400 Mr. R. T. Glazcbrook on the Molecular 



Let P be the electromotive force at the point parallel to axis 



of x } and let us call — — the resistance of the medium ; then 



Ohm's law gives 



us 



and we get 



P ^ 





p _ d¥ df 

 dt dx 



Similarly 



da dyjr 

 ^~ dt dy' 





dR dy/r 



avjc ay i 



(8) 



dt dz 



and these agree exactly with Maxwell (598, B), taking the 

 case when the conductor is at rest. 



Again, substituting in (6) for/ its value from (5), we get, 



if 



dF dG dR 



dx dy dz 



dt dx 2p dx p 3 p dx 



Substituting and reducing, 



dF djr t 1 



dt + dx 



(**+£)=* 



(9) 



(10) 



47T/xC 

 &C, 



C being the conductivity of the medium. And these, again, 

 agree with Maxwell (783), supposing the medium we con- 

 sider is a conductor, so that the quantity K in his expressions 

 is equal to zero. 



By differentiating we have 



dJ_ 



dt 



-VV=°- 



From (8) ~ is the electromotive force at the point parallel 



to x, so far as it does not depend on electromagnetic action, 

 arising, that is, from the action of the free electricity in the 

 medium. And since we consider a conductor, we have 



••• S =°- 

 at 



