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3. On Beats of Imperfect Harmonies

Published online by Cambridge University Press:  15 September 2014

William Thomson
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Extract

According to a usage which has been adopted from the German of Helmholtz by the best English scientific writers on sound, a sound is called a “simple tone,” or without qualification a “tone,” when the variation of pressure of the air in the neighbourhood of the ear which is the immediate excitant of the sense is according to a simple harmonic function of the time; that is to say, when the whole pressure of the air varies in simple proportion to the distance, from a fixed plane, of a point moving uniformly in a circle.

Type
Proceedings 1877-78
Information
Proceedings of the Royal Society of Edinburgh , Volume 9 , 1878 , pp. 602 - 612
Copyright
Copyright © Royal Society of Edinburgh 1878

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References

page 602 note * The old musical usage, according to which the word tone denotes an interval (the major tone or minor tone, or the mean tone of the tempe red scale), though it unfortunately clashes with this recent scientific use of the word tone, can scarcely be abandoned.

page 603 note * Compare “Trans. R.S.E.” April 30th, 1860, “Reduction of Observations of Underground Temperature,” where a short description of Fourier's analysis is to be found.

page 611 note * In every case, to obtain regular beats, each tuning-fork, after being set in vibration by the bow, must be left to itself. The sound is sensibly graver as long as the bow is applied to augment or sustain the vibration than when the fork is left free. Thus, if two tuning-forks nearly, but not quite, in unison, are alternately acted on by the bow and left free, the beats are less rapid during the time the bow is applied to the higher fork, and more rapid while to the lower, than when both forks are vibrating freely.