Mechanical Theory of Heat to the Steam Engine. 369 



the same principles which I have already applied to the treat- 

 ment of several similar cases in a former paper.* 



The steam coming from the boiler passes first into the injuri- 

 ous space, compresses here the steam still present from the pre- 

 vious stroke of the piston, fills the space which thereby becomes 

 free, and acts then by pressure against the piston, which, accord- 

 ing to our assumption, in consequence of a comparatively small 

 load, yields so quickly that the steam cannot follow fast enough 

 to attain in the cylinder the same density as in the boiler. 



Under such circumstances, if only saturated steam passed from 

 the boiler, this would be overheated in the cylinder, inasmuch as 

 the living force of the motion of influx is here converted into 

 heat ; as however the steam carries some finely divided water 

 with it, a part of this will be evaporated by the excess of heat, 

 and will thereby retain the remaining steam in a state of satura- 

 tion. 



We must now propose to ourselves the problem : given, the 

 initial condition of the whole mass to be considered, as well that 

 already contained in the injurious space, as also that newly en- 

 tered from the boiler, further, the quantity of work which is 

 done during the influx by the pressure acting upon the piston, 

 and finally the pressure in the cylinder at the moment of cutting- 

 it off from the boiler, it is required to determine how much of 

 the mass in the cylinder is in the state of steam at this moment. 



33. Let the mass in the injurious space, before the influx which 

 for the sake of generality shall be assumed to be partly fluid and 

 partly in the form of steam, be called ^, and the portion of it, 

 which is in the form of steam p 0 . The pressure of this steam 

 and the absolute temperature which it possesses may for the 

 present be denoted hj p 0 and 2\, without meaning to say that 

 these are exactly the same values which hold good for the con- 

 denser also. The pressure and the temperature in the boiler 



* On the behavior of steam hi expanding under different circumstances, these An- 

 nals, vol. 82, p. 263. Helmholtz, in his report in the progress of physics, published 

 by the Physical Society of Berlin, for the year 1850 and '51, p. 582, says with re- 

 spect to this article and a notice connected with it and communicated in the Philo- 

 sophical Magazine, that in his opinion the same is incorrect in principle, in many 

 points. I have not been able to understand however, the reasons which he assigns 

 for this. Views are ascribed to me -which I never had, and propositions expressed 

 in opposition to them which I have never contested, and which form in fact partly 

 the foundation of my own works on the mechanical theory of heat, while the whole 

 is treated in so general a manner that it has been impossible for me to determine 

 how far these views follow from my words or these propositions are to overthrow 

 my conclusions. I do not therefore see myself obliged to defend my former works 

 against this blame. As however, the development which follows here rests as above 

 mentioned, entirely upon the same views by which I was at that time guided, Helm- 

 holtz will perhaps find in it also the same errors in principle. For this case, I await 

 his objections, only I would then desire him to go into the matter in a somewhat 

 more special manner. 



SECOND SERIES, VOL. XXII, NO. 66. — NOV., 1856. 



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