﻿492 
  Mr. 
  L. 
  Wright 
  on 
  Microscopic 
  Images 
  and 
  Vision. 
  

  

  made 
  chiefly 
  because 
  Dr. 
  Stoney 
  does 
  not 
  seem 
  to 
  recognize 
  

   the 
  true 
  relative 
  proportions, 
  either 
  in 
  maintaining 
  with 
  Abbe 
  

   in 
  such 
  a 
  universal 
  sense 
  that 
  " 
  diffracted 
  light 
  is 
  the 
  machinery 
  

   by 
  which 
  good 
  definition 
  is 
  brought 
  about 
  " 
  ; 
  or 
  when 
  he 
  

   proceeds 
  to 
  illustrate 
  (§35) 
  "the 
  great 
  assistance 
  which 
  is 
  

   rendered 
  to 
  the 
  practical 
  microscopist 
  by 
  Abbe's 
  theory/'' 
  

  

  15. 
  We 
  therefore 
  next 
  consider 
  that 
  illustration. 
  To 
  begin 
  

   with, 
  the 
  resolution 
  of 
  A. 
  pellucida 
  is 
  no 
  real 
  problem 
  at 
  all 
  : 
  

   it 
  is 
  not 
  even 
  of 
  the 
  same 
  nature 
  as 
  the 
  problems 
  which 
  do 
  

   confront 
  the 
  scientific 
  worker. 
  Supposing 
  it 
  were, 
  the 
  latter 
  

   would 
  regard 
  with 
  consternation 
  the 
  elaborate 
  apparatus 
  

   described 
  for 
  producing 
  monochromatic 
  light. 
  This 
  diatom, 
  

   however, 
  has 
  been 
  studied 
  for 
  many 
  years 
  ; 
  the 
  dimensions 
  of 
  

   its 
  structure 
  are 
  known 
  and 
  familiar; 
  and 
  the 
  powers 
  of 
  annular 
  

   illumination 
  have 
  long 
  since 
  been 
  ascertained. 
  It 
  is 
  no 
  

   problem, 
  or 
  one 
  in 
  which 
  help 
  is 
  needed, 
  to 
  take 
  what 
  is 
  really 
  

   a 
  " 
  grating 
  " 
  of 
  this 
  known 
  fineness, 
  and 
  already 
  known 
  to 
  

   have 
  this 
  definite 
  periodicity 
  of 
  structure, 
  and 
  arrange 
  matters 
  

   so 
  as 
  to 
  get 
  the 
  most 
  conspicuous 
  u 
  resolution 
  " 
  of 
  it. 
  The 
  

   problems 
  in 
  which 
  assistance 
  is 
  really 
  wanted, 
  the 
  microscopic 
  

   worker's 
  really 
  " 
  difficult 
  " 
  objects, 
  are 
  such 
  as 
  Dr. 
  Dallinger 
  

   confronted 
  in 
  detecting 
  the 
  spores 
  of 
  a 
  monad, 
  itself 
  only 
  

   60*00 
  °f 
  an 
  nicn 
  * 
  n 
  diameter 
  and 
  themselves 
  only 
  ^ToWo 
  °^ 
  an 
  

   inch 
  ; 
  or 
  more 
  especially 
  (because 
  here 
  was 
  involved 
  real 
  

   " 
  resolution 
  " 
  of 
  fine 
  detail) 
  the 
  process 
  of 
  division 
  in 
  the 
  

   nucleus 
  of 
  a 
  cell, 
  itself 
  only 
  20000 
  °f 
  an 
  mcn 
  l° 
  D 
  g- 
  In 
  such 
  

   cases 
  what 
  will 
  be 
  found 
  and 
  is 
  to 
  be 
  observed 
  is 
  unknown 
  \ 
  

   accurate 
  periodicity 
  of 
  structure 
  is 
  probably 
  absent 
  ; 
  and 
  

   mere 
  artificial 
  force 
  or 
  clearness 
  in 
  ''resolution," 
  even 
  if 
  

   obtainable 
  (which 
  it 
  seldom 
  is) 
  is 
  worthless 
  in 
  comparison 
  

   with 
  known 
  trustworthiness 
  in 
  the 
  image 
  so 
  far 
  as 
  it 
  goes. 
  

   Taking 
  any 
  such 
  case 
  as 
  this 
  for 
  our 
  test-object, 
  and 
  com- 
  

   paring 
  it 
  with 
  the 
  treatment 
  of 
  the 
  A. 
  pellucida 
  as 
  described, 
  

   we 
  shall 
  be 
  able 
  to 
  appreciate 
  the 
  proportion 
  of 
  both 
  truth 
  and 
  

   error 
  — 
  for 
  there 
  is 
  truth 
  as 
  well 
  as 
  error 
  — 
  in 
  the 
  u 
  spectrum 
  " 
  

   theory. 
  

  

  16. 
  We 
  cannot 
  help, 
  in 
  the 
  first 
  place, 
  seeing 
  much 
  error. 
  

   While 
  the 
  minuteness 
  of 
  structure 
  to 
  be 
  detected 
  by 
  

   Dr. 
  Dallinger 
  (in 
  an 
  unknown 
  object) 
  was 
  as 
  great, 
  the 
  

   method 
  of 
  proceeding 
  described 
  for 
  the 
  A. 
  pellucida 
  is 
  im- 
  

   practicable, 
  and 
  would 
  be 
  useless 
  even 
  if 
  practicable. 
  Real 
  

   work 
  has 
  to 
  be 
  done 
  by 
  far 
  different 
  means. 
  The 
  finest 
  

   lenses, 
  used 
  with 
  a 
  wide 
  and 
  solid 
  aplanatic 
  cone 
  of 
  light, 
  

   could 
  alone 
  do 
  such 
  work 
  ; 
  and 
  moreover, 
  earlier 
  lenses 
  of 
  

   1*48 
  N.A. 
  were 
  surpassed 
  in 
  results 
  by 
  apochromatic 
  lenses 
  

   of 
  1'40 
  N.A., 
  better 
  corrected 
  for 
  spherical 
  aberration 
  — 
  the 
  

  

  