﻿HEAT 
  PRODUCED 
  BY 
  THE 
  COMPRESSION 
  OF 
  A. 
  GAS. 
  297 
  

  

  cate 
  galvanometer, 
  and 
  a 
  small 
  thermo-electric 
  battery 
  arranged 
  so 
  that 
  one 
  set 
  of 
  

   the 
  solderings 
  might 
  be 
  within 
  the 
  tube 
  on 
  the 
  side 
  of 
  the 
  entering 
  current 
  of 
  air, 
  

   and 
  the 
  other 
  set 
  within 
  the 
  tube 
  on 
  the 
  side 
  of 
  the 
  current 
  from 
  the 
  orifice. 
  The 
  

   tube 
  on 
  each 
  side 
  of 
  the 
  orifice 
  would 
  need 
  to 
  be 
  bent 
  so 
  as 
  to 
  bring 
  two 
  parts 
  of 
  

   it, 
  at 
  small 
  distances 
  from 
  the 
  orifice 
  on 
  each 
  side, 
  near 
  enough 
  one 
  another 
  to 
  

   admit 
  of 
  the 
  battery 
  being 
  so 
  placed. 
  The 
  only 
  difficulty 
  I 
  can 
  perceive 
  in 
  the 
  

   way 
  of 
  making 
  the 
  necessary 
  arrangements 
  is 
  what 
  might 
  be 
  experienced 
  in 
  

   fitting 
  the 
  two 
  ends 
  of 
  the 
  battery 
  air-tight 
  into 
  the 
  two 
  parts 
  of 
  the 
  tube. 
  It 
  first 
  

   occurred 
  to 
  me 
  that 
  the 
  little 
  battery 
  itself 
  might 
  be 
  placed 
  entirely 
  within 
  the 
  

   tube, 
  and 
  the 
  difference 
  of 
  pressure 
  kept 
  up 
  in 
  the 
  two 
  parts 
  by 
  the 
  middle 
  of 
  the 
  

   battery 
  being 
  fitted 
  nearly 
  air-tight 
  in 
  the 
  tube, 
  by 
  means 
  of 
  wax, 
  or 
  otherwise 
  ; 
  

   but 
  this 
  arrangement 
  would 
  not 
  be 
  satisfactory, 
  as 
  portions 
  of 
  the 
  bars 
  of 
  the 
  

   battery, 
  if 
  not 
  the 
  ends 
  themselves 
  directly, 
  would 
  be 
  altered 
  in 
  temperature, 
  even 
  

   if 
  Mayer's 
  hypothesis 
  were 
  rigorously 
  true, 
  on 
  account 
  of 
  the 
  rushing 
  of 
  the 
  air 
  

   among 
  them. 
  No 
  part 
  of 
  the 
  battery 
  ought 
  to 
  be 
  exposed 
  to 
  the 
  rushing 
  of 
  the 
  

   air 
  in 
  the 
  neighbourhood 
  of 
  the 
  orifice, 
  and 
  therefore 
  the 
  middle 
  of 
  the 
  battery 
  

   would 
  have 
  to 
  be 
  external 
  to 
  the 
  tube, 
  the 
  ends 
  being 
  cemented 
  into 
  the 
  tube 
  by 
  

   some 
  indulating 
  cement 
  sufficiently 
  strong 
  and 
  compact 
  to 
  hold 
  perfectly 
  air-tight 
  

   on 
  the 
  side 
  where 
  the 
  pressure 
  is 
  different 
  from 
  the 
  atmospheric 
  pressure. 
  By 
  

   such 
  means 
  as 
  these 
  I 
  think 
  a 
  very 
  satisfactory 
  series 
  of 
  experiments 
  might 
  easily 
  

   be 
  performed 
  to 
  test 
  Mayer's 
  hypothesis 
  for 
  air 
  through 
  a 
  very 
  wide 
  range 
  of 
  

   temperatures. 
  

  

  18. 
  Should 
  the 
  differential 
  method 
  of 
  experimenting 
  just 
  described 
  indicate 
  

   any 
  difference 
  of 
  temperature 
  whatever 
  on 
  the 
  two 
  sides 
  of 
  the 
  orifice, 
  Mayer's 
  

   hypothesis 
  would 
  be 
  shown 
  to 
  be 
  not 
  exactly 
  fulfilled, 
  and, 
  according 
  as 
  the 
  air 
  

   leaving 
  the 
  orifice 
  is 
  found 
  to 
  be 
  warmer 
  or 
  colder 
  than 
  the 
  entering 
  air, 
  we 
  

   should 
  infer 
  that 
  the 
  heat 
  absorbed, 
  when 
  air 
  expands 
  at 
  a 
  constant 
  temperature, 
  

   is 
  less 
  than 
  or 
  greater 
  than 
  the 
  mechanical 
  effect 
  produced 
  by 
  the 
  expansion. 
  

  

  19. 
  Calorimetrical 
  methods, 
  like 
  those 
  used 
  by 
  Joule, 
  might 
  then 
  be 
  followed 
  

   for 
  actually 
  determining 
  the 
  heat 
  emitted 
  or 
  absorbed 
  by 
  the 
  air 
  . 
  in 
  the 
  neigh- 
  

   bourhood 
  of 
  the 
  orifice, 
  or 
  in 
  the 
  second 
  spiral, 
  in 
  acquiring 
  the 
  temperature 
  of 
  

   the 
  air 
  in 
  the 
  entering 
  stream, 
  and 
  by 
  careful 
  experimenting, 
  it 
  is 
  probable 
  that 
  

   excessively 
  accurate 
  results 
  might 
  be 
  thus 
  obtained 
  for 
  a 
  wide 
  range 
  of 
  tem- 
  

   perature. 
  

  

  20. 
  The 
  result 
  of 
  each 
  experiment 
  would 
  be 
  a 
  value 
  of 
  /x, 
  in 
  terms 
  of 
  Joule's 
  

  

  mechanical 
  equivalent 
  ; 
  to 
  be 
  calculated 
  by 
  the 
  following 
  expression, 
  derived 
  

  

  from 
  equations 
  (5) 
  and 
  (6). 
  

  

  JE 
  

  

  TT 
  

  

  1 
  + 
  Ef 
  _ 
  

  

  fX= 
  tt 
  — 
  .... 
  (7). 
  

  

  1- 
  J 
  

  

  p' 
  u' 
  log 
  -, 
  

  

  VOL. 
  XX. 
  PART 
  II. 
  4 
  L 
  

  

  