returns. This element has a near affinity or relation to > 

 water, because it eagerly takes up rarefied water iota 

 itself, as water again drinks up a portion of air within 

 its contact ; so that air and water, actuated by ether, 

 make the levers and wedges by which nature performs 

 all her changes in bodies. And it serves as the commort 

 medium of communication between us and all bodies. 



The pressure of a column of air upon a square inch 

 only, is equal to fifteen pounds weight. That -upon the 

 surface of a human body generally amounts to at least- 

 thirteen tons weight : seeing all fluids press with an equal 

 force every way, upwards, downwards, sideways, and hi- 

 all directions. 



" But how is it then that our bodies are not crushed - 

 in pieces 1" Our bodies, as well as all others, are filled 

 wit Ji air throughout : and the spring of the internal air 

 is equal to the pressure of that without. And when two 

 equal forces act in contrary directions, they entirely 

 destroy each other's effects: hence, if the ambient air 

 press? upon us, it is all one as if it did not* press at all. 



The elasticity of the air is a counterbalance to its- 

 gravitation. And how necessary is it, that these should 

 balance each other ? Were the power of gravity to be 

 suspended for a moment, and that of elasticity to remain, 

 the atmosphere would instantly be dissipated througlj 

 the infinite regions of space. But while the weight of 

 the air and its elastic force are equal, they produce aa 

 equilibrium among the particles of air, in every part of 

 the atmosphere. 



As the higher it is, the air is more and more expanded,., 

 gravitation being less and less, sa the parts of the air in 

 the upper regions will be expanded, only not to infinity. 

 The air is generally invisible* And it is necessary it- 

 should be so. For as it is the medium through which 

 we see objects, if the parts of it were perceptible, it 

 would render the view of these objects far less perfect 

 and distinct. Hence a greatly magnifying telescope, as 

 it shews the body of air, makes the view ef other objects 

 more confused. 



Yet in some cases you* may seem to see the air. In a 

 very hot summer's day, in an open part of .the country,. 



