﻿Earth's 
  Penetrating 
  Radiation 
  with 
  Wulf 
  Electrometer. 
  751 
  

   may 
  suppose 
  the 
  ionization 
  in 
  the 
  electrometer 
  to 
  be 
  given 
  

  

  by 
  

  

  (i-*) 
  = 
  (i« 
  -.*>-**, 
  

  

  where 
  jjl 
  is 
  the 
  coefficient 
  of 
  absorption 
  of 
  the 
  penetrating 
  

   radiation, 
  d 
  the 
  thickness 
  of 
  the 
  water-screen, 
  and 
  x 
  the 
  

   ionization 
  in 
  the 
  electrometer 
  which 
  is 
  not 
  due 
  to 
  the 
  pene- 
  

   trating 
  radiation. 
  We 
  have 
  then 
  

  

  (5:82-*) 
  = 
  (S'05- 
  l 
  v)e- 
  36 
  ' 
  5 
  ». 
  

  

  For 
  soft 
  gamma 
  rays 
  Rutherford 
  * 
  gives 
  the 
  value 
  "0558 
  

   for 
  /jb 
  and 
  for 
  harder 
  rays 
  the 
  value 
  '0472. 
  The 
  measure- 
  

   ments 
  of 
  Hess 
  f 
  at 
  Vienna 
  on 
  the 
  absorption 
  of 
  gamma 
  rays 
  

   by 
  air 
  also 
  lead 
  to 
  a 
  value 
  for 
  /x 
  for 
  water 
  of 
  '0413. 
  

  

  Applying 
  these 
  values 
  we 
  find 
  the 
  value 
  of 
  x 
  to 
  be 
  as 
  

   follows 
  : 
  — 
  

  

  ju. 
  x 
  (ions 
  per 
  c.c. 
  per 
  sec). 
  

  

  •0558 
  5-48 
  

  

  •0472 
  5-33 
  

  

  •0413 
  5-19 
  

  

  Tn 
  so 
  far 
  as 
  these 
  measurements 
  go 
  then, 
  it 
  would 
  appear 
  

   that 
  5" 
  19 
  ions 
  per 
  c.c. 
  per 
  sec. 
  is 
  the 
  lowest 
  value 
  one 
  should 
  

   have 
  expected 
  to 
  get 
  for 
  the 
  ionization 
  in 
  the 
  zinc 
  vessel 
  

   when 
  all 
  the 
  penetrating 
  radiation 
  was 
  cut 
  off. 
  

  

  In 
  view, 
  however, 
  of 
  the 
  fact 
  that 
  4 
  ions 
  per 
  c.c. 
  per 
  sec. 
  

   was 
  obtained 
  experimentally, 
  the 
  above 
  experiments 
  can 
  

   only 
  be 
  considered 
  as 
  giving 
  a 
  roughly 
  approximate 
  result. 
  

  

  They 
  serve 
  to 
  show, 
  however, 
  that 
  unless 
  there 
  is 
  present 
  at 
  

   the 
  surface 
  of 
  the 
  earth 
  a 
  radiation 
  of 
  a 
  much 
  higher 
  pene- 
  

   trating 
  power 
  than 
  any 
  yet 
  observed, 
  there 
  must 
  be 
  a 
  residual 
  

   ionization 
  in 
  air 
  confined 
  in 
  a 
  zinc 
  vessel 
  (of 
  about 
  4 
  ions 
  

   per 
  c.c. 
  per 
  sec.) 
  when 
  it 
  is 
  not 
  traversed 
  by 
  any 
  radiation 
  

   from 
  an 
  external 
  source. 
  

  

  It 
  would 
  seem, 
  therefore, 
  that 
  this 
  residual 
  ionization 
  must 
  

   be 
  due 
  either 
  to 
  radiation 
  from 
  a 
  minute 
  quantity 
  of 
  radio- 
  

   active 
  matter 
  still 
  remaining 
  in 
  the 
  zinc 
  of 
  which 
  the 
  receiver 
  

   is 
  made, 
  or 
  to 
  a 
  process 
  going 
  on 
  in 
  the 
  gas 
  which 
  results 
  in 
  

   what 
  may 
  be 
  called 
  a 
  spontaneous 
  dissociation 
  of 
  the 
  

   molecules. 
  

  

  If 
  the 
  residual 
  effect 
  were 
  due 
  to 
  active 
  matter 
  in 
  the 
  walls 
  

   of 
  the 
  receiver 
  one 
  should 
  expect 
  that 
  the 
  value 
  obtained 
  for 
  

   "q" 
  would 
  increase 
  if 
  the 
  volume 
  of 
  the 
  receiver 
  were 
  

   diminished. 
  Since 
  the 
  value 
  of 
  4'1 
  ions 
  per 
  c.c. 
  per 
  sec. 
  was 
  

  

  * 
  Rutherford, 
  ' 
  Radioactive 
  Substances 
  and 
  their 
  Transformations,' 
  

   p. 
  266. 
  

  

  t 
  Hess, 
  Phys. 
  Zeit. 
  vol. 
  xii. 
  p. 
  998 
  (1911). 
  

  

  