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. 





