The phosphoroscope was invented by Alexander Edmund Becquerel and used to measure the amount of time that a phosphorescent substance will glow after being irradiated by a brilliant source of light.The phosphoroscope consists of a round metal chamber with a pair of rotating discs inside, arranged so that no light can pass directly through the chamber. The discs have cut-out windows spaced equally at regular angular distances and are turned by the hand crank linked to a gear mechanism. The sample is placed in a specially designed holder into the small opening near the gearing, and it is exposed to the light source through the large rear condensing lens.Engraved on chamber: 'Phosphoroscope de E. Becquerel / J. Duboscq a Parisbecquerel phosphoroscope, phosphoroscope, optical instruments, phosphorescent, alexander edmund becquerel, jules duboscq, france