﻿516 
  F. 
  E. 
  Wright 
  — 
  Methods 
  in 
  Microscopical 
  Petrography. 
  

  

  Table 
  I. 
  

  

  a 
  

  

  siii 
  2 
  a 
  

  

  a 
  

  

  sin 
  2 
  a 
  

  

  a 
  

  

  sin 
  2 
  a 
  

  

  0° 
  

  

  O'OOO 
  00 
  

  

  30° 
  

  

  0-250 
  00 
  

  

  60° 
  

  

  0-750 
  00 
  

  

  1 
  

  

  •000 
  30 
  

  

  1 
  

  

  •265 
  26 
  

  

  1 
  

  

  •764 
  96 
  

  

  " 
  2 
  

  

  •001 
  22 
  

  

  2 
  

  

  •280 
  81 
  

  

  2 
  

  

  •779 
  60 
  

  

  3 
  

  

  •002 
  74 
  

  

  3 
  

  

  •296 
  63 
  

  

  3 
  

  

  •793 
  89 
  

  

  4 
  

  

  •004 
  87 
  

  

  4 
  

  

  •312 
  70 
  

  

  4 
  

  

  •807 
  83 
  

  

  5 
  

  

  0*007 
  60 
  

  

  35 
  

  

  0-328 
  99 
  

  

  65 
  

  

  0-821 
  39 
  

  

  6 
  

  

  •010 
  93 
  

  

  6 
  

  

  •345 
  49 
  

  

  6 
  

  

  •834 
  57 
  

  

  7 
  

  

  •014 
  85 
  

  

  7 
  

  

  •362 
  18 
  

  

  7 
  

  

  •847 
  33 
  

  

  8 
  

  

  •019 
  37 
  

  

  8 
  

  

  •379 
  04 
  

  

  8 
  

  

  •859 
  67 
  

  

  9 
  

  

  •024 
  47 
  

  

  9 
  

  

  •396 
  04 
  

  

  9 
  

  

  •871 
  57 
  

  

  10 
  

  

  0*030 
  15 
  

  

  40 
  

  

  0-413 
  18 
  

  

  70 
  

  

  0-883 
  02 
  

  

  1 
  

  

  •036 
  41 
  

  

  1 
  

  

  •430 
  41 
  

  

  1 
  

  

  •894 
  01 
  

  

  2 
  

  

  •043 
  23 
  

  

  2 
  

  

  •447 
  74 
  

  

  2 
  

  

  •904 
  51 
  

  

  3 
  

  

  •050 
  60 
  

  

  3 
  

  

  •465 
  12 
  

  

  3 
  

  

  •914 
  52 
  

  

  4 
  

  

  •058 
  53 
  

  

  4 
  

  

  •482 
  55 
  

  

  4 
  

  

  •924 
  02 
  

  

  15 
  

  

  0-066 
  99 
  

  

  45 
  

  

  0-500 
  00 
  

  

  75 
  

  

  0*933 
  01 
  

  

  6 
  

  

  •075 
  98 
  

  

  6 
  

  

  •517 
  45 
  

  

  6 
  

  

  •941 
  47 
  

  

  7 
  

  

  •085 
  48 
  

  

  7 
  

  

  •534 
  88 
  

  

  7 
  

  

  •949 
  40 
  

  

  8 
  

  

  •095 
  49 
  

  

  8 
  

  

  •552 
  26 
  

  

  8 
  

  

  •956 
  77 
  

  

  9 
  

  

  •105 
  99 
  

  

  9 
  

  

  •569 
  59 
  

  

  9 
  

  

  •963 
  59 
  

  

  20 
  

  

  0-116 
  98 
  

  

  50 
  

  

  0-586 
  82 
  

  

  80 
  

  

  0-969 
  85 
  

  

  1 
  

  

  •128 
  43 
  

  

  1 
  

  

  •603 
  96 
  

  

  1 
  

  

  •975 
  53 
  

  

  2 
  

  

  •140 
  33 
  

  

  2 
  

  

  •620 
  96 
  

  

  2 
  

  

  •980 
  63 
  

  

  3 
  

  

  •152 
  67 
  

  

  3 
  

  

  •637 
  82 
  

  

  3 
  

  

  •985 
  15 
  

  

  4 
  

  

  •165 
  43 
  

  

  4 
  

  

  •654 
  51 
  

  

  4 
  

  

  •989 
  07 
  

  

  25 
  

  

  0-178 
  61 
  

  

  55 
  

  

  0-671 
  01 
  

  

  85 
  

  

  0992 
  40 
  

  

  6 
  

  

  •192 
  17 
  

  

  6 
  

  

  •687 
  30 
  

  

  6 
  

  

  •995 
  13 
  

  

  1 
  

  

  •206 
  11 
  

  

  7 
  

  

  •703 
  37 
  

  

  7 
  

  

  •997 
  26 
  

  

  8 
  

  

  •220 
  40 
  

  

  8 
  

  

  •719 
  19 
  

  

  8 
  

  

  •998 
  78 
  

  

  9 
  

  

  •235 
  04 
  

  

  9 
  

  

  •734 
  74 
  

  

  9 
  

  

  •999 
  70 
  

  

  30 
  

  

  0-250 
  00 
  

  

  60 
  

  

  0-750 
  00 
  

  

  90 
  

  

  1-000 
  00 
  

  

  Plates 
  II 
  and 
  III 
  should 
  furnish 
  refractive 
  index 
  values 
  

   accurate 
  to 
  about 
  one 
  in 
  the 
  third 
  decimal 
  place. 
  

  

  Examples. 
  — 
  (1) 
  Let 
  2E 
  = 
  60°, 
  the 
  optic 
  axial 
  angle 
  in 
  air 
  

   of 
  a 
  mineral 
  of 
  refractive 
  index 
  /3 
  = 
  1*535. 
  Find 
  the 
  true 
  

   optic 
  axial 
  angle 
  2 
  V. 
  

  

  Pass, 
  on 
  Plate 
  II, 
  along 
  the 
  horizontal 
  line, 
  which 
  cuts 
  the 
  

   ordinate 
  representing 
  the 
  angle 
  E, 
  to 
  its 
  intersection 
  with 
  the 
  

  

  