fflE ELECTRIC LIGHT. 433 



possess a trace of permanent magnetism ; and from such 

 a small beginning Siemens and Wheatstone have taught 

 us to rise by a series of interactions between magnet 

 and armature to a magnetic intensity previously un- 

 approaclied. Conceive the Siemens armature placed 

 between the poles of a suitable electro-magnet. Suppose 

 this latter to possess at starting the faintest trace of 

 magnetism ; when the armature rotates, currents of 

 infinitesimal strength are generated in its coil. Let 

 the ends of that coil be connected with the wire sur- 

 rounding the electro-magnet. The infinitesimal current 

 generated in the armature will then circulate round the 

 magnet, augmenting its intensity by an infinitesimal 

 amount. The strengthened magnet instantly reacts 

 upon the coil which feeds it, producing a current of 

 greater strength. This current again passes round the 

 magnet, which immediately brings its enhanced power 

 to bear upon the coil. By this play of mutual give and 

 take between magnet and armature, the strength of the 

 former is raised in a very brief interval from almost 

 nothing to complete magnetic saturation. Such a 

 magnet and armature 'are able to produce currents of 

 extraordinary power, and if an electric lamp be intro- 

 duced into the common circuit of magnet and armature, 

 we can readily obtain a most powerful light. 1 By this 

 discovery, then, we are enabled to avoid the trouble and 

 expense involved in the employment of permanent 

 magnets ; we are also enabled to drop the exciting 

 magneto-electric machine, and the duplication of the 

 electro-magnets. By it, in short, the electric generator 

 is so far simplified, and reduced in cost, as to enable 



1 In 1867 Mr. Ladd introduced the modification of dividing the 

 armature into two separate coils, one of which fed the electro- 

 magnets, while the other yielded t Ke induced currents. 



