﻿Experiments 
  with 
  the 
  Active 
  Deposit 
  of 
  Thorium. 
  357 
  

  

  interval 
  between 
  succeeding 
  observations 
  and 
  this 
  first 
  

   observation. 
  Column 
  II. 
  gives 
  the 
  deflexion 
  of 
  the 
  electro- 
  

   meter-needle 
  per 
  minute 
  as 
  deduced 
  from 
  observations 
  at 
  

  

  Table 
  I. 
  

  

  Interval 
  since 
  

   1st 
  observation. 
  

  

  Drift 
  of 
  electrometer 
  

  

  needle, 
  

   cm. 
  scale 
  divs./min. 
  

  

  Ionization 
  in 
  either 
  

  

  chamber, 
  

   cm. 
  scale 
  divs./min. 
  

  

  Percentage 
  

   disturbance 
  

   of 
  balance. 
  

  

  hrs. 
  0-0 
  rain. 
  

  

  -1-3 
  

  

  1400 
  

  

  -o-i 
  

  

  „ 
  40-5 
  ., 
  

  

  -0-3 
  

  

  870 
  

  

  -0-035 
  

  

  „ 
  54-5 
  „ 
  

  

  -o-i 
  

  

  740 
  

  

  -0-015 
  

  

  lhr. 
  12 
  ,. 
  

  

  -0-3 
  

  

  600 
  

  

  -0-05 
  

  

  „ 
  41 
  „ 
  

  

  -0-2 
  

  

  430 
  

  

  -0-04 
  

  

  2 
  hrs. 
  5 
  

  

  -002 
  

  

  330 
  

  

  -o-oi 
  

  

  3 
  „ 
  58 
  ,. 
  

  

  -o-i 
  

  

  90 
  

  

  -0-12 
  

  

  5 
  ., 
  „ 
  

  

  -01 
  

  

  43 
  

  

  -0-23 
  

  

  intervals 
  o£ 
  one 
  minute 
  for 
  five 
  minutes. 
  There 
  were, 
  of 
  

   course, 
  considerable 
  probability 
  fluctuations, 
  but 
  the 
  mean 
  

   position 
  was 
  taken 
  in 
  each 
  case. 
  Column 
  III. 
  gives 
  the 
  

   ionization 
  in 
  either 
  chamber 
  as 
  deduced 
  from 
  the 
  curve 
  drawn 
  

   through 
  several 
  observations 
  as 
  the 
  decay 
  proceeded. 
  

   Column 
  IV. 
  gives 
  the 
  percentage 
  disturbance 
  of 
  the 
  balance. 
  

   In 
  these 
  observations 
  the 
  barometric 
  pressure 
  and 
  tempe- 
  

   rature 
  were 
  approximately 
  constant 
  during 
  the 
  experiment, 
  

   otherwise 
  a 
  calculable 
  correction 
  would 
  have 
  been 
  necessary 
  

   owing 
  to 
  the 
  alterations 
  in 
  the 
  ranges 
  of 
  the 
  a 
  particles 
  

   according 
  to 
  the 
  density 
  of 
  the 
  air. 
  

  

  It 
  will 
  be 
  seen 
  that 
  the 
  balance 
  does 
  not 
  change 
  by 
  more 
  

   than 
  0*3 
  per 
  cent, 
  in 
  five 
  hours. 
  Therefore, 
  since 
  the 
  

   a 
  particles 
  of 
  range 
  4*8 
  cm. 
  contribute 
  half 
  the 
  ionization 
  in 
  

   the 
  first 
  chamber 
  the 
  ratio 
  of 
  the 
  numbers 
  of 
  particles 
  of 
  the 
  

   two 
  ranges 
  does 
  not 
  alter 
  by 
  more 
  than 
  06 
  per 
  cent. 
  

  

  Taking 
  the 
  period 
  of 
  either 
  product, 
  say 
  I., 
  as 
  60*5 
  mins., 
  

   i.e. 
  X^O'687 
  hour 
  - 
  1 
  . 
  

  

  In 
  5 
  hours 
  activity 
  of 
  I. 
  falls 
  to 
  a 
  fraction 
  e~ 
  5kl 
  } 
  

  

  .'. 
  ,* 
  5 
  „ 
  „ 
  II. 
  „ 
  „ 
  „ 
  «-^x(l±-006) 
  

  

  — 
  e 
  -oKi 
  g 
  g±-006 
  

  

  — 
  g-5(Ai±-0012^ 
  

  

  \ 
  2 
  =\ 
  1= 
  h-0012, 
  

  

  \ 
  2 
  -\ 
  1 
  /\ 
  1 
  =± 
  -0012/0-687 
  = 
  1/570, 
  

  

  i. 
  e. 
  the 
  transformation 
  constants 
  are 
  the 
  same 
  to 
  within 
  

   1 
  part 
  in 
  570. 
  

  

  