﻿S±G 
  Prof. 
  Skinner 
  and 
  Mr. 
  Tool 
  on 
  the 
  Optical 
  

  

  This 
  fact 
  was 
  made 
  evident 
  by 
  the 
  coefficient 
  of 
  reflexion 
  

   being 
  of 
  a 
  wave 
  form 
  in 
  the 
  red 
  end 
  of 
  the 
  spectrum 
  (arising 
  

   from 
  interference 
  between 
  front 
  and 
  back 
  reflexions) 
  and 
  

   a 
  flat 
  curve 
  in 
  the 
  blue 
  (where 
  the 
  absorption 
  is 
  large). 
  

  

  About 
  11 
  per 
  cent, 
  of 
  the 
  light 
  is 
  reflected 
  at 
  normal 
  

   incidence 
  from 
  the 
  front 
  surface 
  of 
  these 
  films, 
  this 
  value 
  

   being 
  practically 
  the 
  same 
  for 
  all 
  colours. 
  

  

  7. 
  Electrolytic 
  Iron. 
  

  

  As 
  already 
  stated, 
  the 
  electrolytic 
  films 
  were 
  deposited 
  on 
  

   microscope 
  cover-glasses 
  which 
  had 
  been 
  platinized 
  after 
  the 
  

   method 
  of 
  Kundt. 
  As 
  Dearly 
  as 
  could 
  be 
  measured, 
  these 
  

   platinum 
  films 
  were 
  aboul 
  6. 
  10~ 
  7 
  cm. 
  thick 
  in 
  all 
  cases. 
  Asa 
  

   convenient 
  method 
  for 
  measuring 
  the 
  thickness 
  of 
  the 
  various 
  

   iron 
  films 
  with 
  the 
  greatest 
  accuracy, 
  a 
  comparatively 
  thick 
  

   film 
  was 
  deposited, 
  its 
  magnetic 
  rotation 
  observed 
  for 
  the 
  

   more 
  sensitive 
  region 
  of 
  the 
  spectrum 
  (520 
  /jl/j.), 
  and 
  its 
  

   thickness 
  obtained 
  by 
  subtracting 
  the 
  thickness 
  of 
  the 
  

   platinum 
  from 
  the 
  combined 
  thickness 
  as 
  measured 
  according 
  

   to 
  § 
  2. 
  Tlif 
  following 
  table 
  give- 
  the 
  values 
  obtained, 
  the 
  

   thinner 
  film 
  merely 
  serving 
  bo 
  Furnish 
  check-values. 
  

  

  Table 
  IV. 
  

  

  Film. 
  

  

  Thickness 
  x 
  10 
  7 
  (cm.). 
  

  

  Rotation 
  

  

  (degrees). 
  

  

  Rotation 
  

  

  'J 
  hioimees' 
  

  

  Pr 
  + 
  Fe. 
  Pi 
  (appn 
  Fe. 
  

  

  24 
  

   29 
  

  

  41 
  6 
  35 
  

   67 
  6 
  61 
  

  

  ■92 
  

   1*57 
  

  

  263000 
  

   257000 
  

  

  The 
  field-strength 
  used 
  for 
  these 
  measurements 
  was 
  

  

  13,700 
  (c.G.s.). 
  

  

  From 
  the 
  above 
  value 
  of 
  the 
  rotation 
  divided 
  by 
  the 
  

   thickness, 
  the 
  thickness 
  of 
  the 
  other 
  films 
  was 
  calculated 
  

   alter 
  measuring 
  their 
  rotation 
  under 
  the 
  same 
  conditions. 
  

   This 
  assumes 
  that 
  the 
  various 
  films 
  are 
  identical 
  in 
  structure, 
  

   which 
  assumption 
  later 
  results 
  show 
  to 
  be 
  not 
  rigidly 
  correct. 
  

   However, 
  the 
  accuracy 
  obtained 
  by 
  this 
  procedure 
  is 
  probably 
  

   much 
  greater 
  than 
  if 
  the 
  thickness 
  of 
  the 
  thinner 
  films 
  used 
  

   had 
  been 
  measured 
  directly. 
  

  

  Values 
  of 
  the 
  rotation 
  and 
  ellipticity 
  produced 
  by 
  two 
  

   different 
  electrolytic 
  films 
  are 
  found 
  in 
  Table 
  V. 
  and 
  the 
  

   corresponding 
  curves 
  in 
  fig. 
  6 
  (PI. 
  XXIV.) 
  . 
  The 
  form 
  of 
  the 
  

  

  