The larger an arc is, the smaller its radius appears. For example, the three arcs illustrated above belong circles of the same radius.
This entry contributed by Margherita Barile
REFERENCES:
Carraher, R. G. and Thurston, J. B. Optical Illusions and the Visual Arts. New York: Reinhold, 1966.
CITE THIS AS:
Barile, Margherita. "Three-Arc Illusion." From MathWorld–A Wolfram Web Resource, created by Eric W. Weisstein. http://mathworld.wolfram.com/Three-ArcIllusion.html