Abstract
III.
A FINAL proof, if such were needed, is afforded by an experiment, which, though of a striking character, will not necessarily be heard by all persons present, being only well heard by those who sit in certain positions. If a shrill tuning-fork is excited by a blow of the steel mallet, and held opposite a flat wall, part of the waves which it emits strike on the surface, and are reflected. This reflected system of waves, as it passes out into the room, interferes with the direct system. As a result, if the fork, held in the hand be moved toward the wall or from it, a series of maxima and minima of sound will successively reach an ear situated in space at any point near the line of motion, and will be heard as a series of beats; the rapidity with which they succeed one another being proportional to the velocity of the movement of the fork. The fork Dr. Kœnig is using is ut6, which gives wellmarked beats, slow when he moves his arm slowly, quick when he moves it quickly. There are limits to the speed at which the human arm can be moved, and the quickest speed that he can give to his fails to make the beats blend to a tone. But if he will take sol6, vibrating 1½ times as fast, and strike it, and move it away from the wall with the fastest speed that his arm will permit, the beats blend into a short low growl, a non-uniform tone of low pitch, but still having true continuity.
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By Prof. Silvanus P. Thompson . (Communicated by the author' having been read to the Physical Society of London, May 16, 1890.)
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The Researches of Dr. R. R. Kœnig on the Physical Basis of Musical Sounds1. Nature 43, 249–253 (1891). https://doi.org/10.1038/043249a0
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DOI: https://doi.org/10.1038/043249a0