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wardly objects of touch and sight; nor has it form or im age
in any sense which we can conceive of. When, there fore, 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 anything as extended, it is not to be supposed that the thought itself has extension; wher we behold and admire the varieties of colour, 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 anything 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 sensation 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."*
• Reid's Intellectual Powers, Essay ii.
$59. The upozion between the mental and physical change no.
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 connexion between mind and matter in this case as we do in all others. All we know and all we can state with confidence is, that a mental affection is immediately subsequent to an affection or change which is physical. Such is our nature, and such the appointment of Him who made it.
$ 52. Of the 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 acts of the mind itself, and thei agreement or disagreement. Accordingly, we per ceive a tree in the forest or a ship at sea ; and we perceive, also, that an emotion is not a volition, and that reasoning is something different from mere perception. But what we have to say here does.not con.
cern internal perception, but merely that which re. lates to objects'exterior to the mind. Perception, using the term ir
, 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
It will be recollected that the term SENSATION, when applied to the mind, expresses merely the state of the mind, without reference to anything 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
car... ries 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 colour 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 Aattering 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.
Ø 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 have no direct knowledge of the subjective or real essence of matter. Our direct knowledge embraces its qualities or properties, and nothing more. Without proposing to enter into a minute examination of them, it will be proper to recall the 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 pressure, 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 DIVISIBIL-TY 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 54. 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.