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.