succeeding times, when the heat of fashion is a little abated, they will be respected the more for it. If Dr. Woodward's aim was such as I imagine it to have been, he certainly failed of it in some degree. The introducing of gravity into his work might gain him many friends and some few proselytes; but it infused into others a very strong prejudice against him: for this appears to have been the principal reason which moved Mr. Ray to reject his hypothesis of an universal dissolution. He suspected it to be an invention subservient to the new principle of gravity; knowing that the phænomenon, which he would have solved by such a dissolution, was not generally true, and that we have sufficient authorities to prove the contrary *.

Though the nature of my subject hath obliged me here to make so free with Dr. Woodward in one article, I have no desire to lessen his real merit; which is that of having treated the subject of the universal deluge in a manner far superior to all writers who had undertaken it before him. But in the article relating to gravity, to say the best we can of him, he was mistaken.

Ray's Three Discourses, p. 167, 4th edit.

Had

Had the earth been put together in the manner he has supposed, by the attraction of gravity, the natural order of things would have been inverted, and the economy of the world thrown into the utmost confusion. All the water of the globe would have been uppermost all the gold and other metals would have subsided to the central parts. And although the poet has fixed a stigma on his effodiuntur opes, yet had they been carried down to the centre, how many hands had been unemployed, and left to idleness or mischief, for want of necessary labour. What should we have done for instruments of iron and brass; I will not say for warlike and destructive purposes, but for necessary and mechanical uses? To be short, the disposition of things below the surface of the earth is so ordered, that mankind may reap the greatest benefit from it. And does it not plainly demonstrate, at the same time, that though bodies may fall to the earth by what we call gravity, this gravity is but a partial phænomenon, and was never employed as a ruling principle in the conformation of this terraqueous globe? If to the facts here collected we add the density of elementary fire as found by experiment, and the perpetual

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tual efflux of light from the sun, the result of the whole is-gravity does not prevail as an universal principle, either in the heaven above, or in the earth beneath; and consequently, a system of philosophy, which both supposes and requires it to be universal, hath mistaken the agency of nature, and is so far at least contradicted by experience.

CHAP. VI.

The Forces of Attraction and Projection, commonly called Central Forces, will not consist with the Motion of the Planets, even upon the supposition of a Celestial Vacuum.

I

HAVE but one more observation to make

in regard to gravity. I own it to be something in the nature of a digression, and as such I hope it will be excused. This principle then, compounded with a projectile force, will not account for the motion of the heavenly bodies, even allowing the spaces in which they move to be void of all resisting matter. We are under no obligation to grant this; however, let us grant it

for

for argument's sake, and see what will follow.

A body acted upon by two different forces at the same time, will describe the diagonal of a parallelogram, whose sides are respectively equal to the two forces. Experiment shews this to be true; the application of it is what I am here to treat of; and I shall endeavour to be as short and as plain as I possibly can.

The celebrated author of the Principia, as it is universally known to all those who have but dipt into natural philosophy, supposes a planet to be acted upon by a projectile force giving it motion in a right line, which makes a tangent with its orbit. This force, once impressed, is always to continue by his first law of nature. It is also acted upon at the same time by a centripetal force; which some observations upon the moon have induced him to believe is the same with

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* Sir Isaac's first law of nature is this-All bodies continue in their state of rest, or motion, uniformly in a right line, except so much as they are forced to change that state by forces impressed.

Prima lex naturæ, quod unaquæque res quantum in se est, semper in eodem statu perseveret ; sicque quod semel movetur, semper moveri pergat, nec unquam mutetur nisi a causis externis. Vid. Cartesii Princip. Philos. p. 2. sect. 37.

with what is called gravity near the earth's surface. By the former of these forces alone, it would always proceed in the tangent or right line; by the latter, it would fall straight to the centre; by both of them jointly, it will be gradually bent below the tangent, and in a given time, sufficiently small, will describe the diagonal of a parallelogram, whose sides are as the two forces. In a second moment of time, it will describe another, and so on. Now if these parallelograms are imagined to be infinitely small, a series of their diagonals will not sensibly differ from a curve: and thus he accounts for the motion of the planets in curvilinear orbits.

The greatest adversaries' of Sir Isaac Newton must allow the thought to be highly ingenious. A thorough mathematician is so smitten with the elegance of it, and with the wonderful things he has deduced from it in a course of abstruse theorems, in which few are able to follow him but those who do it to a degree of enthusiasm, that they will very hardly be induced to quit their theories for a while, and condescend to examine how this speculation will consist with prac tice.