Temperature coëfficiënt of conductivity of kcal. 
The change of thermai eonduction witli temperature was noticed 
by Forbes [Pliil. Trans. Roy. Soc. Edin. Vol. 33 (1862), p. 133]. 
Generally there is a decrease of conductivity with increase of tem- 
perature and as a similar decrease takes place in the electric con- 
ductivity of metals, it was supposed by Forbes that in general the 
thermai conductivities of metals like their electric, diminished with 
rise of temperature. 
W iEDEMANN and Franz [Pogg. Ann. 89, (1853), 497] appeared to 
show that there is sorne connection bet ween conducting power for 
heat and for electricity. 
For the metals were found not only to follow the same order for 
the two conductivities but in many cases the numbers bore nearly 
the same ratio to each other. 
More recent work has confirmed this supposition. The following 
are some of the valnes for metals of the ratio of the thermai con- 
ductivity and the electrical conductivity or k'c at 18° C. as determ- 
ined by Jaeger and Diesselhorst [Phys. Tech. Reichsanstalt Wiss. 
Abh. 3, (1900)], together with the themperature coëfficiënt of the ratio. 
ïo-io A 
C 
Temp. coeff. 
Cu 
6.65 j 
0.0039 
Ag 
6.86 
0.0037 
Au 
7.09 
0.C037 
Zn 
6.72 
0.0038 
Cd 
7.06 
0.0037 
Pb 
7.15 
0.0040 
Sn 
7.35 
0.0034 
The electron theory of eonduction for heat and for electricity gives 
an explanation of the connection between the two quantities. 
According to that theory the ratio should be proportional to the 
absolute temperature i. e. should have a temp. coeff. 0.00367 and at 
0° C., its value should be 6.3 X 10 10 . The temperature coëfficiënt 
of heat conductivity has been determined by Lorenz [Wied. Ann. 
13, 422, 582 (1881)], Stewart [Proc. Roy. Soc. 53, 151 (1893), 
Lees (Phil. Trans. A. 183, 481 (1892)] etc. 
But the data of only a few elements are available, so it is im- 
possible to obtain a curve with the insufficiënt data, which at present 
