﻿390 
  J. 
  Trowbridge 
  — 
  Electrical 
  Conductivity 
  of 
  the 
  Ether. 
  

  

  direction 
  of 
  the 
  latter. 
  Is 
  it 
  possible 
  that, 
  the 
  ether 
  being 
  

   already 
  under 
  a 
  magnetic 
  stress, 
  the 
  addition 
  of 
  a 
  powerful 
  

   electrostatic 
  stress 
  serves 
  to 
  suddenly 
  break 
  down 
  the 
  ether? 
  

   It 
  is 
  well 
  known 
  that 
  a 
  blast 
  of 
  air 
  imitates 
  the 
  action 
  of 
  the 
  

   magnetic 
  field. 
  It 
  probably 
  does 
  so 
  by 
  blowing 
  out 
  the 
  vol- 
  

   taic 
  arc 
  which 
  tends 
  to 
  form. 
  It 
  may 
  be 
  that 
  the 
  electro- 
  

   dynamic 
  repulsion 
  compels 
  the 
  spark 
  not 
  to 
  follow, 
  so 
  to 
  speak, 
  

   the 
  voltaic 
  arc 
  and 
  its 
  current 
  of 
  heated 
  air. 
  The 
  loud 
  report 
  

   may 
  indicate 
  a 
  sudden 
  stress 
  in 
  the 
  medium, 
  and 
  in 
  the 
  case 
  of 
  

   the 
  Crookes 
  tube 
  the 
  highly 
  rarified 
  medium 
  within 
  it 
  would 
  

   effectually 
  prevent 
  our 
  hearing 
  a 
  similar 
  report. 
  

  

  I 
  next 
  placed 
  the 
  primary 
  spark 
  of 
  the 
  Thomson 
  Tesla 
  trans- 
  

   former 
  near 
  a 
  Crookes 
  tube 
  which 
  was 
  giving 
  out 
  the 
  Rontgen 
  

   rays. 
  I 
  could 
  not 
  perceive 
  any 
  mutual 
  effect. 
  The 
  effect, 
  

   moreover, 
  of 
  ultra 
  violet 
  light 
  on 
  the 
  resistance 
  of 
  sparks 
  in 
  

   air 
  could 
  not 
  be 
  detected. 
  

  

  The 
  method 
  I 
  have 
  outlined 
  enables 
  one 
  to 
  form 
  an 
  estimate 
  

   of 
  the 
  energy 
  incident 
  upon 
  the 
  production 
  of 
  the 
  Rontgen 
  

   rays. 
  It 
  can 
  also 
  measure 
  with 
  greater 
  accuracy 
  the 
  resistance 
  

   of 
  sparks 
  in 
  air 
  and 
  different 
  media. 
  It 
  shows 
  conclusively 
  

   that 
  the 
  discharge 
  in 
  a 
  Crookes 
  tube 
  at 
  the 
  instant 
  when 
  the 
  

   Rontgen 
  rays 
  are 
  being 
  emitted 
  most 
  intensely, 
  is 
  an 
  oscilla- 
  

   tory 
  discharge. 
  In 
  popular 
  language 
  it 
  can 
  be 
  maintained 
  that 
  

   a 
  discharge 
  of 
  lightning 
  a 
  mile 
  long 
  under 
  certain 
  conditions 
  

   encounters 
  no 
  more 
  resistance 
  during 
  its 
  oscillations 
  than 
  one 
  

   of 
  a 
  foot 
  in 
  length. 
  In 
  other 
  words 
  Ohm's 
  law 
  does 
  not 
  hold 
  

   for 
  electric 
  sparks 
  in 
  air 
  or 
  gases. 
  Disruptive 
  discharges 
  in 
  

   gases 
  and 
  in 
  air 
  appear 
  to 
  be 
  of 
  the 
  nature 
  of 
  voltaic 
  arcs. 
  

   Each 
  oscillation 
  can 
  be 
  considered 
  as 
  forming 
  an 
  arc. 
  It 
  is 
  

   well 
  known 
  that 
  a 
  minute 
  spark 
  precedes 
  the 
  formation 
  of 
  the 
  

   voltaic 
  arc 
  in 
  air. 
  The 
  medium 
  is 
  first 
  broken 
  down 
  and 
  then 
  

   the 
  arc 
  follows. 
  I 
  believe 
  that 
  this 
  process 
  occurs 
  also 
  in 
  a 
  

   vacuum 
  and 
  that 
  absolute 
  contact 
  is 
  not 
  necessary 
  to 
  start 
  the 
  

   arc. 
  My 
  experiments 
  lead 
  me 
  to 
  conclude 
  that 
  under 
  very 
  

   high 
  electrical 
  stress 
  the 
  ether 
  breaks 
  down 
  and 
  becomes 
  a 
  good 
  

   conductor. 
  

  

  Jefferson 
  Physical 
  Laboratory, 
  Harvard 
  University. 
  

  

  