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BELL SYSTEM TECHNICAL JOURNAL 



and between them and ground (the operator being considered to be 

 at ground potential) negligibly small. 

 To make the matter more concrete, there is shown in Fig. 6 a 



Fig. 5 — Shielded bridge connected to vacuum tube oscillator and heterodyne detector 



schematic diagram with possible positions of some of the more impor- 

 tant of these admittances indicated as at Ci, C^, etc. (With some 

 exceptions, the capacitance components of these stray admittances 

 substantially determine their full effect. In the diagrams and dis- 

 cussion, therefore, the conductance component will be neglected except 

 where its effect is significantly large.) The capacitances between the 

 two ratio arm coils, Ri and i?2, and from each to ground, are shown 

 as being uniformly distributed along the length of the coils symmet- 

 rically with respect to each other. If this symmetry is perfect these 

 capacitances do not affect the bridge balance. In practise, however, 

 they will only be approximately so, with the result that the two arms 

 will be somewhat unbalanced to alternating currents, the efifect of the 

 unbalance increasing with the frequency. While the ratio arm capaci- 

 tances can be made fairly small, others such as those indicated at 

 Ci, d, Cz, and d will commonly be much larger and hence of greater 

 effect. Capacitances C\ and d are frequently comparatively large 



