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SYMPOSIUM ON AERONAUTICS. 



tion with the filling and ascensional rates to be expected of balloons 

 but also as the best available index of the condition of the atmos- 

 phere with respect to stability. 



Fig. 14. Mean of Wind Observations in " Highs " at 5000 Meters above Sea 



Level, 1907-1912. 



Fig. 16 shows the temperature distribution throughout the year 

 up to the five-kilometer level. It is based on 5 years of observation 

 at Mount Weather. The isotherms are farther apart vertically in 

 the winter than in the summer months, indicating less stable atmos- 

 pheric conditions in the summer months. The decrease in the am- 

 plitude of the annual variation of temperature with height is ap- 

 parent ; also, the difiference in rates of rise and fall of temperature 

 before and after the annual maximum. 



