A similar observation can be made in the case of stringed instruments. If pieces of paper be laid on the strings of a violin, and the bow then drawn across them, the bits of paper will fly off owing to the movements—i.e., the vibrations—of the strings.
That a force applied at one end of several objects in a line or series causes an obvious effect at the other end, can be well illustrated in a simple way. If a number of individuals stand one behind another in a line, each with his hands laid firmly on the shoulders of the one next to him, and the person at the end be pushed, the force will be conveyed through all the intermediate individuals, and cause the unsupported person at the distant end to move. So is it with the particles of which the air is composed. The movements begun in the drum set up by contact corresponding movements or vibrations in the adjacent air, which ultimately reach the hearing subject's ear, thereby affect his brain, and are accompanied by that change in consciousness which he terms "hearing." It will be observed that these events constitute a chain, and a break anywhere will prevent a sound being heard; there is then, in fact, no sound.
Sounds are characterized by pitch, volume, and quality.
The pitch is determined by the number of vibrations that reach the ear within a certain time; the more numerous the sound-waves (vibrations) in a second, the higher the pitch.
Fig. 37 (Tyndall). Meant to illustrate vibrations. The impulse communicated by the ball pushed from the hand to all the intervening ones causes only the last to actually move bodily.
Animals differ a good deal as to the limits of hearing. Cats hear very high-pitched sounds, as of mice, that human beings may not notice, and it is likely that insects hear sounds altogether beyond the limit of the human ear. But it is wonderful how much human beings differ among themselves in regard to this matter. It has surprised the author to find that many persons cannot hear the high-pitched note of certain birds, as the wax-wing.
The lower limit, speaking generally, is for most persons 16 vibrations, and the highest 38000 vibrations a second, according to Helmholtz, hence the entire range of the human ear would be fully 11 octaves; but the practical range of musical sounds is within 40 and 4000 vibrations a second—i.e., about 7 octaves—and, as is well known, even this range is beyond the appreciation of most persons, though as to this much depends on cultivation—attention to the subject extending over a considerable period of time.
The volume, or loudness, of a sound depends on the size of the vibrations, just as one feels a blow from a large object, other things being equal, more than from a small one. The ear drum-head is in the case of a large sound beaten, as it were, more powerfully. The singers that give us bigness of sound instead of quality belabor our ears, so to speak; they treat us as persons of mean understanding—dull intellects; the thing is essentially vulgar.
The quality of a sound is determined by the form of the vibrations. A sound of good quality is to the ear what a beautiful statue or picture is to the eye. As will be explained later, the form or quality depends largely on the shape, etc., of the resonance-chambers above the vocal bands.