﻿394 
  Mr. 
  H. 
  P. 
  Walmsley 
  on 
  the 
  Distribution 
  of 
  the 
  

  

  due 
  solely 
  to 
  the 
  diffusion 
  of 
  the 
  active 
  matter 
  to 
  the 
  

   boundaries 
  of 
  the 
  vessel. 
  If, 
  however, 
  during* 
  the 
  four 
  

   seconds' 
  exposure, 
  an 
  electric 
  field 
  was 
  maintained 
  between 
  

   the 
  wire 
  and 
  the 
  cylinder, 
  an 
  increased 
  amount 
  of 
  active 
  

   deposit 
  was 
  collected. 
  The 
  difference 
  in 
  activity 
  between 
  

   these 
  cases 
  and 
  the 
  former 
  gave 
  the 
  amount 
  of 
  active 
  deposit 
  

   actually 
  collected 
  by 
  tho 
  field. 
  

  

  A 
  large 
  number 
  of 
  experiments 
  were 
  carried 
  out 
  and 
  the 
  

   activities 
  collected 
  by 
  the 
  wire 
  both 
  as 
  anode 
  and 
  as 
  cathode, 
  

   after 
  time 
  intervals 
  varying 
  from 
  0*25 
  min. 
  to 
  7'00 
  mins., 
  

   were 
  determined. 
  Many 
  observations 
  were 
  taken 
  after 
  the 
  

   same 
  time 
  interval, 
  and 
  a 
  most 
  noticeable 
  lack 
  of 
  consistency 
  

   between 
  the 
  readings, 
  and 
  especially 
  those 
  taken 
  on 
  different 
  

   days, 
  was 
  displayed. 
  The 
  latter 
  effect 
  was 
  ultimately 
  found 
  

   to 
  be 
  due 
  to 
  dust, 
  which 
  entered 
  the 
  apparatus 
  during- 
  

   the 
  process 
  of 
  removing 
  one 
  wire 
  and 
  substituting 
  another. 
  

   It 
  was 
  found, 
  however, 
  that 
  applying 
  a 
  strong 
  electric 
  field 
  

   between 
  the 
  wire 
  and 
  cylinder, 
  keeping 
  the 
  tube 
  F 
  in 
  

   position, 
  greatly 
  reduced 
  the 
  variations. 
  Hence 
  before 
  

   making 
  an 
  exposure, 
  the 
  wire 
  was 
  charged 
  to 
  a 
  high 
  

   potential 
  by 
  means 
  of 
  a 
  Wimshurst 
  machine 
  for 
  about 
  two 
  

   or 
  three 
  minutes. 
  This 
  would 
  remove 
  charged 
  dust 
  to 
  the 
  

   boundaries 
  of 
  the 
  vessel. 
  

  

  The 
  radioactive 
  transformations 
  occurring 
  within 
  the 
  

   cylinder 
  are 
  as 
  follows. 
  The 
  emanation 
  (period 
  3'9 
  sees.) 
  

   rapidly 
  decays 
  after 
  its 
  introduction, 
  and 
  produces 
  actinium 
  

   A 
  (period 
  0'002 
  sec), 
  which 
  in 
  turn 
  disintegrates 
  into 
  

   actinium 
  B 
  (period 
  36 
  mins.). 
  The 
  maximum 
  amount 
  of 
  A 
  

   appears 
  after 
  a 
  small 
  fraction 
  of 
  a 
  second, 
  and 
  afterwards 
  

   the 
  amount 
  present 
  is 
  approximately 
  a 
  constant 
  fraction 
  

   (19V0) 
  °^ 
  ^he 
  amoun,: 
  °f 
  emanation 
  present. 
  Hence 
  for 
  

   practical 
  purposes 
  this 
  product 
  may 
  be 
  neglected. 
  The 
  

   maximum 
  amount 
  of 
  B 
  occurs 
  after 
  35*2 
  seconds, 
  at 
  which 
  

   time 
  only 
  0*18 
  per 
  cent, 
  of 
  emanation 
  remains. 
  Hence 
  we 
  

   may 
  assume 
  that 
  the 
  amount 
  of 
  B 
  present, 
  until 
  the 
  maximum 
  

   is 
  reached, 
  is 
  given 
  by 
  (1 
  — 
  e~ 
  kt 
  ), 
  where 
  \ 
  is 
  the 
  decay 
  con- 
  

   stant 
  of 
  the 
  emanation 
  ; 
  and 
  afterwards 
  by 
  e~^K 
  where 
  X 
  1 
  is 
  

   its 
  own 
  decay 
  constant. 
  The 
  first 
  exposure 
  was 
  made 
  after 
  

   an 
  interval 
  of 
  15 
  sees. 
  At 
  this 
  time 
  6*7 
  per 
  cent, 
  of 
  the 
  

   emanation 
  was 
  still 
  untransformed. 
  Hence 
  to 
  make 
  the 
  

   readings 
  comparable 
  with 
  those 
  taken 
  after 
  30 
  sees., 
  a 
  

   7 
  per 
  cent, 
  correction 
  is 
  necessary. 
  Similarly 
  later 
  readings 
  

   require 
  correction 
  for 
  the 
  decay 
  of 
  actinium 
  B. 
  The 
  a-ray 
  

   activity 
  by 
  which 
  the 
  amount 
  of 
  deposit 
  was 
  estimated 
  is 
  

   due 
  to 
  actinium 
  (period 
  2'1 
  mins.). 
  Its 
  maximum 
  occurs 
  

   9*3 
  mins. 
  after 
  that 
  of 
  actinium 
  B, 
  so 
  to 
  obtain 
  full 
  benefit 
  

  

  