must always be able to speak into the transmitter while seated before
the switchboard, and yet allow both of her hands to be free for use.
This was formerly accomplished by suspending an ordinary
granular-carbon transmitter in front of the operator, but a later
development has resulted in the adoption of the so-called breast
transmitter, shown in Fig. 47. This is merely an ordinary
granular-carbon transmitter mounted on a plate which is strapped on
the breast of the operator, the transmitter being provided with a long
curved mouthpiece which projects in such a manner as to lie just in
front of the operator's lips. This device has the advantage of
automatically following the operator in her movements. The breast
transmitter shown in Fig. 47, is that of the Dean Electric Company.

[Illustration: Fig. 48. Transmitter Symbols]

Conventional Diagram. There are several common ways of illustrating
transmitters in diagrams of circuits in which they are employed. The
three most common ways are shown in Fig. 48. The one at the left is
supposed to be a side view of an ordinary instrument, the one in the
center a front view, and the one at the right to be merely a
suggestive arrangement of the diaphragm and the rear electrode. The
one at the right is best and perhaps most common; the center one is
the poorest and least used.




CHAPTER VI

RECEIVERS