PHYSIOLOGY OF COLOR \aSIOK KELLEE. AND MACLEOD. 729 



very satisfactory transitions at the edges between them, all of which 

 are qualities that can be rendered in no way so satisfactorily as by 

 pointilism. 



There can be little doubt that a great part of the peculiar impression 

 produced by pomtilism depends upon the slight movements which the 

 eyeballs are constantly undergoing, even during our most intent fix- 

 ation. This of course produces a certain amount of overlapping of 

 the colors on the retina just as when they are superimposed by means 

 of Maxwell's machine. In the same way vibrations of the eyelids 

 by moving the eyelashes across the palpebral cleft assist in the syn- 

 thesis, this being made evident by half closing the eyes, a method 

 often used in studying pictures. 



The success with which the desired impression can be created in a 

 pointilistic picture often depends upoji the purity of the colored dots, 

 its vibrating quality being at the same time much enhanced by leaving 

 a narrow margin of white around each dot. When this is successfully 

 done there comes into play another physiological process knoAvn as 

 flicker, which can be experimentally produced by rotating disks with 

 black and Avhite sectors at a speed which is just insufficient to cause a 

 uniform gray. The resulting flicker possesses a glittering quality 

 which makes it appear of distmctly greater brightness than the gray 

 which results from complete synthesis. The same thing may be seen 

 by observing the spokes of a wheel revolving at different velocities. 

 Instead of black and white the sectors may be composed of different 

 hues. 



In the flicker experiments the gray remains of the same degree of 

 saturation at whatever rate the disk is revolving, provided it is re- 

 volving more quickly than is necessary to produce complete fusion, 

 and so in pointilistic painting, when the picture is viewed beyond the 

 distance at which fusion occurs the impression is practically that of 

 the older painting. It must be viewed at a distance just short of that 

 which is necessary to produce complete synthesis. The post impres- 

 sionists, such as Cezanne, Matisse, etc., realizing this limitation in 

 pointilism, have been searching after a method by which the color 

 scheme maintains its effect on us at whatever distance the picture is 

 viewed. The physiological principle upon which this depends is 

 that known as contrast, and this we will now proceed to study. 

 Being a property exhibited most strikingly in the case of comple- 

 mentary hues, it becomes necessary for us to have, besides the color 

 triangle, some simple experimental methods by which the comple- 

 mentary hues may be determined. Such methods include the experi- 

 ments of simultaneous and successive contrast, in connection with 

 which many facts of fundamental importance in the use of pigments 

 are brought to light 



