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  XII. 
  On 
  the 
  Emission 
  of 
  Polarized 
  Light 
  by 
  Fluorescent 
  

   Gases. 
  By 
  R. 
  W. 
  Wood, 
  Professor 
  of 
  Experimental 
  Physics, 
  

   Johns 
  Hopkins 
  University*. 
  

  

  PREVIOUS 
  attempts 
  to 
  detect 
  polarized 
  light 
  in 
  the 
  

   emission 
  of 
  fluorescent 
  vapours 
  have 
  yielded 
  negative 
  

   results. 
  Schmidt's 
  observations 
  were 
  made 
  with 
  a 
  nicol 
  only, 
  

   and 
  he 
  failed 
  to 
  detect 
  any 
  difference 
  in 
  the 
  brilliancy 
  of 
  the 
  

   fluorescence 
  as 
  the 
  prism 
  was 
  rotated. 
  

  

  I 
  have 
  always 
  felt 
  that 
  the 
  apparent 
  absence 
  of 
  polarization 
  

   was 
  difficult 
  to 
  reconcile 
  with 
  the 
  theory 
  that 
  the 
  fluorescence 
  

   is 
  merely 
  a 
  re-emission 
  by 
  electrons 
  vibrating 
  synchronously 
  

   with 
  the 
  waves 
  of 
  the 
  exciting 
  light. 
  Quite 
  recently 
  I 
  have 
  

   attacked 
  the 
  problem 
  anew, 
  and 
  by 
  carefully 
  studying 
  the 
  

   conditions 
  have 
  succeeded 
  in 
  getting 
  as 
  much 
  as 
  30 
  per 
  cent, 
  

   of 
  polarized 
  light 
  in 
  the 
  resonance 
  radiation 
  of 
  sodium 
  and 
  

   potassium 
  vapour. 
  The 
  polarization 
  of 
  light 
  produced 
  in 
  this 
  

   way 
  appears 
  to 
  be 
  a 
  wholly 
  new 
  effect, 
  and 
  its 
  study 
  throws 
  

   considerable 
  additional 
  light 
  upon 
  the 
  mechanism 
  of 
  radiation. 
  

  

  The 
  phenomenon 
  was 
  first 
  detected 
  in 
  the 
  case 
  of 
  potassium 
  

   vapour 
  by 
  means 
  of 
  a 
  Savart 
  plate 
  which 
  is 
  capable 
  of 
  

   showing 
  two 
  per 
  cent, 
  of 
  polarization. 
  It 
  was 
  immediately 
  

   picked 
  up 
  in 
  the 
  fluorescence 
  of 
  sodium 
  and 
  iodine, 
  and 
  it 
  is 
  

   probable 
  that 
  other 
  vapours 
  will 
  be 
  found 
  to 
  show 
  it 
  as 
  well. 
  

  

  The 
  apparatus 
  used 
  in 
  the 
  work 
  consisted 
  of 
  a 
  steel 
  tube 
  

   with 
  a 
  lateral 
  branch 
  brazed 
  to 
  its 
  centre 
  for 
  the 
  observation 
  

   of 
  the 
  fluorescent 
  light 
  at 
  an 
  angle 
  of 
  90° 
  with 
  the 
  exciting- 
  

   beam. 
  This 
  tube 
  was 
  used 
  in 
  the 
  earlier 
  work 
  upon 
  fluores- 
  

   cence, 
  before 
  the 
  expedient 
  of 
  " 
  end-on" 
  examination 
  had 
  been 
  

   adopted. 
  The 
  metal 
  was 
  contained 
  in 
  a 
  small 
  retort 
  also 
  

   brazed 
  to 
  the 
  large 
  tube, 
  immediately 
  below 
  the 
  lateral 
  

   observation-tube 
  (fig. 
  1). 
  The 
  light 
  of 
  the 
  arc 
  was 
  focussed 
  

  

  Fijy. 
  1. 
  

  

  "I^jf 
  

  

  by 
  a 
  large 
  lens 
  at 
  the 
  centre 
  of 
  the 
  

   front 
  of 
  the 
  lateral 
  branch. 
  Owinj 
  

   Savart 
  plate 
  it 
  was 
  accessary 
  to 
  e 
  

  

  large 
  tube 
  immediately 
  in 
  

   I 
  to 
  the 
  sensitiveness 
  of 
  the 
  

   iminate 
  all 
  other 
  possible 
  

  

  * 
  Communicated 
  bv 
  the 
  Author. 
  

  

  