Of M. D E LUC. 43 



the breath is the natural phenomenon which is to be explained, 

 or the fcientific experiment by which the theory which M. de 

 Luc refufes, is approved. 



It may be proper here to obferve, that I only confider the 

 diffolving power of air with refpect to water, in order to con- 

 trad it with the precipitation of the difTolved fubftance, when 

 the a<5tion or effect of heat has been diminithed according to 

 the theory. It no ways concerns my proposition, whether it is 

 upon the principle of difTolution or fimple expanfion by heat, 

 that the aqueous vapour is retained in the air, or preferred in 

 a tranfparent ftate. The expreflion of diffolution beft anfwer- 

 ed my purpofe, where the faturation of the atmofphere with 

 humidity was to be expreffed ; therefore I retained it, although 

 I had declared in this Society, when my firfl paper was read 

 and converfed upon, that I did not mean in the leafl to enter 

 into that queftion which ProfefTor Rob is on then put. In like 

 manner, it is abfolutely indifferent to the theory, whether the 

 infpired air or breath acquires its humidity by evaporation, dif- 

 folution, or chemical refolutioh and compofition : Therefore, 

 if this negation, with regard to the origin of water, be intended 

 by M. de Luc as an objection to my proportion, which I 

 think has no relation with that fubject, it would be proper he 

 mould fhow in what refpect that argument of his affects the 

 condenfation of the water contained in the breath, when that 

 breath is mixed with another portion of air. 



I now proceed to the fecond propofition of M. de Luc, 

 which is, That, fuppofing my hypothefis admitted, it does not 

 follow that rain happens in confequence of this caufe ; the or- 

 dinary ftate of the atmofphere being, as he alleges, too dry to 

 admit of this effect. Now, this may be a very good reafon 

 why it mould not always rain, or fhould not rain in that parti- 

 cular ftate of the atmofphere which is moil ordinary; but I 

 believe it will be difficult to perfuade thofe who admit of the 

 hypothefis, that they fhould not apply this principle in the cafe 



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