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XII. Effects of Temperature and Pressure on the Thermal Conriuctiritie* of 

 Solids. Part T. The Effect of Temperature on the Thermal Ci 

 of some Elertrical Insulator*. 



liy CHARLES H. LEES, D.Sc. 

 Inf ARTHUR SnirsTKi:, 



Received November 29, 1904, Read December 15, 1904. 



INTRODUCTION. 



THE question as to whether the thermal conductivity of a solid varies with tempera- 

 ture is an important one, and a considerable amount of attention has been bestowed 

 on it. The experimental work which has l)een done cannot, however, be said to 

 have led to a definite conclusion, owing to the discrepancies tetween the results 

 obtained by different olwervers. Although the more recent of these results have 

 produced a general disbelief of the idea which prevailed a few years ago, that the 

 thermal conductivity of a solid would increase as the temj>erature increased, yet they 

 do not justify the opposite conclusion l>eing drawn. 



Many of the discrepancies may no doubt be put down to the use of materials 

 differing in purity or physical condition, although the effect of a small amount of 

 impurity seems, from experiments which have been made on mixtures, to Ije much 

 less in the case of thermal than it is in the case of electrical conductivity. 



If the thermal conductivity does change with change of temperature, it is of 

 importance that the differences of temperature used in the experimental work should 

 l>e comparatively small, and that the mean temperature of the substance under test 

 should l>e ascertained. Failure to comply with these requirements renders it unwise 

 to take into account many of the older exj>eriment8 in estimating the evidence for 

 and against change of conductivity with temperature. 



A further cause of disagreement may l>e found in the experimental methods used 

 either not being amenable to mathematical treatment, or the treatment not having 

 accurately expressed the experimental conditions. 



Under these circumstances it seemed to me advisable to make a series of deter- 

 minations of the thermal conductivities of a few representative substances under 



VOL. cciv. A 383. 3 K 31.8.05 



