photochronograph

 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.]

 An instrument for the photographic recording of star transits.  [Webster 1913 Suppl.]