FOOTNOTES.
[1] Münsterberg, H., and Campbell, W.W.: PSYCHOLOGICAL REVIEW, I., 1894, p. 441.
[2] In the preceding experiments the cord was definitely to be taken into account in making the judgment. The method of so doing was by running the eye back and forth over the cord preliminary to determining the location of the point.
THE ILLUSION OF RESOLUTION-STRIPES ON THE COLOR-WHEEL.
BY EDWIN B. HOLT.
If a small rod is passed slowly before a rotating disc composed of two differently colored sectors, the rod appears to leave behind it on the disc a number of parallel bands of about the width of the rod and of about the colors, alternately arranged, of the two sectors. These appear not to move, but gradually to fade away.
This phenomenon was first observed by Münsterberg, and by him shown to Jastrow,[1] who, with Moorehouse, has printed a study, without, however, offering an adequate explanation of it.
I. APPARATUS FOR PRODUCING THE ILLUSION.
Any form of color-wheel may be used, but preferably one which is driven by electricity or clock-work, so that a fairly constant speed is assured. Several pairs of paper discs are needed, of the ordinary interpenetrating kind which permit a ready readjustment of the ratios between the two sectors, as follows: one pair consisting of a white and a black disc, one of a light-and a dark-colored disc (light green and dark red have been found admirably suited to the purpose), and a pair of discs distinctly different in color, but equal in luminosity.