CHAPTER XIII.

THE PERCEPTION OF BODY AS PRESENTING STATICAL

ATTRIBUTES.

§ 326. From that class of attributes known to us solely through one or other kind of objective activity; and from that further class known to us through some objective reactivity called forth by a subjective activity; we now pass to that remaining class known to us through a subjective activity only.

In respect of its space-attributes-Bulk, Figure, and Position-body is altogether passive; and the perception of them is wholly due to certain mental operations. Unlike heat, sound, odour, &c., which are presented to consciousness by no acts of our own, but often in spite of our acts—unlike roughness, softness, pliability, &c., of which we become conscious by the union of our own acts with the acts of things; extension under its several modes is cognizable through a wholly-internal co-ordination of impressions: a process in which the extended object has no share. Though the data through which its extension is known, are supplied by the object; yet, as those data are not the extension, and as until they are combined in thought the extension is unknown, it follows that extension is an attribute with which body does not impress us, but which we discover through certain of its other attributes. To an uncritical observer, the visible form of an object seems as much thrust upon his

consciousness by the object itself, as its colour is. But on remembering that the visible form is revealed to him only through certain modifications of light; that these modifications are produced not by the form, but by certain occult properties of the substance having the form; and that if the body had no power of reacting on light, the form would be invisible; it will be seen that the form is known not immediately but mediately. When it is further remembered that in the dark the shape and size of anything are knowable only through tactual and muscular sensations gained by acts of exploration; and that consciousness of the shape and size depends on the thinking of these in certain relations; it will no longer be questioned that in the perception of the space-attributes, the object is wholly passive while the subject is active.

The propriety of distinguishing Bulk, Figure, and Position as statical attributes, may perhaps be questioned. In mechanics, statics and dynamics are allied to one another as closely as the circle is allied to the ellipse, into which it passes by insensible steps; whereas the attributes that are here classed as statical, differ wholly and irreconcilably from those classed as dynamical. The reply is that the terms as now used are to be understood, not in the mechanical sense, but in a more general sense. Statical attributes are those which pertain to body as standing or existing. Dynamical ones are those which pertain to it as acting. If it be admitted that the so-called secondary attributes of body, which, as we find, imply its activity, are rightly termed dynamical; it must be admitted that the so-called primary ones, which, as implying passivity, are their antitheses, may be properly distinguished as statical.

§ 327. Whether the space-attributes of body are any of them knowable through the eyes alone, has been a disputed question. That our perceptions of distance are not originally visual, but result from muscular experiences, which

visual experiences serve to symbolize, is admitted. And that at least one out of the three dimensions of body, involving as it does the idea of greater or less remoteness from us, can be known only through muscular experiences, must also be admitted. But our inability to conceive of colour save as having extension of two dimensions, seems to imply that superficial magnitude is, to a certain extent, knowable by sight. Though it is manifest that superficial magnitude as known by sight is purely relative-that the same surface, according as it is placed close to the eye or a mile off, may occupy the whole field of view, or but an inappreciable portion of it; yet as, while an object is visible at all, it must present some length and breadth, it may be argued that superficial extension in the abstract, is originally perceivable through the eyes, as much as colour is. This conclusion is in one sense true and in another sense untrue. The relation between its untruth and its truth will be best seen by considering first a criticism upon it and then the reply.

Along with the conception of visible superficial extension there goes a conception of distance. Imagine a surface a foot square to be placed a yard from the eye, at right angles to the axis of vision; and imagine that four straight lines are drawn from its angles to the centre of the eye. Suppose now that a surface of six inches square be interposed at half the distance, so as to subtend to the eye the same apparent area; and that another of three inches square be interposed between this and the eye in the same manner; and so on continuously. It is manifest that were it possible to repeat this process ad infinitum, the area subtended by the four converging lines would disappear at the same moment that the distance from the point of convergence disappeared; and that hence, all our experiences conforming as they must to the laws of convergent rays, we can have no conception of a visible superficies without an accompanying conception of a distance between that superficies and the sentient

surface. Consequently, if distance is not conceived à priori, area is not conceived à priori. To this the reply is, that there can be no such series of diminishing areas subtending the same angular space. The argument ignores the structure of the eye; and supposes vision to continue under conditions that must absolutely prevent it. I do not mean only that the supposed diminishing areas will, as their including lines converge, presently come in contact with the eye itself; but I mean that long before they do this, the assumed diminution of the area becomes optically impossible. Though successively diminishing areas subtending the same angular space may be arranged as described so long as the eye is not approached too closely, yet as soon as the limit of its shortest focal adjustment is passed, this no longer holds: the retinal area occupied by the image, while it becomes gradually indefinite, enlarges rather than diminishes. And when we thus see that both the size of the eye and its optical adjustments necessarily enter as factors into the perceptions of visual areas and distances, it becomes manifest that there is a sense in which the consciousness of visual area is pre-determined by the inherited structure; not, indeed, to the same extent as the accompanying sense of colour is so pre-determined, but to some extent-to the extent that the visual organ, by its own size and constitution, furnishes certain limits within which the space-interpretations given to an impression of colour must eventually fall.

But a clearer understanding of the matter will be obtained, if we consider more at length a visual impression as it is received at the periphery of the nervous system. The retina, examined microscopically, presents a tesselated pavement made up of minute rods and cones packed side by side, so that their ends form a surface on which the optical images are received. As far as can be made out, each of these rods and cones is supplied by a separate nerve-fibril; and is, as must be supposed, capable of independent stimulation.

That the joint action of these retinal elements may be the more easily comprehended, let as suppose an analogous structure on a large scale. Imagine that an immense number of fingers could be packed side by side, so that their ends made a flat surface; and that each of them had a separate nervous connexion with the same sensorium. If anything were laid on the flat surface formed by these fingerends, an impression of touch would be given to a certain number of them-a number great in proportion to the size of the thing. And if two things successively laid on them differed in shape as well as in size, there would be a difference not only in the number of finger-ends affected, but also in the kind of combination. What would be the interpretation of any impression thus produced, while as yet no experiences had been accumulated? Would there be any idea of extension? Certainly not a developed idea, though there would be the crude material of an idea. To simplify the question, let the first object laid upon these finger-ends be a straight stick; and let us name the two finger-ends on which its extremes lie, A and Z. If now it be said that the length of the stick will be perceived, it is implied that the distance between A and Z is already known, or in other words, that there is a preexistent idea of a special extension: which is absurd. If it be said that the extension is implied by the simultaneous excitation of B, C, D, E, F, and all the fingers between A and Z, the difficulty is not escaped; for no idea of extension can arise from the simultaneous excitation of these, unless there is a knowledge of their relative positions, which is itself a knowledge of extension. By what process then can the length of the stick become known? It can become known only after the accumulation of certain experiences, by which the series of fingers between A and Z becomes known. If the mass of fingers admits of being moved bodily, as the retina does; and if, in virtue of its movements, something now touched by finger A is next