Section XIV.
Of the motion of very ſmall bodies when agitated by centripetal forces tending to the ſeveral parts of any very great bofy.
Proposition XCIV. Theorem XLVIII.
If two ſimilar mediums be ſeparated from each other by a ſpace terminated on both ſides by parallel planes, and a body in its paſſge through that ſpace be attracted or impelled perpendicular towards either of thoſ mediums, and not agitated or hindered by any other force; and the attraction be every where the ſame at equal diameter from either plane, taken towards the ſame hand of the plane; I ſay that the fine of incidence upon either plane will be to the due of emergence from the other plane, in a given ratio.
Case. 1. Let Aa and Bb (Pl. 25. Fig. 1.) be two parallel planes, and let the body light upon
