﻿y-Rays 
  of 
  Uranium 
  and 
  Radium. 
  647 
  

  

  than 
  in 
  the 
  latter. 
  A 
  determination 
  of 
  X 
  for 
  lead 
  with 
  

   iiraninm 
  X 
  with 
  the 
  new 
  disposition 
  and 
  method 
  o£ 
  working 
  

  

  y-Eays 
  of 
  Uranium. 
  

  

  6 
  7 
  8 
  Q 
  10 
  

  

  All 
  tln'0U2:li 
  1 
  cm. 
  of 
  Lead. 
  

  

  except 
  that 
  the 
  metal 
  was 
  all 
  clamped 
  to 
  the 
  base 
  of 
  the 
  

   electroscope 
  gave 
  a 
  value 
  0*66, 
  which 
  is 
  much 
  nearer 
  to 
  the 
  

   value 
  given 
  in 
  Table 
  I. 
  than 
  to 
  that 
  in 
  Table 
  III. 
  

  

  Considering 
  now 
  the 
  ratio 
  of 
  the 
  absorption 
  coefficients 
  

   for 
  uranium 
  and 
  radium 
  shown 
  in 
  the 
  last 
  column 
  of 
  Table 
  III., 
  

   it 
  will 
  be 
  seen 
  that, 
  excluding 
  the 
  two 
  heaviest 
  substances, 
  

   mercury 
  and 
  lead, 
  and 
  the 
  two 
  lightest, 
  sulphur 
  and 
  paraffin- 
  

   wax, 
  the 
  mean 
  ratio 
  is 
  1'182, 
  and 
  the 
  actual 
  values 
  are 
  

   wonderfully 
  close 
  to 
  this 
  mean. 
  If 
  we 
  exclude 
  also 
  slate, 
  

   which 
  is 
  an 
  indefinite 
  sort 
  of 
  material, 
  the 
  extreme 
  variation 
  

   from 
  the 
  mean 
  value 
  is 
  only 
  2 
  or 
  3 
  per 
  cent. 
  

  

  [It 
  is 
  very 
  interesting 
  to 
  note 
  that 
  the 
  division 
  of 
  the 
  sub- 
  

   stances 
  in 
  Tables 
  II. 
  and 
  III. 
  into 
  three 
  groups, 
  according 
  to 
  

   the 
  values 
  obtained 
  for 
  X/d, 
  is 
  practically 
  the 
  same 
  as 
  the 
  

   division 
  made 
  by 
  Kleeman 
  for 
  totally 
  distinct 
  reasons 
  in 
  his 
  

   study 
  of 
  the 
  secondary 
  radiations 
  generated 
  by 
  y-rays. 
  

   (Compare 
  Phil. 
  Mag. 
  1908, 
  xv. 
  p. 
  644, 
  Tables 
  I. 
  and 
  II.)] 
  

  

  