[ ] 
To the beft: of my Remembrance, this Propofition 
is demonftrated in Dr. Clarkes Notes on Rohaulfs 
Thyjica, and in Monfieur Ledures : And 
it is evident from this alone, that it can only be by a 
Force reprefented by the Sine of the Angle of Con- 
tad that this moveable Body ftrikes the Tangent of 
its Curve. 
Theorem III. 
Let us put Complaifance on the Stretch, and grant 
that Vortexes have a central and centripetal Force 
relative to one Centre O : I fay, that the fpherical 
Vortex will not have as much of this central Force, 
to defend itfelf towards the Poles, as towards the 
Equator. 
Construction. 
Let us take, in the fame Superficies X (fee the Fig- 
p. 420.) T wo Points at Pleafure, the Point A in the Cir- 
cumference of the Equator, and the Point C in the 
Circumference of a fubduple parallel Circle j we will 
give in the Demonftration an equal Velocity to the 
Globules which circulate in thefe Two Circum- 
ferences ; which is the moft favourable Concellion 
imaginable for the Patrons of Vortexes. 
Demonstration. 
It is manifeft, that if the Point A is in an equal 
Space of Time ftruck an equal Number of Times 
as the Point C, and that each Stroke againft the 
Point A be double each Stroke againft the Point C ; 
it is manifeft, I fay, that there is more Force at the 
Equator 
