﻿284 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  12 
  

  

  powerful 
  sound 
  in 
  air 
  signals 
  may 
  be 
  heard 
  varies 
  greatly, 
  and 
  under 
  

   unfavorable 
  weather 
  conditions 
  such 
  signals 
  can 
  be 
  heard 
  only 
  at 
  a 
  

   moderate 
  distance, 
  affording 
  scant 
  protection; 
  there 
  are 
  many 
  cases 
  

   of 
  aberration 
  of 
  the 
  sound, 
  the 
  signal 
  being 
  lost 
  and 
  again 
  picked 
  

   up 
  at 
  a 
  greater 
  distance, 
  and 
  no 
  means 
  are 
  available 
  to 
  the 
  ordinary 
  

   navigator 
  of 
  taking 
  a 
  definite 
  bearing 
  on 
  a 
  sound 
  fog 
  signal. 
  

  

  The 
  steam 
  whistle 
  is 
  a 
  fog 
  signal 
  formerly 
  extensively 
  used; 
  an 
  

   important 
  objection 
  to 
  it 
  is 
  the 
  time 
  required 
  to 
  get 
  it 
  in 
  operation, 
  as 
  

   fog 
  may 
  come 
  with 
  but 
  brief 
  warning 
  and 
  the 
  signal 
  should 
  be 
  in 
  oper- 
  

   ation 
  at 
  once. 
  The 
  most 
  effective 
  sound-producing 
  fog 
  signals 
  are 
  

   the 
  siren 
  and 
  the 
  diaphone 
  using 
  compressed 
  air 
  supplied 
  by 
  air 
  com- 
  

   pressors, 
  driven 
  by 
  internal 
  combustion 
  engines. 
  These 
  signals 
  have 
  

   distinctive 
  notes, 
  and 
  can 
  be 
  started 
  very 
  quickly 
  on 
  the 
  approach 
  of 
  

   fog. 
  In 
  the 
  standard 
  form 
  of 
  siren 
  now 
  used 
  in 
  the 
  Lighthouse 
  Ser- 
  

   vice, 
  a 
  hollow 
  cylinder 
  or 
  rotor, 
  6 
  inches 
  in 
  diameter 
  with 
  peripheral 
  

   slots 
  is 
  revolved 
  in 
  a 
  casing 
  with 
  similar 
  slots, 
  leading 
  to 
  a 
  horn 
  or 
  

   trumpet. 
  The 
  blasts 
  are 
  controlled 
  by 
  clockwork, 
  giving 
  a 
  charac- 
  

   teristic 
  signal 
  at 
  each 
  station. 
  The 
  diaphone 
  is 
  an 
  instrument 
  similar 
  

   to 
  the 
  siren, 
  but 
  having 
  a 
  reciprocating 
  motion 
  instead 
  of 
  a 
  rotary 
  

   one. 
  

  

  Sounding 
  buoys, 
  operated 
  automatically 
  by 
  the 
  sea, 
  are 
  much 
  used 
  

   aids, 
  and 
  serve 
  a 
  very 
  valuable 
  purpose 
  within 
  moderate 
  distances. 
  

   The 
  greater 
  number 
  are 
  the 
  familiar 
  bell 
  buoys; 
  a 
  modification 
  of 
  

   this 
  has 
  recently 
  been 
  made, 
  obtaining 
  a 
  chime 
  effect 
  by 
  means 
  of 
  

   several 
  sizes 
  of 
  gongs, 
  with 
  clappers 
  striking 
  alternately. 
  Bell 
  buoys 
  

   are 
  so 
  balanced 
  as 
  to 
  operate 
  with 
  every 
  slight 
  motion 
  of 
  the 
  waves. 
  

   The 
  whistling 
  buoy 
  is 
  an 
  American 
  invention, 
  and 
  is 
  a 
  valuable 
  aid 
  

   where 
  there 
  is 
  sufficient 
  sea 
  to 
  operate 
  it 
  effectively. 
  Submarine 
  

   bells 
  have 
  been 
  installed 
  on 
  buoys, 
  the 
  movement 
  of 
  the 
  buoy 
  operating 
  

   a 
  large 
  vane, 
  which 
  winds 
  a 
  spring 
  actuating 
  the 
  striking 
  mechanism. 
  

   The 
  most 
  valuable 
  recent 
  improvement 
  is 
  the 
  installation 
  on 
  a 
  buoy 
  of 
  

   a 
  bell 
  operated 
  by 
  carbonic 
  acid 
  gas. 
  The 
  gas 
  tanks 
  are 
  placed 
  in 
  

   receptacles 
  in 
  the 
  buoy, 
  and 
  the 
  bell 
  is 
  struck 
  at 
  uniform 
  intervals 
  by 
  

   a 
  piston 
  actuated 
  by 
  the 
  gas 
  pressure. 
  

  

  About 
  half 
  a 
  century 
  ago 
  considerable 
  research 
  work 
  in 
  sound 
  as 
  af- 
  

   fecting 
  fog 
  signals 
  was 
  done 
  by 
  Joseph 
  Henry, 
  then 
  chairman 
  of 
  the 
  

   Lighthouse 
  Board, 
  as 
  well 
  as 
  Secretary 
  of 
  the 
  Smithsonian 
  Institu- 
  

   tion, 
  and 
  the 
  results 
  were 
  collected 
  in 
  the 
  latter's 
  report 
  for 
  1878. 
  

   About 
  20 
  years 
  ago 
  elaborate 
  comparative 
  tests 
  of 
  fog 
  signal 
  apparatus 
  

   were 
  conducted 
  by 
  the 
  Trinity 
  House 
  of 
  London, 
  at 
  St. 
  Catherines 
  Point, 
  

  

  