METEOROLOGICAL WORK 61 



edge of upper air currents the Signal Corps in the summer of 

 1917 undertook for the first time in history a general program 

 of mapping the upper air currents of the United States, the 

 Atlantic and western Europe in aid of aviation and particularly 

 with reference to trans-Atlantic flight. By the fall of 1918 

 iwenty-six upper air stations, carefully distributed over the 

 United States, were in full operation in place of the one station 

 which had existed before the war. From these stations reports 

 are telegraphed twice daily to the Weather Bureau in Wash- ( 

 ington. From the pilot-balloon observations, charts are con- 

 structed showing the wind-speed and direction at the various 

 levels : for instance, one chart shows the wind-direction and 

 speed near the ground, another chart shows the. wind-direction 

 and speed 500 meters above the ground and additional charts 

 show the wind-direction and speed at the following levels : 

 1,000, 1,500, 2,000, 3,000 and 4,000 meters above the ground. 

 The forecaster at Washington has the various charts before him 

 showing wind and weather conditions prevailing over the 

 United States within an hour and a half after the observations 

 are made. From these charts he prepares the forecast of 

 weather conditions for the various sections of the United States 

 and at the same time prepares a statement of the wind and 

 weather conditions at various altitudes along the various air 

 routes for the use of aerial navigation. This service is al- 

 ready being used by the aerial mail service, and it is also used 

 by the military flyers, as is evidenced by telegraphic requests 

 received at various military meteorological stations for special 

 reports on the weather and wind conditions when long distance 

 flights are contemplated. 



The problem of exploring the upper air currents over the At- 

 lantic was at first thought insoluble on account of the absence 

 of fixed bases, but the success of the Meteorological Service in 

 developing its long-range propaganda balloons has now made 

 possible the mapping of the upper-air highways across the 

 Atlantic, for arrangements are being made to send up both 

 from coastal stations and from trans-Atlantic steamers these 



