AND THE ATMOSPHERE. 20J 



more especially obtains a generic character, by 

 the expansible power which it essentially con- 

 tains. That air possesses this expansible 

 power, is familiarly known to every tyro in 

 physical science. In order to prove it, I shall 

 have less necessity to add new facts to old 

 principles, than to give new principles to old 

 facts. 



Although various external circumstances fre- 

 quently tend to direct this expansive power 

 into different channels ; whenever, air is si- 

 tuated in space free and unconfined its expan- 

 sibility^ acts equally in every direction, ra- 

 diating, as it were, from a centre, it becomes 

 extended to the whole circumference; so that 

 if a small portion of air be enclosed within a 

 bladder, and placed under the receiver of an 

 air-pump, the expansive power which the air 

 jn the bladder possesses, is found gradually to 

 dilate, in proportion as the air external to\the 

 bladder, in the receiver, becomes diminished. 

 The expansive power of air, in every direction, 

 is equally proved by the recoil and bursting of 

 a cannon, when the air in it is too closely com- 

 pressed ; as it is, by the spherical appearance, 

 which every air bubble assumes. It is by 

 virtue of this particular attribute, that every 

 portion of air is in equilibrio with the whole ; 

 that it has as much the power of rising as of 

 falling that it possesses as much of levity, as 



