Square Size Illusions
The squares are all of the same size. Subdividing a square vertically makes it appear wider, while subdividing it horizontally makes it appear taller. The effect becomes apparent when the squares are subdivided even once, and becomes more pronounced as the subdivision becomes finer. We also show the effect of rotation. A square, when rotated so as to stand on a corner, appears larger than one that is standing flat on a side.
 R. G. Carraher and J. B. Thurston, Optical Illusions and the Visual Arts, New York: Van Nostrand Reinhold Company, 1966.
"Square Size Illusions"
Wolfram Demonstrations Project
Published: January 26 2016