BLAIR— AEROLOGY. 



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dolite used with these heights to determine horizontal distance from 

 the starting point. When pilot balloons are used, the rate of ascent 

 can be fairly well determined by means of one of several formulae, 

 based upon the weight of the balloon, its resistance to the air and 

 its ascensional force. It any case the position of a free balloon can 



Fig. 3. Meridional section of the atmosphere. 



be determined independently of the barometric pressure or of the 

 ascensional rate of the balloon if a pair of theodolites, one at either 

 end of a measured base line, is used. By means of any of these 

 methods the observer is able to plot a horizontal projection of the 

 balloon's path. From this plot may be read the wind speed and 

 direction at any time during the ascension. 



One of the first cares of the aeronaut is to put down suitable 

 stations at which aircraft may be housed and repaired. It is im- 



