That part of the telephone into which we speak is called the
transmitter. This is usually a piece of hard rubber having a round
mouthpiece cut through it. At the other side of this mouthpiece is
placed a diaphragm made of a thin piece of metal, which is held m
place by a light spring. Behind this diaphragm, and very close to
it, is placed a carbon button. Between this carbon button and the
diaphragm is a small piece of platinum, which is placed so as to touch
both the button and diaphragm very lightly. This platinum contact
piece is connected with one of the wires running to the primary of
the induction-coil, and the spring attached to the carbon button is
connected with the battery to which the other wire of the primary is
connected. This is all shown in the sketch of a transmitter. (Fig. 13.)
[Illustration: Fig. 13]
A is the mouthpiece; B, the diaphragm; C, the carbon button; D, the
wire at the end of which is the platinum contact; E, the battery; and
F, the induction-coil; P, P are the wires to the primary, and S, S to
the secondary wires.
We will now say a few words about the receiver, and then describe the
manner in which the telephone works.