﻿378 
  An 
  Evaluation 
  of 
  the 
  Absolute 
  Scale 
  of 
  Temperature. 
  

  

  Differences 
  between 
  Gas 
  Thermometers 
  

   (in 
  thousandths 
  of 
  a 
  degree). 
  

  

  i 
  

  

  t. 
  

  

  t]$- 
  

  

  -tn. 
  

  

  tco 
  2 
  - 
  

  

  -*H. 
  

  

  tco 
  2 
  

  

  -*N. 
  

  

  calc. 
  

  

  obs. 
  

   + 
  6 
  

  

  calc. 
  

  

  obs. 
  

  

  calc. 
  

  

  obs. 
  

  

  o 
  

  

  10 
  ... 
  

  

  + 
  6 
  

  

  +23 
  

  

  25 
  

  

  +17 
  

  

  19 
  

  

  20 
  ... 
  

  

  11 
  

  

  10 
  

  

  42 
  

  

  43 
  

  

  31 
  

  

  33 
  

  

  SO 
  ... 
  

  

  14 
  

  

  11 
  

  

  56 
  

  

  54 
  

  

  42 
  

  

  43 
  

  

  40 
  ... 
  

  

  17 
  

  

  11 
  

  

  68 
  

  

  59 
  

  

  51 
  

  

  48 
  

  

  50 
  ... 
  

  

  19 
  

  

  9 
  

  

  74 
  

  

  59 
  

  

  55 
  

  

  50 
  

  

  60 
  ... 
  

  

  19 
  

  

  5 
  

  

  73 
  

  

  53 
  

  

  54 
  

  

  48 
  

  

  70 
  ... 
  

  

  17 
  

  

  1 
  

  

  66 
  

  

  44 
  

  

  49 
  

  

  43 
  

  

  80 
  ... 
  

  

  15 
  

  

  - 
  2 
  

  

  52 
  

  

  31 
  

  

  37 
  

  

  33 
  

  

  90 
  ... 
  

  

  10 
  

  

  - 
  3 
  

  

  31 
  

  

  16 
  

  

  21 
  

  

  19 
  

  

  The 
  Irydrogen 
  and 
  nitrogen 
  scales 
  exhibit 
  a 
  curious 
  reversal 
  

   at 
  80° 
  to 
  90°, 
  which 
  is 
  not 
  reproduced 
  in 
  the 
  calculated 
  

   numbers 
  ; 
  the 
  calculated 
  temperatures 
  are 
  consequently 
  a 
  

   good 
  deal 
  in 
  error 
  there. 
  It 
  will 
  be 
  noticed 
  that 
  the 
  calcu- 
  

   lated 
  difference 
  for 
  t 
  C02 
  — 
  t^ 
  is 
  much 
  more 
  correct 
  than 
  that 
  for 
  

   ^co 
  2 
  — 
  t-H., 
  which 
  seems 
  to 
  show 
  that 
  the 
  anomaly 
  is 
  rather 
  in 
  

   the 
  hydrogen 
  than 
  in 
  the 
  nitrogen 
  scale 
  ; 
  this 
  is 
  another 
  

   point 
  which 
  cannot 
  be 
  cleared 
  up 
  without 
  further 
  experimental 
  

   data. 
  The 
  greatest 
  difference 
  between 
  the 
  observed 
  and 
  

   calculated 
  numbers 
  is 
  o, 
  022 
  ; 
  the 
  mean 
  of 
  all 
  the 
  differences 
  

   0°-008. 
  

  

  Conclusions. 
  

  

  In 
  conclusion 
  one 
  may 
  be 
  permitted 
  to 
  repeat 
  that 
  : 
  — 
  

  

  (1) 
  The 
  absolute 
  temperature 
  of 
  the 
  freezing-point 
  is 
  

   probably 
  within 
  a 
  tenth 
  of 
  a 
  degree 
  of 
  273°. 
  

  

  (2) 
  The 
  divergences 
  between 
  the 
  different 
  gas 
  scales 
  are 
  

   fairly 
  represented 
  by 
  the 
  theory 
  ; 
  but 
  it 
  is 
  not 
  yet 
  possible 
  to 
  

   reduce 
  temperatures 
  to 
  the 
  absolute 
  scale 
  with 
  so 
  high 
  a 
  

   degree 
  of 
  accuracy 
  as 
  it 
  is 
  possible 
  to 
  record 
  them 
  on 
  the 
  

   scale 
  of 
  the 
  mercury 
  thermometer, 
  or 
  on 
  the 
  " 
  normal 
  scale 
  " 
  

   of 
  the 
  Comite 
  internationale. 
  

  

  (3) 
  In 
  order 
  to 
  attain 
  to 
  that 
  degree 
  of 
  accuracy, 
  and 
  to 
  

   settle 
  the 
  value 
  of 
  T 
  to 
  o, 
  05 
  — 
  which 
  seems 
  possible 
  — 
  it 
  is 
  

   necessary 
  : 
  — 
  

  

  (a) 
  To 
  measure 
  the 
  coefficient 
  of 
  pressure 
  for 
  air 
  in 
  the 
  

   same 
  manner 
  as 
  has 
  been 
  done 
  for 
  hydrogen, 
  nitrogen, 
  

   and 
  carbon 
  dioxide 
  by 
  Chappuis, 
  and 
  to 
  extend 
  the 
  

   experiments 
  on 
  all 
  four 
  gases 
  to 
  initial 
  pressures 
  lower 
  

   than 
  one 
  metre 
  of 
  mercury 
  — 
  say 
  for 
  25, 
  50, 
  and 
  75 
  cm. 
  

  

  