Telegraphy - Optical Telegraph

Optical Telegraph

Main articles: Semaphore line (visual telegraphy using signal arms or shutters), flag semaphore (using hand-held flags), signal lamp (visual naval communications) and heliograph (visual communications using reflected sunlight)

The first telegraphs came in the form of optical telegraph including the use of smoke signals, beacons or reflected light, which have existed since ancient times. A semaphore network invented by Claude Chappe operated in France from 1792 through 1846. It helped Napoleon enough to be widely imitated in Europe and the U.S. In the Peninsular War (1807–1814), several similar telegraphs had been used in the Lines of Torres Vedras, by the Anglo-Portuguese army. The Prussian system was put into effect in the 1830s. The last commercial semaphore link ceased operation in Sweden in 1880.

Semaphores were able to convey information more precisely than smoke signals and beacons and consumed no fuel. Messages could be sent at much greater speed than post riders and could serve entire regions. However, like beacons, smoke and reflected light signals they were highly dependent on good weather and daylight to work (practical electrical lighting was not available until about 1880). They required operators and towers every 30 km (20 mi), and could accommodate only about two words per minute. This was useful to governments, but too expensive for most commercial uses other than commodity price information. Electric telegraphs were to reduce the cost of sending a message thirtyfold compared to semaphores, and could be utilized non-stop, 24 hours per day, independent of the weather or daylight.

Elevated locations where optical telegraphs were placed for maximum visibility were renamed to Telegraph Hill, such as Telegraph Hill, San Francisco, and Telegraph Hill in the PNC Bank Arts Center in New Jersey.