C.
The motion of a sound wave must not, however, be confounded with the
motion of the molecules which at any moment form the wave; for during its
passage every molecule concerned in its transference makes only a small
excursion to and fro, the length of the excursion being the amplitude of
vibration, on which the intensity of the sound depends.
Taking the same tuning fork mentioned above, the molecule would take
1/256 of a second to make a full vibration, which is the length of time
it takes for the pulse to travel the length of the sound wave.
For different intensities, the amplitude of vibration of the molecule is
roughly 1/50 to 1/1000000 of an inch. That is to say, in the case of the
same tuning fork, the molecules it causes to vibrate must either travel a
distance of 1/56 or 1/1000000 of an inch forward and back in the 1/256 of
a second or in one direction in the 1/512 of a second.
I might further state that the pitch of the sound depends on the number
of vibrations and the intensity, as already indicated by the amplitude of
stroke--the timbre or quality of the sound depending upon factors which
will be clearly set forth as we advance.
Having now clearly and correctly represented the wave theory of sound,
without touching the physiological effect perceived by means of the ear,
we will proceed to consider it.
Pages:
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140