or outline. The difference between the sensation of form in a still object, as a rainbow, and a moving object, as a flying bird, is not so great as appears at first glance. In both there occurs the feeling of movement. In taking a picture of the rainbow, we must pass the view along the whole curvature exactly as if it were a moving thing describing the extended arc of the heavens. The image that is left is therefore still an impression of movement combined with the optical impression. The main difference lies in this, that in the case of a bird we have the entire image comprehended in the centre of the retina, where the stress of observation lies; in the case of the rainbow, we have an image continued over the whole breadth of the retina, extending from the central point of observation into the vague regions of the circumference. This last makes up our feeling of a continuous image. We have an impression of all the objects that can enter the pupil at one time, which would include a range of about a third of a circle right and left, up and down; and although distinct observation can occur only at a narrow part in the centre of the view, yet some kind of impression is made by the whole, sufficient to give us a sense of continuity. But it is only by moving the eye hither and thither that any distinct view can be obtained, and the impression that the view leaves behind is therefore an impression of lights, shades, and colours, combined with movements. In the observation of still life, there is not the same stimulus to move the eye over the outlines of objects as in the case of moving bodies, hence our attention to still forms is more languid. When the eye is once fixed on an object we are reluctant to lose it, and if the object moves, we follow its course; but we have not the same alacrity in moving the eye along a continuous line or circle. Nevertheless there is a sufficient amount of spontaneous activity in the movements of the eye to prompt this kind of observation, though in a less degree than the other; and by this means we acquire our distinctive impressions of form, figure, or shape. By a circular sweep we are impressed with a ring; by a straight sweep we take in a line; by a sudden change of direction we imbibe an angle. By movements confined to the head and eyes we grasp

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objects lying directly across the view, or with all parts equally distant from the eye; by these movements, combined with altered adaptation to distance, we have figures of objects that retreat from the view, as in looking down a street.

By means of the movements of the eye, we acquire impressions of the visual expanse or apparent magnitude. This visual expanse of bodies is determined by the range or sweep of the eye in passing over their whole extent, or by the fraction of the field of view that they take in. We see a rainbow spanning one-third of the heavens; we see a cloud encircling the sky; we appreciate the dimensions of a picture on the wall as compared with other pictures beside it. The different degrees of movement and tension of the muscles that make the sweep are distinctly felt, and we set down one sweep as more or less than another. We also acquire by repetition standards of comparison for expanses in general, as we acquire standards of weight in the sensibility of the arms.

18. The combination of our feeling of varying distances from the eye, resulting from the movements of adaptation, with the feeling of visual expanse, gives, as we have already seen, the feeling of solidity, or of three dimensions in one continuous object. It has been remarked above, that in seeing a line which crosses the field of view, the impression left consists of a distinct portion of the line corresponding to the centre of the retina continued into indistinctness in the circumference of the retina. So in looking at a retreating line, we have to describe a movement of adaptation as we pass along, and the effect at any one instant would be a distinct view of one portion, while the other portions are indistinct and confused. Thus in a vista of houses, the adaptation that suits the nearest makes the others confused, although still within the field of view, or pictured on the retina; if the middle house is distinct, the two ends of the line will be confused or indistinct. This is the strict visual impression or effect of varying distance, and the combination of this with sweep or expanse realizes the impression of three dimensions, and of solidity. When I look at a cubical block, I have to make a series of movements, right and left, up and down, to

take in the figure and expanse, and as my eye gets on the retreating side I must also adapt for distance, and there results from all this the visual impression of solidity.*

19. The sensation of position or relative situation contains nothing peculiar. The place of an object is ascertained by the distance and direction of it as regards other objects. Thus the place of the sun is determined by the apparent height above the horizon, or the upward sweep of the eye, and by the distance from a cardinal point as determined by a horizontal sweep.

20. I have adverted to the large class of impressions that we receive from moving objects, and to the emotions that they produce, and the permanent imagery that they contribute to the intelligence. A parallel illustration might be afforded in the class of forms, or of objects conceived as having extent and outline, whether at rest or in motion. Every visible thing has dimensions and shape as well as some shade of light or colour, and by these qualities each individual body is discriminated, and impressed upon the optical and mechanical susceptibility of the eye. Some objects have a wide expanse, others are limited; some are straight, others curved; some have a simple outline, as a square or a triangle, others are very complex, and demand many movements to follow them out; as a human figure, a building, or a mass of decorative tracery. The variety of sensation thus arising is very great.

As regards the emotional effect of the visual sensations of objects, I have already remarked on the influence of light and colour, and also on the effect of the single element of distance. When this element is combined with great visual expanse, we have then the sensation of largeness, and of a wide prospect.

*We shall have to remark on this subject again, when considering the acquired perceptions of the eye. In fact, the above statement, as to the indistinctness of the parts of the field of view not falling in the centre of the eye, and not corresponding to the adjustment for distance at the moment, will scarcely correspond to our ordinary experience. The reason of this is, that the mind supplies from the past what the eye does not distinctly see at the time, so that the picture actually realized is not the bare optical impression of the moment, but a much fuller picture which that impression suffices to suggest.

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This feeling is very powerful, and not unlike the feeling of the voluminous in sound; it is a massive and keen emotion allied with the sense of power or great expenditure of force, yet without the feeling of painful exhausting effort. I refer it to the complex sensibility of the eye to colour, expanse, and distance; an aggregate of large and keen sensibility in a minute organ, highly pleasurable for a considerable length of time, and pre-eminently enduring and recoverable as an intellectual element. This is the simplest form of the feeling that we term the sublime.

I may also notice the difference of emotion in straight and in curved forms. Curves appear to gratify the liking we have for waxing and waning motions, as explained when speaking of movements. For this among other reasons to be afterwards considered, they are in general more pleasing than straight forms. Of the three dimensions of space, the up and down is more impressive than the lateral dimension, owing to the sense of weight and support that comes to be inseparable from elevation.

The intellectual imagery derived through the eye from the forms of still life is co-extensive with the visible creation. For the purposes of discrimination and of identification of natural things, and also for the storing of the mind with knowledge and thought, the sensations of objects of sight are available beyond any other class. The eye is kept constantly at work upon the surrounding scene, following the outlines and windings of form, as these extend in every direction; and by the movements thus stimulated each several object is distinguished from those that differ in shape, size, or distance, and identified with itself and those that coincide with it in these peculiarities. The train of movements for a square are recognised as distinct from the train that describes an oval: the outline of a pillar brings on a cycle of motions wholly different from those dictated by the figure of a tree. The property belonging to the mental system of causing movements to cohere that have been described in succession, fixes the series for each different view, and gives a permanent hold of all the distinct forms presented to the eye. This cohering and storing up

process belongs to the intellect, and will be fully treated of in the proper place. What is chiefly notable here is the fact that the impressions of light made on the retina of the eye, and the accompanying muscular impressions rising out of its form-tracing mobility, are, both the one and the other, of a very enduring kind; they take on the coherence that gives them an existence after the fact more easily than any other class of sensible impressions. Neither tastes, nor smells, nor touches, nor sounds, can compare with sights in the property of mental persistence and revivability. Probably no other muscles are equal in susceptibility to the muscles of the eye; hence their educational accomplishments, that is to say, the number of separate forms and combinations that they can retain a hold of, is pre-eminent among the acquirements of the muscular system.