﻿590 
  Mr. 
  A. 
  B. 
  Wood 
  on 
  the 
  Range 
  of 
  the 
  

  

  amount 
  of 
  recoil 
  product 
  received 
  and 
  the 
  pressure 
  in 
  the 
  

   apparatus. 
  Hence 
  in 
  each 
  experiment 
  the 
  activity 
  o£ 
  the 
  

   hemisphere 
  was 
  measured 
  after 
  a 
  15 
  minutes' 
  exposure 
  at 
  a 
  

   certain 
  " 
  standard 
  " 
  pressure. 
  It 
  was 
  then 
  measured 
  at 
  any 
  

   other 
  required 
  pressure. 
  

  

  As 
  in 
  the 
  case 
  of 
  thorium, 
  corrections 
  were 
  made 
  for 
  the 
  

   decay 
  of 
  the 
  active 
  deposit 
  (period 
  36*3 
  mins.) 
  and 
  for 
  the 
  

   decay 
  of 
  actinium 
  D 
  (period 
  4 
  # 
  7 
  mins.) 
  on 
  the 
  hemisphere 
  

   during 
  its 
  removal 
  from 
  the 
  apparatus 
  and 
  measurement 
  of 
  

   its 
  activity. 
  All 
  the 
  results 
  were 
  standardized 
  by 
  reducing 
  

   activities 
  at 
  the 
  standard 
  pressure 
  to 
  the 
  same 
  value, 
  and 
  

   other 
  activities 
  in 
  a 
  corresponding 
  proportion. 
  The 
  curves 
  

   obtained 
  in 
  this 
  way 
  are 
  strikingly 
  similar 
  to 
  those 
  obtained 
  

   in 
  the 
  case 
  of 
  thorium. 
  A 
  rapid 
  fall 
  in 
  activity 
  with 
  increase 
  

   of 
  pressure 
  is 
  observed, 
  the 
  pressure 
  at 
  which 
  the 
  main 
  curve 
  

   (produced) 
  cuts 
  the 
  pressure 
  axis 
  being 
  3*15 
  mm., 
  corre- 
  

   sponding 
  to 
  a 
  range 
  of 
  recoil 
  of 
  nearly 
  0'12 
  mm., 
  i. 
  £., 
  

   practically 
  the 
  same 
  as 
  that 
  of 
  thorium 
  D. 
  

  

  Now 
  the 
  range 
  of 
  the 
  a-particle 
  emitted 
  by 
  actinium 
  C 
  is 
  

   5*4 
  cm. 
  ; 
  consequently, 
  if 
  we 
  assume 
  that 
  the 
  range 
  of 
  the 
  

   recoiling 
  atom 
  is 
  roughly 
  proportional 
  to 
  the 
  range 
  of 
  the 
  

   a-particle 
  — 
  as 
  Wertenstein's 
  * 
  results 
  seem 
  to 
  show— 
  it 
  

   would 
  at 
  once 
  appear 
  that 
  thorium 
  D 
  recoils 
  from 
  the 
  atom 
  

   emitting 
  an 
  a-particle 
  of 
  range 
  4*8 
  cm., 
  namely 
  thorium 
  Ca, 
  

   using 
  the 
  nomenclature 
  adopted 
  by 
  Marsden 
  and 
  Darwin 
  f. 
  

   This 
  result 
  agrees 
  with 
  the 
  deductions 
  of 
  these 
  experimenters 
  

   in 
  their 
  work 
  on 
  ' 
  The 
  Transformations 
  of 
  the 
  Active 
  Deposit 
  

   of 
  Thorium.' 
  

  

  If, 
  on 
  the 
  other 
  hand, 
  thorium 
  D 
  recoiled 
  from 
  thorium 
  C 
  2 
  , 
  

   which 
  emits 
  a-particles 
  of 
  8' 
  6 
  cm. 
  range, 
  one 
  would 
  have 
  

   expected 
  a 
  considerable 
  difference 
  between 
  the 
  ranges 
  of 
  

   recoil 
  of 
  thorium 
  D 
  and 
  actinium 
  D, 
  but 
  no 
  such 
  difference 
  

   was 
  observed. 
  

  

  It 
  has 
  been 
  pointed 
  out 
  above 
  that 
  the 
  experimental 
  curves 
  

   indicated 
  that 
  the 
  recoiling 
  beam 
  was 
  apparently 
  not 
  homo- 
  

   geneous. 
  Many 
  experiments 
  were 
  made 
  to 
  discover 
  the 
  

   cause 
  of 
  this 
  non-homogeneity, 
  but 
  with 
  doubtful 
  success. 
  

   It 
  is 
  obvious, 
  of 
  course, 
  that 
  the 
  condition 
  of 
  the. 
  surf 
  ace 
  of 
  

   the 
  platinum 
  plate 
  has 
  a 
  great 
  influence, 
  but 
  even 
  with 
  plates 
  

   highly 
  polished 
  with 
  rouge 
  the 
  same 
  effect 
  was 
  observed. 
  It 
  

   seems 
  feasible 
  to 
  suppose 
  that 
  the 
  effect 
  is 
  due 
  either 
  to 
  the 
  

   intermingling 
  of 
  the 
  active 
  deposit 
  molecules 
  with 
  those 
  of 
  

   the 
  platinum 
  surface 
  on 
  which 
  they 
  are 
  deposited, 
  or 
  possibly 
  

   to 
  the 
  marked 
  scattering 
  of 
  the 
  recoil 
  atoms 
  in 
  their 
  passage 
  

   through 
  the 
  gas. 
  

  

  * 
  Comptes 
  liendus, 
  civ. 
  p. 
  475 
  (Aug. 
  1912). 
  

   t 
  Proc. 
  Roy. 
  Soc. 
  A, 
  vol. 
  lxxxvii. 
  (1912). 
  

  

  