﻿1875.] 
  Prof. 
  J. 
  Tyndall 
  on 
  Acoustic 
  Reversibility. 
  

  

  161 
  

  

  or 
  the 
  orifice 
  to 
  the 
  end 
  of 
  the 
  tube, 
  the 
  flame 
  was 
  violently 
  agitated 
  

   by 
  the 
  sounding-reed, 
  R. 
  On 
  shifting 
  the 
  tube, 
  or 
  the 
  burner, 
  so 
  

   as 
  to 
  concentrate 
  the 
  sound 
  on 
  a 
  portion 
  of 
  the 
  flame 
  about 
  half 
  an 
  

  

  Fig. 
  1. 
  

  

  inch 
  above 
  the 
  orifice, 
  the 
  action 
  was 
  nil. 
  Concentrating 
  the 
  sound 
  

   upon 
  the 
  burner 
  itself 
  about 
  half 
  an 
  inch 
  below 
  its 
  orifice, 
  there 
  was 
  no 
  

   action. 
  

  

  These 
  experiments 
  demonstrate 
  the 
  localization 
  of 
  " 
  the 
  seat 
  of 
  sensi- 
  

   tiveness," 
  and 
  they 
  prove 
  the 
  flame 
  to 
  be 
  an 
  appropriate 
  instrument 
  for 
  

   the 
  contemplated 
  experiments 
  on 
  reversibility. 
  

  

  The 
  experiments 
  proceeded 
  thus 
  : 
  — 
  The 
  sensitive 
  flame 
  being 
  placed 
  

   close 
  behind 
  a 
  screen 
  of 
  cardboard 
  18 
  inches 
  high 
  by 
  12 
  inches 
  wide, 
  a 
  

   vibrating 
  reed, 
  standing 
  at 
  the 
  same 
  height 
  as 
  the 
  root 
  of 
  the 
  flame, 
  was 
  

   placed 
  at 
  a 
  distance 
  of 
  6 
  feet 
  on 
  the 
  other 
  side 
  of 
  the 
  screen. 
  The 
  

   sound 
  of 
  the 
  reed, 
  in 
  this 
  position, 
  produced 
  a 
  strong 
  agitation 
  of 
  the 
  

   flame. 
  

  

  The 
  whole 
  upper 
  half 
  of 
  the 
  flame 
  was 
  here 
  visible 
  from 
  the 
  reed 
  ; 
  

   hence 
  the 
  necessity 
  of 
  the 
  foregoing 
  experiments 
  to 
  prove 
  the 
  action 
  of 
  

   the 
  sound 
  on 
  the 
  upper 
  portion 
  of 
  the 
  flame 
  to 
  be 
  nil, 
  and 
  that 
  the 
  waves 
  

   had 
  really 
  to 
  bend 
  round 
  the 
  edge 
  of 
  the 
  screen 
  so 
  as 
  to 
  reach 
  the 
  seat 
  of 
  

   sensitiveness 
  in 
  the 
  neighbourhood 
  of 
  the 
  burner. 
  

  

  The 
  positions 
  of 
  the 
  flame 
  and 
  reed 
  were 
  reversed, 
  the 
  latter 
  being 
  

   now 
  close 
  behind 
  the 
  screen, 
  and 
  the 
  former 
  at 
  a 
  distance 
  of 
  6 
  feet 
  

   from 
  it. 
  The 
  sonorous 
  vibrations 
  were 
  without 
  sensible 
  action 
  upon 
  

   the 
  flame. 
  

  

  The 
  experiment 
  was 
  repeated 
  and 
  varied 
  in 
  many 
  ways. 
  Screens 
  of 
  

   various 
  sizes 
  were 
  employed 
  ; 
  and 
  instead 
  of 
  reversing 
  the 
  positions 
  of 
  the 
  

   flame 
  and 
  reed, 
  the 
  screen 
  was 
  moved 
  so 
  as 
  to 
  bring, 
  in 
  some 
  experiments 
  

   the 
  flame, 
  and 
  in 
  other 
  experiments 
  the 
  reed, 
  close 
  behind 
  it. 
  Care 
  was 
  

   also 
  taken 
  that 
  no 
  reflected 
  sound 
  from 
  the 
  walls 
  or 
  ceiling 
  of 
  the 
  labora- 
  

   tory, 
  or 
  from 
  the 
  body 
  of 
  the 
  experimenter, 
  should 
  have 
  any 
  thing 
  to 
  do 
  

   with 
  the 
  effect. 
  In 
  all 
  cases 
  it 
  was 
  shown 
  that 
  the 
  sound 
  was 
  effective 
  

   when 
  the 
  reed 
  was 
  at 
  a 
  distance 
  from 
  the 
  screen 
  and 
  the 
  flame 
  close 
  

  

  