nt
rods, made of carbon and sometimes of metal, such as brass. When the
diaphragm vibrated, the intimacy of contact between the pendant rod
_5_ and the rod _2_ was altered, and thus the resistance of the path
through all of the pendant rods in multiple was changed.

[Illustration: Fig. 39. Multiple-Electrode Transmitter]

A multitude of forms of such transmitters came into use in the early
eighties, and while they in some measure remedied the difficulty
encountered with the Blake transmitter, _i.e._, of not being able to
carry a sufficiently large current, they were all subject to the
effects of extreme sensitiveness, and would rattle or break when
called upon to transmit sounds of more than ordinary loudness.
Furthermore, the presence of such large masses of material, which it
was necessary to throw into vibration by the sound waves, was
distinctly against this form of transmitter. The inertia of the moving
parts was so great that clearness of articulation was interfered with.

Granular Carbon. The idea of employing a mass of granular carbon,
supported between two electrodes, one of which vibrated with the sound
waves and the other was stationary, was proposed by Henry Hunnings in
the early eighties. While this idea forms the basis of all modern
telephone transmitters, yet it did not prevent the almost universal
adoption of the single-contact form of instrument during the next
decade.

Western Electric Solid-Back Transmitter. In the early nineties,
however, the granular-carbon transmitter came into its own with the
advent and wide adoption of the transmitter designed by Anthony C.
White, known as the _White_, or _solid-back_, transmitter. This has
for many years been the standard instrument of the Bell companies
operating throughout the United States, and has found large use
abroad. A horizontal cross-section of this instrument is shown in Fig.
40, and a rear view of the working parts in Fig. 41. The working parts
are all mounted on the front casting _1_. This is supported in a cup
_2_, in turn supported on the lug _3_, which is pivoted on the
transmitter arm or other support. The front and rear electrodes of
this instrument are formed of thin carbon disks shown in solid black.
The rear electrode, the larger one of these disks, is securely
attached by solder to the face of a brass disk having a rearwardly
projecting screw-threaded shank, which serves to hold it and the rear
electrode in place in the bottom of a he