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BELL SYSTEM TECHNICAL JOURNAL 



the principles of shielding were explained in an earlier paper /^ Fig. 13 

 of that paper showing the complete shielding of the balance as con- 

 structed for the measurement of direct capacity by the Colpitts 

 method. Over five million capacity and conductance measurements 

 have been made with the shielded capacity and conductance bridge 

 and in a forthcoming paper Mr. G. A. Anderegg will give details of 

 actual construction of apparatus and of methods of operation as well 

 as some actual representative results. 



Direct Admittance Measurements 



For simplicity, the preceding definitions and methods of measure- 

 ment have been described in terms of capacity, but everything may be 

 generalized, with minor changes only, for the definition and measure- 

 ment of direct admittances with their capacity and conductance 

 components. The essential apparatus change is the addition, in 

 parallel with the variable capacity standards employed, of a variable 

 conductance standard, which shifts direct conductance from one side 

 of the bridge to the other, without changing the total reactance and 

 conductance in the two sides of the bridge. This may be practically 

 realized in a great variety of ways as regards details, which it will 

 suffice to illustrate by Fig. 9, where C , C" , C" , G' , G", indicate the 



pig_ 9 — Variable Direct Conductance and Capacity Standard for Direct Admittance 



Bridge 



continuously variable capacity and conductance standards with 

 enough step-by-step extensions to secure any desired range. 



For the continuously variable conductance standard a slide wire is 

 represented, with a slider made up of two hyperbolic arcs so pro- 

 portioned that, as the slider is moved uniformly in a given oblique 

 direction, conductance is added uniformly on the left and just enough 

 of the wire is short-circuited to produce an equal conductance de- 

 crease on the other side. The arcs are portions of the hyperbola 

 xy = (L^ — 5^)74, where L, S are the total length of the wire and of 

 the portion to be traversed by the slider, and the coordinate axes are 



"The Shielded Balance, El. W., 43, 1904 (647-649). 



