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BELL SYSTEM TECHNICAL JOURNAL 



Since the sensitivity of the bridge network should be a maximum 

 when the unbalance is small, i.e., when a balance is about to be 

 secured, this condition is the one with which the sensitivity calculation 

 is concerned. The capacitance Xb of the bridge network was assumed 

 to vary 10% from the condition of balance and the galvanometer 



Fig. 11 — The variation of the angle between the bridge voltage and the un- 

 balance current for the reactance component and resistance component of non- 

 loaded 19-gauge cable in lengths varying from zero to sixty miles. The curves 

 represent characteristics for frequencies of four, eight and twenty cycles. 



unbalance current, is, was then calculated from equation (3) for each 

 length of line at each frequency. Both the magnitude and phase 

 angle were found. Similarly the resistance r was assumed to vary 

 10% from the condition of balance, Xb remaining balanced, and 

 another set of galvanometer unbalance currents was determined. 

 Such calculations are particularly tedious, involving successive addi- 

 tions and subtractions, multiplications and divisions of complex 

 quantities. The results of these calculations are shown in Figs. 11, 

 12 and 13. Fig. 11 represents the variation in phase angle of i^ with 



