inaSHvtty of Matter, £cc. 105

stantly in vigour; for between every last cen-tripetal impulse, and last projectile force, anew projectile tendency is generated. If itwere otherwise, that is, if the direction werechanged in every part of the orbit, and nonew centripetal force impressed, to help togenerate a new tendency along the tangent;which, I think, implies no contradiction tobe supposed (j>) no body could performabove half a revolution, let the first projectileforce impressed be as great as it can be suppos-ed ; for it is contradictory to suppose that oneindividual impulse should make it move in twoopposite directions; as it ought to do at thetwo extremities of the fame diameter of itscurve. Therefore in this motion, thus con-sidered, there is a constant impairing of the

(p) If a firm unelastie obstacle change the direction ofa moving body, also unelastie, no new force will be im-pressed on it: and if we should suppose this done con-stantly, for half a revolution, it will come up to the cafehere expressed. For, as was said in N 3 n. sect. i.whatever changes the direction of a body in motionwithout adding a new force to it, takes off one of theCompounding forces. And we cannot conceive in onesingle impulse any part of the compounding force to bein quite an opposite direction; especially since compound-ing forces begin to oppose each other, when the angleformed by the lines of their directions becomes obtuse.

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