﻿280 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  12 
  

  

  lights 
  are 
  so 
  spaced 
  that 
  a 
  vessel 
  skirting 
  the 
  coast 
  will 
  always 
  be 
  in 
  

   sight 
  of 
  one 
  of 
  these 
  lights. 
  

  

  There 
  are 
  a 
  great 
  number 
  of 
  smaller 
  lights, 
  such 
  as 
  gas 
  buoys 
  mark- 
  

   ing 
  channels 
  and 
  immediate 
  entrances, 
  and 
  lighthouses 
  and 
  post 
  

   lights 
  marking 
  minor 
  entrances, 
  inside 
  channels, 
  dangers, 
  and 
  river 
  

   channels. 
  

  

  The 
  problems 
  to 
  be 
  solved 
  in 
  providing 
  an 
  effective 
  light 
  for 
  the 
  

   mariner 
  are: 
  most 
  useful 
  location, 
  suitable 
  illuminant, 
  lamp 
  and 
  op- 
  

   tical 
  arrangement 
  to 
  give 
  the 
  required 
  luminous 
  range, 
  height 
  of 
  the 
  

   light 
  for 
  the 
  proper 
  geographic 
  range, 
  and 
  distinctive 
  characteristic 
  

   to 
  avoid 
  confusion 
  with 
  other 
  lighted 
  aids 
  as 
  well 
  as 
  lights 
  for 
  other 
  

   purposes. 
  

  

  Because 
  of 
  expense 
  involved, 
  the 
  number 
  of 
  lights 
  must 
  of 
  course 
  be 
  

   restricted 
  to 
  the 
  most 
  essential 
  locations. 
  They 
  are 
  placed 
  as 
  near 
  

   as 
  practicable 
  to 
  the 
  track 
  of 
  vessels, 
  or 
  to 
  the 
  outer 
  limit 
  of 
  the 
  danger 
  

   to 
  be 
  marked 
  ; 
  large 
  expenditures 
  have 
  sometimes 
  been 
  made 
  so 
  as 
  to 
  

   place 
  a 
  lighthouse 
  in 
  the 
  position 
  most 
  protective 
  to 
  shipping. 
  The 
  

   geographic 
  range, 
  depending 
  on 
  the 
  height 
  of 
  the 
  focal 
  plane 
  above 
  sea 
  

   level, 
  is 
  for 
  the 
  primary 
  lights 
  on 
  low 
  coasts 
  about 
  20 
  nautical 
  miles, 
  

   this 
  distance 
  being 
  sufficient 
  for 
  general 
  navigational 
  purposes. 
  This 
  

   requires 
  a 
  tower 
  of 
  from 
  150 
  to 
  200 
  feet, 
  depending 
  on 
  the 
  elevation 
  of 
  

   the 
  observer 
  on 
  the 
  ship. 
  Adding 
  another 
  100 
  feet 
  to 
  the 
  height 
  of 
  a 
  

   tower 
  of 
  200 
  feet 
  increases 
  the 
  distance 
  of 
  visibility 
  only 
  3V2 
  nautical 
  

   miles. 
  

  

  Illuminants 
  and 
  lighting 
  apparatus. 
  — 
  For 
  illuminant, 
  the 
  primary 
  

   coast 
  lights 
  of 
  this 
  country 
  now 
  use 
  kerosene 
  burned 
  in 
  incandescent 
  

   oil 
  vapor 
  lamps. 
  In 
  this 
  lamp 
  the 
  kerosene, 
  forced 
  into 
  the 
  vapor- 
  

   izer 
  by 
  air 
  pressure, 
  is 
  heated 
  and 
  vaporized, 
  and 
  is 
  burned 
  mixed 
  with 
  

   air 
  under 
  a 
  mantle, 
  which 
  is 
  thus 
  brought 
  to 
  a 
  brilliant 
  incandescence. 
  

   This 
  lamp 
  gives 
  one 
  candlepower 
  of 
  the 
  bare 
  light 
  for 
  about 
  ^/i 
  gallon 
  

   of 
  kerosene 
  a 
  year, 
  as 
  against 
  6 
  gallons 
  a 
  year 
  per 
  candlepower 
  for 
  the 
  

   Argand 
  wick 
  lamp, 
  thus 
  increasing 
  the 
  illuminating 
  efficiency 
  of 
  the 
  

   oil 
  about 
  8 
  times. 
  As 
  an 
  example, 
  when 
  the 
  oil 
  vapor 
  lamp 
  was 
  installed 
  

   at 
  Cape 
  Hatteras 
  lighthouse 
  the 
  power 
  of 
  the 
  light 
  was 
  increased 
  from 
  

   27,000 
  to 
  80,000 
  candles, 
  and 
  the 
  consumption 
  of 
  oil 
  was 
  reduced 
  

   from 
  2,300 
  to 
  1,000 
  gallons 
  a 
  year. 
  Next 
  to 
  kerosene, 
  acetylene 
  gas 
  

   is 
  the 
  most 
  widely 
  used 
  illuminant, 
  supplying 
  nearly 
  1,000 
  lights 
  in 
  

   this 
  service, 
  for 
  the 
  most 
  part 
  unattended 
  beacons 
  on 
  shore, 
  and 
  gas 
  

   buoys. 
  These 
  are 
  nearly 
  all 
  supplied 
  with 
  compressed 
  gas 
  dissolved 
  

   in 
  acetone, 
  in 
  tanks 
  filled 
  with 
  a 
  porous 
  substance; 
  the 
  acetone 
  has 
  the 
  

  

  