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BELL SYSTEM TECHNICAL JOURNAL 



wires reduces the inductance; the curves show that in the case of 

 Ni the inductance passes through zero and is reversed in sign when 

 5 = 1.560. 



When the departure of the circuits from the earth's surface may be 

 neglected, all terms, but the first, on the right-hand side of formulas 

 (17)— (19) drop out, and each reduces to the simple, fundamental 

 grounded circuit formula (4). 



9. Comparison of Theoretical Results with Measurements 

 at 25 and 60 Cycles 



Fig. 9 shows, by means of arrows, the impedances which must be 

 added to each of a large group of measured 25-cycle mutual im- 

 pedances to obtain the results calculated by means of the preceding 

 formulas, on the assumption that the earth has a uniform resistivity 



Fig. 1C — Location of test circuits, the arrow-heads showing the positive directions 

 in the conductors. When circuits are combined in series, with the removal of 

 intermediate grounds, the new circuit designation is shown by the equations. The 

 test circuits >, m and / are large metallic loops from which all grounds have been 

 removed. The horizontal and vertical displacements of the conductor by a few feet, 

 which render the indicated equalities for Jf ^and n only approximate, were allowed 

 for in determining the calculated results for Fig. 9. The grounds of the capital 

 letter circuits were isolated sections of single track about one mile in length; the 

 midpoint of the section is shown as the effective ground but it may have actually- 

 been displaced and have varied with the moisture of the road-bed 



