﻿266 
  Mr. 
  C. 
  C. 
  Paterson 
  on 
  the 
  Proposed 
  

  

  Engineering 
  Society 
  and 
  other 
  bodies 
  took 
  the 
  matter 
  up 
  

   energetically, 
  and 
  the 
  Bureau 
  of 
  Standards, 
  Washington, 
  

   now 
  has 
  the 
  support 
  of 
  the 
  leading 
  institutions 
  in 
  America, 
  

   in 
  defining 
  the 
  value 
  o£ 
  a 
  common 
  standard, 
  to 
  be 
  accepted 
  

   throughout 
  the 
  States. 
  This 
  Institution 
  has 
  ascertained 
  by 
  

   means 
  o£ 
  electric 
  intercomparisons 
  the 
  ratio 
  of 
  their 
  present 
  

   unit 
  to 
  those 
  of 
  Germany, 
  France, 
  and 
  Great 
  Britain 
  respec- 
  

   tively 
  *, 
  and 
  has 
  arranged 
  to 
  adjust 
  the 
  value 
  of 
  the 
  American 
  

   unit 
  as 
  already 
  indicated. 
  

  

  German 
  Unit. 
  — 
  The 
  unit 
  accepted 
  in 
  Germany 
  is 
  the 
  light 
  

   given 
  by 
  the 
  Hefner 
  Lamp 
  burning 
  in 
  an 
  atmosphere 
  at 
  

   normal 
  barometric 
  pressure 
  and 
  containing 
  8*8 
  litres 
  of 
  water 
  

   vapour 
  per 
  cubic 
  metre. 
  The 
  researches 
  of 
  Liebenthal 
  f 
  at 
  

   the 
  Reichsanstalt 
  on 
  the 
  Hefner 
  Lamp 
  and 
  the 
  variation 
  of 
  

   its 
  C.P. 
  with 
  atmospheric 
  change 
  were 
  the 
  earliest 
  systematic 
  

   experiments 
  undertaken 
  of 
  this 
  nature 
  and 
  are 
  too 
  well 
  known 
  

   to 
  require 
  more 
  than 
  passing 
  mention. 
  

  

  French 
  Unit. 
  — 
  The 
  Candle 
  Power 
  Unit 
  adopted 
  by 
  the 
  

   Electrical 
  Industry 
  in 
  France 
  is 
  the 
  Bougie 
  Decimale. 
  This 
  

   is 
  the 
  20th 
  part 
  of 
  the 
  light 
  given 
  out 
  by 
  a 
  sq. 
  cm. 
  of 
  

   platinum 
  at 
  the 
  temperature 
  of 
  solidification. 
  The 
  unit 
  was 
  

   suggested 
  by 
  M. 
  Violle 
  and 
  adopted 
  by 
  the 
  Congres 
  Inter- 
  

   national 
  des 
  Electriciens 
  in 
  1881. 
  

  

  This 
  standard 
  has 
  been 
  found 
  very 
  difficult 
  to 
  reproduce 
  

   and 
  the 
  French 
  authorities 
  still 
  use 
  the 
  Carcel 
  lamp, 
  burning- 
  

   colza 
  oil, 
  as 
  the 
  standard 
  for 
  all 
  photometric 
  work. 
  

  

  A 
  determination 
  of 
  the 
  value 
  of 
  the 
  Carcel 
  lamp 
  in 
  terms 
  

   of 
  the 
  Violle 
  platinum 
  standard 
  has 
  only 
  been 
  made 
  once. 
  

   This 
  was 
  by 
  M. 
  Violle 
  himself 
  in 
  1884 
  J. 
  Measurements 
  

   were 
  made 
  by 
  him 
  using 
  two 
  or 
  three 
  photometric 
  methods, 
  

   and 
  all 
  his 
  values 
  except 
  one 
  showed 
  the 
  bougie 
  decimal 
  to 
  

   be 
  a 
  little 
  less 
  than 
  4 
  per 
  cent, 
  greater 
  than 
  the 
  Carcel 
  unit. 
  

  

  A 
  multiplying 
  factor 
  of 
  I'Ol 
  for 
  the 
  Carcel 
  unit 
  was 
  

   therefore 
  given 
  by 
  him, 
  and 
  has 
  been 
  adopted 
  ever 
  since 
  for 
  

   reducing 
  the 
  values 
  in 
  terms 
  of 
  one 
  standard 
  to 
  those 
  of 
  the 
  

   other. 
  As 
  no 
  account 
  was 
  taken 
  by 
  M. 
  Violle 
  of 
  the 
  pressure 
  

   and 
  humidity 
  of 
  the 
  atmosphere 
  in 
  which 
  the 
  Carcel 
  lamp 
  

   was 
  burning, 
  the 
  accepted 
  figure 
  of 
  1'04 
  must 
  be 
  regarded 
  

   as 
  liable 
  to 
  a 
  certain 
  inaccuracy 
  due 
  to 
  this 
  cause. 
  It 
  should 
  

   be 
  remarked, 
  also 
  §, 
  that 
  no 
  correctino^ 
  factor 
  has 
  as 
  yet 
  been 
  

   determined 
  for 
  the 
  variations 
  in 
  the 
  C.P. 
  of 
  the 
  Carcel 
  lamp 
  

  

  * 
  Kef. 
  cit. 
  

  

  t 
  " 
  Zeitschrift 
  fiir 
  Instrumentenkunde," 
  vol. 
  xv. 
  1895, 
  p. 
  157. 
  

   J 
  Stances 
  of 
  the 
  French 
  Physical 
  Soc, 
  May 
  to 
  July, 
  1884. 
  

   § 
  " 
  Rappoirt 
  de 
  Trois 
  Lamps," 
  Laporte 
  & 
  Jouaust, 
  Bull. 
  Soc. 
  Inst, 
  des 
  

   Elect. 
  2nd 
  s^rie, 
  tome 
  vi. 
  no. 
  58. 
  

  

  