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The eye is a natural organ of sight, by which we see; but the natural organ sees as little as the artificial."

Among other things illustrative of the correctness of what has been said, there is this consideration also. The opinion, that sensation is in the organ or some other material part and not in the soul, is inconsistent with the fundamental and indisputable doctrine of mental identity. "When I say, I see, I hear, I feel, (says the same judicious author,) this implies, that it is one and the same self that performs all these operations. And as it would be absurd to say that my memory, another man's imagination, and a third man's reason may make one individual intelligent being; it would be equally absurd to say, that one piece of matter seeing, another hearing, and a third feeling, may make one and the same percipient being."*

Although the opinion, that sensation is not in the mind but in the body, is unfounded, it is perhaps not surprising, that such a belief should have arisen. If the hand be palsied, there is no sensation of touch; if the ear be stopped, there is no sensation of hearing; if the eye be closed, there is no vision; hence it happens that when we have these sensations, we are led to think of the organ or part of the bodily system, with the origin of which they are connected. When we feel a pain arising from an external cause, it is a natural, and often a useful curiosity, which endeavors to learn the particular place in the body which is affected. This, which we are generally able to ascertain, always arrests our attention more or less. In this way we gradually form a very strong association; and almost unconsciously transfer the place of the inward sensation to that outward part, with which we have so frequently connected it in our thoughts. Although this is clearly a mere fallacy, the circumstance of its being a plausible and tenacious one renders it the more necessary to guard against it.

§. 50. Sensations are not images or resemblances of objects.

But while we are careful to assign sensations their true place in the mind, and to look upon what is outward in the body as merely the antecedents or causes of them, it is a mat* Reid's Intellectual Powers, Essay II.

ter of some consequence to guard against a danger directly the reverse of that which has been remarked on. We are apt to transfer to the sensation, considered as existing in the mind, some of those qualities which belong to the external object. But in point of fact our sensations are by no means copies, pictures, or images of outward objects; nor are they representations of them in any material sense whatever; nor do they possess any of their qualities.

It is true, we often think it otherwise; constantly occupied with external objects, when in the act of contemplation we retire within the mind, we unwarily carry with us the form and qualities of matter, and stamp its likeness on the thought itself. But the thought, whatever it may by the constitution of our nature be the sign of, has no form, and presents no image analogous to what are outwardly objects of touch and sight; nor has it form or image in any sense, which we can conceive of. When, therefore, we have an idea of some object as round, we are not to infer from the existence of the quality in the outward object, that the mental state is possessed of the same quality; when we think of any thing as extended, it is not to be supposed, that the thought itself has extension; when we behold and admire the varieties of color, we are not at liberty to indulge the presumption, that the inward feelings are painted over, and radiant with corresponding hues. There is nothing of the kind, and the admission of such a principle would lead to a multitude of errors.

This subject is illustrated in the following manner by Dr. Reid, whom we have already had repeated occasion to refer to on the subject before us."Pressing my hand with force against the table, I feel pain, and I feel the table to be hard. The pain is a sensation of the mind, and there is nothing that resembles it in the table. The hardness is in the table, nor is there any thing, resembling it in the mind. Feeling is applied to both; but in a different sense; being a word common to the act of sensation, and to that of perceiving by the sense of touch.

"I touch the table gently with my hand, and I feel it to be smooth, hard, and cold. These are qualities of the table perceived by touch; but I perceive them by means of a sensa

tion which indicates them. This sensation not being painful, I commonly give no attention to it. It carries my thought immediately to the thing signified by it, and is itself forgotten, as if it had never been. But by repeating it, and turning my attention to it, and abstracting my thought from the thing signified by it, I find it to be merely a sensation, and that it has no similitude to the hardness, smoothness, or coldness of the table which are signified by it.

"It is indeed difficult, at first, to disjoin things in our attention which have always been conjoined, and to make that an object of reflection which never was so before; but some pains and practice will overcome this difficulty in those, who have got the habit of reflecting on the operations of their own minds.”*

§. 51. The connection between the mental and physical change not susceptible of explanation.

External bodies operate on the senses, before there is any affection of the mind, but it is not easy to say what the precise character and extent of this operation is. We know, that some object capable of affecting the organ must be applied to it in some way either directly or indirectly, and it is a matter of knowledge also, that some change in the organ actually takes place; but further than this, we are involved in uncertainty. All we can undertake to do at present is the mere statement of the facts, viz, the application of an external body, and some change in consequence of it in the organ of

sense.

Subsequently to the change in the organ, either at its extremity and outward developement or in the brain, with which it is connected, and of which it may be considered as making a part, a change in the mind or a new state of the mind immediately takes place. Here also we are limited to the mere statement of the fact. We here touch upon one of those boundaries of the intellect, which men are probably not destined to pass in the present life. We find ourselves unable to resolve and explain the connection between mind and matter in this case as we do in all others. state with confidence is, that a mental affection is immediately subsequent to an affection or change, which is physical.

All we know, and all we can

* Reid's Intellectual Powers, Essay II.

Such is our nature, and such the appointment of Him who made it.

§. 52. Of tho meaning and nature of perception.

We next come to the subject of PERCEPTION, which is intimately connected with that of sensation. This term like many others admits of considerable latitude in its application. In common language we are not only said to have the power of perceiving outward objects, but also of perceiving the agreement or disagreement in the acts of the mind itself. Accordingly we perceive a tree in the forest or a ship at sea, and we also perceive that the whole is greater than a part, and that the three angles of a triangle are equal to two right angles. But what we have to say here does not concern internal perception, but merely that, which relates to objects exterior to the mind.

Perception, using the term in its application to outward objects, differs from sensation, as a whole does from a part; it embraces more. It may be defined, therefore, an affection or state of the mind, which is immediately successive to certain affections of the organ of sense, and which is referred by us to something external as its cause.

It will be recollected that the term SENSATION, when applied to the mind, expresses merely the state of the mind without reference to any thing external, which might be the cause of it, and that it is the name of a truly simple feeling. Perception on the contrary is the name of a complex mental state, including not merely the internal affection of the mind, but also a reference to the exterior cause. Sensation is wholly within ; but Perception carries us, as it were, out of ourselves, and makes us acquainted with the world around us. It is especially by means of this last power, that material nature, in all its varieties of form and beauty, is brought within the range of our inspection. If we had but sensation alone, there would still be form and fragrance, and color, and harmony of sound, but it would seem to be wholly inward. The mind would then become not merely what Leibnitz supposed it to be, a mirror of the universe; it would be to us the universe itself; we could know no other world, no other form of being. Perception prevents the possibility of such a mistake; it undeceives and dissipates the flattering notion, that all things are

in the soul; it leads us to other existences, and in particular to the knowledge of the vast and complicated fabric of the material creation.

§. 53 Of the primary and secondary qualities of matter.

From what has been said, it will be noticed, that SENSATION implies the existence of an external material world as its cause, and that PERCEPTION implies the same existence both as cause and object. As, therefore, the material world comes now so directly and closely under consideration, it' seems proper briefly to advert to that subject. It is hardly necessary to say, that we are altogether ignorant of the subjective or real essence of matter. Our knowledge embraces merely its qualities or properties, and nothing more. Without proposing to enter into a minute examination of them, it' will be proper to recall to recollection here, that the qualities of material bodies have been ranked by writers under the two heads of Primary and Secondary.

The PRIMARY QUALITIES are known by being essential to the existence of all bodies. They are extension, figure, divisibility, and solidity; and some writers have included motion. They are called PRIMARY for the obvious reason, that all men embrace them in the notions which they form of matter, and that they are essential to its existence. All bodies have extension, all bodies have figure, all are capable of division, all possess the attribute of solidity.

By SOLIDITY in bodies, (perhaps some would prefer the term RESISTANCE,) is to be understood that quality, by which a body hinders the approach of others, between which it is interposed. In this sense even water, and all other fluids are solid. If particles of water could be prevented from separating, they would oppose so great resistance, that it would' be impossible for any two bodies, between which they might be, to come in contact. This was shown in an experiment, which was once made at Florence. A quantity of water" was enclosed in a gold ball, which on the most violent pres-" sure could not be made to fill the internal cavity, until the water inside was forced through the pores.-There is reason also for that part of the arrangement, which includes We cannot conceive of a particle so small as

DIVISIBILITY.

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