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Hence Mr. De Luc and foine other philofophers conclude, that 

 the affinity of air to water, if any, no way contributes to eva- 

 poration, but that it is the mere refult of the abforption of caloric 

 by water at its furface, which abforption renders a portion of 

 it fpecifically lighter than the air in contadt with it. Idee s fur la 

 MeteoroL § 2, &c. The denfity, to which vapours thus raifed 

 are capable of arriving, hath certain limiti, each relative to their 

 temperature, being more extenfive in higher temperatures, and 

 narrower in low temperatures. The fpecific gravity of vapour 

 he confiders as lefs than that of air by more tlian one-half, their 

 mafs being above one-half lefs than the mafs of an equal volume 

 of air poffeffing the fame elafticity in the fame circumftances, 

 ibid. § 7. Again, if, fays he, thefe vapours fubfill in any fpace, 

 unmixed with air, in that cafe any prelTure, fuperior to the ex- 

 panfive force which they poffefs in a given temperature, will, by 

 forcing their particles into clofer contad, oblige them to unite, 

 and thus partially condenfe them, or (as he, in my opinion, im- 

 properly calls it) decompofe them ; but if any quantity of air, 

 capable of fupporting this excefs of preffure over their expanfive 

 force, be mixed With them, they will fupport their vaporous 

 ftate, § 14 and 554. 



I muft confefs that the commonly received dodtrine of the fo- 

 lution of vapours in air, at leaft in air of the ufual denfity, on 



plains. 



