The specimen presented here has an overall length of 18 cm and is composed of a cylindrical bar magnet on which a coil is wound, starting from one of the poles; facing the coil and the magnet, and quite close to them, is a thin steel reed which is free to oscillate. The whole is contained inside a black lacquered cylindrical wooden case which is widened on one side to accommodate the coil, and closed on the other.
The magnet is placed along the axis of the case and is held at the free end by a screw which, on passing through the bottom of the case, protrudes on the outside thus allowing regulation of the distance from the steel reed so that it is quite close but does not touch it. The reed is held tightly along its edge by the circular fixing ring of a block of wood carved to the shape of a funnel from which one speaks when the telephone is used as a transmitter or from which one listens when it is used as a receiver.
The ends of the coil are connected by means of two clamping screws fixed to the base of the instrument which are used to connect the telephone to another identical one placed at a distance.
If the reed of the transmitter moves towards or away from the magnet, an induced current is generated in the coil and, on passing through the coil, attracts or repulses the corresponding reed. If the reed of the transmitter oscillates with a certain frequency, the one in the receiver oscillates with the same frequency. ...continues