642 



BELL SYSTEM TECHNICAL JOURNAL 



give the best fit to the curve of mutual impedance at each frequency. 

 The range is not large, extending only from 4.2 X 10~^^ at 60 cycles to 

 2.0 X 10-13 at 1000 cycles. 



Turning to the components of the mutual impedance, however, the 

 agreement is found to be not as good. Fig. 14 shows the measured 

 values of mutual resistance and reactance at 60 cycles and at 500 cycles, 

 also the computed values, the calculations at each frequency being 

 made with the earth conductivity indicated in Table I. At 60 cycles 



0.3 



0.2 



o 0.1 

 o 



m 0.07 



CL 



10 



5 0.06 



'^ 0.03 



Z 

 < 



Q 



ID 



CL 0.02 



5 



< 



D 

 I- 

 D 

 2 0.01 



0.007 



0.005 



0.04 O --^T^- 



20 



30 



50 100 200 300 



HORIZONTAL SEPARATION IN FEET 



500 



1000 



Fig. 13 — Cross Keys tests — Carson theory. Comparison between calculated and 



measured values of mutual impedance. 



the agreement is quite good, but at 500 cycles the departure between 

 calculated and measured values is large. The measured mutual resist- 

 ances are consistently lower than those calculated, while the measured 

 mutual reactances are higher. 



As indicated by the above comparisons, a theory of the kind under 

 discussion leads to results which are in quite good quantitative agree- 

 ment with the experimental results; it is of some interest to discover 

 whether an extension of the theoretical ideas would lead to still closer 

 agreement. It was stated previously that the measurements around 



I 



