﻿Mr. 
  L. 
  Wright 
  on 
  Microscopic 
  Images 
  and 
  Vision. 
  485 
  

  

  special 
  philosophical 
  vice 
  of 
  the 
  mathematicians, 
  the 
  tendency, 
  

   namely, 
  to 
  mistake 
  the 
  sign 
  for 
  the 
  thing 
  signified." 
  

  

  7. 
  This 
  seems 
  further 
  to 
  appear, 
  when 
  we 
  consider 
  the 
  

   reversal 
  of 
  the 
  supposed 
  dynamical 
  system. 
  This, 
  it 
  is 
  sup- 
  

   posed, 
  produces 
  the 
  " 
  best 
  attainable 
  image 
  which 
  the 
  light 
  

   emitted 
  by 
  the 
  object 
  [and 
  grasped 
  by 
  the 
  objective] 
  is 
  capable 
  

   of 
  producing."" 
  Unquestionably 
  the 
  light-waves 
  emitted 
  may 
  

   truly 
  be 
  regarded 
  as 
  a 
  dynamical 
  system 
  ; 
  and 
  may 
  be 
  con- 
  

   ceived 
  as 
  reversed 
  ; 
  and 
  the 
  reversal 
  of 
  the 
  whole 
  actual 
  system 
  

   would 
  produce 
  such 
  an 
  image 
  as 
  described. 
  But 
  it 
  does 
  not 
  

   seem 
  to 
  follow 
  that 
  mere 
  " 
  coalescence 
  and 
  interference 
  of 
  

   uniform 
  plane 
  leaves 
  " 
  involves 
  such 
  a 
  result. 
  Besides 
  what 
  

   has 
  already 
  been 
  said 
  as 
  to 
  the 
  absence 
  of 
  plane-wave 
  cha- 
  

   racter 
  in 
  rays 
  from 
  any 
  self-luminous 
  object, 
  at 
  the 
  very 
  

   minute 
  focal 
  distance 
  of 
  a 
  high-power 
  objective, 
  questions 
  as 
  

   to 
  the 
  longitudinal 
  components 
  in 
  the 
  disturbances, 
  and 
  their 
  

   disposal 
  and 
  influence, 
  and 
  several 
  other 
  questions, 
  would 
  

   seem 
  to 
  need 
  further 
  solution 
  than 
  is 
  known 
  at 
  present, 
  before 
  

   this 
  could 
  be 
  assumed. 
  

  

  In 
  any 
  case, 
  what 
  the 
  reversal 
  of 
  the 
  supposed 
  dynamical 
  

   system 
  must 
  really 
  reproduce 
  as 
  an 
  image 
  at 
  the 
  place 
  of 
  its 
  

   origin, 
  must 
  be 
  the 
  postulated 
  operative 
  cause 
  of 
  the 
  system. 
  

   That, 
  by 
  the 
  hypothesis, 
  is 
  not 
  an 
  actual 
  object 
  and 
  it 
  alone, 
  

   emitting 
  luminous 
  waves, 
  but 
  the 
  object 
  surrounded 
  by 
  an 
  in- 
  

   definite 
  number 
  of 
  identical 
  replicas, 
  emitting 
  identically 
  similar 
  

   plane 
  leaves. 
  This 
  does 
  not 
  represent 
  any 
  object 
  in 
  reality: 
  

   and 
  that 
  fact 
  seems 
  to 
  dispose 
  of 
  such 
  a 
  presentment 
  as 
  a 
  full 
  

   and 
  complete 
  representation 
  of 
  microscopic 
  vision. 
  

  

  The 
  same 
  conclusion 
  follows 
  from 
  Dr. 
  Stoney's 
  directions 
  

   "how 
  to 
  see 
  the 
  rulings" 
  (Phil. 
  Mag. 
  Dec. 
  1896, 
  p. 
  525). 
  

   We 
  first 
  illuminate 
  the 
  object 
  by 
  a 
  near 
  approximation 
  to 
  

   plane 
  waves 
  ; 
  and 
  then 
  behind 
  the 
  lens 
  further 
  exclude 
  every- 
  

   thing 
  but 
  the 
  narrowest 
  pencils 
  of 
  almost 
  exclusively 
  plane 
  

   waves. 
  Thus 
  we 
  produce 
  a 
  " 
  ruling 
  " 
  extending 
  far 
  beyond 
  

   the 
  limits 
  of 
  a 
  true 
  image, 
  and 
  which 
  in 
  other 
  respects 
  is 
  as 
  

   far 
  as 
  possible 
  from 
  being 
  any 
  such. 
  We 
  are 
  really 
  pro- 
  

   ducing, 
  and 
  do 
  produce, 
  easily 
  calculable 
  results 
  of 
  interesting- 
  

   experiments 
  in 
  the 
  interferences 
  of 
  plane 
  waves 
  ; 
  and 
  though 
  

   these 
  results 
  are 
  physically 
  and 
  directly 
  related 
  to 
  the 
  periodic 
  

   structure 
  of 
  the 
  object, 
  considered 
  as 
  an 
  interference-grating, 
  

   they 
  are 
  no 
  trustworthy 
  representation 
  of 
  it. 
  This 
  truth 
  has 
  

   always 
  been 
  recognized 
  and 
  insisted 
  upon 
  by 
  Prof. 
  Abbe 
  and 
  

   his 
  school, 
  resulting 
  in 
  a 
  sort 
  of 
  " 
  counsel 
  of 
  despair 
  " 
  as 
  to 
  

   any 
  truth 
  or 
  certainty 
  in 
  such 
  microscopical 
  images. 
  

  

  8. 
  This 
  brings 
  us 
  back 
  to 
  the 
  more 
  concrete 
  Abbe 
  " 
  spec- 
  

   trum 
  " 
  theory, 
  as 
  already 
  described. 
  But 
  Prof. 
  Abbe 
  

  

  Phil 
  Mag. 
  S. 
  5. 
  Vol. 
  45.' 
  No. 
  277. 
  June 
  1898. 
  2 
  L 
  

  

  