﻿398 
  Mr. 
  H. 
  P. 
  Walmsley 
  on 
  the 
  Distribution 
  of 
  the 
  

  

  from 
  dust, 
  was 
  left 
  undisturbed 
  in 
  the 
  presence 
  of 
  thorium 
  

   emanation 
  for 
  a 
  period 
  of 
  about 
  eighteen 
  hours, 
  and 
  a 
  

   negatively 
  charged 
  rod 
  was 
  then 
  introduced 
  into 
  the 
  vessel 
  

   for 
  one 
  minute, 
  the 
  decay 
  of 
  the 
  radiations 
  from 
  the 
  rod 
  

   after 
  removal 
  was 
  the 
  same 
  as 
  that 
  of 
  a 
  rod 
  which 
  had 
  been 
  

   exposed 
  for 
  a 
  period 
  of 
  eighteen 
  hours. 
  If, 
  however, 
  the 
  

   dust 
  was 
  removed 
  from 
  the 
  air 
  by 
  passing 
  through 
  a 
  plug 
  

   of 
  glass-wool, 
  or 
  by 
  keeping 
  the 
  emanation 
  in 
  an 
  electric 
  

   field, 
  the 
  activity 
  obtained 
  on 
  the 
  rod 
  under 
  similar 
  con- 
  

   ditions 
  decayed 
  with 
  the 
  correct 
  period 
  as 
  deduced 
  from 
  the 
  

   constants 
  of 
  the 
  transformation 
  products. 
  This 
  decisively 
  

   proves 
  that 
  active 
  deposit 
  settles 
  on 
  dust 
  and 
  remains 
  for 
  

   long 
  periods 
  suspended 
  in 
  still 
  air. 
  If 
  the 
  dust 
  had 
  carried 
  

   a 
  negative 
  charge, 
  it 
  is 
  possible 
  that 
  the 
  charge 
  carried 
  by 
  

   the 
  active 
  deposit 
  was 
  not 
  sufficient 
  to 
  neutralize 
  it. 
  In 
  this 
  

   case 
  the 
  dust 
  carrying 
  the 
  active 
  deposit 
  would 
  be 
  collected 
  

   on 
  the 
  positive 
  electrode 
  in 
  an 
  electric 
  field. 
  ^ 
  The 
  experi- 
  

   ments 
  on 
  actinium 
  B 
  have 
  shown 
  that 
  the 
  active 
  deposit 
  in 
  

   dust-free 
  air 
  rapidly 
  diffuses 
  to 
  the 
  sides 
  of 
  the 
  vessel. 
  Dust 
  

   and 
  large 
  nuclei 
  carrying 
  active 
  deposit 
  would 
  probably, 
  

   from 
  their 
  larger 
  size, 
  diffuse 
  much 
  more 
  slowly. 
  In 
  time, 
  

   therefore, 
  it 
  is 
  possible 
  that 
  if 
  an 
  electric 
  field 
  were 
  employed, 
  

  

  Fiff. 
  11. 
  

  

  

  

  

  

  Air 
  

  

  AT 
  ATM 
  

  

  )SPHERIC 
  

  

  

  

  

  PRESSU 
  

  

  RE 
  

  

  4 
  

   *2 
  

  

  

  

  \l 
  

  

  

  

  

  I 
  /(/ITHCO 
  

  

  tl 
  Anode 
  

  

  f 
  /ICTIVIT 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  d 
  

   ^ 
  

  

  

  

  A 
  

  

  

  

  

  

  - 
  1 
  

  

  

  0-5 
  

  

  1-0 
  

  

  1-5 
  2-0 
  . 
  £-5 
  

  

  Time 
  in 
  minutes 
  

  

  3-0 
  

  

  more 
  activity 
  could 
  be 
  collected 
  on 
  the 
  anode 
  than 
  on 
  the 
  

   cathode. 
  This 
  has 
  actually 
  been 
  observed. 
  If 
  the 
  Wims- 
  

   hurst 
  machine 
  were 
  not 
  employed 
  to 
  remove 
  dust-nuclei 
  

   from 
  the 
  chamber 
  before 
  making 
  an 
  exposure, 
  curves 
  of 
  the 
  

   same 
  type 
  as 
  that 
  in 
  fiff. 
  11 
  were 
  obtained. 
  It 
  was 
  found 
  

  

  fio-. 
  11 
  were 
  

  

  