v^rfaily received and known that we Heed not ftay to 
make it good. Now as to the fluid of Air in particular, 
it is evident, as has been already made appear that 'its 
preflure is not always the fame. And 'tis very probable 
(which Experience will determine by making joynt ob- 
iervationsof theBarofcope in feverall places ot the Earth 
at the fame time J that the Airs gravity is not aUke 
chang'd throughout the whole Atmofphere in an Inftant; 
but that the Mercury may have fublided in theBarofcope, 
and confequently the Air become lighter, at London, 
for example, wheii there is no fuch change obferv'd at 
Paris or Edinburgh Now this fuppofition doth give us an 
intelligible account of Winds from the known nature of 
fluids. For when the Air becomes fpecifically lighter in 
one place, or its preffure lelTened, the Neighbouring 
pgrts of the Atmofphere whofe weight is not thus leffen-^, 
ed, run thither in a Current till the Atmofphere therea- 
bouts bereduc'd to an iEquilibrium agaimand according 
to the portion of Air thus chang'd and the leflened or ac- 
quired degrees of the weight and fpring, the currents and 
Winds are lJ:rong or weak, of a long or fhort continu- 
ance. 
- Now Obfervation and Experience do agree with this, 
the Mefcury being found to fubfide for the moft part in 
the Barofcope at the rifing of Winds ; at leafl: it is obferv'd 
to be in motion, and either rifing or falling, or confe- 
quently there is a change in the Atmofpher's preffure at 
that time. And thus v^e have an Intelligible and Aero- 
Statical account, of the afcent of Vapours, of their fal- 
ling down again into rain, and of the currents and Im- 
petuofity of Winds, from this known property, the Va- 
riation of the Atm<ifphere's gravity. 
But I acknowledg the great difficulty remains fliill how 
to account for the differentchanges of the fpecifical gra- 
vity of the Atmofphere j and to this 1 (hall at prefent only 
fay thele two things, i. That it is very ordinary and al- 
lowable 
