﻿834 
  Prof. 
  Skinner 
  and 
  Mr. 
  Tool 
  on 
  the 
  Optical 
  

  

  and 
  ellipticity 
  reverse 
  their 
  direction 
  with 
  respect 
  to 
  the 
  

   magnetizing 
  current. 
  

  

  By 
  varying 
  the 
  method 
  of 
  producing 
  the 
  films 
  of 
  iron 
  we 
  

   have 
  obtained 
  three 
  distinct 
  types, 
  one 
  of 
  which, 
  as 
  stated, 
  

   exhibits 
  a 
  marked 
  absorption 
  region 
  in 
  the 
  visible 
  spectrum, 
  

   while 
  the 
  other 
  two 
  seem 
  to 
  have 
  the 
  centre 
  of 
  such 
  a 
  region 
  

   shifted 
  well 
  out 
  in 
  the 
  ultra-violet. 
  Similar 
  characteristic 
  

   differences 
  are 
  found 
  in 
  films 
  of 
  cobalt. 
  Oathodic 
  films 
  of 
  

   nickel 
  were 
  found 
  to 
  be 
  almost 
  imperceptibly 
  active, 
  though 
  

   electrolytic 
  nickel 
  gives 
  measurable 
  values. 
  

  

  We 
  have 
  also 
  found 
  that 
  a 
  measurable 
  ellipticity 
  is 
  

   imparted 
  to 
  the 
  originally 
  plane-polarized 
  light 
  by 
  all 
  films 
  

   producing 
  a 
  measurable 
  magnetic 
  rotation. 
  

  

  Experimental 
  Methods. 
  

   1. 
  Production 
  of 
  Films. 
  

  

  As 
  stated 
  above, 
  three 
  distinct 
  types 
  of 
  both 
  iron 
  and 
  

   cobalt 
  were 
  obtained 
  — 
  two 
  by 
  the 
  glow 
  current 
  in 
  gases, 
  

   the 
  other 
  by 
  electrolytic 
  deposition. 
  

  

  Iron. 
  — 
  Using 
  a 
  glow 
  current, 
  the 
  films 
  were 
  deposited 
  

   from 
  a 
  circular 
  disk 
  cathode 
  of 
  Swedish 
  iron 
  (diam. 
  10 
  mm.). 
  

   The 
  form 
  of 
  discharge 
  chamber 
  is 
  repre- 
  

   sented 
  in 
  fig. 
  1. 
  To 
  confine 
  the 
  current 
  

   to 
  the 
  face 
  of 
  the 
  cathode 
  K, 
  this 
  was 
  

   backed 
  by 
  a 
  porcelain 
  disk 
  and 
  its 
  stem 
  

   sheathed 
  in 
  porcelain 
  tubing, 
  the 
  tempe- 
  

   rature 
  in 
  some 
  cases 
  running 
  too 
  high 
  for 
  

   glass. 
  The 
  films 
  were 
  deposited 
  on 
  very 
  

   thin 
  (0*1 
  to 
  0'2 
  mm.) 
  microscope 
  cover- 
  

   glasses, 
  selected 
  plane, 
  free 
  from 
  double 
  

   refraction, 
  and 
  of 
  measured 
  magnetic 
  

   rotation 
  — 
  the 
  latter 
  being 
  generally 
  a 
  

   small 
  fraction 
  of 
  that 
  imparted 
  by 
  the 
  

   metal 
  film. 
  To 
  make 
  a 
  film, 
  one 
  of 
  these 
  

   glasses 
  was 
  mounted 
  parallel 
  to 
  the 
  face 
  

   of 
  the 
  cathode- 
  at 
  an 
  adjustable 
  distance 
  

   below 
  it. 
  The 
  discharge 
  chamber 
  was 
  

   then 
  evacuated 
  and 
  usually 
  dried 
  by 
  

   leaving 
  it 
  in 
  connexion 
  with 
  a 
  chamber 
  

   containing 
  phosphorus 
  pentoxide. 
  Dry 
  

   gas 
  (hydrogen, 
  unless 
  otherwise 
  stated) 
  

   was 
  finally 
  admitted 
  to 
  a 
  pressure 
  of 
  one 
  

   to 
  three 
  millimetres 
  of 
  mercury. 
  The 
  

   electric 
  current 
  — 
  -furnished 
  by 
  a 
  1000-volt 
  storage-battery 
  — 
  

   was 
  then 
  passed 
  from 
  the 
  iron 
  disk 
  as 
  cathode. 
  

  

  