An Elementary Treatise on Sound
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1836 Excerpt: ...whose vibrations are executed in equal times with those in which the excursions to an fro of the included sections, are performed in the stopped pipe. Such an aperture is called an embouchure. Vibrations maintained in a Pipe by a Vibrating Disc. a, For, at such a point, the condensations and rarefactions are evanescent, and the amplitudes of the molecular excursions are at a maximum; consequently, there will be no tendency for the air to pass in or out; neither will its motion be impeded, being parallel to the axis of the column and without any lateral bias. b. But let us now conceive the one half (A) of the pipe entirely removed, and in its place a disc substituted exactly closing the aperture, and maintained, by some external cause, constantly in a state of vibration, such, that the performance of one complete. vibration, going and returning, shall exactly occupy as much lime as a sonorous pulse would take to traverse the whole length of the stopped pipe (A + B), or double that of the open one (B). Its first impulse on the air will be propagated along the pipe (B) and reflected at the stopped end, and will again reach the disc just at the moment when the latter is commencing its second impulse. But, the absolute velocity of the disc in its vibrations being excessively minute compared with that of sound, the reflected pulse will undergo a second reflection at the disc, as if it were a fixed stopper. It will, therefore, in its return exactly coincide and conspire with the second original impulse of the disc; and the same process being repeated on every impulse, each will be combined with all its echos, and a musical tone will be drawn forth from the pipe, vastly superior to that which the disc vibrating alone in free air would produce. This is, in fact, the...
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