﻿Barus 
  — 
  Trial 
  of 
  Interferential 
  Induction 
  balance. 
  113 
  

  

  of 
  temperature 
  in 
  iron 
  would 
  be 
  O04: 
  C, 
  which 
  in 
  case 
  of 
  

   several 
  hundred 
  repetitions 
  would 
  be 
  otherwise 
  appreciable. 
  

   Hence 
  this 
  observation, 
  though 
  distinctly 
  marked, 
  must 
  be 
  

   an 
  illusion 
  and 
  due 
  to 
  the 
  fact 
  that 
  the 
  magnetization 
  takes 
  

   place 
  much 
  more 
  'slowly 
  than 
  the 
  demagnetization. 
  It 
  is 
  

   a 
  curious 
  feature, 
  however, 
  that 
  for 
  fields 
  above 
  and 
  below 
  

   the 
  sensitive 
  value 
  in 
  question, 
  continued 
  shifting 
  does 
  not 
  

   occur. 
  

  

  6. 
  The 
  results 
  obtained 
  are 
  applicable 
  to 
  intermittent 
  cur- 
  

   rents 
  of 
  low 
  frequency 
  at 
  once. 
  From 
  the 
  dimensions 
  given, 
  

   the 
  self-induction 
  L 
  of 
  the 
  two 
  helices 
  is 
  not 
  above 
  0*5 
  henry, 
  

   each. 
  If 
  the 
  frequency 
  be 
  kept 
  below 
  100 
  per 
  second, 
  the 
  

   current 
  would 
  not 
  be 
  dephased 
  more 
  than 
  about 
  0'2 
  period 
  

   behind 
  the 
  electromotive 
  force 
  ; 
  and 
  there 
  would 
  be 
  no 
  serious 
  

   interference 
  with 
  visibility 
  from 
  this 
  cause 
  since 
  the 
  partial 
  

   electromotive 
  forces 
  of 
  each 
  helix 
  as 
  well 
  as 
  the 
  total 
  electro- 
  

   motive 
  force 
  are 
  in 
  advance 
  of 
  their 
  respective 
  currents 
  by 
  the 
  

   same 
  fraction 
  of 
  a 
  period. 
  For 
  a 
  simple 
  harmonic 
  variation 
  of 
  

   electromotive 
  force 
  at 
  the 
  source, 
  the 
  impedance 
  introduced 
  at 
  

   each 
  coil 
  for 
  frequencies, 
  0, 
  10, 
  50, 
  100 
  would 
  be 
  about 
  11, 
  34, 
  

   158, 
  316, 
  respectively. 
  To 
  produce 
  appreciable 
  expansion 
  of 
  

   the 
  iron 
  cores 
  one 
  would, 
  therefore, 
  merely 
  have 
  to 
  increase 
  

   the 
  electromotive 
  forces 
  accordingly. 
  

  

  In 
  the 
  following 
  experiments, 
  however, 
  the 
  current 
  is 
  actu- 
  

   ally 
  made 
  and 
  broken. 
  Since 
  the 
  extra 
  current 
  is 
  thus 
  evoked 
  

   and 
  necessarily 
  introduced 
  at 
  the 
  maximum 
  of 
  electromotive 
  

   force, 
  its 
  effect 
  will 
  be 
  a 
  maximum. 
  From 
  the 
  given 
  dimen- 
  

   sions 
  one 
  should 
  expect 
  the 
  current 
  in 
  successive 
  intervals 
  of 
  

   0*01 
  sec. 
  each 
  to 
  be 
  0*20, 
  *37, 
  *50, 
  -60, 
  etc., 
  of 
  the 
  maximum. 
  

   It 
  will 
  thus 
  be 
  necessary, 
  if 
  the 
  frequency 
  is 
  as 
  high 
  as 
  100, 
  to 
  

   use 
  five 
  times 
  the 
  battery 
  power 
  needed 
  in 
  case 
  of 
  continuous 
  

   currents 
  under 
  the 
  same 
  circumstances. 
  This 
  is 
  also 
  the 
  effec- 
  

   tive 
  quantity 
  of 
  current 
  whether 
  one 
  or 
  both 
  helices 
  are 
  in 
  

   circuit, 
  seeing 
  that 
  resistance 
  and 
  self-induction 
  in 
  the 
  two 
  

   cases 
  increase 
  in 
  like 
  ratio. 
  

  

  In 
  the 
  following 
  table 
  I 
  give 
  the 
  results 
  obtained 
  for 
  low 
  

   frequencies, 
  using 
  a 
  Foucault 
  interrupter 
  of 
  the 
  usual 
  pattern. 
  

   The 
  first 
  and 
  third 
  columns 
  show 
  the 
  value 
  of 
  the 
  fields 
  had 
  

   continuous 
  currents 
  been 
  used 
  ; 
  the 
  second 
  and 
  fourth 
  columns 
  

   the 
  corresponding 
  appearance 
  of 
  the 
  interference 
  fringes 
  

   (" 
  clear 
  " 
  denoting 
  maximum 
  visibility). 
  

  

  