﻿Positive 
  Electricity, 
  841 
  

  

  to 
  disappear 
  if 
  the 
  Faraday 
  cylinders 
  are 
  insulated 
  and 
  

   maintained 
  at 
  a 
  potential 
  a 
  few 
  volts 
  above 
  the 
  plate 
  A. 
  

   The 
  ions, 
  which 
  have 
  acquired 
  an 
  energy 
  due 
  to 
  the 
  fall 
  

   through 
  the 
  whole 
  potential-difference 
  of 
  say 
  160 
  volts, 
  will 
  

   be 
  but 
  little 
  afEected 
  by 
  having 
  to 
  go 
  against 
  the 
  difference 
  

   of 
  say 
  20 
  volts, 
  but 
  those 
  ions 
  which 
  have 
  acquired 
  only 
  

   a 
  fraction 
  of 
  this 
  velocity 
  may 
  be 
  wholly 
  stopped 
  by 
  it. 
  On 
  

   raising 
  the 
  potential 
  of 
  the 
  cylinders 
  to 
  about 
  20 
  volts, 
  I 
  

   found 
  that 
  the 
  effect 
  in 
  nearly 
  every 
  case 
  disappears. 
  

  

  There 
  were, 
  however, 
  one 
  or 
  two 
  cases 
  in 
  which 
  it 
  still 
  

   remained 
  ; 
  if 
  the 
  slow 
  moving 
  particles 
  remain 
  neutralized 
  

   for 
  part 
  of 
  their 
  journey 
  between 
  the 
  plate 
  and 
  the 
  cylinder, 
  

   they 
  could 
  not 
  be 
  much 
  affected 
  by 
  the 
  field, 
  and 
  the 
  positive 
  

   particles 
  might 
  still 
  force 
  their 
  way 
  in. 
  

  

  As 
  the 
  question 
  of 
  the 
  existence 
  of 
  small 
  positive 
  ions 
  

   is 
  a 
  very 
  vital 
  one, 
  I 
  have 
  made 
  some 
  other 
  investigations 
  

   with 
  other 
  cases 
  of 
  easily 
  deflected 
  positive 
  ions 
  with 
  the 
  

   object 
  of 
  seeing 
  if 
  the 
  deflexions 
  were 
  in 
  these 
  cases 
  also 
  

   due 
  to 
  the 
  smallness 
  of 
  the 
  velocity 
  rather 
  than 
  to 
  that 
  of 
  

   the 
  mass. 
  

  

  The 
  appearance 
  of 
  the 
  discharge 
  in 
  the 
  neighbourhood 
  of 
  

   the 
  hole 
  in 
  a 
  cathode 
  offers 
  several 
  features 
  of 
  interest 
  ; 
  on 
  

   some 
  of 
  these, 
  light 
  is 
  thrown 
  by 
  the 
  consideration 
  of 
  the 
  

   distribution 
  of 
  the 
  lines 
  of 
  force 
  near 
  the 
  hole 
  before 
  the 
  

   discharge 
  starts. 
  

  

  Let 
  A 
  and 
  B 
  be 
  two 
  parallel 
  metallic 
  plates, 
  B 
  hftving 
  

   a 
  small 
  hole 
  in 
  it. 
  Let 
  us 
  suppose 
  that 
  A 
  is 
  at 
  a 
  higher 
  

   potential 
  than 
  B, 
  then 
  the 
  negative 
  electricity 
  is 
  not 
  uniformly 
  

   distributed 
  over 
  B 
  but 
  is 
  very 
  much 
  concentrated 
  near 
  the 
  

   edge 
  of 
  the 
  hole, 
  the 
  density 
  being 
  infinite 
  at 
  the 
  boundary 
  

   of 
  the 
  hole 
  if 
  the 
  edge 
  is 
  sharp. 
  The 
  electric 
  force 
  is 
  

   proportional 
  to 
  the 
  density, 
  so 
  that 
  up 
  to 
  a 
  distance 
  from 
  the 
  

   hole 
  comparable 
  with 
  the 
  radius 
  of 
  the 
  hole 
  the 
  electric 
  

   intensity 
  is 
  far 
  in 
  excess 
  of 
  its 
  average 
  value. 
  

  

  Again, 
  this 
  accumulation 
  of 
  electricity 
  is 
  not 
  confined 
  to 
  

   the 
  part 
  of 
  the 
  plate 
  facing 
  A. 
  If 
  the 
  plate 
  B 
  is 
  thin 
  in 
  

   comparison 
  with 
  the 
  radius 
  of 
  the 
  hole 
  there 
  will, 
  close 
  to 
  

   the 
  hole, 
  be 
  practically 
  as 
  much 
  electricity 
  on 
  the 
  face 
  of 
  B 
  

   turned 
  away 
  from 
  A 
  as 
  on 
  the 
  side 
  next 
  to 
  A 
  : 
  in 
  fact 
  the 
  

   field 
  of 
  force 
  in 
  the 
  neighbourhood 
  of 
  the 
  hole 
  is 
  much 
  as 
  if 
  

   a 
  fine 
  ring 
  of 
  the 
  same 
  radius 
  as 
  the 
  hole 
  were 
  highly 
  

   electrified 
  and 
  placed 
  by 
  itself 
  in 
  the 
  field. 
  The 
  appearance 
  

   of 
  the 
  discharge 
  through 
  the 
  hole 
  when 
  the 
  pressure 
  is 
  not 
  

   very 
  low 
  illustrates 
  this 
  very 
  well. 
  One 
  of 
  the 
  stages 
  of 
  the 
  

   discharge 
  is 
  shown 
  in 
  fig. 
  9, 
  and 
  it 
  will 
  be 
  seen 
  that 
  this 
  is 
  

  

  