FARM MOTORS 



355 



These shortcomings on the part of the hot-tube igniter, and 

 the rapid development of the electric igniter have caused the 

 general abandonment of the former. 



There are two general classes of electric ignition systems 

 in general use. These systems are generally known as the 

 ' ' make-and-break ' ' system and the ' ' j ump-spark ' ' or high- 

 tension system. Each of these systems has its advantages. 

 The make-and-break system is used largely in connection 

 with stationary engines, while the jump-spark is used with 

 variable-speed motors, like the automobile. 



The Make-and-Break System. In the make-and-break 

 system of electric ignition two electrodes or points are pro- 



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 xS Rod 



fc&ttery of Dry Cells 



Fig. 225. Sketch showing the wiring and essential parts of a make- 

 and-break system of ignition. Four standard dry cells form the usual 

 battery instead of six as shown. 



vided in the compression space of the engine cylinder, and are 

 insulated from each other in such a way that an electric cur- 

 rent will not flow through them unless they are made to 

 touch each other. When an electric current is broken, there 

 is a tendency to produce a spark at the point where the separa- 

 tion takes place. By placing a spark coil in the circuit the size 

 of the spark may be much increased. The system consists 



