V. THE ATMOSPHERE 



PROPERTIES AND USES OF AIR 



We are accustomed to think of fish and other marine life 

 as living in the waters of the ocean. But we are less likely 

 to speak of an atmospheric ocean in the bottom of which 

 birds and human beings live and move. It is calculated 



FlG. 41. Depth and density of the atmosphere. (Tower, Smith & Turton.) 



that one-half of the atmosphere is within four miles of the 

 earth's surface, and twenty-nine thirtieths of it within fifteen 

 miles of sea-level. While probably all of it is inside two 

 hundred miles of the surface, there is no means of knowing 

 positively how far upward it may extend. The highest 

 altitude reached by man is about seven miles. By reason of 



no 



