134 ZV. Blagden’s Experiments cn the 
From the above-mentioned fa£ts it appears, that M. 
Mairan’s pofition, though not deftitute of foundation, was 
enounced by him too generally, and without fufficient precifion. 
^ t 
It is the natural property of water to bear to be cooled a certain 
number of degrees without freezing ; reft favours this pro- 
perty negatively, by giving it no interruption ; but moft kinds 
of agitation interfere with its operation to a greater or lefs de- 
gree, and fome perhaps would prevent it altogether; whilft 
others affedft it fo little, as not to fuperinduce the congelation, 
even when the cooling is brought within one degree of the 
greateft that the water will bear. 
Whatever be the effeft of agitation, there is another caufe 
which much more powerfully haftens the congelation of water. 
It has been long known, that when water is cooled below its 
freezing point, the contaeft of the leaft particle of ice will in- 
ftantly make it congeal, the glacial cryftals /hooting all 
through the liquor, from the fpot where the ice touches it, till 
the whole comes up to the freezing point. Few experiments 
of the minute kind afford a more ftriking fpe&acle than this, 
efpecially when the water has been cooled nearly as much as pof- 
fible below the freezing point ; both from the beautiful manner 
in which the cryftals (hoot through it, and the rapidity with 
r 
which the mercury in the thermometer immerfed in it runs up 
through a fpaceof io or 1 1 degrees, flopping and fixing always 
at 32 in pure water. If from any circumftance, however, as a 
lefs cooling, or the addition of a fait, the (hooting of the ice 
proceed more (lowly, the thermometer will often remain be- 
low the freezing point even after there is much ice in the 
liquor ; and does not rife rapidly, or to its due height, till fome 
of the ice is formed clofe to its bulb ; which exemplifies the 
3 evolution 
