﻿Rotation 
  in 
  Iron 
  Cathode 
  Films. 
  97 
  

  

  factor 
  o£ 
  •321/*281 
  which 
  brings 
  the 
  measured 
  rotation 
  up 
  to 
  

   a' 
  — 
  -299°. 
  Subtracting 
  from 
  this 
  the 
  glass 
  rotation 
  of 
  

   + 
  *143° 
  we 
  get 
  the 
  corrected 
  rotation 
  of 
  —•442°. 
  The 
  pro- 
  

   cess 
  is 
  entirely 
  similar 
  for 
  the 
  case 
  when 
  the 
  liquid 
  is 
  used, 
  

   save 
  that 
  the 
  glass 
  reflecting 
  power 
  is 
  made 
  slightly 
  larger 
  — 
  

   perhaps 
  *045 
  — 
  to 
  take 
  account 
  of 
  the 
  additional, 
  or 
  glass- 
  

   liquid, 
  surface. 
  The 
  cover 
  slips 
  used 
  were 
  of 
  practically 
  the 
  

   same 
  thickness 
  as 
  the 
  glass 
  on 
  which 
  the 
  films 
  themselves 
  

   were 
  deposited 
  and 
  hence 
  the 
  glass 
  rotation 
  was 
  the 
  same 
  in 
  

   either 
  case. 
  

  

  The 
  corrected 
  rotations 
  from 
  the 
  above 
  table 
  have 
  been 
  

   plotted 
  in 
  the 
  curves 
  of 
  PI. 
  I. 
  fig. 
  14. 
  As 
  in 
  all 
  the 
  cases 
  con- 
  

   sidered 
  these 
  are 
  the 
  doubled 
  rotations 
  occurring 
  on 
  reversal 
  

   of 
  magnetization. 
  It 
  will 
  be 
  noted 
  that 
  the 
  curves 
  have 
  the 
  

   same 
  general 
  form 
  as 
  those 
  of 
  the 
  Kerr 
  effect 
  in 
  PL 
  I. 
  figs. 
  6-8, 
  

   but 
  that 
  the 
  rotations 
  are 
  all 
  considerably 
  larger. 
  The 
  

   remarkable 
  feature, 
  however, 
  is 
  that 
  the 
  magnitude 
  of 
  the 
  

   rotations 
  is 
  nearly 
  the 
  same 
  for 
  the 
  three 
  films 
  of 
  very 
  

   different 
  thicknesses, 
  and 
  that 
  the 
  thinnest 
  film 
  shows 
  the 
  

   largest 
  rotation. 
  

  

  Tn 
  the 
  following 
  Table 
  V. 
  (p. 
  98) 
  the 
  results 
  are 
  shown 
  

   of 
  a 
  number 
  of 
  experiments 
  with 
  liquids 
  of 
  optical 
  densities 
  

   ranginor 
  from 
  1'33 
  to 
  1*72. 
  

  

  Discussion 
  of 
  Results. 
  — 
  In 
  Voigt's 
  * 
  recent 
  " 
  Magneto- 
  und 
  

   Electrooptik," 
  which 
  contains 
  the 
  most 
  complete 
  treatment 
  

   of 
  the 
  Kerr 
  phenomenon 
  that 
  has 
  yet 
  appeared, 
  there 
  is 
  

   reached 
  on 
  p. 
  316 
  an 
  expression 
  for 
  the 
  rotation 
  on 
  normal 
  

   reflexion 
  and 
  for 
  polar 
  magnetization 
  — 
  the 
  case 
  we 
  are 
  

   considering 
  — 
  which 
  may 
  be 
  written 
  

  

  „ 
  _. 
  ' 
  Q(k-i) 
  

  

  Rotation 
  = 
  ..= 
  ^^^^-^^ 
  

  

  where 
  Q 
  is 
  a 
  complex 
  which 
  does 
  not 
  contain 
  n, 
  and 
  n 
  and 
  k 
  

   are 
  respectively 
  the 
  refractive 
  index 
  and 
  absorption 
  index 
  of 
  

   the 
  metal. 
  The 
  equations 
  have 
  not 
  been 
  worked 
  out 
  for 
  the 
  

   case 
  of 
  a 
  surrounding 
  medium 
  other 
  than 
  vacuum 
  or 
  air, 
  

   and 
  until 
  this 
  has 
  been 
  done 
  it 
  is 
  useless 
  to 
  attempt 
  any 
  

   satisfactory 
  justification 
  of 
  the 
  above 
  results 
  on 
  theoretical 
  

   grounds. 
  But 
  it 
  is 
  of 
  interest 
  to 
  note 
  that 
  if 
  we 
  grant 
  two 
  

   not 
  unreasonable 
  assumptions 
  f 
  — 
  viz. 
  that 
  the 
  refractive 
  index 
  

  

  * 
  W. 
  Voigt, 
  Magneto- 
  und 
  Electrooptik, 
  Leipzig, 
  1908. 
  

  

  t 
  Experiments 
  now 
  in 
  prosress 
  in 
  this 
  laboratory 
  show 
  that 
  the 
  

   reflecting 
  powers 
  of 
  metals, 
  when 
  overlaid 
  with 
  various 
  liquids, 
  are 
  in 
  

   agreement 
  wilh 
  the 
  well-known 
  formulae 
  for 
  metallic 
  reflexion, 
  if 
  assump- 
  

   tions 
  similar 
  to 
  these 
  are 
  made. 
  In 
  this 
  light 
  they 
  seem 
  extremely 
  

   reasonable. 
  

  

  PJiil 
  Mag. 
  S. 
  6. 
  Vol. 
  18. 
  No. 
  103. 
  July 
  1909. 
  H 
  

  

  