38 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



been found that the depth of easterly winds is much less on this con- 

 tinent than over Europe. The observations also seem to show that 

 temperature changes at the surface of the earth and at altitudes of 

 1 to 2 miles occur simultaneously, thus contradicting previous state- 

 ments that the changes at relatively high levels foreshadow those for 

 low levels twenty-four hours later. It has further developed that 

 the temperature gradients for heat thunderstorms do not accord 

 with those called for by theory. Similarly in hot waves the unusually 

 high temperatures appear to be confined to the strata within half a 

 mile of the earth's surface, wliile the heat wave does not advance 

 abruptly \\dth a solid front like a wall, but is built up gradually over 

 the alTected region. 



Studies of atmospheric electricity and magnetism have been con- 

 tinued along the lines heretofore pursued, while the measurements of 

 the intensity of solar radiation and the percentage of polarization of 

 sky light have been made at Mount Weather and Wasliington as in 

 previous years. The solar radiation records during the five years of 

 observation show marked departures from the monthly and annual 

 mean rates, just as similar records at European observatories during 

 the past twenty-six years also show marked fluctuations in this 

 respect. Tliis study wdll be further pursued during the coming year 

 at four or five additional stations, so located as to be fairly repre- 

 sentative of the different chmatological sections of the country. 



Progress has been made toward installing apparatus for the study 

 of the quantity of vapor in the atmosphere, and the investigation of 

 the properties of different bodies as radiators and as absorbers of 

 radiation. The question of the quantity of water vapor in the atmos- 

 phere is of sufficient importance to justify attempts to determine it, 

 although the amount next the earth's surface is so strongly affected 

 by purely local conditions that its consideration in weather forecast- 

 ing has long since been abandoned. 



Articles discussing the theoretical as well as the practical appfica- 

 tion of the data obtained at Mount Weather and other points appeared 

 in the quarterly buUetin of the Observatory during the year. ^Vhile 

 devoted principaUy to the work at the Observatory, the columns of 

 the bulletm are open to contributions from scientists engaged in 

 corresponding fines of research anywhere in the world. 



FORECASTS AND WARNINGS. 



The application of the Mount Weather investigations to practical 

 forecasting at Waslungton continued during the year, and has proved 

 of material aid in increasing the accuracy and range of the forecasts. 

 A few examples of possibilities in this way will serve to illustrate- 



Sometimes a storm passes eastward without being followed bv 

 expected clearing weather, because a second storm was developing 



