proved by experiment to be the case. This fact is illustrated in the familiar experiment of placing a white tissue paper over black letters on a colored ground, by which the black is practically rendered a neutral gray and the color a light broken color, and in appearance the gray letters receive a color complementary to the color of the page on which they are printed. Each color has its own tone of gray most susceptible to this complementary effect. The truth of this proposition can be perfectly shown on the color wheel by forming with three different sizes of disks a gray ring on a colored surface. For example, select small disks of orange and white of equal size, then a black and a white disk of the second size and an orange and a white disk of the third size. First place the large orange and white disks on the spindle, then join the two medium-sized white and black disks and put them in front of it, and lastly add the small orange and white disks. By rotation the result is the required neutral gray ring on a light orange surface. By the joining of the white disk with each of the orange disks the orange surface may be changed to a variety of tints for trial with the different grays which may be made from the black and white disks, so that the best tones of both orange and gray may be secured. When the best proportions are obtained the effect will be surprising, because when such disks are properly adjusted the complementary effect is so strong in the gray that it appears as a very definite color, a broken green-blue. It is said that the tone of gray should have the same relation to the tone of the color that its complementary would have in order to get best results.
For the same reason if a circle of lightest neutral gray paper, say four inches in diameter, is placed on a piece of yellow paper about six inches square, and another circle just like it is put on a piece of blue paper of similar size, it will be quite difficult to convince any one who has not previously seen the experiment that both gray circles are from the same sheet of paper. The results observed in this experiment are produced by
