THE AUTOMOBILE 277 



Ignition system. The purpose of the ignition system is to 

 explode the gases in the cylinder at the proper time, so that 

 the piston may be forced down. The heat to ignite the gas 

 is furnished by an electric spark. The source of electricity 

 may be either dry cells, storage batteries, or magnetos ; or a 

 combination may be used. The switch that regulates the time 

 of explosion is controlled by contact with the camshaft, 

 which is so set that the explosion occurs at the proper time. 

 A part of the ignition system is an induction coil, which is a 

 device by means of which a current of sufficient strength is 

 formed to cause a spark in the cylinder. The spark plug 

 is composed of two points separated by a short distance, 

 across which the current jumps, producing the spark that 

 sets fire to the gases. 



Lubricating system. In order to prevent friction from 

 wearing out the parts of the engine, they must be kept sup- 

 plied with oil. The lubricating system commonly used 

 consists of a tank for storing the oil, a kind of pump to force 

 the oil to the bearing parts, and piping to take the oil from 

 the tank to the pump and from the pump to the engine. 

 The tank is large enough to hold one or two quarts of oil, 

 and the pump is worked automatically by connection with 

 the crank shaft or other part of the engine. 



Cooling the engine. The combustion of gases in the cylinder 

 produces a large amount of heat, and the cylinder would 

 soon become heated to such a high temperature as to inter- 

 fere seriously with the working of the engine. So some de- 

 vice must be used to keep the cylinder from getting over- 

 heated. This is accomplished by the use of either air or 

 water. The air-cooled engines are constructed in such a 

 way as to expose a large surface for cooling. In most cases 

 fans or some other device are used for forcing drafts of air 

 against the cylinder. 



The air system of cooling has the advantage of simplicity 

 and is much easier to operate, especially in winter when 



