SCIENTIFIC BALLOON ASCENSIONS VON BEZOLD 287 



when we began to investigate the causal connection of the atmos- 

 pheric processes and to trace the latter back to fundamental physical 

 laws. 



When we enter on this problem we must consider the atmosphere 

 as a whole. We can no longer be satisfied with observations that 

 are made in the lowest stratum of air, but have to strive for data 

 from the upper strata and representing all conditions. 



Observations made under ordinary conditions will suffice to give 

 us a picture of the average distribution of temperature, precipita- 

 tion, wind, etc., as well as of their variations, that is to say, they 

 suffice as a basis for climatological studies. By means of such 

 observations, with the help of the graphic weather charts, the phe- 

 nomena of the weather as they follow one after the other, and the 

 connection of the processes that occur together can be made out to 

 very considerable extent. But the explanation of the phenomena is 

 impossible so long as the study is confined to the lowest stratum of air. 



The fundamental generalization that the areas of low barometric 

 pressure are accompanied by cloudiness and precipitation, whereas 

 in the high pressure areas clear, dry weather prevails, becomes 

 intelligible when we consider that in the first case we rave to do 

 with ascending air but in the second case with descending currents. 



From that moment when we recognized what fundamentally 

 different roles the ascending and descending currents play and what 

 incisive importance the vertical movements of the air have for 

 meteorology and climatology, it must have been recognized as 

 a problem of the highest importance to follow along the path of 

 these currents and numerically determine their behavior above and 

 below by exact observations. 



The recognition of the importance of these questions prompted 

 at first the establishment of mountain observatories, and the obser- 

 vations collected there have contributed not a little to advance 

 our understanding of atmospheric processes and to the attainment 

 of new points of view. 



The changes that rising and falling currents of air experience 

 as to temperature and moisture can be followed strictly mathemat- 

 ically by means of the formula? of the mechanical theory of heat, 

 under the assumption that neither mixture with other masses of 

 air nor increase or diminution of heat occurs. In fact such con- 

 siderations enable us to explain a series of phenomena. 



But whether these assumptions actually apply, and to what 

 extent absorption or emission of heat or mixture with other air hav- 

 ing other temperatures and other moisture content, are to be con- 



