( 5IS7 ) 
though as to its particular Effcdls I leave them to the fpe- 
culation of Phyfitiaos 3 and ftiall only add^chat to keep this 
Conjefturc of mine ( for I propofe it as no other ) from 
feemiag as groundlcfi as extravagant , I will annex an Ex- 
pefiment that you will not perhaps diflike , juft as I find it 
rcgifter'd among fome of my loofe Papers, 
I caufed to be blown at the flame of a Lamp three fmall 
round Glals^bubblcs about the bignefs of Hazel-nuts, and 
furnifli'd each of them with a (hort and flenderftem, by 
whofc means they were fo nicely poifed in water^that a ve- 
ry ftnall change of Weight would make them either emerge, 
if they but lightly leaned on the bottom oi the Veflel , or 
Gnk^if they floated on the top of the Water. 
This being done at a time when the Atmofphcre was of 
a convenient Weighty (and fucha feafon is not ordinarily 
difEcuk to be chofen within fome reafonable time to him 
that wants neither attention nor a good Barofcope ) I put 
them in a wide-mouth'd Glals furnifh'd with common Wa- 
ter, and leaving them in a quiet place^where yet they were 
frequently in my eye, and were fufFe r'd to continue many 
weeks (or fome months,) I obferved, as I expecftcd 5 that 
fometimes they would be at the top of the Water, and re- 
main there for divers days, or perhaps Weeks 3 and fome- 
times would fall to the Bottomland after having continued 
there for feme time (longer or (horter) they would again 
emerge^ And though fometimes (efpecially if I removed 
the Veflel that contained them to a Southern Window^) 
they would rife to the Top or fall to the Bottom of the 
Water^ according as the Air was hot or cold 5 yet 'twas 
Dotdiffi^cult to difliinguifli thofe motions from thofe pro- 
duced by the varying Gravity of the Atmofphere» For 
when the Beams of the Sun , or heat of the Ambient Air^ 
by ratifying the Air included in the Bubbles ^ made that 
Air drive out fome of the Water, and confequently made 
the whole Bubble (confiding of Glafs, Air and Water) 
fome what lighter than a bulk of Water equal to itjthough 
the bubble did aeceflarily fwim as long as the included 
Ttttt t Air 
