1^80 



Is cletermiiied by ineasiiriiig tlie resistance of the wire at three knowil 

 teiii|X'ratiire.s. Just ais Koiii.kai'scii Iüih hIiowii tliul the effect of teiii- 

 peniliire on the conductivity of a sohition is very nearly linear, so 

 over coni|iarati\el3' ymall ranges of temperature tlie increase of 

 resistance of pnre inetals is very nearly inoporlioiial In tiie increase 

 in teniperatnre. Hence if R„ is the resistance at a .siamlarci lein|)eratiire, 

 say 0^ ('. and /'( the resistance at a teuiperature /, then we may 

 express the relation between A'„ and A', by an expression of the 

 form lit^ R„{i-\-nt), where ((=:().()()3tï6. There are distinct variations 

 in the value of k. from one element to another. 



It has now been observed that tiie tcmperatnre coëfficiënt of electric 

 condnclivity of elements is distinctly a periodic projjerty of the elements. 



By plotting the valnes of the temperature coefticients given in 

 Landolt and H('»rnstkin's tables well marked periodic curves are 

 obtained. 



~— ^ Atomic weights of elements 



Fig. 2. 



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 coeflicient of ionic mobility of elements (cf. Dhar loc. cit.). 



