﻿Pressure 
  Effect 
  in 
  Corona 
  Discharge. 
  269 
  

  

  At 
  the 
  time 
  marked 
  by 
  the 
  point 
  D, 
  in 
  curve 
  0, 
  a 
  discharge 
  

   current 
  supplying 
  *094 
  watt 
  was 
  switched 
  on. 
  The 
  cooling 
  

   effect 
  of 
  the 
  wind 
  is 
  well 
  shown 
  by 
  the 
  drop 
  in 
  pressure, 
  the 
  

   final 
  value 
  of 
  which 
  was 
  practically 
  that 
  which 
  would 
  have 
  

   been 
  reached 
  after 
  combined 
  action 
  from 
  zero 
  time. 
  

  

  Lastly, 
  mention 
  must 
  be 
  made 
  of 
  an 
  experiment 
  by 
  Warner, 
  

   by 
  which 
  he 
  claims 
  to 
  have 
  shown 
  that 
  instead 
  of 
  a 
  heating 
  

   effect 
  at 
  the 
  instant 
  of 
  starting 
  of 
  the 
  discharge 
  from 
  an 
  

   unheated 
  wire, 
  the 
  gas 
  near 
  the 
  wire 
  actually 
  cools. 
  This 
  

   he 
  deduced 
  from 
  the 
  movement 
  of 
  the 
  spot 
  of 
  a 
  galvanometer 
  

   connected 
  to 
  a 
  thermo-junction, 
  placed 
  in 
  the 
  tube 
  at 
  a 
  

   distance 
  of 
  about 
  4 
  mm. 
  from 
  the 
  axial 
  wire. 
  

  

  The 
  authors 
  repeated 
  this 
  experiment, 
  and 
  found 
  that 
  the 
  

   deflexion 
  observed 
  is 
  not 
  due 
  to 
  a 
  thermo-electric 
  current,, 
  

   but 
  to 
  an 
  electrostatic 
  effect 
  when 
  the 
  thermo-junction 
  takes 
  

   up 
  the 
  potential 
  of 
  the 
  air. 
  Thus 
  this 
  deflexion 
  is 
  also 
  

   observed 
  when 
  the 
  galvanometer 
  is 
  not 
  included 
  in 
  the 
  circuit 
  

   containing 
  the 
  thermo-couple, 
  but 
  is 
  merely 
  in 
  electrical 
  

   contact 
  with 
  it. 
  The 
  cooling 
  of 
  a 
  red-hot 
  wire 
  which 
  Warner 
  

   quotes 
  as 
  occurring 
  when 
  discharge 
  starts 
  from 
  it, 
  is 
  un- 
  

   doubtedly 
  caused 
  by 
  the 
  electric 
  wind 
  which 
  is 
  thus 
  set 
  up. 
  

  

  Summary. 
  

  

  When 
  glow 
  discharge 
  starts 
  between 
  a 
  cylinder 
  and 
  an 
  

   axial 
  wire, 
  in 
  a 
  closed 
  tube 
  at 
  atmospheric 
  pressure, 
  a 
  sudden 
  

   rise 
  of 
  pressure 
  is 
  observed. 
  It 
  has 
  been 
  argued 
  by 
  some 
  

   that 
  this 
  cannot 
  be 
  due 
  to 
  heat 
  generated 
  in 
  the 
  discharge, 
  

   and 
  an 
  alternative 
  theory, 
  that 
  it 
  is 
  due 
  to 
  ionization, 
  has 
  

   been 
  advanced. 
  

  

  In 
  the 
  above 
  paper 
  the 
  authors 
  criticise 
  the 
  argument 
  for 
  the 
  

   ionization 
  theory, 
  and 
  the 
  interpretation 
  of 
  the 
  experimental 
  

   results 
  upon 
  which 
  it 
  is 
  based. 
  They 
  also 
  verify 
  quanti- 
  

   tatively 
  that 
  the 
  effect 
  is 
  purely 
  thermal 
  in 
  origin. 
  

  

  Physics 
  Department, 
  

  

  University 
  of 
  Bristol. 
  

   Jan. 
  7, 
  1918. 
  

  

  Phil. 
  Mag. 
  S. 
  6. 
  Vol. 
  35. 
  No. 
  207. 
  March 
  1918. 
  U 
  

  

  