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130 QUALITY OF SOUNDS OF FLUE-PIPES. [V. § 65.
The regular musical note thus produced is accompanied by a hissing sound, which may be imitated by blowing with the mouth against a knife-edge held in front of it. This sound however contributes nothing to the general effect, being, where a pipe is properly constructed, inaudible except in its immediate neighbourhood.
Stopped wooden flue-pipes of large aperture, blown by only a light pressure of wind, produce sounds which are nearly simple tones; only a trace of partial-tone No. 3 being perceptible. Such tones, like the fork-tones with which they are in fact almost identical, sound sweet and mild, but also tame and spiritless. A greater pressure of wind developes 3 distinctly in addition to 1, and, if it becomes excessive, may spoil the quality by giving the overtone too great an intensity compared to that of the fundamental, or may even extinguish the latter altogether, and so cause the whole sound to jump up an Octave and a Fifth. This result may easily be obtained by blowing with the mouth into a small 6-inch stopped pipe, which can readily be procured at any organ factory.
Stopped pipes of narrow aperture develope the third and fifth partial-tones with distinctness.
In the case of an open pipe the fundamental-tone is never produced by itself. According to the dimen-