On the “Force of Steam or Vapour, €3¢. 55k 
Upon the unmixed gases. However unessential 
the distinction between the gases and vapours 
may be in a chemical sense, their mechanical 
action is very different. By increasing the quan-~ 
tity of any gas in a given space the force of it is 
Proportionally inereased; but increasing ‘the 
quantity of any liquid in a giyen space does not 
at all affect the force of the vapour arising from 
it, On the other hand, by increasing the tem- 
perature of any gas a proportionate increase of 
elasticity ensues; but when the temperature of 
a liquid is increased, the force of vapour from 
it is increased with amazing rapidity, the incre. 
ments of elasticity forming a kind of geometrical 
Progression, to the arithmetical increments of 
heat.—Thus, the ratio of the elastic force of 
_ atmospheric air of 32°to that at 212°, is nearly 
as 5: 73 but the ratio of the force of aqueous 
vapour proceeding from water of 32° and 212°, 
is as 1: 150 nearly, 
The object of the present essay is to determine 
the utmost force that certain vapours, as that 
from water, can exert at different temperatures. 
_ The importance hitherto attached to this enquiry 
has arisen chiefly from the consideration of steam 
asa mechanical agent; and this has directed the 
attention more especially to high temperatures. 
But it will appear from what follows that the 
VOL. y, GG 
