﻿JUNE 
  19, 
  1922 
  PUTNAM: 
  lighthouse; 
  service 
  281 
  

  

  remarkable 
  power 
  of 
  absorbing 
  many 
  times 
  its 
  own 
  volume 
  of 
  gas. 
  

   This 
  makes 
  a 
  safe 
  and 
  economical 
  system 
  for 
  unattended 
  lights 
  and 
  

   buoys. 
  Electricity 
  is 
  not 
  generally 
  used 
  at 
  primary 
  lights 
  because 
  

   of 
  expense, 
  sufficient 
  illuminating 
  power 
  being 
  obtained 
  at 
  much 
  less 
  

   cost 
  with 
  the 
  oil 
  vapor 
  lamp 
  ; 
  electricity 
  is, 
  however, 
  used 
  with 
  great 
  

   advantage 
  at 
  some 
  stations 
  where 
  supply 
  of 
  current 
  is 
  available, 
  par- 
  

   ticularly 
  at 
  harbor 
  stations 
  where 
  distant 
  control 
  is 
  desirable, 
  as 
  a 
  

   station 
  at 
  the 
  end 
  of 
  a 
  breakwater 
  where 
  the 
  light 
  may 
  be 
  controlled 
  

   from 
  the 
  shore 
  end. 
  An 
  automatic 
  arrangement 
  for 
  exchanging 
  lamps 
  

   in 
  case 
  of 
  burnout 
  is 
  used. 
  

  

  The 
  early 
  lighthouses 
  were 
  lighted 
  with 
  open 
  fires, 
  and 
  tallow 
  can- 
  

   dles 
  were 
  used 
  at 
  the 
  Eddy 
  stone 
  light 
  for 
  more 
  than 
  a 
  hundred 
  years. 
  

   Although 
  lighthouses 
  have 
  aided 
  the 
  mariner 
  for 
  more 
  than 
  2,000 
  

   years, 
  most 
  of 
  the 
  progress 
  in 
  illuminating 
  apparatus 
  and 
  fog 
  signals 
  

   has 
  been 
  made 
  during 
  the 
  last 
  century. 
  A 
  hundred 
  years 
  ago 
  coal 
  

   fires 
  and 
  tallow 
  candles 
  had 
  only 
  recently 
  been 
  abandoned 
  at 
  impor- 
  

   tant 
  lighthouses 
  in 
  England, 
  guns 
  were 
  still 
  used 
  as 
  fog 
  signals, 
  and 
  no 
  

   outside 
  lightship 
  had 
  yet 
  been 
  moored 
  off 
  the 
  coast 
  of 
  this 
  country. 
  

   The 
  French 
  physicist, 
  Fresnel, 
  in 
  1822, 
  a 
  hundred 
  years 
  ago 
  this 
  year 
  

   made 
  the 
  greatest 
  single 
  step 
  in 
  the 
  improvement 
  of 
  illuminating 
  ap- 
  

   paratus 
  by 
  developing 
  a 
  built-up 
  annular 
  lens 
  surrounded 
  by 
  rings 
  of 
  

   glass 
  prisms, 
  the 
  central 
  portions 
  of 
  which 
  refract 
  and 
  the 
  outer 
  por- 
  

   tions 
  both 
  reflect 
  and 
  refract 
  the 
  light 
  from 
  a 
  single 
  source 
  lamp 
  

   placed 
  at 
  the 
  focus. 
  This 
  lens 
  was 
  for 
  a 
  fixed 
  light, 
  and 
  its 
  effect 
  was 
  

   to 
  concentrate 
  the 
  light 
  in 
  a 
  plane 
  useful 
  to 
  the 
  mariner, 
  but 
  distributed 
  

   around 
  the 
  horizon. 
  Great 
  progress 
  has 
  since 
  been 
  made 
  by 
  the 
  use 
  

   of 
  lenses 
  constructed 
  in 
  panels, 
  and 
  rotated, 
  thus 
  concentrating 
  

   the 
  light 
  in 
  beams 
  sweeping 
  around 
  the 
  horizon, 
  and 
  showing 
  to 
  the 
  

   mariner 
  a 
  flash 
  or 
  group 
  of 
  flashes 
  with 
  definite 
  characteristic. 
  Great 
  

   illuminating 
  efficiency 
  and 
  much 
  reduced 
  cost 
  have 
  been 
  obtained 
  with 
  

   such 
  apparatus, 
  by 
  using 
  smaller 
  lenses, 
  concentrating 
  the 
  light 
  through 
  

   a 
  small 
  number 
  of 
  panels, 
  and 
  revolving 
  at 
  high 
  speed. 
  The 
  latter 
  is 
  

   made 
  possible 
  by 
  carrying 
  the 
  weight 
  of 
  the 
  rotating 
  lens 
  in 
  mercury 
  

   in 
  an 
  annular 
  trough 
  . 
  The 
  following 
  comparison 
  shows 
  the 
  great 
  ad- 
  

   vantage 
  of 
  the 
  modern 
  lens 
  arrangement 
  : 
  At 
  Seguin, 
  Maine, 
  with 
  first 
  

   order 
  lens 
  72 
  inches 
  in 
  diameter, 
  the 
  light, 
  which 
  is 
  fixed, 
  has 
  22,000 
  

   candlepower. 
  At 
  Molokai, 
  Hawaii, 
  there 
  is 
  a 
  second 
  order 
  two 
  panel 
  

   lens, 
  55 
  inches 
  in 
  diameter, 
  revolving 
  once 
  in 
  20 
  seconds, 
  and 
  giving 
  

   each 
  10 
  seconds 
  a 
  flash 
  of 
  620,000 
  candlepower. 
  At 
  the 
  latter 
  the 
  cost 
  

   of 
  oil 
  per 
  candlepower 
  per 
  year 
  is 
  only 
  about 
  Vso 
  of 
  a 
  cent. 
  With 
  the 
  

  

  