THE ELECTRIC TROLLEY 265 



danger of smoke and sparks elsewhere the electric locomotive 

 is now taking the place of the steam locomotive. In 1915 

 there were 2250 miles of steam railway tracks in the United 

 States that had been changed to electric operation, and some 

 railroads are extending its use to great sections of their lines. 

 The electric locomotive can also be made of much smaller 

 weight than the steam locomotive. But it has to be heavy 

 enough so the drivers will not slip if equally heavy trains 

 are hauled. It is run by motors similar to the ordinary 

 trolley car, but more powerful, and a single engine may draw 

 a whole train of passenger or freight cars. 



SUPPLEMENTARY QUESTIONS FOR CLASS DISCUSSION 



1. What advantages has the trolley over the locomotive? 



2. What parts do the dynamo and the motor play in running 

 the trolley? 



3. In what ways are the dynamo and motor alike?' 



4. How does the motorman control his car ? 



5. What provision is made on the electric cars for protection 

 from accidents ? 



6. How is the electricity produced that runs the cars ? 



7. How does the motor change electricity into action? 



REFERENCES 



Cressey, Discoveries and Inventions of the Twentieth Century, 

 E. P. Button Co., New York City. Chap. 13. 



Harper's Electricity Book for Boys, Harper Bros., New York 

 City. Chap. 10. 



