﻿222 
  Messrs. 
  H. 
  Gr. 
  J. 
  Moseley 
  and 
  C. 
  G. 
  Darwin 
  on 
  

  

  primary 
  beam. 
  As 
  soon 
  as 
  the 
  correct 
  position 
  was 
  de- 
  

   termined, 
  the 
  crystal 
  was 
  turned 
  through 
  an 
  angle 
  A 
  into 
  the 
  

   position 
  d'fined 
  by 
  the 
  telescope 
  S, 
  the 
  lamp, 
  and 
  the 
  plate 
  

   glass. 
  The 
  corresponding 
  position 
  was 
  then 
  found 
  on 
  the 
  

   other 
  side, 
  and 
  the 
  crystal 
  turned 
  through 
  the 
  angle 
  B 
  into 
  

   the 
  standard 
  position, 
  using 
  this 
  time 
  the 
  other 
  side 
  of 
  the 
  

   glass. 
  As 
  the 
  faces 
  of 
  the 
  glass 
  were 
  strictly 
  parallel, 
  the 
  

   special 
  angle 
  was 
  given 
  by 
  ^(A-fB). 
  

  

  The 
  values 
  found 
  for 
  the 
  special 
  angles 
  are 
  tabulated 
  below. 
  

   Those 
  in 
  Tables 
  I. 
  and 
  II. 
  are 
  probably 
  correct 
  to 
  within 
  

   about 
  1', 
  but 
  in 
  Table 
  III. 
  the 
  error 
  may 
  be 
  twice 
  as 
  

   great. 
  

  

  

  Angles 
  of 
  Special 
  Reflexion. 
  

  

  

  

  Table 
  I. 
  

  

  Eocksalt, 
  JSTaCl. 
  

   Cube 
  face. 
  

  

  First 
  Order... 
  

   

  

  13° 
  31' 
  

   •2337 
  

   1-176 
  

  

  0r 
  

  

  11° 
  28' 
  

   •1988 
  

   1-000 
  

  

  ri- 
  

   ll 
  17' 
  

  

  •1956 
  

   •984 
  

  

  9047. 
  

   •1699 
  

   •855 
  

  

  9° 
  29' 
  

   •1647 
  

   •829 
  

  

  sin 
  0x5-030... 
  

  

  Table 
  II. 
  

  

  Potassium 
  

  

  Ferrocyanide, 
  

  

  K 
  4 
  FeCy 
  e 
  .3H 
  2 
  0. 
  

  

  Principal 
  

   cleavage 
  face. 
  

  

  First 
  Order... 
  

   

  

  4° 
  26' 
  

   •0773 
  

   1-168 
  

  

  ft. 
  

  

  3° 
  46r 
  

   •0657 
  

   •995 
  

  

  7i- 
  

  

  3° 
  43|' 
  

   •0650 
  

  

  •982 
  

  

  not 
  

  

  found. 
  

  

  

  sin 
  0X15-11... 
  

  

  Second 
  Order... 
  

   

  

  « 
  2 
  - 
  

   8° 
  55|' 
  

   •1551 
  

   1-172 
  

  

  (3 
  2 
  . 
  

  

  7° 
  33^' 
  

   1315 
  

   •994 
  

  

  y 
  2 
  - 
  

  

  7°2S|' 
  

   •1301 
  

   •983 
  

  

  o 
  2 
  . 
  

  

  not 
  

  

  e 
  2 
  . 
  

   found. 
  

  

  sin 
  

  

  \ 
  sin 
  0X15-11... 
  

  

  Third 
  Order... 
  

   9 
  

  

  a,. 
  

  

  13° 
  28£' 
  

   •2330^ 
  

   1174 
  

  

  11° 
  27' 
  

   •1985 
  

   1-000 
  

  

  y 
  3 
  - 
  

  

  11° 
  16' 
  

  

  •1954 
  

   •984 
  

  

  8 
  3 
  . 
  

  

  9° 
  45^' 
  

   •1695 
  

   •854 
  

  

  £ 
  3' 
  

  

  9° 
  27^' 
  

   •1643 
  

  

  •828 
  

  

  

  ^siu 
  0x15-11... 
  

  

  Table 
  III. 
  

  

  Selenite, 
  

   CaS0 
  4 
  .2H 
  2 
  0. 
  

  

  Principal 
  

   cleavage 
  face. 
  

  

  First 
  Order... 
  

   9 
  

  

  4° 
  59' 
  

   •0869 
  

   1-175 
  

  

  A. 
  

  

  4° 
  16±' 
  

   •0745 
  

   1-009 
  

  

  7i- 
  

  

  4° 
  13^' 
  

  

  •0736 
  

  

  •997 
  

  

  9 
  V 
  

  

  3° 
  39' 
  

   ■0637 
  

   •861 
  

  

  6 
  r 
  

   3° 
  32' 
  

   •0616 
  

   •834 
  

  

  sin0 
  

  

  sin 
  0X13-53... 
  

  

  Second 
  Order.. 
  

   

  

  a 
  2 
  . 
  

  

  9° 
  58f 
  ' 
  

   •1731 
  

   1-172 
  

  

  (3 
  2 
  . 
  

  

  8° 
  30' 
  

   •1478 
  

   1-000 
  

  

  y 
  2 
  - 
  

  

  8° 
  22^' 
  

   •1457 
  

   •985 
  

  

  7° 
  17' 
  

   •1268 
  

   •858 
  

  

  6 
  2 
  . 
  

  

  7° 
  3' 
  

   •1228 
  

   ■830 
  

  

  sin 
  

  

  ±sin 
  0x13-53.. 
  . 
  

  

  