﻿23 
  J- 
  Secondary 
  y 
  Rays 
  due 
  to 
  y 
  Rays 
  of 
  Radium 
  C. 
  

  

  These 
  may 
  be 
  compared 
  with 
  the 
  coefficients 
  of 
  absorption 
  

   of 
  the 
  primary 
  y 
  rays 
  passing 
  through 
  lead 
  *: 
  — 
  

  

  A. 
  

  

  Radium 
  *57-'45 
  

  

  Uranium 
  1*4 
  

  

  Actinium 
  4*7- 
  

  

  •;. 
  

  

  Hence 
  the 
  secondary 
  y 
  rays, 
  due 
  to 
  the 
  primary 
  y 
  rays, 
  

   Using 
  lead, 
  iron, 
  or 
  brick 
  as 
  secondary 
  radiators, 
  are 
  absorbed 
  

   to 
  a 
  degree 
  approximating 
  to 
  that 
  of 
  the 
  primary 
  y 
  rays 
  of 
  

   actinium. 
  It 
  would 
  be 
  interesting 
  to 
  examine 
  the 
  secondary 
  

   y 
  rays 
  due 
  to 
  the 
  primary 
  y 
  rays 
  of 
  actinium. 
  These 
  would 
  

   probably 
  be 
  absorbed 
  even 
  more 
  readily, 
  and 
  would 
  approxi- 
  

   mate 
  more 
  closely 
  to 
  the 
  X 
  rays. 
  The 
  effect 
  would 
  be 
  difficult 
  

   to 
  obtain 
  except 
  with 
  a 
  considerable 
  quantity 
  of 
  actinium. 
  

  

  The 
  reasons 
  for 
  considering 
  the 
  penetrating 
  secondary 
  rays 
  

   to 
  be 
  of 
  the 
  y 
  type, 
  and 
  not 
  of 
  the 
  cathode, 
  are 
  as 
  follows: 
  — 
  

  

  1. 
  There 
  is 
  a 
  well-marked 
  bend 
  in 
  the 
  absorption 
  curves 
  

   shown 
  in 
  the 
  diagrams. 
  This 
  change 
  of 
  character 
  is 
  also 
  well 
  

   marked 
  when 
  the 
  logarithms 
  of 
  the 
  ordinates 
  are 
  plotted. 
  

  

  2. 
  The 
  primary 
  rays 
  penetrate 
  several 
  centimetres 
  into 
  

   substances 
  such 
  as 
  brick 
  or 
  slate 
  ; 
  some 
  of 
  the 
  secondary 
  rays 
  

   emerge 
  from 
  that 
  depth, 
  and 
  will 
  then 
  penetrate 
  several 
  

   millimetres 
  of 
  lead. 
  

  

  3. 
  The 
  values 
  of 
  the 
  coefficients 
  of 
  absorption 
  by 
  lead 
  o£ 
  

   these 
  penetrating 
  rays 
  equal 
  about 
  4, 
  or 
  nearly 
  the 
  value 
  of 
  

   the 
  coefficient 
  of 
  absorption 
  by 
  lead 
  of 
  the 
  primary 
  y 
  rays 
  of 
  

   actinium. 
  

  

  4. 
  If 
  the 
  secondary 
  radiator, 
  such 
  as 
  brick, 
  be 
  placed 
  in 
  a 
  

   strong: 
  magnetic 
  field, 
  the 
  ionization 
  current 
  in 
  the 
  electro- 
  

   scope, 
  due 
  to 
  the 
  penetrating 
  secondary 
  radiation 
  from 
  the 
  

   brick, 
  caused 
  by 
  y 
  rays, 
  is 
  unaffected 
  by 
  the 
  absence 
  or 
  presence 
  

   or 
  direction 
  of 
  the 
  magnetic 
  field. 
  

  

  The 
  laws 
  which 
  govern 
  the 
  magnitude 
  of 
  the 
  secondary 
  

   y 
  radiation 
  are 
  not 
  yet 
  clear. 
  

  

  If 
  possible, 
  further 
  experiments 
  will 
  be 
  made 
  using 
  different 
  

   screens, 
  radiators, 
  and 
  cylinders 
  inclosing 
  the 
  radium. 
  

  

  McGill 
  University, 
  Montreal. 
  

   April 
  L908. 
  

  

  Phil. 
  Mag. 
  Feb. 
  1007. 
  For 
  "Omaha 
  Sea-Salt," 
  read 
  " 
  Enagua 
  Sea-Salt, 
  

   imported 
  1>\ 
  Evans 
  ami 
  Saunders, 
  Toronto." 
  

  

  Phil. 
  Mag. 
  Sept. 
  L906. 
  }>. 
  L09< 
  For 
  "9x10° 
  per 
  c.c. 
  per 
  second," 
  

   read 
  "9x 
  L0 
  H 
  per 
  second." 
  

  

  * 
  Phil. 
  Mag. 
  April 
  L906, 
  

  

  