﻿Homogeneous 
  Secondary 
  Rontgen 
  Radiations. 
  569 
  

  

  Whatever 
  may 
  be 
  the 
  true 
  explanation, 
  these 
  results 
  show 
  

   that 
  the 
  proportionality 
  exhibited 
  after 
  absorption 
  by 
  alumi- 
  

   nium 
  is 
  not 
  general 
  even 
  when 
  copper 
  is 
  the 
  radiating 
  

   substance. 
  This 
  result 
  may 
  be 
  contrasted 
  with 
  the 
  corre- 
  

   sponding 
  phenomena 
  exhibited 
  by 
  the 
  homogeneous 
  radiation 
  

   from 
  silver. 
  In 
  these 
  experiments 
  the 
  homogeneous 
  rays 
  

   disappeared 
  when 
  the 
  primary 
  beam 
  was 
  made 
  more 
  absorbable 
  

   and 
  more 
  efficient 
  as 
  an 
  ionizer 
  of 
  air. 
  The 
  difference 
  is 
  

   almost 
  certainly 
  due 
  to 
  the 
  fact 
  that 
  in 
  the 
  latter 
  case 
  the 
  

   primary 
  radiation 
  passes 
  from 
  one 
  more 
  penetrating 
  to 
  one 
  

   more 
  easily 
  absorbed 
  than 
  the 
  secondary 
  radiation 
  charac- 
  

   teristic 
  of 
  the 
  element 
  exposed 
  to 
  the 
  primary 
  rays. 
  It 
  seems 
  

   highly 
  probable 
  therefore, 
  that 
  with 
  sufficiently 
  absorbable 
  

   primary 
  rays 
  no 
  such 
  relation 
  as 
  that 
  shown 
  by 
  fig. 
  2 
  w 
  r 
  ould 
  

   be 
  obtained, 
  but 
  that 
  the 
  secondary 
  would 
  disappear 
  while 
  

   the 
  primary 
  still 
  produced 
  considerable 
  ionization 
  in 
  air. 
  

   It 
  will 
  be 
  interesting 
  to 
  learn 
  if 
  a 
  primary 
  which 
  ceases 
  to 
  

   stimulate 
  the 
  homogeneous 
  radiation 
  ceases 
  also 
  to 
  produce 
  

   ionization 
  in 
  the 
  radiating 
  substance. 
  We, 
  of 
  course, 
  know 
  

   that 
  elements 
  of 
  the 
  H-S 
  group 
  are 
  ionized, 
  but 
  do 
  not 
  

   emit 
  a 
  homogeneous 
  radiation 
  which 
  can 
  be 
  detected. 
  This 
  

   appears 
  to 
  indicate 
  no 
  necessary 
  connexion 
  between 
  ionization 
  

   and 
  radiation, 
  but 
  is 
  not 
  conclusive 
  for 
  various 
  reasons. 
  

  

  Special 
  Penetrating 
  Power. 
  — 
  In 
  studying 
  the 
  absorption 
  of 
  

   these 
  homogeneous 
  radiations 
  by 
  a 
  number 
  of 
  elements, 
  it 
  

   was 
  found 
  that 
  the 
  relation 
  between 
  the 
  absorption 
  by 
  a 
  

   given 
  substance 
  of 
  the 
  various 
  homogeneous 
  radiations 
  from 
  

   elementary 
  substances 
  and 
  the 
  atomic 
  weight 
  of 
  those 
  

   radiating 
  substances 
  was 
  similar 
  for 
  all 
  absorbing 
  substances, 
  

   except 
  in 
  the 
  case 
  of 
  the 
  radiating 
  and 
  absorbing 
  elements 
  

   being 
  identical 
  or 
  possessing 
  neighbouring 
  atomic 
  weights. 
  

   Each 
  substance 
  appeared 
  to 
  be 
  especially 
  transparent 
  to 
  its 
  

   own 
  radiation, 
  and 
  to 
  a 
  less 
  extent 
  to 
  that 
  from 
  elements 
  of 
  

   neighbouring 
  atomic 
  weight. 
  

  

  The 
  transparency 
  of 
  various 
  elements 
  to 
  an 
  ordinary 
  

   heterogeneous 
  beam 
  of 
  X-rays 
  has 
  been 
  investigated 
  by 
  

   Benoist, 
  who 
  studied 
  the 
  phosphorescence 
  produced 
  by 
  the 
  

   beam 
  after 
  passing 
  through 
  absorbing 
  substances. 
  He 
  com- 
  

   pared 
  the 
  transparencies 
  by 
  finding 
  the 
  mass 
  of 
  a 
  prism 
  o£ 
  

   absorbing 
  substance 
  of 
  definite 
  cross-section, 
  which 
  when 
  

   placed 
  in 
  the 
  path 
  of 
  the 
  beam 
  absorbed 
  it 
  by 
  a 
  definite 
  

   amount. 
  The 
  relation 
  between 
  the 
  transparency 
  so 
  defined 
  

   and 
  measured, 
  and 
  the 
  atomic 
  weight 
  of 
  the 
  absorbing 
  sub- 
  

   stance 
  was 
  shown 
  by 
  a 
  curve 
  similar 
  to 
  that 
  for 
  paper 
  given 
  

   in 
  fig. 
  3. 
  It 
  shows 
  a 
  rapid 
  decline 
  of 
  transparency, 
  with 
  

   increase 
  in 
  atomic 
  weight 
  for 
  low 
  atomic 
  weights, 
  the 
  

  

  