SUIfSATIOIi. 17 



various experiments have been devised, which will be ex- 

 plained in comparing the rival theories of explanation. 



There are ftco theories — tlie psychological and the physio- 

 logical — which attempt to explain the phenomena of con- 

 trast. 



Of these the psychological one was the first to gain prom- 

 inence. Its most able advocate has been Helmholtz. It explains 

 contrast as a decepi^ion of judgment. In ordinary life our 

 sensations have interest for us only so far as they give 

 us practical knowledge. Our chief concern is to recognize 

 objects, and we have no occasion to estimate exactly their 

 absolute brightness and color. Hence we gain no facility 

 in so doing, but neglect the constant changes in their shade, 

 and are very uncertain as to the exact degree of their 

 brightness or tone of their color. When objects are near 

 one another " we are inclined to consider those differences 

 which are clearly and surely perceived as greater than 

 those which appear uncertain in perception or which must 

 be judged by aid of memory," * just as we see a medium- 

 sized man taller than he really is when he stands beside a 

 short man. Such deceptions are more easily possible in 

 the judgment of small differences than of large ones ; 

 also where there is but one element of difference instead of 

 many. In a large number of cases of contrast, in all 

 of which a whitish spot is surrounded on all sides by 

 a colored surface — Meyer's experiment, the mirror experi- 

 ment, colored shadows, etc., soon to be described — the 

 contrast is produced, according to Helmholtz, by the fact 

 that " a colored illumination or a transparent colored cover- 

 ing appears to be spread out over the field, and obser- 

 vation does not show directly that it fails on the white 

 spot."t We therefore believe that we see the latter 

 through the former color. Now 



" Colors have their greatest importance for us in so far as they are 

 properties of bodies and can serve as signs for the recognition of 

 bodies. . . . We have become accustomed, in forming a judgment in 

 regard to the colors of bodies, to eliminate the varying brightness and 



* Helmholtz, Pbysiolog. Optik, p. 393. 

 f Loc. cit. p. 407. 



