﻿10 
  Dr. 
  W. 
  M. 
  Hicks 
  on 
  the 
  Miclwhon-Morleif 
  

  

  first 
  sight 
  owing 
  to 
  the 
  changes 
  produced 
  by 
  actual 
  reflexion 
  

   at 
  a 
  moving 
  surface. 
  The 
  correction 
  due 
  to 
  alteration 
  in 
  the 
  

   angle 
  of 
  reflexion 
  was 
  first 
  introduced 
  by 
  Lorentz, 
  and 
  was 
  

   taken 
  account 
  of 
  in 
  the 
  joint 
  paper 
  by 
  Michelson& 
  Morley 
  in 
  

   1887. 
  But 
  reflexion 
  produces 
  also 
  a 
  change 
  in 
  the 
  wave- 
  

   length 
  of 
  the 
  reflected 
  light. 
  Further, 
  when 
  the 
  source 
  of 
  

   light 
  moves 
  with 
  the 
  apparatus, 
  the 
  light 
  incident 
  at 
  any 
  

   instant 
  on 
  a 
  plate 
  does 
  not 
  come 
  from 
  the 
  position 
  occupied 
  

   by 
  the 
  source 
  at 
  that 
  instant, 
  but 
  from 
  a 
  point 
  which 
  it 
  

   occupied 
  at 
  some 
  interval 
  before 
  ; 
  consequently 
  the 
  angle 
  of 
  

   incidence 
  alters 
  by 
  a 
  small 
  quantity 
  of 
  the 
  first 
  order 
  as 
  the 
  

   direction 
  of 
  drift 
  of 
  the 
  apparatus 
  changes. 
  

  

  The 
  present 
  investigation 
  is 
  undertaken 
  with 
  the 
  view 
  of 
  

   making 
  these 
  corrections. 
  As 
  in 
  a 
  theory 
  of 
  this 
  kind 
  it 
  does 
  

   not 
  seem 
  legitimate 
  to 
  assume 
  beforehand 
  that 
  the 
  ratio 
  of 
  

   the 
  velocity 
  of 
  the 
  earth 
  through 
  the 
  aether 
  to 
  that 
  of 
  light 
  is 
  

   extremely 
  small, 
  the 
  general 
  theory 
  is 
  worked 
  out 
  without 
  

   approximation. 
  It 
  is 
  interesting 
  to 
  see 
  how 
  comparatively 
  

   simple 
  this 
  complete 
  theory 
  is. 
  The 
  principal 
  result 
  of 
  the 
  

   correction 
  is 
  that 
  in 
  the 
  experiment 
  of 
  Michel 
  son 
  & 
  Morley 
  

   the 
  effect 
  to 
  be 
  expected 
  is 
  the 
  reverse 
  of 
  that 
  hitherto 
  

   supposed. 
  

  

  In 
  the 
  actual 
  experiment 
  the 
  light 
  from 
  a 
  flame 
  in 
  the 
  

   focal 
  plane 
  of 
  a 
  lens 
  falls 
  on 
  a 
  small 
  plane-glass 
  plate 
  by 
  

   which 
  it 
  is 
  divided, 
  and 
  the 
  two 
  portions 
  are 
  afterwards 
  

   reflected 
  back 
  to 
  the 
  plate 
  by 
  two 
  small 
  plane 
  mirrors. 
  We 
  

   shall 
  suppose 
  in 
  the 
  first 
  place 
  that 
  the 
  source 
  is 
  a 
  point 
  of 
  

   light 
  or 
  a 
  vertical 
  slit 
  ; 
  so 
  that 
  the 
  incident 
  light 
  consists 
  of 
  

   a 
  single 
  train 
  of 
  parallel 
  waves. 
  

  

  We 
  have 
  thus 
  two 
  mirrors 
  inclined 
  at 
  any 
  given 
  angle, 
  

   and 
  between 
  them 
  a 
  transparent 
  semi-reflecting 
  plate, 
  whose 
  

   plane 
  does 
  not 
  in 
  general 
  pass 
  through 
  the 
  intersection 
  of 
  

   the 
  mirrors. 
  In 
  practice 
  w 
  T 
  e 
  utilize 
  only 
  small 
  portions 
  of 
  

   these 
  planes, 
  but 
  in 
  considering 
  the 
  general 
  theory 
  it 
  is 
  best 
  

   to 
  deal 
  with 
  the 
  complete 
  system 
  of 
  planes 
  and 
  to 
  consider 
  the 
  

   phenomena 
  taking 
  place 
  in 
  the 
  angular 
  space 
  between 
  them. 
  

  

  1. 
  Consider 
  the 
  state 
  of 
  the 
  sether 
  at 
  any 
  given 
  instant, 
  

   and 
  draw 
  the 
  wave 
  diagram, 
  that 
  is 
  a 
  diagram 
  of 
  lines 
  

   representing 
  all 
  the 
  crests 
  (or 
  every 
  nth. 
  crest). 
  

  

  In 
  tig. 
  1, 
  A, 
  B 
  represent 
  the 
  planes 
  of 
  the 
  mirrors, 
  C 
  that 
  

   of 
  the 
  plate. 
  On 
  the 
  plate 
  is 
  incident 
  a 
  train 
  of 
  waves 
  

   (dotted 
  lines), 
  which 
  produces 
  at 
  the 
  plate 
  a 
  train 
  of 
  reflected 
  

   waves 
  (thin 
  broken 
  lines) 
  and 
  of 
  transmitted 
  waves 
  (dotted 
  

   lines). 
  The 
  first 
  set 
  are 
  incident 
  on 
  the 
  mirror 
  plane 
  A 
  and 
  

   produce 
  a 
  train 
  of 
  reflected 
  waves 
  (thin 
  continuous 
  lines). 
  

   The 
  transmitted 
  set 
  fall 
  on 
  the 
  mirror 
  plane 
  B, 
  and 
  produce 
  

  

  