548 PHILOSOPHICAL TRANSACTIONS. [aNNO IjOl^ 



were never without cracks; moreover, it descended to 8CX), and beyond even to 

 1500 ; but in this last experiment the bulb was quite broken, so that the globe 

 of mercury, thoroughly frozen, fell out, and by its fall, of about 3 feet, the 

 globe of mercury became a little compressed, but in the former only some parts 

 of the bulb fell off'. 



Mr. Braun always found that, caeteris paribus, the more intense the natural 

 cold was, the more easy and more expeditiously these experiments succeeded. In 

 continuing them he observed, that double aquafortis was more effectual than 

 simple spirit of nitre; but that if both the aquafortis and Glauber's spirit of 

 nitre, which he sometimes also used, were well prepared, the difference was not 

 very considerable. When his aquafortis was frozen, which often happened, he 

 found the same effects from the frozen parts, when thawed, as from that part of 

 it which remained fluid in the middle of the bottle. Simple spirit of nitre, 

 though it seldom brought the mercury lower than 300 degrees, by the following 

 method he even froze mercury with it. He filled six glasses with snow, as usual, 

 and put the thermometer in one of them, pouring on it the spirit of nitre. 

 When the mercury would fall no lower in this, he in the same manner put it in 

 a 2d, then in a 3d, and so in a 4th; in which 4th immersion the mercury was 

 congealed. Another very considerable difference presented itself in pursuing 

 these inquiries, with regard to the mode of descent of the mercury. He con- 

 stantly and invariably observed, that the mercury descended at first gently, but 

 afterwards very rapidly. But the point at which this impetus begins is not easy 

 to ascertain; as in different experiments it begins very differently, sometimes at 

 about 300, at other times about 350, and even further. In the experiment 

 before-mentioned, in which the mercury fell to 800, it proceeded very regularly 

 to 600: about which point it began to descend, with very great swiftness, and 

 the bulb of the thermometer was broken. The mercury however was perfectly 

 congealed. He frequently observed another remarkable phenomenon, which 

 was, that though the spirit of nitre, the snow, and the mercury in the thermo- 

 meter, were previously reduced to the same temperature, on pouring the spirit 

 of nitre on the snow, the mercury in the thermometer rose. But as this did not 

 always happen, he carefully attended to every circumstance: from which it ap- 

 peared, that this effect arose from his pouring the aquafortis immediately on the 

 bulb of the thermometer, not previously well immersed in the snow. He also 

 observed another effect, twice only : and this was, that after the thermometer 

 had been taken out of the snow and aquafortis, the mercury continued to subside, 

 in the open air, down as far as the congealation of mercury. 



In the course of these inquires, our professor found no difference, whether he 

 made use of long or short thermometers ; whether the tubes were made of the 

 Bohemian, or the glass of Petersburg. Under the same circumstances, the same 



