Off the Beaten Track
in Vol. 23 - July Issue - Year 2022
“Why does it have to be so slow and complicated?” Claude was frustrated by the fact that entrusting a letter to a messenger on horseback or sending notes by homing pigeons was the only way to communicate with his friends in neighboring towns and villages. Surely, there had to be a better way!
Claude Chappe was born in Brûlon, France in December 1763. After completing his studies at the Royal College in La Flèche, he was destined to serve the church as an abbey, but was deprived of his sinecure by the French Revolution. His uncle was an astronomer and scientific explorer whose journal of his trip to Siberia in 1761 fascinated Claude as a child and inspired him to pursue scientific studies. From 1789 to 1793 Claude published five treatises on the transmission of electrical impulses through cables. Having been unsuccessful in his attempt to design an electrical messaging device, he enlisted the help of his three brothers, unemployed like himself, to build a mechanical communication system, also known as an “optical telegraph”.
The brothers developed a system of semaphore relay stations with a series of towers spaced ten to fifteen kilometers apart within line of sight of each other. Each tower would be placed either on an existing support structure, such as a belfry or a tall building, or on a specially built base. Two operators manned each station with two telescopes, one pointed at the previous station and one pointed at the next station. Through his telescope, one operator would see the message coming from the previous station, write it in a book and pass it to his colleague for transmission to the next station. Messages could be sent in either direction down the line.
During the 1790s, the French Revolution was raging, mobs were rampaging through cities and France was at war with other European powers. The French military needed a system that would allow the central government to receive intelligence and issue orders as quickly as possible. After discarding systems using smoke signals and electricity, Claude Chappe decided on an optical system that he called tachygraphy and that the French military renamed telegraphy. The first public demonstration took place on 2nd March 1791 over a distance of sixteen kilometers. Although the message was sent successfully, the system using black and white panels proved slow and complicated. It took the brothers two years to find the right signal transmission system and language code. They determined that two black movable wooden arms, connected by a crossbar, provided the most visible and easily understood way to transmit signals. The arms had metallic counterweights and were controlled by two handles, making the system robust and easy to use. The positions of arms and crossbar together indicated an alphabetic letter. Each of the two-meter-long arms could display seven positions, while the 4.6-meter-long crossbar could assume four different angles, giving 196 symbols altogether (7x7x4). To speed up transmission and improve security, the Chappe brothers developed a code that took 92 of the basic symbols two at a time, giving 8,464 coded words and phrases.
In the summer of 1792, Claude Chappe was asked to set up a line of stations between Paris and Lille, a distance of 230 kilometers, to transmit military dispatches during the war between France and Austria. In 1794 legislators in Paris were stunned when Claude’s telegraph brought news that the French army had captured a city from the Austrians less than an hour after it occurred. New lines spread across France: fifty stations, covering 488 km, between Paris and Strasbourg and another fifty stations between Paris and Lyon. By the early 1800s, France had a network of 556 stations covering a total distance of 4,800 km. The network was further extended to include cities outside of France such as Brussels, Antwerp, Amsterdam, Mainz, Turin, Milan and Venice.
New lines continued to be constructed until 1846, when the appearance of the electric telegraph brought the optical telegraph system to a swift end.
By Giovanni Gregorat, Contributing Editor MFN