﻿Transformations 
  of 
  X-Rays. 
  109 
  

  

  there 
  remains 
  the 
  difficalty 
  of 
  ascerfcaining 
  which 
  particular 
  

   constituents 
  o£ 
  the 
  composite 
  beam 
  are 
  principally 
  concerned 
  

   in 
  producing 
  the 
  phenomena 
  under 
  investigation. 
  

  

  It 
  was 
  thought 
  that 
  useful 
  informatioa 
  concerning 
  the 
  

   nature 
  of 
  X-rays 
  might 
  be 
  obtained 
  if 
  the 
  homogeneous 
  rays 
  

   previously 
  mentioned 
  were 
  used 
  to 
  excite 
  tertiary 
  radiation 
  

   in 
  difEerent 
  substances. 
  

  

  Sagnac 
  has 
  shown 
  that 
  the 
  tertiary 
  X-rays 
  from 
  metals 
  

   exited 
  bv 
  secondary 
  X-rays 
  are 
  more 
  easily 
  absorbed 
  than 
  

   the 
  exciting 
  rays. 
  

  

  Previous 
  experiments'^ 
  had 
  shown 
  that 
  if 
  two 
  substances 
  

   A 
  and 
  B 
  be 
  taken, 
  each 
  of 
  which 
  is 
  found 
  to 
  emit 
  a 
  homo- 
  

   geneous 
  radiation 
  when 
  a 
  suitable 
  primary 
  beam 
  falls 
  upon 
  

   it, 
  the 
  homogeneous 
  radiation 
  from 
  A 
  being 
  more 
  pene- 
  

   trating 
  than 
  that 
  from 
  B, 
  then 
  if 
  a 
  homogeneous 
  beam 
  from 
  

   A 
  be 
  passed 
  through 
  a 
  thin 
  plate 
  of 
  B, 
  tertiary 
  radiation 
  is 
  

   excited 
  in 
  B 
  by 
  the 
  radiation 
  from 
  A, 
  while 
  if 
  the 
  process 
  is 
  

   reversed 
  it 
  is 
  found 
  that 
  the 
  radiation 
  from 
  B 
  excites 
  no 
  

   tertiary 
  radiation 
  in 
  A. 
  

  

  These 
  phenomena 
  were 
  examined 
  in 
  greater 
  detail 
  in 
  the 
  

   experiments 
  described 
  below. 
  

  

  It 
  was 
  found 
  that 
  no 
  trace 
  of 
  a 
  homogeneous 
  tertiary 
  

   radiation 
  could 
  be 
  detected 
  from 
  aluminium 
  when 
  subjected 
  

   to 
  any 
  of 
  the 
  homogeneous 
  radiations 
  from 
  the 
  group 
  of 
  

   metals 
  Cr-Ag, 
  and 
  the 
  amount 
  of 
  scattered 
  radiation 
  pro- 
  

   duced 
  was 
  extremely 
  small 
  when 
  compared 
  with 
  the 
  secondary 
  

   incident 
  beam. 
  

  

  Advantage 
  was 
  taken 
  of 
  these 
  facts, 
  and 
  the 
  primary 
  and 
  

   secondary 
  beams 
  were 
  passed 
  through 
  tubes 
  of 
  thick 
  

   aluminium 
  of 
  rectangular 
  cross-section. 
  This 
  enabled 
  the 
  

   apparatus 
  to 
  be 
  arranged 
  compactly 
  with 
  comparatively 
  short 
  

   distances 
  between 
  the 
  anticathode 
  of 
  the 
  X-ray 
  bulb 
  and 
  the 
  

   secondary 
  radiator, 
  and 
  between 
  the 
  secondary 
  and 
  tertiary 
  

   radiators 
  respectively, 
  a 
  condition 
  essential 
  to 
  secure 
  that 
  the 
  

   ionization 
  produced 
  by 
  the 
  tertiary 
  rays 
  in 
  a 
  suitable 
  ioni- 
  

   zation 
  chamber 
  should 
  be 
  sufficiently 
  intense 
  to 
  ensure 
  

   accurate 
  readings 
  in 
  a 
  reasonably 
  short 
  time, 
  and 
  that 
  the 
  

   direct 
  tertiary 
  radiation 
  should 
  produce 
  an 
  ionization 
  large 
  

   compared 
  with 
  that 
  produced 
  by 
  stray 
  secondary 
  and 
  tertiary 
  

   rays 
  from 
  the 
  surrounding 
  air 
  and 
  neighbouring 
  screens. 
  

  

  The 
  general 
  arrangement 
  of 
  the 
  apparatus 
  is 
  indicated 
  in 
  

   Plan 
  by 
  fig. 
  1. 
  

  

  A 
  rectangular 
  brass 
  tube 
  B 
  lined 
  with 
  aluminium 
  '2 
  cm. 
  

   thick 
  was 
  fitted 
  into 
  an 
  aperture 
  in 
  the 
  lead 
  screen 
  8S 
  sur- 
  

   rounding 
  the 
  X-ray 
  bulb 
  emitting 
  the 
  primary 
  rays, 
  and 
  the 
  

   * 
  Barkia 
  & 
  Sadler, 
  ]*hil. 
  Majr. 
  Oct. 
  1908, 
  pp. 
  5o0-o84. 
  

  

  