32 W. J. M, Rankine on the Air-Engine, 



engine must have been very great, though it was economical 

 of fuel as compared with steam-engines. 



24. Causes of waste of heat in Ericsson's Engine of 1852. 

 — (1.) Imperfect communication of heat from the furnace to 

 the air. — This cause of waste of heat must have operated to a 

 great extent in the engine in question ; for the heating surface 

 was simply the bottom of the expanding cylinder ; at the same 

 time an extensive heating surface was rendered doubly neces- 

 sary by the low pressure of the air ; for, as was long since 

 shown by Dulong and Petit, the power of gases to receive 

 and communicate heat increases with their pressure. 



(2.) Imperfect abstraction of the lost heat. — It has already 

 been stated that there was no provision for abstracting the 

 heat produced in the compressing cylinder ; the direct effect 

 of this would be to cause an additional and unnecessary ex- 

 penditure of power in compressing the air. 



(3.) Communication of heat to the air at improper periods 

 of the stroke. — This cause of waste must have operated to a 

 considerable extent; for the air, after having performed its 

 work, and while in the act of being discharged into the at- 

 mosphere, continued to circulate over the heated bottom of the 

 cylinder, and must have carried away a considerable amount 

 of heat. This heat would not be stored in the regenerator, 

 which must have received no more heat from the escaping 

 air than had been previously abstracted from it by the air 

 when entering, or otherwise the temperature of the regenerator 

 would have gone on continually rising. 



(4.) Expenditure of heat in raising the temperature of the 

 air. — There is reason to believe that in Ericsson's engine, as 

 in Stirling's, the regenerator was adequate to prevent any 

 considerable waste from this cause. 



(5.) Improper arrangement of the changes of volume and 

 pressure. — There is no reason to believe that any material 

 waste arose from this cause. 



It may be observed that Ericsson's engine, as well as Stir- 

 ling's, was absurdly represented by some parties as a "per- 

 petual motion." 



(To be continued?) 



