Meteorological Obfervations. 617 
Experiments om freezing and thawing ina per- 
fe&. vacuum might: give light to»this fubje& : 
as I) fufpect, from the great expanfion of ice, 
that air muft be-generated in the aét of freezing, 
and given out in ithawing. A bit of. ice might 
eafily be diffolved in:the Toricellian vacuum, | to 
afcertain whether it parted with air in thawing.” 
Soon after I received this letter, I-endeavour- 
ed. tor fubject this opinion to, an enaetlnaate 
proof, in the following manner ; 
As much water was put. into the upper end of 
a wide barometer tube, as filled, it to two inches: 
it was ‘then’ frozen in a freezing mixture, the 
tube |was filled with mercury, and.inverted into 
a. veffel, of the, fame.—The mercury’ did not 
remain fufpended. fo -high as, the. ice, but 
there: was. a vacuum, of about a, quarter of: an 
inch between,them.. The place: where. the 
mercury ftood was accurately..marked, and 
the ice was fuffered to thaw, which in about 
half an hour was completely done. The water 
was fupported upon the mercury to the height 
of about. two inches, and the mercury was 
found depreffed very nearly 4 of,an inch, which 
was undoubtedly owing to the preffure of the 
two inches of water. When the tube was 
inclined, the water and mercury entirely 
filled it; a proof that no air had been extri- 
cated during the thawing of the ice. : 
Hhhh I next 
