﻿264 
  Mr. 
  C 
  C. 
  Paterson 
  on 
  the 
  Proposed 
  

  

  agreement 
  between 
  this 
  country, 
  America, 
  and 
  France 
  in 
  

   the 
  matter 
  o£ 
  a 
  common 
  unit 
  o£ 
  Candle 
  Power. 
  

  

  The 
  writer 
  has 
  been 
  conducting 
  the 
  photometric 
  measure- 
  

   ments 
  connected 
  with 
  the 
  work, 
  in 
  this 
  country, 
  and 
  it 
  is 
  the 
  

   intention 
  in 
  this 
  paper 
  to 
  give 
  the 
  results 
  o£ 
  the 
  comparisons 
  

   which 
  have 
  been 
  made, 
  and 
  to 
  explain 
  briefly 
  those 
  facts 
  

   connected 
  with 
  the 
  different 
  standards 
  concerned 
  which 
  have 
  

   a 
  bearing 
  on 
  the 
  agreement 
  which 
  has 
  been 
  reached. 
  

  

  The 
  possibility 
  o£ 
  agreement 
  between 
  the 
  British 
  and 
  

   French 
  units 
  was 
  demonstrated 
  by 
  Dr. 
  Glazebrook 
  in 
  a 
  

   paper 
  on 
  light 
  standards 
  read 
  before 
  the 
  B.A. 
  at 
  Dublin 
  in 
  

   1908 
  *. 
  The 
  chief 
  factor 
  in 
  the 
  present 
  movement 
  has 
  been 
  

   the 
  desire 
  of 
  the 
  authorities 
  in 
  the 
  United 
  States 
  to 
  establish 
  

   one 
  unit 
  for 
  both 
  Gas 
  and 
  Electrical 
  industries 
  in 
  that 
  

   country, 
  and 
  the 
  possibility 
  of 
  their 
  adopting 
  a 
  unit 
  which 
  

   should 
  be 
  identical 
  with 
  those 
  existing 
  in 
  Great 
  Britain 
  and 
  

   France 
  led 
  them 
  to 
  take 
  the 
  initiative 
  in 
  an 
  attempt 
  to 
  obtain 
  

   international 
  cooperation. 
  The 
  agreement 
  which 
  has 
  resulted 
  

   has 
  the 
  approval 
  of 
  the 
  MetropoKtan 
  Gas 
  Referees 
  and 
  now 
  

   forms 
  the 
  subject 
  of 
  an 
  announcement 
  which 
  is 
  reproduced 
  

   on 
  page 
  273. 
  

  

  It 
  is 
  not 
  necessary 
  for 
  the 
  purpose 
  of 
  this 
  paper 
  to 
  enter 
  

   into 
  a 
  detailed 
  description 
  of 
  the 
  various 
  standard 
  lamps 
  and 
  

   units 
  referred 
  to 
  in 
  the 
  memorandum. 
  Dr. 
  J. 
  A. 
  Fleming 
  

   discussed 
  the 
  question 
  of 
  light 
  standards 
  very 
  fully 
  in 
  his 
  

   paper 
  before 
  the 
  Inst, 
  of 
  Elect. 
  Engineers, 
  vol. 
  32, 
  to 
  which 
  

   reference 
  should 
  be 
  made 
  f. 
  Some 
  facts, 
  however, 
  con- 
  

   nected 
  with 
  the 
  units 
  in 
  question 
  have 
  a 
  more 
  especial 
  

   bearing 
  on 
  the 
  experimental 
  results, 
  and 
  should 
  be 
  borne 
  

   in 
  mind 
  in 
  connexion 
  with 
  the 
  table 
  of 
  ratios 
  given 
  on 
  

   pages 
  270, 
  271. 
  

  

  IJie 
  British 
  Unit. 
  — 
  As 
  defined 
  in 
  the 
  above-mentioned 
  

   recommendation, 
  the 
  unit 
  of 
  Candle 
  Power 
  in 
  this 
  country 
  is 
  

   the 
  Harcourt 
  10 
  C.P. 
  Pentane 
  Lamp 
  burning 
  in 
  an 
  atmo- 
  

   sphere 
  at 
  normal 
  barometric 
  pressure 
  and 
  containing 
  8 
  litres 
  

   of 
  water-vapour 
  per 
  cubic 
  metre 
  as 
  measured 
  by 
  a 
  ventilated 
  

   hygrometer. 
  

  

  A 
  difficulty 
  arises 
  in 
  the 
  use 
  of 
  all 
  flame 
  standards 
  in 
  con- 
  

   nexion 
  with 
  the 
  method 
  to 
  be 
  employed 
  for 
  measuring 
  the 
  

   humidity. 
  When 
  flame 
  lamps 
  are 
  burning 
  in 
  a 
  closed 
  room 
  it 
  

   is 
  well 
  known 
  that 
  their 
  candle 
  power 
  diminishes, 
  due 
  probably 
  

   to 
  the 
  vitiation 
  of 
  the 
  air 
  in 
  the 
  immediate 
  neighbourhood 
  

  

  * 
  B.A. 
  Keport, 
  1908, 
  Dublin, 
  *^The 
  Photometric 
  Standard 
  of 
  the 
  

   National 
  Physical 
  Laboratory 
  " 
  ; 
  also 
  * 
  Journal 
  of 
  Gas 
  Liffhtinff,' 
  

   vol. 
  103, 
  1908, 
  p. 
  713. 
  

  

  t 
  See 
  also 
  paper 
  by 
  the 
  aut^.ior, 
  Joiirn. 
  lust. 
  Elect. 
  Eng. 
  vol. 
  xxxviii. 
  

   p. 
  271. 
  

  

  