depression, and every momentary change, to be so truly indicated to the eye that it becomes full of meaning or expression. How well mere light and shade serve to convey what the eye has to learn of a scene or object, may be perceived by examining any of the admi1able engravings which now abound, and which, although made up entirely of degrees of shade, or of black and white, are scarcely inferior in expression to finished paintings.

862. The student of painting soon learns that the hard tracings called outlines, by which he first sketches subjects, do not exist in nature, and have to be again effaced in his finished work; for they mark the place where lights and shades happen to meet. Much may be conveyed to the mind, however, by a mere outline, and particularly if lines of different breadth or thickness are used to indicate the situation of the fainter and deeper shadows.

The subject of chiaroscuro is not so simple as, from the fact of the sun being the great source of light, might at first be supposed; for although this be true, still every body which reflects the sun's light becomes a new source to the bodies around it, and the shading of a picture must have reference to all such sources, and to the different colours of the body itself, and of the neighbouring bodies.

In looking at an extended landscape, it is seen that the near objects, or those in the foreground, are comparatively bright, with their shadows strongly marked, and their peculiar colours everywhere easily distinguishable-as of flowers, fruit, foliage, &c., but of objects farther off and apparently diminished in size, the colours, with increasing distance, become dim, the lights and shadows melt into each other or are confused, and the illumination altogether becomes so faint that the eye at last may see only a certain extent of sombre mountain or plain-appearing bluish, partly owing to the reflected colour of the atmosphere (Art. 834), and partly because the quantity of light which can pierce the great extent of air, is insufficient to exhibit the detail. The ridge called the Blue Mountains in Australia, another of the same name in America, and many others elsewhere, are not really blue, for they possess all the diversity of scenery which the climates can give, but to the eyes which first discovered them, and viewed them from a distance, they all at first appeared blue, and they have retained the name.

In a good picture where, upon canvas stretched on a frame, the artist has disposed the lights, shades, and colours in the very situations and with the intensities which they would have had if coming from the real scene to the eyes, through a plate of glass filling up

Education of the Eye.

631

the frame, all that we have now been saying is strictly exemplified. In the foreground the objects are large and bright, but as they are supposed to become gradually more remote, the size and brightness correspondingly diminish, until at last there is only a dim mixture of bluish or greyish masses forming the boundary of horizon and sky.

863. A child, during what may be called the education of the sense of sight, has a strong perception of the vast differences of appearance which things assume according to their accidental distance from the eye, their position, and their exposure to light; for many of these differences, being at first calculated to deceive the young judgment, have from time to time been noted and recorded. Thus, a boy when he first discovers that a ship which at the near quay, with her sails outspread, concealed from him half the sky, is in an hour or two afterwards seen by him on the distant horizon as a dark speck hardly big enough to hide one star, has his attention strongly awakened, and he feels surprise; or, again, when he learns that the faint blue unchanging mass which he had always observed bound. ing in one direction the view from the home of his youth, is a distant mountain-side thickly inhabited, and covered with dwellings and gardens, where in succession the bright colours of the different seasons periodically glow-he is equally struck. But as soon as experience has enabled him to interpret readily and correctly the visual signs under every variety of circumstance, his attention passes so rapidly from them to the realities-just as it might pass from the paper and printing of a newspaper to the important intelligence communicated by them, that he very soon ceases to reflect that the sign, which in every case similarly suggests the object, is not also in every case like the object, and the same true and complete representation of the reality. The feeling that the sign must be like the thing suggested, becomes at last so strong, that even a difficult effort has to be made by a grown person again to attend to the mere appearances, in any scene of which the realities are known.

864. This attempt to analyse visual appearances, and to estimate truly their connection with realities, is called, as already stated, the study of perspective. When it regards the apparent reduction of size, and the foreshortening of bodies under various circumstances, it is called linear perspective; when it regards the fading of light and the modifying of colour, it is called aërial perspective. As the advanced art of painting depends so much upon the understanding of

532

Perspective in Painting.

these two departments, the gradual progress which it has made in different countries is a measure of the degree in which the common prejudice that things appear exactly as they are has in them been overcome. Where this feeling exists, any untaught person conceives a good painting to be merely a miniature representation drawn according to a certain reduced scale—as of an inch to a yard -and in which all the dimensions of things should be measurable as simply as in the reality-while the colours as to vividness, &c., should perfectly agree with the originals. This statement is remarkably illustrated by the facts, that children in their rude attempts to paint, always aim at realizing such notion of the art, and that such has been the first stage of painting in every country. In Europe, owing to the labours of men of genius, art in painting may be said almost to rival nature, producing impressions on the retina as vivid as those from nature's own scenes, and scarcely distinguishable from them; but in other countries, as in China and India, among the native artists, the early stages of the art may still be studied, In many Chinese pictures, owing to the absence of perspective proportions, an extensive subject is only a collection of portraits of men and things drawn nearly on the same scale, and placed one above another, and where all the colours are as vividly shown as if the objects were only a few feet from the eye; the figures at the bottom, or foreground, are meant to represent the objects nearest to the spectator, while the figures higher up are supposed to be of more remote objects, all appearing as they might be seen in succession by a person who had the power of flying over the country. This kind of representation, although not natural if all viewed at once, may communicate more information than a single common painting, for it is equivalent to a succession of such. In Europe lately the principle has been usefully acted upon for certain purposes, as for representing on one long sheet, or on a succession of sheets connected in a suitable manner, the banks of a river or a line of road. The banks of the Rhine, particularly, have thus been admirably portrayed, so that the spectator directing his eye along the paper, feels almost as if carried in a balloon to view in detail the whole of the enchanting scenery. The bird's-eye view of the ancient city of Cologne, with all its famed architecture, and its noble modern bridge spanning the great river, is a portion of such representation..

Angular Size of Objects.

3rd. Divergence of the rays of light.

E

633

865. This is the next circumstance to be mentioned by which the eye judges of distance. Supposing the line, E F, to mark the place and breadth of the pupil of the eye, the light entering from an object at a, which is near (it is here placed nearer than an object could be seen in reality), is very divergent, or is spreading with a large angle; from

Fig. 209.

the pencil of rays is less divergent, or opens with a smaller angle ; from c it is less divergent still, and so on. Now the eye, to form an image on its retina, requires to exert a bending or converging power exactly proportioned to the divergence of the received rays; and the person has a sense of the effort made, which becomes a kind of measure of the distance of the object. This divergence of the rays entering the eye is an important circumstance in which the most perfect painting must still differ in its effect upon the eye from a natural scene,-for, first, in the natural scene, most of the objects are more distant than their representation can be; and, secondly, while in nature every object according to its distance is sending rays which reach the eye with corresponding divergence, the rays from a picture, which is a single plane surface, come from every part with nearly the same divergence, the eye must feel, therefore, a disappointment in not having to accommodate its power of bending to the different distances attempted to be portrayed on the canvas. It might be expected that this kind of disappointment would be more felt on looking at a common picture placed a few feet from the eye, than at the sort of picture called panorama, which is on a larger scale and proportionately more distant, but such is not always the case. The reason seems to be, that in the former the illusion is not assumed to be complete, for the fact of its being but a picture is not at all concealed, and the eye is therefore at once told to expect a difference of feeling; but in the panorama, the various circumstances are arranged to deceive the eye, if possible, entirely, and to make the spectator believe that the images on the retina are formed by light from the objects themselves. Then to the eye really deceived in all other particulars, the non-accordance with nature in this one, is quickly, and by some persons even painfully felt, so as on their first entering the place, to occasion slight headache or giddiness. The illusion, and consequently the p'casure from

634

Convergence of Optic Axes.

viewing pictures of distant objects, may be made more complete by the spectator using a single lens or a pair of spectacles, of focal distance nearly equal to the distance of the picture from the eye : because such lenses, as already explained, would render all the rays entering the eye nearly parallel, and therefore very nearly such as would reach it from objects at a considerable distance.

4th. Convergence of the axes of the eyes.

866. This is the last circumstance to be considered, by which a person, through the eyes, judges of the distance of objects. In consequence of there being two eyes, on the centres of whose retinas light from any object must fall in order that the person may have a clear vision of it, the axes of both eyes must be directed to the same point of the object. If it be very near, the optical axes will meet and cross each other very near to the face, exhibiting to bystanders the appearance called squinting, as when a man tries to look at the point of his nose; but for objects at greater and greater distances, the optical axes will become less and less oblique, until at length they are nearly parallel to each other. This state occurs, also, when persons are thinking of things not present, and, therefore, seen only by the mind's eye; and the countenance is then said to express contemplation or thoughtfulness. The following figure (fig. 210) serves to explain this part of the subject.

The two circles represent the eye-balls, looking along a middle

line, A B C, directly in front. That line is fitly realized by a common yard measure, or a straight lath of wood, having three pins sticking in it at different distances, as A B and C. While the axes of the