fame in the air-pump (when the preffure is taken off) as in the free air; and therefore fome other cause is to be found: and what more probable, or fo probable as this of gravity or attraction, which manifeftly exerts itself in fome, and is highly probable in all material things m? In the earth itself there is manifeftly fuch a thing as gravity, which might as well be the natural cause of the fphæricity of our globe, as it is in that of leffer maffes; but then, as I demonftrated in the last book, it is alfo evident, that an over-ruling Power, and a wife Providence, not only gave matter this gravitating power, but guided and managed it in the formation of the world.

And now upon fuppofition that gravity had any thing to do in the production of this fphærical figure I am speaking of, the fame it must have alfo in the confervation of that figure. For the fame power it exerted at first, it retajns still; which is as neceffary ftill to the preventing and obviating all extravagant excurfions, and deviations from that figure which may happen through extraordinary

m For the proof of this, I fhall refer to Sir Ifaac Newton's Opticks, Quest. 13. of the fecond edition, and in his Principia, in many places, particularly 1, iii. Prop. 5, 6, 7.

extraordinary commotions and convulfions in any of the globes; fuch as earthquakes are, and other fuch like furious concuffions and emotions that fometimes befal our own globe.

But leaving thefe conjectural matters, let us come to a more evident benefit of gravity, and that is the natural tendency of all bodies to the centre of the globe: this is very manifeft in our own globe. For whatsoever the decays are among earthly things, howfoever their forms are changed, yet their matter remaineth entire, and returneth again to its grand parent the earth: or, to put it in Solomon's words, Eccl. i. 4. " One "generation paffeth away, and another genera❝tion cometh : but the earth abideth for ever.

And an admirable provifion this is for the perpetuity of the globe, and to continue the state and habitability thereof throughout all ages, which would otherwife wafte and decay, or run into the most irreparable and pernicious disorders.

СНАР.

CHA P. II.

THE GUARD WHICH GRAVITY AFFORDS AGAINST

THE CENTRIFUGAL FORCE OF THE SEVERAL

GLOBES.

PON a fuppofition that every of the globes

UPON

revolves round its own axis, (which I have fufficiently proved in the fourth book) we shall find, befides the benefits already specified, another very great ufe of gravity to the good, yea, the very existence of our own and other globes, and that is the prefervation of their integrity against the centrifugal force of this their revolution or diurnal motion. For without fuch a band, as gravity, to keep their parts together, the whirling about of those globes would fhatter them into pieces, and diffipate them abroad into the circumambient fpace. Thus muft it needs befal our own globe, which whirls about at the rate of above 1000

miles an hour", and is compofed of earth and water, materials of much too loofe a texture to prevent the diffipation which the centrifugal force of fuch a rotation must neceffarily occafion about the æquatorial parts, a rotation that would as cafily throw off the parts of the earth, efpecially the waters, as the whirling round of a wheel or a globe, would the loofe duft and water lodged thereon. But by reafon the gravitating power exceeds the centrifugal as 2174 exceeds 7'54064°, that is above 288 times; therefore all parts lie quiet and fecure in their refpective places, and enjoy all the benefits, which I fhewed do accompany this motion without any disturbance from it.

Thus is our own globe guarded by its gravity against the centrifugal force of its rotation. But this is far more remarkable in forte of the other globes. Thus particularly in the fun, whofe ambit is 2582873 miles, and whirls round once

in

The diameter of the earth being 7967'7 miles, according to b. i. chap. 2. note 1. the Ambit thereof is 25031'4 miles, which being divided into 24 hours, makes the revolution to be at the rate of 1043 miles an hour.

This is the proportion, or nearly fo, of the gravitating to the centrifugal force of the earth under the equator, as may be com puted from Sir Ifaac Newton's Princip. I. iii. Prop. 19.

in about 25 days, and confequently doth revolve at the rate of 4262 miles an hour P, which is above four times as faft as the earth; this in a little time would endanger its diffipation, without fuch a provifion as gravity is.

But what is this to the centrifugal force of Jupiter? whofe bulk far exceeds our terraqueous ball, and whofe rotation is performed in lefs than half the time. But from a computation of particulars we shall better eftimate the matter. The diameter of Jupiter being 120653 miles, its circumference is 379043 miles: which revolving round in less than ten hours, is at the rate of 381599 miles an hour at its æquator. And if

the

The Sun's diameter being 822148 miles, the numbers here affigned will naturally follow.

As to the Sun's gravity or attractive power, it is (by the calculation of my friend, the acute and learned Dr. Halley) to the Sun's centrifugal force, as 47000 to 1: the method for finding which, Tee note (r) p. 223.

9 Jupiter's ambit being 379043 miles, and his revolution 9 h. 56', or 596 minutes; the revolution in an hour is, by the loga rithms, thus: