﻿236 
  Prof. 
  R. 
  W. 
  Wood 
  on 
  

  

  If 
  the 
  driving 
  force 
  of 
  cyclones 
  originates 
  in 
  the 
  upper 
  

   portion 
  of 
  the 
  stratosphere 
  where 
  it 
  is 
  locally 
  heated, 
  then 
  

   this 
  heated 
  air 
  must 
  be 
  carried 
  along 
  with 
  the 
  stratosphere 
  

   wind, 
  and 
  the 
  course 
  of 
  the 
  cyclone 
  on 
  the 
  earth's 
  surface 
  

   should 
  indicate 
  the 
  direction 
  of 
  flow 
  of 
  the 
  stratosphere 
  wind 
  

   above. 
  The 
  generally 
  easterly 
  movement 
  of 
  cyclones 
  favours 
  

   this 
  assumption 
  ; 
  but 
  the 
  track 
  of 
  cyclones 
  from 
  south 
  to 
  

   north 
  in 
  North 
  America 
  seems 
  to 
  require 
  explanation. 
  In 
  

   this 
  connexion 
  it 
  is 
  interesting 
  to 
  note 
  that 
  the 
  dust 
  of 
  the 
  

   Krakatoa 
  eruption 
  adhered 
  closely 
  to 
  the 
  area 
  of 
  the 
  equa- 
  

   torial 
  trade 
  winds, 
  except 
  over 
  the 
  Atlantic, 
  where 
  the 
  dust 
  

   was 
  carried 
  to 
  the 
  north 
  apparently 
  along 
  the 
  American 
  

   Cyclone 
  track. 
  

  

  XXVII. 
  Resonance 
  Spectra 
  of 
  Iodine. 
  By 
  R. 
  W. 
  Wood, 
  

   Professor 
  of 
  Experimental 
  Physics, 
  Johns 
  Hopkins 
  

   University* 
  . 
  

  

  [Plates 
  VI.-VI1I.] 
  

  

  SINCE 
  the 
  appearance 
  of 
  the 
  last 
  paper 
  on 
  this 
  subject 
  

   (Phil. 
  Mag. 
  ser. 
  6. 
  vol. 
  xxvi.), 
  the 
  study 
  of 
  these 
  inter- 
  

   esting 
  spectra 
  has 
  been 
  continued 
  without 
  interruption, 
  and 
  

   some 
  new 
  and 
  very 
  important 
  relations 
  have 
  been 
  brought 
  to 
  

   light. 
  As 
  has 
  been 
  shown 
  in 
  previous 
  communications, 
  the 
  

   vapour 
  of 
  iodine 
  in 
  vacuo, 
  when 
  excited 
  to 
  luminosity 
  by 
  the 
  

   light 
  of 
  the 
  Cooper-Hewitt 
  mercury 
  lamp 
  (glass), 
  emits 
  a 
  

   spectrum 
  consisting 
  of 
  a 
  series 
  of 
  doublets, 
  with 
  a 
  separation 
  

   of 
  about 
  1*5 
  AIL, 
  very 
  regularly 
  spaced 
  o 
  along 
  the 
  spectrum 
  

   and 
  separated 
  by 
  intervals 
  of 
  about 
  70 
  AIL 
  These 
  intervals 
  

   increase 
  gradually, 
  however, 
  as 
  we 
  pass 
  away 
  from 
  the 
  green 
  

   mercury 
  line, 
  at 
  which 
  point 
  the 
  doublet 
  series 
  has 
  its 
  origin, 
  

   until, 
  in 
  the 
  extreme 
  reel, 
  the 
  distance 
  between 
  the 
  last 
  two 
  

   doublets 
  observed 
  is 
  about 
  102 
  AIL, 
  and 
  the 
  separation 
  of 
  the 
  

   components 
  of 
  the 
  doublet 
  has 
  increased 
  to 
  2*8 
  AIL 
  By 
  the 
  

   use 
  of 
  dicyanine 
  plates 
  the 
  series 
  has 
  been 
  followed 
  to 
  its 
  

   termination 
  at 
  wave-length 
  7685 
  and 
  the 
  wave-lengths 
  of 
  

   the 
  seven 
  new 
  doublets 
  accurately 
  measured. 
  The 
  doublets 
  are 
  

   not 
  all 
  of 
  uniform 
  intensity, 
  and 
  some 
  are 
  misiing 
  entirely, 
  

   and 
  it 
  is 
  the 
  connexion 
  between 
  this 
  circumstance 
  and 
  the 
  

   way 
  in 
  which 
  the 
  doublet 
  series 
  is 
  related 
  to 
  the 
  band 
  absorp- 
  

   tion 
  spectrum, 
  that 
  is 
  the 
  most 
  interesting 
  point 
  brought 
  out 
  

   by 
  the 
  recent 
  investigations. 
  By 
  varying 
  the 
  conditions 
  of 
  the 
  

   experiment 
  it 
  has 
  been 
  found 
  possible 
  to 
  excite 
  by 
  the 
  green 
  

   mercury 
  line 
  not 
  only 
  the 
  doublet 
  series, 
  but 
  a 
  simplified 
  

   * 
  Communicated 
  by 
  the 
  Author. 
  

  

  