Thermal Conductivity during the Fusion of Metals, 547 



Under the supposition that the lateral loss of heat is 

 negligibly small, we have 



Q=0i + g,=K'8(t 1 + * 1 ); 



^=%lu> ^ =Q M^ 



In an actual case, £3 is slightly less than q 2 , and g^less than 

 q 3 hy nearly the same amount ; hence we may put as the 

 first approximation 



r i 1 f 2 



Since the distances between two junctions of each of the 

 three differential thermocouples «6, <-cL a'b' are equal to 

 each other. t it t 2 , and t 4 in the above relation may be re- 

 placed bv the corresponding deflexions of the galvanometer 

 o\, S 2 , and £ 4 respectively. Moreover, if the distance 

 between two junctions of the differential thermocouple ef 

 and its difference of temperature be respectively denoted by 

 s and Ar, we have 



t- M 



S 



and therefore 



K 1 Qs(8 2 + 8 4 ) 

 2SA*(S 1 + S 2 )' 



In the above relation the determination of the quantity Q 

 is somewhat uncertain. For the heat generated per unit of 

 time in the heating-coil F is accurately known, but a part 

 of it is lost by lateral conduction before flowing into the 

 specimen. It is very difficult to ascertain exactly how much 

 of the heat is thus lost. Hence the absolute values of 

 thermal conductivity obtained by the present method may 

 be somewhat uncertain ; but if we assume that for all 

 temperatures, the above loss is always the same traction of 

 the total heat generated, the relative values of the con- 

 ductivity are perfectly correct. Hence in the present 

 investigation only the relative measurements were made. 



The observation was conducted in the following way : — 

 A constant electric current of about 21 amperes was passed 

 through the heating-coil. After an interval of about one 

 hour, when an approximate stationary state was attained, 

 the temperature of the specimen was first observed, then the 

 readings of the galvanometer corresponding to the junctions 



