92 TRANSMISSION LINE FORMULAS 



Therefore, C is approximately 



i 



4 Iog 6 - + 4 log c 



P V 4 h* + s 2 



Taking as an average case, 



h = 360 inches (30 feet), 

 s = 120 inches (10 feet), 

 p = 0.25 inch, 



we have - = 480, 



p 



2 h , 



and = 6. 



s 



Therefore, = = 



V 4 h 2 + s 2 



Now, logio 480 = 2.681, 



while log 10 = 0.006. 



6 



Thus the capacity is changed by the nearness of the 

 ground by less than J of i%, even with the comparatively 

 wide spacing of 10 feet. 



Tests have shown that the effect of the ground in increas- 

 ing the capacity is even less than the above amount, due 

 partly to the fact that the ground is a poor conductor. 

 As the effect of the ground is so slight, it has been neglected 

 entirely in the calculations in this book. 



REFERENCE. For an alternative proof, see "A Treatise on the Theory 

 of Alternating Currents," by Alexander Russell, 1904, Vol. I. 



See also " The Calculation of Capacity Coefficients for Parallel Suspended 

 Wires," by Frank F. Fowle, Elec. World, Aug. 19, 1911. 



