278 



V. I. FOMINA 



for S determined from the first rise in the VEP curves is close to its true 

 value (when d > 2H) for both double and triple -layered cross-sections. 



When d < 2H the first rise of the asymptotic branch of the VEP curves 

 is brought about by the influence of the vertical contact and the value of S 

 determined from this rise is considerably less than the true transverse con- 

 ductivity, this divergence being the greater for the SN-1 type of VEP the 



smaller is the ratio 



H 





(-0 



^ ^ 9^ 1. 



^ 



V V V V vv] 



I 



\ \ 



\ 

 \ 

 \ 



y 



\ X w 

 X y V 

 / V \ / ■ 







/ \ ,^^ . , , E] Values of -^ 



-(a) b c — ^1 



f ; Fig. 4. a — VEP curves for a horizontally homogeneous medium; b — approximately 

 L i ^|f constructed VEP curves; c — curves of the CV-3s reference graph. 



If the values of S are determined for the terminal branches of observed 

 VEP curves, these values will be very slightly lowered and the lowering will 



decrease as the ratio — • decreases. 

 H 



The maximum increase of Qf^ in relation to {q-^ j^) is observed for separa- 

 tions in which the feed electrode intersects the surface of separation be- 

 tween the media. We may therefore establish the position of the vertical 

 contact by plotting the abscissae of the maximum increase of Qf^ in relation to 

 (Qi,k)L ^long the profile from the centre of each VEP. 



In the case of a triple -layered cross-section a considerable deviation of 

 Qi^ from (^j j^)^ at the minimum of the curve is to be observed. The greatest 

 deviation in the minimum is to be observed in VEP curves obtained when 

 d is close to the abscissa of the minimum. 



