CONDUCTIVITIES OF IRON AND COPPER. 
587 
T. Tct = 1-113 - -00112^ 1-11.3 (1 — -OOU) 
IL ht — 1-130 - ”00112^ = 1-130 (1 - -OOl^). 
The mean value of these results gives 
kt = 1*12 (i - -OOlt). 
Determination of Density and Value of {sd), the Thermal Capacity of Unit Volume of 
Copper. 
The density of the copper was found to be 8-907 at 0° C. Taking this as 8-9, we 
may take the density of copper at f C., as given by 8-9 (1 — -000056^). 
The specific heat of copper at f C. is given by Bede* as -0892 + -000065^. This 
result may be expressed as -0892 (1 + -00073i), hence the value of [sd) at f C. is 
8-9 (1 - -0000560 X -0892 (1 + *000730, 
or 
-794 (1 + -0006740. 
Value of K, the Diffusivity of Copper, in Absolute C.G.S. Units. 
From the results obtained above the value of k at C will be given by 
Kt = {Klsd)t = 1-12 (1 - -OOlO ^ -794 (1 + -0006740. 
That is, 
Kt = 1-41 (1 - -OOU) (1 - -0006740, 
or, 
Kt = 1-41 (1 — -0017^ + -0000007^0- 
This result is probably represented with sufficient accuracy by the formula 
/ct = 1-41 (1 - -00174). 
It AAoll be seen that the results of the experiments here described go to show that 
for both iron and copper the conductivity decreases with rise of temperature. 
* [Recent determinations of tte specific heat of pure copper (probably identical with that used in 
these experiments) give the specific beat at 100° C. as ‘0928. Bride’s formula gives '0957, a value about 
3 per cent, too high. The determinations here referred to were made by J. Jolt, Esq, F.R.S., with bis 
steam calorimeter, and were kindly communicated to me by Mr. James H. Gray, M,A., B.Sc., Glasgow 
University.—12.4.93.] 
4 F 2 
