200 PROPERTIES OF AIR 



Such is the subtilty and invisibility of ga- 

 seous bodies, that like the solar rays, their 

 materiality, for a long time, was disputed. 

 That they possess, however, the essential pro- 

 perty common to all matter ; that they possess 

 extension, or the occupation of space, is deci- 

 dedly proved, by the resistance which they op- 

 pose to bodies moving through them, as well as 

 the power which they possess of excluding 

 other bodies, from occupying the same me- 

 dium, in which they are situated. If any hol- 

 low vessel full of air, as for instance, a common 

 glass tumbler, be inverted on the surface of 

 any liquor, and immersed in it, the resistance 

 which the air opposes to the pressure of the 

 water, prevents the water from entering into 

 it beyond a certain point. If the air in the 

 glass be either condensed, into a smaller vo- 

 lume, or entirely exhausted out of it; instead 

 ef the water preserving the same level which it 

 did before, it immediately rushes in and fills the 

 space which the air had occupied. Indepen- 

 dently of this universal attribute which air. 

 possesses, in common with every other species 

 of matter, it has properties of its own, by which 

 it is essentially known to be what it really is 

 and through which it is distinguished from 

 every other substance. Air is distinguished 

 from liquids, as well as from solids, by the 

 jtenuity and transparency of its parts;. and it 



