48 ANSWERS to the OBJECTIONS 



the atmofphere which is not faturated with humidity. But I 

 have to fhow, that M. de Luc has not reafoned accurately in 

 explaining the reaflumption of the vifible mift into the tranfpa- 

 rent atmofphere. For, though this fact has no immediate con- 

 nection with the queftion in difpute, the condenfation of va- 

 pour ; yet it might be brought in to affect that queftion, by a fort 

 of reafoning, which, though not fcientific, would be fpecious. 



The mift or vifible vapour, according to that reafoning of our 

 author, is evaporated by the heated air : Therefore, that vapour 

 ought not to have been condenfed ; but it was condenfed; therefore 

 it muft have been condenfed upon fome other principle than that 

 which I have alleged is general to all evaporation and conden- 

 fation of humidity. Thus, M. de Luc would, in effect:, 

 though not in terms, make this condenfation to be no conden- 

 fation, or not the condenfation in queftion, becaufe it is not 

 permanent. It is evident, however, that this precipitation of 

 the evaporated water is permanent, fo long as the conditions 

 of its condenfation are continued or remain. But in this cafe 

 of fteam emitted into the open air, thofe conditions of conden- 

 fation cannot continue ; they muft be changed, and the con- 

 denfed vapour muft be again evaporated, fo foon as it meets 

 with a fufHcient quantity of air under-faturated with humidity. 

 Therefore, M. de Luc has endeavoured to explain the evapora- 

 tion of the vifible mift in this cafe, upon a falfe principle, by 

 not taking into consideration the quantity of under-faturated 

 air, which the afcending vapour meets with in the atmo- 

 fphere. 



Thus, whether we confider the explanation which M. de 

 Luc has endeavoured to give, of the condenfation of mift in 

 the cafe of fteam mixed with a body of air, or of the evapo- 

 ration of that mift again when rifing in the atmofphere, there 

 appears to be no folid reafon for his objection to the theory ; 

 and I muft be allowed to maintain, that here alfo, in the cafe 

 of pure vapour, or fteam mixed with a portion of the atmo- 

 fphere, 



