﻿SU 
  Prof. 
  Skinner 
  and 
  Mr. 
  Tool 
  on 
  the 
  Optical 
  

  

  corresponding 
  film. 
  These 
  show 
  that 
  both 
  rotation 
  and 
  

   ellipticity 
  are 
  approximately 
  proportional 
  to 
  the 
  thickness 
  of 
  

   the 
  film, 
  the 
  approximation 
  being 
  on 
  the 
  whole 
  as 
  near 
  as 
  one 
  

   could 
  expect 
  from 
  the 
  conditions 
  of 
  the 
  experiment. 
  These 
  

   values 
  for 
  films 
  3 
  and 
  4 
  are 
  plotted 
  in 
  fig. 
  5, 
  the 
  results 
  from 
  

   3 
  being 
  indicated 
  by 
  the 
  black 
  dots, 
  from 
  4 
  by 
  the 
  circles. 
  

   The 
  transmission 
  values 
  for 
  the 
  same 
  films, 
  given 
  also 
  in 
  

   Table 
  II., 
  serve 
  for 
  calculating 
  the 
  extinction 
  coefficients 
  by 
  

   using 
  the 
  formula 
  

  

  | 
  :; 
  =«-K(*8-*«), 
  

   I4 
  

  

  in 
  which 
  I 
  ;; 
  . 
  I, 
  refer 
  to 
  the 
  ratio 
  in 
  percent, 
  of 
  transmitted 
  

   to 
  the 
  incident 
  light 
  of 
  the 
  two 
  films 
  respectively 
  ; 
  d$ 
  and 
  c/ 
  4 
  

   the 
  thickness 
  of 
  the 
  films 
  in 
  centimetres 
  ; 
  and 
  Iv 
  the 
  ex- 
  

   tinction 
  coefficient 
  -ought. 
  These 
  extinction 
  coefficients 
  are 
  

   also 
  given 
  in 
  Table 
  II. 
  Finally, 
  in 
  the 
  last 
  column 
  of 
  this 
  

   table 
  are 
  given 
  the 
  refractive 
  indices 
  of 
  film 
  .'> 
  as 
  obtained 
  

   according 
  to 
  the 
  method 
  described 
  in 
  § 
  3. 
  They 
  are 
  repre- 
  

   sented 
  in 
  the 
  upper 
  plot 
  of 
  fig. 
  5 
  t 
  and 
  the 
  extinction 
  coefficients 
  

  

  in 
  the 
  lower. 
  

  

  The 
  rotation, 
  ellipticity, 
  and 
  extinction 
  curves 
  are 
  con- 
  

   sistent 
  with 
  each 
  other; 
  but 
  it 
  appears 
  strange 
  that 
  the 
  

   refractive-index 
  enrve 
  -bows 
  no 
  corresponding 
  anomaly 
  in 
  

  

  form 
  in 
  this 
  region. 
  Its 
  slope 
  is, 
  however, 
  opposite 
  in 
  

   direction 
  to 
  that 
  given 
  by 
  other 
  investigators 
  for 
  normal 
  

   iron. 
  The 
  magnitude 
  (2*2 
  to 
  2*4) 
  is 
  about 
  the 
  same 
  here 
  as 
  

   in 
  normal 
  iron. 
  

  

  In 
  Table 
  I 
  II. 
  are 
  recorded 
  the 
  observations 
  of 
  rotation 
  and 
  

   ellipticity 
  of 
  film 
  '2 
  with 
  various 
  field-strengths, 
  the 
  magnitude 
  

   of 
  the 
  latter 
  being 
  determined 
  by 
  the 
  rotation 
  produced 
  in 
  a 
  

   given 
  length 
  of 
  carbon 
  bisulphide. 
  The 
  bottom 
  line 
  of 
  this 
  

   table 
  gives 
  the 
  ratio 
  of 
  the 
  mean 
  of 
  the 
  magnitudes 
  contained 
  

   in 
  each 
  two 
  vertical 
  columns 
  (obtained 
  by 
  ignoring 
  algebraic 
  

   signs). 
  This 
  shows 
  that, 
  within 
  experimental 
  errors, 
  the 
  

   ellipticity 
  bears 
  tbe 
  same 
  ratio 
  to 
  the 
  rotation 
  for 
  all 
  field- 
  

   strengths. 
  Assuming, 
  as 
  has 
  been 
  shown 
  in 
  some 
  cases 
  by 
  

   D\\ 
  Bois 
  * 
  9 
  that 
  the 
  rotation 
  is 
  proportional 
  to 
  the 
  mag- 
  

   netization 
  of 
  the 
  film, 
  we 
  may 
  conclude 
  that 
  the 
  ellipticity 
  

   produced 
  by 
  the 
  film 
  is 
  also 
  proportional 
  to 
  its 
  magnetization. 
  

  

  Observations 
  on 
  light 
  reflected 
  from 
  these 
  films 
  in 
  a 
  

   magnetic 
  field 
  gave 
  no 
  conclusive 
  results, 
  arising 
  partly 
  

   from 
  the 
  fact 
  that 
  so 
  much 
  light 
  is 
  returned 
  from 
  the 
  back 
  

   surface 
  of 
  the 
  film, 
  especially 
  in 
  the 
  red 
  end 
  of 
  the 
  spectrum. 
  

  

  * 
  Du 
  Bois 
  ; 
  Wied. 
  Ann. 
  xxxi. 
  p. 
  941. 
  

  

  