﻿830 
  Prof. 
  R. 
  W. 
  Wood 
  on 
  Resonance 
  

  

  from 
  tho 
  curved 
  glass 
  plates 
  used 
  for 
  the 
  corners 
  of 
  shop 
  

   windows. 
  These 
  were 
  furnished 
  silvered 
  by 
  a 
  mirror-glass 
  

   company 
  at 
  a 
  very 
  small 
  cost, 
  and 
  when 
  mounted 
  as 
  shown 
  

   formed 
  a 
  nearly 
  complete 
  cylindrical 
  reflecting 
  shell 
  over 
  

   half 
  a 
  metre 
  in 
  diameter 
  and 
  in 
  length. 
  The 
  exhausted 
  tube 
  

   containing 
  the 
  iodine 
  and 
  the 
  large 
  Cooper-Hewitt 
  lamp 
  

   were 
  mounted 
  side 
  by 
  side 
  along 
  the 
  axis 
  of 
  the 
  reflecting 
  

   cylinder, 
  the 
  whole 
  arrangement 
  furnishing 
  a 
  sort 
  of 
  " 
  light 
  

   furnace/' 
  in 
  which 
  the 
  iodine 
  vapour 
  glowed 
  with 
  great 
  

   brilliancy. 
  The 
  supports 
  of 
  the 
  large 
  mirrors 
  and 
  the 
  

   parallel 
  tubes 
  are 
  omitted 
  in 
  the 
  diagram 
  to 
  avoid 
  confusion. 
  

  

  Further 
  control 
  of 
  the 
  method 
  of 
  excitation 
  was 
  obtained 
  

   by 
  passing 
  the 
  light 
  of 
  the 
  mercury 
  arc 
  through 
  a 
  large 
  

   glass 
  bulb 
  40 
  cm. 
  in 
  diameter, 
  exhausted 
  save 
  for 
  enough 
  

   bromine 
  vapour 
  to 
  give 
  the 
  transmitted 
  light 
  a 
  good 
  yellow 
  

   colour. 
  The 
  bromine 
  vapour 
  has 
  certain 
  lines 
  in 
  coincidence 
  

   with 
  iodine 
  absorption 
  lines, 
  and 
  by 
  its 
  use 
  as 
  a 
  ray 
  -filter 
  we 
  

   may 
  remove 
  certain 
  frequencies 
  from 
  the 
  green 
  mercury 
  

   line 
  and 
  in 
  consequence 
  throw 
  certain 
  iodine 
  lines 
  out 
  of 
  

   action. 
  

  

  2. 
  Study 
  of 
  the 
  relation 
  between 
  resonance 
  lines 
  (i. 
  e. 
  

   bright 
  lines 
  emitted 
  by 
  the 
  iodine 
  as 
  a 
  result 
  of 
  stimulation 
  

   by 
  more 
  or 
  less 
  monochromatic 
  light) 
  and 
  the 
  complicated 
  

   absorption 
  spectrum, 
  which 
  as 
  I 
  showed 
  in 
  my 
  last 
  paper 
  

   contains 
  about 
  35,000 
  lines 
  between 
  the 
  blue 
  and 
  the 
  red, 
  

   over 
  100 
  fallino- 
  within 
  a 
  region 
  no 
  wider 
  than 
  the 
  distance 
  

   between 
  the 
  yellow 
  sodium 
  lines. 
  In 
  all 
  of 
  my 
  earlier 
  work 
  

   T 
  have 
  been 
  of 
  the 
  opinion 
  that 
  each 
  bright 
  resonance 
  line 
  

   was 
  in 
  coincidence 
  with 
  some 
  one 
  of 
  the 
  numerous 
  dark 
  

   absorption 
  lines, 
  but 
  I 
  now 
  find 
  that 
  this 
  is 
  not 
  the 
  case. 
  

   The 
  direct 
  method 
  of 
  solving 
  this 
  question 
  would 
  be 
  to 
  

   photograph 
  the 
  two 
  spectra 
  in 
  coincidence 
  with- 
  a 
  resolving 
  

   power 
  sufficient 
  to 
  completely 
  resolve 
  the 
  absorption 
  spectrum. 
  

   This 
  can 
  be 
  accomplished 
  only 
  by 
  a 
  spectrograph 
  comparable 
  

   to 
  the 
  one 
  on 
  Mt. 
  Wilson, 
  or 
  my 
  own 
  at 
  East 
  Hampton, 
  and 
  

   to 
  photograph 
  the 
  resonance 
  spectrum 
  under 
  these 
  conditions 
  

   is 
  almost 
  out 
  of 
  the 
  question. 
  There 
  is, 
  however, 
  another 
  

   way 
  in 
  which 
  we 
  may 
  obtain 
  an 
  answer 
  to 
  the 
  question 
  ; 
  we 
  

   may 
  photograph 
  the 
  resonance 
  spectrum 
  after 
  the 
  light 
  has 
  

   been 
  passed 
  through 
  a 
  second 
  tube 
  or 
  bulb 
  containing 
  iodine 
  

   vapour, 
  and 
  see 
  whether 
  the 
  numerous 
  lines 
  forming 
  the 
  

   resonance 
  groups 
  are 
  all 
  weakened 
  to 
  the 
  same 
  degree, 
  as 
  

   would 
  be 
  the 
  case 
  if 
  they 
  were 
  all 
  in 
  coincidence 
  with 
  

   absorption 
  lines 
  of 
  the 
  same 
  intensity. 
  

  

  This 
  is 
  an 
  important 
  point, 
  not 
  only 
  from 
  a 
  theoretical 
  but 
  

   from 
  an 
  experimental 
  standpoint, 
  for 
  in 
  the 
  case 
  of 
  the 
  

  

  