﻿80 
  Prof. 
  H. 
  A. 
  Rowland 
  on 
  Electrical 
  

  

  the 
  whole 
  method 
  (B) 
  is 
  only 
  of 
  special 
  value 
  for 
  — 
  , 
  as 
  two 
  

   adjustments 
  are 
  needed 
  for 
  the 
  others. 
  

  

  Method 
  17. 
  

   (A) 
  W=oo, 
  R 
  = 
  co: 
  

  

  1/ 
  ^B' 
  + 
  B^B'^B,, 
  

  

  M 
  R 
  

  

  // 
  

  

  By 
  this 
  method 
  the 
  self-induction 
  of 
  the 
  mutual 
  induction- 
  

   coil 
  is 
  eliminated. 
  But 
  it 
  is 
  difficult 
  to 
  apply, 
  as 
  two 
  resistances 
  

   must 
  be 
  adjusted, 
  and 
  the 
  adjustment 
  will 
  only 
  hold 
  while 
  the 
  

   current 
  period 
  remains 
  constant. 
  The 
  same 
  remarks 
  apply 
  to 
  

   (B) 
  and 
  (0) 
  following. 
  

  

  (B) 
  R=oo: 
  

  

  W[B 
  ; 
  B"-B'B 
  y/ 
  ] 
  

  

  1/ 
  W'"[B' 
  + 
  B 
  y 
  + 
  B" 
  + 
  B„] 
  + 
  (R 
  7 
  + 
  B,) 
  (B" 
  + 
  B„) 
  

   M 
  -- 
  B„W 
  - 
  

  

  &2ML 
  -rt5tr:^ 
  e 
  ''- 
  e 
  ^^ 
  

  

  17 
  R(R 
  / 
  + 
  R 
  7 
  + 
  R 
  / 
  ' 
  + 
  R 
  / 
  /; 
  + 
  (R' 
  + 
  R,)(R'' 
  + 
  R 
  // 
  ) 
  

   M 
  " 
  RE,, 
  

  

  Method 
  18. 
  

  

  B 
  i 
  B"-B'B 
  tf 
  =0, 
  

   y_ 
  _ 
  1 
  BP 
  R 
  f 
  + 
  R" 
  

   M' 
  + 
  R 
  yi 
  + 
  W 
  " 
  

  

  1/ 
  and 
  M' 
  belong 
  to 
  the 
  same 
  coil. 
  By 
  adjusting 
  the 
  

   Wheatstone 
  bridge 
  first, 
  W 
  can 
  then 
  be 
  afterwards 
  adjusted. 
  

   To 
  find 
  the 
  ratio 
  for 
  any 
  other 
  coil 
  independent 
  of 
  the 
  

  

  induction-coil, 
  we 
  can 
  first 
  find 
  ^ 
  as 
  above. 
  Then 
  add 
  L 
  

  

  M'" 
  

  

  L 
  + 
  L' 
  

  

  to 
  the 
  same 
  circuit, 
  and 
  we 
  can 
  find 
  M/ 
  — 
  . 
  Whence 
  we 
  

  

  can 
  get 
  L. 
  This 
  seems 
  a 
  convenient 
  method 
  if 
  it 
  is 
  sensitive 
  

  

  L' 
  

  

  enough, 
  as 
  the 
  value 
  of 
  ^ 
  should 
  be 
  accurately 
  known 
  for 
  

  

  the 
  inductance 
  standard. 
  

  

  