﻿716 
  Transmission 
  of 
  X 
  Rays 
  through 
  Metals. 
  

  

  were 
  probably 
  crystalline 
  in 
  structure, 
  tbe 
  microcrystals 
  

   giving 
  rise 
  to 
  small 
  pencils 
  o£ 
  radiation 
  from 
  the 
  planes 
  of 
  

   their 
  space-lattices. 
  That 
  such 
  an 
  aggregate 
  of 
  small 
  crystals 
  

   should 
  give 
  rise 
  to 
  a 
  group 
  of 
  streaks 
  of 
  this 
  kind 
  can 
  be 
  

   demonstrated 
  by 
  passing 
  the 
  beam 
  through 
  a 
  collection 
  of 
  

   small 
  crystals 
  specially 
  arranged 
  for 
  the 
  purpose. 
  This 
  was 
  

   done 
  by 
  sprinkling 
  crystalline 
  mercuric 
  oxide 
  on 
  one 
  side 
  of 
  a 
  

   piece 
  of 
  cardboard 
  which 
  was 
  covered 
  with 
  wet 
  gum. 
  The 
  

   specimen 
  was 
  now 
  placed 
  normally 
  in 
  the 
  path 
  of 
  the 
  beam 
  

   with 
  the 
  crystals 
  towards 
  the 
  photographic 
  plate. 
  The 
  re- 
  

   sulting 
  negative 
  was 
  of 
  precisely 
  the 
  nature 
  as 
  shown 
  in 
  

   figs. 
  3, 
  4, 
  & 
  5. 
  This 
  experiment 
  indicates 
  that 
  the 
  matrix 
  in 
  

   which 
  the 
  crystals 
  of 
  the 
  metal 
  sheets 
  are 
  embedded 
  is 
  of 
  

   no 
  account. 
  

  

  When 
  a 
  narrow 
  pencil 
  of 
  light 
  is 
  allowed 
  to 
  pass 
  through 
  

   certain 
  crystals 
  and 
  to 
  fall 
  upon 
  a 
  photographic 
  plate, 
  as 
  in 
  the 
  

   above 
  experiments, 
  similar 
  symmetrical 
  patterns 
  are 
  obtained. 
  

   Experiments 
  carried 
  out 
  by 
  H. 
  S. 
  Allen 
  (' 
  Nature,' 
  xci. 
  

   p. 
  268) 
  have 
  drawn 
  attention 
  to 
  this 
  phenomenon, 
  and 
  show 
  

   that 
  such 
  patterns 
  are 
  only 
  obtained 
  with 
  crystals 
  which 
  

   show 
  a 
  streaky 
  appearance 
  when 
  examined 
  by 
  the 
  naked 
  

   eye. 
  Dr. 
  Tutton 
  ('Nature/ 
  xci. 
  p. 
  268) 
  attributes 
  the 
  

   patterns 
  to 
  " 
  asterism," 
  which, 
  in 
  the 
  case 
  of 
  mica, 
  " 
  is 
  due 
  

   to 
  fine 
  enclosures 
  arranged 
  along 
  the 
  glide 
  planes, 
  and 
  

   parallel 
  to 
  the 
  cleavage 
  plane. 
  Calcite 
  also 
  shows 
  asterism, 
  

   certain 
  crystals 
  held 
  in 
  front 
  of 
  a 
  candle-flame 
  showing 
  a 
  

   radiating 
  star 
  of 
  light. 
  In 
  this 
  case, 
  however, 
  it 
  is 
  due 
  to 
  

   tubular 
  cavities 
  parallel 
  to 
  the 
  glide 
  planes 
  (the 
  rhombohe- 
  

   dron 
  known 
  as 
  e{110}).^ 
  According 
  to 
  H. 
  S. 
  Allen 
  the 
  

   striations 
  in 
  the 
  crystal 
  act 
  just 
  like 
  a 
  diffraction 
  grating. 
  

   It 
  seems 
  that 
  the 
  patterns 
  shown 
  in 
  figs. 
  6 
  & 
  7 
  are 
  to 
  be 
  

   explained 
  in 
  a 
  similar 
  way, 
  being 
  a 
  case 
  of 
  asterism 
  with 
  

   X 
  rays; 
  the 
  striations 
  being 
  produced 
  in 
  the 
  material 
  by 
  the 
  

   process 
  of 
  rolling. 
  

  

  If 
  there 
  is 
  an 
  alignment 
  of 
  the 
  particles 
  within 
  a 
  sheet 
  

   of 
  rolled 
  metal, 
  it 
  should 
  be 
  possible 
  to 
  destroy 
  the 
  arrange- 
  

   ment 
  by 
  heating 
  the 
  specimen, 
  and 
  so 
  bringing 
  it 
  back 
  to 
  its 
  

   original 
  crystalline 
  condition 
  on 
  cooling. 
  In 
  such 
  a 
  case 
  

   one 
  would 
  expect 
  a 
  corresponding 
  change 
  in 
  the 
  pattern. 
  

   This 
  was 
  tried 
  with 
  the 
  aluminium 
  specimen 
  which 
  gave 
  

   the 
  ten-pointed 
  star. 
  The 
  metal 
  was 
  placed 
  upon 
  a 
  flat 
  slab 
  

   and 
  raised 
  to 
  its 
  melting-point 
  and 
  then 
  allowed 
  to 
  cool 
  

   slowly. 
  The 
  resulting 
  photograph 
  with 
  this 
  annealed 
  specimen 
  

   was 
  of 
  the 
  type 
  shown 
  in 
  figs. 
  3, 
  4, 
  and 
  5, 
  all 
  trace 
  of 
  the 
  

   star 
  having 
  disappeared. 
  A 
  portion 
  of 
  the 
  nickel 
  sheet 
  giving 
  

   fig. 
  6 
  was 
  treated 
  in 
  the 
  same 
  way 
  with 
  exactly 
  the 
  same 
  result. 
  

  

  