wards the Poles where they will come nearer to the Axis of their motion, as if you would fuppofe a Body at the Equator which doth endeavour to recede from the Axis of its motion, but because it cannot quite fly off and get away, therefore it will move towards the Poles, that is, it will come nearer to the Axis of its motion than if it had stayed at the Æquator. It seems to me that the Theorift in this part has endeavoured to give us a proof of his great skill in Logicks, for he from a poffible fuppofition, has endeavoured directly to prove its contradictory, that is, because all Bodies do endeavour to recede from the Axis of their motion, therefore they will endeavour to go to the Axis of their motion. But I will now examin his Argument more particularly, and firft I will grant to the Theorist, that all Bodies turned round about any Centre do endeavour to recede from it and fly off in the tangent. For this is both evident to reafon and experience; but fince the Air does always move round the Earth, it is plain that it will alfo endeavour to recede from the Centre of its motion, and by confequence, it will be no hinderance to the water to do the fame, neither can it be faid, that the ftraitness of the Orb will hinder the fluid from receding, fince there is no reafon to affign any fuch ftrait limits to our Globe, for our Air is not enclos'd with walls, but beyond our Atmosphere there lyes a free

and

and open space: befides if there were any fuch ftraitness, without doubt it would be every where equal and the fame, and by confequence, as it hindered the fluid from rifing at the Equator, fo it would alfo hinder its rifing at the Poles, and then there would not in that cafe be any Oval figure at all.

I am fure the Theorift can give no reason why he should make the Air refift the motion of the fluid upwards at the Æquator, and yet yield to its motion upwards at the Poles, fince 'tis certain that the Air preffes as much one way as another: it will by the fame force hinder a fluid from rifing at the Pole, by which it refifted its rifing at the Equator, and therefore it is plain, that the Earth could not upon any fuch account be of an Oblong Spheroidical figure, whofe furface at the Equator is nearer its Centre than its Poles

are.

So far is the Theorifts Opinion diftant from truth in this point, that from the fame very principle of a Centrifugal force it does evidently follow that the furface of the Earth towards the Equator is higher or further diftant from the Centre than it is at the Poles, which is directly contrary to that figure which he supposes it had in its primitive state. Now to prove this, I will fuppofe first, that at the begining of the world the Earth was fluid and spherical, but afterwards God Almighty having given it a motion round its own

Axis,

Axis, all Bodies upon the Earth would describe either the Equator, or Circles parallel to the Equator, and by consequence all would endeavour to recede from the Centre of their motion.

It is to be here obferved, that if a Body doth freely revolve in a Circle about a Centre as the Planets do about the Sun, that its centrifugal force, (or that force by which tal it is drawn towards the Centre) is always equal to its centrifugal force by which it doth endeavour to recede from the Centre: for the force which detains a Body in its orbit must be equal to the force, by which it endeavours to recede from its orbit and fly off in the tangent. This may be clear by the example of a Body turned round a Centre by the help of a thread which detains the Body in its orbit; the thread being stretched by the motion of the Body will endeavour to contract it felf equally towards both ends by which it pull the Centre as much towards the Body as it doth the Body towards the Centre.

Now this Centrifugal force is always proportional to the periphery which each Body defcribes in its diurnal motion by the first Theor. of Hugenius De vi Centrifuga: fo that under the Equator which is the biggest circle the centrifugal force would be greateft, and ftill grow lefs as we approach the Pole where it quite vanifheth, there being there no

diurnal

diurnal rotation. And without doubt all Bodies having this centrifugal force by which they endeavour to recede from the Centre of their motion, would fly off from the Earth if they were not kept in their orbit, by their gravity, or that force by which they are preffed towards the Centre of the Earth, which is much stronger upon our Earth than the centrifugal force; and because the gravity upon the furface of the Earth is always the fame, but the centrifugal force alters and grows lefs the nearer we come to the Poles; it is plain that the gravity under the æquator having a greater force to oppofe it than that which is near the Poles, will not act so strongly in the one place as in the other, and confequently bodies will not be fo heavy under the æquator as at the Poles.

If the Circle * ÆPQP represent the Earth, EQ the æquator, and P P the Poles, if C be a Body in the æquator, it is evident that it will be pulled down by two contrary forces, namely that of its gravity which pulls it towards the Centre, and that of its centrifugal force which pulls it from it. Now if both thefe forces were equal it is evident it would go neither of these ways; but if one were ftronger than the other, it would move where the ftrongeft force pulls it, but only with a velocity which is proportional to the differences of thefe two forces, and therefore

* See Figure 3. Plate II.

it would not defcend fo faft as if there were no centrifugal force pulling against it. That is a Body in the Equator does prefs lefs towards the Centre than at the Pole where there is no centrifugal force to leffen its gravity. Bodies therefore of the fame density are not fo heavy in one place as in the other.

Now in a spherical fluid, all whofe parts gravitate towards the Centre, I think it is evident from the principles of Hydrostaticks and fluidity, that all thofe Bodies which are equally diftant from the Centre, must be equally preft with the weight of the incumbent fluid, and if one part come to be more preffed than another, that which is moft preffed will thrust that out of its place which is leaft, till all the parts come to an æquilibrium one with another, and this is known by a common and eafy experiment, if you take a recurved tube as in the figure, [Fig. 4. Plate II. and fill it with water or any other fluid, it will rife equally in both Legs of the Tube, fo that the furfaces C E and FI are equally preffed by the weight of the incumbent columns BCED, GFIH,. but if one of the Legs of this Tube should be filled with oil, or fome other lighter fluid, and the other with water, the lighter fluid will rife higher than the other, for otherways, these furfaces which are equally distant from the Centre could not be equally preffed.

Juft