BLAIR— AEROLOGY. 



195 



Fig. 7. Mean of Wind Observation in "Lows" at 1000 Meters above Sea 



Level, 1907-1912. 



of this illustration the depth of the atmosphere shown is greatly 

 exaggerated. The units of this general or planetary circulatory 

 system in which the arrows point south are east winds having in 

 the average a north component. Those units in which arrows point 

 north are in general west winds having in the average a south 

 component. 



Especial attention is called to the fact that the air in west winds 

 exerts a greater downward pressure than does the air in east 

 winds. Aside from the fact that a gram mass moving from west to 

 east exerts a greater downward pressure than does a gram mass 

 moving from east to west, it is found that the air in west winds is 

 in general dense for the level it occupies, while the air in east winds 



