﻿82 
  Prof. 
  H. 
  A. 
  Rowland 
  on 
  Electrical 
  

  

  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 
  y 
  is 
  computed 
  from 
  the 
  known 
  

   value 
  of 
  the 
  induction 
  standard. 
  TV 
  is 
  then 
  adjusted 
  and 
  C 
  

   obtained. 
  In 
  general 
  the 
  adjustment 
  can 
  be 
  obtained 
  by 
  

   changing 
  R 
  7 
  and 
  R". 
  The 
  adjustment 
  is 
  independent 
  of 
  the 
  

   current 
  period. 
  

  

  Method 
  23. 
  

   fawLWB^R^ 
  + 
  B'+B,], 
  

  

  — 
  =r 
  + 
  R 
  / 
  + 
  R 
  / 
  . 
  

  

  m 
  

  

  If 
  we 
  make 
  R 
  = 
  we 
  have 
  

  

  &»roL'=rR 
  y 
  

  

  M_ 
  r 
  + 
  R 
  / 
  + 
  R 
  / 
  

   m 
  r 
  

  

  This 
  method 
  requires 
  two 
  simultaneous 
  adjustments. 
  M 
  

   must 
  also 
  be 
  greater 
  than 
  m. 
  As 
  M 
  and 
  1/ 
  belong 
  to 
  the 
  

   same 
  coil, 
  we 
  can 
  consider 
  this 
  method 
  as 
  one 
  for 
  determining 
  

   <m 
  in 
  terms 
  of 
  the 
  M 
  and 
  1/ 
  of 
  some 
  standard 
  coil. 
  

  

  The 
  resistance, 
  A, 
  can 
  be 
  varied 
  to 
  test 
  for, 
  or 
  even 
  correct, 
  

   the 
  error 
  due 
  to 
  electrostatic 
  action 
  between 
  the 
  wires 
  of 
  the 
  

   induction 
  standard. 
  

  

  Method 
  24. 
  

  

  J 
  ± 
  K*J 
  M^/ 
  ^ 
  + 
  R. 
  + 
  RJ 
  

   M, 
  " 
  MV 
  ' 
  M' 
  r-j 
  [f 
  + 
  R 
  / 
  + 
  wy 
  

  

  This 
  is 
  a 
  good 
  method 
  for 
  comparing 
  standards. 
  We 
  first 
  

  

  determine 
  -^~ 
  for 
  each 
  coil 
  by 
  one 
  of 
  the 
  previous 
  methods. 
  

  

  v 
  

   Then 
  we 
  can 
  calculate 
  -7 
  and 
  adjust 
  the 
  other 
  resistances 
  to 
  

  

  balance. 
  

  

  It 
  is 
  independent 
  of 
  the 
  period 
  of 
  the 
  current 
  and 
  suitable 
  

   for 
  standards 
  of 
  equal 
  as 
  well 
  as 
  of 
  different 
  values, 
  as 
  the 
  

   mutual 
  inductances 
  can 
  have 
  any 
  ratio 
  to 
  each 
  other. 
  

  

  For 
  twisted 
  wire 
  coils 
  r 
  t 
  =-r' 
  very 
  nearly. 
  See 
  method 
  23 
  

   for 
  the 
  use 
  of 
  the 
  resistance, 
  A. 
  

  

  