424 Of the P ropagation of Heat 



than in common air ; but not satisfied to rest my in- 

 quiries here, I took the first opportunity that offered, and 

 set myself to repeat the experiments which I had before 

 made with the instruments No. i and No. 2. I plunged 

 this instrument into a mixture of pounded ice and water, 

 where I let it remain till the mercury in the inclosed 

 thermometer had descended to 0°; when, taking it out 

 of this cold mixture, I plunged it suddenly into a vessel 

 of boiling water, and prepared myself to observe the as- 

 cent of the mercury in the inclosed thermometer, as in 

 the foregoing experiments ; but unfortunately the mo- 

 ment the end of the glass body touched the boiling 

 water, it cracked with the Heat at the point where it 

 had been hermetically sealed, and the water rushing into 

 the body spoiled the experiment: and I have not since 

 had an opportunity of providing myself with another 

 instrument to repeat it. 



It having been my intention from the beginning to 

 examine the conducting powers of the artificial airs or 

 gases, the thermometer No. 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 clos- 

 ing the end of the cylinder, I exposed the instrument in 

 freezing water till the mercury in the inclosed thermom- 

 eter had descended to 0° ; when, taking it out of the 

 freezing water, I plunged it into a large vessel of boiling 

 water, and prepared myself to observe the times of heat- 

 ing, as in the former cases ; but an accident happened, 

 which suddenly put a stop to the experiment. Immedi- 

 ately upon plunging the instrument into the boiling 



