96 FIRST YEAR COURSE IN GENERAL SCIENCE 



gravity. The pressure of the air due to its weight is 

 nearly fifteen pounds on a square inch of surface at sea 

 level. This means that the column of air directly above 

 this square inch of surface would weigh about fifteen 

 pounds. 



As one rises to higher levels and leaves some of the air 

 beneath, the pressure becomes less. One of the ways of 



I! " i! 4 





3ft. 



FIG. 44. DENSITY OF THE AIR AT DIFFERENT ELEVATIONS 



1. What is the reason that the air is more dense at sea level than at 

 high elevations? 2. What is the density of the air at the highest mountain 

 known (about 5^ mi. high)? 3. Why would the mercury stand at 1 in. at 

 a height of 15 mi.? 



determining the altitude of a mountain is by measuring the 

 pressure of the atmosphere. Scientists estimate that there 

 is some atmosphere at a height of two hundred miles, but 



