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The Illusion shown above which was discovered by Helmholtz 
in the 19th century. Despite the fact that the two
above figures are identical in size, the white hole looks bigger than the black one in this Illusion.
References
Pappas, T. ``Irradiation Optical Illusion.'' The Joy of Mathematics.
San Carlos, CA: Wide World Publ./Tetra, p. 199, 1989.