| OPTICAL COMMUNICATIONS | |
|
|
|
| "Communicating
with Light : Historical....."
In essence, heliography uses mirrors to reflect sunlight over great distances for the purpose of sending information. The invention of the heliograph is dated 1865. "1865 - Henry Christopher Mance
(1840-1926), of British Army Signal Corps, builds a heliograph, an optical
sunlight-based signalling device. It had tripod-mounted mirrors, with one
mirror linked to a key mechanism. The key tilted the mirror to flash on
and off at the distant station in accordance with the dots and dashes of
the Morse code. Range was line-of-sight, hence hills and mountain tops
were regularly employed, and was limited by atmospheric conditions. A
network of lightweight portable instruments could span ranges of up to 100
miles. (Coe 1993:8, cited in Sterling & Kadrey 1999, note 05.6)." The instruments took on different forms, but the mirrors were planar, about 4-6" in diameter. The instruments were generally held on wooden tripods, providing portability to remote mountain-top locations. The more sophisticated heliographs had mechanisms to allow the mirror to move with, or track, the motion of the sun, as well as morse-code-key operated shutter mechanisms to send flashes of light. The following link contains descriptions of variations of the heliograph: http://www.deadmedia.org/notes/2/027.html Here is a picture of the British version, called the Mance Heliograph:
See The Early History of Data Networks for more information. Around 1885, a system of
heliographs was set up in SE Arizona, and was used by the Army to
communicate during the wars with the Apaches:
|
|
The Heliograph
Look
at the link 
