66 ATMOSPHERE. [Lesson xvi. 



the animal by a debility gradually brought on : to 

 this are also owing many natural phenomena 

 by far too numerous to be mentioned in this 

 place. 



Another property of air, and which indeed is 

 its chief criterion, is its elasticity or springiness ; 

 it is by virtue of this quality that it dilates itself, 

 after the removal of any pressure ; or contracts 

 itself into a less space when it has to sustain a 

 greater pressure. A familiar instance of this qua- 

 lity you may often have observed ; namely, by 

 'having a fresh bladder filled with air ; for when 

 squeezed in the hand the air makes a sensible 

 resistance, but when the hand is taken away, the 

 parts which were compressed, directly restore 

 themselves to their former state. 



I have before observed that th air presses on 

 a square inch with the weight of J5lbs. on a me- 

 dium. Now if we suppose the surface of a full- 

 sized human body to be ten square feet, which is 

 not too much, we shall find, (as it is the nature 

 of the air to press equally in all directions,) that a 

 mart who probably supposes he bears no weight, 

 sustains a pressure of no less than -21,601) Ibs. 

 When we consider that the greater part of us are 

 surrounded with such an astonishing pressure, and 

 that this pressure may in the course of a very few 

 hours be either increased or diminished by more 

 than a thousand pounds weight ; are we never led 

 to reflect upon that POWER who keeps us from 

 utler destruction! Let the Atheist consider what* 



he 



