\Thau"ma*trope\, n. [Gr. ? a wonder + ? to turn.]
(Opt.)
An optical instrument or toy for showing the presistence of
an impression upon the eyes after the luminous object is
withdrawn.
Note: 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 rapidlz 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.