﻿Mr. 
  L. 
  Wright 
  on 
  Microscopic 
  Images 
  and 
  Vision. 
  493 
  

  

  meaning 
  of 
  which 
  we 
  shall 
  see. 
  Supposing- 
  the 
  mieroscopist, 
  

   however, 
  to 
  know 
  or 
  suppose 
  the 
  measure 
  of 
  minuteness 
  in 
  

   the 
  divisions 
  of 
  the 
  cell-nucleus, 
  he 
  would, 
  on 
  the 
  principles 
  

   Dr. 
  Stoney 
  explains, 
  have 
  to 
  employ 
  (with 
  doubtless 
  some 
  

   modification 
  in 
  detail) 
  arrangements 
  for 
  plane-wxve 
  illu- 
  

   mination 
  generically 
  similar 
  to 
  those 
  he 
  describes 
  for 
  the 
  

   diatom. 
  But 
  he 
  would 
  be 
  wrong, 
  and 
  the 
  results 
  would 
  be 
  

   nil 
  *. 
  Dr. 
  Dallino-er 
  had 
  to 
  do 
  such 
  work 
  with 
  a 
  hio-h 
  deo-ree 
  

   of 
  heterogeneous 
  illumination 
  — 
  as 
  close 
  an 
  approach 
  as 
  is 
  

   possible 
  with 
  the 
  lens 
  used, 
  to 
  a 
  self-luminous 
  condition 
  of 
  

   the 
  object. 
  

  

  The 
  image 
  even 
  of 
  the 
  diatom 
  is 
  a 
  false 
  image. 
  It 
  is 
  

   admittedly 
  so 
  in 
  regard 
  to 
  the 
  " 
  spherules," 
  and 
  competent 
  

   judges 
  whom 
  I 
  have 
  consulted 
  are 
  very 
  doubtful 
  whether 
  

   even 
  the 
  breaking 
  up 
  of 
  the 
  striae 
  so 
  shown, 
  is 
  not 
  due 
  to 
  

   false 
  diffraction-fringes 
  from 
  the 
  midrib 
  of 
  the 
  valve, 
  the 
  

   spherules 
  being 
  thus 
  arranged 
  in 
  longitudinal 
  rows 
  far 
  more 
  

   straight 
  than 
  is 
  really 
  the 
  case. 
  Looking 
  at 
  the 
  matter 
  

   theoretically, 
  it 
  will 
  be 
  observed 
  that 
  after 
  having 
  laid 
  down 
  

   how 
  the 
  excellence 
  of 
  the 
  image 
  is 
  in 
  inverse 
  proportion 
  to 
  

   " 
  the 
  degree 
  in 
  which 
  [the 
  state 
  of 
  the 
  light 
  by 
  which 
  the 
  

   object 
  is 
  illuminated] 
  contributes 
  to 
  produce, 
  to 
  modify, 
  or 
  to 
  

   efface 
  detail," 
  he 
  proceeds 
  to 
  obtain 
  this 
  image 
  by 
  almost 
  the 
  

   greatest 
  specialization 
  of 
  the 
  light 
  which 
  is 
  possible. 
  The 
  

   effect 
  of 
  this 
  is 
  to 
  replace 
  the 
  actual 
  detail, 
  by 
  other 
  apparent 
  

   detail 
  which 
  is 
  visually 
  intense, 
  and 
  geometrically 
  sym- 
  

   metrical, 
  to 
  an 
  utterly 
  false 
  degree. 
  

  

  Similar 
  results 
  are 
  traceable 
  in 
  other 
  diatom 
  work 
  by 
  the 
  

   Abbe 
  school, 
  as 
  may 
  be 
  shown 
  by 
  the 
  most 
  familiar 
  test-valve 
  

   of 
  all, 
  a 
  much 
  coarser 
  one, 
  the 
  P. 
  angulatum. 
  Dr. 
  Van 
  

   Heurck 
  has 
  photographed 
  this 
  with 
  the 
  celebrated 
  Abbe- 
  

   Zeiss 
  lens 
  of 
  1*63 
  aperture 
  and 
  dense 
  immersion-fluid 
  and 
  

   medium, 
  by 
  Abbe 
  methods, 
  with 
  an 
  uncorrected 
  condenser 
  ; 
  

   the 
  result 
  is 
  a 
  series 
  of 
  hexagons 
  resembling 
  a 
  honev-comb. 
  

   Dr. 
  Stoney 
  writes 
  f 
  of 
  the 
  same 
  object, 
  that 
  dry 
  objectives 
  

   can 
  only 
  image 
  its 
  details 
  " 
  correctly 
  so 
  far 
  as 
  regards 
  their 
  

   number 
  and 
  position, 
  but 
  any 
  further 
  detail 
  is 
  not 
  correctly 
  

   represented." 
  Immersions 
  embracing 
  most 
  of 
  the 
  first 
  

   spectra, 
  " 
  we 
  now 
  see 
  some 
  detail 
  : 
  the 
  dots 
  appear 
  hexagonal, 
  

   and 
  are 
  separated 
  from 
  one 
  another 
  by 
  walls 
  which 
  are 
  thin, 
  

  

  * 
  Narrow 
  pencils 
  and 
  annuli 
  have 
  of 
  course 
  "been 
  tried, 
  for 
  the 
  contrast 
  

   they 
  give. 
  The 
  probable 
  reason 
  of 
  failure 
  is 
  want 
  of 
  sufficiently 
  regular 
  

   periodicity 
  in 
  the 
  detail. 
  Only 
  such 
  periodic 
  detail 
  is 
  shown 
  better 
  

   by 
  such 
  methods 
  ; 
  all 
  else 
  is 
  " 
  blurred," 
  as 
  Dr. 
  Stoney 
  points 
  out 
  in 
  

   regard 
  to 
  the 
  other 
  features 
  of 
  this 
  diatom 
  itself. 
  

  

  t 
  Modern 
  Microscopy, 
  2nd 
  ed. 
  p. 
  109. 
  

  

  