﻿844 
  

  

  Prof. 
  R. 
  W. 
  Wood 
  on 
  Resonance 
  

  

  with 
  a 
  group 
  formation 
  similar 
  to 
  that 
  which 
  we 
  had 
  in 
  the 
  

   case 
  of 
  the 
  green 
  line. 
  The 
  wave-lengths 
  of 
  the 
  lines 
  are 
  

   given 
  in 
  the 
  following 
  table 
  : 
  — 
  

  

  Excited 
  by 
  Hg 
  577. 
  

  

  Excited 
  by 
  Hg 
  579. 
  

  

  64656 
  

  

  5916- 
  1 
  

  

  64988 
  

  

  

  5938- 
  2 
  

  

  6462- 
  

  

  5910-6 
  4 
  

  

  6494- 
  

  

  

  5935-4 
  5 
  

  

  5457'6 
  

  

  5906-6 
  2 
  

  

  6490- 
  

  

  

  5932- 
  3 
  

  

  Faint 
  broad 
  

  

  5847-3 
  

  

  6409-5 
  

  

  

  5868-3 
  I 
  

  

  band. 
  

  

  5845-4 
  

  

  6405-8 
  

  

  

  58665 
  2 
  

  

  

  58418 
  6 
  

  

  6402-8 
  

  

  

  5863-3 
  6 
  

  

  6302-5 
  

  

  5837-7 
  3 
  

  

  

  

  5860-7 
  3 
  

  

  621)8-2 
  

  

  

  6327-5 
  

  

  

  

  6293-7 
  

  

  57755 
  2 
  

  

  6324-5 
  

  

  

  5795-3 
  2 
  

  

  

  5773-4 
  3 
  

  

  6321-3 
  

  

  

  5792-8 
  3 
  

  

  6217- 
  

  

  57o9-6 
  lOR.R.line. 
  

  

  

  

  5791- 
  10R.R. 
  line. 
  

  

  6214* 
  edges 
  of 
  

  

  5765-8 
  4 
  

  

  6248-6 
  

  

  

  5789-3 
  3 
  

  

  band. 
  

  

  5763-6 
  

  

  6245-7 
  

  

  

  5786- 
  2 
  

  

  6142-5 
  

  

  

  6242-3 
  

  

  

  

  6139- 
  edges 
  of 
  

  

  5705-8 
  1 
  

  

  

  

  5726-3 
  2 
  

  

  band. 
  

  

  5703 
  4 
  2 
  

  

  61664 
  

  

  

  5723-4 
  3 
  

  

  6067-5 
  

  

  5699-8 
  6 
  

  

  6164- 
  

  

  

  5720-3 
  8 
  

  

  6003-3 
  

  

  5696 
  6 
  2 
  

  

  6161-3 
  

  

  

  5717-8 
  3 
  

  

  6059- 
  

  

  5695-6 
  2 
  

  

  6090-3 
  

  

  

  5654-8 
  2 
  

  

  5993-6 
  1 
  

  

  5634-8 
  1 
  

  

  6086-5 
  

  

  

  5651-8 
  4 
  

  

  5988- 
  2 
  

  

  5632- 
  3 
  

  

  6083-8 
  

  

  

  5648-8 
  2 
  

  

  5983-5 
  2 
  

  

  5628-6 
  1 
  

  

  6015- 
  

  

  

  5590* 
  Very 
  faint. 
  

  

  

  5570 
  Very 
  faint. 
  

  

  6012- 
  1 
  

   6008- 
  J 
  

  

  edge 
  of 
  

   band. 
  

  

  

  The 
  wave-length 
  differences 
  between 
  the 
  middle 
  lines 
  of 
  

   these 
  two 
  sets 
  of 
  groups 
  increase 
  gradually 
  as 
  we 
  pass 
  up 
  

   the 
  spectrum, 
  but 
  as 
  the 
  increment 
  varies 
  in 
  a 
  slightly 
  

   irregular 
  manner 
  there 
  seems 
  to 
  be 
  little 
  use 
  in 
  expressing 
  

   it 
  numerically. 
  By 
  applying 
  a 
  pair 
  of 
  compasses 
  to 
  fig. 
  2 
  

   Plate 
  XYI. 
  we 
  can 
  form 
  a 
  good 
  idea 
  of 
  the 
  regularity 
  of 
  the 
  

   spacing, 
  for 
  the 
  spectrum 
  is 
  very 
  nearly 
  normal. 
  

  

  The 
  Band 
  Spectrum 
  and 
  the 
  Line 
  Spectrum 
  : 
  Effect 
  of 
  

   Reducing 
  the 
  Density 
  of 
  the 
  Iodine 
  Vapour. 
  

  

  In 
  the 
  course 
  of 
  the 
  experiments 
  made 
  to 
  determine 
  the 
  

   effect 
  of 
  the 
  absorption 
  upon 
  the 
  resonance 
  spectrum 
  some 
  

   interesting 
  observations 
  were 
  made. 
  As 
  I 
  have 
  shown 
  in 
  

   previous 
  papers, 
  the 
  band 
  spectrum 
  is 
  developed 
  by 
  the 
  

   admixture 
  of 
  helium 
  or 
  gases 
  of 
  its 
  group, 
  at 
  a 
  pressure 
  of 
  a 
  

   few 
  millimetres, 
  with 
  the 
  iodine 
  vapour. 
  The 
  intensity 
  of 
  

   the 
  resonance 
  groups 
  diminishes 
  gradually 
  and 
  that 
  of 
  the 
  

   band 
  spectrum 
  increases 
  proportionally 
  as 
  the 
  pressure 
  of 
  

   the 
  helium 
  increases. 
  The 
  same 
  thing 
  is 
  true, 
  though 
  to 
  a 
  

  

  