198 Historical Review of Experiments 



This glass body was then voided of air by means of 

 mercury. 



The results of the experiments performed with these 

 instruments differed little or not at all from those made 

 with the apparatus previously described, therefore the 

 fact of the transmission of heat through the Torricellian 

 vacuum was established beyond any doubt. 



These results are sufficiently known to the learned 

 world ; now the question arises as to how these results 

 can be reconciled with the theory which at the present 

 day has been adopted in regard to caloric. I must con- 

 fess freely, that, however much I might desire it, I never 

 could reconcile myself to it, because I cannot by any 

 means imagine how heat can be communicated in two 

 ways entirely different from each other. 



Philosophers have made little or no mention of the 

 results of these investigations: I do not assume to ex- 

 plain their silence; if I myself mentioned them as little 

 as they, it is easy to imagine the cause of my silence. 

 It will at least be admitted that I have pointed out 

 plainly enough the doubts which the results of my ex- 

 periments could give rise to. 



I afterwards undertook many other experiments to 

 determine accurately the various degrees of rapidity 

 with which heat passes into mercury when surrounded 

 by common or atmospheric air, by air saturated with 

 moisture, by carbonic acid gas, and by air brought to 

 various degrees of density. 



In the year 1787 I made a series of experiments 

 which are described in the Philosophical Transactions 

 for 1792; my principal object was to investigate the 

 conducting power with regard to heat possessed by vari- 

 ous substances, especially by those which we are accus- 



