THE 

 LONDON, EDINBURGH a.nd DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[FOURTH SERIES.] 



OCTOBER 1856. 



XXXIII. On the Application of the Mechanical Theory of Heat 

 to the Steam-engine. By R. Clausius*. 



1. AS our present modified views respecting the nature and 

 -l\. deportment of heat, which constitute the mechanical 

 theory of heat, had their origin in the well-known fact that heat 

 may b^ employed for producing mechanical work, we may natu- 

 rally anticipate that the theory so originated will in its turn helj) 

 to place this application of heat in a clearer light. At all events 

 the more general views thus obtained must enable us to pro- 

 nounce safely upon the efficiency of the several machines for 

 thus applying heat, as to whether they already perfectly fulfil 

 their purpose, or whether and to what extent they are capable 

 of being perfected. 



Besides these reasons, which apply to all thermo-dynamic 

 machines,^ there are others, applicable more particularly* to the 

 most important of them — the steam-engine, which appear to 

 render a new investigation of the latter, conducted according to 

 the principles of the mechanical theory of heat, desirable. It is 

 precisely with respect to vapour at a maximum density that this 

 new theory has led us to laws which differ essentially from those 

 formerly accepted as true, or at least introduced into former 

 calculations. 



2. I may here be allowed to refer to a fact proved by Rankine 

 and myself, that when a quantity of vapour at its maximum den- 

 sity, enclosed by a surface impenetrable to heat, expands and 

 thereby displaces a moveable part of the enclosing surface, e. g, 

 a piston, with its full force of expansion, a part of the vapour 



* From Poggendorff's Annalen, vol. xcvii. p. 441. 

 Phil. Mag. S. 4. Vol. 12. No. 79. Oct. 1856. R 



