Popular Science Monthly/Volume 31/June 1887/Appearance and Reality in Pictures
By Dr. EUGEN DREHER.
IN the contemplation of the creations of the painter, the mind is stimulated to a degree of activity which the enjoyment of no other form of art-work can induce. A mental operation is provoked of which we are hardly conscious, and which some have attributed to the organization of the visual apparatus, that amounts in effect to the transformation of the flat surfaces of the picture into the appearance of a body or a group standing out or receding in relief. The inquiry as to how the painter can invoke this illusion is usually answered by saying that he knows how to represent objects in perspective; that is, that he is able to arrange the lines of the picture—except that the image is not reversed—so that the adjustment shall correspond essentially with that of the image which is cast upon the photographer's screen or upon the retina of the eye. The process, unperceived and instantaneous in the case of simple objects, by which such representations are given bodily projection, may be followed out in its gradual development in contemplating pictures of a more complex character, as, for instance, a view of the interior of a grand cathedral. Without any change taking place in the image on the retina, the individual objects are gradually lifted one from another; those represented as in the background appear to become larger but at the same time obscure, and those in the fore-ground to grow smaller but more sharply defined. Thus the size we attribute to the objects depends upon the distance we assign to them as well as on the visual angle they subtend. There are, according to this, unconscious processes that fit us for seeing plane surfaces as bodies, provided the picture furnishes suitable points to which our conceptions of corporeal projection may attach themselves. To see a perspective representation of a cube, I must have remaining within me a conception of a cube already acquired by the exercise of my senses; and, without such an acquired conception, the picture would still be to me only a picture or a planimetric feature, without projection. Hence we find that, in looking at pictures, unconscious representations intrude upon the primary conceptions, and change them into secondary ones, by means of which a surface is made to look like a body having projection. This process occurs in all monocular vision, when we interpret the flat retinal image corporeally.
To obtain a proper appreciation of a perspectively correct picture, we must look at it with one eye; for, in looking with two eyes, the duplication of the visual lines that define the position of each point as it is perceived, must cause more or less of the impression of the really plain surface to persist. In this case the corporeal projection becomes confused with the superficial conception, and is more or less modified by it. The effect of perspective is also heightened by looking at the painting through a tube, by means of which it is abstracted from the frame and from its surroundings.
We observe, also, in looking at a picture, the curious phenomenon that, whatever position we may take toward it, it always appears projected, but in aspects which are varied not only in respect to the absolute position of its constituent parts, but also in respect to their mutual relations with one another, to such an extent that from an extremely unfavorable position it appears distorted.
Whenever an artist can not produce the perspective effects he desires in a picture drawn with absolute correctness, he does not hesitate to exaggerate the perspective if he thinks he can thereby enforce a better conception of his design. lie represents distant objects on a smaller scale than strict accuracy demands, and causes us, by unconsciously taking account of the reduction, to see them farther off than we otherwise would do; and he knows how to call our imagination to his help in other ways.
Although the application of perspective devices is usually enough for the purpose, the projection of the design is heightened to a considerable degree, facilitated and brought nearer the appearance of reality by the introduction of effects of light and shade. This also is borrowed from Nature. The shading may, indeed, sometimes define and fix the effect which mere perception fails to convey positively. A square with two diagonals drawn across it may mean simply that, or it may be intended to represent a pyramid. If proper shading is added, the figure is made to mean a pyramid unmistakably.
If we assume that the light is evenly diffused through any space, then, other conditions being equal, those things in the space which are nearer to us will be clearer in appearance in a proportion determined by the rule that the intensity of light diminishes as the square of the distance increases. A point twice as far from the eye as another appears four times as obscure. This normal diminution of intensity is augmented by the darkening which objects undergo in consequence of the interposition of strata of air, or by the effect of "air-perspective," as it is called, in distinction from linear perspective. The painter must take both of these phenomena into account. By the application of a suitable coloring, the effect of air-perspective may be produced in so striking a degree that objects may, by means of it, be made to appear wonderfully remote. This effect, also, is dependent upon our unconscious application of knowledge we have gained from previous experience.
The shadow which all objects cast when exposed to any kind of light is a capital sign of bodily substance. Our conception of bodies is inseparable from that of their shadows. The importance of this phenomenon as an aid to projection is illustrated by the manner in which through them flat letters on signs are made to appear standing out as solid bodies.
The painter is also able to represent motion by taking advantage of the unconscious working of our preconceived impressions. Looking at a masterly marine landscape in the National Gallery at Berlin one day, I could almost see the ship rising and falling upon the waves, and the waves themselves seemed to be in motion as they swelled and swept by the vessel. The painter had seized a single instant in the succession, and had so represented it as to call out the idea of consecutiveness. The question arises, How is the artist to illustrate motion, as he often has to do, say in such a case as that of a rapidly turning wheel, in which we can at no instant distinguish the single spokes, but see only a confusion of flying lines? It is clearly impossible for him to give the exact appearance of motion. He can only seize a given instant or stage, and so manage that it shall represent itself as the effect of the preceding stage and the cause of the following one: A sword-blow must be represented at a decisive point, not at a stage in the descent of the weapon, else the illusion will be destroyed; a pendulum in motion, not at the bottom of its course, where it would seem to be at rest. In painting a galloping horse, no stage of the exact motion is reproduced. The instantaneous photographs have demonstrated that; and also that, if the artist should attempt a reproduction of the kind, he would give any but the effect desired. He makes a more pleasing and probable picture, having, however, no counterpart in Nature, in which he does no violence to her, but, as Schiller has said, "increases the nature that is in Nature."
The theory of color-perceptions is not yet far enough advanced to permit a full explanation of all the phenomena of coloring; still, it is competent in its present condition to give valuable hints concerning the color-effects experienced in the contemplation of paintings.
All the variations in color perceived in Nature may be produced from red, yellow, and blue, or, as others have it, from red, green, and violet, and their combinations. The painter does not possess any of these colors in their purity, but always adulterated with more or less that is foreign to them, and can hardly ever reproduce the exact color he finds in Nature, and it is his task to combine the materials he has so as to give as near as possible an approach to them. How does he, with the deviations he is forced to make, bring about the magic illusion that causes us to perceive in his creations the same endless play of light and color that Nature so lavishly bestows upon her pictures? How does he reproduce the burning glow of the setting sun and the objects it illuminates? He does it by means of a contrast of colors, in which particular shades are given a changed appearance to our perceptions by backing them one against another. When, for instance, a tolerably clear red and a tolerably pure green are put together, both colors appear to undergo a change, and to gain in purity; or, in popular language, the red seems to become redder and the green greener. This proceeds from two causes, one of which is purely mental, and consists in the heightening of the contrast between the two colors when they are brought into comparison with each other; while the other is physical, and depends upon a kind of fatigue which the nervous fibers suffer in consequence of the higher activity which the presentation of the contrast develops in them. As the perception of the red becomes wearied, that of the green becomes more acute, and vice versa, and the two in this manner react upon each other. By a similar process, white reposing upon black appears clearer and purer, while the black seems deeper and darker.
A painter, having to introduce two kinds of light, daylight and candle-light, into his picture, would not be able to represent directly the contrasts which the struggle between the two kinds of light calls forth in Nature, because his colors are so inferior in intensity to the reality. He has to paint the effect in by making the daylight relatively bluer and the candle-light more of a red-yellow than in Nature. He thereby leads us, after an interval, to an illusion of the same character with that which Nature, by the superior intensity of its light, produces in a moment.
In like manner, the painter, by exaggerating the illumination of his objects, reproduces similar effects to those which Nature gives with the full brilliancy of its light; as, for instance, the glow of the snow-fields of the Alps, which the beams of the evening sun clothe as with a garment of fire, in contrast with the dark-blue vault of the sky above them, and with the valleys already hiding themselves in the shadows of night. In all these cases the action of Nature is made more speedy than that of the picture, because the light at its disposal is so much stronger, but the effect of both is in the end of the same character, and the seeming becomes clothed with reality.
The painter must, furthermore, give effect to other color-perceptions which are wholly conditioned upon the organization of the eye. These are the subjective conceptions that show forth the complementary colors. By this term are meant those colors which in combination produce white, as red and green, blue and orange, yellow and violet. The complementary tint also appears after the eye has become fatigued in looking at a particular color, as when the eye has been gazing at green, it turns to a white spot and appears to see it red.
The complementary effects may frequently be observed in Nature. Parts of the sky between bright-red clouds sometimes appear green; and the ground of a wood, the bright-green foliage of which glitters in the sunlight, looks rose-colored. The painter has to take these phenomena into consideration, and, making due allowance for the weakness of his pigments, to incorporate the apparent tints into his picture. Here, again, what Nature with her vivid colors does in an instant, the artist has to bring about more slowly; but the illusion is complete in both cases from the moment our conceptions are brought into accord with it.
There is, furthermore, something in the colors of natural objects which is distinct from the strength and clearness of the illumination, and appears peculiar to certain kinds of light. Among such peculiarities are the metallic luster, the silken sheen, and opalescence, which, although they all proceed from combinations of the spectrum-colors, have not yet been sufficiently investigated to enable us to determine all the circumstances contributing to produce them.
The colors used in painting afford little that is analogous with these lusters. Can the painter produce these effects also by contrast? They appear in pictures by the most eminent masters to be reached almost in perfection. If, however, we inquire whether the painter can reproduce the peculiarities of luster and color which we admire so much in Nature through the contrast of his colors alone, we shall have to admit that he calls other elements into play.
We have already shown how our conceptions of the relations of objects in place are influenced by our unconscious prepossessions. May not these also intrude themselves upon and modify our conceptions of the color and tone of the picture? The connoisseur who has frequently observed the shimmer of the sea, and who has followed with a finely developed perceptive power the transformations of the landscape under a changing light, and who has been in the habit of watching in an æsthetic mood the combination and grouping of the individual features of Nature, is doubtless better able to realize these peculiarities also in works of painting, than he who applies only a sharp but untrained discernment to the gradual development of the idea of the picture.
Thus art, temporarily withdrawing us from Nature by substituting her own creations for the reality, brings us back to Nature as the inexhaustible source whence all its elements are borrowed; and the imagination, also, in its own way, is able to make use of those elements for new creations.—Translated for the Popular Science Monthly from Die Natur.
Colonel Serpa Pinto and Lieutenant Cardozo last year made a successful scientific exploration of the lake-region of Africa. They made a geodetic triangulation of the country from Ibo to Lake Nyassa, whence Lieutenant Cardozo—Colonel Pinto having withdrawn on account of illness—went to Shirva and Blantyre, and by a new road to Quilimane. This is the first scientific work of the kind done in that part of Africa.