CHAPTER VII.
OF THE SENSE OF HEARING.
As the sense of hearing, as well as that of seeing, gives us perceptions of remote objects, so it is subject to similar errors, and may deceive us, when we cannot rectify by the touch, the ideas which it excites. It communicates no distinct intelligence of the distance from whence a sounding body is heard: a great noise far off, and a small one near, produce the same sensation, and, unless we receive aid from some other sense, we can never distinctly tell whether the sound be a great or a small one. It is not till we have, by experience, become acquainted with any particular sound that we can judge of the distance from whence we hear it; but if, for example, we hear the sound of a bell, we are at no great loss to determine its distance, any more than we are of that of a cannon from the report, judging in both cases from similar sounds, which we have been previously acquainted with.
Every body that strikes against another produces a sound which is simple in bodies non-elastic, but is often repeated in such as are elastic. If we strike a bell, a single blow produces a sound, which is repeated while the sonorous body continues to vibrate. These undulations succeed each other so fast, that the ear supposes them one continued sound; whereas, in reality, they form many. A circumstance of this kind happened to myself, for lying on the bed half asleep, I distinctly counted five strokes of the hammer upon the bell of the clock, and rising immediately found it was but the hour of one, and was convinced by examining the machinery that it had struck no more. A person, therefore, who should for the first time, hear the toll of a bell, would very probably be able to distinguish these breaks of sound; and, in fact, we can readily ourselves perceive remission in sounds.
Sounding bodies are of two kinds; those unelastic ones, which being struck, return but a single sound; and those more elastic returning a succession of sounds, which uniting together form a tone. This tone may be considered as a number of sounds produced one after the other by the same body, as we find in a bell, which continues to sound for some time after it is struck. A continuing tone may be also produced from a non-elastic body, by repeating the blow quick and often, as when we beat a drum, or draw a bow along the string of a fiddle.
Considering the subject in this light, we shall find the number of blows or quickness of repetition will have no effect in altering the tone, but only make it more even or more distinct, whereas if we increase the force of the blow by striking the body with double the weight, this will produce a tone twice as loud as the former. From hence we may infer, that all bodies give a louder and graver tone, not in proportion to the number of times they are struck, but to the force that strikes them. And if this be so, those philosophers who make the tone of a sonorous body, a bell, or the string of an harpsichord, for instance, to depend upon the number only of its vibrations, and not the force, have mistaken what is only an effect for a cause. A bell, or an elastic string, can only be considered as a drum beaten; and the frequency of the blows can make no alteration whatsoever in the tone. The largest bells, and the longest and thickest strings, have the most forcible vibrations; and, therefore, their tones will be more loud and more grave in proportion to the size and weight of the body with which they are struck.
If we strike a body incapable of vibration with a double force, or a double mass of matter, it will produce a sound doubly grave. Music has been said, by the ancients, to have been first invented from the blows of different hammers on an anvil. Suppose then we strike an anvil with a hammer of one pound weight, and then with a hammer of two pounds, it is plain that the latter will produce a sound twice as grave as the former. But if we strike with a two pound hammer, and then with a three pound, the last will produce a sound only one third more grave than the former. If we strike with a three, and then with a four, it will likewise follow that the latter will be a quarter part more grave than the former. Now, in the comparing between all those sounds, it is obvious that the difference between one and two is more easily perceived than between two and three, three and four, or any numbers succeeding in the same proportion. The succession of sounds will be, therefore, pleasing in proportion to the ease with which they may be distinguished. That sound which is double the former, or in other words, the octave to the preceding tone, will be the most pleasing harmony. The next to that, which is as two to three, will be most agreeable. And thus universally, those sounds whose differences may be most easily compared are the most agreeable.
It is most certain that the cause of pleasure in all our senses originates from the justness of proportion, and that disproportion never creates a pleasing sensation. The lad whom Mr. Chesselden restored to sights was at first most delighted with those objects which were regular and smooth on the surface; from this it is plain that the ideas we entertain of beauty from the eye originates from regularity and proportion; it is the same with the sense of feeling, smooth, round, and uniform bodies are more pleasing than those which are rough and irregular; why should not therefore the same preference be given by the ear to the proportion of sounds?
Sound has, in common with light, the property of being extensively diffused; and also admits of reflection. The laws of this reflection, it is true, are less understood: all we know is, that sound is reflected by hard bodies, and that their being hollow, sometimes increases the reverberation. A wall or a mountain sometimes reflects sounds so distinct that we are almost induced to suppose it proceeds from them rather than from an opposite quarter. Vaults and hollow rocks also produce distinct echoes.
The internal part of the ear is particularly formed for reflecting sounds, and may, in some measure, be compared to the cavern of a rock. In this cavity sounds are repeated, and by that means conveyed to the membranous part of the lamina, which being an expansion of the auditory nerves transmits them to the mind. The internal cavity of the ear, which is fashioned out in the temporal bone, like a cavern cut into a rock, seems to be fitted for the purposes of echoing sound with the greatest precision.
One of the most common complaints in old age is deafness, which probably proceeds from the rigidity of the nerves in the labyrinth of the ear, augmenting as we advance in years, and when the membranous part of the lamina becomes ossified deafness is the consequence, and is in that case incurable. It sometimes happens from a stoppage of the wax, but it may then be relieved by art. In order to know whether the defect be an internal or art external one, let the deaf person put a repeating watch into his mouth, and if he hears it strike, he may be assured that his disorder proceeds from an external cause, and may be, in some measure, relieved.
It often happens, that people with bad voices, and unmusical ears, hear better with one ear than the other, and suspecting there might be some analogy between the ears and eyes, as those who squint have more strength in one eye than the other, I made several experiments, and always found their defect in judging properly of sounds proceeded from the inequality of their ears, and their receiving by both at the same time unequal sensations, and those persons who hear false also sing false, without knowing it. They also frequently deceive themselves with regard to the side from whence the sound comes, generally supposing the noise to come on the part of the best ear. This, however, is only applicable to those who are born with a defect in the hearing.
Such as are hard of hearing reap the same advantage from the trumpet made for this purpose that short-sighted persons do from concave glasses. As the sight is affected with age so is the hearing, and equally requires the assistance of art. Trumpets for assisting hearing might be easily enlarged, so as to increase sounds, in the same manner that the telescope does bodies; but they could be used to advantage only in places of solitude and stillness, as the neighbouring sounds would mix with the more distant ones, and the whole would produce in the ear nothing but tumult and confusion.
Hearing is a much more necessary sense to man than to any other animal. In the latter it is only a warning against danger, or an encouragement to mutual assistance. In man, it is the source of most of his pleasures, and without it the rest of his senses would be of little benefit. A man born deaf must necessarily be dumb, and his whole sphere of knowledge must be bounded by sensual objects. We shall here notice a singular instance of a young man, who, born deaf, at the age of 24 suddenly acquired the faculty of hearing. The account, which is given in the Memoirs of the Academy of Sciences, 1703, page 18, is in substance as follows:
"A young man, of the town of Chartres, aged about 24, the son of a tradesman, who had been deaf and dumb from his birth, began to speak of a sudden, to the utter astonishment of the whole town. He gave his friends to understand, that for three or four months before, he had heard the sound of the bells, and was greatly surprised at this new and unknown sensation. After some time a kind of water issued from his left ear, and he then heard perfectly well with both. During these three months he listened attentively to all he heard, and accustomed himself to speak softly the words pronounced by others. He laboured hard in perfecting himself in the pronunciation, and in the ideas attached to every sound. At length, supposing himself qualified to break silence, he declared that he could speak, though as yet but imperfectly. Soon after some able divines questioned him concerning his ideas of his past state, and principally with respect to God, his soul, the moral beauty of virtue and deformity of vice. Of these, however, he did not appear to have the slightest conception. He had gone to mass indeed with his parents, had learned to sign himself with the cross, to kneel down, and to assume all the external signs of devotion; but he did all this without comprehending the intention or the cause. He had no idea even of death, but led a life of pure animal instinct, and though entirely taken up with sensual objects, and such as were present, he yet did not seem to have made any reflections upon them. The young man was not, however, in want of understanding, but the understanding of a man deprived of all intercourse with society is so very confined, that the mind is, in some measure, totally under the control of its immediate sensations."
It is possible, nevertheless, to communicate ideas to deaf men, and even to give them precise notions of general subjects, by means of signs, and by writing. A person born deaf, may be taught to read, to write, and even by the motion of the lips to understand what is said to him; a plain proof how much the senses resemble, and may supply the defects of each other.
On this subject it may not be improper to quote a fact, of which I was myself a witness. One M. Pereire, a native of Portugal, who had made it his particular study to teach persons born deaf and dumb, brought to my house a young man who was thus unhappily circumstanced. He was at the age of nineteen, in the month of July, 1746, when M. Pereire undertook to teach him to speak and read. More than four months had not elapsed, when he was capable of pronouncing syllables and words; and in the space of ten months, he perfectly understood, and could, with tolerable distinctness, pronounce about thirteen hundred different words. This education, so favourably begun, was interrupted for nine months by the absence of the master; who then found him far less intelligent than he had left him. His pronunciation was vitiated, and of the words he had learned most of, he retained not the smallest remembrance. M. Pereire accordingly renewed his instructions in the month of February, 1748; and from that time he never left him till June 1749. At one of the meetings of the French Academy this young man was brought them, and had several questions proposed to him in writing. To these his answers, whether written or verbal, were highly satisfactory. His pronunciation, indeed, was slow, and the sound of his voice was harsh; but at these defects there is little cause to wonder, as it is by imitation alone that our organs are enabled to form precise, soft, and well-articulated sounds, and, as this young man was deaf, he could not be expected to imitate what he did not hear; but which harshness, by the assiduity and skill of his master, might, however, in some degree, be corrected afterwards.
In the above case, the expedition of the master, and the progress of the pupil, who indeed seemed to be no wise deficient in point of natural ability and understanding, are an ample proof, that persons born deaf and dumb may, by art, be brought to converse with other men; and I am persuaded that, had this young man been instructed so early as at the age of seven or eight, he would have attained as great a number of ideas as mankind possess in general.