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  Asymmetry 
  of 
  Illumination 
  Curves 
  in 
  Oblique 
  Refraction. 
  

  

  Table 
  VI. 
  

  

  Reflexion 
  grating 
  of 
  two 
  elements. 
  

   a 
  = 
  0*754 
  cm. 
  6 
  = 
  1-446 
  cm. 
  

  

  Angle 
  of 
  Incidence. 
  

  

  Eatio 
  of 
  the 
  1st 
  maxima 
  

   on 
  the 
  right 
  and 
  left. 
  

  

  Observed. 
  | 
  Calculated. 
  

  

  Ratio 
  of 
  the 
  2nd 
  maxima 
  

   on 
  the 
  right 
  and 
  left. 
  

  

  Observed. 
  | 
  Calculated- 
  

  

  89° 
  6' 
  

   89° 
  23 
  

   89° 
  28' 
  

  

  1-43 
  

   225 
  

   2-37 
  

  

  1-40 
  

   201 
  

   2-44 
  

  

  2-09 
  

   3-91 
  

   7-50 
  

  

  201 
  

  

  4-88 
  

   11-06 
  

  

  Table 
  VII. 
  

  

  Reflexion 
  grating 
  of 
  three 
  elements. 
  

   a 
  = 
  0*440 
  cm. 
  6 
  = 
  0*741 
  cm. 
  

  

  Angle 
  

  

  of 
  Incidence. 
  

  

  Ratio 
  of 
  the 
  1st 
  two 
  

  

  Principal 
  Maxima 
  on 
  either 
  

  

  side 
  of 
  the 
  central 
  one. 
  

  

  Ratio 
  of 
  the 
  2nd 
  two 
  

  

  Principal 
  Maxima 
  on 
  either 
  

  

  side 
  of 
  the 
  central 
  one. 
  

  

  

  

  Observed. 
  | 
  Calculated. 
  

  

  Observed. 
  | 
  Calculated. 
  

  

  

  88° 
  49' 
  

  

  1-48 
  

  

  1-43 
  

  

  1-83 
  

  

  1-70 
  

  

  

  89° 
  5' 
  

   89° 
  27' 
  

  

  1-63 
  

   2-65 
  

  

  1-71 
  

  

  2-87 
  

  

  2-90 
  

   X 
  

  

  3-15 
  

  

  more 
  than 
  

   100 
  times. 
  

  

  Summary 
  and 
  Conclusion. 
  

  

  1. 
  The 
  unsymmetrical 
  interference 
  fringes 
  of 
  the 
  light 
  

   obliquely 
  diffracted 
  by 
  two 
  parallel 
  reflecting 
  surfaces 
  in 
  

   the 
  same 
  plane 
  have 
  been 
  observed 
  and 
  photographed. 
  

  

  2. 
  The 
  illumination 
  curve 
  in 
  the 
  diffraction 
  pattern 
  (of 
  

   the 
  Fraunhofer 
  class) 
  due 
  to 
  an 
  obliquely-held 
  reflecting 
  

   surface 
  (which 
  may 
  consist 
  of 
  two 
  or 
  more 
  separate 
  parts 
  in 
  

   the 
  same 
  plane), 
  is 
  found 
  to 
  be 
  markedly 
  asymmetrical, 
  

   corresponding 
  points 
  on 
  either 
  side 
  of 
  the 
  central 
  fringe 
  

   being 
  of 
  very 
  different 
  intensities. 
  As 
  the 
  positions 
  of 
  the 
  

   points 
  of 
  minimum 
  (i. 
  e. 
  zero) 
  illumination 
  are 
  found 
  to 
  be 
  

   in 
  close 
  agreement 
  with 
  those 
  given 
  by 
  the 
  formula 
  of 
  the 
  

   usual 
  type, 
  the 
  asymmetry 
  of 
  the 
  illumination 
  curve 
  may 
  be 
  

   explained 
  as 
  due 
  to 
  the 
  varying 
  obliquity 
  at 
  different 
  points 
  

   in 
  the 
  diffraction 
  pattern. 
  Measurements 
  of 
  the 
  ratio 
  of 
  the 
  

  

  