Quality, kind, or character of musical sounds depends on something very different from loud ness and pitch. We speak of a sound being harsh, or mellow, or rich, &c. We know that a note of the same pitch sounded on a piano, a trumpet, and a violin differs very markedly in quality, and that a note of the same pitch pro duced by the human voice differs from them all. Each instrument, that is to say, has a quality of its own. If a tuning-fork of the same pitch be sounded, we are aware of a great difference. The sound might be called thin, or poor, wanting in quality. It is, indeed, so wanting, for a tuning-fork produces what is called a pure sound. But suppose the tuning fork vibrates 1(X) times per second, and that we take another vibrating 200 times a second ; it will produce a sound the octave of the first. Let us take a third, vibrating 300 times, the octave of the second, a fourth, vibrating 400 times, and so on up to an eighth, vibrating 800 times per second ; then we have a set of forks all related to the first in that they vibrate twice, thrice, four times, &c., as often as the first. If, beginning with the first, they are all sounded one after the other, we perceive the sound of each one immediately after it is pro duced, but the different sounds immediately begin to blend. When all are sounding we are not aware of eight different sounds, but of one sound of a definite pitch and peculiar quality. The pitch is given by the note of the
one with which we began, which is called the fundamental note, and the particular quality is due to the blending of the other notes, which are called overtones or harmonics. The quality may be altered by causing only some of the forks to sound along with the first one; and it is mellow if the forks with fewer vibra tions sound, while it is ringing if those with most vibrations are set going. The quality of the sound produced by a violin string is due, therefore, to it vibrating not only to produce the fundamental note to which it is tuned, but also vibrating so as to produce overtones. A piano wire tuned to the same pitch produces a different set of overtones, and thus has a quality of its own, and so with each different musical instrument. In the language of wave move ment, the pianoforte wire and the violin string may produce the same number of waves in a second of time, but the form of the wave is different in each case, and so the quality differs.
These arc the chief facts to remember regard ing sounds. How the knowledge of them aids in the understanding of the structure of the ear and the perception of sound will be seen immediately.