6 L. J. PETERS AND J. BARDEEN 

If vn 1 =) Re-8ur (9) 
i mae F + = Oa 
where 
B =r. 
When 2/7 is large, the integral becomes 
if 
2moir 
ae 


i ” Jo(8)d8 = r<a (10) 
TO ir 
which is the normal potential for a homogeneous medium of conductivity a1. 
When a/7 is small, the exponentials are approximately equal to unity, and the 
potential becomes 
I 1-k I 
2roir 1 ak k oe Qroor 


Vi= r> a. (11) 
This is the normal potential for a homogeneous medium of conductivity a2. 
EARTH OF CONDUCTIVITY _4 2 
ur2ito-rv/I 
"NORMAL POTENTIAL FOR EARTH OF CONDUCTIVITY Bor 

rfa 
Fig. 3. Theoretical potential curves for two conducting layers. 
This example illustrates a fundamental property of this type of prospect- 
ing. The potentials at points further and further from the electrode are in- 
150 
