Friday, March 23, 2007


Telegraphy (from the Greek words tele = far and graphein = write) is the long-distance transmission of written messages without physical transport of letters, initially over wire. Radiotelegraphy or wireless telegraphy transmits messages using radio. This definition includes recent forms of data transmission such as fax, email, and computer networks in general. (A telegraph is a machine for transmitting and receiving messages over long distances, i.e. for telegraphy. The word telegraph alone generally refers to an electrical telegraph.) Wireless telegraphy is also well-known as CW, for continuous wave (a carrier modulated by on-off keying, as opposed to the earlier radio technique using a spark gap).
Telegraphy messages sent by telegraph operators using Morse code were known as telegrams or cablegrams, frequently shortened to a cable or a wire message. Later, telegrams sent by the Telex network, a switched network of teleprinters similar to the telephone network, were identified as telex messages. Before long distance telephone services were willingly available or affordable, telegram services were very popular. Telegrams were frequently used to confirm business dealings and, unlike e-mail, telegrams were usually used to create binding legal documents for business dealings.
Before fax machines came into general use, wire picture or wire photo was a newspaper picture that was sent from a remote location by a facsimile telegraph. This is why many fax machines have a photo option even today.
Optical telegraphs and smoke signals
The first telegraphs were optical telegraphs, with the use of smoke signals and beacons. These have existed since ancient times. A semaphore network invented by Claude Chappe operated in France from 1792 through 1846. It helped Napoleon enough that it was widely imitated in Europe and the U.S. The last commercial semaphore link left operation in 1880.
Semaphores were able to communicate 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 and smoke signals, they were dependent on good weather to work. They required operators and towers every 30 km (20 mi), and only send 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 thirty-fold compared to semaphore.

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