﻿ON 
  THE 
  MECHANICAL 
  ACTION 
  OF 
  HEAT. 
  563 
  

  

  The 
  approximate 
  positions 
  of 
  the 
  absolutezero 
  contained 
  in 
  this 
  table 
  were 
  

   laid 
  down 
  on 
  the 
  diagram, 
  in 
  which 
  they 
  are 
  marked 
  by 
  crosses. 
  The 
  longitudinal 
  

   divisions 
  represent 
  centigrade 
  degrees 
  divided 
  into 
  tenths 
  ; 
  the 
  transverse 
  divisions, 
  

   atmospheres 
  of 
  pressure 
  at 
  0° 
  centigrade, 
  also 
  divided 
  into 
  tenths. 
  The 
  positions 
  

   of 
  the 
  crosses 
  indicate 
  at 
  once 
  the 
  pressures 
  in 
  the 
  second 
  column 
  of 
  the 
  table, 
  and 
  

   the 
  approximate 
  zeros 
  in 
  the 
  fourth 
  ; 
  and 
  the 
  numbers 
  affixed 
  to 
  them 
  correspond 
  

   with 
  those 
  in 
  the 
  first 
  column. 
  

  

  As 
  the 
  effect 
  of 
  cohesion 
  is 
  greater, 
  and 
  more 
  easily 
  eliminated, 
  in 
  carbonic 
  

   acid 
  gas 
  than 
  in 
  atmospheric 
  air, 
  the 
  determination 
  of 
  the 
  true 
  absolute 
  zero 
  was 
  

   made 
  from 
  the 
  experiments 
  on 
  the 
  former 
  gas. 
  It 
  will 
  be 
  observed 
  that 
  the 
  ap- 
  

   proximate 
  positions 
  of 
  the 
  absolute 
  zero 
  for 
  carbonic 
  acid 
  lie 
  nearly 
  in 
  a 
  straight 
  

   line. 
  A 
  straight 
  line 
  (dotted 
  in 
  the 
  diagram) 
  having 
  been 
  drawn 
  so 
  that 
  it 
  should 
  

   as 
  nearly 
  as 
  possible 
  traverse 
  them, 
  was 
  found 
  to 
  intersect 
  the 
  line 
  corresponding 
  

   to 
  the 
  zero 
  of 
  pressure, 
  that 
  is, 
  to 
  the 
  state 
  of 
  perfect 
  gas, 
  at 
  a 
  point 
  on 
  the 
  scale 
  

   of 
  temperatures 
  274*6 
  centigrade 
  degrees 
  below 
  the 
  temperature 
  of 
  melting 
  ice 
  ; 
  

   which 
  point 
  was 
  accordingly 
  taken 
  as 
  the 
  true 
  absolute 
  zero 
  of 
  the 
  perfect 
  gas 
  

   thermometer. 
  

  

  So 
  far 
  as 
  their 
  irregularity 
  permits, 
  the 
  experiments 
  on 
  atmospheric 
  air 
  con- 
  

   firm 
  this 
  result, 
  for 
  the 
  approximate 
  positions 
  of 
  the 
  absolute 
  zero 
  deduced 
  from 
  

   them, 
  evidently 
  tend 
  towards 
  the 
  very 
  same 
  point 
  on 
  the 
  diagram 
  with 
  those 
  

   deduced 
  from 
  the 
  experiments 
  on 
  carbonic 
  acid. 
  

  

  The 
  values 
  of 
  the 
  coefficient 
  of 
  dilatation 
  and 
  of 
  increase 
  of 
  pressure, 
  of 
  a 
  per- 
  

   fect 
  gas, 
  per 
  degree, 
  in 
  fractions 
  of 
  its 
  volume 
  and 
  pressure, 
  at 
  the 
  temperature 
  of 
  

   melting 
  ice, 
  are 
  accordingly, 
  — 
  

  

  For 
  the 
  Centigrade 
  Scale 
  - 
  974.fi 
  ~ 
  0-00364166 
  

   Fop'Fahrbnheit's 
  Scale 
  494723 
  = 
  0-00202314 
  

  

  