﻿Resonance 
  Spectra 
  of 
  Iodine. 
  247 
  

  

  In 
  the 
  case 
  of 
  the 
  doublets 
  excited 
  by 
  the 
  Cooper-Hewitt 
  

   lamp 
  the 
  companion 
  lines 
  lie 
  on 
  the 
  long 
  wave-length 
  side 
  

   of 
  the 
  main 
  lines, 
  at 
  distances 
  which 
  gradually 
  increase 
  

   with 
  increasing 
  group 
  order. 
  The 
  widths 
  of 
  the 
  doublets 
  in 
  

   the 
  various 
  orders 
  are 
  given 
  in 
  the 
  following 
  table 
  : 
  — 
  

  

  rder. 
  

  

  Width. 
  

  

  Order. 
  

  

  Width 
  

  

  

  

  1-48 
  

  

  15 
  

  

  2-04 
  

  

  1 
  

  

  1-54 
  

  

  17 
  

  

  2-19 
  

  

  3 
  

  

  1-64 
  

  

  18 
  

  

  2-25 
  

  

  5 
  

  

  1-72 
  

  

  20 
  

  

  243 
  

  

  8 
  

  

  1-76 
  

  

  22 
  

  

  2-45 
  

  

  10 
  

  

  1-85. 
  

  

  23 
  

  

  2 
  53 
  

  

  11 
  

  

  1-90 
  

  

  25 
  

  

  2-50 
  

  

  12 
  

  

  1-95 
  

  

  27 
  

  

  2-80 
  

  

  13 
  

  

  1-96 
  

  

  

  

  The 
  increment 
  is 
  not 
  quite 
  regular, 
  and 
  it 
  is 
  my 
  hope 
  that 
  

   a 
  new 
  set 
  of 
  plates 
  made 
  with 
  a 
  more 
  powerful 
  spectrograph 
  

   will 
  show 
  no 
  discrepancies. 
  It 
  is 
  pretty 
  clearly 
  established, 
  

   however, 
  that 
  the 
  distance 
  of 
  the 
  companion 
  line 
  from 
  the 
  

   main 
  line 
  increases 
  progressively. 
  If 
  this 
  is 
  true 
  of 
  the 
  

   companion 
  lines 
  of 
  the 
  other 
  main 
  lines, 
  this 
  circumstance, 
  

   combined 
  with 
  the 
  fact 
  that 
  the 
  group 
  of 
  main 
  lines 
  widens 
  

   as 
  we 
  pass 
  to 
  groups 
  of 
  higher 
  orders, 
  explains 
  fully 
  the 
  fact 
  

   that 
  the 
  groups 
  gradually 
  change 
  in 
  appearance 
  as 
  w 
  T 
  e 
  ascend 
  

   the 
  series. 
  

  

  Groups 
  4, 
  5, 
  6, 
  7, 
  and 
  8 
  are 
  shown 
  by 
  figs, 
  n 
  and 
  o 
  of 
  

   Plate 
  VII., 
  the 
  former 
  excited 
  by 
  the 
  Cooper-Hewitt 
  lamp 
  r 
  

   the 
  latter 
  by 
  the 
  quartz 
  arc 
  at 
  115 
  volts. 
  In 
  the 
  case 
  of 
  

   fig. 
  n 
  we 
  have 
  faint 
  series 
  excited 
  by 
  the 
  two 
  yellow 
  T 
  mercury 
  

   lines, 
  one 
  of 
  which 
  (5790) 
  lies 
  within 
  the 
  fifth 
  order 
  group 
  

   excited 
  by 
  the 
  green 
  line. 
  The 
  lines 
  marked 
  by 
  small 
  crosses 
  

   are 
  the 
  ghosts 
  of 
  the 
  yellow 
  mercury 
  lines, 
  and 
  should 
  not 
  be 
  

   confused 
  with 
  the 
  resonance 
  lines. 
  

  

  In 
  fig. 
  o 
  it 
  will 
  be 
  observed 
  that 
  the 
  doublets 
  shown 
  in 
  

   fig. 
  n 
  have 
  become 
  relatively 
  weak, 
  and 
  that 
  we 
  have 
  a 
  new 
  

   series 
  of 
  strong 
  doublets 
  displaced 
  towards 
  the 
  left 
  with 
  

   respect 
  to 
  the 
  old 
  ones. 
  This 
  is 
  due 
  to 
  the 
  fact 
  that, 
  in 
  the 
  

   case 
  of 
  the 
  quartz 
  arc 
  operating 
  at 
  115 
  volts, 
  the 
  green 
  

   mercury 
  line 
  is 
  strongly 
  reversed 
  and 
  the 
  excitation 
  of 
  

   absorption 
  line 
  No. 
  4 
  (Plate 
  VI. 
  fig. 
  a) 
  becomes 
  relatively 
  

   weak, 
  as 
  it 
  coincides 
  with 
  the 
  reversed 
  core 
  of 
  the 
  mercury 
  

   line. 
  In 
  the 
  seventh 
  order 
  of 
  tig. 
  n 
  there 
  are 
  four 
  lines. 
  

   Two 
  of 
  these, 
  marked 
  by 
  dots, 
  form 
  the 
  doublet 
  excited 
  by 
  

   the 
  green 
  mercury 
  line; 
  the 
  other 
  two 
  belong 
  to 
  a 
  series 
  of 
  

   doublets 
  excited 
  by 
  the 
  yellow 
  line 
  5790. 
  The 
  same 
  con- 
  

   dition 
  is 
  found 
  in 
  the 
  fourth 
  order 
  group, 
  the 
  dotted 
  doublet 
  

   in 
  this 
  case 
  lying 
  to 
  the 
  right 
  of 
  the 
  doublet 
  of 
  order 
  —1 
  

  

  