﻿22 
  C. 
  K. 
  Wead 
  — 
  Intensity 
  of 
  Sound. 
  

  

  Open 
  Diapason 
  stop 
  in 
  an 
  organ, 
  but 
  gave 
  no 
  absolute 
  amount. 
  

   He 
  assumes 
  as 
  a 
  matter 
  of 
  general 
  knowledge 
  that 
  an 
  organ 
  

   builder 
  furnishes 
  a 
  series 
  of 
  pipes 
  of 
  sensibly 
  equal 
  loudness 
  

   (and 
  quality) 
  throughout 
  the 
  scale 
  ; 
  he 
  quotes 
  what 
  he 
  calls 
  

   Topfer's 
  law, 
  that 
  the 
  consumption 
  of 
  wind 
  by 
  pipes 
  belong- 
  

   ing 
  to 
  the 
  same 
  stop 
  varies 
  directly 
  as 
  the 
  length 
  of 
  the 
  pipe, 
  

   and 
  confirms 
  it 
  approximately 
  by 
  experiments 
  ; 
  and 
  so 
  he 
  con- 
  

   cludes 
  that 
  the 
  amount 
  of 
  energy 
  per 
  second 
  necessary 
  to 
  pro- 
  

   duce 
  sounds 
  of 
  equal 
  loudness 
  under 
  similar 
  conditions 
  varies 
  

   inversely 
  as 
  the 
  vibration-frequency. 
  On 
  the 
  other 
  hand 
  M. 
  

   Allard* 
  makes 
  the 
  assumption 
  that 
  the 
  energy 
  per 
  second 
  

   needed 
  to 
  maintain 
  a 
  sound 
  just 
  audible 
  at 
  a 
  given 
  distance 
  

   varies 
  directly 
  as 
  the 
  vibration-frequency, 
  and 
  finds 
  a 
  satisfac- 
  

   tory 
  confirmation 
  of 
  his 
  views 
  in 
  the 
  experiments 
  on 
  the 
  range 
  

   of 
  fog-horns 
  made 
  by 
  various 
  lighthouse 
  boards. 
  But 
  the 
  con- 
  

   dition 
  of 
  the 
  observer 
  will 
  be 
  very 
  different 
  in 
  the 
  two 
  cases 
  ; 
  

   so 
  they 
  are 
  scarcely 
  comparable. 
  

  

  The 
  experiments 
  now 
  to 
  be 
  detailed 
  and 
  discussed 
  are 
  suffi- 
  

   ciently 
  numerous 
  and 
  exact 
  to 
  disprove 
  this 
  alleged 
  law 
  of 
  

   Topfer's, 
  so 
  far 
  at 
  least 
  as 
  one 
  organ 
  is 
  a 
  fair 
  sample 
  of 
  alL 
  

   They 
  were 
  performed 
  on 
  a 
  Hook 
  and 
  Hastings 
  No. 
  11 
  Organ 
  

   in 
  the 
  Congregational 
  Church 
  of 
  Ann 
  Arbor, 
  Mich. 
  : 
  this 
  

   instrument 
  has 
  two 
  manuals 
  of 
  58 
  keys 
  each 
  from 
  C 
  to 
  a 
  //r 
  , 
  the 
  

   great 
  organ 
  having 
  9 
  stops 
  — 
  the 
  seven 
  to 
  be 
  named 
  in 
  table 
  I, 
  

   a 
  2-f 
  7 
  twelfth 
  and 
  a 
  3 
  rank 
  mixture. 
  The 
  pressure 
  of 
  wind 
  

   was 
  very 
  exactly 
  3 
  inches 
  of 
  water, 
  and 
  the 
  total 
  capacity 
  of 
  

   the 
  bellows 
  about 
  35 
  cubic 
  feet 
  ; 
  this 
  quantity 
  of 
  wind 
  would 
  

   leak 
  out 
  in 
  about 
  3 
  minutes. 
  

  

  The 
  only 
  method 
  of 
  experiment 
  available, 
  unless 
  one 
  has 
  a 
  

   very 
  large 
  gas-meter 
  at 
  his 
  disposal, 
  is 
  to 
  fill 
  the 
  bellows 
  and 
  

   determine 
  the 
  time 
  needed 
  for 
  the 
  whole 
  or 
  any 
  definite 
  part 
  

   of 
  its 
  contents 
  to 
  leak 
  out 
  ; 
  then 
  determine 
  similarly 
  the 
  time 
  

   when 
  one 
  or 
  more 
  pipes 
  are 
  sounding. 
  For 
  example, 
  12 
  cu. 
  

   ft. 
  (=A) 
  of 
  air 
  are 
  used; 
  if 
  this 
  leaks 
  out 
  in 
  60 
  seconds 
  the 
  

   leakage 
  is 
  A-=-60= 
  , 
  20 
  cu. 
  ft. 
  per 
  sec; 
  if 
  when 
  a 
  pipe 
  is 
  

   sounding 
  the 
  time 
  is 
  24 
  sec, 
  the 
  flow 
  is 
  then 
  A-r-24=*50 
  cu. 
  ft. 
  

   per 
  sec, 
  and 
  the 
  pipe 
  consumes 
  the 
  difference, 
  that 
  is 
  0*30 
  cu. 
  

   ft. 
  per 
  second 
  ; 
  if 
  this 
  is 
  supplied 
  under 
  a 
  pressure 
  of 
  3 
  inches 
  

   of 
  water 
  =15*6 
  lbs. 
  per 
  sq. 
  ft., 
  the 
  energy 
  used 
  by 
  the 
  pipe 
  

   = 
  '30xl5*6=4-7 
  ft. 
  lbs. 
  per 
  sec. 
  In 
  this 
  way 
  the 
  computa- 
  

   tions 
  have 
  been 
  made 
  for 
  the 
  tables. 
  

  

  Mr. 
  Bosanquet 
  limited 
  his 
  work 
  to 
  observing 
  the 
  times, 
  and 
  

   finding 
  the 
  difference 
  of 
  their 
  reciprocals, 
  thus 
  getting 
  the 
  

   desired 
  relative 
  values. 
  He 
  used 
  a 
  string 
  pendulum, 
  finding 
  

   the 
  time 
  needed 
  for 
  the 
  bellows 
  to 
  empty 
  itself, 
  the 
  u 
  feel 
  " 
  of 
  

   the 
  blowing 
  lever 
  indicating 
  when 
  the 
  bellows 
  is 
  full 
  or 
  empty. 
  

  

  * 
  Comptes 
  Rendus, 
  xcv, 
  10B2. 
  

  

  