The Thaumatrope.
Cut out a piece of card-board of circular form, and affix to it six pieces of string, three on each side. Paint on one side of the card a bird, and on the other a cage, taking care to paint the bird upside down, or the desired effect will not be produced. When showing the toy, take hold of the center strings, between the forefinger and thumb, and twirl the card rapidly around, and the bird will appear snugly ensconced in its cage. The principle on which this effect is produced is, that the image of any object received on the retina or optic nerve is retained on the mind about eight seconds after the object causing the impression is withdrawn, being the memory of the object; consequently, the impression of the painting on one side of the card is not obliterated ere the painting on the other side is brought before the eye. It is easy to understand from this fact how both are seen at once. Many objects will suit the thaumatrope, such as a juggler throwing up two balls on one side, and two balls on the other; and according to the pairs of strings employed, he will appear to throw up two, three, or four balls; the body and legs of a man on one side, and the arms and head on another; a horse and his rider; a mouse and trap. But we leave it to the ingenuity of our readers to devise for themselves.