ried, 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.

A feature in this transmitter that is not found in the White
transmitter is that both the front and the rear electrodes, in fact,
the entire working portions of the transmitter, are insulated from the
exposed metal parts of the instrument. This is accomplished by
insulating the diaphragm and the supporting cup _1_ from the
transmitter front. The terminal _5_ on the cup _1_ forms the
electrical connection for the rear electrode, while the terminal _6_,
which is mounted _on_ but insulated _from_ the cup _1_ and is
connected with the front electrode by a thin flexible connecting
strip, forms the electrical connection for the front electrode.

Kellogg Transmitter. The transmitter of the Kellogg Switchboard and
Supply Company, originally developed by Mr. W.W. Dean and modified by
his successors in the Kellogg Company, is shown in Fig. 43. In this,
the electrode chamber, instead of being mounted in a stationary and
rigid position, as in the case of the White instrument, is mounted on,
and, in fact, forms a part of the diaphragm. The electrode which is
associated with the mica washer instead of moving with the diaphragm,
as in the White instrument, is rigidly connected to a bridge so as to
be as free as possible from all vibrations.

Referring to Fig. 43, which is a horizontal cross-section of the
instrument, _1_ indicates the diaphragm. This is of aluminum and it
has in its center a forwardly deflected portion forming a chamber for
the electrodes. The front electrode _2_ of carbon is backed by a disk
of brass and rigidly secured in the front of this chamber, as clearly
indicated. The rear electrode _3_, also of carbon, is backed by a disk
of brass, and is clamped against the central portion of a mica disk by
means of the enlarged head of stud _6_. A nut _7_, engaging the end of
a screw-threaded shank from the back of the rear electrode, serves to
bind these two parts together securely, clamping the mica washer
between them. The outer edge of the mica washer is clamped to the
main diaphragm _1_ by an aluminum ring and rivets, as clearly
indicated. It is seen, therefore, that the diaphragm itself contains
the electrode chamber as an integral part t