﻿Electric 
  Wind 
  from 
  a 
  Discharging 
  Point. 
  701 
  

  

  (3) 
  The 
  simplest 
  explanation 
  is 
  that 
  this 
  z 
  region 
  is 
  one 
  

   of 
  considerable 
  ionization 
  extending 
  far 
  beyond 
  the 
  limits 
  of 
  

   the 
  glow. 
  This 
  ionization 
  maybe 
  brought 
  about 
  by 
  collisions 
  

   between 
  molecules 
  and 
  ions 
  or 
  other 
  bodies 
  proceeding 
  from 
  

   the 
  glow, 
  or 
  by 
  the 
  emission 
  of 
  certain 
  radiations, 
  possibly 
  

   some 
  intense 
  form 
  of 
  Entladungstrahlen, 
  from 
  the 
  glow 
  

   at 
  the 
  point. 
  In 
  the 
  latter 
  case 
  z 
  might 
  be 
  independent 
  of 
  

   the 
  field 
  F, 
  in 
  that 
  it 
  would 
  be 
  merely 
  a 
  measure 
  of 
  the 
  

   path 
  of 
  these 
  radiations 
  before 
  absorption. 
  Such 
  radiations 
  

   would 
  probably 
  be 
  independent 
  of 
  the 
  distribution 
  of 
  the 
  

   electric 
  field 
  and 
  would 
  be 
  absorbed 
  according 
  to 
  a 
  density 
  

   law, 
  and 
  therefore 
  in 
  a 
  distance 
  inversely 
  proportional 
  to 
  II. 
  

   The 
  experimental 
  evidence 
  is 
  thus 
  in 
  favour 
  of 
  this 
  view, 
  

   although 
  it 
  throws 
  no 
  light 
  on 
  the 
  exact 
  nature 
  of 
  this 
  

   radiation. 
  The 
  radiation 
  would 
  have 
  to 
  be 
  of 
  an 
  extremely 
  

   intense 
  nature 
  because 
  one 
  is 
  dealing 
  with 
  the 
  wind 
  effects 
  

   of 
  a 
  current 
  which 
  is 
  many 
  times 
  greater 
  than 
  the 
  ordinary 
  

   ionization 
  currents 
  at 
  high 
  pressures. 
  

  

  The 
  values 
  of 
  z 
  Q 
  in 
  air 
  and 
  C0 
  2 
  are 
  *2 
  cm. 
  and 
  *46 
  cm. 
  

   respectively. 
  Thus, 
  although 
  z 
  is 
  inversely 
  proportional 
  to 
  

   density 
  in 
  a 
  given 
  gas, 
  there 
  is 
  no 
  such 
  simple 
  relation 
  when 
  

   its 
  values 
  are 
  compared 
  in 
  different 
  gases. 
  If, 
  therefore, 
  z 
  

   is 
  brought 
  about 
  by 
  radiations 
  from 
  the 
  glow 
  at 
  the 
  point, 
  the 
  

   penetrating 
  power 
  of 
  these 
  radiations 
  must 
  depend 
  upon 
  the 
  

   gas 
  in 
  which 
  they 
  are 
  produced. 
  

  

  Summary. 
  

  

  1. 
  An 
  improved 
  apparatus 
  for 
  the 
  measurement 
  of 
  the 
  

   pressure 
  of 
  the 
  electric 
  wind 
  from 
  point-plate 
  discharge 
  under 
  

   different 
  atmospheric 
  pressures 
  has 
  been 
  set 
  up. 
  

  

  2. 
  The 
  curves 
  of 
  wind- 
  pressure 
  p 
  and 
  distance 
  between 
  

   the 
  electrodes 
  z 
  agree 
  in 
  form 
  at 
  normal 
  atmospheric 
  pressure 
  

   with 
  those 
  of 
  other 
  observers 
  and 
  cut 
  the 
  z 
  axis 
  at 
  a 
  distance 
  

   z 
  from 
  the 
  origin. 
  

  

  3. 
  The 
  results 
  at 
  different 
  atmospheric 
  pressures 
  II, 
  in 
  air 
  

   and 
  C0 
  2 
  , 
  show 
  that 
  z 
  is 
  proportional 
  to 
  l/II. 
  This 
  supports 
  

   the 
  view 
  that 
  z 
  is 
  the 
  result 
  of 
  intense 
  ionization 
  possibly 
  

   brought 
  about 
  by 
  radiations 
  from 
  the 
  point, 
  which 
  are 
  

   absorbed 
  in 
  a 
  given 
  gas 
  according 
  to 
  a 
  density 
  law. 
  

  

  The 
  above 
  experiments 
  were 
  carried 
  out 
  in 
  the 
  Physical 
  

   Laboratories 
  of 
  the 
  University 
  of 
  Bristol. 
  

  

  My 
  thanks 
  are 
  due 
  to 
  Dr. 
  A. 
  M. 
  Tyndall 
  for 
  kindly 
  

   suggesting 
  the 
  research, 
  and 
  for 
  constant 
  advice 
  during 
  the 
  

   course 
  of 
  the 
  work, 
  and 
  to 
  Mr. 
  J. 
  D. 
  Fry 
  for 
  help 
  in 
  setting 
  

   up 
  the 
  pressure-gauge. 
  

  

  