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.
Footnotes
[84] Deserted Village, v. 120.
[85] Principles of Moral and Political Science, Part I. c. i. sect. i.
[86] Cowper's Task, Book IV.