• --o Dr. blagden’s Hi/fory of 
done, had the tube been fealed, on account of the great rifk of 
fpoiling the lnftrument in breaking it open lo often. Perhaps 
the above-mentioned appearance of air bubbles, trom the di- 
vided hate of the frozen quicklilver, rqay have depended in part 
upon this expofure to the atmofphere, as well as upon the large 
iize of M. de i/isle’s original thermometers. Under thefe 
circumftances we cannot fuppofe that the inhruments were very 
exact. 
Dr. gmelin on feveral other occafions obferved, that the 
quicklilver in his thermometer looked as it air was interlperfed 
in it. Whenever this happened, it always lublided many de- 
grees below what we now underhand to be the point of mer- 
curial congelation *. The profeflor, totally at a lofs to explain 
fuch a phenomenon, imputes it fometimes to a fundamental 
fault in his inhrument, but which lie could never difeover, and 
at other times to an imaginary elfedt of the intenle cold, in 
expelling or extricating air from the pores of the quicklilver, to 
be abforbed as the cold abated. On the 9th of January, 1738, 
O. S. the mercury funk at once to — 114 0 , after having been 
fiationary two whole days at - 45 0 t- 
The laft obfervations of M. gmelin’s, in which quicklilver 
froze, were made upon his return homeward in a part of Si- 
beria, much nearer the confines of Europe. During the month 
of December, 1742, as he was palling over that branch of the 
Ural or Riphasan mountains which runs between Verchoturic 
and Soli-kamlk, about the 59th degree of N. lat. and fcarcely 
60 degrees E. of Greenwich, his thermometer funk to —41°, 
-70°, and at length into the bulb, though it was graduated 
* Reife. TheiL TI. p.634. 
f Ibid. 
to 
