﻿€38 
  Messrs. 
  F. 
  Soddy 
  and 
  A. 
  S. 
  Russell 
  on 
  the 
  

  

  From 
  the 
  paper, 
  which 
  is 
  merely 
  a 
  preliminary 
  account, 
  

   no 
  conclusion 
  can 
  be 
  formed, 
  in 
  view 
  of 
  the 
  results 
  to 
  be 
  

   ^iven 
  in 
  this 
  section, 
  as 
  to 
  whether 
  the 
  convexity 
  of 
  the 
  

   absorption 
  curve 
  to 
  the 
  origin, 
  which 
  these 
  numbers 
  disclose, 
  

   is 
  due 
  to 
  a 
  real 
  change 
  in 
  the 
  value 
  o£ 
  the 
  absorption 
  

   coefficient. 
  

  

  We 
  obtained 
  for 
  several 
  dispositions 
  results 
  similar 
  to 
  those 
  

   given 
  by 
  Eve 
  and 
  McClelland, 
  and 
  in 
  no 
  case 
  near 
  Wigger''s 
  

   lower 
  value, 
  so 
  we 
  repeated 
  the 
  latter^s 
  work 
  as 
  closely 
  as 
  

   possible. 
  The 
  apparatus 
  consisted 
  of 
  a 
  vertical 
  brass 
  cylinder 
  

   105 
  cm. 
  long, 
  4*5 
  cm. 
  inside 
  diameter, 
  0*5 
  mm. 
  wall 
  thickness 
  

   provided 
  with 
  a 
  central 
  electrode 
  95 
  cm. 
  long 
  passing 
  through 
  

   an 
  insulator 
  and 
  directly 
  connecting 
  with 
  a 
  leaf 
  system 
  inside 
  

   an 
  ordinary 
  brass 
  electroscope. 
  The 
  lead 
  plates 
  were 
  placed 
  

   over 
  the 
  open 
  top 
  end 
  of 
  the 
  cylinder 
  and 
  the 
  radium 
  was 
  

   fixed 
  at 
  a 
  definite 
  height 
  above. 
  The 
  capacity 
  of 
  the 
  arrange- 
  

   ment 
  was 
  30 
  times 
  greater 
  than 
  that 
  of 
  an 
  ordinary 
  leaf 
  

   system. 
  In 
  an 
  experiment 
  with 
  the 
  radium 
  56 
  mm. 
  from 
  the 
  

   top 
  of 
  the 
  cylinder, 
  as 
  used 
  by 
  Wigger, 
  the 
  absorption 
  pro- 
  

   ceeded 
  exponentially 
  from 
  a 
  range 
  of 
  2'^ 
  to 
  4*7 
  cm. 
  of 
  lead, 
  

   the 
  value 
  of 
  the 
  absorption 
  coefficient 
  \ 
  being 
  0*479, 
  instead 
  of 
  

   0'241 
  as 
  stated 
  by 
  him. 
  Wigger, 
  however, 
  appears 
  to 
  have 
  

   calculated 
  his 
  results 
  wrongly. 
  He 
  does 
  not 
  state 
  the 
  natural 
  

   leak 
  of 
  his 
  instrument 
  ; 
  but 
  neglecting 
  this 
  and 
  recalculating 
  

   from 
  his 
  own 
  observations 
  gave 
  a 
  value 
  similar 
  to 
  what 
  w^e 
  

   obtained 
  experimentally. 
  

  

  The 
  effect 
  of 
  increasing 
  the 
  distance 
  of 
  the 
  radium 
  from 
  

   the 
  end 
  of 
  the 
  cylinder 
  to 
  78 
  mm. 
  and 
  100 
  mm. 
  was 
  then 
  

   tried. 
  The 
  leak 
  fell 
  off 
  with 
  great 
  rapidity 
  as 
  the 
  distance 
  of 
  

   the 
  radium 
  was 
  increased, 
  showing 
  that 
  only 
  a 
  few 
  cm. 
  

   of 
  the 
  top 
  end 
  of 
  the 
  long 
  cylinder 
  could 
  be 
  effective 
  in 
  con- 
  

   tributing 
  to 
  the 
  ionization. 
  The 
  curves 
  obtained 
  over 
  the 
  

   same 
  range 
  as 
  before 
  were 
  quite 
  exponential, 
  but 
  the 
  values 
  

   of 
  X 
  were 
  now 
  different, 
  being 
  0*438 
  at 
  78 
  mm. 
  and 
  0*393 
  

   at 
  100 
  mm. 
  This 
  effect 
  of 
  the 
  variation 
  of 
  \ 
  with 
  the 
  distance 
  

   of 
  the 
  source 
  of 
  radiation 
  from 
  the 
  ionization- 
  chamber 
  was 
  

   then 
  investigated 
  with 
  a 
  common 
  form 
  of 
  apparatus. 
  The 
  

   brass 
  electroscope, 
  used 
  in 
  the 
  measurements 
  of 
  section 
  6, 
  

   was 
  mounted 
  on 
  brass 
  pillars 
  on 
  a 
  w^ooden 
  plank 
  one 
  end 
  of 
  

   which 
  was 
  supported 
  on 
  the 
  slate 
  bench 
  while 
  the 
  other 
  was 
  

   supported 
  by 
  two 
  long 
  legs 
  standing 
  on 
  the 
  floor. 
  A 
  large 
  

   hole 
  was 
  cut 
  in 
  the 
  plank 
  so 
  as 
  to 
  allow 
  free 
  passage 
  of 
  

   radiations 
  from 
  beneath 
  the 
  table 
  into 
  the 
  electroscope. 
  The 
  

   base 
  of 
  the 
  electroscope 
  was 
  of 
  lead 
  2*840 
  cm. 
  thick 
  clamped 
  

   up 
  as 
  before. 
  It 
  was 
  found 
  that 
  with 
  5 
  cm. 
  of 
  lead 
  over 
  the 
  

   radium 
  placed 
  on 
  the 
  floor 
  and 
  2*84 
  cm. 
  as 
  base 
  the 
  leak 
  was 
  

  

  