﻿Resonance 
  Spectra 
  of 
  Iodine. 
  249 
  

  

  order, 
  line 
  6 
  being 
  o£ 
  course 
  the 
  unresolved 
  complex 
  of 
  

   emission 
  lines 
  corresponding 
  to 
  the 
  absorption 
  lines 
  covered 
  

   by 
  the 
  green 
  mercury 
  line. 
  Line 
  7 
  is 
  the 
  companion 
  line 
  

   which, 
  together 
  with 
  the 
  "R.R." 
  line 
  corresponding 
  to 
  

   absorption 
  line 
  3, 
  forms 
  the 
  doublet 
  of 
  order. 
  The 
  

   doublets 
  of 
  higher 
  order 
  lie 
  immediately 
  below, 
  the 
  increasing 
  

   distance 
  between 
  the 
  components 
  being 
  very 
  apparent. 
  

  

  Now 
  line 
  2 
  is 
  a 
  companion 
  line 
  to 
  the 
  R.R. 
  line 
  corre- 
  

   sponding 
  to 
  absorption 
  line 
  4, 
  indicated 
  also 
  by 
  line 
  6 
  in 
  

   the 
  diagram. 
  These 
  two 
  lines 
  form 
  another 
  doublet 
  of 
  zero 
  

   order. 
  The 
  higher 
  orders 
  do 
  not 
  lie 
  immediately 
  below, 
  but 
  

   drift 
  to 
  the 
  left, 
  as 
  indicated 
  by 
  the 
  dotted 
  lines. 
  This 
  is 
  

   due 
  to 
  the 
  fact 
  that 
  the 
  constant 
  in 
  the 
  second 
  term 
  of 
  the 
  

   formula 
  is 
  a 
  little 
  less 
  than 
  in 
  the 
  case 
  of 
  the 
  first 
  series 
  of 
  

   doublets 
  considered, 
  in 
  other 
  words 
  the 
  doublets 
  are 
  closer 
  

   together. 
  

  

  In 
  the 
  group 
  of 
  the 
  first 
  order 
  the 
  main 
  line 
  of 
  this 
  series 
  

   of 
  doublets 
  can 
  be 
  separated 
  from 
  the 
  main 
  line 
  of 
  the 
  other 
  

   series 
  only 
  in 
  the 
  fourth 
  order 
  spectrum 
  of 
  the 
  grating. 
  In 
  

   the 
  third 
  order 
  group 
  it 
  is 
  so 
  far 
  detached, 
  that 
  it 
  was 
  con- 
  

   fused 
  for 
  a 
  long 
  time 
  with 
  line 
  5 
  of 
  the 
  first 
  order 
  group. 
  

   If 
  we 
  compare 
  the 
  orders 
  and 
  6 
  we 
  shall 
  see 
  another 
  case 
  

   of 
  this 
  kind 
  : 
  If 
  it 
  were 
  not 
  for 
  this 
  diagram 
  arrangement 
  of 
  

   the 
  groups, 
  we 
  should 
  probably 
  assume 
  that 
  the 
  first 
  line 
  to 
  

   the 
  left 
  of 
  group 
  6 
  corresponded 
  to 
  line 
  1 
  in 
  group 
  0, 
  whereas 
  

   the 
  diagram 
  shows 
  clearly 
  that 
  it 
  corresponds 
  to 
  line 
  2. 
  

   Moreover, 
  it 
  appears 
  in 
  the 
  60-volt 
  excitation, 
  which 
  does 
  

   not 
  bring 
  out 
  lines 
  1 
  and 
  3. 
  

  

  In 
  the 
  construction 
  of 
  the 
  diagram 
  it 
  is, 
  of 
  course, 
  

   necessary 
  to 
  leave 
  blank 
  spaces 
  for 
  the 
  missing 
  orders, 
  

   otherwise 
  the 
  corresponding 
  lines 
  will 
  not 
  lie 
  on 
  a 
  smooth 
  

   curve. 
  

  

  It 
  is 
  a 
  little 
  difficult 
  to 
  explain 
  in 
  words 
  just 
  how 
  this 
  

   diagram 
  is 
  to 
  be 
  interpreted, 
  though 
  it 
  is 
  clear 
  enough 
  if 
  the 
  

   theory 
  of 
  the 
  group 
  formation 
  which 
  I 
  have 
  given 
  is 
  under- 
  

   stood. 
  All 
  of 
  the 
  lines 
  with 
  the 
  exception 
  of 
  6 
  in 
  the 
  order 
  

   orroup 
  must 
  be 
  companion 
  lines, 
  line 
  6 
  being 
  made 
  up 
  of 
  

   the 
  unresolved 
  R.R. 
  lines. 
  In 
  the 
  case 
  of 
  the 
  doublets, 
  the 
  

   superposition 
  of 
  which 
  forms 
  the 
  other 
  groups, 
  we 
  must 
  

   distinguish 
  between 
  what 
  I 
  have 
  called 
  the 
  main 
  line 
  and 
  

   the 
  companion. 
  As 
  we 
  run 
  up 
  the 
  diagram 
  the 
  main 
  lines 
  

   should 
  lie 
  on 
  curves 
  intersecting 
  line 
  6, 
  for 
  example, 
  the 
  

   dotted 
  curve 
  shown 
  which 
  belongs 
  to 
  the 
  2, 
  6 
  doublet. 
  

  

  I 
  have 
  not 
  yet 
  been 
  able 
  to 
  identify 
  certainly 
  any 
  other 
  

   main 
  lines, 
  though 
  I 
  suspect 
  that 
  the 
  one 
  corresponding 
  to 
  

   companion 
  line 
  9 
  descends 
  from 
  line 
  6 
  on 
  a 
  curve 
  sloping 
  

  

  