from
The Collaborative International Dictionary of English v.0.48
Photochronograph \Pho`to*chron"o*graph\, 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.]