554 BELL SYSTEM TECHNICAL JOURNAL 



For the case of X = 10 '\ the corresponding calculations give 

 Z'i2 = -lco(0.391+«'2.27) 

 with }io current in rail, and 



Z'i2 = 4a;( -0.001 -i 0.002) 



with equal and opposite current in rail. It is evident from these 

 figures that the reduction in mutual impedance, due to the current 

 in the rail, is practically independent of the ground conductivity, at 

 least at the separation specified. 



