﻿298 
  Trowbridge 
  and 
  Duane 
  — 
  Velocity 
  of 
  Electric 
  Waves. 
  

  

  The 
  first 
  point 
  in 
  the 
  course 
  of 
  the 
  investigation 
  worthy 
  

   of 
  detailed 
  notice 
  is 
  the 
  production 
  of 
  electric 
  waves 
  along 
  

   parallel 
  wires 
  in 
  such 
  a 
  manner 
  that 
  they 
  are 
  actually 
  visible 
  

   to 
  the 
  eye. 
  The 
  arrangement 
  of 
  the 
  apparatus 
  to 
  accomplish 
  

   this 
  was 
  as 
  follows 
  : 
  

  

  G 
  K 
  

  

  E 
  

  

  

  ■o 
  

  

  1° 
  

  

  J 
  

  

  

  1 
  

  

  

  B 
  

   1 
  

  

  F 
  1 
  

  

  

  H 
  L 
  

  

  A 
  primary 
  condenser 
  A 
  B 
  (Fig. 
  1) 
  was 
  held 
  with 
  its 
  plates 
  in 
  

   vertical 
  planes 
  by 
  means 
  of 
  suitable 
  wooden 
  supports 
  (not 
  rep- 
  

   resented 
  in 
  the 
  figure), 
  and 
  was 
  joined 
  in 
  a 
  circuit 
  B 
  C 
  consisting 
  

   of 
  two 
  wires 
  about 
  75 
  cm 
  long 
  placed 
  l 
  cm 
  apart. 
  In 
  reality 
  this 
  

   circuit 
  JB 
  C 
  should 
  be 
  represented 
  as 
  perpendicular 
  to 
  the 
  plane 
  

   of 
  the 
  paper, 
  (which 
  is 
  taken 
  as 
  the 
  horizontal 
  plane 
  passing 
  

   through 
  the 
  center 
  of 
  the 
  apparatus). 
  The 
  plates 
  of 
  the 
  con- 
  

   denser 
  A 
  B 
  were 
  of 
  sheets 
  of 
  tin 
  foil 
  101 
  X 
  !0 
  cra 
  glued 
  to 
  hard 
  

   rubber 
  sheets 
  and 
  the 
  dielectric 
  between 
  them 
  consisted 
  of 
  

   other 
  similar 
  sheets 
  of 
  hard 
  rubber 
  sufficient 
  in 
  number 
  and 
  

   thickness 
  to 
  make 
  the 
  distance 
  between 
  the 
  condenser 
  plates 
  

   4"2 
  cm 
  . 
  Outside 
  the 
  primary 
  condenser 
  plates 
  and 
  separated 
  from 
  

   them 
  by 
  hard 
  rubber 
  plates, 
  (total 
  thickness 
  *6 
  cm 
  ) 
  were 
  two 
  

   secondary 
  plates 
  E 
  and 
  F 
  each 
  40 
  cm 
  square. 
  To 
  these 
  plates 
  

   was 
  attached 
  the 
  secondary 
  circuit 
  E 
  G- 
  J 
  H 
  F, 
  the 
  form 
  of 
  

   which 
  is 
  represented 
  in 
  fig. 
  1. 
  This 
  latter 
  circuit 
  consisted 
  of 
  

   copper 
  wire, 
  diameter 
  *13 
  cm 
  and 
  its 
  total 
  length 
  from 
  E 
  to 
  F 
  

   was 
  4200 
  cm 
  . 
  A 
  spark 
  gap 
  with 
  spherical 
  terminals 
  2'5 
  ctn 
  in 
  

   diameter 
  was 
  placed 
  at 
  C 
  in 
  the 
  primary 
  circuit, 
  and 
  another 
  

   spark 
  gap 
  with 
  pointed 
  terminals 
  was 
  sometimes 
  inserted 
  at 
  J 
  

   in 
  the 
  secondary 
  circuit, 
  although 
  this 
  latter 
  spark 
  gap 
  had 
  no 
  

   effect 
  upon 
  the 
  phenomena 
  to 
  be 
  described. 
  The 
  primary 
  con- 
  

   denser 
  was 
  charged 
  by 
  means 
  of 
  a 
  large 
  Euhmkorf 
  coil 
  excited 
  

   by 
  five 
  storage 
  cells 
  with 
  a 
  total 
  voltage 
  of 
  ten 
  volts. 
  The 
  

   current 
  from 
  these 
  cells 
  was 
  made 
  and 
  broken 
  by 
  the 
  auto- 
  

   matic 
  interrupter 
  used 
  by 
  Mr. 
  St. 
  John 
  and 
  described 
  by 
  

   him 
  in 
  his 
  paper 
  above 
  referred 
  to. 
  Every 
  time 
  the 
  primary 
  

   condenser 
  was 
  charged, 
  a 
  spark 
  passed 
  at 
  C 
  causing 
  an 
  oscilla- 
  

   tory 
  discharge. 
  These 
  oscillations 
  induced 
  charges 
  on 
  the 
  

   plates 
  E 
  and 
  F 
  which 
  were 
  rapidly 
  reversed 
  in 
  sign, 
  and 
  which 
  

   traveled 
  out 
  along 
  the 
  wires 
  E 
  G- 
  and 
  F 
  H. 
  The 
  dimensions 
  

   of 
  the 
  primary 
  circuit 
  were 
  altered, 
  until 
  by 
  trial 
  it 
  was 
  found 
  

   that 
  a 
  charge 
  of, 
  let 
  us 
  say, 
  positive 
  electricity 
  starting 
  from 
  E 
  

  

  