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
