334 



THE POPULAR SCIENCE MONTHLY. 



nearly to its extreme upper position. The air in eontact with the 

 water-jacket becoming cooled contracts, and the pressure is reduced 

 below the power-piston, which then descends by the force of the at- 

 mosphere. As it reaches the end of its downward stroke and begins 



Pig. 10. 



to ascend, the plunger comes down and the operation is repeated. 

 When the air passes from the heater to the cool cylinder A, it heats 

 the plates of the regenerator and this heat is given off to the cool air, 

 when it is again forced into the heater. The utmost of the heat is thus 

 utilized that is possible. The start in this as in all hot-air and gas 



