For the side of the motion from aphelion to perihelion, that is, the side where the centripetal force is taken to predominate, is still supposed to contain the centrifugal force, though in decreasing proportion as the other increases; and, on the side of the retarded motion, the predominant and ever more predominating centrifugal force is supposed to be present in an exact inverse relation to the centripetal; so that on neither side does one of the two forces ever vanish but only becomes smaller up to the moment of its sudden conversion into the predominant force.