TRANSPORTATION ON LAND 



301 



proved a failure because the car depen'ded upon bat- 

 teries for its electrical energy. The development of 

 the electric generator and ways of distributing the 

 energy gave modern electrical transportation to the 

 world. The first overhead trolley system was built in 

 Kansas City, Missouri, but the first city to replace the 

 old horse-drawn cars with electrically propelled cars 

 was Richmond, Virginia. Modern street railway trans- 

 portation dates from the Richmond experiment about 

 1887. 



In the modern overhead trolley system electrical 

 energy is obtained from generators in a power house, 

 distributed through overhead wires. The car has a 

 trolley wheel at the end of an arm extending above the 

 car. This wheel runs along the supply line and thus 

 connects the electric motors of the car with the elec- 

 trical supply. The rails and earth form a return circuit 

 to the power house for the electricity. Between the 

 trolley and the motors of a car is placed a resistance 

 which can be controlled by a lever in front of the 

 motorman. The resistance in the circuit may be in- 

 creased or decreased by moving the lever. When the 

 car is to be slowed, more resistance is placed in the 

 circuit and less current can reach the motors. When 

 the car is to be speeded up resistance is removed from 

 the circuit and more current reaches the motors. Mo- 

 tors used on street cars are geared directly to the 

 wheels. 



Brakes on the modern street car are of the air type 

 and are controlled by a lever in front of the motorman. 

 Doors on many modern street cars are also opened 

 and closed by means of compressed air. 



In several of the larger cities of this country and 

 Europe electrically propelled trains are used for rapid 

 transportation on elevated lines and in subways. In 

 place of the overhead trolley these systems usually 

 use a third rail to carry the electrical energy from the 

 power house. The third rail is placed beside the track. 

 The cars have an extension arm and a metal shoe 

 which rides along the third rail, much as the trolley 

 wheel moves along the trolley wire. 



On some of the railroads in the mountainous sec- 

 tions of the West electric locomotives have replaced 

 steam. On the steep mountain grades the electric lo- 

 comotives are able to move more heavily loaded trains 

 at a greater speed than the steam locomotives. The 

 locomotives used on these trains are electric power 

 houses on wheels. While the locomotive is climbing 

 a grade it is taking current from the overhead line to 

 drive its powerful motors. When the top is reached 

 and the train starts down the other side, use is made of 

 the force of gravity to move the train. The motors 

 which propelled the train up the mountain now be- 

 come generators and give back to the line nearly 30 



per cent of the electrical energy which they used in 

 climbing. This also serves as a braking device while 

 descending the steep grades. Figure 503 is a picture 

 of a modern electric locomotive in use. 



In several large cities of the country railroads have 



Courtesy the Milwaukee Road 



FIG. 503. MODERN ELECTRIC LOCOMOTIVE 



electrified their lines. This makes for much cleaner 

 and more efficient handling of trains. 



The most recent addition to the devices for land 

 transportation is the bus. It is possible to reach almost 

 any point in the country by buses which run on nearly 

 as exact schedules as the trains. On some lines it is 

 possible to secure sleeping accommodations. 



REFERENCES FOR FURTHER STUDY 

 Texts 



Caldwell and Curtis, Science for Today, Chap. 28 

 Clement, Collister, and Thurston, Our Surroundings, Chap. 



19 

 Hunter and Whitman, Science in Our World of Progress, 



Unit 9 

 Lake, Harley, and Welton, Exploring the World of Science, 



Chap. 25 (part) 

 Pieper and Beauchamp, Everyday Problems in Science, Unit 



17 

 Van Buskirk and Smith, The Science of Everyday Life, Chap. 



20 



Webb and Beauchamp, Science by Obsen>ation and Experi- 

 ment, Unit 3 

 Wood and Carpenter, Our Environment: Uoui We Use and 



Control It, Topic 11 A 



Special references 



Book of Popular Science 



The World Book 



Com f ton's Pictured Encyclopedia 



Holland, Historic Railroads 



