﻿856 
  

  

  Prof. 
  Skinner 
  and 
  Mr. 
  Tool 
  on 
  the 
  Optical 
  

  

  in 
  hydrogen 
  under 
  a 
  comparatively 
  low 
  current- 
  density. 
  

   Compared 
  with 
  iron, 
  they 
  are 
  remarkedly 
  transparent 
  hut 
  

   correspondingly 
  less 
  active 
  in 
  the 
  magnetic 
  field. 
  Fig. 
  11 
  

   (PI. 
  XXIV.) 
  gives 
  curves 
  for 
  die 
  magnetic 
  rotation 
  and 
  ellip* 
  

   ticity 
  of 
  two 
  different 
  films, 
  1870 
  x 
  lO" 
  7 
  and 
  3470 
  x 
  10~ 
  7 
  cm. 
  

   thick 
  respectively. 
  They 
  are 
  strikingly 
  different 
  from 
  all 
  

   other 
  types 
  of 
  films 
  investigated. 
  The 
  rotation 
  is 
  positive 
  

   hut 
  decreases 
  with 
  increasing 
  wave-length 
  ; 
  the 
  ellipticity 
  

   is 
  negative 
  throughout 
  and 
  increases 
  in 
  magnitude 
  with 
  

   increasing 
  wave-length. 
  On 
  comparing 
  these 
  curves 
  with 
  

   those 
  of 
  dark 
  iron 
  (fig. 
  4) 
  we 
  are 
  inclined 
  to 
  think 
  that 
  the 
  

   latter 
  would 
  take 
  this 
  form 
  in 
  the 
  region 
  of 
  the 
  spectrum 
  

   below 
  abonl 
  380 
  fi/j,. 
  

  

  Table 
  XIV. 
  contains 
  the 
  values 
  of 
  magnetic 
  rotation 
  

  

  Table 
  XIV.— 
  Dark 
  Cobalt. 
  

   Thickness: 
  No. 
  2, 
  L870x 
  l<>- 
  ; 
  : 
  Xo. 
  3, 
  3470 
  xlO" 
  7 
  cm. 
  

  

  Field: 
  14,000 
  C.G.S. 
  

  

  Wave- 
  

  

  Rotation 
  ,^ 
  „ 
  

   Thickness* 
  10 
  ^ 
  

  

  Ellipticity 
  

  

  1 
  liicknees' 
  

  

  Transmission 
  

   (per 
  cent.). 
  

  

  Extinct. 
  

  

  Befrac. 
  

  

  length. 
  

  

  

  

  

  

  

  XlO-3. 
  

  

  Index. 
  

  

  No, 
  % 
  

  

  No. 
  3. 
  

  

  \ 
  . 
  _. 
  

  

  No. 
  3. 
  

  

  No. 
  2. 
  

  

  No. 
  :;. 
  

  

  440 
  

  

  

  1 
  :J7 
  

  

  

  :, 
  

  

  

  

  1-98 
  

  

  460 
  

  

  

  1-28 
  

  

  -1-% 
  

  

  -"«»- 
  

  

  •7 
  

  

  •2 
  

  

  

  1*99 
  

  

  480 
  

  

  1*01 
  

  

  1-17 
  

  

  - 
  6 
  4 
  

  

  - 
  9-7 
  

  

  10 
  

  

  •2 
  

  

  10-2 
  

  

  1-98 
  

  

  500 
  

  

  110 
  

  

  L07 
  

  

  - 
  7-6 
  

  

  -10-2 
  

  

  1-5 
  

  

  •3 
  

  

  96 
  

  

  1-96 
  

  

  520 
  

  

  107 
  

  

  1-05 
  

  

  - 
  70 
  

  

  — 
  11 
  7 
  

  

  2-1 
  

  

  •5 
  

  

  9-0 
  

  

  1-96 
  

  

  540 
  

  

  •96 
  

  

  •'•'7 
  

  

  - 
  80 
  

  

  -12-2 
  

  

  31 
  

  

  •75 
  

  

  8-6 
  

  

  1-96 
  

  

  560 
  

  

  •88 
  

  

  •07 
  

  

  - 
  8-8 
  

  

  -lis 
  

  

  4-0 
  

  

  11 
  

  

  8-1 
  

  

  1-96 
  

  

  ;»n 
  

  

  •91 
  

  

  •91 
  

  

  _ 
  ,,.., 
  

  

  -12-8 
  

  

  50 
  

  

  i-3 
  

  

  7-6 
  

  

  1-94 
  

  

  600 
  

  

  •94 
  

  

  •89 
  

  

  -100 
  

  

  -13 
  2 
  

  

  65 
  

  

  2*0 
  

  

  69 
  

  

  198 
  

  

  620 
  

  

  

  

  

  ... 
  

  

  8-7 
  

  

  2-9 
  

  

  6-7 
  

  

  

  630 
  

  

  •70 
  

  

  •80 
  

  

  -'96 
  

  

  -13-5 
  

  

  

  

  

  1-94 
  

  

  040 
  

  

  

  

  

  

  10-6 
  

  

  3-7 
  

  

  6-3 
  

  

  

  660 
  

  

  •61 
  

  

  •76 
  

  

  -ib-o 
  

  

  -142 
  

  

  11-5 
  

  

  4-0 
  

  

  61 
  

  

  1-94 
  

  

  680 
  

  

  ... 
  

  

  ... 
  

  

  

  

  107 
  

  

  5-4 
  

  

  56 
  

  

  

  690 
  

  

  •60 
  

  

  •61 
  

  

  

  -148 
  

  

  

  

  

  1 
  : 
  94 
  

  

  and 
  ellipticity 
  divided 
  by 
  the 
  thickness 
  

  

  figure 
  12) 
  j 
  and 
  of 
  the 
  transmission 
  of 
  the 
  two 
  films 
  

  

  (plotted 
  in 
  

   The 
  

   rotation 
  is 
  proportional 
  to 
  the 
  thickness, 
  hut 
  the 
  ellipticity 
  

   increases 
  more 
  rapidly 
  than 
  the 
  thickness. 
  Were 
  this 
  caused 
  

   by 
  elliptic 
  polarization 
  of 
  the 
  reflected 
  light, 
  this 
  latter 
  

   should 
  be 
  over 
  4.10 
  -3 
  , 
  but 
  a 
  test 
  revealed 
  that 
  one-fortieth 
  

   of 
  that 
  magnitude 
  was 
  not 
  present. 
  This 
  indicates 
  that 
  the 
  

  

  