﻿Telescopic 
  Vision, 
  319 
  

  

  in 
  which 
  almost 
  all 
  inferences 
  arrived 
  at 
  deductively 
  admit 
  

   of 
  satisfactory 
  verification 
  at 
  almost 
  every 
  step, 
  by 
  experi- 
  

   ments 
  with 
  the 
  microscope 
  — 
  an 
  instrument 
  which 
  permits 
  a 
  

   greater 
  range 
  o£ 
  useful 
  conditions 
  to 
  be 
  secured 
  than 
  are 
  

   available 
  with 
  the 
  telescope. 
  

  

  2. 
  In 
  the 
  experimental 
  verifications, 
  which 
  are 
  what 
  we 
  

   shall 
  be 
  chiefly 
  concerned 
  with 
  here, 
  we 
  have 
  to 
  consider 
  

   specially 
  the 
  relation 
  in 
  which 
  two 
  images 
  stand 
  to 
  one 
  

   another. 
  One 
  of 
  these 
  is 
  the 
  familiar 
  image 
  of 
  the 
  celestial 
  

   object 
  presented 
  by 
  the 
  telescope 
  to 
  the 
  eye. 
  Either 
  the 
  

   whole 
  or 
  a 
  part 
  of 
  the 
  other 
  (which 
  we 
  shall 
  find 
  it 
  appropriate 
  

   to 
  call 
  the 
  Concentration 
  Image) 
  can 
  in 
  all 
  cases 
  be 
  formed 
  

   by 
  the 
  same 
  identical 
  light 
  but 
  is 
  an 
  entirely 
  different 
  

   image, 
  as 
  will 
  presently 
  be 
  explained. 
  The 
  advantage 
  of 
  in- 
  

   troducing 
  this 
  concentration 
  image 
  arises 
  from 
  the 
  circum- 
  

   stance 
  that 
  the 
  method 
  of 
  analysis 
  which 
  has 
  proved 
  to 
  be 
  

   the 
  most 
  efficient 
  in 
  tracing 
  out 
  how 
  images 
  are 
  actually 
  

   formed 
  by 
  nature, 
  is 
  the 
  analysis 
  of 
  the 
  light 
  within 
  any 
  

   space 
  occupied 
  by 
  a 
  uniform 
  medium 
  into 
  its 
  constituent 
  

   ufw's 
  (undulations 
  of 
  flat 
  wavelets) 
  — 
  an 
  analysis 
  which 
  can 
  

   be 
  shown 
  to 
  be 
  always 
  possible 
  and 
  legitimate 
  however 
  

   complex 
  the 
  light 
  traversing 
  that 
  part 
  of 
  the 
  medium 
  may 
  be. 
  

   These 
  undulations 
  are 
  innumerable, 
  each 
  consisting 
  of 
  wavelets 
  

   of 
  infinitesimal 
  intensity, 
  each 
  undulation 
  to 
  be 
  thought 
  of 
  as 
  

   pervading 
  the 
  whole 
  of 
  the 
  medium 
  when 
  the 
  medium 
  is 
  

   pictured 
  as 
  extended 
  in 
  all 
  directions 
  without 
  limit, 
  and 
  being 
  

   of 
  such 
  a 
  kind 
  that 
  its 
  wavelets 
  are 
  equidistant, 
  alike, 
  and 
  

   uniform 
  throughout 
  their 
  whole 
  extent 
  in 
  regard 
  to 
  wave- 
  

   length, 
  intensity, 
  and 
  state 
  of 
  polarization 
  *, 
  Moreover, 
  one 
  

   such 
  undulation 
  and 
  one 
  only 
  needs 
  to 
  be 
  recognized 
  as 
  

   travelling 
  in 
  each 
  direction 
  in 
  which 
  light 
  traverses 
  the 
  medium. 
  

   It 
  is 
  by 
  the 
  interferences 
  of 
  these 
  innumerable 
  undulations 
  

   with 
  one 
  another 
  when 
  they, 
  as 
  it 
  were, 
  pour 
  down 
  simulta- 
  

   neously 
  upon 
  the 
  place 
  where 
  the 
  image 
  is 
  formed- 
  -it 
  is 
  by 
  

   these 
  interferences 
  that 
  the 
  image 
  is 
  called 
  into 
  existence 
  

   however 
  intricate 
  it 
  may 
  be. 
  

  

  3. 
  This 
  is 
  by 
  no 
  means 
  the 
  only 
  way 
  in 
  which 
  light 
  can 
  be 
  

   resolved. 
  In 
  fact 
  the 
  number 
  of 
  ways 
  in 
  which 
  light 
  may 
  

   legitimately 
  be 
  resolved 
  has 
  no 
  limit 
  ; 
  and 
  any 
  one 
  of 
  the 
  

   numberless 
  legitimate 
  resolutions, 
  if 
  only 
  ice 
  were 
  able 
  to 
  

   follow 
  out 
  its 
  consequences, 
  would 
  guide 
  us 
  to 
  the 
  same 
  ultimate 
  

   interference 
  effect 
  — 
  in 
  other 
  words, 
  to 
  the 
  same 
  image 
  ; 
  but 
  

   among 
  them 
  the 
  resolution 
  into 
  undulations 
  of 
  absolutely 
  

   uniform 
  and 
  absolutely 
  flat 
  wavelets 
  recommends 
  itself 
  as 
  

   the 
  one 
  by 
  which 
  the 
  student 
  of 
  nature 
  can 
  best 
  appreciate 
  

  

  * 
  See 
  Phil. 
  Mag-, 
  for 
  April 
  1905, 
  p. 
  594, 
  Appendix. 
  

  

  