﻿Dispersion 
  of 
  Sodium 
  Vapoui 
  

  

  141 
  

  

  examination 
  with 
  the 
  spectroscope, 
  however, 
  showed 
  that 
  this 
  

   was 
  not 
  the 
  case, 
  for 
  the 
  spectrum 
  consisted 
  of 
  a 
  diffused 
  red 
  

   band, 
  a 
  very 
  narrow 
  bright 
  band 
  in 
  the 
  case 
  where 
  the 
  D 
  

   lines 
  occur, 
  and 
  a 
  diffused 
  band 
  in 
  the 
  green, 
  in 
  which 
  

   flutings 
  seemed 
  to 
  be 
  present. 
  The 
  general 
  appearance 
  of 
  

   the 
  light 
  reminds 
  one 
  of 
  the 
  fluorescence 
  of 
  uranium 
  glass. 
  

  

  I 
  am 
  at 
  the 
  present 
  time 
  engaged 
  in 
  an 
  investigation 
  of 
  

   the 
  spectrum 
  of 
  this 
  fluorescent 
  light, 
  but 
  am 
  not 
  yet 
  prepared 
  

   to 
  say 
  whether 
  the 
  flutings 
  in 
  the 
  green 
  are 
  discontinuities 
  

   in 
  the 
  emission 
  or 
  due 
  to 
  the 
  absorption 
  o£ 
  the 
  non-luminous 
  

   vapour 
  surrounding 
  the 
  fluorescent 
  vapour. 
  A 
  careful 
  

   photographic 
  study 
  will 
  be 
  necessary 
  before 
  this 
  can 
  be 
  

   decided, 
  for 
  which 
  investigation 
  I 
  am 
  employing 
  an 
  iron 
  tube 
  

   provided 
  with 
  copper 
  jackets 
  at 
  each 
  end, 
  through 
  which 
  

   water 
  circulates. 
  (Fig. 
  7.) 
  The 
  light 
  emitted 
  laterally 
  is 
  

   observed 
  through 
  a 
  second 
  iron 
  tube 
  inserted 
  at 
  a 
  right 
  angle, 
  

   and 
  provided 
  with 
  a 
  glass 
  window. 
  The 
  sodium 
  is 
  placed 
  at 
  

   the 
  junction 
  o£ 
  the 
  tubes, 
  which 
  is 
  then 
  raised 
  to 
  a 
  red 
  heat 
  

   with 
  a 
  blast-lamp. 
  

  

  Fig. 
  7. 
  

  

  So 
  far 
  as 
  I 
  am 
  able 
  to 
  judge 
  by 
  passing 
  the 
  light 
  causing 
  

   the 
  fluorescence 
  through 
  colour-screens, 
  the 
  wave-length 
  of 
  

   the 
  emitted 
  light 
  corresponds 
  very 
  nearly 
  to 
  that 
  of 
  the 
  

   exciting 
  vibrations. 
  Interposing 
  a 
  thin 
  cyanine 
  screen, 
  

   which 
  removes 
  the 
  light 
  in 
  the 
  neighbourhood 
  of 
  the 
  D 
  lines, 
  

   causes 
  no 
  apparent 
  diminution 
  in 
  the 
  intensity 
  of 
  the 
  emitted 
  

   light 
  ; 
  but 
  the 
  spectroscope 
  shows 
  that 
  the 
  bright 
  band 
  at 
  

   wave-length 
  5890 
  has 
  disappeared. 
  A 
  film 
  stained 
  with 
  

   aurantia, 
  which 
  removes 
  everything 
  below 
  the 
  " 
  b 
  " 
  group, 
  

   greatly 
  diminishes 
  the 
  intensity 
  of 
  the 
  fluorescent 
  light, 
  and 
  

   changes 
  its 
  colour 
  to 
  red. 
  A 
  solution 
  of 
  cuprammonium 
  of 
  

   moderate 
  strength 
  removes 
  from 
  the 
  light 
  all 
  of 
  the 
  wave- 
  

   lengths 
  which 
  are 
  capable 
  of 
  exciting 
  the 
  fluorescence. 
  A 
  

   more 
  careful 
  investigation 
  will 
  be 
  necessary 
  before 
  deciding 
  

   whether 
  the 
  wave-length 
  of 
  the 
  emitted 
  light 
  is 
  greater 
  than 
  

   that 
  of 
  the 
  exciting 
  vibrations. 
  My 
  impression 
  is 
  that 
  the 
  

   bright 
  narrow 
  band 
  in 
  the 
  yellow 
  is 
  slightly 
  on 
  the 
  red 
  side 
  

  

  