[ 169 ] 
pours) againft the fides of the mountains, being 
there flopped in its courfe, it mufi; neceffarily afcend 
and pafs over their tops. This air, therefore, will be 
confiderably cooled in its progrefs up the Tides and 
over the tops of the mountains, and confequently 
mufl let go a great part of the watery vapours it 
contains j which will be precipitated in dew and 
nioifture upon the furface of the mountain, where 
it will foak into the earthy parts, or infinuate itfelf 
into the chinks and crevices of the rocks, where being 
colledled, it will afterwards break out in fprings and 
fountains, and become the fource of rivers, which 
aie known always to take their rife in mountainous 
countries j and, on this account, we might have 
fmall fprings and rivers near mountains, although 
there were neither clouds nor rain. But the moi- 
flure, which the air ufually depofites on the moun- 
tains, muft be confiderably increafed by the clouds, 
which are driven againfl them-, and accumulated by 
the winds, for their particles being then prelfed to- 
gether will run into fmall drops of rain. Befides, it 
is well known, that mountains do gather and retain 
the clouds about them by their attradlive force, in 
confequence of which we often fee fome clouds con- 
tinue at reft on the mountains, whilft the others are 
carried on gently by the wind ; hence it is, that 
countries, in the neighbourhood of high mountains, 
are the moft fubjedl to frequent rains. 
Thus I have fhevv^n how the afcent of aqueous va- 
pours, and their conftant cireuladon, by precipitating 
again in moifture, or drops of rain, will arife from the 
dilfolving power of theair, influenced by the viciflitude 
of heat and cold, rarefaction and condenfation. For we 
VoL. LV. 2 find, 
