508 THE APPLICATIONS OF PHYSICAL FORCES. [BOOK iv. 



surface in such a way as to cut off all communication from the 

 source of heat to the air contained in the cylinder. This air, oh the 

 contrary, is in direct contact with the upper surface of the large 

 cylinder, which has double walls, and round which a constant current 

 of cold water is circulating. The chilled air condenses and its 



FIG. 332. Laubereau's hot-air engine. 



elastic force diminishes. The atmospheric pressure becomes the 

 stronger, and the driving piston descends again ; while, on the 

 contrary, the plaster piston rises and exposes the air to a second 

 heating. 



This series of effects is reproduced indefinitely, and gives the 



