﻿262 
  Prof. 
  More 
  and 
  Mr. 
  Maucbly: 
  Action 
  of 
  a 
  Magnetic 
  

  

  a 
  pinkish-white 
  positive 
  column 
  which 
  behaves 
  in 
  all 
  respects 
  

   like 
  a 
  positive 
  column 
  in 
  a 
  Crookes's 
  tube. 
  These 
  phenomena 
  

   led 
  us 
  to 
  believe 
  that 
  there 
  was 
  a 
  true 
  current 
  through 
  the 
  

   glass 
  of: 
  the 
  tube. 
  To 
  test 
  this, 
  a 
  sensitive 
  galvanometer 
  was 
  

   connected 
  with 
  one 
  terminal 
  to 
  earth 
  and 
  the 
  other 
  to 
  the 
  

   insulated 
  gauze 
  screen. 
  A 
  permanent 
  deflexion 
  was 
  obtained, 
  

   indicating 
  a 
  direct 
  current 
  from 
  the 
  earth 
  to 
  the 
  screen; 
  

   reversing 
  the 
  connexions 
  of 
  the 
  galvanometer, 
  the 
  deflexion 
  

   also 
  reversed. 
  A 
  telephone, 
  placed 
  in 
  this 
  circuit, 
  gave 
  a 
  

   distinct 
  sound 
  ; 
  the 
  current, 
  while 
  direct, 
  must 
  therefore 
  be 
  

   intermittent. 
  As 
  a 
  current 
  persists 
  when 
  the 
  cathode 
  and 
  

   screen 
  are 
  both 
  earthed, 
  there 
  must 
  be 
  a 
  virtual 
  cathode 
  on 
  

   or 
  near 
  the 
  inner 
  surface 
  of 
  the 
  glass 
  tube, 
  and 
  a 
  virtual 
  

   anode 
  at 
  a 
  point 
  in 
  the 
  induced 
  column. 
  

  

  Professor 
  Righi 
  places 
  emphasis 
  on 
  the 
  existence 
  of 
  this 
  

   virtual 
  anode 
  as 
  a 
  support 
  to 
  his 
  neutral 
  doublet 
  theory. 
  

   But 
  the 
  fact 
  is, 
  a 
  virtual 
  anode 
  must 
  be 
  present 
  if 
  the 
  gauze 
  

   screen 
  is 
  earthed,, 
  whether 
  there 
  is 
  a 
  magnetic 
  field 
  or 
  not, 
  

   as 
  is 
  shown 
  by 
  the 
  presence 
  of 
  this 
  current 
  through 
  the 
  glass 
  

   of 
  the 
  tube. 
  So 
  far 
  as 
  the 
  division 
  of 
  the 
  induced 
  column 
  

   into 
  two 
  portions, 
  with 
  a 
  virtual 
  anode 
  somewhere 
  near 
  its 
  

   middle, 
  is 
  concerned, 
  that 
  effect 
  may 
  be 
  obtained 
  without 
  a 
  

   magnetic 
  field 
  if 
  we 
  use 
  a 
  Wehnelt 
  cathode 
  and 
  make 
  a 
  

   proper 
  adjustment 
  of 
  pressure, 
  potential, 
  and 
  temperature 
  of 
  

   the 
  cathode 
  strip 
  ; 
  the 
  controlling 
  factor 
  in 
  obtaining 
  this 
  

   effect 
  is 
  thus 
  to 
  force 
  the 
  positive 
  column, 
  <?, 
  out 
  into 
  the 
  

   large 
  tube. 
  Undoubtedly, 
  Professor 
  Righi 
  was 
  compelled 
  

   to 
  use 
  a 
  magnetic 
  field 
  for 
  this 
  purpose, 
  and 
  even 
  to 
  obtain 
  

   any 
  induced 
  column 
  at 
  all, 
  because 
  with 
  the 
  ordinary 
  cathode, 
  

   the 
  potential 
  drop 
  is 
  so 
  great 
  at 
  the 
  cathode 
  that 
  there 
  

   is 
  no 
  force 
  to 
  repel 
  or 
  drive 
  the 
  discharge 
  from 
  the 
  cathode. 
  

   On 
  the 
  other 
  hand, 
  the 
  hot 
  lime 
  reduces 
  the 
  potential 
  drop 
  and 
  

   sends 
  out 
  a 
  stream 
  of 
  cathode 
  rays 
  from 
  the 
  cathode 
  just 
  as 
  

   the 
  magnetic 
  field 
  does. 
  In 
  fact, 
  the 
  induced 
  column 
  in 
  

   the 
  large 
  tube 
  is 
  somewhat 
  unstable 
  and 
  occasionally 
  breaks 
  

   up 
  into 
  striae 
  ; 
  it 
  is 
  possible 
  that 
  this 
  reversed 
  bending 
  by 
  a 
  

   test-magnet 
  is 
  but 
  another 
  phase 
  of 
  the 
  helical 
  twist 
  which 
  

   may 
  be 
  given 
  to 
  the 
  heads 
  of 
  these 
  strise. 
  In 
  one 
  or 
  two 
  in- 
  

   stances 
  we 
  obtained 
  columns 
  which 
  showed 
  two 
  virtual 
  anodes. 
  

   At 
  least, 
  it 
  is 
  not 
  necessary 
  to 
  assume 
  that 
  a 
  virtual 
  anode 
  is 
  

   the 
  limit 
  of 
  the 
  paths 
  of 
  positive 
  ions 
  derived 
  from 
  neutral 
  

   doublets 
  which 
  were 
  originally 
  created 
  by 
  a 
  magnetic 
  field. 
  

  

  The 
  importance 
  of 
  determining 
  the 
  conditions 
  which 
  

   make 
  the 
  discharge 
  intermittent 
  is 
  readily 
  understood 
  when 
  

   it 
  is 
  recalled 
  that 
  Professor 
  Righi 
  states 
  that 
  a 
  virtual 
  anode 
  

   should 
  not 
  be 
  expected 
  unless 
  the 
  discharge 
  is 
  periodic. 
  

  

  

  