Of M. D E L U C. 51 



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

 may propofe in relation to this fubjed, I fliall 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,, 

 fhould truly happen according to the propofition which he has 

 been pleafed to qtieftion 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 mull 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 j 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 q^uantity of air which is not faturated- 

 with vapour. 



Let us now again fuppofe the furrounding atmofphere to be 

 fiilly 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 affumed 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- 



