Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/255



Of the motion of bodies in moveable orbits; and of the motion of the apides.

It i required to make a body move, in a trajectory that revolves about the centre of force, in the ame manner as another body in the ame trajectory at ret.

In the orbit VPK (Pl. 18. Fig. 1.) given by poition, 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 decribes, will be to the area VCP which the line CP decribes at the ame time, as the velocity of the decribing line Cp,