﻿Pressure 
  Effect 
  in 
  Corona 
  Discharge. 
  265 
  

  

  The 
  excess 
  pressure 
  "p" 
  at 
  the 
  wall 
  of 
  the 
  metal 
  tube 
  is 
  

   given 
  by 
  

  

  = 
  [\ 
  = 
  J_ 
  - 
  _?!_ 
  1°& 
  A 
  / 
  a 
  

  

  J 
  a 
  

  

  When 
  "A" 
  is 
  large 
  compared 
  with 
  "a" 
  this 
  approximately 
  

   _ 
  i 
  

  

  4-7T&' 
  

  

  Putting 
  K 
  = 
  1'4 
  cm. 
  /sec, 
  volt/cm., 
  

  

  and 
  i 
  = 
  5x 
  10~ 
  6 
  amp. 
  per 
  cm., 
  

  

  p 
  approximately^ 
  0*003 
  cm. 
  of 
  water. 
  

  

  This 
  is 
  about 
  0*5 
  per 
  cent, 
  of 
  the 
  pressure 
  actually 
  observed 
  

   by 
  the 
  authors 
  under 
  those 
  conditions, 
  and 
  is 
  therefore 
  a 
  

   quantity 
  which 
  may 
  be 
  neglected. 
  

  

  The 
  authors 
  have 
  been 
  able 
  to 
  verify 
  quantitatively 
  that 
  

   the 
  corona 
  pressure 
  effect 
  is 
  solely 
  due 
  to 
  heat 
  generated 
  in 
  

   the 
  discharge, 
  by 
  supplying 
  heat 
  simultaneously 
  from 
  a 
  

   current 
  in 
  the 
  wire 
  and 
  from 
  corona 
  discharge, 
  instead 
  of 
  

   experimenting 
  separately 
  with 
  each 
  source 
  of 
  supply. 
  The 
  

   electric 
  wind 
  thus 
  operates 
  in 
  rapidly 
  conveying 
  heat 
  to 
  the 
  

   wall 
  of 
  the 
  tube 
  from 
  both 
  sources 
  of 
  supply. 
  Let 
  it 
  be 
  

   assumed 
  that 
  the 
  heat 
  from 
  corona 
  discharge 
  is 
  mainly 
  

   evolved 
  close 
  to 
  the 
  wire; 
  then 
  the 
  wind 
  will 
  be 
  almost 
  

   equally 
  effective 
  in 
  distributing 
  heat, 
  whether 
  it 
  comes 
  from 
  

   discharge 
  or 
  from 
  a 
  current 
  in 
  the 
  wire. 
  In 
  other 
  words, 
  if 
  

   the 
  observed 
  pressure 
  rise 
  is 
  due 
  to 
  heat, 
  it 
  should 
  be 
  approxi- 
  

   mately 
  independent 
  of 
  the 
  source 
  of 
  the 
  heat 
  when 
  wind 
  is 
  

   present. 
  Experiments 
  confirming 
  this 
  conclusion 
  are 
  herewith 
  

   described. 
  

  

  Experiments. 
  

  

  The 
  discharge 
  vessel 
  consisted 
  of 
  a 
  platinum 
  wire 
  of 
  diameter 
  

   •006 
  mm. 
  placed 
  along 
  the 
  axis 
  of 
  a 
  horizontal 
  brass 
  tube 
  of 
  

   diameter 
  2*21 
  cm. 
  and 
  length 
  28 
  cm. 
  To 
  a 
  side 
  tube 
  in 
  the 
  

   latter, 
  one 
  limb 
  of 
  an 
  oil 
  manometer 
  was 
  attached. 
  The 
  brass 
  

   tube 
  was 
  closed 
  by 
  ebonite 
  stoppers, 
  through 
  which 
  the 
  axial 
  

   wire 
  passed. 
  The 
  wire 
  was 
  attached 
  to 
  one 
  pole 
  of 
  a 
  high- 
  

   potential 
  dynamo 
  giving 
  voltages 
  up 
  to 
  5500 
  volts. 
  The 
  

   current 
  between 
  wire 
  and 
  tube 
  was 
  measured 
  by 
  a 
  Paul 
  

   microammeter, 
  shunted 
  when 
  necessary. 
  The 
  potential 
  dif- 
  

   ference 
  was 
  measured 
  by 
  a 
  Braun 
  electrometer 
  previously 
  

   calibrated. 
  One 
  terminal 
  of 
  the 
  galvanometer, 
  the 
  case 
  of 
  

  

  