[roo8] 
down. And this CQVtA'mlY {ceteris Paribus,] is to be ad- 
mitted a!fo. 
Onely I add thereto ; that thefe ftatick principles do 
cheiHy take place, when things areotherwife at reft and 
quiet. But when they are in Gommotion, it is many 
times much othervvife. And, in fuch cafes, we muft, 
befidethe refpedlive gravity, take into confideration, the 
force, impuHe, or impetus, that isfuperaddedto there* 
fpe6tive gravity of the partsor matter. 
Thus, if a Bottle befhaken, the fediment at the bot- 
tom, (though heavyer, and for which caufe it did before 
lublide J will be mingled with the fupernatant (finer and 
lighter,) Liquor. And, if a room be fwept, it will (as we 
uie to fpeak,) make a duft : that is, the fmall Earthy 
particles of dull, will rife and mingle with the Jir : not 
becaufe tlicy be lighter then it, (tor we fee that, at lea- 
fure, they will fubfide again,) but becaufe, by a force 
mpon them, they be put into motion. So in a Jetty o£ 
Water (in artificial Waters Works,) the water is throwa 
lapinto the^/r to a great height; not becaufe it fo be- 
comes lighter then the^ir, but becaufe of the force im- 
preilfed. (To fay nothing of a Bullet, ftot upward into 
thejir.) And Bottled Ale, when opened, flyes many 
times upward to a great hight i and fometimes blows^ up 
^he Cork, to releafe it felf from confinement. And, in 
the late Fire Loudon, not Papers only, but other things 
of greater weight, were mounted into the -^^r, and there 
carried aloft for many miles, and fo taken up at more 
then Twenty miles diftance. 
And this I take to be the caufe of Eumes, Vapours, and 
other like matters (moft of them,jwhieh afeend in thtJtr, 
ii@t becaufe lighter then it,but becaufe impelled upward 
eutof the bowels of the Earth, or from thefuperficial 
parts of it, either by fome fubterraneal heats or other 
ferments that put tbem into motion, and force them up- 
ward i whese they remain fufpeadcd. ia the-ii^r, fp long. 
as 
