﻿1036 
  

  

  Mr. 
  F. 
  W. 
  Wheatley 
  on 
  Ionization 
  of 
  

  

  The 
  source 
  of 
  alpha 
  radiation 
  was 
  contained 
  in 
  the 
  brass 
  

   box 
  R 
  let 
  into 
  the 
  plate 
  C 
  and 
  covered 
  with 
  a 
  very 
  thin 
  sheet 
  

   of 
  aluminium 
  flush 
  with 
  the 
  rest 
  of 
  the 
  plate. 
  At 
  the 
  bottom 
  

   of 
  R 
  was 
  a 
  plate 
  of 
  copper 
  evenly 
  coated 
  with 
  polonium, 
  and 
  

   R 
  was 
  made 
  of 
  such 
  a 
  depth 
  and 
  width 
  that 
  every 
  a 
  particle 
  

   passing 
  through 
  the 
  aluminium 
  would 
  reach 
  the 
  plate 
  B 
  even 
  

   when 
  the 
  plates 
  were 
  at 
  their 
  greatest 
  distance 
  apart. 
  

  

  The 
  currents 
  were 
  measured 
  by 
  the 
  zero 
  method 
  of 
  

   Townsend 
  * 
  with 
  a 
  condenser 
  and 
  potentiometer. 
  

  

  The 
  electrometer 
  was 
  enclosed 
  in 
  an 
  earthed 
  lead 
  box 
  

   and 
  all 
  the 
  connexions 
  were 
  provided 
  with 
  earthed 
  tubes. 
  

   Throughout 
  the 
  experiments 
  the 
  upper 
  plate 
  B 
  was 
  kept 
  at 
  

   a 
  positive 
  potential. 
  

  

  In 
  this 
  way 
  every 
  electron 
  formed 
  would 
  reach 
  the 
  plate 
  

   B, 
  and 
  none 
  would 
  be 
  lost 
  on 
  the 
  guard-ring. 
  

  

  Method 
  of 
  conducting 
  the 
  experiments. 
  

   With 
  the 
  larger 
  values 
  of 
  a 
  the 
  formula 
  

   n 
  Q 
  (e* 
  l 
  -l) 
  

  

  may 
  be 
  used 
  to 
  determine 
  a 
  from 
  the 
  current-E.M.F. 
  curves 
  

   corresponding 
  to 
  a 
  distance 
  I 
  between 
  the 
  plates. 
  When 
  it 
  

   is 
  necessary 
  to 
  determine 
  n/n 
  very 
  accurately, 
  it 
  is 
  better 
  to 
  

   be 
  independent 
  of 
  the 
  quantity 
  n 
  and 
  the 
  values 
  of 
  a 
  may 
  

   be 
  determined 
  as 
  follows. 
  

  

  It 
  is 
  advisable 
  to 
  take 
  the 
  distances 
  between 
  the 
  plates 
  

   in 
  the 
  ratio 
  1, 
  2, 
  3, 
  say 
  Z, 
  21, 
  31. 
  

  

  a. 
  

  

  

  I 
  

  

  

  

  

  

  c 
  

  

  

  

  

  A 
  B 
  CD 
  

  

  Let 
  the 
  ionization 
  currents 
  observed 
  for 
  these 
  three 
  

   distances 
  be 
  a, 
  b, 
  c 
  for 
  some 
  particular 
  electromotive 
  force 
  

   (volts 
  per 
  centimetre). 
  

  

  When 
  the 
  plates 
  are 
  at 
  a 
  distance 
  31 
  apart 
  the 
  number 
  of 
  

   electrons 
  generated 
  is 
  c. 
  The 
  number 
  can 
  also 
  be 
  ascertained 
  

  

  * 
  Townsend, 
  Phil. 
  Mag. 
  vi. 
  p. 
  598 
  (1903). 
  

  

  