﻿Rotation 
  in 
  Iron 
  Cathode 
  Films, 
  93 
  

  

  agreement 
  in 
  magnitude 
  of 
  the 
  rotations 
  with 
  those 
  obtained 
  

   with 
  the 
  polished 
  steel 
  surface, 
  as 
  well 
  as 
  the 
  agreement 
  

   with 
  the 
  results 
  of 
  other 
  observers 
  of 
  the 
  Kerr 
  effect 
  — 
  working 
  

   visually 
  — 
  reduced 
  for 
  this 
  same 
  field 
  strength, 
  viz. 
  5700 
  units. 
  

   Moreover 
  some 
  later 
  tests 
  made 
  visually 
  with 
  the 
  aid 
  of 
  an 
  

   ordinary 
  half 
  shade 
  polarimeter 
  on 
  an 
  opaque 
  unoxidized 
  

   film 
  gave 
  a 
  rotation 
  for 
  sodium 
  light, 
  almost 
  identical 
  with 
  

   that 
  of 
  this 
  film. 
  The 
  seat 
  of 
  the 
  Kerr 
  rotation 
  is 
  unquestion- 
  

   ably 
  a 
  thin 
  surface-layer, 
  and 
  the 
  foregoing 
  results 
  allow 
  one 
  

   to 
  say 
  that 
  a 
  layer 
  of 
  less 
  than 
  perhaps 
  20 
  //-/x 
  thickness 
  

   contributes 
  considerably 
  more 
  than 
  half 
  of 
  this 
  rotation 
  ^"^^ 
  

   This 
  is 
  of 
  the 
  same 
  order 
  of 
  magnitude 
  as 
  the 
  thickness 
  of 
  the 
  

   frequently 
  assumed 
  " 
  transition 
  layer 
  ^^ 
  of 
  optical 
  theory. 
  

  

  A 
  third 
  point 
  is 
  the 
  great 
  similarity, 
  if 
  we 
  confine 
  our 
  

   attention 
  to 
  the 
  results 
  for 
  pure 
  iron, 
  of 
  the 
  curves 
  for 
  the 
  

   two 
  cases 
  of 
  rotation. 
  While 
  for 
  the 
  thinner 
  films 
  the 
  Kerr 
  

   rotation 
  curve 
  shows 
  a 
  more 
  rapid 
  decrease 
  on 
  the 
  short 
  

   wave-length 
  side, 
  the 
  forms 
  of 
  the 
  two 
  curves 
  for 
  film 
  15 
  are 
  

   almost 
  identical 
  — 
  at 
  least 
  until 
  beyond 
  IS 
  fjL 
  — 
  as 
  is 
  shown 
  by 
  

   the 
  following 
  Table 
  III. 
  The 
  rotation 
  for 
  the 
  wave-length 
  

   of 
  sodium 
  light 
  is 
  taken 
  as 
  unity 
  in 
  each 
  case. 
  

  

  Table 
  III. 
  

  

  Rotation 
  dispersion 
  of 
  the 
  Faraday 
  and 
  Kerr 
  efiects 
  for 
  

   a 
  pure 
  iron 
  film 
  (15). 
  

  

  Wave- 
  

  

  Transmission 
  

  

  Eeflexion 
  

  

  Wave- 
  

  

  Transmission 
  

  

  Eeflexion 
  

  

  length. 
  

  

  rotation. 
  

  

  rotation. 
  

  

  length. 
  

  

  rotation, 
  i 
  

  

  rotation. 
  

  

  •589,* 
  

  

  1-00 
  

  

  -1-00 
  

  

  1-40 
  

  

  1-71 
  1 
  

  

  -1-70 
  

  

  •70 
  

  

  1-20 
  

  

  -1-16 
  

  

  1-50 
  

  

  1-73 
  

  

  -1^74 
  

  

  •80 
  

  

  1-33 
  

  

  -1-34 
  

  

  1-()U 
  

  

  1-73 
  

  

  -1-74 
  

  

  •90 
  

  

  1-44 
  

  

  -1-42 
  

  

  1-70 
  

  

  1-73 
  

  

  -l-7(> 
  

  

  1-00 
  

  

  1-52 
  

  

  -1-50 
  

  

  1-80 
  

  

  1-71 
  

  

  -1-76 
  

  

  1-10 
  

  

  1-59 
  

  

  -1-56 
  

  

  1-90 
  

  

  1-70 
  

  

  -1-76 
  

  

  1-20 
  

  

  1-64 
  

  

  -1-62 
  

  

  2-00 
  

  

  1-68 
  i 
  

  

  -1-76 
  

  

  1-30 
  

  

  1-68 
  

  

  -1-66 
  

  

  2-10 
  

  

  1-65 
  

  

  -1-76 
  

  

  

  

  

  2-20 
  

  

  1-62 
  

  

  -1-76 
  

  

  It 
  would 
  seem 
  from 
  the 
  above 
  that 
  any 
  explanation 
  of 
  the 
  

   Kerr 
  effect 
  must 
  indicate, 
  more 
  clearly 
  than 
  it 
  does 
  at 
  

   present, 
  its 
  very 
  close 
  connexion 
  with 
  the 
  Faraday 
  rotation 
  ; 
  

   but 
  unfortunately 
  for 
  the 
  generality 
  of 
  this 
  statement 
  the 
  

  

  * 
  We 
  might 
  also 
  say 
  that 
  practically 
  the 
  full 
  value 
  is 
  given 
  by 
  a 
  layer 
  

   60 
  HIM 
  thick, 
  which 
  is 
  about 
  the 
  same 
  thickness 
  as 
  that 
  found 
  by 
  

   Kcenigsberger 
  and 
  Bender 
  (Aim. 
  d. 
  Phys. 
  xxvi. 
  p. 
  763, 
  1908) 
  for 
  

   platinum 
  and 
  gold 
  films 
  vs-hich 
  give 
  the 
  same 
  phase 
  change 
  on 
  reflexion 
  

   as 
  the 
  massive 
  metal. 
  

  

  