﻿G, 
  V. 
  Maclean 
  — 
  Yelocity 
  of 
  Electric 
  Waves 
  in 
  Air. 
  13 
  

  

  the 
  time 
  oscillation 
  of 
  our 
  sparkwouldbel'976xl0~8 
  sees. 
  This 
  

   is 
  then 
  the 
  value 
  of 
  T. 
  "We 
  have 
  already 
  found 
  X, 
  the 
  wave- 
  

   length, 
  to 
  be 
  591*5 
  cms. 
  And 
  since 
  X 
  = 
  YT 
  .*. 
  Y 
  the 
  velocity 
  

  

  X 
  591*5 
  

  

  of 
  the 
  electric 
  wave 
  = 
  ^= 
  ^ 
  ^^.. 
  — 
  ^^ 
  ^ 
  = 
  2*998 
  X 
  10^ 
  ^ 
  centi- 
  

   1 
  I'yToXlO"^ 
  

  

  meters 
  per 
  second 
  or 
  about 
  186,365 
  miles 
  per 
  second. 
  

  

  Professor 
  Trowbridge 
  and 
  Dr. 
  Duane 
  in 
  1895 
  found 
  the 
  

   velocity 
  of 
  electric 
  waves 
  along 
  wires 
  to 
  be 
  2-996x10^^ 
  cms, 
  

   though 
  the 
  mean 
  of 
  seven 
  of 
  their 
  results 
  gave 
  the 
  velocity 
  to 
  

   be 
  3-0024x10^0 
  cms. 
  per 
  second. 
  To 
  make 
  sure 
  the 
  co- 
  

   herer 
  and 
  oscillator 
  were 
  in 
  tune 
  with 
  each 
  other, 
  the 
  

   capacity 
  of 
  the 
  oscillator 
  was 
  altered 
  by 
  doubling 
  the 
  area 
  

   of 
  the 
  tin 
  foil 
  sheets 
  on 
  the 
  glass 
  plate. 
  Sparking 
  at 
  the 
  

   oscillator 
  was 
  again 
  begun 
  and 
  readings 
  taken 
  whereby 
  it 
  

   was 
  seen 
  the 
  positions 
  of 
  the 
  original 
  nodal 
  and 
  anti-nodal 
  

   points 
  were 
  changed. 
  The 
  same 
  thing 
  took 
  place 
  upon 
  alter- 
  

   ing 
  the 
  self-induction. 
  Also 
  separately 
  the 
  self-induction 
  and 
  

   capacity 
  of 
  the 
  coherer 
  were 
  altered, 
  with 
  a 
  similar 
  change 
  in 
  

   the 
  position 
  of 
  the 
  original 
  nodal 
  and 
  anti-nodal 
  points. 
  When 
  

   the 
  wave-length 
  had 
  been 
  determined 
  it 
  seemed 
  desirable 
  to 
  

   test 
  the 
  truth 
  of 
  the 
  theory 
  of 
  Poincare 
  and 
  Bjerknes. 
  It 
  is 
  a 
  

   known 
  fact 
  in 
  the 
  photography 
  of 
  electric 
  oscillation, 
  that 
  it 
  is 
  

   possible 
  to 
  damp 
  out 
  all 
  the 
  oscillations 
  except 
  the 
  fundamental 
  

   by 
  replacing 
  part 
  of 
  the 
  self-induction 
  by 
  a 
  self-induction 
  hav- 
  

   ing 
  a 
  higher 
  resistance. 
  As, 
  for 
  example, 
  interchanging 
  a 
  

   length 
  of 
  copper 
  wire 
  by 
  the 
  same 
  length 
  of 
  graphite. 
  Accord- 
  

   ingly 
  a 
  cylinder 
  of 
  graphite 
  5 
  cms. 
  long 
  was 
  ground 
  down 
  till 
  

   it 
  had 
  the 
  same 
  diameter 
  of 
  the 
  copper 
  wire 
  it 
  was 
  to 
  replace. 
  

   The 
  ends 
  of 
  this 
  rod 
  of 
  graphite 
  were 
  next 
  electroplated 
  with 
  

   copper. 
  Five 
  cms. 
  of 
  one 
  of 
  the 
  copper 
  wires 
  forming 
  the 
  

   self-induction 
  of 
  the 
  coherer 
  were 
  cut 
  out 
  and 
  replaced 
  by 
  

   soldering 
  in 
  the 
  prepared 
  graphite. 
  The 
  coherer 
  and 
  oscil- 
  

   lator 
  circuits 
  had 
  now 
  the 
  same 
  capacity 
  and 
  self-induction 
  as 
  

   before, 
  only 
  the 
  resistance 
  of 
  the 
  self-induction 
  of 
  the 
  coherer 
  

   circuit 
  had 
  been 
  increased. 
  The 
  resistance 
  of 
  the 
  graphite 
  was 
  

   12, 
  ohms. 
  Work 
  was 
  now 
  undertaken 
  under 
  these 
  new 
  con- 
  

   ditions, 
  with 
  the 
  result 
  that 
  the 
  fifty 
  observations 
  thus 
  made 
  

   were 
  identical 
  with 
  those 
  taken 
  under 
  the 
  original 
  conditions. 
  

   The 
  following 
  table 
  gives 
  the 
  measurement 
  taken 
  when 
  the 
  

   graphite 
  was 
  in 
  the 
  circuit. 
  

  

  