﻿612 
  

  

  Dr. 
  J. 
  A. 
  Gray 
  on 
  the 
  Scattering 
  and 
  

  

  than 
  the 
  primary, 
  and 
  this 
  is 
  the 
  explanation 
  usually 
  

   given*. 
  

  

  The 
  writerj 
  came 
  to 
  the 
  conclusion 
  that 
  7 
  rays 
  could 
  be 
  

   directly 
  scattered, 
  but 
  further 
  consideration 
  of 
  the 
  experi- 
  

   ments 
  of 
  Madsenand 
  Florance 
  showed 
  that 
  the 
  interpretation 
  

   of 
  the 
  scattering 
  of 
  7 
  rays 
  given 
  above 
  was 
  probably 
  not 
  

   sufficient, 
  as 
  it 
  appeared 
  that 
  when 
  the 
  intensity 
  of 
  the 
  

   primary 
  rays 
  was 
  diminished 
  by 
  lead, 
  the 
  softer 
  scattered 
  

   rays 
  were 
  not 
  cut 
  down 
  so 
  quickly 
  as 
  one 
  would 
  expect 
  (see 
  

   the 
  tables 
  given 
  below). 
  The 
  question 
  of 
  the 
  scattering 
  of 
  

   7 
  rays 
  has, 
  therefore, 
  been 
  re-examined 
  to 
  some 
  extent, 
  and 
  

   the 
  results 
  obtained 
  show 
  that 
  7 
  rays 
  are 
  not 
  scattered 
  like 
  

   a 
  pencil 
  of 
  «or/3 
  rays, 
  the 
  main 
  explanation 
  of 
  properties 
  

   of 
  the 
  secondary 
  7 
  rays 
  being 
  that 
  when 
  7 
  rays 
  are 
  scattered 
  

   the 
  scattered 
  rays 
  are 
  softer, 
  the 
  softening 
  being 
  greater 
  the 
  

   greater 
  the 
  angle 
  of 
  scattering. 
  In 
  support 
  of 
  this 
  view 
  it 
  

   may 
  be 
  stated 
  that 
  Sadler 
  and 
  MeshamJ 
  have 
  found 
  that 
  

   when 
  homogeneous 
  X 
  rays 
  are 
  scattered 
  in 
  carbon 
  the 
  

   scattered 
  rays 
  are 
  less 
  penetrating. 
  Below 
  are 
  given 
  a 
  

   description 
  of 
  the 
  experiments 
  on 
  secondary 
  7 
  rays, 
  and 
  a 
  

   discussion 
  of 
  the 
  results 
  and 
  their 
  bearing 
  on 
  absorption 
  

   experiments. 
  

  

  Experimental 
  Arrangements 
  and 
  Results. 
  

   Fig. 
  1. 
  

  

  Fig. 
  1 
  (drawn 
  to 
  scale) 
  shows 
  a 
  horizontal 
  section 
  of 
  the 
  

   apparatus 
  used. 
  For 
  a 
  source 
  of 
  7 
  rays, 
  15 
  milligrams 
  of 
  

  

  * 
  Bragg, 
  ' 
  Studies 
  in 
  Radioactivity.' 
  Rutherford, 
  ' 
  Radioactive 
  

   Substances 
  and 
  their 
  Radiations.' 
  

   t 
  Gray, 
  Proc. 
  Roy. 
  Soc. 
  A.lxxxvii. 
  p. 
  489 
  (1912). 
  

   t 
  Sadler 
  and 
  Mesham, 
  Phil.'Mag. 
  xxiv. 
  p. 
  138 
  (1912). 
  

  

  