The Development of the Electromagnetic Telegraph

The electromagnetic telegraph starts with Oersted, who in 1819 found that a magnetized needle would be deflected from its normal position when brought close to a wire carrying a current. A year later, Schweigger found that the deflection was increased if the needle was wrapped with several turns of wire. Soon after, Ampere studied electromagnetism and proposed the use of magnetic needles and coils for the reception of signals.

Ampere's first telegraph system employed a pair of line wires for each character to be sent, which made it of little value. Schilling in 1832 exhibited a system similar to Ampere's, but using fewer line wires. Gauss and Weber in 1833 made further improvements, employing a suspended bar magnet with an attached mirror which reflected a beam of light as a signal detector. The signal currents employed in their apparatus were generated by electromagnetic induction, independently discovered by both Faraday and Henry. Much credit is due Steinheil, who highly perfected the systems of Gauss and Weber, and who discovered that the earth could be used for one side of the connecting circuit. Steinheil also arranged for the messages to be received by several different means, including a code of dots recorded on paper moved by clockwork, acoustically by means of needles which struck bells, and visually by observing the motion of needles.

Wheatstone and Cooke did much to popularize the telegraph and to demonstrate its commercial practicability. Their first system was of the deflecting-needle type, requiring six line wires. It was used with railway systems but was superseded by a type having only two line wires. The independent discoveries of Argo and Davy that an electric current had power to magnetize steel and the development of the electromagnet by Sturgeon in 1825 contributed greatly to the progress of telegraphy. Henry improved the electromagnet and in 1821 successfully used this principle to operate a magnetized bar which rang a bell and transmitted intelligence by code, It remained, however, for Samuel F. B. Morse to apply this principle in a satisfactory manner.