274 SCIENCE OF HOME AND COMMUNITY 



FIG. 103. First stroke (suction). Gas and air admitted to cylinder. 



FIG. 104. Second stroke (compression). Mixture of gas and air compressed. 



FIG. 105. Third stroke (combustion). Mixture is exploded and expands, 

 driving the piston forward. 



Courtesy of Harper & Brothers 

 FIG. 106. Fourth stroke (exhaustion). The burned -out mixture of gas and 



air expelled from the cylinder. 

 THE FOUR-CYCLE GAS ENGINE. 



