﻿610 
  

  

  Mr. 
  T. 
  S. 
  Taylor 
  on 
  the 
  Retardation 
  of 
  

  

  hydrogen 
  cell 
  increased 
  as 
  the 
  range 
  of 
  the 
  entering 
  alpha- 
  

   particle 
  decreased. 
  The 
  particles 
  had 
  to 
  pass 
  through 
  the 
  

   celloidin 
  sheets 
  but 
  this 
  did 
  not 
  influence 
  the 
  effect 
  because, 
  

   as 
  we 
  have 
  seen, 
  the 
  amount 
  by 
  which 
  the 
  range 
  was 
  cut 
  

   down 
  by 
  the 
  celloidin 
  sheets 
  was 
  constant 
  for 
  all 
  positions 
  of 
  

   the 
  cell. 
  Determinations 
  of 
  the 
  air-equivalents 
  in 
  centi- 
  

   metres 
  of 
  three 
  hydrogen 
  cells 
  given 
  in 
  Table 
  I. 
  were 
  made 
  

   for 
  various 
  distances 
  of 
  the 
  cell 
  from 
  the 
  radium 
  and 
  the 
  

   results 
  obtained 
  are 
  recorded 
  in 
  Table 
  III. 
  

  

  Table 
  III. 
  

  

  1 
  

  

  Range 
  of 
  the 
  

  

  

  

  

  a-particle 
  upon 
  

   entering 
  the 
  

  

  A 
  Hydrogen. 
  

  

  B 
  Hydrogen. 
  

  

  C 
  Hydrogen. 
  

  

  hydrogen. 
  

  

  

  

  

  5-2 
  

  

  0-231 
  

  

  0-428 
  

  

  0-762 
  

  

  4-8 
  

  

  0-235 
  

  

  0-434 
  

  

  0776 
  

  

  4-4 
  

  

  0-241 
  

  

  0-442 
  

  

  0-791 
  

  

  4-0 
  

  

  0-247 
  

  

  0-451 
  

  

  0-807 
  

  

  3-6 
  

  

  0-254 
  

  

  0-460 
  

  

  0-831 
  

  

  3-2 
  

  

  0-262 
  

  

  0-470 
  

  

  0-861 
  

  

  2-8 
  

  

  0-271 
  

  

  0-483 
  

  

  0-896 
  

  

  2-4 
  

  

  ! 
  

  

  0-283 
  

  

  0-499 
  

  

  0-938 
  

  

  The 
  reason 
  the 
  maximum 
  range 
  here 
  is 
  5' 
  2 
  cm. 
  instead 
  of 
  

   5*7 
  cm. 
  as 
  it 
  was 
  in 
  Table 
  II. 
  is 
  because 
  the 
  air-equivalent 
  

   of 
  the 
  lower 
  film 
  of 
  celloidin 
  must 
  be 
  subtracted 
  since 
  the 
  

   alpha-particles 
  must 
  pass 
  through 
  it 
  before 
  entering 
  the 
  

   hydrogen. 
  The 
  air-equivalent 
  of 
  the 
  lower 
  film 
  was 
  0'5 
  cm. 
  

  

  Although 
  the 
  air-equivalents 
  of 
  the 
  celloidin 
  sheets 
  

   remained 
  constant, 
  it 
  seemed 
  probable, 
  from 
  the 
  behaviour 
  of 
  

   the 
  hydrogen 
  sheets, 
  that 
  if 
  the 
  same 
  experiments 
  were 
  

   performed 
  in 
  an 
  atmosphere 
  of 
  hydrogen, 
  the 
  hydrogen- 
  

   equivalent 
  * 
  of 
  the 
  celloidin 
  sheet 
  would 
  not 
  remain 
  constant, 
  

   but 
  would 
  decrease 
  as 
  the 
  range 
  of 
  the 
  alpha-particles 
  

   decreased. 
  To 
  investigate 
  this 
  point 
  the 
  apparatus 
  was 
  

   enclosed 
  in 
  an 
  air-tight 
  sheet-iron 
  case, 
  which 
  by 
  several 
  

   partial 
  evacuations 
  and 
  refillings 
  could 
  be 
  filled 
  with 
  practi- 
  

   cally 
  pure 
  hydrogen. 
  With 
  polonium 
  as 
  the 
  source 
  of 
  rays 
  

   the 
  hydrogen 
  equivalents 
  in 
  cms. 
  of 
  sheets 
  of 
  celloidin, 
  

   aluminium, 
  tin^ 
  and 
  gold 
  were 
  determined 
  for 
  various 
  

   distances 
  ot 
  the 
  sheets 
  from 
  the 
  polonium. 
  Only 
  the 
  results 
  

   for 
  the 
  celloidin 
  and 
  A 
  gold 
  are 
  given 
  in 
  Table 
  LY. 
  as 
  they 
  

   are 
  sufficient 
  to 
  illustrate 
  the 
  point 
  in 
  question. 
  

  

  * 
  The 
  hydrogen-equivalent 
  is 
  the 
  amount 
  by 
  which 
  the 
  range 
  of 
  the 
  

   a-particles 
  in 
  hydrogen 
  is 
  cut 
  do-wn 
  by 
  their 
  passage 
  through 
  the 
  sheet. 
  

  

  