EVERY sensation is different from what it would have been if it had been experienced together with, or in sequence to, some other sensation. One of the best illustrations of this "law of relativity" is to be found in contrast, which we shall now study in the sense of sight.
These experiments should be performed in good diffused daylight. Unless otherwise directed, the object must invariably be viewed through the tissue-paper. The foregoing exercise has taught the importance of avoiding fatigue for color and brightness. Make prompt judgments and avoid unnecessary exposure of the eyes to the figures.
1. Brightness-contrast.--Lay the black and the white squares about three centimeters apart upon the background; place a gray bar upon each of them and cover the whole with the tissue-paper. Compare the____________________