24 THE ELECTRIC TELEGRAPH. 



Edinburgh. He divided his thirty wires into twenty-six 

 letters of the alphabet, three signs of punctuation, and one 

 asterisk for indicating the end of a word. The return circuit 

 was formed by a single wire. 



31. In 1825, Mr. Sturgeon, of London, discovered that 

 when a soft iron bar is surrounded by a helix of wire, 

 through which a galvanic current is passing, it acquires 

 a considerable quantity of magnetism, which lasts as long as 

 the current continues in the coil. In this 

 way he constructed some powerful mag- 

 nets. A form which he made, and which 

 acquired an immense lifting power, is 

 shown in Fig. 10. For this purpose, 

 pieces of soft iron were bent in the form 

 of a horse shoe, round the horns of which 

 he wound spirally a length of well insu- 

 10 - lated copper wire. One end of the magnet 



so arranged became a north pole and the other a south pole 

 if the spiral wire were wound in the same direction through- 

 out, supposing the horseshoe to be bent straight. 



The positions of the poles depend, of course, upon the 

 direction in which the spirals are wound, and upon the 

 direction in which the current traverses them, according to 

 the same law as that by which Ampere expressed the posi- 

 tions of the poles of deflected magnets. 



In the coil, Fig. 11, for example, the positive current 

 descending between the observer and the soft iron bar, the 



spiral being right-handed, 

 the north pole would be 

 on the right hand of the 

 observer. 



11 - In order to increase the 



power of electro-magnets the wire has to be wound several 

 times round each of the horns. This is generally done by 

 means of bobbins of wire which can be removed at pleasure. 

 Such magnets have been made with iron cores 3 inches and 

 more in diameter, and over a foot in length, which have 

 carried nearly a ton weight. It is strange that this discovery, 



