3 8 2 NINETEENTH CENTURY. PT. lit 



up by the varying heat on diffeient parts of the earth. The 

 whole subject of electricity and magnetism has been carried 

 in the present century far farther than we can attempt to 

 follow it here, for mathematical knowledge is necessary in 

 order to understand its laws as worked out by Weber and 

 Helmholtz in Germany, and Sir W. Thomson and Clerk- 

 Maxwell in England. 



Invention of the Electric Telegraph by Wheatstone 

 and Cooke, 1837. We have not room to speak here of 

 the electric light, the storage of electricity, and other methods 

 by which this marvellous force has been made the servant 

 of man. But we can hardly close an account of electricity 

 and magnetism without showing how the discovery of 

 these two forces has made it possible for our thoughts to 

 be carried in a few moments of time to the most distant 

 parts of the world. Ever since Volta had shown, in 1800, 

 that an electric current can be sent for any distance along a 

 wire the two ends of which are joined to the poles of a 

 battery, scientific men had speculated whether it might not 

 be possible to use this current for making signals at a 

 distance. The difficulty was how to make the signs at the 

 other end. In 1 8 1 6, Mr. Ronalds, of Hammersmith, hung 

 pith-balls on to a wire, which stood out while the current 

 was flowing, and fell down again when it ceased ; and many 

 other plans were tried, but none succeeded well. 



When Oersted, however, showed in 1819 that an electric 

 current will cause a magnetic needle to turn from side to 

 side, it was clear that here was a means by which signs 

 could be made at any distance ; and accordingly we find 

 that Ampere, in 1830, proposed to work signals by a magnet, 

 and different attempts were made in Europe and America 

 to carry out his idea. The first electric telegraph of any 

 value was patented by Professor Wheatstone and Mr. Cooke 



