﻿596 
  Mr. 
  A. 
  B. 
  Wood 
  on 
  the 
  Range 
  of 
  the 
  

  

  about 
  3*5 
  mm. 
  in 
  air 
  or 
  about 
  16 
  mm. 
  in 
  hydrogen. 
  The 
  

   mean 
  value 
  for 
  the 
  range 
  of 
  recoil 
  was 
  found 
  by 
  this 
  method 
  

   to 
  be 
  '126 
  mm. 
  in 
  air 
  and 
  0*55 
  mm. 
  in 
  hydrogen 
  at 
  atmo- 
  

   spheric 
  pressure. 
  

  

  III. 
  Interpretation 
  of 
  Results. 
  

  

  In 
  the 
  case 
  of 
  recoil 
  from 
  actinium 
  C 
  the 
  results 
  obtained 
  

   by 
  the 
  two 
  methods 
  described 
  above 
  are 
  strikingly 
  similar. 
  

   Both 
  the 
  range 
  of 
  recoil 
  and 
  the 
  form 
  of 
  the 
  absorption 
  

   curves 
  are 
  the 
  same 
  by 
  the 
  two 
  different 
  methods. 
  

  

  The 
  results 
  on 
  the 
  recoil 
  from 
  thorium 
  C 
  are, 
  however, 
  

   not 
  so 
  easy 
  of 
  interpretation. 
  By 
  the 
  first 
  method 
  of 
  experi- 
  

   ment 
  the 
  range 
  of 
  recoil 
  was 
  found 
  to 
  be 
  '12 
  mm. 
  in 
  air 
  at 
  

   atmospheric 
  pressure. 
  Comparing 
  this 
  result 
  with 
  that 
  

   obtained 
  for 
  actinium, 
  it 
  appears 
  as 
  if 
  the 
  recoil 
  product 
  

   came 
  from 
  the 
  atom 
  emitting 
  the 
  a-particle 
  of 
  range 
  4*8 
  cm., 
  

   viz. 
  thorium 
  G. 
  Now 
  it 
  is 
  obvious 
  that 
  the 
  atom 
  emitting 
  

   the 
  S'6 
  cm. 
  range 
  a-particle 
  must 
  have 
  a 
  recoil 
  product 
  of 
  

   longer 
  range 
  than 
  that 
  from 
  actinium 
  C 
  ; 
  consequently, 
  if 
  this 
  

   product 
  has 
  been 
  collected 
  by 
  the 
  hemisphere, 
  it 
  mu>t 
  either 
  

   be 
  rayless 
  or 
  it 
  must 
  have 
  a 
  period 
  of 
  not 
  more 
  than 
  a 
  few 
  

   seconds. 
  The 
  former 
  supposition 
  seems 
  more 
  probable. 
  In 
  

   the 
  experiments 
  on 
  the 
  ionization 
  produced 
  by 
  recoil 
  from 
  

  

  thorium 
  C 
  the 
  form 
  of 
  the 
  absorption 
  curves 
  [— 
  and 
  p) 
  

  

  indicates 
  that 
  the 
  ionization 
  is 
  at 
  first 
  being 
  produced 
  by 
  the 
  

   products 
  recoiling 
  from 
  both 
  thorium 
  (\ 
  and 
  thorium 
  C 
  2 
  , 
  

   whilst 
  after 
  a 
  certain 
  pressure 
  has 
  been 
  reached 
  the 
  ionization 
  

   is 
  produced 
  only 
  by 
  the 
  product 
  from 
  thorium 
  C 
  2 
  . 
  The 
  

   most 
  satisfactory 
  explanation 
  of 
  these 
  two 
  results 
  seems 
  to 
  

   be 
  that 
  thorium 
  D 
  recoils 
  from 
  thorium 
  Ci 
  (emitting 
  a-par- 
  

   ticles 
  of 
  range 
  4°8 
  cm.), 
  whilst 
  the 
  product 
  recoiling 
  from 
  

   thorium 
  C 
  2 
  (emitting 
  a-particles 
  of 
  range 
  8'6 
  cm.) 
  is 
  rayless. 
  

   This 
  result 
  agrees 
  with 
  the 
  scheme 
  suggested 
  by 
  Marsden 
  

   and 
  Darwin 
  * 
  for 
  the 
  disintegration 
  of 
  the 
  thorium 
  series, 
  

  

  viz. 
  : 
  

  

  a(=4*8cm.)/3 
  

   t 
  t 
  

   C 
  a 
  -*D 
  -»? 
  

  

  a 
  a 
  3 
  / 
  

  

  Em. 
  *A 
  > 
  B 
  

  

  \ 
  

  

  a 
  ->c 
  2 
  — 
  ->? 
  

  

  3 
  a(=8-6cm.) 
  

  

  * 
  Loc. 
  cii. 
  

  

  