﻿240 
  Lord 
  Rayleigh 
  : 
  Acoustical 
  JS 
  T 
  otes. 
  

  

  of 
  water 
  may 
  be 
  either 
  directly 
  from 
  a 
  tap 
  or 
  preferably 
  

   from 
  an 
  aspirator 
  bottle. 
  The 
  head 
  of 
  water, 
  about 
  30 
  era., 
  

   must 
  be 
  adjusted 
  ; 
  and 
  it 
  is 
  to 
  be 
  remarked 
  that 
  the 
  

   question 
  is 
  not 
  merely 
  one 
  of 
  accommodating 
  the 
  natural 
  

   pitch 
  of 
  the 
  jet 
  to 
  that 
  of 
  the 
  fork. 
  There 
  is 
  also 
  the 
  phase 
  

   to 
  be 
  considered, 
  for 
  the 
  impact 
  of 
  the 
  drops 
  may 
  check, 
  as 
  

   easily 
  as 
  encourage, 
  an 
  existing 
  vibration. 
  A 
  slight 
  altera- 
  

   tion 
  in 
  the 
  distance 
  between 
  A 
  and 
  B 
  may 
  here 
  be 
  useful. 
  

   In 
  practice 
  attention 
  should 
  be 
  given 
  to 
  the 
  place 
  of 
  resolu- 
  

   tion 
  of 
  the 
  jet, 
  easily 
  discerned 
  in 
  a 
  suitable 
  light. 
  When 
  

   this 
  is 
  brought 
  up 
  as 
  near 
  to 
  the 
  orifice 
  as 
  possible, 
  it 
  will 
  be 
  

   known 
  that 
  the 
  vibration 
  is 
  vigorous 
  and 
  that 
  the 
  phase 
  

   relation 
  is 
  suitable. 
  

  

  The 
  experiment 
  was 
  quite 
  successful. 
  Both 
  the 
  forks 
  

   referred 
  to 
  spoke 
  well 
  and 
  steadily 
  when 
  suitable 
  resonators 
  

   were 
  held 
  near 
  their 
  prongs, 
  But 
  the 
  arrangement 
  is 
  hardly 
  

   to 
  be 
  recommended 
  for 
  general 
  purposes. 
  The 
  use 
  of 
  water 
  

   is 
  messy, 
  and 
  unless 
  care 
  be 
  taken 
  is 
  likely 
  to 
  end 
  in 
  rusting 
  

   the 
  forks. 
  Moreover, 
  the 
  vibrations 
  are 
  not 
  especially 
  

   vigorous— 
  in 
  comparison, 
  for 
  example, 
  with 
  those 
  which 
  

   may 
  be 
  obtained 
  electromagnetically. 
  Another 
  objection 
  is 
  

   to 
  be 
  found 
  in 
  the 
  circumstance 
  that 
  drops 
  of 
  water 
  remaining 
  

   attached 
  to 
  the 
  fork 
  must 
  render 
  the 
  precise 
  pitch 
  uncertain. 
  

  

  Discrimination 
  between 
  Sounds 
  from 
  directly 
  in 
  front 
  and 
  

   directly 
  behind 
  the 
  Observer. 
  

  

  As 
  already* 
  mentioned, 
  I 
  am 
  now 
  unable 
  to 
  make 
  the 
  

   discrimination 
  myself, 
  even 
  in 
  the 
  case 
  of 
  the 
  voice 
  used 
  

   naturally 
  ; 
  so 
  that 
  all 
  that 
  I 
  can 
  report 
  relates 
  to 
  the 
  obser- 
  

   vations 
  of 
  others. 
  It 
  would 
  seem, 
  however, 
  that 
  even 
  youthful 
  

   listeners 
  are 
  not 
  always 
  able 
  to 
  pronounce 
  with 
  certainty. 
  

   In 
  experiments 
  made 
  with 
  some 
  young 
  people 
  in 
  a 
  long- 
  

   corridor, 
  they 
  were 
  able 
  to 
  discriminate 
  among 
  themselves 
  

   whether 
  a 
  voice 
  came 
  from 
  in 
  front 
  or 
  behind, 
  but 
  when 
  I 
  spoke 
  

   they 
  made 
  mistakes. 
  The 
  speaker 
  facing 
  towards 
  the 
  listener 
  

   gave, 
  for 
  example, 
  the 
  numerals 
  one 
  — 
  two 
  — 
  three 
  &c. 
  ; 
  and 
  

   there 
  were 
  enough 
  assistants 
  moving 
  backwards 
  and 
  forwards 
  to 
  

   eliminate 
  information 
  wh 
  ich 
  might 
  otherwise 
  be 
  given 
  by 
  foot- 
  

   steps. 
  Why 
  my 
  voice 
  afforded 
  less 
  foundation 
  for 
  a 
  judgment 
  

   was 
  not 
  clear 
  — 
  possibly 
  in 
  consequence 
  of 
  its 
  graver 
  pitch, 
  

   or 
  because 
  its 
  quality 
  was 
  less 
  familiar. 
  The 
  corridor 
  was 
  so 
  

   long 
  that 
  the 
  observations 
  were 
  not 
  appreciably 
  disturbed 
  by 
  

   echos. 
  

  

  As 
  mentioned 
  before, 
  Mr. 
  Enock 
  is 
  able 
  in 
  many 
  cases 
  to 
  

  

  * 
  Phil. 
  Mag. 
  vol. 
  xiii. 
  p. 
  281 
  (1907). 
  

  

  