SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
Three arc illusion. The three arcs shown give the impression of belonging to circles of increasing radius when viewed from top to bottom. They actually come from circles of the same radius. The illusion is a demonstration that the larger the arc shown, the smaller its radius appears - for short arc segments humans appear to underestimate the curvature. That they are produced by circles of the same radius is demonstrated in image T478/460.
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