Thaumatrope

Optical toy featuring a spinning disk with pictures on each side

A thaumatrope is an optical toy that was popular in the 19th century. A disk with a picture on each side is attached to two pieces of string. When the strings are twirled quickly between the fingers the two pictures appear to blend into one. The toy has traditionally been thought to demonstrate the principle of persistence of vision, a disputed explanation for the cause of illusory motion in stroboscopic animation and film.

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