﻿Homogeneous 
  Secondary 
  Rontgen 
  Radiations. 
  583 
  

  

  into 
  play 
  before 
  the 
  primary 
  pulse 
  has 
  passed 
  and 
  the 
  absorption 
  

   of 
  energy 
  and 
  energy 
  of 
  subsequent 
  radiation 
  are 
  diminished. 
  

   This 
  explains 
  the 
  diminished 
  radiation 
  when 
  the 
  penetrating- 
  

   power 
  of 
  the 
  primary 
  decreases 
  and 
  approximates 
  to 
  that 
  of 
  the 
  

   radiation 
  characteristic 
  of 
  the 
  radiating 
  substance. 
  When 
  the 
  

   primary 
  pulse 
  is 
  thicker 
  than 
  the 
  half- 
  wave 
  characteristic 
  of 
  

   the 
  motion 
  of 
  the 
  electron, 
  the 
  electron 
  is 
  displaced 
  a 
  short 
  

   distance 
  and 
  is 
  gradually 
  brought 
  back 
  by 
  the 
  restoring 
  force 
  

   against 
  a 
  gradually 
  weakening 
  electric 
  force 
  in 
  the 
  primary 
  

   pulse, 
  so 
  that 
  when 
  this 
  has 
  passed, 
  the 
  electron 
  is 
  near 
  its 
  

   position 
  of 
  equilibrium 
  again 
  and 
  the 
  motion 
  and 
  radiation 
  

   produced 
  in 
  the 
  other 
  cases 
  are 
  now 
  absent. 
  It 
  is 
  impossible 
  

   to 
  give 
  an 
  exact 
  solution 
  without 
  some 
  knowledge 
  of 
  the 
  

   distribution 
  of 
  electric 
  force 
  in 
  the 
  primary 
  pulses, 
  of 
  the 
  

   forces 
  binding 
  the 
  disturbed 
  electron 
  to 
  the 
  rest 
  of 
  the 
  atomic 
  

   system, 
  and 
  of 
  the 
  structure 
  of 
  that 
  system; 
  but 
  we 
  may 
  

   consider 
  this 
  to 
  be 
  an 
  approximation 
  to 
  the 
  behaviour 
  of 
  each 
  

   electron 
  directly 
  concerned 
  with 
  the 
  phenomena 
  discussed. 
  

   The 
  number 
  of 
  such 
  electrons 
  may 
  not 
  exceed 
  one 
  in 
  each 
  

   atom 
  of 
  radiating 
  substance. 
  

  

  According 
  to 
  this 
  theory, 
  energy 
  is 
  taken 
  from 
  the 
  primary 
  

   beam 
  and 
  part, 
  at 
  least, 
  appears 
  as 
  secondary 
  homogeneous 
  

   radiation, 
  the 
  rest 
  being 
  transformed 
  into 
  heat. 
  

  

  As 
  the 
  energy 
  of 
  this 
  radiation 
  is 
  quite 
  a 
  considerable 
  

   fraction 
  of 
  the 
  total 
  energy 
  absorbed, 
  we 
  should 
  expect 
  that 
  

   the 
  difference 
  between 
  absorptions 
  of 
  primary 
  rays 
  more 
  or 
  

   less 
  penetrating 
  than 
  the 
  radiation 
  characteristic 
  of 
  the 
  

   absorbing 
  element 
  would 
  be 
  evident 
  from 
  a 
  study 
  of 
  the 
  

   absorption 
  of 
  the 
  various 
  homogeneous 
  beams. 
  But 
  we 
  have 
  

   seen 
  that 
  there 
  is 
  a 
  large 
  absorption 
  of 
  a 
  homogeneous 
  

   radiation 
  by 
  an 
  element 
  which 
  emits 
  a 
  much 
  more 
  easily 
  

   absorbed 
  radiation, 
  because 
  much 
  of 
  the 
  energy 
  is 
  given 
  to 
  

   the 
  electrons 
  ; 
  that 
  for 
  other 
  elements 
  which 
  emit 
  a 
  radiation 
  

   only 
  slightly 
  softer, 
  the 
  absorption 
  is 
  much 
  diminished 
  because 
  

   only 
  a 
  feeble 
  disturbance 
  and 
  consequent 
  secondary 
  radiation 
  

   is 
  set 
  up 
  in 
  the 
  absorber 
  ; 
  and 
  when 
  the 
  radiation 
  charac- 
  

   teristic 
  of 
  the 
  absorbing 
  substance 
  is 
  more 
  penetrating 
  than 
  

   the 
  absorbed 
  radiation, 
  the 
  absorption 
  is 
  small 
  and 
  ho 
  homo- 
  

   geneous 
  secondary 
  radiation 
  is 
  produced. 
  Thus 
  what 
  we 
  have 
  

   previously 
  referred 
  to 
  as 
  the 
  special 
  penetrating 
  power 
  of 
  the 
  

   homogeneous 
  radiations 
  may 
  be 
  explained 
  by 
  the 
  small 
  

   displacement 
  produced 
  in 
  an 
  atom 
  by 
  a 
  radiation 
  more 
  easily 
  

   absorbed, 
  equally 
  absorbed, 
  or 
  slightly 
  more 
  penetrating 
  than 
  

   the 
  radiation 
  characteristic 
  of 
  that 
  atom, 
  for 
  reasons 
  

   indicated. 
  

  

  Though 
  according 
  to 
  such 
  a 
  theory, 
  if 
  the 
  displaced 
  electrons 
  

  

  