in Fig. 16; it will be found that the tint of the gray paper scarcely changes, unless the experimenter sits and stares at the combination for some time. A sheet of thin white tissue-paper is now to be placed 
Fig. 16.—Green and Gray Papers For Experiment on Contrast (One-quarter Size). over the whole, when it will instantly be perceived that the color of the small slip has been converted by contrast into a pale red. Persons seeing this illusion for the first time are always much astonished. Here we have an experiment showing that the contrast produced by strong saturated tints is much feebler than with tints which are pale or mixed with white light, for, by placing tissue-paper over the green sheet, the color of the latter is extraordinarily weakened and mixed with a large quantity of white light. In this experiment it often happens that the red, which is due to contrast alone, seems actually stronger than the green ground itself. If, instead of using a slip of gray paper, we employ one of black, the contrast is less marked, and still less with one of white. It is scarcely necessary to add that, if red paper is employed instead of green, the small gray slips become tinted by contrast with the complementary color—i. e., greenish-blue; the same is true with the other colors. By preparing with India-ink a series of slips of gray paper, ranging from pure white to black, an interesting series of observations can be made on the conditions most favorable for the production of strong contrast-colors. The strongest contrast will be produced in the case of red, orange, and yellow, when the gray slip is a little darker than the color on which it is placed, the reverse being true of green, blue, violet, and purple; in every case the contrast is weaker if the gray slip is much lighter or much darker than the ground. We must expect, then, in painting, to find that neutral gray will be more altered by pale tints of red, orange, or yellow, which are slightly lighter than itself, and that the gray will be less altered by these colors when differing considerably from it in luminosity; analogous conclusions with regard to green, blue, violet, and purple, can also be drawn. Saturated or intense colors in a painting have less effect on white or gray than colors that are pale; this was shown in the preliminary experiment when gray was placed on a ground of strong color. In repeating these experiments it will be noticed that the effect of contrast is stronger with green, blue, and violet, than with red, orange, or yellow—that is to say, it is stronger with the cold than with the warm colors.
We must next examine the effects that are produced by contrasting colors that differ in luminosity or in saturation. If the two colors are identical except in the matter of saturation, it will be found that the one which is more saturated will gain in intensity, while its pale rival
