VOL. LXXIII.J PHILOSOPHICAL TRANSACTIONS. 441 



down out of the air as if dead, and froze immediately, unless they were brought 

 into a warm room. Whenever the door was opened, a fog suddenly formed 

 round it. During the day, short as it was, parhelia and haloes round the sun 

 were frequently seen, and in the night mock moons and haloes about the moon. 

 Finally, our thermometer, not subject to the same deception as the senses, left 

 us no doubt of the excessive cold ; for the quicksilver in it was reduced [on the 

 5th of Jan. O. S.] to — 120° of Fahrenheit's scale ; lower than it had ever 

 hitherto been observed in nature. Little did Mr. G. conceive that, though his 

 thermometer was not subject to the same deception as the senses, it was yet 

 subject to another source of error which defeated all his conclusions : for as soon 

 as the cold became sufficiently great to produce any congelation of the quick- 

 silver, it ceased to be a measure of the temperature ; instead therefore of 120° 

 below 0, the cold most probably did not exceed the point of mercurial congela- 

 tion, or — ; 39°, but by a very few degrees, the great descent of the quicksilver, 

 as it depended on its contraction in the act of freezing, only affording a proof that 

 it had really suffered this change. 



The next instance of mercurial congelation to be found in Gmelin's journal 

 exhibits a very striking example of the force of prejudice. It happened at Yakutsk, 

 lat. 62° N. and long. 130° E. in the winter of 1736 and 1737, and is thus related 

 by the professor. " This winter was unusually mild here, yet we suffered at 

 times very severe cold, being frost-bitten in a sledge within the space of 6 mi- 

 nutes, notwithstanding all our precautions. One day also, a certain person, who 

 has some reputation in the learned world on account of his observations in natural 

 philosophy, informed me by a note, that the quicksilver in his barometer was 

 frozen. I hastened immediately to his house, to see this hitherto incredible 

 wonder of nature. Not feeling by the way the same effects of cold as I had ex- 

 perienced at other times in less distances, I began, before my arrival, to enter- 

 tain suspicions about the congelation of his quicksilver. In fact, I saw that it 

 did not continue in one column, but was divided in different places as into little 

 cylinders which appeared frozen, and in some of these divisions between the 

 quicksilver I perceived an appearance like frozen moisture. It immediately oc- 

 curred to me, that the mercury might have been cleaned with vinegar and salt, 

 and not sufficiently dried. The person acknowledged it had been purified in that 

 manner. This same quicksilver, taken out of the barometer and well-dried, 

 would not freeze again, though exposed to a much greater degree of cold, as 

 shown by the thermometer. We were assured by the inhabitants, that the 

 severest cold of this winter did not approach what they had suffered in other 

 years ; and yet the thermometer fell several times to 72° below O of Fahrenheit's 

 scale, which would be thought, in Germany at least, a very intense frost." The 

 gentleman to whose observation Dr. Gmelin here shows so little respect, says 



vol. xv. 3 L 



