WEATHER BUREAU. 71 



INVESTIGATIONS IN SOLAR RADIATION. 



The necessity of employing untrained observers led to the sus- 

 pension 01 radiation measurements at Santa Fe, N. Mex., between 

 September 12, 1918, and April 23, 1919, and to a marked reduction in 

 the number of measurements at Lincoln, Xebr., during July and 

 August, 1918. By the end of April, 1919, measurements were being 

 obtained as heretofore at both these stations, and also at Madison, 

 AVis., and Washington, D. C. 



The assignment of the official in charge of solar-radiation investi- 

 gations to the editorship of the llonthly Weather Eeview greatly cur- 

 tailed his opportunity for research work. HoAvever, apparatus was 

 tested and an observer trained in its use for the measurement of 

 nocturnal radiation in orchards at Pomona, Calif., and at Medford, 

 Oreg., in connection with the frost-protection investigations of the 

 Weather Bureau. Measurements were also made of the rate at 

 which heat is radiated from different types of oil heaters employed 

 in orchard heating. 



At the end of the fiscal year the work of computing from the 

 radiation measurements available the diurnal and annual variations 

 in radiation intensity with geographical position in the United 

 States, and those which depend principally upon latitude, altitude, and 

 the vapor content of the atmosphere, was well advanced. One of the 

 by-products of the computation has been the determination of the 

 relation between radiation intensity, expressed as a percentage of 

 clear-sky intensity, and the percentage of cloudiness and of the 

 possible hours of sunshine, as observed by eye and recorded auto- 

 matically, respectively, at most Weather Bureau stations. The re- 

 sults of the computation, which will be shown graphically, will soon 

 be ready for publication. 



From the relation between the sun's total, or heat radiation, and 

 the luminous solar radiation, heretofore determined, charts and 

 tables are also being prepared showing the intensity of direct solar 

 illumination on a surface normal to the solar rays, on a horizontal 

 surface, and on vertical surfaces in the plane of the meridian and 

 the prime vertical, respectively, and also the intensity of diffuse 

 sky illumination on a horizontal surface. The illumination data 

 are furnished in response to repeated and urgent requests from 

 illuminating engineers and architects, and must be considered pre- 

 liminary in their character, as the investigation has disclosed the need 

 of extensions in the observational work, especially on the Pacific 

 and Gulf coasts and in the northern tier of States. 



INVESTIGATIONS IN SEISMOLOGY. 



The important work of collecting and publishing earthquake data, 

 begun December 1, 1914, has been continued during the jeav. These 

 data are of two kinds, noninstrumental reports of earthquakes felt 

 and instrumental records, often of quakes imperceptible to the senses 

 and even originating at a great distance. The noninstrumental 

 .reports are rendered by all the regular stations of the Bureau, nearly 

 200 in number, and also by nearly all the Bureau's 4,500 cooperative 

 observers. The instrumental records published by the Bureau have 

 been obtained in' part by instruments owned and operated by the 



