Part 17 (1/2)

THE EAR,

through which we receive those sensations which we call sound

[Illustration: FIG 133--Diagra 133 is a purely diagra the various parts distorted and out of proportion Beginning at the left, we have the _outer ear_, the lobe, to gather in the sound-waves on to the membrane of the tympanum, or drum, to which is attached the first of a series of _ossicles_, or s in the _inner ear_, a cavity surrounded by the bones of the head Inside the inner ear is a watery fluid, P, called _perily water”), i _endolymph_ (”inside water”), also full of fluid Into this fluid project E E E, the ter to the brain

When sound-waves strike the tympanum, they cause it to move inwards and outwards in a series of rapid movements The ossicles operated by the ty O, covered by a htly squeeze the perilymph, which in turn compresses the endolyraphs a sensation of sound to the brain

In Fig 134 we have a h still not in their actual proportions, the components of the ear

The ossicles M, I, and S are respectively the _malleus_ (hammer), _incus_ (anvil), and _stapes_ (stirrup) Each is attached by ligaments to the walls of the middle ear The tympanum moves the malleus, theinto the opening O of Fig 133, which is scientifically known as the _fenestra ovalis_, or ovalAs liquids are practically inco in of the oval, the round , also covered with a membrane When the stapes pushes the oval es out, its elasticity sufficing to put a certain pressure on the perilymph (indicated by the dotted portion of the inner ear)

[Illustration: FIG 134--Diagra the various parts]

The inner ear consists of two main parts, the _cochlea_--so called from its resemblance in shape to a snail's shell--and the _semicircular canals_ Each portion has its perilymph and endolymph, and contains a number of the nerve-ends, which are, however, most numerous in the cochlea We do not know for certain what the functions of the canals and the cochlea are; but it is probable that the foruish between the _intensity_ or loudness of sounds and the direction from which they come, while the latter enables us to determine the _pitch_ of a note In the cochlea are about 2,800 tiny nerve-ends, called the _rods of Corti_ The norive about 33 rods to the sereat scientist Helmholtz has advanced the theory that these little rods are like tiny tuning-forks, each responding to a note of a certain pitch; so that when a string of a piano is sounded and the air vibrations are transmitted to the inner ear, they affect only one of these rods and the part of the brain which it serves, and we have the impression of one particular note It has been proved by experiuish between sounds varying in pitch by only 1/64th of a see of any one Corti fibre This difficulty Hel that in such an ear two adjacent fibres are affected, but one ood ear” for music is presumably one whose Corti rods are very perfect Unlucky people like the gentlenize one tune, and that because people took off their hats when it commenced, are physically deficient Their Corti rods cannot be properly developed

What applies to one single note applies also to the elements of a musical chord A dozen notes may sound simultaneously, but the ear is able to assimilate each and blend it with its fellows; yet it requires a very sensitive and well-trained ear to pick out any one part of a harmony and concentrate the brain's attention on that part

The ear has a es over eleven octaves, but little le octave is possible to the latter The quickest vibrations which strike the eye, as light, have only about twice the rapidity of the slowest; whereas the quickest vibrations which strike the ear, as a musical sound, have more than two thousand tiures, the ordinary ear is sensitive to vibrations ranging from 16 to 38,000 per second The bottom and top notes of a piano make respectively about 40 and 4,000 vibrations a second Of course, some ears, like some eyes, cannot comprehend the whole scale The squeak of bats and the chirrup of crickets are inaudible to sos are able to hear sounds far too shrill to affect the hu part of this wonderful organ is the ty its tension auto our ears” to catch a shrill sound, we tighten theready” for a deep, loud report like that of a gun, we allow the dru 134) communicates with the mouth Its function is probably to keep the air-pressure equal on both sides of the drum When one catches cold the tube is apt to beco unequal pressure and consequent partial deafness

Before leaving this subject, it will be well to remind our more youthful readers that the ear is delicately as well as wonderfullyinto the ear, or a playful blow,the ty it in communication with the inner ear

MUSICAL INSTRUMENTS

These are contrivances for producing sonorous shocks following each other rapidly at regular intervals Musical sounds are distinguished froularity If we shake a nuet only a series of superimposed and chaotic sensations On the other hand, if we strike a tuning-fork, the air is agitated a certain number of times a second, with a pleasant result which we call a note

We will begin our excursion into the region of musical instruments with an examination of that very familiar piece of furniture,

THE PIANOFORTE,

which ” By reat nuisance, the ser-up of tireeably occupied, and is accordingly shown raph or a musical-box Yet the modern piano is a very clever piece of work, admirably adapted for the production of sweet enerally used are the _upright_, with vertical sound-board and wires, and the _grand_, with horizontal sound-board[27]

THE VIBRATION OF STRINGS

As the pianoforte is a stringed instruiven to the subject of the vibration of strings A string in a state of tension emits a note when plucked and allowed to vibrate freely The _pitch_ of the note depends on several conditions:--(1) The dia; (3) the length of the string; (4) the substance of the string Taking them in order:--(1) The number of vibrations per second is inversely proportional to the dia one-quarter of an inch in diaiven tihth of an inch in dia the same, the number of vibrations is directly proportional to the _square root_ of the _tension_: thus, a string strained by a 16-lb weight would vibrate four tiht (3) The nuth_ of the string: thus, a one-foot string would vibrate twice as fast as a two-foot string, strained to the saht

(4) Other things being equal, the rate of vibration is inversely proportional to the square root of the _density_ of the substance: so that a steel ould vibrate th, and tension These facts are ied instru a heavy weight froh tension, and yield a distinct note if struck But the volume of sound will be very small, much too s itself is so li air Now hang the wire froreatly increased, because the string has transe surface of the board

To get the full sound-value of the vibrations of a string, we evidently ought to sosurface In a violin this is effected by straining the strings over a ”bridge” resting on a hollow boxThe loud sound heard proceeds not fro only, but also from the whole surface of the box