﻿636 
  Messrs. 
  F. 
  Soddy 
  and 
  A. 
  S. 
  Russell 
  on 
  the 
  

  

  of 
  times, 
  the 
  rate 
  of 
  leak 
  gradually 
  increased, 
  considerably 
  

   at 
  first 
  and 
  then 
  less 
  rapidly, 
  until 
  a 
  maximum 
  rate 
  was 
  

   reached. 
  This 
  phenomenon 
  was 
  got 
  with 
  different 
  electro- 
  

   scopes, 
  different 
  absorbing 
  plates, 
  and 
  with 
  both 
  radium 
  and 
  

   uranium 
  X. 
  The 
  sign 
  of 
  the 
  charge 
  on 
  the 
  leaf 
  did 
  not 
  seem 
  

   to 
  produce 
  any 
  effect. 
  The 
  maximum 
  rate 
  of 
  leak 
  was 
  found 
  

   in 
  all 
  cases 
  to 
  be 
  about 
  12 
  per 
  cent, 
  greater 
  than 
  the 
  minimum. 
  

   The 
  cause 
  of 
  the 
  steady 
  increase 
  in 
  the 
  rate 
  of 
  leak 
  to 
  a 
  

   maximum 
  remains 
  unknown. 
  We 
  cannot 
  at 
  present 
  give 
  

   any 
  explanation 
  of 
  it. 
  In 
  certain 
  new 
  forms 
  of 
  ionization- 
  

   vessels 
  we 
  are 
  now 
  working 
  with 
  it 
  is 
  not 
  shown. 
  In 
  this 
  

   connexion 
  may 
  be 
  recalled 
  an 
  experiment 
  by 
  G. 
  Jaffe 
  (^Ann. 
  

   Phys, 
  1908, 
  XXV. 
  p. 
  271), 
  who 
  found 
  it 
  to 
  be 
  impossible 
  to 
  

   obtain 
  complete 
  saturation 
  in 
  air 
  at 
  atmospheric 
  pressure 
  

   ionized 
  by 
  the 
  7-rays 
  of 
  radium, 
  even 
  with 
  a 
  potential 
  gradient 
  

   of 
  5000 
  volts 
  per 
  cm. 
  Kleeman 
  (Phil. 
  Mag. 
  1907, 
  xiv. 
  

   p. 
  622) 
  also 
  called 
  attention 
  to 
  gradual 
  fluctuations 
  in 
  mag- 
  

   nitude 
  of 
  5 
  to 
  10 
  per 
  cent, 
  in 
  the 
  values 
  of 
  the 
  leaks 
  obtained 
  

   by 
  using 
  a 
  differential 
  method 
  with 
  two 
  ionization-chambers 
  

   and 
  a 
  steady 
  source 
  of 
  7-rays. 
  He 
  suggested 
  that 
  the 
  ema- 
  

   nation 
  might 
  be 
  coming 
  off 
  from 
  the 
  radium 
  salt 
  inter- 
  

   mittently, 
  causing 
  alterations 
  in 
  the 
  centre 
  of 
  origin 
  of 
  the 
  

   7-rays. 
  This 
  certainly 
  does 
  not 
  apply 
  to 
  our 
  case, 
  for 
  the 
  effect 
  

   is 
  shown 
  also 
  by 
  the 
  y-rays 
  of 
  uranium 
  X, 
  and 
  the 
  irregu- 
  

   larities 
  moreover 
  are 
  quite 
  definite. 
  The 
  effect 
  depends 
  on 
  

   the 
  maintenance 
  during 
  successive 
  observations 
  of 
  the 
  charge 
  

   on 
  the 
  leaf 
  system 
  ; 
  for 
  if 
  with 
  everything 
  in 
  place 
  the 
  

   whole 
  be 
  left 
  undisturbed 
  for 
  a 
  quarter 
  of 
  an 
  hour, 
  and 
  then 
  a 
  

   series 
  of 
  consecutive 
  observations 
  are 
  taken 
  without 
  pause, 
  the 
  

   minimum 
  leak 
  is 
  first 
  obtained, 
  and 
  this 
  gradually 
  increases 
  

   to 
  the 
  maximum. 
  Thus 
  in 
  one 
  experiment 
  6*7 
  mg. 
  of 
  radium 
  

   bromide 
  in 
  a 
  sealed 
  tube 
  was 
  placed 
  below 
  a 
  brass 
  electro- 
  

   scope, 
  the 
  base 
  of 
  which 
  consisted 
  of 
  ^'2^ 
  cm. 
  of 
  lead, 
  and 
  

   everything 
  was 
  left 
  for 
  ten 
  minutes. 
  Consecutive 
  observa- 
  

   tions, 
  then 
  taken 
  over 
  100 
  divisions 
  of 
  the 
  eyepiece 
  scale, 
  

   were, 
  in 
  divisions 
  per 
  minute, 
  111, 
  114, 
  118, 
  120, 
  120, 
  122, 
  

   123-5, 
  124, 
  124-2, 
  125, 
  125, 
  125. 
  If 
  now 
  the 
  radium 
  were 
  

   held 
  up 
  to 
  the 
  side 
  of 
  the 
  instrument 
  for 
  a 
  minute 
  without 
  

   recharging, 
  and 
  the 
  observations 
  repeated, 
  the 
  minimum 
  leak 
  

   was 
  again 
  obtained, 
  and 
  this 
  again 
  increased 
  to 
  the 
  maximum. 
  

   In 
  practice 
  it 
  is 
  easier 
  and 
  quicker 
  thus 
  to 
  obtain 
  the 
  

   minimum 
  leak 
  than 
  the 
  maximum 
  leak, 
  and 
  we 
  have 
  so 
  far 
  

   been 
  concerned 
  to 
  employ 
  a 
  method 
  of 
  working 
  which 
  shall 
  

   avoid 
  these 
  errors 
  and 
  give 
  consistent 
  results. 
  This 
  is 
  

   achieved 
  in 
  the 
  following 
  manner. 
  

  

  After 
  each 
  observation, 
  the 
  leaf 
  being 
  still 
  partially 
  charged, 
  

   6*7 
  mg. 
  of 
  radium 
  bromide 
  in 
  a 
  sealed 
  tube 
  is 
  placed 
  near 
  

  

  