(Imprimerie) Technique de reproduction.
An apparatus for sending telegraphic messages by using a mirror to turn the sun's rays off and on.
Instrument for measuring intensity of sunlight.
Mirror apparatus for signaling by flashes of light
Old method of signaling, used by armies in the late 19th century, which employed sunlight reflected from a mirror to pass messages in Morse code. On a clear day, a heliograph could send over distances in excess of 50 km/30 mi.
Also, an early photographic process by which a permanent image was formed on a glass plate.