SOLAR ENERGY FOR "WATER HEATING — BROOKS 



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FiGDBH 1. — Average hourly solar radiation (direct plus diffuse) received on a horizontal 

 surface at Fresno, Calif., in July and on clear days in December 1933. 



NUMBER OF DAYS OF SUNSHINE 



Reports of the number of clear, partly cloudy, and cloudy days for 

 a large number of stations in each State are published by the United 

 States Department of Agriculture as "Climatological Data" in the 

 United States Monthly Weather Review. A few stations give pyr- 

 heliometer measurements by the week, and several stations report 

 the percentages of possible sunshine, but for a general understanding 

 one must use the rough cloudiness reports. By definition ^ "partly 

 cloudy" indicates sunshine, on the average, for about half the day. 

 In estimating, therefore, the total number of days of available sun- 



8 "Clear" means that the sun is obscured for from to 0.3 of the day ; "partly cloudy" 

 for from 0.4 to 0.7 ; and "cloudy" means that the sun is obscured for from 0.8 to the 

 whole day. 



