ELECTRIC POWER 



145 



161. Electric Motors. The motor has practically the 

 same construction as the dynamo, but its action is that 

 of the dynamo reversed. That is to say, while in the 

 dynamo we cause the coils of the armature to revolve in 

 the field of the magnet, and thus produce a current, in 

 the motor we run a current into the armature, and cause 

 it to revolve, producing motion. The motion of the arma- 

 ture can be passed on, by gear wheels or by belts, to the 

 wheels of a street car, or of whatever is to be set in mo- 

 tion. In other words, in the dynamo we exchange mechan- 

 ical motion for an electric current; but in the motor we 

 exchange the current for mechanical motion. 



Electric motors are used not only for the moving of vehicles, but 

 also for running the machinery of factories, sewing machines, washing 

 machines (cf. Fig. 194), 

 electric fans, vacuum 

 cleaners, etc. c 



Electric Street Cars. 

 In the trolley car the 

 motor is generally under 

 the car, and the current is 

 supplied by the generators (dynamos) of a power house (Fig. 138). 

 The current is carried by a "feed wire" to the trolley wire, or third 

 rail, from which it passes to the motor of the car. The return circuit 

 for the current is through the car track. 



162. Electric Power. Electric power may be generated 

 in dynamos by engines using coal, gasoline, petroleum, 

 etc., as sources of energy, or the power may come from the 

 wind, waterfalls, rapids, or dams. Niagara furnishes power 

 not only for many electric furnaces and for processes of 

 electrolysis, but for lighting cities like Buffalo and Roches- 



FIG. 138. 

 Trolley Car. 



