280 SCIENCE OF HOME AND COMMUNITY 



combinations of gears, which are controlled by a lever. 

 The mechanism for reversing the engine is also located in 

 the gear box. 



Power transmission. Power may be transmitted from 

 the gear set to the wheels by means of sprockets and chains, 

 or by means of a shaft and gears on the rear axle. The chain 

 drive is often used on large motor vehicles, but the gear 

 drive is used largely on the ordinary cars. This has the ad- 

 vantage over the chain drive that it is inclosed and so can 

 easily be kept lubricated and free from dirt. 



Lights. Three means of lighting automobiles have been 

 used : kerosene, gas, and electricity. In the gas systems, 

 a tank containing acetylene gas under pressure is attached 

 to the car. Electricity is now most commonly used. This 

 has the advantages of cleanliness, reliability, and ease of 

 operation, the lights being turned off and on by operating a 

 switch. 



Three types of electric lighting systems are in use: that 

 using the dynamo or magneto; that using the storage 

 battery; and that using both the dynamo and storage 

 battery. In the last system, the current to the lamps is 

 furnished by the battery, but the dynamo keeps the battery 

 charged. This combination system is the one most com- 

 monly used. 



Means of controlling automobiles. The engine is started 

 either by hand or by electricity. At first the clutch is 

 thrown out by means of a foot pedal and then allowed to 

 come back after the engine starts. The direction of the car 

 is controlled by the stearing wheel, which connects with 

 the two front wheels. The speed is controlled by means of 

 two levers on the steering wheel, one of which controls the 

 supply of gas given to the engine, and the other controls the 

 time of sparking. In some cars the supply of gas may also 

 be controlled by a foot pedal. The speed may also be con- 

 trolled by changing the lever in the gear box. The rate of 



