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X. On the Thermal Conductivities of Single and Mixed Solids and Liquids 

 and their Variation with Temperature. 



By CHARLES H. LEES, D.Sc., Assistant Lecturer in Physics in the Oivens College. 

 Communicated by Professor ARTHUR SCHUSTER, F.R.S. 



Received November 30, Read December 16, 1897. 



PART I. CONDUCTIVITIES AND TEMPERATURE COEFFICIENTS OF SOLIDS. 



Sketch of Method, 



IN determining thermal conductivities* of solids not very good conductors of heat, the 

 method least open to objection on theoretical grounds is the one in which a spherical 

 shell of the substance to be tested is filled with, and the exterior surrounded by, some 

 good conductor of heat, the temperatures of the conductors, inside and out, being 

 observed by means of thermometers or thermo-junctions, and maintained constant by 

 heat supplied, e.g., electrically, to the inner conductor at a measured rate (fig. 1). 

 Difficulties, mainly of a mechanical kind, present themselves, however, in the carrying 

 out of this method, which render it advisable to sacrifice some of the theoretical 



simplicity, in order to make the method more practicable. 



Fig. 3. 



Fig. 1. 



Fig. 2. 



DA.CBE 



These difficulties are overcome most easily by having the material to be tested, the 

 conductor to which heat is supplied, and the outside conductors, in the form of flat 

 circular discs of the same diameter (fig. 2), the good-conducting disc, C, to which heat 



* The extremely good account of previous methods and results given by GBAETZ in WINKELMANN'S 

 ' Handbuch der Physik,' vol. 2, pp. 273-314, renders an account of such work unnecessary here. 



5.9.98. 



