VOL. LII.] PHILOSOPHICAL TRANSACTIONS. 545 



at 7 o'clock at 201 ; which last was the greatest degree of cold that had been 

 observed at Petersburg either by himself or others. At 1 o'clock at noon, the 

 thermometer stood at 197- Mr. Braiin had been employed several days before 

 this, in observing the several degrees of cold which different fluids would bear, 

 before they were converted into ice; partly to confirm those things which he had 

 already laid before the academy, and partly to make experiments on liquors which 

 had not yet been examined; as on the days between the 7th and 14th the cold 

 was intense enough to be between the degrees of 181 and igi. When the na- 

 tural cold was so intense as to be at 205, Professor Braun conjectured, that it 

 was of all others the most proper occasion to try the effects of artificial cold, not 

 doubting but that artificial cold would be increased in proportion as the natural 

 was more intense. Aquafortis, which was found by the thermometer to be 204 

 degrees cold, was the greatest part of it frozen, the ice having the appearance of 

 crystals of nitre, which however immediately dissolved in a small degree of heat. 

 This aquafortis which, though frozen at the sides, was liquid in the middle, was 

 poured on pounded ice, in that proportion which was directed by Fahrenheit, the 

 first person who made artificial cold with spirit of nitre. But before the Pro- 

 fessor made this experiment, he by examination found, that both the ice and 

 aquafortis were of the temperature with the air, which was then 204. On the 

 first pouring, the mercury fell 20 degrees ; this spirit was poured off, and fresh 

 put on several times; but it was possible by these means to introduce no more 

 than 30 degrees of cold: so that the mercury in the thermometer fell no lower 

 than 234. Since therefore Fahrenheit could not produce cold greater than that 

 of 40 below the cypher of his thermometer, which corresponds with 210 of 

 that employed by Professor Braun ; nor Reaumur, nor Muschenbroek, who often 

 repeated the same experiment, our author was on the point of giving up this 

 pursuit, as considering this as the greatest degree to which artificial cold could be 

 carried; thinking it sufficient honour to himself to have added 20 degrees to the 

 cold formerly known. 



But reflecting that this was not all the fruit he expected from these experi- 

 ments, he determined to pursue them ; but at the same time however to vary 

 the manner of them. By good fortune his ice was all gone, and he was com- 

 pelled to use snow in its stead, after having first tried, and found the snow of 

 the same degree of cold with the air, at this time 203. The snow, the thermo- 

 meter, and the aquafortis, being of the same temperature, he immersed the 

 thermometer in snow contained in a glass; and at first only poured a few drops 

 of the aquafortis on that part of the snow in which the thermometer was im- 

 mersed: on which he observed the mercury to subside to 26o. Elated by this 

 remarkable success, he immediately conceived hopes that these experiments might 

 be carried further: nor was he deceived in his expectations; for repeating theex- 



VOL. XI. 4 A 



