t 
366 Dr. blagden’s Hijlory of 
g me lin had not any other means of eftimating this but by the 
defcent of his thermometer, which could be depended upon no 
farther than to the point of mercurial congelation. Nay, it is 
not improbable, that the more violent the cold, the lefs would 
the quickfilver appear to link below that point, from the quicker 
freezing and adhefion of the fmall thread of mercury in the 
thermometrical tube. Befides, a part of the quickfilver ex- 
pofed to the air might eafily be frozen, and yet no appearance 
of fuch a change be perceived, if the mafs did not any where 
leparate or divide. And the fa£t, that it actually did freeze 
feveral times during the winter is put beyond all doubt, by the 
linking of the thermometer fo many degrees below the term at 
which that effect begins to take place. The abfurd idea, that 
quickfilver appears to congeal in confequence of water it con- 
tains, was derived, I believe, originally from a whim of Ray- 
mond lully’s. It has been the ufual refuge of thofe gentle- 
men who thought proper to deny that mercury could be made 
lolid by cold ; but is too deflitute of fupport to merit confu- 
tation . 
Profeffor braun mentions, on two different occafions *, that 
the Peterfburg Academy have in their poffeffiou fome obferva- 
tions made in Siberia, which feem to fhew the congelation of 
mercury by natural cold ; but that little credit was given to 
them, becaufe it had at other times been found to retain its 
fluidity when the cold was much more intenfe. Probably the 
obfervations here meant are M. de l’isle de la croyere’s; 
for that gentleman certainly tranfmitted papers to the Academv, 
according to which the mercury became folid as foon as it fell 
about 200° below o of his brother’s thermometer f, cor- 
* Nov. Comment. Petrop. tom. VIII. p. 363. and tom. XI. p. 269. 
f Phil. Tranfaft. vol. LI. p. 673. 
refponding 
