﻿Z. 
  DeFo7'est 
  — 
  Reflection 
  of 
  Hertzian 
  Waves. 
  61 
  

  

  eye-shade. 
  Then 
  by 
  means 
  of 
  an 
  endless 
  cord 
  passed 
  through 
  

   two 
  pulleys 
  and 
  running 
  below 
  the 
  wires, 
  the 
  observer 
  stationed 
  

   at 
  the 
  tube 
  could 
  slide 
  a 
  bridge, 
  attached 
  to 
  the 
  cord 
  by 
  

   wooden 
  clamps, 
  along 
  the 
  wires. 
  

  

  When 
  a 
  node 
  was 
  located 
  by 
  this 
  means, 
  the 
  place 
  was 
  

   marked, 
  a 
  new 
  bridge 
  hung 
  there, 
  and 
  the 
  sliding 
  bridge 
  then 
  

   moved 
  farther 
  along 
  the 
  wires. 
  On 
  each 
  bridge 
  was 
  hung 
  a 
  

   wooden 
  block 
  to 
  hold 
  it 
  fixed 
  in 
  place 
  and 
  in 
  good 
  contact. 
  

   To 
  facilitate 
  measurements 
  a 
  long 
  scale-piece, 
  graduated 
  in 
  

   half-centimeters, 
  was 
  below 
  the 
  wires, 
  and 
  the 
  intervals 
  

   between 
  bridges 
  read 
  therefrom 
  by 
  means 
  of 
  a 
  sliding 
  index 
  

   arm. 
  

  

  For 
  the 
  purposes 
  intended 
  the 
  vacuum 
  tube 
  was 
  the 
  best 
  

   indicator 
  known, 
  though 
  but 
  roughly 
  quantitative. 
  To 
  reduce 
  

   the 
  deforming 
  effect 
  on 
  the 
  standing 
  waves 
  from 
  its 
  capacity 
  

   to 
  a 
  minimum, 
  no 
  electrode 
  nor 
  tinfoil 
  was 
  used, 
  the 
  bare 
  tube 
  

   being 
  laid 
  across 
  the 
  parallel 
  wires. 
  Even 
  then 
  it 
  possessed 
  a 
  

   capacity, 
  as 
  found 
  by 
  a 
  long 
  series 
  of 
  measurements, 
  equivalent 
  

   to 
  a 
  length 
  of 
  -1^"^ 
  of 
  the 
  line. 
  This 
  was 
  independent 
  of 
  the 
  

   wave-lengths 
  used, 
  and 
  was 
  thereafter 
  allowed 
  for 
  in 
  all 
  meas- 
  

   urements 
  of 
  wave-lengths 
  where 
  the 
  tube 
  was 
  present. 
  

  

  Relation 
  hetioeen 
  Change 
  of 
  Phase 
  in 
  Reflection 
  from 
  Open 
  Rnds^ 
  

   and 
  the 
  Frequency. 
  

  

  When 
  an 
  electric 
  wave 
  passes 
  along 
  a 
  conductor 
  we 
  have 
  at 
  

   any 
  point 
  this 
  relation 
  between 
  the 
  E. 
  M. 
  F. 
  and 
  current 
  : 
  

  

  ax 
  at 
  

  

  where 
  <^ 
  = 
  Electro-static 
  potential 
  

  

  C 
  = 
  Current 
  

  

  R 
  = 
  Resistance 
  of 
  the 
  circuit 
  per 
  cm. 
  

  

  L 
  = 
  Self-induction 
  " 
  " 
  " 
  

  

  Let 
  S 
  = 
  Elect, 
  static 
  capacity 
  '* 
  

  

  Q 
  =r 
  Quantity 
  of 
  electricity 
  per 
  unit 
  length. 
  

  

  dx 
  

   Then 
  C 
  = 
  Q 
  ^— 
  = 
  Qy 
  where 
  v 
  =z 
  the 
  velocity 
  of 
  propagation. 
  

  

  dt 
  

  

  . 
  ^+LSy'|t+VRS<^ 
  = 
  

   dx 
  ^ 
  dt 
  ^ 
  ^ 
  

  

  When 
  and 
  where 
  c^ 
  = 
  we 
  have* 
  

  

  Barton, 
  Proc. 
  Royal 
  Soc, 
  vol. 
  liv, 
  p. 
  87, 
  

  

  