cii. XXXV. WHEATSTONE AND COOKE. 357 



end. In 18 16, 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 

 such plans were tried, but none succeeded well. 



When Oersted, however, showed in 18 19 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 fmd that 

 Ampbre, 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 in June 

 1837 ; and during the same year Dr. Steinheil, of Munich, 

 and Professor Morse, of America, both invented telegraphs 

 of rather different kinds. I shall not attempt to describe 

 all of these, but will only explain the simplest principle of an 

 electric telegraph as it is used in England, and to show 

 how it depends upon electricity and magnetism. 



You will see, if you turn back to Figs. 55 and 56, p. 345, 

 that when the electric current flowed round one way, a b c 

 di Fig. 55, the north pole of the needle turned to the west ; 

 when it flowed round the other way, a b c d^ Fig. 56, the north 

 pole turned to the east. Now the signals of the electric tele- 

 graph depend upon this fact, that the direction of the current 

 alters the direction of the magnet. When one man wants 

 to send a message to another, he does it by sending an 

 electric current from a battery along a telegraph wire, so 

 that it passes a magnetic needle either from right to left or 

 from left to right. When it flows round one way, the needle, 

 even if it is a hundred miles off, turns to the right, when it 

 flows round the other way the needle turns to the left ; and 

 it is agreed that so many strokes to the right mean one 



