144 



MAGNETS AND ELECTRICITY 



in the wire, 

 kept moving. 



The current flows as long as the magnet is 

 This is illustrated by Fig. 136. The moving 

 of the magnet causes the wire 

 constantly to pass through 

 new portions of the magnet's 

 field. 



Instead of moving the 

 magnet within a fixed coil, 

 we can keep the coil in mo- 

 tion, while we leave the 

 magnet stationary. This is the principle of the dynamo 

 (Fig. 137). A revolving frame, called the armature, is 

 wound with many separate coils of wire. As each coil ap- 

 proaches and leaves the magnetic field, currents are pro- 

 duced in the wires. These are drawn off, as rapidly as they 



FIG. 136. 



A magnet 'moved into or out of a 

 produces a current in the coil. 



FIG. 137. 



A Direct Current Dynamo, Directly Connected with an Automatic Engine. Courtesy 

 of the Ridgway (Pa.) Dynamo and Engine Co. 



are produced, through wires attached to the poles of the 

 dynamo. The dynamo current may be used for the pro- 

 duction of heat or light, or it may be run into the motors 

 of trolley cars, etc., and used to produce motion. 



