258 Prof. Clau8iu8 on the Application of tlie Mechanical 



the vapour contained in the former raises the piston still higher by 

 its own expansion. After this the cylinder is put in communication 

 with the space C, which shall represent the condenser. We shall 

 suppose the latter to be kept cold by external cooling, and not 

 by injected water, which, as before remarked, causes no essential 

 difference in the results, and yet simplifies our problem. The 

 constant temperature of the condenser shall be Tq. During 

 the connexion of the cylinder with the condenser the piston 

 retraces the whole of its former path, and thus all the vapour* 

 which did not immediately pass by itself into the condenser is 

 driven into it, and there becomes condensed. In order to complete 

 the cycle of operations, it is now necessary to convey the liquid 

 produced by condensation back again into the boiler. This is 

 done by means of the small pump D, whose action is so regu- 

 lated, that at every ascent of the piston just as much liquid is 

 withdrawn from the condenser as entered it by the above con- 

 densation ; and during the descent of the piston this same quan- 

 tity of liquid is forced back into the boiler. As soon as this 

 liquid is again raised in the boiler to the temperature T„ every- 

 thing is once more in its initial condition, and the same series of 

 operations can commence again. Here, therefore, we have a 

 complete circular process. 



In ordinary steam-engines the steam enters the cylinder not 

 only at one end, but alternately at both. But the only differ- 

 ence produced thereby is, that during an ascent and descent of 

 the piston, two circular processes take place instead of one ; and 

 in this case even the determination of the work for one of the 

 processes is sufficient, because from it the total amount of work 

 done during any time can be deduced*. 



19. In making this determination, we shall, as is indeed usual 

 in such cases, consider the cylinder as impenetrable to heat, so 

 that we may neglect the interchange of heat which takes place 

 during a stroke between the walls of the cylinder and the vapour. 



The mass in the cylinder can only consist of vapour at a 

 maximum density, together with some admixed liquid. For it is 

 evident from the foregoing, that during its expansion in the 

 cylinder, after the latter is cut off from the boiler, the vapour 

 cannot pass into the over-heated condition, but must, on the 

 contrary, be partially condensed, provided no heat reaches it 

 from an external source. In other operations hereafter to be 

 mentioned, where this over- heated state might certainly occur, 

 it will be prevented by the small amount of liquid which the 

 vapour always carries with it into the cylinder, and with which 

 it remains in contact. nrff -r , 



The quantity of liquid thus mixed with- the vapour is incon- 



* The space on one side of the piston is a little diminished by the piston- 

 rod, but an allowance can easily be made for this small difference. 



