170 



BELL SYSTEM TECHNICAL JOURNAL 



limiting cases of conductivities X2 and Xi corresponding to the limiting 

 depths zero and infinity. The curves showing the dependence of 

 mutual resistance on the depth and conductivities are put in the 

 simplest form in terms of the two quantities Ihjr and the conductivity 

 ratio X1/X2. Curves of this kind are shown on Fig. 6} 



2b 

 r 



50 



Fig. 6 — D.-C. mutual resistance of wires on surface of two-layer earth; 

 i?(4-B)(a-i) = R{Aa) - R{Ab) + RiBb) - R{Ba). 



^ We are indebted to our colleague Mr. L. L. Lockrow for these curves. Tables 

 from which the function R(r) can be evaluated are published in the Bureau of Mines 

 Technical Paper No. 502. 



