ATMOSPHERIC PRESSURE 



135 



Use of the barometer. The barom- 

 eter may be used to determine eleva- 

 tions. At sea level the barometer will 

 read 30 inches. If the barometer be 

 carried to elevations above sea level, 

 the mercury gradually falls. It falls 

 at the rate of one inch for a rise in 

 elevation of about 910 feet. 



Changes in air pressure are also very 

 closely connected with changes in the 

 weather. In general it may be said 

 that a rapid rise of the mercury in the 

 barometer indicates fair weather, and 

 a rapid fall indicates stormy weather. 

 The barometer is thus of great assist- 

 ance in predicting the general trend 

 of the weather. 



Questions 



1. How can you prove that air has 

 weight ? 



2. What is the weight of a column 

 of air over one square inch at sea 

 level? 



3. Why is not the atmospheric 

 pressure on the top of a mountain the 

 same as it is at the bottom? 



4. 

 scious of the great pressure of the air around us? 



5. What are some of the effects of high altitudes 

 on the human body? 



FIG. 50. A 

 standard mer- 

 curial barom- 



Why are we not always con- eter - 



