﻿580 
  Dr. 
  C. 
  G. 
  Barkla 
  and 
  Mr. 
  C. 
  A. 
  Sadler 
  

  

  on 
  

  

  radiating 
  substance. 
  Indeed, 
  this 
  appears 
  highly 
  improbable, 
  

   for 
  the 
  homogeneous 
  radiation 
  disappears 
  when 
  the 
  primary 
  

   radiation 
  is 
  made 
  " 
  soft 
  " 
  and 
  appears 
  in 
  great 
  intensity 
  when 
  

   the 
  primary 
  is 
  "hard." 
  

  

  If, 
  then, 
  the 
  radiation 
  were 
  emitted 
  simply 
  during 
  the 
  

   process 
  of 
  ionization 
  and 
  were 
  proportional 
  to 
  it, 
  a 
  soft 
  

   primary 
  radiation 
  would 
  produce 
  little 
  or 
  no 
  ionization 
  and 
  

   a 
  more 
  penetrating 
  radiation 
  — 
  (that 
  is 
  one 
  more 
  penetrating 
  

   to 
  most 
  substances) 
  — 
  would 
  produce 
  an 
  ionization 
  at 
  least 
  

   hundreds 
  of 
  times 
  as 
  great. 
  Though 
  experiments 
  have 
  not 
  

   been 
  made 
  on 
  the 
  ionizations 
  produced 
  in 
  these 
  substances 
  

   investigated, 
  such 
  variations 
  in 
  ionization 
  are 
  of 
  a 
  higher 
  

   order 
  of 
  magnitude 
  than 
  any 
  observed. 
  Again, 
  ioni- 
  

   zation 
  is 
  undoubtedly 
  produced 
  in 
  substances 
  of 
  the 
  H-S 
  

   group 
  of 
  elements 
  when 
  homogeneous 
  rays 
  are 
  not 
  emitted 
  

   in 
  appreciable 
  intensity. 
  We, 
  however, 
  do 
  not 
  know 
  anything 
  

   of 
  the 
  homogeneous 
  rays 
  from 
  these 
  substances 
  except 
  that 
  

   they 
  are 
  probably 
  of 
  penetrating 
  type. 
  

  

  The 
  relation 
  between 
  the 
  absorption 
  of 
  a 
  primary 
  radiation 
  

   and 
  the 
  intensity 
  of 
  secondary 
  radiation 
  emitted 
  by 
  the 
  

   absorbing 
  substance, 
  also 
  shows 
  that 
  the 
  emission 
  of 
  homo- 
  

   geneous 
  radiation 
  necessitates 
  a 
  special 
  absorption 
  of 
  the 
  

   primary 
  beam. 
  Also, 
  as 
  far 
  as 
  we 
  can 
  estimate 
  from 
  experi- 
  

   ments 
  made, 
  the 
  energy 
  of 
  the 
  homogeneous 
  radiation 
  is 
  more 
  

   than 
  accounted 
  for 
  by 
  the 
  special 
  absorption 
  necessary 
  to 
  the 
  

   production 
  of 
  that 
  radiation. 
  

  

  Thus 
  in 
  fig. 
  4 
  we 
  have 
  plotted 
  the 
  coefficients 
  of 
  absorption 
  

   of 
  rays 
  from 
  Fe, 
  Co, 
  Ni, 
  Cu, 
  and 
  Zn 
  by 
  Al, 
  Zn, 
  Ag, 
  Sn, 
  Pt 
  

   In 
  each 
  case 
  the 
  radiations 
  absorbed 
  are 
  not 
  — 
  if 
  we 
  generalize 
  

   from 
  results 
  given 
  — 
  capable 
  of 
  stimulating 
  a 
  homogeneous 
  

   radiation 
  characteristic 
  of 
  the 
  absorbing 
  substance, 
  because 
  

   these 
  are 
  of 
  more 
  penetrating 
  type. 
  The 
  curves 
  are 
  similar. 
  But 
  

   when 
  iron 
  is 
  used 
  as 
  the 
  absorbing 
  substance, 
  cobalt 
  radiation, 
  

   which 
  is 
  just 
  more 
  penetrating, 
  is 
  unable 
  to 
  produce 
  more 
  than 
  

   a 
  feeble 
  secondary 
  in 
  the 
  iron, 
  so 
  the 
  decline 
  of 
  the 
  line 
  for 
  Fe 
  

   is 
  not 
  quite 
  so 
  great 
  as 
  would 
  have 
  been 
  expected, 
  because 
  of 
  

   the 
  little 
  extra 
  absorption 
  necessary 
  to 
  set 
  up 
  this 
  slight 
  

   radiation 
  from 
  iron. 
  The 
  copper 
  radiation, 
  which 
  is 
  much 
  

   more 
  penetrating, 
  is 
  able 
  to 
  stimulate 
  an 
  intense 
  radiation 
  in 
  

   iron 
  and 
  at 
  the 
  same 
  time 
  is 
  enormously 
  absorbed. 
  This 
  is 
  

   exhibited 
  by 
  the 
  sudden 
  rise 
  in 
  the 
  Fe 
  curve. 
  Beyond 
  copper, 
  

   the 
  absorption 
  appears 
  to 
  fall 
  again 
  according 
  to 
  the 
  usual 
  

   law, 
  the 
  absorption 
  of 
  the 
  zinc 
  radiation 
  being 
  a 
  little 
  less 
  

   than 
  that 
  of 
  the 
  copper 
  radiation. 
  The 
  stage 
  is 
  thus 
  reached 
  

   when 
  the 
  change 
  in 
  the 
  penetrating 
  power 
  of 
  the 
  primary 
  

   radiation 
  produces 
  no 
  difference 
  in 
  the 
  relative 
  amounts 
  of 
  

  

  