MOTIVE POWER OF HEAT. 193 



Neither steam-engines nor air-engines, however, 

 are nearly perfect; and we do not know in which 

 of the two kinds of machine the nearest approach 

 to perfection may be actually attained. The beau- 

 tiful engine invented by Mr. Stirling of Galston 

 may be considered as an excellent beginning for 

 the air-engine;* and it is only necessary to com- 

 pare this with Newcomen's steam-engine, and con- 

 sider what Watt has effected, to give rise to the 

 most sanguine anticipations of improvement. 



V. On the Economy of Actual Steam-engines. 



56. The steam-engine being universally em- 

 ployed at present as the means for deriving motive 

 power from heat, it is extremely interesting to 

 examine, according to Carnot's theory, the econ- 

 omy actually attained in its use. In the first 



the apparatus, instead of, as in the steam-engine, always 

 in a saturated state. 



* It is probably this invention to which Carnot alludes 

 in the following passage: "II a ete fait, dit-on, tout re- 

 cemment en Angleterre des essais heureujt sur le de- 

 veloppement de la puissance motrice par 1'action de la 

 chaleur sur 1'air atmospherique. Nous ignorons entiere- 

 ment ne quoi ces essais ont consiste, si toutefois ils sont 

 reels." 



