﻿330 
  Trowbridge 
  and 
  Richards 
  — 
  Temperature 
  and 
  

  

  red 
  glow 
  disappeared 
  in 
  the 
  tube, 
  and 
  discovered, 
  on 
  develop- 
  

   ing 
  the 
  photographs 
  which 
  were 
  obtained 
  by 
  means 
  of 
  the 
  

   revolving 
  mirror, 
  that 
  the 
  discharge 
  was 
  non-oscillatory. 
  When, 
  

   however, 
  the 
  resistance 
  in 
  the 
  condenser 
  circuit 
  was 
  dimin- 
  

   ished, 
  the 
  red 
  glow 
  began 
  to 
  appear, 
  and 
  the 
  photographs 
  

   taken 
  when 
  all 
  the 
  resistance 
  except 
  the 
  tube 
  itself 
  was 
  

   removed 
  showed 
  that 
  the 
  discharge 
  was 
  oscillatory. 
  This 
  also 
  

   was 
  evident 
  from 
  the 
  peculiar 
  crackle 
  of 
  the 
  spark, 
  which 
  

   Hertz 
  remarked 
  was 
  essential 
  in 
  performing 
  his 
  experiments 
  

   on 
  electric 
  waves. 
  The 
  apparatus 
  used 
  in 
  this 
  and 
  subsequent 
  

   experiments 
  is 
  sketched 
  in 
  the 
  accompanying 
  diagram 
  (fig. 
  1). 
  

   An 
  examination 
  of 
  our 
  photographs 
  showed 
  the 
  interesting 
  

   fact 
  that 
  there 
  were 
  in 
  general 
  not 
  more 
  than 
  two 
  or 
  three 
  

   complete 
  oscillations; 
  the 
  remaining 
  ones 
  which 
  could 
  have 
  

   been 
  obtained 
  from 
  the 
  given 
  capacity 
  and 
  self-induction 
  hav- 
  

   ing 
  been 
  damped 
  by 
  the 
  resistance 
  of 
  the 
  gas. 
  The 
  question 
  

   immediately 
  arose 
  : 
  what 
  is 
  the 
  resistance 
  of 
  the 
  gas 
  at 
  the 
  

   instant 
  of 
  the 
  discharge 
  ? 
  For 
  if 
  an 
  idea 
  of 
  this 
  can 
  be 
  

   obtained 
  we 
  can 
  get 
  an 
  estimate 
  of 
  the 
  amount 
  of 
  heat 
  devel- 
  

   oped 
  in 
  the 
  gas 
  during 
  each 
  oscillation. 
  A 
  Thomson 
  electro- 
  

   static 
  voltmeter 
  connected 
  to 
  the 
  ends 
  of 
  the 
  hydrogen 
  tube 
  

   indicated 
  a 
  difference 
  of 
  potential 
  of 
  over 
  1,800 
  volts, 
  and 
  this 
  

   difference 
  of 
  potential 
  could 
  only 
  be 
  obtained 
  by 
  substituting 
  

   for 
  the 
  Greissler 
  tube 
  a 
  resistance 
  of 
  many 
  thousand 
  ohms. 
  

   The 
  indications, 
  however, 
  of 
  this 
  instrument 
  in 
  this 
  case 
  are 
  of 
  

   no 
  value 
  ; 
  for 
  we 
  discovered 
  that 
  a 
  resistance 
  of 
  from 
  ten 
  to 
  

   twenty 
  ohms 
  was 
  sufficient 
  to 
  produce 
  the 
  same 
  amount 
  of 
  damp- 
  

   ing 
  which 
  the 
  gas 
  exerted. 
  The 
  resistance 
  of 
  the 
  gas, 
  therefore, 
  

   could 
  not 
  be 
  greater 
  than 
  these 
  amounts.* 
  It 
  is 
  evident, 
  there- 
  

   fore, 
  why 
  the 
  voltmeter 
  gives 
  erroneous 
  readings. 
  On 
  account 
  

   of 
  the 
  inertia 
  of 
  the 
  moving 
  parts 
  and 
  the 
  very 
  short 
  time 
  of 
  

   the 
  discharge, 
  it 
  does 
  not 
  indicate 
  the 
  fall 
  of 
  potential 
  through 
  

   the 
  small 
  resistance 
  of 
  the 
  tube 
  during 
  the 
  instant 
  when 
  the 
  

   discharge 
  passes, 
  but 
  maintains 
  an 
  indication 
  of 
  a 
  high 
  differ- 
  

   ence 
  of 
  potential. 
  

  

  In 
  order 
  to 
  apply 
  systematically 
  this 
  new 
  method 
  of 
  measur- 
  

   ing 
  resistance, 
  our 
  next 
  step 
  was 
  to 
  prepare 
  a 
  series 
  of 
  stand- 
  

   ards, 
  — 
  photographs 
  of 
  the 
  oscillatory 
  sparks 
  of 
  condensers 
  of 
  

   different 
  sizes, 
  damped 
  by 
  known 
  resistances, 
  which 
  were 
  sub- 
  

   stituted 
  for 
  the 
  Geissler 
  tube 
  in 
  the 
  condenser 
  circuit. 
  In 
  all 
  

   these 
  experiments, 
  of 
  course, 
  the 
  small 
  resistance 
  on 
  the 
  left 
  

   hand 
  side 
  of 
  the 
  sketch 
  was 
  cut 
  out 
  by 
  a 
  suitable 
  key. 
  Three 
  

   large 
  Leyden 
  jars, 
  each 
  30 
  centimeters 
  in 
  diameter 
  and 
  50 
  

   centimeters 
  high, 
  having 
  a 
  capacity 
  of 
  6,000 
  electrostatic 
  units 
  

   apiece, 
  were 
  used 
  either 
  singly 
  or 
  together 
  to 
  act 
  as 
  the 
  con- 
  

   denser; 
  the 
  waves 
  generated 
  by 
  these 
  large 
  capacities 
  were 
  

  

  * 
  Damping 
  of 
  electrical 
  oscillations, 
  Proc. 
  Am. 
  Acad., 
  1891. 
  

  

  