C 4*7 3 
Equator than at the parallel Circle. Now the Sup- 
pofition is very certain in both its Parts: For, 
1. Since the Circumference of the Equator is the 
double of that of the parallel Circle, and that being at 
an equal Diftance from the Centre O, (fee Fig. p. 420 ) 
the Globules they contain arc equal to each other j if ♦ 
there be a Thoufand Globules in the Circumference of 
the Parallel, there will be Two thoufand in the Cir- 
cumference of the Equator. And as thefe Globules 
are fuppofed to have in both an equal Velocity, they 
will make (but) One Revolution in the Equator, while 
thofe of the fubduple Circumference will make Two. 
Therefore, in both, there will be Two thoufand 
Strokes employed in the fame Space of Time, againft 
the Points A and C. 
2. Each central Stroke is double at the Equator : 
Becaufe, as there is in both an equal Velocity, and 
that (Lem. II.) each centrifugal Stroke in every 
Circumference is a Fluxion of the firft kind, with 
regard to the Velocity of the Globule which is in 
Motion ; it follows that the centrifugal Strokes both 
in the Equator, and in the parallel Circle, are equal 
to each other. But the central Effort (which is the 
only one by which a Vortex can defend itfelf towards 
the Poles) is at the Point C (Lem. I.) but half the 
centrifugal Effort, Ence it is reprefented by IE fub- 
duple of I C j whereas at the Equator the central 
Effort is the fame with the centrifugal Effort, be- 
caufe the Radius O A is perpendicular on. the fpirical 
Tangent, which correfponds to it. Therefore, 
lii 
Co- 
