﻿•836 
  Sir 
  J. 
  J. 
  Thomson 
  on 
  

  

  be 
  the 
  only 
  direction 
  in 
  which 
  an 
  appreciable 
  number 
  o£ 
  

   Oanalstrahlen 
  or 
  retrograde 
  rays 
  move. 
  

  

  If 
  doublets 
  form 
  an 
  intermediate 
  stage 
  between 
  the 
  ions 
  

   and 
  the 
  atoms, 
  the 
  doublets 
  being 
  the 
  systems 
  formed 
  from 
  

   the 
  molecules 
  of 
  the 
  gas 
  by 
  the 
  ionizing 
  agent, 
  say 
  Rontgen 
  

   rays, 
  then 
  the 
  number 
  of 
  doublets 
  liberated 
  may 
  be 
  enor- 
  

   mously 
  greater 
  than 
  the 
  number 
  of 
  ions 
  set 
  free, 
  so 
  that 
  this 
  

   number 
  may 
  give 
  no 
  indication 
  of 
  the 
  percentage 
  of 
  molecules 
  

   aifected 
  by 
  the 
  rays. 
  

  

  Thus, 
  suppose 
  q 
  doublets 
  are 
  liberated 
  per 
  second 
  per 
  

   cubic 
  centimetre 
  in 
  a 
  gas 
  at 
  a 
  pressure 
  p, 
  let 
  D 
  be 
  the 
  

   number 
  of 
  doublets 
  per 
  cubic 
  centimetre, 
  let 
  jSpD 
  of 
  these 
  

   reunite 
  with 
  the 
  molecules 
  per 
  sec, 
  and 
  7J0D 
  spUt 
  up 
  into 
  

   ions, 
  let 
  jn 
  be 
  the 
  number 
  of 
  positive 
  or 
  negative 
  ions 
  per 
  cc, 
  

   u 
  the 
  coefficient 
  of 
  recombination 
  ; 
  then 
  we 
  have 
  

  

  ~^^j=q-^Dp^yI)p, 
  

   dm 
  j^ 
  2 
  

  

  When 
  things 
  are 
  in 
  a 
  steady 
  state 
  

  

  The 
  saturation 
  current 
  is 
  proportional 
  to 
  the 
  value 
  of 
  

   dm/dt 
  when 
  m 
  is 
  zero 
  ; 
  hence, 
  when 
  things 
  have 
  settled 
  into 
  

   a 
  steady 
  state, 
  the 
  saturation 
  current 
  is 
  proportional 
  to 
  

  

  7 
  

  

  Thus, 
  if 
  7 
  is 
  very 
  small 
  compared 
  with 
  ^, 
  the 
  number 
  of 
  

   ions 
  taken 
  from 
  the 
  gas 
  per 
  second 
  may 
  be 
  very 
  small 
  

   compared 
  with 
  the 
  number 
  of 
  molecules 
  affected 
  by 
  the 
  rays. 
  

   This 
  point 
  is 
  an 
  important 
  one 
  in 
  connexion 
  with 
  the 
  structure 
  

   of 
  the 
  Rontgen 
  rays, 
  the 
  small 
  percentage 
  of 
  the 
  molecules 
  

   decomposed 
  has 
  always 
  been 
  difficult 
  to 
  understand. 
  

  

  If 
  we 
  suppose 
  that 
  the 
  ions 
  are 
  the 
  first 
  product 
  of 
  the 
  

   Rontgen 
  rays 
  on 
  the 
  molecules, 
  this 
  difficulty 
  disappears 
  on 
  

   the 
  assumption 
  that 
  there 
  is 
  a 
  stage 
  intermediate 
  between 
  the 
  

   molecules 
  and 
  the 
  ions. 
  

  

  The 
  values 
  of 
  ejm 
  for 
  the 
  Oanalstrahlen 
  and 
  for 
  the 
  retro- 
  

   grade 
  rays 
  are 
  the 
  same 
  when 
  the 
  pressure 
  is 
  low 
  whatever 
  

   be 
  the 
  gas 
  in 
  the 
  tube. 
  In 
  a 
  former 
  paper 
  I 
  described 
  

   experiments 
  which 
  showed 
  that 
  if 
  a 
  vessel 
  was 
  exhausted 
  

   until 
  the 
  pressure 
  was 
  so 
  low 
  that 
  the 
  discharge 
  would 
  not 
  

   pass, 
  and 
  small 
  quantities 
  of 
  hydrogen, 
  helium, 
  air, 
  oxygen, 
  

  

  