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and th s is at once followed by a mental affection or ? 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. Stiil 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. We say 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 are 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 between them.

$ 62. Design and uses of the senses of smell and taste. It is not unprofitable to delay oftentimes, and contemplate the designs and uses which nature has in view in her works. Although the sense of smell may appear (and perhaps with sufficient reason) to be of less impor

tance than the other senses and the other parts of the animal economy, it is not without its ends. There is evidently design in the position of the organ in reference to the eilluvia, which are the direct subjects of its action, it being placed in the inside of the canal, where the air is continually forced in and out with every breath we draw The organ is precisely adapted, both in its nature and its place, to its appointed medium of communication with other bodies; nor is this the only mark of design attending it. This sense is frequently a source of gratification; and although it is less keen and powerful in men than in many inferior animals, it still has power enough to afford much assistance in this respect, that it often warns us of the presence of objects which experience has found to be injurious to us. The remark has been justly made, that the senses both of taste and smell are of great use in distinguishing bodies that cannot be distinguished by our other senses. They are peculiarly quick and exact in their judgments, especially in discerning, before we can ascertain it in any other way, the beginning and progress of those changes which all bodies are constantly undergoing.

But in both of these senses design and utility are discoverable in reference to food in particular. While the sense of smell guards the entrance of the canal for breathing, the sense of taste has its station at the entrance of the alimentary canal. Hence the food which we consume undergoes the scrutiny of both; an intentional and benevolent provision for protecting men and the animal creation generally against the introduction of what would be noxious to them.

CHAPTER IV.

THE SENSE OF HEARING.

Ø 63. Organ of the sense of hearing FOLLOWING the order which has been proposed, we are next to consider the sense of HEARING. And, in proceed

ing to the consideration of this subject, the reinark 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 at 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 bottom of the eye. Whether this nervous expansion be indispensably 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.

$ 64. Nature of sonorous bodies, and the medium of the communication

of sound. When we leave the bodily organ, and, looking outward, inquire still further for the origin of the sensations which we have by means of the ear, we find them attributable ultimately to the presence and influence of the substances around us.

Those undulations of air, which impinge upon the tympanum, and without which there is no sensation of sound, are caused by the vibrations or oscillations of the particles of certain bodies. The material substances which have this quality are termed sonorous, as wood, brass, iron, &c.; but it exists in different bodies ir very various degrees.

The quality of sonorousness, therefore, in any substance, is properly a susceptibility of motion among its own parts When it is forcibly struck, this motion exists first in itself, and is afterward communicated to the circumambient air The movement of the air which is thus caused, is agaii communicated, like the concentric waves of water agita ted by a stone thrown into it, to other portions successive ly, till it reaches the ear.

The air, accordingly, is the mediuin of communication, between the sonorous body and the tympa.juin of the ear It is true that many solid bodies are good conductors os sound as well as the atmosphere; but as portions of air, through which the vibratory motion must of course pass, are in all cases interposed between that organ and the sounding body, it is not necessary to dwell upon them here. It is sufficient for our present purpose merely to understand, that there is in every sounding body, in the first place, a vibratory motion among its own particles from some cause or other; that this vibration or undulation is communicated from the sounding body to the air, and from one portion of air to another, till it reaches the organ of hearing. Why the internal sensation should at once follow the completion of this process is another inquiry, which we do not undertake to explain. We have before us the antecedent and the consequent, the affection of the organ of hearing by an outward impulse, and the new mental state within ; but the reason of this invariable connexion in two things that are entirely distinct and different, is a matter beyond our limited comprehension

$ 65. 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

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fect, 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

It, is the same in respect to the sensations of sound These sensations exhibit the greatest variety, although the differences are too minute to be separated 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 direc tion, 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 medium, 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.

$ 66. Manner in which we learn the place of sounds. It is a fact worthy of notice in respect to sounds, that we should not know, previous to all experience on the sub

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