[ *29 } 
dividing a body into parts, the furface increafes ac- 
cording to the number of parts, but the proportion 
of fpace occupied (and confequently the fpecific gra- 
vity) remains the fame. Take a cube, whofe iide 
is ten inches, the furface is fix hundred inches, the 
fpace occupied one thoufand cubic inches j divide 
that cube into a thoufand cubes ; the furface will be 
increafed to lix thoufand fquare inches, but the fpace 
occupied will remain a thoufand cubic inches, and 
therefore the fpecific gravity will remain the fame 
and fo on, divide it into as many parts as you pleafe. 
Indeed bodies by an increafe of furface meet a greater 
refiftance in pafling through any medium ; but, I 
think, refiftance and fpecific gravity are here care- 
fully to be diflinguifhed : for that refiftance, which 
prevents the finking of the minute parts of a body, 
in a fluid fpecifically lighter, muft equally retard their 
afeent in the fame fluid ; and therefore can never be 
the caufe of their afeending. 
But let us fuppofe,' that this veficle is formed and 
filled with rarefied air, and afeending through the 
atmofphere ; it is plain, from another caufe, that it 
cannot remain fo during a few feconds of time : for 
no folar or culinary heat can expand air fo as to 
make it permanent in that ftate, in a veficle of va- 
pour afeending through the open atmofphere, for the 
fpace of one minute. For it is evident, that metallic 
bodies, heated many degrees hotter than boiling 
water, and exceedingly larger than, the afeending 
veficle, cool in a few feconds, when expofed to the 
open atmofphere. For inflance, mechanic operators, 
in tempering of fmall drills, only heat them red hot 
in the flame of a lamp, and then weaving them three 
VoL. 4p. S or 
