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   LXV. 
  Intelligence 
  and 
  Miscellaneous 
  Articles. 
  

  

  THE 
  MICHELSON-MORLEY 
  EXPERIMENT. 
  

  

  Physical 
  Laboratory, 
  Univ. 
  of 
  Nebraska. 
  

   February 
  28, 
  1902. 
  

  

  To 
  the 
  Editors 
  of 
  the 
  Philosophical 
  Magazine. 
  

  

  Gentlemen, 
  — 
  

  

  TN 
  the 
  paper 
  of 
  Dr. 
  Hicks, 
  which 
  appeared 
  in 
  the 
  January 
  

   -*- 
  number, 
  discussing 
  the 
  Michelson-Morley 
  experiment, 
  there 
  is 
  

   introduced 
  a 
  term 
  in 
  the 
  expression 
  for 
  the 
  displacement 
  of 
  the 
  

   bands, 
  which 
  it 
  seems 
  to 
  me 
  is 
  at 
  variance 
  with 
  the 
  commonly- 
  

   accepted 
  views 
  concerning 
  the 
  effect 
  of 
  the 
  drift 
  of 
  the 
  aether 
  on 
  

   optical 
  phenomena. 
  

  

  F 
  

  

  He 
  gives 
  the 
  expression 
  T) 
  —c 
  cos 
  2a 
  + 
  D'£ 
  cos 
  a 
  for 
  the 
  

  

  displacement 
  of 
  the 
  bands, 
  and 
  interprets 
  the 
  term 
  D'£ 
  cos 
  a 
  by 
  

   saying 
  that 
  if 
  a 
  photographic 
  plate 
  be 
  exposed 
  where 
  interference 
  

   is 
  taking 
  place, 
  an 
  image 
  of 
  the 
  fringes 
  as 
  they 
  exist 
  at 
  the 
  plane 
  

   of 
  the 
  photographic 
  plate 
  will 
  be 
  printed 
  on 
  the 
  plate, 
  but 
  if 
  an 
  

   image 
  of 
  the 
  fringes 
  be 
  projected 
  on 
  the 
  retina 
  of 
  the 
  eye, 
  by 
  

   focussing 
  the 
  eye 
  directly 
  or 
  with 
  a 
  telescope 
  on 
  a 
  position 
  in 
  

   space, 
  the 
  fringes 
  on 
  the 
  retina 
  will 
  be 
  displaced 
  relatively 
  to 
  those 
  

   in 
  tbe 
  plane 
  on 
  which 
  the 
  eye 
  was 
  focussed. 
  This 
  displacement 
  

   he 
  calls 
  the 
  cos 
  a 
  effect. 
  The 
  distance 
  between 
  the 
  eye 
  and 
  the 
  

   plane 
  of 
  the 
  fringes 
  in 
  space 
  he 
  calls 
  D', 
  and 
  a 
  is 
  approximately 
  

   equal 
  to 
  the 
  angle 
  which 
  the 
  wave-fronts 
  make 
  with 
  the 
  direction 
  

   -of 
  the 
  drift. 
  

  

  Dr. 
  Hicks, 
  therefore, 
  evidently 
  believes 
  in 
  the 
  objective 
  reality 
  

   of 
  the 
  cos 
  a 
  effect, 
  and 
  several 
  times 
  in 
  his 
  paper 
  he 
  speaks 
  of 
  the 
  

   necessity 
  of 
  correcting 
  for 
  or 
  eliminating 
  it. 
  Now 
  a 
  first 
  order 
  

   effect 
  of 
  £ 
  has 
  been 
  looked 
  for 
  by 
  a 
  number 
  of 
  investigators, 
  

   notably 
  Mascart 
  and 
  Ketteler, 
  who 
  were 
  unable 
  to 
  observe 
  any 
  

   such 
  effect. 
  These 
  considerations, 
  taken 
  with 
  the 
  fact 
  that 
  the 
  

   mathematical 
  investigations 
  of 
  Lorentz 
  aud 
  others 
  lead 
  to 
  the 
  

   conclusion 
  that 
  there 
  should 
  be 
  no 
  such 
  effect 
  observable, 
  would 
  

   make 
  it 
  unlikely 
  that 
  the 
  phenomenon 
  to 
  which 
  Dr. 
  Hicks 
  calls 
  

   attention 
  is 
  real. 
  If 
  it 
  were, 
  one 
  might 
  determine 
  £ 
  very 
  simply 
  

   by 
  measuring 
  the 
  displacement 
  observable 
  at 
  different 
  distances 
  

   from 
  the 
  interferometer. 
  It 
  is 
  admissible 
  that 
  there 
  is 
  a 
  dis- 
  

   placement 
  of 
  the 
  fringes 
  relatively 
  to 
  a 
  fixed 
  point 
  in 
  the 
  aether, 
  

   and 
  that 
  this 
  displacement 
  is 
  proportional 
  to 
  D'£ 
  cos 
  a, 
  but 
  there 
  

   is 
  an 
  effect 
  due 
  to 
  the 
  motion 
  of 
  the 
  observer, 
  exactly 
  equal 
  and 
  

   •of 
  opposite 
  sign, 
  which 
  nullifies 
  it. 
  

  

  Dr. 
  Hicks 
  gives 
  the 
  following 
  more 
  complete 
  expression, 
  where 
  

   X 
  is 
  the 
  distance 
  of 
  the 
  central 
  band 
  from 
  the 
  point 
  of 
  intersection 
  

   of 
  the 
  planes 
  of 
  the 
  mirrors, 
  and 
  d 
  sin 
  a 
  is 
  the 
  aberration 
  term, 
  d 
  

   being 
  linear 
  with 
  £. 
  

  

  X 
  = 
  « 
  + 
  & 
  cos 
  2a 
  + 
  c 
  cos 
  a— 
  d 
  sin 
  «♦ 
  

  

  