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. Much discussion has taken place from time to time as to the nature of the larynx as a musical instrument, some being inclined to regard it as most closely allied to a stringed instrument, others to a wind-instrument. It has obviously points of resemblance to both, but the most recent researches make it clearer than ever that it is neither one nor the other, strictly speaking, but that it stands in a class by itself. It is, however, helpful, in considering many questions, to bear in mind its resemblances to both wind and stringed instruments. The vocal bands are not wholly free throughout their length, like the strings of a violin, nor do they bear any great resemblance to the reed of such an instrument as the clarinet, but as in the latter the force causing the vibrations is a blast of air. We have already pointed out that the vocal bands are set into vibration solely by the _expiratory_ blast of air. THE LARYNGOSCOPE.