114 PHILOSOPHICAL TRANSACTIONS. [aNNO I786. 



the two instruments made use of that they should be perfectly alike, yet they 

 might in reality be so far different, either in shape or size, as to occasion a very 

 sensible error in the result of the experiments ; to remove these doubts he made 

 other experiments, with the construction of the instruments varied ; and still 

 with the same results. 



It having been my intention from the beginning to examine the conducting 

 powers of the artificial airs or gasses, the thermometer N° 3 was constructed with 

 a view to those experiments ; and having now provided myself with a stock of 

 those different kinds of airs, I began with fixed air, with which, by means of 

 water, I filled the globe and cylinder containing the thermometer ; and stopping 

 up the two holes in the great stopple closing the end of the cylinder, I exposed 

 the instrument in freezing water till the mercury in the inclosed thermometer 

 had descended to 0^ ; when, taking it out of the freezing water, I plunged it in- 

 to a large vessel of boiling water, and prepared myself to observe the times of 

 heating, as in the former cases ; but an accident happened, which suddenly put a 

 stop to the experiment. Immediately on plunging the instrument into the boil- 

 ing water, the mercury began to rise in the thermometer with such uncommon 

 celerity, that it had passed the first division on the tube, which marked the 10th 

 degree, according to Reaumur's scale, before I was aware of its being yet in mo- 

 tion ; 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 chimney with a great explosion, and the thermometer, which being 

 cemented to it by its tube, was taken along with it, and 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 air saturated with water. 



For this experiment I provided myself with a new thermometer N° 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 

 terminated at one end by a globe 14- inch in diameter. In the centre 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 long, received 

 the end of the tube of the thermometer into a hole bored through its centre or 



