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Sir ISAAC I s ! E W T O N’s Book II.

increase or diminish it in any proportion, we must double ortriple the force that is' requisite to move it with the same cele-rity, or increase or diminish it in the same proportion with thebody. Is the solid, uncompounded particles void of pores,of equal bulk, have their inertia equal, then'this must be ac-curately true : but if matter be of kinds so different from eachother, that the solid elementary particles of the one have agreater inertia than equal solid elementary particles of the otherkind, then it is only when we compare those of the same kind,that we can affirm the inertia to be proportional to the quantityof matter. Such different kinds of matter may exist for oughtwe know ; but it is by diminishing or increasing the number ofdimensions of the pores of bodies that they are condensed orrarified, according to our experience,. and thereby the inertiaof a given bulk increased or diminished.

5. Space is extended without limits, immoveable, uniformand similar in all its parts, and void of all resistance. It con-sists indeed of parts which may be distinguished into otherparts, lest and less, without end, but cannot be separated fromeach other and have their situation and distances changed.

6. Body is extended in space, moveable, bounded by figure,solid, and impenetrable, resisting by its inertia , divisible intoparts, less and less, without end, that may be separated fromeach other and have their situation or distances changed in anymanner.

7. From the succession of our own ideas, and from thesuccessive variations of external objects in the course of nature,we easily acquire the ideas of duration and time, and of theirmeasures. We conceive true or absolute time, to flow uni-