﻿J. 
  Trowbridge 
  — 
  Electrical 
  Conductivity 
  of 
  the 
  Ether. 
  387 
  

  

  Art. 
  XXXYII. 
  — 
  The 
  Electrical 
  Conductivity 
  of 
  the 
  Ether 
  ; 
  

   by 
  John 
  Trowbridge. 
  

  

  I 
  stated 
  in 
  the 
  April 
  number 
  of 
  this 
  Journal 
  that 
  my 
  

   experiments 
  have 
  led 
  me 
  to 
  the 
  conclusion 
  that 
  the 
  chief 
  resist- 
  

   ance 
  in 
  overcoming 
  the 
  apparent 
  resistance 
  of 
  a 
  highly 
  rarified 
  

   medium 
  is 
  encountered 
  at 
  the 
  surface 
  of 
  the 
  electrodes 
  (ueber 
  

   gangschicht) 
  and 
  that 
  when 
  this 
  is 
  overcome 
  the 
  ether 
  offers 
  

   little 
  resistance. 
  The 
  method 
  I 
  have 
  employed 
  seems 
  to 
  me 
  

   to 
  be 
  a 
  very 
  useful 
  one 
  for 
  the 
  study 
  of 
  electrical 
  discharges. 
  

   It 
  may 
  be 
  termed 
  the 
  damping 
  of 
  the 
  additional 
  spark 
  method, 
  

   or 
  the 
  comparison 
  of 
  resistances 
  by 
  the 
  estimation 
  of 
  the 
  damp- 
  

   ing 
  of 
  electrical 
  oscillations.* 
  The 
  electrical 
  circuit 
  is 
  pro- 
  

   vided 
  with 
  two 
  spark 
  gaps. 
  One 
  of 
  these 
  is 
  placed 
  in 
  a 
  gas, 
  

   or 
  under 
  the 
  conditions 
  which 
  are 
  to 
  be 
  examined, 
  while 
  the 
  

   other 
  is 
  photographed 
  according 
  to 
  Feddersen's 
  method 
  by 
  a 
  

   revolving 
  mirror. 
  With 
  cadmium 
  terminals 
  this 
  method 
  

   enables 
  one 
  to 
  estimate 
  the 
  resistance 
  of 
  a 
  spark 
  in 
  air 
  or 
  in 
  

   rarified 
  media 
  to 
  one-half 
  an 
  ohm. 
  

  

  Having 
  at 
  my 
  command 
  a 
  battery 
  giving 
  a 
  voltage 
  of 
  twenty 
  

   thousand, 
  with 
  an 
  internal 
  resistance 
  of 
  only 
  one-quarter 
  of 
  an 
  

   ohm 
  per 
  cell, 
  and 
  capable 
  therefore 
  of 
  giving 
  a 
  very 
  powerful 
  

   current, 
  I 
  first 
  studied 
  the 
  behavior 
  of 
  Crookes 
  tubes 
  which 
  

   were 
  connected 
  to 
  the 
  terminals 
  of 
  this 
  battery. 
  I 
  found 
  that 
  

   no 
  Rontgen 
  rays 
  could 
  be 
  obtained 
  with 
  a 
  voltage 
  of 
  twenty 
  

   thousand. 
  On 
  heating 
  the 
  Crookes 
  tubes, 
  they 
  were 
  filled 
  with 
  

   a 
  pale 
  white 
  light, 
  which 
  showed 
  very 
  faint 
  bands 
  in 
  the 
  green 
  

   when 
  examined 
  by 
  the 
  spectroscope. 
  Then 
  the 
  entire 
  strength 
  

   of 
  the 
  battery 
  appeared 
  to 
  be 
  manifested 
  in 
  the 
  tubes, 
  the 
  elec- 
  

   trodes 
  became 
  red 
  hot 
  — 
  the 
  medium 
  broke 
  down 
  and 
  offered 
  

   no 
  resistance 
  to 
  the 
  current 
  of 
  the 
  battery. 
  This 
  white 
  dis- 
  

   charge 
  showed 
  even 
  at 
  its 
  culminating 
  point 
  no 
  Rontgen 
  rays. 
  

   I 
  then 
  employed 
  the 
  Piante 
  rheostatic 
  machine. 
  This 
  

   apparatus, 
  I 
  think, 
  has 
  not 
  received 
  sufficient 
  attention 
  from 
  

   physicists. 
  In 
  connection 
  with 
  a 
  large 
  battery, 
  it 
  is 
  very 
  

   efficient, 
  and 
  it 
  enables 
  one 
  to 
  form 
  an 
  estimate 
  of 
  the 
  high 
  

   electromotive 
  force 
  that 
  one 
  employs 
  in 
  the 
  study 
  of 
  the 
  

   Rontgen 
  rays. 
  I 
  have 
  slightly 
  modified 
  the 
  form 
  of 
  the 
  

   machine 
  as 
  it 
  is 
  given 
  by 
  Piante. 
  The 
  main 
  principle 
  consists 
  

   in 
  discharging 
  Leyden 
  jars 
  in 
  multiple 
  and 
  then 
  discharging 
  

   them 
  in 
  series. 
  The 
  proportion 
  of 
  the 
  length 
  of 
  spark 
  to 
  the 
  

   number 
  of 
  jars 
  is 
  very 
  close. 
  Knowing 
  the 
  electromotive 
  

   force 
  of 
  the 
  battery 
  which 
  charges 
  the 
  jars, 
  we 
  can 
  estimate 
  

   the 
  voltage 
  necessary 
  to 
  produce 
  sparks 
  of 
  different 
  lengths. 
  I 
  

  

  * 
  Damping 
  of 
  Electrical 
  Oscillations 
  on 
  iron 
  wires, 
  Phil. 
  Mag., 
  Dec, 
  1891. 
  Also 
  

   American 
  Journal 
  of 
  Science, 
  April, 
  1897. 
  

  

  