﻿the 
  Reflexion 
  of 
  the 
  X-rai/s. 
  

  

  227 
  

  

  waves 
  which 
  makes 
  up 
  a 
  characteristic 
  radiation. 
  An 
  

   attempt 
  was 
  made 
  to 
  find 
  over 
  what 
  range 
  of 
  angles 
  reflexion 
  

   of 
  monochromatic 
  radiation 
  occurs. 
  The 
  beam 
  was 
  restricted 
  

   by 
  0*5 
  mm. 
  slits 
  at 
  P 
  and 
  Q, 
  and 
  in 
  order 
  to 
  reduce 
  the 
  

   general 
  reflexion 
  still 
  further 
  a 
  0*5 
  mm. 
  slit 
  was 
  placed 
  in 
  

   front 
  of 
  the 
  detector. 
  The 
  variation 
  of 
  the 
  intensity 
  of 
  

   reflexion 
  with 
  the 
  angle 
  at 
  which 
  the 
  radiation 
  struck 
  the 
  

   crystal 
  of 
  ferrocyanide 
  was 
  then 
  measured 
  in 
  the 
  neighbour- 
  

   hood 
  of 
  the 
  special 
  angles 
  ft 
  and 
  73. 
  Care 
  was 
  taken 
  that 
  

   the 
  reflected 
  beam 
  always 
  entered 
  the 
  detector. 
  The 
  curve 
  

   is 
  shown 
  in 
  tig. 
  4. 
  The 
  two 
  maxima 
  are 
  caused 
  by 
  the 
  

  

  Fiff.4. 
  

  

  ClHNCiNC 
  ANCLE. 
  

  

  selective 
  reflexions 
  at 
  ft 
  and 
  73, 
  while 
  the 
  flat 
  ends 
  of 
  

   the 
  curve 
  represent 
  the 
  general 
  reflexion, 
  which 
  under 
  these 
  

   conditions 
  was 
  small. 
  The 
  shape 
  of 
  this 
  curve 
  is 
  that 
  which 
  

   one 
  would 
  expect 
  with 
  a 
  beam 
  coming 
  from 
  a 
  focus 
  spot 
  on 
  

   the 
  target 
  not 
  more 
  than 
  0*5 
  mm. 
  wide 
  and 
  limited 
  by 
  the 
  

   second 
  slit, 
  if 
  only 
  those 
  rays 
  were 
  reflected 
  which 
  struck 
  

   the 
  crystal 
  at 
  precisely 
  the 
  special 
  angles 
  ft 
  and 
  y 
  :) 
  . 
  Now 
  

   the 
  characteristic 
  rays 
  are 
  known 
  to 
  form 
  only 
  a 
  fraction 
  of 
  

   the 
  primary 
  X-rays, 
  and 
  so 
  the 
  large 
  intensity 
  of 
  the 
  reflected 
  

   beam, 
  when 
  the 
  crystal 
  is 
  set 
  at 
  the 
  special 
  angle, 
  shows 
  thai 
  

   over 
  a 
  finite 
  range 
  of 
  angles 
  of 
  incidence 
  the 
  characteristic 
  

   rays 
  can 
  be 
  reflected. 
  This 
  range 
  cannot 
  be 
  estimated 
  from 
  

   the 
  curve, 
  as 
  tin' 
  exact 
  size 
  of 
  the 
  focus 
  spot 
  is 
  not 
  known, 
  

   but 
  the 
  shape 
  of 
  the 
  curve 
  and 
  also 
  other 
  experiments 
  show 
  

   that 
  it 
  is 
  extremely 
  narrow. 
  The 
  whole 
  range 
  over 
  which 
  

   reflexion 
  can 
  occur 
  i* 
  certainly 
  not 
  more 
  than 
  5', 
  and 
  from 
  

  

  