22 PSYCHOLOGY. 



green and gray. The gray bars appear strongly colored 

 by contrast, although, since they occupy as much space as 

 the green bars, we are not deceiyed into belie-s-ing that we 

 see the former through a green medium. The same is true 

 if we weaye together into a basket pattern narrow strips of 

 green and gray and coyer them with the transparent paper. 



Why, then, if it is a true sensation due to physiological 

 causes, and not an error of judgment, which causes the 

 contrast, does the color disappear when the outlines of the 

 gray scrap are traced, enabling us to recognize it as an 

 independent object ? In the first place, it does not neces- 

 sarily do so, as will easily be seen if the experiment is 

 tried. The contrast-color often remains distinctly yisible 

 in spite of the black outlines. In the second place, there 

 are many adec^uate reasons why the effect should be modi- 

 fied. Simultaneous contrast is always strongest at the 

 border-line of the two fields ; but a narrow black field now 

 separates the two, and itself by contrast strengthens the 

 whiteness of both original fields, which were already little 

 saturated in color ; and on black and on white, contrast- 

 colors show only under the most fayorable circumstances. 

 Even weak objectiye diflerences in color may be made to 

 disappear by such tracing of outlines, as can be seen if we 

 place on a gray background a scrap of faintly-colored 

 paper, cover it with transparent paper and trace its out- 

 lines. Thus we see that it is not the recognition of the 

 contrasting field as an independent object which interferes 

 with its color, but rather a number of entirely explicable 

 physiological disturbances. 



The same may be proved in the case of holding above the 

 tissue paper a second gray scrap and comparing it with that 

 underneath. To avoid the disturbances caused by using 

 papers of different brightness, the second scrap should 

 be made exactly like the first by covering the same gray 

 with the same tissue paper, and carefully cutting a piece 

 about 10 mm. square out of both together. To thoroughly 

 guard against successive contrast, which so easily comjDli- 

 cates the phenomena, we must carefully prevent all previ 

 ous excitation of the retina by colored light. This may be 

 done by arranging thus : Place the sheet of tissue paper 



