﻿Spectra 
  of 
  Iodine 
  under 
  High 
  Dispersion. 
  833 
  

  

  absorption 
  spectrum 
  * 
  with 
  a 
  diagram 
  of 
  a 
  portion 
  of 
  the 
  

   group 
  around 
  the 
  R.R. 
  line 
  immediately 
  above 
  it. 
  The 
  

   seven 
  absorption 
  lines 
  covered 
  by 
  the 
  green 
  Hg 
  line 
  are 
  

   indicated 
  by 
  the 
  arrows. 
  The 
  upper 
  diagram 
  has 
  been 
  

   shitted 
  to 
  the 
  right 
  in 
  order 
  to 
  show 
  as 
  much 
  of 
  the 
  group 
  

   as 
  possible. 
  To 
  bring 
  the 
  two 
  into 
  coincidence 
  the 
  line 
  

   marked 
  Hg 
  should 
  be 
  brought 
  over 
  the 
  seven 
  absorption 
  

   lines. 
  

  

  The 
  circumstance 
  that 
  the 
  group 
  of 
  lines 
  at 
  the 
  R.R. 
  line 
  

   is 
  many 
  times 
  wider 
  than 
  the 
  group 
  of 
  seven 
  absorption 
  lines 
  

   is 
  a 
  very 
  important 
  point, 
  in 
  fact 
  the 
  most 
  important 
  of 
  all, 
  

   for 
  it 
  shows 
  us 
  that 
  each 
  one 
  of 
  the 
  absorption 
  lines 
  

   must 
  be 
  responsible 
  for 
  more 
  than 
  a 
  single 
  line 
  in 
  each 
  

   group. 
  

  

  The 
  R.R. 
  lines 
  of 
  the 
  seven 
  absorption 
  lines 
  would 
  all 
  

   appear 
  superposed 
  with 
  the 
  resolving 
  power 
  employed 
  in 
  

   observations 
  of 
  the 
  resonance 
  spectrum, 
  and 
  the 
  appearance 
  

   of 
  a 
  group 
  of 
  lines 
  at 
  this 
  point 
  shows 
  that 
  each 
  absorption 
  

   line 
  gives 
  us 
  a 
  R.R. 
  line 
  with 
  one 
  or 
  more 
  close 
  companions. 
  

   The 
  R.R. 
  lines 
  are 
  of 
  course 
  superposed 
  in 
  the 
  photographs, 
  

   but 
  the 
  companions 
  are 
  far 
  enough 
  removed 
  to 
  be 
  resolved, 
  

   and 
  taken 
  collectively 
  form 
  the 
  group. 
  As 
  the 
  potential 
  

   drop 
  of 
  the 
  lamp 
  is 
  increased 
  the 
  companion 
  lines 
  increase 
  

   in 
  number, 
  as 
  more 
  and 
  more 
  absorption 
  lines 
  are 
  covered 
  

   by 
  the 
  green 
  line. 
  

  

  This 
  will 
  be 
  more 
  readily 
  understood 
  perhaps 
  by 
  reference 
  

   to 
  fig. 
  2, 
  which 
  is 
  a 
  chart 
  of 
  the 
  groups 
  of 
  the 
  iodine 
  

   resonance 
  spectra 
  excited 
  by 
  the 
  quartz 
  arc 
  under 
  different 
  

   conditions. 
  With 
  140 
  volts 
  potential 
  difference 
  we 
  find 
  

   three 
  very 
  similar 
  groups 
  of 
  lines 
  at 
  wave-lengths 
  5461, 
  

   5525, 
  and 
  5657*1. 
  A 
  characteristic 
  faint 
  triplet 
  to 
  the 
  left, 
  

   a 
  strong 
  triplet 
  in 
  the 
  middle, 
  with 
  two 
  or 
  three 
  faint 
  lines 
  

   to 
  the 
  right. 
  Now 
  the 
  general 
  law 
  of 
  resonance 
  spectra 
  has 
  

   been 
  found 
  to 
  be 
  that 
  the 
  excitation 
  of 
  a 
  single 
  absorption 
  

   line 
  causes 
  the 
  emission 
  of 
  a 
  spectrum 
  of 
  single 
  (usually) 
  

   lines, 
  placed 
  at 
  sensibly 
  equal 
  intervals 
  along 
  a 
  normal 
  

   spectrum, 
  certain 
  lines 
  of 
  the 
  series 
  being 
  often 
  absent. 
  

   Now 
  if 
  the 
  groups 
  or" 
  lines, 
  which 
  appear 
  when 
  a 
  very 
  close 
  

   group 
  of 
  absorption 
  lines 
  are 
  excited 
  (multiplex 
  excitation), 
  

   were 
  formed 
  by 
  the 
  superposition 
  of 
  a 
  number 
  of 
  series 
  of 
  

   equidistant 
  lines, 
  all 
  originating 
  at 
  the 
  same 
  point 
  (so 
  far 
  as 
  

   the 
  resolving 
  power 
  employed 
  is 
  concerned), 
  they 
  would 
  be 
  

   identical 
  in 
  appearance, 
  but 
  their 
  widths 
  would 
  increase 
  

  

  * 
  This 
  photograph 
  was 
  made 
  by 
  Mr. 
  Ellemian 
  of 
  the 
  Mt. 
  Wilson 
  

   Observatory. 
  It 
  was 
  taken 
  on 
  a 
  process 
  plate 
  of 
  a 
  very 
  fine 
  grain 
  and 
  

   bears 
  enlargement 
  much 
  better 
  than 
  my 
  own 
  photographs. 
  

  

  Phil. 
  Maa. 
  S. 
  6. 
  Vol. 
  26. 
  No. 
  155. 
  Nov. 
  1913. 
  3 
  L. 
  

  

  