( 45 ) 
Space that a Particle of Air receding from 
the Center would defcribe in a Second 
by the Action of the centrifugal Force at 
the Circumference of the middle Circle. 
v v 
zm : v : : v : s ; therefore = j \ byHuyghens's 
Rule. Let G and c, exprefs the Force of Gravity* 
and the centrifugal Force at the middle Circle. Since 
the Spaces defcribed in the fame Time by the Action 
of two Forces are as thole Forces S : s : : G : c 3 and 
j G <jj 
— - = c y and fubftituting in this Expreflion in- 
ftead of s , we have 
vv G 
z m S 
. - . f vv G 
lnltead of its equal m , 
c ; and putting 
z rn 
R + r 
c . So that the 
R + r X S 
Ratio of Gravity to the centrifugal Force* at the 
v v G 
middle Circle, is that of G to ■ or that of i 
5 R + rxS 
j which being multiplied by theNum* 
v v 
to i — — - 
R -f r X S 
ber of the revolving Circles R — r, gives for the 
Preflure of the Column of Air R — r proceeding 
from Gravity R — r, and the Pre flure proceeding 
. R — r xv v 
from the centrincal Forces -■ — = — , wherein 
R+rxS 
R — r being a Fa&or common to both, may be 
thrown out of the Expreflion : And fince the Ve- 
locities produced from different Preflures are as the 
fquare Roots of the Preffures, the Velocity Gravity 
would give from the natural Weight or Preflure of 
R — r 
