﻿488 
  Mr. 
  L. 
  Wright 
  on 
  Microscopic 
  Images 
  and 
  Vision. 
  

  

  objective 
  field, 
  a 
  condenser 
  can 
  be 
  selected 
  of 
  such 
  a 
  focal 
  

   length, 
  and 
  other 
  matters 
  so 
  adjusted, 
  that 
  the 
  focal 
  image 
  of 
  

   the 
  coarse 
  grating 
  formed 
  by 
  the 
  condenser, 
  corresponds 
  both 
  

   in 
  intervals 
  and 
  focal 
  plane 
  with 
  the 
  object-grating 
  on 
  the 
  

   stage, 
  and 
  using 
  the 
  same 
  illuminating 
  cone. 
  Remove 
  now 
  

   the 
  coarse 
  grating 
  and 
  place 
  the 
  stage 
  grating 
  centrally: 
  then 
  

   removing 
  the 
  eyepiece 
  and 
  looking 
  down 
  the 
  tube, 
  the 
  dioptric 
  

   beam 
  and 
  its 
  flanking 
  spectra 
  as 
  so 
  often 
  described 
  will 
  be 
  

   seen 
  ; 
  they 
  are 
  the 
  images 
  of 
  the 
  source 
  of 
  light, 
  formed 
  at 
  x 
  

   in 
  fig. 
  1. 
  They 
  interfere 
  and 
  form 
  the 
  image 
  seen 
  by 
  the 
  

   eye-piece, 
  in 
  the 
  Fresnel 
  and 
  Abbe 
  manner. 
  Removing 
  the 
  

   stage 
  grating, 
  and 
  replacing 
  the 
  coarse 
  one 
  over 
  the 
  flame, 
  

   its 
  focal 
  image 
  is 
  now 
  the 
  object. 
  Owing 
  to 
  the 
  heterogeneity 
  

   of 
  the 
  rays, 
  this 
  aerial 
  image 
  emits 
  no 
  spectra 
  — 
  there 
  neither 
  

   are 
  nor 
  can 
  be 
  any 
  such. 
  But 
  it 
  is 
  perfectly 
  resolved. 
  Here 
  

   we 
  have 
  a 
  resolution 
  of 
  3000 
  or 
  6000 
  lines 
  per 
  inch 
  that 
  has 
  

   noplace 
  at 
  all 
  in 
  the 
  "spectrum" 
  theory; 
  which 
  therefore 
  

   can 
  be 
  no 
  complete 
  theory 
  of 
  microscopic 
  vision, 
  though 
  it 
  has 
  

   an 
  important 
  place 
  in 
  it 
  *. 
  

  

  As 
  another 
  expedient, 
  we 
  may 
  place 
  beneath 
  the 
  slide 
  

   a 
  sheet 
  of 
  finely-ground 
  glass. 
  This 
  ground 
  surface 
  refracts 
  

   and 
  reflects 
  the 
  light 
  in 
  countless 
  phases 
  and 
  directions 
  through 
  

   the 
  object, 
  the 
  waves 
  issuing 
  therefrom 
  with 
  similar 
  hetero- 
  

   geneity 
  of 
  character. 
  Here 
  also 
  we 
  must 
  have 
  at 
  least 
  a 
  very 
  

   considerable 
  degree 
  of 
  approximation 
  to 
  the 
  nature 
  of 
  self- 
  

   luminosity 
  ; 
  nor 
  can 
  we 
  get 
  from 
  such 
  illumination 
  any 
  of 
  the 
  

   well-marked 
  "spectra" 
  at 
  x 
  (fig. 
  1), 
  or 
  out-of-focus 
  inter- 
  

   ference-fringes, 
  familiar 
  to 
  us 
  with 
  the 
  Abbe 
  method. 
  The 
  

   difference 
  in 
  character 
  of 
  illumination 
  by 
  such 
  methods, 
  and 
  

   the 
  methods 
  described 
  by 
  Dr. 
  Stoney, 
  is 
  so 
  great, 
  that 
  if 
  the 
  

   u 
  spectrum 
  " 
  theory 
  be 
  completely 
  true, 
  there 
  should 
  at 
  least 
  

   be 
  a 
  uniform 
  and 
  vast 
  deterioration 
  in 
  the 
  image 
  of 
  an 
  object 
  

   thus 
  illuminated. 
  On 
  the 
  contrary, 
  with 
  all 
  good 
  lenses 
  of 
  

   moderate 
  aperture, 
  and 
  slides 
  with 
  any 
  fair 
  amount 
  of 
  opacity 
  

   in 
  details, 
  such 
  an 
  image 
  is 
  about 
  the 
  very 
  best 
  ive 
  can 
  get. 
  

   The 
  excellence 
  of 
  this 
  method 
  of 
  illuminating 
  was 
  first 
  im- 
  

   pressed 
  upon 
  me 
  many 
  years 
  ago 
  by 
  the 
  late 
  Dr. 
  Carpenter 
  ; 
  

   and 
  since 
  I 
  in 
  my 
  turn 
  have 
  recommended 
  it, 
  fresh 
  discovery 
  of 
  

   it 
  has 
  been 
  made 
  by 
  Mr. 
  G. 
  C. 
  Karop 
  f 
  . 
  By 
  its 
  means 
  really 
  

   good 
  moderate 
  powers 
  can 
  be 
  used 
  up 
  to 
  their 
  full 
  aperture, 
  

  

  * 
  Using 
  reduced 
  photographs 
  of 
  perforated 
  zinc, 
  I 
  have 
  similarly 
  used 
  

   their 
  aerial 
  images 
  in 
  comparison 
  with 
  P. 
  angulatumon 
  the 
  stage. 
  Only 
  

   approximately 
  in 
  one 
  respect, 
  because 
  the 
  difficulty 
  of 
  getting 
  sufficiently 
  

   reduced 
  photographs 
  prevented 
  use 
  of 
  the 
  same 
  illuminating 
  cone 
  in 
  the 
  

   two 
  cases. 
  But 
  there 
  is 
  no 
  doubt 
  about 
  the 
  results 
  in 
  all 
  important 
  

   respects. 
  

  

  t 
  Journ. 
  Quekett 
  Microscopical 
  Club, 
  Nov. 
  1896. 
  

  

  