Table 92. 



RELATIVE AMOUNTS OF SOLAR RADIATION RECEIVED ON A 

 HORIZONTAL SURFACE DURING THE YEAR AT DIFFERENT LATITUDES. 



Table 93. 



AIR MASS, M, CORRESPONDING TO DIFFERENT ZENITH DISTANCES 



OF THE SUN. 



Table 94. 



RELATIVE ILLUMINATION INTENSITIES. 



Source of illumination. 



Zenithal sun 



Sky at sunset 



Sky at end of civil twilight 



Zenithal full moon 



Quarter moon 



Starlight 



Intensity. 



Foot-candles. 



9600. O 

 33-00 

 0.40 

 O.02 

 o. 002 

 0.00008 



Ratio to zenithal 

 full moon. 



465000.0 



1650.0 



20.0 



1.0 



o. 1 



0.004 



Smithsonian Tables. 



218 



