Page:The Mathematical Principles of Natural Philosophy - 1729 - Volume 1.djvu/54

10 a pace of our Air, which relatively and in repect of the Earth, remains always the ame, will at one time be one part of the abolute pace into which the Air paes; at another time it will be another part of the ame, and o, abolutely undertood, it will be perpetually mutable.

III. Place is a part of pace which a body takes up, and, is according to the pace, either abolute or relative. I ay, a Part of Space; not the ituation, nor the external urface of the body. For the places of equal Solids, are always equal; but their uperficies, by reaon of their diimilar figures, are often unequal. Poitions properly have no quantity, nor are they o much the places themelves, as the properties of places. The motion of the whole is the ame thing with the um of the motions of the parts, that is, the tranlation of the whole, out of its place, is the ame thing with the um of the tranlations of the parts out of their places; and therefore the Place of the whole, is the ame thing with the Sum of the places of the parts, and for that reaon, it is internal, and in the whole body.

IV. Abolute motion, is the tranlation of a body from one abolute place into another; and Relative motion, the tranlation from one relative place into another. Thus in a Ship under ail, the relative place of a body is that part of the Ship, which the Body poees; or that part of its cavity which the body fills, and which therefore moves together with the Ship: And Relative ret, is the continuance of the Body in the ame part of the Ship, or of its cavity. But Real, abolute ret, is the continuance of the Body in the ame part of that Immovable pace, in which the Ship it elf, its cavity, and all that it contains, is moved. Wherefore, if the Earth is really at ret, the Body Rh