Optical Illusions - Revisited

Below is the most viewed post of all time on my blog.  It was originally posted on May 13, 2010 and since then has had 4,994 hits to date. Going back to each of the links, I understand why it has been so popular.

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I have always been fascinated with optical illusions.  Check out these two websites for more illustrations like the two at the left.  Illusion-Optical. com and NIEHS KIDS' PAGES.
     Also, M. C. Escher, a master of optical illusions, was one of my favorite artists, and I used his work often way back when I taught geometry.