Image unavailable: CRICKET. CICADA. VIOLIN. JEW’S HARP.CRICKET. CICADA. VIOLIN. JEW’S HARP.
Onthe 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.
Nextwe 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.
Image unavailable: VIBRATING STRINGS. ÆOLIAN HARP.VIBRATING STRINGS. ÆOLIAN HARP.
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.
Anapparatus 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.
Theaccompanying illustration is, in fact, a sort of chart as to the vibration of sound.
On the right is shown theÆolian Harp, with its upper lid raised, so as to show the structure of the strings. These are alltuned 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 thirdsad 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.
Inall 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, whichis, 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.
Image unavailable: TRACHEA OF SWAN. TROMBONE.TRACHEA OF SWAN. TROMBONE.
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.
Onthe 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.
Wehave already seen how the air-vibrations poured in at the small end of the trumpet can make resonant notes. We have now to see how the reverse process can be employed, and sounds poured into the larger end be conveyed to the ear.
Image unavailable: EAR-TRUMPET. CONCHA OF HUMAN EAR.EAR-TRUMPET. CONCHA OF HUMAN EAR.
The Ear-trumpet is a familiar example of such an instrument, and, as it is shown in the illustration, there is no need of further description. It is rather remarkable, by the way, that the length of tube does not seem to interfere with the conveyance of sound, as may be seen by the speaking-tubes which are now so common in private houses, hotels, and offices.
I know of one church in which there is a special seat for deaf persons. The reading-desk and pulpit are both fitted with the large ends of Ear-trumpets. From them pass tubes under the flooring, and so into the seat, where they can be applied to the ear of the deaf worshippers.
Onthe right hand is the “Concha,” as it is called, of the human ear, which is evidently constructed for the purpose of collecting and concentrating sounds. Instinctively, if we wishto near any sound more distinctly, we place the open hand behind the ear, so as to enlarge its receptive capacity, and send a greater volume of sound into the ear.
The well-known experiment of holding a shell to the ear so as to hear the murmur of the sea is due to the same cause, the shell collecting, though in a mixed manner, all the surrounding sounds, and making a murmur which really resembles the distant wash of the waves upon the shore.
Image unavailable: SAVAGE TAPPING TREE. SURGEON USING STETHOSCOPE.SAVAGE TAPPING TREE. SURGEON USING STETHOSCOPE.
Then, if we examine the various animals which need acute hearing, either to seize prey or escape from enemies, we shall find that they have large and mobile ears, which can be directed so as to catch the expected sound. The hare, rabbit, and deer are examples of the latter, while the former are well represented by the domestic cat, whose ears are always pricked forward when she hears the scratchings of a mouse.
Anothermost useful appliance is theStethoscope, which enables the skilful surgeon to investigate the interior of the body almost as clearly as if it were transparent. It is perfectly simple, being nothing but a trumpet-shaped piece of wood, formed as shown in the illustration. Sometimes it is hollow, and sometimes solid, but the result is the same,sound being transmitted through wood in a most remarkable manner.
For example, if one end of the longest scaffolding pole be slightly scratched with a pin, the sound will be distinctly heard by any one who places his ear against the other end, though the person who uses the pin can scarcely hear the sound himself. The surgeon, therefore, places the broad end of the Stethoscope upon the patient, and the other upon his ear, taps more or less lightly with his fingers, and by the sounds transmitted through the Stethoscope ascertains the condition of the internal organs.
Onthe left hand is an illustration of the mode in which the Australian savage, without the least idea of the theory of Acoustics, utilises the sound-conducting power of wood. If he wishes to know whether or not a hollow tree is tenanted by an animal of which he is in pursuit, he places his ear against the tree, taps it smartly with his tomahawk, and listens for the movement of the animal inside.
So delicate is this test, that it is employed even when the native is hunting for the large beetle-grubs on which they feed, and which are accounted a luxury even by Europeans, when they have once overcome the prejudice attaching itself to eating, without cookery, fat white grubs as thick and long as a man’s finger.
The Aye-aye is said to eat in exactly the same manner, tapping with its long finger the trunks and branches of trees and, if it hears a maggot inside, gnawing it out.
Oflate years we have had an instrument which enables us to measure the vibrations of sound as accurately as the barometer measures the weight of the atmosphere, the thermometer the temperature, and the photometer the power of light. This is the Siren, which is shown on the right hand of the accompanying illustration.
To explain this instrument fully would require ten times the space which we have at command, and necessitate a greatnumber of drawings. I will, therefore, endeavour to explain its principle in as brief terms as possible.
The reader will observe that at the lower part of the instrument there is a disc pierced with a number of holes, and that above these are two dials. Below the perforated disc, and therefore unseen, is a circular plate, also pierced with holes. When a pipe is attached to the lower part of the instrument, and air propelled through it, the disc begins to revolve, every revolution being recorded by the dials, after the fashion of the ordinary gas-meter.
Image unavailable: GNAT. HUMBLE-BEE. SIREN.GNAT. HUMBLE-BEE. SIREN.
As the pressure is increased, the air, passing through the holes, assumes a rhythmical beat, which soon becomes metamorphosed into musical notes. It is evident, therefore, that, by means of this instrument, the number of vibrations which produce a definite tone can be measured with absolute accuracy by any one who has an ear capable of appreciating a musical note.
It is by means of the Siren that the much-disputed tonic of C will be settled, the Continental and the English C being greatly at variance, and even the English C having been advanced almost a tone since the time of Handel. Much is it to be wished that Italy, the home of song, and England, the patron of song, could unite in their tonic, instead of having systems so widely different that an Italian singer is at a loss with the English pitch, as is an English singer with the Italian pitch.
The Siren is even brought into the service of entomologists, enabling them to measure by the sound the rapidity with which a flying insect moves its wings. By means of this instrumentwe know the origin of the sharp, piercing “ping” of the Gnat, and the heavy, dull boom of the Humble-bee, both of which insects are given in the illustration.
Before taking leave of this subject, I may mention that the instrument is called the Siren because it sings as well under water as in the air, provided that water instead of air be driven through it.
Ourlast page will be given to the phenomenon called by the name ofEcho, which consists in the power of solid substances, whether natural or artificial, of reflecting the waves of sound thrown against them, just as a mirror reflects the waves of light.
Image unavailable: WHISPERING GALLERY.WHISPERING GALLERY.
Very often the Echo is naturally formed, as shown in the illustration, by rocks which cast back the sound—waves thrown against them. This is the case in several parts of Dovedale in Derbyshire, where a pistol shot is reverberated backwards and forwards in a most wonderful manner, and a trumpet blast repeats itself over and over again.
At Walton Hall, the residence of the late C. Waterton, Esq., there is a wonderful Echo, nearly half a mile from the house. Mr. Waterton had discovered the Echo, which proceeded from the walls of the house, and, having found its focus, placed onit a large stone, called the Echo-stone. Any one sitting on this stone, and singing, speaking, or whistling towards the house, heard every sound repeated, as if in mockery.
The celebrated Whispering Gallery in St. Paul’s Cathedral is nothing but an ordinary Echo, though so intensified by the process of radiation, that the sound is transmitted from one side of the dome to the other, just as light or heat is reflected from concave mirrors.
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