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On Dissonance.
Having studied, in the preceding Chapter, the causes and characteristics of beats, we now proceed to inquire into the effects they produce, as they become more and more rapid.
Slow beats in music are not altogether unpleasant; in low tones, and in long sustained chords they often produce a solemn effect: in higher tones, they impart a tremulous or agitating expression; accordingly, modern organs and harmoniums usually have a stop, which, when drawn, brings into play a set of pipes or reeds, so tuned, as to beat with another set, thus imitating the trembling of the human voice and of violins.
When, however, the beats are more rapid, they become unpleasant to the ear. In studying this matter, it will be best to begin with simple tones. Select two C1 tuning-forks, and gradually throw them more and more out of tune, by sticking wax on the prongs of one of them, as described in the last Chapter. Sound the forks together after each addition of wax, and note the effect of the increasing rapidity of the beats. It will be found, that when they number five or six per second, the effect begins to be unpleasant, and becomes harsher and more jarring, as they grow more and more rapid. Of course the beats soon become too rapid to be counted by the unaided ear, but their rate can easily be ascertained by subtracting the vibration numbers of their generators. When the beats amount to about 32 per second,, though they are too rapid to be individually discriminated, yet the resultant sound has the same harsh jarring intermittent character, that it has had all along, only much more disagreeable. The two tones are now at the interval of a semitone, about the worst discord in music, and no one, who tries the above experiment, and notes carefully the effect