544 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK v. 



In these days the metallic threads which serve to transmit human 

 ideas with the velocity of lightning, in the interests of commerce, 

 politics and science, as well as for private correspondence, circle the 

 entire globe. They form a network of prodigious length, which not 

 only covers continents but crosses oceans and seas, and unites all the 

 nations of the world, from Europe to the Indies, China and Japan, 

 Australia and New Zealand, and North and South America. From 

 the American continent this marvellous chain will ultimately cross 

 the whole extent of the Pacific to join Japan and China, and thus 

 complete the circuit round the terrestrial spheroid. We will give 

 further on the statistics of the universal electric telegraph ; but pass 

 now to sketch the history of this marvellous invention. 



To give this history in all its details would require a volume. 

 It must suffice us to indicate rapidly its principal phases, and 

 to show how these phases are connected with the progress of 

 science itself. 



Before the invention of the voltaic pile, the projects for electrical 

 communication, although sufficiently numerous, never had any serious 

 practical application. In Le Sage's system (1774) the electricity of a 

 machine was transmitted by isolated metallic wires to an electroscope 

 whose movements marked the letters of the alphabet; there were in 

 this case 26 wires according to the number of letters. Later, in 

 1798, Bethencourt substituted the discharges of a Leyden jar for those 

 of an ordinary machine, and the system was applied between Aranjuez 

 and Madrid over a distance not less than 27 miles. An analogous 



O 



system was -constructed in 1787 by the French physician Lomond. 

 Reiser in 1794, Cavallo in 1795, Salva in 1796, and Ronald, lastly, in 

 1823, made use also of statical electricity for the transmission of 

 signals, with a modification of the method of indication, as, for 

 instance, the employment of sparks made to discharge upon a 

 fulminating pane. 



The discovery of the voltaic pile directed the attention of inven- 

 tors to a more interesting method, and one much nearer to the true 

 solution. Cox, the American, in 1800, Soammerring in 1811, and lastly 

 Schweigger, the inventor of the multiplier, in 1828, had successively 

 the idea of making use of the chemical properties of the voltaic 

 current. The bubbles of oxygen and hydrogen arising from the decom- 

 position of water gave by their disengagement at one station, various 



