﻿684: 
  Prof. 
  J. 
  J. 
  Thomson 
  on 
  

  

  the 
  only 
  ions 
  besides 
  those 
  o£ 
  hydrogen 
  which 
  can 
  be 
  

   observed 
  in 
  the 
  Canalstrahlen 
  are 
  those 
  of 
  the 
  next 
  highest 
  

   gas 
  helium, 
  which, 
  when 
  the 
  discharge 
  passes 
  through 
  

   helium, 
  can 
  be 
  observed 
  in 
  the 
  Canalstrahlen 
  without 
  

   difficulty. 
  

  

  The 
  places 
  where 
  the 
  neutralization 
  o£ 
  the 
  positive 
  ions 
  by 
  

   the 
  corpuscles 
  takes 
  place 
  will 
  be 
  either 
  quite 
  close 
  to 
  the 
  

   cathode 
  or 
  when 
  the 
  cathode 
  is 
  perforated 
  in 
  the 
  region 
  

   behind 
  the 
  cathode 
  ; 
  for 
  in 
  front 
  of 
  the 
  cathode 
  where 
  the 
  

   positive 
  ions 
  are 
  produced, 
  though 
  the 
  velocity 
  of 
  these 
  ions 
  

   will 
  be 
  small, 
  since 
  they 
  are 
  in 
  a 
  feeble 
  electric 
  field, 
  yet 
  the 
  

   corpuscles 
  which 
  have 
  come 
  from 
  the 
  cathode 
  will 
  have 
  

   passed 
  through 
  a 
  great 
  potential-difference 
  and 
  will 
  .have 
  a 
  

   very 
  high 
  velocity 
  ; 
  thus 
  the 
  relative 
  velocity 
  of 
  the 
  positive 
  

   ions 
  and 
  the 
  corpuscles 
  will 
  be 
  very 
  large. 
  Quite 
  close 
  to 
  

   the 
  cathode 
  the 
  velocity 
  of 
  the 
  corpuscles 
  will 
  be 
  very 
  small, 
  

   and 
  though 
  the 
  velocity 
  of 
  the 
  ion 
  will 
  be 
  much 
  greater 
  than 
  

   in 
  the 
  former 
  case, 
  yet 
  since 
  the 
  mass 
  of 
  the 
  ion 
  is 
  so 
  much 
  

   greater 
  than 
  that 
  of 
  the 
  corpuscle, 
  the 
  velocity 
  acquired 
  by 
  

   the 
  ion 
  under 
  the 
  same 
  potential-difference 
  will 
  be 
  small 
  

   compared 
  with 
  that 
  acquired 
  by 
  the 
  corpuscle, 
  so 
  that 
  the 
  

   relative 
  velocity 
  of 
  the 
  two 
  close 
  to 
  the 
  cathode 
  will 
  be 
  much 
  

   less 
  than 
  at 
  a 
  greater 
  distance 
  in 
  front 
  of 
  it, 
  so 
  that 
  com- 
  

   bination 
  is 
  much 
  more 
  likely 
  to 
  occur 
  near 
  to 
  the 
  cathode, 
  

   or 
  if 
  the 
  cathode 
  is 
  perforated 
  behind 
  it. 
  

  

  If 
  the 
  forces 
  between 
  a 
  small 
  positive 
  ion 
  and 
  an 
  un- 
  

   charged 
  molecule 
  are 
  independent 
  of 
  the 
  atomic 
  weight 
  of 
  

   the 
  molecule, 
  or 
  only 
  increase 
  slowly 
  as 
  the 
  atomic 
  weight 
  

   increases, 
  then 
  such 
  an 
  ion 
  is 
  more 
  likely 
  to 
  attach 
  itself 
  to 
  

   a 
  light 
  molecule 
  than 
  to 
  a 
  heavy 
  one 
  ; 
  for 
  we 
  can 
  show 
  that 
  

   the 
  condition 
  that 
  the 
  ion 
  and 
  the 
  molecule 
  should 
  separate 
  

   is 
  that 
  

  

  M 
  M' 
  V 
  2 
  

   M 
  + 
  M' 
  

  

  should 
  be 
  greater 
  than 
  a 
  certain 
  quantity 
  depending 
  only 
  on 
  

   the 
  force 
  between 
  the 
  systems 
  and 
  their 
  distance 
  apart 
  when 
  

   nearest 
  together. 
  M 
  is 
  the 
  mass 
  of 
  the 
  ion, 
  M' 
  that 
  of 
  the 
  

   molecule, 
  and 
  V 
  the 
  relative 
  velocity 
  of 
  the 
  two 
  at 
  the 
  absidal 
  

   distance. 
  If 
  M' 
  is 
  very 
  large 
  compared 
  with 
  M 
  the 
  condition 
  

   is 
  that 
  Mi* 
  2 
  should 
  be 
  greater, 
  while 
  if 
  M' 
  were 
  equal 
  to 
  M, 
  

   the 
  condition 
  is 
  that 
  -J-Mv 
  2 
  should 
  be 
  greater 
  than 
  the 
  same 
  

   quantity 
  ; 
  thus 
  in 
  the 
  second 
  case 
  the 
  ion 
  would 
  take 
  twice 
  as 
  

   much 
  energy 
  to 
  get 
  free 
  as 
  in 
  the 
  first, 
  and 
  so 
  would 
  be 
  more 
  

   likely 
  to 
  combine 
  with 
  the 
  molecule. 
  

  

  