cooling of Wilier below its freezing Point. 133 
water feparntely, than moving the whole together. I have 
found, that ftriking the bottom of the tumbler againft a board 
would produce inftant congelation, when ftirring the water, or 
fhaking the tumbler in the hand, would have no effect. In 
like manner, when in ftirring the cooled water the quill, or 
flick of glafs, employed for that purpofe, ffrikes againft the 
lide or bottom of the tumbler, the water, which had refifted 
the general ftirring, is often by this percuffion made to freeze. 
The fame effect is produced, and with lefs uncertainty, if the 
quill, or ftick of glafs, be rubbed, and as it were ground, 
againft the fide of the tumbler. But of all fuch methods 
of bringing on the congelation, that which I have found 
to fail the feldomeft, is to rub a bit of wax againft the 
fide of the tumbler under the water; a particular roughnefs 
in the motion is felt, with fome lound, approaching to a 
mufical tremulation, and a cruft of ice is immediately 
perceived under the wax upon the glafs. This efteft of the 
wax I take to be mechanical, depending on its particular ffate 
of confidence. Wood acts in the fame manner, though with 
lefs certainty ; fo does a quill, and likewise glafs ; but the 
latter, being very hard, produces theeffedft with leaft certainty. 
It is a mechanical action upon the water in contact with the 
rubbing fubftance and the glals : for if the outfide of the 
tumbler, or any part of the infide above the water, be rubbed, 
even if it be wet fo as to communicate a limilar feeling of 
tremulation, yet ftill the congelation is not produced. 
All thefe modes of bringing on the congelation lucceed beft,. 
as might be expended, in proportion as the water is more cooled 
below the freezing point. Unlefs the cooling amount to tour 
or five degrees, the fri&ion with wax is often in vain. 
From 
