that boundary will be invisible; and it is just as evident that it is dependent 

 on light-and-shade, since two objects of like color can be differentiated, and 

 two of different colors can be made to appear to blend together, by effects 

 of shadow and light. Light-and-shade is more important than color, because 

 it is primarily an attribute of form, while color is only secondarily so. The 

 reader should look at his hand, or any other small object of elaborate form, 

 and consider the factors of its appearance which enable his eye to perceive 

 it, in its entirety and its details. The form and position of the various por- 

 tions are revealed by the lines of perspective, and by the light-and-shade, 

 that is, the shadows on those parts which are most averted from the prevailing 

 light, and the points of high-light on the reverse portions. We have already 

 seen that these main factors are interdependent on each other. Color, the 

 third factor, plays a much smaller part. A projecting portion, for instance, 

 may be of a different color from the rest, and will then be distinguishable 

 from it by its color alone, but without the line and light-and-shade it would 

 appear merely as a spot of color on the general surface — the projection would 

 not show as such, except in so far as its peculiar color revealed its character- 

 istic outline, — when, as in the case of the counter-shaded animal, the fact of 

 its solid form would be mentally inferred, rather than actually seen, by the 

 observer. On the other hand, there is the color difference between the sur- 

 faces which more directly catch the bluish sky-light, and the relatively orange- 

 colored shadow-portions, etc., aside from other possible color incidents of 

 reflected light; but these are secondary factors, since if the whole object were 

 of a uniform neutral tint, and the color effects of the light were eliminated, 

 the visibility of its various parts would scarcely be decreased. (Drawings in 

 black and white, and photographs, are excellent exponents of this principle.) 

 In just this way the form-variations of all solid objects are revealed to the eye 

 — according to the simple law, that depressions lose light and are therefore 

 darker, and elevations gain light and are therefore brighter; surfaces averted 

 from the prevailing light being equivalent to depressions, and those turned 

 toward it to elevations. It is, then, primarily by the light-and-shade on solid 



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