﻿262 
  Dr. 
  A. 
  M. 
  Tyndall 
  and 
  Miss 
  Searle 
  on 
  the 
  

  

  effect 
  (1) 
  due 
  to 
  discharge, 
  and 
  (2) 
  due 
  to 
  a 
  heating 
  current 
  

   passed 
  through 
  the 
  wire, 
  and 
  has 
  re-affirmed 
  the 
  view 
  that 
  

   the 
  two 
  effects 
  are 
  quite 
  distinct. 
  

  

  Now 
  in 
  the 
  past 
  there 
  has 
  been 
  general 
  agreement 
  among 
  

   physicists 
  that 
  in 
  an 
  ordinary 
  glow 
  discharge 
  the 
  fraction 
  of 
  

   molecules 
  which 
  are 
  ionized 
  is 
  a 
  negligible 
  quantity. 
  It 
  seems 
  

   therefore 
  desirable 
  to 
  settle 
  conclusively 
  what 
  is 
  the 
  origin 
  

   of 
  the 
  pressure 
  rise. 
  

  

  The 
  object 
  of 
  the 
  present 
  paper 
  is 
  to 
  point 
  out 
  several 
  

   fallacies 
  in 
  the 
  arguments 
  of 
  the 
  advocates 
  of 
  the 
  ionization 
  

   theory, 
  and 
  to 
  present 
  a 
  quantitative 
  verification 
  of 
  the 
  

   statement 
  that 
  this 
  sudden 
  rise 
  of 
  pressure 
  accompanying 
  

   the 
  start 
  of 
  corona 
  discharge 
  is 
  purely 
  a 
  thermal 
  effect. 
  

  

  It 
  must 
  first 
  be 
  pointed 
  out 
  that 
  the 
  formula 
  given 
  above, 
  

   upon 
  which 
  the 
  advocates 
  of 
  the 
  ionization 
  theory 
  base 
  much 
  

   of 
  their 
  work, 
  is 
  necessarily 
  incorrect. 
  This 
  may 
  readily 
  be 
  

   seen 
  by 
  applying 
  the 
  test 
  of 
  dimensions 
  to 
  the 
  terms 
  of 
  the 
  

   equation. 
  Before 
  the 
  dimensions 
  of 
  the 
  two 
  terms 
  can 
  be 
  

   equated, 
  the 
  left-hand 
  term 
  must 
  be 
  multiplied 
  by 
  a 
  time 
  " 
  t." 
  

   The 
  equation 
  then 
  takes 
  the 
  form 
  it 
  would 
  have 
  if 
  the 
  

   pressure 
  effect 
  was 
  due 
  entirely 
  to 
  heat 
  generated 
  in 
  a 
  

   vessel 
  of 
  constant 
  volume, 
  from 
  which 
  the 
  radiation 
  losses 
  

   were 
  always 
  a 
  constant 
  fraction 
  of 
  the 
  heat 
  supplied. 
  If 
  

   reference 
  be 
  made 
  to 
  the 
  proof 
  of 
  this 
  formula 
  in 
  Kunz's 
  

   paper, 
  it 
  will 
  be 
  seen 
  that 
  in 
  steps 
  1 
  and 
  4 
  a 
  time 
  factor 
  has 
  

   been 
  erroneously 
  omitted. 
  

  

  But 
  this 
  does 
  not 
  dispose 
  of 
  a 
  further 
  argument 
  which 
  has 
  

   been 
  brought 
  forward 
  : 
  namely, 
  that 
  the 
  pressure 
  effect 
  at 
  

   the 
  start 
  of 
  the 
  discharge 
  is 
  far 
  too 
  sudden 
  to 
  be 
  accounted 
  

   for 
  by 
  heat 
  generated 
  during 
  discharge, 
  and 
  that 
  the 
  rise 
  

   in 
  pressure 
  due 
  to 
  the 
  latter 
  is 
  only 
  appreciable 
  after 
  the 
  

   discharge 
  has 
  been 
  passing 
  for 
  some 
  time. 
  

  

  Thus 
  Warner 
  has 
  published 
  a 
  number 
  of 
  curves 
  showing 
  

   that 
  the 
  " 
  corona 
  pressure 
  " 
  reached 
  its 
  full 
  value 
  within 
  

   3 
  seconds 
  of 
  the 
  start 
  of 
  discharge, 
  whereas 
  in 
  the 
  corre- 
  

   sponding 
  effect 
  produced 
  by 
  heating 
  the 
  wire 
  this 
  did 
  

   not 
  occur 
  until 
  about 
  15 
  seconds 
  after 
  the 
  heating 
  current 
  

   was 
  switched 
  on. 
  Moreover, 
  the 
  rise 
  in 
  pressure 
  produced 
  

   by 
  the 
  dissipation 
  of 
  a 
  given 
  amount 
  of 
  energy 
  in 
  the 
  wire 
  

   was 
  much 
  greater 
  than 
  that 
  accompanying 
  the 
  same 
  dissi- 
  

   pation 
  of 
  energy 
  in 
  the 
  glow 
  discharge. 
  

  

  But 
  the 
  argument 
  that 
  the 
  pressure 
  effects 
  in 
  the 
  two 
  

   cases 
  must 
  therefore 
  be 
  different 
  in 
  origin 
  entirely 
  break* 
  

  

  