THE E7E AS A SENSORY APPARATUS. 547 



will seem dark gray, with a white patch on it; an effect due 

 to the greater excitability of the retinal parts previously 

 rested by the black, when compared with the sensation 

 aroused elsewhere by light from the white wall acting on the 

 previously stimulated parts of the visual surface. All persons 

 will recall many instances of such phenomena, which are es- 

 pecially noticeable soon after rising in the morning. Similar 

 things may be noticed with colors; after looking at a red 

 patch the eye turned on a white wall sees a blue-green patch; 

 the elements causing red sensations having been fatigued, the 

 white, mixed light from the wall now excites on that region 

 of the retina only the other primary color sensations. The 

 blending of colors so as to secure their greatest effect depends 

 on this fact; red and green go well together because each 

 rests the parts of the visual apparatus most excited by the 

 other, and so each appears bright and vivid as the eye wan- 

 ders to and fro; while red and orange together, each exciting 

 and exhausting mainly the same visual elements, render dull, 

 r or in popular phrase " kill," one another. 



Contrasts. If a well-defined black surface be looked at on 

 a larger white one the parts of the latter close to the black look 

 whiter than the rest, and the parts of the black near the 

 white blacker than the rest; so, also, if a green patch be 

 looked at on a red surface each color is heightened near where 

 they meet. This phenomenon is largely due to fatigue and 

 deficient fixation : the retinal parts not excited and fatigued 

 by the black or the green are brought by a movement of the 

 organ so as to receive light from the white or red surface; 

 phenomena due to this cause are known as those of successive 

 contrast. Even in the case of perfect fixation, however, some- 

 thing of the same kind is seen; black looks blacker near 

 white and green greener near red when the eye has not 

 moved in the least from one to the other. A small piece of 

 light gray paper put on a sheet of red, which latter is then 

 covered accurately with a sheet of semi-transparent tissue- 

 paper, assumes the complementary color of the red, i.e., IOOKS 

 bluish green ; and gray on a green sheet under similar cir- 

 cumstances looks pink. Such phenomena are known as those 

 of simultaneous contrast, and are explained on psychological 

 grounds by those who accept Young's theory of color vision. 

 Just as a medium-sized man looks short beside a tall one, so, 

 it is said, a black surface looks blacker near a white one, or a 



