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Subject: Dead Media Working Notes 05.6
Dead Media: The Heliograph, the Heliotrope
From: bruces_AT_well.com (Bruce Sterling)
Source: The Telegraph: A History of Morse's Invention
and its Predecessors in the United States by Lewis Coe
TK 5115 C54 1993 McFarland and Company, Publishers
ISBN 0-89950-736-0
page 8
"One of the most successful and widely used visual
signalling systems, the heliograph, did not appear until
1865, long after most visual systems were considered
obsolete. The factor that established the heliograph was
the existence of the Morse alphabet of dots and dashes,
widely used for land telegraph and submarine cable
operations. The ancients understood the principles of
reflected sunlight, but no one ever got around to devising
a code for the letters of the alphabet. Signal codes of
some type had existed long before Morse, but none of them
ever reached a level of universal acceptance, and they
were mostly forgotten by the time Morse published his
code.
"Early in the nineteenth century, Gauss, a German
mathematician, had discovered the tremendous potential of
the sun's rays reflected from a plane mirror. Through
experiments he was able to demonstrate that even a small
mirror one inch square could send flashes that could be
seen over a distance of seven miles. The silvered glass
mirror, invented in 1840 by Justin Liebeg, paved the way
for the heliograph. (...)
"Like the American army, the British did not have a
separate Signal Corps organization until the 1860s. The
first British signal school was established at Chatham in
1865. Shortly after, a young officer named Henry
Christopher Mance (1840-1926) became interested in
signalling with the sun. Mance, later to be knighted for
his achievements in engineering, knew of the use of mirror
instruments called heliotropes in the triangulation of
India. The Indian survey, one of the great engineering
projects of the nineteenth century, required accurate
location of high mountain peaks to serve as control points
fot the ground survey. Bright fire pots were used at
night and the heliotropes by day. It is not know whether
any Morse code signalling was done by heliotrope, but it
is certain that prearranged signals were exchanged.
(...) "The simple and effective instrument that Mance
invented was to be an important part of military
communications for the next 40 years. Limited to use in
sunlight, the heliograph became the most efficient visual
signalling device ever known. In preradio days it was
often the only means of communication that could span
ranges of up to 100 miles with a lightweight portable
instrument.
"The Mance instrument employed tripod-mounted
mirrors, with one mirror linked to a key mechanism. The
key tilted the mirror enough to turn the flash on and off
at the distant station in accordance with the dots and
dashes of the Morse code. Range was line-of-sight, with
atmospheric conditions establishing the upper limit. The
British army found the Mance heliograph ideally suited to
field operations in India and Afghanistan. It was used to
transmit daily reports and orders to and from the remote
mountain posts and for tactical communications when troops
were in the field. (One hundred ten years later, TV
pictures were to show Afghan guerilla units using British
pattern heliographs in their conflict with the Russians.)
The present Afghans have found the helio useful for the
same reason as their British enemies of old; namely, a
simple uncomplicated mechanism that requires no batteries
or complex maintenance."
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