General Science Part 24

270. The Individuality of Instruments. It has been shown that a piano string when struck by a hammer, or a violin string when bowed, or a mandolin string when plucked, vibrates not only as a whole, but also in segments, and as a result gives forth not a simple tone, as we are accustomed to think, but a very complex tone consisting of the fundamental and one or more overtones. If the string whose fundamental note is lower C (128 vibrations per second) is thrown into vibration, the tone produced may contain, in addition to the prominent fundamental, any one or more of the following overtones: C', G'', C'', E'', C''', etc.

The number of overtones actually present depends upon a variety of circ.u.mstances: in the piano, it depends largely upon the location of the hammer; in the violin, upon the place and manner of bowing.

Mechanical differences in construction account for prominent and numerous overtones in some instruments and for feeble and few overtones in others. The oboe, for example, is so constructed that only the high overtones are present, and hence the sound gives a "pungent" effect; the clarinet is so constructed that the even-numbered overtones are killed, and the presence of only odd-numbered overtones gives individuality to the instrument. In these two instruments we have vibrating air columns instead of vibrating strings, but the laws which govern vibrating strings are applicable to vibrating columns of air, as we shall see later. It is really the presence or absence of overtones which enables us to distinguish the note of the piano from that of the violin, flute, or clarinet. If overtones could be eliminated, then middle C, or any other note on the piano, would be indistinguishable from that same note sounded on any other instrument. The fundamental note in every instrument is the same, but the overtones vary with the instrument and lend individuality to each. The presence of high overtones in the oboe and the presence of odd-numbered overtones in the clarinet enable us to distinguish without fail the sounds given out by these instruments.

The richness and individuality of an instrument are due, not only to the overtones which accompany the fundamental, but also to the "forced" vibrations of the inclosing case, or of the sounding board.

If a vibrating tuning fork is held in the hand, the sound will be inaudible except to those quite near; if, however, the base of the fork is held against the table, the sound is greatly intensified and becomes plainly audible throughout the room.

The vibrations of the fork are transmitted to the table top and throw it into vibrations similar to its own, and these additional vibrations intensify the original sound. Any fork, no matter what its frequency, can force the surface of the table into vibration, and hence the sound of any fork will be intensified by contact with a table or box.

This is equally true of strings; if stretched between two posts and bowed, the sound given out by a string is feeble, but if stretched over a sounding board, as in the piano, or over a wooden sh.e.l.l, as in the violin, the sound is intensified. Any note of the instrument will force the sounding body to vibrate, thus reenforcing the volume of sound, but some tones, or modes of vibration, do this more easily than others, and while the sounding board or sh.e.l.l always responds, it responds in varying degree. Here again we have not only enrichment of sound but also individuality of instruments.

271. The Kinds of Stringed Instruments. Stringed instruments may be grouped in the following three cla.s.ses:--

_a_. Instruments in which the strings are set into motion by hammers--piano.

_b_. Instruments in which the strings are set into motion by bowing--violin, viola, violoncello, double ba.s.s.

_c_. Instruments in which the strings are set into motion by plucking--harp, guitar, mandolin.

[Ill.u.s.tration: FIG. 186.--1, violin; 2, viola; 3, violoncello; 4, double ba.s.s.]

_a_. The piano is too well known to need comment. In pa.s.sing, it may be mentioned that in the construction of the modern concert piano approximately 40,000 separate pieces of material are used. The large number of pieces is due, partly, to the fact that the single string corresponding to any one key is usually replaced by no less than three or four similar strings in order that greater volume of sound may be obtained. The hammer connected to a key strikes four or more strings instead of one, and hence produces a greater volume of tone.

_b_. The viola is larger than the violin, has heavier and thicker strings, and is pitched to a lower key; in all other respects the two are similar. The violoncello, because of the length and thickness of its strings, is pitched a whole octave lower than the violin; otherwise it is similar. The unusual length and thickness of the strings of the double ba.s.s make it produce very low notes, so that it is ordinarily looked upon as the "ba.s.s voice" of the orchestra.

_c_. The harp has always been considered one of the most pleasing and perfect of musical instruments. Here the skilled performer has absolutely free scope for his genius, because his fingers can pluck the strings at will and hence regulate the overtones, and his feet can regulate at will the tension, and hence the pitch of the strings.

Guitar and mandolin are agreeable instruments for amateurs, but are never used in orchestral music.

[Ill.u.s.tration: FIG. 187.--A harp.]

272. Wind Instruments. In the so-called wind instruments, sound is produced by vibrating columns of air inclosed in tubes or pipes of different lengths. The air column is thrown into vibration either directly, by blowing across a narrow opening at one end of a pipe as in the case of the whistle, or indirectly, by exciting vibrations in a thin strip of wood or metal, called a reed, which in turn communicates its vibrations to the air column within.

The shorter the air column, the higher the pitch. This agrees with the law of vibrating strings which gives high pitches for short lengths.

[Ill.u.s.tration: FIG. 188.--Open organ pipes of different pitch.]

The pitch of the sound emitted by a column of air vibrating within a pipe varies according to the following laws:

1. The shorter the pipe, the higher the pitch.

2. The pitch of a note emitted by an open pipe is one octave higher than that of a closed pipe of equal length.

3. Air columns vibrate in segments just as do strings, and the tone emitted by a pipe of given length is complex, consisting of the fundamental and one or more overtones. The greater the number of overtones present, the richer the tone produced.

273. How the Various Pitches are Produced. With a pipe of fixed length, for example, the clarinet (Fig. 189, 1), different pitches are obtained by pressing keys which open holes in the tube and thus shorten or lengthen the vibrating air column and produce a rise or fall in pitch. Changes in pitch are also produced by variation in the player's breathing. By blowing hard or gently, the number of vibrations of the reed is increased or decreased and hence the pitch is altered.

[Ill.u.s.tration: FIG. 189--1, clarinet; 2, oboe; 3, flute.]

In the oboe (Fig. 189, 2) the vibrating air column is set into motion by means of two thin pieces of wood or metal placed in the mouthpiece of the tube. Variations in pitch are produced as in the clarinet by means of stops and varied breathing. In the flute, the air is set into motion by direct blowing from the mouth, as is done, for instance, when we blow into a bottle or key.

The sound given out by organ pipes is due to air blown across a sharp edge at the opening of a narrow tube. The air forced across the sharp edge is thrown into vibration and communicates its vibration to the air within the organ pipe. For different pitches, pipes of different lengths are used: for very low pitches long, closed pipes are used; for very high pitches short, open pipes are used. The mechanism of the organ is such that pressing a key allows the air to rush into the communicating pipe and a sound is produced characteristic of the length of the pipe.

[Ill.u.s.tration: FIG. 190.--1, horn; 2, trumpet; 3, trombone.]

[Ill.u.s.tration: FIG. 191.--1, kettledrum; 2, ba.s.s drum; 3, cymbals.]

[Ill.u.s.tration: FIG. 192.--The seating arrangement of the Philadelphia orchestra.]

In the bra.s.s wind instruments such as horn, trombone, and trumpet, the lips of the player vibrate and excite the air within. Varying pitches are obtained partly by the varying wind pressure of the musician; if he breathes fast, the pitch rises; if he breathes slowly, the pitch falls. All of these instruments, however, except the trombone possess some valves which, on being pressed, vary the length of the tube and alter the pitch accordingly. In the trombone, valves are replaced by a section which slides in and out and shortens or lengthens the tube.

274. The Percussion Instruments. The percussion instruments, including kettledrums, ba.s.s drums, and cymbals, are the least important of all the musical instruments; and are usually of service merely in adding to the excitement and general effect of an orchestra.

In orchestral music the various instruments are grouped somewhat as shown in Figure 192.

CHAPTER XXIX

SPEAKING AND HEARING

[Ill.u.s.tration: 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 coa.r.s.er. 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 hoa.r.s.eness 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 surpa.s.sing 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 pa.s.s 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, bra.s.s 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.

[Ill.u.s.tration: 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 ca.n.a.l, 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 ca.n.a.l 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 pa.s.ses 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 acc.u.mulates, 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.

[Ill.u.s.tration: FIG. 195.--A vibrating tuning fork traces a curved line on smoked gla.s.s.]