The Semaphore Telegraph

(Important in The Mistaken Wife)

Claude Chappe developed the first modern system of optical telegraphy in 1793*.  After experimenting with synchronised pendulum clocks and sliding panel frames, Chappe and his brothers successfully tested a device consisting of a pivoting beam and arms, whose relative positions could designate signs for letters and numerals.  The National Assembly approved construction of a line from Paris to Lille, which was completed in the summer of 1794.  The famous watchmaker, Abraham-Louis Breguet, helped to design the pulley and gearing systems, and mathematician Gaspard Monge designed an improved code.  Stations were built approximately 10 km apart, often on a hill or utilising a church tower.  The speed of transmission varied according to the weather, but a message could be sent from Paris to Lille in approximately half an hour.  The system did not work at night; attempts to fasten lanterns to the pivoting arms proved unsuccessful.  To improve the security of transmissions, only certain stations decoded a message before passing it on.  Most were entrusted only with the control codes that preceded and followed the actual message.  In October 1794 construction of a second line, from Paris to Strasbourg, was approved, and by 1800 stations were spreading across the country.  Although hailed as a benefactor of France, Chappe endured chronic funding problems and criticism from adversaries, and he committed suicide in 1805.  His brothers continued to develop and expand the system, however, and by the end of the Napoleonic era France had 224 stations over one thousand miles of telegraph routes. With further improvements and expansions, Chappe’s semaphore continued in operation until 1853, when it was replaced by the electric telegraph.

*Lord George Murray’s shutter telegraph was inspired by reports of the Chappe semaphore.  Construction of the first line between London and Deal, with a branch to Sheerness, began in 1795.