VOICE, SPEECH, AND GESTURE. I. THE VOICE. GENERAL PRINCIPLES OF ACOUSTICS. WHEN a gong is struck, it is thrown into a series of vibrations, and, as a result, the surrounding ocean of air is set a-trembling. Each particle taps the one next to it, and thus the commotion, or ware, advances, much in the same way as it may do along a row of billiard balls, placed at short intervals, when the end ball is struck. This transference of vibration through the atmosphere is termed a sound-wave, which is thus purely physical in its nature. Let us now suppose the wave to strike upon the ear; an impression is flashed along the nerves of hearing to the brain, and a sound is heard. There are thus two kinds of sound, and it is very important to distinguish clearly between them-the sound of the natural philosopher, which is a purely physical phenomenon, and the sound of the mental philosopher, which is a purely psychical phenomenon. We may conveniently term the one "physical sound," and the other "psychical sound." Physical sound generally originates in the vibration of some solid body. It is thus that the human voice originates, viz., in the vibrations of the vocal chords. The sound-wave may be conducted not only through gaseous media like the atmosphere, but also through solids and liquids. Thus, by placing the ear to the earth, the clatter of distant horses' hoofs may be heard -a fact well known to the savage warrior. Similarly, a person with his head under water can distinctly hear the sounds produced outside; indeed, all sound-waves which strike the ear have to pass through a layer of fluid before they reach the auditory nerve. The fact that physical sound can be conducted through a solid medium is of practical interest to the physician. Let the ears be closed. Now strike a tuningfork and bring it into contact with the skull-the note will be distinctly heard, the sound reaching the auditory nerve through the solid skull. Now, if a deaf person can hear a tuning-fork when applied to the head in this way, we have proof positive that the nervous portion of the hearing organ is in working order, and that the fault must lie with that part whose function it is to receive the impression of the sound-wavewith the receptive apparatus. PITCH. The pitch of a sound depends upon the rapidity of the vibrations; the more rapid the rate of vibration, the higher the pitch. Only those vibrations within a certain range are capable of being perceived as sound-of producing the sensation of sound. Below a certain rate and above a certain rate they fail to arouse the hearing organ into activity-they fall, as it were, upon a deaf ear. Speaking generally, it is found that if the vibrations are more than 38,000 and less than 20,000 a second, they cannot be heard. There are some, however, whose upward range of perception is greater than this, just as there are others whose downward range is greater. The difference of people in this respect is very curious. "The squeak of a bat," writes Tyndall, "the sound of a cricket, even the chirrup of the common housesparrow, are unheard by some people who for lower sounds possess a sensitive ear." The same writer has referred to a case of short auditory range noticed by himself in crossing the Weregern Alp with a friend. "The grass on each side of the path swarmed with insects, which to me rent the air with their shrill chirruping. My friend heard nothing of this, the insect music lying beyond his limit of audition."+ Musical sound has a much more limited range than that indicated; vibrations below 40 and above 4,000 a second are not heard as musical tones, such sounds as they evoke being destitute of musical quality. The human voice ranges, on an average, over two octaves. It should be noticed that the speaking voice ranges in pitch as well as the singing voice. In ordinary speaking, pitch ranges within five notes, but it may be I made to extend over an octave. Individuals differ very considerably in the pitch of their speaking voice. In women and children it is about an octave higher than in men. The loudness of sound depends upon the amplitude of the vibrations. Thus, if a violin string be gently touched, it will yield a soft sound; but if the string be plucked some distance out of its position of rest and there let go, the sound produced will be much louder; for in the latter case the amplitude of vibration, or distance which the string travels on either side of its position of rest, will be much greater than in the former. It will be observed that the vibrations become less and less ample as the sound dies away; nevertheless, the rate remains the same, for otherwise the pitch of the sound would fall. In bass voices the vibrations of the vocal chords during loud phonation may sometimes actually be observed by means of the laryngoscope, the conditions in such cases being favourable for the observationnamely, slowness, together with considerable amplitude of vibration. TIMBRE. Timbre, or quality of tone, enables us to distinguish different sounds of the same pitch from one another. If the same note is sounded on the violin, organ, or piano, or uttered by the human voice, we can at once recognise the difference, even though the pitch is the same; and similarly, we can distinguish between the various vowel sounds. The explanation of timbre lies in the fact that musical sounds are not simple, but compound. Each note consists of a primary or fundamental set of vibrations, which determines the pitch, and of a number of superadded vibrations which determine the timbre. Thus the fundamental note of, let us say, the middle G is the same on any instrument, but the superadded sounds. are different in each case, and hence the difference in timbre. The vibrations which thus reinforce the primary vibrations are termed harmonics or overtones. Their production can, perhaps, be best understood in the case of strings. When a violin string is struck it vibrates as a whole, producing the fundamental note, but it also divides into a number of separate parts which vibrate independently, and it is these latter vibrations which yield the overtones. Now it will at once be seen that if we can by any means strengthen an overtone, or group of overtones, we can modify very considerably the timbre of a sound. This can be done, and is done, in the case both of musical instruments and of the human voice, the modification being effected by consonance and resonance, the latter of which, so far as the human voice is concerned, is the more important. CONSONANCE. Let a violin string be attached by one end to a horizontal rod (Fig. 1) and at the other end let a weight be suspended so as to stretch the string. If the string be now plucked, it will yield a faint, thin sound-a sound of small volume. If now the string be fixed in a violin. so as to be in connection with the sounding board, the note emitted by it when struck will be much louder. In the former case only a small surface of air comes in contact with the vibrating body; in the latter the |