The String and Reed.
It has previously been mentioned that all sounds are owing to vibrations of the air. But there are many ways of producing these vibrations, and each mode gives a different quality of tone. We have already seen, by means of the drum, how sound is produced by percussion. We shall now see how sounds can be produced by the vibrations of a String.
If the string of a bow be pulled and smartly loosed, the result is a distinctly musical sound, higher or lower according to the length and tension of the string. Perhaps some of my readers may recall the passage in Homer’s “Odyssey,” where Ulysses strings the fatal bow:—
“Heedless he heard them; but disdained reply,
The bow perusing with exactest eye.
Then, as some heavenly minstrel, taught to sing
High notes responsive to the trembling string,
To some new strain when he adapts the lyre,
Or the dumb lute refits with vocal wire,
Relaxes, strains, and draws them to and fro;
So the great master drew the mighty bow,
And drew with ease. One hand aloft displayed
The bending horns, and one the string essayed.
From his essaying hand the string let fly,
Twanged short and sharp, like the shrill swallow’s cry.”
The Harp is, in fact, nothing but a magnified bow, with a number of strings of graduated length and tension. Some very beautiful experiments have been made on this subject by the Rev. Sir F. A. G. Ouseley, Professor of Music at Oxford, who stretched a string of sixty-four feet in length, and found that although, when vibrating, it must produce a note, there was no human ear that could distinguish it. Yet, if combined with other musical instruments, it would probably do its work well. The theory of the vibrations will be briefly described on another page.
These vibrations may be produced in various manners. The string may be pulled with the fingers, as in the harp, the guitar, the zither, or even the violin, &c., in pizzicato passages.
The old harpsichord, now an instrument vanished into the shadows of the past, pulled the strings with little strips of quill, acting like the thumb-ring of the zither-player. The “plectrum” of the ancients acted in the same manner, and the Japanese have at the present day a sort of guitar played with a plectrum. I have heard it, but cannot particularly admire the effect, the notes appearing to be without feeling, and as if they were played on a barrel-organ.
Sometimes, as in our modern pianos, the strings are struck by hammers instead of being pulled by fingers, plectrum, or goose-quill.
The most ingenious mode of causing musical vibration is the Bow, which is too familiar to need a detailed description. Suffice it to say that it really is a modified bow, the place of the string being supplied by a flat band of horsehair, which is drawn over the string, and so causes it to vibrate. In order to enable the bow to grip the string, it is rubbed with resin almost as often as a billiard-player chalks his cue.
Some skill is required even in producing a sound by the bow. It looks as if any one could do it, but a novice, if he extorts any sound at all, never rises above a squeak. When I took my first violin lessons, nearly thirty years ago, I was so horrified at the discordant sounds elicited from the instrument, that I retired to the topmost garret of the house in order not to hurt any one’s feelings except my own.
On the left hand of the illustration is seen a well-known example of the imitation of Nature by Art. This is the common Cricket, whose loud shrill call is more familiar than agreeable.
Some years ago, while engaged on my “Insects at Home,” I gave much time to the examination of the structures by which such a sound can be produced. On the under side of the wing-covers, or “elytra,” as they are scientifically termed, are notched ridges, which, when examined with a moderate power of the microscope, have something of this appearance ~~~~~~~. The friction of these notches produces the musical sound, which, as the reader will see, is exactly analogous to the friction of the bow upon the string.
Next we come to the Vibrator, sometimes called the Reed. It is introduced into various musical instruments, such, for example, as the harmonium, the clarionet, the oboe, the bassoon, and various organ pipes.
The simplest form of the Vibrator is shown in the Jew’s Harp, as it is popularly called, though it is not a harp, and has nothing to do with Jews.
The word is really a mistaken pronunciation of “jaw’s harp,” because the instrument is held against the teeth, while its tongue is vibrated by strokes of the finger. These vibrations affect the air within the mouth, and, by expanding or contracting the mouth, the sound is lowered or raised according to the laws of Acoustics. Of course, the range of notes is very small, being limited to those of the common chord, and even they being attainable only by a practised performer. Very good effects, however, have been produced by means of a series of Jew’s Harps, set to different tones by loading the end of the tongue with sealing-wax or similar substances.
An apparatus constructed on the same principle is to be found in the vocal organs of the male Cicada. If one of these insects be examined on the lower surface, two curious and nearly circular flaps will be seen, just at the junction of the thorax with the abdomen. It is by the action of these two little vibrators that the insect is able to produce a sound so loud, that in calm weather it may be heard at the distance of a mile.
The accompanying illustration is, in fact, a sort of chart as to the vibration of sound.
On the right is shown the Æolian Harp, with its upper lid raised, so as to show the structure of the strings. These are all tuned to the same note, the present D being generally accepted as being most free from false tuning, and less liable for the errors of “temperament.” Several of the strings are an octave lower than the others, but the tonic is always the same.
The instrument is placed in a current of air, generally in a window, with the sash let down upon it, and the air-currents set the strings vibrating in a most wonderful manner.
There is no need for human fingers to touch them, but they automatically divide themselves into the component parts of the common chord, and produce octaves, fifths, and thirds ad infinitum.
On the left hand of the same illustration is exhibited a string of the same length and tension, vibrating in two different ways. The upper figure shows it divided into three portions, each of which gives the fifth above the tonic, and all of which, when sounding simultaneously, give a fulness and richness to the tone which could only be attained otherwise by three distinct instruments. All players of stringed instruments know how invaluable are these harmonics, without which many passages of well-known music could not be played, and which are produced by “damping,” and not pressing the strings.
So, if the string be lightly touched, or damped at the crossing portion at either end, the result will be that the string divides itself into three portions, and all three resound simultaneously.
The lower string is vibrating in thirds, having divided itself into four portions. If it were damped in the middle, it would divide itself into two portions, and sound octaves.
The subject is a most interesting one, but our space is nearly exhausted, and we must pass to another branch of it.
In all brass instruments furnished with a mouthpiece, and not with a reed, the notes are obtained by vibrations of the enclosed air, caused by the movement of the lips. They are all set to some definite tonic, sometimes C natural, but mostly to a flat tone, such as B flat or E flat.
Taking the ordinary military trumpet or bugle as an example, we have (when we have learned how to play it), first, the tonic. By alteration of the lips we get the octave above the tonic. Then comes the fifth; then the third, which is, in fact, another octave; and then a few other notes, the truth of which depends on the ear of the player.
Now, all these notes are obtained by means of the lips, which set the column of air vibrating, and divide it into harmonics. The apparently complicated bugle-calls of the army are nearly all formed from four notes only, i.e. (taking C as the tonic) C G C E G.
The Trombone, which is shown on the right hand of the illustration, has the advantage of being lengthened at will, and thus giving the performer a fresh tonic, and consequently another series of harmonics. Valved and keyed instruments have a similar advantage, the one acting by lengthening, and the other by shortening, the column of air. The former is infinitely the better plan, as it sets more harmonics vibrating, and consequently gives a greater richness of tone.
A familiar example of this is to be found in the Ophicleide and Euphonium. The former is eight feet in total length, and alters its tonic by eleven keys, which shorten the column of air. The latter is of the same length, but, by the employment of valves, can be made sixteen feet in length. Consequently the euphonium has practically killed the ophicleide, just as the ophicleide killed the serpent. The cornet-à-pistons, the brass contra-basso, the flugel horn, the tenor sax-horn, &c., are all constructed on the same principle.
On the left hand of the illustration is shown the wonderful apparatus by means of which the Swan produces its far-resounding cry. The windpipe, or “trachea,” as it is technically named, passes down the neck, protected by the bones, until it reaches the chest. There it leaves them, enters the cavity of the chest, and contorts itself in such a manner as to obtain greater length, just as is the case with the trombone and valved instruments.