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First. Mr, De Sauffure and General Roy have proved that 

 water in its foHd ftate evaporates in every degree of cold between 

 o and 32°, as it is w^ell known to do in its liquid ftate, and in far 

 greater proportion in all degrees fuperior to 32*^. 



Secondly. Though water evaporates more quickly and irl great&r 

 quantity hi vacuo than in open air (and confcquently its evapo- 

 ration cannot be attributed to its affinity to air) yet it w'ould 

 fpeedily be condenfed back 'again into water by contaft with 

 colder bodies if it did not adhere to air, which therefore chiefly 

 Tupports it in a vaporous ftate, and thus the different opinions of 

 philofophers on this fubjed may be reconciled. Mr. Sauffure has 

 Ihewn that the power of air to fupport vapor diminifhes with its 

 denfity, but not in the fame ratio, even though the heat fhould 

 continue unaltered. This power, therefore, depends partly on 

 its temperature, and partly on its denfity; an-d hervce invifible 

 vapor abounds more in the lower than in the middle ftrata of 

 the atmofphere, Mr. Lambert, in the memoirs of Berlin for the 

 year 1772, has fhewn that the quantity of vapor at different eleva- 

 tions in the atmofphere is generally as the fquares of the mercurial 

 altitudes at thofe elevaticJns, which I believe to be true in all heights 

 to us acceffible ; but in the very higheft regions, which are occupied 

 chiefly by inflammable air, I am inclined to think that vapor is 

 more abundant than in thfe middle ftrata, as water adheres more 

 ftrongly to this air than to refpirable air, and it is probably this 

 circumftance that gave rife to the great mift obferved in 1783. 



Thirdly, To the delicate experiments of Mr, Sauffure we 

 are alfo indebted for the interefting difcovery that a cubic foot 



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