on the Subject of Heat. 199 



tomed to use for clothing. The instrument which I 

 used in these experiments, and which I called ^passage- 

 thermometer^ differs but slightly from that described 

 above. I fixed the bulb of a mercurial thermometer 

 half an inch in diameter within a glass glpbe an inch 

 and a half in diameter, with a long cylindrical neck ; 

 I then filled the space between the outer surface of the 

 thermometer bulb and the inner surface of the glass 

 globe with a certain quantity of the substance whose 

 conducting power was to be determined, and allowed 

 the instrument to cool in a mixture of pounded ice and 

 water. As soon as the thermometer showed me that 

 its bulb (which was in the middle of the glass globe) 

 had acquired and retained constantly the temperature 

 of the cooling mixture (that is, o of Reaumur's scale), 

 I took the apparatus out of this cold mixture, plunged 

 it into boiling water, observed the times required for 

 the heat to pass into the bulb of the thermometer 

 through the surrounding substance, and inserted them 

 in a table, noting every ten degrees as accurately as 

 possible. 



Since the water into which I plunged my appara- 

 tus was kept constantly boiling, it is evident that the 

 outside of the instrument, that is, the outer surface of 

 the globe, was always of the same temperature ; hence 

 the more or less rapid heating of the thermometer 

 bulb within the globe indicated the resistance which 

 the covering of the bulb offered to the passage of 

 the heat from the inner surface of the globe to the bulb 

 of the thermometer. 



In this way I made several experiments; but as I 

 was inconvenienced by the steam rising from the boil- 

 ing water, and so experienced difficulty in noting the 



