58 
Steam Engine^ 
of all elastic fluids of whatever kind into liquids ; and we 
ought not to despair of effecting it in low terhperatures 
and by strong pressure exerted upon the unmixed gases. 
However unessential the distinction between the gases 
and vapours may be in a chemical sense, their mechanical 
action is very difftrent. By increasing the quantity of 
any gas in a given space the force of it is proportionally 
increased ; but increasing the quantity of any liquid in a 
given space does not at all affect the force of the vapour 
arising from it. On the other hand, by increasing the 
temperature of any gas a proportionate increase of elasti- 
city ensues ; but when the temperature of a liquid is in- 
creased, the force of vapour from it is increased with 
amazing rapidity, the increments of elasticity forming a 
kind of geometrical progression, to the arithmetical incre- 
ments of heat. — Thus, the ratio of the elastic force of at- 
mospheric air of 32^, to that at 212'^, is nearly as 3 : 7 ; 
but the ratio of the force of aqueous vapour proceeding 
from ’ivater of 32^ and 212^', is as 1 : 150 nearly. 
The object of the present essay is to determine the ut- 
most force that certain vapours, as that from water, can 
exert at diflcrent temperatures. The importance hitherto 
attached to this enquiry has arisen chiefly from the consi- 
deration of steam as a mechanical agent ; and this has 
directed the attention more especially to high temperatures. 
But it will appear from what folio v/s that the progress of 
philosophy is more immediately interested in accurate ob* 
servations on the force of steam in low temperatures* 
Dlflerent authors have published accounts of their expe- 
riments on the force of steam : I have on a former occa- 
sion (Meteorological Essays, page 134) given a table of 
forces for every from 80^ to 212*^. The author of 
the article Steam,” in the Encyclopedia Britannica, has 
done the same from 52 • to 280"^ : and M. Bettancourt, in 
the Memoirs dcs scatnms etrangeres” for 1790, (see Hut- 
