﻿58 
  L. 
  DeForest 
  — 
  Reflection 
  of 
  Hertzian 
  Waves. 
  

  

  Akt. 
  YII. 
  — 
  Reflection 
  of 
  IleHzian 
  Waves 
  at 
  the 
  Ends 
  of 
  

   Parallel 
  Wires 
  ; 
  by 
  Lee 
  DeFokest. 
  

  

  Since 
  tlie 
  famous 
  experiments 
  of 
  Hertz 
  on 
  electric 
  waves 
  in 
  

   wires, 
  investigators 
  in 
  this 
  field 
  have 
  found 
  most 
  useful 
  the 
  

   arrangement 
  known 
  as 
  the 
  Lecher 
  system, 
  or 
  adaptations 
  of 
  this. 
  

   In 
  its 
  original 
  form 
  this 
  consists 
  essentially 
  of 
  two 
  condensers, 
  

   each 
  of 
  two 
  metal 
  plates, 
  hung 
  parallel. 
  One 
  pair 
  of 
  these 
  is 
  

   connected 
  to 
  the 
  secondary 
  terminals 
  of 
  an 
  induction 
  coil, 
  with 
  

   a 
  spark 
  gap 
  in 
  the 
  circuit. 
  From 
  the 
  other 
  pair 
  of 
  plates 
  lead 
  

   off 
  two 
  long 
  parallel 
  wires. 
  

  

  By 
  the 
  action 
  of 
  the 
  coil 
  the 
  primary 
  plates 
  are 
  charged 
  

   with 
  equal 
  and 
  opposite 
  quantities 
  of 
  electricity, 
  which 
  dis- 
  

   charge 
  across 
  the 
  gap, 
  when 
  the 
  tension 
  has 
  been 
  raised 
  suffi- 
  

   ciently 
  high. 
  Rapid 
  oscillations 
  of 
  a 
  period 
  depending 
  on 
  the 
  

   capacity 
  of 
  the 
  entire 
  system 
  are 
  thus 
  set 
  up, 
  which 
  induce 
  

   corresponding 
  impulses 
  in 
  the 
  secondary 
  plates. 
  Electric 
  

   waves 
  surge 
  over 
  the 
  two 
  wires, 
  to 
  be 
  reflected 
  at 
  their 
  ends 
  

   with 
  a 
  change 
  in 
  intensity 
  and 
  phase 
  depending 
  on 
  the 
  nature 
  

   of 
  the 
  terminal 
  arrangement. 
  

  

  Thus 
  standing 
  waves 
  are 
  set 
  up 
  in 
  the 
  wires, 
  which 
  are 
  the 
  

   better 
  defined, 
  the 
  more 
  nearly 
  the 
  length 
  of 
  the 
  wires 
  

   approaches 
  an 
  integral 
  number 
  of 
  half 
  wave-lengths. 
  

  

  The 
  ease 
  with 
  which 
  these 
  standing 
  waves 
  can 
  here 
  be 
  

   measured, 
  and 
  the 
  symmetry 
  and 
  simplicity 
  of 
  the 
  whole 
  

   arrangement, 
  make 
  this 
  system 
  of 
  the 
  greatest 
  usefulness 
  in 
  all 
  

   researches 
  where 
  the 
  phenomena 
  of 
  waves 
  in 
  wires 
  are 
  to 
  be 
  

   studied. 
  

  

  At 
  the 
  nodes 
  of 
  these 
  standing 
  waves, 
  a 
  conducting 
  body, 
  as 
  

   a 
  wire 
  bridge, 
  may 
  be 
  placed 
  across 
  both 
  wires 
  without 
  inter- 
  

   fering 
  with 
  the 
  action 
  beyond. 
  

  

  At 
  an 
  other 
  point, 
  however, 
  such 
  a 
  bridge 
  harms 
  the 
  effect, 
  

   producing 
  extinction 
  of 
  the 
  glow 
  in 
  a 
  vacuum 
  tube 
  placed 
  

   across 
  the 
  two 
  wires 
  at 
  their 
  ends. 
  

  

  By 
  such 
  means 
  Lecher 
  was 
  enabled 
  to 
  measure 
  readily 
  half 
  

   wave-lengths, 
  between 
  successive 
  bridges 
  ; 
  and 
  inasmuch 
  as 
  

   theory 
  has 
  shown 
  the 
  velocity 
  of 
  propagation 
  in 
  such 
  a 
  system 
  

   to 
  be 
  that 
  of 
  light, 
  he 
  could 
  compute 
  the 
  period 
  of 
  the 
  

   vibration. 
  

  

  With 
  such 
  an 
  apparatus, 
  or 
  with 
  the 
  improved 
  form 
  intro- 
  

   duced 
  by 
  Blondlot, 
  an 
  enormous 
  amount 
  of 
  work 
  in 
  determin- 
  

   ing 
  dielectric 
  constants, 
  indices 
  of 
  reflection, 
  electric 
  dispersion, 
  

   etc., 
  in 
  fluids, 
  has 
  been 
  accomplished, 
  notably 
  by 
  German 
  physi- 
  

   cists. 
  Quantitative 
  experiments 
  have 
  been 
  made 
  with 
  bolom- 
  

   eter, 
  electrometer, 
  or 
  thermo-electric 
  means, 
  and 
  thus 
  the 
  atten- 
  

   uation 
  and 
  curves 
  of 
  the 
  standing 
  waves 
  determined. 
  

  

  