thoſe forces ought to be impreſs'd, that the motions of the globes might be moſt augmented. that is, we might diſcover their hindermoſt faces, or thoſe which, in the circular motion, do follow. But the faces which follow being known, and conſequently, the oppoſite ones that precede, we ſhould likewiſe know the determination of their motions. And thus we might find both the quantity and the determination of this circular motion, ev'n in an immenſe vacuum, where there was nothing external or ſenſible with which the globes could be compar'd. But now if in that ſpace ſome remote bodies were plac'd that kept always a given poſition one to another, as the Fixt Stars do in our regions; we cou'd not indeed determine from the relative tranſlation of the globes among thoſe bodies, whether the motion did belong to the globes or to the bodies. But if we obſerv'd the cord, and found that its tenſion was that very tenſion which the motions of the globes requir'd, we might conclude the motion to be in the globes. and the bodies to be at reſt; and then, laſtly, from the tranſlation of the globes among the bodies, we ſhould find the determination of their motions. But how we are to collect the true motions from their cauſes, effects, and apparent differences; and vice versa, how from the motions, either true or apparent, we may come to the knowledge of their cauſes and effects, ſhall be explain'd more at large in the following Tract. For to this end it was that I
compos'd it.
