in various Substances. 441 



periments made upon different days will have different 

 results, and of course, strictly speaking, cannot be com- 

 pared together; but the temperature of pounded ice 

 and water is ever the same, and of course the results of 

 the experiments are uniform. 



In heating the thermometer, I did not in general bring 

 it to the temperature of the boiling water, as this tem- 

 perature, as I have just observed, is variable; but when 

 the mercury had attained the 75 of its' scale, I immedi- 

 ately took it out of the boiling water, and plunged it in- 

 to the ice and water ; or, which I take to be still more 

 accurate, suffering the mercury to rise a degree or two 

 above 75, and then taking it out of the boiling water, I 

 held it over the vessel containing the pounded ice and 

 water, ready to plunge it into that mixture the moment 

 the mercury, descending, passes the 75. 



Having a watch at my ear which beat half seconds 

 (which I counted), I noted the time of the passage of 

 the mercury over the divisions of the thermometer, 

 marking 70 and every tenth degree from it, descending 

 to 10 of the scale. I continued the cooling to o, or 

 the temperature of the ice and water, in very few in- 

 stances, as this took up much time, and was attended 

 with no particular advantage, the determination of the 

 times taken up in cooling 60 degrees of Reaumur's 

 scale that is to say, from 70 to 10 being quite suffi- 

 cient to ascertain the conducting power of any body 

 whatever. 



During the time of cooling in ice and water, the 

 thermometer was constantly moved about in this mix- 

 ture from one place to another ; and there was always so 

 much pounded ice mixed with the water that the ice ap- 

 peared above the surface of the water, the vessel, which 



