[ 166 ] 
the thermometer had been taken out of the fnow and 
aquafortis, the mercury continued to fubfide, in the 
open air, down as low as the congealation of mer- 
cury. 
In the courfe of thefe inquiries, our profeffor found 
no difference, whether he made ufe of long or fhort 
thermometers j whether the tubes were made of the 
Bohemian, or the glafs of Peterfburg. Under the 
fame circumftances, the fame effedts were always 
produced, making an allowance for the different 
contraction of the different glaffes, under fo fevere a 
degree of cold. But if thefe tubes were filled with 
different mercury, there was then a fenfible dif- 
ference 5 inafmuch as mercury revived from fubli- 
mate did not fubfide fo faft in the thermometer, as 
that did, which was lefs pure. He has even found, 
that he has been able to congeal the lefs pure mer- 
cury, at a time when he could not bring the revived 
mercury lower than 300 degrees : but this he would, 
till farther trials have been made, not have confi dered 
as a general axiom. 
From thefe experiments, our author conceives it 
demonftrated, that heat alone is the caufe of the flui- 
dity of mercury, as it is that of water and other 
fluids. If, therefore, any part of the world docs 
exifl, in which fo great a degree of cold prevails, 
as to make mercury folid, there is no doubt, but 
that mercury ought to appear there as a body 
equally firm and confident, as the reft of the metals 
do here: that mercury, upon congealing, becomes 
its own ice, however different the mercurial ice may 
be from that of water, or other liquids. The idea 
of freezing does or can comprehend nothing more 
than 
6 
