photochronograph

n. [ Photo- + chronograph. ] 1. (Physics) An instrument for recording minute intervals of time. The record is made by the power of a magnetic field, due to an electric signaling current, to turn the plane of polarization of light. A flash, coinciding in time and duration with the signal, is thus produced and is photographed on a moving plate. [ Webster 1913 Suppl. ]

2. (Astron.) An instrument for the photographic recording of star transits. [ Webster 1913 Suppl. ]