﻿482 
  Mr. 
  B. 
  S. 
  Cohen 
  on 
  Production 
  of 
  Small 
  

  

  frequency 
  depends 
  on 
  the 
  free 
  period 
  of 
  the 
  apparatus 
  

   can 
  be 
  utilized. 
  The 
  method, 
  however, 
  is 
  untrustworthy, 
  

   and 
  the 
  output 
  small. 
  

  

  The 
  wave 
  form 
  is 
  also 
  far 
  from 
  sinusoidal, 
  as 
  might 
  be 
  

   expected 
  when 
  it 
  is 
  considered 
  that 
  it 
  is 
  influenced 
  by 
  the 
  

   action 
  of 
  the 
  polarized 
  electromagnet 
  in 
  the 
  receiver. 
  Fig. 
  4 
  

   (PI. 
  XVI.) 
  shows 
  the 
  wave 
  form 
  using 
  the 
  local 
  battery 
  type 
  of 
  

   telephone 
  instrument. 
  

  

  Mr. 
  A. 
  Campbell's 
  modification 
  of 
  the 
  humming 
  telephone 
  

   consists 
  of 
  a 
  steel 
  bar 
  with 
  a 
  free 
  period 
  of 
  the 
  frequency 
  

   desired, 
  and 
  this 
  is 
  set 
  in 
  motion 
  by 
  a 
  polarized 
  electro- 
  

   magnet, 
  which 
  has 
  attached 
  to 
  it 
  a 
  light 
  microphone, 
  which 
  

   maintains 
  the 
  interaction 
  and 
  supplies 
  current 
  to 
  the 
  external 
  

   circuit 
  through 
  a 
  transformer. 
  This 
  apparatus 
  is 
  more 
  reliable 
  

   than 
  the 
  humming 
  telephone. 
  The 
  output, 
  however, 
  is 
  limited 
  

   by 
  the 
  transmitter* 
  and 
  the 
  wave 
  form 
  is 
  similar 
  to 
  that 
  

   of 
  the 
  ordinary 
  humming 
  telephone 
  *. 
  

  

  Organ 
  Pipes 
  etc. 
  — 
  Organ 
  pipes, 
  other 
  wind 
  instruments, 
  

   and 
  tuning 
  forks 
  sounding 
  in 
  transmitters, 
  were 
  experimented 
  

   on 
  for 
  a 
  short 
  time, 
  and 
  might 
  under 
  certain 
  conditions 
  give 
  

   satisfactory 
  results. 
  It 
  is 
  difficult 
  to 
  avoid 
  trouble, 
  however, 
  

   with 
  all 
  such 
  arrangements, 
  owing 
  to 
  irregularities 
  intro- 
  

   duced 
  by 
  the 
  transmitters 
  and 
  to 
  their 
  limited 
  output. 
  

  

  Vibrating 
  Wire 
  Interrupters. 
  — 
  The 
  vibrating 
  wire 
  inter- 
  

   rupter 
  described 
  by 
  Wien, 
  Orlich, 
  Campbell, 
  and 
  others, 
  

   has 
  when 
  suitably 
  modified 
  given 
  very 
  satisfactory 
  results, 
  

   and 
  I 
  propose 
  to 
  describe 
  a 
  special 
  form 
  of 
  this 
  apparatus 
  f. 
  

   It 
  has 
  been 
  found 
  very 
  difficult 
  to 
  construct 
  a 
  vibrating 
  wire 
  

   which 
  will 
  run 
  reliably 
  at 
  a 
  frequency 
  much 
  above 
  300^, 
  

   and 
  I 
  have 
  been 
  unable 
  to 
  find 
  references 
  to 
  wires 
  which 
  

   could 
  be 
  maintained 
  in 
  vibration 
  at 
  a 
  frequency 
  higher 
  than 
  

   500^-. 
  The 
  output 
  is 
  also 
  very 
  limited, 
  and 
  the 
  frequency 
  

   difficult 
  to 
  determine 
  and 
  vary. 
  

  

  In 
  order 
  to 
  overcome 
  these 
  drawbacks 
  the 
  instrument 
  illus- 
  

   trated 
  in 
  fig. 
  5 
  (PI. 
  XVII.) 
  has 
  been 
  designed. 
  The 
  upper 
  figure 
  

   shows 
  details 
  of 
  the 
  mercury 
  cups 
  and 
  electromagnet, 
  and 
  the 
  

   lower 
  figure 
  gives 
  a 
  general 
  view 
  of 
  the 
  whole 
  instrument. 
  

   The 
  wire 
  is 
  steel, 
  1*06 
  mm. 
  in 
  diameter, 
  and 
  supports 
  a 
  soft 
  

   iron 
  armature 
  which 
  is 
  maintained 
  in 
  vibration 
  by 
  an 
  electro- 
  

  

  * 
  For 
  further 
  particulars 
  of 
  these 
  devices 
  see 
  Note 
  by 
  R. 
  Appleyard, 
  

   Elect. 
  Rev. 
  pp. 
  57 
  & 
  656, 
  vol. 
  xxvi. 
  1890 
  ; 
  Paper 
  on 
  Humming 
  Tele- 
  

   phones, 
  F. 
  Gill, 
  Journal 
  I. 
  E. 
  E. 
  vol. 
  xxxi. 
  1901 
  ; 
  A. 
  Campbell, 
  Proc. 
  

   Royal 
  Soc. 
  p. 
  208, 
  June 
  12th, 
  1906: 
  J. 
  E. 
  Taylor, 
  Journal 
  I. 
  E. 
  E. 
  

   p. 
  396, 
  vol. 
  xxxi. 
  1901; 
  E. 
  Dolezalek, 
  Zeitschrift 
  fiir 
  Instrument 
  en- 
  

   kunde, 
  p. 
  240, 
  Aug-. 
  1903. 
  

  

  f 
  (1) 
  Max 
  Wien, 
  Wied. 
  Ann. 
  xlii. 
  p. 
  593 
  (1891). 
  

  

  do. 
  do. 
  xliv. 
  p. 
  681 
  & 
  p. 
  689 
  (1891). 
  

  

  (2) 
  Orlich, 
  Elentrotechn. 
  Zeitsch. 
  vol. 
  xxvi. 
  (1903). 
  

  

  