﻿<y-Rays 
  of 
  Uranium 
  ami 
  Radium, 
  

  

  645 
  

  

  0-6 
  

  

  1-2 
  2-4 
  3-6 
  4-8 
  6-0 
  7-2 
  84 
  3-6 
  lo-, 
  

   y-Rays 
  of 
  Radium. 
  All 
  througli 
  1 
  cm. 
  of 
  Lead. 
  

  

  l^-Q 
  

  

  The 
  mean 
  value 
  of 
  Xjcl 
  for 
  all 
  substances 
  having 
  a 
  density 
  

   between 
  the 
  range 
  of 
  from 
  2-Q 
  to 
  S'S 
  is 
  for 
  radium 
  '040, 
  and 
  

   for 
  uranium 
  X 
  '047. 
  It 
  may 
  be 
  noted 
  that 
  the 
  deviations 
  

   from 
  the 
  mean 
  value 
  are, 
  considering 
  the 
  nature 
  of 
  the 
  expe- 
  

   riment, 
  very 
  small 
  indeed. 
  This 
  is 
  largely 
  due 
  to 
  the 
  pre- 
  

   cautions 
  taken 
  each 
  time 
  to 
  secure 
  the 
  minimum 
  leak 
  referred 
  

   to 
  before. 
  

  

  Thus 
  Xjcl 
  for 
  uranium 
  X 
  for 
  zinc 
  gave 
  a 
  value 
  of 
  '0465 
  

   twice 
  on 
  different 
  occasions. 
  Repeating 
  the 
  experiment 
  

   under 
  exactly 
  similar 
  conditions, 
  on 
  the 
  same 
  day 
  as 
  one 
  of 
  

   the 
  measurements, 
  except 
  that 
  the 
  leak 
  was 
  taken 
  without 
  

   thorough 
  ionization 
  of 
  the 
  air 
  in 
  the 
  electroscope 
  before 
  each 
  

  

  