Sidebilder
PDF
ePub

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 qualities or properties of malleability, fusibility, solubility, permeability, and the like.

C 2

Perrepion is a no

[merged small][merged small][merged small][merged small][ocr errors]
[ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][merged small]

Ø 17. Nature and importance of the senses as a source of knowledge.

It 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.

[ocr errors][ocr errors]

0 18. Connexion of the brain with sensation and perception. (I.) It may perhaps be asked, Whether these views are 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 or perception of roughness.

CHAPTER III.

THE SENSES OF SMELL AND TASTE.

[ocr errors][merged small]

§ 17. Nature and importance of the senses as a source of knowledge.

It 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.

0 18. Connexion of the brain with sensation and perception. (I.) It may perhaps be asked, Whether these views are 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 or perception of roughness.

« ForrigeFortsett »