﻿388 
  J. 
  Trowbridge 
  — 
  Electrical 
  Conductivity 
  of 
  the 
  Ether. 
  

  

  speedily 
  found 
  that 
  at 
  least 
  one 
  hundred 
  thousand 
  volts 
  were 
  

   necessary 
  to 
  produce 
  the 
  Rontgen 
  rays 
  and 
  they 
  were 
  produced 
  

   more 
  intensely 
  as 
  I 
  increased 
  the 
  voltage, 
  certainly 
  to 
  the 
  point 
  

   of 
  five 
  hundred 
  thousand 
  volts. 
  

  

  In 
  order 
  to 
  ascertain 
  whether 
  the 
  discharges 
  through 
  the 
  

   Crookes 
  tubes 
  when 
  the 
  Rontgen 
  rays 
  were 
  apparently 
  pro- 
  

   duced 
  most 
  strongly 
  were 
  oscillatory, 
  I 
  first 
  placed 
  a 
  Geissler 
  

   tube 
  in 
  the 
  circuit 
  with 
  the 
  Crookes 
  tube 
  and 
  carefully 
  

   observed 
  the 
  appearance 
  of 
  the 
  two 
  electrodes 
  of 
  the 
  Geissler 
  

   tube. 
  They 
  were 
  quite 
  alike 
  and 
  indicated 
  an 
  oscillatory 
  dis- 
  

   charge. 
  I 
  then 
  replaced 
  the 
  latter 
  tube 
  by 
  a 
  small 
  spark 
  gap 
  

   and 
  photographed 
  it 
  in 
  a 
  rapidly 
  revolving 
  mirror. 
  The 
  pho- 
  

   tograph 
  showed 
  at 
  least 
  ten 
  oscillations 
  with 
  a 
  period 
  of 
  about 
  

   one 
  ten-millionth 
  of 
  a 
  second 
  with 
  the 
  Crookes 
  tube 
  and 
  the 
  cir- 
  

   cuit 
  I 
  employed. 
  Furthermore, 
  applying 
  the 
  method 
  of 
  esti- 
  

   mating 
  resistances 
  by 
  the 
  method 
  of 
  damping, 
  I 
  found 
  that 
  

   the 
  resistance 
  of 
  the 
  rarified 
  medium 
  was 
  less 
  than 
  five 
  ohms. 
  

   The 
  energy, 
  therefore, 
  at 
  the 
  moment 
  of 
  the 
  emission 
  of 
  the 
  

   Rontgen 
  rays, 
  was 
  not 
  far 
  from 
  three 
  million 
  horse 
  power, 
  act- 
  

   ing 
  for 
  one 
  millionth 
  of 
  a 
  second. 
  I 
  employed 
  also 
  a 
  Crookes 
  

   tube 
  with 
  an 
  aluminum 
  mirror 
  of 
  about 
  two 
  centimeters 
  focus. 
  

   The 
  resistance 
  of 
  this 
  tube 
  to 
  the 
  discharge 
  was 
  the 
  same 
  as 
  

   that 
  in 
  which 
  the 
  mirror 
  had 
  a 
  focal 
  length 
  of 
  six 
  centimeters. 
  

   Incidentally, 
  there 
  seems 
  to 
  be 
  no 
  advantage 
  in 
  shortening 
  the 
  

   distance 
  between 
  the 
  cathode 
  and 
  the 
  anode 
  — 
  by 
  employing 
  a 
  

   mirror 
  of 
  short 
  focus. 
  Struck 
  by 
  the 
  fact 
  that 
  the 
  distance 
  

   between 
  the 
  electrodes 
  did 
  not 
  appear 
  to 
  make 
  any 
  appreciable 
  

   difference 
  in 
  the 
  resistance 
  of 
  the 
  Crookes 
  tube, 
  I 
  replaced 
  the 
  

   latter 
  by 
  a 
  spark 
  gap 
  of 
  six 
  inches 
  in 
  length 
  in 
  air, 
  and 
  photo- 
  

   graphed 
  the 
  spark 
  in 
  another 
  gap 
  in 
  air 
  in 
  the 
  same 
  circuit. 
  

   This 
  latter 
  gap 
  was 
  one-quarter 
  of 
  an 
  inch. 
  The 
  photographs 
  

   showed 
  on 
  an 
  average 
  the 
  same 
  number 
  of 
  oscillations 
  whether 
  

   the 
  additional 
  spark 
  gap 
  was 
  six 
  inches 
  in 
  length 
  or 
  one 
  inch 
  in 
  

   length. 
  I 
  found, 
  moreover, 
  that 
  on 
  increasing 
  the 
  electromo- 
  

   tive 
  force 
  the 
  resistance 
  of 
  the 
  sparks 
  in 
  air 
  decreased. 
  By 
  

   quickly 
  drawing 
  apart 
  the 
  terminals 
  of 
  my 
  large 
  battery 
  I 
  can 
  

   produce 
  a 
  flaming 
  discharge 
  in 
  air 
  of 
  about 
  three 
  feet 
  in 
  

   length. 
  Rhigi 
  has 
  also 
  observed 
  the 
  same 
  phenomenon 
  with 
  

   sparks 
  from 
  an 
  electrical 
  machine. 
  We 
  see 
  that 
  no 
  increase 
  in 
  

   resistance 
  results. 
  I 
  then 
  placed 
  the 
  secondary 
  spark 
  gap 
  in 
  a 
  

   receiver 
  and 
  studied 
  the 
  resistance 
  offered 
  by 
  rarified 
  air 
  at 
  the 
  

   point 
  when 
  long 
  ribbon 
  light 
  white 
  disruptive 
  discharges 
  can 
  

   be 
  obtained. 
  This 
  point 
  is 
  at 
  about 
  100 
  cm 
  pressure. 
  The 
  

   resistance 
  of 
  such 
  discharges 
  of 
  about 
  six 
  inches 
  in 
  length 
  in 
  a 
  

   receiver 
  containing 
  air 
  at 
  this 
  pressure 
  is 
  two 
  or 
  three 
  ohms 
  

   more 
  than 
  sparks 
  of 
  one 
  quarter 
  of 
  an 
  inch 
  in 
  air, 
  which 
  have 
  

   a 
  resistance 
  of 
  from 
  2 
  to 
  3 
  ohms. 
  On 
  measuring 
  by 
  the 
  above 
  

  

  