LESSON XVI. 



ON THE ATMOSPHERE. 



Diffusing gently its enlivening pow'r, 

 The genial Air we all around us feel 

 Cheering though unexplor'd by human sight. 



we have now finished our survey of the hea- 

 venly bodies, our inquiries may naturally descend 

 to the Earth we inhabit : and here the first thing 

 which attracts our attention is, that thin, transpa- 

 rent, and fluid body, called Air, which surrounds 

 this terraqueous globe, and covers it to a consider- 

 able height. Or, if we include in our definition 

 the whole of the fluid mass, consisting of air, 

 electric matter, aqueous and other vapours, which 

 surrounds the Earth, and partakes of all its motions; 

 we then make use of the word Atmosphere, as a 

 term comprising the whole. Beside the different 

 kinds of air, it is manifest that the whole mass of 

 the atmosphere contains a considerable quantity 

 of water, together with an heterogeneous collec- 

 tion of particles exhaled from all solid or fluid 

 bodies on the surface of the Earth. These, how- 

 ever, are transformed into a fluid mass called 

 Atmospheric Air, which is that transparent, colour- 

 less fluid which every where invests this elobe, 

 possessing permanent elasticity and gravity. It is 

 composed of four gases, but principally of 78 parts 

 of nitrogen and 22 of oxygen gas in bulk ; and in- 

 E 3 weigh U 



