[ '2H .] 
that the flrong current in the Seine impeded the 
congelation : motion will certainly hinder the parts 
of fluid bodies from acquiring a regular arrange- 
ment; but it may be doubted whether it will wholly 
prevent their coalefcence, in any cafe where the 
degree of heat is lefs than what would keep them 
fluid if they were quiefeent. We have frequent in- 
ftances in chemiflry, of faturated folutions of fdts 
reti'iaining perfedlly fluid whili^ at reft, and of form- 
ing thick coagulums upon the leaft motion. Melted 
metals, glafs, refins, See. appear to continue fluid 
for a longer time, after being taken from the fire, 
by having their parts moved, than if they are left at 
reft ; becaufe the fuperficies which is expofed to 
the air is conftantly changing, and the whole mafs 
becomes uniformly cold and fixed at once, as foon 
as it has parted with the heat neceftary for its fufion. 
The moft rapid rivers would probably experience a - 
flmilar change, did the cold in the atmofphere con- 
tinue long enough to be communicated to the whole 
body of the water : for upon taking the thermo- 
meter out of the fnow, which laid upon the bank 
of the river, and immerfing it into the water, it 
fuddenly rofe 26°, and flood at 32°, or higher ; fo 
that the air was very confiderably colder than the 
water : nor is this at all to be wondered at, when we 
confider that great degrees of cold may be fuddenly 
produced in the atmofphere by caufes which do not 
immediately operate upon other bodies. Thus the 
influx of colder air from the northern latitudes, or 
the'delcent of that which always remains exceeding- 
ly cold in the up(.^r parts of the atmofphere in the 
fame 
6 
