220 Examination of the received Doifrines 



preflure, or the contrary, and that it will we have already 

 fufficient evidence, of what kind is the heat ? According to 

 the received do6lrine, it is neither fenfible nor latent heat; foF 

 that heat which, united to oxygen and azot, forms atmo- 

 fpheric air, is not fenjible, and that which raifes the tempe- 

 rature of bodies is not latent: but this heat conjlitutes one- 

 half, two-thirds, three-fourths, or four-fifths of atmofpberic 

 air (according to the number of atmofpheres comprefied into 

 one), is a conftituent chemical ingredient of the atmofphere, 

 and therefore latent heat : and yet it raifes the temperature 

 of other bodies, without being fepjrated from its union with 

 the oxygen and azot by the exercije of any chemical affinity ; 

 therefore it is fenjible heat. 



The doctrine feems evidently to ftand oppofed to itfelf; 

 or (hall we, to avoid this conclufion, fav that heat has a third 

 mode of exiftence, in which it may be called sensiblet 

 latent caloric! Abfurd as fuch a pofition might be, 

 it would not be more fo than the doctrine of latent heat, 

 taking that term in its common acceptation. 



I meant to have troubled the Society with a few further 

 remarks on this interefting fubje6t, but, havipg already en- 

 croached further upon its time than I at firft intended, muft 

 defer them for the prefent. 



To conclude : The doctrine of latent and fenfible heat ap- 

 pears to me to have arifen from a want of due attention to 

 the facts eftabliihed by the veteran Black refpe&ing the dif- 

 ferent capacities of bodies for heat. This eminent chemilt 

 was the firft who propofed any thing rational on this fubject, 

 and, when the beautiful fimplicity of the firft principles 

 which he eftabliflied is duly attended to, it appears wonderful 

 to me that the fimple and permanent ftructure that might, 

 have been reared upon them fhould have efcaped his faga r 

 cious observation. Having eftabliihed this incontrovertible 

 fact, that different fubftances have different capacities for 

 heat, this truth of itfelf necefiarily embraced another, which, 

 though it could not poflibly efcape obfervation, has never 

 been applied as it ought; namely, that in every chemical 

 combination' we effect we are altering the capacities of bodies 

 for heat, and consequently deranging the equilibrium ; for 

 9 the 



