EFFECTS OF FAULTY VISION IN PAINTING. 183 



that, for instance, an intense or strongly illuminated red can be per- 

 ceived as such, while a less intense red appears green. This moderate 

 degree of color-blindness does not always deter people from painting. 

 A proof of this I saw at the last year's Exhibition, in a picture which 

 represented a cattle-market. The roofs of the surrounding houses 

 were all painted "red on the sunny side, green in the shadow; but 

 what particularly struck me the oxen also were red in the sun, green 

 in the shadow. The slighter degrees of this anomaly, in the form of 

 an insufficient perception of colors, have probably been the real cause 

 why several great artists, who have become famous on account of the 

 beauty of their drawing and the richness of their compositions, have 

 failed to attain an equal degree of perfection in coloring. 



In opposition to these isolated cases, I have to draw your attention 

 to other cases which happen more frequently, and in advanced age, in 

 consequence of a change in the perception of colors. They do not 

 arise from a deficient function of the nervous apparatus of the eye, but 

 in consequence of a change in the color of the lens. 



The lens always gets rather yellow at an advanced age, and with 

 many people the intensity of the discoloration is considerable. This, 

 however, does not essentially diminish the power of vision. In order 

 to get a distinct idea of the effect of this discoloration, it is best to 

 make experiments with yellow glasses of the corresponding shade. 

 Only, the experiment must be continued for some time, because at first 

 every thing looks yellow to us. But the eye gets soon accustomed to 

 the color, or rather it becomes dulled with regard to it, and then 

 things appear again in their true light and color. This is at least the 

 case with all objects of a somewhat bright and deep color. A careful 

 examination, however, shows that a pale blue, or rather a certain small 

 quantity of blue, cannot be perceived even after a very prolonged ex- 

 periment, and after the eye has long got accustomed to the yellow 

 color, because the yellow glass really excludes it. This must, of 

 course, exercise a considerable influence when looking at pictures, on 

 account of the great difference which necessarily exists between real 

 objects and their representation in pictures. 



These differences are many and great, as has been so thoroughly 

 explained by Helmholtz. Let us for a moment waive the considera- 

 tion of the difference produced by transmitting an object seen as a 

 body on to a simple flat surface, and consider only the intensity of 

 light and color. The intensity of light proceeding from the sun and 

 reflected by objects is so infinitely greater than the strongest light re- 

 flected from a picture, that the proportion expressed in numbers is far 

 beyond our comprehension. There is also so great a difference be- 

 tween the color of light, or of an illuminated object, and the pigments 

 employed in painting, that it appears wonderful that the art of paint- 

 ing can, by the use of them, produce such perfect optical delusions. 

 It can, of course, ODly produce optical delusions, never a real optical 



