The action of this transmitter is as follows:  Sound waves are concentrated against the center of the diaphragm by the mouth-piece, which is of the familiar form.  These waves impinge against the diaphragm, causing it to vibrate, and this, in turn, produces similar vibrations in the front electrode.  The vibrations of the front electrode are permitted by the elasticity of the mica washer 6.  The rear electrode is, however, held stationary within the heavy chambered block 4 and which in turn is held immovable by its rigid mounting.  As a result, the front electrode approaches and recedes from the rear electrode, thus compressing and decompressing the mass of granular carbon between them.  As a result, the intimacy of contact between the electrode plates and the granules and also between the granules themselves is altered, and the resistance of the path from one electrode to the other through the mass of granules is varied.

New Western Electric Transmitter.  The White transmitter was the prototype of a large number of others embodying the same features of having the rear electrode mounted in a stationary cup or chamber and the front electrode movable with the diaphragm, a washer of mica or other flexible insulating material serving to close the front of the electrode chamber and at the same time to permit the necessary vibration of the front electrode with the diaphragm.

[Illustration:  Fig. 42.  New Western Electric Transmitter]

One of these transmitters, embodying these same features but with modified details, is shown in Fig. 42, this being the new transmitter manufactured by the Western Electric Company.  In this the bridge of the original White transmitter is dispensed with, the electrode chamber being supported by a pressed metal cup 1, which supports the chamber as a whole.  The electrode cup, instead of being made of a solid block as in the White instrument, is composed of two portions, a cylindrical or tubular portion 2 and a back 3.  The cylindrical portion is externally screw-threaded so as to engage an internal screw thread in a flanged opening in the center of the cup 1.  By this means the electrode chamber is held in place in the cup 1, and by the same means the mica washer 4 is clamped between the flange in this opening and the tubular portion 2 of the electrode chamber.  The front electrode is carried, as in the White transmitter, on the mica washer and is rigidly attached to the center of the diaphragm so as to partake of the movement thereof.  It will be seen, therefore, that this is essentially a White transmitter, but with a modified mounting for the electrode chamber.