﻿International 
  Unit 
  of 
  Candle 
  Power. 
  273 
  

  

  approaches 
  the 
  figure 
  0-90. 
  The 
  mean 
  o£ 
  all 
  the 
  ratios 
  

   Hefner/Pentane 
  comes 
  to 
  0'90o 
  and 
  those 
  o£ 
  Hefner/Bougie 
  

   Dec. 
  to 
  0-895, 
  so 
  that 
  although 
  the 
  comparisons 
  between 
  the 
  

   Pentane 
  and 
  Bougie 
  Decimale 
  units 
  indicate 
  a 
  difference 
  o£ 
  

   0-8 
  per 
  cent., 
  the 
  same 
  units 
  compared 
  through 
  the 
  Hefner 
  

   Standard 
  only 
  appear 
  to 
  differ 
  by 
  0*5 
  per 
  cent. 
  

  

  The 
  author's 
  acknowledgments 
  are 
  due 
  to 
  Dr. 
  R. 
  T. 
  

   Glazebrook, 
  F.R.S., 
  Director 
  o£ 
  the 
  National 
  Physical 
  

   Laboratory. 
  

  

  Appendix. 
  

  

  €opy 
  of 
  Announcement 
  made 
  in 
  France^ 
  America, 
  and 
  Great 
  

   Britain, 
  relative 
  to 
  the 
  proposed 
  Internationcd 
  Unit 
  of 
  Light. 
  

  

  In 
  order 
  to 
  determine 
  as 
  accurately 
  as 
  possible 
  the 
  relations 
  

   between 
  the 
  photometric 
  units 
  of 
  America, 
  France, 
  Grermany, 
  

   and 
  Great 
  Britain, 
  comparisons 
  have 
  been 
  made 
  at 
  different 
  

   times 
  during 
  the 
  past 
  few 
  years 
  at 
  the 
  Bureau 
  of 
  Standards, 
  

   AVashington 
  ; 
  at 
  the 
  Laboratoire 
  Central 
  d^Electricite, 
  Paris 
  ; 
  

   at 
  the 
  Physikalisch-Technische 
  Peichsanstalt, 
  Berlin, 
  and 
  at 
  

   the 
  National 
  Physical 
  Laboratory, 
  London. 
  

  

  The 
  unit 
  of 
  light 
  at 
  the 
  Bureau 
  of 
  Standards 
  has 
  been 
  

   maintained 
  through 
  the 
  medium 
  of 
  a 
  series 
  of 
  incandescent 
  

   ■electric 
  lamps, 
  the 
  values 
  of 
  which 
  were 
  originally 
  intended 
  

   to 
  be 
  in 
  agreement 
  with 
  the 
  British 
  unit, 
  being 
  made 
  

   100/88 
  times 
  the 
  Hefner 
  unit. 
  

  

  The 
  unit 
  of 
  light 
  at 
  the 
  Laboratoire 
  Central 
  is 
  the 
  bougie 
  

   decimale, 
  which 
  is 
  the 
  twentieth 
  part 
  of 
  the 
  standard 
  defined 
  

   by 
  the 
  International 
  Conference 
  on 
  Units 
  of 
  1884, 
  and 
  which 
  

   is 
  taken, 
  in 
  accordance 
  with 
  the 
  experiments 
  of 
  Violle, 
  as 
  

   0'104 
  of 
  the 
  Carcel 
  lamp. 
  

  

  The 
  unit 
  of 
  light 
  at 
  the 
  Physikalisch-Technische 
  Reichs- 
  

   anstalt 
  is 
  that 
  given 
  by 
  the 
  Hefner 
  lamp 
  burning 
  at 
  normal 
  

   barometric 
  pressure 
  (76 
  cm.) 
  in 
  an 
  atmosphere 
  containing 
  

   88 
  litres 
  of 
  water- 
  vapour 
  per 
  cubic 
  metre. 
  

  

  The 
  unit 
  of 
  light 
  at 
  the 
  National 
  Physical 
  Laboratory 
  is 
  

   that 
  given 
  by 
  the 
  10 
  candle 
  power 
  Harcourt 
  Pentane 
  lamp 
  

   burning 
  at 
  normal 
  barometric 
  pressure 
  (76 
  cm.) 
  in 
  an 
  

   atmosphere 
  containing 
  8 
  litres 
  of 
  water-vapour 
  per 
  cubic 
  

   metre. 
  

  

  In 
  addition 
  to 
  the 
  direct 
  inter 
  comparison 
  of 
  flame 
  standards 
  

   carried 
  out 
  recently 
  by 
  the 
  national 
  laboratories 
  in 
  Europe, 
  

   one 
  comparison 
  was 
  made 
  in 
  1906 
  and 
  two 
  in 
  1908 
  between 
  

   the 
  American 
  and 
  European 
  units 
  by 
  means 
  o£ 
  carefully 
  

   seasoned 
  carbon 
  filament 
  electric 
  standards, 
  and 
  as 
  a 
  result 
  

  

  