Of M. DE LUC. 53 



be thought that I omit to anfwer any thing which M. de Luc 

 may propofe in relation to this fubjed, I mail now examine 

 this laft ftatement which he has given of the cafe, and endea- 

 vour to (how, that every thing which he fuppofes to appear, 

 mould truly happen according to the proportion which he has 

 been pleafed to queftion or deny. 



In fuppofing the cafe of a body of warm and humid air en- 

 vironed by the cold atmofphere, M. de Luc does not here 

 mention what degree of faturation or humidity he fuppofes in 

 the external air. Now, upon this will very much depend the 

 confequences of mixing the fmall portion of humid air with 

 an indefinite portion of the furrounding atmofphere. If we 

 fuppofe, as, from other parts of his writing, M. de Luc in- 

 clines to do, that the atmofphere is not fully faturated, then all 

 the appearances muft follow which he has fuppofed ', that is to 

 fay, that there is firft to be a vifible condenfation in the mix- 

 ture of the two airs ; but as this compound mafs, or warmed 

 air, mixes with the colder, by rifing and difperfing in the at- 

 mofphere, the condenfed humidity is at laft to be totally evapo- 

 rated or diffolved in the quantity of air which is not faturated 

 with vapour. 



Let us now again fuppofe the furrounding atmofphere to be 

 fully faturated or impregnated with humidity, then, in mixing 

 with it the warm humid air of the chamber, there is reafon to 

 conclude, that the condenfation of humidity would remain 

 permanent, although it might not remain vifible, if in fmall 

 quantity and greatly difperfed in the atmofphere. But this will 

 require fome explanation. 



According to the principle aflumed in my propofition, it 

 is equal portions of the unequally heated airs, that, upon mix- 

 ture, fhould produce the greateft condenfation of humidity y 

 and that, in proportion as a very fmall quantity of one or other 

 is employed, that is to fay, in proportion to the inequality of 

 the mixed bodies, the fmaller quantity of condenfation will 



be 



