﻿188 
  Prof. 
  R. 
  W. 
  Wood 
  on 
  the 
  Emission 
  of 
  

  

  imagine 
  as 
  a 
  rough 
  model 
  of 
  our 
  molecule 
  a 
  hollow 
  sphere 
  

   with 
  a 
  wire 
  passing 
  through 
  its 
  centre, 
  along 
  which 
  a 
  bead 
  

   can 
  slide. 
  Consider 
  the 
  polarized 
  exciting 
  waves 
  as 
  travelling 
  

   along 
  the 
  x 
  axis 
  towards 
  the 
  origin 
  (fig. 
  2), 
  with 
  their 
  

  

  Fig. 
  2. 
  

  

  yvw* 
  

  

  direction 
  of 
  vibration 
  parallel 
  to 
  the 
  z 
  axis. 
  It 
  is 
  clear 
  that 
  

   the 
  bead 
  will 
  vibrate 
  with 
  the 
  greatest 
  amplitude 
  when 
  the 
  

   direction 
  of 
  the 
  wire 
  is 
  also 
  parallel 
  to 
  the 
  z 
  axis. 
  If 
  the 
  wire 
  

   lies 
  in 
  the 
  x 
  y 
  plane 
  no 
  vibration 
  will 
  occur. 
  In 
  other 
  

   positions 
  there 
  will 
  be 
  vibrations 
  of 
  greater 
  or 
  less 
  amplitude, 
  

   according 
  to 
  the 
  component 
  of 
  the 
  force 
  in 
  the 
  light 
  which 
  

   is 
  directed 
  along 
  the 
  wire. 
  We 
  may 
  represent 
  the 
  fluorescent 
  

   gas 
  by 
  an 
  enormous 
  number 
  of 
  these 
  vibrators 
  with 
  their 
  

   wires 
  pointing 
  in 
  all 
  possible 
  directions. 
  The 
  vibrations 
  of 
  

   the 
  beads 
  along 
  the 
  wires 
  can 
  each 
  be 
  resolved 
  into 
  two 
  com- 
  

   ponents, 
  one 
  parallel 
  to 
  the 
  x 
  axis, 
  the 
  other 
  parallel 
  to 
  the 
  z 
  

   axis, 
  and 
  the 
  integrated 
  effects 
  of 
  these 
  components, 
  or 
  rather 
  

   of 
  their 
  squares, 
  will 
  give 
  us 
  the 
  measure 
  of 
  the 
  intensity 
  of 
  

   the 
  emitted 
  radiation 
  vibrating 
  parallel 
  to 
  the 
  x 
  and 
  z 
  axes. 
  

   These 
  integrals 
  stand 
  in 
  the 
  ratio 
  of 
  6 
  to 
  2, 
  which 
  means, 
  since 
  

   the 
  total 
  intensity 
  is 
  8, 
  and 
  their 
  difference 
  is 
  4, 
  that 
  we 
  are 
  

   to 
  expect 
  a 
  polarization 
  of 
  50 
  per 
  cent, 
  with 
  a 
  vibration 
  

   direction 
  parallel 
  to 
  the 
  z 
  axis. 
  By 
  experiment 
  we 
  find 
  only 
  

   30 
  per 
  cent. 
  

  

  As 
  the 
  percentage 
  of 
  polarization 
  appears 
  to 
  decrease 
  as 
  

   the 
  temperature 
  of 
  the 
  tube 
  is 
  raised, 
  it 
  is 
  possible 
  that 
  at 
  

   lower 
  temperatures 
  than 
  any 
  which 
  can 
  be 
  employed 
  satis- 
  

   factorily, 
  the 
  percentage 
  may 
  be 
  higher. 
  As 
  to 
  possible 
  

   depolarizing 
  agencies, 
  rotation 
  of 
  the 
  molecule 
  would 
  doubtless 
  

   act 
  in 
  this 
  way 
  if 
  the 
  electrons 
  continued 
  to 
  emit 
  light 
  after 
  

   the 
  cessation 
  of 
  the 
  incident 
  light, 
  or 
  — 
  expressing 
  it 
  in 
  terms 
  

   of 
  our 
  imaginary 
  model 
  — 
  if 
  the 
  head 
  on 
  the 
  wire 
  continued 
  

   to 
  vibrate 
  after 
  the 
  wire 
  turned 
  into 
  the 
  : 
  y 
  plane. 
  It 
  must 
  

   he 
  remembered, 
  however, 
  that 
  sodium 
  Is 
  regarded 
  as 
  mona- 
  

   tomic, 
  and 
  the 
  question 
  arises 
  ;i- 
  to 
  whether 
  we 
  can 
  ascribe 
  

  

  