﻿250 
  Prof. 
  R. 
  W. 
  Wood 
  on 
  

  

  to 
  the 
  left 
  at 
  a 
  lesser 
  angle 
  than 
  the 
  dotted 
  curves, 
  i. 
  e., 
  at 
  

   about 
  the 
  angle 
  taken 
  by 
  companion 
  line 
  3. 
  

  

  Various 
  modifications 
  in 
  the 
  conditions 
  of 
  excitation 
  have 
  

   been 
  made 
  with 
  a 
  view 
  of 
  establishing 
  which 
  absorption 
  lines 
  

   are 
  responsible 
  for 
  the 
  various 
  doublets. 
  

  

  For 
  example, 
  it 
  was 
  found 
  that 
  the 
  lateral 
  emission 
  and 
  

   the 
  end-on 
  emission 
  of 
  a 
  Cooper-Hewitt 
  lamp 
  showed 
  a 
  very- 
  

   different 
  intensity 
  distribution 
  in 
  the 
  green 
  mercury 
  line, 
  as 
  

   shown 
  by 
  figs, 
  r 
  and 
  *, 
  Plate 
  VIII. 
  , 
  which 
  were 
  made 
  with 
  a 
  

   very 
  fine 
  plane 
  grating 
  by 
  Dr. 
  Anderson. 
  If 
  the 
  iodine 
  

   vapour 
  is 
  excited 
  by 
  the 
  lateral 
  emission 
  of 
  the 
  lamp, 
  as 
  with 
  

   the 
  " 
  light-fnrnace 
  " 
  companion 
  line 
  No. 
  1 
  appeals 
  in 
  addition 
  

   to 
  the 
  strong 
  doublets. 
  See 
  and 
  +1 
  orders 
  of 
  fig. 
  j 
  % 
  

   Plate 
  VII. 
  After 
  several 
  failures 
  I 
  succeeded 
  in 
  obtaining 
  

   a 
  record 
  of 
  the 
  iodine 
  resonance 
  excited 
  by 
  the 
  end-on 
  

   emission, 
  and 
  in 
  this 
  spectrum 
  companion 
  line 
  No. 
  2 
  appeared 
  

   also. 
  Now 
  companion 
  line 
  No. 
  1 
  does 
  not 
  appear 
  in 
  the 
  case 
  

   of 
  excitation 
  by 
  the 
  quartz 
  arc 
  operating 
  at 
  35 
  volts, 
  and 
  the 
  

   short 
  wave-length 
  satellite 
  of 
  the 
  green 
  line 
  is 
  weaker, 
  with 
  

   respect 
  to 
  the 
  main 
  line, 
  in 
  this 
  case, 
  than 
  in 
  the 
  case 
  of 
  the 
  

   Cooper-Hewitt 
  lamp, 
  as 
  is 
  shown 
  by 
  figs, 
  t 
  and 
  u, 
  Plate 
  VIII. 
  

   (t 
  being 
  the 
  Cooper-Hewitt 
  line 
  and 
  u 
  the 
  quartz 
  arc). 
  This 
  

   makes 
  it 
  appear 
  probable 
  that 
  companion 
  line 
  No. 
  1 
  arises 
  

   from 
  the 
  excitation 
  of 
  the 
  absorption 
  line 
  which 
  is 
  in 
  

   coincidence 
  with 
  the 
  short 
  wave-length 
  satellite. 
  

  

  Companion 
  line 
  No. 
  2 
  is 
  probably 
  due 
  to 
  the 
  excitation 
  of 
  

   absorption 
  line 
  No. 
  4. 
  It 
  comes 
  out 
  with 
  excitation 
  by 
  the 
  

   " 
  end-on 
  " 
  emission 
  of 
  the 
  Cooper-Hewitt 
  lamp 
  owing 
  to 
  

   the 
  broadening 
  of 
  the 
  main 
  line 
  which 
  occurs 
  under 
  this 
  

   condition, 
  and 
  for 
  the 
  same 
  reason 
  it 
  is 
  the 
  first 
  line 
  to 
  appear 
  

   when 
  the 
  terminal 
  voltage 
  of 
  the 
  quartz 
  arc 
  is 
  increased. 
  No 
  

   very 
  definite 
  conclusions 
  have 
  been 
  drawn 
  from 
  the 
  numerous 
  

   experiments 
  which 
  have 
  been 
  made 
  with 
  the 
  exciting 
  light 
  

   filtered 
  through 
  bromine 
  vapour 
  and 
  nitrogen 
  tetroxide. 
  

   With 
  a 
  potential 
  of 
  90 
  volts 
  on 
  the 
  quartz 
  arc 
  companion 
  

   lines 
  4 
  and 
  5 
  appear. 
  If 
  the 
  exciting 
  light 
  is 
  filtered 
  through 
  

   bromine 
  vapour 
  contained 
  in 
  an 
  exhausted 
  bulb 
  about 
  30 
  cm. 
  

   in 
  diameter, 
  line 
  No. 
  5 
  disappears 
  in 
  the 
  groups 
  of 
  order 
  

   and 
  + 
  1. 
  In 
  the 
  third 
  order 
  group 
  line 
  No. 
  5 
  is 
  much 
  

   stronger 
  than 
  4 
  and 
  bromine 
  filtration 
  of 
  the 
  exciting 
  light 
  

   equalizes 
  the 
  intensity. 
  Line 
  No. 
  4 
  must 
  therefore 
  be 
  due 
  

   to 
  the 
  excitation 
  of 
  an 
  absorption 
  line 
  which 
  is 
  not 
  in 
  

   coincidence 
  with 
  a 
  bromine 
  line, 
  and 
  which 
  is 
  first 
  covered 
  

   by 
  the 
  mercury 
  line 
  when 
  the 
  lamp 
  operates 
  at 
  90 
  volts. 
  

   This 
  seems 
  to 
  be 
  absorption 
  line 
  No. 
  5, 
  while 
  the 
  other 
  

  

  