738 ANNUAL KEPORT SMITHSONIAN INSTITUTION^ 1913. 



different spectral hues are brought to a focus on the retina. The rays 

 of slow vibration, as at the red end of the spectrum, are less readily 

 focused than those which vibrate quickly, as at the violet end. Con- 

 sequently, when red rays are in focus, violet rays are overfocused and 

 vice versa. The application of these principles in art depends on the 

 fact that our judgment of distance is partly associated with the 

 amount of effort which we must make in order to accommodate our 

 vision. At rest the optical apparatus of the eye is accommodated 

 for distant objects so that when these come nearer than a certain 

 point an effort is required to make the focusing stronger. From the 

 amount of this effort we judge in part of the distance of the object. 

 Now, it takes more effort to focus red than green or blue rays so that 

 we always tend to locate a red object as being nearer than one that is 

 blue or green. These facts can be very beautifully demonstrated by 

 looking at red and green lamps placed side by side; the green light 

 appears to be behind the red. And in picture painting the same 

 principles can be applied, and seem to be so in many of the post-im- 

 pressionists' paintings; objects are brought forward by being colored 

 in the reds and they are pushed back by the use of blues and violets. 

 These facts bring us to a discussion of the influence of the blue- 

 violet line which so many post-impressionists are using to outline ob- 

 jects to which they desire, without shading, to give the impression of 

 rotundit}'-, or more correctly, of projection. The effect of such a line 

 is perhaps best demonstrated in still-life studies where its existence 

 at the edges of, say, a vase, will, when the picture is viewed at such a 

 distance that the line just disappears, cause the vase not only to 

 stand forward from its background but also make it appear rotund, 

 as if shaded toward the edges. The line is sometimes used in land- 

 scape pictures with the object of holding the pattem together. These 

 effects are most marked when the object is painted in hues that are 

 considerably removed from blue on the chromatic circle, or are of 

 much less saturation (more removed toward neutrality). Similar 

 effects can sometimes be obtained by the use of a black line, but none 

 of the flaring hues can be successfully employed for making it. It 

 is difficult to explain the action of these outlines : indeed, it is almost 

 certain that several factors play a role in producing the illusion 

 which they create. When the line is a blue one and the prevailing 

 hue of the color field which it borders tends toward yellow a syn- 

 thetic gi'ay will result at a certain distance, thus creating the impres- 

 sion that some space exists between the object and its surroundings. 

 Wlien a black line separates two colored areas there occurs a certain 

 amount of irradiation on to it of the neighboring hues, which there- 

 fore undergo a more or less sudden lowering of intensity at its edges, 

 wliich become more and more pronounced toward the middle of the 

 line until the hues finally meet and partly overlap, thus producing a 



