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 ordered it.

§ 13. 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 a 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 organs of sense, and which is referred by us to something external as its cause.

§ 14. Perception makes us acquainted with a material world. 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 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 colour, and harmony of sound, but it would seem to be wholly inward The mind would seem to constitute everything; 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.

§ 15. 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. It is hardly necessary to ay, 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 state here, that the qualities of materiał 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 reason already distinctly referred to, 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 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.

§ 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 it 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 colour, may possess also, in relation to other bodies, the qualitics or properties of malleability, fusibility, solubility, permeability, and the like.

C 2

CHAPTER III.

THE SENSES OF SMELL AND TASTE.

17. Nature and importance of the senses as a source of knowledge. Ir is desirable to keep clearly in mind the precise relation 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 he were the only being in existence.

◊ 18. Connexion of the brain with sensation and perception (1.) It may perhaps be asked, Whether these views ae 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 a: perception of roughness.