Transportation on Land 335 



of the motor. A motor transforms electrical energy into mechanical 

 energy. 



The generator consists of coils of wire and a shaft in the field of an 

 electromagnet. 



A magneto comprises coils of wire which move through the field 

 of a permanent magnet. 



r An alternating current (A. C.) generator delivers into the external 

 circuit a frequently reversing current, just as it is produced in the coils 

 ef the armature. 



( A direct current (D. C.) generator, by means of the commutator, 

 delivers into the external circuit a current in one direction only. 

 ; In general, a motor may be used as a generator, and a generator 

 aig a motor. 



^Jthe electromagnet consists of a soft iron core wound with insulated 

 wire. ' 



The transformer has two coils, a primary and a secondary, upon 

 a common core. It is used to step up or step down the voltage of an 

 alternating current. 



To transmit a small current at high voltage is more economical 

 than to transmit a large current at low voltage. 



The successful use of gasoline motors in vehicles depends upon 

 electric ignition. 



Gasoline engines are of two types, the one-in-four working stroke, 

 or four-cycle, and the one-in-two working stroke, or two-cycle. 



Electricity for ignition purposes is derived from a magneto or from 

 a battery. 



A battery consists of several cells connected with wires. 



The two types of cells most used for ignition are the dry cell, and 

 the secondary (storage) cell. 



The current for the dry cell (a primary cell) is due to the chemical 

 action of the zinc and sal ammoniac. 



The electric current of a secondary cell is due to chemical changes 

 which are reversed when a current passes in the opposite direction. 



REVIEW QUESTIONS 



1. What progress has been made in recent years in electrifying 

 steam railways? 2. Why has the Milwaukee railroad electrified its 

 lines in the mountains of Montana? 3. How does one electric loco- 

 motive help another in the mountains? 4. How is the train going 

 down grade made to help in furnishing energy for trains going up 

 grade? 5. What natural resources are used for developing the 



