Sfeant Engine , 57 
ty, at 30® below that temperature it has half the force,, 
and at 40® above it, double the force : and so in other li- 
quids. Moreover, the force of aqueous vapour of 60® 
is nearly equal to half inch of mercury^ when admitted 
into a torriceilian vacuum ; and water of the same tempe- 
rature, confined with perfectly dry air, increases the elas- 
ticity to just the saitie amount. 
3. The quantity of any liquid evaporated in the open 
air is directly as the force of steam from such liquid at its 
temperature, all other circumstances being the same. 
4. Ail elastic fiuids expand the same quantity by 
heat : and this expansion is very nearly in the same equa- 
ble way as that of mercury ; at least from 32^ to 212®.— 
It seems probable the expansion of each particle of the 
same fluid, or its sphere of influence, is directly as the 
quantity of heat combined with it ; and consequently the 
expansion of the fluid as the cube of the temperature, reck- 
oned from the point of total privation* 
Having now stated the chief principles which seem to 
be established from the following series of facts and ob- 
servations, I shall proceed to treat of them under the se- 
veral heads* 
On the force of steam or vapour from vjater and varU 
ous other liquids^ both in a vacuum and in air. 
The term steam or vapour is equally applied to those 
elastic fluids which, by cold and pressure of certain known 
degrees, are reduced wholly or in part into a liquid states 
Such are the elastic fluids arising from water, alcohol, 
ether, ammonia, mercury, &c. Other elastic fiuids that 
eannol be reduced, or rather that have not yet been redu- 
ced, into a liquid state by the united agency of those two 
powers, are commonly denominated gases. There caii 
!| scarcely be a doubt entertained respecting the reducibility 
Vol. JL H 
