﻿22 
  Diffraction 
  phenomena 
  in 
  the 
  Focal 
  Plane 
  of 
  a 
  Telescope, 
  

  

  solution 
  of 
  the 
  problem 
  either 
  as 
  mathematical 
  formula 
  or 
  as 
  

   graphical 
  representation. 
  

  

  For 
  the 
  latter 
  purpose 
  we 
  draw 
  the 
  concentric 
  circles 
  

   representing 
  lines 
  of 
  equal 
  intensity 
  for 
  the 
  luminous 
  source, 
  

   and 
  similar 
  lines 
  of 
  equal 
  negative 
  intensity 
  for 
  the 
  imaginary 
  

   source 
  occupying 
  the 
  dark 
  space; 
  by 
  the 
  process 
  above 
  

   described 
  we 
  get 
  a 
  series 
  of 
  lines 
  of 
  equal 
  intensity 
  due 
  

   to 
  these 
  sources. 
  In 
  the 
  annexed 
  diagrams 
  (figs. 
  10 
  and 
  11) 
  

   Fig. 
  10. 
  Fig. 
  11. 
  

  

  1 
  give 
  a 
  portion 
  of 
  these 
  lines 
  in 
  the 
  neighbourhood 
  of 
  the 
  

   rim 
  of 
  the 
  luminous 
  source 
  (a 
  = 
  co), 
  when 
  there 
  is 
  a 
  dark 
  

   circular 
  disk 
  (a 
  = 
  40) 
  ; 
  the 
  lines 
  are 
  drawn 
  for 
  equal 
  inter- 
  

   vals 
  O'l 
  of 
  the 
  intensity. 
  Fig. 
  10 
  represents 
  the 
  lines 
  when 
  

   the 
  dark 
  disk 
  touches 
  the 
  rim, 
  and 
  fig. 
  11 
  when 
  the 
  nearest 
  

   distance 
  between 
  it 
  and 
  the 
  rim 
  is 
  equal 
  to 
  1. 
  In 
  both 
  figures 
  

   the 
  dotted 
  lines 
  give 
  the 
  boundaries 
  of 
  the 
  luminous 
  source. 
  

  

  