﻿408 
  Prof. 
  R. 
  W. 
  Wood 
  on 
  the 
  Electrical 
  Resonance 
  of 
  

  

  coloured 
  films 
  were 
  examined 
  by 
  polarized 
  light. 
  To 
  enu- 
  

   merate 
  all 
  of 
  the 
  different 
  effects 
  which 
  I 
  have 
  recorded 
  in 
  

   ray 
  note-book 
  would 
  require 
  too 
  much 
  space, 
  and 
  I 
  shall 
  

   only 
  mention 
  two 
  or 
  three 
  typical 
  effects. 
  The 
  arrangement 
  

   of 
  the 
  apparatus 
  was 
  as 
  follows. 
  The 
  light 
  of 
  a 
  Welsbach 
  

   burner 
  passed 
  through 
  a 
  Nicol 
  prism 
  mounted 
  in 
  an 
  opaque 
  

   screen 
  in 
  such 
  a 
  way 
  that 
  it 
  could 
  be 
  turned 
  through 
  a 
  right 
  

   angle, 
  then 
  through 
  the 
  coloured 
  film 
  at 
  oblique 
  incidence, 
  

   and 
  then 
  into 
  the 
  direct-vision 
  spectroscope. 
  It 
  was 
  found 
  

   in 
  the 
  case 
  of 
  one 
  of 
  the 
  purple 
  films, 
  which 
  had 
  a 
  strong 
  

   absorption-band 
  in 
  the 
  yellow-green, 
  that 
  this 
  band 
  was 
  only 
  

   present 
  when 
  tbe 
  electric 
  vector 
  was 
  parallel 
  to 
  the 
  plane 
  of 
  

   incidence. 
  When 
  the 
  electric 
  vector 
  was 
  parallel 
  to 
  the 
  

   surface 
  the 
  spectrum 
  appeared 
  continuous. 
  In 
  every 
  case 
  

   the 
  colour 
  was 
  much 
  more 
  pronounced 
  when 
  tbe 
  electric 
  

   vector 
  had 
  a 
  component 
  normal 
  to 
  the 
  surface. 
  On 
  turning 
  

   the 
  nicol 
  from 
  one 
  position 
  to 
  the 
  other, 
  no 
  motion 
  of 
  the 
  

   absorption-band 
  could 
  be 
  detected 
  in 
  this 
  film, 
  the 
  change 
  

   consisting 
  in 
  a 
  gradual 
  fading 
  away. 
  In 
  other 
  films, 
  how- 
  

   ever, 
  I 
  have 
  sometimes 
  found 
  that 
  the 
  absorption 
  -band 
  shifts 
  

   its 
  position 
  when 
  the 
  nicol 
  is 
  turned. 
  For 
  example, 
  in 
  the 
  

   case 
  of 
  a 
  film 
  which 
  showed 
  an 
  absorption-band 
  a 
  little 
  below 
  

   the 
  D 
  lines 
  with 
  the 
  electric 
  vector 
  perpendicular 
  to 
  the 
  

   plane 
  of 
  incidence, 
  on 
  turning 
  the 
  nicol 
  the 
  band 
  moved 
  

   along 
  into 
  the 
  red 
  and 
  became 
  broader 
  and 
  fainter, 
  the 
  effect 
  

   being 
  similar 
  to 
  that 
  produced 
  by 
  cooling 
  the 
  film. 
  

  

  When 
  the 
  films 
  are 
  viewed 
  between 
  two 
  nicols 
  more 
  com- 
  

   plicated 
  effects 
  are 
  obtained, 
  which 
  I 
  shall 
  omit 
  for 
  the 
  

   present 
  as 
  they 
  have 
  not 
  yet 
  been 
  carefully 
  studied. 
  

  

  Until 
  someone 
  has 
  calculated 
  the 
  behaviour 
  of 
  a 
  sheet 
  

   of 
  resonators 
  at 
  oblique 
  incidence 
  with 
  reference 
  to 
  waves 
  

   polarized 
  in 
  and 
  at 
  right 
  angles 
  to 
  the 
  plane 
  of 
  incidence, 
  

   it 
  will 
  be 
  impossible 
  to 
  say 
  whether 
  the 
  polarization 
  experi- 
  

   ments 
  are 
  in 
  accordance 
  with 
  the 
  resonance 
  hypothesis 
  or 
  

   not. 
  It 
  seems 
  to 
  me, 
  however, 
  that 
  the 
  results 
  obtained 
  with 
  

   polarized 
  light 
  will 
  be 
  the 
  means 
  of 
  eventually 
  determining 
  

   the 
  exact 
  cause 
  of 
  the 
  colours, 
  or 
  at 
  least 
  in 
  deciding 
  in 
  favour 
  

   of, 
  or 
  against, 
  the 
  theory 
  of 
  electrical 
  resonance. 
  

  

  Electrical 
  Conductivity 
  of 
  the 
  Films. 
  

   The 
  coloured 
  films 
  are 
  apparently 
  non-conducting. 
  Inas- 
  

   much 
  as 
  it 
  was 
  difficult 
  to 
  make 
  sure 
  that 
  the 
  films 
  were 
  

   deposited 
  up 
  to 
  and 
  against 
  the 
  " 
  sealed-in 
  " 
  electrodes, 
  a 
  

   bulb 
  was 
  fitted 
  with 
  a 
  ground 
  joint 
  through 
  which 
  the 
  wires 
  

   passed 
  as 
  shown 
  in 
  fig. 
  4. 
  After 
  the 
  film 
  had 
  been 
  depoisted 
  

   the 
  joint 
  was 
  turned, 
  causing 
  the 
  tips 
  of 
  the 
  wire 
  to 
  be 
  drawn 
  

  

  