﻿116 
  Mr. 
  S. 
  K. 
  Mitra 
  on 
  the 
  Asymmetry 
  of 
  

  

  Table 
  IV. 
  

  

  a=-754cm. 
  6 
  = 
  1-446 
  cm. 
  X 
  = 
  -0000435 
  cm. 
  

   i 
  = 
  89°29'-90. 
  

  

  Interference 
  Minima. 
  

  

  Calculated 
  

   90° 
  -e. 
  

  

  Observed 
  

   90° 
  -0. 
  

  

  1st 
  on 
  the 
  right. 
  

  

  25'72 
  

  

  25' 
  -62 
  

  

  1st 
  on 
  the 
  left. 
  

  

  33"75 
  

  

  33' 
  45 
  

  

  2nd,, 
  ., 
  „ 
  

  

  40' 
  -08 
  

  

  39 
  '-94 
  

  

  5th 
  „ 
  „ 
  „ 
  54 
  K 
  94 
  

  

  54'-96 
  

  

  The 
  Asymmetry 
  of 
  the 
  Illumination- 
  Curves. 
  

  

  As 
  remarked 
  above, 
  there 
  is 
  a 
  very 
  marked 
  difference 
  in 
  

   the 
  luminosity 
  of 
  the 
  corresponding 
  bands 
  on 
  either 
  side 
  of 
  

   the 
  central 
  fringe 
  of 
  the 
  pattern 
  due 
  to 
  the 
  reflecting 
  surface 
  

   of 
  two 
  elements. 
  Similar 
  effects 
  are 
  also 
  noticeable 
  when 
  

   the 
  reflecting 
  surface 
  consists 
  of 
  three 
  elements. 
  Figs. 
  V 
  

   and 
  VI 
  in 
  the 
  Plate 
  reproduce 
  two 
  photographs 
  obtained 
  

   with 
  a 
  reflecting 
  surface 
  consisting 
  of 
  three 
  elements. 
  The 
  

   difference 
  between 
  the 
  intensities 
  of 
  the 
  2nd 
  principal 
  

   maximum 
  on 
  either 
  side 
  of 
  the 
  central 
  one 
  is 
  very 
  evident 
  

   in 
  the 
  reproductions 
  and 
  might 
  be 
  made 
  out 
  even 
  in 
  respect 
  

   of 
  the 
  secondary 
  maxima 
  on 
  either 
  side. 
  This 
  asymmetry 
  

   demands 
  an 
  explanation. 
  As 
  is 
  shown 
  by 
  the 
  measurements 
  

   given 
  in 
  Tables 
  I. 
  to 
  IV., 
  the 
  positions 
  of 
  the 
  minima 
  of 
  

   illumination 
  are 
  in 
  good 
  agreement 
  with 
  those 
  calculated 
  

   from 
  the 
  formula 
  of 
  the 
  usual 
  type, 
  which 
  are 
  obtained 
  on 
  

   the 
  assumption 
  that 
  each 
  of 
  the 
  elements 
  into 
  which 
  the 
  

   reflecting 
  surface 
  may 
  be 
  divided 
  diffracts 
  light 
  strictly 
  

   in 
  proportion 
  to 
  its 
  area, 
  and 
  that 
  the 
  phase 
  and 
  intensity 
  of 
  

   the 
  disturbance 
  incident 
  on 
  the 
  surface 
  are 
  the 
  same 
  as 
  when 
  

   the 
  waves 
  travel 
  undisturbed. 
  Further, 
  the 
  intensities 
  at 
  

   the 
  points 
  of 
  minimum 
  illumination 
  are 
  shown 
  by 
  observa- 
  

   tion 
  and 
  by 
  the 
  photographs 
  to 
  be 
  zero, 
  in 
  agreement 
  with 
  

   the 
  results 
  indicated 
  by 
  these 
  formulae. 
  On 
  the 
  other 
  hand, 
  

   the 
  difference 
  in 
  the 
  intensity 
  at 
  corresponding 
  points 
  of 
  the 
  

   pattern 
  on 
  either 
  side 
  of 
  the 
  central 
  fringe 
  remains 
  unex- 
  

   plained 
  according 
  to 
  such 
  formulae 
  unless 
  regarded 
  as 
  an 
  

   obliquity 
  effect. 
  

  

  