HISTORY OF DYNAMICAL THEORY OF HEAT 331 



proceeding to maintain it by a series of experimental reductio ad ab- 

 surdum. 



Premising that the temperature of a body could not be increased 

 unless either its " capacity " were diminished from some cause, or 

 heat were added to it from still other bodies in contact, and observing 

 a production of heat to be consequent on friction or percussion, he 

 enumerated the following as including all possible explanations of the 

 phenomenon consistent with the assumption of caloric : 



First, the production by the friction of a specific diminution in the 

 " capacity " of the body, whereby caloric would be disengaged, and thus 

 made sensible. This was the supposition which Count Rumford showed 

 to be quite incompatible with the inexhaustibility of the supply. 



Second, the liberation of caloric during some slow process of com- 

 bustion accompanying the friction, the source in this case being the 

 oxygen of the surrounding medium. This contingency was likewise 

 anticipated by Rumford, who failed to detect any indications of such 

 an action. 



And, third, the production of some occult change in the bodies 

 rubbed, whereby they might acquire the property of abstracting an 

 unusual quantity of heat-substance from surrounding matter. 



His argument against the existence of caloric depended, therefore, 

 upon showing that these different suppositions were all contrary to 

 the indications of experiment, whence the inference as to the unten- 

 ability of the hypothesis itself. But, although this method of reason- 

 ing has been characterized as " somewhat confused," the following 

 experiments upon which it was based are now considered classical. 



Two parallelopipedons of ice, initially at. a temperature of 29 Fahr., 

 were fastened in an apparatus by which they might be rubbed to- 

 gether, and kept in a continued and violent friction with each other. 

 They thus were almost wholly melted, the temperature of the result- 

 ing water being " ascertained to be 35, after remaining in an atmos- 

 phere of a lower temperature for some minutes." The fusion also was 

 observed to take place only at the rubbing surface. 



From this experiment it was therefore to be inferred that the 

 " capacity " of a body was not necessarily diminished by friction ; 

 for, according to the discoveries of Black, the melting of a quantity 

 of ice could only take place with the absorption of a definite quantity 

 of heat its latent heat of fusion. 



Upon the second supposition, Davy remarked : 



" From this experiment it is likewise evident that the increase of tempera- 

 ture consequent on friction cannot arise from the decomposition of the oxygen 

 gas in contact, for ice has no attraction for oxygen. Since the increase of tem- 

 perature consequent on friction cannot arise from the diminution of capacity or 

 oxidation of the acting bodies, the only remaining supposition is, that it arises 

 from an absolute quantity of heat added to them, which heat must be attracted 

 from the bodies in contact. Then friction must induce some change in bodies 

 enabling them to attract heat from the bodies in contact." 



