The optical telegraph preceded the electrical telegraph. It was faster than riding couriers for bringing a message over long distances. Types of optical telegraph are the semaphore, ship flags, smoke signals, and beacons. The distance that an optical telegraph can bridge is limited by geography, the shape of the earth, weather, and the sharpness of the human eye. In practical use, most optical telegraphs used relay leagues to bridge longer distances.

There was in France at the end of the 18th century a complete and working installation of optical telegraph. During the Revolutionary period, a French inventor, Claude Chappe (1763-1805), convinced the Deputies to set up a huge network between major cities. It was used for army and national communications till the 1850s.

A chain of semaphores was built in England during the Napoleonic Wars in the 19th century to warn London of a French invasion. The chain ran from the Admiralty in Whitehall to Portsmouth in the English Channel. As a result there are several locations still called Telegraph Hill. There is a restored example on a hill at Chatley Heath in Surrey.

In the 1850s, U.S. Army Major Albert J. Myer, a surgeon by training, developed a system using left or right movements of a flag (or torch or lantern at night), similar to the Morse code of dots and dashes. This is sometimes called the wig-wag method of signaling. More mobile than previous means of optical telegraphy, this code was used extensively by Signal Corps troops on both sides in the American Civil War. (Its first use in battle was by Confederate Lieutenant Edward Porter Alexander at the First Battle of Bull Run in 1861.)

Throughout Chinese history, smoke signals were used as communication tool during war time. Until these days, the Chinese phrase 烽火 (feng1 huo3, fire signals) is still used as a synonym for war.

See also

• Childs Hill for an example of a Telegraph Hill

External links

• Albert Myer's 1864 A Manual of Signals: For The Use Of Signal Officers In The Field
• The telegraph chain to Faversham from the Admiralty