﻿226 
  J. 
  Trowbridge 
  — 
  Electrical 
  Oscillations 
  on 
  Iron 
  Wires. 
  

  

  Beside 
  the 
  short 
  lead 
  wires 
  above 
  described, 
  the 
  discharging 
  

   circuit 
  consisted 
  of 
  the 
  two 
  parallel 
  wires 
  30 
  cm. 
  apart 
  and 
  510 
  

   cm. 
  long. 
  These 
  were 
  the 
  only 
  portions 
  of 
  the 
  apparatus 
  

   changed 
  during 
  the 
  experiment, 
  and 
  they 
  were 
  replaced 
  by 
  

   wires 
  of 
  different 
  material 
  and 
  of 
  different 
  size. 
  The 
  other 
  

   conditions 
  — 
  length 
  of 
  spark, 
  lead 
  wires, 
  and 
  the 
  copper 
  cross 
  

   wire 
  connecting 
  the 
  outer 
  end 
  of 
  the 
  long 
  parallel 
  wires 
  — 
  

   remained 
  undisturbed 
  throughout 
  the 
  experiment. 
  

  

  The 
  Leyden 
  jar 
  was 
  charged 
  each 
  time 
  as 
  nearly 
  as 
  possible 
  

   to 
  the 
  same 
  potential, 
  judging 
  by 
  the 
  number 
  of 
  turns 
  given 
  

   the 
  Holtz 
  machine. 
  It 
  is 
  unfortunate 
  that 
  no 
  more 
  accurate 
  

   means 
  of 
  measuring 
  it 
  were 
  at 
  hand, 
  although 
  the 
  different 
  

   negatives 
  showed 
  but 
  slight 
  variation. 
  The 
  capacity 
  of 
  the 
  

   jar 
  to 
  alternations 
  of 
  this 
  period 
  was 
  5060 
  electrostatic 
  units. 
  

  

  I 
  describe 
  the 
  discharging 
  portion 
  of 
  the 
  apparatus 
  minutely, 
  

   for 
  the 
  success 
  of 
  an 
  investigation 
  of 
  this 
  nature 
  depends 
  upon 
  

   the 
  suppression 
  of 
  all 
  sparks 
  save 
  that 
  which 
  one 
  wishes 
  to 
  

   observe 
  ; 
  and 
  the 
  method 
  surely 
  and 
  completely 
  accomplished 
  

   this. 
  The 
  photograph 
  of 
  the 
  spark 
  could 
  thus 
  be 
  made 
  to 
  fall 
  

   very 
  accurately 
  on 
  the 
  sensitive 
  plate. 
  When 
  one 
  considers 
  

   that 
  the 
  image 
  of 
  the 
  spark 
  was 
  flying 
  through 
  the 
  air 
  on 
  a 
  

   circle 
  of 
  a 
  radius 
  of 
  ten 
  feet 
  with 
  a 
  velocity 
  of 
  a 
  mile 
  a 
  second, 
  

   it 
  will 
  be 
  seen 
  that 
  an 
  extremely 
  small 
  deviation 
  in 
  the 
  point 
  

   of 
  contact 
  between 
  the 
  cutting 
  tool 
  and 
  the 
  type-metal 
  would 
  

   have 
  thrown 
  the 
  image 
  entirely 
  off 
  the 
  sensitive 
  plate. 
  A 
  

   singular 
  phenomenon 
  was 
  noticed 
  in 
  this 
  connection. 
  When 
  

   a 
  comparatively 
  low 
  potential 
  was 
  used, 
  such 
  as 
  that 
  afforded 
  by 
  

   the 
  air 
  condenser 
  used 
  in 
  our 
  previous 
  investigation, 
  the 
  cut- 
  

   ting 
  tool 
  ploughed 
  two 
  or 
  three 
  millimeters 
  along 
  the 
  surface 
  

   of 
  the 
  type-metal 
  before 
  a 
  spark 
  passed 
  at 
  the 
  point 
  in 
  the 
  

   circuit 
  where 
  it 
  was 
  desired. 
  With 
  higher 
  potentials 
  this 
  

   phenomenon 
  was 
  also 
  observed, 
  but 
  the 
  extent 
  of 
  cutting 
  was 
  

   diminished. 
  

  

  It 
  is 
  possible 
  that 
  the 
  insulating 
  wax 
  may 
  have 
  melted 
  

   under 
  the 
  sudden 
  blow 
  of 
  the 
  cutting 
  tool, 
  and, 
  flowing 
  around 
  

   it, 
  prevented 
  instant 
  contact. 
  This 
  seems 
  to 
  us 
  improbable, 
  

   for 
  a 
  deep 
  and 
  clear-cut 
  groove 
  was 
  made 
  in 
  the 
  soft 
  type- 
  

   metal. 
  Great 
  attention 
  was 
  paid 
  to 
  the 
  solid 
  structure 
  of 
  this 
  

   contact 
  apparatus. 
  It 
  was 
  entirely 
  separate 
  from 
  the 
  support 
  

   of 
  the 
  revolving 
  parts, 
  and 
  was 
  perfectly 
  steady. 
  

  

  The 
  other 
  end 
  of 
  the 
  armature 
  shaft 
  was 
  lengthened 
  into 
  a 
  

   cylindrical 
  chronograph, 
  similar 
  to 
  that 
  described 
  in 
  the 
  article 
  

   already 
  cited, 
  and 
  its 
  performance 
  left 
  nothing 
  to 
  be 
  desired. 
  

   A 
  small 
  Ruhmkorf 
  coil, 
  excited 
  by 
  two 
  storage 
  cells, 
  and 
  inter- 
  

   rupted 
  by 
  a 
  seconds 
  pendulum, 
  gave 
  a 
  record 
  of 
  the 
  speed 
  of 
  

   the 
  mirror. 
  The 
  stylus 
  which 
  drew 
  the 
  spiral 
  turns 
  on 
  the 
  

   barrel 
  of 
  the 
  chronograph 
  was 
  drawn 
  along 
  the 
  barrel 
  by 
  

  

  