glass, no trace of green effect will be produced, but a gray either slightly yellow or blue, according to the relative strength of the colors in the glass and the silk. This same effect would be secured if the yellow light of the setting sun illuminated the same material, but under such conditions everything else would be similarly affected so that the effect would not be so apparent.
The idea that all color is derived from the three primaries, red, yellow and blue, is so generally believed that our best writers among artists, colorists and educators have repeated it for many years. George Barnard, an English artist, in a very valuable book on water color painting, speaking of the colors of the spectrum which may be re-combined to form white light, says that if the yellow and blue rays are combined they produce green.
Chevreul also states in his invaluable book on color contrasts that yellow and blue threads woven into a texture, side by side, produce green. This statement is the more remarkable because the writer was a very careful investigator and is but another evidence of the strong hold which the Newton and Brewster theory has had on the public mind for so many years.
The story is told of an artist who wished to introduce into a composition of still life a blue vase with a bit of yellow lace thrown over a portion of it, and having been educated to believe that yellow and blue made green, gave a green effect to the portion of the vase covered by the lace. Had he known that blue and yellow light combined make gray instead of green he would have avoided the error.
The fact that gray is the product of blue and yellow light is sometimes taken advantage of in forming backgrounds in lithographic printing, in which a stippling of alternate clots of yellow and blue, very close together but not overlapping, is used to produce a beautifully transparent gray much more pleasing than any one tint of gray. This result is clue to the blending of the two colors in the eye with the same effect as the colors of two rotating disks are mingled. The fact that there is a dif-
