[ *s 8 ] 
mercury in fome of the barometers and thermome- 
ters made ufe of for experiments in Siberia had been 
frozen : but fince that in greater degrees of cold, the 
mercury continued fluid in other barometers and 
thermometers, the immobility and hardnefs obferved 
in fome of thefe inflruments, was attributed more 
probably to the lead or the bifmuth, with which the 
mercury had been adulterated, and was not con- 
fidered as a real freezing of the mercury : but this 
has been fince put out of all doubt ; fince it is cer- 
tain, that pure mercury would not freeze under fuch 
fmall degrees of cold, great as they were for natural 
cold. The experiments, which the profeflor made, 
in order to congeal mercury, demonftrate this molt 
evidently ; befides which, they exhibit new pheno- 
mena. 
There happened at Peterfburg, on the 14th of 
December 1759, a very great froft, equal if not 
more intenfe than any which had been obferved 
there : for, between nine and ten o’clock in the 
morning, Delifle’s thermometer flood at 205 ; at 
feven o’clock, at 20 i; which laft was the greatefl: 
degree of cold, that had been obferved at Peterfburg, 
either by himfelf or others. At one o’clock at noon, 
the thermometer flood at 197. Mr. Braun had been 
employed, feveral days before this, in obferving the 
feveral degrees of cold, which different fluids would 
bear, before they were converted into ice ; partly to 
confirm thofe things which he had already laid be- 
fore the academy; and partly to make experiments 
upon liquors, which had not yet been examined ; as 
on the days between the 7th and 14th the cold was 
intenfe 
