This transmitter does not make use of a mica washer or diaphragm, but employs a felt washer which surrounds the shank of the rear electrode and serves to close and seal the carbon containing cup.  By this means the granular carbon is retained in the chamber and the necessary flexibility or freedom of motion is permitted between the front and the rear electrodes.  As in the Kellogg and the later Bell instruments, the entire working parts of this transmitter are insulated from the metal containing case, the inner chamber, formed by the cup 2 and the diaphragm 3, being insulated from the transmitter front and its locking ring by means of insulating washers, as shown.

Fig. 44.  Automatic Electric Company Transmitter

Monarch Transmitter.  The transmitter of the Monarch Telephone Manufacturing Company, shown in Fig. 45, differs from both the stationary-cup and the vibrating-cup types, although it has the characteristics of both.  It might be said that it differs from each of these two types of transmitters in that it has the characteristics of both.

This transmitter, it will be seen, has two flexible mica washers between the electrodes and the walls of the electrode cup.  The front and the back electrodes are attached to the diaphragm and the bridge, respectively, by a method similar to that employed in the solid-back transmitters, while the carbon chamber itself is free to vibrate with the diaphragm as is characteristic of the Kellogg transmitter.

[Illustration:  Fig. 45.  Monarch Transmitter]

An aluminum diaphragm is employed, the circumferential edge of which is forwardly deflected to form a seat.  The edge of the diaphragm rests against and is separated from the brass front by means of a one-piece gasket of specially treated linen.  This forms an insulator which is not affected by heat or moisture.  As in the transmitters previously described, the electrodes are firmly soldered to brass disks which have solid studs extending from their centers.  In the case of both the front and the rear electrodes, a mica disk is placed over the supporting stud and held in place by a brass hub which has a base of the same size as the electrode.  The carbon-chamber wall consists of a brass ring to which are fastened the mica disks of the front and the back electrodes by means of brass collars clamped over the edge of the mica and around the rim of the brass ring forming the chamber.

[Illustration:  MAIN OFFICE BUILDING, BERKELEY, CALIFORNIA Containing Automatic Equipment, Forming Part of Larger System Operating in San Francisco and Vicinity.  Bay Cities Home Telephone Company.]