Such instruments are well fitted to perform the role of electrical
interrupters, and it was in such a character that one of them figured in
the Exhibition of the Upper School of Telegraphy as a type of an
interrupter for testing piles.
When it is desired to test a pile to ascertain the practicability of
employing it in telegraphy, it is necessary to make it perform a work
which shall be as nearly as possible identical with that which it will
be called on to do, until it is used up, to estimate the duration of
such work, to measure regularly the constants of the pile, the
electro-motive power, and the internal resistance. Usually, in
telegraphy, this work consists in sending over a line of a certain
resistance intermittent currents, through the intermedium of suitable
manipulators. It suffices then to cause the branches of the electro
tuning fork to play the role of one of these manipulators. For doing
this the tuning fork carries two insulating ebonite or ivory strips, B B
(Fig. 3), which, at every oscillation, abut against vertical brass
springs, r. Each of these latter is located in front of the platinized
point of a screw, v, which is affixed to a small metallic tongue. The
springs and tongues are insulated from each other, and are mounted on a
piece which may be moved by a screw, V, so as to cause the springs of
the strips, B B', to approach or recede according to the amplitude of
the instrument's vibrations.
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