﻿852 
  Prof. 
  Skinner 
  and 
  Mr. 
  Tool 
  on 
  the 
  Optical 
  

  

  wave- 
  lengths 
  for 
  which 
  values 
  were 
  obtained 
  for 
  all 
  fields, 
  

   is 
  given 
  at 
  the 
  bottom 
  of 
  the 
  table 
  (corrections 
  having 
  first 
  

   been 
  made 
  for 
  difference 
  in 
  field-strength}. 
  As 
  with 
  both 
  the 
  

   dark 
  and 
  the 
  electrolytic 
  types, 
  this 
  shows 
  also 
  the 
  ellipticity 
  

   proportional 
  to 
  the 
  rotation, 
  hence 
  we 
  assume 
  it 
  to 
  be 
  

   proportional 
  to 
  the 
  magnetization 
  .of 
  the 
  iron. 
  

  

  Fig. 
  LO 
  shows 
  tin- 
  variation 
  in 
  magnetic 
  rotation 
  of 
  the 
  

   three 
  types 
  of 
  films 
  with 
  the 
  strength 
  of 
  field. 
  The 
  curves 
  

   for 
  electrolytic 
  and 
  metallic 
  films 
  (plotted 
  from 
  Tables 
  VII, 
  

   and 
  XI.) 
  are 
  (put.' 
  parallel: 
  that 
  lor 
  the 
  dark 
  (Table 
  III.) 
  

   reaches 
  practically 
  a 
  maximum 
  magnitude 
  at 
  an 
  intensity 
  as 
  

   low 
  as 
  5000 
  lines, 
  though 
  the 
  others 
  Mill 
  show 
  an 
  observable 
  

   increase 
  ai 
  L5,000. 
  

  

  Tl 
  1( 
  . 
  effect 
  of 
  reflexiou 
  in 
  a 
  magnetic 
  field 
  is 
  given 
  for 
  

   film 
  15 
  in 
  the 
  following 
  table:— 
  

  

  Table 
  XII. 
  

   Field: 
  L3,200 
  o.G.s. 
  

  

  •length 
  

  

  Rotation 
  (deg.) 
  

  

  Ellipticity 
  xlO 
  3 
  ... 
  

  

  110 
  

  

  Leo 
  

  

  520 
  

  

  560 
  • 
  

  

  600 
  

  

  660 
  

  

  680 
  

  

  -•!•_' 
  

  

  -•12 
  

  

  -•13 
  

  

  -12 
  

  

  -11 
  

  

  -•15 
  

  

  -•13 
  

  

  

  -2-34 
  

  

  -2-20 
  

  

  -212 
  

  

  -2-16 
  

  

  -1-92 
  

  

  -201 
  

  

  The 
  rotation 
  and 
  ellipticity 
  arc 
  both 
  negative, 
  as 
  found 
  in 
  

   the 
  case 
  of 
  electrolytic 
  films, 
  tin- 
  rotation 
  in 
  both 
  being 
  of 
  

   about 
  the 
  Bame 
  magnitude 
  

  

  The 
  ellipticity 
  of 
  the 
  metallic 
  type 
  (which 
  was 
  found 
  to 
  be 
  

   the 
  same 
  on 
  both 
  air 
  and 
  glass 
  faces 
  of 
  the 
  film) 
  decreases 
  

   slightly 
  with 
  increasing 
  wave-length, 
  and 
  averages 
  about 
  

   four 
  times 
  that 
  obtained 
  from 
  the 
  electrolytic 
  type. 
  The 
  

   results 
  in 
  Table 
  XII. 
  are 
  plotted 
  in 
  fig. 
  8. 
  

  

  9. 
  Elliptic 
  Polarization 
  produced 
  by 
  Transmission 
  

   should 
  be 
  Proportional 
  to 
  the 
  Thickness. 
  

  

  It 
  may 
  be 
  easily 
  proved 
  that 
  any 
  ellipticity 
  arising 
  from 
  

   differential 
  absorption, 
  of 
  the 
  two 
  circular 
  components 
  into 
  

   which 
  the 
  light 
  is 
  assumed 
  to 
  be 
  resolved, 
  should, 
  for 
  the 
  

   magnitudes 
  observed 
  here, 
  be 
  simply 
  proportional 
  to 
  the 
  

   thickness 
  of 
  the 
  film. 
  

  

  Let 
  A 
  r 
  and 
  Ai 
  be 
  the 
  amplitudes 
  of 
  the 
  " 
  right 
  and 
  

   "left" 
  vibrations 
  respectively. 
  These 
  superposed 
  produce 
  

   an 
  elliptic 
  vibration 
  whose 
  major 
  axis 
  is 
  twice 
  their 
  sum, 
  

  

  