Optical telegraphy. Historical artwork of a light- signalling device used in optical telegraphy. This is a Mangin projector, invented by colonel Mangin in the early 1880s. It was designed to be used as either a reflector of sunlight or an oil-fuelled lamp. The range over which it could be seen varied from 20-100 kilometres, depending on the weather, whether it was day or night, and whether it used sunlight or oil. It was used by the military to send messages by optical telegraphy. Mangin was a French colonel, and the projector was used by the French in Tunisia, and later by many other armies, including the British, Russians and Belgians. From La Telegraphie Historique (Alexis Belloc, 1888).