The story
From diplo- (“double”) + Ancient Greek εἶδος (eîdos, “image”) + -scope.
Etymology from Wiktionary, CC BY-SA 4.0.
dipleidoscope
Today it means: An instrument for determining the time of apparent noon. It consists of two mirrors and a plane glass 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 centre is on the meridian. Full definition →