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KF5JRV > TECH 26.04.16 13:27l 79 Lines 4206 Bytes #999 (0) @ WW
BID : 2070_KF5JRV
Read: GUEST
Subj: Optical Telegraph
Path: IW8PGT<CX2SA<N0KFQ<KF5JRV
Sent: 160426/1119Z 2070@KF5JRV.#NWAR.AR.USA.NA BPQ1.4.65
The Optical Telegraph: Faster than a Messenger on Horseback
March 2, 1791 - 1794
On March 2, 1791 inventor Claude Chappe sent his brother the
first transmission over their optical telegraph: "si vous reussissez,
vous serez bient“t couvert de gloire" (If you succeed, you will soon
bask in glory). The initial experimental line ran between Brulon and
Parc‚.
Having been appointed and charged with establishing a line of stations
between Paris and Lille, a distance of 230 kilometres (about 143 miles),
Claude Chappe succeeded in completing his first optical telegraph, or
semaphore telegraph. The Chappe telegraph was used to carry dispatches
for the war between France and Austria, and communicated news of a French
capture of Cond‚-sur-l'Escaut from the Austrians less than an hour
after it occurred.
Chappe's system was the first widely adopted system to transmit
messages overland faster than a messager or horseback can carry a
message over a good road system. That speed had remained essentially
fixed since Roman times. The first symbol of a message to Lille
would pass through 15 stations in only nine minutes. The speed of
the line varied with the weather, but the line to Lille typically
transferred 36 symbols, a complete message, in about 32 minutes.
Paris to Strasbourg with 50 stations was the next line and soon
others followed.
"In the Chappe system messages were encrypted and translated by
semaphore signals built on the tops of towers miles apart. A
telegrapher in the next tower would read the semaphore signals
through a telescope and retransmit the message to the following
tower. This process would be repeated, with error-correction
checks in place at each repetition, until the message reached the
end of the line. Because optical telegraph systems using semaphores
required that messages be continually restransmitted from tower to
tower, there was no fail-safe way to eliminate error. Furthermore
it was necessary to encrypt all messages so that the operators
would not be privy to secret information. Thus only the directors
of the system and the inspectors were allowed to know the code
for message signals. The two operators in each signaling tower
knew only the limited set of control codes used for error
correction, clock synchronizations, etc. The actual codes were
written in codebooks. Claude Chappe's 1795 codebook had 8,940
words and phrases. By 1799 he had added four supplementary
codebooks with additional words and phrases, and names of places
and people. Thus each message had to include a citation of the
code book employed"
"All signals on the semphore telegraph were passed one at a time,
in strictly synchronus fashion. The operators were required to
check [by telescope] their neighboring stations every few minutes
for new signals, and reproduce them as quickly as possible. The
operator then had to verify that the next station inline
reproduced the signal correctly, and set an error signal if it
failed to do so. Each symbol had to be recorded in a logbook,
as soon as it was carried to completion. Since no symbolic or
numeric code system for representing the semaphore positions
was described this was done in the form of little
pictograms. . . " (Hotzmann & Pehrson, The Early History of Data
Networks [1995] 87).
The Chappe optical telegraph eventually covered France with "a
network of 556 stations stretching a total distance of 4,800
kilometres." It was be used for military and national communications
until the 1850s.
"By 1824, the Chappe brothers were promoting the semaphore lines
for commercial use, especially to transmit the costs of commodities.
Napoleon Bonaparte saw the military advantage in being able to
transmit information between locations, and carried a portable
semaphore with his headquarters. This allowed him to coordinate
forces and logistics over longer distances than any other army
of his time. However because stations had to be within sight of
each other, and because the efficient operation of the network
required well trained and disciplined operators, the costs of
administration and wages were a continuous source of financial
difficulties."
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