Text: "It has been found by experiment that not only does the intensity of sound vary with the amplitude of the vibrations of the sounding body; but as nearly as the square of the amplitude. For instance, if a piano string can be made to vibrate so that the width of swing in its motion is one-fiftieth of an inch, and if another piano string giving the same pitch can be made to vibrate with an amplitude of one twenty-fifth of an inch, then the second will have an amplitude twice that of the first and its intensity will be approximately four times as great." Piano Tuning and Allied Arts "intensity varies as the square of the amplitude" Handbook of Acoustics, page 138

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