﻿6SS 
  Prof. 
  J. 
  J. 
  Thomson 
  

  

  on 
  

  

  moving 
  primary 
  cathode 
  rays 
  was 
  produced 
  from 
  the 
  hot 
  

   Wehnelt 
  cathode 
  C, 
  these 
  passed 
  through 
  a 
  hole 
  in 
  the 
  

   anode 
  A, 
  the 
  anode 
  was 
  earthed, 
  the 
  primary 
  rays 
  passed 
  

   over 
  the 
  top 
  of 
  the 
  side 
  tube, 
  T 
  ; 
  across 
  the 
  top 
  of 
  the 
  tube 
  

   were 
  stretched 
  two 
  parallel 
  pieces 
  of 
  wire 
  gauze 
  about 
  a 
  

   millimetre 
  apart 
  : 
  the 
  upper 
  gauze 
  was 
  earthed, 
  the 
  other 
  

   could 
  be 
  charged 
  negatively 
  by 
  connecting 
  it 
  with 
  the 
  

   negative 
  terminal 
  of 
  a 
  battery 
  of 
  small 
  storage-cells, 
  the 
  

   positive 
  terminal 
  of 
  which 
  was 
  earthed. 
  When 
  the 
  lower 
  

   gauze 
  was 
  earthed 
  as 
  well 
  as 
  the 
  upper, 
  the 
  tube 
  was 
  filled 
  

   with 
  the 
  glow 
  due 
  to 
  the 
  secondary 
  rays. 
  When 
  the 
  lower 
  

   gauze 
  was 
  charged 
  to 
  a 
  negative 
  potential 
  of 
  about 
  40 
  volts, 
  

   this 
  glow 
  became 
  exceedingly 
  faint 
  ; 
  but 
  that 
  the 
  gas 
  below 
  

   the 
  gauze 
  was 
  ionized 
  was 
  shown 
  by 
  the 
  fact 
  that 
  when 
  the 
  

   negative 
  potential 
  of 
  the 
  lower 
  gauze 
  was 
  increased 
  to 
  about 
  

   200 
  volts, 
  a 
  potential 
  quite 
  insufficient 
  to 
  produce 
  luminosity 
  

   in 
  an 
  unionized 
  gas, 
  the 
  tube 
  again 
  became 
  full 
  of 
  luminous 
  

   glow. 
  Thus 
  something 
  capable 
  of 
  ionizing 
  the 
  gas 
  was 
  able 
  

   to 
  traverse 
  the 
  strong 
  electric 
  field. 
  There 
  are 
  two 
  sources 
  

   of 
  ionization 
  which 
  have 
  to 
  be 
  eliminated 
  before 
  we 
  can 
  

   assign 
  this 
  ionization 
  to 
  the 
  existence 
  of 
  neutral 
  systems 
  

   traversing 
  the 
  electric 
  field, 
  — 
  the 
  ultra-violet 
  light 
  coming 
  

   from 
  the 
  luminous 
  discharge 
  in 
  the 
  main 
  tube, 
  and 
  soft 
  

   Rontgen 
  rays 
  produced 
  by 
  the 
  slowly 
  moving 
  primary 
  cathode 
  

   rays. 
  To 
  test 
  whether 
  it 
  was 
  due 
  to 
  ultra-violet, 
  a 
  thin 
  plate 
  

   of 
  quartz 
  was 
  placed 
  over 
  the 
  top 
  of 
  the 
  upper 
  gauze 
  : 
  with 
  

   this 
  arrangement 
  no 
  luminosity 
  could 
  be 
  detected 
  in 
  the 
  side 
  

   tube 
  under 
  the 
  conditions 
  as 
  to 
  potential 
  and 
  so 
  on 
  which 
  

   gave 
  bright 
  luminosity 
  in 
  the 
  tube 
  when 
  the 
  quartz 
  was 
  

   absent. 
  Hence 
  I 
  conclude 
  that 
  the 
  luminosity 
  was 
  not 
  due 
  to 
  

   ultra-violet 
  light. 
  To 
  test 
  whether 
  it 
  was 
  due 
  to 
  soft 
  Rontgen 
  

   rays, 
  taking 
  the 
  quartz 
  away, 
  I 
  got 
  a 
  bright 
  luminosity 
  in 
  

   the 
  side 
  tube 
  with 
  the 
  primary 
  rays 
  passing 
  horizontally 
  

   down 
  the 
  tube, 
  then 
  by 
  means 
  of 
  a 
  magnet 
  I 
  bent 
  the 
  primary 
  

   rays 
  so 
  that 
  they 
  struck 
  the 
  glass 
  of 
  the 
  tube 
  just 
  above 
  the 
  

   side 
  tube, 
  the 
  path 
  of 
  the 
  rays 
  being 
  represented 
  by 
  the 
  dotted 
  

   line 
  of 
  the 
  figure. 
  This 
  made 
  the 
  rays 
  themselves 
  further 
  

   from 
  the 
  side 
  tube, 
  but 
  brought 
  the 
  places 
  where 
  they 
  struck 
  

   the 
  glass, 
  the 
  sources 
  of 
  the 
  Rontgen 
  rays, 
  much 
  nearer 
  to 
  

   that 
  tube 
  : 
  so 
  that 
  if 
  the 
  ionization 
  in 
  the 
  side 
  tube 
  were 
  due 
  

   to 
  Rontgen 
  rays 
  it 
  should 
  be 
  increased 
  by 
  the 
  introduction 
  

   of 
  the 
  magnet, 
  while 
  if 
  it 
  were 
  due 
  to 
  the 
  neutral 
  doublets 
  it 
  

   would 
  be 
  diminished. 
  As 
  a 
  matter 
  of 
  fact 
  the 
  luminosity 
  in 
  

   the 
  side 
  tube 
  almost 
  disappeared 
  when 
  the 
  rays 
  were 
  deflected 
  

   in 
  this 
  way, 
  showing 
  that 
  it 
  was 
  not 
  due 
  to 
  Rontgen 
  rays, 
  

  

  