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

by Thomas Brown

We are able, indeed,—not while we continue to look at the sphere, but with a sort of mental effort, afterwards to separate the colour from the convexity, and to imagine the same colour united with any other surface, plane or concave,—the reason of which is very evident. Our sensation of colour has not been uniformly associated with one species of extension, but with all its varieties; and may, therefore, be suggested in possible coexistence with all. In all these varieties, however, two dimensions have been constantly implied; and, therefore, the association of colour with these is complete and indissoluble. If every surface in nature had been convex, it is by no means improbable, that we should have found the same difficulty, in attempting to separate colour from convexity, which we now find, in attempting to separate it from mere length and breadth.

It is the same, in various other affections of the mind, as in our sensations. There are feelings, which we cannot separate from other feelings, and which, we yet know, must have been originally separate. I might refer to the silent growth and maturity of almost every passion, of which the mind is susceptible. But there is sufficient proof, even in affections, which seem instantaneous. The mother, when she looks at her babe, cannot behold it without feelings, very different from those, which the same form and colour, in another infant, would have excited; and yet, impossible as it is to separate, in this case, the mere visual sensation, from that emotion of happy and instant fondness which accompanies it, there is surely no natural connexion of the emotion, with the mere length, and breadth, and colour.

The impossibility of separating the sensation of colour from the notion of extension, it appears, then, is not a decisive proof of an original connexion of these; for, if it were decisive, it would prove still more;—and we might, from this alone, assert with equal confidence, the original visual perception of three dimensions, as that of two, and of the magnitude and figure, which we term tangible, as much as of those, which we have chosen to term visible. It is surely as little possible for us, when we open our eyes on some wide and magnificent landscape, to separate the colour, as a mere visual sensation, from the field, the mountain, the forest, the stream, the sky, as to separate it from the half inch, or inch of our retina, of the perception of which we have no consciousness in any case; and it is too much for those who deny the immediate perception of those greater magnitudes, to urge, in proof of the necessary original perception of this inch or half inch, what, if valid in any respect, must establish no less the proposition which they deny, than the proposition which they affirm.

But, it will be said, there is truly a certain figure of the part of the retina, on which the light falls. The fact is undeniable. But the question is, not whether such a figure exist, but whether the perception of the figure necessarily form a part of the sensation. The brain, and nervous system in general, are of a certain form, when they are affected in any manner. But it does not therefore, follow,—as the fact sufficiently shows,—that the knowledge of this form constitutes any part of the changeful feeling of the moment. To confine ourselves, however, to the mere senses,—it is not in the organ of sight only, that the nervous matter is of a certain shape:—it is expanded into some shape or other, in every organ. When the whole, or a part, therefore, of the olfactory organ, is affected by the rays of odour, if I may so term them, we might, with exactly the same ground for our belief, suppose, that the knowledge of a certain extension must accompany the fragrance, because a certain nervous expanse is, in this case, affected, as that the notion of a certain extension must, for the same reason, and for the same reason alone, accompany the sensation of colour. It is because the same light, which acts upon the organ of one person, may be made visible to another, that we conceive it more peculiarly to be figured, as it were, on the nervous expanse, when it is not in itself truly more figured, than the number of coexisting particles of odour, which affect the nerve of smell. We cannot exhibit the particles of odour, however, acting on the nostril of any one. But, when the eye is dissected from its orbit, we can show the image of a luminous body, distinctly formed upon the retina. We, the observers of the dissected eye, have thus a clearer notion of the length and breadth of the nervous matter affected in the one case than in the other. But it is not in the dissected eye that vision takes place; and as the living eye, and the living nostrils, are alike affected in more than one physical point, we must surely admit, that in both cases, and in both cases equally, a certain length and breadth are affected, and that there is an olfactory figure as truly as a visible figure. The mere visibility of the image to another person cannot alter the nature of the organic affection itself to the sentient individual. If the olfactory figure be not necessarily accompanied with the perception of extension, there is no stronger reason a priori, to suppose that what is termed the visible figure,—which is nothing more than a similar affection of a nervous expanse,—should be accompanied with the knowledge of the part of the retina affected.

These arguments, however, though they seem to me to invalidate completely the only arguments which I can imagine to be urged in support of our original perception of figure by the eye, are negative only. But there is also a positive argument, which seems to me truly decisive, against the supposed necessary perception of visible figure,—that it implies the blending of things which cannot be blended. If the mere visual sensation of colour imply, in itself, no figure, I can conceive it to be blended with any figure; but not so, if it imply, in itself, a fixed definite figure, so essential to the very sensation of the colour, that without it the colour could not for a single moment be perceived. During the whole time, then, in which I am gazing on a wide landscape, there is, according to the opinion of those who contend for the necessary perception of visible figure, not colour merely, but a certain small coloured expanse, of definite outline, constantly perceived—since, without this, colour itself could not be perceived; and, during all this time, there is also a notion of a figure of a very different kind, of three dimensions, and of magnitude almost infinitely greater, combined, not with colour merely, but with the same coloured expanse. There must, therefore, be some possible combination of these forms and magnitudes; since it is the colour which we perceive that is blended with the tangible magnitudes suggested. Now, though there are certain feelings which may coexist and unite, it appears to me, that there are others which cannot be so blended. I may combine, for example, my notion of a plane or convex surface, with my notion of whiteness or blueness, hardness or softness, roughness or smoothness; but I cannot blend my notions of these two surfaces, the plane and the convex, as one surface, both plane and convex, more than I can think of a whole which is less than a fraction of itself, or a square, of which the sides are not equal, and the angles equal only to three right angles. The same blue or white surface cannot appear to me, then, at once plane and convex, as it must do if there be a visible figure of one exact outline coexisting with the tactual figure which is of a different outline; nor, even though the surface were in both cases plane, can it appear to me, at the same moment, half an inch square, and many feet square. All this must be done, however, as often as we open our eyes, if there be truly any perception of visible figure coexisting with the mere suggestions of touch. The visible figure of the sphere, on which I fix my gaze, is said to be a plane of two dimensions inseparable from colour, and this inseparable colour must yet be combined with the sphere, which I perceive distinctly to be convex. According to the common theory, therefore, it is at once, to my perception, convex and plane; and, if the sphere be a large one, it is perceived, at the same moment, to be a sphere of many feet in diameter, and a plane circular surface of the diameter of a quarter of an inch. The assertion of so strange a combination of incongruities would, indeed, require some powerful arguments to justify it; yet is has been asserted, not merely without positive evidence, as if not standing in need of any proof, but in absolute opposition to our consciousness; and the only arguments which we can ever imagine to be urged for it, are, as we have seen, of no weight,—or would tend as much to prove the original visual perception of tangible figures, as of the figure that is termed visible.

Is it not at least more probable, therefore, that though, like the particles of odour when they act upon our nostrils, the rays of light affect a portion of the retina, so as to produce on it an image, which, if the eye were separated from its orbit, and its coats dissected, might be a distinct visible figure to the eye of another observer; this figure of the portion of the retina affected, enters as little into the simple original sensation of sight, as the figure of the portion of the olfactory nervous expanse, when it is affected, enters into the sensations of smell?—and that, when the simple affection of sight is blended with the ideas of suggestion, in what are termed the acquired perceptions of vision,—as, for example, in the perception of a sphere,—it is colour only which is blended with the large convexity, and not a small coloured plane?—which small coloured plane being necessarily limited in extent and form, so as never to be larger than the retina itself, cannot blend with various forms and magnitudes, and which, if it could even be supposed to constitute a part of the convexity of a sphere perceived by us, still could not diffuse its own limited and inseparable colour over the whole magnitude of the sphere.

I have stated to you my own opinion with respect to visible figure,—an opinion, which to myself, I confess, appears almost certain, or, at least, far more probable than the opinion generally entertained, that has no evidence in our consciousness at any one moment of vision to support it. But on subjects of this kind, which are in themselves so very subtile, and, therefore, so liable to error, I must beg you, at all times, and especially when the opposite sentiment has the authority of general belief, to consider any opinion, which I may submit to you, as offered more to your reflection, than for your passive adoption of it. If I wish you,—reverently, indeed, but still freely,—to weigh the evidence of doctrines of philosophy, which are sanctioned even by the greatest names of every age, I must wish you still more, because it will be still more your duty, to weigh well the evidence of opinions that come to you, with no other authority than that of one very fallible individual.

In looking back on the senses which we have been considering, what a boundless field do we seem already to have been endeavouring to traverse? and how admirable would the mind have been, even though it had been capable of no other office than that of representing, in the union of all its sensations, as in a living mirror of the universe, the splendid conceptions of the great Being who formed it; or, rather of creating a-new in itself, that very universe which it represents and admires?

Such is the power of the senses;—of

——“senses, that inherit earth and heavens,