Mr. J. Gill on the Dynamical Theory of Heat. 91 



liquid. This collapse should evidently be sudden, and each 

 particle in assuming the liquid state should, for the moment, 

 leave an almost perfect vacuum in the space it occupied in con- 

 tact with the cold walls of the condenser. The void is instantly 

 occupied by a fresh particle of vapour, which in its turn col- 

 lapses, and so the process continues as long as vapour remains 

 to be condensed. It may be conceived that the particles of 

 vapour thus rapidly precipitated into a vacuous space, bounded 

 on the outside by the hard metallic walls of the condenser, must 

 strike with violence against these surfaces, and generate heat by 

 this molecular battering. 



It may be replied that the internal work done by the remain- 

 ing particles of vapour in forcing their fellows down the preci- 

 pice of the vacuum should cause an amount of chilling of the 

 mass by an actual disappearance of heat equal to that generated 

 by the percussive action of the particles against the sides of the 

 condenser. To this I would answer that, until some good account 

 can be given of the actual excess of work-producing power which 

 high-pressure steam is allowed to possess as compared with steam 

 of low pressure, weight for weight, and which is apparently lost 

 by the quiet condensation of the steam in the vessel which con- 

 tains it, we may suppose some unacknowledged form of energy 

 to exist in the steam distinct from mere molecular motion, though 

 always acting in cooperation with it, and more than sufficient to 

 cause the violent fall of the vapour particles against the walls of 

 the condenser, thus generating heat in excess of what is fairly 

 due to the constitution of the steam. 



The very nature of steam suggests the idea that, as far as 

 quantitative heat is concerned, each individual particle should 

 have a fixed specific temperature, the general temperature of 

 any given mass resulting simply from the number of particles in 

 a given space, or, in other words, the distance of the particles 

 from each other, and consequently the amplitude of their mole- 

 cular motions. Thus it is certainly reasonable to conceive of a 

 fall of temperature in expanding steam without any idea of abso- 

 lute loss of heat. However this may be, I would beg to impress 

 on the attention of physicists who may be making further expe- 

 rimental researches on this interesting point, the importance of 

 guarding against all probable causes of error which can be fore- 

 seen, keeping in mind the results obtained by Seguin and Hirn, 

 and also the experiments of Siemens, in which high-pressure 

 steam seemed to superheat itself by tumultuous expansion. 

 I remain, Sir, 



Your most obedient Servant, 



Joseph Gill. 



Palermo, January 4, 1864. 



