﻿Striatlons 
  hi 
  the 
  Electric 
  Discharge. 
  4^5 
  

  

  movement 
  of 
  the 
  ions 
  is 
  in 
  the 
  same 
  direction 
  at 
  all 
  parts 
  o£ 
  

   the 
  tube 
  ; 
  thus, 
  whenever 
  the 
  electric 
  force 
  is 
  negative, 
  there 
  

   must 
  be 
  ions 
  movino- 
  ao-ainst 
  the 
  electric 
  force 
  instead 
  of 
  

   with 
  it. 
  Now 
  the 
  validity 
  of 
  the 
  method 
  of 
  the 
  wire 
  elec- 
  

   trodes 
  depends 
  upon 
  the 
  assumption 
  that 
  the 
  ions 
  in 
  the 
  

   neighbourhood 
  of 
  the 
  tip 
  of 
  these 
  electrodes 
  follow 
  the 
  lines 
  

   of 
  force, 
  that 
  if, 
  for 
  example, 
  the 
  tip 
  were 
  at 
  a 
  higher 
  poten- 
  

   tial 
  than 
  the 
  gas 
  so 
  that 
  the 
  force 
  on 
  a 
  positive 
  ion 
  were 
  

   away 
  from 
  the 
  tip, 
  negative 
  ions 
  would 
  follow 
  the 
  direction 
  

   of 
  the 
  force 
  acting 
  upon 
  them, 
  and 
  run 
  into 
  the 
  tip 
  and 
  lower 
  

   its 
  potential 
  until 
  it 
  became 
  the 
  same 
  as 
  that 
  of 
  the 
  gas 
  in 
  

   its 
  neighbourhood. 
  But 
  if 
  the 
  ions 
  do 
  not 
  follow 
  the 
  electric 
  

   force, 
  and 
  the 
  existence 
  of 
  a 
  negative 
  force 
  implies 
  that 
  some 
  

   of 
  them 
  at 
  any 
  rate 
  do 
  not, 
  we 
  have 
  no 
  right 
  to 
  assume 
  that 
  

   the 
  potential 
  of 
  the 
  wire 
  is 
  the 
  same 
  as 
  that 
  of 
  the 
  gas. 
  In 
  

   some 
  simple 
  cases 
  it 
  is 
  evident 
  that 
  it 
  would 
  not 
  be 
  so. 
  

   Thus 
  suppose 
  the 
  wire 
  were 
  exposed 
  to 
  a 
  stream 
  of 
  cathode 
  

   rays, 
  and 
  that 
  there 
  were 
  no 
  positive 
  ions 
  in 
  its 
  neighbour- 
  

   hood, 
  then 
  it 
  is 
  evident 
  that 
  the 
  wire 
  w^ould 
  acquire 
  the 
  

   potential 
  of 
  the 
  cathode 
  from 
  which 
  the 
  rays 
  started 
  and 
  not 
  

   that 
  of 
  the 
  gns 
  around 
  the 
  wire. 
  

  

  For 
  these 
  reasons 
  I 
  felt 
  that 
  the 
  existence 
  of 
  a 
  negative 
  

   force 
  could 
  not 
  be 
  established 
  by 
  means 
  of 
  wire 
  electrodes, 
  

   and 
  I 
  adopted 
  an 
  entirely 
  different 
  method 
  of 
  measuring 
  the 
  

   electric 
  force 
  along 
  the 
  discharge-tube. 
  The 
  principle 
  of 
  

   this 
  method 
  is 
  as 
  follows 
  : 
  imagine 
  a 
  very 
  fine 
  pencil 
  of 
  

   cathode 
  rays, 
  travelling 
  at 
  right 
  angles 
  to 
  the 
  line 
  joining 
  the 
  

   cathode 
  and 
  anode, 
  to 
  pass 
  through 
  the 
  discharge-tube. 
  As 
  

   it 
  crosses 
  the 
  discharge 
  at 
  any 
  place 
  it 
  will 
  be 
  acted 
  upon 
  by 
  

   the 
  electric 
  force 
  at 
  the 
  point 
  of 
  the 
  discharge^ 
  and 
  will 
  be 
  

   deflected 
  by 
  an 
  amount 
  proportional 
  to 
  the 
  electric 
  force. 
  

   The 
  deflexion 
  will 
  be 
  from 
  the 
  cathode 
  of 
  the 
  discharge-tube 
  

   if 
  the 
  force 
  is 
  positive, 
  towards 
  it 
  if 
  the 
  force 
  is 
  negative. 
  

   If 
  very 
  small 
  pencils 
  of 
  cathode 
  rays 
  are 
  used 
  the 
  disturbance 
  

   of 
  the 
  electric 
  field 
  in 
  the 
  discharge-tube 
  due 
  to 
  the 
  negative 
  

   charge 
  on 
  the 
  rays 
  is 
  quite 
  insignificant, 
  and 
  there 
  is 
  none 
  

   of 
  that 
  distortion 
  of 
  the 
  striations 
  which, 
  to 
  a 
  greater 
  or 
  less 
  

   extent, 
  always 
  occurs 
  when 
  exploring 
  metallic 
  electrodes 
  are 
  

   used. 
  

  

  The 
  arrangement 
  by 
  which 
  this 
  principle 
  is 
  carried 
  out 
  in 
  

   practice 
  is 
  shown 
  in 
  fig. 
  2. 
  The 
  cathode 
  and 
  anode 
  are 
  

   fastened 
  together 
  by 
  a 
  piece 
  of 
  glass-rod 
  and 
  fastened 
  to 
  a 
  

   float, 
  floating 
  on 
  the 
  top 
  of 
  a 
  mercury 
  column. 
  By 
  raising 
  or 
  

   lowering 
  the 
  column 
  the 
  anode 
  and 
  cathode 
  can 
  be 
  moved 
  up 
  

   and 
  down 
  the 
  discharge-tube. 
  This 
  arrangement 
  is 
  the 
  same 
  

   as 
  that 
  used 
  with 
  the 
  wire 
  detectors 
  and 
  shown 
  in 
  fig. 
  3. 
  

  

  