Semaphore

Chappe pioneers a long-range, rapid, visual signaling system.

In Paris in 1791, a little-known engineer and inventor named Claude Chappe (1763-1805) began to experiment with an optical signaling system or visual telegraph. His ambition was to send complex messages via a succession of towers using a combination of signaling arms. Three years later, in 1794, working with the aid of his four brothers, Chappe demonstrated his first optical semaphore. His string of fifteen towers placed within sight of each other was able to transmit a message 120 miles (190 km) from Paris to Lille in only nine minutes. The project's burdensome costs were borne by a French leadership who were recently at war with Austria and eager for any strategic advantage in communication.

     Each tower was topped by a 30-foot (9 m) mast to which a rotating arm was attached with smaller, counterbalanced wooden arms at its ends. These could move through the horizontal and vertical and in a series of seven 45-degree positions to produce 196 combinations of letters, numbers, and selected words. The semaphore's indicators seemed almost to mimic the outstretched arms of human, and were painted black to provide maximum contrast against blue or cloudy skies. Telescopes were fitted to each tower so that its operators could relay messages on. Because spies could easily see the messages, a code book consisting of secret phrased and words was introduced for emergencies. Chappe's semaphore proved such a success that new lines of towers were soon constructed, radiating out from the French capital cities such as Dunkirk, Brussels, and Antwerp.

“[Electricity] had to be abandoned when no adequate insulators could be found for the wires.” Abraham Chappe on his brother’s experiment