﻿

  Earth's 
  Penetrating 
  Radiation 
  with 
  Wulf 
  Electrometer. 
  749 
  

  

  that 
  this 
  layer 
  of 
  sand 
  and 
  clay 
  acted 
  as 
  a 
  screen 
  and 
  cut 
  off 
  

   entirely 
  the 
  excess 
  radiation 
  from 
  the 
  shale 
  underneath. 
  

  

  Another 
  illustration 
  of 
  a 
  screening 
  effect 
  was 
  obtained 
  in 
  

   the 
  reading 
  taken 
  on 
  the 
  surface 
  of 
  the 
  ground 
  back 
  about 
  

   30 
  metres 
  from 
  the 
  opening 
  into 
  the 
  clay 
  bank. 
  At 
  this 
  

   station 
  no 
  direct 
  radiation 
  could 
  reach 
  the 
  instrument 
  Irom 
  

   the 
  shale, 
  and 
  the 
  radiation 
  from 
  the 
  clay 
  deposits 
  could 
  only 
  

   reach 
  it 
  after 
  passing 
  through 
  the 
  surface-layer 
  of 
  sandy 
  

   loam, 
  which 
  was 
  about 
  one 
  metre 
  thick. 
  The 
  reading 
  at 
  this 
  

   station 
  was 
  only 
  6'S2 
  ions 
  per 
  c.c. 
  per 
  sec. 
  From 
  this 
  low 
  

   value 
  it 
  was 
  evident 
  that 
  the 
  sandy 
  loam 
  contained 
  considerably 
  

   less 
  active 
  matter 
  than 
  the 
  clays 
  and 
  also 
  that 
  it 
  acted 
  as 
  a 
  

   screen 
  to 
  absorb 
  the 
  radiation 
  coming 
  from 
  the 
  clay 
  lying 
  

   below 
  it. 
  

  

  It 
  may 
  be 
  added, 
  in 
  regard 
  to 
  these 
  various 
  deposits, 
  that 
  

   it 
  was 
  the 
  shale 
  which 
  was 
  used 
  in 
  making 
  the 
  red-coloured 
  

   bricks 
  and 
  the 
  clays 
  in 
  making 
  the 
  light-coloured 
  ones. 
  

  

  V. 
  On 
  the 
  Penetrating 
  Radiation 
  from 
  the 
  Atmosphere. 
  

  

  In 
  several 
  previous 
  communications 
  by 
  one 
  of 
  us 
  * 
  and 
  by 
  

   0. 
  S. 
  Wright 
  f 
  , 
  attention 
  has 
  been 
  drawn 
  to 
  the 
  fact 
  that 
  the 
  

   ionization 
  in 
  a 
  closed 
  vessel 
  is 
  very 
  much 
  less 
  over 
  the 
  water 
  

   of 
  Lake 
  Ontario 
  than 
  it 
  is 
  at 
  points 
  on 
  the 
  neighbouring 
  

   land. 
  Further, 
  in 
  measurements 
  made 
  on 
  the 
  lake 
  with 
  a 
  

   zine 
  receiver 
  of 
  about 
  21 
  litres 
  capacity 
  and 
  a 
  Wilson 
  

   electrometer 
  the 
  value 
  of 
  " 
  q 
  " 
  has 
  been 
  shown 
  to 
  be 
  about 
  

   4*46 
  ions 
  per 
  c.c. 
  per 
  sec. 
  

  

  On 
  repeating 
  these 
  measurements 
  with 
  a 
  Wulf 
  electro- 
  

   meter 
  the 
  mean 
  of 
  a 
  number 
  of 
  sets 
  of 
  observations 
  gave 
  a 
  

   value 
  of 
  4*93 
  ions 
  per 
  c.c. 
  per 
  sec. 
  for 
  " 
  5," 
  which 
  is 
  slightly 
  

   higher 
  than 
  the 
  value 
  previously 
  obtained 
  with 
  the 
  larger 
  

   receiver. 
  These 
  observations 
  were 
  carried 
  out 
  on 
  a 
  small 
  

   skiff 
  about 
  2 
  kilometres 
  from 
  the 
  shore, 
  at 
  a 
  point 
  where 
  the 
  

   water 
  was 
  about 
  20 
  metres 
  deep. 
  

  

  In 
  a 
  second 
  set 
  of 
  observations 
  made 
  at 
  this 
  point 
  on 
  the 
  

   skiff' 
  the 
  electrometer 
  was 
  plac3d 
  for 
  protection 
  in 
  a 
  metal 
  

   box 
  of 
  aluminium-bronze 
  with 
  walls 
  a 
  little 
  over 
  one 
  centi- 
  

   metre 
  thick. 
  In 
  these 
  measurements 
  the 
  value 
  of 
  4*81 
  ions 
  

   per 
  c.c. 
  per 
  sec. 
  was 
  obtained 
  for 
  " 
  q". 
  

  

  In 
  a 
  third 
  set 
  the 
  metal 
  box 
  containing 
  the 
  electrometer 
  

   was 
  lowered 
  into 
  the 
  water 
  to 
  a 
  depth 
  of 
  about 
  eight 
  metres, 
  

   and 
  in 
  these 
  experiments 
  the 
  average 
  reading 
  obtained 
  was 
  

   4" 
  7 
  7 
  ions 
  per 
  c.c. 
  per 
  sec. 
  From 
  this 
  result 
  it 
  would 
  appear 
  

  

  * 
  Phys. 
  Rev. 
  vol. 
  xxvi. 
  No. 
  6, 
  p. 
  526 
  (1908). 
  

   t 
  Phil. 
  Mag. 
  ser. 
  6, 
  No. 
  17, 
  p. 
  295 
  (1909). 
  

  

  