THE CONQUEST OF NATURE 



between the poles of a powerful electromagnet. These 

 coils of wire constitute what is called an armature. When 

 the current is switched on it passes through this arma- 

 ture, as well as through the electromagnet, and the mutual 

 attractions and repulsions between the magnetic poles 

 and the electric current in the coils of wire, cause the 

 armature to revolve with such tremendous energy as 

 to move the train the motion of its axis being trans- 

 mitted to the axle of the car-wheels by a simple gearing. 



All this is simple enough if we regard only the how 

 and not the why of the phenomena. Ignoring the why 

 for the moment, let us seek the origin of the current 

 which, by being conducted through the armature, 

 has produced the striking effect we have just witnessed. 

 This current reaches the car through an overhead or 

 underground wire. All that is essential is that some con- 

 ducting medium, such as an iron rail, or a copper wire, 

 shall form an unbroken connection between the motor 

 apparatus and the central dynamo where the power is 

 generated the return circuit being made either by 

 another wire or by the ordinary rails. 



The central dynamo in question will be found, if we 

 visit the power-house, to be a ponderous affair, sugges- 

 tive to the untechnical mind of impenetrable mysteries. 

 Yet in reality it is a device essentially the same in con- 

 struction as the motor which drives the train. That 

 is to say, its unit of construction consists of a wire- 

 wound armature revolving on an axis and fitted between 

 the poles of an electromagnet. Here, however, the 

 sequence of phenomena is reversed, for the armature, 

 instead of receiving a current of electricity, is made to 



[i74] 



