in various Substances. 



415 



By these experiments it appears that the conducting 

 power of air is to that of the Torricellian vacuum as 

 9 If to 16^^ inversely, or as 1000 to 603. 



To determine whether the same law would hold good 

 when the heated thermometers, instead of being plunged 

 into freezing water, were suffered to cool in the open 

 air, I made the following experiments. The thermom- 

 eters No. I and No. 1 being again heated in boiling 

 water, as in the last experiments, I took them out of 

 the water, and suspended them in the middle of a large 

 room, where the air (which appeared to be perfectly at 

 rest, the windows and doors being all shut) was warm to 

 the 1 6th degree of Reaumur's thermometer, and the 

 times of cooling were observed as follows : — 



Here the difference in the conducting powers of air 

 and of the Torricellian vacuum appears to be nearly the 

 same as in the foregoing experiments, being as 6^-^ to 

 lo^f inversely, or as looo to 605. I could not observe 

 the time of cooling from 80'' to 70°, being at that time 

 busied in suspending the instruments. 



