Sftasi* Theory of Heat to the Steam-engine. 



that the machine goes so slowly, or that the influx canal is so 

 wide, that the same pressure p^ exists in the cylinder as in the 

 boiler. This case therefore gives the maximum of work. If 

 with equal influx of vapour the velocity of motion is greater, or 

 with equal velocity of motion the influx of vapour is smaller, we 

 obtain from the same quantity of vapour a less quantity of work. 



32. Before we now proceed to consider connectedly the same 

 series of processes according to the mechanical theory of heat, it 

 will be best to submit one of the same, which requires especial in- 

 vestigation, to a separate treatment in order at once to establish 

 the results which have reference thereto. I refer to the entrance 

 of vapour into the vicious space and into the cylinder y when it has 

 there to overcome a smaller pressure than that with which it was 

 forced out of the boiler. In this investigation I can proceed ac- 

 cording to the same principles as those which I have employed 

 in a former memoir* when treating similar cases. 



The vapour from the boiler first enters the vicious space, here 

 compresses the vapour of small density which still remains from 

 the former stroke, fills up the space thus becoming free, and 

 then presses against the piston, which, in consequence of its 

 assumed comparatively small charge, recedes so quickly that the 

 vapour cannot follow it quickly enough to reach the same den- 

 .sity in the cylinder as it had in the boiler. 



If saturated vapour alone issued from the boiler, it must under 

 such circumstances become over-heated in the cylinder, for the 

 vis viva of the entering mass is here converted into heat ; as the 

 vapour, however, carries with it some finely divided drops of 

 water, a part of the latter will be evaporated by the surplus heat, 

 and thus the remaining vapour will be maintained in its saturated 

 condition. 



* " T Jeber das Verhalten des Dampfes bei der Ausdehnung imter verschie- 

 denenUmstanden/' Pogg. Ann. vol. Ixxxii. p. 263. With reference to this 

 memoir, and to a notice connected therewith, which appeared in the Philo- 

 sophical Magazine, Helraholtz,in his report published in the Fortschritten der 

 Physik, by the Physical Society of Berlin (years 1850 and 1851, p. 682), is of 

 opinion that the principle is in many points incorrect. I have not, however, 

 beea able to understand the reasons he adduces in support of this opinion. 

 Views are ascribed to me which I never held, and, on the other hand, theorems 

 enunciated which I never disputed, and which, indeed, partially constitute the 

 basis upon which my own researches in the mechanical theory of heat are 

 founded ; at the same time so great a generality is maintained throughout, 

 that I found it impossible to recognize how far those views ought to follow 

 from my words, and these theorems contradict my conclusions. I do not 

 therefore feel myself called upon to defend my former researches against 

 this censure. As the following development, however, rests precisely upon 

 the same views which before served me, Helmholtz will probably again find 

 the same inaccuracy of principle. In such a case I shall look forward to 

 his objections, and request him merely to enter somewhat more specially 



into the subject. _ ')<. ^^ ■:A':}m-l^ ..'^..^t ,; . ,:, .- j,.,;,,^ :.-.:■;:=..•. -v*,., r 



