Sir I s a a c Newton’s Book I.

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mption; but continues always in the fame place, till removedby fome power applied to it.

9. A g a i n, whenever a body is once in motion, it continuesin that motion fome time after the moving power has quittedit, and it is left to it felf. Now if the body continue to movebut a ftngle moment, after the moving power has left it, therecan no reafon be affigned, why it fliould ever ftop withoutfome external force. For it is plain, that this continuance ofthe motion is caufed only by the body’s having already mov-ed, the foie operation of the power upon the body being theputting it in motion; therefore that motion continued will e-qually be the caufe of its farther motion, and fo on withoutend. The only doubt that can remain, is, whether this motioncommunicated continues intire, after the power, that caufedit, ceafes to ad; or whether it does not gradually languifh anddecreafe. And this fufpicion cannot be removed by a tranfi-ent and flight obfervation on bodies, but will be fully clearedup by thofe more accurate proofs of the laws of motion,which are to be confidered in the next chapter.

10. Lastly, bodies in motion appear to affed a ftraightcourfe without any deviation, unlefs when difturbed by fomeadventitious power ading upon them. If a body be thrownperpendicularly upwards or downwards, it appears to continuein the fame ftraight line during the whole time of its motion.If a body be thrown in any other diredion, it is found to de-viate from the line, in which it began to move, more and

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