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Nowfincethe air Is an heterogeneous fluid, containing 
in it particles of another body, and yet retaining a 
perfed: tranfparency, which is the criterion of a true 
ibiution in other cafes, why fliould we not infer from 
analogy, that in this cafe alfo it indicates a true folution 
of water in air ? efpecially when we confider that 
there are hardly any two fluids that may not, by 
themfelves, or by the means of fome third body, be 
fo thoroughly incorporated, that one of them may 
be properly faid to be diflblved in the other. But 
the truth of this will be further confirmed, by com- 
- paring the properties of common folutions with thofe 
of evaporation j which I fliall now do in feveral 
inftances. 
Firftj when a body is immerfed in a fluid that 
diflblves it ; for inftance, a lump of fait in water ; we 
fee the fait foon begin to diflblve and impregnate with 
its particles the water that furrounds it, which will 
then appear thick and loaded ; and if the water be 
at refl, the folution will proceed very flowly; but if it 
be ftirred about, the fait will foon be intirely diflblved. 
How exadlly does this correfpond with what Dr. 
Halley remarked in an experiment made on the eva- 
poration of water in a clofe room ? Phil. Tranf. 
N® 192. “ The fame obfervations (fays he) do 
likewife fhew an odd quality in the vapours of wa- 
“ ter, which is that of adhering to the furface that 
“ exhales them, which they clothe, as it were, 
“ with a fleece of vapourous air, which once in- 
vefting it, the vapour rifes afterwards in much lefs 
** quantity.” Here we fee, that the air, which lay 
at reft over the water, appeared thick, and loaded 
with aqueous particles 3 and then the evaporation 
• VoL. LV. X proceeded 
