﻿748 
  Prof. 
  McLennan 
  and 
  Mr. 
  McLeod 
  : 
  Measurement 
  

  

  s 
  on 
  

  

  the 
  Physical 
  Laboratory, 
  which 
  was 
  constructed 
  of 
  stone 
  and 
  

   white 
  brick, 
  and 
  as 
  these 
  values 
  were 
  uniformly 
  lower 
  than 
  

   those 
  obtained 
  in 
  the 
  residence 
  referred 
  to, 
  it 
  was 
  thought 
  

   that 
  possibly 
  the 
  higher 
  values 
  might 
  be 
  due 
  to 
  a 
  measurable 
  

   excess 
  of 
  radio-active 
  matter 
  contained 
  in 
  the 
  bricks 
  of 
  the 
  

   residential 
  structure. 
  

  

  As 
  the 
  bricks 
  for 
  both 
  structures 
  were 
  made 
  from 
  different 
  

   deposits 
  in 
  the 
  same 
  brick-yard 
  a 
  series 
  of 
  measurements 
  was 
  

   made 
  in 
  the 
  neighbourhood 
  of 
  these 
  different 
  deposits, 
  and 
  it 
  

   was 
  found 
  that 
  the 
  surmise 
  was 
  correct. 
  

  

  In 
  this 
  particular 
  brick-yard 
  the 
  surface-layer 
  is 
  a 
  sandy 
  

   loam 
  about 
  one 
  metre 
  thick 
  ; 
  below 
  these 
  there 
  is 
  a 
  series 
  of 
  

   strata 
  of 
  glacial 
  clays, 
  each 
  stratum 
  ranging 
  from 
  4 
  to 
  10 
  

   metres 
  in 
  thickness. 
  Below 
  the 
  clay 
  is 
  a 
  deposit 
  of 
  Lorraine 
  

   shale 
  some 
  250 
  metres 
  in 
  depth. 
  This 
  brick-yard, 
  which 
  has 
  

   been 
  worked 
  for 
  over 
  fifty 
  years, 
  now 
  consists 
  of 
  a 
  great 
  

   opening 
  in 
  the 
  face 
  of 
  a 
  hill 
  and 
  a 
  huge 
  cylindrical 
  cavity 
  

   in 
  front 
  of 
  this 
  opening 
  and 
  extending 
  down 
  into 
  the 
  shale. 
  

   The 
  depth 
  of 
  the 
  cavity 
  at 
  present 
  is 
  about 
  25 
  metres 
  and 
  

   the 
  length 
  of 
  its 
  diameter 
  is 
  about 
  the 
  same. 
  The 
  sides 
  of 
  

   the 
  opening 
  in 
  the 
  face 
  of 
  the 
  hill 
  as 
  it 
  stands 
  consist 
  of 
  a 
  

   series 
  of 
  terraces, 
  each 
  of 
  which 
  consists 
  of 
  one 
  particular 
  

   deposit 
  of 
  clay. 
  This 
  system 
  of 
  terraces 
  in 
  the 
  clays, 
  it 
  will 
  

   be 
  seen, 
  provided 
  an 
  excellent 
  means 
  of 
  investigating 
  the 
  

   radiation 
  from 
  each 
  deposit 
  in 
  turn, 
  and 
  when 
  readings 
  were 
  

   taken 
  on 
  each 
  terrace 
  it 
  was 
  found 
  that 
  these 
  gave 
  values 
  for 
  

   " 
  q 
  " 
  extending 
  from 
  8 
  to 
  9 
  ions 
  per 
  c.c. 
  per 
  sec. 
  with 
  a 
  mean 
  

   value 
  of 
  about 
  8*84. 
  

  

  In 
  the 
  shale 
  pit, 
  however, 
  much 
  higher 
  readings 
  were 
  

   obtained. 
  These 
  were 
  taken 
  at 
  different 
  points 
  on 
  the 
  base 
  

   of 
  the 
  pit 
  and 
  on 
  a 
  number 
  of 
  ledges 
  which 
  were 
  accessible. 
  

   The 
  values 
  found 
  for 
  " 
  g" 
  in 
  the 
  shale-pit 
  ranged 
  from 
  12 
  to 
  

   14*8 
  ions 
  per 
  c.c. 
  per 
  sec, 
  the 
  lower 
  values 
  being 
  obtained 
  

   when 
  the 
  stations 
  were 
  taken 
  at 
  points 
  near 
  surfaces 
  which 
  

   were 
  weathered, 
  and 
  the 
  higher 
  ones 
  when 
  the 
  observation 
  

   stations 
  were 
  close 
  to 
  places 
  where 
  the 
  surface 
  of 
  the 
  shale 
  

   had 
  been 
  recently 
  exposed. 
  

  

  As 
  an 
  illustration 
  of 
  how 
  definitely 
  the 
  comparatively 
  

   strong 
  radiation 
  from 
  the 
  shale 
  producing 
  the 
  high 
  ionization 
  

   was 
  localized, 
  a 
  particular 
  measurement 
  may 
  be 
  cited. 
  

  

  The 
  stratum 
  immediately 
  above 
  the 
  shale 
  consisted 
  partly 
  

   of 
  sand 
  and 
  partly 
  of 
  clay. 
  At 
  one 
  particular 
  point 
  this 
  

   layer 
  was 
  about 
  2*5 
  metres 
  thick, 
  and 
  it 
  extended 
  up 
  to 
  the 
  

   face 
  of 
  the 
  opening 
  of 
  the 
  pit 
  in 
  the 
  shale. 
  The 
  reading 
  

   obtained 
  on 
  this 
  layer 
  at 
  a 
  point 
  about 
  6 
  metres 
  back 
  from 
  

   the 
  edge 
  was 
  only 
  8*67 
  ions 
  per 
  c.c. 
  per 
  sec, 
  which 
  shows 
  

  

  