96 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



members of the technical staff of the bureau and is now being suc- 

 cessfully used in recording solar radiation intensities. 



The evaporation program inaugurated in 1916 has been continued. 

 Regular reports are being rendered by 47 stations, and the results 

 are published in the State Section Reports. An annual summary 

 for all stations appears in the statistical section of the annual report 

 of the Chief of the Weather Bureau. 



Investigations of the relation between anemometer cup movement 

 and actual wind velocity, begun more than 20 years ago by Prof. 

 C. F. Marvin and limited in scope at that time by the difficulty of 

 obtaining high velocities, have been resumed, and as a result the rela- 

 tions are now known up to 113 miles an hour actual velocity. This 

 investigation has been conducted jointly by Messrs. Fergusson and 

 Covert of the instrument division, using the wind tunnel of the 

 Bureau of Standards, which was primarily constructed for the study 

 of problems in aviation, and in which high velocities under control 

 are easily produced. Many other forms of anemometers, different 

 sizes of cups, and lengths of arms, were also made subjects of experi- 

 ment, with a view to the early design of an anemometer to record 

 true wind velocities, and the preparation of corrections applicable 

 to the records of the Weather Bureau, which are all on a uniform 

 basis of indicated velocities. 



Exhibits. — An exhibit to show the 'activities of the Weather Bu- 

 reau has been prepared for the Brazilian Centennial Exposition, also 

 three self-demonstrating exhibits and one instrumental exhibit to 

 accompany the Government exhibits sent over circuits routed to 

 State fairs in the United States. This work is carried on cooper- 

 atively with the Office of Exhibits. 



As a result of the wide distribution of Farmers' Bulletin No. 842, 

 Modern Methods of Protection Against Lightning, the Weather 

 Bureau is being called upon with increasing frequency to answer let- 

 ters of inquiry in regard to methods to be used in particular in- 

 stances. R. N. Covert has been named Weather Bureau repre- 

 sentative on a committee to formulate a code whose purpose is to 

 specify safe practice in lightning protective measures. 



INVESTIGATIONS IN SOLAR RADIATION. 



Continuous registration of the quantity of heat received from the 

 sun at the surface of the earth from day to day has been maintained 

 at Washington, D. C, since 1909; at Madison, Wis., since 1911; and 

 at Lincoln, Nebr., since 1915. In addition, on clear days the intensity 

 of direct solar radiation has been measured at the above stations and 

 also at Santa Fe, N. Mex. At the latter station these measurements 

 Avere discontinued at the end of March, 1922, when the Weather 

 Bureau office was moved to the new Federal building, which does not 

 afford suitable exposure for pyrheliometers ; and at Lincoln, Nebr., 

 the registration of the heat energy received from the sun has been 

 discontinued temporarily on account of a defect in the recording 

 pyrheliometer. It is expected that the early completion of a record- 

 ing pyrheliometer of improved design will make it possible to replace 

 this defective instrument in the near future. 



In addition to heat measurements, the intensity of direct sunlight 

 and of diffuse skylight has been measured on almost every day at 



