of the beams. Thus, for instance, if in a microphone with a horizontal
sound plate, as illustrated in Fig. 3, the carbon rollers are pressed
upward by outward force, it is evident that only a very trifling
rolling and disturbing motion can occur, and only small pieces of
carbon can be knocked off, which would act injuriously as a secondary
contact. The same may be said of the journals of microphones with
vertical sound plates, as represented in Fig. 2, when the carbon
rollers are pressed in the direction of the arrow, _p_, that is to
say, against the sound plate. In this case the journals, _a_, are
fixed in the flutings of the beams, _b_, in a direction given them by
the power and gravity operating on them, which is clearly represented
in the accompanying design, Fig. 2.

[Illustration: FIG. 1.
FIG. 2.
FIG. 3.
THE MIX AND GENEST TELEPHONE]

In all such cases the regulating contrivance applied to brake the
carbon rollers in their motion has the result that only the
oscillations transmitted from the sound plate on to the contacts come
in operation, whereas disturbing mechanical shocks resulting from any
outward influences occasion very insignificant vibrations, which are
not perceptible in the telephone. The separate contacts thus form a
firm system with the sound plate, so that the former are influenced in
their motions and effects solely and alone by the shocks and
oscillations which operate direct on these sound plates. The roller
motion of the carbon is thus removed, and the distinctness of the
words spoken is greatly augmented.