the Congelation of Shuickfilver. ^62 
fuftei the fra ok e to afcend as it iffued from the chimnies. 
“ Birds feli down out of the air as if dead, and froze imme- 
diately, unlels they were brought into a warm room* 
“ Whenever the door was opened, a fog fuddenly formed round it. 
“ During the day, fhort as it was, parhelia and haloes round the 
“ lun were frequently feen, and in the night mock moons and 
“ haloes about the moon. Finally, our thermometer, not fub- 
<c jecl to the fame deception as the fenfes, left us no doubt of 
“ the exceffive cold ; for the quickfilver in it was reduced” [on 
the 5th of Jan. O. S.] “ to - 120° of Fahrenheit’s fcale, 
lower than it had ever hitherto been obferved in nature.” 
Thus far Profefior gmelin. Little did he conceive that, 
though Ins thermometer was not lubject to the fame deception 
as the lenfes, it lay expofed to another lource of error which 
defeated all his conclufions : for as foon as the cold became luf- 
ficiently great to produce any congelation of the quickfilver, it 
ceafed to be a meafure of the temperature ; in head, therefore, 
of 120 0 below o, the cold mold probably did not exceed the 
point of mercurial congelation, or - 39 0 , but by a very few’ de- 
grees, the great defcent of the quickfilver, as it depended upon 
its contraction in the act of freezing, only affording a proof 
that it had really luffered this change. 
VV e mult here ouferve, that Dr. gmelin’s thermometers 
were conftru died by M. Joseph Nicholas de l’isle, brother 
to the gentleman who went upon this expedition, on the prin- 
ciple invented bv himfelf, and which hill bears his name. At 
prefent fuch thermometers are always, made bv determinimr 
• J J £y. 
two fixed points, of which tire uppermoft, or that of boiling- 
water, is afiumed as o, and the lowermoft, or the point of 
melting ice, as 150% the fcale being counted downward ; but 
in their original conftruftion, when the utility of fixed points. 
was. 
