1 84 THE POPULAR SCIENCE MONTHLY. 



identity ; that is to say, the image which is traced in our eye by rea, 

 objects is not identical with the image produced in our eye by the pict- 

 ure. This is best observed by changing the light. Whoever paints in 

 London has but too frequent opportunities of observing this. A little 

 more or less fog, the reflection of a cloud, illuminated by the sun, suf- 

 fices to alter entirely the coloring of the picture, while the coloring of 

 natural objects is not changed in the same manner. 



Let us now return to our experiment with the yellow glass, and we 

 shall find that it aflect6 our eye very much in the same way as a yellow 

 tint in the light, and therefore modifies natural objects in quite a dif- 

 ferent degree from pictures. If we continue the experiment for a con- 

 siderable time, the difference becomes more and more essential. As I 

 said before, the eye becomes dulled with regard to the yellow light, 

 and thus sees Nature again in its normal coloring. The small quantity 

 of blue light which is excluded by the yellow glass produces no sen- 

 sible difference, as the difference is equalized by a diminution of sensi- 

 bility with regard to yellow. In the picture, on the contrary, there is 

 found in many places only as nmch blue as is perfectly absorbed by 

 the yellow glass, and this,, therefore, can never be perceived, however 

 long we continue the experiment. Even for those parts of the picture 

 which have been painted with the most intense blue the painter could 

 produce, the quantity of blue excluded by the yellow glass will make 

 itself felt, because its power is not so small with regard to pigments as 

 with regard to the blue in Nature. 



Imagine, now, that, in the course of years, one of the transparent 

 media in the eye of a painter had gradually become yellowish, and 

 that this yellow had by degrees considerably increased in intensity, 

 and you will easily understand the influence it must exercise upon his 

 work. He will see in Nature almost every thing correctly ; but in his 

 picture every thing will appear to him yellowish, and consequently he 

 will paint it too blue. Does he not perceive this himself? Does he 

 not believe it if told of it ? Were this the case, it would be easy for 

 him to correct the fault, since an artist can paint in a yellower or 

 bluer tone, as he chooses. These are two questions which are easily 

 answered by psychological experience. He does not perceive it him- 

 self, because he does not remember that he formerly saw in a different 

 way. Our remembrance with regard to opinions, sensations, percep- 

 tions, etc., which have become gradually modified in the course of 

 years not by any external influence or sudden impression, but by a 

 gradual change in our own physical or mental individuality is almost 

 nil. 



He does not believe it I would not say because an artist rarely 

 recognizes what others tell him with regard to his works, but because 

 with him, as with every one else, the impressions received through his 

 own eye have a stronger power of conviction than any thing else. 

 " Senen geht vor Sagen " (" Seeing is believing "), says the old adage. 



