﻿J. 
  Trowbridge 
  — 
  Electrical 
  Oscillations 
  on 
  Iron 
  Wires. 
  227 
  

  

  means 
  of 
  a 
  small 
  heavily 
  loaded 
  carriage, 
  which, 
  on 
  being 
  

   released 
  at 
  the 
  moment 
  the 
  lever 
  arm 
  threw 
  the 
  type-metal 
  in 
  

   contact 
  with 
  the 
  cutting 
  tool, 
  descended 
  an 
  inclined 
  plane 
  of 
  

   adjustable 
  height. 
  

  

  A 
  small 
  Topler-Holtz 
  machine 
  charged 
  a 
  large 
  Leyden 
  jar, 
  

   and 
  it 
  was 
  found 
  to 
  work 
  admirably 
  in 
  all 
  states 
  of 
  the 
  weather. 
  

   The 
  apparatus 
  which 
  I 
  have 
  thus 
  described 
  was 
  the 
  result 
  of 
  

   the 
  experience 
  of 
  the 
  previous 
  year, 
  and 
  worked 
  for 
  months 
  

   without 
  failure 
  ; 
  and 
  the 
  taking 
  of 
  photographs 
  of 
  the 
  oscilla- 
  

   tory 
  discharge 
  by 
  it 
  became 
  a 
  mere 
  matter 
  of 
  routine. 
  

  

  The 
  following 
  cases 
  were 
  tried 
  : 
  

  

  (1.) 
  When 
  the 
  long 
  parallel 
  wires 
  were 
  of 
  copper 
  (diameter 
  

   •087 
  cm.), 
  the 
  number 
  of 
  double 
  oscillations 
  visible 
  on 
  the 
  

   negatives 
  averaged 
  quite 
  uniformly 
  9 
  or 
  9 
  '5. 
  

  

  (2.) 
  When 
  the 
  wires 
  were 
  of 
  German 
  silver 
  (diameter 
  

   •061 
  cm.), 
  three 
  oscillations 
  were 
  visible. 
  

  

  (3.) 
  But 
  when 
  an 
  annealed 
  iron 
  wire 
  (diameter 
  "087 
  cm.) 
  was 
  

   substituted, 
  only 
  the 
  first 
  return 
  oscillation 
  was 
  distinctly 
  visi- 
  

   ble, 
  with 
  occasionally 
  a 
  trace 
  of 
  the 
  first 
  duplicate 
  discharge. 
  

  

  (4c.) 
  On 
  substituting 
  fine 
  copper 
  wire 
  (diameter 
  *027 
  cm.), 
  

   five 
  complete 
  oscillations 
  were 
  quite 
  uniformly 
  visible. 
  

  

  (5.) 
  Fine 
  German 
  silver 
  wire 
  (*029 
  cm.), 
  nickel 
  wire 
  

   (•019 
  cm.),* 
  soft 
  iron 
  ("027 
  cm.), 
  and 
  piano 
  steel 
  wire 
  ("027 
  cm.), 
  

   gave 
  but 
  faintly 
  the 
  first 
  return 
  discharge 
  after 
  the 
  pilot 
  spark. 
  

  

  The 
  pilot 
  sparks 
  were 
  in 
  all 
  cases 
  strong. 
  

  

  The 
  single 
  return 
  discharge 
  through 
  the 
  iron 
  wire 
  did 
  not 
  

   admit 
  of 
  measurement 
  sufficiently 
  accurate 
  to 
  furnish 
  any 
  basis 
  

   for 
  calculation 
  of 
  its 
  self-induction. 
  The 
  time 
  did 
  not 
  appar- 
  

   ently 
  differ, 
  if 
  at 
  all, 
  by 
  more 
  than 
  fourteen 
  or 
  fifteen 
  per 
  cent. 
  

   Some 
  general 
  reasoning 
  based 
  upon 
  the 
  number 
  of 
  oscillations 
  

   may 
  be 
  of 
  interest. 
  It 
  must 
  be 
  acknowledged, 
  however, 
  that 
  

   this 
  reasoning 
  is 
  open 
  to 
  criticism, 
  although 
  it 
  affords 
  the 
  most 
  

   plausible 
  explanation. 
  The 
  phenomenon 
  itself 
  is 
  not 
  a 
  doubt- 
  

   ful 
  one. 
  

  

  The 
  time 
  of 
  a 
  double 
  oscillation 
  for 
  the 
  large-sized 
  copper 
  

   wire 
  was 
  '0000020 
  sec. 
  ; 
  for 
  the 
  small 
  copper 
  wire, 
  '0000021 
  

   sec. 
  The 
  others 
  as 
  far 
  as 
  could 
  be 
  determined 
  did 
  not 
  differ 
  

   much 
  from 
  these 
  values, 
  and 
  for 
  this 
  purpose 
  either 
  is 
  suffi- 
  

   ciently 
  accurate. 
  Denote 
  by 
  W 
  the 
  ohmic 
  resistance 
  of 
  the 
  

   parallel 
  wires 
  to 
  alternating 
  currents 
  of 
  this 
  periodicity 
  ; 
  by 
  R, 
  

   the 
  resistance 
  to 
  steady 
  currents. 
  

  

  />=— 
  = 
  3,000,000 
  (piratically). 
  

   Taking 
  the 
  cases 
  up 
  in 
  order 
  : 
  

  

  * 
  Obtained 
  by 
  the 
  kindness 
  of 
  Joseph 
  Wharton, 
  Esq., 
  of 
  Philadelphia. 
  

  

  