Sect. XII.
of Natural Philosophy.
263
Section XII.
Of the attractive forces of ſphærical bodies.
Proposition LXX. Theorem XXX.
If to every point of a ſphærical ſurface there tend equal centripetal forces decreaſing in the duplicate ratio of the disſtances from thoſe points; I ſay that a corpuſcle placed within that ſuperficies will not be attracted by thoſe forces any way.
Let HIKL (Pl. 21. Fig. 4.) be that ſphærical ſuperficies, and P a corpuſcle placed within. Through P let there be drawn to this ſuperficies the two lines HK, IL, intercepting very ſmall arcs HI, KL; and becauſe (by cor. 3. lem. 7.) the triangles HPI, LPK are alike, thoſe arcs will be propor-
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tional
