432 PHILOSOPHICAL TRANSACTIONS. [ANNO 1783. 



aqua fortis and pounded ice, by means of which his thermometer was reduced to 

 — 6q°, lower, by almost 30 degrees, than it had fallen in any preceding experi- 

 ments of this nature. 



Animated by the hope that a still greater degree of cold might be produced, he 

 entered on the experiment anew ; and all his pounded ice being expended, he was 

 fortunately obliged to substitute snow in its place. With this fresh mixture he 

 had the satisfaction of seeing the mercury in his thermometer sink to — 100°, 

 and in successive experiments to — 244° and — 352°. Surprized at so unex- 

 pected an event, he drew the instrument out of the mixture, and.carefully exa- 

 mined its bulb, to see if it had received any injury ; but he found it perfectly 

 entire, and perceived a much more unexpected phenomenon, that the quicksilver 

 was fixed, and remained immoveable above 12 minutes. On repeating the same 

 experiment with another thermometer, graduated no lower than — 220°, all the 

 mercury sunk into the ball, and became solid as before, not beginning to re- 

 ascend till after a still longer interval of time. 



From these appearances the professor very justly concluded, that the quick- 

 silver in both instruments had been fixed or frozen by the cold ; but as the evi- 

 dence was not yet complete, he only ventured to propose the congelation of mer- 

 cury as a probable truth, at the next meeting of the Academy held 3 days after- 

 wards ; and in the mean time was making preparations to acquire more palpable 

 proofs of the fact. The thermometers ordered with this view were not ready till 

 the 25th of December O. S. when, in company with the celebrated ^Epinus, pro- 

 fessor of physics, he performed the experiment with similar materials, and as 

 soon as he found the quicksilver immoveable, broke the bulb of his thermome- 

 ter. Now all his doubts were removed ; he obtained a solid shining metallic 

 mass, which extended under the strokes of a pestle, in hardness rather inferior 

 to lead, and yielding a dull dead sound like that metal. Professor ^Epinus was 

 occupied at the same time in similar experiments, employing both thermometers 

 and simple tubes of a large bore ; with which last he remarked, that the quick- 

 silver in them fell sensibly on freezing, and assumed a concave surface ; also, 

 that the congealed pieces would sink in fluid mercury ; all evident proofs of its 

 great contraction. These observations were frequently repeated during the 

 winter, with some variety in the circumstances and phenomena, by Prof. Braun, 

 and many other persons. 



When the season for experiments requiring cold was past, Prof. Braun em- 

 ployed himself in drawing up a general account of such as he had then made, 

 which he communicated to the Petersburg Academy, Sept. 6, 17G0, O. S. and 

 printed soon afterwards as a separate dissertation. Five years afterwards, Prof. 

 Braun again addressed the public on the same subject, under the title ol " Sup- 

 plements" to his former dissertation. Here he declares, that since the first dis- 



