﻿Absolute 
  Method 
  of 
  Graduating 
  a 
  Thermometer. 
  227 
  

  

  meteorological 
  investigations 
  ; 
  and 
  many, 
  perhaps 
  most, 
  low 
  

   Canadian 
  temperatures 
  have 
  been 
  observed 
  on 
  these 
  instru- 
  

   ments. 
  

  

  My 
  own 
  belief 
  is 
  that 
  for 
  ordinary 
  meteorological 
  uses 
  

   the 
  idea 
  was 
  by 
  no 
  means 
  bad, 
  and 
  that 
  it 
  might, 
  for 
  very 
  

   low 
  temperatures, 
  when 
  accuracy 
  of 
  o, 
  i 
  or 
  o, 
  2 
  F. 
  is 
  good 
  

   enough, 
  be 
  carried 
  farther. 
  

  

  Instead 
  of 
  trying 
  to 
  make 
  the 
  scale 
  of 
  the 
  mercury 
  or 
  

   spirit 
  thermometer 
  coincide 
  with 
  that 
  of 
  a 
  gas 
  thermometer 
  

   at 
  three 
  points 
  only, 
  one 
  might, 
  if 
  one 
  knew 
  the 
  natural 
  scale 
  

   well 
  enough, 
  make 
  it 
  coincide 
  at 
  a 
  considerably 
  larger 
  number 
  

   of 
  points. 
  The 
  calculated 
  alterations 
  to 
  make 
  to 
  the 
  data 
  

   supplied 
  by 
  calibration 
  would 
  not 
  entail 
  any 
  very 
  serious 
  

   trouble. 
  

  

  The 
  other 
  reason 
  for 
  dwelling 
  on 
  the 
  facts 
  is 
  that 
  they 
  are 
  

   at 
  least 
  strongly 
  suggestive 
  that 
  the 
  glass 
  employed 
  in 
  this 
  

   country 
  for 
  making 
  thermometers 
  is 
  not 
  quite 
  so 
  uniform 
  as 
  

   one 
  would 
  like 
  it 
  to 
  be. 
  The 
  figures 
  given 
  in 
  § 
  18 
  for 
  the 
  

   freezing-point 
  of 
  mercury 
  on 
  the 
  natural 
  scales 
  of 
  twenty 
  

   English 
  glass 
  thermometers 
  showed 
  a 
  difference 
  of 
  o, 
  35 
  F. 
  

   between 
  the 
  extremes. 
  I 
  was 
  inclined 
  to 
  attribute 
  the 
  greater 
  

   part 
  of 
  this 
  to 
  possible 
  errors 
  of 
  reading, 
  or 
  impurity 
  of 
  the 
  

   mercury 
  used 
  on 
  one 
  or 
  two 
  occasions 
  in 
  the 
  bath. 
  A 
  direct 
  

   comparison, 
  however, 
  of 
  the 
  two 
  extreme 
  thermometers,, 
  

   freshly 
  recalibrated, 
  in 
  the 
  same 
  bath 
  of 
  freezing 
  mercury 
  

   fairly 
  confirmed 
  the 
  previously 
  observed 
  difference. 
  The 
  

   result 
  is 
  perhaps 
  not 
  absolutely 
  conclusive, 
  because 
  the 
  

   purity 
  of 
  the 
  mercury 
  inside 
  thermometers 
  has 
  to 
  be 
  taken 
  

   for 
  granted 
  : 
  and 
  if 
  this 
  confidence 
  is 
  misplaced, 
  the 
  point 
  at 
  

   which 
  the 
  consequences 
  would 
  be 
  most 
  serious 
  would 
  likely 
  

   be 
  the 
  freezing-point 
  of 
  mercury 
  itself. 
  

  

  [To 
  be 
  continued.] 
  

  

  XXV. 
  On 
  Lord 
  Kelvin's 
  Absolute 
  Method 
  of 
  Graduating 
  a 
  

   Thermometer. 
  By 
  J. 
  Rose-Innes, 
  B.Sc* 
  

  

  IN 
  a 
  paper 
  " 
  On 
  the 
  Thermal 
  Effects 
  of 
  Fluids 
  in 
  Motion 
  " 
  

   Lord 
  Kelvin 
  has 
  given 
  the 
  cooling 
  effects 
  exhibited 
  by 
  

   various 
  gases 
  in 
  passing 
  through 
  a 
  porous 
  plug 
  ; 
  and 
  he 
  

   found 
  that 
  the 
  effects 
  for 
  any 
  one 
  gas 
  kept 
  at 
  the 
  same 
  

   initial 
  temperature 
  were 
  proportional 
  to 
  the 
  difference 
  of 
  

   pressure 
  on 
  the 
  two 
  sides 
  of 
  the 
  plug 
  (Reprinted 
  Papers, 
  vol. 
  i. 
  

   pp. 
  333-455). 
  He 
  also 
  found 
  that 
  the 
  cooling 
  effect 
  for 
  any 
  

   one 
  gas 
  per 
  unit 
  difference 
  of 
  pressure 
  varies 
  as 
  the 
  inverse 
  

   square 
  of 
  the 
  absolute 
  temperature 
  ; 
  and 
  this 
  rule 
  succeeds 
  

   * 
  Communicated 
  by 
  the 
  Physical 
  Society 
  : 
  read 
  Dec. 
  10, 
  1897. 
  

  

  