Chap. i. PHILOSOPHICAL DISCOVERIES. 299

that might form a system os an inferior order. But we do notfind that nature carries this subordination so far, unless wewould consider the motion of projectiles, near the surfaces ofthe secondary planets, as an example of this kind.

7. It is next to be considered, where this point of rest of thecommon centre of gravity of the system is to be found ; andit is plain from what we have already seen, that it can neverbe far removed from the sun, because the matter in the sunvastly exceeds the matter in all the planets taken together :and, from what we said of the centre of gravity above, it ap-pears that it is always nearer the greater body in proportion asit is greater. 'Jupiter is the largest of the planets, and yet isbut ~ of the fun, so that their centre of gravity must be1067 times nearer the sim than Jupiter ; and as the distance ofJupiter is little more than 1067 semidiameters of the fun, itfollows that the centre of gravity of the fun and Jupiter can-not be much above the surface of the sun. Saturn is less thanJupiter both in bulk and density, and the centre of gravity ofthe Sun and Saturn falls within the body of the fun : andthus it easily appears, that tho’ all the planets were on one sideof the fun in one line, the centre of gravity of the fun andthem all could scarcely be above a semi-diameter of the sunfrom his surface : and this is the farthest that the fun is everremoved from that centre. It appears, therefore, that tho’the fun is in perpetual agitation about this centre, yet, beingalways so near it, he may very well be considered by astrono-mers as the centre of the solar system. Thus, tho’ the ter-raqueous globe receives an impression from every power thatmoves projectiles in the air, and is, to speak accurately, agi-tated a little by these powers with a very complex motion, yetwe consider it as at rest, neglecting such exceeding minuteactions and their effects.

CCq 2

CHAP.