Although the movements of this latter are not, as we know, of the
nature of ordinary sonorous vibrations, it was thought that they might
prove to be in opposite directions on the two sides of the plate, and
that one of the contacts might be compressed while the other was free.
So notwithstanding the advantages of this arrangement, it was thought
necessary to place the plate vertically in order to give the same
regulation to the two contacts which it is essential should be
identical. But it became difficult to regulate by weight; and even to
succeed in regulating at all, it became necessary to employ two
parallel diaphragms, vibrating in unison, and each carrying its
contact, but in opposite directions. Afterwards, the horizontal
arrangement was again adopted; but, by a clever combination, the two
principles applied by Dr. Herz--derivation and inversion--were united.
The current is then led to a double contact, where it divides. This
contact is arranged under the plate in such a way that its two points
of variable resistance act in opposite directions to each other, or,
in some apparatus, so that one of the points has no variation, while
the other is in action. The result that occurs may be easily imagined.
The system has been experimented with under different forms; in one
case the derivation is simple, that is, a single one of the currents
being sent into the line, while in another case it is double, each of
the branches being provided with a bobbin and communicating with the
receiver.
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