﻿C>$2 
  Prof. 
  J. 
  J. 
  Thomson 
  

  

  on 
  

  

  ions 
  seem, 
  in 
  the 
  ionization 
  chamber, 
  to 
  be 
  moving 
  more 
  

   rapidly 
  than 
  the 
  negative, 
  for 
  with 
  no 
  electric 
  field 
  in 
  that 
  

   chamber 
  both 
  cylinder 
  and 
  disk 
  acquire 
  a 
  positive 
  charge 
  

   when 
  the 
  magnetic 
  field 
  is 
  strong. 
  

  

  With 
  the 
  apparatus 
  we 
  have 
  been 
  describing 
  we 
  can 
  

   measure 
  simultaneously 
  the 
  values 
  of 
  ejm 
  for 
  the 
  ions 
  and 
  

   the 
  Canalstrahlen 
  in 
  the 
  same 
  vessel, 
  and 
  the 
  experiments 
  

   we 
  have 
  described 
  show 
  that 
  we 
  can 
  get 
  a 
  complete 
  change 
  

   in 
  the 
  character 
  of 
  the 
  ions 
  without 
  any 
  change 
  in 
  the 
  nature 
  

   of 
  the 
  Canalstrahlen 
  ; 
  this 
  is, 
  I 
  think, 
  strong 
  evidence 
  that 
  

   the 
  particles 
  composing 
  the 
  Canalstrahlen 
  are 
  the 
  same 
  from 
  

   whatever 
  source 
  they 
  may 
  be 
  derived. 
  

  

  It 
  might, 
  however, 
  be 
  urged 
  that 
  although 
  the 
  tube 
  might 
  

   be 
  cleared 
  of 
  hydrogen 
  to 
  begin 
  with, 
  this 
  gas 
  might 
  be 
  

   driven 
  by 
  the 
  discharge 
  out 
  of 
  the 
  cathode 
  and 
  that 
  this 
  

   might 
  be 
  the 
  source 
  of 
  the 
  Canalstrahlen, 
  and 
  I 
  have 
  

   noticed 
  a 
  phenomenon 
  which 
  at 
  first 
  sight 
  suggests 
  this 
  view. 
  

   I 
  have 
  observed 
  that 
  under 
  some 
  conditions 
  there 
  is 
  a 
  lag 
  

   amounting 
  in 
  some 
  cases 
  to 
  half 
  a 
  minute 
  or 
  so 
  between 
  

   starting 
  the 
  discharge 
  and 
  the 
  appearance 
  of 
  the 
  phosphor- 
  

   escence 
  due 
  to 
  the 
  canal-rays 
  ; 
  this 
  might 
  be 
  explained 
  by 
  

   supposing 
  that 
  it 
  takes 
  time 
  to 
  liberate 
  sufficient 
  hydrogen 
  

   to 
  produce 
  appreciable 
  Canalstrahlen. 
  I 
  have 
  made 
  many 
  

   experiments 
  on 
  this 
  lag 
  and 
  these 
  show 
  that 
  it 
  has 
  no 
  special 
  

   connexion 
  with 
  hydrogen, 
  but 
  is 
  due 
  to 
  an 
  alteration 
  in 
  the 
  

   pressure 
  of 
  the 
  gas 
  produced 
  by 
  the 
  discharge. 
  It 
  is 
  well 
  

   known 
  that 
  the 
  Canalstrahlen 
  are 
  only 
  well 
  developed 
  when 
  

   the 
  pressure 
  in 
  the 
  tube 
  is 
  between 
  certain 
  limits. 
  It 
  is 
  only 
  

   when 
  the 
  initial 
  pressure 
  is 
  near 
  to, 
  but 
  outside, 
  one 
  of 
  these 
  

   limits 
  that 
  the 
  lag 
  occurs, 
  and 
  then 
  the 
  alteration 
  in 
  pressure 
  

   which 
  occurs 
  when 
  the 
  discharge 
  passes 
  may 
  accumulate 
  

   until 
  the 
  pressure 
  is 
  brought 
  within 
  the 
  required 
  limits. 
  

   That 
  this, 
  and 
  not 
  the 
  introduction 
  of 
  hydrogen 
  rather 
  than 
  

   any 
  other 
  gas, 
  is 
  the 
  explanation 
  of 
  the 
  lag 
  is 
  I 
  think 
  proved 
  

   in 
  the 
  following 
  experiments 
  : 
  — 
  If 
  the 
  presence 
  of 
  hydrogen 
  

   were 
  all 
  that 
  is 
  wanted 
  for 
  the 
  Canalstrahlen, 
  then 
  the 
  lag 
  

   should 
  not 
  occur 
  when 
  the 
  tube 
  is 
  filled 
  with 
  hydrogen 
  : 
  we 
  

   find 
  that 
  the 
  lag 
  occurs 
  when 
  the 
  tube 
  is 
  filled 
  with 
  hydrogen, 
  

   as 
  well 
  as 
  when 
  great 
  precautions 
  have 
  been 
  taken 
  to 
  remove 
  

   this 
  gas 
  from 
  the 
  tube. 
  Again, 
  in 
  a 
  tube 
  from 
  which 
  

   hydrogen 
  has 
  been 
  removed 
  and 
  the 
  lag 
  is 
  well 
  developed, 
  

   the 
  admission 
  of 
  a 
  small 
  quantity 
  of 
  dry 
  air 
  will 
  remove 
  the 
  

   lag 
  just 
  as 
  effectively 
  as 
  the 
  admission 
  of 
  hydrogen. 
  When 
  

   once 
  the 
  lag 
  has 
  been 
  got 
  rid 
  of 
  it 
  is 
  necessary 
  to 
  give 
  the 
  

   tube 
  a 
  long 
  rest 
  from 
  the 
  discharge 
  before 
  it 
  returns. 
  The 
  

   fact 
  that 
  the 
  lag 
  may 
  be 
  destroyed 
  by 
  admitting 
  a 
  small 
  

  

  

  