858 



PERCEPTION OF COLORS. 



added. Therefore, any color-mixture may be produced by a color of the 

 spectrum plus white. (2) The less white the colors contain, the more 

 saturated they are said to be; the more white they contain, the less 

 saturated do they appear. The degree of saturation of a color dimin- 

 ishes with the intensity of the illumination. In a steadily increasing 

 illumination, the colors become more nearly white, and at the same time 

 they lose more and more their specific character; for example, in a bright 

 light, yellow readily passes into white. 



As the pigment of the macula lutea partly absorbs certain colored lights, 

 an explanation is afforded for the fact that colors seen by the macula alone have 

 a different appearance from those seen by other portions of the retina. 



Since the time of Newton, attempts have been made to construct a so-called 

 geometric color-chart, on which any mixed color can be found, according to the 

 principle of construction of the center of gravity. The accompanying figure 

 shows such a color-chart: white is placed in the middle, and different colors are 

 represented at points in the curve surrounding it. From the center (white) 

 to each of these points of the curve, lines may be drawn and each color may be 

 conceived as applied to the line in such a manner that, commencing at white, 

 there is the lightest tint, and then gradually more saturated ones, until, finally, 

 at the point of the curve designated by the name of the color the latter appears 



in a pure saturated form. Be- 

 tween violet and red, their mixed 

 color, purple, is indicated. In 

 order to determine from this 

 chart the mixed color produced 

 by any two colors of the spectrum, 

 the points of these colors should 

 be connected by a straight line; 

 in each point weights may be 

 conceived as placed correspond- 

 ing to the units of intensity of 

 these colors. Then the position 

 of the center of gravity of the 

 two in the connecting line indi- 

 cates the situation of the mixed 

 color in the color-chart. The 

 mixed color of two spectral colors 

 lies in the straight line that con- 

 nects the two color-points on the 

 color-chart. It is easily seen, 

 FIG. 300. Geometric Color-chart. further, that the impression of 



the mixed color corresponds to 

 an intermediate spectral color 



mixed with white. The complementary color of any spectral color is found by 

 drawing a line from the point of this color through white, until it intersects the op- 

 posite edge of the color-chart. The point of intersection gives the complemen- 

 tary color. If pure white is to be made from a mixture of two complementary 

 >rs, the color lying nearest white on the connecting line must be especially 

 strong, for then only would the center of gravity of the connecting line be 

 situated in the point white. 



The color-chart permits, further, of the determination of the mixed color 

 produced by three or more colors. For example, the colors designated by the 

 nts a (pale yellow), b (comparatively saturated greenish blue) and c (com- 

 paratively saturated blue) are chosen for mixing. In the three points are placed 

 weights that represent the intensities of the colors, and the center of gravity 

 riangle a b c is determined; this will lie at p. It is obvious, however, that 

 s mixed impression, whitish-greenish-blue can be produced also by the color 

 greenish-blue + white (according to rule i), for p can just as well be the center 

 of gravity of two weights that lie on the line connecting greenish-blue and white. 

 Around the color-chart a triangle V Gr R may be drawn, enclosing the figure 

 The three primary or fundamental colors, red, green and violet, 

 lie in the angles of the triangle. It is evident that every colored impression, 

 that is any point of the color-chart, may be determined by placing at the angles 



Violet 



Cyan blue 



Indigo 



Orange 



