﻿574 
  Prof. 
  J. 
  S. 
  Townsend 
  on 
  the 
  Conductivity 
  

  

  not 
  arise 
  from 
  the 
  collisions 
  of 
  the 
  negative 
  ions. 
  The 
  curve 
  

   for 
  this 
  gas 
  obtained 
  with 
  Rontgen 
  rays 
  practically 
  coincides 
  

   with 
  that 
  obtained 
  with 
  ultra-violet 
  light 
  over 
  a 
  large 
  range 
  

   of 
  forces. 
  It 
  lies 
  slightly 
  above 
  the 
  latter 
  curve. 
  

  

  We 
  cannot 
  expect 
  a 
  closer 
  resemblance 
  between 
  the 
  two 
  

   sets 
  of 
  curves 
  as 
  there 
  are 
  other 
  effects, 
  besides 
  the 
  one 
  I 
  

   have 
  mentioned, 
  which 
  make 
  it 
  difficult 
  to 
  obtain 
  very 
  

   accurate 
  determinations 
  of 
  the 
  quantity 
  ex. 
  with 
  Rontgen 
  rays. 
  

   The 
  initial 
  distribution 
  of 
  ions 
  is 
  not 
  uniform 
  between 
  the 
  

   plates, 
  and 
  the 
  secondary 
  radiation 
  carries 
  a 
  charge 
  which 
  

  

  X 
  

  

  introduces 
  complications. 
  The 
  larger 
  values 
  of 
  — 
  can 
  only 
  

  

  be 
  obtained 
  from 
  experiments 
  at 
  low 
  press 
  ures, 
  and 
  in 
  these 
  

   cases 
  the 
  initial 
  ionization 
  is 
  small 
  and 
  of 
  the 
  same 
  order 
  as 
  

   the 
  charge 
  carried 
  by 
  the 
  secondary 
  radiation. 
  This 
  method 
  

   is 
  therefore 
  not 
  suited 
  for 
  the 
  determination 
  of 
  the 
  larger 
  

  

  values 
  of 
  - 
  . 
  It 
  ought 
  to 
  be 
  easy 
  to 
  determine 
  these 
  numbers 
  

  

  with 
  ultra-violet 
  light, 
  and 
  I 
  hope 
  to 
  continue 
  the 
  experi- 
  

   ments 
  with 
  air 
  and 
  carbonic 
  acid, 
  so 
  as 
  to 
  obtain 
  the 
  maximum 
  

   values 
  of 
  a 
  for 
  these 
  gases. 
  

  

  The 
  curve 
  which 
  I 
  have 
  given 
  for 
  hydrogen 
  practically 
  

  

  reaches 
  the 
  maximum 
  value 
  of 
  — 
  , 
  which 
  is 
  about 
  5'2. 
  

  

  p 
  X 
  

  

  8. 
  The 
  results 
  obtained 
  with 
  the 
  smaller 
  values 
  of 
  — 
  are 
  

  

  . 
  P 
  

   sufficient 
  to 
  lead 
  to 
  the 
  conclusion 
  that 
  the 
  negative 
  ions 
  

  

  generated 
  in 
  a 
  gas 
  by 
  the 
  motion 
  of 
  the 
  zinc 
  ions 
  set 
  free 
  by 
  

   ultra-violet 
  light 
  are 
  identical 
  with 
  the 
  ions 
  produced 
  by 
  

   Rontgen 
  rays 
  in 
  the 
  same 
  gas. 
  The 
  experiments 
  with 
  ultra- 
  

   violet 
  light 
  show 
  that 
  the 
  negative 
  ions 
  produced 
  in 
  any 
  gas 
  

   by 
  the 
  motion 
  of 
  the 
  ions 
  from 
  the 
  zinc 
  plate 
  are 
  identical 
  

   with 
  the 
  zinc 
  ions 
  themselves. 
  Consequently 
  the 
  negative 
  

   ions 
  produced 
  by 
  Rontgen 
  rays 
  in 
  any 
  of 
  these 
  gases 
  are 
  

   exactly 
  the 
  same 
  as 
  the 
  ions 
  set 
  free 
  by 
  ultra-violet 
  light 
  from 
  

   a 
  zinc 
  plate. 
  

  

  We 
  are 
  also 
  led 
  to 
  conclude 
  from 
  the 
  experiments, 
  that 
  

   these 
  negative 
  ions 
  are 
  small 
  compared 
  with 
  the 
  molecules 
  of 
  

   any 
  of 
  the 
  gases. 
  A 
  molecule 
  of 
  a 
  gas 
  makes 
  more 
  than 
  

   four 
  times 
  the 
  number 
  of 
  collisions 
  that 
  a 
  negative 
  ion 
  makes 
  

   in 
  going 
  through 
  the 
  same 
  distance 
  of 
  the 
  gas 
  at 
  a 
  given 
  

   pressure. 
  Also, 
  the 
  property 
  which 
  they 
  possess 
  of 
  generating 
  

   new 
  ions 
  does 
  not 
  belong 
  to 
  the 
  positive 
  ions 
  under 
  similar 
  

   conditions 
  of 
  force 
  and 
  pressure. 
  These 
  properties 
  of 
  the 
  

   negative 
  ion 
  show 
  that 
  it 
  must 
  be 
  small 
  both 
  as 
  regards 
  

  

  