Sound. An affection of the medium in which we live, by vibrations like those which are produced in water, when a stone is thrown into it. It travels at the rate of 1,142 feet in a second, and different vibrations affect the different gases which constitute the atmosphere, and hence their various simultaneous tones. But the same gas may be variously affected, and, hence, different pitches of tone, or octaves. If a string perform 100 vibrations in a second, the ear receives 100 strokes, which we call sound ; and, if another makes 200 vibrations, the first is lower or flatter, and the latter higher and sharper, but according every other time, so that in flat sound-there are fewer vibrations than in sharp sounds. Every key of the piano-forte contains a determinate number of vibrations, which accord at regular intervals, and are completed in a second. The note marked C makes 100 vibrations in a second; but the note C, three octaves higher, makes 1,600 vibrations in the same time. It appears, by experiment, that we cannot determine the sound of a string which makes less than 30 vibrations in a second, because it is too low, nor of one which makes more than 7,552 vibrations in a second, because too high. These limits determine the power of the human ear. The eight notes of an octave are in length as follow; - 128-144-160-180-192-216-240-256 - and these are the proportions of strings which sound the diatonic scale, in which, at certain intervals of 2, 3, and 5, the vibrations correspond.