Chap. i. PHILOSOPHY. 43

this power of inactivity is in every body proportional to thequantity of the folid matter in it. But although we have noabfolute proof, that all the matter in the univerfe is uniform,and poffeffes this power of inactivity in the lame degree; yetwe can with certainty compare together the different degreesof this power of inactivity in different bodies. Particularlythis power is proportional to the weight of bodies, as Sir IsaacNewton has demonftrated a . However, notwithftandingthat this power of inactivity in any body can be more certain-ly known, than the quantity of folid matter in it; yet fincethere is no reafon to fufpeCt that one is not proportional to theother, we fhall hereafter fpeak without hefitation of the quan-tity of matter in bodies, as the meafure of the degree of theirpower of inactivity.

15*. This being eftablifhed, we may now compare theeffects of the fame power upon different bodies, as hither-to we have fhewn the effects of different powers upon thelame body. And here if we limit the word motion to thepeculiar fenfe given to it in philofophy, we may comprehendall that is to be faid upon this head under one fhort precept;that the fame power, to whatever body it is applied, will al-ways produce the fame degree of motion. But here motiondoes not fignify the degree of celerity or velocity with whicha body moves, in which fenfe only we have hitherto ufed it;but it is made ufe of particularly in philofophy to fignify theforce with which a body moves: as if two bodies A and B be-

1 Princ, Philof. L. II. prop. 24. corol. 7. Sec alfo B. II, Ch. 5. § 3. of this trcatife.

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