A property near a kin to the preceding, is this, that if a place is mov'd, whatever is placed therein moves along with it; and therefore a body, which is mov'd from a place in motion, partakes alſo of the motion of its place. Upon which account all motions from places in motion, are no other than parts of entire and abſolute motions; and every entire motion is compoſed out of the motion of the body out of its firſt place, and the motion of this place out of its place, and ſo on; until we come to ſome immovable place, as in the before mention'd example of the Sailor. Wherefore entire and abſolute motions can be no otherwiſe determin'd than by immovable places; and for that reaſon I did before refer thoſe abſolute motions to immovable places, but relative ones to moveable places. Now no other places are immovable, but thoſe that, from infinity to infinity, do all retain the ſame given poſitions one to another; and upon this account, muſt ever remain unmov'd; and do thereby conſtitute, what I call, immovable ſpace.
The Cauſes by which true and relative motions are diſtinguiſhed, one from the other, are the forces impreſs'd upon bodies to generate motion. True motion is neither generated nor alter'd, but by ſome force impreſs'd upon the body moved: but relative motion may be generated or alter'd without any force impreſs'd upon the body. For it is ſufficient only to impreſs ſome force on other bodies with which the former is compar'd, that by their giving way, that relation may be chang'd, in which the relative reſt or motion of this other body did conſiſt. Again, True motion ſuffers always ſome change from any force impreſs'd upon the moving body; but Relative motion does not neceſſarily undergo any change, by ſuch forces. For if
the ſame forces are likewiſe impreſs'd on thoſe other
