38 Mr. Davies Gilbert's observations on the steam engine. 
From this document it appears, that several of the large 
engines now at work in Cornwall, are actually performing a 
duty about one quarter part greater than would be the whole 
efficiency of steam, unaided by expansive working, or by high 
pressure ; assuming that fourteen cubic feet of water is the 
quantity converted into steam by a bushel of coal ; but other 
engines, apparently similar in every respect, fail in perform- 
ing half this duty ; and no satisfactory cause has yet been 
assigned for the important difference. 
As examples of the power and energies of the human 
mind, these applications of fire, through the medium of an 
elastic fluid, to mechanical purposes, stand pre-eminently dis- 
tinguished: as elaborate contrivances useful to man, steam 
engines are confessedly without a rival. 
No series of investigations can therefore be more worthy 
of minute and accurate attention than one which may enable 
us to connect by general laws, the temperatures, the densities, 
the elasticities, the capacities for heat, and the quantities ren- 
dered latent in assuming the elastic form ; first for steam, 
and then, if possible, for all other bodies capable of existing 
in a gaseous state, both in contact with their generating 
fluids, and in complete separation from them. 
I have gone more at length into the principles of the steam 
engine, than the immediate object of this Paper either re- 
quires or can warrant ; but I trust that the Society will admit 
the great importance of the subject as an excuse ; a subject 
with which local circumstances have rendered me familiar 
during the whole of my life. 
