_Series No. XV._--The figures in each pair of this series were full-faced, and of the same shape and size, but one was gray and the other colored, the gray being seen first to the left, and then to the right. The colors used were of Prang's series (Gray, R., Y., G., B., V.). In No. 1 the figures were in the form of a six-pointed star, and gray was compared with red. In No. 2 the figures were elliptical, and gray was compared with yellow. In No. 3 a broad circular band of gray was compared with the same figure in green. In No. 4 the figures were kite-shaped, and gray was compared with blue. In No. 5 a circular surface of gray was compared with a circular surface of violet. The objects compared were exposed at the same time, under the usual conditions. As might perhaps be expected, the colored surfaces proved to be the more persistent in ideation, showing a general average of 37.81 seconds per minute as against 30.90 seconds for the gray. The distinctness of the process of color apprehension is reflected in the notes: "In the colored images I find the color rather than the form occupying my attention; the image seems like an area of color, as though I were close to a wall and could not see the boundary;" and then we have the significant addition, "yet I feel myself going about in the colored area." Again: "In the gray the outline was more distinct than in the colors; the color seems to come up as a shade, and the outline does not come with it." Or again: "The gray has a more sharply defined outline than the color." This superior definiteness in outline of the gray figures is subject to exceptions, and one subject reports 'the green outline more distinct than the gray.' And even so brilliant a color as yellow did not always obscure the boundary: "The yellow seems to burn into my head," says one of the subjects, "but the outline was distinct." The reports in regard to this color (yellow) are in fact rather striking, and are sometimes given in terms of energy, as though the subject were distinctly conscious of an active process (objectified) set up in the apprehension of this color. The reports run: "The yellow has an expansive power; there seemed to be no definite outline." "The yellow seemed to exert a power over the gray to suppress it; its power was very strong; it seemed to be aggressive." TABLE XVI.