[ 7° J 



\YC contemplate this hypothcfis, it prcfents nothing but incom- 

 patibiUties with our adtual knowledge of the operation of fire. 



Secondly, Our author's demand, that we admit a degree of 

 heat adlmg with the greatefl; poflible iutenfity, and yet producing 

 no change in the fubltances acted upon, is not only gratuitous, 

 as he himfelf ftems to allow, but incompatible with all phy- 

 fical inquiry, and a mere petito principii. No caufe can be traced 

 but by its efFedts, that is, by the changes it has produced ; if 

 thefc are fuppofed null, all inquiry mufl ceafe. To avoid 

 this objedlion, and countenance this fuppofition, our author 

 further demands a degree of compreflion under which the adlion 

 of heat could produce no change ; but this being another new 

 and independent fuppofition, fliould itfelf be proved to be pro- 

 bable, or at leaft poflible, which our author neither has done, 

 nor, as far as I can fee, can do ; and even, with the help of 

 this double fuppofition, it cannot be proved that pure calcareous 

 earths can at all be melted with or without emitting their fixed air, 

 as this fufion has never yet been eflfedled either by concentrated 

 folar heat, or by the help of pui-e air, or by any other contrivance 

 of art; and if it could, how could the fliells, with which it 

 is in fundry inftances filled, efcape fufion, and remain unblended 

 with the common mafs in which they were imbedded ? 



Our author will probably reply, that many difiiculties alfo 

 accom.pany the fuppofition of an aqueous folution, and this 

 I freely confefs. In tlie a<n;ual con; itution of things, both 

 phyfical and moral, many inexplicable difficulties occur, but 



muft 



