﻿Dr. 
  C. 
  Chree*s 
  Notes 
  on 
  Thermometry. 
  

  

  221 
  

  

  ning 
  of 
  the 
  exposure 
  to 
  a 
  fixed 
  temperature, 
  that 
  it 
  tends 
  

   probably 
  to 
  a 
  maximum 
  with 
  prolonged 
  exposure, 
  and 
  that 
  it 
  

   is 
  greatest 
  in 
  glasses 
  containing 
  lead. 
  Together 
  with 
  the 
  

   permanent 
  rise 
  of 
  zero 
  there 
  may 
  exist 
  a 
  temporary 
  depres- 
  

   sion, 
  and 
  as 
  the 
  latter 
  wears 
  off, 
  on 
  the 
  thermometer's 
  being 
  

   exposed 
  to 
  a 
  normal 
  temperature, 
  the 
  permanent 
  rise 
  appa- 
  

   rently 
  increases. 
  

  

  Owing 
  to 
  the 
  permanent 
  rise 
  of 
  zero, 
  wholly 
  erroneous 
  

   conclusions 
  would 
  be 
  drawn 
  as 
  to 
  the 
  natural 
  scale 
  of 
  a 
  ther- 
  

   mometer 
  unless 
  it 
  had 
  previously 
  been 
  exposed 
  to 
  a 
  course 
  of 
  

   treatment 
  tending 
  to 
  reduce 
  to 
  a 
  minimum 
  the 
  permanent 
  

   effect 
  of 
  exposure 
  to 
  any 
  temperature 
  within 
  the 
  range 
  to 
  which 
  

   the 
  comparison 
  is 
  to 
  be 
  extended 
  *. 
  Generally 
  speaking, 
  

   the 
  treatment 
  consists 
  in 
  exposing 
  the 
  thermometer 
  for 
  some 
  

   time, 
  preferably 
  on 
  more 
  than 
  one 
  occasion, 
  to 
  a 
  temperature 
  

   higher 
  than 
  any 
  at 
  which 
  the 
  comparison 
  is 
  to 
  be 
  made, 
  and 
  

   allowing 
  it 
  to 
  cool 
  slowly 
  f. 
  

  

  § 
  15. 
  At 
  the 
  Bureau 
  International 
  the 
  comparison 
  of 
  the 
  

   verve 
  dur 
  and 
  hydrogen 
  scales 
  has 
  been 
  extended 
  to 
  the 
  range 
  

   100° 
  C. 
  to 
  200° 
  C, 
  use 
  being 
  made 
  of 
  the 
  variable 
  boiling- 
  

   point 
  method 
  already 
  referred 
  to. 
  The 
  following 
  resume 
  

   of 
  the 
  results 
  is 
  given 
  in 
  the 
  " 
  Proces- 
  Verbaux 
  " 
  J 
  of 
  the 
  

   International 
  Committee. 
  

  

  Table 
  VI. 
  

  

  Temperature 
  centigrade 
  ... 
  

  

  110°. 
  

  

  120°. 
  

  

  130°. 
  

  

  140°. 
  

  

  150°. 
  

  

  §=verre 
  dur— 
  hydrogen- 
  "1 
  

   reading. 
  j 
  

  

  -•037 
  

  

  -•063 
  

  

  -•075 
  

  

  - 
  074 
  

  

  -•060 
  

  

  Temperature 
  centigrade 
  ... 
  

  

  160°. 
  

  

  170°. 
  

  

  180°. 
  

   4-043 
  

  

  190°. 
  

  

  200°. 
  

  

  d 
  verre 
  dur 
  — 
  hydrogen- 
  \ 
  

   reading. 
  J 
  

  

  -•034 
  

  

  + 
  •001 
  

  

  +•086 
  

  

  +i25 
  

  

  The 
  results 
  are 
  said 
  to 
  accord 
  fairly 
  with 
  the 
  formula 
  § 
  

   S=^(100-010- 
  3 
  {4-22377x10- 
  2 
  + 
  -88486164x10- 
  3 
  (100-^) 
  

  

  + 
  •39993 
  xl0- 
  5 
  (l00-0 
  2 
  }, 
  

   where 
  t 
  is 
  verve 
  dur 
  temperature. 
  

  

  * 
  Cf. 
  Crafts, 
  Comptes 
  Send 
  us, 
  vol. 
  xciv. 
  1882, 
  p. 
  1298. 
  

  

  f 
  It 
  is 
  desirable 
  tb.it 
  such 
  treatment 
  should 
  r 
  recede 
  calibration 
  or 
  

   division. 
  If 
  it 
  alters 
  the 
  coefficients 
  a 
  lf 
  a 
  2) 
  &c. 
  in 
  (2) 
  it 
  really 
  alters 
  

   the 
  natural 
  scale 
  of 
  the 
  glass. 
  

  

  X 
  Stances 
  de 
  1895, 
  Paris, 
  1896, 
  p. 
  44. 
  

  

  § 
  The 
  factor 
  10— 
  3 
  is 
  not 
  in 
  the 
  original 
  but 
  appears 
  necessary. 
  

   Phil. 
  Mag. 
  S. 
  5. 
  Vol. 
  45. 
  No. 
  274. 
  March 
  1898. 
  " 
  R 
  

  

  