AA1 PHILOSOPHICAL TRANSACTIONS. [ANNO 1783. 



Dr. B., seems to have been no other than one of his associates in the commission, 

 M. de L'Isle de la Croyere, probably the first person on earth who saw quick- 

 silver reduced to a solid form by cold, and ventured to credit the testimony of 

 his senses. As to the objection, that the same mercury did not freeze with a 

 greater degree of cold, it is of no avail; for M. Gmelin had not any other means 

 of estimating this but by the descent of his thermometer, which could not be 

 depended on farther than to the point of mercurial congelation. The absurd 

 idea, that quicksilver appears to congeal in consequence of water it contains, 

 was derived, it seems, originally from a whim of Raymond Lully's. It has been 

 the usual refuge of those gentlemen who thought proper to deny that mercury 

 could be made solid by cold; but it is too destitute of support to merit confu- 

 tation. 



Another set of observations, in the course of which the mercury frequently 

 congealed, were made by Dr. Gmelin at Kirenga fort, lat. 57i n. long. 108 e. 

 in the winter of 1737 and 1738. His thermometer on different days stood at 

 — 108°, — 86°, — 100°, — 113°, and several intermediate degrees. Some ex- 

 traordinary appearances, which very much perplexed him in these observations, 

 not only admit of a ready solution from Mr. Hutchins's determination of the 

 freezing point of quicksilver, but also confirm it with wonderful precision. 

 Another instance occurred at Kirenga fort a few days afterwards, explicable in the 

 same manner. On Dec. 2Q, o. s., Dr. Gmelin found his thermometer, which 

 had been standing at — 40° early in the morning, sunk down to — 100° at 4 in 

 the afternoon. He subjoins the following remark. " I observed some air in the 

 thermometer, separating the quicksilver for the space of about 6 degrees. Yester- 

 day evening I took notice of a similar appearance, except that the air was not then 

 collected into one place, but lay scattered in several. I considered it as an acci- 

 dental fault in the instrument, and attempted to expel it by means of a steel wire, 

 but could not bear the cold. In the barometer also some very small air-bubbles 

 were perceived. Next morning only a very few minute air-bubbles remained in the 

 quicksilver of the thermometer, which had then risen to — 44°, and not the least 

 vestige of them was to be seen in the barometer." It cannot be doubted, but 

 these appearances proceeded from a congelation of the mercury in Gmelin's in- 

 struments. On several other occasions Dr. G. observed that the quicksilver in 

 his thermometer looked as if air was interspersed in it. Whenever this hap- 

 pened, it always subsided many degrees below what we now understand to be the 

 point of mercurial congelation. The professor, totally at a loss to explain such 

 a phenomenon, imputes it sometimes to a fundamental fault in his instrument, 

 but which he could never discover, and at other times to an imaginary effect of 

 the intense cold, in expelling or extricating air from the pores of the quicksilver, 

 to be absorbed as the cold abated. On the 9th of January 1738, o. s., the mer- 



