bodies, with which the compariſon is made, that the relative poſition may be preſerved, then that condition will be preſerv'd, in which the relative motion conſiſits. And therefore, any relative motion may be changed, when the true motion remains unalter'd, and the relative may be preſerv'd, when the true ſuffers ſome change. Upon which accounts, true motion does by no means conſiſt in ſuch relations.
The Effects which diſtinguiſh abſolute from relative motion are, the forces of receding from the axe of circular motion. For there are no ſuch forces in circular motion purely relative, but in a true and abſolute circular motion, they are greater or leſs, according to the quantity of the motion. If a veſſel, hung by a long cord, is ſo often turned about that the cord is ſtrongly twiſted, then fill'd with water, and held at reſt together with the water; after by the ſudden action of another force, it is whirl'd about the contrary way, and while the cord is untwiſting it ſelf the veſſel continues for ſome time in this motion; the ſurface of the water will at firſt be plain, as before the veſſel began to move: but the veſſel, by gradually communicating its motion to the water, will make it begin ſenſibly to revolve, and recede by little and little from the middle, and aſcend to the ſides of the veſſel, forming it ſelf into a concave figure, (as I have experienced) and the ſwifter the motion becomes, the higher will the water riſe, till at laſt, performing its revolutions in the ſame times with the veſſel, it becomes relatively at reſt in it. This aſcent of the water ſhews its endeavour to recede from the axe of its motion; and the true and abſolute circular motion of the water, which is here directly contrary to the relative, diſcovers it ſelf and may be meaſured by this endeavour. At firſt,
when the relative motion of the water in the veſſel was
