in various Substances. 425 



water, the mercury began to rise in the thermometer 

 with such uncommon celerity that it had passed the 

 first division upon the tube (which marked the loth de- 

 gree, according to Reaumur's scale) before I was aware 

 of its being yet in motion; and having thus missed the 

 opportunity of observing the time elapsed when the 

 mercury arrived at that point, I was preparing to observe 

 its passage of the next, when all of a sudden the stopple 

 closing the end of the cylinder was blown up the chim- 

 ney with a great explosion, and the thermometer, which, 

 being cemented to it by its tube, was taken along with 

 it, was broken to pieces, and destroyed in its fall. 



This unfortunate experiment, though it put a stop for 

 the time to the inquiries proposed, opened the way to 

 other researches not less interesting. Suspecting that 

 the explosion was occasioned by the rarefaction of the 

 water which remained attached to the inside of the globe 

 and cylinder after the operation of filling them with 

 fixed air, and thinking it more than probable that the 

 uncommon celerity with which the mercury rose in the 

 thermometer was principally owing to the same cause, I 

 was led to examine the conducting power of moist air, or 

 airsaturated with water. 



For this experiment I provided myself with a new 

 thermometer No. 4, the bulb of which, being of the 

 same form as those already described (viz. globular), was 

 also of the same size, or half an inch in diameter. To 

 receive this thermometer a glass cylinder was provided, 

 8 lines in diameter, and about 14 inches long, and ter- 

 minated at one end by a globe i-|- inch in diameter. In 

 the center of this globe the bulb of the thermometer 

 was confined, by means of the stopple which closed the 

 end of the cylinder ; which stopple, being near 2 inches 



