﻿J. 
  Trowbridge 
  — 
  Does 
  a 
  Vacuum 
  conduct 
  Electricity 
  f 
  343 
  

  

  Art. 
  XXXII. 
  — 
  Does 
  a 
  Vacuum 
  conduct 
  Electricity? 
  / 
  by 
  

   John 
  Trowbridge. 
  

  

  This 
  question 
  has 
  been 
  answered 
  affirmatively 
  by 
  Edlund, 
  

   and 
  negatively 
  by 
  the 
  latest 
  researches 
  of 
  Professor 
  J. 
  J. 
  

   Thomson. 
  Some 
  recent 
  experiments 
  of 
  my 
  own 
  lead 
  me 
  to 
  

   believe 
  that 
  the 
  principal 
  resistance 
  resides 
  at 
  the 
  boundary 
  

   between 
  the 
  highly 
  rarified 
  space 
  in 
  a 
  Crookes 
  tube, 
  for 
  

   instance, 
  and 
  the 
  electrodes. 
  I 
  find 
  by 
  photography 
  that 
  the 
  

   electrical 
  discharge 
  which 
  produces 
  the 
  Pontgen 
  rays 
  oscillates 
  

   and 
  the 
  number 
  of 
  oscillations 
  gave 
  in 
  the 
  tube 
  experimented 
  

   with 
  a 
  resistance 
  in 
  the 
  tube 
  at 
  the 
  moment 
  of 
  discharge 
  of 
  

   only 
  live 
  ohms. 
  In 
  the 
  case 
  of 
  a 
  disruptive 
  discharge 
  of 
  elec- 
  

   tricity, 
  therefore, 
  after 
  the 
  initial 
  resistance 
  of 
  the 
  medium 
  breaks 
  

   clown 
  it 
  exhibits 
  hardly 
  any 
  resistance 
  during 
  the 
  oscillations 
  of 
  

   the 
  discharge. 
  I 
  produced 
  the 
  proper 
  conditions 
  by 
  employing 
  

   a 
  Plante 
  rheostatic 
  machine* 
  or 
  in 
  other 
  words 
  an 
  arrangement 
  

   by 
  means 
  of 
  which 
  Leyden 
  jars 
  can 
  be 
  charged 
  in 
  multiple 
  

   and 
  discharged 
  in 
  series. 
  A 
  highly 
  disruptive 
  spark 
  can 
  thus 
  

   be 
  obtained 
  with 
  a 
  storage 
  battery 
  of 
  ten 
  thousand 
  cells. 
  This 
  

   Plante 
  accumulator 
  does 
  not 
  reverse 
  its 
  poles 
  and 
  is 
  therefore 
  

   extremely 
  useful 
  in 
  studying 
  the 
  Pontgen 
  phenomenon. 
  I 
  

   was 
  extremely 
  interested, 
  however, 
  in 
  discovering 
  that 
  the 
  

   electrical 
  discharge 
  through 
  the 
  Crookes 
  tube 
  at 
  the 
  moment 
  

   when 
  the 
  Pontgen 
  rays 
  were 
  being 
  produced 
  most 
  strongly 
  

   was 
  an 
  oscillatory 
  one, 
  of 
  a 
  high 
  period, 
  about 
  ten 
  million 
  

   oscillations 
  per 
  second 
  in 
  the 
  case 
  I 
  examined. 
  Perfect 
  defini- 
  

   tion, 
  therefore, 
  cannot 
  be 
  obtained 
  even 
  with 
  the 
  use 
  of 
  an 
  

   electrical 
  machine 
  unless 
  care 
  is 
  taken 
  to 
  shield 
  the 
  anode 
  from 
  

   the 
  photographic 
  plate. 
  

  

  By 
  applying 
  the 
  same 
  method 
  to 
  electrical 
  sparks 
  in 
  air, 
  I 
  

   have 
  discovered 
  that 
  a 
  spark 
  of 
  six 
  inches 
  indicates 
  little 
  if 
  any 
  

   more 
  resistance 
  than 
  a 
  spark 
  of 
  one 
  inch. 
  The 
  sparks 
  there- 
  

   fore 
  do 
  not 
  follow 
  Ohm's 
  law. 
  All 
  my 
  experiments 
  lead 
  me 
  to 
  

   believe 
  that 
  a 
  disruptive 
  discharge 
  of 
  electricity 
  encounters 
  its 
  

   chief 
  resistance 
  at 
  the 
  going 
  over 
  layer 
  between 
  the 
  electrodes 
  

   and 
  the 
  medium 
  ; 
  and 
  that 
  during 
  the 
  discharge 
  in 
  a 
  highly 
  

   rarified 
  medium 
  very 
  little 
  resistance 
  is 
  encountered. 
  By 
  the 
  

   method 
  employed 
  an 
  increase 
  or 
  diminution 
  of 
  resistance 
  of 
  

   half 
  an 
  ohm 
  can 
  be 
  detected. 
  The 
  resistance 
  of 
  the 
  Crookes 
  

   tube 
  to 
  the 
  disruptive 
  discharges 
  seems 
  to 
  diminish 
  with 
  the 
  

   increase 
  of 
  rarefaction 
  or 
  the 
  nearer 
  we 
  approach 
  a 
  vacuum. 
  

  

  * 
  Comptes 
  Rendus, 
  lxxxv, 
  p. 
  794, 
  1877. 
  

   Jefferson 
  Physical 
  Laboratory, 
  March 
  9, 
  1897. 
  

  

  