LIII.) These colored disks are slit on one side from center to circumference, and therefore by interlocking two or more they may be adjusted so that either occupies any desired percentage of the whole area, which may be very precisely determined by a scale of 100 segments shown on the outer edge of a larger disk on which the colored disks are superimposed. When connected with the color- wheel and adjusted as may be desired, and then rapidly revolved, the two or more distinct colors resolve themselves into a single uniform composite color, whose elements are shown, in their relative proportion, by the scale surrounding the disks.[1]
The scales (both horizontal and vertical) of the present work are all prepared directly from definite color-wheel formulæ, based on carefully calculated curves; the thirty-six pure spectrum hues, represented
- ↑ See the colored figure on the frontispiece of this work, which clearly illustrates this method of color measurement. Larger disks of spectrum red, green, and violet are interlocked and adjusted so that they present, respectively, 32, 42. and 26 per cent, of the circumference ; superimposed on these is a single smaller disk of neutral gray , and on this two still smaller disks of black and white, the former occupying 79, the latter 21, per cent, of the area. The result of this combination of colors, when the disks are rapidly revolved, is that the entire surface becomes a uniform neutral gray precisely like the middle disk, which blends so completely with the color inside and outside its limits that no trace of division can be detected. Hence, neutral gray equals a combination of red 32, green 42, and violet 26 per cent., and also equals a combination of black 79 and white 21 per cent. As further illustrating the point, it may be mentioned that not only does the above-mentioned combination of the three primary colors equal neutral gray but so also does the combination of any color ("secondary" or "tertiary' as well as primary) with its complementary, though the darkness or lightness of the gray varies somewhat, as the following table shows:
Spectrum Color. Complementary Color. Equivalent Gray. Name. Per Cent. Per Cent. Composition. Black. White. Red 44 56 Blue 41 + Green 59. 72.5 27.5 Orange 28.5 71.5 Blue 51.5 + Green 48.5. 69 31 Yellow 33 67 Blue 60.5 + Violet 39.5. 64 36 Green 51 49 Red 57.5 + Violet 42.5. 73 27 Blue 64 36 Yellow 82 + Orange 18. 62 37 Violet 62.5 37.5 Yellow 69 + Green 31. 61.5 38.5
