and bridles. For as the natural tendency of all impreft motion is in ftrait lines, fo when motion was given to the planets, this motion (although as I faid it was artificially made, perpendicularly to the radii, yet) would carry them quite away in their tangents, fo that they would never return again. But being thus detained by gravity, another admirable provifion is, that, 2. They are moved in orbs: which orbs are formed of a motion compounded of this rectilinear impulse, impreft upon the planets, and the tendency of their gravity to the centres. In which motion a third thing very remarkable is, That the impulfe or velocity which is imparted by the first mover to every planet, and the gravity of each planet, are fo nearly equal to what is required to make a body describe a circle, that the orbits of the planets are not very eccentrical, but nearly circular. As is particularly remarkable in Venus, and the earth; and more especially in the whole fyftem of Jupiter's fatellites. And an admirable. work this is. For fhould the velocity of any planet be double to what would make it move in a circle, the planet would go away in infinitum, without ever returning again in any orb whatfoever. Or fhould one half of the velocity be taken away, the planet would defcend obliquely towards the fun, until it became four times nearer

the

the fun than before; and then afcend again to its former place, defcribing a very eccentrical orb. And by afcending and defcending alternately, it would be heated fixteen times more at one time than another. Which uneven heat would make the planet unfit for habitation. And the fame thing would happen, if the determination of its motion should be altered, fo as to become very oblique to the radius drawn from the planet to the fun. But these things being accurately adjufted, and contempered, make the whole fyftem to be a work of incomparable convenience and beauty; a work the beft contrived for the benefit of the world's inhabitants, and to set forth the curiofity and skill of the infinite Workman.

It is manifeft therefore that the fyftem of the planets is not to be reckoned a matter of chance, or a thing owing to a neceffity of nature, but the work of a kind and wife Agent. And that this is fo, will be farther manifeft from the cafe of comets, whose motions, directions, and orbs, being utterly different from thofe of the planets, demonftrate the planetary fyftem to have been modeled by counfel, and not by a neceffity of nature, or left to chance. For as for the motion of comets, it is so far from being always the fame way, that they move fometimes contrary to one

another.

another. And as for their planes and directions, they lie every way. And as for their orbs, they are exceedingly eccentrical. And by the bye this eccentricity is an admirable contrivance of the Creator, to prevent the comets from disturbing either the planets, or one another, by their mutual attractions. For by this means, they have a large and fufficient room to revolve in; and by afcending to very great heights above the fyftem of the planets, and spending almost all their time in the remote regions of the universe, at vaft distances both from the planets, and from one another, they do not incommode either the planets, or themfelves; as otherwife they would have done, fhould they have moved in the fame plane with the planets, For had they done so, they would have been apt fometimes to have come too near the planets and have difturbed their motions, and perhaps have dashed upon them alfo. But all thefe circumftances are fo well adjufted, and fo wifely regulated by the Divine Providence, that the fyftem could not have been better contrived, either for convenience or beauty.

And now upon this highly probable, I might fay phyfically certain, theory of gravity acting in the motion of the globes, we have another cxquifite

quifite nicety in the works of the creation, that justly deserves the greatest admiration and praise; that among fo many immenfe moving maffes, they should all obferve their due bounds, keep the moft proper paths appointed for their convenience and good, and at all times answer the great ends to which they minifter in the creation, Particularly, that the habitable globes fhould always remain at fuch due distances, and move in fuch proper orbits, as are beft for them. And that the comets too, fhould at the fame time pass in paths utterly different, but yet fuch, in all probability, as may render them also of very great ufe to fome or other parts of the world; whether we look upon them as places of torment (as hath been faid) or bodies appointed for the refreshment and recruit of the fun, or any of his planets, as Sir Ifaac Newton conjectureth in his Principia, 1. iii. Prop. 41, & 42.

"

And now from the confideration of what I have fhewn in this fixth book, to be either highly probable, or very certain concerning gravity, we have another manifeft demonftration of the infinite Creator's wifdom and care, and another

cogent argument to excite the highest veneration and praise in his creatures.

BOOK

BOOK VII.

Of the PROVISION made for

LIGHT AND HEAT

THROUGHOUT THE UNIVERSE,

СНАР. 1.

OF THE LIGHT AND HEAT OF THE FIXT STARS AND

SUN.

AS light and heat are two of the most useful

things in the univerfe, fo the infinitely wife and kind Creator hath made an excellent provifion for these things, in all probability for every globe throughout the univerfe, but particularly for those of our own fyftem. For it is very

manifeft that every globe we fee, doth fhine with its own native, or with borrowed light. Event all thofe immenfe bodies at the greatest distance from us, the fixt stars, which, I have before faid,

are