THE 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 

 unapproached. Conceive the Siemens armature placed 

 between the poles of a suitable electro-magnet. Sup- 

 pose 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 cur- 

 rent 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 it 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 mag- 

 net and armature are able to produce currents of ex- 

 traordinary 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.* By this 

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

 expense involved in the employment of permanent mag- 

 nets; 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 



* Tn 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 the induced currents. 



