﻿the 
  Illumination 
  Curves 
  in 
  Oblique 
  Refraction. 
  115 
  

  

  For 
  photographs 
  II, 
  III, 
  and 
  IV, 
  the 
  actual 
  values 
  o£ 
  6 
  

   for 
  the 
  interference 
  minima 
  were 
  calculated 
  from 
  the 
  known 
  

   constants 
  a, 
  b, 
  i, 
  \ 
  and 
  compared 
  with 
  the 
  observed 
  values. 
  

   These 
  are 
  shown 
  in 
  Tables 
  II. 
  , 
  III., 
  and 
  IV. 
  

  

  Table 
  II. 
  

  

  a 
  = 
  0*754 
  em. 
  5=1*446 
  cm. 
  \= 
  "0000435 
  cm. 
  

   ; 
  = 
  89°15'-27. 
  

  

  Interference 
  Minima. 
  

  

  Calculated 
  diffraction 
  

   angle, 
  90° 
  - 
  9 
  

   (in 
  minutes). 
  

  

  Observed 
  diffraction 
  

   angle, 
  90°- 
  9 
  

   (in 
  minutes). 
  

  

  2nd 
  on 
  the 
  right. 
  

  

  35'-98 
  

  

  35'-85 
  

  

  1st 
  „ 
  „ 
  

  

  41' 
  97 
  

  

  41'-83 
  

  

  1st 
  „ 
  „ 
  left. 
  

  

  47' 
  -21 
  

  

  46'-95 
  

  

  2nd 
  „ 
  „ 
  „ 
  

  

  51"92 
  

  

  52'-05 
  

  

  5th 
  „ 
  „ 
  „ 
  

  

  64'-02 
  

  

  63'95 
  

  

  Table 
  III. 
  

  

  a 
  =0-754 
  cm. 
  6=1-446 
  cm. 
  \= 
  -0000435 
  cm. 
  

  

  i 
  = 
  89°22'"75. 
  

  

  Interference 
  Minima. 
  

  

  Calculated 
  

   90° 
  -9. 
  

  

  Observed 
  

   90° 
  -9. 
  

  

  2nd 
  on 
  the 
  right. 
  

  

  26'-15 
  

  

  26'-12 
  

  

  1st 
  „ 
  „ 
  

  

  33'-88 
  

  

  33'-85 
  

  

  1st 
  ,, 
  „ 
  left. 
  

  

  40' 
  -25 
  

  

  4O'-09 
  

  

  2nd 
  „ 
  „ 
  „ 
  

  

  45'-69 
  

  

  45''70 
  

  

  5th 
  „ 
  „ 
  „ 
  

  

  58'-90 
  

  

  58'-75 
  

  

  I 
  2 
  

  

  