﻿Dr. 
  C. 
  Chree's 
  Notes 
  on 
  Thermometry. 
  315 
  

  

  and 
  when 
  it 
  and 
  the 
  corresponding 
  part 
  of 
  the 
  stem 
  are 
  raised 
  

   in 
  temperature 
  from 
  t' 
  to 
  t 
  the 
  volume 
  increases 
  to 
  

  

  v 
  Q 
  (t 
  + 
  x 
  — 
  t 
  l 
  )(l 
  + 
  a 
  l 
  t 
  + 
  a 
  2 
  t*-{-. 
  .)• 
  

   Thus 
  

  

  =v 
  (t 
  + 
  x 
  — 
  t 
  l 
  )(l 
  + 
  a 
  L 
  t 
  + 
  a 
  2 
  t 
  2 
  + 
  . 
  .) 
  ; 
  

   whence 
  

  

  _ 
  (t-tJit-t^lA^^ 
  + 
  jAz-azXt 
  + 
  t') 
  + 
  . 
  .} 
  

  

  (l 
  + 
  <M 
  + 
  a 
  2 
  * 
  2 
  + 
  . 
  .)(1 
  + 
  A 
  1 
  * 
  / 
  + 
  . 
  .) 
  " 
  " 
  lZ 
  ° 
  ; 
  

  

  As 
  a 
  first 
  approximation, 
  with 
  the 
  notation 
  of 
  (4), 
  

  

  x=e 
  x 
  (t-tj) 
  (i-i*)* 
  (27) 
  

  

  As 
  already 
  stated, 
  e 
  x 
  is 
  approximately 
  the 
  reciprocal 
  of 
  

   the 
  number 
  of 
  degree 
  volumes 
  included 
  in 
  the 
  bulb 
  up 
  to 
  

   the 
  zero 
  mark. 
  It 
  is 
  a 
  constant 
  for 
  any 
  particular 
  kind 
  of 
  

   glass, 
  and 
  in 
  all 
  ordinary 
  kinds 
  of 
  glass 
  it 
  is 
  a 
  little 
  less 
  than 
  

   1/6000. 
  Knowing 
  the 
  glass, 
  we 
  should 
  at 
  once 
  know 
  the 
  

   correction 
  provided 
  we 
  knew 
  t' 
  . 
  

  

  In 
  reality, 
  of 
  course, 
  the 
  emergent 
  column 
  varies 
  in 
  

   temperature 
  from 
  base 
  to 
  summit, 
  so 
  that 
  t' 
  must 
  be 
  regarded 
  

   as 
  its 
  mean 
  temperature. 
  To 
  determine 
  t 
  1 
  directly, 
  the 
  

   Reichsanstalt 
  employ 
  a 
  " 
  Faden-thermometer," 
  placed 
  appar- 
  

   ently 
  with 
  its 
  very 
  elongated 
  bulb 
  closely 
  adjacent 
  to 
  the 
  

   emergent 
  column. 
  Taking 
  the 
  reading 
  of 
  this 
  auxiliary 
  

   thermometer 
  for 
  f, 
  and 
  replacing 
  e 
  1 
  in 
  (27) 
  by 
  1/6100, 
  they 
  

   claim, 
  as 
  already 
  stated, 
  to 
  obtain 
  with 
  thermometers 
  of 
  Jena 
  

   glass 
  59 
  m 
  corrected 
  temperature-readings 
  which 
  are 
  consistent 
  

   to 
  0°*1 
  C. 
  even 
  up 
  to 
  500° 
  C. 
  This 
  practice 
  of 
  the 
  Reichs- 
  

   anstalt 
  seems 
  a 
  development 
  of 
  an 
  idea 
  which 
  originated 
  

   w 
  r 
  ith 
  Regnault 
  |. 
  

  

  The 
  theoretical 
  aspects 
  of 
  the 
  case 
  are 
  discussed 
  by 
  

   Guillaume 
  J, 
  who 
  refers 
  to 
  the 
  work 
  of 
  Regnault, 
  Mousson, 
  

   Wullner, 
  Holzmann, 
  Thorpe, 
  Mills, 
  and 
  Thiesen, 
  

  

  § 
  32. 
  In 
  comparing 
  high-range 
  thermometers 
  at 
  the 
  Kew 
  

   Observatory 
  I 
  have 
  used 
  a 
  formula 
  

  

  x=G(t-t 
  1 
  )(t-t') 
  (28) 
  

  

  * 
  This 
  formula 
  supplies 
  a 
  correction 
  to 
  the 
  reading 
  of 
  a 
  maximum 
  

   thermometer 
  taken 
  when 
  the 
  surrounding 
  temperature 
  is 
  t', 
  if 
  t 
  — 
  t 
  

   represent 
  the 
  number 
  of 
  degrees 
  in 
  the 
  detached 
  column. 
  {Of. 
  Leyst, 
  

   Rep. 
  fur 
  Meteorologie, 
  vol. 
  xiv. 
  1891.) 
  

  

  t 
  Relation 
  des 
  Expei-iences, 
  vol. 
  i. 
  p. 
  225. 
  

  

  % 
  Thermometrie, 
  pp. 
  188-193. 
  

  

  