T. Deighton 



•217 



simple manner the volume of soil through which the practically important 

 portion of the current flows. 



The method of attacking the problem adopted by Mascart and 

 Joubert, viz. by electrical flux and tubes of How leads to complications 

 when applied to cases other than the two selected. Since we are using 

 an alternating current, we may probably treat the matter from the 

 electrostatic point of view at any one moment, instead of considering 

 it generall}' from electrodvnamic considerations, without any serious 

 error. 



X 



Let A and B (Fig. 3) be two electrodes, supposed small, in an isotropic 

 conducting medium. We may assume that at any moment an ion at 

 any point P in the median plane PC'P' is subject to two forces, one acting 

 from A, represented in magnitude and direction by PX, and one towards 

 2?, represented in magnitude and direction by FY . These wnll be equal 

 at any point in PVP' and will have a resultant FZ which may be taken 

 to represent the force tending to move the ion at the moment which 

 will be proportional to the current, since assuming Ohms law, the mean 

 velocity of the ions resolved in the direction in which the force acts 

 varies as the force. 



Thus the current density at any point on the median plane FCF' 

 will be proportional to FZ at that point. 



