[ 1^7 ] 
particles lefs apt to run into drops, and fall down 
in rain. And thus we generally find, by expe- 
rience, that the rarefied and condenfed ftates of the 
atmofpherc are refpeaively attended with rain and 
fair weather ; though this does not happen at all 
times, for the air, though rarefied, may not then 
abound rnuch with aqueous vapours, having already 
parted with a good deal of them j fo likewife, when 
the air is denfe and heavy, it. may then be much 
loaded with vapours, which will increafe its weight ; . 
and indeed it muft be fo after a long continuance of. 
iair weather, fo that we may then . have rain even 
before the atmofphere changes to a rarer date. 
Upon this principle I think we may account for 
the changes of the weather, which ufually attend, 
the rifing and falling of the mercury in the baro- 
meter, better than by faying, that when the air 
grows rarer and lighter, it cannot by the laws of. 
hydroftaticks fo well fupport the clouds and vapours, 
and therefore muft permit them to fall down in 
drops of rain ; for when the air grows rarer, although 
the clouds will defcend into a lower and denfer part 
of it, yet they will be there fupported^ and I do 
not fee why their particles fhould be more apt to run. 
into drops there, than when they were higher up, un- 
•lefs^ they received fome addition from the water de- 
polited among them, by the rarefied air, in the 
rnanner I have juft now mentioned. For fince the 
air is rarefied gradually, the clouds can defcend but 
very flowly ; and, therefore,, their particles will not 
be fo much prefted together by the refiftance they 
meet with in their defcent, as they generally are .by 
the winds which blow. upon them. 
When 
