the tuning-fork throw the air into
vibrations which are conveyed to the ear and produce the sensation of
sound. The duration of time occupied in the vibrations of the tuning-fork
is therefore independent of the space passed over. The greater or less
energy expended does not influence the duration of time occupied by the
vibration; it only influences the amplitude of the vibration.

The second quality of musical sounds is the pitch, and the pitch depends
upon the number of vibrations that a sounding body makes in each second of
time. The most unmusical ear can distinguish a high note from a low one,
even when the interval is not great. Low notes are characterised by a
relatively small number of vibrations, and as the pitch rises so the number
of vibrations increase. 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. Although notes are of the
same loudness and pitch when played on different instruments or spoken or
sung by different individuals, yet even a person with no ear for music can
easily detect a difference in the quality of the sound and is able to
recognise the nature of the instrument or the timbre of the voice. This
difference in the timbre