As there are a great many other applications of electricity of which we have to treat,—the Electric Light, and Mr. Edison’s other inventions,—our space will not permit a much more detailed account of the telegraph, but there are some incidents connected with its progress which it would be as well to mention.
Fig. 256.—Electric cable.
Fig. 257.—Ocean cable.
Alexander Bain, about 1840, attempted to produce a printing telegraph, and in 1846 he actually accomplished a registering apparatus, which was an application of the principles of Dyar and Davy. But although Bain’s system was good, Morse had the advantage of possession in the United States, where it was tried, and Bain went out of fashion. Bain’s system was, in fact, the present chemical “automatic” telegraph, which has been perfected for rapid transmission.
Bakewell’s instrument, which has been improved upon by later electricians, is termed the fac-simile telegraph. The message to be sent is written with a pen which has been dipped in varnish (for ink), and the characters are inscribed upon prepared tinfoil. The message is then put upon a cylinder covered with prepared paper, and has a pointer attached. There is a precisely similar cylinder at the receiving station. When the cylinders are simultaneously set going, the point at one will trace a spiral line as the first (transmitting) point passes round its cylinder. However, as the latter “stylus” meets the varnish letters a break occurs, and these spaces are exactly reproduced as blanks at the other end, and the form of the letters can be seen. Coselli, in his adaptation, caused dark letters to be registered on a white ground, and thus simplified matters. Since then we have had printing telegraphs, and dials, and writing machines, one of which will be described presently.
Submarine telegraphs were, it is said, first suggested by Salvá in 1797, and Wheatstone, in 1840, declared that it was quite possible to connect England and France by wire. Morse and Calt experimented with submarine cables in America, and Lieutenant Siemens first applied gutta-percha to the wires as an insulator in the Prussian line of telegraph across the Rhine. The English laid a wire between Dover and Calais, which was broken, but successfully relaid. And so on, till in 1857 the great project of the Atlantic cable was broached. We give illustrations of the cables; the circumstances connected with the laying of which, and the enthusiasm over the successful accomplishment of the task, must be in the memory of all. The readings of the messages were shown by delicate galvanometers, the beam of light being reflected from a mirror. This cable was lost, and in 1862 Mr. Field came over to urge the importance of the submarine cable between this country and America. The cable was shipped on the Great Eastern in 1865, and was 2,186 miles long. It consisted of seven copper wires twisted, and covered with gutta-percha. The outside coating consists of ten iron wires surrounded by manilla yarn. But this cable broke, and a third was made and laid in 1866. The old cable was then recovered and spliced. There are some two hundred cables now in existence, the last being the Cape cable, laid when the Boer War was engaging our attention. The transmitting apparatus of Mr. Varley and Sir W. Thomson has greatly accelerated the rapidity of messages, and Thomson’s syphon recorder farther increased the speed.
The following description of a new system is from Scribner’s Magazine for 1880:—
“New Telegraphic System.