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appropriate orga; (2.) The change or sensation in the mind; and, (3.) The reference of the sensation to the external body as its cause.
22. Of the sense and the sensations of taste
The tongue,. which is covered with numerous nervous papillæ, forms essentially the organ of taste, although the papillæ are found scattered in other parts of the cavity of the mouth. The application of any sapid body to this organ immediately causes in it a change or affection; and that is at once followed by a mental affection or a new state of the mind. In this way we have the sensations and perceptions, to which we give the names sweet, bitter, sour, acrid, &c.
Having experienced the inward sensation, the affections of the mind are then referred by us to something external as their cause. We do not, however, always, nor even generally, distinguish the qualities which constitute this cause by separate and appropriate designations; but express them by the names that are employed for the internal feeling, viz., sweetness, bitterness, sourness, &c. This reference of what is internally experienced to its external cause is very rapidly made; so that we at once say of one apple it is sweet, and of another it is sour. Still it is to be kept in mind, that, in point of fact, it is subsequent, both in the order of nature and of time, to the mere sensation; although we may not be able, in consequence of its rapidity, to mark distinctly the progress of the mental action from the one to the other. As in the case of smells, which have already been remarked upon, the reference is the result of our former experience.
of one body it is sweet, and of another it is sour, beCause we have ever observed that the mental states indicated by those terms have always existed in connexion with the presence of those bodies.
Whenever, therefore, we say of any bodies that they ar sweet, bitter, sour, or apply any other epithets expressive of sapid qualities, we mean to be understood to say that such bodies are fitted, in the constitution of things, to cause in the mind the sensations of sweetness, bitterness, and sourness, or other sensations expressed by
denominations of taste. Or, in other words, that they are the established antecedents of such mental states, as there is, further than this, no necessary connexion be tween them.
THE SENSE OF HEARING.
23. Organ of the sense of hearing.
FOLLOWING the order which has been proposed, we are next to consider the sense of HEARING. And, in proceeding to the consideration of this subject, the remark is a very obvious one, that we should be unable to hear if we had not a sense designed for, and appropriate to, that result. The air, when put strongly in motion, is distinctly perceived by the touch; but no impression which it could make on that sense would cause that internal feeling which is termed a sensation of sound. Our Creator, therefore, has taken care that these sensations shall have their own organ; and it is obviously one of precise and elaborate workmanship.
The ear is designedly planted in a position where, with the greatest ease, it takes cognizance of whatever is going on in the contiguous atmosphere. When we examine it externally, we not only find it thus favourably situated, but presenting a hollowed and capacious surface, so formed as to grasp and gather in the undulations of air, continually floating and in motion around it. Without, however, delaying to give a minute description of the internal construction of the ear, which belongs rather to the physiologist, it will answer our present purpose merely to add, that these undulations are conducted by it through various windings, till they are brought in a state of concentration, as it were, against the membrane called the TYMPANUM.-It is worthy of notice, that on the internal surface of this membrane (the drum, as it is popularly called) there is a nerve spread out in a manner analogous to the expansion of the optic nerve at the bot
tom of the eye. Whether this nervous expansion be in dispensably necessary to the result or not, it is certain that a pressure upon or affection of the tympanum by the external air, is followed by a new state of the mind, known as the sensation or perception of sound.
24. Varieties of the sensation of sound.
The sensations which we thus become possessed of by the hearing are far more numerous than the words and the forms of speech, having relation to them in different languages, would lead us to suppose. It will help to illustrate this subject if we recur a moment to the sense of TASTE. The remark has somewhere been made to this effect, and probably with much truth, that if a person were to examine five hundred different wines, he would hardly find two of them of precisely the same flavour. The diversity is almost endless, although there is no language which distinguishes each variety of taste by a separate name. It is the same in respect to the sensations of sound. These sensations exhibit the greatest variety, although their differences are too minute to be separately and distinctly represented by language.
These views will appear the less objectionable when it is remembered that sounds differ from each other both in the tone and in the strength of the tone. It is remarked by Dr. Reid, that five hundred variations of tone may be perceived by the ear, also an equal number of variations in the strength of the tone; making; as he expressly informs us, by a combination of the tones and of the degrees of strength, more than twenty thousand simple sounds, differing either in tone or strength.
In a perfect tone, a great many undulations of elastic air are required, which must be of equal duration and extent, and follow each other with perfect regularity. Each undulation is made up of the advance and retreat of innumerable particles, whose motions are all uniform in direction, force, and time. Accordingly, there will be varieties also and shades of difference in the same tone, arising from the position and manner of striking the sonorous body, from the constitution of the elastic medi um, and from the state of the organ of hearing.
Different instruments, such as a flute, a violin, and a bass-viol, may all sound the same tone, and yet be easily distinguishable. A considerable number of human voices may sound the same note, and with equal strength, and yet there will be some difference. The same voice, while it maintains the proper distinctions of sound, may yet be varied many ways by sickness or health, youth or age, and other alterations in our bodily condition to which we are incident.
25. Manner in which we learn the place of sounds.
It is a fact particularly worthy of notice in respect to sounds, that we should not know, previous to all experience on the subject, whether a sound came from the right or left, from above or below, from a smaller or greater distance. And this will appear the less surprising when we remember that the undulations of air are always changed from their original direction by the channels and the windings of the ear before they strike the tympanum. Abundant facts confirm this statement.
Dr. Reid mentions, that once, as he was lying in bed, having been put into a fright, he heard his own heart beat. He took it to be some one knocking at the door, and arose and opened the door oftener than once before he discovered that the sound was in his own breast. Some traveller has related that, when he first heard the roaring of a lion in a desert wilderness, not seeing the animal, he did not know on what side to apprehend danger, as the sound seemed to him to proceed from the ground, and to enclose a circle, of which he and his companions stood in the centre.
It is by custom or experience that we learn to distinguish the place of things, and, in some measure also, their nature, by means of their sound. It is thus that we learn that one noise is in a contiguous room, that another is above our heads, and another is in the street. And what seems to be an evidence of this is, that when we are in a strange place, after all our experience, we very frequently find ourselves mistaken in these respects
If a man born deaf were suddenly made to hear, he would probably consider his first sensations of sound as
originating wholly within himself. But in process of time we learn not only to refer the origin of sounds to a position above or below, to the right or left; but to connect each particular sound with a particular external cause, referring one to a bell as its appropriate external cause, another to a flute, another to a trumpet.
THE SENSE OF TOUCH.
◊ 26. Of the sense of touch in general and its sensations. WE are next to consider the sense of TOUCH. principal organ of this sense is the hand, although it is not limited to that part of our frame, but is diffused over the whole body. The hand principally arrests our attention as the organ of this sense, because, being furnished with various articulations, it is easily moveable by the muscles, and can readily adapt itself to the various changes of form in the objects to which it is applied.
The senses, which have hitherto been examined, are more simple and uniform in their results than that of the touch. By the ear we merely possess that sensation which we denominate hearing; we have the knowledge of sounds, and that is all. By the palate we acquire a knowledge of tastes, and by the sense of smelling we become acquainted with the odours of bodies. The knowledge which is directly acquired by all these senses is limited to the qualities which have been mentioned By the sense of touch, on the contrary, we become acquainted not with one merely, but with a variety of qualities, such as the following, heat and cold, hardness and softness, roughness and smoothness, solidity or resistance, extension, and figure; and, in particular, it gives occasion for the origin of the antecedent and more general notion of externality.
§ 27. Idea of externality suggested in connexion with the touch. If man were possessed of the sense of smell alone, it would be found that the earliest elements of his knowl