of Electricity through Metals. 195 



put it equal toTkl. Thus, if X is the external electric force 



and _ M(Xp+kT) 



w 

 or w X 



BE*"" T* 



This relation between 1 and a is represenl i d graphically 

 by a straight line, and the value of I corresponding to any 

 value of Xo can be determined In' finding where this line 

 intersects the curve 



I=NMF(#). 



The effects corresponding to any finite value of I will U 

 the same as if I doublets per unit volume pointed in the 

 direction of the electric force, while the axes of the resi were 

 uniformly distributed in nil directions ; and we may picture 

 the substance as containing a number of chains of polarized 

 atoms whose doubletsall point, in the direction of the electric 

 force as in fig. 2. 



o© e© e© & it r v 



<r 



So far as we have gone there bas been nothing to differ- 

 entiate between insulators and metals ; in each of these the 

 doublets set under the electric field and give to the substance 

 specific inductive capacity, the value of which is proportional 



lo the value of I when X,, ifl unit v. 



It will be uoticed thai the electrons in til'- atoms of the 

 substance will be under the influence of {'<,!•<■■ <1 by 



ueighbouring polarized atoms. Thus in ti - presented 



in the figure these forces tend t<> make the electrons in A 

 move towards B, and those in B to (' and so on. On this 

 theory the peculiarity of metals is that electrons, not 

 necessarily nor probably those in the doublets, are very easily 

 abstracted by these forces from the atoms when these are 

 crowded together. Thus we may suppose thai under these 

 forcos an electron is torn from A and goes :<> B, another 

 from B going to 0, and so on along the line, — the electrons 

 passing along the chain of atoms like a company in single 

 file passing over a series of stepping-stones. Let as suppose 



o 2 



