Lectures on the Philosophy of the Human Mind (Vol. 1 of 3)

by Thomas Brown

Footnotes

[79] Pope's Essay on Criticism, v. 374—381.

[80] Quintus Curtius, lib. v. cap. 7.

[81] Mart. Scrib. Book I. c. 7. with some exclusions.

[82] Page 98, 99.

[83] Gray de Princip. Cogit. lib. i. v. 64–80.

[LECTURE XXII.]

ON THE FEELINGS ASCRIBED TO THE SENSE OF TOUCH,—AND ANALYSIS OF THESE FEELINGS.

In my Last Lecture, Gentlemen, I finished the remarks which I had to offer, on our sense of hearing; and in the conclusion of it, had begun the consideration of a very important order of our feelings, those which belong to the sense of touch.

Of these, I may mention, in the first place, the sensations of heat and cold,—sensations that arise from affections of our nerves of touch, or at least from affections of nerves, which, as equally diffused and intermingled with them, it is impossible to distinguish from those which constitute our organ of touch, the same wide surface rendering us sensible, as it were, at every point of warmth as of pressure.

I have also remarked to you, how little analogy there is of our sensations of warmth, to the other sensations commonly ascribed to this organ; and the great difference of the feelings, has led some physiologists to believe, that the organs of sensations so different, must themselves be different. But even though the sensations were as dissimilar as is supposed, there is no reason a priori to believe,—and to experience, it is evident, that, in this case, we cannot appeal, so as to derive from it any ground for believing,—that sensations, which are very different, must arise from affections of different organs. As far, indeed, as we can safely appeal to experience, in this very case, there are sensations which we never hesitate in referring to our tactual nerves, as different from the more common sensations ascribed to touch, as the sensation of warmth itself. I allude to the pain of puncture or laceration of the skin. Indeed, if the brain be ultimately the great organ of all our sensations, it is evident that we must refer to affections of one sensorial organ, not the various feelings of touch only, but, with them the still greater variety of feelings, that constitute our sensations of smell, taste, sound, and colour.

But are we indeed sure, that there truly is that great dissimilarity supposed, or may not our belief of it arise from our reference to touch of sensations that truly do not belong to it? Such, at least, is the opinion, to which, I think, a nicer analysis will lead us. The primary original feelings, which we owe to our mere organ of touch, I consider as of a kind, all of which are far more analogous to the sensations of warmth, or of pain on puncture, than to the perceptions of form and hardness, which are generally regarded as tangible. Before entering on the analysis, however, it will be necessary to consider, what are the sensations which we are supposed to owe to this organ.

The sensations of heat and cold,—as received from our organ of touch,—we may almost lay out of account in our analytical inquiry. It is unnecessary to dwell on them, or even to repeat, in application to them, the argument, which has been already applied more than once to the sensations before considered. It is quite evident, that, in classing our warmth or chillness, as a sensation,—and not as a feeling that has arisen spontaneously in the mind,—we are influenced by that experience, which has previously given us the belief of objects external,—at least, of our own corporeal frame,—and that, if we had been unsusceptible of any other sensations, than those of heat and cold, we should as little have believed these to arise directly from a corporeal cause, as any of our feelings of joy or sorrow. The same remark may be applied to the painful sensations of puncture and laceration.

It is only to the other more important information ascribed to the sense of touch, therefore, that our attention is to be directed.

By touch, we are commonly said to be made acquainted with extension, magnitude, divisibility, figure, motion, solidity, liquidity, viscidity, hardness, softness, roughness, smoothness. These terms, I readily allow, are very convenient for expressing notions of certain forms or states of bodies, that are easily distinguishable. But, though specifically distinguishable, they admit generically of very considerable reduction and simplification. Hardness and softness, for example, are expressive only of greater or less resistance,—roughness is irregularity of resistance, when there are intervals between the points that resist, or when some of these points project beyond others,—smoothness is complete uniformity of resistance,—liquidity, viscidity, are expressive of certain degrees of yieldingness to our effort, which solidity excludes, unless when the effort employed is violent. All, in short, I repeat, are only different species or degrees of that which we term resistance, whatever it may be, which impedes our continued effort, and impedes it variously as the substances without are themselves various. Such is one order, then, of the feelings commonly ascribed to the sense which we are at present considering.

To proceed to the other supposed tangible qualities, before included in our enumeration,—figure is the boundary of extension, as magnitude is that which it comprehends; and divisibility, if we consider the apparent continuity of the parts which we divide, is only extension under another name. If we except motion, therefore, which is not permanent, but accidental,—and the knowledge of which is evidently secondary to the knowledge which we acquire of our organs of sense, before which the objects are said to move, and secondary in a much more important sense, as resulting not from any direct immediate organic state of one particular moment, but from a comparison of sensations past and present,—all the information, which we are supposed to receive primarily and directly from touch, relates to modifications of resistance and extension.

Though it is to the sense of touch, however, that the origin of the knowledge of these is generally ascribed, I am inclined to think, in opposition to this opinion, that in both cases, the reference is wrongly made,—that if we had the sense of touch only, we should not be sensible of resistance, nor, I conceive, even of extension,—and that we seem to perceive the varieties of extension and resistance immediately by touch only, because the simple original tactual feeling has become representative of these, in the same manner, and for the same reason, as we seem to perceive the varieties of distance immediately by the eye. The sense of touch has unquestionably, like all our other senses, its own peculiar feelings, though, for the simple original feelings, attached to the affections of this most extensive of organs, we have unfortunately no name, but that which is applied in popular, and even in philosophic language, to all the affections of the mind. Our joy or grief, hope or fear, love or hate, I before remarked, we term feelings, as readily and frequently, as we use this term to express our sensations of touch; and that, which, however restricted in its original meaning, is now the common name of our mental affections of every class, has, by this extension, unfortunately, become a very unfit one, for distinguishing a limited order of those affections.

Whatever be the term, which we may use, however, there is, and must be, a sensation peculiar to touch, without regard to the extent or quantity of the surface impressed,—as there is, in colour, a sensation peculiar to vision, without regard to the extent of the portion of the retina on which the light may have fallen. Every physical point of our organ of touch, when existing in a certain state, is capable of inducing in the mind a peculiar feeling, though no other physical point of the organ were affected,—as every physical point of the retina, though but a single ray of light were admitted to the eye, is capable of inducing in the mind a peculiar affection of vision; and when many such physical points are affected together, by some impressing surface, the form of which we think that we discover immediately by touch, it is from experience only that we can learn the vicinity of the physical points of our own tactual surface thus impressed, and consequently the continued extension of the object which impresses them. Before we have so much knowledge of external things, as to know even that we have any bodily organs whatever,—and it is of this state of absolute ignorance alone that we must think, as often as we speculate on the information which our senses separately afford,—when we know as little of our bodily frame, as of that material universe, of which we know nothing, we cannot, by the very terms of this supposition, know that different points of our organ of touch are affected in a certain manner,—that these points are contiguous to each other—and that the mass affecting these contiguous points must consequently itself be composed of points, that are, in like manner, contiguous. We know nothing of our organs—we know nothing of any external masses—but a certain feeling is excited in our mind; and it is this simple feeling alone, whatever it may be, which constitutes the direct elementary sensation of touch, though this simple elementary sensation, like many other sensations, may afterwards be so blended with other feelings, as to become significant of them, and even to seem to involve them, as if originally and necessarily coexisting.

It is impossible for us at present, indeed, to have a body impressed on us, without the immediate notion of something external and extended,—as it is impossible for one, whose sight is perfect, to open his eyes, in the light of day, without perceiving, as it were immediately, the long line of variegated landscape, in the scenery before him:—the one impossibility is exactly equal to the other; yet we know, in the case of vision, that all which we immediately perceive, at the very moment, when our eyes seem to comprehend the worlds of half infinity, in the hemisphere on Which we gaze, is a small expanse of light,—if even, which I greatly doubt, there truly be, in our original perceptions of this sense, so much of extension, as is implied in the smallest possible expanse. In touch, in like manner, I conceive, that the immediate sensation, though, like colour, it may now seem inseparable from extension and outness,—if, on the authority of Berkeley, I may venture to use that barbarous but expressive term,—was, like colour, originally distinct from them,—that, by the mere original sensations of this organ, in short, we could as little know the existence of an impressing body, as, by the mere original sensations of vision, we could learn that such a body existed at the extremity of the room in which we sit.

In defining sensation, when we began our inquiry into its nature, I stated it to be that affection of the mind, which is immediately subsequent to the affection of certain organs, induced by the action of external bodies; and I admitted, that, in this definition two assumptions were made,—the existence of foreign changeable external bodies, as separate from the mind,—and the existence of organs, also separate from the mind, and in relation to it truly external, like other bodies, but forming a permanent part of our corporeal frame, and capable of being affected, in a certain manner, by the other bodies, of which the existence was assumed. As far as our analytical inquiry has yet proceeded, these assumptions are assumptions still. We have not been able to detect, in the sensations considered by us, more than in any of our internal pleasures or pains, any circumstances that seem to be indicative of a material world without.

Our analytical inquiry itself, however, even in attempting to trace the circumstances, in which the belief originates, must proceed on that very belief. Accordingly, in examining our senses of smell, taste, and hearing, I uniformly took for granted the existence of odoriferous, sapid, and vibrating bodies, and considered merely, whether the sensations, excited by these, were, of themselves, capable of communicating to us any knowledge of the external and independent existence of the bodies which excited them.

In the present stage of our inquiry, I must, in like manner, take for granted the existence of bodies, which act, by their contiguity or pressure, on our organ of touch, as the odoriferous or sapid particles, act on our nerves of smell and taste—not that I assume this belief, as existing in the mind whose intellectual acquisitions are the subject of inquiry,—for, in that case, the inquiry itself would be superfluous. I assume it, merely as existing in the mind of us the inquirers,—and only, because it is impossible, without such an assumption to make the suppositions that are necessary for the inquiry. All our language is at present adapted to a system of external things. There is no direct vocabulary of scepticism; and even the most cautious and philosophic inquirer, therefore, must often be obliged to express his doubt, or his dissent, in language that implies affirmation. In the present case, when we attempt to analyse our sensations, it is impossible to speak of the circumstances in which the infant is placed, or, I may say even, to speak of the infant himself, without that assumption which we have been obliged to make. The real existence of an external universe, and the belief of that existence, are, however, in themselves, perfectly separate and distinct; and it is not the existence of an external world, which we are now endeavouring to establish as an object of belief. We are only endeavouring, in our analysis of the sensations afforded by our different organs, to ascertain in what circumstance the belief arises. There might be a world of suns and planets, though there were no human being, whose mind could be affected with belief of it; and even the most zealous defenders of the reality of external nature must admit, that, though no created thing but ourselves were in existence, our mind might still have been so constituted, as to have the very series of feelings, which form at present its successive phenomena, and which are ascribed in no small number to the action of external things.

Are the primary sensations derived from the organ of touch, then, of such a kind as to afford us that knowledge, which they are supposed to give of things without?

Let us imagine a being, endowed with the sense of touch, and with every other sense and faculty of our mind, but not with any previous knowledge of his own corporeal frame, or of other things external,—and let us suppose a small body, of any shape, to be pressed, for the first time, on his open hand. Whatever feelings mere touch can give, directly of itself, would of course be the same in this case, as now, when our knowledge is increased, and complicated, from many other sources.

Let the body, thus impressed, be supposed to be a small cube, of the same temperature with the hand itself, that all consideration of heat or cold may be excluded, and the feeling produced be as simple as possible.

What, then, may we suppose the consequent feeling to be?

It will, I conceive, be a simple feeling of the kind of which I have already spoken, as capable of arising from the affection of a single point of our organ of touch,—a feeling that varies indeed with the quantity of pressure, as the sensation of fragrance varies with the number of the odorous particles, but involves as little the notion of extension, as that notion is involved in the mere fragrance of a violet or a rose. The connection of this original tactual feeling, however, with that of extension, is, now, so indissoluble, as, indeed, it could not fail to become, in the circumstance in which it has uniformly arisen, that it is almost impossible to conceive it as separate. We may perhaps, however, make a near approach to the conception of it, by using the gentle gradual pressure of a small pointed body, which, in the various slight feelings, excited by it,—before it penetrate the cuticle, or cause any considerable pain,—may represent, in some measure, the simple and immediate effect, which pressure in any case produces,—exclusively of the associate feelings which it indirectly suggests.

Such of you, as have the curiosity to try the experiment, with any small bodies, not absolutely pointed,—such as the head of a pin, or any body of similar dimensions,—will be astonished to feel, how very slightly, if at all, the notion of extension or figure is involved in the feeling, even after all the intimate associations of our experience;—certainly far less than the notion of longitudinal distance seems to us to be involved in the immediate affections of our sense of sight. It is an experiment, therefore, which I must request you not to neglect to make.

But the pressure of such a large body, as the cube, which we have supposed to be pressed against our organ of touch, now awakens very different feelings. We perceive, as it were immediately, form and hardness. May not, then, the knowledge of resistance and extension, and consequently the belief of the essential qualities of matter,—be originally communicated by the affections of this organ?

The feeling of resistance,—to begin with this,—is, I conceive, to be ascribed, not to our organ of touch, but to our muscular frame, to which I have already more than once directed your attention, as forming a distinct organ of sense; the affections of which, particularly as existing in combination with other feelings, and modifying our judgments concerning these, (as in the case of distant vision, for example,) are not less important than those of our other sensitive organs. The sensations of this class, are, indeed, in common circumstances, so obscure, as to be scarcely heeded or remembered by us; but there is probably no contraction, even of a single muscle, which is not attended with some faint degree of sensation, that distinguishes it from the contractions of other muscles, or from other degrees of contraction of the same muscle. I must not be understood, however, as meaning that we are able, in this manner, by a sort of instinctive anatomy, to perceive and number our own muscles, and when many of them are acting together, as they usually do, to distinguish each from each; for, till we study the internal structure of our frame, we scarcely know more, than that we have limbs which move at our will, and we are altogether ignorant of the complicated machinery which is subservient to the volition. But each motion of the visible limb, whether produced by one or more of the invisible muscles, is accompanied with a certain feeling, that may be complex, indeed, as arising from various muscles, but which is considered by the mind as one; and it is this particular feeling, accompanying the particular visible motion,—whether the feeling and the invisible parts contracted be truly simple or compound,—which we distinguish from every other feeling accompanying every other quantity of contraction. It is as if a man, born blind, were to walk, for the first time, in a flower garden. He would distinguish the fragrance of one parterre from the fragrance of another, though he might be altogether ignorant of the separate odours united in each; and might even consider as one simple perfume, what was, in truth, the mingled product of a thousand.

Obscure as our muscular sensations are in common circumstances, there are other circumstances,—which I pointed out to you in treating before of this subject,—in which they make themselves abundantly manifest. I need not refer to the diseased state of the muscles, in which they become painfully sensible; and I will admit, that the reference to such a morbid state, in which the structure may be supposed to be altered by the disease, would perhaps scarcely be a fair one. It is sufficient to refer to phenomena of which every one must have been conscious innumerable times, and which imply no disease nor lasting difference of state. What is the feeling of fatigue, for example, but a muscular feeling? that is to say, a feeling of which our muscles are as truly the organ, as our eye or ear is the organ of sight or hearing. When a limb has been long exercised, without sufficient intervals of rest, the repetition of the contraction of its muscles is accompanied, not with a slight and obscure sensation, but with one which amounts, if it be gradually increased, to severe pain, and which before it arrives at this, has passed progressively through various stages of uneasiness. Even when there has been no previous fatigue, we cannot make a single powerful effort at any time, without being sensible of the muscular feeling connected with this effort. Of the pleasure which attends more moderate exercise, every one must have been conscious in himself, even in his years of maturity, when he seldom has recourse to it for the pleasure alone; and must remember, still more the happiness which it afforded him in other years, when happiness was of less costly and laborious production than at present. By that admirable provision, with which nature accommodates the blessings which she gives, to the wants that stand in need of them, she has, in that early period,—when the pleasure of mental freedom, and the ambitions of busy life, are necessarily excluded,—made ample amends to the little slave of affection, in that disposition to spontaneous pleasure, which renders it almost an effort to be sad, as if existence itself were delight; giving him a fund of independent happiness in the very air which she has poured around him, and the ready limbs which move through it, almost without his bidding. In that beautiful passage, in which Goldsmith describes the sounds that come in one mingled murmur from the village, who does not feel the force of the happiness which is comprised in the single line, that speaks of

“The playful children, just let loose from school?”[84]

It is not the mere freedom from the intellectual task of which we think; it is much more, that burst of animal pleasure, which is felt in every limb, when the long constraint that has repressed it is removed, and the whole frame is given once more to all the freedom of nature. It is by the pleasure of exertion, and the pain of inexertion, that we are roused from that indolence, into which, with great injury to society, that requires our contribution of active aid, we otherwise might sink;—as we are roused, in like manner, by the pleasure of food, and the pain of hunger, to take the aliment that is necessary for our individual sustenance; and though the mere aliment is, indeed, more important for life, it is not more important for happiness than that pleasure of activity which calls and forces us from our slothful repose.

“Thee, too, My Paridel,—I saw thee there,

Stretch'd on the rack of a too easy chair.”

With the same happy provision with which she has considered the young of our own species, Nature has, in the other animals, whose sources of general pleasure are still more limited than in the child, converted their muscular frame into an organ of delight. It is not in search of richer pasture that the horse gallops over his field, or the goat leaps from rock to rock; it is for the luxury of the exercise itself. “If the shell-fish on the shore,” says Dr Ferguson, “perform no visible action but that of opening and closing his shell, to receive the brine that accommodates, or to exclude the foul matter that annoys him, there are other animals that, in the opposite extreme, are active; and for whom Nature seems to administer the means of supply, merely as a restorative of that strength which they are so freely to waste in the seemingly sportive or violent exercises to which they are disposed.”[85]

“The bounding fawn, that darts across the glade,

When none pursues, through mere delight of heart,

And spirits buoyant, with excess of glee;

The horse as wanton, and almost as fleet,

That skims the spacious meadow at full speed,

Then stops, and snorts, and, throwing high his heels,

Starts to the voluntary race again;

The very kine, that gambol at high noon,—

The total herd,—receiving first from one,

That leads the dance, a summons to be gay;

Though wild their strange vagaries, and uncouth

Their efforts, yet resolved, with one consent,

To give such act and utterance as they may

To ecstacy, too big to be suppress'd.”[86]

It is this appearance of happy life which spreads a charm over every little group, with which Nature animates her scenery; and he who can look without interest on the young lamb, as it frolics around the bush, may gaze, indeed, on the magnificent landscape as it opens before him,—but it will be with an eye which looks languidly, and in vain, for pleasure which it cannot find.

These observations, on our muscular pains and pleasures, in conformity with that view of them which I endeavoured to give you, in a former lecture, are not digressive now, nor uselessly repeated. It is of great importance for the applications which we have to make, that you should be fully aware that our muscular frame, is not merely a part of the living machinery of motion, but is also truly an organ of sense. When I move my arm, without resistance, I am conscious of a certain feeling; when the motion is impeded, by the presence of an external body, I am conscious of a different feeling, arising partly, indeed, from the mere sense of touch, in the moving limb compressed, but not consisting merely in this compression, since, when the same pressure is made by a foreign force, without any muscular effort on my part, my general feeling is very different. It is the feeling of this resistance to our progressive effort, (combined, perhaps, with the mere tactual feeling) which forms what we term, our feeling of solidity or hardness; and, without it, the tactual feeling would be nothing more, than a sensation indifferent or agreeable, or disagreeable or severely painful, according to the force of the pressure, in the particular case; in the same way, as the matter of heat, acting, in different degrees, on this very organ of touch, and on different portions of its surface, at different times, produces all the intermediate sensations, agreeable, disagreeable, or indifferent, from the pain of excessive cold, to the pain of burning; and produces them in like manner, without suggesting the presence of any solid body, external to ourselves.

Were the cube, therefore, in the case supposed, pressed, for the first time, on the hand, it would excite a certain sensation, indeed, but not that of resistance, which always implies a muscular effort that is resisted, and consequently not that of hardness, which is a mode of resistance. It would be very different, however, if we fairly made the attempt to press against it; for, then, our effort would be impeded, and the consequent feeling of resistance would arise; which, as co-existing in this case, and in every case of effort, with the particular sensation of touch, might afterwards be suggested by it, on the simple recurrence of the same sensation of touch, so as to excite the notion of hardness, in the body touched, without the renewal of any muscular effort on our part, in the same manner as the angular surfaces of the cube, if we chance to turn our eye on it, are suggested by the mere plane of colour, which it presents to our immediate vision, and which is all that our immediate vision would, of itself, have made known to us. The feeling of resistance, then, I trust, it will be admitted, and consequently of hardness, and all the other modes of resistance, is a muscular, not a tactual feeling.

But though the resistance or hardness of the cube, as implying some counter effort, may not be immediately sensible to our superficial organ of touch, are not its dimensions so perceived? Its cubical form, it will be allowed, cannot be felt, as only one of its surfaces is supposed to be pressed upon the hand; but, is not at least this square surface perceived immediately? In short, does not touch, originally and immediately, convey to us the knowledge of extension?

With our present complete belief of external things, indeed, and especially of our organs of sense, the most important of these, the origin of our knowledge of extension, seems to us a matter of very easy explanation. The square surface presses on our organ of touch,—it affects not a single physical point merely, but a portion of the organ, corresponding exactly, in surface with itself; and the perception of the similar square, it will be said, thus immediately arises. But, in all this easy explanation, it is very strangely forgotten, that the feeling, whatever it may be, which the impression of the square surface produces, is not itself the square configuration of our tactual organ, corresponding with that surface, but the state of a very different substance, which is as little square, as it is round or elliptical,—which is, indeed, from its own absolute simplicity, incapable of resemblance in shape to any thing; and the resemblance of which, therefore, to the shape of the mere organ, is as little to be expected in the sensations of touch,—as that other state of mind, which constitutes the sensation of the fragrance of a rose, can be expected to resemble the shape of the odorous particles themselves, or of the organ of smell, which is affected by them. The very knowledge which touch is supposed to give, is, in this case, most inconsistently, assumed, as existing in the mind, before the very touch which is supposed to give it. If, indeed, the mind could know, that a part of its external corporeal organ is compressed into the form of a square, or that another square surface is compressing that organ, the difficulty would be at an end; for it would, then, most undoubtedly, have that very knowledge of extension, the origin of which we seek. But it is not explained, how the mind, which alone can have sensation or knowledge, and which certainly is not square itself, is to be made acquainted with the squareness of its own corporeal organ, or of the foreign body; nor, indeed, how the squareness of the mere external organ should produce this particular affection of the mind, more than if the organ were compressed into the shape of a polygon of one thousand sides.

Let it be supposed, that, when a small cube is pressed on the hand, one hundred physical points of the organ of touch are affected in a certain manner. We have, it is said, an immediate perception of a square surface. Let it next be supposed, that, instead of one hundred of these continuous points of the organ, an equal number of points, at various distances in the surface of the body, are affected in the same manner. On this supposition it will scarcely be said, that the perception of a square would arise, when there is no square, more than any other imaginable form, in the space comprehended in the pressure. Yet what difference is there, in these two cases, to a mind that is, by supposition, absolutely ignorant of every bodily organ, and consequently alike ignorant of the nearness or distance of the points of the organ of touch? In both cases, one hundred points, equally sensible, are affected, and are affected precisely in the same manner;—and there is truly no difference, unless we tacitly suppose the mind to be conscious of the bodily frame, and, therefore, of the continuity of certain points of the organ of touch, with the other points that are proximate to them,—a sort of knowledge, for which it would not be easy to account, and which it is impossible to conceive, without conceding the very point in question. A little attentive reflection on the circumstances of these two cases, will, perhaps, aid you in freeing your minds from the illusive belief, of which it may not be easy for you at first to divest yourselves,—that the continuity and similarity of shape, which are known to us the inquirers, are known also to that little sentient being, whose first elements of knowledge we are endeavouring to trace.

We are too apt to forget, in inquiries of this sort, that it is not in our organ of touch merely, that a certain extent of the nervous extremity of our sensorial organ is affected. This occurs, equally, in every other organ. In the superficial expansion of the nerves of hearing, smell, taste, for example, it is not a point merely that is affected, but a number of continuous points, precisely, as in the superficial organ of touch; and if, therefore, the notion of extension in general, or of figure, which is limited extension, arose whenever a part of the nervous expansion was affected in any way, we should derive these notions as much from a taste, or a smell, or a sound, as from any of the configurations or affections of our organ of touch.

It is not, therefore, merely because a certain limited part of the sensorial organ is affected, that we have the notion of the square surface, in the case supposed by us: for, if this alone were necessary, we should have square inches, and half inches, and various other forms, rectilinear or curvilinear, of fragrance and sound.

But, it may perhaps be urged, though all our organs must, indeed, exist equally with our organ of touch of a certain shape when affected,—and though the sensorial figure of our other organs, is not accompanied with any of those mental affections, which constitute the perception of angular or curvilinear figure, there is something, in the nature of that part of the sensorial organ, which terminates on the general surface of the body, that impresses the mind, immediately, with a sensation, corresponding with the exact figure, in which the organ may itself exist. When the square, therefore, in the case imagined by us, is impressed upon the organ, the mental affection which constitutes our notion of a square may immediately arise, though it would not arise from the similar squareness of our organs of smell or hearing.

In answer to this mere supposition, I may remark, that the sensorial organ of touch exists, at every moment, of a certain shape, and that we yet have no perception of this shape, so as to be able to delineate the whole extent of our tactual organ, in the same manner as we could delineate the impressing square, in the case supposed: or, if it be said, that the configuration of the organ does not excite this mental affection, in the quiescent state of the part, but only when it is itself affected, I may remark, that we are as little able to delineate its figure, when we are exposed to the action of heat, which yet acts most powerfully upon this very organ, inducing sensations, at least as vivid as those of hardness or figure.

It may still, however, be contended, for in a question of this sort I wish fairly to imagine every possible argument—it may still be contended, that, though the organ of touch has no effect, in this way merely as configured, and might, in any other configuration operate, precisely in the same manner, on the sentient mind,—still the harmony of the bodily and mental changes is so arranged by nature, that the organic state in touch, whatever it may be, is immediately followed by the knowledge of the extension of the impressing body,—in the same manner as a certain state of the organ of smell, whatever that state may be, is immediately followed by that affection of the mind, which constitutes our sensation of the fragrance of a rose. Though this argument, in truth, rather begs the question, than attempts to meet it, let us give to it all the force which it may claim. The accurate determination of the point may, indeed, seem, at first almost impossible; since in whatever manner the seeming perception may arise, it must be admitted, that we now seem to perceive extension, as it were immediately, by touch; though not more immediately than in vision we seem to perceive the positions of objects in different distances before our eyes.—But there is, fortunately, at least one test, which the point in question still admits. If the apparent perception of extension by touch, be truly and originally immediate, and not acquired, like the apparent perception of distance in vision, so as to involve a sort of intellectual measurement or suggestion of some sort, after the primary sensation,—the perception must be constant and universal, not confined to a few simple and familiar forms, which, if we can distinguish these alone, we may be supposed to have learned from experience, but extending to forms of every kind; for it would certainly be a very strange abuse of the license of supposition, to imagine that we perceive a square immediately, but not a circle, or a circle but not a square, or indeed any other figure. Even at present, then—though the circumstances of the trial,—when the experience of many years must have exhausted so many varieties of form, associating the notion of these with the particular tactual feeling whatever that may be—are surely very unfavourable to the opinion which I maintain,—even at present, I may safely trust to experiment, the determination of the question. When a body which we do not see, is pressed on any part of our tactual organ, do we immediately discover its form,—as immediately, as we are sensible of fragrance, when our organ of smell is in a healthy state, and an odoriferous body is presented to it, or of sound, when a cannon is fired beside us? This we certainly should do, if figure were as direct an object of the sense of touch, as fragrance and sound are of the senses of smell and hearing. Even though it be a form of the simplest kind, square, round, triangular, that is thus pressed upon our palm, we scarcely distinguish the precise species of figure for a moment, and are long before we can convince ourselves, that we have perceived its exact magnitude, in the determination of which, after all, we shall very probably be mistaken, if we confine ourselves to the mere intellectual measurement; though we should even add to the immediate sensation of touch, all the discriminating skill of our judgment and reflection. But, if the body be irregular in form,—however slight the irregularity may be, and of a species that would not perplex in the slightest degree our sense of sight, and which certainly, therefore, should perplex as little our sense of touch, which is supposed to be still more immediately perceptive of form,—we are incapable for some time, and I may even say are incapable altogether, of fixing, with precision, its magnitude and figure—that very magnitude and figure which are yet said to be the direct objects of touch. Of this a single trial may convince any one; it is a trial which as it seems to me decisive, I must request you to make. Are we then entitled to say, in the case of the square surface of the cube pressed upon our hand, that though we cannot discover other forms and magnitudes, we yet discover its extension, and consequently its figure, by the immediate sense of touch?—or may we not rather conclude with confidence, that what is true of other forms is true of this also, that it is only in consequence of more frequent experience we have learned as it were to distinguish, with some degree of certainty, the simpler forms, which, as mere forms, are not more direct objects of the sense of touch than forms the most irregular, and that without such experience, therefore, our mere sense of touch is incapable of informing us of the figure of bodies, immediately and originally.

If then the knowledge of extension be not derived from our immediate sense of touch, it must be derived from some other source, which allows it to be associated with the feelings of touch, and afterwards suggested by these, in the same manner as distant extent, in the case of vision, is suggested by a few slight varieties of colour. Let us endeavour, then, since some such source there must be, to discover what the source is.