﻿304 
  Trowbridge 
  and 
  Duane 
  — 
  Velocity 
  of 
  Electric 
  Waves. 
  

  

  was 
  determined 
  to 
  one 
  part 
  in 
  five 
  hundred 
  by 
  means 
  of 
  an 
  

   electric 
  chronograph. 
  

  

  Number 
  of 
  

  

  Distance 
  between 
  

  

  Velocity 
  

  

  revolutions 
  

  

  two 
  successive 
  

  

  of 
  

  

  of 
  mirror 
  

  

  points 
  on 
  plate. 
  

  

  Waves. 
  

  

  per 
  sec. 
  

  

  cm. 
  

  

  cm- 
  

  

  71'2 
  

  

  •05608 
  

  

  2-819 
  X 
  10 
  10 
  

  

  70-85 
  

  

  •05600 
  

  

  2-810 
  X 
  10 
  10 
  

  

  70-7 
  

  

  •05532 
  

  

  2-835 
  X 
  10 
  10 
  

  

  71-3 
  

  

  •05637 
  

  

  2-808 
  X 
  10 
  10 
  

  

  70-8 
  

  

  •05611 
  

  

  Average. 
  

  

  2-808 
  X 
  10 
  10 
  

  

  

  2-816 
  X 
  10 
  10 
  

  

  69-2 
  

  

  •05340 
  

  

  2-988 
  X 
  10 
  10 
  

  

  The 
  last 
  line 
  in 
  the 
  table 
  contains 
  the 
  results 
  of 
  measure- 
  

   ments 
  on 
  photographs 
  of 
  the 
  primary 
  spark 
  instead 
  of 
  the 
  

   secondary. 
  In 
  this 
  case 
  the 
  distance 
  from 
  the 
  mirror 
  to 
  the 
  

   photographic 
  plate 
  was 
  311*5 
  crn 
  . 
  In 
  spite 
  of 
  the 
  fact 
  that 
  the 
  

   last 
  value 
  of 
  the 
  velocity 
  is 
  much 
  nearer 
  that 
  of 
  the 
  velocity 
  

   of 
  light, 
  and 
  of 
  the 
  ratio 
  of 
  the 
  two 
  systems 
  of 
  electrical 
  units 
  

   than 
  the 
  average 
  of 
  the 
  first 
  five, 
  we 
  do 
  not 
  think 
  it 
  can 
  be 
  

   relied 
  upon, 
  for 
  two 
  reasons. 
  First 
  because 
  of 
  the 
  possible 
  

   error 
  introduced 
  by 
  the 
  fact 
  that 
  the 
  two 
  circuits 
  had 
  not 
  

   exactly 
  the 
  same 
  period 
  of 
  oscillation 
  ; 
  and 
  second 
  because 
  the 
  

   distances 
  measured 
  on 
  the 
  photographic 
  plate 
  were 
  only 
  about 
  

   •05 
  cm 
  , 
  instead 
  of 
  l'00 
  cm 
  . 
  

  

  The 
  generally 
  accepted 
  value 
  for 
  the 
  velocity 
  of 
  light 
  is 
  

   2-998 
  X 
  10 
  10 
  centimeters. 
  At 
  present 
  it 
  does 
  not 
  seem 
  to 
  us 
  

   likely, 
  judging 
  from 
  the 
  table 
  as 
  it 
  stands, 
  and 
  from 
  a 
  considera- 
  

   tion 
  of 
  the 
  possible 
  errors 
  in 
  the 
  various 
  measurements, 
  that 
  the 
  

   total 
  error 
  in 
  our 
  determination 
  can 
  be 
  as 
  great 
  as 
  the 
  differ- 
  

   ence 
  between 
  the 
  average 
  just 
  given 
  and 
  2'998 
  X 
  10 
  10 
  . 
  

  

  Whether 
  this 
  discrepancy 
  is 
  due 
  to 
  the 
  fact 
  that 
  the 
  circuit 
  

   may 
  not 
  have 
  been 
  long 
  enough 
  in 
  comparison 
  with 
  the 
  

   length 
  of 
  the 
  waves 
  to 
  allow 
  of 
  their 
  full 
  development, 
  or 
  not, 
  

   we 
  do 
  not 
  undertake 
  to 
  say. 
  If 
  the 
  bends 
  in 
  the 
  circuit 
  at 
  

   M 
  and 
  M' 
  have 
  a 
  retarding 
  effect 
  upon 
  the 
  waves, 
  this 
  

   fact 
  can 
  be 
  very 
  easily 
  discovered 
  and 
  allowed 
  for. 
  As 
  yet 
  

   we 
  have 
  not 
  had 
  time 
  to 
  investigate 
  the 
  question. 
  We 
  there- 
  

   fore 
  publish 
  the 
  results 
  above 
  tabulated 
  as 
  a 
  preliminary 
  

   record, 
  hoping 
  to 
  refine 
  upon 
  the 
  measurements 
  in 
  several 
  

   important 
  particulars, 
  and 
  to 
  extend 
  the 
  investigation 
  to 
  

   circuits 
  of 
  different 
  sizes 
  and 
  shapes, 
  one 
  of 
  which 
  will 
  

   probably 
  be 
  a 
  long 
  circuit 
  of 
  some 
  300 
  meters 
  running 
  out 
  of 
  

   doors, 
  and 
  at 
  a 
  considerable 
  distance 
  above 
  the 
  ground. 
  

  

  In 
  the 
  final 
  paper, 
  too, 
  we 
  hope 
  to 
  publish 
  a 
  great 
  many 
  

   details 
  of 
  the 
  method, 
  together 
  with 
  some 
  interesting 
  phenom- 
  

  

  