﻿848 
  Prof. 
  Skinner 
  and 
  Mr. 
  Tool 
  on 
  the 
  Optical 
  

  

  their 
  curves 
  in 
  fig. 
  7. 
  The 
  rotation 
  is 
  proportional 
  to 
  the 
  

   thickness 
  throughout, 
  but 
  with 
  the 
  ellipticity 
  this 
  is 
  true 
  

   only 
  in 
  the 
  blue 
  end 
  of 
  the 
  spectrum, 
  a 
  considerable 
  diver- 
  

   gence 
  being 
  evident 
  in 
  the 
  red. 
  A 
  more 
  remarkable 
  variation 
  

   in 
  these 
  electrolytic 
  films 
  is 
  found 
  on 
  comparing 
  the 
  rotation 
  

   curve 
  in 
  this 
  figure 
  with 
  that 
  plotted 
  from 
  Lobach's 
  results 
  

   (I.e.) 
  which 
  is 
  also 
  given. 
  The 
  magnitudes 
  are 
  not 
  only 
  

   greatly 
  different, 
  but 
  the 
  rotation 
  in 
  our 
  films 
  increases 
  more 
  

   rapidly 
  toward 
  the 
  red 
  than 
  in 
  his, 
  thus 
  showing 
  that 
  the 
  

   difference 
  in 
  values 
  cannot 
  be 
  accounted 
  for 
  by 
  assuming 
  an 
  

   error 
  in 
  thickness 
  measurements. 
  

  

  The 
  extinction 
  coefficients 
  of 
  this 
  type 
  of 
  iron 
  were 
  obtained 
  

   by 
  measuring 
  the 
  transmission 
  of 
  a 
  very 
  thin 
  film 
  of 
  definite 
  

   thickness, 
  then 
  repeating 
  the 
  measurements 
  after 
  depositing 
  

   over 
  this. 
  Two 
  films 
  were 
  thus 
  tested, 
  giving 
  as 
  mean 
  results 
  

   the 
  values 
  found 
  in 
  Table 
  VI. 
  The 
  corresponding 
  curve 
  is 
  

   plotted 
  in 
  fig, 
  7. 
  Compared 
  with 
  dark 
  iron 
  it 
  is 
  noticed 
  that 
  

   this 
  extinction-curve 
  is 
  much 
  Hatter 
  than 
  that 
  of 
  fig. 
  5, 
  

   a 
  fact 
  we 
  should 
  expect 
  Brom 
  the 
  great 
  difference 
  in 
  form 
  of 
  

   the 
  curves 
  of 
  rotation 
  and 
  ellipticity. 
  Another 
  remarkable 
  

   difference 
  between 
  these 
  films 
  and 
  those 
  of 
  the 
  dark 
  iron 
  is 
  

   the 
  relative 
  magnitudes 
  of 
  rotation, 
  ellipticity, 
  and 
  extinction. 
  

   With 
  the 
  same 
  thickness 
  the 
  magnetic 
  effects 
  of 
  electrolytic 
  

   iron 
  are 
  aboui 
  forty 
  times 
  that 
  of 
  the 
  dark, 
  while 
  the 
  

   extinction 
  ranges 
  Erom 
  ten 
  to 
  thirty 
  times. 
  

  

  The 
  effect 
  on 
  rotation 
  and 
  ellipticity 
  of 
  varying 
  the 
  strength 
  

   of 
  the 
  magnetic 
  field 
  is 
  shown 
  in 
  the 
  following 
  table, 
  obtained 
  

   from 
  film 
  24 
  with 
  a 
  wave-length 
  of 
  f>2() 
  nn. 
  

  

  Table 
  VII. 
  

  

  Field-#trengtli 
  Rotation 
  Ellipticity 
  

   (cleg.)- 
  XlO 
  3 
  . 
  

  

  Klli]>ticity 
  xl(R 
  

   Rota! 
  ion 
  

  

  9,500 
  GO 
  12-7 
  

   10,800 
  -05 
  13-8 
  

   12,800 
  "69 
  148 
  

   15,000 
  77 
  102 
  

  

  212 
  

   21*2 
  

  

  21 
  :> 
  

   21-2 
  

  

  As 
  with 
  dark 
  iron, 
  the 
  ellipticity 
  changes 
  with 
  the 
  mag- 
  

   netizing 
  force 
  at 
  the 
  same 
  rate 
  as 
  the 
  rotation, 
  as 
  shown 
  by 
  

   the 
  last 
  column 
  of 
  this 
  table. 
  

  

  Light 
  reflected 
  from 
  an 
  electrolytic 
  film 
  (No. 
  22) 
  was 
  

  

  