﻿54 
  Rowland 
  and 
  Penniman 
  — 
  Electrical 
  Measurements. 
  

  

  and 
  the 
  self-inductance 
  of 
  this 
  coil 
  is 
  changed 
  until 
  there 
  is 
  no 
  

   deflection, 
  as 
  in 
  the 
  case 
  of 
  the 
  standard. 
  " 
  The 
  accuracy 
  with 
  

   which 
  this 
  can 
  be 
  done 
  depends 
  on 
  the 
  accuracy 
  with 
  which 
  

   R+r 
  can 
  be 
  set 
  or 
  1 
  part 
  in 
  10000. 
  This 
  method 
  therefore 
  

   gives 
  a 
  means 
  of 
  comparing 
  and 
  constructing 
  coils 
  to 
  agree 
  in 
  

   self-inductance 
  to 
  within 
  1 
  part 
  in 
  10000 
  with 
  a 
  standard. 
  

  

  Method 
  6. 
  Zero 
  Method 
  for 
  the 
  coynparison 
  of 
  Self 
  inductance 
  

  

  loith 
  capacity. 
  

  

  This 
  method 
  resembles 
  Method 
  12 
  and 
  the 
  connections 
  are 
  

   made 
  as 
  in 
  the 
  figures 
  when 
  both 
  the 
  hanging 
  coil 
  and 
  fixed 
  

   coils 
  of 
  the 
  electrodynamometer 
  are 
  shunted 
  off 
  the 
  main 
  cir- 
  

   cuit. 
  

  

  Let 
  the 
  currents 
  be 
  denoted 
  by 
  C„£«^^, 
  C,£^'(^^+0i), 
  C^e^X^^+^a), 
  

   Q^tm-\-^,)^2iwdLC^e{ibt-\-(p,), 
  The 
  resistance 
  by 
  R'', 
  r\ 
  R 
  and 
  r. 
  

   The 
  capacity 
  by 
  C. 
  The 
  self-inductance 
  by 
  L. 
  A' 
  and 
  A'' 
  are 
  

   reversing 
  commutators 
  and 
  F 
  the 
  terminals 
  of 
  the 
  fixed 
  coils 
  

   and 
  H 
  the 
  terminals 
  of 
  the 
  hanging 
  coil 
  of 
  the 
  electrodyna- 
  

   mometer. 
  

  

  If 
  now 
  a 
  periodic 
  electromotive 
  force 
  is 
  applied 
  to 
  the 
  termi- 
  

   nals 
  A 
  and 
  B 
  the 
  equations 
  connecting 
  the 
  different 
  currents 
  

   are 
  as 
  below, 
  from 
  which 
  equations 
  the 
  quantity 
  Qfi^ 
  cos 
  

   (jfi 
  — 
  ^g) 
  is 
  to 
  be 
  found, 
  which 
  is 
  proportional 
  to 
  the 
  deflection. 
  

   From 
  the 
  figure 
  

  

  