I 204 ] 
APPENDIX TO THE PRECEDING PAPER. 
On the changes of volume produced in gases in different states oj 
density , by heat. 
Read May 1, 1823. 
In investigating the laws of the elastic forces exerted by 
vapours or gases raised from liquids by increase of tempe- 
rature under compression, one of the most important circum- 
stances to be considered is the rate of the expansion, or what 
is equivalent, of the elastic force, in atmospheres in different - 
states of density. 
It has been shown by the experiments of M. M. Dalton 
and Gay Lussac, that elastic fluids of very different specific 
gravities expand equally by equal increments of temperature, 
or, as it may be more correctly expressed, according to the 
elucidations of M. M. Dulong and Petit, that mercury and 
air, or gases, are equivalent in their expansions for any 
number of degrees in the thermometrical scale between the 
freezing and boiling points of water ; and the early researches 
of M. Amontons seemed to show that the increase of the 
spring or elastic force of air by increase of temperature, was 
in the direct ratio of its density. I am not however acquainted 
with any direct researches upon the changes of volume pro- 
duced in gases in very different states of condensation and 
rarefaction by changes of temperature, and the importance of 
the enquiry, in relation to the subject of my last communica- 
