﻿Resonance 
  Spectra 
  of 
  Iodine. 
  251 
  

  

  component, 
  which 
  is 
  removed 
  by 
  filtration 
  of 
  the 
  exciting 
  

   light 
  through 
  bromine, 
  is 
  probably 
  due 
  to 
  absorption 
  

   line 
  6. 
  

  

  With 
  a 
  potential 
  of 
  110 
  volts 
  on 
  the 
  lamp, 
  companion 
  line 
  

   No. 
  3 
  appears, 
  and 
  this 
  also 
  is 
  removed 
  by 
  the 
  bromine 
  

   filtration 
  of 
  the 
  exciting 
  light, 
  as 
  is 
  shown 
  by 
  figs, 
  p 
  and 
  q, 
  

   Plate 
  VIII., 
  in 
  which 
  q 
  is 
  the 
  resonance 
  spectrum 
  obtained 
  

   when 
  the 
  exciting 
  light 
  is 
  filtered 
  through 
  bromine. 
  It 
  

   appears 
  to 
  be 
  due 
  to 
  the 
  stimulation 
  of 
  absorption 
  line 
  7 
  

   which 
  is 
  in 
  coincidence 
  with 
  a 
  bromine 
  line. 
  

  

  The 
  difficulty 
  in 
  interpreting 
  the 
  results 
  obtained 
  is 
  due 
  to 
  

   the 
  fact 
  that 
  the 
  mercury 
  line 
  widens 
  both 
  to 
  the 
  right 
  and 
  

   left 
  as 
  the 
  voltage 
  increases, 
  so 
  that 
  two 
  absorption 
  lines 
  

   may 
  be 
  attacked 
  simultaneously. 
  If 
  this 
  happens, 
  we 
  can 
  

   differentiate 
  between 
  them 
  only 
  if 
  one 
  of 
  them 
  is 
  in 
  coin- 
  

   cidence 
  with 
  a 
  bromine 
  line 
  and 
  the 
  other 
  not. 
  What 
  is 
  

   most 
  needed 
  just 
  now 
  is 
  one 
  or 
  more 
  other 
  filters 
  similar 
  to 
  

   bromine 
  vapour, 
  but 
  I 
  have 
  not 
  been 
  able 
  to 
  find 
  anything 
  

   with 
  sufficiently 
  narrow 
  lines, 
  though 
  I 
  have 
  tried 
  a 
  number 
  

   of 
  vapours 
  which 
  looked 
  promising. 
  What 
  would 
  be 
  still 
  

   better 
  would 
  be 
  to 
  alter 
  the 
  wave-length 
  of 
  a 
  narrow 
  exciting 
  

   line 
  so 
  as 
  to 
  cause 
  it 
  to 
  pass 
  by 
  degrees 
  from 
  one 
  absorption 
  

   line 
  to 
  the 
  next. 
  

  

  Excitation 
  by 
  the 
  Yellow 
  Lines. 
  

  

  The 
  resonance 
  spectra 
  excited 
  by 
  the 
  two 
  yellow 
  lines 
  have 
  

   not 
  been 
  completely 
  investigated 
  as 
  yet, 
  though 
  a 
  large 
  

   number 
  of 
  photographs 
  have 
  been 
  made. 
  Each 
  yellow 
  line 
  

   excites 
  a 
  series 
  of 
  nearly 
  equidistant 
  groups 
  which 
  resemble 
  

   roughly 
  the 
  groups 
  excited 
  by 
  the 
  green 
  line. 
  Six 
  pairs 
  of 
  

   these 
  groups, 
  from 
  —1 
  order 
  to 
  + 
  4 
  order, 
  photographed 
  

   with 
  rather 
  low 
  dispersion 
  are 
  shown 
  by 
  fig. 
  i, 
  Plate 
  VI. 
  In 
  

   this 
  case 
  the 
  excitation 
  was 
  by 
  the 
  quartz 
  mercury 
  arc 
  

   operating 
  at 
  140 
  volts, 
  the 
  green 
  line 
  having 
  been 
  cut 
  off 
  

   by 
  means 
  of 
  a 
  glass 
  trough 
  filled 
  with 
  a 
  solution 
  of 
  eosine. 
  

   Some 
  difficulty 
  was 
  found 
  in 
  securing 
  the 
  spectrum 
  excited 
  

   by 
  the 
  Cooper-Hewitt 
  arc, 
  as 
  the 
  yellow 
  lines 
  are 
  com- 
  

   paratively 
  weak 
  in 
  this 
  case, 
  but 
  satisfactory 
  results 
  were 
  

   finally 
  obtained 
  with 
  the 
  light 
  furnace, 
  the 
  iodine 
  tube 
  being 
  

   wrapped 
  around 
  with 
  a 
  sheet 
  of 
  gelatine 
  stained 
  to 
  a 
  deep 
  

   orange-yellow. 
  

  

  In 
  this 
  case 
  each 
  yellow 
  line 
  excited 
  a 
  series 
  of 
  doublets, 
  

   but 
  both 
  series 
  were 
  much 
  more 
  irregular 
  than 
  the 
  series 
  

   excited 
  by 
  the 
  green 
  line. 
  

  

  