vifible by their gathering into thick and dark Clouds, by 
the falling down of Clouds and Mifts on the tops of 
Hills, and thick fogs in the Air, and by their dropping 
down into rain, fnow, 6cc. and that thefe do ufually fail 
-out only when the Mercury (ubfides alitde, and confe* 
quently when the Atmofphere's gravity is lefs, is the con- 
ftiint obfervation of thofe who have had occafion to take 
notice of the changes of: the Barofcope. And thus you fee 
how this Hypothelis for the afcent of Vapours and falling 
down of rain, grounded on the changes of the Atmol* 
ph<2re's gravity anfwers daily obfervation & experience' 
Againft this It may be objeSted, that it is obfeTvable 
many times that even when theMercury in theBarokope 
is riling there will be rain, and particularly fometimes in 
North Eaft Winds. To this I anfwer that the Vapours 
will fall down into rain not only when the fpecifieal gra- 
vity of the atmofphere is leffened, but alfo if the Clouds 
have been carried for fome while towajrdsone quarter of 
the Heavens by theWinds,Sc then if theWindsdo fudden- 
ly change into another quarter thefe Vapours,which were 
formerly fcattered into fmall particles and fo did eafily 
float, are fuddenly driven together into little drops and 
fo milft needs fall down into rain, and therefore the fal- 
ling of rain while the Mercury is rifing is obfervable only 
upon the fudden change of contrary Winds. 
But let us confider in the next place whether thofe fre- 
quent cemmotionsin the Air which we call Winds, may 
not be accounted for upon the fame Principles, and this 
we fhall do as formerly by looking into the nature of a 
fluid in the general and of the Air in particular, a%to flu- 
ids in general!, that knowm definition of Archimedes is 
univerfally acknowledged, Qiiod earum partium minus 
prefTxexpellantur amag!'s preiEs, fo that iftherebeany 
portion of a fluid of a far lefTe preiTurc and refillance then 
the reft, the whole fluid runs in a current thither, till all 
be reduc'd to an Equilibrium. This principle is fo uni- 
B h S verfally 
