﻿L. 
  De 
  Forest 
  — 
  Reflection 
  of 
  Hertzian 
  Waves. 
  65 
  

  

  any 
  system 
  hehind 
  it, 
  but 
  only 
  by 
  those 
  between 
  it 
  and 
  the 
  

   sonrce. 
  

  

  The 
  half 
  wave-length 
  w^as 
  fixed 
  by 
  two 
  bridges, 
  at 
  the 
  

   desired 
  distance 
  apart, 
  attached 
  to 
  a 
  strip 
  of 
  wood 
  and 
  always 
  

   moved 
  together 
  back 
  and 
  forth 
  along 
  the 
  line. 
  The 
  nodes 
  

   thns 
  located 
  were 
  naturally 
  broader 
  and 
  less 
  defined 
  than 
  when 
  

   but 
  one 
  bridge 
  was 
  shifted. 
  

  

  Although 
  the 
  whole 
  range 
  of 
  half 
  wave-lengths 
  was 
  

   attempted, 
  at 
  intervals 
  of 
  2-5^'^, 
  only 
  a 
  few 
  could 
  be 
  satisfac- 
  

   torily 
  observed. 
  This 
  was 
  due 
  to 
  the 
  necessity 
  for 
  a 
  double 
  

   resonance 
  to 
  secure 
  a 
  glow 
  in 
  the 
  tube. 
  The 
  system 
  defined 
  

   by 
  the 
  two 
  bridges 
  kept 
  one 
  half 
  wave-length 
  apart 
  must 
  be 
  in 
  

   resonance 
  both 
  with 
  the 
  end 
  system 
  and 
  with 
  the 
  part 
  in 
  front 
  

   including 
  the 
  exciter. 
  

  

  Had 
  it 
  been 
  feasible 
  to 
  employ 
  much 
  longer 
  wires, 
  100"^, 
  

   this 
  necessity 
  would 
  not 
  have 
  existed 
  with 
  the 
  limited 
  wave- 
  

   trains 
  sent 
  out 
  by 
  the 
  exciter. 
  

  

  Eegarding 
  the 
  bare 
  ends 
  as 
  two 
  spheres 
  of 
  the 
  radius 
  of 
  the 
  

   wires, 
  the 
  static 
  capacity 
  as 
  calculated 
  graphically 
  by 
  the 
  

   methods 
  of 
  inverse 
  points 
  was 
  found 
  to 
  be 
  

  

  S^ 
  = 
  -45 
  C. 
  G. 
  S. 
  

  

  Thus 
  the 
  actual 
  capacity 
  for 
  the 
  bare 
  ends, 
  for 
  these 
  rapid 
  

   oscillations, 
  is 
  seen 
  to 
  be 
  very 
  much 
  greater 
  than 
  that 
  calculated 
  

   for 
  static 
  charges, 
  and 
  varies 
  with 
  the 
  frequency. 
  The 
  curves 
  

   in 
  Fig. 
  2 
  show^ 
  a 
  slight 
  decrease 
  in 
  the 
  change 
  of 
  phase 
  by 
  reflec- 
  

   tion 
  with 
  increasing 
  frequency, 
  and 
  a 
  more 
  marked 
  falling 
  off 
  

   in 
  the 
  end 
  capacity. 
  This 
  decrease 
  in 
  capacity 
  with 
  period 
  is 
  

   to 
  be 
  expected. 
  

  

  With 
  two 
  brass 
  balls 
  on 
  the 
  ends, 
  l-So'"^ 
  diam., 
  2-55^'^ 
  

   between 
  centers, 
  the 
  lost 
  length 
  in 
  reflection 
  is 
  of 
  course 
  much 
  

   more 
  marked. 
  The 
  extreme 
  limits 
  of 
  the 
  balls 
  were 
  here 
  

   taken 
  as 
  marking 
  the 
  end 
  of 
  the 
  wares. 
  

  

  The 
  reflection 
  throughout 
  seemed 
  much 
  better 
  for 
  these 
  balls 
  

   at 
  ends 
  than 
  for 
  bare 
  ends 
  ; 
  the 
  nodes 
  were 
  always 
  more 
  easily 
  

   located 
  and 
  clearly 
  defined. 
  There 
  was 
  no 
  difference 
  in 
  the 
  

   character 
  of 
  the 
  reflection 
  with 
  the 
  bare 
  ends, 
  whether 
  these 
  

   were 
  cut 
  off 
  square 
  or 
  tapered 
  to 
  fine 
  points. 
  

  

  By 
  Maxwell's 
  method 
  the 
  calculated 
  static 
  capacity 
  of 
  the 
  

   balls 
  is 
  1'15 
  C. 
  G. 
  S. 
  units. 
  The 
  observed 
  capacities 
  for 
  these 
  

   oscillations 
  are 
  from 
  2 
  to 
  5 
  times 
  greater 
  than 
  this 
  — 
  a 
  much 
  

   smaller 
  discrepancy 
  than 
  for 
  the 
  case 
  of 
  bare 
  ends. 
  The 
  radia- 
  

   tion 
  from 
  the 
  balls 
  is 
  much 
  less. 
  

  

  In 
  the 
  curves 
  given 
  the 
  figures 
  for 
  amounts 
  lost 
  in 
  refiection 
  

  

  cannot 
  be 
  defined 
  closer 
  than 
  dc 
  O'S^"", 
  because 
  of 
  the 
  broad 
  

  

  nodes 
  found, 
  allowing 
  an 
  error 
  of 
  from 
  2 
  to 
  4 
  per 
  cent 
  in 
  the 
  

  

  angles 
  of 
  change 
  of 
  phase. 
  

  

  Am. 
  Jour. 
  Sci. 
  —Fourth 
  Series, 
  Yol. 
  YIII, 
  No. 
  43.— 
  July, 
  1899. 
  

   5 
  

  

  