TRACTION ENGINES 459 



the point of ignition in the engine in order to reduce the 

 power at low speed, or else shifting the power from one 

 set of gears to another. Generally in an engine where the 

 power is shifted there are only two speeds, a high and a 

 low. 



On the road. About the same caution should be exer- 

 cised in handling a gasoline traction engine through soft 

 and muddy places and over bridges as in handling a steam 

 engine. But there is practically no caution to be taken 

 in climbing hills other than that taken on level ground. 

 Upon descending a hill a strong and effective brake 

 should always be at the control of the operator. 



Traction. As a rule gasoline traction engines are much 

 lighter than steam traction engines. Consequently their 

 tractive power is correspondingly less. And for heavy 

 traction work the size of the engine must be increased 

 in order to add to the tractive power. 



