Chap. 2. PHILOSOPHY.

6 1

this metal being the most weighty of any body known to us.This glals they empty of the air contained within it, and bymoving a wire, which passes through the top of the glals, theylet the feather and the heavy body fall together ; and it is al-ways found, that as the two bodies begin to descend at thefame time, so they accompany each other in the fall, andcome to the bottom at the very fame instant, as near as the eyecan judge. Thus, as far as this experiment can be dependedon, it is certain, that the effect of the power of gravity uponeach body is proportional to the quantity of solid matter, or tothe power of inactivity in each body. For in the limitedsense, which we have given above to the word motion, it hasbeen shewn, that the fame force gives to all bodies the famedegree ess motion, and different forces communicate differentdegrees of motion proportional to the respective powers \ Inthis cafe, if the power of gravity were to act equally upon thefeather, and upon the more solid body, the solid body woulddescend so much flower than the feather, as to have no great-er degree of motion than the feather: but as both bodies de-scend with equal swiftness, the degree of motion in the solidbody is greater than in the feather, bearing the lame propor-tion to it, as the quantity of matter in the solid body to thequantity of matter in the feather. Therefore the effect ofgravity on. the solid body is greater than on the feather, in pro-portion to the greater degree of motion communicated; thatis, the effect of the power of gravity on the solid body bears-the lame proportion to its effect on the feather, as the quanti-ty

* Chap. I. § 25, z6, 27, compared with § 15, &c.