﻿672 
  Prof. 
  J. 
  J. 
  Thomson 
  on 
  

  

  combination 
  does 
  not 
  take 
  place. 
  We 
  have 
  seen 
  that 
  the 
  

   particles 
  in 
  the 
  Canal 
  strahlen 
  have 
  a 
  velocity 
  of 
  the 
  order 
  

   of 
  2 
  x 
  10 
  s 
  cm. 
  /sec. 
  With 
  a 
  velocity 
  snch 
  as 
  this 
  their 
  kinetic 
  

   energy 
  would 
  be 
  equal 
  to 
  the 
  mean 
  kinetic 
  energy 
  of 
  the 
  

   molecules 
  of 
  a 
  gas 
  at 
  a 
  temperature 
  of 
  many 
  hundred 
  thousand 
  

   degrees 
  absolute; 
  and 
  though, 
  as 
  I 
  have 
  shown 
  in 
  ' 
  Conduction 
  

   of 
  Electricity 
  through 
  Gases/ 
  2nd 
  edition, 
  p. 
  360, 
  a 
  positive 
  

   ion 
  might 
  be 
  expected 
  to 
  combine 
  with 
  a 
  corpuscle 
  if 
  its 
  

   velocity 
  were 
  but 
  a 
  little 
  less 
  than 
  this, 
  it 
  would 
  not 
  be 
  likely 
  

   to 
  do 
  so 
  with 
  an 
  uncharged 
  molecule 
  where 
  the 
  attraction 
  

   would 
  be 
  very 
  much 
  less. 
  If 
  we 
  take 
  the 
  case 
  of 
  a 
  positive 
  

   ion 
  of 
  mass 
  ?n 
  projected 
  with 
  a 
  velocity 
  V 
  at 
  right 
  angles 
  to 
  

   the 
  line 
  joining 
  it 
  with 
  a 
  molecule 
  of 
  mass 
  M, 
  and 
  at 
  a 
  given 
  

   distance 
  from 
  it, 
  the 
  condition 
  that 
  the 
  ion 
  should 
  be 
  able 
  to 
  

   get 
  away 
  from 
  the 
  molecule 
  is 
  that 
  

  

  mV*. 
  M 
  

  

  should 
  be 
  greater 
  than 
  a 
  certain 
  quantity 
  depending 
  on 
  the 
  

   force 
  between 
  the 
  molecules 
  and 
  the 
  ion 
  and 
  the 
  apsidal 
  

   distance 
  between 
  them. 
  Kow 
  if 
  the 
  force 
  were 
  independent 
  

   of 
  the 
  mass 
  of 
  the 
  molecule, 
  we 
  see 
  that 
  it 
  would 
  require 
  a 
  

   greater 
  value 
  of 
  mV 
  2 
  to 
  separate 
  the 
  ion 
  from 
  the 
  molecule, 
  

   when 
  M 
  is 
  small 
  compared 
  with 
  m, 
  than 
  when 
  it 
  is 
  large. 
  Thus 
  

   if 
  the 
  kinetic 
  energy 
  of 
  the 
  ions 
  were 
  gradually 
  to 
  diminish 
  say 
  

   by 
  collisions 
  with 
  the 
  molecules, 
  then 
  if 
  there 
  were 
  molecules 
  

   of 
  different 
  masses 
  in 
  the 
  gas 
  through 
  which 
  the 
  Canalstrahlen 
  

   are 
  moving, 
  combination 
  would 
  occur 
  first 
  with 
  the 
  molecules 
  

   of 
  smallest 
  mass, 
  while 
  the 
  heaviest 
  molecules 
  would 
  be 
  the 
  

   last 
  to 
  combine. 
  The 
  lightest 
  molecules 
  would 
  thus 
  have 
  the 
  

   first 
  pick 
  of 
  the 
  ions, 
  which 
  would 
  therefore 
  tend 
  to 
  be 
  

   absorbed 
  by 
  the 
  lightest 
  gases. 
  The 
  force 
  between 
  an 
  ion 
  

   and 
  a 
  molecule 
  is 
  proportional 
  to 
  the 
  volume 
  of 
  the 
  molecule 
  ; 
  

   and 
  if 
  the 
  volume 
  of 
  a 
  molecule 
  were 
  to 
  increase 
  as 
  rapidly 
  

   as 
  its 
  mass, 
  the 
  preceding 
  considerations 
  would 
  not 
  be 
  valid. 
  

   We 
  have 
  every 
  reason, 
  however, 
  to 
  believe 
  that 
  the 
  changes 
  in 
  

   the 
  volume 
  of 
  the 
  molecules 
  are 
  not 
  comparable 
  with 
  the 
  

   changes 
  in 
  the 
  masses 
  : 
  that, 
  for 
  example, 
  the 
  volume 
  of 
  a 
  

   molecule 
  of 
  oxygen, 
  instead 
  of 
  being 
  sixteen 
  times 
  that 
  of 
  a 
  

   molecule 
  of 
  hydrogen, 
  is 
  hardly 
  more 
  than 
  twice, 
  so 
  that 
  the 
  

   increase 
  in 
  the 
  forces 
  exerted 
  by 
  the 
  heavier 
  molecules 
  

   is 
  not 
  sufficient 
  to 
  counteract 
  the 
  influence 
  of 
  the 
  increased 
  

   mass. 
  

  

  