﻿956 
  Dr. 
  G. 
  Johnstone 
  Stoney 
  on 
  

  

  we 
  have 
  here 
  resolved 
  the 
  incident 
  light 
  are 
  of 
  the 
  complex 
  

   type 
  referred 
  to 
  in 
  § 
  31 
  (August 
  no. 
  of 
  the 
  Phil. 
  Mag. 
  p. 
  337), 
  

   that 
  is 
  to 
  say, 
  they 
  are 
  ufW's 
  the 
  waves 
  of 
  which 
  need 
  not 
  

   be 
  alike 
  except 
  as 
  regards 
  wave-length, 
  but 
  in 
  which, 
  through- 
  

   out 
  the 
  whole 
  extent 
  of 
  each 
  wave, 
  there 
  will 
  be 
  no 
  difference 
  

   between 
  one 
  part 
  of 
  that 
  wave 
  and 
  another 
  part 
  of 
  the 
  same 
  

   wave. 
  Restrictions 
  seem 
  to 
  limit 
  the 
  differences 
  that 
  actually 
  

   prevail 
  between 
  the 
  successive 
  waves 
  on 
  any 
  one 
  u£W, 
  

   consequent 
  upon 
  events 
  that 
  go 
  on 
  within 
  the 
  superficial 
  

   molecules 
  of 
  visible 
  matter. 
  This 
  is 
  a 
  subject 
  one 
  part 
  of 
  

   which 
  is 
  discussed 
  in 
  a 
  paper 
  in 
  Vol. 
  IV. 
  of 
  the 
  Scientific 
  

   Transactions 
  of 
  the 
  Royal 
  Dublin 
  Society 
  (1891), 
  p. 
  563, 
  

   from 
  which 
  discussion 
  it 
  appears 
  that 
  the 
  Light 
  emitted 
  by 
  a 
  

   visible 
  body 
  i- 
  due 
  to 
  the 
  activities 
  of 
  the 
  negative 
  electrons 
  

   within 
  its 
  molecule-, 
  and 
  that 
  the 
  motion 
  of 
  any 
  one 
  electron, 
  

   however 
  intricate 
  it> 
  path, 
  is 
  resolvable 
  into 
  elliptic 
  partials 
  

   each 
  of 
  which 
  will 
  emit 
  light 
  of 
  a 
  definite 
  wave-length 
  *. 
  

  

  CHAPTER 
  7. 
  

  

  Analysis 
  of 
  a 
  beam 
  of 
  light. 
  

  

  When 
  we 
  intend 
  that 
  the 
  light 
  incident 
  upon 
  object 
  z 
  

   in 
  our 
  experimental 
  apparatus 
  (see 
  Plate 
  XII.) 
  shall 
  be 
  

   diffused 
  light, 
  we 
  employ 
  a 
  >ource 
  of 
  light 
  wdiich 
  we 
  have 
  

   called 
  cr. 
  A 
  part 
  of 
  this 
  light 
  will 
  ultimately 
  become 
  the 
  

   image 
  of 
  z' 
  which 
  may 
  then 
  be 
  >v(m 
  in 
  the 
  pro-telescope 
  T' 
  

   at 
  ./ 
  ' 
  : 
  and 
  in 
  order 
  to 
  trace 
  how 
  this 
  comes 
  to 
  pass 
  we 
  have 
  

   divided 
  the 
  advance 
  of 
  the 
  light 
  from 
  a 
  to 
  x' 
  into 
  three 
  

   stages. 
  

  

  64. 
  The 
  first 
  stage 
  of 
  this 
  progress, 
  wdiich 
  is 
  from 
  a 
  to 
  z', 
  

   we 
  have 
  studied 
  in 
  the 
  last 
  chapter, 
  and 
  have 
  found 
  that 
  if 
  

   a 
  be 
  divided 
  into 
  n 
  sufficiently 
  small 
  patches 
  da 
  u 
  da 
  2 
  , 
  &c, 
  

   each 
  of 
  these 
  will 
  transmit 
  towards 
  object 
  z' 
  a 
  single 
  stellade 
  

   of 
  light 
  (light 
  of 
  the 
  kind 
  we 
  receive 
  from 
  stars), 
  and 
  that 
  

   each 
  of 
  these 
  stellades 
  will 
  consist 
  of 
  m 
  uf 
  W's 
  (undulations 
  

   of 
  flat 
  waves), 
  one 
  for 
  each 
  of 
  the 
  m 
  wave-lengths 
  of 
  which 
  

   we 
  have 
  found 
  that 
  white 
  light 
  may 
  legitimately 
  be 
  regarded 
  

   as 
  consisting 
  — 
  along 
  with 
  a 
  residuum 
  of 
  light 
  obeying 
  a 
  

   different 
  law 
  of 
  propagation, 
  which 
  however 
  at 
  the 
  middle 
  

   of 
  object 
  z' 
  and 
  for 
  a 
  certain 
  distance 
  round 
  that 
  point 
  is 
  so 
  

  

  * 
  We 
  have 
  some 
  reason 
  to 
  suspect 
  that 
  the 
  more 
  definite 
  motions 
  of 
  

   negative 
  electrons 
  are 
  accompanied 
  by 
  surgings 
  of 
  the 
  associated 
  positive 
  

   electricity. 
  It 
  may 
  be 
  to 
  these 
  less 
  definite 
  displacements 
  of 
  positive 
  

   electricity 
  that 
  we 
  are 
  to 
  look 
  for 
  the 
  explanation 
  of 
  subsidiary 
  effects 
  

   which 
  ha^e 
  been 
  observed, 
  even 
  possibly 
  including 
  anomalous 
  dispersion. 
  

  

  