﻿■■ 
  

  

  90 
  

  

  Mr. 
  Nalinimohan 
  Basu 
  on 
  the 
  Diffraction 
  of 
  

  

  up 
  to 
  2 
  cm. 
  Table 
  III. 
  shows 
  the 
  observed 
  values, 
  the 
  values 
  

   calculated 
  from 
  my 
  formulae, 
  and 
  the 
  values 
  according 
  to 
  

   Schuster's 
  formula 
  (which 
  would 
  be 
  valid 
  for 
  a 
  sharp 
  dif- 
  

   fracting 
  edge 
  in 
  the 
  same 
  position) 
  . 
  To 
  calculate 
  the 
  posi- 
  

   tions 
  of 
  the 
  minima 
  given 
  by 
  the 
  relations 
  n\=2d0 
  2 
  -\-2a6 
  3 
  , 
  

   and 
  a?' 
  = 
  '2dd 
  + 
  3a0 
  2 
  /2, 
  the 
  first 
  equation 
  was 
  solved 
  for 
  by 
  

   Horner's 
  method, 
  and 
  the 
  resulting 
  values 
  substituted 
  in 
  the 
  

   second 
  equation. 
  The 
  measurements 
  of 
  the 
  width 
  of 
  the 
  first 
  

   band 
  were 
  rather 
  rough 
  on 
  account 
  of 
  the 
  indefiniteness 
  of 
  

   its 
  outer 
  edge. 
  The 
  agreement 
  between 
  the 
  observed 
  widths 
  

   and 
  the 
  widths 
  calculated 
  from 
  my 
  formulae 
  is 
  seen 
  to 
  be 
  

   fairly 
  satisfactory 
  for 
  values 
  of 
  d 
  up 
  to 
  3 
  mm. 
  For 
  larger 
  

   values 
  of 
  d 
  the 
  observed 
  widths 
  agree 
  more 
  closely 
  with 
  those 
  

   calculated 
  from 
  Schuster's 
  formula, 
  as 
  explained 
  in 
  paragraphs 
  

   11 
  and 
  14 
  above. 
  

  

  Theory 
  of 
  the 
  Fringes 
  between 
  the 
  edge 
  and 
  the 
  source 
  of 
  light. 
  

  

  16. 
  As 
  already 
  remarked 
  in 
  paragraph 
  7, 
  the 
  direct 
  and 
  

   the 
  reflected 
  pencils 
  tend 
  to 
  separate 
  into 
  distinct 
  parts 
  of 
  

   the 
  field 
  when 
  the 
  focal 
  plane 
  of 
  the 
  observing 
  microscope 
  is 
  

  

  Fig. 
  3. 
  

  

  put 
  forward 
  so 
  as 
  to 
  lie 
  between 
  the 
  edge 
  of 
  the 
  cylinder 
  

   and 
  the 
  source 
  of 
  light. 
  Why 
  this 
  is 
  so 
  will 
  be 
  readily 
  

   understood 
  on 
  a 
  reference 
  to 
  fig. 
  3. 
  The 
  rays 
  reflected 
  

  

  