40 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



WEATHER BUREAU. 



The work of the Weatlior Bureau during the year has been carried 

 on along accustomed lines. Its practical operations have consisted 

 in the collection and dissemination of weather information and the 

 issue of forecasts and warnings, and its remaining energies have been 

 devoted to the study of meteorological problems yet unsolved. The 

 routine work has been characterized by extension into new fields 

 wherever opportunity was offered, mainly in the fruit-growing dis- 

 tricts of the West, where spring frost warnings have been distributed 

 under a more specialized system. The marine work has been enlarged 

 to include meteorological charts for the Great Lakes and the Indian 

 Ocean, which were formerly not represented in the series of ocean 

 meteorological charts. Studies of conditions in the upper atmos- 

 phere, of solar radiation, and of the effect of climate on forests and 

 stream flow constitute the special investigations conducted by the 

 bureau during the year. 



STUDIES OF THE UPPER ATMOSPHERE. 



Kite flights at the Mount Weather Observatory and sounding-bal- 

 loon campaigns at Huron, S. Dak., and Fort Omaha, Nebr., during 

 the year completed four consecutive years of kite and balloon records. 

 The results obtained during the year have been highly satisfactory. 

 There were three distinct branches of this investigation: (1) Sound- 

 ings of the upper air over Mount Weather, Va., by means of kites and 

 captive balloons; (2) soundings of the air at great altitudes by means 

 of free balloons carrying meteorological instruments; and (3) a 

 study of temperature and pressure changes in the lower layers of 

 the air at summit and base stations in the mountains of Colorado. 



The exploration of the atmosphere by means of sounding balloons 

 has become an international work. While a matter of general 

 scientific interest, its importance to the Weather Bureau naturally 

 hinges on the expectation that the facts disclosed may eventually 

 be utilized in the improvement of weather forecasts. The discovery 

 of conditions in the upper atmosphere altogether different from those 

 formerly supposed to exist has been described in previous reports. 

 The most important of these discoveries is the existence of a region 

 in which a fall in temperature with increasing altitude ceases to take 

 place. This stratum is encountered between 6 and 7 miles above the 

 earth's surface and continues upward to an indefinite height. It is 

 usually referred to as " the upper inversion." The most interesting 

 facts regarding the upper inversion have to do with its variations in 

 temperature and the movement of its winds. 



Contrary to the order prevailing at the surface of the earth, the 

 lowest temperatures of the upper inversion are found in equatorial 



