THE ELECTRIC DELL 319 



of the coil. This shows that the ends of the helix have mag- 

 netic power but not the sides. 



If a soft iron nail (Fig. 212) or its equivalent is slipped 

 within the coil, the lifting and attractive power of the coil is 

 increased, and comparatively heavy weights can be lifted. 



A coil of wire traversed by an electric current 

 and containing a core of soft iron has the power 

 of attracting and moving heavy iron objects ; that is, 

 it acts like a magnet. Such an arrangement is 

 called an electromagnet. As soon as the current 

 ceases to flow, the electromagnet loses its power and 

 becomes merely iron and wire without magnetic 

 properties. 



If many cells are used, the strength of the electro- 

 magnet is increased, and if the coil is wound closely, FIG. 212. 

 as in Figure 213, instead of loosely, as in Figure Coil and 



soft iron 



211, the magnetic strength is still further increased, rod. 

 The strength of any electromagnet 

 depends upon the number of coils wound on 

 the iron core and upon the strength of the 

 current which is sent through the coils. 



To increase the strength of the electromagnet 

 still further, the so-called horseshoe shape is 

 used (Fig. 214). In such an arrangement there 

 is practically the strength of two separate elec- 

 tromagnets. 



297. The Electric Bell. The ringing of the 

 electric bell is due to the attractive power of 

 an electromagnet. By the pushing of a button 

 FIG. 213. An (Fig. 215) connection is made with a battery, 



electromagnet. 



and current nows through the wire wound on 

 the iron spools, and further to the screw P which presses 

 against the soft iron strip or armature S; and from 5 the 



