﻿Recoil 
  Atoms 
  from 
  Thorium 
  C 
  and 
  Actinium 
  C. 
  589 
  

  

  the 
  magnitude 
  or 
  direction 
  of 
  the 
  field. 
  It 
  is 
  of 
  course 
  

   possible 
  to 
  suppose 
  that 
  some 
  of 
  the 
  recoil 
  atoms 
  acquire 
  a 
  

   negative 
  charge 
  in 
  travelling 
  through 
  the 
  gas, 
  and 
  would 
  

   thus 
  collect 
  on 
  the 
  positive 
  electrode. 
  The 
  possibility 
  o£ 
  the 
  

   reversal 
  of 
  the 
  charge 
  on 
  the 
  recoil 
  atoms 
  due 
  to 
  dust 
  is 
  

   supported 
  by 
  some 
  experiments 
  of 
  Mr. 
  Walmsley 
  * 
  in 
  this 
  

   laboratory. 
  No 
  definite 
  evidence, 
  however, 
  in 
  support 
  of 
  

   such 
  a 
  view 
  was 
  obtained 
  by 
  the 
  author. 
  

  

  This 
  diffusion 
  effect 
  makes 
  it 
  difficult 
  to 
  determine 
  the 
  

   exact 
  pressure 
  at 
  which 
  the 
  recoiling 
  atoms 
  just 
  fail 
  to 
  reach 
  

   the 
  hemisphere 
  ; 
  but 
  by 
  continuing 
  the 
  main 
  portion 
  of 
  the 
  

   curve 
  to 
  cut 
  the 
  pressure-axis 
  (as 
  shown 
  by 
  the 
  dotted 
  line 
  

   in 
  fig. 
  2), 
  a 
  fairly 
  consistent 
  result 
  is 
  obtained. 
  The 
  mean 
  

  

  Fig. 
  2. 
  

  

  93 
  

  

  <^40 
  

  

  is 
  

  

  I 
  30 
  

  

  120 
  

  

  \ 
  

  

  

  

  

  

  

  A 
  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  

  -00 
  o- 
  

  

  

  I 
  2 
  3 
  4 
  5 
  6 
  

  

  Pressure 
  in 
  mms 
  — 
  <- 
  

  

  value 
  of 
  this 
  pressure 
  for 
  all 
  experiments 
  is 
  3 
  # 
  25 
  mm. 
  Now 
  

   the 
  internal 
  radius 
  of 
  the 
  hemisphere 
  in 
  the 
  above 
  experi- 
  

   ments 
  was 
  28 
  mm., 
  consequently 
  the 
  range 
  of 
  recoil 
  of 
  

   thorium 
  D 
  in 
  air 
  at 
  atmospheric 
  pressure 
  is 
  0*12 
  mm. 
  

  

  A 
  number 
  of 
  experiments 
  were 
  also 
  made 
  in 
  hydrogen, 
  

   the 
  curves 
  being 
  similar 
  to 
  those 
  obtained 
  for 
  air. 
  In 
  this 
  

   case, 
  however, 
  it 
  was 
  found 
  that 
  the 
  range 
  was 
  a 
  little 
  over 
  

   four 
  times 
  the 
  range 
  in 
  air. 
  

  

  (b) 
  Recoil 
  from 
  Actinium 
  C. 
  

  

  On 
  account 
  of 
  the 
  relatively 
  rapid 
  decay 
  of 
  actinium 
  active 
  

   deposit, 
  it 
  was 
  necessary 
  to 
  perform 
  many 
  experiments 
  to 
  

   determine 
  a 
  single 
  curve 
  showing 
  the 
  relation 
  between 
  the 
  

  

  * 
  Loc. 
  cit. 
  

  

  