Section IX.
Of the motion of bodies in moveable orbits; and of the motion of the apſides.
Proposition XLIII. Problem XXX.
It iſ required to make a body move, in a trajectory that revolves about the centre of force, in the ſame manner as another body in the ſame trajectory at reſt.
In the orbit VPK (Pl. 18. Fig. 1.) given by poſition, let the body P revolve, proceeding from V towards K. From the centre C let there be continually drawn Cp, equal to CP, making the angle VCp proportional to the angle VCP; and the area which the line Cp deſcribes, will be to the area VCP which the line CP deſcribes at the ſame time, as the velocity of the deſcribing line Cp,
