i7i varioiLS 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, suff^ering 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 0°, 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 



