II. A. Rowland — Electrical Measurement. 439 



Method 9. 

 WM-:*=B,[a» + B I+ *p] • 



Making R" = oo and r -f- R' = r we have 



-6 a L'M+ ^- or & 2 L'M- X = R (r + R,) 



c (J ' 



Taking two observations we can eliminate 5 2 I/M and we 

 have 



M 

 J=»K,{r-(r)'} 



Knowing I/M we can find C'. Throwing out C (i. e., mak- 

 ing it oo ) we can find 6 a L'M in absolute measure : then put in 

 C and find its value as above. 



To correct for self induction in R„ we have for case R 7/ = oo, 

 the exact equation 



6 2 L'M- ^ = R,(r + R,) + 5 a [L' + L ,-M]L,- ^ 



The correction, therefore, nearly vanishes for two twisted 

 wires in a coil where 1/ — M = and C is taken out. 



Method 10. 



- WM + — or b*M - — = 

 c c 



[R;R''-R ; R']{r[R' + R' / + R / + RJ + (R' + R / )(R" + R // ) } 

 [R' + R" + R ; + RJ 2 



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

 reduces. But it is more general and always gives zero deflec- 

 tion when adjusted, however M is connected. To throw out 

 C make it oo. 



Method 11. 

 L-M 



e 

 L + M 



= rR + & 2 (J— M) (L-M) 



= rB, + b*(l + M) (L + M) 



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. Method 8, however, is better for this. 



