﻿^Transmission 
  of 
  X 
  Rays 
  through 
  Metals. 
  7 
  1 
  5 
  

  

  Fig. 
  5 
  was 
  obtained 
  with 
  platinum 
  (0*1 
  mm. 
  thick). 
  A 
  

   specimen 
  of: 
  hard 
  wood 
  (liyniim 
  vitce) 
  of 
  thickness 
  such 
  

   -p. 
  5 
  as 
  to 
  have 
  stopping 
  power 
  approximately 
  

  

  equal 
  to 
  that 
  of 
  one 
  millimetre 
  of 
  aluminium 
  

   4 
  if 
  f 
  gave 
  rise 
  to 
  no 
  such 
  markings. 
  

  

  \ 
  fa' 
  The 
  metal 
  specimens 
  mentioned 
  above 
  

  

  -*=. 
  A&fa 
  ^ 
  were 
  taken 
  from 
  the 
  laboratory 
  stores, 
  where 
  

   _ 
  ^^ 
  "^ 
  they 
  had 
  remained 
  unused 
  for 
  several 
  years. 
  

   *f. 
  . 
  V 
  Wishing 
  to 
  make 
  experiments 
  with 
  nickel 
  

   / 
  /* 
  J 
  \, 
  and 
  aluminium, 
  I 
  found 
  it 
  necessary 
  to 
  roll 
  

   out 
  new 
  specimens, 
  as 
  none 
  of 
  suitable 
  thick- 
  

   ness 
  were 
  available. 
  These 
  two 
  samples 
  yielded 
  entirely 
  

   different 
  results. 
  

  

  Fig. 
  6 
  shows 
  a 
  perfectly 
  symmetrical 
  pattern 
  obtained 
  

   with 
  the 
  nickel 
  (0*28 
  mm. 
  thick) 
  con- 
  

   sisting 
  of 
  four 
  diffuse 
  patches 
  which 
  

   fade 
  away 
  towards 
  their 
  edges, 
  gradu- 
  

   ally 
  merging 
  into 
  the 
  general 
  fogging 
  

   of 
  the 
  plate. 
  No 
  other 
  streaks 
  or 
  

   patches 
  were 
  visible 
  on 
  the 
  negative, 
  

   and 
  the 
  patches 
  forming 
  the 
  pattern 
  

   showed 
  no 
  evidence 
  of 
  structure. 
  The 
  

   same 
  description 
  applies 
  to 
  the 
  nature 
  

   of 
  the 
  pattern 
  obtained 
  with 
  the 
  

   aluminium 
  (1/0 
  mm. 
  thick). 
  The 
  

   emergent 
  radiation 
  in 
  this 
  case 
  gave 
  

   rise 
  to 
  a 
  symmetrical 
  ten-pointed 
  star 
  

   (see 
  fig. 
  7). 
  It 
  was 
  found 
  that 
  the 
  orientation 
  of 
  the 
  

   pattern 
  was 
  independent 
  of 
  that 
  of 
  the 
  X-ray 
  tube, 
  while, 
  on 
  

   the 
  other 
  hand, 
  a 
  rotation 
  of 
  the 
  

   metal 
  sheet 
  produced 
  a 
  corresponding- 
  

   rotation 
  of 
  the 
  pattern 
  on 
  the 
  plate. 
  

   Precisely 
  the 
  same 
  pattern 
  was 
  

   reproduced 
  by 
  using 
  an 
  entirely 
  dif- 
  

   ferent 
  part 
  of 
  the 
  same 
  metal 
  sheet. 
  

   This 
  seemed 
  remarkable 
  at 
  first 
  sight, 
  

   but 
  further 
  investigation 
  showed 
  that 
  

   the 
  axis 
  of 
  symmetry 
  AB 
  in 
  both 
  cases 
  

   «p 
  sg 
  \ 
  i 
  life 
  (fig 
  s 
  - 
  6 
  & 
  7) 
  was 
  parallel 
  to 
  the 
  di- 
  

  

  ; 
  j 
  rection 
  in 
  which 
  the 
  material 
  had 
  been 
  

  

  Hi^' 
  W? 
  \W 
  ^ 
  rolled. 
  This 
  fact 
  supplies 
  a 
  key 
  to 
  

   the 
  explanation. 
  

   • 
  g 
  It 
  must 
  be 
  borne 
  in 
  mind 
  that 
  the 
  

  

  specimens 
  yielding 
  spots 
  were 
  all 
  well 
  

   aged, 
  while 
  those 
  yielding 
  symmetrical 
  patterns 
  were 
  freshly 
  

   rolled 
  for 
  the 
  purpose. 
  The 
  former, 
  through 
  age 
  or 
  annealing, 
  

  

  