﻿920 
  Dr. 
  Norman 
  Campbell 
  on 
  a 
  

  

  8. 
  These 
  measurements 
  were 
  made 
  with 
  polonium 
  as 
  a 
  

   source 
  o£ 
  a 
  rays 
  ; 
  no 
  difference 
  could 
  be 
  detected 
  if 
  it 
  was 
  

   replaced 
  by 
  ThO, 
  or 
  when 
  absorbing 
  sheets 
  were 
  placed 
  

   between 
  the 
  source 
  and 
  the 
  chamber. 
  Experiments 
  were 
  

   also 
  made 
  in 
  which 
  X 
  rays 
  were 
  used 
  in 
  place 
  of! 
  a 
  rays, 
  the 
  

   intensity 
  of 
  the 
  rays 
  and 
  their 
  hardness 
  being 
  varied 
  by 
  

   means 
  of 
  absorbing 
  screens. 
  No 
  dependence 
  of 
  the 
  maximum 
  

   values 
  of 
  i/I 
  on 
  the 
  nature 
  or 
  the 
  intensity 
  of 
  the 
  rays 
  could 
  

   be 
  detected*, 
  but 
  the 
  range 
  of 
  pressure 
  over 
  which 
  the 
  

   maximum 
  values 
  of 
  i/I 
  were 
  obtained 
  extended 
  notably 
  

   further 
  in 
  the 
  direction 
  of 
  high 
  pressures 
  when 
  X 
  rays 
  were 
  

   used, 
  especially 
  when 
  V 
  was 
  small. 
  The 
  magnitude 
  of 
  I 
  for 
  

   a 
  given 
  value 
  of 
  p 
  and 
  I 
  was 
  not 
  very 
  different 
  in 
  the 
  ex- 
  

   periments 
  with 
  the 
  different 
  kinds 
  of 
  rays. 
  

  

  9. 
  These 
  results 
  were 
  obtained 
  before 
  the 
  theory 
  of 
  § 
  2 
  had 
  

   been 
  worked 
  out, 
  but 
  it 
  was 
  immediately 
  obvious 
  that 
  they 
  

   could 
  not 
  be 
  reconciled 
  with 
  the 
  theory 
  of 
  conduction 
  which 
  

   regards 
  only 
  recombination. 
  According 
  to 
  that 
  theory, 
  i/I 
  

   is 
  approximately 
  a 
  function 
  of 
  V/V 
  p 
  , 
  where 
  

  

  Y 
  P 
  =21l,y/ 
  a 
  .(k 
  i 
  + 
  k 
  1 
  ) 
  

  

  {a 
  is 
  the 
  coefficient 
  of 
  recombination.) 
  Now 
  (k 
  x 
  -\- 
  £ 
  2 
  )~V 
  p, 
  

   a 
  increases 
  somewhat 
  with 
  the 
  pressure 
  but 
  is 
  almost 
  inde- 
  

   pendent 
  of 
  the 
  nature 
  of 
  the 
  gas, 
  Ix 
  ql, 
  ^p. 
  Hence 
  for 
  

   changes 
  of 
  pressure, 
  Yp 
  should 
  increase 
  with 
  p 
  more 
  rapidly 
  

   than 
  p 
  3/2 
  , 
  for 
  changes 
  of 
  I 
  it 
  should 
  increase 
  as 
  I 
  2 
  , 
  for 
  

  

  q1/2 
  

  

  changes 
  in 
  the 
  gas 
  should 
  change 
  ns~~- 
  — 
  r 
  , 
  and 
  for 
  changes 
  

  

  of 
  q 
  should 
  change 
  as 
  q 
  1 
  / 
  2 
  . 
  The 
  constancy 
  of 
  the 
  relation 
  of 
  

   i/I 
  to 
  Y 
  while 
  these 
  quantities 
  vary 
  over 
  the 
  range 
  observed 
  

   in 
  these 
  experiments 
  is 
  quite 
  irreconcilable 
  with 
  the 
  view 
  

   that 
  i/I 
  is 
  determined 
  by 
  Y/Y 
  p 
  . 
  

  

  On 
  the 
  other 
  hand, 
  if 
  the 
  experimental 
  conditions 
  can 
  be 
  

   supposed 
  to 
  be 
  such 
  that 
  the 
  theory 
  leading 
  to 
  (15) 
  is 
  

   applicable, 
  the 
  identity 
  of 
  the 
  relation 
  of 
  i/l 
  to 
  V 
  for 
  all 
  

   pressures, 
  gases, 
  and 
  distances 
  between 
  the 
  electrodes 
  and 
  

   intensities 
  of 
  ionization 
  is 
  at 
  once 
  explained. 
  Moreover, 
  there 
  

   is 
  quantitative 
  agreement 
  between 
  theory 
  and 
  experiment. 
  

   In 
  the 
  case 
  of 
  both 
  air 
  and 
  hydrogen 
  it 
  is 
  possible 
  to 
  find 
  a 
  

   small 
  range 
  of 
  pressure 
  within 
  which 
  i/I 
  has 
  its 
  maximum 
  

   value 
  for 
  both 
  small 
  and 
  large 
  values 
  of 
  V. 
  The 
  following- 
  

   table 
  gives 
  these 
  values 
  ; 
  the 
  figures 
  are 
  the 
  means 
  obtained 
  

  

  * 
  The 
  greatest 
  difference 
  in 
  the 
  value 
  of 
  i/I 
  which 
  could 
  possibly 
  have 
  

   escaped 
  detection 
  varied 
  from 
  0005 
  when 
  V>4 
  to 
  0015 
  when 
  V=0\L. 
  

  

  