Early Electric Telegraphs
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Benjamin Franklin defined the basic principles of electricity in his book Experiments and Observations on Electricity, published in London in 1751. Electricity was a constant force in nature that moved between a positive and negative charge, was conducted over a distance by certain metals such as tin and lead, but not conducted by insulating materials such as silk and glass. A spark would complete a circuit between two conductors separated by a short distance. Certain materials such as human hair would "stand on end" when conducting a small amount of electricity. In 1774, Georges Louis Lesage built a telegraph in Geneva using 26 insulated wires for each letter of the alphabet. When an electric current was applied to a wire at one end, it would move a ball suspended from the wire at the other end striking a bell. Joseph Henry designed a simpler device in 1831 using an electromagnet to move a metal bar that would strike a bell.
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Volta portrait from
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Alessandro Volta in 1800 invented the voltaic pile, an early electric battery, that used a chemical reaction to produce an electric current when a disc soaked with a salt solution was placed between discs of silver and zinc. Francisco Salva in 1805 used a voltaic pile to produce a hydrogen signal and Harrison Gray Dyar built and 8-mile line on Long Island in 1827 that produced a chemical discoloration on a moving strip of litmus paper. Alexander Bain of Scotland patented a chemical telegraph in 1848 that made blue marks on a special paper and competed for a number of years with the Morse in the United States.
Hans Oersted in 1819 discovered that a magnetic needle moved when an electric current was sent through a nearby wire. Andre Ampere in 1820 made a device with 26
needles and 26 wires to signal each letter of the alphabet, and similar needle telegraphs were built over the next 20 years by Carl Gauss, Wilhelm Weber, Henry and Edward Highton. William Cooke and Charles Wheatstone built a device for the London and Birmingham Railway in 1837 that used a wire coil to cause 5 needles, later a single needle, to point to different locations on a dial corresponding to an alphabet code. Wheatstone pioneered bipolar transmission that later became the basis of the duplex and quadraplex telegraphs. Unlike Morse, who used only the single positive polarity of the electrical current switched off and on to represent a dot or dash, Wheatstone reversed his current between a positive and negative polarity to represent his code. Wheatstone also was one of the first to recognize the importance of Georg Ohm's discovery in 1827 that the resistance of certain materials changed the strength of the electrical current. Baron Schilling developed a needle telegraph in Russia in 1832, using a 2-element code in which left and right movements of the needle represented letters of the alphabet. K.A. Steinheil in Germany developed a single-needle telegraph with a dot-dash code in 1836 and persuaded Bavaria to build a national line, the first government-sponsored telegraph line. Werner von Siemens in Germany developed the
pointer telegraph in 1847 and founded Telegraphen-Bauanstalt that became the electronics giant Siemens AG.
© 1999-2005 by Steven E. Schoenherr. All rights reserved. |
