an instrument by which the several proportions of musical sounds and intervals, as well in the natural as in the tempered scales, are tried. Originally it had, as its name implies, only one string; but it is better constructed with two; for, by means of the additional string, an opportunity is afforded of judging of the harmony of two tempered notes in every possible variety of temperament. The monochord is called the harmonical canon. Its invention is ascribed to Pythagoras.