318 



BELL SYSTEM TECHNICAL JOURNAL 



short-circuited terminals or by applying a formula due to G. A, 

 Campbell.^ 



Acknowledgments 



I am indebted to Mr. E. D. Sunde for a suggestion which brought 

 this theorem into focus for me; Dr. H. M. Trueblood has aided in 

 eliminating certain weak points in the proof; to Mr. R. M. Foster I 

 owe a number of improvements, aside from that mentioned in the 

 footnote, in the general spirit of the paper. My chief acknowledgment, 

 however, as indicated by the footnotes referring to his work, is to 

 Dr. G. A. Campbell ; I should like the paper to be taken as an instance 

 of the fertility and generality of the methods and results of network 

 analysis he has introduced. 



* "Direct Capacity Measurement," Bell System Technical Journal, I, 1, pp. 18-38 

 (July, 1922). The formula, given on page 34, requires modification only to the extent 

 of substituting impedances for capacities; for four terminals the direct impedance, 

 Dij, between terminals i and j is given by: 



D.i = 



2Aij ' 



where A,j is the co-factor of the element in row i, column _;" of the determinant: 



A = 



The elements of the determinant are the driving-point impedances between terminals 

 indicated by the subscripts (all other terminals open), namely, Zi2:i2, ^13:13, etc., 

 written for brevity Zn, Z13, etc. 



