200 Sir H. Davy on the application of liquids formed 
temperature ; but the exact law is not yet determined ; and 
the result is a complicated one, and depends upon circum- 
stances which require to be ascertained by experiment. Thus 
the ratio of the elastic force, dependent upon pressure, is to 
be combined with that of the expansive force dependent upon 
temperature ; and the greater loss of radiant heat at high tem- 
peratures, and the developement of latent heat in compres- 
sion, and the necessity for its re-absorption in expansion (as 
the rationale of the subject is at present understood) must 
awaken some doubts as to the economical results to be ob- 
tained by employing the steam of water under very great 
pressures, and at very elevated temperatures. 
No such doubts, however, can arise with respect to the 
use of such liquids, as require for their existence even a 
compression equal to that of the weight of 30 or 40 atmo- 
spheres : and where common temperatures, or slight eleva- 
tions of them, are sufficient to produce an immense elastic 
force ; and when the principal question to be discussed, is 
whether the effect of mechanical motion is to be most easily 
produced by an increase or diminution of heat by artificial 
means. 
With the assistance of Mr. Faraday I have made some 
experiments on this subject, and the results have answered 
my most sanguine expectations. Sulphuretted hydrogen, 
which condenses readily at 3 0 F., under a pressure equal 
to that which balances the elastic force of an atmosphere 
compressed to had its elastic force increased so as to 
equal that of an atmosphere compressed to T y by an in- 
crease of 47 0 of temperature. Liquid muriatic acid at 3 °, 
exerted an elastic force equivalent to that of an atmosphere 
compressed to ; by an increase of 22 0 , it gained an elastic 
