﻿206 
  Dr. 
  C. 
  Chree's 
  Notes 
  on 
  Thermometry. 
  

  

  English 
  text-book 
  where 
  particulars 
  of 
  recent 
  work 
  may 
  be 
  

   found. 
  The 
  following 
  discussion 
  is 
  intended 
  partly 
  to 
  supply 
  

   this 
  want. 
  Few 
  of 
  the 
  subjects 
  it 
  deals 
  with 
  are 
  novel, 
  

   except 
  in 
  details 
  ; 
  and 
  several 
  are 
  discussed 
  at 
  much 
  greater 
  

   length 
  in 
  Dr. 
  Guillaume's 
  admirable 
  work 
  i 
  Thermometrie 
  

   de 
  Precision? 
  in 
  the 
  publications 
  of 
  the 
  Bureau 
  International, 
  

   and 
  in 
  those 
  of 
  the 
  Phys. 
  tech. 
  Reich 
  sanstalt 
  at 
  Charlotten- 
  

   burg. 
  I 
  am 
  indebted 
  to 
  these 
  sources 
  for 
  many 
  of 
  the 
  

   details 
  mentioned 
  here. 
  I 
  have, 
  however, 
  adopted 
  an 
  

   independent 
  standpoint, 
  and 
  have 
  further 
  considered 
  the 
  

   bearing 
  of 
  recent 
  work 
  on 
  the 
  methods 
  in 
  general 
  use 
  in 
  this 
  

   country. 
  

  

  The 
  ideal 
  mercury-thermometer 
  is 
  one 
  which 
  accommodates 
  

   itself 
  at 
  once 
  and 
  completely 
  to 
  the 
  temperature 
  it 
  is 
  for 
  the 
  

   time 
  being 
  exposed 
  to, 
  and 
  which 
  when 
  exposed 
  to 
  a 
  given 
  

   temperature 
  supplies 
  an 
  invariable 
  reading. 
  

  

  The 
  departures 
  from 
  this 
  ideal 
  will 
  be 
  discussed 
  presently, 
  

   after 
  we 
  have 
  considered 
  the 
  nature 
  of 
  the 
  temperature-scale 
  

   of 
  an 
  imaginary 
  glass-mercury 
  thermometer 
  free 
  from 
  all 
  the 
  

   deficiencies. 
  

  

  § 
  2. 
  For 
  the 
  laws 
  of 
  thermal 
  expansion 
  of 
  mercury 
  and 
  

   glass 
  we 
  may 
  assume 
  provisionally 
  

  

  V=V 
  (1 
  + 
  A 
  1 
  *+A 
  2 
  * 
  2 
  + 
  ..),.... 
  (1) 
  

  

  v=v 
  (l 
  + 
  a 
  1 
  t 
  + 
  a 
  2 
  t*+ 
  . 
  .) 
  (2) 
  

  

  Here 
  t 
  denotes 
  temperature 
  on 
  a 
  standard 
  scale, 
  which 
  we 
  

   may 
  suppose 
  that 
  of 
  the 
  hydrogen-thermometer 
  of 
  the 
  Bureau 
  

   International 
  ; 
  Y 
  is 
  the 
  volume 
  at 
  0° 
  C, 
  and 
  V 
  at 
  t° 
  C. 
  of 
  a 
  

   given 
  mass 
  of 
  mercury, 
  A 
  1} 
  A 
  2 
  , 
  &c, 
  constants 
  defining 
  its 
  

   expansion 
  ; 
  v 
  is 
  the 
  volume 
  at 
  0° 
  C, 
  and 
  « 
  at 
  ^° 
  C. 
  of 
  a 
  

   • 
  given 
  mass 
  of 
  glass, 
  a 
  ly 
  a 
  2 
  , 
  &e. 
  expansion-constants 
  for 
  the 
  

   'particular 
  kind 
  of 
  glass. 
  

  

  The 
  natural 
  scale 
  of 
  the 
  thermometer 
  corresponds 
  to 
  the 
  

   case 
  when 
  its 
  stem 
  between 
  the 
  divisions 
  and 
  100 
  — 
  which 
  

   answer 
  to 
  the 
  freezing- 
  and 
  boiling-points 
  of 
  pure 
  water 
  

   under 
  a 
  standard 
  pressure 
  — 
  is 
  subdivided 
  into 
  100 
  equal 
  

   volumes. 
  Degree 
  divisions 
  below 
  0° 
  C. 
  or 
  above 
  100° 
  C. 
  

   should 
  equal 
  in 
  volume 
  those 
  of 
  the 
  fundamental 
  interval 
  

   0° 
  to 
  100°. 
  Suppose 
  that 
  t 
  and 
  t-\-x 
  are 
  corresponding 
  tem- 
  

   peratures 
  on 
  the 
  hydrogen 
  and 
  glass-mercury 
  scales. 
  At 
  

   0° 
  C. 
  the 
  volume 
  of 
  the 
  mercury 
  is 
  equal 
  to 
  the 
  internal 
  

   volume 
  V 
  of 
  the 
  thermometer 
  bulb, 
  including 
  the 
  stem 
  up 
  

   to 
  the 
  zero 
  mark. 
  At 
  temperature 
  t° 
  C. 
  the 
  volume 
  of 
  the 
  

   mercury 
  is 
  equal 
  to 
  that 
  of 
  the 
  bulb 
  and 
  of 
  t 
  + 
  cc 
  stem- 
  

  

  