heliographs

Quelle: http://www.aqpl43.dsl.pipex.com/MUSEUM/COMMS/heliograph/heliograph.htm

The Heliograph was a simple but highly effective instrument for instantaneous optical communication over 50 miles or more in the 19th century.

Its major uses were for military and survey work. It was still in serious use at least up to 1935, for example by Glubb Pasha's Arab Legion in Palestine.

The classic heliograph is the Mance pattern, devised by Sir Henry Mance at Bombay in 1869. See illustration below.

A British Mark V Mance pattern 5-inch heliograph. The operating key is behind the mirror.

Under ordinary conditions, a flash could be seen 30 miles (48 km) with the naked eye and much farther with a telescope.

Heliographs could be used with moonlight, but at much reduced range.

Speed was 5 to 12 words per minute, depending on the Morse skills of the operators.