n. [ Gr. qay^ma a wonder + tre`pein to turn. ] (Opt.) An optical instrument or toy for showing the persistence of an impression upon the eyes after the luminous object is withdrawn. [ 1913 Webster ]

☞ It consists of a card having on its opposite faces figures of two different objects, or halves of the same object, as a bird and a cage, which, when the card is whirled rapidly round a diameter by the strings that hold it, appear to the eye combined in a single picture, as of a bird in its cage. [ 1913 Webster ]