fore in all the matter contiguous to the perimeter of the magnus orbis, muſt be of the ſame denſity as the Earth. But now that which lies between the magnus orbis and the orb of Satum muſt have either an equal or greater denſity. For to make the conſtitution of the vortex permanent, the parts of leſs denſity muſt he near the centre, and thoſe of greater denſity muſt go farther from it. For ſince the periodic times of the Planets are in the ſeſquiplicate ratio of their diſtances from the Sun, the periods of the parts of the vortices muſt alſo preſerve the ſame ratio. Thence it will follow that the centrifugal forces of the parts of the vortex muſt be reciprocally as the ſquares of their diſtances. Thoſe parts therefore which are more remote from the centre endeavour to recede from it with leſs force; whence if their denſity be deficient, they muſt yield to the greater force with which the parts that lie nearer the centre endeavour to aſcend. Therefore the denſer parts will aſcend; and thoſe of leſs denſity will deſcend; and there will be a mutual change of places, till all the fluid matter in the whole vortex be ſo adjuſted and diſpoſed, that being reduced to an equilibrium its parts become quieſcent. If two fluids of different denſity be contained in the ſame veſſel; it will certainly come to paſs that the fluid of greater denſity will ſink the loweſt; and by a like reaſoning it follows that the denſer parts of the vortex by their greater centrifugal force will aſcend to the higheſt places. Therefore all that far greater part of the vortex which lies without the Earth's orb, will have a denſity, and by conſequence a vis inertia anſwering to the bulk of the matter, which cannot be leſs than
the denſity and vis inertia of the Earth. But from
