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Can your eyes deceive you? Adjust the size of the white polygon on the right until you think it is equal to the black polygon on the left. Then check your selection by moving the white polygon over the black one. This illusion was discovered by Helmholtz in the century.
Contributed by: Sándor Kabai (October 2008)
Open content licensed under CC BY-NC-SA
Wolfram Demonstrations Project
Published: October 14 2008