TELEGRAPH

any device or system that allows the transmission of information by coded signal over distance. Many telegraphic systems have been used over the centuries, but the term is most often understood to refer to the electric telegraph, which was developed in the mid-19th century and for more than 100 years was the principal means of transmitting printed information by wire or radio wave. This article begins with a brief description of notable pre-electric visual telegraph systems and then traces the development of electric telegraphy. any system that allows the transmission of encoded information by signal across a distance. The word was coined about 1792 from the Greek tele, far, and graphein, to write, but the principle is far older. While telegraph systems have used a variety of signaling methods and devices, the term is most often applied to the electric telegraph developed in the 19th century. The earliest forms of telegraphy were probably smoke, fire, or drum signals. In the late 18th century optical telegraphs were invented by Claude Chappe in France and by George Murray in England. Called semaphores, these telegraphs relayed messages from hilltop to hilltop with the aid of telescopes. Chappe's system used a vertical timber holding a movable crossbar with indicators at each end that could assume various configurations, like a signalman with flags. Murray's system used a large tower-mounted box with six panels that opened and closed in different combinations according to a code. Rapid development of telegraph systems came with the discovery that electric impulses could be used to transmit signals along a wire. Among the many electric systems attempted was the needle telegraph, based on Hans Christian rsted's discovery in 1819 that an electric current caused an adjacent magnetized needle or pointer to deflect. The Cooke and Wheatstone five-needle telegraph of 1837 utilized this phenomenon with a panel imprinted with letters and numerals to which the five needles pointed singly or in pairs. This apparatus was widely used in Great Britain, especially for railroad signaling. The development of the electromagnet about that time provided the American inventor Samuel Morse with a way to transmit and receive electric signals. Together with Alfred Vail, his partner from 1837, Morse developed the simple operator key, something like a single typewriter key, which when depressed completed an electric circuit and sent a signal to a distant receiver, which was originally a device that embossed a series of dots and dashes on a paper roll. The use of dots and dashes to represent letters, numbers, and operating functions became known as the Morse Code. About 1856 a sounding key was developed; skilled operators could listen to what the key said and write the messages directly, or, after 1878, type them. Telegraph lines quickly spread across North America and Europe in the 1840s, and were extended to Asia, Africa, and Australia later in the century. Because of the size and high cost of telegraph systems and their importance in international affairsthey were seen by European powers as critical strategic resources that would rationalize colonial administration and improve military security (especially in British India), and by emerging nations like Russia and China as aids to economic and social modernizationtelegraph companies were among the largest business enterprises of the 19th century, and included firms that were privately held, state-subsidized, or state-owned. With growing telegraph traffic, refinements were necessary. The duplex circuit, developed in Germany, made it possible for messages to travel simultaneously in opposite directions on the same line. Thomas Edison devised a quadruplex in 1874 that permitted four messages to travel at once, two going in either direction. The most revolutionary innovation belonged to Jean-Maurice-mile Baudot. His time-division multiplex, invented in 1871, consisted of a brush arm that traveled around a copper ring divided into equal sectors. In each sector there were five contacts that would be opened or closed in one of 32 possible combinations, each five-bit combination encoding a letter or symbol. As the brush arm moved in its circle it would pick up a code combination from one sector and then the next and so on. As many messages as there were sectors could be sent simultaneously. The Baudot Code was widely used in teleprinters. By the end of the 19th century the world was crisscrossed by telegraph lines, including numerous cables across the Atlantic Ocean. Some early telegraphs using keyboards and typewheels were capable of producing tapes of printed messages, which were long used in stock tickers. In 1903 Donald Murray of England combined Baudot's time-division multiplex system and its five-level code with a system for punching tape devised by Wheatstone to produce a system that transmitted page form telegrams. Between 1924 and 1928 the simplex printer or teleprinter, commonly known by the American Telephone and Telegraph trade name Teletype, was developed to serve the simple back-and-forth needs of business communication through subscription networks such as telex. Teleprinters in 1933 were capable of printing up to 500 characters per minute. By 1964 improved teleprinters were using the American Standard Code for Information Interchange, a seven-level code capable of producing 128 alphanumeric and control signals. Some versions produced 900 characters per minute. The invention and technical improvement of the telephone at first made a new range of technology available to telegraphy, particularly in the field of high-speed transmission. Other important developments in telegraphy in the 20th century included the use of microwave radio links, satellite transmission, and computerized switching. By the end of the century, though, the growing capacity of the telephone system to support high-speed data transmission (particularly facsimile and electronic mail) reduced the telegraph system to a minor role in telecommunication. Additional reading George Shiers (ed.), The Electric Telegraph: An Historical Anthology (1977); Lewis Coe, The Telegraph: A History of Morse's Invention and Its Predecessors in the United States (1993); and Paul Israel, From Machine Shop to Industrial Laboratory: Telegraphy and the Changing Context of American Invention, 18301920 (1992), detail the development of the telegraph in the United States and Europe and include many excellent illustrations of a wide range of devices and systems related to telegraphy. Robert Luther Thompson, Wiring a Continent: The History of the Telegraph Industry in the United States, 18321866 (1947, reissued 1972), describes in detail the industry's formative years and includes copies of Congressional acts and industrial agreements affecting the development of this industry. Brooke Hindle, Emulation and Invention (1981), deals with the evolution of new technology, including Morse's development of the telegraph. Roger L. Freeman, Reference Manual for Telecommunications Engineering, 2nd ed. (1993), is a technical sourcebook containing standards for various types of communication. Clare D. McGillem