134 MILLIKAN— METEOROLOGICAL WORK 



H. Warning of weather conditions favorable for use of gas by 



enemy. 

 K. Probable accuracy or odds in favor of forecast. 



Most of the aerological data was obtained from theodolite ob- 

 servations on pilot balloons. The extent to which our knowledge 

 of the upper air has been, and is being, extended by this pilot bal- 

 loon work may be seen from the fact that before the war there 

 existed but one station in the United States where pilot balloon 

 explorations were regularly carried on. Within a year of the in- 

 ception of the meteorological service in the United States Army, 

 thirty-seven complete stations for the obtaining of both surface and 

 upper air data in aid of aviation and the artillery had been estab- 

 lished in the United States and equipped with special aircraft theo- 

 dolites and pilot balloons, neither of which had ever been produced 

 before in this country. Further, twenty such stations had been 

 established by our forces abroad. For the manning of this service, 

 about five hundred specially selected men had been trained in this 

 country, and three hundred and fourteen of them sent abroad, while 

 about two hundred were held for work in the United States. 



The scientific interest in this service centers about four distinct 

 problems : 



1. The extension of our knowledge of the law of motion of pilot 

 balloons. 



2. The procurement of data and the development of methods 

 for the preparation of artillery range tables. 



3. The development of long range propaganda balloons. 



4. The charting of the upper air in the United States and over- 

 seas in aid of aviation. 



I. The Extension of Our Knoivledge of the Lazv of Motion of 

 Pilot Balloons. — Prior to the development of the meteorological 

 service of the army there had been made in the United States per- 

 haps one hundred pilot balloon flights in which the balloons had 

 been followed by the two-theodolite method — the only method which 

 permits of real accuracy — and in several European countries there 

 had been a somewhat greater number, but the data was incomplete 

 and fragmentary. 



Within the past year approximately five thousand such observa- 



