[ ti ] 



SECT. V. 



Of the Contents of the Air. 



Did not the acid vigor of the mine, 



Roll'd from fo many thund'ring chimneys, tame 



The putrid fleams that overfwarm the fky ; 



This cauftic venom would perhaps corrode 



Thofe tender cells that draw the vital air, 



In vain with all their unctuous rills bedew'd^^. 



THAT thin, tranfparent, invifible fluid, called 

 the atmofphere, which furrounds the earth, 

 rifes to a considerable height above its furface. 

 Although invifible to us, it is a real fubftance, 

 excluding other fubftances from the fpace which 

 it occupies, and, like other fluids, preffes equally 

 ki all directions: its weight is the caufe of the 

 fufpenfion of mercury in the barometer, and is to 

 that of water as 1 to 900, or 15 pounds upon 

 every fquare inch of the earth. 



It chiefly confifts of two elaftic fluids, or 

 gafesf^, poffefled of very different and oppofite 

 properties ; it contains alfo other gafes, or fub- 

 ftances, fufpended or diffolvcd in it, but in fmall 

 quantity. Thefe two fluids, or gafes, are diftin- 



(d) Armftrong's Art of preferving Health, p. 51. 



(e) Gas, from gafcht (German) an eruption of wind; any 

 matter fubtilized by heat into an elaftic aeriform ftate. 



M guifhed 



