725 



TABLE 819.— ILLUMINATION DUE TO DIRECT SUNLIGHT, SKY LIGHT, AND 

 TOTAL ON HORIZONTAL AND VERTICAL PLANES 2 " 



The solar altitude, h, is expressed in angular units, the illumination, /, in foot-candles. 

 The subscripts p and h designate the evaluation of illumination on the perpendicular 

 (facing the sun) and horizontal planes. The additional subscripts, d, s, and t, designate 

 direct sunlight, sky light and total light (direct sunlight plus sky light). 



251 Jones, L. A., and Condit, H. R., Journ. Opt. Soc. Amer., vol. 38, p. 147, 1948. 



TABLE 820.— MEAN INTENSITY / FOR 24 HOURS OF SOLAR RADIATION ON A 

 HORIZONTAL SURFACE AT THE TOP OF THE ATMOSPHERE AND 

 THE SOLAR RADIATION A, IN TERMS OF THE SOLAR RADIATION, 

 A a , AT EARTH'S MEAN DISTANCE FROM THE SUN 



Average annual solar energy received per square dekameter of horizontal surface in kilowatt 

 hours. U. S. : Lincoln, 160,906; Mount Weather, 148,824; Washington, 145,403; New York, 

 106,460; Chicago 97,856. Other countries: Toronto, 139,523; Johannesburg, 175,696; Davos 

 Platz, 174,043; South Kensington, 78,569; Stockholm, 79,267. 



SMITHSONIAN PHYSICAL TABLES 



