68 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE. 



owned and operated by the bureau itself, one at Washington, D. C, 

 the other at Northfield, Vt. The remainder are furnished through 

 cooperation with various agencies at 18 additional stations distrib- 

 uted from Panama to Alaska and from the Hawaiian Islands to 

 Porto Rico. 



During the calendar year 1917, 112 earthquakes were felt within 

 the borders of the United States proper. The great majority of 

 these produced no damage whatever, and none any material damage. 



SOLAR RADIATION INVESTIGATIONS. 



Continuous records of the total amount of radiation received on a 

 horizontal surface from the sun and slcy were obtained throughout 

 the year at Washington, D. C, Madison, Wis., and Lincoln, Nebr. 

 Measurements of the intensity of direct solar radiation have been 

 made at the above stations, and also at Santa Fe, N. Mex., whenever 

 atmospheric conditions have been suitable, and at Washington and 

 Madison the percentage of polarization of sky light has been meas- 

 ured. A monthly summary of the results has been published in the 

 Monthly Weather Review. 



Experience has shown the superiority of the silver-block type of 

 Marvin pyrheliometer over the spiral-ribbon type. Two new instru- 

 ments of the former type have therefore been constructed and stand- 

 ardized during the year to replace instruments of the spiral-ribbon 

 type in use at Lincoln and Madison. A similar change in the instru- 

 mental equipment has also been made at Santa Fe, so that all four 

 pyrheliometric stations are now equipped with the new and im- 

 proved form of Marvin pyrheliometer. 



Persistent requests have been received from various sources for the 

 cooperation of the Weather Bureau in a project having for its object 

 the determination of sky brightness, or the intensity of natural light- 

 ing, in various sections of the United States, at different seasons of 

 the year and hours of the day, and under various atmospheric condi- 

 tions. Some preliminary work has been done along this line. 



A program for meteorological observations was planned for about 

 55 Weather Bureau stations in or near the path of total obscuration 

 of the sun during the eclipse of June 8, 1918. In addition, a special 

 station for measuring both incoming and outgoing radiation during 

 the eclipse was established at Goldendale, Wash., at the center of the 

 path of totality. The complete program was carried out as planned, 

 although weather conditions at some points were unfavorable. 



The Office of Solar Radiation Investigations at Camp American 

 University has cooperated with the experiment station of the Bureau 

 of Mines (now the Chemical Warfare Service, National Army) in 

 determining the prevailing meteorological conditions during experi- 

 ments in the open air. 



AGRICULTURAL METEOROLOGY. 



With the growth and extension of the service rendered by the 

 Weather Bureau and represented by its great weather and crop serv- 

 ice, the establishment of the Division of Agricultural Meteorology to 

 handle all such work under capable direction was the natural out- 

 come. This organization became effective February 21, 1916, and has 



