﻿308 
  Dr. 
  C. 
  (Three's 
  Notes 
  on 
  Thermometry. 
  

  

  Applying 
  the 
  mathematical 
  theory 
  of 
  elasticity, 
  Guillaume* 
  

   has 
  deduced 
  a 
  very 
  simple 
  relation 
  between 
  the 
  external 
  and 
  

   internal 
  pressure 
  coefficients, 
  measured 
  of 
  course 
  in 
  the 
  same 
  

   units. 
  Calling 
  these 
  coefficients 
  ft 
  e 
  and 
  /3; 
  respectively, 
  as 
  

   Guillaume 
  does, 
  this 
  relation 
  may 
  be 
  written 
  

  

  A 
  — 
  fie 
  = 
  C, 
  

  

  where 
  c 
  is 
  proportional 
  to 
  the 
  difference 
  between 
  the 
  com- 
  

   pressibility 
  of 
  mercury 
  and 
  that 
  of 
  the 
  particular 
  glass 
  of 
  

   which 
  the 
  thermometer 
  is 
  made. 
  Thus 
  in 
  all 
  thermometers 
  

   of 
  the 
  same 
  glass 
  /3i—/3 
  e 
  should 
  be 
  constant. 
  Taking 
  the 
  

   units 
  recommended 
  above, 
  viz. 
  rise 
  of 
  1° 
  in 
  reading 
  and 
  1 
  mm. 
  

   of 
  mercury 
  pressure, 
  the 
  results 
  deduced 
  at 
  the 
  Bureau 
  

   International 
  * 
  and 
  the 
  Reichsanstalt 
  f 
  are 
  as 
  follows 
  : 
  — 
  

  

  Glass. 
  (/3i-/3 
  e 
  )xl07. 
  

  

  Verve 
  dur 
  154 
  J 
  

  

  Jena 
  glass 
  16 
  m 
  . 
  . 
  . 
  . 
  143 
  

  

  ,, 
  . 
  . 
  DJ 
  . 
  . 
  . 
  . 
  J.OO 
  

  

  § 
  27. 
  In 
  determining 
  fi 
  e 
  the 
  thermometer, 
  immersed 
  in 
  a 
  

   liquid, 
  is 
  exposed 
  to 
  various 
  air 
  pressures, 
  from 
  an 
  atmosphere 
  

   downwards 
  §. 
  The 
  fact 
  that 
  the 
  changes 
  of 
  pressure 
  tend 
  to 
  

   affect 
  the 
  temperature 
  of 
  the 
  liquid 
  is 
  pointed 
  out 
  in 
  the 
  

   publications 
  of 
  the 
  Reichsanstalt 
  ||, 
  and 
  it 
  is 
  apparently 
  re- 
  

   commended 
  that 
  water 
  — 
  preferably 
  near 
  4° 
  C. 
  — 
  should 
  be 
  

   used 
  rather 
  than 
  glycerine 
  or 
  mercury 
  Tf. 
  

  

  Observations 
  of 
  the 
  thermometer 
  alternately 
  in 
  the 
  vertical 
  

   and 
  horizontal 
  positions, 
  at 
  any 
  convenient 
  temperature, 
  

   supply 
  the 
  means 
  of 
  calculating 
  /3i. 
  The 
  Sevres-pattern 
  

   hypsometer 
  is 
  specially 
  adapted 
  for 
  this 
  purpose. 
  The 
  experi- 
  

   mental 
  determination 
  of 
  fti, 
  however, 
  is 
  not 
  so 
  easy 
  as 
  it 
  looks. 
  

   In 
  a 
  horizontal 
  thermometer 
  the 
  end 
  of 
  the 
  mercury 
  column 
  

   loses 
  its 
  symmetrical 
  shape 
  — 
  especially 
  in 
  a 
  large 
  bore 
  — 
  and 
  

   the 
  reading 
  becomes 
  uncertain. 
  There 
  is 
  also 
  apt 
  to 
  be 
  trouble 
  

   through 
  the 
  capillary 
  effect. 
  Capillarity 
  causes 
  a 
  pressure 
  on 
  

   the 
  mercury 
  and 
  bulb. 
  Unless 
  this 
  is 
  constant, 
  which 
  ceases 
  

  

  * 
  Thermometrie, 
  pp. 
  102-103. 
  

  

  t 
  Wiss. 
  Abhandl. 
  vol. 
  i. 
  p. 
  70 
  (1894). 
  

  

  X 
  Schuster 
  and 
  Gannon, 
  Phil. 
  Trans. 
  1895, 
  p. 
  436, 
  take 
  1 
  cm. 
  of 
  mercury- 
  

   pressure 
  for 
  the 
  unit 
  instead 
  of 
  1 
  mm., 
  giving 
  154 
  XlO 
  -6 
  for 
  the 
  Bureau 
  

   International's 
  value 
  of 
  /% 
  — 
  j3 
  e 
  in 
  verve 
  dur. 
  Schuster 
  and 
  Gannon 
  appar- 
  

   ently 
  think 
  141 
  would 
  be 
  more 
  exact 
  than 
  154. 
  

  

  § 
  See 
  Guillaume's 
  Thermometrie, 
  p. 
  103. 
  

  

  || 
  Wiss. 
  Abhandl. 
  vol. 
  ii. 
  1895, 
  pp. 
  7-8. 
  

  

  •f[ 
  See 
  Lord 
  Kelvin's 
  ' 
  Mathematical 
  and 
  Physical 
  Papers,' 
  vol. 
  iii. 
  

   pp. 
  236-239 
  ; 
  also 
  Joule, 
  Phil. 
  Trans. 
  1859, 
  pp. 
  133-136. 
  

  

  