﻿the 
  Velocity 
  of 
  Light. 
  335 
  

  

  3. 
  Does 
  the 
  dragging 
  along 
  (entrainement) 
  of 
  the 
  light 
  

   waves 
  in 
  the 
  air-vortex 
  close 
  to 
  the 
  mirror 
  affect 
  the 
  dis- 
  

   placement 
  ? 
  

  

  These 
  criticisms 
  have 
  been 
  carefully 
  considered 
  by 
  H. 
  A. 
  

   Lorentz"*, 
  who 
  states 
  that 
  " 
  Quoiqir'elles 
  (quelques 
  considera- 
  

   tions 
  . 
  . 
  .) 
  laissent 
  encore 
  beaucoup 
  a 
  desirer 
  au 
  point 
  de 
  vue 
  

   de 
  la 
  rigueur, 
  elles 
  me 
  semblent 
  bien 
  propres 
  a 
  dissiper 
  les 
  

   doutes 
  que 
  je 
  viens 
  de 
  rappeler." 
  

  

  It 
  seems 
  to 
  me 
  that 
  M. 
  Lorentz 
  has 
  satisfactorily 
  answered 
  

   M. 
  Corner's 
  questions 
  ; 
  and 
  my 
  own 
  estimate 
  of 
  the 
  most 
  

   probable 
  value 
  of 
  V 
  agrees 
  with 
  the 
  second 
  result 
  given 
  on 
  

   p. 
  334, 
  namely, 
  

  

  V 
  = 
  299,890±60. 
  

  

  Nevertheless 
  an 
  experimental 
  determination 
  which 
  should 
  

   more 
  or 
  less 
  completely 
  avoid 
  the 
  necessity 
  for 
  the 
  considera- 
  

   tion 
  of 
  these 
  questions, 
  or 
  at 
  least 
  materially 
  diminish 
  any 
  

   error 
  which 
  could 
  possibly 
  arise, 
  even 
  if 
  they 
  were 
  valid 
  ; 
  

   and 
  which, 
  in 
  any 
  case, 
  would 
  furnish 
  one 
  more 
  independent 
  

   result 
  to 
  be 
  combined 
  with 
  the 
  very 
  few 
  reliable 
  ones 
  already 
  

   obtained, 
  — 
  would 
  surely 
  be 
  welcome. 
  

  

  The 
  preceding 
  exposition 
  makes 
  it 
  clear 
  that 
  the 
  measure- 
  

   ments 
  and 
  observations 
  to 
  be 
  combined 
  with 
  or 
  to 
  be 
  com- 
  

   pared 
  with 
  the 
  velocity 
  of 
  light, 
  namely 
  : 
  

  

  (1) 
  Astronomical 
  observations 
  of 
  L, 
  

  

  (2) 
  Electromagnetic 
  ratio 
  v, 
  

  

  (3) 
  Velocity 
  of 
  Hertzian 
  oscillations, 
  

  

  are 
  all 
  capable 
  of 
  measurement 
  with 
  an 
  order 
  of 
  accuracy 
  

   which 
  even 
  now 
  approaches, 
  if 
  does 
  not 
  equal, 
  that 
  of 
  the 
  

   measurement 
  of 
  the 
  velocity 
  of 
  light. 
  

  

  This, 
  it 
  seems 
  to 
  me, 
  is 
  a 
  sufficient 
  excuse 
  — 
  if 
  any 
  were 
  

   needed 
  — 
  for 
  once 
  more 
  attacking 
  the 
  problem. 
  

  

  The 
  following 
  plan 
  suggested 
  itself 
  during 
  the 
  experiments 
  

   upon 
  the 
  " 
  Relative 
  Motion 
  of 
  the 
  Earth 
  and 
  the 
  Luminiferous 
  

   .Ether 
  "f. 
  

  

  The 
  essential 
  feature 
  is 
  the 
  combination 
  of 
  a 
  grating 
  with 
  

   a 
  revolving 
  mirror, 
  which 
  combination 
  acts 
  as 
  a 
  toothed 
  

   wheel, 
  the 
  grating-space 
  representing 
  the 
  distance 
  between 
  

   the 
  teeth, 
  the 
  radius 
  being 
  the 
  distance 
  from 
  the 
  revolving 
  

   mirror 
  to 
  grating. 
  

  

  It 
  was 
  proposed 
  to 
  utilize 
  this 
  combination 
  in 
  an 
  attempt 
  

   to 
  solve 
  the 
  problem 
  of 
  the 
  " 
  relative 
  motion 
  " 
  by 
  measuring 
  

   the 
  velocity 
  of 
  light 
  in 
  one 
  direction, 
  that 
  is, 
  without 
  return- 
  

   ing 
  the 
  light 
  to 
  the 
  source. 
  This 
  was 
  before 
  the 
  celebrated 
  work 
  

  

  * 
  "Sur 
  la 
  methode 
  du 
  miroir 
  tournant 
  pour 
  la 
  determination 
  de 
  la 
  

   vitesse 
  de 
  la 
  lumiere." 
  Arch. 
  Neer. 
  des 
  Sciences, 
  ser. 
  ii. 
  t. 
  vi. 
  p. 
  303. 
  

   t 
  Am. 
  Journ. 
  of 
  Science, 
  vol. 
  xxxiv. 
  Nov. 
  1887. 
  

  

  