﻿832 
  Sir 
  J. 
  J. 
  Thomson 
  on 
  

  

  I 
  have 
  made 
  many 
  determinations 
  of 
  the 
  velocity 
  of 
  

   Canalstrahlen 
  at 
  different 
  pressures 
  using 
  tubes 
  of 
  very 
  

   different 
  shapes, 
  and 
  the 
  results 
  were 
  so 
  nearly 
  constant 
  in 
  

   spite 
  of 
  the 
  wide 
  variations 
  in 
  the 
  conditions, 
  that 
  I 
  was 
  led 
  

   to 
  suspect 
  that 
  the 
  velocity 
  of 
  the 
  positive 
  rays 
  was 
  not 
  

   influenced 
  to 
  any 
  great 
  extent 
  by 
  the 
  strength 
  of 
  the 
  electric 
  

   field 
  in 
  the 
  tube. 
  To 
  test 
  this 
  matter 
  in 
  as 
  direct 
  a 
  way 
  as- 
  

   possible 
  I 
  used 
  the 
  following 
  method. 
  

  

  This 
  discharge 
  was 
  produced 
  by 
  a 
  large 
  induction-coil 
  ; 
  the 
  

   discharge-tube, 
  fig. 
  8, 
  had 
  a 
  perforated 
  cathode 
  faced 
  with 
  

   calcium, 
  so 
  that 
  the 
  discharge 
  would 
  pass 
  at 
  very 
  low 
  

   pressures 
  without 
  sparking 
  through 
  the 
  glass 
  walls 
  of 
  the 
  

   tube 
  and 
  breaking 
  the 
  apparatus. 
  The 
  anode 
  A 
  was 
  an 
  

   aluminium 
  cylinder 
  perforated 
  with 
  a 
  very 
  small 
  hole^ 
  

   When 
  the 
  discharge 
  was 
  passing 
  through 
  the 
  tube 
  a 
  pencil 
  

   of 
  cathode 
  rays 
  passed 
  through 
  the 
  hole 
  and 
  produced 
  a 
  

   small 
  well-defined 
  spot 
  on 
  the 
  fluorescent 
  willemite 
  screen 
  S^ 
  

   placed 
  at 
  the 
  anode 
  end 
  of 
  the 
  tube. 
  

  

  During 
  their 
  path 
  up 
  to 
  the 
  screen 
  after 
  leaving 
  the 
  anode 
  

   they 
  could 
  be 
  exposed 
  to 
  a 
  known 
  magnetic 
  field 
  produced 
  

   by 
  an 
  electromagnet, 
  and 
  the 
  distance 
  through 
  which 
  the 
  

   spot 
  moved 
  when 
  the 
  magnet 
  was 
  put 
  on 
  enabled 
  us 
  to> 
  

   calculate 
  the 
  velocity 
  of 
  the 
  cathode 
  rays. 
  

  

  The 
  Canalstrahlen 
  after 
  passing 
  through 
  the 
  aperture 
  in 
  

   the 
  cathode 
  pass 
  along 
  a 
  metal 
  tube 
  of 
  very 
  fine 
  bore 
  (one 
  

   of 
  the 
  perforated 
  needles 
  used 
  for 
  hypodermic 
  injections) 
  

   and 
  emerge 
  between 
  two 
  parallel 
  vertical 
  metallic 
  plates 
  

   (4 
  mm. 
  apart 
  in 
  one 
  set 
  of 
  experiments, 
  3 
  mm. 
  in 
  another) 
  

   which 
  can 
  be 
  connected 
  with 
  the 
  terminals 
  of 
  a 
  battery 
  of 
  

   small 
  storage-cells 
  ; 
  the 
  rays 
  are 
  thus 
  exposed 
  to 
  a 
  strong 
  

   electric 
  field 
  and 
  are 
  deflected 
  horizontally. 
  

  

  Two 
  poles 
  (about 
  the 
  same 
  length 
  as 
  these 
  plates) 
  of 
  a 
  

   powerful 
  electromagnet 
  of 
  the 
  Du 
  Bois 
  pattern, 
  are 
  placed 
  

   on 
  either 
  side 
  of 
  the 
  tube, 
  and 
  the 
  horizontal 
  magnetic 
  field 
  

   due 
  to 
  this 
  magnet 
  deflects 
  the 
  rays 
  in 
  a 
  vertical 
  direction 
  ► 
  

   The 
  deflexion 
  of 
  the 
  rays 
  is 
  measured 
  by 
  the 
  deflexion 
  of 
  the 
  

  

  