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which they might be to come in contact. shown in an experiment which was once made at Flor

A quantity of water was enclosed in a gold ball, which, on the most violent pressure, could not be made to fill ihe internal cavity until the water inside was forced through the pores,

There is reason also for that part of the arrangement which includes DIVISIBILITY. We cannot conceive of a particle so small as not to be susceptible of division. And to that small particle must belong, not only divisibility, but the qualities of solidity, extension, and figure.

Ø 16. Of the secondary qualities of matter. The SECONDARY qualities of bodies are of two kinds. (1.) Those which have relation to the perceiving and sentient mind; (2.) Those which have relation to other bodies.

Under the first class are to be included sound, colour, taste, smell, hardness and softness, heat and cold, roughness and smoothness, &c. When we say of a body it has sound, we imply in this remark that it possesses qualities which will cause certain effects in the mind; the term sound being applicable, by the use of language, both to the qualities of the external object and to the effect produced within. When we say ic has colour, we always make a like reference to the mind, which beholds and contemplates it; and it is the same of the other secondary qualities of this description.

The other class of secondary qualities, (or properties, as they are not unfrequently termed,) those which have relation to other material bodies, are exceedingly various and numerous. The material substance which, in relation to the mind, possesses the qualities of sound and col. our, may possess also, in relation to other bodies, the qual. itics or properties of malleability, fusibility, solubility, permeability, and the like.





010. Nature and importance of the senses as a source of knowledgs.

It is desirable to keep clearly in mind the precise re lation of the senses to the origin, progress, and amount of our knowledge, and to possess, if possible, a correct understanding of their true value. In a certain sense, the possession of the bodily organs with which we are furnished, is not essential and prerequisite to the possession of that knowledge which we are accustomed to ascribe to them. There is nothing unwarrantable and unreasonable in the supposition, that the knowledge which we now have by their means might have been possessed without their aid, either immediately, or in some way altogether different. Their use and indispensableness in the acquisition of a certain portion of what men are permitted to know, is a matter of arrangement and appointment on the part of our Maker. It is undoubtedly an evidence of the correctness of this remark, that the Supreme Being has a full acquaintance with all those outward objects which present themselves to our notice, without being indebted to any material instrumentality and mediation. He perceives in another way, or, rather, all knowledge is inherent in, and originally and unalterably essential to himself.

It is not so, as we have reason to believe, with any other beings, and certainly not with man. Although a great part of his knowledge relates to material things, he is so formed, and his constitution is so ordered, that he is wholly dependent for it on the senses.-Deprive him of the ear, and all nature becomes silent; deprive him of the

eye, and the sun and moon withdraw their light, and the universe becomes darkened; deprive him of the sense of touch, and he is then entirely insulated, and as much cut off from all communication with others as if be were the only being in existence.

g 18. Connexion of the brain with sensation and perception (I.) It may perhaps be asked, Whether these views 2.e intended to exclude the brain, as having a connexion with the senses in the results which are here ascribed to them? And this inquiry leads us to observe, (what has been before alluded to, that the brain is a prominent organ in the material part of the process of sensation and of external perception. The senses evidently cannot be separated from the nervous system. But the substance which is found in the nerves, excepting the coat in which it is enveloped, is the same as in the brain, being of the same soft and fibrous texture, and in continuity with it As a general statement, when the brain has been in any way injured, the inward sensation, which would otherwise be distinct on the presence of an external body, is imperfect. Also, if the nerve be injured, or if its continuity be disturbed by the pressure of a tight ligature, the effect is the same; a circumstance which goes to confirm the alleged identity of substance in the two.

(II.) The brain, therefore, and whatever of the same substance is in continuity with it, particularly the nerves, constitutes the sensorial organ, which, in the subordinate organs of taste, smell, sight, touch, and hearing, presents itself under different modifications to external objects. On this organ, the sensorial, as thus explained, an impression must be made before there can be sensation and perception.

An impression, for instance, is made on that part of the sensorial organ called the auditory nerve, and a state of mind immediately succeeds which is variously termed, according to the view in which it is contemplated, either the sensation or the perception of sound.

An impression is made by the rays of light on that 'expansion of the optic nerve which forms what is called the RETINA of the eye, and the intellectual principle is immediately brought into that new position, which is termed visual perception or a perception of sight.

The hand is impressed on a body of an uneven and rough surface, and immediately consequent on this application and pressure is that state of mind which is termed a sensation o' perception of roughness.

$ 19. Order in which the senses are to be considered. In considering those ideas which we become possessed of by means of the senses, it is natural to begin with that sense which will cause us the least difficulty in the analysis of its results; and to proceed to others successively: as we find them increasing in importance. It may not be altogether easy to apply this principle with strictness, but it will answer all the purpose for which it is here introduced, if we consider the senses in the following order, the smell, taste, hearing, touch, and sight.

The mind holds a communication with the material world by means of the sense of smelling. All animal and vegetable bodies (and the same will probably hold good of other bodies, though generally in a less degree) are continually sending out effluvia of great subtilty, These small particles are rapidly and widely scattered abroad in the neighbourhood of the body from which they proceed. No sentient being can come within the circumference occupied by these continually moving and volatile atoms, without experiencing effects from it.

$ 20. Of the sense and sensations of smell. The medium through which we have the sensations and perceptions of smell, is the organ which is termed the olfactory nerve, situated principally in the nostrils, but partly in some continuous cavities. When some odoriferous particles, sent from external objects, affect this organ, there is a certain state of mind produced which varies with the nature of the odoriferous bodies. But we can no more infer from the sensation itself merely, that there exists any necessary connexion between the smell and the external objects, than that there exists a connexion between the emotions of joy and sorrow and the same obe jects. It might indeed be suggested to us by the change in our mental states, that there must be some cause or antecedent to the change, but this suggestion would be far from implying the necessity of a corporeal cause.

(II.) How then does it happen, that we are not merely sensible of the particular sensation, but refer it at once to sole external object, to the rose, or the honeysuckle ? In answer it may be remarked, it' we had always been

destitute of the senses of sight and touch, this reference never could have been made; but, having been furnished with them by the beneficent Author of our being, we ipake this reference by experience. When we have seen the rose, when we have been near to it and handled it, we have uniformly been conscious of that state of mind which we term a sensation of smell. When we have come into the neighbourhood of the honeysuckle, or when it has been gathered and presented to us, we have been reminded of its fragrance. And thus, having learned by experience that the presence of the odoriferous body is always attended with the sensations of smell, we form the habi of attributing the sensations to that body as their cause

$ 21. Of perceptions of smell in distinction from sensativns. The mental reference spoken of in the last section is made with almost as much promptness as if it were necessarily involved in the sensation itself. It is at least so rapid, that we find ourselves utterly unable to mark the mind's progress from the inward feeling to the conception of the outward cause. Nor is this inability surpri. sing, when we consider that we have repeated this pro cess, both in this and in analogous cases, from our earli est childhood. No object has ever been present to u: capable of operating on the senses, where this process ha: not been gone through. The result of this long-continued and frequent repetition has been an astonishing quicka ness in the mental action; so much so that the mind leaps outward with the rapidity of lightning, to be present with, and to comprehend the causes of the feeling within.

This view, it will be seen, helps in illustrating the nature of PERCEPTION as distinguished from sensation. The outlines of that distinction have already been given; and every one of the senses, as well as that now under consideration, will furnish proofs and illustrations of it. Aco cordingly, when we are said to perceive the smell, or to have perceptions of the smell of a body, the rapid process which has been described is gone through, and the three things which were involved in the lefinition of Perception, already given, are supposed to exist; (1.) The presence of the odoriferous bosly and the affection of its

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