afterwards change their adjustment to suit an object six feet distant, we are distinctly conscious of the change, and of the degree or amount of it; we know that the change is greater than in extending the adjustment to a three-feet object, while it is less than we should have to go through for a twenty-feet object. Thus in the alterations of the eyes for near and far, we have a distinctive consciousness of amount or degree, no less than in the movements for right and left, up and down. Feelings of the same nature as active exertion in any part of the body gives rise to, are thus incorporated with the sensibility to colour; the luminous impression is associated with action on our part, and is no longer a purely passive state. We find that the light changes as our action changes, we recognise in it a certain connexion with our movements; an association springs up between the passive emotion and the active energy of the visible organ, or rather with the body generally; for the changes of view are owing as much to movements of the head and trunk as to the sweep of the eye within its own orbit.

We have not yet attained to the perception or knowledge of any outward thing as the source of colour, and the occasion of the varying movements and adjustments of the eyes. We have discriminating feelings of colour, the discriminative sense of active energies, and the association of the two in one fact, but nothing to reveal or suggest external things; we have merely the means of comparing a number of various mental states. Nor do I see how with the eye alone we can ever pass from the internal consciousness to the external perception, to the recognition, knowledge, and belief of things out of or apart from ourselves, the causes of those internal states. Many have contended for, and many more assumed, this power as attaching to vision. But in so doing they seem to me to have fallen into a confusion of idea respecting the mental nature of this perception of an outer world, as I shall now endeavour to explain.

35. It is I believe admitted on all hands that the recognition of an outer world apart from self is mixed up with the perception of such qualities as extension, form, and remoteness,

DISTANCE IMPLIES LOCOMOTIVE EFFORT.

365 called Primary qualities of matter. Heat, odour, taste, colour alone, do not suggest external and independent objects, being for this reason termed the Secondary qualities of bodies. I shall fasten, therefore, on the two facts of remoteness and extension, both which imply outward existence in so far as we recognise and believe in the reality of a material world apart from the mind. With regard to those two qualities,-the distance of a thing from the seeing eye and the dimensions of a body in space, I affirm that they cannot be perceived through the medium of sight alone.

It appears

Take first the case of Distance or remoteness. to me that the very meaning of this quality, the full import of the fact implied in it,-is such as cannot be taken in by mere sight. For what do we mean when we say that an object is four yards distant from where we stand? I imagine that among other things we understand this, namely, that it would take a certain number of paces to come up to it, or to reduce the distance from four yards to two yards. The possibility of a certain amount of locomotion is implied in the very idea of distance. The eye would be distinctly aware of a change when the distance was reduced from four yards to two, but it has of itself no knowledge of the cause or accompanying incidents of that change. These are measured by our other activities, and in the case of great distances, by the locomotive energy and continuance requisite to pass from the one to the other. In the case of objects within reach of the hand, the movements of the arm give the measure of distance; they supply the accompanying fact that makes distance something more than an unknown visible impression. When we say that a thing has been shifted from a position of six inches distance from the eye to a position of twelve, we imply that with the change of ocular effect there has been another change corresponding to a certain definite movement of the hand and arm in a forward direction; and unless by supposing this additional action, we have no key whatever to the change that has come over our visible impression of the thing in question. I say, therefore, that distance cannot be perceived by the eye, because the idea of distance by its very nature

implies feelings and measurements out of the eye, and located in the other active organs,—the locomotive and other moving members. If our notion of distance did not reveal to us the fact that by so many steps, or by a certain swing of the arm or bend of the body, we should make a definite change in the appearance of the object, it would not be a notion of distance; there might be an ocular effect, but not a revelation of distance. Granting that the eye is very distinctly affected by every change in the remoteness of a visible object from six inches to a mile, that it recognises a variation of impression all through this interval, this would not answer the question, how far is the object removed at each step? I do not see even how it could tell which way the thing was moving. The actual distance means so many inches, feet, or yards, and of these we have no measure by the eye; indeed they have no relevancy as regards the eye; they concern the locomotive and other mechanical movements, but not the movements of sight.

With the active exertion of the body in locomotion we have a definite muscular feeling; we recognise one exertion as greater or less than another; the feeling of a long stride is different from a short; six paces are attended by a different consciousness from four. We acquire permanent and revivable impressions of these exertions when any one has been often repeated, as for example, pacing the length of a room. We can compare any new case with this old habitual effort, and there results a consciousness of more or less. This I take to be our starting point in the feeling of distance traversed, or of linear extension in general: this is the source of our perception, and the measure and standard of reference when we arrive at the same notion by other means. When, along with a forward movement, we behold a steadily varying change of appearance in the objects before us, we associate the change with the locomotive effort, and after many repetitions we firmly connect the one with the other. We then know what is implied in a certain feeling in the eye, a certain adjustment of the lenses and a certain inclination of the axes, of all which we are conscious; we know that these things are connected with

IMPORT OF DISTANCE AND EXTENSION.

367

the further experience of a definite locomotive energy needing to be expended in order to alter this consciousness to some other consciousness. Apart from this association, the eye feeling might be recognised as differing from other eye feelings, but there would be no other perception in the case. Experience connects these differences of ocular adjustment with the various exertions of the body at large, and the one can then imply and reveal the others. The feeling we have when the eyes are parallel and vision distinct is associated with a great and prolonged effort of walking, in other words, with a long distance. An inclination of the eyes of two degrees, is associated with two paces to bring us up to the nearest limit of vision, or with a stretch of some other kind measured in the last resort by pacing, or by passing the hand along the object. The change from an inclination of 30° to an inclination of 10°, is associated with a given sweep of the arm carrying the hand forward over eight inches and a half.

36. I maintain therefore that distance from the eye, and lineal extent in any direction, means a definite amount of bodily movement experienced in connexion with the change of visible impression in passing from one point to another. If we next attend to the sweep of the eye over the field of view, as required by an object extended laterally, we shall find in the same manner that this sweep gives a most distinctive consciousness, so that a larger sweep can be discriminated from a smaller; but it gives no information besides. It tells of no outward thing, so far as I can make out; certainly it does not tell of extension, for this simple reason, that extension means a given movement of the body. If I say that a log of wood I see before me is six yards long, I mean that it would take a certain number of my paces to traverse its length: the visual impression of itself cannot mean or imply any fact of this kind, until experience has connected the sweep of the with the sweep of the legs or other moveable parts.

eye

Accordingly, I hold, as regards extension in general, that this is a feeling derived in the first instance from the locomotive or moving organs; that a definite amount of movement of these comes to be associated with the sweep and adjustments and

other effects of the eye; and that the notion when full grown is a compound of locomotion, touch, and vision, the one implying and recalling the others. A certain movement of the eye, as the sweep over a table, gives us the sense of that table's magnitude, when it recals or revives the extent and direction of arm movement necessary to compass the length, breadth, and height of the table. Previous to this experience the sight of the table would be a mere visible effect, differing consciously from other visible effects as one stomachic pain differs from another, but not suggesting any foreign effect whatever. It could not suggest magnitude, because magnitude is not magnitude if it do not mean the extent of movement of the arms or limbs that would be needed to compass the object; and this can be gained in no other way but by actual trial by these very organs.

37. The conclusion, therefore, is that extension, size, or magnitude, owes not only its origin but its essential import or meaning to a combination of different effects associated together under the cohesive principle we are now considering. Extension, or space, as a quality, has no other origin and no other meaning than the association of these different sensitive and motor effects. The coalition of sensations of sight and touch with felt motive energies explains everything that belongs to our notion of extended magnitude or space. This view has both its supporters and its opponents. Of the opposition, I shall content myself with referring to Sir William Hamilton, who expresses himself on the subject in the following terms:-'The opinions so generally prevalent, that through touch, or touch and muscular feeling, or touch and sight, or touch, muscular feeling, and sight, that through these senses exclusively, we are percipient of extension, &c., I do not admit. On the contrary, I hold that all sensations whatsoever, of which we are conscious, as one out of another, eo ipso, afford us the condition of immediately and necessarily apprehending extension; for in the consciousness itself of such reciprocal outness is actually involved a perception of difference of place in space, and, consequently, of the extended.'-Dissertations on Reid, p. 861. The statement here made that all sensations, of which