Transportation on Land 321 



not be unlike that of the automobile within the past twenty 

 years. Less than twenty years ago there were fewer than 

 fifty automobiles in the country, and these were fantastic, 

 almost impossible contrivances. To-day the automobile is 

 everywhere in rapidly increasing numbers. In a similar way we 

 may consider the present and the future of electricity in long 

 distance transportation. To-day the alternating current is 

 generated for transmission over long distances and then con- 

 verted into the direct current for most effective use. To-morrow 

 generators will be made which will generate direct current at 

 high tension and potential for long distance transmission, and do 

 away with the present expensive process and machinery for 

 rectifying or changing the alternating into the direct or contin- 

 uous current (pages 327-8). 



142. The electric motor. The electric motor changes elec- 

 tric energy, transmitted by wires from a battery or a generator, 

 into power to do work or mechanical energy. The electric 

 generator (page 325) takes in mechan- 

 ical energy derived from steam or 

 falling water and gives out electrical 

 energy. The simplest form of the 

 motor is illustrated in Fig. 100. 

 When an electric current passes along 

 the wire that lies between the poles 

 of a magnet, the wire is made to move FlG - * 00< ~~ Dia s ram showing 



,7 now a motor works. 



in the direction of the dotted line. If 



the direction of the current is reversed, the wire will move 

 in another direction. This does not resemble a motor, but it 

 acts exactly like one. Suppose you have a coil of wire, as in 

 Fig. 101, and the electric current causes the coil to move from 

 dotted line to present position. At just this point where the 

 coil would stop, the current is reversed, with the result that 

 the coil continues to move through another half turn. Revers- 

 ing the current at this point causes the coil to be carried be- 

 yond the next stopping point. With the continued reversal 



