hereof. The entire
structure of the diaphragm, the front and back electrodes, and the
granular carbon within are permanently assembled in the factory and
cannot be dissociated without destroying some of the parts. The rear
electrode is held rigidly in place by the bridge _5_ and the stud _6_,
this stud passing through a block _9_ mounted on the bridge but
insulated from it. The stud _6_ is clamped in the block _9_ by means
of the set screw _8_, so as to hold the rear electrode in proper
position after this position has been determined.

[Illustration: Fig. 43. Kellogg Transmitter]

In this transmitter, as in the transmitter shown in Fig. 42, all of
the working parts are insulated from the exposed metal casing. The
diaphragm is insulated from the front of the instrument by means of a
washer _4_ of impregnated cloth, as indicated. The rear electrode is
insulated from the other portions of the instrument by means of the
mica washer and by means of the insulation between the block _9_ and
the bridge _5_. The terminal for the rear electrode is mounted on the
block _9_, while the terminal for the front electrode, shown at _10_,
is mounted on, but insulated from, the bridge. This terminal _10_ is
connected with the diaphragm and therefore with the front electrode by
means of a thin, flexible metallic connection. This transmitter is
provided with damping springs similar to those of the White
instrument.

It is claimed by advocates of this type of instrument that, in
addition to the ordinary action due to the compression and
decompression of the granular carbon between the electrodes, there
exists another action due to the agitation of the granules as the
chamber is caused to vibrate by the sound waves. In other words, in
addition to the ordinary action, which may be termed _the piston
action between the electrodes_, it is claimed that the general
shaking-up effect of the granules when the chamber vibrates produces
an added effect. Certain it is, however, that transmitters of this
general type are very efficient and have proven their capability of
giving satisfactory service through long periods of time.

Another interesting feature of this instrument as it is now
manufactured is the use of a transmitter front that is struck up from
sheet metal rather than the employment of a casting as has ordinarily
been the practice. The formation of the supporting lug for the
transmitter from the sheet metal which forms the rear casing