THE ATMOSPHERE 



59 



In the table, what is the relative density (a) of dry air 

 and of saturated air at the same temperatures ; (6) of air 

 whether dry or saturated as the temperature is increased? 

 What is true of the amounts of water vapor held by the air 

 as its temperature is lowered? 



3. What must be true of barometer readings (a) in a 

 warm moisture-laden atmosphere; (b) in a cold dry at- 

 mosphere ? With a temperature stationary or rising, what 

 is the probable cause of a falling barometer? What is the 

 reasoning that forecasts rainfall when there is any consid- 

 erable fall in the mercury column of the barometer? 



CURRENTS IN THE ATMOSPHERE 



1. In the first paragraph under 

 Ventilation, what was true of 

 the relative temperatures of the 

 air in the two chimneys ? What 

 will the air in the box do because 

 of these conditions? Explain 

 why the air goes down one 

 chimney and then on through 

 the box. What is true of the 

 temperature of the warmed air 



FIG. 23. Convection currents 



after it leaves the chimney ? in air. 



