#### Some interesting optical illusions

Posted by: blitzer

Date: 2008-10-30 17:56:14

Two congruent circles are surrounded by other circles, one of them surrounded by large congruent circles, and the other surrounded by small congruent circles. The one sưrounded by small circles seems to be bigger.

http://en.wikipedia.org/wiki/Lilac_chaser

Stare at the black + for 20-30 seconds.

http://en.wikipedia.org/wiki/Caf%C3%A9_wall_illusion

Parallel lines appear to be bent.

http://en.wikipedia.org/wiki/Image:Revolving_circles.svg

Move your head back and forth.

http://en.wikipedia.org/wiki/Missing_square_puzzle

Four objects are formed to make a 13 by 5 right triangle. When rearranged, they seem to form a triangle with the same proportions, except with 1 missing square.

http://en.wikipedia.org/wiki/Fraser_spiral_illusion

A spiral? Not really.