﻿Resonance 
  Spectra 
  of 
  Iodine, 
  243 
  

  

  overlapping 
  which 
  gives 
  rise 
  to 
  considerable 
  irregularity 
  in 
  

   appearance, 
  especially 
  in 
  the 
  green 
  region. 
  The 
  emission 
  

   spectrum 
  of 
  iodine, 
  electrically 
  excited 
  in 
  a 
  vacuum-tube, 
  

   closely 
  resembles 
  the 
  absorption 
  spectrum, 
  though 
  they 
  are 
  

   not 
  exactly 
  complementary, 
  as 
  has 
  been 
  shown 
  recently 
  

   (Wood 
  and 
  Kimura, 
  Astrophysical 
  Journal, 
  Sept. 
  1917). 
  

   Now 
  the 
  green 
  line 
  of 
  mercury, 
  which 
  excites 
  the 
  series 
  of 
  

   doublets, 
  lies 
  just 
  within 
  the 
  head 
  of 
  a 
  well-marked 
  band 
  in 
  

   the 
  emission 
  spectrum, 
  and 
  it 
  will 
  be 
  observed 
  that 
  the 
  

   doublets 
  of 
  order 
  +1 
  and 
  +3 
  are 
  similarly 
  located. 
  This 
  

   was 
  ascertained 
  by 
  superposing 
  the 
  resonance 
  spectrum 
  on 
  a 
  

   band 
  emission 
  spectrum. 
  It 
  is 
  less 
  well 
  shown, 
  except 
  for 
  

   the 
  doublet 
  of 
  the 
  + 
  3 
  order, 
  by 
  fig. 
  d, 
  Plate 
  VI., 
  which 
  was 
  

   taken 
  under 
  conditions 
  not 
  well 
  suited 
  to 
  emphasize 
  the 
  

   heads 
  of 
  the 
  bands, 
  the 
  line 
  spectrum 
  being 
  too 
  prominent. 
  

   The 
  three 
  bands 
  above 
  specified 
  appear 
  as 
  emission 
  bands 
  

   accompanying 
  the 
  doublets 
  when 
  the 
  iodine 
  is 
  excited 
  in 
  

   vacuo, 
  as 
  shown 
  diagrammatically 
  by 
  fig. 
  2, 
  in 
  which 
  the 
  

  

  Fig. 
  2. 
  

  

  doublets 
  have 
  been 
  drawn 
  a 
  little 
  longer 
  than 
  the 
  lines 
  

   forming 
  the 
  bands. 
  The 
  band 
  accompanying 
  the 
  doublet 
  of 
  

   order 
  is 
  not 
  as 
  strongly 
  developed 
  as 
  the 
  other 
  two, 
  and 
  

   only 
  its 
  head 
  shows 
  in 
  fig. 
  /, 
  Plate 
  VI. 
  

  

  By 
  comparing 
  the 
  plates 
  of 
  the 
  resonance 
  spectrum 
  with 
  

   those 
  of 
  the 
  band 
  spectrum, 
  it 
  has 
  been 
  found 
  that 
  the 
  

   doublet 
  of 
  the 
  fourth 
  order 
  also 
  lies 
  just 
  within 
  the 
  head 
  of 
  

   a 
  band. 
  Above 
  this 
  point 
  the 
  relations 
  have 
  not 
  yet 
  been 
  

   exactly 
  determined, 
  for 
  the 
  band 
  spectrnm 
  accompanying 
  

   the 
  resonance 
  doublets 
  has 
  not 
  yet 
  been 
  photographed 
  in 
  the 
  

   red. 
  Though 
  the 
  fourth 
  order 
  doublet, 
  which 
  is 
  faint, 
  lies 
  

   near 
  the 
  head 
  of 
  a 
  band 
  shown 
  on 
  the 
  plate 
  made 
  of 
  the 
  

   electrically 
  excited 
  vapour, 
  it 
  does 
  not 
  occupy 
  a 
  correspond- 
  

   ing 
  position 
  with 
  respect 
  to 
  the 
  band 
  which 
  forms 
  a 
  member 
  

   of 
  the 
  simpler 
  system 
  shown 
  in 
  fig. 
  A, 
  the 
  spacing 
  of 
  which 
  

   is 
  two-fifths 
  of 
  the 
  distance 
  between 
  the 
  doublets, 
  i. 
  e., 
  there 
  

   are 
  five 
  bands 
  between 
  the 
  doublets 
  of 
  first 
  and 
  third 
  order. 
  

  

  It 
  will 
  be 
  necessary 
  to 
  trace 
  this 
  simpler 
  band 
  spectrum 
  

   throughout 
  the 
  orange 
  and 
  red 
  region, 
  before 
  we 
  can 
  be 
  sure 
  

  

  