﻿450 
  Sir 
  J. 
  J. 
  Thomson 
  on 
  

  

  The 
  heaping 
  up 
  of 
  the 
  negative 
  electricity 
  at 
  the 
  head 
  of 
  

   the 
  striations 
  seems 
  to 
  me 
  to 
  be 
  the 
  most 
  important 
  factor 
  in 
  

   the 
  production 
  of 
  striations. 
  

  

  This 
  concentration 
  of 
  the 
  negative 
  electricity 
  at 
  regular 
  

   intervals 
  along 
  the 
  discharge 
  may 
  be 
  explained 
  as 
  follows. 
  

   Consider 
  a 
  stream 
  of 
  negative 
  corpuscles 
  ])rojected 
  from 
  the 
  

   neighbourhood 
  of 
  the 
  cathode 
  with 
  considerable 
  velocity 
  : 
  

   they 
  will 
  collide 
  against 
  the 
  molecules 
  of 
  the 
  gas, 
  and 
  thereby 
  

   lose 
  velocity 
  : 
  if 
  the 
  electric 
  field 
  acting 
  on 
  them 
  is 
  not 
  

   sufficiently 
  intense 
  to 
  restore 
  the 
  velocity 
  lost 
  by 
  the 
  collisions, 
  

   the 
  corpuscles 
  will 
  lose 
  velocity 
  as 
  they 
  travel 
  through 
  the 
  

   ^as, 
  thus 
  the 
  corpuscles 
  in 
  the 
  rear 
  will 
  gain 
  on 
  those 
  in 
  

   front, 
  and 
  therefore 
  the 
  density 
  of 
  the 
  corpuscles 
  and 
  there- 
  

   fore 
  of 
  the 
  negative 
  electricity 
  will 
  be 
  greater 
  in 
  the 
  front, 
  

  

  and 
  by 
  the 
  equation 
  -^ 
  =4:7rp, 
  when 
  X 
  is 
  the 
  electric 
  force, 
  

  

  w 
  the 
  distance 
  from 
  the 
  cathode, 
  and 
  p 
  the 
  density 
  of 
  the 
  

   electricity, 
  the 
  electric 
  force 
  will 
  increase 
  rapidly 
  in 
  conse- 
  

   quence 
  of 
  this 
  concentration. 
  This 
  increase 
  in 
  the 
  force 
  will 
  

   increase 
  the 
  velocity 
  of 
  the 
  particles 
  in 
  front. 
  If 
  the 
  increase 
  

   in 
  velocity 
  is 
  not 
  sufficient 
  to 
  make 
  the 
  corpuscles 
  ionize 
  the 
  

   gas 
  by 
  collision, 
  the 
  congestion 
  will 
  be 
  relieved 
  by 
  the 
  

   gradually 
  increasing 
  velocity 
  of 
  the 
  corpuscles 
  in 
  front, 
  and 
  

   there 
  will 
  be 
  no 
  periodicity 
  either 
  in 
  the 
  density 
  of 
  the 
  

   electricity 
  or 
  the 
  electric 
  force. 
  If, 
  however, 
  the 
  force 
  in- 
  

   creases 
  so 
  that 
  the 
  corpuscles 
  produce 
  ions 
  by 
  collision 
  quite 
  

   a 
  different 
  state 
  of 
  affairs 
  will 
  occur 
  ; 
  suppose 
  that 
  when 
  the 
  

   corpuscles 
  get 
  to 
  a 
  place 
  P, 
  their 
  velocity 
  is 
  sufficient 
  to 
  

   produce 
  ionization. 
  On 
  the 
  anode 
  side 
  of 
  P 
  positive 
  and 
  

   negative 
  ions 
  will 
  be 
  produced, 
  the 
  positive 
  ones 
  will 
  crowd 
  

   towards 
  P, 
  the 
  negative 
  ones 
  will 
  move 
  away 
  from 
  it 
  ; 
  the 
  

   consequence 
  will 
  be 
  that 
  there 
  will 
  be 
  an 
  excess 
  of 
  positive 
  elec- 
  

   trification 
  on 
  the 
  anode 
  side 
  of 
  P: 
  now 
  positive 
  electrification 
  

   implies 
  a 
  diminution 
  in 
  the 
  electric 
  force 
  as 
  we 
  move 
  towards 
  

   the 
  anode, 
  thus 
  the 
  electric 
  force 
  will 
  fall. 
  When 
  it 
  has 
  

   fallen 
  below 
  the 
  value 
  required 
  for 
  ionization 
  the 
  negative 
  

   electricity 
  will 
  as 
  before 
  begin 
  to 
  accumulate 
  in 
  the 
  front 
  of 
  

   the 
  stream, 
  and 
  the 
  electric 
  force 
  will 
  again 
  increase 
  to 
  the 
  

   value 
  required 
  for 
  ionization 
  when 
  the 
  process 
  will 
  be 
  repeated. 
  

   We 
  shall 
  in 
  this 
  way 
  get 
  a 
  periodicity 
  in 
  the 
  electric 
  force 
  

   such 
  as 
  is 
  observed 
  in 
  the 
  striated 
  discharge. 
  Thus 
  on 
  this 
  

   view 
  the 
  concave 
  side 
  of 
  the 
  bright 
  head 
  of 
  the 
  striation 
  acts 
  

   as 
  a 
  cathode, 
  the 
  corresponding 
  anode 
  being 
  the 
  convex 
  side 
  

   of 
  the 
  bright 
  head 
  of 
  the 
  adjacent 
  striation 
  on 
  the 
  anode 
  side. 
  

   Between 
  these 
  two 
  places 
  we 
  have 
  a 
  complete 
  discharge, 
  

   forming 
  a 
  unit 
  by 
  the 
  combination 
  of 
  which 
  the 
  whole 
  dis- 
  

   charge 
  is 
  built 
  up. 
  The 
  ions 
  which 
  carry 
  the 
  current 
  through 
  

  

  