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98 SIMPLE TONES [V. §49.
a pianoforte note of the same pitch the fork-tone is wanting in richness and vivacity, and produces an impression of greater depth, so that one is at first inclined to think the fork employed must be an Octave too low.
It is a direct inference from the general theory of the nature of quality that simple tones can differ only in pitch and intensity. Accordingly we find that tuning-forks of the same pitch, mounted on resonance-boxes and set gently vibrating by a resined fiddle-bow, exhibit, whatever be their forms and sizes, differences of loudness only. When made to sound with equal intensity by suitable bowing, their tones are absolutely undistinguishable from each other.
49. Sounding strings vibrate so rapidly that their movements cannot be followed directly by the eye. It will be well, therefore, that we should examine how the slower and more easily controllable vibrations of non-sounding strings are performed, before treating the proper subject of this section. Take a flexible caoutchouc tube ten or fifteen feet long and fasten its ends to two fixed objects separated from each other by that distance. The tube can be set in periodic vibration by impressing a swaying movement upon it with the hand near either ex-