﻿Rowland 
  and 
  Penniman 
  — 
  Electrical 
  Measurements. 
  53 
  

  

  Cor- 
  Com. 
  

  

  Period 
  

  

  . 
  Coils. 
  

  

  R". 
  

  

  Correc. 
  

  

  

  Queen. 
  

  

  R 
  + 
  r. 
  

  

  rec. 
  

  

  Average. 
  

  

  K\ 
  

  

  Ratio. 
  

  

  40 
  

  

  P1 
  + 
  P2 
  

  

  + 
  c 
  

  

  902-4 
  

  

  -14-55 
  

  

  887-85 
  

  

  60+5 
  

  

  2306-3 
  

  

  —-62 
  

  

  2307-98 
  

  

  1 
  

  

  2-5995 
  

  

  u 
  

  

  u 
  

  

  a 
  

  

  a 
  

  

  ? 
  

  

  2310-9 
  

  

  a 
  

  

  

  2 
  

  

  

  133 
  

  

  u' 
  

  

  

  a 
  

  

  a 
  

  

  56 
  + 
  5 
  

  

  57 
  +5 
  

  

  2304-1 
  

   2305-4 
  

  

  a 
  

  

  2304-13 
  

  

  1 
  

   2 
  

  

  2-5951 
  

  

  40 
  

  

  u 
  

  

  A 
  

  

  902-43 
  

  

  a 
  

   a 
  

  

  887-88 
  

  

  85+5 
  

   106 
  + 
  5 
  

  

  4703- 
  

  

  4724-2 
  

  

  a 
  

  

  a 
  

  

  4712-98 
  

  

  1 
  

   2 
  

  

  5-3080 
  

  

  133 
  

  

  i( 
  

  

  902-4 
  

  

  " 
  

  

  887-85 
  

  

  82+5 
  

   85+5 
  

  

  4704-2 
  

   4707 
  

  

  a' 
  

  

  4704-98 
  

  

  1 
  

   2 
  

  

  5-2991 
  

  

  40 
  

  

  A 
  + 
  C 
  

   -2M 
  

  

  902-35 
  

  

  

  887-8 
  

  

  a 
  

  

  1146 
  + 
  5 
  

   1227+5 
  

  

  9149-5 
  

   9233-5 
  

  

  a 
  

   a 
  

  

  9190-88 
  

  

  1 
  

   2 
  

  

  10-3515 
  

  

  133 
  

  

  u 
  

  

  902-4 
  

  

  a 
  

  

  887-85 
  

  

  1170 
  + 
  5 
  

  

  9171-7 
  

  

  " 
  

  

  

  1 
  

  

  

  u 
  

  

  a 
  

  

  u 
  

  

  " 
  

  

  " 
  

  

  1194 
  + 
  5 
  

  

  9191-7 
  

  

  a 
  

  

  9181-08 
  

  

  2 
  

  

  10-3395 
  

  

  40 
  

  

  A 
  + 
  C 
  

   + 
  2M 
  

  

  u 
  

  

  902-35 
  

  

  a 
  

  

  887-8 
  

  

  a 
  

  

  111+5 
  

  

  146 
  + 
  5 
  

  

  2550-9 
  

   2556-4 
  

  

  a 
  

  

  255303 
  

  

  1 
  

   2 
  

  

  2-8716 
  

  

  133 
  

  

  u 
  

  

  u 
  

  

  a 
  

  

  a 
  

  

  c 
  

  

  a 
  

  

  38+5 
  

   38 
  + 
  5 
  

  

  2548-7 
  

   2548-7 
  

  

  a 
  

  

  2548-08 
  

  

  1 
  

   9 
  

  

  2-8701 
  

  

  40 
  

  

  A 
  + 
  C 
  

  

  902-6 
  

  

  " 
  

  

  888-05 
  

  

  123 
  

  

  5852- 
  

  

  " 
  

  

  

  1 
  

  

  

  u 
  

  

  it 
  

  

  a 
  

  

  a 
  

  

  " 
  

  

  169 
  

  

  5898- 
  

  

  a 
  

  

  5880-13 
  

  

  2 
  

  

  6-6225 
  

  

  133 
  

  

  " 
  

  

  a 
  

  

  a 
  

  

  a 
  

  

  134 
  

  

  5863-5 
  

  

  a 
  

  

  

  1 
  

  

  

  " 
  

  

  u 
  

  

  C( 
  

  

  a 
  

  

  a 
  

  

  140 
  

  

  5869- 
  

  

  a 
  

  

  5865-63 
  

  

  2 
  

  

  6-6054 
  

  

  The 
  above 
  results 
  show 
  to 
  what 
  accuracy 
  self-inductances 
  of 
  

   different 
  values 
  can 
  be 
  compared 
  to 
  each 
  other, 
  or 
  to 
  one 
  of 
  

   the 
  self-inductances 
  taken 
  as 
  a 
  standard. 
  The 
  reason 
  that 
  the 
  

   agreenaent 
  between 
  the 
  different 
  determinations 
  is 
  not 
  greater 
  

   than 
  it 
  is, 
  even 
  though 
  the 
  electrodynamometer 
  was 
  sensitive 
  

   to 
  a 
  change 
  of 
  1 
  part 
  in 
  10000 
  in 
  R 
  + 
  ?', 
  is 
  that 
  there 
  was 
  

   always 
  some 
  little 
  heating 
  of 
  the 
  resistances, 
  and 
  although 
  they 
  

   were 
  measured 
  in 
  each 
  determination 
  on 
  a 
  Wheatstone 
  bridge, 
  

   still 
  it 
  was 
  impossible 
  to 
  determine 
  the 
  exact 
  resistance 
  at 
  the 
  

   time 
  that 
  the 
  experiment 
  was 
  made. 
  This 
  slight 
  effect 
  of 
  the 
  

   heating 
  of 
  the 
  resistances 
  would 
  not 
  enter 
  in 
  the 
  comparison 
  

   of 
  two 
  nearly 
  equal 
  self-inductances, 
  that 
  is 
  the 
  comparison 
  of 
  

   a 
  coil 
  with 
  a 
  standard. 
  The 
  accuracy 
  of 
  this 
  comparison 
  can 
  

   be 
  made 
  to 
  depend 
  on 
  the 
  accuracy 
  with 
  which 
  E-+r 
  can 
  be 
  

   determined 
  for 
  zero 
  deflection, 
  and 
  this 
  can 
  be 
  done 
  to 
  about 
  1 
  

   part 
  in 
  10000. 
  To 
  do 
  this, 
  first 
  the 
  standard 
  coil 
  and 
  the 
  coil 
  

   to 
  be 
  compared 
  are 
  substituted 
  in 
  turn 
  in 
  place 
  of 
  L 
  in 
  figure 
  ; 
  

   they 
  are 
  thus 
  compared 
  separately 
  to 
  a 
  third 
  coil. 
  But 
  as 
  the 
  

   standard 
  and 
  the 
  coil 
  to 
  be 
  compared 
  are 
  nearly 
  equal 
  in 
  self- 
  

   inductance, 
  the 
  difference 
  or 
  self-inductance 
  can 
  be 
  determined 
  

   by 
  the 
  amount 
  necessary 
  to 
  change 
  "R 
  + 
  r, 
  and 
  this 
  change 
  will 
  

   be 
  nearly 
  independent 
  of 
  the 
  slight 
  heating 
  of 
  the 
  resistances. 
  

   To 
  make 
  a 
  coil 
  of 
  the 
  same 
  self-inductance 
  as 
  the 
  standard, 
  the 
  

   standard 
  is 
  placed 
  in 
  the 
  R-f-r 
  circuit 
  and 
  the 
  value 
  of 
  R+r 
  is 
  

   found 
  that 
  produces 
  no 
  deflection. 
  The 
  coil 
  to 
  be 
  compared 
  is 
  

   then 
  substituted 
  in 
  place 
  of 
  the 
  standard 
  keeping 
  R-f?' 
  fixed, 
  

  

  