﻿378 
  

  

  Prof. 
  McLennan 
  and 
  Mr. 
  Kennedy 
  

  

  tlie 
  

  

  no 
  means 
  warrantable; 
  and 
  from 
  the 
  results 
  of 
  additional 
  

   measurements 
  it 
  has 
  been 
  found 
  necessary 
  to 
  modify 
  the 
  

   conclusions 
  mentioned 
  in 
  the 
  earlier 
  notices. 
  

  

  In 
  measuring 
  and 
  comparing 
  the 
  activities 
  of 
  the 
  different 
  

   salts, 
  these 
  were 
  each 
  spread 
  out 
  in 
  turn 
  in 
  uniform 
  layers 
  

   on 
  a 
  shallow 
  tray 
  w 
  T 
  hich 
  was 
  placed 
  on 
  the 
  bottom 
  of 
  the 
  

  

  ionizing 
  chamber 
  shown 
  in 
  fig. 
  1, 
  

  

  which 
  w 
  r 
  as 
  40 
  cm. 
  long, 
  

  

  Fio-. 
  1. 
  

  

  '///////, 
  

  

  7ZZ7?77, 
  

  

  26 
  cm. 
  wide, 
  and 
  28 
  cms. 
  deep. 
  The 
  saturation 
  currents 
  

   through 
  the 
  air 
  in 
  the 
  chamber 
  were 
  measured 
  with 
  a 
  sensi- 
  

   tive 
  quadrant 
  electrometer, 
  and 
  were 
  taken 
  as 
  measures 
  of 
  

   the 
  activities 
  of 
  the 
  different 
  salts. 
  

  

  II. 
  Relation 
  of 
  Activity 
  to 
  Area 
  of 
  Salt 
  exposed. 
  

  

  Before 
  proceeding 
  with 
  the 
  examination 
  of 
  the 
  different 
  

   salts 
  some 
  preliminary 
  measurements 
  were 
  made 
  on 
  the 
  

   activity 
  of 
  potassium 
  sulphate 
  when 
  different 
  areas 
  of 
  a 
  layer 
  

   of 
  this 
  salt 
  were 
  exposed 
  to 
  the 
  air 
  in 
  the 
  chamber. 
  A 
  layer 
  

   of 
  the 
  salt 
  some 
  6 
  mm. 
  in 
  thickness 
  w 
  7 
  as 
  placed 
  in 
  the 
  tray 
  

   mentioned 
  above, 
  which 
  was 
  35 
  cms. 
  long 
  and 
  18 
  cms. 
  wide, 
  

   and 
  then 
  covered 
  with 
  a 
  thick 
  plate 
  of 
  metal 
  divided 
  into 
  

   sections 
  18 
  cms. 
  long, 
  and 
  5 
  cms. 
  wide. 
  These 
  sections 
  were, 
  

   one 
  after 
  another, 
  removed 
  from 
  the 
  tray, 
  so 
  that 
  larger 
  and 
  

   larger 
  areas 
  of 
  the 
  salt 
  were 
  left 
  exposed 
  to 
  the 
  air 
  in 
  the 
  

   chamber. 
  The 
  saturation 
  current 
  corresponding 
  to 
  each 
  

   area 
  was 
  measured, 
  and 
  the 
  values 
  which 
  are 
  given 
  in 
  Table 
  I. 
  

   and 
  plotted 
  in 
  fig. 
  2, 
  show 
  that 
  the 
  saturation 
  currents 
  were 
  

  

  