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rLLUSION. 471 ILLtrSION. the aniJles of the square, so that we perceive which should include the square. No one whose not a circle at all, but four ares apparently be- vision is normal can escape these illusions; their lono'ing to circles of less radius than the circle occurrence is, as we shall see, intrinsic to the E Fig. 5. CONSTANT illusions of extent (trom Titehener. Experimental Ps,rcbology). The vertical dimensions appear to be greater than the horizontal dimensions of all the figures. FiQ. 6. VARIABLE ILLUSIONS OF DiHECTios (A the Bering flpure, B Wundt's figure). The parallel lines ab and cd in A seem to be nearer together at the ends than in the middle. In B the opposite ia the case,
