[ i68 ] 
When the atmofphere is much fatu rated with wa- 
ter, and grows colder or rarer than it was before, wc 
fhall then perceive the lower air begin to part with 
fome of the water it contains, which will fall infen- 
iibly to the ground, or adhere to the walls of houfes, 
or other bodies expofed to it, and make them be- 
come damp and wet. And if the moifture fettles 
on the fmooth furfaces of cold bodies, fuch as mar- 
ble or other ftoncs, whofe pores cannot imbibe it, it 
will cover them with a kind of dew, and then thofe 
bodies are vulgarly faid to fweat. 
At this time the hygrometer being affedled by the 
moidiure will point to wet^ and, as we perceive from 
thence, that the air is difpofed to part with the wa- 
ter it contains, we may generally expedl rain. But 
when the air again grows warm or denfe, it will be 
able again to dilTolve, and take up the water it before 
depofited, and the moifture on the bodies expofed 
to it will difappear, the hygrometer will point lo dry, 
and we may then promife ourfelves fair weather. 
I obferved before, that, if a bottle be filled with a 
very cold liquor, and expofed to the warm air, a 
dew will foon be formed on its furface by the moi- 
flure which the cold air depofites. Now if we fup- 
pofe this body flill to retain the fame degree of cold, 
whilfi: the air pafles over it, the dew on its furface 
will continually increafe, and run down its fides in 
fmall ftreams of water. This feems to be exadtly 
the cafe of mountains, whofe tops reach into the colder 
parts of the atmofphere ; and which, therefore, are 
themfelves colder than the air is in general. For when 
the wind blows the lower parts of the atmofphere 
(which are the warmeft and mofl: replete with va- 
pours) 
