466 THE EFFECT OF TEMPERATURE ON THE THERMAL CONDUCTIVITIES, ETC. 



Remarks on the Preceding Results. 



The agreement of the results obtained at the higher temperatures with results 

 previously known has been shown in the notes to the tables to be very good in the 

 cases of paraffin wax, ice, and glycerine, but not all that could be desired in the cases 

 of naphthaline and ft naphthol. It should, however, not be overlooked that crystals 

 in general possess different conductivities in different directions, and that considerable 

 differences may be caused by the different methods in which the crystals in a cooling 

 mass, e.g., of naphthaline, arrange themselves with respect to those directions which 

 are ultimately to become the lines of flow of heat. 



Whatever the arrangement of the crystals in^any particular sample of a substance, 

 if that sample is tested at different temperatures, the results express the variation 

 with temperature of the thermal conductivity of that sample in some fixed direction, 

 and enable the question as to whether conductivity increases or decreases with 

 increase of temperature to be answered. 



The curves expressing the results of the experiments show that there is a marked 

 increase of the thermal conductivities of ice, naphthaline, aniline, and nitrophenol as 

 the temperature is decreased, a slight increase (in terms of the hydrogen scale only) 

 in the cases of ft naphthol and diphenylamine, and possibly of paraffin wax, and an 

 increase to a maximum at 80 with a decrease beyond in the case of glycerine. 



These facts point to the conclusion that the effect of temperature on the thermal 

 conductivities of electrical insulators is mainly, if not entirely, determined by the 

 physical and chemical nature of each substance, and cannot be stated for electrical 

 insulators generally, although there seems on the average to be a tendency towards 

 higher conductivities at lower temperatures. 



In two cases, i.e., those of ice and aniline, the thermal conductivity of the solid is 

 much greater than that of the liquid ; while in another, glycerine, the conductivities 

 in the two states near the melting-point are almost identical. 



