A heliograph is a solar telegraph system that signals by flashes of sunlight reflected by a mirror. The flashes are produced by momentarily pivoting the mirror, or by interrupting the beam with a shutter. The heliograph was a simple but effective instrument for instantaneous optical communication over long distances during the late 19th and early 20th centuries. Its main uses were military, survey and forest protection work. Heliographs were standard issue in the British and Australian armies until the 1960s, and were used by the Pakistani army as late as 1975.
Fig. 1: Signaling with a Mance heliograph, Alaska-Canada border, 1910.
Fig. 2: German heliograph made by R. Fuess in Berlin (on display at the Museum of Communication in Frankfurt)
Fig. 3 Ottoman heliograph crew at Huj during World War I, 1917
Ruins of German Schutztruppe on top of Dikwillem, where the Germans used to have a Heliographic Station (Bird's eye view 2017)
Morse code is a method used in telecommunication to encode text characters as standardized sequences of two different signal durations, called dots and dashes, or dits and dahs. Morse code is named after Samuel Morse, one of the early developers of the system adopted for electrical telegraphy.
This Morse key was originally used by Gotthard railway, later by a shortwave radio amateur
Single needle telegraph instrument
Telegraph key and sounder. The signal is "on" when the knob is pressed, and "off" when it is released. Length and timing of the dits and dahs are entirely controlled by the telegraphist.
Morse code receiver that records on paper tape
