﻿z82 
  Dr. 
  C. 
  G. 
  Barkla 
  and 
  Mr. 
  C. 
  A. 
  Sadler 
  

  

  on 
  

  

  The 
  zinc 
  radiation 
  is 
  unable 
  to 
  set 
  up 
  radiations 
  in 
  these 
  

   elements, 
  as 
  they 
  are 
  of 
  more 
  penetrating 
  type. 
  The 
  absorp- 
  

   tions 
  are, 
  however, 
  not 
  sufficiently 
  abnormal 
  to 
  speak 
  of 
  with 
  

   certainty. 
  The 
  effect 
  is 
  more 
  clearly 
  shown 
  by 
  the 
  curve 
  

   obtained 
  from 
  the 
  homogeneous 
  radiation 
  from 
  silver 
  (fig. 
  3). 
  

  

  These 
  results 
  show 
  that 
  a 
  substance 
  whose 
  characteristic 
  

   radiation 
  is 
  equally 
  or 
  more 
  penetrating 
  than 
  the 
  radiation 
  

   incident 
  upon 
  it, 
  does 
  not 
  absorb 
  that 
  radiation 
  so 
  much 
  as 
  

   when 
  the 
  incident 
  is 
  of 
  more 
  penetrating 
  type 
  and 
  able 
  to 
  

   stimulate 
  a 
  secondary 
  radiation 
  in 
  that 
  substance. 
  As 
  the 
  

   penetrating 
  power 
  of 
  the 
  incident 
  radiation 
  (as 
  measured 
  by 
  

   most 
  substances) 
  increases, 
  the 
  absorption 
  increases 
  up 
  to 
  a 
  

   certain 
  point. 
  A 
  definite 
  portion 
  of 
  the 
  absorption 
  thus 
  

   appears 
  to 
  be 
  connected 
  with 
  the 
  secondary 
  radiation, 
  and 
  

   may 
  be 
  proportional 
  to 
  it. 
  But 
  this 
  does 
  not 
  conclusively 
  

   show 
  that 
  ionization, 
  or 
  some 
  kind 
  of 
  disruption 
  in 
  the 
  atom 
  

   is 
  not 
  the 
  cause 
  of 
  the 
  radiation, 
  for 
  the 
  absorption 
  of 
  a 
  

   certain 
  amount 
  of 
  energy 
  of 
  the 
  primary 
  beam 
  might 
  be 
  

   required 
  to 
  produce 
  the 
  instability 
  which 
  liberates 
  more 
  

   energy. 
  

  

  The 
  facts 
  that 
  the 
  homogeneous 
  rays 
  have 
  invariably 
  been 
  

   found 
  more 
  easily 
  absorbed 
  than 
  the 
  primary 
  rays 
  producing 
  

   them, 
  and, 
  in 
  the 
  cases 
  investigated, 
  that 
  the 
  homogeneous 
  

   rays 
  disappear 
  when 
  the 
  primary 
  becomes 
  more 
  easily 
  

   absorbed, 
  indicate 
  a 
  relation 
  between 
  primary 
  and 
  secondary 
  

   which 
  would 
  be 
  difficult 
  to 
  explain 
  if 
  this 
  radiation 
  were 
  

   directly 
  due 
  to 
  a 
  disruption 
  of 
  any 
  kind 
  taking 
  place 
  in 
  the 
  

   atom. 
  It 
  appears 
  rather 
  that 
  the 
  radiation 
  is 
  due 
  to 
  what 
  

   may 
  be 
  regarded 
  as 
  quite 
  a 
  normal 
  behaviour 
  of 
  an 
  atom 
  

   after 
  it 
  has 
  been 
  passed 
  over 
  by 
  Rontgen 
  pulses, 
  such 
  as 
  a 
  

   free 
  vibration 
  of 
  electrons. 
  

  

  Let 
  us 
  consider 
  the 
  passage 
  of 
  an 
  electromagnetic 
  pulse, 
  in 
  

   which 
  the 
  electric 
  field 
  is 
  un 
  directional, 
  over 
  an 
  electron 
  

   with 
  a 
  free 
  period 
  of 
  vibration 
  much 
  longer 
  than 
  double 
  the 
  

   time 
  taken 
  for 
  the 
  pulse 
  to 
  pass 
  over 
  it. 
  (In 
  this 
  case 
  the 
  

   Rontgen 
  pulse 
  is 
  thinner 
  and 
  more 
  penetrating 
  than 
  the 
  half- 
  

   wave 
  produced 
  by 
  the 
  free 
  vibration 
  of 
  the 
  electron.) 
  The 
  

   electron 
  receives 
  an 
  impulse 
  and 
  is 
  left 
  with 
  kinetic 
  energy 
  

   after 
  the 
  pulse 
  has 
  passed. 
  Consequently 
  it 
  is 
  then 
  acted 
  upon 
  

   by 
  forces 
  called 
  into 
  play 
  in 
  the 
  atom 
  itself. 
  These 
  produce 
  

   a 
  motion 
  which 
  is 
  characteristic 
  of 
  the 
  atom 
  of 
  which 
  the 
  

   electron 
  forms 
  a 
  part, 
  and 
  this 
  results 
  in 
  radiation 
  — 
  probably 
  

   the 
  homogeneous 
  radiation 
  discussed 
  in 
  this 
  paper. 
  

  

  When 
  the 
  thickness 
  of 
  the 
  primary 
  pulse 
  approaches 
  the 
  

   half-wave 
  length 
  characteristic 
  of 
  the 
  vibratory 
  motion 
  of 
  the 
  

   electron 
  in 
  the 
  atom, 
  the 
  restoring 
  force 
  in 
  the 
  atom 
  is 
  brought 
  

  

  