France Builds Visual Telegraph


In July 1794 Claude Chappe, assisted by two of his brothers, completed a telegraph line consisting of fifteen stations between Paris and Lille. The first telegram on the 210 km Paris-Lille line was sent on 15 August 1794. It reported the recapture of Le Quesnoy.

Long-distance optical telegraphy is a technology dating back thousands of years. Written records exist, for example, of an Ancient Greek system of torches used to transmit the 24 letters of the Greek alphabet along relay chains. But the first modern system of visual telegraphy was established in France during its Revolutionary era under the direction of Claude Chappe.

Chappe was born in Brulon, France, in 1763. He planned to join the clergy, but shifted his focus to scientific pursuits with the outbreak of the French Revolution. With his brothers, he discovered that long-distance messages could be sent using combinations of simple signals. In 1791, Chappe and his brothers created a prototype of an optical semaphore. Over the next few years, they improved the device’s coding and obtained government support. Their invention would be dubbed the “télégraphe,” a French word from the Greek for “far writer.”

The Chappe brothers devised a system of semaphores employing linear arms to send signals. The semaphore was a long rotating bar (the regulator) with two smaller rotating arms (the indicators) on its ends attached to weights. An operator controlled the semaphore through a system of ropes and pulleys.The regulator was hinged to a vertical pole and could move vertically or obliquely. Each indicator could be adjusted to seven positions 45 degrees apart. In all, 98 positions were possible, but six signals were reserved for special indications. Each of the 92 positions corresponded to a page in a code book, which, in turn, contained 92 symbols on each of its 92 pages. As a result, operators could send a code pair that could generate one of 8,464 (92 x 92) signs.

This system expanded rapidly in the late 1790s. A line of 230 km connected Paris and Lille by May 1794, and a second line from Paris to Strasbourg was completed in 1798. Each station was about 10 to 15 km apart and manned by two operators. Napoleon Bonaparte took power in 1799 and saw the telegraph as a vital tool for battle. He ordered the system’s expansion, and even proposed a line across the English Channel to prepare for an invasion of the island. By the early 1800s, four lines linked to Paris, and by the middle of the century, reached across Western Europe and Northern Africa.

Although the English installed electrical telegraph lines as early as 1837, the French only began to replace their optical system in 1846, with some hesitation. Early French electrical telegraph systems, in fact, used the old French code, with its thousands of symbols, rather than the simpler Morse Code.

Further Reading

J-M. Dilhac, "The Telegraph of Claude Chappe: An Optical Telecommunication Network for the XVIIIrd Century."