ASTRONOMY.

PART II.

PHYSICAL ASTRONOMY.

Sect. I.

6f the forces which retain the Flanets in

THEIR ORBITS.

236. If a body gravitating to a fixed centre,have a projectile motion impressed on it, in a linenot passing through the centre, it will move in acurve ; and the straight line drawn from the bo-dy to the centre; will describe areas proportionalto the times.

JPrincip, Math, lib, i. prop. I.

P 3 a. Conversely,