THE TRIANGLE SWING

1. Imagine that on a white card before you a black equilateral triangle, one inch high, has been drawn. To the left of the wide base, put a black dot; to the right put another black dot.
2. Now, with a sigh, point your nose to one black dot, slide. across the card to the other, back and forth. Pay no attention to the triangle which seems to slip aside, in the opposite direction, as you travel from dot to dot. Do you get this illusion of motion?
3. Turn the triangle upside down so that it stands on its peak. This time,-place the black dots to left and right of the point.
4. Swing your attention from dot to dot rhythmically again. The sharp point will actually seem to shift a bit from side to side in the opposite direction. The triangle takes care of itself, slipping out of the way so that you can see first one dot then the other.

A dot is restful to see or think about because it requires no -mental interpretation.