_High Speed._ This curve shows very well indeed what seems to be typical of the relations between the intensity of the moving light and the apparent curvature of the front edge of the image. With the lowest degrees of intensity the amount of the curvature is very little. Sometimes it was difficult to measure it at all. The light was so faint and the speed so rapid that probably very little reënforcement or irradiation took place, although what did occur would show its presence most prominently, since, on account of the high speed at which the pendulum moved, any part of the image which should come into consciousness ahead of the rest, even by a very little time, would appear considerably in advance of the rest of the image in space. Of course a certain amount of time would be required for the stimulus to spread itself over the retina, since it has to overcome a certain amount of resistance in the nerve-layers, and if this time were not given, the curvature of the resulting image would be of course decreased. As the light brightened, however, the curvature increased rapidly, until finally, when the intensity of the light neared its highest point, the curvature ceased becoming greater, and finally decreased. The mean error in eight judgments taken by two people for each intensity of light was about .099 in. [Illustration: High Speed] [Illustration: Middle Speed] [Illustration: Low Speed] The measurements with the middle speed were very similar. The curvature with the lowest intensity of light was somewhat greater than when this same light moved with the highest speed. The maximum point of curvature was reached with a light of less intensity, and the curvature was less. When yet higher intensities were used, the curve decreased rapidly. The amount of curvature was also much less with the brightest light than with the higher speed. The following table shows the judgments of three observers for this speed: MIDDLE SPEED Intensities. 1 2 3 4 5 6 7 8 9 First Subject. 8 10 9 11 10 9 9 7 8 10 11 13 13 10 11 10 9 8 10 10 11 11 9 8 8 7 7 10 11 11 14 10 12 8 9 9 10 11 10 11 9 9 7 10 7 11 11 11 13 10 10 9 10 7 Second Subject. 10 9 11 11 12 8 11 7 8 12 14 13 14 15 14 10 9 9 10 14 13 13 12 11 11 10 9 11 14 13 13 13 12 12 10 9 13 11 13 14 12 12 10 9 9 13 12 13 14 12 12 11 11 9