﻿J. 
  Trowbridge 
  — 
  Electrical 
  Oscillations 
  on 
  Iron 
  Wires. 
  225 
  

  

  that 
  the 
  magnetic 
  susceptibility 
  of 
  iron 
  does 
  not 
  play 
  any 
  part 
  

   in 
  the 
  case 
  of 
  such 
  rapid 
  motions.* 
  

  

  Although 
  the 
  impulsive 
  impedance 
  is 
  apparently 
  not 
  affected 
  

   by 
  the 
  magnetic 
  character 
  of 
  the 
  wire, 
  experiments 
  lead 
  me 
  to 
  

   believe 
  that 
  discharges 
  of 
  the 
  quick 
  period 
  of 
  a 
  Leyden 
  jar 
  are 
  

   affected 
  very 
  appreciably 
  by 
  the 
  magnetic 
  nature 
  of 
  iron, 
  steel, 
  

   and 
  nickel 
  conductors. 
  This 
  effect 
  is 
  so 
  great 
  that 
  it 
  dampens 
  

   the 
  electrical 
  oscillations, 
  and 
  makes 
  it 
  difficult 
  to 
  determine 
  

   whether 
  the 
  time 
  of 
  oscillation 
  is 
  also 
  affected 
  by 
  the 
  permea- 
  

   bility 
  of 
  the 
  conductor. 
  

  

  The 
  apparatus 
  employed 
  was 
  similar 
  to 
  that 
  described 
  in 
  the 
  

   investigation 
  of 
  electrical 
  oscillations 
  with 
  an 
  air 
  condenser. 
  f 
  

   Certain 
  important 
  modifications, 
  however, 
  were 
  made. 
  The 
  

   plane 
  mirror 
  which 
  was 
  used 
  in 
  the 
  former 
  research 
  was 
  re- 
  

   placed 
  by 
  a 
  concave 
  mirror 
  of 
  ten 
  feet 
  focus 
  and 
  three 
  and 
  a 
  

   half 
  inches 
  in 
  radius. 
  This 
  mirror 
  w^as 
  mounted 
  upon 
  the 
  end 
  

   of 
  the 
  armature 
  shaft 
  of 
  a 
  one-half 
  horse 
  power 
  electric 
  motor. 
  

  

  The 
  discharging 
  apparatus 
  consisted 
  of 
  a 
  sharp 
  cutting 
  tool, 
  

   insulated, 
  and 
  mounted 
  on 
  the 
  edge 
  of 
  the 
  rotating 
  disk 
  bear- 
  

   ing 
  the 
  mirror. 
  It 
  was 
  metallically 
  connected 
  with 
  a 
  grooved 
  

   ring 
  of 
  brass 
  mounted 
  upon 
  the 
  shaft 
  and 
  insulated 
  from 
  it 
  by 
  

   hard 
  rubber. 
  Around 
  this 
  was 
  wound 
  a 
  copper 
  wire, 
  one 
  end 
  

   of 
  which 
  was 
  connected 
  with 
  the 
  discharging 
  wire, 
  and 
  the 
  

   other 
  drawn 
  taut 
  by 
  a 
  rubber 
  band- 
  The 
  electrical 
  discharge 
  

   was 
  thrown 
  on 
  to 
  the 
  circuit 
  by 
  thrusting 
  forward 
  a 
  lever 
  

   which 
  brought 
  a 
  solid 
  hinged 
  frame 
  containing 
  a 
  strip 
  of 
  soft 
  

   type-metal 
  into 
  contact 
  with 
  the 
  rapidly 
  revolving 
  steel-cutting 
  

   tool. 
  An 
  electrical 
  contact 
  was 
  thus 
  insured 
  by 
  the 
  tool 
  cut- 
  

   ting 
  a 
  groove 
  in 
  the 
  strip 
  of 
  type-metal. 
  In 
  order 
  to 
  avoid 
  a 
  

   spark 
  at 
  the 
  contact, 
  the 
  tyj)e-metal 
  was 
  thickly 
  covered 
  with 
  a 
  

   wax 
  of 
  peculiar 
  composition. 
  The 
  only 
  spark 
  that 
  occurred, 
  

   therefore, 
  was 
  the 
  one 
  the 
  oscillations 
  of 
  which 
  I 
  desired 
  to 
  

   study. 
  At 
  each 
  trial 
  the 
  type-metal 
  was 
  moved 
  so 
  as 
  to 
  expose 
  

   a 
  new 
  cutting 
  surface. 
  The 
  type-metal 
  was 
  insulated 
  from 
  the 
  

   rest 
  of 
  the 
  apparatus, 
  but 
  connected 
  with 
  the 
  outer 
  coating 
  of 
  

   the 
  Leyden 
  jar 
  ; 
  first 
  both 
  terminals 
  of 
  the 
  Holtz 
  machine 
  were 
  

   thrown 
  off, 
  and 
  immediately 
  after 
  the 
  cutting 
  tool, 
  ploughing 
  

   its 
  way 
  through 
  the 
  type-metal, 
  placed 
  the 
  outer 
  coating 
  of 
  the 
  

   Leyden 
  jar 
  in 
  circuit 
  with 
  one 
  of 
  the 
  two 
  parallel 
  wires 
  lead- 
  

   ing 
  to 
  the 
  terminals 
  of 
  the 
  spark. 
  The 
  other 
  wire 
  was 
  per- 
  

   manently 
  in 
  connection 
  with 
  the 
  inner 
  coating 
  of 
  the 
  jar. 
  

  

  * 
  •• 
  Ersetzen 
  wir 
  den 
  bisherigen 
  Kupferdraht 
  durch 
  einen 
  dickeren 
  oder 
  diin- 
  

   nefen 
  Kupferdraht 
  oder 
  durch 
  eiuen 
  Draht 
  aus 
  anderem 
  Metall. 
  so 
  behalten 
  die 
  

   Kcotenpunkte 
  ihre 
  Lager 
  bei. 
  Die 
  Fortplanzun^sgeschwindigkeit 
  in 
  alien 
  sclchen 
  

   Drahten 
  ist 
  daher 
  gleich, 
  und 
  wir 
  sind 
  berechtigt, 
  von 
  derselben 
  als 
  einer 
  bestimm- 
  

   ten 
  Geschwindigkeit 
  zu 
  reden. 
  Auch 
  Eisendrahte 
  machen 
  keine 
  Ausnahme 
  von 
  

   der 
  allgemeinen 
  Regel. 
  die 
  Magnetisirbarkeit 
  des 
  Eisens 
  kommt 
  also 
  bei 
  so 
  

   schmalen 
  Bewegungen 
  nicht 
  in 
  Betracht." 
  — 
  Ann. 
  der 
  Physik 
  und 
  Chemie. 
  Xo. 
  34. 
  

   1888, 
  p. 
  558. 
  

  

  f 
  Proceedings 
  of 
  Am. 
  Acad, 
  of 
  Arts 
  and 
  Sci., 
  vol. 
  xxv, 
  p. 
  109. 
  

  

  