The accompanying sketch shows two optical illusions, the first having a perfect circle on the outside edge appears to be flattened at the points A, and the arcs of the circle, B, appear to be more rounding. In the second figure the circle appears to have an oval form with the distance from C to C greater than from D to D. A compass applied to the circles in either figures will show that they are perfectly round. --Contributed by Norman S. Brown, Chippewa Falls, Wis.

Ill: The Two Illusions