SEC. IV,] OF NATURAL PHILOSOPHY. 2S9 density is reciprocally as SP the distance from the centre, a body will re volve in this spiral. Q.E.D. COR. 1. The velocity in any place P, is always the same wherewith a body in a non-resisting medium with the same centripetal force would re volve in a circle, at the same distance SP from the centre. COR. 2. The density of the medium, if the distance SP be given, is as OS OS TTp, but if that distance is not given, as ^ ^5. And thence a spiral may be fitted to any density of the medium. COR. 3. The force of the resistance in any place P is to the centripetal force in the same place as