152 Thermal Conductivities of Copper and Iron. [Mar. 23, 



(&.) The bar was protected from currents of air and external 

 radiation by surrounding it by a trough of sheet zinc. 



The range of temperature over which the observations extended 

 was from 15° C. to about 220° 0. 



The iron bar used was a square j-inch bar of ordinary wrought 

 iron; the copper bar was a round ^-inch bar of pure electrolytic 

 copper. The reduction of the data of experiment was effected by the 

 aid of curves drawn to a scale sufficiently large to secure the neces- 

 sary accuracy. 



In the case of the copper bar two distinct determinations, I and II, 

 were made under different conditions, and the observations reduced 

 separately. The results of these two determinations agreed within 

 rather less than If per cent. 



In order to reduce diffusivity to absolute conductivity, the densities 

 of the iron and copper were determined hydrostatically, and the varia- 

 tion of the specific heat of iron with the temperature was determined 

 by Bunsen's calorimeter with the result that the specific heat at f C 

 was found to be given by— s t = 0' 1095 (1 + 0*000080. For the specific 

 heat of copper the result given by Bede (s t = 0-0892 + 0-0000650 

 was taken. 



The final results obtained are indicated by the formulae given 

 below, and tend to show that for both copper and iron the conduc- 

 tivity decreases with rise of temperature. 



Results for Iron in G.G.S. Units. 

 Diffusivity, /c, at t° C. is given by — 



K t = 0-208(1-0-00175 0, 

 and the absolute thermal conductivity, k, by — 

 h = 0-172 (1-0-0011 0- 



Results for Oopper in G.G.8. Units. 

 Diffusivity, k, at t° C. is given by — 



I. K t = 1-370(1-0-00125 0. 

 II. Kt = 1-391 (1-0-00120 1). 



The mean of these results is taken as — 



K f = 1-38 (1-0-0012 0, 



and the value of the absolute conductivity, k, is then given by — 



h = 1-10 (1-0-00053 0- 



