This can be proved in many ways. Take, for example,
two tuning-forks of different size: the shorter produces a considerably
higher pitched note than the longer one. If a mirror be attached to one of
the prongs of each fork, and a beam of light be cast upon each mirror
successively and then reflected in a revolving mirror, the oscillating spot
of light is converted into a series of waves; and if the waves obtained by
reflecting the light from the mirror of the smaller one be counted and
compared with those reflected from the mirror attached to the larger fork,
it will be found that the number of waves reflected from the smaller fork
is proportionally to the difference in the pitch more numerous than the
waves reflected from the larger. The air is thrown into corresponding
periodic vibrations according to the rate of vibration of the
sound-producing body.
Thirdly, the quality, timbre, or klang depends upon the overtones, in
respect to which I could cite many experiments to prove that whenever a
body vibrates, other bodies near it may be set in vibration, but only on
condition that such bodies shall be capable themselves of producing the
same note. A number of different forms of resonators can be used to
illustrate this law; a law indeed which is of the greatest importance in
connection with the mechanism of the human voice.
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