mation will not enable us to decide between them. The second fuppofition is, that the earth, being a mixed mass fomewhat fluid, took, as it might do, its prefent form, by the joint action of the mutual gravitation of its parts and its rotatory motion. This, as we have faid, is a point in the history of the earth, which our obfervations are not fufficient to determine. For a very small depth below the furface (but extremely fmall, lefss perhaps, than an eight thousandth part, compared with the depth of the centre) we find veftiges of ancient fluidity. But this fluidity must have gone down many hundred times further than we can penetrate, to enable the earth to take its prefent oblate form; and, whether any traces of this kind exist to that depth, we are ignorant. Calculations were made a few years ago of the mean density of the earth, by comparing the force of its attraction with the force of attraction of a rock of granite, the bulk of which could be afcertained: and the upshot of the calculation was, that the earth upon an average, through its whole fphere, has twice the denfity of granite, or about five times that of water. Therefore it cannot be a hollow fhell, as fome have for

merly fuppofed: nor can its internal parts be occupied by central fire, or by water. The folid parts must greatly exceed the fluid parts: and the probability is, that it is a folid mafs throughout, compofed of fubftances, more ponderous the deeper we go. Nevertheless, we may conceive the prefent face of the earth to have originated from the revolution of a sphere, covered with a furface of a compound mixture; the fluid and folid parts feparating, as the furface became quiefcent. Here then comes in the moderating hand of the Creator. If the water had exceeded its prefent proportion, even but by a trifling quantity compared with the whole globe, all the land would have been covered: had there been much less than there is, there would not have been enough to fertilize the continent. Had the exficcation been progreffive, fuch as we may fuppofe to have been produced by an evaporating heat, how came it to flop at the point at which we fee it? Why did it not ftop fooner; why at all? The mandate of the Deity will account for this nothing elfe will.

IV. OF CENTRIPETAL FORCES. By virtue of the fimpleft law that can be imagined, viz. that a body continues in the ftate in which

it is, whether of motion or reft; and, if in motion, goes on in the line in which it was proceeding, and with the fame velocity, unlefs there be fome caufe for change; by virtue, I fay, of this law, it comes to pafs (what may appear to be a strange confequence) that cafes arife, in which attraction, inceffantly drawing a body towards a centre, never brings, nor ever will bring, the body to that centre, but keep it in eternal circulation round it. If it were poffible to fire off a cannon ball with a velocity of five miles in a fecond, and the refiftance of the air could be taken away, the cannon ball would for ever wheel round the earth, instead of falling down upon it. This is the principle which fuftains the heavenly motions. The Deity having appointed this law to matter, than which, as we have said before, no law could be more fimple, has turned it to a wonderful account in conftructing planetary fyftems.

The actuating cause in these systems, is an attraction which varies reciprocally as the square of the distance: that is, at double the distance, has a quarter of the force; at half the distance, four times the ftrength; and fo on. Now, concerning this law of variation,

we have three things to obferve; first, that attraction, for any thing we know about it, was just as capable of one law of variation as of another: fecondly; that, out of an infinite number of poffible laws, those which were admiffible for the purpose of fupporting the heavenly motions, lay within certain narrow limits: thirdly; that of the admiffible laws, or those which come within the limits prescribed, the law that actually prevails is the moft beneficial. So far as these propofitions can be made out, we may be faid, I think, to prove choice and regulation; choice, out of boundless variety; and regulation, of that which, by its own nature, was, in respect of the property regulated, indifferent and indefinite.

I. First then, attraction, for any thing we know about it, was originally indifferent to all laws of variation depending upon change of distance, i. e. just as susceptible of one law as of another. It might have been the same at all diftances. It might have increased as the diftance increased. Or it might have diminished with the increase of the diftance, yet in ten thousand different proportions from the prefent. It might have followed no stated law at

all.

all. If attraction be, what Cotes with many other Newtonians have thought it, a primordial property of matter, not dependent upon, or traceable to, any other material cause, then, by the very nature and definition of a primordial property, it stood indifferent to all laws. If it be the agency of fomething immaterial, then alfo, for any thing we know of it, it was indifferent to all laws. If the revolution of bodies round a centre depend upon vortices, neither are these limited to one law more than another.

There is, I know, an account given of attraction, which should seem, in its very cause, to affign to it the law, which we find it to obferve, and which, therefore, makes that law, a law, not of choice, but of neceffity: and it is the account, which afcribes attraction to an emanation from the attracting body. It is probable, that the influence of fuch an emanation will be proportioned to the fpiffitude of the rays, of which it is compofed: which fpiffitude, fuppofing the rays to iffue in right lines on all fides from a point, will be reciprocally as the fquare of the distance. The mathematics of this folution we do not call in queftion: the queftion with us is, whether there

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