Frazer's Spiral Illusion

This spiral design is not a spiral at all. Trace the lines around the circle from any point and you will discover that what looks like a continuous line is really separate circles.
     The continuous spiral effect is caused by orange line segments that cross the circles at an extreme angle. They give the circles a "twisted cord" effect and distort them into a illusionary spiral.

Credits: Frazer, The British Journal of Psychology, 1908.
Art: R. Ausbourne