﻿356 
  Messrs. 
  E. 
  Marsden 
  and 
  R. 
  H. 
  Wilson 
  on 
  some 
  

  

  Marsden 
  and 
  Darwin 
  agree 
  that 
  amounts 
  of 
  C 
  and 
  C 
  a 
  are 
  

   deposited 
  on 
  the 
  plate 
  in 
  the 
  same 
  proportion 
  as 
  they 
  exist 
  

   in 
  the 
  active 
  deposit 
  as 
  ordinarily 
  collected. 
  The 
  ionizations 
  

   due 
  to 
  the 
  a 
  particles 
  of 
  ranges 
  4*8 
  cm. 
  and 
  8*6 
  era. 
  were 
  

   balanced 
  against 
  one 
  another, 
  as 
  shown 
  in 
  fig. 
  2. 
  

  

  Fig. 
  2. 
  

  

  To 
  Electrometer 
  

  

  + 
  200 
  V. 
  

  

  ZOO 
  V. 
  

  

  The 
  a. 
  particles 
  from 
  the 
  nickel 
  plate 
  S 
  passed 
  through 
  a 
  

   canalising 
  grid 
  into 
  two 
  ionization 
  chambers 
  A 
  and 
  B 
  of 
  

   depth 
  2'0 
  and 
  2' 
  6 
  cm. 
  respectively, 
  the 
  electrodes 
  being 
  

   rings 
  covered 
  with 
  thin 
  foils 
  of 
  aluminium 
  equivalent 
  to 
  

   05 
  mm. 
  of 
  air 
  in 
  stopping 
  power 
  of 
  a 
  particles. 
  The 
  

   ol 
  particles 
  of 
  range 
  4*8 
  cm. 
  penetrated 
  about 
  1*6 
  cm. 
  into 
  

   the 
  first 
  chamber, 
  whilst 
  those 
  of 
  range 
  S'6 
  cm. 
  penetrated 
  

   both 
  chambers 
  and 
  struck 
  the 
  electrode 
  Y 
  about 
  0*7 
  cm. 
  from 
  

   the 
  end 
  of 
  their 
  range. 
  X 
  was 
  charged 
  to 
  +200 
  volts 
  and 
  

   Y 
  to 
  —200 
  volts, 
  whilst 
  Z 
  was 
  connected 
  to 
  a 
  Dolezaiek 
  

   electrometer. 
  Balance 
  was 
  made 
  as 
  accurately 
  as 
  possible 
  

   by 
  the 
  adjustment 
  of 
  S, 
  Z, 
  and 
  Y. 
  

  

  In 
  these 
  circumstances 
  it 
  could 
  be 
  calculated 
  that 
  the 
  

   ionization 
  due 
  to 
  the 
  a. 
  particles 
  of 
  range 
  4*8 
  cm. 
  was 
  just 
  

   about 
  50 
  per 
  cent, 
  of 
  the 
  total 
  ionization 
  in 
  the 
  first 
  chamber. 
  

   It 
  was 
  hoped 
  to 
  detect 
  any 
  difference 
  in 
  the 
  periods 
  by 
  a 
  

   change 
  in 
  the 
  balance 
  as 
  the 
  source 
  decayed. 
  A 
  typical 
  set 
  

   of 
  readings 
  is 
  given 
  in 
  Table 
  I. 
  

  

  The 
  first 
  observation 
  was 
  made 
  about 
  twenty 
  minutes 
  after 
  

   the 
  nickel 
  plate 
  was 
  withdrawn 
  from 
  the 
  solution, 
  so 
  that 
  the 
  

   thorium 
  D 
  was 
  in 
  equilibrium. 
  ( 
  Column 
  I. 
  gives 
  the 
  time 
  

  

  