﻿Mr. 
  L. 
  Wright 
  on 
  Microscopic 
  Images 
  and 
  Vision. 
  499 
  

  

  much 
  sharper 
  and 
  " 
  finer 
  '* 
  images 
  of 
  bacteria, 
  in 
  fact 
  the 
  

   only 
  images 
  worth 
  having. 
  Prof. 
  Abbe 
  accounted 
  for 
  this 
  

   observational 
  fact, 
  in 
  an 
  article 
  * 
  expressly 
  contradicting 
  any 
  

   advantage 
  whatever 
  to 
  the 
  image 
  (as 
  an 
  image) 
  from 
  a 
  wide 
  

   cone, 
  on 
  the 
  ground 
  that 
  the 
  wide 
  cone, 
  owing 
  to 
  its 
  more 
  

   sharply 
  defined 
  focal 
  plane 
  (want 
  of 
  "penetration"), 
  makes 
  

   invisible 
  the 
  transparent 
  tissues 
  in 
  which 
  the 
  bacteria 
  are 
  

   situate. 
  But 
  he 
  fails 
  to 
  account 
  for 
  the 
  fact 
  that 
  it 
  is 
  just 
  

   the 
  same 
  w 
  7 
  ith 
  bacteria 
  in 
  invisible 
  culture-media 
  or 
  sputum 
  ; 
  

   and 
  that 
  the 
  advantage 
  really 
  consists 
  in 
  the 
  much 
  greater 
  

   sharpness 
  or 
  thinness 
  of 
  the 
  images 
  of 
  the 
  bacteria 
  them- 
  

   selves 
  ; 
  in 
  truth 
  of 
  contour, 
  so 
  that 
  square 
  ends 
  are 
  shown 
  

   square 
  and 
  not 
  rounded 
  ; 
  and 
  in 
  the 
  fact 
  that 
  there 
  are 
  no 
  

   blurred 
  edges 
  or 
  diffraction- 
  fringes 
  round 
  them, 
  as 
  appear 
  with 
  

   a 
  narrow 
  cone. 
  In 
  fact, 
  many 
  allied 
  bacteria 
  cannot 
  be 
  distin- 
  

   guished 
  at 
  all 
  by 
  the 
  microscopic 
  methods 
  still 
  too 
  current 
  in 
  

   our 
  schools, 
  which 
  have 
  taken 
  their 
  methods 
  from 
  Germany. 
  

  

  So 
  also, 
  when 
  Mr. 
  Baugh 
  visited 
  the 
  famed 
  Jena 
  workshop 
  

   in 
  1895, 
  he 
  was 
  told 
  by 
  Prof. 
  Zimmermann, 
  one 
  of 
  the 
  

   scientific 
  start' 
  (who 
  has 
  himself 
  published 
  a 
  work 
  on 
  micro- 
  

   scopy), 
  that 
  in 
  photographing 
  they 
  found 
  no 
  difference 
  in 
  

   results 
  obtained 
  by 
  the 
  chromatic 
  and 
  achromatic 
  condensers 
  ; 
  

   which 
  is 
  equivalent 
  to 
  the 
  statement 
  that 
  they 
  knew 
  of 
  no 
  

   better 
  results 
  than 
  those 
  from 
  a 
  0'50 
  cone. 
  Our 
  English 
  

   results 
  are 
  quite 
  different. 
  Mr. 
  A. 
  Pringle, 
  wmose 
  splendid 
  

   photographic 
  work 
  on 
  bacteria 
  is 
  well 
  known, 
  often 
  uses 
  the 
  

   largest 
  aplanatic 
  cones 
  ; 
  and, 
  to 
  quote 
  once 
  more 
  our 
  

   recognized 
  authority 
  on 
  microscopic 
  practice 
  f 
  , 
  " 
  Photo- 
  

   micrography 
  with 
  a 
  small 
  cone 
  is 
  quite 
  easy, 
  as 
  great 
  contrast 
  

   can 
  be 
  secured 
  [the 
  reason 
  has 
  been 
  shown 
  in 
  foregoing 
  

   paragraphs]. 
  With 
  a 
  large 
  cone 
  difficulties 
  begin 
  — 
  difficulties 
  

   of 
  adjustment, 
  difficulties 
  of 
  lens 
  correction, 
  difficulties 
  of 
  

   exposure, 
  and 
  difficulties 
  of 
  development. 
  If, 
  so 
  far 
  as 
  our 
  

   experience 
  goes, 
  a 
  good 
  photo-micrograph 
  is 
  required, 
  these 
  

   difficulties 
  must 
  be 
  mastered." 
  

  

  21. 
  This 
  quotation 
  leads 
  us 
  to 
  the 
  prejudicial 
  effect 
  of 
  the 
  

   theory 
  (or 
  rather 
  of 
  its 
  undue 
  preponderance) 
  upon 
  micro- 
  

   scopic 
  objectives. 
  The 
  mode 
  of 
  illumination 
  directly 
  influences 
  

   the 
  quality 
  of 
  the 
  objective 
  ; 
  because 
  the 
  all-important 
  point 
  

   of 
  correction 
  for 
  spherical 
  aberration 
  has 
  commanding 
  influence 
  

   upon 
  the 
  cone 
  of 
  heterogeneous 
  rays 
  which 
  can 
  be 
  used 
  with 
  

   it. 
  This 
  does 
  not 
  appear 
  under 
  the 
  Abbe 
  method 
  ; 
  and 
  

   accordingly 
  Strahl 
  positively 
  maintains 
  J 
  that 
  " 
  the 
  influence 
  

  

  * 
  Journ. 
  R. 
  M. 
  S., 
  Dec. 
  1889. 
  

  

  t 
  Dallinger, 
  p. 
  3(55. 
  

  

  X 
  Journ. 
  R. 
  M. 
  S. 
  Dec. 
  1895. 
  

  

  