﻿242 
  Lord 
  Rayleigh 
  : 
  Acoustical 
  Notes. 
  

  

  breast, 
  or 
  it 
  may 
  stand 
  upon 
  the 
  table, 
  e. 
  g. 
  at 
  dinner. 
  In 
  a 
  

   large 
  model 
  there 
  are 
  two 
  microphones, 
  as 
  described, 
  con- 
  

   nected 
  in 
  parallel. 
  The 
  instruments 
  upon 
  which 
  I 
  experi- 
  

   mented 
  were 
  kindly 
  lent 
  me 
  by 
  a 
  friend 
  who 
  had 
  found 
  them 
  

   efficient, 
  though 
  fatiguing 
  to 
  the 
  ear. 
  

  

  For 
  my 
  purpose 
  the 
  microphone 
  and 
  telephone 
  were 
  placed 
  

   in 
  separate 
  rooms, 
  so 
  that 
  nothing 
  could 
  be 
  heard 
  except 
  

   through 
  the 
  instrument. 
  The 
  reproduction 
  of 
  speech, 
  given 
  

   at 
  about 
  one 
  foot 
  away 
  from 
  the 
  microphone, 
  was 
  better 
  than 
  

   anything 
  I 
  had 
  ever 
  heard 
  before. 
  The 
  first 
  impression 
  was 
  

   that 
  all 
  the 
  consonantal 
  sounds 
  were 
  completely 
  rendered, 
  but 
  

   this 
  turned 
  out 
  to 
  be 
  an 
  illusion. 
  In 
  listening 
  to 
  the 
  numerals, 
  

   given 
  in 
  order, 
  the 
  observer 
  would 
  feel 
  confident 
  that 
  he 
  

   heard 
  the 
  fin 
  Jive 
  and 
  the 
  s 
  in 
  six. 
  But 
  if 
  the 
  initial 
  sound 
  

   was 
  prolonged 
  — 
  fffive, 
  s 
  s 
  s 
  i.v, 
  the 
  observer 
  could 
  not 
  tell 
  

   until 
  he 
  heard 
  the 
  sequel 
  which 
  it 
  was 
  going 
  to 
  be. 
  Further, 
  

   if 
  the 
  sounds 
  were 
  given 
  as 
  s 
  s 
  ive, 
  /fix, 
  they 
  were 
  heard 
  

   normally 
  as 
  five 
  and 
  six. 
  It 
  was 
  plain 
  that 
  there 
  was 
  no 
  

   difference 
  in 
  the 
  rendering 
  off 
  and 
  s. 
  I 
  am 
  informed 
  that 
  

   this 
  is 
  a 
  well-known 
  difficulty 
  in 
  ordinary 
  telephoning, 
  and 
  

   that 
  in 
  spelling 
  a 
  name 
  containing/ 
  or 
  s 
  it 
  is 
  usual 
  to 
  say 
  "/ 
  

   for 
  Friday 
  " 
  or 
  " 
  s 
  for 
  Saturday." 
  But 
  the 
  articulation 
  of 
  

   the 
  acousticon 
  is 
  so 
  superior 
  that 
  it 
  was 
  surprising 
  to 
  find 
  the 
  

   failure 
  complete. 
  The 
  characterisation 
  of 
  sh 
  was 
  not 
  much 
  

   better, 
  though 
  after 
  a 
  little 
  practice 
  I 
  could 
  distinguish 
  it 
  

   from 
  ^ 
  or/, 
  but 
  probably 
  only 
  by 
  a 
  greater 
  loudness. 
  

  

  These 
  failures 
  might 
  have 
  been 
  ascribed 
  to 
  my 
  rather 
  

   defective 
  hearing, 
  but 
  other 
  observers 
  with 
  normal 
  hearing 
  

   did 
  no 
  better. 
  When, 
  however, 
  the 
  iron 
  plate 
  of 
  the 
  tele- 
  

   phone 
  was 
  replaced 
  by 
  one 
  three 
  times 
  as 
  thick, 
  a 
  difference 
  

   between 
  /and 
  s 
  could 
  be 
  detected, 
  though 
  both 
  were 
  rather 
  

   weak. 
  The 
  above 
  observations 
  were 
  made 
  with 
  the 
  small 
  

   model 
  and 
  usually 
  with 
  but 
  one 
  battery 
  cell. 
  In 
  the 
  case 
  of 
  

   the 
  large 
  model 
  microphone 
  and 
  with 
  two 
  cells 
  in 
  action, 
  it 
  

   was 
  just 
  possible 
  to 
  hear 
  some 
  difference 
  between 
  f 
  and 
  s, 
  the 
  

   usual 
  iron 
  plate 
  of 
  the 
  telephone 
  being 
  employed. 
  

  

  The 
  question 
  arises 
  as 
  to 
  how 
  the 
  acousticon 
  aids 
  defective 
  

   hearing. 
  A 
  failure 
  to 
  distinguish 
  f 
  and 
  s 
  seems 
  a 
  bad 
  

   beginning. 
  I 
  could 
  not 
  find 
  that 
  the 
  general 
  loudness 
  of 
  

   speech 
  was 
  increased 
  by 
  the 
  instrument. 
  When 
  the 
  speaker 
  

   stood 
  some 
  20 
  feet 
  away 
  from 
  the 
  microphone, 
  I 
  could 
  hear 
  

   better 
  directly 
  from 
  the 
  situation 
  of 
  the 
  microphone 
  than 
  

   when 
  in 
  the 
  further 
  room 
  I 
  listened 
  through 
  the 
  instrument. 
  

   Possibly 
  a 
  clue 
  may 
  be 
  found 
  in 
  the 
  behaviour 
  of 
  the 
  acousticon 
  

   in 
  presence 
  of 
  low 
  notes. 
  These 
  are 
  very 
  feebly 
  transmitted. 
  

   Pure 
  tones 
  from 
  forks 
  making 
  128, 
  256, 
  384 
  vibrations 
  per 
  

   second, 
  held 
  in 
  front 
  of 
  Helmholtz 
  resonators 
  and 
  close 
  to 
  the 
  

  

  