﻿324 
  "Dr. 
  C. 
  Chree's 
  Notes 
  on 
  Thermometry. 
  

  

  by 
  adopting 
  the 
  vertical 
  as 
  the 
  standard 
  position. 
  The 
  actual 
  

   readings 
  of 
  a 
  correctly 
  divided 
  thermometer, 
  after 
  allowance 
  

   is 
  made 
  for 
  any 
  secular 
  change 
  of 
  zero, 
  are 
  likely 
  to 
  give 
  at 
  

   ordinary 
  atmospheric 
  temperatures 
  — 
  where 
  nearly 
  all 
  very 
  

   exact 
  absolute 
  measurements 
  are 
  made 
  — 
  results 
  agreeing 
  with 
  

   those 
  of 
  the 
  hydrogen 
  thermometer 
  to 
  within 
  0°*1 
  C. 
  To 
  

   those 
  physicists 
  and 
  chemists 
  who 
  are 
  accustomed 
  to 
  record 
  

   temperatures 
  to 
  C, 
  001 
  C, 
  or 
  even 
  o, 
  0001 
  C, 
  this 
  may 
  seem 
  

   a 
  paltry 
  claim 
  : 
  but 
  it 
  does 
  not 
  seem 
  so 
  to 
  many 
  scientific 
  

   men 
  whose 
  interests 
  extend 
  beyond 
  the 
  temperature 
  of 
  the 
  

   thermometer 
  to 
  that 
  of 
  its 
  surroundings. 
  For 
  many 
  purposes, 
  

   including 
  even 
  some 
  investigations 
  of 
  high 
  scientific 
  import- 
  

   ance, 
  the 
  measurement 
  of 
  temperatures 
  to 
  0°'001 
  C. 
  is 
  just 
  as 
  

   futile 
  as 
  the 
  use 
  of 
  10 
  figure 
  logarithms 
  in 
  handling 
  data 
  in 
  

   which 
  the 
  fourth 
  significant 
  figure 
  is 
  uncertain. 
  

  

  On 
  the 
  other 
  hand, 
  there 
  unquestionably 
  exist 
  physical 
  and 
  

   chemical 
  investigations, 
  tending 
  to 
  increase 
  in 
  number, 
  in 
  

   which 
  the 
  absolute 
  determination 
  of 
  temperatures 
  with 
  the 
  

   highest 
  possible 
  precision 
  is 
  of 
  fundamental 
  importance. 
  For 
  

   these, 
  in 
  the 
  mean 
  time, 
  English 
  glass 
  thermometers 
  and 
  

   ordinary 
  British 
  methods 
  are 
  not 
  suitable. 
  However 
  good 
  

   the 
  workmanship, 
  and 
  however 
  accurate 
  the 
  calibration, 
  there 
  

   exist 
  the 
  following 
  defects 
  : 
  — 
  

  

  1. 
  Ice 
  readings 
  corresponding 
  to 
  infinitely 
  prolonged 
  ex- 
  

   posure 
  to 
  0° 
  C. 
  are 
  not 
  practically 
  obtainable 
  ; 
  and 
  ordinary 
  

   ice 
  readings 
  being 
  affected 
  to 
  some 
  extent 
  by 
  the 
  previous 
  

   temperature 
  are 
  not 
  strictly 
  comparable, 
  

  

  2. 
  So 
  long 
  as 
  changes 
  of 
  3 
  J 
  inches 
  of 
  mercury 
  in 
  baro- 
  

   metric 
  pressure 
  are 
  possible, 
  and 
  occasions 
  arise 
  for 
  the 
  im- 
  

   mersion 
  of 
  thermometers 
  in 
  heavy 
  liquids, 
  corrections 
  for 
  

   external 
  pressure 
  cannot 
  always 
  be 
  avoided. 
  

  

  3. 
  Unless 
  frequently 
  subjected 
  to 
  temperature-cycles 
  of 
  

   considerable 
  range 
  an 
  ordinary 
  English 
  glass 
  thermometer 
  is 
  

   apt 
  to 
  be 
  influenced 
  for 
  days, 
  it 
  may 
  be 
  weeks, 
  by 
  exposure 
  

   to 
  any 
  temperature 
  much 
  over 
  120° 
  F. 
  

  

  4. 
  For 
  accuracy 
  of 
  an 
  order 
  higher 
  than 
  0°*1 
  F. 
  it 
  is 
  

   certainly 
  unsafe 
  to 
  assume 
  the 
  natural 
  scale 
  of 
  an 
  English 
  

   glass 
  thermometer 
  identical 
  with 
  that 
  of 
  the 
  hydrogen 
  or 
  

   nitrogen 
  thermometer, 
  ever 
  for 
  the 
  restricted 
  range 
  22° 
  F. 
  

   to 
  212° 
  F. 
  

  

  5. 
  Whether 
  through 
  variety 
  in 
  the 
  constitution 
  of 
  the 
  glass 
  

   or 
  differences 
  in 
  its 
  treatment, 
  the 
  natural 
  scales 
  of 
  ordinary 
  

   English 
  glass 
  thermometers 
  do 
  not 
  appear 
  sufficiently 
  ac- 
  

   cordant 
  to 
  render 
  practicable 
  the 
  use 
  of 
  any 
  general 
  table 
  of 
  

   reductions 
  to 
  a 
  standard 
  scale 
  of 
  temperature. 
  

  

  For 
  leave 
  to 
  publish 
  particulars 
  of 
  experiments 
  made 
  at 
  

  

  