Section 29 of 36 - Table of Contents
CHAPTER XXIX SPEAKING AND HEARING [Illustration: FIG. 193.--The vibration of the vocal cords produces the sound of the human voice.] 275. Speech. The human voice is the most perfect of musical instruments. Within the throat, two elastic bands are attached to the windpipe at the place commonly called Adam's apple; these flexible bands have received the name of vocal cords, since by their vibration all speech is produced. In ordinary breathing, the cords are loose and are separated by a wide opening through which air enters and leaves the lungs. When we wish to speak, muscular effort stretches the cords, draws them closer together, and reduces the opening between them to a narrow slit, as in the case of the organ pipe. If air from the lungs is sent through the narrow slit, the vocal cords or bands are thrown into rapid vibration and produce sound. The pitch of the sound depends upon the tension of the stretched membranes, and since this can be altered by muscular action, the voice can be modulated at will. In times of excitement, when the muscles of the body in general are in a state of great tension, the pitch is likely to be uncommonly high. Women's voices are higher than men's because the vocal cords are shorter and finer; even though muscular tension is relaxed and the cords are made looser, the pitch of a woman's voice does not fall so low as that of a man's voice since his cords are naturally much longer and coarser. The difference between a soprano and an alto voice is merely one of length and tension of the vocal cords. Successful singing is possible only when the vocal cords are readily flexible and when the singer can supply a steady, continuous blast of air through the slit between the cords. The hoarseness which frequently accompanies cold in the head is due to the thickening of the mucous membrane and to the filling up of the slit with mucus, because when this happens, the vocal cords cannot vibrate properly. The sounds produced by the vocal cords are transformed into speech by the help of the tongue and lips, which modify the shape of the mouth cavity. Some of the lower animals have a speaking apparatus similar to our own, but they cannot perfectly transform sound into speech. The birds use their vocal cords to beautiful advantage in singing, far surpassing us in many ways, but the power of speech is lacking. 276. The Ear. The pulses created in the air by a sounding body are received by the ear and the impulses which they impart to the auditory nerve pass to the brain and we become conscious of a sound. The ear is capable of marvelous discrimination and accuracy. "In order to form an idea of the extent of this power imagine an auditor in a large music hall where a full band and chorus are performing. Here, there are sounds mingled together of all varieties of pitch, loudness, and quality; stringed instruments, wood instruments, brass instruments, and voices, of many different kinds. And in addition to these there may be all sorts of accidental and irregular sounds and noises, such as the trampling and shuffling of feet, the hum of voices, the rustle of dress, the creaking of doors, and many others. Now it must be remembered that the only means the ear has of becoming aware of these simultaneous sounds is by the condensations and rarefactions which reach it; and yet when the sound wave meets the nerves, the nerves single out each individual element, and convey to the mind of the hearer, not only the tones and notes of every instrument in the orchestra, but the character of every accidental noise; and almost as distinctly as if each single tone or noise were heard alone."--POLE. [Illustration: FIG. 194.--The ear.] 277. The Structure of the Ear. The external portion of the ear acts as a funnel for catching sound waves and leading them into the canal, where they strike upon the ear drum, or tympanic membrane, and throw it into vibration. Unless the ear drum is very flexible there cannot be perfect response to the sound waves which fall upon it; for this reason, the glands of the canal secrete a wax which moistens the membrane and keeps it flexible. Lying directly back of the tympanic membrane is a cavity filled with air which enters by the Eustachian tube; from the throat air enters the Eustachian tube, moves along it, and passes into the ear cavity. The dull crackling noise noticed in the ear when one swallows is due to the entrance and exit of air in the tube. Several small bones stretch across the upper portion of the cavity and make a bridge, so to speak, from the ear drum to the far wall of the cavity. It is by means of these three bones that the vibrations of the ear drum are transmitted to the inner wall of the cavity. Behind the first cavity is a second cavity so complex and irregular that it is called the labyrinth of the ear. This labyrinth is filled with a fluid in which are spread out the delicate sensitive fibers of the auditory nerves; and it is to these that the vibrations must be transmitted. Suppose a note of 800 vibrations per second is sung. Then 800 pulses of air will reach the ear each second, and the ear drum, being flexible, will respond and will vibrate at the same rate. The vibration of the ear drum will be transmitted by the three bones and the fluid to the fibers of the auditory nerves. The impulses imparted to the auditory nerve reach the brain and in some unknown way are translated into sound. 278. Care of the Ear. Most catarrhal troubles are accompanied by an oversupply of mucus which frequently clogs up the Eustachian tube and produces deafness. For the same reason, colds and sore throat sometimes induce temporary deafness. The wax of the ear is essential for flexibility of the ear drum; if an extra amount accumulates, it can be got rid of by bathing the ear in hot water, since the heat will melt the wax. The wax should never be picked out with pin or sharp object except by a physician, lest injury be done to the tympanic membrane. 279. The Phonograph. The invention of the phonograph by Edison in 1878 marked a new era in the popularity and dissemination of music. Up to that time, household music was limited to those who were rich enough to possess a real musical instrument, and who in addition had the understanding and the skill to use the instrument. The invention of the phonograph has brought music to thousands of homes possessed of neither wealth nor skill. That the music reproduced by a phonograph is not always of the highest order does not, in the least, detract from the interest and wonder of the instrument. It can reproduce what it is called upon to reproduce, and if human nature demands the commonplace, the instrument will be made to satisfy the demand. On the other hand, speeches of famous men, national songs, magnificent opera selections, and other pleasing and instructive productions can be reproduced fairly accurately. In this way the phonograph, perhaps more than any other recent invention, can carry to the "shut-ins" a lively glimpse of the outside world and its doings. [Illustration: FIG. 195.--A vibrating tuning fork traces a curved line on smoked glass.] The phonograph consists of a cylinder or disk of wax upon which the vibrations of a sensitive diaphragm are recorded by means of a fine metal point. The action of the pointer in reporting the vibrations of a diaphragm is easily understood by reference to a tuning fork. Fasten a stiff bristle to a tuning fork by means of wax, allowing the end of the point to rest lightly upon a piece of smoked glass. If the glass is drawn under the bristle a straight line will be scratched on the glass, but if the tuning fork is struck so that the prongs vibrate back and forth, then the straight line changes to a wavy line and the type of wavy line depends upon the fork used. In the phonograph, a diaphragm replaces the tuning fork and a cylinder (or a disk) coated with wax replaces the glass plate. When the speaker talks or the singer sings, his voice strikes against a delicate diaphragm and throws it into vibration, and the metal point attached to it traces on the wax of a moving cylinder a groove of varying shape and appearance called the "record." Every variation in the speaker's voice is repeated in the vibrations of the metal disk and hence in the minute motion of the pointer and in the consequent record on the cylinder. The record thus made can be placed in any other phonograph and if the metal pointer of this new phonograph is made to pass over the tracing, the process is reversed and the speaker's voice is reproduced. The sound given out in the this way is faint and weak, but can be strengthened by means of a trumpet attached to the phonograph. [Illustration: FIG. 196.--A phonograph. In this machine the cylinder is replaced by a revolving disk.]Prev Next All
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