m 
is determined by rneasuring the resistance of the w.ire at three knowti 
temperatures. Just as Kohlhaüsch has shown that the effect of tem- 
perature on the conductivity of a solution is very nearly linear, so 
over coinparatively small ranges of temperature the increase of 
resistance of pure rnetals is very nearly proportional to the increase 
in temperature. Hence if R 0 is the resistance af a Standard temperature, 
say 0° C. and R t the resistance at a temperature t, then we may 
express the relation between R 0 and R t by an expression of the 
form R t = R 0 (1 where « = 0.00366. There are dfstinct variations 
in the value of «, from one element to another. 
It has now been observed that the temperature coëfficiënt of eleetric 
conductivity of elements is distinctly a periodic property of fhe elements. 
By plotting the values of the temperature coefficients given in 
Landolt and Börnstkin’s tables well marked periodic curves are 
obtained. 
Elements of the same group lie very nearly on a straight line 
and occupy similar positions on the curve. 
This curve resembles the one that is obtained by plotting the 
temperature coëfficiënt of ionic mobility of elements (of. Dhar loc. eik). 
