444 H. A. Rowland — Electrical Measurement. 







Method 20. 









R'^-rR^O 





M 

 L 



R" M 



-B, + R„'L' ' 

 any value. 



w r,/ l w 



"R"(R, + R„) S ' L' ~R' + R" 



L>M; 1/ 



In case of a standard inductance, M and L are known, espe- 

 cially when the wires are twisted. 



The method can then be used for determining any other in- 

 ductance, L', and is very convenient for the purpose. 



R /; and R, + R /7 are first calculated from the inductance 

 standard. The "Wheatstone bridge is then adjusted and W 

 varied until a balance is obtained. This balance is independent 

 of the current period, as also in the next two methods. 







Method 21. 









RR // -R"R / = 





1 



R+R, 



" R, 



L' (R' + R,) 2 L' 

 M 7-R, ' I ' 



_R'+R y 



r 



1>M. 



This is Niven's method adapted to alternating currents. See 

 remarks to method 20. 



Methods 20 and 21 are specially useful when one wishes to 

 set up an apparatus for measuring self induction, as the resist- 

 ances R\ R /; , R /5 R /y can be adjusted once for all in case of a 

 given inductance standard and only W or r need be varied 

 afterwards. 



Method 22. 



This is Carey Foster's method adapted to alternating cur- 

 rents and changed by making R" finite instead of zero. 



The ratio of R' + R ; to R 7 is computed from the known 

 value of the induction standard. R" is then adjusted and C 

 obtained. In general the adjustment can be obtained by 

 changing R / and R". The adjustment is independent of the 

 current period. 



Method 23. 



tfmlj' = rU t + R[r -f R' + RJ 



= r + R' + R, 



m 



