This constant varies very little from steel to malleable cast iron, and
it may be taken as equal to 818270.
Thus, then, we have a means of constructing a tuning fork in which two
of the three quantities, n, e, l, are given in advance. Experience
proves that no errors are committed exceeding one or two per cent.
It is seen from this that there is a means of increasing the mass of the
instrument without changing anything in the thickness, the length or,
consequently, the number of vibrations, and this is by increasing the
_breadth_.
It is in this way that I have succeeded in having long massive tuning
forks made of malleable iron, giving no more than 12 to 15 vibrations
per second, and vibrating with perfect regularity. Fig. 2, annexed,
shows one of these instruments of about 55 centimeters length, whose
breadth, E, is from 5 to 6 centimeters, and which makes about fifteen
double vibrations per second only.
[Illustration: FIG. 2.--THE ELECTRICAL TUNING FORK.]
This number might be still further reduced, but at the expense of our
being led to exaggerate the longitudinal dimensions of the apparatus in
such a way as to make it inconvenient. The object may be attained more
simply by loading the branches with slides supporting leaden weights, M,
of 500 grammes each. By fixing these slides at different points on the
branches, the number of vibrations can be made to vary from simple to
double, and even triple.
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