PHYSIOLOGY OF COLOE VISION KELLER AND MACLEOD. 731 



modify the colored impression created b}^ shifting the eyes to another 

 part. It is improbable, however, that any artist has laid on his pig- 

 ments with this object in view. Nevertheless, successive contrast 

 may assist us greatly in the actual determination of the comple- 

 mentary hue. Thus, to take again our example of the gray wall 

 against the green background, we may exaggerate the effect of the 

 green on the gray by regarding the green for some time and then 

 shifting the gaze to the wall, when its purplish hue will be found to 

 l)e much intensified. 



Simultaneous contrast, on the other hand, is of paramount impor- 

 tance in art; indeed, it is as important in the final impression pro- 

 duced by a painting or a design as any other quality which this may 

 possess. This importance depends on the fact that when two colored 

 surfaces are placed in apposition each becomes changed as if it were 

 mixed to a certain extent with the complementary hue of the other; 

 or if a gray or a tint of low saturation (see p. 733) is apposed against 

 a saturated color field it will assume a complementary hue of greater 

 or less saturation, according to the relative area of brightness of the 

 apposing areas. By applying these principles in picture painting 

 unsaturated hues may be caused to assume much greater degrees of 

 saturation, while, if the apposition be false, hues in themselves of 

 almost complete saturation may become dull and subdued. 



To the artist it comes to be of the highest importance that he 

 possess some easily remembered scheme by which he can predict these 

 contrast effects. The color triangle may be thus employed, but a 

 simpler, though perhaps less scientific device, for the same purpose is 

 the chromatic circle of Rood (fig. 2). To construct such a circle we 

 must laiow the wave lengths of the various colors which we desire to 

 contrast.^ The differences ip wave lengths are then calculated so as 

 to correspond to angular differences, these angles being formed by 

 the radii of the circle. As in the color triangle, opposite radii will 

 ]oin complementary colors and the center will represent white light; 

 i. e., the nearer the center the less will be the saturation of the color. 



If one such circle, drawn on transparent paper, be superimposed on 

 another, the effect which is produced by contrasting two colors can be 

 readily ascertained. Thus, suppose we desire to determine the influ- 

 ence which red has when contrasted with the other colors. Having 

 accurately superimposed the two circles we move the transparent one 

 so that the point on it which corresponds to red is displaced along 

 the line joining red and its complimentary, blue-gi*een. The colors on 

 the upper circle will now stand in positions on the lower correspond- 

 ing to the changes in hue and saturation which they would have 

 suffered by contrast with red. Thus orange will stand nearer the 



1 This can be done by comparing the colors with those of a highly magnified spectrum 

 of white light alongside of which is a scale of wave lengths. 



