Mr. J. Gill on the Dynamical Theory of Heat. 9 



defined), and it is mathematically demonstrated that heat should 

 disappear in such cases and might be transformed into the work 

 done, it may be freely admitted that the work performed by the 

 expansion of isolated steam is accompanied by a corresponding 

 disappearance of heat. This disappearance of heat, if the steam 

 is saturated, should cause a corresponding condensation of part 

 of the mass, or an equivalent amount of cooling if the steam is 

 sufficiently superheated to bear abstraction of heat without con- 

 densing. If a reservoir of saturated steam be put in free com- 

 munication with a cylinder and loaded piston, the piston's out- 

 ward motion would be accompanied by an expansion of the 

 whole mass of steam, and a condensation of steam-particles 

 throughout the mass equivalent to the amouut of work done by 

 the piston. If, now (the communication with the working cylin- 

 der being closed), fresh steam from some other source be forced 

 into the reservoir until its original pressure is recovered, the 

 compression thus effected should reevaporate the liquid particles 

 of condensed steam, and the general mass of steam should be- 

 come again dry, or merely saturated. If yet a further quantity 

 of steam equal to a stroke of the working piston be injected into 

 the reservoir, the mass of steam should become superheated ; and 

 the fall of temperature and pressure consequent on the succeed- 

 ing stroke would now bring back the steam to its initial state 

 of saturation. Thus it would seem that heat should equally 

 disappear from an isolated mass of steam doing work by expan- 

 sion, whether the steam be saturated or superheated ; but in the 

 case here imagined the disappearance of heat would be from the 

 whole mass in the reservoir and cylinder together. 



In the circumstances above imagined, the source of a conti- 

 nuance of work would be the injection of a continued supply of 

 steam into the reservoir; and the operations of injecting and 

 withdrawing steam being intermittent and occurring at alterna- 

 ting intervals, a corresponding fluctuation of density and tem- 

 perature would occur in the whole mass, with periodic superheat- 

 ing or condensation, as the case might be, but without perma- 

 nent disappearance of heat except in the cylinder, the contents 

 of which formed part of the general mass during the working 

 stroke, and participated in the general loss of heat assumed to 

 be transformed into the work done. Thus, if the cylinder be yu 

 of the volume of the reservoir, the disappearance of heat from 

 the cylinder itself would be T l o of the whole heat supposed to 

 disappear ; the remaining -fjy would be replaced in the reservoir 

 by the succeeding stroke of the injecting pump, while the con- 

 tents of the cylinder would be discharged into the condenser in 

 the state in which the fluid remained at the end of the work- 

 ing stroke. 



