﻿300 
  Trowbridge 
  and 
  Duane 
  — 
  Velocity 
  of 
  Electric 
  Waves. 
  

  

  of 
  two 
  pieces 
  of 
  wire 
  insulated 
  with 
  rubber, 
  bent 
  into 
  circles 
  

   of 
  about 
  2 
  cm 
  radius, 
  and 
  fastened 
  to 
  a 
  bit 
  of 
  pine 
  wood 
  by 
  

   means 
  of 
  a 
  heavy 
  coating 
  of 
  paraffine. 
  The 
  two 
  wires 
  of 
  the 
  

   secondary 
  circuit 
  passed 
  through 
  holes 
  in 
  this 
  bit 
  of 
  wood 
  in 
  

   such 
  a 
  manner 
  as 
  to 
  pass 
  through 
  the 
  centers 
  of 
  the 
  two 
  circles. 
  

   In 
  the 
  early 
  part 
  of 
  the 
  investigation 
  the 
  bolometer 
  and 
  

   galvanoscope 
  were 
  placed 
  at 
  a 
  sufficient 
  distance 
  from 
  the 
  oscil- 
  

   lating 
  circuits 
  to 
  prevent 
  any 
  direct 
  action 
  of 
  one 
  on 
  the 
  other, 
  

   and 
  the 
  leads 
  running 
  from 
  the 
  circular 
  conductors 
  to 
  the 
  bolome- 
  

   ter 
  consisted 
  of 
  long 
  line 
  wires. 
  Later 
  when 
  longer 
  circuits 
  

   and 
  longer 
  waves 
  were 
  experimented 
  with, 
  great 
  inconvenience 
  

   was 
  experienced 
  from 
  the 
  long 
  leads 
  since 
  their 
  relative 
  

   position 
  had 
  considerable 
  effect 
  upon 
  the 
  galvanoscope 
  deflec- 
  

   tions. 
  In 
  order 
  to 
  obviate 
  this 
  difficulty 
  short 
  leads 
  of 
  heavily 
  

   insulated 
  wire 
  were 
  used 
  and 
  the 
  bolometer 
  was 
  placed 
  on 
  

   wheels 
  and 
  moved 
  along 
  from 
  place 
  to 
  place. 
  A 
  bolometric 
  

   study 
  of 
  the 
  circuit 
  just 
  described 
  showed 
  the 
  character 
  

   of 
  the 
  oscillation 
  to 
  be 
  that 
  mentioned, 
  namely, 
  nodes 
  at 
  the 
  

   points 
  G, 
  J 
  and 
  H, 
  and 
  maximum 
  accumulations 
  at 
  the 
  points 
  

   K 
  and 
  L. 
  A 
  careful 
  run 
  was 
  made 
  from 
  one 
  end 
  of 
  the 
  cir- 
  

   cuit 
  to 
  the 
  other, 
  which 
  furnished 
  data 
  from 
  which 
  a 
  very 
  

   regular 
  curve 
  was 
  drawn. 
  

  

  Two 
  points 
  deserve 
  notice 
  here, 
  before 
  we 
  pass 
  on 
  to 
  the 
  

   next 
  arrangement 
  of 
  the 
  apparatus. 
  First 
  the 
  automatic 
  cur- 
  

   rent 
  interrupter 
  that 
  worked 
  so 
  beautifully 
  in 
  connection 
  with 
  

   the 
  Hertz 
  vibrator 
  would 
  not 
  function 
  well, 
  when 
  the 
  vibrator 
  

   was 
  replaced 
  by 
  the 
  circuit 
  and 
  condenser 
  just 
  described. 
  For 
  

   a 
  detailed 
  description 
  of 
  this 
  interrupter 
  we 
  must 
  again 
  

   refer 
  to 
  Mr. 
  St. 
  John's 
  paper. 
  The 
  essential 
  feature 
  of 
  the 
  

   apparatus 
  was 
  this 
  : 
  the 
  circuit 
  was 
  interrupted 
  by 
  the 
  regular 
  

   periodic 
  lifting 
  of 
  a 
  platinum 
  plunger 
  from 
  a 
  glass 
  cup 
  par- 
  

   tially 
  filled 
  with 
  mercury. 
  Alcohol 
  was 
  poured 
  over 
  the 
  

   surface 
  of 
  the 
  mercury 
  in 
  order 
  to 
  keep 
  it 
  clean, 
  and 
  this 
  

   effectually 
  stopped 
  the 
  sparking 
  when 
  the 
  Hertz 
  vibrator 
  

   was 
  used. 
  When, 
  however, 
  the 
  induction 
  coil 
  was 
  used 
  to 
  

   charge 
  the 
  large 
  condensers, 
  violent 
  sparks 
  occurred 
  at 
  the 
  

   point 
  where 
  the 
  plunger 
  left 
  the 
  mercury, 
  almost 
  any 
  one 
  

   of 
  which 
  was 
  sufficiently 
  strong 
  to 
  blow 
  the 
  alcohol 
  out 
  of 
  

   the 
  cup. 
  As 
  the 
  same 
  current 
  in 
  the 
  primary 
  of 
  the 
  induc- 
  

   tion 
  coil 
  was 
  used 
  in 
  the 
  two 
  cases, 
  the 
  most 
  probable 
  explana- 
  

   tion 
  of 
  this 
  is 
  the 
  following. 
  The 
  capacity 
  of 
  the 
  condenser 
  

   being 
  considerably 
  greater 
  than 
  that 
  of 
  the 
  two 
  plates 
  in 
  the 
  

   Hertz 
  vibrator, 
  the 
  current 
  in 
  the 
  secondary 
  of 
  the 
  induction 
  

   coil 
  in 
  the 
  first 
  case 
  must 
  have 
  been 
  much 
  greater 
  than 
  that 
  in 
  

   the 
  second 
  case. 
  Hence 
  the 
  reaction 
  of 
  the 
  secondary 
  current 
  

   on 
  the 
  primary 
  of 
  the 
  induction 
  coil, 
  must 
  have 
  been 
  much 
  

   greater. 
  This 
  would 
  cause 
  a 
  greater 
  reaction 
  of 
  the 
  sec- 
  

  

  