We reproduce herewith, in Fig. 1, a cut showing in projection one of the
simplest forms of the apparatus.
[Illustration: FIG. 1.--CONSTANT VIBRATOR.]
If we imagine the platinum or steel style, s, of the figure to be done
away with, as well as the platinized plate, I, and its communication
with the negative pole of the pile, P, we shall have the ordinary
instrument kept in operation electrically by the aid of the
electro-magnet, E, the style, s, the interrupting plate, I, and the
pile.
If we preserve the parts above mentioned, the instrument will possess
the property of having vibrations of a constant amplitude if sufficient
energy be kept up in the pile. In fact, when the amplitude is
sufficiently great to cause the style, s, to touch the plate, I, it
will be seen that at such a moment the current no longer passes through
the electromagnet, and the vibration is no longer maintained. The
amplitude cannot exceed an extent which shall permit the style, s, to
touch I.
Under such conditions, the duration of the vibrations remains exactly
constant, as does also the vibratory intensity of the entire instrument.
The measurement of time, then, by an instrument of this kind is, indeed,
as perfect as it could well be.
This complication in the arrangement of the apparatus has no importance
as regards those tuning forks the number of whose vibrations exceeds a
hundred per second, for in such a case these are given an amplitude of a
few millimeters only; but it would be of importance with regard to
instruments whose number of vibrations is very small, and to which it
might be desirable to give great amplitude; for then, as I have long ago
shown, the duration of the oscillation would depend a little on the
amplitude, but a very little, it is true.
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