﻿634 
  Messrs. 
  F. 
  Soddy 
  and 
  A. 
  S. 
  Russell 
  on 
  tl 
  

  

  It 
  will 
  be 
  seen 
  from 
  the 
  other 
  curves 
  that 
  after 
  a 
  certain 
  

   initial 
  thickness 
  of 
  matter 
  has 
  been 
  penetrated, 
  corresponding 
  

  

  Fig. 
  1. 
  

  

  5 
  6 
  7 
  8 
  

   TH/C^A'ESS 
  (cm) 
  

  

  to 
  1 
  cm. 
  of 
  lead, 
  or 
  an 
  equivalent 
  thickness 
  of 
  other 
  sub- 
  

   stances, 
  the 
  absorption 
  follows 
  an 
  exponential 
  law 
  represented 
  

   by 
  the 
  equation 
  

  

  K^2) 
  

  

  ^^-Kh-h)^ 
  

  

  where 
  ^i 
  and 
  t^ 
  refer 
  to 
  thicknesses 
  in 
  centimetres, 
  \ty) 
  and 
  

   1(^2) 
  to 
  the 
  corresponding 
  ionizations, 
  and 
  X 
  is 
  a 
  constant, 
  

   which 
  is 
  usually 
  termed 
  " 
  the 
  absorption 
  coefficient." 
  Owing 
  

   to 
  the 
  obliquity 
  of 
  part 
  of 
  the 
  beam 
  this 
  absorption 
  coefficient 
  

   departs 
  slightly 
  from 
  the 
  true 
  absorption 
  coefficient 
  corre- 
  

   sponding 
  to 
  the 
  X 
  of 
  the 
  theoretical 
  equation 
  

  

  which 
  represents 
  the 
  exponential 
  absorption 
  of 
  a 
  parallel 
  

   homogeneous 
  radiation 
  passing 
  through 
  the 
  absorbing 
  plate 
  

   normally 
  to 
  its 
  surface. 
  It 
  can 
  be 
  shown, 
  for 
  example, 
  to 
  be 
  

  

  