﻿the 
  Kefiexion 
  of 
  the 
  X-rays 
  

  

  225 
  

  

  much 
  more 
  penetrating, 
  had 
  a 
  slight 
  maximum 
  iu 
  the 
  neigh- 
  

   bourhood 
  of 
  this 
  angle. 
  

  

  The 
  different 
  orders 
  and 
  different 
  types 
  of 
  characteristic 
  

   were 
  by 
  no 
  means 
  equally 
  conspicuous. 
  The 
  relative 
  in- 
  

   tensities 
  after 
  subtracting 
  the 
  effect 
  of 
  the 
  general 
  reflexion 
  

   are 
  given 
  for 
  the 
  case 
  of 
  ferrocyanide 
  in 
  Table 
  IV. 
  The 
  

  

  Table 
  IV. 
  

   Intensity 
  of 
  Select 
  ice 
  Reflexions* 
  

  

  

  cc. 
  

  

  0. 
  

  

  y. 
  d. 
  

  

  e. 
  

  

  First 
  Order 
  

  

  Second 
  Order 
  

  

  oS 
  

  

  28 
  

  

  > 
  

  

  — 
  

  

  Third 
  Order 
  

  

  Corrected 
  forab- 
  "1 
  

   sorption 
  by 
  air 
  J 
  

  

  5S 
  

   99 
  

  

  100 
  

  

  140 
  

  

  74 
  

  

  100 
  

  

  44 
  

   56 
  

  

  14 
  

   17 
  

  

  relative 
  intensities 
  found 
  for 
  the 
  different 
  types 
  of 
  radiation 
  

  

  have 
  little 
  definite 
  meaning. 
  In 
  the 
  first 
  place 
  they 
  have 
  

  

  been 
  cut 
  down 
  by 
  absorption 
  to 
  very 
  different 
  extents. 
  If 
  

  

  allowance 
  were 
  made 
  for 
  absorption 
  in 
  glass, 
  air, 
  and 
  mica, 
  

  

  probably 
  the 
  true 
  intensities 
  would 
  be 
  in 
  the 
  same 
  order 
  as 
  

  

  the 
  wave-lengths, 
  a, 
  being 
  the 
  strongest 
  and 
  e 
  much 
  the 
  

  

  i 
  • 
  

   weakest. 
  Id 
  the 
  second 
  place, 
  definite 
  evidence 
  was 
  obtained 
  

  

  that 
  the 
  relative 
  strengths 
  depended 
  on 
  the 
  state 
  of 
  the 
  tube. 
  

   The 
  weaker 
  types, 
  indeed, 
  almost 
  disappeared 
  sometimes 
  as 
  

   the 
  t 
  tibe 
  became 
  hard, 
  and 
  flashed 
  up 
  again 
  when 
  its 
  condition 
  

   was 
  altered. 
  The 
  strength 
  of 
  the 
  radiation 
  7 
  relative 
  to 
  its 
  

   neighbour 
  f 
  3 
  altered 
  from 
  70 
  per 
  cent, 
  to 
  IK) 
  per 
  cent, 
  in 
  the 
  

   course 
  of 
  one 
  short 
  experiment. 
  Comparison 
  between 
  the 
  

   different 
  orders 
  i.^ 
  more 
  profitable. 
  Jt 
  will 
  lie 
  seen 
  from 
  

   Table 
  IV. 
  that 
  in 
  ferrocyanide 
  the 
  third 
  order 
  was 
  enor- 
  

   mously 
  the 
  most 
  conspicuous, 
  since 
  tin 
  1 
  general 
  reflexion 
  

   was 
  so 
  much 
  less 
  intense 
  al 
  these 
  large 
  angles. 
  The 
  

   sixth 
  order 
  was 
  quite 
  easily 
  found, 
  the 
  fourth 
  order 
  in 
  t 
  

   at 
  all. 
  These 
  facts 
  can 
  be 
  very 
  simply 
  explained. 
  If 
  the 
  

   crystal 
  structure 
  completely 
  repeats 
  itself 
  only 
  every 
  three 
  

   Layers, 
  the 
  distance 
  between 
  the 
  first 
  and 
  fourth 
  layers 
  gives 
  

   the 
  fundamental 
  distance 
  d 
  in 
  equation 
  (1). 
  It 
  is 
  possible 
  

   either 
  that 
  the 
  three 
  layers 
  are 
  at 
  nearly 
  but 
  not 
  quite 
  the 
  

   same 
  distance 
  apart, 
  or 
  that 
  every 
  third 
  layer 
  is 
  especially 
  

   rich 
  in 
  the 
  heavy 
  atoms, 
  iron 
  for 
  example, 
  which 
  mosl 
  

   Phil 
  Mag. 
  S. 
  6. 
  Vol. 
  26. 
  No. 
  151. 
  July 
  1913. 
  Q 
  

  

  