252 THE POPULAR SCIENCE MONTHLY. 



in which particular shades are given a changed appearance to our per- 

 ceptions 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 popu- 

 lar 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 nerv- 

 ous fibers suffer in consequence of the higher activity which the pre- 

 sentation 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 rela- 

 tively 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 char- 

 acter 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-percep- 

 tions which are wholly conditioned upon the organization of the eye. 

 These are the subjective conceptions that show forth the complement- 

 ary 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 



