Optical Devices

In CyberArts seminar we are learning about Thaumatrope. 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. Stretching the strings will ensure that they continue to wind and unwind. 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.
So by drawing pictures on two discs, and spun in such a way you can see the two pictures become one while still spinning. So it becomes a optical illusion, confusing your brian seeing the two pictures at a time.
The invention of the thaumatrope, means "turning marvel" or "wonder turner," has often been credited to the astronomer Sir John Herschel.