Chap. i. PHILOSOPHY.

37

thofe halves, or the whole greater body, will require themoving power to be doubled. *

17. That the moving power being in this fenfe doubled,fhould juft double likewife the velocity of the fame body,feems near as evident, if we conftder, that the effect of thepower applied muft needs be the fame, whether that powerbe applied to the body at once, or in parts. Suppofe then thedouble power not applied to the body at once, but half of itfirft, and afterwards the other half; it is not conceivable forwhat reafon the half laft applied ftiould come to have a dif-ferent effect upon the body, from that which is applied nr ft,as it muft have, if the velocity of the body was not juft dou-bled by the application of it. So far as experience can deter-mine, we fee nothing to favour fuch a fuppofttion. We can-not indeed ( by reafon of the conftant motion of the earth )make trial upon any body perfe&ly at reft, whereby to feewhether a power applied in that cafe would have a differenteffect, from what it has, when the body is already moving ;but we find no alteration in the effcdt of the fame powei onaccount of any difference there may be in the motion of thebody, when the power is applied. The earth does not al-ways carry bodies with the fame degree of velocity ; yet wefind the vifible effects of any power applied to the fame bo-dy to be at all times the very fame : and a bale of goods, orother moveable body lying in a fhip is as eafily removedfrom place to place, while the fhip is under fail, if its motionbe fteady, as when it is fixed at anchor.

18. Now