﻿Dr. 
  0. 
  Chree's 
  Notes 
  on 
  Thermometry. 
  317 
  

  

  The 
  values 
  obtained 
  for 
  C 
  in 
  formula 
  (28) 
  at 
  Kew 
  Ob- 
  

   servatory 
  have 
  varied 
  from 
  one 
  thermometer 
  to 
  another. 
  A 
  

   good 
  deal 
  seems 
  to 
  depend 
  on 
  the 
  fineness 
  of 
  the 
  bore 
  and 
  

   the 
  thickness 
  of 
  the 
  enveloping 
  glass. 
  Even 
  with 
  a 
  given 
  

   thermometer 
  so 
  much 
  depends 
  on 
  the 
  conditions 
  to 
  which 
  

   its 
  stem 
  is 
  exposed, 
  that 
  corrections, 
  whether 
  from 
  a 
  general 
  

   formula 
  or 
  from 
  direct 
  experiment 
  under 
  one 
  definite 
  set 
  of 
  

   conditions, 
  are 
  of 
  uncertain 
  value. 
  If 
  corrections 
  are 
  to 
  be 
  

   deduced 
  from 
  a 
  particular 
  experiment, 
  the 
  conditions 
  ought 
  

   to 
  be 
  made 
  as 
  similar 
  as 
  possible 
  to 
  those 
  in 
  which 
  the 
  

   thermometer 
  will 
  normally 
  be 
  employed. 
  The 
  nature 
  of 
  the 
  

   ventilation 
  over 
  the 
  surface 
  of 
  the 
  hot 
  liquid 
  seems 
  to 
  

   have 
  a 
  large 
  influence 
  on 
  the 
  temperature 
  of 
  the 
  emergent 
  

   column 
  and 
  also, 
  one 
  would 
  suspect, 
  on 
  the 
  height 
  of 
  

   the 
  point 
  where 
  the 
  emergent 
  column 
  has 
  its 
  mean 
  tem- 
  

   perature. 
  

  

  Welsh's 
  Method 
  of 
  Graduation, 
  

  

  § 
  33. 
  Forty 
  years 
  ago, 
  when 
  Mr. 
  John 
  Welsh, 
  F.R.S., 
  was 
  

   Superintendent 
  of 
  Kew 
  Observatory, 
  the 
  accurate 
  pointing 
  

   of 
  thermometers 
  at 
  temperatures 
  within 
  40° 
  or 
  50° 
  F. 
  of 
  the 
  

   normal 
  boiling-point 
  of 
  water 
  presented 
  serious 
  difficulties 
  to 
  

   makers. 
  At 
  the 
  same 
  time 
  thermometers 
  with 
  such 
  a 
  range 
  

   as 
  172° 
  F. 
  to 
  212° 
  F. 
  were 
  considerably 
  in 
  demand 
  for 
  

   estimating 
  heights 
  of 
  mountains 
  &c. 
  by 
  hypsometric 
  obser- 
  

   vations. 
  It 
  was 
  probably 
  this 
  combination 
  of 
  circumstances 
  

   that 
  led 
  Mr. 
  Welsh 
  to 
  initiate 
  the 
  method 
  to 
  which 
  his 
  name 
  

   is 
  here 
  attached. 
  The 
  only 
  description 
  of 
  the 
  method 
  

   published 
  by 
  Welsh, 
  so 
  far 
  as 
  I 
  know, 
  is 
  a 
  brief 
  note 
  entitled 
  

   " 
  Instructions 
  for 
  the 
  Graduation 
  of 
  Boiling-point 
  Thermo- 
  

   meters, 
  intended 
  for 
  the 
  Measurement 
  of 
  Heights," 
  B.A. 
  

   Report 
  for 
  1856, 
  Transactions 
  of 
  Sections, 
  p. 
  49. 
  

  

  In 
  this 
  he 
  gives 
  only 
  numerical 
  results 
  for 
  a 
  particular 
  

   case. 
  Briefly 
  stated, 
  the 
  method 
  consists 
  in 
  comparing 
  the 
  

   thermometer 
  with 
  a 
  standard, 
  not 
  in 
  its 
  final 
  state, 
  but 
  in 
  

   a 
  preliminary 
  state 
  when 
  it 
  contains 
  a 
  larger 
  quantity 
  of 
  

   mercury. 
  

  

  In 
  the 
  particular 
  case 
  described 
  by 
  Welsh, 
  the 
  excess 
  of 
  

   mercury 
  in 
  the 
  preliminary 
  state 
  is 
  such 
  that 
  the 
  thermo- 
  

   meter 
  reads 
  212° 
  F. 
  when 
  the 
  real 
  temperature 
  is 
  82° 
  F., 
  the 
  

   extra 
  mercury, 
  filling 
  130 
  Fahrenheit 
  degree-divisions, 
  being 
  

   thrown 
  off 
  between 
  the 
  preliminary 
  and 
  final 
  states. 
  Data 
  

   applicable 
  to 
  the 
  range 
  172° 
  to 
  212° 
  F. 
  in 
  the 
  final 
  state 
  are 
  

   obtained 
  from 
  a 
  comparison 
  in 
  the 
  initial 
  state 
  between 
  the 
  

   temperatures 
  42° 
  and 
  82° 
  F. 
  

  

  Phil. 
  Mag. 
  S. 
  5. 
  Vol. 
  45. 
  No. 
  275. 
  April 
  1898. 
  Z 
  

  

  