted by a vibrator, they are strong enough to produce a noise which can be heard in all parts of a room, and consequently the call may be given in this way. If the currents are due to telephonic transmission, the instrument is applied to the ear, care being taken to put the finger on the button G, and the exchange of correspondence takes place as in ordinary instruments; but it is simpler and more manageable to insert a second telephone in the circuit for this purpose. When the box is inverted on its mouthpiece, and the button G ceases to press on the spring D G, the battery current reacts on the vibrator of the instrument, and sends the call to the corresponding station, following this route: I D A C B E, line, earth and battery; and the call goes on until the correspondent breaks the current by taking up his instrument, thus warning the other that he is ready to listen.