Page:Heroes of the telegraph (IA cu31924031222494).djvu/26

 and clumsy, was nevertheless used not only for scientific, but for general correspondence. Steinheil, of Munich, simplified it, and added an alarm in the form of a bell.

In 1836, Steinheil also devised a recording telegraph, in which the movable needles indicated the message by marking dots and dashes with printer's ink on a ribbon of travelling paper, according to an artificial code in which the fewest signs were given to the commonest letters in the German language. With this apparatus the message was registered at the rate of six words a minute. The early experimenters, as we have seen, especially Salvá, had utilised the ground as the return part of the circuit; and Salvá had proposed to use it on his telegraph, but Steinheil was the first to demonstrate its practical value. In trying, on the suggestion of Gauss, to employ the rails of the Nürenberg to Fürth railway as the conducting line for a telegraph in the year 1838, he found they would not serve; but the failure led him to employ the earth as the return half of the circuit.

In 1837, Stratingh, of Groninque, Holland, devised a telegraph in which the signals were made by electro-magnets actuating the hammers of two gongs or bells of different tone; and M. Amyot invented an automatic sending key in the nature of a musical box. From 1837-8, Edward Davy, a Devonshire surgeon, exhibited a needle telegraph in London, and proposed one based on the discovery of Arago, that a piece of soft iron is temporarily magnetised by the passage of an electric current through a coil surrounding it. This principle was further applied by Morse in his electro-magnetic printing telegraph. Davy was a prolific inventor, and also sketched out a telegraph in which the gases evolved from water which was decomposed by the current actuated a recording pen. But