﻿Lord 
  Rayleigh 
  : 
  Acoustical 
  Sotes. 
  245 
  

  

  so 
  that 
  the 
  maximum 
  effect 
  occurs 
  when 
  

  

  CJU 
  2 
  = 
  1, 
  

  

  i. 
  e., 
  when 
  the 
  natural 
  frequency 
  of 
  the 
  circuit 
  coincides 
  with 
  

   that 
  o£ 
  the 
  imposed 
  force. 
  For 
  this 
  pitch 
  the 
  self-induction 
  

   is 
  compensated. 
  The 
  effect 
  of 
  short-circuiting 
  the 
  condenser 
  

   may 
  be 
  represented 
  by 
  taking 
  C 
  = 
  co 
  . 
  If, 
  apart 
  from 
  phase, 
  

   the 
  current 
  is 
  unaltered 
  by 
  short-circuiting 
  the 
  condenser, 
  

   the 
  capacity 
  in 
  action 
  must 
  be 
  equal 
  to 
  one-half 
  of 
  the 
  most 
  

   favourable 
  capacity, 
  or 
  else 
  must 
  be 
  so 
  great 
  as 
  not 
  to 
  be 
  

   distinguishable 
  in 
  experiment 
  from 
  infinity. 
  It 
  is 
  to 
  be 
  noted 
  

   that 
  the 
  accurate 
  compensation 
  of 
  self-induction 
  can 
  be 
  

   effected 
  for 
  only 
  one 
  pitch, 
  and 
  that 
  in 
  practice 
  the 
  

   advantage 
  will 
  be 
  limited 
  to 
  a 
  range 
  of 
  pitch 
  not 
  exceeding 
  

   an 
  octave. 
  

  

  Such 
  experiments 
  as 
  I 
  have 
  been 
  able 
  to 
  make 
  did 
  not 
  

   exhibit 
  any 
  improvement 
  in 
  articulation 
  as 
  the 
  result 
  of 
  

   including 
  a 
  condenser 
  in 
  the 
  circuit. 
  It 
  is 
  possible 
  that 
  the 
  

   simple 
  theory 
  above 
  stated 
  is 
  too 
  much 
  interfered 
  with 
  by 
  

   complications 
  such 
  as 
  eddy-currents 
  in 
  the 
  iron 
  or 
  hysteresis 
  

   in 
  the 
  action 
  of 
  the 
  condenser. 
  A 
  distinct 
  resonance 
  could 
  

   be 
  attained 
  in 
  the 
  region 
  of 
  the 
  higher 
  notes 
  of 
  my 
  harmonium 
  

   (about 
  2000 
  vibrations 
  per 
  second) 
  when 
  an 
  additional 
  self- 
  

   induction 
  was 
  included 
  in 
  the 
  circuit. 
  Such 
  resonance 
  

   would 
  be 
  practically 
  limited 
  to 
  a 
  region 
  including 
  3 
  or 
  4 
  semi- 
  

   tones, 
  and 
  when 
  at 
  the 
  best 
  pitch 
  the 
  condenser 
  was 
  put 
  out 
  

   of 
  action 
  by 
  a 
  short-circuiting 
  key 
  there 
  was 
  a 
  very 
  marked 
  

   falling 
  off 
  of 
  intensity. 
  It 
  is 
  probable 
  that 
  this 
  subject 
  has 
  

   already 
  received 
  attention 
  from 
  those 
  engaged 
  in 
  the 
  endeavour 
  

   to 
  improve 
  the 
  telephone 
  as 
  a 
  practical 
  instrument 
  ; 
  if 
  not, 
  I 
  

   think 
  it 
  would 
  be 
  worthy 
  of 
  investigation. 
  There 
  should 
  be 
  

   no 
  great 
  difficulty 
  in 
  securing 
  several 
  electrical 
  resonances 
  at 
  

   pitches 
  suitably 
  distributed, 
  in 
  addition 
  to 
  the 
  mechanical 
  

   resonance 
  of 
  the 
  plate. 
  

  

  If 
  my 
  memory 
  serves 
  me, 
  it 
  was 
  observed 
  in 
  the 
  early 
  days 
  

   of 
  telephony 
  that 
  the 
  sounds 
  remained 
  audible 
  even 
  though 
  

   the 
  usual 
  ferrotype 
  plate 
  were 
  replaced 
  by 
  one 
  of 
  other 
  

   material. 
  The 
  experiment 
  is 
  easily 
  tried. 
  When 
  a 
  telephone 
  

   provided 
  with 
  a 
  copper 
  or 
  aluminium 
  plate 
  was 
  included 
  in 
  a 
  

   circuit 
  with 
  a 
  battery 
  (of 
  one 
  or 
  two 
  cells) 
  and 
  a 
  simple 
  

   carbon 
  microphone 
  (after 
  Hughes), 
  the 
  ticking 
  of 
  a 
  watch 
  

   placed 
  near 
  the 
  microphone 
  was 
  easily 
  audible, 
  and 
  (it 
  hap- 
  

   pened) 
  with 
  different 
  quality 
  in 
  the 
  two 
  cases. 
  On 
  the 
  other 
  

   hand 
  a 
  plate 
  of 
  mica 
  was 
  silent 
  under 
  similar 
  conditions, 
  

   although 
  when 
  the 
  excitation 
  is 
  very 
  violent, 
  as 
  with 
  a 
  make- 
  

   and-break 
  arrangement, 
  sounds 
  may 
  be 
  heard 
  without 
  a 
  plate 
  

  

  