﻿from 
  Actinium 
  in 
  Uniform 
  Electric 
  Fields. 
  751 
  

  

  From 
  Carr's 
  results 
  * 
  it 
  is 
  known 
  that 
  460 
  volts 
  is 
  the 
  

   spark 
  potential 
  for 
  a 
  pressure 
  of 
  9 
  mm. 
  with 
  the 
  plates 
  

   2 
  mm. 
  apart. 
  Consequently 
  for 
  all 
  voltages 
  above 
  450 
  the 
  

   exposures 
  were 
  made 
  with 
  a 
  current 
  passing 
  between 
  the 
  

   plates. 
  This 
  would 
  mean 
  that 
  a 
  large 
  number 
  of 
  ions 
  were 
  

   present 
  between 
  the 
  terminals 
  during 
  the 
  exposure 
  ; 
  and 
  it 
  

   is 
  interesting 
  to 
  note 
  that 
  the 
  presence 
  of 
  these 
  ions 
  resulted 
  

   in 
  a 
  considerable 
  increase 
  in 
  the 
  activity 
  of 
  the 
  two 
  plates. 
  

   But 
  just 
  how 
  this 
  result 
  is 
  brought 
  about 
  is 
  difficult 
  to 
  explain 
  

   as 
  the 
  exact 
  relation 
  which 
  exists 
  between 
  the 
  number 
  of 
  ions 
  

   present 
  in 
  a 
  gas 
  and 
  the 
  active 
  deposit 
  particles 
  is 
  still 
  obscure, 
  

   and 
  it 
  will 
  be 
  necessary 
  to 
  make 
  additional 
  experiments 
  before 
  

   the 
  question 
  can 
  be 
  cleared 
  up. 
  

  

  One 
  of 
  the 
  main 
  questions 
  left 
  open 
  in 
  the 
  present 
  investi- 
  

   gation 
  is 
  the 
  cause 
  of 
  the 
  decrease 
  in 
  activity 
  of 
  the 
  electrodes 
  

   in 
  the 
  three 
  different 
  gases 
  at 
  the 
  low 
  pressures. 
  

  

  It 
  seems 
  fair 
  to 
  conclude 
  from 
  the 
  results 
  that 
  in 
  the 
  region 
  

   of 
  low 
  pressures 
  there 
  was 
  a 
  gradual 
  decrease 
  both 
  in 
  the 
  

   excess 
  of 
  positively 
  charged 
  deposit 
  particles, 
  and 
  also 
  in 
  

   the 
  total 
  number 
  of 
  the 
  particles 
  present 
  in 
  the 
  space 
  between 
  

   the 
  electrodes. 
  

  

  The 
  experiments, 
  however, 
  do 
  not 
  show 
  whether 
  this 
  de- 
  

   crease 
  was 
  due 
  to 
  a 
  falling 
  off 
  in 
  the 
  amount 
  of 
  emanation 
  

   coming 
  into 
  this 
  space 
  or 
  in 
  the 
  amount 
  of 
  emanation 
  and 
  

   deposit 
  particles 
  passing 
  directly 
  through 
  it 
  into 
  the 
  outer 
  

   chamber 
  of 
  the 
  apparatus. 
  From 
  the 
  fact 
  that 
  at 
  the 
  low 
  

   pressures 
  as 
  well 
  as 
  the 
  high 
  ones 
  the 
  activity 
  fell 
  away 
  as 
  

   the 
  distance 
  of 
  the 
  salt 
  from 
  the 
  electrodes 
  was 
  increased, 
  

   it 
  would 
  seem 
  that 
  the 
  decrease 
  mentioned 
  above 
  was 
  due 
  to 
  

   decrease 
  in 
  the 
  amount 
  of 
  emanation 
  entering 
  the 
  space 
  

   between 
  the 
  electrodes. 
  The 
  matter, 
  however, 
  is 
  not 
  clear, 
  

   and 
  consequently 
  the 
  explanation 
  of 
  the 
  decrease 
  must 
  

   be 
  deferred 
  until 
  the 
  scope 
  of 
  the 
  investigation 
  can 
  be 
  

   extended. 
  

  

  In 
  conclusion 
  I 
  desire 
  to 
  thank 
  Professor 
  McLennan 
  for 
  

   the 
  selection 
  of 
  the 
  subject, 
  and 
  for 
  the 
  very 
  helpful 
  sugges- 
  

   tions 
  be 
  has 
  offered 
  from 
  time 
  to 
  time 
  during 
  the 
  investigation. 
  

  

  Physical 
  Laboratory, 
  

   University 
  of 
  Toronto. 
  

   May 
  26th, 
  1909. 
  

  

  • 
  rhil. 
  Trans, 
  cci. 
  pp. 
  403-433. 
  

  

  