30 W. J. M. Rankine on the Means of 



penditure of heat whatsoever, except losses by conduction 

 and radiation. This amounted to representing Stirling's air- 

 engine as a machine for creating power out of nothing, popu- 

 larly called a "perpetual motion" It is very probable that 

 the promulgation of that erroneous theory may have led scien- 

 tific and practical men to regard the real performances of this 

 engine as delusive, and may have been the cause which, not- 

 withstanding its economy as compared with steam-engines, 

 prevented the extension of its use beyond the Dundee 

 Foundry. 



(5.) Imperfect arrangement of the series of changes of vo- 

 lume and pressure. — It is not likely that in Stirling's engine 

 any material amount of waste arose from this cause, for the 

 series of changes in question would be regulated by the rela- 

 tive motions of the piston and plungers ; and those motions 

 being susceptible of adjustment, as in the case of the piston 

 and slide-valve of a steam-engine, would be fixed, by trial, so 

 as to act in the manner found to be most advantageous. 



From all that has been stated, it appears, — that the principal 

 causes of waste of heat in Stirling's engine were — first, defi- 

 ciency of heating surface, and, secondly, communication of heat 

 to the air during that part of the stroke when it was not being 

 expanded ; — that the latter cause was sufficient of itself to 

 double, or nearly to double, the theoretical consumption of 

 fuel ; that the actual consumption of fuel was triple the theo- 

 retical consumption ; but that, notwithstanding such defects, 

 the engine was economical as compared with steam-engines. 



22. Ericsson's Engine of 1852. — In this engine the com- 

 pression and expansion of the air were performed in two dif- 

 ferent cylinders, and at each stroke the air which had been 

 used was expelled into the atmosphere, a fresh supply of air 

 being at the same time taken in to perform the next stroke. 

 This process of expelling the used air, and taking in fresh air 

 corresponded to the process C of the cycle ; for the air ex- 

 pelled being, while in the cylinder, at a high temperature, 

 was driven through a regenerator of wire gauze, and there 

 left its sensible heat. This mode of working involved a great 

 practical disadvantage, especially for marine purposes ; for the 

 cylinders had to be made large enough to contain the requi- 



