196 



SYMPOSIUM ON AERONAUTICS. 



is light for its level. That air is heavy or light for the level it 

 occupies depends upon its humidity and its temperature and on the 

 fact that descending air heats at the adiabatic rate while condensa- 

 tion of the moisture in ascending air offsets to a greater or less 

 degree the adiabatic cooling that accompanies the ascent. It is also 

 true that, compared with moist air, dry air absorbs but little radiated 



Fig. 8. Mean of Wind Observations in "Highs" at 2000 Meters above Sea 



Level, 1907-1912. 



heat. This difference in adiabatic rates of cooling and heating 

 effectively prevents the mixing of the airs in question. The west 

 winds in general follow the irregularities of the bottoms, solid earth, 

 water, or aerial, over which they flow and are in consequence gusty 

 winds. East winds are not likely to be thrown into gusts by irregu- 



