712 



MAGNETIC INDUCTION. 



the keeper becomes a north pole ; the other end therefore 

 a south pole. This other end again becomes also a south 

 pole by the inductive action of the adjoining pole of the 

 electro-magnet, which is a north pole. Thus either 

 pole produces not only the effect which is due to its 

 individual influence, but it also adds to the action of 

 the other, and the total attraction exerted by both poles 

 together is consequently more than double that which 



B 



FIG. 361 (anproj.; real size}. 



would be exerted if each pole were to act alone. Thus 

 the small electro-magnet represented in fig. 361 A will 

 support, by means of a keeper, a weight of several 

 hundred grammes; the larger electro-magnet, fig. 361 

 B, will support a considerable number of kilogrammes, 

 the current of a single Grove's or Bunsen's cell being 

 used in either case. With very large electro-magnets, 



