﻿478 
  Mr. 
  J. 
  S. 
  Townsend 
  on 
  Applications 
  of 
  

  

  Let 
  us 
  find 
  the 
  distance 
  of 
  a 
  particle 
  x 
  which 
  in 
  a 
  time 
  

   t 
  would 
  reach 
  the 
  side 
  : 
  we 
  have 
  

  

  f°10 
  9 
  2 
  _ 
  10 
  W 
  

   t= 
  — 
  ! 
  -^ 
  x 
  ax 
  — 
  

  

  

  ro 
  12 
  36 
  ' 
  

  

  when 
  t= 
  A 
  we 
  have 
  x 
  = 
  ^_ 
  _ 
  . 
  

  

  So 
  that 
  in 
  the 
  case 
  we 
  are 
  considering 
  a 
  layer 
  of 
  1*5 
  x 
  10~~ 
  3 
  

   thickness 
  of 
  the 
  gas 
  would 
  have 
  its 
  conductivity 
  destroyed 
  

   in 
  jq 
  of 
  a 
  second 
  owing 
  to 
  the 
  mutual 
  attraction 
  between 
  each 
  

   ion 
  and 
  its 
  image. 
  The 
  ratio 
  of 
  this 
  volume 
  to 
  the 
  total 
  

  

  volume 
  of 
  the 
  tube 
  is 
  , 
  which 
  becomes 
  3 
  x 
  10 
  ~ 
  2 
  

  

  irr 
  

  

  when 
  r='l. 
  Hence 
  in 
  this 
  case 
  the 
  loss 
  of 
  conductivity 
  due 
  

   to 
  the 
  carriers 
  attracting 
  themselves 
  up 
  to 
  the 
  sides 
  is 
  small 
  

   compared 
  with 
  the 
  loss 
  of 
  conductivity 
  due 
  to 
  diffusion. 
  

  

  7. 
  When 
  there 
  is 
  an 
  excess 
  of 
  carriers 
  charged 
  with 
  elec- 
  

   tricity 
  of 
  one 
  kind 
  the 
  gas 
  not 
  only 
  conducts 
  but 
  exhibits 
  the 
  

   properties 
  of 
  a 
  charged 
  body. 
  The 
  motion 
  of 
  the 
  carriers 
  in 
  

   such 
  a 
  gas 
  is 
  somewhat 
  complicated, 
  as 
  both 
  the 
  diffusion 
  and 
  

   the 
  effect 
  of 
  mutual 
  repulsion 
  have 
  to 
  be 
  taken 
  into 
  account. 
  

   When 
  the 
  charge 
  per 
  c. 
  c. 
  is 
  small 
  we 
  can 
  leave 
  the 
  latter 
  

   effect 
  out 
  of 
  account 
  and 
  consider 
  only 
  the 
  diffusion. 
  The 
  equa- 
  

   tions 
  (5) 
  Section 
  II. 
  can 
  then 
  be 
  applied 
  to 
  charged 
  gases, 
  

   and 
  we 
  can 
  look 
  upon 
  them 
  as 
  particular 
  cases 
  of 
  conducting 
  

   gases. 
  The 
  properties 
  of 
  these 
  gases 
  vary 
  in 
  many 
  ways 
  in 
  

   regard 
  to 
  their 
  power 
  of 
  retaining 
  their 
  conductivity; 
  thus 
  

   some 
  of 
  them 
  can 
  be 
  passed 
  along 
  tubing, 
  bubbled 
  though 
  

   liquids, 
  or 
  sent 
  through 
  gauze 
  or 
  wool 
  without 
  losing 
  more 
  

   than 
  from 
  20 
  to 
  50 
  per 
  cent, 
  of 
  their 
  conductivity, 
  whereas 
  

   others 
  are 
  made 
  perfect 
  non-conductors 
  when 
  similarly 
  treated. 
  

   The 
  equations 
  (5) 
  Section 
  II. 
  show 
  that 
  rate 
  of 
  loss 
  of 
  con- 
  

   ductivity 
  by 
  coming 
  into 
  contact 
  with 
  conductors 
  increases 
  

   very 
  rapidly 
  with 
  V 
  the 
  velocity 
  of 
  the 
  carrier 
  under 
  an 
  elec- 
  

   tromotive 
  force 
  of 
  1 
  volt 
  per 
  centimetre. 
  We 
  should, 
  there- 
  

   fore, 
  expect 
  that 
  for 
  those 
  gases 
  which 
  retain 
  their 
  conduc- 
  

   tivity 
  after 
  bubbling 
  through 
  liquids 
  &c. 
  the 
  value 
  of 
  V 
  is 
  

   small 
  compared 
  with 
  its 
  value 
  for 
  gases 
  which 
  retain 
  none 
  of 
  

   their 
  conductivity 
  after 
  similar 
  treatment. 
  In 
  support 
  of 
  this 
  

   explanation 
  we 
  have 
  the 
  following 
  results 
  : 
  — 
  The 
  conductivity 
  

   of 
  a 
  gas 
  which 
  has 
  been 
  made 
  a 
  conductor 
  by 
  means 
  of 
  Hontgen 
  

   rays 
  is 
  destroyed 
  by 
  passing 
  the 
  gas 
  through 
  wool 
  or 
  bubbling 
  

   through 
  sulphuric 
  acid, 
  and 
  the 
  velocity 
  of 
  the 
  carrier 
  under 
  

   an 
  electromotive 
  force 
  of 
  a 
  volt 
  per 
  centimetre 
  is 
  (for 
  air) 
  

  

  