I3 3 ' 7> . Blagden’s Experiments on the 
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and furface of the water may prevent their ludden cooling. 
And one of the mod: convenient veflfels for the purpofe is a 
round body terminating in a neck, the body to be lurrounded 
with the frigorific mixture, whilft the water in the neck is 
kept above the freezing point. 
Thefe are the principal facts with which my experiments 
have furnifhed me relative to the cooling of water below its 
point of congelation. I fee no general cirqumftance that ap- 
plies to them all. At one time I thought that much depended 
on reducing the water into thin plates ; an idea which was 
principally fuggefted by the more ready congelation of the 
edges of the water where it rifes up as a thin film on the fides, 
and by the effect of extraneous fubftances floating in the water 
to haflen its freezing, which might be fuppofed frequently in 
their motions to intercept fmall portions of the fluid, and form 
it into thin plates. Agitation likewife might by reducing 
the water in fome part or another into flmilar plates. And as 
water impregnated with air appeared lefs capable of being 
cooled than the fame water deprived of its air, it feemed not 
impoflible that the air might a£t likewife by producing thin 
plates in different parts of the fluid. With a view to this hy« 
pothefls I made feveral experiments. Into a tumbler with 
diddled water I put a quantity of fand, which fettled loofely 
to the bottom, and left the water above as tranfparent as be- 
fore. This tumbler being placed in the frigorific mixture, 
the water bore to be cooled as well as it had done without this 
addition. Laying thin bits of glafs upon one another at the 
bottom of* the tumbler, in place of the fand, I found no dif- 
ference in the effect. By this latter experiment it was more- 
over proved, that points in the water do not perceptibly facili- 
tate its crydallifation into ice. Now the thin plates or wedges 
of 
