Dipleidoscope \Di*plei"do*scope\, n. [Gr. ? double + ? image +
   -scope.] (Astron.)
   An instrument for determining the time of apparent noon. It
   consists of two mirrors and a plane glass disposed in the
   form of a prism, so that, by the reflections of the sun's
   rays from their surfaces, two images are presented to the
   eye, moving in opposite directions, and coinciding at the
   instant the sun's center is on the meridian.
   [1913 Webster]