﻿Spectra 
  of 
  Iodine 
  under 
  High 
  Dispersion. 
  839 
  

  

  groups, 
  and 
  since 
  fig. 
  6 
  of 
  PI. 
  XVI. 
  shows 
  us 
  that 
  now 
  ab- 
  

   sorption 
  line 
  Xo. 
  2 
  is 
  excited 
  by 
  the 
  further 
  broadening 
  of 
  

   the 
  green 
  line, 
  we 
  may 
  regard 
  companion 
  line 
  4 
  as 
  due 
  to 
  

   this 
  absorption 
  line. 
  At 
  90 
  volts 
  potential 
  we 
  have 
  ab- 
  

   sorption 
  line 
  No. 
  5 
  picked 
  up 
  by 
  the 
  exciting 
  radiation, 
  and 
  

   companion 
  line 
  Xo. 
  9 
  appears. 
  It 
  is 
  extremely 
  difficult 
  to 
  

   make 
  out 
  which 
  lines 
  are 
  associated 
  in 
  this 
  way, 
  and 
  I 
  have 
  

   spent 
  many 
  hours 
  in 
  examining 
  and 
  comparing 
  the 
  photo- 
  

   graphs. 
  Certain 
  points 
  which 
  1 
  could 
  not 
  explain 
  made 
  it 
  

   seem 
  imperative 
  to 
  obtain 
  photographs 
  of 
  the 
  groups 
  of 
  

   resonance 
  lines 
  under 
  the 
  highest 
  dispersion 
  possible, 
  and 
  I 
  

   accordingly 
  shifted 
  to 
  the 
  fourth 
  order 
  spectrum 
  of 
  the 
  large 
  

   grating, 
  and 
  secured 
  a 
  series 
  of 
  excellent 
  photographs 
  of 
  the 
  

   1st 
  and 
  3rd 
  order 
  groups, 
  with 
  the 
  quartz 
  arc 
  running 
  wuth 
  

   various 
  potential 
  drops, 
  and 
  with 
  the 
  Cooper-Hewitt 
  lamp. 
  

   Enlargements 
  of 
  the 
  1st 
  order 
  group 
  are 
  reproduced 
  on 
  

   PI. 
  XV. 
  tig. 
  7. 
  The 
  most 
  interesting 
  point 
  brought 
  out 
  was 
  

   that 
  line 
  Xo. 
  1 
  of 
  the 
  group 
  was 
  a 
  close 
  doublet, 
  and 
  that 
  the 
  

   component 
  of 
  longer 
  wave-length 
  disappeared 
  if 
  the 
  exciting 
  

   light 
  was 
  filtered 
  through 
  bromine 
  vapour. 
  The 
  bromine 
  

   filtration 
  of 
  the 
  exciting 
  light 
  also 
  causes 
  the 
  disappearance 
  

   of 
  line 
  Xo. 
  3 
  from 
  the 
  resonance 
  group, 
  as 
  I 
  showed 
  in 
  the 
  

   earlier 
  paper. 
  Owing 
  to 
  the 
  improved 
  definition 
  shown 
  by 
  

   the 
  10-foot 
  spectrograph 
  since 
  its 
  burial, 
  I 
  was 
  enabled 
  to 
  

   get 
  a 
  more 
  satisfactory 
  photograph 
  of 
  the 
  bromine 
  and 
  iodine 
  

   absorption 
  spectra 
  in 
  coincidence 
  than 
  the 
  one 
  obtained 
  last 
  

   summer. 
  It 
  is 
  reproduced 
  on 
  PL 
  XYI. 
  fig. 
  3, 
  the 
  group 
  of 
  

   seven 
  iodine 
  lines 
  with 
  which 
  we 
  are 
  concerned 
  being 
  indicated 
  

   by 
  the 
  arrows. 
  The 
  bromine 
  vapour 
  removes 
  from 
  the 
  green 
  

   mercury 
  line 
  those 
  frequencies 
  which 
  are 
  capable 
  of 
  stimu- 
  

   lating 
  the 
  iodine 
  lines 
  3, 
  6, 
  and 
  7, 
  the 
  removal 
  being 
  most 
  

   complete 
  in 
  the 
  case 
  of 
  line 
  3, 
  for 
  which 
  the 
  coincidence 
  is 
  

   absolute. 
  The 
  photographs 
  taken 
  with 
  high 
  dispersion 
  show 
  

   that 
  line 
  5 
  of 
  the 
  resonance 
  group, 
  which 
  I 
  have 
  called 
  the 
  

   core 
  line, 
  becomes 
  double 
  and 
  finally 
  triple 
  as 
  the 
  potential 
  

   of 
  the 
  exciting 
  arc 
  is 
  increased. 
  On 
  the 
  theory 
  of 
  the 
  

   formation 
  of 
  the 
  groups 
  which 
  I 
  have 
  suggested, 
  this 
  would 
  

   mean 
  that 
  the 
  core 
  lines 
  corresponding 
  to 
  the 
  different 
  

   absorption 
  lines 
  are 
  not 
  in 
  exact 
  coincidence, 
  as 
  was 
  at 
  first 
  

   supposed. 
  I 
  have 
  given 
  in 
  fig. 
  3 
  a 
  diagram 
  of 
  the 
  1st 
  order 
  

   group 
  as 
  obtained 
  with 
  high 
  dispersion 
  and 
  with 
  the 
  exciting 
  

   lamp 
  operating 
  at 
  different 
  potentials, 
  and 
  also 
  a 
  diagram 
  

   which 
  represents, 
  as 
  nearly 
  as 
  I 
  am 
  able 
  to 
  say 
  at 
  the 
  

   present 
  time, 
  the 
  decomposition 
  of 
  the 
  group 
  into 
  its 
  con- 
  

   stituents. 
  The 
  number 
  of 
  the 
  iodine 
  absorption 
  line 
  which 
  

  

  