ELECTRICAL MEASUREMENT BY ALTERNATING CURRENTS 305 



The correction, therefore, nearly vanishes for two twisted wires in a 

 coil where U M = and C is taken out. 



Method 10. 



c c 



\_R,R" - R lt R'-\ \rlR' + R" + R,+ fl,,] + ( + R) (R" + ) \ 



This can be used in the same manner as 9 to which it readily reduces. 

 But it is more general and always gives zero deflection when adjusted, 

 however M is connected. To throw out (7 make it oo . 



Method 11. 

 L M_ 



c 

 L + M 



- M} (L- M} 



c 



For the upper equation the last term may be made small and the 

 method may be useful for determining L M when c is known. 

 Me'thod 8, however, is better for this. 



Method 12. 



L' = R+R' 

 I ~ r 



Should the circuits R and r also have small self inductances, L and I, 

 we can use the exact equation 



rR 



When L' and Z are approximately known, we can write the following, 

 using the approximate value on the right side of the equation 

 L'_ R+R'T, Lr L r , VLl , 



I ' r 

 Taking out L' and putting a condenser, (7, in R we have 



For a condenser, R can be small or zero. 

 20 



