cooling of Water below its freezing Point . i V) 
of water, which muft be intercepted by the bits of fand or 
glafs, feem very analogous to fuch as may be produced by 
floating particles of extraneous matter ; and therefore the effect 
of the latter is probably to be afcribed to fome other caufe, 
fuch as haftening the cooling, or rendering it lefs uniform, or, 
perhaps, communicating motion to the fluid. 
In the preceding inftances, however, the water may be con- 
fidered as conftituting, by its adhefion, a fort of continued 
body with the fubftance it touches ; and it might be fuppofed 
that, if one or both furfaces of the thin plate were in contact 
with air only, the congelation would take place. I therefore 
put down fome air, retained by a fmall difh of wax, into the 
water to be cooled, and let it flay there till the whole was 
reduced many degrees below the freezing point ; but no conge- 
lation enfued : I then contrived to turn up the difli of wax in 
the water, fo that the air it had carried down, efcaping from 
under it, afcended as a bubble to the top of the water, and 
there burft : ftill the water retained its fluidity, notwithftanding 
the contact of a loofe bubble of fuch cold air, and the motion 
produced by its explofion on the furface. In other experiments, 
I have indeed feen the burfting of a bubble on the furface ap- 
parently bring on the congelation ; but feemingly from the 
agitation it occafioned. And though a wetted furface, or a 
fmall thin portion of water, freeze in general more readily 
than a larger mafs, yet I have feen inftances of a jar cooled 
many degrees below the freezing point, and the water and air 
in it equally cold, which had, notwithftanding, upon its in- 
fide, from the furface of the water to an inch or more above 
it, an evident dew that remained quite fluid, and rendered the 
furface of the glafs wet. Under the fame circumftances alio, I 
have raifed the thermometer out of the cooled w 7 ater, without 
occafioning any congelation in the adhering thin film of that 
T a fluid. 
