﻿312 
  Dr. 
  C. 
  Chree's 
  Notes 
  on 
  Thermometry. 
  

  

  The 
  depression, 
  being 
  A 
  at 
  the 
  freezing- 
  and 
  A 
  + 
  8(100 
  — 
  t') 
  

   at 
  the 
  boiling-point, 
  would 
  require 
  to 
  be 
  given 
  throughout 
  by 
  

  

  A 
  +8^(100— 
  r>) 
  

  

  if 
  the 
  adoption 
  of 
  the 
  vertical 
  position 
  alone 
  were 
  to 
  suffice. 
  

   Thus 
  above 
  the 
  chamber 
  the 
  depression 
  actually 
  found 
  would 
  

   be 
  too 
  small 
  by 
  

  

  B{(t/l00)(100-r 
  , 
  )-{t-T 
  , 
  )\=BT 
  / 
  (100-t)/100; 
  

  

  while 
  below 
  the 
  chamber 
  it 
  would 
  be 
  too 
  large 
  by 
  

  

  StVIOO. 
  

  

  Consequently 
  we 
  can 
  accomplish 
  our 
  object 
  by 
  simply 
  

   shortening 
  each 
  degree-division, 
  whether 
  above 
  or 
  below 
  the 
  

   chamber, 
  by 
  cV/100 
  of 
  its 
  natural 
  length 
  (i. 
  e. 
  the 
  length 
  of 
  

   stem 
  whose 
  volume 
  would 
  be 
  one-hundredth 
  of 
  the 
  funda- 
  

   mental 
  interval). 
  This 
  is 
  equivalent 
  to 
  the 
  following 
  rule 
  : 
  — 
  

   Determine 
  the 
  freezing- 
  and 
  boiling-points 
  in 
  the 
  vertical 
  

   position 
  ; 
  calculate 
  from 
  a 
  calibration 
  where 
  the 
  divisions 
  

   ti 
  and 
  t 
  2 
  immediately 
  below 
  and 
  above 
  the 
  chamber 
  would 
  

   come 
  in 
  the 
  usual 
  way, 
  but 
  mark 
  the 
  former 
  point 
  lower 
  by 
  

   S^t'/IOO 
  and 
  the 
  latter 
  higher 
  by 
  8(100-* 
  2 
  )t7100 
  than 
  

   according 
  to 
  the 
  calculation 
  ; 
  subdivide 
  the 
  stem 
  between 
  the 
  

   divisions 
  and 
  t 
  lf 
  t 
  2 
  and 
  100, 
  into 
  equal 
  volumes. 
  

  

  This 
  instruction 
  supposes 
  8 
  to 
  be 
  known. 
  To 
  determine 
  it 
  

   observe 
  the 
  difference 
  D 
  in 
  the 
  boiling-point 
  readings 
  obtained 
  

   with 
  the 
  thermometer 
  vertical 
  and 
  horizontal, 
  then 
  

  

  S 
  = 
  D-h-(t 
  + 
  100-t'), 
  

  

  where 
  t' 
  has 
  its 
  previous 
  meaning, 
  while 
  t 
  is 
  the 
  number 
  of 
  

   degree-divisions 
  between 
  the 
  centre 
  of 
  the 
  bulb 
  and 
  the 
  zero- 
  

   point. 
  It 
  must 
  be 
  remembered 
  that 
  the 
  correction 
  is 
  a 
  small 
  

   one, 
  so 
  that 
  we 
  may 
  safely 
  use 
  in 
  our 
  calculation 
  of 
  8 
  the 
  

   values 
  obtained 
  for 
  t 
  and 
  ¥ 
  when 
  the 
  correction 
  is 
  neglected. 
  

  

  In 
  practice, 
  for 
  moderate 
  accuracy, 
  the 
  simplest 
  plan 
  would 
  

   be 
  to 
  mark 
  off 
  two 
  points 
  one 
  slightly 
  below, 
  the 
  other 
  

   slightly 
  above 
  the 
  chamber, 
  by 
  comparison 
  with 
  an 
  ordinary 
  

   standard 
  thermometer 
  of 
  the 
  same 
  kind 
  of 
  glass, 
  both 
  ther- 
  

   mometers 
  being 
  vertical. 
  Subdividing 
  the 
  two 
  portions 
  of 
  

   stem 
  included 
  between 
  these 
  marked 
  points 
  and 
  the 
  respective 
  

   fundamental 
  points 
  into 
  equal 
  volumes, 
  we 
  attain 
  our 
  object. 
  

  

  If 
  a 
  chamber 
  existed 
  above 
  the 
  100° 
  C. 
  mark, 
  the 
  only 
  

   change 
  required 
  would 
  be 
  a 
  raising 
  of 
  all 
  the 
  degree-divisions 
  

   .above 
  the 
  chamber 
  — 
  relative 
  to 
  the 
  positions 
  calculated 
  in 
  

  

  