Thamatrope
A thaumatrope is a small disc, held on opposite sides of its circumference by pieces of string. An image is drawn on each side of the disc, and is selected in such a way that when the disc is spun, the two images appear to become superimposed. To spin the disc, one string is held in a hand, and the disc is rotated to wind the string. Then, both strings are held, and the disc is allowed to rotate. Gently stretching the strings will ensure that they continue to unwind and rewind. This motion causes the disc to rotate, first in one direction and then in the opposite. The faster the disc rotates, the greater the clarity of the illusion.
Although the thaumatrope does not produce animated scenes, it relies on the same persistence of vision principle that other optical toys use to create illusions of motion. Persistence of vision is the eye's ability to retain an image for roughly 1/20 of a second after the object is gone. In this case, the eye continues to see the two images on either side of the thaumatrope shortly after each has disappeared. As the thaumatrope spins, the series of quick flashes is interpreted as one continuous image.
Source: Laura Hayes and John Howard Wileman Exhibit of Optical Toys
Although the thaumatrope does not produce animated scenes, it relies on the same persistence of vision principle that other optical toys use to create illusions of motion. Persistence of vision is the eye's ability to retain an image for roughly 1/20 of a second after the object is gone. In this case, the eye continues to see the two images on either side of the thaumatrope shortly after each has disappeared. As the thaumatrope spins, the series of quick flashes is interpreted as one continuous image.
Source: Laura Hayes and John Howard Wileman Exhibit of Optical Toys