﻿Secondary 
  7 
  Rays 
  due 
  to 
  7 
  Rays 
  of 
  Radium 
  C. 
  225 
  

  

  In 
  this 
  case 
  the 
  order 
  of 
  secondary 
  radiation 
  is 
  that 
  of 
  

   density. 
  

  

  The 
  remarkable 
  dissimilarity 
  in 
  the 
  two 
  cases 
  is 
  at 
  first 
  

   sight 
  perplexing, 
  and 
  the 
  object 
  of 
  the 
  present 
  paper 
  is 
  to 
  

   explain 
  to 
  some 
  extent 
  the 
  cause 
  of 
  the 
  apparent 
  differences. 
  

  

  In 
  the 
  first 
  place 
  it 
  must 
  be 
  pointed 
  out 
  that 
  a 
  comparison 
  

   of 
  the 
  two 
  tables 
  above 
  given 
  is 
  an 
  unfair 
  one, 
  because 
  the 
  

   first 
  table 
  really 
  shows 
  secondary 
  radiation 
  of 
  the 
  X-ray 
  

   type, 
  for 
  the 
  cathode 
  rays 
  were 
  absorbed 
  by 
  air 
  before 
  they 
  

   reached 
  the 
  testing 
  apparatus. 
  But 
  the 
  second 
  table 
  gives 
  

   mainly 
  the 
  cathode 
  secondary 
  radiation 
  due 
  to 
  7 
  rays, 
  for 
  in 
  

   this 
  case 
  the 
  cathode 
  rays 
  produce 
  a 
  much 
  greater 
  effect 
  in 
  

   the 
  electroscope 
  than 
  the 
  secondary 
  rays 
  of 
  the 
  7 
  type. 
  

  

  A 
  few 
  experiments 
  recently 
  made 
  may 
  be 
  worth 
  recording. 
  

   The 
  X 
  rays 
  from 
  a 
  very 
  hard 
  tube 
  were 
  employed, 
  such 
  as 
  

   were 
  used 
  in 
  some 
  previous 
  experiments 
  to 
  compare 
  the 
  

   ionizations 
  of 
  various 
  gases 
  by 
  7 
  and 
  X 
  rays. 
  These 
  hard 
  

   penetrating 
  % 
  rays 
  were 
  found 
  fo 
  ionize 
  gases 
  almost 
  in 
  the 
  

   same 
  manner 
  as 
  7 
  rays. 
  In 
  the 
  present 
  case 
  the 
  X 
  rays 
  

   struck 
  plates 
  of 
  the 
  substances 
  named 
  in 
  Table 
  III., 
  and 
  the 
  

   incident 
  secondary 
  rays 
  were 
  measured 
  by 
  the 
  electroscope, 
  

  

  Table 
  III. 
  

  

  Secondary 
  Rays 
  from 
  X 
  and 
  7 
  Rays. 
  

   Cathode 
  rays 
  removed 
  by 
  absorption. 
  

  

  Q 
  t 
  -r> 
  v 
  a. 
  Thickness 
  

   Secondary 
  Radiator. 
  

  

  111 
  cms. 
  

  

  X. 
  

  

  7- 
  

  

  Books 
  (edges) 
  11 
  

  

  Paraffin 
  4 
  

  

  280 
  

   230 
  

  

  170 
  

  

  160 
  

  

  125 
  

  

  103 
  

  

  61 
  

  

  58 
  

  

  2-5 
  

   20 
  

   27 
  

   3-0 
  

   36 
  

   3-0 
  

   1-7 
  

   3 
  8 
  

   10 
  

   3-3 
  

  

  65 
  

  

  Brick 
  6 
  

  

  „ 
  14 
  

  

  Slate 
  6 
  

  

  Wood 
  11 
  

  

  Cement 
  '.. 
  21 
  

  

  Lead 
  5 
  

  

  Iron 
  5 
  

  

  

  described 
  later, 
  used 
  throughout 
  these 
  experiments. 
  The 
  

   cathode 
  secondary 
  rays 
  w^ere 
  absorbed 
  by 
  the 
  air 
  between 
  

   the 
  secondary 
  radiator 
  and 
  the 
  electroscope. 
  The 
  incident 
  

  

  * 
  Phil. 
  A[ao-. 
  Xov. 
  1904. 
  

  

  