546 PHILOSOPHICAL TRANSACTIONS. [aNNO I761. 



periment in the same simple manner, he poured on only some more aquafortis, 

 and immediately the mercury fell to 380. On which he immersed the thermo- 

 meter in another glass filled with snow, before it had lost any of this acquired 

 cold; and at length by this 3d experiment the mercury subsided to 47 degrees. 

 When he observed this enormous degree of cold he could scarcely give credit to 

 his eyes, and believed his thermometer broken. But to his infinite satisfaction, 

 on taking out his thennometer, he found it whole: though the mercury was im- 

 moveable, and continued so in the open air 12 minutes. He carried his thermo- 

 meter into a chamber, where the temperature of the air was 125 degrees; and 

 after some minutes the mercury, being restored to its fluidity, began to rise. But 

 to be certain v/hether this thermometer had received any injury, and whether it 

 would yet correspond with his thermometer which he keeps as a standard, he 

 suspended them together, and in 20 minutes the thermometers corresponded one 

 with the other. 



The thermometers which our author usually employs have a spherical bulb, 

 and their scale is divided into 1 200 parts, of which 600 are above the cypher, 

 which denotes the heat of boiling water, and 600 below that heat. A thermo- 

 meter of this construction was used in investigating the heat of boiling mercury 

 and oils. He had another thermometer, of which the scale went no lower than 

 360 degrees below the cypher, denoting the heat of boiling water. He repeated 

 the former experiment with this, and the mercury very soon descended so that 

 the whole was contained in the bulb, which however it did not quite fill. The 

 mercury in this bulb was immoveable, even though he shook the thermometer: 

 till after about a quarter of an hour, it began to ascend in the open air ; and 

 it continued to ascend till it became higher than the circumambient air seemed to 

 indicate. He was struck with this extraordinary phenomenon, and very atten- 

 tively looked at the mercury in this thermometer, and found certain air bubbles 

 interspersed with the mercury, which were not in that of the other thermometer. 

 From these, and other experiments, he was satisfied that the mercury in these 

 thermometers had been fixed and congealed by the cold. 



Hitherto our Professor had only seen the mercury fixed within the bulb of his 

 thermometers. These he was unwilling to break. He was however desirous of 

 examining the mercury in its fixed state, and therefore determined to break his 

 thermometers in the next experiments. It was several days before he got other 

 thermometers which exactly corresponded with those he had already employed. 

 When these were procured the natural cold had somewhat relented. In the 

 former experiment the thermometer stood at 204: it was now at 199. In 

 making the experiment he varied the manner a little. He first put the bulb of 

 the thermometer into a glass of snow, gently pressed down, before he poured 

 on the aquafortis: he then, in another glass, poured the aquafortis on the snow 



