﻿246 
  Lord 
  Rayleigh 
  : 
  Acoustical 
  Notes. 
  

  

  at 
  all. 
  The 
  telephone 
  employed 
  was 
  bipolar 
  and 
  of 
  modern 
  

   manufacture. 
  

  

  In 
  another 
  experiment 
  the 
  permanent 
  steel 
  magnets 
  were 
  

   removed 
  from 
  the 
  telephone 
  and 
  replaced 
  by 
  a 
  soft-iron 
  U 
  

   which 
  could 
  be 
  magnetized 
  at 
  will 
  by 
  an 
  independent 
  electric 
  

   current, 
  the 
  coils 
  and 
  pole-pieces 
  of 
  the 
  telephone 
  remaining 
  

   undisturbed. 
  Without 
  a 
  magnetizing 
  current 
  but 
  little 
  of 
  the 
  

   ticks 
  of 
  the 
  watch 
  could 
  be 
  heard 
  from 
  the 
  copper 
  plate, 
  but 
  

   when 
  the 
  soft 
  iron 
  was 
  magnetized 
  the 
  sounds 
  became 
  distinct 
  

   as 
  before. 
  

  

  I 
  had 
  supposed 
  at 
  first 
  that 
  this 
  experiment 
  might 
  dis- 
  

   criminate 
  between 
  the 
  two 
  possible 
  explanations 
  of 
  the 
  sound, 
  

   the 
  one 
  depending 
  upon 
  traces 
  of 
  iron 
  as 
  an 
  impurity 
  in 
  the 
  

   copper 
  or 
  aluminium, 
  the 
  other 
  invoking 
  the 
  action 
  of 
  

   induced 
  currents 
  circulating 
  in 
  the 
  metallic 
  plates. 
  But 
  it 
  

   appears 
  that 
  in 
  either 
  case 
  the 
  efficiency 
  would 
  be 
  promoted 
  

   by 
  a 
  high 
  constant 
  magnetization 
  of 
  the 
  pole-pieces. 
  

  

  The 
  copper 
  disk, 
  weighing 
  about 
  one 
  gram, 
  was 
  of 
  a 
  kind 
  

   unlikely 
  to 
  contain 
  appreciable 
  iron 
  and 
  its 
  action 
  was 
  not 
  

   affected 
  by 
  washing 
  with 
  hydrochloric 
  acid. 
  When 
  a 
  mica 
  

   disk, 
  which 
  of 
  itself 
  gave 
  no 
  sound, 
  was 
  dusted 
  over 
  with 
  1 
  mg. 
  

   of 
  fine 
  iron 
  filings 
  attached 
  with 
  varnish, 
  only 
  a 
  very 
  faint 
  

   sound 
  could 
  be 
  made 
  out. 
  A 
  similar 
  mica 
  disk 
  coated 
  with 
  

   -| 
  gm. 
  of 
  copper 
  filings 
  from 
  the 
  same 
  material 
  as 
  that 
  of 
  the 
  

   disk, 
  yielded 
  no 
  sound. 
  A 
  similar 
  telephone 
  with 
  copper 
  disk 
  

   was 
  included 
  in 
  the 
  circuit 
  for 
  the 
  sake 
  of 
  rapid 
  comparison 
  

   throughout 
  the 
  experiments. 
  

  

  From 
  these 
  results 
  it 
  appeared 
  unlikely 
  that 
  the 
  effects 
  

   were 
  to 
  be 
  attributed 
  to 
  traces 
  of 
  iron 
  in 
  the 
  other 
  metals, 
  

   and 
  this 
  conclusion 
  was 
  confirmed 
  in 
  a 
  varied 
  form 
  of 
  the 
  

   experiment 
  tried 
  later. 
  Mr. 
  Enock 
  prepared 
  two 
  flat 
  coils 
  

   of 
  fine 
  covered 
  copper 
  wire 
  weighing 
  together 
  about 
  2 
  gms. 
  

   These 
  were 
  mounted 
  separately 
  on 
  pieces 
  of 
  mica 
  afterwards 
  

   cemented 
  with 
  wax 
  to 
  the 
  main 
  disk 
  so 
  as 
  to 
  encircle 
  the 
  mag- 
  

   netic 
  poles. 
  W 
  hen 
  the 
  ends 
  of 
  the 
  flat 
  coils 
  were 
  disconnected, 
  

   nothing 
  was 
  heard 
  ; 
  but 
  on 
  completing 
  the 
  circuit 
  of: 
  one 
  or 
  

   both 
  coils 
  the 
  effects 
  were 
  very 
  distinct, 
  both 
  with 
  the 
  carbon 
  

   microphone 
  and 
  watch 
  as 
  before 
  used 
  or 
  with 
  another 
  arrange- 
  

   ment 
  giving 
  a 
  more 
  powerful 
  action. 
  We 
  may 
  conclude, 
  I 
  

   think, 
  that 
  the 
  sounds 
  of 
  a 
  copper 
  disk 
  are 
  due 
  to 
  alternating 
  

   currents 
  induced 
  in 
  it 
  and 
  reacting 
  upon 
  the 
  nearly 
  constant 
  

   magnetism 
  of 
  the 
  pole-pieces. 
  

  

  Terling 
  Place, 
  Witbam, 
  

   Jan. 
  1908. 
  

  

  