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BELL SYSTEM TECHNICAL JOURNAL 



image distance has been shown above to be of the order of thejength 

 of the conductors. To illustrate this fact, in Fig. 8 four dotted curves 

 have been added to the curve of Fig. 5 showing the mutual induct- 

 ances of the two parallel grounded conductors when they are in the 



j i ' i i 1 1 1 



j i i i i 1 1 1 



?//;.://///m'/////////. 



apt 

 o.oi 



i i i i i i 1 1 



J 1 i i i 1 1 1 



Fig. 8 — Mutual Neumann integral between grounded filaments forming opposite 



sides of a rectangle with unit separation, on the surface of the earth (from Fig. 5) 



and between the same filaments when one or both of the filaments is raised above 



or depressed below the surface of the earth as shown by the insert 



four positions indicated by iVi, iV 2 , N 3 and Ni on the insert of Fig. 8, 

 calculated by formulas (28)-(30) of the appendix, which are special 

 cases of (35), (36), (39) and (40). When the conductors are long, the 

 relative change in the mutual inductance is small. Depressing the 



